bims-moremu 2025-07-20 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2025–07–20
39 papers selected by
Anna Vainshtein, Craft Science Inc.

Aldehyde Oxidase 1 Deficiency Enhances Aerobic Exercise Performance by Promoting Skeletal Muscle Adaptation and Improving Mitochondrial Function.
Aging in the Skeletal Muscle Revealed by Molecular Immunohistochemical Imaging.
Cellular repressor of E1A-stimulated genes 1 enhances skeletal muscle performance through the stimulation of muscle differentiation and Akt-mTOR signaling pathway activation.
Molecular constraints of sarcopenia in the ageing muscle.
Skeletal muscle stem cell mitochondria are transferred to muscle fibers in response to a hypertrophic stimulus.
An integrative framework linking molecular signatures and locomotory phenotypes in space-induced sarcopenia.
Fibrillin-Related Proteins Control Calcium Homeostasis in Dystrophic Muscle Across Species.
Targeting the canonical ER stress IRE1α/XBP1 pathway counteracts pancreatic cancer-induced skeletal muscle wasting.
A Self-Renewing Biomimetic Skeletal Muscle Construct Engineered using Induced Myogenic Progenitor Cells.
Proteomic and Metabolomic Profiling Nominates Druggable Targets and Biomarkers for Pulmonary Arterial Hypertension-Associated Myopathy and Exercise Intolerance in Male Monocrotaline Rats.
Klotho deficiency promotes skeletal muscle weakness and is associated with impaired motor unit connectivity.
Deletion of Skeletal Muscle Mitochondrial Glutamic-Oxaloacetic Transaminase (GOT2) Enhances Oxaloacetate Inhibition of Succinate Dehydrogenase and Alters Substrate Selectivity.
Distinct systemic metabolic features in limb-girdle muscular dystrophy type R1 mouse models as a potential early pathogenic signature.
Hb-EGF directs systemic muscle repair.
Protective effects of Salubrinal against H2O2-induced muscle wasting via eIF2α/ATF4 signaling pathway.
Intramuscular adipose tissue restricts functional muscle recovery.
Exploring lncRNA-Mediated Mechanisms in Muscle Regulation and Their Implications for Duchenne Muscular Dystrophy.
Time-of-day effects on muscle mitochondria following short-term ablation of satellite cells.
Muscle in Endocrinology: From Skeletal Muscle Hormone Regulation to Myokine Secretion and Its Implications in Endocrine-Metabolic Diseases.
In vitro mechanical stretch inhibits differentiation of mouse myoblast C2C12 cells without sustained eIF2α phosphorylation.
Morphological differences in myofibre size and shape: A comparative study of the soleus, gastrocnemius, triceps brachii and vastus lateralis in humans and mice.
Sirtuin 3 modulation by high phosphates: a potential mechanism in muscle aging and sarcopenia.
Impact of Aerobic Training on Transcriptomic Changes in Skeletal Muscle of Rats with Cardiac Cachexia.
Mutations in Hsp40 co-chaperone change the unique canonical inter-domain interactions stimulating LGMDD1 myopathy.
The titin N2A-MARP signalosome constrains muscle longitudinal hypertrophy in response to stretch.
A systemically deliverable lipid-conjugated siRNA targeting DUX4 as an facioscapulohumeral muscular dystrophy therapeutic.
Combinatory Treatment to Alleviate Cellular Stress and Improve Skeletal Muscle Phenotype in Spinal Muscular Atrophy.
Microalgae empower skeletal muscle via increased force production and viability.
Muscle very long-chain ceramides associate with insulin resistance independently of obesity.
Impact of Mitochondrial A3243G Mutation on Skeletal Muscle Energy Metabolism: Evidence from Human Induced Pluripotent Stem Cell-Derived Skeletal Muscle Cells.
Irisin Prevents the Effects of Simulated Microgravity on Bone and Muscle Differentiation Markers.
ATF3 as a molecular nexus linking ferroptosis regulation to sarcopenia pathogenesis via PI3K/Akt pathway activation.
Menstrual cycle influence on skeletal muscle mitochondrial respiration in humans.
Proteomic aging signatures across mouse organs and life stages.
Inhibition of AhR improves cortical bone and skeletal muscle function via preservation of neuromuscular junctions.
The copper chaperone ATOX1 exhibits differential protein-protein interactions and contributes to skeletal myoblast differentiation.
Tendon's 'first aid' response - new insights into acute tendon molecular reprogramming after rupture.
Eli Lilly in $650M pact to boost muscle.
The insulin-like peptide INS-27 mediates a muscle-to-neuron feedback signal coupling muscle activity with AMPA receptor trafficking.

FASEB J. 2025 Jul 31. 39(14): e70815

Aldehyde Oxidase 1 Deficiency Enhances Aerobic Exercise Performance by Promoting Skeletal Muscle Adaptation and Improving Mitochondrial Function.

Yan Liu, Qi-Quan Wang, Tian-E Huang, Meng Yao, Ben-Hui Wang, Chun-Ping Huang, Shu Wang, Yi-Fan Lu, Xin-Qiang Lan, Xiao-Li Tian, Yang Xiang.

  Aerobic exercise has significant health benefits, including preventing chronic diseases like sarcopenia. It strongly depends on muscle fiber types, with higher oxidative fiber ratios enhancing endurance. However, the molecular mechanisms underlying aerobic exercise capacity remain incompletely understood. In this study, we identified 395 genes associated with muscle fiber types, among which 39 were linked to metabolic pathways. Notably, we focused on aldehyde oxidase 1 (AOX1), a molybdenum flavin enzyme, due to its unique non-mitochondrial localization, suggesting a potential causal role in regulating muscle metabolism. We further revealed a significant downregulation of Aox1 mRNA expression in the skeletal muscle of mice after two weeks of exercise training, indicating its involvement in exercise adaptation. To further explore this link, we generated Aox1 knockout (KO) mice and subjected them to endurance capacity tests. Aox1 KO mice exhibited significantly enhanced exercise endurance compared to wild-type (WT) controls, accompanied by a shift toward a more oxidative muscle phenotype, as indicated by an increased proportion of oxidative fibers. Mechanistically, Aox1 KO mice exhibit increased expression of PGC-1α, enhanced mitochondrial function, and increased capillary density in skeletal muscle, facilitating improved oxygen delivery and utilization during exercise. Additionally, in vitro experiments using C2C12 myotubes revealed that Aox1 knockdown alleviated starvation- and TNF-α-induced muscle atrophy, which partially mimics sarcopenia, highlighting its protective role against aging- and stress-induced muscle damage. These findings identify AOX1 as a negative regulator of aerobic exercise capacity and stress resilience, advancing our understanding of skeletal muscle adaptation and highlighting AOX1 as a potential target for improving exercise performance and mitigating sarcopenia.

Keywords:  AOX1; aerobic exercise; capillary density; mitochondria; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.1096/fj.202500240R
Int J Mol Sci. 2025 Jun 22. pii: 5986. [Epub ahead of print]26(13):

Aging in the Skeletal Muscle Revealed by Molecular Immunohistochemical Imaging.

Manuela Malatesta, Barbara Cisterna.

  The skeletal muscle is a complex organ mainly composed of multinucleated fibres responsible for contractile activity, but it also contains postnatal myogenic stem cells (i.e., satellite cells), connective cells and nervous cells. The skeletal muscle is severely affected by aging, undergoing a progressive reduction in muscle mass, strength and endurance in a condition known as sarcopenia. The mechanisms underlying sarcopenia still need to be completely clarified, but they are undoubtedly multifactorial, involving all cell types constituting the skeletal muscle. Immunohistochemistry has widely been used to investigate skeletal muscle aging, identifying age-related molecular alterations in the various myofibre components, as well as in the satellite cells and peri-fibre environment. The wide range of immunohistochemical data reported in this review is proof of the primary role played by this long-established, yet modern, technique. Its high specificity for the molecules of interest, and the possibility of imaging and quantifying the signal in the real histological or cytological sites where these molecules are located and active, makes immunohistochemistry a unique and irreplaceable tool among the laboratory techniques in biomedicine.

Keywords:  extracellular matrix; immunolabelling; mitochondria; myonuclei; neuromuscular junction; sarcolemma; sarcopenia; sarcoplasmic reticulum; satellite cells; vascularization

DOI:  https://doi.org/10.3390/ijms26135986
PLoS One. 2025 ;20(7): e0328485

Cellular repressor of E1A-stimulated genes 1 enhances skeletal muscle performance through the stimulation of muscle differentiation and Akt-mTOR signaling pathway activation.

Ayumi Goto, Michihiro Hashimoto, Sho Yokogawa, Yuzu Naruse, Hitoshi Yamashita.

Cellular repressor of E1A-stimulated genes 1 (CREG1), a glycoprotein secreted by various cell types, plays a crucial role in cellular differentiation and energy metabolism. While previous research has linked CREG1 deficiency in skeletal muscles to impaired exercise capacity and altered muscle fiber-type composition, its specific role in skeletal muscle function and differentiation remains unclear. In this study, we investigated the impact of CREG1 on muscle performance and fiber-type composition in adipocyte P2-CREG1-transgenic (Tg) mice and explored muscle differentiation in C2C12 myotubes. Tg mice exhibited significantly improved muscle performance compared to wild-type mice, as indicated by enhanced grip strength. Additionally, the proportion of type IIx fiber in the soleus muscle was significantly increased in Tg mice, along with a tendency towards elevated Myh1 mRNA expression. Enhanced CREG1 expression and activation of the Akt-mTOR signaling pathway, which is involved in muscle protein synthesis, were observed in the skeletal muscles of Tg mice. In C2C12 myotubes, Creg1 knockdown appears to decrease myoblast determination protein 1 (Myod1) expression, while recombinant CREG1 treatment restored Myod1 expression and promoted Akt-mTOR phosphorylation. These findings suggest that CREG1 stimulates muscle differentiation by enhancing protein synthesis, thereby influencing skeletal muscle function.

