bims-moremu 2024-06-09 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024‒06‒09
thirty papers selected by
Anna Vainshtein, Craft Science Inc.

Cellular interactions and microenvironment dynamics in skeletal muscle regeneration and disease.
Endothelial cell signature in muscle stem cells validated by VEGFA-FLT1-AKT1 axis promoting survival of muscle stem cell.
Transcriptomic gene signatures measure satellite cell activity in muscular dystrophies.
The effects of exercise and mitochondrial transplantation alone or in combination against Doxorubicin-induced skeletal muscle atrophy.
Loss of endogenous estrogen alters mitochondrial metabolism and muscle clock-related protein Rbm20 in female mdx mice.
Setdb1 protects genome integrity in murine muscle stem cells to allow for regenerative myogenesis and inflammation.
STAT3 inhibition recovers regeneration of aged muscles by restoring autophagy in muscle stem cells.
Spaceflight on the ISS changed the skeletal muscle proteome of two astronauts.
Effects of endurance training under calorie restriction on energy substrate metabolism in mouse skeletal muscle and liver.
Skeletal muscle PGC-1α remodels mitochondrial phospholipidome but does not alter energy efficiency for ATP synthesis.
Higher expression of denervation-responsive genes is negatively associated with muscle volume and performance traits in the study of muscle, mobility, and aging (SOMMA).
Expression of mitochondrial oxidative stress response genes in muscle is associated with mitochondrial respiration, physical performance, and muscle mass in the Study of Muscle, Mobility, and Aging.
Changes in protein fluxes in skeletal muscle during sequential stages of muscle regeneration after acute injury in male mice.
Diacylglycerol kinase delta overexpression improves glucose clearance and protects against the development of obesity.
Agent-based model demonstrates the impact of nonlinear, complex interactions between cytokinces on muscle regeneration.
Exercise training alters skeletal muscle microvascular endothelial cell properties in recent postmenopausal females.
miR-27b-3p reduces muscle fibrosis during chronic skeletal muscle injury by targeting TGF-βR1/Smad pathway.
Identification of nicotinamide N-methyltransferase as a promising therapeutic target for sarcopenia.
Muscle-specific pyruvate kinase isoforms, PKM1 and PKM2, regulate mammalian SWI/SNF proteins and histone 3 phosphorylation during myoblast differentiation.
Skeletal Muscle Mitochondrial Morphology Negatively Affected in Mice Lacking Xin.
SPNS1 ablation drives skeletal muscle atrophy by disrupting mitophagy, mitochondrial function, and apoptosis in mice.
Skeletal muscle myosin heavy chain protein fragmentation as a potential marker of protein degradation in response to resistance training and disuse atrophy.
Nuclear receptor Nur77 and Yin-Yang 1 synergistically increase mitochondrial abundance and activity in macrophages.
RASopathies - what they reveal about RAS/MAPK signaling in skeletal muscle development.
Cell type mapping of inflammatory muscle diseases highlights selective myofiber vulnerability in inclusion body myositis.
Skeletal myotubes expressing ALS mutant SOD1 induce pathogenic changes, impair mitochondrial axonal transport, and trigger motoneuron death.
Recent advances in understanding the mechanisms in skeletal muscle of interaction between exercise and frontline antihyperglycemic drugs.
Mitochondrial mechanisms in the pathogenesis of chronic inflammatory musculoskeletal disorders.
Styxl2 regulates de novo sarcomere assembly by binding to non-muscle myosin IIs and promoting their degradation.
Acetate derived from the intestinal tract has a critical role in maintaining skeletal muscle mass and strength in mice.

Front Cell Dev Biol. 2024 ;12 1385399

Cellular interactions and microenvironment dynamics in skeletal muscle regeneration and disease.

Cristina Rodríguez, Filipa Timóteo-Ferreira, Gabriella Minchiotti, Silvia Brunelli, Ombretta Guardiola.

  Skeletal muscle regeneration relies on the intricate interplay of various cell populations within the muscle niche-an environment crucial for regulating the behavior of muscle stem cells (MuSCs) and ensuring postnatal tissue maintenance and regeneration. This review delves into the dynamic interactions among key players of this process, including MuSCs, macrophages (MPs), fibro-adipogenic progenitors (FAPs), endothelial cells (ECs), and pericytes (PCs), each assuming pivotal roles in orchestrating homeostasis and regeneration. Dysfunctions in these interactions can lead not only to pathological conditions but also exacerbate muscular dystrophies. The exploration of cellular and molecular crosstalk among these populations in both physiological and dystrophic conditions provides insights into the multifaceted communication networks governing muscle regeneration. Furthermore, this review discusses emerging strategies to modulate the muscle-regenerating niche, presenting a comprehensive overview of current understanding and innovative approaches.

Keywords:  endothelial cells; fibro-adipogenic progenitors; macrophages; muscle niche dynamics; muscle stem cells; muscular dystrophies; regenerative medicine strategies; skeletal muscle regeneration

DOI:  https://doi.org/10.3389/fcell.2024.1385399
Elife. 2024 Jun 06. pii: e73592. [Epub ahead of print]13

Endothelial cell signature in muscle stem cells validated by VEGFA-FLT1-AKT1 axis promoting survival of muscle stem cell.

Mayank Verma, Yoko Asakura, Xuerui Wang, Kasey Zhou, Mahmut Ünverdi, Allison P Kann, Robert S Krauss, Atsushi Asakura.

  Endothelial and skeletal muscle lineages arise from common embryonic progenitors. Despite their shared developmental origin, adult endothelial cells (ECs) and muscle stem cells (MuSCs) (satellite cells) have been thought to possess distinct gene signatures and signaling pathways. Here we shift this paradigm by uncovering how adult MuSC behavior is affected by the expression of a subset of EC transcripts. We used several computational analyses including single-cell RNAseq to show that MuSCs express low levels of canonical EC markers in mice. We demonstrate that MuSC survival is regulated by one such prototypic endothelial signaling pathway (VEGFA-FLT1). Using pharmacological and genetic gain- and loss-of-function studies, we identify the FLT1-AKT1 axis as the key effector underlying VEGFA-mediated regulation of MuSC survival. All together, our data support that the VEGFA-FLT1-AKT1 pathway promotes MuSC survival during muscle regeneration, and highlights how the minor expression of select transcripts is sufficient for affecting cell behavior.

Keywords:  developmental biology; mouse; regenerative medicine; stem cells

DOI:  https://doi.org/10.7554/eLife.73592
iScience. 2024 Jun 21. 27(6): 109947

Transcriptomic gene signatures measure satellite cell activity in muscular dystrophies.

Elise N Engquist, Anna Greco, Leo A B Joosten, Baziel G M van Engelen, Christopher R S Banerji, Peter S Zammit.

  The routine need for myonuclear turnover in skeletal muscle, together with more sporadic demands for hypertrophy and repair, are performed by resident muscle stem cells called satellite cells. Muscular dystrophies are characterized by muscle wasting, stimulating chronic repair/regeneration by satellite cells. Here, we derived and validated transcriptomic signatures for satellite cells, myoblasts/myocytes, and myonuclei using publicly available murine single cell RNA-Sequencing data. Our signatures distinguished disease from control in transcriptomic data from several muscular dystrophies including facioscapulohumeral muscular dystrophy (FSHD), Duchenne muscular dystrophy, and myotonic dystrophy type I. For FSHD, the expression of our gene signatures correlated with direct counts of satellite cells on muscle sections, as well as with increasing clinical and pathological severity. Thus, our gene signatures enable the investigation of myogenesis in bulk transcriptomic data from muscle biopsies. They also facilitate study of muscle regeneration in transcriptomic data from human muscle across health and disease.

