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Cocanougher BT, Liu SW, Francescatto L, Behura A, Anneling M, Jackson DG, Deak KL, Hornik CD, ElMallah MK, Pizoli CE, Smith EC, Tan KGQ, McDonald MT. The severity of MUSK pathogenic variants is predicted by the protein domain they disrupt. HGG ADVANCES 2024; 5:100288. [PMID: 38566418 PMCID: PMC11070630 DOI: 10.1016/j.xhgg.2024.100288] [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: 11/28/2023] [Revised: 03/27/2024] [Accepted: 03/27/2024] [Indexed: 04/04/2024] Open
Abstract
Biallelic loss-of-function variants in the MUSK gene result in two allelic disorders: (1) congenital myasthenic syndrome (CMS; OMIM: 616325), a neuromuscular disorder that has a range of severity from severe neonatal-onset weakness to mild adult-onset weakness, and (2) fetal akinesia deformation sequence (OMIM: 208150), a form of pregnancy loss characterized by severe muscle weakness in the fetus. The MUSK gene codes for muscle-specific kinase (MuSK), a receptor tyrosine kinase involved in the development of the neuromuscular junction. Here, we report a case of neonatal-onset MUSK-related CMS in a patient harboring compound heterozygous deletions in the MUSK gene, including (1) a deletion of exons 2-3 leading to an in-frame MuSK protein lacking the immunoglobulin 1 (Ig1) domain and (2) a deletion of exons 7-11 leading to an out-of-frame, truncated MuSK protein. Individual domains of the MuSK protein have been elucidated structurally; however, a complete MuSK structure generated by machine learning algorithms has clear inaccuracies. We modify a predicted AlphaFold structure and integrate previously reported domain-specific structural data to suggest a MuSK protein that dimerizes in two locations (Ig1 and the transmembrane domain). We analyze known pathogenic variants in MUSK to discover domain-specific genotype-phenotype correlations; variants that lead to a loss of protein expression, disruption of the Ig1 domain, or Dok-7 binding are associated with the most severe phenotypes. A conceptual model is provided to explain the severe phenotypes seen in Ig1 variants and the poor response of our patient to pyridostigmine.
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Affiliation(s)
- Benjamin T Cocanougher
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA.
| | - Samuel W Liu
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA
| | | | - Alexander Behura
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA
| | - Mariele Anneling
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA
| | - David G Jackson
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA
| | - Kristen L Deak
- Department of Pathology, Duke University, Durham, NC, USA
| | - Chi D Hornik
- Department of Pediatrics, Duke University, Durham, NC, USA
| | - Mai K ElMallah
- Department of Pediatrics, Duke University, Durham, NC, USA
| | - Carolyn E Pizoli
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Pediatric Neurology, Duke University, Durham, NC, USA
| | - Edward C Smith
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Pediatric Neurology, Duke University, Durham, NC, USA
| | - Khoon Ghee Queenie Tan
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA
| | - Marie T McDonald
- Department of Pediatrics, Duke University, Durham, NC, USA; Division of Medical Genetics, Duke University, Durham, NC, USA.
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Jang J, Kim Y, Song T, Park S, Kim HJ, Koh JH, Cho Y, Park SY, Sadayappan S, Kwak HB, Wolfe RR, Kim IY, Choi CS. Free essential amino acid feeding improves endurance during resistance training via DRP1-dependent mitochondrial remodelling. J Cachexia Sarcopenia Muscle 2024. [PMID: 38881251 DOI: 10.1002/jcsm.13519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2023] [Revised: 05/15/2024] [Accepted: 05/16/2024] [Indexed: 06/18/2024] Open
Abstract
BACKGROUND Loss of muscle strength and endurance with aging or in various conditions negatively affects quality of life. Resistance exercise training (RET) is the most powerful means to improve muscle mass and strength, but it does not generally lead to improvements in endurance capacity. Free essential amino acids (EAAs) act as precursors and stimuli for synthesis of both mitochondrial and myofibrillar proteins that could potentially confer endurance and strength gains. Thus, we hypothesized that daily consumption of a dietary supplement of nine free EAAs with RET improves endurance in addition to the strength gains by RET. METHODS Male C57BL6J mice (9 weeks old) were assigned to control (CON), EAA, RET (ladder climbing, 3 times a week), or combined treatment of EAA and RET (EAA + RET) groups. Physical functions focusing on strength or endurance were assessed before and after the interventions. Several analyses were performed to gain better insight into the mechanisms by which muscle function was improved. We determined cumulative rates of myofibrillar and mitochondrial protein synthesis using 2H2O labelling and mass spectrometry; assessed ex vivo contractile properties and in vitro mitochondrial function, evaluated neuromuscular junction (NMJ) stability, and assessed implicated molecular singling pathways. Furthermore, whole-body and muscle insulin sensitivity along with glucose metabolism, were evaluated using a hyperinsulinaemic-euglycaemic clamp. RESULTS EAA + RET increased muscle mass (10%, P < 0.05) and strength (6%, P < 0.05) more than RET alone, due to an enhanced rate of integrated muscle protein synthesis (19%, P < 0.05) with concomitant activation of Akt1/mTORC1 signalling. Muscle quality (muscle strength normalized to mass) was improved by RET (i.e., RET and EAA + RET) compared with sedentary groups (10%, P < 0.05), which was associated with increased AchR cluster size and MuSK activation (P < 0.05). EAA + RET also increased endurance capacity more than RET alone (26%, P < 0.05) by increasing both mitochondrial protein synthesis (53%, P < 0.05) and DRP1 activation (P < 0.05). Maximal respiratory capacity increased (P < 0.05) through activation of the mTORC1-DRP1 signalling axis. These favourable effects were accompanied by an improvement in basal glucose metabolism (i.e., blood glucose concentrations and endogenous glucose production vs. CON, P < 0.05). CONCLUSIONS Combined treatment with balanced free EAAs and RET may effectively promote endurance capacity as well as muscle strength through increased muscle protein synthesis, improved NMJ stability, and enhanced mitochondrial dynamics via mTORC1-DRP1 axis activation, ultimately leading to improved basal glucose metabolism.
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Affiliation(s)
- Jiwoong Jang
- Integrative Metabolic Fluxomics Lab, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Internal Medicine, Gil Medical Center, Gachon University, Incheon, Korea
| | - Yeongmin Kim
- Integrative Metabolic Fluxomics Lab, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon, Korea
| | - Taejeong Song
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, Center for Cardiovascular Research, University of Cincinnati, Cincinnati, Ohio, USA
| | - Sanghee Park
- Integrative Metabolic Fluxomics Lab, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Korea
| | - Hee-Joo Kim
- Integrative Metabolic Fluxomics Lab, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon, Korea
| | - Jin-Ho Koh
- Integrative Metabolic Fluxomics Lab, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Korea
| | - Yoonil Cho
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon, Korea
| | - Shi-Young Park
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Gachon Biomedical Convergence Institute, Gachon University Gil Medical Center, Incheon, Korea
| | - Sakthivel Sadayappan
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, Center for Cardiovascular Research, University of Cincinnati, Cincinnati, Ohio, USA
| | - Hyo-Bum Kwak
- Department of Kinesiology, Inha University, Incheon, Korea
- Institute of Sports & Arts Convergence, Inha University, Incheon, Korea
- Department of Biomedical Science, Program in Biomedical Science & Engineering, Inha University, Incheon, Korea
| | - Robert R Wolfe
- Department of Geriatrics, Center for Translational Research in Aging and Longevity, Donald W. Reynolds Institute on Aging, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
| | - Il-Young Kim
- Integrative Metabolic Fluxomics Lab, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Korea
| | - Cheol Soo Choi
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea
- Department of Internal Medicine, Gil Medical Center, Gachon University, Incheon, Korea
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Korea
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3
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Dziadkowiak E, Baczyńska D, Waliszewska-Prosół M. MuSK Myasthenia Gravis-Potential Pathomechanisms and Treatment Directed against Specific Targets. Cells 2024; 13:556. [PMID: 38534400 DOI: 10.3390/cells13060556] [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: 02/13/2024] [Revised: 03/17/2024] [Accepted: 03/19/2024] [Indexed: 03/28/2024] Open
Abstract
Myasthenia gravis (MG) is an autoimmune disease in which autoantibodies target structures within the neuromuscular junction, affecting neuromuscular transmission. Muscle-specific tyrosine kinase receptor-associated MG (MuSK-MG) is a rare, often more severe, subtype of the disease with different pathogenesis and specific clinical features. It is characterized by a more severe clinical course, more frequent complications, and often inadequate response to treatment. Here, we review the current state of knowledge about potential pathomechanisms of the MuSK-MG and their therapeutic implications as well as ongoing research in this field, with reference to key points of immune-mediated processes involved in the background of myasthenia gravis.
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Affiliation(s)
- Edyta Dziadkowiak
- Department of Neurology, Wroclaw Medical University, Borowska 213, 50-556 Wroclaw, Poland
| | - Dagmara Baczyńska
- Department of Molecular and Cellular Biology, Wroclaw Medical University, Borowska 211A, 50-556 Wroclaw, Poland
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Uyen Dao TM, Barbeau S, Messéant J, Della-Gaspera B, Bouceba T, Semprez F, Legay C, Dobbertin A. The collagen ColQ binds to LRP4 and regulates the activation of the Muscle-Specific Kinase-LRP4 receptor complex by agrin at the neuromuscular junction. J Biol Chem 2023; 299:104962. [PMID: 37356721 PMCID: PMC10382678 DOI: 10.1016/j.jbc.2023.104962] [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: 04/20/2022] [Revised: 06/09/2023] [Accepted: 06/13/2023] [Indexed: 06/27/2023] Open
Abstract
Collagen Q (ColQ) is a nonfibrillar collagen that plays a crucial role at the vertebrate neuromuscular junction (NMJ) by anchoring acetylcholinesterase to the synapse. ColQ also functions in signaling, as it regulates acetylcholine receptor clustering and synaptic gene expression, in a manner dependent on muscle-specific kinase (MuSK), a key protein in NMJ formation and maintenance. MuSK forms a complex with low-density lipoprotein receptor-related protein 4 (LRP4), its coreceptor for the proteoglycan agrin at the NMJ. Previous studies suggested that ColQ also interacts with MuSK. However, the molecular mechanisms underlying ColQ functions and ColQ-MuSK interaction have not been fully elucidated. Here, we investigated whether ColQ binds directly to MuSK and/or LRP4 and whether it modulates agrin-mediated MuSK-LRP4 activation. Using coimmunoprecipitation, pull-down, plate-binding assays, and surface plasmon resonance, we show that ColQ binds directly to LRP4 but not to MuSK and that ColQ interacts indirectly with MuSK through LRP4. In addition, we show that the LRP4 N-terminal region, which contains the agrin-binding sites, is also crucial for ColQ binding to LRP4. Moreover, ColQ-LRP4 interaction was reduced in the presence of agrin, suggesting that agrin and ColQ compete for binding to LRP4. Strikingly, we reveal ColQ has two opposing effects on agrin-induced MuSK-LRP4 signaling: it constitutively reduces MuSK phosphorylation levels in agrin-stimulated myotubes but concomitantly increases MuSK accumulation at the muscle cell surface. Our results identify LRP4 as a major receptor of ColQ and provide new insights into mechanisms of ColQ signaling and acetylcholinesterase anchoring at the NMJ.
