bims-moremu 2023-11-12 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–11–12
thirty-six papers selected by
Anna Vainshtein, Craft Science Inc.

Treadmill training does not enhance skeletal muscle recovery following disuse atrophy in older male mice.
Mass Spectrometry-Based Proteomic Technology and Its Application to Study Skeletal Muscle Cell Biology.
Impact of biological sex and sex hormones on molecular signatures of skeletal muscle at rest and in response to distinct exercise training modes.
Two zebrafish cacna1s loss-of-function variants provide models of mild and severe CACNA1S-related myopathy.
From workout to molecular switches: How does skeletal muscle produce, sense, and transduce subcellular redox signals?
Mitophagy Activation by Urolithin A to Target Muscle Aging.
Role of Actin-Binding Proteins in Skeletal Myogenesis.
TAZ stimulates exercise-induced muscle satellite cell activation via Pard3-p38 MAPK-TAZ signalling axis.
Improved endurance capacity of diabetic mice during SGLT2 inhibition: Role of AICARP, an AMPK activator in the soleus.
Absence of the primary cilia formation gene Talpid3 impairs muscle stem cell function.
Exercise attenuates polyglutamine-mediated neuromuscular degeneration in a mouse model of spinal and bulbar muscular atrophy.
The potassium-glycogen interaction on force and excitability in mouse skeletal muscle: implications for fatigue.
Tropomyosin 3 (TPM3) function in skeletal muscle and in myopathy.
6-day Dry Immersion leads to downregulation of slow-fiber type and mitochondria-related genes expression.
Low extracellular magnesium induces phenotypic and metabolic alterations in C2C12-derived myotubes.
Temporal dynamics of muscle mitochondrial uncoupling-induced integrated stress response and ferroptosis defense.
Acetate and succinate benefit host muscle energetics as exercise-associated post-biotics.
Skeletal muscle regeneration failure in ischemic-damaged limbs is associated with pro-inflammatory macrophages and premature differentiation of satellite cells.
Native lamin A/C proteomes and novel partners from heart and skeletal muscle in a mouse chronic inflammation model of human frailty.
11-beta-hydroxysteroid dehydrogenase type 1 (HSD11B1) gene expression in muscle is linked to reduced skeletal muscle index in sarcopenic patients.
Regulating Striated Muscle Contraction: Through Thick and Thin.
snRNA-seq analysis in multinucleated myogenic FSHD cells identifies heterogeneous FSHD transcriptome signatures associated with embryonic-like program activation and oxidative stress-induced apoptosis.
Mechanisms and effects of metformin on skeletal muscle disorders.
Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice.
A transcriptomics-based drug repositioning approach to identify drugs with similar activities for the treatment of muscle pathologies in spinal muscular atrophy (SMA) models.
Sarcopenia: still in relative definition-penia and severe treatment-penia.
Combinatorial activation of the WNT-dependent fibrogenic program by distinct complement subunits in dystrophic muscle.
DNA hypomethylation characterizes genes encoding tissue-dominant functional proteins in liver and skeletal muscle.
Antioxidants restore store-operated Ca2+ entry in patient-iPSC-derived myotubes with tubular aggregate myopathy-associated Ile484ArgfsX21 STIM1 mutation via upregulation of binding immunoglobulin protein.
Protocol for isolating mice skeletal muscle myoblasts and myotubes via differential antibody validation.
Construct and criterion validity of muscle ultrasonography for assessment of skeletal muscle in patients recovering from COVID-19.
Transcriptome analysis reveals genes associated with stem cell activation by physical exercise in the dentate gyrus of aged p16Ink4a knockout mice.
The adaptive antioxidant response during fasting-induced muscle atrophy is oppositely regulated by ZEB1 and ZEB2.
66Mouse models of accelerated aging in musculoskeletal research for assessing frailty, sarcopenia, and osteoporosis - a review.
Skeletal muscle-derived extracellular vesicles transport glycolytic enzymes to mediate muscle-to-bone crosstalk.
FNIP1 abrogation promotes functional revascularization of ischemic skeletal muscle by driving macrophage recruitment.

Front Physiol. 2023 ;14 1263500

Treadmill training does not enhance skeletal muscle recovery following disuse atrophy in older male mice.

Elena M Yee, Carson T Hauser, Jonathan J Petrocelli, Naomi M M P de Hart, Patrick J Ferrara, Princess Bombyck, Zachary J Fennel, Lisha van Onselen, Sohom Mookerjee, Katsuhiko Funai, J David Symons, Micah J Drummond.

  Introduction: A hallmark of aging is poor muscle recovery following disuse atrophy. Efficacious strategies to enhance muscle recovery following disuse atrophy in aging are non-existent. Prior exercise training could result in favorable muscle morphological and cellular adaptations that may promote muscle recovery in aging. Here, we characterized the impact of exercise training on skeletal muscle inflammatory and metabolic profiles and cellular remodeling and function, together with femoral artery reactivity prior to and following recovery from disuse atrophy in aged male mice. We hypothesized that 12 weeks of treadmill training in aged male mice would improve skeletal muscle cellular remodeling at baseline and during recovery from disuse atrophy, resulting in improved muscle regrowth. Methods: Physical performance, ex vivo muscle and vascular function, tissue and organ mass, hindlimb muscle cellular remodeling (macrophage, satellite cell, capillary, myofiber size, and fibrosis), and proteolytic, inflammatory, and metabolic muscle transcripts were evaluated in aged exercise-trained and sedentary mice. Results: We found that at baseline following exercise training (vs. sedentary mice), exercise capacity and physical function increased, fat mass decreased, and endothelial function improved. However, exercise training did not alter tibialis anterior or gastrocnemius muscle transcriptional profile, macrophage, satellite cell, capillarity or collagen content, or myofiber size and only tended to increase tibialis mass during recovery from disuse atrophy. Conclusion: While exercise training in old male mice improved endothelial function, physical performance, and whole-body tissue composition as anticipated, 12 weeks of treadmill training had limited impact on skeletal muscle remodeling at baseline or in response to recovery following disuse atrophy.

Keywords:  aging; atrophy; exercise; function; inflammation; muscle regrowth

DOI:  https://doi.org/10.3389/fphys.2023.1263500
Cells. 2023 Nov 01. pii: 2560. [Epub ahead of print]12(21):

Mass Spectrometry-Based Proteomic Technology and Its Application to Study Skeletal Muscle Cell Biology.

Paul Dowling, Dieter Swandulla, Kay Ohlendieck.

  Voluntary striated muscles are characterized by a highly complex and dynamic proteome that efficiently adapts to changed physiological demands or alters considerably during pathophysiological dysfunction. The skeletal muscle proteome has been extensively studied in relation to myogenesis, fiber type specification, muscle transitions, the effects of physical exercise, disuse atrophy, neuromuscular disorders, muscle co-morbidities and sarcopenia of old age. Since muscle tissue accounts for approximately 40% of body mass in humans, alterations in the skeletal muscle proteome have considerable influence on whole-body physiology. This review outlines the main bioanalytical avenues taken in the proteomic characterization of skeletal muscle tissues, including top-down proteomics focusing on the characterization of intact proteoforms and their post-translational modifications, bottom-up proteomics, which is a peptide-centric method concerned with the large-scale detection of proteins in complex mixtures, and subproteomics that examines the protein composition of distinct subcellular fractions. Mass spectrometric studies over the last two decades have decisively improved our general cell biological understanding of protein diversity and the heterogeneous composition of individual myofibers in skeletal muscles. This detailed proteomic knowledge can now be integrated with findings from other omics-type methodologies to establish a systems biological view of skeletal muscle function.

Keywords:  mass spectrometry; muscle cell biology; muscle proteomics; myology; organelle proteomics

DOI:  https://doi.org/10.3390/cells12212560
Cell Metab. 2023 Nov 07. pii: S1550-4131(23)00379-0. [Epub ahead of print]35(11): 1996-2010.e6

Impact of biological sex and sex hormones on molecular signatures of skeletal muscle at rest and in response to distinct exercise training modes.

Mark W Pataky, Surendra Dasari, Kelly L Michie, Kyle J Sevits, A Aneesh Kumar, Katherine A Klaus, Carrie J Heppelmann, Matthew M Robinson, Rickey E Carter, Ian R Lanza, K Sreekumaran Nair.

  Substantial divergence in cardio-metabolic risk, muscle size, and performance exists between men and women. Considering the pivotal role of skeletal muscle in human physiology, we investigated and found, based on RNA sequencing (RNA-seq), that differences in the muscle transcriptome between men and women are largely related to testosterone and estradiol and much less related to genes located on the Y chromosome. We demonstrate inherent unique, sex-dependent differences in muscle transcriptional responses to aerobic, resistance, and combined exercise training in young and older cohorts. The hormonal changes with age likely explain age-related differential expression of transcripts. Furthermore, in primary human myotubes we demonstrate the profound but distinct effects of testosterone and estradiol on amino acid incorporation to multiple individual proteins with specific functions. These results clearly highlight the potential of designing exercise programs tailored specifically to men and women and have implications for people who change gender by altering their hormone profile.

