Role Of P53 In The Regulation Of NF-?B And MAPK Activity And Insulin Resistance

Objectives: Elevated free fatty acids(FFAs)are fundamental to the pathogenesis of hepatic insulin resistance.However,the molecular mechanisms of insulin resistance remain not completely understood.Tumor suppressor protein p53 has been demonstrated to be a regulator of glucose homeostasis.Recent studies also have shown that NF-?B and MAPK signaling pathways are involved in pathogenesis of insulin resistance.However,there are little studies about the influence of p53 on NF-?B and MAPK signaling in insulin resistance.The present study examined the expression levels of p53,NF-?B p65,p38 and ERK1/2MAPK in two mouse models of insulin resistance and two palmitate acid-induced in vitro models.To better understand therole of p53 in the regulation of NF-?B and MAPK activity and insulin resistance,we explored the effect of p53 agonist(Nutlin-3)and antagonist(pifithrin-?)on insulin resistance and protein levels of NF-?B p65,p38 and ERK1/2MAPK.Our results show the role of p53 in the regulation of insulin resistance via NF-?B and MAPK signaling pathways and suggest that p53 could be a new target for the treatment of diabetes.Methods:(1)Palmitic acid stimulated 3T3-L1 and HepG2 cells were used as in vitro models,and high fat diet induced C57BL/6J mice and ob/ob mice were used as in vivo models of insulin resistance.Protein levels of p53,NF-?B p65,p38 and ERK1/2MAPK were examined by immunoblotting.The expression of insulin receptor(IR),insulin receptor substrate(IRS-1)proteins and AKT,which are related to the regulation of glucose metabolism,were also investigated.(2)HepG2 cells were treated with a p53 agonist(Nutlin-3)or antagonist(pifithrin-?).Glucose consumption were measured,and protein levels of NF-?B p-p65,p-p38 and p-ERK1/2 MAPK were examined byWestern blot analysis.(3)HepG2 cells were treated with palmitate acid in combination with Nutlin-3,a p53 agonist.Glucose consumption were measured.Western blot analysis was used to examine the protein expression of NF-?B p-p65,p-p38 MAPK,p-ERK1/2.Results:(1)Down-expression of p53 and up-expression of intranuclear p65 were observed in insulin resistance model of 3T3-L1 cells.P53 was also downexpressed and p-p65 was upexpressed in insulin resistance model of HepG2 cells.Meanwhile,p-p38 and p-ERK1/2 MAPK were up-regulated in palmitate induced HepG2 cells.In adipose tissue and liver tissue of two in vivo insulin resistance models,the expression of p53 decreased while intranuclear p65 and p50 increased compared with the control group.Meanwhile,we observed that p-p38 and p-ERK1/2 were up-regulated in insulin resistant liver tissue of C57BL/6J and ob/ob mice.(2)Treatment of HepG2 cells with Nutlin-3 improved insulin resistance.In HepG2 cells,Nutlin-3 significantly increased phosphorylation levels of cantly increased the IR,AKT and decreased the phosphorylation levels of p70s6 k.The expression levels of p-p65,p-p38,p-ERK1/2 were reduced.Conversely,PFT induced insulin resistance and decreased phosphorylation levels of IR,AKT and increased the phosphorylation levels of p70s6 k.The expression levels of p-p65,p-p38,p-ERK1/2 were increased.(3)We also found that Nutlin-3 can increase the expression of p53 in PA induced insulin resistance model,and increase the level of glucose consumption while NF-?B/p65 and p38/ERK1/2 MAPK signaling pathways were suppresed in HepG2 cell line.Conclusions:(1)Down-expression of p53 and up-expression of p-p65 or intranuclear p65 were observed in insulin resistance model of 3T3-L1 and HepG2 cells,as well as in adipose tissue and liver tissue of two in vivo insulin resistance models.Meanwhile,p-p38 and p-ERK1/2 MAPK were up-regulated in palmitate induced HepG2 cells and in liver tissue of C57BL/6J and ob/ob mice.(2)In HepG2 cells,Nutlin-3 significantly increased phosphorylation levels of IR,AKT and decreased the phosphorylation levels of p70s6 k.The expression levels of NF-?B p-p65,p-p38,p-ERK1/2MAPK were reduced.Conversely,PFT decreased phosphorylation levels of IR,AKT and increased the phosphorylation levels of p70s6 k.The expression levels of p-p65,p-p38,p-ERK1/2 were increased.(3)Nutlin-3 can increase the expression of p53 in PA induced insulin resistance model,and increase the level of glucose consumption while NF-?B/p65 and p38/ERK1/2 MAPK signaling pathways were suppresed in HepG2 cell line.In a word,our data shed new light on that p53 may be improve insulin resistance via regulating NF-?B/MAPK signaling pathways.