bims-moremu 2024-09-22 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024‒09‒22
37 papers selected by
Anna Vainshtein, Craft Science Inc.

Exercise training and changes in skeletal muscle mitochondrial proteins: from blots to "omics".
Calorie restriction and rapamycin distinctly restore non-canonical ORF translation in the muscles of aging mice.
Vgll2 as an integrative regulator of mitochondrial function and contractility specific to skeletal muscle.
Hypomethylation in promoters of PGC-1α involved in exercise-driven skeletal muscular alterations in old age.
Age-related histone H3.3 accumulation associates with a repressive chromatin in mouse tibialis anterior muscle.
Tilted but not down: Exercise during bed rest improves mitochondrial function in older adults.
Engineered Myovascular Tissues for Studies of Endothelial/Satellite Cell Interactions.
The androgen receptor in mesenchymal progenitors regulates skeletal muscle mass via Igf1 expression in male mice.
Ubiquitylomics: An Emerging Approach for Profiling Protein Ubiquitylation in Skeletal Muscle.
Resistance training suppresses accumulation of senescent fibro-adipogenic progenitors and senescence-associated secretory phenotype in aging rat skeletal muscle.
Irisin Ameliorates Muscle Atrophy by Inhibiting the Upregulation of the Ubiquitin‒Proteasome System in Chronic Kidney Disease.
Myonuclear position and blood vessel organization during skeletal muscle postnatal development.
Temporal expression of mitochondrial life cycle markers during acute and chronic overload of rat plantaris muscles.
N-acetylaspartate promotes glycolytic-to-oxidative fiber-type switch and resistance to atrophic stimuli in myotubes.
Effect of Lactational Low-Protein Diet on Skeletal Muscle during Adulthood and Ageing in Male and Female Mouse Offspring.
Sex-Specific Skeletal Muscle Gene Expression Responses to Exercise Reveal Novel Direct Mediators of Insulin Sensitivity Change.
Comparative transcriptomics of broad-spectrum and synthetic cannabidiol treated C2C12 skeletal myotubes.
Cell transplantation-mediated dystrophin supplementation efficacy in Duchenne muscular dystrophy mouse motor function improvement demonstrated by enhanced skeletal muscle fatigue tolerance.
Mesenchymal Stromal Cell Transplantation Ameliorates Fibrosis and microRNA Dysregulation in Skeletal Muscle Ischaemia.
Anabolic deficits and divergent unfolded protein response underlie skeletal and cardiac muscle growth impairments in the Yoshida hepatoma tumor model of cancer cachexia.
Unlocking the potential of exercise: harnessing myokines to delay musculoskeletal aging and improve cognitive health.
In vitro immuno-prevention of nitration/dysfunction of myogenic stem cell activator HGF, towards developing a strategy for age-related muscle atrophy.
High-Intensity Interval Training Mitigates Sarcopenia and Suppresses the Myoblast Senescence Regulator EEF1E1.
Ameliorated cellular hallmarks of myotonic dystrophy in hybrid myotubes from patient and unaffected donor cells.
Transcriptome Analysis of Differentially Expressed Genes and Molecular Pathways Involved in C2C12 Cells Myogenic Differentiation.
Dysregulated FOXO1 activity drives skeletal muscle intrinsic dysfunction in amyotrophic lateral sclerosis.
Skeletal muscle loss and sarcopenia in obesity pharmacotherapy.
Dual role of the S5 segment in type 1 ryanodine receptor channel gating.
Pathomechanisms of Monoallelic variants in TTN causing skeletal muscle disease.
Freeze-dried porous collagen scaffolds for the repair of volumetric muscle loss injuries.
Exercise Alleviates Cardiovascular Diseases by Improving Mitochondrial Homeostasis.
Functional study of the ST6GAL2 gene regulating skeletal muscle growth and development.
Elucidating the effect of drug-induced mitochondrial dysfunction on insulin signaling and glucose handling in skeletal muscle cell line (C2C12) in vitro.
Agonist antibody to MuSK protects mice from MuSK myasthenia gravis.
Age-related breakdown in networks of inter-muscular coordination.
Sarcopenia.
Assessing muscle protein synthesis rates in vivo in humans: the deuterated water (2H2O) method.

Crit Rev Biochem Mol Biol. 2024 Sep 17. 1-23

Exercise training and changes in skeletal muscle mitochondrial proteins: from blots to "omics".

Elizabeth G Reisman, Nikeisha J Caruana, David J Bishop.

  Mitochondria are essential, membrane-enclosed organelles that consist of ∼1100 different proteins, which allow for many diverse functions critical to maintaining metabolism. Highly metabolic tissues, such as skeletal muscle, have a high mitochondrial content that increases with exercise training. The classic western blot technique has revealed training-induced increases in the relatively small number of individual mitochondrial proteins studied (∼5% of the >1100 proteins in MitoCarta), with some of these changes dependent on the training stimulus. Proteomic approaches have identified hundreds of additional mitochondrial proteins that respond to exercise training. There is, however, surprisingly little crossover in the mitochondrial proteins identified in the published human training studies. This suggests that to better understand the link between training-induced changes in mitochondrial proteins and metabolism, future studies need to move beyond maximizing protein detection to adopting methods that will increase the reliability of the changes in protein abundance observed.

Keywords:  Mitochondria; fiber type; proteins; proteomics; skeletal muscle; training

DOI:  https://doi.org/10.1080/10409238.2024.2383408
NPJ Regen Med. 2024 Sep 19. 9(1): 23

Calorie restriction and rapamycin distinctly restore non-canonical ORF translation in the muscles of aging mice.

Nitish Mittal, Meric Ataman, Lionel Tintignac, Daniel J Ham, Lena Jörin, Alexander Schmidt, Michael Sinnreich, Markus A Ruegg, Mihaela Zavolan.

Loss of protein homeostasis is one of the hallmarks of aging. As such, interventions that restore proteostasis should slow down the aging process and improve healthspan. Two of the most broadly used anti-aging interventions that are effective in organisms from yeast to mammals are calorie restriction (CR) and rapamycin (RM) treatment. To identify the regulatory mechanisms by which these interventions improve the protein homeostasis, we carried out ribosome footprinting in the muscle of mice aged under standard conditions, or under long-term treatment with CR or RM. We found that the treatments distinctly impact the non-canonical translation, RM primarily remodeling the translation of upstream open reading frames (uORFs), while CR restores stop codon readthrough and the translation of downstream ORFs. Proteomics analysis revealed the expression of numerous non-canonical ORFs at the protein level. The corresponding peptides may provide entry points for therapies aiming to maintain muscle function and extend health span.

DOI: https://doi.org/10.1038/s41536-024-00369-9
J Cell Physiol. 2024 Sep 17. e31436

Vgll2 as an integrative regulator of mitochondrial function and contractility specific to skeletal muscle.

Masahiko Honda, Ryota Inoue, Kuniyuki Nishiyama, Takeshi Ueda, Akiyoshi Komuro, Hisayuki Amano, Ryoichi Sugisawa, Suman Dash, Jun Shirakawa, Hitoshi Okada.

  During skeletal muscle adaptation to physiological or pathophysiological signals, contractile apparatus and mitochondrial function are coordinated to alter muscle fiber type. Although recent studies have identified various factors involved in modifying contractile proteins and mitochondrial function, the molecular mechanisms coordinating contractile and metabolic functions during muscle fiber transition are not fully understood. Using a gene-deficient mouse approach, our previous studies uncovered that vestigial-like family member 2 (Vgll2), a skeletal muscle-specific transcription cofactor activated by exercise, is essential for fast-to-slow adaptation of skeletal muscle. The current study provides evidence that Vgll2 plays a role in increasing muscle mitochondrial mass and oxidative capacity. Transgenic Vgll2 overexpression in mice altered muscle fiber composition toward the slow type and enhanced exercise endurance, which contradicted the outcomes observed with Vgll2 deficiency. Vgll2 expression was positively correlated with the expression of genes related to mitochondrial function in skeletal muscle, mitochondrial DNA content, and protein abundance of oxidative phosphorylation complexes. Additionally, Vgll2 overexpression significantly increased the maximal respiration of isolated muscle fibers and enhanced the suppressive effects of endurance training on weight gain. Notably, no additional alteration in expression of myosin heavy chain genes was observed after exercise, suggesting that Vgll2 plays a direct role in regulating mitochondrial function, independent of its effect on contractile components. The observed increase in exercise endurance and metabolic efficiency may be attributed to the acute upregulation of genes promoting fatty acid utilization as a direct consequence of Vgll2 activation facilitated by endurance exercise. Thus, the current study establishes that Vgll2 is an integrative regulator of mitochondrial function and contractility in skeletal muscle.

Keywords:  endurance training; mitochondrial function; muscle fiber; oxidative phosphorylation; respiration; weight gain

DOI:  https://doi.org/10.1002/jcp.31436
Open Life Sci. 2024 ;19(1): 20220959

Hypomethylation in promoters of PGC-1α involved in exercise-driven skeletal muscular alterations in old age.

Qiaowei Li, Qin Liu, Zhong Lin, Wenwen Lin, Feng Huang, Pengli Zhu.

