Msxl-modulated muscle satellite cells retain a primitive state and exhibit an enhanced capacity for osteogenic differentiation

Multipotent muscle satellite cells (MuSCs) have been identified as potential seed cells for bone tissue engineering. However, MuSCs exhibit a rapid loss of sternness after in vitro culturing, thereby compromising their therapeutic efficiency. Muscle segment homeobox gene 1 (msxl) has been found to induce the dedifferentiation of committed progenitor cells, as well as terminally differentiated myotubes. In this study, a Tet-off retroviral gene delivery system was used to modulate msxl expression. After ten passages, MuSCs that did not express msx-1 (e.g., the non-msxl group) were compared with MuSCs with induced msx-1 expression (e.g., the msxl group). The latter group exhibited a more juvenile morphology, it contained a significantly lower percentage of senescent cells characterized by positive beta-galactosidase staining, and it exhibited increased proliferation and a higher proliferation index. Immunocytochemical stainings further detected a more primitive gene expression profile for the msxl group, while osteogenic differentiation assays and ectopic bone formation assays demonstrated an improved capacity for the msxl group to undergo osteogenic differentiation. These results suggest that transient expression of msxl in MuSCs can retain a primitive state, thereby enhancing their capacity for osteogenic differentiation and restoring the potential for MuSCs to serve as seed cells for bone tissue engineering.