| Objectives:Insulin stimulates both nitric oxide (NO)-dependent vasodilation and endothelin-1(ET-1)-dependent vasoconstriction. However, the cellular mechanisms that control the dual vascular effects of insulin remain unclear. This study aimed to investigate the roles of the multi-domain adaptor protein APPL1in modulating vascular actions of insulin in mice and in endothelial cells.Research Design and Methods:Both APPL1knockout mice and transgenic mice were generated to evaluate its physiological roles on vascular reactivity and insulin signaling in endothelial cells.Results:Insulin potently induced NO-dependent relaxations in mesenteric arteries of8-week-old mice, whereas this effect of insulin was progressively impaired with ageing or upon development of high fat diet-induced obesity. Transgenic expression of APPL1prevented ageing-and obesity-induced impairment in insulin-induced vasodilation, and reversed obesity-induced augmentation in insulin-evoked ET-1-dependent vasoconstriction. By contrast, genetic disruption of APPL1shifted the effects of insulin from vasodilation to vasoconstriction. At the molecular level, insulin-elicited activation of Akt and eNOS and production of NO were enhanced in APPL1transgenic mice, but were abrogated in APPL1knockout mice. Conversely, insulin-induced ERK1/2phosphorylation and ET-1expression was augmented in APPL1knockout mice, but was diminished in APPL1transgenic mice. In endothelial cells, APPL1potentiated insulin-stimulated Akt activation by competing with the Akt inhibitor Tribble-3, and suppressed ERK1/2signaling by altering the phosphorylation status of its upstream kinase Raf-1. Furthermore, over-expression of APPL1could improve high fat diet induced hyperglycemia and hyperinsulinemia.Conclusions:APPL1plays a key role in coordinating the vasodilator and vasoconstrictor effects of insulin, by modulating Akt-dependent NO production and ERK1/2-mediated ET-1secretion in the endothelium. |
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