Nicotinamide and pyridoxine stimulate muscle stem cell expansion and enhance regenerative capacity during aging.

Skeletal muscle relies on resident muscle stem cells (MuSCs) for growth and repair. Aging and muscle diseases impair MuSC function, leading to stem cell exhaustion and regenerative decline that contribute to the progressive loss of skeletal muscle mass and strength. In the absence of clinically available nutritional solutions specifically targeting MuSCs, we used a human myogenic progenitor high-content imaging screen of natural molecules from food to identify nicotinamide (NAM) and pyridoxine (PN) as bioactive nutrients that stimulate MuSCs and have a history of safe human use.

A dual-color PAX7 and MYF5 in vivo reporter to investigate muscle stem cell heterogeneity in regeneration and aging.

Increasing evidence suggests that the muscle stem cell (MuSC) pool is heterogeneous. In particular, a rare subset of PAX7-positive MuSCs that has never expressed the myogenic regulatory factor MYF5 displays unique self-renewal and engraftment characteristics. However, the scarcity and limited availability of protein markers make the characterization of these cells challenging.

A Tead1-Apelin axis directs paracrine communication from myogenic to endothelial cells in skeletal muscle.

Apelin (Apln) is a myokine that regulates skeletal muscle plasticity and metabolism and declines during aging. Through a yeast one-hybrid transcription factor binding screen, we identified the TEA domain transcription factor 1 (Tead1) as a novel regulator of the promoter. Single-cell analysis of regenerating muscle revealed that the apelin receptor () is enriched in endothelial cells, whereas is enriched in myogenic cells.

An engineered multicellular stem cell niche for the 3D derivation of human myogenic progenitors from iPSCs.

Fate decisions in the embryo are controlled by a plethora of microenvironmental interactions in a three-dimensional niche. To investigate whether aspects of this microenvironmental complexity can be engineered to direct myogenic human-induced pluripotent stem cell (hiPSC) differentiation, we here screened murine cell types present in the developmental or adult stem cell niche in heterotypic suspension embryoids. We identified embryonic endothelial cells and fibroblasts as highly permissive for myogenic specification of hiPSCs.

Muscle Stem Cell Quiescence: Controlling Stemness by Staying Asleep.

Muscle stem cells (MuSCs) are tissue-resident stem cells required for growth and repair of skeletal muscle, that are otherwise maintained in a cell-cycle-arrested state called quiescence. While quiescence was originally believed to be a state of cellular inactivity, increasing evidence suggests that quiescence is dynamically regulated and contributes to stemness, the long-term capacity to maintain regenerative functions. Here, we review the current understanding of MuSC quiescence and highlight recently discovered molecular markers, which differentiate depth of quiescence and influence self-renewal capacity.

Aging Disrupts Muscle Stem Cell Function by Impairing Matricellular WISP1 Secretion from Fibro-Adipogenic Progenitors.

Research on age-related regenerative failure of skeletal muscle has extensively focused on the phenotypes of muscle stem cells (MuSCs). In contrast, the impact of aging on regulatory cells in the MuSC niche remains largely unexplored. Here, we demonstrate that aging impairs the function of mouse fibro-adipogenic progenitors (FAPs) and thereby indirectly affects the myogenic potential of MuSCs.

Isolation, Culture, and Immunostaining of Skeletal Muscle Myofibers from Wildtype and Nestin-GFP Mice as a Means to Analyze Satellite Cell.

Multinucleated myofibers, the functional contractile units of adult skeletal muscle, harbor mononuclear Pax7 myogenic progenitors on their surface between the myofiber basal lamina and plasmalemma. These progenitors, known as satellite cells, are the primary myogenic stem cells in adult muscle. This chapter describes our laboratory protocols for isolating, culturing, and immunostaining intact myofibers from mouse skeletal muscle as a means for studying satellite cell dynamics.

Refilins are short-lived Actin-bundling proteins that regulate lamellipodium protrusion dynamics.

Refilins (RefilinA and RefilinB) are members of a novel family of Filamin binding proteins that function as molecular switches to conformationally alter the Actin filament network into bundles. We show here that Refilins are extremely labile proteins. An N-terminal PEST/DSG(X)S motif mediates ubiquitin-independent rapid degradation.

Isolation of Mouse Periocular Tissue for Histological and Immunostaining Analyses of the Extraocular Muscles and Their Satellite Cells.

