bims-moremu 2024-08-25 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024–08–25
29 papers selected by
Anna Vainshtein, Craft Science Inc.

The clockwork of champions: Influence of circadian biology on exercise performance.
Hydrogel biomaterials that stiffen and soften on demand reveal that skeletal muscle stem cells harbor a mechanical memory.
Muscle-derived IL-1β regulates EcSOD expression via the NBR1-p62-Nrf2 pathway in muscle during cancer cachexia.
Quantifying Muscle Regeneration: Activated Muscle Satellite Cells and New Regenerated Myofibers in Chronic and Acute Degeneration Models.
Involvement of lysophosphatidic acid-LPA1-YAP signaling in healthy and pathological FAPs migration.
Skeletal muscle adaptations following eccentric contractions are not mediated by keratin 18.
Sarcopenia is attenuated by mairin in SAMP8 mice via the inhibition of FAPs fibrosis through the AMPK-TGF-β-SMAD axis.
The human AMPKγ3 R225W mutation negatively impacts site-1 nucleotide binding and does not enhance basal AMPKγ3-associated activity nor glycogen production in human or mouse skeletal muscle.
Critical variables regulating age-related anabolic responses to protein nutrition in skeletal muscle.
Insights into the influence of high-intensity interval training on skeletal muscle clock gene expression in insulin-resistant individuals.
Physical exercise in amyotrophic lateral sclerosis: a potential co-adjuvant therapeutic option to counteract disease progression.
High mobility group box 1 (HMGB1) is a potential disease biomarker in cell and mouse models of Duchenne muscular dystrophy.
Fatiguing exercise reduces cellular passive Young's modulus in human vastus lateralis muscle.
Unlocking peak performance: The role of Nrf2 in enhancing exercise outcomes and training adaptation in humans.
BCL2L13 at endoplasmic reticulum-mitochondria contact sites regulates calcium homeostasis to maintain skeletal muscle function.
Pathophysiological role of connexin and pannexin hemichannels in neuromuscular disorders.
In dystrophic mdx hindlimb muscles where fibrosis is limited versican haploinsufficiency transiently improves contractile function without reducing inflammation.
Proteomic Profiling of Hindlimb Skeletal Muscle Disuse in a Murine Model of Sepsis.
Reduced myotube diameter induced by combined inhibition of transforming growth factor-β type I receptors Acvr1b and Tgfbr1 is associated with enhanced β1-syntrophin expression.
Muscle memory in humans: evidence for myonuclear permanence and long-term transcriptional regulation after strength training.
Duchenne muscular dystrophy skeletal muscle cells derived from human induced pluripotent stem cells recapitulate various calcium dysregulation pathways.
Extracellular vesicles may provide an alternative detoxification pathway during skeletal muscle myoblast ageing.
Quercetin induces a slow myofiber phenotype in engineered human skeletal muscle tissues.
Five days of bed rest in young and old adults: Retainment of skeletal muscle mass with neuromuscular electrical stimulation.
Succinate dehydrogenase-complex II regulates skeletal muscle cellular respiration and contractility but not muscle mass in genetically induced pulmonary emphysema.
MicroRNAs and their Modulatory Effect on the Hallmarks of Osteosarcopenia.
Small molecule inhibition of glycogen synthase I reduces muscle glycogen content and improves biomarkers in a mouse model of Pompe disease.
SPECIFIC TENSION OF HUMAN MUSCLE IN VIVO: A SYSTEMATIC REVIEW.
Mechanoresponsive regulation of myogenesis by the force-sensing transcriptional regulator Tono.

Free Radic Biol Med. 2024 Aug 19. pii: S0891-5849(24)00607-5. [Epub ahead of print]224 78-87

The clockwork of champions: Influence of circadian biology on exercise performance.

Stuart J Hesketh, Karyn A Esser.

  Exercise physiology and circadian biology are distinct and long-standing fields. Recently they have seen increased integration, largely due to the discovery of the molecular components of the circadian clock and recognition of human exercise performance differences over time-of-day. Circadian clocks, ubiquitous in cells, regulate a daily tissue specific program of gene expression that contribute to temporal patterns of physiological functions over a 24-h cycle. Understanding how circadian clock function in skeletal muscle, as well as other tissues contribute to exercise performance is still in the very early stages. This review provides background on this emerging field with a review of early exercise and time-of-day studies in both human and animals. We then move into the role of the circadian clock and its daily program of gene expression in skeletal muscle with a focus on specific metabolic and physiological outputs that vary over time-of-day. Lastly, we discuss the recognition that the timing of exercise communicates with the skeletal muscle circadian clock to adjust its phase settings and why this maybe important for performance and health.

Keywords:  Circadian rhythm; Endurance; Exercise physiology; Molecular clock; Performance; Skeletal muscle; Strength

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.08.020
Proc Natl Acad Sci U S A. 2024 Aug 27. 121(35): e2406787121

Hydrogel biomaterials that stiffen and soften on demand reveal that skeletal muscle stem cells harbor a mechanical memory.

Christopher M Madl, Yu Xin Wang, Colin A Holbrook, Shiqi Su, Xuechen Shi, Fitzroy J Byfield, Gwendoline Wicki, Iris A Flaig, Helen M Blau.

  Muscle stem cells (MuSCs) are specialized cells that reside in adult skeletal muscle poised to repair muscle tissue. The ability of MuSCs to regenerate damaged tissues declines markedly with aging and in diseases such as Duchenne muscular dystrophy, but the underlying causes of MuSC dysfunction remain poorly understood. Both aging and disease result in dramatic increases in the stiffness of the muscle tissue microenvironment from fibrosis. MuSCs are known to lose their regenerative potential if cultured on stiff plastic substrates. We sought to determine whether MuSCs harbor a memory of their past microenvironment and if it can be overcome. We tested MuSCs in situ using dynamic hydrogel biomaterials that soften or stiffen on demand in response to light and found that freshly isolated MuSCs develop a persistent memory of substrate stiffness characterized by loss of proliferative progenitors within the first three days of culture on stiff substrates. MuSCs cultured on soft hydrogels had altered cytoskeletal organization and activity of Rho and Rac guanosine triphosphate hydrolase (GTPase) and Yes-associated protein mechanotransduction pathways compared to those on stiff hydrogels. Pharmacologic inhibition identified RhoA activation as responsible for the mechanical memory phenotype, and single-cell RNA sequencing revealed a molecular signature of the mechanical memory. These studies highlight that microenvironmental stiffness regulates MuSC fate and leads to MuSC dysfunction that is not readily reversed by changing stiffness. Our results suggest that stiffness can be circumvented by targeting downstream signaling pathways to overcome stem cell dysfunction in aged and disease states with aberrant fibrotic tissue mechanics.

Keywords:  dynamic hydrogels; fibrosis; mechanical memory; mechanotransduction; muscle stem cells

DOI:  https://doi.org/10.1073/pnas.2406787121
J Physiol. 2024 Aug 21.

Muscle-derived IL-1β regulates EcSOD expression via the NBR1-p62-Nrf2 pathway in muscle during cancer cachexia.

Mami Yamada, Eiji Warabi, Hisashi Oishi, Vitor A Lira, Mitsuharu Okutsu.