Keywords:  aerobic exercise; estradiol; estrogen; gender; primary human myotubes; protein synthesis; resistance exercise; sex differences; testosterone; transcriptome

DOI:  https://doi.org/10.1016/j.cmet.2023.10.010
Hum Mol Genet. 2023 Oct 31. pii: ddad178. [Epub ahead of print]

Two zebrafish cacna1s loss-of-function variants provide models of mild and severe CACNA1S-related myopathy.

Yukari Endo, Linda Groom, Sabrina M Wang, Emanuela Pannia, Nigel W Griffiths, Jenica L M Van Gennip, Brian Ciruna, Jocelyn Laporte, Robert T Dirksen, James J Dowling.

  CACNA1S-related myopathy, due to pathogenic variants in the CACNA1S gene, is a recently described congenital muscle disease. Disease associated variants result in loss of gene expression and/or reduction of Cav1.1 protein stability. There is an incomplete understanding of the underlying disease pathomechanisms and no effective therapies are currently available. A barrier to the study of this myopathy is the lack of a suitable animal model that phenocopies key aspects of the disease. To address this barrier, we generated knockouts of the two zebrafish CACNA1S paralogs, cacna1sa and cacna1sb. Double knockout fish exhibit severe weakness and early death, and are characterized by the absence of Cav1.1 α1 subunit expression, abnormal triad structure, and impaired excitation-contraction coupling, thus mirroring the severe form of human CACNA1S-related myopathy. A double mutant (cacna1sa homozygous, cacna1sb heterozygote) exhibits normal development, but displays reduced body size, abnormal facial structure, and cores on muscle pathologic examination, thus phenocopying the mild form of human CACNA1S-related myopathy. In summary, we generated and characterized the first cacna1s zebrafish loss-of-function mutants, and show them to be faithful models of severe and mild forms of human CACNA1S-related myopathy suitable for future mechanistic studies and therapy development.

Keywords:  Cav1.1; congenital myopathy; excitation contraction coupling; zebrafish

DOI:  https://doi.org/10.1093/hmg/ddad178
Free Radic Biol Med. 2023 Nov 02. pii: S0891-5849(23)01076-6. [Epub ahead of print]209(Pt 2): 355-365

From workout to molecular switches: How does skeletal muscle produce, sense, and transduce subcellular redox signals?

Carlos Henriquez-Olguin, Roberto Meneses-Valdes, Paraskevi Kritsiligkou, Eduardo Fuentes-Lemus.

  Skeletal muscle is crucial for maintaining human health and overall quality of life. Acute exercise introduces a multifaceted intracellular stress, with numerous post-translational modifications believed to underpin the health benefits of sustained exercise training. Reactive oxygen species (ROS) are posited to serve as second messengers, triggering cytoprotective adaptations such as the upregulation of enzymatic scavenger systems. However, a significant knowledge gap exists between the generation of oxidants in muscle and the exact mechanisms driving muscle adaptations. This review delves into the current research on subcellular redox biochemistry and its role in the physiological adaptations to exercise. We propose that the subcellular regulation of specific redox modifications is key to ensuring specificity in the intracellular response.

Keywords:  Exercise training; Hydrogen peroxide; Mitochondria; Redox signaling; Skeletal muscle

DOI:  https://doi.org/10.1016/j.freeradbiomed.2023.10.404
Calcif Tissue Int. 2023 Nov 05.

Mitophagy Activation by Urolithin A to Target Muscle Aging.

Julie Faitg, Davide D'Amico, Chris Rinsch, Anurag Singh.

  The age-related loss of skeletal muscle function starts from midlife and if left unaddressed can lead to an impaired quality of life. A growing body of evidence indicates that mitochondrial dysfunction is causally involved with muscle aging. Muscles are tissues with high metabolic requirements, and contain rich mitochondria supply to support their continual energy needs. Cellular mitochondrial health is maintained by expansing of the mitochondrial pool though mitochondrial biogenesis, by preserving the natural mitochondrial dynamic process, via fusion and fission, and by ensuring the removal of damaged mitochondria through mitophagy. During aging, mitophagy levels decline and negatively impact skeletal muscle performance. Nutritional and pharmacological approaches have been proposed to manage the decline in muscle function due to impaired mitochondria bioenergetics. The natural postbiotic Urolithin A has been shown to promote mitophagy, mitochondrial function and improved muscle function across species in different experimental models and across multiple clinical studies. In this review, we explore the biology of Urolithin A and the clinical evidence of its impact on promoting healthy skeletal muscles during age-associated muscle decline.

Keywords:  Aging; Mitochondria; Mitophagy; Muscle health; Urolithin A

DOI:  https://doi.org/10.1007/s00223-023-01145-5
Cells. 2023 Oct 25. pii: 2523. [Epub ahead of print]12(21):

Role of Actin-Binding Proteins in Skeletal Myogenesis.

Mai Thi Nguyen, Raju Dash, Kyuho Jeong, Wan Lee.

  Maintenance of skeletal muscle quantity and quality is essential to ensure various vital functions of the body. Muscle homeostasis is regulated by multiple cytoskeletal proteins and myogenic transcriptional programs responding to endogenous and exogenous signals influencing cell structure and function. Since actin is an essential component in cytoskeleton dynamics, actin-binding proteins (ABPs) have been recognized as crucial players in skeletal muscle health and diseases. Hence, dysregulation of ABPs leads to muscle atrophy characterized by loss of mass, strength, quality, and capacity for regeneration. This comprehensive review summarizes the recent studies that have unveiled the role of ABPs in actin cytoskeletal dynamics, with a particular focus on skeletal myogenesis and diseases. This provides insight into the molecular mechanisms that regulate skeletal myogenesis via ABPs as well as research avenues to identify potential therapeutic targets. Moreover, this review explores the implications of non-coding RNAs (ncRNAs) targeting ABPs in skeletal myogenesis and disorders based on recent achievements in ncRNA research. The studies presented here will enhance our understanding of the functional significance of ABPs and mechanotransduction-derived myogenic regulatory mechanisms. Furthermore, revealing how ncRNAs regulate ABPs will allow diverse therapeutic approaches for skeletal muscle disorders to be developed.

Keywords:  actin dynamics; actin-binding proteins; differentiation; myogenesis; non-coding RNA; proliferation

DOI:  https://doi.org/10.3390/cells12212523
J Cachexia Sarcopenia Muscle. 2023 Nov 03.

TAZ stimulates exercise-induced muscle satellite cell activation via Pard3-p38 MAPK-TAZ signalling axis.

Kyung Min Kim, Gi Don Yoo, Woong Heo, Ho Taek Oh, Jeekeon Park, Somin Shin, Youjin Do, Mi Gyeong Jeong, Eun Sook Hwang, Jeong-Ho Hong.

   BACKGROUND: Exercise stimulates the activation of muscle satellite cells, which facilitate the maintenance of stem cells and their myogenic conversion during muscle regeneration. However, the underlying mechanism is not yet fully understood. This study shows that the transcriptional co-activator with PDZ-binding motif (TAZ) stimulates muscle regeneration via satellite cell activation.
METHODS: Tazf/f mice were crossed with the paired box gene 7 (Pax7)creERT2 mice to generate muscle satellite cell-specific TAZ knockout (sKO) mice. Mice were trained in an endurance exercise programme for 4 weeks. Regenerated muscles were harvested and analysed by haematoxylin and eosin staining. Muscle tissues were also analysed by immunofluorescence staining, immunoblot analysis and quantitative reverse transcription PCR (qRT-PCR). For the in vitro study, muscle satellite cells from wild-type and sKO mice were isolated and analysed. Mitochondrial DNA was quantified by qRT-PCR using primers that amplify the cyclooxygenase-2 region of mitochondrial DNA. Quiescent and activated satellite cells were stained with MitoTracker Red CMXRos to analyse mitochondria. To study the p38 mitogen-activated protein kinase (MAPK)-TAZ signalling axis, p38 MAPK was activated by introducing the MAPK kinase 6 plasmid into satellite cells and also inhibited by treatment with the p38 MAPK inhibitor, SB203580.
RESULTS: TAZ interacts with Pax7 to induce Myf5 expression and stimulates mammalian target of rapamycin signalling for satellite cell activation. In sKO mice, TAZ depletion reduces muscle satellite cell number by 38% (0.29 ± 0.073 vs. 0.18 ± 0.034, P = 0.0082) and muscle regeneration. After muscle injury, TAZ levels (2.59-fold, P < 0.0001) increase in committed cells compared to self-renewing cells during asymmetric satellite cell division. Mechanistically, the polarity protein Pard3 induces TAZ (2.01-fold, P = 0.008) through p38 MAPK, demonstrating that the p38 MAPK-TAZ axis is important for muscle regeneration. Physiologically, endurance exercise training induces muscle satellite cell activation and increases muscle fibre diameter (1.33-fold, 43.21 ± 23.59 vs. 57.68 ± 23.26 μm, P = 0.0004) with increased TAZ levels (1.76-fold, P = 0.017). However, sKO mice had a 39% reduction in muscle satellite cell number (0.20 ± 0.03 vs. 0.12 ± 0.02, P = 0.0013) and 24% reduction in muscle fibre diameter compared to wild-type mice (61.07 ± 23.33 vs. 46.60 ± 24.29 μm, P = 0.0006).
CONCLUSIONS: Our results demonstrate a novel mechanism of TAZ-induced satellite cell activation after muscle injury and exercise, suggesting that activation of TAZ in satellite cells may ameliorate the muscle ageing phenotype and may be an important target protein for the drug development in sarcopenia.

