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Fish LA, Ewing MD, Jaime D, Rich KA, Xi C, Wang X, Feder RE, Wharton KA, Rich MM, Arnold WD, Fallon JR. The MuSK-BMP pathway regulates synaptic Nav1.4 localization and muscle excitability. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.24.563837. [PMID: 37961580 PMCID: PMC10634800 DOI: 10.1101/2023.10.24.563837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
The neuromuscular junction (NMJ) is the linchpin of nerve-evoked muscle contraction. Broadly considered, the function of the NMJ is to transduce a nerve action potential into a muscle fiber action potential (MFAP). Efficient information transfer requires both cholinergic signaling, responsible for the generation of endplate potentials (EPPs), and excitation, the activation of postsynaptic voltage-gated sodium channels (Nav1.4) to trigger MFAPs. In contrast to the cholinergic apparatus, the signaling pathways that organize Nav1.4 and muscle fiber excitability are poorly characterized. Muscle-specific kinase (MuSK), in addition to its Ig1 domain-dependent role as an agrin-LRP4 receptor, is also a BMP co-receptor that binds BMPs via its Ig3 domain and shapes BMP-induced signaling and transcriptional output. Here we probed the function of the MuSK-BMP pathway at the NMJ using mice lacking the MuSK Ig3 domain ('ΔIg3-MuSK'). Synapses formed normally in ΔIg3-MuSK animals, but the postsynaptic apparatus was fragmented from the first weeks of life. Anatomical denervation was not observed at any age examined. Moreover, spontaneous and nerve-evoked acetylcholine release, AChR density, and endplate currents were comparable to WT. However, trains of nerve-evoked MFAPs in ΔIg3-MuSK muscle were abnormal as revealed by increased jitter and blocking in single fiber electromyography. Further, nerve-evoked compound muscle action potentials (CMAPs), as well as twitch and tetanic muscle torque force production, were also diminished. Finally, Nav1.4 levels were reduced at ΔIg3-MuSK synapses but not at the extrajunctional sarcolemma, indicating that the observed excitability defects are the result of impaired localization of this voltage-gated ion channel at the NMJ. We propose that MuSK plays two distinct roles at the NMJ: as an agrin-LRP4 receptor necessary for establishing and maintaining cholinergic signaling, and as a BMP co-receptor required for maintaining proper Nav1.4 density, nerve-evoked muscle excitability and force production. The MuSK-BMP pathway thus emerges as a target for modulating excitability and functional innervation, which are defective in conditions such as congenital myasthenic syndromes and aging.
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Affiliation(s)
- L. A. Fish
- Neuroscience Graduate Program, Brown University, Providence, RI 02912
- Carney Institute for Brain Science, Brown University, Providence, RI 02912
| | - M. D. Ewing
- Department of Neuroscience, Brown University, Providence, RI 02912
| | - D. Jaime
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912
| | - K. A. Rich
- Neuroscience Graduate Program, Ohio State University, Columbus, OH 43210
| | - C. Xi
- Biotechnology Graduate Program, Brown University, Brown University, Providence, RI 02912
| | - X. Wang
- Department of Neuroscience Cell Biology and Physiology, Wright State University, Dayton, OH 45435
| | - R. E. Feder
- Department of Neuroscience, Brown University, Providence, RI 02912
| | - K. A. Wharton
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912
| | - M. M. Rich
- Department of Neuroscience Cell Biology and Physiology, Wright State University, Dayton, OH 45435
| | - W. D. Arnold
- NextGen Precision Health Institute, University of Missouri, Columbia, MO 62511
| | - J. R. Fallon
- Carney Institute for Brain Science, Brown University, Providence, RI 02912
- Department of Neuroscience, Brown University, Providence, RI 02912
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2
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Kwan HLR, Chan ZCK, Bi X, Kutkowska J, Prószyński TJ, Chan CB, Lee CW. Nerve-independent formation of membrane infoldings at topologically complex postsynaptic apparatus by caveolin-3. SCIENCE ADVANCES 2023; 9:eadg0183. [PMID: 37327338 PMCID: PMC10275590 DOI: 10.1126/sciadv.adg0183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Accepted: 05/12/2023] [Indexed: 06/18/2023]
Abstract
Junctional folds are unique membrane specializations developed progressively during the postnatal maturation of vertebrate neuromuscular junctions (NMJs), but how they are formed remains elusive. Previous studies suggested that topologically complex acetylcholine receptor (AChR) clusters in muscle cultures undergo a series of transformations, resembling the postnatal maturation of NMJs in vivo. We first demonstrated the presence of membrane infoldings at AChR clusters in cultured muscles. Live-cell super-resolution imaging further revealed that AChRs are gradually redistributed to the crest regions and spatially segregated from acetylcholinesterase along the elongating membrane infoldings over time. Mechanistically, lipid raft disruption or caveolin-3 knockdown not only inhibits membrane infolding formation at aneural AChR clusters and delays agrin-induced AChR clustering in vitro but also affects junctional fold development at NMJs in vivo. Collectively, this study demonstrated the progressive development of membrane infoldings via nerve-independent, caveolin-3-dependent mechanisms and identified their roles in AChR trafficking and redistribution during the structural maturation of NMJs.
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Affiliation(s)
- Hui-Lam Rachel Kwan
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Zora Chui-Kuen Chan
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Xinyi Bi
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
- School of Biological Sciences, Faculty of Science, The University of Hong Kong, Hong Kong, China
| | - Justyna Kutkowska
- Łukasiewicz Research Network – PORT Polish Center for Technology Development, Wrocław, Poland
| | - Tomasz J. Prószyński
- Łukasiewicz Research Network – PORT Polish Center for Technology Development, Wrocław, Poland
| | - Chi Bun Chan
- School of Biological Sciences, Faculty of Science, The University of Hong Kong, Hong Kong, China
| | - Chi Wai Lee
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
- Golden Meditech Centre for NeuroRegeneration Sciences, Hong Kong Baptist University, Hong Kong, China
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3
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Massih B, Veh A, Schenke M, Mungwa S, Seeger B, Selvaraj BT, Chandran S, Reinhardt P, Sterneckert J, Hermann A, Sendtner M, Lüningschrör P. A 3D cell culture system for bioengineering human neuromuscular junctions to model ALS. Front Cell Dev Biol 2023; 11:996952. [PMID: 36866276 PMCID: PMC9973451 DOI: 10.3389/fcell.2023.996952] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 01/16/2023] [Indexed: 02/16/2023] Open
Abstract
The signals that coordinate and control movement in vertebrates are transmitted from motoneurons (MNs) to their target muscle cells at neuromuscular junctions (NMJs). Human NMJs display unique structural and physiological features, which make them vulnerable to pathological processes. NMJs are an early target in the pathology of motoneuron diseases (MND). Synaptic dysfunction and synapse elimination precede MN loss suggesting that the NMJ is the starting point of the pathophysiological cascade leading to MN death. Therefore, the study of human MNs in health and disease requires cell culture systems that enable the connection to their target muscle cells for NMJ formation. Here, we present a human neuromuscular co-culture system consisting of induced pluripotent stem cell (iPSC)-derived MNs and 3D skeletal muscle tissue derived from myoblasts. We used self-microfabricated silicone dishes combined with Velcro hooks to support the formation of 3D muscle tissue in a defined extracellular matrix, which enhances NMJ function and maturity. Using a combination of immunohistochemistry, calcium imaging, and pharmacological stimulations, we characterized and confirmed the function of the 3D muscle tissue and the 3D neuromuscular co-cultures. Finally, we applied this system as an in vitro model to study the pathophysiology of Amyotrophic Lateral Sclerosis (ALS) and found a decrease in neuromuscular coupling and muscle contraction in co-cultures with MNs harboring ALS-linked SOD1 mutation. In summary, the human 3D neuromuscular cell culture system presented here recapitulates aspects of human physiology in a controlled in vitro setting and is suitable for modeling of MND.