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Affiliation(s)
- Thi Minh Uyen Dao
- Université Paris Cité, CNRS, Saints-Pères Paris Institute for the Neurosciences, Paris, France
| | - Susie Barbeau
- Université Paris Cité, CNRS, Saints-Pères Paris Institute for the Neurosciences, Paris, France
| | - Julien Messéant
- Université Paris Cité, CNRS, Saints-Pères Paris Institute for the Neurosciences, Paris, France
| | | | - Tahar Bouceba
- Sorbonne Université, CNRS, IBPS, Protein Engineering Platform, Paris, France
| | - Fannie Semprez
- Université Paris Cité, CNRS, Saints-Pères Paris Institute for the Neurosciences, Paris, France
| | - Claire Legay
- Université Paris Cité, CNRS, Saints-Pères Paris Institute for the Neurosciences, Paris, France
| | - Alexandre Dobbertin
- Université Paris Cité, CNRS, Saints-Pères Paris Institute for the Neurosciences, Paris, France.
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5
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Prömer J, Barresi C, Herbst R. From phosphorylation to phenotype - Recent key findings on kinase regulation, downstream signaling and disease surrounding the receptor tyrosine kinase MuSK. Cell Signal 2023; 104:110584. [PMID: 36608736 DOI: 10.1016/j.cellsig.2022.110584] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 12/16/2022] [Accepted: 12/31/2022] [Indexed: 01/04/2023]
Abstract
Muscle-specific kinase (MuSK) is the key regulator of neuromuscular junction development. MuSK acts via several distinct pathways and is responsible for pre- and postsynaptic differentiation. MuSK is unique among receptor tyrosine kinases as activation and signaling are particularly tightly regulated. Initiation of kinase activity requires Agrin, a heparan sulphate proteoglycan derived from motor neurons, the low-density lipoprotein receptor-related protein-4 (Lrp4) and the intracellular adaptor protein Dok-7. There is a great knowledge gap between MuSK activation and downstream signaling. Recent studies using omics techniques have addressed this knowledge gap, thereby greatly contributing to a better understanding of MuSK signaling. Impaired MuSK signaling causes severe muscle weakness as described in congenital myasthenic syndromes or myasthenia gravis but the underlying pathophysiology is often unclear. This review focuses on recent advances in deciphering MuSK activation and downstream signaling. We further highlight latest break-throughs in understanding and treatment of MuSK-related disorders and discuss the role of MuSK in non-muscle tissue.
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Affiliation(s)
- Jakob Prömer
- Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria
| | - Cinzia Barresi
- Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria
| | - Ruth Herbst
- Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
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6
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Jang J, Koh JH, Kim Y, Kim HJ, Park S, Chang Y, Jung J, Wolfe RR, Kim IY. Balanced Free Essential Amino Acids and Resistance Exercise Training Synergistically Improve Dexamethasone-Induced Impairments in Muscle Strength, Endurance, and Insulin Sensitivity in Mice. Int J Mol Sci 2022; 23:ijms23179735. [PMID: 36077132 PMCID: PMC9456044 DOI: 10.3390/ijms23179735] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 08/23/2022] [Accepted: 08/25/2022] [Indexed: 11/16/2022] Open
Abstract
Our previous study shows that an essential amino acid (EAA)-enriched diet attenuates dexamethasone (DEX)-induced declines in muscle mass and strength, as well as insulin sensitivity, but does not affect endurance. In the present study, we hypothesized that the beneficial effects will be synergized by adding resistance exercise training (RET) to EAA, and diet-free EAA would improve endurance. To test hypotheses, mice were randomized into the following four groups: control, EAA, RET, and EAA+RET. All mice except the control were subjected to DEX treatment. We evaluated the cumulative rate of myofibrillar protein synthesis (MPS) using 2H2O labeling and mass spectrometry. Neuromuscular junction (NMJ) stability, mitochondrial contents, and molecular signaling were demonstrated in skeletal muscle. Insulin sensitivity and glucose metabolism using 13C6-glucose tracing during oral glucose tolerance tests were analyzed. We found that EAA and RET synergistically improve muscle mass and/or strength, and endurance capacity, as well as insulin sensitivity, and glucose metabolism in DEX-treated muscle. These improvements are accomplished, in part, through improvements in myofibrillar protein synthesis, NMJ, fiber type preservation, and/or mitochondrial biogenesis. In conclusion, free EAA supplementation, particularly when combined with RET, can serve as an effective means that counteracts the adverse effects on muscle of DEX that are found frequently in clinical settings.
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Affiliation(s)
- Jiwoong Jang
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon 21999, Korea
- Department of Internal Medicine, Gil Medical Center, Gachon University, Incheon 21565, Korea
| | - Jin-Ho Koh
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon 21565, Korea
| | - Yeongmin Kim
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon 21999, Korea
| | - Hee-Joo Kim
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon 21999, Korea
| | - Sanghee Park
- Department of Internal Medicine, Gil Medical Center, Gachon University, Incheon 21565, Korea
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon 21565, Korea
| | - Yewon Chang
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon 21999, Korea
| | - Jiyeon Jung
- Department of Health Sciences and Technology, GAIHST, Gachon University, Incheon 21999, Korea
| | - Robert R. Wolfe
- Department of Geriatrics, Center for Translational Research in Aging and Longevity, Donald W. Reynolds Institute on Aging, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Il-Young Kim
- Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon 21999, Korea
- Department of Molecular Medicine, College of Medicine, Gachon University, Incheon 21565, Korea
- Correspondence: ; Tel.: +82-32-899-6685
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7
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Boëx M, Cottin S, Halliez M, Bauché S, Buon C, Sans N, Montcouquiol M, Molgó J, Amar M, Ferry A, Lemaitre M, Rouche A, Langui D, Baskaran A, Fontaine B, Messéant J, Strochlic L. The cell polarity protein Vangl2 in the muscle shapes the neuromuscular synapse by binding to and regulating the tyrosine kinase MuSK. Sci Signal 2022; 15:eabg4982. [PMID: 35580169 DOI: 10.1126/scisignal.abg4982] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The development of the neuromuscular junction (NMJ) requires dynamic trans-synaptic coordination orchestrated by secreted factors, including Wnt family morphogens. To investigate how these synaptic cues in NMJ development are transduced, particularly in the regulation of acetylcholine receptor (AChR) accumulation in the postsynaptic membrane, we explored the function of Van Gogh-like protein 2 (Vangl2), a core component of Wnt planar cell polarity signaling. We found that conditional, muscle-specific ablation of Vangl2 in mice reproduced the NMJ differentiation defects seen in mice with global Vangl2 deletion. These alterations persisted into adulthood and led to NMJ disassembly, impaired neurotransmission, and deficits in motor function. Vangl2 and the muscle-specific receptor tyrosine kinase MuSK were functionally associated in Wnt signaling in the muscle. Vangl2 bound to and promoted the signaling activity of MuSK in response to Wnt11. The loss of Vangl2 impaired RhoA activation in cultured mouse myotubes and caused dispersed, rather than clustered, organization of AChRs at the postsynaptic or muscle cell side of NMJs in vivo. Our results identify Vangl2 as a key player of the core complex of molecules shaping neuromuscular synapses and thus shed light on the molecular mechanisms underlying NMJ assembly.
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Affiliation(s)
- Myriam Boëx
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Steve Cottin
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Marius Halliez
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Stéphanie Bauché
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Céline Buon
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Nathalie Sans
- Institut National de la Santé et de la Recherche Médicale, Neurocentre Magendie, UMR-S 1215, Bordeaux 33077, France.,Université Bordeaux, Neurocentre Magendie, Bordeaux, 33000, France
| | - Mireille Montcouquiol
- Institut National de la Santé et de la Recherche Médicale, Neurocentre Magendie, UMR-S 1215, Bordeaux 33077, France.,Université Bordeaux, Neurocentre Magendie, Bordeaux, 33000, France
| | - Jordi Molgó
- Université Paris-Saclay, Commissariat à l'Energie Atomique et aux énergies Alternatives, Institut des Sciences du Vivant Frédéric Joliot, Département Médicaments et Technologies pour la Santé, Equipe Mixte de Recherche CNRS 9004, Service d'Ingénierie Moléculaire pour la Santé, Gif-sur-Yvette 91191, France
| | - Muriel Amar
- Université Paris-Saclay, Commissariat à l'Energie Atomique et aux énergies Alternatives, Institut des Sciences du Vivant Frédéric Joliot, Département Médicaments et Technologies pour la Santé, Equipe Mixte de Recherche CNRS 9004, Service d'Ingénierie Moléculaire pour la Santé, Gif-sur-Yvette 91191, France
| | - Arnaud Ferry
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Mégane Lemaitre
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Phénotypage du Petit Animal, Paris 75013, France
| | - Andrée Rouche
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Dominique Langui
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut du Cerveau et de la Moelle, Plate-forme d'Imagerie Cellulaire Pitié-Salpêtrière, Paris 75013, France
| | - Asha Baskaran
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut du Cerveau et de la Moelle, Plate-forme d'Imagerie Cellulaire Pitié-Salpêtrière, Paris 75013, France
| | - Bertrand Fontaine
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France.,Assistance Publique-Hôpitaux de Paris (AP-HP) Service de Neuro-Myologie, Hôpital Universitaire Pitié-Salpêtrière, Paris 75013, France
| | - Julien Messéant
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
| | - Laure Strochlic
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Institut de Myologie, Centre de Recherche en Myologie, Paris 75013, France
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Alvarez-Suarez P, Nowak N, Protasiuk-Filipunas A, Yamazaki H, Prószyński TJ, Gawor M. Drebrin Regulates Acetylcholine Receptor Clustering and Organization of Microtubules at the Postsynaptic Machinery. Int J Mol Sci 2021; 22:9387. [PMID: 34502296 PMCID: PMC8430516 DOI: 10.3390/ijms22179387] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 08/20/2021] [Accepted: 08/24/2021] [Indexed: 01/07/2023] Open
Abstract
Proper muscle function depends on the neuromuscular junctions (NMJs), which mature postnatally to complex "pretzel-like" structures, allowing for effective synaptic transmission. Postsynaptic acetylcholine receptors (AChRs) at NMJs are anchored in the actin cytoskeleton and clustered by the scaffold protein rapsyn, recruiting various actin-organizing proteins. Mechanisms driving the maturation of the postsynaptic machinery and regulating rapsyn interactions with the cytoskeleton are still poorly understood. Drebrin is an actin and microtubule cross-linker essential for the functioning of the synapses in the brain, but its role at NMJs remains elusive. We used immunohistochemistry, RNA interference, drebrin inhibitor 3,5-bis-trifluoromethyl pyrazole (BTP2) and co-immunopreciptation to explore the role of this protein at the postsynaptic machinery. We identify drebrin as a postsynaptic protein colocalizing with the AChRs both in vitro and in vivo. We also show that drebrin is enriched at synaptic podosomes. Downregulation of drebrin or blocking its interaction with actin in cultured myotubes impairs the organization of AChR clusters and the cluster-associated microtubule network. Finally, we demonstrate that drebrin interacts with rapsyn and a drebrin interactor, plus-end-tracking protein EB3. Our results reveal an interplay between drebrin and cluster-stabilizing machinery involving rapsyn, actin cytoskeleton, and microtubules.
