bims-moremu 2022-11-27 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2022–11–27
33 papers selected by
Anna Vainshtein, Craft Science Inc.

RNA-Sequencing Reveals Upregulation and a Beneficial Role of Autophagy in Myoblast Differentiation and Fusion.
PCM1 labelling reveals myonuclear and nuclear dynamics in skeletal muscle across species.
Targeted ablation of Fn14 receptor improves exercise capacity and inhibits neurogenic muscle atrophy.
Measurement of skeletal muscle glucose uptake in mice in response to acute treadmill running.
Systemic AAV9.BVES Delivery Ameliorates Muscular Dystrophy in a Mouse Model of LGMDR25.
Skeletal and Cardiac Muscle Calcium Transport Regulation in Health and Disease.
Exercise alters the circadian rhythm of REV-ERB-α and downregulates autophagy-related genes in peripheral and central tissues.
SENP7 deSUMOylase-governed transcriptional program coordinates sarcomere assembly and is targeted in muscle atrophy.
Pharmacological inhibition of HDAC6 improves muscle phenotypes in dystrophin-deficient mice by downregulating TGF-β via Smad3 acetylation.
Genetic ablation of Toll-like Receptor 4 seems to activate the apoptosis pathway in the skeletal muscle of mice after acute physical exercise.
Vitamin D status modulates mitochondrial oxidative capacities in skeletal muscle: role in sarcopenia.
α-Synuclein aggregation causes muscle atrophy through neuromuscular junction degeneration.
Huntingtin regulates calcium fluxes in skeletal muscle.
Disrupted T-tubular network accounts for asynchronous calcium release in MTM1 deficient skeletal muscle.
The role of NLRP3 inflammasome in inflammation-related skeletal muscle atrophy.
CRISPR-mediated correction of skeletal muscle Ca2+ handling in a novel DMD patient-derived pluripotent stem cell model.
The hairpin region of WNT7A is sufficient for binding to the Frizzled7 receptor and to elicit signaling in myogenic cells.
Major histocompatibility complex I-induced endoplasmic reticulum stress mediates the secretion of pro-inflammatory muscle-derived cytokines.
Mammalian Target of Rapamycin (mTOR) Signaling at the Crossroad of Muscle Fiber Fate in Sarcopenia.
Lactate Activates AMPK Remodeling of the Cellular Metabolic Profile and Promotes the Proliferation and Differentiation of C2C12 Myoblasts.
Functional Nutrients to Ameliorate Neurogenic Muscle Atrophy.
Skeletal muscle mitochondrial inertia associates with carnitine acetyltransferase activity and physical function in humans.
Depletion of CD206+ M2-like macrophages induces fibro-adipogenic progenitors activation and muscle regeneration.
Fast and slow skeletal myosin binding protein-C and aging.
Myostatin Knockout Affects Mitochondrial Function by Inhibiting the AMPK/SIRT1/PGC1α Pathway in Skeletal Muscle.
Statins Induce Locomotion and Muscular Phenotypes in Drosophila melanogaster That Are Reminiscent of Human Myopathy: Evidence for the Role of the Chloride Channel Inhibition in the Muscular Phenotypes.
Titin force in muscle cells alters lattice order, thick and thin filament protein formation.
Characterization of the dystrophin-associated protein complex by mass spectrometry.
The role of exerkines on brain mitochondria: a mini-review.
Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging.
Revisiting skeletal myopathy and exercise training in heart failure: Emerging role of myokines.
Artificial intelligence workflow quantifying muscle features on Hematoxylin-Eosin stained sections reveals dystrophic phenotype amelioration upon treatment.
The phosphorylation of AMPKβ1 is critical for increasing autophagy and maintaining mitochondrial homeostasis in response to fatty acids.

Cells. 2022 Nov 10. pii: 3549. [Epub ahead of print]11(22):

RNA-Sequencing Reveals Upregulation and a Beneficial Role of Autophagy in Myoblast Differentiation and Fusion.

Pengcheng Lyu, Honglin Jiang.

  Myoblast differentiation is a complex process whereby the mononuclear muscle precursor cells myoblasts express skeletal-muscle-specific genes and fuse with each other to form multinucleated myotubes. The objective of this study was to identify potentially novel mechanisms that mediate myoblast differentiation. We first compared transcriptomes in C2C12 myoblasts before and 6 days after induction of myogenic differentiation by RNA-seq. This analysis identified 11,046 differentially expressed genes, of which 5615 and 5431 genes were upregulated and downregulated, respectively, from before differentiation to differentiation. Functional enrichment analyses revealed that the upregulated genes were associated with skeletal muscle contraction, autophagy, and sarcomeres while the downregulated genes were associated with ribonucleoprotein complex biogenesis, mRNA processing, ribosomes, and other biological processes or cellular components. Western blot analyses showed an increased conversion of LC3-I to LC3-II protein during myoblast differentiation, further demonstrating the upregulation of autophagy during myoblast differentiation. Blocking the autophagic flux in C2C12 cells with chloroquine inhibited the expression of skeletal-muscle-specific genes and the formation of myotubes, confirming a positive role for autophagy in myoblast differentiation and fusion.

Keywords:  RNA-seq; autophagy; differentiation; myoblast; myotube

DOI:  https://doi.org/10.3390/cells11223549
Am J Physiol Cell Physiol. 2022 Nov 21.

PCM1 labelling reveals myonuclear and nuclear dynamics in skeletal muscle across species.

Mark R Viggars, Daniel J Owens, Claire Stewart, Catherine Coirault, Abigail L Mackey, Jonathan C Jarvis.

  Myonuclei transcriptionally regulate muscle fibres during homeostasis and adaptation to exercise. Their cellular location and quantity are important when characterising phenotypes of myopathies, the effect of treatments and to understand the roles of satellite cells in muscle adaptation and muscle 'memory'. Difficulties arise in identifying myonuclei due to their proximity to the sarcolemma and closely residing interstitial cell neighbours. We aimed to determine to what extent PCM1 isa specific marker of myonuclei in-vitro and in-vivo. Single isolated myofibres and transverse sections from mice and humans were studied from several models including Wild-type and Lamin A/C mutant mice after functional overload and damage and recovery in humans following forced eccentric contractions. Fibres were immuno-labelled for PCM1, Pax7 and DNA. C2C12 myoblasts were also studied to investigate changes in PCM1 localisation during myogenesis. PCM1 labelled the nuclear envelope of myonuclei in mature myofibres and in newly formed myotubes, but also labelled centrosomes in proliferating myogenic precursors which may or may not fuse to join the myofibre syncytium. It also labelled non-myogenic nuclei near the sarcolemma especially in regenerating areas of the Lmna+/ΔK32 mouse and damaged human muscle. While PCM1 is not completely specific to myonuclei, the impact of false-positive identification of interstitial cells on myonuclei counts would be small in healthy muscle. PCM1 may prove useful as a marker of satellite cell dynamics due to the distinct change in localisation during differentiation, revealing satellite cells in their quiescent (PCM1-), proliferating (PCM1+ centrosome), and pre-fusion states (PCM1+ nuclear envelope).

Keywords:  Macrophage; Myonuclei; PCM1; Satellite Cell; Skeletal Muscle

DOI:  https://doi.org/10.1152/ajpcell.00285.2022
FASEB J. 2022 Dec;36(12): e22666

Targeted ablation of Fn14 receptor improves exercise capacity and inhibits neurogenic muscle atrophy.

Meiricris Tomaz da Silva, Aniket S Joshi, Tatiana E Koike, Anirban Roy, Kavya Mathukumalli, Danesh H Sopariwala, Vihang A Narkar, Ashok Kumar.

