bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2022‒08‒28
twenty-one papers selected by
Anna Vainshtein
Craft Science Inc.
  1. Exercise improves high-fat diet-induced metabolic disorder by promoting HDAC5 degradation through the ubiquitin-proteasome system in skeletal muscle.
  2. Caveolin-3 regulates the activity of Ca2+/calmodulin-dependent protein kinase II in C2C12 cells.
  3. BECN1F121A mutation increases autophagic flux in aged mice and improves aging phenotypes in an organ-dependent manner.
  4. Metabolic Pathways and Ion Channels Involved in Skeletal Muscle Atrophy: A Starting Point for Potential Therapeutic Strategies.
  5. Mitochondrial dynamics maintain muscle stem cell regenerative competence throughout adult life by regulating metabolism and mitophagy.
  6. Percutaneous electrical stimulation-induced muscle contraction prevents the decrease in ribosome RNA and ribosome protein during pelvic hindlimb suspension.
  7. The Contribution of Genetics to Muscle Disuse, Retraining, and Aging.
  8. RSPO3 is a novel contraction-inducible factor identified in an "in vitro exercise model" using primary human myotubes.
  9. Laminin α5_CD239_Spectrin is a candidate association that compensates the linkage between the basement membrane and cytoskeleton in skeletal muscle fibers.
  10. The mitochondrial protein OPA1 regulates the quiescent state of adult muscle stem cells.
  11. Skeletal-Muscle-Specific Overexpression of Chrono Leads to Disruption of Glucose Metabolism and Exercise Capacity.
  12. Effects of lactate administration on hypertrophy and mTOR signaling activation in mouse skeletal muscle.
  13. Age-related muscle anabolic resistance: inevitable or preventable?
  14. Downregulating Mitochondrial DNA Polymerase γ in the Muscle Stimulated Autophagy, Apoptosis, and Muscle Aging-Related Phenotypes in Drosophila Adults.
  15. Ablation of Ghrelin Receptor Mitigates the Metabolic Decline of Aging Skeletal Muscle.
  16. Contributions of Titin and Collagen to Passive Stress in Muscles from mdm Mice with a Small Deletion in Titin's Molecular Spring.
  17. ATAC-Seq of a Single Myofiber from Mus musculus.
  18. Regulatory role of RNA N6-methyladenosine modifications during skeletal muscle development.
  19. Potential Satellite Cell-Linked Biomarkers in Aging Skeletal Muscle Tissue: Proteomics and Proteogenomics to Monitor Sarcopenia.
  20. 5 fluorouracil disrupts skeletal muscle immune cells and impairs skeletal muscle repair and remodeling.
  21. Prescription of Resistance Training for Sarcopenic Older Adults: Does it Require Specific Attention?
  1. Appl Physiol Nutr Metab. 2022 Aug 23.
    Exercise improves high-fat diet-induced metabolic disorder by promoting HDAC5 degradation through the ubiquitin-proteasome system in skeletal muscle.
    Song Huang, Xinyue Zheng, Xinyu Zhang, Zhe Jin, Sujuan Liu, Li Fu, Yanmei Niu.
      Histone deacetylase 4/5 are essential for regulating metabolic gene expression, AMPKα2 regulates HDAC4/5 activity and the expression of MuRF1 during exercise. In this study, we used wild type and AMPKα2-/- mice to explore the potential regulatory relationship between AMPKα2 and HDAC4/5 expression during exercise. Firstly, we fed C57BL/6J mice with high-fat diet for eight-week to assess the effects of high-fat diet on skeletal muscle metabolism and HDAC4/5 expression. We then performed a six-week treadmill exercise on both wild type and AMPKα2-/- mice. After exercise, the expressions of HDAC4/5 were examined in both gastrocnemius and soleus. The citrate synthase activity and proteins involved in skeletal muscle oxidative process were assessed. To determine the relationship of HDAC4/5 and skeletal muscle oxidative capacity, citrate synthase activity was assessed after silencing HDAC4/5. Moreover, HDAC5 ubiquitination and the association of MuRF1 to HDAC5 were also investigated. Our results showed that six-week exercise increased the skeletal muscle oxidative capacity and decreased HDAC4/5 expression only in soleus. HDAC5 silencing increased C2C12 cells oxidative capacity. Proteasome inhibition by MG132 abolished exercise-induced HDAC5 degradation mediated by MuRF1-ubiquitin-proteasome system. However, the UPS did not dominantly account for exercise-induced HDAC4 degradation. Exercise up-regulated MuRF1-HDAC5 association in wild type mice but not in AMPKα2-/- mice. Our results revealed that six-week exercise increased the skeletal muscle oxidative capacity and promoted HDAC5 degradation in soleus through the UPS, MuRF1 mediated HDAC5 ubiquitination. Although AMPKα2 played partial role in regulating MuRF1 expression and HDAC5 ubiquitination, exercise-induced HDAC5 degradation did not fully depend on AMPKα2.
    DOI:  https://doi.org/10.1139/apnm-2022-0174
  2. Am J Physiol Cell Physiol. 2022 Aug 22.
    Caveolin-3 regulates the activity of Ca2+/calmodulin-dependent protein kinase II in C2C12 cells.