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Affiliation(s)
- Bita Massih
- Institute of Clinical Neurobiology, University Hospital Würzburg, Würzburg, Germany
| | - Alexander Veh
- Institute of Clinical Neurobiology, University Hospital Würzburg, Würzburg, Germany
| | - Maren Schenke
- Institute for Food Quality and Safety, Research Group Food Toxicology and Alternative/Complementary Methods to Animal Experiments, University of Veterinary Medicine Hannover, Hannover, Germany
| | - Simon Mungwa
- Institute of Clinical Neurobiology, University Hospital Würzburg, Würzburg, Germany
| | - Bettina Seeger
- Institute for Food Quality and Safety, Research Group Food Toxicology and Alternative/Complementary Methods to Animal Experiments, University of Veterinary Medicine Hannover, Hannover, Germany
| | - Bhuvaneish T. Selvaraj
- Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
- UK Dementia Research Institute at University of Edinburgh, University of Edinburgh, Edinburgh, United Kingdom
- Anne Rowling Regenerative Neurology Clinic, University of Edinburgh, Edinburgh, United Kingdom
| | - Siddharthan Chandran
- Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
- UK Dementia Research Institute at University of Edinburgh, University of Edinburgh, Edinburgh, United Kingdom
- Anne Rowling Regenerative Neurology Clinic, University of Edinburgh, Edinburgh, United Kingdom
| | - Peter Reinhardt
- Center for Regenerative Therapies Dresden, Technische Universität Dresden, Dresden, Germany
| | - Jared Sterneckert
- Center for Regenerative Therapies Dresden, Technische Universität Dresden, Dresden, Germany
- Medical Faculty Carl Gustav Carus of TU Dresden, Dresden, Germany
| | - Andreas Hermann
- Translational Neurodegeneration Section “Albrecht-Kossel”, Department of Neurology, University Medical Center Rostock, Rostock, Germany
- Center for Transdisciplinary Neurosciences Rostock, University Medical Center Rostock, Rostock, Germany
- Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE) Rostock/Greifswald, Rostock, Germany
| | - Michael Sendtner
- Institute of Clinical Neurobiology, University Hospital Würzburg, Würzburg, Germany
| | - Patrick Lüningschrör
- Institute of Clinical Neurobiology, University Hospital Würzburg, Würzburg, Germany
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4
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Zou S, Pan BX. Post-synaptic specialization of the neuromuscular junction: junctional folds formation, function, and disorders. Cell Biosci 2022; 12:93. [PMID: 35718785 PMCID: PMC9208267 DOI: 10.1186/s13578-022-00829-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 06/05/2022] [Indexed: 11/14/2022] Open
Abstract
Post-synaptic specialization is critical to the neurotransmitter release and action potential conduction. The neuromuscular junctions (NMJs) are the synapses between the motor neurons and muscle cells and have a more specialized post-synaptic membrane than synapses in the central nervous system (CNS). The sarcolemma within NMJ folded to form some invagination portions called junctional folds (JFs), and they have important roles in maintaining the post-synaptic membrane structure. The NMJ formation and the acetylcholine receptor (AChR) clustering signal pathway have been extensively studied and reviewed. Although it has been suggested that JFs are related to maintaining the safety factor of neurotransmitter release, the formation mechanism and function of JFs are still unclear. This review will focus on the JFs about evolution, formation, function, and disorders. Anticipate understanding of where they are coming from and where we will study in the future.
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Ding Q, Kesavan K, Lee KM, Wimberger E, Robertson T, Gill M, Power D, Chang J, Fard AT, Mar JC, Henderson RD, Heggie S, McCombe PA, Jeffree RL, Colditz MJ, Hilliard MA, Ng DCH, Steyn FJ, Phillips WD, Wolvetang EJ, Ngo ST, Noakes PG. Impaired signaling for neuromuscular synaptic maintenance is a feature of Motor Neuron Disease. Acta Neuropathol Commun 2022; 10:61. [PMID: 35468848 PMCID: PMC9040261 DOI: 10.1186/s40478-022-01360-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 04/06/2022] [Indexed: 11/17/2022] Open
Abstract
A central event in the pathogenesis of motor neuron disease (MND) is the loss of neuromuscular junctions (NMJs), yet the mechanisms that lead to this event in MND remain to be fully elucidated. Maintenance of the NMJ relies upon neural agrin (n-agrin) which, when released from the nerve terminal, activates the postsynaptic Muscle Specific Kinase (MuSK) signaling complex to stabilize clusters of acetylcholine receptors. Here, we report that muscle from MND patients has an increased proportion of slow fibers and muscle fibers with smaller diameter. Muscle cells cultured from MND biopsies failed to form large clusters of acetylcholine receptors in response to either non-MND human motor axons or n-agrin. Furthermore, levels of expression of MuSK, and MuSK-complex components: LRP4, Caveolin-3, and Dok7 differed between muscle cells cultured from MND patients compared to those from non-MND controls. To our knowledge, this is the first time a fault in the n-agrin-LRP4-MuSK signaling pathway has been identified in muscle from MND patients. Our results highlight the n-agrin-LRP4-MuSK signaling pathway as a potential therapeutic target to prolong muscle function in MND.
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6
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Deschenes MR, Flannery R, Hawbaker A, Patek L, Mifsud M. Adaptive Remodeling of the Neuromuscular Junction with Aging. Cells 2022; 11:cells11071150. [PMID: 35406714 PMCID: PMC8997609 DOI: 10.3390/cells11071150] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 03/24/2022] [Accepted: 03/24/2022] [Indexed: 02/06/2023] Open
Abstract
Aging is associated with gradual degeneration, in mass and function, of the neuromuscular system. This process, referred to as “sarcopenia”, is considered a disease by itself, and it has been linked to a number of other serious maladies such as type II diabetes, osteoporosis, arthritis, cardiovascular disease, and even dementia. While the molecular causes of sarcopenia remain to be fully elucidated, recent findings have implicated the neuromuscular junction (NMJ) as being an important locus in the development and progression of that malady. This synapse, which connects motor neurons to the muscle fibers that they innervate, has been found to degenerate with age, contributing both to senescent-related declines in muscle mass and function. The NMJ also shows plasticity in response to a number of neuromuscular diseases such as amyotrophic lateral sclerosis (ALS) and Lambert-Eaton myasthenic syndrome (LEMS). Here, the structural and functional degradation of the NMJ associated with aging and disease is described, along with the measures that might be taken to effectively mitigate, if not fully prevent, that degeneration.
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7
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Zhang C, Joshi A, Liu Y, Sert O, Haddix SG, Teliska LH, Rasband A, Rodney GG, Rasband MN. Ankyrin-dependent Na + channel clustering prevents neuromuscular synapse fatigue. Curr Biol 2021; 31:3810-3819.e4. [PMID: 34289389 DOI: 10.1016/j.cub.2021.06.052] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 06/09/2021] [Accepted: 06/17/2021] [Indexed: 01/18/2023]
Abstract
Skeletal muscle contraction depends on activation of clustered acetylcholine receptors (AchRs) and muscle-specific Na+ channels (Nav1.4). Some Nav1.4 channels are highly enriched at the neuromuscular junction (NMJ), and their clustering is thought to be essential for effective muscle excitation. However, this has not been experimentally tested, and how NMJ Na+ channels are clustered is unknown. Here, using muscle-specific ankyrinR, ankyrinB, and ankyrinG single, double, and triple-conditional knockout mice, we show that Nav1.4 channels fail to cluster only after deletion of all three ankyrins. Remarkably, ankyrin-deficient muscles have normal NMJ morphology, AchR clustering, sarcolemmal levels of Nav1.4, and muscle force, and they show no indication of degeneration. However, mice lacking clustered NMJ Na+ channels have significantly reduced levels of motor activity and their NMJs rapidly fatigue after repeated nerve-dependent stimulation. Thus, the triple redundancy of ankyrins facilitates NMJ Na+ channel clustering to prevent neuromuscular synapse fatigue.
