bims-moremu 2024-08-11 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024–08–11
23 papers selected by
Anna Vainshtein, Craft Science Inc.

A molecular pathway for cancer cachexia-induced muscle atrophy revealed at single-nucleus resolution.
Mitigating disuse-induced skeletal muscle atrophy in ageing: Resistance exercise as a critical countermeasure.
Enhanced secretion of promyogenic exosomes by quiescent muscle cells.
TMEM16A regulates satellite cell mediated skeletal muscle regeneration by ensuring a moderate level of caspase 3 activity.
Different outcomes of endurance and resistance exercise in skeletal muscles of Oculopharyngeal muscular dystrophy.
The benefits of exercise on aging: focus on muscle biomarkers.
Inhibition of Sesn2 has negative regulatory effects on the myogenic differentiation of C2C12 myoblasts.
Relationships between endurance exercise training-induced muscle fiber-type shifting and autophagy in slow- and fast-twitch skeletal muscles of mice.
A comprehensive single-cell RNA transcriptomic analysis identifies a unique SPP1+ macrophages subgroup in aging skeletal muscle.
Systemic and tissue-specific spexin response to acute treadmill exercise in rats.
Generation of Bidimensional and Three-Dimensional Muscle Culture Systems.
Effects of intensified training with insufficient recovery on joint level and single muscle fibre mechanical function: The role of myofibrillar Ca2+ sensitivity.
Enhanced expression of the myogenic factor Myocyte enhancer factor-2 in imaginal disc myoblasts activates a partial, but incomplete, muscle development program.
DNA Electrotransfer Regulates Molecular Functions in Skeletal Muscle.
Interactions between myoblasts and macrophages under high glucose milieus result in inflammatory response and impaired insulin sensitivity.
Are Aminoglycoside Antibiotics TRPing Your Metabolic Switches?
Integration of single-cell datasets depicts profiles of macrophages and fibro/adipogenic progenitors in dystrophic muscle.
GDF15 is dispensable for the insulin-sensitizing effects of chronic exercise.
Harmonization of experimental procedures to assess mitochondrial respiration in human permeabilized skeletal muscle fibers.
The foundation of excitation-contraction coupling in skeletal muscle: Communication between the transverse tubules and sarcoplasmic reticulum.
Peroxiredoxin 2 Regulates DAF-16/FOXO Mediated Mitochondrial Remodelling in Response to Exercise that is Disrupted in Ageing.
Sex differences in human performance.
Mitochondrial fragmentation in early differentiation of human MB135 myoblasts: Role of mitochondrial ROS production in the absence of depolarization.

Cell Rep. 2024 Aug 07. pii: S2211-1247(24)00916-1. [Epub ahead of print]43(8): 114587

A molecular pathway for cancer cachexia-induced muscle atrophy revealed at single-nucleus resolution.

Yichi Zhang, Matthieu Dos Santos, Huocong Huang, Kenian Chen, Puneeth Iyengar, Rodney Infante, Patricio M Polanco, Rolf A Brekken, Chunyu Cai, Ambar Caijgas, Karla Cano Hernandez, Lin Xu, Rhonda Bassel-Duby, Ning Liu, Eric N Olson.

  Cancer cachexia is a prevalent and often fatal wasting condition that cannot be fully reversed with nutritional interventions. Muscle atrophy is a central component of the syndrome, but the mechanisms whereby cancer leads to skeletal muscle atrophy are not well understood. We performed single-nucleus multi-omics on skeletal muscles from a mouse model of cancer cachexia and profiled the molecular changes in cachexic muscle. Our results revealed the activation of a denervation-dependent gene program that upregulates the transcription factor myogenin. Further studies showed that a myogenin-myostatin pathway promotes muscle atrophy in response to cancer cachexia. Short hairpin RNA inhibition of myogenin or inhibition of myostatin through overexpression of its endogenous inhibitor follistatin prevented cancer cachexia-induced muscle atrophy in mice. Our findings uncover a molecular basis of muscle atrophy associated with cancer cachexia and highlight potential therapeutic targets for this disorder.

Keywords:  AAV; CP: Cancer; CP: Metabolism; atrophy; cachexia; denervation; myogenin; myostatin; single nucleus ATAC-seq; single nucleus RNA-seq; single nucleus multiome

DOI:  https://doi.org/10.1016/j.celrep.2024.114587
Exp Physiol. 2024 Aug 06.

Mitigating disuse-induced skeletal muscle atrophy in ageing: Resistance exercise as a critical countermeasure.

James McKendry, Giulia Coletta, Everson A Nunes, Changhyun Lim, Stuart M Phillips.

  The gradual deterioration of physiological systems with ageing makes it difficult to maintain skeletal muscle mass (sarcopenia), at least partly due to the presence of 'anabolic resistance', resulting in muscle loss. Sarcopenia can be transiently but markedly accelerated through periods of muscle disuse-induced (i.e., unloading) atrophy due to reduced physical activity, sickness, immobilisation or hospitalisation. Periods of disuse are detrimental to older adults' overall quality of life and substantially increase their risk of falls, physical and social dependence, and early mortality. Disuse events induce skeletal muscle atrophy through various mechanisms, including anabolic resistance, inflammation, disturbed proteostasis and mitochondrial dysfunction, all of which tip the scales in favour of a negative net protein balance and subsequent muscle loss. Concerningly, recovery from disuse atrophy is more difficult for older adults than their younger counterparts. Resistance training (RT) is a potent anabolic stimulus that can robustly stimulate muscle protein synthesis and mitigate muscle losses in older adults when implemented before, during and following unloading. RT may take the form of traditional weightlifting-focused RT, bodyweight training and lower- and higher-load RT. When combined with sufficient dietary protein, RT can accelerate older adults' recovery from a disuse event, mitigate frailty and improve mobility; however, few older adults regularly participate in RT. A feasible and practical approach to improving the accessibility and acceptability of RT is through the use of resistance bands. Moving forward, RT must be prescribed to older adults to mitigate the negative consequences of disuse atrophy.

