Mechanisms Of Interferon Regulatory Factor 6(IRF6)in Development Of Nonalcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease(NAFLD)has become the leading cause of chronic liver disease and the rapidly growing health problem,which affecting one third of adults and an increasing number of children in the developed countries.NAFLD encompasses a histological spectrum,ranging from simple steatosis to non-alcoholic steatohepatitis(NASH),the latter of which is complicated with different degrees of fibrosis.The pathogenesis of NAFLD is closely correlated with and exacerbates insulin resistance,metabolic disorder,lipotoxicity,oxidative stress,endoplasmic reticulum(ER)stress,mitochondrial dysfunction,adipose tissue dysfunction,innate immunity disorder,cytokine secretion and gut microbiota.NAFLD places a crushing burden on the world and there is an urgent need to find effective treatment strategies.To seek potential targets for the treatment of NAFLD,we performed differential gene analysis on the RNA-Seq public database of high-fat diet-induced mouse NAFLD model.Four differentially expressed genes(DEGs)have been highilighted for their significantly and consistently changed expression levels in all these 6 datasets.Notably,IRF6 was the only one down-regulated DEG.We thus hypothesized that it may be intimately involved in NAFLD progression.We found that IRF6 protein level and m RNA level were down-regulated in the liver of high-fat,high-cholesterol diet(HFHC)and high-fat diet(HFD)mice as well as in primary hepatocytes challenged by palmitic acid(PA)and oleic acid(OA)for 24 h.Interestingly,the down-regulation of IRF6 is independent of the classical proteasome pathway.Instead,the high fat-induced Cp G island methylation in the IRF6 promoter region directly inhibits IRF6 transcription.Our functional studies demonstrated that IRF6 overexpression inhibits PA/OA induced lipid droplet accumulation in vitro.Furthermore,hepatocyte-specific knockout of IRF6(IRF-HKO)mice exhibited significantly exacerbated insulin resistance and lipids accumulation in response to HFD administration in vivo.The accumulation of these results indicates that IRF6 is an inhibitor of NAFLD.Considering that IRF6 is mainly localized in the nucleus of hepatocytes,we speculated that it may function as a classical regulatory factor.Therefore,we combined the Ch IP-Seq with RNA-Seq to identify the molecular mechanism and regulatory target genes of IRF6 function.We found that IRF6 can directly bind to the promoter region of PPARγ.A negative correlation between IRF6 and PPARγ was verified in vitro.IRF6 knockdown promoted PPARγ expression,while overexpression of IRF6 inhibited PPARγ expression.IRF6 knockdown promoted transcription of PPARγ downstream target genes and promoted lipid synthesis and fatty acid uptake.We further found that Pparγ knockout largely abolished IRF6 downregulation-aggravated lipid accumulation in hepatocytes after PO treatment,indicating that PPARγ mediates the function of IRF6 to regulate lipid metabolism.In summary,IRF6 plays an important role as a transcription factor in NAFLD development.IRF6 improves non-alcoholic fatty liver disease and metabolic disorders by inhibiting the transcription of PPARγ.Our study identified IRF6-PPARγ as a key regulatory axis of hepatic steatosis,providing new potential targets and scientific evidence for the treatment of NAFLD,further enhancing the understanding of the pathogenesis of nonalcoholic fatty liver disease.