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Affiliation(s)
- Chuansheng Zhang
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Abhijeet Joshi
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Yanhong Liu
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Ozlem Sert
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Seth G Haddix
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Lindsay H Teliska
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Anne Rasband
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - George G Rodney
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Matthew N Rasband
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA.
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8
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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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Zelada D, Bermedo-García F, Collao N, Henríquez JP. Motor function recovery: deciphering a regenerative niche at the neuromuscular synapse. Biol Rev Camb Philos Soc 2020; 96:752-766. [PMID: 33336525 PMCID: PMC7986695 DOI: 10.1111/brv.12675] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 11/20/2020] [Accepted: 11/25/2020] [Indexed: 12/13/2022]
Abstract
The coordinated movement of many organisms relies on efficient nerve–muscle communication at the neuromuscular junction (NMJ), a peripheral synapse composed of a presynaptic motor axon terminal, a postsynaptic muscle specialization, and non‐myelinating terminal Schwann cells. NMJ dysfunctions are caused by traumatic spinal cord or peripheral nerve injuries as well as by severe motor pathologies. Compared to the central nervous system, the peripheral nervous system displays remarkable regenerating abilities; however, this capacity is limited by the denervation time frame and depends on the establishment of permissive regenerative niches. At the injury site, detailed information is available regarding the cells, molecules, and mechanisms involved in nerve regeneration and repair. However, a regenerative niche at the final functional step of peripheral motor innervation, i.e. at the mature neuromuscular synapse, has not been deciphered. In this review, we integrate classic and recent evidence describing the cells and molecules that could orchestrate a dynamic ecosystem to accomplish successful NMJ regeneration. We propose that such a regenerative niche must ensure at least two fundamental steps for successful NMJ regeneration: the proper arrival of incoming regenerating axons to denervated postsynaptic muscle domains, and the resilience of those postsynaptic domains, in morphological and functional terms. We here describe and combine the main cellular and molecular responses involved in each of these steps as potential targets to help successful NMJ regeneration.
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Affiliation(s)
- Diego Zelada
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
| | - Francisca Bermedo-García
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
| | - Nicolás Collao
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
| | - Juan P Henríquez
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
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10
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Boehm I, Alhindi A, Leite AS, Logie C, Gibbs A, Murray O, Farrukh R, Pirie R, Proudfoot C, Clutton R, Wishart TM, Jones RA, Gillingwater TH. Comparative anatomy of the mammalian neuromuscular junction. J Anat 2020; 237:827-836. [PMID: 32573802 PMCID: PMC7542190 DOI: 10.1111/joa.13260] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 05/28/2020] [Accepted: 05/28/2020] [Indexed: 12/11/2022] Open
Abstract
The neuromuscular junction (NMJ)—a synapse formed between lower motor neuron and skeletal muscle fibre—represents a major focus of both basic neuroscience research and clinical neuroscience research. Although the NMJ is known to play an important role in many neurodegenerative conditions affecting humans, the vast majority of anatomical and physiological data concerning the NMJ come from lower mammalian (e.g. rodent) animal models. However, recent findings have demonstrated major differences between the cellular anatomy and molecular anatomy of human and rodent NMJs. Therefore, we undertook a comparative morphometric analysis of the NMJ across several larger mammalian species in order to generate baseline inter‐species anatomical reference data for the NMJ and to identify animal models that better represent the morphology of the human NMJ in vivo. Using a standardized morphometric platform (‘NMJ‐morph’), we analysed 5,385 individual NMJs from lower/pelvic limb muscles (EDL, soleus and peronei) of 6 mammalian species (mouse, cat, dog, sheep, pig and human). There was marked heterogeneity of NMJ morphology both within and between species, with no overall relationship found between NMJ morphology and muscle fibre diameter or body size. Mice had the largest NMJs on the smallest muscle fibres; cats had the smallest NMJs on the largest muscle fibres. Of all the species examined, the sheep NMJ had the most closely matched morphology to that found in humans. Taken together, we present a series of comprehensive baseline morphometric data for the mammalian NMJ and suggest that ovine models are likely to best represent the human NMJ in health and disease.
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Affiliation(s)
- Ines Boehm
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK
| | - Abrar Alhindi
- School of Medicine, UNESP-São Paulo State University, Botucatu, Sao Paulo, Brazil.,Faculty of Medicine, Department of Anatomy, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Ana S Leite
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK.,School of Medicine, UNESP-São Paulo State University, Botucatu, Sao Paulo, Brazil
| | - Chandra Logie
- The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, UK
| | - Alyssa Gibbs
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK
| | - Olivia Murray
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK
| | - Rizwan Farrukh
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK
| | - Robert Pirie
- The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, UK
| | | | - Richard Clutton
- The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, UK
| | - Thomas M Wishart
- The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, UK
| | - Ross A Jones
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK
| | - Thomas H Gillingwater
- Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, UK.,Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK
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11
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Pęziński M, Daszczuk P, Pradhan BS, Lochmüller H, Prószyński TJ. An improved method for culturing myotubes on laminins for the robust clustering of postsynaptic machinery. Sci Rep 2020; 10:4524. [PMID: 32161296 PMCID: PMC7066178 DOI: 10.1038/s41598-020-61347-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 02/20/2020] [Indexed: 01/03/2023] Open
Abstract
Motor neurons form specialized synapses with skeletal muscle fibers, called neuromuscular junctions (NMJs). Cultured myotubes are used as a simplified in vitro system to study the postsynaptic specialization of muscles. The stimulation of myotubes with the glycoprotein agrin or laminin-111 induces the clustering of postsynaptic machinery that contains acetylcholine receptors (AChRs). When myotubes are grown on laminin-coated surfaces, AChR clusters undergo developmental remodeling to form topologically complex structures that resemble mature NMJs. Needing further exploration are the molecular processes that govern AChR cluster assembly and its developmental maturation. Here, we describe an improved protocol for culturing muscle cells to promote the formation of complex AChR clusters. We screened various laminin isoforms and showed that laminin-221 was the most potent for inducing AChR clusters, whereas laminin-121, laminin-211, and laminin-221 afforded the highest percentages of topologically complex assemblies. Human primary myotubes that were formed by myoblasts obtained from patient biopsies also assembled AChR clusters that underwent remodeling in vitro. Collectively, these results demonstrate an advancement of culturing myotubes that can facilitate high-throughput screening for potential therapeutic targets for neuromuscular disorders.
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Affiliation(s)
- Marcin Pęziński
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Patrycja Daszczuk
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Bhola Shankar Pradhan
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.,Łukasiewicz Research Network - PORT Polish Center for Technology Development, Wrocław, Poland
| | - Hanns Lochmüller
- Department of Neuropediatrics and Muscle Disorders, Faculty of Medicine, Medical Centre, University of Freiburg, Freiburg, Germany.,Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada.,Division of Neurology, Department of Medicine, The Ottawa Hospital, Ottawa, Canada
| | - Tomasz J Prószyński
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland. .,Łukasiewicz Research Network - PORT Polish Center for Technology Development, Wrocław, Poland.