Keywords:  disease; model organism; musculoskeletal medicine; specialized functions of cells; transcriptomics

DOI:  https://doi.org/10.1016/j.isci.2024.109947
J Muscle Res Cell Motil. 2024 Jun 01.

The effects of exercise and mitochondrial transplantation alone or in combination against Doxorubicin-induced skeletal muscle atrophy.

Gokhan Burcin Kubat, Oner Ulger, Ozbeyen Atalay, Tugba Fatsa, Ibrahim Turkel, Berkay Ozerklig, Ertugrul Celik, Emrah Ozenc, Gulcin Simsek, Meltem Tuncer.

  Doxorubicin (DOX) is a chemotherapy drug used to treat various types of cancer, but it is associated with significant side effects such as skeletal muscle atrophy. Exercise has been found to prevent skeletal muscle atrophy through the modulation of mitochondrial pathways. Mitochondrial transplantation (MT) may mitigate toxicity, neurological disorders, kidney and liver injury, and skeletal muscle atrophy. The objective of this study was to evaluate the effects of MT, exercise, and MT with exercise on DOX-induced skeletal muscle atrophy. Male Sprague Dawley rats were randomly assigned to the following groups: control, DOX, MT with DOX, exercise with DOX, and exercise with MT and DOX. A 10-day treadmill running exercise and MT (6.5 µg/100 µL) to tibialis anterior (TA) muscle were administered prior to a single injection of DOX (20 mg/kg). Our data showed that exercise and MT with exercise led to an increase in cross-sectional area of the TA muscle. Exercise, MT and MT with exercise reduced inflammation and maintained mitochondrial enzyme activity. Additionally, exercise and MT have been shown to regulate mitochondrial fusion/fission. Our findings revealed that exercise and MT with exercise prevented oxidative damage. Furthermore, MT and MT with exercise decreased apoptosis and MT with exercise triggered mitochondrial biogenesis. These findings demonstrate the importance of exercise in the prevention of skeletal muscle atrophy and emphasize the significant benefits of MT with exercise. To the best of our knowledge, this is the first study to demonstrate the therapeutic effects of MT with exercise in DOX-induced skeletal muscle atrophy.

Keywords:  Doxorubicin; Exercise; Mitochondria; Mitochondrial transplantation; Skeletal muscle atrophy

DOI:  https://doi.org/10.1007/s10974-024-09676-6
FASEB J. 2024 Jun 15. 38(11): e23718

Loss of endogenous estrogen alters mitochondrial metabolism and muscle clock-related protein Rbm20 in female mdx mice.

Cara A Timpani, Didier Debrincat, Stephanie Kourakis, Rebecca Boyer, Luke E Formosa, Joel R Steele, Haijian Zhang, Ralf B Schittenhelm, Aaron P Russell, Emma Rybalka, Angus Lindsay.

  Female carriers of a Duchenne muscular dystrophy (DMD) gene mutation manifest exercise intolerance and metabolic anomalies that may be exacerbated following menopause due to the loss of estrogen, a known regulator of skeletal muscle function and metabolism. Here, we studied the impact of estrogen depletion (via ovariectomy) on exercise tolerance and muscle mitochondrial metabolism in female mdx mice and the potential of estrogen replacement therapy (using estradiol) to protect against functional and metabolic perturbations. We also investigated the effect of estrogen depletion, and replacement, on the skeletal muscle proteome through an untargeted proteomic approach with TMT-labelling. Our study confirms that loss of estrogen in female mdx mice reduces exercise capacity, tricarboxylic acid cycle intermediates, and citrate synthase activity but that these deficits are offset through estrogen replacement therapy. Furthermore, ovariectomy downregulated protein expression of RNA-binding motif factor 20 (Rbm20), a critical regulator of sarcomeric and muscle homeostasis gene splicing, which impacted pathways involving ribosomal and mitochondrial translation. Estrogen replacement modulated Rbm20 protein expression and promoted metabolic processes and the upregulation of proteins involved in mitochondrial dynamics and metabolism. Our data suggest that estrogen mitigates dystrophinopathic features in female mdx mice and that estrogen replacement may be a potential therapy for post-menopausal DMD carriers.

Keywords:  Duchenne muscular dystrophy; Rbm20; dystrophin; estrogen; metabolism; metabolomics; mitochondria; molecular clock; proteomics; skeletal muscle

DOI:  https://doi.org/10.1096/fj.202400329R
Dev Cell. 2024 Jun 05. pii: S1534-5807(24)00329-0. [Epub ahead of print]

Setdb1 protects genome integrity in murine muscle stem cells to allow for regenerative myogenesis and inflammation.

Pauline Garcia, William Jarassier, Caroline Brun, Lorenzo Giordani, Fany Agostini, Wai Hing Kung, Cécile Peccate, Jade Ravent, Sidy Fall, Valentin Petit, Tom H Cheung, Slimane Ait-Si-Ali, Fabien Le Grand.

  The histone H3 lysine 9 methyltransferase SETDB1 controls transcriptional repression to direct stem cell fate. Here, we show that Setdb1 expression by adult muscle stem cells (MuSCs) is required for skeletal muscle regeneration. We find that SETDB1 represses the expression of endogenous retroviruses (ERVs) in MuSCs. ERV de-repression in Setdb1-null MuSCs prevents their amplification following exit from quiescence and promotes cell death. Multi-omics profiling shows that chromatin decompaction at ERV loci activates the DNA-sensing cGAS-STING pathway, entailing cytokine expression by Setdb1-null MuSCs. This is followed by aberrant infiltration of inflammatory cells, including pathological macrophages. The ensuing histiocytosis is accompanied by myofiber necrosis, which, in addition to progressive MuSCs depletion, completely abolishes tissue repair. In contrast, loss of Setdb1 in fibro-adipogenic progenitors (FAPs) does not impact immune cells. In conclusion, genome maintenance by SETDB1 in an adult somatic stem cell is necessary for both its regenerative potential and adequate reparative inflammation.

Keywords:  SETDB1; cGAS-STING pathway; endogeneous retrovirus; inflammation; muscle regeneration; muscle stem cells; necrosis; transposable element

DOI:  https://doi.org/10.1016/j.devcel.2024.05.012
Life Sci Alliance. 2024 Aug;pii: e202302503. [Epub ahead of print]7(8):

STAT3 inhibition recovers regeneration of aged muscles by restoring autophagy in muscle stem cells.

Giorgia Catarinella, Andrea Bracaglia, Emilia Skafida, Paola Procopio, Veronica Ruggieri, Cristina Parisi, Marco De Bardi, Giovanna Borsellino, Luca Madaro, Pier Lorenzo Puri, Alessandra Sacco, Lucia Latella.

Age-related reduction in muscle stem cell (MuSC) regenerative capacity is associated with cell-autonomous and non-cell-autonomous changes caused by alterations in systemic and skeletal muscle environments, ultimately leading to a decline in MuSC number and function. Previous studies demonstrated that STAT3 plays a key role in driving MuSC expansion and differentiation after injury-activated regeneration, by regulating autophagy in activated MuSCs. However, autophagy gradually declines in MuSCs during lifespan and contributes to the impairment of MuSC-mediated regeneration of aged muscles. Here, we show that STAT3 inhibition restores the autophagic process in aged MuSCs, thereby recovering MuSC ability to promote muscle regeneration in geriatric mice. We show that STAT3 inhibition could activate autophagy at the nuclear level, by promoting transcription of autophagy-related genes, and at the cytoplasmic level, by targeting STAT3/PKR phosphorylation of eIF2α. These results point to STAT3 inhibition as a potential intervention to reverse the age-related autophagic block that impairs MuSC ability to regenerate aged muscles. They also reveal that STAT3 regulates MuSC function by both transcription-dependent and transcription-independent regulation of autophagy.

