Heart stem cells discovered

US researchers have discovered that the heart contains a type of stem cell that can divide and produce new heart cells after birth, which might allow the organ to repair itself. The surprise finding could lead to new therapies for damage caused by heart attacks. The researchers, based at the University of California, San Diego, say the cells are very rare - only a few hundred remain in the heart after birth, and this number decreases with age. The study, reported in Nature, is described as 'truly ground-breaking' by UK scientist Jeremy Pearson, of the British Heart Foundation (BHF).

Until now, it was thought that the 'master' cells which give rise to specialised heart cells are only present during the organ's early development in the womb. But the scientists found some of these 'cardiac progenitor cells' in the hearts of adult mice, and also in newborn human hearts. They identified the elusive cells by looking for tissue with an active version of a gene called islet-1, which is switched on in cardiac progenitor cells. 'These are very rare cells, which accounts for why they have not yet been reported', said study leader Kenneth Chien.

A few hundred of the progenitor cells produced millions of heart muscle cells in the laboratory, say the researchers. They are not true stem cells, since they can only divide and multiply a certain number of times - unlike stem cells, which can divide indefinitely. However,  like stem cells, they could still potentially be used to repair heart damage. Heart attacks leave scar tissue, which does not work like proper heart muscle. One day, it might be possible to treat heart attack patients with progenitor cells taken from their own hearts, grown in the laboratory and transplanted back. However, Chien stresses that 'therapeutic use of these cells is many years away'.

Jeremy Pearson, associate medical director of the BHF, said the paper provides 'the first clear description' of stem cells present in the heart. 'Their work is truly ground-breaking' he said, adding that it could lead to new ways to treat congenital heart defects, as well as heart attack damage. However, US expert Elizabeth Nabel cautioned that 'we don't know whether these cells can even be grown from a normal adult heart, or a diseased adult heart'.