Studies on the host response to influenza A virus infections in

Transcription

University of Veterinary Medicine Hannover
Helmholtz Centre for Infection Research Braunschweig
Department: Infection Genetics
Studies on the host response to influenza A
virus infections in mouse knock-out mutants
Thesis
Submitted in partial fulfilment of the requirements for the degree
Doctor rerum naturalium
(Dr. rer. nat.)
awarded by the University of Veterinary Medicine Hannover
by
Nora Kühn née Mehnert
Freiberg
Hannover, Germany, 2015
Supervisor:
Supervision group:
Prof. Dr. Klaus Schughart
Prof. Dr. Georg Herrler
Prof. Dr. Dr. Luka Cicin-Sain
1st evaluation:
Prof. Dr. Klaus Schughart
Helmholtz Centre for Infection Research, Braunschweig
Prof. Dr. Georg Herrler
University of Veterinary Medicine, Hannover
Prof. Dr. Dr. Luka Cicin-Sain
Helmholtz Centre for Infection Research, Braunschweig
2nd evaluation:
Prof. Dr. Martin Schwemmle
University Medical Center, Freiburg
Date of final exam:
April 30, 2015
Parts of this thesis have been published or submitted in:
PLOS Pathogens (Manuscript I)
submitted (Manuscript II)
PLOS ONE (Manuscript III)
i
Abstract
Studies on the host response to influenza A virus infections in mouse knockout mutants
Nora Kühn
Influenza A virus (IAV) infection poses a significant public health problem worldwide
and treatment is limited due to occurring virus resistances. The influenza virus hemagglutinin (HA), which mediates viral entry into the target cells, has to be cleaved by
host proteases to mature into an active form. Host proteases responsible for cleavage
activation represent potential new targets for antiviral therapy. Ubiquitously expressed
subtilisin-like proteases are known to activate highly pathogenic avian influenza viruses.
However, other tissue- and cell-specific proteases are involved in the activation of human
influenza viruses with monobasic HA cleavage site. Recently, type II transmembrane
serine proteases (TTSPs) have been described as cleavage activators in cell culture.
The goal of my thesis was to examine the in vivo role of three host cell proteases
TMPRSS2, TMPRSS4 and TMPRSS11D after IAV infection in mouse knock-out models.
Here, I demonstrated that deletion of the host protease TMPRSS2 inhibited the
spread of mono-basic H1N1 IAV, including the pandemic 2009 H1N1. Tmprss2 deficient mice were completely protected from body weight loss and death after infection. Impairment of lung function and lung pathology was strongly reduced. Also,
after infection with the mono-basic H3N2 IAV, body weight loss and mortality were
less severe in Tmprss2 -deficient mice than in control mice but not completely inhibited.
These observations suggest that for cleavage activation of H3 viruses other proteases
besides TMPRSS2 are involved in vivo.
Deletion of TMPRSS4 did not protect mice from body weight loss, death and virus
spread upon infection with H3N2 IAV. However, Tmprss2-/- Tmprss4-/- double knockout mice showed strongly reduced body weight loss and mortality as well as decreased
viral spread and lung pathology in comparison to wild type mice. However, protection
was still not complete. Therefore, I analyzed the role of a third protease, TMPRSS11D,
for H3N2 IAV activation. Tmprss11d-/- mice exhibited also decreased mortality demonstrating that it may also be involved in cleavage activation of H3 HA in vivo.
In addition, I successfully established pulse oximetry to measure oxygen saturation
after infection in different mouse strains. Oxygen saturation correlates with pathophysiological changes in the lung after IAV infection and with viral titer.
In summary, the results of my thesis work demonstrated the involvement of several proteases in HA cleavage in vivo. H1 is completely dependent on TMPRSS2. In
contrast, H3 can be activated by TMPRSS2, TMPRSS4 and also by TMPRSS11D.
Therefore, all three proteases represent suitable targets for new antivirals fighting human IAV infections.
ii
Zusammenfassung
Analyse der Wirtsantwort auf Influenza A Infektion in Knock-out Mausstämmen
Nora Kühn
Influenza A Virus (IAV)-Infektionen stellen weltweit eines der größten Gesundheitsprobleme dar. Steigende Anzahlen auftretender Resistenzen gegenüber antiviralen
Medikamenten erschwert die Bekämpfung von IAV-Infektionen. Die Aktivierung des
Oberflächenproteins Hämaglutinin (HA) durch Wirtsproteasen ist ein essentieller Schritt
bei der Replikation des Influenza Virus’. Aufgrund ihrer wichtigen Funktion in der
Virusvermehrung sind Wirtsproteasen daher ein vielversprechender Angriffspunkt in
der Entwicklung neuer Medikamente gegen Influenzainfektionen. Hochpathogene aviäre
Virusstämme werden überall im Körper von subtilisin-ähnlichen Proteasen gespalten.
Im Gegensatz dazu können humane Influenzaviren mit einer monobasischen Spaltstelle, abhängig vom Gewebe, von verschiedenen Wirtsproteasen aktiviert werden. In
diversen in vitro Studien wurden Mitglieder der Typ II Transmembran-Serinproteasen
als Enzyme der HA-Aktivierung von Influenzaviren beschrieben.
Die Zielsetzung meiner Doktorarbeit war, die in vivo Funktion der Wirtsproteasen
TMPRSS2, TMPRSS4 und TMPRSS11D nach einer IAV-Infektion mit Hilfe von
Knock-out Mausstämmen zu untersuchen.
In meiner Doktorarbeit konnte ich zeigen, dass das Ausschalten der Wirtsprotease
TMPRSS2 die Ausbreitung des monobasischen H1N1 Virus, sowohl des Maus adaptierten PR8 Virus’ als auch des pandemischen Influenza H1N1 2009 Virus’, inhibiert.
Nach der Infektion waren Tmprss2 Knock-out Mäuse vollständig vor Gewichtsverlust
und einem letalen Krankheitsverlauf geschützt. Weiterhin war die Auswirkung der Infektion auf Lungenfunktion als wie auch auf die Lungenpathologie sehr gering. Auch
nach Infektion mit einem weiteren humanpathogenen Influenza Subtypen H3N2, waren
Gewichtsverlust und Mortalität in Tmprss2 Knock-out Mäusen weniger schwerwiegend
als in den Kontrolltieren. Allerdings konnte kein vollständiger Schutz beobachtet werden. Aufgrund dieser Ergebnisse kann geschlussfolgert werden, dass H3 noch von
weiteren Wirtsproteasen aktiviert werden kann.
Im Gegensatz zu Tmprss2, zeigten Tmprss4 -defiziente Mäuse nach einer H3N2 IAV
Infektion keinen Unterschied im Gewichtsverlust, Mortalität und viraler Ausbreitung
in der Lunge. Allerdings waren Tmprss2Tmprss4 Doppel-Knock-out Mäuse resistenter
gegenüber H3N2 in Bezug auf Gewichtsverlust, Sterberate, Dissemination von viralen
Partikeln und Lungenpathologie. Eine komplette Resistenz gegenüber H3N2 konnte
allerdings immer noch nicht beobachtet werden. Um weitere H3-aktivierende Wirtsproteasen zu identifizieren, wurde mit Hilfe von Tmprss11d Knock-out Mäusen die
Rolle von TMPRSS11D in der H3N2 Pathogenese untersucht. Tmprss11d Knock-out
Mäuse wiesen eine höhere Überlebensrate als die Kontrolltiere auf, und somit kon-
iii
nte ich zeigen, dass TMPRSS11D, neben TMPRSS2 und TMPRSS4, ebenfalls an der
H3-Spaltung in vivo beteiligt ist.
Um den Infektionsverlauf und die Lungenfunktion nach einer IAV Infektion präziser
zu beschreiben, habe ich die Pulsoxymetrie als alternative Methode zur Körpergewichtsmessung etabliert. Nach der Infektion korreliert die Sauerstoffsättigung mit der viralen
Replikation als auch mit pathophysiologischen Veränderungen in der Lunge.
Zusammengefasst zeigte ich in meiner Doktorarbeit die Beteiligung verschiedener
Wirtsproteasen an der HA Aktivierung im Mausmodell. Die H1-Spaltung ist komplett abhängig von der Aktivität von TMPRSS2. Im Gegensatz dazu wird H3 von
TMPRSS2, TMPRSS4 und TMPRSS11D gespalten. Aufgrund dieser Ergebnisse
stellen diese drei Proteasen geeignete und vielversprechende Targets für innovative
Strategien zur Bekämpfung von Influenza Infektionen dar.
iv
Table of Contents
1 Introduction
1.1 Biology of influenza A virus . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.1 Aetiology and classification . . . . . . . . . . . . . . . . . . . . .
1.1.2 Structure of viral particle . . . . . . . . . . . . . . . . . . . . . .
1.1.3 Replication cycle . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Importance of host proteases for influenza virus infection . . . . . . . .
1.2.1 Proteolytic activation of the hemagglutinin . . . . . . . . . . . .
1.2.2 Involvement of host proteases in the cleavage of mammalian influenza viruses . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.3 Type II transmembrane serine proteases . . . . . . . . . . . . . .
1.3 Treatment and prevention of influenza . . . . . . . . . . . . . . . . . . .
1.4 Mouse as a model for influenza research . . . . . . . . . . . . . . . . . .
5
6
9
11
2 Objectives
14
3 Results
3.1 Manuscript I: TMPRSS2 is essential for Influenza H1N1 virus pathogenesis in mice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Manuscript II: Tmprss2 and Tmprss4 facilitate proteolytic activation of
H3N2 Influenza A virus hemagglutinin in mice . . . . . . . . . . . . . .
3.3 Manuscript III: Cellular changes in blood indicate severe respiratory disease during influenza infections in mice . . . . . . . . . . . . . . . . . .
15
4 Contribution to manuscripts
39
5 Unpublished Data
5.1 TMPRSS11D is involved in cleavage activation of H3N2 hemagglutinin
in mice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Additional results for Tmprss2 knock-out mutant . . . . . . . . . . . . .
5.2.1 Lung homogenate of H1N1 infected Tmprss2-/- mice is less infectious than homogenate from wild type lungs . . . . . . . . . . . .
5.2.2 Tmprss2 -deficient mice are completely protected after H1N1 WSN
influenza virus infection . . . . . . . . . . . . . . . . . . . . . . .
5.2.3 Tmprss2 -deficient mice are not completely protected after H3N2
influenza virus infection . . . . . . . . . . . . . . . . . . . . . . .
5.3 FLT3 signaling is critical for the host response after Influenza A infection
40
6 Discussion & Perspectives
53
References
60
v
1
1
1
2
3
4
4
15
16
38
40
43
43
44
46
47
1 Introduction
Seasonal influenza, commonly called ”flu”, is caused by influenza viruses and poses a
serious threat to human health. In humans, the influenza virus infects the respiratory tract and typical symptoms include chills, fever, muscle pains, severe headache,
coughing, weakness and general discomfort (Behrens et al., 2006; Modrow et al., 2010).
The human influenza viruses are transmitted between people by inhaling droplets from
an infected person who is sneezing or coughing. Furthermore the transmission via
direct skin-to-skin contact or indirect contact with contaminated surfaces is possible
(Behrens et al., 2006; Neumann and Kawaoka, 2015). Infections with seasonal human
influenza viruses exhibit a low mortality rate in healthy individuals (Reid and Taubenberger, 2003; Taubenberger and Morens, 2008). In contrast, infections are more severe
in young children, elderly, people with respiratory and cardiac diseases as well as immunosuppressed people (Behrens et al., 2006; Taubenberger and Morens, 2008). Fatal
outcome is often associated with development of bacterial pneumonia (Boyd et al.,
2006).
Seasonal epidemics turn up every year, usually in the winter months in temperate
climates. Pandemic outbreaks caused by a new influenza substrain my occur at unpredictable intervals (Taubenberger and Morens, 2008; Taubenberger and Kash, 2010).
The Spanish influenza 1918 was the most severe pandemic when estimated 30 % of
the world’s population was infected and around 30-50 million people died (Simonsen,
1999; Taubenberger and Morens, 2008). In the last 100 years three further influenza
epidemics occurred: Asian influenza in 1957, Hong Kong influenza in 1968, Russian flu
1977 and Swine-origin influenza in 2009 (Kilbourne, 2006).
For a better control of influenza disease, basic and clinical research mostly focusses
on understanding epidemiology, pathogenicity, species-transmission as well as molecular determinants of the host defense and virus virulence.
1.1 Biology of influenza A virus
1.1.1 Aetiology and classification
Influenza viruses belong to the Orthomyxoviridae family and are grouped into the
three genera, Influenza virus A, Influenza virus B and Influenza virus C which differ
in their pathogenicity and host tropism. In contrast to influenza A viruses, type B
and C exclusively infect humans. Human influenza A and B cause seasonal epidemics.
However, influenza A virus (IAV) represents the most severe type, because it mutates
much faster than influenza B viruses. Large original reservoirs of IAVs exist in aquatic
birds of the order Anseriformes (ducks, geese, swans, etc.) and Charadriiformes (gulls,
terns, etc.). Apart from waterfowls, other birds and mammals can be infected. Based
on the two surface proteins hemagglutinin (HA) and neuraminidase (NA), IAVs are
classified into subtypes. A total of 16 HA (H1-H16) and 9 NA types (N1-N9) have
been found. Additionally, two new subtypes, denoted as H17 and H18 as well as
1
1.1
Biology of influenza A virus
N10 and N11, were recently discovered in bats (Tong et al., 2013). Two subtypes
are currently circulating in humans: H1N1 and H3N2. IAV isolates are named by
their strain, type (A, B or C), host, place of first isolation, number of the strain, year
of subtype isolation and antigenic subtype (Hay et al., 2001), for example, influenza
A/mallard/Memphis/123/95 (H5N1).
1.1.2 Structure of viral particle
Influenza viruses are roughly spherically or pleomorphically shaped with a diameter of
80-120 nm (Palese and Shaw, 2007; Bouvier and Palese, 2008; Modrow et al., 2010).
Viral particles are enveloped by a host cell-derived lipid membrane, in which three
proteins are embedded. The surface protein HA is a homotrimeric integral membrane
glycoprotein which is responsible for the attachment of the virus to sialic acids (SA)
moieties on the host cell surface. Cleavage of the inactive precursor HA0 into the
two active subunits HA1 and HA2 primes influenza HA fusion activity (reviewed by
Böttcher-Friebertshäuser et al. (2014)). The homotetrameric surface protein NA is able
to cleave SAs from glycolipids or glycoproteins. This function is essential to release
new virions which are attached to SAs from infected host cells (Palese et al., 1974).
Furthermore, the ion channel protein M2 is integrated in the envelope and is required
for influx of protons in the endosomes which results in a confirmational change of the
virus core and subsequent uncoating (Pinto et al., 1992). The matrix 1 protein (M1)
builds the inner surface of the virion and interacts with the cytoplasmic domains of
HA and NA proteins, as well as with viral ribonucleoprotein (vRNP) complexes. The
viral genome is covered by the nucleoprotein (NP) which mediates transport of RNPs
to the nucleus and controls viral genome replication (Nayak et al., 2004, 2009). Each
genomic segment is associated with three proteins: polymerase basic protein 1 and
2 (PB1 and PB2) and the polymerase acidic protein (PA). PB1 contains highly conserved motifs common to all RNA-dependent polymerases and both the PB1 and the
PB2 proteins are involved in the transcription. The PA induces proteolytic degradation
of coexpressed proteins and is suggested to be involved in the vRNA synthesis whereas
specific functions during the replication are not known yet (Huarte et al., 2001). Moreover, the nonstructural protein 1 (NS1) is involved in the transcription. It increases
the initiation of viral mRNA translation and, in addition the NS1, binds to double
stranded RNA to inhibit the activation of the host immune system (Hale et al., 2008).
The NS2 protein, which is also known as nuclear export protein (NEP), mediates the
export of newly produced RNPs out of the nucleus (Paterson and Fodor, 2012).
The entire IAV genome is 13,588 bases long and consists of eight negative-sense,
single-stranded viral RNA (vRNA) segments, which encode 11 open reading frames
(ORFs) (Figure 1) (Bouvier and Palese, 2008). The helical hairpin formed by the 3’ and 5’ - ends of the vRNA segments are non-coding. These regions include the mRNA
polyadenylation signal as well as packaging signals for the virus assembly and they
function as promoter for vRNA replication by the viral polymerase complex (Compans
et al., 1972; Murti et al., 1988).
2
1.1
Biology of influenza A virus
Figure 1: Influenza A virus virion (Source: Nelson and Holmes (2007)
1.1.3 Replication cycle
In the initial step of the influenza virus life cycle, HA binds to SA receptors on glycoproteins or glycolipids which are expressed on the host cell surface (Bouvier and
Palese, 2008; Taubenberger and Kash, 2010). The virion then enters the cell by endocytosis (Figure 2 (step 1)) (Lakadamyali et al., 2004). The low endosomal pH value in
endosomes triggers the conformational change in the HA and subsequently membrane
fusion activity. This results in release of vRNPs into the host cell cytoplasm and subsequent transport into the nucleus (Figure 2 (step 2)) (Stegmann, 2000; Sieczkarski and
Whittaker, 2005; Cros and Palese, 2003). In the nucleus the polymerase complex starts
to synthesize two positive-sense RNA species: mRNA templates for viral protein synthesis and complementary RNA (cRNA) as template for more copies of negative-sense,
genomic vRNA (Figure 2 (step 3)). PB1 and PB2 proteins use 5’-capped primers
from host mRNA transcripts. This cap-snatching mechanism initiates viral mRNA
synthesis and inhibits host cell translation and transcription. Viral mRNA segments
are exported and translated like host mRNAs (Figure 2 (step 4)) (Samji, 2009).
The envelope proteins HA, NA and M2 are translated on membrane-bound ribosomes. After translation, these proteins are transported to the endoplasmic reticulum
where folding and glycosylation (only HA and NA) take place (Figure 2 (step 5)). In
the Golgi apparatus envelope proteins are post-translational modified and directed to
the cell membrane for viral assembly via Golgi vesicles (Figure 2 (step 6)) (Samji,
2009).
Remaining viral proteins (PB1, PB2, PA, NP, NS1, NS2 and M1) are transported
back to the host nucleus where due to newly synthesized vRNAs, new vRNPs are
produced (Figure 2 (step 7)). Subsequently, vRNPs are coated with M1 proteins and
transported to the plasma membrane containing high amounts of envelope proteins
(Baudin et al., 2001; Boulo et al., 2007). Due to the accumulation of M1 protein at
3
1.2
Importance of host proteases for influenza virus infection
Figure 2: Replication cycle of influenza A virus (source: Neumann et al. (2009)
the cytoplasmic side of lipid bilayer, viral budding is initiated (Figure 2 (step 8)). The
cellular membrane protrudes and covers the nucleocapsid, and new virions bud from
the cell. The NA protein abrogate the interaction of HA with SA receptors and viral
particle can be released from the host cell (Figure 2 (step 9)) (Nayak et al., 2004).
1.2 Importance of host proteases for influenza virus infection
1.2.1 Proteolytic activation of the hemagglutinin
HA is necessary for viral infectivity, because it mediates viral attachment and fusion
with host cells. After assembly of new virions, the HA has to be activated to acquire its
membrane fusion potential. Therefore, host cell proteases have to cleave the precursor
protein HA0 into the two subunits HA1 and HA2 which remain covalently connected by
a disulfide bond (Klenk and Garten, 1994; Garten and Klenk, 1999; Steinhauer, 1999).
Cleavage site sequences determine which type of cellular host protease can cleave HA
(Horimoto and Kawaoka, 2005).
Already 20 years ago, a strict correlation between cleavage site and pathogenicity was reported for avian influenza viruses. Low pathogenic avian influenza viruses
(LPAIV) contain in their HA a monobasic cleavage site with either a single Arg or
Lys residue. Monobasic cleavage sites are cleaved by trypsin-like proteases which are
mainly expressed in the respiratory and gastrointestinal tract and monobasic viruses
therefore cause only local infections (Klenk and Garten, 1994; Garten and Klenk, 1999).
Highly pathogenic avian influenza viruses (HPAIV) contain a polybasic cleavage site
with the consensus motif R-X-R/K-R (Bosch et al., 1981; Webster and Rott, 1987;
Perdue et al., 1997). Polybasic motives can be recognized by eukaryotic subtilisin-like
4
1.2
proteases which are ubiquitously expressed. This allows HPIAV to spread systemically,
which is associated with a severe disease outcome (Stieneke-Grober et al., 1992). High
pathogenicity of HPIAV can be also caused by a lack of a carbohydrate side chain or
several amino acids close to the cleavage site, which increase the cleavability (Kawaoka
et al., 1984; Deshpande et al., 1987; Ohuchi et al., 1989, 1991; Skehel and Wiley, 2000).
1.2.2 Involvement of host proteases in the cleavage of mammalian influenza viruses
For quite some years, the host proteases of the respiratory tract are object of many in
vitro and in vivo studies. In the 1970s, cleavage of the HA0 by trypsin and trypsin-like
proteases as well as by some other proteases like akrosin and urokinase was detected
in vitro (Lazarowitz et al., 1973; Klenk et al., 1975). Until today, just few proteases
were described in vivo. The trypsin-like protease tryptase Clara was isolated from rat
bronchoalveolar lavage. Tryptase Clara can cleave HA from IAV and is inhibited by
the protease inhibitors aprotinin, leupeptin and lung surfactant (Kido et al., 1993).
Results from Sakai and colleagues suggested an increased activity of tryptase Clara
after infection with Sendai virus (murine parainfluenza virus type 1) in the rat respiratory tract (Sakai et al., 1994). Furthermore, the trypsin-like protease mini-plasmin,
which was extracted from rat lung tissue, is able to cleave HA of various IVA strains
in vitro (Murakami et al., 2001). The distinct expression of tryptase Clara and miniplasmin suggest that in different sections of respiratory tract several host proteases
might activate influenza viruses (Kido et al., 1992; Ogasawara et al., 1992; Murakami
et al., 2001; Towatari et al., 2002). However, the role of these two proteases in influenza
pathogenesis in vivo remains to be elucidated.
A severe progression of IAV infection is often associated with bacterial superinfections (Scheiblauer et al., 1992; Kuiken and Taubenberger, 2008). Tashiro and colleagues reported that certain bacteria, including Staphylococcus aureus and Aerococcus
viridans, are able to secrete influenza virus activating proteases. Because of this coinfected mice reveales a more severe IAV infection course than mice infected with only
one pathogen (Tashiro et al., 1987). Whether increased viral spread in humans is associated with the expression of HA-activating bacterial proteases by bacteria, remains
to be determined.
The laboratory strain A/WSN/33 (H1N1) was extensively passaged in different
animals. This virus is able to replicate in cultured cells in absence of exogenous trypsin
(Choppin, 1969; Castrucci and Kawaoka, 1993). In contrast to other human influenza
viruses, A/WSN/33 NA binds serum plasminogen which activates HA after conversion
to plasmin (Lazarowitz et al., 1973; Schulman and Palese, 1977; Goto and Kawaoka,
1998).
An in vitro study with primary human adenoid epithelial cells (HAECs) that simulate the upper respiratory tract of humans demonstrated cell-associated activation of
IAV by serine proteases (Zhirnov et al., 2002). In the following years the type II transmembrane serine proteases (TTSPs) were subject to many in vitro studies to identify
the responsible host proteases for human influenza virus.
5
1.2
1.2.3 Type II transmembrane serine proteases
Böttcher and colleagues reported that TTSPs might be host proteases which are responsible for activation of human influenza viruses and LPAIV. They showed in transfected
MDCK cells that TMPRSS2 (transmembrane serine protease 2) and TMPRSS11D
(HAT: human airway trypsin-like protease) can cleavage activate HA of human influenza viruses H1N1, H2N9 and H3N2 (Böttcher et al., 2006). A further member of
the TTSP family, TMPRSS4, was shown to cleave H1 in vitro (Chaipan et al., 2009;
Bertram et al., 2010). Apart from human influenza viruses, two members MSPL (mosaic serine protease large form) and its splice variant TMPRSS13 of the TTSP family
can activate HPAIVs with a low efficiency recognition site for furin (Okumura et al.,
2010). Other enveloped viruses are also cleaved by different members of the TTSP family. TMPRSS2 activates the human metapneumovirus (HMPV), which is necessary for
a multiplicative replication in target cells (Shirogane et al., 2008). In addition the coronavirus SARS-CoV spike protein is activated by TMPRSS2 (Matsuyama et al., 2010;
Shulla et al., 2011), and also TMPRSS11D enhances SARS-CoV entry (Kam et al.,
2009).
