Resveratrol Inhibits Hepatic Steatosis By Inducing Autophagy

Non-alcoholic fatty liver disease(NAFLD) has become the most common cause of chronic liver injury worldwide. However, there is currently no satisfactory therapeutic strategy for NAFLD. Resveratrol(RSV) is a natural polyphenol that has been reported to attenuate NAFLD, though its underlying mechanism is unclear. Recently, autophagy has been identified as a critical protective mechanism during the development of NAFLD. It has been reported that droplets could been partly or completely wrapped by the doublemembrane-structured autolipophagosome vesicles, with which are transported to lysosomes and then degraded into fatty acids. Increasing autophagy induces β-oxidation, thus attenuating hepatic steatosis; meanwhile, lipid accumulates in the liver of autophagy-related gene 7(ATG7) knockout mice.Studies have shown that, RSV can inhibit the inflammatory response of endothelial cells by activating autophagy.Therefore, we propose that RSV inhibits hepatic steatosis by inducing autophagy in hepatic cells.We established hepatic steatosis cell model using palmitic acid(PA), and NAFLD mouse model using high-fat diet. First, we observed the protective effects of RSV on hepatic steatosis with oil red O staining, HE staining, triglycerides(TG) content detection. Second, we studied the mechanism of the protective effects of RSV on hepatic steatosis. Here, we treated cells with autophagy agonist, autophagy inhibitors, siRNA, and then detected autophagy using confocal laser scanning, transmission electron microscopy. At last, we further studied c AMP/PRKA/AMPK/SIRT1 signaling pathway in RSV inducing autophagy in hepatic cells. We treated cells with inhibitors and siRNAs of adenylate cyclase(Adenylyl cyclase, AC),protein kinase A(Protein kinase A,PRKA),AMP-activated protein kinase(Adenosine 5’-monophosphate activated protein kinase,AMPK),sirtuin 1(Silent information regulator 1, SIRT1) and then detected the expression of AC,PRKA, AMPK, SIRT1 using western blot technique.The main results and conclusions are as follows:(1) RSV decreases TG content in PA-treated HepG2 cells, suggesting its potential in inhibiting hepatic steatosis.(2) Autophagy plays an important role in inhibiting hepatic steatosis.RSV induces autophagy in Hep G2 cells in dose-and time-dependent way. RSV’s effects on hepatic steatosis significantly decrease when autophagy is inhibited.(3) Sirt1 signaling plays a key role in the regulation of RSV-induced autophagy.RSV prominently increases the content of cAMP in HepG2 cells, upregulate the expression of PRKA, activates AMPK and thus induces the expression of SIRT1; After using siRNA to knock down PRKA, AC, AMPK and SIRT1 gene, or inhibitors to inhibit the activities of PRKA,AC,AMPK and SIRT1, RSV-induced autophagy is remarkably inhibited. All of the above show that, c AMP/PRKA/AMPK/SIRT1 signaling plays a key role in the regulation of RSV-induced autophagy.In conclusion, RSV inhibits hepatic steatosis by activating SIRT1-related signaling pathway to induce autophagy, thus preventing NAFLD.