DOI: https://doi.org/10.26508/lsa.202302503
NPJ Microgravity. 2024 Jun 05. 10(1): 60

Spaceflight on the ISS changed the skeletal muscle proteome of two astronauts.

Marta Murgia, Jörn Rittweger, Carlo Reggiani, Roberto Bottinelli, Matthias Mann, Stefano Schiaffino, Marco V Narici.

Skeletal muscle undergoes atrophy and loss of force during long space missions, when astronauts are persistently exposed to altered gravity and increased ionizing radiation. We previously carried out mass spectrometry-based proteomics from skeletal muscle biopsies of two astronauts, taken before and after a mission on the International Space Station. The experiments were part of an effort to find similarities between spaceflight and bed rest, a ground-based model of unloading, focused on proteins located at the costameres. We here extend the data analysis of the astronaut dataset and show compartment-resolved changes in the mitochondrial proteome, remodeling of the extracellular matrix and of the antioxidant response. The astronauts differed in their level of onboard physical exercise, which correlated with their respective preservation of muscle mass and force at landing in previous analyses. We show that the mitochondrial proteome downregulation during spaceflight, particularly the inner membrane and matrix, was dramatic for both astronauts. The expression of autophagy regulators and reactive oxygen species scavengers, however, showed partially opposite expression trends in the two subjects, possibly correlating with their level of onboard exercise. As mitochondria are primarily affected in many different tissues during spaceflight, we hypothesize that reactive oxygen species (ROS) rather than mechanical unloading per se could be the primary cause of skeletal muscle mitochondrial damage in space. Onboard physical exercise might have a strong direct effect on the prevention of muscle atrophy through mechanotransduction and a subsidiary effect on mitochondrial quality control, possibly through upregulation of autophagy and anti-oxidant responses.

DOI: https://doi.org/10.1038/s41526-024-00406-3
J Physiol Sci. 2024 Jun 07. 74(1): 32

Effects of endurance training under calorie restriction on energy substrate metabolism in mouse skeletal muscle and liver.

Kenya Takahashi, Yu Kitaoka, Hideo Hatta.

  We investigated whether calorie restriction (CR) enhances metabolic adaptations to endurance training (ET). Ten-week-old male Institute of Cancer Research (ICR) mice were fed ad libitum or subjected to 30% CR. The mice were subdivided into sedentary and ET groups. The ET group performed treadmill running (20-25 m/min, 30 min, 5 days/week) for 5 weeks. We found that CR decreased glycolytic enzyme activity and monocarboxylate transporter (MCT) 4 protein content, while enhancing glucose transporter 4 protein content in the plantaris and soleus muscles. Although ET and CR individually increased citrate synthase activity in the plantaris muscle, the ET-induced increase in respiratory chain complex I protein content was counteracted by CR. In the soleus muscle, mitochondrial enzyme activity and protein levels were increased by ET, but decreased by CR. It has been suggested that CR partially interferes with skeletal muscle adaptation to ET.

Keywords:  Calorie restriction; Endurance training; Enzyme; Gluconeogenesis; Liver; Mitochondria; Skeletal muscle; Transporter

DOI:  https://doi.org/10.1186/s12576-024-00924-5
bioRxiv. 2024 May 26. pii: 2024.05.22.595374. [Epub ahead of print]

Skeletal muscle PGC-1α remodels mitochondrial phospholipidome but does not alter energy efficiency for ATP synthesis.

Takuya Karasawa, Ran Hee Choi, Cesar A Meza, J Alan Maschek, James E Cox, Katsuhiko Funai.

  Background: Exercise training is thought to improve the mitochondrial energy efficiency of skeletal muscle. Some studies suggest exercise training increases the efficiency for ATP synthesis by oxidative phosphorylation (OXPHOS), but the molecular mechanisms are unclear. We have previously shown that exercise remodels the lipid composition of mitochondrial membranes, and some of these changes could contribute to improved OXPHOS efficiency (ATP produced by O2 consumed or P/O). Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a transcriptional co-activator that coordinately regulates exercise-induced adaptations including mitochondria. We hypothesized that increased PGC-1α activity is sufficient to remodel mitochondrial membrane lipids and promote energy efficiency.Methods: Mice with skeletal muscle-specific overexpression of PGC-1α (MCK-PGC-1α) and their wildtype littermates were used for this study. Lipid mass spectrometry and quantitative PCR were used to assess muscle mitochondrial lipid composition and their biosynthesis pathway. The abundance of OXPHOS enzymes was determined by western blot assay. High-resolution respirometry and fluorometry analysis were used to characterize mitochondrial bioenergetics (ATP production, O2 consumption, and P/O) for permeabilized fibers and isolated mitochondria.
Results: Lipidomic analyses of skeletal muscle mitochondria from wildtype and MCK-PGC-1α mice revealed that PGC-1α increases the concentrations of cone-shaped lipids such as phosphatidylethanolamine (PE), cardiolipin (CL), and lysophospholipids, while decreases the concentrations of phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidic acid (PA). However, while PGC-1α overexpression increased the abundance of OXPHOS enzymes in skeletal muscle and the rate of O2 consumption (JO2), P/O values were unaffected with PGC-1α in permeabilized fibers or isolated mitochondria.
Conclusions: Collectively, overexpression of PGC-1α promotes the biosynthesis of mitochondrial PE and CL but neither PGC-1α nor the mitochondrial membrane lipid remodeling induced in MCK-PGC-1α mice is sufficient to increase the efficiency for mitochondrial ATP synthesis. These findings suggest that exercise training may increase OXPHOS efficiency by a PGC-1α-independent mechanism, and question the hypothesis that mitochondrial lipids directly affect OXPHOS enzymes to improve efficiency for ATP synthesis.

Keywords:  exercise; mitochondria; phospholipids; skeletal muscle

DOI:  https://doi.org/10.1101/2024.05.22.595374
Aging Cell. 2024 Jun 03. e14115

Higher expression of denervation-responsive genes is negatively associated with muscle volume and performance traits in the study of muscle, mobility, and aging (SOMMA).

Cole J Lukasiewicz, Gregory J Tranah, Daniel S Evans, Paul M Coen, Haley N Barnes, Zhiguang Huo, Karyn A Esser, Xiping Zhang, Christopher Wolff, Kevin Wu, Nancy E Lane, Steven B Kritchevsky, Anne B Newman, Steven R Cummings, Peggy M Cawthon, Russell T Hepple.

