bims-moremu 2024-11-10 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024–11–10
thirty-two papers selected by
Anna Vainshtein, Craft Science Inc.

SMN depletion impairs skeletal muscle formation and maturation in a mouse model of SMA.
Comparative analysis of acute eccentric contraction-induced changes to the skeletal muscle transcriptome in young and aged mice and humans.
Exercise-induced interactions between skeletal muscle and bone via myokines and osteokine in mice: Role of FNDC5/irisin, IGF-1, and osteocalcin.
The sodium/ascorbic acid co-transporter SVCT2 distributes in a striated membrane-enriched domain at the M-band level in slow-twitch skeletal muscle fibers.
Therapeutic potential of omaveloxolone in counteracting muscle atrophy post-denervation: a multi-omics approach.
Synthetic injectable and porous hydrogels for the formation of skeletal muscle fibers: Novel perspectives for the acellular repair of substantial volumetric muscle loss.
The L27 domain of MPP7 enhances TAZ-YY1 cooperation to renew muscle stem cells.
NAD+: An Old but Promising Therapeutic Agent for Skeletal Muscle Ageing.
Acute exercise boosts NAD+ metabolism of human peripheral blood mononuclear cells.
Resistance but not endurance training suppresses glucocorticoid-induced leucine zipper (GILZ) expression in human skeletal muscle.
Ythdf2 facilitates precursor miR-378/miR-378-5p maturation to support myogenic differentiation.
Urinary titin as an early biomarker of skeletal muscle proteolysis and atrophy in various catabolic conditions.
Extracellular matrix-mimicking cryogels composed of methacrylated fucoidan enhance vascularized skeletal muscle regeneration following volumetric muscle loss.
Activation of the apelin/APJ system by vitamin D attenuates age-related muscle atrophy.
The Spatial-Temporal Alternative Splicing Profile Reveals the Functional Diversity of FXR1 Isoforms in Myogenesis.
Stable oxidative posttranslational modifications alter the gating properties of RyR1.
Acute high-intensity muscle contraction moderates AChR gene expression independent of rapamycin-sensitive mTORC1 pathway in rat skeletal muscle.
Temporal variation in p38-mediated regulation of DUX4 in facioscapulohumeral muscular dystrophy.
Dilated cardiomyopathy-associated skeletal muscle actin (ACTA1) mutation R256H disrupts actin structure and function and causes cardiomyocyte hypocontractility.
C2C12 myoblasts differentiate into myofibroblasts via the TGF-β1 signaling pathway mediated by Fibulin2.
Massive sarcomerogenesis in human skeletal muscle following long-term eccentric exercise intervention.
Post-exercise hot-water immersion is not effective for ribosome biogenesis in rat skeletal muscle.
Sodium danshensu modulates skeletal muscle fiber type formation and metabolism by inhibiting pyruvate kinase M1.
Magnetic 3D bioprinting of skeletal muscle spheroid for a spheroid-based screening assay.
Effects of cannabidiol on AMPKα2 /HIF-1α/BNIP3/NIX signaling pathway in skeletal muscle injury.
Mitochondrial quality control measures, systemic inflammation, and lower-limb muscle power in older adults: a PROMPT secondary analysis.
Protocol for muscle fiber type and cross-sectional area analysis in cryosections of whole lower mouse hindlimbs.
The combined influences of local heat application and resistance exercise on the acute mRNA response of skeletal muscle.
Comment on 'Diagnosis of Sarcopenia by Evaluating Skeletal Muscle Mass by Adjusted Bioimpedance Analysis Validated With Dual-Energy X-Ray Absorptiometry' by Cheng et al.
Direct conversion of urine-derived cells into functional motor neuron-like cells by defined transcription factors.
Flywheel resistance training promotes unique muscle architectural and performance-related adaptations in young adults.
Motor unit adaptation to disuse: crossing the threshold from firing rate suppression to neuromuscular junction transmission.

Hum Mol Genet. 2024 Nov 06. pii: ddae162. [Epub ahead of print]

SMN depletion impairs skeletal muscle formation and maturation in a mouse model of SMA.

Hong Liu, Lucia Chehade, Marc-Olivier Deguise, Yves De Repentigny, Rashmi Kothary.

  Spinal muscular atrophy (SMA) is characterized by low levels of the ubiquitously expressed Survival Motor Neuron (SMN) protein, leading to progressive muscle weakness and atrophy. Skeletal muscle satellite cells play a crucial role in muscle fiber maintenance, repair, and remodelling. While the effects of SMN depletion in muscle are well documented, its precise role in satellite cell function remains largely unclear. Using the Smn2B/- mouse model, we investigated SMN-depleted satellite cell biology through single fiber culture studies. Myofibers from Smn2B/- mice were smaller in size, shorter in length, had reduced myonuclear domain size, and reduced sub-synaptic myonuclear clusters-all suggesting impaired muscle function and integrity. These changes were accompanied by a reduction in the number of myonuclei in myofibers from Smn2B/- mice across all disease stages examined. Although the number of satellite cells in myofibers was significantly reduced, those remaining retained their capacity for myogenic activation and proliferation. These findings support the idea that a dysregulated myogenic process could be occurring as early in muscle stem cells during muscle formation and maturation in SMA. Targeting those pathways could offer additional options for combinatorial therapies for SMA.

Keywords:  muscle satellite cells; myofiber; myonuclear domain; single fiber culture

DOI:  https://doi.org/10.1093/hmg/ddae162
Am J Physiol Regul Integr Comp Physiol. 2024 Nov 04.

Comparative analysis of acute eccentric contraction-induced changes to the skeletal muscle transcriptome in young and aged mice and humans.

Jake R Boykin, Jennifer L Steiner, Grant R Laskin, Michael D Roberts, Cynthia Vied, Craig Rg Willis, Timothy Etheridge, Bradley S Gordon.

  Adaptations to skeletal muscle following resistance exercise are due in part to changes to the skeletal muscle transcriptome. While transcriptional changes in response to resistance exercise occur in young and aged muscle, aging alters this response. Rodent models have served great utility in defining regulatory factors that underscore the influence of mechanical load and aging on changes to skeletal muscle phenotype. Unilateral eccentric contractions in young and aged rodents are widely used to model resistance exercise in humans. However, the extent to which unilateral eccentric contractions in young and aged rodents mimics the transcriptional response in humans remains unknown. We re-analyzed two publicly available RNA sequencing datasets from young and aged mice and humans that were subjected to acute eccentric contractions to define key similarities and differences to the muscle transcriptional response following this exercise modality. The effect of aging on the number of contraction-sensitive genes, the distribution patterns of those genes into unique/common categories, and the cellular pathways associated with the differentially expressed genes (DEGs) were similar in mice and humans. However, there was little overlap between species when comparing specific contraction-sensitive DEGs within the same age group. There were strong intraspecies relationships for the common transcription factors predicted to influence the contraction-sensitive gene sets, whereas interspecies relationships were weak. Overall, these data demonstrate key similarities between mice and humans for the contraction-induced changes to the muscle transcriptome, but we posit species-specific responses exist and should be taken into consideration when attempting to translate rodent eccentric exercise models.

Keywords:  aging; gene expression; resistance exercise; transcription factors

DOI:  https://doi.org/10.1152/ajpregu.00224.2024
Bone. 2024 Oct 31. pii: S8756-3282(24)00303-X. [Epub ahead of print]190 117314

Exercise-induced interactions between skeletal muscle and bone via myokines and osteokine in mice: Role of FNDC5/irisin, IGF-1, and osteocalcin.

Junpei Hatakeyama, Shota Inoue, Hanlin Jiang, Ryo Yokoi, Hideki Moriyama.

