Evidence for multiple satellite cell populations and a non-myogenic cell type that is regulated differently in regenerating and growing skeletal muscle

We have performed studies to determine if different populations of satellite cells provide nuclei to growing and regenerating skeletal muscle fibers. Satellite cells were isolated from regenerating or growing anterior tibialis muscles, and their phenotypic properties were compared in vitro. Isolates from regenerating muscle contained 31% satellite cells, and those from control muscle contained 66% satellite cells, as determined by their expression of desmin. Among the desmin-positive satellite cells present from each preparation, two distinct populations of satellite cells were evident. Approximately 28% of satellite cell colonies were composed of only large cells, contained less than 50 cells/colony, and were designated as type 1 colonies. The remainder of satellite cell colonies isolated from either regenerating or control muscles were primarily composed of small cells, contained from 60 to 150 cells/colony, and were designated as type 2 colonies. Despite dramatic differences in the ratio of myogenic to non-myogenic cell types, satellite cells from regenerating and control muscles formed myotubes and expressed myosin heavy chain at similar levels. Treatment of regenerating cultures with dexamethasone resulted in a 16% increase in the number of desmin-positive colonies and dramatically decreased the proliferation of non-myogenic cells. These results suggest that at least two distinct populations of satellite cells can be isolated from regenerating and control skeletal muscles, and that non-myogenic cells are differentially regulated in regenerating versus non-regenerating environments.