bims-moremu 2023-04-16 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023‒04‒16
33 papers selected by
Anna Vainshtein
Craft Science Inc.

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice.
Skeletal muscle atrophy, regeneration, and dysfunction in heart failure: Impact of exercise training.
Sox11 is enriched in myogenic progenitors but dispensable for development and regeneration of skeletal muscle.
Increased mitochondrial surface area and cristae density in the skeletal muscle of strength athletes.
Specification of skeletal muscle fiber-type is determined by the calcineurin/NFATc1 signaling pathway during muscle regeneration.
Intramuscular IL-10 Administration Enhances the Activity of Myogenic Precursor Cells and Improves Motor Function in ALS Mouse Model.
Altered muscle niche contributes to myogenic deficit in the D2- mdx model of severe DMD.
Insulin, dibutyryl-cAMP, and glucose modulate expression of patatin-like domain containing protein 7 in cultured human myotubes.
Skeletal muscle dysfunctions in pulmonary arterial hypertension: Effects of aerobic exercise training.
Validation of Human Skeletal Muscle Tissue Chip Autonomous Platform to Model Age-Related Muscle Wasting in Microgravity.
CRISPR-EDITING THERAPY FOR DUCHENNE MUSCULAR DYSTROPHY.
Mir-302a/TWF1 Axis Impairs the Myogenic Differentiation of Progenitor Cells through F-Actin-Mediated YAP1 Activation.
Nerve pathology is prevented by linker proteins in mouse models for LAMA2-related muscular dystrophy.
Tceal7 Regulates Skeletal Muscle Development through Its Interaction with Cdk1.
Interaction between poly-A binding protein PABPC4 and nuclear receptor corepressor NCoR1 modulates a metabolic stress response.
Single cell analysis reveals satellite cell heterogeneity for proinflammatory chemokine expression.
Muscle Mechanics and Thick Filament Activation: An Emerging Two-Way Interaction for the Vertebrate Striated Muscle Fine Regulation.
New Findings: Hindlimb Unloading Causes Nucleocytoplasmic Ca2+ Overload and DNA Damage in Skeletal Muscle.
Myokine Musclin Is Critical for Exercise-Induced Cardiac Conditioning.
Main Pathogenic Mechanisms and Recent Advances in COPD Peripheral Skeletal Muscle Wasting.
The history-dependent features of muscle force production: A challenge to the cross-bridge theory and their functional implications.
Tectorigenin targets PKACα to promote GLUT4 expression in skeletal muscle and improve insulin resistance in vitro and in vivo.
Blood flow restriction does not alter the early hypertrophic signaling and short-term adaptive response to resistance exercise when performed to task failure.
The effect of single-leg disuse on skeletal muscle strength and size in the non-immobilized leg of uninjured adults: A meta-analysis.
Exercise training impacts skeletal muscle remodelling induced by metabolic syndrome in ZSF1 rats through metabolism regulation.
The Potential Modulatory Effects of Exercise on Skeletal Muscle Redox Status in Chronic Kidney Disease.
Plasma proteomic changes in response to exercise training are associated with cardiorespiratory fitness adaptations.
Targeted Demethylation of the TGFβ1 mRNA Promotes Myoblast Proliferation via Activating the SMAD2 Signaling Pathway.
Perturbing the muscle work loop paradigm to unravel the neuromechanics of unsteady locomotion.
Direct electrical stimulation impacts on neuromuscular junction morphology on both stimulated and unstimulated contralateral soleus.
Exercise training remodels inguinal white adipose tissue through adaptations in innervation, vascularization, and the extracellular matrix.
The Role of the Piezo1 Mechanosensitive Channel in the Musculoskeletal System.
The relationship between epigenetic age and the hallmarks of aging in human cells.

Cell Mol Life Sci. 2023 Apr 13. 80(5): 122

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice.

Vitor Rosetto Muñoz, José Diego Botezelli, Rafael Calais Gaspar, Alisson L da Rocha, Renan Fudoli Lins Vieira, Barbara Moreira Crisol, Renata Rosseto Braga, Matheus Brandemarte Severino, Susana Castelo Branco Ramos Nakandakari, Gabriel Calheiros Antunes, Sérgio Q Brunetto, Celso D Ramos, Lício Augusto Velloso, Fernando Moreira Simabuco, Leandro Pereira de Moura, Adelino Sanchez Ramos da Silva, Eduardo Rochete Ropelle, Dennys Esper Cintra, José Rodrigo Pauli.

  OBJECTIVE: Intriguingly, hyperinsulinemia, and hyperglycemia can predispose insulin resistance, obesity, and type 2 diabetes, leading to metabolic disturbances. Conversely, physical exercise stimulates skeletal muscle glucose uptake, improving whole-body glucose homeostasis. Therefore, we investigated the impact of short-term physical activity in a mouse model (Slc2a4+/-) that spontaneously develops hyperinsulinemia and hyperglycemia even when fed on a chow diet.METHODS: Slc2a4+/- mice were used, that performed 5 days of endurance or strength exercise training. Further analysis included physiological tests (GTT and ITT), skeletal muscle glucose uptake, skeletal muscle RNA-sequencing, mitochondrial function, and experiments with C2C12 cell line.
RESULTS: When Slc2a4+/- mice were submitted to the endurance or strength training protocol, improvements were observed in the skeletal muscle glucose uptake and glucose metabolism, associated with broad transcriptomic modulation, that was, in part, related to mitochondrial adaptations. The endurance training, but not the strength protocol, was effective in improving skeletal muscle mitochondrial activity and unfolded protein response markers (UPRmt). Moreover, experiments with C2C12 cells indicated that insulin or glucose levels could contribute to these mitochondrial adaptations in skeletal muscle.
CONCLUSIONS: Both short-term exercise protocols were efficient in whole-body glucose homeostasis and insulin resistance. While endurance exercise plays an important role in transcriptome and mitochondrial activity, strength exercise mostly affects post-translational mechanisms and protein synthesis in skeletal muscle. Thus, the performance of both types of physical exercise proved to be a very effective way to mitigate the impacts of hyperglycemia and hyperinsulinemia in the Slc2a4+/- mouse model.

Keywords:  Hyperinsulinemia; Mitochondrial adaptations; Physical exercise; Skeletal muscle

DOI:  https://doi.org/10.1007/s00018-023-04771-2
J Sport Health Sci. 2023 Apr 09. pii: S2095-2546(23)00040-6. [Epub ahead of print]

Skeletal muscle atrophy, regeneration, and dysfunction in heart failure: Impact of exercise training.

Harrison Gallagher, Paul W Hendrickse, Marcelo G Pereira, T Scott Bowen.

  This review highlights some established and some more contemporary mechanisms responsible for heart failure-induced skeletal muscle wasting and weakness. We first describe the effects of heart failure on the relationship between protein synthesis and degradation rates, which determine muscle mass, the involvement of the satellite cells for continual muscle regeneration, and changes in myofiber calcium homeostasis linked to contractile dysfunction. We then highlight key mechanistic effects of both aerobic and resistance exercise training on skeletal muscle in heart failure and outline its application as a beneficial treatment. Overall, heart failure causes multiple impairments related to autophagy, anabolic-catabolic signaling, satellite cell proliferation, and calcium homeostasis, which together promote fiber atrophy, contractile dysfunction, and impaired regeneration. Although both wasting and weakness are partly rescued by aerobic and resistance exercise training in heart failure, the effects of satellite cell dynamics remain poorly explored.

Keywords:  Calcium; Exercise training; Heart failure; Satellite cells; Skeletal muscle wasting

DOI:  https://doi.org/10.1016/j.jshs.2023.04.001
bioRxiv. 2023 Mar 31. pii: 2023.03.30.534956. [Epub ahead of print]

Sox11 is enriched in myogenic progenitors but dispensable for development and regeneration of skeletal muscle.

Stephanie N Oprescu, Nick Baumann, Xiyue Chen, Qiang Sun, Yu Zhao, Feng Yue, Huating Wang, Shihuan Kuang.

