bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2022–11–06
29 papers selected by
Anna Vainshtein, Craft Science Inc.



  1. FEBS Open Bio. 2022 Nov 03.
      When skeletal muscle is damaged, satellite cells (SCs) are activated to proliferate rapidly and fuse with the damaged muscle fibers to form new muscle fibers, thereby promoting muscle growth and remodeling and repair of trauma. Exosomes from differentiating human skeletal muscle cells trigger myogenesis of stem cells and provide biochemical cues for skeletal muscle regeneration. Therefore, we hypothesised that when muscles are injured, myoblast-derived exosomes may regulate muscle repair and regeneration. Here, we investigated the underlying mechanism by applying C2C12-derived exosomes to injured mouse skeletal muscles. The expression levels of skeletal muscle regeneration factors Pax7 and lipid-promoting factor PPARγ were upregulated, while the expression levels of fibrosis factors collagen-1 and α-SMA decreased. The expression of PCNA was elevated after applying C2C12-derived exosomes to SCs. Application of C2C12-derived exosomes to fibro-adipogenic progenitors (FAPs) resulted in an increase in PPARγ expression and adipogenesis capacity, while α-SMA expression and fibrosis capacity decreased. Analysis of the transcriptome and proteome of SCs after treatment with exosomes showed the involvement of multiple biological processes, including proliferation and differentiation of SCs, muscle regeneration, skeletal muscle atrophy, and the inflammatory response after muscle injury. Hence, our data suggest that C2C12-derived exosomes can promote the regeneration of skeletal muscle fibers, accelerate the production of fat from damaged muscles, inhibit the fibrosis of damaged muscles, and accelerate injury repair, which is related to exosome-mediated regulation of the proliferation of SCs, differentiation of FAPs, and modulation of SC mRNA expression and protein formation and decomposition.
    Keywords:  C2C12-derived exosomes; FAPs; SCs; myoblast; repair and regeneration; skeletal muscle
    DOI:  https://doi.org/10.1002/2211-5463.13504
  2. Mol Metab. 2022 Nov 01. pii: S2212-8778(22)00192-2. [Epub ahead of print] 101623
       OBJECTIVES: The Mitochondrial Unfolded Protein Response (UPRmt) is a compartment-specific mitochondrial quality control (MQC) mechanism that uses the transcription factor ATF5 to induce the expression of protective enzymes to restore mitochondrial function. Acute exercise is a stressor that has the potential to temporarily disrupt organellar protein homeostasis, however, the roles of ATF5 and the UPRmt in maintaining basal mitochondrial content, function and exercise-induced MQC mechanisms in skeletal muscle are not known.
    METHODS: ATF5 KO and WT mice were examined at rest or after a bout of acute endurance exercise. We measured protein content in whole muscle, nuclear, cytosolic and mitochondrial fractions, in addition to mRNA transcript levels in whole muscle. Using isolated mitochondria, we quantified rates of oxygen consumption and ROS emission to observe the effects of the absence of ATF5 on organelle function.
    RESULTS: ATF5 KO mice exhibited a larger and less functional muscle mitochondrial pool, most likely a culmination of enhanced biogenesis via increased PGC-1 α expression, and attenuated mitophagy. The absence of ATF5 resulted in a reduction in antioxidant proteins and increases in mitochondrial ROS emission, cytosolic cytochrome c, and the expression of mitochondrial chaperones. KO muscle also displayed enhanced exercise-induced stress kinase signaling, but a blunted mitophagic and UPRmt gene expression response, complemented by significant increases in the basal mRNA abundance and nuclear localization of ATF4. Instead of promoting its nuclear translocation, acute exercise caused the enrichment of ATF5 in mitochondrial fractions. We also identified PGC-1 α as an additional regulator of the basal expression of UPRmt genes.
    CONCLUSION: The transcription factor ATF5 retains a critical role in the maintenance of mitochondrial homeostasis and the appropriate response of muscle to acute exercise for the optimization of mitochondrial quality control.
    Keywords:  Exercise; Mitochondria; Mitochondrial Quality Control; Mitochondrial Unfolded Protein Response (UPR(mt)); Protein Homeostasis; Skeletal Muscle
    DOI:  https://doi.org/10.1016/j.molmet.2022.101623
  3. Front Physiol. 2022 ;13 1056479
      
    Keywords:  aging; oxidative stress; sarcopenia; senescence; skeletal muscle
    DOI:  https://doi.org/10.3389/fphys.2022.1056479
  4. Front Immunol. 2022 ;13 953272
      Interleukin 6 (IL-6) acts as a pro and anti-inflammatory cytokine, has an intense correlation with exercise intensity, and activates various pathways such as autophagy and mitochondrial unfolded protein response. Also, IL-6 is interconnected to circadian clock-related inflammation and can be suppressed by the nuclear receptor subfamily 1, group D, member 1 (Nr1d1, protein product REV-ERBα). Since IL-6 is linked to physical exercise-modulated metabolic pathways such as autophagy and mitochondrial metabolism, we investigated the relationship of IL-6 with REV-ERBα in the adaptations of these molecular pathways in response to acute intense physical exercise in skeletal muscle. The present study was divided into three experiments. In the first one, wild-type (WT) and IL-6 knockout (IL-6 KO) mice were divided into three groups: Basal time (Basal; sacrificed before the acute exercise), 1 hour (1hr post-Ex; sacrificed 1 hour after the acute exercise), and 3 hours (3hr post-Ex; sacrificed 3 hours after the acute exercise). In the second experiment, C2C12 cells received IL-6 physiological concentrations or REV-ERBα agonist, SR9009. In the last experiment, WT mice received SR9009 injections. After the protocols, the gastrocnemius muscle or the cells were collected for reverse transcription-quantitative polymerase chain reaction (RTq-PCR) and immunoblotting techniques. In summary, the downregulation of REV-ERBα, autophagic flux, and most mitochondrial genes was verified in the IL-6 KO mice independent of exercise. The WT and IL-6 KO treated with SR9009 showed an upregulation of autophagic genes. C2C12 cells receiving IL-6 did not modulate the Nr1d1 mRNA levels but upregulated the expression of some mitochondrial genes. However, when treated with SR9009, IL-6 and mitochondrial gene expression were upregulated in C2C12 cells. The autophagic flux in C2C12 suggest the participation of REV-ERBα protein in the IL-6-induced autophagy. In conclusion, the present study verified that the adaptations required through physical exercise (increases in mitochondrial content and improvement of autophagy machinery) might be intermediated by an interaction between IL-6 and REVERBα.
