Proteomic host responses and growth properties of highly pathogenic H5N1 and novel H7N9 avian influenza strains
Influenza viruses cause significant mortality and morbidity worldwide due to seasonal oubreaks as well as occassional, and sometimes devastating, pandemics. Estimates state that approximately 5% of the adult and 20% of the child population is infected yearly, leading to approximately a half-million deaths and three million severe infections in non-pandemic years. Aside from globally-circulating strains, zoonotic outbreaks caused by avian strains are a constant threat. In 1997, the first human cases of H5N1 infections occurred and since then strains of this subtype have killed approximately 700 people causing a severe disease with as high as 60% lethality rate. In March 2013, a strain of the H7N9 subtype started an epizootic in China causing a severe respiratory disease reminiscent of H5N1 infections and with a 20% case fatality rate. In this thesis, we have studied the host responses as well the viral replication kinetics of H5N1 and H7N9 strains and compared then to those of mild H1N1 seasonal and 2009 pandemic strains. During early infections of A549 cells, we have shown that the H5N1 virus induced a more profound and functional change to the host proteome. All viruses induced the NRF2-mediated oxidative stress responses and the H7N9 and H5N1 strains downregulated fibronectin, a host protein vital to infection for human strains. Using mathematical modeling and extensive growth kinetic analysis, we showed that the H5N1 and H7N9 strains had higher peak titers and faster growth kinetics. This was due to an higher infection rate for the H7N9 strain and an higher production rate for the H5N1 strain, compared to the human viruses. Conversely, the 2009 pandemic H1N1 strain had the poorest replication kinetics, longest eclipse phase and lowest infection rates. These results point towards the higher level of cellular disruption during infection with highly pathogenic strains of influenza, which may be indicative of the more profound changes required to support growth of viruses with faster kinetics to higher titers. Furthermore, the greater changes in the cellular proteome that we have characterized in vitro may be connected to the significantly greater virulence associated with infection by avian viruses in vivo, opening a novel and productive avenue of investigation to understand viral virulence mechanisms.
Influenza, Proteomics, iTRAQ, H5N1, H7N9, Modeling, NRF2, Fibronectin