  Skeletal muscle atrophy is a prevalent complication in multiple chronic diseases and disuse conditions. Fibroblast growth factor-inducible 14 (Fn14) is a member of the TNF receptor superfamily and a bona fide receptor of the TWEAK cytokine. Accumulating evidence suggests that Fn14 levels are increased in catabolic conditions as well as during exercise. However, the role of Fn14 in the regulation of skeletal muscle mass and function remains poorly understood. In this study, through the generation of novel skeletal muscle-specific Fn14-knockout mice, we have investigated the muscle role of Fn14 in the regulation of exercise capacity and denervation-induced muscle atrophy. Our results demonstrate that there was no difference in skeletal muscle mass between control and muscle-specific Fn14-knockout mice. Nevertheless, the deletion of Fn14 in skeletal muscle significantly improved exercise capacity and resistance to fatigue. This effect of Fn14 deletion is associated with an increased proportion of oxidative myofibers and higher capillaries number per myofiber in skeletal muscle. Furthermore, our results demonstrate that targeted deletion of Fn14 inhibits denervation-induced muscle atrophy in adult mice. Deletion of Fn14 reduced the expression of components of the ubiquitin-proteasome system and non-canonical NF-kappa B signaling in denervated skeletal muscle, as well as increased the phosphorylation of Akt kinase and FoxO3a transcription factor. Collectively, our results demonstrate that targeted inhibition of Fn14 improves exercise tolerance and inhibits denervation-induced muscle atrophy in adult mice.

Keywords:  FOXO; NF-kappa B; angiogenesis; cytokine signaling; skeletal muscle atrophy

DOI:  https://doi.org/10.1096/fj.202201583R
J Biol Methods. 2022 ;9(3): e162

Measurement of skeletal muscle glucose uptake in mice in response to acute treadmill running.

Lisbeth Liliendal Valbjørn Møller, Steffen Henning Raun, Andreas Mæchel Fritzen, Lykke Sylow.

  Skeletal muscle contractions stimulate glucose uptake into the working muscles during exercise. Because this signaling pathway is independent of insulin, exercise constitutes an important alternative pathway to increase glucose uptake, also in insulin-resistant muscle. Therefore, much effort is being put into understanding the molecular regulation of exercise-stimulated glucose uptake by skeletal muscle. To delineate the causal molecular mechanisms whereby muscle contraction or exercise regulate glucose uptake, the investigation of genetically manipulated rodents is necessary. Presented here is a modified and optimized protocol assessing exercise-induced muscle glucose uptake in mice in response to acute treadmill running. Using this high-throughput protocol, running capacity can accurately and reproducibly be determined in mice, and basal- and exercise-stimulated skeletal muscle glucose uptake and intracellular signaling can precisely and dose-dependently be measured in awake mice in vivo without the need for catheterization and with minimal loss of blood.

Keywords:  AMPK; exercise; glucose uptake; muscle; muscle contraction

DOI:  https://doi.org/10.14440/jbm.2022.385
Mol Ther. 2022 Nov 24. pii: S1525-0016(22)00670-0. [Epub ahead of print]

Systemic AAV9.BVES Delivery Ameliorates Muscular Dystrophy in a Mouse Model of LGMDR25.

Haiwen Li, Peipei Wang, Ethan Hsu, Kelsey M Pinckard, Kristin I Stanford, Renzhi Han.

Limb-girdle muscular dystrophy type R25 (LGMDR25) is caused by recessive mutations in BVES encoding a cAMP binding protein, characterized by progressive muscular dystrophy with deteriorating muscle function and impaired cardiac conduction in patients. There is currently no therapeutic treatment for LGMDR25 patients. Here we report the efficacy and safety of recombinant adeno-associated virus 9 (AAV9)-mediated systemic delivery of human BVES driven by a muscle-specific promoter MHCK7 (AAV9.BVES) in BVES-knockout (BVES-KO) mice. AAV9.BVES efficiently transduced the cardiac and skeletal muscle tissues when intraperitoneally injected into neonatal BVES-KO mice. AAV9.BVES dramatically improved body weight gain, muscle mass, muscle strength and exercise performance in BVES-KO mice regardless of sex. AAV9.BVES also significantly ameliorated the histopathological features of muscular dystrophy. The heart rate reduction was also normalized in BVES-KO mice under exercise-induced stress following systemic AAV9.BVES delivery. Moreover, intravenous AAV9.BVES administration into adult BVES-KO mice after the disease onset also resulted in substantial improvement in body weight, muscle mass, muscle contractility, and stress-induced heart rhythm abnormality. No obvious toxicity was detected. Taken together, these results provide the proof-of-concept evidence to support the AAV9.BVES gene therapy for LGMDR25.

DOI: https://doi.org/10.1016/j.ymthe.2022.11.012
Biosci Rep. 2022 Nov 22. pii: BSR20211997. [Epub ahead of print]

Skeletal and Cardiac Muscle Calcium Transport Regulation in Health and Disease.

Mark A Valentim, Aditya N Brahmbhatt, A Russell Tupling.

  In healthy muscle, the rapid release of calcium ions (Ca2+) with excitation-contraction (E-C) coupling, results in elevations in Ca2+ concentrations which can exceed 10-fold that of resting values. The sizable transient changes in Ca2+ concentrations are necessary for the activation of signaling pathways which rely on Ca2+ as a second messenger, including those involved with force generation, fiber type distribution and hypertrophy. However, prolonged elevations in intracellular Ca2+ can result in the unwanted activation of Ca2+ signaling pathways that cause muscle damage, dysfunction, and disease. Muscle employs several calcium handling and calcium transport proteins that function to rapidly return Ca2+ concentrations back to resting levels following contraction. This review will detail our current understanding of calcium handling during the decay phase of intracellular calcium transients in healthy skeletal and cardiac muscle. We will also discuss how impairments in Ca2+ transport can occur and how mishandling of Ca2+ can lead to the pathogenesis and/or progression of skeletal muscle myopathies and cardiomyopathies.

Keywords:  NCX; SERCA; muscle; phospholamban; sarcolipin; sarcoplasmic reticulum

DOI:  https://doi.org/10.1042/BSR20211997
Sci Rep. 2022 Nov 21. 12(1): 20006

Exercise alters the circadian rhythm of REV-ERB-α and downregulates autophagy-related genes in peripheral and central tissues.

Alisson L da Rocha, Ana P Pinto, Bruno L S Bedo, Gustavo P Morais, Luciana C Oliveira, Ruither O G Carolino, Jose R Pauli, Fernando M Simabuco, Leandro P de Moura, Eduardo R Ropelle, Dennys E Cintra, Donato A Rivas, Adelino S R da Silva.

The transcriptional repressor REV-ERB-α, encoded by Nuclear Receptor Subfamily 1 Group D Member 1 (Nr1d1), has been considered to play an essential role in the skeletal muscle oxidative capacity adaptation and muscle mass control. Also, this molecule regulates autophagy via the repression of autophagy-related genes both in skeletal muscle and brain regions. Classically, training programs based on endurance or strength characteristics enhance skeletal muscle mass content and/or oxidative capacity, leading to autophagy activation in several tissues. Thus, it seems that REV-ERB-α regulates similar responses induced by exercise. However, how this molecule responds to different exercise models/intensities in different tissues is still unclear. Therefore, the main aim was to characterize the responses of REV-ERB-α and autophagy-related genes to different exercise protocols (endurance/interval run/strength) in distinct tissues (gastrocnemius, soleus and hippocampus). Since REV-ERB-α presents a circadian rhythm, the analyses were performed in a time-course manner. The endurance and strength groups attenuated REV-ERB-α transcriptional response during the time course in gastrocnemius and soleus. Conversely, the interval group enhanced the Nr1d1 expression in the hippocampus. All protocols downregulated the REV-ERB-α protein levels in gastrocnemius following the exercise session with concomitant nuclear exclusion. The major autophagy-related genes presented downregulation after the exercise session in all analyzed tissues. Altogether, these results highlight that REV-ERB-α is extremely sensitive to physical exercise stimuli, including different models and intensities in skeletal muscle and the hippocampus.

DOI: https://doi.org/10.1038/s41598-022-24277-4
Cell Rep. 2022 Nov 22. pii: S2211-1247(22)01576-5. [Epub ahead of print]41(8): 111702

SENP7 deSUMOylase-governed transcriptional program coordinates sarcomere assembly and is targeted in muscle atrophy.