    Keywords:  C2C12 cells; Nr1d1; autophagic flux; genetic deletion; mitochondria; pharmacological treatment
    DOI:  https://doi.org/10.3389/fimmu.2022.953272
  5. Front Physiol. 2022 ;13 975652
      The skeletal muscle tissue can adapt to exercise and environmental stressors with a remarkable plasticity. Prolonged cold stress exposure has been associated to increased skeletal muscle capillarization. Angioadaptation refers to the coordinated molecular and cellular processes that influence the remodeling of skeletal muscle microvasculature. Two cell types are central to angioadaptation: the myocytes, representing an important source of angiokines; and the skeletal muscle endothelial cell (SMECs), targets of these angiokines and main constituents of muscle capillaries. The influence of cold stress on skeletal muscle angioadaptation remains largely unknown, particularly with respect to myocyte-specific angiokines secretion or endothelial cell angioadaptive responses. Here, we use an in vitro model to investigate the impact of cold stress (28°C versus 37°C) on C2C12 myotubes and SMECs. Our main objectives were to evaluate: 1) the direct impact of cold stress on C2C12 cellular expression of angiokines and their release in the extracellular environment; 2) the indirect impact of cold stress on SMECs migration via these C2C12-derived angiokines; and 3) the direct effect of cold stress on SMECs angioadaptive responses, including migration, proliferation, and the activation of the vascular endothelial growth factor receptor-2 (VEGFR2). Cold stress reduced the secretion of angiokines in C2C12 myotubes culture media irrespective their pro-angiogenic or angiostatic nature. In SMECs, cold stress abrogated cell proliferation and reduced the activation of VEGFR2 despite a greater expression of this receptor. Finally, SMECs pre-conditioned to cold stress displayed an enhanced migratory response when migration was stimulated in rewarming conditions. Altogether our results suggest that cold stress may be overall angiostatic. However, cold stress accompanied by rewarming may be seen as a pro-angiogenic stressor for SMECs. This observation questions the potential for using pre-cooling in sport-performance or therapeutic exercise prescription to enhance skeletal muscle angioadaptive responses to exercise.
    Keywords:  TSP-1; VEGF-A; angioadaptation; angiogenesis; angiokine; proteome; thrombospondin
    DOI:  https://doi.org/10.3389/fphys.2022.975652
  6. Nanomedicine. 2022 Oct 26. pii: S1549-9634(22)00109-5. [Epub ahead of print] 102623
      In a context of drug repurposing, pentamidine (PTM), an FDA-approved antiparasitic drug, has been proposed to reverse the splicing defects associated in myotonic dystrophy type 1 (DM1). However, clinical use of PTM is hinder by substantial toxicity, leading to find alternative delivery strategies. In this work we proposed hyaluronic acid-based nanoparticles as a novel encapsulation strategy to efficiently deliver PTM to skeletal muscles cells. In vitro studies on C2C12 myoblasts and myotubes showed an efficient nanoparticles' internalization with minimal toxicity. More interestingly, our findings evidenced for the first time the endosomal escape of hyaluronic acid-based nanocarriers. Ex vivo studies showed an efficient nanoparticles' internalization within skeletal muscle fibers. Finally, the therapeutic efficacy of PTM-loaded nanosystems to reduce the number of nuclear foci has been demonstrated in a novel DM1 in vitro model. So far, current data demonstrated the potency of hyaluronic acid-based nanosystems as efficient nanocarrier for delivering PTM into skeletal muscle and mitigate DM1 pathology.
    Keywords:  Biomaterials; C2C12 cells; DM1 cell model; Muscular dystrophies; Nanoparticles
    DOI:  https://doi.org/10.1016/j.nano.2022.102623
  7. Curr Opin Genet Dev. 2022 Oct 26. pii: S0959-437X(22)00108-3. [Epub ahead of print]77 101999
      We are living longer, but our healthspan has not increased. The goal of regenerative medicine is to increase quality of life through an understanding of the cellular and molecular processes that underlie effective tissue repair in order to restore damaged tissues. The drivers of muscle regeneration are the muscle stem cells that cycle between quiescent and activated states to meet tissue regenerative demands. Here we review recent findings on the role of the niche, or tissue microenvironment, in the modulation of muscle stem cell plasticity and the mechanisms responsible for the drastic loss of stem cell function with aging. These new studies unveil fundamental mechanisms of stem cell plasticity with broad relevance to other tissues and lay the foundation for the development of therapeutic strategies to boost the regenerative potential of aged muscle stem cells.