    Michio Matsunobe, Norio Motohashi, Eito Aoki, Tsukasa Tominari, Masaki Inada, Yoshitsugu Aoki.
      Caveolins, encoded by the Cav gene family, are the main components of caveolae. Caveolin-3 (Cav3) is specifically expressed in muscle cells. Mutations in Cav3 are responsible for a group of muscle diseases called caveolinopathies, and Cav3 deficiency is associated with sarcolemmal membrane alterations, disorganization of T-tubules, and disruption of specific cell-signaling pathways. However, Cav3 overexpression increases the number of sarcolemmal caveolae and muscular dystrophy-like regenerating muscle fibers with central nuclei, suggesting that the alteration of Cav3 expression levels or localization influences muscle cell functions. Here we used mouse C2C12 myoblasts in which Cav3 expression was suppressed with short hairpin RNA and found that Cav3 suppression impaired myotube differentiation without affecting the expression of MyoD and Myog. We also observed an increase of intracellular Ca2+ levels, total calpain activity, and Ca2+-dependent calmodulin kinase II (CaMKII) levels in Cav3-depleted myoblasts. Importantly, those phenotypes due to Cav3 suppression were caused by the ryanodine receptor activation. Furthermore, pharmacological inhibition of CaMKII rescued the impairment of myoblast differentiation due to Cav3 knockdown. Our results suggest that Cav3 regulates intracellular Ca2+ concentrations by modulating ryanodine receptor activity in muscle cells and that CaMKII suppression in muscle could be a novel therapy for caveolinopathies.
    Keywords:  Calcium; Caveolin; Myogenic cells; Myopathy; Skeletal muscle
    DOI:  https://doi.org/10.1152/ajpcell.00077.2022
  3. Autophagy. 2022 Aug 21. 1-9
    BECN1F121A mutation increases autophagic flux in aged mice and improves aging phenotypes in an organ-dependent manner.
    Salwa Sebti, Zhongju Zou, Michael U Shiloh.
      Macroautophagy/autophagy is necessary for lifespan extension in multiple model organisms and autophagy dysfunction impacts age-related phenotypes and diseases. Introduction of an F121A mutation into the essential autophagy protein BECN1 constitutively increases basal autophagy in young mice and reduces cardiac and renal age-related changes in longer lived Becn1F121A mutant mice. However, both autophagic and lysosomal activities decline with age. Thus, whether autophagic flux is maintained during aging and whether it is enhanced in Becn1F121A mice is unknown. Here, we demonstrate that old wild-type mice maintained functional autophagic flux in heart, kidney and skeletal muscle but not liver, and old Becn1F121A mice had increased autophagic flux in those same organs compared to wild type. In parallel, Becn1F121A mice were not protected against age-associated hepatic phenotypes but demonstrated reduced skeletal muscle fiber atrophy. These findings identify an organ-specific role for the ability of autophagy to impact organ aging phenotypes.
    Keywords:  Aging; BECN1; autophagic flux; liver; mouse; skeletal muscle
    DOI:  https://doi.org/10.1080/15548627.2022.2111852
  4. Cells. 2022 Aug 18. pii: 2566. [Epub ahead of print]11(16):
    Metabolic Pathways and Ion Channels Involved in Skeletal Muscle Atrophy: A Starting Point for Potential Therapeutic Strategies.
    Ileana Canfora, Nancy Tarantino, Sabata Pierno.
      Skeletal muscle tissue has the important function of supporting and defending the organism. It is the largest apparatus in the human body, and its function is important for contraction and movements. In addition, it is involved in the regulation of protein synthesis and degradation. In fact, inhibition of protein synthesis and/or activation of catabolism determines a pathological condition called muscle atrophy. Muscle atrophy is a reduction in muscle mass resulting in a partial or complete loss of function. It has been established that many physiopathological conditions can cause a reduction in muscle mass. Nevertheless, it is not well known the molecular mechanisms and signaling processes causing this dramatic event. There are multiple concomitant processes involved in muscle atrophy. In fact, the gene transcription of some factors, oxidative stress mechanisms, and the alteration of ion transport through specific ion channels may contribute to muscle function impairment. In this review, we focused on the molecular mechanisms responsible for muscle damage and potential drugs to be used to alleviate this disabling condition.
    Keywords:  atrophy; disuse; hindlimb unloading; ion channels; sarcopenia; skeletal muscle
    DOI:  https://doi.org/10.3390/cells11162566
  5. Cell Stem Cell. 2022 Aug 19. pii: S1934-5909(22)00304-6. [Epub ahead of print]
    Mitochondrial dynamics maintain muscle stem cell regenerative competence throughout adult life by regulating metabolism and mitophagy.
    Xiaotong Hong, Joan Isern, Silvia Campanario, Eusebio Perdiguero, Ignacio Ramírez-Pardo, Jessica Segalés, Pablo Hernansanz-Agustín, Andrea Curtabbi, Oleg Deryagin, Angela Pollán, José A González-Reyes, José M Villalba, Marco Sandri, Antonio L Serrano, José A Enríquez, Pura Muñoz-Cánoves.