Keywords:  anabolism; catabolism; muscle unloading; physical activity; sarcopenia

DOI:  https://doi.org/10.1113/EP091937
Front Cell Dev Biol. 2024 ;12 1381357

Enhanced secretion of promyogenic exosomes by quiescent muscle cells.

Prabhavathy Devan, Ananga Ghosh, Pallavi Rao T, Swasti Raychaudhuri, Harikrishna Adicherla, Himadri Devanshi, Pallavi Kshetrapal, Jyotsna Dhawan.

  Signaling interactions are important during skeletal muscle regeneration, where muscle cells in distinct states (quiescent, reactivated, proliferating and differentiated) must coordinate their response to injury. Here, we probed the role of secreted small extracellular vesicles (sEV/exosomes) using a culture model of physiologically relevant cell states seen in muscle regeneration. Unexpectedly, G0 myoblasts exhibited enhanced secretion of sEV (∼150 nm) displaying exosome markers (Alix, TSG101, flotillin-1, and CD9), and increased expression of Kibra, a regulator of exosome biogenesis. Perturbation of Kibra levels confirmed a role in controlling sEV secretion rates. Purified sEVs displayed a common exosome marker-enriched proteome in all muscle cell states, as well as state-specific proteins. Exosomes derived from G0 cells showed an antioxidant signature, and were most strongly internalized by differentiated myotubes. Functionally, donor exosomes from all muscle cell states could activate an integrated Wnt reporter in target cells, but only G0-derived exosomes could induce myogenic differentiation in proliferating cells. Taken together, we provide evidence that quiescence in muscle cells is accompanied by enhanced secretion of exosomes with distinct uptake, cargo and signal activating features. Our study suggests the novel possibility that quiescent muscle stem cells in vivo may play a previously under-appreciated signaling role during muscle homeostasis.

Keywords:  G0; KIBRA; SEV; Wnt; differentiation; exosomes; myoblast; quiescence

DOI:  https://doi.org/10.3389/fcell.2024.1381357
Stem Cells. 2024 Aug 04. pii: sxae048. [Epub ahead of print]

TMEM16A regulates satellite cell mediated skeletal muscle regeneration by ensuring a moderate level of caspase 3 activity.

Zhiyuan Sun, Xinqi Shan, Chun'e Fan, Lutao Liu, Shuai Li, Jiahui Wang, Na Zhou, Minsheng Zhu, Huaqun Chen.

  It has been documented that caspase 3 activity is necessary for skeletal muscle regeneration, but how its activity is regulated is largely unknown. Our previous report shows that intracellular TMEM16A, a calcium activated chloride channel, significantly regulates caspase 3 activity in myoblasts during skeletal muscle development. By using a mouse line with satellite cell (SC)-specific deletion of TMEM16A, we examined the role of TMEM16A in regulating caspase 3 activity in SC (or SC-derived myoblast) as well as skeletal muscle regeneration. The mutant animals displayed apparently impaired regeneration capacity in adult muscle along with enhanced ER stress and elevated caspase 3 activity in Tmem16a-/- SC derived myoblasts. Blockade of either excessive ER stress or caspase 3 activity by small molecules significantly restored the inhibited myogenic differentiation of Tmem16a-/- SCs, indicating that excessive caspase 3 activity resulted from TMEM16A deletion contributes to the impaired muscle regeneration and the upstream regulator of caspase 3 was ER stress. Our results revealed an essential role of TMEM16A in satellite cell mediated skeletal muscle regeneration by ensuring a moderate level of caspase 3 activity.

Keywords:  ER stress; TMEM16A; caspase 3; muscle regeneration; satellite cell

DOI:  https://doi.org/10.1093/stmcls/sxae048
J Cachexia Sarcopenia Muscle. 2024 Aug 07.

Different outcomes of endurance and resistance exercise in skeletal muscles of Oculopharyngeal muscular dystrophy.

Alexis Boulinguiez, Jamila Dhiab, Barbara Crisol, Laura Muraine, Ludovic Gaut, Corentin Rouxel, Justine Flaire, Hadidja-Rose Mouigni, Mégane Lemaitre, Benoit Giroux, Lucie Audoux, Benjamin SaintPierre, Arnaud Ferry, Vincent Mouly, Gillian Butler-Browne, Elisa Negroni, Alberto Malerba, Capucine Trollet.

   BACKGROUND: Exercise is widely considered to have beneficial impact on skeletal muscle aging. In addition, there are also several studies demonstrating a positive effect of exercise on muscular dystrophies. Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant inherited neuromuscular disorder caused by mutations in the PAPBN1 gene. These mutations consist in short (1-8) and meiotically stable GCN trinucleotide repeat expansions in its coding region responsible for the formation of PAPBN1 intranuclear aggregates. This study aims to characterize the effects of two types of chronic exercise, resistance and endurance, on the OPMD skeletal muscle phenotype using a relevant murine model of OPMD.
METHODS: In this study, we tested two protocols of exercise. In the first, based on endurance exercise, FvB (wild-type) and A17 (OPMD) mice underwent a 6-week-long motorized treadmill protocol consisting in three sessions per week of running 20 cm/s for 20 min. In the second protocol, based on resistance exercise generated by chronic mechanical overload (OVL), surgical removal of gastrocnemius and soleus muscles was performed, inducing hypertrophy of the plantaris muscle. In both types of exercise, muscles of A17 and FvB mice were compared with those of respective sedentary mice. For all the groups, force measurement, muscle histology, and molecular analyses were conducted.
RESULTS: Following the endurance exercise protocol, we did not observe any major changes in the muscle physiological parameters, but an increase in the number of PABPN1 intranuclear aggregates in both tibialis anterior (+24%, **P = 0.0026) and gastrocnemius (+18%, ****P < 0.0001) as well as enhanced collagen deposition (+20%, **P = 0.0064 in the tibialis anterior; +35%, **P = 0.0042 in the gastrocnemius) in the exercised A17 OPMD mice. In the supraphysiological resistance overload protocol, we also observed an increased collagen deposition (×2, ****P < 0.0001) in the plantaris muscle of A17 OPMD mice which was associated with larger muscle mass (×2, ****P < 0.0001) and fibre cross sectional area (×2, ***P = 0.0007) and increased absolute maximal force (×2, ****P < 0.0001) as well as a reduction in PABPN1 aggregate number (-16%, ****P < 0.0001).
CONCLUSIONS: Running exercise and mechanical overload led to very different outcome in skeletal muscles of A17 mice. Both types of exercise enhanced collagen deposition but while the running protocol increased aggregates, the OVL reduced them. More importantly OVL reversed muscle atrophy and maximal force in the A17 mice. Our study performed in a relevant model gives an indication of the effect of different types of exercise on OPMD muscle which should be further evaluated in humans for future recommendations as a part of the lifestyle of individuals with OPMD.

