bims-moremu 2025-04-20 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2025–04–20
thirty-two papers selected by
Anna Vainshtein, Craft Science Inc.

NOR-1 Overexpression Elevates Myoglobin Expression via PERM1 and Enhances Mitochondrial Function and Endurance in Skeletal Muscles of Aged Mice.
HDAC11 deficiency regulates age-related muscle decline and sarcopenia.
Melatonin and Exercise Restore Myogenesis and Mitochondrial Dynamics Deficits Associated With Sarcopenia in iMS-Bmal1-/- Mice.
Modelling Skeletal Muscle Ageing and Repair In Vitro.
AAV capsids target muscle-resident cells with different efficiencies-A comparative study between AAV8, AAVMYO, and AAVMYO2.
RNF138 regulates skeletal muscle differentiation via the Wnt/β-catenin signaling pathway.
Krüppel-like factor 5 remodels lipid metabolism in exercised skeletal muscle.
Loss of popdc3 Impairs Mitochondrial Function and Causes Skeletal Muscle Atrophy and Reduced Swimming Ability in Zebrafish.
Consecutive skeletal muscle PGC-1α overexpression: A double-edged sword for mitochondrial health in the aging brain.
Mitochondrial Dynamics: Deciphering the Role of HDL-C in Regulating Mitochondrial Function and Fatty Acid Oxidation in Human Skeletal Muscle.
HD6277 Suppresses Muscle Atrophy by Promoting Myogenic Factors and Inhibiting Proteolysis in Aged Mice.
The role of microRNAs in dexamethasone-induced skeletal muscle atrophy.
Immunoproteasome subunit PSMB8 promotes skeletal muscle regeneration by regulating macrophage phenotyping switch in mice.
A Novel Research Paradigm for Sarcopenia of Limb Muscles: Lessons From the Perpetually Working Diaphragm's Anti-Aging Mechanisms.
The mechanism of EGF in promoting skeletal muscle post-injury regeneration.
Parp3 assists muscle function and skeletal muscle differentiation by selectively adjusting H3K27me3 enrichment.
Sex-specific skeletal muscle gene expression responses to exercise reveal novel direct mediators of insulin sensitivity change.
Systemic effect of combined functional overload and endurance-type swimming exercise on whole-body metabolism in mice.
A genetic variant in SMAD7 acts as a modifier of LMNA-associated muscular dystrophy, implicating SMAD signaling as a therapeutic target.
Resistance exercise-induced circulating factors influence the damaged skeletal muscle proteome in a sex-dependent manner.
DNA hypermethylation preceded by H3K27 trimethylation is linked to downregulation of gene expression in disuse muscle atrophy in male mice.
Human skeletal muscle mitochondrial pathways are impacted by a neuropathologic diagnosis of Alzheimer's disease.
Myosin relaxation states in skeletal muscle fibers of rats and mice: Effects of sex and adiposity.
L-Arginine Activates the Neuregulin-1/ErbB Receptor Signaling Pathway and Increases Utrophin mRNA Levels in C2C12 Cells.
Quantitative measurement of morphometric indicators of skeletal muscle cell behaviour and quality.
Submaximal eccentric training during immobilization does not prevent serial sarcomere loss or impairments in mechanical function in old or young rats.
ATM knock out alters calcium signalling and augments contraction in skeletal muscle cells differentiated from human urine-derived stem cells.
An Update on Reported Variants in the Skeletal Muscle α-Actin (ACTA1) Gene.
Housing Temperature Impacts the Systemic and Tissue-Specific Molecular Responses to Cancer in Mice.
GL261 glioblastoma induces delayed body weight gain and stunted skeletal muscle growth in young mice.
Role of IL-16 in age-related skeletal muscle atrophy: an integrated study.
Autophagy, ER-phagy and ER dynamics during cell differentiation.

FASEB J. 2025 Apr 30. 39(8): e70542

NOR-1 Overexpression Elevates Myoglobin Expression via PERM1 and Enhances Mitochondrial Function and Endurance in Skeletal Muscles of Aged Mice.

Hector G Paez, Christopher R Pitzer, Peter J Ferrandi, Junaith S Mohamed, Stephen E Alway.

  Skeletal muscle health and function deteriorate with age, ultimately leading to impaired mobility and disability. Exercise is among the most effective interventions to mitigate muscle dysfunction in aging and reverse deficits. However, low attrition and an impaired capacity to exercise may limit its utility in improving muscle function in aged persons. Therefore, it is crucial to advance our mechanistic understanding of the molecular transducers of exercise to identify new and innovative drug targets to improve muscle health. Transcriptomic profiling of the human response to exercise has revealed that the nuclear receptor NR4A3 (NOR-1) is among the most responsive genes to acute exercise. Previously, we observed that in vitro knockdown of NOR-1 alters metabolic signaling in C2C12 myotubes. Specifically, we found that expression of PERM1, CKMT2, myoglobin, and mTORC1 signaling were perturbed during the knockdown of NOR-1. Herein, we extend these findings and observe that a NOR-1-PERM1-myoglobin axis regulates myoglobin expression in vitro. Furthermore, we found that aging is associated with reduced skeletal muscle NOR-1 expression. Although it is well known that exercise improves aged muscle function, whether overexpression of the exercise-responsive gene NOR-1 can confer benefits and improve muscle function in an aged context has not been evaluated. We found that the overexpression of NOR-1 in aged muscle results in enhanced muscle endurance, mitochondrial respiration, and elevated expression of NOR-1 responsive genes that we previously identified in loss of function studies. However, we also observed that overexpression of NOR-1 did not improve maximal muscle torque production and resulted in a small but significant loss of muscle wet weight that was concomitant with elevated autophagy signaling. Our data suggest that NOR-1 expression may reduce muscle fatigability and that NOR-1 drives myoglobin expression in a PERM1-dependent manner.

Keywords:  aging; autophagy; fatigue; mitochondria; muscle

DOI:  https://doi.org/10.1096/fj.202500375R
Geroscience. 2025 Apr 12.

HDAC11 deficiency regulates age-related muscle decline and sarcopenia.

Renato Odria, Aina Cardús, Clara Gomis-Coloma, Marta Balanyà-Segura, Alexandra Mercado-Amarilla, Pau Maestre-Mora, Andrea Poveda-Sabuco, Joan Carles Domingo, Gisela Nogales-Gadea, Jose A Gomez-Sanchez, Erica Hurtado, Mònica Suelves.

  Sarcopenia, defined as the progressive loss of skeletal muscle mass and function associated with ageing, has devastating effects in terms of reducing the quality of life of older people. Muscle ageing is characterised by muscle atrophy and decreased capacity for muscle repair, including a reduction in the muscle stem cell pool that impedes recovery after injury. Histone deacetylase 11 (HDAC11) is the newest member of the HDAC family and it is highly expressed in skeletal muscle. Our group recently showed that genetic deficiency in HDAC11 increases skeletal muscle regeneration, mitochondrial function and globally improves muscle performance in young mice. Here, we explore for the first time the functional consequences of HDAC11 deficiency in old mice, in homeostasis and during muscle regeneration. Aged mice lacking HDAC11 show attenuated muscle atrophy and postsynaptic fragmentation of the neuromuscular junction, but no significant differences in the number or diameter of myelinated axons of peripheral nerves. Maintenance of the muscle stem cell reservoir and advanced skeletal muscle regeneration after injury are also observed. HDAC11 depletion enhances mitochondrial fatty acid oxidation and attenuates age-associated alterations in skeletal muscle fatty acid composition, reducing drastically the omega-6/omega-3 fatty acid ratio and improving significantly the omega-3 index, providing an explanation for improved muscle strength and fatigue resistance and decreased mortality. Taken together, our results point to HDAC11 as a new target for the treatment of sarcopenia. Importantly, selective HDAC11 inhibitors have recently been developed that could offer a new therapeutic approach to slow the ageing process.

Keywords:  Fatty acid oxidation; HDAC11; Muscle atrophy; Omega-6/omega-3 fatty acid ratio; Sarcopenia; Skeletal muscle regeneration

DOI:  https://doi.org/10.1007/s11357-025-01611-y
J Pineal Res. 2025 Apr;77(3): e70049

Melatonin and Exercise Restore Myogenesis and Mitochondrial Dynamics Deficits Associated With Sarcopenia in iMS-Bmal1-/- Mice.

Yolanda Ramírez-Casas, José Fernández-Martínez, María Martín-Estebané, Paula Aranda-Martínez, Alba López-Rodríguez, Sergio Esquivel-Ruiz, Yang Yang, Germaine Escames, Darío Acuña-Castroviejo.

