Role of Mononuclear Cardiomyocytes in Cardiac Turnover and Regeneration

PURPOSE OF REVIEW: The typical remodeling process after cardiac injury is scarring and compensatory hypertrophy. The limited regeneration potential of the adult heart is thought to be due to the post-mitotic status of postnatal cardiomyocytes, which are mostly binucleated and/or polyploid. Nevertheless, there is evidence for cardiomyocyte turnover in the adult heart. The purpose of this review is to describe the recent findings regarding the proliferative potential of mononuclear cardiomyocytes and to evaluate their function in cardiac turnover and disease. RECENT FINDINGS: There is overwhelming evidence from carbon-dating in humans and multi-isotope imaging mass spectrometry in mice that there is a very low but detectable level of turnover of cardiomyocytes in the heart. The source of this renewal is not clear, but recent evidence points to a population of mononuclear, diploid cardiomyocytes that are still capable of authentic cell division. Controversy arises when their role in cardiac repair is considered, as some studies claim that they contribute to repair by cell division while other studies do not find evidence for hyperplasia but hypertrophy. Stimulation of the mononuclear cardiomyocyte population has been proposed as a therapeutic strategy in cardiac disease. SUMMARY: The studies reviewed here agree on the existence of a low annual cardiomyocyte turnover rate which can be attributed to the proliferation of mononuclear cardiomyocytes. Potential roles of mononucleated cardiomyocytes in cardiac repair after injury are discussed.