Mamta Amrute-Nayak, Luis Vincens Gand, Bushra Khan, Tim Holler, Ekaterini Kefalakes, Maike Kosanke, Theresia Kraft, Arnab Nayak.

  Disorganization of the basic contractile unit of muscle cells, i.e., the sarcomeres, leads to suboptimal force generation and is a hallmark of muscle atrophy. Here, we demonstrate that the nuclear role of SENP7 deSUMOylase is pivotal for sarcomere organization. SENP7 expression is temporally upregulated in mature muscle cells and directly regulates transcription of the myosin heavy chain (MyHC-IId) gene. We identify SENP7-dependent deSUMOylation of flightless-1 (Fli-I) as a signal for Fli-I association with scaffold attachment factor b1 (Safb1). SENP7 deficiency leads to higher Fli-I SUMOylation and lower chromatin residency of Safb1, thus generating transcriptionally incompetent chromatin conformation on MyHC-IId. Consequently, lower expression of MyHC-IId causes sarcomere disorganization and disrupted muscle cell contraction. Remarkably, cachexia signaling impedes the SENP7-governed transcriptional program, leading to muscle atrophy, with profound loss of motor protein MyHC-IId. We propose a SENP7-driven distinct transcription program as paramount for muscle cell function, which was found targeted in cachexia.

Keywords:  CP: Developmental biology; CP: Molecular biology; SUMOylation; cachexia; chromatin signaling; epigenetics; muscle atrophy; sarcomere organization; skeletal muscle

DOI:  https://doi.org/10.1016/j.celrep.2022.111702
Nat Commun. 2022 Nov 19. 13(1): 7108

Pharmacological inhibition of HDAC6 improves muscle phenotypes in dystrophin-deficient mice by downregulating TGF-β via Smad3 acetylation.

Alexis Osseni, Aymeric Ravel-Chapuis, Edwige Belotti, Isabella Scionti, Yann-Gaël Gangloff, Vincent Moncollin, Laetitia Mazelin, Remi Mounier, Pascal Leblanc, Bernard J Jasmin, Laurent Schaeffer.

The absence of dystrophin in Duchenne muscular dystrophy disrupts the dystrophin-associated glycoprotein complex resulting in skeletal muscle fiber fragility and atrophy, associated with fibrosis as well as microtubule and neuromuscular junction disorganization. The specific, non-conventional cytoplasmic histone deacetylase 6 (HDAC6) was recently shown to regulate acetylcholine receptor distribution and muscle atrophy. Here, we report that administration of the HDAC6 selective inhibitor tubastatin A to the Duchenne muscular dystrophy, mdx mouse model increases muscle strength, improves microtubule, neuromuscular junction, and dystrophin-associated glycoprotein complex organization, and reduces muscle atrophy and fibrosis. Interestingly, we found that the beneficial effects of HDAC6 inhibition involve the downregulation of transforming growth factor beta signaling. By increasing Smad3 acetylation in the cytoplasm, HDAC6 inhibition reduces Smad2/3 phosphorylation, nuclear translocation, and transcriptional activity. These findings provide in vivo evidence that Smad3 is a new target of HDAC6 and implicate HDAC6 as a potential therapeutic target in Duchenne muscular dystrophy.

DOI: https://doi.org/10.1038/s41467-022-34831-3
Cell Biochem Funct. 2022 Nov 22.

Genetic ablation of Toll-like Receptor 4 seems to activate the apoptosis pathway in the skeletal muscle of mice after acute physical exercise.

Bruno B Marafon, Ana P Pinto, Larissa G de Vicente, Alisson L da Rocha, Fernando M Simabuco, Eduardo R Ropelle, Leandro P de Moura, Dennys E Cintra, José R Pauli, Adelino S R da Silva.

  Many conditions, such as inflammation and physical exercise, can induce endoplasmic reticulum (ER) stress. Toll-like Receptor 4 (TLR4) can trigger inflammation and ER stress events. However, there are still no data in the literature regarding the role of TLR4 in ER stress during exercise in skeletal muscle. Therefore, the current investigation aimed to verify the responses of ER stress markers in wild-type (WT) and Tlr4 global knockout (KO) mice after acute and chronic physical exercise protocols. Eight-week-old male WT and KO mice were submitted to acute (moderate or high intensity) and chronic (4-week protocol) treadmill exercises. Under basal conditions, KO mice showed lower performance in the rotarod test. Acute high-intensity exercise increased eIF2α protein in the WT group. After the acute high-intensity exercise, there was an increase in Casp3 and Ddit3 mRNA for the KO mice. Acute moderate exercise increased the cleaved Caspase-3/Caspase-3 in the KO group. In response to chronic exercise, the KO group showed no improvement in any performance evaluation. The 4-week chronic protocol did not generate changes in ATF6, CHOP, p-IRE1α, p-eIF2α/eIF2α, and cleaved Caspase-3/Caspase-3 ratio but reduced BiP protein compared with the KO-Sedentary group. These results demonstrate the global deletion of Tlr4 seems to have the same effects on UPR markers of WT animals after acute and chronic exercise protocols but decreased performance. The cleaved Caspase-3/Caspase-3 ratio may be activated by another pathway other than ER stress in Tlr4 KO animals.

Keywords:  Toll-like Receptor-4 (TLR4); apoptosis; knockout model; physical exercise

DOI:  https://doi.org/10.1002/cbf.3765
Commun Biol. 2022 Nov 24. 5(1): 1288

Vitamin D status modulates mitochondrial oxidative capacities in skeletal muscle: role in sarcopenia.

Jérôme Salles, Audrey Chanet, Christelle Guillet, Anouk Mm Vaes, Elske M Brouwer-Brolsma, Christophe Rocher, Christophe Giraudet, Véronique Patrac, Emmanuelle Meugnier, Christophe Montaurier, Philippe Denis, Olivier Le Bacquer, Adeline Blot, Marion Jourdan, Yvette Luiking, Matthew Furber, Miriam Van Dijk, Nicolas Tardif, Y Yves Boirie, Stéphane Walrand.

Skeletal muscle mitochondrial function is the biggest component of whole-body energy output. Mitochondrial energy production during exercise is impaired in vitamin D-deficient subjects. In cultured myotubes, loss of vitamin D receptor (VDR) function decreases mitochondrial respiration rate and ATP production from oxidative phosphorylation. We aimed to examine the effects of vitamin D deficiency and supplementation on whole-body energy expenditure and muscle mitochondrial function in old rats, old mice, and human subjects. To gain further insight into the mechanisms involved, we used C2C12 and human muscle cells and transgenic mice with muscle-specific VDR tamoxifen-inducible deficiency. We observed that in vivo and in vitro vitamin D fluctuations changed mitochondrial biogenesis and oxidative activity in skeletal muscle. Vitamin D supplementation initiated in older people improved muscle mass and strength. We hypothesize that vitamin D supplementation is likely to help prevent not only sarcopenia but also sarcopenic obesity in vitamin D-deficient subjects.

DOI: https://doi.org/10.1038/s42003-022-04246-3
J Cachexia Sarcopenia Muscle. 2022 Nov 23.

α-Synuclein aggregation causes muscle atrophy through neuromuscular junction degeneration.

Qiumei Yang, Yanyan Wang, Chunsong Zhao, Shimin Pang, Jing Lu, Piu Chan.