    DOI:  https://doi.org/10.1016/j.gde.2022.101999
  8. Tissue Eng Regen Med. 2022 Nov 01.
       BACKGROUND: Skeletal muscles play many important roles in the human body and any malfunction or disorder of the skeletal muscles can lead to a reduced quality of life. Some skeletal dysfunctions are acquired, such as sarcopenia but others are congenital. Duchenne muscular dystrophy (DMD) is one of the most common forms of hereditary muscular dystrophy and is caused by a deficiency of the protein, Dystrophin. Currently, there is no clear treatment for DMD, there are only methods that can alleviate the symptoms of the disease. Mesenchymal stem cells, including tonsil-derived mesenchymal stem cells (TMSCs) have been shown to differentiate into skeletal muscle cells (TMSC-myocyte) and can be one of the resources for the treatment of DMD. Skeletal muscle cell characteristics of TMSC-myocytes have been confirmed through changes in morphology and expression of skeletal muscle markers such as Myogenin, Myf6, and MYH families after differentiation.
    MEOTHDS: Based on these characteristics, TMSC-myocytes have been transplanted into mdx mice, a mouse model of DMD, to investigate whether they can help improve the symptoms of DMD. The red fluorescent protein gene was transduced into TMSC (TMSC-R) for tracking transplanted cells.
    RESULTS: Prior to transplantation (TP), it was confirmed whether TMSC-R-myocytes had the same differentiation potential as TMSC-myocytes. Increased expression of dystrophin and autophagy markers in the TP group compared with the sham group was confirmed in the gastrocnemius muscle 12 weeks after TP.
    CONCLUSION: These results demonstrate muscle regeneration and functional recovery of mdx via autophagy activation following TMSC-myocyte TP.
    Keywords:  Differentiation; Duchenne muscular dystrophy; Mdx; Tonsil-derived mesenchymal stem cells
    DOI:  https://doi.org/10.1007/s13770-022-00489-7
  9. Geroscience. 2022 Nov 02.
      The age-related decline in skeletal muscle mass and function is known as sarcopenia. Sarcopenia progresses based on complex processes involving protein dynamics, cell signaling, oxidative stress, and repair. We have previously found that 8-week treatment with elamipretide improves skeletal muscle function, reverses redox stress, and restores protein S-glutathionylation changes in aged female mice. This study tested whether 8-week treatment with elamipretide also affects global phosphorylation in skeletal muscle consistent with functional improvements and S-glutathionylation. Using female 6-7-month-old mice and 28-29-month-old mice, we found that phosphorylation changes did not relate to S-glutathionylation modifications, but that treatment with elamipretide did partially reverse age-related changes in protein phosphorylation in mouse skeletal muscle.
    Keywords:  Aging; Mitochondria; Phosphorylation; Proteomics; S-Glutathionylation; Sarcopenia
    DOI:  https://doi.org/10.1007/s11357-022-00679-0
  10. Cell Signal. 2022 Oct 31. pii: S0898-6568(22)00271-6. [Epub ahead of print] 110509
      Cancer-associated cachexia (CAC) is a multifactorial wasting syndrome characterized by loss of skeletal muscle. Interleukin-11 (IL11), one of the IL6 family cytokines, is highly expressed in various types of cancer including cancers frequently associated with cachexia. However, the impact of IL11 on muscle metabolism remains to be determined. Since one of the mechanisms of muscle wasting in cachexia is defective muscle regeneration due to impaired myogenic differentiation, we examined the effect of IL11 on the differentiation of C2C12 mouse myoblasts. Treatment of C2C12 cells with recombinant mouse IL11 resulted in decreased myotube formation. In addition, IL11 treatment reduced the protein and mRNA levels of myosin heavy chain (MHC), a marker of myogenic differentiation. Moreover, the levels of myogenic regulatory factors including myogenin and Mrf4 were significantly reduced by IL11 treatment. IL11 treatment increased the number of BrdU-positive cells and the level of phosphorylated retinoblastoma (Rb) protein, while the levels of p21Waf1 and p27Kip1 were reduced by IL11 treatment in differentiating C2C12 cells, suggesting that IL11 interferes with cell cycle exit during the early stages of myogenic differentiation. Consistent with this, IL11 treatment at the late stage of differentiation did not affect myotube formation and MHC expression. IL11 treatment resulted in an activation of ERK, STAT3, and AKT in differentiating C2C12 cells. However, only ERK inhibitors including PD98059 and U0126 were able to ameliorate the suppressive effect of IL11 on the expression of MHC and myogenin. Additionally, pretreatment with PD98059 and U0126 resulted in improved myotube formation and reduced BrdU staining in IL11-treated cells. Together, our results suggest that IL11 inhibits myogenic differentiation through delayed cell cycle exit in an ERK-dependent manner. To our knowledge, this study is the first to demonstrate an inhibitory role of IL11 in myogenic differentiation and identifies the previously unrecognized role of IL11 as a possible mediator of CAC.
