This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Conversion of green-fluorescent protein (GFP) positive marrow cells to skeletal muscle cells has been demonstrated and is the focus of this project. We have determined that donor GFP+ marrow cells have converted to muscle cells by colocalizing GFP and desmin in morphologically characteristic muscle fibers. We have found increasing levels of marrow conversion or transdifferentiation to skeletal muscle cells by altering the specifics of the transplant regimen including cell number, timing of transplant and mode of cell delivery (i.e. local injection vs systemic infusion or mobilization of transplanted cells). We have also found that the number of conversion events changes with different mobilization regimens and that subsets of marrow cells, give higher rates of conversion than unseparated marrow cells. The nature of the skeletal muscle injury, radiation or direct cardiotoxin injection, is also critical in determining the level of transdifferentiation of marrow to muscle cells seen in vivo. In preliminary studies using a cardiotoxin muscle injury in previously transplanted mice, combined with radiation and direct injection of different populations of marrow cells we have obtained conversion rates up to12%, i.e. 12% of the muscle fibers were GFP+ skeletal muscle cells. This project evaluates the specifics of muscle injury which will lead to high-level conversion of marrow to muscle and to explore which particular cell type can give rise to muscle at the highest frequency, the timing of transplant suitable for such conversions and the number of cells necessary to obtain significant muscle conversion.
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