Mechanism Of Oxytocin Improving Body Weight And Energy Metabolism In Obese Mice By Promoting Fat Differentiation

Objective: The aim of this study is to examine the effects of oxytocin on the energy metabolism in brown,beige and white adipose tissues,and the effect of oxytocin on differentiation of C3H10T1/2 cells.Moreover,the underlying mechanisms for oxytocin improving body weight gain and energy metabolism in obese mice were investigated.Methods:(1)The 12 week old C57BL/6J male mice were fed at 6°C for 8 days.The hypothalamus,interscapular brown adipose tissue(BAT),inguinal white adipose tissue(i WAT)and epididymal white adipose tissue(e WAT)were collected.The m RNA expression of oxytocin in hypothalamus and oxytocin receptor(OTR)and uncoupling protein-1(UCP1)gene in BAT,i WAT and e WAT were detected by q RT-PCR.Plasma oxytocin levels were detected by electroluminescence.(2)The C57BL/6J male mice were fed with high fat diet(HFD)for 8 weeks to induce obesity model.Then the mice were divided into two groups: control group(HFD only),group oxytocin(oxytocin subcutaneous injection with osmotic micropump).All the mice were fed with HFD for additional 4 weeks.Food intake,body weight and rectal temperature were observed.The glucose tolerance test(GTT)and insulin tolerance test(ITT)were performed.The plasma levels of epinephrine(E),norepinephrine(NE),triglyceride(TG)and total cholesterol(TC)were detected.BAT in the interscapular region,i WAT and e WAT were collected and weighed.The morphological changes of these adipose tissues were observed by HE staining.The m RNA expression of UCP1 was detected by q RT-PCR.The protein expression of UCP1 was detected by Western blot.The liver was collected and weighed.The contents of TC and TG were observed by HE staining and oil red staining.(3)Bone marrow mesenchymal stem cells C3H10T1/2 were incubated with differentiated medium in the absence or presence of recombinant oxytocin(25,50,100 ng/ml)for 8days.The m RNA expressions of PPARα,PPARγ,UCP1,CIDEA,PPARγc1α,DIO2,ELOVL3,NNMT,RETN and PRDM16 were detected by q RT-PCR,and the protein expressions of UCP1 and PRDM16 were detected by Western blot.(4)LV-PRDM16 sh RNA was used to knock down the expression of PRDM16 in C3H10T1/2 cells,then oxytocin was added to intervene.The expression of UCP1,CIDEA and DIO2 was detected by q RT-PCR and the expression of UCP1 protein was detected by Western blot.Results:(1)The level of plasma oxytocin was increased(P < 0.05),and the expression of hypothalamic oxytocin m RNA was increased(P < 0.05).The m RNA expression of OTR and UCP1 in BAT and i WAT were increased(P < 0.05),while there was no change in e WAT.(2)Oxytocin reduced the weight gain and increased the rectal temperature in HFD induced obese mice(P < 0.05).The food intake,the plasma level of E and NE levels had no difference between the two groups.(3)The fasting insulin level in oxytocin group was lower than that in control group.GTT and ITT showed that glucose in oxytocin group was lower than that in control group(P <0.05).(4)The weight of i WAT and e WAT in oxytocin group decreased(P < 0.05),but the weight of BAT in interscapular region did not change.The accumulation of lipid droplets in BAT decreased,the diameter of adipocytes in i WAT decreased,and the adipocytes in e WAT decreased(P < 0.05).The m RNA and protein expression of UCP1 in BAT and i WAT increased in oxytocin group(P < 0.05).There was no significant difference in the expression of UCP1 in e WAT(P > 0.05).(5)In oxytocin group,the contents of TC and TG in liver decreased(P < 0.05),but the levels of TC and TG in plasma did not change significantly.There was no change in liver weight.(6)Compared with the control group,the expression of PPARα,PPARγ,UCP1,CIDEA,PPARγc1α,DIO2 and ELOVL3 increased,the expression of NNMT and RETN decreased,the expression of PRDM16 increased,and the expression of UCP1 and PRDM16 increased in a dose-dependent manner(P < 0.05).(7)With the knockdown of PRDM16 expression,UCP1,CIDEA and DIO2 m RNA expression and UCP1 protein expression in C3H10T1/2 cells were lower than those in control group(P < 0.05).Conclusion: Oxytocin can induce browning of adipose tissue and increase its thermogenesis,so as to improve weight gain,glucose metabolism and fatty liver,and thus combat obesity and metabolic disorders.