Glucagon-like Peptide 1 Ameliorates Hepatocellular Steatosis Via The FXR Autophagy Pathway

BackgroundNowadays,nonalcoholic fatty Liver disease(NAFLD)has become a major public health problem in China,and the end-stage liver disease caused by it will aggravate the economical burden to society and families.NAFLD is defined as a clinicopathological syndrome characterized by intrahepatic steatosis except for alcohol and other definite liver-damaging factors,which is an acquired metabolic stress-induced liver injury closely related to insulin resistance and genetic susceptibility.NAFLD leads to nonalcoholic steatohepatitis,which will progress to end-stage liver disease and even induce hepatocellular carcinoma if it develops into liver cirrhosis without being controlled.So far,no drug with definite curative effect on NAFLD has been found,and no country has approved drugs to treat NAFLD.How to use effective ways to prevent and treat NAFLD and stop its progress is an urgent problem to be solved.Glucagonlike peptide 1(GLP-1),as a popular target in type 2 diabetes,has been shown to activate autophagy in hepatocytes to alleviate lipid accumulation.Farnesoid X receptor(FXR),as a negative regulator of autophagy transcription signaling factor,aggravates hepatic steatosis by inhibiting autophagy.Therefore,this study is to explore whether GLP-1 could regulate the autophagy pathway through FXR and alleviate the lipid damage of hepatocytes,so as to provide a reference for the NAFLD treatment.Objective1.To explore the effect of GLP-1 on lipid metabolism in the hepatocellular steatosis model.2.To explore the mechanism of GLP-1 regulating FXR to activate autophagy pathway and alleviate lipid deposition in the hepatocellular steatosis model.Methods1.The human hepatocellular carcinoma cell lines(HepG2)were used to construct the hepatocellular steatosis model induced by sodium palmitate(PA).Oil red O staining,CCK-8 test,intracellular triglyceride(TG)and malondialdehyde(MDA)content determination were used to assess the effect of the model construction.The expression of GLP-1 R and FXR were detected by Western blot and immunofluorescencen,and the expression of autophagy-related protein LC3 and p62 were detected by Western blot.2.Exendin-4(Ex-4)was used to treat the hepatocellular steatosis model,and Exendin-9(Ex-9)was used to inhibit Ex-4.Hepatocellular lipid deposition was measuered by CCK-8 test,oil red O staining,intracellular TG and MDA content determination.Western blot,real-time polymerase chain reaction(RT-PCR)and immunofluorescence were used to detect the expression of GLP-1 R and FXR.Western blot and RT-PCR were used to detect the expression of mTOR and autophagy-related proteins.3.HepG2 cells with knock-down FXR were constructed by siRNA,and the lipid deposition was measuered by oil red O staining,intracellular TG and MDA content determination.The expression of GLP-1 R and FXR was detected by Western blot,RTPCR and immunofluorescence,and the expression of mTOR and autophagy-related proteins was detected by Western blot and RT-PCR.Results1.Ex-4 alleviated lipid deposition,and reduced intracellular TG and MDA in the hepatocellular steatosis model.2.Ex-4 reduced the expression of FXR in the hepatocellular steatosis model,and activated autophagy through the mTOR pathway,increassing the expression of LC3 and reducing the expression of p62.3.After knocking FXR down in HepG2 cells by siRNA,intracellular lipid deposition was reduced and the autophagy pathway was activated.Conclusion1.GLP-1 can alleviate lipid damage significantly in the hepatocellular steatosis model,protect liver from lipotoxicity,and delays the progression of NAFLD.2.GLP-1 can inhibit the mTOR signaling pathway to activate autophagy in HepG2 cells,increase the expression of FXR,mTOR and LC3,and reduce the expression of GLP-1 R and p62,thereby alleviating hepatocellular steatosis.3.HepG2 with knock-down FXR may up-regulate the expression of LC3,downregulat the expression of p62,and eliminate the protective effect of Ex-4 on hepatocellular steatosis.