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AIMS: Insulin (Ins) resistance (IRES) associates to increased cardiovascular risk as observed in metabolic syndrome. Chronic stimulation of beta-adrenergic receptors (betaAR) due to exaggerated sympathetic nervous system activity is involved in the pathogenesis of IRES. The cellular levels of G protein coupled receptor kinase 2 (GRK2) increase during chronic betaAR stimulation, leading to betaAR desensitization. We tested the hypothesis that GRK2 plays a role in betaAR-induced IRES. METHODS AND RESULTS: We evaluated Ins-induced glucose uptake and signalling responses in vitro in cell overexpressing the beta(2)AR, the GRK2, or the catalytically dead mutant GRK2-DN. In a model of increased adrenergic activity, IRES and elevated cellular GRK2 levels, the spontaneously hypertensive rats (SHR) we performed the intravenous glucose tolerance test load. To inhibit GRK2, we synthesized a peptide based on the catalytical sequence of GRK2 conjugated with the antennapedia internalization sequence (Ant-124). Ins in human kidney embryonic (HEK-293) cells causes rapid accumulation of GRK2, tyrosine phosphorylation of Ins receptor substrate 1 (IRS1) and induces glucose uptake. In the same cell type, transgenic beta(2)AR overexpression causes GRK2 accumulation associated with significant deficit of IRS1 activation and glucose uptake by Ins. Similarly, transgenic GRK2 overexpression prevents Ins-induced tyrosine phosphorylation of IRS1 and glucose uptake, whereas GRK2-DN ameliorates glucose extraction. By immunoprecipitation, GRK2 binds IRS1 but not the Ins receptor in an Ins-dependent fashion, which is lost in HEK-GRK2 cells. Ant-124 improves Ins-induced glucose uptake in HEK-293 and HEK-GRK2 cells, but does not prevent GRK2/IRS1 interaction. In SHR, Ant-124 infusion for 30 days ameliorates IRES and IRS1 tyrosine phosphorylation. CONCLUSION: Our results suggest that GRK2 mediates adrenergic IRES and that inhibition of GRK2 activity leads to increased Ins sensitivity both in cells and in animal model of IRES.

Downregulation of hypoxia-inducible factor 1 (HIF-1) and vascular endothelial growth factor (VEGF) are shown to be involved in age-dependent impairment of angiogenesis. In this study, we explore whether prior exercise is able to affect these molecular patterns favorably and to enhance neoangiogenesis in old Wistar rats with hind-limb ischemia. At day 7 after surgery, HIF-1alpha and VEGF expression increased in the ischemic muscle of trained animals. Exercise increased capillary density and limb perfusion as revealed by histologic, angiographic, and dyed bead techniques. Furthermore, exercise capacity and limb trophism have significantly improved in trained aged rats. In these animals, the reduction of VEGF serum levels has reflected the comprehensive improvement in local ischemia evoked by exercise. In conclusion, prior exercise represents a valid tool to counteract age-related molecular alterations resulting in impaired angiogenesis in response to ischemia.