Impaired cross-activation of β3 integrin and VEGFR-2 on endothelial progenitor cells with aging decreases angiogenesis in response to hypoxia

Background: The mechanism by which vascular regeneration declines with aging is not fully understood. An interaction between integrin and vascular endothelial growth factor receptor-2 (VEGFR-2) plays a substantial role in angiogenesis. Here, we investigated whether aging impairs this interaction in endothelial progenitor cells (EPCs) under hypoxia. Methods and results: Aging reduced the blood flow and vessel density in ischemic muscles in mice. Levels of phosphorylated Src (p-Src), p-beta(3), and p-VEGFR-2 in acute ischemia were reduced in the muscles of aged mice compared to young mice. The hypoxia-inducible factor (HIF)-1 alpha stabilizer deferoxamine improved the age-related impairment of angiogenesis, but this effect was diminished by LY290004, an inhibitor of phosphatidylinositol 3-kinase. Deferoxamine improved the reduction in chronic ischemia-induced beta(3)-integrin and VEGFR-2 phosphorylation in the muscles of aged mice; this effect was also diminished by LY290004. In EPCs, we identified the molecular requirements for VEGF-mediated beta(3)-integrin and VEGFR-2 cross-activation in vitronectin-induced cell adhesion under acute hypoxia. We demonstrated that c-Src controlled the adhesion- and VEGF-induced beta(3) tyrosine phosphorylation in hypoxia. Aging enhanced the hypoxia-induced EPC apoptosis and impaired several c-Src-related VEGF-induced receptor events, including beta(3) tyrosine activation, ligand binding, cell adhesion, and tubulogenesis in cultured EPCs of animals and those of humans. Conclusions: These data suggest that the aging-related decline in angiogenic action in response to ischemia is mediated by the impairment of cross-activation between beta(3) and VEGFR-2 in EPCs, which is partially associated with decreased HIF-1 alpha stability. (C) 2013 Elsevier Ireland Ltd. All rights reserved.