Abstract
Hepatic steatosis can progress to the clinical condition of non-alcoholic steatohepatitis (NASH), which is a precursor of more serious liver diseases. The novel PKC isoforms δ and ε are activated by lipid metabolites and have been implicated in lipid-induced hepatic disease. Using a methionine- and choline-deficient (MCD) dietary model of NASH, we addressed the question of whether hepatic PKCδ and PKCε are activated. With progression from steatosis to steatohepatitis, there was activation and increased PKCδ protein content coincident with hepatic endoplasmic reticulum (ER) stress parameters. To examine whether similar changes could be induced in vitro, McA-RH 7777 (McA) hepatoma cells were used. We observed that McA cells stored triglyceride and released alanine aminotransferase (ALT) when treated with MCD medium in the presence of fatty acids. Further, MCD medium with palmitic acid, but not oleic or linoleic acids, maximally activated PKCδ and stimulated ER stress. In PKCδ knockdown McA cells, MCD/fatty acid medium-induced ALT release and ER stress induction were completely blocked, but triglyceride storage was not. In addition, a reduction in the uptake of propidium iodide and the number of apoptotic nuclei and a significant increase in cell viability and DNA content were observed in PKCδ knockdown McA cells incubated in MCD medium with palmitic acid. Our studies show that PKCδ activation and protein levels are elevated in an animal model of steatohepatitis, which was recapitulated in a cell model, supporting the conclusion that PKCδ plays a role in ALT release, the ER stress signal, and cell death.