Keywords:  Atrophy; Exercise; Fibrosis; OPMD; PAPBN1; Skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13546
Aging (Albany NY). 2024 Aug 08. 16

The benefits of exercise on aging: focus on muscle biomarkers.

Robin Grolaux, Bernadette Jones-Freeman, Macsue Jacques, Nir Eynon.

  The focus on maintaining health and vitality (e.g., good healthspan) in later life has become increasingly important as the world's population is getting older. In the last decade, advances in aging research have identified biomarkers like DNA methylation (DNAm) and gene expression, offering insights into both chronological and biological aging. This understanding opens up possibilities for interventions that can slow down molecular aspects of the aging process. Exploring the impact of exercise on these biomarkers in human skeletal muscle (a critical tissue for metabolism, thermogenesis and movement) reveals its potential to foster healthier aging.

Keywords:  OMICs; biomarkers; epigenetics; exercise; skeletal muscle

DOI:  https://doi.org/10.18632/aging.206064
Mol Biomed. 2024 Aug 09. 5(1): 31

Inhibition of Sesn2 has negative regulatory effects on the myogenic differentiation of C2C12 myoblasts.

Zubiao Song, Qing Lin, Jiahui Liang, Weixi Zhang.

  Sestrin2 (Sesn2) has been previously confirmed to be a stress-response molecule. However, the influence of Sesn2 on myogenic differentiation remains elusive. This study was conducted to analyze the role of Sesn2 in the myogenic differentiation of C2C12 myoblasts and related aspects in mdx mice, an animal model of Duchenne muscular dystrophy (DMD). Our results showed that knockdown of Sesn2 reduced the myogenic differentiation capacity of C2C12 myoblasts. Predictive analysis from two databases suggested that miR-182-5p is a potential regulator of Sesn2. Further experimental validation revealed that overexpression of miR-182-5p decreased both the protein and mRNA levels of Sesn2 and inhibited myogenesis of C2C12 myoblasts. These findings suggest that miR-182-5p negatively regulates myogenesis by repressing Sesn2 expression. Extending to an in vivo model of DMD, knockdown of Sesn2 led to decreased Myogenin (Myog) expression and increased Pax7 expression, while its overexpression upregulated Myog levels and enhanced the proportion of slow-switch myofibers. These findings indicate the crucial role of Sesn2 in promoting myogenic differentiation and skeletal muscle regeneration, providing potential therapeutic targets for muscular dystrophy.

Keywords:  Duchenne muscular dystrophy; Myogenic differentiation; Sestrin2; Slow-twitch myofibers; miR-182-5p

DOI:  https://doi.org/10.1186/s43556-024-00193-z
Phys Act Nutr. 2024 Jun;28(2): 23-34

Relationships between endurance exercise training-induced muscle fiber-type shifting and autophagy in slow- and fast-twitch skeletal muscles of mice.

Insu Kwon, Kyoung Soo Kim, Youngil Lee.

   PURPOSE: Endurance exercise induces muscle fiber-type shifting and autophagy; however, the potential role of autophagy in muscle fiber-type transformation remains unclear. This study examined the relationship between muscle fiber-type shifting and autophagy in the soleus (SOL) and extensor digitorum longus (EDL) muscles, which are metabolically discrete muscles.
METHODS: Male C57BL/6J mice were randomly assigned to sedentary control (CON) and exercise (EXE) groups. After 1 week of acclimation to treadmill running, the mice in the EXE group ran at 12-15 m/min, 60 min/day, 5 days/week for 6 weeks. All mice were sacrificed 90 min after the last exercise session, and the targeted tissues were rapidly dissected. The right side of the tissues was used for western blot analysis, whereas the left side was subjected to immunohistochemical analysis.
RESULTS: Endurance exercise resulted in muscle fiber-type shifting (from type IIa to type I) and autophagy (an increase in LC3-II) in the SOL muscle. However, muscle fiber-type transformation and autophagy were not correlated in the SOL and EDL muscles. Interestingly, in contrast to the canonical autophagy signaling pathways, our study showed that exercise-induced autophagy concurs with enhanced anabolic (increased p-AKTSer473/AKT and p-mTOR/mTORSer2448 ratios) and suppressed catabolic (reduced p-AMPKThr172/AMPK ratio) states.
CONCLUSION: Our findings demonstrate that chronic endurance exercise-induced muscle fiber-type transformation and autophagy occur in a muscle-specific manner (e.g., SOL). More importantly, our study suggests that endurance training-induced SOL muscle fiber-type transition may underlie metabolic modulations caused by the AMPK and AKT/mTOR signaling pathways rather than autophagy.