      Skeletal muscle regeneration depends on the correct expansion of resident quiescent stem cells (satellite cells), a process that becomes less efficient with aging. Here, we show that mitochondrial dynamics are essential for the successful regenerative capacity of satellite cells. The loss of mitochondrial fission in satellite cells-due to aging or genetic impairment-deregulates the mitochondrial electron transport chain (ETC), leading to inefficient oxidative phosphorylation (OXPHOS) metabolism and mitophagy and increased oxidative stress. This state results in muscle regenerative failure, which is caused by the reduced proliferation and functional loss of satellite cells. Regenerative functions can be restored in fission-impaired or aged satellite cells by the re-establishment of mitochondrial dynamics (by activating fission or preventing fusion), OXPHOS, or mitophagy. Thus, mitochondrial shape and physical networking controls stem cell regenerative functions by regulating metabolism and proteostasis. As mitochondrial fission occurs less frequently in the satellite cells in older humans, our findings have implications for regeneration therapies in sarcopenia.
    Keywords:  Drp1; OXPHOS; aging; metabolism; mitochondria; mitochondrial dynamics; mitophagy; muscle regeneration; muscle stem cells; satellite cells
    DOI:  https://doi.org/10.1016/j.stem.2022.07.009
  6. J Appl Physiol (1985). 2022 Aug 25.
    Percutaneous electrical stimulation-induced muscle contraction prevents the decrease in ribosome RNA and ribosome protein during pelvic hindlimb suspension.
    Takaya Kotani, Yuki Tamura, Karina Kouzaki, Hikaru Kato, Mako Isemura, Koichi Nakazato.
      Skeletal muscle unloading leads to muscle atrophy. Ribosome synthesis has been implicated as an important skeletal muscle mass regulator owing to its translational capacity. Muscle unloading induces a reduction in ribosome synthesis and content, with muscle atrophy. Percutaneous electrical muscle stimulation (pEMS)-induced muscle contraction is widely used in clinics to improve muscle mass. However, its efficacy in rescuing the reduction in ribosomal synthesis has not been addressed thus far. We examined the effects of daily pEMS treatment on ribosome synthesis and content during mouse hindlimb unloading. Male C57BL/6J mice were randomly assigned to sedentary (SED) and hindlimb unloading by pelvic suspension (HU) groups. Muscle contraction was triggered by pEMS treatment of the right gastrocnemius muscle of a subset of the HU group (HU+pEMS). Hindlimb unloading for 6 days significantly lowered 28S rRNA, rpL10, and rpS3 expression, which was rescued by daily pEMS treatment. The protein expression of phospho-p70S6K and UBF was significantly higher in the HU+pEMS than in the HU group. The mRNA expression of ribophagy receptor Nufip1 increased in both the HU and HU+pEMS groups. Protein light chain 3 (LC3)-II expression and the LC3-II/LC3-I ratio were increased by HU, but pEMS attenuated this increase. Our findings indicate that during HU, daily pEMS treatment prevents the reduction in the levels of some proteins associated with ribosome synthesis. Additionally, the HU-induced activation of ribosome degradation may be attenuated. These data provide insights into ribosome content regulation and the mechanism of attenuation of muscle atrophy by pEMS treatment during muscle disuse.
    Keywords:  Hindlimb unloading; Muscle atrophy; Ribophagy; Ribosome synthesis
    DOI:  https://doi.org/10.1152/japplphysiol.00204.2022
  7. Genes (Basel). 2022 Aug 01. pii: 1378. [Epub ahead of print]13(8):
    The Contribution of Genetics to Muscle Disuse, Retraining, and Aging.
    Giuseppe Sirago, Anna Picca, Emiliana Giacomello, Emanuele Marzetti, Luana Toniolo.
      Genetic background may partly explain differences in muscle responses to internal or external stimuli. Muscle disuse involves various degrees of skeletal muscle atrophy due to inactivity and mechanical unloading. Whether and to which extent genetic background impacts disuse atrophy and retraining in individuals of different ages are currently unclear. Here, we provide a brief overview of relevant literature on the contribution of genetics to muscle disuse, retraining, and aging, and offer a perspective on unanswered questions on the subject that may open new venues for research.
    Keywords:  exercise; genetic variants; muscle atrophy
    DOI:  https://doi.org/10.3390/genes13081378
  8. Sci Rep. 2022 Aug 22. 12(1): 14291
    RSPO3 is a novel contraction-inducible factor identified in an "in vitro exercise model" using primary human myotubes.
    Tadahisa Takahashi, Yuqing Li, Weijian Chen, Mazvita R Nyasha, Kazumi Ogawa, Kazuaki Suzuki, Masashi Koide, Yoshihiro Hagiwara, Eiji Itoi, Toshimi Aizawa, Masahiro Tsuchiya, Naoki Suzuki, Masashi Aoki, Makoto Kanzaki.
