beta-Blockers Promote Angiogenesis in the Mouse Aortic Ring Assay

Recent results indicate that the reduction of beta-adrenergic signaling impairs angiogenesis under ischemic conditions. Because angiogenesis may occur in the absence of ischemia, it remains to be determined whether and how beta-adrenergic signaling regulates angiogenesis, which develops under normoxic conditions. The effect of beta-adrenergic ligands on angiogenesis was investigated using 3-dimensional cultures of mouse aortic rings embedded in collagen type I, in which luminized microvessels develop in response to vascular endothelial growth factor (VEGF). Under normoxic conditions, both isoproterenol, a beta-adrenergic receptor (beta-AR) agonist, and forskolin, an adenylate cyclase activator, were unable to influence aortic microvessel sprouting. On the contrary, treatment with propranolol, a beta-AR antagonist, caused an approximately 70% increase in VEGF-mediated microvessel sprouting. This effect was abolished in rings from both double beta-AR and beta(1)-AR knockout mice, but not in rings from beta 2-AR knockout mice. Significant increases in microvessel sprouting were also observed when mouse aortic rings from C57BL/6 mice were treated with the beta(1)-AR-selective antagonists metoprolol and bisoprolol or with the beta(2)-AR-selective antagonist ICI 118,551. Conversely, carvedilol, a nonselective beta-AR antagonist, was unable to affect aortic sprouting. These findings suggest that some beta-blockers display proangiogenic activity through a mechanism that is independent of their ability to antagonize catecholamine action. The present results also identify a new function for beta-AR signaling as a facilitator for VEGF-mediated angiogenesis and have implications for understanding the mechanisms that regulate angiogenic responses under normoxic conditions.