  Skeletal muscle and bone interact to maintain their structure and function. Physical exercise is the most effective and easily applicable strategy to maintain their functions; however, exercise-induced interactions by soluble factors remained elusive. Our study aimed to identify exercise-induced interactions between muscle and bone by examining (1) the effects of myokine on bone and (2) the effects of osteocalcin (OCN) on skeletal muscle. To understand the effects of exercise-induced myokines on bone, we examined the effects of FNDC5 for aerobic exercise and IGF-1 for resistance exercise using a muscle-specific myokine overexpression model. To examine OCN effects on muscle, mice were intraperitoneally administered OCN-neutralizing antibody during long-term exercise. Our result showed that aerobic exercise tended to increase serum HA-tag protein attached to FNDC5 in muscle-specific overexpression groups. In addition, osteoblastic activation was increased only after aerobic exercise with HA/FNDC5 overexpression. Resistance exercise did not alter circulating HA-tag (muscle-derived IGF-1) and bone metabolism after IGF-1/HA overexpression. In the OCN study, aerobic exercise enhanced endurance capacity by restoring muscle glycogen content; however, OCN neutralization returned these to baseline. After resistance exercise, OCN suppression inhibited muscle hypertrophy and strength gains by preventing protein synthesis. Our results suggest that aerobic exercise following FNDC5 muscle overexpression promotes osteoblast activity, which may be partially caused by muscle-derived FNDC5 secretion. In addition, OCN was necessary for muscle adaptation in both aerobic and resistance exercises.

Keywords:  Aerobic exercise; Bone; Mice; Resistance exercise; Skeletal muscle

DOI:  https://doi.org/10.1016/j.bone.2024.117314
Biol Res. 2024 Nov 06. 57(1): 79

The sodium/ascorbic acid co-transporter SVCT2 distributes in a striated membrane-enriched domain at the M-band level in slow-twitch skeletal muscle fibers.

Daniel Sandoval, Jessica Mella, Jorge Ojeda, Francisca Bermedo-García, Marcela Low, Sylvain Marcellini, Maite A Castro, Mariana Casas, Enrique Jaimovich, Juan Pablo Henríquez.

   BACKGROUND: Vitamin C plays key roles in cellular homeostasis, functioning as a potent antioxidant and a positive regulator of cell differentiation. In skeletal muscle, the vitamin C/sodium co-transporter SVCT2 is preferentially expressed in oxidative slow fibers. SVCT2 is up-regulated during the early fusion of primary myoblasts and decreases during initial myotube growth, indicating the relevance of vitamin C uptake via SVCT2 for early skeletal muscle differentiation and fiber-type definition. However, our understanding of SVCT2 expression and function in adult skeletal muscles is still limited.
RESULTS: In this study, we demonstrate that SVCT2 exhibits an intracellular distribution in chicken slow skeletal muscles, following a highly organized striated pattern. A similar distribution was observed in human muscle samples, chicken cultured myotubes, and isolated mouse myofibers. Immunohistochemical analyses, combined with biochemical cell fractionation experiments, reveal a strong co-localization of SVCT2 with intracellular detergent-soluble membrane fractions at the central sarcomeric M-band, where it co-solubilizes with sarcoplasmic reticulum proteins. Remarkably, electrical stimulation of cultured myofibers induces the redistribution of SVCT2 into a vesicular pattern.
CONCLUSIONS: Our results provide novel insights into the dynamic roles of SVCT2 in different intracellular compartments in response to functional demands.

Keywords:  M-band; SVCT2; Sarcoplasmic reticulum; Skeletal muscle; Vitamin C

DOI:  https://doi.org/10.1186/s40659-024-00554-6
J Transl Med. 2024 Nov 02. 22(1): 991

Therapeutic potential of omaveloxolone in counteracting muscle atrophy post-denervation: a multi-omics approach.

Sulong Wang, Xin Yang, Kai Liu, Debin Xiong, Ainizier Yalikun, Yimurang Hamiti, Aihemaitijiang Yusufu.

   BACKGROUND: Muscle atrophy caused by denervation is common in neuromuscular diseases, leading to loss of muscle mass and function. However, a comprehensive understanding of the overall molecular network changes during muscle denervation atrophy is still deficient, hindering the development of effective treatments.
METHOD: In this study, a sciatic nerve transection model was employed in male C57BL/6 J mice to induce muscle denervation atrophy. Gastrocnemius muscles were harvested at 3 days, 2 weeks, and 4 weeks post-denervation for transcriptomic and proteomic analysis. An integrative multi-omics approach was utilized to identify key genes essential for disease progression. Targeted proteomics using PRM was then employed to validate the differential expression of central genes. Combine single-nucleus sequencing results to observe the expression levels of PRM-validated genes in different cell types within muscle tissue.Through upstream regulatory analysis, NRF2 was identified as a potential therapeutic target. The therapeutic potential of the NRF2-targeting drug Omaveloxolone was evaluated in the mouse model.
RESULT: This research examined the temporal alterations in transcripts and proteins during muscle atrophy subsequent to denervation. A comprehensive analysis identified 54,534 transcripts and 3,218 proteins, of which 23,282 transcripts and 1,852 proteins exhibited statistically significant changes at 3 days, 2 weeks, and 4 weeks post-denervation. Utilizing multi-omics approaches, 30 hubgenes were selected, and PRM validation confirmed significant expression variances in 23 genes. The findings highlighted the involvement of mitochondrial dysfunction, oxidative stress, and metabolic disturbances in the pathogenesis of muscle atrophy, with a pronounced impact on type II muscle fibers, particularly type IIb fibers. The potential therapeutic benefits of Omaveloxolone in mitigating oxidative stress and preserving mitochondrial morphology were confirmed, thereby presenting novel strategies for addressing muscle atrophy induced by denervation. GSEA analysis results show that Autophagy, glutathione metabolism, and PPAR signaling pathways are significantly upregulated, while inflammation-related and neurodegenerative disease-related pathways are significantly inhibited in the Omaveloxolone group.GSR expression and the GSH/GSSG ratio were significantly higher in the Omaveloxolone group compared to the control group, while MuSK expression was significantly lower than in the control group.
CONCLUSION: In our study, we revealed the crucial role of oxidative stress, glucose metabolism, and mitochondrial dysfunction in denervation-induced muscle atrophy, identifying NRF2 as a potential therapeutic target. Omaveloxolone was shown to stabilize mitochondrial function, enhance antioxidant capacity, and protect neuromuscular junctions, thereby offering promising therapeutic potential for treating denervation-induced muscle atrophy.

Keywords:  Multi-omics research; NRF2; Omaveloxolone; Oxidative stress; Peripheral nerve injury; Skeletal muscle atrophy

DOI:  https://doi.org/10.1186/s12967-024-05810-7
J Tissue Eng. 2024 Jan-Dec;15:15 20417314241283148

Synthetic injectable and porous hydrogels for the formation of skeletal muscle fibers: Novel perspectives for the acellular repair of substantial volumetric muscle loss.

Louise Griveau, Marion Bouvet, Emilie Christin, Cloé Paret, Lauriane Lecoq, Sylvie Radix, Thomas Laumonier, Jerome Sohier, Vincent Gache.

