Monitoring and interpretation of intracranial pressure

Elevated circulating free fatty acids (FFA) contribute to the development of hepatic steatosis and promote hepatocyte apoptosis by incompletely defined mechanisms. Although the death ligand TRAIL has been implicated in a variety of pathologic liver diseases, the role of TRAIL in mediating apoptosis of FFA-induced steatotic hepatocytes is unknown. Aim: we examined TRAIL cytotoxicity in an in vitro model of hepatocyte steatosis induced by FFA. Methods: Hepatocytes (Huh7 cells, HepG2 cells and primary rat hepatocytes) were rendered steatotic by incubation with oleic acid. Apoptosis was assessed morphologically and biochemically by caspase activity. TRAIL receptor regulation was examined using immunoblot analysis and siRNA for targeted knockdown. JNK inhibition was attained with SP600125. Results: Oleic acid sensitized the cells to TRAIL but not TNF- á cytotoxicity. Free fatty acid sensitization to TRAIL occurred at much lower concentrations than required for FFA-mediated sensitization to Fas, or FFA-induced lipoapoptosis. Oleic acid treatment led to upregulation of the cognate TRAIL receptor death receptor 5 (DR5) but not death receptor 4 (DR4). The upregulation of DR5 was c-jun N-terminal Kinase (JNK)-dependent. siRNA targeted knockdown of either DR5 or DR4 demonstrated that DR5 was responsible for FFA sensitization to TRAIL killing. DR5 expression was enhanced in steatotic human liver samples. Our results suggest that free fatty acid induced hepatocyte steatosis sensitizes to TRAIL by a DR5-mediated-JNK-dependent mechanism.