  Exercise training can significantly improve skeletal muscle mitochondrial function and has been proven to be highly relevant to alterations in skeletal muscle DNA methylation. However, it remains unclear whether late-in-life exercise has an effect on promoter methylation of PGC-1α, a key regulator of mitochondrial biogenesis. Here we employed two distinct exercise modalities, constant medium intensity exercise training (CMIT) and high-intensity interval exercise training (HIIT), to investigate their impacts on PGC-1α expression and methylation regulation in skeletal muscle of aged mice. The results revealed a notable decrease in PGC-1α expression in skeletal muscle of aged mice, accompanied by elevated methylation levels of the PGC-1α promoter, and increased DNA methyltransferase (DNMT) protein expressions. However, both forms of exercise training significantly corrected PGC-1α epigenetic changes, increased PGC-1α expression, and ameliorated skeletal muscle reduction. Furthermore, exercise training led to elevated expression of proteins related to mitochondrial biogenesis and energy metabolism in skeletal muscle, improving mitochondrial structure and function. In conclusion, late-in-life exercise improved skeletal muscle function, morphology, and mitochondria biogenesis, which may be associated with hypomethylation in promoters of PGC-1α and increased content of skeletal muscle PGC-1α. Notably, there was no clear difference between HIIT and CMIT in PGC-1α expression and skeletal muscle function.

Keywords:  DNA methylation; PGC-1α; exercise; sarcopenia

DOI:  https://doi.org/10.1515/biol-2022-0959
J Physiol Sci. 2024 Sep 14. 74(1): 41

Age-related histone H3.3 accumulation associates with a repressive chromatin in mouse tibialis anterior muscle.

Ryo Masuzawa, Hemilce Karina Rosa Flete, Junya Shimizu, Fuminori Kawano.

  The present study aimed to investigate age-related changes in histone variant H3.3 and its role in the aging process of mouse tibialis anterior muscle. H3.3 level significantly increased with age and correlated with H3K27me3 level. Acute exercise successfully upregulated the target gene expression in 8-wk-old mice, whereas no upregulation was noted in 53-wk-old mice. H3K27me3 level was increased at these loci in response to acute exercise in 8-wk-old mice. However, in 53-wk-old mice, H3.3 and H3K27me3 levels were increased at rest and were not affected by acute exercise. Furthermore, forced H3.3 expression in the skeletal muscle of 8-wk-old mice led to a gradual improvement in motor function. The results suggest that age-related H3.3 accumulation induces the formation of repressive chromatin in the mouse tibialis anterior muscle. However, H3.3 accumulation also appears to play a positive role in enhancing skeletal muscle function.

Keywords:  Aging; Chromatin immunoprecipitation; Epigenetics; Exercise; Histone modification

DOI:  https://doi.org/10.1186/s12576-024-00935-2
J Physiol. 2024 Sep 18.

Tilted but not down: Exercise during bed rest improves mitochondrial function in older adults.

Anna E Kupraty, Bridget Coyle-Asbil.



Keywords:  ageing; bed rest; exercise metabolism; mitochondrial dynamics; muscle atrophy; oxidative stress

DOI:  https://doi.org/10.1113/JP287143
Acta Biomater. 2024 Sep 17. pii: S1742-7061(24)00536-1. [Epub ahead of print]

Engineered Myovascular Tissues for Studies of Endothelial/Satellite Cell Interactions.

Torie Broer, Nick Tsintolas, Karly Purkey, Stewart Hammond, Sophia DeLuca, Tianyu Wu, Ishika Gupta, Alastair Khodabukus, Nenad Bursac.

  In the native skeletal muscle, capillaries reside in close proximity to muscle stem cells (satellite cells, SCs) and regulate SC numbers and quiescence through partially understood mechanisms difficult to study in vivo. This challenge could be addressed by the development of a 3-dimensional (3D) in vitro model of vascularized skeletal muscle harboring both a pool of quiescent SCs and a robust network of capillaries. Still, studying interactions between SCs and endothelial cells (ECs) within a tissue-engineered muscle environment has been hampered by the incompatibility of commercially available EC media with skeletal muscle differentiation. In this study, we first optimized co-culture media and cellular ratios to generate highly functional vascularized human skeletal muscle tissues ("myovascular bundles") with contractile properties (∼10 mN/mm2) equaling those of avascular, muscle-only tissues ("myobundles"). Within one week of muscle differentiation, ECs in these tissues formed a dense network of capillaries that co-aligned with muscle fibers and underwent initial lumenization. Incorporating vasculature within myobundles increased the total SC number by 82%, with SC density and quiescent signature being increased proximal (≤20μm) to EC networks. In vivo, at two weeks post-implantation into dorsal window chambers in nude mice, vascularized myobundles exhibited improved calcium handling compared to avascular implants. In summary, we engineered highly functional myovascular tissues that enable studies of the roles of EC-SC crosstalk in human muscle development, physiology, and disease. STATEMENT OF SIGNIFICANCE: In native skeletal muscle, intricate relationships between vascular cells and muscle stem cells ("satellite cells") play critical roles in muscle growth and regeneration. Current methods for in vitro engineering of contractile skeletal muscle do not recreate capillary networks present in vivo. Our study for the first time generates in vitro robustly vascularized, highly functional engineered human skeletal muscle tissues. Within these tissues, satellite cells are more abundant and, similar as in vivo, they are more dense and less proliferative proximal to endothelial cells. Upon implantation in mice, vascularized engineered muscles show improved calcium handling compared to muscle-only implants. We expect that this versatile in vitro system will enable studies of muscle-vasculature crosstalk in human development and disease.

Keywords:  satellite cell; skeletal muscle; tissue engineering; vascularization; window chamber

DOI:  https://doi.org/10.1016/j.actbio.2024.09.020
Proc Natl Acad Sci U S A. 2024 Sep 24. 121(39): e2407768121

The androgen receptor in mesenchymal progenitors regulates skeletal muscle mass via Igf1 expression in male mice.

Hiroshi Sakai, Hideaki Uno, Harumi Yamakawa, Kaori Tanaka, Aoi Ikedo, Akiyoshi Uezumi, Yasuyuki Ohkawa, Yuuki Imai.

  Androgens exert their effects primarily by binding to the androgen receptor (AR), a ligand-dependent nuclear receptor. While androgens have anabolic effects on skeletal muscle, previous studies reported that AR functions in myofibers to regulate skeletal muscle quality, rather than skeletal muscle mass. Therefore, the anabolic effects of androgens are exerted via nonmyofiber cells. In this context, the cellular and molecular mechanisms of AR in mesenchymal progenitors, which play a crucial role in maintaining skeletal muscle homeostasis, remain largely unknown. In this study, we demonstrated expression of AR in mesenchymal progenitors and found that targeted AR ablation in mesenchymal progenitors reduced limb muscle mass in mature adult, but not young or aged, male mice, although fatty infiltration of muscle was not affected. The absence of AR in mesenchymal progenitors led to remarkable perineal muscle hypotrophy, regardless of age, due to abnormal regulation of transcripts associated with cell death and extracellular matrix organization. Additionally, we revealed that AR in mesenchymal progenitors regulates the expression of insulin-like growth factor 1 (Igf1) and that IGF1 administration prevents perineal muscle atrophy in a paracrine manner. These findings indicate that the anabolic effects of androgens regulate skeletal muscle mass via, at least in part, AR signaling in mesenchymal progenitors.

Keywords:  Igf1; androgen receptor; mesenchymal progenitors; skeletal muscle

DOI:  https://doi.org/10.1073/pnas.2407768121
J Cachexia Sarcopenia Muscle. 2024 Sep 16.

Ubiquitylomics: An Emerging Approach for Profiling Protein Ubiquitylation in Skeletal Muscle.

Samuel O Lord, Harvey E Johnston, Rahul S Samant, Yu-Chiang Lai.

  Skeletal muscle is a highly adaptable tissue, finely tuned by various physiological and pathological factors. Whilst the pivotal role of skeletal muscle in overall health is widely acknowledged, unravelling the underlying molecular mechanisms poses ongoing challenges. Protein ubiquitylation, a crucial post-translational modification, is involved in regulating most biological processes. This widespread impact is achieved through a diverse set of enzymes capable of generating structurally and functionally distinct ubiquitin modifications on proteins. The complexity of protein ubiquitylation has presented significant challenges in not only identifying ubiquitylated proteins but also characterising their functional significance. Mass spectrometry enables in-depth analysis of proteins and their post-translational modification status, offering a powerful tool for studying protein ubiquitylation and its biological diversity: an approach termed ubiquitylomics. Ubiquitylomics has been employed to tackle different perspectives of ubiquitylation, including but not limited to global quantification of substrates and ubiquitin linkages, ubiquitin site recognition and crosstalk with other post-translational modifications. As the field of mass spectrometry continues to evolve, the usage of ubiquitylomics has unravelled novel insights into the regulatory mechanisms of protein ubiquitylation governing biology. However, ubiquitylomics research has predominantly been conducted in cellular models, limiting our understanding of ubiquitin signalling events driving skeletal muscle biology. By integrating the intricate landscape of protein ubiquitylation with dynamic shifts in muscle physiology, ubiquitylomics promises to not only deepen our understanding of skeletal muscle biology but also lay the foundation for developing transformative muscle-related therapeutics. This review aims to articulate how ubiquitylomics can be utilised by researchers to address different aspects of ubiquitylation signalling in skeletal muscle. We explore methods used in ubiquitylomics experiments, highlight relevant literature employing ubiquitylomics in the context of skeletal muscle and outline considerations for experimental design.

