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Korb A, Tajbakhsh S, Comai GE. Functional specialisation and coordination of myonuclei. Biol Rev Camb Philos Soc 2024; 99:1164-1195. [PMID: 38477382 DOI: 10.1111/brv.13063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Revised: 01/30/2024] [Accepted: 02/02/2024] [Indexed: 03/14/2024]
Abstract
Myofibres serve as the functional unit for locomotion, with the sarcomere as fundamental subunit. Running the entire length of this structure are hundreds of myonuclei, located at the periphery of the myofibre, juxtaposed to the plasma membrane. Myonuclear specialisation and clustering at the centre and ends of the fibre are known to be essential for muscle contraction, yet the molecular basis of this regionalisation has remained unclear. While the 'myonuclear domain hypothesis' helped explain how myonuclei can independently govern large cytoplasmic territories, novel technologies have provided granularity on the diverse transcriptional programs running simultaneously within the syncytia and added a new perspective on how myonuclei communicate. Building upon this, we explore the critical cellular and molecular sources of transcriptional and functional heterogeneity within myofibres, discussing the impact of intrinsic and extrinsic factors on myonuclear programs. This knowledge provides new insights for understanding muscle development, repair, and disease, but also opens avenues for the development of novel and precise therapeutic approaches.
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Affiliation(s)
- Amaury Korb
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
| | - Shahragim Tajbakhsh
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
| | - Glenda E Comai
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
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2
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Schellino R, Boido M, Vrijbloed JW, Fariello RG, Vercelli A. Synergistically Acting on Myostatin and Agrin Pathways Increases Neuromuscular Junction Stability and Endurance in Old Mice. Aging Dis 2024; 15:893-910. [PMID: 37548943 PMCID: PMC10917542 DOI: 10.14336/ad.2023.0713-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Accepted: 07/13/2023] [Indexed: 08/08/2023] Open
Abstract
Sarcopenia is the primary cause of impaired motor performance in the elderly. The current prevailing approach to counteract such condition is increasing the muscle mass through inhibition of the myostatin system: however, this strategy only moderately improves muscular strength, not being able to sustain the innervation of the hypertrophic muscle per se, leading to a progressive worsening of motor performances. Thus, we proposed the administration of ActR-Fc-nLG3, a protein that combines the soluble activin receptor, a strong myostatin inhibitor, with the C-terminal agrin nLG3 domain. This compound has the potential of reinforcing neuro-muscular stability to the hypertrophic muscle. We previously demonstrated an enhancement of motor endurance and ACh receptor aggregation in young mice after ActR-Fc-nLG3 administration. Now we extended these observations by demonstrating that also in aged (2 years-old) mice, long-term administration of ActR-Fc-nLG3 increases in a sustained way both motor endurance and muscle strength, compared with ActR-Fc, a myostatin inhibitor, alone. Histological data demonstrate that the administration of this biological improves neuromuscular stability and fiber innervation maintenance, preventing muscle fiber atrophy and inducing only moderate hypertrophy. Moreover, at the postsynaptic site we observe an increased folding in the soleplate, a likely anatomical substrate for improved neurotransmission efficiency in the NMJ, that may lead to enhanced motor endurance. We suggest that ActR-Fc-nLG3 may become a valid option for treating sarcopenia and possibly other disorders of striatal muscles.
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Affiliation(s)
- Roberta Schellino
- Department of Neuroscience Rita Levi-Montalcini, University of Turin, Turin 10126, Italy
- Neuroscience Institute Cavalieri Ottolenghi, University of Turin, Orbassano, 10043 Italy
| | - Marina Boido
- Department of Neuroscience Rita Levi-Montalcini, University of Turin, Turin 10126, Italy
- Neuroscience Institute Cavalieri Ottolenghi, University of Turin, Orbassano, 10043 Italy
| | | | | | - Alessandro Vercelli
- Department of Neuroscience Rita Levi-Montalcini, University of Turin, Turin 10126, Italy
- Neuroscience Institute Cavalieri Ottolenghi, University of Turin, Orbassano, 10043 Italy
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3
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Fernández-Martínez J, Ramírez-Casas Y, Yang Y, Aranda-Martínez P, Martínez-Ruiz L, Escames G, Acuña-Castroviejo D. From Chronodisruption to Sarcopenia: The Therapeutic Potential of Melatonin. Biomolecules 2023; 13:1779. [PMID: 38136651 PMCID: PMC10741491 DOI: 10.3390/biom13121779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 12/04/2023] [Accepted: 12/07/2023] [Indexed: 12/24/2023] Open
Abstract
Sarcopenia is an age-related condition that involves a progressive decline in muscle mass and function, leading to increased risk of falls, frailty, and mortality. Although the exact mechanisms are not fully understood, aging-related processes like inflammation, oxidative stress, reduced mitochondrial capacity, and cell apoptosis contribute to this decline. Disruption of the circadian system with age may initiate these pathways in skeletal muscle, preceding the onset of sarcopenia. At present, there is no pharmacological treatment for sarcopenia, only resistance exercise and proper nutrition may delay its onset. Melatonin, derived from tryptophan, emerges as an exceptional candidate for treating sarcopenia due to its chronobiotic, antioxidant, and anti-inflammatory properties. Its impact on mitochondria and organelle, where it is synthesized and crucial in aging skeletal muscle, further highlights its potential. In this review, we discuss the influence of clock genes in muscular aging, with special reference to peripheral clock genes in the skeletal muscle, as well as their relationship with melatonin, which is proposed as a potential therapy against sarcopenia.