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12
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Ge D, Noakes PG, Lavidis NA. What are Neurotransmitter Release Sites and Do They Interact? Neuroscience 2020; 425:157-168. [DOI: 10.1016/j.neuroscience.2019.11.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2019] [Revised: 11/10/2019] [Accepted: 11/11/2019] [Indexed: 12/22/2022]
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13
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Pérez V, Bermedo-Garcia F, Zelada D, Court FA, Pérez MÁ, Fuenzalida M, Ábrigo J, Cabello-Verrugio C, Moya-Alvarado G, Tapia JC, Valenzuela V, Hetz C, Bronfman FC, Henríquez JP. The p75 NTR neurotrophin receptor is required to organize the mature neuromuscular synapse by regulating synaptic vesicle availability. Acta Neuropathol Commun 2019; 7:147. [PMID: 31514753 PMCID: PMC6739937 DOI: 10.1186/s40478-019-0802-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 09/01/2019] [Indexed: 02/07/2023] Open
Abstract
The coordinated movement of organisms relies on efficient nerve-muscle communication at the neuromuscular junction. After peripheral nerve injury or neurodegeneration, motor neurons and Schwann cells increase the expression of the p75NTR pan-neurotrophin receptor. Even though p75NTR targeting has emerged as a promising therapeutic strategy to delay peripheral neuronal damage progression, the effects of long-term p75NTR inhibition at the mature neuromuscular junction have not been elucidated. We performed quantitative neuroanathomical analyses of the neuromuscular junction in p75NTR null mice by laser confocal and electron microscopy, which were complemented with electromyography, locomotor tests, and pharmacological intervention studies. Mature neuromuscular synapses of p75NTR null mice show impaired postsynaptic organization and ultrastructural complexity, which correlate with altered synaptic function at the levels of nerve activity-induced muscle responses, muscle fiber structure, force production, and locomotor performance. Our results on primary myotubes and denervated muscles indicate that muscle-derived p75NTR does not play a major role on postsynaptic organization. In turn, motor axon terminals of p75NTR null mice display a strong reduction in the number of synaptic vesicles and active zones. According to the observed pre and postsynaptic defects, pharmacological acetylcholinesterase inhibition rescued nerve-dependent muscle response and force production in p75NTR null mice. Our findings revealing that p75NTR is required to organize mature neuromuscular junctions contribute to a comprehensive view of the possible effects caused by therapeutic attempts to target p75NTR.
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Affiliation(s)
- Viviana Pérez
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Center for Advanced Microscopy (CMA BioBio), Universidad de Concepción, Concepción, Chile
| | - Francisca Bermedo-Garcia
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Center for Advanced Microscopy (CMA BioBio), Universidad de Concepción, Concepción, Chile
| | - Diego Zelada
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Center for Advanced Microscopy (CMA BioBio), Universidad de Concepción, Concepción, Chile
| | - Felipe A Court
- Center for Integrative Biology, Faculty of Sciences, Universidad Mayor; FONDAP Center for Geroscience, Brain Health and Metabolism, Santiago, Chile
| | - Miguel Ángel Pérez
- Laboratory of Neural Plasticity, Center for Neurobiology and Integrative Physiology, Faculty of Sciences, Institute of Physiology, Universidad de Valparaíso, Valparaíso, Chile
- Present Address: Health Sciences School, Universidad de Viña del Mar, Viña del Mar, Chile
| | - Marco Fuenzalida
- Laboratory of Neural Plasticity, Center for Neurobiology and Integrative Physiology, Faculty of Sciences, Institute of Physiology, Universidad de Valparaíso, Valparaíso, Chile
| | - Johanna Ábrigo
- Laboratory of Muscle Pathologies, Fragility and Aging, Department of Biological Sciences, Faculty of Life Sciences, Millennium Institute on Immunology and Immunotherapy, Universidad Andrés Bello, Santiago, Chile
| | - Claudio Cabello-Verrugio
- Laboratory of Muscle Pathologies, Fragility and Aging, Department of Biological Sciences, Faculty of Life Sciences, Millennium Institute on Immunology and Immunotherapy, Universidad Andrés Bello, Santiago, Chile
| | - Guillermo Moya-Alvarado
- Department of Physiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Juan Carlos Tapia
- Department of Biomedical Sciences, Faculty of Health Sciences, Universidad de Talca, Talca, Chile
| | - Vicente Valenzuela
- Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago, Chile
- Center for Geroscience, Brain Health and Metabolism, Santiago, Chile
- Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, University of Chile, Santiago, Chile
| | - Claudio Hetz
- Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago, Chile
- Center for Geroscience, Brain Health and Metabolism, Santiago, Chile
- Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, University of Chile, Santiago, Chile
- Buck Institute for Research on Aging, Novato, CA, 94945, USA
| | - Francisca C Bronfman
- Department of Physiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile.
- Center for Aging and Regeneration (CARE), Institute of Biomedical Sciences (ICB), Faculty of Medicine and Faculty of Life Sciences, Universidad Andrés Bello, Santiago, Chile.
| | - Juan Pablo Henríquez
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Center for Advanced Microscopy (CMA BioBio), Universidad de Concepción, Concepción, Chile.
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14
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Abstract
This article discusses antibodies associated with immune-mediated myasthenia gravis and the pathologic action of these antibodies at the neuromuscular junctions of skeletal muscle. To explain how these antibodies act, we consider the physiology of neuromuscular transmission with emphasis on 4 features: the structure of the neuromuscular junction; the roles of postsynaptic acetylcholine receptors and voltage-gated Na+ channels and in converting the chemical signal from the nerve terminal into a propagated action potential on the muscle fiber that triggers muscle contraction; the safety factor for neuromuscular transmission; and how the safety factor is reduced in different forms of autoimmune myasthenia gravis.
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Affiliation(s)
- Robert L Ruff
- Department of Neurology, Case Western University School of Medicine, The Metro Health System, 2500 Metro Health Drive, Cleveland, OH 44109, USA; Department of Neurosciences, Case Western Reserve University, Cleveland, OH, USA
| | - Robert P Lisak
- Department of Neurology, Wayne State University School of Medicine, 8D University Health Center, 4201 St Antoine, Detroit, MI 48201, USA; Department of Biochemistry, Microbiology and Immunology, Wayne State University, Detroit, MI, USA.
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15
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McMacken GM, Spendiff S, Whittaker RG, O’Connor E, Howarth RM, Boczonadi V, Horvath R, Slater CR, Lochmüller H. Salbutamol modifies the neuromuscular junction in a mouse model of ColQ myasthenic syndrome. Hum Mol Genet 2019; 28:2339-2351. [PMID: 31220253 PMCID: PMC6606850 DOI: 10.1093/hmg/ddz059] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2019] [Revised: 03/14/2019] [Accepted: 03/15/2019] [Indexed: 12/23/2022] Open
Abstract
The β-adrenergic agonists salbutamol and ephedrine have proven to be effective as therapies for human disorders of the neuromuscular junction, in particular many subsets of congenital myasthenic syndromes. However, the mechanisms underlying this clinical benefit are unknown and improved understanding of the effect of adrenergic signalling on the neuromuscular junction is essential to facilitate the development of more targeted therapies. Here, we investigated the effect of salbutamol treatment on the neuromuscular junction in the ColQ deficient mouse, a model of end-plate acetylcholinesterase deficiency. ColQ-/- mice received 7 weeks of daily salbutamol injection, and the effect on muscle strength and neuromuscular junction morphology was analysed. We show that salbutamol leads to a gradual improvement in muscle strength in ColQ-/- mice. In addition, the neuromuscular junctions of salbutamol treated mice showed significant improvements in several postsynaptic morphological defects, including increased synaptic area, acetylcholine receptor area and density, and extent of postjunctional folds. These changes occurred without alterations in skeletal muscle fibre size or type. These findings suggest that β-adrenergic agonists lead to functional benefit in the ColQ-/- mouse and to long-term structural changes at the neuromuscular junction. These effects are primarily at the postsynaptic membrane and may lead to enhanced neuromuscular transmission.
