Growth-factor-mediated cardiac stem cell activation in myocardial regeneration.

The concept of an intrinsic regenerative capacity of the adult mammalian myocardium owing to the presence of cardiac stem cells (CSCs) in the atria and ventricles is starting to be accepted by the cardiovascular research community. The identification of this cell population has improved the prospects for developing successful clinical protocols for human myocardial regeneration. In the normal adult myocardium, only a small fraction of CSCs undergo amplification and differentiation to replace the parenchymal cells lost by normal wear and tear. Physiological or pathological stimuli cause substantial activation of CSCs, which is mediated by a paracrine feedback loop between myocytes and CSCs. In response to stress, the myocytes produce growth factors and cytokines, for which CSCs have receptors, and autocrine, self-sustaining activation of growth-factor production is simultaneously triggered in the CSCs. These findings from human and animal studies led us to test whether in situ activation of CSCs by growth factors would be as effective as transplantation of CSCs into the regenerating myocardium after ischemia in an animal model that has relevance to humans. In a porcine model, we produced extensive and functionally relevant myocardial regeneration. Here, we discuss the properties of endogenous myocardial stem cells that might be exploited to produce clinical myocardial regeneration without the need for cell transplantation.