bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2023‒10‒01
forty papers selected by
Anna Vainshtein, Craft Science Inc.
  1. DOCK3 regulates normal skeletal muscle regeneration and glucose metabolism.
  2. A Novel Imaging Method (FIM-ID) Reveals that Myofibrillogenesis Plays a Major Role in the Mechanically Induced Growth of Skeletal Muscle.
  3. Bleomycin-treated myoblasts undergo p21-associated cellular senescence and have severely impaired differentiation.
  4. Age-related changes of skeletal muscle metabolic response to contraction are also sex-dependent.
  5. Identification of a muscle-specific isoform of VMA21 as a potent actor in X-linked myopathy with excessive autophagy pathogenesis.
  6. Emergence and Progression of Behavioral Motor Deficits and Skeletal Muscle Atrophy across the Adult Lifespan of the Rat.
  7. Toward Ameliorating Insulin Resistance: Targeting a Novel PAK1 Signaling Pathway Required for Skeletal Muscle Mitochondrial Function.
  8. Muscle-specific overexpression of Atg2 gene and endurance exercise delay age-related deteriorations of skeletal muscle and heart function via activating the AMPK/Sirt1/PGC-1α pathway in male Drosophila.
  9. Anabolic Resistance in the Pathogenesis of Sarcopenia in the Elderly: Role of Nutrition and Exercise in Young and Old People.
  10. Biological sex divergence in transcriptomic profiles during the onset of hindlimb unloading-induced atrophy.
  11. Extracellular matrix contribution to disease progression and dysfunction in myopathy.
  12. Metabolic crosstalk between skeletal muscle cells and liver through IRF4-FSTL1 in nonalcoholic steatohepatitis.
  13. Redox Profile of Skeletal Muscles: Implications for Research Design and Interpretation.
  14. Effects of the order of endurance and high intensity interval exercise in combined training on mice skeletal muscle metabolism.
  15. Dipyridamole activates adenosine A2B receptor and AMPK/cAMP signaling and promotes myogenic differentiation of myoblastic C2C12 cells.
  16. Metformin Protects Rat Skeletal Muscle from Physical Exercise-Induced Injury.
  17. mRNA in situ hybridization exhibits unbalanced nuclear/cytoplasmic dystrophin transcript repartition in Duchenne myogenic cells and skeletal muscle biopsies.
  18. Studying Muscle Transcriptional Dynamics at Single-molecule Scales in Drosophila.
  19. The Effect of SERCA Activation on Functional Characteristics and Signaling of Rat Soleus Muscle upon 7 Days of Unloading.
  20. Dimethyl fumarate modulates the dystrophic disease program following short-term treatment.
  21. Cryo-EM structures of Myomaker reveal a molecular basis for myoblast fusion.
  22. Effects of autoimmune abnormalities on skeletal muscle regeneration after needle puncture in mice.
  23. Anserine is expressed in human cardiac and skeletal muscles.
  24. Highly contractile 3D tissue engineered skeletal muscles from human iPSCs reveal similarities with primary myoblast-derived tissues.
  25. FLII Modulates the Myogenic Differentiation of Progenitor Cells via Actin Remodeling-Mediated YAP1 Regulation.
  26. The long non-coding RNA lnc-H19 is important for endurance exercise by maintaining slow muscle fiber types.
  27. Shank3 related muscular hypotonia is accompanied by increased intracellular calcium concentrations and ion channel dysregulation in striated muscle tissue.
  28. Role of Fyn and the interleukin-6-STAT-3-autophagy axis in sarcopenia.
  29. Cellular and molecular evidence that synaptic Schwann cells contribute to aging of mouse neuromuscular junctions.
  30. Splicing regulation of GFPT1 muscle-specific isoform and its roles in glucose metabolisms and neuromuscular junction.
  31. Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis.
  32. Time-Dependent Changes in Muscle IGF1-IGFBP5-PAPP System after Sciatic Denervation.
  33. Cancer Cachexia: Underlying Mechanisms and Potential Therapeutic Interventions.
  34. The Mitochondrial Calcium Uniporter (MCU): Molecular Identity and Role in Human Diseases.
  35. Effects of exercise prehabilitation on muscle atrophy and contractile properties in hindlimb-unloaded rats.
  36. Evidence for multi-scale power amplification in skeletal muscle.
  37. Dependence of myosin filament structure on intracellular calcium concentration in skeletal muscle.
  38. DDAH1 Protects against Cardiotoxin-Induced Muscle Injury and Regeneration.
  39. Exploring the Therapeutic Potential of Ethyl 3-Hydroxybutyrate in Alleviating Skeletal Muscle Wasting in Cancer Cachexia.
  40. Myosin-binding protein C forms C-links and stabilizes OFF states of myosin.
  1. FASEB J. 2023 10;37(10): e23198
    DOCK3 regulates normal skeletal muscle regeneration and glucose metabolism.
    Adrienne Samani, Muthukumar Karuppasamy, Katherine G English, Colin A Siler, Yimin Wang, Jeffrey J Widrick, Matthew S Alexander.
      DOCK (dedicator of cytokinesis) is an 11-member family of typical guanine nucleotide exchange factors (GEFs) expressed in the brain, spinal cord, and skeletal muscle. Several DOCK proteins have been implicated in maintaining several myogenic processes such as fusion. We previously identified DOCK3 as being strongly upregulated in Duchenne muscular dystrophy (DMD), specifically in the skeletal muscles of DMD patients and dystrophic mice. Dock3 ubiquitous KO mice on the dystrophin-deficient background exacerbated skeletal muscle and cardiac phenotypes. We generated Dock3 conditional skeletal muscle knockout mice (Dock3 mKO) to characterize the role of DOCK3 protein exclusively in the adult muscle lineage. Dock3 mKO mice presented with significant hyperglycemia and increased fat mass, indicating a metabolic role in the maintenance of skeletal muscle health. Dock3 mKO mice had impaired muscle architecture, reduced locomotor activity, impaired myofiber regeneration, and metabolic dysfunction. We identified a novel DOCK3 interaction with SORBS1 through the C-terminal domain of DOCK3 that may account for its metabolic dysregulation. Together, these findings demonstrate an essential role for DOCK3 in skeletal muscle independent of DOCK3 function in neuronal lineages.
    Keywords:  DOCK3; GLUT4 processing; regeneration; skeletal muscle
    DOI:  https://doi.org/10.1096/fj.202300386RR
  2. bioRxiv. 2023 Sep 15. pii: 2023.09.13.557204. [Epub ahead of print]
    A Novel Imaging Method (FIM-ID) Reveals that Myofibrillogenesis Plays a Major Role in the Mechanically Induced Growth of Skeletal Muscle.
    Kent W Jorgenson, Jamie E Hibbert, Ramy K A Sayed, Anthony N Lange, Joshua S Godwin, Paulo H C Mesquita, Bradley A Ruple, Mason C McIntosh, Andreas N Kavazis, Michael D Roberts, Troy A Hornberger.
      An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the number of myofibrils (i.e., myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (FIM-ID). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a foundationally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it.
    DOI:  https://doi.org/10.1101/2023.09.13.557204
  3. Geroscience. 2023 Sep 26.
    Bleomycin-treated myoblasts undergo p21-associated cellular senescence and have severely impaired differentiation.
    Michael Kamal, Sophie Joanisse, Gianni Parise.
      As we age, the ability to regenerate and repair skeletal muscle damage declines, partially due to increasing dysfunction of muscle resident stem cells-satellite cells (SC). Recent evidence implicates cellular senescence, which is the irreversible arrest of proliferation, as a potentiator of SC impairment during aging. However, little is known about the role of senescence in SC, and there is a large discrepancy in senescence classification within skeletal muscle. The purpose of this study was to develop a model of senescence in skeletal muscle myoblasts and identify how common senescence-associated biomarkers respond. Low-passage C2C12 myoblasts were treated with bleomycin or vehicle and then evaluated for cytological and molecular senescence markers, proliferation status, cell cycle kinetics, and differentiation potential. Bleomycin treatment caused double-stranded DNA breaks, which upregulated p21 mRNA and protein, potentially through NF-κB and senescence-associated super enhancer (SASE) signaling (p < 0.01). Consequently, cell proliferation was abruptly halted due to G2/M-phase arrest (p < 0.01). Bleomycin-treated myoblasts displayed greater senescence-associated β-galactosidase staining (p < 0.01), which increased over several days. These myoblasts remained senescent following 6 days of differentiation and had significant impairments in myotube formation (p < 0.01). Furthermore, our results show that senescence can be maintained despite the lack of p16 gene expression in C2C12 myoblasts. In conclusion, bleomycin treatment provides a valid model of damage-induced senescence that was associated with elevated p21, reduced myoblast proliferation, and aberrant cell cycle kinetics, while confirming that a multi-marker approach is needed for the accurate classification of senescence within skeletal muscle.
    Keywords:  Aging; Bleomycin; Myoblast; Senescence; Skeletal muscle
    DOI:  https://doi.org/10.1007/s11357-023-00929-9
  4. J Physiol. 2023 Sep 23.
    Age-related changes of skeletal muscle metabolic response to contraction are also sex-dependent.
    Matthew D Campbell, Danijel Djukovic, Daniel Raftery, David J Marcinek.