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Affiliation(s)
- Grace M McMacken
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle Upon Tyne, UK
| | - Sally Spendiff
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle Upon Tyne, UK
- Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada
| | - Roger G Whittaker
- Institute of Neuroscience, Newcastle University, Newcastle Upon Tyne, UK
| | - Emily O’Connor
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle Upon Tyne, UK
| | - Rachel M Howarth
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle Upon Tyne, UK
| | - Veronika Boczonadi
- Institute of Neuroscience, Newcastle University, Newcastle Upon Tyne, UK
| | - Rita Horvath
- Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK
| | - Clarke R Slater
- Institute of Neuroscience, Newcastle University, Newcastle Upon Tyne, UK
| | - Hanns Lochmüller
- Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada
- Department of Neuropediatrics and Muscle Disorders, Medical Center – University of Freiburg, Faculty of Medicine, Freiburg, Germany
- Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia, Spain
- Division of Neurology, Department of Medicine, The Ottawa Hospital, Ottawa, Canada
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16
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Rodrigues AZC, Wang ZM, Messi ML, Delbono O. Sympathomimetics regulate neuromuscular junction transmission through TRPV1, P/Q- and N-type Ca 2+ channels. Mol Cell Neurosci 2019; 95:59-70. [PMID: 30763691 PMCID: PMC6394868 DOI: 10.1016/j.mcn.2019.01.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Revised: 01/24/2019] [Accepted: 01/26/2019] [Indexed: 01/10/2023] Open
Abstract
Increasing evidence indicates that, first, the sympathetic nervous system interacts extensively with both vasculature and skeletal muscle fibers near neuromuscular junctions (NMJs) and, second, its neurotransmitter, noradrenaline, influences myofiber molecular composition and function and motor innervation. Since sympathomimetic agents have been reported to improve NMJ transmission, we examined whether two in clinical use, salbutamol and clenbuterol, affect the motor axon terminal via extracellular Ca2+ and molecular targets, such as TRPV1 and P/Q- and N-type voltage-activated Ca2+ channels. Electrophysiological recordings in ex-vivo preparations of peroneal nerves and lumbricalis muscles from young adult mice focused on spontaneous miniature end-plate potentials and singly and repetitively evoked end-plate potentials. Adding one dose of salbutamol or clenbuterol to the nerve/muscle preparation or repeatedly administering salbutamol to a mouse for 4 weeks increased spontaneous and evoked synaptic vesicle release but induced a steep decline in EPP amplitude in response to repetitive nerve stimulation. These effects were mediated primarily by ω-agatoxin IVA-sensitive P/Q-type and secondarily by ω-conotoxin GVIA-sensitive N-type Ca2+ channels. Presynaptic arvanil-sensitive TRPV1 channels seem to regulate Ca2+ at the motor neuron terminal at rest, while putative presynaptic β-adrenergic receptors may mediate sympathomimetic and catecholamine effects on presynaptic Ca2+ channels during NMJ activation.
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Affiliation(s)
- Anna Zaia Carolina Rodrigues
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States of America; Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC, United States of America
| | - Zhong-Min Wang
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States of America
| | - María Laura Messi
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States of America
| | - Osvaldo Delbono
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States of America; Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC, United States of America.
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17
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Causes and consequences of age-related changes at the neuromuscular junction. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.04.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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18
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Petralia RS, Wang YX, Mattson MP, Yao PJ. Invaginating Structures in Mammalian Synapses. Front Synaptic Neurosci 2018; 10:4. [PMID: 29674962 PMCID: PMC5895750 DOI: 10.3389/fnsyn.2018.00004] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 03/19/2018] [Indexed: 12/26/2022] Open
Abstract
Invaginating structures at chemical synapses in the mammalian nervous system exist in presynaptic axon terminals, postsynaptic spines or dendrites, and glial processes. These invaginating structures can be divided into three categories. The first category includes slender protrusions invaginating into axonal terminals, postsynaptic spines, or glial processes. Best known examples of this category are spinules extending from postsynaptic spines into presynaptic terminals in forebrain synapses. Another example of this category are protrusions from inhibitory presynaptic terminals invaginating into postsynaptic neuronal somas. Regardless of the direction and location, the invaginating structures of the first category do not have synaptic active zones within the invagination. The second category includes postsynaptic spines invaginating into presynaptic terminals, whereas the third category includes presynaptic terminals invaginating into postsynaptic spines or dendrites. Unlike the first category, the second and third categories have active zones within the invagination. An example of the second category are mossy terminal synapses of the hippocampal CA3 region, in which enlarged spine-like structures invaginate partly or entirely into mossy terminals. An example of the third category is the neuromuscular junction (NMJ) where substantial invaginations of the presynaptic terminals invaginate into the muscle fibers. In the retina, rod and cone synapses have invaginating processes from horizontal and bipolar cells. Because horizontal cells act both as post and presynaptic structures, their invaginating processes represent both the second and third category. These invaginating structures likely play broad yet specialized roles in modulating neuronal cell signaling.
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Affiliation(s)
| | - Ya-Xian Wang
- Advanced Imaging Core, NIDCD/NIH, Bethesda, MD, United States
| | - Mark P Mattson
- Laboratory of Neurosciences, National Institute on Aging, Intramural Research Program, Baltimore, MD, United States
| | - Pamela J Yao
- Laboratory of Neurosciences, National Institute on Aging, Intramural Research Program, Baltimore, MD, United States
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19
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Kaminski HJ, Alnosair E, Algahtani RM. Clinical trials for myasthenia gravis: a historical perspective. Ann N Y Acad Sci 2018; 1413:5-10. [PMID: 29377153 DOI: 10.1111/nyas.13545] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2017] [Revised: 10/09/2017] [Accepted: 10/10/2017] [Indexed: 11/30/2022]
Abstract
Symposia dedicated to myasthenia gravis and related disorders date back to 1947 and serve as markers of the progress for the field. We provide a brief historical review of therapy development through the lens of the publications that arose from the close to quinquennial meetings that have been supported nearly since their inception by the Myasthenia Gravis Foundation of America and the New York Academy of Sciences. One can appreciate great advances, false starts, and dead ends that are found in all fields of medicine. We tally up the score card for MG and find points scored, but the win is not yet close.
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Affiliation(s)
- Henry J Kaminski
- Department of Neurology, GW-Medical Faculty Associates, George Washington University, Washington, DC
| | - Eman Alnosair
- Department of Neurology, GW-Medical Faculty Associates, George Washington University, Washington, DC
| | - Rami M Algahtani
- Department of Neurology, GW-Medical Faculty Associates, George Washington University, Washington, DC
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20
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Plomp JJ, Huijbers MGM, Verschuuren JJGM. Neuromuscular synapse electrophysiology in myasthenia gravis animal models. Ann N Y Acad Sci 2017; 1412:146-153. [PMID: 29068559 DOI: 10.1111/nyas.13507] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 08/30/2017] [Accepted: 09/06/2017] [Indexed: 12/12/2022]
Abstract
The neuromuscular junction (NMJ) forms the synaptic connection between a motor neuron and a skeletal muscle fiber. In order to achieve a sustained muscle contraction, this synapse has to reliably transmit motor neuronal action potentials onto the muscle fiber. To guarantee successful transmission even during intense activation of the NMJ, a safety factor of neuromuscular transmission exists. In the neuromuscular disorder myasthenia gravis (MG), autoantibodies are directed against acetylcholine receptors or, in the rarer variants, against other postsynaptic NMJ proteins. This causes loss of functional acetylcholine receptors, which compromises the safety factor of neuromuscular transmission, leading to the typical fatigable muscle weakness of MG. With intracellular microelectrode measurement of (miniature) endplate potentials at NMJs in ex vivo nerve-muscle preparations from MG animal models, these functional synaptic defects have been determined in much detail. Here, we describe the electrophysiological events at the normal NMJ and the pathoelectrophysiology at NMJs of animal models for MG.