Keywords:  exercise; muscle regeneration; muscle satellite cell; sarcopenia

DOI:  https://doi.org/10.1002/jcsm.13348
J Cachexia Sarcopenia Muscle. 2023 Nov 08.

Improved endurance capacity of diabetic mice during SGLT2 inhibition: Role of AICARP, an AMPK activator in the soleus.

Shintaro Nakamura, Yasutaka Miyachi, Akihito Shinjo, Hisashi Yokomizo, Masatomo Takahashi, Kohta Nakatani, Yoshihiro Izumi, Hiroko Otsuka, Naoichi Sato, Ryuichi Sakamoto, Takashi Miyazawa, Takeshi Bamba, Yoshihiro Ogawa.

   BACKGROUND: Diabetes is associated with an increased risk of deleterious changes in muscle mass and function or sarcopenia, leading to physical inactivity and worsening glycaemic control. Given the negative energy balance during sodium-glucose cotransporter-2 (SGLT2) inhibition, whether SGLT2 inhibitors affect skeletal muscle mass and function is a matter of concern. However, how SGLT2 inhibition affects the skeletal muscle function in patients with diabetes remains insufficiently explored. We aimed to explore the effects of canagliflozin (CANA), an SGLT2 inhibitor, on skeletal muscles in genetically diabetic db/db mice focusing on the differential responses of oxidative and glycolytic muscles.
METHODS: Db/db mice were treated with CANA for 4 weeks. We measured running distance and handgrip strength to assess skeletal muscle function during CANA treatment. At the end of the experiment, we performed a targeted metabolome analysis of the skeletal muscles.
RESULTS: CANA treatment improved the reduced endurance capacity, as revealed by running distance in db/db mice (414.9 ± 52.8 vs. 88.7 ± 22.7 m, P < 0.05). Targeted metabolome analysis revealed that 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranosyl 5'-monophosphate (AICARP), a naturally occurring AMP-activated protein kinase (AMPK) activator, increased in the oxidative soleus muscle (P < 0.05), but not in the glycolytic extensor digitorum longus muscle (P = 0.4376), with increased levels of AMPK phosphorylation (P < 0.01).
CONCLUSIONS: This study highlights the potential role of the AICARP/AMPK pathway in oxidative rather than glycolytic skeletal muscles during SGLT2 inhibition, providing novel insights into the mechanism by which SGLT2 inhibitors improve endurance capacity in patients with type 2 diabetes.

Keywords:  AICARP; AMPK; SGLT2 inhibitor; endurance exercise; fatty acid oxidation; skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13350
Commun Biol. 2023 11 04. 6(1): 1121

Absence of the primary cilia formation gene Talpid3 impairs muscle stem cell function.

Victor Martinez-Heredia, Danielle Blackwell, Sujith Sebastian, Timothy Pearson, Gi Fay Mok, Laura Mincarelli, Charlotte Utting, Leighton Folkes, Ernst Poeschl, Iain Macaulay, Ulrike Mayer, Andrea Münsterberg.

Skeletal muscle stem cells (MuSC) are crucial for tissue homoeostasis and repair after injury. Following activation, they proliferate to generate differentiating myoblasts. A proportion of cells self-renew, re-enter the MuSC niche under the basal lamina outside the myofiber and become quiescent. Quiescent MuSC have a primary cilium, which is disassembled upon cell cycle entry. Ex vivo experiments suggest cilia are important for MuSC self-renewal, however, their requirement for muscle regeneration in vivo remains poorly understood. Talpid3 (TA3) is essential for primary cilia formation and Hedgehog (Hh) signalling. Here we use tamoxifen-inducible conditional deletion of TA3 in MuSC (iSC-KO) and show that regeneration is impaired in response to cytotoxic injury. Depletion of MuSC after regeneration suggests impaired self-renewal, also consistent with an exacerbated phenotype in TA3iSC-KO mice after repeat injury. Single cell transcriptomics of MuSC progeny isolated from myofibers identifies components of several signalling pathways, which are deregulated in absence of TA3, including Hh and Wnt. Pharmacological activation of Wnt restores muscle regeneration, while purmorphamine, an activator of the Smoothened (Smo) co-receptor in the Hh pathway, has no effect. Together, our data show that TA3 and primary cilia are important for MuSC self-renewal and pharmacological treatment can efficiently restore muscle regeneration.

DOI: https://doi.org/10.1038/s42003-023-05503-9
J Cachexia Sarcopenia Muscle. 2023 Nov 08.

Exercise attenuates polyglutamine-mediated neuromuscular degeneration in a mouse model of spinal and bulbar muscular atrophy.

Tomoki Hirunagi, Hideaki Nakatsuji, Kentaro Sahashi, Mikiyasu Yamamoto, Madoka Iida, Genki Tohnai, Naohide Kondo, Shinichiro Yamada, Ayuka Murakami, Seiya Noda, Hiroaki Adachi, Gen Sobue, Masahisa Katsuno.

   BACKGROUND: Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder caused by the expansion of trinucleotide cytosine-adenine-guanine (CAG) repeats, which encodes a polyglutamine (polyQ) tract in the androgen receptor (AR) gene. Recent evidence suggests that, in addition to motor neuron degeneration, defective skeletal muscles are also the primary contributors to the pathogenesis in SBMA. While benefits of physical exercise have been suggested in SBMA, underlying mechanism remains elusive.
METHODS: We investigated the effect of running exercise in a transgenic mouse model of SBMA carrying human AR with 97 expanded CAGs (AR97Q). We assigned AR97Q mice to exercise and sedentary control groups, and mice in the exercise group received 1-h forced running wheel (5 m/min) 5 days a week for 4 weeks during the early stage of the disease. Motor function (grip strength and rotarod performance) and survival of each group were analysed, and histopathological and biological features in skeletal muscles and motor neurons were evaluated.
RESULTS: AR97Q mice in the exercise group showed improvement in motor function (~40% and ~50% increase in grip strength and rotarod performance, respectively, P < 0.05) and survival (median survival 23.6 vs. 16.7 weeks, P < 0.05) with amelioration of neuronal and muscular histopathology (~1.4-fold and ~2.8-fold increase in motor neuron and muscle fibre size, respectively, P < 0.001) compared to those in the sedentary group. Nuclear accumulation of polyQ-expanded AR in skeletal muscles and motor neurons was suppressed in the mice with exercise compared to the sedentary mice (~50% and ~30% reduction in 1C2-positive cells in skeletal muscles and motor neurons, respectively, P < 0.05). We found that the exercise activated 5'-adenosine monophosphate-activated protein kinase (AMPK) signalling and inhibited mammalian target of rapamycin pathway that regulates protein synthesis in skeletal muscles of SBMA mice. Pharmacological activation of AMPK inhibited protein synthesis and reduced polyQ-expanded AR proteins in C2C12 muscle cells.
CONCLUSIONS: Our findings suggest the therapeutic potential of exercise-induced effect via AMPK activation in SBMA.

Keywords:  AMPK; exercise; polyglutamine disease; spinal and bulbar muscular atrophy

DOI:  https://doi.org/10.1002/jcsm.13344
J Physiol. 2023 Nov 07.

The potassium-glycogen interaction on force and excitability in mouse skeletal muscle: implications for fatigue.

Simeon P Cairns, Jean-Marc Renaud.

