bims-moremu 2022-10-02 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2022–10–02
thirty-six papers selected by
Anna Vainshtein, Craft Science Inc.

Aging, Skeletal Muscle, and Epigenetics.
Actin maturation requires the ACTMAP/C19orf54 protease.
The fibrotic niche impairs satellite cell function and muscle regeneration in mouse models of Marfan syndrome.
miR-106b is a novel target to promote muscle regeneration and restore satellite stem cell function in injured Duchenne dystrophic muscle.
Loss of full-length dystrophin expression results in major cell-autonomous abnormalities in proliferating myoblasts.
FOXO signaling pathway in skeletal muscle atrophy.
Growth hormone/IGF-I-dependent signaling restores decreased expression of the myokine SPARC in aged skeletal muscle.
Exercise intervention mitigates zebrafish age-related sarcopenia via alleviating mitochondrial dysfunction.
(-)-Epicatechin modulates the expression of myomiRs implicated in exercise response in mouse skeletal muscle.
Antagonism Between DUX4 and DUX4c Highlights a Pathomechanism Operating Through β-Catenin in Facioscapulohumeral Muscular Dystrophy.
Phosphoproteomic mapping reveals distinct signaling actions and activation of muscle protein synthesis by Isthmin-1.
Urotensin receptor acts as a novel target for ameliorating fasting-induced skeletal muscle atrophy.
Assessing and enhancing migration of human myogenic progenitors using directed iPS cell differentiation and advanced tissue modelling.
The INSR/AKT/mTOR pathway regulates the pace of myogenesis in a syndecan-3-dependent manner.
Reduced adenosine diphosphate sensitivity in skeletal muscle mitochondria increases reactive oxygen species production in mouse models of aging and oxidative stress but not denervation.
FUS Mutation Causes Disordered Lipid Metabolism in Skeletal Muscle Associated with ALS.
Mitochondria-ER cooperation: NLRX1 detects mitochondrial protein import stress and promotes mitophagy through the ER protein RRBP1.
The non-modifiable factors age, gender, and genetics influence resistance exercise.
Proteomic features of skeletal muscle adaptation to resistance exercise training as a function of age.
Neuromuscular function in experimental disuse - a prime suspect?
Effects of Endurance Training on Metabolic Enzyme Activity and Transporter Proteins in Skeletal Muscle of Ovariectomized Mice.
Cancer cachexia as a multiorgan failure: Reconstruction of the crime scene.
Effects of Broad-spectrum Antibiotic Treatment or Germ-free Status on Endurance Performance and Exercise Adaptations in Mice.
Sex differences in the impact of resistance exercise load on muscle damage: A protocol for a randomised parallel group trial.
Target formation in muscle fibres indicates reinnervation - a proteomic study in muscle samples from peripheral neuropathies.
Single-cell RNA-seq reveals interferon-induced guanylate-binding proteins are linked with sarcopenia.
The role of the dystrophin glycoprotein complex in muscle cell mechanotransduction.
Loss of skeletal muscle mass is not specific to type 2 diabetes.
Simultaneous monitoring of mouse grip strength, force profile, and cumulative force profile distinguishes muscle physiology following surgical, pharmacologic and diet interventions.
Modulating Myogenesis: An Optimized In Vitro Assay to Pharmacologically Influence Primary Myoblast Differentiation.
Role of exosomes and exosomal microRNA in muscle-Kidney crosstalk in chronic kidney disease.
Retinoic acid and RARγ maintain satellite cell quiescence through regulation of translation initiation.
Age- and time-dependent mitochondrial genotoxic and myopathic effects of beta-guanidinopropionic acid, a creatine analog, on rodent skeletal muscles.
An interplay between BRD4 and G9a regulates skeletal myogenesis.
Antagonistic control of active surface integrins by myotubularin and phosphatidylinositol 3-kinase C2β in a myotubular myopathy model.
Megaconial congenital muscular dystrophy due to novel CHKB variants: a case report and literature review.

Plast Reconstr Surg. 2022 Oct 01. 150 27S-33S

Aging, Skeletal Muscle, and Epigenetics.

Claire E Stewart, Adam P Sharples.

SUMMARY: We are living in an aging society. In 2019, 1 billion individuals were already aged over 60. The number of people in this demographic is predicted to reach 1.4 billion by 2030 and 2.1 billion by 2050 (WHO). In the USA, individuals over 65 represent the fastest growing segment of the population (US census bureau). Similar trends are seen in the UK, with 16.2 million people already aged over 60, equivalent to 24% of the total population (Age UK; https://www.ageuk.org.uk/globalassets/age-uk/documents/reports-and-publications/later_life_uk_factsheet.pdf). Indeed, in the UK, people over the age of 60 outnumbered those under the age of 18, for the first time in 2008. This statistic still prevails today. Because of medical and biopharmaceutical progress, lifespan is increasing rapidly, but healthspan is failing to keep up. If we are to increase healthy living, then we need to begin to understand the mechanisms of how we age across the life course, so that relevant interventions may be developed to facilitate "life in our years," not simply "years in our life." It is reported that only 25% of aging is genetically predetermined. This fits with observations of some families aging very quickly and poorly and others aging slowly and well. If this is indeed the case and the rate of aging is not fixed, then this knowledge provides a significant opportunity to manipulate the impact of environmental influencers of age. With that in mind, it begs the question of what are the mechanisms of aging and is there potential to manipulate this process on an individual-by-individual basis? The focus of this article will be on the process of muscle wasting with aging (sarcopenia) and the potential of exercise and its underlying mechanisms to reverse or delay sarcopenia. There will be a focus on epigenetics in muscle wasting and the capability of exercise to change our skeletal muscle epigenetic profile for the good. The article ends with considerations relating to facial aging, Botox treatment, and gene editing as a tool for plastic surgeons in the future.

DOI: https://doi.org/10.1097/PRS.0000000000009670
Science. 2022 Sep 30. 377(6614): 1533-1537

Actin maturation requires the ACTMAP/C19orf54 protease.

Peter Haahr, Ricardo A Galli, Lisa G van den Hengel, Onno B Bleijerveld, Justina Kazokaitė-Adomaitienė, Ji-Ying Song, Lona J Kroese, Paul Krimpenfort, Marijke P Baltissen, Michiel Vermeulen, Coen A C Ottenheijm, Thijn R Brummelkamp.

Protein synthesis generally starts with a methionine that is removed during translation. However, cytoplasmic actin defies this rule because its synthesis involves noncanonical excision of the acetylated methionine by an unidentified enzyme after translation. Here, we identified C19orf54, named ACTMAP (actin maturation protease), as this enzyme. Its ablation resulted in viable mice in which the cytoskeleton was composed of immature actin molecules across all tissues. However, in skeletal muscle, the lengths of sarcomeric actin filaments were shorter, muscle function was decreased, and centralized nuclei, a common hallmark of myopathies, progressively accumulated. Thus, ACTMAP encodes the missing factor required for the synthesis of mature actin and regulates specific actin-dependent traits in vivo.

DOI: https://doi.org/10.1126/science.abq5082
Acta Physiol (Oxf). 2022 Sep 27. e13889

The fibrotic niche impairs satellite cell function and muscle regeneration in mouse models of Marfan syndrome.

Meiricris Tomaz da Silva, Audrei R Santos, Tatiana E Koike, Tabata L Nascimento, Andrei Rozanski, Darko Bosnakovski, Lygia V Pereira, Ashok Kumar, Michael Kyba, Elen H Miyabara.

   AIM: It has been suggested that the proliferation and early differentiation of myoblasts are impaired in Marfan syndrome (MFS) mice during muscle regeneration. However, the underlying cellular and molecular mechanisms remain poorly understood. Here, we investigated muscle regeneration in MFS mouse models by analyzing the influence of the fibrotic niche on satellite cell function.
METHODS: In vivo, ex-vivo and in vitro experiments were performed. In addition, we evaluated the effect of the pharmacological inhibition of fibrosis using Ang-(1-7) on regenerating skeletal muscles of MFS mice.
RESULTS: Skeletal muscle of MFS mice shows increased accumulation of collagen fibers (81.2%), number of fibroblasts (157.1%) and fibro-adipogenic progenitor cells (80.6%), and Smad2/3 signaling (110.5%), in response to injury compared with wild-type mice. There was an increased number of proinflammatory and anti-inflammatory macrophages (3.6 and 3.1-fold, respectively) in regenerating muscles of wild-type mice, but not in the regenerating muscles of MFS mice. Our data show that proliferation and differentiation of satellite cells are altered (p≤0.05) in MFS mice. Myoblast transplantation assay revealed that the regenerating muscles from MFS mice have reduced satellite cell self-renewal capacity (74.7%). In addition, we found that treatment with Ang-(1-7) reduces fibrosis (71.6%) and ameliorates satellite cell dysfunction (p≤0.05) and muscle contractile function (p≤0.05) in MFS mice.
CONCLUSION: The fibrotic niche, caused by Fbn1 mutations, reduces the myogenic potential of satellite cells, affecting structural and functional muscle regeneration. In addition, the fibrosis inhibitor Ang-(1-7) partially counteracts satellite cell abnormalities and restores myofiber size and contractile force in regenerating muscles.

