: Major trauma can cause volumetric muscle loss (VML) resulting in life-long disability. Although skeletal muscle is capable of remarkable regenerative potential, when injury is massive and destroys the underlying architecture, regeneration is aborted and is characterized instead by scar tissue formation. The standard of care in such injuries is wound closure, leaving little hope for functional recovery. The promise of regenerative medicine is the full regeneration of damaged tissues, either by promoting repair from endogenous stem cells or by the transplantation of cells to enhance regeneration. Perhaps the best example of this is skin grafting in the setting of massive tissue loss in burn victims. The fact that grafted skin contains endogenous stem cells assures that the graft will not only restore function acutely but also chronically as the stem cells function to replenish skin cells that are lost during the normal turnover of the tissue. Likewise, the long-term goal of regenerative medicine is to be able to restore damaged tissue and maintain that tissue for the full lifetime of the individual. Major advances have been made in the culture and transplantation of muscle stem cells (MuSCs, also known as "satellite cells") in recent decades, primarily in rodent models of muscle injury and degenerative disease. It has been known for over 40 years that transplanted myoblasts, the more differentiated progeny of MuSCs, can contribute to new muscle formation in the host. However, it has long been recognized that those cells have limited regenerative capacity and fail to form new stem cells. By contrast, recent studies have shown that quiescent MuSCs have a much greater capacity to regenerate tissue and to form new skeletal muscle, and that even very few MuSCs are capable of remarkable regenerative capacity if maintained under optimal conditions, such as when still attached to the muscle fiber that they are associated with in vivo. The goals of the studies outlined in this proposal are to develop methods to generate artificial muscle fibers (AMFs) upon which MuSCs can be seeded in order to enhance their regenerative potential. We have extensive preliminary data showing enhancement of MuSC function when associated with AMFs. In this proposal, we will use highly purified human MuSCs to test for our ability to bioengineer AMFs in order to enhance the regenerative potential of freshly isolated MuSCs to engage in repair of a chronic VML model in the mouse. We will use standardized injuries to host mouse muscle producing VML, and we will test for regenerative capacity of transplanted cells, either alone or in association with AMFs, to restore tissue structure and function. Analyses will include non-invasive imaging, physiological muscle function testing, and both histological and immunohistochemical analysis of tissue regeneration. In addition, we will perform detailed molecular analyses of human MuSCs directly after isolation or after self-renewal in mice following transplantation. Our long-term goal is to establish conditions for the maintenance or even expansion of human MuSCs in culture while still being able to maintain or restore the remarkable regenerative potential they exhibit in their native environment. The overall goal of this proposal is to develop a scalable technology using AMFs to enhance MuSC transplantation for the treatment of volumetric muscle loss. This will have direct and immediate relevance to Veterans who are suffering from skeletal muscle injuries, injuries that have limited their functional capacity and that, to date, have no hope of further recovery. Our goal is to develop a therapeutic approach to muscle tissue repair based upon a deep understanding of the basic stem cell biology, a state-of-the-art application of materials science to these clinical challenges, and a firm commitment to the clinical/translational mission to improve the health and quality of life of Veterans whose function and further rehabilitation is limited by the lack of effective therapeutic options.
The major focus of our work is to use muscle stem cells to repair muscle tissue that has sustained major traumatic injury, a clinical challenge faced by a large number of Veterans and often referred to as Volumetric Muscle Loss. Muscle stem cells are most effective in repairing muscle when they are in their native state, namely deeply embedded in muscle tissue. Therefore, we will attempt to reconstruct that native state by placing human muscle stem cells in association with components that mimic the environment that those cells experience in the body. To do this, we will create artificial muscle fibers and develop culture conditions that are optimal for human muscle stem cells. We will test whether maintaining the cells under those conditions renders them particularly effective after transplantation to repair the injured muscle o a mouse. Our long-term goal is to be able to repair entire regions of damaged human muscle by transplanting human stem cells to contribute to the repair of muscle fibers, the regeneration of muscle tissue, and the restoration of muscle function.