title: Inflammasomes, cell explosions, and pathogenesis: exploring the role of RNA virus-induced programmed cell death as a mechanism of protection or of viral pathogenesis
Creators: name: Wallace, Hannah L.
Publisher: name: Memorial University of Newfoundland
publisherIdentifier: https://ror.org/04haebc03
publisherIdentifierScheme: ROR
Year: 2025

description: Programmed cell death (PCD), namely apoptosis, pyroptosis, and necroptosis, have been reported in the context of many viral infections. However, the role that PCD plays during infection, whether it acts as a mechanism of pathogenesis or as an innate immune response to aid in viral clearance, is unclear. Apoptosis is generally thought of as a non-inflammatory form of PCD while pyroptosis and necroptosis are considered inflammatory. Apoptosis, mediated by caspase-3, results in chromatin condensation and cell blebbing. Pyroptosis, mediated by caspase-1 and gasdermin-D, and necroptosis, mediated by RIPK3 and pMLKL, both result in pore formation in the cell membrane and subsequent lysis of the cell. RNA viruses have been the cause of well-known large-scale virus outbreaks over the last century including HIV, Ebola, Influenza A viruses (IAVs), and SARS-CoV-2. RNA viruses are of particular interest due to their high mutation rates and association with increased likelihood of pandemics. Hepatitis C virus (HCV) and IAVs are two types of RNA viruses with substantial public health implications. HCV is a blood-borne virus that, if left untreated, will lead to chronic infection in ~80% of individuals. Despite curative drug treatment for HCV, some individuals still develop liver disease, even in the absence of virus infection, necessitating research to understand the cause of ongoing liver disease and inflammation. IAVs have been the causative agent of several pandemics in the last century and are constantly a concern for public health agencies. While seasonal human IAVs have been studied extensively in the context of cell death, IAVs from non-human hosts, such as birds and swine, have not been studied in this context despite their pandemic potential. The goal of the research for this thesis was a better understanding of pathogenesis, the role of PCD, and the mechanisms by which PCD is induced by RNA virus infections. Chapter 1 introduces these topics. Chapter 2 focuses on our investigation of apoptosis and pyroptosis induction by HCV. We found significant crosstalk between the apoptosis and pyroptosis pathways during HCV infection and showed that PCD was necessary for efficient virus propagation. Chapter 3 traces our investigation of the trigger of HCV-induced pyroptosis in hepatocytes, finding that fully infectious virus production was necessary to trigger pyroptosis in HCV-infected Huh-7.5 cells. We also attempted to identify mechanisms by which bystander pyroptosis could be occurring and investigated the role of immune cells in bystander pyroptosis, finding that THP-1 cells are susceptible to bystander pyroptosis induced by HCV. Chapter 4 outlines our investigation of PCD induced by two IAVs of avian-origin and two of swine-origin. We found that the two avian viruses preferentially induced different forms of PCD and that one of these viruses was unexpectedly able to infect human lung cells while the other abortively infected the lung cells. The two swine viruses both induced all three forms of PCD albeit to different extents. Given the importance of RNA viruses to public health and the substantial number of disease outbreaks caused by them, understanding how these viruses cause disease is an important academic and globally relevant pursuit. The clearer understanding of the mechanisms of cell death contributing to viral pathogenesis or innate immune clearance presented here may aid in drug development and help prioritize research on viruses most likely to cause future outbreaks. Overall, the work presented in this thesis adds to the growing body of research that aims to understand the role of PCD during virus infection.