To date, conventional wisdom has subscribed only limited use to stem cells derived from adult tissues, indicating a certain inability to develop and mature into other tissues or organs of the body. It is the ability of stem cells to form into other tissues or organs that has heralded a new era in research, inspiring great hope that debilitating diseases and conditions could some day be cured.

Adult stem cells are the easiest to access but their potential appeared limited. Over the last two years, research from the laboratory of Dr. Michael Rudnicki, Senior Scientist and Program director at the OHRI and Professor at the University of Ottawa, has effectively challenged that notion.

It was thought that only satellite cells surrounding muscle fibres could mediate skeletal muscle regeneration until recently, when Dr. Rudnicki's group found that adult stem cells not only participate in muscle tissue regeneration but also spawn satellite cells. A certain population of these stem cells, which are recognized by the cell surface proteins CD45 and Sca1 (stem cell antigen-1), is involved in normal muscle tissue repair, but is only triggered into the muscle cell development pathway by injury.

The group also demonstrated that a protein called Pax7 is required to turn adult stem cells into muscle cells during regeneration. In earlier work, the researchers showed that that CD45:Sca1 cells taken from regenerating muscle in mice lacking Pax7 could not become muscle cells. And they showed that by putting Pax7 gene back into CD45:Sca1 cells taken from uninjured muscle, they were able to generate cells that readily differentiate into muscle cells. They observed the production of muscle-forming cells that not only gave rise to differentiated muscle cells, but also provided a new approach to tissue repair.

Dr. Rudnicki and his team have effectively demonstrated that Pax7 is not only necessary to repair muscle tissue, it is sufficient. It was previously found that the Pax7 gene was required to form muscle making stem cells. In this new study, introduction of Pax7 with a virus into stem cells forced the cells to become muscle making cells, opening the door for treatment of disorders such as Muscular Dystrophy.

The implications of such findings could some day lead to drastic improvements for those suffering from Muscular Dystrophy.

Michael Rudnicki explains "This work demonstrates that Pax7 represents a key protein in the chain of events that directs stem cells to repair muscle. We now need to identify drugs that can activate Pax7 towards developing new therapies for the treatment of these devastating diseases."

The findings were published in Public Library of Science, a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. The material can be accessed by logging onto www.plos.org.

"After 20 years in research on muscular dystrophy, it has become clear to me that the best hope for those with neuromuscular disorders is through regeneration of the damaged muscle and that stem cells provide the means to achieving this," explained Dr. Ronald Worton, CEO of the OHRI. "Dr. Rudnicki's group has led the way in demonstrating how this might be done in a controlled way."

The research was supported by grants from the Muscular Dystrophy Association, the National Institutes of Health, the Canadian Institutes of Health Research, the Howard Hughes Medical Institute and the Canada Research Chair Program.

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