  Oxidative stress contributes to the loss of skeletal muscle mass and function in cancer cachexia. However, this outcome may be mitigated by an improved endogenous antioxidant defence system. Here, using the well-established oxidative stress-inducing muscle atrophy model of Lewis lung carcinoma (LLC) in 13-week-old male C57BL/6J mice, we demonstrate that extracellular superoxide dismutase (EcSOD) levels increase in the cachexia-prone extensor digitorum longus muscle. LLC transplantation significantly increased interleukin-1β (IL-1β) expression and release from extensor digitorum longus muscle fibres. Moreover, IL-1β treatment of C2C12 myotubes increased NBR1, p62 phosphorylation at Ser351, Nrf2 nuclear translocation and EcSOD protein expression. Additional studies in vivo indicated that intramuscular IL-1β injection is sufficient to stimulate EcSOD expression, which is prevented by muscle-specific knockout of p62 and Nrf2 (i.e. in p62 skmKO and Nrf2 skmKO mice, respectively). Finally, since an increase in circulating IL-1β may lead to unwanted outcomes, we demonstrate that targeting this pathway at p62 is sufficient to drive muscle EcSOD expression in an Nrf2-dependent manner. In summary, cancer cachexia increases EcSOD expression in extensor digitorum longus muscle via muscle-derived IL-1β-induced upregulation of p62 phosphorylation and Nrf2 activation. These findings provide further mechanistic evidence for the therapeutic potential of p62 and Nrf2 to mitigate cancer cachexia-induced muscle atrophy. KEY POINTS: Oxidative stress plays an important role in muscle atrophy during cancer cachexia. EcSOD, which mitigates muscle loss during oxidative stress, is upregulated in 13-week-old male C57BL/6J mice of extensor digitorum longus muscles during cancer cachexia. Using mouse and cellular models, we demonstrate that cancer cachexia promotes muscle EcSOD protein expression via muscle-derived IL-1β-dependent stimulation of the NBR1-p62-Nrf2 signalling pathway. These results provide further evidence for the potential therapeutic targeting of the NBR1-p62-Nrf2 signalling pathway downstream of IL-1β to mitigate cancer cachexia-induced muscle atrophy.

Keywords:  NBR1; Nrf2; SQSTM1/p62; extracellular superoxide dismutase; interleukin‐1β; muscle atrophy; skeletal muscle

DOI:  https://doi.org/10.1113/JP286460
Methods Mol Biol. 2024 Aug 21.

Quantifying Muscle Regeneration: Activated Muscle Satellite Cells and New Regenerated Myofibers in Chronic and Acute Degeneration Models.

Antonio Fernando Ribeiro Junior, Brandow Willy Souza, Mariz Vainzof.

  Regeneration is a remarkable characteristic of the skeletal muscle. Triggered by common lesions, regeneration is stimulated resulting in muscle fiber repair and restoration of muscle homeostasis in normal muscle. In genetic dystrophic muscle, the cycle of degeneration/regeneration is an endless loop that leads to impaired regeneration and substitution of muscle fibers by connective and adipose tissue, causing muscle weakness. Identification and characterization of muscle regeneration steps can help discover potential therapy targets for muscle diseases and aging. Muscle regeneration markers such as the number of satellite cells in the muscle, the proportion of activated satellite cells, and the quantity of regenerating muscle fiber can be quantified using immunolabeling.Here we are presenting a quantitative method to measure muscle regeneration that can be applied to different proposals. To demonstrate the protocol applicability, we used models for acute and chronic muscle injuries. As model of acute degeneration, a wild-type C57BL6 mice with muscle injury induced by electroporation was used, and the muscle was analyzed after 5 and 10 days post-injury. DMDmdx mouse muscle was used as a model of chronic degeneration. The methodologies presented here are among the gold standard methodologies for muscle regeneration analysis and can be easily applied to any type of muscle regeneration study.

Keywords:  Developmental myosin; Electroporation; Immunofluorescence; Muscle regeneration; Muscular dystrophies; Neuromuscular disease; PAX7; Satellite cells; Skeletal muscle

DOI:  https://doi.org/10.1007/7651_2024_564
Matrix Biol. 2024 Aug 15. pii: S0945-053X(24)00107-0. [Epub ahead of print]

Involvement of lysophosphatidic acid-LPA1-YAP signaling in healthy and pathological FAPs migration.

Alexia Bock-Pereda, Meilyn Cruz-Soca, Felipe S Gallardo, Adriana Córdova-Casanova, Cristian Gutierrez-Rojas, Jennifer Faundez-Contreras, Jerold Chun, Juan Carlos Casar, Enrique Brandan.

  Skeletal muscle fibrosis is defined as the excessive accumulation of extracellular matrix (ECM) components and is a hallmark of muscular dystrophies. Fibro-adipogenic progenitors (FAPs) are the main source of ECM, and thus have been strongly implicated in fibrogenesis. In skeletal muscle fibrotic models, including muscular dystrophies, FAPs undergo dysregulations in terms of proliferation, differentiation, and apoptosis, however few studies have explored the impact of FAPs migration. Here, we studied fibroblast and FAPs migration and identified lysophosphatidic acid (LPA), a signaling lipid central to skeletal muscle fibrogenesis, as a significant migration inductor. We identified LPA receptor 1 (LPA1) mediated signaling as crucial for this effect through a mechanism dependent on the Hippo pathway, another pathway implicated in fibrosis across diverse tissues. This cross-talk favors the activation of the Yes-associated protein 1 (YAP) and Transcriptional coactivator with PDZ-binding motif (TAZ), leading to increased expression of fibrosis-associated genes. This study reveals the role of YAP in LPA-mediated fibrotic responses as inhibition of YAP transcriptional coactivator activity hinders LPA-induced migration in fibroblasts and FAPs. Moreover, we found that FAPs derived from the mdx4cv mice, a murine model of Duchenne muscular dystrophy, display a heightened migratory phenotype due to enhanced LPA signaling compared to wild-type FAPs. Remarkably, we found that the inhibition of LPA1 or YAP transcriptional coactivator activity in mdx4cv FAPs reverts this phenotype. In summary, the identified LPA-LPA1-YAP pathway emerges as a critical driver of skeletal muscle FAPs migration and provides insights into potential novel targets to mitigate fibrosis in muscular dystrophies.

Keywords:  Duchenne Muscular Dystrophy; FAPs; LPA; YAP/TAZ; cell migration

DOI:  https://doi.org/10.1016/j.matbio.2024.08.005
J Appl Physiol (1985). 2024 Aug 22.

Skeletal muscle adaptations following eccentric contractions are not mediated by keratin 18.

Muni Swamy Ganjayi, Samuel W Frank, Thomas A Krauss, Michael L York, Robert J Bloch, Cory W Baumann.

  The molecular mechanisms that drive muscle adaptations after eccentric exercise training are multifaceted and likely impacted by age. Previous studies have reported that many genes and proteins respond differently in young and older muscles following training. Keratin 18 (Krt18), a cytoskeletal protein involved in force transduction and organization, was found to be upregulated after muscles performed repeated bouts of eccentric contractions, with higher levels observed in young muscle compared to older muscle. Therefore, the purpose of this study was to determine if Krt18 mediates skeletal muscle adaptations following eccentric exercise training. The anterior crural muscles of Krt18 knockout (KO) and wild-type (WT) mice were subjected to either a single bout or repeated bouts of eccentric contractions, with isometric torque assessed across the initial and final bouts. Functionally, Krt18 KO and WT mice did not differ prior to performing any eccentric contractions (p≥0.100). Muscle strength (tetanic isometric torques) and the ability to adapt to eccentric exercise training were also consistent across strains at all time points (p≥0.169). Stated differently, immediate strength deficits and the recovery of strength following a single or multiple bouts of eccentric contractions were similar between Krt18 KO and WT mice. In summary, the absence of Krt18 does not impede the muscle's ability to adapt to repeated eccentric contractions, suggesting it is not essential for exercise-induced remodeling.