      Mitochondria adapt to increased energy demands during muscle contraction by acutely altering metabolite fluxes and substrate oxidation. With age, an impaired mitochondrial metabolic response may contribute to reduced exercise tolerance and decreased skeletal muscle mass, specific force, increased overall fatty depositions in the skeletal muscle, frailty and depressed energy maintenance. We hypothesized that elevated energy stress in mitochondria with age alters the capacity of mitochondria to utilize different substrates following muscle contraction. To test this hypothesis, we used in vivo electrical stimulation to simulate high-intensity intervals (HII) or low intensity steady-state (LISS) exercise in young (5-7 months) and aged (27-29 months) male and female mice to characterize effects of age and sex on mitochondrial substrate utilization in skeletal muscle following contraction. Mitochondrial respiration using glutamate decreased in aged males following HII and glutamate oxidation was inhibited following HII in both the contracted and non-stimulated muscle of aged female muscle. Analyses of the muscle metabolome of female mice indicated that changes in metabolic pathways induced by HII and LISS contractions in young muscle are absent in aged muscle. To test improved mitochondrial function on substrate utilization following HII, we treated aged females with elamipretide (ELAM), a mitochondrially-targeted peptide shown to improve mitochondrial bioenergetics and restore redox status in aged muscle. ELAM removed inhibition of glutamate oxidation and showed increased metabolic pathway changes following HII, suggesting rescuing redox status and improving bioenergetic function in mitochondria from aged muscle increases glutamate utilization and enhances the metabolic response to muscle contraction in aged muscle. KEY POINTS: Acute local contraction of gastrocnemius can systemically alter mitochondrial respiration in non-stimulated muscle. Age-related changes in mitochondrial respiration using glutamate or palmitoyl carnitine following contraction are sex-dependent. Respiration using glutamate after high-intensity contraction is inhibited in aged female muscle. Metabolite level and pathway changes following muscle contraction decrease with age in female mice. Treatment with the mitochondrially-targeted peptide elamipretide can partially rescue metabolite response to muscle contraction.
    Keywords:  age; high-intensity intervals; low-intensity steady-state; metabolism; mitochondrial adaptation; sarcopenia; sex specific effects
    DOI:  https://doi.org/10.1113/JP285124
  5. Hum Mol Genet. 2023 Sep 26. pii: ddad164. [Epub ahead of print]
    Identification of a muscle-specific isoform of VMA21 as a potent actor in X-linked myopathy with excessive autophagy pathogenesis.
    Ilaria Cocchiararo, Olivia Cattaneo, Jayasimman Rajendran, Florent Chabry, Mélanie Cornut, Hadrien Soldati, Anne Bigot, Kamel Mamchaoui, Sara Gibertini, Axelle Bouche, Daniel J Ham, Thomas Laumonier, Alexandre Prola, Perrine Castets.
      Defective lysosomal acidification is responsible for a large range of multi-systemic disorders associated with impaired autophagy. Diseases caused by mutations in the VMA21 gene stand as exceptions, specifically affecting skeletal muscle (X-linked Myopathy with Excessive Autophagy, XMEA) or liver (Congenital Disorder of Glycosylation). VMA21 chaperones vacuolar (v-) ATPase assembly, which is ubiquitously required for proper lysosomal acidification. The reason VMA21 deficiencies affect specific, but divergent tissues remains unknown. Here, we show that VMA21 encodes a yet-unreported long protein isoform, in addition to the previously described short isoform, which we name VMA21-120 and VMA21-101, respectively. In contrast to the ubiquitous pattern of VMA21-101, VMA21-120 was predominantly expressed in skeletal muscle, and rapidly up-regulated upon differentiation of mouse and human muscle precursors. Accordingly, VMA21-120 accumulated during development, regeneration and denervation of mouse skeletal muscle. In contrast, neither induction nor blockade of autophagy, in vitro and in vivo, strongly affected VMA21 isoform expression. Interestingly, VMA21-101 and VMA21-120 both localized to the sarcoplasmic reticulum of muscle cells, and interacted with the v-ATPase. While VMA21 deficiency impairs autophagy, VMA21-101 or VMA21-120 overexpression had limited impact on autophagic flux in muscle cells. Importantly, XMEA-associated mutations lead to both VMA21-101 deficiency and loss of VMA21-120 expression. These results provide important insights into the clinical diversity of VMA21-related diseases and uncover a muscle-specific VMA21 isoform that potently contributes to XMEA pathogenesis.
    Keywords:  VMA21; XMEA; autophagy; myogenesis; v-ATPase
    DOI:  https://doi.org/10.1093/hmg/ddad164
  6. Biology (Basel). 2023 Aug 28. pii: 1177. [Epub ahead of print]12(9):
    Emergence and Progression of Behavioral Motor Deficits and Skeletal Muscle Atrophy across the Adult Lifespan of the Rat.
    Max GrönholdtKlein, Ali Gorzi, Lingzhan Wang, Erik Edström, Eric Rullman, Mikael Altun, Brun Ulfhake.
      The facultative loss of muscle mass and function during aging (sarcopenia) poses a serious threat to our independence and health. When activities of daily living are impaired (clinical phase), it appears that the processes leading to sarcopenia have been ongoing in humans for decades (preclinical phase). Here, we examined the natural history of sarcopenia in male outbred rats to compare the occurrence of motor behavioral deficits with the degree of muscle wasting and to explore the muscle-associated processes of the preclinical and clinical phases, respectively. Selected metrics were validated in female rats. We used the soleus muscle because of its long duty cycles and its importance in postural control. Results show that gait and coordination remain intact through middle age (40-60% of median lifespan) when muscle mass is largely preserved relative to body weight. However, the muscle shows numerous signs of remodeling with a shift in myofiber-type composition toward type I. As fiber-type prevalence shifted, fiber-type clustering also increased. The number of hybrid fibers, myofibers with central nuclei, and fibers expressing embryonic myosin increased from being barely detectable to a significant number (5-10%) at late middle age. In parallel, TGFβ1, Smad3, FBXO32, and MuRF1 mRNAs increased. In early (25-month-old) and advanced (30-month-old) aging, gait and coordination deteriorate with the progressive loss of muscle mass. In late middle age and early aging due to type II atrophy (>50%) followed by type I atrophy (>50%), the number of myofibers did not correlate with this process. In advanced age, atrophy is accompanied by a decrease in SCs and βCatenin mRNA, whereas several previously upregulated transcripts were downregulated. The re-expression of embryonic myosin in myofibers and the upregulation of mRNAs encoding the γ-subunit of the nicotinic acetylcholine receptor, the neuronal cell adhesion molecule, and myogenin that begins in late middle age suggest that one mechanism driving sarcopenia is the disruption of neuromuscular connectivity. We conclude that sarcopenia in rats, as in humans, has a long preclinical phase in which muscle undergoes extensive remodeling to maintain muscle mass and function. At later time points, these adaptive mechanisms fail, and sarcopenia becomes clinically manifest.
    Keywords:  aging; behavior; denervation; dynapenia; sarcopenia; skeletal muscle atrophy
    DOI:  https://doi.org/10.3390/biology12091177
  7. Antioxidants (Basel). 2023 Aug 22. pii: 1658. [Epub ahead of print]12(9):
    Toward Ameliorating Insulin Resistance: Targeting a Novel PAK1 Signaling Pathway Required for Skeletal Muscle Mitochondrial Function.
    Rekha Balakrishnan, Pablo A Garcia, Rajakrishnan Veluthakal, Janice M Huss, Joseph M Hoolachan, Debbie C Thurmond.
      The p21-activated kinase 1 (PAK1) is required for insulin-stimulated glucose uptake in skeletal muscle cells. However, whether PAK1 regulates skeletal muscle mitochondrial function, which is a central determinant of insulin sensitivity, is unknown. Here, the effect of modulating PAK1 levels (knockdown via siRNA, overexpression via adenoviral transduction, and/or inhibition of activation via IPA3) on mitochondrial function was assessed in normal and/or insulin-resistant rat L6.GLUT4myc and human muscle (LHCN-M2) myotubes. Human type 2 diabetes (T2D) and non-diabetic (ND) skeletal muscle samples were also used for validation of the identified signaling elements. PAK1 depletion in myotubes decreased mitochondrial copy number, respiration, altered mitochondrial structure, downregulated PGC1α (a core regulator of mitochondrial biogenesis and oxidative metabolism) and PGC1α activators, p38 mitogen-activated protein kinase (p38MAPK) and activating transcription factor 2 (ATF2). PAK1 enrichment in insulin-resistant myotubes improved mitochondrial function and rescued PGC1α expression levels. Activated PAK1 was localized to the cytoplasm, and PAK1 enrichment concurrent with p38MAPK inhibition did not increase PGC1α levels. PAK1 inhibition and enrichment also modified nuclear phosphorylated-ATF2 levels. T2D human samples showed a deficit for PGC1α, and PAK1 depletion in LHCN-M2 cells led to reduced mitochondrial respiration. Overall, the results suggest that PAK1 regulates muscle mitochondrial function upstream of the p38MAPK/ATF2/PGC1α-axis pathway.
    Keywords:  PAK1; insulin resistance; mitochondria; skeletal muscle; type 2 diabetes
    DOI:  https://doi.org/10.3390/antiox12091658
  8. FASEB J. 2023 Nov;37(11): e23214
    Muscle-specific overexpression of Atg2 gene and endurance exercise delay age-related deteriorations of skeletal muscle and heart function via activating the AMPK/Sirt1/PGC-1α pathway in male Drosophila.
    Jing-Feng Wang, Deng-Tai Wen, Shi-Jie Wang, Ying-Hui Gao, Xin-Yuan Yin.
