Effects Of Txnip On Geniposide Regulating Endoplasmic Reticulum Stress In Pancreatic Beta Cells

Under endoplasmic reticulum stress(ERS)conditions,cells activate a signaling network named unfolded protein response(UPR)to enhance the adaptation to the change of environment,to antagonize ERS,and to stabilize the cellular homeostasis.A large number of references show that UPR plays an essential role on the development and prevention of type 2 diabetes mellitus(T2DM).Our previous works demonstrated that geniposide could affect the redox state by regulating the degradation of thioredoxin-interacting protein(Txnip),a key player on the regulation of cellular redox state,improve the function of cells,and prevent the cell apoptosis induced by high glucose in pancreatic beta cells.But unfortunately,the mechanisms about that keep to be explored.In this study,we determined the effects of geniposide on UPR in high glucose-treated pancreatic beta INS-1 cells,and analyzed the association between UPR and geniposide regulating Txnip degradation induced by high glucose.The results indicated that geniposide enhanced the phosphorylation of PERK/eIF2α and IRE1α,two key molecules of UPR signal pathway,and pre-incubation with GSK2656157,an inhibitor for PERK,and STF-083010,an inhibitor for IRE1α could attenuate the role of geniposide on Txnip degradation in high glucose-treated INS-1 cells significantly.Furthermore,RNAi on PERK and IRE1α also prevented the effects of geniposideon Txnip degradation in pancreatic beta cells.All these data suggested that geniposide regulating the degradation of Txnip induced by high glucose might be involved in its role on UPR,which was beneficial to enhance the adaptation,and increase the viability in high glucose-cultured pancreatic beta cells.To investigate the effect of Txnip on geniposide improving the function of pancreatic beta cells,firstly,we evaluated the effect of geniposide on the cell viability induced by glucolipotoxicity(16.7 mM glucose and 0.2 mM palimate),the results demonstrated that geniposide could increase the cell viability significantly in INS-1 cells.Secondly,we compared the influence of geniposide on the expression of apoptotic proteins including OH-1,Bcl-2,Bax and cleaved caspase-3 in Txnip knockdown and normal cultured INS-1cells.Data showed that,knockdown of Txnip could noticeably increase the protein levels of OH-1 and Bcl-2,but decrease the level of Bax and cleaved caspase-3,and geniposide could further potentiate these effects.In the end,we evaluated the effects of geniposide onthe protein levels of apoptotic proteins in the pancreatic tissue of Txnip-/-mice,the results indicated that,although Txnip knockout had no significant role on the levels of apoptotic proteins,but geniposide significantly increased the protein levels of HO-1 and Bcl-2 in high glucose/high lipid(HFD)-feeded Txnip-/-mice.All the data showed in this study suggested that UPR molecules play an essential role on geniposide regulating txnip degradation induced by high glucose in pancreatic beta cells,but Txnip was not the only way of geniposide antagonizing endoplasmic reticulum stress.