bims-moremu 2023-11-26 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–11–26
35 papers selected by
Anna Vainshtein, Craft Science Inc.

Muscle Progenitor Cell Fusion in the Maintenance of Skeletal Muscle.
Serine synthesis pathway enzyme PHGDH is critical for muscle cell biomass, anabolic metabolism and mTORC1 signaling.
Heme oxygenase-1: A potential therapeutic target for improving skeletal muscle atrophy.
Fiber type traps: revisiting common misconceptions about skeletal muscle fiber types with application to motor control, biomechanics, physiology, and biology.
MicroRNA-92b in the skeletal muscle regulates exercise capacity via modulation of glucose metabolism.
Myospreader improves gene editing in skeletal muscle by myonuclear propagation.
Targeting Epigenetic Regulators with HDAC and BET Inhibitors to Modulate Muscle Wasting.
Altered m6A RNA methylation governs denervation-induced muscle atrophy by regulating ubiquitin proteasome pathway.
Physical activity of mice on dietary sulfur amino acid restriction is influenced by age of diet initiation and biological sex.
Conserved and species-specific transcriptional responses to daily programmed resistance exercise in rat and mouse.
Mass Spectrometry-Based Multiomics Identifies Metabolic Signatures of Sarcopenia in Rhesus Monkey Skeletal Muscle.
Sarcopenia: no consensus, no diagnostic criteria, and no approved indication-How did we get here?
The Molecular Mechanisms of Fuel Utilization during Exercise.
Melatonin Alleviates the Impairment of Muscle Bioenergetics and Protein Quality Control Systems in Leptin-Deficiency-Induced Obesity.
Signatures of Cysteine Oxidation on Muscle Structural and Contractile Proteins Are Associated with Physical Performance and Muscle Function in Older Adults: Study of Muscle, Mobility and Aging (SOMMA).
Hallmarks of ageing in human skeletal muscle and implications for understanding the pathophysiology of sarcopenia in women and men.
Transcriptome profile of subsynaptic myonuclei at the neuromuscular junction in embryogenesis.
Unravelling the Role of Cancer Cell-Derived Extracellular Vesicles in Muscle Atrophy, Lipolysis, and Cancer-Associated Cachexia.
Expression of mitochondrial oxidative stress response genes in muscle is associated with mitochondrial respiration, physical performance, and muscle mass in the Study of Muscle, Mobility and Aging (SOMMA).
Cpt1a silencing in AgRP neurons improves cognitive and physical capacity and promotes healthy aging in male mice.
Polydatin inhibited TNF-α-induced apoptosis of skeletal muscle cells through AKT-mediated p38 MAPK and NF-κB pathways.
One Week of Single Leg Immobilization Lowers Muscle Connective Protein Synthesis Rates in Healthy, Young Adults.
The role of the circadian clock system in mitochondrial trans-sulfuration pathway and tissue remodeling.
Development of a Cre-recombination-based color-switching reporter system for cell fusion detection.
Uncoupling Protein 3 Promotes the Myogenic Differentiation of Type IIb Myotubes in C2C12 Cells.
Associations of Objective and Self-Reported Physical Activity and Sedentary Behavior with Skeletal Muscle Energetics: The Study of Muscle, Mobility and Aging (SOMMA).
Electrical impedance myography detects dystrophin-related muscle changes in mdx mice.
Age Is Just a Number: Progress and Obstacles in the Discovery of New Candidate Drugs for Sarcopenia.
Preventive Effects of Collagen-Derived Dipeptide Prolyl-Hydroxyproline against Dexamethasone-Induced Muscle Atrophy in Mouse C2C12 Skeletal Myotubes.
Age-related nitration/dysfunction of myogenic stem cell activator HGF.
Skeletal muscle gene expression signatures of obese high- and low- responders to endurance exercise training.
Childhood adverse life events and skeletal muscle mitochondrial function.
Mitochondrial phosphoproteomes are functionally specialized across tissues.
Skeletal muscle energetics explain the sex disparity in mobility impairment in the Study of Muscle, Mobility and Aging (SOMMA).
Congenital myasthenic syndrome from a MUSK gene mutation.

Results Probl Cell Differ. 2024 ;71 257-279

Muscle Progenitor Cell Fusion in the Maintenance of Skeletal Muscle.

Jarred M Whitlock.

  Skeletal muscle possesses a resident, multipotent stem cell population that is essential for its repair and maintenance throughout life. Here I highlight the role of this stem cell population in muscle repair and regeneration and review the genetic control of the process; the mechanistic steps of activation, migration, recognition, adhesion, and fusion of these cells; and discuss the novel recognition of the membrane signaling that coordinates myogenic cell-cell fusion, as well as the identification of a two-part fusogen system that facilitates it.

Keywords:  Cell-cell fusion; Fusogen; Muscle progenitor cell; Myogenesis; Phospholipid scrambling; Satellite cell; Skeletal muscle

DOI:  https://doi.org/10.1007/978-3-031-37936-9_13
Am J Physiol Endocrinol Metab. 2023 Nov 22.

Serine synthesis pathway enzyme PHGDH is critical for muscle cell biomass, anabolic metabolism and mTORC1 signaling.

Sakari Mäntyselkä, Kalle Kolari, Philipp Baumert, Laura Ylä-Outinen, Lauri Kuikka, Suvi Lahtonen, Perttu Permi, Henning Wackerhage, Elina Kalenius, Riikka Kivelä, Juha J Hulmi.

  Cells use glycolytic intermediates for anabolism e.g., via the serine synthesis and pentose phosphate pathways. However, we still understand poorly how these metabolic pathways contribute to skeletal muscle cell biomass generation. The first aim of this study was therefore to identify enzymes that limit protein synthesis, myotube size, and proliferation in skeletal muscle cells. We inhibited key enzymes of glycolysis, the pentose phosphate pathway, and serine synthesis pathway to evaluate their importance in C2C12 myotube protein synthesis. Based on the results of this first screen, we then focused on the serine synthesis pathway enzyme phosphoglycerate dehydrogenase (PHGDH). We used two different PHGDH inhibitors and mouse C2C12 and human primary muscle cells to study the importance and function of the PHGDH. Both myoblasts and myotubes incorporated glucose-derived carbon into proteins, RNA, and lipids and we showed that PHGDH is essential in these processes. PHGDH inhibition decreased protein synthesis, myotube size, and myoblast proliferation without cytotoxic effects. The decreased protein synthesis in response to PHGDH inhibition appears to occur mainly mTORC1 dependently as was evident from experiments with insulin-like growth factor 1 and rapamycin. Further metabolomics analyses revealed that PHGDH inhibition accelerated glycolysis and altered amino acid, nucleotide, and lipid metabolism. Lastly, we found that supplementing an antioxidant and redox modulator N-acetylcysteine partially rescued the decreased protein synthesis and mTORC1 signaling during PHGDH inhibition. The data suggest that PHGDH activity is critical for skeletal muscle cell biomass generation from glucose, and that it regulates protein synthesis and mTORC1 signaling.

Keywords:  Glycolysis; Metabolic reprogramming; Protein synthesis; Warburg effect; mTORC1

DOI:  https://doi.org/10.1152/ajpendo.00151.2023
Exp Gerontol. 2023 Nov 18. pii: S0531-5565(23)00256-5. [Epub ahead of print] 112335

Heme oxygenase-1: A potential therapeutic target for improving skeletal muscle atrophy.

Qin Xiao, Chen-Chen Sun, Chang-Fa Tang.

  Skeletal muscle atrophy is a common muscle disease that is directly caused by an imbalance in protein synthesis and degradation. At the histological level, it is mainly characterized by a reduction in muscle mass and fiber cross-sectional area (CSA). Patients with skeletal muscle atrophy present with reduced motor ability, easy fatigue, and poor life quality. Heme oxygenase-1 (HO-1) is an inducible enzyme that catalyzes the degradation of heme and has attracted much attention for its anti-oxidation effects. In addition, there is growing evidence that HO-1 plays an important role in anti-inflammatory, anti-apoptosis, pro-angiogenesis, and maintaining skeletal muscle homeostasis, making it a potential therapeutic target for improving skeletal muscle atrophy. Here, we review the pathogenesis of skeletal muscle atrophy, the biology of HO-1 and its regulation, and the biological function of HO-1 in skeletal muscle homeostasis, with a specific focus on the role of HO-1 in skeletal muscle atrophy, aiming to observe the therapeutic potential of HO-1 for skeletal muscle atrophy.

Keywords:  HO-1; HO-1 inducer; Skeletal muscle atrophy; Skeletal muscles homeostasis; Therapeutic target

DOI:  https://doi.org/10.1016/j.exger.2023.112335
J Appl Physiol (1985). 2023 Nov 23.