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Affiliation(s)
- Jaap J Plomp
- Department of Neurology, Leiden University Medical Centre, Leiden, the Netherlands
| | - Maartje G M Huijbers
- Department of Neurology, Leiden University Medical Centre, Leiden, the Netherlands.,Department of Human Genetics, Leiden University Medical Centre, Leiden, the Netherlands
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21
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Petralia RS, Wang YX, Mattson MP, Yao PJ. Invaginating Presynaptic Terminals in Neuromuscular Junctions, Photoreceptor Terminals, and Other Synapses of Animals. Neuromolecular Med 2017; 19:193-240. [PMID: 28612182 PMCID: PMC6518423 DOI: 10.1007/s12017-017-8445-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 06/01/2017] [Indexed: 10/19/2022]
Abstract
Typically, presynaptic terminals form a synapse directly on the surface of postsynaptic processes such as dendrite shafts and spines. However, some presynaptic terminals invaginate-entirely or partially-into postsynaptic processes. We survey these invaginating presynaptic terminals in all animals and describe several examples from the central nervous system, including giant fiber systems in invertebrates, and cup-shaped spines, electroreceptor synapses, and some specialized auditory and vestibular nerve terminals in vertebrates. We then examine mechanoreceptors and photoreceptors, concentrating on the complex of pre- and postsynaptic processes found in basal invaginations of the cell. We discuss in detail the role of vertebrate invaginating horizontal cell processes in both chemical and electrical feedback mechanisms. We also discuss the common presence of indenting or invaginating terminals in neuromuscular junctions on muscles of most kinds of animals, and especially discuss those of Drosophila and vertebrates. Finally, we consider broad questions about the advantages of possessing invaginating presynaptic terminals and describe some effects of aging and disease, especially on neuromuscular junctions. We suggest that the invagination is a mechanism that can enhance both chemical and electrical interactions at the synapse.
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Affiliation(s)
- Ronald S Petralia
- Advanced Imaging Core, NIDCD/NIH, 35A Center Drive, Room 1E614, Bethesda, MD, 20892-3729, USA.
| | - Ya-Xian Wang
- Advanced Imaging Core, NIDCD/NIH, 35A Center Drive, Room 1E614, Bethesda, MD, 20892-3729, USA
| | - Mark P Mattson
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD, 21224, USA
| | - Pamela J Yao
- Laboratory of Neurosciences, NIA/NIH, Baltimore, MD, 21224, USA
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22
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Super-Resolution Microscopy Reveals a Nanoscale Organization of Acetylcholine Receptors for Trans-Synaptic Alignment at Neuromuscular Synapses. eNeuro 2017; 4:eN-NWR-0232-17. [PMID: 28798955 PMCID: PMC5550840 DOI: 10.1523/eneuro.0232-17.2017] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 07/24/2017] [Accepted: 07/25/2017] [Indexed: 11/30/2022] Open
Abstract
The neuromuscular junction (NMJ) is a chemical synapse formed between motoneurons and skeletal muscle fibers. The vertebrate NMJ uses acetylcholine (ACh) as the neurotransmitter and features numerous invaginations of the postsynaptic muscle membrane termed junctional folds. ACh receptors (AChRs) are believed to be concentrated on the crest of junctional folds but their spatial organization remains to be fully understood. In this study, we utilized super-resolution microscopy to examine the nanoscale organization of AChRs at NMJ. Using Structured Illumination Microscopy, we found that AChRs appear as stripes within the pretzel-shaped mouse NMJs, which however, do not correlate with the size of the crests of junctional folds. By comparing the localization of AChRs with several pre- and postsynaptic markers of distinct compartments of NMJs, we found that AChRs are not distributed evenly across the crest of junctional folds as previously thought. Instead, AChR stripes are more closely aligned with the openings of junctional folds as well as with the presynaptic active zone. Using Stochastic Optical Reconstruction Microscopy (STORM) for increased resolution, we found that each AChR stripe contains an AChR-poor slit at the center that is equivalent to the size of the opening of junctional folds. Together, these findings indicate that AChRs are largely localized to the edges of crests surrounding the opening of folds to align with the presynaptic active zones. Such a nanoscale organization of AChRs potentially enables trans-synaptic alignment for effective synaptic transmission of NMJs.
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23
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van der Pijl EM, van Putten M, Niks EH, Verschuuren JJGM, Aartsma-Rus A, Plomp JJ. Characterization of neuromuscular synapse function abnormalities in multiple Duchenne muscular dystrophy mouse models. Eur J Neurosci 2016; 43:1623-35. [PMID: 27037492 DOI: 10.1111/ejn.13249] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 03/22/2016] [Accepted: 03/23/2016] [Indexed: 11/30/2022]
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked myopathy caused by dystrophin deficiency. Dystrophin is present intracellularly at the sarcolemma, connecting actin to the dystrophin-associated glycoprotein complex. Interestingly, it is enriched postsynaptically at the neuromuscular junction (NMJ), but its synaptic function is largely unknown. Utrophin, a dystrophin homologue, is also concentrated at the NMJ, and upregulated in DMD. It is possible that the absence of dystrophin at NMJs in DMD causes neuromuscular transmission defects that aggravate muscle weakness. We studied NMJ function in mdx mice (lacking dystrophin) and wild type mice. In addition, mdx/utrn(+/-) and mdx/utrn(-/-) mice (lacking utrophin) were used to investigate influences of utrophin levels. The three Duchenne mouse models showed muscle weakness when comparatively tested in vivo, with mdx/utrn(-/-) mice being weakest. Ex vivo muscle contraction and electrophysiological studies showed a reduced safety factor of neuromuscular transmission in all models. NMJs had ~ 40% smaller miniature endplate potential amplitudes compared with wild type, indicating postsynaptic sensitivity loss for the neurotransmitter acetylcholine. However, nerve stimulation-evoked endplate potential amplitudes were unchanged. Consequently, quantal content (i.e. the number of acetylcholine quanta released per nerve impulse) was considerably increased. Such a homeostatic compensatory increase in neurotransmitter release is also found at NMJs in myasthenia gravis, where autoantibodies reduce acetylcholine receptors. However, high-rate nerve stimulation induced exaggerated endplate potential rundown. Study of NMJ morphology showed that fragmentation of acetylcholine receptor clusters occurred in all models, being most severe in mdx/utrn(-/-) mice. Overall, we showed mild 'myasthenia-like' neuromuscular synaptic dysfunction in several Duchenne mouse models, which possibly affects muscle weakness and degeneration.
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Affiliation(s)
- Elizabeth M van der Pijl
- Department of Neurology, Leiden University Medical Centre, Research Building S5-P, P.O. Box 9600 2300 RC, Leiden, The Netherlands
| | - Maaike van Putten
- Department of Human Genetics, Leiden University Medical Centre, Leiden, The Netherlands
| | - Erik H Niks
- Department of Neurology, Leiden University Medical Centre, Research Building S5-P, P.O. Box 9600 2300 RC, Leiden, The Netherlands
| | - Jan J G M Verschuuren
- Department of Neurology, Leiden University Medical Centre, Research Building S5-P, P.O. Box 9600 2300 RC, Leiden, The Netherlands
| | - Annemieke Aartsma-Rus
- Department of Human Genetics, Leiden University Medical Centre, Leiden, The Netherlands
| | - Jaap J Plomp
- Department of Neurology, Leiden University Medical Centre, Research Building S5-P, P.O. Box 9600 2300 RC, Leiden, The Netherlands
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24
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da Silva AJ, Trindade MAS, Santos DOC, Lima RF. Maximum-likelihood q-estimator uncovers the role of potassium at neuromuscular junctions. BIOLOGICAL CYBERNETICS 2016; 110:31-40. [PMID: 26721559 DOI: 10.1007/s00422-015-0673-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2013] [Accepted: 12/05/2015] [Indexed: 06/05/2023]
Abstract
Recently, we demonstrated the existence of nonextensive behavior in neuromuscular transmission (da Silva et al. in Phys Rev E 84:041925, 2011). In this letter, we first obtain a maximum-likelihood q-estimator to calculate the scale factor ([Formula: see text]) and the q-index of q-Gaussian distributions. Next, we use the indexes to analyze spontaneous miniature end plate potentials in electrophysiological recordings from neuromuscular junctions. These calculations were performed assuming both normal and high extracellular potassium concentrations [Formula: see text]. This protocol was used to test the validity of Tsallis statistics under electrophysiological conditions closely resembling physiological stimuli. The analysis shows that q-indexes are distinct depending on the extracellular potassium concentration. Our letter provides a general way to obtain the best estimate of parameters from a q-Gaussian distribution function. It also expands the validity of Tsallis statistics in realistic physiological stimulus conditions. In addition, we discuss the physical and physiological implications of these findings.
