bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2022–11–20
35 papers selected by
Anna Vainshtein, Craft Science Inc.
  1. Molecular Responses to Acute Exercise and Their Relevance for Adaptations in Skeletal Muscle to Exercise Training.
  2. Twist2-expressing cells reside in human skeletal muscle and are responsive to aging and resistance exercise training.
  3. Essential roles of the cytokine oncostatin M in crosstalk between muscle fibers and immune cells in skeletal muscle after aerobic exercise.
  4. Parkin deficiency exacerbates fasting-induced skeletal muscle wasting in mice.
  5. A ubiquitous endocrine disruptor tributyltin induces muscle wasting and retards muscle regeneration.
  6. Tripartite motif-containing protein 32 (TRIM32) regulates Ca2+ movement in skeletal muscle.
  7. Elevated CD47 is a hallmark of dysfunctional aged muscle stem cells that can be targeted to augment regeneration.
  8. Activation of eIF4E-binding-protein-1 rescues mTORC1-induced sarcopenia by expanding lysosomal degradation capacity.
  9. PGC-1β modulates catabolism and fiber atrophy in the fasting-response of specific skeletal muscle beds.
  10. Fndc5/irisin is regulated by myogenesis stage, irisin, muscle type and training.
  11. CRISPR-Cas9 Correction of Duchenne Muscular Dystrophy in Mice by a Self-Complementary AAV Delivery System.
  12. Mechanisms of cooperative cell-cell interactions in skeletal muscle regeneration.
  13. Restoration of Dystrophin Expression in Mdx-Derived Muscle Progenitor Cells Using CRISPR/Cas9 System and Homology-Directed Repair Technology.
  14. Identifying FDA-Approved Drugs that Upregulate Utrophin A as a Therapeutic Strategy for Duchenne Muscular Dystrophy.
  15. Requirement for PINCH in skeletal myoblast differentiation.
  16. Prior AICAR induces elevated glucose uptake concomitant with greater γ3-AMPK activation and reduced membrane cholesterol in skeletal muscle from 26-month-old rats.
  17. DUSP1 promotes muscle atrophy by inhibiting myocyte differentiation in cachectic patients.
  18. The adhesion G-protein-coupled receptor Gpr116 is essential to maintain the skeletal muscle stem cell pool.
  19. Regulation of protein and oxidative energy metabolism are down-regulated in the skeletal muscles of Asiatic black bears during hibernation.
  20. PGC-1α in the myofibers regulates the balance between myogenic and adipogenic progenitors affecting muscle regeneration.
  21. Cilia-Mediated Insulin/Akt and ST2/JNK Signaling Pathways Regulate the Recovery of Muscle Injury.
  22. Myokines derived from contracting skeletal muscle suppress anabolism in MCF7 breast cancer cells by inhibiting mTOR.
  23. Does the regulation of skeletal muscle influence cognitive function? A scoping review of pre-clinical evidence.
  24. RACK1 is evolutionary conserved in satellite stem cell activation and adult skeletal muscle regeneration.
  25. Mitochondria: Key modulators of skeletal muscle remodeling.
  26. Single cell sequencing maps skeletal muscle cellular diversity as disease severity increases in dystrophic mouse models.
  27. Skeletal muscle 99mTechnetium-pyrophosphate scan: more questions than answers.
  28. Identification of Subproteomic Markers for Skeletal Muscle Profiling.
  29. Public Health Need, Molecular Targets, and Opportunities for the Accelerated Development of Function-Promoting Therapies: Proceedings of a National Institute on Aging Workshop.
  30. Current Strategies of Muscular Dystrophy Therapeutics: An Overview.
  31. Metformin suppresses progression of muscle aging via activation of the AMP kinase-mediated pathways in Drosophila adults.
  32. Extracellular Vesicles as Communicators of Senescence in Musculoskeletal Aging.
  33. Single-molecule imaging reveals how mavacamten and PKA modulate ATP turnover in skeletal muscle myofibrils.
  34. Exercise sustains the hallmarks of health.
  35. Interactive regulation of DNA demethylase gene TET1 and m6A methyltransferase gene METTL3 in myoblast differentiation.
  1. Physiol Rev. 2022 Nov 17.
    Molecular Responses to Acute Exercise and Their Relevance for Adaptations in Skeletal Muscle to Exercise Training.
    Brendan Egan, Adam P Sharples.
      Repeated, episodic bouts of skeletal muscle contraction undertaken frequently as structured exercise training is a potent stimulus for physiological adaptation in many organs. Specifically in skeletal muscle, remarkable plasticity is demonstrated by the remodeling of muscle structure and function in terms of muscular size, force, endurance, and contractile velocity as a result of the functional demands induced by various types of exercise training. This plasticity, and the mechanistic basis for adaptations to skeletal muscle in response to exercise training, is underpinned by activation and/or repression of molecular pathways and processes induced in response to each individual acute exercise session. These pathways include the transduction of signals arising from neuronal, mechanical, metabolic, and hormonal stimuli through complex signal transduction networks, which are linked to a myriad of effector proteins involved in the regulation of pre- and post-transcriptional processes, and protein translation and degradation processes. This review therefore describes acute exercise-induced signal transduction and the molecular responses to acute exercise in skeletal muscle including emerging concepts such as epigenetic pre- and post-transcriptional regulation, and the regulation of protein translation and degradation. A critical appraisal of methodological approaches and the current state of knowledge informs a series of recommendations offered as future directions in the field.
    Keywords:  aerobic; gene expression; metabolism; resistance; transcription
    DOI:  https://doi.org/10.1152/physrev.00054.2021
  2. FASEB J. 2022 Dec;36(12): e22642
    Twist2-expressing cells reside in human skeletal muscle and are responsive to aging and resistance exercise training.
    Nick Gaulton, Griffen Wakelin, Laura V Young, Scott Wotherspoon, Michael Kamal, Gianni Parise, Joshua P Nederveen, Andy Holwerda, Lex B Verdijk, Luc J C van Loon, Tim Snijders, Adam P Johnston.
      Skeletal muscle is maintained and repaired by sub-laminar, Pax7-expressing satellite cells. However, recent mouse investigations have described a second myogenic progenitor population that resides within the myofiber interstitium and expresses the transcription factor Twist2. Twist2-expressing cells exclusively repair and maintain type IIx/b muscle fibers. Currently, it is unknown if Twist2-expressing cells are present in human skeletal muscle and if they function as myogenic progenitors. Here, we perform a combination of single-cell RNA sequencing analysis and immunofluorescence staining to demonstrate the identity and localization of Twist2-expressing cells in human skeletal muscle. Twist2-expressing cells were identified to be anatomically and transcriptionally comparable to fibro-adipogenic progenitors (FAPs) and lack expression of typical satellite cell markers such as Pax7. Comparative analysis revealed that human and mouse Twist2-expressing cells were highly transcriptionally analogous and resided within the same anatomical structures in vivo. Examination of young and aged skeletal muscle biopsy samples revealed that Twist2-positive cells are more prevalent in aged muscle and increase following 12-weeks of resistance exercise training (RET) in humans. However, the quantity of Twist2-positive cells was not correlated with indices of muscle mass or muscle fiber cross-sectional area (CSA) in young or older muscle, and their abundance was surprisingly, negatively correlated with CSA and myonuclear domain size following RET. Taken together, we have identified cells expressing Twist2 in human skeletal muscle which are responsive to aging and exercise. Further examination of their myogenic potential is warranted.
    Keywords:  Twist2; aging; progenitor cells; sarcopenia; skeletal muscle
    DOI:  https://doi.org/10.1096/fj.202201349RR
  3. J Biol Chem. 2022 Nov 09. pii: S0021-9258(22)01129-2. [Epub ahead of print] 102686
    Essential roles of the cytokine oncostatin M in crosstalk between muscle fibers and immune cells in skeletal muscle after aerobic exercise.
    Tadasuke Komori, Yoshihiro Morikawa.