   BACKGROUND: Sarcopenia is common in patients with Parkinson's disease (PD), showing mitochondrial oxidative stress in skeletal muscle. The aggregation of α-synuclein (α-Syn) to induce oxidative stress is a key pathogenic process of PD; nevertheless, we know little about its potential role in regulating peripheral nerves and the function of the muscles they innervate.
METHODS: To investigate the role of α-Syn aggregation on neuromuscular system, we used the Thy1 promoter to overexpress human α-Syn transgenic mice (mThy1-hSNCA). hα-Syn expression was evaluated by western blot, and its localization was determined by confocal microscopy. The impact of α-Syn aggregation on the structure and function of skeletal muscle mitochondria and neuromuscular junctions (NMJs), as well as muscle mass and function were characterized by flow cytometry, transmission electron microscopy, Seahorse XF24 metabolic assay, and AAV9 in vivo injection. We assessed the regenerative effect of mitochondrial-targeted superoxide dismutase (Mito-TEMPO) after skeletal muscle injury in mThy1-hSNCA mice.
RESULTS: Overexpressed hα-Syn protein localized in motor neuron axons and NMJs in muscle and formed aggregates. α-Syn aggregation increased the number of abnormal mitochondrial in the intramuscular axons and NMJs by over 60% (P < 0.01), which inhibited the release of acetylcholine (ACh) from presynaptic vesicles in NMJs (P < 0.05). The expression of genes associated with NMJ activity, neurotransmission and regulation of reactive oxygen species (ROS) metabolic process were significantly decreased in mThy1-hSNCA mice, resulting in ROS production elevated by ~220% (P < 0.05), thereby exacerbating oxidative stress. Such process altered mitochondrial spatial relationships to sarcomeric structures, decreased Z-line spacing by 36% (P < 0.05) and increased myofibre apoptosis by ~10% (P < 0.05). Overexpression of α-Syn altered the metabolic profile of muscle satellite cells (MuSCs), including basal respiratory capacity (~170% reduction) and glycolytic capacity (~150% reduction) (P < 0.05) and decreased cell migration and fusion during muscle regeneration (~60% and ~40%, respectively) (P < 0.05). We demonstrated that Mito-TEMPO treatment could restore the oxidative stress status (the complex I/V protein and enzyme activities increased ~200% and ~150%, respectively), which caused by α-Syn aggregation, and improve the ability of muscle regeneration after injury. In addition, the NMJ receptor fragmentation and ACh secretion were also improved.
CONCLUSIONS: These results reveal that the α-synuclein aggregation plays an important role in regulating acetylcholine release from neuromuscular junctions and induces intramuscular mitochondrial oxidative stress, which can provide new insights into the aetiology of muscle atrophy in patients with Parkinson's disease.

Keywords:  Area; Muscle atrophy; Neuromuscular junction; Oxidative stress; Parkinson's disease; α-Synuclein

DOI:  https://doi.org/10.1002/jcsm.13123
J Gen Physiol. 2023 Jan 02. pii: e202213103. [Epub ahead of print]155(1):

Huntingtin regulates calcium fluxes in skeletal muscle.

Mathilde Chivet, Maximilian McCluskey, Anne Sophie Nicot, Julie Brocard, Mathilde Beaufils, Diane Giovannini, Benoit Giannesini, Brice Poreau, Jacques Brocard, Sandrine Humbert, Frédéric Saudou, Julien Fauré, Isabelle Marty.

The expression of the Huntingtin protein, well known for its involvement in the neurodegenerative Huntington's disease, has been confirmed in skeletal muscle. The impact of HTT deficiency was studied in human skeletal muscle cell lines and in a mouse model with inducible and muscle-specific HTT deletion. Characterization of calcium fluxes in the knock-out cell lines demonstrated a reduction in excitation-contraction (EC) coupling, related to an alteration in the coupling between the dihydropyridine receptor and the ryanodine receptor, and an increase in the amount of calcium stored within the sarcoplasmic reticulum, linked to the hyperactivity of store-operated calcium entry (SOCE). Immunoprecipitation experiments demonstrated an association of HTT with junctophilin 1 (JPH1) and stromal interaction molecule 1 (STIM1), both providing clues on the functional effects of HTT deletion on calcium fluxes. Characterization of muscle strength and muscle anatomy of the muscle-specific HTT-KO mice demonstrated that HTT deletion induced moderate muscle weakness and mild muscle atrophy associated with histological abnormalities, similar to the phenotype observed in tubular aggregate myopathy. Altogether, this study points toward the hypotheses of the involvement of HTT in EC coupling via its interaction with JPH1, and on SOCE via its interaction with JPH1 and/or STIM1.

DOI: https://doi.org/10.1085/jgp.202213103
J Physiol. 2022 Nov 21.

Disrupted T-tubular network accounts for asynchronous calcium release in MTM1 deficient skeletal muscle.

Peter Szentesi, Beatrix Dienes, Candice Kutchukian, Tamas Czirjak, Ana Buj-Bello, Vincent Jacquemond, Laszlo Csernoch.

   KEY POINTS: Myotubular myopathy is a fatal disease due to genetic deficiency in the phosphoinositide phosphatase MTM1. Although causes are known and corresponding gene-therapy strategies are developed, there is no mechanistic understanding of the disease-associated muscle function failure. Resolving this issue is of primary interest both for fundamental knowledge of how MTM1 is critical for healthy muscle function but also for establishing the related cellular mechanisms most primarily or stringently affected by the disease, and thus of potential interest as therapy targets. The mathematical modelling approach used in the present work proves that the disease-associated alteration of the plasma membrane invagination network is sufficient to explain dysfunctions of excitation-contraction coupling, providing the first integrated quantitative framework explaining the associated contraction failure.
ABSTRACT: In mammalian skeletal muscle propagation of surface membrane depolarization into the interior of the muscle fibre along the transverse (T-) tubular network is essential for the synchronized release of calcium from the sarcoplasmic reticulum (SR) via Ryanodine receptors (RyR) in response to the conformational change in the voltage-sensor dihydropyridine receptors. Deficiency in 3-phosphoinositide phosphatase myotubularin (MTM1) has been reported that disruption of T-tubules results in impaired SR calcium release. Here confocal calcium transients recorded in muscle fibres of MTM1-deficient mice were compared to results from a model where propagation of the depolarization along the T-tubules was modelled mathematically with disruptions in the network assumed to modify the access and transmembrane resistances as well as the capacitance. If, in simulations, T-tubules were assumed to be partially or completely inaccessible to the depolarization and RyR at these points to be prime for calcium-induced calcium release, all features of measured SR calcium release could be reproduced. We conclude that the inappropriate propagation of the depolarization into the fibre interior is the initial critical cause of severely impaired SR calcium release in MTM1 deficiency, while Ca2+ -triggered opening of RyRs provides an alleviating support to the diseased process. Abstract figure legend In mammalian skeletal muscle the surface membrane depolarization propagates into the interior of the muscle fibre along the transverse (T-) tubular network and synchronizes the release of calcium from the sarcoplasmic reticulum (SR) via Ryanodine receptors (RyR). Deficiency in 3-phosphoinositide phosphatase myotubularin (MTM1) results in the disruption of the T-tubules and the appearance of delayed SR calcium release. Calcium transients recorded in muscle fibres of MTM1-deficient mice were compared to results when the propagation of the depolarization along the T-tubules was modelled mathematically. If T-tubules were assumed to be partially or completely inaccessible to the depolarization all features of measured SR calcium release could be reproduced. Thus the inappropriate propagation of the depolarization into the fibre interior is the initial critical cause of severely impaired SR calcium release in MTM1 deficiency, while Ca2+ -triggered opening of RyRs provides an alleviating support to the diseased process. This article is protected by copyright. All rights reserved.

Keywords:  MTM1; T-tubule; calcium release; ryanodine receptor; sarcoplasmic reticulum

DOI:  https://doi.org/10.1113/JP283650
Front Immunol. 2022 ;13 1035709

The role of NLRP3 inflammasome in inflammation-related skeletal muscle atrophy.

Yukun Liu, Dongfang Wang, Tianyu Li, Fan Yang, Zhanfei Li, Xiangjun Bai, Yuchang Wang.

  Skeletal muscle atrophy is a common complication in survivors of sepsis, which affects the respiratory and motor functions of patients, thus severely impacting their quality of life and long-term survival. Although several advances have been made in investigations on the pathogenetic mechanism of sepsis-induced skeletal muscle atrophy, the underlying mechanisms remain unclear. Findings from recent studies suggest that the nucleotide-binding and oligomerisation domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, a regulator of inflammation, may be crucial in the development of skeletal muscle atrophy. NLRP3 inhibitors contribute to the inhibition of catabolic processes, skeletal muscle atrophy and cachexia-induced inflammation. Here, we review the mechanisms by which NLRP3 mediates these responses and analyse how NLRP3 affects muscle wasting during inflammation.