The TTSPs include 20 family members and possess a specific domain structure:
a short intracellular N-terminus, a transmembrane domain and a large extracellular
C-terminus (Figure 3). On the basis of protein domains at the C-terminus, TTSPs
are divided into four subfamilies: HAT/DESC subfamily including TMPRSS11D, hepsin/Tmprss subfamily including TMPRSS2 and TMPRSS4, matriptase subfamily and
corin subfamily (Szabo et al., 2003; Szabo and Bugge, 2008; Choi et al., 2009; Bertram
et al., 2010). The TTSPs are synthesized as zymogens and are activated by cleavage
of a highly conserved motif at the C-terminal into the mature form (Szabo and Bugge,
2008).
The protease family of TTSPs possesses important functions in embryonic development and mammalian tissue homeostasis. Furthermore, TTSP proteases are subject to
intensive studies regarding the involvement in several diseases, including cancer, due
to dysregulated expression. Because of over-expression in a great variety of tumors,
TTSPs are suggested as novel markers of tumor growth and possible targets for new
cancer therapies (Szabo and Bugge, 2008).
TMPRSS2
The TTSP family member TMPRSS2 (also known as epitheliasin) is localized on chromosome 21 (mouse: chromosome 16) and contains 14 exons and 13 introns (http:
//www.ensemble.org/index.html). Like other TTSPs, TMPRSS2 is synthesized as a
zymogen which needs to be proteolytically activated. Cleavage can result in release of
an enzymatically active protease into the extracellular space (Afar et al., 2001; Szabo
and Bugge, 2008). The soluble form possesses only minimal enzyme activity which
is not sufficient to support cleavage of influenza virus HA (Böttcher-Friebertshäuser
et al., 2013).
6
1.2
Figure 3: Domain organization of human TTSPs (source: Choi et al. (2009)
7
1.2
TMPRSS2 is highly expressed in prostate epithelial cells and lower levels of mRNA
have been found in epithelia of the gastrointestinal, urogenital and respiratory tracts
(Donaldson et al., 2002; Szabo et al., 2003; Szabo and Bugge, 2008). Furthermore,
TMPRSS2 expression was described in human bronchial epithelium, type II pneumocytes and alveolar macrophages (Bertram et al., 2010, 2012). Immuno-histochemical
studies showed expression of TMPRSS2 in cardiac myocytes, suggesting that it may
lead to influenza-associated myocarditis (Bertram et al., 2012). Donaldson and colleagues reported the regulatory function of TMPRSS2 for epithelial sodium channels
which control the airway surface liquid volume and therefore the efficiency of mucociliary clearance (Donaldson et al., 2002). In addition, a huge number of studies
investigated the association of TMPRSS2 in prostate carcinogenesis. TMPRSS2 is
overexpressed in prostate cancer tissue and chromosomal fusion of Tmprss2 gene with
genes encoding for ETS (E-twenty six) family transcription factors have been found
which are used as a prognostic marker of prostate carcinogenesis (Szabo et al., 2003;
Szabo and Bugge, 2008; Choi et al., 2009; Tomlins et al., 2009; Bertram et al., 2010).
Mice deficient in Tmprss2 developed normally, survived to adulthood with no differences in protein levels and exhibited no discernible abnormalities in organ histology
and function (Kim et al., 2006).
TMPRSS4
TMPRSS4 is localized on chromosome 11 (mouse: chromosome 9) and consists of 13
exons and 12 introns (http://www.ensemble.org/index.html). Several studies addressed the physiological role of TMPRSS4, but the specific role is still unclear. Three
substrates have been identified so far: HA of influenza virus (Bertram et al., 2010),
urokinase-type plasminogen activator (Min et al., 2014) and the epithelial sodium channel (Passero et al., 2012). An increased expression of TMPRSS4 was associated with
increased progression and metastatic potential of several cancers, including gastric,
liver, lung, ovarian, pancreatic and thyroid cancer (Choi et al., 2009; de Aberasturi
and Calvo, 2015). Min and colleagues reported that active TMPRSS4 protease domain can be released from cells in culture (Min et al., 2014) and therefore may be
suitable as biomarker for cancer diagnostics.
TMPRSS4 mRNA was detected in the gastrointestinal tract (esophagus, stomach,
small intestine and colon), urogenital tract (kidney and bladder), in mouse bronchiolaralveolar epithelial cells and in human lung tissue (Wallrapp et al., 2000; Planes et al.,
2005; Chaipan et al., 2009). In zebrafish embryos, TMPRSS4 is necessary for normal
organogenesis. Tmprss4 morpholino knock-down resulted in severe defects in tissue
development and cell differentiation (Ohler and Becker-Pauly, 2011). Interestingly,
Tmprss4 -deficient mice do not exert any obvious phenotype (unpublished data).
8
1.3
Treatment and prevention of influenza
TMPRSS11D
In humans, the TTSP family member TMPRSS11D is localized on chromosome
4 (mouse: chromosome 5) (http://www.ensemble.org/index.html). Originally,
TMPRSS11D was found in sputum of patients with chronic bronchitis and bronchial
asthma (Yasuoka et al., 1997). Different studies reported TMPRSS11D expression in
human trachea, larynx, bronchi, nasal epithelium, tongue, organs of the gastrointestinal tract, skin, testis and brain (Yasuoka et al., 1997; Böttcher et al., 2006; Szabo and
Bugge, 2008; Bertram et al., 2012).
The physiological role of TMPRS11D is still unknown.
Upregulation of
TMPRSS11D is connected with inflammatory processes (Iwakiri et al., 2004). In vitro
studies support a possible role for TMPRSS11D in respiratory homeostasis during immune reaction, because it can influence the capacity to increase mucin gene expression,
control fibrin deposition as well as stimulate bronchial fibroblast proliferation in epithelial cells (Miki et al., 2003; Chokki et al., 2004; Matsushima et al., 2006). Furthermore,
TMPRSS11D can cleave and inactivate the urokinase receptor (Upar) and thus impact
cell movement during airway inflammation (Beaufort et al., 2007). In chronic airway
diseases like asthma, high concentrations of TMPRSS11D are released into the airway
fluids (Yasuoka et al., 1997; Yamaoka et al., 1998; Szabo and Bugge, 2008).
Tmprss11d knock-out mice showed no defects in embryonic development, health and
long-term survival (Sales et al., 2011).
1.3 Treatment and prevention of influenza
Vaccination provides the most effective protection against seasonal influenza viruses.
Annual vaccine contains antigens from two influenza A viruses and one influenza B
virus of the most widespread strains. However, these vaccines fail to provide broadly
protective and long-lasting immunity. Also, they will not be effective against new
strain variants or zoonotic influenza viruses which may cause pandemics. However,
novel insights into the correlation of influenza protection and broadly B- and T-cell
protective immune response provided promising strategies for innovative vaccine development. Examples of new broadly acting antigen candidates represent conserved
surface antigens like epitopes in the NA and M2 protein or the stem region of the HA
protein (Reperant et al., 2014).
Furthermore, intervention with influenza virus replication cycle provides numerous
targets for new antiviral drugs. Present options to combat influenza virus infections
include only two classes of antiviral compounds. These drugs target viral entry and
release of new virions from infected cells. Amantadine and rimantadine block the M2
ion channel and thereby inhibit proton influx into the virus particle and uncoating of
the incoming virion (Hay et al., 1985). The M2 protein of influenza B viruses has a
different amino acid sequence (Pinto and Lamb, 2007). Therefore, amantanes are only
effective against influenza A viruses. These drugs have to be administered early after
9
1.3
Treatment and prevention of influenza
infection and are often associated with serious side effects. A further disadvantage of
using amantadine and rimantadine is the rapid occurrence of viral resistances (Monto
and Arden, 1992).
A second class of antivirals including zanamivir, oseltamivir and peramivir inhibits
the NA protein of IAV by preventing release of the influenza virus from infected cells.
NA inhibitors represent the most important tools for treating influenza A and B virus
infections (Mendel and Sidwell, 1998; Colman, 1999). However, rapid emergence of
resistant viral strains has also limited the use of NA inhibitors.
The limited number of antiviral drug targets emphasizes the urgent need for developing new antiviral strategies. Recent studies mainly include the improvement of
existing drugs which are directed against M2 and NA (Wei et al., 2011; Weight et al.,
2011; Lee et al., 2012). Other strategies inhibiting other antiviral targets in particular the viral RNA-dependent RNA polymerase (RdRP), NP and NS1 (Loregian et al.,
2014) are under development. Furthermore, combinatorial therapies targeting multiple
viral protein functions to achieve greater antiviral effects and to reduce the emergence
of drug resistances have been proposed (Ilyushina et al., 2006). In mice, the combined
use of amantadine and oseltamivir has shown synergism effects (Ilyushina et al., 2007).
IAV replication is strictly dependent on host functions, since a plethora of host proteins is required during the virus life cycle (Karlas et al., 2010; Konig et al., 2010). Targeting host proteins for antiviral strategies could avoid drug resistance. As described
above, host proteases are needed to cleavage activate the IAV HA. Therefore, protease
inhibitors have been investigated as potential anti-influenza agents (Kido et al., 2007).
For example, protease inhibitor aprotinin demonstrated anti-influenza activity in vitro,
in mice and also in humans (Zhirnov et al., 1984, 1996, 2002). Aprotinin is approved in
clinical practice to prevent post-operative bleeding. In Russia, clinical studies were performed on the usage of aprotinin to treat seasonal and swine-origin pandemic influenza
(Zhirnov et al., 2011). A further possible approach to inhibit viral-host interactions is
the removal of terminal SA residues from glycoproteins and glycolipids. A new drug
candidate is the recombinant fusion protein DAS181 (Fludase) that removes SA from
the receptors in the airway (Malakhov et al., 2006; Nicholls et al., 2013). Inhibitory
activity of DAS181 against many seasonal strains of IAV including oseltamivir-resistant
H1N1 could be demonstrated in preclinical studies (Nicholls et al., 2008; Triana-Baltzer
et al., 2009). In addition, after inhaling DAS181, a significant decrease of viral load
could be observed in influenza infected patients in a recent clinical study (Moss et al.,
2012). Importins and molecular chaperons may represent other antiviral targets due
to their function in nuclear translocation of vRNP components. Resa-Infante and coworkers reported enhanced survival and lower pathology of importin-α7-deficient mice
after H1N1 IAV infection (Resa-Infante et al., 2014).
Next to cell entry mechanisms, also host-signaling pathways are crucial for viral
replication. For example, members of the downstream mitogen-activated protein kinase
(MAPKs) pathway play a major role in vRNP trafficking (Marjuki et al., 2006). In
vivo inhibition of p38 MAPK reduced viral titer and increased survival after lethal
10
1.4
Mouse as a model for influenza research
infection with H5N1 IAV in mice. Furthermore, virus-induced cytokine expression
was diminished because p38 MAPK regulates IFN induction and controls signaling
(Börgeling et al., 2014). Inhibitors that block MAPKs signaling as well as the NFκB pathway are under development (Loregian et al., 2014). Cellular constituents are
used by influenza viruses to produce new RNAs, proteins, and lipid envelopes. For
this reason, strategies involving the host cell metabolism are another possibility for
the development of new antivirals. The lipid soluble mediator protectin D1 (PD1) was
reported to have anti-inflammatory and specific anti-influenza activity by blocking the
nuclear export of viral RNA molecules (Morita et al., 2013). Furthermore, induction of
cellular antiviral response by small molecules is subject of intensive research to find new
anti-influenza drugs. For example, short synthetic RNA molecules are substrates for
the host pathogen sensor RIG-I and showed the potential to induce a potent antiviral
response which inhibited virus replication (Ranjan et al., 2010; Goulet et al., 2013).
In the last years, research to identify novel host factors involved in influenza virus
replication increased constantly, because the possibility of blocking different viral and/or
host targets may allow the generation of novel antivirals.
1.4 Mouse as a model for influenza research
It is important to understand the mechanism of IAV infection and the course of disease
in the host. However, human individuals respond differently to IAV infection and in
vitro and in silico models are not able to simulate the human physiological and immunological complexity. A few studies used influenza-infected volunteers to observe the
symptomatic and virological aspects (Carrat et al., 2008; Huang et al., 2011), but ethical reasons limit extensive experiments in humans. Furthermore, the human population
exhibits a high genetic variability and environmental as well as individual parameters,
like preexisting illnesses, smoking and nutrition would need to be accounted for or to
be controlled in studies with humans. Because of this, animal models are essential to
understand host factors affecting influenza virus pathogenesis, transmission and immune response. Furthermore, animal models are important for pre-clinical testing to
assess the efficiency of therapeutic interventions (Thangavel and Bouvier, 2014). In
the past, several animal models have been established for influenza research including mice, cotton rats, syrian hamsters, guinea pigs, ferrets, dogs, cats, domestic swine
and non-human primates like rhesus, cynomolgus macaques and marmosets (Barnard,
2009; Tripp and Tompkins, 2009; Bouvier and Lowen, 2010; Eichelberger and Green,
2011; Moncla et al., 2013).
In 1933, influenza virus was isolated for the first time by filtering the throat washings of an influenza patient. The filtrate was then inoculated into the nares of ferrets,
which then expressed influenza-like illness (Smith, 1933; Evans, 1966). Because they
show similar disease symptoms as humans (fever, malaise, anorexia, coughing, nasal
secretion), ferrets are a valuable model for influenza research (Smith, 1933; Belser
et al., 2011). Next to clinical signs, another strength of the ferret model is their susceptibility to human IAV isolates without prior adaptation and airborne transmission
11
1.4
from one infected animal to another. On the other hand, the ferret model has disadvantages in high costs of housing, limited availability and few ferret-specific immunological
reagents. Furthermore, ferrets are outbred and thus not suitable for genetic studies
(van der Laan et al., 2008).
In contrast, the mouse model which was established in 1934 for influenza virus infections, has many advantages (Andrewes et al., 1934). Mice are small, easy to handle,
they breed very fast and costs for housing are relatively low. In addition, many wellcharacterized inbred mouse strains as well as a huge amount of research reagents are
available and allow highly reproducible studies (van der Laan et al., 2008). Inbred
strains show different susceptibility after IAV according to their genetic background,
virus strain and infection dose (Srivastava et al., 2009). Natural variation of the genetic
background of inbred strains provides an important resource to study complex diseases
involving interaction of multiple genes. Because many genes responsible for complex
diseases are homologues between mice and humans, the mouse model is crucial for the
identification of genetic risk factors in humans. Furthermore, spontaneous mutations
often cause phenotypes that mimic human genetic diseases (Simpson et al., 1997; Linder, 2001). In addition, a huge amount of knock-out, knock-in and transgenic mouse
strains are available for infection research. After infection with IAV, parameters like
body weight loss and survival, viral load in the lungs and lung pathology are commonly
monitored (Sidwell et al., 1999; Srivastava et al., 2009; Wilk and Schughart, 2012).
The main drawback of the mouse model is the difference in symptoms compared to
humans after an IAV infection, since they do not sneeze, cough or have fever. Typical
signs in influenza-infected mice are anorexia, lethargy, fur ruffling from lack of grooming, dehydration and restricted movements (Bouvier and Lowen, 2010; Belser et al.,
2011). Furthermore, the commonly used mouse strains C57BL/6 and BALB/c cannot
be infected directly with human influenza isolates (Bouvier and Lowen, 2010). Thus,
human IAV isolates have to be passaged serially through mouse lungs to adapt them
(Hirst, 1947; Tripp and Tompkins, 2009). However, not all IAV strains have to be
adapted. Notable exceptions are the 1918 H1N1, the 2009 pandemic H1N1 and several
avian influenza strains (e.g. H5N1) as well as the novel H7N9 virus that emerged in
China in 2013 (Bouvier and Lowen, 2010; Hai et al., 2013).
Genomes from humans and mice are 95% homologous (Gregory et al., 2002). Therefore, mice represent a perfect animal model to study gene functions whereby phenotyping of knock-out mice is one important methodology (Austin et al., 2004; Dinnyes and
Szmolenszky, 2005; Brown and Hancock, 2006). The two main methods to generate
knock-out mice are gene targeting and gene trapping (Guan et al., 2010). Gene targeting is the method of choice for site-directed mutagenesis to create loss-of function
(knock-out) mutants (Hogan and Lyons, 1988). As an alternative to gene targeting,
gene trapping as well as N-ethyl-N-nitrosourea (ENU) induced mutagenesis was developed and represent random mutation techniques (Kothary et al., 1988; Gossler et al.,
1989; Abuin et al., 2007). This gene targeting method is not specific and allows to
knock-out large numbers of genes in short time (Takeuchi, 1997; Zambrowicz et al.,
1998). The knock-out mouse project (KOMP) was initiated to knock out all mouse
12
1.4
genes creating convenient resources for the scientific research. Many gene approaches
have been developed for different targeting constructs that carry a deletion or insertion in the gene to be mutated and a region of homology which can recombine with
the targeted gene locus. Zinc-finger proteins and transcription activator-like effectors
(TALEs) with site-specific DNA-binding specificities increase the targeting efficiency
(Boch, 2011). The CRISPR/Cas system has been discovered recently and allows an
even more efficient gene editing and it is now possible to generate genetically engineered mice within weeks (Horvath and Barrangou, 2010; Wiedenheft et al., 2012).
This technique allows to target up to five genes simultaneously in ES cells to create
multiple knock-out mice in one step (Wang et al., 2013).
13
2 Objectives
Influenza epidemics and reoccurring pandemics are responsible for significant global
morbidity and mortality. Currently, only two therapies are approved to treat influenza
virus infections that target the viral proteins neuraminidase and M2. Due to the high
genetic variability of the influenza virus, selection pressure results rapidly in development of resistance. Therefore, a major emphasis of recent research is focusing on the
identification of host cell factors essential for the virus life cycle. These factors might
be suitable targets for novel antiviral therapies in humans.
One possible intervention would be to block host cell protease-mediated cleavage
of influenza virus hemagglutinin (HA). HA cleavage activation is necessary for viral
infectivity. In human and mice, several proteases, e.g. TMPRSS2, TMPRSS4 and
TMPRSS11D (HAT) have been shown to cleave influenza virus HA in vitro.
The main objective of my thesis was to analyze the role of the host cell proteases
TMPRSS2, TMPRSS4 and TMPRSS11D after influenza A virus infection in vivo using
mouse knock-out mutants.
Mice deficient for Tmprss2 and Tmprss4 should be analyzed after infection with
influenza A virus subtypes that are presently circulating in humans. Body weight
loss and survival, virus spread, HA cleavage as well as the lung pathology should be
examined to evaluate the role of TMPRSS2 and TMPRSS4 in cleavage activation, virus
replication and pathogenesis of H1N1 and H3N2. Therefore, single and double knockout Tmprss2 and Tmprss4 mice were be studied. Also, a third protease, TMPRSS11D,
should be studied in knock-out mice to assess its role for H3 viral pathogenesis in vivo.
In addition, pulse oximetry should be established as an additional measurement to
better follow the pathophysiology after influenza A virus infection in the mouse model.
14
3 Results
3.1 Manuscript I: TMPRSS2 is essential for Influenza H1N1 virus pathogenesis
in mice
Bastian Hatesuer1 , Stephanie Bertram1 , Nora Mehnert1 , Mahmoud M. Bahgat, Peter S. Nelson, Stefan Pöhlmann2 , Klaus Schughart2
1 These authors contributed equally to this work
2 SP and KS also contributed equally to this work
PLoS Pathog. 2013; 9(12): e1003774. doi: 10.1371/journal.ppat.1003774
Annual influenza epidemics and occasional pandemics pose a severe threat to human health. Host cell factors required for viral spread but not for cellular survival
are attractive targets for novel approaches to antiviral intervention. The cleavage activation of the influenza virus hemagglutinin (HA) by host cell proteases is essential
for viral infectivity. However, it is unknown which proteases activate influenza viruses
in mammals. Several candidates have been identified in cell culture studies, leading
to the concept that influenza viruses can employ multiple enzymes to ensure their
cleavage activation in the host. Here, we show that deletion of a single HA-activating
protease gene, Tmprss2, in mice inhibits spread of mono-basic H1N1 influenza viruses,
including the pandemic 2009 swine influenza virus. Lung pathology was strongly reduced and mutant mice were protected from weight loss, death and impairment of lung
function. Also, after infection with mono-basic H3N2 influenza A virus body weight
loss and survival was less severe in Tmprss2 mutant compared to wild type mice. As
expected, Tmprss2 -deficient mice were not protected from viral spread and pathology
after infection with multi-basic H7N7 influenza A virus. In conclusion, these results
identify TMPRSS2 as a host cell factor essential for viral spread and pathogenesis of
mono-basic H1N1 and H3N2 influenza A viruses.
15
3.2
Manuscript II: Tmprss2 and Tmprss4 facilitate proteolytic activation of H3N2 Influenza A virus
hemagglutinin in mice
3.2 Manuscript II: Tmprss2 and Tmprss4 facilitate proteolytic activation of
H3N2 Influenza A virus hemagglutinin in mice
Nora Kühn1 , Ruth L. O. Stricker1 , Silke Bergmann2 , Nadine Kasnitz3 , Anna Keppner4 ,
Siegfried Weiß3 , Edith Hummler4 , Bastian Hatesuer1¶ , Klaus Schughart1,2¶*
Author affiliations:
1
Department of Infection Genetics, Helmholtz Centre for Infection Research, University
of Veterinary Medicine Hanover, 38124 Braunschweig, Germany
2
Department of Microbiology, Immunology and Biochemistry, University of Tennessee
Health Science Center, 38163 Memphis, USA
3
Department of Molecular Immunology, Helmholtz Centre for Infection Research, 38124
Braunschweig, Germany
4
Department of Pharmacology and Toxicology, University of Lausanne, 1005 Lausanne,
Switzerland
*
Corresponding author
E-mail: [email protected]
¶
These authors contributed equally.
Submitted
Abstract
Cleavage of influenza virus hemagglutinin (HA) by host cell proteases is necessary for
viral activation and infectivity. In humans and mice, several candidate proteases, e.g.
TMPRSS2, TMPRSS4 and TMPRSS11d (HAT) have been shown to cleave influenza
virus HA in vitro and may thus represent suitable targets for therapeutic intervention. Recently, we reported that inactivation of a single HA-activating protease gene,
Tmprss2, in knock-out mice inhibits spread of H1N1 influenza viruses. However, after
infection of Tmprss2 knock-out mice with H3N2 only a slight increase was observed in
survival and mice still lost body weight. In this study, we investigated an additional
trypsin-like protease, TMPRSS4. Both TMPRSS2 and TMPRSS4 are expressed in the
same cell types of the mouse lung. Deletion of Tmprss4 alone in knock-out mice does
not protect them from body weight loss and death upon infection with H3N2 influenza
virus. In contrast, Tmprss2-/- Tmprss4-/- double knock-out mice showed a strongly reduced virus spread and lung pathology in addition to reduced body weight loss and
mortality. Thus, our results identified TMPRSS4 as a second host cell protease that,
in addition to TMPRSS2, is able to cleavage activate the HA of H3N2 influenza virus
HA in vivo.
16
3.2
Author summary
Influenza epidemics and reoccurring pandemics are responsible for significant global
morbidity and mortality. Due to high variability of the virus genome, resistance to
available antiviral drugs is frequently observed and new targets for treatment of influenza are needed. Host cell factors essential for processing of the virus hemagglutinin
represent very suitable drug targets because the virus is dependent on these host factors for replication. We reported previously that Tmprss2 -deficient mice are protected
against H1N1 virus infections, but only slight protection against H3N2 was observed.
Here, we show that deletion of two host proteases, Tmprss2 and Tmprss4, reduced
viral spread as well as lung pathology strongly and resulted in increased survival after
H3N2 infection. Thus, TMPRSS4 represents another host cell factor that is involved
in cleavage activation of H3N2 Influenza viruses in vivo.