      The physiological significance of skeletal muscle as a secretory organ is now well known but we can only speculate as to the existence of as-yet-unidentified myokines, especially those upregulated in response to muscle contractile activity. We first attempted to establish an "insert-chamber based in vitro exercise model" allowing the miniature but high cell-density culture state enabling highly developed contractile human myotubes to be readily obtained by applying electric pulse stimulation (EPS). By employing this in vitro exercise model, we identified R-spondin 3 (RSPO3) as a novel contraction-inducible myokine produced by cultured human myotubes. Contraction-dependent muscular RSPO3 mRNA upregulation was confirmed in skeletal muscles of mice subjected to sciatic nerve mediated in situ contraction as well as those of mice after 2 h of running. Pharmacological in vitro experiments demonstrated a relatively high concentration of metformin (millimolar range) to suppress the contraction-inducible mRNA upregulation of human myokines including RSPO3, interleukin (IL)-6, IL-8 and CXCL1. Our data also suggest human RSPO3 to be a paracrine factor that may positively participate in the myogenesis processes of myoblasts and satellite cells. Thus, the "insert chamber-based in vitro exercise model" is a potentially valuable research tool for investigating contraction-inducible biological responses of human myotubes usually exhibiting poorer contractility development even in the setting of EPS treatment.
    DOI:  https://doi.org/10.1038/s41598-022-18190-z
  9. Matrix Biol Plus. 2022 Aug;15 100118
    Laminin α5_CD239_Spectrin is a candidate association that compensates the linkage between the basement membrane and cytoskeleton in skeletal muscle fibers.
    Yamato Kikkawa, Masumi Matsunuma, Ryuji Kan, Yuji Yamada, Keisuke Hamada, Motoyoshi Nomizu, Yoichi Negishi, Shushi Nagamori, Tatsushi Toda, Minoru Tanaka, Motoi Kanagawa.
      The linkage between the basement membrane (BM) and cytoskeleton is crucial for muscle fiber stability and signal transduction. Mutations in the linkage molecules can cause various types of muscular dystrophies. The different severities and times of onset suggest that compensatory linkages occur at the sarcolemma. Cluster of differentiation 239 (CD239) binds to the α5 subunit of laminin-511 extracellularly and is connected to spectrin intracellularly, resulting in a linkage between the BM and cytoskeleton. In this study, we explored the linkage of laminin α5_CD239_spectrin in skeletal muscles. Although laminin α5, CD239, and spectrin were present in embryonic skeletal muscles, they disappeared in adult skeletal muscle tissues, except for the soleus and diaphragm. Laminin α5_CD239_spectrin was localized in the skeletal muscle tissues of Duchenne muscular dystrophy and congenital muscular dystrophy mouse models. The experimental regeneration of skeletal muscle increased the CD239-mediated linkage, indicating that it responds to regeneration, but not to genetic influence. Furthermore, in silico analysis showed that laminin α5_CD239_spectrin was upregulated by steroid therapy for muscular dystrophy. Therefore, CD239-mediated linkage may serve as a therapeutic target to prevent the progression of muscular dystrophy.
    Keywords:  BCAM; Basement membrane; CD239; Laminin; Muscular dystrophy; Spectrin
    DOI:  https://doi.org/10.1016/j.mbplus.2022.100118
  10. Cell Stem Cell. 2022 Aug 19. pii: S1934-5909(22)00333-2. [Epub ahead of print]
    The mitochondrial protein OPA1 regulates the quiescent state of adult muscle stem cells.
    Nicole Baker, Steven Wade, Matthew Triolo, John Girgis, Damian Chwastek, Sarah Larrigan, Peter Feige, Ryo Fujita, Colin Crist, Michael A Rudnicki, Yan Burelle, Mireille Khacho.
      Quiescence regulation is essential for adult stem cell maintenance and sustained regeneration. Our studies uncovered that physiological changes in mitochondrial shape regulate the quiescent state of adult muscle stem cells (MuSCs). We show that MuSC mitochondria rapidly fragment upon an activation stimulus, via systemic HGF/mTOR, to drive the exit from deep quiescence. Deletion of the mitochondrial fusion protein OPA1 and mitochondrial fragmentation transitions MuSCs into G-alert quiescence, causing premature activation and depletion upon a stimulus. OPA1 loss activates a glutathione (GSH)-redox signaling pathway promoting cell-cycle progression, myogenic gene expression, and commitment. MuSCs with chronic OPA1 loss, leading to mitochondrial dysfunction, continue to reside in G-alert but acquire severe cell-cycle defects. Additionally, we provide evidence that OPA1 decline and impaired mitochondrial dynamics contribute to age-related MuSC dysfunction. These findings reveal a fundamental role for OPA1 and mitochondrial dynamics in establishing the quiescent state and activation potential of adult stem cells.
    Keywords:  G-alert; GSH; OPA1; ROS; adult muscle stem cells; aging; glutathione; mTOR; mitochondrial dynamics; quiescence; reactive oxygen species; stem cell activation; stem cell maintenance; systemic factors
    DOI:  https://doi.org/10.1016/j.stem.2022.07.010
  11. Life (Basel). 2022 Aug 15. pii: 1233. [Epub ahead of print]12(8):
    Skeletal-Muscle-Specific Overexpression of Chrono Leads to Disruption of Glucose Metabolism and Exercise Capacity.
