A study in the August 2007 issue of Nature Medicine reports that stem cells help the heart to regenerate after injury, but not during normal ageing.
The question of whether stem cells exist in the heart that can generate muscle cells during ageing or after injury has been highly controversial. To resolve this controversy, Richard Lee and colleagues have taken a novel genetic approach that overcomes many of the technological limitations of previous work. These authors used a genetically modified mouse in which mature heart cells (but not cardiac stem cells) are labelled with a fluorescent protein early in the life of the animal. The authors reasoned that, if stem cells replenish the heart, the percentage of labelled heart cells would decrease over time. But if they don't, the percentage would remain unchanged. So, they looked for the fluorescent label as their mice got older or in response to injury.
The researchers found that, during normal ageing, the percentage of labelled heart cells did not change. By contrast, after heart attack and another form of heart injury, the percentage of labelled heart cells decreased. So, cardiac stem cells replenish heart cells in response to injury, but not as the heart ages. These findings should help sway those who have been sceptical of the existence of heart stem cells. The physiological basis for the intriguing difference between stem cell function in injured and ageing hearts remains to be explored.
Richard Lee (Brigham and Women's Hospital, Harvard Medical School, Cambridge, MA, USA)
Abstract available online.
(C) Nature Medicine press release.
Message posted by: Trevor M. D'Souza