Keywords:  Marfan syndrome; angiotensin-1-7; fibrosis; satellite cell function; skeletal muscle regeneration

DOI:  https://doi.org/10.1111/apha.13889
Mol Ther Nucleic Acids. 2022 Sep 13. 29 769-786

miR-106b is a novel target to promote muscle regeneration and restore satellite stem cell function in injured Duchenne dystrophic muscle.

Lara Rodriguez-Outeiriño, Francisco Hernandez-Torres, Felicitas Ramirez de Acuña, Alberto Rastrojo, Carlota Creus, Alejandra Carvajal, Luis Salmeron, Marisol Montolio, Patricia Soblechero-Martin, Virginia Arechavala-Gomeza, Diego Franco, Amelia Eva Aranega.

  Satellite cells (SCs), muscle stem cells, display functional heterogeneity, and dramatic changes linked to their regenerative capabilities are associated with muscle-wasting diseases. SC behavior is related to endogenous expression of the myogenic transcription factor MYF5 and the propensity to enter into the cell cycle. Here, we report a role for miR-106b reinforcing MYF5 inhibition and blocking cell proliferation in a subset of highly quiescent SC population. miR-106b down-regulation occurs during SC activation and is required for proper muscle repair. In addition, miR-106b is increased in dystrophic mice, and intramuscular injection of antimiR in injured mdx mice enhances muscle regeneration promoting transcriptional changes involved in skeletal muscle differentiation. miR-106b inhibition promotes the engraftment of human muscle stem cells. Furthermore, miR-106b is also high in human dystrophic muscle stem cells and its inhibition improves intrinsic proliferative defects and increases their myogenic potential. This study demonstrates that miR-106b is an important modulator of SC quiescence, and that miR-106b may be a new target to develop therapeutic strategies to promote muscle regeneration improving the regenerative capabilities of injured dystrophic muscle.

Keywords:  MT: Non-coding RNAs; miR-106b; muscle regeneration; muscular dystrophy; satellite cell; stemness

DOI:  https://doi.org/10.1016/j.omtn.2022.08.025
Elife. 2022 09 27. pii: e75521. [Epub ahead of print]11

Loss of full-length dystrophin expression results in major cell-autonomous abnormalities in proliferating myoblasts.

Maxime R F Gosselin, Virginie Mournetas, Malgorzata Borczyk, Suraj Verma, Annalisa Occhipinti, Justyna Róg, Lukasz Bozycki, Michal Korostynski, Samuel C Robson, Claudio Angione, Christian Pinset, Dariusz C Gorecki.

  Duchenne muscular dystrophy (DMD) affects myofibers and muscle stem cells, causing progressive muscle degeneration and repair defects. It was unknown whether dystrophic myoblasts-the effector cells of muscle growth and regeneration-are affected. Using transcriptomic, genome-scale metabolic modelling and functional analyses, we demonstrate, for the first time, convergent abnormalities in primary mouse and human dystrophic myoblasts. In Dmdmdx myoblasts lacking full-length dystrophin, the expression of 170 genes was significantly altered. Myod1 and key genes controlled by MyoD (Myog, Mymk, Mymx, epigenetic regulators, ECM interactors, calcium signalling and fibrosis genes) were significantly downregulated. Gene ontology analysis indicated enrichment in genes involved in muscle development and function. Functionally, we found increased myoblast proliferation, reduced chemotaxis and accelerated differentiation, which are all essential for myoregeneration. The defects were caused by the loss of expression of full-length dystrophin, as similar and not exacerbated alterations were observed in dystrophin-null Dmdmdx-βgeo myoblasts. Corresponding abnormalities were identified in human DMD primary myoblasts and a dystrophic mouse muscle cell line, confirming the cross-species and cell-autonomous nature of these defects. The genome-scale metabolic analysis in human DMD myoblasts showed alterations in the rate of glycolysis/gluconeogenesis, leukotriene metabolism, and mitochondrial beta-oxidation of various fatty acids. These results reveal the disease continuum: DMD defects in satellite cells, the myoblast dysfunction affecting muscle regeneration, which is insufficient to counteract muscle loss due to myofiber instability. Contrary to the established belief, our data demonstrate that DMD abnormalities occur in myoblasts, making these cells a novel therapeutic target for the treatment of this lethal disease.

Keywords:  DMD; dystrophin; human; mdx; medicine; mouse; myoblast; transcriptomics

DOI:  https://doi.org/10.7554/eLife.75521
Am J Pathol. 2022 Sep 26. pii: S0002-9440(22)00286-3. [Epub ahead of print]

FOXO signaling pathway in skeletal muscle atrophy.

Kun Chen, Peng Gao, Zongchao Li, Aonan Dai, Ming Yang, Siyu Chen, Jingyue Su, Zhenhan Deng, Liangjun Li.

  Skeletal muscle atrophy is the consequence of protein degradation exceeding protein synthesis due to disease, aging and physical inactivity. Patients with skeletal muscle atrophy have decreased muscle mass and fiber cross-sectional area, thereby suffering reduced survival quality and motor function. The forkhead box O (FOXO) signaling pathway plays an important role in the pathogenesis of skeletal muscle atrophy by regulating E3 ubiquitin ligases and some autophagy factors. However, the mechanism of FOXO signaling pathway leading to skeletal muscle atrophy is still unclear and needs to be further explored. The development of treatment strategies for skeletal muscle atrophy has been a thorny clinical problem. FOXO-targeted therapy to treat skeletal muscle atrophy is a promising approach, and an increasing number of relevant studies have been reported. In this paper, we reviewed the mechanism and therapeutic targets of the FOXO signaling pathway mediating skeletal muscle atrophy, and provided some new ideas for the clinical treatment of this condition.

Keywords:  Atrogin-1; FOXO signaling pathway; IGF-1/PI3K/AKT signaling pathway; MuRF-1; skeletal muscle atrophy

DOI:  https://doi.org/10.1016/j.ajpath.2022.09.003
J Mol Med (Berl). 2022 Sep 30.

Growth hormone/IGF-I-dependent signaling restores decreased expression of the myokine SPARC in aged skeletal muscle.

Sebastian Mathes, Alexandra Fahrner, Edlira Luca, Jan Krützfeldt.

  Skeletal muscle exerts many beneficial effects on the human body including the contraction-dependent secretion of peptides termed myokines. We have recently connected the myokine secreted protein acidic and rich in cysteine (SPARC) to the formation of intramuscular adipose tissue (IMAT) in skeletal muscle from aged mice and humans. Here, we searched for inducers of SPARC in order to uncover novel treatment approaches for IMAT. Endurance exercise in mice as well as forskolin treatment in vitro only modestly activated SPARC levels. However, through pharmacological treatments in vitro, we identified IGF-I as a potent inducer of SPARC expression in muscle cells, likely through a direct activation of its promoter via phosphatidylinositol 4,5-bisphospate 3-kinase (PI3K)-dependent signaling. We employed two different mouse models of growth hormone (GH)/IGF-I deficiency to solidify our understanding of the relationship between IGF-I and SPARC in vivo. GH administration robustly increased intramuscular SPARC levels (3.5-fold) in GH releasing hormone receptor-deficient mice and restored low intramuscular SPARC expression in skeletal muscle from aged mice. Intramuscular glycerol injections induced higher levels of adipocyte markers (adiponectin, perilipin) in aged compared to young mice, which was not prevented by GH treatment. Our study provides a roadmap for the study of myokine regulation during aging and demonstrates that the GH/IGF-I axis is critical for SPARC expression in skeletal muscle. Although GH treatment did not prevent IMAT formation in the glycerol model, targeting SPARC by exercise or by activation of IGF-I signaling might offer a novel therapeutic strategy against IMAT formation during aging. KEY MESSAGES : IGF-I regulates the myokine SPARC in muscle cells directly at the promoter level. GH/IGF-I is able to restore the decreased SPARC levels in aged skeletal muscle. The glycerol model induces higher adipocyte markers in aged compared to young muscle. GH treatment does not prevent IMAT formation in the glycerol model.

