Curcumin Improves Palmitate-induced Insulin Resistance In Human Umbilical Vein Endothelial Cells By Maintaining Proteostasis In Endoplasmic Reticulum

Objective: Diabetes has become one of the major noninfectious chronic diseases affecting the health of the global population,and its prevalence is increasing year by year.Insulin resistance is prone to lead to type 2 diabetes mellitus,which plays an important role in the development of diabetes and complications.At the same time,studies have shown that the damage of vascular endothelial cells is closely related to the development of cardiovascular complications in diabetes.Insulin resistance therapy targeting vascular endothelial cells may have beneficial effects in preventing diabetes-related cardiovascular diseases.Curcumin is the main bioactive component of plant Curcuma longa,which has anti-oxidative stress and anti-inflammatory effects,and can improve diabetes and diabetic complications,but its effect on vascular endothelium remains to be further studied.In this study,we investigated the effects of curcumin on insulin resistance in human umbilical vein endothelial cells(HUVECs)induced by palmitate.Methods: HUVECs were cultured in phenol red-free Medium 200 medium containing1% low serum growth supplement(LSGS).The expression of symbol proteins and their phosphorylation were detected by western blot.Peptidase activity,glucose uptake and protein aggregation were detected by related assay kits,respectively.Results:(1)Palmitate reduced the phosphorylation of AKT Thr308 stimulated by insulin,increased the level of endoplasmic reticulum stress markers,the ratio of LC3-II to LC3-I and the peptidase activity of 20 S proteasome,while endoplasmic reticulum stress inhibitor 4-Phenylbutyric acid(PBA)reversed the above changes.(2)Curcumin significantly improved the phosphorylation of AKT Thr308 induced by insulin stimulation,reversed the adverse effects of palmitate on the translocation of glucose transporter 4(GLUT4)on plasma membrane and the uptake of 2-DG induced by insulin stimulation,and significantly reduced the expression of endoplasmic reticulum stress markers,protein aggregation,the phosphorylation of JNK Thr183 and IRS-1Ser307 and the peptidase activity of 20 S proteasome after palmitate treatment,while increased the LC3 expression,the ratio of LC3-II to LC3-1,and the autophagy flux.(3)Compared to control group,autophagy protein 5(Atg5)knockdown inhibited the phosphorylation of AKT Thr308,translocation of GLUT4 and uptake of 2-DG stimulated by insulin,eliminated the beneficial effects of curcumin on endoplasmic reticulum stress,exacerbated ubiquitination of total protein,restored protein aggregation and the phosphorylation of AKT Thr308 and IRS-1 Ser307.Conclusion: Curcumin-activated autophagy could maintain protein homeostasis in endoplasmic reticulum,attenuate endoplasmic reticulum stress,inhibit JNK/IRS-1pathway,and improve insulin resistance.