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Affiliation(s)
- Paloma Alvarez-Suarez
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Natalia Nowak
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Anna Protasiuk-Filipunas
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Hiroyuki Yamazaki
- Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan;
| | - Tomasz J. Prószyński
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Marta Gawor
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
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9
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Myostatin Inhibition-Induced Increase in Muscle Mass and Strength Was Amplified by Resistance Exercise Training, and Dietary Essential Amino Acids Improved Muscle Quality in Mice. Nutrients 2021; 13:nu13051508. [PMID: 33947024 PMCID: PMC8146053 DOI: 10.3390/nu13051508] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 04/23/2021] [Accepted: 04/27/2021] [Indexed: 12/16/2022] Open
Abstract
It has been frequently reported that myostatin inhibition increases muscle mass, but decreases muscle quality (i.e., strength/muscle mass). Resistance exercise training (RT) and essential amino acids (EAAs) are potent anabolic stimuli that synergistically increase muscle mass through changes in muscle protein turnover. In addition, EAAs are known to stimulate mitochondrial biogenesis. We have investigated if RT amplifies the anabolic potential of myostatin inhibition while EAAs enhance muscle quality through stimulations of mitochondrial biogenesis and/or muscle protein turnover. Mice were assigned into ACV (myostatin inhibitor), ACV+EAA, ACV+RT, ACV+EAA +RT, or control (CON) over 4 weeks. RT, but not EAA, increased muscle mass above ACV. Despite differences in muscle mass gain, myofibrillar protein synthesis was stimulated similarly in all vs. CON, suggesting a role for changes in protein breakdown in muscle mass gains. There were increases in MyoD expression but decreases in Atrogin-1/MAFbx expression in ACV+EAA, ACV+RT, and ACV+EAA+RT vs. CON. EAA increased muscle quality (e.g., grip strength and maximal carrying load) without corresponding changes in markers of mitochondrial biogenesis and neuromuscular junction stability. In conclusion, RT amplifies muscle mass and strength through changes in muscle protein turnover in conjunction with changes in implicated signaling, while EAAs enhance muscle quality through unknown mechanisms.
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10
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Rodríguez Cruz PM, Cossins J, Beeson D, Vincent A. The Neuromuscular Junction in Health and Disease: Molecular Mechanisms Governing Synaptic Formation and Homeostasis. Front Mol Neurosci 2020; 13:610964. [PMID: 33343299 PMCID: PMC7744297 DOI: 10.3389/fnmol.2020.610964] [Citation(s) in RCA: 87] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 10/30/2020] [Indexed: 12/28/2022] Open
Abstract
The neuromuscular junction (NMJ) is a highly specialized synapse between a motor neuron nerve terminal and its muscle fiber that are responsible for converting electrical impulses generated by the motor neuron into electrical activity in the muscle fibers. On arrival of the motor nerve action potential, calcium enters the presynaptic terminal, which leads to the release of the neurotransmitter acetylcholine (ACh). ACh crosses the synaptic gap and binds to ACh receptors (AChRs) tightly clustered on the surface of the muscle fiber; this leads to the endplate potential which initiates the muscle action potential that results in muscle contraction. This is a simplified version of the events in neuromuscular transmission that take place within milliseconds, and are dependent on a tiny but highly structured NMJ. Much of this review is devoted to describing in more detail the development, maturation, maintenance and regeneration of the NMJ, but first we describe briefly the most important molecules involved and the conditions that affect their numbers and function. Most important clinically worldwide, are myasthenia gravis (MG), the Lambert-Eaton myasthenic syndrome (LEMS) and congenital myasthenic syndromes (CMS), each of which causes specific molecular defects. In addition, we mention the neurotoxins from bacteria, snakes and many other species that interfere with neuromuscular transmission and cause potentially fatal diseases, but have also provided useful probes for investigating neuromuscular transmission. There are also changes in NMJ structure and function in motor neuron disease, spinal muscle atrophy and sarcopenia that are likely to be secondary but might provide treatment targets. The NMJ is one of the best studied and most disease-prone synapses in the nervous system and it is amenable to in vivo and ex vivo investigation and to systemic therapies that can help restore normal function.
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Affiliation(s)
- Pedro M. Rodríguez Cruz
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| | - Judith Cossins
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| | - David Beeson
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| | - Angela Vincent
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
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11
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A Role of Lamin A/C in Preventing Neuromuscular Junction Decline in Mice. J Neurosci 2020; 40:7203-7215. [PMID: 32817327 DOI: 10.1523/jneurosci.0443-20.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 08/10/2020] [Accepted: 08/11/2020] [Indexed: 12/13/2022] Open
Abstract
During aging, skeletal muscles become atrophic and lose contractile force. Aging can also impact the neuromuscular junction (NMJ), a synapse that transmits signals from motoneurons to muscle fibers to control muscle contraction. However, in contrast to muscle aging that has been studied extensively, less is known about the molecular mechanisms of NMJ aging although its structure and function are impaired in aged animals. To this end, we performed RNA sequencing (RNA-seq) analysis to identify genes whose expression in synapse-rich region is altered. Gene ontology (GO) analysis highlighted genes relating to nuclear structure or function. In particular, lamin A/C, an intermediate filament protein critical for the interphase nuclear architecture, was reduced. Remarkably, mutation of lamin A/C in muscles or motoneurons had no effect on NMJ formation in either sex of mice, but the muscle mutation caused progressive denervation, acetylcholine receptor (AChR) cluster fragmentation, and neuromuscular dysfunction. Interestingly, rapsyn, a protein critical to AChR clustering, was reduced in mutant muscle cells; and expressing rapsyn in muscles attenuated NMJ deficits of HSA-Lmna-/- mice. These results reveal a role of lamin A/C in NMJ maintenance and suggest that nuclear dysfunction or deficiency may contribute to NMJ deficits in aged muscles.SIGNIFICANCE STATEMENT This study provides evidence that lamin A/C, a scaffolding component of the nuclear envelope, is critical to maintaining the NMJ in mice. Its muscle-specific mutation led to progressive NMJ degeneration in vivo We showed that the mutation reduced the level of rapsyn, a protein necessary for acetylcholine receptor (AChR) clustering; and expression of rapsyn in muscles attenuated NMJ deficits of HSA-Lmna-/- mice. These results reveal a role of lamin A/C in NMJ maintenance and suggest that nuclear dysfunction or deficiency may contribute to NMJ deficits in aged muscles.
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12
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Liu Y, Qiao K, Yan C, Song J, Huan X, Luo S, Lu J, Zhao C, Xi J. Congenital myasthenia syndrome in a Chinese family with mutations in MUSK: A hotspot mutation and literature review. J Clin Neurosci 2020; 76:161-165. [PMID: 32253145 DOI: 10.1016/j.jocn.2020.03.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 03/01/2020] [Accepted: 03/20/2020] [Indexed: 11/30/2022]
Abstract
Congenital myasthenic syndrome (CMS) caused by mutations in MUSK is very rare and the genotype-phenotype relationship in MUSK related CMS is still unclear. Here we identified two patients carrying a homozygous hotspot mutation, c.308A > G in MUSK from a Chinese family. Both of them presented predominant bulbar weakness and atrophy of bilateral temporalis and masticatory muscles. To address the phenotype-genotype relationship, a total of 27 MUSK related CMS patients were reviewed. Patients with nonsense, frameshift or splicing mutations showed earlier onset (10/13 vs 2/14 neonatal onset, p = 0.0018) and more occurrence of vocal cord paralysis or stridor (8/13 vs 0/14, p = 0.0006), indicating a more severe phenotype. Comparing with patients carrying other missense mutations, the four patients carrying a homozygous c.308A > G mutation showed the female predominance (4/10 vs 4/4) and dramatic exacerbation after emotional or physiological stresses (2/10 vs 4/4) like pregnancy, menstrual periods and infection. All these indicated a genotype-phenotype relationship in MUSK-related CMS.
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Affiliation(s)
- Yiqi Liu
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Kai Qiao
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Chong Yan
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Jie Song
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Xiao Huan
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Sushan Luo
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Jiahong Lu
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Chongbo Zhao
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China
| | - Jianying Xi
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China.
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13
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Herbst R. MuSk function during health and disease. Neurosci Lett 2019; 716:134676. [PMID: 31811897 DOI: 10.1016/j.neulet.2019.134676] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Revised: 12/02/2019] [Accepted: 12/04/2019] [Indexed: 02/06/2023]
Abstract
The receptor tyrosine kinase MuSK (muscle-specific kinase) is the key signaling molecule during the formation of a mature and functional neuromuscular junction (NMJ). Signal transduction events downstream of MuSK activation induce both pre- and postsynaptic differentiation, which, most prominently, includes the clustering of acetylcholine receptors (AChRs) at synaptic sites. MuSK activation requires a complex interplay between its co-receptor Lrp4 (low-density lipoprotein receptor-related protein-4), the motor neuron-derived heparan-sulfate proteoglycan Agrin and the intracellular adaptor protein Dok-7. A tight regulation of MuSK kinase activity is crucial for proper NMJ development. Defects in MuSK signaling are the cause of muscle weakness as reported in congenital myasthenic syndromes and myasthenia gravis. This review focuses on recent structure-based analyses of MuSK, Agrin, Lrp4 and Dok-7 interactions and their function during MuSK activation. Conclusions about the regulation of the MuSK kinase that were derived from molecular structures will be highlighted. In addition, the role of MuSK during development and disease will be discussed.
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Affiliation(s)
- Ruth Herbst
- Medical University of Vienna, Center for Pathophysiology, Infectiology and Immunology, Kinderspitalgasse 15, 1090 Vienna, Austria.
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14
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Issop Y, Hathazi D, Khan MM, Rudolf R, Weis J, Spendiff S, Slater CR, Roos A, Lochmüller H. GFPT1 deficiency in muscle leads to myasthenia and myopathy in mice. Hum Mol Genet 2019; 27:3218-3232. [PMID: 29905857 PMCID: PMC6121184 DOI: 10.1093/hmg/ddy225] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2018] [Accepted: 06/05/2018] [Indexed: 11/13/2022] Open
Abstract
Glutamine-fructose-6-phosphate transaminase 1 (GFPT1) is the rate-limiting enzyme in the hexosamine biosynthetic pathway which yields precursors required for protein and lipid glycosylation. Mutations in GFPT1 and other genes downstream of this pathway cause congenital myasthenic syndrome (CMS) characterized by fatigable muscle weakness owing to impaired neurotransmission. The precise pathomechanisms at the neuromuscular junction (NMJ) owing to a deficiency in GFPT1 is yet to be discovered. One of the challenges we face is the viability of Gfpt1−/− knockout mice. In this study, we use Cre/LoxP technology to generate a muscle-specific GFPT1 knockout mouse model, Gfpt1tm1d/tm1d, characteristic of the human CMS phenotype. Our data suggest a critical role for muscle derived GFPT1 in the development of the NMJ, neurotransmission, skeletal muscle integrity and highlight that a deficiency in skeletal muscle alone is sufficient to cause morphological postsynaptic NMJ changes that are accompanied by presynaptic alterations despite the conservation of neuronal GFPT1 expression. In addition to the conventional morphological NMJ changes and fatigable muscle weakness, Gfpt1tm1d/tm1d mice display a progressive myopathic phenotype with the presence of tubular aggregates in muscle, characteristic of the GFPT1-CMS phenotype. We further identify an upregulation of skeletal muscle proteins glypican-1, farnesyltransferase/geranylgeranyltransferase type-1 subunit α and muscle-specific kinase, which are known to be involved in the differentiation and maintenance of the NMJ. The Gfpt1tm1d/tm1d model allows for further investigation of pathophysiological consequences on genes and pathways downstream of GFPT1 likely to involve misglycosylation or hypoglycosylation of NMJs and muscle targets.