Keywords:  diGly; mass spectrometry; proteomics; skeletal muscle; ubiquitin

DOI:  https://doi.org/10.1002/jcsm.13601
Geroscience. 2024 Sep 19.

Resistance training suppresses accumulation of senescent fibro-adipogenic progenitors and senescence-associated secretory phenotype in aging rat skeletal muscle.

Yung-Li Hung, Ayami Sato, Yuka Takino, Akihito Ishigami, Shuichi Machida.

  Accumulation of senescent cells in tissues contributes to multiple aging-related pathologies. Senescent fibro-adipogenic progenitors (FAPs) contribute to aging-related muscle atrophy. Resistance training can help to maintain skeletal muscle mass, improve mobility, and reduce certain health risks commonly associated with aging. We investigated, using rat model, the impact of resistance training on FAPs in aging skeletal muscle, which remains unclear. Twenty-two-month-old female rats were divided into sedentary and training groups. The training group rodents were trained to climb a ladder while bearing a load for 20 training sessions over 2 months, after which, the flexor hallucis longus muscles were collected and analyzed. Senescent cells were identified using a senescence-associated β-galactosidase stain and p21 immunohistochemistry (IHC), and FAPs were identified using platelet-derived growth factor receptor alpha IHC. The results indicate that resistance training in rats prevented aging-associated skeletal muscle atrophy and suppressed M2 polarization of macrophages. The number of senescent cells was significantly reduced in the 24-month-old training group, with most of them being FAPs. Conversely, the number of senescent FAPs increased significantly in the 24-month-old sedentary group compared with that in the 18-month-old sedentary group. The number of senescent FAPs in the 24-month-old training group decreased significantly. Resistance training also suppressed the senescence-associated secretory phenotype (SASP). The killer T cell-specific marker, CD8α, was elevated in the skeletal muscles of the aging rats following resistance training, indicating upregulation of recognition and elimination of senescent cells. Overall, resistance training suppressed the accumulation of senescent FAPs and acquisition of SASP in aging skeletal muscles.

Keywords:  Fibro-adipogenic progenitors; Resistance training; Sarcopenia; Senescent cells

DOI:  https://doi.org/10.1007/s11357-024-01338-2
Calcif Tissue Int. 2024 Sep 16.

Irisin Ameliorates Muscle Atrophy by Inhibiting the Upregulation of the Ubiquitin‒Proteasome System in Chronic Kidney Disease.

Shiyuan Wang, Yajing Pan, Qi Pang, Aihua Zhang.

  Muscle atrophy is a common complication of chronic kidney disease (CKD). Irisin, a novel muscle cytokine, protects against muscle atrophy, but its specific role in CKD-associated muscle atrophy requires further elucidation. Because the ubiquitin-proteasome system (UPS) plays an important role in CKD muscle atrophy, our study will explore whether irisin affects UPS and alleviate CKD-associated muscle atrophy. In this study, an adenine-fed mouse model of CKD and urotension II (UII)-induced C2C12 myotubes were used as in vivo and in vitro models of muscle atrophy. The results showed that renal function, mouse weight, and the cross-sectional area (CSA) of skeletal muscles were significantly improved in CKD mice treated with irisin. Moreover, irisin effectively mitigated the decreases in phosphorylated Forkhead box O 3a (p-FOXO3A) levels and increases in the levels of E3 ubiquitin ligases, such as muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx/atrogin1), in both the muscles of CKD mice and UII-induced C2C12 myotubes. In addition, irisin significantly increased the expression levels of myogenic differentiation factor D (MyoD) in the muscles of CKD mice. Our study is the first to demonstrate that irisin ameliorates skeletal muscle atrophy by inhibiting UPS upregulation and improving satellite cell differentiation in CKD.

Keywords:  Chronic kidney disease; Irisin; Skeletal muscle atrophy; Ubiquitin proteasome system; Urotension II

DOI:  https://doi.org/10.1007/s00223-024-01283-4
Development. 2024 Sep 17. pii: dev.202548. [Epub ahead of print]

Myonuclear position and blood vessel organization during skeletal muscle postnatal development.

Catarina Sequeira, Lou Martha Wackerbarth, Andreia Pena, Mafalda Sá-Pereira, Cláudio A Franco, Edgar R Gomes.

  Skeletal muscle development is a complex process involving myoblast fusion to generate multinucleated fibers. Myonuclei first align in the center of the myotubes before migrating to the periphery of the myofiber. Blood vessels (BVs) are important contributors to the correct development of skeletal muscle, and myonuclei are found next to BVs in adult muscle. Here, we show that most myonuclear migration to the periphery occurs between E17.5 and P1. Furthermore, myonuclear accretion after P7 does not result in centrally nucleated myofibers as observed in the embryo. Instead, myonuclei remain at the periphery of the myofiber without moving to the center. Finally, we show that hypovascularization of skeletal muscle alters the interaction between myonuclei and BVs, suggesting that BVs may contribute to myonuclear positioning during skeletal muscle postnatal development. Overall, this work provides a comprehensive analysis of skeletal muscle development during the highly dynamic postnatal period, bringing new insights about myonuclear positioning and its interaction with BVs.

Keywords:  Blood vessels; Nuclear positioning; Postnatal development; Skeletal muscle

DOI:  https://doi.org/10.1242/dev.202548
Front Physiol. 2024 ;15 1420276

Temporal expression of mitochondrial life cycle markers during acute and chronic overload of rat plantaris muscles.

Jon-Philippe K Hyatt, Emilie J Lu, Gary E McCall.

  Skeletal muscle hypertrophy is generally associated with a fast-to-slow phenotypic adaptation in both human and rodent models. Paradoxically, this phenotypic shift is not paralleled by a concomitant increase in mitochondrial content and aerobic markers that would be expected to accompany a slow muscle phenotype. To understand the temporal response of the mitochondrial life cycle (i.e., biogenesis, oxidative phosphorylation, fission/fusion, and mitophagy/autophagy) to hypertrophic stimuli, in this study, we used the functional overload (FO) model in adult female rats and examined the plantaris muscle responses at 1 and 10 weeks. As expected, the absolute plantaris muscle mass increased by ∼12 and 26% at 1 and 10 weeks following the FO procedure, respectively. Myosin heavy-chain isoform types I and IIa significantly increased by 116% and 17%, respectively, in 10-week FO plantaris muscles. Although there was a general increase in protein markers associated with mitochondrial biogenesis in acute FO muscles, this response was unexpectedly sustained under 10-week FO conditions after muscle hypertrophy begins to plateau. Furthermore, the early increase in mito/autophagy markers observed under acute FO conditions was normalized by 10 weeks, suggesting a cellular environment favoring mitochondrial biogenesis to accommodate the aerobic demands of the plantaris muscle. We also observed a significant increase in the expression of mitochondrial-, but not nuclear-, encoded oxidative phosphorylation (OXPHOS) proteins and peptides (i.e., humanin and MOTS-c) under chronic, but not acute, FO conditions. Taken together, the temporal response of markers related to the mitochondrial life cycle indicates a pattern of promoting biogenesis and mitochondrial protein expression to support the energy demands and/or enhanced neural recruitment of chronically overloaded skeletal muscle.

Keywords:  MOTS-c; autophagy; biogenesis; mitophagy; myosin heavy chain; oxidative phosphorylation

DOI:  https://doi.org/10.3389/fphys.2024.1420276
Cell Death Dis. 2024 Sep 19. 15(9): 686

N-acetylaspartate promotes glycolytic-to-oxidative fiber-type switch and resistance to atrophic stimuli in myotubes.

Serena Castelli, Enrico Desideri, Leonardo Laureti, Federica Felice, Angela De Cristofaro, Silvia Scaricamazza, Giacomo Lazzarino, Maria Rosa Ciriolo, Fabio Ciccarone.

N-acetylaspartate (NAA) is a neuronal metabolite that can be extruded in extracellular fluids and whose blood concentration increases in several neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Aspartoacylase (ASPA) is the enzyme responsible for NAA breakdown. It is abundantly expressed in skeletal muscle and most other human tissues, but the role of NAA catabolism in the periphery is largely neglected. Here we demonstrate that NAA treatment of differentiated C2C12 muscle cells increases lipid turnover, mitochondrial biogenesis and oxidative metabolism at the expense of glycolysis. These effects were ascribed to NAA catabolism, as CRISPR/Cas9 ASPA KO cells are insensitive to NAA administration. Moreover, the metabolic switch induced by NAA was associated with an augmented resistance to atrophic stimuli. Consistently with in vitro results, SOD1-G93A ALS mice show an increase in ASPA levels in those muscles undergoing the glycolytic to oxidative switch during the disease course. The impact of NAA on the metabolism and resistance capability of myotubes supports a role for this metabolite in the phenotypical adaptations of skeletal muscle in neuromuscular disorders.

DOI: https://doi.org/10.1038/s41419-024-07047-0
Nutrients. 2024 Sep 01. pii: 2926. [Epub ahead of print]16(17):

Effect of Lactational Low-Protein Diet on Skeletal Muscle during Adulthood and Ageing in Male and Female Mouse Offspring.