  Sarcopenia, a condition associated with aging, involves progressive loss of muscle mass, strength, and function, leading to impaired mobility, health, and increased mortality. The underlying mechanisms remain unclear, which limits the development of effective therapeutic interventions. Emerging evidence implicates chronodisruption as a key contributor to sarcopenia, emphasizing the role of Bmal1, a circadian clock gene critical for muscle integrity and mitochondrial function. In a skeletal muscle-specific and inducible Bmal1 knockout model (iMS-Bmal1-/-), we observed hallmark features of sarcopenia, including disrupted rhythms, impaired muscle function, and mitochondrial dysfunction. Exercise and melatonin treatment reversed these deficits independently of Bmal1. Building on these findings, the present study elucidates several mechanisms underlying these changes and the pathways by which melatonin and exercise exert their beneficial effects. Our findings indicate that iMS-Bmal1-/- mice exhibit reduced expression of satellite cell and muscle regulatory factors, indicating impaired muscle regeneration. While mitochondrial respiration remained unchanged, notable alterations in mitochondrial dynamics disrupted mitochondria in skeletal muscle. In addition, these mice showed alterations in muscle energy metabolism, compromised antioxidant defense, and inflammatory response. Remarkably, exercise and/or melatonin successfully mitigated these deficits, restoring muscle health in Bmal1-deficient mice. These findings position exercise and melatonin as promising therapeutic candidates for combating sarcopenia and emphasize the need to elucidate the molecular pathways underlying their protective effects.

Keywords:  Bmal1; exercise; melatonin; mitochondrial dysfunction; myogenesis; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.1111/jpi.70049
J Tissue Eng Regen Med. 2023 ;2023 9802235

Modelling Skeletal Muscle Ageing and Repair In Vitro.

Janelle Tarum, Hans Degens, Mark D Turner, Claire Stewart, Craig Sale, Lívia Santos.

Healthy skeletal muscle can regenerate after ischaemic, mechanical, or toxin-induced injury, but ageing impairs that regeneration potential. This has been largely attributed to dysfunctional satellite cells and reduced myogenic capacity. Understanding which signalling pathways are associated with reduced myogenesis and impaired muscle regeneration can provide valuable information about the mechanisms driving muscle ageing and prompt the development of new therapies. To investigate this, we developed a high-throughput in vitro model to assess muscle regeneration in chemically injured C2C12 and human myotube-derived young and aged myoblast cultures. We observed a reduced regeneration capacity of aged cells, as indicated by an attenuated recovery towards preinjury myotube size and myogenic fusion index at the end of the regeneration period, in comparison with younger muscle cells that were fully recovered. RNA-sequencing data showed significant enrichment of KEGG signalling pathways, PI3K-Akt, and downregulation of GO processes associated with muscle development, differentiation, and contraction in aged but not in young muscle cells. Data presented here suggest that repair in response to in vitro injury is impaired in aged vs. young muscle cells. Our study establishes a framework that enables further understanding of the factors underlying impaired muscle regeneration in older age.

DOI: https://doi.org/10.1155/2023/9802235
Mol Ther Methods Clin Dev. 2025 Jun 12. 33(2): 101451

AAV capsids target muscle-resident cells with different efficiencies-A comparative study between AAV8, AAVMYO, and AAVMYO2.

Timothy J McGowan, Nicolas Lewerenz, Eleonora Maino, Marco Thürkauf, Lena Jörin, Markus A Rüegg.

  Adeno-associated viruses (AAVs) of different serotypes are commonly used in gene therapies and gene interrogation studies to deliver transgenes to skeletal muscle in humans and mice. While efficient muscle fiber transduction is possible, little is known of their capacity to transduce muscle-residing mononuclear cells. Here, we addressed this question for AAV8 and the two myotropic AAVs, AAVMYO and AAVMYO2, by engineering them to express the tdTomato gene. AAVs were then injected intramuscularly or intravenously at two different doses into adult mice followed by flow-cytometry-based isolation of endothelial cells, immune cells, muscle stem cells, and fibro-adipogenic progenitor cells from the tibialis anterior muscle. Overall, we noted varying rates of tdTomato expression across all cell types. Transduction efficiency fluctuated in AAV serotype-dependent, titer-dependent, administration-dependent, and cell-dependent manners. By visualizing AAV DNA in vivo, we confirmed that AAV8, AAVMYO, and AAVMYO2 deliver transgenes to muscle-residing mononuclear cells. We show that mononuclear cells are also successfully transduced in the dy W /dy W mouse model of LAMA2-related muscular dystrophy. Altogether, we demonstrate that muscle-residing mononuclear cells are transduced by AAVs and provide an insightful guidance for researchers aiming to target muscle-resident mononuclear cells in their studies.

Keywords:  AAV; AAV8; AAVMYO; AAVMYO2; endothelial cells; fibro-adipogenic progenitor cells; gene therapy; immune cells; muscle stem cells; skeletal muscle

DOI:  https://doi.org/10.1016/j.omtm.2025.101451
Theranostics. 2025 ;15(10): 4446-4464

RNF138 regulates skeletal muscle differentiation via the Wnt/β-catenin signaling pathway.

Wenhao Wang, Zhuohua Wang, Rourong Li, Weiyi Huang, Qiao Ling, Xiaoxiao Li, Zan Li, Manqi Cao, Zhihui Zhang, Qingrong Sun, Zhijuan Liang, Hua-An Zhang, Xuan Jiang, Chuwen Lin, Yaoqing Chen, Bo Zhao, Yu Zhao, Ji-An Pan, Xiaoxue Peng.

  Rationale: Myogenesis is a strictly regulated process driven by signaling pathways activating muscle-specific gene expression. During myogenesis, muscle stem cells exhibit DNA damage response (DDR) features, which are essential for myoblast differentiation and skeletal muscle regeneration. However, the specific roles of DDR-associated proteins in these processes are not yet fully understood. Methods: Gene knockdown and knockout were used in cell and animal models to study RNF138's function in myoblast differentiation and skeletal muscle regeneration. Multi-omics profiling, including transcriptomics and proteomics, was conducted to identify the key proteins regulated by RNF138 in myogenesis. Protein turnover assays were utilized to investigate RNF138's role in APC protein turnover. Immunofluorescence microscopy was performed to confirm the protein colocalization and subcellular localization. Results: RNF138 expression increases during myoblast differentiation and in regenerating myofibers following muscle injury. Knockdown of RNF138 in C2C12 myoblasts impairs myogenic differentiation and fusion. Additionally, Rnf138-deficient mice exhibit delayed muscle regeneration following cardiotoxin-induced injury. Multi-omics profiling, including transcriptomics and proteomics, reveals that Wnt/β-catenin signaling, a key driver of myogenic differentiation, is enhanced by RNF138. Mechanistically, RNF138 stabilizes β-catenin and enhances its nuclear localization by facilitating lysosomal degradation of APC, a component of the β-catenin degradation complex responsible for mediating the export of β-catenin from the nucleus to the cytoplasm for further ubiquitin-proteasome degradation. Conclusions: We reveal a noncanonical role for RNF138, an E3 ubiquitin ligase, as a positive regulator of myoblast differentiation and skeletal muscle regeneration via the Wnt/β-catenin pathway. This finding highlights the noncanonical function of RNF138 beyond its known roles in DDR and other cellular processes. Therefore, RNF138 provides a potential link between DDR and myoblast differentiation, offering new insights into the molecular regulation of muscle regeneration.

Keywords:  RNF138; Wnt/β-catenin; adenomatous polyposis coli; skeletal muscle differentiation

DOI:  https://doi.org/10.7150/thno.110925
Mol Metab. 2025 Apr 16. pii: S2212-8778(25)00061-4. [Epub ahead of print] 102154

Krüppel-like factor 5 remodels lipid metabolism in exercised skeletal muscle.

Konstantin Schneider-Heieck, Joaquín Pérez-Schindler, Jonas Blatter, Laura M de Smalen, Wandrille Duchemin, Stefan A Steurer, Bettina Karrer-Cardel, Danilo Ritz, Christoph Handschin.

  Regular physical activity induces a variety of health benefits, preventing and counteracting diseases caused by a sedentary lifestyle. However, the molecular underpinnings of skeletal muscle plasticity in exercise remain poorly understood. We identified a role of the Krüppel-Like Factor 5 (Klf5) in this process, in particular in the regulation of lipid homeostasis. Surprisingly, gain- and loss-of-function studies in muscle in vivo revealed seemingly opposite functions of Klf5 in the response to an acute exercise bout and chronic training, modulating lipid oxidation and synthesis, respectively. Thus, even though only transiently induced, the function of Klf5 is complex and fundamental for a normal long-term training response. These findings highlight the importance of this mediator of external stress response to adaptive remodeling of skeletal muscle tissue.