  A reduced muscle glycogen content and potassium (K+ ) disturbances across muscle membranes occur concomitantly during repeated intense exercise and together may contribute to skeletal muscle fatigue. Therefore, we examined whether raised extracellular K+ concentration ([K+ ]o ) (4 to 11 mM) interacts with lowered glycogen to reduce force production. Isometric contractions were evoked in isolated mouse soleus muscles (37°C) using direct supramaximal field stimulation. (1) Glycogen declined markedly in non-fatigued muscle with >2 h exposure in glucose-free physiological saline compared with control solutions (11 mM glucose), i.e. to <45% control. (2) Severe glycogen depletion was associated with increased 5'-AMP-activated protein kinase activity, indicative of metabolic stress. (3) The decline of peak tetanic force at 11 mM [K+ ]o was exacerbated from 67% initial at normal glycogen to 22% initial at lowered glycogen. This was due to a higher percentage of inexcitable fibres (71% vs. 43%), yet without greater sarcolemmal depolarisation or smaller amplitude action potentials. (4) Returning glucose while at 11 mM [K+ ]o increased both glycogen and force. (5) Exposure to 4 mM [K+ ]o glucose-free solutions (15 min) did not increase fatiguability during repeated tetani; however, after recovery there was a greater force decline at 11 mM [K+ ]o at lower than normal glycogen. (6) An important exponential relationship was established between relative peak tetanic force at 11 mM [K+ ]o and muscle glycogen content. These findings provide direct evidence of a synergistic interaction between raised [K+ ]o and lowered muscle glycogen as the latter shifts the peak tetanic force-resting EM relationship towards more negative resting EM due to lowered sarcolemmal excitability, which hence may contribute to muscle fatigue. KEY POINTS: Diminished muscle glycogen levels and raised extracellular potassium concentrations ([K+ ]o ) occur simultaneously during intense exercise and together may contribute to muscle fatigue. Prolonged exposure of isolated non-fatigued soleus muscles of mice to glucose-free physiological saline solutions markedly lowered muscle glycogen levels, as does fatigue then recovery in glucose-free solutions. For both approaches, the subsequent decline of maximal force at 11 mM [K+ ]o , which mimics interstitial [K+ ] levels during intense exercise, was exacerbated at lowered compared with normal glycogen. This was mainly due to many more muscle fibres becoming inexcitable. We established an important relationship that provides evidence of a synergistic interaction between raised [K+ ]o and lowered glycogen content to reduce force production. This paper indicates that partially lowered muscle glycogen (and/or metabolic stress) together with elevated interstitial [K+ ] interactively lowers muscle force, and hence may diminish performance especially during repeated high-intensity exercise.

Keywords:  action potential; glycogen; potassium; sarcolemmal excitability; skeletal muscle fatigue

DOI:  https://doi.org/10.1113/JP285129
Skelet Muscle. 2023 Nov 07. 13(1): 18

Tropomyosin 3 (TPM3) function in skeletal muscle and in myopathy.

Matthias R Lambert, Emanuela Gussoni.

  The tropomyosin genes (TPM1-4) contribute to the functional diversity of skeletal muscle fibers. Since its discovery in 1988, the TPM3 gene has been recognized as an indispensable regulator of muscle contraction in slow muscle fibers. Recent advances suggest that TPM3 isoforms hold more extensive functions during skeletal muscle development and in postnatal muscle. Additionally, mutations in the TPM3 gene have been associated with the features of congenital myopathies. The use of different in vitro and in vivo model systems has leveraged the discovery of several disease mechanisms associated with TPM3-related myopathy. Yet, the precise mechanisms by which TPM3 mutations lead to muscle dysfunction remain unclear. This review consolidates over three decades of research about the role of TPM3 in skeletal muscle. Overall, the progress made has led to a better understanding of the phenotypic spectrum in patients affected by mutations in this gene. The comprehensive body of work generated over these decades has also laid robust groundwork for capturing the multiple functions this protein plays in muscle fibers.

Keywords:  Congenital myopathy; Rare diseases; Skeletal muscle; TPM3; Thin filaments; Tropomyosin

DOI:  https://doi.org/10.1186/s13395-023-00327-x
Am J Physiol Endocrinol Metab. 2023 Nov 08.

6-day Dry Immersion leads to downregulation of slow-fiber type and mitochondria-related genes expression.

Kristina A Sharlo, Natalia A Vilchinskaya, Sergey A Tyganov, Olga V Turtikova, Irina D Lvova, Ksenia V Sergeeva, Ilya V Rukavishnikov, Boris S Shenkman, Elena S Tomilovskaya, Oleg I Orlov.

  The soleus muscle in humans is responsible for maintaining an upright posture and participates in walking and running. Under muscle disuse, it undergoes molecular signaling changes that result in altered force and work capacity. The triggering mechanisms and pathways of these changes are not yet fully understood. In this article, we aimed to detect the molecular pathways that are involved in the unloading-induced alterations in the human soleus muscle under 6-days of dry immersion. A 6-day dry immersion led to the downregulation of mitochondrial biogenesis and dynamics markers, upregulation of calcium-dependent CaMK II phosphorylation, enhanced PGC1α promoter region methylation and altered muscle micro-RNA expression, without affecting p-AMPK content or fiber-type transformation.

Keywords:  dry immersion; gene expression; mitochondria; muscle unloading; skeletal muscle

DOI:  https://doi.org/10.1152/ajpendo.00284.2023
Sci Rep. 2023 11 08. 13(1): 19425

Low extracellular magnesium induces phenotypic and metabolic alterations in C2C12-derived myotubes.

Monica Zocchi, Marco Bartolini, Jeanette A Maier, Sara Castiglioni.

Magnesium (Mg) has a pivotal role in upholding skeletal muscle health and optimizing performance. Its deficiency decreases muscle strength, and an association has been reported between Mg intake and sarcopenia. To gain a comprehensive understanding of the repercussions arising from low Mg concentrations on muscle behavior, we employed an in vitro model utilizing C2C12-derived myotubes. Myotubes cultured in low Mg show a significant reduction of thickness and a concomitant down-regulation of myosin heavy chain (MyHC), Myog and Myomixer. In parallel, myotubes shape their metabolism. Glycolysis is inhibited and beta-oxidation increases. These metabolic changes are consistent with the increase of MyHC I (slow) vs. MyHC II (fast) expression. We identified an essential player in these changes, namely nitric oxide (NO), as the increase in NO production appeared to orchestrate the observed modifications in myotube behavior and metabolism under low Mg conditions. Understanding these underlying mechanisms may pave the way for targeted interventions to ameliorate muscle-related conditions associated with Mg deficiency and contribute to enhancing overall muscle health and function.

DOI: https://doi.org/10.1038/s41598-023-46543-9
Front Endocrinol (Lausanne). 2023 ;14 1277866

Temporal dynamics of muscle mitochondrial uncoupling-induced integrated stress response and ferroptosis defense.

Carla Igual Gil, Alina Löser, Kristina Lossow, Maria Schwarz, Daniela Weber, Tilman Grune, Anna P Kipp, Susanne Klaus, Mario Ost.

  Mitochondria play multifaceted roles in cellular function, and impairments across domains of mitochondrial biology are known to promote cellular integrated stress response (ISR) pathways as well as systemic metabolic adaptations. However, the temporal dynamics of specific mitochondrial ISR related to physiological variations in tissue-specific energy demands remains unknown. Here, we conducted a comprehensive 24-hour muscle and plasma profiling of male and female mice with ectopic mitochondrial respiratory uncoupling in skeletal muscle (mUcp1-transgenic, TG). TG mice are characterized by increased muscle ISR, elevated oxidative stress defense, and increased secretion of FGF21 and GDF15 as ISR-induced myokines. We observed a temporal signature of both cell-autonomous and systemic ISR in the context of endocrine myokine signaling and cellular redox balance, but not of ferroptotic signature which was also increased in TG muscle. We show a progressive increase of muscle ISR on transcriptional level during the active phase (night time), with a subsequent peak in circulating FGF21 and GDF15 in the early resting phase. Moreover, we found highest levels of muscle oxidative defense (GPX and NQO1 activity) between the late active to early resting phase, which could aim to counteract excessive iron-dependent lipid peroxidation and ferroptosis in muscle of TG mice. These findings highlight the temporal dynamics of cell-autonomous and endocrine ISR signaling under skeletal muscle mitochondrial uncoupling, emphasizing the importance of considering such dissociation in translational strategies and sample collection for diagnostic biomarker analysis.

Keywords:  FGF21; GDF15; circadian rhythm; ferroptosis; integrated stress response; mitochondrial uncoupling; oxidative stress; skeletal muscle

DOI:  https://doi.org/10.3389/fendo.2023.1277866
Physiol Rep. 2023 Nov;11(21): e15848

Acetate and succinate benefit host muscle energetics as exercise-associated post-biotics.

Ahmed Ismaeel, Taylor R Valentino, Benjamin Burke, Jensen Goh, Tolulope P Saliu, Fatmah Albathi, Allison Owen, John J McCarthy, Yuan Wen.

  Recently, the gut microbiome has emerged as a potent modulator of exercise-induced systemic adaptation and appears to be crucial for mediating some of the benefits of exercise. This study builds upon previous evidence establishing a gut microbiome-skeletal muscle axis, identifying exercise-induced changes in microbiome composition. Metagenomics sequencing of fecal samples from non-exercise-trained controls or exercise-trained mice was conducted. Biodiversity indices indicated exercise training did not change alpha diversity. However, there were notable differences in beta-diversity between trained and untrained microbiomes. Exercise significantly increased the level of the bacterial species Muribaculaceae bacterium DSM 103720. Computation simulation of bacterial growth was used to predict metabolites that accumulate under in silico culture of exercise-responsive bacteria. We identified acetate and succinate as potential gut microbial metabolites that are produced by Muribaculaceae bacterium, which were then administered to mice during a period of mechanical overload-induced muscle hypertrophy. Although no differences were observed for the overall muscle growth response to succinate or acetate administration during the first 5 days of mechanical overload-induced hypertrophy, acetate and succinate increased skeletal muscle mitochondrial respiration. When given as post-biotics, succinate or acetate treatment may improve oxidative metabolism during muscle hypertrophy.