      Crosstalk between muscle fibers and immune cells is well known in the processes of muscle repair after exercise, especially resistance exercise. In aerobic exercise, however, this crosstalk is not fully understood. In the present study, we found that macrophages, especially anti-inflammatory (M2) macrophages, and neutrophils accumulated in skeletal muscles of mice 24 h after a single bout of an aerobic exercise. The expression of oncostatin M (OSM), a member of the IL-6 family of cytokines, was also increased in muscle fibers immediately after the exercise. Additionally, we determined that deficiency of OSM in mice inhibited the exercise-induced accumulation of M2 macrophages and neutrophils, while intramuscular injection of OSM increased these immune cells in skeletal muscles. Furthermore, the chemokines related to the recruitment of macrophages and neutrophils were induced in skeletal muscles after aerobic exercise, which were attenuated in OSM-deficient mice. Among them, CC chemokine ligand (CCL) 2, CCL7, and CXC chemokine ligand (CXCL) 1 were induced by OSM in skeletal muscles. Next, we analyzed the direct effects of OSM on the skeletal muscle macrophages, because the OSM receptor β subunit was expressed predominantly in macrophages in the skeletal muscle. OSM directly induced the expression of these chemokines and anti-inflammatory markers in the skeletal muscle macrophages. From these findings, we conclude that OSM is essential for aerobic exercise-induced accumulation of M2 macrophages and neutrophils in the skeletal muscle partly through the regulation of chemokine expression in macrophages.
    Keywords:  chemokine; cytokine; exercise; macrophage; neutrophil; skeletal muscle
    DOI:  https://doi.org/10.1016/j.jbc.2022.102686
  4. NPJ Parkinsons Dis. 2022 Nov 17. 8(1): 159
    Parkin deficiency exacerbates fasting-induced skeletal muscle wasting in mice.
    Nesibe Peker, Mridula Sharma, Ravi Kambadur.
      Parkinson's Disease (PD) is a chronic and progressive neurodegenerative disease manifesting itself with tremors, muscle stiffness, bradykinesia, dementia, and depression. Mutations of mitochondrial E3 ligase, PARKIN, have been associated with juvenile PD. Previous studies have characterized muscle atrophy and motor deficits upon loss of functional Parkin in fly and rodent models. However, the mechanisms behind pathophysiology of Parkin deficient muscle remains to be elusive. Here, results suggested that knock down of Parkin significantly increases proteolytic activities in skeletal muscle cell line, the C2C12 myotubes. However, the atrogene levels increase moderately in Parkin deficient cell line. To further investigate the role of Parkin in skeletal muscle atrophy, Parkin knock out (KO) and wild type mice were subjected to 48 h starvation. After 48 h fasting, a greater reduction in skeletal muscle weights was observed in Parkin KO mice as compared to age matched wild type control, suggesting elevated proteolytic activity in the absence of Parkin. Subsequent microarray analyses revealed further enhanced expression of FOXO and ubiquitin pathway in fasted Parkin KO mice. Furthermore, a greater reduction in the expression of cytoskeleton genes was observed in Parkin KO mice following 48 h fasting. Collectively, these results suggest that Parkin deficiency exacerbates fasting-induced skeletal muscle wasting, through upregulating genes involved in catabolic activities in skeletal muscle.
    DOI:  https://doi.org/10.1038/s41531-022-00419-3
  5. J Cachexia Sarcopenia Muscle. 2022 Nov 16.
    A ubiquitous endocrine disruptor tributyltin induces muscle wasting and retards muscle regeneration.
    Hsien-Chun Chiu, Rong-Sen Yang, Te-I Weng, Chen-Yuan Chiu, Kuo-Cheng Lan, Shing-Hwa Liu.
       BACKGROUND: Organotin pollutant tributyltin (TBT) is an environmental endocrine disrupting chemical and is a known obesogen and diabetogen. TBT can be detected in human following consumption of contaminated seafood or water. The decrease in muscle strength and quality has been shown to be associated with type 2 diabetes in older adults. However, the adverse effects of TBT on the muscle mass and function still remain unclear. Here, we investigated the effects and molecule mechanisms of low-dose TBT on skeletal muscle regeneration and atrophy/wasting using the cultured skeletal muscle cell and adult mouse models.
    METHODS: The mouse myoblasts (C2C12) and differentiated myotubes were used to assess the in vitro effects of low-dose tributyltin (0.01-0.5 μM). The in vivo effects of TBT at the doses of 5 and 25 μg/kg/day (n = 6/group), which were five times lower than the established no observed adverse effect level (NOAEL) and equal to NOAEL, respectively, by oral administration for 4 weeks on muscle wasting and muscle regeneration were evaluated in a mouse model with or without glycerol-induced muscle injury/regeneration.
    RESULTS: TBT reduced myogenic differentiation in myoblasts (myotube with 6-10 nuclei: 53.9 and 35.8% control for 0.05 and 0.1 μM, respectively, n = 4, P < 0.05). TBT also decreased myotube diameter, upregulated protein expression levels of muscle-specific ubiquitin ligases (Atrogin-1 and MuRF1), myostatin, phosphorylated AMPKα, and phosphorylated NFκB-p65, and downregulated protein expression levels of phosphorylated AKT and phosphorylated FoxO1 in myotubes (0.2 and 0.5 μM, n = 6, P < 0.05). Exposure of TBT in mice elevated body weight, decreased muscle mass, and induced muscular dysfunction (5 and 25 μg/kg, P > 0.05 and P < 0.05, respectively, n = 6). TBT inhibited soleus muscle regeneration in mice with glycerol-induced muscle injury (5 and 25 μg/kg, P > 0.05 and P < 0.05, respectively, n = 6). TBT upregulated protein expression levels of Atrogin-1, MuRF1, myostatin, and phosphorylated AMPKα and downregulated protein expression level of phosphorylated FoxO1 in the mouse soleus muscles (5 and 25 μg/kg, P > 0.05 and P < 0.05, respectively, n = 6).
    CONCLUSIONS: This study demonstrates for the first time that low-dose TBT significantly inhibits myogenic differentiation and triggers myotube atrophy in a cell model and significantly decreases muscle regeneration and muscle mass and function in a mouse model. These findings suggest that low-dose TBT exposure may be an environmental risk factor for muscle regeneration inhibition, atrophy/wasting, and disease-related myopathy.
    Keywords:  Environmental pollutants; Muscle regeneration; Muscle wasting; Tributyltin
    DOI:  https://doi.org/10.1002/jcsm.13119
  6. Am J Physiol Cell Physiol. 2022 Nov 14.
    Tripartite motif-containing protein 32 (TRIM32) regulates Ca2+ movement in skeletal muscle.
    Jun Hee Choi, Seung Yeon Jeong, Jooho Kim, Jin Seok Woo, Eun Hui Lee.
      Mutations in tripartite motif-containing protein 32 (TRIM32), especially in NHL repeats, have been found in skeletal muscle in patients with type 2H limb-girdle muscular dystrophy (LGMD2H). However, the roles of the NHL repeats of TRIM32 in skeletal muscle functions have not been well addressed. In the present study, to examine the functional role(s) of the TRIM32 NHL repeats in skeletal muscle, TRIM32-binding proteins in skeletal muscle were first searched using a binding assay and MALDI-TOF/TOF. Sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 1a (SERCA1a) was found to be a TRIM32-binding protein. Next, a deletion mutant of TRIM32 missing the NHL repeats (NHL-Del) was expressed in mouse primary skeletal myotubes during myoblast differentiation into myotubes. Ca2+ movement in the myotubes was examined using single-cell Ca2+ imaging. Unlike wild-type (WT) TRIM32, NHL-Del did not enhance the amount of Ca2+ release from the sarcoplasmic reticulum (SR), Ca2+ release for excitation-contraction (EC) coupling or extracellular Ca2+ entry via store-operated Ca2+ entry (SOCE). In addition, even compared with the vector control, NHL-Del resulted in reduced SOCE due to reduced expression of extracellular Ca2+-entry channels. Transmission electron microscopy (TEM) observation of the myotubes revealed that NHL-Del induced the formation of abnormal vacuoles and tubular structures in the cytosol. Therefore, by binding to SERCA1a via its NHL repeats, TRIM32 may participate in the regulation of Ca2+ movement for skeletal muscle contraction and the formation of cellular vacuoles and tubular structures in skeletal muscle. Functional defects in TRIM32 due to mutations in NHL repeats may be pathogenic toward LGMD2H.