    Shiyi He, Lu Yan, Rongxin Zhu, Hao Wei, Jianxiong Wang, Lan Zheng, Ying Zhang.
      Disruption of circadian rhythms is related to disorders of glucose metabolism, and the molecular clock also exists in skeletal muscle. The ChIP-derived repressor of network oscillator (Chrono) and brain and muscle ARNT-like 1 (Bmal1) are core circadian components. Chrono is considered to be the repressor of Bmal1, and the Chrono-Bmal1 pathway is important in regulating the circadian rhythm; it has been speculated that this pathway could be a new mechanism for regulating glucose metabolism. The purpose of this study was to investigate the effects of Chrono on glucose metabolism in skeletal muscle and exercise capacity by using mice with skeletal-muscle-specific overexpression of Chrono (Chrono TG) and wild-type (WT) mice as the animal models. The results of this cross-sectional study indicated that the Chrono TG mice had an impaired glucose tolerance, lower exercise capacity, and higher levels of nonfasted blood glucose and glycogen content in skeletal muscle compared to WT mice. In addition, the Chrono TG mice also showed a significant increase in the amount of Chrono bound to Bmal1 according to a co-IP analysis; a remarkable decrease in mRNA expression of Tbc1d1, Glut4, Hk2, Pfkm, Pdp1, Gbe1, and Phka1, as well as in activity of Hk and protein expression of Ldhb; but higher mRNA expression of Pdk4 and protein expression of Ldha compared with those of WT mice. These data suggested the skeletal-muscle-specific overexpression of Chrono led to a greater amount of Chrono bound to Bmal1, which then could affect the glucose transporter, glucose oxidation, and glycogen utilization in skeletal muscle, as well as exercise capacity.
    Keywords:  Chrono; exercise capacity; glucose metabolism; mice; skeletal muscle
    DOI:  https://doi.org/10.3390/life12081233
  12. Physiol Rep. 2022 Aug;10(16): e15436
    Effects of lactate administration on hypertrophy and mTOR signaling activation in mouse skeletal muscle.
    Takanaga Shirai, Yu Kitaoka, Kazuki Uemichi, Katsuyuki Tokinoya, Kohei Takeda, Tohru Takemasa.
      Lactate is a metabolic product of glycolysis and has recently been shown to act as a signaling molecule that induces adaptations in oxidative metabolism. In this study, we investigated whether lactate administration enhanced muscle hypertrophy and protein synthesis responses during resistance exercise in animal models. We used male ICR mice (7-8 weeks old) were used for chronic (mechanical overload induced by synergist ablation: [OL]) and acute (high-intensity muscle contraction by electrical stimulation: [ES]) resistance exercise models. The animals were intraperitoneally administrated a single dose of sodium lactate (1 g/kg of body weight) in the ES study, and once a day for 14 consecutive days in the OL study. Two weeks of mechanical overload increased plantaris muscle wet weight (main effect of OL: p < 0.05) and fiber cross-sectional area (main effect of OL: p < 0.05), but those were not affected by lactate administration. Following the acute resistance exercise by ES, protein synthesis and phosphorylation of p70 S6 kinase and ribosomal protein S6, which are downstream molecules in the anabolic signaling cascade, were increased (main effect of ES: p < 0.05), but lactate administration had no effect. This study demonstrated that exogenous lactate administration has little effect on the muscle hypertrophic response during resistance exercise using acute ES and chronic OL models. Our results do not support the hypothesis that elevated blood lactate concentration induces protein synthesis responses in skeletal muscle.
    Keywords:  hypertrophy; lactate; mTOR signaling, protein synthesis; skeletal muscle
    DOI:  https://doi.org/10.14814/phy2.15436
  13. Nutr Rev. 2022 Aug 26. pii: nuac062. [Epub ahead of print]
    Age-related muscle anabolic resistance: inevitable or preventable?
    Alan A Aragon, Kevin D Tipton, Brad J Schoenfeld.
      Age-related loss of muscle mass, strength, and performance, commonly referred to as sarcopenia, has wide-ranging detrimental effects on human health, the ramifications of which can have serious implications for both morbidity and mortality. Various interventional strategies have been proposed to counteract sarcopenia, with a particular emphasis on those employing a combination of exercise and nutrition. However, the efficacy of these interventions can be confounded by an age-related blunting of the muscle protein synthesis response to a given dose of protein/amino acids, which has been termed "anabolic resistance." While the pathophysiology of sarcopenia is undoubtedly complex, anabolic resistance is implicated in the progression of age-related muscle loss and its underlying complications. Several mechanisms have been proposed as underlying age-related impairments in the anabolic response to protein consumption. These include decreased anabolic molecular signaling activity, reduced insulin-mediated capillary recruitment (thus, reduced amino acid delivery), and increased splanchnic retention of amino acids (thus, reduced availability for muscular uptake). Obesity and sedentarism can exacerbate, or at least facilitate, anabolic resistance, mediated in part by insulin resistance and systemic inflammation. This narrative review addresses the key factors and contextual elements involved in reduction of the acute muscle protein synthesis response associated with aging and its varied consequences. Practical interventions focused on dietary protein manipulation are proposed to prevent the onset of anabolic resistance and mitigate its progression.