Keywords:  damage; exercise; injury; intermediate filaments; strength

DOI:  https://doi.org/10.1152/japplphysiol.00496.2024
Gene. 2024 Aug 17. pii: S0378-1119(24)00754-6. [Epub ahead of print]931 148873

Sarcopenia is attenuated by mairin in SAMP8 mice via the inhibition of FAPs fibrosis through the AMPK-TGF-β-SMAD axis.

Wen Zhong, Huanan Jia, Haiyan Zhu, Yuan Tian, Wei Huang, Qiyue Yang.

  Sarcopenia has become a prominent health problem among the elderly because of its adverse consequence, including physical disabilities and death. Fibro-adipogenic progenitors (FAPs) exhibit adipogenic and fibrogenic potencies and regulate skeletal muscle development, which plays important role in sarcopenia. Mairin, as an ingredient of Astragalus membranaceus, has the effect of anti-fibrosis. Therefore, we predicted that mairin targeted the fibrosis of FAPs and then affected sarcopenia. To verify our ideas, mairin (30 mg/kg/day or 60 mg/kg/day) was given to senescence accelerated mouse-prone 8 (SAMP8) mice by oral administration. Aging led to loss of weight, skeletal muscle mass, strength, and function, and an increase in muscle atrophy and fibrosis, while mairin administration inhibited physiological decline caused by aging. Similarly, mairin (20 μM or 40 μM) treatment enhanced FAP proliferation but blocked the differentiation into fibroblasts. Mechanically, mairin played an anti-fibrotic role via AMP-activated protein kinase-transforming growth factor beta-drosophila mothers against decapentaplegic protein (AMPK-TGF-β-SMAD) axis, as evidenced by increased phosphorylation of AMPKα and decreased TGF-β and phosphorylated-SMAD2/3. In addition, the potential target genes of mairin were explored by mRNA sequencing in our study. In conclusion, mairin may interfere with the AMPK/TGF-β/SMAD pathway to repress the fibrosis of FAPs and eventually ameliorate sarcopenia.

Keywords:  AMPK-TGF-β-SMAD; FAPs; Fibrosis; Mairin; Sarcopenia

DOI:  https://doi.org/10.1016/j.gene.2024.148873
Acta Physiol (Oxf). 2024 Aug 22. e14213

The human AMPKγ3 R225W mutation negatively impacts site-1 nucleotide binding and does not enhance basal AMPKγ3-associated activity nor glycogen production in human or mouse skeletal muscle.

Nicolas O Eskesen, Rasmus Kjøbsted, Jesper Bratz Birk, Nicolai S Henriksen, Nicoline R Andersen, Stine Ringholm, Henriette Pilegaard, Jørgen F P Wojtaszewski.

   AIM: AMP-activated protein kinase (AMPK) is activated during cellular energy perturbation. AMPK complexes are composed of three subunits and several variants of AMPK are expressed in skeletal muscle. The regulatory AMPKγ3 subunit is predominantly expressed in fast-twitch muscle fibers. A human AMPKγ3 R225W mutation has been described. The mutation increases the total pool of AMPK activity in cells cultured from R225W carrier muscle and is associated with increased glycogen levels in mature skeletal muscle. This led to the idea of AMPKγ3 being involved in the regulation of skeletal muscle glycogen levels. Evidence for this causative link remains to be provided.
METHODS: We studied muscle biopsies from human carriers of the AMPKγ3 R225W mutation and we developed a novel AMPKγ3 R225W knock-in mouse model (KI HOM). Through in vitro, in situ, and ex vivo techniques, we investigated AMPK activity, AMPK function, and glycogen levels in skeletal muscle of humans and mice.
RESULTS: In human carriers, the basal AMPKγ3-associated activity was reduced when assayed in the absence of exogenous AMP. No difference was observed when assayed under AMP saturation, which was supported by findings in muscle of KI HOM mice. Furthermore, effects of AICAR/muscle contraction on AMPKγ3-associated activity were absent in KI HOM muscle. Muscle glycogen levels were not affected by the mutation in human carriers or in KI HOM mice.
CONCLUSIONS: The AMPKγ3 R225W mutation does not impact the AMPK-associated activity in human skeletal muscle and the mutation is not linked to glycogen accumulation. The R225W mutation ablates the AMPKγ3-associated activation by AICAR/muscle contractions, presumably due to loss of nucleotide binding in the CBS 1 domain of AMPKγ3.

Keywords:  AICAR; AMPK; glycogen; muscle contraction; skeletal muscle

DOI:  https://doi.org/10.1111/apha.14213
Front Nutr. 2024 ;11 1419229

Critical variables regulating age-related anabolic responses to protein nutrition in skeletal muscle.

Colleen S Deane, Jake Cox, Philip J Atherton.

  Protein nutrition is critical for the maintenance of skeletal muscle mass across the lifecourse and for the growth of muscle in response to resistance exercise - both acting via the stimulation of protein synthesis. The transient anabolic response to protein feeding may vary in magnitude and duration, depending on, e.g., timing, dose, amino acid composition and delivery mode, which are in turn influenced by physical activity and age. This review aims to: (i) summarise the fundamental metabolic responses of muscle to protein feeding, (ii) discuss key variables regulating muscle anabolic responses to protein feeding, and (iii) explore how these variables can be optimised for muscle anabolism in response to physical activity and ageing.

Keywords:  ageing; exercise; muscle; nutrition; protein

DOI:  https://doi.org/10.3389/fnut.2024.1419229
J Physiol. 2024 Aug 19.

Insights into the influence of high-intensity interval training on skeletal muscle clock gene expression in insulin-resistant individuals.

Krystel Desjardins, Shima Taherkhani, Lyane Méthot, Victoria Castonguay, Jean-Philippe Leduc-Gaudet.



Keywords:  circadian rhythm; exercise training; insulin resistance; mitochondria; skeletal muscle

DOI:  https://doi.org/10.1113/JP286939
Front Cell Dev Biol. 2024 ;12 1421566

Physical exercise in amyotrophic lateral sclerosis: a potential co-adjuvant therapeutic option to counteract disease progression.

Gianmarco Fenili, Silvia Scaricamazza, Alberto Ferri, Cristiana Valle, Maria Paola Paronetto.

  Amyotrophic lateral sclerosis (ALS) is a fatal disorder characterized by the selective degeneration of upper and lower motor neurons, leading to progressive muscle weakness and atrophy. The mean survival time is two to five years. Although the hunt for drugs has greatly advanced over the past decade, no cure is available for ALS yet. The role of intense physical activity in the etiology of ALS has been debated for several decades without reaching a clear conclusion. The benefits of organized physical activity on fitness and mental health have been widely described. Indeed, by acting on specific mechanisms, physical activity can influence the physiology of several chronic conditions. It was shown to improve skeletal muscle metabolism and regeneration, neurogenesis, mitochondrial biogenesis, and antioxidant defense. Interestingly, all these pathways are involved in ALS pathology. This review will provide a broad overview of the effect of different exercise protocols on the onset and progression of ALS, both in humans and in animal models. Furthermore, we will discuss challenges and opportunities to exploit physiological responses of imposed exercise training for therapeutic purposes.

