275-LB: Mitochondrial Fission Factor Can Be a Key Factor in the Regulation of Hepatic Lipid Metabolism

Abstract

Nonalcoholic fatty liver disease (NAFLD) develops into nonalcoholic steatohepatitis (NASH) when fat accumulates in the liver, leading to hepatocyte apoptosis, inflammation and fibrosis. No effective treatments for NASH have been established. Mitochondria are important organelles that play a central role in de novo lipogenesis and fatty acid β-oxidation. We have shown that mitochondrial fission is enhanced by short-term high-fat diet (HFD) loading, but is impaired by long-term. We speculated that mitochondrial fission inhibition is associated with the development of NASH and generated mice deletion of hepatocyte-specific mitochondrial fission factor (KO) mice. Conditioning HFD, KO mice showed inhibition of hepatocyte mitochondrial fission, increased ER stress and decreased triglyceride secretion from the liver. The hepatic triglyceride contents had significantly increased in KO mice compared to control (CONT), and histological analysis showed a marked increase in large lipid droplets (LDs). In addition to marked fat accumulation, hepatic apoptosis, inflammation and fibrosis were increased in the livers of KO mice, indicating the development of NASH. We noted that large LDs were increased in KO mice and added an additional analysis to determine how mitochondrial fission inhibition is involved in LDs formation in the liver. Oleic acid is a representative monounsaturated fatty acid that promotes LDs deposition in hepatocytes and is mildly cytotoxic by inducing ER stress and apoptosis. Loading primary cultured hepatocytes (PH) with oleic acid increased the number of smaller LDs in PH of CONT mice, whereas LDs in cells of KO mice became larger. Gene expression of Cidec, which acts on the fusion of LDs, was increased in the liver of KO mice, suggesting that inhibition of mitochondrial fission may induce the fusion of LDs and the enlargement of intracellular LDs in the liver. Further analysis is planned, as inhibition of mitochondrial fission may be involved in changes of LDs morphology. Disclosure Y. Takeichi: None. T. Miyazawa: None. Y. Ogawa: None.