Introduction
Influenza viruses pose major threats to public health as they are responsible for epidemics and pandemics resulting in high morbidity and mortality worldwide. Several
pandemics such as the Spanish flu (1918), Asian flu (1957) and Hong Kong flu (1968)
caused millions of deaths in the last century (Cox and Subbarao, 2000). Furthermore, hundreds of thousands people die from seasonal influenza infections every year
(http://www.who.int). Currently, only two therapies targeting the viral proteins
neuraminidase and M2 are approved to treat influenza. Therefore, novel viral or host
targets for antiviral strategies blocking viral replication or inhibiting cellular proteins
necessary for the virus life cycle are urgently needed (Loregian et al., 2014). Host
proteases represent a very promising group for antiviral targets. Proteolytic cleavage
of the precursor hemagglutinin (HA0 ) into HA1 and HA2 subunits by proteases of the
host is essential for fusion of HA with the endosomal membrane and thus represents an
essential step for infectivity of the virus (Klenk et al., 1975; Lazarowitz and Choppin,
1975). The majority of influenza viruses, including low pathogenic avian and human
influenza viruses, carry a single arginine (R) residue at the cleavage site. These HAs
are cleaved by host trypsin-like proteases (Steinhauer, 1999; Murakami et al., 2001;
Towatari et al., 2002; Kido et al., 2007). In vitro studies with cultured human respiratory epithelium cells demonstrated the involvement of several membrane-associated
proteases (Zhirnov et al., 2002). Cell culture studies further identified transmembrane
serine proteases TMPRSS2, TMPRSS4 and TMPRSS11D (transmembrane protease,
serine 2; transmembrane protease, serine 4; transmembrane protease, serine 11d) as
enzymes being able to cleave the HA of H1 and H3 influenza virus subtypes (Böttcher
et al., 2006; Bertram et al., 2010; Böttcher-Friebertshäuser et al., 2011). We previously
showed that deletion of Tmprss2 in knock-out mice strongly limits viral spread and
lung pathology after H1N1 influenza A virus infection (Hatesuer et al., 2013). An essential role for TMPRSS2 in cleavage activation and viral spread was also reported for
H7N9 influenza A virus (Sakai et al., 2014; Tarnow et al., 2014). We also demonstrated
that deletion of Tmprss2 slightly reduced body weight loss and mortality in mice after
17
3.2
H3N2 infection compared to wild type mice but did not protect mice from lethal infections (Hatesuer et al., 2013). Therefore, in addition to TMPRSS2 other trypsin-like
proteases of the respiratory tract are able to cleave the hemagglutinin of H3 influenza
virus subtypes.
In this study, we investigated the role of Tmprss4 in the context of influenza A virus
replication and pathogenesis in experimentally infected mice. We showed that knockout of Tmprss4 alone did not protect mice from lethal H3N2 influenza A infections.
In contrast, Tmprss2-/- Tmprss4-/- double knock-out mice showed a massively reduced
viral spread and lung pathology and also reduced body weight loss and mortality.
Results
Tmprss2 and Tmprss4 are co-expressed in alveolar and bronchial regions
It was described previously that Tmprss2 is expressed in type II pneumocytes and
bronchial epithelium (Bertram et al., 2012), the main target cells for influenza A viruses
(Koerner et al., 2012; Weinheimer et al., 2012). TMPRSS4 is an additional protease
with in vitro HA cleavage potential (Chaipan et al., 2009; Bertram et al., 2010). Therefore, we examined the expression profile of Tmprss4 in mouse lung tissues. We performed in-situ hybridization (ISH) analyses to differentiate between alveolar epithelial
cells type I (AECI) and type II (AEC II) in non-infected mouse lungs. As shown in
Fig. 1A, round and mostly cuboidal shaped AECII were detected by expression of the
cell-type specific marker surfactant associated protein C (Sftpc, stained blue). Thin
and flat AECI cells could be identified by expression of the cell-type specific marker
aquaporin 5 (Aqp5, stained red). In addition we used immunohistochemical staining to
detect expression of both proteases Tmprss2 and Tmprss4. Staining in cuboidal and
granular cells of alveolar tissue representing AECII cells (Fig. 1B) as well as in the
bronchiolar epithelium (Fig. 1C) could be observed.
18
3.2
Figure 1: Tmprss2 and Tmprss4 are expressed in bronchial and alveolar regions. In-situ hybridization of lung slides from non-infected C57BL/6J lungs with probes specific for AECI (Aqp5 ) and
AECII (Sftpc) (A; bright field: left, fluorescence: right, magnification: 20x). In both images, AECI
(Aqp5 ) were stained in red and AECII (Sftpc) in blue. Cryo-sections of lungs from non-infected
C57BL/6J mice were stained for TMPRSS2 (red) and TMPRSS4 (blue) (B, C, magnification: 40x).
Tmprss2 and Tmprss4 were co-expressed in round, granular and roughly cuboidal shaped cells in
the alveolar region (B) and in bronchial epithelium cells (C).
19
3.2
Deletion of Tmprss4 does not affect body weight loss and viral replication in H1N1 and
H3N2 infected mice
We used mice carrying a deletion in the Tmprss4 gene to study the role of TMPRSS4
during influenza infection in vivo. RT-PCR analysis of knock-out lung tissue confirmed
the absence of full length Tmprss4 transcript (S1 Fig.). Tmprss4 -deficient mice showed
normal reproduction rates, development and growth patterns and no obvious abnormal
phenotype (unpublished data).
Wild type as well as Tmprss4-/- mice were infected with mouse-adapted PR8M
(A/PuertoRico/8/34, H1N1). Both, wild type and Tmprss4-/- mice lost weight after
infection to the same degree and with comparable courses. They also showed similar mortality rates (Fig. 2A). Similar results were obtained after infection with two
additional H1N1 virus variants (PR8F, A/WSN/33, S2A-B Fig.) and after infection
with a multi-basic, mouse-adapted H7N7 virus (SC35M, A/Seal/Massachusetts/1/80,
S2C Fig.). After infection with 2x103 Focus Forming Units (FFU) of mouse-adapted
H3N2 virus (A/HongKong/01/68 (Haller et al., 1979) body weight loss and survival
was not different between the two mouse strains (Fig. 2B). Also no statistic significant
difference was observed after infection with a lower dose (10 FFU) of H3N2 virus (Fig.
2C). Measurement of viral loads in lungs of infected mice revealed similar viral loads in
wild type and Tmprss4 knock-out mice at days 2, 3, and 4 p.i. (Fig. 3). These results
showed that loss of Tmprss4 in knock-out mice does not protect mice from virus replication, spreading or pathogenesis after infection with H3N2 or H1N1 influenza virus in
comparison to wild type mice.
20
3.2
Figure 2: Tmprss4-/- mice are not resistant to H1N1 and H3N2 infection. Eight to eleven weeks
old female mice were infected with 2x105 FFU mouse-adapted PR8M (A/PuertoRico/8/34; A)
or 2x103 FFU mouse-adapted H3N2 (A/HongKong/01/68; B) and 10 FFU H3N2 (C) influenza
virus by intra-nasal application. Body weight loss was monitored until day 14 p.i. Mice with a
weight loss of more than 30% of the starting bodyweight were euthanized and recorded as dead.
Weight loss data represent mean values +/- SEM. No differences in body weight loss were observed
between knock-out and wild type mice.
21
3.2
Figure 3: Tmprss4 knock-out mice show similar viral loads in lungs as wild type mice after
H3N2 influenza A virus infection. Eight to eleven weeks old female mice were infected with
2x103 FFU mouse-adapted H3N2 influenza virus by intra-nasal application and infectious particles
were determined in lung homogenates. Individual values, mean and SEM are presented. Viral load
was not significant different in infected wild type compared to infected homozygous mutant mice
at days 2 to 4 p.i.
Tmprss2-/- Tmprss4-/- double knock-out mice are protected from severe pathogenesis and
showed reduced virus replication after H3N2 infection
Since both Tmprss2 and Tmprss4, are able to cleave H3 hemagglutinin in vitro and
are expressed in influenza virus target cells, we hypothesized that H3N2 virus may
be processed by both TTSPs in vivo. Therefore, we generated Tmprss2-/- Tmprss4-/double knock-out mice and infected them with 2x103 FFU H3N2 virus. Indeed, infected
double mutant mice showed significant less and delayed loss of body weight compared
to wild type mice as well as to Tmprss2-/- and Tmprss4-/- single knock-out mice (Fig.
4A). Furthermore, viral load was lower in double knock-out mice than in wild-type
mice after infection with 2x103 FFU H3N2 at days 2 to 8 p.i. (Fig. 4B). However, this
difference was not statistical significant. In bronchoalveolar lavage (BAL), less H3 as
well as processed HA1 was detected in infected double knock-out mice compared to
wild type mice (S3 Fig.). In addition, the weight of wild type lungs increased stronger
between days 2 to 8 post infection compared to knock-out lungs (Fig. 4C) indicating
less infiltration of immune cells and accumulation of fluid in alveoli. After infection
with H3N2, the peripheral blood revealed similar degrees of lymphopenia during the
first two days p.i. in both wild type and knock-out mice, followed by an increase of
lymphocytes in both knock-out and wild type mice (Fig. 4D). Similar granulocytosis
was observed in both strains on days 2 to 6 p.i. However, the relative number of
granulocytes increased to higher levels in wild type mice compared to double knockout mice (Fig. 4D). Also, granulocyte numbers remained high at later time points
in the wild type which can be interpreted as a typical indicator for severe influenza
infection (Fig. 4D) (Dengler et al., 2014).
22
3.2
Figure 4: Tmprss2-/- Tmprss4-/- double knock-out mice show reduced body weight loss and mortality after infection with H3N2 influenza A virus infection. Eight to eleven weeks old
female mice were infected with 2x103 FFU mouse-adapted H3N2 influenza virus by intra-nasal
application and body weight and survival (A) was monitored until day 14 p.i. In addition to mice
that were found dead, mice with a weight loss of more than 30% of the starting body weight
were euthanized and recorded as dead. Infectious particles were determined in lung homogenates
(B); individual values, mean and SEM are presented. Relative lung weight was determined by
weighing freshly prepared lungs and determining the percent ratio of lung weight to body weight;
individual values, mean and SEM are shown (C). Hematological parameters in blood were measured with the VetScan HM5 system and kinetics of absolute numbers of white blood cells (WBC),
lymphocytes (Lym), monocytes (Mon) and granulocytes (Gr) were determined (D). Homozygous
Tmprss2-/- Tmprss4-/- knock-out mice lost significantly less body weight than wild type mice (e.g. p
<0,0001 at day 2, and p <0,0001 at day 4, using Mann-Whitney-U test); Tmprss2-/- and Tmprss4-/mice showed significantly reduced mortality compared to wild type mice (p <0,0001 , using log rank
test) as well as to the single knock-out mice. Data for Tmprss2-/- mice in (A) and (B) were taken
from Hatesuer et al. (2013) and are included for comparison with Tmprss4-/- and double knock-out
mice. Viral load was higher in infected wild type mice compared to infected homozygous mutant
mice at days 2, 4 and 6 p.i. However, this difference was not statistically significant. At day 8 p.i.
all wild type mice died or had to be euthanized. Furthermore, lung weights were higher in infected
wild type mice compared to infected Tmprss2-/- Tmprss4-/- knock-out mice. In the hemograms,
lymphocyte numbers decreased until day 2 p.i., and granulocytes increased in wild type mice on
day 2 p.i. and in Tmprss2-/- Tmprss4-/- knock-out mice to a lesser degree.
23
3.2
Immuno-histochemical analyses of viral antigen on day 2 p.i. revealed similar spread
of infection in bronchiolar epithelial cells in wild type and Tmprss2-/- Tmprss4-/- mice
(Fig. 5 A,B). However, on day 2 p.i. H3N2 virus was detected in alveolar regions of wild
type lungs whereas no spreading of virus to these lung regions occurred in double knockout mice (Fig. 5 C,D). On day 6 p.i. mutant lungs showed limited virus spreading in
alveolar cells (Fig. 5 F) indicating that virus is still replicating and continues to spread
in double knock-out. Wild type lungs showed a strong increase in lung infiltrates at
day 6 p.i. and hemorrhages as well as edema were observed (Fig. 5 E,G). In contrast,
less infiltrates and reduced pathogenesis could be found in Tmprss2-/- Tmprss4-/- lungs
(Fig. 5 F,H).
Discussion
Seasonal influenza viruses as well as new emerging subtypes pose a major threat to
human health. Influenza viruses are dependent on host cell factors for cell entry and
replication. The identification of such host factors and the understanding of their role
during influenza life cycle is of great importance for the development of novel therapeutic targets. Proteolytic cleavage of influenza virus HA by host proteases may
represent a suitable process for intervention. In particular host proteases that exhibit
trypsin-like activity, such as TMPRSS2, TMPRSS4, TMPRSS11D (HAT), ST14 (matriptase), KLK5, KLK12, TMPRSS11E (DESC1) and TMPRSS13 (MSPL) were shown
to cleave influenza virus HAs with a monobasic cleavage site and support multi-cycle
virus replication in cell culture (Böttcher et al., 2006; Chaipan et al., 2009; Hamilton et al., 2012; Hamilton and Whittaker, 2013; Zmora et al., 2014). On the other
hand, the trypsin-like proteases prostasin, hepsin, TMPRSS3, TMPRSS6, TMPRSS9,
TMPRSS10, TMPRSS11B and TMPRSS11F did not activate HA upon co-expression
in mammalian cells (Bertram et al., 2010; Böttcher-Friebertshäuser et al., 2010; Zmora
et al., 2014).
We showed previously that TMPRSS2 is required for H1 cleavage activation in vivo
(Hatesuer et al., 2013). Tmprss2-/- mutant mice are completely protected from mortality after infection with several H1N1 viruses (Hatesuer et al., 2013). In addition,
infection with 10 FFU A/HK/01/68 (H3N2) virus, which also carries a mono-basic
cleavage site in the HA, resulted in reduced body weight loss and lower mortality in
Tmprss2-/- mice compared to wild type mice. However, this difference was less pronounced after infection with increased virus dose. Therefore, we investigated whether
a further protease may also be involved in cleavage activation of H3N2 viruses.
Here, we showed for the first time that H3 hemagglutinin can recruit different host
proteases for cleavage activation. Deletion of Tmprss4-/- alone in single knock-out mice
did not have a significant effect with respect to body weight loss, survival or pathology.
However, deletion of both Tmprss2-/- and Tmprss4-/- in double-knock out mice strongly
and significantly improved morbidity and survival after H3N2 infection. Nevertheless
infected mice still showed limited body weight loss indicating residual activity and
spreading of viral particles.
24
3.2
Figure 5: Tmprss2-/- Tmprss4-/- double knock-out mice exhibit milder lung pathology and reduced viral spread into alveolar regions after infection with H3N2 virus. Eight to
eleven weeks old female mice were infected with 2x103 FFU mouse-adapted H3N2 influenza virus by
intra-nasal application. Serial lung sections were stained on day 2, 4 and 6 p.i. with anti-influenza
antibody and haematoxylin (A-F) or with haematoxylin/eosin (G-H). Magnification: A-B, E-H
10x and C-D 40x. On day 2 p.i. virus-infected cells were observed mainly in bronchiolar regions of
knock-out mice and in bronchiolar as well as alveolar regions in wild type mice (A-D). Both wild
type and mutant mice showed viral spreading into alveolar regions on day 6 p.i. However, in wild
type lungs the tissue was more densely consolidated with higher numbers of infiltrating immune
cells compared to Tmprss2-/- Tmprss4-/- knock-out mice (E-J). Furthermore, hemorrhages as well
as edema were observed in C57BL/6J infected lungs indicating more severe pathology (G-H).
25
3.2
Several studies have addressed the physiological role of TMPRSS4 so far and three
specific substrates could been identified: HA of influenza virus (Bertram et al., 2010),
urokinase-type plasminogen activator (PLAU) (Min et al., 2014) and the epithelial
sodium channel (SCNN1A) (Passero et al., 2012). An increased expression of Tmprss4-/was associated with increased progression and metastatic potential of several cancers
(de Aberasturi and Calvo, 2015). TMPRSS4 transcripts were detected in the gastrointestinal tract (esophagus, stomach, small intestine and colon), the urogenital tract
(kidney and bladder), in mouse bronchiolar-alveolar epithelial cells and in human lung
tissue (Wallrapp et al., 2000; Planes et al., 2005; Chaipan et al., 2009). In lung tissue, TMPRSS2 expression was described in human bronchial epithelium, AECII cells
and alveolar macrophages (Bertram et al., 2010, 2012). We confirmed expression of
Tmprss2-/- and Tmprss4-/- in the alveolar region and bronchial epithelium cells of
murine lungs. Both proteases were co-expressed in granular and roughly cuboidal
shaped cells, representing AECII cells. In other studies, influenza A virus antigens
were detected almost exclusively in AECII cells and to a lower degree in alveolar
macrophages (Koerner et al., 2012; Weinheimer et al., 2012). This co-localization of
host proteases and virus strongly suggests that both proteases may be involved in HA
maturation.
It should be noted, that deletion of Tmprss2-/- did not change the tropism of H3N2
virus infection in mice. This is consistent with the observation that both proteins are
expressed in the same cell types. Thus, after removal of Tmprss2-/- alone, Tmprss4-/is still able to activate HA of H3N2 viruses. Only after deletion of both proteases, survival rate increased due to reduced viral load in lungs. Although virus replication was
decreased, we still observed processed HA protein, viral spreading and pathology. From
these data we conclude, that in addition to TMPRSS2 and TMPRSS4 further proteases
are able to cleave and activate the hemagglutinin of H3N2. Different proteases were
shown to activate H3 in vitro (Böttcher et al., 2006; Hamilton et al., 2012; Hamilton
and Whittaker, 2013; Zmora et al., 2014). Transmembrane protease, serine 11d (TMPRSS11D; HAT) is mainly expressed in murine trachea and bronchi and is thought to
cleave HA mainly in the upper regions of the lower respiratory tract (Hansen et al.,
2004; Sales et al., 2011; Tarnow et al., 2014). Furthermore, kallikrein-related peptidase
5 (KLK5) was described to cleave H1 and H3 HA (Hamilton and Whittaker, 2013),
tryptase beta 2 (TPSB2; tryptase Clara) was reported to cleave H3 (Kido et al., 2007),
and suppression of tumorigenicity 14 (colon carcinoma) (ST14; matriptase) cleaves H3
to a certain degree (Hamilton et al., 2012). A recent study also reported that the host
proteases transmembrane protease, serine 11e (TMPRSS11E; DESC1) and transmembrane protease, serine 13 (TMPRSS13; MSPL) are capable of cleaving H1, H2 and H3
HA in vitro (Zmora et al., 2014).
In summary, our in vivo results provide further important insights into the involvement of host proteases for influenza HA processing. We validated proteases as
important targets for the development of new influenza antiviral drugs. Several broad
spectrum protease inhibitors have been reported to block influenza virus in cell culture
and in vivo (Zhirnov et al., 1984; Zhirnov, 1987; Ovcharenko and Zhirnov, 1994; Bah-
26
3.2
gat et al., 2011; Zhirnov et al., 2011). However, treatment of patients with such broad
inhibitors may cause considerable side effects. Tmprss4-/- and Tmprss2-/- Tmprss4-/mice are healthy and do not show any obvious phenotype in the absence of infection.
Thus, specific inhibition of these proteases would be more appropriate for treating an
acute influenza infection. Our studies suggest that an inhibitor targeting TMPRSS2
and TMPRSS4 would be well suitable to block replication of H1N1 and, to a major
degree, H3N2 influenza infections, which represent the majority of seasonal subtypes
infecting humans each year. It should, however, be noted that our results were obtained in the mouse model and the development or use of any potential inhibitor will
require validation studies in humans.
Materials and Methods
Virus, mice and plasmids
Original stocks of viruses were obtained from Stefan Ludwig, University of Münster
(PR8M, A/PuertoRico/8/34 H1N1, Münster Variant; A/WSN/33 H1N1), from Peter
Stäheli, University of Freiburg (PR8F, A/PuertoRico/8/34 H1N1, Freiburg variant,
SC35M A/Seal/Massachusetts/1/80 (H7N7) (Gabriel et al., 2005; Hoffmann et al.,
2000) and from Otto Haller, University of Freiburg (A/Hong Kong/01/68, (Haller
et al., 1979)). The low virulent H1N1 mouse-adapted virus PR8M and the high virulent
mouse-adapted H1N1 PR8F virus isolates have been described previously (Blazejewska
et al., 2011). Virus stocks for all infections were prepared by infection of 10-day-old
embryonated chicken eggs. Knock-out mice were generated by using a replacement
vector targeting the Tmprss4 gene in 129SVEV ES cells. Germline chimeras were
obtained and crossed to Flp-mice and Nestin-CRE deleter mice. Homozygous knockout mice were then backcrossed to C57BL/6J for seven generations to generate the
knock-out strain B6;129-Tmprss4tm1.1Hum (Tmprss4-/- ) used in our studies. Mutant
Tmprss4-/- mice were maintained on a mixed C57BL/6J (95%) – 129 (5%) background.
Homozygous mutant mice were genotyped by PCR analysis. Genotyping of Tmprss4
alleles was carried out using a three primer strategy (P1 5’GGT CAG ATG TAA
AAG GTA GAC3’, P2 5’GCT AGG TTC CTT GTT CCT G3’, P3 5’ CAT GGA
TGT GAC CAT TGT GC3’) that allowed to distinguish between wild type (yielding a
200 bp product) and knock-out (yielding a 500 bp product) alleles, respectively (unpublished data). Double knock-out B6.129S1-Tmprss2tm1Tsyk Tmptss4tm1.1Hum mice were
generated by interbreeding of Tmprss2-/- and Tmprss4-/- homozygous mice. B6.129S1Tmprss2tm1Tsyk mice were described previously (Hatesuer et al., 2013; Kim et al., 2006).
As controls, C57BL/6J mice were obtained from Janvier, France.
RNA isolation, purification and RT-PCR analysis
Total RNA was prepared from lungs using the RNeasy Midi Kit (Qiagen, Hilden,
Germany) following the manufacturer’s protocol. cDNA was synthetized using the
27
3.2
BioscriptTM (Bioline GmbH, Germany). Subsequently, Taq polymerase (REDTaq,
Sigma-Aldrich) and gene-specific primers (exon 4: P1 5’CAG TTG TGT GAC GGC
CAC3’, exon 11: P2 5’CAC AGC ATC TCA GCG GTC A3’) were used for PCR
amplification of the Tmprss4-/- specific gene fragment.
Infection of mice and measurement of body weight and survival
For infection experiments, female mice at the age of 8-11 weeks were anesthetized
by intra-peritoneal injection of ketamin-xylazine solution (85% NaCl [0.9%], 10% ketamine, 5% xylazine; 200 µl per 20g body weight). Infection was performed by intranasal application of virus solution in 20 µl of sterile phosphate-buffered saline. Subsequently, survival and body weight loss were monitored until day 14 p.i. In addition
to mice that were found dead, mice with a weight loss of more than 30% of the starting
body weight were euthanized and recorded as dead.
Determining infectious particles
Viral load in infected lungs was determined on MDCK II (Madin-Darby Canine Kidney
II) cells using the FFU assay as described earlier (Blazejewska et al., 2011). The
detection limit of the assay was 80 infectious particles/lung. Thus, for samples where
no virus was detected, data points were set to 80 FFU/lung.
Hematology
For monitoring of hematological parameters, hearts were punctuated and blood was
collected in EDTA tubes. Numbers of lymphocytes (Lym), granulocytes (Gr) and
monocytes (Mon) in the blood were determined immediately using the hematologic
system VetScan HM5 (Abaxis).
Immunohistochemical, immunofluorescence analyses and in-situ hybridization
Lungs were prepared and immersion-fixed for 24 hours in 4% buffered formaldehyde
solution (pH 7.4), dehydrated in a series of graded ethanol and embedded in paraffin.