DOI: https://doi.org/10.1371/journal.pone.0328485
Front Aging. 2025 ;6 1588014

Molecular constraints of sarcopenia in the ageing muscle.

S Damanti, E Senini, R De Lorenzo, A Merolla, S Santoro, C Festorazzi, M Messina, G Vitali, C Sciorati, A A Manfredi, P Rovere-Querini.

  Sarcopenia, the age-related loss of skeletal muscle mass, strength, and function, is driven by a convergence of molecular, cellular, hormonal, nutritional, and neurological alterations. Skeletal muscle comprises multinucleated fibers supported by satellite cells-muscle stem cells essential for repair and regeneration. With age, both the structure and function of these components deteriorate: myonuclei become disorganized, gene expression skews toward catabolic, inflammatory, and fibrotic pathways, and satellite cell numbers and activity decline. Concurrently, mitochondrial dysfunction, impaired proteostasis, and vascular rarefaction limit energy availability and regenerative capacity. Neurodegeneration and age-related muscle fibers denervation further exacerbate muscle loss, particularly affecting fast-twitch fibers, and reduce motor unit integrity. These neural deficits, alongside changes at the neuromuscular junction, contribute to functional decline and diminished contractility. Hormonal changes-including reduced levels of growth hormone, testosterone, and IGF-1-undermine anabolic signaling and promote muscle atrophy. Nutritional factors are also pivotal: anorexia of aging and reduced dietary protein intake lead to suboptimal nutrient availability. Compounding this is anabolic resistance, a hallmark of aging muscle, in which higher levels of dietary protein and amino acids are required to stimulate muscle protein synthesis effectively. Physical inactivity and immobility, often secondary to chronic illness or frailty, further accelerate sarcopenia by promoting disuse atrophy. The molecular constraints of sarcopenia are deeply intertwined with non-molecular mechanisms-such as neuromuscular degeneration, hormonal shifts, inadequate nutrition, and reduced physical activity-creating a complex and self-reinforcing cycle that impairs muscle maintenance and regeneration in the elderly. This review synthesizes current evidence on these interconnected factors, highlighting opportunities for targeted interventions to preserve muscle health across the lifespan.

Keywords:  ageing; constraints; molecular mechainsm; muscle; sarcopenia

DOI:  https://doi.org/10.3389/fragi.2025.1588014
Function (Oxf). 2025 Jul 17. pii: zqaf031. [Epub ahead of print]

Skeletal muscle stem cell mitochondria are transferred to muscle fibers in response to a hypertrophic stimulus.

Jensen Goh, Julia G Williams, Sarah E Ogle, Jai K Joshi, Logan N Scott, Benjamin I Burke, Alex R Keeble, Nicholas T Thomas, Christopher S Fry, Ahmed Ismaeel, John J McCarthy.

  The fusion of skeletal muscle stem cell (MuSC) to myofibers during hypertrophy has exclusively focused on the transfer of the MuSC nucleus, leaving the fate of other MuSC organelles, such as mitochondria, largely unexplored. The objective of this study was to determine if MuSCs transfer their mitochondria upon myofiber fusion in response to a hypertrophic stimulus. To achieve this goal, we specifically labeled MuSC mitochondria with Dendra2 fluorescence by crossing the MuSC-specific CreER (Pax7CreER/CreER) mouse with the Rosa26-Dendra2 mouse to generate the Pax7-Dendra2 mouse. To induce the fusion of MuSC to myofibers, Pax7-Dendra2 mice underwent synergist ablation surgery to induce mechanical overload (MOV) of plantaris muscle for 3, 7 and 14 days. To track MuSC proliferation, a mini-osmotic pump was implanted at the time of MOV to continuously deliver EdU. At the designated time, plantaris muscles were excised and processed for immunohistochemistry to quantify Dendra2 + myofibers. There was a progressive increase in Dendra2-positive fibers across the MOV time course. Three distinct patterns or domains of Dendra2 fluorescence within myofibers were identified and designated as newly fused (NF), crescent (CS) or diffuse (DF). From these Dendra2 + domain types, we inferred MuSC fusion dynamics which indicated MuSC fusion occurred prior to mechanical overload day 3 (MOV-3) and preferentially with Type 2A fibers. Quantification of EdU + myonuclei found the majority of early (MOV < 3 days) MuSC fusion was division-independent, while proliferating MuSCs contributed primarily to later fusion events. The results of this study provide the first evidence that MuSC mitochondria are transferred to myofibers upon fusion during hypertrophy while, unexpectedly, revealing a greater complexity in MuSC fusion than previously recognized.

Keywords:  mitochondrial transfer; muscle stem cell; satellite cell; stem cell dynamics; stem cell fusion

DOI:  https://doi.org/10.1093/function/zqaf031
bioRxiv. 2025 May 08. pii: 2025.05.03.652040. [Epub ahead of print]

An integrative framework linking molecular signatures and locomotory phenotypes in space-induced sarcopenia.

Brendan K Ball, Hammad F Khan.

Age-related skeletal muscle deterioration, referred to as sarcopenia, poses significant risks to astronaut health and mission success during spaceflight, yet its multisystem drivers remain poorly understood. While terrestrial sarcopenia manifests gradually through aging, spaceflight induces analogous musculoskeletal decline within weeks, providing an accelerated model to study conserved atrophy mechanisms. Here, we introduced an integrative framework combining cross-species genetic analysis with physiological modeling to understand mechanistic pathways in space-induced sarcopenia. By analyzing rodent and human datasets, we identified conserved molecular pathways underlying microgravity-induced muscle atrophy, revealing shared regulators of neuromuscular signaling including pathways related to neurotransmitter release and regulation, mitochondrial function, and synaptic integration. Building upon these molecular insights, we developed a physiologically grounded central pattern generator model that reproduced spaceflight-induced locomotion deficits in mice. This multi-scale approach established mechanistic connections between transcriptional changes and impaired movement kinetics while identifying potential therapeutic targets applicable to both spaceflight and terrestrial aging-related muscle loss.

DOI: https://doi.org/10.1101/2025.05.03.652040
bioRxiv. 2025 Jun 11. pii: 2025.06.09.658655. [Epub ahead of print]

Fibrillin-Related Proteins Control Calcium Homeostasis in Dystrophic Muscle Across Species.

D Marchiafava, A G Vidal-Gadea.

Duchenne muscular dystrophy (DMD) involves progressive muscle degeneration associated with calcium dysregulation, but the mechanisms linking extracellular matrix (ECM) integrity to calcium homeostasis remain unclear. We investigated whether MUA- 3, a fibrillin-related ECM protein in Caenorhabditis elegans , contributes to calcium regulation in dystrophic muscle. Using fluorescent calcium imaging in transgenic worms expressing muscle-specific GCaMP2, we found that downregulating mua-3 selectively elevated resting calcium levels in healthy muscle but had no effect in dystrophic ( dys-1 ) muscle, suggesting impaired MUA-3 function in dystrophy. Despite altered calcium dynamics, mua-3 downregulation did not affect locomotor function. In human dystrophic myoblasts, we observed significantly elevated sarcoplasmic calcium levels concurrent with substantial downregulation of fibrillin genes FBN1/FBN2. These findings demonstrate that fibrillin-related proteins regulate calcium homeostasis across species, suggesting that ECM integrity directly contributes to cellular calcium control in muscle. This work identifies a conserved mechanism linking extracellular matrix stability to intracellular calcium regulation and suggests that targeting ECM-calcium coupling may offer new therapeutic approaches for muscular dystrophy.

DOI: https://doi.org/10.1101/2025.06.09.658655
bioRxiv. 2025 May 05. pii: 2025.05.05.652304. [Epub ahead of print]

Targeting the canonical ER stress IRE1α/XBP1 pathway counteracts pancreatic cancer-induced skeletal muscle wasting.

Aniket S Joshi, Meiricris Tomaz da Silva, Anh Tuan Vuong, Bowen Xu, Ravi K Singh, Ashok Kumar.

Cancer-driven cachexia is a deleterious syndrome which involves progressive loss of skeletal muscle mass with or without fat loss, fatigue, and weakness that cannot be reversed by nutritional intake. Recent studies have shown deregulation of endoplasmic reticulum (ER)-induced unfolded protein response (UPR) pathways in skeletal muscles in various catabolic conditions, including cancer growth. However, the role of individual arms of the UPR in regulation of muscle mass remains poorly understood. Here, we demonstrate that the IRE1α/XBP1 arm of the UPR stimulates the activation of ubiquitin-proteasome system, autophagy, JAK-STAT3 signaling, and fatty acid oxidation in skeletal muscle of the KPC mouse model of pancreatic cancer cachexia. Furthermore, our results show that IRE1α/XBP1 pathway is a key contributor to cachexia as targeted ablation of XBP1 transcription factor in mouse skeletal muscle inhibits KPC tumor-induced muscle wasting. Transcriptionally active XBP1 protein binds to the promoter region of multiple genes whose products are involved in skeletal muscle wasting. Treatment of KPC tumor-bearing mice with 4µ8C, a small molecule IRE1α inhibitor, reverses cachexia-induced molecular changes and improves skeletal muscle mass and strength. Altogether, our study highlights that the IRE1α/XBP1 signaling axis mediates pancreatic cancer-induced muscle wasting and inhibition of this pathway could be a potential approach to mitigate muscle wasting in pancreatic cancer patients.