  In severe skeletal muscle damage, muscle tissue regeneration process has to face the loss of resident muscle stem cells (MuSCs) and the lack of connective tissue necessary to guide the regeneration process. Biocompatible and standardized 3D structures that can be injected to the muscle injury site, conforming to the defect shape while actively guiding the repair process, holds great promise for skeletal muscle tissue regeneration. In this study, we explore the use of an injectable and porous lysine dendrimer/polyethylene glycol (DGL/PEG) hydrogel as an acellular support for skeletal muscle regeneration. We adjusted the DGL/PEG composition to achieve a stiffness conducive to the attachment and proliferation of murine immortalized myoblasts and human primary muscle stems cells, sustaining the formation and maturation of muscle fibers in vitro. We then evaluated the potential of one selected "myogenic-porous hydrogel" as a supportive structure for muscle repair in a large tibialis anterior muscle defect in rats. This injectable and porous formulation filled the defect, promoting rapid cellularization with the presence of endothelial cells, macrophages, and myoblasts, thereby supporting neo-myogenesis more specifically at the interface between the wound edges and the hydrogel. The selected porous DGL/PEG hydrogel acted as a guiding scaffold at the periphery of the defect, facilitating the formation and anchorage of aligned muscle fibers 21 days after injury. Overall, our results indicate DGL/PEG porous injectable hydrogel potential to create a pro-regenerative environment for muscle cells after large skeletal muscle injuries, paving the way for acellular treatment in regenerative muscle medicine.

Keywords:  Volumetric muscle loss; injectable and porous hydrogels; regenerative muscle medicine

DOI:  https://doi.org/10.1177/20417314241283148
EMBO Rep. 2024 Nov 04.

The L27 domain of MPP7 enhances TAZ-YY1 cooperation to renew muscle stem cells.

Anwen Shao, Joseph L Kissil, Chen-Ming Fan.

  Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renew, to support a lifetime of regenerative capacity. Here we study the renewal of skeletal muscle stem cell (MuSC) during regeneration. The transcriptional co-factors TAZ/YAP (via the TEAD transcription factors) regulate cell cycle and growth while the transcription factor YY1 regulates metabolic programs for MuSC activation. We show that MPP7 and AMOT join TAZ and YY1 to regulate a selected number of common genes that harbor TEAD and YY1 binding sites. Among these common genes, Carm1 can direct MuSC renewal. We demonstrate that the L27 domain of MPP7 enhances the interaction as well as the transcriptional activity of TAZ and YY1, while AMOT acts as an intermediate to bridge them together. Furthermore, MPP7, TAZ and YY1 co-occupy the promoters of Carm1 and other common downstream genes. Our results define a renewal program comprised of two progenitor transcriptional programs, in which selected key genes are regulated by protein-protein interactions, dependent on promoter context.

Keywords:  Muscle Regeneration; Renewal Division; Stem Cells; Tiered Regulation; Transcription

DOI:  https://doi.org/10.1038/s44319-024-00305-4
Ageing Res Rev. 2023 Oct 28. pii: S1568-1637(23)00265-9. [Epub ahead of print] 102106

NAD+: An Old but Promising Therapeutic Agent for Skeletal Muscle Ageing.

Yingying Xu, Weihua Xiao.

  More than a century after the discovery of nicotinamide adenine dinucleotide (NAD+), our understanding of the molecule's role in the biology of ageing continues to evolve. As a coenzyme or substrate for many enzymes, NAD+ governs a wide range of biological processes, including energy metabolism, genomic stability, signal transduction, and cell fate. NAD+ deficiency has been recognised as a bona fide hallmark of tissue degeneration, and restoring NAD+ homeostasis helps to rejuvenate multiple mechanisms associated with tissue ageing. The progressive loss of skeletal muscle homeostasis with age is directly associated with high morbidity, disability and mortality. The aetiology of skeletal muscle ageing is complex, involving mitochondrial dysfunction, senescence and stem cell depletion, autophagy defects, chronic cellular stress, intracellular ion overload, immune cell dysfunction, circadian clock disruption, microcirculation disorders, persistent denervation, and gut microbiota dysbiosis. This review focuses on the therapeutic potential of NAD+ restoration to alleviate the above pathological factors and discusses the effects of in vivo administration of different NAD+ boosting strategies on skeletal muscle homeostasis, aiming to provide a reference for combating skeletal muscle ageing.

Keywords:  NAD(+) boosting; NAD(+) metabolism; Skeletal muscle ageing; Therapies

DOI:  https://doi.org/10.1016/j.arr.2023.102106
Brain Behav Immun. 2024 Nov 03. pii: S0889-1591(24)00687-1. [Epub ahead of print]

Acute exercise boosts NAD+ metabolism of human peripheral blood mononuclear cells.

David Walzik, Niklas Joisten, Alexander Schenk, Sina Trebing, Kirill Schaaf, Alan J Metcalfe, Polyxeni Spiliopoulou, Johanna Hiefner, Adrian McCann, Carsten Watzl, Per Magne Ueland, Sebastian Gehlert, Anna Worthmann, Charles Brenner, Philipp Zimmer.

  Nicotinamide adenine dinucleotide (NAD+) coenzymes are the central electron carriers in biological energy metabolism. Low NAD+ levels are proposed as a hallmark of ageing and several diseases, which has given rise to therapeutic strategies that aim to tackle these conditions by boosting NAD+ levels. As a lifestyle factor with preventive and therapeutic effects, exercise increases NAD+ levels across various tissues, but so far human trials are mostly focused on skeletal muscle. Given that immune cells are mobilized and redistributed in response to acute exercise, we conducted two complementary trials to test the hypothesis that a single exercise session alters NAD+ metabolism of peripheral blood mononuclear cells (PBMCs). In a randomized crossover trial (DRKS00017686) with 24 young adults (12 female) we show that acute exercise increases gene expression and protein abundance of several key NAD+ metabolism enzymes with high conformity between high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT). In a longitudinal exercise trial (DRKS00029105) with 12 young adults (6 female) we confirm these results and reveal that - similar to skeletal muscle - NAD+ salvage is pivotal for PBMCs in response to exercise. Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of NAD+ salvage pathway, displayed a pronounced increase in gene expression during exercise, which was accompanied by elevated intracellular NAD+ levels and reduced serum levels of the NAD+ precursor nicotinamide. These results demonstrate that acute exercise triggers NAD+ biosynthesis of human PBMCs with potential implications for immunometabolism, immune effector function, and immunological exercise adaptions.

Keywords:  Exercise; Immune cell; Metabolism; NAD(+); Nicotinamide adenine dinucleotide; PBMC

DOI:  https://doi.org/10.1016/j.bbi.2024.11.004
Eur J Appl Physiol. 2024 Nov 05.

Resistance but not endurance training suppresses glucocorticoid-induced leucine zipper (GILZ) expression in human skeletal muscle.

Sebastian Paul, Lars Donath, Jessica Hoppstädter, Anne Hecksteden.

   PURPOSE: Within human skeletal muscle, statin treatment leads to elevated levels of the glucocorticoid-induced leucine zipper (GILZ). Further, GILZ mediates the muscle-related side effects of statins. Physical exercise leads to GILZ suppression, in a mechanosensitive manner. Given that statin treatment is rarely tolerated by habitually exercising individuals due to statin-associated muscle symptoms (SAMS), it appears that the opposing regulation of GILZ facilitates this detrimental interaction of two key measures of cardiovascular prevention, specifically for exercise modalities with high muscle strain. Similarly, opposing regulation of atrophy associated genes (atrogenes) may be a further mechanism. If confirmed, these results might have implications for the exercise prescription of statin-users.
METHODS: A systematic search of the Gene Expression Omnibus (GEO) repository for studies reporting the acute effects of either endurance (END), conventional resistance (RT), or eccentric resistance training (ECC) was conducted. GILZ, as well as the expression of pivotal atrogenes (e.g., muscle atrophy F-box, cathepsin L, etc.) were quantified.
RESULTS: 15 studies with 204 participants (22 females; 182 males) were included. RT resulted in the highest GILZ suppression, significantly differing from the expressional change after END ( - 0.46 ± 1.11 vs. - 0.07 ± 1.08), but not from ECC ( - 0.46 ± 1.11 vs. - 0.46 ± 0.95). Similar results were seen for various atrogenes.
CONCLUSION: Our results strengthen the assumption that mechanical loading can be considered a key mediator of exercise-induced changes in GILZ and atrogene expression.