Sections (0.5 µm) were cut from three evenly distributed levels of paraffin blocks and
stained with haematoxylin and eosin. For immunohistochemical studies, sections were
stained overnight at 4 ◦ C with a primary antibody against influenza A virus nucleoprotein (clone hb65; ATCC, Wessel, Germany). Subsequently, tissue sections were
incubated for 30 min with HRP-labeled goat-anti-mouse IgG2a (Biozol) and counterstained with haematoxylin (Rimmelzwaan et al., 2001). For immunofluorescence
analyses, 12 µm thick cryo-sections were air-dried, fixed in acetone at −20 ◦ C and rehydrated in PBS. Slides were blocked with anti-FCR (1:500, purified rat anti-mouse
CD16/CD32). Primary antibodies used were: rabbit anti-TMPRSS4 polyclonal antibody AF350 conjugated (Bioss) and rabbit anti-TMPRSS2 antibody Cy5 conjugated
(antikoerper-online.de). After staining, the slides were washed with PBS, dried and
28
3.2
mounted with Neo-Mount (Merck, Darmstadt, Germany). Analyses were performed
using a Zeiss LSM510 laser scanning microscope with a 40x oil immersion objective.
For in-situ hybridization (ISH) studies of alveolar epithelial cells type I (AECI) and
alveolar epithelial cells type II (AEC II) 5 µm thick formalin-fixed, paraffin-embedded
lung tissue sections were used with the QuantiGene ViewRNA ISH Tissue Assay kit
(Affymetrix, Cleveland, OH) following the manufacturer’s instructions. TYPE6 (Sftpc
for AECII) and TYPE1 (Aqp5 for AECI) QuantiGene View RNA probes were generated, based on Affymetrix probesets. Gen Bank Accession number for TYPE6 (Sftpc):
NM 011359, region 2-784; for TYPE1 (Aqp5): NM 009701, region 239-1533. Pretreatment was performed for 10 min at 90 − 95 ◦ C and protease digestion for 20 min at
40 ◦ C. Slides were stained with Fast red for TYPE1 probes. TYPE6 probes were detected with Fast blue. Slides were then counterstained with Gill’s Hematoxylin. A
negative control (antisense) was run in parallel and showed no hybridization signals
(not shown) (Gen Bank Accession number TYPE1 (Sftpc-neg): region 23-803 covered
by probeset NM 011359-N; TYPE1 (Aqp5-neg): region 172-1122 covered by probeset
NM 009701-N). Bright field images were recorded using Aperio Scanscope and analyzed with Aperio Imagescope software. For detection of fluorescence images, the Zeiss
LSM710 laser scanning microscope was used with a 20x objective.
Western Blot
Broncho-alveolar lavage (BAL) samples were prepared on day 1 and 3 p.i. and mixed
with 2x SDS gel-loading buffer, heated to 95 ◦ C for 2 min, sonicated for 5 min and centrifuged for 2 min at 16,000xg. The supernatant was loaded onto a SDS-polyacrylamide
gel (5% stacking gel, 12% resolving gel) and the protein samples were separated for
45 min with 230 V. Subsequently, protein samples were transferred to a membrane
TM
R
(Immobilon
Transfer membrane, Merck Millipore) in a Mini Trans-Blot
Electrophoretic Transfer cell system for 1 h at 100 V. The membrane was incubated with
blocking buffer (5% non-fat dry milk powder dissolved in TBST) for 30 min and subsequently with primary antibody (1:10000 in TBST, rabbit polyclonal antibody to
H3N2 HA, Sino Biological Inc. and 1:3000, rabbit polyclonal antibody to Influenza
virus NP antibody, GeneTex) over night. After 3 washing steps with TBST, the membrane was placed in HRP-conjugated anti-rabbit secondary antibody (1:10000 in TBST,
Anti-Rabbit IgG, Sigma-Aldrich) for 90 min. The membrane was washed three times
with TBST and incubated with substrate (Immobilon Western Chemiluminescent HRP
Substrate, Merck Millipore). Positive signals from the membrane were recorded with
a FujiFilm LAS-3000 documentation system.
Acknowledgements
We would like to thank the animal caretakers at the Central Animal Facilities at the
HZI for maintaining the mice for this study, Karin Lammert and Heike Petrat for
excellent technical assistance. Original stocks of influenza A viruses were obtained
from Peter Stäheli (University of Freiburg), Stefan Ludwig (University of Münster)
29
3.2
and Otto Haller (University of Freiburg). The work described here was part of a PhD
thesis work by NK at the University of Veterinary Medicine Hannover, Germany.
Supporting information
S1: Figure 6 - Genomic PCR confirms deletion of Tmprss4 locus.
S2: Figure 7 - Tmprss4-/- mice were not resistant to H1N1 and H7N7 influenza virus
infection.
S3: Figure 8 - The hemagglutinin of H3N2 influenza virus was processed in BAL of
Tmprss2-/- Tmprss4-/- knock-out mice.
30
3.2
Figure 6: Genomic PCR confirms deletion of Tmprss4 locus. RNA was extracted from Tmprss4-/and C57BL/6J lungs and amplified by RT-PCR. As negative control, no RNA was used in the
reverse transcriptase reaction. The deletion of exon 8 and 9 results in a shorter fragment (563 bp)
in Tmprss4-/- mice. In lungs from wild type mice the full length fragment (890 bp) from exon 4
up to exon 9 was obtained. The size of bands was determined using the 2 log DNA ladder (NEB).
31
3.2
Figure 7: Tmprss4-/- mice were not resistant to H1N1 and H7N7 influenza virus infection. Eight
to eleven weeks old female mice were infected with 2x103 FFU mouse-adapted PR8F (H1N1; A)
and 2x103 FFU WSN (H1N1; B) or 2x104 FFU mouse-adapted SC35M (H7N7; C) influenza virus.
Body weight loss was monitored until day 14 p.i. Mice with a weight loss of more than 30% of
the starting bodyweight were euthanized and recorded as dead. Weight loss data represent mean
values +/- SEM. No significant differences in body weight loss were observed between knock-out
and wild type mice.
32
3.2
Figure 8: The hemagglutinin of H3N2 influenza virus was processed in BAL of
Tmprss2-/- Tmprss4-/- knock-out mice. BAL from infected wild type and Tmprss2-/- Tmprss4-/female mice was harvested at day 1 and day 3 after infection with 2x103 FFU mouse-adapted H3N2.
As negative controls, BAL from mock-infected mutant and control mice were prepared at day 3.
The samples were mixed with the loading buffer and loaded undiluted. BAL samples were then
analyzed for HA by Western blots. In the BAL from knock-out mice lower amounts of viral proteins
were detected reflecting lower viral loads measured in the FFU assay. However, HA was still processed. As a loading control, a membrane with the same samples was incubated with anti-influenza
NP antibody confirming that equal amounts of protein were loaded for knock-out and wild type
mice.
33
Manuscript II References
Bahgat, M. M., P. Blazejewska, and K. Schughart (2011). Inhibition of lung serine
proteases in mice: a potentially new approach to control influenza infection. Virol
J 8, 27.
Bertram, S., I. Glowacka, I. Steffen, A. Kuhl, and S. Pohlmann (2010). Novel insights
into proteolytic cleavage of influenza virus hemagglutinin. Rev Med Virol 20 (5),
298–310.
Bertram, S., A. Heurich, H. Lavender, S. Gierer, S. Danisch, P. Perin, J. M. Lucas,
P. S. Nelson, S. Pohlmann, and E. J. Soilleux (2012). Influenza and sars-coronavirus
activating proteases tmprss2 and hat are expressed at multiple sites in human respiratory and gastrointestinal tracts. PLoS One 7 (4), e35876.
Blazejewska, P., L. Koscinski, N. Viegas, D. Anhlan, S. Ludwig, and K. Schughart
(2011). Pathogenicity of different pr8 influenza a virus variants in mice is determined
by both viral and host factors. Virology 412 (1), 36–45.
Böttcher, E., T. Matrosovich, M. Beyerle, H. D. Klenk, W. Garten, and M. Matrosovich
(2006). Proteolytic activation of influenza viruses by serine proteases tmprss2 and
hat from human airway epithelium. J Virol 80 (19), 9896–8.
Böttcher-Friebertshäuser, E., C. Freuer, F. Sielaff, S. Schmidt, M. Eickmann, J. Uhlendorff, T. Steinmetzer, H. D. Klenk, and W. Garten (2010). Cleavage of influenza virus
hemagglutinin by airway proteases tmprss2 and hat differs in subcellular localization
and susceptibility to protease inhibitors. J Virol 84 (11), 5605–14.
Böttcher-Friebertshäuser, E., D. A. Stein, H. D. Klenk, and W. Garten (2011). Inhibition of influenza virus infection in human airway cell cultures by an antisense
peptide-conjugated morpholino oligomer targeting the hemagglutinin-activating protease tmprss2. J Virol 85 (4), 1554–62.
Chaipan, C., D. Kobasa, S. Bertram, I. Glowacka, I. Steffen, T. S. Tsegaye, M. Takeda,
T. H. Bugge, S. Kim, Y. Park, A. Marzi, and S. Pohlmann (2009). Proteolytic
activation of the 1918 influenza virus hemagglutinin. J Virol 83 (7), 3200–11.
Cox, N. J. and K. Subbarao (2000). Global epidemiology of influenza: past and present.
Annu Rev Med 51, 407–21.
de Aberasturi, A. L. and A. Calvo (2015). Tmprss4: an emerging potential therapeutic
target in cancer. Br J Cancer 112 (1), 4–8.
Dengler, L., N. Kühn, D. L. Shin, B. Hatesuer, K. Schughart, and E. Wilk (2014). Cellular changes in blood indicate severe respiratory disease during influenza infections
in mice. PLoS One 9 (7), e103149.
34
Gabriel, G., B. Dauber, T. Wolff, O. Planz, H. D. Klenk, and J. Stech (2005). The
viral polymerase mediates adaptation of an avian influenza virus to a mammalian
host. Proc Natl Acad Sci U S A 102 (51), 18590–5.
Haller, O., H. Arnheiter, and J. Lindenmann (1979). Natural, genetically determined
resistance toward influenza virus in hemopoietic mouse chimeras. role of mononuclear
phagocytes. J Exp Med 150 (1), 117–26.
Hamilton, B. S., D. W. Gludish, and G. R. Whittaker (2012). Cleavage activation of
the human-adapted influenza virus subtypes by matriptase reveals both subtype and
strain specificities. J Virol 86 (19), 10579–86.
Hamilton, B. S. and G. R. Whittaker (2013). Cleavage activation of humanadapted influenza virus subtypes by kallikrein-related peptidases 5 and 12. J Biol
Chem 288 (24), 17399–407.
Hansen, I. A., M. Fassnacht, S. Hahner, F. Hammer, M. Schammann, S. R. Meyer,
A. B. Bicknell, and B. Allolio (2004). The adrenal secretory serine protease asp is
a short secretory isoform of the transmembrane airway trypsin-like protease. Endocrinology 145 (4), 1898–905.
Hatesuer, B., S. Bertram, N. Mehnert, M. M. Bahgat, P. S. Nelson, S. Pohlman, and
K. Schughart (2013). Tmprss2 is essential for influenza h1n1 virus pathogenesis in
mice. PLoS Pathog 9 (12), e1003774.
Hoffmann, E., J. Stech, I. Leneva, S. Krauss, C. Scholtissek, P. S. Chin, M. Peiris, K. F.
Shortridge, and R. G. Webster (2000). Characterization of the influenza a virus gene
pool in avian species in southern china: was h6n1 a derivative or a precursor of h5n1?
J Virol 74 (14), 6309–15.
Kido, H., Y. Okumura, H. Yamada, T. Q. Le, and M. Yano (2007). Proteases essential
for human influenza virus entry into cells and their inhibitors as potential therapeutic
agents. Curr Pharm Des 13 (4), 405–14.
Kim, T. S., C. Heinlein, R. C. Hackman, and P. S. Nelson (2006). Phenotypic analysis
of mice lacking the tmprss2-encoded protease. Mol Cell Biol 26 (3), 965–75.
Klenk, H. D., R. Rott, M. Orlich, and J. Blodorn (1975). Activation of influenza a
viruses by trypsin treatment. Virology 68 (2), 426–39.
Koerner, I., M. N. Matrosovich, O. Haller, P. Staeheli, and G. Kochs (2012). Altered
receptor specificity and fusion activity of the haemagglutinin contribute to high virulence of a mouse-adapted influenza a virus. J Gen Virol 93 (Pt 5), 970–9.
Lazarowitz, S. G. and P. W. Choppin (1975). Enhancement of the infectivity of influenza a and b viruses by proteolytic cleavage of the hemagglutinin polypeptide.
Virology 68 (2), 440–54.
35
Loregian, A., B. Mercorelli, G. Nannetti, C. Compagnin, and G. Palu (2014). Antiviral
strategies against influenza virus: towards new therapeutic approaches. Cell Mol Life
Sci.
Min, H. J., M. K. Lee, J. W. Lee, and S. Kim (2014). Tmprss4 induces cancer cell
invasion through pro-upa processing. Biochem Biophys Res Commun 446 (1), 1–7.
Murakami, M., T. Towatari, M. Ohuchi, M. Shiota, M. Akao, Y. Okumura, M. A.
Parry, and H. Kido (2001). Mini-plasmin found in the epithelial cells of bronchioles
triggers infection by broad-spectrum influenza a viruses and sendai virus. Eur J
Biochem 268 (10), 2847–55.
Ovcharenko, A. V. and O. P. Zhirnov (1994). Aprotinin aerosol treatment of influenza
and paramyxovirus bronchopneumonia of mice. Antiviral Res 23 (2), 107–18.
Passero, C. J., G. M. Mueller, M. M. Myerburg, M. D. Carattino, R. P. Hughey,
and T. R. Kleyman (2012). Tmprss4-dependent activation of the epithelial sodium
channel requires cleavage of the gamma-subunit distal to the furin cleavage site. Am
J Physiol Renal Physiol 302 (1), F1–8.
Planes, C., C. Leyvraz, T. Uchida, M. A. Angelova, G. Vuagniaux, E. Hummler,
M. Matthay, C. Clerici, and B. Rossier (2005). In vitro and in vivo regulation
of transepithelial lung alveolar sodium transport by serine proteases. Am J Physiol
Lung Cell Mol Physiol 288 (6), L1099–109.
Rimmelzwaan, G. F., T. Kuiken, G. van Amerongen, T. M. Berstebroer, and R. A.
Fouchier (2001). Pathogenesis of influenza a (h5n1) virus infection in a primate
model. J Virol 75, 6687–6691.
Sakai, K., Y. Ami, M. Tahara, T. Kubota, M. Anraku, M. Abe, N. Nakajima,
T. Sekizuka, K. Shirato, Y. Suzaki, A. Ainai, Y. Nakatsu, K. Kanou, K. Nakamura, T. Suzuki, K. Komase, E. Nobusawa, K. Maenaka, M. Kuroda, H. Hasegawa,
Y. Kawaoka, M. Tashiro, and M. Takeda (2014). The host protease tmprss2 plays a
major role in in vivo replication of emerging h7n9 and seasonal influenza viruses. J
Virol 88 (10), 5608–16.
Sales, K. U., J. P. Hobson, R. Wagenaar-Miller, R. Szabo, A. L. Rasmussen, A. Bey,
M. F. Shah, A. A. Molinolo, and T. H. Bugge (2011). Expression and genetic loss
of function analysis of the hat/desc cluster proteases tmprss11a and hat. PLoS
One 6 (8), e23261.
Steinhauer, D. A. (1999). Role of hemagglutinin cleavage for the pathogenicity of
influenza virus. Virology 258 (1), 1–20.
Tarnow, C., G. Engels, A. Arendt, F. Schwalm, H. Sediri, A. Preuss, P. S. Nelson,
W. Garten, H. D. Klenk, G. Gabriel, and E. Böttcher-Friebertshäuser (2014). Tmprss2 is a host factor that is essential for pneumotropism and pathogenicity of h7n9
influenza a virus in mice. J Virol.
36
Towatari, T., M. Ide, K. Ohba, Y. Chiba, M. Murakami, M. Shiota, M. Kawachi,
H. Yamada, and H. Kido (2002). Identification of ectopic anionic trypsin i in rat
lungs potentiating pneumotropic virus infectivity and increased enzyme level after
virus infection. Eur J Biochem 269 (10), 2613–21.
Wallrapp, C., S. Hahnel, F. Muller-Pillasch, B. Burghardt, T. Iwamura, M. Ruthenburger, M. M. Lerch, G. Adler, and T. M. Gress (2000). A novel transmembrane
serine protease (tmprss3) overexpressed in pancreatic cancer. Cancer Res 60 (10),
2602–6.
Weinheimer, V. K., A. Becher, M. Tonnies, G. Holland, J. Knepper, T. T. Bauer,
P. Schneider, J. Neudecker, J. C. Ruckert, K. Szymanski, B. Temmesfeld-Wollbrueck,
A. D. Gruber, N. Bannert, N. Suttorp, S. Hippenstiel, T. Wolff, and A. C. Hocke
(2012). Influenza a viruses target type ii pneumocytes in the human lung. J Infect
Dis 206 (11), 1685–94.
Zhirnov, O. P. (1987). High protection of animals lethally infected with influenza virus
by aprotinin-rimantadine combination. J Med Virol 21 (2), 161–7.
Zhirnov, O. P., M. R. Ikizler, and P. F. Wright (2002). Cleavage of influenza a virus
hemagglutinin in human respiratory epithelium is cell associated and sensitive to
exogenous antiproteases. J Virol 76 (17), 8682–9.
Zhirnov, O. P., H. D. Klenk, and P. F. Wright (2011). Aprotinin and similar protease
inhibitors as drugs against influenza. Antiviral Res 92 (1), 27–36.
Zhirnov, O. P., A. V. Ovcharenko, and A. G. Bukrinskaya (1984). Suppression of
influenza virus replication in infected mice by protease inhibitors. J Gen Virol 65 (
Pt 1), 191–6.
Zmora, P., P. Blazejewska, A. S. Moldenhauer, K. Welsch, I. Nehlmeier, Q. Wu,
H. Schneider, S. Pohlmann, and S. Bertram (2014). Desc1 and mspl activate influenza a viruses and emerging coronaviruses for host cell entry. J Virol 88 (20),
12087–97.
37
3.3
Manuscript III: Cellular changes in blood indicate severe respiratory disease during influenza infections
in mice
3.3 Manuscript III: Cellular changes in blood indicate severe respiratory disease
during influenza infections in mice
Leonie Dengler, Nora Kühn, Dai-Lun Shin, Bastian Hatesuer, Klaus Schughart and
Esther Wilk
PLoS One. 2014; 9(7): e103149. doi: 10.1371/journal.pone.0103149
Influenza A infection is a serious threat to human and animal health. Many of the
biological mechanisms of the host-pathogen-interactions are still not well understood
and reliable biomarkers indicating the course of the disease are missing. The mouse
is a valuable model system enabling us to study the local inflammatory host response
and the influence on blood parameters under controlled circumstances. Here, we compared the lung and peripheral changes after PR8 (H1N1) influenza A virus infection
in C57BL/6J and DBA/2J mice using virus variants of different pathogenicity resulting in non-lethal and lethal disease. We monitored hematological and immunological
parameters revealing that the granulocyte to lymphocyte ratio in the blood represents
an early indicator of severe disease progression already two days after influenza A infection in mice. These findings might be relevant to optimize early diagnostic options
of severe influenza disease and to monitor successful therapeutic treatment in humans.
38
4 Contribution to manuscripts
Manuscript I: TMPRSS2 is essential for Influenza H1N1 virus pathogenesis in mice
For this manuscript, I performed the majority of the experimental studies. I analyzed
virus replication by foci assay, antibody titer against viral proteins by ELISA and
oxygen saturation by pulse oximetry after H1N1 infection. Furthermore, I prepared
the lungs for histopathological analyses. I infected Tmprss2-/- and Tmprss2+/+ mice
with H3N2, observed body weight loss and survival and determined viral load in the
lungs. In addition, I contributed to the writing of the manuscript.
Manuscript II: Tmprss2 and Tmprss4 facilitate proteolytic activation of H3N2 Influenza
A virus hemagglutinin in mice
I was centrally involved in the study design and performed the majority of experiments.
I infected the mice and determined body weight loss and survival, viral load and lung
immunohistochemical analysis. Furthermore I performed the RT-PCR analysis, immunofluorescence staining of lungs and the western blot. I prepared all figures, legends
and wrote the manuscript draft.
Manuscript III: Cellular changes in blood indicate severe respiratory disease during
influenza infections in mice
For this manuscript, I established the arterial oxygen saturation measurement. I infected DBA/2J and C57BL/6J mice with H1N1 influenza A virus and determined the
oxygen saturation during the whole infection process and prepared the appropriate
figure.
39
5 Unpublished Data
5.1 TMPRSS11D is involved in cleavage activation of H3N2 hemagglutinin in
mice
Introduction
We reported previously that the deletion of Tmprss2 in mice protects the host against
virus spread and lung pathology after H1N1 influenza virus infection (Hatesuer et al.,
2013). In addition, TMPRSS2 is responsible for the cleavage activation of H7N9
(Tarnow et al., 2014; Sakai et al., 2014). Furthermore, TMPRSS2 and TMPRSS4
can activate H3, as we detected a strongly reduced viral spread and lung pathology
as well as reduced mortality in double knock-out mice after H3N2 infection (unpublished data). This study also showed that Tmprss2-/- Tmprss4-/- mice are not fully protected against H3N2 infection indicating the involvement of further proteases. Bertram
and colleagues demonstrated co-expression of TMPRSS2 and TMPRSS11D in type 2
pneumocytes whereas TMPRSS11D was expressed at a lower level in these cell types
(Bertram et al., 2012). Furthermore, TMPRSS11D was expressed in epithelial cells
of the trachea and occasionally in type I pneumocytes. Also, cleavage of influenza
virus HA from H1N1 and H3N2 subtypes and multicycle virus replication in vitro were
demonstrated (Böttcher et al., 2006). The results from in vitro studies and expression
of TMPRSS11D in influenza target cells suggest its participation in H3 cleavage activation in vivo. To address the involvement of TMPRSS11D in vivo, I analyzed pathology
in Tmprss11d-/- knock-out mice.
Materials & Methods
Infection of mice and measurement of body weight loss and survival. Mutant FVBTmprss11d-/- mice were generated as described previously (Sales et al., 2011). Genotyping of the mice was performed by Southern blot (Sales et al., 2011). As controls,
FVB/NRj mice were obtained from Janvier, France. For infection experiments, female mice at the age of 8-11 weeks were anesthetized by intra-peritoneal injection of
Ketamin-Xylazine solution in sterile NaCl (50 mg/ml Ketamine, Invesa Arzneimittel
GmbH, Freiburg; 2 % Xylazine, Bayer Health-Care, Leverkusen) with a dose adjusted
to the individual body weight. Infection was performed by intranasal application of
virus solution in 20 µl of sterile phosphate-buffered saline. Subsequently, survival and
body weight loss were monitored until day 14 p.i. In addition to mice that were found
dead, mice with a weight loss of more than 30% of the starting body weight were
euthanized and recorded as dead.
Determining infectious particles. Viral load in infected lungs and tracheas was determined on MDCK II (Madin-Darby Canine Kidney II) cells using the FFU assay as
described earlier (Blazejewska et al., 2011). The detection limit of the assay is at 80
infectious particles/lung. Thus, the data points were set to 80 FFU/lung for samples
with no virus detected.
40
5.1
TMPRSS11D is involved in cleavage activation of H3N2 hemagglutinin in mice
Results & Discussion
In absence of infection, Tmprss11d-deficient mice exhibit normal reproduction, development and growth patterns (Sales et al., 2011).
The mouse-adapted PR8M virus (A/PuertoRico/8/34 H1N1, Münster variant
(Blazejewska et al., 2011)) was inoculated intranasally into wild type and Tmprss11d-/mice. All FVB/NRj and Tmprss11d-/- mice lost weight after infection without any significant difference in weight loss curve and survival (Figure 4A). After infection with
10 FFU of H3N2 virus (A/HongKong/01/68 (Haller et al., 1979)), mortality was significantly decreased (p-value: 0,041 using Mann Whitney U test) in Tmprss11d-/- mice
compared to wild type mice (Figure 4B). However, no significant difference in body
weight loss was detected. After increasing the infection dose of mouse-adapted H3N2
virus (2x103 FFU), both mouse strains lost weight and reached critical weight within
5 up to 7 days. Body weight loss and survival were not significantly different between
wild type and Tmprss11d-/- mice at this infection dose (Figure 4C).