  With aging skeletal muscle fibers undergo repeating cycles of denervation and reinnervation. In approximately the 8th decade of life reinnervation no longer keeps pace, resulting in the accumulation of persistently denervated muscle fibers that in turn cause an acceleration of muscle dysfunction. The significance of denervation in important clinical outcomes with aging is poorly studied. The Study of Muscle, Mobility, and Aging (SOMMA) is a large cohort study with the primary objective to assess how aging muscle biology impacts clinically important traits. Using transcriptomics data from vastus lateralis muscle biopsies in 575 participants we have selected 49 denervation-responsive genes to provide insights to the burden of denervation in SOMMA, to test the hypothesis that greater expression of denervation-responsive genes negatively associates with SOMMA participant traits that included time to walk 400 meters, fitness (VO2peak), maximal mitochondrial respiration, muscle mass and volume, and leg muscle strength and power. Consistent with our hypothesis, increased transcript levels of: a calciumdependent intercellular adhesion glycoprotein (CDH15), acetylcholine receptor subunits (CHRNA1, CHRND, CHRNE), a glycoprotein promoting reinnervation (NCAM1), a transcription factor regulating aspects of muscle organization (RUNX1), and a sodium channel (SCN5A) were each negatively associated with at least 3 of these traits. VO2peak and maximal respiration had the strongest negative associations with 15 and 19 denervation-responsive genes, respectively. In conclusion, the abundance of denervationresponsive gene transcripts is a significant determinant of muscle and mobility outcomes in aging humans, supporting the imperative to identify new treatment strategies to restore innervation in advanced age.

Keywords:  denervation; gene expression profiling; muscle; neuromuscular junction; skeletal

DOI:  https://doi.org/10.1111/acel.14115
Aging Cell. 2024 Jun 03. e14114

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

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

  Gene expression in skeletal muscle of older individuals may reflect compensatory adaptations in response to oxidative damage that preserve tissue integrity and maintain function. Identifying associations between oxidative stress response gene expression patterns and mitochondrial function, physical performance, and muscle mass in older individuals would further our knowledge of mechanisms related to managing molecular damage that may be targeted to preserve physical resilience. To characterize expression patterns of genes responsible for the oxidative stress response, RNA was extracted and sequenced from skeletal muscle biopsies collected from 575 participants (≥70 years old) from the Study of Muscle, Mobility, and Aging. Expression levels of 21 protein-coding RNAs related to the oxidative stress response were analyzed in relation to six phenotypic measures, including maximal mitochondrial respiration from muscle biopsies (Max OXPHOS), physical performance (VO2 peak, 400-m walking speed, and leg strength), and muscle size (thigh muscle volume and whole-body D3Cr muscle mass). The mRNA level of the oxidative stress response genes most consistently associated across outcomes are preferentially expressed within the mitochondria. Higher expression of mRNAs that encode generally mitochondria located proteins SOD2, TRX2, PRX3, PRX5, and GRX2 were associated with higher levels of mitochondrial respiration and VO2 peak. In addition, greater SOD2, PRX3, and GRX2 expression was associated with higher physical performance and muscle size. Identifying specific mechanisms associated with high functioning across multiple performance and physical domains may lead to targeted antioxidant interventions with greater impacts on mobility and independence.

Keywords:  aging; cohort study; gene expression; mitochondria; muscle; oxidative stress

DOI:  https://doi.org/10.1111/acel.14114
Sci Rep. 2024 Jun 07. 14(1): 13172

Changes in protein fluxes in skeletal muscle during sequential stages of muscle regeneration after acute injury in male mice.

Alec Bizieff, Maggie Cheng, Kelvin Chang, Hussein Mohammed, Naveed Ziari, Edna Nyangau, Mark Fitch, Marc K Hellerstein.

  Changes in protein turnover play an important role in dynamic physiological processes, including skeletal muscle regeneration, which occurs as an essential part of tissue repair after injury. The inability of muscle tissue to recapitulate this regenerative process can lead to the manifestation of clinical symptoms in various musculoskeletal diseases, including muscular dystrophies and pathological atrophy. Here, we employed a workflow that couples deuterated water (2H2O) administration with mass spectrometry (MS) to systematically measure in-vivo protein turnover rates across the muscle proteome in 8-week-old male C57BL6/J mice. We compared the turnover kinetics of over 100 proteins in response to cardiotoxin (CTX) induced muscle damage and regeneration at unique sequential stages along the regeneration timeline. This analysis is compared to gene expression data from mRNA-sequencing (mRNA-seq) from the same tissue. The data reveals quantitative protein flux signatures in response to necrotic damage, in addition to sequential differences in cell proliferation, energy metabolism, and contractile gene expression. Interestingly, the mRNA changes correlated poorly with changes in protein synthesis rates, consistent with post-transcriptional control mechanisms. In summary, the experiments described here reveal the signatures and timing of protein flux changes during skeletal muscle regeneration, as well as the inability of mRNA expression measurements to reveal changes in directly measured protein turnover rates. The results of this work described here provide a better understanding of the muscle regeneration process and could help to identify potential biomarkers or therapeutic targets.

Keywords:  Flux proteomics; In-vivo regeneration; Mass spectrometry; Muscle damage; Muscle injury; Stable isotope labeling

DOI:  https://doi.org/10.1038/s41598-024-62115-x
Metabolism. 2024 Jun 04. pii: S0026-0495(24)00166-5. [Epub ahead of print] 155939

Diacylglycerol kinase delta overexpression improves glucose clearance and protects against the development of obesity.

Maxence Jollet, Flavia Tramontana, Lake Q Jiang, Melissa L Borg, Mladen Savikj, Michael S Kuefner, Julie Massart, Thais de Castro Barbosa, Louise Mannerås-Holm, Antonio Checa, Nicolas J Pillon, Alexander V Chibalin, Marie Björnholm, Juleen R Zierath.

  BACKGROUND AND AIM: Diacylglycerol kinase (DGK) isoforms catalyze an enzymatic reaction that removes diacylglycerol (DAG) and thereby terminates protein kinase C signaling by converting DAG to phosphatidic acid. DGKδ (type II isozyme) downregulation causes insulin resistance, metabolic inflexibility, and obesity. Here we determined whether DGKδ overexpression prevents these metabolic impairments.METHODS: We generated a transgenic mouse model overexpressing human DGKδ2 under the myosin light chain promoter (DGKδ TG). We performed deep metabolic phenotyping of DGKδ TG mice and wild-type littermates fed chow or high-fat diet (HFD). Mice were also provided free access to running wheels to examine the effects of DGKδ overexpression on exercise-induced metabolic outcomes.
RESULTS: DGKδ TG mice were leaner than wild-type littermates, with improved glucose tolerance and increased skeletal muscle glycogen content. DGKδ TG mice were protected against HFD-induced glucose intolerance and obesity. DGKδ TG mice had reduced epididymal fat and enhanced lipolysis. Strikingly, DGKδ overexpression recapitulated the beneficial effects of exercise on metabolic outcomes. DGKδ overexpression and exercise had a synergistic effect on body weight reduction. Microarray analysis of skeletal muscle revealed common gene ontology signatures of exercise and DGKδ overexpression that were related to lipid storage, extracellular matrix, and glycerophospholipids biosynthesis pathways.
CONCLUSION: Overexpression of DGKδ induces adaptive changes in both skeletal muscle and adipose tissue, resulting in protection against high fat diet-induced obesity. DGKδ overexpression recapitulates exercise-induced adaptations on energy homeostasis and skeletal muscle gene expression profiles.

Keywords:  Exercise; Glucose metabolism; Lipid metabolism; Lipid species; Obesity

DOI:  https://doi.org/10.1016/j.metabol.2024.155939
Elife. 2024 Jun 03. pii: RP91924. [Epub ahead of print]13

Agent-based model demonstrates the impact of nonlinear, complex interactions between cytokinces on muscle regeneration.

Megan Haase, Tien Comlekoglu, Alexa Petrucciani, Shayn M Peirce, Silvia S Blemker.