Fiber type traps: revisiting common misconceptions about skeletal muscle fiber types with application to motor control, biomechanics, physiology, and biology.

Silvia S Blemker, Susan V Brooks, Karyn A Esser, Katherine R Saul.

  Skeletal muscle is a highly complex tissue that is studied by scientists from a wide spectrum of disciplines, including motor control, biomechanics, exercise science, physiology, cell biology, genetics, regenerative medicine, orthopedics, and engineering. While this diversity in perspectives has led to many important discoveries, historically there has been limited overlap in discussions across fields. This has led to misconceptions and oversimplifications about muscle biology which can create confusion and potentially slow scientific progress across fields. The purpose of this synthesis paper is to bring together research perspectives across multiple muscle fields to identify common assumptions related to muscle fiber type that are points of concern to clarify. These assumptions include: 1) classification by myosin isoform and fiber oxidative capacity is equivalent, 2) fiber cross-sectional area is a surrogate marker for myosin isoform or oxidative capacity, and 3) muscle force-generating capacity can be inferred from myosin isoform. We address these 3 fiber type traps and provide some context for how these misunderstandings can and do impact experimental design, computational modeling, and interpretations of findings, from the perspective of a range of fields. We stress the dangers of generalizing findings about "muscle fiber types" among muscles or across species or sex, and we note the importance for precise use of common terminology across the muscle fields.

Keywords:  fiber type; myosin; skeletal muscle

DOI:  https://doi.org/10.1152/japplphysiol.00337.2023
J Cachexia Sarcopenia Muscle. 2023 Nov 20.

MicroRNA-92b in the skeletal muscle regulates exercise capacity via modulation of glucose metabolism.

Shu Yang, Guangyan Yang, Xinyu Wang, Lixing Li, Yanchun Li, Jiaqing Xiang, Lin Kang, Zhen Liang.

   BACKGROUND: Exercise mimetics is a proposed class of therapeutics that specifically mimics or enhances the therapeutic effects of exercise. Muscle glycogen and lactate extrusion are critical for physical performance. The mechanism by which glycogen and lactate metabolism are manipulated during exercise remains unclear. This study aimed to assess the effect of miR-92b on the upregulation of exercise training-induced physical performance.
METHODS: Adeno-associated virus (AAV)-mediated skeletal muscle miR-92b overexpression in C57BLKS/J mice, and global knockout of miR-92b mice were used to explore the function of miR-92b in glycogen and lactate metabolism in skeletal muscle. AAV-mediated UGP2 or MCT4 knockdown in WT or miR-92 knockout mice was used to confirm whether miR-92b regulates glycogen and lactate metabolism in skeletal muscle through UGP2 and MCT4. Body weight, muscle weight, grip strength, running time and distance to exhaustion, and muscle histology were assessed. The expression levels of muscle mass-related and function-related proteins were analysed by immunoblotting or immunostaining.
RESULTS: Global knockout of miR-92b resulted in normal body weight and insulin sensitivity, but higher glycogen content before exercise exhaustion (0.8538 ± 0.0417 vs. 1.043 ± 0.040, **P = 0.0087), lower lactate levels after exercise exhaustion (4.133 ± 0.2589 vs. 3.207 ± 0.2511, *P = 0.0279), and better exercise capacity (running distance to exhaustion, 3616 ± 86.71 vs. 4231 ± 90.29, ***P = 0.0006; running time to exhaustion, 186.8 ± 8.027 vs. 220.8 ± 3.156, **P = 0.0028), as compared with those observed in the control mice. Mice skeletal muscle overexpressing miR-92b (both miR-92b-3p and miR-92b-5p) displayed lower glycogen content before exercise exhaustion (0.6318 ± 0.0231 vs. 0.535 ± 0.0194, **P = 0.0094), and higher lactate accumulation after exercise exhaustion (4.5 ± 0.2394 vs. 5.467 ± 0.1892, *P = 0.01), and poorer exercise capacity (running distance to exhaustion, 4005 ± 81.65 vs. 3228 ± 149.8, ***P<0.0001; running time to exhaustion, 225.5 ± 7.689 vs. 163 ± 6.476, **P = 0.001). Mechanistic analysis revealed that miR-92b-3p targets UDP-glucose pyrophosphorylase 2 (UGP2) expression to inhibit glycogen synthesis, while miR-92b-5p represses lactate extrusion by directly target monocarboxylate transporter 4 (MCT4). Knockdown of UGP2 and MCT4 reversed the effects observed in the absence of miR-92b in vivo.
CONCLUSIONS: This study revealed regulatory pathways, including miR-92b-3p/UGP2/glycogen synthesis and miR-92b-5p/MCT4/lactate extrusion, which could be targeted to control exercise capacity.

Keywords:  Exercise capacity; Glycogen synthesis; Lactate extrusion; Skeletal muscle; miR-92b

DOI:  https://doi.org/10.1002/jcsm.13377
bioRxiv. 2023 Nov 06. pii: 2023.11.06.565807. [Epub ahead of print]

Myospreader improves gene editing in skeletal muscle by myonuclear propagation.

Kiril K Poukalov, M Carmen Valero, Derek R Muscato, Leanne M Adams, Heejae Chun, Young Il Lee, Nadja S Andrade, Zane Zeier, H Lee Sweeney, Eric T Wang.

Successful CRISPR/Cas9-based gene editing in skeletal muscle is dependent on efficient propagation of Cas9 to all myonuclei in the myofiber. However, nuclear-targeted gene therapy cargos are strongly restricted to their myonuclear domain of origin. By screening nuclear localization signals and nuclear export signals, we identify "Myospreader", a combination of short peptide sequences that promotes myonuclear propagation. Appending Myospreader to Cas9 enhances protein stability and myonuclear propagation in myoblasts and myofibers. AAV-delivered Myospreader dCas9 better inhibits transcription of toxic RNA in a myotonic dystrophy mouse model. Furthermore, Myospreader Cas9 achieves higher rates of gene editing in CRISPR reporter and Duchenne muscular dystrophy mouse models. Myospreader reveals design principles relevant to all nuclear-targeted gene therapies and highlights the importance of the spatial dimension in therapeutic development.

DOI: https://doi.org/10.1101/2023.11.06.565807
Int J Mol Sci. 2023 Nov 16. pii: 16404. [Epub ahead of print]24(22):

Targeting Epigenetic Regulators with HDAC and BET Inhibitors to Modulate Muscle Wasting.

Lorenzo Nevi, Noora Pöllänen, Fabio Penna, Giuseppina Caretti.

  Epigenetic changes contribute to the profound alteration in the transcriptional program associated with the onset and progression of muscle wasting in several pathological conditions. Although HDACs and their inhibitors have been extensively studied in the field of muscular dystrophies, the potential of epigenetic inhibitors has only been marginally explored in other disorders associated with muscle atrophy, such as in cancer cachexia and sarcopenia. BET inhibitors represent a novel class of recently developed epigenetic drugs that display beneficial effects in a variety of diseases beyond malignancies. Based on the preliminary in vitro and preclinical data, HDACs and BET proteins contribute to the pathogenesis of cancer cachexia and sarcopenia, modulating processes related to skeletal muscle mass maintenance and/or metabolism. Thus, epigenetic drugs targeting HDACs and BET proteins may emerge as promising strategies to reverse the catabolic phenotype associated with cachexia and sarcopenia. Further preclinical studies are warranted to delve deeper into the molecular mechanisms associated with the functions of HDACs and BET proteins in muscle atrophy and to establish whether their epigenetic inhibitors represent a prospective therapeutic avenue to alleviate muscle wasting.

Keywords:  BET proteins; HDACs; cachexia; epigenetics; muscle wasting; sarcopenia

DOI:  https://doi.org/10.3390/ijms242216404
J Transl Med. 2023 Nov 23. 21(1): 845

Altered m6A RNA methylation governs denervation-induced muscle atrophy by regulating ubiquitin proteasome pathway.

Junjie Sun, Hai Zhou, Zehao Chen, Han Zhang, Yanzhe Cao, Xinlei Yao, Xin Chen, Boya Liu, Zihui Gao, Yuntian Shen, Lei Qi, Hualin Sun.

