Role Of YAP In Adipose Tissue Function And The Obesity Related Metabolic Diseases

Background: The incidence of obesity has increased in modern societies worldwide,which increases the risk of diabetes,cerebrovascular disease,coronary heart disease,high blood pressure and hyperlipidemia.Therefore,the elucidation of molecular mechanisms of obesity is important to develop new therapeutic targets of obesity and related disease.The Hippo-YAP signaling pathway was first found in Drosophila as an important pathway for the regulation of tissue and organ development.In mammals,the core component of this pathway is the kinase system consisting of upstream Mst1/2 and downstream YAP/TAZ.In the proliferative state,YAP/TAZ is not phosphorylated,but is transcribed into the nucleus as a secondary transcription factor binding to the TEAD family transcription factor,which binds to the promoter region of the downstream target gene.Although the functional role of the Hippo-YAP pathway in other tissues is widely studied,YAP is relatively scarce in the application of adipogenesis and adipose tissue function.Objective: To study the role of YAP in adipocyte differentiation,lipolysis and obesity-related metabolic disorders and the underlying mechanisms.Method: Two adipose tissue specific YAP transgenic mice?YAPtgfAP2cre+ and YAPtgf AdCre+?were developed to study the role of YAP in adipose tisuuse function.The preadipocytes and mature adipocytes were isolated by enzyme digestion.The preadipicytes were treated with differentiating solutions DMI,which promoted differentiation of the preadipocytes.The levels of P-YAP?ser127?and YAP protein were detected by Western blot.RT-PCR was used to detect the expression of YAP.The effect of Hippo-YAP on lipolysis was tested by measuring the glycerol level in medium.Real-time quantitative PCR and Western Blot were used to analyze the expression of lipolytic-related molecules.Wild type mice were treated by high fat diet for 3 days,8 weeks and 12 weeks and then the levels of YAP mRNA,p-YAP?ser127?and YAP protein were detected.The YAPtg^fAP2^Cre+ and YAPtgf AdCre+ mice and control mice were treated with high fat diet for 12 weeks.IPGTT was performed.Plasma TG and CHO level were tested.The hepatic lipid was extracted and measured.All results were analyzed by T test or analysis of variance,with P <0.05 as the significant difference in the presence of criteria.Results: In the early stage of obesity?3-day HFD treatment?,the expression of P-YAP and the mRNA level of YAP in adipose tissue were significantly increased and the total protein level of YAP was decreased.After a long-term HFD treatment?8 weeks and 12 weeks?,P-YAP and the mRNA level of YAP in adipose tissue were aslo incrased.However,the the total protein level of YAP was not changed compared with that of mice treated by nomal diet.During the process of the preadipocytes differentation into mature adipocytes,the protein level of pYAP?ser127?was significantly increased and that of T--YAP was decrased.The YAP overexpressed preadipocytes showed inhibited differentation and suppressed C/EBP? level.In addition,the glycerol released from mature adipocytes in transgenic mice were increased than that of the control mice.These data indicated YAP inhibited the differentiation of preadipocytes and promoted the lipolysis of mature adipocyte.To study the role of YAP in adipose tissue in obesity-related metabolic disorder,we treated the YAPtgfAP2cre+ and YAPtgf AdCre+ mice and control mice with HFD for 12 weeks.Fat weight and fat/body weight decreased in YAPtg^fAP2^Cre+mice as well as YAPtgf AdCre+ mice when compared with the control mice.Both types YAP transgenic mice showed smaller size of adipocytes,increased plasm and hepatic TG level.YAPtgf AdCre+ mice showed aggravated insuin resistance evidenced by IPGTT.Conclusion: The protein level of p-YAP and mRNA level of YAP were increased by HFD.YAP can inhibit the differentiation of preadipocytes and promote the lipolysis of mature adipocyte,which leads to obesity-induced dyslipidemia,fatty liver disease and insulin resistance.