To follow up the observed difference in survival, we investigated hematological parameters in peripheral blood as an indicator for the inflammatory host response and
disease progression (Dengler et al., 2014). After infection with 10 FFU H3N2, no difference in the ratio of granulocytes to lymphocytes was observed at any time point
(Figure 5A). In addition a similar viral load in lungs of wild type mice and Tmprss11d
knock-out mice was observed (Figure 5B).
From these results, we conclude that TMPRSS11D also participates in the processing of H3N2 HA in vivo. Nevertheless, the tissue-specificity of TMPRSS11D activation
and biological significance still remains unclear. Sales and co-workers revealed high expression of Tmprss11d gene transcripts in murine and human trachea and only a minor
signal in lungs (Sales et al., 2011). Therefore, I hypothesize that the main tissue of
cleavage activation by TMPRSS11D is in trachea, whereby TMPRSS2 and TMPRSS4
cleave H3 in lung tissue. To validate this theory, further experiments are planned.
41
5.1
TMPRSS11D is involved in cleavage activation of H3N2 hemagglutinin in mice
Figure 4: Tmprss11d-deficient mice show reduced mortality after infection with 10 FFU H3N2
influenza A virus. Eight to eleven weeks old female mice were infected with 2x105 FFU PR8M
H1N1 (A), 10 FFU (B) and 2x103 FFU (C) mouse-adapted H3N2 influenza virus by intra-nasal
application. Body weight loss was monitored until day 14 p.i. Mice with a weight loss of more
than 30 % of the starting bodyweight were euthanized and recorded as dead. Weight loss data
represent mean values +/- SEM. After infection with H1N1 no differences in body weight loss and
survival were observed (A). No differences in body weight loss were recorded between Tmprss11d-/and wild type mice after infection with 10 FFU of H3N2 (B). However, mortality was significantly
decreased (p-value: 0.041, using Log-Rank test) in Tmprss11d-/- mice compared to wild type mice
(B). After increasing the infection dose to 2x103 FFU H3N2, no difference in body weight loss and
survival was detected (C).
42
5.2
Additional results for Tmprss2 knock-out mutant
Figure 5: Hemogram of peripheral blood and viral load in the lungs of Tmprss11d-/- mice after
infection with H3N2 influenza A virus. Eight to eleven weeks old female mice were infected
with 10 FFU mouse-adapted H3N2 influenza virus by intra-nasal application. Hematological parameters in the heart blood were measured with the VetScan HM5 system and the normalized
ratio of granulocytes to lymphocytes (ratio(dx)=([granulocytes(dx)]/[lymphocytes[dx])/ratio(d0))
was calculated from absolute cell counts (A). The granulocyte to lymphocyte ratio exhibited no
differences between Tmprss11d-/- mice and the control mice. Infectious particles were determined
in lung homogenates. Individual values, mean and SEM are presented (B). Viral load was not
significantly different in infected wild type mice compared to infected homozygous mutant mice at
days 1 to 5 p.i.
5.2 Additional results for Tmprss2 knock-out mutant
5.2.1 Lung homogenate of H1N1 infected Tmprss2-/- mice is less infectious than
homogenate from wild type lungs
Deletion of Tmprss2 in mice strongly limits viral spread and lung pathology after
H1N1 influenza infection. After infection with H1N1 PR8M virus, only non-processed
HA0 protein was detected in mutants whereas the cleavage product HA1 was found in
infected wild type mice (Hatesuer et al., 2013). To further validate the lack of cleavage
activation in knock-out mice, I inoculated highly susceptible DBA/2J mice with lung
homogenates from infected Tmprss2-/- mice.
Material & Methods
Mouse infections. Five female Tmprss2-/- and Tmprss2+/+ mice at the age of 8-11
weeks were anesthetized by intra-peritoneal injection of Ketamin-Xylazine solution in
sterile NaCl (50 mg/ml Ketamine, Invesa Arzneimittel GmbH, Freiburg; 2 % Xylazine,
Bayer Health-Care, Leverkusen) with a dose adjusted to the individual body weight.
Infection of 2x105 FFU H1N1 PR8M was performed by intranasal application of virus
solution in 20 µl of sterile phosphate-buffered saline. One day p.i. lungs were harvested,
homogenized and five female DBA/2J mice at the age of 9 weeks were infected with
lung homogenates from Tmprss2-/- and Tmprss2+/+ mice. Subsequently, survival and
body weight loss were monitored until day 14 p.i. In addition to mice that were found
dead, mice with a weight loss of more than 30 % of the starting body weight were
euthanized and recorded as dead.
43
5.2
Figure 6: Highly susceptible DBA/2J mice survived infection with Tmprss2-/- lung homogenate.
9 weeks old DBA/2J were infected with 20 µl lung homogenates from H1N1 infected Tmprss2-/and Tmprss2+/+ mice by intra-nasal application. Survival and body weight loss were monitored
until day 14 p.i. Mice with a weight loss of more than 30 % of the starting body weight were
euthanized and recorded as dead. After infection with H1N1 with mutant and wild type lung
homogenate weight loss was significant different between both groups. Survival was significantly
increased in DBA/2J infected with mutant lung homogenate (p-value: 0.0035, Log-rank Test).
DBA/2J mice are highly susceptible to IAV infection. For infection with H1N1 PR8M
(A/PuertoRico/8/34 H1N1 Münster variant (Blazejewska et al., 2011)), the LD50 is 20
FFU (Srivastava et al., 2009). Lung homogenates of PR8M infected Tmprss2-/- and
Tmprss2+/+ mice were inoculated intranasally into DBA/2J mice. DBA/2J infected
with Tmprss2+/+ lung homogenate lost weight rapidly and died within 9 days p.i. In
contrast, body weight loss in DBA/2J mice that were infected with lung homogenates
of Tmprss2-/- mice started two days later and 80 % of infected DBA/2J mice regained
body weight after 11 days and survived (Figure 6).
These results confirm the low infectivity of lung homogenates from H1N1 IAV infected Tmprss2-/- mice. After infection of Tmprss2 -deficient mice with PR8M H1N1
virus, no processing of the HA0 was detected in BAL, but an initial increase in virus
titers was detected in the first two days p.i. Virus used for infection had been grown in
embryonated chicken eggs whereby HA could be activated and passed one replication
cycle. Lung homogenates were taken at day 1 p.i. with 2x105 FFU PR8M H1N1.
Thus, also remaining activated virus from the initial infection could cause the weight
loss in DBA/2J mice. However, the amount of infectious particles in Tmprss2-/- lung
homogenates was presumably lower than 20 FFU, resulting in a sublethal infection for
DBA/2J mice.
5.2.2 Tmprss2 -deficient mice are completely protected after H1N1 WSN influenza
virus infection
The laboratory strain A/WSN/33 (H1N1) is also able to enhance proteolytic activation
of the HA via its NA protein. In contrast to other human influenza viruses, A/WSN/33
NA binds serum plasminogen which activates HA after being converted to plasmin
44
5.2
Figure 7: TMPRSS2 is essential for spread and pathogenesis of H1N1 A/WSN/33 virus. Eight
to eleven weeks old female mice were infected with 2x103 FFU A/ WSN/33 influenza virus by
intra-nasal application. Body weight loss was monitored until day 14 p.i. Mice with a weight loss
of more than 30 % of starting bodyweight were euthanized and recorded as dead. Weight loss data
represent mean values +/- SEM. After infection with H1N1 WSN body weight loss was significantly
different in wild type and homozygous mutant mice.
(Lazarowitz et al., 1973; Schulman and Palese, 1977; Goto and Kawaoka, 1998). To
further investigate this possibility, I infected Tmprss2 -deficient mice with A/WSN/33
H1N1.
Material & Methods
Infection of mice. Female mice at the age of 8-11 weeks were anesthetized by intraperitoneal injection of Ketamin-Xylazine solution in sterile NaCl (50 mg/ml Ketamine,
Invesa Arzneimittel GmbH, Freiburg; 2 % Xylazine, Bayer Health-Care, Leverkusen)
with a dose adjusted to individual body weight. Infection was performed by intranasal
application of virus solution in 20 µl of sterile phosphate-buffered saline.
Upon intranasal infection of Tmprss2-/- and Tmprss2+/+ mice with WSN, wild type
mice lost weight significantly whereas mutant mice did not exhibit body weight loss
and showed no signs of disease (Figure 7). A special characteristic of A/WSN/33 is
the ability to replicate in cultured cells in the absence of exogenous trypsin (Choppin,
1969; Castrucci and Kawaoka, 1993). A/WSN/33 NA could recruit plasminogen, which
activates HA upon transformation to plasmin(Goto and Kawaoka, 1998). However, in
my studies, I could show that in the absence of TMPRSS2, A/WSN/33 virus is not
able to cause a severe infection course in mice. These results demonstrate that plasmin
alone is not sufficient to efficiently cleave HA of A/WSN/33 in mouse lung tissue and
that HA is primarily cleaved by TMPRSS2.
45
5.2
5.2.3 Tmprss2 -deficient mice are not completely protected after H3N2 influenza virus
infection
We demonstrated that Tmprss2-/- mice exhibit slightly reduced body weight loss
and mortality compared to wild type mice after infection with 2x103 FFU H3N2
(A/HongKong/01/68 (Haller et al., 1979)). However, viral load in lungs was not different between mutant and wild type mice. After decreasing infection dose to 10 FFU
of H3N2, Tmprss2 -deficient mice showed no body weight loss and no further sigh of
disease. In contrast, wild type lost body weight and 30 % of mice succumbed as
consequence of infection (Hatesuer et al., 2013).
To determine whether the different outcome in body weight loss and survival after
infection with 10 FFU H3N2 was also reflected by decreased lung pathology, I compared
viral load in lungs of Tmprss2 -deficient and wild type mice.
Material & Methods
Infection of mice. Female mice at the age 8-11 weeks were anesthetized by intraperitoneal injection of Ketamin-Xylazine solution in sterile NaCl (50 mg/ml Ketamine,
Invesa Arzneimittel GmbH, Freiburg; 2 % Xylazine, Bayer Health-Care, Leverkusen)
with a dose adjusted to the individual body weight. Infection was performed by intranasal application of virus solution in 20 µl of sterile phosphate-buffered saline. Lung
homogenates were prepared at different time points p.i. Determining infectious particles. Viral load in infected lungs was determined on MDCK II (Madin-Darby Canine
Kidney II) cells using the FFU assay as described earlier (Blazejewska et al., 2011).
Detection limit of the assay is 80 infectious particles/lung. Thus, for samples where no
virus was detected, data points were set to 80 FFU/lung.
Tmprss2-/- and control mice were infected intranasally with 10 FFU H3N2 and at day
1, 3, 5 and 8 p.i., viral titer in lungs was determined. At all time points, mutant
and control mice revealed similar viral titers. However, a high variation in titer was
observed in infected mutant mice (Figure 8).
Despite differences in body weight loss and survival, similar outcomes for viral spread
were observed in Tmprss2 knock-out and wild type mice indicating the participation
of other host proteases in H3 cleavage activation. The high variation in both groups
could be caused by the low infection dose of 10 FFU. Especially in the first days p.i.
with low doses, virus may replicates in mice with different rates. An increased number
of mice may reduce the variation.
46
5.3
FLT3 signaling is critical for the host response after Influenza A infection
Figure 8: Tmprss2 -deficient mice knock-out mice show similar viral loads in lungs as wild type
mice after H3N2 influenza A virus infection. Eight to eleven weeks old female mice were
infected with 10 FFU mouse-adapted H3N2 influenza virus by intra-nasal application. Infectious
particles were determined in lung homogenates. Individual values, mean and SEM are presented.
Three mice per time point were analyzed. Viral load was not significantly different in infected wild
type mice compared to infected homozygous mutant mice at days 1 to 8 p.i.
5.3 FLT3 signaling is critical for the host response after Influenza A infection
FMS-like tyrosine kinase 3 (FLT3) is a hematopoietic receptor tyrosine kinase important for development of many immune cells including dendritic cells (DC) and natural
killer (NK) cells. Binding of its ligand FLT3L results in stimulation of progenitor cell
growth in bone marrow and blood. The Flt3wmfl/wmfl (warmflash - wmfl) strain was
identified in an ENU (N-ethyl-N-nitrosourea) mutagenesis screen for susceptibility to
mouse cytomegalovirus (MCMV) (Eidenschenk et al., 2010). The induced point mutation (G to A) causes a shift of splice donor site and an in-frame deletion of two
amino acids in Flt3 resulting in a non-functional protein. FLT3 was shown to mediate
DC-driven activation of NK cells during MCMV infection. Flt3wmfl/wmfl mice failed to
control viral infection and revealed increased viral titers (Eidenschenk et al., 2010).
The phenotype of Flt3wmfl/wmfl mice after influenza infection is not known. Thus, this
strain was used to study NK cell and DC function and to determine the functional role
of Flt3 during influenza infection.
Material & Methods
Mouse infections. Female Flt3wmfl/wmfl and C57BL/6J mice at the age of 8-11 weeks
were anesthetized by intra-peritoneal injection of Ketamin-Xylazine solution in sterile
NaCl (50 mg/ml Ketamine, Invesa Arzneimittel GmbH, Freiburg; 2 % Xylazine, Bayer
Health-Care, Leverkusen) with a dose adjusted to the individual body weight. Infection
was performed by intranasal application of virus solution in 20 µl of sterile phosphatebuffered saline. Subsequently, survival and body weight loss were monitored until day
47
5.3
14 p.i. In addition to mice that were found dead, mice with a weight loss of more than
30 % of the starting body weight were euthanized and recorded as dead.
Determining infectious particles. Viral load in infected lungs was determined on MDCK
II (Madin-Darby Canine Kidney II) cells using the FFU assay as described earlier
(Blazejewska et al., 2011). Detection limit of the assay is 80 infectious particles/lung.
Hematology. For monitoring hematological parameters, peri-orbital sinus was punctuated and blood was collected in EDTA tubes. Numbers of lymphocytes (Lym),
granulocytes (Gr) and monocytes (Mon) were immediately determined in eye blood
immediately using the hematologic system VetScan HM5 (Abaxis).
Flt3wmfl/wmfl mice of the same sex and age are smaller and lighter in body weight than
wild type mice (Eidenschenk et al., 2010). Furthermore, Flt3wmfl/wmfl mice exhibit a
thin fur and show increased urine loss, although no pathological obvious abnormalities
can be found in skin, pancreas and kidney. Flt3wmfl/wmfl mutants showed an increased
susceptibility to IAV infection compared to wild type mice. After infection with H1N1
PR8M virus, Flt3wmfl/wmfl mice lost weight rapidly and, depending on the infection
dose, survived (Figure 9: A - 2x102 FFU) or died 4 to 8 days p.i. (Figure 9: B - 2x103
and C - 2x105 FFU). In contrast, wild type controls regained body weight after day 7
and survived infections with all infection doses. To investigate whether the low survival
rates of Flt3wmfl/wmfl mice are related to high viral load, we analyzed the amount of viral
particles in the lung. For all three infection doses, I did not find significant differences
in viral load between mutant and wild type mice (Figure 9: A-C).
To follow up the observed difference in survival, I looked for changes in hematological parameters in peripheral blood as an indicator for inflammatory host response and
disease progression (Dengler et al., 2014). Non-lethal infection with 2x102 FFU H1N1
PR8M induced a lymphopenia during first 3 days p.i. in wild type mice (Figure 10 A).
In contrast, the amount of lymphocytes remained on a constant level in Flt3wmfl/wmfl
mice. Furthermore, a stronger increase of granulocytes up to day 8 p.i. was observed
in Flt3wmfl/wmfl mutants. In wild type mice, I observed only a slight increase of granulocytes followed by a decrease after day 6 p.i. in wild type mice (Figure 10 A,B). The
ratio of lymphocytes to granulocytes correlates well with severity of infection (Dengler
et al., 2014). While only a slight increase over time was observed in wild type mice, a
significant higher ratio could be detected in Flt3wmfl/wmfl mice (Figure 10 C).
To determine the granulocyte influx into lung, bronchoalveolar lavage (BAL) was analyzed with the VetScan system (Figure 11). In contrast to wild type mice, a stronger
increase of white blood cells and lymphocytes was detected in Flt3wmfl/wmfl mice after PR8M H1N1 infection (Figure 11 A,B). After 5 days p.i., granulocytes in BAL
of Flt3wmfl/wmfl mice increased strongly, whereas the amount in control mice started
decreasing from day 3 p.i. (Figure 11 C).
48
5.3
Figure 9: Comparison of body weight loss, survival and viral load after infection with different
doses of H1N1 PR8M. 9-11 weeks old mice were infected with (A) 2x102 FFU, (B) 2x103 FFU
and (C) 2x105 FFU PR8M H1N1 influenza virus by intra-nasal application. Survival and body
weight loss were monitored until day 14 p.i. Mice with a weight loss of more than 30 % of starting
body weight were euthanized and recorded as dead. Infectious particles were determined from lung
homogenates at different time points p.i. (Statistics: Mann Whitney U test *: p-value <0,05).
Flt3wmfl/wmfl mice lost weight rapidly and depending on infection dose they survived (A - 2x102
FFU) or died 4 to 8 days post infection (B - 2x103 and C - 2x105 FFU). In contrast, wild type
controls regained body weight after day 7 and survived for all infection doses. For all three infection
doses we could not find significant differences in viral load between mutant and wild type mice
(A-C).
49
5.3
Figure 10: Hematological parameters in peripheral blood exhibited differences in Flt3wmfl/wmfl
and wild type mice. 9-11 weeks old mice were infected with 2x102 FFU PR8M H1N1
influenza virus by intra-nasal application. After different time points p.i. blood from (A)
Flt3wmfl/wmfl and (B) C57BL/6J mice was collected by puncturing retro-orbital sinus followed
by the analysis via the VetScan system. Normalized ratio of granulocytes to lymphocytes
(ratio(dx)=([granulocytes(dx)]/[lymphocytes[dx])/ratio(d0)) was calculated from absolute cell
counts (C). Flt3wmfl/wmfl mutants revealed a higher increase up to day 8 p.i. in granulocytes
in contrast to wild type (Statistics: Mann Whitney U test *: p-value <0,05).
50
5.3
Figure 11: Granulocyte influx in the lung. 9-11 weeks old mice were infected with 2x102 FFU PR8M
H1N1 influenza virus by intra-nasal application. BAL of Flt3wmfl/wmfl and C57BL/6J mice was
harvested and analyzed by the VetScan system (A, B). Absolute amount of granulocytes after
influenza infection are shown in C. After infection Flt3 mutants determined a higher increase of
white blood cells, lymphocytes and granulocytes compared to wild type mice (Statistics: Mann
Whitney U test *: p-value <0,05).
51
5.3
Eidenschenk and colleagues reported an increased susceptibility of Flt3wmfl/wmfl mice
to mouse cytomegalovirus (MCMV) infection and showed a reduced NK cell response
which is caused by a defective DC signaling (Eidenschenk et al., 2010). My experiments demonstrate that Flt3wmfl/wmfl mice are more susceptible to influenza A H1N1
infection than wild type controls. Often, increased susceptibility to influenza infections is accompanied by higher viral load in lungs (Blazejewska et al., 2011; Boon
et al., 2011). However, the high susceptibility of Flt3wmfl/wmfl was not associated with
increased viral load. On the other hand, analysis of hematological parameters revealed
a stronger increase in white blood cells and granulocytes in Flt3wmfl/wmfl in blood and
lung indicating a higher inflammation and a more severe course of infection.
Based on my results, I hypothesize that Flt3wmfl/wmfl mice are more susceptible because of a combination of hyper-inflammatory response to IAV infection and physical
impairments, e.g. small growth, increased urine loss and thin fur. Further experiments are needed to examine the role of DC and NK cells in the immune response of
Flt3wmfl/wmfl mice. Flow cytometry (by Friederike Schäkel) and transcriptome studies
have been performed but have to be analyzed in detail.
52
6 Discussion & Perspectives
Due to genetic drift, the genome of influenza viruses is constantly changing. These
genetic changes result in antigenic different viruses. Thus, vaccines have to be adapted
and immunization protection has to be repeated every season. Furthermore, such
mutations can lead to the emergence of virus variants that are resistant to most or in
the worst case to all of the currently available drugs. During its life cycle, influenza virus
requires many host proteins for replication, virus assembly and maturation. Such host
proteins are attractive targets for therapeutic intervention because the virus cannot
easily escape by generating resistance. Cleavage activation of influenza virus HA is
essential for viral infectivity. Thus, host proteins responsible for HA cleavage activation
were object of intensive research in the last years.
Others had previously shown that the TTSPs TMPRSS2, TMPRSS4 and
TMPRSS11D can activate influenza hemagglutinin of the subtypes H1 and H3 in vitro
(Böttcher et al., 2006; Bertram et al., 2010; Böttcher-Friebertshäuser et al., 2011). To
evaluate the role of such proteases in vivo, I investigated viral replication and pathogenesis in different knock-out mouse models.
Human influenza viruses infect cells which express α2,6-linked forms of sialic acid
(SA) (Skehel and Wiley, 2000; Modrow et al., 2010; Bouvier and Palese, 2008; Taubenberger and Kash, 2010). Viral spread into alveolar epithelium and infection of this
tissue is known for pandemic influenza viruses, including the swine-origin influenza
virus 2009 (Kuiken and Taubenberger, 2008; Taubenberger and Morens, 2008; Yeh
et al., 2010). Various cell types, including goblet cells, type I and type II pneumocytes, and alveolar macrophages were reported to be targets of viral infection. Type
I pneumocytes represent 8 % of all lung cells but cover >95 % of alveolar surface and
are responsible for gas exchange and fluid homeostasis. More cuboidal type II pneumocytes account for 15 % of total cells in the lung and can differentiate into type I
pneumocytes (Herzog et al., 2008). To study which cells are targeted by influenza
virus, Weinheimer and colleagues used a human ex vivo lung model and reported that
seasonal and pandemic influenza viruses (subtypes H1N1 and H3N2) predominantly infect type II pneumocytes (Weinheimer et al., 2012). Additional studies obtained similar
results after pathological examination of fatal human cases and cell tropism in mice
(Shieh et al., 2010; Koerner et al., 2012). Type II pneumocytes have a high number of
mitochondria and endoplasmic reticulum indicating high metabolic activity which may
be the main reason for preferred influenza virus targeting (Weinheimer et al., 2012).
TMPRSS2 is expressed in the human bronchial epithelium, type II pneumocytes and
in alveolar macrophages (Bertram et al., 2010, 2012). Furthermore a co-expression
of TMPRSS2 with α2, 6-linked SA in type II pneumocytes and alveolar macrophages
was shown, suggesting that TMPRSS2 might support viral replication in these cells
(Bertram 2012).
In my thesis, I investigated the role of TMPRSS2 in influenza virus replication
and pathogenesis in experimentally infected mice. After infection of Tmprss2 -deficient
mice with H1N1 virus, the mice were protected from body weight loss, death and
53
6. Discussion & Perspectives
impairment of lung function. Furthermore, viral spread was strongly inhibited and
mice were protected from severe lung pathology. In contrast to wild type mice, the
HA precursor protein was not processed in BAL of infected Tmprss2-/- mice. However,
from day 1 to day 2 p.i., an initial increase of viral titer in lungs was observed. After
day 2 p.i., the viral titer started to decrease.
The mice were infected with a virus produced in embryonated chicken eggs and
thus virus carries an activated HA (Gotoh et al., 1990, 1992). Therefore, the virus
can perform at least one replication cycle. In addition, it is possible that at least
one further protease facilitates H1 cleavage activation and allows limited viral spread.
However, if this was the case, this marginal viral spread could be controlled by the
antiviral immune response since Tmprss2-/- mice showed no signs of clinical symptoms
after high dose H1N1 virus infection. The resistant phenotype of Tmprss2 -deficient
mice after H1N1 influenza virus infection was confirmed by two other groups (Sakai
et al., 2014; Tarnow et al., 2014).
