Muscle biology
Abstract
Facioscapulohumeral muscular dystrophy (FSHD) is driven by aberrant expression of the early embryonic transcription factor Double Homeobox 4 (DUX4), yet the mechanisms linking low, sporadic DUX4 activity to progressive muscle degeneration remain unclear. Here, we identify cellular senescence as a central and early mechanism in FSHD pathogenesis. Analysis of patient muscle transcriptomes revealed strong enrichment of senescence and senescence-associated secretory phenotype (SASP) programs that correlated with DUX4 activity, clinical severity, and histopathological changes. Notably, these signatures were detectable even in STIR-negative muscles, defining a prodystrophic state characterized by early molecular alterations preceding overt MRI-detectable inflammation and highlighting their potential utility as early biomarkers of disease activity. Using an FSHD mouse model, we show that DUX4-induced muscle injury rapidly triggers senescence, which then progressively expands. Fibroadipogenic progenitors and macrophages emerged as the principal senescent populations and key sources of pro-inflammatory and profibrotic SASP signals. Importantly, senescence was therapeutically modifiable. Treatment with the nucleoside reverse transcriptase inhibitor lamivudine (3TC), which inhibits LINE-1 reverse transcriptase activity, significantly reduced senescence, inflammation, and fibrosis while promoting muscle regeneration. These findings identify cellular senescence as a tractable driver of FSHD and warrant senotherapeutic strategies, particularly lamivudine, for clinical intervention in FSHD.
Authors
Usuk Jung, Erdong Wei, Ana Mitanoska, Philipp Heher, Kenric Chen, Haseeb Ahsan, Xu Zhang, Giorgio Tasca, Paul D. Robbins, Nathan K. LeBrasseur, Michael Kyba, Darko Bosnakovski
Abstract
Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, most of which are large exon deletions that result in loss of dystrophin protein. Adenine base editing (ABE) enables permanent gene correction by modifying splice sites to cause exon skipping and restoration of the DMD open reading frame. We previously demonstrated that adeno-associated virus 9–mediated (AAV9-mediated) delivery of adenine base editors allows efficient gene editing in mouse models of DMD. However, conventional AAV-based gene delivery approaches are complicated by their limited packaging capacity and high-dose-related toxicity. Here, we describe a single AAV vector encoding a compact adenine base editor, SlugABE8e, and a single-guide RNA, which enable efficient editing in a humanized DMD mouse model at a lower dose using the muscle-tropic MyoAAV4 capsid. Systemic MyoAAV4A delivery in juvenile DMD mice efficiently restored dystrophin expression in the heart and skeletal muscles. This molecular rescue was accompanied by reduced serum creatine kinase activity and diminished muscle pathology. A liver-detargeted MyoAAV4E-off capsid eliminated viral entry and editing in the liver. We also explored a high-fidelity base editor, SlugHF-ABE8e(V106W), which showed similar on-target and off-target editing to SlugABE8e. Together, these findings establish an all-in-one AAV strategy that efficiently mitigates DMD disease progression.
Authors
Yu-Chung Pien, Hui Li, Gabrielle Bulliard, Huachun Liu, Mateusz Z. Durbacz, Zhisheng Xu, Andreas C. Chai, Francesco Chemello, Efrain Sanchez-Ortiz, Nerea Zabaleta, Luk H. Vandenberghe, Ning Liu, Eric N. Olson
Abstract
Pain is a common and disabling feature of myotonic disorders, yet its biological basis remains poorly understood and no targeted analgesic therapies currently exist. Here, we demonstrate that skeletal muscle hyperexcitability is sufficient to initiate a persistent pain state independent of inflammation, nerve injury, or overt tissue damage. Using complementary pharmacological and genetic models of myotonia resulting from loss of the voltage-gated skeletal muscle chloride channel ClC-1 function, we show that transient and chronic myotonia produce robust mechanical, thermal, and cold hypersensitivity, as well as spontaneous pain-like behavior. Notably, pain-like behaviors induced by transient myotonia persist long after overt motor symptoms have resolved, suggesting that a transient episode of muscle hyperexcitability is sufficient to trigger prolonged alterations in nociceptive processing. Physiological recordings revealed altered excitability of dorsal root ganglion and superficial dorsal horn neurons and enhanced sensory-evoked activity in the parabrachial nucleus, indicating altered nociceptive processing across multiple levels of the pain neuraxis. Transient myotonia increased total sodium current density in sensory neurons, with a shift toward a greater tetrodotoxin-resistant current fraction. Pharmacological inhibition with the NaV1.8-directed analgesic Suzetrigine markedly attenuated pain-like behaviors in both models of myotonia. Together, these findings establish a link between myotonia and persistent alterations in nociceptive processing and identify NaV1.8-directed analgesia as a promising therapeutic strategy for myotonia-associated pain.