    Keywords:  LGMD2H; NHL repeats; SERCA1a; TRIM32; skeletal muscle
    DOI:  https://doi.org/10.1152/ajpcell.00426.2022
  7. Cell Stem Cell. 2022 Nov 14. pii: S1934-5909(22)00427-1. [Epub ahead of print]
    Elevated CD47 is a hallmark of dysfunctional aged muscle stem cells that can be targeted to augment regeneration.
    Ermelinda Porpiglia, Thach Mai, Peggy Kraft, Colin A Holbrook, Antoine de Morree, Veronica D Gonzalez, Keren I Hilgendorf, Laure Frésard, Angelica Trejo, Sriram Bhimaraju, Peter K Jackson, Wendy J Fantl, Helen M Blau.
      In aging, skeletal muscle strength and regenerative capacity decline, due in part to functional impairment of muscle stem cells (MuSCs), yet the underlying mechanisms remain elusive. Here, we capitalize on mass cytometry to identify high CD47 expression as a hallmark of dysfunctional MuSCs (CD47hi) with impaired regenerative capacity that predominate with aging. The prevalent CD47hi MuSC subset suppresses the residual functional CD47lo MuSC subset through a paracrine signaling loop, leading to impaired proliferation. We uncover that elevated CD47 levels on aged MuSCs result from increased U1 snRNA expression, which disrupts alternative polyadenylation. The deficit in aged MuSC function in regeneration can be overcome either by morpholino-mediated blockade of CD47 alternative polyadenylation or antibody blockade of thrombospondin-1/CD47 signaling, leading to improved regeneration in aged mice, with therapeutic implications. Our findings highlight a previously unrecognized age-dependent alteration in CD47 levels and function in MuSCs, which underlies reduced muscle repair in aging.
    Keywords:  CyTOF; U1 snRNA; aging; alternative polyadenylation; antisense morpholino oligonucleotide; in vivo antibody blockade; muscle stem cells; paracrine signaling; regeneration; thrombospondin-1/CD47 signaling
    DOI:  https://doi.org/10.1016/j.stem.2022.10.009
  8. J Cachexia Sarcopenia Muscle. 2022 Nov 17.
    Activation of eIF4E-binding-protein-1 rescues mTORC1-induced sarcopenia by expanding lysosomal degradation capacity.
    Elisa M Crombie, Seonyoung Kim, Stuart Adamson, Han Dong, Tzu-Chiao Lu, Yiju Wu, Yajun Wu, Yotam Levy, Nolan Stimple, Wing Moon R Lam, Hwee Weng D Hey, Dominic J Withers, Ao-Lin Hsu, Boon Huat Bay, Julien Ochala, Shih-Yin Tsai.
       BACKGROUND: Chronic mTORC1 activation in skeletal muscle is linked with age-associated loss of muscle mass and strength, known as sarcopenia. Genetic activation of mTORC1 by conditionally ablating mTORC1 upstream inhibitor TSC1 in skeletal muscle accelerates sarcopenia development in adult mice. Conversely, genetic suppression of mTORC1 downstream effectors of protein synthesis delays sarcopenia in natural aging mice. mTORC1 promotes protein synthesis by activating ribosomal protein S6 kinases (S6Ks) and inhibiting eIF4E-binding proteins (4EBPs). Whole-body knockout of S6K1 or muscle-specific over-expression of a 4EBP1 mutant transgene (4EBP1mt), which is resistant to mTORC1-mediated inhibition, ameliorates muscle loss with age and preserves muscle function by enhancing mitochondria activities, despite both transgenic mice showing retarded muscle growth at a young age. Why repression of mTORC1-mediated protein synthesis can mitigate progressive muscle atrophy and dysfunction with age remains unclear.
    METHODS: Mice with myofiber-specific knockout of TSC1 (TSC1mKO), in which mTORC1 is hyperactivated in fully differentiated myofibers, were used as a mouse model of sarcopenia. To elucidate the role of mTORC1-mediated protein synthesis in regulating muscle mass and physiology, we bred the 4EBP1mt transgene or S6k1 floxed mice into the TSC1mKO mouse background to generate 4EBP1mt-TSC1mKO or S6K1-TSC1mKO mice, respectively. Functional and molecular analyses were performed to assess their role in sarcopenia development.
    RESULTS: Here, we show that 4EBP1mt-TSC1mKO, but not S6K1-TSC1mKO, preserved muscle mass (36.7% increase compared with TSC1mKO, P < 0.001) and strength (36.8% increase compared with TSC1mKO, P < 0.01) at the level of control mice. Mechanistically, 4EBP1 activation suppressed aberrant protein synthesis (two-fold reduction compared with TSC1mKO, P < 0.05) and restored autophagy flux without relieving mTORC1-mediated inhibition of ULK1, an upstream activator of autophagosome initiation. We discovered a previously unidentified phenotype of lysosomal failure in TSC1mKO mouse muscle, in which the lysosomal defect was also conserved in the naturally aged mouse muscle, whereas 4EBP1 activation enhanced lysosomal protease activities to compensate for impaired autophagy induced by mTORC1 hyperactivity. Consequently, 4EBP1 activation relieved oxidative stress to prevent toxic aggregate accumulation (0.5-fold reduction compared with TSC1mKO, P < 0.05) in muscle and restored mitochondrial homeostasis and function.
    CONCLUSIONS: We identify 4EBP1 as a communication hub coordinating protein synthesis and degradation to protect proteostasis, revealing therapeutic potential for activating lysosomal degradation to mitigate sarcopenia.
    Keywords:  mRNA translation; mTORC1; mitochondrial dysfunction; protein degradation; sarcopenia
    DOI:  https://doi.org/10.1002/jcsm.13121
  9. Mol Metab. 2022 Nov 15. pii: S2212-8778(22)00212-5. [Epub ahead of print] 101643
    PGC-1β modulates catabolism and fiber atrophy in the fasting-response of specific skeletal muscle beds.
    Svenia Schmid, Barbara Heim-Kupr, Joaquín Pérez-Schindler, Shivani Mansingh, Markus Beer, Nitish Mittal, Nikolaus Ehrenfeuchter, Christoph Handschin.
       OBJECTIVE: Skeletal muscle is a pivotal organ for the coordination of systemic metabolism, constituting one of the largest storage site for glucose, lipids and amino acids. Tight temporal orchestration of protein breakdown in times of fasting has to be balanced with preservation of muscle mass and function. However, the molecular mechanisms that control the fasting response in muscle are poorly understood.
    METHODS: We now have identified a role for the peroxisome proliferator-activated receptor γ coactivator 1β (PGC-1β) in the regulation of catabolic pathways in this context in muscle-specific loss-of-function mouse models.
    RESULTS: Muscle-specific knockouts for PGC-1β experience mitigated muscle atrophy in fasting, linked to reduced expression of myostatin, atrogenes, activation of AMP-dependent protein kinase (AMPK) and other energy deprivation signaling pathways. At least in part, the muscle fasting response is modulated by a negative effect of PGC-1β on the nuclear factor of activated T-cells 1 (NFATC1).
    CONCLUSIONS: Collectively, these data highlight the complex regulation of muscle metabolism and reveal a new role for muscle PGC-1β in the control of proteostasis in fasting.
    Keywords:  PGC-1β; atrophy; fasting; myostatin; skeletal muscle; ubiquitin proteasome
    DOI:  https://doi.org/10.1016/j.molmet.2022.101643
  10. Am J Transl Res. 2022 ;14(10): 7063-7079
    Fndc5/irisin is regulated by myogenesis stage, irisin, muscle type and training.
    Gal Lavi, Avital Horwitz, Ofira Einstein, Reut Zipori, Ofri Gross, Ruth Birk.
       OBJECTIVES: Irisin, a novel myokine that responds to exercise, was initially identified as a regulator of fat tissue metabolism. We aimed to investigate fibronectin type III domain-containing protein 5 (Fndc5)/irisin, auto/para-crine role in different muscle fibers, different activities, and muscle cell differentiation.
    METHODS: Using in-vitro, ex-vivo, and in-vivo muscle models, Fndc5 was studied at the physiological and molecular levels.
