Overexpression of Cardiomyocyte α_1A-Adrenergic Receptors Attenuates Postinfarct Remodeling by Inducing Angiogenesis Through Heterocellular Signaling

Objective-Stimulation of cardiac α_1A-adrenergic receptors (α_1A-AR) has been proposed for treatment of heart failure, since it increases myocardial contractility. We investigated a different mechanism, induction of angiogenesis. Approach and Results-Four to 6 weeks after permanent coronary artery occlusion, transgenic rats with cardiomyocyte-specific α_1A-adrenergic receptor overexpression had less remodeling than their nontransgenic littermates, with less fibrosis, hypertrophy and lung weight, and preserved left ventricular ejection fraction and wall stress (all P<0.05). Coronary blood flow, measured with microspheres, increased in the infarct zone in transgenic rats compared with nontransgenic littermates (1.4±0.2 versus 0.5±0.08 mL min^-1 g^-1; P<0.05), which is consistent with angiogenesis, as reflected by a 20% increase in capillary density in the zone adjacent to the infarct. The question arose, how does transgenic overexpression of a gene in cardiomyocytes induce angiogenesis? We identified a paracrine mechanism, whereby vascular endothelial growth factor-A mRNA and protein were increased in isolated transgenic cardiomyocytes and also by nontransgenic littermate cardiomyocytes treated with an α_1A-agonist, resulting in angiogenesis. Conditioned medium from cultured cardiomyocytes treated with an α_1A agonist enhanced human umbilical vein endothelial cell tubule formation, which was blocked by an anti-vascular endothelial growth factor-A antibody. Moreover, improved cardiac function, blood flow, and increased capillary density after chronic coronary artery occlusion in transgenic rats were blocked by either a mitogen ERK kinase (MEK) or a vascular endothelial growth factor-A inhibitor. Conclusion-Cardiomyocyte-specific overexpression of the α_1A-adrenergic receptors resulted in enhanced MEK-dependent cardiomyocyte vascular endothelial growth factor-A expression, which stimulates angiogenesis via a paracrine mechanism involving heterocellular cardiomyocyte/endothelial cell signaling, protecting against remodeling and heart failure after chronic coronary artery occlusion.