DOI: https://doi.org/10.1101/2025.05.05.652304
Adv Funct Mater. 2024 Jan;pii: adfm.202300571. [Epub ahead of print]34(1):

A Self-Renewing Biomimetic Skeletal Muscle Construct Engineered using Induced Myogenic Progenitor Cells.

Inseon Kim, Seunghun S Lee, Adhideb Ghosh, Stephen J Ferguson, Ori Bar-Nur.

  Skeletal muscle represents a highly organized tissue that primarily regenerates by myogenic stem cells. Mimicking an in vitro skeletal muscle differentiation program that contains self-renewing muscle stem cells and aligned myotubes is considered challenging. This study presents the engineering of a biomimetic muscle construct that can self-regenerate and produce aligned myotubes using induced myogenic progenitor cells (iMPCs), a heterogeneous culture consisting of skeletal muscle stem, progenitor, and differentiated cells. Utilizing electrospinning, polycaprolactone (PCL) substrates are fabricated to facilitate iMPC-differentiation into aligned myotubes by controlling PCL fiber orientation. Newly-conceived constructs contain organized multinucleated myotubes alongside self-renewing stem cells, whose differentiation capacity is augmented by Matrigel supplementation. Furthermore, this work utilizes single-cell RNA-sequencing (scRNA-seq) to demonstrate that iMPC-derived constructs faithfully recapitulate a step-wise myogenic differentiation program. Notably, when subjected to a damaging myonecrotic agent, self-renewing stem cells rapidly differentiate into aligned myotubes within the constructs, akin to skeletal muscle repair in vivo. Finally, this study demonstrates that the iMPC derivation protocol can be adapted to engineer human myoblast-derived muscle constructs containing aligned myotubes, showcasing potential for translational applicability. Taken together, this work reports a novel in vitro system that mirrors myogenic regeneration and skeletal muscle alignment for basic research and regenerative medicine.

Keywords:  induced myogenic progenitor cells; myogenic differentiation; skeletal muscle regeneration; tissue engineering

DOI:  https://doi.org/10.1002/adfm.202300571
J Heart Lung Transplant. 2025 Jul 10. pii: S1053-2498(25)02101-1. [Epub ahead of print]

Proteomic and Metabolomic Profiling Nominates Druggable Targets and Biomarkers for Pulmonary Arterial Hypertension-Associated Myopathy and Exercise Intolerance in Male Monocrotaline Rats.

Phablo Abreu, Ryan Moon, Jenna B Mendelson, Todd Markowski, LeeAnn Higgins, Kevin Murray, Candace Guerrero, Jeffrey Blake, Sasha Z Prisco, Kurt W Prins.

   BACKGROUND: Pulmonary arterial hypertension (PAH) is a rare but debilitating condition that causes exercise intolerance and ultimately death. Skeletal muscle derangements contribute to depressed exercise capacity in PAH, but the mechanisms underlying muscle dysfunction including the changes in muscle biology based on fiber type are understudied.
METHODS: We evaluated exercise capacity, muscle histopathology, mitochondrial density, mitochondrial proteomics, and metabolomics/lipidomics of quadriceps (predominately fast fibers) and soleus (predominately slow fibers) muscles in the monocrotaline (MCT) rat model of PAH.
RESULTS: MCT rats exhibited impaired exercise capacity. Surprisingly, there were divergent atrophic and metabolic remodeling in the quadriceps and soleus muscles of MCT rats. In the quadriceps, there was a mild atrophic response only in type II fibers. In contrast, both type I and II fibers atrophied in the soleus. Both muscles exhibited fibrotic infiltration, but mitochondrial density was reduced in the quadriceps only. Mitochondrial proteomics and tissue metabolomics/lipidomics profiling demonstrated the two muscles exhibited distinct responses as the quadriceps had impairments in oxidative phosphorylation/fat metabolism and storage of triacylglycerides. However, the soleus showed signs of proteasome deficiencies and alterations in phosphatidylcholine/phosphatidylethanolamine homeostasis. Finally, profiling of metabolites/lipids in the serum identified potential novel biomarkers of exercise intolerance in PAH including the dimethylarginine pathway, cysteine, and triacylglycerides.
CONCLUSION: Our data suggest differential cachectic and metabolic responses occur in PAH-induced myopathy. We nominate mitochondrial biogenesis and proteasome activation as potential druggable targets for PAH-myopathy.

Keywords:  Exercise capacity; Myopathy; metabolomics; proteomics

DOI:  https://doi.org/10.1016/j.healun.2025.06.034
bioRxiv. 2025 Jun 17. pii: 2025.06.11.659129. [Epub ahead of print]

Klotho deficiency promotes skeletal muscle weakness and is associated with impaired motor unit connectivity.

Linda A Bean, Connor Thomas, Juan F Villa, Alexander J Fitt, Areli Jannes S Javier, Akanksha Agrawal, Hanna Whitney, Guilherme Nascimento Dos Santos, Kenneth E White, Joshua R Huot, Steven S Welc.

Muscle wasting and weakness are important clinical problems that impact quality of life and health span by restricting mobility and independence, and by increasing the risk for physical disability. The molecular basis for this has not been fully determined. Klotho expression is downregulated in conditions associated with muscle wasting, including aging, chronic kidney disease, and myopathy. The objective of this study was to investigate a mechanistic role for Klotho in regulating muscle wasting and weakness. Body weight, lean mass, muscle mass, and myofiber caliber were reduced in Klotho-deficient mice. In the tibialis anterior muscle of Klotho null mice, type IIa myofibers were resistant to changes in size, and muscle composition differed with a higher concentration of type IIb fibers to the detriment of type IIx fibers. Glycolytic enzymatic activity also increased. The composition of the soleus muscle was unaffected and myofiber caliber was reduced comparably in type I, IIa, and IIx fibers. Muscle contractile function declined in Klotho-deficient mice, as evidenced by reduced absolute twitch and torque, and decreased rates of contraction and relaxation. RNA-sequencing analysis identified increased transcriptional expression of synaptic and fetal sarcomeric genes, which prompted us to test effects on muscle innervation. Klotho-deficiency induced morphological remodeling of the neuromuscular junction, myofiber denervation, and a functional loss of motor units. Loss of motor units correlated with absolute torque. Collectively, our findings have uncovered a novel mechanism through which Klotho-deficiency leads to alterations to the muscle synapse affecting motor unit connectivity that likely influences muscle wasting and weakness.
Key points summary: Maintaining skeletal muscle mass and function is critical to preserve physical capacity and independence. Clinical observations implicate longevity factor ⍺Klotho as a key regulator of muscle mass and weakness. Low Klotho levels are reported to correlate with muscle weakness and frailty.Using Klotho null mice, our study shows that Klotho-deficiency promotes skeletal muscle weakness and impaired motor unit connectivity.RNA-sequencing analysis identified altered expression of sarcomeric and synaptic genes suggesting changes to the muscle synapse in Klotho-deficient mice.Histopathological analyses revealed Klotho-deficiency is associated with reduced myofiber caliber, altered muscle composition, and increased prevalence of NCAM+ denervated fibers. Imaging of the NMJ further showed morphological changes and reduced area of synaptic contact.Overall, our findings show that Klotho regulates the structure and function of the NMJ affecting motor unit connectivity which may have an important role in the pathogenesis of muscle wasting and weakness.

DOI: https://doi.org/10.1101/2025.06.11.659129
FASEB J. 2025 Jul 31. 39(14): e70825

Deletion of Skeletal Muscle Mitochondrial Glutamic-Oxaloacetic Transaminase (GOT2) Enhances Oxaloacetate Inhibition of Succinate Dehydrogenase and Alters Substrate Selectivity.

Brian D Fink, Ritu Som, Liping Yu, William I Sivitz.

  Oxaloacetate (OAA) is converted to aspartate by mitochondrial glutamic-oxaloacetic transaminase 2 (GOT2) along with the conversion of glutamate to alpha-ketoglutarate (α-KG). Glutamate can also be directly converted to α-KG by glutamate dehydrogenase. In past work, we found that in skeletal muscle mitochondria energized by succinate alone, oxaloacetate accumulates and inhibits succinate dehydrogenase (complex II) in a manner dependent on inner membrane potential (ΔΨ). Here, we tested the hypothesis that deleting GOT2 would increase OAA concentrations, decrease complex II-energized respiration, and alter the selectivity of succinate versus glutamate for energy. Incubating wild-type mitochondria with succinate and glutamate revealed that increments in ADP increased OAA and caused a preferential use of glutamate for energy. Deletion of GOT2 compared to wild-type decreased complex II energized respiration, increased OAA, and decreased consumption of glutamate relative to succinate. OAA accumulation was also associated with decreased conversion of succinate to fumarate and malate. These findings are consistent with GOT2 control of metabolite flow through succinate dehydrogenase via regulation of OAA and consequent inhibition of succinate dehydrogenase. In contrast to respiration energized at complex II, when mitochondria were energized at complex I by pyruvate + malate, respiration did not differ between GOT2KO and WT mitochondria, and oxaloacetate was not detectable. In summary, GOT2 and OAA mediate complex II respiration and mitochondrial energy substrate selectivity.