      Atg2 is a key gene in autophagy formation and plays an important role in regulating aging progress. Exercise is an important tool to resist oxidative stress in cells and delay muscle aging. However, the relationship between exercise and the muscle Atg2 gene in regulating skeletal muscle aging remains unclear. Here, overexpression or knockdown of muscle Atg2 gene was achieved by constructing the AtgUAS/MhcGal4 system in Drosophila, and these flies were also subjected to an exercise intervention for 2 weeks. The results showed that both overexpression of Atg2 and exercise significantly increased the climbing speed, climbing endurance, cardiac function, and lifespan of aging flies. They also significantly up-regulated the expression of muscle Atg2, AMPK, Sirt1, and PGC-1α genes, and they significantly reduced muscle malondialdehyde and triglyceride. These positive benefits were even more pronounced when the two were combined. However, the effects of Atg2 knockdown on skeletal muscle, heart, and lifespan were reversed compared to its overexpression. Importantly, exercise ameliorated age-related changes induced by Atg2 knockdown. Therefore, current results confirmed that both overexpression of muscle Atg2 and exercise delayed age-related deteriorations of skeletal muscle, the heart function, and lifespan, and exercise could also reverse age-related changes induced by Atg2 knockdown. The molecular mechanism is related to the overexpression of the Atg2 gene and exercise, which increase the activity of the AMPK/Sirt1/PGC-1α pathway, oxidation and antioxidant balance, and lipid metabolism in aging muscle.
    Keywords:  AMPK/Sirt1/PGC-1α; Atg2; cardiac function; endurance exercise; muscle aging
    DOI:  https://doi.org/10.1096/fj.202301312R
  9. Nutrients. 2023 Sep 20. pii: 4073. [Epub ahead of print]15(18):
    Anabolic Resistance in the Pathogenesis of Sarcopenia in the Elderly: Role of Nutrition and Exercise in Young and Old People.
    Caterina Tezze, Marco Sandri, Paolo Tessari.
      The development of sarcopenia in the elderly is associated with many potential factors and/or processes that impair the renovation and maintenance of skeletal muscle mass and strength as ageing progresses. Among them, a defect by skeletal muscle to respond to anabolic stimuli is to be considered. Common anabolic stimuli/signals in skeletal muscle are hormones (insulin, growth hormones, IGF-1, androgens, and β-agonists such epinephrine), substrates (amino acids such as protein precursors on top, but also glucose and fat, as source of energy), metabolites (such as β-agonists and HMB), various biochemical/intracellular mediators), physical exercise, neurogenic and immune-modulating factors, etc. Each of them may exhibit a reduced effect upon skeletal muscle in ageing. In this article, we overview the role of anabolic signals on muscle metabolism, as well as currently available evidence of resistance, at the skeletal muscle level, to anabolic factors, from both in vitro and in vivo studies. Some indications on how to augment the effects of anabolic signals on skeletal muscle are provided.
    Keywords:  exercise; intracellular signals; nutrition; protein foods; protein synthesis; sarcopenia; skeletal muscle
    DOI:  https://doi.org/10.3390/nu15184073
  10. Am J Physiol Cell Physiol. 2023 Sep 25.
    Biological sex divergence in transcriptomic profiles during the onset of hindlimb unloading-induced atrophy.
    Stavroula Tsitkanou, Francielly Morena da Silva, Ana Regina Cabrera, Eleanor R Schrems, Kevin A Murach, Tyrone A Washington, Megan E Rosa-Caldwell, Nicholas P Greene.
      Disuse-induced muscle atrophy is a common clinical problem observed mainly in older adults, intensive care units patients, or astronauts. Previous studies presented biological sex divergence in progression of disuse-induced atrophy along with differential changes in molecular mechanisms possibly underlying muscle atrophy. The aim of this study was to perform transcriptomic profiling of male and female mice during the onset and progression of unloading disuse-induced atrophy. Male and female mice underwent hindlimb unloading (HU) for 24, 48, 72 and 168h (n=8/group). Muscles were weighed for each cohort and gastrocnemius was used for RNA-sequencing analysis. Females exhibited muscle loss as early as 24h of HU, while males after 168h of HU. In males, pathways related to proteasome degradation were upregulated throughout 168-h HU, while in females these pathways were upregulated up to 72-h HU. Lcn2, a gene contributing to regulation of myogenesis, was upregulated by 6.46-19.86-fold across all time points in females only. A reverse expression of Fosb, a gene related to muscle degeneration, was observed between males (4.27-fold up) and females (4.57-fold down) at 24-h HU. Mitochondrial pathways related to TCA cycle were highly downregulated at 168h of HU in males, while in females this downregulation was less pronounced. Collagen-related pathways were consistently downregulated throughout 168-h HU only in females, suggesting a potential biological sex-specific protective mechanism against disuse-induced fibrosis. In conclusion, females may have protection against HU-induced skeletal muscle mitochondrial degeneration and fibrosis through transcriptional mechanisms, although they may be more vulnerable to HU-induced muscle wasting compared to males.
    Keywords:  Muscle atrophy; disuse; fibrosis; hindlimb unloading; mitochondria
    DOI:  https://doi.org/10.1152/ajpcell.00352.2023
  11. Am J Physiol Cell Physiol. 2023 Sep 25.
    Extracellular matrix contribution to disease progression and dysfunction in myopathy.
    Ashlee M Long, GaHyun Lee, Alexis Demonbreun, Elizabeth M McNally.
      Myopathic processes affect skeletal muscle and heart. In the muscular dystrophies, which are a subset of myopathies, muscle cells are gradually replaced by fibrosis and fat, impairing muscle function as well as regeneration and repair. In addition to skeletal muscle, these genetic disorders often also affect the heart, where fibrofatty infiltration progressively accumulates in the myocardium, impairing heart function. While considerable effort has focused on gene-corrective and gene-replacement approaches to stabilize myofibers and cardiomyocytes, the continual and ongoing deposition of extracellular matrix itself contributes to tissue and organ dysfunction. Transcriptomic and proteomic profiling, along with high resolution imaging and biophysical measurements, have been applied to define extracellular matrix components and their role in contributing to cardiac and skeletal muscle weakness. More recently, decellularization methods have been adapted to an on-slide format to preserve the spatial geography of the extracellular matrix, allowing new insight into matrix remodeling and its direct role in suppressing regeneration in muscle. This review highlights recent literature with focus on the extracellular matrix and molecular mechanisms that contribute to muscle and heart fibrotic disorders. We will also compare how the myopathic matrix differs from healthy matrix, emphasizing how the pathological matrix contributes to disease.
    Keywords:  Extracellular matrix; decellularization; fibrosi; heart; muscle
    DOI:  https://doi.org/10.1152/ajpcell.00182.2023
  12. Nat Commun. 2023 Sep 28. 14(1): 6047
    Metabolic crosstalk between skeletal muscle cells and liver through IRF4-FSTL1 in nonalcoholic steatohepatitis.
    Shanshan Guo, Yonghao Feng, Xiaopeng Zhu, Xinyi Zhang, Hui Wang, Ruwen Wang, Qiongyue Zhang, Yiming Li, Yan Ren, Xin Gao, Hua Bian, Tiemin Liu, Huanqing Gao, Xingxing Kong.
      Inter-organ crosstalk has gained increasing attention in recent times; however, the underlying mechanisms remain unclear. In this study, we elucidate an endocrine pathway that is regulated by skeletal muscle interferon regulatory factor (IRF) 4, which manipulates liver pathology. Skeletal muscle specific IRF4 knockout (F4MKO) mice exhibited ameliorated hepatic steatosis, inflammation, and fibrosis, without changes in body weight, when put on a nonalcoholic steatohepatitis (NASH) diet. Proteomics analysis results suggested that follistatin-like protein 1 (FSTL1) may constitute a link between muscles and the liver. Dual luciferase assays showed that IRF4 can transcriptionally regulate FSTL1. Further, inducing FSTL1 expression in the muscles of F4MKO mice is sufficient to restore liver pathology. In addition, co-culture experiments confirmed that FSTL1 plays a distinct role in various liver cell types via different receptors. Finally, we observed that the serum FSTL1 level is positively correlated with NASH progression in humans. These data indicate a signaling pathway involving IRF4-FSTL1-DIP2A/CD14, that links skeletal muscle cells to the liver in the pathogenesis of NASH.
    DOI:  https://doi.org/10.1038/s41467-023-41832-3
  13. Antioxidants (Basel). 2023 Sep 07. pii: 1738. [Epub ahead of print]12(9):
    Redox Profile of Skeletal Muscles: Implications for Research Design and Interpretation.
    Olga Vasileiadou, George G Nastos, Panagiotis N Chatzinikolaou, Dimitrios Papoutsis, Dimitra I Vrampa, Spyridon Methenitis, Nikos V Margaritelis.
      Mammalian skeletal muscles contain varying proportions of Type I and II fibers, which feature different structural, metabolic and functional properties. According to these properties, skeletal muscles are labeled as 'red' or 'white', 'oxidative' or 'glycolytic', 'slow-twitch' or 'fast-twitch', respectively. Redox processes (i.e., redox signaling and oxidative stress) are increasingly recognized as a fundamental part of skeletal muscle metabolism at rest, during and after exercise. The aim of the present review was to investigate the potential redox differences between slow- (composed mainly of Type I fibers) and fast-twitch (composed mainly of Type IIa and IIb fibers) muscles at rest and after a training protocol. Slow-twitch muscles were almost exclusively represented in the literature by the soleus muscle, whereas a wide variety of fast-twitch muscles were used. Based on our analysis, we argue that slow-twitch muscles exhibit higher antioxidant enzyme activity compared to fast-twitch muscles in both pre- and post-exercise training. This is also the case between heads or regions of fast-twitch muscles that belong to different subcategories, namely Type IIa (oxidative) versus Type IIb (glycolytic), in favor of the former. No safe conclusion could be drawn regarding the mRNA levels of antioxidant enzymes either pre- or post-training. Moreover, slow-twitch skeletal muscles presented higher glutathione and thiol content as well as higher lipid peroxidation levels compared to fast-twitch. Finally, mitochondrial hydrogen peroxide production was higher in fast-twitch muscles compared to slow-twitch muscles at rest. This redox heterogeneity between different muscle types may have ramifications in the analysis of muscle function and health and should be taken into account when designing exercise studies using specific muscle groups (e.g., on an isokinetic dynamometer) or isolated muscle fibers (e.g., electrical stimulation) and may deliver a plausible explanation for the conflicting results about the ergogenic potential of antioxidant supplements.
