Hematopoietic progenitor cells residing in muscle engraft into bone marrow following transplantation.

Hematopoietic and mesenchymal stem cells can potentially be the same cell type or adhere simultaneously in both bone marrow (BM) and muscle. In this study, we asked whether murine BM-derived cells could be tracked in muscle tissue after BM transplantation and whether muscle-derived cells have hematopoietic potential. To answer the first question, we transplanted BM from male BALB/c mice into irradiated female recipients and analyzed for engraftment. We used quantitative polymerase chain reaction (PCR) and fluorescent in situ hybridization techniques for Y chromosome-specific gene probes. A high number of BM-derived cells were located in both the intravascular and extravascular spaces in muscle tissue after BM transplantation. To answer the second question, we analyzed colony-forming potential in vitro with soft-agar assays and the competitive engraftment potential in vivo of muscle-derived cells. Engraftment levels of male cell populations were tested by quantitative PCR. The long-term engraftment potential of muscle-derived cells was low compared with that of BM. We conclude that there is intensive cellular trafficking between BM and muscle tissue. The engraftment potential of muscle-derived stem cells into BM is low and corresponds to the low amounts of hematopoietic colony-forming cells found in muscle tissue.