Resistin Impairs Insulin Signaling And Promotes Endothelial Apoptosis Via Induction Of Endoplasmic Reticulum Stress

ObjectivesInsulin induces vasorelaxation via stimulation of nitric oxide(NO) production in endothelium. It has been shown that adipocyte-derived resistin inhibits insulin-induced vasorelaxation and induces endothelial activation, the underlying the mechanisms are not defined. The present study tested the hypothesis whether resistin inhibits insulin-stimulated NO production and induces endothelial damage via induction of endoplasmic reticulum(ER) in endothelium.MethodsHuman umbilical vein endothelial cells(HUVECs) were incubated with either tunicamycin(an inducer of ER stress, from 1?g/ml to 20?g/ml) or resistin(from 10ng/ml to 100ng/ml) for 1 hour or 24 hours. In some experiments, the cells were preincubated with TUDCA(ER stress inhibits) or insulin(100 nm/L) for 15 minutes before tunicamycin or resistin treatment. The protein expression of ER stress markers GRP78, Phosphor-JNK, or insulin signaling molecules including Phosphor-Akt and Phosphor-e NOS were determined by Western blot. The m RNA expression of proinflammatory cytokines tumor nuclear factor(TNF)? and inteleukin(IL)-6 was determined by real-time PCR. To investigate the effects of resistin on endothelial apoptosis, the protein expression of caspase 3 was determined in HUVECs treated with resistin.In HUVECs, either resistin or tunicanmycin dose-dependently increased the expression of GRP78 and JNK phosphorylation, suggesting that resistin induces ER stress in endothelial cells. Incubation of HUVECs with insulin increased phosphorylation of Akt(Tyr 473) and e NOS(ser 1179), resistin inhibited insulin-induced phosphorylation of Akt and e NOS, TUDCA reversed inhibitory effects of resistin on Akt and e NOS phosphorylation accompanied with decreased expression of ER stress markers GRP78 and JNK phosphorylation. Moreover, resistin increased the expression of proinflammatory genes TNF-? and IL-6, and apoptosis protein caspase 3, which were also prevented by TUDCA treatment.ConclusionsOur results demonstrated that resistin induced ER stress in endothelial cells, resulting in impairment of insulin-stimulated NO production and induction of endothelial inflammation and apoptosis. These results contribute to the scientific basis of the development of new strategies for the treatment of cardiovascular and metabolic diseases. Results...