    Keywords:  antioxidants; enzymes; fibers; oxidative stress; redox; skeletal muscle
    DOI:  https://doi.org/10.3390/antiox12091738
  14. Am J Physiol Regul Integr Comp Physiol. 2023 Sep 25.
    Effects of the order of endurance and high intensity interval exercise in combined training on mice skeletal muscle metabolism.
    Takanaga Shirai, Kazuki Uemichi, Tohru Takemasa.
      Endurance exercise (EE) mainly improves oxidative capacity, whereas, high intensity interval exercise (HIIE) improves also glycolytic capacity. There is a growing body of evidence that suggests that combining endurance exercise (EE) with high-intensity interval exercise (HIIE) can lead to improved athletic performance and fitness outcomes compared to either form of exercise alone. This study aimed to elucidate whether the order in which EE and HIIE are performed in combined training affected oxidative metabolism and glycolysis in mice skeletal muscle. 7 weeks of age male ICR mice were divided into 3 groups: CON (Control), EE-HIIE, HIIE-EE. The total training period was 3 weeks (3 times / week). Mice performed running on a treadmill as endurance exercise and swimming with a weight load of 10% of body weight as swimming. EE prior to HIIE (EE-HIIE) improved running performance in the maximal EE capacity test (all-out test) and partly enhanced the expression levels of molecular signals involved in glycolysis when compared with HIIE prior to EE (HIIE-EE). The order of exercise did not, however, impact the expression of proteins related to mitochondrial dynamics, including those involved in the morphological changes of mitochondria through repeated fusion and fission, as well as oxidative energy metabolism. The findings suggest that the order of exercise has no significant impact on the expression of proteins associated with glycolytic and oxidative energy metabolism. Nevertheless, our results indicate that the order of EE-HIIE may enhance running performance.
    Keywords:  Combined training; Endurance exercise; High intensity interval exercise; Oxidative and glycolytic metabolism; Skeletal muscle
    DOI:  https://doi.org/10.1152/ajpregu.00077.2023
  15. Front Pharmacol. 2023 ;14 1247664
    Dipyridamole activates adenosine A2B receptor and AMPK/cAMP signaling and promotes myogenic differentiation of myoblastic C2C12 cells.
    Miguel Marco-Bonilla, Raquel Herencia, María Fresnadillo, Fernando Huete-Toral, Gonzalo Carracedo, Raquel Largo, Gabriel Herrero-Beaumont, Aránzazu Mediero.
      Introduction: Sarcopenia is defined as a loss of muscle mass and strength. ATP homeostasis is crucial during myogenesis. We determined how the purinergic system modulates myogenesis using dipyridamole (blocks adenosine taken up by the cells) and tenofovir (inhibits ATP release) in a myoblast cell line. Methods: C2C12 cells were differentiated in the presence/absence of tenofovir/dipyridamole, with/without the A2B selective inhibitor PSB-603. Extra-/intracellular nucleotides were examined via HPLC. The expression of muscle differentiation proteins (Pax7, Mif5, MyoD, MyoG, and MHC), PKA/CREB, adenosine receptors (A1, A2A, A2B, and A3), ATP-channel pannexin-1 and the P2X7 receptor was analyzed via WB and RT-PCR. cAMP and AMPK activation was measured. Results: Tenofovir increased intracellular ATP and reduced extracellular adenosine, decreasing Pax7 expression and increasing MHC expression prematurely. Dipyridamole increased intracellular AMP and extracellular adenosine, counteracting the premature myogenesis promoted by tenofovir. All adenosine receptors were expressed during differentiation with dipyridamole, increasing A2B expression. Tenofovir maintained inactive AMPK and decreased cAMP levels, as well as PKAα and pCREB expression, which were recovered with dipyridamole. Discussion: Adenosine and ATP act as mediators in muscle myogenesis. The blockade of ATP release by tenofovir promotes premature myogenesis, with dipyridamole counteracting the premature differentiation promoted by tenofovir via the adenosine A2B receptor and cAMP/AMPK pathways. Therefore, dipyridamole might be of interest as a therapeutic approach in sarcopenia.
    Keywords:  A2B receptor; adenosine; dipyridamole; muscle; sarcopenia
    DOI:  https://doi.org/10.3389/fphar.2023.1247664
  16. Biomedicines. 2023 Aug 22. pii: 2334. [Epub ahead of print]11(9):
    Metformin Protects Rat Skeletal Muscle from Physical Exercise-Induced Injury.
    Giuliana Abbadessa, Eleonora Maniscalco, Loredana Grasso, Jasmin Popara, Federica Di Scipio, Francesco Franco, Daniele Mancardi, Fabio Pigozzi, Paolo Borrione, Giovanni Nicolao Berta, Silvia Racca.
      Metformin (Met) is a drug commonly prescribed in type 2 diabetes mellitus. Its efficacy is due to the suppression of hepatic gluconeogenesis, enhancement of peripheral glucose uptake and lower glucose absorption by the intestine. Recent studies have reported Met efficacy in other clinical applications, such as age-related diseases. Despite the wide clinical use of Met, its mechanism of action on muscle and its effect on muscle performance are unclear. We investigated the effects of Met combined with training on physical performance (PP) in healthy rats receiving Met for 8 weeks while undergoing daily moderate exercise. We evaluated the following: PP through graded endurance exercise test performed before the beginning of the training protocol and 48 h before the end of the training period; blood ALT, AST, LDH and CK-MB levels in order to address muscle damage; and several blood and muscle myokines and the expression of factors believed to be involved in muscle adaptation to exercise. Our data demonstrate that Met does not improve the positive effects of exercise on performance, although it protects myocytes from exercise-induced damage. Moreover, given that Met positively affects exercise-induced muscle adaptation, our data support the idea of the therapeutic application of Met when muscle function and structure are compromised.
    Keywords:  metformin; muscle adaptation; physical performance; skeletal muscle; training
    DOI:  https://doi.org/10.3390/biomedicines11092334
  17. Sci Rep. 2023 09 24. 13(1): 15942
    mRNA in situ hybridization exhibits unbalanced nuclear/cytoplasmic dystrophin transcript repartition in Duchenne myogenic cells and skeletal muscle biopsies.
    Maria Sofia Falzarano, Martina Mietto, Fernanda Fortunato, Marianna Farnè, Fernanda Martini, Pierpaolo Ala, Rita Selvatici, Francesco Muntoni, Alessandra Ferlini.
      To gain insight on dystrophin (DMD) gene transcription dynamics and spatial localization, we assayed the DMD mRNA amount and defined its compartmentalization in myoblasts, myotubes, and skeletal muscle biopsies of Duchenne muscular dystrophy (DMD) patients. Using droplet digital PCR, Real-time PCR, and RNAscope in situ hybridization, we showed that the DMD transcript amount is extremely reduced in both DMD patients' cells and muscle biopsies and that mutation-related differences occur. We also found that, compared to controls, DMD transcript is dramatically reduced in the cytoplasm, as up to 90% of it is localized in nuclei, preferentially at the perinuclear region. Using RNA/protein colocalization experiments, we showed that about 40% of nuclear DMD mRNA is localized in the nucleoli in both control and DMD myogenic cells. Our results clearly show that mutant DMD mRNA quantity is strongly reduced in the patients' myogenic cells and muscle biopsies. Furthermore, mutant DMD mRNA compartmentalization is spatially unbalanced due to a shift in its localization towards the nuclei. This abnormal transcript repartition contributes to the poor abundance and availability of the dystrophin messenger in cytoplasm. This novel finding also has important repercussions for RNA-targeted therapies.
    DOI:  https://doi.org/10.1038/s41598-023-43134-6
  18. J Vis Exp. 2023 Sep 08.
    Studying Muscle Transcriptional Dynamics at Single-molecule Scales in Drosophila.
    Emma Leroux, Nourhene Ammar, Savannah Moinet, Thierry Pecot, Hadi Boukhatmi.
      Skeletal muscles are large syncytia made up of many bundled myofibers that produce forces and enable body motion. Drosophila is a classical model to study muscle biology. The combination of both Drosophila genetics and advanced omics approaches led to the identification of key conserved molecules that regulate muscle morphogenesis and regeneration. However, the transcriptional dynamics of these molecules and the spatial distribution of their messenger RNA within the syncytia cannot be assessed by conventional methods. Here we optimized an existing single-molecule RNA fluorescence in situ hybridization (smFISH) method to enable the detection and quantification of individual mRNA molecules within adult flight muscles and their muscle stem cells. As a proof of concept, we have analyzed the mRNA expression and distribution of two evolutionary conserved transcription factors, Mef2 and Zfh1/Zeb. We show that this method can efficiently detect and quantify single mRNA molecules for both transcripts in the muscle precursor cells, adult muscles, and muscle stem cells.
    DOI:  https://doi.org/10.3791/65713
  19. Biomolecules. 2023 09 06. pii: 1354. [Epub ahead of print]13(9):
    The Effect of SERCA Activation on Functional Characteristics and Signaling of Rat Soleus Muscle upon 7 Days of Unloading.
    Kristina A Sharlo, Irina D Lvova, Sergey A Tyganov, Ksenia A Zaripova, Svetlana P Belova, Tatiana Y Kostrominova, Boris S Shenkman, Tatiana L Nemirovskaya.
