β2-adrenergic receptor stimulation improves endothelial progenitor cell-mediated ischemic neoangiogenesis

RATIONALE: Endothelial progenitor cells (EPCs) are present in the systemic circulation and home to sites of ischemic injury where they promote neoangiogenesis. β₂-Adrenergic receptor (β₂AR) plays a critical role in vascular tone regulation and neoangiogenesis. OBJECTIVE: We aimed to evaluate the role of β₂AR on EPCs' function. METHODS AND RESULTS: We firstly performed in vitro analysis showing the expression of β₂AR on EPCs. Stimulation of wild-type EPCs with β-agonist isoproterenol induced a significant increase of Flk-1 expression on EPCs as assessed by fluorescence-activated cell sorter. Moreover, β₂AR stimulation induced a significant increase of cell proliferation, improved the EPCs migratory activity, and enhanced the EPCs' ability to promote endothelial cell network formation in vitro. Then, we performed in vivo studies in animals model of hindlimb ischemia. Consistent with our in vitro results, in vivo EPCs' treatment resulted in an improvement of impaired angiogenic phenotype in β₂AR KO mice after induction of ischemia, whereas no significant amelioration was observed when β₂AR knock out (KO) EPCs were injected. Indeed, wild-type-derived EPCs' injection resulted in a significantly higher blood flow restoration in ischemic hindlimb and higher capillaries density at histological analysis as compared with not treated or β₂AR KO EPC-treated mice. CONCLUSIONS: The present study provides the first evidence that EPCs express a functional β₂AR. Moreover, β₂AR stimulation results in EPCs proliferation, migration, and differentiation, enhancing their angiogenic ability, both in vitro and in vivo, leading to an improved response to ischemic injury in animal models of hindlimb ischemia.