US scientists have discovered 'cardiac master cells' that are able to transform into any of the three main forms of heart tissue. The heart has long been thought of as unable to regenerate itself when damaged. This research gives hope that therapies may be developed, possibly using human embryonic stem cells (ES cells), to help patients with heart disease, or after heart attacks. Two groups of scientists independently discovered two different types of precursor heart cells, one that is able to produce three of the major types of heart tissue, the other only two. The teams used genetic mapping techniques in experimental mice to identify muscle-building stem cells in the hearts of embryonic animals.
Kenneth Chien of Harvard Medical School, who led one of the research teams, traced cells expressing the islet-1 gene, which has previously been linked with cells in cardiac muscle. After tracing the islet-expressing cells they were surprised to find that they gave rise to cardiac muscle, smooth muscle and endothelial cells. The second team, led by Stuart Orkin, also of Harvard Medical School, traced cells expressing a gene known as Nkx2.5. This gene is known as 'tinman' in fruit flies, as when it is switched off the flies develop without a heart. The cells expressing Nkx2.5 gave rise to two of the major types of cardiac tissue, the researchers suspect that the islet-1 expressing cells are the parent cells of the second type of cell but this has yet to be proved.
There have been many attempts to repair damaged hearts using some form of stem cell. Until now the work has been hampered by lack of knowledge as to which cells should be used. Generally trials have focused on injecting precursor blood or muscle cells, but these have had little success. The next step in this research is to attempt to coax human ES cells to develop into the kind of precursor or master cell that the researchers have identified in mice. These could then be injected into the heart, with the potential to repair damaged areas of muscle or the crucial epithelial cells that form the lining of coronary blood vessels.
Chien explained the future direction of the research saying, 'It's the beginning of being able to harness the power of embryonic stem cells for generating specific tissues. We have no reason to believe this can't be transposed into the human context'. Professor Peter Weissberg , medical director of the British Heart Foundation, cautiously welcomed the research telling the BBC, 'Such findings are very promising...These are early steps in the long road to discovering how to repair a damaged heart'. The work is published in the journal Cell. A third paper identifying a precursor cell to all three forms of heart tissue identified using a different marker is published in Developmental Cell, a sister publication of Cell. This paper is published by Gordon Keller and his team from Mount Sinai School of Medicine in New York.