      Skeletal muscle abnormalities and atrophy during unloading are accompanied by the accumulation of excess calcium in the sarcoplasm. We hypothesized that calcium accumulation may occur, among other mechanisms, due to the inhibition of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) activity. Consequently, the use of the SERCA activator will reduce the level of calcium in the sarcoplasm and prevent the negative consequences of muscle unloading. Wistar rats were randomly assigned into one of three groups (eight rats per group): control rats with placebo (C), 7 days of unloading/hindlimb suspension with placebo (7HS), and 7 days of unloading treated with SERCA activator CDN1163 (7HSC). After seven days of unloading the soleus muscle, the 7HS group displayed increased fatigue in the ex vivo test, a significant increase in the level of calcium-dependent CaMK II phosphorylation and the level of tropomyosin oxidation, as well as a decrease in the content of mitochondrial DNA and protein, slow-type myosin mRNA, and the percentage of slow-type muscle fibers. All of these changes were prevented in the 7HSC group. Moreover, treatment with CDN1163 blocked a decrease in the phosphorylation of p70S6k, an increase in eEF2 phosphorylation, and an increase in MuRF-1 mRNA expression. Nevertheless, there were no differences in the degree of fast and slow muscle fiber atrophy between the 7HS and 7HSC groups. Conclusion: SERCA activation during 7 days of unloading prevented an increase in soleus fatigue, the decrease of slow-type myosin, mitochondrial markers, and markers of calcium homeostasis but had no effect on muscle atrophy.
    Keywords:  AMPK; ATP; MAFbx; MuRF1; muscle atrophy; soleus muscle unloading
    DOI:  https://doi.org/10.3390/biom13091354
  20. JCI Insight. 2023 Sep 26. pii: e165974. [Epub ahead of print]
    Dimethyl fumarate modulates the dystrophic disease program following short-term treatment.
    Cara A Timpani, Stephanie Kourakis, Danielle A Debruin, Dean G Campelj, Nancy Pompeani, Narges Dargahi, Angelo Patrick R Bautista, Ryan M Bagaric, Elya J Ritenis, Lauren Sahakian, Didier Debrincat, Nicole Stupka, Patricia Hafner, Peter G Arthur, Jessica R Terrill, Vasso Apostolopoulos, Judy B De Haan, Nuri Gueven, Dirk Fischer, Emma Rybalka.
      New medicines are urgently required to treat the fatal neuromuscular disease, Duchenne muscular dystrophy (DMD). Dimethyl fumarate (DMF) is a potent immunomodulatory small molecule nuclear erythroid 2-related factor 2 (Nrf2) activator with current clinical utility in the treatment of multiple sclerosis and psoriasis that could be effective for DMD and rapidly translatable. Here, we tested two weeks of daily 100mg/kg DMF versus 5mg/kg standard care prednisone (PRED) treatment in juvenile mdx mice with early symptomatic DMD. Both drugs modulated seed genes driving the DMD disease program and improved force production in fast-twitch muscle. However, only DMF showed pro-mitochondrial effects, protected contracting muscles from fatigue, improved histopathology and augmented clinically compatible muscle function tests. DMF may be a more selective modulator of the DMD disease program than PRED warranting follow-up longitudinal studies to evaluate disease modifying impact.
    Keywords:  Drug therapy; Muscle Biology; Neuromuscular disease; Skeletal muscle; Therapeutics
    DOI:  https://doi.org/10.1172/jci.insight.165974
  21. Nat Struct Mol Biol. 2023 Sep 28.
    Cryo-EM structures of Myomaker reveal a molecular basis for myoblast fusion.
    Tao Long, Yichi Zhang, Linda Donnelly, Hui Li, Yu-Chung Pien, Ning Liu, Eric N Olson, Xiaochun Li.
      The fusion of mononucleated myoblasts produces multinucleated muscle fibers leading to the formation of skeletal muscle. Myomaker, a skeletal muscle-specific membrane protein, is essential for myoblast fusion. Here we report the cryo-EM structures of mouse Myomaker (mMymk) and Ciona robusta Myomaker (cMymk). Myomaker contains seven transmembrane helices (TMs) that adopt a G-protein-coupled receptor-like fold. TMs 2-4 form a dimeric interface, while TMs 3 and 5-7 create a lipid-binding site that holds the polar head of a phospholipid and allows the alkyl tails to insert into Myomaker. The similarity of cMymk and mMymk suggests a conserved Myomaker-mediated cell fusion mechanism across evolutionarily distant species. Functional analyses demonstrate the essentiality of the dimeric interface and the lipid-binding site for fusogenic activity, and heterologous cell-cell fusion assays show the importance of transcellular interactions of Myomaker protomers for myoblast fusion. Together, our findings provide structural and functional insights into the process of myoblast fusion.
    DOI:  https://doi.org/10.1038/s41594-023-01110-8
  22. Exp Biol Med (Maywood). 2023 Sep 26. 15353702231198073
    Effects of autoimmune abnormalities on skeletal muscle regeneration after needle puncture in mice.
    Misato Masugi, Osamu Ichii, Yuki Otani, Takashi Namba, Yasuhiro Kon.
      Regeneration of injured skeletal muscles is supported by the activation of satellite cells, and excessive traumatic injuries may trigger abnormal processes, such as fibrosis. Because the participation of immune cells is crucial during skeletal muscle repair, systemic autoimmune diseases impair their regeneration. This study focused on a traumatic injury by injection and investigated the effect of autoimmune diseases on skeletal muscle regeneration. Male mice of MRL/MpJ-Faslpr/lpr and MRL/MpJ (6-7 months old) were used for autoimmune disease and healthy groups. The abdominal walls punctured by a needle were histologically analyzed at 1, 3, and 8 days postinjection. In both groups, injured skeletal muscle tissues showed necrosis and inflammatory cell infiltrations on day 1, increased cell density at 3 days, and regenerative myotubes with central nuclei without fibrosis at 8 days. Gr-1+ neutrophils at injured skeletal muscle were abundant at 1 day, and then substantially decreased starting from 3 days in both groups. The number of CD3+ T cells was remarkably higher in MRL/MpJ-Faslpr/lpr than that in MRL/MpJ at 1 day, and a similar tendency was observed in B220+ B cells. The numbers of IBA1+ macrophages and bromodeoxyuridine-incorporating cells tended to be higher at 3 days, and those of the latter, mainly proliferating paired-box-7+ satellite cells, showed significance at other time points and negatively correlated with the autoimmune disease indices, such as spleen weights or serum autoantibody level. Thus, this result suggested that injured skeletal muscle by minor trauma is normally regenerated regardless of the effects of autoimmune diseases, although lymphocyte infiltrations during these processes were more severe in MRL/MpJ-Faslpr/lpr.
    Keywords:  Autoimmune disease; MRL/MpJ-Faslpr/lpr; histopathology; injection; muscle regeneration; skeletal muscle
    DOI:  https://doi.org/10.1177/15353702231198073
  23. Physiol Rep. 2023 Oct;11(19): e15833
    Anserine is expressed in human cardiac and skeletal muscles.
    Lívia de Souza Gonçalves, Wagner Ribeiro Pereira, Rafael Pires da Silva, Guilherme Carvalho Yamaguchi, Victor Henrique Carvalho, Bianca Scigliano Vargas, Leonardo Jensen, Marisa Helena Gennari de Medeiros, Hamilton Roschel, Guilherme Giannini Artioli.
      We evaluated whether anserine, a methylated analog of the dipeptide carnosine, is present in the cardiac and skeletal muscles of humans and whether the CARNMT1 gene, which encodes the anserine synthesizing enzyme carnosine-N-methyltransferase, is expressed in human skeletal muscle. We found that anserine is present at low concentrations (low micromolar range) in both cardiac and skeletal muscles, and that anserine content in skeletal muscle is ~15 times higher than in cardiac muscle (cardiac muscle: 10.1 ± 13.4 μmol·kg-1 of dry muscle, n = 12; skeletal muscle: 158.1 ± 68.5 μmol·kg-1 of dry muscle, n = 11, p < 0.0001). Anserine content in the heart was highly variable between individuals, ranging from 1.4 to 45.4 μmol·kg-1 of dry muscle, but anserine content was not associated with sex, age, or body mass. We also showed that CARNMT1 gene is poorly expressed in skeletal muscle (n = 10). This is the first study to demonstrate that anserine is present in the ventricle of the human heart. The presence of anserine in human heart and the confirmation of its expression in human skeletal muscle open new avenues of investigation on the specific and differential physiological functions of histidine dipeptides in striated muscles.
    Keywords:  anserine; carnosine-N-methyltransferase; heart; human; muscle
    DOI:  https://doi.org/10.14814/phy2.15833
  24. Stem Cell Reports. 2023 Sep 20. pii: S2213-6711(23)00313-2. [Epub ahead of print]
    Highly contractile 3D tissue engineered skeletal muscles from human iPSCs reveal similarities with primary myoblast-derived tissues.
    Erik van der Wal, Alessandro Iuliano, Stijn L M In 't Groen, Anjali P Bholasing, Dominik Priesmann, Preeti Sharma, Bianca den Hamer, Vittorio Saggiomo, Marcus Krüger, W W M Pim Pijnappel, Jessica C de Greef.
      Skeletal muscle research is transitioning toward 3D tissue engineered in vitro models reproducing muscle's native architecture and supporting measurement of functionality. Human induced pluripotent stem cells (hiPSCs) offer high yields of cells for differentiation. It has been difficult to differentiate high-quality, pure 3D muscle tissues from hiPSCs that show contractile properties comparable to primary myoblast-derived tissues. Here, we present a transgene-free method for the generation of purified, expandable myogenic progenitors (MPs) from hiPSCs grown under feeder-free conditions. We defined a protocol with optimal hydrogel and medium conditions that allowed production of highly contractile 3D tissue engineered skeletal muscles with forces similar to primary myoblast-derived tissues. Gene expression and proteomic analysis between hiPSC-derived and primary myoblast-derived 3D tissues revealed a similar expression profile of proteins involved in myogenic differentiation and sarcomere function. The protocol should be generally applicable for the study of personalized human skeletal muscle tissue in health and disease.