   BACKGROUND: Denervation-induced muscle atrophy is complex disease involving multiple biological processes with unknown mechanisms. N6-methyladenosine (m6A) participates in skeletal muscle physiology by regulating multiple levels of RNA metabolism, but its impact on denervation-induced muscle atrophy is still unclear. Here, we aimed to explore the changes, functions, and molecular mechanisms of m6A RNA methylation during denervation-induced muscle atrophy.
METHODS: During denervation-induced muscle atrophy, the m6A immunoprecipitation sequencing (MeRIP-seq) as well as enzyme-linked immunosorbent assay analysis were used to detect the changes of m6A modified RNAs and the involved biological processes. 3-deazidenosine (Daa) and R-2-hydroxyglutarate (R-2HG) were used to verify the roles of m6A RNA methylation. Through bioinformatics analysis combined with experimental verification, the regulatory roles and mechanisms of m6A RNA methylation had been explored.
RESULTS: There were many m6A modified RNAs with differences during denervation-induced muscle atrophy, and overall, they were mainly downregulated. After 72 h of denervation, the biological processes involved in the altered mRNA with m6A modification were mainly related to zinc ion binding, ubiquitin protein ligase activity, ATP binding and sequence-specific DNA binding and transcription coactivator activity. Daa reduced overall m6A levels in healthy skeletal muscles, which reduced skeletal muscle mass. On the contrary, the increase in m6A levels mediated by R-2HG alleviated denervation induced muscle atrophy. The m6A RNA methylation regulated skeletal muscle mass through ubiquitin-proteasome pathway.
CONCLUSION: This study indicated that decrease in m6A RNA methylation was a new symptom of denervation-induced muscle atrophy, and confirmed that targeting m6A alleviated denervation-induced muscle atrophy.

Keywords:  Denervation; Muscle atrophy; Ubiquitin–proteasome pathway; m6A

DOI:  https://doi.org/10.1186/s12967-023-04694-3
Sci Rep. 2023 Nov 23. 13(1): 20609

Physical activity of mice on dietary sulfur amino acid restriction is influenced by age of diet initiation and biological sex.

Diana Cooke, Gene P Ables.

Sulfur amino acid restriction (SAAR)-the reduction of methionine and cysteine concentrations either in the diet or by genetic manipulation-promotes health span and extends lifespan, but its effects on physical activity remain unclear. We investigated whether age of diet initiation and biological sex could influence physical activity in mice fed either a control diet (CF, 0.86% methionine w/w) or SAAR (0.12% methionine w/w). Quadriceps femoris muscle mass is smaller in SAAR than in CF mice. Young mice fed a chronic SAAR diet at 8 weeks of age exhibited improved wire hang and running wheel activities compared to young CF mice, while aged mice showed comparable results. The effects of chronic SAAR on physical activity was mildly influenced by sex as observed in middle-aged male SAAR mice who showed minor improvements than CF males while middle-aged females displayed no discernible effects. Muscle mass is minimally affected by changes in markers of protein synthesis, autophagy and atrophy. Improvements to physical activity in young SAAR mice could be partially attributed to increased skeletal muscle mitochondrial activity. Furthermore, SAAR in C2C12 myotubes increased citrate synthase protein expression and enhanced succinyl dehydrogenase enzyme activity compared to CF myotubes. Overall, our data reveal that SAAR can improve mouse physical activity without compromising muscle proteostasis. This is partially due to enhanced mitochondrial activity, but the effects are influenced by age of diet initiation and sex.

DOI: https://doi.org/10.1038/s41598-023-47676-7
FASEB J. 2023 Dec;37(12): e23299

Conserved and species-specific transcriptional responses to daily programmed resistance exercise in rat and mouse.

Mark R Viggars, Hazel Sutherland, Christopher P Cardozo, Jonathan C Jarvis.

  Mice are often used in gain or loss of function studies to understand how genes regulate metabolism and adaptation to exercise in skeletal muscle. Once-daily resistance training with electrical nerve stimulation produces hypertrophy of the dorsiflexors in rat, but not in mouse. Using implantable pulse generators, we assessed the acute transcriptional response (1-h post-exercise) after 2, 10, and 20 days of training in free-living mice and rats using identical nerve stimulation paradigms. RNA sequencing revealed strong concordance in the timecourse of many transcriptional responses in the tibialis anterior muscles of both species including responses related to "stress responses/immediate-early genes, and "collagen homeostasis," "ribosomal subunits," "autophagy," and "focal adhesion." However, pathways associated with energy metabolism including "carbon metabolism," "oxidative phosphorylation," "mitochondrial translation," "propanoate metabolism," and "valine, leucine, and isoleucine degradation" were oppositely regulated between species. These pathways were suppressed in the rat but upregulated in the mouse. Our transcriptional analysis suggests that although many pathways associated with growth show remarkable similarities between species, the absence of an actual growth response in the mouse may be because the mouse prioritizes energy metabolism, specifically the replenishment of fuel stores and intermediate metabolites.

Keywords:  exercise; functional electrical stimulation; metabolism; muscle atrophy; muscle hypertrophy; transcription

DOI:  https://doi.org/10.1096/fj.202301611R
J Proteome Res. 2023 Nov 22.

Mass Spectrometry-Based Multiomics Identifies Metabolic Signatures of Sarcopenia in Rhesus Monkey Skeletal Muscle.

Melissa R Pergande, Katie J Osterbauer, Kevin M Buck, David S Roberts, Nina N Wood, Priya Balasubramanian, Morgan W Mann, Kalina J Rossler, Gary M Diffee, Ricki J Colman, Rozalyn M Anderson, Ying Ge.

  Sarcopenia is a progressive disorder characterized by age-related loss of skeletal muscle mass and function. Although significant progress has been made over the years to identify the molecular determinants of sarcopenia, the precise mechanisms underlying the age-related loss of contractile function remains unclear. Advances in "omics" technologies, including mass spectrometry-based proteomic and metabolomic analyses, offer great opportunities to better understand sarcopenia. Herein, we performed mass spectrometry-based analyses of the vastus lateralis from young, middle-aged, and older rhesus monkeys to identify molecular signatures of sarcopenia. In our proteomic analysis, we identified proteins that change with age, including those involved in adenosine triphosphate and adenosine monophosphate metabolism as well as fatty acid beta oxidation. In our untargeted metabolomic analysis, we identified metabolites that changed with age largely related to energy metabolism including fatty acid beta oxidation. Pathway analysis of age-responsive proteins and metabolites revealed changes in muscle structure and contraction as well as lipid, carbohydrate, and purine metabolism. Together, this study discovers new metabolic signatures and offers new insights into the molecular mechanisms underlying sarcopenia for the evaluation and monitoring of a therapeutic treatment of sarcopenia.

Keywords:  bottom-up proteomics; multiomics; nonhuman primate; sarcopenia; skeletal muscle; untargeted metabolomics

DOI:  https://doi.org/10.1021/acs.jproteome.3c00474
Geroscience. 2023 Nov 24.

Sarcopenia: no consensus, no diagnostic criteria, and no approved indication-How did we get here?

William J Evans, Jack Guralnik, Peggy Cawthon, James Appleby, Francesco Landi, Lindsay Clarke, Bruno Vellas, Luigi Ferrucci, Ronenn Roubenoff.

  In addition to the role of skeletal muscle in movement and locomotion, muscle plays a critical role in a broad array of metabolic processes that can contribute to improved health or risk of disease. The age-associated loss of muscle has been termed sarcopenia. The muscle is the primary site of insulin-stimulated glucose disposal and the largest component of basal metabolic rate, directly and indirectly affects bone density, produces myokines with pleiotropic effect on muscle and other tissues including the brain, and stores essential amino acids essential for the maintenance of protein synthesis during periods of reduced food intake and stress. As such, not surprisingly deterioration of skeletal muscle health, typically operationalized as decline of muscle mass and muscle strength is both a powerful risk factor and main consequence of chronic diseases, disability, and loss of independence, and it is one of the strongest risk factors for mortality. However, skeletal muscle remains one of the most plastic of all tissues, with rapid changes in rates of protein synthesis and degradation in response to physical activity and inactivity, inflammation, and nutritional and hormonal status. This has made the development of pharmacological therapies to increase muscle mass (or prevent loss), an important goal for decades. However, while remarkable advances in the understanding of molecular and cellular regulation of muscle protein metabolism have occurred recently, there are no approved drugs for the treatment of sarcopenia, the loss of skeletal muscle affecting millions of older people. The goal of this paper is to describe the possible reasons for the lack of new and effective pharmacotherapies to treat one of the most important risk factors for age-associated disease and loss of independence.

Keywords:  Body composition; Functional capacity; Muscle mass; Regulatory approval; Sarcopenia

DOI:  https://doi.org/10.1007/s11357-023-01016-9
Biology (Basel). 2023 Nov 19. pii: 1450. [Epub ahead of print]12(11):

The Molecular Mechanisms of Fuel Utilization during Exercise.

Anna Pi, Sneha Damal Villivalam, Sona Kang.