Moussira Alameddine, Atilla Emre Altinpinar, Ufuk Ersoy, Ioannis Kanakis, Ioanna Myrtziou, Susan E Ozanne, Katarzyna Goljanek-Whysall, Aphrodite Vasilaki.

  Sarcopenia is characterised by the loss of skeletal muscle mass and function, which leads to a high risk of increased morbidity and mortality. Maternal malnutrition has been linked to impaired development of skeletal muscle of the offspring; however, there are limited studies that report the long-term effect of a maternal low-protein diet during lactation on the ageing of skeletal muscles. This study aimed to examine how a maternal low-protein diet (LPD) during lactation affects skeletal muscle ageing in the offspring. Pups born from control mothers were lactated by mothers fed with an LPD. Post-weaning, mice were either maintained on an LPD or switched to a control, normal-protein diet (NPD). In males, an LPD mainly affected the size of the myofibres without a major effect on fibre number and led to reduced grip strength in ageing mice (24 months). Female mice from mothers on an LPD had a lower body and muscle weight at weaning but caught up with control mice at 3 months. During ageing, the muscle weight, myofibre number and survival rate of female pups were significantly affected. These findings highlight the effect of an LPD during lactation on skeletal muscle ageing, the lifespan of offspring and the importance of sexual dimorphism in response to dietary challenges.

Keywords:  ageing; lactation; low-protein diet (LPD); sarcopenia; skeletal muscle

DOI:  https://doi.org/10.3390/nu16172926
medRxiv. 2024 Sep 08. pii: 2024.09.07.24313236. [Epub ahead of print]

Sex-Specific Skeletal Muscle Gene Expression Responses to Exercise Reveal Novel Direct Mediators of Insulin Sensitivity Change.

S Ma, M C Morris, M J Hubal, L M Ross, K M Huffman, C G Vann, N Moore, E R Hauser, A Bareja, R Jiang, E Kummerfeld, M D Barberio, J A Houmard, W B Bennett, J L Johnson, J A Timmons, G Broderick, V B Kraus, C F Aliferis, W E Kraus.

BACKGROUND: Understanding the causal pathways, systems, and mechanisms through which exercise impacts human health is complex. This study explores molecular signaling related to whole-body insulin sensitivity (Si) by examining changes in skeletal muscle gene expression. The analysis considers differences by biological sex, exercise amount, and exercise intensity to identify potential molecular targets for developing pharmacologic agents that replicate the health benefits of exercise.METHODS: The study involved 53 participants from the STRRIDE I and II trials who completed eight months of aerobic training. Skeletal muscle gene expression was measured using Affymetrix and Illumina technologies, while pre- and post-training Si was assessed via an intravenous glucose tolerance test. A novel gene discovery protocol, integrating three literature-derived and data-driven modeling strategies, was employed to identify causal pathways and direct causal factors based on differentially expressed transcripts associated with exercise intensity and amount.
RESULTS: In women, the transcription factor targets identified were primarily influenced by exercise amount and were generally inhibitory. In contrast, in men, these targets were driven by exercise intensity and were generally activating. Transcription factors such as ATF1, CEBPA, BACH2, and STAT1 were commonly activating in both sexes. Specific transcriptional targets related to exercise-induced Si improvements included TACR3 and TMC7 for intensity-driven effects, and GRIN3B and EIF3B for amount-driven effects. Two key signaling pathways mediating aerobic exercise-induced Si improvements were identified: one centered on estrogen signaling and the other on phorbol ester (PKC) signaling, both converging on the epidermal growth factor receptor (EGFR) and other relevant targets.
CONCLUSIONS: The signaling pathways mediating Si improvements from aerobic exercise differed by sex and were further distinguished by exercise intensity and amount. Transcriptional adaptations in skeletal muscle related to Si improvements appear to be causally linked to estrogen and PKC signaling, with EGFR and other identified targets emerging as potential skeletal muscle-specific drug targets to mimic the beneficial effects of exercise on Si.

DOI: https://doi.org/10.1101/2024.09.07.24313236
Physiol Rep. 2024 Sep;12(18): e70059

Comparative transcriptomics of broad-spectrum and synthetic cannabidiol treated C2C12 skeletal myotubes.

Scott H Gillham, Paige L Cole, Mark R Viggars, Andy H Nolan, Graeme L Close, Daniel J Owens.

  Cannabidiol (CBD) is widely used in sports for recovery, pain management, and sleep improvement, yet its effects on muscle are not well understood. This study aimed to determine the transcriptional response of murine skeletal muscle myotubes to broad-spectrum CBD and synthetic CBD (sCBD). Differentiated C2C12 myotubes were treated with 10 μM CBD, sCBD, or vehicle control (DMSO) for 24 h before RNA extraction. Poly-A tail-enriched mRNA libraries were constructed and sequenced using 2 × 50 bp paired-end sequencing. CBD and sCBD treatment induced 4489 and 1979 differentially expressed genes (DEGs; p < 0.001, FDR step-up <0.05), respectively, with common upregulation of 857 genes and common downregulation of 648 genes. Common upregulated DEGs were associated with "response to unfolded protein," "cell redox homeostasis," "endoplasmic reticulum stress," "oxidative stress," and "cellular response to hypoxia." Common downregulated DEGs were linked to "sarcomere organization," "skeletal muscle tissue development," "regulation of muscle contraction," and "muscle contraction." CBD treatment induced unique DEGs compared to sCBD. The data indicate CBD may induce mild cellular stress, activating pathways associated with altered redox balance, unfolded protein response, and endoplasmic reticulum stress. We hypothesize that CBD interacts with muscle and may elicit a "mitohormetic" effect that warrants further investigation.

Keywords:  cannabidiol; skeletal muscle; transcriptome

DOI:  https://doi.org/10.14814/phy2.70059
Stem Cell Res Ther. 2024 Sep 19. 15(1): 313

Cell transplantation-mediated dystrophin supplementation efficacy in Duchenne muscular dystrophy mouse motor function improvement demonstrated by enhanced skeletal muscle fatigue tolerance.

Clémence Kiho Bourgeois Yoshioka, Nana Takenaka-Ninagawa, Megumi Goto, Mayuho Miki, Daiki Watanabe, Masamichi Yamamoto, Tomoki Aoyama, Hidetoshi Sakurai.

  BACKGROUND: Duchenne muscular dystrophy (DMD) is an incurable neuromuscular disease leading to progressive skeletal muscle weakness and fatigue. Cell transplantation in murine models has shown promise in supplementing the lack of the dystrophin protein in DMD muscles. However, the establishment of novel, long-term, relevant methods is needed to assess its efficiency on the DMD motor function. By applying newly developed methods, this study aimed to evaluate the functional and molecular effects of cell therapy-mediated dystrophin supplementation on DMD muscles.METHODS: Dystrophin was supplemented in the gastrocnemius of a 5-week-old immunodeficient DMD mouse model (Dmd-null/NSG) by intramuscular xenotransplantation of healthy human immortalized myoblasts (Hu5/KD3). A long-term time-course comparative study was conducted between wild-type, untreated DMD, and dystrophin supplemented-DMD mouse muscle functions and histology. A novel GO-ATeam2 transgenic DMD mouse model was also generated to assess in vivo real-time ATP levels in gastrocnemius muscles during repeated contractions.
RESULTS: We found that 10.6% dystrophin supplementation in DMD muscles was sufficient to prevent low values of gastrocnemius maximal isometric contraction torque (MCT) at rest, while muscle fatigue tolerance, assessed by MCT decline after treadmill running, was fully ameliorated in 21-week-old transplanted mice. None of the dystrophin-supplemented fibers were positive for muscle damage markers after treadmill running, with 85.4% demonstrating the utilization of oxidative metabolism. Furthermore, ATP levels in response to repeated muscle contractions tended to improve, and mitochondrial activity was significantly enhanced in dystrophin supplemented-fibers.
CONCLUSIONS: Cell therapy-mediated dystrophin supplementation efficiently improved DMD muscle functions, as evaluated using newly developed evaluation methods. The enhanced muscle fatigue tolerance in 21-week-old mice was associated with the preferential regeneration of damage-resistant and oxidative fibers, highlighting increased mitochondrial activity, after cell transplantation. These findings significantly contribute to a more in-depth understanding of DMD pathogenesis.

Keywords:  Cell transplantation; Duchenne muscular dystrophy mouse model; Dystrophin supplementation; GO-ATeam2 transgenic mouse model; In vivo ATP imaging; Mitochondrial activity; Motor function evaluation; Muscle fatigue tolerance; Oxidative slow fibers

DOI:  https://doi.org/10.1186/s13287-024-03922-x
Stem Cells. 2024 Sep 16. pii: sxae058. [Epub ahead of print]

Mesenchymal Stromal Cell Transplantation Ameliorates Fibrosis and microRNA Dysregulation in Skeletal Muscle Ischaemia.

Clara Sanz-Nogués, Alan J Keane, Michael Creane, Sean O Hynes, Xizhe Chen, Caomhán J Lyons, Emma Horan, Stephen J Elliman, Katarzyna Goljanek-Whysall, Timothy O'Brien.

