bims-moremu 2023-05-21 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–05–21
33 papers selected by
Anna Vainshtein, Craft Science Inc.

Blocking muscle wasting via deletion of the muscle-specific E3 ligase MuRF1 impedes pancreatic tumor growth.
Adenosine monophosphate-activated protein kinase is elevated in human cachectic muscle and prevents cancer-induced metabolic dysfunction in mice.
Inhibiting de novo ceramide synthesis restores mitochondrial and protein homeostasis in muscle aging.
Macrophage Involvement in Aging-Associated Skeletal Muscle Regeneration.
Exploring mitochondrial morphology in skeletal muscle: Implications for highly trained individuals.
Secreted ADAMTS-like 2 promotes myoblast differentiation by potentiating Wnt signaling.
High-intensity interval training in the form of isometric contraction improves fatigue resistance in dystrophin-deficient muscle.
Molecular clocks, satellite cells, and skeletal muscle regeneration.
Rapid restitution of contractile dysfunction by synthetic copolymers in dystrophin-deficient single live skeletal muscle fibers.
The D84G mutation in STIM1 causes nuclear envelope dysfunction and myopathy in mice.
Effect of RONS-Induced Intracellular Redox Homeostasis in 6-NBDG/Glucose Uptake in C2C12 Myotubes and Single Isolated Skeletal Muscle Fibres.
Loss of transcriptional heterogeneity in aged human muscle stem cells.
IL-4 Signaling Promotes Myoblast Differentiation and Fusion by Enhancing the Expression of MyoD, Myogenin, and Myomerger.
Filamin-A-interacting protein 1 (FILIP1) is a dual compartment protein linking myofibrils and microtubules during myogenic differentiation and upon mechanical stress.
Muscle fusogens go viral for gene delivery to skeletal muscle.
SPSB1-mediated inhibition of TGF-β receptor-II impairs myogenesis in inflammation.
Caloric Restriction Combined with Immobilization as Translational Model for Sarcopenia Expressing Key-Pathways of Human Pathology.
Androgen receptor coordinates muscle metabolic and contractile functions.
A Scoping Review Investigating the "Gene-Dosage Theory" of Mitochondrial DNA in the Healthy Skeletal Muscle.
SESN1 is a FOXO3 effector that counteracts human skeletal muscle ageing.
Z-Disk-Associated Plectin (Isoform 1d): Spatial Arrangement, Interaction Partners, and Role in Filamin C Homeostasis.
Establishment of Skeletal Myogenic Progenitors from Non-Human Primate Induced Pluripotent Stem Cells.
Insight into muscle stem cell regeneration and mechanobiology.
Allosteric modulation of ryanodine receptor RyR1 by nucleotide derivatives.
Pathophysiological mechanisms of reduced physical activity: insights from the human step reduction model and animal analogues.
Exercise Improves Metabolism and Alleviates Atherosclerosis via Muscle-Derived Extracellular Vesicles.
An in silico FSHD muscle fibre for modelling DUX4 dynamics and predicting the impact of therapy.
Arntl deficiency in myeloid cells reduces neutrophil recruitment and delays skeletal muscle repair.
A Systematic Review investigating the Effectiveness of Exercise training in Glycogen Storage Diseases.
Adiposity is associated with widespread transcriptional changes and downregulation of longevity pathways in aged skeletal muscle.
Increased tetanic calcium in early fatigue of mammalian muscle fibers is accompanied by accelerated force development despite a decreased force.
Sarcopenia and noncoding RNAs: A comprehensive review.
Conserved multi-tissue transcriptomic adaptations to exercise training in humans and mice.

Commun Biol. 2023 05 13. 6(1): 519

Blocking muscle wasting via deletion of the muscle-specific E3 ligase MuRF1 impedes pancreatic tumor growth.

Daria Neyroud, Orlando Laitano, Aneesha Dasgupta, Christopher Lopez, Rebecca E Schmitt, Jessica Z Schneider, David W Hammers, H Lee Sweeney, Glenn A Walter, Jason Doles, Sarah M Judge, Andrew R Judge.

Cancer-induced muscle wasting reduces quality of life, complicates or precludes cancer treatments, and predicts early mortality. Herein, we investigate the requirement of the muscle-specific E3 ubiquitin ligase, MuRF1, for muscle wasting induced by pancreatic cancer. Murine pancreatic cancer (KPC) cells, or saline, were injected into the pancreas of WT and MuRF1-/- mice, and tissues analyzed throughout tumor progression. KPC tumors induces progressive wasting of skeletal muscle and systemic metabolic reprogramming in WT mice, but not MuRF1-/- mice. KPC tumors from MuRF1-/- mice also grow slower, and show an accumulation of metabolites normally depleted by rapidly growing tumors. Mechanistically, MuRF1 is necessary for the KPC-induced increases in cytoskeletal and muscle contractile protein ubiquitination, and the depression of proteins that support protein synthesis. Together, these data demonstrate that MuRF1 is required for KPC-induced skeletal muscle wasting, whose deletion reprograms the systemic and tumor metabolome and delays tumor growth.

DOI: https://doi.org/10.1038/s42003-023-04902-2
J Cachexia Sarcopenia Muscle. 2023 May 16.

Adenosine monophosphate-activated protein kinase is elevated in human cachectic muscle and prevents cancer-induced metabolic dysfunction in mice.

Steffen H Raun, Mona S Ali, Xiuqing Han, Carlos Henríquez-Olguín, T C Phung Pham, Roberto Meneses-Valdés, Jonas R Knudsen, Anna C H Willemsen, Steen Larsen, Thomas E Jensen, Ramon Langen, Lykke Sylow.

   BACKGROUND: Metabolic dysfunction and cachexia are associated with poor cancer prognosis. With no pharmacological treatments, it is crucial to define the molecular mechanisms causing cancer-induced metabolic dysfunction and cachexia. Adenosine monophosphate-activated protein kinase (AMPK) connects metabolic and muscle mass regulation. As AMPK could be a potential treatment target, it is important to determine the function for AMPK in cancer-associated metabolic dysfunction and cachexia. We therefore established AMPK's roles in cancer-associated metabolic dysfunction, insulin resistance and cachexia.
METHODS: In vastus lateralis muscle biopsies from n = 26 patients with non-small cell lung cancer (NSCLC), AMPK signalling and protein content were examined by immunoblotting. To determine the role of muscle AMPK, male mice overexpressing a dominant-negative AMPKα2 (kinase-dead [KiDe]) specifically in striated muscle were inoculated with Lewis lung carcinoma (LLC) cells (wild type [WT]: n = 27, WT + LLC: n = 34, mAMPK-KiDe: n = 23, mAMPK-KiDe + LLC: n = 38). Moreover, male LLC-tumour-bearing mice were treated with (n = 10)/without (n = 9) 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) to activate AMPK for 13 days. Littermate mice were used as controls. Metabolic phenotyping of mice was performed via indirect calorimetry, body composition analyses, glucose and insulin tolerance tests, tissue-specific 2-[3H]deoxy-d-glucose (2-DG) uptake and immunoblotting.
RESULTS: Patients with NSCLC presented increased muscle protein content of AMPK subunits α1, α2, β2, γ1 and γ3 ranging from +27% to +79% compared with control subjects. In patients with NSCLC, AMPK subunit protein content correlated with weight loss (α1, α2, β2 and γ1), fat-free mass (α1, β2 and γ1) and fat mass (α1 and γ1). Tumour-bearing mAMPK-KiDe mice presented increased fat loss and glucose and insulin intolerance. LLC in mAMPK-KiDe mice displayed lower insulin-stimulated 2-DG uptake in skeletal muscle (quadriceps: -35%, soleus: -49%, extensor digitorum longus: -48%) and the heart (-29%) than that in non-tumour-bearing mice. In skeletal muscle, mAMPK-KiDe abrogated the tumour-induced increase in insulin-stimulated TBC1D4thr642 phosphorylation. The protein content of TBC1D4 (+26%), pyruvate dehydrogenase (PDH; +94%), PDH kinases (+45% to +100%) and glycogen synthase (+48%) was increased in skeletal muscle of tumour-bearing mice in an AMPK-dependent manner. Lastly, chronic AICAR treatment elevated hexokinase II protein content and normalized phosphorylation of p70S6Kthr389 (mTORC1 substrate) and ACCser212 (AMPK substrate) and rescued cancer-induced insulin intolerance.
CONCLUSIONS: Protein contents of AMPK subunits were upregulated in skeletal muscle of patients with NSCLC. AMPK activation seemed protectively inferred by AMPK-deficient mice developing metabolic dysfunction in response to cancer, including AMPK-dependent regulation of multiple proteins crucial for glucose metabolism. These observations highlight the potential for targeting AMPK to counter cancer-associated metabolic dysfunction and possibly cachexia.

