Dissecting the molecular pathways required for the generation and maintenance of induced myogenic progenitors (iMPCs) and assessing their potential for gene therapy

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Skeletal muscle is a regenerative tissue that is mostly comprised of differentiated myofibers responsible for contraction and thus movement. In addition,muscle contains a rare population of stem cells termed satellite cells, which are in a quiescent state under homeostatic conditions but undergo activation upon tissue injury. Once activated, satellite cells proliferate and form uncommitted myoblasts, which then differentiate and fuse with other myoblasts to regenerate damaged tissue. Remarkably, individual satellite cells have the capacity to produce myofibers and replenish the satellite cell niche when transplanted into damaged muscle. Satellite cells hold a great promise for muscle tissue generation. Although they can be explanted in culture for a limited period of time using growth factors and/or small compounds they cannot be expanded at numbers required for clinical use. Recently, the host lab has demonstrated the transdifferentiation of skin fibroblasts into myogenic stem-¬like cells that proliferate in culture and produce myofibers in vitro and in vivo. However, it is unclear to what extent these induced myogenic progenitor cells (iMPCs) resemble satellite cells. Also, the genetic that the “transdifferentiation” of fibroblasts to iMPCs underlie, remain elusive. Decoding these molecular mechanisms is key for understanding cell fate transitions beyond muscle stem cell generation and will be important for evaluating the iMPC’s potential for gene therapy approaches. •Objective 1. Are iMPC subsets molecularly and functionally equivalent to satellite cells? The first aim will be to compare gene expression and chromatin accessibility signatures between purified iMPCs and satellite cells using satellite cell reporter mice.•Objective 2. How do transcription factors and small molecules synergize to alter the epigenetic, gene expression and differentiation state mechanistically? Ectopic expression of the transcription factor MyoD alone is insufficient, while the expression of MyoD and treatment with a chemical cocktail is sufficient to establish a myogenic stem/progenitor-like state. We, therefore, aim to understand how exposure of skin fibroblasts to certain chemicals facilitates a chromatin state, that allows MyoD binding and thus a progenitor-¬like program.•Objective 3: Establish proof-of-principle evidence for the utility of iMPCs in gene and cell therapyWe hypothesize that the established iMPC culture system could be useful to study pathological myogenesis ex vivo. iMPCs should facilitate the introduction or correction of disease-associated mutations, which has therapeutic relevance. The goal of this aim is therefore to gather evidence that (i) iMPCs can be derived from dystrophic mouse models to study disease phenotypes, (ii) iMPCs are amenable to gene correction and (iii) corrected iMPCs differentiate into healthy myofibers upon transplantation.