Mechanism Of Hsp90 Modulating Lipotoxicity Through Endoplasmic Reticulum Stress In INS-1E Cells

Elevated free fatty acids accompanied by obesity can cause lipotoxicity and lead to pancreatic islet cells injury.However,the cell lipotoxicity,INS-1E cells were treated with palmitate(PA group).Compared with control group,apoptosis rate increased in PA group.Then palmitate treated cells and control cells were detected by liquid chromatography-tandem mass spectrometry(LC-MS/MS)label-free protein quantification and 317 different proteins were identified,in which Hsp90 was found decreased in palmitate treated cells compared with the control group.The result was validated by Western blot.Hsp90 is an important molecular chaperone to maintain cell survival.Previous studies have shown that Hsp90 inhibitors may kill tumor cells through the endoplasmic reticulum stress(ERS)-apoptosis pathway(PERK-CHOP pathway and IRE1α-JNK pathway).Therefore,this study aims to investigate the mechanism of Hsp90 mediated ERS-apoptosis pathway to further reveal the molecular mechanism of lipotoxicity in pancreatic β-cells.First,the protein expressions in ERS-apoptosis pathway were detected by Western blot.The results showed that compared with control group,ERS-apoptosis pathway related proteins p-PERK,CHOP,p-IRE1α,p-JNK and apoptosis related enzyme cleaved-caspase3 were increased in PA treatment group,while endoplasmic reticulum molecular chaperone BiP was down-regulated.Then,Hsp90 of INS-1E cells was knocked down by Lentivirus-RNAi to imitate decreased Hsp90 in palmitate treated cells.The results showed that compared to the negative control group,cell apoptosis rate and ERS-apoptosis pathway related proteins p-PERK,CHOP,p-IRE1α,p-JNK were increased,while ER molecular chaperone BiP was decreased after knocking down Hsp90 in INS-1E cells.Second,INS-1E cells were overexpressed of Hsp90 by Lentivirus,and then treated with palmitate.Compared to negative control group treated with PA,its cell apoptosis rate and p-PERK,CHOP,p-IRE1α,p-JNK,cleaved-caspase 3 levels were down regulated,while BiP levels was up regulated.We conclude that:(1)Hsp90 in INS-1E cells were decreased under lipotoxicity,which may lead to down-regulation of endoplasmic reticulum molecular chaperone-BiP,and activation of ERS-apoptosis pathway,PERK-CHOP pathway and IRE1α-JNK pathway,and finally cause apoptosis in INS-1E cells;(2)Over expression of Hsp90 in INS-1E cells,may alleviate lipotoxicity induced-apoptosis and protect the β-cells by increasing the expression of endoplasmic reticulum molecular chaperones BiP,and inhibiting ERS-apoptosis pathway,PERK-CHOP pathway and IRE1α-JNK pathway.