Keywords:  AMP-activated protein kinase (AMPK); cancer cachexia; glucose metabolism; insulin resistance; skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13238
Sci Transl Med. 2023 May 17. 15(696): eade6509

Inhibiting de novo ceramide synthesis restores mitochondrial and protein homeostasis in muscle aging.

Tanes I Lima, Pirkka-Pekka Laurila, Martin Wohlwend, Jean David Morel, Ludger J E Goeminne, Hao Li, Mario Romani, Xiaoxu Li, Chang-Myung Oh, Dohyun Park, Sandra Rodríguez-López, Julijana Ivanisevic, Hector Gallart-Ayala, Barbara Crisol, Florence Delort, Sabrina Batonnet-Pichon, Leonardo R Silveira, Lakshmi Sankabattula Pavani Veera Venkata, Anil K Padala, Suresh Jain, Johan Auwerx.

Disruption of mitochondrial function and protein homeostasis plays a central role in aging. However, how these processes interact and what governs their failure in aging remain poorly understood. Here, we showed that ceramide biosynthesis controls the decline in mitochondrial and protein homeostasis during muscle aging. Analysis of transcriptome datasets derived from muscle biopsies obtained from both aged individuals and patients with a diverse range of muscle disorders revealed that changes in ceramide biosynthesis, as well as disturbances in mitochondrial and protein homeostasis pathways, are prevalent features in these conditions. By performing targeted lipidomics analyses, we found that ceramides accumulated in skeletal muscle with increasing age across Caenorhabditis elegans, mice, and humans. Inhibition of serine palmitoyltransferase (SPT), the rate-limiting enzyme of the ceramide de novo synthesis, by gene silencing or by treatment with myriocin restored proteostasis and mitochondrial function in human myoblasts, in C. elegans, and in the skeletal muscles of mice during aging. Restoration of these age-related processes improved health and life span in the nematode and muscle health and fitness in mice. Collectively, our data implicate pharmacological and genetic suppression of ceramide biosynthesis as potential therapeutic approaches to delay muscle aging and to manage related proteinopathies via mitochondrial and proteostasis remodeling.

DOI: https://doi.org/10.1126/scitranslmed.ade6509
Cells. 2023 04 22. pii: 1214. [Epub ahead of print]12(9):

Macrophage Involvement in Aging-Associated Skeletal Muscle Regeneration.

Chang-Yi Cui, Luigi Ferrucci, Myriam Gorospe.

  The skeletal muscle is a dynamic organ composed of contractile muscle fibers, connective tissues, blood vessels and nerve endings. Its main function is to provide motility to the body, but it is also deeply involved in systemic metabolism and thermoregulation. The skeletal muscle frequently encounters microinjury or trauma, which is primarily repaired by the coordinated actions of muscle stem cells (satellite cells, SCs), fibro-adipogenic progenitors (FAPs), and multiple immune cells, particularly macrophages. During aging, however, the capacity of skeletal muscle to repair and regenerate declines, likely contributing to sarcopenia, an age-related condition defined as loss of muscle mass and function. Recent studies have shown that resident macrophages in skeletal muscle are highly heterogeneous, and their phenotypes shift during aging, which may exacerbate skeletal muscle deterioration and inefficient regeneration. In this review, we highlight recent insight into the heterogeneity and functional roles of macrophages in skeletal muscle regeneration, particularly as it declines with aging.

Keywords:  aging; fibro-adipogenic progenitor; macrophage; regeneration; repair; satellite cell; skeletal muscle

DOI:  https://doi.org/10.3390/cells12091214
J Physiol. 2023 May 18.

Exploring mitochondrial morphology in skeletal muscle: Implications for highly trained individuals.

Blair MacLeod.



Keywords:  mitochondria; mitochondrial cristae; resistance exercise; skeletal muscle; strength training; weightlifting

DOI:  https://doi.org/10.1113/JP284873
Matrix Biol. 2023 May 13. pii: S0945-053X(23)00060-4. [Epub ahead of print]

Secreted ADAMTS-like 2 promotes myoblast differentiation by potentiating Wnt signaling.

Nandaraj Taye, Mukti Singh, Clair Baldock, Dirk Hubmacher.

  Myogenesis is the process that generates multinucleated contractile myofibers from muscle stem cells during skeletal muscle development and regeneration. Myogenesis is governed by myogenic regulatory transcription factors, including MYOD1. Here, we identified the secreted matricellular protein ADAMTS-like 2 (ADAMTSL2) as part of a Wnt-dependent positive feedback loop which augmented or sustained MYOD1 expression and thus promoted myoblast differentiation. ADAMTSL2 depletion resulted in severe retardation of myoblast differentiation in vitro and its ablation in myogenic precursor cells resulted in aberrant skeletal muscle architecture. Mechanistically, ADAMTSL2 potentiated WNT signaling by binding to WNT ligands and WNT receptors. We identified the WNT-binding ADAMTSL2 peptide, which was sufficient to promote myogenesis in vitro. Since ADAMTSL2 was previously described as a negative regulator of TGFβ signaling in fibroblasts, ADAMTSL2 now emerges as a signaling hub that could integrate WNT, TGFβ and potentially other signaling pathways within the dynamic microenvironment of differentiating myoblasts during skeletal muscle development and regeneration.

Keywords:  ADAMTS proteases; ADAMTSL proteins; Extracellular matrix; acromelic dysplasia; geleophysic dysplasia; skeletal muscle

DOI:  https://doi.org/10.1016/j.matbio.2023.05.003
J Physiol. 2023 May 15.

High-intensity interval training in the form of isometric contraction improves fatigue resistance in dystrophin-deficient muscle.

Nao Yamauchi, Katsuyuki Tamai, Iori Kimura, Azuma Naito, Nao Tokuda, Yuki Ashida, Norio Motohashi, Yoshitsugu Aoki, Takashi Yamada.

  Duchenne muscular dystrophy (DMD) is a genetic muscle-wasting disorder characterised by progressive muscle weakness and easy fatigability. Here we examined whether high-intensity interval training (HIIT) in the form of isometric contraction improves fatigue resistance in skeletal muscle from dystrophin-deficient mdx52 mice. Isometric HIIT was performed on plantar flexor muscles in vivo with supramaximal electrical stimulation every other day for 4 weeks (a total of 15 sessions). In the non-trained contralateral gastrocnemius muscle from mdx52 mice, the decreased fatigue resistance was associated with a reduction in the amount of PGC-1α, citrate synthase activity, mitochondrial respiratory complex II, LC3B-II/I ratio, and mitophagy-related gene expression (i.e., Pink1, parkin, Bnip3, and Bcl2l13) as well as an increase in the phosphorylation levels of Src Tyr416 and Akt Ser473, the amount of p62, and the percentage of Evans blue dye-positive area. Isometric HIIT restored all these alterations and markedly improved fatigue resistance in mdx52 muscles. Moreover, an acute bout of HIIT increased the phosphorylation levels of AMPK Thr172, ACC Ser79, Ulk1 Ser555, and Drp1 Ser616 in mdx52 muscles. Thus, our data show that HIIT with isometric contractions significantly mitigates histological signs of pathology and improves fatigue resistance in dystrophin-deficient muscles. These beneficial effects can be explained by the restoration of mitochondrial function via AMPK-dependent induction of the mitophagy program and de novo mitochondria biogenesis. KEY POINTS: Skeletal muscle fatigue is often associated with Duchenne muscular dystrophy (DMD) and leads to an inability to perform daily tasks, profoundly decreasing quality of life. We examined the effect of high-intensity interval training (HIIT) in the form of isometric contraction on fatigue resistance in skeletal muscle from the mdx52 mouse model of DMD. Isometric HIIT counteracted the reduced fatigue resistance as well as dystrophic changes in skeletal muscle of mdx52 mice. This beneficial effect could be explained by the restoration of mitochondrial function via AMPK-dependent mitochondrial biogenesis and the induction of mitophagy program in the dystrophic muscles. Abstract figure legend As a result of the loss of dystrophin, increased production of NADPH oxidase 2 (NOX2)- and mitochondria-derived reactive oxygen species (ROS) causes mitochondrial Ca2+ overload as well as an activation of Src/Akt pathway. This then leads to mitochondrial dysfunction and perturbation of mitophagy, which contribute to dystrophic pathology and decreased fatigue resistance due to accumulation of damaged mitochondria in dystrophin-deficient muscle. High-intensity interval training (HIIT) with isometric contractions mitigates dystrophic alterations and improves fatigue resistance, presumably via AMPK-dependent mitochondrial turnover; dysfunctional mitochondria are eliminated via mitophagy and replaced through de novo mitochondria biogenesis. This article is protected by copyright. All rights reserved.

