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New type of muscle stem cell identified


Summary of research

The Myology group of the University Pierre et Marie Curie in Paris has recently identified a new population of muscle stem cells. This study shows that these muscle stem cells called ‘progenitor interstitial cells’ (PICs) can be isolated from the muscles of very young mice. Once they are isolated and cultured in the laboratory, PICs are able to form new muscle. Indeed, once they are reintroduced into the damaged muscles of mice, they help muscle repair as efficiently as satellite cells, the professional muscle stem cells. This work has identified a new source of stem cells in the muscle. However, whether PICs are present in adult muscles and contribute to their regeneration in muscle disease, are all questions that need further study.

What is the idea behind this study and what did this study show?

Regeneration and repair of damaged muscles relies on the activity of resident stem cells. Stem cells are a reservoir of cells that, when activated, are instructed to form new tissue. In the case of skeletal muscle, this regenerative capacity has been mainly attributed to a type of muscle stem cell, called satellite cells. These cells are found close to the muscle fibre and are considered the master muscle stem cells. Just recently, different cells other than satellite cells had been shown to be helping in muscle regeneration. However, up until now these cells had not been identified and located.

In this study, performed by the group of Dr. Sassoon, the scientists looked at the muscles of mice during the first 2-3 weeks after birth. They found a new type of muscle stem cell located between the muscle fibres, in what is called the interstitium of the muscle, so the authors called them Progenitor Interstitial Cells, or PICs. They showed that PICs are more abundant at birth and their number declines in adults, just as for satellite cells. They isolated them from the muscles of young mice and tested the cell’s behaviour in the laboratory. These experiments showed that these cells behave like satellite cells, forming new muscle fibres. Next, they tested if PICs could do this when in the mice. So, they reintroduced PICs into the muscle of mice that had been damaged and they showed that PICs are able to form new muscle tissue as efficiently as satellite cells.

 

What does this mean for patients?

In muscle diseases such as Duchenne muscular dystrophy the muscles weaken and start to waste away. The muscle is lost because the body cannot adequately regenerate and/or repair itself during the progression of the disease. Therefore, promoting the regeneration potential of muscle stem cells would be one way to prevent muscle loss.

Up to now satellite cells were considered the main type of cells involved in skeletal muscle regeneration. However, in muscle affected by muscle disease and in aged muscles, satellite cells are eventually exhausted and show a limited regenerative potential. The identification of a new muscle stem cell type represents a new possibility for therapeutic approaches. These cells could be exploited to regenerate diseased or aged muscles. Moreover, the fact that PICs can be easily isolated and grown in the laboratory makes them possible candidates for cell-therapy. In fact, it may be possible to increase the numbers of   PICs in the laboratory and then reintroduce them to repopulate damaged muscles.

Nevertheless, before this becomes real and applicable to patients a lot of further work needs to be done. For example, the role of PICs in adult muscle has yet to be investigated. The number of PICs declines after birth and their contribution in adult skeletal muscle regeneration is still unknown. Moreover, PICs have only up to now been identified in mice. Whether these cells are also present in human muscles and whether they could also be isolated from humans is a topic for further study.

 

Further information and links

This scientific work and summary were supported by funding from the European Community’s Seventh Framework Programme project OPTISTEM.