A person with heart failure will lose heart muscle cells known as cardiomyocytes, so the only way to reverse heart failure is to make more of these cells.
Researchers from Children's Hospital in Boston, Massachusetts have discovered a new group of stem cells that can give rise to cardiomyocytes. Located in the outermost layer of the heart, the stem cells could one day play a critical role in regenerating injured heart tissue. The discovery was published online in the journal Nature on June 22, 2008.
In 2006, scientists identified another cardiac stem cell, marked by the expression of a gene called Nkx2-5, with the potential of becoming either heart muscle or cells lining blood vessels in the organ's left-sided chambers. Other United States researchers also discovered a related progenitor heart cell that produces the same cell types in the right-sided heart chambers.
For the first time, the new research shows that new heart stem cells can also be derived from a third type of cardiac stem cell, located within the surface of the organ and identifiable through its expression of a gene called Wt1.
The researchers also showed that the cells from the heart's outer lining (known as the epicardium) could metamorphose into cardiomyocytes and smooth muscle cells, endothelial cells, which line the interior of blood vessels, and fibroblasts, found in connective tissue. When regenerating tissue, it is necessary to regenerate the whole tissue and not just the cardiomyocytes.
Their discovery of the new stem cells was purely an accident. In order to study the role a different gene in the epicardium, the researchers labeled cells in live mouse embryos with red fluorescent protein. Unexpectedly, they saw that these epicardial cells were becoming cardiomycytes. It was indeed a lucky observation.
The next challenge for the researchers is for them to figure out how a progenitor stem cell decides to become a certain type of functioning cell within the heart, and then how to develop methods to trick the stem cells into transforming into the desired tissue.
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