Keywords:  exercise; metagenomics; microbiome; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.15848
Genome Med. 2023 Nov 10. 15(1): 95

Skeletal muscle regeneration failure in ischemic-damaged limbs is associated with pro-inflammatory macrophages and premature differentiation of satellite cells.

Kevin W Southerland, Yueyuan Xu, Derek T Peters, Xin Lin, Xiaolin Wei, Yu Xiang, Kaileen Fei, Lindsey A Olivere, Jeremy M Morowitz, James Otto, Qunsheng Dai, Christopher D Kontos, Yarui Diao.

   BACKGROUND: Chronic limb-threatening ischemia (CLTI), a severe manifestation of peripheral arterial disease (PAD), is associated with a 1-year limb amputation rate of approximately 15-20% and substantial mortality. A key feature of CLTI is the compromised regenerative ability of skeletal muscle; however, the mechanisms responsible for this impairment are not yet fully understood. In this study, we aim to delineate pathological changes at both the cellular and transcriptomic levels, as well as in cell-cell signaling pathways, associated with compromised muscle regeneration in limb ischemia in both human tissue samples and murine models of CLTI.
METHODS: We performed single-cell transcriptome analysis of ischemic and non-ischemic muscle from the same CLTI patients and from a murine model of CLTI. In both datasets, we analyzed gene expression changes in macrophage and muscle satellite cell (MuSC) populations as well as differential cell-cell signaling interactions and differentiation trajectories.
RESULTS: Single-cell transcriptomic profiling and immunofluorescence analysis of CLTI patient skeletal muscle demonstrated that ischemic-damaged tissue displays a pro-inflammatory macrophage signature. Comparable results were observed in a murine CLTI model. Moreover, integrated analyses of both human and murine datasets revealed premature differentiation of MuSCs to be a key feature of failed muscle regeneration in the ischemic limb. Furthermore, in silico inferences of intercellular communication and in vitro assays highlight the importance of macrophage-MuSC signaling in ischemia induced muscle injuries.
CONCLUSIONS: Collectively, our research provides the first single-cell transcriptome atlases of skeletal muscle from CLTI patients and a murine CLTI model, emphasizing the crucial role of macrophages and inflammation in regulating muscle regeneration in CLTI through interactions with MuSCs.

Keywords:  Chronic limb-threatening ischemia; Macrophage polarization; Murine hindlimb ischemia; Muscle satellite cells; Peripheral arterial disease; Single-cell transcriptome analysis; Skeletal muscle regeneration

DOI:  https://doi.org/10.1186/s13073-023-01250-y
Front Cell Dev Biol. 2023 ;11 1240285

Native lamin A/C proteomes and novel partners from heart and skeletal muscle in a mouse chronic inflammation model of human frailty.

Fatima D Elzamzami, Arushi Samal, Adith S Arun, Tejas Dharmaraj, Neeti R Prasad, Alex Rendon-Jonguitud, Lauren DeVine, Jeremy D Walston, Robert N Cole, Katherine L Wilson.

  Clinical frailty affects ∼10% of people over age 65 and is studied in a chronically inflamed (Interleukin-10 knockout; "IL10-KO") mouse model. Frailty phenotypes overlap the spectrum of diseases ("laminopathies") caused by mutations in LMNA. LMNA encodes nuclear intermediate filament proteins lamin A and lamin C ("lamin A/C"), important for tissue-specific signaling, metabolism and chromatin regulation. We hypothesized that wildtype lamin A/C associations with tissue-specific partners are perturbed by chronic inflammation, potentially contributing to dysfunction in frailty. To test this idea we immunoprecipitated native lamin A/C and associated proteins from skeletal muscle, hearts and brains of old (21-22 months) IL10-KO versus control C57Bl/6 female mice, and labeled with Tandem Mass Tags for identification and quantitation by mass spectrometry. We identified 502 candidate lamin-binding proteins from skeletal muscle, and 340 from heart, including 62 proteins identified in both tissues. Candidates included frailty phenotype-relevant proteins Perm1 and Fam210a, and nuclear membrane protein Tmem38a, required for muscle-specific genome organization. These and most other candidates were unaffected by IL10-KO, but still important as potential lamin A/C-binding proteins in native heart or muscle. A subset of candidates (21 in skeletal muscle, 30 in heart) showed significantly different lamin A/C-association in an IL10-KO tissue (p < 0.05), including AldoA and Gins3 affected in heart, and Lmcd1 and Fabp4 affected in skeletal muscle. To screen for binding, eleven candidates plus prelamin A and emerin controls were arrayed as synthetic 20-mer peptides (7-residue stagger) and incubated with recombinant purified lamin A "tail" residues 385-646 under relatively stringent conditions. We detected strong lamin A binding to peptides solvent exposed in Lmcd1, AldoA, Perm1, and Tmem38a, and plausible binding to Csrp3 (muscle LIM protein). These results validated both proteomes as sources for native lamin A/C-binding proteins in heart and muscle, identified four candidate genes for Emery-Dreifuss muscular dystrophy (CSRP3, LMCD1, ALDOA, and PERM1), support a lamin A-interactive molecular role for Tmem38A, and supported the hypothesis that lamin A/C interactions with at least two partners (AldoA in heart, transcription factor Lmcd1 in muscle) are altered in the IL10-KO model of frailty.

Keywords:  AldoA; Emery-Dreifuss muscular dystrophy; Fam210a; Lmcd1; Perm1; Phf2; Tmem38a; lamin A

DOI:  https://doi.org/10.3389/fcell.2023.1240285
Aging Clin Exp Res. 2023 Nov 09.

11-beta-hydroxysteroid dehydrogenase type 1 (HSD11B1) gene expression in muscle is linked to reduced skeletal muscle index in sarcopenic patients.

Sabine Schluessel, Wei Zhang, Hanna Nowotny, Martin Bidlingmaier, Stefan Hintze, Sonja Kunz, Sebastian Martini, Stefan Mehaffey, Peter Meinke, Carl Neuerburg, Ralf Schmidmaier, Benedikt Schoser, Nicole Reisch, Michael Drey.

   BACKGROUND: Glucocorticoids play a significant role in metabolic processes and pathways that impact muscle size, mass, and function. The expression of 11-beta-hydroxysteroid dehydrogenase type 1 (HSD11B1) has been previously described as a major regulator of skeletal muscle function in glucocorticoid-induced muscle atrophy and aging humans. Our study aimed to investigate glucocorticoid metabolism, including the expression of HSD11B1 in skeletal muscle, in patients with sarcopenia.
METHODS: Muscle biopsies were taken from the vastus lateralis muscle of thirty-three patients over 60 years of age with hip fractures. Sarcopenia status was assessed according to the criteria of the European Working Group on Sarcopenia in Older People 2. Skeletal muscle mass was measured by bioelectrical impedance analysis. Cortisol and cortisone concentrations were measured in serum. Gene expression analysis of HSD11B1, NR3C1, FBXO32, and TRIM63 in muscle biopsies was performed. Serial cross sections of skeletal muscle were labeled with myosin heavy chain slow (fiber type-1) and fast (fiber type-2) antibodies.
RESULTS: The study included 33 patients (21 women) with a mean age of 82.5 ± 6.3 years, 17 patients revealed sarcopenic (n = 16 non-sarcopenic). Serum cortisone concentrations were negatively correlated with muscle mass (ß = - 0.425; p = 0.034) and type-2 fiber diameter (ß = - 0.591; p = 0.003). Gene expression of HSD11B1 (ß = - 0.673; p = 0.008) showed a negative correlation with muscle mass in the sarcopenic group. A significant correlation was found for the non-sarcopenic group for NR3C1 (ß = 0.548; p = 0.028) and muscle mass.
CONCLUSION: These findings suggest a pathogenetic role of HSD11B1 in sarcopenic muscle.

Keywords:  FBXO32; Glucocorticoids; HSD11B1; NR3C1; Sarcopenia; TRIM63

DOI:  https://doi.org/10.1007/s40520-023-02574-w
Annu Rev Physiol. 2023 Nov 06.

Regulating Striated Muscle Contraction: Through Thick and Thin.

Elisabetta Brunello, Luca Fusi.