Keywords:  Klf5; exercise; lipid metabolism; skeletal muscle; stress response; transcriptional regulation

DOI:  https://doi.org/10.1016/j.molmet.2025.102154
J Cachexia Sarcopenia Muscle. 2025 Apr;16(2): e13794

Loss of popdc3 Impairs Mitochondrial Function and Causes Skeletal Muscle Atrophy and Reduced Swimming Ability in Zebrafish.

Chen-Chen Sun, Zhang-Lin Chen, Dong Yang, Jiang-Ling Xiao, Xiang-Tao Chen, Xi-Yang Peng, Xiu-Shan Wu, Chang-Fa Tang.

   BACKGROUND: The Popeye domain containing 3 (POPDC3) protein is essential for the maintenance of skeletal muscle homeostasis. POPDC3 is a pathogenic variant gene of limb-girdle muscular dystrophy (LGMD), and its variants lead to LGMDR26. At the animal level, zebrafish larvae with popdc3 mutations develop tail curls and muscle atrophy. However, the mechanism of skeletal muscle atrophy induced by POPDC3 variants/loss remains unclear.
METHODS: Eight-month-old male WT and popdc3 mKO zebrafish were used for this research. Loli Track (Denwmark) and Loligo Swimming Respirometer were used to observe the zebrafish's swimming ability. The zebrafish skeletal muscle structure and cross-sectional area (CSA) were observed and counted by transmission electron microscopy (TEM), H&E and wheat germ agglutinin (WGA). Enriched genes and signalling pathways were analysed using RNA sequencing, and the effects of popdc3 mKO on zebrafish skeletal muscle mitochondrial respiration, biogenesis and dynamics were examined to investigate possible mechanisms.
RESULTS: The swimming ability of popdc3 mKO zebrafish was reduced, and as evidenced by the reluctance to move, fewer movement trajectories, the total distance travelled (p < 0.001), the average velocity of movement (p < 0.001), oxygen consumption (MO2) (p < 0.01), maximum oxygen consumption (MO2max) (p < 0.05), critical swimming speed (Ucrit) (p < 0.01) and relative swimming speed (Ucrit-r) (p < 0.01) were significantly decreased and increased of the exhaustive swimming time (p < 0.01). In addition, loss of popdc3 reduced zebrafish skeletal muscle weight (p < 0.001), muscle/body weight (p < 0.01), myofibre size and CSA (p < 0.01), increased protein degradation (ubiquitination and autophagy) (p < 0.05) and decreased protein synthesis (p < 0.05), suggesting that popdc3 deficiency induces zebrafish skeletal muscle atrophy. Further, popdc3 mKO zebrafish mitochondrial function is reduced, as evidenced by impaired mitochondrial respiration, decreased biogenesis and kinetic imbalance (p < 0.05).
CONCLUSIONS: POPDC3, a Popeye protein, plays an important role in controlling mitochondrial function and skeletal muscle mass and strength. Loss of popdc3 decreases mitochondrial respiration and mitochondrial biogenesis, disrupting kinetic homeostasis, which induces mitochondrial dysfunction and impaired protein turnover (reduced synthesis and increased degradation), leading to zebrafish skeletal muscle atrophy.

Keywords:  POPDC3; mitochondrial dysfunction; protein homeostasis; skeletal muscle atrophy; skeletal muscle mass

DOI:  https://doi.org/10.1002/jcsm.13794
Biochim Biophys Acta Mol Basis Dis. 2025 Apr 12. pii: S0925-4439(25)00196-6. [Epub ahead of print]1871(6): 167851

Consecutive skeletal muscle PGC-1α overexpression: A double-edged sword for mitochondrial health in the aging brain.

Lei Zhou, Soroosh Mozaffaritabar, Erika Koltai, Smaragda Giannopoulou, Attila Kolonics, Yaodong Gu, Ricardo A Pinho, Ildiko Miklossy, Istvan Boldogh, Zsolt Radák.

  Mitochondrial dysfunction is a critical contributor to age-related functional declines in skeletal muscle and brain. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is essential for mitochondrial biogenesis and function during aging. While skeletal muscle-specific overexpression of PGC-1α is known to mimic exercise-induced benefits in young animals, its chronic systemic effects on aging tissues remain unclear. This study aimed to determine the lifelong impact of skeletal muscle-specific PGC-1α overexpression on mitochondrial health, oxidative stress, inflammation, and cognitive function in aged mice. We established three experimental groups: young wild-type mice (3-4 months old), aged wild-type mice (25-27 months old), and aged mice with skeletal muscle-specific PGC-1α overexpression (24-27 months old). In skeletal muscle, aging led to significant reductions in mitochondrial biogenesis markers, including PGC-1α, FNDC5, and mtDNA content. PGC-1α overexpression reversed this decline, elevating the expression of PGC-1α, SIRT1, LONP1, SDHA, CS, TFAM, eNOS, and mtDNA levels, suggesting preserved mitochondrial biogenesis. However, FNDC5 and SIRT3 were paradoxically suppressed, indicating potential compensatory feedback mechanisms. PGC-1α overexpression also enhanced anabolic signaling, as evidenced by increased phosphorylation of mTOR and S6, and reduced FOXO1 expression, favoring a muscle growth-promoting environment. Moreover, aging impaired mitochondrial dynamics by downregulating MFN1, MFN2, OPA1, FIS1, and PINK1. While PGC-1α overexpression did not restore fusion-related proteins, it further reduced fission-related protein and enhanced mitophagy proteins, as evidenced by increased PINK1 phosphorylation. In contrast, in the hippocampus, muscle-specific PGC-1α overexpression exacerbated age-associated mitochondrial biogenesis decline. Expression levels of key mitochondrial markers, including PGC-1α, SIRT1, CS, FNDC5, Cytochrome C, and TFAM, were further reduced compared to aged wild-type controls. mTOR phosphorylation was also significantly suppressed, whereas cognition-related proteins (BDNF, VEGF, eNOS) and performance in behavioral tests remained unchanged. Importantly, skeletal muscle-specific PGC-1α overexpression triggered pronounced oxidative stress and inflammatory responses in both skeletal muscle and the hippocampus. In skeletal muscle, elevated levels of protein carbonyls, IκB-α, NF-κB, TNF-α, SOD2, and NRF2 were observed, accompanied by a reduction in the DNA repair enzyme OGG1. Notably, similar patterns were detected in the hippocampus, including increased expression of protein carbonyls, iNOS, NF-κB, TNF-α, SOD2, GPX1, and NRF2, alongside decreased OGG1 levels. These findings suggest that the overexpression of PGC-1α in skeletal muscle may have contributed to systemic oxidative stress and inflammation. In conclusion, skeletal muscle-specific PGC-1α overexpression preserves mitochondrial biogenesis and enhances anabolic signaling in aging muscle but concurrently induces oxidative stress and inflammatory responses, which may adversely affect mitochondrial health in the brain. These results emphasize the complex role of the skeletal muscle PGC-1α during aging.

Keywords:  Aging; Hippocampus; Inflammation; Mitochondrial biogenesis; Oxidative stress; PGC-1α; Skeletal muscle

DOI:  https://doi.org/10.1016/j.bbadis.2025.167851
Am J Physiol Heart Circ Physiol. 2025 Apr 15.

Mitochondrial Dynamics: Deciphering the Role of HDL-C in Regulating Mitochondrial Function and Fatty Acid Oxidation in Human Skeletal Muscle.

Mauricio Castro-Sepulveda, Francesca Amati.

  XXXX.

Keywords:  Mitochondria; cholesterol; metabolism; physiology; skeletal muscle

DOI:  https://doi.org/10.1152/ajpheart.00219.2025
J Cachexia Sarcopenia Muscle. 2025 Apr;16(2): e13805

HD6277 Suppresses Muscle Atrophy by Promoting Myogenic Factors and Inhibiting Proteolysis in Aged Mice.

Joo Won Kim, SukHwan Yun, Min Jeong Park, Eyun Song, Sooyeon Jang, Ahreum Jang, Kyung Mook Choi, Sei Hyun Baik, Hwan-Jin Hwang, Hye Jin Yoo.