Keywords:  glutamic‐oxaloacetic transaminase‐2; mitochondria; mitochondrial complex II; mitochondrial inner membrane potential; oxaloacetate; respiration; skeletal muscle; succinate dehydrogenase

DOI:  https://doi.org/10.1096/fj.202501071R
Biochim Biophys Acta Mol Basis Dis. 2025 Jul 09. pii: S0925-4439(25)00331-X. [Epub ahead of print]1871(7): 167983

Distinct systemic metabolic features in limb-girdle muscular dystrophy type R1 mouse models as a potential early pathogenic signature.

Fumiko Shinkai-Ouchi, Yoshiki Itoh, Mayumi Shindo, Kyohei Mikami, Yoshinobu Iguchi, Shoji Hata, Rie Tsutsumi, Yuna Izumi-Mishima, Kyoka Machida, Yuki Suzuki, Hiroshi Sakaue, Yasuko Ono.

  Limb-girdle muscular dystrophy type R1 (LGMDR1, formerly LGMD2A) is a genetic disorder caused by mutations in CAPN3 and is characterized by progressive proximal limb muscle weakness. The CAPN3 gene product, calpain-3/CAPN3/p94, is a member of the intracellular cysteine protease superfamily predominantly expressed in the skeletal muscle. LGMDR1 pathogenesis has been investigated separately using mouse models: CAPN3:C129S [knock-in (KI)] mice, which express a proteolytically inactive variant, and CAPN3 knockout (KO) mice. These studies propose that CAPN3 bears both proteolytic activity-dependent and -independent functions and that the loss of either or both affects phenotypes. Here, we report a side-by-side, long-term analysis of KI and KO mice to comprehensively understand the LGMDR1 pathology in terms of CAPN3 function. Their physiques were comparable to those of wild-type animals, but age-dependent LGMDR1 symptoms were observed by histochemical analysis, with more severe symptoms observed in KO mice. Quantitative muscle proteomics and gene ontology analyses revealed more diverse changes in the KO mice than in the KI mice. Of the associated terms, "metabolic process" was the most affected across the genotype and age groups. Metabolomic analysis suggested that the skeletal muscles of these mice had an imbalance in the branched-chain amino acid catabolic pathway. Furthermore, a reduction in lipids and glycogen was observed in the liver of KO mice, suggesting that a systemic energy deficit occurs during CAPN3 deficiency. Altogether, our results suggest that muscular dysfunction in LGMDR1 models is associated with compromised systemic energy balance and that the extent of perturbation is implicated in disease severity.

Keywords:  Calpain-3; Energy homeostasis; Limb-girdle muscular dystrophy R1/2A; Metabolism; Muscle-liver crosstalk; Skeletal muscle proteomics

DOI:  https://doi.org/10.1016/j.bbadis.2025.167983
bioRxiv. 2025 Jun 08. pii: 2025.06.04.657846. [Epub ahead of print]

Hb-EGF directs systemic muscle repair.

Haley C Dean, Vishnu M Saraswathy, Amulya Saini, Tiffany Ou, Jennifer McAdow, Amruta Tendolkar, Mayssa H Mokalled, A N Johnson.

Regenerative capacity varies between tissues, species, and stages of the life cycle. What is less appreciated is that regenerative capacity also varies with the magnitude of the injury, even within a single tissue. Vertebrate skeletal muscle efficiently regenerates following minor injuries; however, extensive injuries may result in incomplete repair, which can be debilitating. To understand if small- and large-scale muscle injuries activate distinct regenerative programs, we developed a systemic muscle injury model in zebrafish. Transcriptomic analysis of muscle and non-muscle tissues revealed that systemic and local muscle injuries elicit distinct molecular responses, both quantitatively and qualitatively. Systemic muscle injury activated the expression of Heparin binding epidermal-like growth factor (Hb-EGF) in the epidermis, and Hb-EGF is necessary for systemic muscle repair. Conversely, local muscle injury did not induce Hb-EGF expression and Hb-EGF was not required for local muscle repair. These studies suggest that large- and small-scale muscle injuries activate different regenerative programs, resulting in either systemic or local repair.

DOI: https://doi.org/10.1101/2025.06.04.657846
Front Pharmacol. 2025 ;16 1607606

Protective effects of Salubrinal against H2O2-induced muscle wasting via eIF2α/ATF4 signaling pathway.

Siming Lin, Jingying Wu, Guili Lian, Weibin Wu, Weixiao Chen, Ai Chen, Li Luo, Liangdi Xie.

   Background: Endoplasmic reticulum stress (ERS) plays a critical role in skeletal muscle physiology and pathology, though the precise mechanisms remain unclear. Salubrinal, a selective inhibitor of eIF2α dephosphorylation, has been shown as a potential therapeutic agent for various conditions, but its effects on sarcopenia are not well understood. This study investigated the protective effects of salubrinal against H2O2-induced muscle cell injury and its impact on the eIF2α/ATF4 signaling pathway.
Methods: Gastrocnemius muscle samples from aged mice were used and cultured C2C12 myotubes were also used to explore the effects of Salubrinal through Western blotting, immunofluorescence, and apoptosis assays.
Results: Our results demonstrated that H2O2 treatment induced significant muscle cell damage, evidenced by reduced MHC1 expression and increased apoptosis. Salubrinal, in a concentration-dependent manner, mitigated these effects, preserving MHC1 expression and reducing apoptosis. Furthermore, salubrinal enhanced the expression of p-eIF2α and ATF4, suggesting that its protective effects are mediated through the eIF2α/ATF4 pathway.
Conclusion: These findings highlight salubrinal's potential as a therapeutic agent for muscle wasting conditions, particularly those related to oxidative stress and ERS.

Keywords:  aging; endoplasmic reticulum stress; salubrinal; sarcopenia; skeletal muscle atrophy

DOI:  https://doi.org/10.3389/fphar.2025.1607606
Cell Rep. 2025 Jul 15. pii: S2211-1247(25)00792-2. [Epub ahead of print]44(8): 116021

Intramuscular adipose tissue restricts functional muscle recovery.

Alessandra M Norris, Victoria R Palzkill, Ambili B Appu, Kiara E Fierman, Christian D Noble, Terence E Ryan, Daniel Kopinke.

  With age and disease, skeletal muscle is progressively lost and replaced by fibrotic scar and intramuscular adipose tissue (IMAT). While strongly correlated, it remains unclear whether IMAT has a functional impact on muscle. In the present study, we evaluated the impact of IMAT on muscle regeneration by creating a mouse model where the cellular origin of IMAT, fibro/adipogenic progenitors (FAPs), is prevented from differentiating into adipocytes (mFATBLOCK model). We found that blocking IMAT after an adipogenic injury allowed muscle to regenerate more efficiently, resulting in enhanced functional recovery. Our data explain why acute muscle injuries featuring IMAT infiltration, such as rotator cuff tears and acute denervation injuries, exhibit poor regeneration and lead to a loss of muscle function. It also demonstrates the therapeutic importance of preventing IMAT formation in acute injuries in order to maximize regeneration and minimize loss in muscle mass and function.

Keywords:  CP: Metabolism; fatty fibrosis; fibro/adipogenic progenitors; intramuscular adipose tissue; muscle regeneration; rotator cuff tear

DOI:  https://doi.org/10.1016/j.celrep.2025.116021
Int J Mol Sci. 2025 Jun 24. pii: 6032. [Epub ahead of print]26(13):

Exploring lncRNA-Mediated Mechanisms in Muscle Regulation and Their Implications for Duchenne Muscular Dystrophy.

Abdolvahab Ebrahimpour Gorji, Zahra Roudbari, Kasra Ahmadian, Vahid Razban, Masoud Shirali, Karim Hasanpur, Tomasz Sadkowski.

  Duchenne muscular dystrophy (DMD) manifests as a hereditary condition that diminishes muscular strength through the progressive degeneration of structural muscle tissue, which is brought about by deficiencies in the dystrophin protein required for the integrity of muscle cells. DMD is among four different types of dystrophinopathy disorders. Current studies have established that long non-coding RNAs (lncRNAs) play a significant role in determining the trajectory and overall prognosis of chronic musculoskeletal conditions. LncRNAs are different in terms of their lengths, production mechanisms, and operational modes, but they do not produce proteins, as their primary activity is the regulation of gene expression. This research synthesizes current literature on the role of lncRNAs in the regulation of myogenesis with a specific focus on certain lncRNAs leading to DMD increments or suppressing muscle biological functions. LncRNAs modulate skeletal myogenesis gene expression, yet pathological lncRNA function is linked to various muscular diseases. Some lncRNAs directly control genes or indirectly control miRNAs with positive or negative effects on muscle cells or the development of DMD. The research findings have significantly advanced our knowledge about the regulatory function of lncRNAs on muscle growth and regeneration processes and DMD diseases.

Keywords:  DMD; LncRNA; gene regulation; skeletal muscle

DOI:  https://doi.org/10.3390/ijms26136032
Front Physiol. 2025 ;16 1613184

Time-of-day effects on muscle mitochondria following short-term ablation of satellite cells.

Ryan E Kahn, Fawzan Dinnunhan, Guadalupe Meza, Richard L Lieber, Orly Lacham-Kaplan, John A Hawley, Sudarshan Dayanidhi.