Keywords:  fatigue resistance; high-intensity interval training; isometric contraction; mitochondria; muscular dystrophy

DOI:  https://doi.org/10.1113/JP284532
Am J Physiol Cell Physiol. 2023 May 15.

Molecular clocks, satellite cells, and skeletal muscle regeneration.

Ryan E Kahn, Sudarshan Dayanidhi, Orly Lacham-Kaplan, John A Hawley.

  Skeletal muscle comprises approximately 50% of individual body mass and plays vital roles in locomotion, heat production, and whole-body metabolic homeostasis. This tissue exhibits a robust diurnal rhythm which is under control of the suprachiasmatic nucleus (SCN) region of the hypothalamus. The SCN acts as a 'central' co-ordinator of circadian rhythms, while cell-autonomous 'peripheral' clocks are located within almost all other tissues/organs in the body. Synchronization of peripheral clocks in muscle (and other tissues) together with the central clock is crucial to ensure temporally coordinated physiology across all organ systems. By virtue of its mass, human skeletal muscle contains the largest collection of peripheral clocks, but within muscle resides a local stem cell population, satellite cells (SC's), which have their own functional molecular clock independent of the numerous muscle clocks. Skeletal muscle has a daily turnover rate of 1-2%, so the regenerative capacity of this tissue is important for whole-body homeostasis/repair and depends on successful SC myogenic progression (i.e., proliferation, differentiation and fusion). Emerging evidence suggests SC-mediated muscle regeneration may, in part, be regulated by molecular clocks involved in SC-specific diurnal transcription. Here we provide insight on molecular clock regulation of muscle regeneration/repair and provide a novel perspective on the interplay between SC-specific molecular clocks, myogenic programs, and cell cycle kinetics that underpin myogenic progression.

Keywords:  cell cycle; circadian rhythms; muscle stem cells; myogenesis; myogenic regulatory factors

DOI:  https://doi.org/10.1152/ajpcell.00073.2023
Skelet Muscle. 2023 May 19. 13(1): 9

Rapid restitution of contractile dysfunction by synthetic copolymers in dystrophin-deficient single live skeletal muscle fibers.

Dongwoo Hahn, Joseph D Quick, Brian R Thompson, Adelyn Crabtree, Benjamin J Hackel, Frank S Bates, Joseph M Metzger.

  Duchenne muscular dystrophy (DMD) is caused by the lack of dystrophin, a cytoskeletal protein essential for the preservation of the structural integrity of the muscle cell membrane. DMD patients develop severe skeletal muscle weakness, degeneration, and early death. We tested here amphiphilic synthetic membrane stabilizers in mdx skeletal muscle fibers (flexor digitorum brevis; FDB) to determine their effectiveness in restoring contractile function in dystrophin-deficient live skeletal muscle fibers. After isolating FDB fibers via enzymatic digestion and trituration from thirty-three adult male mice (9 C57BL10, 24 mdx), these were plated on a laminin-coated coverslip and treated with poloxamer 188 (P188; PEO75-PPO30-PEO75; 8400 g/mol), architecturally inverted triblock (PPO15-PEO200-PPO15, 10,700 g/mol), and diblock (PEO75-PPO16-C4, 4200 g/mol) copolymers. We assessed the twitch kinetics of sarcomere length (SL) and intracellular Ca2+ transient by Fura-2AM by field stimulation (25 V, 0.2 Hz, 25 °C). Twitch contraction peak SL shortening of mdx FDB fibers was markedly depressed to 30% of the dystrophin-replete control FDB fibers from C57BL10 (P < 0.001). Compared to vehicle-treated mdx FDB fibers, copolymer treatment robustly and rapidly restored the twitch peak SL shortening (all P < 0.05) by P188 (15 μM = + 110%, 150 μM = + 220%), diblock (15 μM = + 50%, 150 μM = + 50%), and inverted triblock copolymer (15 μM = + 180%, 150 μM = + 90%). Twitch peak Ca2+ transient from mdx FDB fibers was also depressed compared to C57BL10 FDB fibers (P < 0.001). P188 and inverted triblock copolymer treatment of mdx FDB fibers increased the twitch peak Ca2+ transient (P < 0.001). This study shows synthetic block copolymers with varied architectures can rapidly and highly effectively enhance contractile function in live dystrophin-deficient skeletal muscle fibers.

Keywords:  Calcium handling; Contractile function; Duchenne muscular dystrophy; Dystrophin; Membrane stabilizing copolymer; Skeletal muscle

DOI:  https://doi.org/10.1186/s13395-023-00318-y
bioRxiv. 2023 May 03. pii: 2023.05.03.539279. [Epub ahead of print]

The D84G mutation in STIM1 causes nuclear envelope dysfunction and myopathy in mice.

Victoria Bryson, Chaojian Wang, Zirui Zhou, Kavisha Singh, Noah Volin, Eda Yildirim, Paul Rosenberg.

Stromal interaction molecule 1 (STIM1) is a Ca 2+ sensor located in the sarcoplasmic reticulum (SR) of skeletal muscle where it is best known for its role in store operated Ca 2+ entry (SOCE). Genetic syndromes resulting from STIM1 mutations are recognized as a cause of muscle weakness and atrophy. Here, we focus on a gain of function mutation that occurs in humans and mice (STIM1 +/D84G mice) where muscles exhibit constitutive SOCE. Unexpectedly, this constitutive SOCE did not affect global Ca 2+ transients, SR Ca 2+ content or excitation contraction coupling (ECC) and was therefore unlikely to underlie the reduced muscle mass and weakness observed in these mice. Instead, we demonstrate that the presence of D84G STIM1 in the nuclear envelope of STIM1 +/D84G muscle disrupts nuclear-cytosolic coupling causing severe derangement in nuclear architecture, DNA damage, and altered lamina A associated gene expression. Functionally, we found D84G STIM1 reduced the transfer of Ca 2+ from the cytosol to the nucleus in myoblasts resulting in a reduction of [Ca 2+ ] N . Taken together, we propose a novel role for STIM1 in the nuclear envelope that links Ca 2+ signaling to nuclear stability in skeletal muscle.

DOI: https://doi.org/10.1101/2023.05.03.539279
Int J Mol Sci. 2023 Apr 29. pii: 8082. [Epub ahead of print]24(9):

Effect of RONS-Induced Intracellular Redox Homeostasis in 6-NBDG/Glucose Uptake in C2C12 Myotubes and Single Isolated Skeletal Muscle Fibres.

Escarlata Fernández-Puente, Eva Martín-Prieto, Carlos Manuel Márquez, Jesús Palomero.

  The glucose uptake in skeletal muscle is essential to produce energy through ATP, which is needed by this organ to maintain vital functions. The impairment of glucose uptake compromises the metabolism and function of skeletal muscle and other organs and is a feature of diabetes, obesity, and ageing. There is a need for research to uncover the mechanisms involved in the impairment of glucose uptake in skeletal muscle. In this study, we adapted, developed, optimised, and validated a methodology based on the fluorescence glucose analogue 6-NBDG, combined with a quantitative fluorescence microscopy image analysis, to determine the glucose uptake in two models of skeletal muscle cells: C2C12 myotubes and single fibres isolated from muscle. It was proposed that reactive oxygen and nitrogen species (RONS) and redox homeostasis play an important role in the modulation of intracellular redox signalling pathways associated with glucose uptake. In this study, we prove that the prooxidative intracellular redox environment under oxidative eustress produced by RONS such as hydrogen peroxide and nitric oxide improves glucose uptake in skeletal muscle cells. However, when oxidation is excessive, oxidative distress occurs, and cellular viability is compromised, although there might be an increase in the glucose uptake. Based on the results of this study, the determination of 6-NBDG/glucose uptake in myotubes and skeletal muscle cells is feasible, validated, and will contribute to improve future research.

Keywords:  6-NBDG; C2C12 myotubes; ROS; glucose uptake; hydrogen peroxide; insulin resistance; nitric oxide; quantitative fluorescence microscopy; redox homeostasis; skeletal muscle fibres

DOI:  https://doi.org/10.3390/ijms24098082
PLoS One. 2023 ;18(5): e0285018

Loss of transcriptional heterogeneity in aged human muscle stem cells.

