Relaxin, cardiac stem cells and heart regeneration

The notion that the adult heart of mammals including humans contain a small population of resident cardiac progenitor/stem cells (CSCs) have questioned the traditional paradigm of the myocardium as a post-mitotic terminally differentiated tissue. These cells, however, are relatively scarce and unable to be recruited in large number at the site of tissue damage. This has sparkled novel interest in the identification of molecules capable of stimulating the regenerative potentials of CSCs in their microenvironment. In this context, the peptide hormone relaxin (RLX), recently validated as a cardiovascular hormone, deserves a key place. This article summarizes the most recent findings of our group on the ability of RLX to modulate growth and differentiation of mouse neonatal cardiomyocytes, suggesting that this hormone, for which the heart is both a source and target organ, may participate in the endogenous mechanisms of myocardial repair/regeneration. Moreover, we have recently observed that RLX, by a Notch-1-mediated mechanism, inhibits cardiac myofibroblast differentiation and function, suggesting that the known anti-fibrotic effects of RLX may be part of a complex network of actions whereby this hormone facilitates cardiac stem cell growth and improves myocardial regeneration.