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Affiliation(s)
- Yasmin Issop
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle, UK
| | - Denisa Hathazi
- Leibniz-Institut für Analytische Wissenschaften-ISAS e.V, Dortmund, Germany
| | - Muzamil Majid Khan
- Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany
| | - Rüdiger Rudolf
- Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.,Interdisciplinary Center for Neurosciences, University of Heidelberg, Heidelberg, Germany.,Institute of Molecular and Cell Biology, Mannheim University of Applied Sciences, Mannheim, Germany
| | - Joachim Weis
- Institute of Neuropathology, RWTH Aachen University Hospital, Aachen, Germany
| | - Sally Spendiff
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle, UK
| | - Clarke R Slater
- Institute of Neuroscience, Newcastle University, Newcastle, UK
| | - Andreas Roos
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle, UK.,Leibniz-Institut für Analytische Wissenschaften-ISAS e.V, Dortmund, Germany
| | - Hanns Lochmüller
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle, UK.,Department of Neuropediatrics and Muscle Disorders,Faculty of Medicine, Medical Center - University of Freiburg, Freiburg, Germany.,Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia, Spain
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15
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Animal Models of the Neuromuscular Junction, Vitally Informative for Understanding Function and the Molecular Mechanisms of Congenital Myasthenic Syndromes. Int J Mol Sci 2018; 19:ijms19051326. [PMID: 29710836 PMCID: PMC5983836 DOI: 10.3390/ijms19051326] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 04/24/2018] [Accepted: 04/25/2018] [Indexed: 01/16/2023] Open
Abstract
The neuromuscular junction is the point of contact between motor nerve and skeletal muscle, its vital role in muscle function is reliant on the precise location and function of many proteins. Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders of neuromuscular transmission with 30 or more implicated proteins. The use of animal models has been instrumental in determining the specific role of many CMS-related proteins. The mouse neuromuscular junction (NMJ) has been extensively studied in animal models of CMS due to its amenability for detailed electrophysiological and histological investigations and relative similarity to human NMJ. As well as their use to determine the precise molecular mechanisms of CMS variants, where an animal model accurately reflects the human phenotype they become useful tools for study of therapeutic interventions. Many of the animal models that have been important in deconvolving the complexities of neuromuscular transmission and revealing the molecular mechanisms of disease are highlighted.
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16
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O'Connor E, Töpf A, Zahedi RP, Spendiff S, Cox D, Roos A, Lochmüller H. Clinical and research strategies for limb-girdle congenital myasthenic syndromes. Ann N Y Acad Sci 2018; 1412:102-112. [PMID: 29315608 DOI: 10.1111/nyas.13520] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 09/05/2017] [Accepted: 09/12/2017] [Indexed: 12/21/2022]
Abstract
Congenital myasthenic syndromes (CMS) are a group of rare disorders that cause fatigable muscle weakness due to defective signal transmission at the neuromuscular junction, a specialized synapse between peripheral motor neurons and their target muscle fibers. There are now over 30 causative genes that have been reported for CMS. Of these, there are 10 that are associated with a limb-girdle pattern of muscle weakness and are thus classed as LG-CMS. Next-generation sequencing and advanced methods of data sharing are likely to uncover further genes that are associated with similar clinical phenotypes, contributing to better diagnosis and effective treatment of LG-CMS patients. This review highlights clinical and pathological hallmarks of LG-CMS in relation to the underlying genetic defects and pathways. Tailored animal and cell models are essential to elucidate the exact function and pathomechanisms at the neuromuscular synapse that underlie LG-CMS. The integration of genomics and proteomics data derived from these models and patients reveals new and often unexpected insights that are relevant beyond the rare genetic disorder of LG-CMS and may extend to the functioning of mammalian synapses in health and disease more generally.
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Affiliation(s)
- Emily O'Connor
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Ana Töpf
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - René P Zahedi
- Leibniz-Institut für Analytische Wissenschaften, ISAS e.V., Dortmund, Germany
| | - Sally Spendiff
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Daniel Cox
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Andreas Roos
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK.,Leibniz-Institut für Analytische Wissenschaften, ISAS e.V., Dortmund, Germany
| | - Hanns Lochmüller
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
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17
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Rizzuto E, Pisu S, Nicoletti C, Del Prete Z, Musarò A. Measuring Neuromuscular Junction Functionality. J Vis Exp 2017. [PMID: 28809841 DOI: 10.3791/55227] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Neuromuscular junction (NMJ) functionality plays a pivotal role when studying diseases in which the communication between motor neuron and muscle is impaired, such as aging and amyotrophic lateral sclerosis (ALS). Here we describe an experimental protocol that can be used to measure NMJ functionality by combining two types of electrical stimulation: direct muscle membrane stimulation and the stimulation through the nerve. The comparison of the muscle response to these two different stimulations can help to define, at the functional level, potential alterations in the NMJ that lead to functional decline in muscle. Ex vivo preparations are suited to well-controlled studies. Here we describe an intensive protocol to measure several parameters of muscle and NMJ functionality for the soleus-sciatic nerve preparation and for the diaphragm-phrenic nerve preparation. The protocol lasts approximately 60 min and is conducted uninterruptedly by means of a custom-made software that measures the twitch kinetics properties, the force-frequency relationship for both muscle and nerve stimulations, and two parameters specific to NMJ functionality, i.e. neurotransmission failure and intratetanic fatigue. This methodology was used to detect damages in soleus and diaphragm muscle-nerve preparations by using SOD1G93A transgenic mouse, an experimental model of ALS that ubiquitously overexpresses the mutant antioxidant enzyme superoxide dismutase 1 (SOD1).
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Affiliation(s)
- Emanuele Rizzuto
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome;
| | - Simona Pisu
- Institute Pasteur Cenci-Bolognetti, DAHFMO-Unit of Histology and Medical Embryology, Sapienza University of Rome
| | - Carmine Nicoletti
- Institute Pasteur Cenci-Bolognetti, DAHFMO-Unit of Histology and Medical Embryology, Sapienza University of Rome
| | - Zaccaria Del Prete
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome; Center for Life Nano Science@Sapienza, Istituto Italiano di Tecnologia
| | - Antonio Musarò
- Institute Pasteur Cenci-Bolognetti, DAHFMO-Unit of Histology and Medical Embryology, Sapienza University of Rome; Center for Life Nano Science@Sapienza, Istituto Italiano di Tecnologia;
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18
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Luan X, Tian W, Cao L. Limb-girdle congenital myasthenic syndrome in a Chinese family with novel mutations in MUSK gene and literature review. Clin Neurol Neurosurg 2016; 150:41-45. [DOI: 10.1016/j.clineuro.2016.08.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Revised: 08/04/2016] [Accepted: 08/21/2016] [Indexed: 11/16/2022]
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19
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MuSK Kinase Activity is Modulated By A Serine Phosphorylation Site in The Kinase Loop. Sci Rep 2016; 6:33583. [PMID: 27666825 PMCID: PMC5035991 DOI: 10.1038/srep33583] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 08/31/2016] [Indexed: 11/16/2022] Open
Abstract
The neuromuscular junction (NMJ) forms when a motor neuron contacts a muscle fibre. A reciprocal exchange of signals initiates a cascade of signalling events that result in pre- and postsynaptic differentiation. At the centre of these signalling events stands muscle specific kinase (MuSK). MuSK activation, kinase activity and subsequent downstream signalling are crucial for NMJ formation as well as maintenance. Therefore MuSK kinase activity is tightly regulated to ensure proper NMJ development. We have identified a novel serine phosphorylation site at position 751 in MuSK that is increasingly phosphorylated upon agrin stimulation. S751 is also phosphorylated in muscle tissue and its phosphorylation depends on MuSK kinase activity. A phosphomimetic mutant of S751 increases MuSK kinase activity in response to non-saturating agrin concentrations . In addition, basal MuSK and AChR phosphorylation as well as AChR cluster size are increased. We believe that the phosphorylation of S751 provides a novel mechanism to relief the autoinhibition of the MuSK activation loop. Such a lower autoinhibition could foster or stabilize MuSK kinase activation, especially during stages when no or low level of agrin are present. Phosphorylation of S751 might therefore represent a novel mechanism to modulate MuSK kinase activity during prepatterning or NMJ maintenance.
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20
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Durmuş H, Ayhan Ö, Çırak S, Deymeer F, Parman Y, Franke A, Eiber N, Chevessier F, Schlötzer-Schrehardt U, Clemen CS, Hashemolhosseini S, Schröder R, Hemmrich-Stanisak G, Tolun A, Serdaroğlu-Oflazer P. Neuromuscular endplate pathology in recessive desminopathies: Lessons from man and mice. Neurology 2016; 87:799-805. [PMID: 27440146 DOI: 10.1212/wnl.0000000000003004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2015] [Accepted: 05/17/2016] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To assess the clinical, genetic, and myopathologic findings in 2 cousins with lack of desmin, the response to salbutamol in one patient, and the neuromuscular endplate pathology in a knock-in mouse model for recessive desminopathy. METHODS We performed clinical investigations in the patients, genetic studies for linkage mapping, exome sequencing, and qPCR for transcript quantification, assessment of efficacy of (3-month oral) salbutamol administration by muscle strength assessment, 6-minute walking test (6MWT), and forced vital capacity, analysis of neuromuscular endplate pathology in a homozygous R349P desmin knock-in mouse by immunofluorescence staining of the hind limb muscles, and quantitative 3D morphometry and expression studies of acetylcholine receptor genes by quantitative PCR. RESULTS Both patients had infantile-onset weakness and fatigability, facial weakness with bilateral ptosis and ophthalmoparesis, generalized muscle weakness, and a decremental response over 10% on repetitive nerve stimulation. Salbutamol improved 6MWT and subjective motor function in the treated patient. Genetic analysis revealed previously unreported novel homozygous truncating desmin mutation c.345dupC leading to protein truncation and consequent fast degradation of the mutant mRNA. In the recessive desminopathy mouse with low expression of the mutant desmin protein, we demonstrated fragmented motor endplates with increased surface areas, volumes, and fluorescence intensities in conjunction with increased α and γ acetylcholine receptor subunit expression in oxidative soleus muscle. CONCLUSIONS The patients were desmin-null and had myopathy, cardiomyopathy, and a congenital myasthenic syndrome. The data from man and mouse demonstrate that the complete lack as well as the markedly decreased expression of mutant R349P desmin impair the structural and functional integrity of neuromuscular endplates.