    Keywords:  C2C12; IL6 family cytokines; Interleukin-11; Myogenesis; cachexia
    DOI:  https://doi.org/10.1016/j.cellsig.2022.110509
  11. Hum Gene Ther. 2022 Oct 31.
      Duchenne muscular dystrophy (DMD) is a fatal muscle disease caused by dystrophin deficiency. Dystrophin consists of the amino terminus, central rod domain with 24 spectrin-like repeats and four hinges (H), cysteine-rich domain, and carboxyl terminus. Several highly abbreviated micro-dystrophins are currently in clinical trials. They all carry H1 and H4. Here we investigated whether these two hinges are essential for micro-dystrophin function in murine DMD models. Three otherwise identical micro-dystrophins were engineered to contain H1 and/or H4 and were named H1/H4 (with both H1 and H4), ∆H1 (without H1), and ∆H4 (without H4). These constructs were packaged in adeno-associated virus serotype-9 and delivered to the tibialis anterior muscle of 3-month-old male mdx4cv mice (1E12 vector genome particles/muscle). Three months later, we detected equivalent micro-dystrophin expression in total muscle lysate. However, only H1/H4 and ∆H1 showed correct sarcolemmal localization. ∆H4 mainly existed as subsarcolemmal aggregates. H1/H4 and ∆H1, but not ∆H4, fully restored the dystrophin-associated protein complex and significantly improved the specific muscle force. Eccentric contraction-induced force decline was best protected by H1/H4, followed by ∆H1, but not by ∆H4. Next, we compared H1/H4 and ∆H1 in 6-week-old male mdx mice by intravenous injection (1E13 vector genome particles/mouse). Four months post-injection, H1/H4 significantly outperformed ∆H1 in extensor digitorum longus muscle force measurements but two constructs yielded comparable ECG improvements. We conclude that H4 is essential for micro-dystrophin function and H1 facilitates force production. Our findings will help develop next-generation micro-dystrophin gene therapy.
    DOI:  https://doi.org/10.1089/hum.2022.180
  12. FASEB J. 2022 Dec;36(12): e22628
      Exercise training enhances oxidative capacity whereas detraining reduces mitochondrial content in skeletal muscle. The strategy to suppress the detraining-induced reduction of mitochondrial content has not been fully elucidated. As previous studies reported that branched-chain amino acid (BCAA) ingestion increased mitochondrial content in skeletal muscle, we evaluated whether BCAA supplementation could suppress the detraining-induced reduction of mitochondrial content. Six-week-old male Institute of Cancer Research (ICR) mice were randomly divided into four groups as follows: control (Con), endurance training (Tr), detraining (DeTr), and detraining with BCAA supplementation (DeTr + BCAA). Mice in Tr, DeTr, and DeTr + BCAA performed treadmill running exercises [20-30 m/min, 60 min, 5 times/week, 4 weeks]. Then, mice in DeTr and DeTr + BCAA were administered with water or BCAA [0.6 mg/g of body weight, twice daily] for 2 weeks of detraining. In whole skeletal muscle, mitochondrial enzyme activities and protein content were decreased after 2 weeks of detraining, but the reduction was suppressed by BCAA supplementation. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein content, a master regulator of mitochondrial biogenesis, was decreased by detraining irrespective of BCAA ingestion. Regarding mitochondrial degradation, BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3), a mitophagy-related protein, was significantly higher in the Tr group than in the DeTr + BCAA group, but not different from in the DeTr group. With respect to mitochondrial quality, BCAA ingestion did not affect oxygen consumption rate (OCR) and reactive oxygen species (ROS) production in isolated mitochondria. Our findings suggest that BCAA ingestion suppresses the detraining-induced reduction of mitochondrial content partly through inhibiting mitophagy.
    Keywords:  branched-chain amino acid; detraining; mitochondria; mitochondrial biogenesis; mitophagy; skeletal muscle
    DOI:  https://doi.org/10.1096/fj.202200588R
  13. Elife. 2022 Oct 31. pii: e81121. [Epub ahead of print]11
      Neonatal brachial plexus injury (NBPI) causes disabling and incurable muscle contractures that result from impaired longitudinal growth of denervated muscles. This deficit in muscle growth is driven by increased proteasome-mediated protein degradation, suggesting a dysregulation of muscle proteostasis. The myostatin (MSTN) pathway, a prominent muscle-specific regulator of proteostasis, is a putative signaling mechanism by which neonatal denervation could impair longitudinal muscle growth, and thus a potential target to prevent NBPI-induced contractures. Through a mouse model of NBPI, our present study revealed that pharmacologic inhibition of MSTN signaling induces hypertrophy, restores longitudinal growth, and prevents contractures in denervated muscles of female but not male mice, despite inducing hypertrophy of normally innervated muscles in both sexes. Additionally, the MSTN-dependent impairment of longitudinal muscle growth after NBPI in female mice is associated with perturbation of 20S proteasome activity, but not through alterations in canonical MSTN signaling pathways. These findings reveal a sex dimorphism in the regulation of neonatal longitudinal muscle growth and contractures, thereby providing insights into contracture pathophysiology, identifying a potential muscle-specific therapeutic target for contracture prevention, and underscoring the importance of sex as a biological variable in the pathophysiology of neuromuscular disorders.
    Keywords:  developmental biology; mouse
    DOI:  https://doi.org/10.7554/eLife.81121
  14. Front Cell Dev Biol. 2022 ;10 986930
      Oculopharyngeal muscular dystrophy (OPMD) is a late-onset dominant disease that primarily affects craniofacial muscles. Despite the fact that the genetic cause of OPMD is known to be expansion mutations in the gene encoding the nuclear polyadenosine RNA binding protein PABPN1, the molecular mechanisms of pathology are unknown and no pharmacologic treatments are available. Due to the limited availability of patient tissues, several animal models have been employed to study the pathology of OPMD. However, none of these models have demonstrated functional deficits in the muscles of the pharynx, which are predominantly affected by OPMD. Here, we used a knock-in mouse model of OPMD, Pabpn1 +/A17 , that closely genocopies patients. In Pabpn1 +/A17 mice, we detected impaired pharyngeal muscle function, and impaired pharyngeal satellite cell proliferation and fusion. Molecular studies revealed that basal autophagy, which is required for normal satellite cell function, is higher in pharynx-derived myoblasts than in myoblasts derived from limb muscles. Interestingly, basal autophagy is impaired in cells derived from Pabpn1 +/A17 mice. Pabpn1 knockdown in pharyngeal myoblasts failed to recapitulate the autophagy defect detected in Pabpn1 +/A17 myoblasts suggesting that loss of PABPN1 function does not contribute to the basal autophagy defect. Taken together, these studies provide the first evidence for pharyngeal muscle and satellite cell pathology in a mouse model of OPMD and suggest that aberrant gain of PABPN1 function contributes to the craniofacial pathology in OPMD.