    Keywords:  3D-tissue engineering; contractile force; drug screening; induced pluripotent stem cells; myoblasts; myofiber; organ-on-a-chip; personalized medicine; satellite cell; skeletal muscle
    DOI:  https://doi.org/10.1016/j.stemcr.2023.08.014
  25. Int J Mol Sci. 2023 Sep 20. pii: 14335. [Epub ahead of print]24(18):
    FLII Modulates the Myogenic Differentiation of Progenitor Cells via Actin Remodeling-Mediated YAP1 Regulation.
    Mai Thi Nguyen, Quoc Kiet Ly, Hyun-Jung Kim, Wan Lee.
      The dynamic rearrangement of the actin cytoskeleton plays an essential role in myogenesis, which is regulated by diverse mechanisms, such as mechanotransduction, modulation of the Hippo signaling pathway, control of cell proliferation, and the influence of morphological changes. Despite the recognized importance of actin-binding protein Flightless-1 (FLII) during actin remodeling, the role played by FLII in the differentiation of myogenic progenitor cells has not been explored. Here, we investigated the roles of FLII in the proliferation and differentiation of myoblasts. FLII was found to be enriched in C2C12 myoblasts, and its expression was stable during the early stages of differentiation but down-regulated in fully differentiated myotubes. Knockdown of FLII in C2C12 myoblasts resulted in filamentous actin (F-actin) accumulation and inhibited Yes-associated protein 1 (YAP1) phosphorylation, which triggers its nuclear translocation from the cytoplasm. Consequently, the expressions of YAP1 target genes, including PCNA, CCNB1, and CCND1, were induced, and the cell cycle and proliferation of myoblasts were promoted. Moreover, FLII knockdown significantly inhibited the expression of myogenic regulatory factors, i.e., MyoD and MyoG, thereby impairing myoblast differentiation, fusion, and myotube formation. Thus, our findings demonstrate that FLII is crucial for the differentiation of myoblasts via modulation of the F-actin/YAP1 axis and suggest that FLII is a putative novel therapeutic target for muscle wasting.
    Keywords:  FLII; actin remodeling; differentiation; mechanotransduction; myogenesis
    DOI:  https://doi.org/10.3390/ijms241814335
  26. J Biol Chem. 2023 Sep 22. pii: S0021-9258(23)02309-8. [Epub ahead of print] 105281
    The long non-coding RNA lnc-H19 is important for endurance exercise by maintaining slow muscle fiber types.
    Yongqi Yue, Yanru Yue, Zeyu Fan, Yingying Meng, Chenglong Wen, Yalong An, Ying Yao, Xiao Li.
      Skeletal muscle consists of different muscle fiber types whose heterogeneity is characterized by different metabolic patterns and expression of MyHC isomers. The transformation of muscle fiber types is regulated by a complex molecular network in which long non-coding RNAs (lncRNAs) play an important role. In this study, we found that lnc-H19 is more enriched in slow muscle fibers. In vitro, interference of lnc-H19 by siRNA significantly promoted the expression of fast muscle fiber gene MyHC IIB and inhibited the expression of the slow muscle fiber gene MyHC I, thereby leading to a fast muscle fiber phenotype. Additionally, interference of lnc-H19 significantly inhibited mRNA expression of the mitochondrial genes, such as COX5A, COX -2, UQCRFSL, FABP3 and CD36. Overexpression of lnc-H19 resulted in an opposite result. In vivo, knockdown of lnc-H19 by AAV-shRNA-H19 suppressed the mRNA expression of the slow muscle fiber gene MyHC I and the protein expression of slow-MyHC. Simultaneously, mitochondria were reduced in number, swollen and vacuolated. The activities of succinate dehydrogenase (SDH), lactic dehydrogenase (LDH), and superoxide dismutase (SOD) were significantly inhibited, and malondialdehyde (MDA) content was significantly increased, indicating that deficiency of lnc-H19 leads to decreased oxidative metabolism and antioxidant capacity in muscle. Further, inhibition of lnc-H19 decreased the weight-bearing swimming time and limb suspension time of mice. In conclusion, our results revealed the role of lnc-H19 in maintaining slow muscle fiber types and maintaining exercise endurance, which may help to further improve the regulatory network of lnc-H19 in muscle function.
    Keywords:  Lnc-H19; endurance exercise; mitochondria; myofiber type
    DOI:  https://doi.org/10.1016/j.jbc.2023.105281
  27. Front Cell Dev Biol. 2023 ;11 1243299
    Shank3 related muscular hypotonia is accompanied by increased intracellular calcium concentrations and ion channel dysregulation in striated muscle tissue.
    Berra Yildiz, Lisa Schiedt, Medhanie Mulaw, Jürgen Bockmann, Sarah Jesse, Anne-Kathrin Lutz, Tobias M Boeckers.
      Phelan-McDermid syndrome (PMS) is a syndromic form of Autism Spectrum Disorders (ASD) classified as a rare genetic neurodevelopmental disorder featuring global developmental delay, absent or delayed speech, ASD-like behaviour and neonatal skeletal muscle hypotonia. PMS is caused by a heterozygous deletion of the distal end of chromosome 22q13.3 or SHANK3 mutations. We analyzed striated muscles of newborn Shank3Δ11(-/-) animals and found a significant enlargement of the sarcoplasmic reticulum as previously seen in adult Shank3Δ11(-/-) mice, indicative of a Shank3-dependent and not compensatory mechanism for this structural alteration. We analyzed transcriptional differences by RNA-sequencing of muscle tissue of neonatal Shank3Δ11(-/-) mice and compared those to Shank3(+/+) controls. We found significant differences in gene expression of ion channels crucial for muscle contraction and for molecules involved in calcium ion regulation. In addition, calcium storage- [i.e., Calsequestrin (CSQ)], calcium secretion- and calcium-related signaling-proteins were found to be affected. By immunostainings and Western blot analyses we could confirm these findings both in Shank3Δ11(-/-) mice and PMS patient muscle tissue. Moreover, alterations could be induced in vitro by the selective downregulation of Shank3 in C2C12 myotubes. Our results emphasize that SHANK3 levels directly or indirectly regulate calcium homeostasis in a cell autonomous manner that might contribute to muscular hypotonia especially seen in the newborn.
    Keywords:  ASD; RNA-sequencing; Shank3; immunohistochemistry; muscular hypotonia; neurodevelopmental disorders; western blot
    DOI:  https://doi.org/10.3389/fcell.2023.1243299
  28. iScience. 2023 Oct 20. 26(10): 107717
    Role of Fyn and the interleukin-6-STAT-3-autophagy axis in sarcopenia.
    Tsuyoshi Sasaki, Eijiro Yamada, Ryota Uehara, Shuichi Okada, Hirotaka Chikuda, Masanobu Yamada.
      Sarcopenia is the progressive loss of muscle mass wherein Fyn regulates STAT3 to decrease autophagy. To elucidate the role of inflammation in Fyn-STAT3-dependent autophagy and sarcopenia, here we aimed to investigate the underlying mechanisms using two mouse models of primary and secondary sarcopenia: (1) tail suspension and (2) sciatic denervation. In wild-type mice, the expression of Fyn and IL-6 increased significantly. The expression and phosphorylation levels of STAT3 were also significantly augmented, while autophagic activity was abolished. To investigate Fyn-dependency, we used tail suspension with Fyn-null mice. In tail-suspended wild-type mice, IL-6 expression was increased; however, it was abolished in Fyn-null mice, which maintained autophagy and the expression and ablation of STAT3 phosphorylation. In conclusion, Fyn was found to be associated with the IL-6-STAT3-autophagy axis in sarcopenia. This finding permits a better understanding of sarcopenia-associated metabolic diseases and the possible development of therapeutic interventions.
    Keywords:  Biological sciences; Disease
    DOI:  https://doi.org/10.1016/j.isci.2023.107717
  29. Aging Cell. 2023 Sep 28. e13981
    Cellular and molecular evidence that synaptic Schwann cells contribute to aging of mouse neuromuscular junctions.
    Robert Louis Hastings, Mary Flordelys Avila, Emma Suneby, Devin Juros, Anson O'Young, Jason Peres da Silva, Gregorio Valdez.
      Age-induced degeneration of the neuromuscular junction (NMJ) is associated with motor dysfunction and muscle atrophy. While the impact of aging on the NMJ presynapse and postsynapse is well-documented, little is known about the changes perisynaptic Schwann cells (PSCs), the synaptic glia of the NMJ, undergo during aging. Here, we examined PSCs in young, middle-aged, and old mice in three muscles with different susceptibility to aging. Using light and electron microscopy, we found that PSCs acquire age-associated cellular features either prior to or at the same time as the onset of NMJ degeneration. Notably, we found that aged PSCs fail to completely cap the NMJ even though they are more abundant in old compared with young mice. We also found that aging PSCs form processes that either intrude into the synaptic cleft or guide axonal sprouts to innervate other NMJs. We next profiled the transcriptome of PSCs and other Schwann cells (SCs) to identify mechanisms altered in aged PSCs. This analysis revealed that aged PSCs acquire a transcriptional pattern previously shown to promote phagocytosis that is absent in other SCs. It also showed that aged PSCs upregulate unique pro-inflammatory molecules compared to other aged SCs. Interestingly, neither synaptogenesis genes nor genes that are typically upregulated by repair SCs were induced in aged PSCs or other SCs. These findings provide insights into cellular and molecular mechanisms that could be targeted in PSCs to stave off the deleterious effects of aging on NMJs.
    Keywords:  NMJ; aging; perisynaptic Schwann cell; synapses; synaptic glia; terminal Schwann cell
    DOI:  https://doi.org/10.1111/acel.13981
  30. iScience. 2023 Oct 20. 26(10): 107746
    Splicing regulation of GFPT1 muscle-specific isoform and its roles in glucose metabolisms and neuromuscular junction.