Authors
Tyler S. Nelson, Aida Calderon-Rivera, Heather N. Allen, Alaina L Waters, Emanuel Loeza-Alcocer, Jorge B. Pineda-Farias, Narges Pachenari, Santiago Loya-Lopez, Kimberly Gomez, Erick J. Rodriguez-Palma, Paz Duran, Michael S. Gold, Rajesh Khanna
Abstract
Mutations in the survival of motor neuron 1 (SMN1) can reduce functional SMN protein levels, which causes Spinal Muscular Atrophy (SMA), a disease affecting the nervous system and peripheral tissues, including the immune system. Yet, SMN expression across immune cell subsets and the impact of SMN-modulating therapies on the immune system remains underexplored. We found that in neonatal mouse spleen, SMN expression was highest in B cells, which were massively reduced in SMA mice. In human PBMCs from adults, DCs and monocytes expressed the highest SMN levels, whereas SMA patients showed reduced DC and increased B cell frequencies. Patients receiving systemic versus CNS-restricted therapy showed similar differences in immune cell composition and SMN levels. Similarly, an exploratory cohort including untreated patients did not indicate a substantial treatment-specific effect relative to controls. To assess the impact of differentiation on SMN, PMA-treated THP-1 cells were analyzed, revealing enhanced aberrant SMN splicing and increased SMN-positive Cajal bodies. In conclusion, SMN levels vary across immune cell types, and reduced SMN levels are associated with altered immune cell composition. Immune alterations and decreased SMN levels were observed in both treated and untreated SMA patients and may contribute to dysfunctions of the immune system in SMA.
Authors
Ines Tapken, Katharina Rahmel-Stein, Christine Ehlers, Federica Cieri, Nora T. Detering, Tobias Schüning, Bogdan Bjelica, Charlotte Mindermann, Svenja Neuhoff, Linda-Isabell Schmitt, Markus Leo, Tim Hagenacker, Sabine Illsinger, Elia Di Schiavi, Theresa Graalmann, Susanne Petri, Ulrich Kalinke, Peter Claus
Abstract
We previously identified a muscular dystrophy caused by biallelic variants in JAG2, whose protein product Jagged2 JAGGED2 (JAG2) is a canonical Notch NOTCH ligand. However, the disease mechanism remains unclear, particularly with respect to muscle stem cell (MuSC) function and muscle regeneration. We examined the consequences of JAG2 deficiency and modeled pathogenic JAG2 variants in vitro and in vivo, the latter in mouse and fly models and with particular attention to the MuSC-muscle endothelial cell (MuEC) niche. We found that both Jag2 deficiency and overexpression of pathogenic JAG2 variants impaired NOTCHNotch signaling and myogenic self-renewal and differentiation. Hypomorphic Jag2 mutant (Jag2sm) mice display depleted MuSCs, corresponding with impaired muscle regeneration in those mice. Co-culture experiments and the examination of cell-type-specific Jag2 conditional knockout mice demonstrated that MuEC-specific Jag2 knockout resulted in reduced MuSC self-renewal, while MuSC-specific Jag2 knockout resulted in reduced myogenic differentiation. Human reference JAG2, but not human pathogenic variants of JAG2, rescued the deficiency of Serrate (Ser), the Drosophila ortholog of JAG2. Therefore, pathogenic variants in JAG2 impair muscle development and regeneration through disrupted cell-autonomous cis-inhibition and non-autonomous trans-activation involving NOTCHNotch signaling dysfunction. Our findings indicate that optimizing JAG2-mediated NOTCHNotch signaling is a potential therapeutic approach for JAG2-related muscular dystrophy.
