Differential Gene Expression in Liver Tissue and Blood From Individuals With Chronic Viral Hepatitis With or Without a Complicating Hepatoma or Autoimmune Liver Disease

The objective of this study is to identify genes that are specifically up or down regulated in chronic viral hepatitis and autoimmune liver disease and then to examine how these expression patterns relate (if at all) to clinical outcome. The expression pattern of thousands of genes should provide extremely powerful statistical tools to distinguish between different pathophysiological states. It is well recognized that neither hepatitis B or hepatitis C is directly cytotoxic, their effect appears to be mediated via an immune response. Similarly in individuals with autoimmune liver disease e.g. primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH) immune mediated mechanisms appear to be the cause of their liver disease although the eliciting antigen(s) remain unknown. The pattern of gene expression can give clues as to both the cause and the pathogenesis of disease. For instance, if a disease is caused by an infection, a specific cytokine response is observed which will be different if this infection is viral or bacterial or parasitic. It is also possible that a certain pattern of response would be elicited if the disease is caused as a response to xenobiotic. In patients with autoimmune liver disease, it is possible that an endogenous and/or an exogenous antigen initiates the disease with a subsequent autoimmune response. Finally, it is also possible that a completely unexpected series of cellular events is responsible for pathogenesis, and the microarray experiments will enable us to discover these processes.

HCV - The molecular genetics of hepatitis C viral infection HCV molecular biology: HCV is a positive-stranded RNA Flaviviridae virus with a 9.6kB genome. The genome encodes a polyprotein of approximately 3000 amino acids which is subsequently cleaved by host and virus-specific proteases to yield 4 structural and 6 nonstructural polypeptides. The 4 functional proteins include a metalloproteinase (NS5A), serine protease (NS3/NS4A), RNA helicase (NS3), and a RNA-dependent RNA polymerase (NS5B). Six different genotypes of HCV have been described, with genotype 1 being the most prevalent worldwide and genotype 4 being the most prevalent in the Middle East.

The various genotypes interact differently with the host immune system, though the molecular basis for this is unclear. Chronic infection by genotypes 1 and 4 is notoriously resistant to treatment with IFN, while genotypes 2 and 3 have relatively better responses. This difference may be in part due to mutations in the NS5A protein. In cellular models NS5A can interact with IFN-induced antiviral enzymes such as 2'5'OAS. Other HCV proteins likely interact with cellular proteins to alter responses to immune and IFN antiviral mechanisms: HCV core protein dampens lymphocytic Th1 responses and influences IRF, Jak/STAT and iNOS pathways. Although these results suggest how the virus may alter known cellular pathways, viral evasion of the immune system is multifactorial and clearly complex.

Research Hypothesis: The processes that lead to persistence of acute HCV infection are related, at a molecular level, to those that drive HCV resistance to IFN therapy. Elucidating the specifics of the host/viral response in both of these contexts will provide novel targets for small-molecule antiviral therapy which can be applied both to acute and chronicHCV.

Progress Report: CIHR 106800 We have established a large and growing tissue and RNA registry for the study of liver disease, and have performed a comprehensive gene array analysis of chronic HCV. Some of our most important findings are detailed here.