Keywords:  AKT/mTOR; AMPK; LC3-II; exercise training adaptation; extensor digitorum longus; muscle fiber-type; soleus

DOI:  https://doi.org/10.20463/pan.2024.0013
Sci Rep. 2024 Aug 06. 14(1): 18156

A comprehensive single-cell RNA transcriptomic analysis identifies a unique SPP1+ macrophages subgroup in aging skeletal muscle.

Wen Bi, Mengyue Yang, Mengjia Shi, Mirong Hou, Changqing Jiang, Gang Fan, Weiming Guo.

  Senescence of skeletal muscle (SkM) has been a primary contributor to senior weakness and disability in recent years. The gradually declining SkM function associated with senescence has recently been connected to an imbalance between damage and repair. Macrophages (Mac) are involved in SkM aging, and different macrophage subgroups hold different biological functions. Through comprehensive single-cell transcriptomic analysis, we first compared the metabolic pathways and biological functions of different types of cells in young (Y) and old (O) mice SkM. Strikingly, the Mac population in mice SkM was also explored, and we identified a unique Mac subgroup in O SkM characterized by highly expressed SPP1 with strong senescence and adipogenesis features. Further work was carried out on the metabolic and biological processes for these Mac subgroups. Besides, we verified that the proportion of the SPP1+ Mac was increased significantly in the quadriceps tissues of O mice, and the senotherapeutic drug combination dasatinib + quercetin (D + Q) could dramatically reduce its proportion. Our study provides novel insight into the potential role of SPP1+ Mac in SkM, which may serve as a senotherapeutic target in SkM aging.

Keywords:  Cell senescence; SPP1+ macrophages; Senolytics; Single-cell sequencing; Skeletal muscle

DOI:  https://doi.org/10.1038/s41598-024-69284-9
Peptides. 2024 Aug 05. pii: S0196-9781(24)00134-7. [Epub ahead of print] 171281

Systemic and tissue-specific spexin response to acute treadmill exercise in rats.

Ibrahim Turkel, Berkay Ozerklig, Burak Yazgan, Ahmet Emrah Ozenc, Gokhan Burcin Kubat, Gulcin Simsek, Muhammed Mustafa Atakan, Sukran Nazan Kosar.

  Spexin (SPX) is a 14-amino-acid peptide that plays an important role in the regulation of metabolism and energy homeostasis. It is well known that a variety of bioactive molecules released into the circulation by organs and tissues in response to acute and chronic exercise, known as exerkines, mediate the benefits of exercise by improving metabolic health. However, it is unclear whether acute exercise affects SPX levels in the circulation and peripheral tissues. This study aimed to determine whether acute treadmill exercise induces plasma SPX levels, as well as mRNA expression and immunostaining of SPX in skeletal muscle, adipose tissue, and liver. Male Sprague Dawley rats were divided into sedentary and acute exercise groups. Plasma, soleus (SOL), extensor digitorum longus (EDL), adipose tissue, and liver samples were collected at six time points (0, 1, 3, 6, 12, and 24h) following 60min of acute treadmill exercise at a speed of 25m/min and 0% grade. Acute exercise increased plasma SPX levels and induced mRNA expression of Spx in the SOL, EDL, and liver. Immunohistochemical analysis demonstrated that acute exercise led to a decrease in SPX immunostaining in the liver. Taken together, these findings suggest that SPX increases in response to acute exercise as a potential exerkine candidate, and the liver may be one of the sources of acute exercise-induced plasma SPX levels in rats. However, a comprehensive analysis is needed to fully elucidate the systemic response of SPX to acute exercise, as well as the tissue from which SPX is secreted.

Keywords:  Adipose tissue; Exercise; Exerkine, Skeletal muscle; Liver; Spexin

DOI:  https://doi.org/10.1016/j.peptides.2024.171281
Methods Mol Biol. 2024 ;2835 229-247

Generation of Bidimensional and Three-Dimensional Muscle Culture Systems.

Marianna Cosentino, Antonio Musarò.

  Skeletal muscle is a postmitotic tissue composed of contractile myofibers that are oriented and connected to different layers of connective tissue. Nevertheless, adult muscle fibers retain the capacity to regenerate in response to damage, activating the classical muscle stem cell compartment, namely, satellite cells (SCs), which are mitotically quiescent cells until required for growth or repair and are localized between the basal lamina and sarcolemma of myofibers. The transition of SCs from the quiescent state toward activation, commitment, and differentiation involves the genetic and epigenetic adaptation to novel biological functions, entailing dynamic changes in the protein expression profile. Interestingly, some of the activities and signaling regulating proliferation, commitment, differentiation, and survival/apoptosis of satellite cells have been also partially recapitulated in vitro, taking advantage of robust markers, reliable techniques, and reproducible protocols. Over the years, different techniques of muscular cell culture have been designed including primary cultures from embryonic or postnatal muscle, myogenic cell line, and three-dimensional (3D) skeletal muscle construct. Typical two-dimensional (2D) muscle cell culture cannot fully recapitulate the complexity of living muscle tissues, restricting their usefulness for physiological studies. The development of functional 3D culture models represents a valid alternative to overcome the limitations of already available in vitro model, increasing our understanding of the roles played by the various cell types and how they interact. In this chapter, the development of bidimensional and three-dimensional cell cultures have been described, improving the technical aspect of satellite cell isolation, the best culture-based conditions for muscle cell growth and differentiation, and the procedures required to develop a three-dimensional skeletal muscle construct.

Keywords:  Cell culture; Muscle differentiation; Muscle primary culture; Satellite cells isolation; Three-dimensional bioengineered muscle

DOI:  https://doi.org/10.1007/978-1-0716-3995-5_19
Appl Physiol Nutr Metab. 2024 Aug 09.

