Muscle-derived stem cells for musculoskeletal tissue regeneration and repair.

Muscle recently has been identified as a good source of adult stem cells that can differentiate into cells of different lineages. The most well-known muscle progenitor cells are satellite cells, which not only contribute to the replenishment of the myogenic cell pool but also can become osteoblasts, adipocytes and chondrocytes. Other populations of stem cells that appear to be distinct from satellite cells also have been discovered recently. Muscle-derived stem cells (MDSCs) can be divided into two major categories based on these cells' varied abilities to differentiate into myogenic lineages. Interestingly, MDSCs that can differentiate readily into myogenic cells are usually CD45-. In contrast, MDSCs with less myogenic potential are CD45+. Various lines of evidence suggest that different populations of MDSCs are closely related. Furthermore, MDSCs appear to be closely related to endothelial cells or pericytes of the capillaries surrounding myofibers. When used in tissue engineering applications, MDSCs--particularly those genetically engineered to express growth factors--have been demonstrated to possess great potential for the regeneration and repair of muscle, bone and cartilage. Further research is necessary to delineate the relationship between different populations of MDSCs and between MDSCs and other adult stem cells, to investigate their developmental origin, and to determine the regulatory pathways and factors that control stem cell self-renewal, proliferation and differentiation. This knowledge could greatly enhance the usefulness of muscle-derived stem cells, as well as other adult stem cells, for tissue repair and regeneration applications. Copyright 2004 Elsevier B.V.