  Muscle regeneration is a complex process due to dynamic and multiscale biochemical and cellular interactions, making it difficult to identify microenvironmental conditions that are beneficial to muscle recovery from injury using experimental approaches alone. To understand the degree to which individual cellular behaviors impact endogenous mechanisms of muscle recovery, we developed an agent-based model (ABM) using the Cellular-Potts framework to simulate the dynamic microenvironment of a cross-section of murine skeletal muscle tissue. We referenced more than 100 published studies to define over 100 parameters and rules that dictate the behavior of muscle fibers, satellite stem cells (SSCs), fibroblasts, neutrophils, macrophages, microvessels, and lymphatic vessels, as well as their interactions with each other and the microenvironment. We utilized parameter density estimation to calibrate the model to temporal biological datasets describing cross-sectional area (CSA) recovery, SSC, and fibroblast cell counts at multiple timepoints following injury. The calibrated model was validated by comparison of other model outputs (macrophage, neutrophil, and capillaries counts) to experimental observations. Predictions for eight model perturbations that varied cell or cytokine input conditions were compared to published experimental studies to validate model predictive capabilities. We used Latin hypercube sampling and partial rank correlation coefficient to identify in silico perturbations of cytokine diffusion coefficients and decay rates to enhance CSA recovery. This analysis suggests that combined alterations of specific cytokine decay and diffusion parameters result in greater fibroblast and SSC proliferation compared to individual perturbations with a 13% increase in CSA recovery compared to unaltered regeneration at 28 days. These results enable guided development of therapeutic strategies that similarly alter muscle physiology (i.e. converting extracellular matrix [ECM]-bound cytokines into freely diffusible forms as studied in cancer therapeutics or delivery of exogenous cytokines) during regeneration to enhance muscle recovery after injury.

Keywords:  agent-based model; cell biology; computational biology; cytokine dynamics; mouse; muscle regeneration; skeletal muscle; systems biology

DOI:  https://doi.org/10.7554/eLife.91924
J Physiol. 2024 Jun 01.

Exercise training alters skeletal muscle microvascular endothelial cell properties in recent postmenopausal females.

L B Nørregaard, C C Hansen, K A Wickham, S Møller, K Olsen, T Ehlers, J Bangsbo, Y Hellsten.

  The present study examined and compared the impact of exercise training on redox and molecular properties of human microvascular endothelial cells derived from skeletal muscle biopsies from sedentary recent (RPF, ≤ 5 years as postmenopausal) and late (LPF, ≥ 10 years as postmenopausal) postmenopausal females. Resting skeletal muscle biopsies were obtained before and after 8 weeks of intense aerobic exercise training for isolation of microvascular endothelial cells and determination of skeletal muscle angiogenic proteins and capillarisation. The microvascular endothelial cells were analysed for mitochondrial respiration and production of reactive oxygen species (ROS), glycolysis and proteins related to vascular function, redox balance and oestrogen receptors. Exercise training led to a reduced endothelial cell ROS formation (∼50%; P = 0.009 and P = 0.020 for intact and permeabilized cells (state 3), respectively) in RPF only, with no effect on endothelial mitochondrial capacity in either group. Basal endothelial cell lactate formation was higher (7%; P = 0.028), indicating increased glycolysis, after compared to before the exercise training period in RPF only. Baseline endothelial G protein-coupled oestrogen receptor (P = 0.028) and muscle capillarisation (P = 0.028) was lower in LPF than in RPF. Muscle vascular endothelial growth factor protein was higher (32%; P = 0.002) following exercise training in LPF only. Exercise training did not influence endothelial cell proliferation or skeletal muscle capillarisation in either group, but the CD31 level in the muscle tissue, indicating endothelial cell content, was higher (>50%; P < 0.05) in both groups. In conclusion, 8 weeks of intense aerobic exercise training reduces ROS formation and enhances glycolysis in microvascular endothelial cells from RPF but does not induce skeletal muscle angiogenesis. KEY POINTS: Late postmenopausal females have been reported to achieve limited vascular adaptations to exercise training. There is a paucity of data on the effect of exercise training on isolated skeletal muscle microvascular endothelial cells (MMECs). In this study the formation of reactive oxygen species in MMECs was reduced and glycolysis increased after 8 weeks of aerobic exercise training in recent but not late postmenopausal females. Late postmenopausal females had lower levels of G protein-coupled oestrogen receptor in MMECs and lower skeletal muscle capillary density at baseline. Eight weeks of intense exercise training altered MMEC properties but did not induce skeletal muscle angiogenesis in postmenopausal females.

Keywords:  angiogenesis; capillarisation; endothelial cells; exercise training; metabolism; mitochondrial function; postmenopausal females

DOI:  https://doi.org/10.1113/JP286269
J Orthop Surg Res. 2024 Jun 02. 19(1): 329

miR-27b-3p reduces muscle fibrosis during chronic skeletal muscle injury by targeting TGF-βR1/Smad pathway.

Hang Yao, Jin Qian, Xu-Ting Bian, Lin Guo, Kang-Lai Tang, Xu Tao.

  BACKGROUND: Fibrosis is a significant pathological feature of chronic skeletal muscle injury, profoundly affecting muscle regeneration. Fibro-adipogenic progenitors (FAPs) have the ability to differentiate into myofibroblasts, acting as a primary source of extracellular matrix (ECM). the process by which FAPs differentiate into myofibroblasts during chronic skeletal muscle injury remains inadequately explored.METHOD: mouse model with sciatic nerve denervated was constructed and miRNA expression profiles between the mouse model and uninjured mouse were analyzed. qRT/PCR and immunofluorescence elucidated the effect of miR-27b-3p on fibrosis in vivo and in vitro. Dual-luciferase reporter identified the target gene of miR-27b-3p, and finally knocked down or overexpressed the target gene and phosphorylation inhibition of Smad verified the influence of downstream molecules on the abundance of miR-27b-3p and fibrogenic differentiation of FAPs.
RESULT: FAPs derived from a mouse model with sciatic nerves denervated exhibited a progressively worsening fibrotic phenotype over time. Introducing agomiR-27b-3p effectively suppressed fibrosis both in vitro and in vivo. MiR-27b-3p targeted Transforming Growth Factor Beta Receptor 1 (TGF-βR1) and the abundance of miR-27b-3p was negatively regulated by TGF-βR1/Smad.
CONCLUSION: miR-27b-3p targeting the TGF-βR1/Smad pathway is a novel mechanism for regulating fibrogenic differentiation of FAPs. Increasing abundance of miR-27b-3p, suppressing expression of TGF-βR1 and inhibiting phosphorylation of smad3 presented potential strategies for treating fibrosis in chronic skeletal muscle injury.

Keywords:  Fibro-adipogenic progenitors; Fibrosis; MicroRNAs; Muscle injury

DOI:  https://doi.org/10.1186/s13018-024-04733-9
Aging Cell. 2024 Jun 05. e14236

Identification of nicotinamide N-methyltransferase as a promising therapeutic target for sarcopenia.

Rui Liang, Qiao Xiang, Miao Dai, Taiping Lin, Dongmei Xie, Quhong Song, Yu Liu, Jirong Yue.

