bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2021‒06‒13
forty-nine papers selected by
Anna Vainshtein
Craft Science Inc.

  1. Function (Oxf). 2021 ;2(1): zqaa033
      Satellite cells are required for postnatal development, skeletal muscle regeneration across the lifespan, and skeletal muscle hypertrophy prior to maturity. Our group has aimed to address whether satellite cells are required for hypertrophic growth in mature skeletal muscle. Here, we generated a comprehensive characterization and transcriptome-wide profiling of skeletal muscle during adaptation to exercise in the presence or absence of satellite cells in order to identify distinct phenotypes and gene networks influenced by satellite cell content. We administered vehicle or tamoxifen to adult Pax7-DTA mice and subjected them to progressive weighted wheel running (PoWeR). We then performed immunohistochemical analysis and whole-muscle RNA-seq of vehicle (SC+) and tamoxifen-treated (SC-) mice. Further, we performed single myonuclear RNA-seq to provide detailed information on how satellite cell fusion affects myonuclear transcription. We show that while skeletal muscle can mount a robust hypertrophic response to PoWeR in the absence of satellite cells, growth, and adaptation are ultimately blunted. Transcriptional profiling reveals several gene networks key to muscle adaptation are altered in the absence of satellite cells.
    Keywords:  Pax7; adaptation; exercise; hypertrophy; muscle function; muscle stem cell; satellite cell
  2. Acta Physiol (Oxf). 2021 Jun 07. e13702
      AIM: Mechanosensitive Piezo1 ion channels emerged recently as important contributors to various vital functions including modulation of the blood supply to skeletal muscles. The specific Piezo1 channel agonist Yoda1 was shown to regulate the tone of blood vessels similarly to physical exercise. However, the direct role of Piezo1 channels in muscle function has been little studied so far. We therefore investigated the action of Yoda1 on the functional state of skeletal muscle precursors (satellite cells and myotubes) as well as on adult muscle fibers.METHODS: Immunostaining, electrophysiological intracellular recordings and Ca2+ imaging experiments were performed to localize and assess the effect of the chemical activation of Piezo1 channels with Yoda1, on myogenic precursors, adult myofibers and at the adult neuromuscular junction.
    RESULTS: Piezo1 channels were detected by immunostaining in satellite cells and myotubes as well as in adult myofibers. In the skeletal muscle precursors, Yoda1 treatment stimulated the differentiation and cell fusion rather than the proliferation of satellite cells. Moreover, in myotubes, Yoda1 induced significant [Ca2+ ]i transients, without detectable [Ca2+ ]i response in adult myofibers. Furthermore, although expression of Piezo1 channels was detected around the muscle endplate region, Yoda1 application did not alter either the nerve-evoked or spontaneous synaptic activity or muscle contractions in adult myofibers.
    CONCLUSION: Our data indicate that the chemical activation of Piezo1 channels specifically enhances the differentiation of skeletal muscle precursors, suggesting a possible new strategy to promote muscle regeneration.
    Keywords:  Piezo1 channels; Yoda1; myogenesis; myotubes; satellite cells; skeletal muscle myofibers
  3. Nat Commun. 2021 06 08. 12(1): 3450
      The epigenetic mechanisms coordinating the maintenance of adult cellular lineages and the inhibition of alternative cell fates remain poorly understood. Here we show that targeted ablation of the histone chaperone HIRA in myogenic cells leads to extensive transcriptional modifications, consistent with a role in maintaining skeletal muscle cellular identity. We demonstrate that conditional ablation of HIRA in muscle stem cells of adult mice compromises their capacity to regenerate and self-renew, leading to tissue repair failure. Chromatin analysis of Hira-deficient cells show a significant reduction of histone variant H3.3 deposition and H3K27ac modification at regulatory regions of muscle genes. Additionally, we find that genes from alternative lineages are ectopically expressed in Hira-mutant cells via MLL1/MLL2-mediated increase of H3K4me3 mark at silent promoter regions. Therefore, we conclude that HIRA sustains the chromatin landscape governing muscle cell lineage identity via incorporation of H3.3 at muscle gene regulatory regions, while preventing the expression of alternative lineage genes.
  4. Mol Ther Nucleic Acids. 2021 Jun 04. 24 923-938
      Cancer cachexia is a kind of whole-body metabolic disorder syndrome accompanied by severe wasting of muscle tissue in which cancer exosomes may be involved. Analysis of clinical samples showed that the serum exosome concentrations were correlated with the development of cancer cachexia. Exosomes secreted by C26 cells could decrease the diameter of C2C12 myotubes in vitro and decrease mouse muscle strength and tibialis anterior (TA) muscle weight in vivo. GW4869, an inhibitor of exosome excretion, ameliorated muscle wasting in C26 tumor-bearing mice. MicroRNA (miRNA) sequencing (miRNA-seq) analysis suggested that miR-195a-5p and miR-125b-1-3p were richer in C26 exosomes than in exosomes secreted from MC38 cells (non-cachexic). Both miR-195a-5p and miR-125b-1-3p mimics could induce atrophy of C2C12 myoblasts. Downregulation of Bcl-2 and activation of the apoptotic signaling pathway were observed in C2C12 myoblasts transfected with miR-195a-5p and miR-125b-1-3p mimics, in the gastrocnemius muscle of C26 tumor-bearing mice and in the TA muscle injected with C26 exosomes. Results of dual-luciferase assay confirmed the targeting of miR-195a-5p/miR-125b-1-3p to Bcl-2. Overexpression of Bcl-2 successfully reversed atrophy of C2C12 myoblasts induced by the two miRNA mimics. These results suggested that cancer exosome enriched miRNAs might induce muscle atrophy by targeting Bcl-2-mediated apoptosis.
    Keywords:  apoptosis; cancer cachexia; exosome; miRNA; skeletal muscle wasting
  5. BioDrugs. 2021 Jun 07.
      The debilitating neuromuscular disorders Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA), which harm 1 in 5000 newborn males and 1 in 11,000 newborns, respectively, are marked by progressive muscle wasting among other complications. While DMD causes generalized muscle weakness due to the absence of the dystrophin protein, SMA patients generally face motor neuron degeneration because of the lack of the survival motor neuron (SMN) protein. Many of the most promising therapies for both conditions restore the absent proteins dystrophin and SMN. Antisense oligonucleotide-mediated exon skipping and inclusion therapies are advancing clinically with the approved DMD therapies casimersen, eteplirsen, golodirsen, and viltolarsen, and the SMA therapy nusinersen. Existing antisense therapies focus on skeletal muscle for DMD and motor neurons for SMA, respectively. Through innovative techniques, such as peptide conjugation and multi-exon skipping, these therapies could be optimized for efficacy and applicability. By contrast, gene replacement therapy is administered only once to patients during treatment. Currently, only onasemnogene abeparvovec for SMA has been approved. Safety shortcomings remain a major challenge for gene therapy. Nevertheless, gene therapy for DMD has strong potential to restore dystrophin expression in patients. In light of promising functional improvements, antisense and gene therapies stand poised to elevate the lives of patients with DMD and SMA.
  6. Front Physiol. 2021 ;12 679152
      Skeletal muscle wasting in patients with diabetes mellitus (DM) is a complication of decreased muscle mass and strength, and is a serious risk factor that may result in mortality. Deteriorated differentiation of muscle precursor cells, called myoblasts, in DM patients is considered to be one of the causes of muscle wasting. We recently developed myogenetic oligodeoxynucleotides (myoDNs), which are 18-base single-strand DNAs that promote myoblast differentiation by targeting nucleolin. Herein, we report the applicability of a myoDN, iSN04, to myoblasts isolated from patients with type 1 and type 2 DM. Myogenesis of DM myoblasts was exacerbated concordantly with a delayed shift of myogenic transcription and induction of interleukins. Analogous phenotypes were reproduced in healthy myoblasts cultured with excessive glucose or palmitic acid, mimicking hyperglycemia or hyperlipidemia. iSN04 treatment recovered the deteriorated differentiation of plural DM myoblasts by downregulating myostatin and interleukin-8 (IL-8). iSN04 also ameliorated the impaired myogenic differentiation induced by glucose or palmitic acid. These results demonstrate that myoDNs can directly facilitate myoblast differentiation in DM patients, making them novel candidates for nucleic acid drugs to treat muscle wasting in patients with DM.
    Keywords:  diabetes mellitus; myoblast; myogenetic oligodeoxynucleotide; myogenic differentiation; skeletal muscle
  7. Stem Cells Int. 2021 ;2021 9955691
      The Pax7+ muscle stem cells (MuSCs) are essential for skeletal muscle homeostasis and muscle regeneration upon injury, while the molecular mechanisms underlying muscle stem cell fate determination and muscle regeneration are still not fully understood. N6-methyladenosine (m6A) RNA modification is catalyzed by METTL3 and plays important functions in posttranscriptional gene expression regulation and various biological processes. Here, we generated muscle stem cell-specific METTL3 conditional knockout mouse model and revealed that METTL3 knockout in muscle stem cells significantly inhibits the proliferation of muscle stem cells and blocks the muscle regeneration after injury. Moreover, knockin of METTL3 in muscle stem cells promotes the muscle stem cell proliferation and muscle regeneration in vivo. Mechanistically, METTL3-m6A-YTHDF1 axis regulates the mRNA translation of Notch signaling pathway. Our data demonstrated the important in vivo physiological function of METTL3-mediated m6A modification in muscle stem cells and muscle regeneration, providing molecular basis for the therapy of stem cell-related muscle diseases.