Keywords:  ICUAW; NLRP3; inflammasome; metabolic syndrome; pyroptosis; sepsis; skeletal muscle

DOI:  https://doi.org/10.3389/fimmu.2022.1035709
Neuromuscul Disord. 2022 Nov 01. pii: S0960-8966(22)00702-7. [Epub ahead of print]

CRISPR-mediated correction of skeletal muscle Ca2+ handling in a novel DMD patient-derived pluripotent stem cell model.

Cristina Morera, Jihee Kim, Amaia Paredes-Redondo, Muriel Nobles, Denis Rybin, Robert Moccia, Anna Kowala, Jinhong Meng, Seth Garren, Pentao Liu, Jennifer E Morgan, Francesco Muntoni, Nicolas Christoforou, Jane Owens, Andrew Tinker, Yung-Yao Lin.

  Mutations in the dystrophin gene cause the most common and currently incurable Duchenne muscular dystrophy (DMD) characterized by progressive muscle wasting. Although abnormal Ca2+ handling is a pathological feature of DMD, mechanisms underlying defective Ca2+ homeostasis remain unclear. Here we generate a novel DMD patient-derived pluripotent stem cell (PSC) model of skeletal muscle with an isogenic control using clustered regularly interspaced short palindromic repeat (CRISPR)-mediated precise gene correction. Transcriptome analysis identifies dysregulated gene sets in the absence of dystrophin, including genes involved in Ca2+ handling, excitation-contraction coupling and muscle contraction. Specifically, analysis of intracellular Ca2+ transients and mathematical modeling of Ca2+ dynamics reveal significantly reduced cytosolic Ca2+ clearance rates in DMD-PSC derived myotubes. Pharmacological assays demonstrate Ca2+ flux in myotubes is determined by both intracellular and extracellular sources. DMD-PSC derived myotubes display significantly reduced velocity of contractility. Compared with a non-isogenic wildtype PSC line, these pathophysiological defects could be rescued by CRISPR-mediated precise gene correction. Our study provides new insights into abnormal Ca2+ homeostasis in DMD and suggests that Ca2+ signaling pathways amenable to pharmacological modulation are potential therapeutic targets. Importantly, we have established a human physiology-relevant in vitro model enabling rapid pre-clinical testing of potential therapies for DMD.

Keywords:  CRISPR; Ca(2+) handling; Duchenne muscular dystrophy; Dystrophin; Human pluripotent stem cells

DOI:  https://doi.org/10.1016/j.nmd.2022.10.007
Comput Struct Biotechnol J. 2022 ;20 6348-6359

The hairpin region of WNT7A is sufficient for binding to the Frizzled7 receptor and to elicit signaling in myogenic cells.

Manuel Schmidt, Christine Poser, Christina Janster, Julia von Maltzahn.

  Wnt signaling is essential for embryonic development and tissue homeostasis. So far, little is known about the importance and functional relevance of the different regions in WNT proteins including regions in their C-terminus identified as hairpin and linker. However, it was shown that the C-terminus of WNT7A comprising the linker and the hairpin region is sufficient to elicit signaling. Here, we demonstrate that actually the hairpin region of WNT7A in its C-terminus is fully sufficient to induce non-canonical signaling in myogenic cells while the linker region alone did not show biological activity. Of note, all known non-canonical signaling branches of WNT7A signaling in skeletal muscle were activated by the hairpin region of WNT7A thereby inducing hypertrophy in myotubes, symmetric expansion of satellite stem cells and migration of myoblasts. Furthermore, we demonstrate that the linker region in the C-terminus of WNT7A binds to the FZD7 receptor while it does not activate non-canonical Wnt signaling. However, the hairpin and the linker region of WNT7A can activate canonical Wnt signaling independent of each other suggesting that specificity of downstream signaling might be depending on those specific regions in the C-terminus.

Keywords:  Hypertrophy; Muscle stem cell; Myogenesis; Satellite cell; Wnt signaling; Wnt7a

DOI:  https://doi.org/10.1016/j.csbj.2022.10.047
J Cell Mol Med. 2022 Nov 25.

Major histocompatibility complex I-induced endoplasmic reticulum stress mediates the secretion of pro-inflammatory muscle-derived cytokines.

Anastasia Thoma, Kate E Earl, Katarzyna Goljanek-Whysall, Adam P Lightfoot.

  Major histocompatibility complex (MHC) I is an important component of intracellular antigen presentation. However, improper expression of MHC I upon the cell surface has been associated with several autoimmune diseases. Myositis is a rare acquired autoimmune disease which targets skeletal muscle, and MHC I overexpression on the surface of muscle fibres and immune cell infiltration are clinical hallmarks. MHC I overexpression may have an important pathogenic role, mediated by the activation of the endoplasmic reticulum (ER) stress response. Given the evidence that muscle is a diverse source of cytokines, we aimed to investigate whether MHC I overexpression can modify the profile of muscle-derived cytokines and what role the ER stress pathway may play. Using C2C12 myoblasts we overexpressed MHC I with a H-2kb vector in the presence or absence of salubrinal an ER stress pathway modifying compound. MHC I overexpression induced ER stress pathway activation and elevated cytokine gene expression. MHC I overexpression caused significant release of cytokines and chemokines, which was attenuated in the presence of salubrinal. Conditioned media from MHC I overexpressing cells induced in vitro T-cell chemotaxis, atrophy of healthy myotubes and modified mitochondrial function, features which were attenuated in the presence of salubrinal. Collectively, these data suggest that MHC I overexpression can induce pro-inflammatory cytokine/chemokine release from C2C12 myoblasts, a process which appears to be mediated in-part by the ER stress pathway.

Keywords:  ER stress; major histocompatibility complex (MHC) I; myokines; skeletal muscle

DOI:  https://doi.org/10.1111/jcmm.17621
Int J Mol Sci. 2022 Nov 10. pii: 13823. [Epub ahead of print]23(22):

Mammalian Target of Rapamycin (mTOR) Signaling at the Crossroad of Muscle Fiber Fate in Sarcopenia.

Giuseppe Sirago, Anna Picca, Riccardo Calvani, Hélio José Coelho-Júnior, Emanuele Marzetti.

  The mammalian target of rapamycin (mTOR) is a major regulator of skeletal myocyte viability. The signaling pathways triggered by mTOR vary according to the type of endogenous and exogenous factors (e.g., redox balance, nutrient availability, physical activity) as well as organismal age. Here, we provide an overview of mTOR signaling in skeletal muscle, with a special focus on the role played by mTOR in the development of sarcopenia. Intervention strategies targeting mTOR in sarcopenia (e.g., supplementation of plant extracts, hormones, inorganic ions, calorie restriction, and exercise) have also been discussed.

Keywords:  aging; atrogenes; autophagy; calorie restriction; mitophagy; neuromuscular junction; protein degradation; protein synthesis; rapalogs; skeletal muscle

DOI:  https://doi.org/10.3390/ijms232213823
Int J Mol Sci. 2022 Nov 13. pii: 13996. [Epub ahead of print]23(22):

Lactate Activates AMPK Remodeling of the Cellular Metabolic Profile and Promotes the Proliferation and Differentiation of C2C12 Myoblasts.

Yu Zhou, Xi Liu, Caihua Huang, Donghai Lin.

  Lactate is a general compound fuel serving as the fulcrum of metabolism, which is produced from glycolysis and shuttles between different cells, tissues and organs. Lactate is usually accumulated abundantly in muscles during exercise. It remains unclear whether lactate plays an important role in the metabolism of muscle cells. In this research, we assessed the effects of lactate on myoblasts and clarified the underlying metabolic mechanisms through NMR-based metabonomic profiling. Lactate treatment promoted the proliferation and differentiation of myoblasts, as indicated by significantly enhanced expression levels of the proteins related to cellular proliferation and differentiation, including p-AKT, p-ERK, MyoD and myogenin. Moreover, lactate treatment profoundly regulated metabolisms in myoblasts by promoting the intake and intracellular utilization of lactate, activating the TCA cycle, and thereby increasing energy production. For the first time, we found that lactate treatment evidently promotes AMPK signaling as reflected by the elevated expression levels of p-AMPK and p-ACC. Our results showed that lactate as a metabolic regulator activates AMPK, remodeling the cellular metabolic profile, and thereby promoting the proliferation and differentiation of myoblasts. This study elucidates molecular mechanisms underlying the effects of lactate on skeletal muscle in vitro and may be of benefit to the exploration of lactate acting as a metabolic regulator.