  Sarcopenia is a significant geriatric syndrome that involves the loss of skeletal muscle mass and strength. Due to its substantial endocrine role, the metabolic microenvironment of skeletal muscle undergoes changes with age. Examining the pathogenesis of sarcopenia through focusing on metabolic dysregulation could offer insights for developing more effective intervention strategies. In this study, we analyzed the transcriptomics data to identify specific genes involved in the regulation of metabolism in skeletal muscle during the development of sarcopenia. Three machine learning algorithms were employed to screen key target genes exhibiting strong correlations with metabolism, which were further validated using RNA-sequencing data and publicly accessible datasets. Among them, the metabolic enzyme nicotinamide N-methyltransferase (NNMT) was elevated in sarcopenia, and predicted sarcopenia with an area under the curve exceeding 0.7, suggesting it as a potential therapeutic target for sarcopenia. As expected, inhibition of NNMT improved the grip strength in aging mice and alleviated age-related decline in the mass index of the quadriceps femoris muscles and whole-body lean mass index. Additionally, the NNMTi treatment increased the levels of nicotinamide adenine dinucleotide (NAD+) content, as well as PGC1α and p-AMPK expression in the muscles of both the D-galactose-treated mouse model and naturally aging mouse model. Overall, this work demonstrates NNMT as a promising target for preventing age-related decline in muscle mass and strength.

Keywords:  NAD+; NNMT; diagnostic biomarker; metabolic dysregulation; sarcopenia

DOI:  https://doi.org/10.1111/acel.14236
FASEB J. 2024 Jun 15. 38(11): e23702

Muscle-specific pyruvate kinase isoforms, PKM1 and PKM2, regulate mammalian SWI/SNF proteins and histone 3 phosphorylation during myoblast differentiation.

Monserrat Olea-Flores, Tapan Sharma, Odette Verdejo-Torres, Imaru DiBartolomeo, Paul R Thompson, Teresita Padilla-Benavides, Anthony N Imbalzano.

  Pyruvate kinase is a glycolytic enzyme that converts phosphoenolpyruvate and ADP into pyruvate and ATP. There are two genes that encode pyruvate kinase in vertebrates; Pkm and Pkl encode muscle- and liver/erythrocyte-specific forms, respectively. Each gene encodes two isoenzymes due to alternative splicing. Both muscle-specific enzymes, PKM1 and PKM2, function in glycolysis, but PKM2 also has been implicated in gene regulation due to its ability to phosphorylate histone 3 threonine 11 (H3T11) in cancer cells. Here, we examined the roles of PKM1 and PKM2 during myoblast differentiation. RNA-seq analysis revealed that PKM2 promotes the expression of Dpf2/Baf45d and Baf250a/Arid1A. DPF2 and BAF250a are subunits that identify a specific sub-family of the mammalian SWI/SNF (mSWI/SNF) of chromatin remodeling enzymes that is required for the activation of myogenic gene expression during differentiation. PKM2 also mediated the incorporation of DPF2 and BAF250a into the regulatory sequences controlling myogenic gene expression. PKM1 did not affect expression but was required for nuclear localization of DPF2. Additionally, PKM2 was required not only for the incorporation of phosphorylated H3T11 in myogenic promoters but also for the incorporation of phosphorylated H3T6 and H3T45 at myogenic promoters via regulation of AKT and protein kinase C isoforms that phosphorylate those amino acids. Our results identify multiple unique roles for PKM2 and a novel function for PKM1 in gene expression and chromatin regulation during myoblast differentiation.

Keywords:  H3 phosphorylation; SWI/SNF; chromatin remodeling enzymes; gene regulation; myoblast differentiation; pyruvate kinase

DOI:  https://doi.org/10.1096/fj.202400784R
Biochem Cell Biol. 2024 Jun 06.

Skeletal Muscle Mitochondrial Morphology Negatively Affected in Mice Lacking Xin.

Grace Martin, Dhuha Al-Sajee, Molly Gingrich, Rimsha Chattha, Michael Akcan, Cynthia M F Monaco, Meghan C Hughes, Christopher G R Perry, Irena A Rebalka, Mark A Tarnopolsky, Thomas James Hawke.

Altered mitochondrial structure and function are implicated in the functional decline of skeletal muscle. Numerous cytoskeletal proteins are known to affect mitochondrial homeostasis, but this complex network is still being unraveled. Here, we investigated mitochondrial alterations in mice lacking the cytoskeletal adapter protein, XIN (XIN-/-). XIN-/- and wild-type littermate male and female mice were fed a chow or high-fat diet (HFD; 60% kcal fat) for 8 weeks before analyses of their skeletal muscles was conducted. Immuno-electron microscopy (EM) and immunofluorescence staining revealed XIN in the mitochondria and peri-mitochondrial areas, as well as the myoplasm. Intermyofibrillar mitochondria in chow-fed XIN-/- mice were notably different from wild-type (large, and/or swollen in appearance). Succinate Dehydrogenase and Cytochrome Oxidase IV staining indicated greater evidence of mitochondrial enzyme activity in XIN-/- mice. No difference in body mass gains or glucose handling was observed between cohorts with HFD. However, EM revealed significantly greater mitochondrial density with evident structural abnormalities (swelling, reduced cristae density) in XIN-/- mice. Absolute Complex I and II-supported respiration was not different between groups, but relative to mitochondrial density, was significantly lower in XIN-/-. These results provide the first evidence for a role of XIN in maintaining mitochondrial morphology and function.

DOI: https://doi.org/10.1139/bcb-2024-0034
Genes Dis. 2024 Sep;11(5): 101083

SPNS1 ablation drives skeletal muscle atrophy by disrupting mitophagy, mitochondrial function, and apoptosis in mice.

Xianzhong Zhang, Fengmin Zhang, Haofan Wu, Zhen Yu, Chengle Zhuang.

DOI: https://doi.org/10.1016/j.gendis.2023.101083
bioRxiv. 2024 May 25. pii: 2024.05.24.595789. [Epub ahead of print]

Skeletal muscle myosin heavy chain protein fragmentation as a potential marker of protein degradation in response to resistance training and disuse atrophy.

Daniel L Plotkin, Madison L Mattingly, Derick A Anglin, J Max Michel, Joshua S Godwin, Mason C McIntosh, João G A Bergamasco, Maíra C Scarpelli, Vitor Angleri, Lemuel W Taylor, Darryn S Willoughby, C Brooks Mobley, Andreas N Kavazis, Carlos Ugrinowitsch, Cleiton A Libardi, Michael D Roberts.

We sought to examine how resistance exercise (RE), cycling exercise, and disuse atrophy affect myosin heavy chain (MyHC) protein fragmentation in humans. In the first study (1boutRE), younger adult men (n=8; 5±2 years of RE experience) performed a lower body RE bout with vastus lateralis (VL) biopsies obtained immediately before, 3-, and 6-hours post-exercise. In the second study (10weekRT), VL biopsies were obtained in untrained younger adults (n=36, 18 men and 18 women) before and 24 hours (24h) after their first/naïve RE bout. These participants also engaged in 10 weeks (24 sessions) of resistance training and donated VL biopsies before and 24h after their last RE bout. VL biopsies were also examined from a third acute cycling study (n=7) and a fourth study involving two weeks of leg immobilization (n=20, 15 men and 5 women) to determine how MyHC fragmentation was affected. In the 1boutRE study, the fragmentation of all MyHC isoforms (MyHC Total ) increased 3 hours post-RE (∼ +200%, p=0.018) and returned to pre-exercise levels by 6 hours post-RE. Immunoprecipitation of MyHC Total revealed ubiquitination levels remained unaffected at the 3- and 6-hour post-RE time points. Interestingly, a greater increase in magnitude for MyHC type IIa versus I isoform fragmentation occurred 3-hours post-RE (8.6±6.3-fold versus 2.1±0.7-fold, p=0.018). In all 10weekRT participants, the first/naïve and last RE bouts increased MyHC Total fragmentation 24h post-RE (+65% and +36%, respectively; p<0.001); however, the last RE bout response was attenuated compared to the first bout (p=0.045). The first/naïve bout response was significantly elevated in females only (p<0.001), albeit females also demonstrated a last bout attenuation response (p=0.002). Although an acute cycling bout did not alter MyHC Total fragmentation, ∼8% VL atrophy with two weeks of leg immobilization led to robust MyHC Total fragmentation (+108%, p<0.001), and no sex-based differences were observed. In summary, RE and disuse atrophy increase MyHC protein fragmentation. A dampened response with 10 weeks of resistance training, and more refined responses in well-trained men, suggest this is an adaptive process. Given the null polyubiquitination IP findings, more research is needed to determine how MyHC fragments are processed. Moreover, further research is needed to determine how aging and disease-associated muscle atrophy affect these outcomes, and whether MyHC fragmentation is a viable surrogate for muscle protein turnover rates.

