Muscle biology
Abstract
While glucagon-like peptide-1 receptor agonists (GLP-1RAs) like semaglutide are effective in treating obesity, up to 45% of the resulting weight loss can be attributed to skeletal muscle loss. Given the critical role of skeletal muscle in health and mobility, this may have long-term adverse consequences. Herein we investigated whether oral ketone ester supplementation could prevent semaglutide-induced muscle loss and explored the underlying molecular mechanisms. Obese, glucose-intolerant mice received vehicle, semaglutide, or semaglutide plus a β-hydroxybutyrate–generating ketone ester for three weeks. Body composition, muscle strength, and endurance were assessed longitudinally. Semaglutide monotherapy reduced lean mass, impaired muscle strength, and suppressed mitochondrial gene expression while elevating atrophy-related genes in skeletal muscle samples. Co-administration with ketone ester preserved skeletal muscle mass and function without compromising fat loss. Mechanistically, ketone ester co-treatment prevented semaglutide-induced changes in mitochondrial and atrophy-related gene expression, suggesting mitochondrial defects and impaired ketone metabolism contribute to GLP-1RA-induced muscle loss. Together, these findings demonstrate that ketone ester supplementation can maintain muscle mass and performance during semaglutide-driven weight loss. These preclinical findings support ketone therapy as a promising strategy to counteract the sarcopenia-promoting effects of GLP-1RAs and warrant clinical evaluation to assess its translational potential.
Authors
Yasser Abuetabh, Mya A. Schmidt, Masaaki Naganuma, Ramana Vaka, Mahmoud A. El-Ghiaty, Shelly Braun, Ethan A. Kwan, Matthieu C.P. Zolondek, Darius Sahid, Laibah Khan, Rajat K. Shandal, Ashley L. Trudeau, Yaning Li, Sufyan O. Malik, Qiuyu Sun, Danica K. Roth, Daniela Y. Morales-Llamas, Jody L. Levasseur, Mourad Ferdaoussi, Richard P. Fahlman, Jason R.B. Dyck
Abstract
The composition of mitochondrial membrane lipids is crucial to cellular respiration, as seen in Barth syndrome (BTHS), a rare disease affecting skeletal muscle, heart, and neutrophils. In BTHS, mutations in the tafazzin (TAZ) gene reduce remodeling of the mitochondrial phospholipid, cardiolipin, causing mitochondrial dysfunction in skeletal muscle and heart. Here, we investigated effects of altering polyunsaturated fatty acid content in cardiolipin using preclinical models of BTHS. In vitro, the absence of TAZ did not impair omega-3 fatty acid incorporation into cardiolipin and resulted in increased turnover of these acyl chains. To examine this in a functional model, we generated a muscle-specific knockout mouse of TAZ (TAZ MKO), which recapitulated the human phenotype in skeletal muscle. Supplementing the diet of TAZ MKO with fish-oil-derived omega-3 fatty acids prevented lean mass loss, improved mitochondrial respiration, altered mitochondrial structure, and revealed moderate improvements in the stress response. Surprisingly, no diet-induced changes to cardiolipin species were observed in the TAZ MKO, but other phospholipids were altered by both genotype and diet, revealing complex regulation and potential compensation. Overall, this work provides evidence that omega-3 fatty acid supplementation is beneficial in muscle lacking TAZ to improve quality of life when added to current BTHS treatments.
Authors
Katharina B. Kuentzel, Ana Vranešević, Samuel A.J. Trammell, Fabian Finger, Jesper F. Havelund, Yvette L. Schooneveldt, Ivan Bradić, Nicoline R. Andersen, Anna S. Hassing, Katja T. Michler, Martin R. Larsen, Zachary Gerhart-Hines, Steven M. Claypool, Jonas T. Treebak, Andreas M. Fritzen, Matthew P. Gillum, Steen Larsen, Nils Færgeman, Trisha J. Grevengoed
Abstract
Duchenne muscular dystrophy (DMD) is a lethal pediatric striated muscle disease caused by loss of dystrophin for which there is no cure. Cardiomyopathy is the leading cause of death amongst individuals with DMD, and effective therapeutics to treat DMD cardiomyopathy are a major unmet clinical need. This work investigated adeno-associated viral (AAV) gene therapy approaches to treat DMD cardiomyopathy by overexpression of the calcium binding proteins S100A1 and apoptosis repressor with caspase recruitment domains (ARC). Using the severe D2.mdx mouse model of DMD, we identified that S100A1 gene therapy improves the diastolic dysfunction associated with DMD cardiomyopathy, whereas ARC gene therapy prolongs survival. The combination of both S100A1 and ARC in a single bicistronic vector improves the long-term cardiac outcome and histopathology of D2.mdx mice, development of heart failure caused by micro-dystrophin expression, and exhibits safety via intracoronary delivery in a canine model of DMD. In addition to robust cardiac benefits, S100A1-ARC gene therapy benefits D2.mdx skeletal muscle function and histopathology when driven by a striated muscle promoter. Together, these findings indicate that S100A1-ARC gene therapy represents an effective treatment for DMD cardiomyopathy and may have therapeutic benefits in treating other forms of cardiomyopathy and muscle pathologies.