   Introduction: Endurance exercise capacity fluctuates by time-of-day due, in part, to molecular clock effects on muscle physiology. As endurance-based exercise relies predominantly on mitochondria for the conversion of cellular energy, fluctuations observed in endurance capacity have been attributed to diurnal variation in mitochondrial respiration and molecular clock KO animals exhibiting blunted mitochondrial function/content. Recently, a circadian profiling of satellite cells (SCs) demonstrated molecular clock, metabolic, and mitochondrial genes exhibit robust oscillation over 24 h while long-term SC ablation impairs endurance exercise capacity. These lines of evidence suggest SC molecular clocks may influence mitochondrial respiration according to time-of-day. We determined whether mitochondrial respiration differs by time-of-day in the presence and absence of SCs in oxidative (soleus, SOL) and glycolytic (tibialis anterior, TA) muscle.
Methods: Utilizing a Pax7CRE-ERT2/+; Rosa26DTA/+ mouse model capable of SC ablation (SC+, SC-), we conducted experiments in either the morning, afternoon, or evening.
Results: In both SOL and TA, respiratory coupling ratio (RCR) was lowest and Leak-state respiration (TA) was highest in the morning with no differences observed following SC ablation. Utilizing a submaximal ex vivo fatigue protocol that relies predominantly on mitochondrial energy, we observed that submaximal fatiguability was lower in the morning than afternoon in glycolytic muscle (EDL) (morning-SC + : 54 ± 5; afternoon-SC + : 36 ± 6 contractions until fatigue, p < 0.05), which corresponded with peak/trough Bmal1 and CLOCK gene expression in muscle.
Discussion: Collectively, the results from the current study suggest that SCs influence mitochondria in a time-of-day manner.

Keywords:  contractility; molecular clocks; muscle fatigue; muscle mitochondria; satellite cells

DOI:  https://doi.org/10.3389/fphys.2025.1613184
J Clin Med. 2025 Jun 25. pii: 4490. [Epub ahead of print]14(13):

Muscle in Endocrinology: From Skeletal Muscle Hormone Regulation to Myokine Secretion and Its Implications in Endocrine-Metabolic Diseases.

Pedro Iglesias.

  Skeletal muscle, traditionally recognized for its motor function, has emerged as a key endocrine organ involved in metabolic regulation and interorgan communication. This narrative review addresses the dual role of muscle as a target tissue for classical hormones-such as growth hormone (GH), insulin-like growth factor type 1 (IGF-1), thyroid hormones, and sex steroids-and as a source of myokines, bioactive peptides released in response to muscle contraction that exert autocrine, paracrine, and endocrine effects. Several relevant myokines are discussed, such as irisin and Metrnl-like myokines (Metrnl), which mediate exercise-associated metabolic benefits, including improved insulin sensitivity, induction of thermogenesis in adipose tissue, and immunometabolic modulations. It also examines how muscle endocrine dysfunction, caused by chronic inflammation, hormone resistance, or sedentary lifestyle, contributes to the development and progression of metabolic diseases such as obesity, type 2 diabetes, and sarcopenia, highlighting the importance of muscle mass in the prognosis of these pathologies. Finally, the therapeutic potential of interventions aimed at preserving or enhancing muscle function-through physical exercise, hormone therapy and anabolic agents-is highlighted, together with the growing research on myokines as biomarkers and pharmacological targets. This review expands the understanding of muscle in endocrinology, proposing an integrative approach that recognizes its central role in metabolic health and its potential to innovate the clinical management of endocrine-metabolic diseases.

Keywords:  brain-derived neurotrophic factor; endocrine–metabolic diseases; fibroblast growth factor 21; fibronectin type III domain-containing protein 5; interleukin-15; interleukin-6; irisin; leukemia inhibitory factor; meteorin-like; myokine; myonectin; myostatin; secreted protein acidic and rich in cysteine; skeletal muscle

DOI:  https://doi.org/10.3390/jcm14134490
Biochem Biophys Res Commun. 2025 Jul 14. pii: S0006-291X(25)01065-4. [Epub ahead of print]778 152350

In vitro mechanical stretch inhibits differentiation of mouse myoblast C2C12 cells without sustained eIF2α phosphorylation.

Kazuaki Mori, Toru Asahi, Kosuke Kataoka, Yoshikatsu Akiyama.

  Mechanical stretch critically influences skeletal muscle physiology, yet its role in myoblast differentiation and the associated molecular mechanisms have not been fully clarified. This study investigated the effects of uniaxial cyclic mechanical stretch (UnCyMSt) on differentiation of mouse myoblast C2C12 cells, focusing particularly on the potential involvement of eukaryotic initiation factor 2 alpha (eIF2α), a key regulator maintaining muscle stem cell quiescence. To apply mechanical stretch, C2C12 cells were cultured on polydimethylsiloxane surfaces covalently immobilized with collagen (Col-GA-PDMS), ensuring stable cell adhesion under UnCyMSt, whereas cells cultured on physically adsorbed collagen surfaces (Col-PDMS) detached under similar conditions. Under differentiation conditions, UnCyMSt markedly inhibited myoblast differentiation, as evidenced by suppressed expression of the differentiation marker myogenin. Additionally, stretched cells aligned perpendicular to the direction of mechanical stretch application. Given the established role of phosphorylated eIF2α (p-eIF2α) in maintaining myoblast quiescence, we investigated whether UnCyMSt inhibits differentiation by modulating eIF2α phosphorylation at serine 51. UnCyMSt did not prevent the progressive dephosphorylation of eIF2α during differentiation induction. Correspondingly, expression levels of activating transcription factor 4 (ATF4), downstream of p-eIF2α, also decreased under UnCyMSt. Our results demonstrate that UnCyMSt inhibits C2C12 myoblast differentiation without sustained phosphorylated eIF2α, suggesting the involvement of alternative mechanosensitive signaling pathways. These findings provide new insights into mechanical regulation of muscle differentiation and highlight the need for further exploration into stretch-responsive molecular mechanisms influencing myogenesis.

Keywords:  C2C12 cells; Mechanical stretch; Mechanotransduction; Myoblast differentiation; Polydimethylsiloxane; eIF2α signalling

DOI:  https://doi.org/10.1016/j.bbrc.2025.152350
J Anat. 2025 Jul 17.

Morphological differences in myofibre size and shape: A comparative study of the soleus, gastrocnemius, triceps brachii and vastus lateralis in humans and mice.

Casper Soendenbroe, Rene B Svensson, Bettina Mittendorfer, S Peter Magnusson, Abigail L Mackey, Jesper L Andersen.

  Certain skeletal muscles are specialized for their functional roles, yet direct comparisons of cellular morphology of distinct muscles beyond fibre type distribution are limited. This study investigated myofibre morphology in predominantly slow, fast and mixed fibre muscles in humans and mice, with the aim of establishing reference values for muscle-specific myofibre size and shape. Nine healthy young men (Age: 26 ± 1 years, BMI: 23 ± 1 kg/m2) had muscle biopsies taken from soleus, triceps brachii and vastus lateralis muscles. Additionally, the soleus and gastrocnemius muscles were harvested from 7 male C57BL/6 mice. Muscle samples were analysed by ATPase (human) or immunofluorescence (mouse) stainings of fibre type specific cross-sectional area, perimeter and Shape Factor Index (SFI; fibre perimeter2/4 × π × fibre cross-sectional area). In humans, type I fibres had 30%-40% larger CSA and 4%-7% higher SFI in soleus (1.54 ± 0.06) compared to triceps brachii (1.47 ± 0.05) and vastus lateralis (1.43 ± 0.04). Type IIa fibres SFI were 10%-11% higher in soleus (1.61 ± 0.08) compared to triceps brachii (1.45 ± 0.04) and vastus lateralis (1.45 ± 0.08). Soleus type I fibres were more heterogeneous in terms of size and shape compared to other muscles. Analyses of mouse muscle showed a similar pattern, in that CSA and SFI were higher in type I and IIa fibres of the soleus compared to the gastrocnemius. These findings suggest a consistent morphological characteristic of soleus fibres across species, with potentially important implications for future biomedical research.

Keywords:  locomotion; myofibre morphology; shape factor; skeletal muscle

DOI:  https://doi.org/10.1111/joa.70025
Am J Transl Res. 2025 ;17(6): 4187-4197

Sirtuin 3 modulation by high phosphates: a potential mechanism in muscle aging and sarcopenia.

Chao Xu, Ling Xiong, Junhu Chen, Qingcheng Liu, Fang Wang, Xianxian Fu, Juan Huo, Yufei Bu, Shiyu Chen, Qian Liu.

