Rationale There is growing evidence that the myocardium responds to injury by recruiting c-kit+ cardiac progenitor cells to the damage tissue. Even though the ability of exogenously introducing c-kit+ cells to injured myocardium has been established, the capability of recruiting these cells through modulation of local signaling pathways by gene transfer has not been tested. Objective To determine whether stem cell factor gene transfer mediates cardiac regeneration in a rat myocardial infarction model, through survival and recruitment of c-kit+ progenitors and cell-cycle activation in cardiomyocytes, and explore the mechanisms involved. Methods and Results Infarct size, cardiac function, cardiac progenitor cells recruitment, fibrosis, and cardiomyocyte cell-cycle activation were measured at different time points in controls (n=10) and upon stem cell factor gene transfer (n=13) after myocardial infarction. We found a regenerative response because of stem cell factor overexpression characterized by an enhancement in cardiac hemodynamic function: an improvement in survival; a reduction in fibrosis, infarct size and apoptosis; an increase in cardiac c-kit+ progenitor cells recruitment to the injured area; an increase in cardiomyocyte cell-cycle activation; and Wnt/β-catenin pathway induction. Conclusions Stem cell factor gene transfer induces c-kit+ stem/progenitor cell expansion in situ and cardiomyocyte proliferation, which may represent a new therapeutic strategy to reverse adverse remodeling after myocardial infarction.

Stem cell and gene therapies are being pursued as strategies for repairing damaged cardiac tissue following myocardial infarction in an attempt to prevent heart failure. The chemokine receptor-4 (CXCR4) and its ligand, CXCL12, play a critical role in stem cell recruitment post-acute myocardial infarction. Whereas progenitor cell migration via the CXCL12/CXCR4 axis is well characterized, little is known about the molecular mechanisms of CXCR4 mediated modulation of cardiac hypertrophy and failure. We used gene therapy to test the effects of CXCR4 gene delivery on adverse ventricular remodeling due to pressure overload. We assessed the effect of cardiac overexpression of CXCR4 during trans-aortic constriction (TAC) using a cardiotropic adeno-associated viral vector (AAV9) carrying the CXCR4 gene. Cardiac overexpression of CXCR4 in mice with pressure overload prevented ventricular remodeling, preserved capillary density and maintained function as determined by echocardiography and in vivo hemodynamics. In isolated adult rat cardiac myocytes, CXCL12 treatment prevented isoproterenol induced hypertrophy and interrupted the calcineurin/NFAT pathway. Finally, a complex involving the L-type calcium channel, β2-adenoreceptor, and CXCR4 (Cav1.2/β2AR/CXCR4) was identified in healthy cardiac myocytes and was shown to dissociate as a consequence of heart failure. CXCR4 administered to the heart via gene transfer prevents pressure overload induced heart failure. The identification of CXCR4 participation in a Cav1.2-β2AR regulatory complex provides further insight into the mechanism by which CXCR4 modulates calcium homeostasis and chronic pressure overload responses in the cardiac myocyte. Together these results suggest AAV9.CXCR4 gene therapy is a potential therapeutic approach for congestive heart failure.