   BACKGROUND: G protein-coupled receptor 40 (GPR40) acts as a modulator of various physiological functions, including glycaemic lowering, anti-inflammation and antioxidative stress, in several tissues. However, the role of GPR40 in skeletal muscles remains unclear.
METHODS: To investigate the roles of muscle GPR40, C2C12 myoblasts and myotubes were stimulated with palmitate and HD6277, a GPR40 agonist. Muscle strength and myofiber thickness were measured in obese and aged mice fed HD6277.
RESULTS: In C2C12 myoblasts, the addition of HD6277 induced phosphorylated Akt levels and expression of the myogenic factors, myogenin (MyoG), myocyte enhancer factor 2C (Mef2c) and myosin heavy chain (MyHC, p < 0.05). These changes resulted in accelerated muscle differentiation from myoblasts to myotubes (MyHC-positive area +56.52%; myotube width +34.08% vs. Veh, p < 0.05). In C2C12 myotubes, a palmitate-mediated decrease in the phosphorylation of forkhead box protein O1A (FOXO1A) and increase in the expression of E3 ubiquitin ligases, atrogin-1 and muscle RING-finger protein 1 (MuRF1) were reversed by HD6277 (p < 0.05). Additionally, HD6277 inhibited palmitate-induced apoptotic events such as the Bcl-2 (Bcl2)-associated X protein (Bax)/Bcl-2 ratio, caspase 3 cleavage and nuclear fragmentation in C2C12 myoblasts and myotubes (p < 0.05). These beneficial HD6277-mediated actions disappeared after the addition of an Akt inhibitor (p < 0.05). Similar to in vitro studies, HD6277 administration in obese and aged mice increased myogenic factors and decreased E3 ubiquitin ligase expression and apoptotic events (p < 0.05). HD6277 increased muscle strength (+9.88% vs. Aged, p < 0.05) and myofiber thickness (+29.01% vs. Aged, p < 0.05) in aging mice but only improved myofiber thickness (+11.84% vs. HFD, p < 0.05) in obese mice.
CONCLUSION: HD6277 can increase myogenic factors and reduce E3 ligase-mediated proteolysis to inhibit muscle atrophy in aged mice. Our results suggest that GPR40 agonists may have potential as therapeutic agents for sarcopenia.

Keywords:  GPR40; muscle atrophy; myoblast; myogenic factors; myotube; sarcopenia

DOI:  https://doi.org/10.1002/jcsm.13805
Exp Gerontol. 2025 Apr 16. pii: S0531-5565(25)00078-6. [Epub ahead of print] 112749

The role of microRNAs in dexamethasone-induced skeletal muscle atrophy.

Subi Ren, Jie Chai, Lijuan Zhang, JiGang Li, Xi Long, Tinghuan Zhang.

  Muscle atrophy is characterized by a decrease in muscle mass, strength, and activity. Recently, it was determined that microRNAs (miRNAs) can regulate muscle atrophy and that dexamethasone (Dex), an allergy and autoimmune disorder treatment that can induce muscle atrophy. Therefore, this study was designed to identify miRNAs expressed in Dex-induced muscle atrophy in mice using small RNA sequencing. A total of 820 miRNAs were identified, with 58 miRNAs expressed explicitly in atrophic muscles. Dex-induced muscle atrophy miRNAs clustered separately from the differential miRNAs in aging, disuse, and cancer-induced muscle atrophy models. The target genes of Dex-induced muscle atrophy miRNAs were independently enriched in inositol phosphate metabolism, hypoxia-inducible factor-1 signaling pathway, etc. Of note, there was a significant increase in the volume of fat cells and adipose weight in the Dex group, suggesting that fat deposition during Dex-induced skeletal muscle atrophy is a unique and typical feature. SIMPLE SUMMARY: Dexamethasone (Dex) is a glucocorticoid used to treat allergic and autoimmune diseases, but excessive use can lead to skeletal muscle atrophy. We used dexamethasone (Dex) to build a muscle atrophy model in mice, and obvious changes had taken place in mouse body weight, muscle tissue morphology and related genes. A large number of microRNAs were found to be differentially expressed, and their functions were enriched in pathways related to muscle development. At the same time, we compared the similarities and differences of microRNAs and their functions between Dex induced muscle atrophy model and other muscle atrophy models. Finally, we were surprised to find that Dex induced muscle atrophy is specifically accompanied by the accumulation of body fat.

Keywords:  Dexamethasone; Lipid deposition; Muscle atrophy; microRNAs

DOI:  https://doi.org/10.1016/j.exger.2025.112749
Am J Physiol Cell Physiol. 2025 Apr 16.

Immunoproteasome subunit PSMB8 promotes skeletal muscle regeneration by regulating macrophage phenotyping switch in mice.

Yanhong Zhang, Shiyao Hong, Fan Zhang, Kexin Yao, Shuhui Jin, Shijuan Gao, Yan Liu, Yulin Li, Congcong Zhang.

  Immunoproteasomes regulate the degradation of ubiquitin-coupled proteins and cell differentiation. However, its precise role in skeletal muscle regeneration remains unclear. In this study, we found that expression of the immunoproteasome subunit PSMB8 increased significantly in young muscles after cardiotoxin-induced injury, whereas its expression was downregulated in injured aged mice. Genetic knockout or pharmacological inhibition of the immunoproteasome subunit PSMB8 resulted in impaired muscle regeneration, and increased interstitial fibrosis. PSMB8 inhibition by siRNA or inhibitor decreased the differentiation ability of myoblasts. There was increased infiltration of inflammatory cells, especially Ly6Chi pro-inflammatory macrophages, in Psmb8 deficient muscles. In vitro, Psmb8 deficient macrophages expressed higher levels of pro-inflammatory cytokines and lower levels of anti-inflammatory cytokines after phagocytosis of myoblast debris, which was associated with increased activation of the NF-κB signaling pathway. Inhibition of the NF-κB pathway improves the regeneration ability and attenuates interstitial fibrosis in Psmb8 deficient muscles after injury. The overexpression of Psmb8 by adenovirus could also improve the regenerative ability of aged muscles.

Keywords:  Immunoproteasome; inflammation; macrophage; muscle regeneration; myoblast fusion; phagocytosis

DOI:  https://doi.org/10.1152/ajpcell.00965.2024
J Cachexia Sarcopenia Muscle. 2025 Apr;16(2): e13797

A Novel Research Paradigm for Sarcopenia of Limb Muscles: Lessons From the Perpetually Working Diaphragm's Anti-Aging Mechanisms.

Enhui Li, Rui Wang, Yanli Li, Xiang Zan, Shufen Wu, Yiru Yin, Xiaorong Yang, Litian Yin, Yu Zhang, Jianguo Li, Xin Zhao, Ce Zhang.

   BACKGROUND: Skeletal muscle function and mass continuously decrease during aging. Most studies target limb muscles owing to their direct impact on mobility and falls risk. The diaphragm (DIA), also a type of skeletal muscle with different phenotype, has received less attention. Comparative research of the DIA and limb muscles can reveal their distinct aging characteristics. Critically, the potential endogenous anti-aging mechanisms of DIA that may provide new insights into the mechanisms of sarcopenia in limb muscles remain scarce.
METHODS: Treadmill and grip tests assessed limb muscle function, while a lung function system evaluated respiratory function in both adult (6-month-old) and old (22-month-old) mice. Histological assessments evaluated muscle mass in both the DIA and tibialis anterior (TA). Transcriptome sequencing identified differentially expressed genes (DEGs) between the DIA and TA with aging. Adeno-associated virus (AAV)-encoding short hairpin (sh) RNA targeting gene was injected into adult mice's TA muscles to knockdown target gene level in TA, and AAV-gene was injected into old mice's TA to overexpress target gene level.
RESULTS: Old mice displayed significantly reduced running distance (p = 0.0026), maximal speed (p = 0.0019), time to exhaustion (p = 0.0033) and grip strength (p = 0.0055) compared with adult mice, alongside TA's weight loss, decreased myofibre cross-sectional area (CSA) and autophagy deficiency. However, lung function indicators (respiratory rate, tidal volume, minute ventilation volume, forced vital capacity and ratio of forced expiratory volume in 100 or 200 ms to forced vital capacity), as well as DIA weight and morphology remained stable in old mice. Transcriptional analysis revealed 61 DEGs, with significant upregulation or downregulation observed in TA, but without changes in DIA during aging. Smox (spermine oxidase) is one of the DEGs, responsible for catalysing the conversion of spermine to spermidine. It was reported that in muscle atrophy models such as limb immobilisation, fasting and denervation, Smox's levels are positively correlated with muscle mass and function. Additionally, an increase in Smox also promotes mitochondrial biogenesis. In our study, AAV-shSmox adult mice decreased running distance, speed and time, myofibre CSA alongside mitochondrial function, compared with controls. In contrast, old mice with Smox overexpression showed enhanced mitochondrial function.
CONCLUSIONS: In conclusion, this study reveals aging diversities of TA and DIA, explores the sarcopenia of limb muscles based on the anti-aging properties of DIA, which offers a novel perspective on limb sarcopenia. Our findings suggest Smox as a potential target for developing strategies to mitigate sarcopenia progression.

