The Role And Mechanism Of P53/PXR-SCD1 Axis In Nonalcoholic Fatty Liver Disease

Backgrounds and Aims:Nonalcoholic fatty liver disease(NAFLD)is the most common chronic liver disease in China.p53 is a tumor suppressor protein,which can not only regulate the cell cycle and inhibit the tumorigenesis,but also participate in the regulation of multiple processes of glucose and lipid metabolism.Currently,it has been found that p53 can regulate fat metabolism and participate in the occurrence and development of NAFLD.Pregnane X receptor(PXR),a nuclear receptor closely related to liver metabolism,was shown regulated by p53.The purpose of this study was to investigate the role of p53 and PXR in the development of NAFLD and its molecular mechanism.Materials and Methods:Human normal liver cell line,L02;human liver cancer cell line,Hep G2;and mouse normal liver cell line,AML12 were stimulated by palmitic acid(PA)to induce NAFLD cell model.C57BL/6 mice with p53 wild type or knockout were fed with the high fat diet(HFD)for 8 weeks to establish the animal model of NAFLD,and steatosis was detected by HE staining,oil red O staining and triglyceride determination.Cells were treated with si RNA or p53 agonist/inhibitor,and the expression of NAFLD-related genes and proteins were detected by RT-PCR,western blot and immunohistochemistry.The regulation of p53 on PXR and SCD1 in vivo was verified by intraperitoneal injection of p53 agonist.Transcriptional regulation of SCD1 by p53/PXR was detected by double luciferase reporting assay.The interaction between p53 and PXR was detected by immunoprecipitation.In Hep G2 cells and primary hepatocytes,p53 and PXR si RNA were used to verify that the improvement of NAFLD in p53 knockdown models is regulated by PXR.Results:In the NAFLD mice model induced by HFD,the expression of p53 m RNA and protein in the liver were significantly increased.The establishment of NAFLD model by HFD showed that the liver steatosis was significantly reduced in p53 knockout mice compared with the wild type model.In addition,inhibition of p53 in Hep G2 and AML12 reduced the steatosis in NAFLD cell models;moreover,PA-induced steatosis was attenuated in primary hepatocytes from p53 knockout mice than in p53 wild type cells.In NAFLD cells and mouse models,the p53 pathway was activated,nuclear expression of PXR increased,and SCD1 expression was up-regulated.While in p53 knockout mice,there was no significant change in the expression of PXR in the nucleus and no significant difference in the expression of SCD1,compared with the mice fed with normal diet.In Hep G2 cells,p53 agonist induced PXR to transfer to nucleus and induce the expression of SCD1.In vivo,intraperitoneal injection of p53 agonist could induce PXR transfer to nucleus and SCD1 expression was up-regulated in p53 wild-type mice cells,too.Dual luciferase reporting experiments showed that activation of p53 could enhance the transcriptional activation of SCD1 by PXR,which was weakened by the knockdown of PXR and enhanced by the overexpression of PXR.The Co-IP experiment indicated the interaction between p53 and PXR,and after knockdown of PXR with si RNA,the improvement of NAFLD caused by p53 knockdown or/and knockout was reversed,indicating that the role of p53 in NAFLD was mediated by PXR.Conclusion:p53 interacts with PXR to transcriptional regulate SCD1 and then regulate the occurrence and development of NAFLD.The p53/PXR-SCD1 axis provides a new perspective on the pathogenesis of NAFLD and a potential target for the treatment of NAFLD.