Keywords:  Atrogenes; Cardiovascular disease; Exercise; GILZ; Gene expression

DOI:  https://doi.org/10.1007/s00421-024-05644-7
Cell Mol Life Sci. 2024 Nov 06. 81(1): 445

Ythdf2 facilitates precursor miR-378/miR-378-5p maturation to support myogenic differentiation.

Kaiping Deng, Yalong Su, Zhipeng Liu, Silu Hu, Caifang Ren, Wurilege Wei, Yixuan Fan, Yanli Zhang, Feng Wang.

  Ythdf2 is known to mediate mRNA degradation in an m6A-dependent manner, and it has been shown to play a role in skeletal muscle differentiation. Recently, Ythdf2 was also found to bind to m6A-modified precursor miRNAs and regulate their maturation. However, it remains unknown whether this mechanism is related to the regulation of myogenesis by Ythdf2. Here, we observed that Ythdf2 knockdown significantly suppressed myotube formation and impacted miRNAs expression during myogenic differentiation. Through integrated analysis of miRNA and mRNA sequencing data, miR-378 and miR-378-5p were identified as important targets of Ythdf2 in myogenesis. Mechanically, Ythdf2 was found to interact with core components of the pre-miRNA processor complex, namely DICER1 and TARBP2, thereby facilitating the maturation of pre-miR-378/miR-378-5p in an m6A-dependent manner and resulting in an increase in the expression levels of mature miR-378 and miR-378-5p. Moreover, the downregulation of either miR-378 or miR-378-5p significantly inhibited myotube formation, while the forced expression of miR-378 or miR-378-5p could partially rescued Ythdf2 knockdown-induced suppression of myogenic differentiation by activating the mTOR pathway. Collectively, our results for the first time suggest that Ythdf2 regulates myogenic differentiation via mediating pre-miR-378/miR-378-5p maturation, which might provide new insights into the molecular mechanisms underlying m6A modification in the regulation of myogenesis.

Keywords:  Skeletal muscle development; Ythdf2; miR-378; miR-378-5p; pre-miRNA processing

DOI:  https://doi.org/10.1007/s00018-024-05456-0
Biochem Biophys Res Commun. 2024 Oct 28. pii: S0006-291X(24)01454-2. [Epub ahead of print]737 150918

Urinary titin as an early biomarker of skeletal muscle proteolysis and atrophy in various catabolic conditions.

Mizusa Hyodo, Kazuhiro Nomura, Rie Tsutsumi, Yuna Izumi-Mishima, Hibiki Kawaguchi, Ayuka Kawakami, Kanako Hara, Yuki Suzuki, Taku Shirakawa, Kayo Osawa, Masafumi Matsuo, Hiroshi Sakaue.

  Skeletal muscle atrophy impairs quality of life and increases the risk of disease, but current methods for assessment of muscle mass have several limitations. We here investigated the urinary concentration of a fragment of the muscle protein titin as a potential biomarker for the early detection of skeletal muscle atrophy. Four mouse models with different atrophy pathways were studied: those of cardiotoxin-induced acute muscle injury, cast-induced muscle immobilization, lipopolysaccharide-induced sepsis, and streptozotocin-induced diabetes. In all four models, urinary titin levels increased early, concurrent with or preceding upregulation of the atrophy-related genes for atrogin-1 and MuRF-1. The increase in the urinary titin concentration was thus associated with initial muscle damage and the onset of proteolysis, rather than with late-stage muscle wasting. Our findings suggest that urinary titin is a promising biomarker for detection of the onset of skeletal muscle catabolism and prediction of the subsequent development of atrophy in different catabolic states. Noninvasive measurement of urinary titin may therefore allow the earlier detection of skeletal muscle proteolysis compared with conventional techniques.

Keywords:  Muscle atrophy; Muscle catabolism; Muscle inflammation; Skeletal muscle; Titin

DOI:  https://doi.org/10.1016/j.bbrc.2024.150918
Int J Biol Macromol. 2024 Nov 02. pii: S0141-8130(24)07931-5. [Epub ahead of print] 137122

Extracellular matrix-mimicking cryogels composed of methacrylated fucoidan enhance vascularized skeletal muscle regeneration following volumetric muscle loss.

Dimulati Maimaiti, Xiaoyang Ge, Chengyue Wang, Jinuo Liu, Guanyu Yang, Dachuan Zhang, Yong Xu, Fan He, Xi Chen.

  Volumetric muscle loss (VML) significantly impairs the inherent regenerative ability of skeletal muscle and results in chronic functional impairment. Polysaccharides in the muscle extracellular matrix are crucial for regulating cell proliferation and differentiation. Recent studies indicate that fucoidan has beneficial effects on musculoskeletal conditions. However, the impact of fucoidan on skeletal muscle regeneration remains poorly understood. In this study, methacrylated fucoidan (FuMA) was synthesized through chemical grafting of the methacryloyl group onto fucoidan. In vitro experiments demonstrated that treatment with FuMA significantly up-regulated the expression of myogenic markers and promoted the formation of myotubes in C2C12 myoblast cells. Importantly, FuMA treatment led to a significant enhancement in mitochondrial energy metabolism of myoblasts via activation of the NRF2 antioxidant signaling pathway. To further investigate the regenerative properties in repairing skeletal muscle defects, we fabricated a dual crosslinked cryogel consisting of FuMA and methacrylated gelatin (GelMA) with a porous and interconnected structure. In a rat tibialis anterior muscle VML model, implantation of the FuMA/GelMA cryogel effectively promoted the regeneration of muscle fibers, reduced collagen deposition, and facilitated the formation of new blood vessels. Hence, polysaccharide-based cryogels represent a promising implantable biomimetic scaffold for facilitating skeletal muscle regeneration following severe injuries.

Keywords:  Cryogels; Methacrylated fucoidan; Mitochondrial function; NRF2; Skeletal muscle; Volumetric muscle loss

DOI:  https://doi.org/10.1016/j.ijbiomac.2024.137122
Life Sci. 2024 Oct 31. pii: S0024-3205(24)00795-1. [Epub ahead of print]359 123205

Activation of the apelin/APJ system by vitamin D attenuates age-related muscle atrophy.

Yoo Jeong Lee, Gyu Hee Kim, Da Som Lee, Hyeon-Ju Jeong, Joo Hyun Lim.

   AIMS: Age-related frailty and reduced physical activity contribute to a degenerative loss of muscle mass, function, and strength, which is known as sarcopenia. Increasing evidence has shown that vitamin D has beneficial effects on the muscle health. However, the molecular mechanisms of vitamin D have not been fully elucidated. In this study, we aimed to demonstrate whether vitamin D can overcome muscle atrophy due to aging, especially with respect to the regulation of myokines.
MAIN METHODS: Young (3-month-old) and aged (18-month-old) C57BL/6 mice were assigned to the following 3 groups: normal diet (1000 IU/kg), vitamin D3-supplemented diet (20,000 IU/kg), and normal diet plus exercise for 4 months.
KEY FINDINGS: We found that the reduction in muscle strength and mass due to aging was reversed by vitamin D3 supplementation. The levels of markers involved in muscle atrophy and cellular senescence in the muscle of the aged mice were substantially decreased by vitamin D3. Interestingly, we observed that the expression of apelin and its receptor (APJ), which is known to be secreted after exercise, significantly increased in aged muscles with a vitamin D3-supplemented diet but not in the young mice. Moreover, circulating interleukin-6 (IL-6) and growth differentiation factor 8 (GDF8) levels were significantly increased in the aged mice but were restored by vitamin D3 treatment.
SIGNIFICANCE: Our present data indicate that vitamin D3 supplementation ameliorates aging-induced muscle atrophy and senescence, similar to the effects of exercise, suggesting the positive impact of vitamin D as an intervention strategy to prevent aging-induced metabolic diseases.

