Human and rat hepatic stellate cells produce stem cell factor: a possible mechanism for mast cell recruitment in liver fibrosis

Background/Aims: Mast cell numbers are markedly increased in advanced liver fibrosis. Stem cell factor may recruit mast cells to the liver following injury as it induces mast cell proliferation, survival and differentiation from resident tissue precursors. This study examines stem cell factor production in human fibrotic liver and by hepatic stellate cells during culture in vitro. Methods: Stem cell factor production was examined in human fibrotic livers by ELISA and in human and rat hepatic stellate cell cultures using reverse transcription-polymerase chain reaction (RT-PCR), Northern blotting, Western blotting and immunocyto-chemistry. Co-culture studies examined adhesion between hepatic stellate cells and purified mast cells. Results: RT-PCR showed stem cell factor mRNA was more consistently expressed in fibrotic human livers relative to normal, and ELISA confirmed this by showing stem cell factor protein was significantly increased 2–3-fold in homogenates of human cirrhotic liver (primary biliary cirrhosis, primary sclerosing cholangitis) relative to normal. RT-PCR detected stem cell factor mRNA in human and rat hepatic stellate cells activated by culture on plastic. This was confirmed by Western blotting, which showed that freshly isolated hepatic stellate cells expressed relatively little 30 kD stem cell factor compared to late primary culture activated hepatic stellate cells (14 day) and passaged hepatic stellate cells. As assessed by fluorescence immunocytochemistry, stem cell factor protein was homogeneously expressed by populations of culture-activated rat hepatic stellate cells. During coculture, purified human skinmast cells adhered to hepatic stellate cell monolayers on plastic, and this adherence was inhibited >50% by addition of antibodies against stem cell factor. Conclusions: Hepatic stellate cells activated in vitro produce stem cell factor. These cells may play an important role in recruiting mast cells to liver during injury and fibrosis.