Transcription factors (TFs) play key roles in regulating the differentiation and function of stem cells, including muscle satellite cells (MuSCs), a resident stem cell population responsible for postnatal regeneration of the skeletal muscle. Sox11 belongs to the Sry-related HMG-box (SOX) family of TFs that play diverse roles in stem cell behavior and tissue specification. Analysis of single-cell RNA-sequencing (scRNA-seq) datasets identify a specific enrichment of Sox11 mRNA in differentiating but not quiescent MuSCs. Consistent with the scRNA-seq data, Sox11 levels increase during differentiation of murine primary myoblasts in vitro. scRNA-seq data comparing muscle regeneration in young and old mice further demonstrate that Sox11 expression is reduced in aged MuSCs. Age-related decline of Sox11 expression is associated with reduced chromatin contacts within the topologically associated domains. Unexpectedly, Myod1 Cre -driven deletion of Sox11 in embryonic myoblasts has no effects on muscle development and growth, resulting in apparently healthy muscles that regenerate normally. Pax7 CreER or Rosa26 CreER driven (MuSC-specific or global) deletion of Sox11 in adult mice similarly has no effects on MuSC differentiation or muscle regeneration. These results identify Sox11 as a novel myogenic differentiation marker with reduced expression in quiescent and aged MuSCs, but the specific function of Sox11 in myogenesis remain to be elucidated.

DOI: https://doi.org/10.1101/2023.03.30.534956
J Physiol. 2023 Apr 12.

Increased mitochondrial surface area and cristae density in the skeletal muscle of strength athletes.

Javier Botella, Camilla T Schytz, Thomas F Pehrson, Rune Hokken, Simon Laugesen, Per Aagaard, Charlotte Suetta, Britt Christensen, Niels Ørtenblad, Joachim Nielsen.

  Mitochondria are the cellular organelles responsible for resynthesising the majority of ATP. In skeletal muscle, there is an increased ATP turnover during resistance exercise to sustain the energetic demands of muscle contraction. Despite this, little is known regarding the mitochondrial characteristics of chronically strength-trained individuals and any potential pathways regulating the strength-specific mitochondrial remodelling. Here, we investigated the mitochondrial structural characteristics in skeletal muscle of strength athletes and age-matched untrained controls. The mitochondrial pool in strength athletes was characterised by increased mitochondrial cristae density, decreased mitochondrial size, and increased surface-to-volume ratio, despite similar mitochondrial volume density. We also provide a fibre-type and compartment specific assessment of mitochondria morphology in human skeletal muscle, which reveals across groups a compartment-specific influence on mitochondrial morphology that is largely independent of fibre-type. Furthermore, we show that resistance exercise leads to signs of mild mitochondrial stress, without an increase in the number of damaged mitochondria. Using publicly available transcriptomic data we show that acute resistance exercise increases the expression of markers of mitochondrial biogenesis, fission, and mitochondrial unfolded protein responses (UPRmt ). Further, we observed an enrichment of the UPRmt in the basal transcriptome of strength-trained individuals. Together, these findings show that strength athletes possess a unique mitochondrial remodelling, which minimises the space required for mitochondria. We propose that the concurrent activation of markers of mitochondrial biogenesis and mitochondrial remodelling pathways (fission and UPRmt ) with resistance exercise may be partially responsible for the observed mitochondrial phenotype of strength athletes. KEY POINTS: Untrained individuals and strength athletes possess comparable skeletal muscle mitochondrial volume density. In contrast, strength athletes'mitochondria are characterised by increased cristae density, decreased size, and increased surface-to-volume ratio. Type I fibres have an increased number of mitochondrial profiles with minor differences in the mitochondrial morphological characteristics compared to type II fibres. The mitochondrial morphology is distinct across the subcellular compartments in both groups, with subsarcolemmal mitochondria being bigger in size when compared to intermyofibrillar. Acute resistance exercise leads to signs of mild morphological mitochondrial stress accompanied by increased gene expression of markers of mitochondrial biogenesis, fission, and mitochondrial unfolded protein response (UPRmt). Abstract figure legend: Mitochondria are the cellular organelles responsible for resynthesising the majority of ATP. The present study aimed to investigate the mitochondrial structural characteristics of strength athletes when compared to age-matched untrained individuals. Here we show that the mitochondria of strength athletes have an increased mitochondrial cristae density, increased number of profiles, and an increased surface-to-volume ratio; despite similar mitochondrial volumetric density. Furthermore, we show that human type I fibres, when compared to type II fibres, are characterised by an increased number of mitochondrial profiles without differences in their morphological characteristics. Finally, we show that acute resistance exercise leads to mild signs of mitochondrial morphological stress and an increased expression of markers of mitochondrial biogenesis, fission, and mitochondrial unfolded protein response (UPRmt ). This article is protected by copyright. All rights reserved.

Keywords:  Mitochondria; Olympic weightlifting; cristae density; resistance exercise; skeletal muscle; strength

DOI:  https://doi.org/10.1113/JP284394
Biochem Biophys Res Commun. 2023 Mar 22. pii: S0006-291X(23)00317-0. [Epub ahead of print]659 20-28

Specification of skeletal muscle fiber-type is determined by the calcineurin/NFATc1 signaling pathway during muscle regeneration.

Junchul Shin, Aki Nunomiya, Kohsuke Gonda, Ryoichi Nagatomi.

  Skeletal muscle fiber type specification is changeable during muscle regeneration following cardiotoxin (CTX) injection; however, the mechanism of muscle fiber shift in regenerating muscle fibers remains unclear. Furthermore, it is unclear as to which factors determine skeletal muscle fiber types in regenerating muscle fibers. Previous studies showed that CTX-induced muscle damage resulted in a temporary hypoxic condition, indicating that hypoxia-inducible factor (HIF)-1α may be involved in muscle fiber type transition. Stabilization of HIF-1α has been shown to result in muscle fiber type transition toward slow-twitch phenotype through the calcineurin/nuclear factor activated T cell 1 (NFATc1) signaling pathway. Therefore, the aim of the present study was to determine whether the calcineurin/NFATc1 pathway is a key mediator of skeletal muscle fiber type transition during muscle regeneration. We found that CTX-induced muscle damage resulted in transient ischemia and HIF-1α expression in skeletal muscle. Additionally, it shifted the muscle fiber type proportion toward a slow-twitch phenotype in the soleus muscle (37.5% in the control muscle vs. 61.3% in the damaged muscle; p < 0.01) three weeks after muscle damage. Moreover, the NFATc1 protein levels increased in damaged muscle, and blockage of the calcineurin/NFATc1 signaling pathway by tacrolimus (FK-506) treatment substantially decreased the number of slow-twitch muscle fibers in the soleus muscle. This study demonstrated that CTX-induced muscle injury results in transient ischemia in hind limb muscle and stabilizes HIF-1α. Moreover, muscle damage increased oxidative phenotype muscle fibers through the calcineurin/NFATc1 signaling pathway during muscle regeneration.

Keywords:  Calcineurin; Hypoxia-inducible factor α; NFATc1; Type I muscle Fiber

DOI:  https://doi.org/10.1016/j.bbrc.2023.03.032
Cells. 2023 Mar 26. pii: 1016. [Epub ahead of print]12(7):

Intramuscular IL-10 Administration Enhances the Activity of Myogenic Precursor Cells and Improves Motor Function in ALS Mouse Model.

Paola Fabbrizio, Cassandra Margotta, Jessica D'Agostino, Giuseppe Suanno, Lorenzo Quetti, Caterina Bendotti, Giovanni Nardo.

  Amyotrophic Lateral Sclerosis (ALS) is the most common adult motor neuron disease, with a poor prognosis, a highly unmet therapeutic need, and a burden on health care costs. Hitherto, strategies aimed at protecting motor neurons have missed or modestly delayed ALS due to a failure in countering the irreversible muscular atrophy. We recently provided direct evidence underlying the pivotal role of macrophages in preserving skeletal muscle mass. Based on these results, we explored whether the modulation of macrophage muscle response and the enhancement of satellite cell differentiation could effectively promote the generation of new myofibers and counteract muscle dysfunction in ALS mice. For this purpose, disease progression and the survival of SOD1G93A mice were evaluated following IL-10 injections in the hindlimb skeletal muscles. Thereafter, we used ex vivo methodologies and in vitro approaches on primary cells to assess the effect of the treatment on the main pathological signatures. We found that IL-10 improved the motor performance of ALS mice by enhancing satellite cells and the muscle pro-regenerative activity of macrophages. This resulted in delayed muscle atrophy and motor neuron loss. Our findings provide the basis for a suitable adjunct multisystem therapeutic approach that pinpoints a primary role of muscle pathology in ALS.