    Keywords:  PABPN1; autophagy; craniofacial muscles; dysphagia; muscular dystrophy; oculopharyngeal muscular dystrophy; satellite cells
    DOI:  https://doi.org/10.3389/fcell.2022.986930
  15. Cureus. 2022 Sep;14(9): e29655
      Skeletal muscle is a major anatomic structural component of the human body. Myopathy, defined as skeletal muscle disease, may offend any of the body's 650 muscles and encompasses an extended array of acute and chronic abnormalities. Muscle disease can be categorized according to etiology as congenital, traumatic, infectious, or neoplastic. The concept of the diversity of multiple muscular disease processes signifies an important role for imaging in the detection and characterization of myopathy. However, despite the exquisite physiological properties of skeletal muscle, muscle imaging has not received attention equal to that of bones and joints. Accordingly, this article provides an indication of the most suitable imaging modalities for myopathy and reviews a multitude of primary and systemic muscle derangements, with an emphasis on magnetic resonance (MR) imaging findings. Because these patterns of MR imaging abnormality bespeak the widespread nature of myopathy, we illustrate typical examples of muscle disease processes to simplify diagnosis.
    Keywords:  disease; edema; fat; mass; mri; muscle; muscle disease; myopathy; patterns
    DOI:  https://doi.org/10.7759/cureus.29655
  16. Nat Commun. 2022 Nov 04. 13(1): 6622
      Mitochondrial networks provide coordinated energy distribution throughout muscle cells. However, pathways specifying mitochondrial networks are incompletely understood and it is unclear how they might affect contractile fiber-type. Here, we show that natural energetic demands placed on Drosophila melanogaster muscles yield native cell-types among which contractile and mitochondrial network-types are regulated differentially. Proteomic analyses of indirect flight, jump, and leg muscles, together with muscles misexpressing known fiber-type specification factor salm, identified transcription factors H15 and cut as potential mitochondrial network regulators. We demonstrate H15 operates downstream of salm regulating flight muscle contractile and mitochondrial network-type. Conversely, H15 regulates mitochondrial network configuration but not contractile type in jump and leg muscles. Further, we find that cut regulates salm expression in flight muscles and mitochondrial network configuration in leg muscles. These data indicate cell type-specific regulation of muscle mitochondrial network organization through evolutionarily conserved transcription factors cut, salm, and H15.
    DOI:  https://doi.org/10.1038/s41467-022-34445-9
  17. Trends Microbiol. 2022 Oct 29. pii: S0966-842X(22)00286-4. [Epub ahead of print]
      The gut microbiota represents a 'metabolic organ' that can regulate human metabolism. Intact gut microbiota contributes to host homeostasis, whereas compositional perturbations, termed dysbiosis, are associated with a wide range of diseases. Recent evidence demonstrates that dysbiosis, and the accompanying loss of microbiota-derived metabolites, results in a substantial alteration of skeletal muscle metabolism. As an example, bile acids, produced in the liver and further metabolized by intestinal microbiota, are of considerable interest since they regulate several host metabolic pathways by activating nuclear receptors, including the farnesoid X receptor (FXR). Indeed, alteration of gut microbiota may lead to skeletal muscle atrophy via a bile acid-FXR pathway. This Review aims to suggest a new pathway that connects different mechanisms, involving the gut-muscle axis, that are often seen as unrelated, and, starting from preclinical studies, we hypothesize new strategies aimed at optimizing skeletal muscle functionality.
    Keywords:  bile acid; gut microbiota; metabolism; next-generation sequencing; skeletal muscle
    DOI:  https://doi.org/10.1016/j.tim.2022.10.003
  18. Front Cardiovasc Med. 2022 ;9 1000067
      Impaired biomolecules and cellular organelles are gradually built up during the development and aging of organisms, and this deteriorating process is expedited under stress conditions. As a major lysosome-mediated catabolic process, autophagy has evolved to eradicate these damaged cellular components and recycle nutrients to restore cellular homeostasis and fitness. The autophagic activities are altered under various disease conditions such as ischemia-reperfusion cardiac injury, sarcopenia, and genetic myopathies, which impact multiple cellular processes related to cellular growth and survival in cardiac and skeletal muscles. Thus, autophagy has been the focus for therapeutic development to treat these muscle diseases. To develop the specific and effective interventions targeting autophagy, it is essential to understand the molecular mechanisms by which autophagy is altered in heart and skeletal muscle disorders. Herein, we summarize how autophagy alterations are linked to cardiac and skeletal muscle defects and how these alterations occur. We further discuss potential pharmacological and genetic interventions to regulate autophagy activities and their applications in cardiac and skeletal muscle diseases.
