Intrinsic Muscle Stem Cell Dysfunction Contributes to Impaired Regeneration in the mdx Mouse.

Background: Duchenne muscular dystrophy (DMD) is a devastating disease characterized by progressive muscle wasting that leads to diminished lifespan. In addition to the inherent weakness of dystrophin-deficient muscle, the dysfunction of resident muscle stem cells (MuSC) significantly contributes to disease progression.

Methods: Using the mdx mouse model of DMD, we performed an in-depth characterization of disease progression and MuSC function in dystrophin-deficient skeletal muscle using immunohistology, isometric force measurements, transcriptomic analysis and transplantation assays.

The mitochondrial protein OPA1 regulates the quiescent state of adult muscle stem cells.

Quiescence regulation is essential for adult stem cell maintenance and sustained regeneration. Our studies uncovered that physiological changes in mitochondrial shape regulate the quiescent state of adult muscle stem cells (MuSCs). We show that MuSC mitochondria rapidly fragment upon an activation stimulus, via systemic HGF/mTOR, to drive the exit from deep quiescence.

GLI3 regulates muscle stem cell entry into G and self-renewal.

Satellite cells are required for the growth, maintenance, and regeneration of skeletal muscle. Quiescent satellite cells possess a primary cilium, a structure that regulates the processing of the GLI family of transcription factors. Here we find that GLI3 processing by the primary cilium plays a critical role for satellite cell function.

Analysis of human satellite cell dynamics on cultured adult skeletal muscle myofibers.

Background: Maintaining stem cells in physiologically relevant states is necessary to understand cell and context-specific signalling paradigms and to understand complex interfaces between cells in situ. Understanding human stem cell function is largely based on tissue biopsies, cell culture, and transplantation into model organisms.

Methods: Here, we describe a method to isolate post-mortem intact human muscle myofibers and culture muscle stem cells within the niche microenvironment to assay cellular dynamics, stem cell identity, stem cell hierarchy, and differentiation potential.

Isolation of satellite cells and transplantation into mice for lineage tracing in muscle.

Limited methods exist to assay the direct effects of therapeutic intervention on muscle stem cell fate, proliferation or differentiation in an in vivo context. Here we provide an optimized protocol for muscle stem cell isolation and transplantation into mice to deconvolute heterogeneity within isolated stem cell populations. Viable and pure cell populations are isolated within 2 h and can then be used for therapeutic intervention or transplantation to uncover the repopulating and differentiation potential in mice, a physiologically relevant in vivo context.

EGFR-Aurka Signaling Rescues Polarity and Regeneration Defects in Dystrophin-Deficient Muscle Stem Cells by Increasing Asymmetric Divisions.

Loss of dystrophin expression in Duchenne muscular dystrophy (DMD) causes progressive degeneration of skeletal muscle, which is exacerbated by reduced self-renewing asymmetric divisions of muscle satellite cells. This, in turn, affects the production of myogenic precursors and impairs regeneration and suggests that increasing such divisions may be beneficial. Here, through a small-molecule screen, we identified epidermal growth factor receptor (EGFR) and Aurora kinase A (Aurka) as regulators of asymmetric satellite cell divisions.

Orienting Muscle Stem Cells for Regeneration in Homeostasis, Aging, and Disease.

Muscle stem cells, or satellite cells, are required for skeletal muscle maintenance, growth, and repair. Following satellite cell activation, several factors drive asymmetric cell division to generate a stem cell and a proliferative progenitor that forms new muscle. The balance between symmetric self-renewal and asymmetric division significantly impacts the efficiency of regeneration.

Muscle stem cells.

Feige and Rudnicki introduce muscle stem cells.

Direct Reprogramming of Mouse Fibroblasts into Functional Skeletal Muscle Progenitors.

Skeletal muscle harbors quiescent stem cells termed satellite cells and proliferative progenitors termed myoblasts, which play pivotal roles during muscle regeneration. However, current technology does not allow permanent capture of these cell populations in vitro. Here, we show that ectopic expression of the myogenic transcription factor MyoD, combined with exposure to small molecules, reprograms mouse fibroblasts into expandable induced myogenic progenitor cells (iMPCs).