Keywords:   Smox ; aging; diaphragm; limb skeletal muscles; sarcopenia; transcriptome

DOI:  https://doi.org/10.1002/jcsm.13797
Differentiation. 2025 Apr 07. pii: S0301-4681(25)00029-5. [Epub ahead of print]143 100862

The mechanism of EGF in promoting skeletal muscle post-injury regeneration.

Huaixin Teng, Yongze Liu, Ruotong Hao, Lu Zhang, Xiaoyu Zhang, Shufeng Li, Shuang Li, Huili Tong.

  Epidermal Growth Factor (EGF) is a multifunctional cytokine that plays an important role in the growth and development of skeletal muscle. In this study, a mouse skeletal muscle post-injury regeneration model and the C2C12 myoblasts cell line were used to elucidate the molecular mechanism by which EGF promotes myoblast proliferation and differentiation and then improves skeletal muscle post-injury regeneration. EGF regulates the activities of p38-MAPK and PI3K/AKT/mTOR signaling pathways through the Epidermal Growth Factor Receptor (EGFR), thereby promoting the proliferation and differentiation of myoblasts. This finding will support the treatment of skeletal muscle injury, which is of great value in resolving muscle health problems such as muscular atrophy and sarcopenia.

Keywords:  Differentiation; EGF; Proliferation; Regeneration; Skeletal muscle

DOI:  https://doi.org/10.1016/j.diff.2025.100862
iScience. 2025 Apr 18. 28(4): 112267

Parp3 assists muscle function and skeletal muscle differentiation by selectively adjusting H3K27me3 enrichment.

Zuleyha Yildirim, Aurélia Noll, Kathline Martin-Hernandez, Jean-Christophe Amé, Najat Hanini, Nadia Messaddeq, Isabelle Robert, Bernardo Reina San Martin, Gunn Hildrestrand, Magnar Bjoras, Françoise Dantzer.

  Poly(ADP-ribose) polymerase 3 (Parp3) is known for its role in DNA repair, mitotic division, and cancer aggressiveness. Still, its physiological roles have yet to be defined. Here, we combined in vivo studies using Parp3-deficient mice with in cellulo studies to explore the involvement of Parp3 in skeletal muscle function and muscle differentiation. We show that Parp3 contributes to skeletal muscle integrity and promotes myogenic differentiation. Mechanistically, we show that Parp3 promotes the enrichment of the repressive histone mark H3K27me3 onto a panel of selected genes. For some genes, Parp3 also helps the binding of Ezh2, the histone methyltransferase that catalyzes H3K27me3. Moreover, Parp3 ADP-ribosylates Ezh2 in vitro. Altogether, these findings unveil Parp3 as a driver of efficient murine skeletal myogenesis in vitro and muscle function in young adults, and highlight an epigenetic control of gene expression.

Keywords:  Cell biology; Epigenetics; Model organism; Molecular mechanism of gene regulation; Molecular network

DOI:  https://doi.org/10.1016/j.isci.2025.112267
NAR Mol Med. 2025 Apr;2(2): ugaf010

Sex-specific skeletal muscle gene expression responses to exercise reveal novel direct mediators of insulin sensitivity change.

Sisi Ma, Monica J Hubal, Matthew C Morris, Leanna M Ross, Kim M Huffman, Christopher G Vann, Nadia Moore, Elizabeth R Hauser, Akshay Bareja, Rong Jiang, Eric Kummerfeld, Matthew D Barberio, Joseph A Houmard, William C Bennett, Johanna L Johnson, James A Timmons, Gordon Broderick, Virginia B Kraus, Constantin F Aliferis, William E Kraus.

Understanding how exercise improves whole-body insulin sensitivity (Si) involves complex molecular signaling. This study examines skeletal muscle gene expression changes related to Si, considering sex differences, exercise amount, and intensity to identify pharmacologic targets mimicking exercise benefits. Fifty-three participants from STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise) I and II completed eight months of aerobic training. Gene expression was assessed via Affymetrix and Illumina technologies, and Si was measured using intravenous glucose tolerance tests. A novel discovery protocol integrating literature-derived and data-driven modeling identified causal pathways and direct transcriptional targets. In women, exercise amount primarily influenced transcription factor targets, which were generally inhibitory, while in men, exercise intensity drove activating targets. Common transcription factors included ATF1, CEBPA, BACH2, and STAT1. Si-related transcriptional targets included TACR3 and TMC7 for intensity-driven effects, and GRIN3B and EIF3B for amount-driven effects. Two key pathways mediating Si improvements were identified: estrogen signaling and protein kinase C (PKC) signaling, both converging on the epidermal growth factor receptor (EGFR) and other relevant targets. The molecular pathways underlying Si improvements varied by sex and exercise parameters, highlighting potential skeletal muscle-specific drug targets such as EGFR to replicate the metabolic benefits of exercise.

DOI: https://doi.org/10.1093/narmme/ugaf010
Am J Physiol Endocrinol Metab. 2025 Apr 18.

Systemic effect of combined functional overload and endurance-type swimming exercise on whole-body metabolism in mice.

Takanaga Shirai, Kazuki Uemichi, Ryoto Iwai, Hayato Shinkai, Tomohiro Iwata, Riku Tanimura, Shunsuke Sugiyama, Tohru Takemasa.

  In this study, we examined the effects of concurrent functional overload and endurance exercise on muscle hypertrophy, mitochondrial function, and systemic adaptations in male mice. The mice were assigned to three groups: Sham (Sham), overload-induced hypertrophy (OL), and overload with concurrent 60-min free swimming (5 time/week) (OL+Swim), over a four-weeks. While OL promoted muscle hypertrophy and protein synthesis through the Akt/mTOR signaling pathway, the addition of swimming (OL+Swim) attenuated these effects, resulting in less pronounced muscle growth and a smaller increase in myofiber cross-sectional area. Notably, the OL+Swim group exhibited enhanced mitochondrial activity and glycogen content compared with the OL group. Both the OL and OL+Swim groups showed elevated rates of protein synthesis, with a significant upregulation of AMPK and PGC-1α in the OL+Swim group, suggesting enhanced mitochondrial biogenesis and adaptation. Concurrent training also resulted in systemic benefits, including reduced inguinal and epididymal white adipocyte size, improved mitochondrial enzyme activities in adipose and liver tissues, and higher levels of FNDC5, FGF21, and BDNF in serum, which contributed to enhanced muscle protein synthesis in cultured muscle cells. These results highlight the trade-offs between muscle hypertrophy and metabolic health in mice and underscore the importance of balanced training regimens to optimize overall metabolic health and muscle function. Our results provide further insight into how concurrent strength and endurance training can be optimized for health and performance benefits.

Keywords:  endurance exercise; hypertrophy; myotenectomy; oxidative metabolism; skeletal muscle; systemic effect

DOI:  https://doi.org/10.1152/ajpendo.00433.2024
Sci Adv. 2025 Apr 18. 11(16): eads7903

A genetic variant in SMAD7 acts as a modifier of LMNA-associated muscular dystrophy, implicating SMAD signaling as a therapeutic target.

Nathaniel P Mohar, Christopher J Langland, Zachary Darr, Jill Viles, Steven A Moore, Benjamin W Darbro, Lori L Wallrath.

Mutations in LMNA cause multiple types of muscular dystrophy (LMNA-MD). The symptoms of LMNA-MD are highly variable and sensitive to genetic background. To identify genetic contributions to this phenotypic variability, we performed whole-genome sequencing on four siblings possessing the same LMNA mutation with differing degrees of skeletal muscle disease severity. We identified a variant in SMAD7 that segregated with severe muscle disease. To functionally test the SMAD7 variant, we generated a Drosophila model possessing the LMNA mutation and the SMAD7 variant in the orthologous fly genes. The SMAD7 variant increased SMAD signaling and enhanced muscle defects caused by the mutant lamin. Conversely, overexpression of wild-type SMAD7 rescued muscle function. These findings were extended to humans by showing that SMAD signaling is increased in muscle biopsy tissue from individuals with LMNA-MD compared to age-matched controls. Collectively, our findings support SMAD7 as the first functionally tested genetic modifier for LMNA-MD and suggest components of the SMAD pathway as therapeutic targets.

DOI: https://doi.org/10.1126/sciadv.ads7903
Physiol Rep. 2025 Apr;13(7): e70291

Resistance exercise-induced circulating factors influence the damaged skeletal muscle proteome in a sex-dependent manner.