Keywords:  AMPK; C2C12 myoblasts; NMR-based metabonomics; lactate; metabolic regulator

DOI:  https://doi.org/10.3390/ijms232213996
Metabolites. 2022 Nov 21. pii: 1149. [Epub ahead of print]12(11):

Functional Nutrients to Ameliorate Neurogenic Muscle Atrophy.

Viviana Moresi, Alessandra Renzini, Giorgia Cavioli, Marilia Seelaender, Dario Coletti, Giuseppe Gigli, Alessia Cedola.

  Neurogenic muscle atrophy is a debilitating condition that occurs from nerve trauma in association with diseases or during aging, leading to reduced interaction between motoneurons and skeletal fibers. Current therapeutic approaches aiming at preserving muscle mass in a scenario of decreased nervous input include physical activity and employment of drugs that slow down the progression of the condition yet provide no concrete resolution. Nutritional support appears as a precious tool, adding to the success of personalized medicine, and could thus play a relevant part in mitigating neurogenic muscle atrophy. We herein summarize the molecular pathways triggered by denervation of the skeletal muscle that could be affected by functional nutrients. In this narrative review, we examine and discuss studies pertaining to the use of functional ingredients to counteract neurogenic muscle atrophy, focusing on their preventive or curative means of action within the skeletal muscle. We reviewed experimental models of denervation in rodents and in amyotrophic lateral sclerosis, as well as that caused by aging, considering the knowledge generated with use of animal experimental models and, also, from human studies.

Keywords:  aging; muscle wasting; natural compounds; neurodegenerative diseases; nutraceuticals; sarcopenia

DOI:  https://doi.org/10.3390/metabo12111149
JCI Insight. 2022 Nov 22. pii: e163855. [Epub ahead of print]

Skeletal muscle mitochondrial inertia associates with carnitine acetyltransferase activity and physical function in humans.

Rodrigo F Mancilla, Lucas Lindeboom, Lotte Grevendonk, Joris Hoeks, Timothy R Koves, Deborah M Muoio, Patrick Schrauwen, Vera Schrauwen-Hinderling, Matthijs Kc Hesselink.

   BACKGROUND: At the onset of exercise, the speed at which PCr decreases towards a new steady state (PCr on-kinetics), reflects the readiness to activate mitochondrial ATP synthesis, which is secondary to Acetyl-CoA availability in skeletal muscle. We hypothesized that PCr on-kinetics are slower in metabolically compromised and older individuals, and associated with low carnitine acetyl-transferase (CrAT) protein activity and compromised physical function.
METHODS: We applied 31P-Magnetic Resonance Spectroscopy (MRS) to assess PCr on-kinetics in two cohorts of human volunteers. Cohort 1: patients with type 2 diabetes, obese, lean trained and untrained individuals. Cohort 2: young and older individuals with normal physical activity and older trained. Previous results of CrAT protein activity and acetylcarnitine content in muscle tissue were used to explore the underlying mechanisms of PCr on-kinetics, along with various markers of physical function.
RESULTS: PCr on-kinetics were significantly slower in metabolically compromised and older individuals (indicating mitochondrial inertia) as compared to young and older trained volunteers, regardless of in vivo skeletal muscle oxidative capacity (P<0.001). Mitochondrial inertia correlated with reduced CrAT protein activity, low acetylcarnitine content and also with functional outcomes (P<0.001).
CONCLUSION: PCr on-kinetics are significantly slower in metabolically compromised and older individuals with normal physical activity compared to young and older trained, regardless of in vivo skeletal muscle oxidative capacity, indicating greater mitochondrial inertia. Thus, PCr on-kinetics are a currently unexplored signature of skeletal muscle mitochondrial metabolism, tightly linked to functional outcomes. Skeletal muscle mitochondrial inertia might emerge as a target of intervention to improve physical function.
TRIAL REGISTRATION:
CLINICALTRIALS: gov: NCT01298375 and clinicaltrials.gov: NCT03666013.
FUNDING: R.M and M.H were granted with an EFSD/Lilly grant from the European Foundation for the Study of Diabetes (EFSD). V.S was supported by an ERC staring grant (Grant no. 759161) "MRS in Diabetes".

Keywords:  Aging; Diabetes; Metabolism; Mitochondria; Skeletal muscle

DOI:  https://doi.org/10.1172/jci.insight.163855
Nat Commun. 2022 Nov 21. 13(1): 7058

Depletion of CD206+ M2-like macrophages induces fibro-adipogenic progenitors activation and muscle regeneration.

Allah Nawaz, Muhammad Bilal, Shiho Fujisaka, Tomonobu Kado, Muhammad Rahil Aslam, Saeed Ahmed, Keisuke Okabe, Yoshiko Igarashi, Yoshiyuki Watanabe, Takahide Kuwano, Koichi Tsuneyama, Ayumi Nishimura, Yasuhiro Nishida, Seiji Yamamoto, Masakiyo Sasahara, Johji Imura, Hisashi Mori, Martin M Matzuk, Fujimi Kudo, Ichiro Manabe, Akiyoshi Uezumi, Takashi Nakagawa, Yumiko Oishi, Kazuyuki Tobe.

Muscle regeneration requires the coordination of muscle stem cells, mesenchymal fibro-adipogenic progenitors (FAPs), and macrophages. How macrophages regulate the paracrine secretion of FAPs during the recovery process remains elusive. Herein, we systemically investigated the communication between CD206+ M2-like macrophages and FAPs during the recovery process using a transgenic mouse model. Depletion of CD206+ M2-like macrophages or deletion of CD206+ M2-like macrophages-specific TGF-β1 gene induces myogenesis and muscle regeneration. We show that depletion of CD206+ M2-like macrophages activates FAPs and activated FAPs secrete follistatin, a promyogenic factor, thereby boosting the recovery process. Conversely, deletion of the FAP-specific follistatin gene results in impaired muscle stem cell function, enhanced fibrosis, and delayed muscle regeneration. Mechanistically, CD206+ M2-like macrophages inhibit the secretion of FAP-derived follistatin via TGF-β signaling. Here we show that CD206+ M2-like macrophages constitute a microenvironment for FAPs and may regulate the myogenic potential of muscle stem/satellite cells.

DOI: https://doi.org/10.1038/s41467-022-34191-y
Geroscience. 2022 Nov 21.

Fast and slow skeletal myosin binding protein-C and aging.

L R Perazza, G Wei, L V Thompson.

  Aging is associated with skeletal muscle strength decline and cardiac diastolic dysfunction. The structural arrangements of the sarcomeric proteins, such as myosin binding protein-C (MyBP-C) are shown to be pivotal in the pathogenesis of diastolic dysfunction. Yet, the role of fast (fMyBP-C) and slow (sMyBP-C) skeletal muscle MyBP-C remains to be elucidated. Herein, we aimed to characterize MyBP-C and its paralogs in the fast tibialis anterior (TA) muscle from adult and old mice. Immunoreactivity preparations showed that the relative abundance of the fMyBP-C paralog was greater in the TA of both adult and old, but no differences were noted between groups. We further found that the expression level of cardiac myosin binding protein-C (cMyBP-C), an important modulator of cardiac output, was lowered by age. Standard SDS-PAGE along with Pro-Q Diamond phosphoprotein staining did not identify age-related changes in phosphorylated MyBP-C proteins from TA and cardiac muscles; however, it revealed that MyBP-C paralogs in fast skeletal and cardiac muscle were highly phosphorylated. Mass spectrometry further identified glycogen phosphorylase, desmin, actin, troponin T, and myosin regulatory light chain 2 as phosphorylated myofilament proteins in both ages. MyBP-C protein-bound carbonyls were determined using anti-DNP immunostaining and found the carbonyl level of fMyBP-C, sMyBP-C, and cMyBP-C to be similar between old and adult animals. In summary, our data showed some differences regarding the MyBP-C paralog expression and identified an age-related reduction of cMyBP-C expression. Future studies are needed to elucidate which are the age-driven post-translational modifications in the MyBP-C paralogs.