Keywords:  Amyotrophic Lateral Sclerosis; macrophages; mouse models; myogenic precursor cells; skeletal muscle

DOI:  https://doi.org/10.3390/cells12071016
bioRxiv. 2023 Mar 28. pii: 2023.03.27.534413. [Epub ahead of print]

Altered muscle niche contributes to myogenic deficit in the D2- mdx model of severe DMD.

Davi A G Mázala, Ravi Hindupur, Young Jae Moon, Fatima Shaikh, Iteoluwakishi H Gamu, Dhruv Alladi, Georgiana Panci, Michèle Weiss-Gayet, Bénédicte Chazaud, Terence A Partridge, James S Novak, Jyoti K Jaiswal.

Lack of dystrophin is the genetic basis for the Duchenne muscular dystrophy (DMD). However, disease severity varies between patients, based on specific genetic modifiers. D2- mdx is a model for severe DMD that exhibits exacerbated muscle degeneration and failure to regenerate even in the juvenile stage of the disease. We show that poor regeneration of juvenile D2- mdx muscles is associated with enhanced inflammatory response to muscle damage that fails to resolve efficiently and supports excessive accumulation of fibroadipogenic progenitors (FAPs). Unexpectedly, the extent of damage and degeneration of juvenile D2- mdx muscle is reduced in adults and is associated with the restoration of the inflammatory and FAP responses to muscle injury. These improvements enhance myogenesis in the adult D2- mdx muscle, reaching levels comparable to the milder (B10- mdx ) mouse model of DMD. Ex vivo co-culture of healthy satellite cells (SCs) with the juvenile D2- mdx FAPs reduced their fusion efficacy and in vivo glucocorticoid treatment of juvenile D2 mouse improved muscle regeneration. Our findings indicate that aberrant stromal cell response contributes to poor myogenesis and greater muscle degeneration in dystrophic juvenile D2- mdx muscles and reversal of this reduces pathology in adult D2- mdx mouse muscle, identifying these as therapeutic targets to treat dystrophic DMD muscles.

DOI: https://doi.org/10.1101/2023.03.27.534413
Front Endocrinol (Lausanne). 2023 ;14 1139303

Insulin, dibutyryl-cAMP, and glucose modulate expression of patatin-like domain containing protein 7 in cultured human myotubes.

Katarina Miš, Ana-Marija Lulić, Tomaž Marš, Sergej Pirkmajer, Maja Katalinić.

  Expression of patatin-like phospholipase domain containing protein 7 (PNPLA7), also known as neuropathy target esterase-related esterase (NRE), a lysophospholipase, increases with fasting and decreases with feeding in mouse skeletal muscle, indicating it is regulated by insulin, counterregulatory hormones, such as glucocorticoids and catecholamines, and/or nutrients. In cultured mouse adipocytes insulin reduces Pnpla7 expression, underscoring the possibility that insulin regulates PNPLA7 in skeletal muscle. The first aim of this study was to establish whether PNPLA7 is functionally expressed in cultured human skeletal muscle cells. The second aim was to determine whether PNPLA7 is regulated by insulin, glucocorticoids, cAMP/protein kinase A pathway, and/or glucose. Cultured human skeletal muscle cells expressed PNPLA7 mRNA and protein. Gene silencing of PNPLA7 in myoblasts reduced the phosphorylation of 70 kDa ribosomal protein S6 kinase and ribosomal protein S6 as well as the abundance of α1-subunit of Na+,K+-ATPase and acetyl-CoA carboxylase, indirectly suggesting that PNPLA7 is functionally important. In myotubes, insulin suppressed PNPLA7 mRNA at 1 g/L glucose, but not at low (0.5 g/L) or high (4.5 g/L) concentrations. Treatment with synthetic glucocorticoid dexamethasone and activator of adenylyl cyclase forskolin had no effect on PNPLA7 regardless of glucose concentration, while dibutyryl-cAMP, a cell-permeable cAMP analogue, suppressed PNPLA7 mRNA at 4.5 g/L glucose. The abundance of PNPLA7 protein correlated inversely with the glucose concentrations. Collectively, our results highlight that PNPLA7 in human myotubes is regulated by metabolic signals, implicating a role for PNPLA7 in skeletal muscle energy metabolism.

Keywords:  NRE; PNPLA7; cultured human myotubes; dexamethasone; dibutyryl-cAMP; forskolin; glucose; insulin

DOI:  https://doi.org/10.3389/fendo.2023.1139303
Front Physiol. 2023 ;14 1148146

Skeletal muscle dysfunctions in pulmonary arterial hypertension: Effects of aerobic exercise training.

Filipe Rios Drummond, Luciano Bernardes Leite, Denise Coutinho de Miranda, Lucas Rios Drummond, Victor Neiva Lavorato, Leôncio Lopes Soares, Clóvis Andrade Neves, Antônio José Natali.

  Pulmonary arterial hypertension is associated with skeletal muscle myopathy and atrophy and impaired exercise tolerance. Aerobic exercise training has been recommended as a non-pharmacological therapy for deleterious effects imposed by pulmonary arterial hypertension. Aerobic physical training induces skeletal muscle adaptations via reduced inflammation, improved anabolic processes, decreased hypoxia and regulation of mitochondrial function. These benefits improve physical exertion tolerance and quality of life in patients with pulmonary arterial hypertension. However, the mechanisms underlying the therapeutic potential of aerobic exercise to skeletal muscle disfunctions in patients with pulmonary arterial hypertension are not well understood yet. This minireview highlights the pathways involved in skeletal muscle adaptations to aerobic exercise training in patients with pulmonary arterial hypertension.

Keywords:  aerobic exercise; effort; myopathy; physical performance; pulmonary hypertension

DOI:  https://doi.org/10.3389/fphys.2023.1148146
Res Sq. 2023 Mar 29. pii: rs.3.rs-2631490. [Epub ahead of print]

Validation of Human Skeletal Muscle Tissue Chip Autonomous Platform to Model Age-Related Muscle Wasting in Microgravity.

Maddalena Parafati, Shelby Giza, Tushar Shenoy, Jorge Mojica-Santiago, Meghan Hopf, Legrand Malany, Don Platt, Paul Kuehl, Isabel Moore, Zachary Jacobs, Gentry Barnett, Christine Schmidt, William McLamb, Paul Coen, Twyman Clements, Siobhan Malany.

Microgravity-induced muscle atrophy experienced by astronauts shares similar physiological changes to muscle wasting experienced by older adults, known as sarcopenia. These shared attributes provide a rationale for investigating microgravity-induced molecular changes in human bioengineered muscle cells that may also mimic the progressive underlying pathophysiology of sarcopenia. Here, we report the results of an experiment that incorporated three-dimensional myobundles derived from muscle biopsies from young and older adults, that were integrated into an autonomous CubeLabâ"¢, and flown to the International Space Station (ISS) aboard SpaceX CRS-21 in December 2020 as part of the NIH/NASA funded Tissue Chips in Space program. Global transcriptomic RNA-Seq analysis comparing the myobundles in space and on the ground revealed downregulation of shared transcripts related to myoblast proliferation and muscle differentiation for those in space. The analysis also revealed differentially expressed gene pathways related to muscle metabolism unique to myobundles derived from the older cohort exposed to the space environment compared to ground controls. Gene classes related to inflammatory pathways were uniquely modulated in flight samples cultured from the younger cohort compared to ground controls. Our muscle tissue chip platform provides a novel approach to studying the cell autonomous effects of microgravity on muscle cell biology that may not be appreciated on the whole organ or organism level and sets the stage for continued data collection from muscle tissue chip experimentation in microgravity. Thus, we also report on the challenges and opportunities for conducting autonomous tissue-on-chip CubeLab TM payloads on the ISS.

DOI: https://doi.org/10.21203/rs.3.rs-2631490/v1
Hum Gene Ther. 2023 Apr 14.

CRISPR-EDITING THERAPY FOR DUCHENNE MUSCULAR DYSTROPHY.

Francesco Chemello, Eric N Olson, Rhonda Bassel-Duby.

Duchenne muscular dystrophy (DMD) is a debilitating genetic disorder that results in progressive muscle degeneration and weakness. DMD is caused by mutations in the gene encoding dystrophin protein, a membrane-associated protein required for maintenance of muscle structure and function. Although the genetic mutations causing the disease are well known, no curative therapies have been developed to date. The advent of genome editing technologies provides new opportunities to correct the underlying mutations responsible for DMD. These mutations have been successfully corrected in human cells, mice, and large animal models through different strategies based on CRISPR-Cas9 gene editing. Ideally, CRISPR-editing could offer a one-time treatment for DMD by correcting the genetic mutations and enabling normal expression of the repaired gene. However, numerous challenges remain to be addressed, including optimization of gene editing, delivery of gene editing components to all the muscles of the body, and the suppression of possible immune responses to the CRISPR-editing therapy. This review provides an overview of the recent advances toward CRISPR-editing therapy for DMD and discusses the opportunities and the remaining challenges in the path to clinical translation.