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Affiliation(s)
- Hacer Durmuş
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany.
| | - Özgecan Ayhan
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Sebahattin Çırak
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Feza Deymeer
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Yeşim Parman
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Andre Franke
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Nane Eiber
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Frederic Chevessier
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Ursula Schlötzer-Schrehardt
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Christoph S Clemen
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Said Hashemolhosseini
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Rolf Schröder
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Georg Hemmrich-Stanisak
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Aslıhan Tolun
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
| | - Piraye Serdaroğlu-Oflazer
- From the Department of Neurology (H.D., F.D., Y.P., P.S.-O.), Faculty of Medicine, Istanbul University; Department of Molecular Biology and Genetics (Ö.A., A.T.), Boğaziçi University, Istanbul, Turkey; Children's National Medical Center (S.Ç.), Research Center for Genetic Medicine, Washington, DC; Department of Pediatrics, Institute for Human Genetics, and Center for Molecular Medicine, University Hospital Cologne; Institute of Clinical Molecular Biology (A.F., G.H.-S.), Christian-Albrechts-University of Kiel; Institute of Biochemistry (N.E., S.H.), Institute of Neuropathology (F.C., R.S.), and Department of Ophthalmology (U.S.-S.), Friedrich-Alexander-University of Erlangen-Nuremberg; and Center for Biochemistry, Institute of Biochemistry I, Medical Faculty (C.S.C.), University of Cologne, Germany
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21
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O'Connor E, Töpf A, Müller JS, Cox D, Evangelista T, Colomer J, Abicht A, Senderek J, Hasselmann O, Yaramis A, Laval SH, Lochmüller H. Identification of mutations in the MYO9A gene in patients with congenital myasthenic syndrome. Brain 2016; 139:2143-53. [PMID: 27259756 PMCID: PMC4958899 DOI: 10.1093/brain/aww130] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 04/20/2016] [Indexed: 12/13/2022] Open
Abstract
Congenital myasthenic syndromes are a group of rare and genetically heterogenous disorders resulting from defects in the structure and function of the neuromuscular junction. Patients with congenital myasthenic syndrome exhibit fatigable muscle weakness with a variety of accompanying phenotypes depending on the protein affected. A cohort of patients with a clinical diagnosis of congenital myasthenic syndrome that lacked a genetic diagnosis underwent whole exome sequencing in order to identify genetic causation. Missense biallelic mutations in the MYO9A gene, encoding an unconventional myosin, were identified in two unrelated families. Depletion of MYO9A in NSC-34 cells revealed a direct effect of MYO9A on neuronal branching and axon guidance. Morpholino-mediated knockdown of the two MYO9A orthologues in zebrafish, myo9aa/ab, demonstrated a requirement for MYO9A in the formation of the neuromuscular junction during development. The morphants displayed shortened and abnormally branched motor axons, lack of movement within the chorion and abnormal swimming in response to tactile stimulation. We therefore conclude that MYO9A deficiency may affect the presynaptic motor axon, manifesting in congenital myasthenic syndrome. These results highlight the involvement of unconventional myosins in motor axon functionality, as well as the need to look outside traditional neuromuscular junction-specific proteins for further congenital myasthenic syndrome candidate genes.
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Affiliation(s)
- Emily O'Connor
- 1 John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, UK
| | - Ana Töpf
- 1 John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, UK
| | - Juliane S Müller
- 2 Wellcome Trust Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Daniel Cox
- 1 John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, UK
| | - Teresinha Evangelista
- 1 John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, UK
| | - Jaume Colomer
- 3 Neuromuscular Unit, Neurology Department, Fundación Sant Joan de Déu, Hospital Materno-Infantil Sant Joan de Déu, Passeig Sant Joan de Déu, 2, 08950 Esplugues de Llobregat, Barcelona, Spain
| | - Angela Abicht
- 4 Friedrich-Baur-Institute, Ludwig-Maximilians-University, 80336 Munich, Germany
| | - Jan Senderek
- 4 Friedrich-Baur-Institute, Ludwig-Maximilians-University, 80336 Munich, Germany
| | - Oswald Hasselmann
- 5 Children's Hospital of Eastern Switzerland, Department of Neuropediatrics, Claudiusstrasse 6, 9006 St. Gallen, Switzerland
| | - Ahmet Yaramis
- 6 Paediatric Neurology Unit, Diyarbakır Memorial Hospital, Turkey
| | - Steven H Laval
- 1 John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, UK
| | - Hanns Lochmüller
- 1 John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, UK
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22
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Eguchi T, Tezuka T, Miyoshi S, Yamanashi Y. Postnatal knockdown of dok-7 gene expression in mice causes structural defects in neuromuscular synapses and myasthenic pathology. Genes Cells 2016; 21:670-6. [PMID: 27091576 DOI: 10.1111/gtc.12370] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 03/08/2016] [Indexed: 02/01/2023]
Abstract
The neuromuscular junction (NMJ) is a synapse between a motor neuron and skeletal muscle and is required for muscle contraction. The formation and maintenance of NMJs are governed by the muscle-specific receptor tyrosine kinase MuSK. We previously showed that the muscle cytoplasmic protein Dok-7 is an essential activator of MuSK. Indeed, mice lacking either Dok-7 or MuSK form no NMJs, and defects in the human DOK7 gene underlie a congenital myasthenic syndrome (an NMJ disorder). However, it remains unproven whether Dok-7 is required for the postnatal maintenance of NMJs. In this study, we generated recombinant adeno-associated virus (AAV) vectors encoding short hairpin RNAs targeting the mouse dok-7 gene (AAV-shD7). Systemic administration of AAV-shD7 into 2-week-old mice down-regulated dok-7 expression in muscle and induced myasthenic symptoms including reduction in body weight and motor function. Moreover, AAV-shD7 treatment suppressed MuSK-dependent gene expression of NMJ components and reduced the size of NMJs. These results demonstrate that correct, physiological levels of dok-7 expression are required for the postnatal maintenance of NMJs.
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Affiliation(s)
- Takahiro Eguchi
- Division of Genetics, Department of Cancer Biology, The Institute of Medical Science, The University of Tokyo, Tokyo, 108-8639, Japan
| | - Tohru Tezuka
- Division of Genetics, Department of Cancer Biology, The Institute of Medical Science, The University of Tokyo, Tokyo, 108-8639, Japan
| | - Sadanori Miyoshi
- Division of Genetics, Department of Cancer Biology, The Institute of Medical Science, The University of Tokyo, Tokyo, 108-8639, Japan
| | - Yuji Yamanashi
- Division of Genetics, Department of Cancer Biology, The Institute of Medical Science, The University of Tokyo, Tokyo, 108-8639, Japan
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23
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Shen C, Xiong WC, Mei L. LRP4 in neuromuscular junction and bone development and diseases. Bone 2015; 80:101-108. [PMID: 26071838 DOI: 10.1016/j.bone.2015.05.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/28/2014] [Revised: 05/04/2015] [Accepted: 05/08/2015] [Indexed: 02/08/2023]
Abstract
Low-density lipoprotein receptor-related protein 4 (LRP4) is a member of the low-density lipoprotein receptor (LDLR) family. Recent studies have revealed multiple functions and complex signaling mechanisms of LRP4 in different organs and tissues. LPR4 mutation or malfunction has been implicated in neurological disorders including congenital myasthenic syndrome, myasthenia gravis, and diseases of bone or kidney. This article is part of a Special Issue entitled "Muscle Bone Interactions".
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Affiliation(s)
- Chengyong Shen
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912, USA; Department of Neurology, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912, USA
| | - Wen-Cheng Xiong
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912, USA; Department of Neurology, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912, USA
| | - Lin Mei
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912, USA; Department of Neurology, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912, USA.
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24
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Evangelista T, Hanna M, Lochmüller H. Congenital Myasthenic Syndromes with Predominant Limb Girdle Weakness. J Neuromuscul Dis 2015; 2:S21-S29. [PMID: 26870666 PMCID: PMC4746746 DOI: 10.3233/jnd-150098] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Congenital myasthenic syndromes are a heterogeneous group of genetically determined disorders characterized by impaired neuromuscular transmission. They usually present from birth to childhood and are characterised by exercise induced weakness and fatigability. Genotype-phenotype correlations are difficult. However, in some patients particular phenotypic aspects may point towards a specific genetic defect. The absence of ptosis and ophthalmoparesis in patients with limb-girdle weakness makes the diagnosis of a neuromuscular transmission defect particularly challenging (LG-CMS). This is illustrated by a well-documented case published by Walton in 1956. The diagnosis of LG-CMS is secured by demonstrating a neuromuscular transmission defect with single fibre EMG or repetitive nerve stimulation, in the absence of auto-antibodies. Ultimately, a genetic test is required to identify the underlying cause and assure counselling and optimization of treatment. LG-CMS are inherited in autosomal recessive traits, and are often associated with mutations in DOK7 and GFPT1, and less frequently with mutations in COLQ, ALG2, ALG14 and DPAGT. Genetic characterization of CMS is of the upmost importance when choosing the adequate treatment. Some of the currently used drugs can either ameliorate or aggravate the symptoms depending on the underlying genetic defect. The drug most frequently used for the treatment of CMS is pyridostigmine an acetylcholinesterase inhibitor. However, pyridostigmine is not effective or is even detrimental in DOK7- and COLQ-related LG-CMS, while beta-adrenergic agonists (ephedrine, salbutamol) show some sustained benefit. Standard clinical trials may be difficult, but standardized follow-up of patients and international collaboration may help to improve the standards of care of these conditions.
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Affiliation(s)
- Teresinha Evangelista
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Newcastle University, Newcastle upon Tyne, UK
| | - Mike Hanna
- UCL MRC Centre for Neuromuscular Disease, Institute of Neurology and National Hospital for Neurology and Neurosurgery, Queen Square, London, United Kingdom
| | - Hanns Lochmüller
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Newcastle University, Newcastle upon Tyne, UK
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25
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Tintignac LA, Brenner HR, Rüegg MA. Mechanisms Regulating Neuromuscular Junction Development and Function and Causes of Muscle Wasting. Physiol Rev 2015; 95:809-52. [DOI: 10.1152/physrev.00033.2014] [Citation(s) in RCA: 224] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The neuromuscular junction is the chemical synapse between motor neurons and skeletal muscle fibers. It is designed to reliably convert the action potential from the presynaptic motor neuron into the contraction of the postsynaptic muscle fiber. Diseases that affect the neuromuscular junction may cause failure of this conversion and result in loss of ambulation and respiration. The loss of motor input also causes muscle wasting as muscle mass is constantly adapted to contractile needs by the balancing of protein synthesis and protein degradation. Finally, neuromuscular activity and muscle mass have a major impact on metabolic properties of the organisms. This review discusses the mechanisms involved in the development and maintenance of the neuromuscular junction, the consequences of and the mechanisms involved in its dysfunction, and its role in maintaining muscle mass during aging. As life expectancy is increasing, loss of muscle mass during aging, called sarcopenia, has emerged as a field of high medical need. Interestingly, aging is also accompanied by structural changes at the neuromuscular junction, suggesting that the mechanisms involved in neuromuscular junction maintenance might be disturbed during aging. In addition, there is now evidence that behavioral paradigms and signaling pathways that are involved in longevity also affect neuromuscular junction stability and sarcopenia.
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Affiliation(s)
- Lionel A. Tintignac
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Hans-Rudolf Brenner
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Markus A. Rüegg
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
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26
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MuSK frizzled-like domain is critical for mammalian neuromuscular junction formation and maintenance. J Neurosci 2015; 35:4926-41. [PMID: 25810523 DOI: 10.1523/jneurosci.3381-14.2015] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The muscle-specific kinase MuSK is one of the key molecules orchestrating neuromuscular junction (NMJ) formation. MuSK interacts with the Wnt morphogens, through its Frizzled-like domain (cysteine-rich domain [CRD]). Dysfunction of MuSK CRD in patients has been recently associated with the onset of myasthenia, common neuromuscular disorders mainly characterized by fatigable muscle weakness. However, the physiological role of Wnt-MuSK interaction in NMJ formation and function remains to be elucidated. Here, we demonstrate that the CRD deletion of MuSK in mice caused profound defects of both muscle prepatterning, the first step of NMJ formation, and synapse differentiation associated with a drastic deficit in AChR clusters and excessive growth of motor axons that bypass AChR clusters. Moreover, adult MuSKΔCRD mice developed signs of congenital myasthenia, including severe NMJs dismantlement, muscle weakness, and fatigability. We also report, for the first time, the beneficial effects of lithium chloride, a reversible inhibitor of the glycogen synthase kinase-3, that rescued NMJ defects in MuSKΔCRD mice and therefore constitutes a novel therapeutic reagent for the treatment of neuromuscular disorders linked to Wnt-MuSK signaling pathway deficiency. Together, our data reveal that MuSK CRD is critical for NMJ formation and plays an unsuspected role in NMJ maintenance in adulthood.