Keywords:  Aging; Growth hormone; IGF-I; IMAT; SPARC; Skeletal muscle

DOI:  https://doi.org/10.1007/s00109-022-02260-w
FEBS J. 2022 Sep 27.

Exercise intervention mitigates zebrafish age-related sarcopenia via alleviating mitochondrial dysfunction.

Chen-Chen Sun, Dong Yang, Zhang-Lin Chen, Jiang-Ling Xiao, Qin Xiao, Cheng-Li Li, Zuo-Qiong Zhou, Xi-Yang Peng, Chang Fa Tang.

  Sarcopenia is a common disorder that leads to a progressive decrease in skeletal muscle function in elderly people. Exercise effectively prevents or delays the onset and progression of sarcopenia. However, the molecular mechanisms underlying how exercise intervention improves skeletal muscle atrophy remain unclear. In this study, we found that 21-month-old zebrafish had a decreased swimming ability, reduced muscle fiber cross-sectional area, unbalanced protein synthesis, and degradation, increased oxidative stress, and mitochondrial dysfunction, which suggests zebrafish are a valuable model for sarcopenia. Eight weeks of exercise intervention attenuated these pathological changes in sarcopenia zebrafish. Moreover, the effects of exercise on mitochondrial dysfunction were associated with the activation of the AMPK/SIRT1/PGC-1α axis and 15-PGDH downregulation. Our results reveal potential therapeutic targets and indicators to treat age-related sarcopenia using exercise intervention.

Keywords:  15-PGDH; AMPK/SIRT1/PGC-1α; Exercise; Mitochondrial Homeostasis; Sarcopenia

DOI:  https://doi.org/10.1111/febs.16637
Gene. 2022 Sep 26. pii: S0378-1119(22)00727-2. [Epub ahead of print] 146907

(-)-Epicatechin modulates the expression of myomiRs implicated in exercise response in mouse skeletal muscle.

Carlos Palma-Flores, Paola B Zárate-Segura, José Manuel Hernández-Hernández, Sergio de Los Santos, Andrea S Tejeda-Gómez, Luis Javier Cano-Martínez, Patricia Canto, Jorge Omar Garcia-Rebollar, Ramón M Coral-Vázquez.

  The flavanol (-)-epicatechin has exercise-mimetic properties. Besides, several miRNAs play a role in modulating the adaptation of the muscle to different training protocols. However, notwithstanding all information, few studies aimed to determine if (-)-epicatechin can modify the expression of miRNAs related to skeletal muscle development and regeneration. Mice were treated for fifteen days by oral gavage with the flavanol (-)-epicatechin. After treatment, the quadriceps of the mice was dissected, and total RNA was extracted. The expression level of miR-133, -204, -206, -223, -486, and -491 was analyzed by qRT-PCR. We also used bioinformatic analysis to predict the participation of these miRNAs in different skeletal muscle signal transduction pathways. Additionally, we analyzed the level of the myogenic proteins MyoD and myogenin by Western blot and measured the cross-sectional area of muscle fibers stained with E&H. (-)-Epicatechin upregulated the expression of miR-133, -204, -206, -223, and -491 significantly, which was associated with an increase in the level of the myogenic proteins MyoD and Myogenin and an augment in the fiber size. The bioinformatics analysis showed that the studied miRNAs might participate in different signal transduction pathways related to muscle development and adaptation. Our results showed that (-)-epicatechin upregulated miRNAs that participate in skeletal exercise muscle adaptation, induced muscle hypertrophy, and increased the level of myogenic proteins MyoD and MyoG.

Keywords:  (−)-epicatechin; MyoD; Myogenin; hypertrophy; myomiRs; skeletal Muscle

DOI:  https://doi.org/10.1016/j.gene.2022.146907
Front Cell Dev Biol. 2022 ;10 802573

Antagonism Between DUX4 and DUX4c Highlights a Pathomechanism Operating Through β-Catenin in Facioscapulohumeral Muscular Dystrophy.

Massimo Ganassi, Nicolas Figeac, Magalie Reynaud, Huascar Pedro Ortuste Quiroga, Peter S Zammit.

  Aberrant expression of the transcription factor DUX4 from D4Z4 macrosatellite repeats on chromosome 4q35, and its transcriptome, associate with pathogenesis in facioscapulohumeral muscular dystrophy (FSHD). Forced DUX4 expression halts skeletal muscle cell proliferation and induces cell death. DUX4 binds DNA via two homeodomains that are identical in sequence to those of DUX4c (DUX4L9): a closely related transcriptional regulator encoded by a single, inverted, mutated D4Z4 unit located centromeric to the D4Z4 macrosatellite array on chromosome 4. However, the function and contribution of DUX4c to FSHD pathogenesis are unclear. To explore interplay between DUX4, DUX4c, and the DUX4-induced phenotype, we investigated whether DUX4c interferes with DUX4 function in human myogenesis. Constitutive expression of DUX4c rescued the DUX4-induced inhibition of proliferation and reduced cell death in human myoblasts. Functionally, DUX4 promotes nuclear translocation of β-CATENIN and increases canonical WNT signalling. Concomitant constitutive expression of DUX4c prevents β-CATENIN nuclear accumulation and the downstream transcriptional program. DUX4 reduces endogenous DUX4c levels, whereas constitutive expression of DUX4c robustly suppresses expression of DUX4 target genes, suggesting molecular antagonism. In line, DUX4 expression in FSHD myoblasts correlates with reduced DUX4c levels. Addressing the mechanism, we identified a subset of genes involved in the WNT/β-CATENIN pathway that are differentially regulated between DUX4 and DUX4c, whose expression pattern can separate muscle biopsies from severely affected FSHD patients from healthy. Finally, blockade of WNT/β-CATENIN signalling rescues viability of FSHD myoblasts. Together, our study highlights an antagonistic interplay whereby DUX4 alters cell viability via β-CATENIN signalling and DUX4c counteracts aspects of DUX4-mediated toxicity in human muscle cells, potentially acting as a gene modifier for FSHD severity. Importantly, direct DUX4 regulation of the WNT/β-CATENIN pathway informs future therapeutic interventions to ameliorate FSHD pathology.

Keywords:  DUX4; DUX4L9; DUX4c; FSHD; WNT signalling; facioscapulohumeral muscular dystrophy; proliferation; β-CATENIN

DOI:  https://doi.org/10.3389/fcell.2022.802573
Elife. 2022 Sep 28. pii: e80014. [Epub ahead of print]11

Phosphoproteomic mapping reveals distinct signaling actions and activation of muscle protein synthesis by Isthmin-1.

Meng Zhao, Niels Banhos Dannieskiold-Samsøe, Livia Ulicna, Quennie Nguyen, Laetitia Voilquin, David E Lee, James P White, Zewen Jiang, Nickeisha Cuthbert, Shrika Paramasivam, Ewa Bielczyk-Maczynska, Capucine Van Rechem, Katrin J Svensson.

  The secreted protein Isthmin-1 (Ism1) mitigates diabetes by increasing adipocyte and skeletal muscle glucose uptake by activating the PI3K-Akt pathway. However, while both Ism1 and insulin converge on these common targets, Ism1 has distinct cellular actions suggesting divergence in downstream intracellular signaling pathways. To understand the biological complexity of Ism1 signaling, we performed phosphoproteomic analysis after acute exposure, revealing overlapping and distinct pathways of Ism1 and insulin. We identify a 53 % overlap between Ism1 and insulin signaling and Ism1-mediated phosphoproteome-wide alterations in ~ 450 proteins that are not shared with insulin. Interestingly, we find several unknown phosphorylation sites on proteins related to protein translation, mTOR pathway and, unexpectedly, muscle function in the Ism1 signaling network. Physiologically, Ism1 ablation in mice results in altered proteostasis, including lower muscle protein levels under fed and fasted conditions, reduced amino acid incorporation into proteins, and reduced phosphorylation of the key protein synthesis effectors Akt and downstream mTORC1 targets. As metabolic disorders such as diabetes are associated with accelerated loss of skeletal muscle protein content, these studies define a non-canonical mechanism by which this anti-diabetic circulating protein controls muscle biology.

Keywords:  cell biology; mouse

DOI:  https://doi.org/10.7554/eLife.80014
Pharmacol Res. 2022 Sep 24. pii: S1043-6618(22)00414-5. [Epub ahead of print] 106468

Urotensin receptor acts as a novel target for ameliorating fasting-induced skeletal muscle atrophy.

