The role of muscle cells in bone repair

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Failure of bone healing leads to significant pain and disability, such that augmentation of fracture repair is a dynamic and important field of study. A full understanding of bone repair is necessary before we can hope to introduce novel successful therapies. We believe that a improved understanding of the origins of the cells involved with bone healing may lead to new surgical, drug and cell-based therapies for the treatment of recalcitrant bone repair. Stem cells originating from the bone marrow and periosteum are known to differentiate into mature bone cells and produce bone. However, these tissues are damaged or have poor access to the site of bone injury in many severe open fractures. In these cases, bone repair often initiates in a region adjacent to an opposing muscle. This has led us to speculate that cells from the muscle may directly contribute to bone repair. Published studies, which have be confirmed by our group, have demonstrated the strong potential for muscle-derived progenitor cells (satellite cells) to become bone-like in response to stimuli such as bone morphogenic proteins. To put bone-forming potential of muscle cells in perspective, we plan to expand on these studies and compare mouse satellite cells with mouse bone marrow stem cells. In addition, we plan to use a transgenic mouse whose muscle cells become permanently genetically transformed to stain blue. This mouse will allow us to assess the fate of muscle cells and their contribution to bone formation in ectopic bone formation and fracture repair models. This study will explore on the most basic level the cellular contribution of muscle to bone repair. The results of this research project will significantly influence our therapeutic directions for improving fracture repair in the future.