Mechanisms of Hepatitis C virus induced hepatocyte injury.

HCV disease is a global problem, with over 2% of the world?s population infected, some 180 million people. Although the disease may take decades to progress, the majority of chronically infected people will eventually show signs of liver damage. In the last few years the incidence of HCV-associated liver failure has increased considerably in the U.K. and several studies have predicted a further 50 - 100% increase in the next decade. HCV-associated liver failure is now the leading indicator for liver transplantation in the UK. Unfortunately the only current therapy (pegylated interferon + ribavirin) is expensive, has significant side effects and is often ineffective. Hence, there is an urgent need for new approaches to treat this disease.

One of the prime functions of the liver is the synthesis of bile, which is kept separate from the blood supply by a polarized barrier between the biliary vessels and the rest of the liver. Several manifestations of liver injury associated with HCV infection involve some degree of failure of this biliary system, leading to the liver being damaged by bile acid. HCV entry into cells involves proteins involved in cell polarization, notably the tight junction protein Claudin?1. We have shown that HCV infected cells have an altered polarity and express excessive quantities of Vascular Endothelial Growth Factor (VEGF), a protein which disrupts cell polarization. Depolarisation is mediated via two structural components of the virus, the envelope proteins E1 and E2, that sequester Claudin-1 protein within the cell and stimulate VEGF expression. Treatment of HCV infected cultures with an antibody that inhibits VEGF activity abrogates new rounds of HCV infection, providing an exciting new avenue for antiviral intervention. It is worth noting that, if this approach is validated during the course of this study, suitable VEGF antagonists are already approved for the treatment of various advanced cancers, and we would anticipate the process of drug development to be considerably accelerated.

Hepatitis C virus (HCV) primarily infects hepatocytes within the liver, with the majority of infected subjects developing progressive disease including chronic hepatitis, cirrhosis and hepatocellular carcinoma. However, the mechanisms underlying liver injury are poorly defined. Many tissues in the body contain polarised cells and hepatocytes are known to polarise with tight junctions separating their apical canalicular and basolateral domains. Hepatic polarity is critical to the function of the liver. Cholestasis occurs when tight junctions lose function permitting the leakage of proteins and bile acids between apical and basal compartments. Recent advances allowing the propagation of HCV in cell culture have demonstrated that viral infection disrupts hepatocellular tight junctions and induces vascular endothelial growth factor (VEGF) expression. VEGF is an angiogenic factor expressed in many tumours. We have shown that VEGF can disrupt hepatocellular tight junctions and promote HCV infection of polarized HepG2 cells. Current evidence suggests that the viral encoded E1E2 glycoproteins induce the relocalisation of tight junction proteins in a VEGF-dependent manner. We propose to investigate the effect(s) of HCV glycoproteins, cloned from subjects with or without cholestasis, on TJ protein localization, function and VEGF expression. We will evaluate both the VEGF-dependency of virus induced changes in hepatocyte polarity and the efficacy of VEGF antagonists on HCV induced changes in cellular polarity. Several VEGF antagonists are under evaluation for the treatment of diverse cancers. These data suggest that targeting VEGF may provide a new approach for the treatment of HCV infection and related HCC metastasis.