DOI: https://doi.org/10.1089/hum.2023.053
Int J Mol Sci. 2023 Mar 28. pii: 6341. [Epub ahead of print]24(7):

Mir-302a/TWF1 Axis Impairs the Myogenic Differentiation of Progenitor Cells through F-Actin-Mediated YAP1 Activation.

Mai Thi Nguyen, Wan Lee.

  Actin cytoskeleton dynamics have been found to regulate myogenesis in various progenitor cells, and twinfilin-1 (TWF1), an actin-depolymerizing factor, plays a vital role in actin dynamics and myoblast differentiation. Nevertheless, the molecular mechanisms underlying the epigenetic regulation and biological significance of TWF1 in obesity and muscle wasting have not been explored. Here, we investigated the roles of miR-302a in TWF1 expression, actin filament modulation, proliferation, and myogenic differentiation in C2C12 progenitor cells. Palmitic acid, the most prevalent saturated fatty acid (SFA) in the diet, decreased the expression of TWF1 and impeded myogenic differentiation while increasing the miR-302a levels in C2C12 myoblasts. Interestingly, miR-302a inhibited TWF1 expression directly by targeting its 3'UTR. Furthermore, ectopic expression of miR-302a promoted cell cycle progression and proliferation by increasing the filamentous actin (F-actin) accumulation, which facilitated the nuclear translocation of Yes-associated protein 1 (YAP1). Consequently, by suppressing the expressions of myogenic factors, i.e., MyoD, MyoG, and MyHC, miR-302a impaired myoblast differentiation. Hence, this study demonstrated that SFA-inducible miR-302a suppresses TWF1 expression epigenetically and impairs myogenic differentiation by facilitating myoblast proliferation via F-actin-mediated YAP1 activation.

Keywords:  YAP1; differentiation; miR-302a; myogenesis; proliferation; twinfilin-1

DOI:  https://doi.org/10.3390/ijms24076341
PNAS Nexus. 2023 Apr;2(4): pgad083

Nerve pathology is prevented by linker proteins in mouse models for LAMA2-related muscular dystrophy.

Judith R Reinhard, Emanuela Porrello, Shuo Lin, Pawel Pelczar, Stefano C Previtali, Markus A Rüegg.

  LAMA2-related muscular dystrophy (LAMA2 MD or MDC1A) is a devastating congenital muscular dystrophy that is caused by mutations in the LAMA2 gene encoding laminin-α2, the long chain of several heterotrimeric laminins. Laminins are essential components of the extracellular matrix that interface with underlying cells. The pathology of LAMA2 MD patients is dominated by an early-onset, severe muscular dystrophy that ultimately leads to death by respiratory insufficiency. However, pathology in nonmuscle tissues has been described. Prior work in the dyW /dyW mouse model for LAMA2 MD has shown that two linker proteins, mini-agrin and αLNNd, when expressed in skeletal muscle fibers, greatly increase survival from a few months up to more than 2 years. However, the restoration of skeletal muscle function accentuates the pathology in nonmuscle tissue in dyW /dyW mice, first and foremost in the peripheral nerve resulting in paralysis of the hind limbs. We now show that the expression of the two linker proteins in all tissues ameliorates the muscular dystrophy and prevents the appearance of the hind limb paralysis. Importantly, the same ameliorating effect of the linker proteins was seen in dy3K /dy3K mice, which represent the most severe mouse model of LAMA2 MD. In summary, these data show that the two linker proteins can compensate the loss of laminin-α2 in muscle and peripheral nerve, which are the two organs most affected in LAMA2 MD. These results are of key importance for designing appropriate expression constructs for mini-agrin and αLNNd to develop a gene therapy for LAMA2 MD patients.

Keywords:  MDC1A; laminin; merosin; myelination; radial sorting

DOI:  https://doi.org/10.1093/pnasnexus/pgad083
Int J Mol Sci. 2023 Mar 27. pii: 6264. [Epub ahead of print]24(7):

Tceal7 Regulates Skeletal Muscle Development through Its Interaction with Cdk1.

Zhenzhen Xiong, Mengni Wang, Jianhua Wu, Xiaozhong Shi.

  We have previously reported Tceal7 as a muscle-specific gene that represses myoblast proliferation and promotes myogenic differentiation. The regulatory mechanism of Tceal7 gene expression has been well clarified recently. However, the underlying mechanism of Tceal7 function in skeletal muscle development remains to be elucidated. In the present study, we have generated an MCK 6.5 kb-HA-Tceal7 transgenic model. The transgenic mice are born normally, while they have displayed defects in the growth of body weight and skeletal muscle myofiber during postnatal development. Although four RxL motifs have been identified in the Tceal7 protein sequence, we have not detected any direct protein-protein interaction between Tceal7 and Cyclin A2, Cyclin B1, Cylin D1, or Cyclin E1. Further analysis has revealed the interaction between Tceal7 and Cdk1 instead of Cdk2, Cdk4, or Cdk6. Transgenic overexpression of Tceal7 reduces phosphorylation of 4E-BP1 Ser65, p70S6K1 Thr389, and Cdk substrates in skeletal muscle. In summary, these studies have revealed a novel mechanism of Tceal7 in skeletal muscle development.

Keywords:  Cdk1; Tceal7; skeletal muscle development

DOI:  https://doi.org/10.3390/ijms24076264
J Biol Chem. 2023 Apr 12. pii: S0021-9258(23)00344-7. [Epub ahead of print] 104702

Interaction between poly-A binding protein PABPC4 and nuclear receptor corepressor NCoR1 modulates a metabolic stress response.

Oliveira Ag, Oliveira Ld, Cruz Mv, Guimarães Dspsf, Lima Ti, B C Santos-Fávero, Luchessi Ad, B A Pauletti, Leme Ap, Bajgelman Mc, Afonso J, Regitano Lca, Carvalho Hf, Carneiro Em, Kobarg J, Perissi V, Auwerx J, Silveira Lr.

  Mitochondria are organelles known primarily for generating ATP via the oxidative phosphorylation process. Environmental signals are sensed by whole organisms or cells and markedly affect this process, leading to alterations in gene transcription and, consequently, changes in mitochondrial function and biogenesis. The expression of mitochondrial genes is finely regulated by nuclear transcription factors, including nuclear receptors and their coregulators. Among the best-known coregulators is the nuclear receptor corepressor 1 (NCoR1). Muscle-specific knockout of NCoR1 in mice induces an oxidative phenotype, improving glucose and fatty acid metabolism. However, the mechanism by which NCoR1 is regulated remains elusive. In this work, we identified the Poly A Binding Protein (PABPC4) as a new NCoR1 interactor. Unexpectedly, we found that silencing of PABPC4 induced an oxidative phenotype in both C2C12 and MEF cells as indicated by increased oxygen consumption, mitochondria content, and reduced lactate production. Mechanistically, we demonstrated that PABPC4 silencing increased the ubiquitination and consequent degradation of NCoR1, leading to the derepression of PPAR-regulated genes. As a consequence, cells with PABPC4 silencing had a greater capacity to metabolize lipids, reduced intracellular lipid droplets and reduced cell death. Interestingly, in conditions known to induce mitochondrial function and biogenesis, both mRNA expression and PABPC4 protein content were markedly reduced. Our study, therefore, suggests that the lowering of PABPC4 expression may represent an adaptive event required to induce mitochondrial activity in response to metabolic stress in skeletal muscle cells. As such, the NCoR1-PABPC4 interface might be a new road to the treatment of metabolic diseases.

Keywords:  NCoR1; PABPC4; metabolism; mitochondria; nuclear receptors; transcription corepressor

DOI:  https://doi.org/10.1016/j.jbc.2023.104702
Front Cell Dev Biol. 2023 ;11 1084068

Single cell analysis reveals satellite cell heterogeneity for proinflammatory chemokine expression.

Alexander B Andre, Katherina P Rees, Samantha O'Connor, Grant W Severson, Jason M Newbern, Jeanne Wilson-Rawls, Christopher L Plaisier, Alan Rawls.