The extraocular muscles (EOMs) comprise a group of highly specialized skeletal muscles controlling eye movements. Although a number of unique features of EOMs including their sparing in Duchenne muscular dystrophy have drawn a continuous interest, knowledge about these hard to reach muscles is still limited. The goal of this chapter is to provide detailed methods for the isolation and histological analysis of mouse EOMs.

Expression profile and overexpression outcome indicate a role for βKlotho in skeletal muscle fibro/adipogenesis.

Regeneration of skeletal muscles is required throughout life to ensure optimal performance. Therefore, a better understanding of the resident cells involved in muscle repair is essential. Muscle repair relies on satellite cells (SCs), the resident myogenic progenitors, but also involves the contribution of interstitial cells including fibro/adipocyte progenitors (FAPs).

Myogenic-specific ablation of Fgfr1 impairs FGF2-mediated proliferation of satellite cells at the myofiber niche but does not abolish the capacity for muscle regeneration.

Skeletal muscle satellite cells (SCs) are Pax7(+) myogenic stem cells that reside between the basal lamina and the plasmalemma of the myofiber. In mature muscles, SCs are typically quiescent, but can be activated in response to muscle injury. Depending on the magnitude of tissue trauma, SCs may divide minimally to repair subtle damage within individual myofibers or produce a larger progeny pool that forms new myofibers in cases of overt muscle injury.

Extraocular muscle satellite cells are high performance myo-engines retaining efficient regenerative capacity in dystrophin deficiency.

Extraocular muscles (EOMs) are highly specialized skeletal muscles that originate from the head mesoderm and control eye movements. EOMs are uniquely spared in Duchenne muscular dystrophy and animal models of dystrophin deficiency. Specific traits of myogenic progenitors may be determinants of this preferential sparing, but very little is known about the myogenic cells in this muscle group.

Ancestral Myf5 gene activity in periocular connective tissue identifies a subset of fibro/adipogenic progenitors but does not connote a myogenic origin.

Extraocular muscles (EOM) represent a unique muscle group that controls eye movements and originates from head mesoderm, while the more typically studied body and limb muscles are somite-derived. Aiming to investigate myogenic progenitors (satellite cells) in EOM versus limb and diaphragm of adult mice, we have been using flow cytometry in combination with myogenic-specific Cre-loxP lineage marking for cell isolation. While analyzing cells from the EOM of mice that harbor Myf5(Cre)-driven GFP expression, we identified in addition to the expected GFP(+) myogenic cells (presumably satellite cells), a second dominant GFP(+) population distinguished as being Sca1(+), non-myogenic, and exhibiting a fibro/adipogenic potential.

Moderate-intensity treadmill running promotes expansion of the satellite cell pool in young and old mice.

Satellite cells, the myogenic progenitors located at the myofibre surface, are essential for the repair of adult skeletal muscle. There is ample evidence for an age-linked decline in the number of satellite cells and performance in limb muscles. Hence, an effective means of activating and expanding the satellite cell pool may enhance muscle maintenance and reduce the impact of age-associated muscle deterioration (sarcopaenia).

A contemporary atlas of the mouse diaphragm: myogenicity, vascularity, and the Pax3 connection.

The thoracic diaphragm is a unique skeletal muscle composed of costal, crural, and central tendon domains. Although commonly described in medical textbooks, newer insights into the diaphragm cell composition are scarce. Here, using reporter mice, combined with gene expression analyses of whole tissues and primary cultures, we compared the diaphragm domains and their myogenic progenitors (i.

Down-regulation of MyoD by calpain 3 promotes generation of reserve cells in C2C12 myoblasts.

Calpain 3 is a calcium-dependent cysteine protease that is primarily expressed in skeletal muscle and is implicated in limb girdle muscular dystrophy type 2A. To date, its best characterized function is located within the sarcomere, but this protease is found in other cellular compartments, which suggests that it exerts multiple roles. Here, we present evidence that calpain 3 is involved in the myogenic differentiation process.

Up-regulation of calcium-dependent proteolysis in human myoblasts under acute oxidative stress.

The reduced regenerative potential of muscle fibres, most likely due to a decreased number and/or function of satellite cells, could play a significant role in the progression of muscle ageing. Accumulation of reactive oxygen species has been clearly correlated to sarcopenia and could contribute to the impairment of satellite cell function. In this work we have investigated the effect of oxidative stress generated by hydrogen peroxide in cultured human skeletal muscle satellite cells.