SUMOylation Of ERp44 Enhances Ero1α ER Retention Contributing To The Pathogenesis Of Obesity And Insulin Resistance

Purpose:With the development of high-resolution mass spectrometry and optimization of data analysis,numerous post-translational modificated protein molecules involved in the pathogenesis of type 2 diabetes have been discovered.As the only E2 conjugating enzyme for the SUMO system,Ubc9-mediated SUMOylation has been recognized to regulate diverse biological processes,including protein interaction,subcellular localization,protein stability and so on.However,its impact on adipocytes relevant to obesity and insulin resistance is yet to be elucidated.Our previous studies found that ER stress in white adipocyte of obese mice was increased,accompanied by the Ubc9 expression up-regulation.In addition,Ubc9 expression in white adipose tissue was positively correlated with BMI.HFD challenge induced ER stress and rendered adipocyte to undergo a SUMOylation turnover,leading to adipocyte dysfunction,obesity,and insulin resistance.The purpose of current project is to demonstrate the role of SUMOylation in the regulation of adipocytic metabolism and the related mechanisms during the course of T2D development.Methods:We established adipocyte-specific Ubc9 deletion mice to explore the effects of Ubc9 on obesity and metabolic disorders induced by high-fat diet in adult mice.The molecular targets of SUMOylation were explored by liquid chromatography-mass spectrometry,and the regulatory mechanism of SUMOylation in T2D was analyzed.Results:Adipocyte-specific depletion of Ubc9(Adipo Q-Cre-Ubc9^fl/fl,Ubc9^AKO)protected mice from high fat diet（HFD）-induced obesity,insulin resistance,and hepatosteatosis.The Ubc9^AKO mice were featured by the reduced HFD-induced endoplasmic reticulum（ER）stress and inflammatory response.Mechanically,over nutrition rendered adipocytes to undergo a SUMOylation turnover characterized by the change of SUMOylation levels and substrates.ERp44 displayed the highest change in terms of SUMOylation levels of substrates involved in ER-related functions.Ubc9 mediated ERp44 SUMOylation at lysine 76（K76）located within the a thioredoxin（TRX）-like domain to enhance its degradation,thereby suppressing its covalent binding to Ero1α,an oxidase that exists in the ER but lack of ER retention motif,and reducing endoplasmic reticulum stress by promoting Ero1αsecretion.Conclusions and interpretation:Disruption of ERp44 SUMOylation reduced Ero1αER retention coupled with improved adaptive response in the ER to chronic metabolic stress along with enhanced lipolysis and repressed lipogenesis.Collectively,our data suggest that modulation of ERp44 SUMOylation in adipocytes could be a feasible strategy against obesity and insulin resistance in clinical settings.