Myocardial regeneration: expanding the repertoire of thymosin β4 in the ischemic heart.

Efficient cardiac regeneration postinfarction (MI) requires the replacement of lost cardiomyocytes, formation of new coronary vessels and appropriate modulation of the inflammatory response. However, insight into how to stimulate repair of the human heart is currently limited. Using the embryonic paradigm of regeneration, we demonstrated that the actin-binding peptide thymosin β4 (Tβ4), required for epicardium-derived coronary vasculogenesis, can recapitulate its embryonic role and activate quiescent adult epicardial cells (EPDCs). Once stimulated, EPDCs facilitate neovascularization of the ischemic adult heart and, moreover, contribute bona fide cardiomyocytes. EPDC-derived cardiomyocytes structurally and functionally integrate with resident muscle to regenerate functional myocardium, limiting pathological remodeling, and effecting an improvement in cardiac function. Alongside pro-survival and anti-inflammatory properties, these regenerative roles, via EPDCs, markedly expand the range of therapeutic benefits of Tβ4 to sustain and repair the myocardium after ischemic damage.