Role of vascular endothelial insulin sensitisation in vascular repair in systemic insulin resistance

Abstract

BackgroundInsulin resistance is an independent risk factor for cardiovascular disease. Murine models with global insulin receptor haploinsufficiency (IRKO) show endothelial dysfunction and impaired vascular repair, potentially related to reduced number and function of endothelial progenitor cells and bioavailability of nitric oxide. We hypothesise that endothelium-specific insulin sensitisation, in the context of global insulin resistance, could reverse these vascular abnormalities. Therefore, we have bred IRKO mice with HIRECO mice, which overexpress a human insulin receptor in endothelial cells under the transcriptional regulation of the Tie-2 promoter-enhancer. MethodsDouble-transgenic offspring from HIRECO mice crossed with IRKO mice (HIRECOxIRKO) were compared with IRKO mice after confirming genotype with PCR on DNA extracted from ear samples. Metabolic assessment was done with glucose-tolerance and insulin-tolerance tests, and ELISA was used to measure plasma insulin concentrations. Blood pressure (BP) was measured with tail cuff plethysmography. Femoral artery denuding injury was induced with an angioplasty guide-wire; 4 days later, vessels were explanted after perfusion with Evans blue dye to quantify endothelial denudation. Circulating progenitor cells (CPCs, positive for Sca-1/Flk-1) were counted in peripheral venous blood by fluorescence-activated cell sorting. Continuous data were expressed as means (SD) and analysed with paired and unpaired Student's t tests as appropriate (significance at p<0·05). A minimum of five of each mouse type was used in each comparison, unless otherwise stated. FindingsHIRECOxIRKO and IRKO mice had similar growth profiles (weight at 4 months 28·3 g [3·0] vs 27·4 [0·9], p=0·51) and systolic BP (98 mm Hg [12·4] vs 106 [10·4], p=0·28), with comparable insulin sensitivity on tolerance tests. Basal plasma insulin concentrations were also similar (0·70 ng/mL [0·50] vs 0·76 [0·47], p=0·78; n=7), though HIRECOxIRKO did not display the post prandial hyperinsulinaemia seen in IRKO mice previously and in this study. Vascular repair was significantly enhanced in HIRECOxIRKO after femoral artery wire injury (HIRECOxIRKO 56·9% regeneration [11·1] vs IRKO 46·0% [5·1], p=0·048). This repair was not associated with any improvement in numbers of CPCs, which were similar in the two groups of mice (HIRECOxIRKO 90 Sca-1/Flk-1 positive cells [27] vs IRKO 105 [42], p=0·99]. InterpretationIn HIRECOxIRKO mice, restoration of vascular repair occurred after endothelial wire injury, which has been previously demonstrated as impaired in IRKO mice. This restoration happened even with comparable glucoregulation and BP, suggesting that the effect is related specifically to endothelial insulin sensitisation despite insulin resistance in traditional target tissues. These data are early and exploratory, and sample size was small and from murine colonies; nonetheless, they seem to support the possibility of vascular endothelial insulin sensitisation as a potential therapeutic target in insulin resistant states. A mechanism remains to be established and we are planning assays of endothelial function, angiogenesis, and downstream insulin molecular signalling. FundingBritish Heart Foundation.