Effects of intensified training with insufficient recovery on joint level and single muscle fibre mechanical function: The role of myofibrillar Ca2+ sensitivity.

Olivia P Roussel, Christopher Pignanelli, Emma F Hubbard, Alexandra M Coates, Arthur Cheng, Jamie F Burr, Geoffrey Alonzo Power.

Intense exercise training with insufficient recovery time is associated with reductions in neuromuscular performance. However, it is unclear how single muscle fibre mechanical function and myofibrillar Ca2+ sensitivity contribute to these impairments. We investigated the effects of overload training on joint-level neuromuscular performance and cellular-level mechanical function. Fourteenathletes (4 female, 10 male) underwent a 3-week intensified training protocol consisting of up to 150% of their regular training hours with three additional high-intensity training sessions per week. Neuromuscular performance of the knee extensors was assessed via maximum voluntary contraction (MVC) force, electrically evoked twitch contractions, and a force-frequency relationship. Muscle biopsies were taken from the vastus lateralis to assess single fibre mechanical function. Neither MVC force nor twitch parameters were altered following training (all p>0.05), but a rightward shift in the force-frequency curve was observed with average reduction in force of 6-27% across frequencies 5-20Hz (all p<0.05). In single fibres, maximal force output was not reduced following training, but there was a rightward shift in the force-pCa curve driven by a 6% reduction in Ca2+ sensitivity (p<0.05). These data indicate intensified training leads to impaired Ca2+ sensitivity at the single fibre level, which in part explains impaired neuromuscular function at the joint level during lower frequencies of activation. This is an important consideration for athletes, as performance is often assessed at maximal levels of activation, and these underlying impairments in force generation may be less obvious.

DOI: https://doi.org/10.1139/apnm-2024-0189
Dev Biol. 2024 Aug 05. pii: S0012-1606(24)00209-4. [Epub ahead of print]

Enhanced expression of the myogenic factor Myocyte enhancer factor-2 in imaginal disc myoblasts activates a partial, but incomplete, muscle development program.

Elizabeth M Trujillo, Samuel R Lee, Antonio Aguayo, Tylee Torosian, Richard M Cripps.

  The Myocyte enhancer factor-2 (MEF2) transcription factor plays a vital role in orchestrating muscle differentiation. While MEF2 cannot effectively induce myogenesis in naïve cells, it can potently accelerate myogenesis in mesodermal cells. This includes in Drosophila melanogaster imaginal disc myoblasts, where triggering premature muscle gene expression in these adult muscle progenitors has become a paradigm for understanding the regulation of the myogenic program. Here, we investigated the global consequences of MEF2 overexpression in the imaginal wing disc myoblasts, by combining RNA-sequencing with RT-qPCR and immunofluorescence. We observed the formation of sarcomere-like structures that contained both muscle and cytoplasmic myosin, and significant upregulation of muscle gene expression, especially genes essential for myofibril formation and function. These transcripts were functional since numerous myofibrillar proteins were detected in discs using immunofluorescence. Interestingly, muscle genes whose expression is restricted to the adult stages were not activated in these adult myoblasts. These studies confirm a broad activation of the myogenic program in response to MEF2 expression and suggest that additional regulatory factors are required for promoting the adult muscle-specific program. Our findings contribute to understanding the regulatory mechanisms governing muscle development and highlight the multifaceted role of MEF2 in orchestrating this intricate process.

Keywords:  Drosophila; MEF2; Myocyte enhancer factor-2; Myosin; myoblast; myogenesis

DOI:  https://doi.org/10.1016/j.ydbio.2024.08.004
Bioelectricity. 2024 Jun;6(2): 80-90

DNA Electrotransfer Regulates Molecular Functions in Skeletal Muscle.

Amanda Sales Conniff, Jared Tur, Kristopher Kohena, Min Zhang, Justin Gibbons, Loree C Heller.

   Background: Tissues, such as skeletal muscle, have been targeted for the delivery of plasmid DNA (pDNA) encoding vaccines and therapeutics. The application of electric pulses (electroporation or electrotransfer) increases cell membrane permeability to enhance plasmid delivery and expression. However, the molecular effects of DNA electrotransfer on the muscle tissue are poorly characterized.
Materials and Methods: Four hours after intramuscular plasmid electrotransfer, we evaluated gene expression changes by RNA sequencing. Differentially expressed genes were analyzed by gene ontology (GO) pathway enrichment analysis.
Results: GO analysis highlighted many enriched molecular functions. The terms regulated by pulse application were related to muscle stress, the cytoskeleton and inflammation. The terms regulated by pDNA injection were related to a DNA-directed response and its control. Several terms regulated by pDNA electrotransfer were similar to those regulated by pulse application. However, the terms related to pDNA injection differed, focusing on entry of the plasmid into the cells and intracellular trafficking.
Conclusion: Each muscle stimulus resulted in specific regulated molecular functions. Identifying the unique intrinsic molecular changes driven by intramuscular DNA electrotransfer will aid in the design of preventative and therapeutic gene therapies.

Keywords:  RNA sequencing; electroporation; electrotransfer; molecular functions; plasmid; skeletal muscle

DOI:  https://doi.org/10.1089/bioe.2022.0041
World J Diabetes. 2024 Jul 15. 15(7): 1589-1602

Interactions between myoblasts and macrophages under high glucose milieus result in inflammatory response and impaired insulin sensitivity.

Wei Luo, Yue Zhou, Li-Ying Wang, Lei Ai.