    Keywords:  autophagy; cardiomyopathy; gene therapy; heart disease; mitophagy; muscular dystrophy; myopathy; skeletal muscle disease
    DOI:  https://doi.org/10.3389/fcvm.2022.1000067
  19. NMR Biomed. 2022 Nov 04. e4869
      Rodent models of Duchenne muscular dystrophy (DMD) often do not recapitulate the severity of muscle wasting and resultant fibro-fatty infiltration observed in DMD patients. Having recently documented severe muscle wasting and fatty deposition in two preclinical models of muscular dystrophy (Dysferlin-null and mdx mice) through apolipoprotein E (ApoE) gene deletion without and with cholesterol-, triglyceride-rich Western diet supplementation, we sought to determine whether magnetic resonance imaging and spectroscopy (MRI and MRS) could be used to detect, characterize, and compare lipid deposition in mdx-ApoE knockout (KO) to mdx mice in a diet-dependent manner. MRI revealed that both mdx and mdx-ApoE mice exhibited elevated proton relaxation time constants (T2 ) in their lower hindlimbs irrespective of diet, indicating both chronic muscle damage and fatty tissue deposition. The mdx-ApoE mice on a Western diet (mdx-ApoEW ) presented with greatest fatty tissue infiltration in the posterior compartment of the hindlimb compared to other groups as detected by MRI/MRS. High-resolution magic angle spinning (HR-MAS) confirmed elevated lipid deposition in the posterior compartments of mdx-ApoEW mice in vivo and ex vivo, respectively. In conclusion, the mdx-ApoEW model recapitulates some of the extreme fatty tissue deposition observed clinically in DMD muscle but typically absent in mdx mice. This preclinical model will help facilitate the development of new imaging modalities directly relevant to the image contrast generated in DMD, and help to refine MR based biomarkers and their relationship to tissue structure and disease progression.
    Keywords:  Duchenne muscular dystrophy; fibro-fatty infiltration; magnetic resonance imaging and spectroscopy; mouse; muscle tissues; time domain nuclear magnetic resonance
    DOI:  https://doi.org/10.1002/nbm.4869
  20. J Gen Physiol. 2022 Dec 05. pii: e202213230. [Epub ahead of print]154(12):
      In skeletal muscle excitation-contraction (E-C) coupling, depolarization of the plasma membrane triggers Ca2+ release from the sarcoplasmic reticulum (SR), referred to as depolarization-induced Ca2+ release (DICR). DICR occurs through the type 1 ryanodine receptor (RyR1), which physically interacts with the dihydropyridine receptor Cav1.1 subunit in specific machinery formed with additional essential components including β1a, Stac3 adaptor protein, and junctophilins. Exome sequencing has accelerated the discovery of many novel mutations in genes encoding DICR machinery in various skeletal muscle diseases. However, functional validation is time-consuming because it must be performed in a skeletal muscle environment. In this study, we established a platform of the reconstituted DICR in HEK293 cells. The essential components were effectively transduced into HEK293 cells expressing RyR1 using baculovirus vectors, and Ca2+ release was quantitatively measured with R-CEPIA1er, a fluorescent ER Ca2+ indicator, without contaminant of extracellular Ca2+ influx. In these cells, [K+]-dependent Ca2+ release was triggered by chemical depolarization with the aid of inward rectifying potassium channel, indicating a successful reconstitution of DICR. Using the platform, we evaluated several Cav1.1 mutations that are implicated in malignant hyperthermia and myopathy. We also tested several RyR1 inhibitors; whereas dantrolene and Cpd1 inhibited DICR, procaine had no effect. Furthermore, twitch potentiators such as perchlorate and thiocyanate shifted the voltage dependence of DICR to more negative potentials without affecting Ca2+-induced Ca2+ release. These results well reproduced the findings with the muscle fibers and the cultured myotubes. Since the procedure is simple and reproducible, the reconstituted DICR platform will be highly useful for the validation of mutations and drug discovery for skeletal muscle diseases.
    DOI:  https://doi.org/10.1085/jgp.202213230
  21. Antioxid Redox Signal. 2022 Oct 31.
       SIGNIFICANCE: Cancer is frequently associated with the appearance of cachexia, a multifactorial wasting syndrome. Cachexia develops either as a result of tumor progression or as a side effect of anticancer treatments, especially of standard chemotherapy, eventually representing the direct cause of death in up to one third of all cancer patients. Cachexia, within its multi-organ affection, is characterized by severe loss of muscle mass and function, representing the most relevant subject of preclinical and clinical investigation.
    RECENT ADVANCES: The pathogenesis of muscle wasting in cancer- and chemotherapy-induced cachexia is complex and encompasses heightened protein catabolism and reduced anabolism, disrupted mitochondria and energy metabolism and even neuromuscular junction dismantling. The mechanisms underlying these alterations are still controversial, especially concerning the molecular drivers that could be targeted for anti-cachexia therapies. Inflammation and mitochondrial oxidative stress are among the principal candidates, the latter being extensively discussed in the present review.
    CRITICAL ISSUES: Several approaches have been tested in order to modulate the redox homeostasis in tumor hosts and to counteract cancer- and chemotherapy-induced muscle wasting, from exercise training to distinct classes of direct or indirect antioxidants. We herein report the most relevant results obtained in both preclinical and clinical trials.
    FUTURE DIRECTIONS: Including the assessment and the treatment of altered redox balance in the clinical management of cancer patients is still a big challenge. The available evidence suggests that fortifying the antioxidant defenses either by pharmacological or non-pharmacological strategies will likely improve cachexia and eventually the outcome of a broad cancer patient population.