Keywords:  ALS; exercise; muscle atrophy; neurodegenerative disease; physical activity

DOI:  https://doi.org/10.3389/fcell.2024.1421566
Biol Open. 2024 Aug 19. pii: bio.060542. [Epub ahead of print]

High mobility group box 1 (HMGB1) is a potential disease biomarker in cell and mouse models of Duchenne muscular dystrophy.

Rebecca A Slick, Jessica Sutton, Margaret Haberman, Benjamin S O'Brien, Jennifer A Tinklenberg, Aashay Mardikar, Mariah J Prom, Margaret Beatka, Melanie Gartz, Mark Vanden Avond, Emily Siebers, David L Mack, J Patrick Gonzalez, Allison D Ebert, Kanneboyina Nagaraju, Michael W Lawlor.

  Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disorder affecting 1:3500 male births and associated with myofiber degeneration, regeneration, and inflammation. Glucocorticoid treatments have been the standard of care due to immunomodulatory/immunosuppressive properties but novel genetic approaches, including exon skipping and gene replacement therapy, are currently being developed. The identification of additional biomarkers to assess DMD-related inflammatory responses and the potential efficacy of these therapeutic approaches are thus of critical importance. The current study utilizes RNA sequencing of skeletal muscle from two mdx mouse models to identify high mobility group box 1 (HMGB1) as a candidate biomarker potentially contributing to DMD-related inflammation. HMGB1 protein content was increased in a human iPSC-derived skeletal myocyte model of DMD and microdystrophin treatment decreased HMGB1 back to control levels. In vivo, HMGB1 protein levels were increased in vehicle treated B10-mdx skeletal muscle compared to B10-WT and significantly decreased in B10-mdx animals treated with adeno-associated virus (AAV)-microdystrophin. However, HMGB1 protein levels were not increased in D2-mdx skeletal muscle compared to D2-WT, demonstrating a strain-specific difference in DMD-related immunopathology.

Keywords:  Biomarker; Duchenne muscular dystrophy; HMGB1; Muscle differentiation; RNA sequencing

DOI:  https://doi.org/10.1242/bio.060542
Exp Physiol. 2024 Aug 20.

Fatiguing exercise reduces cellular passive Young's modulus in human vastus lateralis muscle.

Grace E Privett, Austin W Ricci, Larry L David, Karen Wiedenfeld Needham, Yong How Tan, Karina H Nakayama, Damien M Callahan.

  Previous studies demonstrated that acute fatiguing exercise transiently reduces whole-muscle stiffness, which might contribute to increased risk of injury and impaired contractile performance. We sought to elucidate potential intracellular mechanisms underlying these reductions. To that end, the cellular passive Young's modulus was measured in muscle fibres from healthy, young males and females. Eight volunteers (four male and four female) completed unilateral, repeated maximal voluntary knee extensions until task failure, immediately followed by bilateral percutaneous needle muscle biopsy of the post-fatigued followed by the non-fatigued control vastus lateralis. Muscle samples were processed for mechanical assessment and separately for imaging and phosphoproteomics. Fibres were passively (pCa 8.0) stretched incrementally to 156% of initial sarcomere length to assess Young's modulus, calculated as the slope of the resulting stress-strain curve at short (sarcomere length = 2.4-3.0 µm) and long (sarcomere length = 3.2-3.8 µm) lengths. Titin phosphorylation was assessed by liquid chromatography followed by high-resolution mass spectrometry. The passive modulus was significantly reduced in post-fatigued versus control fibres from male, but not female, participants. Post-fatigued samples showed altered phosphorylation of five serine residues (four located within the elastic region of titin) but did not exhibit altered active tension or sarcomere ultrastructure. Collectively, these results suggest that acute fatigue is sufficient to alter phosphorylation of skeletal titin in multiple locations. We also found reductions in the passive modulus, consistent with prior reports in the literature investigating striated muscle stiffness. These results provide mechanistic insight contributing to the understanding of dynamic regulation of whole-muscle tissue mechanics in vivo. HIGHLIGHTS: What is the central question of this study? Previous studies have shown that skeletal muscle stiffness is reduced following a single bout of fatiguing exercise in whole muscle, but it is not known whether these changes manifest at the cellular level, and their potential mechanisms remain unexplored. What is the main finding and its importance? Fatiguing exercise reduces cellular stiffness in skeletal muscle from males but not females, suggesting that fatigue alters tissue compliance in a sex-dependent manner. The phosphorylation status of titin, a potential mediator of skeletal muscle cellular stiffness, is modified by fatiguing exercise. Previous studies have shown that passive skeletal muscle stiffness is reduced following a single bout of fatiguing exercise. Lower muscle passive stiffness following fatiguing exercise might increase risk for soft-tissue injury; however, the underlying mechanisms of this change are unclear. Our findings show that fatiguing exercise reduces the passive Young's modulus in skeletal muscle cells from males but not females, suggesting that intracellular proteins contribute to reduced muscle stiffness following repeated loading to task failure in a sex-dependent manner. The phosphorylation status of the intracellular protein titin is modified by fatiguing exercise in a way that might contribute to altered muscle stiffness after fatiguing exercise. These results provide important mechanistic insight that might help to explain why biological sex impacts the risk for soft-tissue injury with repeated or high-intensity mechanical loading in athletes and the risk of falls in older adults.

Keywords:  cellular stiffness; fatigue; passive mechanics; skeletal muscle; titin

DOI:  https://doi.org/10.1113/EP092072
Free Radic Biol Med. 2024 Aug 14. pii: S0891-5849(24)00597-5. [Epub ahead of print]

Unlocking peak performance: The role of Nrf2 in enhancing exercise outcomes and training adaptation in humans.

Miriam Martinez-Canton, Victor Galvan-Alvarez, Marcos Martin-Rincon, Jose A L Calbet, Angel Gallego-Selles.

  Since the discovery of the nuclear factor erythroid-derived 2-like 2 (Nrf2) transcription factor thirty years ago, it has been shown that it regulates more than 250 genes involved in a multitude of biological processes, including redox balance, mitochondrial biogenesis, metabolism, detoxification, cytoprotection, inflammation, immunity, autophagy, cell differentiation, and xenobiotic metabolism. In skeletal muscle, Nrf2 signalling is primarily activated in response to perturbation of redox balance by reactive oxygen species or electrophiles. Initial investigations into human skeletal muscle Nrf2 responses to exercise, dating back roughly a decade, have consistently indicated that exercise-induced ROS production stimulates Nrf2 signalling. Notably, recent studies employing Nrf2 knockout mice have revealed impaired skeletal muscle contractile function characterised by reduced force output and increased fatigue susceptibility compared to wild-type counterparts. These deficiencies partially stem from diminished basal mitochondrial respiratory capacity and an impaired capacity to upregulate specific mitochondrial proteins in response to training, findings corroborated by inducible muscle-specific Nrf2 knockout models. In humans, baseline Nrf2 expression in skeletal muscle correlates with maximal oxygen uptake and high-intensity exercise performance. This manuscript delves into the mechanisms underpinning Nrf2 signalling in response to acute exercise in human skeletal muscle, highlighting the involvement of ROS, antioxidants and Keap1/Nrf2 signalling in exercise performance. Furthermore, it explores Nrf2's role in mediating adaptations to chronic exercise and its impact on overall exercise performance. Additionally, the influence of diet and certain supplements on basal Nrf2 expression and its role in modulating acute and chronic exercise responses are briefly addressed.