  8. Front Bioeng Biotechnol. 2021 ;9 652970
      Mesenchymal stromal cells (MSCs) are multipotent cells found in different tissues: bone marrow, peripheral blood, adipose tissues, skeletal muscle, perinatal tissues, and dental pulp. MSCs are able to self-renew and to differentiate into multiple lineages, and they have been extensively used for cell therapy mostly owing to their anti-fibrotic and immunoregulatory properties that have been suggested to be at the basis for their regenerative capability. MSCs exert their effects by releasing a variety of biologically active molecules such as growth factors, chemokines, and cytokines, either as soluble proteins or enclosed in extracellular vesicles (EVs). Analyses of MSC-derived secretome and in particular studies on EVs are attracting great attention from a medical point of view due to their ability to mimic all the therapeutic effects produced by the MSCs (i.e., endogenous tissue repair and regulation of the immune system). MSC-EVs could be advantageous compared with the parental cells because of their specific cargo containing mRNAs, miRNAs, and proteins that can be biologically transferred to recipient cells. MSC-EV storage, transfer, and production are easier; and their administration is also safer than MSC therapy. The skeletal muscle is a very adaptive tissue, but its regenerative potential is altered during acute and chronic conditions. Recent works demonstrate that both MSCs and their secretome are able to help myofiber regeneration enhancing myogenesis and, interestingly, can be manipulated as a novel strategy for therapeutic interventions in muscular diseases like muscular dystrophies or atrophy. In particular, MSC-EVs represent promising candidates for cell free-based muscle regeneration. In this review, we aim to give a complete picture of the therapeutic properties and advantages of MSCs and their products (MSC-derived EVs and secreted factors) relevant for skeletal muscle regeneration in main muscular diseases.
    Keywords:  atrophy; extracellular vesicles; mesenchymal stromal cells; muscle; muscle regeneration; muscular dystrophy; secretome
  9. Metabolism. 2021 Jun 03. pii: S0026-0495(21)00103-7. [Epub ahead of print] 154803
      BACKGROUND AND AIMS: A diminution in skeletal muscle mitochondrial function due to ectopic lipid accumulation and excess nutrient intake is thought to contribute to insulin resistance and the development of type 2 diabetes. However, the functional integrity of mitochondria in insulin-resistant skeletal muscle remains highly controversial.METHODS: 19 healthy adults (age:28.4 ± 1.7 years; BMI:22.7 ± 0.3 kg/m2) received an overnight intravenous infusion of lipid (20% Intralipid) or saline followed by a hyperinsulinemic-euglycemic clamp to assess insulin sensitivity using a randomized crossover design. Skeletal muscle biopsies were obtained after the overnight lipid infusion to evaluate activation of mitochondrial dynamics proteins, ex-vivo mitochondrial membrane potential, ex-vivo oxidative phosphorylation and electron transfer capacity, and mitochondrial ultrastructure.
    RESULTS: Overnight lipid infusion increased dynamin related protein 1 (DRP1) phosphorylation at serine 616 and PTEN-induced kinase 1 (PINK1) expression (P = 0.003 and P = 0.008, respectively) in skeletal muscle while reducing mitochondrial membrane potential (P = 0.042). The lipid infusion also increased mitochondrial-associated lipid droplet formation (P = 0.011), the number of dilated cristae, and the presence of autophagic vesicles without altering mitochondrial number or respiratory capacity. Additionally, lipid infusion suppressed peripheral glucose disposal (P = 0.004) and hepatic insulin sensitivity (P = 0.014).
    CONCLUSIONS: These findings indicate that activation of mitochondrial fission and quality control occur early in the onset of insulin resistance in human skeletal muscle. Targeting mitochondrial dynamics and quality control represents a promising new pharmacological approach for treating insulin resistance and type 2 diabetes.
  10. J Tissue Eng. 2021 Jan-Dec;12:12 20417314211022092
      Extracellular vesicles (EVs) hold value as accessible biomarkers for understanding cellular differentiation and related pathologies. Herein, EV biomarkers in models of skeletal muscle dormancy and differentiation have been comparatively profiled using Raman spectroscopy (RS). Significant variations in the biochemical fingerprint of EVs were detected, with an elevation in peaks associated with lipid and protein signatures during early myogenic differentiation (day 2). Principal component analysis revealed a clear separation between the spectra of EVs derived from myogenic and senescent cell types, with non-overlapping interquartile ranges and population median. Observations aligned with nanoparticle tracking data, highlighting a significant early reduction in EV concentration in senescent myoblast cultures as well as notable variations in EV morphology and diameter. As differentiation progressed physical and biochemical differences in the properties of EVs became less pronounced. This study demonstrates the applicability of RS as a high-resolution analytical method for profiling biochemical changes in EVs during early myogenesis.
    Keywords:  Raman spectroscopy; Vesicle; analytical; differentiation; skeletal muscle
  11. Front Physiol. 2021 ;12 668600
      The mechanisms involved in the development of skeletal muscle fibers have been studied in the last 70 years and yet many aspects of this process are still not completely understood. A myriad of in vivo and in vitro invertebrate and vertebrate animal models has been used for dissecting the molecular and cellular events involved in muscle formation. Among the most used animal models for the study of myogenesis are the rodents rat and mouse, the fruit fly Drosophila, and the birds chicken and quail. Here, we describe the robustness and advantages of the chick primary muscle culture model for the study of skeletal myogenesis. In the myoblast culture obtained from embryonic chick pectoralis muscle it is possible to analyze all the steps involved in skeletal myogenesis, such as myoblast proliferation, withdrawal from cell cycle, cell elongation and migration, myoblast alignment and fusion, the assembly of striated myofibrils, and the formation of multinucleated myotubes. The fact that in vitro chick myotubes can harbor hundreds of nuclei, whereas myotubes from cell lines have only a dozen nuclei demonstrates the high level of differentiation of the autonomous chick myogenic program. This striking differentiation is independent of serum withdrawal, which points to the power of the model. We also review the major pro-myogenic and anti-myogenic molecules and signaling pathways involved in chick myogenesis, in addition to providing a detailed protocol for the preparation of embryonic chick myogenic cultures. Moreover, we performed a bibliometric analysis of the articles that used this model to evaluate which were the main explored topics of interest and their contributors. We expect that by describing the major findings, and their advantages, of the studies using the embryonic chick myogenic model we will foster new studies on the molecular and cellular process involved in muscle proliferation and differentiation that are more similar to the actual in vivo condition than the muscle cell lines.
    Keywords:  chick embryo; muscle differentiation; myoblast; myogenesis; myotube; skeletal muscle
  12. Cell Rep. 2021 Jun 08. pii: S2211-1247(21)00574-X. [Epub ahead of print]35(10): 109223
      During aging, the regenerative capacity of skeletal muscle decreases due to intrinsic changes in muscle stem cells (MuSCs) and alterations in their niche. Here, we use quantitative mass spectrometry to characterize intrinsic changes in the MuSC proteome and remodeling of the MuSC niche during aging. We generate a network connecting age-affected ligands located in the niche and cell surface receptors on MuSCs. Thereby, we reveal signaling by integrins, Lrp1, Egfr, and Cd44 as the major cell communication axes perturbed through aging. We investigate the effect of Smoc2, a secreted protein that accumulates with aging, primarily originating from fibro-adipogenic progenitors. Increased levels of Smoc2 contribute to the aberrant Integrin beta-1 (Itgb1)/mitogen-activated protein kinase (MAPK) signaling observed during aging, thereby causing impaired MuSC functionality and muscle regeneration. By connecting changes in the proteome of MuSCs to alterations of their niche, our work will enable a better understanding of how MuSCs are affected during aging.
    Keywords:  Integrin; Smoc2; aging; extracellular matrix; muscle stem cell; niche; pERK; proteomics; satellite cell; skeletal muscle
  13. J Sport Health Sci. 2021 Jun 08. pii: S2095-2546(21)00067-3. [Epub ahead of print]
      BACKGROUND: Exercise is beneficial for muscle atrophy. Peroxisome proliferator-activated receptor gamma (PPARγ) and microRNA-29b (miR-29b) have been reported to be responsible for angiotensin Ⅱ (AngⅡ)-induced muscle atrophy. However, it is unclear whether exercise can protect AngⅡ-induced muscle atrophy by targeting PPARγ/miR-29b.METHODS: Skeletal muscle atrophy in both control group and run group was established by AngⅡ infusion and after 1 week exercise training mice was sacrificed and muscle weight was determined. Myofiber size was measured by hematoxylin-eosin (HE) and wheat germ agglutinin (WGA) staining. Apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The expression level of muscle atrogenes, including F-box only protein 32 (FBXO32, also called Atrogin-1) and muscle specific RING-finger 1 (MuRF-1), the phosphorylation level of protein kinase B (PKB, also called AKT)/forkhead box O3A (FOXO3A)/mammalian target of rapamycin (mTOR) pathway proteins, the expression level of PPARγ and apoptosis-related proteins including B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X (Bax), cysteine-aspartic acid protease 3 (caspase-3) and cleaved-caspase-3, were determined by western blot. The expression level of miR-29b was checked by reverse transcription quantitative polymerase chain reaction (RT-qPCR). A PPARγ inhibitor (T0070907) or miR-29b overexpression adeno-associated virus serotype-8 (AAV8) was used to demonstrate whether PPARγ activation or miR-29b inhibition mediates the beneficial effects of exercise in AngⅡ-induced muscle atrophy.
