Rat hepatic stellate cell expression of α2-macroglobulin is a feature of cellular activation: implications for matrix remodelling in hepatic fibrosis

Abstract

1. Hepatic stellate cells are key mediators of hepatic fibrosis. We have studied hepatic stellate cell expression of the collagenase and general protease inhibitor alpha2-macroglobulin after activation in tissue culture and in response to certain cytokines. 2. Hepatic stellate cells isolated by Pronase-collagenase digestion were activated by culture on uncoated plastic. By Northern analysis hepatic stellate cells undergoing activation (5 days) expressed alpha2-macroglobulin mRNA and alpha2-macroglobulin could be immunolocalized to hepatic stellate cells from 5 to 15 days of culture. 3. By ELISA of cell culture supernatants hepatic stellate cell secretion of alpha2-macroglobulin was found to increase from 2. 78+/-1.13 ng x ml-1 x microgram-1 DNA per 24 h at 5 days of culture (n=8) to 13.55+/-4.64 ng x ml-1 x microgram-1 DNA per 24 h at 15 days of culture (n=7). Stimulation of hepatic stellate cells with interleukin-6 at 5 days caused a significant increase in alpha2-macroglobulin expression as did exposure to Kupffer-cell conditioned medium. However, exposure of hepatic stellate cells to interleukin-1, transforming growth factor-beta1 and tumour necrosis factor-alpha had no significant effect. 4. During profibrotic liver injury plasma alpha2-macroglobulin levels were found to increase to between 850% and 250% of the control value (100%) after bile duct ligation (72 h to 13 days respectively), and to 1166% and 1106% of the control value during progressive CCl4-induced fibrosis (24 h to 4 weeks respectively). 5. These data suggest that hepatic stellate cells are a potential source of the potent protease inhibitor alpha2-macroglobulin, expression of which may inhibit matrix remodelling during progressive fibrosis.