Lin Yin, Na Li, Weihua Jia, Nuoqi Wang, Meidai Liang, Jiamin Shang, Guifen Qiang, Guanhua Du, Xiuying Yang.

  Urotensin receptor (UT) is a G-protein-coupled receptor, whose endogenous ligand is urotensin-II (U-II). Skeletal muscle mass is regulated by various conditions, such as nutritional status, exercise, and diseases. Previous studies have pointed out that the urotensinergic system is involved in skeletal muscle metabolism and function, but its mechanism remains unclear, especially given the lack of research on the effect and mechanism of fasting. In this study, UT receptor knockout mice were generated to evaluate whether UT has effects on fasting induced skeletal muscle atrophy. Furthermore, the UT antagonist palosuran (3, 10, 30mg/kg) was intraperitoneally administered daily for 5 days to clarify the therapeutic effect of UT antagonism. Our results found the mice that fasted for 48hours exhibited skeletal muscle atrophy, accompanied by enhanced U-II levels in both skeletal muscles and blood. UT receptor knockout effectively prevented fasting-induced skeletal muscle atrophy. The UT antagonist ameliorated fasting-induced muscle atrophy in mice as determined by increased muscle strengths, weights, and muscle fiber areas (including fast, slow, and mixed types). In addition, the UT antagonist reduced skeletal muscle atrophic markers, including F-box only protein 32 (FBXO32) and tripartite motif containing 63 (TRIM63). Moreover, the UT antagonist was also observed to enhance PI3K/AKT/mTOR while inhibiting autophagy signaling. In summary, our study provides the first evidence that UT antagonism may represent a novel therapeutic approach for the treatment of fasting-induced skeletal muscle atrophy.

Keywords:  Urotensin-II; fasting; palosuran; skeletal muscle atrophy; urotensin receptor

DOI:  https://doi.org/10.1016/j.phrs.2022.106468
EMBO Mol Med. 2022 Sep 26. e14526

Assessing and enhancing migration of human myogenic progenitors using directed iPS cell differentiation and advanced tissue modelling.

SungWoo Choi, Giulia Ferrari, Louise A Moyle, Kirsty Mackinlay, Naira Naouar, Salma Jalal, Sara Benedetti, Christine Wells, Francesco Muntoni, Francesco Saverio Tedesco.

  Muscle satellite stem cells (MuSCs) are responsible for skeletal muscle growth and regeneration. Despite their differentiation potential, human MuSCs have limited in vitro expansion and in vivo migration capacity, limiting their use in cell therapies for diseases affecting multiple skeletal muscles. Several protocols have been developed to derive MuSC-like progenitors from human induced pluripotent stem (iPS) cells (hiPSCs) to establish a source of myogenic cells with controllable proliferation and differentiation. However, current hiPSC myogenic derivatives also suffer from limitations of cell migration, ultimately delaying their clinical translation. Here we use a multi-disciplinary approach including bioinformatics and tissue engineering to show that DLL4 and PDGF-BB improve migration of hiPSC-derived myogenic progenitors. Transcriptomic analyses demonstrate that this property is conserved across species and multiple hiPSC lines, consistent with results from single cell motility profiling. Treated cells showed enhanced trans-endothelial migration in transwell assays. Finally, increased motility was detected in a novel humanised assay to study cell migration using 3D artificial muscles, harnessing advanced tissue modelling to move hiPSCs closer to future muscle gene and cell therapies.

Keywords:  cell migration; cell therapy; iPS cells; muscular dystrophy; tissue engineering

DOI:  https://doi.org/10.15252/emmm.202114526
Matrix Biol. 2022 Sep 21. pii: S0945-053X(22)00116-0. [Epub ahead of print]

The INSR/AKT/mTOR pathway regulates the pace of myogenesis in a syndecan-3-dependent manner.

Fiona K Jones, Alexander Phillips, Andrew R Jones, Addolorata Pisconti.

  Muscle stem cells (MuSCs) are indispensable for muscle regeneration. A multitude of extracellular stimuli direct MuSC fate decisions from quiescent progenitors to differentiated myocytes. The activity of these signals is modulated by coreceptors such as syndecan-3 (SDC3). We investigated the global landscape of SDC3-mediated regulation of myogenesis using a phosphoproteomics approach which revealed, with the precision level of individual phosphosites, the large-scale extent of SDC3-mediated regulation of signal transduction in MuSCs. We then focused on INSR/AKT/mTOR as a key pathway regulated by SDC3 during myogenesis and mechanistically dissected SDC3-mediated inhibition of insulin receptor signaling in MuSCs. SDC3 interacts with INSR ultimately limiting signal transduction via AKT/mTOR. Both knockdown of INSR and inhibition of AKT rescue Sdc3-/- MuSC differentiation to wild type levels. Since SDC3 is rapidly downregulated at the onset of differentiation, our study suggests that SDC3 acts a timekeeper to restrain proliferating MuSC response and prevent premature differentiation.

Keywords:  AKT; Muscle stem cell; differentiation; insulin signaling; mTOR; proteoglycan

DOI:  https://doi.org/10.1016/j.matbio.2022.09.004
JCSM Rapid Commun. 2021 Jan-Jun;4(1):4(1): 75-89

Reduced adenosine diphosphate sensitivity in skeletal muscle mitochondria increases reactive oxygen species production in mouse models of aging and oxidative stress but not denervation.

Gavin Pharaoh, Jacob Brown, Rojina Ranjit, Zoltan Ungvari, Holly Van Remmen.

   Background: Mitochondrial bioenergetics are sensitive to adenosine diphosphate (ADP) concentration. Reactive oxygen species (ROS) production and respiration [oxygen consumption rate (OCR)] are altered at physiological ADP concentrations (i.e. ADP insensitivity) in aged human muscle. Here, we investigate ADP sensitivity in mouse muscle mitochondria.
Methods: We measured OCR and ROS production in permeabilized gastrocnemius fibres using an ADP titration protocol and the Oroboros O2k respirometer and fluorometer. We measured changes in ADP sensitivity in muscle from mice at different ages, after sciatic nerve transection (denervation), and in response to increased oxidative stress (Sod1 -/- mice). Further, we asked whether the mitochondrial-targeted peptide SS-31 can modulate ADP insensitivity and contractile function in the Sod1 -/- mouse model.
Results: Reduced ADP sensitivity is associated with increases in mitochondrial ROS production in aged (62%) and Sod1 -/- (33%) mice. The maximal capacity to produce ROS does not increase with age, and there is no effect of age on ADP sensitivity for OCR in mouse gastrocnemii. Denervation does not induce ADP insensitivity for either ROS generation or OCR. Treatment of Sod1 -/- mice with SS-31 increases ADP sensitivity for both OCR and ROS, decreases maximal ROS production (~40%), and improves resistance to muscle fatigue.
Conclusions: Adenosine diphosphate sensitivity for ROS production decreases in aged mouse gastrocnemius muscle fibres, although aged mice do not exhibit a difference in OCR. Denervation does not induce ADP insensitivity; however, insensitivity to ADP is induced in a model of oxidative stress. ADP insensitivity could contribute to muscle fatigue, and SS-31 may be the first drug capable of targeting this aging phenotype.

Keywords:  ADP sensitivity; Mitochondria; Oroboros O2k respirometry and fluorometry; Reactive oxygen species (ROS) production; Sarcopenia

DOI:  https://doi.org/10.1002/rco2.29
Mol Neurobiol. 2022 Sep 28.

FUS Mutation Causes Disordered Lipid Metabolism in Skeletal Muscle Associated with ALS.

Binbin Zhou, Yilei Zheng, Xiaobing Li, Huifang Dong, Jiaxi Yu, Yang Zou, Min Zhu, Yanyan Yu, Xin Fang, Meihong Zhou, Wei Zhang, Yun Yuan, Zhaoxia Wang, Jianwen Deng, Daojun Hong.

  Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by dysfunction of the upper and lower motor neurons resulting in muscle weakness and wasting. Recently, several studies on ALS patients and ALS animal models indicated that intramuscular toxicity played a role in ALS disease progression; however, the mechanisms driving this are unknown. In this study, we explored the possible dysfunction of lipid metabolism in myocytes associated with ALS. Initially, skeletal muscle from 41 ALS patients, as well as 53 non-ALS control subjects, was investigated, and we identified that lipid droplet accumulation in the muscle fibers of ALS patients was significantly increased, especially in patients with FUS mutations. A myoblast (C2C12) cell line expressing mutant FUS (FUS-K510Q) was able to induce lipid droplet accumulation and mitochondrial dysfunction. Consistently, transgenic flies expressing FUS-K510Q under a muscle-specific driver showed elevated triglyceride levels in the flight muscles, as well as locomotor defects. Biochemical analysis of C2C12 cells and fly muscle tissues showed upregulation of PLIN2, and downregulation of ATGL and CPT1A, indicating inhibition of lipolysis and fatty acid β-oxidation in muscle cells with FUS mutations. Our study provided a potential explanation for the pathogenesis associated with lipid droplets accumulating in skeletal muscle in ALS. Our data also suggested that disordered lipid metabolism and mitochondrial dysfunction play a crucial role in intramuscular toxicity in ALS.