  Peripheral arterial disease (PAD) is associated with lower-extremity muscle wasting. Hallmark features of PAD-associated skeletal muscle pathology include loss of skeletal muscle mass, reduced strength and physical performance, increased inflammation, fibrosis, and adipocyte infiltration. At the molecular level, skeletal muscle ischaemia has also been associated with gene and microRNA (miRNA) dysregulation. Mesenchymal stromal cells (MSCs) have been shown to enhance muscle regeneration and improve muscle function in various skeletal muscle injuries. This study aimed to evaluate the effects of intramuscularly delivered human umbilical cord-derived MSCs (hUC-MSCs) on skeletal muscle ischaemia. Herein, we report an hUC-MSC-mediated amelioration of ischaemia-induced skeletal muscle atrophy and function via enhancement of myofibre regeneration, reduction of tissue inflammation, adipocyte accumulation, and tissue fibrosis. These changes were observed in the absence of cell-mediated enhancement of blood flow recovery as measured by Laser Doppler imaging. Furthermore, reduced tissue fibrosis in the hUC-MSC-treated group was associated with upregulation of miR-1, miR-133a, and miR-29b and downregulation of targeted pro-fibrotic genes such as Col1a1 and Fn1. Our results support the use of hUC-MSCs as a novel approach to reduce fibrosis and promote skeletal muscle regeneration after ischaemic injury in patients with PAD.

Keywords:  fibrosis; mesenchymal stromal cells; microRNAs; muscle ischaemia; peripheral arterial disease

DOI:  https://doi.org/10.1093/stmcls/sxae058
Physiol Rep. 2024 Sep;12(18): e70044

Anabolic deficits and divergent unfolded protein response underlie skeletal and cardiac muscle growth impairments in the Yoshida hepatoma tumor model of cancer cachexia.

Daniel J Belcher, Nina Kim, Blanca Navarro-Llinas, Maria Möller, Francisco J López-Soriano, Silvia Busquets, Gustavo A Nader.

  Cancer cachexia manifests as whole body wasting, however, the precise mechanisms governing the alterations in skeletal muscle and cardiac anabolism have yet to be fully elucidated. In this study, we explored changes in anabolic processes in both skeletal and cardiac muscles in the Yoshida AH-130 ascites hepatoma model of cancer cachexia. AH-130 tumor-bearing rats experienced significant losses in body weight, skeletal muscle, and heart mass. Skeletal and cardiac muscle loss was associated with decreased ribosomal (r)RNA, and hypophosphorylation of the eukaryotic factor 4E binding protein 1. Endoplasmic reticulum stress was evident by higher activating transcription factor mRNA in skeletal muscle and growth arrest and DNA damage-inducible protein (GADD)34 mRNA in both skeletal and cardiac muscles. Tumors provoked an increase in tissue expression of interferon-γ in the heart, while an increase in interleukin-1β mRNA was apparent in both skeletal and cardiac muscles. We conclude that compromised skeletal muscle and heart mass in the Yoshida AH-130 ascites hepatoma model involves a marked reduction translational capacity and efficiency. Furthermore, our observations suggest that endoplasmic reticulum stress and tissue production of pro-inflammatory factors may play a role in the development of skeletal and cardiac muscle wasting.

Keywords:  cancer; inflammation; ribosomal RNA; unfolded protein response; wasting

DOI:  https://doi.org/10.14814/phy2.70044
Front Physiol. 2024 ;15 1338875

Unlocking the potential of exercise: harnessing myokines to delay musculoskeletal aging and improve cognitive health.

Xing Gao, Yiyan Chen, Peng Cheng.

  Objectives: This review aims to summarize the common physiological mechanisms associated with both mild cognitive impairment (MCI) and musculoskeletal aging while also examining the relevant literature on how exercise regulation influences the levels of shared myokines in these conditions.Methods: The literature search was conducted via databases such as PubMed (including MEDLINE), EMBASE, and the Cochrane Library of Systematic Reviews. The searches were limited to full-text articles published in English, with the most recent search conducted on 16 July 2024. The inclusion criteria for this review focused on the role of exercise and myokines in delaying musculoskeletal aging and enhancing cognitive health. The Newcastle‒Ottawa Scale (NOS) was utilized to assess the quality of nonrandomized studies, and only those studies with moderate to high quality scores, as per these criteria, were included in the final analysis. Data analysis was performed through narrative synthesis.
Results: The primary outcome of this study was the evaluation of myokine expression, which included IL-6, IGF-1, BDNF, CTSB, irisin, and LIF. A total of 16 studies involving 633 older adults met the inclusion criteria. The current exercise modalities utilized in these studies primarily consisted of resistance training and moderate-to high-intensity cardiovascular exercise. The types of interventions included treadmill training, elastic band training, aquatic training, and Nordic walking training. The results indicated that both cardiovascular exercise and resistance exercise could delay musculoskeletal aging and enhance the cognitive functions of the brain. Additionally, different types and intensities of exercise exhibited varying effects on myokine expression.
Conclusion: Current evidence suggests that exercise mediates the secretion of specific myokines, including IL-6, IGF-1, BDNF, CTSB, irisin, and LIF, which establish self-regulatory circuits between the brain and muscle. This interaction enhances cognitive function in the brain and improves skeletal muscle function. Future research should focus on elucidating the exact mechanisms that govern the release of myokines, the correlation between the intensity of exercise and the secretion of these myokines, and the distinct processes by which myokines influence the interaction between muscle and the brain.

Keywords:  Alzheimer’s disease; exercise; mild cognitive impairment; muscle-brain loop; musculoskeletal aging; myokines

DOI:  https://doi.org/10.3389/fphys.2024.1338875
Aging Cell. 2024 Sep 19. e14337

In vitro immuno-prevention of nitration/dysfunction of myogenic stem cell activator HGF, towards developing a strategy for age-related muscle atrophy.

Sakiho Tanaka, Alaa Elgaabari, Miyumi Seki, So Kuwakado, Kahona Zushi, Junri Miyamoto, Shoko Sawano, Wataru Mizunoya, Kenshiro Ehara, Naruha Watanabe, Yohei Ogawa, Hikaru Imakyure, Reina Fujimaru, Rika Osaki, Kazuki Shitamitsu, Kaoru Mizoguchi, Tomoki Ushijima, Takahiro Maeno, Takashi Nakashima, Takahiro Suzuki, Mako Nakamura, Judy E Anderson, Ryuichi Tatsumi.

  In response to peroxynitrite (ONOO-) generation, myogenic stem satellite cell activator HGF (hepatocyte growth factor) undergoes nitration of tyrosine residues (Y198 and Y250) predominantly on fast IIa and IIx myofibers to lose its binding to the signaling receptor c-met, thereby disturbing muscle homeostasis during aging. Here we show that rat anti-HGF monoclonal antibody (mAb) 1H41C10, which was raised in-house against a synthetic peptide FTSNPEVRnitroY198EV, a site well-conserved in mammals, functions to confer resistance to nitration dysfunction on HGF. 1H41C10 was characterized by recognizing both nitrated and non-nitrated HGF with different affinities as revealed by Western blotting, indicating that the paratope of 1H41C10 may bind to the immediate vicinity of Y198. Subsequent experiments showed that 1H41C10-bound HGF resists peroxynitrite-induced nitration of Y198. A companion mAb-1H42F4 presented similar immuno-reactivity, but did not protect Y198 nitration, and thus served as the control. Importantly, 1H41C10-HGF also withstood Y250 nitration to retain c-met binding and satellite cell activation functions in culture. The Fab region of 1H41C10 exerts resistivity to Y250 nitration possibly due to its localization in the immediate vicinity to Y250, as supported by an additional set of experiments showing that the 1H41C10-Fab confers Y250-nitration resistance which the Fc segment does not. Findings highlight the in vitro preventive impact of 1H41C10 on HGF nitration-dysfunction that strongly impairs myogenic stem cell dynamics, potentially pioneering cogent strategies for counteracting or treating age-related muscle atrophy with fibrosis (including sarcopenia and frailty) and the therapeutic application of investigational HGF drugs.

Keywords:  c‐met binding; hepatocyte growth factor (HGF); monoclonal antibody; muscle atrophy; peroxynitrite; rat; resident myogenic stem satellite cell; tyrosine nitration

DOI:  https://doi.org/10.1111/acel.14337
J Cachexia Sarcopenia Muscle. 2024 Sep 14.

High-Intensity Interval Training Mitigates Sarcopenia and Suppresses the Myoblast Senescence Regulator EEF1E1.

Yaoshan Dun, Wenliang Zhang, Yang Du, Kangling Xie, Yuan Liu, Cui Li, Ling Qiu, Siqian Fu, Thomas P Olson, Yuqiong Long, Baiyang You, Suixin Liu.