Authors
David W. Hammers, Cora C. Hart, Eli A. Zerpa, Karen I. Laurent, Young il Lee, Margaret M. Sleeper, H. Lee Sweeney
Abstract
Immune responses against transgene products can compromise AAV-mediated gene transfer. Although several factors influencing this immunogenicity have been described, the early in vivo events driving CD8+ T cell activation remain poorly defined. Here, we examined antigen presentation kinetics following intramuscular AAV administration in mice. Strikingly, viral genomes were detected in draining lymph nodes as early as one hour post-injection, and transgene-derived peptides were presented to CD8+ T cells from day 1, resulting in progressive activation and first cell divisions detected at day 4. Removal of the injection site demonstrated that AAV particles reaching draining lymph nodes within the first hour were sufficient to induce cytotoxic transgene-specific CD8+ T cells. Finally, AAV vectors incorporating different muscle-specific promoters and regulatory sequences were evaluated. Although muscle-specific, all promoters exhibited variable transgene expression in dendritic cells in vitro, correlating with early T-cell activation in vivo; notably, those associated with higher early antigen presentation induced robust T cell response, whereas reduced presentation correlated with absence of CD8+ T cells. These findings reveal an unexpectedly early onset of transgene-derived epitope presentation, modulated by promoter specificity, which critically shapes CD8+ T cell response. This provides a rationale for evaluating and mitigating AAV immunogenicity in gene therapy design.
Authors
Lindsay Jeanpierre, Coralie Pecquet, Hanadi Saliba, Pauline Finard, Stéphane Terry, Gianni Tavella, Inès Guesmia, Sylvie Boutin, Bérangère Bertin, Sofia Benkhelifa-Ziyyat, Giuseppe Ronzitti, David-Alexandre Gross
Abstract
Centronuclear myopathies (CNMs) are rare congenital disorders characterized by muscle weakness, fiber hypotrophy, and organelle mislocalization. Most cases arise from mutations in MTM1 or DNM2, encoding myotubularin and dynamin-2, respectively. DNM2 is a GTPase that binds lipids, oligomerizes around membranes, and mediates fission. We previously showed that DNM2 levels are elevated in MTM1-CNM patients and Mtm1–/y mice, and that normalizing DNM2 rescues disease phenotypes. However, the specific DNM2 functions driving pathology remain unclear. Here, we expressed AAV-delivered WT and DNM2 mutants in WT and Mtm1–/y mouse muscles to disrupt specific DNM2 molecular functions. In WT mice, overexpression of WT DNM2 and most mutants induced CNM-like phenotypes, including reduced force, fiber hypotrophy, and centralized nuclei, consistent with gain-of-function mechanisms. The lipid-binding-defective mutant K562E did not induce disease-like phenotype. In Mtm1–/y mice, K562E mutant markedly improved muscle force, mass, and fiber size, while others failed to rescue. Therefore, we generated Mtm1–/y Dnm2K562E/+ mice, which showed full rescue of survival, motor function, and muscle force, with improved muscle mass, fiber size, and organelle positioning despite persistently elevated DNM2 levels. This study reveals that DNM2 lipid binding, not protein abundance or GTPase activity, drives pathology, and represents the most rational therapeutic target for DNM2 therapy in MTM1-CNM.