    RESULTS: Exercise can significantly attenuate AngⅡ-induced muscle atrophy, which is demonstrated by increased skeletal muscle weight, cross-sectional area of myofiber, and activation of AKT/mTOR signaling and by decreased atrogenes expressions and apoptosis. In AngⅡ-induced muscle atrophy mice models, PPARγ was elevated while miR-29b was decreased by exercise. The protective effects of exercise in AngⅡ-induced muscle atrophy were inhibited by a PPARγ inhibitor (T0070907) or miR-29b overexpression AAV8.
    CONCLUSION: Exercise attenuates AngⅡ-induced muscle atrophy by activation of PPARγ and suppression of miR-29b.
    Keywords:  Angiotensin Ⅱ; Exercise; Muscle atrophy; PPARγ; miR-29b
  14. J Physiol. 2021 Jun 07.
      Passive skeletal muscle mechanical properties of whole muscle are not as well understood as muscle's active mechanical properties. Both the structural basis for passive mechanical properties and the properties themselves are challenging to determine because it is not clear which structures within skeletal muscle actually bear passive loads and there are not established standards by which to make mechanical measurements. Evidence suggests that titin bears the majority of the passive load within the single muscle cell. However, at larger scales, such as fascicles and muscles, there is emerging evidence that the extracellular matrix (ECM) bears the majority of the load. Complicating the ability to quantify and compare across size scales, muscles, and species, definitions of muscle passive properties such as stress, strain, modulus and stiffness can be made relative to many reference parameters. These uncertainties make a full understanding of whole muscle passive mechanical properties and modeling these properties very difficult. Future studies defining the specific load bearing structures and their composition and organization are required to fully understand passive mechanics of the whole muscle and develop therapies to treat disorders in which passive muscle properties are altered such as muscular dystrophy, traumatic laceration, and contracture due to upper motor neuron lesion as seen in spinal cord injury, stroke and cerebral palsy. Abstract figure legend Schematic representation of passive load bearing at various skeletal muscle scales. In the sarcomere (upper left), load is borne by the giant elastic protein titin and, to a lesser extent, desmin. The myofilaments actin and myosin are responsible for active force production. Sarcomeres in series (myofibrils) connect to the fiber surface at specialized focal adhesions called costameres at which desmin and other cytoskeletal proteins converge (upper right). Muscle fibers are embedded in a connective tissue matrix (lower left) composed primarily of basal lamina collagen type IV. At larger scales, passive load is borne in the perimysium (lower right) by perimysial cables that seem to be composed of collagen types 1 and 3 and this is where the majority of passive load is borne. This article is protected by copyright. All rights reserved.
  15. FASEB J. 2021 Jul;35(7): e21686
      Unbalanced copper (Cu2+ ) homeostasis is associated with the developmental defects of vertebrate myogenesis, but the underlying molecular mechanisms remain elusive. In this study, it was found that Cu2+ stressed zebrafish embryos and larvae showed reduced locomotor speed as well as loose and decreased myofibrils in skeletal muscle, coupled with the downregulated expression of muscle fiber markers mylpfa and smyhc1l and the irregular arrangement of myofibril and sarcomere. Meanwhile, the Cu2+ stressed zebrafish embryos and larvae also showed significant reduction in the expression of H3K4 methyltransferase smyd1b transcripts and H3K4me3 protein as well as in the binding enrichment of H3K4me3 on gene mylpfa promoter in skeletal muscle cells, suggesting that smyd1b-H3K4me3 axis mediates the Cu2+ -induced myofibrils specification defects. Additionally, whole genome DNA methylation sequencing unveiled that the gene smyd5 exhibited significant promoter hyper-methylation and increased expression in Cu2+ stressed embryos, and the ectopic expression of smyd5 in zebrafish embryos also induced the myofibrils specification defects as those observed in Cu2+ stressed embryos. Moreover, Cu2+ was shown to suppress myofibrils specification and smyd1b promoter transcriptional activity directly independent of the integral function of copper transporter cox17 and atp7b. All these data may shed light on the linkage of unbalanced copper homeostasis with specific gene promoter methylation and epigenetic histone protein modification as well as the resultant signaling transduction and the myofibrillogenesis defects.
    Keywords:   smyd1b ; smyd5 ; Cu2+; histone protein; methylation; myofibrillogenesis
  16. Mitochondrion. 2021 Jun 02. pii: S1567-7249(21)00075-1. [Epub ahead of print]
      Skeletal muscle is composed of fiber types that differ in mitochondrial content, antioxidant capacity, and susceptibility to apoptosis. Ceramides have been linked to oxidative stress-mediated apoptotic intracellular signalling and the enzyme neutral sphingomyelinase (nSMase) is, in part, responsible for generating these ceramides through the hydrolysis of sphingomyelin. Despite the role of ceramides in mediating apoptosis, there is a gap in the literature regarding nSMase in skeletal muscle mitochondria. This study aimed to characterize total nSMase activity and individual isoform expression in isolated subsarcolemmal (SS) mitochondria from soleus, diaphragm, plantaris, and extensor digitorum longus (EDL). Total nSMase activity did not differ between muscle types. nSMase2 content was detectable in all muscles and higher in EDL, soleus, and plantaris compared to diaphragm whereas nSMase3 was undetectable in all muscles. Finally, total nSMase activity positively correlated to nSMase2 protein content in soleus but not the other muscles. These findings suggest that nSMase associated with SS mitochondria may play a role in intracellular signalling processes involving ceramides in skeletal muscle and nSMase2 may be the key isoform, specifically in slow twitch muscle like soleus. Further studies are needed to fully elucidate the specific contribution of nSMase, along with the role of the various isoforms and mitochondrial subpopulation in generating mitochondrial ceramides in skeletal muscle, and its potential effects on mediating apoptosis.
    Keywords:  diaphragm; extensor digitorum longus; plantaris; soleus; subsarcolemmal
  17. Int J Chron Obstruct Pulmon Dis. 2021 ;16 1661-1675
      Background: Exposure to cigarette smoke (CS) is the main risk factor for chronic obstructive pulmonary disease (COPD). CS not only causes chronic airway inflammation and lung damage but also is involved in skeletal muscle dysfunction (SMD). Previous studies have shown that histone deacetylase 2 (HDAC2) plays an important role in the progression of COPD. The aim of this study was to determine the role of HDAC2 in CS-induced skeletal muscle atrophy and senescence.Methods: Gastrocnemius muscle weight and cross-sectional area (CSA) were measured in mice with CS-induced emphysema, and changes in the expression of atrophy-related markers and senescence-related markers were detected. In addition, the relationship between HDAC2 expression and skeletal muscle atrophy and senescence was also investigated.
    Results: Mice exposed to CS for 24 weeks developed emphysema and gastrocnemius atrophy and exhibited a decrease in gastrocnemius weight and skeletal muscle cross-sectional area. In addition, the HDAC2 protein levels were significantly decreased while the levels of atrophy-associated markers, including MURF1 and MAFbx, and senescence-associated markers, including P53 and P21, were significantly increased in the gastrocnemius muscle. In vitro, the exposure of C2C12 cells to cigarette smoke extract (CSE) significantly increased the MAFbx and MURF1 protein levels and decreased the HDAC2 protein levels. Moreover, overexpression of HDAC2 significantly ameliorated CSE-induced atrophy and senescence and reversed the increased MURF1, MAFbx, P53, and P21 expression in C2C12 cells. In addition, CSE treatment significantly increased the IKK and NF-κB p65 protein levels, and PTDC (an NF-kB inhibitor) ameliorated atrophy and senescence.
    Conclusion: Our findings suggest that HDAC2 plays an important role in CS-induced skeletal muscle atrophy and senescence, possibly through the NF-κB pathway.
    Keywords:  atrophy; histone deacetylase 2; nuclear factor-ҡB; senescence; skeletal muscle
  18. Sci Adv. 2021 Jun;pii: eabd7924. [Epub ahead of print]7(24):
      Muscle stem cells (satellite cells) are distributed throughout the body and have heterogeneous properties among muscles. However, functional topographical genes in satellite cells of adult muscle remain unidentified. Here, we show that expression of Homeobox-A (Hox-A) cluster genes accompanied with DNA hypermethylation of the Hox-A locus was robustly maintained in both somite-derived muscles and their associated satellite cells in adult mice, which recapitulates their embryonic origin. Somite-derived satellite cells were clearly separated from cells derived from cranial mesoderm in Hoxa10 expression. Hoxa10 inactivation led to genomic instability and mitotic catastrophe in somite-derived satellite cells in mice and human. Satellite cell-specific Hoxa10 ablation in mice resulted in a decline in the regenerative ability of somite-derived muscles, which were unobserved in cranial mesoderm-derived muscles. Thus, our results show that Hox gene expression profiles instill the embryonic history in satellite cells as positional memory, potentially modulating region-specific pathophysiology in adult muscles.
