Therapeutic Mechanisms of Cardiac Progenitors in Ischemic Cardiomyopathy

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Ischemic heart disease is a leading cause of death worldwide. Given the limited regenerative capacity of the human heart following myocardial injury, stem cell-based therapies, including the recent cKit+ cell therapy have emerged as a promising approach for improving cardiac repair and function. Clinical and preclinical data suggests that benefits of cKit+ cell transplantation include improved cardiac function and myocardial mass. However, the ability of cKit+ CPCs to differentiate into cardiomyocytes as a significant mode of cardiac repair is controversial. Published data from our group has established the beneficial effects of stem cell factor (SCF), the ligand for cKit, in improving the abundance of cKit+ cells, angiogenesis and cardiac function in both rat and pig models of ischemic cardiomyopathy. Further, our preliminary data suggest that secreted paracrine factors, particularly the membrane-bound exosomes, may mediate most of the pro-angiogenic paracrine activity of the SCF-treated cKit+ cell. Our central hypothesis is that mobilization of a heterogeneous group of endogenous CPCs using gene transfer for the receptor tyrosine cKit ligand stem cell factor (SCF) can enhance cardiac tissue repair following myocardial injury via their paracrine secretion. We will test the necessary and sufficient conditions of SCF-induced CPC recruitment using the MI model of heart failure in swine to evaluate the roles of SCF-induced cKit, PW1 and PDGFR expressing CPCs in myocardial repair, regeneration and restoration of function. We will test the hypothesis that cKit, PW1 and PDGFR progenitor cells are sufficient for SCF induced cardiac repair by gain of function experiments using SCF modRNA. We will test the hypothesis that cKit, PW1 and PDGFR progenitor cells are necessary for cardiac repair by loss of function experiments using shRNA-mediated knockdown of cKit, PDGFR and PW1 receptors. RNAs will be delivered one-week post-MI by the clinically relevant intracoronary route and animals will be evaluated for survival, cardiac remodeling, cardiac function, cell-specific proliferation and differentiation and the molecular mechanisms involved. We will determine the role of paracrine secretion from cKit+ CPCs in SCF-induced cardiac repair. Our preliminary data suggest that exosomes, and not the exosomes-depleted fraction from swine post-MI cKit- secretome have pro-angiogenic activity. Using specific expertise for exosomes research, we will identify the miRNA expression of cKit+ exosomes in response to SCF. In addition, we will investigate the functional mechanisms of cKit+ exosomes-induced proliferation and contractile function of cardiomyocytes and angiogenesis of endothelial cells in vitro. Finally, we will determine the therapeutic benefits of cKit exosomes in a swine model of heart failure.