  Background: The expression of proinflammatory signals at the site of muscle injury are essential for efficient tissue repair and their dysregulation can lead to inflammatory myopathies. Macrophages, neutrophils, and fibroadipogenic progenitor cells residing in the muscle are significant sources of proinflammatory cytokines and chemokines. However, the inducibility of the myogenic satellite cell population and their contribution to proinflammatory signaling is less understood. Methods: Mouse satellite cells were isolated and exposed to lipopolysaccharide (LPS) to mimic sterile skeletal muscle injury and changes in the expression of proinflammatory genes was examined by RT-qPCR and single cell RNA sequencing. Expression patterns were validated in skeletal muscle injured with cardiotoxin by RT-qPCR and immunofluorescence. Results: Satellite cells in culture were able to express Tnfa, Ccl2, and Il6, within 2 h of treatment with LPS. Single cell RNA-Seq revealed seven cell clusters representing the continuum from activation to differentiation. LPS treatment led to a heterogeneous pattern of induction of C-C and C-X-C chemokines (e.g., Ccl2, Ccl5, and Cxcl0) and cytokines (e.g., Tgfb1, Bmp2, Il18, and Il33) associated with innate immune cell recruitment and satellite cell proliferation. One cell cluster was enriched for expression of the antiviral interferon pathway genes under control conditions and LPS treatment. Activation of this pathway in satellite cells was also detectable at the site of cardiotoxin induced muscle injury. Conclusion: These data demonstrate that satellite cells respond to inflammatory signals and secrete chemokines and cytokines. Further, we identified a previously unrecognized subset of satellite cells that may act as sensors for muscle infection or injury using the antiviral interferon pathway.

Keywords:  chemokines; inflammation; interferon; muscle repair; satellite cells; scRNA-seq

DOI:  https://doi.org/10.3389/fcell.2023.1084068
Int J Mol Sci. 2023 Mar 27. pii: 6265. [Epub ahead of print]24(7):

Muscle Mechanics and Thick Filament Activation: An Emerging Two-Way Interaction for the Vertebrate Striated Muscle Fine Regulation.

Lorenzo Marcucci.

  Contraction in striated muscle is classically described as regulated by calcium-mediated structural changes in the actin-containing thin filaments, which release the binding sites for the interaction with myosin motors to produce force. In this view, myosin motors, arranged in the thick filaments, are basically always ready to interact with the thin filaments, which ultimately regulate the contraction. However, a new "dual-filament" activation paradigm is emerging, where both filaments must be activated to generate force. Growing evidence from the literature shows that the thick filament activation has a role on the striated muscle fine regulation, and its impairment is associated with severe pathologies. This review is focused on the proposed mechanical feedback that activates the inactive motors depending on the level of tension generated by the active ones, the so-called mechanosensing mechanism. Since the main muscle function is to generate mechanical work, the implications on muscle mechanics will be highlighted, showing: (i) how non-mechanical modulation of the thick filament activation influences the contraction, (ii) how the contraction influences the activation of the thick filament and (iii) how muscle, through the mechanical modulation of the thick filament activation, can regulate its own mechanics. This description highlights the crucial role of the emerging bi-directional feedback on muscle mechanical performance.

Keywords:  SRX; dual filament activation; mechanosensing mechanism; thick filament regulation

DOI:  https://doi.org/10.3390/ijms24076265
Cells. 2023 Apr 03. pii: 1077. [Epub ahead of print]12(7):

New Findings: Hindlimb Unloading Causes Nucleocytoplasmic Ca2+ Overload and DNA Damage in Skeletal Muscle.

Huajian Yang, Huiping Wang, Fangyang Pan, Yuxi Guo, Liqi Cao, Wenjing Yan, Yunfang Gao.

  Disuse atrophy of skeletal muscle is associated with a severe imbalance in cellular Ca2+ homeostasis and marked increase in nuclear apoptosis. Nuclear Ca2+ is involved in the regulation of cellular Ca2+ homeostasis. However, it remains unclear whether nuclear Ca2+ levels change under skeletal muscle disuse conditions, and whether changes in nuclear Ca2+ levels are associated with nuclear apoptosis. In this study, changes in Ca2+ levels, Ca2+ transporters, and regulatory factors in the nucleus of hindlimb unloaded rat soleus muscle were examined to investigate the effects of disuse on nuclear Ca2+ homeostasis and apoptosis. Results showed that, after hindlimb unloading, the nuclear envelope Ca2+ levels ([Ca2+]NE) and nucleocytoplasmic Ca2+ levels ([Ca2+]NC) increased by 78% (p < 0.01) and 106% (p < 0.01), respectively. The levels of Ca2+-ATPase type 2 (Ca2+-ATPase2), Ryanodine receptor 1 (RyR1), Inositol 1,4,5-tetrakisphosphate receptor 1 (IP3R1), Cyclic ADP ribose hydrolase (CD38) and Inositol 1,4,5-tetrakisphosphate (IP3) increased by 470% (p < 0.001), 94% (p < 0.05), 170% (p < 0.001), 640% (p < 0.001) and 12% (p < 0.05), respectively, and the levels of Na+/Ca2+ exchanger 3 (NCX3), Ca2+/calmodulin dependent protein kinase II (CaMK II) and Protein kinase A (PKA) decreased by 54% (p < 0.001), 33% (p < 0.05) and 5% (p > 0.05), respectively. In addition, DNase X is mainly localized in the myonucleus and its activity is elevated after hindlimb unloading. Overall, our results suggest that enhanced Ca2+ uptake from cytoplasm is involved in the increase in [Ca2+]NE after hindlimb unloading. Moreover, the increase in [Ca2+]NC is attributed to increased Ca2+ release into nucleocytoplasm and weakened Ca2+ uptake from nucleocytoplasm. DNase X is activated due to elevated [Ca2+]NC, leading to DNA fragmentation in myonucleus, ultimately initiating myonuclear apoptosis. Nucleocytoplasmic Ca2+ overload may contribute to the increased incidence of myonuclear apoptosis in disused skeletal muscle.

Keywords:  hindlimb unloading; nuclear Ca2+ regulation; nuclear apoptosis; skeletal muscle

DOI:  https://doi.org/10.3390/cells12071077
Int J Mol Sci. 2023 Mar 30. pii: 6525. [Epub ahead of print]24(7):

Myokine Musclin Is Critical for Exercise-Induced Cardiac Conditioning.

Matthew P Harris, Shemin Zeng, Zhiyong Zhu, Vitor A Lira, Liping Yu, Denice M Hodgson-Zingman, Leonid V Zingman.

  This study investigates the role and mechanisms by which the myokine musclin promotes exercise-induced cardiac conditioning. Exercise is one of the most powerful triggers of cardiac conditioning with proven benefits for healthy and diseased hearts. There is an emerging understanding that muscles produce and secrete myokines, which mediate local and systemic "crosstalk" to promote exercise tolerance and overall health, including cardiac conditioning. The myokine musclin, highly conserved across animal species, has been shown to be upregulated in response to physical activity. However, musclin effects on exercise-induced cardiac conditioning are not established. Following completion of a treadmill exercise protocol, wild type (WT) mice and mice with disruption of the musclin-encoding gene, Ostn, had their hearts extracted and exposed to an ex vivo ischemia-reperfusion protocol or biochemical studies. Disruption of musclin signaling abolished the ability of exercise to mitigate cardiac ischemic injury. This impaired cardioprotection was associated with reduced mitochondrial content and function linked to blunted cyclic guanosine monophosphate (cGMP) signaling. Genetic deletion of musclin reduced the nuclear abundance of protein kinase G (PKGI) and cyclic adenosine monophosphate (cAMP) response element binding (CREB), resulting in suppression of the master regulator of mitochondrial biogenesis, peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α), and its downstream targets in response to physical activity. Synthetic musclin peptide pharmacokinetic parameters were defined and used to calculate the infusion rate necessary to maintain its plasma level comparable to that observed after exercise. This infusion was found to reproduce the cardioprotective benefits of exercise in sedentary WT and Ostn-KO mice. Musclin is essential for exercise-induced cardiac protection. Boosting musclin signaling might serve as a novel therapeutic strategy for cardioprotection.

Keywords:  cardioprotection; exercise; heart disease; ischemia; musclin; natriuretic peptide; osteocrin; pharmacokinetics; preconditioning; reperfusion; stress resistance

DOI:  https://doi.org/10.3390/ijms24076525
Int J Mol Sci. 2023 Mar 29. pii: 6454. [Epub ahead of print]24(7):

Main Pathogenic Mechanisms and Recent Advances in COPD Peripheral Skeletal Muscle Wasting.