   OBJECTIVES: To investigate the role of elevated phosphate levels in muscle aging, and to elucidate the underlying molecular mechanisms by which high phosphate conditions regulate muscle aging and explore the potential therapeutic role of SIRT3 activation.
METHODS: Young (5-month-old) and aged (24-month-old) C57BL/6 mice were compared in terms of body weight, muscle strength, and serum sodium levels. Additionally, C2C12 myoblasts were exposed to 20 mM β-glycerophosphate (BGP) to simulate high phosphate conditions. Cellular senescence was assessed using senescence-associated β-galactosidase (SA-β-GAL) staining and Western blot analysis (P53, P62, and P21). The role of SIRT3 in muscle cell senescence was further investigated by treating C2C12 cells with the SIRT3 activator 2-APQC.
RESULTS: Aged mice exhibited significantly higher body weight, reduced grip strength, and elevated serum sodium levels compared to young mice, indicating muscle aging. BGP treatment in C2C12 cells induced cellular senescence, as evidenced by elevated SA-β-GAL activity and upregulation of senescence markers P53, P62, and P21. Furthermore, high phosphate levels impaired cell migration and differentiation. Activation of SIRT3 by 2-APQC alleviated these effects, restoring autophagic activity and reversing muscle cell dysfunction.
CONCLUSIONS: Elevated serum sodium and phosphate levels are associated with muscle aging in mice. High phosphate induces cellular senescence and impairs muscle function, while SIRT3 activation mitigates these effects, highlighting its potential as a therapeutic target for sarcopenia. Dietary phosphate restriction and activation of SIRT3 may represent effective strategies for combating age-related muscle degeneration.

Keywords:  Muscle aging; SIRT3; high phosphate; muscle function; sarcopenia; senescence-associated β-galactosidase

DOI:  https://doi.org/10.62347/JWEY8421
Int J Mol Sci. 2025 Jul 07. pii: 6525. [Epub ahead of print]26(13):

Impact of Aerobic Training on Transcriptomic Changes in Skeletal Muscle of Rats with Cardiac Cachexia.

Daniela Sayuri Inoue, Quinten W Pigg, Dillon R Harris, Dongmei Zhang, Devon J Boland, Mariana Janini Gomes.

  Cardiac cachexia (CC) is an advanced stage of heart failure (HF) characterized by structural and functional abnormalities in skeletal muscle, leading to muscle loss. Aerobic training provides benefits; however, the underlying molecular mechanisms remain poorly understood. This study aimed to investigate the therapeutic effects of aerobic training on transcriptomic alterations associated with disease progression in cachectic skeletal muscle. HF was induced in male Wistar rats by a single monocrotaline injection (60 mg/Kg). Aerobic training consisted of 30 min treadmill running at ~55% of maximal capacity, 5×/week for 4 weeks. Assessments included body mass, right ventricle mass, skeletal muscle fiber size and exercise tolerance. RNA-seq analysis was performed on the medial gastrocnemius muscle. Sedentary cachectic rats exhibited 114 differentially expressed genes (DEGs) while exercised cachectic rats had only 18 DEGs. Enrichment pathways analyses and weighted gene co-expression network analysis (WGCNA) identified potential key genes involved in disrupted lipid metabolism in sedentary cachectic rats, which were not observed in the exercised cachectic rats. Validation of DEGs related to lipid metabolism confirmed that Dgat2 gene expression was modulated by aerobic training in CC rats. These findings suggest that aerobic training mitigates transcriptional alterations related to lipid metabolism in rats with CC, highlighting its therapeutic potential.

Keywords:  exercise; metabolism; muscular remodeling; pulmonary arterial hypertension; transcriptome

DOI:  https://doi.org/10.3390/ijms26136525
bioRxiv. 2025 May 03. pii: 2025.05.02.651952. [Epub ahead of print]

Mutations in Hsp40 co-chaperone change the unique canonical inter-domain interactions stimulating LGMDD1 myopathy.

Ankan K Bhadra, Geetika Aggarwal, Anshuman Jaysingh, Daniel Chen, Jil Daw, Conrad C Weihl, Heather L True.

Limb-girdle muscular dystrophy D1 (LGMDD1) is a rare, dominantly inherited neuromuscular disorder caused by mutations in the HSP40 co-chaperone DNAJB6, primarily in the GF or J-domains. Currently, no treatments are available, and a challenge in understanding the disease is identifying a specific client protein for DNAJB6 in skeletal muscle. Our previous research indicated that LGMDD1 GF domain mutants in Sis1 exhibit substrate-specific effects, influenced by HSP70 activity. Herein, we found that novel mutations in the J-domain similarly affected chaperone function. The J-domain mutants exhibited variable substrate processing, reduced binding affinity to client-substrate, and decreased stimulation of Ssa1 ATP hydrolysis, with these effects being substrate-conformer-specific. Our simulation studies noted differences in inter-domain interactions linked to the mutants, which influence the Hsp40-Hsp70 ATPase cycle. These mechanistic insights enhance our understanding of LGMDD1 myopathy and help to identify potential treatment strategies in the future.
Teaser: Recalibrating the inter-domain interface of the mutant protein could potentially serve as a key therapeutic strategy for LGMDD1 myopathy.

DOI: https://doi.org/10.1101/2025.05.02.651952
bioRxiv. 2025 Jun 25. pii: 2025.06.19.660595. [Epub ahead of print]

The titin N2A-MARP signalosome constrains muscle longitudinal hypertrophy in response to stretch.

Robbert van der Pijl, Jochen Gohlke, Joshua Strom, Eva Peters, Shengyi Shen, Stefan Conijn, Zaynab Hourani, Stephan Lange, Ju Chen, Paul Langlais, Siegfried Labeit, Henk Granzier, Coen Ottenheijm.

Titin-based mechanosensing is a key driver of trophic signaling in muscle, yet the downstream pathways linking titin sensing to muscle remodeling remain poorly understood. To investigate these signaling mechanisms, we utilized unilateral diaphragm denervation (UDD), an in vivo model that induces titin-stiffness-dependent hypertrophy via mechanical stretch. Using UDD in rats and mice, we characterized the longitudinal hypertrophic response and distinguished stretch-induced signaling from denervation effects by performing global transcriptomic and proteomic analyses following UDD and bilateral diaphragm denervation (BDD) in rats. Our findings identified upregulation of titin-associated muscle ankyrin repeat proteins (MARPs). Subsequent phosphorylation enrichment mass spectrometry in mouse diaphragm highlighted the involvement of the N2A-element. UDD in MARP knockout (KO) mice resulted in enhanced longitudinal hypertrophy, with Western blot analysis revealing activation of the mTOR pathway. Furthermore, pharmacological inhibition of mTORC1 with rapamycin suppressed longitudinal hypertrophy, demonstrating that mTOR signaling regulates titin-mediated hypertrophic growth in a MARP-dependent manner. These findings establish MARPs as key modulators of titin-based mechanotransduction and highlight mTORC1 as a central regulator of longitudinal muscle hypertrophy.

DOI: https://doi.org/10.1101/2025.06.19.660595
Mol Ther Methods Clin Dev. 2025 Sep 11. 33(3): 101513

A systemically deliverable lipid-conjugated siRNA targeting DUX4 as an facioscapulohumeral muscular dystrophy therapeutic.

Katelyn Daman, Jing Yan, Annabelle Biscans, Dimas Echeverria, Taisia Shmushkovich, Alexey Wolfson, Julia F Alterman, Anastasia Khvorova, Charles P Emerson.

  Facioscapulohumeral muscular dystrophy (FSHD) is the third most diagnosed muscular dystrophy. The disease is caused by genetic and epigenetic disruptions that result in misexpression of the germline transcription factor DUX4 in skeletal muscle, leading to muscle toxicity and turnover. As a gene misexpressed exclusively in muscle, DUX4 is a suitable for muscle-targeted small interfering RNA (siRNA) knockdown therapy. Here we identify a DUX4-targeting siRNA, DU01, that potently knocks down the expression of DUX4 target genes in FSHD patient-derived myotubes ex vivo. Further, DU01 conjugated with the lipid docosanoic acid (DCA) is systemically deliverable to mice by subcutaneous injection to achieve greater than 50% knockdown of DUX4 target genes in FSHD patient muscle xenografts. These findings identify the DCA-conjugated DUX4 siRNA, DCA-siRNADUX4, as a disease-targeting therapeutic for clinical development.

Keywords:  FSHD; lipid-conjugated siRNA; muscular dystrophy; siRNA; xenograft

DOI:  https://doi.org/10.1016/j.omtm.2025.101513
Circ Res. 2025 Jul 14.

Combinatory Treatment to Alleviate Cellular Stress and Improve Skeletal Muscle Phenotype in Spinal Muscular Atrophy.

Wenshu Zeng, Xiaohui Kong, Arianne Caudal, Shane Rui Zhao, Christina Alamana, Juan Melesio, Lu Ren, Jessica Guzman, Paul D Pang, Kelly Howell, Karen S Chen, John W Day, Joseph C Wu.



Keywords:  induced pluripotent stem cells; muscle, skeletal; muscular atrophy, spinal; phenotype; reactive oxygen species

DOI:  https://doi.org/10.1161/CIRCRESAHA.124.325931
Sci Adv. 2025 Jul 18. 11(29): eadw5786

Microalgae empower skeletal muscle via increased force production and viability.

Xiang Wang, Claire Schirmer, Elena Totter, Simone Schuerle.

Engineered skeletal muscle holds potential for tissue engineering and biohybrid robotics applications. However, current strategies face challenges in enhancing force generation while maintaining stability and scalability of the muscle, largely due to insufficient oxygenation and limited nutrient delivery. In this study, we present an engineering approach to address these limitations by coculturing Chlamydomonas reinhardtii (C. reinhardtii), a photosynthetic unicellular green microalga, with C2C12 myoblasts in a hydrogel matrix. Leveraging the photosynthetic activity of C. reinhardtii, our microalgae-empowered muscle (MAM) constructs exhibited superior contractility and almost three times higher active force generation compared to conventional muscle constructs. MAM showed higher cellular viability and reduced tissue damage, attributed to in situ oxygenation and nutrient supply provided by microalgal photosynthesis. In addition, improved myotube alignment was observed in MAM, which contributed to enhanced force generation. Our findings showcase the potential of photosynthetic microalgae as a functional component in engineered skeletal muscle, offering a solution to longstanding challenges in muscle engineering.

