Isolation of Progenitors that Exhibit Myogenic/Osteogenic Bipotency In Vitro by Fluorescence-Activated Cell Sorting from Human Fetal Muscle

Fluorescence-activated cell sorting (FACS) strategies to purify distinct cell types from the pool of fetal human myofiber-associated (hMFA) cells were developed. We demonstrate that cells expressing the satellite cell marker PAX7 are highly enriched within the subset of CD45(-)CD11b(-)GlyA(-)CD31(-)CD34(-)CD56(int)ITGA7(hi) hMFA cells. These CD45(-)CD11b(-)GlyA(-)CD31(-)CD34(-)CD56(int)ITGA7(hi) cells lack adipogenic capacity but exhibit robust, bipotent myogenic and osteogenic activity in vitro and engraft myofibers when transplanted into mouse muscle. In contrast, CD45(-)CD11b(-)GlyA(-)CD31(-)CD34(+) fetal hMFA cells represent stromal constituents of muscle that do not express PAX7, lack myogenic function, and exhibit adipogenic and osteogenic capacity in vitro. Adult muscle likewise contains PAX7(+) CD45(-)CD11b(-)GlyA(-)CD31(-)CD34(-)CD56(int)ITGA7(hi) hMFA cells with in vitro myogenic and osteogenic activity, although these cells are present at lower frequency in comparison to their fetal counterparts. The ability to directly isolate functionally distinct progenitor cells from human muscle will enable novel insights into muscle lineage specification and homeostasis.