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Affiliation(s)
- José Fernández-Martínez
- Centro de Investigación Biomédica, Facultad de Medicina, Departamento de Fisiología, Instituto de Biotecnología, Parque Tecnológico de Ciencias de la Salud, Universidad de Granada, 18016 Granada, Spain; (J.F.-M.); (Y.R.-C.); (P.A.-M.); (L.M.-R.); (G.E.)
- Instituto de Investigación Biosanitaria (Ibs.Granada), Hospital Universitario San Cecilio, 18016 Granada, Spain
| | - Yolanda Ramírez-Casas
- Centro de Investigación Biomédica, Facultad de Medicina, Departamento de Fisiología, Instituto de Biotecnología, Parque Tecnológico de Ciencias de la Salud, Universidad de Granada, 18016 Granada, Spain; (J.F.-M.); (Y.R.-C.); (P.A.-M.); (L.M.-R.); (G.E.)
- Instituto de Investigación Biosanitaria (Ibs.Granada), Hospital Universitario San Cecilio, 18016 Granada, Spain
| | - Yang Yang
- Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, Faculty of Life Sciences and Medicine, Northwest University, Xi’an 710069, China;
| | - Paula Aranda-Martínez
- Centro de Investigación Biomédica, Facultad de Medicina, Departamento de Fisiología, Instituto de Biotecnología, Parque Tecnológico de Ciencias de la Salud, Universidad de Granada, 18016 Granada, Spain; (J.F.-M.); (Y.R.-C.); (P.A.-M.); (L.M.-R.); (G.E.)
- Instituto de Investigación Biosanitaria (Ibs.Granada), Hospital Universitario San Cecilio, 18016 Granada, Spain
| | - Laura Martínez-Ruiz
- Centro de Investigación Biomédica, Facultad de Medicina, Departamento de Fisiología, Instituto de Biotecnología, Parque Tecnológico de Ciencias de la Salud, Universidad de Granada, 18016 Granada, Spain; (J.F.-M.); (Y.R.-C.); (P.A.-M.); (L.M.-R.); (G.E.)
- Instituto de Investigación Biosanitaria (Ibs.Granada), Hospital Universitario San Cecilio, 18016 Granada, Spain
| | - Germaine Escames
- Centro de Investigación Biomédica, Facultad de Medicina, Departamento de Fisiología, Instituto de Biotecnología, Parque Tecnológico de Ciencias de la Salud, Universidad de Granada, 18016 Granada, Spain; (J.F.-M.); (Y.R.-C.); (P.A.-M.); (L.M.-R.); (G.E.)
- Instituto de Investigación Biosanitaria (Ibs.Granada), Hospital Universitario San Cecilio, 18016 Granada, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Instituto de Salud Carlos III (ISCIII), 28029 Madrid, Spain
| | - Darío Acuña-Castroviejo
- Centro de Investigación Biomédica, Facultad de Medicina, Departamento de Fisiología, Instituto de Biotecnología, Parque Tecnológico de Ciencias de la Salud, Universidad de Granada, 18016 Granada, Spain; (J.F.-M.); (Y.R.-C.); (P.A.-M.); (L.M.-R.); (G.E.)