    Keywords:  muscle mass; muscle protein synthesis; protein intake; protein timing; resistance training
    DOI:  https://doi.org/10.1093/nutrit/nuac062
  14. Biomolecules. 2022 Aug 11. pii: 1105. [Epub ahead of print]12(8):
    Downregulating Mitochondrial DNA Polymerase γ in the Muscle Stimulated Autophagy, Apoptosis, and Muscle Aging-Related Phenotypes in Drosophila Adults.
    Mika Ozaki, Tuan Dat Le, Yoshihiro H Inoue.
      Reactive oxygen species, generated as by-products of mitochondrial electron transport, can induce damage to mitochondrial DNA (mtDNA) and proteins. Here, we investigated whether the moderate accumulation of mtDNA damage in adult muscles resulted in accelerated aging-related phenotypes in Drosophila. DNA polymerase γ (Polγ) is the sole mitochondrial DNA polymerase. The muscle-specific silencing of the genes encoding the polymerase subunits resulted in the partial accumulation of mtDNA with oxidative damage and a reduction in the mtDNA copy number. This subsequently resulted in the production of abnormal mitochondria with reduced membrane potential and, consequently, a partially reduced ATP quantity in the adult muscle. Immunostaining indicated a moderate increase in autophagy and mitophagy in adults with RNA interference of Polγ (PolγRNAi) muscle cells with abnormal mitochondria. In adult muscles showing continuous silencing of Polγ, malformation of both myofibrils and mitochondria was frequently observed. This was associated with the partially enhanced activation of pro-apoptotic caspases in the muscle. Adults with muscle-specific PolγRNAi exhibited a shortened lifespan, accelerated age-dependent impairment of locomotor activity, and disturbed circadian rhythms. Our findings in this Drosophila model contribute to understanding how the accumulation of mtDNA damage results in impaired mitochondrial activity and how this contributes to muscle aging.
    Keywords:  DNA polymeraseγ; Drosophila; autophagy; mitochondria; muscle aging
    DOI:  https://doi.org/10.3390/biom12081105
  15. Genes (Basel). 2022 Jul 30. pii: 1368. [Epub ahead of print]13(8):
    Ablation of Ghrelin Receptor Mitigates the Metabolic Decline of Aging Skeletal Muscle.
    Colleen O'Reilly, Ligen Lin, Hongying Wang, James Fluckey, Yuxiang Sun.
      The orexigenic hormone ghrelin has multifaceted roles in health and disease. We have reported that ablation of the ghrelin receptor, growth hormone secretagogue receptor (GHS-R), protects against metabolic dysfunction of adipose tissues in aging. Our further observation interestingly revealed that GHS-R deficiency phenocopies the effects of myokine irisin. In this study, we aim to determine whether GHS-R affects the metabolic functions of aging skeletal muscle and whether GHS-R regulates the muscular functions via irisin. We first studied the expression of metabolic signature genes in gastrocnemius muscle of young, middle-aged and old mice. Then, old GHS-R knockout (Ghsr-/-) mice and their wild type counterparts were used to assess the impact of GHS-R ablation on the metabolic characteristics of gastrocnemius and soleus muscle. There was an increase of GHS-R expression in skeletal muscle during aging, inversely correlated with the decline of metabolic functions. Remarkedly the muscle of old GHS-R knockout (Ghsr-/-) mice exhibited a youthful metabolic profile and better maintenance of oxidative type 2 muscle fibers. Furthermore, old Ghsr-/- mice showed improved treadmill performance, supporting better functionality. Also intriguing to note was the fact that old GHS-R-ablated mice showed increased expression of the irisin precursor FNDC5 in the muscle and elevated plasma irisin levels in circulation, which supports a potential interrelationship between GHS-R and irisin. Overall, our work suggests that GHS-R has deleterious effects on the metabolism of aging muscle, which may be at least partially mediated by myokine irisin.
    Keywords:  GHS-R; aging; irisin; skeletal muscle
    DOI:  https://doi.org/10.3390/genes13081368
  16. Int J Mol Sci. 2022 Aug 09. pii: 8858. [Epub ahead of print]23(16):
    Contributions of Titin and Collagen to Passive Stress in Muscles from mdm Mice with a Small Deletion in Titin's Molecular Spring.
    Pabodha Hettige, Dhruv Mishra, Henk Granzier, Kiisa Nishikawa, Matthew J Gage.