Next to H1N1, also H3N2 is circulating during seasonal outbreaks in humans. It was
shown in vitro that TMPRSS2 can cleave mono-basic H3 influenza viruses (Böttcher
et al., 2006). Surprisingly, H3N2 influenza virus was able to replicate in Tmprss2-/mice. Nevertheless, body weight loss and mortality in Tmprss2 -deficient mice were
significantly reduced in a dose-dependent manner. However, compared to wild type
lungs, viral load was not significantly lower in mutants. Additional TMPRSS2 in vivo
studies obtained similar results depending on the infection dose. Sakai and colleagues
infected Tmprss2 -deficient mice with different doses of A/Guizhou-X (H3N2) whereby
mutants showed 100 % survival for all doses in contrast to the more susceptible controls
(Sakai et al., 2014). In contrast, Tarnow and colleagues observed no differences between
mutants and wild type mice after infection with a high dose of A/Aichi/2/68 (H3N2)
(Tarnow et al., 2014). In summary, in vivo results of different groups indicate an
involvement of TMPRSS2 in H3N2 cleavage activation, but additional proteases must
be involved in this process.
Also, TMPRSS2 was shown to be essential for viral spread and pathogenicity of the
human H7N9 isolate A/Anhui/1/13. Tmprss2-/- mice showed no sign of disease after
infection with H7N9, in contrast to highly susceptible wild type (Sakai et al., 2014;
Tarnow et al., 2014). The H7N9 isolate contains a monobasic cleavage site (Gao et al.,
2013) and is mainly cleaved by TMPRSS2.
Next, I investigated the role of TMPRSS4 in the context of IAV replication and
pathogenesis in mice. TMPRSS4 transcripts were detected in the gastrointestinal
tract (esophagus, stomach, small intestine and colon), the urogenital tract (kidney
and bladder), in mouse bronchiolar-alveolar epithelial cells and in human lung tissue
(Wallrapp et al., 2000; Planes et al., 2005; Chaipan et al., 2009). Until now, it had not
been examined whether TMPRSS4 is expressed by type II pneumocytes, the target
cells of influenza viruses. Using immune-histochemical staining, I observed expression
of TMPRSS4 in the alveolar region and bronchial epithelium cells of murine lungs.
TMPRSS2 and TMPRSS4 were co-expressed in granular and roughly cuboidal shaped
54
cells representing type II pneumocytes. This co-localization of host proteases in viral
target cells strongly suggests that both proteases may be involved in HA maturation.
Indeed, deletion of Tmprss4 in knock-out mice did not have significant effect with
respect to body weight loss, survival and pathology after H3N2 influenza virus infection.
However, deletion of both Tmprss2 and Tmprss4 in double-knock out mice strongly
and significantly improved morbidity and survival after H3N2 infection. The viral
load and pathology was reduced compared to wild type mice, but the HA precursor
was still processed into HA1 and HA2 and enabled the virus to spread into alveolar
regions. From these data, I conclude that in addition to TMPRSS2 and TMPRSS4
even more proteases must be able to cleave and activate H3. However, enhanced
protection of double knock-out mice relative to each single knock-out strain indicates
that both proteins facilitate H3 activation and can, at least partially, complement each
other functionally. Bertram and colleagues knocked down TMPRSS2 and TMPRSS4
via siRNA in Caco-2 cells and demonstrated that expression of both proteases was
essential for the efficient trypsin-independent spread of influenza virus (Bertram et al.,
2010). Thereby, viral release was more efficiently inhibited after knock-down of both,
TMPRSS2 and TMPRSS4, in contrast to single knock-down. In these in vitro studies,
a PR8 (H1N1) influenza virus was used to infect the Caco-2 cells (Bertram et al.,
2010). However the results from Bertram and co-workers support our assumption of
functionally complementation of TMPRSS2 and TMPRSS4 whereby I observed this
functionally complementation after H3N2 virus infection only.
From our knock-out studies we conclude that in addition to TMPRSS2 and
TMPRSS4 other proteases participate in H3 cleavage activation in vivo. Bertram and
colleagues demonstrated the co-expression of TMPRSS2 and TMPRSS11D in type II
pneumocytes whereas TMPRSS11D was expressed to a lesser extent. Furthermore,
TMPRSS11D was expressed by occasional type I pneumocytes (Bertram et al., 2012).
TMPRSS11D was demonstrated to cleave influenza virus HA from H1N1 and H3N2
and support multicycle virus replication in vitro (Böttcher et al., 2006). However, the
role of TMPRSS11D in influenza virus pathogenesis in the infected host has yet to be
clarified. Since TMPRSS11D was shown to cleave influenza A virus H3 in cell culture,
it was another promising candidate for the H3 cleavage activation (Böttcher et al.,
2006).
Therefore, the objective of my third protease project was to analyze the role of
TMPRSS11D in activation and spread of H3N2 influenza viruses in the murine airways.
To prove the suggestion that TMPRSS11D is involved in H3 cleavage activation in vivo,
Tmprss11d-deficient mice were infected with influenza A and investigated. With a low
infection dose of 10 FFU of mouse-adapted H3N2 virus, significant lower mortality
was determined in Tmprss11d-/- mice. After increasing the H3N2 infection dose, no
difference between knock-out and control mice could be observed. RT-PCR analysis
from mouse tissue showed that TMPRSS11D is mainly expressed in larynx, trachea,
bronchi and just marginally in lungs (Sales et al., 2011; Tarnow et al., 2014). In contrast, TMPRSS2 mRNA transcripts were found in all sections of the lower respiratory
system in mice (Tarnow et al., 2014). Therefore, TMPRSS11D may support cleavage
55
activation of H3 in murine trachea and bronchi, whereas TMPRSS2 and TMPRSS4
cleave H3 in bronchial epithelium and type II pneumocytes.
In future studies, it would be important to investigate H3 cleavage in a mouse line
that is deficient for all three host proteases. My results also pose a more general question: Why is H3N2 cleavage activation, in contrast to H1N1, supported by several
proteases? By crystallography, it was shown that the H3 cleavage site is located in
a loop which contains 19 amino acids from which 8 protrude from the surface of the
HA trimer (Chen et al., 1998). It is thus conceivable that the protrusion of the HA
loop provides a more easy access for several proteases. For this structural analysis, the
arginine 329 at the cleavage site was replaced by glutamine, R329Q, to prevent tryptic
cleavage during the protein purification. By means of this amino acid change, Chen
and co-workers solved the structure of a non-cleaved H3 (Chen et al., 1998). However, this amino acid change might have destroyed non-covalent interactions between
the cleavage site and other domains of the HA protein resulting in the protrusion of
the loop. Crystallization of a non-modified H3 protein may help to clarify the loop
structure. Furthermore, protease accessibility is mainly controlled by two factors: first,
insertion of amino acids upstream of the cleavage site was reported to enhance protease
accessibility and therefore cleavability of HA (Khatchikian et al., 1989; Ohuchi et al.,
1991) and second, carbohydrate residues near the cleavage site may mask its recognition by proteases (Kawaoka and Webster, 1989; Ohuchi et al., 1989). The increased
accessibility of the H3 cleavage loop may allow cleavability by several proteases.
In my thesis, I confirmed the involvement of at least three host proteases in H3
cleavage activation, but my results also indicated that more proteases in different parts
of the airways may be involved. As early as 1992, Kido and colleagues purified the
extracellular protease TPSB2 (tryptase clara) from bronchiolar epithelial Clara cells
in rat lungs (Kido et al., 1992). TPSB2 was also shown to cleave HA of A/Aichi/2/68
(H3N2) and activate infectivity of IAV in a dose-dependent way in vitro (Kido et al.,
1992, 2007). Mice deficient for Tpsb2 showed a defective link between adaptive and
innate immunity after trichinella spiralis infection (Shin et al., 2008). However, the
role of TPSB2 in HA cleavage activation in vivo is presently not known. ST14 (matriptase) is highly expressed in a membrane-bound form throughout the respiratory
tract. Immunohistochemical reactivity of ST14 was detected in nasal mucosa, alveolar
and bronchiole epithelium (Oberst et al., 2003). However, Hamilton and colleagues determined that secreted, catalytic domain has the ability to cleavage activate influenza
virus HA. Thereby ST14 cleaved HA of particular strains within the H1 subtype but
not H2 and H3 subtypes (Hamilton et al., 2012). Baron and colleagues demonstrated
that H9N2 viruses with R-S-S-R or R-S-R-R cleavage sites are activated by ST14 in addition to TMPRSS2 and TMPRSS11D (Baron et al., 2013). In a recent study by Zmora
and co-workers, seven TTSPs previously reported to be expressed in the lung were investigated for their ability to activate H3 in transfected 293T cells (Zmora et al., 2014).
TMPRSS11E (Desc) and TMPRSS13 (MSPL) were able to cleave HA of H1, H2 and H3
subtypes and were co-localized with HA in infected cells. The proteases TMPRSS11F,
PRSS8 (prostasin), TMPRSS11B, TMPRSS9 and TMPRSS10 showed no cleavage ac-
56
tivity after co-expression with HA (Zmora et al., 2014). Therefore, TMPRSS11E and
TMPRSS13 would be promising other candidates to test their role for H3 activation
in vivo. Furthermore, KLK5 and KLK12, two members of the kallikrein-related peptidase family were analyzed for HA cleavage activity (Hamilton and Whittaker, 2013).
Cleavage specificity of KLK5 and KLK12 closely resembled the cleavage site of HA and
KLK12 expression has been observed in tracheal epithelial cells (Shaw and Diamandis, 2007). Both peptidases exhibited a preference for particular influenza subtypes in
vitro. KLK5 cleaved the H1 and H3 subtypes most efficiently and KLK12 cleaved H1
and H2 (Hamilton and Whittaker, 2013). However, their contribution to H3 cleavage
activation in vivo was not determined yet.
Bacterial infections could support virus propagation by the release of bacterial proteases that also facilitate cleavage of HA. Staphylococcus aureus (S. aureus) was reported to secrete proteases, which could cleave the HA of certain influenza strains in
vitro. Thereby, activation of HA was specific for bacteria and virus strains (Tashiro
et al., 1987). Furthermore, a protease secreted by Aerococcus viridans (A. viridans) was
reported to cleave HA of different influenza virus isolates and co-infections in mice led
to severe outcome (Scheiblauer et al., 1992). Thus far, HA-activating proteases from
S.aureus and A. viridans have not been investigated and the contribution of bacteria
to cleavage activation of influenza viruses in murine and human airways still remains
to be demonstrated (Böttcher-Friebertshäuser et al., 2013).
Due to their crucial role for virus infectivity, HA-activating host cell proteases
are potential drug targets. As early as 30 years ago, Zhirnov and colleagues found
that the natural inhibitor aprotinin suppresses influenza virus replication. Aprotinin
was shown to protect mice from lethal IAV infection and significantly reduced virus
titers and pathology in bronchi and lungs by inhibiting HA cleavage (Zhirnov et al.,
2011). Furthermore, inhalation of aerosolized aprotinin in patients with seasonal influenza significantly reduced duration of the disease without causing side effects in
a clinical trial (Zhirnov et al., 1996). Numerous studies reported that TMPRSS2,
TMPRSS4, TMPRSS11D, TPSB2 and trypsin are highly sensitive to aprotinin inhibition in cell culture experiments (Zhirnov et al., 1982a,b; Kido et al., 1992, 1993;
Böttcher-Friebertshäuser et al., 2010; Murakami et al., 2001; Towatari et al., 2002; Sato
et al., 2003). In addition, several synthetic host protease inhibitors are under development. Inhibition of TMPRSS2 activity in cell culture by peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) or peptide mimics (BAPA) of TMPRSS2
was shown to significantly reduce virus titers and to delay virus propagation. The
combination of protease inhibitor and oseltamivir was highly synergistic and decreased
virus propagation efficiently (Böttcher-Friebertshäuser et al., 2011, 2012; Meyer et al.,
2013). Recently, the serine protease inhibitor HAI-2 (SPINT2) that reside on the
plasma membrane of several tissues, were shown to inhibit HA cleavage of humanadapted H1 and H3 subtypes. HAI-2 inhibited influenza virus infection in in vitro and
prolonged the survival of infected mice (Hamilton et al., 2014). Furthermore, substrate
analogue peptide mimic inhibitors of TMPRSS11D showed significant suppression of influenza virus replication in vitro (Böttcher et al., 2009; Böttcher-Friebertshäuser et al.,
57
2010; Sielaff et al., 2011).
Targeting HA-activating proteases is a new approach for anti-influenza therapy. Until recently, a lack of knowledge about relevant proteases, concerns about toxicity and
possible side effects have limited the development of novel antivirals. In Germany, aprotinin was approved for pancreatitis and post-operative bleeding (Fritz and Wunderer,
1983). Due to potential severe side effects (kidney failure) aprotinin was withdrawn
from the market between 2007 and 2013. The Committee for Medicinal Products for
Human Use recommended the reenactment of admission to the market in 2013. In Russia, aprotinin was tested for influenza treatment in clinical trials, whereas used doses
were clearly lower than those usually used in cardio-thoracic surgery (Zhirnov et al.,
1996, 2011). To decrease side effects it will be necessary to develop highly specific
inhibitors to deactivate as few proteases possible . Knocking out two proteases caused
no obvious phenotype in our Tmprss2-/- Tmprss4-/- mice. They exhibited normal reproduction, development and growth patterns. My work provided new insights about
the subtype specific cleavage activation of three host proteases in vivo. I assumed in
vivo validation of all candidates which are proposed for HA activation in vitro, since
for instance TMPRSS4 and TMPRSS11D are not involved in cleavage of H1 in mice
but cleavage could be shown in cell culture studies.
In conclusion, protease inhibitors are able to suppress several proteases in different
airway compartments to prevent viral pathogenesis of seasonal influenza A viruses.
However, more research is necessary to find all responsible proteases that are involved
in HA activation in vivo. Alternatively, a combination of different proteases inhibitors
or administration of classical NA inhibitor in addition to protease inhibitors could be
an efficient strategy to treat severe IAV infections. Since TMPRSS2 and TMPRSS11D
support also cleavage activation of influenza B viruses, SARS coronavirus and the
human metapneumovirus in vitro, they might play a role in the spread of different
respiratory viruses (Shirogane et al., 2008; Matsuyama et al., 2010; Shulla et al., 2011;
Böttcher-Friebertshäuser et al., 2012). Therefore, targeting host proteases could provide new antiviral strategies for several severe and pandemic viruses.
Further studies are necessary to obtain a comprehensive understanding of the HA
subtype specificity of host proteases. Therefore, the physiological roles of many TTSPs
have to be clarified. To complete our understanding why some HA subtypes are substrates of several proteases and why H1 and monobasic H7 are primarily processed by
TMPRSS2, protein structure analysis of TTSP members and HA-protease complexes
are required. These crystal structures could provide more information about cleavage
site accessibility. In addition, identification of additional host proteases responsible
for H3 activation in different airway compartments is important for the development
of specific protease inhibitors. Already generated inhibitors, like the peptide mimic
BAPA, should be examined in mice to confirm results in vivo and to determine potential side effects.
In a smaller part of my thesis, I established pulse oximetry as an additional measurement to body weight loss to better follow physiopathology after IAV infection.
58
Pulse oximetry is a widespread technique for non-invasive measuring of oxygen saturation of arterial blood, based on different absorption spectra of oxygenated and
R
deoxygenated hemoglobin. The MouseOx
system was generated for measurement of
non-anesthetized animals. However, sensor clips which were fixed in the neck caused
stress and even small movements of the mice resulted in error messages. Furthermore,
behavior of mice was different depending on the inbred mouse strain. Consequently, the
measurement procedure had to be adjusted to the inbred strain. The results showed
a decrease in lung function of different inbred mouse strains during the course of infection. However, during the first days post infection, oxygen saturation was still high
and decreased much later whereas loss in body weight was evident about three days
earlier. Regeneration of oxygen saturation started after clearance of virus about two
days later than recovery of body weight. Though body weight loss was more severe in
mice after administration of virus high doses or of highly virulent virus, reduction in
blood oxygen saturation did not increase accordingly. In conclusion, measurement of
blood oxygen saturation by pulse oximetry in mice reflects pathophysiological changes
after IAV infection but does not provide a robust measurement for severity of disease.
59
References
Abuin, A., G. M. Hansen, and B. Zambrowicz (2007). Gene trap mutagenesis. Handb
Exp Pharmacol (178), 129–47.
Afar, D. E., I. Vivanco, R. S. Hubert, J. Kuo, E. Chen, D. C. Saffran, A. B. Raitano,
and A. Jakobovits (2001). Catalytic cleavage of the androgen-regulated TMPRSS2
protease results in its secretion by prostate and prostate cancer epithelia. Cancer
Res 61 (4), 1686–92.
Andrewes, C. H., P. P. Laidlaw, and W. Smith (1934). Lancet 2, 859–861.
Austin, C. P., J. F. Battey, A. Bradley, M. Bucan, M. Capecchi, F. S. Collins, W. F.
Dove, G. Duyk, S. Dymecki, J. T. Eppig, F. B. Grieder, N. Heintz, G. Hicks, T. R.
Insel, A. Joyner, B. H. Koller, K. C. Lloyd, T. Magnuson, M. W. Moore, A. Nagy,
J. D. Pollock, A. D. Roses, A. T. Sands, B. Seed, W. C. Skarnes, J. Snoddy, P. Soriano, D. J. Stewart, F. Stewart, B. Stillman, H. Varmus, L. Varticovski, I. M. Verma,
T. F. Vogt, H. von Melchner, J. Witkowski, R. P. Woychik, W. Wurst, G. D. Yancopoulos, S. G. Young, and B. Zambrowicz (2004). The knockout mouse project.
Nat Genet 36 (9), 921–4.
Barnard, D. L. (2009). Animal models for the study of influenza pathogenesis and
therapy. Antiviral Res 82 (2), A110–22.
Baron, J., C. Tarnow, D. Mayoli-Nussle, E. Schilling, D. Meyer, M. Hammami,
F. Schwalm, T. Steinmetzer, Y. Guan, W. Garten, H. D. Klenk, and E. BottcherFriebertshauser (2013). Matriptase, HAT, and TMPRSS2 activate the hemagglutinin
of H9N2 influenza A viruses. J Virol 87 (3), 1811–20.
Baudin, F., I. Petit, W. Weissenhorn, and R. W. Ruigrok (2001). In vitro dissection
of the membrane and RNP binding activities of influenza virus M1 protein. Virology 281 (1), 102–8.
Beaufort, N., D. Leduc, H. Eguchi, K. Mengele, D. Hellmann, T. Masegi, T. Kamimura,
S. Yasuoka, F. Fend, M. Chignard, and D. Pidard (2007). The human airway trypsinlike protease modulates the urokinase receptor (uPAR, CD87) structure and functions. Am J Physiol Lung Cell Mol Physiol 292 (5), L1263–72.
Behrens, G., R. Gottschalk, L. G¸rtler, T. C. Harder, C. Hoffmann, B. S. Kamps,
S. Korsman, W. Preiser, G. Reyes-Teran, M. Stoll, O. Werner, and G. van Zyl
(2006). Influenza Report 2006. Flying Publisher.
Belser, J. A., J. M. Katz, and T. M. Tumpey (2011). The ferret as a model organism
to study influenza A virus infection. Dis Model Mech 4 (5), 575–9.
Bertram, S., I. Glowacka, P. Blazejewska, E. Soilleux, P. Allen, S. Danisch, I. Steffen,
S. Y. Choi, Y. Park, H. Schneider, K. Schughart, and S. Pohlmann (2010). TMPRSS2
and TMPRSS4 facilitate trypsin-independent spread of influenza virus in Caco-2
cells. J Virol 84 (19), 10016–25.
Bertram, S., I. Glowacka, I. Steffen, A. Kuhl, and S. Pohlmann (2010). Novel insights
into proteolytic cleavage of influenza virus hemagglutinin. Rev Med Virol 20 (5),
298–310.
60
References
Bertram, S., A. Heurich, H. Lavender, S. Gierer, S. Danisch, P. Perin, J. M. Lucas,
P. S. Nelson, S. Pohlmann, and E. J. Soilleux (2012). Influenza and SARS-coronavirus
activating proteases TMPRSS2 and HAT are expressed at multiple sites in human
respiratory and gastrointestinal tracts. PLoS One 7 (4), e35876.
Blazejewska, P., L. Koscinski, N. Viegas, D. Anhlan, S. Ludwig, and K. Schughart
(2011). Pathogenicity of different PR8 influenza A virus variants in mice is determined by both viral and host factors. Virology 412 (1), 36–45.
Boch, J. (2011). TALEs of genome targeting. Nat Biotechnol 29 (2), 135–6.
Boon, A., D. Finkelstein, M. Zheng, G. Liao, J. Allard, K. Klumpp, R. Webster,
G. Peltz, and R. Webby (2011). H5N1 influenza virus pathogenesis in genetically
diverse mice is mediated at the level of viral load. mBio 2(5).
Börgeling, Y., M. Schmolke, D. Viemann, C. Nordhoff, J. Roth, and S. Ludwig (2014).
Inhibition of p38 mitogen-activated protein kinase impairs influenza virus-induced
primary and secondary host gene responses and protects mice from lethal H5N1
infection. J Biol Chem 289 (1), 13–27.
Bosch, F. X., W. Garten, H. D. Klenk, and R. Rott (1981). Proteolytic cleavage
of influenza virus hemagglutinins: primary structure of the connecting peptide between HA1 and HA2 determines proteolytic cleavability and pathogenicity of Avian
influenza viruses. Virology 113 (2), 725–35.
Böttcher, E., C. Freuer, T. Steinmetzer, H. D. Klenk, and W. Garten (2009). MDCK
cells that express proteases TMPRSS2 and HAT provide a cell system to propagate
influenza viruses in the absence of trypsin and to study cleavage of HA and its
inhibition. Vaccine 27 (45), 6324–9.
Böttcher, E., T. Matrosovich, M. Beyerle, H. D. Klenk, W. Garten, and M. Matrosovich
(2006). Proteolytic activation of influenza viruses by serine proteases TMPRSS2 and
HAT from human airway epithelium. J Virol 80 (19), 9896–8.
Böttcher-Friebertshäuser, E., C. Freuer, F. Sielaff, S. Schmidt, M. Eickmann, J. Uhlendorff, T. Steinmetzer, H. D. Klenk, and W. Garten (2010). Cleavage of influenza
virus hemagglutinin by airway proteases TMPRSS2 and HAT differs in subcellular
localization and susceptibility to protease inhibitors. J Virol 84 (11), 5605–14.
Böttcher-Friebertshäuser, E., W. Garten, M. Matrosovich, and H. D. Klenk (2014). The
hemagglutinin: a determinant of pathogenicity. Curr Top Microbiol Immunol 385,
3–34.
Böttcher-Friebertshäuser, E., H. D. Klenk, and W. Garten (2013). Activation of influenza viruses by proteases from host cells and bacteria in the human airway epithelium. Pathog Dis 69 (2), 87–100.
Böttcher-Friebertshäuser, E., Y. Lu, D. Meyer, F. Sielaff, T. Steinmetzer, H. D. Klenk,
and W. Garten (2012). Hemagglutinin activating host cell proteases provide promising drug targets for the treatment of influenza A and B virus infections. Vaccine 30 (51), 7374–80.
61
References
Böttcher-Friebertshäuser, E., D. A. Stein, H. D. Klenk, and W. Garten (2011). Inhibition of influenza virus infection in human airway cell cultures by an antisense
peptide-conjugated morpholino oligomer targeting the hemagglutinin-activating protease TMPRSS2. J Virol 85 (4), 1554–62.
Boulo, S., H. Akarsu, R. W. Ruigrok, and F. Baudin (2007). Nuclear traffic of influenza
virus proteins and ribonucleoprotein complexes. Virus Res 124 (1-2), 12–21.
Bouvier, N. M. and A. C. Lowen (2010). Animal Models for Influenza Virus Pathogenesis and Transmission. Viruses 2 (8), 1530–1563.
Bouvier, N. M. and P. Palese (2008). The biology of influenza viruses. Vaccine 26
Suppl 4, D49–53.
Boyd, M., K. Clezy, R. Lindley, and R. Pearce (2006). Pandemic influenza: clinical
issues. Med J Aust 185, S44–7.
