The Mechanisms Of Liraglutide Induced Weight Loss Through Browning Of White Fat By Activation Of P38MAPK Pathway

Objective Treatment of T2 DM patients with obese has been a medical difficulty,because traditional drugs always induce weight gain accompanied with lowering glycemia.Glucagon like peptide-1(GLP-1)receptor agonists can both lower glycemia and reduce the weight,by now,the mechanisms of weight loss have not been fully elucidated.It has been demonstrated that GLP-1 can promote lipolysis through c AMP pathway in a concentration dependent manner,but the mechanisms have not been established.Moreover,it has been shown that changes in NPs and FGF21 in circulation is associated with activation of browning in white adipose tissue(WAT).In this study,we will investigate whether liraglutide induced weight loss is related to elevation of plasma NPs and FGF21 levels.And further experiments both in vivo and in vitro to verify the mechanism of GLP-1 induced browning in WAT.Method 1.Thirty-one outpatients with type 2 diabetes accompanied with obesity were subcutaneously administered 12 weeks liraglutide.Body composition and abdominal visceral,subcutaneous adipose tissue areas were assessed at pre-and post-treatment with DXA and abdominal CT scanning.The plasma ANP and BNP concentrations were quantified by commercial ELISA Kit,in order to explore the relationships between liraglutide induced change in body composition and browning in WAT.2.High fat diet induced obese c57BL/6 mice were administrated with liraglutide in the concentration of 400 g/kg and 200 g/kg respectively,and the changes in body weight and adipose tissue content were observed.HE staining was used to observe the morphological changes.Immuno fluorescence staining,real-time PCR and western blot were used to measure the expression of UCP-1.Furthermore,the expression of PKA,p-PKA,p38 MAPK,p-p38 MAPK and other factors associated with browning of WAT including PRDM16,Cidea and Tbx1 in m RNA and protein level to explore the possible mechanism of liraglutide induced browning in WAT.3.Differentiated 3T3-L1 adiocytes were treated with liraglutide in different concentration gradient and with adding in PKA inhibitor and p38 MAPK inhibitor.The factors associated with browning of WAT were detected by immuno fluorescence staining,real-time PCR and Western blot,in order to verify that the mechanisms of liraglutide induced weight loss through promoting browning in WAT by activating p38 MAPK to promote UCP1.Result 1.liraglutide treatment significantly reduced body weight,fat tissue,abdominal adipose especially in visceral fat,which were significantly associated with the elevation of plasma NPs levels(p < 0.001),suggesting liraglutide induced weight loss was related to browning in WAT.2.After 8 weeks liraglutide administration,the body weight and fat mass in obese mice were significantly reduced(P < 0.01).HE staining showed adipocytes in perirenal(PRWAT)and inguinal subcutaneous adipose tissue(IWAT)partly acquired brown-like morphological characteristics.UCP-1m RNA and protein were elevated in both PRWAT and IWAT,and phosphorylation of PKA and p38 MAPK were significantly increased(P < 0.05).The m RNA and protein of PGC-1?,FGF21,PRDM16,CIDEA,Tb X-1and CD137 were also significantly elevated with liraglutide treatment(P < 0.05),especially in UCP-1?PGC-1? andp-p38 MAPK,which increased in a liraglutide concentration manner.3.In differentiated 3T3-L1,phosphorylation of p38 MAPK were significantly inhibited by PKA inhibitor,and GLP-1RA induced increasing UCP-1 and other factors associated in browing of WAI were obviously attenuated by inhibition of PKA and p38 MAPK.Conclusion 1.liraglutide significantly induced adipose tissue and weight loss in T2 DM patients with obesity might be associated with browning in WAT.Liraglutide can promote browning in the perirenal and inguinal fat by activating PKA and p38 MAPK and resultant promoting PGC-1? and UCP-1,suggesting the mechanisms of GLP-1 induced weight loss might related to browning in WAT by activating c AMP/PKA/p38 MAPK pathway.