- Instituto de Investigación Biosanitaria (Ibs.Granada), Hospital Universitario San Cecilio, 18016 Granada, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Instituto de Salud Carlos III (ISCIII), 28029 Madrid, Spain
- UGC de Laboratorios Clínicos, Hospital Universitario San Cecilio, 18016 Granada, Spain
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Bagley JR, Denes LT, McCarthy JJ, Wang ET, Murach KA. The myonuclear domain in adult skeletal muscle fibres: past, present and future. J Physiol 2023; 601:723-741. [PMID: 36629254 PMCID: PMC9931674 DOI: 10.1113/jp283658] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Accepted: 01/06/2023] [Indexed: 01/12/2023] Open
Abstract
Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. The nuclei of muscle fibres (myonuclei) are usually situated peripherally which complicates the equitable distribution of gene products. Myonuclear abundance can also change under conditions such as hypertrophy and atrophy. Specialised zones in muscle fibres have different functions and thus distinct synthetic demands from myonuclei. The complex structure and regulatory requirements of multinuclear muscle cells understandably led to the hypothesis that myonuclei govern defined 'domains' to maintain homeostasis and facilitate adaptation. The purpose of this review is to provide historical context for the myonuclear domain and evaluate its veracity with respect to mRNA and protein distribution resulting from myonuclear transcription. We synthesise insights from past and current in vitro and in vivo genetically modified models for studying the myonuclear domain under dynamic conditions. We also cover the most contemporary knowledge on mRNA and protein transport in muscle cells. Insights from emerging technologies such as single myonuclear RNA-sequencing further inform our discussion of the myonuclear domain. We broadly conclude: (1) the myonuclear domain can be flexible during muscle fibre growth and atrophy, (2) the mechanisms and role of myonuclear loss and motility deserve further consideration, (3) mRNA in muscle is actively transported via microtubules and locally restricted, but proteins may travel far from a myonucleus of origin and (4) myonuclear transcriptional specialisation extends beyond the classic neuromuscular and myotendinous populations. A deeper understanding of the myonuclear domain in muscle may promote effective therapies for ageing and disease.
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Affiliation(s)
- James R. Bagley
- Muscle Physiology Laboratory, Department of Kinesiology, San Francisco State University, San Francisco, California
| | | | - John J. McCarthy
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky
- Department of Physiology, College of Medicine, University of Kentucky
| | - Eric T. Wang
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics, University of Florida, Gainesville, Florida
- Myology Institute, University of Florida
- Genetics Institute, University of Florida
| | - Kevin A. Murach
- Exercise Science Research Center, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas
- Cell and Molecular Biology Graduate Program, University of Arkansas
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Rose N, Estrada Chavez B, Sonam S, Nguyen T, Grenci G, Bigot A, Muchir A, Ladoux B, Cadot B, Le Grand F, Trichet L. Bioengineering a miniaturized in vitro 3D myotube contraction monitoring chip to model muscular dystrophies. Biomaterials 2023; 293:121935. [PMID: 36584444 DOI: 10.1016/j.biomaterials.2022.121935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Revised: 11/17/2022] [Accepted: 11/27/2022] [Indexed: 12/15/2022]
Abstract
Quantification of skeletal muscle functional contraction is essential to assess the outcomes of therapeutic procedures for neuromuscular disorders. Muscle three-dimensional "Organ-on-chip" models usually require a substantial amount of biological material, which rarely can be obtained from patient biopsies. Here, we developed a miniaturized 3D myotube culture chip with contraction monitoring capacity at the single cell level. Optimized micropatterned substrate design enabled to obtain high culture yields in tightly controlled microenvironments, with myotubes derived from primary human myoblasts displaying spontaneous contractions. Analysis of nuclear morphology confirmed similar myonuclei structure between obtained myotubes and in vivo myofibers, as compared to 2D monolayers. LMNA-related Congenital Muscular Dystrophy (L-CMD) was modeled with successful development of diseased 3D myotubes displaying reduced contraction. The miniaturized myotube technology can thus be used to study contraction characteristics and evaluate how diseases affect muscle organization and force generation. Importantly, it requires significantly fewer starting materials than current systems, which should substantially improve drug screening capability.
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Affiliation(s)
- Nicolas Rose
- Sorbonne Université, Inserm UMRS 974, Centre de Recherche en Myologie, 75013, Paris, France.
| | - Berenice Estrada Chavez
- Sorbonne Université, Inserm UMRS 974, Centre de Recherche en Myologie, 75013, Paris, France.
| | - Surabhi Sonam
- Université Paris Cité, CNRS, Institut Jacques Monod, F-75013, Paris, France.
| | - Thao Nguyen
- Université Paris Cité, CNRS, Institut Jacques Monod, F-75013, Paris, France.
| | - Gianluca Grenci
- Mechanobiology Institute, National University of Singapore, 117411, Singapore.
| | - Anne Bigot
- Sorbonne Université, Inserm UMRS 974, Centre de Recherche en Myologie, 75013, Paris, France.
| | - Antoine Muchir
- Sorbonne Université, Inserm UMRS 974, Centre de Recherche en Myologie, 75013, Paris, France.