  Exercise is widely recognized for its positive impact on human health and well-being. The process of utilizing substrates in skeletal muscle during exercise is intricate and governed by complex mechanisms. Carbohydrates and lipids serve as the primary fuel sources for skeletal muscle during exercise. It is now understood that fuel selection during exercise is not solely determined by physical activity itself but is also influenced by the overall metabolic state of the body. The balance between lipid and carbohydrate utilization significantly affects exercise capacity, including endurance, fatigue, and overall performance. Therefore, comprehensively understanding the regulation of substrate utilization during exercise is of utmost importance. The aim of this review is to provide an extensive overview of the current knowledge regarding the pathways involved in the regulation of substrate utilization during exercise. By synthesizing existing research, we can gain a holistic perspective on the intricate relationship between exercise, metabolism, and fuel selection. This advanced understanding has the potential to drive advancements in the field of exercise science and contribute to the development of personalized exercise strategies for individuals looking to optimize their performance and overall health.

Keywords:  exercise; fuel utilization; skeletal muscle

DOI:  https://doi.org/10.3390/biology12111450
Antioxidants (Basel). 2023 Nov 03. pii: 1962. [Epub ahead of print]12(11):

Melatonin Alleviates the Impairment of Muscle Bioenergetics and Protein Quality Control Systems in Leptin-Deficiency-Induced Obesity.

Yaiza Potes, Andrea Díaz-Luis, Juan C Bermejo-Millo, Zulema Pérez-Martínez, Beatriz de Luxán-Delgado, Adrian Rubio-González, Iván Menéndez-Valle, José Gutiérrez-Rodríguez, Juan J Solano, Beatriz Caballero, Ignacio Vega-Naredo, Ana Coto-Montes.

  Leptin is critically compromised in the major common forms of obesity. Skeletal muscle is the main effector tissue for energy modification that occurs as a result of the effect of endocrine axes, such as leptin signaling. Our study was carried out using skeletal muscle from a leptin-deficient animal model, in order to ascertain the importance of this hormone and to identify the major skeletal muscle mechanisms affected. We also examined the therapeutic role of melatonin against leptin-induced muscle wasting. Here, we report that leptin deficiency stimulates fatty acid β-oxidation, which results in mitochondrial uncoupling and the suppression of mitochondrial oxidative damage; however, it increases cytosolic oxidative damage. Thus, different nutrient-sensing pathways are disrupted, impairing proteostasis and promoting lipid anabolism, which induces myofiber degeneration and drives oxidative type I fiber conversion. Melatonin treatment plays a significant role in reducing cellular oxidative damage and regulating energy homeostasis and fuel utilization. Melatonin is able to improve both glucose and mitochondrial metabolism and partially restore proteostasis. Taken together, our study demonstrates melatonin to be a decisive mitochondrial function-fate regulator in skeletal muscle, with implications for resembling physiological energy requirements and targeting glycolytic type II fiber recovery.

Keywords:  leptin; melatonin; metabolism; mitochondria; obesity; skeletal muscle

DOI:  https://doi.org/10.3390/antiox12111962
medRxiv. 2023 Nov 08. pii: 2023.11.07.23298224. [Epub ahead of print]

Signatures of Cysteine Oxidation on Muscle Structural and Contractile Proteins Are Associated with Physical Performance and Muscle Function in Older Adults: Study of Muscle, Mobility and Aging (SOMMA).

Nicholas J Day, Shane S Kelly, Li-Yung Lui, Tyler A Mansfield, Matthew J Gaffrey, Jesse B Trejo, Tyler J Sagendorf, Kwame Attah, Ronald J Moore, Collin M Douglas, Anne B Newman, Stephen B Kritchevsky, Philip A Kramer, David J Marcinek, Paul M Coen, Bret H Goodpaster, Russell T Hepple, Peggy M Cawthon, Vladislav A Petyuk, Karyn A Esser, Wei-Jun Qian, Steven R Cummings.

Oxidative stress is considered a contributor to declining muscle function and mobility during aging; however, the underlying molecular mechanisms remain poorly described. We hypothesized that greater levels of cysteine (Cys) oxidation on muscle proteins are associated with decreased measures of mobility. Herein, we applied a novel redox proteomics approach to measure reversible protein Cys oxidation in vastus lateralis muscle biopsies collected from 56 subjects in the Study of Muscle, Mobility and Aging (SOMMA), a community-based cohort study of individuals aged 70 years and older. We tested whether levels of Cys oxidation on key muscle proteins involved in muscle structure and contraction were associated with muscle function (leg power and strength), walking speed, and fitness (VO 2 peak on cardiopulmonary exercise testing) using linear regression models adjusted for age, sex, and body weight. Higher oxidation levels of select nebulin Cys sites were associated with lower VO 2 peak, while greater oxidation of myomesin-1, myomesin-2, and nebulin Cys sites was associated with slower walking speed. Higher oxidation of Cys sites in key proteins such as myomesin-2, alpha-actinin-2, and skeletal muscle alpha-actin were associated with lower leg power and strength. We also observed an unexpected correlation (r = 0.48) between a higher oxidation level of 8 Cys sites in alpha-actinin-3 and stronger leg power. Despite this observation, the results generally support the hypothesis that Cys oxidation of muscle proteins impair muscle power and strength, walking speed, and cardiopulmonary fitness with aging.

DOI: https://doi.org/10.1101/2023.11.07.23298224
Clin Sci (Lond). 2023 Nov 29. 137(22): 1721-1751

Hallmarks of ageing in human skeletal muscle and implications for understanding the pathophysiology of sarcopenia in women and men.

Antoneta Granic, Karen Suetterlin, Tea Shavlakadze, Miranda D Grounds, Avan A Sayer.

  Ageing is a complex biological process associated with increased morbidity and mortality. Nine classic, interdependent hallmarks of ageing have been proposed involving genetic and biochemical pathways that collectively influence ageing trajectories and susceptibility to pathology in humans. Ageing skeletal muscle undergoes profound morphological and physiological changes associated with loss of strength, mass, and function, a condition known as sarcopenia. The aetiology of sarcopenia is complex and whilst research in this area is growing rapidly, there is a relative paucity of human studies, particularly in older women. Here, we evaluate how the nine classic hallmarks of ageing: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication contribute to skeletal muscle ageing and the pathophysiology of sarcopenia. We also highlight five novel hallmarks of particular significance to skeletal muscle ageing: inflammation, neural dysfunction, extracellular matrix dysfunction, reduced vascular perfusion, and ionic dyshomeostasis, and discuss how the classic and novel hallmarks are interconnected. Their clinical relevance and translational potential are also considered.

Keywords:  hallmarks of ageing; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.1042/CS20230319
J Neurochem. 2023 Nov 23.

Transcriptome profile of subsynaptic myonuclei at the neuromuscular junction in embryogenesis.

Bisei Ohkawara, Masaomi Kurokawa, Akinori Kanai, Kiyomi Imamura, Guiying Chen, Ruchen Zhang, Akio Masuda, Koichi Higashi, Hiroshi Mori, Yutaka Suzuki, Ken Kurokawa, Kinji Ohno.

  Skeletal muscle fiber is a large syncytium with multiple and evenly distributed nuclei. Adult subsynaptic myonuclei beneath the neuromuscular junction (NMJ) express specific genes, the products of which coordinately function in the maintenance of the pre- and post-synaptic regions. However, the gene expression profiles that promote the NMJ formation during embryogenesis remain largely unexplored. We performed single-nucleus RNA sequencing (snRNA-seq) analysis of embryonic and neonatal mouse diaphragms, and found that each myonucleus had a distinct transcriptome pattern during the NMJ formation. Among the previously reported NMJ-constituting genes, Dok7, Chrna1, and Chrnd are specifically expressed in subsynaptic myonuclei at E18.5. In the E18.5 diaphragm, ca. 10.7% of the myonuclei express genes for the NMJ formation (Dok7, Chrna1, and Chrnd) together with four representative β-catenin regulators (Amotl2, Ptprk, Fam53b, and Tcf7l2). Additionally, the temporal gene expression patterns of these seven genes are synchronized in differentiating C2C12 myoblasts. Amotl2 and Ptprk are expressed in the sarcoplasm, where β-catenin serves as a structural protein to organize the membrane-anchored NMJ structure. In contrast, Fam53b and Tcf7l2 are expressed in the myonucleus, where β-catenin serves as a transcriptional coactivator in Wnt/β-catenin signaling at the NMJ. In C2C12 myotubes, knockdown of Amotl2 or Ptprk markedly, and that of Fam53b and Tcf7l2 less efficiently, impair the clustering of acetylcholine receptors. In contrast, knockdown of Fam53b and Tcf7l2, but not of Amotl2 or Ptprk, impairs the gene expression of Slit2 encoding an axonal attractant for motor neurons, which is required for the maturation of motor nerve terminal. Thus, Amotl2 and Ptprk exert different roles at the NM compared to Fam53b and Tcf7l2. Additionally, Wnt ligands originating from the spinal motor neurons and the perichondrium/chondrocyte are likely to work remotely on the subsynaptic nuclei and the myotendinous junctional nuclei, respectively. We conclude that snRNA-seq analysis of embryonic/neonatal diaphragms reveal a novel coordinated expression profile especially in the Wnt/β-catenin signaling that regulate the formation of the embryonic NMJ.