Keywords:  Nrf2 signalling; ROS; exercise; free radicals; keap1; performance; polyphenols

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.08.011
iScience. 2024 Aug 16. 27(8): 110510

BCL2L13 at endoplasmic reticulum-mitochondria contact sites regulates calcium homeostasis to maintain skeletal muscle function.

Dogan Grepper, Cassandra Tabasso, Nadège Zanou, Axel K F Aguettaz, Mauricio Castro-Sepulveda, Dorian V Ziegler, Sylviane Lagarrigue, Yoan Arribat, Adrien Martinotti, Ammar Ebrahimi, Jean Daraspe, Lluis Fajas, Francesca Amati.

  The physical connection between mitochondria and endoplasmic reticulum (ER) is an essential signaling hub to ensure organelle and cellular functions. In skeletal muscle, ER-mitochondria calcium (Ca2+) signaling is crucial to maintain cellular homeostasis during physical activity. High expression of BCL2L13, a member of the BCL-2 family, was suggested as an adaptive response in endurance-trained human subjects. In adult zebrafish, we found that the loss of Bcl2l13 impairs skeletal muscle structure and function. Ca2+ signaling is altered in Bcl2l13 knockout animals and mitochondrial complexes activity is decreased. Organelle fractioning in mammalian cells shows BCL2L13 at mitochondria, ER, and mitochondria-associated membranes. ER-mitochondria contact sites number is not modified by BCL2L13 modulation, but knockdown of BCL2L13 in C2C12 cells changes cytosolic Ca2+ release and mitochondrial Ca2+ uptake. This suggests that BCL2L13 interaction with mitochondria and ER, and its role in Ca2+ signaling, contributes to proper skeletal muscle function.

Keywords:  cell biology; pharmacology

DOI:  https://doi.org/10.1016/j.isci.2024.110510
J Physiol. 2024 Aug 22.

Pathophysiological role of connexin and pannexin hemichannels in neuromuscular disorders.

Walter Vásquez, Carlos A Toro, Christopher P Cardozo, Luis A Cea, Juan C Sáez.

  A growing body of research has provided evidence that de novo expression of connexin hemichannels and upregulation of pannexin hemichannels (Cx HCs and Panx HCs, respectively) in the cytoplasmic membrane of skeletal muscle (sarcolemma) are critical steps in the pathogenesis of muscle dysfunction of many genetic and acquired muscle diseases. This review provides an overview of the current understanding of the molecular mechanisms regulating the expression of Cx and Panx HCs in skeletal muscle, as well as their roles in both muscle physiology and pathologies. Additionally, it addresses existing gaps in knowledge and outlines future challenges in the field.

Keywords:  connexons; inflammation; muscle atrophy; pannexons

DOI:  https://doi.org/10.1113/JP286173
Am J Physiol Cell Physiol. 2024 Aug 19.

In dystrophic mdx hindlimb muscles where fibrosis is limited versican haploinsufficiency transiently improves contractile function without reducing inflammation.

Danielle Debruin, Natasha L Mcrae, Alex B Addinsall, Daniel R McCulloch, Robert G Barker, Didier Debrincat, Alan Hayes, Robyn M Murphy, Nicole Stupka.

  Versican is increased with inflammation and fibrosis, and is upregulated in Duchenne muscular dystrophy. In fibrotic diaphragm muscles from dystrophic mdx mice, genetic reduction of versican attenuated macrophage infiltration and improved contractile function. Versican is also implicated in myogenesis. Here, we investigated whether versican modulated mdx hindlimb muscle pathology, where inflammation and regeneration are increased - but fibrosis is minimal. Immunohistochemistry and qRT-PCR were used to assess how fiber type and glucocorticoids (α-methylprednisolone) modify versican expression. To genetically reduce versican, female mdx and male versican haploinsufficient (hdf) mice were bred resulting in male mdx-hdf and mdx (control) pups. Versican expression, contractile function, and pathology were evaluated in hindlimb muscles. Versican immunoreactivity was greater in slow versus fast hindlimb muscles. Versican mRNA transcripts were reduced by α-methylprednisolone in soleus, but not in fast extensor digitorum longus, muscles. In juvenile (6-week-old) mdx-hdf mice, versican expression was most robustly decreased in soleus muscles leading to improved force output and a modest reduction in fatiguability. These functional benefits were not accompanied by decreased inflammation. Muscle architecture, regeneration markers, and fiber type also did not differ between mdx-hdf mice and mdx littermates. Improvements in soleus contractile function were not retained in adult (20-week-old) mdx-hdf mice. In conclusion, soleus muscles from juvenile mdx mice were most responsive to pharmacological or genetic approaches targeting versican; however, the benefits of versican reduction were limited due to low fibrosis. Pre-clinical matrix research in dystrophy should account for muscle phenotype (including age) and the interdependence between the inflammation and fibrosis.

Keywords:  Duchenne muscular dystrophy;.; inflammation; macrophage; provisional extracellular matrix; versican

DOI:  https://doi.org/10.1152/ajpcell.00320.2024
Crit Care Explor. 2024 Aug 01. 6(8): e1144

Proteomic Profiling of Hindlimb Skeletal Muscle Disuse in a Murine Model of Sepsis.

Franccesco P Boeno, Luiz Fernando W Roesch, Philip A Efron, Orlando Laitano.

CONTEXT: Sepsis leads to multiple organ dysfunction and negatively impacts patient outcomes. Skeletal muscle disuse is a significant comorbidity in septic patients during their ICU stay due to prolonged immobilization.
HYPOTHESIS: Combination of sepsis and muscle disuse will promote a unique proteomic signature in skeletal muscle in comparison to disuse and sepsis separately.
METHODS AND MODELS: Following cecal ligation and puncture (CLP) or Sham surgeries, mice were subjected to hindlimb suspension (HLS) or maintained normal ambulation (NA). Tibialis anterior muscles from 24 C57BL6/J male mice were harvested for proteomic analysis. Proteomic profiles were assessed using nano-liquid chromatography with tandem mass spectrometry, followed by data analysis including Partial Least Squares Discriminant Analysis (PLS-DA), to compare the differential protein expression across groups.
RESULTS: A total of 2876 differentially expressed proteins were identified, with marked differences between groups. In mice subjected to CLP and HLS combined, there was a distinctive proteomic signature characterized by a significant decrease in the expression of proteins involved in mitochondrial function and muscle metabolism, alongside a marked increase in proteins related to muscle degradation pathways. The PLS-DA demonstrated a clear separation among experimental groups, highlighting the unique profile of the CLP/HLS group. This suggests an important interaction between sepsis-induced inflammation and disuse atrophy mechanisms in sepsis-induced myopathy.
INTERPRETATIONS AND CONCLUSIONS: Our findings reveal a complex proteomic landscape in skeletal muscle exposed to sepsis and disuse, consistent with an exacerbation of muscle protein degradation under these combined stressors. The identified proteins and their roles in cellular stress responses and muscle pathology provide potential targets for intervention to mitigate muscle dysfunction in septic conditions, highlighting the importance of addressing both sepsis and disuse concurrently in clinical and experimental settings.

DOI: https://doi.org/10.1097/CCE.0000000000001144
J Cell Physiol. 2024 Aug 20. e31418

Reduced myotube diameter induced by combined inhibition of transforming growth factor-β type I receptors Acvr1b and Tgfbr1 is associated with enhanced β1-syntrophin expression.

