Several experiments in animals and a few clinical trials in human patients have shown that implanting skeletal muscle cells isolated from muscle biopsies into the heart after a heart attack can help the heart to some degree, but the implanted skeletal muscle cells do not integrate into the existing heart muscle mass and the skeletal muscle cells do not differentiate into heart muscle cells.
Experiments like those mentioned above utilized muscle satellite cells. Muscle satellite cells are a resident stem cell population that respond to muscle damage and divide to form skeletal muscle cells form new muscle. Satellite cells are a perfect example of a unipotent stem cell, which is to say a cell that makes one type of terminally differentiated cell type.
Skeletal muscles, however, have another cell population called muscle-derived stem cells or MDSCs. MDSCs express an entirely different set of cell surface proteins than satellite cells, and have the capacity to differentiate into skeletal muscle, smooth muscle, bone, tendon, nerve, endothelial and hematopoietic cells. MDSCs grow well in culture, tolerate low oxygen conditions quite well, and show excellent regenerative potential.
Other laboratories have managed to culture MDSCs in collagen and produce beating heart muscle cells. Others have observed MDSCs forming a proper myocardium under certain conditions. Several studies have established the ability to MDSCs to treat laboratory animals that have suffered a heart attack. The most recent work from Sekiya and others has established that cell sheets made from MDSCs can reduce dilation of the left ventricle, increased capillary density, and promoted recovery without causing erratic heat beat patterns.
Despite their obvious efficacy. MDSCs remain difficult to isolate in high enough numbers to therapeutic purposes. None of the cell surface molecules sported by MDSCs are unique to those cells. Therefore, getting clean cultures of MDSCs remains a challenge. Still, these cells represent some of the best hopes for regenerative medicine in the heart. These cells do form heart muscle cells and heal ailing hearts. They can be grown in bioreactors to high numbers and can also be combined with engineered materials to shore up a damaged heart and mediate its regeneration. While the use of MDSCs is still in its infancy, the promise certainly is there.