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27
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Engel AG, Shen XM, Selcen D, Sine SM. Congenital myasthenic syndromes: pathogenesis, diagnosis, and treatment. Lancet Neurol 2015; 14:420-34. [PMID: 25792100 PMCID: PMC4520251 DOI: 10.1016/s1474-4422(14)70201-7] [Citation(s) in RCA: 336] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The congenital myasthenic syndromes (CMS) are a diverse group of genetic disorders caused by abnormal signal transmission at the motor endplate, a special synaptic contact between motor axons and each skeletal muscle fibre. Most CMS stem from molecular defects in the muscle nicotinic acetylcholine receptor, but they can also be caused by mutations in presynaptic proteins, mutations in proteins associated with the synaptic basal lamina, defects in endplate development and maintenance, or defects in protein glycosylation. The specific diagnosis of some CMS can sometimes be reached by phenotypic clues pointing to the mutated gene. In the absence of such clues, exome sequencing is a useful technique for finding the disease gene. Greater understanding of the mechanisms of CMS have been obtained from structural and electrophysiological studies of the endplate, and from biochemical studies. Present therapies for the CMS include cholinergic agonists, long-lived open-channel blockers of the acetylcholine receptor ion channel, and adrenergic agonists. Although most CMS are treatable, caution should be exercised as some drugs that are beneficial in one syndrome can be detrimental in another.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
| | - Xin-Ming Shen
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - Duygu Selcen
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - Steven M Sine
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, USA
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28
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Abstract
The neuromuscular junction (NMJ) is a synapse between motor neurons and skeletal muscle fibers, and is critical for control of muscle contraction. Its formation requires neuronal agrin that acts by binding to LRP4 to stimulate MuSK. Mutations have been identified in agrin, MuSK, and LRP4 in patients with congenital myasthenic syndrome, and patients with myasthenia gravis develop antibodies against agrin, LRP4, and MuSK. However, it remains unclear whether the agrin signaling pathway is critical for NMJ maintenance because null mutation of any of the three genes is perinatal lethal. In this study, we generated imKO mice, a mutant strain whose LRP4 gene can be deleted in muscles by doxycycline (Dox) treatment. Ablation of the LRP4 gene in adult muscle enabled studies of its role in NMJ maintenance. We demonstrate that Dox treatment of P30 mice reduced muscle strength and compound muscle action potentials. AChR clusters became fragmented with diminished junctional folds and synaptic vesicles. The amplitude and frequency of miniature endplate potentials were reduced, indicating impaired neuromuscular transmission and providing cellular mechanisms of adult LRP4 deficiency. We showed that LRP4 ablation led to the loss of synaptic agrin and the 90 kDa fragments, which occurred ahead of other prejunctional and postjunctional components, suggesting that LRP4 may regulate the stability of synaptic agrin. These observations demonstrate that LRP4 is essential for maintaining the structural and functional integrity of the NMJ and that loss of muscle LRP4 in adulthood alone is sufficient to cause myasthenic symptoms.
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29
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Wilbe M, Ekvall S, Eurenius K, Ericson K, Casar-Borota O, Klar J, Dahl N, Ameur A, Annerén G, Bondeson ML. MuSK: a new target for lethal fetal akinesia deformation sequence (FADS). J Med Genet 2015; 52:195-202. [PMID: 25612909 DOI: 10.1136/jmedgenet-2014-102730] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
BACKGROUND Fetal akinesia deformation sequence syndrome (FADS, OMIM 208150) is characterised by decreased fetal movement (fetal akinesia) as well as intrauterine growth restriction, arthrogryposis, and developmental anomalies (eg, cystic hygroma, pulmonary hypoplasia, cleft palate, and cryptorchidism). Mutations in components of the acetylcholine receptor (AChR) pathway have previously been associated with FADS. METHODS AND RESULTS We report on a family with recurrent fetal loss, where the parents had five affected fetuses/children with FADS and one healthy child. The fetuses displayed no fetal movements from the gestational age of 17 weeks, extended knee joints, flexed hips and elbows, and clenched hands. Whole exome sequencing of one affected fetus and the parents was performed. A novel homozygous frameshift mutation was identified in muscle, skeletal receptor tyrosine kinase (MuSK), c.40dupA, which segregated with FADS in the family. Haplotype analysis revealed a conserved haplotype block suggesting a founder mutation. MuSK (muscle-specific tyrosine kinase receptor), a component of the AChR pathway, is a main regulator of neuromuscular junction formation and maintenance. Missense mutations in MuSK have previously been reported to cause congenital myasthenic syndrome (CMS) associated with AChR deficiency. CONCLUSIONS To our knowledge, this is the first report showing that a mutation in MuSK is associated with FADS. The results support previous findings that CMS and/or FADS are caused by complete or severe functional disruption of components located in the AChR pathway. We propose that whereas milder mutations of MuSK will cause a CMS phenotype, a complete loss is lethal and will cause FADS.
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Affiliation(s)
- Maria Wilbe
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Sara Ekvall
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Karin Eurenius
- Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden
| | - Katharina Ericson
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden Department of Pathology and Cytology, Uppsala University Hospital, Uppsala, Sweden
| | - Olivera Casar-Borota
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden Department of Pathology and Cytology, Uppsala University Hospital, Uppsala, Sweden
| | - Joakim Klar
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Niklas Dahl
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Adam Ameur
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Göran Annerén
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Marie-Louise Bondeson
- Science for Life Laboratory, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
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30
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Ferry A, Joanne P, Hadj-Said W, Vignaud A, Lilienbaum A, Hourdé C, Medja F, Noirez P, Charbonnier F, Chatonnet A, Chevessier F, Nicole S, Agbulut O, Butler-Browne G. Advances in the understanding of skeletal muscle weakness in murine models of diseases affecting nerve-evoked muscle activity, motor neurons, synapses and myofibers. Neuromuscul Disord 2014; 24:960-72. [PMID: 25042397 DOI: 10.1016/j.nmd.2014.06.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 05/23/2014] [Accepted: 06/01/2014] [Indexed: 12/13/2022]
Abstract
Disease processes and trauma affecting nerve-evoked muscle activity, motor neurons, synapses and myofibers cause different levels of muscle weakness, i.e., reduced maximal force production in response to voluntary activation or nerve stimulation. However, the mechanisms of muscle weakness are not well known. Using murine models of amyotrophic lateral sclerosis (SOD1(G93A) transgenic mice), congenital myasthenic syndrome (AChE knockout mice and Musk(V789M/-) mutant mice), Schwartz-Jampel syndrome (Hspg2(C1532YNEO/C1532YNEO) mutant mice) and traumatic nerve injury (Neurotomized wild-type mice), we show that the reduced maximal activation capacity (the ability of the nerve to maximally activate the muscle) explains 52%, 58% and 100% of severe weakness in respectively SOD1(G93A), Neurotomized and Musk mice, whereas muscle atrophy only explains 37%, 27% and 0%. We also demonstrate that the impaired maximal activation capacity observed in SOD1, Neurotomized, and Musk mice is not highly related to Hdac4 gene upregulation. Moreover, in SOD1 and Neurotomized mice our results suggest LC3, Fn14, Bcl3 and Gadd45a as candidate genes involved in the maintenance of the severe atrophic state. In conclusion, our study indicates that muscle weakness can result from the triggering of different signaling pathways. This knowledge may be helpful in designing therapeutic strategies and finding new drug targets for amyotrophic lateral sclerosis, congenital myasthenic syndrome, Schwartz-Jampel syndrome and nerve injury.
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Affiliation(s)
- Arnaud Ferry
- Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, UMR S794, INSERM U974, CNRS UMR 7215, Institut de Myologie, Paris F-75013, France; Université Paris Descartes, Sorbonne Paris Cité, Paris F-75006, France.
| | - Pierre Joanne
- Université Paris Diderot, Sorbonne Paris Cité, CNRS EAC 4413, Unit of Functional and Adaptive Biology, Laboratory of Stress and Pathologies of the Cytoskeleton, Paris F-75013, France
| | - Wahiba Hadj-Said
- Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, UMR S794, INSERM U974, CNRS UMR 7215, Institut de Myologie, Paris F-75013, France
| | - Alban Vignaud
- Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, UMR S794, INSERM U974, CNRS UMR 7215, Institut de Myologie, Paris F-75013, France
| | - Alain Lilienbaum
- Université Paris Diderot, Sorbonne Paris Cité, CNRS EAC 4413, Unit of Functional and Adaptive Biology, Laboratory of Stress and Pathologies of the Cytoskeleton, Paris F-75013, France
| | - Christophe Hourdé
- Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, UMR S794, INSERM U974, CNRS UMR 7215, Institut de Myologie, Paris F-75013, France
| | - Fadia Medja
- Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, UMR S794, INSERM U974, CNRS UMR 7215, Institut de Myologie, Paris F-75013, France
| | - Philippe Noirez
- Université Paris Descartes, Sorbonne Paris Cité, Laboratoire de Biologie de la Nutrition EA 2498, Paris, France
| | - Frederic Charbonnier
- Université Paris Descartes, Sorbonne Paris Cité, CESeM, UMR 8194 CNRS, Paris F-75006, France
| | - Arnaud Chatonnet
- Universités Montpellier 1 et 2, INRA, UMR 866, Montpellier, France
| | - Frederic Chevessier
- Universitätsklinikum Erlangen, Neuropathologisches Institut, Erlangen, Germany
| | - Sophie Nicole
- Université Pierre et Marie Curie - Paris 6, INSERM U975, Centre de recherche de l'Institut Cerveau Moelle, CNRS UMR 7225, Paris, France
| | - Onnik Agbulut
- Université Paris Diderot, Sorbonne Paris Cité, CNRS EAC 4413, Unit of Functional and Adaptive Biology, Laboratory of Stress and Pathologies of the Cytoskeleton, Paris F-75013, France
| | - Gillian Butler-Browne
- Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, UMR S794, INSERM U974, CNRS UMR 7215, Institut de Myologie, Paris F-75013, France
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31
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Abstract
PURPOSE OF REVIEW Congenital myasthenic syndromes (CMSs) form a heterogeneous group of genetic diseases characterized by a dysfunction of neuromuscular transmission because of mutations in numerous genes. This review will focus on the causative genes recently identified and on the therapy of CMSs. RECENT FINDINGS Advances in exome sequencing allowed the discovery of a new group of genes that did not code for the known molecular components of the neuromuscular junction, and the definition of a new group of glycosylation-defective CMS. Rather than the specific drugs used, some of them having been known for decades, it is the rigorous therapeutic strategy that is now offered to the patient in relation to the identified mutated gene that is novel and promising. SUMMARY In addition to the above main points, we also present new data on the genes that were already known with an emphasis on the clinic and on animal models that may be of use to understand the pathophysiology of the disease. We also stress not only the diagnosis difficulties between congenital myopathies and CMSs, but also the continuum that may exist between the two.