      Muscular dystrophy with myositis (mdm) is a naturally occurring mutation in the mouse Ttn gene that results in higher passive stress in muscle fibers and intact muscles compared to wild-type (WT). The goal of this study was to test whether alternative splicing of titin exons occurs in mdm muscles, which contain a small deletion in the N2A-PEVK regions of titin, and to test whether splicing changes are associated with an increase in titin-based passive tension. Although higher levels of collagen have been reported previously in mdm muscles, here we demonstrate alternative splicing of titin in mdm skeletal muscle fibers. We identified Z-band, PEVK, and C-terminus Mex5 exons as splicing hotspots in mdm titin using RNA sequencing data and further reported upregulation in ECM-associated genes. We also treated skinned mdm soleus fiber bundles with trypsin, trypsin + KCl, and trypsin + KCL + KI to degrade titin. The results showed that passive stress dropped significantly more after trypsin treatment in mdm fibers (11 ± 1.6 mN/mm2) than in WT fibers (4.8 ± 1 mN/mm2; p = 0.0004). The finding that treatment with trypsin reduces titin-based passive tension more in mdm than in WT fibers supports the hypothesis that exon splicing leads to the expression of a stiffer and shorter titin isoform in mdm fibers. After titin extraction by trypsin + KCl + KI, mdm fibers (6.7 ± 1.27 mN/mm2) had significantly higher collagen-based passive stress remaining than WT fibers (2.6 ± 1.3 mN/mm2; p = 0.0014). We conclude that both titin and collagen contribute to higher passive tension of mdm muscles.
    Keywords:  KCl; KI; exon splicing; fiber bundles; soleus; titin extraction; trypsin
    DOI:  https://doi.org/10.3390/ijms23168858
  17. Bio Protoc. 2022 Jun 20. pii: e4452. [Epub ahead of print]12(12):
    ATAC-Seq of a Single Myofiber from Mus musculus.
    Korin Sahinyan, Darren M Blackburn, Vahab D Soleimani.
      Chromatin accessibility is a key determinant of gene expression that can be altered under different physiological and disease conditions. Skeletal muscle is made up of myofibers that are highly plastic and adaptive. Therefore, assessing the genome-wide chromatin state of myofibers under various conditions is very important to gain insight into the epigenetic state of myonuclei. The rigid nature of myofibers, as well as the low number of myonuclei that they contain, have rendered genome-wide studies with myofibers challenging. In recent years, ATAC-Seq from whole muscle and single nucleus ATAC-Seq have been performed. However, these techniques cannot distinguish between different fiber and cell types present in the muscle. In addition, due to the limited depth capacity obtained from single nucleus ATAC-Seq, an extensive comparative analysis cannot be performed. Here, we introduce a protocol where we combine the isolation of a single myofiber with OMNI ATAC-Seq. This protocol allows for genome-wide analysis of accessible chromatin regions of a selected single myofiber at a sufficient depth for comparative analysis under various physiological and disease conditions. This protocol can also allow for a specific myofiber to be selected, such as a regenerating myofiber. In the future, this protocol can help identify global changes in chromatin state under various conditions, as well as between different types of myofibers. Graphical abstract.
    Keywords:   ATAC-Seq ; Chromatin Accessibility ; Epigenetics ; Single myofiber ; Skeletal Muscle
    DOI:  https://doi.org/10.21769/BioProtoc.4452
  18. Front Cell Dev Biol. 2022 ;10 929183
    Regulatory role of RNA N6-methyladenosine modifications during skeletal muscle development.
    Baojun Yu, Jiamin Liu, Juan Zhang, Tong Mu, Xiaofang Feng, Ruoshuang Ma, Yaling Gu.
      Functional cells in embryonic myogenesis and postnatal muscle development undergo multiple stages of proliferation and differentiation, which are strict procedural regulation processes. N6-methyladenosine (m6A) is the most abundant RNA modification that regulates gene expression in specific cell types in eukaryotes and regulates various biological activities, such as RNA processing and metabolism. Recent studies have shown that m6A modification-mediated transcriptional and post-transcriptional regulation plays an essential role in myogenesis. This review outlines embryonic and postnatal myogenic differentiation and summarizes the important roles played by functional cells in each developmental period. Furthermore, the key roles of m6A modifications and their regulators in myogenesis were highlighted, and the synergistic regulation of m6A modifications with myogenic transcription factors was emphasized to characterize the cascade of transcriptional and post-transcriptional regulation during myogenesis. This review also discusses the crosstalk between m6A modifications and non-coding RNAs, proposing a novel mechanism for post-transcriptional regulation during skeletal muscle development. In summary, the transcriptional and post-transcriptional regulatory mechanisms mediated by m6A and their regulators may help develop new strategies to maintain muscle homeostasis, which are expected to become targets for animal muscle-specific trait breeding and treatment of muscle metabolic diseases.
    Keywords:  N6-methyladenosine (m6A) modification; epigenetic; myogenesis; skeletal muscle development; transcriptional regulation
    DOI:  https://doi.org/10.3389/fcell.2022.929183
  19. Proteomes. 2022 Aug 19. pii: 29. [Epub ahead of print]10(3):
    Potential Satellite Cell-Linked Biomarkers in Aging Skeletal Muscle Tissue: Proteomics and Proteogenomics to Monitor Sarcopenia.
    Diego Fernández-Lázaro, Evelina Garrosa, Jesús Seco-Calvo, Manuel Garrosa.
