Study On The Role And Mechanism Of Interleukin-6 In Mouse Fat Formation

Obesity is one of the most serious health problems,troubling the humanity in the 21~stt century.Excessive obesity can lead to a series of metabolic diseases such as hypertension and atherosclerosis.Obesity can be defined as excess fat tissue due to the increase in the size and numeber of adipose cells.Therefore,controlling the number and size of adipocytes is a effective strategy for obesity prevention and treatment.IL-6 is a kind of pro-inflammatory cytokine.Recent studies have shown that IL-6 would affect mouse body weight,fat content and energy metabolism.However,the specific effect of IL-6 on adipogenesis and its mechanism is little reported.In the present study,we used mouse white adipose tissue derived SVF cells and IL-6knock-out mice to study the effects of IL-6 on adipogenesis.Firstly,the effects of different concentrations of IL-6 on white fat formation were detected by Oil Red O staining,qRT-PCR and Western Blotting,and the optimal concentration of IL-6 was determined.Secondly,we found that IL-6 activated the STAT3 signaling pathway.Nic,the inhibitor of STAT3 signaling pathway,reversed the inhibition of IL-6 on fat formation.Subsequently,the critical role of PPAR?in SVF cells adipogenesis was evaluated.Finally,differences of blood fat,white adipose tissue,brown adipose tissue and liver between wild type mice and IL-6 gene knock-out mice were used to test the role of IL-6 on regulating fat formation in vivo.The main results are as follows:(1)The effect of different concentration of IL-6 on the white fat formation of SVF cells:Cells were treated with 1 ng/m L,2 ng/m L and 5 ng/m L IL-6.Results showed that the number of white adipose cells and the mRNA and protein levels of the white fat markers was clearly decreased,suggesting that IL-6 inhibits the white fat formation of SVF cells.In the subsequent experiments,we choose 2ng/m L as the optical concentration.(2)IL-6 has no effect on cell proliferation of SVF cells:SVF cells were treated with IL-6 for 24h,the results of Edu proliferation test showed that IL-6 could not affect the growth of SVF cells.(3)IL-6 stimulates STAT3 signaling pathway:The result of Western Blotting showed that IL-6 stimulated STAT3 signaling pathway at 15 min.Then,SVF cells were treated with STAT3 inhibitor Nic for 30min,followed by induction of differentiation by AS with or without IL-6.Results indicated that Nic increased lipid accumulation and adipogenesis-related markers compared with treated with IL-6 alone.These findings suggested that IL-6 palys a significant role in the inhibition of adipogenesis via activation of STAT3 signaling pathways.(4)IL-6 decreased the expression of the key transcription factors-PPAR?:Pretreatment with PPAR?activator Ros increased the adipocyte differentiation of SVF cells.However,co-treatment with IL-6 and Ros decreased the number of fat droplet and the levels of these correlation transcription factors compared with Ros-treated cells.These results showed that IL-6 inhibits adipogenesis through the downregulation of PPAR?which mediated by STAT3signaling pathway.(5)The influence of IL-6 gene knock-out in fat formation:We performed qRT-PCR,Western Blotting and HE staining to analyze the difference of blood fat,WAT,BAT,and liver between wild-type mice and IL-6 knock-out mice.Results indicated that the content of TG,TC and VLDL-c was almost no differnence in female mouse of two groups,but in male,the content of these had the trend of decreasing in IL-6 knock-out group.Additionally,the ratio of WAT and body weight seemed to be increased,and the weight percentage of the liver was down-regulated in IL-6 knockout group.This was consistent with the previous results.Finally,compared with wild-type mice,the BAT weight percentage of IL-6 knock-out mice was no significant change in female but increased in the male.This suggests that there may be gender difference when IL-6 effects brown fat.The above results show that IL-6 plays a significant inhibitory role in the process of fat formation,and the effect is achieved through the downregulation of PPAR?which mediated by STAT3 signal pathway.This study can give us a more comprehensive understanding in the role of IL-6 in fat formation and its molecular mechanism.Moreover,it may provide some new guide for the prevention and treatment of obesity.