    RESULTS: Following training, C57BL/6 mice (n=10) were subject to fast and slow-twitch muscles dissection and molecular analysis. Isolated mice (C57BL/6, n=14) slow and fast-twitch muscles were subject to electrical aerobic and anaerobic pulses stimulation (EPS). L6 muscle cells differentiation was characterized by Fndc5 differentiation-depended expression pattern parallel with significant hypertrophy, Myogenin elevation, and overlapping Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (Pgc-1α) expression pattern. Exogenous irisin significantly altered Fndc5 expression; augmented at early differentiation (3-4-fold, P<0.05) and decreased (2-fold, P<0.05) at late differentiation. Training induced a significant elevation in Fndc5/irisin and Pgc-1α expression levels in all muscle types compared to the sedentary state, where soleus muscle (slow) Fndc5 expression levels were significantly higher compared to levels in all other fast muscles (3-140-fold, P<0.001). Similarly, following EPS, Fndc5 expression levels were significantly augmented in the soleus slow muscle following both aerobic and anaerobic activity (3-3.5-fold, P<0.05) compared to extensor digitorum longus (fast) muscle.
    CONCLUSIONS: Muscle cell's Fndc5 expression has a differentiation-depended pattern paralleling Pgc-1α expression and hypertrophy. Irisin autocrinally and significantly regulate Fndc5 and Pgc-1α in a differentiation-depended manner. Muscle Fndc5 expression levels are dependent on fiber type and activity type.
    Keywords:  FNDC5; Irisin; Pgc-1α; muscle; myogenesis
  11. Methods Mol Biol. 2023 ;2587 411-425
    CRISPR-Cas9 Correction of Duchenne Muscular Dystrophy in Mice by a Self-Complementary AAV Delivery System.
    Yu Zhang, Rhonda Bassel-Duby, Eric N Olson.
      Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disorder, caused by mutations in the DMD gene coding dystrophin. Applying clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (CRISPR-Cas) for therapeutic gene editing represents a promising technology to correct this devastating disease through elimination of underlying genetic mutations. Adeno-associated virus (AAV) has been widely used for gene therapy due to its low immunogenicity and high tissue tropism. In particular, CRISPR-Cas9 gene editing components packaged by self-complementary AAV (scAAV) demonstrate robust viral transduction and efficient gene editing, enabling restoration of dystrophin expression throughout skeletal and cardiac muscle in animal models of DMD. Here, we describe protocols for cloning CRISPR single guide RNAs (sgRNAs) into a scAAV plasmid and procedures for systemic delivery of AAVs into a DMD mouse model. We also provide methodologies for quantification of dystrophin restoration after systemic CRISPR-Cas9-mediated correction of DMD.
    Keywords:  Adeno-associated virus; DMD mouse model; Dystrophin; Gene editing; sgRNA
    DOI:  https://doi.org/10.1007/978-1-0716-2772-3_21
  12. Inflamm Regen. 2022 Nov 16. 42(1): 48
    Mechanisms of cooperative cell-cell interactions in skeletal muscle regeneration.
    Hiroyuki Koike, Ichiro Manabe, Yumiko Oishi.
      Skeletal muscles have an extraordinary capacity to regenerate themselves when injured. Skeletal muscle stem cells, called satellite cells, play a central role in muscle regeneration via three major steps: activation, proliferation, and differentiation. These steps are affected by multiple types of cells, such as immune cells, fibro-adipogenic progenitor cells, and vascular endothelial cells. The widespread use of single-cell sequencing technologies has enabled the identification of novel cell subpopulations associated with muscle regeneration and their regulatory mechanisms. This review summarizes the dynamism of the cellular community that controls and promotes muscle regeneration, with a particular focus on skeletal muscle stem cells.
    Keywords:  Inflammation; Macrophage; Single-cell RNA sequencing; Skeletal muscle stem cells; Tissue regeneration
    DOI:  https://doi.org/10.1186/s41232-022-00234-6
  13. Methods Mol Biol. 2023 ;2587 455-464
    Restoration of Dystrophin Expression in Mdx-Derived Muscle Progenitor Cells Using CRISPR/Cas9 System and Homology-Directed Repair Technology.
    Yue Jin, Yan Shen, Il-Man Kim, Neal L Weintraub, Mark Hamrick, Yaoliang Tang.
      Duchenne muscular dystrophy (DMD) is a progressive myopathy caused by mutations in genes encoding dystrophin proteins that ultimately lead to depletion of myogenic progenitor cells (MPCs). Several approaches have been used to correctly express the dystrophin gene in induced pluripotent stem cells (iPSCs), including deletion of mutated exon 23 (ΔEx23) by clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated gene 9 (Cas9)-mediated gene editing technology. However, this approach is labor-intensive due to individual colony picking and genotyping to verify allelic modification. Here, we present a protocol to restore the function of the dystrophin gene by using homology-directed repair (HDR)-based CRISPR/Cas9 and inducing myogenic program of reprogrammed iPSCs from Mdx mice by inducible muscle-specific transcription factor MyoD.
    Keywords:  CRISPR-Cas9-HDR gene editing; Duchenne muscular dystrophy; iPSC-derived myoprogenitors
    DOI:  https://doi.org/10.1007/978-1-0716-2772-3_23
  14. Methods Mol Biol. 2023 ;2587 495-510
    Identifying FDA-Approved Drugs that Upregulate Utrophin A as a Therapeutic Strategy for Duchenne Muscular Dystrophy.
    Christine Péladeau, Bernard J Jasmin.
      Duchenne muscular dystrophy (DMD) is a neuromuscular disease caused by mutations and deletions within the DMD gene, which result in a lack of dystrophin protein at the sarcolemma of skeletal muscle fibers. The absence of dystrophin fragilizes the sarcolemma and compromises its integrity during cycles of muscle contraction, which, progressively, leads to reductions in muscle mass and function. DMD is thus a progressive muscle-wasting disease that results in a loss of ambulation, cardiomyopathy , respiratory impairment, and death. Although there is presently no cure for DMD, recent advances have led to many promising treatments. One such approach entails increasing expression of a homologous protein to dystrophin, named utrophin A, which is endogenously expressed in both healthy and DMD muscle fibers. Upregulation of utrophin A all along the sarcolemma of DMD muscle fibers can, in part, compensate for the absence of dystrophin. Over the years, our laboratory has focused a significant portion of our efforts in identifying and characterizing drugs and small molecules for their ability to target utrophin A and cause its overexpression. As part of these efforts, we have recently developed a novel ELISA-based high-throughput drug screen, to identify FDA-approved drugs that increase the expression of utrophin A in muscle cells in culture as well as in dystrophic mice. Here, we describe our overall strategy to identify and characterize several FDA-approved drugs that upregulate utrophin A expression and provide details on all experimental approaches. Such strategy has the potential to lead to the rapid development of novel therapeutics for DMD.
    Keywords:  Disease; Drug screen; Duchenne muscular dystrophy; ELISA; FDA-approved drugs; Muscle; Utrophin
    DOI:  https://doi.org/10.1007/978-1-0716-2772-3_26
  15. Cell Tissue Res. 2022 Nov 17.
    Requirement for PINCH in skeletal myoblast differentiation.
    Huimin Liao, Fei Wang, Ke Lu, Xiaolei Ma, Jie Yan, Lina Luo, Yunfu Sun, Xingqun Liang.
      PINCH, an adaptor of focal adhesion complex, plays essential roles in multiple cellular processes and organogenesis. Here, we ablated PINCH1 or both of PINCH1 and PINCH2 in skeletal muscle progenitors using MyoD-Cre. Double ablation of PINCH1 and PINCH2 resulted in early postnatal lethality with reduced size of skeletal muscles and detachment of diaphragm muscles from the body wall. PINCH mutant myofibers failed to undergo multinucleation and exhibited disrupted sarcomere structures. The mutant myoblasts in culture were able to adhere to newly formed myotubes but impeded in cell fusion and subsequent sarcomere genesis and cytoskeleton organization. Consistent with this, expression of integrin β1 and some cytoskeleton proteins and phosphorylation of ERK and AKT were significantly reduced in PINCH mutants. However, N-cadherin was correctly expressed at cell adhesion sites in PINCH mutant cells, suggesting that PINCH may play a direct role in myoblast fusion. Expression of MRF4, the most highly expressed myogenic factor at late stages of myogenesis, was abolished in PINCH mutants that could contribute to observed phenotypes. In addition, mice with PINCH1 being ablated in myogenic progenitors exhibited only mild centronuclear myopathic changes, suggesting a compensatory role of PINCH2 in myogenic differentiation. Our results revealed a critical role of PINCH proteins in myogenic differentiation.