Emilie Barruet, Katharine Striedinger, Pauline Marangoni, Jason H Pomerantz.

Age-related loss of muscle mass and function negatively impacts healthspan and lifespan. Satellite cells function as muscle stem cells in muscle maintenance and regeneration by self-renewal, activation, proliferation and differentiation. These processes are perturbed in aging at the stem cell population level, contributing to muscle loss. However, how representation of subpopulations within the human satellite cell pool change during aging remains poorly understood. We previously reported a comprehensive baseline of human satellite cell (Hu-MuSCs) transcriptional activity in muscle homeostasis describing functional heterogenous human satellite cell subpopulations such as CAV1+ Hu-MUSCs. Here, we sequenced additional satellite cells from new healthy donors and performed extended transcriptomic analyses with regard to aging. We found an age-related loss of global transcriptomic heterogeneity and identified new markers (CAV1, CXCL14, GPX3) along with previously described ones (FN1, ITGB1, SPRY1) that are altered during aging in human satellite cells. These findings describe new transcriptomic changes that occur during aging in human satellite cells and provide a foundation for understanding functional impact.

DOI: https://doi.org/10.1371/journal.pone.0285018
Cells. 2023 04 29. pii: 1284. [Epub ahead of print]12(9):

IL-4 Signaling Promotes Myoblast Differentiation and Fusion by Enhancing the Expression of MyoD, Myogenin, and Myomerger.

Mitsutoshi Kurosaka, Yung-Li Hung, Shuichi Machida, Kazuhisa Kohda.

  Myoblast fusion is essential for skeletal muscle development, growth, and regeneration. However, the molecular mechanisms underlying myoblast fusion and differentiation are not fully understood. Previously, we reported that interleukin-4 (IL-4) promotes myoblast fusion; therefore, we hypothesized that IL-4 signaling might regulate the expression of the molecules involved in myoblast fusion. In this study, we showed that in addition to fusion, IL-4 promoted the differentiation of C2C12 myoblast cells by inducing myoblast determination protein 1 (MyoD) and myogenin, both of which regulate the expression of myomerger and myomaker, the membrane proteins essential for myoblast fusion. Unexpectedly, IL-4 treatment increased the expression of myomerger, but not myomaker, in C2C12 cells. Knockdown of IL-4 receptor alpha (IL-4Rα) in C2C12 cells by small interfering RNA impaired myoblast fusion and differentiation. We also demonstrated a reduction in the expression of MyoD, myogenin, and myomerger by knockdown of IL-4Rα in C2C12 cells, while the expression level of myomaker remained unchanged. Finally, cell mixing assays and the restoration of myomerger expression partially rescued the impaired fusion in the IL-4Rα-knockdown C2C12 cells. Collectively, these results suggest that the IL-4/IL-4Rα axis promotes myoblast fusion and differentiation via the induction of myogenic regulatory factors, MyoD and myogenin, and myomerger.

Keywords:  NFATc2; interleukin-4; muscle differentiation; myoblast fusion; myogenic regulatory factors; myomaker; myomerger

DOI:  https://doi.org/10.3390/cells12091284
Cell Tissue Res. 2023 May 13.

Filamin-A-interacting protein 1 (FILIP1) is a dual compartment protein linking myofibrils and microtubules during myogenic differentiation and upon mechanical stress.

Valentina Grande, Julia Schuld, Peter F M van der Ven, Oliver J Gruss, Dieter O Fürst.

  Variations in the gene encoding filamin-A-interacting protein 1 (FILIP1) were identified to be associated with a combination of neurological and muscular symptoms. While FILIP1 was shown to regulate motility of brain ventricular zone cells, a process important for corticogenesis, the function of the protein in muscle cells has been less well characterized. The expression of FILIP1 in regenerating muscle fibres predicted a role in early muscle differentiation. Here we analysed expression and localization of FILIP1 and its binding partners filamin-C (FLNc) and microtubule plus-end-binding protein EB3 in differentiating cultured myotubes and adult skeletal muscle. Prior to the development of cross-striated myofibrils, FILIP1 is associated with microtubules and colocalizes with EB3. During further myofibril maturation its localization changes, and FILIP1 localizes to myofibrillar Z-discs together with the actin-binding protein FLNc. Forced contractions of myotubes by electrical pulse stimulation (EPS) induce focal disruptions in myofibrils and translocation of both proteins from Z-discs to these lesions, suggesting a role in induction and/or repair of these structures. The immediate proximity of tyrosylated, dynamic microtubules and EB3 to lesions implies that also these play a role in these processes. This implication is supported by the fact that in nocodazole-treated myotubes that lack functional microtubules, the number of lesions induced by EPS is significantly reduced. In summary, we here show that FILIP1 is a cytolinker protein that is associated with both microtubules and actin filaments, and might play a role in the assembly of myofibrils and their stabilization upon mechanical stress to protect them from damage.

Keywords:  Filamin-A-interacting protein 1; Mechanical stress protection; Myofibrillogenesis; Skeletal muscle differentiation; Z-disc proteins

DOI:  https://doi.org/10.1007/s00441-023-03776-4
Cell. 2023 May 11. pii: S0092-8674(23)00417-8. [Epub ahead of print]186(10): 2041-2043

Muscle fusogens go viral for gene delivery to skeletal muscle.

Devin E Gibbs, April D Pyle.

Viruses and multinucleated cells rely on fusogens to facilitate the fusion of their membranes. In this issue of Cell, Millay and colleagues demonstrate that replacing viral fusogens with mammalian skeletal muscle fusogens leads to the specific transduction of skeletal muscle and the ability to deliver gene therapy constructs in a therapeutically relevant muscle disease.

DOI: https://doi.org/10.1016/j.cell.2023.04.021
J Cachexia Sarcopenia Muscle. 2023 May 20.

SPSB1-mediated inhibition of TGF-β receptor-II impairs myogenesis in inflammation.

Yi Li, Niklas Dörmann, Björn Brinschwitz, Melanie Kny, Elisa Martin, Kirsten Bartels, Ning Li, Priyanka Voori Giri, Stefan Schwanz, Michael Boschmann, Susanne Hille, Britta Fielitz, Tobias Wollersheim, Julius Grunow, Stephan B Felix, Steffen Weber-Carstens, Friedrich C Luft, Oliver J Müller, Jens Fielitz.

   BACKGROUND: Sepsis-induced intensive care unit-acquired weakness (ICUAW) features profound muscle atrophy and attenuated muscle regeneration related to malfunctioning satellite cells. Transforming growth factor beta (TGF-β) is involved in both processes. We uncovered an increased expression of the TGF-β receptor II (TβRII)-inhibitor SPRY domain-containing and SOCS-box protein 1 (SPSB1) in skeletal muscle of septic mice. We hypothesized that SPSB1-mediated inhibition of TβRII signalling impairs myogenic differentiation in response to inflammation.
METHODS: We performed gene expression analyses in skeletal muscle of cecal ligation and puncture- (CLP) and sham-operated mice, as well as vastus lateralis of critically ill and control patients. Pro-inflammatory cytokines and specific pathway inhibitors were used to quantitate Spsb1 expression in myocytes. Retroviral expression plasmids were used to investigate the effects of SPSB1 on TGF-β/TβRII signalling and myogenesis in primary and immortalized myoblasts and differentiated myotubes. For mechanistical analyses we used coimmunoprecipitation, ubiquitination, protein half-life, and protein synthesis assays. Differentiation and fusion indices were determined by immunocytochemistry, and differentiation factors were quantified by qRT-PCR and Western blot analyses.
RESULTS: SPSB1 expression was increased in skeletal muscle of ICUAW patients and septic mice. Tumour necrosis factor (TNF), interleukin-1β (IL-1β), and IL-6 increased the Spsb1 expression in C2C12 myotubes. TNF- and IL-1β-induced Spsb1 expression was mediated by NF-κB, whereas IL-6 increased the Spsb1 expression via the glycoprotein 130/JAK2/STAT3 pathway. All cytokines reduced myogenic differentiation. SPSB1 avidly interacted with TβRII, resulting in TβRII ubiquitination and destabilization. SPSB1 impaired TβRII-Akt-Myogenin signalling and diminished protein synthesis in myocytes. Overexpression of SPSB1 decreased the expression of early (Myog, Mymk, Mymx) and late (Myh1, 3, 7) differentiation-markers. As a result, myoblast fusion and myogenic differentiation were impaired. These effects were mediated by the SPRY- and SOCS-box domains of SPSB1. Co-expression of SPSB1 with Akt or Myogenin reversed the inhibitory effects of SPSB1 on protein synthesis and myogenic differentiation. Downregulation of Spsb1 by AAV9-mediated shRNA attenuated muscle weight loss and atrophy gene expression in skeletal muscle of septic mice.
CONCLUSIONS: Inflammatory cytokines via their respective signalling pathways cause an increase in SPSB1 expression in myocytes and attenuate myogenic differentiation. SPSB1-mediated inhibition of TβRII-Akt-Myogenin signalling and protein synthesis contributes to a disturbed myocyte homeostasis and myogenic differentiation that occurs during inflammation.

