Hepatitis C virus-replicating hepatocytes induce fibrogenic activation of hepatic stellate cells

Background & Aims: The mechanism by which hepatitis C virus induces liver fibrosis remains largely obscure. To characterize the profibrogenic potential of hepatitis C virus, we used the hepatitis C virus replicon cell line Huh-7 5-15, which stably expresses the nonstructural hepatitis C virus genes NS3 through NS5B, and hepatic stellate cells as fibrogenic effector cells. Methods: Rat and human hepatic stellate cells were incubated with conditioned media from replicon cells, and expression of fibrosis-related genes was quantified by using real-time polymerase chain reaction, protein, and functional assays. Transforming growth factor beta 1 activity was determined by bioassay. Results: Hepatitis C virus replicon cells release factors that differentially modulate hepatic stellate cell expression of key genes involved in liver fibrosis in a clearly profibrogenic way, up-regulating procollagen alpha 1(I) and procollagen alpha 1(III) and down-regulating fibrolytic matrix metalloproteinases. Transforming growth factor beta 1 expression and bioactivity were increased severalfold in hepatitis C virus-replicating vs mock-transfected hepatoma cells. However, transforming growth factor beta 1 activity was responsible for only 50% of the profibrogenic activity. Conclusions: Hepatitis C virus nonstructural genes induce an increased expression of transforming growth factor beta 1 and other profibrogenic factors in infected hepatocytes. The direct induction of profibrogenic mediators by hepatitis C virus in infected hepatocytes explains the frequent observation of progressive liver fibrosis despite a low level of inflammation and suggests novel targets for antifibrotic therapies in chronic hepatitis C.