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32
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The neuromuscular junction: Selective remodeling of synaptic regulators at the nerve/muscle interface. Mech Dev 2013; 130:402-11. [DOI: 10.1016/j.mod.2012.09.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Revised: 09/18/2012] [Accepted: 09/21/2012] [Indexed: 11/19/2022]
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Grandič M, Aráoz R, Molgó J, Turk T, Sepčić K, Benoit E, Frangež R. The non-competitive acetylcholinesterase inhibitor APS12-2 is a potent antagonist of skeletal muscle nicotinic acetylcholine receptors. Toxicol Appl Pharmacol 2012; 265:221-8. [PMID: 23046821 DOI: 10.1016/j.taap.2012.09.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 09/28/2012] [Accepted: 09/30/2012] [Indexed: 10/27/2022]
Abstract
APS12-2, a non-competitive acetylcholinesterase inhibitor, is one of the synthetic analogs of polymeric alkylpyridinium salts (poly-APS) isolated from the marine sponge Reniera sarai. In the present work the effects of APS12-2 were studied on isolated mouse phrenic nerve-hemidiaphragm muscle preparations, using twitch tension measurements and electrophysiological recordings. APS12-2 in a concentration-dependent manner blocked nerve-evoked isometric muscle contraction (IC(50)=0.74 μM), without affecting directly-elicited twitch tension up to 2.72 μM. The compound (0.007-3.40 μM) decreased the amplitude of miniature endplate potentials until a complete block by concentrations higher than 0.68 μM, without affecting their frequency. Full size endplate potentials, recorded after blocking voltage-gated muscle sodium channels, were inhibited by APS12-2 in a concentration-dependent manner (IC(50)=0.36 μM) without significant change in the resting membrane potential of the muscle fibers up to 3.40 μM. The compound also blocked acetylcholine-evoked inward currents in Xenopus oocytes in which Torpedo (α1(2)β1γδ) muscle-type nicotinic acetylcholine receptors (nAChRs) have been incorporated (IC(50)=0.0005 μM), indicating a higher affinity of the compound for Torpedo (α1(2)β1γδ) than for the mouse (α1(2)β1γε) nAChR. Our data show for the first time that APS12-2 blocks neuromuscular transmission by a non-depolarizing mechanism through an action on postsynaptic nAChRs of the skeletal neuromuscular junction.
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Affiliation(s)
- Marjana Grandič
- Institute of Physiology, Pharmacology and Toxicology, Veterinary Faculty, University of Ljubljana, Gerbičeva 60, SI-1000 Ljubljana, Slovenia
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34
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Takahashi Y, Sugiyama M, Ueda Y, Itoh T, Yagyu K, Shiraishi H, Ukeba-Terashita Y, Nakanishi M, Nagashima T, Imai T, Motomura M, Saitoh S. Childhood-onset anti-MuSK antibody positive myasthenia gravis demonstrates a distinct clinical course. Brain Dev 2012; 34:784-6. [PMID: 22277190 DOI: 10.1016/j.braindev.2011.12.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Revised: 10/27/2011] [Accepted: 12/29/2011] [Indexed: 11/19/2022]
Abstract
Anti-muscle-specific tyrosine kinase antibody (MuSK-Ab) is the second most frequent autoantibody identified in adult patients with myasthenia gravis (MG). Adult patients with MuSK-Ab demonstrate characteristic clinical features but very little information is available for childhood-onset patients with MuSK-positive MG. We report a childhood-onset female patient with MuSK-positive MG. This patient showed basic clinical features compatible with adult-onset MuSK-positive MG, but some features, including spontaneous improvement, are distinct from those in adult patients. Serial examination of MuSK-Ab titers revealed a gross correlation with clinical severity despite significantly high titers throughout the clinical course. Therefore, childhood-onset MuSK-positive MG may demonstrate a distinct clinical characteristics in the early period of illness.
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Affiliation(s)
- Yumi Takahashi
- Department of Pediatrics, Graduate School of Medicine, Hokkaido University, Sapporo, Japan
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35
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Chaouch A, Beeson D, Hantaï D, Lochmüller H. 186th ENMC International Workshop: Congenital myasthenic syndromes 24–26 June 2011, Naarden, The Netherlands. Neuromuscul Disord 2012; 22:566-76. [DOI: 10.1016/j.nmd.2011.12.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 12/13/2011] [Indexed: 12/24/2022]
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36
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Molecular mechanisms underlying maturation and maintenance of the vertebrate neuromuscular junction. Trends Neurosci 2012; 35:441-53. [PMID: 22633140 DOI: 10.1016/j.tins.2012.04.005] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 04/09/2012] [Accepted: 04/15/2012] [Indexed: 01/22/2023]
Abstract
The vertebrate neuromuscular junction (NMJ), a peripheral synapse formed between motoneuron and skeletal muscle, is characterized by a protracted postnatal period of maturation and life-long maintenance. In neuromuscular disorders such as congenital myasthenic syndromes (CMSs), disruptions of NMJ maturation and/or maintenance are frequently observed. In particular, defective neuromuscular transmission associated with structural and molecular abnormalities at the pre- and postsynaptic membranes, as well as at the synaptic cleft, has been reported in these patients. Here, we review recent advances in the understanding of molecular and cellular events that mediate NMJ maturation and maintenance. The underlying regulatory mechanisms, including key molecular regulators at the presynaptic nerve terminal, synaptic cleft, and postsynaptic muscle membrane, are discussed.
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37
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Mori S, Yamada S, Kubo S, Chen J, Matsuda S, Shudou M, Maruyama N, Shigemoto K. Divalent and monovalent autoantibodies cause dysfunction of MuSK by distinct mechanisms in a rabbit model of myasthenia gravis. J Neuroimmunol 2012; 244:1-7. [DOI: 10.1016/j.jneuroim.2011.12.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Revised: 11/07/2011] [Accepted: 12/05/2011] [Indexed: 12/21/2022]
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38
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Engel AG. Current status of the congenital myasthenic syndromes. Neuromuscul Disord 2012; 22:99-111. [PMID: 22104196 PMCID: PMC3269564 DOI: 10.1016/j.nmd.2011.10.009] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Revised: 10/11/2011] [Accepted: 10/13/2011] [Indexed: 01/04/2023]
Abstract
Congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is compromised by one or more specific mechanisms. Clinical, electrophysiologic, and morphologic studies have paved the way for detecting CMS-related mutations in proteins residing in the nerve terminal, the synaptic basal lamina, and in the postsynaptic region of the motor endplate. The disease proteins identified to date include choline acetyltransferase (ChAT), the endplate species of acetylcholinesterase (AChE), β2-laminin, the acetylcholine receptor (AChR), rapsyn, plectin, Na(v)1.4, the muscle specific protein kinase (MuSK), agrin, downstream of tyrosine kinase 7 (Dok-7), and glutamine-fructose-6-phosphate transaminase 1 (GFPT1). Myasthenic syndromes associated with centronuclear myopathies were recently recognized. Analysis of properties of expressed mutant proteins contributed to finding improved therapy for most CMS. Despite these advances, the molecular basis of some phenotypically characterized CMS remains elusive. Moreover, other types of CMS and disease genes likely exist and await discovery.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN 55905, United States.
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39
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SUTO JI. Development of an Efficient Method for Genotyping at the <i>gd</i> Locus in NC/Sgn Mice Based on PCR-RFLP Analysis. J Vet Med Sci 2012; 74:1003-6. [DOI: 10.1292/jvms.12-0010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Jun-ichi SUTO
- Agrogenomics Research Center, National Institute of Agrobiological Sciences
- Agrogenomics Research Center, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305–8634, Japan
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40
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Chevessier F, Peter C, Mersdorf U, Girard E, Krejci E, McArdle JJ, Witzemann V. A new mouse model for the slow-channel congenital myasthenic syndrome induced by the AChR εL221F mutation. Neurobiol Dis 2011; 45:851-61. [PMID: 22178625 DOI: 10.1016/j.nbd.2011.10.024] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2011] [Revised: 09/29/2011] [Accepted: 10/28/2011] [Indexed: 11/24/2022] Open
Abstract
We have generated a new mouse model for congenital myasthenic syndromes by inserting the missense mutation L221F into the ε subunit of the acetylcholine receptor by homologous recombination. This mutation has been identified in man to cause a mild form of slow-channel congenital myasthenic syndrome with variable penetrance. In our mouse model we observe as in human patients prolonged endplate currents. The summation of endplate potentials may account for a depolarization block at increasing stimulus frequencies, moderate reduced muscle strength and tetanic fade. Calcium and intracellular vesicle accumulation as well as junctional fold loss and organelle degeneration underlying a typical endplate myopathy, were identified. Moreover, a remodeling of neuromuscular junctions occurs in a muscle-dependent pattern expressing variable phenotypic effects. Altogether, this mouse model provides new insight into the pathophysiology of congenital myasthenia and serves as a new tool for deciphering signaling pathways induced by excitotoxicity at peripheral synapses.
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Affiliation(s)
- Frédéric Chevessier
- Department of Molecular Neurobiology, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany
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41
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Mori S, Kubo S, Akiyoshi T, Yamada S, Miyazaki T, Hotta H, Desaki J, Kishi M, Konishi T, Nishino Y, Miyazawa A, Maruyama N, Shigemoto K. Antibodies against muscle-specific kinase impair both presynaptic and postsynaptic functions in a murine model of myasthenia gravis. THE AMERICAN JOURNAL OF PATHOLOGY 2011; 180:798-810. [PMID: 22142810 DOI: 10.1016/j.ajpath.2011.10.031] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Revised: 10/04/2011] [Accepted: 10/25/2011] [Indexed: 01/17/2023]
Abstract
Antibodies against acetylcholine receptors (AChRs) cause pathogenicity in myasthenia gravis (MG) patients through complement pathway-mediated destruction of postsynaptic membranes at neuromuscular junctions (NMJs). However, antibodies against muscle-specific kinase (MuSK), which constitute a major subclass of antibodies found in MG patients, do not activate the complement pathway. To investigate the pathophysiology of MuSK-MG and establish an experimental autoimmune MG (EAMG) model, we injected MuSK protein into mice deficient in complement component five (C5). MuSK-injected mice simultaneously developed severe muscle weakness, accompanied by an electromyographic pattern such as is typically observed in MG patients. In addition, we observed morphological and functional defects in the NMJs of EAMG mice, demonstrating that complement activation is not necessary for the onset of MuSK-MG. Furthermore, MuSK-injected mice exhibited acetylcholinesterase (AChE) inhibitor-evoked cholinergic hypersensitivity, as is observed in MuSK-MG patients, and a decrease in both AChE and the AChE-anchoring protein collagen Q at postsynaptic membranes. These findings suggest that MuSK is indispensable for the maintenance of NMJ structure and function, and that disruption of MuSK activity by autoantibodies causes MG. This mouse model of EAMG could be used to develop appropriate medications for the treatment of MuSK-MG in humans.