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Affiliation(s)
- A J da Silva
- Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, CEP 31270-901, Brazil.
- Instituto de Humanidades, Artes e Ciências, Universidade Federal do Sul da Bahia, Itabuna, Bahia, CEP 45613-204, Brazil.
| | - M A S Trindade
- Departamento de Ciências Exatas e da Terra, Universidade do Estado da Bahia, Alagoinhas, Bahia, CEP 48040-210, Brazil
| | - D O C Santos
- Instituto de Humanidades, Artes e Ciências, Universidade Federal do Sul da Bahia, Itabuna, Bahia, CEP 31270-901, Brazil
| | - R F Lima
- Departamento de Fisiologia e Farmacologia, Faculdade de Medicina, Universidade Federal do Ceará, Fortaleza, Ceará, CEP 60430-270, Brazil
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Slater CR. The functional organization of motor nerve terminals. Prog Neurobiol 2015; 134:55-103. [DOI: 10.1016/j.pneurobio.2015.09.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 08/28/2015] [Accepted: 09/05/2015] [Indexed: 12/19/2022]
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Arnold WD, Feldman DH, Ramirez S, He L, Kassar D, Quick A, Klassen TL, Lara M, Nguyen J, Kissel JT, Lossin C, Maselli RA. Defective fast inactivation recovery of Nav 1.4 in congenital myasthenic syndrome. Ann Neurol 2015; 77:840-50. [PMID: 25707578 DOI: 10.1002/ana.24389] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 02/10/2015] [Accepted: 02/11/2015] [Indexed: 11/06/2022]
Abstract
OBJECTIVE To describe the unique phenotype and genetic findings in a 57-year-old female with a rare form of congenital myasthenic syndrome (CMS) associated with longstanding muscle fatigability, and to investigate the underlying pathophysiology. METHODS We used whole-cell voltage clamping to compare the biophysical parameters of wild-type and Arg1457His-mutant Nav 1.4. RESULTS Clinical and neurophysiological evaluation revealed features consistent with CMS. Sequencing of candidate genes indicated no abnormalities. However, analysis of SCN4A, the gene encoding the skeletal muscle sodium channel Nav 1.4, revealed a homozygous mutation predicting an arginine-to-histidine substitution at position 1457 (Arg1457His), which maps to the channel's voltage sensor, specifically D4/S4. Whole-cell patch clamp studies revealed that the mutant required longer hyperpolarization to recover from fast inactivation, which produced a profound use-dependent current attenuation not seen in the wild type. The mutant channel also had a marked hyperpolarizing shift in its voltage dependence of inactivation as well as slowed inactivation kinetics. INTERPRETATION We conclude that Arg1457His compromises muscle fiber excitability. The mutant fast-inactivates with significantly less depolarization, and it recovers only after extended hyperpolarization. The resulting enhancement in its use dependence reduces channel availability, which explains the patient's muscle fatigability. Arg1457His offers molecular insight into a rare form of CMS precipitated by sodium channel inactivation defects. Given this channel's involvement in other muscle disorders such as paramyotonia congenita and hyperkalemic periodic paralysis, our study exemplifies how variations within the same gene can give rise to multiple distinct dysfunctions and phenotypes, revealing residues important in basic channel function.
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Affiliation(s)
- W David Arnold
- Department of Neurology, Ohio State University Wexner Medical Center, Columbus, OH
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Plomp JJ, Morsch M, Phillips WD, Verschuuren JJGM. Electrophysiological analysis of neuromuscular synaptic function in myasthenia gravis patients and animal models. Exp Neurol 2015; 270:41-54. [PMID: 25620417 DOI: 10.1016/j.expneurol.2015.01.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Revised: 01/07/2015] [Accepted: 01/16/2015] [Indexed: 12/21/2022]
Abstract
Study of the electrophysiological function of the neuromuscular junction (NMJ) is instrumental in the understanding of the symptoms and pathophysiology of myasthenia gravis (MG), an autoimmune disorder characterized by fluctuating and fatigable muscle weakness. Most patients have autoantibodies to the acetylcholine receptor at the NMJ. However, in recent years autoantibodies to other crucial postsynaptic membrane proteins have been found in previously 'seronegative' MG patients. Electromyographical recording of compound and single-fibre muscle action potentials provides a crucial in vivo method to determine neuromuscular transmission failure while ex vivo (miniature) endplate potential recordings can reveal the precise synaptic impairment. Here we will review these electrophysiological methods used to assess NMJ function and discuss their application and typical results found in the diagnostic and experimental study of patients and animal models of the several forms of MG.
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Affiliation(s)
- Jaap J Plomp
- Department of Neurology, Leiden University Medical Centre, Leiden, The Netherlands.
| | - Marco Morsch
- Motor Neuron Disease Research Group, Macquarie University, Sydney, Australia
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Patel V, Oh A, Voit A, Sultatos LG, Babu GJ, Wilson BA, Ho M, McArdle JJ. Altered active zones, vesicle pools, nerve terminal conductivity, and morphology during experimental MuSK myasthenia gravis. PLoS One 2014; 9:e110571. [PMID: 25438154 PMCID: PMC4249869 DOI: 10.1371/journal.pone.0110571] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Accepted: 09/15/2014] [Indexed: 11/18/2022] Open
Abstract
Recent studies demonstrate reduced motor-nerve function during autoimmune muscle-specific tyrosine kinase (MuSK) myasthenia gravis (MG). To further understand the basis of motor-nerve dysfunction during MuSK-MG, we immunized female C57/B6 mice with purified rat MuSK ectodomain. Nerve-muscle preparations were dissected and neuromuscular junctions (NMJs) studied electrophysiologically, morphologically, and biochemically. While all mice produced antibodies to MuSK, only 40% developed respiratory muscle weakness. In vitro study of respiratory nerve-muscle preparations isolated from these affected mice revealed that 78% of NMJs produced endplate currents (EPCs) with significantly reduced quantal content, although potentiation and depression at 50 Hz remained qualitatively normal. EPC and mEPC amplitude variability indicated significantly reduced number of vesicle-release sites (active zones) and reduced probability of vesicle release. The readily releasable vesicle pool size and the frequency of large amplitude mEPCs also declined. The remaining NMJs had intermittent (4%) or complete (18%) failure of neurotransmitter release in response to 50 Hz nerve stimulation, presumably due to blocked action potential entry into the nerve terminal, which may arise from nerve terminal swelling and thinning. Since MuSK-MG-affected muscles do not express the AChR γ subunit, the observed prolongation of EPC decay time was not due to inactivity-induced expression of embryonic acetylcholine receptor, but rather to reduced catalytic activity of acetylcholinesterase. Muscle protein levels of MuSK did not change. These findings provide novel insight into the pathophysiology of autoimmune MuSK-MG.