Authors
Raquel Gómez-Oca, Xènia Massana-Muñoz, David Reiss, Juliana De Carvalho Neves, Nadege Diedhiou, Roberto Silva-Rojas, Belinda S. Cowling, Marie Goret, Jocelyn Laporte
Abstract
Skeletal muscle pathology is a critical but poorly understood contributor to neuromuscular degeneration in spinal and bulbar muscular atrophy (SBMA), a CAG/polyglutamine (polyQ) expansion disorder caused by mutation in the androgen receptor (AR). Using a gene-targeted SBMA mouse model, we applied single-nucleus RNA sequencing to identify a disease-specific population of skeletal muscle myonuclei that replaced normal myonuclear subtypes. This transition was associated with dysregulation of the pathway governed by PGC-1α, a central regulator of myofiber specification and metabolic identity. PGC-1α dysfunction in SBMA muscle was age-, hormone-, and polyQ length–dependent and was partially rescued by subcutaneous delivery of AR-targeted antisense oligonucleotides. Integrated ChIP-seq and RNA-seq analyses revealed that aberrant PGC-1α activity promoted the expression of a distinct set of myofiber specification genes while downregulating those that define healthy Type IIb and Type IIx myonuclei. We propose a model in which this dysfunction arose downstream of polyQ-mediated sequestration of PGC-1α cofactors MEF2, CREB, and CBP, leading to transcriptional reprogramming and cellular dysfunction. These findings implicated PGC-1α dysregulation as a key event linking AR polyQ expansion to skeletal muscle degeneration and suggested a shared mechanism for polyQ-mediated muscle pathology across related neurodegenerative diseases.
Authors
Curtis J. Kuo, Laura B. Chopp, Zhigang Yu, Luhan Ni, Hien T. Zhao, Janghoo Lim, Andrew P. Lieberman
Abstract
Lysophosphatidic acid (LPA) is a bioactive lipid that signals through G protein–coupled receptors (LPA1–6) and regulates multiple cellular processes, including fibrosis. Although LPA signaling has been implicated in fibrotic diseases in several organs, its role in skeletal muscle remains unclear. Here, we show that LPA/LPA1 signaling promotes fibrogenesis after sciatic nerve transection. Denervation induces differential expression of LPA signaling axis components and a transient early increase in intramuscular LPA levels. Pharmacological inhibition of LPA1/3 with Ki16425, or genetic deletion of LPA1, reduces extracellular matrix accumulation and expansion of fibro/adipogenic progenitors (FAPs) in denervated muscle. Although LPA blockade suppresses atrophy-related gene expression, it does not fully preserve myofiber size. Mechanistically, denervation increases YAP/TAZ expression, nuclear localization in FAPs, and transcriptional activity, effects that are attenuated by LPA axis inhibition. Furthermore, pharmacological inhibition of YAP/TAZ with verteporfin reduces fibrosis after denervation, supporting their role as critical downstream mediators. Finally, transient denervation activates the LPA axis, promotes muscle fibrosis, reduces axonal density in the sciatic nerve, and increases neuromuscular junction instability, effects reversed by Ki16425. Together, these findings identify the LPA/LPA1/YAP/TAZ pathway as a key driver of denervation-induced muscle fibrosis and a potential therapeutic target in neuromuscular disorders.
Authors
Meilyn Cruz-Soca, Adriana Córdova-Casanova, Jennifer Faundez-Contreras, Nicolás W. Martínez, Francesca Vaccaro-Rivera, Sebastián Bazaes-Astorga, Cristian Gutiérrez-Rojas, Felipe S. Gallardo, Daniela L. Rebolledo, Felipe A. Court, Jerold Chun, Carlos P. Vio, Soledad Matus, Juan Carlos Casar, Enrique Brandan
Abstract
X-linked myotubular myopathy (XLMTM) is a rare genetic disorder that typically presents at birth with progressive muscle weakness and respiratory difficulties and is caused by myotubularin-1 (MTM1) gene mutations. Here we examine the role of phosphatidylinositol-4-phosphate 3-kinase catalytic subunit type 2 beta (PIK3C2B), a lipid kinase that interacts with MTM1, in XLMTM in various models. We examined the effect of BLU3797, a novel, highly potent, selective, orally bioavailable PIK3C2B inhibitor, on survival, muscle development, myofiber phenotypes, and gene expression in MTM1-/y mice. PIK3C2B-deficient XLMTM animals demonstrated increased survival, restored muscle function, fewer myofibers with centralized nuclei, and normalization of disease-associated molecular markers. BLU3797 alleviated the XLMTM phenotype in a dose-dependent and reversible manner. Loss of functional PIK3C2B in XLMTM mice promoted a more differentiated, adult-like myofiber profile, which was strongly associated with normalization of disease surrogates and a reduction in markers of early muscle development and regeneration. BLU3797 treatment appears to modulate the expression of microRNAs associated with satellite cell activation and myofiber fusion. These findings indicate that PIK3C2B inhibition with BLU3797 effectively reverses the XLMTM disease phenotype by enhancing muscle function and promoting development toward a more mature state.
