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

1. Hepatic stellate cells are key mediators of hepatic fibrosis. We have studied hepatic stellate cell expression of the collagenase and general protease inhibitor alpha 2-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 alpha 2-macroglobulin mRNA and alpha 2-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 alpha 2-macroglobulin was found to increase from 2.78 +/- 1.13 ng.ml(-1).mu g(-1) DNA per 24 h at 5 days of culture (n = 8) to 13.55 +/- 4.64 ng.ml(-1).mu g(-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 alpha 2-macroglobulin expression as did exposure to Kupffer-cell conditioned medium. However, exposure of hepatic stellate cells to interleukin-1, transforming growth factor-beta(1) and tumour necrosis factor-alpha had no significant effect. 4. During profibrotic liver injury plasma alpha 2-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 CCl(4)-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 alpha 2-macroglobulin, expression of which may inhibit matrix remodelling during progressive fibrosis.