   BACKGROUND: Skeletal muscle handles about 80% of insulin-stimulated glucose uptake and become the major organ occurring insulin resistance (IR). Many studies have confirmed the interactions between macrophages and skeletal muscle regulated the inflammation and regeneration of skeletal muscle. However, despite of the decades of research, whether macrophages infiltration and polarization in skeletal muscle under high glucose (HG) milieus results in the development of IR is yet to be elucidated. C2C12 myoblasts are well-established and excellent model to study myogenic regulation and its responses to stimulation. Further exploration of macrophages' role in myoblasts IR and the dynamics of their infiltration and polarization is warranted.
AIM: To evaluate interactions between myoblasts and macrophages under HG, and its effects on inflammation and IR in skeletal muscle.
METHODS: We detected the polarization status of macrophages infiltrated to skeletal muscles of IR mice by hematoxylin and eosin and immunohistochemical staining. Then, we developed an in vitro co-culture system to study the interactions between myoblasts and macrophages under HG milieus. The effects of myoblasts on macrophages were explored through morphological observation, CCK-8 assay, Flow Cytometry, and enzyme-linked immunosorbent assay. The mediation of macrophages to myogenesis and insulin sensitivity were detected by morphological observation, CCK-8 assay, Immunofluorescence, and 2-NBDG assay.
RESULTS: The F4/80 and co-localization of F4/80 and CD86 increased, and the myofiber size decreased in IR group (P < 0.01, g = 6.26). Compared to Mc group, F4/80+CD86+CD206- cells, tumor necrosis factor-α (TNFα), inerleukin-1β (IL-1β) and IL-6 decreased, and IL-10 increased in McM group (P < 0.01, g > 0.8). In McM + HG group, F4/80+CD86+CD206- cells, monocyte chemoattractant protein 1, TNFα, IL-1β and IL-6 were increased, and F4/80+CD206+CD86- cells and IL-10 were decreased compared with Mc + HG group and McM group (P < 0.01, g > 0.8). Compered to M group, myotube area, myotube number and E-MHC were increased in MMc group (P < 0.01, g > 0.8). In MMc + HG group, myotube area, myotube number, E-MHC, GLUT4 and glucose uptake were decreased compared with M + HG group and MMc group (P < 0.01, g > 0.8).
CONCLUSION: Interactions between myoblasts and macrophages under HG milieus results in inflammation and IR, which support that the macrophage may serve as a promising therapeutic target for skeletal muscle atrophy and IR.

Keywords:  Chronic inflammation; Cross-talk; Glucose toxicity; Insulin sensitivity; Macrophages phenotype; Myoblasts

DOI:  https://doi.org/10.4239/wjd.v15.i7.1589
Cells. 2024 Jul 29. pii: 1273. [Epub ahead of print]13(15):

Are Aminoglycoside Antibiotics TRPing Your Metabolic Switches?

Alfredo Franco-Obregón, Yee Kit Tai.

  Transient receptor potential (TRP) channels are broadly implicated in the developmental programs of most tissues. Amongst these tissues, skeletal muscle and adipose are noteworthy for being essential in establishing systemic metabolic balance. TRP channels respond to environmental stimuli by supplying intracellular calcium that instigates enzymatic cascades of developmental consequence and often impinge on mitochondrial function and biogenesis. Critically, aminoglycoside antibiotics (AGAs) have been shown to block the capacity of TRP channels to conduct calcium entry into the cell in response to a wide range of developmental stimuli of a biophysical nature, including mechanical, electromagnetic, thermal, and chemical. Paradoxically, in vitro paradigms commonly used to understand organismal muscle and adipose development may have been led astray by the conventional use of streptomycin, an AGA, to help prevent bacterial contamination. Accordingly, streptomycin has been shown to disrupt both in vitro and in vivo myogenesis, as well as the phenotypic switch of white adipose into beige thermogenic status. In vivo, streptomycin has been shown to disrupt TRP-mediated calcium-dependent exercise adaptations of importance to systemic metabolism. Alternatively, streptomycin has also been used to curb detrimental levels of calcium leakage into dystrophic skeletal muscle through aberrantly gated TRPC1 channels that have been shown to be involved in the etiology of X-linked muscular dystrophies. TRP channels susceptible to AGA antagonism are critically involved in modulating the development of muscle and adipose tissues that, if administered to behaving animals, may translate to systemwide metabolic disruption. Regenerative medicine and clinical communities need to be made aware of this caveat of AGA usage and seek viable alternatives, to prevent contamination or infection in in vitro and in vivo paradigms, respectively.

Keywords:  adipogenesis; antimicrobial resistance; diabetes; inflammation; insulin resistance; magnetic fields; mitohormesis; muscle–adipose crosstalk; myokines; regenerative medicine

DOI:  https://doi.org/10.3390/cells13151273
Exp Cell Res. 2024 Aug 05. pii: S0014-4827(24)00288-X. [Epub ahead of print]442(1): 114197

Integration of single-cell datasets depicts profiles of macrophages and fibro/adipogenic progenitors in dystrophic muscle.

Alessandra Vitaliti, Alessio Reggio, Marta Colletti, Angela Galardi, Alessandro Palma.

  Single-cell technologies have recently expanded the possibilities for researchers to gain, at an unprecedented resolution level, knowledge about tissue composition, cell complexity, and heterogeneity. Moreover, the integration of data coming from different technologies and sources also offers, for the first time, the possibility to draw a holistic portrait of how cells behave to sustain tissue physiology during the human lifespan and disease. Here, we interrogated and integrated publicly available single-cell RNAseq data to advance the understanding of how macrophages, fibro/adipogenic progenitors, and other cell types establish gene regulatory networks and communicate with each other in the muscle tissue. We identified altered gene signatures and signaling pathways associated with the dystrophic condition, including an enhanced Spp1-Cd44 signaling in dystrophic macrophages. We shed light on the differences among dystrophic muscle aging, considering wild type, mdx, and more severe conditions as in the case of the mdx-2d model. Contextually, we provided details on existing communication relations between muscle niche cell populations, highlighting increased interactions and distinct signaling events that these cells stablish in the dystrophic microenvironment. We believe our findings can help scientists to formulate and test new hypotheses by moving towards a more complete understanding of muscle regeneration and immune system biology.

