A Study On The Effects Of Er Stress On Lipid Metabolism Homeostasis And The Underlying Mechanism

Adipose tissues,as an endocrinal organ,play important roles in the regulation of lipid storage and lipid metabolism.Lipid metabolism homeostasis represented the balance of body metabolism which regulated by nutrition,genetic background and environment.The endoplasmic reticulum?ER?performs important functions related to the synthesis,folding and transport of proteins.The ER of adipose tissue also plays a critical role in lipid transportation and regulates lipid metabolism.When the folding capacity of the ER cannot cope with the high load of unfolded and misfolded proteins,ER homeostasis is disturbed and ER stress is promoted.The imbalance of Ca²⁺homeostasis and the disorder of lipid metabolism as a consequence of ER stress.Studies found obesity and chemicals?such as Tunicamycin,TM?induced ER stress of adipose tissue led to disorder of lipid metabolism,but it's underlying mechanism still unclear.In this study,TM was used to induce ER stress of mice adipocytes and adipose tissue.We intend to discover its effects on adipose lipid metabolism and on hepatic lipid metabolism;discover the connection between adipokines?adiponectin and leptin?and ER stress;and define the regulation mechanisms between ER stress and disorder of lipid metabolism,inflammation,autophagy and apoptosis.This study will illustrate the underlying mechanisms that how ER stress of adipose tissue affects hepatic lipid metabolism by transporting adiposcytes-derived exosomes to liver.The main results are listed as followed:1.Established ER stress model of adipose tissue and adipocytes by using tunicamycin?TM?treatment.The expression level of ER stress indicators,such as Chop,GRP78 and members of Atf family,were all enhanced.TM treatment reducd the body weight and lipid size,and along with inflammation of adipose tissue and insuin resistance.In addition,TM induced adipocytes ER stress and decreased the levels of adiponectin and leptin,which leading to the disorder of lipid metabolism.However,ER stress was inhibited by using 4-PBA,and reduced the increasing of FFA.2.ER stress and dyslipidemia was inhibited by adiponectin and AdipoR1,the receptor of adiponectin.Adiponectin also reduced cellular Ca²⁺concentration,and alleviated dyslipidemia induced by the disturbulance of FFA.Additionally,adiponectin up-regulated the expression of PPAR?via enhancing the phosphorylation level of AMPK/PKC.Further study found PPAR?was the transcriptional regulator of Atf2,one of the important ER stress indicators.Adiponectin activated AMPK/PKC/PPAR?signals to block the transcription of Atf2,then inhibited the accumulation of FFA and Ca²⁺of adipocytes,relieving dyslipidemia and adipocytes apoptosis.3.RNA-seq analyzation was used to discover the interaction of leptin and ER stress.We found leptin inhibited ER stress and closely related with autophagy and inflammation of adipocytes.Leptin activated leptin receptor and the downstream JAK2/ATAT3 signal pathway,and then inhibited ER stress-induced autophagy by redcuing autophagy flux and autophagosome formation.In addition,leptin increased the expression of Klf4.Klf4 was the negative transcriptional regulator of Atf4,which means leptin inhibited ER stress and autophagy by the regulation of Klf4.Moreover,leptin inhibited authophagy by regulting the formation of ATF4 and ATG5 complex.Leptin then alleviated dyslipidemia and inflammation of adipose tissue.4.Adipocytes-dervied exosome?TM ATEx?was isolated from the adipocytes pre-treated with TM.The PHK26-labled exosome was injected into mice.Results showed TM ATEx triggered hepatic ER stress and caused hepatic dyslipidemia,which leading to hepatic steatosis and inflammation.Proteomics sequencing showed ER stress changed the protein expression of adiposcytes-derived exosomes,and the exosomal proteins can transport to liver.The exosomal protein Akr1b7,located in cytoplasm,had the most significant increasing.Bioinformatics analyzation showed Akr1b7 invovled in the regulation of lipid metabolism,we then found TM ATEx increased hepatic Akr1b7 level,then led to the inceaseing of glycerol.And the increasing of glycerol caused hepatic ER stress and dyslipidemia.In summary,our study showed the mechanism that ER stress of adipocytes led to dyslipidemia by the regulation of Atf2 and Atf4.Adiponection and leptin interacted with ER stress to inhibited adipocyte autopagy,apoptosis and inflammation.We also found TM ATEx delivered Akr1b7 to liver and involved in the regulation of hepatic dyslipidemia.Finally,this study illustrated the underlying mechanism of how ER stress-induced lipid metabolism disorder.This study will lay a molecular basis for the mouldability of lipid metabolism,and give important theoretical basis for the improvement of meat quality.