Keywords:  APJ; Apelin; Myokine; Sarcopenia; Vitamin D

DOI:  https://doi.org/10.1016/j.lfs.2024.123205
Adv Sci (Weinh). 2024 Nov 05. e2405157

The Spatial-Temporal Alternative Splicing Profile Reveals the Functional Diversity of FXR1 Isoforms in Myogenesis.

Wei Wang, Xinhao Fan, Weiwei Liu, Yuxin Huang, Shuhong Zhao, Yalan Yang, Zhonglin Tang.

  Alternative splicing (AS) is a fundamental mechanism contributing to proteome diversity, yet its comprehensive landscape and regulatory dynamics during skeletal muscle development remain largely unexplored. Here, the temporal AS profiles are investigated during myogenesis in five vertebrates, conducting comprehensive profiling across 27 developmental stages in skeletal muscle and encompassing ten tissues in adult pigs. The analysis reveals a pervasive and evolutionarily conserved pattern of alternative exon usage throughout myogenic differentiation, with hundreds of skipped exons (SEs) showing developmental regulation, particularly within skeletal muscle. Notably, this study identifies a muscle-specific SE (exon 15) within the Fxr1 gene, whose AS generates two dynamically expressed isoforms with distinct functions: the isoform without exon 15 (Fxr1E15 -) regulates myoblasts proliferation, while the isoform incorporating exon 15 (Fxr1E15+) promotes myogenic differentiation and fusion. Transcriptome analysis suggests that specifically knocking-down Fxr1E15+ isoform in myoblasts modulates differentiation by influencing gene expression and splicing of specific targets. The increased inclusion of exon 15 during differentiation is mediated by the binding of Rbm24 to the intron. Furthermore, in vivo experiments indicate that the Fxr1E15+ isoform facilitates muscle regeneration. Collectively, these findings provide a comprehensive resource for AS studies in skeletal muscle development, underscoring the diverse functions and regulatory mechanisms governing distinct Fxr1 isoforms in myogenesis.

Keywords:  FXR1; RBM24; alternative splicing; muscle regeneration; myogenesis

DOI:  https://doi.org/10.1002/advs.202405157
J Gen Physiol. 2024 Dec 02. pii: e202313515. [Epub ahead of print]156(12):

Stable oxidative posttranslational modifications alter the gating properties of RyR1.

Maarten M Steinz, Nicole Beard, Emily Shorter, Johanna T Lanner.

The ryanodine receptor type 1 (RyR1) is a Ca2+ release channel that regulates skeletal muscle contraction by controlling Ca2+ release from the sarcoplasmic reticulum (SR). Posttranslational modifications (PTMs) of RyR1, such as phosphorylation, S-nitrosylation, and carbonylation are known to increase RyR1 open probability (Po), contributing to SR Ca2+ leak and skeletal muscle dysfunction. PTMs on RyR1 have been linked to muscle dysfunction in diseases like breast cancer, rheumatoid arthritis, Duchenne muscle dystrophy, and aging. While reactive oxygen species (ROS) and oxidative stress induce PTMs, the impact of stable oxidative modifications like 3-nitrotyrosine (3-NT) and malondialdehyde adducts (MDA) on RyR1 gating remains unclear. Mass spectrometry and single-channel recordings were used to study how 3-NT and MDA modify RyR1 and affect Po. Both modifications increased Po in a dose-dependent manner, with mass spectrometry identifying 30 modified residues out of 5035 amino acids per RyR1 monomer. Key modifications were found in domains critical for protein interaction and channel activation, including Y808/3NT in SPRY1, Y1081/3NT and H1254/MDA in SPRY2&3, and Q2107/MDA and Y2128/3NT in JSol, near the binding site of FKBP12. Though these modifications did not directly overlap with FKBP12 binding residues, they promoted FKBP12 dissociation from RyR1. These findings provide detailed insights into how stable oxidative PTMs on RyR1 residues alter channel gating, advancing our understanding of RyR1-mediated Ca2+ release in conditions associated with oxidative stress and muscle weakness.

DOI: https://doi.org/10.1085/jgp.202313515
Exp Physiol. 2024 Nov 05.

Acute high-intensity muscle contraction moderates AChR gene expression independent of rapamycin-sensitive mTORC1 pathway in rat skeletal muscle.

Yuhei Makanae, Satoru Ato, Karina Kouzaki, Yuki Tamura, Koichi Nakazato.

  The relationship between mechanistic target of rapamycin complex 1 (mTORC1) activation after resistance exercise and acetylcholine receptor (AChR) subunit gene expression remains largely unknown. Therefore, we aimed to investigate the effect of electrical stimulation-induced intense muscle contraction, which mimics acute resistance exercise, on the mRNA expression of AChR genes and the signalling pathways involved in neuromuscular junction (NMJ) maintenance, such as mTORC1 and muscle-specific kinase (MuSK). The gastrocnemius muscle of male adult Sprague-Dawley rats was isometrically exercised. Upon completion of muscle contraction, the rats were euthanized in the early (after 0, 1, 3, 6 or 24 h) and late (after 48 or 72 h) recovery phases and the gastrocnemius muscles were removed. Non-exercised control animals were euthanized in the basal state (control group). In the early recovery phase, Agrn gene expression increased whereas LRP4 decreased without any change in the protein and gene expression of AChR gene subunits. In the late recovery phase, Agrn, Musk, Chrnb1, Chrnd and Chrne gene expression were altered and agrin and MuSK protein expression increased. Moreover, mTORC1 and protein kinase B/Akt-histone deacetylase 4 (HDAC) were activated in the early phase but not in the late recovery phase. Furthermore, rapamycin, an inhibitor of mTORC1, did not disturb changes in AChR subunit gene expression after muscle contraction. However, rapamycin addition slightly increased AChR gene expression, while insulin did not impact it in rat L6 myotube. These results suggest that changes in the AChR subunits after muscle contraction are independent of the rapamycin-sensitive mTORC1 pathway.

Keywords:  acetylcholine receptor; mTORC1; muscle contraction

DOI:  https://doi.org/10.1113/EP091006
Sci Rep. 2024 11 02. 14(1): 26437

Temporal variation in p38-mediated regulation of DUX4 in facioscapulohumeral muscular dystrophy.

Rajanikanth Vangipurapu, Jonathan Oliva, Amelia Fox, Francis M Sverdrup.

  Facioscapulohumeral muscular dystrophy (FSHD) is a degenerative muscle disease caused by loss of epigenetic silencing and ectopic reactivation of the embryonic double homeobox protein 4 gene (DUX4) in skeletal muscle. The p38 MAP kinase inhibitor losmapimod is currently being tested in FSHD clinical trials due to the finding that p38 inhibition suppresses DUX4 expression in preclinical models. However, the role of p38 in regulating DUX4 at different myogenic stages has not been investigated. We used genetic and pharmacologic tools in FSHD patient-derived myoblasts/myocytes to explore the temporal role of p38 in differentiation-induced DUX4 expression. Deletion of MAPK14/11 or inhibition of p38α/β caused a significant reduction in early differentiation-dependent increases in DUX4 and DUX4 target gene expression. However, in MAPK14/11 knockout cells, there remains a differentiation-associated increase in DUX4 and DUX4 target gene expression later in differentiation. Furthermore, pharmacologic inhibition of p38α/β only partially decreased DUX4 and DUX4 target gene expression in late differentiating myotubes. In xenograft studies, p38α/β inhibition by losmapimod failed to suppress DUX4 target gene expression in late FSHD xenografts. Our results show that while p38 is critical for DUX4 expression during early myogenesis, later in myogenesis a significant level of DUX4 expression is independent of p38α/β activity.