Keywords:  Wnt signaling; myonucleus; myotendinous junction; neuromuscular junction; skeletal muscle; β-catenin

DOI:  https://doi.org/10.1111/jnc.16013
Cells. 2023 Nov 09. pii: 2598. [Epub ahead of print]12(22):

Unravelling the Role of Cancer Cell-Derived Extracellular Vesicles in Muscle Atrophy, Lipolysis, and Cancer-Associated Cachexia.

Akbar L Marzan, Sai V Chitti.

  Cancer-associated cachexia is a metabolic syndrome that causes significant reduction in whole-body weight due to excessive loss of muscle mass accompanied by loss of fat mass. Reduced food intake and several metabolic abnormalities, such as increased energy expenditure, excessive catabolism, and inflammation, are known to drive cachexia. It is well documented that cancer cells secrete EVs in abundance which can be easily taken up by the recipient cell. The cargo biomolecules carried by the EVs have the potential to alter the signalling pathways and function of the recipient cells. EV cargo includes proteins, nucleic acids, lipids, and metabolites. Tumour-secreted EVs have been found to alter the metabolic and biological functions of adipose and muscle tissue, which aids in the development of the cachexia phenotype. To date, no medical intervention or FDA-approved drug exists that can completely reverse cachexia. Therefore, understanding how cancer-derived EVs contribute to the onset and progression of cancer-associated cachexia may help with the identification of new biomarkers as well as provide access to novel treatment alternatives. The goal of this review article is to discuss the most recent research on cancer-derived EVs and their function in cellular crosstalk that promotes catabolism in muscle and adipose tissue during cancer-induced cachexia.

Keywords:  browning; cancer-associated cachexia; extracellular vesicles; lipolysis; muscle atrophy

DOI:  https://doi.org/10.3390/cells12222598
medRxiv. 2023 Nov 06. pii: 2023.11.05.23298108. [Epub ahead of print]

Expression of mitochondrial oxidative stress response genes in muscle is associated with mitochondrial respiration, physical performance, and muscle mass in the Study of Muscle, Mobility and Aging (SOMMA).

Gregory J Tranah, Haley N Barnes, Peggy M Cawthon, Paul M Coen, Karyn A Esser, Russell T Hepple, Zhiguang Huo, Philip A Kramer, Frederico G S Toledo, Daniel S Evans, Steven R Cummings.

Gene expression in skeletal muscle of older individuals may reflect compensatory adaptations in response to oxidative damage that preserve tissue integrity and maintain function. Identifying associations between oxidative stress response gene expression patterns and mitochondrial function, physical performance, and muscle mass in older individuals would further our knowledge of mechanisms related to managing molecular damage that may be targeted to preserve physical resilience. To characterize expression patterns of genes responsible for the oxidative stress response, RNA was extracted and sequenced from skeletal muscle biopsies collected from 575 participants (≥70 years old) from the Study of Muscle, Mobility and Aging. Expression levels of twenty-one protein coding RNAs related to the oxidative stress response were analyzed in relation to six phenotypic measures, including: maximal mitochondrial respiration from muscle biopsies (Max OXPHOS), physical performance (VO 2 peak, 400m walking speed, and leg strength), and muscle size (thigh muscle volume and whole-body D3Cr muscle mass). The mRNA level of the oxidative stress response genes most consistently associated across outcomes are preferentially expressed within the mitochondria. Higher expression of mRNAs that encode generally mitochondria located proteins SOD2 , TRX2 , PRX3 , PRX5 , and GRX2 were associated with higher levels of mitochondrial respiration and VO 2 peak. In addition, greater SOD2, PRX3, and GRX2 expression was associated with higher physical performance and muscle size. Identifying specific mechanisms associated with high functioning across multiple performance and physical domains may lead to targeted antioxidant interventions with greater impacts on mobility and independence.

DOI: https://doi.org/10.1101/2023.11.05.23298108
Aging Cell. 2023 Nov 22. e14047

Cpt1a silencing in AgRP neurons improves cognitive and physical capacity and promotes healthy aging in male mice.

Kevin Ibeas, Christian Griñán-Ferré, Maria Del Mar Romero, David Sebastián, Marianela Bastías-Pérez, Roberto Gómez, M Carmen Soler-Vázquez, Sebastián Zagmutt, Mercè Pallás, Margarida Castell, Denise D Belsham, Paula Mera, Laura Herrero, Dolors Serra.

  Orexigenic neurons expressing agouti-related protein (AgRP) and neuropeptide Y in the arcuate nucleus (ARC) of the hypothalamus are activated in response to dynamic variations in the metabolic state, including exercise. We previously observed that carnitine palmitoyltransferase 1a (CPT1A), a rate-limiting enzyme of mitochondrial fatty acid oxidation, is a key factor in AgRP neurons, modulating whole-body energy balance and fluid homeostasis. However, the effect of CPT1A in AgRP neurons in aged mice and during exercise has not been explored yet. We have evaluated the physical and cognitive capacity of adult and aged mutant male mice lacking Cpt1a in AgRP neurons (Cpt1a KO). Adult Cpt1a KO male mice exhibited enhanced endurance performance, motor coordination, locomotion, and exploration compared with control mice. No changes were observed in anxiety-related behavior, cognition, and muscle strength. Adult Cpt1a KO mice showed a reduction in gastrocnemius and tibialis anterior muscle mass. The cross-sectional area (CSA) of these muscles were smaller than those of control mice displaying a myofiber remodeling from type II to type I fibers. In aged mice, changes in myofiber remodeling were maintained in Cpt1a KO mice, avoiding loss of physical capacity during aging progression. Additionally, aged Cpt1a KO mice revealed better cognitive skills, reduced inflammation, and oxidative stress in the hypothalamus and hippocampus. In conclusion, CPT1A in AgRP neurons appears to modulate health and protects against aging. Future studies are required to clarify whether CPT1A is a potential antiaging candidate for treating diseases affecting memory and physical activity.

Keywords:  AgRP neurons; CPT1A; aging; cognitive behavior; physical activity

DOI:  https://doi.org/10.1111/acel.14047
Gen Physiol Biophys. 2023 Nov;42(6): 521-529

Polydatin inhibited TNF-α-induced apoptosis of skeletal muscle cells through AKT-mediated p38 MAPK and NF-κB pathways.

Yongli Liu, Fang Xie, Changhuai Lu, Zongbo Zhou, Shudong Li, Jia Zhong, Qian Li, Xianfang Shao.

Skeletal muscle atrophy severely impacts one's quality of life. The effects and mechanism of polydatin on skeletal muscle atrophy are unclear. This study investigated the effects and mechanism of polydatin on TNF-α-induced skeletal muscle cells. The skeletal muscle cell atrophy model was established by inducing C2C12 cells with TNF-α. Cell viability, IL-1β levels and cell apoptosis were assessed. The mRNA and protein expression levels of apoptosis-related proteins were measured. Meanwhile, the binding of polydatin to AKT was analyzed by molecular docking. TNF-α reduced cell fusion and viability while up-regulated IL-1β level and promoted cell apoptosis. TNF-α activated AKT, NF-κB, and p38 MAPK signaling pathways. Polydatin reversed these effects induced by TNF-α, with a low concentration being more effective. Polydatin was predicted to bind to GLY162, PHE161, GLU198, THR195 and GLU191 sites of AKT protein through van der Waals force and conventional hydrogen bonds. Overexpression of AKT led to increased phosphorylation levels of AKT, p38, and p65 proteins, as well as IL-1β levels and cell apoptosis. Polydatin inhibited TNF-α-induced apoptosis of C2C12 cells by regulating NF-κB and p38 MAPK signaling pathways through AKT. This suggests that polydatin shows promise as a new drug for the treatment of skeletal muscle atrophy.

DOI: https://doi.org/10.4149/gpb_2023027
Med Sci Sports Exerc. 2023 Nov 23.

One Week of Single Leg Immobilization Lowers Muscle Connective Protein Synthesis Rates in Healthy, Young Adults.

Andrew M Holwerda, Michelle E G Weijzen, Antoine Zorenc, Joan Senden, Guus H J Jetten, Lisanne H P Houben, Lex B Verdijk, Luc J C van Loon.

