Muscle biology
Abstract
Skeletal muscle frequently experiences oxygen depletion, especially during exercise, and the alpha subunit of the hypoxia-inducible factors (HIF1α and HIF2α) plays a crucial role in mediating cellular adaptation to low oxygen levels. However, although significant, the absence of an appropriate experimental mouse model leaves the precise roles of HIFα in myofibers unclear. Therefore, this study developed mice with myofiber-specific knockouts of prolyl hydroxylase proteins (PHDs), in which HIFα is stabilized, and inducible myofiber-specific overexpression of stable HIF1α or HIF2α to explore the role of HIFα in myofibers. Using three distinct mouse models, we found that HIF1α increased the number of oxidative fibers but paradoxically impaired exercise performance and mitochondrial function. Comparatively, HIF2α exerted protection mechanisms against glucose intolerance and diet-induced obesity. Notably, HIF2α stabilization in skeletal muscle markedly elevated erythropoietin (EPO) levels in muscle and serum but not in the kidney and liver, suggesting skeletal muscle is a previously unrecognized site of EPO production in the body. Thus, this study demonstrates the distinct roles of HIF1α and HIF2α in skeletal muscle, newly uncovering that the PHD-HIF2α axis produces EPO from myofibers.
Authors
Junhyeong Lee, Merc Emil Matienzo, Sangyi Lim, Edzel Evallo, Yeongsin Kim, Sujin Jang, Keon Kim, Chang Hyeon Choi, Youn Ho Han, Chang-Min Lee, Tae-Il Jeon, Sang-Ik Park, Jun Wu, Dong-il Kim, Min-Jung Park
Abstract
Muscle cell fusion is critical for the formation and maintenance of multinucleated myotubes during skeletal muscle development and regeneration. However, the molecular mechanisms directing cell-cell fusion are not fully understood. Here, we identified platelet-derived growth factor receptor β (PDGFRβ) signaling as a key modulator of myocyte function in adult muscle cells. Our findings demonstrated that genetic deletion of Pdgfrb enhanced muscle regeneration and increased myofiber size, whereas Pdgfrb activation impaired muscle repair. Inhibition of PDGFRβ activity promoted myonuclear accretion in both mouse and human myotubes, whereas PDGFRβ activation stalled myotube development by preventing cell spreading to limit fusion potential. Furthermore, PDGFRβ activity cooperated with TGF-β signaling to regulate myocyte size and fusion. Mechanistically, PDGFRβ signaling required STAT1 activation, and blocking STAT1 phosphorylation enhanced myofiber repair and size during regeneration. Collectively, PDGFRβ signaling acts as a regenerative checkpoint and represents a potential clinical target to improve skeletal muscle repair.
Authors
Siwen Xue, Abigail M. Benvie, Jamie E. Blum, Benjamin D. Cosgrove, Anna E. Thalacker-Mercer, Daniel C. Berry
Abstract
Statins lower cholesterol, reducing the risk of heart disease, and are among the most frequently prescribed drugs. Approximately 10% of individuals develop statin-associated muscle symptoms (SAMS; myalgias, rhabdomyolysis, and muscle weakness), often rendering them statin intolerant. The mechanism underlying SAMS remains poorly understood. Patients with mutations in the skeletal muscle ryanodine receptor 1 (RyR1)/calcium release channel can be particularly intolerant of statins. High-resolution structures revealed simvastatin binding sites in the pore region of RyR1. Simvastatin stabilized the open conformation of the pore and activated the RyR1 channel. In a mouse expressing a mutant RyR1-T4709M found in a patient with profound statin intolerance, simvastatin caused muscle weakness associated with leaky RyR1 channels. Cotreatment with a Rycal drug that stabilizes the channel closed state prevented simvastatin-induced muscle weakness. Thus, statin binding to RyR1 can cause SAMS, and patients with RyR1 mutations may represent a high-risk group for statin intolerance.
Authors
Gunnar Weninger, Haikel Dridi, Steven Reiken, Qi Yuan, Nan Zhao, Linda Groom, Jennifer Leigh, Yang Liu, Carl Tchagou, Jiayi Kang, Alexander Chang, Estefania Luna-Figueroa, Marco C. Miotto, Anetta Wronska, Robert T. Dirksen, Andrew R. Marks
Abstract
BACKGROUND. Spinal muscular atrophy (SMA) is a rare genetic neuromuscular disease caused by deletions or mutations of the survival motor neuron 1 gene. Despite the availability of genetically-based treatments for SMA, functional impairments and weakness persist in treated symptomatic individuals. This study addresses whether additional treatment after gene transfer therapy could provide further clinical benefits. METHODS. Interim Day 302 findings are described from the phase 4 open-label RESPOND trial evaluating nusinersen in participants aged ≤ 36 months who had suboptimal clinical status following onasemnogene abeparvovec (OA) treatment, as determined by the investigator. RESULTS. Thirty-seven participants included in the interim analysis were symptomatic at the time of OA administration. Most (92%) had two survival motor neuron 2 gene copies. Age at first nusinersen dose (median [range]) was 9.1 (3–33) months for participants with two SMN2 copies and 34.2 (31–36) months for those with three SMN2 copies, while time from OA dose to first nusinersen dose (median [range]) was 6.3 (3–31) and 13.3 (10–22) months, respectively. Participants had elevated neurofilament light chain (NfL) levels and low compound muscle action potential (CMAP) amplitudes at baseline, suggesting active neurodegeneration and severe denervation at study entry. Improvements from baseline were observed across a range of outcomes at Day 302, including motor function outcomes (HINE-2 and CHOP-INTEND total score), achievement of independent sitting, NfL levels, CMAP, and investigator- and caregiver-reported outcomes. Mean NfL levels decreased rapidly from baseline to Day 183 and remained low at Day 302. Mean ulnar and peroneal CMAP amplitudes increased. No safety concerns were identified. CONCLUSION. Improvements in clinical and biomarker outcomes support the benefit of nusinersen treatment in infants and children with suboptimal clinical status following OA. TRIAL REGISTRATION. ClinicalTrials.gov ID, NCT04488133; EudraCT number, 2020-003492-18. FUNDING. This study was sponsored by Biogen (Cambridge, MA, USA).