Keywords:  CRISPR knockout; FSHD; Facioscapulohumeral muscular dystrophy; Losmapimod; p38-dependent and independent myogenic regulation and DUX4 expression

DOI:  https://doi.org/10.1038/s41598-024-77911-8
Proc Natl Acad Sci U S A. 2024 Nov 12. 121(46): e2405020121

Dilated cardiomyopathy-associated skeletal muscle actin (ACTA1) mutation R256H disrupts actin structure and function and causes cardiomyocyte hypocontractility.

Ankit Garg, Silvia Jansen, Lina Greenberg, Rui Zhang, Kory J Lavine, Michael J Greenberg.

  Skeletal muscle actin (ACTA1) mutations are a prevalent cause of skeletal myopathies consistent with ACTA1's high expression in skeletal muscle. Rare de novo mutations in ACTA1 associated with combined cardiac and skeletal myopathies have been reported, but ACTA1 represents only ~20% of the total actin pool in cardiomyocytes, making its role in cardiomyopathy controversial. Here we demonstrate how a mutation in an actin isoform expressed at low levels in cardiomyocytes can cause cardiomyopathy by focusing on a unique ACTA1 variant, R256H. We previously identified this variant in a family with dilated cardiomyopathy, who had reduced systolic function without clinical skeletal myopathy. Using a battery of multiscale biophysical tools, we show that R256H has potent effects on ACTA1 function at the molecular scale and in human cardiomyocytes. Importantly, we demonstrate that R256H acts in a dominant manner, where the incorporation of small amounts of mutant protein into thin filaments is sufficient to disrupt molecular contractility, and that this effect is dependent on the presence of troponin and tropomyosin. To understand the structural basis of this change in regulation, we resolved a structure of R256H filaments using cryoelectron microscopy, and we see alterations in actin's structure that have the potential to disrupt interactions with tropomyosin. Finally, we show that ACTA1R256H/+ human-induced pluripotent stem cell cardiomyocytes demonstrate reduced contractility and sarcomeric organization. Taken together, we demonstrate that R256H has multiple effects on ACTA1 function that are sufficient to cause reduced contractility and establish a likely causative relationship between ACTA1 R256H and clinical cardiomyopathy.

Keywords:  actin; cardiomyopathy; contractility; muscle

DOI:  https://doi.org/10.1073/pnas.2405020121
Gene. 2024 Oct 26. pii: S0378-1119(24)00929-6. [Epub ahead of print] 149048

C2C12 myoblasts differentiate into myofibroblasts via the TGF-β1 signaling pathway mediated by Fibulin2.

Yongqiang Yang, Lei Li, Jun Fei, Zhong Li.

  Myoblast cells play a critical role in the regeneration of skeletal muscle following injury. It has been reported that local elevation of transforming growth factor-β1(TGF-β1) after skeletal muscle injury induces differentiation of myoblast cells into myofibroblasts.However, the mechanisms underlying this differentiation process remain incompletely understood. In this study, we found that Fibulin2 expression significantly increases in myoblast cells in response to TGF-β1 stimulation.Elevated Fibulin2 levels enhance the expression of fibrotic markers, mediated through phosphorylation of Smad2.Conversely, downregulation of Fibulin2 in myoblast cells inhibits the upregulation of fibrotic markers induced by TGF-β1 stimulation.Extracellular secretion of Fibulin2 activates the TGF-β1-Smad2 pathway, thereby promoting the upregulation of fibrotic markers.Hence, Fibulin2 and TGF-β1 form a positive feedback loop that facilitates differentiation of myoblast cells into myofibroblasts.

Keywords:  C2C12 myoblasts; Fibulin2; Myofibroblasts; TGF-β1

DOI:  https://doi.org/10.1016/j.gene.2024.149048
J Sport Health Sci. 2024 Oct 25. pii: S2095-2546(24)00161-3. [Epub ahead of print] 101003

Massive sarcomerogenesis in human skeletal muscle following long-term eccentric exercise intervention.

Heiliane de Brito Fontana, Walter Herzog.

DOI: https://doi.org/10.1016/j.jshs.2024.101003
Am J Physiol Regul Integr Comp Physiol. 2024 Nov 04.

Post-exercise hot-water immersion is not effective for ribosome biogenesis in rat skeletal muscle.

Takaya Kotani, Yuki Tamura, Karina Kouzaki, Kazushige Sasaki, Koichi Nakazato.

  Ribosome biogenesis is an important regulator of skeletal muscle hypertrophy induced by repeated bouts of resistance exercise (RE). Hot-water immersion (HWI), a widely used post-exercise recovery strategy, activates the mechanistic target of rapamycin (mTOR) signaling, a key regulator of ribosome biogenesis in skeletal muscle. However, the effect of HWI on skeletal muscle ribosome biogenesis is not well understood. Here, we aimed to investigate the effects of HWI and post-exercise HWI on ribosome biogenesis using a rat RE model. Male Sprague-Dawley rats were randomly assigned to HWI and non-HWI groups. In both groups, the right leg was isometrically exercised using transcutaneous electrical stimulation, while the left leg was used as an internal non-RE control. Following RE, both limbs were immersed in hot water (41.2 ± 0.03℃) for 20 min under isoflurane anesthesia in the HWI group and the gastrocnemius muscles were sampled at 3 and 24 h post-exercise. HWI significantly increased mTOR signaling and c-Myc mRNA expression, whereas post-exercise HWI significantly increased transcription initiation factor-IA mRNA expression. However, neither HWI nor post-exercise HWI enhanced 45S pre-rRNA expression, ribosomal RNA, or ribosomal protein content. Additionally, HWI tended to decrease 28S rRNA and 18S rRNA content, widely used markers of ribosome content. These results suggest that HWI as a post-exercise recovery is not effective in activating ribosome biogenesis.

Keywords:  heat stress; mechanistic target of rapamycin signaling; resistance exercise; ribophagy; skeletal muscle hypertrophy

DOI:  https://doi.org/10.1152/ajpregu.00068.2024
Front Pharmacol. 2024 ;15 1467620

Sodium danshensu modulates skeletal muscle fiber type formation and metabolism by inhibiting pyruvate kinase M1.

Yunxia Zhang, Xiaoxiao Wu, Ruoqi Li, Mengru Sui, Guoyin Li, Shuhua Fan, Mingsheng Yang, Qiuping Liu, Xiaomeng Liu, Changjing Wu, Lili Li.

  Sodium Danshensu (SDSS) is extracted from Salvia miltiorrhiza and has many pharmacological effects. However, little is known about its effects on muscle fiber formation and metabolism. Here, we aimed to investigated the role and molecular mechanisms of SDSS in modulating the formation of skeletal muscle fiber. C2C12 cells were incubated in differentiation medium with or without SDSS for 4 days. C57BL/6 mice were orally administered SDSS by gavage once a day for 8 weeks. Grip strength, treadmill, muscle weight, western blotting, qPCR, immunofluorescence staining and H&E staining were performed. SDSS target proteins were searched through drug affinity responsive target stability (DARTS) and mass spectrometry analysis. Furthermore, molecular docking was carried out for Pyruvate kinase M1 (PKM1). The effect of PKM1 on myosin heavy chain (MyHCs) gene expression was verified by knockdown of PKM1 experiment. SDSS induced oxidative muscle fiber-related gene expression, and inhibited glycolytic fiber-related gene expression in C2C12 cells. Muscle mass, the percentage of slow oxidative fibers, succinic dehydrogenase activity, muscle endurance, glucose tolerance, and the expression of the MyHC1 and MyHC2a genes increased while MyHC2b expression, lactate dehydrogenase activity, and the percentage of glycolytic muscle fibers decreased in SDSS-treated mice. Mechanistically, SDSS bound to the pyruvate kinase PKM1 and significantly repressed its activity. PKM1 inhibited MyHC1 and MyHC2a expression but promoted MyHC2b expression. SDSS also significantly attenuated the effects of PKM1 on muscle fiber-related gene expression in C2C12 cells. Our findings indicate that SDSS promotes muscle fiber transformation from the glycolytic type to the oxidative type by inhibiting PKM1 activity, which provide a new idea for treating muscle atrophy, muscle metabolism diseases and improving animal meat production.