PURPOSE: Short periods of limb immobilization lower myofibrillar protein synthesis rates. Within skeletal muscle, the extracellular matrix of connective proteins is recognized as an important factor determining the capacity to transmit contractile force. Little is known regarding the impact of immobilization and subsequent recovery on muscle connective protein synthesis rates. This study examined the impact of one week of leg immobilization and two weeks of subsequent ambulant recovery on daily muscle connective protein synthesis rates.
METHODS: Thirty healthy, young (24 ± 5 y) men were subjected to 7 days of one-legged knee immobilization followed by 14 days of ambulant recovery. Deuterium oxide ingestion was applied over the entire period and muscle biopsy samples were collected before immobilization, after immobilization, and after recovery to measure muscle connective protein synthesis rates and mRNA expression of key extracellular matrix proteins (collagen I, collagen III), glycoproteins (fibronectin, tenascin-C), and proteoglycans (fibromodulin, and decorin). A two-way repeated measures (time x leg) ANOVA was used to compare changes in muscle connective protein synthesis rates during immobilization and recovery.
RESULTS: During immobilization, muscle connective protein synthesis rates were lower in the immobilized (1.07 ± 0.30 %/d) compared with the non-immobilized (1.48 ± 0.44 %/d; P < 0.01) leg. When compared to the immobilization period, connective protein synthesis rates in the immobilized leg increased during subsequent recovery (1.48 ± 0.64 %/d; P < 0.01). Following recovery, skeletal muscle collagen I, collagen III, fibronectin, fibromodulin, and decorin mRNA expression increased when compared to the post-immobilization timepoint (all P < 0.001).
CONCLUSIONS: One week of leg immobilization lowers muscle connective protein synthesis rates. Muscle connective protein synthesis rates increase during subsequent ambulant recovery, which is accompanied by increased mRNA expression of key extracellular matrix proteins.

DOI: https://doi.org/10.1249/MSS.0000000000003342
Can J Physiol Pharmacol. 2023 Nov 18.

The role of the circadian clock system in mitochondrial trans-sulfuration pathway and tissue remodeling.

Suresh C Tyagi, Sathnur Pushpakumar, Utpal Sen, Oluwaseun E Akinterinwa, Yuting Zheng, Sri Prakash L Mokshagundam, Dinesh K Kalra, Mahavir Singh.

Hydrogen sulfide (H2S) is a product of epigenetics that involves trans-sulfuration pathway for clearance of homocysteine (Hcy), thereby mitigating skeletal muscle's pathological remodeling. Although master circadian clock regulator that is known as brain and muscle aryl hydrocarbon receptor nuclear translocator like protein 1 (i.e., BMAL1) is associated with S-adenosylhomocysteine hydrolase and Hcy metabolism but how trans-sulfuration is influenced by circadian clock remains unexplored. We hypothesize that alterations in functioning of circadian clock during sleep/wake cycle affect skeletal muscle. To test this, we measured MMP-2 and MMP-9. We also studied MMP-13 that is influenced by growth arrest and DNA damage-45 during sleep/wake cycle. Wild type and cystathionine β synthase deficient (CBS-/+) mice were treated with H2S and subjected for measurement of trans-sulfuration factors from skeletal muscle. Results suggested robust activation of MMPs in wake mice versus sleep indicating "1-carbon metabolic dysregulation" which takes place during muscular dystrophy. Interestingly, levels of CBS, cystathionine γ lyase, MTHFR, phosphatidylethanolamine N-methyltransferase, and Hcy-protein bound paraoxonase 1 were attenuated CBS-/+. H2S treatment mitigated the changes. Levels of mitochondrial peroxisome proliferator-activated receptor-gamma coactivator 1-α and mitofusin-2 were improved by H2S. Our findings suggest participation of circadian clock in trans-sulfuration pathway that affects skeletal muscle and mitochondrial regeneration.

DOI: https://doi.org/10.1139/cjpp-2023-0186
Biochem Biophys Res Commun. 2023 Nov 17. pii: S0006-291X(23)01325-6. [Epub ahead of print]690 149231

Development of a Cre-recombination-based color-switching reporter system for cell fusion detection.

Toshifumi Asano, Philipp Sasse, Takao Nakata.

  Cell fusion plays a key role in the development and formation of tissues and organs in several organisms. Skeletal myogenesis is assessed in vitro by cell shape and gene and protein expression using immunofluorescence and immunoblotting assays. However, these conventional methods are complex and do not allow for easy time-course observation in living cells. Therefore, this study aimed to develop a Cre recombination-based fluorescent reporter system to monitor cell-cell fusion. We combined green and red fluorescent proteins with a Cre-loxP system to detect syncytium formation using a fluorescent binary switch. This allowed us to visualize mononucleated cells with green fluorescence before fusion and multinucleated syncytia with red fluorescence by conditional expression after cell fusion. The formation of multinuclear myotubes during myogenic differentiation was detected by the change in fluorescence from green to red after Cre-mediated recombination. The distribution of the fluorescence signal correlated with the expression of myogenic differentiation markers. Moreover, red reporter fluorescence intensity was correlated with the number of nuclei contained in the red fluorescent-positive myotubes. We also successfully demonstrated that our fusion monitoring system is applicable to the formation of skeletal muscle myotube and placental syncytiotrophoblast. These results suggest that the color-switching fluorescent reporter system, using Cre-mediated recombination, could be a robust tool used to facilitate the study of cell-to-cell fusion.

Keywords:  Cell fusion; Cre-loxP; Fluorescent reporter; Multinuclear cell; Myoblast; Trophoblast

DOI:  https://doi.org/10.1016/j.bbrc.2023.149231
Genes (Basel). 2023 Nov 07. pii: 2049. [Epub ahead of print]14(11):

Uncoupling Protein 3 Promotes the Myogenic Differentiation of Type IIb Myotubes in C2C12 Cells.

Ziwei You, Jieyu Wang, Faliang Li, Wei Hei, Meng Li, Xiaohong Guo, Pengfei Gao, Guoqing Cao, Chunbo Cai, Bugao Li.

  Uncoupling protein 3 (Ucp3) is an important transporter within mitochondria and is mainly expressed in skeletal muscle, brown adipose tissue and the myocardium. However, the effects of Ucp3 on myogenic differentiation are still unclear. This study evaluated the effects of Ucp3 on myogenic differentiation, myofiber type and energy metabolism in C2C12 cells. Gain- and loss-of-function studies revealed that Ucp3 could increase the number of myotubes and promote the myogenic differentiation of C2C12 cells. Furthermore, Ucp3 promoted the expression of the type IIb myofiber marker gene myosin heavy chain 4 (Myh4) and decreased the expression of the type I myofiber marker gene myosin heavy chain 7 (Myh7). In addition, energy metabolism related to the expression of PPARG coactivator 1 alpha (Pgc1-α), ATP synthase, H+ transportation, mitochondrial F1 complex, alpha subunit 1 (Atp5a1), lactate dehydrogenase A (Ldha) and lactate dehydrogenase B (Ldhb) increased with Ucp3 overexpression. Ucp3 could promote the myogenic differentiation of type IIb myotubes and accelerate energy metabolism in C2C12 cells. This study can provide the theoretical basis for understanding the role of Ucp3 in energy metabolism.

Keywords:  C2C12 cells; Ucp3; energy metabolism; myogenic differentiation; types of myotubes

DOI:  https://doi.org/10.3390/genes14112049
medRxiv. 2023 Nov 06. pii: 2023.11.05.23298134. [Epub ahead of print]

Associations of Objective and Self-Reported Physical Activity and Sedentary Behavior with Skeletal Muscle Energetics: The Study of Muscle, Mobility and Aging (SOMMA).

Yujia Susanna Qiao, Terri L Blackwell, Peggy M Cawthon, Paul M Coen, Steven R Cummings, Giovanna Distefano, Samaneh Farsijani, Daniel E Forman, Bret H Goodpaster, Stephen B Kritchevsky, Theresa Mau, Frederico G S Toledo, Anne B Newman, Nancy W Glynn.

Background: Skeletal muscle energetics decline with age, and physical activity (PA) has been shown to counteract these declines in older adults. Yet, many studies were based on self-reported PA or structured exercise interventions. We examined the associations of objective daily PA and sedentary behavior (SB) with skeletal muscle energetics and also compared with self-reported PA and SB. We also explored the extent to which PA would attenuate the associations of age with muscle energetics.
Methods: Among the Study of Muscle, Mobility and Aging (SOMMA) enrolled older adults, 810 (mean age=76±5, 58% women) had maximal muscle oxidative capacity measured ex vivo via high-resolution respirometry of permeabilized myofibers (maxOXPHOS) and in vivo by 31 Phosphorus magnetic resonance spectroscopy (ATP max ). Objective PA was measured using the wrist-worn ActiGraph GT9X over 7-days to capture sedentary behavior (SB), light, and moderate-to-vigorous PA (MVPA). Self-reported SB, MVPA, and all exercise-related PA were assessed with The Community Healthy Activities Model Program for Seniors questionnaire. Linear regression models with progressive covariate adjustments evaluated the associations between SB, PA and muscle energetics, and the attenuation of the age / muscle energetic association by PA.
Results: Every 30 minutes more objective MVPA was associated with 0.65 pmol/s*mg higher maxOXPHOS and 0.012 mM/sec higher ATP max , after adjustment for age, site/technician and sex. More time spent in objective light+MVPA was significantly associated with higher ATP max , but not maxOXPHOS. In contrast, every 30 minutes spent in objective SB was associated with 0.43 pmol/s*mg lower maxOXPHOS and 0.004 mM/sec lower ATP max . Only associations with ATP max held after further adjusting for socioeconomic status, body mass index, lifestyle factors and multimorbidities. Self-reported MVPA and all exercise-related activities, but not SB, yielded similar associations with maxOXPHOS and ATP max . Lastly, age was only significantly associated with muscle energetics in men. Adjusting for objective time spent in MVPA attenuated the age association with ATP max by nearly 60% in men.
Conclusion: More time spent in daily PA, especially MVPA, were associated with higher muscle energetics. Interventions that increase higher intensity activity might offer potential therapeutic interventions to slow the age-related decline in muscle energetics. Our work also emphasizes the importance of taking PA into consideration when evaluating associations related to skeletal muscle energetics.

