How to Mend a Broken Heart: Stem Cells

By Colin Barras, New Scientist, July 29, 2007

According to a team of researchers, stem cells may help repair damaged tissue after a heart attack.

Stem cells played a significant role in repairing damaged hearts in a study that was conducted using mice. But whether it is cells from elsewhere in the body or actual heart cells that are doing the repair is a continuing point of investigation.

So that their heart muscle cells could be stained with a fluorescent protein, Richard Lee of the Harvard Medical School in Boston and colleagues genetically engineered mice.

Around 80 per cent of the heart muscle cells in young mice picked up the stain. Demonstrating that heart muscle cells are not normally replaced in life, the stain level remained the same as the mice aged stated researchers. But, suggesting that new muscle cells are formed in response to injury was a drop to 70% in stained cell count when heart attacks were induced in the mice.

Lee thinks that a limited ability to self-heal would characterize the adult mouse heart and align it with the study results.

"The mechanism to activate cardiac regeneration is present, but it's inadequate," he says. "Could that be because mammals don't have enough [heart] stem cells? There are other theories as well. We need to understand what is holding the system back, so that we can devise a strategy to turn that brake off."

But Kenneth Chien of the Massachusetts General Hospital in Boston is not yet convinced that Lee's team has identified heart stem cells in the mice. Heart stem cells were only first discovered last year, and although the paper provides many answers, Chien thinks it also raises several questions.

"The evidence is circumstantial because the data is not related to finding the pool of new cells and tagging it, but simply showing that the existing pool changes," Chien says. "The most important question now is: can you identify that new pool? Are they pre-existing immature cardiac muscle cells? Or are they [stem cells] from the heart or elsewhere in the body?"