Authors
Crystal M. Proud, Richard S. Finkel, Julie A. Parsons, Riccardo Masson, John F. Brandsema, Nancy L. Kuntz, Richard Foster, Wenjing Li, Ross Littauer, Jihee Sohn, Stephanie Fradette, Bora Youn, Angela D. Paradis
Abstract
A single bout of exercise improves muscle insulin sensitivity for up to 48 hours via the AMP-activated protein kinase (AMPK). Limb ischemia activates AMPK in muscle, and subsequent reperfusion enhances insulin-stimulated vasodilation, potentially eliciting a more pronounced exercise effect with reduced workload. Here, we investigated the combined effect of upper leg intermittent ischemia-reperfusion (IIR) and continuous knee-extension exercise on muscle insulin sensitivity regulation. We found that IIR-exercise potentiated AMPK activation and muscle insulin sensitivity. The potentiating effect of IIR-exercise on muscle insulin sensitivity was associated with increased insulin-stimulated blood flow in parallel with enhanced phosphorylation of endothelial nitric oxide synthase. Metabolomics analyses demonstrated a suppression of muscle medium-chain acylcarnitines during IIR-exercise, which correlated with insulin sensitivity and was consistent with findings in isolated rat muscle treated with Decanoyl-L-carnitine. Collectively, combining IIR with low-to-moderate intensity exercise may represent a promising intervention to effectively enhance muscle insulin sensitivity. This approach could offer potential for mitigating muscle insulin resistance in clinical settings and among individuals with lower physical activity levels.
Authors
Kohei Kido, Janne R. Hingst, Johan Onslev, Kim A. Sjøberg, Jesper B. Birk, Nicolas O. Eskesen, Tongzhu Zhou, Kentaro Kawanaka, Jesper F. Havelund, Nils J. Færgeman, Ylva Hellsten, Jørgen F.P. Wojtaszewski, Rasmus Kjøbsted
Abstract
Authors
Masahiko Shigemura, Felix L. Nunez-Santana, S.Marina Casalino-Matsuda, David Kirchenbuechler, Radmila Nafikova, Fei Chen, Zhan Yu, Yuliana V. Sokolenko, Estefani Diaz, Suchitra Swaminathan, Suror Mohsin, Rizaldy P. Scott, Lynn C. Welch, Chitaru Kurihara, Emilia Lecuona, G.R. Scott Budinger, Peter H. S. Sporn, Jacob I. Sznajder, Ankit Bharat
Abstract
Facioscapulohumeral muscular dystrophy (FSHD) is a genetic muscle disease caused by ectopic expression of the toxic protein DUX4, resulting in muscle weakness. However, the mechanism by which DUX4 exerts its toxicity remains unclear. In this study, we observed abnormal iron accumulation in muscles of patients with FSHD and in muscle-specific DUX4-expressing (DUX4-Tg) mice. Treatment with iron chelators, an iron-deficient diet, and genetic modifications inhibiting intracellular uptake of iron did not improve but rather exacerbated FSHD pathology in DUX4-Tg mice. Unexpectedly, however, iron supplementation, either from a high-iron diet or intravenous iron administration, resulted in remarkable improvement in grip strength and running performance in DUX4-Tg mice. Iron supplementation suppressed abnormal iron accumulation and the ferroptosis-related pathway involving increased lipid peroxidation in DUX4-Tg muscle. Muscle-specific DUX4 expression led to retinal vasculopathy, a part of FSHD pathology, which was prevented by iron administration. Furthermore, high-throughput compound screening of the ferroptosis pathway identified drug candidates including Ferrostatin-1 (Fer-1), a potent inhibitor of lipid peroxidation. Treatment with Fer-1 dramatically improved physical function in DUX4-Tg mice. Our findings demonstrate that DUX4-provoked toxicity is involved in the activation of the ferroptosis-related pathway and that supplementary iron could be a promising and readily available therapeutic option for FSHD.