Andi Shi, Chuqi He, Kirsten Otten, Gang Wu, Tymour Forouzanfar, Rob C I Wüst, Richard T Jaspers.

  Simultaneous inhibition of transforming growth factor-β (TGF-β) type I receptors Acvr1b and Tgfbr1 signalling has been associated with excessive skeletal muscle hypertrophy in vivo. However, it remains unclear whether the increased muscle mass in vivo is a direct result of inhibition of intracellular TGF-β signalling or whether this is an indirect effect of an altered extracellular anabolic environment. Here, we tested whether individual or simultaneous knockdown of TGF-β type I receptors in C2C12 myotubes was sufficient to induce muscle hypertrophy. The expression levels of TGF-β type I receptors Acvr1b and Tgfbr1 in myotubes were knocked down individually or in combination in the absence or presence of TGF-β1 and myostatin. Knocking down either Acvr1b or Tgfbr1 did not significantly change cell phenotype. Unexpectedly, simultaneous knockdown of both receptors reduced C2C12 myotube diameter, mRNA expression levels of Hgf, Ccn2 and Mymx with or without TGF-β1 and myostatin administration. In spite of decreased phosphorylation of Smad2/3, phosphorylation of P70S6K was reduced. In addition, the gene expression level of β1-syntrophin (Sntb1), which encodes a protein associated with the dystrophin-glycoprotein complex, was increased. Parallel experiments where Sntb1 gene expression was reduced showed an increase in myotube diameter and fusion of C2C12 myoblasts. Together, these results indicate that the knockdown of both TGF-β type I receptors reduced myotube diameter. This atrophic effect was attributed to reduced protein synthesis signalling and an increased expression of β1-syntrophin. These results have implications for our fundamental understanding of how TGF-β signalling regulates skeletal muscle size.

Keywords:  Acvr1b; TGF‐β type I receptor; Tgfbr1; myotubes; β1‐syntrophin

DOI:  https://doi.org/10.1002/jcp.31418
J Physiol. 2024 Aug 19.

Muscle memory in humans: evidence for myonuclear permanence and long-term transcriptional regulation after strength training.

Kristoffer Toldnes Cumming, Stefan Markus Reitzner, Marit Hanslien, Kenneth Skilnand, Olivier R Seynnes, Oscar Horwath, Niklas Psilander, Carl Johan Sundberg, Truls Raastad.

  The objective of this work was to investigate myonuclear permanence and transcriptional regulation as mechanisms for cellular muscle memory after strength training in humans. Twelve untrained men and women performed 10 weeks of unilateral elbow-flexor strength training followed by 16 weeks of de-training. Thereafter, 10 weeks' re-training was conducted with both arms: the previously trained arm and the contralateral untrained control arm. Muscle biopsies were taken from the trained arm before and after both training periods and from the control arm before and after re-training. Muscle biopsies were analysed for fibre cross-sectional area (fCSA), myonuclei and global transcriptomics (RNA sequencing). During the first training period, myonuclei increased in type 1 (13 ± 17%) and type 2 (33 ± 23%) fibres together with a 30 ± 43% non-significant increase in mixed fibre fCSA (P = 0.069). Following de-training, fCSA decreased in both fibre types, whereas myonuclei were maintained, resulting in 33% higher myonuclear number in previously trained vs. control muscle in type 2 fibres. Furthermore, in the previously trained muscle, three differentially expressed genes (DEGs; EGR1, MYL5 and COL1A1) were observed. Following re-training, the previously trained muscle showed larger type 2 fCSA compared to the control (P = 0.035). However, delta change in type 2 fCSA was not different between muscles. Gene expression was more dramatically changed in the control arm (1338 DEGs) than in the previously trained arm (822 DEGs). The sustained higher number of myonuclei in the previously trained muscle confirms myonuclear accretion and permanence in humans. Nevertheless, because of the unclear effect on the subsequent hypertrophy with re-training, the physiological benefit remains to be determined. KEY POINTS: Muscle memory is a cellular mechanism that describes the capacity of skeletal muscle fibres to respond differently to training stimuli if the stimuli have been previously encountered. This study overcomes past methodological limitations related to the choice of muscles and analytical procedures. We show that myonuclear number is increased after strength training and maintained during de-training. Increased myonuclear number and differentially expressed genes related to muscle performance and development in the previously trained muscle did not translate into a clearly superior responses during re-training. Because of the unclear effect on the subsequent hypertrophy and muscle strength gain with re-training, the physiological benefit remains to be determined.

Keywords:  CSA; gene expression; muscle fibre; skeletal muscle

DOI:  https://doi.org/10.1113/JP285675
Cell Calcium. 2024 Aug 13. pii: S0143-4160(24)00101-5. [Epub ahead of print]123 102943

Duchenne muscular dystrophy skeletal muscle cells derived from human induced pluripotent stem cells recapitulate various calcium dysregulation pathways.

Arnaud Delafenêtre, Charles-Albert Chapotte-Baldacci, Léa Dorémus, Emmanuelle Massouridès, Marianne Bernard, Matthieu Régnacq, Jérôme Piquereau, Aurélien Chatelier, Christian Cognard, Christian Pinset, Stéphane Sebille.

  Duchenne muscular dystrophy (DMD) is an X-linked progressive muscle degenerative disease, caused by mutations in the dystrophin gene and resulting in premature death. As a major secondary event, an abnormal elevation of the intracellular calcium concentration in the dystrophin-deficient muscle contributes to disease progression in DMD. In this study, we investigated the specific functional features of induced pluripotent stem cell-derived muscle cells (hiPSC-skMCs) generated from DMD patients to regulate intracellular calcium concentration. As compared to healthy hiPSC-skMCs, DMD hiPSC-skMCs displayed specific spontaneous calcium signatures with high levels of intracellular calcium concentration. Furthermore, stimulations with electrical field or with acetylcholine perfusion induced higher calcium response in DMD hiPSC-skMCs as compared to healthy cells. Finally, Mn2+ quenching experiments demonstrated high levels of constitutive calcium entries in DMD hiPSC-skMCs as compared to healthy cells. Our findings converge on the fact that DMD hiPSC-skMCs display intracellular calcium dysregulation as demonstrated in several other models. Observed calcium disorders associated with RNAseq analysis on these DMD cells highlighted some mechanisms, such as spontaneous and activated sarcoplasmic reticulum (SR) releases or constitutive calcium entries, known to be disturbed in other dystrophin-deficient models. However, store operated calcium entries (SOCEs) were not found to be dysregulated in our DMD hiPSC-skMCs model. These results suggest that all the mechanisms of calcium impairment observed in other animal models may not be as pronounced in humans and could point to a preference for certain mechanisms that could correspond to major molecular targets for DMD therapies.

Keywords:  Calcium channels; Duchenne muscular dystrophy; Dystrophin; Induced pluripotent stem cells; Skeletal muscle cells

DOI:  https://doi.org/10.1016/j.ceca.2024.102943
J Extracell Biol. 2024 Aug;3(8): e171

Extracellular vesicles may provide an alternative detoxification pathway during skeletal muscle myoblast ageing.

María Fernández-Rhodes, Emma Buchan, Stephanie D Gagnon, Jiani Qian, Lee Gethings, Rebecca Lees, Ben Peacock, Andrew J Capel, Neil R W Martin, Pola Goldberg Oppenheimer, Mark P Lewis, Owen G Davies.

