Modulation of stellate cell proliferation and gene expression by rat hepatocytes: effect of toxic iron overload.

Mechanisms by which hepatocytes and transdifferentiated hepatic stellate cells (HSC) initiate liver fibrosis in chronic iron toxicity are unknown. This study was to determine if factors in media from control and iron-loaded rat hepatocyte cultures modulate HSC gene expression and proliferation. Conditioned medium (CM) from both control and iron-loaded hepatocytes increased serum-stimulated DNA synthesis by HSC to 140% of control values (P<0.05). Heating CM (15 min, 80 degrees C) caused a suppression of DNA synthesis that was partially reversed by a TGF-beta-neutralizing antibody. Addition of TGF-beta1 reproduced the suppression. Levels in HSC of mRNA for collagen type I, collagen type IV, TGF-beta, and plasminogen activator inhibitor-1 were unaffected by exposure to CM but increased significantly when CM from iron-loaded hepatocytes was heat-treated. In HepG2 cell cultures, iron loading increased total (but not activated) TGF-beta secretion into the medium approximately 2-fold. We conclude that increased secretion of latent TGF-beta by hepatocytes injured by iron is a potential factor influencing fibrogenic behavior of HSC.