THE discovery of heart stem cells in 2006 raised hopes that new treatments for heart disease would soon follow. Now, it seems heart stem cells may already help to repair the damage after a heart attack, if only to a limited degree.
Richard Lee of the Harvard Medical School and colleagues genetically engineered mice so that their heart muscle cells could be stained with a fluorescent protein. Only 80 per cent of the heart muscle cells in young mice picked up the stain. However, as the mice aged, this level remained the same, suggesting that adult mice don't normally make new heart muscle cells. When the team induced heart attacks in the mice, the number of stained cells dropped to 70 per cent, while the overall number of heart cells remained about the same, suggesting that new muscle cells can form in response to injury (Nature Medicine, DOI: 10.1038/nm1618).
Lee thinks that the adult mouse heart has a limited ability to repair itself. "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? 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 isn't convinced. "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?"