Keywords:  Amyotrophic laterals sclerosis; Fused in sarcoma; Lipid metabolism; Mitochondrial dysfunction; Skeletal muscle

DOI:  https://doi.org/10.1007/s12035-022-03048-2
Autophagy. 2022 Sep 28.

Mitochondria-ER cooperation: NLRX1 detects mitochondrial protein import stress and promotes mitophagy through the ER protein RRBP1.

Samuel A Killackey, Yuntian Bi, Dana J Philpott, Damien Arnoult, Stephen E Girardin.

  Mitochondria rely on efficient protein import across their membranes for optimal function. We have shown that numerous mitochondrial stressors all converge on a common pathway disrupting this import efficiency. We identified a novel pathway involving NLRX1 and RRBP1 that responds to this import stress, resulting in LC3 lipidation, mitochondrial targeting and ultimate degradation. Furthermore, we demonstrated the relevance of this mitophagy axis in murine skeletal muscle following acute exercise. We propose that mitochondrial protein import stress is an underlying, common trigger for mitophagy, offering a novel avenue for therapeutic exploration and mechanistic insight.

Keywords:  Autophagy; NLR; exercise; import; mitochondria; mitophagy; proteostasis

DOI:  https://doi.org/10.1080/15548627.2022.2129763
Front Aging. 2022 ;3 1005848

The non-modifiable factors age, gender, and genetics influence resistance exercise.

Claudio Viecelli, Collin Y Ewald.

  Muscle mass and force are key for movement, life quality, and health. It is well established that resistance exercise is a potent anabolic stimulus increasing muscle mass and force. The response of a physiological system to resistance exercise is composed of non-modifiable (i.e., age, gender, genetics) and modifiable factors (i.e., exercise, nutrition, training status, etc.). Both factors are integrated by systemic responses (i.e., molecular signaling, genetic responses, protein metabolism, etc.), consequently resulting in functional and physiological adaptations. Herein, we discuss the influence of non-modifiable factors on resistance exercise: age, gender, and genetics. A solid understanding of the role of non-modifiable factors might help to adjust training regimes towards optimal muscle mass maintenance and health.

Keywords:  age; gender; genetics; modifier; resistance exercise

DOI:  https://doi.org/10.3389/fragi.2022.1005848
Geroscience. 2022 Sep 26.

Proteomic features of skeletal muscle adaptation to resistance exercise training as a function of age.

Colleen S Deane, Bethan E Phillips, Craig R G Willis, Daniel J Wilkinson, Ken Smith, Nahoko Higashitani, John P Williams, Nathaniel J Szewczyk, Philip J Atherton, Atsushi Higashitani, Timothy Etheridge.

  Resistance exercise training (RET) can counteract negative features of muscle ageing but older age associates with reduced adaptive capacity to RET. Altered muscle protein networks likely contribute to ageing RET adaptation; therefore, associated proteome-wide responses warrant exploration. We employed quantitative sarcoplasmic proteomics to compare age-related proteome and phosphoproteome responses to RET. Thigh muscle biopsies were collected from eight young (25 ± 1.1 years) and eight older (67.5 ± 2.6 years) adults before and after 20 weeks supervised RET. Muscle sarcoplasmic fractions were pooled for each condition and analysed using Isobaric Tags for Relative and Absolute Quantification (iTRAQ) labelling, tandem mass spectrometry and network-based hub protein identification. Older adults displayed impaired RET-induced adaptations in whole-body lean mass, body fat percentage and thigh lean mass (P > 0.05). iTRAQ identified 73 differentially expressed proteins with age and/or RET. Despite possible proteomic stochasticity, RET improved ageing profiles for mitochondrial function and glucose metabolism (top hub; PYK (pyruvate kinase)) but failed to correct altered ageing expression of cytoskeletal proteins (top hub; YWHAZ (14-3-3 protein zeta/delta)). These ageing RET proteomic profiles were generally unchanged or oppositely regulated post-RET in younger muscle. Similarly, RET corrected expression of 10 phosphoproteins altered in ageing, but these responses were again different vs. younger adults. Older muscle is characterised by RET-induced metabolic protein profiles that, whilst not present in younger muscle, improve untrained age-related proteomic deficits. Combined with impaired cytoskeletal adhesion responses, these results provide a proteomic framework for understanding and optimising ageing muscle RET adaptation.

Keywords:  Ageing; Hub protein; Network analysis; Phosphoproteome; Proteomics

DOI:  https://doi.org/10.1007/s11357-022-00658-5
J Physiol. 2022 Sep 26.

Neuromuscular function in experimental disuse - a prime suspect?

Casper Soendenbroe.



Keywords:  denervation; disuse; muscle function; neuromuscular

DOI:  https://doi.org/10.1113/JP283800
Med Sci Sports Exerc. 2022 Sep 28.

Effects of Endurance Training on Metabolic Enzyme Activity and Transporter Proteins in Skeletal Muscle of Ovariectomized Mice.

Kenya Takahashi, Yu Kitaoka, Yutaka Matsunaga, Hideo Hatta.

PURPOSE: Estrogen deficiency or insufficiency can occur under several conditions, leading to negative health outcomes. To establish an effective countermeasure against estrogen loss, we investigated the effects of endurance training on ovariectomy (OVX)-induced metabolic disturbances.
METHODS: Female ICR mice underwent OVX or sham operations. On day 7 of recovery, the mice were randomized to remain either sedentary or undergo 5 weeks of treadmill running (15-20 m/min, 60 min, 5 days/week). During week 5 of the training, all animals performed a treadmill running test (15 m/min, 60 min).
RESULTS: Following the experimental period, OVX resulted in greater gains in body mass, fat mass, and triglyceride content in the gastrocnemius muscle. OVX enhanced phosphofructokinase activity in the plantaris muscle and decreased lactate dehydrogenase (LDH) activity in the plantaris and soleus muscles. OVX decreased the protein content of NDUFB8, a mitochondrial respiratory chain subunit, but did not decrease the activities of other mitochondrial proteins or enzymes. Endurance training significantly enhanced mitochondrial enzyme activity and protein content in the skeletal muscles. While OVX increased the respiratory exchange ratio during the treadmill running test, and post-exercise blood lactate levels, endurance training normalized these parameters.
CONCLUSIONS: The present findings suggest that endurance training is a viable strategy to counteract the negative metabolic consequences in hypoestrogenism.

DOI: https://doi.org/10.1249/MSS.0000000000003045
Front Cell Dev Biol. 2022 ;10 960341

Cancer cachexia as a multiorgan failure: Reconstruction of the crime scene.

Michele Ferrara, Maria Samaden, Elena Ruggieri, Emilie Vénéreau.

  Cachexia is a devastating syndrome associated with the end-stage of several diseases, including cancer, and characterized by body weight loss and severe muscle and adipose tissue wasting. Although different cancer types are affected to diverse extents by cachexia, about 80% of all cancer patients experience this comorbidity, which highly reduces quality of life and response to therapy, and worsens prognosis, accounting for more than 25% of all cancer deaths. Cachexia represents an urgent medical need because, despite several molecular mechanisms have been identified, no effective therapy is currently available for this devastating syndrome. Most studies focus on skeletal muscle, which is indeed the main affected and clinically relevant organ, but cancer cachexia is characterized by a multiorgan failure. In this review, we focus on the current knowledge on the multiple tissues affected by cachexia and on the biomarkers with the attempt to define a chronological pathway, which might be useful for the early identification of patients who will undergo cachexia. Indeed, it is likely that the inefficiency of current therapies might be attributed, at least in part, to their administration in patients at the late stages of cachexia.

Keywords:  adipose tissue; brain; cancer cachexia; gut; immune system; liver; pancreas; skeletal muscle

DOI:  https://doi.org/10.3389/fcell.2022.960341
Med Sci Sports Exerc. 2022 Sep 28.

Effects of Broad-spectrum Antibiotic Treatment or Germ-free Status on Endurance Performance and Exercise Adaptations in Mice.