    Keywords:  Cell fusion; Cytoskeleton organization; Integrin pathway; PINCH; Skeletal myogenesis
    DOI:  https://doi.org/10.1007/s00441-022-03701-1
  16. Facets (Ott). 2022 Jan;7 774-791
    Prior AICAR induces elevated glucose uptake concomitant with greater γ3-AMPK activation and reduced membrane cholesterol in skeletal muscle from 26-month-old rats.
    Haiyan Wang, Amy Zheng, Edward B Arias, Gregory D Cartee.
      Attenuated skeletal muscle glucose uptake (GU) has been observed with advancing age. It is important to elucidate the mechanisms linked to interventions that oppose this detrimental outcome. Earlier research using young rodents and (or) cultured myocytes reported that treatment with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR; an AMP-activated protein kinase (AMPK) activator) can increase γ3-AMPK activity and reduce membrane cholesterol content, each of which has been proposed to elevate GU. However, the effect of AICAR treatment on γ3-AMPK activity and membrane cholesterol in skeletal muscle of aged animals has not been reported. Our purpose was to evaluate the effects of AICAR treatment on these potential mechanisms for enhanced glucose uptake in the skeletal muscle of aged animals. Epitrochlearis muscles from 26-27-month-old male rats were isolated and incubated ± AICAR, followed by 3 h incubation without AICAR, and then incubation with 3-O-methyl-[3 H] glucose (to assess GU ± insulin). Muscles were also analyzed for γ3-AMPK activity and membrane cholesterol content. Prior AICAR treatment led to increased γ3-AMPK activity, reduced membrane cholesterol content, and enhanced glucose uptake in skeletal muscle from aged rats. These observations revealed that two potential mechanisms for greater GU previously observed in younger animals and (or) cell models are also potentially relevant for enhanced GU by muscles from older animals.
    Keywords:  AMP-activated protein kinase; aging; cholesterol; glucose transport; insulin sensitivity; skeletal muscle
    DOI:  https://doi.org/10.1139/facets-2021-0166
  17. Front Oncol. 2022 ;12 1040112
    DUSP1 promotes muscle atrophy by inhibiting myocyte differentiation in cachectic patients.
    Xiangyu Sui, Xiangyu Mao, Guohao Wu, Qingyang Meng.
       Background: Skeletal muscle atrophy is the major hallmark of cancer cachexia. The mechanisms underlying muscle wasting remain elusive in cachectic patients. Our research seeks to identify differentially expressed genes (DEGs) between non-cachectic and cachectic cancer patients and elucidate their functions.
    Methods: We screened the DEGs of skeletal muscle between patients with and without cachexia from microarray data. Biological function of DEGs is analyzed through gene enrichment analysis, while an interaction network is constructed to visualize how genes are related. A Spearman's correlation analysis demonstrated the clinical significance of DUSP1 related to cancer cachexia. Skeletal muscle samples were collected and histomorphology studies were conducted. Function of DUSP1 on myogenesis was clarified by qPCR, western blotting, and immunofluorescence.
    Results: We screened 324 DEGs in skeletal muscle from patients with and without cachexia. The results of the gene enrichment analysis indicated that inflammatory cytokines and immune responses contribute significantly to the pathological condition of cachexia. DUSP1 was one of the key genes in the regulating network. DUSP1 protein and mRNA levels were increased significantly in skeletal muscle tissues from patients with cancer cachexia. DUSP1 expression in cachectic group was found to have negative correlation with SMA, prealbumin and BMI and positive correlation with TNFα, IL6 and weight loss. Significant changes of myogenesis related genes were observed in myocyte after DUSP1 was overexpressed and knocked down.
    Conclusion: In skeletal muscle of cachectic patients, DUSP1 expression was observed to be higher and thus DUSP1 promote muscle atrophy by inhibiting myogenesis. DUSP1 is expected to be a specific target in cancer cachexia for preventing and treating muscle atrophy.
    Keywords:  DUSP1; cancer cachexia; muscle atrophy; myogenesis; skeletal muscle
    DOI:  https://doi.org/10.3389/fonc.2022.1040112
  18. Cell Rep. 2022 Nov 15. pii: S2211-1247(22)01516-9. [Epub ahead of print]41(7): 111645
    The adhesion G-protein-coupled receptor Gpr116 is essential to maintain the skeletal muscle stem cell pool.
    Charlotte Sénéchal, Ryo Fujita, Solène Jamet, Arhamatoulaye Maiga, Junio Dort, Zakaria Orfi, Nicolas A Dumont, Michel Bouvier, Colin Crist.
      Skeletal muscle is populated with a reservoir of quiescent muscle stem cells (MuSCs), which regenerate the tissue after injury. Here, we show that the adhesion G-protein-coupled receptor Gpr116 is essential for long-term maintenance of the MuSC pool. Quiescent MuSCs express high levels of Gpr116, which is rapidly downregulated upon MuSC activation. MuSCs deficient for Gpr116 exhibit progressive depletion over time and are defective in self-renewal. Adhesion G-protein-coupled receptors contain an agonistic peptide sequence, called the "Stachel" sequence, within their long N-terminal ectodomains. Stimulation of MuSCs with the GPR116 Stachel peptide delays MuSC activation and differentiation. Stachel peptide stimulation of GPR116 leads to strong interaction with β-arrestins. Stimulation of GPR116 increases the nuclear localization of β-arrestin1, where it interacts with cAMP response element binding protein to regulate gene expression. Altogether, we propose a model by which GPR116 maintains the MuSC pool via nuclear functions of β-arrestin1.
    Keywords:  CP: Stem cell research; GPR116; adhesion G-protein-coupled receptor; muscle stem cell; regeneration; skeletal muscle; β-arrestin1
    DOI:  https://doi.org/10.1016/j.celrep.2022.111645
  19. Sci Rep. 2022 Nov 16. 12(1): 19723
    Regulation of protein and oxidative energy metabolism are down-regulated in the skeletal muscles of Asiatic black bears during hibernation.
    Mitsunori Miyazaki, Michito Shimozuru, Yu Kitaoka, Kenya Takahashi, Toshio Tsubota.
      Hibernating animals exhibit an unexplained physiological characteristic of skeletal muscles being atrophy resistance, in which case muscle mass and strength remain almost unchanged both before and after hibernation. In this study, we examined the alterations in the regulatory systems of protein and energy metabolism in the skeletal muscles of Asiatic black bears during hibernation. Skeletal muscle samples (vastus lateralis muscle) were collected from identical individuals (n = 8) during the active (July) and hibernating (February) periods, while histochemical and biochemical analyses were performed. We observed no significant alterations in body weight, muscle fiber size, and fiber type composition during the active and hibernating periods, indicating that the skeletal muscles of bears are very well preserved during hibernation. In hibernating bear skeletal muscles, both regulatory pathways of muscle protein synthesis (Akt/mechanistic target of rapamycin and mitogen-activated protein kinase systems) and proteolysis (ubiquitin-proteasome and autophagy systems) were down-regulated. Gene expression levels of factors regulating oxidative metabolism were also decreased in hibernating bear skeletal muscles. This is likely an adaptive strategy to minimize the energy wasting of amino acids and lipids during hibernation, which is accompanied by a prolonged period of disuse and starvation.
    DOI:  https://doi.org/10.1038/s41598-022-24251-0
  20. iScience. 2022 Nov 18. 25(11): 105480
    PGC-1α in the myofibers regulates the balance between myogenic and adipogenic progenitors affecting muscle regeneration.
    Marc Beltrà, Fabrizio Pin, Domiziana Costamagna, Robin Duelen, Alessandra Renzini, Riccardo Ballarò, Lorena Garcia-Castillo, Ambra Iannuzzi, Viviana Moresi, Dario Coletti, Maurilio Sampaolesi, Fabio Penna, Paola Costelli.