    DOI:  https://doi.org/10.1089/ars.2022.0149
  22. Physiol Rep. 2022 Nov;10(21): e15481
      The use of non-steroidal anti-inflammatory drugs (NSAIDs) for treatment of musculoskeletal injuries is commonplace in the general, athletic, and military populations. While NSAIDs have been studied in a variety of tissues, the effects of NSAIDs on skeletal muscle have not been fully defined. To address this, we investigated the degree to which the cyclooxygenase (COX)-2-selective NSAID celecoxib affects muscle cell proliferation, differentiation, anabolic signaling, and mitochondrial function in primary human skeletal myoblasts and myotubes. Primary muscle cells were treated with celecoxib or NS-398 (a pharmacological inhibitor of COX-2) as a control. Celecoxib administration significantly reduced myoblast proliferation, viability, fusion, and myotube area in a dose-dependent manner, whereas NS-398 had no effect on any of these outcomes. Celecoxib treatment was also associated with reduced phosphorylation of ribosomal protein S6 in myoblasts, and reduced phosphorylation of AKT, p70S6K, S6, and ERK in myotubes. In contrast, NS-398 did not alter phosphorylation of these molecules in myoblasts or myotubes. In myoblasts, celecoxib significantly reduced mitochondrial membrane potential and respiration, as evidenced by the decreased citric acid cycle (CAC) intermediates cis-aconitic acid, alpha-keto-glutarate acid, succinate acid, and malic acid. Similar results were observed in myotubes, although celecoxib also reduced pyruvic acid, citric acid, and fumaric acid. NS-398 did not affect CAC intermediates in myoblasts or myotubes. Together, these data reveal that celecoxib inhibits proliferation, differentiation, intracellular signaling, and mitochondrial function in primary human myoblasts and myotubes independent of its function as a COX-2 inhibitor.
    Keywords:  celecoxib; cyclooxygenase; inflammation; mitochondria; myoblast; non-steroidal anti-inflammatory drug (NSAID)
    DOI:  https://doi.org/10.14814/phy2.15481
  23. Sports Med. 2022 Nov 05.
       BACKGROUND AND OBJECTIVE: This systematic review with meta-analysis investigated the influence of resistance training proximity-to-failure on muscle hypertrophy.
    METHODS: Literature searches in the PubMed, SCOPUS and SPORTDiscus databases identified a total of 15 studies that measured muscle hypertrophy (in healthy adults of any age and resistance training experience) and compared resistance training performed to: (A) momentary muscular failure versus non-failure; (B) set failure (defined as anything other than momentary muscular failure) versus non-failure; or (C) different velocity loss thresholds.
    RESULTS: There was a trivial advantage for resistance training performed to set failure versus non-failure for muscle hypertrophy in studies applying any definition of set failure [effect size=0.19 (95% confidence interval 0.00, 0.37), p=0.045], with no moderating effect of volume load (p=0.884) or relative load (p=0.525). Given the variability in set failure definitions applied across studies, sub-group analyses were conducted and found no advantage for either resistance training performed to momentary muscular failure versus non-failure for muscle hypertrophy [effect size=0.12 (95% confidence interval -0.13, 0.37), p=0.343], or for resistance training performed to high (>25%) versus moderate (20-25%) velocity loss thresholds [effect size=0.08 (95% confidence interval -0.16, 0.32), p=0.529].
    CONCLUSION: Overall, our main findings suggest that (i) there is no evidence to support that resistance training performed to momentary muscular failure is superior to non-failure resistance training for muscle hypertrophy and (ii) higher velocity loss thresholds, and theoretically closer proximities-to-failure do not always elicit greater muscle hypertrophy. As such, these results provide evidence for a potential non-linear relationship between proximity-to-failure and muscle hypertrophy.
    DOI:  https://doi.org/10.1007/s40279-022-01784-y
  24. Nat Biotechnol. 2022 Nov 03.
      Spatial transcriptomics reveals the spatial context of gene expression, but current methods are limited to assaying polyadenylated (A-tailed) RNA transcripts. Here we demonstrate that enzymatic in situ polyadenylation of RNA enables detection of the full spectrum of RNAs, expanding the scope of sequencing-based spatial transcriptomics to the total transcriptome. We demonstrate that our spatial total RNA-sequencing (STRS) approach captures coding RNAs, noncoding RNAs and viral RNAs. We apply STRS to study skeletal muscle regeneration and viral-induced myocarditis. Our analyses reveal the spatial patterns of noncoding RNA expression with near-cellular resolution, identify spatially defined expression of noncoding transcripts in skeletal muscle regeneration and highlight host transcriptional responses associated with local viral RNA abundance. STRS requires adding only one step to the widely used Visium spatial total RNA-sequencing protocol from 10x Genomics, and thus could be easily adopted to enable new insights into spatial gene regulation and biology.
    DOI:  https://doi.org/10.1038/s41587-022-01517-6
  25. Neurology. 2022 Nov 01. pii: 10.1212/WNL.0000000000201294. [Epub ahead of print]
      Molecular therapies exploit understanding of pathogenic mechanisms to reconstitute impaired gene function or manipulate flawed RNA expression. These therapies include 1) RNA interference by antisense oligonucleotides, 2) mRNA modification using small molecules, and 3) gene replacement therapy, the viral-mediated intracellular delivery of exogenous nucleic acids to reverse a genetic defect. Several molecular therapies are approved for treating spinal muscular atrophy (SMA), a recessive genetic disorder caused Survival Motor Neuron (SMN)1 gene mutations. SMA involves degeneration of lower motor neurons, which leads to progressive muscle weakness, hypotonia, and hypotrophy. Onasemnogene abeparvovec is a gene replacement therapy for SMA that uses Adeno Associated Virus delivery of functional SMN1 cDNA to motor neurons. Two other molecular therapies modulate SMN2 transcription: nusinersen, an antisense oligonucleotide, and risdiplam, a small molecule designed to modify faulty mRNA expression. The most suitable individualized treatment for SMA is not established. Here, we describe remarkable clinical improvement in a 4-month-old patient with SMA type 1 who received onasemnogene abeparvovec therapy. This case represents an explanatory bridge from bench to bedside with regard to therapeutic approaches for genetic disorders in neurology. Knowledge of the detailed mechanisms underlying genetic neurological disorders, particularly monogenic conditions, is paramount for developing tailored therapies. When multiple disease-modifying therapies are available, early genetic diagnosis is crucial for appropriate therapy selection, highlighting the importance of early identification and intervention. A combination of drugs, each targeting unique genetic pathomechanisms, may provide additional clinical benefits.
