Objective: Increased cardiac stromal cell-derived factor-1α (SDF-1α) 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-1α expression in ischemic heart. However, the mechanism underlying heme oxygenase-1/CO-induced cardiac SDF-1α expression remains elusive. This study aims to investigate the signaling pathway and the transcriptional factor that mediate CO-induced SDF-1α gene expression and cardioprotection.
Approach and results: CO gas and a CO-releasing compound, tricarbonyldichlororuthenium (II) dimer, dose-dependently induced SDF-1α expression in primary neonatal cardiomyocytes and H9C2 cardiomyoblasts. Promoter luciferase-reporter assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation demonstrated that the activator protein 2α (AP-2α) mediated tricarbonyldichlororuthenium (II) dimer-induced SDF-1α gene transcription. Tricarbonyldichlororuthenium (II) dimer induced AP-2α expression via protein kinase B (AKT)-dependent signaling. AKT inhibition or AP-2α knockdown reduced tricarbonyldichlororuthenium (II) dimer-induced SDF-1α expression. Coronary ligation induced transient increases of cardiac AP-2α and SDF-1α 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-2α and SDF-1α 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-1α expression and cardioprotection was ablated by intramyocardial injection of lentivirus bearing specific short hairpin RNA targeting AP-2α.
Conclusions: Our data demonstrate that AKT-dependent upregulation of AP-2α is essential for CO-induced SDF-1α expression and myocardial repair after ischemic injury.