  BACKGROUND: The optimal exercise regimen for alleviating sarcopenia remains uncertain. This study aimed to investigate the efficacy of high-intensity interval training (HIIT) over moderate-intensity continuous training (MICT) in ameliorating sarcopenia.METHODS: We conducted a randomized crossover trial to evaluate plasma proteomic reactions to acute HIIT (four 4-min high-intensity intervals at 70% maximal capacity alternating with 4 min at 30%) versus MICT (constant 50% maximal capacity) in inactive adults. We explored the relationship between a HIIT-specific protein relative to MICT, identified via comparative proteomic analysis, eukaryotic translation elongation factor 1 epsilon 1 (EEF1E1) and sarcopenia in a paired case-control study of elderly individuals (aged over 65). Young (3 months old) and aged (20 months old) mice were randomized to sedentary, HIIT and MICT groups (five sessions/week for 4 weeks; n = 8 for each group). Measurements included skeletal muscle index, hand grip strength, expression of atrophic markers Atrogin1 and MuRF1 and differentiation markers MyoD, myogenin and MyHC-II via western blotting. We examined the impact of EEF1E1 siRNA and recombinant protein on D-galactose-induced myoblast senescence, measuring senescence-associated β-galactosidase and markers like p21 and p53.
RESULTS: The crossover trial, including 10 sedentary adults (32 years old, IQR 31-32) demonstrated significant alterations in the abundance of 21 plasma proteins after HIIT compared with MICT. In the paired case-control study of 84 older adults (84 years old, IQR 69-81; 52% female), EEF1E1 was significantly increased in those with sarcopenia compared to those without (14.68 [95%CI, 2.02-27.34] pg/mL, p = 0.03) and was associated with skeletal muscle index (R2 = 0.51, p < 0.001) and hand grip strength (R2 = 0.54, p < 0.001). In the preclinical study, aged mice exhibited higher EEF1E1 mRNA and protein levels in skeletal muscle compared to young mice, accompanied by a lower muscle mass and strength, increased cellular senescence and protein degradation markers and reduced muscle differentiation efficiency (all p < 0.05). HIIT reduced EEF1E1 expression and mitigated age-related muscle decline and atrophy in aged mice more effectively than MICT. Notably, EEF1E1 downregulation via siRNA significantly counteracted D-galactose-induced myoblast senescence as evidenced by reduced markers of muscle protein degradation and improved muscle differentiation efficiency (all p < 0.05). Conversely, treatments that increased EEF1E1 levels accelerated the senescence process (p < 0.05). Further exploration indicated that the decrease in EEF1E1 was associated with increased SIRT1 level and enhanced autophagy.
CONCLUSIONS: This study highlights the potential of HIIT as a promising approach to prevent and treat sarcopenia while also highlighting EEF1E1 as a potential intervention target.

Keywords:  EEF1E1; autophagy; high‐intensity interval training; sarcopenia; senescence

DOI:  https://doi.org/10.1002/jcsm.13600
Stem Cell Res Ther. 2024 Sep 15. 15(1): 302

Ameliorated cellular hallmarks of myotonic dystrophy in hybrid myotubes from patient and unaffected donor cells.

Renée H L Raaijmakers, C Rosanne M Ausems, Marieke Willemse, Sarah A Cumming, Baziel G M van Engelen, Darren G Monckton, Hans van Bokhoven, Derick G Wansink.

BACKGROUND: Cell-based strategies are being explored as a therapeutic option for muscular dystrophies, using a variety of cell types from different origin and with different characteristics. Primary pericytes are multifunctional cells found in the capillary bed that exhibit stem cell-like and myogenic regenerative properties. This unique combination allows them to be applied systemically, presenting a promising opportunity for body-wide muscle regeneration. We previously reported the successful isolation of ALP+ pericytes from skeletal muscle of patients with myotonic dystrophy type 1 (DM1). These pericytes maintained normal growth parameters and myogenic characteristics in vitro despite the presence of nuclear (CUG)n RNA foci, the cellular hallmark of DM1. Here, we examined the behaviour of DM1 pericytes during myogenic differentiation.METHODS: DMPK (CTG)n repeat lengths in patient pericytes were assessed using small pool PCR, to be able to relate variation in myogenic properties and disease hallmarks to repeat expansion. Pericytes from unaffected controls and DM1 patients were cultured under differentiating conditions in vitro. In addition, the pericytes were grown in co-cultures with myoblasts to examine their regenerative capacity by forming hybrid myotubes. Finally, the effect of pericyte fusion on DM1 disease hallmarks was investigated.
RESULTS: Small pool PCR analysis revealed the presence of somatic mosaicism in pericyte cell pools. Upon differentiation to myotubes, DMPK expression was upregulated, leading to an increase in nuclear foci sequestering MBNL1 protein. Remarkably, despite the manifestation of these disease biomarkers, patient-derived pericytes demonstrated myogenic potential in co-culture experiments comparable to unaffected pericytes and myoblasts. However, only the unaffected pericytes improved the disease hallmarks in hybrid myotubes. From 20% onwards, the fraction of unaffected nuclei in myotubes positively correlated with a reduction of the number of RNA foci and an increase in the amount of free MBNL1.
CONCLUSIONS: Fusion of only a limited number of unaffected myogenic precursors to DM1 myotubes already ameliorates cellular disease hallmarks, offering promise for the development of cell transplantation strategies to lower disease burden.

DOI: https://doi.org/10.1186/s13287-024-03913-y
Mol Biotechnol. 2024 Sep 18.

Transcriptome Analysis of Differentially Expressed Genes and Molecular Pathways Involved in C2C12 Cells Myogenic Differentiation.

Lingjian Tao, Weixing Huang, Zhiyan Li, Wei Wang, Xinhuan Lei, Jiangjie Chen, Xiaoting Song, Fangying Lu, Shaohua Fan, Liwei Zhang.

  Muscles are essential tissues responsible for movement, stability, and metabolism, playing a crucial role in human health and well-being. A comprehensive understanding of muscle differentiation processes is imperative for combating muscle degenerative diseases such as muscular dystrophy. In this study, C2C12 cells were induced to differentiate into myotubes in vitro. Phenotypic changes were observed utilizing Gimsa and immunofluorescent staining techniques. RNA sequencing was conducted at distinct time points (0, 2, 4, and 7 days) during the differentiation process. To elucidate the underlying molecular mechanisms, differential expression analysis, gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and Gene Set Enrichment Analysis (GSEA) were performed. Soft clustering of time series gene expression was employed to establish the expression patterns of differentially expressed genes (DEGs) at various time points during myogenesis. Additionally, quantitative reverse transcription PCR was utilized to validate gene expression from RNA-seq data at the mRNA level. Throughout the myogenic differentiation of C2C12 cells, notable morphological changes were observed, with myoblasts forming multinucleated myotubes by day 4 and plump elongated structures by day 7. Gene expression analysis revealed a substantial increase in DEGs as differentiation progressed, with a significant rise in DEGs from day 0 to day 7. Enrichment analysis highlighted key biological processes and pathways involved, including signal transduction and immune system processes, as well as pathways like chemokine and calcium signaling. Noise-robust soft clustering identified distinct temporal gene expression patterns, categorizing genes into upregulated, downregulated, and biphasic response clusters. The MYH family exhibited diverse expression changes, with Myh3, Myh13, Myh6, Myh7, Myh2, Myh8, Myh14, Myh7b, Myh1, and Myh4 upregulated, Myh10, Myh9, and Myh12 downregulated. Key transcription factors displayed dynamic expression patterns, which was crucial for the regulation of myoblast differentiation. A comprehensive and dynamic transcriptomic analysis of the C2C12 myoblast differentiation process has significantly enhanced our understanding of the key genes and biological pathways involved in myogenesis.

Keywords:  C2C12 cell; Myoblast; Myogenic differentiation; RNA sequencing

DOI:  https://doi.org/10.1007/s12033-024-01259-7
Acta Neuropathol. 2024 Sep 16. 148(1): 43

Dysregulated FOXO1 activity drives skeletal muscle intrinsic dysfunction in amyotrophic lateral sclerosis.

Mónica Zufiría, Oihane Pikatza-Menoio, Maddi Garciandia-Arcelus, Xabier Bengoetxea, Andrés Jiménez, Amaia Elicegui, María Levchuk, Olatz Arnold-García, Jon Ondaro, Pablo Iruzubieta, Laura Rodríguez-Gómez, Uxoa Fernández-Pelayo, Mikel Muñoz-Oreja, Ana Aiastui, José Manuel García-Verdugo, Vicente Herranz-Pérez, Miren Zulaica, Juan José Poza, Rebeca Ruiz-Onandi, Roberto Fernández-Torrón, Juan Bautista Espinal, Mario Bonilla, Ana Lersundi, Gorka Fernández-Eulate, Javier Riancho, Ainara Vallejo-Illarramendi, Ian James Holt, Amets Sáenz, Edoardo Malfatti, Stéphanie Duguez, Lorea Blázquez, Adolfo López de Munain, Gorka Gerenu, Francisco Gil-Bea, Sonia Alonso-Martín.

