Researchers from the laboratory of Jonas Frisén at the Karolinska Institutet in Sweden have recently put radioactive carbon from nuclear bomb tests to good use, testing whether the adult human heart has the ability to repair itself. So how does that work? Well, a sharp rise in atmospheric radioactive carbon in the 1950-60s due to nuclear testing and its subsequent incorporation into genomic DNA provides a method to measure cell age and turnover.
Previous studies have successfully applied this technique to the study of cell regeneration in the human heart, although this still remains a contentious point. This resolution of the quandary is important, as if cardiomyocytes, the cells which make up the contractile tissue of the heart, have some level of endogenous regenerative capacity, we may be able to exogenously promote repair of the damaged heart.
In this new study, the researchers provided an integrated model of heart cell generation and turnover in humans through the study of heart tissue from 29 deceased individuals of various ages.
This demonstrated that:
- Cardiomyocyte number actually remains constant over the human lifespan
- Cardiomyocyte turnover is highest in early childhood and decreases gradually throughout life to <1% per year in adulthood, with similar turnover rates throughout the myocardium.
- Hearts grow in size with age due to cells increasing in size, rather than in number
- Overall, heart cells regeneration occurs on a modest scale, with only 40% replaced during a lifetime.
- Endothelial and mesenchymal cell number increase substantially from childhood into adulthood
- Endothelial cells have a high turnover rate (>15% per year)
- Mesenchymal cells have a more limited adult renewal rate (<4% per year).
The authors note that these findings should aid the development of new therapeutic strategies aiming to treat heart attacks and heart disease, and hopefully this will put an end to the uncertainty surrounding the regenerative capacity of the adult human heart. So, researchers in the field take heart! Read this explosive study here at Cell, June, 2015.