      Skeletal muscle repair is accomplished by satellite cells (MuSCs) in cooperation with interstitial stromal cells (ISCs), but the relationship between the function of these cells and the metabolic state of myofibers remains unclear. This study reports an altered proportion of MuSCs and ISCs (including adipogenesis-regulatory cells; Aregs) induced by the transgenic overexpression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) in the myofibers (MCK-PGC-1α mice). Although PGC-1α-driven increase of MuSCs does not accelerate muscle regeneration, myogenic progenitors isolated from MCK-PGC-1α mice and transplanted into intact and regenerating muscles are more prone to fuse with recipient myofibers than those derived from wild-type donors. Moreover, both young and aged MCK-PGC-1α animals exhibit reduced perilipin-positive areas when challenged with an adipogenic stimulus, demonstrating low propensity to accumulate adipocytes within the muscle. Overall, these results unveil that increased PGC-1α expression in the myofibers favors pro-myogenic and anti-adipogenic cell populations in the skeletal muscle.
    Keywords:  Cell biology; Developmental biology; Physiology
    DOI:  https://doi.org/10.1016/j.isci.2022.105480
  21. Adv Sci (Weinh). 2022 Nov 14. e2202632
    Cilia-Mediated Insulin/Akt and ST2/JNK Signaling Pathways Regulate the Recovery of Muscle Injury.
    Daishi Yamakawa, Junya Tsuboi, Kousuke Kasahara, Chise Matsuda, Yuhei Nishimura, Tatsuya Kodama, Naoyuki Katayama, Masatoshi Watanabe, Masaki Inagaki.
      Following injury, skeletal muscle regenerates but fatty tissue accumulation is seen in aged muscle or muscular dystrophies. Fibro/adipogenic progenitors (FAPs) are key players in these events; however, the effect of primary cilia on FAPs remains unclear. Here, it is reported that genetic ablation of trichoplein (TCHP), a ciliary regulator, induces ciliary elongation on FAPs after injury, which promotes muscle regeneration while inhibiting adipogenesis. The defective adipogenic differentiation of FAPs is attributed to dysfunction of cilia-dependent lipid raft dynamics, which is critical for insulin/Akt signaling. It is also found that interleukin (IL) 13 is substantially produced by intramuscular FAPs, which are upregulated by ciliary elongation and contribute to regeneration. Mechanistically, upon injury, long cilia excessively activate the IL33/ST2/JNK axis to enhance IL13 production, facilitating myoblast proliferation and M2 macrophage polarization. The results indicate that FAPs organize the regenerative responses to skeletal muscle injury via cilia-mediated insulin/Akt and ST2/JNK signaling pathways.
    Keywords:  adipogenesis; fibro/adipogenic progenitors; interleukin 13; interleukin 33; lipid raft; primary cilia; skeletal muscle regeneration
    DOI:  https://doi.org/10.1002/advs.202202632
  22. Front Physiol. 2022 ;13 1033585
    Myokines derived from contracting skeletal muscle suppress anabolism in MCF7 breast cancer cells by inhibiting mTOR.
    Amanda R Davis, Chelsea G Goodenough, Kim C Westerlind, Robert Strange, John W Deaver, Patrick J Ryan, Steven E Riechman, James D Fluckey.
       There is strong evidence that physical activity has a profound protective effect against multiple types of cancer. Here, we show that this effect may be mediated by factors released from skeletal muscle during simulated exercise, in situ, which suppress canonical anabolic signaling in breast cancer. We report attenuated growth of MCF7 breast cancer cells in the presence of a rodent-derived exercise conditioned perfusate, independent of prior exercise training. This reduction was concomitant with increased levels of DEPTOR protein and reduced mTOR activity.
    Keywords:  cell culture; electrical stimulation; myokines; protein synthesis; tumor suppression
    DOI:  https://doi.org/10.3389/fphys.2022.1033585
  23. J Orthop Translat. 2023 Jan;38 76-83
    Does the regulation of skeletal muscle influence cognitive function? A scoping review of pre-clinical evidence.
    Chaoran Liu, Pui Yan Wong, Simon Kwoon Ho Chow, Wing Hoi Cheung, Ronald Man Yeung Wong.
       Background: Cognitive impairment is a major challenge for elderlies, as it can progress in a rapid manner and effective treatments are limited. Sarcopenic elderlies have a higher risk of dementia. This scoping review aims to reveal whether muscle is a mediator of cognitive function from pre-clinical evidence.
    Methods: PubMed, Embase, and Web of Science were searched to Feb 2nd, 2022, using the keywords (muscle) AND (cognition OR dementia OR Alzheimer) AND (mouse OR rat OR animal). The PRISMA guideline was used in this study.
    Results: A total of 17 pre-clinical studies were selected from 7638 studies. 4 studies reported that muscle atrophy and injury harmed memory, functional factors, and neurons in the brain for rodents with or without Alzheimer's disease (AD). 3 studies observed exercise induced muscle to secrete factors, including lactate, fibronectin type III domain-containing protein 5 (FNDC5), and cathepsin B, which plays essential roles in the elevation of cognitive functions and brain-derived neurotrophic factor (BDNF) levels. Muscle-targeted treatments including electrical stimulation and intramuscular injections had effective remote effects on the hippocampus. 6 studies showed that muscle-specific overexpression of scFv59 and Neprilysin, or myostatin knockdown alleviated AD symptoms. 1 study showed that muscle insulin resistance also led to deficient hippocampal neurogenesis in MKR mice.
    Conclusions: The skeletal muscle is involved in the mediation of cognitive function. The evidence was established by the response in the brain (altered number of neurons, functional factors, and other AD pathological characteristics) with muscle atrophy or injury, muscle secretory factors, and muscle-targeted treatments.
    The translational potential of this paper: This study summarizes the current evidence in how muscle affects cognition in molecular levels, which supports muscle-specific treatments as potential clinical strategies to prevent cognitive dysfunction.
    Keywords:  Animal model; Brain; Cognitive function; Muscle; Review
    DOI:  https://doi.org/10.1016/j.jot.2022.10.001
  24. Cell Death Discov. 2022 Nov 18. 8(1): 459
    RACK1 is evolutionary conserved in satellite stem cell activation and adult skeletal muscle regeneration.
    Elisabetta Catalani, Silvia Zecchini, Matteo Giovarelli, Agnese Cherubini, Simona Del Quondam, Kashi Brunetti, Federica Silvestri, Paulina Roux-Biejat, Alessandra Napoli, Silvia Rosanna Casati, Marcello Ceci, Nicla Romano, Silvia Bongiorni, Giorgio Prantera, Emilio Clementi, Cristiana Perrotta, Clara De Palma, Davide Cervia.
      Skeletal muscle growth and regeneration involves the activity of resident adult stem cells, namely satellite cells (SC). Despite numerous mechanisms have been described, different signals are emerging as relevant in SC homeostasis. Here we demonstrated that the Receptor for Activated C-Kinase 1 (RACK1) is important in SC function. RACK1 was expressed transiently in the skeletal muscle of post-natal mice, being abundant in the early phase of muscle growth and almost disappearing in adult mature fibers. The presence of RACK1 in interstitial SC was also detected. After acute injury in muscle of both mouse and the fruit fly Drosophila melanogaster (used as alternative in vivo model) we found that RACK1 accumulated in regenerating fibers while it declined with the progression of repair process. To note, RACK1 also localized in the active SC that populate recovering tissue. The dynamics of RACK1 levels in isolated adult SC of mice, i.e., progressively high during differentiation and low compared to proliferating conditions, and RACK1 silencing indicated that RACK1 promotes both the formation of myotubes and the accretion of nascent myotubes. In Drosophila with depleted RACK1 in all muscle cells or, specifically, in SC lineage we observed a delayed recovery of skeletal muscle after physical damage as well as the low presence of active SC in the wound area. Our results also suggest the coupling of RACK1 to muscle unfolded protein response during SC activation. Collectively, we provided the first evidence that transient levels of the evolutionarily conserved factor RACK1 are critical for adult SC activation and proper skeletal muscle regeneration, favoring the efficient progression of SC from a committed to a fully differentiated state.