  Amyotrophic Lateral Sclerosis (ALS) is a multisystemic neurodegenerative disorder, with accumulating evidence indicating metabolic disruptions in the skeletal muscle preceding disease symptoms, rather than them manifesting as a secondary consequence of motor neuron (MN) degeneration. Hence, energy homeostasis is deeply implicated in the complex physiopathology of ALS and skeletal muscle has emerged as a key therapeutic target. Here, we describe intrinsic abnormalities in ALS skeletal muscle, both in patient-derived muscle cells and in muscle cell lines with genetic knockdown of genes related to familial ALS, such as TARDBP (TDP-43) and FUS. We found a functional impairment of myogenesis that parallels defects of glucose oxidation in ALS muscle cells. We identified FOXO1 transcription factor as a key mediator of these metabolic and functional features in ALS muscle, via gene expression profiling and biochemical surveys in TDP-43 and FUS-silenced muscle progenitors. Strikingly, inhibition of FOXO1 mitigated the impaired myogenesis in both the genetically modified and the primary ALS myoblasts. In addition, specific in vivo conditional knockdown of TDP-43 or FUS orthologs (TBPH or caz) in Drosophila muscle precursor cells resulted in decreased innervation and profound dysfunction of motor nerve terminals and neuromuscular synapses, accompanied by motor abnormalities and reduced lifespan. Remarkably, these phenotypes were partially corrected by foxo inhibition, bolstering the potential pharmacological management of muscle intrinsic abnormalities associated with ALS. The findings demonstrate an intrinsic muscle dysfunction in ALS, which can be modulated by targeting FOXO factors, paving the way for novel therapeutic approaches that focus on the skeletal muscle as complementary target tissue.

Keywords:  Amyotrophic lateral sclerosis; FOXO1; FUS; Glycolysis; Myogenesis; TDP-43

DOI:  https://doi.org/10.1007/s00401-024-02794-y
Nat Rev Endocrinol. 2024 Sep 18.

Skeletal muscle loss and sarcopenia in obesity pharmacotherapy.

David C D Hope, Tricia M-M Tan.

DOI: https://doi.org/10.1038/s41574-024-01041-4
Commun Biol. 2024 Sep 18. 7(1): 1108

Dual role of the S5 segment in type 1 ryanodine receptor channel gating.

Takashi Murayama, Yuya Otori, Nagomi Kurebayashi, Toshiko Yamazawa, Hideto Oyamada, Takashi Sakurai, Haruo Ogawa.

The type 1 ryanodine receptor (RyR1) is a Ca2+ release channel in the sarcoplasmic reticulum that is essential for skeletal muscle contraction. RyR1 forms a channel with six transmembrane segments, in which S5 is the fifth segment and is thought to contribute to pore formation. However, its role in channel gating remains unclear. Here, we performed a functional analysis of several disease-associated mutations in S5 and interpreted the results with respect to the published RyR1 structures to identify potential interactions associated with the mutant phenotypes. We demonstrate that S5 plays a dual role in channel gating: the cytoplasmic side interacts with S6 to reduce the channel activity, whereas the luminal side forms a rigid structural base necessary for S6 displacement in channel opening. These results deepen our understanding of the molecular mechanisms of RyR1 channel gating and provide insight into the divergent disease phenotypes caused by mutations in S5.

DOI: https://doi.org/10.1038/s42003-024-06787-1
Hum Mol Genet. 2024 Sep 15. pii: ddae136. [Epub ahead of print]

Pathomechanisms of Monoallelic variants in TTN causing skeletal muscle disease.

Jochen Gohlke, Johan Lindqvist, Zaynab Hourani, Sarah Heintzman, Paola Tonino, Bakri Elsheikh, Ana Morales, Matteo Vatta, Arthur Burghes, Henk Granzier, Jennifer Roggenbuck.

  Pathogenic variants in the titin gene (TTN) are known to cause a wide range of cardiac and musculoskeletal disorders, with skeletal myopathy mostly attributed to biallelic variants. We identified monoallelic truncating variants (TTNtv), splice site or internal deletions in TTN in probands with mild, progressive axial and proximal weakness, with dilated cardiomyopathy frequently developing with age. These variants segregated in an autosomal dominant pattern in 7 out of 8 studied families. We investigated the impact of these variants on mRNA, protein levels, and skeletal muscle structure and function. Results reveal that nonsense-mediated decay likely prevents accumulation of harmful truncated protein in skeletal muscle in patients with TTNtvs. Splice variants and an out-of-frame deletion induce aberrant exon skipping, while an in-frame deletion produces shortened titin with intact N- and C-termini, resulting in disrupted sarcomeric structure. All variant types were associated with genome-wide changes in splicing patterns, which represent a hallmark of disease progression. Lastly, RNA-seq studies revealed that GDF11, a member of the TGF-β superfamily, is upregulated in diseased tissue, indicating that it might be a useful therapeutic target in skeletal muscle titinopathies.

Keywords:   TTN deletion; TTNtv; Dominant titinopathy; Titin; titinopathy pathomechanisms

DOI:  https://doi.org/10.1093/hmg/ddae136
bioRxiv. 2024 Sep 03. pii: 2024.08.30.610194. [Epub ahead of print]

Freeze-dried porous collagen scaffolds for the repair of volumetric muscle loss injuries.

Ivan M Basurto, Ryann D Boudreau, Geshani C Bandara, Samir A Muhammad, George J Christ, Steven R Caliari.

Volumetric muscle loss (VML) injuries are characterized by the traumatic loss of skeletal muscle resulting in permanent damage to both tissue architecture and electrical excitability. To address this challenge, we previously developed a 3D aligned collagen-glycosaminoglycan (CG) scaffold platform that supported in vitro myotube alignment and maturation. In this work, we assessed the ability of CG scaffolds to facilitate functional muscle recovery in a rat tibialis anterior (TA) model of VML. Functional muscle recovery was assessed following implantation of either non-conductive CG or electrically conductive CG-polypyrrole (PPy) scaffolds at 4, 8, and 12 weeks post-injury by in vivo electrical stimulation of the peroneal nerve. After 12 weeks, scaffold-treated muscles produced maximum isometric torque that was significantly greater than non-treated tissues. Histological analysis further supported these reparative outcomes with evidence of regenerating muscle fibers at the material-tissue interface in scaffold-treated tissues that was not observed in non-repaired muscles. Scaffold-treated muscles possessed higher numbers of M1 and M2 macrophages at the injury while conductive CG-PPy scaffold-treated muscles showed significantly higher levels of neovascularization as indicated by the presence of pericytes and endothelial cells, suggesting a persistent wound repair response not observed in non-treated tissues. Finally, only tissues treated with non-conductive CG scaffolds displayed neurofilament staining similar to native muscle, further corroborating isometric contraction data. Together, these findings show that CG scaffolds can facilitate improved skeletal muscle function and endogenous cellular repair, highlighting their potential use as therapeutics for VML injuries.

DOI: https://doi.org/10.1101/2024.08.30.610194
J Am Heart Assoc. 2024 Sep 18. e036555

Exercise Alleviates Cardiovascular Diseases by Improving Mitochondrial Homeostasis.

Huijie Zhang, Yuxuan Zhang, Jiaqiao Zhang, Dandan Jia.

  Engaging in regular exercise and physical activity contributes to delaying the onset of cardiovascular diseases (CVDs). However, the physiological mechanisms underlying the benefits of regular exercise or physical activity in CVDs remain unclear. The disruption of mitochondrial homeostasis is implicated in the pathological process of CVDs. Exercise training effectively delays the onset and progression of CVDs by significantly ameliorating the disruption of mitochondrial homeostasis. This includes improving mitochondrial biogenesis, increasing mitochondrial fusion, decreasing mitochondrial fission, promoting mitophagy, and mitigating mitochondrial morphology and function. This review provides a comprehensive overview of the benefits of physical exercise in the context of CVDs, establishing a connection between the disruption of mitochondrial homeostasis and the onset of these conditions. Through a detailed examination of the underlying molecular mechanisms within mitochondria, the study illuminates how exercise can provide innovative perspectives for future therapies for CVDs.

Keywords:  cardiovascular diseases; exercise; exerkines; mitochondrial homeostasis

DOI:  https://doi.org/10.1161/JAHA.124.036555
Heliyon. 2024 Sep 15. 10(17): e37311

Functional study of the ST6GAL2 gene regulating skeletal muscle growth and development.

Tao Wang, Bo Ran, Yingyu Luo, Jideng Ma, Jing Li, Penghao Li, Mingzhou Li, Diyan Li.

  ST6GAL2, a member of the sialoglycosyltransferase family, primarily localizes within the cellular Golgi apparatus. However, the role of the ST6GAL2 gene in skeletal muscle growth and development remains elusive. In this study, the impact of the ST6GAL2 gene on the proliferation, differentiation, and apoptosis of primary chicken myoblasts at the cellular level was investigated. Quantitative fluorescent PCR was used to measure the expression levels of genes. Subsequently, using gene knockout mice, we assessed its effects on skeletal muscle growth and development in vivo. Our findings reveal that the ST6GAL2 gene promotes the expression of cell cycle and proliferation-related genes, including CCNB2 and PCNA, and apoptosis-related genes, such as Fas and Caspase-9. At the individual level, double knockout of ST6GAL2 inhibited the formation of both fast and slow muscle fibers in the quadriceps, extensor digitorum longus, and tibial anterior muscle, while promoting their formation in the gastrocnemius and soleus. These results collectively demonstrate that the ST6GAL2 gene facilitates the proliferation, apoptosis, and fusion processes of primary chicken myoblasts. Additionally, it promotes the enlargement of cross-sectional muscle fiber areas and regulates the formation of fast and slow muscle fibers at the individual level, albeit inhibiting muscle fusion. This study provides valuable insights into the role of the ST6GAL2 gene in promoting proliferation of skeletal muscle.

