Roles of AKT and sphingosine kinase in the antiapoptotic effects of bile duct ligation in mouse liver

Tumor necrosis factor (TNF) receptor- and Fas-mediated apoptosis are major death processes of hepatocytes in liver disease. Although antiapoptotic effects in the injured liver promote chronic hepatitis and carcinogenesis, scant information is known about these mechanisms. To explore this issue, we compared acute liver injury after TNF-α or anti-Fas antibody (Jo2) between livers from sham-operated mice and chronic injured liver via bile duct ligation (BDL). BDL inhibited hepatocyte apoptosis induced by TNF-α but not by Jo2. On the other hand, BDL inhibited the massive hemorrhage seen in livers treated with either TNF-α or Jo2. Inactivation of AKT blocked the antiapoptotic effect of BDL. Sphingosine kinase knockout mice also lost the antihemorrhagic effect of BDL and attenuated the antiapoptotic effects of BDL. In bile duct-ligated livers, hepatic stellate cells (HSCs) were activated and produced tissue inhibitor of metalloproteinase 1 in a sphingosine kinase (SphK)-1-dependent mechanism. In conclusion, BDL exerts antiapoptotic effects that appear to require activation of AKT in hepatocytes and SphK in HSCs.