Authors
Kodai Nakamura, Huascar-Pedro Ortuste-Quiroga, Naoki Horii, Shin Fujimaki, Toshiro Moroishi, Keiichi I. Nakayama, Shinjiro Hino, Yoshihiko Saito, Ichizo Nishino, Yusuke Ono
Abstract
The dystrophin-glycoprotein complex (DGC) is composed of peripheral and integral membrane proteins at the muscle cell membrane that link the extracellular matrix with the intracellular cytoskeleton. While it is well-established that genetic mutations that disrupt the structural integrity of DGC result in numerous muscular dystrophies, the three-dimensional structure of the complex has remained elusive. Two recent elegant cryoEM structures of DGC illuminate its molecular architecture and reveal the unique structural placement of sarcospan (SSPN) within the complex. SSPN, a 25-kDa tetraspanin-like protein, anchors beta-dystroglycan to the beta-, gamma- and delta-sarcoglycan trimer, supporting biochemical studies that SSPN is a core element for DGC assembly and stabilization. Here, we advance these studies by revealing that SSPN provides scaffolding in gamma-sarcoglycanopathies enabling substitution of gamma-sarcoglycan by its homolog, zeta-sarcoglycan, leading to the structural integrity of the DGC and prevention of limb-girdle muscular dystrophy R5. Three-dimensional modeling reveals that zeta-sarcoglycan preserves protein-protein interactions with the sarcospan, sarcoglycans, dystroglycan, and dystrophin. The structural integrity of the complex maintains myofiber attachment to the extracellular matrix and protect the cell membrane from contraction-induced damage. These findings demonstrate that sarcospan prevents limb-girdle muscular dystrophy R5 by remodeling of the sarcoglycan complex composition.
Authors
Ekaterina I. Mokhonova, Daniel Helzer, Ravinder Malik, Hafsa Mamsa, Jackson Walker, Mark Maslanka, Tess S. Fleser, Mohammad H. Afsharinia, Shiheng Liu, Johan Holmberg, Z. Hong Zhou, Eric J. Deeds, Kirk C. Hansen, Elizabeth M. McNally, Rachelle H. Crosbie
MuSK cysteine-rich domain antibodies are pathogenic in a mouse model of autoimmune myasthenia gravis
Abstract
The neuromuscular junction (NMJ), synapse between the motor neuron terminal and a skeletal muscle fiber is crucial, throughout life, in maintaining the reliable neurotransmission required for functional motricity. Disruption of this system leads to neuromuscular disorders, such as auto-immune myasthenia gravis (MG), the most common form of NMJ diseases. MG is caused by autoantibodies directed mostly against the acetylcholine receptor (AChR) or the muscle-specific kinase MuSK. Several studies report immunoreactivity to the Frizzled-like cysteine-rich Wnt-binding domain of MuSK (CRD) in patients, although the pathogenicity of the antibodies involved remains unknown. We showed here that the immunoreactivity to MuSK CRD induced by the passive transfer of anti-MuSKCRD antibodies in mice led to typical MG symptoms, characterized by a loss of body weight and a locomotor deficit. The functional and morphological integrity of the NMJ was compromised with a progressive decay of neurotransmission and disruption of the structure of pre- and post-synaptic compartments. We found that anti-MuSKCRD antibodies completely abolished Agrin-mediated AChR clustering by decreasing the Lrp4-MuSK interaction. These results provide the first demonstration of the role of the MuSK CRD in MG pathogenesis and improve our understanding of the underlying pathophysiological mechanisms.
Authors
Marius Halliez, Steve Cottin, Axel You, Céline Buon, Antony Grondin, Léa S. Lippens, Megane Lemaitre, Jérome Ezan, Charlotte Isch, Yann Rufin, Mireille Montcouquiol, Nathalie Sans, Bertrand Fontaine, Julien Messéant, Rozen Le Panse, Laure Strochlic
Abstract
Gene replacement therapies mediated by adeno-associated viral (AAV) vectors represent a promising approach for treating genetic diseases. However, their modest packaging capacity (~4.7 kb) remains an important constraint and significantly limits their application for genetic disorders involving large genes. A prominent example is Duchenne muscular dystrophy (DMD), whose protein product dystrophin is generated from an 11.2 kb segment of the DMD mRNA. Here, we explored methods that enable efficient expression of full-length dystrophin via triple AAV co-delivery. This method exploits the protein trans-splicing mechanism mediated by split inteins. We identified a combination of efficient and specific split intein pairs that enables the reconstitution of full-length dystrophin from three dystrophin fragments. We show that systemic delivery of low doses of the myotropic AAVMYO1 in mdx4cv mice leads to efficient expression of full-length dystrophin in the hindlimb, diaphragm, and heart muscles. Notably, muscle morphology and physiology were significantly improved in triple AAV-treated mdx4cv mice versus saline-treated controls. This method shows the feasibility of expressing large proteins from several fragments that are delivered using low doses of myotropic AAV vectors. It can be adapted to other large genes involved in disorders for which gene replacement remains challenged by the modest AAV cargo capacity.
Authors
Hichem Tasfaout, Timothy S. McMillen, Theodore R. Reyes, Christine L. Halbert, Rong Tian, Michael Regnier, Jeffrey S. Chamberlain
Copyright © 2026 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)