Force generation in striated muscle is primarily controlled by structural changes in the actin-containing thin filaments triggered by an increase in intracellular calcium concentration. However, recent studies have elucidated a new class of regulatory mechanisms, based on the myosin-containing thick filament, that control the strength and speed of contraction by modulating the availability of myosin motors for the interaction with actin. This review summarizes the mechanisms of thin and thick filament activation that regulate the contractility of skeletal and cardiac muscle. A novel dual-filament paradigm of muscle regulation is emerging, in which the dynamics of force generation depends on the coordinated activation of thin and thick filaments. We highlight the interfilament signaling pathways based on titin and myosin-binding protein-C that couple thin and thick filament regulatory mechanisms. This dual-filament regulation mediates the length-dependent activation of cardiac muscle that underlies the control of the cardiac output in each heartbeat. Expected final online publication date for the Annual Review of Physiology, Volume 86 is February 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

DOI: https://doi.org/10.1146/annurev-physiol-042222-022728
Hum Mol Genet. 2023 Nov 02. pii: ddad186. [Epub ahead of print]

snRNA-seq analysis in multinucleated myogenic FSHD cells identifies heterogeneous FSHD transcriptome signatures associated with embryonic-like program activation and oxidative stress-induced apoptosis.

Dongxu Zheng, Annelot Wondergem, Susan Kloet, Iris Willemsen, Judit Balog, Stephen J Tapscott, Ahmed Mahfouz, Anita van den Heuvel, Silvère M van der Maarel.

  The sporadic nature of DUX4 expression in FSHD muscle challenges comparative transcriptome analyses between FSHD and control samples. A variety of DUX4 and FSHD-associated transcriptional changes have been identified, but bulk RNA-seq strategies prohibit comprehensive analysis of their spatiotemporal relation, interdependence and role in the disease process. In this study, we used single-nucleus RNA-sequencing of nuclei isolated from patient- and control-derived multinucleated primary myotubes to investigate the cellular heterogeneity in FSHD. Taking advantage of the increased resolution in snRNA-sequencing of fully differentiated myotubes, two distinct populations of DUX4-affected nuclei could be defined by their transcriptional profiles. Our data provides insights into the differences between these two populations and suggests heterogeneity in two well-known FSHD-associated transcriptional aberrations: increased oxidative stress and inhibition of myogenic differentiation. Additionally, we provide evidence that DUX4-affected nuclei share transcriptome features with early embryonic cells beyond the well-described cleavage stage, progressing into the 8-cell and blastocyst stages. Altogether, our data suggests that the FSHD transcriptional profile is defined by a mixture of individual and sometimes mutually exclusive DUX4-induced responses and cellular state-dependent downstream effects.

Keywords:  DUX4; FSHD; cellular heterogeneity; muscular dystrophy; single-nucleus RNA-sequencing

DOI:  https://doi.org/10.1093/hmg/ddad186
Front Neurol. 2023 ;14 1275266

Mechanisms and effects of metformin on skeletal muscle disorders.

Ren Shang, Jing Miao.

  Skeletal muscle disorders are mostly genetic and include several rare diseases. With disease progression, muscle fibrosis and adiposis occur, resulting in limited mobility. The long course of these diseases combined with limited treatment options affect patients both psychologically and economically, hence the development of novel treatments for neuromuscular diseases is crucial to obtain a better quality of life. As a widely used hypoglycemic drug in clinical practice, metformin not only has anti-inflammatory, autophagy-regulating, and mitochondrial biogenesis-regulating effects, but it has also been reported to improve the symptoms of neuromuscular diseases, delay hypokinesia, and regulate skeletal muscle mass. However, metformin's specific mechanism of action in neuromuscular diseases requires further elucidation. This review summarizes the evidence showing that metformin can regulate inflammation, autophagy, and mitochondrial biogenesis through different pathways, and further explores its mechanism of action in Duchenne muscular dystrophy, statin-associated muscle disorders, and age-related sarcopenia. This review clarifies the directions of future research on therapy for neuromuscular diseases.

Keywords:  autophagy; inflammation; metformin; mitochondrial biogenesis; skeletal muscle disorders

DOI:  https://doi.org/10.3389/fneur.2023.1275266
Am J Physiol Endocrinol Metab. 2023 Nov 08.

Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice.

Curtis C Hughey, Deanna P Bracy, Ferrol I Rome, Mickael Goelzer, E Patrick Donahue, Benoit Viollet, Marc Foretz, David H Wasserman.

  Regular exercise elicits adaptations in glucose and lipid metabolism that allow the body to meet energy demands of subsequent exercise bouts more effectively and mitigate metabolic diseases including fatty liver. Energy discharged during the acute exercise bouts that comprise exercise training may be a catalyst for liver adaptations. During acute exercise, liver glycogenolysis and gluconeogenesis are accelerated to supply glucose to working muscle. Lower liver energy state imposed by gluconeogenesis and related pathways activates AMP-activated protein kinase (AMPK), which conserves ATP partly by promoting lipid oxidation. This study tested the hypothesis that AMPK is necessary for liver glucose and lipid adaptations to training. Liver-specific AMPKα1α2 knockout (AMPKα1α2fl/fl+AlbCre) mice and littermate controls (AMPKα1α2fl/fl) completed sedentary and exercise training protocols. Liver nutrient fluxes were quantified at rest or during acute exercise following training. Liver metabolites and molecular regulators of metabolism were assessed. Training increased liver glycogen in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. The inability to increase glycogen led to lower glycogenolysis, glucose production, and circulating glucose during acute exercise in trained AMPKα1α2fl/fl+AlbCre mice. Deletion of AMPKα1α2 attenuated training-induced declines in liver diacylglycerides. In particular, training lowered the concentration of unsaturated and elongated fatty acids comprising diacylglycerides in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. Training increased liver triacylglycerides and the desaturation and elongation of fatty acids in triacylglycerides of AMPKα1α2fl/fl+AlbCre mice. These lipid responses were independent of differences in tricarboxylic acid cycle fluxes. In conclusion, AMPK is required for liver training adaptations that are critical to glucose and lipid metabolism.

Keywords:  aerobic exercise; gluconeogenesis; glycogenolysis; metabolic flux analysis; mitochondrial oxidative metabolism

DOI:  https://doi.org/10.1152/ajpendo.00289.2023
Hum Mol Genet. 2023 Nov 08. pii: ddad192. [Epub ahead of print]

A transcriptomics-based drug repositioning approach to identify drugs with similar activities for the treatment of muscle pathologies in spinal muscular atrophy (SMA) models.

Joseph M Hoolachan, Eve McCallion, Emma R Sutton, Özge Çetin, Paloma Pacheco-Torres, Maria Dimitriadi, Suat Sari, Gavin J Miller, Magnus Okoh, Lisa M Walter, Peter Claus, Matthew J A Wood, Daniel P Tonge, Melissa Bowerman.

  Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder caused by the reduction of survival of motor neuron (SMN) protein levels. Although three SMN-augmentation therapies are clinically approved that significantly slow down disease progression, they are unfortunately not cures. Thus, complementary SMN-independent therapies that can target key SMA pathologies and that can support the clinically approved SMN-dependent drugs are the forefront of therapeutic development. We have previously demonstrated that prednisolone, a synthetic glucocorticoid (GC) improved muscle health and survival in severe Smn-/-;SMN2 and intermediate Smn2B/- SMA mice. However, long-term administration of prednisolone can promote myopathy. We thus wanted to identify genes and pathways targeted by prednisolone in skeletal muscle to discover clinically approved drugs that are predicted to emulate prednisolone's activities. Using an RNA-sequencing, bioinformatics, and drug repositioning pipeline on skeletal muscle from symptomatic prednisolone-treated and untreated Smn-/-; SMN2 SMA and Smn+/-; SMN2 healthy mice, we identified molecular targets linked to prednisolone's ameliorative effects and a list of 580 drug candidates with similar predicted activities. Two of these candidates, metformin and oxandrolone, were further investigated in SMA cellular and animal models, which highlighted that these compounds do not have the same ameliorative effects on SMA phenotypes as prednisolone; however, a number of other important drug targets remain. Overall, our work further supports the usefulness of prednisolone's potential as a second-generation therapy for SMA, identifies a list of potential SMA drug treatments and highlights improvements for future transcriptomic-based drug repositioning studies in SMA.

Keywords:  animal models; drug repurposing; skeletal muscle; spinal muscular atrophy; transcriptomics

DOI:  https://doi.org/10.1093/hmg/ddad192
Metabolism. 2023 Nov 01. pii: S0026-0495(23)00321-9. [Epub ahead of print] 155717

Sarcopenia: still in relative definition-penia and severe treatment-penia.

Stergios A Polyzos, Christos S Mantzoros.



Keywords:  Muscle mass; Muscle strength; Physical performance; Sarcopenia; Sarcopenic obesity; Skeletal muscle

DOI:  https://doi.org/10.1016/j.metabol.2023.155717
EMBO Mol Med. 2023 Nov 06. e17405

Combinatorial activation of the WNT-dependent fibrogenic program by distinct complement subunits in dystrophic muscle.

Francesca Florio, Sara Vencato, Filomena T Papa, Michela Libergoli, Eyemen Kheir, Imen Ghzaiel, Thomas A Rando, Yvan Torrente, Stefano Biressi.