  19. Nat Commun. 2021 06 09. 12(1): 3471
      Exercise training prevents multiple diseases, yet the molecular mechanisms that drive exercise adaptation are incompletely understood. To address this, we create a computational framework comprising data from skeletal muscle or blood from 43 studies, including 739 individuals before and after exercise or training. Using linear mixed effects meta-regression, we detect specific time patterns and regulatory modulators of the exercise response. Acute and long-term responses are transcriptionally distinct and we identify SMAD3 as a central regulator of the exercise response. Exercise induces a more pronounced inflammatory response in skeletal muscle of older individuals and our models reveal multiple sex-associated responses. We validate seven of our top genes in a separate human cohort. In this work, we provide a powerful resource ( ) that expands the transcriptional landscape of exercise adaptation by extending previously known responses and their regulatory networks, and identifying novel modality-, time-, age-, and sex-associated changes.
  20. Front Endocrinol (Lausanne). 2021 ;12 682012
      During aging and menopausal transition in women, a progressive muscle degeneration (i.e. decrease in quality and muscle function) occurs. This muscle dysfunction, caused by decreased proliferation of muscle satellite cells, increased levels of inflammatory markers, and altered levels of sex hormones, exposes women to a raised incidence of sarcopenia. In this regard, hormonal balance and, in particular, estradiol, seems to be essential in skeletal muscle function. The role of the estradiol on satellite cells and the release of inflammatory cytokines in menopausal women are reviewed. In particular, estradiol has a beneficial effect on the skeletal muscle by stimulating satellite cell proliferation. Skeletal muscle can respond to estrogenic hormonal control due to the presence of specific receptors for estradiol at the level of muscle fibers. Additionally, estradiol can limit inflammatory stress damage on skeletal muscle. In this review, we primarily focused on the role of estradiol in sarcopenia and on the possibility of using Estradiol Replacement Therapy, which combined with nutritional and physical activity programs, can counteract this condition representing a valid tool to treat sarcopenia in women.
    Keywords:  aging; endocrinology; hormones; menopause; muscle
  21. Free Radic Biol Med. 2021 Jun 03. pii: S0891-5849(21)00351-8. [Epub ahead of print]172 82-89
      High intensity exercise is a popular mode of exercise to elicit similar or greater adaptive responses compared to traditional moderate intensity continuous exercise. However, the molecular mechanisms underlying these adaptive responses are still unclear. The purpose of this pilot study was to compare high and low intensity contractile stimulus on the Nrf2-mediated redox stress response in mouse skeletal muscle. An intra-animal design was used to control for variations in individual responses to muscle stimulation by comparing a stimulated limb (STIM) to the contralateral unstimulated control limb (CON). High Intensity (HI - 100Hz), Low Intensity (LI - 50Hz), and Naïve Control (NC - Mock stimulation vs CON) groups were used to compare these effects on Nrf2-ARE binding, Keap1 protein, and downstream gene and protein expression of Nrf2 target genes. Muscle stimulation significantly increased Nrf2-ARE binding in LI-STIM compared to LI-CON (p = 0.0098), while Nrf2-ARE binding was elevated in both HI-CON and HI-STIM compared to NC (p = 0.0007). The Nrf2-ARE results were mirrored in the downregulation of Keap1, where Keap1 expression in HI-CON and HI-STIM were both significantly lower than NC (p = 0.008) and decreased in LI-STIM compared to LI-CON (p = 0.015). In addition, stimulation increased NQO1 protein compared to contralateral control regardless of stimulation intensity (p = 0.019), and HO1 protein was significantly higher in high intensity compared to the Naïve control group (p = 0.002). Taken together, these data suggest a systemic redox signaling exerkine is activating Nrf2-ARE binding and is intensity gated, where Nrf2-ARE activation in contralateral control limbs were only seen in the HI group. Other research in exercise induced Nrf2 signaling support the general finding that Nrf2 is activated in peripheral tissues in response to exercise, however the specific exerkine responsible for the systemic signaling effects is not known. Future work should aim to delineate these redox sensitive systemic signaling mechanisms.
    Keywords:  High intensity exercise; Muscle contraction; Nrf2-Keap1; Redox signaling
  22. FASEB J. 2021 Jul;35(7): e21714
      We tested the hypothesis that cancer cachexia progression would induce oxidative post-translational modifications (Ox-PTMs) associated with skeletal muscle wasting, with different responses in muscles with the prevalence of glycolytic and oxidative fibers. We used cysteine-specific isotopic coded affinity tags (OxICAT) and gel-free mass spectrometry analysis to investigate the cysteine Ox-PTMs profile in the proteome of both plantaris (glycolytic) and soleus (oxidative) muscles in tumor-bearing and control rats. Histological analysis revealed muscle atrophy in type II fibers in plantaris muscle, with no changes in plantaris type I fibers and no differences in both soleus type I and II fibers in tumor-bearing rats when compared to healthy controls. Tumor progression altered the Ox-PTMs profile in both plantaris and soleus. However, pathway analysis including the differentially oxidized proteins revealed tricarboxylic acid cycle and oxidative phosphorylation as main affected pathways in plantaris muscle from tumor-bearing rats, while the same analysis did not show main metabolic pathways affected in the soleus muscle. In addition, cancer progression affected several metabolic parameters such as ATP levels and markers of oxidative stress associated with muscle atrophy in plantaris muscle, but not in soleus. However, isolated soleus from tumor-bearing rats had a reduced force production capacity when compared to controls. These novel findings demonstrate that tumor-bearing rats have severe muscle atrophy exclusively in glycolytic fibers. Cancer progression is associated with cysteine Ox-PTMs in the skeletal muscle, but these modifications affect different pathways in a glycolytic muscle compared to an oxidative muscle, indicating that intrinsic muscle oxidative capacity determines the response to cancer cachectic effects.
    Keywords:  aerobic metabolism; atrophy; cancer cachexia; fiber type; muscle wasting
  23. Exerc Sport Sci Rev. 2021 Jun 05.
      ABSTRACT: Breast Cancer gene 1 (BRCA1) is a large, multi-functional protein that regulates a variety of mechanisms in multiple different tissues. Our work established that Brca1 is expressed in skeletal muscle and localizes to the mitochondria and nucleus. Here, we propose BRCA1 expression is critical for the maintenance of force production and mitochondrial respiration in skeletal muscle.
  24. Tissue Eng Part A. 2021 Jun 09.
      Advances in the engineering of comprehensive skeletal muscle models in vitro will improve drug screening platforms and can lead to better therapeutic approaches for the treatment of skeletal muscle injuries. To this end, a vascularized tissue-engineered skeletal muscle (TE-SkM) model that includes adipocytes was developed in order to better emulate the intramuscular adipose tissue that is observed in skeletal muscles of patients with diseases like diabetes. Muscle precursor cells (MPCs) cultured with and without microvessels derived from adipose tissue (microvascular fragments; MVFs) were used to generate TE-SkM constructs, with and without a microvasculature, respectively. TE-SkM constructs were treated with adipogenic induction media to induce varying levels of adipogenesis. With a delayed addition of induction media to allow for angiogenesis, a robust microvasculature in conjunction with an increased content of adipocytes was achieved. The augmentation of vascularized TE-SkM constructs with adipocytes caused a reduction in maturation (compaction), mechanical integrity (Young's Modulus), and myotube and vessel alignment. An increase in basal glucose uptake was seen in both levels of adipogenic induction, and a diminished insulin-stimulated glucose uptake was associated with the higher level of adipogenic differentiation, and the greater number of adipocytes. Impact Statement The findings of the current study represent the effectiveness of employing a combinatorial approach involving MPCs and MVFs to create a vascularized TE-SkM model with adipocytes that induces structural and metabolic changes. This model is a platform to support the discovery of mechanisms underlying the phenomena of intramuscular adipose tissue that is characteristic of the skeletal muscles of patients with diseases.
  25. J Appl Physiol (1985). 2021 Jun 10.
      AIM: The maintenance of healthy and functional mitochondria is the result of a complex mitochondrial turnover and herein quality-control program which includes both mitochondrial biogenesis and autophagy of mitochondria. The aim of this study was to examine the effect of an intensified training load on skeletal muscle mitochondrial quality control in relation to changes in mitochondrial oxidative capacity, maximal oxygen consumption and performance in highly trained endurance athletes.METHODS: 27 elite endurance athletes performed high intensity interval exercise followed by moderate intensity continuous exercise 3 days per week for 4 weeks in addition to their usual volume of training. Mitochondrial oxidative capacity, abundance of mitochondrial proteins, markers of autophagy and antioxidant capacity of skeletal muscle were assessed in skeletal muscle biopsies before and after the intensified training period.
    RESULTS: The intensified training period increased several autophagy markers suggesting an increased turnover of mitochondrial and cytosolic proteins. In permeabilized muscle fibers, mitochondrial respiration was ~20 % lower after training although some markers of mitochondrial density increased by 5-50%, indicative of a reduced mitochondrial quality by the intensified training intervention. The antioxidative proteins UCP3, ANT1, and SOD2 were increased after training, whereas we found an inactivation of aconitase. In agreement with the lower aconitase activity, the amount of mitochondrial LON protease that selectively degrades oxidized aconitase, was doubled.
