The Role Of Survivin In Adipose Tissue Remodeling And Metabolic Homeostasis

Objective:Based on our previous study on Survivin,we aim to further investigate the regulation of survivin expression and degration in fat,and the role of survivin on adipose tissue remodeling and energy metabolism homeostasis in vivo and in vitro using adipocyte specific Survivin knock-out（SKO）mice.Methods:We investigated the expressional level of survivin in adipose tissue from“Fast and Refed”,short term HFD feeding and fat specific m TOR1 pathway activated mice in vivo.Meanwhile,we also detected the survivin expression in the liver of HFD fed mice to compare with adipose tissue.Next,we treated adipocytes with branched chain amino acid（BCAA）,phosphatidic acid（PA）,which directly activate the m TORC1 pathway,and m TORC1 activator 3BDO for investigating their effect on survivin expression in vitro.We also tested the survivin degradation pathway by fetal bovine serum（FBS）and glucose depletion in the medium.SKO mice were obtained by crossing survivin^loxp/loxpmice with Adiponectin-Cre^+/-mice,and the overall metabolic phenotype of SKO mice was observed under regular chow diet and HFD feeding conditions.The thermogenic function of BAT and SAT of SKO and control（Con）mice was detected under cold exposure.The SAT and BAT vascular stromal fraction cells（SVF）from SKO and Con mice were isolated and differentiated into mature adipocytes,and the effect of survivin depletion on differentiation,lipid starage,lipolysis,thermogenic gene and protein expression were detected in mature adipocytes.Mitochondrial oxidative phosphorylation function was tested by seahorse,and mitochondria content was evaluated using mito-traker green.Results:First,Refeeding and 3 days HFD feeding could upregulated survivin expression in adipose tissue.And survivin expression also upregulated in adipose tissue and adipocytes from m TORC1 signaling pathway activated mice.The BCAA and PA in the medium enhanced survivin expression in mature adipocytes via m TORC1 signaling in vitro.In addition,FBS and glucose depletion in the medium promoted survivin degradation through the proteasome pathway in adipocytes.When fed with regular chow diet,the BAT mass of SKO mice significantly reduced,and the expressional level of thermogenic protein Ucp1 also decreased.However,there was no significant difference between SKO and Con mice in overall metabolic phenotypes in terms of body weight,food intake,glucose tolerance,and insulin tolerance.Under HFD feeding conditions,although there was no significant difference in body weight between Con and SKO mice,but the ratio of SAT and BAT mass to body weight of SKO mice was significantly lower than that of Con mice,meanwhile the ratio of liver tissue weight to body weight significantly increased,and the ITT and IPGTT results showed that SKO mice developed insulin resistance and glucose intolerence,and the blood glucose levels between two groups were most significant at 30 minutes after insulin or glucose injection（p=0.02,p=0.019,respectively）.Under cold exposure,the thermogenic genes and proteins expression significantly reduced in BAT and SAT of SKO mice compared with Con mice.Moreover,the expressional levels of thermogenic genes and protein,and mitochondrial oxidative phosphorylation function reduced in primary beige and brown adipocytes from SKO mice without effecting their differentiation and lipolysis function,meanwhile the signal transduction and transcriptional activation factor 1（STAT1）,which negetively regulated thermogenesis,expression level was increased.Besides,survivin overexpression in beige adipocytes up-regulated the Ucp1protein expression without having effect on differentiation.Conclusion:Survivin expression in fat is regulated by nutrition sensing m TORC1 pathway in vivo and in vitro.Survivin in mature adipocytes is indispensable for maintening normal BAT mass and function,and the proper expansion of SAT under overnutrition in vivo.In vitro,Survivin positively regulates the thermogenesis and mitochondrial oxidative phosphorylation in beige and brown adipocytes.Our study firstly revealded the key role of survivin in maintaining the adipose tissue homeostatis and energy metabolism in vivo.