Pauline Henrot, Isabelle Dupin, Pierre Schilfarth, Pauline Esteves, Léo Blervaque, Maéva Zysman, Fares Gouzi, Maurice Hayot, Pascal Pomiès, Patrick Berger.

  Chronic obstructive pulmonary disease (COPD) is a worldwide prevalent respiratory disease mainly caused by tobacco smoke exposure. COPD is now considered as a systemic disease with several comorbidities. Among them, skeletal muscle dysfunction affects around 20% of COPD patients and is associated with higher morbidity and mortality. Although the histological alterations are well characterized, including myofiber atrophy, a decreased proportion of slow-twitch myofibers, and a decreased capillarization and oxidative phosphorylation capacity, the molecular basis for muscle atrophy is complex and remains partly unknown. Major difficulties lie in patient heterogeneity, accessing patients' samples, and complex multifactorial process including extrinsic mechanisms, such as tobacco smoke or disuse, and intrinsic mechanisms, such as oxidative stress, hypoxia, or systemic inflammation. Muscle wasting is also a highly dynamic process whose investigation is hampered by the differential protein regulation according to the stage of atrophy. In this review, we report and discuss recent data regarding the molecular alterations in COPD leading to impaired muscle mass, including inflammation, hypoxia and hypercapnia, mitochondrial dysfunction, diverse metabolic changes such as oxidative and nitrosative stress and genetic and epigenetic modifications, all leading to an impaired anabolic/catabolic balance in the myocyte. We recapitulate data concerning skeletal muscle dysfunction obtained in the different rodent models of COPD. Finally, we propose several pathways that should be investigated in COPD skeletal muscle dysfunction in the future.

Keywords:  cachexia; interleukin; metabolism; myocyte

DOI:  https://doi.org/10.3390/ijms24076454
J Biomech. 2023 Apr 07. pii: S0021-9290(23)00148-3. [Epub ahead of print]152 111579

The history-dependent features of muscle force production: A challenge to the cross-bridge theory and their functional implications.

Daniel Hahn, Seong-Won Han, Venus Joumaa.

  The cross-bridge theory predicts that muscle force is determined by muscle length and the velocity of active muscle length changes. However, before the formulation of the cross-bridge theory, it had been observed that the isometric force at a given muscle length is enhanced or depressed depending on active muscle length changes before that given length is reached. These enhanced and depressed force states are termed residual force enhancement (rFE) and residual force depression (rFD), respectively, and together they are known as the history-dependent features of muscle force production. In this review, we introduce early attempts in explaining rFE and rFD before we discuss more recent research from the past 25 years which has contributed to a better understanding of the mechanisms underpinning rFE and rFD. Specifically, we discuss the increasing number of findings on rFE and rFD which challenge the cross-bridge theory and propose that the elastic element titin plays a role in explaining muscle history-dependence. Accordingly, new three-filament models of force production including titin seem to provide better insight into the mechanism of muscle contraction. Complementary to the mechanisms behind muscle history-dependence, we also show various implications for muscle history-dependence on in-vivo human muscle function such as during stretch-shortening cycles. We conclude that titin function needs to be better understood if a new three-filament muscle model which includes titin, is to be established. From an applied perspective, it remains to be elucidated how muscle history-dependence affects locomotion and motor control, and whether history-dependent features can be changed by training.

Keywords:  Active force; Cross-bridges; Force-length relationship; Force-velocity relationship; Passive force enhancement; Residual force depression; Residual force enhancement; Stiffness; Stretch-shortening cycle; Titin

DOI:  https://doi.org/10.1016/j.jbiomech.2023.111579
Int J Biol Sci. 2023 ;19(5): 1579-1596

Tectorigenin targets PKACα to promote GLUT4 expression in skeletal muscle and improve insulin resistance in vitro and in vivo.

Xinlei Yao, Lei Liu, Wenjun Shao, Miao Bai, Xiaohan Ding, Geng Wang, Shuyue Wang, Lihua Zheng, Ying Sun, Guannan Wang, Yanxin Huang, Chunlei Yu, Zhenbo Song, Yongli Bao, Shaonian Yang, Luguo Sun.

  The decreased expression and dysfunction of glucose transporter 4 (GLUT4), the insulin-responsive glucose transporter, are closely related to the occurrence of insulin resistance (IR). To improve the expression of GLUT4 may represent a promising strategy to prevent and treat IR and type 2 diabetes (T2DM). Here, we demonstrate that the natural compound tectorigenin (TG) enhances GLUT4 expression, glucose uptake and insulin responsiveness via activating AMP-activated protein kinase (AMPK)/myocyte enhancer factor 2 (MEF2) signaling in both normal and IR skeletal muscle cells and tissues. Accordingly, prophylactic and therapeutic uses of TG can significantly ameliorate IR and hyperglycemia in T2DM mice. Mechanistically, we identify protein kinase A catalytic subunit α (PKACα) as the target of TG to increase GLUT4 expression and TG-PKACα binding promotes the dissociation of PKACα from the regulatory subunits, leading to the activation of PKA/AMPK signaling. PKACα knockdown in local quadriceps muscles almost completely abolished the therapeutic effects of TG on IR and T2DM, as well as the enhancement on AMPK signaling and GLUT4 expression in skeletal muscle. This study supports TG as a new drug candidate to treat IR and its related diseases, but also enriches our knowledge of PKA signaling in glucose metabolism in skeletal muscle.

Keywords:  AMPK; GLUT4; PKACα; insulin resistance; tectorigenin

DOI:  https://doi.org/10.7150/ijbs.80125
J Appl Physiol (1985). 2023 Apr 13.

Blood flow restriction does not alter the early hypertrophic signaling and short-term adaptive response to resistance exercise when performed to task failure.

Christopher Pignanelli, Graham P Holloway, Jamie F Burr.

  Previous research supports that low-load resistance exercise with BFR (LL-BFR) acutely increases physiological responses and muscle mass accrual compared to low-load resistance exercise (LL-RE) alone. However, most studies have work-matched LL-BFR and LL-RE. Completing sets to similar perceived efforts, thereby allowing for a variable amount of work, may provide a more ecologically valid approach to compare LL-BFR and LL-RE. This study aimed to examine acute signaling and training responses following LL-RE or LL-BFR performed to task failure. Ten participants had each leg randomly assigned to perform LL-RE or LL-BFR. Muscle biopsies were obtained before and two-hours after the first exercise bout and after 6-weeks of training for Western blot and immunohistochemistry analyses. Repeated measure ANOVA and intraclass coefficients (ICC) were used to compare responses of each condition. After exercise, AKT(T308) phosphorylation increased after LL-RE and LL-BFR (both ~145% of baseline, p<0.05) and trended for p70 S6K(T389) (LL-RE: ~158% and LL-BFR: ~137%, p=0.06). BFR did not alter these responses, resulting in fair-excellent ICCs for signaling proteins involved in anabolism (ICCAKT(T308)=0.889, p=0.001; ICCAKT(S473) =0.519, p=0.074; ICCp70 S6K(T389)=0.514, p=0.105). After training, muscle fiber cross-sectional area and vastus lateralis whole-muscle thickness were similar between conditions (ICC≥ 0.637, p≤0.031). Similar acute and chronic responses between conditions and high ICC values between legs suggest that both LL-BFR and LL-RE performed by the same person result in similar adaptations. These data support the concept that sufficient muscular exertion is a key factor for training-induced muscle hypertrophy with low-load resistance exercise independent of total work and blood flow.

Keywords:  Ischemia; Maximal repetitions; Oxygen availability; Volitional fatigue

DOI:  https://doi.org/10.1152/japplphysiol.00529.2022
J Appl Physiol (1985). 2023 Apr 13.

The effect of single-leg disuse on skeletal muscle strength and size in the non-immobilized leg of uninjured adults: A meta-analysis.

Nicholas Preobrazenski, Ian Janssen, Chris McGlory.