    CONCLUSION: Together, this suggests that mitochondrial respiratory function is impaired during the initial recovery from a period of intensified endurance training while mitochondrial quality control is slightly activated in highly trained skeletal muscle.
    Keywords:  athletes; endurance; mitochondrial oxidative capacity; mitochondrial quality-control; mitophagy
  26. Appl Physiol Nutr Metab. 2021 Jun 11.
      PUFA-derived bioactive lipid mediators called oxylipins have been shown to influence muscle growth, inflammation and repair in select muscles. Since individual oxylipins have varying effects and potencies, broad profiling in differing muscle types is required to further understand their overall effects. In addition, diet and sex are key determinants of oxylipin levels. Therefore, to provide comprehensive data on oxylipin profiles in rat soleus (SO), red gastrocnemius (RG), and white gastrocnemius (WG) muscles, female and male weanling Sprague-Dawley rats were provided control or experimental diets enriched in n-3 (ω-3) or n-6 (ω-6) PUFA for 6 weeks. Free oxylipin analysis by HPLC/MS/MS revealed that SO muscle had 25% more oxylipins and 4-13 times greater oxylipin mass than WG muscle. Dietary n-3 PUFA, α-linolenic acid, EPA, and DHA, each increased n-3 oxylipins derived directly from their precursors and several that were not direct precursors, while reducing arachidonic acid derived oxylipins. Dietary linoleic acid had few effects on oxylipins. Oxylipins with a sex effect were higher in females in SO and RG. Oxylipins generally reflected the effects of diet and sex on PUFA, but there were exceptions. These fundamental oxylipin profile data provide groundwork knowledge and context for future research on muscle oxylipin functions. Novelty • Rat soleus (SO) compared to red (RG) and white gastrocnemius (WG) muscles have a higher number and greater mass of oxylipins. • Oxylipins generally reflect diet effects on PUFA in all muscles, but there are notable exceptions. • Oxylipins in SO and RG are higher in females.
  27. Med Sci Sports Exerc. 2021 Jun 11.
      PURPOSE: This study was designed to probe the effect of downhill running on microtubule acetylation and autophagic flux in rat skeletal muscle.METHODS: Sprague-Dawley rats were subjected to an exercise protocol of a 90-min downhill run with a slope of -16° and a speed of 16 m/min, and then the soleus was sampled at 0 h, 12 h, 24 h, 48 h, and 72 h after exercise. Protein expression levels of microtubule-associated protein 1 light chain 3 (LC3), p62/sequestosome 1 (p62), α-tubulin and acetylated α-tubulin (AcK40 α-tubulin) were detected by Western blotting. Alpha-tubulin was costained with acetylated α-tubulin (AcK40 α-tubulin) or cytoplasmic dynein intermediate chain in a single muscle fiber, and LC3 was costained with lysosomal associated membrane protein 1 (LAMP1) in cryosections. To assess autophagic flux in vivo, colchicine or vehicle was injected intraperitoneally 3 days before the exercise experiment, and the protein levels of LC3 and p62 were measured by Western blotting.
    RESULTS: Downhill running induced a significant increase in the protein levels of LC3-II and p62, while the level and proportion of AcK40 α-tubulin were markedly decreased. Furthermore, the amount of dynein on α-tubulin was decreased after downhill running, and autophagosomes accumulated in the middle of myofibrils. Importantly, LC3-II flux was decreased following downhill running compared with that in the control group.
    CONCLUSIONS: A bout of downhill running decreases microtubule acetylation, which may impair dynein recruitment and autophagosome transportation, causing blocked autophagic flux.
  28. Dev Dyn. 2021 Jun 06.
      BACKGROUND: The growth of most bony tuberosities, like the deltoid tuberosity (DT), rely on the transmission of muscle forces at the tendon-bone attachment during skeletal growth. Tuberosities distribute muscle forces and provide mechanical leverage at attachment sites for joint stability and mobility. The genetic factors that regulate tuberosity growth remain largely unknown. In mouse embryos with global deletion of fibroblast growth factor 9 (Fgf9), the DT size is notably enlarged. In this study, we explored the tissue-specific regulation of DT size using both global and targeted deletion of Fgf9.RESULTS: We showed that cell hypertrophy and mineralization dynamics of the DT, as well as transcriptional signatures from skeletal muscle but not bone, were influenced by the global loss of Fgf9. Loss of Fgf9 during embryonic growth led to increased chondrocyte hypertrophy and reduced cell proliferation at the DT attachment site. This endured hypertrophy and limited proliferation may explain the abnormal mineralization patterns and locally dysregulated expression of markers of endochondral development in Fgf9null attachments. We then showed that targeted deletion of Fgf9 in skeletal muscle leads to postnatal enlargement of the DT.
    CONCLUSION: Taken together, we discovered that Fgf9 may play an influential role in muscle-bone crosstalk during embryonic and postnatal development. This article is protected by copyright. All rights reserved.
    Keywords:  Bone shape; Enthesis; Mechanics; Muscle; Skeleton
  29. Am J Physiol Cell Physiol. 2021 06 09.
      Animal models clearly illustrate that the maintenance of skeletal muscle mass depends on the function and interaction of a heterogeneous population of resident and infiltrating mononuclear cells. Several lines of evidence suggest that mononuclear cells also play a role in muscle wasting in humans, and targeting these cells may open new treatment options for intervention or prevention in sarcopenia. Methodological and ethical constraints have perturbed exploration of the cellular characteristics and function of mononuclear cells in human skeletal muscle. Thus, investigations of cellular phenotypes often depend on immunohistochemical analysis of small tissue samples obtained by needle biopsies, which do not match the deep phenotyping of mononuclear cells obtained from animal models. Here, we have developed a protocol for Fluorescence Activated Cell Sorting (FACS), based on single-cell RNA-sequencing data, for quantifying and characterizing mononuclear cell populations in human skeletal muscle. Muscle stem cells, fibro-adipogenic progenitors, and two subsets of macrophages (CD11c+/-) are present in needle biopsies in comparable quantities per milligram tissue to open surgical biopsies. We find that direct cell isolation is preferable due to a substantial shift in transcriptome when using pre-culture before the FACS procedure. Finally, in vitro validation of the cellular phenotype of muscle stem cells, fibro-adipogenic progenitors, and macrophages confirms population specific traits. This study demonstrates that mononuclear cell populations can be quantified and subsequently analyzed from needle biopsy material and opens the perspective for future clinical studies of cellular mechanisms in muscle wasting.
    Keywords:  Biopsy; Mononuclear cells; Skeletal muscle
  30. Commun Biol. 2021 Jun 08. 4(1): 703
      Random errors in protein synthesis are prevalent and ubiquitous, yet their effect on organismal health has remained enigmatic for over five decades. Here, we studied whether mice carrying the ribosomal ambiguity (ram) mutation Rps2-A226Y, recently shown to increase the inborn error rate of mammalian translation, if at all viable, present any specific, possibly aging-related, phenotype. We introduced Rps2-A226Y using a Cre/loxP strategy. Resulting transgenic mice were mosaic and showed a muscle-related phenotype with reduced grip strength. Analysis of gene expression in skeletal muscle using RNA-Seq revealed transcriptomic changes occurring in an age-dependent manner, involving an interplay of PGC1α, FOXO3, mTOR, and glucocorticoids as key signaling pathways, and finally resulting in activation of a muscle atrophy program. Our results highlight the relevance of translation accuracy, and show how disturbances thereof may contribute to age-related pathologies.
  31. Aging (Albany NY). 2021 Jun 07.
    Keywords:  NAD +; SIRT; aging; deacetylation; skeletal muscle
  32. Cell Biosci. 2021 Jun 05. 11(1): 105
      BACKGROUND: The neuromuscular junction (NMJ) is a peripheral synapse critical to muscle contraction. Like acetylcholine receptors (AChRs), many essential proteins of NMJ are extremely concentrated at the postjunctional membrane. However, the mechanisms of synapse-specific concentration are not well understood; furthermore, it is unclear whether signaling molecules critical to NMJ formation and maintenance are also locally transcribed.RESULTS: We studied the β-gal activity encoded by a lacZ cassette driven by the promoter of the Lrp4 gene. As reported for Lrp4 mRNA, β-gal was in the central region in embryonic muscles and at the NMJ after its formation. However, β-gal was no longer in the central areas of muscle fibers in Lrp4 or MuSK mutant mice, indicating a requirement of Lrp4/MuSK signaling. This phenotype could be rescued by transgenic expression of LRP4 with a transmembrane domain but not soluble ECD in Lrp4 mutant mice. β-gal and AChR clusters were distributed in a broader region in lacZ/ECD than that of heterozygous lacZ/+ mice, indicating an important role of the transmembrane domain in Lrp4 signaling. Synaptic β-gal activity became diffused after denervation or treatment with µ-conotoxin, despite its mRNA was increased, indicating synaptic Lrp4 mRNA enrichment requires muscle activity. β-gal was also diffused in aged mice but became re-concentrated after muscle stimulation. Finally, Lrp4 mRNA was increased in C2C12 myotubes by Wnt ligands in a manner that could be inhibited by RKI-1447, an inhibitor of ROCK in Wnt non-canonical signaling. Injecting RKI-1447 into muscles of adult mice diminished Lrp4 synaptic expression.