DOI: https://doi.org/10.1126/sciadv.adw5786
Mol Metab. 2025 Jul 11. pii: S2212-8778(25)00119-X. [Epub ahead of print] 102212

Muscle very long-chain ceramides associate with insulin resistance independently of obesity.

Søren Madsen, Harry B Cutler, Kristen C Cooke, Meg Potter, Jasmine Khor, Christoph D Rau, Stewart Wc Masson, Anna Howell, Zora Modrusan, Anthony S Don, Jacqueline Stöckli, Alexis Diaz Vegas, David E James.

Lipids, in particular ceramides and diacylglycerols (DAGs), are implicated in insulin resistance (IR), however their precise roles remain unclear. Here, we leverage natural genetic variation to examine muscle lipids and systemic IR in 399 Diversity Outbred Australia mice fed either chow or a high-fat diet. Adipose tissue mass was significantly associated with 55% of muscle lipid features and whole-body insulin sensitivity, with DAGs as the only lipid class enriched in this association. To disentangle the contribution of adiposity and muscle lipids to whole-body insulin sensitivity, we employed two independent approaches: (1) a linear model correcting muscle lipid features for adipose tissue mass to assess their relationship with insulin sensitivity, and (2) stratifying mice into insulin sensitivity quartiles within adiposity bins. Both revealed that very long-chain ceramides, but not DAGs, were linked to IR. RNA sequencing and proteomics from the same muscles further associated these very long-chain ceramides with cellular stress, mitochondrial dysfunction, and protein synthesis. Meanwhile, DAGs correlated with leptin gene expression in skeletal muscle, suggesting they originate from contaminating adipocytes rather than myocytes per se. We propose that many muscle lipids, including DAGs, associate with muscle and systemic IR due to accumulation of adipose tissue rather than directly influencing muscle insulin sensitivity. By addressing the relationship between adiposity and metabolic state, we identified very long-chain muscle ceramides as being highly associated with IR independently of adiposity.

DOI: https://doi.org/10.1016/j.molmet.2025.102212
Stem Cells Dev. 2025 Jul 16.

Impact of Mitochondrial A3243G Mutation on Skeletal Muscle Energy Metabolism: Evidence from Human Induced Pluripotent Stem Cell-Derived Skeletal Muscle Cells.

Ritsuko Oikawa, Kenichi Yokota, Junji Fujikura, Tomoya Uchimura, Kazutoshi Miyashita, Kaori Hayashi, Hidetoshi Sakurai, Masakatsu Sone.

  The study of skeletal muscle disorders in patients with mitochondrial diseases is crucial for gaining insights into disease physiology; however, their molecular mechanisms have not been fully elucidated. We previously established human-induced pluripotent stem (iPS) cells in two patients with the mitochondrial DNA (mtDNA) A3243G mutation and isolated iPS cell clones with either undetectable or high levels of mutations. In the present study, we established skeletal muscle cells from iPS cells with mutation-high and mutation-undetectable clones and comparatively analyzed their mitochondrial functions. Fluorescence immunostaining, fusion index, and qRT-PCR revealed no differences in the morphology, differentiation efficiency, or expression levels of skeletal muscle markers between the mutation-high and mutation-undetectable clones. However, the basal oxygen consumption rate, an indicator of mitochondrial respiration, and adenosine triphosphate (ATP) production were reduced in the mutation-high clones of patients 1 and 2. In addition, the extracellular acidification rate, an indicator of glycolytic activity, was reduced in mutation-high clones of patient 2, who exhibited a more severe clinical phenotype. In the mutation-high clones of both patients, mitochondrial Complex I activity and mtDNA copy number were also reduced, whereas the expression levels of peroxisome proliferator-activated receptor gamma coactivator 1α and glucose transporter type 4 were upregulated, indicating compensation for ATP deficiency. These findings reveal the effects of mitochondrial disorders on energy metabolism in skeletal muscles and provide novel insights into skeletal muscle dysfunction in patients with mitochondrial diseases.

Keywords:  induced pluripotent stem cells; mitochondria; mitochondrial disease; oxygen consumption rate; skeletal muscle

DOI:  https://doi.org/10.1177/15473287251359330
FASEB Bioadv. 2025 Jul;7(7): e70032

Irisin Prevents the Effects of Simulated Microgravity on Bone and Muscle Differentiation Markers.

Lorenzo Sanesi, Roberta Zerlotin, Alessio Campiolo, Angela Oranger, Manuela Dicarlo, Clelia Suriano, Ameneh Ghadiri, Graziana Colaianni, Maria Grano, Sara Tavella, Silvia Colucci.

  Microgravity exposure affects both tissues and cells, and, in this regard, one of the most affected targets is the skeletal muscle system due to the significant loss of bone and muscle mass leading to osteoporosis and sarcopenia, respectively. Several efforts are underway to counteract the effects of microgravity, and recent studies on irisin, a myokine with anabolic effects on the musculoskeletal system, have shown promising results. Due to the practical challenges of conducting experiments in actual microgravity, different devices generating a simulated microgravity condition on Earth have been developed. Here, we exposed myoblasts, osteoblasts, osteocytes to a random position machine (RPM) for five days to assess microgravity effect on the expression of key differentiation factors in cells untreated or treated with irisin. In myoblasts (C2C12), exposure to RPM led to increased expression of early myogenesis maker genes Pax7 (p = 0.0016), Myf5 (p = 0.0005) and MyoD (p = 0.0009). Irisin treatment in the last 8 h of RPM cultures prevented these increases by returning Pax7 (p = 0.0008) and MyoD (p = 0.01) to control values, and only partially Myf5. In bone cells, exposure to RPM for 5 days showed no effect in osteoblasts (MC3T3) but decreased the expression of Pdpn (p = 0.0285) and Dmp-1 (p = 0.0423) genes in osteocytes (MLO-Y4). Irisin treatment completely prevented the decline in Pdpn (p = 0.293) and Dmp-1 (p = 0.0339) levels. Overall, our data showed that the impact of RPM exposure keeps myoblasts and osteocytes in a proliferative state, and irisin treatment restores them to their baseline biological condition, suggesting that irisin can counteract the changes induced by simulated microgravity.

Keywords:  bone; irisin; microgravity; muscle; myoblasts; osteoblasts; osteocytes; random position machine

DOI:  https://doi.org/10.1096/fba.2025-00085
Exp Gerontol. 2025 Jul 14. pii: S0531-5565(25)00159-7. [Epub ahead of print] 112830

ATF3 as a molecular nexus linking ferroptosis regulation to sarcopenia pathogenesis via PI3K/Akt pathway activation.

Zhi Chen, Dingxiang Hu, Chengjian Wu, Zhengru Wu, Jiajun Lin, Wenge Liu.

   PURPOSE: Sarcopenia, characterized by progressive skeletal muscle loss and weakness, has unclear pathogenesis and lacks targeted therapies. Emerging evidence implicates ferroptosis in sarcopenia progression, though its regulatory mechanisms remain undefined. This study investigates the ferroptosis-sarcopenia interplay, identifies core regulators and elucidates their molecular basis.
METHODS: The experimental design combined in vivo and in vitro approaches using SAMP8 mice and C2C12 myoblast. Sarcopenia phenotypes were systematically characterized through functional assessments of mice, histomorphological analysis of gastrocnemius muscle, and quantification of iron deposition. Bioinformatics cross-analysis was performed by intersecting the sarcopenia-related gene expression dataset (GSE175495) with ferroptosis-associated genes from the FerrDb database, identifying ATF3 as a hub gene. Validation was conducted through Western blot (WB) and quantitative real-time PCR (qPCR). For mechanistic exploration, ferroptosis was induced in C2C12 cells using ferric ammonium citrate (FAC, 500 μM, 48 h), followed by lentivirus-mediated ATF3 overexpression. The regulatory role of ATF3 in ferroptosis was assessed via reactive oxygen species (ROS) assay, malondialdehyde (MDA) quantification, and FerroOrange fluorescent probe for intracellular iron detection. Transcriptome sequencing of ATF3-dysregulated cell lines was performed, and GO/ KEGG enrichment analyses were applied to identify critical signaling pathways. Functional validation was further conducted using pathway-specific inhibitors.
RESULTS: Aged SAMP8 mice exhibited hallmark sarcopenia characteristics including 31 % reduction in grip strength, 42 % decrease in muscle fiber cross-sectional area, and 2.1-fold elevation in intramuscular iron content. Molecular analysis revealed age-dependent downregulation of ATF3 expression (57 % protein decrease, 63 % mRNA reduction). ATF3 overexpression in C2C12 cells significantly attenuated ferroptosis, evidenced by 45-52 % reductions in ROS/MDA levels and reversal of atrophy-related protein expression. Transcriptomic profiling identified 773 differentially expressed genes functionally enriched in PI3K/Akt signaling, with ATF3 overexpression inducing 3.2-fold activation of p-Akt. Crucially, pharmacological PI3K inhibition completely abolished ATF3-mediated ferroptosis suppression, establishing pathway dependency.
CONCLUSION: These findings demonstrate that ATF3 serves as a critical molecular nexus linking ferroptosis regulation to sarcopenia pathogenesis through PI3K/Akt pathway activation.