Keywords:  Aging; Muscle contractility; Phosphorylation

DOI:  https://doi.org/10.1007/s11357-022-00689-y
Int J Mol Sci. 2022 Nov 08. pii: 13703. [Epub ahead of print]23(22):

Myostatin Knockout Affects Mitochondrial Function by Inhibiting the AMPK/SIRT1/PGC1α Pathway in Skeletal Muscle.

Mingjuan Gu, Zhuying Wei, Xueqiao Wang, Yang Gao, Dong Wang, Xuefei Liu, Chunling Bai, Guanghua Su, Lei Yang, Guangpeng Li.

  Myostatin (Mstn) is a major negative regulator of skeletal muscle mass and initiates multiple metabolic changes. The deletion of the Mstn gene in mice leads to reduced mitochondrial functions. However, the underlying regulatory mechanisms remain unclear. In this study, we used CRISPR/Cas9 to generate myostatin-knockout (Mstn-KO) mice via pronuclear microinjection. Mstn-KO mice exhibited significantly larger skeletal muscles. Meanwhile, Mstn knockout regulated the organ weights of mice. Moreover, we found that Mstn knockout reduced the basal metabolic rate, muscle adenosine triphosphate (ATP) synthesis, activities of mitochondrial respiration chain complexes, tricarboxylic acid cycle (TCA) cycle, and thermogenesis. Mechanistically, expressions of silent information regulator 1 (SIRT1) and phosphorylated adenosine monophosphate-activated protein kinase (pAMPK) were down-regulated, while peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) acetylation modification increased in the Mstn-KO mice. Skeletal muscle cells from Mstn-KO and WT were treated with AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR), and the AMPK inhibitor Compound C, respectively. Compared with the wild-type (WT) group, Compound C treatment further down-regulated the expression or activity of pAMPK, SIRT1, citrate synthase (CS), isocitrate dehydrogenase (ICDHm), and α-ketoglutarate acid dehydrogenase (α-KGDH) in Mstn-KO mice, while Mstn knockout inhibited the AICAR activation effect. Therefore, Mstn knockout affects mitochondrial function by inhibiting the AMPK/SIRT1/PGC1α signaling pathway. The present study reveals a new mechanism for Mstn knockout in regulating energy homeostasis.

Keywords:  AMPK/SIRT1/PGC-1α; CRISPR/Cas9; knockout; mitochondrial; myostatin; skeletal muscle

DOI:  https://doi.org/10.3390/ijms232213703
Cells. 2022 Nov 08. pii: 3528. [Epub ahead of print]11(22):

Statins Induce Locomotion and Muscular Phenotypes in Drosophila melanogaster That Are Reminiscent of Human Myopathy: Evidence for the Role of the Chloride Channel Inhibition in the Muscular Phenotypes.

Mohamed H Al-Sabri, Neha Behare, Ahmed M Alsehli, Samuel Berkins, Aadeya Arora, Eirini Antoniou, Eleni I Moysiadou, Sowmya Anantha-Krishnan, Patricia D Cosmen, Johanna Vikner, Thiago C Moulin, Nourhene Ammar, Hadi Boukhatmi, Laura E Clemensson, Mathias Rask-Andersen, Jessica Mwinyi, Michael J Williams, Robert Fredriksson, Helgi B Schiöth.

  The underlying mechanisms for statin-induced myopathy (SIM) are still equivocal. In this study, we employ Drosophila melanogaster to dissect possible underlying mechanisms for SIM. We observe that chronic fluvastatin treatment causes reduced general locomotion activity and climbing ability. In addition, transmission microscopy of dissected skeletal muscles of fluvastatin-treated flies reveals strong myofibrillar damage, including increased sarcomere lengths and Z-line streaming, which are reminiscent of myopathy, along with fragmented mitochondria of larger sizes, most of which are round-like shapes. Furthermore, chronic fluvastatin treatment is associated with impaired lipid metabolism and insulin signalling. Mechanistically, knockdown of the statin-target Hmgcr in the skeletal muscles recapitulates fluvastatin-induced mitochondrial phenotypes and lowered general locomotion activity; however, it was not sufficient to alter sarcomere length or elicit myofibrillar damage compared to controls or fluvastatin treatment. Moreover, we found that fluvastatin treatment was associated with reduced expression of the skeletal muscle chloride channel, ClC-a (Drosophila homolog of CLCN1), while selective knockdown of skeletal muscle ClC-a also recapitulated fluvastatin-induced myofibril damage and increased sarcomere lengths. Surprisingly, exercising fluvastatin-treated flies restored ClC-a expression and normalized sarcomere lengths, suggesting that fluvastatin-induced myofibrillar phenotypes could be linked to lowered ClC-a expression. Taken together, these results may indicate the potential role of ClC-a inhibition in statin-associated muscular phenotypes. This study underlines the importance of Drosophila melanogaster as a powerful model system for elucidating the locomotion and muscular phenotypes, promoting a better understanding of the molecular mechanisms underlying SIM.

Keywords:  CLC-1; ClC-a; Drosophila melanogaster; Hmgcr; PKCtheta (PKCθ); Pkcdelta (Pkcδ); chelerythrine; fluvastatin; lipotoxicity; locomotion; mitochondrial dysfunction; myopathy; sarcomere; skeletal muscle chloride channel; statin-induced myopathy; statins

DOI:  https://doi.org/10.3390/cells11223528
Proc Natl Acad Sci U S A. 2022 Nov 29. 119(48): e2209441119

Titin force in muscle cells alters lattice order, thick and thin filament protein formation.

Anthony L Hessel, Weikang Ma, Nicole Mazara, Paige E Rice, Devin Nissen, Henry Gong, Michel Kuehn, Thomas Irving, Wolfgang A Linke.

  Skeletal muscle force production is increased at longer compared to shorter muscle lengths because of length-dependent priming of thick filament proteins in the contractile unit before contraction. Using small-angle X-ray diffraction in combination with a mouse model that specifically cleaves the stretch-sensitive titin protein, we found that titin cleavage diminished the length-dependent priming of the thick filament. Strikingly, a titin-sensitive, length-dependent priming was also present in thin filaments, which seems only possible via bridge proteins between thick and thin filaments in resting muscle, potentially myosin-binding protein C. We further show that these bridges can be forcibly ruptured via high-speed stretches. Our results advance a paradigm shift to the fundamental regulation of length-dependent priming, with titin as the key driver.

Keywords:  X-ray diffraction; elasticity; length-dependent activation; mouse; ultrastructure

DOI:  https://doi.org/10.1073/pnas.2209441119
Mass Spectrom Rev. 2022 Nov 24. e21823

Characterization of the dystrophin-associated protein complex by mass spectrometry.

Emily H Canessa, Rita Spathis, James S Novak, Aaron Beedle, Kanneboyina Nagaraju, Luca Bello, Elena Pegoraro, Eric P Hoffman, Yetrib Hathout.

  The dystrophin-associated protein complex (DAPC) is a highly organized multiprotein complex that plays a pivotal role in muscle fiber structure integrity and cell signaling. The complex is composed of three distinct interacting subgroups, intracellular peripheral proteins, transmembrane glycoproteins, and extracellular glycoproteins subcomplexes. Dystrophin protein nucleates the DAPC and is important for connecting the intracellular actin cytoskeletal filaments to the sarcolemma glycoprotein complex that is connected to the extracellular matrix via laminin, thus stabilizing the sarcolemma during muscle fiber contraction and relaxation. Genetic mutations that lead to lack of expression or altered expression of any of the DAPC proteins are associated with different types of muscle diseases. Hence characterization of this complex in healthy and dystrophic muscle might bring insights into its role in muscle pathogenesis. This review highlights the role of mass spectrometry in characterizing the DAPC interactome as well as post-translational glycan modifications of some of its components such as α-dystroglycan. Detection and quantification of dystrophin using targeted mass spectrometry are also discussed in the context of healthy versus dystrophic skeletal muscle.