DOI: https://doi.org/10.1101/2024.05.24.595789
FEBS Lett. 2024 Jun 02.

Nuclear receptor Nur77 and Yin-Yang 1 synergistically increase mitochondrial abundance and activity in macrophages.

Duco S Koenis, Inkie J A Evers-van Gogh, Pieter B van Loenen, Wilbert Zwart, Eric Kalkhoven, Carlie J M de Vries.

  Mitochondrial biogenesis requires precise regulation of both mitochondrial-encoded and nuclear-encoded genes. Nuclear receptor Nur77 is known to regulate mitochondrial metabolism in macrophages and skeletal muscle. Here, we compared genome-wide Nur77 binding site and target gene expression in these two cell types, which revealed conserved regulation of mitochondrial genes and enrichment of motifs for the transcription factor Yin-Yang 1 (YY1). We show that Nur77 and YY1 interact, that YY1 increases Nur77 activity, and that their binding sites are co-enriched at mitochondrial ribosomal protein gene loci in macrophages. Nur77 and YY1 co-expression synergistically increases Mrpl1 expression as well as mitochondrial abundance and activity in macrophages but not skeletal muscle. As such, we identify a macrophage-specific Nur77-YY1 interaction that enhances mitochondrial metabolism.

Keywords:  macrophage; mitochondria; nuclear receptor; skeletal muscle; transcriptional regulation

DOI:  https://doi.org/10.1002/1873-3468.14942
Dis Model Mech. 2024 Jun 01. pii: dmm050609. [Epub ahead of print]17(6):

RASopathies - what they reveal about RAS/MAPK signaling in skeletal muscle development.

Katherine A Rauen, William E Tidyman.

  RASopathies are rare developmental genetic syndromes caused by germline pathogenic variants in genes that encode components of the RAS/mitogen-activated protein kinase (MAPK) signal transduction pathway. Although the incidence of each RASopathy syndrome is rare, collectively, they represent one of the largest groups of multiple congenital anomaly syndromes and have severe developmental consequences. Here, we review our understanding of how RAS/MAPK dysregulation in RASopathies impacts skeletal muscle development and the importance of RAS/MAPK pathway regulation for embryonic myogenesis. We also discuss the complex interactions of this pathway with other intracellular signaling pathways in the regulation of skeletal muscle development and growth, and the opportunities that RASopathy animal models provide for exploring the use of pathway inhibitors, typically used for cancer treatment, to correct the unique skeletal myopathy caused by the dysregulation of this pathway.

Keywords:  Cardio-facio-cutaneous syndrome; Costello syndrome; Myopathy; Neurofibromatosis type 1; RAS pathway; RASopathy; Rare disorder; Skeletal myogenesis; Treatment

DOI:  https://doi.org/10.1242/dmm.050609
Nat Aging. 2024 Jun 04.

Cell type mapping of inflammatory muscle diseases highlights selective myofiber vulnerability in inclusion body myositis.

Sven Wischnewski, Thomas Thäwel, Chiseko Ikenaga, Anna Kocharyan, Celia Lerma-Martin, Amel Zulji, Hans-Werner Rausch, David Brenner, Leonie Thomas, Michael Kutza, Brittney Wick, Tim Trobisch, Corinna Preusse, Maximilian Haeussler, Jan Leipe, Albert Ludolph, Angela Rosenbohm, Ahmet Hoke, Michael Platten, Jochen H Weishaupt, Clemens J Sommer, Werner Stenzel, Thomas E Lloyd, Lucas Schirmer.

Inclusion body myositis (IBM) is the most prevalent inflammatory muscle disease in older adults with no effective therapy available. In contrast to other inflammatory myopathies such as subacute, immune-mediated necrotizing myopathy (IMNM), IBM follows a chronic disease course with both inflammatory and degenerative features of pathology. Moreover, causal factors and molecular drivers of IBM progression are largely unknown. Therefore, we paired single-nucleus RNA sequencing with spatial transcriptomics from patient muscle biopsies to map cell-type-specific drivers underlying IBM pathogenesis compared with IMNM muscles and noninflammatory skeletal muscle samples. In IBM muscles, we observed a selective loss of type 2 myonuclei paralleled by increased levels of cytotoxic T and conventional type 1 dendritic cells. IBM myofibers were characterized by either upregulation of cell stress markers featuring GADD45A and NORAD or protein degradation markers including RNF7 associated with p62 aggregates. GADD45A upregulation was preferentially seen in type 2A myofibers associated with severe tissue inflammation. We also noted IBM-specific upregulation of ACHE encoding acetylcholinesterase, which can be regulated by NORAD activity and result in functional denervation of myofibers. Our results provide promising insights into possible mechanisms of myofiber degeneration in IBM and suggest a selective type 2 fiber vulnerability linked to genomic stress and denervation pathways.

DOI: https://doi.org/10.1038/s43587-024-00645-9
bioRxiv. 2024 May 26. pii: 2024.05.24.595817. [Epub ahead of print]

Skeletal myotubes expressing ALS mutant SOD1 induce pathogenic changes, impair mitochondrial axonal transport, and trigger motoneuron death.

Pablo Martínez, Mónica Silva, Sebastián Abarzúa, María Florencia Tevy, Enrique Jaimovich, Martha Constantine-Paton, Fernando J Bustos, Brigitte van Zundert.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the loss of motoneurons (MNs), and despite progress, there is no effective treatment. A large body of evidence shows that astrocytes expressing ALS-linked mutant proteins cause non-cell autonomous toxicity of MNs. Although MNs innervate muscle fibers and ALS is characterized by the early disruption of the neuromuscular junction (NMJ) and axon degeneration, there are controversies about whether muscle contributes to non-cell-autonomous toxicity to MNs. In this study, we generated primary skeletal myotubes from myoblasts derived from ALS mice expressing human mutant SOD1 G93A (termed hereafter mutSOD1). Characterization revealed that mutSOD1 skeletal myotubes display intrinsic phenotypic and functional differences compared to control myotubes generated from non-transgenic (NTg) littermates. Next, we analyzed whether ALS myotubes exert non-cell-autonomous toxicity to MNs. We report that conditioned media from mutSOD1 myotubes (mutSOD1-MCM), but not from control myotubes (NTg-MCM), induced robust death of primary MNs in mixed spinal cord cultures and compartmentalized microfluidic chambers. Our study further revealed that applying mutSOD1-MCM to the MN axonal side in microfluidic devices rapidly reduces mitochondrial axonal transport while increasing Ca2+ transients and reactive oxygen species (i.e., H 2 O 2 ). These results indicate that soluble factor(s) released by mutSOD1 myotubes cause MN axonopathy that leads to lethal pathogenic changes.