Brown, S. D. and J. M. Hancock (2006). The mouse genome. Genome Dyn 2, 33–45.
Carrat, F., E. Vergu, N. M. Ferguson, M. Lemaitre, S. Cauchemez, S. Leach, and A. J.
Valleron (2008). Time lines of infection and disease in human influenza: a review of
volunteer challenge studies. Am J Epidemiol 167 (7), 775–85.
Castrucci, M. R. and Y. Kawaoka (1993). Biologic importance of neuraminidase stalk
length in influenza A virus. J Virol 67 (2), 759–64.
Chaipan, C., D. Kobasa, S. Bertram, I. Glowacka, I. Steffen, T. S. Tsegaye, M. Takeda,
T. H. Bugge, S. Kim, Y. Park, A. Marzi, and S. Pohlmann (2009). Proteolytic
activation of the 1918 influenza virus hemagglutinin. J Virol 83 (7), 3200–11.
Chen, J., K. H. Lee, D. A. Steinhauer, D. J. Stevens, J. J. Skehel, and D. C. Wiley
(1998). Structure of the hemagglutinin precursor cleavage site, a determinant of
influenza pathogenicity and the origin of the labile conformation. Cell 95 (3), 409–
17.
Choi, S. Y., S. Bertram, I. Glowacka, Y. W. Park, and S. Pohlmann (2009). Type
II transmembrane serine proteases in cancer and viral infections. Trends Mol
Med 15 (7), 303–12.
Chokki, M., S. Yamamura, H. Eguchi, T. Masegi, H. Horiuchi, H. Tanabe,
T. Kamimura, and S. Yasuoka (2004). Human airway trypsin-like protease increases
mucin gene expression in airway epithelial cells. Am J Respir Cell Mol Biol 30 (4),
470–8.
Choppin, P. W. (1969). Replication of influenza virus in a continuous cell line: high
yield of infective virus from cells inoculated at high multiplicity. Virology 39 (1),
130–4.
Colman, P. M. (1999). A novel approach to antiviral therapy for influenza. J Antimicrob
Chemother 44 Suppl B, 17–22.
Compans, R. W., J. Content, and P. H. Duesberg (1972). Structure of the ribonucleoprotein of influenza virus. J Virol 10 (4), 795–800.
62
References
Cros, J. F. and P. Palese (2003). Trafficking of viral genomic RNA into and out of the
nucleus: influenza, Thogoto and Borna disease viruses. Virus Res 95 (1-2), 3–12.
de Aberasturi, A. L. and A. Calvo (2015). TMPRSS4: an emerging potential therapeutic target in cancer. Br J Cancer 112 (1), 4–8.
Dengler, L., N. Kühn, D. L. Shin, B. Hatesuer, K. Schughart, and E. Wilk (2014).
Cellular Changes in Blood Indicate Severe Respiratory Disease during Influenza Infections in Mice. PLoS One 9 (7), e103149.
Deshpande, K. L., V. A. Fried, M. Ando, and R. G. Webster (1987). Glycosylation
affects cleavage of an H5N2 influenza virus hemagglutinin and regulates virulence.
Proc Natl Acad Sci U S A 84 (1), 36–40.
Dinnyes, A. and A. Szmolenszky (2005). Animal cloning by nuclear transfer: state-ofthe-art and future perspectives. Acta Biochim Pol 52 (3), 585–8.
Donaldson, S. H., A. Hirsh, D. C. Li, G. Holloway, J. Chao, R. C. Boucher, and S. E.
Gabriel (2002). Regulation of the epithelial sodium channel by serine proteases in
human airways. J Biol Chem 277 (10), 8338–45.
Eichelberger, M. C. and M. D. Green (2011). Animal models to assess the toxicity,
immunogenicity and effectiveness of candidate influenza vaccines. Expert Opin Drug
Metab Toxicol 7 (9), 1117–27.
Eidenschenk, C., K. Crozat, P. Krebs, R. Arens, D. Popkin, C. N. Arnold, A. L. Blasius,
C. A. Benedict, E. M. Moresco, Y. Xia, and B. Beutler (2010). Flt3 permits survival
during infection by rendering dendritic cells competent to activate NK cells. Proc
Natl Acad Sci U S A 107 (21), 9759–64.
Evans, D. G. (1966). Wilson Smith. 1987-1965. Biogr. Mem. Fellows R. SOc. 12 (1).
Fritz, H. and G. Wunderer (1983). Biochemistry and applications of aprotinin, the
kallikrein inhibitor from bovine organs. Arzneimittelforschung 33 (4), 479–94.
Gao, R., B. Cao, Y. Hu, Z. Feng, D. Wang, W. Hu, J. Chen, Z. Jie, H. Qiu, K. Xu,
X. Xu, H. Lu, W. Zhu, Z. Gao, N. Xiang, Y. Shen, Z. He, Y. Gu, Z. Zhang, Y. Yang,
X. Zhao, L. Zhou, X. Li, S. Zou, Y. Zhang, X. Li, L. Yang, J. Guo, J. Dong, Q. Li,
L. Dong, Y. Zhu, T. Bai, S. Wang, P. Hao, W. Yang, Y. Zhang, J. Han, H. Yu, D. Li,
G. F. Gao, G. Wu, Y. Wang, Z. Yuan, and Y. Shu (2013). Human infection with a
novel avian-origin influenza A (H7N9) virus. N Engl J Med 368 (20), 1888–97.
Garten, W. and H. D. Klenk (1999). Understanding influenza virus pathogenicity.
Trends Microbiol 7 (3), 99–100.
Gossler, A., A. L. Joyner, J. Rossant, and W. C. Skarnes (1989). Mouse embryonic
stem cells and reporter constructs to detect developmentally regulated genes. Science 244 (4903), 463–5.
Goto, H. and Y. Kawaoka (1998). A novel mechanism for the acquisition of virulence
by a human influenza A virus. Proc Natl Acad Sci U S A 95 (17), 10224–8.
63
References
Gotoh, B., T. Ogasawara, T. Toyoda, N. M. Inocencio, M. Hamaguchi, and Y. Nagai
(1990). An endoprotease homologous to the blood clotting factor X as a determinant
of viral tropism in chick embryo. EMBO J 9 (12), 4189–95.
Gotoh, B., F. Yamauchi, T. Ogasawara, and Y. Nagai (1992). Isolation of factor
Xa from chick embryo as the amniotic endoprotease responsible for paramyxovirus
activation. FEBS Lett 296 (3), 274–8.
Goulet, M. L., D. Olagnier, Z. Xu, S. Paz, S. M. Belgnaoui, E. I. Lafferty, V. Janelle,
M. Arguello, M. Paquet, K. Ghneim, S. Richards, A. Smith, P. Wilkinson,
M. Cameron, U. Kalinke, S. Qureshi, A. Lamarre, E. K. Haddad, R. P. Sekaly,
S. Peri, S. Balachandran, R. Lin, and J. Hiscott (2013). Systems analysis of a RIG-I
agonist inducing broad spectrum inhibition of virus infectivity. PLoS Pathog 9 (4),
e1003298.
Gregory, S. G., M. Sekhon, J. Schein, S. Zhao, K. Osoegawa, C. E. Scott, R. S. Evans,
P. W. Burridge, T. V. Cox, C. A. Fox, R. D. Hutton, I. R. Mullenger, K. J. Phillips,
J. Smith, J. Stalker, G. J. Threadgold, E. Birney, K. Wylie, A. Chinwalla, J. Wallis, L. Hillier, J. Carter, T. Gaige, S. Jaeger, C. Kremitzki, D. Layman, J. Maas,
R. McGrane, K. Mead, R. Walker, S. Jones, M. Smith, J. Asano, I. Bosdet, S. Chan,
S. Chittaranjan, R. Chiu, C. Fjell, D. Fuhrmann, N. Girn, C. Gray, R. Guin, L. Hsiao,
M. Krzywinski, R. Kutsche, S. S. Lee, C. Mathewson, C. McLeavy, S. Messervier,
S. Ness, P. Pandoh, A. L. Prabhu, P. Saeedi, D. Smailus, L. Spence, J. Stott, S. Taylor, W. Terpstra, M. Tsai, J. Vardy, N. Wye, G. Yang, S. Shatsman, B. Ayodeji,
K. Geer, G. Tsegaye, A. Shvartsbeyn, E. Gebregeorgis, M. Krol, D. Russell, L. Overton, J. A. Malek, M. Holmes, M. Heaney, J. Shetty, T. Feldblyum, W. C. Nierman,
J. J. Catanese, T. Hubbard, R. H. Waterston, J. Rogers, P. J. de Jong, C. M. Fraser,
M. Marra, J. D. McPherson, and D. R. Bentley (2002). A physical map of the mouse
genome. Nature 418 (6899), 743–50.
Guan, C., C. Ye, X. Yang, and J. Gao (2010). A review of current large-scale mouse
knockout efforts. Genesis 48 (2), 73–85.
Hai, R., M. Schmolke, V. H. Leyva-Grado, R. R. Thangavel, I. Margine, E. L. Jaffe,
F. Krammer, A. Solorzano, A. Garcia-Sastre, P. Palese, and N. M. Bouvier (2013).
Influenza A(H7N9) virus gains neuraminidase inhibitor resistance without loss of in
vivo virulence or transmissibility. Nat Commun 4, 2854.
Hale, B. G., R. E. Randall, J. Ortin, and D. Jackson (2008). The multifunctional NS1
protein of influenza A viruses. J Gen Virol 89 (Pt 10), 2359–76.
Haller, O., H. Arnheiter, and J. Lindenmann (1979). Natural, genetically determined
resistance toward influenza virus in hemopoietic mouse chimeras. Role of mononuclear phagocytes. J Exp Med 150 (1), 117–26.
Hamilton, B. S., C. Chung, S. Y. Cyphers, V. D. Rinaldi, V. C. Marcano, and G. R.
Whittaker (2014). Inhibition of influenza virus infection and hemagglutinin cleavage
by the protease inhibitor HAI-2. Biochem Biophys Res Commun.
Hamilton, B. S., D. W. Gludish, and G. R. Whittaker (2012). Cleavage activation of
the human-adapted influenza virus subtypes by matriptase reveals both subtype and
strain specificities. J Virol 86 (19), 10579–86.
64
References
Hamilton, B. S. and G. R. Whittaker (2013). Cleavage activation of humanadapted influenza virus subtypes by kallikrein-related peptidases 5 and 12. J Biol
Chem 288 (24), 17399–407.
Hatesuer, B., S. Bertram, N. Mehnert, M. M. Bahgat, P. S. Nelson, S. Pohlman, and
K. Schughart (2013). Tmprss2 is essential for influenza H1N1 virus pathogenesis in
mice. PLoS Pathog 9 (12), e1003774.
Hay, A. J., V. Gregory, A. R. Douglas, and Y. P. Lin (2001). The evolution of human
influenza viruses. Philos Trans R Soc Lond B Biol Sci 356 (1416), 1861–70.
Hay, A. J., A. J. Wolstenholme, J. J. Skehel, and M. H. Smith (1985). The molecular
basis of the specific anti-influenza action of amantadine. EMBO J 4 (11), 3021–4.
Herzog, E. L., A. R. Brody, T. V. Colby, R. Mason, and M. C. Williams (2008). Knowns
and unknowns of the alveolus. Proc Am Thorac Soc 5 (7), 778–82.
Hirst, G. K. (1947). STUDIES ON THE MECHANISM OF ADAPTATION OF INFLUENZA VIRUS TO MICE. J Exp Med 86 (5), 357–66.
Hogan, B. and K. Lyons (1988). Gene targeting. Getting nearer the mark. Nature 336 (6197), 304–5.
Horimoto, T. and Y. Kawaoka (2005). Influenza: lessons from past pandemics, warnings from current incidents. Nat Rev Microbiol 3 (8), 591–600.
Horvath, P. and R. Barrangou (2010). CRISPR/Cas, the immune system of bacteria
and archaea. Science 327 (5962), 167–70.
Huang, Y., A. K. Zaas, A. Rao, N. Dobigeon, P. J. Woolf, T. Veldman, N. C. Oien,
M. T. McClain, J. B. Varkey, B. Nicholson, L. Carin, S. Kingsmore, C. W. Woods,
G. S. Ginsburg, and A. O. Hero (2011). Temporal dynamics of host molecular
responses differentiate symptomatic and asymptomatic influenza a infection. PLoS
Genet 7 (8), e1002234.
Huarte, M., J. J. Sanz-Ezquerro, F. Roncal, J. Ortin, and A. Nieto (2001). PA subunit from influenza virus polymerase complex interacts with a cellular protein with
homology to a family of transcriptional activators. J Virol 75 (18), 8597–604.
Ilyushina, N. A., N. V. Bovin, R. G. Webster, and E. A. Govorkova (2006). Combination chemotherapy, a potential strategy for reducing the emergence of drug-resistant
influenza A variants. Antiviral Res 70 (3), 121–31.
Ilyushina, N. A., E. Hoffmann, R. Salomon, R. G. Webster, and E. A. Govorkova (2007).
Amantadine-oseltamivir combination therapy for H5N1 influenza virus infection in
mice. Antivir Ther 12 (3), 363–70.
Iwakiri, K., M. Ghazizadeh, E. Jin, M. Fujiwara, T. Takemura, S. Takezaki, S. Kawana,
S. Yasuoka, and O. Kawanami (2004). Human airway trypsin-like protease induces
PAR-2-mediated IL-8 release in psoriasis vulgaris. J Invest Dermatol 122 (4), 937–44.
Kam, Y. W., Y. Okumura, H. Kido, L. F. Ng, R. Bruzzone, and R. Altmeyer (2009).
Cleavage of the SARS coronavirus spike glycoprotein by airway proteases enhances
virus entry into human bronchial epithelial cells in vitro. PLoS One 4 (11), e7870.
65
References
Karlas, A., N. Machuy, Y. Shin, K. P. Pleissner, A. Artarini, D. Heuer, D. Becker,
H. Khalil, L. A. Ogilvie, S. Hess, A. P. Maurer, E. Muller, T. Wolff, T. Rudel, and
T. F. Meyer (2010). Genome-wide RNAi screen identifies human host factors crucial
for influenza virus replication. Nature 463 (7282), 818–22.
Kawaoka, Y., C. W. Naeve, and R. G. Webster (1984). Is virulence of H5N2 influenza
viruses in chickens associated with loss of carbohydrate from the hemagglutinin?
Virology 139 (2), 303–16.
Kawaoka, Y. and R. G. Webster (1989). Interplay between carbohydrate in the stalk
and the length of the connecting peptide determines the cleavability of influenza
virus hemagglutinin. J Virol 63 (8), 3296–300.
Khatchikian, D., M. Orlich, and R. Rott (1989). Increased viral pathogenicity after insertion of a 28S ribosomal RNA sequence into the haemagglutinin gene of an
influenza virus. Nature 340 (6229), 156–7.
Kido, H., Y. Okumura, H. Yamada, T. Q. Le, and M. Yano (2007). Proteases essential
for human influenza virus entry into cells and their inhibitors as potential therapeutic
agents. Curr Pharm Des 13 (4), 405–14.
Kido, H., K. Sakai, Y. Kishino, and M. Tashiro (1993). Pulmonary surfactant is a
potential endogenous inhibitor of proteolytic activation of Sendai virus and influenza
A virus. FEBS Lett 322 (2), 115–9.
Kido, H., Y. Yokogoshi, K. Sakai, M. Tashiro, Y. Kishino, A. Fukutomi, and
N. Katunuma (1992). Isolation and characterization of a novel trypsin-like protease
found in rat bronchiolar epithelial Clara cells. A possible activator of the viral fusion
glycoprotein. J Biol Chem 267 (19), 13573–9.
Kilbourne, E. D. (2006). Influenza pandemics of the 20th century. Emerging Infectious
Diseases 12, 9–14.
Kim, T. S., C. Heinlein, R. C. Hackman, and P. S. Nelson (2006). Phenotypic analysis
of mice lacking the Tmprss2-encoded protease. Mol Cell Biol 26 (3), 965–75.
Klenk, H. D. and W. Garten (1994). Host cell proteases controlling virus pathogenicity.
Trends Microbiol 2 (2), 39–43.
Klenk, H. D., R. Rott, M. Orlich, and J. Blodorn (1975). Activation of influenza A
viruses by trypsin treatment. Virology 68 (2), 426–39.
Koerner, I., M. N. Matrosovich, O. Haller, P. Staeheli, and G. Kochs (2012). Altered
receptor specificity and fusion activity of the haemagglutinin contribute to high virulence of a mouse-adapted influenza A virus. J Gen Virol 93 (Pt 5), 970–9.
Konig, R., S. Stertz, Y. Zhou, A. Inoue, H. H. Hoffmann, S. Bhattacharyya, J. G.
Alamares, D. M. Tscherne, M. B. Ortigoza, Y. Liang, Q. Gao, S. E. Andrews,
S. Bandyopadhyay, P. De Jesus, B. P. Tu, L. Pache, C. Shih, A. Orth, G. Bonamy,
L. Miraglia, T. Ideker, A. Garcia-Sastre, J. A. Young, P. Palese, M. L. Shaw, and
S. K. Chanda (2010). Human host factors required for influenza virus replication.
Nature 463 (7282), 813–7.
66
References
Kothary, R., S. Clapoff, A. Brown, R. Campbell, A. Peterson, and J. Rossant (1988).
A transgene containing lacZ inserted into the dystonia locus is expressed in neural
tube. Nature 335 (6189), 435–7.
Kuiken, T. and J. K. Taubenberger (2008). Pathology of human influenza revisited.
Vaccine 26 Suppl 4, D59–66.
Lakadamyali, M., M. J. Rust, and X. Zhuang (2004). Endocytosis of influenza viruses.
Microbes Infect 6 (10), 929–36.
Lazarowitz, S. G., A. R. Goldberg, and P. W. Choppin (1973). Proteolytic cleavage
by plasmin of the HA polypeptide of influenza virus: host cell activation of serum
plasminogen. Virology 56 (1), 172–80.
Lee, C. M., A. K. Weight, J. Haldar, L. Wang, A. M. Klibanov, and J. Chen (2012).
Polymer-attached zanamivir inhibits synergistically both early and late stages of
influenza virus infection. Proc Natl Acad Sci U S A 109 (50), 20385–90.
Linder, C. C. (2001). The influence of genetic background on spontaneous and genetically engineered mouse models of complex diseases. Lab Anim (NY) 30 (5), 34–9.
Loregian, A., B. Mercorelli, G. Nannetti, C. Compagnin, and G. Palu (2014). Antiviral
strategies against influenza virus: towards new therapeutic approaches. Cell Mol Life
Sci.
Malakhov, M. P., L. M. Aschenbrenner, D. F. Smee, M. K. Wandersee, R. W. Sidwell,
L. V. Gubareva, V. P. Mishin, F. G. Hayden, D. H. Kim, A. Ing, E. R. Campbell,
M. Yu, and F. Fang (2006). Sialidase fusion protein as a novel broad-spectrum
inhibitor of influenza virus infection. Antimicrob Agents Chemother 50 (4), 1470–9.
Marjuki, H., M. I. Alam, C. Ehrhardt, R. Wagner, O. Planz, H. D. Klenk, S. Ludwig,
and S. Pleschka (2006). Membrane accumulation of influenza A virus hemagglutinin triggers nuclear export of the viral genome via protein kinase Calpha-mediated
activation of ERK signaling. J Biol Chem 281 (24), 16707–15.
Matsushima, R., A. Takahashi, Y. Nakaya, H. Maezawa, M. Miki, Y. Nakamura,
F. Ohgushi, and S. Yasuoka (2006). Human airway trypsin-like protease stimulates
human bronchial fibroblast proliferation in a protease-activated receptor-2-dependent
pathway. Am J Physiol Lung Cell Mol Physiol 290 (2), L385–95.
Matsuyama, S., N. Nagata, K. Shirato, M. Kawase, M. Takeda, and F. Taguchi (2010).
Efficient activation of the severe acute respiratory syndrome coronavirus spike protein
by the transmembrane protease TMPRSS2. J Virol 84 (24), 12658–64.
Mendel, D. B. and R. W. Sidwell (1998). Influenza virus resistance to neuraminidase
inhibitors. Drug Resist Updat 1 (3), 184–9.
Meyer, D., F. Sielaff, M. Hammami, E. Böttcher-Friebertshäuser, W. Garten, and
T. Steinmetzer (2013). Identification of the first synthetic inhibitors of the type II
transmembrane serine protease TMPRSS2 suitable for inhibition of influenza virus
activation. Biochem J 452, 331–43.
67
References
Miki, M., Y. Nakamura, A. Takahashi, Y. Nakaya, H. Eguchi, T. Masegi, K. Yoneda,
S. Yasuoka, and S. Sone (2003). Effect of human airway trypsin-like protease on
intracellular free Ca2+ concentration in human bronchial epithelial cells. J Med
Invest 50 (1-2), 95–107.
Min, H. J., M. K. Lee, J. W. Lee, and S. Kim (2014). TMPRSS4 induces cancer cell
invasion through pro-uPA processing. Biochem Biophys Res Commun 446 (1), 1–7.
Modrow, S., D. Falke, U. Truyen, and H. Schätzl (2010). Molekulare Virologie (3. ed.).
Spektrum Akademischer Verlag GmbH Heidelberg-Berlin.
Moncla, L. H., T. M. Ross, J. M. Dinis, J. T. Weinfurter, T. D. Mortimer, N. SchultzDarken, K. Brunner, r. Capuano, S. V., C. Boettcher, J. Post, M. Johnson, C. E.
Bloom, A. M. Weiler, and T. C. Friedrich (2013). A novel nonhuman primate model
for influenza transmission. PLoS One 8 (11), e78750.
Monto, A. S. and N. H. Arden (1992). Implications of viral resistance to amantadine
in control of influenza A. Clin Infect Dis 15 (2), 362–7; discussion 368–9.
Morita, M., K. Kuba, A. Ichikawa, M. Nakayama, J. Katahira, R. Iwamoto,
T. Watanebe, S. Sakabe, T. Daidoji, S. Nakamura, A. Kadowaki, T. Ohto, H. Nakanishi, R. Taguchi, T. Nakaya, M. Murakami, Y. Yoneda, H. Arai, Y. Kawaoka, J. M.
Penninger, M. Arita, and Y. Imai (2013). The lipid mediator protectin D1 inhibits
influenza virus replication and improves severe influenza. Cell 153 (1), 112–25.
Moss, R. B., C. Hansen, R. L. Sanders, S. Hawley, T. Li, and R. T. Steigbigel (2012).
A phase II study of DAS181, a novel host directed antiviral for the treatment of
influenza infection. J Infect Dis 206 (12), 1844–51.
Murakami, M., T. Towatari, M. Ohuchi, M. Shiota, M. Akao, Y. Okumura, M. A.
Parry, and H. Kido (2001). Mini-plasmin found in the epithelial cells of bronchioles
triggers infection by broad-spectrum influenza A viruses and Sendai virus. Eur J
Biochem 268 (10), 2847–55.
Murti, K. G., R. G. Webster, and I. M. Jones (1988). Localization of RNA polymerases
on influenza viral ribonucleoproteins by immunogold labeling. Virology 164 (2), 562–
6.
Nayak, D. P., R. A. Balogun, H. Yamada, Z. H. Zhou, and S. Barman (2009). Influenza
virus morphogenesis and budding. Virus Res 143 (2), 147–61.
Nayak, D. P., E. K. Hui, and S. Barman (2004). Assembly and budding of influenza
virus. Virus Res 106 (2), 147–65.
Nelson, M. and E. Holmes (2007). The evolution of epidemic influenza. Nature Reviews
Genetics 8, 196–205.
Neumann, G. and Y. Kawaoka (2015). Transmission of influenza a viruses. Virology 479-480, 234–246.
Neumann, G., T. Noda, and Y. Kawaoka (2009). Emergence and pandemic potential
of swine-origin H1N1 influenza virus. Nature 459, 931–939.
68
References
Nicholls, J. M., L. M. Aschenbrenner, J. C. Paulson, E. R. Campbell, M. P. Malakhov,
D. F. Wurtman, M. Yu, and F. Fang (2008). Comment on: concerns of using sialidase
fusion protein as an experimental drug to combat seasonal and pandemic influenza.
