Abstract 10696: Enhancing Endothelial Insulin Sensitivity Reduces NO Bioavailability: a role for NADPH Oxidase-Derived Reactive Oxygen Species
Insulin resistance in the whole body and endothelium is a hallmark of type 2 diabetes. Insulin resistance at the level of the endothelium reduces bioavailability of the anti-atherosclerotic signalling radical nitric oxide (NO). The effect of enhancing insulin sensitivity in the endothelium remains an open question. We studied the effects of increasing insulin signalling in the endothelium using novel transgenic mice, over-expression of the Type A human Insulin Receptor (HIRECO) in the endothelium, under direction of the Tie-2 promoter-enhancer. Semi-quantitative RT-PCR was carried out on tissues and endothelial cells from aorta and lungs to confirm significantly increased levels of human insulin receptor mRNA, while the protein expression was confirmed by immunohistochemistry on aortic sections in HIRECO and wild type mice. No significant changes in morphological features, metabolic phenotypes, such as fasting glucose levels and glucocompetence or blood pressure regulation were observed between the HIRECO and wild type (WT) littermates. HIRECO mice had significant endothelial dysfunction demonstrated by a blunted response to acetylcholine (Emax, WT vs. HIRECO: 84±3% vs. 68±3% respectively; p>0.05). No difference in endothelium-independent response to sodium nitroprusside was observed in HIRECO mice. The impaired aortic response to acetylcholine was normalized by the specific NADPH oxidase inhibitor peptide, gp91ds-tat, (Emax: 93±5%; p<0.06) as well as the superoxide dismutase mimetic, Mn(III)TmPyP. Isolated aortic rings of HIRECO exhibited a hypercontractile response to phenylephrine compared to wild type mice (log EC50, WT vs. HIRECO: 6.96±0.03 vs. 7.24±0.08, p<0.01). Basal NO bioactivity was decreased in HIRECO compared to wild type littermates (Emax upon exposure to eNOS inhibitor, L-N mono-methyl arginine in phenylephrine-constricted aorta, WT vs. HIRECO: 144±27.9% vs. 32±33%; p<0.05). These data demonstrate enhanced oxidative stress in a novel murine model of increased insulin signalling in the endothelium, leading to reduced bioavailability of nitric oxide. Our study also demonstrates for the first time, that increased insulin sensitivity in the endothelium elevates superoxide anion levels.
- © 2011 by American Heart Association, Inc.