The research, conducted in mice, employed Embryonic Stem (ES) cells. In humans, ES cells can give rise to all the cells of the body, except for those in the placenta. In their study, the scientists used ES cells in mice to form less "powerful" cells called multipotent cells, which by themselves can only give rise to a limited number of cell types. Until recently, it was believed that the three cell types in the heart-cardiac, smooth muscle and endothelial-were most likely produced by different sources. However, the scientists found evidence for the existence of a single multipotent cell, the cardiac progenitor cell, which can give rise to all the three major tissues in the heart. While the research was carried out in mice, the findings are expected to apply to humans as well.
The different tissues in the heart serve diverse functions: The cardiac muscle makes up the heart itself, and its contractions enable the heart to pump blood to different parts of the body. The smooth muscle, on the other hand, is found in the walls of the heart's blood vessels, and facilitates the constriction and dilation of blood vessels. Endothelial cells, which line the interior surface of blood vessels, serve many functions like controlling the passage of materials into and out of the bloodstream. Given the diversity of these cells, Dr. Chein found it surprising that a single multipotent cell could form these three different cell types.
Dr. Stuart Orkin of Howard Hughes Medical Institute and Children's Hospital Boston, who led a second group that independently came to similar conclusions, said, "Instead of multiple different cell types migrating and coming together to form the heart, the heart comes from stem cells that give rise to multiple cell types in the same local environment-a simpler way of building the organ … And because these cells can make multiple cell types, they could be more useful in repairing the heart than any single kind of cell."
Human ES cells have captured the attention of biologists as powerful agents for advancing the field of regenerative medicine. These cells are immortal, and have almost unlimited development potential. ES cells hold great promise for the therapy of various diseases and disorders including diabetes, heart failure, Parkinson's disease, leukemia and spinal cord injury.
Research into ES cells is expected to give scientists important insights into understanding how human development occurs from the embryo stage onwards. Such research will reveal information about the transmission of birth defects, which could in turn be used to seek prevention and treatment of such disorders. Furthermore, stem cell research could help to identify targets for drugs and test potential therapeutics. Additionally, stem cells are being investigated to facilitate the development of gene therapy, which aims to eliminate defective genes in the body and establish normal functions.
Significant progress has been made in the last decade in the field of stem cell research, especially in avenues like blood and the nervous system. For example, research has established that a single multipotent cell, called the hematopoietic stem cell, can give rise to all the cells in blood, including red and white blood cells.
However, stem cell research is largely still in its infancy. A lot of work must be conducted before such cells can be implemented for widespread therapeutic use to address, for instance, Parkinson's disease. As Casey Guenthner '08 said, "Parkinson's disease is caused by degeneration of particular population of dopamine neurons in the brain. In animal models of Parkinson's disease, as well as in humans, there has been limited success at transplanting stem cell-like cells into the degenerated brain area and having them differentiate into dopamine neurons. However, current study may eventually enhance our understanding of how stem cells 'decide' what type of cell to become-knowledge that may one day be applied to developing better techniques for growing cells and specifically inducing them to become dopamine neurons."
Today, scientists are investigating several aspects of ES cell biology, including how to direct these cells to selectively create a few or a single cell type. Different genetic techniques like RNA interference are being employed in such research.
The study conducted in mice raises new hopes for the treatment of heart diseases and disorders. Presently, the use of ES cells in cardiac regenerative procedures, primarily investigated in mice, carries the risk of cancer resulting from uncontrolled growth of these cells. In addition, scientists have experienced problems in producing a sufficient number of heart cells from ES cells. However, a single multipotent cell that has relatively limited development potential and is more specific to the heart is likely to be less risky, more effective and not to suffer from the limitations of other ES-based systems.
Dr. Chien said, "Embryonic stem cells are difficult to use for heart regeneration because of the danger of teratomas (i.e. cancers). If we can get around that threat by cloning master cardiovascular stem cells, that would be a major advance." The findings also suggest that the cardiac multipotent cell shares many similarities with the hematopoietic stem cell, which is known to regenerate all blood cell lineages.
Until recently, scientists believed that the heart lacked the ability to regenerate after being damaged. However, Professor Peter Weissberg, medical director of the British Heart Foundation, reportedly said at on www.bbc.co.uk that "these studies, coupled with other recent discoveries, suggest that there may be certain cells within the heart which have the capacity to become new heart and blood vessel cells ... by studying how these cells change into mature, functioning heart cells we will ultimately understand the molecular mechanisms required to form new heart cells … These are early steps in the long road to discovering how to repair a damaged heart."