      Sarcopenia (Sp) is the loss of skeletal muscle mass associated with aging which causes an involution of muscle function and strength. Satellite cells (Sc) are myogenic stem cells, which are activated by injury or stress, and repair muscle tissue. With advancing age, there is a decrease in the efficiency of the regenerative response of Sc. Diagnosis occurs with the Sp established by direct assessments of muscle. However, the detection of biomarkers in real-time biofluids by liquid biopsy could represent a step-change in the understanding of the molecular biology and heterogeneity of Sp. A total of 13 potential proteogenomic biomarkers of Sp by their physiological and biological interaction with Sc have been previously described in the literature. Increases in the expression of GDF11, PGC-1α, Sirt1, Pax7, Pax3, Myf5, MyoD, CD34, MyoG, and activation of Notch signaling stimulate Sc activity and proliferation, which could modulate and delay Sp progression. On the contrary, intensified expression of GDF8, p16INK4a, Mrf4, and activation of the Wnt pathway would contribute to early Sp development by directly inducing reduced and/or altered Sc function, which would attenuate the restorative capacity of skeletal muscle. Additionally, tissue biopsy remains an important diagnostic tool. Proteomic profiling of aged muscle tissues has shown shifts toward protein isoforms characteristic of a fast-to-slow transition process and an elevated number of oxidized proteins. In addition, a strong association between age and plasma values of growth differentiation factor 15 (GDF-15) has been described and serpin family A member 3 (serpin A3n) was more secreted by atrophied muscle cells. The identification of these new biomarkers holds the potential to change personalized medicine because it could predict in real time the course of Sp by monitoring its evolution and assessing responses to potential therapeutic strategies.
    Keywords:  aging; biomarkers; liquid biopsy; muscle satellite cells; proteogenomic; proteomics; sarcopenia; tissue biopsy
    DOI:  https://doi.org/10.3390/proteomes10030029
  20. J Appl Physiol (1985). 2022 Aug 25.
    5 fluorouracil disrupts skeletal muscle immune cells and impairs skeletal muscle repair and remodeling.
    Brandon N VanderVeen, Thomas D Cardaci, Sarah S Madero, Sierra J McDonald, Brooke M Bullard, Robert L Price, James A Carson, Daping Fan, E Angela Murphy.
      5-fluorouracil (5FU) remains a first line chemotherapeutic for several cancers despite its established adverse side effects. Reduced blood counts with cytotoxic chemotherapies not only expose patients to infection and fatigue, but can disrupt tissue repair and remodeling, leading to lasting functional deficits. We sought to characterize the impact of 5FU-induced leukopenia on skeletal muscle in the context of remodeling. First, C57BL/6 mice were subjected to multiple dosing cycles of 5FU and skeletal muscle immune cells were assessed. Second, mice given 1 cycle of 5FU were subjected to 1.2% BaCl2 i.m. to induce muscle damage. One cycle of 5FU induced significant body weight loss, but only 3 dosing cycles of 5FU induced skeletal muscle mass loss. One cycle of 5FU reduced skeletal muscle CD45+ immune cells with a particular loss of infiltrating CD11b+Ly6cHi monocytes. While CD45+ cells returned following 3 cycles, CD11b+CD68+ macrophages were reduced with 3 cycles and remained suppressed at 1 month following 5FU administration. One cycle of 5FU blocked the increase in CD45+ immune cells 4 days following BaCl2; however, there was a dramatic increase in CD11b+Ly6g+ neutrophils and a loss of CD11b+Ly6cHi monocytes in damaged muscle with 5FU compared to PBS. These perturbations resulted in increased collagen production 14 and 28 days following BaCl2 and a reduction in centralized nuclei and mCSA compared to PBS. Together, these results demonstrate that cytotoxic 5FU impairs muscle damage repair and remodeling concomitant with a loss of immune cells that persists beyond the cessation of treatment.
    Keywords:  Chemotherapy; Macrophages; Monocytes; Muscle Remodeling; Muscle Repair
    DOI:  https://doi.org/10.1152/japplphysiol.00325.2022
  21. Ageing Res Rev. 2022 Aug 17. pii: S1568-1637(22)00162-3. [Epub ahead of print] 101720
    Prescription of Resistance Training for Sarcopenic Older Adults: Does it Require Specific Attention?
    Hélio José Coelho-Júnior, Anna Picca, Riccardo Calvani, Emanuele Marzetti.
      Sarcopenia is an age-related neuromuscular disease characterized by substantial muscle atrophy, dynapenia and/or loss of physical function. Sarcopenia progression increases the risk for numerous negative events, including falls, disability, hospitalization, nursing home placement, and death. As such, this condition is recognized as an important topic in gerontology and geriatrics. The best approach to counteract the development and progression of sarcopenia is actively debated. Resistance training (RT) has received special attention in this context, owing to large number of studies showing its ability to produce significant improvements in sarcopenia-related parameters. Recommendations to guide RT prescription for older adults with different conditions, including people who have traits of sarcopenia, have been published. Some authors have argued that RT guidelines for older adults are similar to one another, which may indicate that the presence of sarcopenia does not require specific physical exercise programs. However, older people with sarcopenia might present with peculiar physical, biomechanical, physiological, and psychosocial characteristics that, in our view, are not taken into adequate consideration in existing exercise guidelines. Here, we present evidence to support the view that RT prescription for older adults with sarcopenia is complex, multifactorial, and still needs more evidence.
    Keywords:  Elderly; Frailty; Multicomponent exercise; Strength training
    DOI:  https://doi.org/10.1016/j.arr.2022.101720
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