  Fibrosis is associated with compromised muscle functionality in Duchenne muscular dystrophy (DMD). We report observations with tissues from dystrophic patients and mice supporting a model to explain fibrosis in DMD, which relies on the crosstalk between the complement and the WNT signaling pathways and the functional interactions of two cellular types. Fibro-adipogenic progenitors and macrophages, which populate the inflamed dystrophic muscles, act as a combinatorial source of WNT activity by secreting distinct subunits of the C1 complement complex. The resulting aberrant activation of the WNT signaling in responsive cells, such as fibro-adipogenic progenitors, contributes to fibrosis. Indeed, pharmacological inhibition of the C1r/s subunits in a murine model of DMD mitigated the activation of the WNT signaling pathway, reduced the fibrogenic characteristics of the fibro-adipogenic progenitors, and ameliorated the dystrophic phenotype. These studies shed new light on the molecular and cellular mechanisms responsible for fibrosis in muscular dystrophy and open to new therapeutic strategies.

Keywords:  Duchenne muscular dystrophy; complement C1 complex; fibro-adipogenic progenitors; fibrosis; skeletal muscle regeneration

DOI:  https://doi.org/10.15252/emmm.202317405
Sci Rep. 2023 11 05. 13(1): 19118

DNA hypomethylation characterizes genes encoding tissue-dominant functional proteins in liver and skeletal muscle.

Hideki Maehara, Toshiya Kokaji, Atsushi Hatano, Yutaka Suzuki, Masaki Matsumoto, Keiichi I Nakayama, Riku Egami, Takaho Tsuchiya, Haruka Ozaki, Keigo Morita, Masaki Shirai, Dongzi Li, Akira Terakawa, Saori Uematsu, Ken-Ichi Hironaka, Satoshi Ohno, Hiroyuki Kubota, Hiromitsu Araki, Fumihito Miura, Takashi Ito, Shinya Kuroda.

Each tissue has a dominant set of functional proteins required to mediate tissue-specific functions. Epigenetic modifications, transcription, and translational efficiency control tissue-dominant protein production. However, the coordination of these regulatory mechanisms to achieve such tissue-specific protein production remains unclear. Here, we analyzed the DNA methylome, transcriptome, and proteome in mouse liver and skeletal muscle. We found that DNA hypomethylation at promoter regions is globally associated with liver-dominant or skeletal muscle-dominant functional protein production within each tissue, as well as with genes encoding proteins involved in ubiquitous functions in both tissues. Thus, genes encoding liver-dominant proteins, such as those involved in glycolysis or gluconeogenesis, the urea cycle, complement and coagulation systems, enzymes of tryptophan metabolism, and cytochrome P450-related metabolism, were hypomethylated in the liver, whereas those encoding-skeletal muscle-dominant proteins, such as those involved in sarcomere organization, were hypomethylated in the skeletal muscle. Thus, DNA hypomethylation characterizes genes encoding tissue-dominant functional proteins.

DOI: https://doi.org/10.1038/s41598-023-46393-5
FASEB Bioadv. 2023 Nov;5(11): 453-469

Antioxidants restore store-operated Ca2+ entry in patient-iPSC-derived myotubes with tubular aggregate myopathy-associated Ile484ArgfsX21 STIM1 mutation via upregulation of binding immunoglobulin protein.

Fusako Sakai-Takemura, Fumiaki Saito, Ken'ichiro Nogami, Yusuke Maruyama, Ahmed Elhussieny, Kiichiro Matsumura, Shin'ichi Takeda, Yoshitsugu Aoki, Yuko Miyagoe-Suzuki.

  Store-operated Ca2+ entry (SOCE) is indispensable for intracellular Ca2+ homeostasis in skeletal muscle, and constitutive activation of SOCE causes tubular aggregate myopathy (TAM). To understand the pathogenesis of TAM, we induced pluripotent stem cells (iPSCs) from a TAM patient with a rare mutation (c.1450_1451insGA; p. Ile484ArgfsX21) in the STIM1 gene. This frameshift mutation produces a truncated STIM1 with a disrupted C-terminal inhibitory domain (CTID) and was reported to diminish SOCE. Myotubes induced from the patient's-iPSCs (TAM myotubes) showed severely impaired SOCE, but antioxidants greatly restored SOCE partly via upregulation of an endoplasmic reticulum (ER) chaperone, BiP (GRP78), in the TAM myotubes. Our observation suggests that antioxidants are promising tools for treatment of TAM caused by reduced SOCE.

Keywords:  Stromal interaction molecule 1; antioxidants; binding immunoglobulin protein; calcium; calcium release‐activated calcium channel protein 1 (ORAI1); induced pluripotent stem cells; skeletal muscle; store‐operated Ca2+ entry; tubular aggregate myopathy

DOI:  https://doi.org/10.1096/fba.2023-00069
STAR Protoc. 2023 Nov 07. pii: S2666-1667(23)00558-0. [Epub ahead of print]4(4): 102591

Protocol for isolating mice skeletal muscle myoblasts and myotubes via differential antibody validation.

Dominique C Stephens, Margaret Mungai, Amber Crabtree, Heather K Beasley, Edgar Garza-Lopez, Larry Vang, Kit Neikirk, Zer Vue, Neng Vue, Andrea G Marshall, Kyrin Turner, Jian-Qiang Shao, Bishnu Sarker, Sandra Murray, Jennifer A Gaddy, Jamaine Davis, Steven M Damo, Antentor O Hinton.

  Isolation of skeletal muscles allows for the exploration of many complex diseases. Here, we present a protocol for isolating mice skeletal muscle myoblasts and myotubes that have been differentiated through antibody validation. We describe steps for collecting and preparing murine skeletal tissue, myoblast cell maintenance, plating, and cell differentiation. We then detail procedures for cell incubation, immunostaining, slide preparation and storage, and imaging for immunofluorescence validation.

Keywords:  Cell Culture; Cell Isolation; Model Organisms

DOI:  https://doi.org/10.1016/j.xpro.2023.102591
Front Physiol. 2023 ;14 1231538

Construct and criterion validity of muscle ultrasonography for assessment of skeletal muscle in patients recovering from COVID-19.

Kirby P Mayer, Kate Kosmac, Yuan Wen, Selina M Parry, Sanjay Dhar, Sarah Foster, Jonathan Starck, Ashley A Montgomery-Yates, Esther E Dupont-Versteegden, Anna G Kalema.

  Background: The purpose was to investigate the content, construct, and criterion validity of muscle ultrasound in a mixed cohort of participants recovering from mild and critical COVID-19. Methods: A secondary analysis of a prospective cross-sectional study was conducted on data obtained from a battery of muscle and physical function assessments including a muscle biopsy and muscle ultrasonography (US). Rectus femoris (RF) muscle thickness (mT), quadricep complex (QC) mT, RF muscle cross-sectional area (CSA) using 2D freeform trace and estimated from Feret's diameter, and RF echo intensity (EI) were assessed with US. Muscle fiber CSA, fiber type, protein content in muscle fibers, extracellular matrix content (ECM; wheat-germ agglutin), and percent area of collagen in ECM (picrosirius red) were examined from vastus lateralis muscle biopsies. Spearman rho correlations (r) were performed to assess validity of ultrasound parameters. Results: Thirty-three individuals participated including 11 patients surviving critical COVID-19, 15 individuals recovering from mild-COVID, and 7 controls. There were several significant correlations between RF mT, QC mT, RF CSA, and RF EI with age, comorbid burden, body-mass index, and measures of muscle strength, muscle power, and physical function (range r = 0.35-0.83). RF Feret's CSA correlated to CSA of type II muscle fibers (r = 0.41, p = 0.022) and the average size of all muscle fibers (r = 0.39, p = 0.031). RF EI was correlated with collagen in muscle ECM (r = 0.53, p = 0.003) and protein content in muscle tissue (r = -0.52, p = 0.012). Conclusion: Muscle size and quality measured using US has moderate content and construct validity, and to lesser extent, fair to moderate criterion validity in a mixed cohort of individuals recovering from COVID. Muscle ultrasound quality (EI) appears to be sensitive at detecting muscle dysfunction as it is associated with strength, power, physical function, and collagen distribution in a mixed group of individuals recovering from COVID-19.

Keywords:  ICU-acquired weakness; critical illness; muscle dysfunction; muscle ultrasound; muscle wasting; post-intensive care syndrome; skeletal muscle

DOI:  https://doi.org/10.3389/fphys.2023.1231538
Front Cell Dev Biol. 2023 ;11 1270892

Transcriptome analysis reveals genes associated with stem cell activation by physical exercise in the dentate gyrus of aged p16Ink4a knockout mice.

Laura Micheli, Giorgio D'Andrea, Teresa Maria Creanza, Daniel Volpe, Nicola Ancona, Raffaella Scardigli, Felice Tirone.