DOI: https://doi.org/10.1101/2023.11.05.23298134
Skelet Muscle. 2023 Nov 18. 13(1): 19

Electrical impedance myography detects dystrophin-related muscle changes in mdx mice.

Tetsuaki Hiyoshi, Fuqiang Zhao, Rina Baba, Takeshi Hirakawa, Ryosuke Kuboki, Kazunori Suzuki, Yoshiro Tomimatsu, Patricio O'Donnell, Steve Han, Neta Zach, Masato Nakashima.

   BACKGROUND: The lack of functional dystrophin protein in Duchenne muscular dystrophy (DMD) causes chronic skeletal muscle inflammation and degeneration. Therefore, the restoration of functional dystrophin levels is a fundamental approach for DMD therapy. Electrical impedance myography (EIM) is an emerging tool that provides noninvasive monitoring of muscle conditions and has been suggested as a treatment response biomarker in diverse indications. Although magnetic resonance imaging (MRI) of skeletal muscles has become a standard measurement in clinical trials for DMD, EIM offers distinct advantages, such as portability, user-friendliness, and reduced cost, allowing for remote monitoring of disease progression or response to therapy. To investigate the potential of EIM as a biomarker for DMD, we compared longitudinal EIM data with MRI/histopathological data from an X-linked muscular dystrophy (mdx) mouse model of DMD. In addition, we investigated whether EIM could detect dystrophin-related changes in muscles using antisense-mediated exon skipping in mdx mice.
METHODS: The MRI data for muscle T2, the magnetic resonance spectroscopy (MRS) data for fat fraction, and three EIM parameters with histopathology were longitudinally obtained from the hindlimb muscles of wild-type (WT) and mdx mice. In the EIM study, a cell-penetrating peptide (Pip9b2) conjugated antisense phosphorodiamidate morpholino oligomer (PPMO), designed to induce exon-skipping and restore functional dystrophin production, was administered intravenously to mdx mice.
RESULTS: MRI imaging in mdx mice showed higher T2 intensity at 6 weeks of age in hindlimb muscles compared to WT mice, which decreased at ≥ 9 weeks of age. In contrast, EIM reactance began to decline at 12 weeks of age, with peak reduction at 18 weeks of age in mdx mice. This decline was associated with myofiber atrophy and connective tissue infiltration in the skeletal muscles. Repeated dosing of PPMO (10 mg/kg, 4 times every 2 weeks) in mdx mice led to an increase in muscular dystrophin protein and reversed the decrease in EIM reactance.
CONCLUSIONS: These findings suggest that muscle T2 MRI is sensitive to the early inflammatory response associated with dystrophin deficiency, whereas EIM provides a valuable biomarker for the noninvasive monitoring of subsequent changes in skeletal muscle composition. Furthermore, EIM reactance has the potential to monitor dystrophin-deficient muscle abnormalities and their recovery in response to antisense-mediated exon skipping.

Keywords:  Cell-penetrating peptide conjugated antisense phosphorodiamidate morpholino oligomer; Duchenne muscular dystrophy; Electric impedance myography; Magnetic resonance imaging; mdx mice

DOI:  https://doi.org/10.1186/s13395-023-00331-1
Cells. 2023 Nov 11. pii: 2608. [Epub ahead of print]12(22):

Age Is Just a Number: Progress and Obstacles in the Discovery of New Candidate Drugs for Sarcopenia.

Hyun-Jun Kim, Da-Woon Jung, Darren Reece Williams.

  Sarcopenia is a disease characterized by the progressive loss of skeletal muscle mass and function that occurs with aging. The progression of sarcopenia is correlated with the onset of physical disability, the inability to live independently, and increased mortality. Due to global increases in lifespan and demographic aging in developed countries, sarcopenia has become a major socioeconomic burden. Clinical therapies for sarcopenia are based on physical therapy and nutritional support, although these may suffer from low adherence and variable outcomes. There are currently no clinically approved drugs for sarcopenia. Consequently, there is a large amount of pre-clinical research focusing on discovering new candidate drugs and novel targets. In this review, recent progress in this research will be discussed, along with the challenges that may preclude successful translational research in the clinic. The types of drugs examined include mitochondria-targeting compounds, anti-diabetes agents, small molecules that target non-coding RNAs, protein therapeutics, natural products, and repositioning candidates. In light of the large number of drugs and targets being reported, it can be envisioned that clinically approved pharmaceuticals to prevent the progression or even mitigate sarcopenia may be within reach.

Keywords:  aging; drug discovery; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.3390/cells12222608
Biomolecules. 2023 Nov 05. pii: 1617. [Epub ahead of print]13(11):

Preventive Effects of Collagen-Derived Dipeptide Prolyl-Hydroxyproline against Dexamethasone-Induced Muscle Atrophy in Mouse C2C12 Skeletal Myotubes.

Yoshifumi Kimira, Konosuke Osawa, Yoshihiro Osawa, Hiroshi Mano.

  Glucocorticoids, commonly used to manage inflammatory diseases, can induce muscle atrophy by accelerating the breakdown of muscle proteins. This research delves into the influence of Prolyl-hydroxyproline (Pro-Hyp), a collagen-derived peptide, on muscle atrophy induced with dexamethasone (DEX), a synthetic glucocorticoid, in mouse C2C12 skeletal myotubes. Exposure to DEX (10 μM) for 6 days resulted in a decrease in myotube diameter, along with elevated mRNA and protein levels of two muscle-atrophy-related ubiquitin ligases, muscle atrophy F-box (MAFbx, also known as atrogin-1) and muscle ring finger 1 (MuRF-1). Remarkably, treatment with 0.1 mM of Pro-Hyp mitigated the reduction in myotube thickness caused by DEX, while promoting the phosphorylation of Akt, mammalian target of rapamycin (mTOR), and forkhead box O3a (Foxo3a). This led to the inhibition of the upregulation of the ubiquitin ligases atrogin-1 and MuRF-1. These findings indicate the potential significance of Pro-Hyp as a promising therapeutic target for countering DEX-induced muscle atrophy.

Keywords:  Prolyl-hydroxyproline; collagen-derived peptide; mouse C2C12 skeletal myotubes; muscle atrophy; ubiquitin ligases

DOI:  https://doi.org/10.3390/biom13111617
Aging Cell. 2023 Nov 20. e14041

Age-related nitration/dysfunction of myogenic stem cell activator HGF.

Alaa Elgaabari, Nana Imatomi, Hirochika Kido, Takashi Nakashima, Shoko Okuda, Yoshitaka Manabe, Shoko Sawano, Wataru Mizunoya, Ryuki Kaneko, Sakiho Tanaka, Takahiro Maeno, Yuji Matsuyoshi, Miyumi Seki, So Kuwakado, Kahona Zushi, Nasibeh Daneshvar, Mako Nakamura, Takahiro Suzuki, Kenji Sunagawa, Judy E Anderson, Ronald E Allen, Ryuichi Tatsumi.

  Mechanical perturbation triggers activation of resident myogenic stem cells to enter the cell cycle through a cascade of events including hepatocyte growth factor (HGF) release from its extracellular tethering and the subsequent presentation to signaling-receptor c-met. Here, we show that with aging, extracellular HGF undergoes tyrosine-residue (Y) nitration and loses c-met binding, thereby disturbing muscle homeostasis. Biochemical studies demonstrated that nitration/dysfunction is specific to HGF among other major growth factors and is characterized by its locations at Y198 and Y250 in c-met-binding domains. Direct-immunofluorescence microscopy of lower hind limb muscles from three age groups of rat, provided direct in vivo evidence for age-related increases in nitration of ECM-bound HGF, preferentially stained for anti-nitrated Y198 and Y250-HGF mAbs (raised in-house) in fast IIa and IIx myofibers. Overall, findings highlight inhibitory impacts of HGF nitration on myogenic stem cell dynamics, pioneering a cogent discussion for better understanding age-related muscle atrophy and impaired regeneration with fibrosis (including sarcopenia and frailty).