Authors
Andrew Shearer, Melissa L. Brooks, Maxine M. Chen, Thiwanka Samarakoon, John Hsieh, Gramoz Kondakci, Emanuele Perola, Jason Brubaker, Kristina Fetalvero, Stefanie Schalm, Joana Caetano-Lopes
Abstract
Limb-girdle muscular dystrophy R2 (LGMD R2) is an autosomal recessive disorder caused by dysferlin deficiency, leading to progressive muscle weakness and wasting. The lack of reliable clinical biomarkers has limited disease monitoring and therapeutic evaluation. Here, we identified Disabled-2 (DAB2) as a molecular and clinical indicator of disease state in LGMD R2. Transcriptomic profiling revealed a significant upregulation of DAB2 in induced pluripotent stem cell–derived (iPSC-derived) myotubes from patients, a finding validated in muscle biopsies from 14 dysferlin-deficient individuals and in dysferlin-deficient Bla/J mice, where DAB2 levels increased with disease progression. Importantly, AAV-mediated expression of full-length dysferlin restored DAB2 levels, supporting its value as a dynamic readout of disease activity for both disease monitoring and therapeutic response. Given the established role of DAB2 in clathrin-mediated endocytosis, particularly in LDL receptor internalization and cholesterol homeostasis, and the pathological lipid accumulation reported in LGMD R2, we investigated its contribution to lipid dysregulation. High DAB2 expression paralleled lipid deposition in patient muscles, iPSC-derived myotubes, and mouse tissue, whereas siRNA-mediated DAB2 knockdown reduced lipid accumulation in LGMD R2 myotubes. Collectively, these findings suggest that DAB2 functions as a mechanistic link between dysferlin deficiency, altered lipid handling, and disease severity, and they highlight its potential as a prognostic marker and therapeutic response measure for LGMD R2.
Authors
Celine Bruge, Nathalie Bourg, Emilie Pellier, Quentin Miagoux, Manon Benabides, Noella Grossi, Hassan Hayat, Margot Jarrige, Helene Polveche, Valeria Agostini, Anthony Brureau, Stephane Vassilopoulos, Teresinha Evangelista, Gorka Fernández-Eulate, Tanya Stojkovic, Isabelle Richard, Xavier Nissan
Abstract
Thyroid hormone signaling is an essential regulator of skeletal muscle development, function, and metabolism, yet the specific signaling pathways required for muscle regeneration are not yet defined. We used scRNA-seq and the FUCCI (fluorescent ubiquitination-based cell cycle indicator) reporter mouse model to examine how hypothyroidism impacts repair processes after cardiotoxin-induced injury in mice. During regeneration, and up to 2 months after injury, hypothyroid muscles displayed smaller myofibers and a shift to slower oxidative fiber types. scRNA-seq of tibialis anterior muscle during regeneration revealed that hypothyroidism reduced myogenic-lineage diversity. Cell cycle analysis confirmed delayed cell cycle progression at 5 and 14 days after injury, with skeletal muscle stem cells stalled at the G1/S transition, hindering differentiation. Transcriptomic data revealed altered nonmyogenic dynamics, including elevated activated fibro-adipogenic progenitors (FAPs) early in repair and persistent proinflammatory macrophages. Integrative regulon and ligand-receptor analysis further demonstrated that triiodothyronine acted through dual modes: a direct transcriptional control of myogenic cell cycle and oxidative programs and an indirect paracrine remodeling mediated by FAP and immune signaling networks. This study identified what we believe to be novel effects of hypothyroidism on myogenic heterogeneity and impaired tissue repair, offering insights into muscle-wasting mechanisms relevant to hypothyroidism-associated myopathy and sarcopenia.
Authors
Paola Aguiari, Valentina Villani, Yan-Yun Liu, Gianni Carraro, Gregory A. Brent, Laura Perin, Anna Milanesi
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