Noah T Hutchinson, Selena S Wang, Jack Dokhanchi, Rodney W Johnson, Thomas W Buford, Jacob M Allen, Jeffrey A Woods.

PURPOSE: Endurance exercise alters the gut microbiome independently of diet. The extent to which gut microbes are responsible for physiologic adaptations to exercise training is unknown. The purpose of these experiments was to determine the role of gut microbes in performance and muscle adaptation to six weeks of voluntary wheel running (VWR) in mice.
METHODS: We depleted microbes with broad-spectrum antibiotic treatment (ABX) and used germ-free (GF) mice to determine effects on adaptations to VWR. Male and female C57Bl/6 mice (n = 56) were assigned to daily VWR or sedentary conditions. After the intervention, treadmill endurance and glucose tolerance were assessed, and gastrocnemius and soleus tissues were harvested and analyzed for citrate synthase (CS) enzyme activity and expression of exercise training-sensitive genes.
RESULTS: ABX treatment and GF status resulted in VWR volumes ~22% and 26% lower than controls, respectively. Analysis of variance revealed that while VWR increased treadmill endurance, ABX had no effect. GF status significantly reduced treadmill performance in trained GF mice post-training. VWR increased gastrocnemius CS enzyme activity in all groups, and ABX and GF status did not reduce the VWR effect. VWR also increased muscle expression of PGC1a, but this was not affected by ABX treatment.
CONCLUSIONS: ABX treatment and GF status reduced VWR behavior but did not affect VWR-induced adaptations in endurance capacity, CS activity, or expression of muscle metabolic genes. However, GF status reduced endurance capacity. These data indicated that reducing microbes in adulthood does not inhibit endurance-training adaptations in C57Bl/6 mice, but that GF mice possess a reduced responsiveness to endurance exercise training, perhaps due to a developmental defect associated with lack of microbes from birth.

DOI: https://doi.org/10.1249/MSS.0000000000003051
PLoS One. 2022 ;17(9): e0275221

Sex differences in the impact of resistance exercise load on muscle damage: A protocol for a randomised parallel group trial.

Alice G Pearson, Lindsay S Macnaughton, Karen Hind.

INTRODUCTION: Resistance training can induce skeletal muscle hypertrophy and strength gains, but is also associated with acute muscle damage, characterised by muscle soreness, impaired muscle function, and structural damage to muscle cell membranes and its components. These consequences can be detrimental to future exercise performance and dampen long-term training adaptations. Previous research has considered resistance exercise intensity as a factor in exercise-induced muscle damage (EIMD), though a clear direction of the findings has not yet been established. Further, female populations are heavily underrepresented in this field of study. Therefore, we here propose a study protocol designed to examine sex differences in the muscle damage response to resistance exercise performed with low or high loads in a population of untrained, young adults.
METHODS: This study will employ a randomised parallel group design. Twenty-four males and 24 females will perform an acute leg-based resistance exercise session at either 30% (low-load) or 80% (high-load) of their pre-determined one-repetition maximum (1RM). Maximal leg strength will be determined by a 1RM test 3 wk before and 72 and 168 h after the exercise bout. Additionally, muscle damage will be assessed immediately before the exercise bout and immediately, 24, 48, 72, and 168 h after the exercise bout through measures of muscle soreness, limb circumference, range of motion, and serum concentrations of creatine kinase and interleukin-6. The outcomes of this trial could inform sex-specific resistance training recommendations and help bridge the sex data gap in sport and exercise science research.

DOI: https://doi.org/10.1371/journal.pone.0275221
Neuropathol Appl Neurobiol. 2022 Sep 30. e12853

Target formation in muscle fibres indicates reinnervation - a proteomic study in muscle samples from peripheral neuropathies.

Karsten Krause, Britta Eggers, Julian Uszkoreit, Stefan Eulitz, Robert Rehmann, Anne K Güttsches, Anja Schreiner, Peter F M van der Ven, Dieter O Fürst, Katrin Marcus, Matthias Vorgerd, Rudolf A Kley.

   AIMS: Target skeletal muscle fibres - defined by different concentric areas in oxidative enzyme staining - can occur in patients with neurogenic muscular atrophy. Here, we used our established hypothesis-free proteomic approach with the aim to decipher the protein composition of targets. We also searched for potential novel interactions between target proteins.
METHODS: Targets and control areas were laser microdissected from skeletal muscle sections of 20 patients with neurogenic muscular atrophy. Samples were analysed by a highly sensitive mass spectrometry approach enabling a relative protein quantification. Results were validated by immunofluorescence studies. Protein interactions were investigated by yeast two-hybrid assays, coimmunoprecipitation experiments and bimolecular fluorescence complementation.
RESULTS: More than 1,000 proteins were identified. Among these, 55 proteins were significantly over-represented and 40 proteins significantly under-represented in targets compared to intraindividual control samples. The majority of over-represented proteins was associated with the myofibrillar Z-disc and actin dynamics, followed by myosin and myosin-associated proteins, proteins involved in protein biosynthesis, and chaperones. Under-represented proteins were mainly mitochondrial proteins. Functional studies revealed that the LIM domain of the over-represented protein LIMCH1 interacts with isoform A of Xin actin-binding repeat-containing protein 1 (XinA).
CONCLUSIONS: Especially proteins involved in myofibrillogenesis are over-represented in target structures, which indicates an ongoing process of sarcomere assembly and/or remodelling within this specific area of the muscle fibres. We speculate that target structures are the result of reinnervation processes in which filamin C-associated myofibrillogenesis is tightly regulated by the BAG3-associated protein quality system.

Keywords:  Filamins; LIMCH1; Laser microdissection; Mass spectrometry; Proteomics; Reinnervation; Skeletal muscle; Target fibre

DOI:  https://doi.org/10.1111/nan.12853
J Cachexia Sarcopenia Muscle. 2022 Sep 26.

Single-cell RNA-seq reveals interferon-induced guanylate-binding proteins are linked with sarcopenia.

Zhi Peng, Ruoyu Zhang, Xiaolin Kuang, Chen Yu, Shiwei Niu, Yongjun Du, Di Lu, Shaobo Li, Zhaowei Teng, Sheng Lu.

   BACKGROUND: Sarcopenia is defined as an age-related progressive loss of muscle mass and/or strength. Although different factors can contribute to this disease, the underlying mechanisms remain unclear. We assessed transcriptional heterogeneity in skeletal muscles from sarcopenic and control mice at single-cell resolution.
METHODS: A mouse model was established to study sarcopenic skeletal muscles. Single-cell RNA-seq was performed on tibialis anterior (TA) muscle cells collected from sarcopenic and control mice. A series of bioinformatic analyses were carried out to identify and compare different cell types under different conditions. Immunofluorescence staining and western blotting were used to validate the findings from single-cell experiments. Tube formation assays were conducted to further evaluate the effects of Gbp2 on endothelial cells during angiogenesis.
RESULTS: A murine sarcopenia model was successfully established using a senescence-accelerated mouse strain (SAMP6, n = 5). Sarcopenia phenotype was induced by administration of dexamethasone (20 mg/kg) and reduced physical activity. Senescence-resistant mice strain (SAMR1) and SAMP6 strain with similar activity but injected with PBS were recruited as two control groups. As signs of sarcopenia, body weight, muscle cell counts and cross-sectional fibre area were all significantly decreased in sarcopenic mice (P value = 0.004, 0.03 and 0.035, respectively). After quality control, 13 612 TA muscle single-cell transcriptomes were retained for analysis. Fourteen cell clusters were identified from the profiled cells. Among them, two distinct endothelial subtypes were found to be dominant in the sarcopenia group (42.2% cells) and in the two control groups (59.1% and 47.9% cells), respectively. 191 differentially expressed genes were detected between the two endothelial subtypes. Sarcopenia-specific endothelial cell subtype exhibited a dramatic increase in the interferon family genes and the interferon-inducible guanylate-binding protein (GBP) family gene expressions. For example, Igtp and Gbp2 in sarcopenic endothelial cells were 5.4 and 13.3 times higher than those in the control groups, respectively. We further validated our findings in muscle specimens of sarcopenia patients and observed that GBP2 levels were increased in endothelial cells of a subset of patients (11 of 40 patients, 27.5%), and we identified significantly higher CD31 and GBP2 co-localization (P value = 0.001128). Finally, we overexpressed Gbp2 in human umbilical vein endothelial cells in vitro. The endothelial cells with elevated Gbp2 expression displayed compromised tube formation.
CONCLUSIONS: Our single-cell-based results suggested that endothelial cells may play critical roles in sarcopenia development through interferon-GBP signalling pathways, highlighting new therapeutic directions to slow down or even reverse age-related sarcopenia.