    DOI:  https://doi.org/10.1038/s41420-022-01250-8
  25. Semin Cell Dev Biol. 2022 Nov 11. pii: S1084-9521(22)00291-9. [Epub ahead of print]
    Mitochondria: Key modulators of skeletal muscle remodeling.
    Joe Quadrilatero.
      
    DOI:  https://doi.org/10.1016/j.semcdb.2022.10.004
  26. iScience. 2022 Nov 18. 25(11): 105415
    Single cell sequencing maps skeletal muscle cellular diversity as disease severity increases in dystrophic mouse models.
    Kholoud K Saleh, Haibin Xi, Corey Switzler, Emily Skuratovsky, Matthew A Romero, Peggie Chien, Devin Gibbs, Lily Gane, Michael R Hicks, Melissa J Spencer, April D Pyle.
      Duchenne muscular dystrophy (DMD) is caused by out-of-frame mutations in the DMD gene resulting in the absence of a functional dystrophin protein, leading to a devastating and progressive lethal muscle-wasting disease. Little is known about cellular heterogeneity as disease severity increases. Advances in single-cell RNA sequencing (scRNA-seq) enabled us to explore skeletal muscle-resident cell populations in healthy, dystrophic, and severely dystrophic mouse models. We found increased frequencies of activated fibroblasts, fibro-adipogenic progenitor cells, and pro-inflammatory macrophages in dystrophic gastrocnemius muscles and an upregulation of extracellular matrix genes on endothelial cells in dystrophic and severely dystrophic muscles. We observed a pronounced risk of clotting, especially in the severely dystrophic mice with increased expression of plasminogen activator inhibitor-1 in endothelial cells, indicating endothelial cell impairment as disease severity increases. This work extends our understanding of the severe nature of DMD which should be considered when developing single or combinatorial approaches for DMD.
    Keywords:  Animal physiology; Biological sciences; Cellular physiology; Natural sciences; Omics; Physiology; Transcriptomics
    DOI:  https://doi.org/10.1016/j.isci.2022.105415
  27. Muscle Nerve. 2022 Nov 16.
    Skeletal muscle 99mTechnetium-pyrophosphate scan: more questions than answers.
    Marcus V Pinto, Teerin Liewluck.
      
    DOI:  https://doi.org/10.1002/mus.27754
  28. Methods Mol Biol. 2023 ;2596 291-302
    Identification of Subproteomic Markers for Skeletal Muscle Profiling.
    Paul Dowling, Stephen Gargan, Dieter Swandulla, Kay Ohlendieck.
      The biochemical and cell biological profiling of contractile fiber types and subcellular structures plays a central role in basic and applied myology. Mass spectrometry-based proteomics presents an ideal approach for the systematic identification of proteomic and subproteomic markers. These representative components of fast versus slow muscle fibers and their subcellular fractions are highly useful for in-depth surveys of skeletal muscle adaptations to physiological challenges, as well as the improvement of diagnostic, prognostic, and therapy-monitoring methodologies in muscle pathology. This chapter outlines the identification of subproteomic markers for skeletal muscle profiling based on bottom-up and top-down approaches, including fluorescence two-dimensional difference gel electrophoresis (2D-DIGE).
    Keywords:  DIGE; Proteomics; Skeletal muscle; Subcellular marker; Subproteomics
    DOI:  https://doi.org/10.1007/978-1-0716-2831-7_20
  29. J Gerontol A Biol Sci Med Sci. 2022 Nov 18. pii: glac181. [Epub ahead of print]
    Public Health Need, Molecular Targets, and Opportunities for the Accelerated Development of Function-Promoting Therapies: Proceedings of a National Institute on Aging Workshop.
    Rosaly Correa-de-Araujo, Shalender Bhasin.
       BACKGROUND: People ≥ 65 years are expected to live a substantial portion of their remaining lives with a limiting physical condition and the numbers of affected individuals will increase substantially due to the growth of the population of older adults worldwide. The age-related loss of muscle mass, strength, and function is associated with an increased risk of physical disabilities, falls, loss of independence, metabolic disorders, and mortality. The development of function-promoting therapies to prevent and treat age-related skeletal muscle functional limitations is a pressing public health problem.
    METHODS: On March 20-22, 2022, the National Institute on Aging (NIA) held a workshop entitled "Development of Function-Promoting Therapies: Public Health Need, Molecular Targets, and Drug Development."
    RESULTS: The workshop covered a variety of topics including advances in muscle biology, novel candidate molecules, findings from randomized trials, and challenges in the design of clinical trials and regulatory approval of function-promoting therapies. Leading academic investigators, representatives from the National Institutes of Health (NIH) and the U.S. Food and Drug Administration (FDA), professional societies, pharmaceutical industry, and patient advocacy organizations shared research findings and identified research gaps and strategies to advance the development of function-promoting therapies. A diverse audience of 397 national and international professionals attended the conference.
    CONCLUSIONS: Function-promoting therapies to prevent and treat physical disabilities associated with aging and chronic diseases are a public health imperative. Appropriately powered, well-designed clinical trials and synergistic collaboration among academic experts, patients and stakeholders, the NIH and the FDA, and the pharmaceutical industry are needed to accelerate the development of function-promoting therapies.
    Keywords:  Age-related muscle dysfunction; Clinical performance; Functional decline; Mobility disability; Sarcopenia; Skeletal muscle function deficit
    DOI:  https://doi.org/10.1093/gerona/glac181
  30. Methods Mol Biol. 2023 ;2587 3-30
    Current Strategies of Muscular Dystrophy Therapeutics: An Overview.
    Kenji Rowel Q Lim, Toshifumi Yokota.
      Muscular dystrophies are a group of genetic disorders characterized by varying degrees of progressive muscle weakness and degeneration. They are clinically and genetically heterogeneous but share the common histological features of dystrophic muscle. There is currently no cure for muscular dystrophies, which is of particular concern for the more disabling and/or lethal forms of the disease. Through the years, several therapies have encouragingly been developed for muscular dystrophies and include genetic, cellular, and pharmacological approaches. In this chapter, we undertake a comprehensive exploration of muscular dystrophy therapeutics under current development. Our review includes antisense therapy, CRISPR, gene replacement, cell therapy, nonsense suppression, and disease-modifying small molecule compounds.
    Keywords:  Antisense oligonucleotides; CRISPR; Cell therapy; Gene replacement; Muscular dystrophy; Nonsense suppression; Small molecule compounds
    DOI:  https://doi.org/10.1007/978-1-0716-2772-3_1
  31. Eur Rev Med Pharmacol Sci. 2022 Nov;pii: 30158. [Epub ahead of print]26(21): 8039-8056
    Metformin suppresses progression of muscle aging via activation of the AMP kinase-mediated pathways in Drosophila adults.
    S Suzuta, H Nishida, M Ozaki, N Kohno, T D Le, Y H Inoue.
       OBJECTIVE: Metformin, a medicine used for the treatment of type 2 diabetes, was previously reported to suppress age-dependent hyperproliferation of intestinal stem cells in Drosophila. Here, we aimed to investigate its anti-aging effects on other tissues, such as adult muscle and elucidate the mechanisms underlying the anti-ageing effect.
    MATERIALS AND METHODS: To evaluate the anti-muscle ageing effect of Metformin, we visualized ubiquitinated protein aggregates accumulated in adult muscle as the flies age by immunostaining and measured the total pixel size of the aggregates. We altered gene expression in the muscle by induction of dsRNA against the relevant mRNAs or mRNAs encoding the constitutively active mutant proteins using the Gal4/UAS system. We determined the mRNA levels by quantitative Real Time-Polymerase Chain Reaction (QRT-PCR).
    RESULTS: Continuous metformin feeding significantly extended the lifespan of Drosophila adults. Furthermore, the feeding suppressed the aging-dependent accumulation of ubiquitinated aggregates in adult muscle. To delineate the mechanism through which metformin influences the muscle aging phenotype, we induced the constitutively active AMPK specifically in the muscles and found that the activation of the AMPK-mediated pathway was sufficient for the anti-aging effect of Metformin. Furthermore, the AMPK-mediated downregulation of Tor-mediated pathways, subsequent induction of an eIF-4E inhibitor were involved in the effect. These genetic data suggested that the metformin effect is related to the partial suppression of protein synthesis in ribosomes. Furthermore, metformin stimulated autophagy induction in adult muscles.