  The effects of single-leg immobilization on changes in skeletal muscle strength and size in the non-immobilized leg remains controversial. Some studies have shown decreases, or even increases, in skeletal muscle strength and size of the non-immobilized leg, thus challenging its role as an internal control. Here we meta-analyze changes in knee extensor strength and size in the non-immobilized leg of non-injured adults who participated in single-leg disuse studies. We extracted data from the non-immobilized leg of participants from 15 of 40 studies included in our previous meta-analysis on single-leg disuse. Single-leg disuse had a trivial effect on knee extensor strength (Hedges gav = -0.13 [-0.23, -0.03], p<0.01, -3.6±5.6%, N=13 studies, n=194 participants) and no impact on knee extensor size (0.06 [-0.06, 0.19], p=0.21, 0.8±2.9%, N=9, n=107) in the non-immobilized leg. By comparison, single-leg disuse had a large effect on knee extensor strength (-0.85 [-1.01, -0.69], p<0.01, -20.4±6.4%; mean difference between legs = 16.8±7.8% [12.8, 20.8], p<0.001) and a medium effect on knee extensor size (-0.40 [-0.55, -0.25], p<0.01, -7.0±4%; mean difference = 7.8±5.6% [11.6, 4.0], p<0.002). These results highlight the utility of the non-immobilized leg to act as an internal control in single-leg immobilization studies.

Keywords:  immobilization; muscle disuse; size; skeletal muscle; strength

DOI:  https://doi.org/10.1152/japplphysiol.00147.2023
Biochim Biophys Acta Mol Basis Dis. 2023 Apr 06. pii: S0925-4439(23)00075-3. [Epub ahead of print] 166709

Exercise training impacts skeletal muscle remodelling induced by metabolic syndrome in ZSF1 rats through metabolism regulation.

Rita Nogueira-Ferreira, Inês Santos, Rita Ferreira, Dulce Fontoura, Cláudia Sousa-Mendes, Inês Falcão-Pires, André Lourenço, Adelino Leite-Moreira, Iola F Duarte, Daniel Moreira-Gonçalves.

  Metabolic syndrome (MetS), characterized by a set of conditions that include obesity, hypertension, and dyslipidemia, is associated with increased cardiovascular risk. Exercise training (EX) has been reported to improve MetS management, although the underlying metabolic adaptations that drive its benefits remain poorly understood. This work aims to characterize the molecular changes induced by EX in skeletal muscle in MetS, focusing on gastrocnemius metabolic remodelling. 1H NMR metabolomics and molecular assays were employed to assess the metabolic profile of skeletal muscle tissue from lean male ZSF1 rats (CTL), obese sedentary male ZSF1 rats (MetS-SED), and obese male ZF1 rats submitted to 4 weeks of treadmill EX (5 days/week, 60 min/day, 15 m/min) (MetS-EX). EX did not counteract the significant increase of body weight and circulating lipid profile, but had an anti-inflammatory effect and improved exercise capacity. The decreased gastrocnemius mass observed in MetS was paralleled with glycogen degradation into small glucose oligosaccharides, with the release of glucose-1-phosphate, and an increase in glucose-6-phosphate and glucose levels. Moreover, sedentary MetS animals' muscle exhibited lower AMPK expression levels and higher amino acids' metabolism such as glutamine and glutamate, compared to lean animals. In contrast, the EX group showed changes suggesting an increase in fatty acid oxidation and oxidative phosphorylation. Additionally, EX mitigated MetS-induced fiber atrophy and fibrosis in the gastrocnemius muscle. EX had a positive effect on gastrocnemius metabolism by enhancing oxidative metabolism and, consequently, reducing susceptibility to fatigue. These findings reinforce the importance of prescribing EX programs to patients with MetS.

Keywords:  Gastrocnemius; Metabolic syndrome; Metabolism; Metabolomics; Treadmill exercise

DOI:  https://doi.org/10.1016/j.bbadis.2023.166709
Int J Mol Sci. 2023 Mar 23. pii: 6017. [Epub ahead of print]24(7):

The Potential Modulatory Effects of Exercise on Skeletal Muscle Redox Status in Chronic Kidney Disease.

Sara Mendes, Diogo V Leal, Luke A Baker, Aníbal Ferreira, Alice C Smith, João L Viana.

  Chronic Kidney Disease (CKD) is a global health burden with high mortality and health costs. CKD patients exhibit lower cardiorespiratory and muscular fitness, strongly associated with morbidity/mortality, which is exacerbated when they reach the need for renal replacement therapies (RRT). Muscle wasting in CKD has been associated with an inflammatory/oxidative status affecting the resident cells' microenvironment, decreasing repair capacity and leading to atrophy. Exercise may help counteracting such effects; however, the molecular mechanisms remain uncertain. Thus, trying to pinpoint and understand these mechanisms is of particular interest. This review will start with a general background about myogenesis, followed by an overview of the impact of redox imbalance as a mechanism of muscle wasting in CKD, with focus on the modulatory effect of exercise on the skeletal muscle microenvironment.

Keywords:  chronic kidney disease; exercise; oxidative stress; reactive oxygen species (ROS); skeletal muscle wasting

DOI:  https://doi.org/10.3390/ijms24076017
JCI Insight. 2023 Apr 10. pii: e165867. [Epub ahead of print]8(7):

Plasma proteomic changes in response to exercise training are associated with cardiorespiratory fitness adaptations.

Jeremy M Robbins, Prashant Rao, Shuliang Deng, Michelle J Keyes, Usman A Tahir, Daniel H Katz, Pierre M Jean Beltran, François Marchildon, Jacob L Barber, Bennet Peterson, Yan Gao, Adolfo Correa, James G Wilson, J Gustav Smith, Paul Cohen, Robert Ross, Claude Bouchard, Mark A Sarzynski, Robert E Gerszten.

  Regular exercise leads to widespread salutary effects, and there is increasing recognition that exercise-stimulated circulating proteins can impart health benefits. Despite this, limited data exist regarding the plasma proteomic changes that occur in response to regular exercise. Here, we perform large-scale plasma proteomic profiling in 654 healthy human study participants before and after a supervised, 20-week endurance exercise training intervention. We identify hundreds of circulating proteins that are modulated, many of which are known to be secreted. We highlight proteins involved in angiogenesis, iron homeostasis, and the extracellular matrix, many of which are novel, including training-induced increases in fibroblast activation protein (FAP), a membrane-bound and circulating protein relevant in body-composition homeostasis. We relate protein changes to training-induced maximal oxygen uptake adaptations and validate our top findings in an external exercise cohort. Furthermore, we show that FAP is positively associated with survival in 3 separate, population-based cohorts.

Keywords:  Cardiology; Cardiovascular disease; Extracellular matrix; Metabolism; Proteomics

DOI:  https://doi.org/10.1172/jci.insight.165867
Cells. 2023 Mar 24. pii: 1005. [Epub ahead of print]12(7):

Targeted Demethylation of the TGFβ1 mRNA Promotes Myoblast Proliferation via Activating the SMAD2 Signaling Pathway.

Kaiping Deng, Zhipeng Liu, Xiaodan Li, Zhen Zhang, Yixuan Fan, Qunhao Huang, Yanli Zhang, Feng Wang.

  Recent evidence suggested that N6-methyladenosine (m6A) methylation can determine m6A-modified mRNA fate and play an important role in skeletal muscle development. It was well known that transforming growth factor beta 1 (TGFβ1) is involved in a variety of cellular processes, such as proliferation, differentiation, and apoptosis. However, little is known about the m6A-mediated TGFβ1 regulation in myogenesis. Here, we observed an increase in endogenous TGFβ1 expression and activity during myotube differentiation. However, the knockdown of TGFβ1 inhibits the proliferation and induces cell apoptosis of myoblast. Moreover, we found that m6A in 5'-untranslated regions (5'UTR) of TGFβ1 promote its decay and inhibit its expression, leading to the blockage of the TGFβ1/SMAD2 signaling pathway. Furthermore, the targeted specific demethylation of TGFβ1 m6A using dCas13b-FTO significantly increased the TGFβ1-mediated activity of the SMAD2 signaling pathway, promoting myoblast proliferation. These findings suggest that TGFβ1 is an essential regulator of myoblast growth that is negatively regulated by m6A. Overall, these results highlight the critical role of m6A-mediated post-transcriptional regulation in myogenesis.

Keywords:  TGFβ1; cell proliferation; dCas13b; m6A; myoblast

DOI:  https://doi.org/10.3390/cells12071005
J Exp Biol. 2023 Apr 01. pii: jeb243561. [Epub ahead of print]226(7):

Perturbing the muscle work loop paradigm to unravel the neuromechanics of unsteady locomotion.

Simon Sponberg, Emily Abbott, Gregory S Sawicki.

