A new report in the June 1 issue of the journal Cell, a publication of Cell Press, confirms the existence of some apparently uncommitted stem cells amongst cells responsible for generating the bulging biceps of body builders and the rippling abs of fitness buffs.
The findings could lead to new muscle-regenerating therapiesincluding cell transplantation regimens and stem cell-replenishing drugsfor people with various muscle-wasting diseases, including muscular dystrophies. Ultimately, such treatments might also help keep people strong as they age, according to the researchers.
A team led by Michael Rudnicki of the Ottawa Health Research Institute in Canada found that so-called satellite cells in muscle actually include a mix of cells already committed to their muscular fate and others that behave like more versatile stem cells. The cells had widely been considered by scientists as a homogeneous population of dedicated muscle progenitors. Moreover, Rudnicki's team showed that injection of the "satellite stem cells" into the muscles of mice successfully replenished the animals regenerative reservoir of cells.
"We've found that there are two types of satellite cell90% that are already committed to becoming muscle and another 10% with characteristics normally attributed to stem cells," Rudnicki said. "It's not been shown yet, but these muscle stem cells might even have the capacity to make other tissues, such as bone and fat."
"We've also shown that these satellite stem cells, when transplanted into muscle, can repopulate the regenerative cell niche. This is a very significant advance in our understanding of satellite cell biology that will require us to rethink decades of research. It also opens new avenues for therapeutic treatment of muscular diseases."
Skeletal muscle fibers are essentially long, tubular cells, each of which includes hundreds of nuclei. The fibers are surrounded by a coating of collagen and other glycoproteins with satellite cells sandwiched in between. First discovered in the 1960s, satellite cells are known to be responsible for the growth, maintenance, and repair of skeletal muscle after birth. The normally quiet restorative cells spring into action in response to the stress of weight-bearing or trauma.
Yet much about the mechanisms controlling satellite cells identity and development had remained uncertain, Rudnicki said. Earlier studies had even suggested that satellite cells might originate from muscle cells that had essentially regressed, or dedifferentiated, to a more primitive developmental state.