The Regulation Of Autophagy In Adipocytes And Mechanism Of Bcl2l13 In Adipose Tissue Browning

In recent years,the global incidence of obesity has rapidly increased,which urges us to explore new mechanisms of obesity and new methods to prevent and treat obesity.Autophagy is a lysosomal pathway by which intracellular organelles and proteins are degraded to supply the cell with energy and to maintain cellular homeostasis.Autophagy plays important role in energy metabolism.Therefore,the study of autophagy in adipocytes and/or adipose tissues will provide new targets and ideas for the prevention and treatment of obesity and its related metabolic diseases.Adipose tissue is the most plastic organ in the body and is often undergoes dynamic remodeling in response to different energy status.In obesity,the adipose tissue undergoes dynamic remodeling,including changes in the number and size of the adipocytes and affect the microenvironment of expanded adipose tissues,accompanied by alterations in angiogenesis,extracellular matrix remodeling,inflammatory infiltration and so on.Activation of the sympathetic nervous system often induce a white-to-brown fat conversion and accompanied by a dynamic evolution of mitochondria.In this study,we investigated the role of autophagy in the adipose tissue remodeling both in vivo and in vitro,mainly including the adipose tissue of simple obese individuals and high fat diets induced obesity mice,and 3T3L1 adipocytes or primary adipocytes.Section ?.Autophagy changes in adipose tissue of obese individuals and related affects on adipocytes functionObjective: This section aim to investigate the autophagy changes in adipose tissue of obese individuals and the regulation of autophagy mediated by obesity related inflammation in the homeostasis of adipose tissue.Methods: RNA-seq analysis was examined in the visceral(omentum majus)adipose tissue of paired normal and obesity,and the results were verificated in vivo and in vitro.The functions of obesity-associated adipose inflammation on autophagy-lysosomal response in adipocytes were further studied in vitro.Results: Transcriptome analysis showed that a large number of differentially expressed lysosomal/autophagic genes were up-regulated in the omental adipose tissue of obese individuals and the activation of inflammation related genes were observed in obesity;Microarry database of 3T3L1 adipocytes treated with TNF? at different time points was analyzed and revealed that TNF? caused a major up-regulation of lysosomal/autophagic genes at 2 and/or 24 hours,whereas down-regulation at 6 days;Tweleve lysosomal/autophagic genes were identified as the common different expression genes both in human omental adipose tissue and 3T3-L1 adipocytes by venn analysis;Co-expression network was constructed to identify the core lysosomal/autophagic genes with pivotal roles in adipocytes for the response to TNF? treatment and found that CTSB(Cathepsin B)may play a pivotal role in gene interactions and regulation;In vivo,high fat diets mainly induced lysosomal/autophagic genes expression in mature adipocytes of mouse epididymal adipose tissue;In vitro,short-term TNF? stimulation not only upregulate lysosomal/autophagic genes and SQSTM1/p62 expression,but also promote autophagy and lipolysis;Lipid droplet protein perilipin(PLIN1)was degraded by autophagy-lysosomal pathway,PLIN1 can be ubiquitinated and directly interact with SQSTM1/p62;TNF? induced autophagy is a more selective process that signals through SQSTM1/p62 and can selectively degrade PLIN1.The degradation of PLIN1 is dependent on Cathepsin B activity.Conclusions: Our study indicates changes of autophagy in obese individual adipose tissue are closely related to the activation of inflammation and lysosomal/autophagic genes,and the proinflammatory cytokine TNF? can activate adipocyte autophagy,thus impair the storage of triglyceride in adipocytes.Section ?.Bcl2l13 is essential for adipose tissue browningIn recent years,adipose tissue browning is a new target for the treatment of obesity.Adipose tissue browning is often accompanied by the dynamic evolution of mitochondria.However,regulation of mitochondrial dynamic in this process is not yet clear.We compared the mitophagy related genes in an adipocyte database of rosiglitazone,a PPAR? receptor agonist,and found that rosiglitazone can significantly up-regulate the expression of Bcl2l13 both in differentiated 3T3L1 adipocytes and C3H10T1/2 adipocytes.Bcl2l13 is a newly reported mitophagy receptor,and its function in adipocytes has not been reported yet.In this section,we explored the function and mechanism of Bcl2l13 in the process of adipose tissue browning in vitro and in vivo,respectively.Rosiglitazone up-regulated the expression of Bcl2113 in 3T3L1 adipocytes.Bcl2113 was gradually increased in the process of primary adipocytes differentiation towards brown adipocytes,and the expression of Bcl2l13 was found to be highly expressed in brown adipose tissue.Correspondingly,both cold stimulation and ?3 receptor agonist CL316243 significantly up-regulated Bcl2l13 in the subcutaneous adipose tissue of mice.In addition,lentiviral knockdown Bcl2l13 in primary adipocytes significantly inhibited adipocyte browning.This study highlights the role of Bcl2l13 in the adipose tissue browning and suggests that Bcl2l13 may serve as a potential target for the treatment of obesity.