    DOI:  https://doi.org/10.1212/WNL.0000000000201294
  26. Nat Commun. 2022 Nov 04. 13(1): 6661
      Parkin, an E3 ubiquitin ligase, plays an essential role in mitochondrial quality control. However, the mechanisms by which Parkin connects mitochondrial homeostasis with cellular metabolism in adipose tissue remain unclear. Here, we demonstrate that Park2 gene (encodes Parkin) deletion specifically from adipose tissue protects mice against high-fat diet and aging-induced obesity. Despite a mild reduction in mitophagy, mitochondrial DNA content and mitochondrial function are increased in Park2 deficient white adipocytes. Moreover, Park2 gene deletion elevates mitochondrial biogenesis by increasing Pgc1α protein stability through mitochondrial superoxide-activated NAD(P)H quinone dehydrogenase 1 (Nqo1). Both in vitro and in vivo studies show that Nqo1 overexpression elevates Pgc1α protein level and mitochondrial DNA content and enhances mitochondrial activity in mouse and human adipocytes. Taken together, our findings indicate that Parkin regulates mitochondrial homeostasis by balancing mitophagy and Pgc1α-mediated mitochondrial biogenesis in white adipocytes, suggesting a potential therapeutic target in adipocytes to combat obesity and obesity-associated disorders.
    DOI:  https://doi.org/10.1038/s41467-022-34468-2
  27. J Nephrol. 2022 Nov 02.
      Increased muscle protein catabolism leading to muscle wasting is a prominent feature of the syndrome of protein-energy wasting (PEW) in patients with chronic kidney disease (CKD). PEW and muscle wasting are induced by factors such as inflammation, oxidative stress and metabolic acidosis that activate the ubiquitin-proteasome system, the main regulatory mechanism of skeletal muscle degradation. Whether deficiency of nuclear factor erythroid 2-related factor 2 (NRF2), which regulates expression of antioxidant proteins protecting against oxidative damage triggered by inflammation, may exacerbate PEW has yet to be examined in aging patients with CKD. This review focuses on the hypothesis that NRF2 is involved in the maintenance of muscle mass and explores whether sustained activation of NRF2 by non-pharmacological interventions using nutraceutical activators to improve redox homeostasis could be a plausible strategy to prevent skeletal muscle disorders, including muscle wasting, sarcopenia and frailty associated with PEW in aging CKD patients.
    Keywords:  Chronic kidney disease; Inflammation; Muscle wasting; NRF2; Oxidative stress
    DOI:  https://doi.org/10.1007/s40620-022-01484-w
  28. Front Physiol. 2022 ;13 958333
      Background: Peripheral muscle weakness can be measured quantitatively in long COVID patients. Mechanomyography (MMG) is an alternative tool to measure muscle strength non-invasively. Objective: This literature review aims to provide evidence on the efficacy of MMG in measuring muscle strength for long COVID patients and to determine the physiological factors that may affect the use of MMG in assessing muscle performance. Methods: A systematic literature review was conducted using EBSCO's MEDLINE Complete. A total of five out of 2,249 potential publications fulfilled the inclusion criteria. Results: The selected studies addressed muscle performance based on the physiological effects of age, gender, and physical activity level. MMG is sensitive in measuring muscle strength for long COVID patients due to its higher signal-to-noise ratio and lightweight accelerometers. Its neglectable skin impedance and low risk of influences during the recording of surface motions make MMG a reliable tool. Conclusion: Muscle performance is affected by age, gender, and physical activity level. Sensors, such as MMG, as well as the length of the muscle and the characteristics of the muscle activity, are important considerations when choosing a sensor for diagnostic evaluation. The efficacy of MMG in measuring muscle strength for long COVID patients and the physiological factors that may affect the use of MMG in assessing muscle performance are discussed.
    Keywords:  long COVID; mechanomyography; muscle strength; physiology; skeletal muscles
    DOI:  https://doi.org/10.3389/fphys.2022.958333
  29. J Endocr Soc. 2022 Oct 26. 6(12): bvac151
      In mammals, adipose tissues and skeletal muscles (SkMs) play a major role in the regulation of energy homeostasis. Recent studies point to a possibility of dynamic interplay between these 2 sites during development that has pathophysiological implications. Among adipose depots, brown adipose tissue (BAT) is the major energy-utilizing organ with several metabolic features that resemble SkM. Both organs are highly vascularized, innervated, and rich in mitochondria and participate in defining the whole-body metabolic rate. Interestingly, in large mammals BAT depots undergo a striking reduction and concomitant expansion of white adipose tissue (WAT) during postnatal development that shares temporal and molecular overlap with SkM maturation. The correlation between BAT to WAT transition and muscle development is not quite apparent in rodents, the predominantly used animal model. Therefore, the major aim of this article is to highlight this process in mammals with larger body size. The developmental interplay between muscle and BAT is closely intertwined with sexual dimorphism that is greatly influenced by hormones. Recent studies have pointed out that sympathetic inputs also determine the relative recruitment of either of the sites; however, the role of gender in this process has not been studied. Intriguingly, higher BAT content during early postnatal and pubertal periods positively correlates with attainment of better musculature, a key determinant of good health. Further insight into this topic will help in detailing the developmental overlap between the 2 seemingly unrelated tissues (BAT and SkM) and design strategies to target these sites to counter metabolic syndromes.
    Keywords:  adipose tissue; brown fat; larger mammals; myogenesis; perinatal development; skeletal muscle
    DOI:  https://doi.org/10.1210/jendso/bvac151