Keywords:  Fibro/adipogenic progenitors; Genomics; Macrophages; Muscle regeneration; Single-cell

DOI:  https://doi.org/10.1016/j.yexcr.2024.114197
Cell Rep. 2024 Aug 02. pii: S2211-1247(24)00906-9. [Epub ahead of print]43(8): 114577

GDF15 is dispensable for the insulin-sensitizing effects of chronic exercise.

Axel Labour, Marlène Lac, Lucas Frassin, Benjamin Lair, Enda Murphy, Claire Maslo, Laurent Monbrun, Marie-Lou Calmy, Marie Marquès, Nathalie Viguerie, Geneviève Tavernier, Pierre Gourdy, Donal O'Gorman, Emilie Montastier, Claire Laurens, Alexandra Montagner, Cedric Moro.

  Growth and differentiation factor 15 (GDF15) has recently emerged as a weight loss and insulin-sensitizing factor. Growing evidence also supports a role for GDF15 as a physiological, exercise-induced stress signal. Here, we tested whether GDF15 is required for the insulin-sensitizing effects of exercise in mice and humans. At baseline, both under a standard nutritional state and high-fat feeding, GDF15 knockout (KO) mice display normal glucose tolerance, systemic insulin sensitivity, maximal speed, and endurance running capacity when compared to wild-type littermates independent of sex. When submitted to a 4-week exercise training program, both lean and obese wild-type and GDF15 KO mice similarly improve their endurance running capacity, glucose tolerance, systemic insulin sensitivity, and peripheral glucose uptake. Insulin-sensitizing effects of exercise training were also unrelated to changes in plasma GDF15 in humans. In summary, we here show that GDF15 is dispensable for the insulin-sensitizing effects of chronic exercise.

Keywords:  CP: Metabolism; GDF15; exercise; exerkine; glucose tolerance; insulin sensitivity; mice

DOI:  https://doi.org/10.1016/j.celrep.2024.114577
Free Radic Biol Med. 2024 Aug 01. pii: S0891-5849(24)00585-9. [Epub ahead of print]

Harmonization of experimental procedures to assess mitochondrial respiration in human permeabilized skeletal muscle fibers.

Carolina Doerrier, Pau Gama-Perez, Dominik Pesta, Giovanna Distefano, Stine D Soendergaard, Karoline Maise Chroeis, Alba Gonzalez-Franquesa, Bret H Goodpaster, Clara Prats, Marta Sales-Pardo, Roger Guimera, Paul M Coen, Erich Gnaiger, Steen Larsen, Pablo M Garcia-Roves.

   AIM: High-resolution respirometry in human permeabilized muscle fibers is extensively used for analysis of mitochondrial adaptions to nutrition and exercise interventions, and is linked to athletic performance. However, the lack of standardization of experimental conditions limits quantitative inter- and intra-laboratory comparisons.
METHODS: In our study, an international team of investigators measured mitochondrial respiration of permeabilized muscle fibers obtained from three biopsies (vastus lateralis) from the same healthy volunteer to avoid inter-individual variability. High-resolution respirometry assays were performed together at the same laboratory to assess whether the heterogenity in published results are due to the effects of respiration media (MiR05 versus Z) with or without the myosin inhibitor blebbistatin at low- and high-oxygen regimes.
RESULTS: Our findings reveal significant differences between respiration media for OXPHOS and ET capacities supported by NADH&succinate-linked substrates at different oxygen concentrations. Respiratory capacities were approximately 1.5-fold higher in MiR05 at high-oxygen regimes compared to medium Z near air saturation. The presence or absence of blebbistatin in human permeabilized muscle fiber preparations was without effect on oxygen flux.
CONCLUSION: Our study constitutes a basis to harmonize and establish optimum experimental conditions for respirometric studies of permeabilized human skeletal muscle fibers to improve reproducibility.

Keywords:  O(2) regime; blebbistatin; high-resolution respirometry; mitochondrial respiration; permeabilized skeletal muscle fibers; respiration medium MiR05; respiration medium Z

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.07.039
Adv Physiol Educ. 2024 Aug 08.

The foundation of excitation-contraction coupling in skeletal muscle: Communication between the transverse tubules and sarcoplasmic reticulum.

Jack A Rall.

  The expression excitation-contraction (EC) coupling in skeletal muscle was coined in 1952 (1). The term evolved narrowly to include only the processes at the triad that intervene between depolarization of the transverse tubular (T-tubular) membrane and Ca2+ release from the sarcoplasmic reticulum (SR). From 1970 to 1988, the foundation of EC coupling was elucidated. The channel through which Ca2+ was released during activation was located in the SR by its specific binding to the plant insecticide ryanodine. This channel was called the ryanodine receptor (RyR). The RyR contained four subunits that together constituted the "SR foot" structure that traversed the gap between the SR and the T-tubular membrane. Ca2+ channels, also called dihydropyridine receptors (DHPRs), were located in the T-tubular membrane at the triadic junction and shown to be essential for EC coupling. There was a precise relationship between the two channels. Four DHPRs, organized as tetrads, were superimposed on alternate RyRs. This structure was consistent with the proposal that EC coupling was mediated via a movement of intramembrane charge in the T-tubular system. The speculation was that the DHPR acted as a voltage sensor transferring information to the RyRs of the SR by protein-protein interaction causing the release of Ca2+ from the SR. A great deal of progress was made by 1988 toward understanding EC coupling. However, the ultimate question of how voltage-sensing is coupled to opening of the SR Ca2+ release channel remains unresolved.