Keywords:  ATF3; Ferroptosis; PI3K/ Akt pathway; Sarcopenia

DOI:  https://doi.org/10.1016/j.exger.2025.112830
Physiol Rep. 2025 Jul;13(13): e70458

Menstrual cycle influence on skeletal muscle mitochondrial respiration in humans.

W Bradley Nelson, Brandon S Pfeifer, Ashley R Lovell, Erik D Marchant, Briell V Mitchell, Erin L Atkinson, Trevor L Murphy, Sydney L Poulsen, Jay R K Baird, Chad R Hancock, Robert D Hyldahl.

  The menstrual cycle influences function in various tissues in the body. We sought to determine if menstrual cycle phase could influence mitochondrial function in skeletal muscle in females. Twenty-nine females with regular menstrual cycles were randomized to have a vastus lateralis muscle biopsy during either the early follicular or luteal phase. High-resolution respirometry was used to determine mitochondrial respiration on permeabilized muscle fibers. Glutamate/malate LEAK respiration was significantly higher during the luteal phase compared to the early follicular phase. Glutamate/malate/succinate LEAK respiration was the same during both menstrual cycle phases, as was maximal coupled and uncoupled respiration. There were no differences in fatty acid-supported respiration. The fatty acid-supported coupling efficiency ratios of 1-OcM (octanoylcarnitine/malate) LEAK over maximal coupled respiration and 1-OcM LEAK over maximal uncoupled respiration were both significantly higher in mitochondria from the early follicular phase than in the luteal phase. Mitochondrial H2O2 emission (glutamate/malate/succinate supported) was significantly increased in muscle from the early follicular phase. We detected no differences in mitochondrial content using citrate synthase activity between phases of the menstrual cycle. Collectively, our observations demonstrate a limited influence of the menstrual cycle on certain measures of submaximal respiration, coupling efficiencies, and H2O2 emission.

Keywords:  menstrual cycle phase; mitochondrial respiration; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.70458
EMBO J. 2025 Jul 15.

Proteomic aging signatures across mouse organs and life stages.

Enzo Scifo, Sarah Morsy, Ting Liu, Kan Xie, Kristina Schaaf, Daniele Bano, Dan Ehninger.

  Aging is associated with the accumulation of molecular damage, functional decline, increasing disease prevalence, and ultimately mortality. Although our system-wide understanding of aging has significantly progressed at the genomic and transcriptomic levels, the availability of large-scale proteomic datasets remains limited. To address this gap, we have conducted an unbiased quantitative proteomic analysis in male C57BL/6J mice, examining eight key organs (brain, heart, lung, liver, kidney, spleen, skeletal muscle, and testis) across six life stages (3, 5, 8, 14, 20, and 26-month-old animals). Our results reveal age-associated organ-specific as well as systemic proteomic alterations, with the earliest and most extensive changes observed in the kidney and spleen, followed by liver and lung, while the proteomic profiles of brain, heart, testis, and skeletal muscle remain more stable. Isolation of the non-blood-associated proteome allowed us to identify organ-specific aging processes, including oxidative phosphorylation in the kidney and lipid metabolism in the liver, alongside shared aging signatures. Trajectory and network analyses further reveal key protein hubs linked to age-related proteomic shifts. These results provide a system-level resource of protein changes during aging in mice, and identify potential molecular regulators of age-related decline.

Keywords:  Aging; Mass Spectrometry; Mouse Organs; Protein Trajectories; SureQuant

DOI:  https://doi.org/10.1038/s44318-025-00509-x
JCI Insight. 2025 Jul 15. pii: e192047. [Epub ahead of print]

Inhibition of AhR improves cortical bone and skeletal muscle function via preservation of neuromuscular junctions.

Kanglun Yu, Sagar Vyavahare, Dima W Alhamad, Husam Bensreti, Ling Ruan, Anik Tuladhar, Caihong Dai, Joseph C Shaver, Alok Tripathi, Kehong Ding, Rafal Pacholczyk, Marion A Cooley, Roger Zhong, Maribeth H Johnson, Jie Chen, Wendy B Bollag, Carlos M Isales, William D Hill, Mark W Hamrick, Sadanand Fulzele, Meghan E McGee-Lawrence.

  The aryl hydrocarbon receptor (AhR) is proposed to mediate the frailty-promoting effects of the tryptophan metabolite kynurenine (Kyn), which increases with age in mice and humans. The goal of the current study was to test whether administration of pharmacological AhR inhibitors, BAY2416964 and CH-223191, could abrogate musculoskeletal decline in aging mice. Female C57BL/6 mice (18 months old) were treated with vehicle (VEH) or BAY2416964 (30 mg/kg) via daily oral gavage 5 days/week for 8 weeks. A second AhR antagonist, CH-223191, was administered to 16-month-old male and female C57BL/6 mice via intraperitoneal injections (3.3 mg/kg) 3 days/week for 12 weeks. While grip strength declined over time in VEH-treated mice, BAY2416964 preserved grip strength in part by improving integrity of neuromuscular junctions, an effect replicated during in vitro studies with siRNA against AhR. Cortical bone mass was also greater in BAY2416964- than VEH-treated mice. Similarly, CH-223191 treatment improved cortical bone and showed beneficial effects in skeletal muscle, including reducing oxidative stress as compared to VEH-treated animals. Transcriptomic and proteomic data from BAY2416964-treated mice supported a positive impact of BAY2416964 on molecular targets that affect neuromuscular junction function. Taken together, these data support AhR as a therapeutic target for improving musculoskeletal health during aging.

Keywords:  Aging; Bone biology; Osteoclast/osteoblast biology; Osteoporosis; Skeletal muscle

DOI:  https://doi.org/10.1172/jci.insight.192047
bioRxiv. 2025 Jul 10. pii: 2025.07.08.663731. [Epub ahead of print]

The copper chaperone ATOX1 exhibits differential protein-protein interactions and contributes to skeletal myoblast differentiation.

Nathan Ferguson, Yu Zhang, Alexandra M Perez, Allison T Mezzell, Vinit C Shanbhag, Michael J Petris, Katherine E Vest.

Copper is an essential but potentially toxic nutrient required for a variety of biological functions. Mammalian cells use a complex network of copper transporters and metallochaperones to maintain copper homeostasis. Previous work investigating the role of copper in various disease states has highlighted the importance of copper transporters and metallochaperones. However, questions remain about how copper distribution changes under dynamic conditions like tissue differentiation. We previously reported that the copper exporter ATP7A is required for skeletal myoblast differentiation and that its expression changes in a differentiation dependent manner. Here, we sought to further understand the ATP7A-mediated copper export pathway by examining ATOX1, the copper chaperone that delivers copper to ATP7A. To investigate the role of ATOX1 in a dynamic cellular context, we characterized its binding partners during myoblast differentiation using the proximity labeling protein APEX2 to biotinylate proteins near ATOX1. We discovered that the ATOX1 interactome undergoes dramatic changes as myoblasts differentiate. These dynamic interactions correlate with distinct phenotypes of ATOX1 deficiency in proliferating and differentiated cells. Together, our results highlight the dynamic interactome of ATOX1 and its contribution to myoblast differentiation.

DOI: https://doi.org/10.1101/2025.07.08.663731
J Physiol. 2025 Jul 16.

Tendon's 'first aid' response - new insights into acute tendon molecular reprogramming after rupture.

M V Franchi, C S Fry, M Kjaer.



Keywords:  tendon; tendon acute rupture; transcriptomics

DOI:  https://doi.org/10.1113/JP289048
Nat Biotechnol. 2025 Jul;43(7): 1025

Eli Lilly in $650M pact to boost muscle.

DOI: https://doi.org/10.1038/s41587-025-02753-2
PLoS Genet. 2025 Jul 18. 21(7): e1011786

The insulin-like peptide INS-27 mediates a muscle-to-neuron feedback signal coupling muscle activity with AMPA receptor trafficking.

Bethany J Rennich, Regina M Powers, Samantha Moores, Molly Hodul, Peter Juo.

Regulation of AMPA Receptor (AMPAR) levels at synapses controls synaptic strength and is a major mechanism underlying learning and memory. Growing evidence indicates that AMPAR trafficking can be regulated by extracellular factors. Here, we show that the insulin-like peptide INS-27 mediates a muscle-to-neuron signal that promotes surface levels of the C. elegans AMPAR GLR-1 at synapses in pre-motor AVA interneurons that reside two synaptic layers upstream of the neuromuscular junction. Mutants lacking cholinergic neuromuscular signaling or muscle activity trigger an increase in surface GLR-1 levels in upstream AVA neurons. Genetic data suggest that this signal is dependent on the dense-core vesicle regulator unc-31/CAPS, the insulin-like peptide INS-27, which is one of the most highly expressed neuropeptides in muscle, and the Insulin/IGF-1 receptor DAF-2. ins-27 loss-of-function mutants exhibit decreased surface GLR-1 levels and defects in glutamatergic behavior. Further, loss of neuromuscular junction signaling stimulates secretion of INS-27 from muscle in an unc-31/CAPS-dependent manner. Our data support a model in which INS-27 is released from muscle and signals via DAF-2/Insulin/IGF-1 receptors to promote surface levels of GLR-1 in AVA neurons. Our study reveals a potential feedback signal that couples muscle activity with surface AMPARs in upstream neurons.

DOI: https://doi.org/10.1371/journal.pgen.1011786