  Throughout adulthood neural stem cells divide in neurogenic niches-the dentate gyrus of the hippocampus and the subventricular zone-producing progenitor cells and new neurons. Stem cells self-renew, thus preserving their pool. Furthermore, the number of stem/progenitor cells in the neurogenic niches decreases with age. We have previously demonstrated that the cyclin-dependent kinase inhibitor p16Ink4a maintains, in aged mice, the pool of dentate gyrus stem cells by preventing their activation after a neurogenic stimulus such as exercise (running). We showed that, although p16Ink4a ablation by itself does not activate stem/progenitor cells, exercise strongly induced stem cell proliferation in p16Ink4a knockout dentate gyrus, but not in wild-type. As p16Ink4a regulates stem cell self-renewal during aging, we sought to profile the dentate gyrus transcriptome from p16Ink4a wild-type and knockout aged mice, either sedentary or running for 12 days. By pairwise comparisons of differentially expressed genes and by correlative analyses through the DESeq2 software, we identified genes regulated by p16Ink4a deletion, either without stimulus (running) added, or following running. The p16Ink4a knockout basic gene signature, i.e., in sedentary mice, involves upregulation of apoptotic, neuroinflammation- and synaptic activity-associated genes, suggesting a reactive cellular state. Conversely, another set of 106 genes we identified, whose differential expression specifically reflects the pattern of proliferative response of p16 knockout stem cells to running, are involved in processes that regulate stem cell activation, such as synaptic function, neurotransmitter metabolism, stem cell proliferation control, and reactive oxygen species level regulation. Moreover, we analyzed the regulation of these stem cell-specific genes after a second running stimulus. Surprisingly, the second running neither activated stem cell proliferation in the p16Ink4a knockout dentate gyrus nor changed the expression of these genes, confirming that they are correlated to the stem cell reactivity to stimulus, a process where they may play a role regulating stem cell activation.

Keywords:  adult neurogenesis; aging; dentate gyrus; neural stem cells; p16INK4a; physical exercise; running; self-renewal

DOI:  https://doi.org/10.3389/fcell.2023.1270892
Proc Natl Acad Sci U S A. 2023 Nov 14. 120(46): e2301120120

The adaptive antioxidant response during fasting-induced muscle atrophy is oppositely regulated by ZEB1 and ZEB2.

Chiara Ninfali, Marlies Cortés, M C Martínez-Campanario, Verónica Domínguez, Lu Han, Ester Tobías, Anna Esteve-Codina, Carlos Enrich, Belén Pintado, Gloria Garrabou, Antonio Postigo.

  Reactive oxygen species (ROS) serve important homeostatic functions but must be constantly neutralized by an adaptive antioxidant response to prevent supraphysiological levels of ROS from causing oxidative damage to cellular components. Here, we report that the cellular plasticity transcription factors ZEB1 and ZEB2 modulate in opposing directions the adaptive antioxidant response to fasting in skeletal muscle. Using transgenic mice in which Zeb1 or Zeb2 were specifically deleted in skeletal myofibers, we show that in fasted mice, the deletion of Zeb1, but not Zeb2, increased ROS production and that the adaptive antioxidant response to fasting essentially requires ZEB1 and is inhibited by ZEB2. ZEB1 expression increased in fasted muscles and protected them from atrophy; conversely, ZEB2 expression in muscles decreased during fasting and exacerbated muscle atrophy. In fasted muscles, ZEB1 reduces mitochondrial damage and increases mitochondrial respiratory activity; meanwhile, ZEB2 did the opposite. Treatment of fasting mice with Zeb1-deficient myofibers with the antioxidant triterpenoid 1[2-cyano-3,12-dioxool-eana-1,9(11)-dien-28-oyl] trifluoro-ethylamide (CDDO-TFEA) completely reversed their altered phenotype to that observed in fasted control mice. These results set ZEB factors as potential therapeutic targets to modulate the adaptive antioxidant response in physiopathological conditions and diseases caused by redox imbalance.

Keywords:  NRF2; ZEB1 and ZEB2; antioxidant response; muscle atrophy; reactive oxygen species

DOI:  https://doi.org/10.1073/pnas.2301120120
Ageing Res Rev. 2023 Nov 05. pii: S1568-1637(23)00277-5. [Epub ahead of print] 102118

66Mouse models of accelerated aging in musculoskeletal research for assessing frailty, sarcopenia, and osteoporosis - a review.

Dilara Yılmaz, Neashan Mathavan, Esther Wehrle, Gisela A Kuhn, Ralph Müller.

  Musculoskeletal aging encompasses the decline in bone and muscle function, leading to conditions such as frailty, osteoporosis, and sarcopenia. Unraveling the underlying molecular mechanisms and developing effective treatments are crucial for improving the quality of life for those affected. In this context, accelerated aging models offer valuable insights into these conditions by displaying the hallmarks of human aging. Herein, this review focuses on relevant mouse models of musculoskeletal aging with particular emphasis on frailty, osteoporosis, and sarcopenia. Among the discussed models, PolgA mice in particular exhibit hallmarks of musculoskeletal aging, presenting early-onset frailty, as well as reduced bone and muscle mass that closely resemble human musculoskeletal aging. Ultimately, findings from these models hold promise for advancing interventions targeted at age-related musculoskeletal disorders, effectively addressing the challenges posed by musculoskeletal aging and associated conditions in humans.

Keywords:  Musculoskeletal aging; PolgA; accelerated aging mouse models; frailty; osteoporosis; sarcopenia

DOI:  https://doi.org/10.1016/j.arr.2023.102118
Cell Metab. 2023 Nov 07. pii: S1550-4131(23)00382-0. [Epub ahead of print]35(11): 2028-2043.e7

Skeletal muscle-derived extracellular vesicles transport glycolytic enzymes to mediate muscle-to-bone crosstalk.

Shixing Ma, Xiaotao Xing, Haisen Huang, Xin Gao, Xun Xu, Jian Yang, Chengcheng Liao, Xuanhao Zhang, Jinglun Liu, Weidong Tian, Li Liao.

  Identification of cues originating from skeletal muscle that govern bone formation is essential for understanding the crosstalk between muscle and bone and for developing therapies for degenerative bone diseases. Here, we identified that skeletal muscle secreted multiple extracellular vesicles (Mu-EVs). These Mu-EVs traveled through the bloodstream to reach bone, where they were phagocytized by bone marrow mesenchymal stem/stromal cells (BMSCs). Mu-EVs promoted osteogenic differentiation of BMSCs and protected against disuse osteoporosis in mice. The quantity and bioactivity of Mu-EVs were tightly correlated with the function of skeletal muscle. Proteomic analysis revealed numerous proteins in Mu-EVs, some potentially regulating bone metabolism, especially glycolysis. Subsequent investigations indicated that Mu-EVs promoted the glycolysis of BMSCs by delivering lactate dehydrogenase A into these cells. In summary, these findings reveal that Mu-EVs play a vital role in BMSC metabolism regulation and bone formation stimulation, offering a promising approach for treating disuse osteoporosis.

Keywords:  aerobic glycolysis; bone marrow mesenchymal stem/stromal cells; extracellular vesicles; glycolytic enzyme; lactate dehydrogenase A; skeletal muscle

DOI:  https://doi.org/10.1016/j.cmet.2023.10.013
Nat Commun. 2023 Nov 06. 14(1): 7136

FNIP1 abrogation promotes functional revascularization of ischemic skeletal muscle by driving macrophage recruitment.

Zongchao Sun, Likun Yang, Abdukahar Kiram, Jing Yang, Zhuangzhuang Yang, Liwei Xiao, Yujing Yin, Jing Liu, Yan Mao, Danxia Zhou, Hao Yu, Zheng Zhou, Dengqiu Xu, Yuhuan Jia, Chenyun Ding, Qiqi Guo, Hongwei Wang, Yan Li, Li Wang, Tingting Fu, Shijun Hu, Zhenji Gan.

Ischaemia of the heart and limbs attributable to compromised blood supply is a major cause of mortality and morbidity. The mechanisms of functional angiogenesis remain poorly understood, however. Here we show that FNIP1 plays a critical role in controlling skeletal muscle functional angiogenesis, a process pivotal for muscle revascularization during ischemia. Muscle FNIP1 expression is down-regulated by exercise. Genetic overexpression of FNIP1 in myofiber causes limited angiogenesis in mice, whereas its myofiber-specific ablation markedly promotes the formation of functional blood vessels. Interestingly, the increased muscle angiogenesis is independent of AMPK but due to enhanced macrophage recruitment in FNIP1-depleted muscles. Mechanistically, myofiber FNIP1 deficiency induces PGC-1α to activate chemokine gene transcription, thereby driving macrophage recruitment and muscle angiogenesis program. Furthermore, in a mouse hindlimb ischemia model of peripheral artery disease, the loss of myofiber FNIP1 significantly improved the recovery of blood flow. Thus, these results reveal a pivotal role of FNIP1 as a negative regulator of functional angiogenesis in muscle, offering insight into potential therapeutic strategies for ischemic diseases.

DOI: https://doi.org/10.1038/s41467-023-42690-9