Novel Paracrine Action of Endothelium enhances Glucose Uptake in Muscle and Fat

Rationale: A hallmark of type 2 diabetes is insulin resistance, which leads to increased endothelial cell production of superoxide and a simultaneous reduction in availability of the vasoprotective signalling radical, nitric oxide (NO). We recently demonstrated in preclinical models that type 2 diabetes simultaneously causes resistance to insulin like growth factor-1 (IGF-1) mediated glucose lowering and endothelial NO release.

Objective: To examine the effect of insulin and IGF-1 resistance specifically in endothelial cells in vivo.

Methods and Results: We generated mice expressing mutant IGF-1 receptors (mIGF-1R), which form non-functioning hybrid receptors with native insulin receptors (IR) and IGF-1R, directed to endothelial cells under control of the Tie2 promoter-enhancer. Despite endothelial cell insulin and IGF-1 resistance, mutant IGF-1R endothelial cell over-expressing mice (mIGFREO) had enhanced insulin and IGF-1 mediated systemic glucose disposal, lower fasting free fatty acids and triglycerides. In hyperinsulinaemic-euglycaemic clamp studies, mIGFREO had increased glucose disposal and increased glucose uptake into muscle and fat, in response to insulin. mIGFREO had increased NADPH oxidase 4 (Nox4) expression due to reduced expression of the microRNA, miR-25. Consistent with increased Nox4, mIGFREO endothelial cells generated increased hydrogen peroxide (H2O2), with no increase in superoxide. Treatment with catalase, a dismutase restored insulin tolerance to wild type levels in mIGFREO.

Conclusions: Combined insulin and IGF-1 resistance restricted to the endothelium leads to a potentially favourable adaptation in contrast to pure insulin resistance, with increased Nox4-derived H2O2 generation mediating enhanced whole-body insulin sensitivity.