    CONCLUSIONS: This study demonstrates that synapse-specific enrichment of Lrp4 mRNA requires a coordinated interaction between Lrp4/MuSK signaling, muscle activity, and Wnt non-canonical signaling. Thus, the study provides a new mechanism for Lrp4 mRNA enrichment. It also provides a potential target for the treatment of NMJ aging and other NMJ-related diseases.
    Keywords:  Lrp4; Muscle activity; Neuromuscular junction; Wnt non-canonical signaling; β-gal
  33. Magn Reson Med. 2021 Jun 09.
      PURPOSE: Multislice arterial spin labeling (ASL) MRI acquisitions are currently challenging in skeletal muscle because of long transit times, translating into low-perfusion SNR in distal slices when large spatial coverage is required. However, fiber type and oxidative capacity vary along the length of healthy muscles, calling for multislice acquisitions in clinical studies. We propose a new variant of flow alternating inversion recovery (FAIR) that generates sufficient ASL signal to monitor exercise-induced perfusion changes in muscle in two distant slices.METHODS: Label around and between two 7-cm distant slices was created by applying the presaturation/postsaturation and selective inversion modules selectively to each slice (split-label multislice FAIR). Images were acquired using simultaneous multislice EPI. We validated our approach in the brain to take advantage of the high resting-state perfusion, and applied it in the lower leg muscle during and after exercise, interleaved with a single-slice FAIR as a reference.
    RESULTS: We show that standard multislice FAIR leads to an underestimation of perfusion, while the proposed split-label multislice approach shows good agreement with separate single-slice FAIR acquisitions in brain, as well as in muscle following exercise.
    CONCLUSION: Split-label FAIR allows measuring muscle perfusion in two distant slices simultaneously without losing sensitivity in the distal slice.
    Keywords:  ASL; FAIR; MRI; muscle; perfusion
  34. Aging Cell. 2021 Jun 08. e13415
      Cellular senescence has emerged as a significant and potentially tractable mechanism of aging and multiple aging-related conditions. Biomarkers of senescent cell burden, including molecular signals in circulating immune cells and the abundance of circulating senescence-related proteins, have been associated with chronological age and clinical parameters of biological age in humans. The extent to which senescence biomarkers are affected by interventions that enhance health and function has not yet been examined. Here, we report that a 12-week structured exercise program drives significant improvements in several performance-based and self-reported measures of physical function in older adults. Impressively, the expression of key markers of the senescence program, including p16, p21, cGAS, and TNFα, were significantly lowered in CD3+ T cells in response to the intervention, as were the circulating concentrations of multiple senescence-related proteins. Moreover, partial least squares discriminant analysis showed levels of senescence-related proteins at baseline were predictive of changes in physical function in response to the exercise intervention. Our study provides first-in-human evidence that biomarkers of senescent cell burden are significantly lowered by a structured exercise program and predictive of the adaptive response to exercise.
    Keywords:  aging; immune cells; inflammation; senotherapeutics
  35. Front Med (Lausanne). 2021 ;8 649748
      Background: Sarcopenia is a muscle disease in loss of muscle strength, mass, and function associated with aging. Although protective effects of exercise on muscle mass and function are generally recognized, research findings in sarcopenic adults are inconsistent. It is necessary to conduct a systematic review to determine the effects of exercise on muscle strength, body composition, and physical performance in older adults with sarcopenia, and to examine the potential moderators including sociodemographic characteristics and exercise-related factors. Methods: Six electronical academic databases (Medline, Embase, CINAHL, Scopus, Cochrane Library, and SPORTDiscus) were used to retrieve the eligible studies from inception to May 2020. Two reviewers independently selected and extracted the data from each included study, and effect sizes were calculated by employing random-effect models with 95% confidential interval (CI). The Physiotherapy Evidence Database (PEDro) scale was used to assess study quality. Results: Seventeen studies (985 participants with sarcopenia, aged 67.6-86 years) were included in this review study. The meta-analytic results showed significant improvements in muscle strength [grip strength, SMD = 0.30, 95% CI (0.15, 0.45), I 2 = 6%, p < 0.01; knee extension, SMD = 0.32, 95% CI (0.15, 0.50), I 2 = 0%, p < 0.01; and chair and stand, SMD = 0.56, 95% CI (0.30, 0.81), I 2 = 36%, p < 0.01], in physical performance [timed up and go, SMD = 0.74, 95% CI (0.48, 1.00), I 2 = 0%, p < 0.01; and gait speed, SMD = 0.59, 95% CI (0.35, 0.82), I 2 = 62%, p < 0.01], and in body composition [skeletal muscle mass index, SMD = 0.37, 95% CI (0.15, 0.58), I 2 = 16%, p < 0.01; and appendicular skeletal muscle, SMD = 0.31, 95% CI (0.13, 0.49), I 2 = 20%, p < 0.01]. However, there were no significant differences in other body composition (SMD = 0.20-0.36). Additionally, meta-regression revealed that the higher percent of female participants was significantly associated with improved gait speed (β = 0.0096, p = 0.03) and decreased skeletal muscle mass index (β = -0.0092, p = 0.01). Conclusions: The current meta-analysis suggests that exercise is a beneficial therapy, which has protective effects for older adults with sarcopenia. Some beneficial effects may be moderated by gender and exercise intensity.
    Keywords:  meta—analysis; muscle function; physical exercise; physical performance; sarcopenia
  36. J Frailty Aging. 2021 ;10(3): 226-232
      Detection of sarcopenia in primary care is a first and essential step in community-dwelling older adults before implementing preventive interventions against the onset of disabling conditions. In fact, leaving this condition undiagnosed and untreated can impact on the individual's quality of life and function, as well as on healthcare costs. This article summarizes the many instruments today available for promoting an earlier and prompter detection of sarcopenia in primary care, combining insights about its clinical management. Primary care physicians may indeed play a crucial role in the identification of individuals exposed to the risk of sarcopenia or already presenting this condition. To confirm the suspected diagnosis, several possible techniques may be advocated, but it is important that strategies are specifically calibrated to the needs, priorities and resources of the setting where the evaluation is conducted. To tackle sarcopenia, nutritional counselling and physical activity programs are today the two main interventions to be proposed. Multicomponent and personalized exercise programs can (and should) be prescribed by primary care physicians, taking advantage of validated programs ad hoc designed for this purpose (e.g., the Vivifrail protocol). It is possible that, in the next future, new pharmacological treatments may become available for tackling the skeletal muscle decline. These will probably find application in those individuals non-responding to lifestyle interventions.
    Keywords:  Skeletal muscle; aging; geriatrics; muscle strength; physical function
  37. Exerc Sport Sci Rev. 2021 Jun 08.
      ABSTRACT: Neuromuscular electrical stimulation (NMES) applied to skeletal muscles is an effective rehabilitation and exercise training modality. However, the relatively low muscle force and rapid muscle fatigue induced by NMES limits the stimulus provided to the neuromuscular system, and subsequent adaptations. We hypothesise that adaptations to NMES will be enhanced by the use of specific stimulation protocols and adjuvant interventions.
  38. Skelet Muscle. 2021 Jun 09. 11(1): 15
      BACKGROUND: Diabetes-related muscle wasting is one of the devastating complications of diabetes, which is associated with muscle autophagy due to insulin-mediated glucose starvation. However, treatment for diabetes-related muscle wasting is limited. Our previous study already found that niclosamide ethanolamine salt has the therapeutic effects on insulin deficiency of type 1 diabetes mice and muscle wasting induced by doxorubicin. Therefore, we aim to investigate the therapeutic effects of niclosamide ethanolamine salt on diabetes-induced muscle wasting and to explore whether the mechanism is associated with muscle autophagy.METHODS: Type 1 diabetes mice were induced by intraperitoneal injection of streptozotocin, then were fed with regular diet supplemented with 10 g/kg niclosamide ethanolamine salt. The whole experiment lasted for 8 weeks. At the end of the study, grip strength, weights of tibialis anterior, gastrocnemius, soleus, and extensor digitorum longus muscle were measured. Tibialis anterior muscles stained with PAS were used for evaluating the fiber cross sectional area. Immunofluorescence analysis of myosin heavy chain expression in extensor digitorum longus and soleus muscle was used for determining the composition of the muscle fiber type. Electronic microscopy was applied to observe the autophagy in the atrophied muscle. Serum insulin levels and fasting blood glucose were also measured. Tissues of gastrocnemius muscle were used for detecting the expression of the proteins related to autophagy.
    RESULTS: In this study, we found that niclosamide ethanolamine salt could ameliorate muscle atrophy in the type 1 diabetes mice as well, such as enhancing the declined grip strength, improving limb weight and increasing the numbers of glycolytic muscle fiber. Electron microscopy also confirmed that there did exist abundant autophagic vacuoles in the atrophied muscle of the type 1 diabetes mice. Specifically, niclosamide ethanolamine salt could reduce the over expression of autophagy-related proteins, including p-AMPK (Thr172), FoxO3a, p-ULK1 (Ser555), LC3B II, and p-p38 in gastrocnemius muscle of the type 1 diabetes mice.