Keywords:  age-related muscle atrophy; fast myofiber; fibrosis; hepatocyte growth factor (HGF); peroxynitrite; regeneration; resident myogenic stem cell; tyrosine nitration

DOI:  https://doi.org/10.1111/acel.14041
J Clin Endocrinol Metab. 2023 Nov 21. pii: dgad677. [Epub ahead of print]

Skeletal muscle gene expression signatures of obese high- and low- responders to endurance exercise training.

Leona Kovac, Thomas Goj, Meriem Ouni, Martin Irmler, Markus Jähnert, Johannes Beckers, Martin Hrabe de Angelis, Andreas Peter, Anja Moller, Andreas L Birkenfeld, Cora Weigert, Annette Schürmann.

   CONTEXT: Exercise training is known to improve glucose tolerance and reverse insulin resistance in persons with obesity. However, some individuals fail to improve or even decline in their clinical traits following exercise intervention.
OBJECTIVE: This study focused on gene expression and DNA methylation signatures in skeletal muscle of low- (LRE) and high-responders (RES) to 8 weeks of supervised endurance training.
METHODS: We performed skeletal muscle gene expression and DNA methylation analyses in LRE and RES before and after exercise intervention. Additionally, we applied the least absolute shrinkage and selection operator (LASSO) approach to identify predictive marker genes of exercise outcome.
RESULTS: We show that the two groups differ markedly already before the intervention. RES were characterized by lower expression of genes involved in DNA replication and repair, and higher expression of extracellular matrix (ECM) components. LASSO approach identified several novel candidates (e.g. ZCWPW2, FOXRED1, STK40), which have not been previously described in the context of obesity and exercise response. Following the intervention, LRE reacted with expression changes of genes related to inflammation and apoptosis, RES with genes related to mitochondrial function. LRE exhibited significantly higher expression of ECM components compared to RES, suggesting improper remodeling and potential negative effects on insulin sensitivity. Between 45 and 70% of differences in gene expression could be linked to differences in DNA methylation.
CONCLUSION: Together, our data offer an insight into molecular mechanisms underlying differences in response to exercise and provide potential novel markers for the success of intervention.

Keywords:  DNA methylation; LASSO; exercise; gene expression; obesity; responders

DOI:  https://doi.org/10.1210/clinem/dgad677
medRxiv. 2023 Nov 08. pii: 2023.11.07.23298177. [Epub ahead of print]

Childhood adverse life events and skeletal muscle mitochondrial function.

Kate A Duchowny, Theresa Mau, L Grisell Diaz-Ramierz, Li-Yung Lui, David J Marcinek, Frederico G S Toledo, Peggy M Cawthon, Russell T Hepple, Philip A Kramer, Anne B Newman, Stephen B Kritchevsky, Steven R Cummings, Paul M Coen, Anthony J A Molina.

Social stress experienced in childhood is associated with adverse health later in life. Mitochondrial function has been implicated as a mechanism for how stressful life events "get under the skin" to influence physical wellbeing. Using data from the Study of Muscle, Mobility and Aging (n=879, 59% women), linear models examined whether adverse childhood events (i.e., physical abuse) were associated with two measures of skeletal muscle mitochondrial energetics in older adults: (1) maximal adenosine triphosphate production (ATP max ) and (2) maximal state 3 respiration (Max OXPHOS). Forty-five percent of the sample reported experiencing 1+ adverse childhood event. After adjustment, each additional event was associated with -0.07 SD (95% CI= - 0.12, -0.01) lower ATP max . No association was observed with Max OXPHOS. Adverse childhood events are associated with lower ATP production in later life. Findings indicate that mitochondrial function may be a mechanism in understanding how early social stress influences health in later life.

DOI: https://doi.org/10.1101/2023.11.07.23298177
Life Sci Alliance. 2024 Feb;pii: e202302147. [Epub ahead of print]7(2):

Mitochondrial phosphoproteomes are functionally specialized across tissues.

Fynn M Hansen, Laura S Kremer, Ozge Karayel, Isabell Bludau, Nils-Göran Larsson, Inge Kühl, Matthias Mann.

Mitochondria are essential organelles whose dysfunction causes human pathologies that often manifest in a tissue-specific manner. Accordingly, mitochondrial fitness depends on versatile proteomes specialized to meet diverse tissue-specific requirements. Increasing evidence suggests that phosphorylation may play an important role in regulating tissue-specific mitochondrial functions and pathophysiology. Building on recent advances in mass spectrometry (MS)-based proteomics, we here quantitatively profile mitochondrial tissue proteomes along with their matching phosphoproteomes. We isolated mitochondria from mouse heart, skeletal muscle, brown adipose tissue, kidney, liver, brain, and spleen by differential centrifugation followed by separation on Percoll gradients and performed high-resolution MS analysis of the proteomes and phosphoproteomes. This in-depth map substantially quantifies known and predicted mitochondrial proteins and provides a resource of core and tissue-specific mitochondrial proteins (mitophos.de). Predicting kinase substrate associations for different mitochondrial compartments indicates tissue-specific regulation at the phosphoproteome level. Illustrating the functional value of our resource, we reproduce mitochondrial phosphorylation events on dynamin-related protein 1 responsible for its mitochondrial recruitment and fission initiation and describe phosphorylation clusters on MIGA2 linked to mitochondrial fusion.

DOI: https://doi.org/10.26508/lsa.202302147
medRxiv. 2023 Nov 09. pii: 2023.11.08.23298271. [Epub ahead of print]

Skeletal muscle energetics explain the sex disparity in mobility impairment in the Study of Muscle, Mobility and Aging (SOMMA).

Philip A Kramer, Paul M Coen, Peggy M Cawthon, Giovanna Distefano, Steven R Cummings, Bret H Goodpaster, Russell T Hepple, Stephen B Kritchevsky, Eric G Shankland, David J Marcinek, Frederico G S Toledo, Kate A Duchowny, Sofhia V Ramos, Stephanie Harrison, Anne B Newman, Anthony J A Molina.

The age-related decline in muscle mitochondrial energetics contributes to the loss of mobility in older adults. Women experience a higher prevalence of mobility impairment compared to men, but it is unknown whether sex-specific differences in muscle energetics underlie this disparity. In the Study of Muscle, Mobility and Aging (SOMMA), muscle energetics were characterized using in vivo phosphorus-31 magnetic resonance spectroscopy and high-resolution respirometry of vastus lateralis biopsies in 773 participants (56.4% women, age 70-94 years). A Short Physical Performance Battery score ≤ 8 was used to define lower-extremity mobility impairment. Muscle mitochondrial energetics were lower in women compared to men (e.g. Maximal Complex I&II OXPHOS: Women=55.06 +/- 15.95; Men=65.80 +/- 19.74; p<0.001) and in individuals with mobility impairment compared to those without (e.g., Maximal Complex I&II OXPHOS in women: SPPB≥9=56.59 +/- 16.22; SPPB≤8=47.37 +/- 11.85; p<0.001). Muscle energetics were negatively associated with age only in men (e.g., Maximal ETS capacity: R=-0.15, p=0.02; age/sex interaction, p=0.04), resulting in muscle energetics measures that were significantly lower in women than men in the 70-79 age group but not the 80+ age group. Similarly, the odds of mobility impairment were greater in women than men only in the 70-79 age group (70-79 age group, OR age-adjusted =1.78, 95% CI=1.03, 3.08, p=0.038; 80+ age group, OR age-adjusted =1.05, 95% CI=0.52, 2.15, p=0.89). Accounting for muscle energetics attenuated up to 75% of the greater odds of mobility impairment in women. Women had lower muscle mitochondrial energetics compared to men, which largely explain their greater odds of lower-extremity mobility impairment.

DOI: https://doi.org/10.1101/2023.11.08.23298271
Pract Neurol. 2023 Nov 20. pii: pn-2023-003945. [Epub ahead of print]

Congenital myasthenic syndrome from a MUSK gene mutation.

Antonia McLean, Ian Wilson.

  Slowly progressive neuromuscular symptoms often have a genetic basis. We present the case of a woman in her 40s with gradually progressive symmetrical weakness and respiratory muscle involvement. Extensive investigation found no specific cause. After a novel neuromuscular gene panel became available, we identified a mutation in the MUSK gene (muscle-specific kinase), confirming a diagnosis of congenital myasthenic syndrome. This group of rare disorders are caused by mutations in genes encoding the neuromuscular junction.

Keywords:  MYASTHENIA; NEUROGENETICS; NEUROMUSCULAR

DOI:  https://doi.org/10.1136/pn-2023-003945