P38γ Modulates The Lipid Metabolism In Non-alcoholic Fatty Liver Disease By Regulating The JAK-STAT Signaling Pathway

Objective: Non-Alcoholic Fatty Liver Disease(NAFLD)is one of the most common chronic liver diseases in the world,and its incidence increases yearly.In the pathogenesis of NAFLD,the "multiple strikes" theory is a widely accepted view that steatosis,lipid toxicity and inflammation.The disease begins with excessive accumulation of triglycerides in the liver,which in turn leads to liver cell damage,steatosis,inflammation and so on.Therefore,inhibition of lipid accumulation in liver is an effective strategy to treat fatty liver.P38γ is one of the four subtypes of P38 mitogen activated protein kinases(P38 MAPKs)that regulates cell cycle entry and hepatoma.Recent studies have shown that P38γ deficient in myeloid cells are resistant to diet-induced fatty liver disease,hepatic triglyceride accumulation and glucose tolerance,suggesting the importance of P38γ in the pathogenesis of NAFLD.However,the applicability of the underlying molecular mechanisms of P38γ as a target for disease therapy remains poorly understood.In this study,we investigated the effect of P38γ on lipid accumulation in NAFLD.In addition,the possible mechanisms of the P38γ and Janus kinase signal transducers and transcriptional activators(JAK-STAT)signaling pathways in NAFLD were investigated.Method: In vivo,a mouse model of NAFLD was established by feeding C57BL/6J mice a methionine and choline deficient diet(MCD),and the expression level of P38γin mouse liver was detected.Then adeno-associated virus(AAV9-Sh RNA-P38γ)and its control plasmid were injected into C57BL/6J mice via the caudal vein to create P38γknockdown mice.The expression levels of SREBP-1c,PPAR-α and ACOX-1 were detected by Western blot and RT-qPCR,respectively.In vitro,AML-12 was induced by free fatty acids(FFA)in mouse liver cells.P38γ-siRNA and p EGFP-C1-P38γ were used to silence and overexpress P38γ,and the expression levels of SREBP-1c,PPAR-α and ACOX-1 were detected by Western blot and RT-qPCR,respectively.The effect of P38γon the apoptosis of FFA-induced AML-12 cells was evaluated by flow cytometry.Finally,Western blot was used to detect the effect of P38γ on the activation of JAK-STAT signaling pathway and lipid accumulation.Results: In vivo,the results of HE staining and Oil Red O staining showed that the animal model of NAFLD was established successfully.Immunohistochemistry,Western blot and RT-qPCR results showed that P38γ was up-regulated in the liver of NAFLD model mice.After silting P38γ,the degree of liver injury and lipid accumulation were alleviated in mice.And the expression level of SREBP-1c,a key transcription factor foe de novo lipid synthesis,was reduced,while the expression levels of PPAR-α,a lipid oxidation-related regulator,and its related target gene such as ACOX-1were increased.In vitro,P38γ silencing increased the expression levels of PPAR-α and related target gene ACOX-1,and suppressed the expression level of SREBP-1c.Conversely,after overexpression of P38γ,the expression level of SREBP-1c was increased,while the expression levels of PPAR-α and ACOX-1 were decreased,and promoted the apoptosis rate of AML-12 cells induced by FFA.Finally,we found that P38γ significantly activated the JAK-STAT signaling pathway.After silting P38γ,the expression levels of P-JAK3 and P-STAT5 a,the target protein of JAK-STAT signaling pathway,were significantly inhibited,while the expression levels of P-JAK3 and P-STAT5 a were significantly increased after P38γ overexpression.In addition,P38γ-siRNA and JAK-STAT signaling pathway inhibitor BD750 significantly inhibited the activation of JAK-STAT signaling pathway.Compared with P38γ-siRNA group,the expression levels of PPAR-α,ACOX-1 and SREBP-1c in P38γ-siRNA+BD750 coculture group were not significantly changed.Conclusions: These results suggested that P38γ regulated lipid metabolism in NAFLD by regulating JAK-STAT signaling pathway,and targeting P38γ can inhibit lipid accumulation in fatty liver disease.