    CONCLUSION: Niclosamide ethanolamine salt could ameliorate muscle wasting. The mechanisms underlying might be associated with inhibition of muscle autophagy.
    Keywords:  Autophagy; Diabetes-related muscle wasting; Niclosamide ethanolamine salt
  39. Histochem Cell Biol. 2021 Jun 10.
      Studies in differentiating skeletal muscle cells in vitro have revealed that the microtubule-organizing center shifts from the centrosome to the perinuclear sites. As the Golgi apparatus surrounds the nucleus in a myotube, it is unclear whether microtubules are nucleated at the nuclear envelope or at the surrounding Golgi apparatus. In this study, we investigated the positional relationship between the microtubule nucleating sites and the Golgi apparatus in C2C12 myotubes and in primary cultured mouse skeletal myotubes. We focused on gaps in the perinuclear Golgi apparatus where the nuclear envelope was not covered with the Golgi apparatus. In microtubule regrowth assay, microtubule regrowth after cold-nocodazole depolymerization of preexisting microtubules was not found at the gap of the perinuclear Golgi apparatus. Most of the microtubule regrowth was detected at the CDK5RAP2 (CDK5 regulatory subunit-associated protein 2)-rich spots on the perinuclear Golgi apparatus. Disruption of the perinuclear Golgi apparatus with brefeldin A treatment eliminated the perinuclear microtubule regrowth. The Golgi apparatus of undifferentiated myoblasts and those at the cytoplasm of myotubes were also the microtubule nucleating sites. From these observations, we concluded that most of the perinuclear microtubule nucleation occurs on the Golgi apparatus surrounding the nucleus.
    Keywords:  CDK5RAP2; Golgi apparatus; MTOC; Microtubule nucleation; Skeletal muscle cell
  40. iScience. 2021 May 21. 24(5): 102488
      Targeting the signaling pathway of growth differentiation factor 8 (GDF8), also known as myostatin, has been regarded as a promising strategy to increase muscle mass in the elderly and in patients. Accumulating evidence in animal models and clinical trials has indicated that a rational approach is to inhibit a limited number of transforming growth factor β (TGF-β) family ligands, including GDF8 and activin A, without affecting other members. Here, we focused on one of the endogenous antagonists against TGF-β family ligands, follistatin-like 3 (FSTL3), which mainly binds and neutralizes activins, GDF8, and GDF11. Although bivalent human FSTL3 Fc-fusion protein was rapidly cleared from mouse circulation similar to follistatin (FST)-Fc, monovalent FSTL3-Fc (mono-FSTL3-Fc) generated with the knobs-into-holes technology exhibited longer serum half-life. Systemic administration of mono-FSTL3-Fc in mice induced muscle fiber hypertrophy and increased muscle mass in vivo. Our results indicate that the monovalent FSTL3-based therapy overcomes the difficulties of current anti-GDF8 therapies.
    Keywords:  Human metabolism; Musculoskeletal medicine; Physiology
  41. Biomed Res. 2021 ;42(3): 115-119
      The basement membrane (BM), with collagen IV as a major component, plays an important role in the maintenance of muscle structure and its robustness. To investigate the effects of aging on factors related to BM construction, we compared the expression status of these factors in 3- and 20-month-old male Wistar rats. The expression levels of Col4a1 and Col4a2 (encoding collagen IV), Sparc (involved in collagen IV functionalization), and Mmp14 (a collagen IV degradation factor) were decreased. These results suggest that aging suppresses collagen IV synthetic and degradative factors and affects BM-related factors in the steady state.
  42. Mol Metab. 2021 Jun 04. pii: S2212-8778(21)00108-3. [Epub ahead of print] 101263
      OBJECTIVE: Abscisic acid (ABA) is a plant hormone also present and active in animals. In mammals, ABA regulates blood glucose levels by stimulating insulin-independent glucose uptake and metabolism in adipocytes and myocytes, through its receptor LANCL2. The objective of this study was to investigate whether another member of the LANCL protein family, LANCL1, also behaves as an ABA receptor and, if so, which functional effects are mediated by LANCL1.METHODS: ABA binding to human recombinant LANCL1 was explored by equilibrium binding experiments with [3H]ABA, by circular dichroism and by surface plasmon resonance. Rat L6 myoblasts overexpressing either LANCL1 or LANCL2, or silenced for the expression of both proteins, were used to investigate basal and ABA-stimulated transport of a fluorescent glucose analog (NBDG) and the signaling pathway downstream of the LANCL proteins, by means of Western blot and qPCR analysis. Finally, glucose tolerance and sensitivity to ABA were compared in LANCL2-/- and wild-type (WT) siblings.
    RESULTS: Human recombinant LANCL1 binds ABA with a Kd between 1 and 10 μM, depending on the assay, i.e. in a concentration range that lies in between the low and high-affinity ABA binding sites of LANCL2. In L6 myoblasts, LANCL1 and LANCL2 similarly, i) stimulate both basal and ABA-triggered NBDG uptake (4-fold), ii) activate transcription and protein expression of the glucose transporters GLUT4 and GLUT1 (4-6-fold) and of the signaling proteins AMPK/PGC-1α/Sirt1 (2-fold), iii) stimulate mitochondrial respiration (5-fold) and expression of the skeletal muscle (SM) uncoupling proteins sarcolipin (3-fold) and UCP3 (12-fold). LANCL2-/- mice have a reduced glucose tolerance compared with WT; they spontaneously overexpress LANCL1 in the SM and respond to chronic ABA treatment (1 μg/Kg body weight/day) with an improved glycemia response to glucose load and an increased SM transcription of GLUT4 and GLUT1 (20-fold), of the AMPK/PGC-1α/Sirt1 pathway and of sarcolipin, UCP3 and NAMPT (4-6-fold).
    CONCLUSIONS: LANCL1 behaves as an ABA receptor, with a somewhat lower affinity for ABA as compared with LANCL2, but with overlapping effector functions, stimulating glucose uptake and expression of muscle glucose transporters, mitochondrial uncoupling and respiration, via the AMPK/PGC-1α/Sirt1 pathway. Receptor redundancy may have been advantageous in animal evolution, given the role of the ABA/LANCL system in insulin-independent stimulation of cell glucose uptake and energy metabolism.
    Keywords:  LANCL1; UCP3; abscisic acid; cell respiration; glucose transporters; sarcolipin
  43. Sci Rep. 2021 Jun 08. 11(1): 12062
      Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive muscle weakness. Skeletal muscle is a prime source for biomarker discovery since it is one of the earliest sites to manifest disease pathology. From a prior RNA sequencing project, we identified FGF23 as a potential muscle biomarker in ALS. Here, we validate this finding with a large collection of ALS muscle samples and found a 13-fold increase over normal controls. FGF23 was also increased in the SOD1G93A mouse, beginning at a very early stage and well before the onset of clinical symptoms. FGF23 levels progressively increased through end-stage in the mouse. Immunohistochemistry of ALS muscle showed prominent FGF23 immunoreactivity in the endomysial connective tissue and along the muscle membrane and was significantly higher around grouped atrophic fibers compared to non-atrophic fibers. ELISA of plasma samples from the SOD1G93A mouse showed an increase in FGF23 at end-stage whereas no increase was detected in a large cohort of ALS patients. In conclusion, FGF23 is a novel muscle biomarker in ALS and joins a molecular signature that emerges in very early preclinical stages. The early appearance of FGF23 and its progressive increase with disease progression offers a new direction for exploring the molecular basis and response to the underlying pathology of ALS.
  44. EMBO Mol Med. 2021 Jun 07. e13591
      Cachexia syndrome develops in patients with diseases such as cancer and sepsis and is characterized by progressive muscle wasting. While iNOS is one of the main effectors of cachexia, its mechanism of action and whether it could be targeted for therapy remains unexplored. Here, we show that iNOS knockout mice and mice treated with the clinically tested iNOS inhibitor GW274150 are protected against muscle wasting in models of both septic and cancer cachexia. We demonstrate that iNOS triggers muscle wasting by disrupting mitochondrial content, morphology, and energy production processes such as the TCA cycle and acylcarnitine transport. Notably, iNOS inhibits oxidative phosphorylation through impairment of complexes II and IV of the electron transport chain and reduces ATP production, leading to energetic stress, activation of AMPK, suppression of mTOR, and, ultimately, muscle atrophy. Importantly, all these effects were reversed by GW274150. Therefore, our data establish how iNOS induces muscle wasting under cachectic conditions and provide a proof of principle for the repurposing of iNOS inhibitors, such as GW274150 for the treatment of cachexia.