    CONCLUSIONS: Our results suggest that metformin can be regarded as an anti-aging compound in Drosophila muscle. The stimulation of autophagy was also involved in the anti-aging effect, which delayed the progression of muscle aging in Drosophila adults.
    DOI:  https://doi.org/10.26355/eurrev_202211_30158
  32. JBMR Plus. 2022 Nov;6(11): e10686
    Extracellular Vesicles as Communicators of Senescence in Musculoskeletal Aging.
    Monica Correa Alfonzo, Ahmed Al Saedi, Sadanand Fulzele, Mark W Hamrick.
      Extracellular vesicles (EVs), including exosomes and microvesicles, are released by numerous cell types. EVs are now acknowledged as playing a critical role in cell-cell communication in healthy aging as well as in age-related diseases. Recently it was shown that senescence, a key hallmark of aging, increases the secretion of EVs. Moreover, EVs can transport proteins and microRNAs (miRNAs) that are key components of the senescence-associated secretory phenotype (SASP). Here we review evidence that SASP-related miRNAs are involved in musculoskeletal degeneration with aging. Specifically, senescence-related miRNAs are elevated in EVs released by skeletal muscle myocytes and fibro-adipogenic progenitor cells with aging and disuse atrophy, respectively. Many of these same senescence-related miRNAs are detected in EVs from the synovial fluid of patients with osteoarthritis, and these miRNAs can contribute to cartilage degeneration. Finally, senescence-associated miRNAs are secreted from bone marrow-derived stem (stromal) cells impacting neighboring hematopoietic stem cells and circulating in the blood. The senescence-associated miRNA mir-34a, which is known to target Wnt and Notch pathways as well as the cell survival factors Sirt1 and Bcl2, is detected in EVs from human and animal subjects with muscle atrophy, bone loss, and osteoarthritis. These findings suggest that suppressing the secretion of EV-derived, senescence-related miRNAs, such as miR-34a, or increasing levels of competing endogenous long noncoding RNAs, such as MALAT1 that inhibit miR-34a, may help to improve musculoskeletal function with aging. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
    Keywords:  EXOSOMES; MALAT1; OSTEOARTHRITIS; OSTEOPOROSIS; SARCOPENIA; miR‐34a
    DOI:  https://doi.org/10.1002/jbm4.10686
  33. J Gen Physiol. 2023 Jan 02. pii: e202213087. [Epub ahead of print]155(1):
    Single-molecule imaging reveals how mavacamten and PKA modulate ATP turnover in skeletal muscle myofibrils.
    Matvey Pilagov, Laurens W H J Heling, Jonathan Walklate, Michael A Geeves, Neil M Kad.
      Muscle contraction is controlled at two levels: the thin and the thick filaments. The latter level of control involves three states of myosin heads: active, disordered relaxed (DRX), and super-relaxed (SRX), the distribution of which controls the number of myosins available to interact with actin. How these are controlled is still uncertain. Using fluorescently labeled ATP, we were able to spatially assign the activity of individual myosins within the sarcomere. We observed that SRX comprises 53% of all heads in the C-zone compared with 35% and 44% in the P- and D-zones, respectively. The recently FDA-approved hypertrophic cardiomyopathy drug, mavacamten (mava), significantly decreased DRX, favoring SRX in both the C- and D-zones at 60% and 63%, respectively. Since thick filament regulation is in part regulated by the myosin-binding protein-C (MyBP-C), we also studied PKA phosphorylation. This had the opposite effect as mava, specifically in the C-zone where it decreased SRX to 34%, favoring DRX. These results directly show that excess concentrations of mava do increase SRX, but the effect is limited across the sarcomere, suggesting mava is less effective on skeletal muscle. In addition, we show that PKA directly affects the contractile machinery of skeletal muscle leading to the liberation of repressed heads. Since the effect is focused on the C-zone, this suggests it is likely through MyBP-C phosphorylation, although our data suggest that a further reserve of myosins remain that are not accessible to PKA treatment.
    DOI:  https://doi.org/10.1085/jgp.202213087
  34. J Sport Health Sci. 2022 Oct 29. pii: S2095-2546(22)00103-X. [Epub ahead of print]
    Exercise sustains the hallmarks of health.
    Yan Qiu, Benjamin Fernández-García, H Immo Lehmann, Guoping Li, Guido Kroemer, Carlos López-Otín, Junjie Xiao.
      Exercise has long been known for its active role in improving physical fitness and sustaining health. Regular moderate-intensity exercise improves all aspects of human health and is widely accepted as a preventative and therapeutic strategy for various diseases. It is well-documented that exercise maintains and restores homeostasis at the organismal, tissue, cellular, and molecular levels to stimulate positive physiological adaptations that consequently protect against various pathological conditions. Here we mainly summarize how moderate-intensity exercise affects the major hallmarks of health, including the integrity of barriers, containment of local perturbations, recycling and turnover, integration of circuitries, rhythmic oscillations, homeostatic resilience, hormetic regulation, as well as repair and regeneration. Furthermore, we summarize the current understanding of the mechanisms responsible for beneficial adaptations in response to exercise. This review aimed at providing a comprehensive summary of the vital biological mechanisms through which moderate-intensity exercise maintains health and opens a window for its application in other health interventions. We hope that continuing investigation in this field will further increase our understanding of the processes involved in the positive role of moderate-intensity exercise and thus get us closer to the identification of new therapeutics that improve quality of life.
    Keywords:  Beneficial effects of exercise; Exercise-related physiological adaptations; Hallmarks of health; Moderate-intensity exercise; Therapeutic exercise
    DOI:  https://doi.org/10.1016/j.jshs.2022.10.003
  35. Int J Biol Macromol. 2022 Nov 11. pii: S0141-8130(22)02639-3. [Epub ahead of print]
    Interactive regulation of DNA demethylase gene TET1 and m6A methyltransferase gene METTL3 in myoblast differentiation.
    Xinran Yang, Chugang Mei, Sayed Haidar Abbas Raza, Xinhao Ma, Jianfang Wang, Jiawei Du, Linsen Zan.
      DNA methylation (5mC) and mRNA N6-methyladenosine (m6A) play an essential role in gene transcriptional regulation. DNA methylation has been well established to be involved in skeletal muscle development. Interacting regulatory mechanisms between DNA methylation and mRNA m6A modification have been identified in a variety of biological processes. However, the effect of m6A on skeletal muscle differentiation and the underlying mechanisms are still unclear. It is also unknown whether there is an interaction between DNA methylation and mRNA m6A modification in skeletal myogenesis. In the present study, we used m6A-IP-qPCR, LC-MS/MS and dot blot assays to determine that the DNA demethylase gene, TET1, exhibited increased m6A levels and decreased mRNA expression during bovine skeletal myoblast differentiation. Dual-luciferase reporter assays and RIP experiments demonstrated that METTL3 suppressed TET1 expression by regulating TET1 mRNA stability in a m6A-YTHDF2-dependent manner. Furthermore, TET1 mediated DNA demethylation of itself, MYOD1 and MYOG, thereby stimulating their expression to promote myogenic differentiation. Ectopic expression of TET1 rescued the effect of METTL3 knockdown on reduced myotubes. In contrast, TET1 knockdown impaired the myogenic differentiation promoted by METTL3 overexpression. Moreover, ChIP experiments found that TET1 could bind and demethylate METTL3 DNA, which enhanced METTL3 expression. In addition, TET1 knockdown decreased m6A levels. ChIP assays also showed that TET1 knockdown contributed to the binding of H3K4me3 and H3K27me3 to METTL3 DNA. Our results revealed a negative feedback regulatory loop between TET1 and METTL3 in myoblast differentiation, which unveiled the interplay among DNA methylation, RNA methylation and histone methylation in skeletal myogenesis.
    Keywords:  DNA methylation; Histone methylation; METTL3; Myoblast differentiation; TET1; mRNA m(6)A methylation
    DOI:  https://doi.org/10.1016/j.ijbiomac.2022.11.081
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