Hui-Ying Luk, Danielle E Levitt, Casey R Appell, Nigel C Jiwan.

  Muscle recovery after damage is mediated by circulating factors and intracellular signaling pathways. Our previous studies have demonstrated that resistance exercise (RE)-induced circulating factors elicited sex-differential responses in damaged muscle. However, the global effects of these circulating factors on damaged muscle are largely understudied. We examined the differential effects of RE-induced circulating factors and sex on the damaged muscle proteome. Damaged vastus lateralis muscle from 3 men and 3 women from a parent study were analyzed. Participants completed 2 identical bouts of unilateral eccentric knee extensions immediately followed by either upper body RE to induce circulating factors (EXE) or 20-min seated rest (CON). Muscle biopsies collected from the damaged leg at 24 h were used. 900 proteins were identified by LC-MS/MS analysis. Ingenuity Pathway Analysis was used to detect activation prediction using z-scores for functional and pathway analyses. In men, 79 proteins were downregulated and 15 were upregulated in EXE versus CON. These differentially expressed proteins were associated with immunological and inflammatory signaling pathways. Biological functions of the differentially expressed proteins in EXE vs. CON in men include inactivating acute inflammatory signaling, neutrophil extracellular trap signaling, ROS production, and activating IL-12 signaling. These results underline that RE-induced circulating factors have a sex-specific effect on the damaged muscle proteome, where immune signaling is altered in men but not women. Given that the immune response is critical for recovery from muscle damage, these results highlight the potential role of RE-induced circulating factors that could be essential in mediating muscle recovery.

Keywords:  eccentric exercise; hormones; inflammation; muscle recovery

DOI:  https://doi.org/10.14814/phy2.70291
Physiol Rep. 2025 Apr;13(7): e70317

DNA hypermethylation preceded by H3K27 trimethylation is linked to downregulation of gene expression in disuse muscle atrophy in male mice.

Junya Shimizu, Fuminori Kawano.

  Disuse muscle atrophy can result in downregulated gene expression vital to muscle integrity, yet the mechanisms driving this downregulation remain unclear. Epigenetic alterations regulate transcriptional potential, with repressive changes suppressing gene expression. This study explored epigenetic mechanisms of gene downregulation during disuse muscle atrophy. Male C57BL/6J mice underwent hindlimb suspension for 3 or 7 days. The vastus intermedius (VI) muscle was analyzed, showing unchanged mass on day 3, but on day 7, decreased mass and reduced fiber size were assessed via immunohistochemistry. Corresponding to this atrophy timing, qPCR analysis revealed nine downregulated genes on day 7, which were selected for epigenetic analysis; collectively, they showed no downregulation on day 3. Among the nine genes, methylated DNA immunoprecipitation revealed significantly elevated DNA methylation (hypermethylation) in the upstream regions of transcription start sites (TSS) on day 7, which overall negatively correlated with gene expression. Histone marks (H3K27me3, H3K4me3, H3.3, and total H3) were also assessed using chromatin immunoprecipitation, revealing that the repressive histone mark H3K27me3 increased in the regions on day 3 but decreased on day 7. These findings suggest that DNA hypermethylation in the upstream regions preceded by H3K27me3 enrichment contributes to the downregulation of gene expression during disuse muscle atrophy.

Keywords:  DNA methylation; H3K27me3; disuse muscle atrophy; epigenetic alterations; gene expression

DOI:  https://doi.org/10.14814/phy2.70317
Neurobiol Dis. 2025 Apr 16. pii: S0969-9961(25)00132-9. [Epub ahead of print] 106916

Human skeletal muscle mitochondrial pathways are impacted by a neuropathologic diagnosis of Alzheimer's disease.

Chelsea N Johnson, Mara R Evans, Anneka E Blankenship, Casey S John, Michaella J Rekowski, Michael P Washburn, Andy Phan, Cynthia M Gouvion, Mohammad Haeri, Russell H Swerdlow, Paige C Geiger, Jill K Morris.

  Alzheimer's disease (AD) is associated with reduced lean mass and impaired skeletal muscle mitochondrial and motor function. Although primary mitochondrial defects in AD may underlie these findings, molecular alterations in AD have not been thoroughly examined in human skeletal muscle. Here, we used two human skeletal muscle types, quadriceps (n = 81) and temporalis (n = 66), to compare the proteome of individuals with a neuropathologic AD diagnosis based on AD Neuropathologic Change (ADNPC+: n = 54 temporalis, 44 quadriceps) to controls (ADNPC-: n = 27 temporalis, 22 quadriceps). We determined the effects of ADNPC status within each muscle and within apolipoprotein E4 (APOE4) carriers and APOE4 non-carriers. Pathways that support mitochondrial metabolism, including oxidative phosphorylation, were downregulated in skeletal muscle of ADNPC+ versus ADNPC- individuals. Similar mitochondrial effects were observed across muscle types and APOE4 carrier groups, but nearly four times as many proteins were altered in temporalis versus quadriceps tissue and mitochondrial effects were most pronounced in APOE4 carriers compared to APOE4 non-carriers. Of all detected oxidative phosphorylation proteins, the expression of ~29-61 % (dependent on muscle/APOE4 carrier group) significantly correlated with AD progression, ranked by Clinical Dementia Rating and ADNPC scores. Of these, 23 proteins decreased in expression with greater AD progression in all skeletal muscle type and APOE4 carrier groups. This is the first study to assess differences in the human skeletal muscle proteome in the context of AD. Our work shows that systemic mitochondrial alterations in AD extend to skeletal muscle and these effects are amplified by APOE4 and correlate with AD progression.

Keywords:  APOE4; Alzheimer's disease; Mitochondria; Proteomics; Quadriceps; Skeletal muscle; Temporalis

DOI:  https://doi.org/10.1016/j.nbd.2025.106916
Physiol Rep. 2025 Apr;13(7): e70336

Myosin relaxation states in skeletal muscle fibers of rats and mice: Effects of sex and adiposity.

Zachery A Roloff, Lien A Phung, Luke A Weyrauch, Philip C Woods, Shawna L McMillin, Brian P Sullivan, Rebecca Barok, Naixin Zhang, Katherine A Murphy, Timothy D O'Connell, Brendan J Dougherty, David D Thomas, Mark S Miller, Dawn A Lowe.

  Myosin disordered- and super-relaxed states (DRX and SRX, respectively) in skeletal muscle fibers are hypothesized to play key roles in thermogenesis and basal metabolic energy expenditure, raising potential for novel therapeutic targets for obesity and other metabolic diseases. Limited studies have investigated relationships between body composition or biological sex and myosin relaxed states. Using fluorescence-based single-nucleotide turnover, we report quantitative relationships of diet-induced adiposity and sex with biochemical parameters of myosin relaxed states of rodent muscle fibers. Our main findings were: (1) adiposity had minimal to no effect on parameters of relaxed myosin states measured in fibers from rats and mice, (2) fibers from female rats and mice had 10%-20% shorter SRX lifetimes than those from males (p ≤ 0.035), (3) in rats, females had shorter DRX lifetimes than males, and (4) myosin heavy chain isoform had negligible impact on parameters of relaxed myosin states. We conclude that skeletal muscle energy utilization during rest, as measured by myosin ATPase, is affected minimally by adiposity, but differs by sex. Continued exploration of the metabolic implications of myosin transitioning between SRX and DRX will provide further understanding of muscle thermogenesis and whole-body metabolism; in so doing, sex as a biological factor should be considered.

Keywords:  ATPase; SRX; adiposity; myosin; myosin heavy chain

DOI:  https://doi.org/10.14814/phy2.70336
Biochem Res Int. 2025 ;2025 2171745

L-Arginine Activates the Neuregulin-1/ErbB Receptor Signaling Pathway and Increases Utrophin mRNA Levels in C2C12 Cells.

Gladys Tapia, Sebastián Fuenzalida, Constanza Rivera, Pía Apablaza, Mónica Silva, Enrique Jaimovich, Nevenka Juretić.