    Paniz Farshadyeganeh, Mohammad Nazim, Ruchen Zhang, Bisei Ohkawara, Kazuki Nakajima, Mohammad Alinoor Rahman, Farhana Nasrin, Mikako Ito, Jun-Ichi Takeda, Kenji Ohe, Yuki Miyasaka, Tamio Ohno, Akio Masuda, Kinji Ohno.
      Glutamine:fructose-6-phosphate transaminase 1 (GFPT1) is the rate-limiting enzyme of the hexosamine biosynthetic pathway (HBP). A 54-bp exon 9 of GFPT1 is specifically included in skeletal and cardiac muscles to generate a long isoform of GFPT1 (GFPT1-L). We showed that SRSF1 and Rbfox1/2 cooperatively enhance, and hnRNP H/F suppresses, the inclusion of human GFPT1 exon 9 by modulating recruitment of U1 snRNP. Knockout (KO) of GFPT1-L in skeletal muscle markedly increased the amounts of GFPT1 and UDP-HexNAc, which subsequently suppressed the glycolytic pathway. Aged KO mice showed impaired insulin-mediated glucose uptake, as well as muscle weakness and fatigue likely due to abnormal formation and maintenance of the neuromuscular junction. Taken together, GFPT1-L is likely to be acquired in evolution in mammalian striated muscles to attenuate the HBP for efficient glycolytic energy production, insulin-mediated glucose uptake, and the formation and maintenance of the neuromuscular junction.
    Keywords:  Biochemistry; Biological sciences; Physiology
    DOI:  https://doi.org/10.1016/j.isci.2023.107746
  31. Acta Neuropathol. 2023 Sep 29.
    Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis.
    Christopher Nelke, Christina B Schroeter, Lukas Theissen, Corinna Preusse, Marc Pawlitzki, Saskia Räuber, Vera Dobelmann, Derya Cengiz, Felix Kleefeld, Andreas Roos, Benedikt Schoser, Anna Brunn, Eva Neuen-Jacob, Jana Zschüntzsch, Sven G Meuth, Werner Stenzel, Tobias Ruck.
      Inclusion body myositis (IBM) is unique across the spectrum of idiopathic inflammatory myopathies (IIM) due to its distinct clinical presentation and refractoriness to current treatment approaches. One explanation for this resistance may be the engagement of cell-autonomous mechanisms that sustain or promote disease progression of IBM independent of inflammatory activity. In this study, we focused on senescence of tissue-resident cells as potential driver of disease. For this purpose, we compared IBM patients to non-diseased controls and immune-mediated necrotizing myopathy patients. Histopathological analysis suggested that cellular senescence is a prominent feature of IBM, primarily affecting non-myogenic cells. In-depth analysis by single nuclei RNA sequencing allowed for the deconvolution and study of muscle-resident cell populations. Among these, we identified a specific cluster of fibro-adipogenic progenitors (FAPs) that demonstrated key hallmarks of senescence, including a pro-inflammatory secretome, expression of p21, increased β-galactosidase activity, and engagement of senescence pathways. FAP function is required for muscle cell health with changes to their phenotype potentially proving detrimental. In this respect, the transcriptomic landscape of IBM was also characterized by changes to the myogenic compartment demonstrating a pronounced loss of type 2A myofibers and a rarefication of acetylcholine receptor expressing myofibers. IBM muscle cells also engaged a specific pro-inflammatory phenotype defined by intracellular complement activity and the expression of immunogenic surface molecules. Skeletal muscle cell dysfunction may be linked to FAP senescence by a change in the collagen composition of the latter. Senescent FAPs lose collagen type XV expression, which is required to support myofibers' structural integrity and neuromuscular junction formation in vitro. Taken together, this study demonstrates an altered phenotypical landscape of muscle-resident cells and that FAPs, and not myofibers, are the primary senescent cell type in IBM.
    Keywords:  Acetylcholine receptor; Complement; Inclusion body myositis; Myofiber; Senescence; Single nuclei
    DOI:  https://doi.org/10.1007/s00401-023-02637-2
  32. Int J Mol Sci. 2023 Sep 14. pii: 14112. [Epub ahead of print]24(18):
    Time-Dependent Changes in Muscle IGF1-IGFBP5-PAPP System after Sciatic Denervation.
    Ana Isabel Martín, Álvaro Moreno-Rupérez, Elena Nebot, Miriam Granado, Daniel Jaque, M Paz Nieto-Bona, Asunción López-Calderón, Teresa Priego.
      Denervation-induced muscle atrophy is a frequent cause of skeletal muscle diseases. However, the role of the most important muscle growth factor, insulin-like growth factor (IGF-1), in this process is poorly understood. IGF-1 activity is controlled by six IGF-1 binding proteins (IGFBPs). In skeletal muscle, IGFBP-5 seems to have an important role in atrophic processes. Furthermore, pappalysins (PAPP-A) modulate muscle growth by increasing IGF-1 bioavailability through IGFBP cleavage. We aimed to study the time-dependent changes in the IGF1-IGFBP5-PAPP system and its regulators in gastrocnemius muscle after sciatic denervation. Gastrocnemius atrophy and overexpression of IGF-1 was observed from day 3 post-denervation. The proteolytic factors measured were elevated from day 1 post-denervation onwards. Expression of both IGFBP-5 and pappalysins were increased on days 1 and 3. Subsequently, on days 7 to 14 pappalysins returned to control levels while IGFBP-5 remained elevated. The ratio IGFBP-5/PAPP-A was correlated with the main proteolytic markers. All data suggest that the initial increase of pappalysins could facilitate the IGF-1 action on muscle growth, whereas their subsequent decrease could lead to further muscle wasting.
    Keywords:  IGF-1; IGFBP-5; pappalysins; skeletal muscle atrophy
    DOI:  https://doi.org/10.3390/ijms241814112
  33. Metabolites. 2023 Sep 20. pii: 1024. [Epub ahead of print]13(9):
    Cancer Cachexia: Underlying Mechanisms and Potential Therapeutic Interventions.
    Dean Directo, Sang-Rok Lee.
      Cancer cachexia, a multifactorial metabolic syndrome developed during malignant tumor growth, is characterized by an accelerated loss of body weight accompanied by the depletion of skeletal muscle mass. This debilitating condition is associated with muscle degradation, impaired immune function, reduced functional capacity, compromised quality of life, and diminished survival in cancer patients. Despite the lack of the known capability of fully reversing or ameliorating this condition, ongoing research is shedding light on promising preclinical approaches that target the disrupted mechanisms in the pathophysiology of cancer cachexia. This comprehensive review delves into critical aspects of cancer cachexia, including its underlying pathophysiological mechanisms, preclinical models for studying the progression of cancer cachexia, methods for clinical assessment, relevant biomarkers, and potential therapeutic strategies. These discussions collectively aim to contribute to the evolving foundation for effective, multifaceted counteractive strategies against this challenging condition.
    Keywords:  cachexia; exercise; inflammation; metabolic reprogramming; mitochondrial dysfunction; proteolysis
    DOI:  https://doi.org/10.3390/metabo13091024
  34. Biomolecules. 2023 Aug 25. pii: 1304. [Epub ahead of print]13(9):
    The Mitochondrial Calcium Uniporter (MCU): Molecular Identity and Role in Human Diseases.
    Donato D'Angelo, Rosario Rizzuto.
      Calcium (Ca2+) ions act as a second messenger, regulating several cell functions. Mitochondria are critical organelles for the regulation of intracellular Ca2+. Mitochondrial calcium (mtCa2+) uptake is ensured by the presence in the inner mitochondrial membrane (IMM) of the mitochondrial calcium uniporter (MCU) complex, a macromolecular structure composed of pore-forming and regulatory subunits. MtCa2+ uptake plays a crucial role in the regulation of oxidative metabolism and cell death. A lot of evidence demonstrates that the dysregulation of mtCa2+ homeostasis can have serious pathological outcomes. In this review, we briefly discuss the molecular structure and the function of the MCU complex and then we focus our attention on human diseases in which a dysfunction in mtCa2+ has been shown.
    Keywords:  MCU; cancer; cardiovascular diseases; metabolic diseases; mitochondrial Ca2+ signaling; neurodegenerative disorders; skeletal muscle diseases
    DOI:  https://doi.org/10.3390/biom13091304
  35. Muscle Nerve. 2023 Sep 29.
    Effects of exercise prehabilitation on muscle atrophy and contractile properties in hindlimb-unloaded rats.
    Hyo-Seong Yeo, Jae-Young Lim.
      INTRODUCTION/AIMS: Effective strategies for rapid recovery after surgery are needed. Therefore, we investigated the effects of exercise prehabilitation (EP) and hindlimb unloading (HU) on muscle loss and contractility.METHODS: Twenty-two Sprague-Dawley rats (12 wk old) were divided into normal control (NCON, n = 5), hindlimb unloading control (HCON, n = 10), and exercise prehabilitation followed by hindlimb unloading (Ex-preH, n = 7) groups. Ex-PreH performed exercise training for 14 days before hindlimb unloading for 14 days. Body composition was evaluated, along with muscle strength and function. The soleus (SOL) and extensor digitorum longus (EDL) muscle contractile properties were analyzed at the whole-muscle level. The titin concentration and myosin heavy chain (MHC) type composition were analyzed.
    RESULTS: There were no effects of Ex-preH on total mass, lean mass, or muscle weight. Physical function was significantly higher in the Ex-preH group than in the HCON group (39.5° vs. 35.7°). The SOL twitch force (19.6 vs. 7.1 mN/m2 ) and specific force (107.3 vs. 61.2 mN/m2 ) were greater in Ex-preH group than in HCON group. EDL shortening velocity was higher in Ex-preH group than in HCON group (13.2 vs. 5.0 FL/s). The SOL full-length titin level was higher in Ex-preH group than in HCON group.