DOI: https://doi.org/10.1101/2024.05.24.595817
Physiol Rep. 2024 Jun;12(11): e16093

Recent advances in understanding the mechanisms in skeletal muscle of interaction between exercise and frontline antihyperglycemic drugs.

Sean A Newsom, Matthew M Robinson.

  Regular exercise and antihyperglycemic drugs are front-line treatments for type-2 diabetes and related metabolic disorders. Leading drugs are metformin, sodium-glucose cotransporter-2 inhibitors, and glucagon-like peptide 1 receptor agonists. Each class has strong individual efficacy to treat hyperglycemia, yet the combination with exercise can yield varied results, some of which include blunting of expected metabolic benefits. Skeletal muscle insulin resistance contributes to the development of type-2 diabetes while improvements in skeletal muscle insulin signaling are among key adaptations to exercise training. The current review identifies recent advances into the mechanisms, with an emphasis on skeletal muscle, of the interaction between exercise and these common antihyperglycemic drugs. The review is written toward researchers and thus highlights specific gaps in knowledge and considerations for future study directions.

Keywords:  aerobic; glucagon‐like peptide 1 receptor agonist; metformin; mitochondria; resistance; sodium‐glucose cotransporter‐2 inhibitor

DOI:  https://doi.org/10.14814/phy2.16093
Cell Biosci. 2024 Jun 08. 14(1): 76

Mitochondrial mechanisms in the pathogenesis of chronic inflammatory musculoskeletal disorders.

Kailun Wu, Ju-Sheng Shieh, Ling Qin, Jiong Jiong Guo.

  Chronic inflammatory musculoskeletal disorders characterized by prolonged muscle inflammation, resulting in enduring pain and diminished functionality, pose significant challenges for the patients. Emerging scientific evidence points to mitochondrial malfunction as a pivotal factor contributing to these ailments. Mitochondria play a critical role in powering skeletal muscle activity, but in the context of persistent inflammation, disruptions in their quantity, configuration, and performance have been well-documented. Various disturbances, encompassing alterations in mitochondrial dynamics (such as fission and fusion), calcium regulation, oxidative stress, biogenesis, and the process of mitophagy, are believed to play a central role in the progression of these disorders. Additionally, unfolded protein responses and the accumulation of fatty acids within muscle cells may adversely affect the internal milieu, impairing the equilibrium of mitochondrial functioning. The structural discrepancies between different mitochondrial subsets namely, intramyofibrillar and subsarcolemmal mitochondria likely impact their metabolic capabilities and susceptibility to inflammatory influences. The release of signals from damaged mitochondria is known to incite inflammatory responses. Intriguingly, migrasomes and extracellular vesicles serve as vehicles for intercellular transfer of mitochondria, aiding in the removal of impaired mitochondria and regulation of inflammation. Viral infections have been implicated in inducing stress on mitochondria. Prolonged dysfunction of these vital organelles sustains oxidative harm, metabolic irregularities, and heightened cytokine release, impeding the body's ability to repair tissues. This review provides a comprehensive analysis of advancements in understanding changes in the intracellular environment, mitochondrial architecture and distribution, biogenesis, dynamics, autophagy, oxidative stress, cytokines associated with mitochondria, vesicular structures, and associated membranes in the context of chronic inflammatory musculoskeletal disorders. Strategies targeting key elements regulating mitochondrial quality exhibit promise in the restoration of mitochondrial function, alleviation of inflammation, and enhancement of overall outcomes.

Keywords:  Chronic inflammatory musculoskeletal disorders; Extracellular vesicles; Mitochondrial calcium overload; Mitochondrial dynamics; Mitochondrial dysfunction; Mitophagy; Oxidative stress

DOI:  https://doi.org/10.1186/s13578-024-01259-9
Elife. 2024 Jun 03. pii: RP87434. [Epub ahead of print]12

Styxl2 regulates de novo sarcomere assembly by binding to non-muscle myosin IIs and promoting their degradation.

Xianwei Chen, Yanfeng Li, Jin Xu, Yong Cui, Qian Wu, Haidi Yin, Yuying Li, Chuan Gao, Liwen Jiang, Huating Wang, Zilong Wen, Zhongping Yao, Zhenguo Wu.

  Styxl2, a poorly characterized pseudophosphatase, was identified as a transcriptional target of the Jak1-Stat1 pathway during myoblast differentiation in culture. Styxl2 is specifically expressed in vertebrate striated muscles. By gene knockdown in zebrafish or genetic knockout in mice, we found that Styxl2 plays an essential role in maintaining sarcomere integrity in developing muscles. To further reveal the functions of Styxl2 in adult muscles, we generated two inducible knockout mouse models: one with Styxl2 being deleted in mature myofibers to assess its role in sarcomere maintenance, and the other in adult muscle satellite cells (MuSCs) to assess its role in de novo sarcomere assembly. We find that Styxl2 is not required for sarcomere maintenance but functions in de novo sarcomere assembly during injury-induced muscle regeneration. Mechanistically, Styxl2 interacts with non-muscle myosin IIs, enhances their ubiquitination, and targets them for autophagy-dependent degradation. Without Styxl2, the degradation of non-muscle myosin IIs is delayed, which leads to defective sarcomere assembly and force generation. Thus, Styxl2 promotes de novo sarcomere assembly by interacting with non-muscle myosin IIs and facilitating their autophagic degradation.

Keywords:  Styxl2; autophagy; developmental biology; mouse; non-muscle myosin II; pseudophosphatase; sarcomere assembly; zebrafish

DOI:  https://doi.org/10.7554/eLife.87434
Physiol Rep. 2024 Jun;12(11): e16047

Acetate derived from the intestinal tract has a critical role in maintaining skeletal muscle mass and strength in mice.

Saki Kobayashi, Katsutaro Morino, Takuya Okamoto, Mitsumi Tanaka, Shogo Ida, Natsuko Ohashi, Koichiro Murata, Tsuyoshi Yanagimachi, Juro Sakai, Hiroshi Maegawa, Yukihiro Fujita, Shinji Kume.

  Acetate is a short-chain fatty acid (SCFA) that is produced by microbiota in the intestinal tract. It is an important nutrient for the intestinal epithelium, but also has a high plasma concentration and is used in the various tissues. Acetate is involved in endurance exercise, but its role in resistance exercise remains unclear. To investigate this, mice were administered either multiple antibiotics with and without oral acetate supplementation or fed a low-fiber diet. Antibiotic treatment for 2 weeks significantly reduced grip strength and the cross-sectional area (CSA) of muscle fiber compared with the control group. Intestinal concentrations of SCFAs were reduced in the antibiotic-treated group. Oral administration of acetate with antibiotics prevented antibiotic-induced weakness of skeletal muscle and reduced CSA of muscle fiber. Similarly, a low-fiber diet for 1 year significantly reduced the CSA of muscle fiber and fecal and plasma acetate concentrations. To investigate the role of acetate as an energy source, acetyl-CoA synthase 2 knockout mice were used. These mice had a shorter lifespan, reduced skeletal muscle mass and smaller CSA of muscle fiber than their wild type littermates. In conclusion, acetate derived from the intestinal microbiome can contribute to maintaining skeletal muscle performance.

Keywords:  acetate; microbiome; short‐chain fatty acid; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.16047