Keywords:  charge movement; dihydropyridine receptor; ryanodine receptor; sarcoplasmic reticulum; transverse tubules

DOI:  https://doi.org/10.1152/advan.00086.2024
Mol Metab. 2024 Aug 06. pii: S2212-8778(24)00134-0. [Epub ahead of print] 102003

Peroxiredoxin 2 Regulates DAF-16/FOXO Mediated Mitochondrial Remodelling in Response to Exercise that is Disrupted in Ageing.

Qin Xia, Penglin Li, José C Casas-Martinez, Antonio Miranda-Vizuete, Emma McDermott, Peter Dockery, Katarzyna Goljanek-Whysall, Brian McDonagh.

  Ageing is associated with mitochondrial dysfunction and increased oxidative stress. Exercise generates endogenous reactive oxygen species (ROS) and promotes rapid mitochondrial remodelling. We investigated the role of Peroxiredoxin 2 (PRDX-2) in mitochondrial adaptations to exercise and ageing using Caenorhabditis elegans as a model system. PRDX-2 was required for the mitochondrial remodelling in response to exercise mediated by DAF-16 transcription factor activation and regulation of mitochondrial fusion gene eat-3. Employing an acute exercise and recovery cycle, we demonstrated exercise-induced mitochondrial ER contact sites (MERCS) assembly and mitochondrial remodelling dependent on PRDX-2 and DAF-16 signalling. There was increased mitochondrial fragmentation, elevated ROS and an altered redox state of PRDX-2 concomitant with impaired DAF-16 nuclear localisation during ageing. Similarly, the prdx-2 mutant strain exhibited increased mitochondrial fragmentation and a failure to activate DAF-16 required for mitochondrial fusion. Collectively, our data highlight the critical role of PRDX-2 in orchestrating mitochondrial remodelling in response to a physiological stress by regulating DAF-16 nuclear localisation.

Keywords:  Ageing; C. elegans; DAF-16; Exercise; Mitochondrial ER Contact Sites; Peroxiredoxin 2

DOI:  https://doi.org/10.1016/j.molmet.2024.102003
J Physiol. 2024 Aug 06.

Sex differences in human performance.

Sandra K Hunter, Jonathon W Senefeld.

  Sex as a biological variable is an underappreciated aspect of biomedical research, with its importance emerging in more recent years. This review assesses the current understanding of sex differences in human physical performance. Males outperform females in many physical capacities because they are faster, stronger and more powerful, particularly after male puberty. This review highlights key sex differences in physiological and anatomical systems (generally conferred via sex steroids and puberty) that contribute to these sex differences in human physical performance. Specifically, we address the effects of the primary sex steroids that affect human physical development, discuss insight gained from an observational study of 'real-world data' and elite athletes, and highlight the key physiological mechanisms that contribute to sex differences in several aspects of physical performance. Physiological mechanisms discussed include those for the varying magnitude of the sex differences in performance involving: (1) absolute muscular strength and power; (2) fatigability of limb muscles as a measure of relative performance; and (3) maximal aerobic power and endurance. The profound sex-based differences in human performance involving strength, power, speed and endurance, and that are largely attributable to the direct and indirect effects of sex-steroid hormones, sex chromosomes and epigenetics, provide a scientific rationale and framework for policy decisions on sex-based categories in sports during puberty and adulthood. Finally, we highlight the sex bias and problem in human performance research of insufficient studies and information on females across many areas of biology and physiology, creating knowledge gaps and opportunities for high-impact studies.

Keywords:  athletic performance; endurance; exercise; fatigability; gender; muscle strength; sex; sex hormones

DOI:  https://doi.org/10.1113/JP284198
Life Sci. 2024 Aug 02. pii: S0024-3205(24)00531-9. [Epub ahead of print]354 122941

Mitochondrial fragmentation in early differentiation of human MB135 myoblasts: Role of mitochondrial ROS production in the absence of depolarization.

Daniil A Chernyavskij, Konstantin G Lyamzaev, Olga Yu Pletjushkina, Fei Chen, Anna Karpukhina, Yegor S Vassetzky, Boris V Chernyak, Ekaterina N Popova.

   AIMS: Study of the role of mitochondria-generated reactive oxygen species (mtROS) and mitochondrial polarization in mitochondrial fragmentation at the initial stages of myogenesis.
MAIN METHODS: Mitochondrial morphology, Drp1 protein phosphorylation, mitochondrial electron transport chain components content, mtROS and mitochondrial lipid peroxidation levels, and mitochondrial polarization were evaluated on days 1 and 2 of human MB135 myoblasts differentiation. A mitochondria-targeted antioxidant SkQ1 was used to elucidate the effect of mtROS on mitochondria.
KEY FINDINGS: In immortalized human MB135 myoblasts, mitochondrial fragmentation began on day 1 of differentiation before the myoblast fusion. This fragmentation was preceded by dephosphorylation of p-Drp1 (Ser-637). On day 2, an increase in the content of some mitochondrial proteins was observed, indicating mitochondrial biogenesis stimulation. Furthermore, we found that myogenic differentiation, even on day 1, was accompanied both by an increased production of mtROS, and lipid peroxidation of the inner mitochondrial membrane. SkQ1 blocked these effects and partially reduced the level of mitochondrial fragmentation, but did not affect the dephosphorylation of p-Drp1 (Ser-637). Importantly, mitochondrial fragmentation at early stages of MB135 differentiation was not accompanied by depolarization, as an important stimulus for mitochondrial fragmentation.
SIGNIFICANCE: Mitochondrial fragmentation during early myogenic differentiation depends on mtROS production rather than mitochondrial depolarization. SkQ1 only partially inhibited mitochondrial fragmentation, without significant effects on mitophagy or early myogenic differentiation.

Keywords:  Mitochondrial fragmentation; Mitochondrial membrane potential (ΔΨm); Mitochondrial reactive oxygen species (mtROS); Myogenesis; Myogenic differentiation

DOI:  https://doi.org/10.1016/j.lfs.2024.122941