Ischemic neoangiogenesis enhanced by β₂-adrenergic receptor overexpression: A novel role for the endothelial adrenergic system

β₂-Adrenergic receptors (β₂ARs) are widely expressed, although their physiological relevance in many tissues is not yet fully understood. In vascular endothelial cells, they regulate NO release and vessel tone. Here we provide novel evidence that β₂ARs can regulate neoangiogenesis in response to chronic ischemia. We used in vivo adenoviral-mediated gene transfer of the human β₂AR to the endothelium of the rat femoral artery and increased β₂AR signaling resulting in ameliorated angiographic blood flow and hindlimb perfusion after chronic ischemia. Histological analysis confirmed that β₂AR overexpression also produced benefits on capillary density. The same maneuver partially rescued impaired angiogenesis in spontaneously hypertensive rats (SHR), whereas gene delivery of the G-protein-coupling defective mutant Ile164 β₂AR failed to provide ameliorations. Stimulation of endogenous and overexpressed β₂AR on endothelial cells in vitro was found to regulate cell number by inducing proliferation and [³H]-thymidine incorporation through means of extracellular receptor-activated kinase and vascular endothelial growth factor. The β₂AR also has novel effects on endothelial cell number through stimulation of proapoptosis and antiapoptosis pathways involving p38 mitogen-activated protein kinase and PI3-kinase/Akt activation. Therefore, β₂ARs play a critical role in endothelial cell proliferation and function including revascularization, suggesting a novel and physiologically relevant role in neoangiogenesis in response to ischemia.