  Skeletal muscle (SM) acts as a secretory organ, capable of releasing myokines and extracellular vesicles (SM-EVs) that impact myogenesis and homeostasis. While age-related changes have been previously reported in murine SM-EVs, no study has comprehensively profiled SM-EV in human models. To this end, we provide the first comprehensive comparison of SM-EVs from young and old human primary skeletal muscle cells (HPMCs) to map changes associated with SM ageing. HPMCs, isolated from young (24 ± 1.7 years old) and older (69 ± 2.6 years old) participants, were immunomagnetically sorted based on the presence of the myogenic marker CD56 (N-CAM) and cultured as pure (100% CD56+) or mixed populations (MP: 90% CD56+). SM-EVs were isolated using an optimised protocol combining ultrafiltration and size exclusion chromatography (UF + SEC) and their biological content was extensively characterised using Raman spectroscopy (RS) and liquid chromatography mass spectrometry (LC-MS). Minimal variations in basic EV parameters (particle number, size, protein markers) were observed between young and old populations. However, biochemical fingerprinting by RS highlighted increased protein (amide I), lipid (phospholipids and phosphatidylcholine) and hypoxanthine signatures for older SM-EVs. Through LC-MS, we identified 84 shared proteins with functions principally related to cell homeostasis, muscle maintenance and transcriptional regulation. Significantly, SM-EVs from older participants were comparatively enriched in proteins involved in oxidative stress and DNA/RNA mutagenesis, such as E3 ubiquitin-protein ligase TTC3 (TTC3), little elongation complex subunit 1 (ICE1) and Acetyl-CoA carboxylase 1 (ACACA). These data suggest SM-EVs could provide an alternative pathway for homeostasis and detoxification during SM ageing.

Keywords:  LC‐MS/MS; Raman spectroscopy; ageing; extracellular vesicles; human primary cells; skeletal muscle

DOI:  https://doi.org/10.1002/jex2.171
FASEB J. 2024 Aug 31. 38(16): e70009

Quercetin induces a slow myofiber phenotype in engineered human skeletal muscle tissues.

Akitoshi Nagai, Yoshihisa Kaneda, Takayuki Izumo, Yoshihiro Nakao, Hiroyuki Honda, Kazunori Shimizu.

Skeletal muscle comprises slow and fast myofibers, with slow myofibers excelling in aerobic metabolism and endurance. Quercetin, a polyphenol, is reported to induce slow myofibers in rodent skeletal muscle both in vitro and in vivo. However, its effect on human myofiber types remains unexplored. In this study, we evaluated quercetin's impact on slow myofiber induction using human skeletal muscle satellite cells. In a two-dimensional culture, quercetin enhanced gene expression, contributing to muscle differentiation, and significantly expanded the area of slow-type myosin heavy chain positive cells. It also elevated the gene expression of Pgc1α, an inducer of slow myofibers. Conversely, quercetin did not affect mitochondrial abundance, fission, or fusion, but it did increase the gene expression of Cox7A2L, which aids in promoting mitochondrial supercomplexity and endurance, and Mb, which contributes to oxidative phosphorylation. In a three-dimensional culture, quercetin significantly extended the time to peak tension and half relaxation time of the engineered human skeletal muscle tissues constructed on microdevices. Moreover, quercetin enhanced the muscle endurance of the tissues and curbed the rise in lactate secretion from the exercised tissues. These findings suggest that quercetin may induce slow myofibers in human skeletal muscle.

DOI: https://doi.org/10.1096/fj.202400914RR
Physiol Rep. 2024 Aug;12(16): e16166

Five days of bed rest in young and old adults: Retainment of skeletal muscle mass with neuromuscular electrical stimulation.

Sofie K Hansen, Pernille Hansen, Hanne Nygaard, Hans D Grønbæk, Tania W Berry, Camilla M Olsen, Per Aagaard, Lars G Hvid, Jakob Agergaard, Flemming Dela, Charlotte Suetta.

  The consequences of short-term disuse are well known, but effective countermeasures remain elusive. This study investigated the effects of neuromuscular electrical stimulation (NMES) during 5 days of bed rest on retaining lower limb muscle mass and muscle function in healthy young and old participants. One leg received NMES of the quadriceps muscle (3 × 30min/day) (NMES), and the other served as a control (CON). Isometric quadriceps strength (MVC), rate of force development (RFD), lower limb lean mass, and muscle thickness were assessed pre-and post-intervention. Muscle thickness remained unaltered with NMES in young and increased in old following bed rest, while it decreased in CON legs. In old participants, mid-thigh lean mass (MTLM) was preserved with NMES while decreased in CON legs. In the young, only a tendency to change with bed rest was detected for MTLM. MVC and early-phase RFD decreased in young and old, irrespective of NMES. In contrast, late-phase RFD was retained in young participants with NMES, while it decreased in young CON legs, and in the old, irrespective of NMES. NMES during short-term bed rest preserved muscle thickness but not maximal muscle strength. While young and old adults demonstrated similar adaptive responses in preventing the loss of skeletal muscle thickness, RFD was retained in the young only.

Keywords:  aging; atrophy; disuse; muscle strength

DOI:  https://doi.org/10.14814/phy2.16166
Sci Adv. 2024 Aug 23. 10(34): eado8549

Succinate dehydrogenase-complex II regulates skeletal muscle cellular respiration and contractility but not muscle mass in genetically induced pulmonary emphysema.

Joseph Balnis, Ankita Tufts, Emily L Jackson, Lisa A Drake, Diane V Singer, David Lacomis, Chun Geun Lee, Jack A Elias, Jason D Doles, L James Maher, Annie Jen, Joshua J Coon, David Jourd'heuil, Harold A Singer, Catherine E Vincent, Ariel Jaitovich.

Reduced skeletal muscle mass and oxidative capacity coexist in patients with pulmonary emphysema and are independently associated with higher mortality. If reduced cellular respiration contributes to muscle atrophy in that setting remains unknown. Using a mouse with genetically induced pulmonary emphysema that recapitulates muscle dysfunction, we found that reduced activity of succinate dehydrogenase (SDH) is a hallmark of its myopathic changes. We generated an inducible, muscle-specific SDH knockout mouse that demonstrates lower mitochondrial oxygen consumption, myofiber contractility, and exercise endurance. Respirometry analyses show that in vitro complex I respiration is unaffected by loss of SDH subunit C in muscle mitochondria, which is consistent with the pulmonary emphysema animal data. SDH knockout initially causes succinate accumulation associated with a down-regulated transcriptome but modest proteome effects. Muscle mass, myofiber type composition, and overall body mass constituents remain unaltered in the transgenic mice. Thus, while SDH regulates myofiber respiration in experimental pulmonary emphysema, it does not control muscle mass or other body constituents.

DOI: https://doi.org/10.1126/sciadv.ado8549
Curr Osteoporos Rep. 2024 Aug 20.

MicroRNAs and their Modulatory Effect on the Hallmarks of Osteosarcopenia.

William J Silva, André Cruz, Gustavo Duque.