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Affiliation(s)
- Shuuichi Mori
- Department of Geriatric Medicine, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan
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42
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Punga AR, Lin S, Oliveri F, Meinen S, Rüegg MA. Muscle-selective synaptic disassembly and reorganization in MuSK antibody positive MG mice. Exp Neurol 2011; 230:207-17. [DOI: 10.1016/j.expneurol.2011.04.018] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2011] [Revised: 04/15/2011] [Accepted: 04/21/2011] [Indexed: 11/25/2022]
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43
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Punga AR, Maj M, Lin S, Meinen S, Rüegg MA. MuSK levels differ between adult skeletal muscles and influence postsynaptic plasticity. Eur J Neurosci 2011; 33:890-8. [PMID: 21255125 DOI: 10.1111/j.1460-9568.2010.07569.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Muscle-specific tyrosine kinase (MuSK) is involved in the formation and maintenance of the neuromuscular junction (NMJ), and is necessary for NMJ integrity. As muscle involvement is strikingly selective in pathological conditions in which MuSK is targeted, including congenital myasthenic syndrome with MuSK mutation and MuSK antibody-seropositive myasthenia gravis, we hypothesized that the postsynaptic response to MuSK-agrin signalling differs between adult muscles. Transcript levels of postsynaptic proteins were compared between different muscles in wild-type adult mice. MuSK expression was high in the soleus and sternomastoid muscles and low in the extensor digitorum longus (EDL) and omohyoid muscles. The acetylcholine receptor (AChR) α subunit followed a similar expression pattern, whereas expression of Dok-7, Lrp4 and rapsyn was comparable between the muscles. We subsequently examined muscles in mice that overexpressed a miniaturized form of neural agrin or MuSK. In these transgenic mice, the soleus and sternomastoid muscles responded with formation of ectopic AChR clusters, whereas such clusters were almost absent in the EDL and omohyoid muscles. Electroporation of Dok-7 revealed its important role as an activator of MuSK in AChR cluster formation in adult muscles. Together, our findings indicate for the first time that adult skeletal muscles harbour different endogenous levels of MuSK and that these levels determine the ability to form ectopic AChR clusters upon overexpression of agrin or MuSK. We believe that these findings are important for our understanding of adult muscle plasticity and the selective muscle involvement in neuromuscular disorders in which MuSK is diminished.
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Affiliation(s)
- Anna R Punga
- Department of Neurobiology/Pharmacology, Biozentrum, University of Basel, Basel, Switzerland.
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44
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Vrolix K, Fraussen J, Molenaar PC, Losen M, Somers V, Stinissen P, De Baets MH, Martínez-Martínez P. The auto-antigen repertoire in myasthenia gravis. Autoimmunity 2010; 43:380-400. [PMID: 20380581 DOI: 10.3109/08916930903518073] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Myasthenia Gravis (MG) is an antibody-mediated autoimmune disorder affecting the postsynaptic membrane of the neuromuscular junction (NMJ). MG is characterized by an impaired signal transmission between the motor neuron and the skeletal muscle cell, caused by auto-antibodies directed against NMJ proteins. The auto-antibodies target the nicotinic acetylcholine receptor (nAChR) in about 90% of MG patients. In approximately 5% of MG patients, the muscle specific kinase (MuSK) is the auto-antigen. In the remaining 5% of MG patients, however, antibodies against the nAChR or MuSK are not detectable (idiopathic MG, iMG). Although only the anti-nAChR and anti-MuSK auto-antibodies have been demonstrated to be pathogenic, several other antibodies recognizing self-antigens can also be found in MG patients. Various auto-antibodies associated with thymic abnormalities have been reported, as well as many non-MG-specific auto-antibodies. However, their contribution to the cause, pathology and severity of the disease is still poorly understood. Here, we comprehensively review the reported auto-antibodies in MG patients and discuss their role in the pathology of this autoimmune disease.
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Affiliation(s)
- Kathleen Vrolix
- Division of Neuroscience, School of Mental Health and Neuroscience, Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands
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45
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Dupuis L, Echaniz-Laguna A. Skeletal muscle in motor neuron diseases: therapeutic target and delivery route for potential treatments. Curr Drug Targets 2010; 11:1250-61. [PMID: 20840067 PMCID: PMC4834127 DOI: 10.2174/1389450111007011250] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2009] [Accepted: 05/04/2010] [Indexed: 12/12/2022]
Abstract
Lower motor neuron (LMN) degeneration occurs in several diseases that affect patients from neonates to elderly and can either be genetically transmitted or occur sporadically. Among diseases involving LMN degeneration, spinal muscular atrophy (SMA) and spinal bulbar muscular atrophy (Kennedy's disease, SBMA) are pure genetic diseases linked to loss of the SMN gene (SMA) or expansion of a polyglutamine tract in the androgen receptor gene (SBMA) while amyotrophic lateral sclerosis (ALS) can either be of genetic origin or occur sporadically. In this review, our aim is to put forward the hypothesis that muscle fiber atrophy and weakness might not be a simple collateral damage of LMN degeneration, but instead that muscle fibers may be the site of crucial pathogenic events in these diseases. In SMA, the SMN gene was shown to be required for muscle structure and strength as well as for neuromuscular junction formation, and a subset of SMA patients develop myopathic pathology. In SBMA, the occurrence of myopathic histopathology in patients and animal models, along with neuromuscular phenotype of animal models expressing the androgen receptor in muscle only has lead to the proposal that SBMA may indeed be a muscle disease. Lastly, in ALS, at least part of the phenotype might be explained by pathogenic events occuring in skeletal muscle. Apart from its potential pathogenic role, skeletal muscle pathophysiological events might be a target for treatments and/or be a preferential route for targeting motor neurons.
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Affiliation(s)
- Luc Dupuis
- Inserm, U692, Strasbourg, F-67085 France.
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46
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Maselli RA, Arredondo J, Cagney O, Ng JJ, Anderson JA, Williams C, Gerke BJ, Soliven B, Wollmann RL. Mutations in MUSK causing congenital myasthenic syndrome impair MuSK-Dok-7 interaction. Hum Mol Genet 2010; 19:2370-9. [PMID: 20371544 PMCID: PMC2876883 DOI: 10.1093/hmg/ddq110] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We describe a severe congenital myasthenic syndrome (CMS) caused by two missense mutations in the gene encoding the muscle specific receptor tyrosine kinase (MUSK). The identified MUSK mutations M605I and A727V are both located in the kinase domain of MuSK. Intracellular microelectrode recordings and microscopy studies of the neuromuscular junction conducted in an anconeus muscle biopsy revealed decreased miniature endplate potential amplitudes, reduced endplate size and simplification of secondary synaptic folds, which were consistent with postsynaptic deficit. The study also showed a striking reduction of the endplate potential quantal content, consistent with additional presynaptic failure. Expression studies in MuSK deficient myotubes revealed that A727V, which is located within the catalytic loop of the enzyme, caused severe impairment of agrin-dependent MuSK phosphorylation, aggregation of acetylcholine receptors (AChRs) and interaction of MuSK with Dok-7, an essential intracellular binding protein of MuSK. In contrast, M605I, resulted in only moderate impairment of agrin-dependent MuSK phosphorylation, aggregation of AChRs and interaction of MuSK with Dok-7. There was no impairment of interaction of mutants with either the low-density lipoprotein receptor-related protein, Lrp4 (a co-receptor of agrin) or with the mammalian homolog of the Drosophila tumorous imaginal discs (Tid1). Our findings demonstrate that missense mutations in MUSK can result in a severe form of CMS and indicate that the inability of MuSK mutants to interact with Dok-7, but not with Lrp4 or Tid1, is a major determinant of the pathogenesis of the CMS caused by MUSK mutations.
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Affiliation(s)
- Ricardo A Maselli
- Department of Neurology, School of Veterinary Medicine, University of California Davis, Davis, CA 95618, USA.
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47
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Shi L, Butt B, Ip FCF, Dai Y, Jiang L, Yung WH, Greenberg ME, Fu AKY, Ip NY. Ephexin1 is required for structural maturation and neurotransmission at the neuromuscular junction. Neuron 2010; 65:204-16. [PMID: 20152127 DOI: 10.1016/j.neuron.2010.01.012] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/24/2009] [Indexed: 12/24/2022]
Abstract
The maturation of neuromuscular junctions (NMJs) requires the topological transformation of postsynaptic acetylcholine receptor (AChR)-containing structures from a simple plaque to an elaborate structure composed of pretzel-like branches. This maturation process results in the precise apposition of the presynaptic and postsynaptic specializations. However, little is known about the molecular mechanisms underlying the plaque-to-pretzel transition of AChR clusters. In this study, we identify an essential role for the RhoGEF ephexin1 in the maturation of AChR clusters. Adult ephexin1(-/-) mice exhibit severe muscle weakness and impaired synaptic transmission at the NMJ. Intriguingly, when ephexin1 expression is deficient in vivo, the NMJ fails to mature into the pretzel-like shape, and such abnormalities can be rescued by re-expression of ephexin1. We further demonstrate that ephexin1 regulates the stability of AChR clusters in a RhoA-dependent manner. Taken together, our findings reveal an indispensible role for ephexin1 in regulating the structural maturation and neurotransmission of NMJs.
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Affiliation(s)
- Lei Shi
- Department of Biochemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China
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48
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Abstract
CollagenQ (ColQ) plays an important structural role at vertebrate neuromuscular junctions (NMJs) by anchoring and accumulating acetylcholinesterase (AChE) in the extracellular matrix (ECM). Moreover, ColQ interacts with perlecan/dystroglycan and the muscle-specific receptor tyrosine kinase (MuSK), key molecules in the NMJ formation. MuSK promotes acetylcholine receptor (AChR) clustering in a process mediated by rapsyn, a cytoplasmic protein that stimulates AChR packing in clusters and regulates synaptic gene transcription. Here, we investigated a regulatory role for ColQ by comparing the clustering and expression of synaptic proteins in wild type and ColQ-deficient muscle cells in culture and at NMJ. We show first that AChR clusters are smaller and more densely packed in the absence of ColQ both in vitro and in vivo. Second, we find that like AChRs and rapsyn, MuSK mRNA levels are increased in cultured cells but not in muscles lacking ColQ. However, membrane-bound MuSK is decreased both in vitro and in vivo suggesting that ColQ controls MuSK sorting or stabilization in the muscle membrane. In line with this, our data show that activation of the MuSK signaling pathway is altered in the absence of ColQ leading to (1) perturbation of AChR clustering and/or beta-AChR subunit phosphorylation and (2) modifications of AChR mRNA level due to the lack of ColQ-MuSK interaction. Together, our results demonstrate that ColQ, in addition to its structural role, has important regulatory functions at the synapse by controlling AChR clustering and synaptic gene expression through its interaction with MuSK.
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49
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Abstract
The heparan sulfate proteoglycan agrin is best known for its essential role during formation, maintenance and regeneration of the neuromuscular junction. Mutations in agrin-interacting proteins are the genetic basis for a number of neuromuscular disorders. However, agrin is widely expressed in many tissues including neurons and glial cells of the brain, where its precise function is much less understood. Fewer synapses develop in brains that lack agrin, consistent with a function of agrin during CNS synaptogenesis. Recently, a specific transmembrane form of agrin (TM-agrin) was identified that is concentrated at that interneuronal synapses in the brain. Clustering or overexpression of TM-agrin leads to the formation of filopodia-like processes, which might be precursors for CNS synapses. Agrin is subject to defined and activity-dependent proteolytic cleavage by neurotrypsin at synapses and dysregulation of agrin processing might contribute to the development of mental retardation. This review summarizes what is known about the role of agrin during synapse formation at the neuromuscular junction and in the developing CNS and will discuss additional functions of agrin in the adult CNS, in particular during BBB formation, during recovery after traumatic brain injury and in the etiology of diseases, including Alzheimer’s disease and mental retardation.
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Affiliation(s)
- Stephan Kröger
- Department of Physiological Genomics, Ludwig-Maximilians University, Schillerstrasse 46, D-80336 Munich, Germany
| | - Heike Pfister
- Department of Physiological Genomics, Ludwig-Maximilians University, Schillerstrasse 46, D-80336 Munich, Germany
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