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OBJECTIVE- Insulin stimulates both nitric oxide (NO>dependent vasodilation and endothelin-1 (ET-l)-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 multidomain adaptor protein APPLI in modulating vascular actions of insulin in mice and in endothelial cells.
RESEARCH DESIGN AND METHODS- Both APPLI knockout mice and APPLI transgenic mice were generated to evaluate APPLl's physiological roles in regulating vascular reactivity and insulin signaling in endothelial cells.
RESULTS - Insulin potently induced NO-dependent relaxations in mesenteric arteries of 8-week-old mice, whereas this effect of insulin was progressively impaired with ageing or upon development of obesity induced by high-fat diet Transgenic expression of APPLI prevented age- and obesity-induced impairment in insulininduced vasodilation and reversed obesity-induced augmentation in insulin-evoked ??-1-dependent vasoconstriction. By contrast, genetic disruption of APPLI shifted the effects of insulin from vasodilation to vasoconstriction. At the molecular level, insulinelicited activation of protein kinase B (Akt) and endothelial NO synthase and production of NO were enhanced in APPLI transgenic mice but were abrogated in APPLI knockout mice. Conversely, insulin-induced extracellular signal-related kinase (ERK) 1/2 phosphorylation and ETl expression was augmented in APPLI knockout mice but was diminished in APPLI transgenic mice. In endothelial cells, APPLI potentiated insulin-stimulated Akt activation by competing with the Akt inhibitor Tribbles 3 (TRB3) and suppressed ERK1/2 signaling by altering the phosphorylation status of its upstream kinase Raf-1.
CONCLUSIONS- APPLI plays a key role in coordinating the vasodilator and vasoconstrictor effects of insulin by modulating Akt-dependent NO production and ERKl/2-mediated ET-I secretion in the endothelium. Diabetes 60:3044-3054, 2011
Insulin is not only a principal regulator of glucose homeostasis but also a vasoactive hormone involved in modulation of vascular tone (1). In the vasculature, insulin exerts both vasodilator and vasoconstrictor effects by promoting the endothelial production of nitric oxide (NO) and the release of endothelin-1 (ET-I) (2). msulin-sümulated NO production in endothelial cells is mediated by the phosphatidylinositol 3-kinase (PI 3-K)/ protein kinase B (Akt) signaling cascade, which in turn phosphorylates and activates endothelial NO synthase (eNOS) (3). On the other hand, insulin-induced expression and secretion of the vasoconstrictor ET-I is mediated by the extracellular signal-regulated kinase (ERK) 1/2 mitogenactivated protein kinase (MAPK) signaling pathway in vascular endothelium (4)....