Activator Protein-2α Mediates Carbon Monoxide-Induced Stromal Cell-Derived Factor-1α Expression and Vascularization in Ischemic Heart

Objective-Increased cardiac stromal cell-derived factor-1 alpha (SDF-1 alpha) expression promotes neovascularization and myocardial repair after ischemic injury through recruiting stem cells and reducing cardiomyocyte death. Previous studies have shown that heme oxygenase-1 and its reaction byproduct, carbon monoxide (CO), induce SDF-1 alpha expression in ischemic heart. However, the mechanism underlying heme oxygenase-1/CO-induced cardiac SDF-1 alpha expression remains elusive. This study aims to investigate the signaling pathway and the transcriptional factor that mediate CO-induced SDF-1 alpha gene expression and cardioprotection. Approach and Results-CO gas and a CO-releasing compound, tricarbonyldichlororuthenium (II) dimer, dose-dependently induced SDF-1 alpha expression in primary neonatal cardiomyocytes and H9C2 cardiomyoblasts. Promoter luciferase-reporter assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation demonstrated that the activator protein 2 alpha(AP-2 alpha) mediated tricarbonyldichlororuthenium (II) dimer-induced SDF-1 alpha gene transcription. Tricarbonyldichlororuthenium (II) dimer induced AP-2 alpha expression via protein kinase B (AKT)-dependent signaling. AKT inhibition or AP-2 alpha knockdown reduced tricarbonyldichlororuthenium (II) dimer-induced SDF-1 alpha expression. Coronary ligation induced transient increases of cardiac AP-2 alpha and SDF-1 alpha expression, which were declined at 1 week postinfarction in mice. Periodic exposure of coronary-ligated mice to CO (250 ppm for 1 hour/day, 6 days) resumed the induction of AP-2 alpha and SDF-1 alpha gene expression in infarcted hearts. Immunohistochemistry and echocardiography performed at 4 weeks after coronary ligation revealed that CO treatment enhanced neovascularization in the myocardium of peri-infarct region and improved cardiac function. CO-mediated SDF-1 alpha expression and cardioprotection was ablated by intramyocardial injection of lentivirus bearing specific short hairpin RNA targeting AP-2 alpha. Conclusions-Our data demonstrate that AKT-dependent upregulation of AP-2 alpha is essential for CO-induced SDF-1 alpha expression and myocardial repair after ischemic injury. (Arterioscler Thromb Vasc Biol. 2013; 33: 785-794.)