Keywords:  Cell proliferation and apoptosis; Induced differentiation; Knockout mice; Primary myoblast; ST6GAL2; Skeletal muscle

DOI:  https://doi.org/10.1016/j.heliyon.2024.e37311
PLoS One. 2024 ;19(9): e0310406

Elucidating the effect of drug-induced mitochondrial dysfunction on insulin signaling and glucose handling in skeletal muscle cell line (C2C12) in vitro.

Auxiliare Kuretu, Mamosheledi Mothibe, Phikelelani Ngubane, Ntethelelo Sibiya.

Efavirenz, tenofovir, rifampicin, simvastatin, lamotrigine and clarithromycin are known potential mitochondrial toxicants. Mitochondrial toxicity has been reported to disrupt the chain of events in the insulin signalling pathway. Considering the upward trajectory of diabetes mellitus prevalence, studies which seek to uncover probable risk factors for developing diabetes should be encouraged. This study aimed to evaluate the intracellular mechanisms leading to the development of insulin resistance in the presence of various conventional pharmacological agents reported as potential mitochondrial toxicants in skeletal muscle cell line. Differentiated C2C12 preparations were exposed to multiple concentrations of efavirenz, tenofovir, rifampicin, simvastatin, lamotrigine, and clarithromycin, separately. Glucose handling was evaluated by observing the changes in insulin-stimulated glucose uptake and assessing the changes in GLUT4 translocation, GLUT4 expression and Akt expression. The changes in mitochondrial function were evaluated by assessing mitochondrial membrane integrity, cellular ATP production, generation of intracellular reactive oxygen species, expression of tafazzin and quantification of medium malonaldehyde. Insulin stimulated glucose uptake was perturbed in C2C12 pre-treated with potential mitotoxicants. Additionally, ATP synthesis, alterations in mitochondrial membrane potential, excessive accumulation of ROS and malonaldehyde were observed in the presence of potential mitotoxicants. Particularly, we observed suppression of proteins involved in the insulin signalling pathway and maintenance of mitochondrial function namely GLUT4, Akt and tafazzin. Mitochondrial toxicants can potentially induce insulin resistance emanating from mitochondrial dysfunction. These new findings will contribute to the understanding of underlying mechanisms involved in the development of insulin resistance linked to mitochondrial dysfunction.

DOI: https://doi.org/10.1371/journal.pone.0310406
Proc Natl Acad Sci U S A. 2024 Sep 24. 121(39): e2408324121

Agonist antibody to MuSK protects mice from MuSK myasthenia gravis.

Julien Oury, Begona Gamallo-Lana, Leah Santana, Christophe Steyaert, Dana L E Vergoossen, Adam C Mar, Bernhardt Vankerckhoven, Karen Silence, Roeland Vanhauwaert, Maartje G Huijbers, Steven J Burden.

  Myasthenia gravis (MG) is a chronic and severe disease of the skeletal neuromuscular junction (NMJ) in which the effects of neurotransmitters are attenuated, leading to muscle weakness. In the most common forms of autoimmune MG, antibodies attack components of the postsynaptic membrane, including the acetylcholine receptor (AChR) or muscle-specific kinase (MuSK). MuSK, a master regulator of NMJ development, associates with the low-density lipoprotein-related receptor 4 (Lrp4) to form the signaling receptor for neuronal Agrin, a nerve-derived synaptic organizer. Pathogenic antibodies to MuSK interfere with binding between MuSK and Lrp4, inhibiting the differentiation and maintenance of the NMJ. MuSK MG can be debilitating and refractory to treatments that are effective for AChR MG. We show here that recombinant antibodies, derived from MuSK MG patients, cause severe neuromuscular disease in mice. The disease can be prevented by a MuSK agonist antibody, presented either prophylactically or after disease onset. These findings suggest a therapeutic alternative to generalized immunosuppression for treating MuSK MG by selectively and directly targeting the disease mechanism.

Keywords:  autoimmune disease; myasthenia gravis; neuromuscular; synapse; therapeutic antibody

DOI:  https://doi.org/10.1073/pnas.2408324121
Geroscience. 2024 Sep 17.

Age-related breakdown in networks of inter-muscular coordination.

Sergi Garcia-Retortillo, Óscar Abenza, Fidanka Vasileva, Natàlia Balagué, Robert Hristovski, Andrew Wells, Jason Fanning, Jeff Kattula, Plamen Ch Ivanov.

  Assessing inter-muscular coordination in older adults is crucial, as it directly impacts an individual's ability for independent functioning, injury prevention, and active engagement in daily activities. However, the precise mechanisms by which distinct muscle fiber types synchronize their activity across muscles to generate coordinated movements in older adults remain unknown. Our objective is to investigate how distinct muscle groups dynamically synchronize with each other in young and older adults during exercise. Thirty-five young adults and nine older adults performed one bodyweight squat set until exhaustion. Simultaneous surface electromyography (sEMG) recordings were taken from the left and right vastus lateralis, and left and right erector spinae. To quantify inter-muscular coordination, we first obtained ten time series of sEMG band power for each muscle, representing the dynamics of different muscle fiber types. Next, we calculated the bivariate equal-time Pearson's cross-correlation for each pair of sEMG band power time series across all leg and back muscles. The main results show (i) an overall reduction in the degree of inter-muscular coordination, and (ii) increased stratification of the inter-muscular network in older adults compared to young adults. These findings suggest that as individuals age, the global inter-muscular network becomes less flexible and adaptable, hindering its ability to reorganize effectively in response to fatigue or other stimuli. This network approach opens new avenues for developing novel network-based markers to characterize multilevel inter-muscular interactions, which can help target functional deficits and potentially reduce the risk of falls and neuro-muscular injuries in older adults.

Keywords:  Aging; Complex systems; Inter-muscular coordination; Muscle fibers; Network physiology; Skeletal muscles

DOI:  https://doi.org/10.1007/s11357-024-01331-9
Nat Rev Dis Primers. 2024 Sep 19. 10(1): 68

Sarcopenia.

Avan A Sayer, Rachel Cooper, Hidenori Arai, Peggy M Cawthon, Marie-Josiane Ntsama Essomba, Roger A Fielding, Miranda D Grounds, Miles D Witham, Alfonso J Cruz-Jentoft.

Sarcopenia is the accelerated loss of skeletal muscle mass and function commonly, but not exclusively, associated with advancing age. It is observed across many species including humans in whom it can lead to decline in physical function and mobility as well as to increased risk of adverse outcomes including falls, fractures and premature mortality. Although prevalence estimates vary because sarcopenia has been defined in different ways, even using a conservative approach, the prevalence is between 5% and 10% in the general population. A life course framework has been proposed for understanding not only the occurrence of sarcopenia in later life but also influences operating at earlier life stages with potentially important implications for preventive strategies. Harnessing progress in understanding the hallmarks of ageing has been key to understanding sarcopenia pathophysiology. Considerable convergence in approaches to diagnosis of sarcopenia has occurred over the last 10 years, with a growing emphasis on the central importance of muscle strength. Resistance exercise is currently the mainstay of treatment; however, it is not suitable for all. Hence, adjunctive and alternative treatments to improve quality of life are needed. An internationally agreed approach to definition and diagnosis will enable a step change in the field and is likely to be available in the near future through the Global Leadership Initiative in Sarcopenia.

DOI: https://doi.org/10.1038/s41572-024-00550-w
J Nutr. 2024 Sep 13. pii: S0022-3166(24)01029-0. [Epub ahead of print]

Assessing muscle protein synthesis rates in vivo in humans: the deuterated water (2H2O) method.

Andrew M Holwerda, Philip J Atherton, Kenneth Smith, Daniel J Wilkinson, Stuart M Phillips, Luc J C van Loon.

  Skeletal muscle tissue is in a constant state of turnover, with muscle tissue protein synthesis and breakdown rates ranging between 1-2 % across the day in vivo in humans. Muscle tissue remodeling is largely controlled by the up- and down-regulation of muscle tissue protein synthesis rates. Research studies generally apply stable isotope labeled amino acids to assess muscle protein synthesis rates in vivo in humans. Following labeled amino acid administration in a laboratory setting, muscle tissue samples are collected over several hours to assess the incorporation rate of these labeled amino acids in muscle tissue protein. To allow quantification of bulk muscle protein synthesis rates over more prolonged periods, the use of deuterated water methodology has regained much interest. Ingestion of daily boluses of deuterium oxide (2H2O) results in 2H-enrichment of the body water pool. The available 2H-atoms become incorporated into endogenously synthesized alanine primarily through transamination of pyruvate in the liver. With 2H-alanine widely available to all tissues, it becomes incorporated into de novo synthesized tissue proteins. Assessing the increase in tissue protein-bound 2H-alanine enrichment in muscle biopsy samples over time allows for calculation of muscle protein synthesis rates over several days or even weeks. As the deuterated water method allows for assessment of muscle tissue protein synthesis rates under free living conditions in non-laboratory settings, there is an increasing interest in its application. This manuscript describes the theoretical background of the deuterated water method and offers a comprehensive tutorial to correctly apply the method to determine bulk muscle protein synthesis rates in vivo in humans.

Keywords:  Aging; Dietary Protein; Exercise; Muscle Atrophy; Muscle hypertrophy

DOI:  https://doi.org/10.1016/j.tjnut.2024.09.012