Many research groups in the stem cell field are engaged in a search for sources of useful tissue-specific cells in the body, developing means of identification and isolation. This runs in parallel with efforts to reprogram more easily obtained cells, such as from skin samples, into a range of different types for therapy and research. Both approaches add value in the near term, expanding the range of tissues in which regeneration might be greatly enhanced. The heart is of particular interest as it normally has little capacity for repair, and is of course the cause of a great many fatal problems as we age. Here is an example of progress in identifying existing cell populations that support heart tissue:
Endothelial cells residing in the coronary arteries can function as cardiac stem cells to produce new heart muscle tissue. The findings [offer] insights into how the heart maintains itself and could lead to new strategies for repairing the heart when it fails after a heart attack. The heart has long been considered to be an organ without regenerative potential. Recent findings, however, have demonstrated that new heart muscle cells are generated at a low rate, suggesting the presence of cardiac stem cells. The source of these cells was unknown.
[Researchers] postulated that the endothelial cells that line blood vessels might have the potential to generate new heart cells. They knew that endothelial cells give rise to other cell types, including blood cells, during development. Now, using sophisticated technologies to "track" cells in a mouse model, they have demonstrated that endothelial cells in the coronary arteries generate new cardiac muscle cells in healthy hearts. They found two populations of cardiac stem cells in the coronary arteries - a quiescent population in the media layer and a proliferative population in the adventitia (outer) layer.
The finding that coronary arteries house a cardiac stem cell niche has interesting implications. Coronary artery disease would impact this niche. "Our study suggests that coronary artery disease could lead to heart failure not only by blocking the arteries and causing heart attacks, but also by affecting the way the heart is maintained and regenerated."