J Antimicrob Chemother 62 (2), 426–8; author reply 428–9.
Nicholls, J. M., R. B. Moss, and S. M. Haslam (2013). The use of sialidase therapy for
respiratory viral infections. Antiviral Res 98 (3), 401–9.
Oberst, M. D., B. Singh, M. Ozdemirli, R. B. Dickson, M. D. Johnson, and C. Y.
Lin (2003). Characterization of matriptase expression in normal human tissues. J
Histochem Cytochem 51 (8), 1017–25.
Ogasawara, T., B. Gotoh, H. Suzuki, J. Asaka, K. Shimokata, R. Rott, and Y. Nagai
(1992). Expression of factor X and its significance for the determination of paramyxovirus tropism in the chick embryo. EMBO J 11 (2), 467–72.
Ohler, A. and C. Becker-Pauly (2011). Morpholino knockdown of the ubiquitously
expressed transmembrane serine protease TMPRSS4a in zebrafish embryos exhibits
severe defects in organogenesis and cell adhesion. Biol Chem 392 (7), 653–64.
Ohuchi, M., M. Orlich, R. Ohuchi, B. E. Simpson, W. Garten, H. D. Klenk, and R. Rott
(1989). Mutations at the cleavage site of the hemagglutinin after the pathogenicity
of influenza virus A/chick/Penn/83 (H5N2). Virology 168 (2), 274–80.
Ohuchi, R., M. Ohuchi, W. Garten, and H. D. Klenk (1991). Human influenza virus
hemagglutinin with high sensitivity to proteolytic activation. J Virol 65 (7), 3530–7.
Okumura, Y., E. Takahashi, M. Yano, M. Ohuchi, T. Daidoji, T. Nakaya, E. Bottcher,
W. Garten, H. D. Klenk, and H. Kido (2010). Novel type II transmembrane serine
proteases, MSPL and TMPRSS13, Proteolytically activate membrane fusion activity
of the hemagglutinin of highly pathogenic avian influenza viruses and induce their
multicycle replication. J Virol 84 (10), 5089–96.
Palese, P. and M. L. Shaw (2007). Orthomyxoviridae: the viruses and their replication.
(5th edn. ed.). Fields Virology.
Palese, P., K. Tobita, M. Ueda, and R. W. Compans (1974). Characterization of temperature sensitive influenza virus mutants defective in neuraminidase. Virology 61 (2),
397–410.
Passero, C. J., G. M. Mueller, M. M. Myerburg, M. D. Carattino, R. P. Hughey, and
T. R. Kleyman (2012). TMPRSS4-dependent activation of the epithelial sodium
channel requires cleavage of the gamma-subunit distal to the furin cleavage site. Am
J Physiol Renal Physiol 302 (1), F1–8.
Paterson, D. and E. Fodor (2012). Emerging roles for the influenza A virus nuclear
export protein (NEP). PLoS Pathog 8 (12), e1003019.
Perdue, M. L., M. Garcia, D. Senne, and M. Fraire (1997). Virulence-associated sequence duplication at the hemagglutinin cleavage site of avian influenza viruses.
Virus Res 49 (2), 173–86.
69
References
Pinto, L. H., L. J. Holsinger, and R. A. Lamb (1992). Influenza virus M2 protein has
ion channel activity. Cell 69 (3), 517–28.
Pinto, L. H. and R. A. Lamb (2007). Controlling influenza virus replication by inhibiting its proton channel. Mol Biosyst 3 (1), 18–23.
Planes, C., C. Leyvraz, T. Uchida, M. A. Angelova, G. Vuagniaux, E. Hummler,
M. Matthay, C. Clerici, and B. Rossier (2005). In vitro and in vivo regulation
of transepithelial lung alveolar sodium transport by serine proteases. Am J Physiol
Lung Cell Mol Physiol 288 (6), L1099–109.
Ranjan, P., L. Jayashankar, V. Deyde, H. Zeng, W. G. Davis, M. B. Pearce, J. B.
Bowzard, M. A. Hoelscher, V. Jeisy-Scott, M. E. Wiens, S. Gangappa, L. Gubareva,
A. Garcia-Sastre, J. M. Katz, T. M. Tumpey, T. Fujita, and S. Sambhara (2010).
5’PPP-RNA induced RIG-I activation inhibits drug-resistant avian H5N1 as well as
1918 and 2009 pandemic influenza virus replication. Virol J 7, 102.
Reid, A. H. and J. K. Taubenberger (2003). The origin of the 1918 pandemic influenza
virus: a continuing enigma. J Gen Virol 84 (Pt 9), 2285–92.
Reperant, L. A., G. F. Rimmelzwaan, and A. D. Osterhaus (2014). Advances in influenza vaccination. F1000Prime Rep 6, 47.
Resa-Infante, P., R. Thieme, T. Ernst, P. C. Arck, H. Ittrich, R. Reimer, and G. Gabriel
(2014). Importin-alpha7 is required for enhanced influenza A virus replication in the
alveolar epithelium and severe lung damage in mice. J Virol 88 (14), 8166–79. R.
Sakai, K., Y. Ami, M. Tahara, T. Kubota, M. Anraku, M. Abe, N. Nakajima,
T. Sekizuka, K. Shirato, Y. Suzaki, A. Ainai, Y. Nakatsu, K. Kanou, K. Nakamura, T. Suzuki, K. Komase, E. Nobusawa, K. Maenaka, M. Kuroda, H. Hasegawa,
Y. Kawaoka, M. Tashiro, and M. Takeda (2014). The host protease TMPRSS2 plays
a major role in in vivo replication of emerging H7N9 and seasonal influenza viruses.
J Virol 88 (10), 5608–16.
Sakai, K., T. Kohri, M. Tashiro, Y. Kishino, and H. Kido (1994). Sendai virus infection
changes the subcellular localization of tryptase Clara in rat bronchiolar epithelial
cells. Eur Respir J 7 (4), 686–92.
Sales, K. U., J. P. Hobson, R. Wagenaar-Miller, R. Szabo, A. L. Rasmussen, A. Bey,
M. F. Shah, A. A. Molinolo, and T. H. Bugge (2011). Expression and genetic loss of
function analysis of the HAT/DESC cluster proteases TMPRSS11A and HAT. PLoS
One 6 (8), e23261.
Samji, T. (2009). Influenza A: understanding the viral life cycle. Yale J Biol Med 82 (4),
153–9.
Sato, M., S. Yoshida, K. Iida, T. Tomozawa, H. Kido, and M. Yamashita (2003).
A novel influenza A virus activating enzyme from porcine lung: purification and
characterization. Biol Chem 384 (2), 219–27.
Scheiblauer, H., M. Reinacher, M. Tashiro, and R. Rott (1992). Interactions between
bacteria and influenza A virus in the development of influenza pneumonia. J Infect
Dis 166 (4), 783–91.
70
References
Schulman, J. L. and P. Palese (1977). Virulence factors of influenza A viruses: WSN
virus neuraminidase required for plaque production in MDBK cells. J Virol 24 (1),
170–6.
Shaw, J. L. and E. P. Diamandis (2007). Distribution of 15 human kallikreins in tissues
and biological fluids. Clin Chem 53 (8), 1423–32.
Shieh, W. J., D. M. Blau, A. M. Denison, M. Deleon-Carnes, P. Adem, J. Bhatnagar,
J. Sumner, L. Liu, M. Patel, B. Batten, P. Greer, T. Jones, C. Smith, J. Bartlett,
J. Montague, E. White, D. Rollin, R. Gao, C. Seales, H. Jost, M. Metcalfe, C. S.
Goldsmith, C. Humphrey, A. Schmitz, C. Drew, C. Paddock, T. M. Uyeki, and S. R.
Zaki (2010). 2009 pandemic influenza A (H1N1): pathology and pathogenesis of 100
fatal cases in the United States. Am J Pathol 177 (1), 166–75.
Shin, K., G. F. Watts, H. C. Oettgen, D. S. Friend, A. D. Pemberton, M. F. Gurish,
and D. M. Lee (2008). Mouse mast cell tryptase mMCP-6 is a critical link between
adaptive and innate immunity in the chronic phase of Trichinella spiralis infection.
J Immunol 180 (7), 4885–91.
Shirogane, Y., M. Takeda, M. Iwasaki, N. Ishiguro, H. Takeuchi, Y. Nakatsu,
M. Tahara, H. Kikuta, and Y. Yanagi (2008). Efficient multiplication of human
metapneumovirus in Vero cells expressing the transmembrane serine protease TMPRSS2. J Virol 82 (17), 8942–6.
Shulla, A., T. Heald-Sargent, G. Subramanya, J. Zhao, S. Perlman, and T. Gallagher
(2011). A transmembrane serine protease is linked to the severe acute respiratory
syndrome coronavirus receptor and activates virus entry. J Virol 85 (2), 873–82.
Sidwell, R. W., K. W. Bailey, P. A. Bemis, M. H. Wong, E. J. Eisenberg, and J. H.
Huffman (1999). Influence of treatment schedule and viral challenge dose on the
in vivo influenza virus-inhibitory effects of the orally administered neuraminidase
inhibitor GS 4104. Antivir Chem Chemother 10 (4), 187–93.
Sieczkarski, S. B. and G. R. Whittaker (2005). Characterization of the host cell entry
of filamentous influenza virus. Arch Virol 150 (9), 1783–96.
Sielaff, F., E. Bottcher-Friebertshauser, D. Meyer, S. M. Saupe, I. M. Volk, W. Garten,
and T. Steinmetzer (2011). Development of substrate analogue inhibitors for the
human airway trypsin-like protease HAT. Bioorg Med Chem Lett 21 (16), 4860–4.
Simonsen, L. (1999). The global impact of influenza on morbidity and mortality.
Vaccine 17 Suppl 1, S3–10.
Simpson, E. M., C. C. Linder, E. E. Sargent, M. T. Davisson, L. E. Mobraaten, and
J. J. Sharp (1997). Genetic variation among 129 substrains and its importance for
targeted mutagenesis in mice. Nat Genet 16 (1), 19–27.
Skehel, J. J. and D. C. Wiley (2000). Receptor binding and membrane fusion in virus
entry: the influenza hemagglutinin. Annu Rev Biochem 69, 531–69.
Smith, W. (1933). A Virus Obtained From Influenza Patients. The Lancet 222 (5732),
66–68.
71
References
Srivastava, B., P. Blazejewska, M. Hessmann, D. Bruder, R. Geffers, S. Mauel, A. D.
Gruber, and K. Schughart (2009). Host genetic background strongly influences the
response to influenza a virus infections. PLoS One 4 (3), e4857.
Stegmann, T. (2000). Membrane fusion mechanisms: the influenza hemagglutinin
paradigm and its implications for intracellular fusion. Traffic 1 (8), 598–604.
Steinhauer, D. A. (1999). Role of hemagglutinin cleavage for the pathogenicity of
influenza virus. Virology 258 (1), 1–20.
Stieneke-Grober, A., M. Vey, H. Angliker, E. Shaw, G. Thomas, C. Roberts, H. D.
Klenk, and W. Garten (1992). Influenza virus hemagglutinin with multibasic cleavage
site is activated by furin, a subtilisin-like endoprotease. EMBO J 11 (7), 2407–14.
Szabo, R. and T. H. Bugge (2008). Type II transmembrane serine proteases in development and disease. Int J Biochem Cell Biol 40 (6-7), 1297–316.
Szabo, R., Q. Wu, R. B. Dickson, S. Netzel-Arnett, T. M. Antalis, and T. H. Bugge
(2003). Type II transmembrane serine proteases. Thromb Haemost 90 (2), 185–93.
Takeuchi, T. (1997). A gene trap approach to identify genes that control development.
Dev Growth Differ 39 (2), 127–34.
Tarnow, C., G. Engels, A. Arendt, F. Schwalm, H. Sediri, A. Preuss, P. S. Nelson,
W. Garten, H. D. Klenk, G. Gabriel, and E. Böttcher-Friebertshäuser (2014). TMPRSS2 is a host factor that is essential for pneumotropism and pathogenicity of
H7N9 influenza A virus in mice. J Virol.
Tashiro, M., P. Ciborowski, H. D. Klenk, G. Pulverer, and R. Rott (1987). Role
of Staphylococcus protease in the development of influenza pneumonia. Nature 325 (6104), 536–7.
Taubenberger, J. K. and J. C. Kash (2010). Influenza virus evolution, host adaptation,
and pandemic formation. Cell Host Microbe 7 (6), 440–51.
Taubenberger, J. K. and D. M. Morens (2008). The pathology of influenza virus
infections. Annu Rev Pathol 3, 499–522.
Thangavel, R. R. and N. M. Bouvier (2014). Animal models for influenza virus pathogenesis, transmission, and immunology. J Immunol Methods 410, 60–79.
Tomlins, S. A., A. Bjartell, A. M. Chinnaiyan, G. Jenster, R. K. Nam, M. A. Rubin,
and J. A. Schalken (2009). ETS gene fusions in prostate cancer: from discovery to
daily clinical practice. Eur Urol 56 (2), 275–86.
Tong, S., X. Zhu, Y. Li, M. Shi, J. Zhang, M. Bourgeois, H. Yang, X. Chen, S. Recuenco,
J. Gomez, L. M. Chen, A. Johnson, Y. Tao, C. Dreyfus, W. Yu, R. McBride, P. J.
Carney, A. T. Gilbert, J. Chang, Z. Guo, C. T. Davis, J. C. Paulson, J. Stevens,
C. E. Rupprecht, E. C. Holmes, I. A. Wilson, and R. O. Donis (2013). New world
bats harbor diverse influenza A viruses. PLoS Pathog 9 (10), e1003657.
Towatari, T., M. Ide, K. Ohba, Y. Chiba, M. Murakami, M. Shiota, M. Kawachi,
H. Yamada, and H. Kido (2002). Identification of ectopic anionic trypsin I in rat
lungs potentiating pneumotropic virus infectivity and increased enzyme level after
virus infection. Eur J Biochem 269 (10), 2613–21.
72
References
Triana-Baltzer, G. B., L. V. Gubareva, A. I. Klimov, D. F. Wurtman, R. B. Moss,
M. Hedlund, J. L. Larson, R. B. Belshe, and F. Fang (2009). Inhibition of neuraminidase inhibitor-resistant influenza virus by DAS181, a novel sialidase fusion
protein. PLoS One 4 (11), e7838.
Tripp, R. A. and S. M. Tompkins (2009). Animal models for evaluation of influenza
vaccines. Curr Top Microbiol Immunol 333, 397–412.
van der Laan, J. W., C. Herberts, R. Lambkin-Williams, A. Boyers, A. J. Mann,
and J. Oxford (2008). Animal models in influenza vaccine testing. Expert Rev
Vaccines 7 (6), 783–93.
Wallrapp, C., S. Hahnel, F. Muller-Pillasch, B. Burghardt, T. Iwamura, M. Ruthenburger, M. M. Lerch, G. Adler, and T. M. Gress (2000). A novel transmembrane
serine protease (TMPRSS3) overexpressed in pancreatic cancer. Cancer Res 60 (10),
2602–6.
Wang, H., H. Yang, C. S. Shivalila, M. M. Dawlaty, A. W. Cheng, F. Zhang, and
R. Jaenisch (2013). One-step generation of mice carrying mutations in multiple
genes by CRISPR/Cas-mediated genome engineering. Cell 153 (4), 910–8.
Webster, R. G. and R. Rott (1987). Influenza virus A pathogenicity: the pivotal role
of hemagglutinin. Cell 50 (5), 665–6.
Wei, G., W. Meng, H. Guo, W. Pan, J. Liu, T. Peng, L. Chen, and C. Y. Chen (2011).
Potent neutralization of influenza A virus by a single-domain antibody blocking M2
ion channel protein. PLoS One 6 (12), e28309.
Weight, A. K., J. Haldar, L. Alvarez de Cienfuegos, L. V. Gubareva, T. M. Tumpey,
J. Chen, and A. M. Klibanov (2011). Attaching zanamivir to a polymer markedly
enhances its activity against drug-resistant strains of influenza a virus. J Pharm
Sci 100 (3), 831–5.
Weinheimer, V. K., A. Becher, M. Tonnies, G. Holland, J. Knepper, T. T. Bauer,
P. Schneider, J. Neudecker, J. C. Ruckert, K. Szymanski, B. Temmesfeld-Wollbrueck,
A. D. Gruber, N. Bannert, N. Suttorp, S. Hippenstiel, T. Wolff, and A. C. Hocke
(2012). Influenza A viruses target type II pneumocytes in the human lung. J Infect
Dis 206 (11), 1685–94.
Wiedenheft, B., S. H. Sternberg, and J. A. Doudna (2012). RNA-guided genetic silencing systems in bacteria and archaea. Nature 482 (7385), 331–8.
Wilk, E. and K. Schughart (2012). The Mouse as Model System to Study HostPathogen Interactions in Influenza A Infections. Current Protocols in Mouse Biology 2, 177–205.
Yamaoka, K., K. Masuda, H. Ogawa, K. Takagi, N. Umemoto, and S. Yasuoka (1998).
Cloning and Characterization of the cDNA for Human Airway Trypsin-like Protease.
J Biol Chem 273, 11895–11901.
Yasuoka, S., T. Ohnishi, S. Kawano, S. Tsuchihashi, M. Ogawara, K. Masuda, K. Yamaoka, M. Takahashi, and T. Sano (1997). Purification, characterization, and localization of a novel trypsin-like protease found in the human airway. Am J Respir Cell
Mol Biol 16 (3), 300–8. Y.
73
References
Yeh, E., R. F. Luo, L. Dyner, D. K. Hong, N. Banaei, E. J. Baron, and B. A. Pinsky
(2010). Preferential lower respiratory tract infection in swine-origin 2009 A(H1N1)
influenza. Clin Infect Dis 50 (3), 391–4.
Zambrowicz, B. P., G. A. Friedrich, E. C. Buxton, S. L. Lilleberg, C. Person, and
A. T. Sands (1998). Disruption and sequence identification of 2,000 genes in mouse
embryonic stem cells. Nature 392 (6676), 608–11.
Zhirnov, O. P., M. R. Ikizler, and P. F. Wright (2002). Cleavage of influenza a virus
hemagglutinin in human respiratory epithelium is cell associated and sensitive to
exogenous antiproteases. J Virol 76 (17), 8682–9.
Zhirnov, O. P., L. S. Kirzhner, A. V. Ovcharenko, and N. A. Malyshev (1996). Clinical
effectiveness of aprotinin aerosol in influenza and parainfluenza. Vestn Ross Akad
Med Nauk (5), 26–31.
Zhirnov, O. P., H. D. Klenk, and P. F. Wright (2011). Aprotinin and similar protease
inhibitors as drugs against influenza. Antiviral Res 92 (1), 27–36.
Zhirnov, O. P., A. V. Ovcharenko, and A. G. Bukrinskaya (1982a). Protective effect of
protease inhibitors in influenza virus infected animals. Arch Virol 73 (3-4), 263–72.
Zhirnov, O. P., A. V. Ovcharenko, and A. G. Bukrinskaya (1982b). Proteolytic activation of influenza WSN virus in cultured cells is performed by homologous plasma
enzymes. J Gen Virol 63 (2), 469–74.
Zhirnov, O. P., A. V. Ovcharenko, and A. G. Bukrinskaya (1984). Suppression of
influenza virus replication in infected mice by protease inhibitors. J Gen Virol 65 (
Pt 1), 191–6.
Zmora, P., P. Blazejewska, A. S. Moldenhauer, K. Welsch, I. Nehlmeier, Q. Wu,
H. Schneider, S. Pohlmann, and S. Bertram (2014). DESC1 and MSPL activate
influenza A viruses and emerging coronaviruses for host cell entry. J Virol 88 (20),
12087–97.
74
Affidavit
I herewith declare that I autonomously carried out the PhD-thesis entitled ”Studies on
the host response to influenza A virus infections in mouse knock-out mutants”.
No third party assistance has been used. I did not receive any assistance in return
for payment by consulting agencies or any other person. No one received any kind of
payment for direct or indirect assistance in correlation to the content of the submitted
thesis.
I conducted the project at the following institution:
Hemholtz Center for Infection Research, Infection Genetics
The thesis has not been submitted elsewhere for an exam, as thesis or for evaluation
in a similar context. I hereby affirm the above statement to be complete and true to
the best of my knowledge.
Braunschweig, 02/22/2015
Nora Kühn
I
Acknowledgement
Mein besonderer Dank gilt Prof. Dr. Klaus Schughart für die Möglichkeit, meine
Doktorarbeit in der Abteilung ”Infektionsgenetik” anfertigen zu können. Für seine
Unterstützung, Anregungen sowie die Möglichkeit diverse nationale und internationale
Konferenzen zu besuchen bin ich ihm sehr dankbar.
Auch bei Dr. Bastian Hatesuer möchte ich mich für seine exzellente Betreuung,
wertvollen Ratschläge sowie Kritiken und ständige Unterstützung danken. Ohne ihn
wäre die Entdeckungsreise durch die Welt der Proteasen nicht möglich gewesen.
Ich danke den Mitgliedern meiner Betreuungsgruppe, Prof. Dr. Georg Herrler und
Prof. Dr. Dr. Luka Cicin-Sain, für die Anregungen und interessanten Diskussionen.
Im Besonderen möchte ich den Technischen Assistenten der Abteilung danken. Vor
allem ohne die Hilfe von Karin Lammert hätte ich oft die Flut an Genotypisierungen
nicht bewältigen können. Auch bei Sylvana Foth möchte ich mich für die Unterstützung
bei organisatorischen Belangen danken.
Weiterhin danke ich Dr. Ruth Stricker für die großartige Zusammenarbeit und für
die Hilfe bei der Etablierung des Western Blotts, Dr. Esther Wilk danke ich für die
vielen wertvollen Ratschläge in Sachen Immunologie und Dr. Heike Kollmus für ihre
entscheidende Hilfe im Kampf mit dem Southern Blot sowie für ihre konstruktive Kritik
während meiner Projektpräsentationen.
Besonders danke ich auch Dr. Leonie Dengler und Sarah Leist für die tolle Arbeitsatmosphäre, Unterstützung in allen Lebensbereichen und dafür, dass sie mir auch an
düsteren Tagen stets ein Lächeln ins Gesicht gezaubert haben.
Der ganzen Abteilung ”Infektionsgenetik” gebührt mein Dank für die gute Arbeitsatmosphäre und tolle Zusammenarbeit.
Dr. Silke Bergmann danke ich für die Anfertigung der In-situ-Färbungen und auch für
die schöne gemeinsame Zeit in Braunschweig.
Bei Nadine Kasnitz möchte ich mich für die Hilfe am Konfokal-Mikroskop und für die
vielen Tipps bezüglich der Fluoreszenzfärbung bedanken.
Friederike Schäkel danke ich für ihre hervorragende Arbeit während ihrer Bachelorarbeit in unserer Gruppe.
Weiter möchte ich auch den Tierpflegern des HZIs sowie Anna Rinkel und Marina Pils
aus der Mauspathologie für die gute Zusammenarbeit danken.
Meinen Eltern Josefine und Hans-Jürgen Mehnert danke ich für die allgegenwärtige
Unterstützung. Ohne ihre Hilfe und ihren Glauben an mich hätte ich bisher nicht so
viel in meinem Leben erreicht.
Ein besonderer Dank gebührt meinem Mann Markus Kühn. Ich danke ihm für seine
grenzenlose Liebe, Unterstützung, Geduld und Motivation.
Nora Kühn
Braunschweig, Februar 2015
II

Studies on the host response to influenza A virus infections in

Transcription

Documents pareils

Influenza A H7N9 (A/Hangzhou/1/2013) Hemagglutinin Protein

The 1999–2000 avian influenza (H7N1) epidemic in Italy

A nosocomial outbreak of 2009 pandemic influenza A (H1N1) in a

African Swine Fever Definition Affected species Pathogens Modes of

TamiFlu and FluMist - Natural Solutions Foundation

Le septembre 2011 - The Ottawa Hospital Foundation

Corpus Octobre 2006

Equine and canine influenza: a review of current events

Consultation with Health Care Professionals and Influenza