  L-arginine induces the expression of utrophin in skeletal muscle cells, so it has been proposed as a pharmacological treatment to attenuate the symptoms of Duchenne muscular dystrophy (DMD). On the other hand, it has been described that one of the pathways that participates in the expression of utrophin in muscle is the Neuregulin-1 (NRG-1)/ErbB receptors pathway. Several studies have postulated that disintegrin and metalloprotease-17 (ADAM17) causes the proteolytic processing of NRG of transmembrane, allowing the release of NRG to the medium, which when joining its ErbB receptor activates the signaling pathway that triggers utrophin transcription. The aim of this study was to evaluate the effect of L-arginine in the activation of NRG-1/ErbB pathway and utrophin mRNA levels in C2C12 cells, and the participation of ADAM17 in this process. Our results indicate that L-arginine induces phosphorylation of ErbB2 and increases utrophin mRNA levels in C2C12 myotubes, with a maximum increase of 2-fold at 4 h post-stimulation. This effect is not observed when the myotubes are stimulated in the presence of GM6001 (general metalloprotease inhibitor) or PD-158780 (specific inhibitor of ErbB receptor phosphorylation). Experiments performed by flow cytometry suggest that L-arginine stimulates ADAM17 activation in our study model. Furthermore, immunofluorescence analysis supports our findings that L-arginine stimulates ADAM17 increase in treated myotubes. However, our results using pharmacological inhibitors suggest that ADAM17 does not participate in utrophin expression in C2C12 cells treated with L-arginine. The results obtained help to clarify the mechanism of action of L-arginine in the expression of utrophin in muscle cells, which will contribute to the design of new therapeutic strategies in pathologies such as DMD.

Keywords:  ADAM17; C2C12; L-arginine; Neuregulin; skeletal muscle

DOI:  https://doi.org/10.1155/bri/2171745
J R Soc Interface. 2025 Apr;22(225): 20240634

Quantitative measurement of morphometric indicators of skeletal muscle cell behaviour and quality.

David Hardman, Katharina Hennig, Inês Belo Martins, William Roman, Edgar R Gomes, Miguel O Bernabeu.

  In vitro culturing of effective human-induced pluripotent stem cell-derived skeletal muscle cells (hiPSC-SMCs) has proven to be challenging. Progress is hindered by the limited range of metrics applied to assess experimental success. We present a semi-automated workflow for segmenting, tracking and quantifying migration and fusion behaviour in live and static images of myoblast and myotube cells. Workflow outputs are validated against manually labelled images and the metrics applied to images from case studies of in vitro cultures of primary mouse muscle cells under varying culture media conditions, mouse primary cells undergoing optogenetic stimulation and hiPSC-SMC. We show culture media-dependent differences in cell fusion dynamics and increased acetylcholine receptors in myonuclei under optogenetic stimulation. We show that myoblasts have greater persistence and proliferation in primary mouse cells than hiPSC, and cell-cell fusion occurred earlier but at a steadier rate in primary mouse cells.

Keywords:  acetylcholine receptor; muscle cell; myonuclei; myotube; quantification

DOI:  https://doi.org/10.1098/rsif.2024.0634
J Gerontol A Biol Sci Med Sci. 2025 Apr 15. pii: glaf082. [Epub ahead of print]

Submaximal eccentric training during immobilization does not prevent serial sarcomere loss or impairments in mechanical function in old or young rats.

Avery Hinks, Ethan Vlemmix, Geoffrey A Power.

  The age-related loss of muscle mass is partly driven by a reduction in serial sarcomere number (SSN), and further SSN loss occurs during immobilization. SSN is associated with optimal force and power production and muscle passive tension, thus immobilization-induced SSN loss is especially a concern for older individuals who are often subjected to forced muscle disuse with illness and injury. We previously showed that submaximal eccentric resistance training increased SSN and improved muscle function in old rats. The present study investigated whether this training could prevent the losses of SSN and function when performed intermittently during immobilization. 10 old (32 months) and 10 young (8 months) rats underwent unilateral casting of the plantar flexors in a shortened position for 2 weeks. Thrice weekly, casts were removed for isokinetic eccentric resistance training. Pre- and post-training we assessed in-vivo maximum isometric torque at ankle angles corresponding to stretched and neutral muscle lengths, the passive torque-angle relationship, and isotonic power. The soleus and medial gastrocnemius were harvested for SSN measurements, with the untrained leg as a control. In old and young rats, muscles of the casted leg had smaller muscle wet weights (20-40%), physiological cross-sectional area (16-20%), and SSN (7-29%) than the control leg. Furthermore, maximum isometric torque (37-46%) and isotonic power (≈70%) decreased, and passive torque increased (+≈400%) from pre- to post-training for both age groups. Thus, irrespective of age, submaximal eccentric resistance training 3 days/week was ineffective for preventing the losses of muscle contractile tissue and mechanical function during casting.

Keywords:  Casting; aging; force-length relationship; passive force; power; sarcomerogenesis

DOI:  https://doi.org/10.1093/gerona/glaf082
Cell Death Discov. 2025 Apr 15. 11(1): 177

ATM knock out alters calcium signalling and augments contraction in skeletal muscle cells differentiated from human urine-derived stem cells.

Giulia Dematteis, Giulia Lecchi, Giulia Boni, Diana Pendin, Carla Distasi, Mariagrazia Grilli, Dmitry Lim, Luigia Grazia Fresu, Maria Talmon.

Ataxia-telangiectasia (A-T) is a rare neurodegenerative disorder caused by the deficiency of the serine/threonine kinase ataxia telangiectasia mutated (ATM) protein, whose loss of function leads to altered cell cycle, apoptosis, oxidative stress balance and DNA repair after damage. The clinical manifestations are multisystemic, among them cerebellar degeneration and muscular ataxia. The molecular mechanism by which ATM loss leads to A-T is still uncertain and, currently only symptomatic treatments are available. In this study, we generated a functional skeletal muscle cell model that recapitulates A-T and highlights the role of ATM in calcium signalling and muscle contraction. To this aim, by using CRISPR/Cas9 technology, we knocked out the ATM protein in urine-derived stem cells (USCs) from healthy donors. The resulting USCs-ATM-KO maintained stemness but showed G2/S cell cycle progression and an inability to repair DNA after UV damage. Moreover, they showed increased cytosolic calcium release after ATP stimulation to the detriment of the mitochondria. The alterations of calcium homoeostasis were maintained after differentiation of USCs-ATM-KO into skeletal muscle cells (USC-SkMCs) and correlated with impaired cell contraction. Indeed, USC-SkMCs-ATM-KO contraction kinetics were dramatically accelerated compared to control cells. These results highlight the relevant function of ATM in skeletal muscle, which is not only dependent on a non-functional neuronal communication, paving the way for future studies on a muscular interpretation of A-T ataxia.

DOI: https://doi.org/10.1038/s41420-025-02485-x
Hum Mutat. 2024 ;2024 6496088

An Update on Reported Variants in the Skeletal Muscle α-Actin (ACTA1) Gene.

Joshua S Clayton, Mridul Johari, Rhonda L Taylor, Lein Dofash, Georgina Allan, Gavin Monahan, Peter J Houweling, Gianina Ravenscroft, Nigel G Laing.

  The ACTA1 gene encodes skeletal muscle alpha-actin, which forms the core of the sarcomeric thin filament in adult skeletal muscle. ACTA1 represents one of six highly conserved actin proteins that have all been associated with human disease. The first 15 pathogenic variants in ACTA1 were reported in 1999, which expanded to 177 in 2009. Here, we update on the now 607 total variants reported in LOVD, HGMD, and ClinVar, which includes 343 reported pathogenic/likely pathogenic (P/LP) variants. We also provide suggested ACTA1-specific modifications to ACMG variant interpretation guidelines based on our analysis of known variants, gnomAD reports, and pathogenicity in other actin isoforms. Using these criteria, we report a total of 447 P/LP ACTA1 variants. From a clinical perspective, the number of reported ACTA1 disease phenotypes has grown from five to 20, albeit with some overlap. The vast majority (74%) of ACTA1 variants cause nemaline myopathy (NEM), but there are increasing numbers that cause cardiomyopathy and novel phenotypes such as distal myopathy. We highlight challenges associated with identifying genotype-phenotype correlations for ACTA1. Finally, we summarize key animal models and review the current state of preclinical treatments for ACTA1 disease. This update provides important resources and recommendations for the study and interpretation of ACTA1 variants.

Keywords:  ACTA1; actin; mutation update; nemaline myopathy; neuromuscular disease; rare disease; variants

DOI:  https://doi.org/10.1155/2024/6496088
J Cachexia Sarcopenia Muscle. 2025 Apr;16(2): e13781

Housing Temperature Impacts the Systemic and Tissue-Specific Molecular Responses to Cancer in Mice.

Andrea Irazoki, Emma Frank, Tang Cam Phung Pham, Jessica L Braun, Amy M Ehrlich, Mark Haid, Fabien Riols, Camilla Hartmann Friis Hansen, Anne-Sofie Rydal Jørgensen, Nicoline Resen Andersen, Laura Hidalgo-Corbacho, Roberto Meneses-Valdes, Mona Sadek Ali, Steffen Henning Raun, Johanne Louise Modvig, Samantha Gallero, Steen Larsen, Zach Gerhart-Hines, Thomas Elbenhardt Jensen, Maria Rohm, Jonas T Treebak, Val Andrew Fajardo, Lykke Sylow.