  Muscle function during movement is more than a simple, linear transformation of neural activity into force. The classic work loop technique has pioneered our understanding of muscle, but typically only characterizes function during unperturbed movement cycles, such as those experienced during steady walking, running, swimming and flying. Yet perturbations away from steady movement often place greater demands on muscle structure and function and offer a unique window into muscle's broader capacity. Recently, studies in diverse organisms from cockroaches to humans have started to grapple with muscle function in unsteady (perturbed, transient and fluctuating) conditions, but the vast range of possible parameters and the challenge of connecting in vitro to in vivo experiments are daunting. Here, we review and organize these studies into two broad approaches that extend the classic work loop paradigm. First, in the top-down approach, researchers record length and activation patterns of natural locomotion under perturbed conditions, replay these conditions in isolated muscle work loop experiments to reveal the mechanism by which muscle mediates a change in body dynamics and, finally, generalize across conditions and scale. Second, in the bottom-up approach, researchers start with an isolated muscle work loop and then add structural complexity, simulated loads and neural feedback to ultimately emulate the muscle's neuromechanical context during perturbed movement. In isolation, each of these approaches has several limitations, but new models and experimental methods coupled with the formal language of control theory give several avenues for synthesizing an understanding of muscle function under unsteady conditions.

Keywords:  Closed loop feedback control; Muscle force production; Neuromechanics; Perturbation; Tendon elasticity; Unsteady locomotion

DOI:  https://doi.org/10.1242/jeb.243561
J Cachexia Sarcopenia Muscle. 2023 Apr 15.

Direct electrical stimulation impacts on neuromuscular junction morphology on both stimulated and unstimulated contralateral soleus.

Young Il Lee, Nicola Cacciani, Ya Wen, Xiang Zhang, Yvette Hedström, Wesley Thompson, Lars Larsson.

  BACKGROUND: There is increasing evidence of crosstalk between organs. The neuromuscular junction (NMJ) is a peripheral chemical synapse whose function and morphology are sensitive to acetylcholine (ACh) release and muscle depolarization. In an attempt to improve our understanding of NMJ plasticity and muscle crosstalk, the effects of unilateral direct electrical stimulation of a hindlimb muscle on the NMJ were investigated in rats exposed long-term post-synaptic neuromuscular blockade.METHODS: Sprague Dawley rats were subjected to post-synaptic blockade of neuromuscular transmission by systemic administration of α-cobrotoxin and mechanically ventilated for up to 8 days and compared with untreated sham operated controls and animals exposed to unilateral chronic electrical stimulation 12 h/day for 5 or 8 days.
RESULTS: NMJs produced axonal and glial sprouts (growth of processes that extend beyond the confines of the synapse defined by high-density aggregates of acetylcholine receptors [AChRs]) in response to post-synaptic neuromuscular blockade, but less than reported after peripheral denervation or pre-synaptic blockade. Direct electrical soleus muscle stimulation reduced the terminal Schwann cell (tSC) and axonal sprouting in both stimulated and non-stimulated contralateral soleus. Eight days chronic stimulation reduced (P < 0.001) the number of tSC sprouts on stimulated and non-stimulated soleus from 6.7 ± 0.5 and 6.9 ± 0.5 sprouts per NMJ, respectively, compared with 10.3 ± 0.9 tSC per NMJ (P < 0.001) in non-stimulated soleus from rats immobilized for 8 days. A similar reduction of axonal sprouts (P < 0.001) was observed in stimulated and non-stimulated contralateral soleus in response to chronic electrical stimulation. RNAseq-based gene expression analyses confirmed a restoring effect on both stimulated and unstimulated contralateral muscle. The cross-over effect was paralleled by increased cytokine/chemokine levels in stimulated and contralateral unstimulated muscle as well as in plasma.
CONCLUSIONS: Motor axon terminals and terminal Schwann cells at NMJs of rats subjected to post-synaptic neuromuscular blockade exhibited sprouting responses. These axonal and glial responses were likely dampened by a muscle-derived myokines released in an activity-dependent manner with both local and systemic effects.

Keywords:  Chronic electrical stimulation; Crossover effect; Neuromuscular junction; Post-synaptic neuromuscular blockade; Soleus muscle; Terminal sprouting

DOI:  https://doi.org/10.1002/jcsm.13235
Cell Rep. 2023 Apr 13. pii: S2211-1247(23)00403-5. [Epub ahead of print]42(4): 112392

Exercise training remodels inguinal white adipose tissue through adaptations in innervation, vascularization, and the extracellular matrix.

Pasquale Nigro, Maria Vamvini, Jiekun Yang, Tiziana Caputo, Li-Lun Ho, Nicholas P Carbone, Danae Papadopoulos, Royce Conlin, Jie He, Michael F Hirshman, Joseph D White, Jacques Robidoux, Robert C Hickner, Søren Nielsen, Bente K Pedersen, Manolis Kellis, Roeland J W Middelbeek, Laurie J Goodyear.

  Inguinal white adipose tissue (iWAT) is essential for the beneficial effects of exercise training on metabolic health. The underlying mechanisms for these effects are not fully understood, and here, we test the hypothesis that exercise training results in a more favorable iWAT structural phenotype. Using biochemical, imaging, and multi-omics analyses, we find that 11 days of wheel running in male mice causes profound iWAT remodeling including decreased extracellular matrix (ECM) deposition and increased vascularization and innervation. We identify adipose stem cells as one of the main contributors to training-induced ECM remodeling, show that the PRDM16 transcriptional complex is necessary for iWAT remodeling and beiging, and discover neuronal growth regulator 1 (NEGR1) as a link between PRDM16 and neuritogenesis. Moreover, we find that training causes a shift from hypertrophic to insulin-sensitive adipocyte subpopulations. Exercise training leads to remarkable adaptations to iWAT structure and cell-type composition that can confer beneficial changes in tissue metabolism.

Keywords:  Adipo-Clear; CP: Metabolism; CP: Molecular biology; ECM; NEGR1; PRDM16; exercise; innervation; proteomics; spatial transcriptomics; vascularization; white adipose tissue

DOI:  https://doi.org/10.1016/j.celrep.2023.112392
Int J Mol Sci. 2023 Mar 30. pii: 6513. [Epub ahead of print]24(7):

The Role of the Piezo1 Mechanosensitive Channel in the Musculoskeletal System.

Beatrix Dienes, Tamás Bazsó, László Szabó, László Csernoch.

  Since the recent discovery of the mechanosensitive Piezo1 channels, many studies have addressed the role of the channel in various physiological or even pathological processes of different organs. Although the number of studies on their effects on the musculoskeletal system is constantly increasing, we are still far from a precise understanding. In this review, the knowledge available so far regarding the musculoskeletal system is summarized, reviewing the results achieved in the field of skeletal muscles, bones, joints and cartilage, tendons and ligaments, as well as intervertebral discs.

Keywords:  Piezo1; Yoda1; bone; calcium homeostasis; cartilage; joint; ligament; mechanosensitive channels; skeletal muscle; tendon

DOI:  https://doi.org/10.3390/ijms24076513
Nat Aging. 2022 Jun;2(6): 484-493

The relationship between epigenetic age and the hallmarks of aging in human cells.

Sylwia Kabacik, Donna Lowe, Leonie Fransen, Martin Leonard, Siew-Lan Ang, Christopher Whiteman, Sarah Corsi, Howard Cohen, Sarah Felton, Radhika Bali, Steve Horvath, Ken Raj.

Epigenetic clocks are mathematically derived age estimators that are based on combinations of methylation values that change with age at specific CpGs in the genome. These clocks are widely used to measure the age of tissues and cells1,2. The discrepancy between epigenetic age (EpiAge), as estimated by these clocks, and chronological age is referred to as EpiAge acceleration. Epidemiological studies have linked EpiAge acceleration to a wide variety of pathologies, health states, lifestyle, mental state and environmental factors2, indicating that epigenetic clocks tap into critical biological processes that are involved in aging. Despite the importance of this inference, the mechanisms underpinning these clocks remained largely uncharacterized and unelucidated. Here, using primary human cells, we set out to investigate whether epigenetic aging is the manifestation of one or more of the aging hallmarks previously identified3. We show that although epigenetic aging is distinct from cellular senescence, telomere attrition and genomic instability, it is associated with nutrient sensing, mitochondrial activity and stem cell composition.

DOI: https://doi.org/10.1038/s43587-022-00220-0