Keywords:  Critical illness myopathy; Inflammation-induced muscle atrophy; Myogenic differentiation; SPSB1; Sepsis; TGFβ receptor II

DOI:  https://doi.org/10.1002/jcsm.13252
Aging Dis. 2023 Jun 01. 14(3): 937-957

Caloric Restriction Combined with Immobilization as Translational Model for Sarcopenia Expressing Key-Pathways of Human Pathology.

Jelle C B C de Jong, Martien P M Caspers, Nanda Keijzer, Nicole Worms, Joline Attema, Christa de Ruiter, Serene Lek, Arie G Nieuwenhuizen, Jaap Keijer, Aswin L Menke, Robert Kleemann, Lars Verschuren, Anita M van den Hoek.

The prevalence of sarcopenia is increasing while it is often challenging, expensive and time-consuming to test the effectiveness of interventions against sarcopenia. Translational mouse models that adequately mimic underlying physiological pathways could accelerate research but are scarce. Here, we investigated the translational value of three potential mouse models for sarcopenia, namely partial immobilized (to mimic sedentary lifestyle), caloric restricted (CR; to mimic malnutrition) and a combination (immobilized & CR) model. C57BL/6J mice were calorically restricted (-40%) and/or one hindleg was immobilized for two weeks to induce loss of muscle mass and function. Muscle parameters were compared to those of young control (4 months) and old reference mice (21 months). Transcriptome analysis of quadriceps muscle was performed to identify underlying pathways and were compared with those being expressed in aged human vastus lateralis muscle-biopsies using a meta-analysis of five different human studies. Caloric restriction induced overall loss of lean body mass (-15%, p<0.001), whereas immobilization decreased muscle strength (-28%, p<0.001) and muscle mass of hindleg muscles specifically (on average -25%, p<0.001). The proportion of slow myofibers increased with aging in mice (+5%, p<0.05), and this was not recapitulated by the CR and/or immobilization models. The diameter of fast myofibers decreased with aging (-7%, p<0.05), and this was mimicked by all models. Transcriptome analysis revealed that the combination of CR and immobilization recapitulated more pathways characteristic for human muscle-aging (73%) than naturally aged (21 months old) mice (45%). In conclusion, the combination model exhibits loss of both muscle mass (due to CR) and function (due to immobilization) and has a remarkable similarity with pathways underlying human sarcopenia. These findings underline that external factors such as sedentary behavior and malnutrition are key elements of a translational mouse model and favor the combination model as a rapid model for testing the treatments against sarcopenia.

DOI: https://doi.org/10.14336/AD.2022.1201
J Cachexia Sarcopenia Muscle. 2023 May 20.

Androgen receptor coordinates muscle metabolic and contractile functions.

Kamar Ghaibour, Mélanie Schuh, Sirine Souali-Crespo, Céline Chambon, Anouk Charlot, Joe Rizk, Daniela Rovito, Anna-Isavella Rerra, Qingshuang Cai, Nadia Messaddeq, Joffrey Zoll, Delphine Duteil, Daniel Metzger.

   BACKGROUND: Androgens are anabolic steroid hormones that exert their function by binding to the androgen receptor (AR). We have previously established that AR deficiency in limb muscles impairs sarcomere myofibrillar organization and decreases muscle strength in male mice. However, despite numerous studies performed in men and rodents, the signalling pathways controlled by androgens via their receptor in skeletal muscles remain poorly understood.
METHODS: Male ARskm-/y (n = 7-12) and female ARskm-/- mice (n = 9), in which AR is selectively ablated in myofibres of musculoskeletal tissue, and male AR(i)skm-/y , in which AR is selectively ablated in post-mitotic skeletal muscle myofibres (n = 6), were generated. Longitudinal monitoring of body weight, blood glucose, insulin, lipids and lipoproteins was performed, alongside metabolomic analyses. Glucose metabolism was evaluated in C2C12 cells treated with 5α-dihydrotestosterone (DHT) and the anti-androgen flutamide (n = 6). Histological analyses on macroscopic and ultrastructural levels of longitudinal and transversal muscle sections were conducted. The transcriptome of gastrocnemius muscles from control and ARskm-/y mice was analysed at the age of 9 weeks (P < 0.05, 2138 differentially expressed genes) and validated by RT-qPCR analysis. The AR (4691 peaks with false discovery rate [FDR] < 0.1) and H3K4me2 (47 225 peaks with FDR < 0.05) cistromes in limb muscles were determined in 11-week-old wild-type mice.
RESULTS: We show that disrupting the androgen/AR axis impairs in vivo glycolytic activity and fastens the development of type 2 diabetes in male, but not in female mice. In agreement, treatment with DHT increases glycolysis in C2C12 myotubes by 30%, whereas flutamide has an opposite effect. Fatty acids are less efficiently metabolized in skeletal muscles of ARskm-/y mice and accumulate in cytoplasm, despite increased transcript levels of genes encoding key enzymes of beta-oxidation and mitochondrial content. Impaired glucose and fatty acid metabolism in AR-deficient muscle fibres is associated with 30% increased lysine and branched-chain amino acid catabolism, decreased polyamine biosynthesis and disrupted glutamate transamination. This metabolic switch generates ammonia (2-fold increase) and oxidative stress (30% increased H2 O2 levels), which impacts mitochondrial functions and causes necrosis in <1% fibres. We unravel that AR directly activates the transcription of genes involved in glycolysis, oxidative metabolism and muscle contraction.
CONCLUSIONS: Our study provides important insights into diseases caused by impaired AR function in musculoskeletal system and delivers a deeper understanding of skeletal muscle pathophysiological dynamics that is instrumental to develop effective treatment for muscle disorders.

Keywords:  androgen receptor; genomics; metabolism; skeletal muscle; type 2 diabetes

DOI:  https://doi.org/10.1002/jcsm.13251
Int J Mol Sci. 2023 May 02. pii: 8154. [Epub ahead of print]24(9):

A Scoping Review Investigating the "Gene-Dosage Theory" of Mitochondrial DNA in the Healthy Skeletal Muscle.

Zandra Overgaard Pedersen, Britt Staevnsbo Pedersen, Steen Larsen, Tina Dysgaard.

  This review provides an overview of the evidence regarding mtDNA and valid biomarkers for assessing mitochondrial adaptions. Mitochondria are small organelles that exist in almost all cells throughout the human body. As the only organelle, mitochondria contain their own DNA, mitochondrial DNA (mtDNA). mtDNA-encoded polypeptides are subunits of the enzyme complexes in the electron transport chain (ETC) that are responsible for production of ATP to the cells. mtDNA is frequently used as a biomarker for mitochondrial content, since changes in mitochondrial volume are thought to induce similar changes in mtDNA. However, some exercise studies have challenged this "gene-dosage theory", and have indicated that changes in mitochondrial content can adapt without changes in mtDNA. Thus, the aim of this scoping review was to summarize the studies that used mtDNA as a biomarker for mitochondrial adaptions and address the question as to whether changes in mitochondrial content, induce changes in mtDNA in response to aerobic exercise in the healthy skeletal muscle. The literature was searched in PubMed and Embase. Eligibility criteria included: interventional study design, aerobic exercise, mtDNA measurements reported pre- and postintervention for the healthy skeletal muscle and English language. Overall, 1585 studies were identified. Nine studies were included for analysis. Eight out of the nine studies showed proof of increased oxidative capacity, six found improvements in mitochondrial volume, content and/or improved mitochondrial enzyme activity and seven studies did not find evidence of change in mtDNA copy number. In conclusion, the findings imply that mitochondrial adaptions, as a response to aerobic exercise, can occur without a change in mtDNA copy number.

