The insulin-like growth factor-1 receptor is a negative regulator of nitric oxide bioavailability and insulin sensitivity in the endothelium
Abbas A., Imrie H., Viswambharan H., Sukumar P., Rajwani A., Cubbon RM., Gage M., Smith J., Galloway S., Yuldeshava N., Kahn M., Xuan S., Grant PJ., Channon KM., Beech DJ., Wheatcroft SB., Kearney MT.
OBJECTIVE - In mice, haploinsufficiency of the IGF-1 receptor (IGF-1R +/2), at a whole-body level, increases resistance to inflammation and oxidative stress, but the underlying mechanisms are unclear. We hypothesized that by forming insulin-resistant heterodimers composed of one IGF-1Rαβ and one insulin receptor (IR), IRαβ complex in endothelial cells (ECs), IGF-1R reduces free IR, which reduces EC insulin sensitivity and generation of the antioxidant/anti-inflammatory signaling radical nitric oxide (NO). RESEARCH DESIGN AND METHODS - Using a number of complementary gene-modified mice with reduced IGF-1R at a whole-body level and specifically in EC, and complementary studies in EC in vitro, we examined the effect of changing IGF-1R/IR stoichiometry on EC insulin sensitivity and NO bioavailability. RESULTS - IGF-1R+/2 mice had enhanced insulin-mediated glucose lowering. Aortas from these mice were hypocontractile to phenylephrine (PE) and had increased basal NO generation and augmented insulin-mediated NO release from EC. To dissect EC from whole-body effects we generated mice with EC-specific knockdown of IGF-1R. Aortas from these mice were also hypocontractile to PE and had increased basal NO generation. Whole-body and EC deletion of IGF-1R reduced hybrid receptor formation. By reducing IGF-1R in IR-haploinsufficient mice we reduced hybrid formation, restored insulin-mediated vasorelaxation in aorta, and insulin stimulated NO release in EC. Complementary studies in human umbilical vein EC in which IGF-1R was reduced using siRNA confirmed that reducing IGF-1R has favorable effects on NO bioavailability and EC insulin sensitivity. CONCLUSIONS - These data demonstrate that IGF-1R is a critical negative regulator of insulin sensitivity and NO bioavailability in the endothelium. © 2011 by the American Diabetes Association.