| | - Benoît Ladoux
- Université Paris Cité, CNRS, Institut Jacques Monod, F-75013, Paris, France.
| | - Bruno Cadot
- Sorbonne Université, Inserm UMRS 974, Centre de Recherche en Myologie, 75013, Paris, France.
| | - Fabien Le Grand
- Institut NeuroMyoGène, Université Claude Bernard Lyon 1, CNRS UMR 5310, INSERM U1217, 69008, Lyon, France.
| | - Léa Trichet
- Sorbonne Université, CNRS UMR 7574, Laboratoire de Chimie de La Matière Condensée de Paris, 75005, Paris, France.
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Lamin V, Verry J, Dokun OS, Kronemberger A, Wong T, Lira VA, Dokun AO. microRNA-29a Regulates ADAM12 Through Direct Interaction With ADAM12 mRNA and Modulates Postischemic Perfusion Recovery. J Am Heart Assoc 2022; 11:e025727. [PMID: 35946473 PMCID: PMC9496313 DOI: 10.1161/jaha.122.025727] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 06/27/2022] [Indexed: 11/20/2022]
Abstract
Background Peripheral artery disease is caused by atherosclerotic occlusion of vessels outside the heart and most commonly affects vessels of the lower extremities. Angiogenesis is a part of the postischemic adaptation involved in restoring blood flow in peripheral artery disease. Previously, in a murine hind limb ischemia model of peripheral artery disease, we identified ADAM12 (a disintegrin and metalloproteinase gene 12) as a key genetic modifier of postischemic perfusion recovery. However, less is known about ADAM12 regulation in ischemia. MicroRNAs are a class of small, noncoding, single-stranded RNAs that regulate gene expression primarily through transcriptional repression of messenger RNA (mRNA). We showed microRNA-29a (miR-29a) modulates ADAM12 expression in the setting of diabetes and ischemia. However, how miR-29a modulates ADAM12 is not known. Moreover, the physiological effects of miR-29a modulation in a nondiabetic setting is not known. Methods and Results We overexpressed or inhibited miR-29a in ischemic mouse gastrocnemius and tibialis anterior muscles, and quantified the effect on perfusion recovery, ADAM12 expression, angiogenesis, and skeletal muscle regeneration. In addition, using RNA immunoprecipitation-based anti-miR competitive assay, we investigated the interaction of miR-29a and ADAM12 mRNA in mouse microvascular endothelial cell, skeletal muscle, and human endothelial cell lysates. Ectopic expression of miR-29a in ischemic mouse hind limbs decreased ADAM12 mRNA expression, increased skeletal muscle injury, decreased skeletal muscle function, and decreased angiogenesis and perfusion recovery, with no effect on skeletal muscle regeneration and myofiber cross-sectional area following hind limb ischemia. RNA immunoprecipitation-based anti-miR competitive assay studies showed miR-29a antagomir displaced miR-29a and ADAM12 mRNA from the AGO-2 (Argonaut-2) complex in a dose dependent manner. Conclusions Taken together, the data show miR-29a suppresses ADAM12 expression by directly binding to its mRNA, resulting in impaired skeletal muscle function, angiogenesis, and poor perfusion. Hence, elevated levels of miR-29a, as seen in diabetes and aging, likely contribute to vascular pathology, and modulation of miR-29a could be a therapeutic target.
