Increased expression of connective tissue growth factor in fibrotic human liver and in activated hepatic stellate cells

Abstract

Background/Aims: Connective tissue growth factor is a recently described mitogenic protein implicated in a variety of fibrotic disorders. Connective tissue growth factor may be a downstream mediator of the pro-fibrotic and mitogenic actions of transforming growth factor-β, promoting extracellular matrix deposition and fibrogenesis. As transforming growth factor-β is considered important to the pathogenesis of hepatic fibrosis, we examined the possible contribution of connective tissue growth factor to this process. Methods: Connective tissue growth factor expression was examined in normal and fibrotic human and rat livers using RT-PCR and ribonuclease protection assays, and in primary cultures of rat hepatic stellate cells by Northern and Western blotting. Results: Ribonuclease protection assays demonstrated connective tissue growth factor mRNA was increased 3–5-fold in human fibrotic liver compared with normal. RT-PCR showed this mRNA was increased in carbon-tetrachloride-treated rat liver. Northern analysis showed connective tissue growth factor mRNA was increasingly expressed during progressive activation of cultured rat hepatic stellate cells. Western analysis confirmed that freshly isolated hepatic stellate cells secreted relatively little connective tissue growth factor compared with hepatic stellate cells activated in culture. Hepatic stellate cells stimulated with transforming growth factor-β1 showed increased expression of connective tissue growth factor mRNA and protein. Conclusions: Connective tissue growth factor mRNA is consistently upregulated in human liver cirrhosis of various aetiologies, supporting a role for this growth factor in hepatic fibrogenesis. Our studies suggest that hepatic stellate cells may be an important source of hepatic connective tissue growth factor in vivo, particularly following stimulation with transforming growth factor-β.