Authors
Minoru Tanaka, Nam Chul Kim, Isabelle Draper, Hannah R. Littel, Mekala Gunasekaran, Johnnie Turner, Natalya M. Wells, Qasim Mujteba, Yoko Asakura, Peter B. Kang, Atsushi Asakura
Abstract
Coenzyme A (CoA) facilitates fatty acid synthesis, energy production, gene regulation, and antioxidant function. While CoA biosynthesis is well-characterized, the mechanisms governing CoA degradation remain poorly understood. Here, we identify the Metazoan Homolog of SpoT, MESH1, as a CoA phosphatase that dephosphorylates CoA at the 3’ position of the ribose ring to form dephospho-CoA (dp-CoA). Recent studies have shown that CoA, similar to glutathione (GSH), is a cysteine-derived metabolite that protects cells against ferroptosis. Ferroptosis induced by blocking cystine import depletes CoA biosynthesis, while CoA restoration rescues cells from ferroptosis. We found that MESH1 knockdown preserved CoA levels by preventing its degradation, contributing to ferroptosis protection, indicating the bifunctional role of MESH1 in regulating CoA and previously reported NADPH. Mechanistically, MESH1 knockdown elevates CoA levels, maintaining functional mitochondrial thioredoxin system, thereby preventing mitochondrial lipid peroxidation. In Drosophila, we found that dMesh1 overexpression leads to ferroptosis-mediated muscle atrophy, which can be rescued by increasing CoA and NADPH levels. Taken together, these findings establish MESH1 as a key phosphatase that governs ferroptosis sensitivity by coordinating CoA and NADPH homeostasis, unveiling a novel link between CoA degradation, mitochondrial integrity, and muscle health.
Authors
Chao-Chieh Lin, Joshua Rose, Alexander A. Mestre, Chien-Kuang C. Ding, Ssu-Yu Chen, Sze Mun Choy, Kah Yong Goh, Weiyi Jiang, Wen Xing Lee, Qizhou Jiang, Yanting Chen, Tianai Sun, Jianli Wu, Yueqi Chen, Yunju Oh, Pyeonghwa Jeong, Jiyong Hong, Kenon Chua, Michael C. Fitzgerald, Guo-Fang Zhang, Hong-Wen Tang, Pei Zhou, Jen-Tsan Chi
Abstract
The immune system is not only essential for host defense, but it is also involved in tissue maintenance and disease pathogenesis. Macrophages play a key role in tissue repair, fibrosis, and tumorigenesis, but the mechanisms underlying their multifunctionality have not been fully explored. Here, we identified Mrep (Ly6ChiCX3CR1loPDPN+CD9+) as a crucial subset of macrophages for muscle regeneration after muscle injury. Muscle regeneration required Mrep-derived activin A, which was produced via the TLR4/TIR domain–containing adapter-inducing interferon-β/TANK-binding kinase 1/interferon regulatory factor 3/7 signaling pathway in response to muscle injury. Mrep exerted pathological effects by secreting activin A in a model of genetically induced heterotopic ossification (HO), which was suppressed by TLR4 inhibition. Thus, this study elucidates the context-dependent functions of macrophages and the link between injury and HO, suggesting that Mrep is a potential therapeutic target for regenerating muscles and suppressing HO.
Authors
Wenqiang Yin, Kazuo Okamoto, Asuka Terashima, Warunee Pluemsakunthai, Takehito Ono, Taku Ito-Kureha, Shizuo Akira, Yoshinobu Hashizume, Roland Baron, Satoshi Ueha, Kouji Matsushima, Martin M. Matzuk, Yuji Mishina, Hiroshi Takayanagi
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
Copyright © 2026 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)