Keywords:  MyHCs; muscle fiber; muscle metabolism; pyruvate kinase; sodium danshensu

DOI:  https://doi.org/10.3389/fphar.2024.1467620
SLAS Discov. 2024 Oct 26. pii: S2472-5552(24)00052-2. [Epub ahead of print] 100190

Magnetic 3D bioprinting of skeletal muscle spheroid for a spheroid-based screening assay.

Chayanit Chaweewannakorn, Khin The Nu Aye, Joao N Ferreira.

  Over the past decade, there has been a rapid development in the use of magnetic three dimensional (3D) based cell culture systems. Concerning the skeletal muscle, 3D culture systems can provide biological insights for translational clinical research in the fields of muscle physiology and metabolism. These systems can enhance the cell culture environment by improving spatially-oriented cellular assemblies and morphological features closely mimicking the in vivo tissues/organs, since they promote strong interactions between cells and the extracellular matrix (ECM). However, the time-consuming and complex nature of 3D traditional culture techniques pose a challenge to the widespread adoption of 3D systems. Herein, a bench protocol is presented for creating an innovative, promptly assembled and user-friendly culture platform for the magnetic 3D bioprinting of skeletal muscle spheroids. Our protocol findings revealed consistent morphological outcomes and the functional development of skeletal muscle tissue, as evidenced by the expression of muscle-specific contractile proteins and myotubes and the responsiveness to stimulation with cholinergic neurotransmitters. This proof-of-concept protocol confirmed the future potential for further validation and application of spheroid-based assays in human skeletal muscle research.

Keywords:  3D cell culture; bioprinting; magnetic; nanoparticles; skeletal muscle

DOI:  https://doi.org/10.1016/j.slasd.2024.100190
Front Pharmacol. 2024 ;15 1450513

Effects of cannabidiol on AMPKα2 /HIF-1α/BNIP3/NIX signaling pathway in skeletal muscle injury.

Zhiquan Hou, Zhifang Wang, Jun Zhang, Yunen Liu, Zhonghua Luo.

  Cannabidiol: (CBD) is a non-psychoactive natural active ingredient from cannabis plant, which has many pharmacological effects, including neuroprotection, antiemetic, anti-inflammatory and anti-skeletal muscle injury. However, the mechanism of its effect on skeletal muscle injury still needs further research. In order to seek a scientifically effective way to combat skeletal muscle injury during exercise, we used healthy SD rats to establish an exercise-induced skeletal muscle injury model by treadmill training, and systematically investigated the effects and mechanisms of CBD, a natural compound in the traditional Chinese medicine Cannabis sativa L., on combating skeletal muscle injury during exercise. CBD effectively improved the fracture of skeletal muscle tissue and reduced the degree of inflammatory cell infiltration. Biochemical indexes such as CK, T, Cor, LDH, SOD, MDA, and GSH-Px in serum of rats returned to normal. Combining transcriptome and network analysis results, CBD may play a protective role in exercise-induced skeletal muscle injury through HIF-1 signaling pathway. The experimental results implied that CBD could down-regulate the expression of IL-6, NF-κB, TNF-α, Keap1, AMPKα2, HIF-1α, BNIP3 and NIX, and raised the protein expression of IL-10, Nrf2 and HO-1. These results indicate that the protective effect of CBD on exercise-induced skeletal muscle injury may be related to the inhibition of oxidative stress and inflammation, thus inhibiting skeletal muscle injury through AMPKα2/HIF-1α/BNIP3/NIX signal pathways.

Keywords:  cannabidiol; exercise-induced skeletal muscle injury; inflammation; oxidative stress; transcriptome sequencing

DOI:  https://doi.org/10.3389/fphar.2024.1450513
J Nutr Health Aging. 2024 Nov 05. pii: S1279-7707(24)00496-2. [Epub ahead of print]28(12): 100408

Mitochondrial quality control measures, systemic inflammation, and lower-limb muscle power in older adults: a PROMPT secondary analysis.

Helio José Coelho-Junior, Emanuele Marzetti, Casey L Sexton, Kevin Wu, Robert Mankowski, Stephen D Anton, Christiaan Leeuwenburgh, Anna Picca.

   OBJECTIVES: The study was conducted to explore associations between markers of mitochondrial quality control (MQC) from vastus lateralis muscle biopsies, serum inflammatory markers, and measures of muscle power assessed by two different tools in a sample of older adults.
DESIGN: Secondary analysis of data collected in the PeppeR develOpMental ProjecT (PROMPT) at the University of Florida (Gainesville, FL, USA).
METHODS: Forty-three older adults (n = 20 women) were included in the study. Muscle volume of the calf and thigh was quantified by three-dimensional magnetic resonance imaging. Lower-limb muscle power was estimated using 5-time sit-to-stand (5STS) muscle power equations and isokinetic test. Protein markers of MQC were measured in muscle samples by Western immoblotting (n = 12-23), while type I and II fiber cross-sectional area (CSA) and their proportion were quantified using immunohistochemistry (n = 12). Cytochrome C oxidase enzyme activity was measured spectrophotometrically. Finally, inflammatory markers were quantified in the serum using a multiplex immunoassay (n = 39).
RESULTS: Mean age of participants was 78.1 ± 5.5 years, and the average body mass index was 26.2 ± 4.5 kg/m2. Markers of mitochondrial biogenesis (i.e., PGC-1α), mitochondrial import proteins (i.e., cHsp70 and mtHsp70), and type I fiber CSA were significantly associated with muscle power estimated via both 5STS muscle power equations and isokinetic test (p < 0.05). Specific associations were also found according to the muscle power assessment method. 5STS muscle power measures were negatively correlated with ClvCasp3, P-AMPK, T-AMPK, P-p38, GM-CSF, INF-γ, IL1b, IL6, IL8, and TNF-α, whereas positive associations were found with BAX (p < 0.05). In contrast, isokinetic measures were significantly and positively correlated with RIP140, Hsp60, and type II muscle fiber CSA (p < 0.05).
CONCLUSIONS: Markers of mitochondrial biogenesis (PGC-1α), mitochondrial import proteins (cHsp70 and mtHsp70), and type I muscle fiber CSA were significantly linked to lower-limb muscle power in older adults. These results suggest that muscle power is influenced by mitochondrial signaling. We also found that the relationship between mitochondrial mediators, inflammatory markers, and muscle power varied according to the assessment tool used.

Keywords:  Apoptosis; Inflammaging; Mitochondria; Muscle aging; Physical performance; Sarcopenia

DOI:  https://doi.org/10.1016/j.jnha.2024.100408
STAR Protoc. 2024 Nov 01. pii: S2666-1667(24)00589-6. [Epub ahead of print]5(4): 103424

Protocol for muscle fiber type and cross-sectional area analysis in cryosections of whole lower mouse hindlimbs.

Edmund Battey, Matthieu Dos Santos, Dipsikha Biswas, Pascal Maire, Kei Sakamoto.

  We outline a protocol to visualize all mouse lower hindlimb skeletal muscles simultaneously. We describe procedures for orientating the whole lower hindlimb in gum tragacanth prior to freezing, simplifying the proceeding experimental steps, and enhancing the comprehensiveness of characterizations. We then detail steps for quantifying muscle fiber size and fiber type characteristics in a single cryosection using histochemistry and immunofluorescence. This protocol can be applied to histological and (immuno)histochemical evaluations such as muscle regeneration, fibrosis, enzymatic activity, and glycogen content.