Keywords:  Endothelial cell; Guanylate-binding protein; Interferon; Sarcopenia; Single-cell RNA-seq; Skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13091
Commun Biol. 2022 Sep 27. 5(1): 1022

The role of the dystrophin glycoprotein complex in muscle cell mechanotransduction.

Darren Graham Samuel Wilson, Andrew Tinker, Thomas Iskratsch.

Dystrophin is the central protein of the dystrophin-glycoprotein complex (DGC) in skeletal and heart muscle cells. Dystrophin connects the actin cytoskeleton to the extracellular matrix (ECM). Severing the link between the ECM and the intracellular cytoskeleton has a devastating impact on the homeostasis of skeletal muscle cells, leading to a range of muscular dystrophies. In addition, the loss of a functional DGC leads to progressive dilated cardiomyopathy and premature death. Dystrophin functions as a molecular spring and the DGC plays a critical role in maintaining the integrity of the sarcolemma. Additionally, evidence is accumulating, linking the DGC to mechanosignalling, albeit this role is still less understood. This review article aims at providing an up-to-date perspective on the DGC and its role in mechanotransduction. We first discuss the intricate relationship between muscle cell mechanics and function, before examining the recent research for a role of the dystrophin glycoprotein complex in mechanotransduction and maintaining the biomechanical integrity of muscle cells. Finally, we review the current literature to map out how DGC signalling intersects with mechanical signalling pathways to highlight potential future points of intervention, especially with a focus on cardiomyopathies.

DOI: https://doi.org/10.1038/s42003-022-03980-y
World J Diabetes. 2022 Aug 15. 13(8): 665-667

Loss of skeletal muscle mass is not specific to type 2 diabetes.

Bo Zhou, Ying-Qi Jin, Lian-Ping He.

  Skeletal muscle is a massive insulin-sensitive tissue in the body. Loss of muscle mass is associated with mitochondrial dysfunction, and is often a result of diabetes. Insulin deficiency or insulin resistance can only be seen as reduced skeletal muscle mass. Diabetes is caused by insulin deficiency or insulin resistance; however, insulin resistance is not unique to diabetics. Insulin resistance also exists in many diseases.

Keywords:  Diabetics; Insulin deficiency; Insulin resistance; Skeletal muscle mass

DOI:  https://doi.org/10.4239/wjd.v13.i8.665
Sci Rep. 2022 Sep 30. 12(1): 16428

Simultaneous monitoring of mouse grip strength, force profile, and cumulative force profile distinguishes muscle physiology following surgical, pharmacologic and diet interventions.

Joseph J Munier, Justin T Pank, Amie Severino, Huan Wang, Peixiang Zhang, Laurent Vergnes, Karen Reue.

Grip strength is a valuable preclinical assay to study muscle physiology in disease and aging by directly determining changes in muscle force generation in active laboratory mice. Existing methods to statistically evaluate grip strength, however, have limitations in the power and scope of the physiological features that are assessed. We therefore designed a microcontroller whose serial measure of resistance-based force enables the simultaneous readout of (1) peak grip strength, (2) force profile (the non-linear progress of force exerted throughout a standard grip strength trial), and (3) cumulative force profile (the integral of force with respect to time of a single grip strength trial). We hypothesized that muscle pathologies of different etiologies have distinct effects on these parameters. To test this, we used our apparatus to assess the three muscle parameters in mice with impaired muscle function resulting from surgically induced peripheral pain, genetic peripheral neuropathy, adverse muscle effects induced by statin drug, and metabolic alterations induced by a high-fat diet. Both surgically induced peripheral nerve injury and statin-associated muscle damage diminished grip strength and force profile, without affecting cumulative force profile. Conversely, genetic peripheral neuropathy resulting from lipin 1 deficiency led to a marked reduction to all three parameters. A chronic high-fat diet led to reduced grip strength and force profile when normalized to body weight. In high-fat fed mice that were exerted aerobically and allowed to recover for 30 min, male mice exhibited impaired force profile parameters, which female mice were more resilient. Thus, simultaneous analysis of peak grip strength, force profile and cumulative force profile distinguishes the muscle impairments that result from distinct perturbations and may reflect distinct motor unit recruitment strategies.

DOI: https://doi.org/10.1038/s41598-022-20665-y
Curr Protoc. 2022 Sep;2(9): e565

Modulating Myogenesis: An Optimized In Vitro Assay to Pharmacologically Influence Primary Myoblast Differentiation.

Cordell A VanGenderen, Jules A Granet, Romina L Filippelli, Yiyang Liu, Natasha C Chang.

  The intentional pharmacological manipulation of myogenesis is an important technique for understanding the underlying mechanisms of muscle differentiation and disease etiology. Using the pharmacological agent metformin as an example molecule, we present a systematic approach to examine the impact of pharmacological agents on the myogenic program. This consists of optimizing the in vitro differentiation of primary myoblast cells followed by the generation of a dose-response curve for a respective pharmaceutical. To assess myogenic differentiation, we utilized three approaches (incorporating both transcriptional and protein techniques) to assess the effects of biologically active agents on the in vitro differentiation of primary myogenic progenitors. First, the immunofluorescent visualization of myosin heavy chain (MYHC), which is expressed in differentiated myofibers, is used to obtain the fusion index, a quantitative read-out of differentiation efficiency. Second, quantitative reverse transcription PCR (RT-qPCR) reveals the expression of myogenic factors (Pax7, Myf5, Myod, Myog, Myh2) at the transcript level. Third, western blotting is used to assess the protein expression levels of the myogenic markers (PAX7, MYF5, MYOD, MYOG, and MYHC). By monitoring the expression of these various myogenic factors during the differentiation process, the relative cellular state and differentiation status between samples can be determined. Combined, these approaches enable the successful assessment of the impact of pharmacological agents on myogenic differentiation. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Immunofluorescence assay for qualitative and quantitative assessment of pharmacological agents on in vitro myogenic differentiation Support Protocol 1: Evaluating myogenic gene expression by RT-qPCR Support Protocol 2: Evaluating myogenic protein expression by western blot.

Keywords:  in vitro differentiation; metformin; myogenesis; pharmacological modulation; primary myoblast

DOI:  https://doi.org/10.1002/cpz1.565
Front Cell Dev Biol. 2022 ;10 951837

Role of exosomes and exosomal microRNA in muscle-Kidney crosstalk in chronic kidney disease.

Sijie Zhou, Gladys Lai Ying Cheing, Alex Kwok Kuen Cheung.

  Chronic kidney disease (CKD) is a progressive damage of kidneys that can no longer serve the blood-filtering function, and is a life-threatening condition. Skeletal muscle wasting is a common complication of CKD. Yet the relationship between kidney and skeletal muscle in CKD remains unclear. Exosomes, a type of small membrane-bound vesicles released from cells to the extracellular environment, have increasingly received attention due to their potential as mediators of crosstalk between kidneys and different organs, including skeletal muscle. This mini-review summarizes the recent findings that point to the role of exosomes in the cross-talk between kidney and skeletal muscle in CKD. Understanding of the contents and the mechanism of exosome release may prone exosomes be the potential therapeutic targets for CKD.

Keywords:  chronic kidney disease; crosstalk; exosomes; microRNA; skeletal muscle

DOI:  https://doi.org/10.3389/fcell.2022.951837
Cell Death Dis. 2022 Sep 29. 13(9): 838

Retinoic acid and RARγ maintain satellite cell quiescence through regulation of translation initiation.

Wenzhe Luo, Yueyuan Xu, Ruige Liu, Yinlong Liao, Sheng Wang, Haoyuan Zhang, Xinyun Li, Heng Wang.

In adult skeletal muscle, satellite cells are in a quiescent state, which is essential for the future activation of muscle homeostasis and regeneration. Multiple studies have investigated satellite cell proliferation and differentiation, but the molecular mechanisms that safeguard the quiescence of satellite cells remain largely unknown. In this study, we purposely activated dormant satellite cells by using various stimuli and captured the in vivo-preserved features from quiescence to activation transitions. We found that retinoic acid signaling was required for quiescence maintenance. Mechanistically, retinoic acid receptor gamma (RARγ) binds to and stimulates genes responsible for Akt dephosphorylation and subsequently inhibits overall protein translation initiation in satellite cells. Furthermore, the alleviation of retinoic acid signaling released the satellite cells from quiescence, but this restraint was lost in aged cells. Retinoic acid also preserves the quiescent state during satellite cell isolation, overcoming the cellular stress caused by the isolation process. We conclude that active retinoic acid signaling contributes to the maintenance of the quiescent state of satellite cells through regulation of the protein translation initiation process.

