Approximately 1.8% of the population in the United States has antibody to HCV and the infection rate is increasing. Multiple retrospective, case-control and population-based studies have demonstrated that infection with the hepatitis C virus (HCV) is a significant risk factor for the development of insulin resistance, hepatic steatosis and type 2 diabetes mellitus which confer an increased risk for hepatic fibrosis, cirrhosis and hepatocellular carcinoma. The site (hepatic vs. peripheral) and severity of insulin resistance in HCV infection has never been systematically examined in humans. In addition, the cause-effect relationship between insulin resistance and hepatic steatosis in HCV infection has not been clarified. In this proposal, the hypothesis to be tested is that human HCV infection results in specific changes in gene expression that leads to significant hepatic insulin resistance which provides a 'fertile ground' for the development of hepatic steatosis. In Aim 1, the site and severity of insulin resistance (IR) in patients with hepatitis C infection will be assessed by stepped insulin-euglycemic clamp before and following anti-viral therapy. The results will be compared with a group of weight matched normal controls and individuals with non-alcoholic fatty liver disease. In Aim 2, directed and global gene profiling will be performed on biopsy samples of subjects studied in Aim 1 to test the hypothesis that HCV infection results in a distinct pattern of gene expression that is responsible for the induction of hepatic insulin resistance. The output of the gene arrays will be analyzed by different but complimentary methods: i) Gene Set Enrichment Analysis, a robust method for determining coordinated changes in gene expression of a priori defined sets of functionally related genes, ii) identification of networks of related genes populated with genes which have significant differences in expression, iii) performing a novel 'index gene network enrichment analysis' using index genes to generate networks which can be statistically compared between conditions. The results of these studies will provide the first data on the physiological mechanisms of insulin resistance and the relationship to the development of steatosis and will provide the first insight into the molecular mechanism mechanisms underlying HCV-induced insulin resistance.