Keywords:  Cell Biology; Cell isolation; Cell separation/fractionation; Metabolism; Microscopy; Model Organisms; Molecular Biology

DOI:  https://doi.org/10.1016/j.xpro.2024.103424
Front Physiol. 2024 ;15 1473241

The combined influences of local heat application and resistance exercise on the acute mRNA response of skeletal muscle.

Mark L McGlynn, Alejandro M Rosales, Christopher W Collins, Dustin R Slivka.

   Introduction: The development and maintenance of the skeletal muscle is crucial for the support of daily function. Heat, when applied locally, has shown substantial promise in the maintenance of the muscle. The purpose of this study was to determine the combined effects of local heat application and acute resistance exercise on gene expression associated with the human muscle growth program.
Materials and methods: Participants (n = 12, 26 ± 7 years, 1.77 ± 0.07 m, 79.6 ± 15.4 kg, and 16.1 ± 11.6 %BF) completed an acute bilateral bout of resistance exercise consisting of leg press (11 ± 2 reps; 170 ± 37 kg) and leg extension (11 ± 1 reps; 58 ± 18 kg). Participants wore a thermal wrap containing circulating fluid (40°C, exercise + heat; EX + HT) during the entire experimental period and 4 h post-exercise, while the other leg served as an exercise-only (EX) control. Biopsies of the vastus lateralis were collected (Pre, Post, and 4hPost) for gene expression analyses.
Results: Intramuscular temperatures increased (Post, +2.2°C ± 0.7°C, and p < 0.001; 4hPost, +2.5°C ± 0.6°C, and p < 0.001) and were greater in the EX + HT leg post-exercise (+0.35°C ± 0.3°C, and p = 0.005) and after 4hPost (+2.1°C ± 0.8°C and p < 0.001). MYO-D1 mRNA was greater in the EX + HT leg vs. the EX (fold change = 2.74 ± 0.42 vs. 1.70 ± 0.28, p = 0.037). No other genes demonstrated temperature sensitivity when comparing both legs (p > 0.05). mRNA associated with the negative regulator, myostatin (MSTN), decreased post-exercise (p = 0.001) and after 4 h (p = 0.001). mRNA associated with proteolysis decreased post-exercise (FBXO32, p = 0.001; FOXO3a, p = 0.001) and after 4 h (FBXO32, p = 0.001; FOXO3a, p = 0.027).
Conclusion: The elevated transcription of the myogenic differentiation factor 1 (MYO-D1) after exercise in the heated condition may provide a mechanism by which muscle growth could be enhanced.

Keywords:  gene expression; myogenic; myogenic differentiation factor 1; myogenin; myostatin; proteolytic

DOI:  https://doi.org/10.3389/fphys.2024.1473241
J Cachexia Sarcopenia Muscle. 2024 Nov 07.

Comment on 'Diagnosis of Sarcopenia by Evaluating Skeletal Muscle Mass by Adjusted Bioimpedance Analysis Validated With Dual-Energy X-Ray Absorptiometry' by Cheng et al.

Hyunjee Kim.

DOI: https://doi.org/10.1002/jcsm.13587
Sci Rep. 2024 11 06. 14(1): 27011

Direct conversion of urine-derived cells into functional motor neuron-like cells by defined transcription factors.

Hiroaki Nagai, Masayo Saito, Hidehisa Iwata.

  Direct cell-type conversion of somatic cells into cell types of interest has garnered great attention because it circumvents rejuvenation and preserves the hallmarks of cellular aging (unlike induced pluripotent stem cells [iPSCs]) and is more suitable for modeling diseases with strong age-related and epigenetic contributions. Fibroblasts are commonly used for direct conversion; however, obtaining these cells requires highly invasive skin biopsies. Urine-derived cells (UDCs) are an alternative cell source and can be obtained via noninvasive procedures. Herein, induced motor neuron-like cells (iMNs) were generated from UDCs by transducing transcription factors involved in motor neuron (MN) differentiation. iMNs exhibited neuronal morphology, upregulation of pan-neuron and MN markers, and MN functionality, including spontaneous calcium oscillation and bungarotoxin-positive neuromuscular junction formation, when co-cultured with myotubes. Altogether, the findings of this study indicated that UDCs can be converted to functional MNs. This technology may allow us to understand disease pathogenesis and progression and discover biomarkers and drugs for MN-related diseases at the population level.

Keywords:  Direct conversion; Direct reprogramming; Motor neurons; Urine-derived cells

DOI:  https://doi.org/10.1038/s41598-024-73759-0
Eur J Sport Sci. 2024 Nov 05.

Flywheel resistance training promotes unique muscle architectural and performance-related adaptations in young adults.

Nile F Banks, Alexander C Berry, Emily M Rogers, Nathaniel D M Jenkins.

  The purpose of this study was to examine the skeletal muscle hypertrophic, architectural, and performance-related adaptations in response to volume-matched, total-body flywheel versus traditional resistance training in a randomized, non-exercise controlled study in physically active young adults. Thirty-one healthy young adults (24 ± 3 y) were randomized to 10 weeks of traditional resistance training (TRT; n = 7F/5M), flywheel training (FWRT; n = 7F/4M), or a habitual activity control (CON; n = 5F/3M). Maximal voluntary isometric torque (MVIT), one repetition-maximum (1RM) for the free weight squat and bench press, three repetition work maximum (3Wmax) for the flywheel squat and bench press, countermovement jump height, and broad jump distance, as well as site-specific muscle hypertrophy, fascicle length (FL), and pennation angle, were measured. Both TRT and FWRT increased MVIT (p ≤ 0.021) and FFM (p ≤ 0.032) compared to CON. However, TRT promoted superior improvements in free weight squat and bench 1RM (p < 0.001), and FWRT improved flywheel 3Wmax squat and bench (p < 0.001). FWRT increased the FL and cross-sectional area of the distal VL, countermovement jump height, and broad jump distance (p ≤ 0.048), whereas TRT increased the pennation angle and cross-sectional area of the proximal VL. Therefore, 10 weeks of volume-matched, total-body traditional, and flywheel resistance training similarly increased maximal isometric strength and fat-free mass. However, FWRT promoted unique skeletal muscle architectural adaptations that likely contributed to region-specific VL hypertrophy and jump performance improvements. Thus, FWRT provides a novel training stimulus that promotes architectural adaptations that support improved athletic performance in a manner that is not provided by traditional resistance exercise training.

Keywords:  countermovement jump; isoinertial exercise; muscle hypertrophy; muscle plasticity; resistance exercise

DOI:  https://doi.org/10.1002/ejsc.12215
J Physiol. 2024 Nov 04.

Motor unit adaptation to disuse: crossing the threshold from firing rate suppression to neuromuscular junction transmission.

Mathew Piasecki.

  Neural conditioning to scenarios of muscle disuse is undoubtedly a cause of functional decrements that typically exceed losses of muscle size. Yet establishing the relative contribution of neural adaptation and the specific location in the motor pathway remains technically challenging. Several studies of healthy humans have targeted this system and have established that motor unit firing rate is suppressed following disuse, with a number of critical caveats. It is suppressed in the immobilized limb only, at relative and absolute force levels, and preferentially targets lower-threshold motor units. Concomitantly, electrophysiological investigation of neuromuscular junction transmission (NMJ) stability of lower-threshold motor units reveals minimal change following disuse. These findings contrast with numerous other methods, which show clear involvement of the NMJ but are unable to characterize the motor unit to which they belong. It is physiologically plausible that decrements observed following disuse are a result of suppressed firing rate of lower-threshold motor units and impairment of transmission of the NMJ of higher-threshold motor units. As such, motor units within the pool should be viewed in light of their varying susceptibility to disuse.

Keywords:  disuse; firing rate; motoneuron; neuromuscular junction

DOI:  https://doi.org/10.1113/JP284159