Keywords:  CS; aerobic exercise; citrate synthase; electron transport chain; mitochondrial DNA; mitochondrial adaptions; mitochondrial content; mtDNA

DOI:  https://doi.org/10.3390/ijms24098154
Cell Prolif. 2023 May 17. e13455

SESN1 is a FOXO3 effector that counteracts human skeletal muscle ageing.

Ying Jing, Yuesheng Zuo, Liang Sun, Zheng-Rong Yu, Shuai Ma, Huifang Hu, Qian Zhao, Daoyuan Huang, Weiqi Zhang, Juan Carlos Izpisua Belmonte, Yang Yu, Jing Qu, Guang-Hui Liu, Si Wang.

Sarcopenia, a skeletal muscle disorder in which loss of muscle mass and function progresses with age, is associated with increased overall frailty, risk of falling and mortality in the elders. Here, we reveal that SESN1 safeguards skeletal muscle from ageing downstream of the longevity gene FOXO3, which we recently reported is a geroprotector in primate skeletal muscle. Knockdown of SESN1 mimicked the human myotube ageing phenotypes observed in the FOXO3-deficient human myotubes, whereas genetic activation of SESN1 alleviated human myotube senescence. Of note, SESN1 was identified as a protective secretory factor against muscle atrophy. Administration of recombinant SESN1 protein attenuated senescence of human myotubes in vitro and facilitated muscle regeneration in vivo. Altogether, we unveil a key role of SESN1 downstream of FOXO3 in protecting skeletal muscle from ageing, providing diagnostic biomarkers and intervention strategies for counteracting skeletal muscle ageing and related diseases.

DOI: https://doi.org/10.1111/cpr.13455
Cells. 2023 04 26. pii: 1259. [Epub ahead of print]12(9):

Z-Disk-Associated Plectin (Isoform 1d): Spatial Arrangement, Interaction Partners, and Role in Filamin C Homeostasis.

Lilli Winter, Ilona Staszewska-Daca, Stefan Zittrich, Fatiha Elhamine, Michaela M Zrelski, Katy Schmidt, Irmgard Fischer, Christian Jüngst, Astrid Schauss, Wolfgang H Goldmann, Robert Stehle, Gerhard Wiche.

  Plectin, a highly versatile cytolinker protein, is crucial for myofiber integrity and function. Accordingly, mutations in the human gene (PLEC) cause several rare diseases, denoted as plectinopathies, with most of them associated with progressive muscle weakness. Of several plectin isoforms expressed in skeletal muscle and the heart, P1d is the only isoform expressed exclusively in these tissues. Using high-resolution stimulated emission depletion (STED) microscopy, here we show that plectin is located within the gaps between individual α-actinin-positive Z-disks, recruiting and bridging them to desmin intermediate filaments (Ifs). Loss of plectin in myofibril bundles led to a complete loss of desmin Ifs. Loss of Z-disk-associated plectin isoform P1d led to disorganization of muscle fibers and slower relaxation of myofibrils upon mechanical strain, in line with an observed inhomogeneity of muscle ultrastructure. In addition to binding to α-actinin and thereby providing structural support, P1d forms a scaffolding platform for the chaperone-assisted selective autophagy machinery (CASA) by directly interacting with HSC70 and synpo2. In isoform-specific knockout (P1d-KO) mouse muscle and mechanically stretched plectin-deficient myoblasts, we found high levels of undigested filamin C, a bona fide substrate of CASA. Similarly, subjecting P1d-KO mice to forced swim tests led to accumulation of filamin C aggregates in myofibers, highlighting a specific role of P1d in tension-induced proteolysis activated upon high loads of physical exercise and muscle contraction.

Keywords:  chaperone-assisted selective autophagy; cytolinker; desmin intermediate filaments; myofibril; plectin; skeletal muscle

DOI:  https://doi.org/10.3390/cells12091259
Cells. 2023 04 13. pii: 1147. [Epub ahead of print]12(8):

Establishment of Skeletal Myogenic Progenitors from Non-Human Primate Induced Pluripotent Stem Cells.

June Baik, Carolina Ortiz-Cordero, Alessandro Magli, Karim Azzag, Sarah B Crist, Aline Yamashita, James Kiley, Sridhar Selvaraj, Ricardo Mondragon-Gonzalez, Elizabeth Perrin, John P Maufort, Jody L Janecek, Rachael M Lee, Laura Hocum Stone, Parthasarathy Rangarajan, Sabarinathan Ramachandran, Melanie L Graham, Rita C R Perlingeiro.

  Pluripotent stem (PS) cells enable the scalable production of tissue-specific derivatives with therapeutic potential for various clinical applications, including muscular dystrophies. Given the similarity to human counterparts, the non-human primate (NHP) is an ideal preclinical model to evaluate several questions, including delivery, biodistribution, and immune response. While the generation of human-induced PS (iPS)-cell-derived myogenic progenitors is well established, there have been no data for NHP counterparts, probably due to the lack of an efficient system to differentiate NHP iPS cells towards the skeletal muscle lineage. Here, we report the generation of three independent Macaca fascicularis iPS cell lines and their myogenic differentiation using PAX7 conditional expression. The whole-transcriptome analysis confirmed the successful sequential induction of mesoderm, paraxial mesoderm, and myogenic lineages. NHP myogenic progenitors efficiently gave rise to myotubes under appropriate in vitro differentiation conditions and engrafted in vivo into the TA muscles of NSG and FKRP-NSG mice. Lastly, we explored the preclinical potential of these NHP myogenic progenitors in a single wild-type NHP recipient, demonstrating engraftment and characterizing the interaction with the host immune response. These studies establish an NHP model system through which iPS-cell-derived myogenic progenitors can be studied.

Keywords:  RNA sequencing; induced pluripotent stem cells; muscle regeneration; muscular dystrophy; myogenesis; non-human primate; stem cell therapy

DOI:  https://doi.org/10.3390/cells12081147
Stem Cell Res Ther. 2023 May 12. 14(1): 129

Insight into muscle stem cell regeneration and mechanobiology.

Kuin Tian Pang, Larry Sai Weng Loo, Sean Chia, Francesca Yi Teng Ong, Hanry Yu, Ian Walsh.

  Stem cells possess the unique ability to differentiate into specialized cell types. These specialized cell types can be used for regenerative medicine purposes such as cell therapy. Myosatellite cells, also known as skeletal muscle stem cells (MuSCs), play important roles in the growth, repair, and regeneration of skeletal muscle tissues. However, despite its therapeutic potential, the successful differentiation, proliferation, and expansion processes of MuSCs remain a significant challenge due to a variety of factors. For example, the growth and differentiation of MuSCs can be greatly influenced by actively replicating the MuSCs microenvironment (known as the niche) using mechanical forces. However, the molecular role of mechanobiology in MuSC growth, proliferation, and differentiation for regenerative medicine is still poorly understood. In this present review, we comprehensively summarize, compare, and critically analyze how different mechanical cues shape stem cell growth, proliferation, differentiation, and their potential role in disease development (Fig. 1). The insights developed from the mechanobiology of stem cells will also contribute to how these applications can be used for regenerative purposes using MuSCs.

Keywords:  Mechanobiology; Skeletal muscle stem cells; Stiffness; Strain; Topography; Viscoelasticity

DOI:  https://doi.org/10.1186/s13287-023-03363-y
Structure. 2023 May 03. pii: S0969-2126(23)00132-6. [Epub ahead of print]

Allosteric modulation of ryanodine receptor RyR1 by nucleotide derivatives.

Spencer Cholak, James W Saville, Xing Zhu, Alison M Berezuk, Katharine S Tuttle, Omid Haji-Ghassemi, Francisco J Alvarado, Filip Van Petegem, Sriram Subramaniam.

  The coordinated release of Ca2+ from the sarcoplasmic reticulum (SR) is critical for excitation-contraction coupling. This release is facilitated by ryanodine receptors (RyRs) that are embedded in the SR membrane. In skeletal muscle, activity of RyR1 is regulated by metabolites such as ATP, which upon binding increase channel open probability (Po). To obtain structural insights into the mechanism of RyR1 priming by ATP, we determined several cryo-EM structures of RyR1 bound individually to ATP-γ-S, ADP, AMP, adenosine, adenine, and cAMP. We demonstrate that adenine and adenosine bind RyR1, but AMP is the smallest ATP derivative capable of inducing long-range (>170 Å) structural rearrangements associated with channel activation, establishing a structural basis for key binding site interactions that are the threshold for triggering quaternary structural changes. Our finding that cAMP also induces these structural changes and results in increased channel opening suggests its potential role as an endogenous modulator of RyR1 conductance.