DOI: https://doi.org/10.1038/s41419-022-05284-9
Geroscience. 2022 Sep 30.

Age- and time-dependent mitochondrial genotoxic and myopathic effects of beta-guanidinopropionic acid, a creatine analog, on rodent skeletal muscles.

Allen Herbst, Judd M Aiken, Chiye Kim, Danielle Gushue, Debbie McKenzie, Timothy M Moore, Jin Zhou, Austin N Hoang, Solbie Choi, Jonathan Wanagat.

  Beta-guanidinopropionic acid (GPA) is a creatine analog suggested as a treatment for hypertension, diabetes, and obesity, which manifest primarily in older adults. A notable side effect of GPA is the induction of mitochondrial DNA deletion mutations. We hypothesized that mtDNA deletions contribute to muscle aging and used the mutation promoting effect of GPA to examine the impact of mtDNA deletions on muscles with differential vulnerability to aging. Rats were treated with GPA for up to 4 months starting at 14 or 30 months of age. We examined quadriceps and adductor longus muscles as the quadriceps exhibits profound age-induced deterioration, while adductor longus is maintained. GPA decreased body and muscle mass and mtDNA copy number while increasing mtDNA deletion frequency. The interactions between age and GPA treatment observed in the quadriceps were not observed in the adductor longus. GPA had negative mitochondrial effects in as little as 4 weeks. GPA treatment exacerbated mtDNA deletions and muscle aging phenotypes in the quadriceps, an age-sensitive muscle, while the adductor longus was spared. GPA has been proposed for use in age-associated diseases, yet the pharmacodynamics of GPA differ with age and include the detrimental induction of mtDNA deletions, a mitochondrial genotoxic stress that is pronounced in muscles that are most vulnerable to aging. Further research is needed to determine if the proposed benefits of GPA on hypertension, diabetes, and obesity outweigh the detrimental mitochondrial and myopathic side effects.

Keywords:  Aging; Creatine; Genetics; Guanidinopropionic acid; Mitochondria; Skeletal muscle

DOI:  https://doi.org/10.1007/s11357-022-00667-4
Front Cell Dev Biol. 2022 ;10 978931

An interplay between BRD4 and G9a regulates skeletal myogenesis.

Naidi Yang, Dipanwita Das, Shilpa Rani Shankar, Pierre-Alexis Goy, Ernesto Guccione, Reshma Taneja.

  Histone acetylation and methylation are epigenetic modifications that are dynamically regulated by chromatin modifiers to precisely regulate gene expression. However, the interplay by which histone modifications are synchronized to coordinate cellular differentiation is not fully understood. In this study, we demonstrate a relationship between BRD4, a reader of acetylation marks, and G9a, a writer of methylation marks in the regulation of myogenic differentiation. Using loss- and gain-of-function studies, as well as a pharmacological inhibition of its activity, we examined the mechanism by which BRD4 regulates myogenesis. Transcriptomic analysis using RNA sequencing revealed that a number of myogenic differentiation genes are downregulated in Brd4-depleted cells. Interestingly, some of these genes were upregulated upon G9a knockdown, indicating that BRD4 and G9a play opposing roles in the control of myogenic gene expression. Remarkably, the differentiation defect caused by Brd4 knockdown was rescued by inhibition of G9a methyltransferase activity. These findings demonstrate that the absence of BRD4 results in the upregulation of G9a activity and consequently impaired myogenic differentiation. Collectively, our study identifies an interdependence between BRD4 and G9a for the precise control of transcriptional outputs to regulate myogenesis.

Keywords:  acetylation; differentiation; methylation; muscle; reader; writer

DOI:  https://doi.org/10.3389/fcell.2022.978931
Proc Natl Acad Sci U S A. 2022 Oct 04. 119(40): e2202236119

Antagonistic control of active surface integrins by myotubularin and phosphatidylinositol 3-kinase C2β in a myotubular myopathy model.

Paula Samsó, Philipp A Koch, York Posor, Wen-Ting Lo, Hassane Belabed, Marc Nazare, Jocelyn Laporte, Volker Haucke.

  X-linked centronuclear myopathy (XLCNM) is a severe human disease without existing therapies caused by mutations in the phosphoinositide 3-phosphatase MTM1. Loss of MTM1 function is associated with muscle fiber defects characterized by impaired localization of β-integrins and other components of focal adhesions. Here we show that defective focal adhesions and reduced active β-integrin surface levels in a cellular model of XLCNM are rescued by loss of phosphatidylinositiol 3-kinase C2β (PI3KC2β) function. Inactivation of the Mtm1 gene impaired myoblast differentiation into myotubes and resulted in reduced surface levels of active β1-integrins as well as corresponding defects in focal adhesions. These phenotypes were rescued by concomitant genetic loss of Pik3c2b or pharmacological inhibition of PI3KC2β activity. We further demonstrate that a hitherto unknown role of PI3KC2β in the endocytic trafficking of active β1-integrins rather than rescue of phosphatidylinositol 3-phosphate levels underlies the ability of Pik3c2b to act as a genetic modifier of cellular XLCNM phenotypes. Our findings reveal a crucial antagonistic function of MTM1 and PI3KC2β in the control of active β-integrin surface levels, thereby providing a molecular mechanism for the adhesion and myofiber defects observed in XLCNM. They further suggest specific pharmacological inhibition of PI3KC2β catalysis as a viable treatment option for XLCNM patients.

Keywords:  endocytosis; focal adhesions; integrins; myotubular myopathy; phosphoinositides

DOI:  https://doi.org/10.1073/pnas.2202236119
Skelet Muscle. 2022 Sep 29. 12(1): 23

Megaconial congenital muscular dystrophy due to novel CHKB variants: a case report and literature review.

Francesca Magri, Sara Antognozzi, Michela Ripolone, Simona Zanotti, Laura Napoli, Patrizia Ciscato, Daniele Velardo, Giulietta Scuvera, Valeria Nicotra, Antonella Giacobbe, Donatella Milani, Francesco Fortunato, Manuela Garbellini, Monica Sciacco, Stefania Corti, Giacomo Pietro Comi, Dario Ronchi.

   BACKGROUND: Choline kinase beta (CHKB) catalyzes the first step in the de novo biosynthesis of phosphatidyl choline and phosphatidylethanolamine via the Kennedy pathway. Derangement of this pathway might also influence the homeostasis of mitochondrial membranes. Autosomal recessive CHKB mutations cause a rare form of congenital muscular dystrophy known as megaconial congenital muscular dystrophy (MCMD).
CASE PRESENTATION: We describe a novel proband presenting MCMD due to unpublished CHKB mutations. The patient is a 6-year-old boy who came to our attention for cognitive impairment and slowly progressive muscular weakness. He was the first son of non-consanguineous healthy parents from Sri Lanka. Neurological examination showed proximal weakness at four limbs, weak osteotendinous reflexes, Gowers' maneuver, and waddling gate. Creatine kinase levels were mildly increased. EMG and brain MRI were normal. Left quadriceps skeletal muscle biopsy showed a myopathic pattern with nuclear centralizations and connective tissue increase. Histological and histochemical staining suggested subsarcolemmal localization and dimensional increase of mitochondria. Ultrastructural analysis confirmed the presence of enlarged ("megaconial") mitochondria. Direct sequencing of CHKB identified two novel defects: the c.1060G > C (p.Gly354Arg) substitution and the c.448-56_29del intronic deletion, segregating from father and mother, respectively. Subcloning of RT-PCR amplicons from patient's muscle RNA showed that c.448-56_29del results in the partial retention (14 nucleotides) of intron 3, altering physiological splicing and transcript stability. Biochemical studies showed reduced levels of the mitochondrial fission factor DRP1 and the severe impairment of mitochondrial respiratory chain activity in patient's muscle compared to controls.
CONCLUSIONS: This report expands the molecular findings associated with MCMD and confirms the importance of considering CHKB variants in the differential diagnosis of patients presenting with muscular dystrophy and mental retardation. The clinical outcome of MCMD patients seems to be influenced by CHKB molecular defects. Histological and ultrastructural examination of muscle biopsy directed molecular studies and allowed the identification and characterization of an intronic mutation, usually escaping standard molecular testing.

Keywords:  Choline kinase beta (CHKB); Enlarged mitochondria; Megaconial congenital muscular dystrophy; Mitochondrial dynamics

DOI:  https://doi.org/10.1186/s13395-022-00306-8