Regulation of hepatocyte proliferation after subtotal liver resection in rats

Abstract

Hepatocyte proliferation is the main cellular mechanism of liver regeneration. However, after removal of more than 80 % of the liver mass, a temporary block of hepatocyte proliferation is observed, which may be the cause of impaired regeneration during transplantation and liver resection in the clinical practice. The current study aims to analyze the molecular mechanisms of hepatocyte proliferation impairment after subtotal liver resection in rats. In male Wistar rats, a model of liver regeneration after subtotal resection is reproduced - removal of more than 80 % of liver mass. Using the methods of immunohistochemistry, PCR-RT, western blot, possible molecular mechanisms of slowing down the proliferation of hepatocytes were studied. It was found that expression of cyclin D1 and E increased only 30 hours after surgery. Their appearance coincides with the beginning of transcription of genes for Cyclins D1 and E1 at 30 h after surgery. The corresponding increase in concentrations of cyclin D, and E proteins is further delayed till 48 h after surgery. These results indicate that, in this particular model, hepatocytes are reluctant to undergo transition between G0- and G1 -phases of cell cycle. We have observed a prolonged decrease in the expression of protooncogene C-met (the hepatocyte growth factor receptor-encoding gene Met). We have also observed an increase in expression of the transforming growth factor beta-1 receptor-encoding gene TgfbrII. At the same time, irreversible block of hepatocyte proliferation was prevented by expression of certain factors, notably of the TWEAK/ Fn14 signaling pathway: concentrations of the corresponding proteins in remnant livers have peaked from 24 h to 48 h after surgery. Thus, after subtotal liver resection, the remaining hepatocytes are exposed to a large scope of both mitogenic and antimitogenic factors. Proliferative behavior of hepatocytes in remnant livers is determined by fine balance of these factors. The prevalence of antimitogenic factors in the early period after surgery delays the onset of hepatocyte proliferation.