Heart Factory or Fiction? Cardiac Progenitor Cells and Regeneration
In the Christian tradition, the doctrine of regeneration considers the "deceitful...and wicked" heart a vessel for accepting God, and thereby being born again. Indeed, many cultures have invested the heart with powers well beyond its biological role in maintaining systemic perfusion. However, the heart's capacity for renewal was limited to metaphor until relatively recently, when science revealed a very literal interpretation of cardiac regeneration. Contrary to longstanding belief, it now appears that new cardiomyocytes are created after birth, and that cardiomyocyte renewal continues in the aging human heart. Most studies estimate that the annual rate of myocyte renewal is roughly 1%, though other groups suggest that up to 40% of a heart's cardiomyocytes might be regenerated each year. These new cells may arise from resident cardiac progenitor cells, from proliferation of pre-existing cardiomyocytes, or from migratory populations of epicardial cells. Regardless of their origin, their number and inherent function seem insufficient to heal the profoundly injured heart, as roughly 300,000 Americans die every year of heart failure. Of course, the more sanguine among us view this striking burden of disease as a therapeutic opportunity, and clinical trials of myocardial regeneration using various cell types and preparations already have been conducted. Early trials in the field used bone marrow derived stem cells with mixed results. More recently, two trials have investigated the use of cardiac progenitor cells and their findings have been somewhat promising. Though treatment with stem cells appears safe, enthusiasm for their expanded use is restrained by the acknowledgement that both evidence of meaningful clinical benefit and clear mechanisms of benefit are lacking. Thus, rigorous ongoing investigation of stem cell biology in the heart will be essential in clarifying whether therapeutic cardiac regeneration could indeed become a reality.
- Received October 3, 2013.
- Accepted October 11, 2013.