   PURPOSE OF THE REVIEW: Osteosarcopenia is a geriatric syndrome associated with disability and mortality. This review summarizes the key microRNAs that regulate the hallmarks of sarcopenia and osteoporosis. Our objective was to identify components similarly regulated in the pathology and have therapeutic potential by influencing crucial cellular processes in both bone and skeletal muscle.
RECENT FINDINGS: The simultaneous decline in bone and muscle in osteosarcopenia involves a complex crosstalk between these tissues. Recent studies have uncovered several key mechanisms underlying this condition, including the disruption of cellular signaling pathways that regulate bone remodeling and muscle function and regeneration. Accordingly, emerging evidence reveals that dysregulation of microRNAs plays a significant role in the development of each of these hallmarks of osteosarcopenia. Although the recent recognition of osteosarcopenia as a single diagnosis of bone and muscle deterioration has provided new insights into the mechanisms of these underlying age-related diseases, several knowledge gaps have emerged, and a deeper understanding of the role of common microRNAs is still required. In this study, we summarize current evidence on the roles of microRNAs in the pathogenesis of osteosarcopenia and identify potential microRNA targets for treating this condition. Among these, microRNAs-29b and -128 are upregulated in the disease and exert adverse effects by inhibiting IGF-1 and SIRT1, making them potential targets for developing inhibitors of their activity. MicroRNA-21 is closely associated with the occurrence of muscle and bone loss. Conversely, microRNA-199b is downregulated in the disease, and its reduced activity may be related to increased myostatin and GSK3β activity, presenting it as a target for developing analogues that restore its function. Finally, microRNA-672 stands out for its ability to protect skeletal muscle and bone when expressed in the disease, highlighting its potential as a possible therapy for osteosarcopenia.

Keywords:  Bone-muscle crosstalk; MicroRNAs; Non-coding RNA; Osteoporosis; Osteosarcopenia; Sarcopenia

DOI:  https://doi.org/10.1007/s11914-024-00880-4
Am J Physiol Endocrinol Metab. 2024 Aug 22.

Small molecule inhibition of glycogen synthase I reduces muscle glycogen content and improves biomarkers in a mouse model of Pompe disease.

Rafael Calais Gaspar, Ikki Sakuma, Ali Nasiri, Brandon T Hubbard, Traci E LaMoia, Brooks P Leitner, Samnang Tep, Yannan Xi, Eric M Greene, Julie C Ullman, Kitt Falk Petersen, Gerald I Shulman.

  Pompe disease is a rare genetic disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA). This enzyme is responsible for breaking down glycogen, leading to the abnormal accumulation of glycogen, which results in progressive muscle weakness and metabolic dysregulation. In this study, we investigated the hypothesis that the small molecule inhibition of glycogen synthase I (GYS1) may reduce muscle glycogen content and improve metabolic dysregulation in a mouse model of Pompe disease. To address this hypothesis, we studied four groups of male mice: a control group of wild-type B6129SF1/J mice fed either regular chow (WT) or a GYS1 inhibitor (MZ-101) diet (WT-GYS1), and Pompe model mice B6;129-Gaatm1Rabn/J fed either regular chow (GAA-KO) or MZ-101 diet (GAA-GYS1) for 7 days. Our findings revealed that GAA-KO mice exhibited abnormal glycogen accumulation in the gastrocnemius, heart, and diaphragm. In contrast, inhibiting GYS1 reduced glycogen levels in all tissues compared to GAA-KO mice. Furthermore, GAA-KO mice displayed reduced spontaneous activity during the dark cycle compared to WT mice, while GYS1 inhibition counteracted this effect. Compared to GAA-KO mice, GAA-GYS1 mice exhibited improved glucose tolerance and whole-body insulin sensitivity. These improvements in insulin sensitivity could be attributed to increased AMPK phosphorylation in the gastrocnemius of WT-GYS1 and GAA-GYS1 mice. Additionally, the GYS1 inhibitor led to a reduction in the phosphorylation of GSS641 and the LC3 autophagy marker. Together, our results suggest that targeting GYS1 could serve as a potential strategy for treating glycogen storage disorders and metabolic dysregulation.

Keywords:  Pompe disease; muscle glucose metabolism

DOI:  https://doi.org/10.1152/ajpendo.00175.2024
J Appl Physiol (1985). 2024 Aug 22.

SPECIFIC TENSION OF HUMAN MUSCLE IN VIVO: A SYSTEMATIC REVIEW.

Lomas S Persad, Zheng Wang, Paula A Pino, Benjamin I Binder-Markey, Kenton R Kaufman, Richard L Lieber.

  The intrinsic force production capability of human muscle can be expressed as "Specific Tension," or, the maximum force generated per cross-sectional area of muscle fibers. This value can be used to determine, for example, whether muscle quality changes during exercise, atrophy, disease, or hypertrophy. A value of 22.5 N/cm2 for mammalian muscle has generally become accepted based on detailed studies of small mammals. Determining the specific tension of human muscle is much more challenging since almost all determinations are indirect. Calculation of human muscle specific tension requires an understanding of that muscle's contribution to joint torque, its activation magnitude, tendon compliance, and joint moment arm. Determining any of these parameters is technically challenging in humans and thus, it is no surprise that human specific tension values reported vary from 2 to 73 N/cm2. In this systematic review, we screened 1,506 published papers and identified 29 studies published between 1983 and 2023 that used appropriate methods and which reported 95 human specific tension values. We have weighted each parameter based on whether it was directly measured, estimated, or calculated based on the literature, with decreasing weighting used for the more indirect methods. Based on this exhaustive review of the relevant human literature, we suggest that the most accurate value that should be used for human muscle specific tension is 26.8 N/cm2.

Keywords:  Muscle stress; joint torque; magnetic resonance imaging; physiological cross-sectional area; ultrasound

DOI:  https://doi.org/10.1152/japplphysiol.00296.2024
Curr Biol. 2024 Aug 14. pii: S0960-9822(24)01018-2. [Epub ahead of print]

Mechanoresponsive regulation of myogenesis by the force-sensing transcriptional regulator Tono.

Xu Zhang, Jerome Avellaneda, Maria L Spletter, Sandra B Lemke, Pierre Mangeol, Bianca H Habermann, Frank Schnorrer.

  Muscle morphogenesis is a multi-step program, starting with myoblast fusion, followed by myotube-tendon attachment and sarcomere assembly, with subsequent sarcomere maturation, mitochondrial amplification, and specialization. The correct chronological order of these steps requires precise control of the transcriptional regulators and their effectors. How this regulation is achieved during muscle development is not well understood. In a genome-wide RNAi screen in Drosophila, we identified the BTB-zinc-finger protein Tono (CG32121) as a muscle-specific transcriptional regulator. tono mutant flight muscles display severe deficits in mitochondria and sarcomere maturation, resulting in uncontrolled contractile forces causing muscle rupture and degeneration during development. Tono protein is expressed during sarcomere maturation and localizes in distinct condensates in flight muscle nuclei. Interestingly, internal pressure exerted by the maturing sarcomeres deforms the muscle nuclei into elongated shapes and changes the Tono condensates, suggesting that Tono senses the mechanical status of the muscle cells. Indeed, external mechanical pressure on the muscles triggers rapid liquid-liquid phase separation of Tono utilizing its BTB domain. Thus, we propose that Tono senses high mechanical pressure to adapt muscle transcription, specifically at the sarcomere maturation stages. Consistently, tono mutant muscles display specific defects in a transcriptional switch that represses early muscle differentiation genes and boosts late ones. We hypothesize that a similar mechano-responsive regulation mechanism may control the activity of related BTB-zinc-finger proteins that, if mutated, can result in uncontrolled force production in human muscle.

Keywords:  BTB-zinc finger; Drosophila; development; mechanical pressure; mechanobiology; mitochondria; muscle; phase separation; sarcomere; transcription

DOI:  https://doi.org/10.1016/j.cub.2024.07.079