Keywords:  RyR1; Ryanodine Receptor; cryo-EM; nucleotide binding

DOI:  https://doi.org/10.1016/j.str.2023.04.009
Acta Physiol (Oxf). 2023 May 13. e13986

Pathophysiological mechanisms of reduced physical activity: insights from the human step reduction model and animal analogues.

Fabio Sarto, Roberto Bottinelli, Martino V Franchi, Simone Porcelli, Bostjan Simunič, Rado Pišot, Marco V Narici.

  Physical inactivity represents a heavy burden for modern societies and is spreading worldwide, it is a recognised pandemic and is the fourth cause of global mortality. Not surprisingly, there is an increasing interest in longitudinal studies on the impact of reduced physical activity on different physiological systems. This narrative review focuses on the pathophysiological mechanisms of step reduction (SR), an experimental paradigm that involves a sudden decrease in participants' habitual daily steps to a lower level, mimicking the effects of a sedentary lifestyle. Analogous animal models of reduced physical activity, namely the "wheel-lock" and the "cage reduction" models, which can provide the foundation for human studies, are also discussed. The empirical evidence obtained thus far shows that even brief periods of reduced physical activity can lead to substantial alterations in skeletal muscle health and metabolic function. In particular, decrements in lean/muscle mass, muscle function, muscle protein synthesis, cardiorespiratory fitness, endothelial function and insulin sensitivity, together with an increased fat mass and inflammation, have been observed. Exercise interventions seem particularly effective for counteracting these pathophysiological alterations induced by periods of reduced physical activity. A direct comparison of SR with other human models of unloading, such as bed rest and lower limb suspension/immobilisation, is presented. In addition, we propose a conceptual framework aiming to unravel the mechanisms of muscle atrophy and insulin resistance in the specific context of reduced ambulatory activity. Finally, methodological considerations, knowledge gaps and future directions for both animal and human models are also discussed in the review.

Keywords:  Cage reduction; disuse; inactivity; insulin sensitivity; muscle atrophy; wheel-lock

DOI:  https://doi.org/10.1111/apha.13986
Aging Dis. 2023 Jun 01. 14(3): 952-965

Exercise Improves Metabolism and Alleviates Atherosclerosis via Muscle-Derived Extracellular Vesicles.

Yixiao Wang, Yunnan Liu, Siyan Zhang, Na Li, Changyang Xing, Chen Wang, Jia Wang, Mengying Wei, Guodong Yang, Lijun Yuan.

Regular exercise maintains a healthy metabolic profile, while the underlying mechanisms have not been fully elucidated. Extracellular vesicles serve as an important mediator in intercellular communication. In this study, we aimed to explore whether exercise-induced extracellular vesicles (EVs) of skeletal muscle origins contribute to exercise-related protective effects on metabolism. We found that the twelve weeks of swimming training improved glucose tolerance, reduced visceral lipid accumulation, alleviated liver damage, and inhibited atherosclerosis progression in both obese WT mice and ApoE-/- mice, which could be partially blocked by EV biogenesis repression. Injection of skeletal muscle-derived EVs from exercised C57BL/6J mice (twice a week for 12 weeks) had similar protective effects on both obese WT mice and ApoE-/- mice as exercise itself. Mechanistically, these exe-EVs could be endocytosed by major metabolic organs, especially the liver and adipose tissue. With the protein cargos rich in mitochondrial and fatty acid oxidation-related components, exe-EVs remodeled metabolism towards beneficial cardiovascular outcomes. Our study here has shown that exercise remodels metabolism towards beneficial cardiovascular outcomes at least partially via the skeletal muscle secreted EVs. Therapeutic delivery of exe-EVs or the analogues could be promising for prevention of certain cardiovascular and metabolic diseases.

DOI: https://doi.org/10.14336/AD.2022.1131
Elife. 2023 May 15. pii: e88345. [Epub ahead of print]12

An in silico FSHD muscle fibre for modelling DUX4 dynamics and predicting the impact of therapy.

Matthew V Cowley, Johanna Pruller, Massimo Ganassi, Peter S Zammit, Christopher R S Banerji.

  Facioscapulohumeral muscular dystrophy (FSHD) is an incurable myopathy linked to over-expression of the myotoxic transcription factor DUX4. Targeting DUX4 is the leading therapeutic approach, however it is only detectable in 0.1-3.8% of FSHD myonuclei. How rare DUX4 drives FSHD and the optimal anti-DUX4 strategy is unclear. We combine stochastic gene expression with compartment models of cell states, building a simulation of DUX4 expression and consequences in FSHD muscle fibres. Investigating iDUX4 myoblasts, scRNAseq and snRNAseq of FSHD muscle we estimate parameters including DUX4 mRNA degradation, transcription and translation rates and DUX4 target gene activation rates. Our model accurately recreates the distribution of DUX4 and target gene positive cells seen in scRNAseq of FSHD myocytes. Importantly we show DUX4 drives significant cell death despite expression in only 0.8% of live cells. Comparing scRNAseq of unfused FSHD myocytes to snRNAseq of fused FSHD myonuclei, we find evidence of DUX4 protein syncytial diffusion and estimate its rate via genetic algorithms. We package our model into freely available tools, to rapidly investigate consequences of anti-DUX4 therapy.

Keywords:  cell biology; computational biology; human; systems biology

DOI:  https://doi.org/10.7554/eLife.88345
Sci Rep. 2023 Apr 25. 13(1): 6747

Arntl deficiency in myeloid cells reduces neutrophil recruitment and delays skeletal muscle repair.

Aiko Watanabe, Hiroyuki Koike, Naoki Kumagami, Shigeki Shimba, Ichiro Manabe, Yumiko Oishi.

After a muscle injury, a process comprising inflammation, repair, and regeneration must occur in a time-sensitive manner for skeletal muscle to be adequately repaired and regenerated. This complex process is assumed to be controlled by various myeloid cell types, including monocytes and macrophages, though the mechanism is not fully understood. Aryl hydrocarbon receptor nuclear translocator-like (Arntl or Bmal1) is a transcription factor that controls the circadian rhythm and has been implicated in regulating myeloid cell functions. In the present study, we generated myeloid cell-specific Arntl conditional knockout (cKO) mice to assess the role of Arntl expressed in myeloid cell populations during the repair process after muscle injury. Myeloid cell-specific Arntl deletion impaired muscle regeneration after cardiotoxin injection. Flow cytometric analyses revealed that, in cKO mice, the numbers of infiltrating neutrophils and Ly6Chi monocytes within the injured site were reduced on days 1 and 2, respectively, after muscle injury. Moreover, neutrophil migration and the numbers of circulating monocytes were significantly reduced in cKO mice, which suggests these effects may account, at least in part, for the impaired regeneration. These findings suggest that Arntl, expressed in the myeloid lineage regulates neutrophil and monocyte recruitment and is therefore required for skeletal muscle regeneration.

DOI: https://doi.org/10.1038/s41598-023-33830-8
Ther Adv Rare Dis. 2022 Jan-Dec;3:3 26330040221076497

A Systematic Review investigating the Effectiveness of Exercise training in Glycogen Storage Diseases.

Claire Bordoli, Elaine Murphy, Ian Varley, Graham Sharpe, Philip Hennis.

   Introduction: Glycogen storage diseases (GSDs) are rare inborn errors of carbohydrate metabolism typically with skeletal muscle and liver involvement. In those with skeletal muscle involvement, the majority display symptoms of exercise intolerance which can cause profound exercise limitation and impair everyday living and quality of life (QoL). There are no curative treatments for GSDs, thus therapeutic options, such as exercise training, are aimed at improving QoL by alleviating signs and symptoms. In order to investigate the effectiveness of exercise training in adults with GSDs, we systematically reviewed the literature.
Methods: In this review we conducted searches within SCOPUS and MEDLINE to identify potential papers for inclusion. These papers were independently assessed for inclusion and quality by two authors. We identified 23 studies which included aerobic training, strength training or respiratory muscle training in patients with McArdles (n = 41) and Pompe disease (n = 139).
Results: In McArdle disease, aerobic exercise training improved aerobic capacity (VO2 peak) by 14-111% with further benefits to functional capacity and well-being. Meanwhile, strength training increased muscle peak power by 100-151% and reduced disease severity. In Pompe disease, a combination of aerobic and strength training improved VO2 peak by 9-10%, muscle peak power by 64%, functional capacity and well-being. Furthermore, respiratory muscle training (RMT) improved respiratory muscular strength [maximum inspiratory pressure (MIP) increased by up to 65% and maximum expiratory pressure (MEP) by up to 70%], with additional benefits shown in aerobic capacity, functional capacity and well-being.
Conclusion: This adds to the growing body of evidence which suggests that supervised exercise training is safe and effective in improving aerobic capacity and muscle function in adults with McArdle or Pompe disease. However, the literature base is limited in quality and quantity with a dearth of literature regarding exercise training in other GSD subtypes.