    Keywords:  cachexia; cancer; iNOS; inflammation; metabolism
  45. Am J Physiol Cell Physiol. 2021 06 09.
      Maintaining mitochondrial function and dynamics is crucial for cellular health. In muscle, defects in mitochondria result in severe myopathies where accumulation of damaged mitochondria causes deterioration and dysfunction. Importantly, understanding the role of mitochondria in disease is a necessity to determine future therapeutics. One of the most common myopathies is mitochondrial encephalopathy lactic acidosis stroke-like episodes (MELAS), which has no current treatment. Recently, MELAS patients treated with rapamycin exhibited improved clinical outcomes. However, the cellular mechanisms of rapamycin effects in MELAS patients are currently unknown. In this study, we used cultured skin fibroblasts as a window into the mitochondrial dysfunction evident in MELAS cells, as well as to study the mechanisms of rapamycin action, compared to control, healthy individuals. We observed that mitochondria from patients were fragmented, had a 3-fold decline in the average speed of motility, a 2-fold reduced mitochondrial membrane potential and a 1.5-2-fold decline in basal respiration. Despite the reduction in mitochondrial function, mitochondrial import protein Tim23 was elevated in patient cell lines. MELAS fibroblasts exhibited increased MnSOD levels and lysosomal function when compared to healthy controls. Treatment of MELAS fibroblasts with rapamycin for 24 hrs resulted in increased mitochondrial respiration compared to control cells, a higher lysosome content, and a greater localization of mitochondria to lysosomes. Our studies suggest that rapamycin has the potential to improve cellular health even in the presence of mtDNA defects, primarily via an increase in lysosomal content.
    Keywords:  human fibroblasts; lysosomes; mitochondrial health; mitochondrial myopathies
  46. Front Pharmacol. 2021 ;12 687491
      The ongoing loss of skeletal muscle is a central event of cancer cachexia, and its consequences include adverse effects on patient's quality of life and survival. Alpinetin (Alp), a natural plant-derived flavonoid obtained from Alpinia katsumadai Hayata, has been reported to possess potent anti-inflammatory and antitumor activities. This study aimed to explore the therapeutic effect and underlying mechanism of Alp in the prevention of cancer cachexia. We found that Alp (25-100 μM) dose-dependently attenuated Lewis lung carcinoma-conditioned medium-induced C2C12 myotube atrophy and reduced expression of the E3 ligases Atrogin-1 and MuRF1. Moreover, Alp administration markedly improved vital features of cancer cachexia in vivo with visible reduction of the loss of tumor-free body weight and wasting of multiple tissues, including skeletal muscle, epididymal fat, and decreased expression of Atrogin-1 and MuRF1 in cachectic muscle. Alp suppressed the elevated spleen weight and serum concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6. Further, Alp treatment remained protective against cancer cachexia in the advanced stage of tumor growth. Molecular docking results suggested that Alp was docked into the active site of PPARγ with the docking score of -7.6 kcal/mol, forming a hydrogen bond interaction with PPARγ protein amino acid residue HIS449 with a bond length of 3.3 Å. Mechanism analysis revealed that Alp activated PPARγ, resulting in the downregulated phosphorylation of NF-κB and STAT3 in vitro and in vivo. PPARγ inhibition induced by GW9662 notably attenuated the improvement of Alp on the above cachexia phenomenon, indicating that PPARγ activation mediated the therapeutic effect of Alp. These findings suggested that Alp might be a potential therapeutic candidate against cancer cachexia.
    Keywords:  C2C12 myotube; GW9662; PPARγ; alpinetin; cancer cachexia; skeletal muscle
  47. Sports Med. 2021 Jun 07.
      BACKGROUND: The relationship between exercise-induced muscle damage (EIMD) indicators and acute training loads (TL) is yet to be reviewed extensively in semi-elite and elite athlete populations.OBJECTIVES: The objectives of this systematic review and meta-analysis were threefold: (1) to evaluate studies of EIMD following the initial period of the preseason in semi-elite and elite athletes: (2) to examine acute physiological and performance responses across two periods of the season with similar TL; and (3) to examine acute physiological and performance responses to acute changes in TL during the season.
    METHODS: The CINAHL, PubMed, Scopus, SPORTDiscus and Web of Science databases were systematically searched for studies that investigated: (1) semi-elite or elite athletes in team or individual sports following a periodised training programme; and (2) measured acute responses to training. Studies were excluded if: (1) conducted in animals; (2) non-English language; or (3) a conference abstract, review or case report. The Kmet Quality Scoring of Quantitative Studies tool was used for study appraisal.
    SYNTHESIS METHODS: Data were quantitatively analysed by generating forest plots to report test statistics for statistical significance and inter-trial heterogeneity.
    RESULTS: Of the included studies (n = 32), athletes experienced greater creatine kinase (CK) concentrations (Z = 4.99, p < 0.00001, I2 = 74%), inflammatory factors and other indirect measures of muscle damage in the initial phase of the preseason period compared to the off-season; there were no changes in CK (Z = 1.43, p = 0.15, I2 = 74%) across two time points of similar TL; and there were concurrent increases in CK with increases in TL (Z = 4.26, p < 0.0001, I2 = 36%) and vice versa (Z = 4.33, p < 0.0001, I2 = 79%).The qualitative analysis identified that the response of inflammatory factors and other indirect measures of muscle damage to changes in load were inconclusive.
    LIMITATIONS: This review included varying age, sex, sports and competition levels. The group level meta-analysis failed to identify within-athlete or position-specific differences across time.
    CONCLUSION: Blood biomarkers of EIMD may not differ across periods of similar TL, however can be considered a sensitive monitoring tool for assessing responses following acute TL changes in semi-elite and elite athletes.
  48. Int J Med Sci. 2021 ;18(12): 2480-2492
      Background: Trans-cinnamaldehyde (tCA), a bioactive component found in Cinnamomum cassia, has been reported to exhibit anti-inflammatory and antioxidant effects, but its efficacy in muscle cells has yet to be found. In this study, we investigated the inhibitory effect of tCA on inflammatory and oxidative stress induced by lipopolysaccharide (LPS) in C2C12 mouse skeletal myoblasts. Methods: To investigate the anti-inflammatory and antioxidant effects of tCA in LPS-treated C2C12 cells, we measured the levels of pro-inflammatory mediator, cytokines, and reactive oxygen species (ROS). To elucidate the mechanism underlying the effect of tCA, the expression of genes involved in the expression of inflammatory and oxidative regulators was also investigated. We further evaluated the anti-inflammatory and antioxidant efficacy of tCA against LPS in the zebrafish model. Results: tCA significantly inhibited the LPS-induced release of pro-inflammatory mediators and cytokines, which was associated with decreased expression of their regulatory genes. tCA also suppressed the expression of Toll-like receptor 4 (TLR4) and myeloid differentiation factor, and attenuated the nuclear translocation of nuclear factor-kappa B (NF-κB) and the binding of LPS to TLR4 on the cell surface in LPS-treated C2C12 cells. Furthermore, tCA abolished LPS-induced generation of ROS and expression levels of ROS producing enzymes, NADPH oxidase 1 (NOX1) and NOX2. However, tCA enhanced the activation of nuclear translocation of nuclear factor-E2-related factor 2 (Nrf2) and the expression of heme oxygenase-1 (HO-1) in LPS-stimulated C2C12 myoblasts. In addition, tCA showed strong protective effects against NO and ROS production in LPS-injected zebrafish larvae. Conclusions: Our findings suggest that tCA exerts its inhibitory ability against LPS-induced inflammatory and antioxidant stress in C2C12 myoblasts by targeting the TLR4/NF-κB, which might be mediated by the NOXs and Nrf2/HO-1 pathways.
    Keywords:  Nrf2/HO-1.; TLR4/NF-κB; Trans-cinnamaldehyde; inflammation; oxidative stress
  49. Phys Ther. 2021 Jun 09. pii: pzab144. [Epub ahead of print]
      OBJECTIVE: Although neuromuscular electrical stimulation (NMES) has been used as a safe and relevant complement to voluntary resistance training, its effectiveness in increasing quadriceps femoris muscle strength and mass in healthy young and older adults has not been determined. The aim of this scoping review was to assess the effects of NMES on quadriceps muscle strength and mass in healthy young and older adults.METHODS: CENTRAL, Pedro, MEDLINE, PubMed were searched from inception to September 2019. Randomized controlled trials (RCTs) that compared NMES with control group or voluntary resistance training for healthy young and older adults were included. Study characteristics, primary and secondary outcome parameters, and details of the NMES intervention were extracted by 2 reviewers. Only studies for which full text was available in English were included.
    RESULTS: Thirty-two RCTs including 796 healthy participants were identified as being eligible for young adults, and 5 RCTs including 123 healthy participants were identified as being eligible for older adults. The available evidence strongly suggests that NMES improves quadriceps muscle strength as compared with control group in young adults, but its efficacy seems lower than that of voluntary resistance training. The available limited evidence regarding the effects of NMES on quadriceps muscle mass compared to control in young adults is inconclusive, with 3 RCTs showing positive effects and 3 RCTs not showing positive effects. The very limited available evidence from 2 RCTs in older adults suggests that NMES might be beneficial for increasing quadriceps muscle strength and mass.
    CONCLUSION: Overall, the evidence indicates that NMES is an efficacious method for increasing quadriceps muscle strength in young adults, whereas its impact on muscle mass requires further investigations. In addition, the effectiveness of NMES needs to be confirmed in older adults on the basis of more high-quality RCTs with larger sample sizes.
    IMPACT: This scoping review of 87 RCTs including 919 people is the first study to show that the use of NMES increases quadriceps muscle strength in young adults and might improve quadriceps muscle strength as compared to control interventions in older adults. In both young and older adults, the effects of NMES on quadriceps muscle mass are still unclear.
    Keywords:  Exercise training; Muscle atrophy; Neuromuscular electrical stimulation; Physical therapy; Scoping review