New source of heart stem cells ...( Researchers at Children's Hospital B...)

Researchers at Children's Hospital Boston are continuing to document the heart's earliest origins. Now, they have pinpointed a new, previously unrecognized group of stem cells that give rise to cardiomyocytes, or heart muscle cells. These stem cells, located in the surface of the heart, or epicardium, advance the hope of being able to regenerate injured heart tissue.

This finding, published online by the journal Nature on June 22, comes on the heels of parallel cardiac stem cell discoveries in 2006, at both Children's and Massachusetts General Hospital. Then, the Children's team found that a specific stem cell or progenitor, marked by expression of a gene called Nkx2-5, forms many components of the heart: heart muscle cells, vascular smooth muscle cells, and the endothelial cells lining blood vessels in the heart's left-sided chambers. The team at MGH found a related progenitor, marked by expression of the Isl1 gene, that produces these same cell-types in the right-sided heart chambers.

Now, researchers at Children's have shown that heart muscle cells can also be derived from a third type of cardiac progenitor, located within the epicardium and identifiable through its expression of a gene called Wt1.

"There's a lot of interest in finding places to obtain new cardiomyocytes, because in heart failure, you lose cardiomyocytes, so the only way to reverse heart failure is to make more of these cells," said William Pu, MD, a pediatric cardiologist at Children's who was the study's senior investigator.

Although epicardial cells are known to give rise to smooth muscle and endothelial cells during coronary vessel formation, nobody previously thought that epicardial cells might turn into cardiomyocytes. "I couldn't believe it at first, myself," said Bin Zhou, MD, a research fellow in Pu's laboratory and the study's first author.

The results were independently corroborated by researchers from the University of Ca
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