ApoE Deficiency Promotes Non-alcoholic Fatty Liver Disease In Mice Via Impeding AMPK/mTOR Mediated Autophagy

Backgrounds:The pathogenesis of non-alcoholic fatty liver disease considered liver damage caused by inflammation and oxidative stress due to excessive accumulation of hepatic fat.Excessive accumulation of hepatic fat is related to fat production and metabolism.Therefore,most of the drugs used to treat NAFLD are based on reducing the content of fat in the body and liver.However,the mechanism of the process from excessive accumulation of fat to inflammation,oxidative stress,and liver damage is not clear.Fat metabolism of the body is mainly in the liver.Excessive accumulation of fat can lead to excessive mitochondrialb-oxidation and the production of electron transport chain enzyme activity in the liver,which increases more reactive oxygen species?ROS?and damages mitochondrial function.Mitochondrial dysfunction will further promote the development and deterioration of the nonalcoholic fatty liver.Mitochondrial fission and fusion play a key role in maintaining mitochondrial function.Adenosine phosphate activated protein kinase?AMPK?is the key molecule regulating mitochondrial quality control.AMPK activated can make mitochondria elongate/fuse and proliferate,thus maintaining and producing healthy mitochondria,produce more ATP and less ROS.AMPK can activate autophagy by direct phosphorylation and inhibition of mTOR.Autophagy can regulate the mitochondrial fission and fusion,maintain the function and quality of mitochondria,regulate lipid metabolism,improve insulin resistance and reduce oxidative stress,and protect hepatocytes by reducing the damage of hepatocytes.Apolipoprotein E?ApoE?is an important component of lipoproteins and regulates plasma lipoprotein and cholesterol concentrations.About 75%of ApoE is synthesized in liver parenchymal cells.ApoE has anti-inflammatory and antioxidative properties and ApoE could affect the level of autophagy in astrocytes.ApoE deficiency causes atherosclerosis,dyslipidemia,and other metabolic syndromes.ApoE knockout(ApoE^-/-)mice showed spontaneous inflammation and high cholesterol levels compared with wild type?WT?mice.ApoE^-/-mice fed a high-fat diet can rapidly develop non-alcoholic steatohepatitis?NASH?.The mechanism of ApoE^-/-mouse liver from fat accumulation to inflammatory oxidative stress and liver injury has not been reported,and whether ApoE is related to inflammatory,oxidative stress and liver injury in NAFLD has not been reported.Aim:This study aimed to explore the changes in AMPK/mTOR pathway,autophagy level and mitochondrial function in the process of liver from fat accumulation to inflammatory oxidative stress and liver injury,and to explore the relationship between ApoE and NAFLD.Methods:Eight-week-old WT mice and ApoE^-/-mice were divided into normal diet groups and a high-fat diet group.In the agonist group,ApoE^-/-mice were fed with the high-fat diet,500 mg/g AICAR was injected intraperitoneally three times a week;ApoE^-/-mice were fed with the high-fat diet,1 mg/kg rapamycin was injected intraperitoneally every two days.The levels of AST,ALT,lipid in serum,lipid and ATP the n liver were detected by kit,the pathological changes in the liver were detected by H&E,Masson,oil red staining and projection electron microscopy,and the levels of liver-related proteins were detected by immunofluorescence,immunohistochemistry and Western blot.Result:1.At 16 weeks of age,ApoE^-/-mice only had hepatic lipid accumulation,no obvious fatty degeneration and liver damage,AMPK/mTOR pathway,autophagy level,mitochondrial dysfunction,inflammation,and oxidative stress;2.After 8 weeks of the high-fat diet,the lipid levels of serum and liver,and hepatic injury were significantly increased in the ApoE^-/--HFD group compared to other groups.ApoE^-/-mice exhibited increased deposition of fat in liver tissue.The PGC1a,NRF1,ATP,p-AMPK,AMPK,Beclin1,and LC3 levels were downregulated and ROS,p-mTOR,and mTOR were increased in the ApoE^-/--HFD group compared to WT-HFD group;3.After treated with AMPK and autophagy activators,AICAR and rapamycin,these pathologies and protein levels can be rescued in ApoE^-/-mice liver.Conclusion:In conclusion,ApoE deficiency inhibited the AMPK/mTOR pathway,decreased autophagy levels,impaired mitochondrial function in the liver,and lead to NAFLD,which indicates ApoE may regulate AMPK/mTOR pathway by modulating hepatic mitochondrial function in NAFLD.