    DISCUSSION: Exercise prehabilitation did not prevent muscle mass loss followed by muscle wasting, although it minimized the reduction of physical function. Therefore, exercise prehabilitation should be considered for rapid functional recovery after disuse due to surgery and injuries.
    Keywords:  MHC type; contractile properties; exercise prehabilitation; hindlimb unloading; titin
    DOI:  https://doi.org/10.1002/mus.27979
  36. J Exp Biol. 2023 Sep 28. pii: jeb.246070. [Epub ahead of print]
    Evidence for multi-scale power amplification in skeletal muscle.
    Jarrod C Petersen, Thomas J Roberts.
      Many animals use a combination of skeletal muscle and elastic structures to amplify power output for fast motions. Among vertebrates, tendons in series with skeletal muscle are often implicated as the primary power-amplifying spring, but muscles contain elastic structures at all levels of organization, from the muscle-tendon to the extracellular matrix to elastic proteins within sarcomeres. The present study uses ex vivo muscle preparations in combination with high-speed video to quantify power output, as the product of force and velocity, at several levels of muscle organization to determine where power amplification occurs. Dynamic ramp-shortening contractions in isolated frog flexor digitorum superficialis brevis were compared with isotonic power output to identify power amplification within muscle fibers, the muscle belly, free tendon, and elements external to the muscle-tendon. Energy accounting revealed that artifact from compliant structures outside of the muscle-tendon unit contributed significant peak instantaneous power. This compliance included deflection of clamped bone that stored and released energy contributing 195.22±33.19 W kg-1±s.e.m. to the peak power output. In addition, we find that power detected from within the muscle fascicles for dynamic shortening ramps was 338.78±16.03 W kg-1±s.e.m., or nearly twice the maximum isotonic power output of 195.23±8.82 W kg-1±s.e.m. Measurements of muscle belly and muscle-tendon unit also demonstrated significant power amplification. These data suggest that intramuscular tissues, as well as bone, have the capacity to store and release energy to amplify whole-muscle power output.
    Keywords:  Elastic recoil; Frog; Locomotion; Power amplification; Skeletal muscle
    DOI:  https://doi.org/10.1242/jeb.246070
  37. J Gen Physiol. 2023 Dec 04. pii: e202313393. [Epub ahead of print]155(12):
    Dependence of myosin filament structure on intracellular calcium concentration in skeletal muscle.
    Marco Caremani, Luca Fusi, Massimo Reconditi, Gabriella Piazzesi, Theyencheri Narayanan, Malcolm Irving, Vincenzo Lombardi, Marco Linari, Elisabetta Brunello.
      Contraction of skeletal muscle is triggered by an increase in intracellular calcium concentration that relieves the structural block on actin-binding sites in resting muscle, potentially allowing myosin motors to bind and generate force. However, most myosin motors are not available for actin binding because they are stabilized in folded helical tracks on the surface of myosin-containing thick filaments. High-force contraction depends on the release of the folded motors, which can be triggered by stress in the thick filament backbone, but additional mechanisms may link the activation of the thick filaments to that of the thin filaments or to intracellular calcium concentration. Here, we used x-ray diffraction in combination with temperature-jump activation to determine the steady-state calcium dependence of thick filament structure and myosin motor conformation in near-physiological conditions. We found that x-ray signals associated with the perpendicular motors characteristic of isometric force generation had almost the same calcium sensitivity as force, but x-ray signals associated with perturbations in the folded myosin helix had a much higher calcium sensitivity. Moreover, a new population of myosin motors with a longer axial periodicity became prominent at low levels of calcium activation and may represent an intermediate regulatory state of the myosin motors in the physiological pathway of filament activation.
    DOI:  https://doi.org/10.1085/jgp.202313393
  38. Antioxidants (Basel). 2023 Sep 13. pii: 1754. [Epub ahead of print]12(9):
    DDAH1 Protects against Cardiotoxin-Induced Muscle Injury and Regeneration.
    Fei Feng, Bingqing Cui, Li Fang, Ting Lan, Kai Luo, Xin Xu, Zhongbing Lu.
      Nitric oxide (NO) is an important biological signaling molecule affecting muscle regeneration. The activity of NO synthase (NOS) is regulated by dimethylarginine dimethylaminohydrolase 1 (DDAH1) through degradation of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA). To investigate the role of DDAH1 in muscle injury and regeneration, muscle-specific Ddah1-knockout mice (Ddah1MKO) and their littermates (Ddah1f/f) were used to examine the progress of cardiotoxin (CTX)-induced muscle injury and subsequent muscle regeneration. After CTX injection, Ddah1MKO mice developed more severe muscle injury than Ddah1f/f mice. Muscle regeneration was also delayed in Ddah1MKO mice on Day 5 after CTX injection. These phenomena were associated with higher serum ADMA and LDH levels as well as a great induction of inflammatory response, oxidative stress and cell apoptosis in the gastrocnemius (GA) muscle of Ddah1MKO mice. In the GA muscle of CTX-treated mice, Ddah1 deficiency decreased the protein expression of M-cadherin, myogenin, Bcl-2, peroxiredoxin 3 (PRDX3) and PRDX5, and increased the protein expression of MyoD, TNFα, Il-6, iNOS and Bax. In summary, our data suggest that DDAH1 exerts a protective role in muscle injury and regeneration.
    Keywords:  DDAH1; cardiotoxin; muscle regeneration; oxidative stress
    DOI:  https://doi.org/10.3390/antiox12091754
  39. Biomolecules. 2023 Aug 30. pii: 1330. [Epub ahead of print]13(9):
    Exploring the Therapeutic Potential of Ethyl 3-Hydroxybutyrate in Alleviating Skeletal Muscle Wasting in Cancer Cachexia.
    Yu Zhou, Ruohan Lu, Fusheng Lin, Shu Chen, Qi-Qing He, Guoyang Wu, Caihua Huang, Donghai Lin.
      Cachexia (CAC) is a debilitating metabolic syndrome. Although dietary interventions are attractive, long-term adherence to specific diets is difficult to maintain and can lead to systemic side effects. Ethyl 3-hydroxybutyrate (EHB) is a commonly used food additive found in wine and Tribolium castaneum. In this study, we investigated the effects of EHB administration in cachectic mice. After a single intraperitoneal injection of EHB into mice, 3-hydroxybutyrate (3-HB) levels were significantly increased in the serum and gastrocnemius of mice. The administration of EHB alleviated cachexia-related symptoms, ameliorated skeletal muscle atrophy, and improved survival in cachectic mice. In addition, the supplementation of cachectic mice with 3-HB by EHB administration significantly reduced tumor weights, indicating the anti-tumor effects of 3-HB. Remarkably, the addition of 3-HB to the culture medium significantly attenuated the C2C12 myotube atrophy induced by the culture supernatant of CT26 cell lines, highlighting its potential to counteract the destructive effects of tumor-derived elements on muscle tissue. NMR-based metabolomics analysis provided insights into the underlying mechanisms and revealed that the anti-cachexia effects of 3-HB treatment can be attributed to three key mechanisms: the promotion of the TCA cycle and the attenuation of proteolysis, the promotion of protein synthesis and the improvement of metabolic homeostasis, and a reduction in inflammation and an enhancement of the antioxidant capacity. This study provided compelling evidence for the protective effects of 3-HB treatment on the cachectic gastrocnemius and highlighted the efficacy of EHB administration as a ketone supplementation approach to achieve nutritional ketosis without the need for dietary restriction.
    Keywords:  3-hydroxybutyrate; Ethyl 3-hydroxybutyrate; cancer cachexia; ketogenic diet; metabonomics
    DOI:  https://doi.org/10.3390/biom13091330
  40. bioRxiv. 2023 Sep 12. pii: 2023.09.10.556972. [Epub ahead of print]
    Myosin-binding protein C forms C-links and stabilizes OFF states of myosin.
    Anthony L Hessel, Nichlas M Engels, Michel Kuehn, Devin Nissen, Rachel L Sadler, Weikang Ma, Thomas C Irving, Wolfgang A Linke, Samantha P Harris.
      Contraction force in muscle is produced by the interaction of myosin motors in the thick filaments and actin in the thin filaments and is fine-tuned by other proteins such as myosin-binding protein C (MyBP-C). One form of control is through the regulation of myosin heads between an ON and OFF state in passive sarcomeres, which leads to their ability or inability to interact with the thin filaments during contraction, respectively. MyBP-C is a flexible and long protein that is tightly bound to the thick filament at its C-terminal end but may be loosely bound at its middle- and N-terminal end (MyBP-C C1C7 ). Under considerable debate is whether the MyBP-C C1C7 domains directly regulate myosin head ON/OFF states, and/or link thin filaments ("C-links"). Here, we used a combination of mechanics and small-angle X-ray diffraction to study the immediate and selective removal of the MyBP-C C1C7 domains of fast MyBP-C in permeabilized skeletal muscle. After cleavage, the thin filaments were significantly shorter, a result consistent with direct interactions of MyBP-C with thin filaments thus confirming C-links. Ca 2+ sensitivity was reduced at shorter sarcomere lengths, and crossbridge kinetics were increased across sarcomere lengths at submaximal activation levels, demonstrating a role in crossbridge kinetics. Structural signatures of the thick filaments suggest that cleavage also shifted myosin heads towards the ON state - a marker that typically indicates increased Ca 2+ sensitivity but that may account for increased crossbridge kinetics at submaximal Ca 2+ and/or a change in the force transmission pathway. Taken together, we conclude that MyBP-C C1C7 domains play an important role in contractile performance which helps explain why mutations in these domains often lead to debilitating diseases.
    DOI:  https://doi.org/10.1101/2023.09.10.556972
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