In this study, treatment of C57BL/6J (wild type, WT) mice fed a high-fat diet (HFD) with retinoic acid (RA) decreased body weight and subcutaneous and visceral fat content, reversed the apparent hepatosteatosis, and reduced hepatic intracellular triglyceride and serum alanine transaminase (ALT) and aspartate aminotransferase (AST) concentrations. Moreover, RA treatment improved glucose tolerance and insulin sensitivity in WT mice fed a HFD. However, these RA-induced effects in WT mice fed a HFD were alleviated in liver specific Sirtuin 1 (Sirt1) deficient (LKO) mice fed a HFD. Furthermore, RA also could not improve glucose tolerance and insulin sensitivity in LKO mice fed a HFD. The mechanism studies indicated that RA indeed increased the expression of hepatic Sirt1 and superoxide dismutase 2 (Sod2), and inhibited the expression of sterol regulatory element binding protein 1c (Srebp-1c) in WT mice in vivo and in vitro. RA decreased mitochondrial reactive oxygen species (ROS) production in WT primary hepatocytes and increased mitochondrial DNA (mtDNA) copy number in WT mice liver. However, these RA-mediated molecular effects were also abolished in the liver and primary hepatocytes from LKO mice. In summary, RA protected against HFD-induced hepatosteatosis by decreasing Srebp-1c expression and improving antioxidant capacity through a Sirt1-mediated mechanism.
Keywords: Sirt1; lipid metabolism; non-alcoholic fatty liver disease; oxidative stress; retinoic acid.