Keywords:  dystroglycans; dystrophin; laminin; mass spectrometry; sarcoglycans

DOI:  https://doi.org/10.1002/mas.21823
J Appl Physiol (1985). 2022 Nov 23.

The role of exerkines on brain mitochondria: a mini-review.

Junwon Heo, Emily E Noble, Jarrod A Call.

  Exercise benefits many organ systems, including having a panacea-like effect on the brain. For example, aerobic exercise improves cognition and attention and reduces the risk of brain-related diseases, such as dementia, stress, and depression. Recent advances suggest that endocrine signaling from peripheral systems, such as skeletal muscle, mediates the effects of exercise on the brain. Consequently, it has been proposed that factors secreted by all organs in response to physical exercise should be more broadly termed the "exerkines". Accumulating findings suggest that exerkines derived from skeletal muscle, liver, and adipose tissues directly impact brain mitochondrial function. Mitochondria play a pivotal role in regulating neuronal energy metabolism, neurotransmission, cell repair, and maintenance in the brain, and therefore exerkines may act via impacting brain mitochondria to improve brain function and disease resistance. Therefore, herein we review studies investigating the impact of muscle-, liver-, and adipose tissue-derived exerkines on brain cognitive and metabolic function via modulating mitochondrial bioenergetics, content, and dynamics under healthy and/or disease conditions.

Keywords:  Adipokines; Exercise; Hepatokines; Mitochondria; Myokines

DOI:  https://doi.org/10.1152/japplphysiol.00565.2022
Biol Rev Camb Philos Soc. 2022 Nov 22.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging.

Georgios Mavropalias, Marni Boppart, Kayley M Usher, Miranda D Grounds, Kazunori Nosaka, Anthony J Blazevich.

  Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

Keywords:  ECM remodelling; collagen; connective tissue; exercise; fascia

DOI:  https://doi.org/10.1111/brv.12916
Metabolism. 2022 Nov 21. pii: S0026-0495(22)00226-8. [Epub ahead of print]138 155348

Revisiting skeletal myopathy and exercise training in heart failure: Emerging role of myokines.

Robinson Ramírez-Vélez, Arantxa González, Antonio García-Hermoso, Iñigo Latasa Amézqueta, Mikel Izquierdo, Javier Díez.

  Exercise intolerance remains a major unmet medical need in patients with heart failure (HF). Skeletal myopathy is currently considered as the major limiting factor for exercise capacity in HF patients. On the other hand, emerging evidence suggest that physical exercise can decrease morbidity and mortality in HF patients. Therefore, mechanistic insights into skeletal myopathy may uncover critical aspects for therapeutic interventions to improve exercise performance in HF. Emerging data reviewed in this article suggest that the assessment of circulating myokines (molecules synthesized and secreted by skeletal muscle in response to contraction that display autocrine, paracrine and endocrine actions) may provide new insights into the pathophysiology, phenotyping and prognostic stratification of HF-related skeletal myopathy. Further studies are required to determine whether myokines may also serve as biomarkers to personalize the modality and dose of physical training prescribed for patients with HF and exercise intolerance. In addition, the production and secretion of myokines in patients with HF may interact with systemic alterations (e.g., inflammation and metabolic disturbances), frequently present in patients with HF. Furthermore, myokines may exert beneficial or detrimental effects on cardiac structure and function, which may influence adverse cardiac remodelling and clinical outcomes in HF patients. Collectively, these data suggest that a deeper knowledge on myokines regulation and actions may lead to the identification of novel physical exercise-based therapeutic approaches for HF patients.

Keywords:  Biomarkers; Heart failure; Myokines; Personalized training; Physical exercise; Skeletal myopathy

DOI:  https://doi.org/10.1016/j.metabol.2022.155348
Sci Rep. 2022 Nov 19. 12(1): 19913

Artificial intelligence workflow quantifying muscle features on Hematoxylin-Eosin stained sections reveals dystrophic phenotype amelioration upon treatment.

Marie Reinbigler, Jérémie Cosette, Zoheir Guesmia, Simon Jimenez, Catalin Fetita, Elisabeth Brunet, Daniel Stockholm.

Cell segmentation is a key step for a wide variety of biological investigations, especially in the context of muscle science. Currently, automated methods still struggle to perform skeletal muscle fiber quantification on Hematoxylin-Eosin (HE) stained histopathological whole slide images due to low contrast. On the other hand, the Deep Learning algorithm Cellpose offers new perspectives considering its increasing adoption for segmentation of a wide range of cells. Combining two open-source tools, Cellpose and QuPath, we developed MyoSOTHES, an automated Myofibers Segmentation wOrkflow Tuned for HE Staining. MyoSOTHES enables solving segmentation inconsistencies encountered by default Cellpose model in presence of large range size cells and provides information related to muscle Feret's diameter distribution and Centrally Nucleated Fibers, thus depicting muscle health and treatment effects. MyoSOTHES achieves high quality segmentation compared to baseline workflow with a detection F1-score increasing from 0.801 to 0.919 and a Root Mean Square Error (RMSE) on diameter improved by 31%. MyoSOTHES was validated on an animal study featuring gene transfer in [Formula: see text]-Sarcoglycanopathy, for which dose-response effect is visible and conclusions drawn are consistent with those previously published. MyoSOTHES thus paves the way for wide quantification of HE stained muscle sections and retrospective analysis of HE labeled slices used in laboratories for decades.

DOI: https://doi.org/10.1038/s41598-022-24139-z
Proc Natl Acad Sci U S A. 2022 Nov 29. 119(48): e2119824119

The phosphorylation of AMPKβ1 is critical for increasing autophagy and maintaining mitochondrial homeostasis in response to fatty acids.

Eric M Desjardins, Brennan K Smith, Emily A Day, Serge Ducommun, Matthew J Sanders, Joshua P Nederveen, Rebecca J Ford, Stephen L Pinkosky, Logan K Townsend, Robert M Gutgesell, Rachel Lu, Kei Sakamoto, Gregory R Steinberg.

  Fatty acids are vital for the survival of eukaryotes, but when present in excess can have deleterious consequences. The AMP-activated protein kinase (AMPK) is an important regulator of multiple branches of metabolism. Studies in purified enzyme preparations and cultured cells have shown that AMPK is allosterically activated by small molecules as well as fatty acyl-CoAs through a mechanism involving Ser108 within the regulatory AMPK β1 isoform. However, the in vivo physiological significance of this residue has not been evaluated. In the current study, we generated mice with a targeted germline knock-in (KI) mutation of AMPKβ1 Ser108 to Ala (S108A-KI), which renders the site phospho-deficient. S108A-KI mice had reduced AMPK activity (50 to 75%) in the liver but not in the skeletal muscle. On a chow diet, S108A-KI mice had impairments in exogenous lipid-induced fatty acid oxidation. Studies in mice fed a high-fat diet found that S108A-KI mice had a tendency for greater glucose intolerance and elevated liver triglycerides. Consistent with increased liver triglycerides, livers of S108A-KI mice had reductions in mitochondrial content and respiration that were accompanied by enlarged mitochondria, suggestive of impairments in mitophagy. Subsequent studies in primary hepatocytes found that S108A-KI mice had reductions in palmitate- stimulated Cpt1a and Ppargc1a mRNA, ULK1 phosphorylation and autophagic/mitophagic flux. These data demonstrate an important physiological role of AMPKβ1 Ser108 phosphorylation in promoting fatty acid oxidation, mitochondrial biogenesis and autophagy under conditions of high lipid availability. As both ketogenic diets and intermittent fasting increase circulating free fatty acid levels, AMPK activity, mitochondrial biogenesis, and mitophagy, these data suggest a potential unifying mechanism which may be important in mediating these effects.

Keywords:  AMPK; NAFLD; autophagy; fat oxidation; mitochondria

DOI:  https://doi.org/10.1073/pnas.2119824119