Keywords:  endurance training; exercise; glycogen storage disease; respiratory training; review; strength training

DOI:  https://doi.org/10.1177/26330040221076497
J Cachexia Sarcopenia Muscle. 2023 May 18.

Adiposity is associated with widespread transcriptional changes and downregulation of longevity pathways in aged skeletal muscle.

EpiGen Global Research Consortium

   BACKGROUND: Amongst healthy older people, a number of correlates of impaired skeletal muscle mass and function have been defined. Although the prevalence of obesity is increasing markedly in this age group, information is sparse about the particular impacts of obesity on ageing skeletal muscle or the molecular mechanisms that underlie this and associated disease risk.
METHODS: Here, we examined genome-wide transcriptional changes using RNA sequencing in muscle biopsies from 40 older community-dwelling men from the Hertfordshire Sarcopenia Study with regard to obesity (body mass index [BMI] >30 kg/m2 , n = 7), overweight (BMI 25-30, n = 19), normal weight (BMI < 25, n = 14), and per cent and total fat mass. In addition, we used EPIC DNA methylation array data to investigate correlations between DNA methylation and gene expression in aged skeletal muscle tissue and investigated the relationship between genes within altered regulatory pathways and muscle histological parameters.
RESULTS: Individuals with obesity demonstrated a prominent modified transcriptional signature in muscle tissue, with a total of 542 differentially expressed genes associated with obesity (false discovery rate ≤0.05), of which 425 genes were upregulated when compared with normal weight. Upregulated genes were enriched in immune response (P = 3.18 × 10-41 ) and inflammation (leucocyte activation, P = 1.47 × 10-41 ; tumour necrosis factor, P = 2.75 × 10-15 ) signalling pathways and downregulated genes enriched in longevity (P = 1.5 × 10-3 ) and AMP-activated protein kinase (AMPK) (P = 4.5 × 10-3 ) signalling pathways. Furthermore, differentially expressed genes in both longevity and AMPK signalling pathways were associated with a change in DNA methylation, with a total of 256 and 360 significant cytosine-phosphate-guanine-gene correlations identified, respectively. Similar changes in the muscle transcriptome were observed with respect to per cent fat mass and total fat mass. Obesity was further associated with a significant increase in type II fast-fibre area (P = 0.026), of which key regulatory genes within both longevity and AMPK pathways were significantly associated.
CONCLUSIONS: We provide for the first time a global transcriptomic profile of skeletal muscle in older people with and without obesity, demonstrating modulation of key genes and pathways implicated in the regulation of muscle function, changes in DNA methylation associated with such pathways and associations between genes within the modified pathways implicated in muscle regulation and changes in muscle fibre type.

Keywords:  AMPK; DNA methylation; adiposity; gene expression; longevity; skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13255
FASEB J. 2023 Jun;37(6): e22978

Increased tetanic calcium in early fatigue of mammalian muscle fibers is accompanied by accelerated force development despite a decreased force.

Cecilia Leijding, Ida Viken, Joseph D Bruton, Daniel C Andersson, Arthur J Cheng, Håkan Westerblad.

  During the initial phase of fatigue induced by repeated contractions in fast-twitch muscle fibers, tetanic force decreases despite increasing tetanic free cytosolic [Ca2+ ] ([Ca2+ ]cyt ). Here, we hypothesized that the increase in tetanic [Ca2+ ]cyt nevertheless has positive effects on force in early fatigue. Experiments on enzymatically isolated mouse flexor digitorum brevis (FDB) fibers showed that an increase in tetanic [Ca2+ ]cyt during ten 350 ms contractions required trains of electrical pulses to be elicited at short intervals (≤2 s) and at high frequencies (≥70 Hz). Mechanically dissected mouse FDB fibers showed greater decrease in tetanic force when the stimulation frequency during contractions was gradually reduced to prevent the increase in tetanic [Ca2+ ]cyt . Novel analyses of data from previous studies revealed an increased rate of force development in the tenth fatiguing contraction in mouse FDB fibers, as well as in rat FDB and human intercostal fibers. Mouse FDB fibers deficient in creatine kinase showed no increase in tetanic [Ca2+ ]cyt and slowed force development in the tenth contraction; after injection of creatine kinase to enable phosphocreatine breakdown, these fibers showed an increase in tetanic [Ca2+ ]cyt and accelerated force development. Mouse FDB fibers exposed to ten short contractions (43 ms) produced at short intervals (142 ms) showed increased tetanic [Ca2+ ]cyt accompanied by a marked (~16%) increase in the developed force. In conclusion, the increase in tetanic [Ca2+ ]cyt in early fatigue is accompanied by accelerated force development, which under some circumstances can counteract the decline in physical performance caused by the concomitant decrease in maximum force.

Keywords:  calcium; force development; inorganic phosphate; muscle fibers; parvalbumin; skeletal muscle fatigue

DOI:  https://doi.org/10.1096/fj.202300401R
J Cell Physiol. 2023 May 14.

Sarcopenia and noncoding RNAs: A comprehensive review.

Soudeh Ghafouri-Fard, Arian Askari, Bashdar Mahmud Hussen, Mohammad Taheri, Arda Kiani.

  Sarcopenia is an elderly disease and is related to frailty and loss of muscle mass (atrophy) of older adults. The exact molecular mechanisms contributing to the pathogenesis of disease are yet to be discovered. In recent years, the role of noncoding RNAs in the pathogenesis of almost every kind of malignant and nonmalignant conditions is pinpointed. Regarding their regulatory function, there have been an increased number of studies on the role of noncoding RNAs in the progress of sarcopenia. In this manuscript, we review the role of microRNAs and long noncoding RNAs in development and progression of disease. We also discuss their potential as therapeutic targets in this condition.

Keywords:  lncRNA; miRNAs; muscle atrophy; noncoding RNA; sarcopenia

DOI:  https://doi.org/10.1002/jcp.31031
Cell Rep. 2023 May 12. pii: S2211-1247(23)00510-7. [Epub ahead of print]42(5): 112499

Conserved multi-tissue transcriptomic adaptations to exercise training in humans and mice.

Timothy M Moore, Sindre Lee, Thomas Olsen, Marco Morselli, Alexander R Strumwasser, Amanda J Lin, Zhenqi Zhou, Aaron Abrishami, Steven M Garcia, Jennifer Bribiesca, Kevin Cory, Kate Whitney, Theodore Ho, Timothy Ho, Joseph L Lee, Daniel H Rucker, Christina Q A Nguyen, Akshay T S Anand, Aidan Yackly, Lorna Q Mendoza, Brayden K Leyva, Claudia Aliman, Daniel J Artiga, Yonghong Meng, Sarada Charugundla, Calvin Pan, Vida Jedian, Marcus M Seldin, In Sook Ahn, Graciel Diamante, Montgomery Blencowe, Xia Yang, Etienne Mouisel, Matteo Pellegrini, Lorraine P Turcotte, Kåre I Birkeland, Frode Norheim, Christian A Drevon, Aldons J Lusis, Andrea L Hevener.

  Physical activity is associated with beneficial adaptations in human and rodent metabolism. We studied over 50 complex traits before and after exercise intervention in middle-aged men and a panel of 100 diverse strains of female mice. Candidate gene analyses in three brain regions, muscle, liver, heart, and adipose tissue of mice indicate genetic drivers of clinically relevant traits, including volitional exercise volume, muscle metabolism, adiposity, and hepatic lipids. Although ∼33% of genes differentially expressed in skeletal muscle following the exercise intervention are similar in mice and humans independent of BMI, responsiveness of adipose tissue to exercise-stimulated weight loss appears controlled by species and underlying genotype. We leveraged genetic diversity to generate prediction models of metabolic trait responsiveness to volitional activity offering a framework for advancing personalized exercise prescription. The human and mouse data are publicly available via a user-friendly Web-based application to enhance data mining and hypothesis development.

Keywords:  CP: Metabolism; CP: Molecular biology; HMDP; exercise; genetics; multi-omics; physical activity; physiology; systems biology

DOI:  https://doi.org/10.1016/j.celrep.2023.112499