   BACKGROUND: Cancer cachexia, affecting up to 80% of patients with cancer, is characterized by muscle and fat loss with functional decline. Preclinical research seeks to uncover the molecular mechanisms underlying cachexia to identify potential targets. Housing laboratory mice at ambient temperature induces cold stress, triggering thermogenic activity and metabolic adaptations. Yet, the impact of housing temperature on preclinical cachexia remains unknown.
METHODS: Colon 26 carcinoma (C26)-bearing and PBS-inoculated (Ctrl) mice were housed at standard (ST; 20°C-22°C) or thermoneutral temperature (TN; 28°C-32°C). They were monitored for body weight, composition, food intake and systemic factors. Upon necropsy, tissues were weighed and used for evaluation of ex vivo force and respiration, or snap frozen for biochemical assays.
RESULTS: C26 mice lost 7.5% body weight (p = 0.0001 vs. Ctrls), accounted by decreased fat mass (-35%, p < 0.0001 vs. Ctrls), showing mild cachexia irrespective of housing temperature. All C26 mice exhibited reduced force (-40%, p < 0.0001 vs. Ctrls) and increased atrogene expression (3-fold, p < 0.003 vs. Ctrls). Cancer altered white adipose tissue (WAT)'s functional gene signature (49%, p < 0.05 vs. Ctrls), whereas housing temperature reduced brown adipose tissue (BAT)'s (-78%, p < 0.05 vs. ST Ctrl). Thermogenic capacity measured by Ucp1 expression decreased upon cancer in both WAT and BAT (-93% and -63%, p < 0.0044 vs. Ctrls). Cancer-driven glucose intolerance was noted at ST (26%, p = 0.0192 vs. ST Ctrl), but restored at TN (-23%, p = 0.005 vs. ST C26). Circulating FGF21, GDF-15 and IL-6 increased in all C26 mice (4-fold, p < 0.009 vs. Ctrls), with a greater effect on IL-6 at TN (76%, p = 0.0018 vs. ST C26). Tumour and WAT Il6 mRNA levels remained unchanged, while cancer induced skeletal muscle (SkM) Il6 (2-fold, p = 0.0016 vs. Ctrls) at both temperatures. BAT Il6 was only induced in C26 mice at TN (116%, p = 0.0087 vs. ST C26). At the bioenergetics level, cancer increased SkM SERCA ATPase activity at ST (4-fold, p = 0.0108 vs. ST Ctrl) but not at TN. In BAT, O2 consumption enhanced in C26 mice at ST (119%, p < 0.03 vs. ST Ctrl) but was blunted at TN (-44%, p < 0.0001 vs. ST C26). Cancer increased BAT ATP levels regardless of temperature (2-fold, p = 0.0046 vs. Ctrls), while SERCA ATPase activity remained unchanged at ST and decreased at TN (-59%, p = 0.0213 vs. TN Ctrl).
CONCLUSIONS: In mild cachexia, BAT and SkM bioenergetics are susceptible to different housing temperatures, which influences cancer-induced alterations in glucose metabolism and systemic responses.

Keywords:  bioenergetics; cancer cachexia; cold‐induced stress; thermogenic tissues; thermoneutrality

DOI:  https://doi.org/10.1002/jcsm.13781
Am J Physiol Regul Integr Comp Physiol. 2025 Apr 18.

GL261 glioblastoma induces delayed body weight gain and stunted skeletal muscle growth in young mice.

Joshua R Huot, Nicholas A Jamnick, Fabrizio Pin, Patrick D Livingston, Chandler S Callaway, Andrea Bonetto.

   INTRODUCTION: The survival rate for children and adolescents has increased to over 85%. However, there is limited understanding of the impact of pediatric cancers on muscle development and physiology. Given that brain tumors alone account for 26% of all pediatric cancers, this study aimed to investigate the skeletal muscle consequences of tumor growth in young mice.
METHODS: C2C12 myotubes were co-cultured with GL261 murine glioblastoma cells to assess myotube size. GL261 cells were then injected subcutaneously into 4-week-old male C57BL/6J mice. Animals were euthanized 28 days post-GL261 implantation. Muscle function was tested in vivo and ex vivo. Muscle protein synthesis was estimated via the SUnSET method, and gene/protein expression levels were assessed via Western blotting and qPCR.
RESULTS: In vitro, the C2C12 cultures exposed to GL261 exhibited myotube atrophy, consistent with a disrupted anabolic/catabolic balance. In vivo, carcass, heart, and fat mass were significantly reduced in the tumor-bearing mice. Skeletal muscle growth was impeded in the GL261 hosts, along with smaller muscle CSA. Both in vivo muscle torque and the ex vivo EDL muscle force were unchanged. At molecular level, the tumor hosts displayed reduced estimations of muscle protein synthesis and increased muscle protein ubiquitination, in disagreement with decreased muscle ubiquitin ligase mRNA expression.
CONCLUSIONS: Overall, we showed that GL261 tumors impact the growth of pediatric mice by stunting skeletal muscle development, decreasing muscle mass, reducing muscle fiber size, diminishing muscle protein synthesis, and altering protein catabolism signaling.

Keywords:  animal model; bone; cachexia; cancer; glioblastoma; muscle

DOI:  https://doi.org/10.1152/ajpregu.00035.2025
BMC Musculoskelet Disord. 2025 Apr 17. 26(1): 379

Role of IL-16 in age-related skeletal muscle atrophy: an integrated study.

Wenliang Fan, Zhibang Zhao, Liqiang Wang, Qingbo Chu.

   BACKGROUND: In this study, we aim to explore the roles of IL-16 in sarcopenia based on older orthopedic patients and animal research.
METHODS: This clinical research in this study was an observational investigation and included all the older patients with orthopedic trauma admitted to our department between January 2021 and January 2022. Patients were identified with sarcopenia if they have both low hand grip strength (HGS) and low appendicular skeletal muscle mass (ASM). Propensity score matching (PSM) was performed to reduce the bias caused by the co-factors and levels of IL-16 between normal patients and patients with sarcopenia were compared. In animal research, mice were treated with IL-16 to identify the effects of IL-16 on muscle function and muscle mass. Then the sarcopenia models were established and the anti-IL-16 was performed to identify the potential therapeutical effect of targeting IL-16.
RESULTS: 421 individuals were included in the clinical study, and 77 were identified as sarcopenia. In the matched populations, the serum levels of IL-16 of individuals with low HGS, ASM, and sarcopenia were significantly higher than normal individuals (all p < 0.001). The mice treated with IL-16 showed significantly impaired muscle function and physical performance and loss of muscle mass. Using anti-IL-16 antibodies may rescue the sarcopenia traits caused by botulinum toxin type A.
CONCLUSION: Individuals with high levels of IL-16 may have a significantly high risk of sarcopenia. IL-16 impairs muscle function and physical performance and leads to muscle atrophy in mice, and these effects could be reduced by targeting IL-16.

Keywords:  Cytokines; IL-16; Inflammaging; Muscle atrophy; Sarcopenia

DOI:  https://doi.org/10.1186/s12891-025-08633-9
J Mol Biol. 2025 Apr 11. pii: S0022-2836(25)00217-7. [Epub ahead of print] 169151

Autophagy, ER-phagy and ER dynamics during cell differentiation.

Michele Cillo, Viviana Buonomo, Anna Vainshtein, Paolo Grumati.

  The endoplasmic reticulum (ER) is a multifunctional organelle essential for protein and lipid synthesis, ion transport and inter-organelle communication. It comprises a highly dynamic network of membranes that continuously reshape to support a wide range of cellular processes. During cellular differentiation, extensive remodelling of both ER architecture and its proteome is required to accommodate alterations in cell morphology and function. Autophagy, and ER-phagy in particular, plays a pivotal role in reshaping the ER, enabling cells to meet their evolving needs and adapt to developmental cues. Despite the ER's critical role in cellular differentiation, the mechanisms responsible for regulating its dynamics are not fully understood. Emerging evidence suggests that transcriptional and post-translational regulation play a role in fine-tuning ER-phagy and the unfolded protein response (UPR). This review explores the molecular basis of autophagy and ER-phagy, highlighting their role in ER remodelling during cellular differentiation. A deeper understanding of these processes could open new avenues for targeted therapeutic approaches in conditions where ER remodelling is impaired.

Keywords:  Cell Differentiation; Development; Endoplasmic Reticulum

DOI:  https://doi.org/10.1016/j.jmb.2025.169151