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Affiliation(s)
- Victor Lamin
- Division of Endocrinology and Metabolism, Carver College of MedicineUniversity of IowaIowa CityIA
| | - Joseph Verry
- Division of Endocrinology and Metabolism, Carver College of MedicineUniversity of IowaIowa CityIA
| | - Olumayowa S. Dokun
- Division of Endocrinology and Metabolism, Carver College of MedicineUniversity of IowaIowa CityIA
| | - Ana Kronemberger
- Fraternal Order of Eagles Diabetes Research Center, Carver College of MedicineUniversity of IowaIowa CityIA
- Department of Health and Human Physiology, College of Liberal Arts and SciencesUniversity of IowaIowa CityIA
| | - Thomas Wong
- Division of Endocrinology and Metabolism, Carver College of MedicineUniversity of IowaIowa CityIA
| | - Vitor A. Lira
- Fraternal Order of Eagles Diabetes Research Center, Carver College of MedicineUniversity of IowaIowa CityIA
- Department of Health and Human Physiology, College of Liberal Arts and SciencesUniversity of IowaIowa CityIA
| | - Ayotunde O. Dokun
- Division of Endocrinology and Metabolism, Carver College of MedicineUniversity of IowaIowa CityIA
- Fraternal Order of Eagles Diabetes Research Center, Carver College of MedicineUniversity of IowaIowa CityIA
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Roman W, Muñoz-Cánoves P. Muscle is a stage, and cells and factors are merely players. Trends Cell Biol 2022; 32:835-840. [DOI: 10.1016/j.tcb.2022.03.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 02/28/2022] [Accepted: 03/02/2022] [Indexed: 12/25/2022]
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Viggars MR, Wen Y, Peterson CA, Jarvis JC. Automated cross-sectional analysis of trained, severely atrophied and recovering rat skeletal muscles using MyoVision 2.0. J Appl Physiol (1985) 2022; 132:593-610. [PMID: 35050795 DOI: 10.1152/japplphysiol.00491.2021] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The number of myonuclei within a muscle fiber is an important factor in muscle growth, but its regulation during muscle adaptation is not well understood. We aimed to elucidate the timecourse of myonuclear dynamics during endurance training, loaded and concentric resistance training, and nerve silencing-induced disuse atrophy with subsequent recovery. We modified tibialis anterior muscle activity in free-living rats with electrical stimulation from implantable pulse generators, or with implantable osmotic pumps delivering tetrodotoxin (TTX) to silence the motor nerve without transection. We used the updated, automated software MyoVision to measure fiber type-specific responses in whole tibialis anterior cross-sections (~8000 fibers each). Seven days of continuous low frequency stimulation (CLFS) reduced muscle mass (-12%), increased slower myosin isoforms and reduced IIX/IIB fibers (-32%) and substantially increased myonuclei especially in IIX/IIB fibers (55.5%). High load resistance training (Spillover), produced greater hypertrophy (~16%) in muscle mass and fiber cross-sectional area (CSA) than low load resistance training (concentric, ~6%) and was associated with myonuclear addition in all fiber types (35-46%). TTX-induced nerve silencing resulted in progressive loss in muscle mass, fiber CSA, and myonuclei per fiber cross-section (-50.7%, -53.7%, -40.7%, respectively at 14 days). Myonuclear loss occurred in a fiber type-independent manner, but subsequent recovery during voluntary habitual activity suggested that type IIX/IIB fibers contained more new myonuclei during recovery from severe atrophy. This study demonstrates the power and accuracy provided by the updated MyoVision software and introduces new models for studying myonuclear dynamics in training, detraining, retraining, repeated disuse, and recovery.
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Affiliation(s)
- Mark Robert Viggars
- Research Institute for Sport & Exercise Sciences, grid.4425.7Liverpool John Moores University, Liverpool, United Kingdom.,Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida, United States.,Myology Institute, University of Florida, Gainesville, Florida, United States
| | - Yuan Wen
- Department of Physiology, College of Medicine, University of Kentucky, Lexington, Kentucky, United States.,Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, United States.,MyoAnalytics, LLC, Lexington, Kentucky, United States
| | - Charlotte A Peterson
- Department of Physiology, College of Medicine, University of Kentucky, Lexington, Kentucky, United States.,Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, United States
| | - Jonathan C Jarvis
- Research Institute for Sport & Exercise Sciences, grid.4425.7Liverpool John Moores University, Liverpool, United Kingdom
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Lifetime analysis of mdx skeletal muscle reveals a progressive pathology that leads to myofiber loss. Sci Rep 2020; 10:17248. [PMID: 33057110 PMCID: PMC7560899 DOI: 10.1038/s41598-020-74192-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Accepted: 09/23/2020] [Indexed: 02/06/2023] Open
Abstract
The muscular dystrophy X-linked mouse (mdx) is the most commonly used preclinical model for Duchenne muscular dystrophy. Although disease progression in the mouse does not perfectly model the human disease, it shares many pathological features. Early characterizations of the model reported severe pathology through early adulthood followed by disease stabilization. As a result, research in the mdx mouse has largely focused on early adulthood. The overarching goal of this study is to improve the understanding of the mdx mouse model by tracking pathological features of the disease throughout life. We performed a thorough characterization of myofiber pathology in mdx mice from 2 weeks to 2 years of age. We report that individual mdx muscle fibers undergo progressive hypertrophy that continues through the lifespan. Despite massive hypertrophy on the myofiber level, we report no hypertrophy on the muscle level. These seemingly contradictory findings are explained by previously underappreciated myofiber loss in mdx mice. We conclude that due to myofiber loss, in combination with the progressive nature of other pathological features, aged mdx muscle tissue provides reliable benchmarks for disease progression that may be valuable in testing the efficacy of therapeutics for Duchenne muscular dystrophy.
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