Stem Cells. 2017 Jul;35(7):1815-1834. doi: 10.1002/stem.2639.

Slow-Myofiber Commitment by Semaphorin 3A Secreted from Myogenic Stem Cells.

Tatsumi R1, Suzuki T1,2,3, Do MQ1, Ohya Y1, Anderson JE4, Shibata A1, Kawaguchi M1, Ohya S1, Ohtsubo H1, Mizunoya W1, Sawano S1, Komiya Y1, Ichitsubo R1, Ojima K5, Nishimatsu SI2, Nohno T2, Ohsawa Y6, Sunada Y6, Nakamura M7, Furuse M1, Ikeuchi Y1, Nishimura T3, Yagi T8, Allen RE9.

Author information

Abstract

Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secreted protein, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle injury; however, its physiological significance is still unknown. Here we show that Sema3A impacts slow-twitch fiber generation through a signaling pathway, cell-membrane receptor (neuropilin2-plexinA3) → myogenin-myocyte enhancer factor 2D → slow myosin heavy chain. This novel axis was found by small interfering RNA-transfection experiments in myoblast cultures, which also revealed an additional element that Sema3A-neuropilin1/plexinA1, A2 may enhance slow-fiber formation by activating signals that inhibit fast-myosin expression. Importantly, satellite cell-specific Sema3A conditional-knockout adult mice (Pax7CreERT2 -Sema3Afl °x activated by tamoxifen-i.p. injection) provided direct in vivo evidence for the Sema3A-driven program, by showing that slow-fiber generation and muscle endurance were diminished after repair from cardiotoxin-injury of gastrocnemius muscle. Overall, the findings highlight an active role for satellite cell-secreted Sema3A ligand as a key “commitment factor” for the slow-fiber population during muscle regeneration. Results extend our understanding of the myogenic stem-cell strategy that regulates fiber-type differentiation and is responsible for skeletal muscle contractility, energy metabolism, fatigue resistance, and its susceptibility to aging and disease. Stem Cells 2017;35:1815-1834.

KEYWORDS:

Muscle endurance; Myogenin; Regeneration; Resident myogenic stem satellite cells; Semaphorin 3A; Slow-twitch myofiber

PMID: 28480592

 

Supplemental Discussion:

Possible agonization of Sema3A-dependent signaling by functional food ingredients 

This study presented a model for time-coordinated progression of slow-fiber commitment and maturation in muscle regeneration (see Fig. 7).  Sema3A ligand is secreted from early-differentiated myoblasts (in a HGF/syndecan2, 4-dependent manner, shown in dashed-line box) and impacts slow-fiber commitment through neuropilin2-plexinA3 → myogenin (and MEF2D/HDAC7) slow MyHC.  The model includes additional elements to suppress fast-MyHC expression (red-dotted lines) and slow-MyHC (black dashed-line).  At the subsequent growth-phase, slow-MyHC-positive myotubes establish the motor innervation that contributes to fiber-type maturation through a calcium/calcineurin signaling pathway, along with configuration of regenerated capillaries and transcriptional PGC1α/PPARδ-circuitry (not depicted in Fig. 7).  It is worth noting again that the slow MyHC-expression pathway modeled here is activated by the association of Sema3A ligands with the binding-receptor neuropilin2; therefore it is possible that ligands other than Sema3A bind to neuropilin2 to generate the signal for slow-fiber formation.  We have already found a promising natural agonist in food ingredients; briefly, 500 ng/ml apple polyphenol (APP; prepared from unripe apples) or 10 ng/ml chlorogenic acid (a major component of APP) up-regulates the expression of myogenin, MEF2D and slow MyHC without changing the level of Sema3A.  These findings indicate that chlorogenic acid may agonize the Sema3A response in primary cultures of satellite cells (Tatsumi et al., manuscript in preparation).  The functional application of such in vitro findings was supported by our in vivo study, in which 8 wks of a diet containing 5%-APP significantly improved the endurance of calf muscles in young-adult Fischer F344 rats, and a diet of 0.5% APP increased the proportion of fatigue-resistant fibers and myoglobin in Sprague-Dawley rats [1, 2].  Future in vivo and in vitro experiments on satellite cell-specific Sema3A-cKO mice will be designed to help develop novel strategies to promote directional increases in slow or fast fibers, depending on applications to human sports and health sciences.  Perhaps the most important studies will be those directed to combating the loss of the fiber-type balance that is part of age-related atrophy, and toward meat-animal production in particular niche markets.  Additionally, a recent report showed that Sema3A signaling through its motor neuron neuropilin1 receptor may trigger a progressive distal axonopathy and muscle denervation in the SOD1G93A mouse model of human familial amyotrophic lateral sclerosis (fALS) [3, 4].  The effects of satellite cell-specific Sema3A-cKO on the phenotypes of the SOD1G93A mouse would provide significant insights into the pathophysiology of fALS and the possible pathogenic roles of Sema3A over-expression for which an increase in axon repulsion could contribute to neurodegenerative diseases affecting both lower and upper motor neurons.  These many ideas are now accessible through advances in our understanding of mechanisms underlying slow-fiber formation in muscle regenerating fibers under conditional control of satellite-cell derived Sema3A.

 

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