MED1 Regulates Nonalcoholic Fatty Liver Via SREBP1/ACC Axis

Nonalcoholic fatty liver disease（NAFLD）is the most common liver disease in the world.It is closely related to obesity,diabetes,atherosclerosis and others.At present,there is still a lack of effective and reliable therapeutic drugs in clinic.Previous studies have shown that transcriptional coactivator MED1 plays an important role in liver lipid and energy metabolism.The pre-experimental study in our research group found that MED1expression was increased in the liver of obese（ob/ob）mice.The expressions of SREBP1c and lipid anabolic genes were decreased in the livers of MED1^ΔLiv-ob/ob mice.Therefore,this study hypothesized that MED1 may regulate the occurrence of obese fatty liver through SREBP1c/ACC axis.In current study,ob/ob and MED1^ΔLiv-ob/ob mice were used as animal models.The effects of liver MED1 deletion on fatty liver formation and lipid metabolism in obese mice were analyzed by histopathology and RNA-seq.By the loss of function experiment,the molecular relationship between MED1 and SREBP1c/ACC axis in hepatocytes was clarified.Using Co IP and Ch IP techniques,and the molecular mechanism of MED1 regulating NAFLD was revealed.This study provides a theoretical and experimental basis for further exploring the pathogenesis of NAFLD and developing MED1 as a new target for the treatment of obese fatty liver.The main experimental results have listed as follows:1.Liver MED1 knockdown/deletion in obese mice was successfully established.MED1 deficency in liver remarkably alleviatedhepatic steatosis,triglyceride content and inflammatory infiltration of visceral adipose tissue in obese mice.2.Transcriptome analysis inlivers from ob/ob and MED1^ΔLiv-ob/ob mice screeneded that 1203 differential expressed genes（DEGs）.Go and KEGG enrichment analysis found that these DEGs were mainly enriched in PPAR signal pathway,unsaturated fatty acid biosynthesis pathway,fatty acid decomposition pathway and steroid hormone synthesis pathway.Through liver transcriptome analysis and RT-PCR verification,the genes related to lipid metabolism affected by MED1,such as acetyl Co A carboxylase（ACC）,stearyl COA desaturase 1（SCD1）,cell death inducing DNA fragmentation factor similar protein A（Cidea）were obtained.It suggests that MED1 may participate in the formation of fatty liver by affecting the expression of genes related to lipid anabolism.3.Hep G2 cells were treated with palmitic acid PA to simulate liver steatosis in vivo and small interfering RNA（si MED1）was used to interfere with the m RNA level of MED1,which showed that the deletion of MED1 can significantly reduce the lipid deposition in Hep G2 cells induced by PA.It is suggested that MED1 may participate in hepatic steatosis by affecting hepatocyte lipid synthesis.4.Co IP results showed that there was protein interaction between MED1and SREBP1c.Bioinformatics predicted that three SRE sites were located in the promoter region of ACC gene.Ch IP experiment further showed that the deletion of MED1 reduced the enrichment of SREBP1c in the promoter region of ACC gene.Liver MED1 deficency also caused a reduced enrichment of H3K4me1 and H3K27ac in the promoter region of ACC gene.