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MESH Headings
- Animals
- Female
- Immunization, Passive
- Mice
- Motor Endplate/pathology
- Motor Endplate/physiopathology
- Motor Neurons/pathology
- Myasthenia Gravis, Autoimmune, Experimental/immunology
- Myasthenia Gravis, Autoimmune, Experimental/metabolism
- Myasthenia Gravis, Autoimmune, Experimental/pathology
- Myasthenia Gravis, Autoimmune, Experimental/physiopathology
- Neural Conduction
- Neurotransmitter Agents/metabolism
- Protein Structure, Tertiary
- Rats
- Receptor Protein-Tyrosine Kinases/chemistry
- Receptor Protein-Tyrosine Kinases/immunology
- Receptors, Cholinergic/metabolism
- Synaptic Vesicles/metabolism
- Vaccination
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Affiliation(s)
- Vishwendra Patel
- Department of Pharmacology and Physiology, New Jersey Medical School-Rutgers University, Newark, New Jersey, United States of America
| | - Anne Oh
- Department of Pharmacology and Physiology, New Jersey Medical School-Rutgers University, Newark, New Jersey, United States of America
| | - Antanina Voit
- Department Cell Biology and Molecular Medicine, New Jersey Medical School-Rutgers University, Newark, New Jersey, United States of America
| | - Lester G. Sultatos
- Department of Pharmacology and Physiology, New Jersey Medical School-Rutgers University, Newark, New Jersey, United States of America
| | - Gopal J. Babu
- Department Cell Biology and Molecular Medicine, New Jersey Medical School-Rutgers University, Newark, New Jersey, United States of America
| | - Brenda A. Wilson
- Department of Microbiology, University of Illinois, Urbana-Champaign, Illinois, United States of America
| | - Mengfei Ho
- Department of Microbiology, University of Illinois, Urbana-Champaign, Illinois, United States of America
| | - Joseph J. McArdle
- Department of Pharmacology and Physiology, New Jersey Medical School-Rutgers University, Newark, New Jersey, United States of America
- * E-mail:
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Arnold AS, Gill J, Christe M, Ruiz R, McGuirk S, St-Pierre J, Tabares L, Handschin C. Morphological and functional remodelling of the neuromuscular junction by skeletal muscle PGC-1α. Nat Commun 2014; 5:3569. [PMID: 24686533 PMCID: PMC4846352 DOI: 10.1038/ncomms4569] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 03/06/2014] [Indexed: 11/09/2022] Open
Abstract
The neuromuscular junction (NMJ) exhibits high morphological and functional plasticity. In the mature muscle, the relative levels of physical activity are the major determinants of NMJ function. Classically, motor neuron-mediated activation patterns of skeletal muscle have been thought of as the major drivers of NMJ plasticity and the ensuing fibre-type determination in muscle. Here we use muscle-specific transgenic animals for the peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) as a genetic model for trained mice to elucidate the contribution of skeletal muscle to activity-induced adaptation of the NMJ. We find that muscle-specific expression of PGC-1α promotes a remodelling of the NMJ, even in the absence of increased physical activity. Importantly, these plastic changes are not restricted to post-synaptic structures, but extended to modulation of presynaptic cell morphology and function. Therefore, our data indicate that skeletal muscle significantly contributes to the adaptation of the NMJ subsequent to physical activity.
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Affiliation(s)
- Anne-Sophie Arnold
- Biozentrum, Division of Pharmacology/Neurobiology, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
| | - Jonathan Gill
- Biozentrum, Division of Pharmacology/Neurobiology, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
| | - Martine Christe
- 1] Biozentrum, Division of Pharmacology/Neurobiology, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland [2]
| | - Rocío Ruiz
- Department of Medical Physiology and Biophysics, School of Medicine University of Seville, Avda. Sánchez Pizjuan 4, 41009 Sevilla, Spain
| | - Shawn McGuirk
- Department of Biochemistry, Rosalind and Morris Goodman Cancer Centre, McGill University, 3655 promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6
| | - Julie St-Pierre
- Department of Biochemistry, Rosalind and Morris Goodman Cancer Centre, McGill University, 3655 promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6
| | - Lucía Tabares
- Department of Medical Physiology and Biophysics, School of Medicine University of Seville, Avda. Sánchez Pizjuan 4, 41009 Sevilla, Spain
| | - Christoph Handschin
- Biozentrum, Division of Pharmacology/Neurobiology, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
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Fewou SN, Plomp JJ, Willison HJ. The pre-synaptic motor nerve terminal as a site for antibody-mediated neurotoxicity in autoimmune neuropathies and synaptopathies. J Anat 2013; 224:36-44. [PMID: 23937354 DOI: 10.1111/joa.12088] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/11/2013] [Indexed: 12/20/2022] Open
Abstract
The pre-synaptic motor nerve terminal is a highly complex and dynamic compartment within the lower motor neuron responsible for converting electrical signals into secreted chemicals. This self-renewing process of synaptic transmission is accomplished by the calcium-triggered fusion of neurotransmitter-containing vesicles with the plasma membrane and the subsequent retrieval and recycling of vesicle components. Besides this conventional physiological role, the highly active process of vesicle fusion and re-uptake into endosomal sorting pathways acts as a conduit for entry of a range of substances into the intracellular compartment of the motor nerve terminal. Whilst this entry portal sub-serves many vital physiological processes, such as those mediated by neurotrophin trafficking, there is also the potential for substantial pathological consequences resulting from uptake of noxious agents, including autoantibodies, viruses and toxins. These may act locally to induce disease within the nerve terminal, or traffic beyond to the motor neuron cell body and central nervous system to exert their pathological effects. This review focuses on the recent evidence that the ganglioside-rich pre-synaptic membrane acts as a binding site for potentially neurotoxic serum autoantibodies that are present in human autoimmune motor neuropathies. Autoantibodies that bind surface antigens induce membrane lytic effects, whereas their uptake attenuates local injury and transfers any potential pathological consequences to the intracellular compartment. Herein the thesis is explored that a balance exists between local injury at the exofacial leaflet of the pre-synaptic membrane and antibody uptake, which dictates the overall level and site of motor nerve injury in this group of disorders.
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Affiliation(s)
- Simon N Fewou
- Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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31
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Mechanisms associated with the pathogenicity of antibodies against muscle-specific kinase in myasthenia gravis. Autoimmun Rev 2013; 12:912-7. [DOI: 10.1016/j.autrev.2013.03.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/12/2013] [Indexed: 12/27/2022]
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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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Hernandez-Oliveira e Silva S, Rostelato-Ferreira S, Rocha-e-Silva TAA, Randazzo-Moura P, Dal-Belo CA, Sanchez EF, Borja-Oliveira CR, Rodrigues-Simioni L. Beneficial effect of crotamine in the treatment of myasthenic rats. Muscle Nerve 2013; 47:591-3. [PMID: 23460475 DOI: 10.1002/mus.23714] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/26/2012] [Indexed: 11/06/2022]
Abstract
INTRODUCTION Crotamine is a basic, low-molecular-weight peptide that, at low concentrations, improves neurotransmission in isolated neuromuscular preparations by modulating sodium channels. In this study, we compared the effects of crotamine and neostigmine on neuromuscular transmission in myasthenic rats. METHODS We used a conventional electromyographic technique in in-situ neuromuscular preparations and a 4-week treadmill program. RESULTS During the in-situ electromyographic recording, neostigmine (17 μg/kg) caused short-term facilitation, whereas crotamine induced progressive and sustained twitch-tension enhancement during 140 min of recording (50 ± 5%, P < 0.05). On the treadmill evaluation, rats showed significant improvement in exercise tolerance, characterized by a decrease in the number of fatigue episodes after 2 weeks of a single-dose treatment with crotamine. CONCLUSIONS These results indicate that crotamine is more efficient than neostigmine for enhancing muscular performance in myasthenic rats, possibly by improving the safety factor of neuromuscular transmission.
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Serra A, Ruff RL, Leigh RJ. Neuromuscular transmission failure in myasthenia gravis: decrement of safety factor and susceptibility of extraocular muscles. Ann N Y Acad Sci 2013; 1275:129-35. [PMID: 23278588 DOI: 10.1111/j.1749-6632.2012.06841.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An appropriate density of acetylcholine receptors (AChRs) and Na(+) channels (NaChs) in the normal neuromuscular junction (NMJ) determines the magnitude of safety factor (SF) that guarantees fidelity of neuromuscular transmission. In myasthenia gravis (MG), an overall simplification of the postsynaptic folding secondary to NMJ destruction results in AChRs and NaChs depletion. Loss of AChRs and NaChs accounts, respectively, for 59% and 40% reduction of the SF at the endplate, which manifests as neuromuscular transmission failure. The extraocular muscles (EOM) have physiologically less developed postsynaptic folding, hence a lower baseline SF, which predisposes them to dysfunction in MG and development of fatigue during "high performance" eye movements, such as saccades. However, saccades in MG show stereotyped, conjugate initial components, similar to normal, which might reflect preserved neuromuscular transmission fidelity at the NMJ of the fast, pale global fibers, which have better developed postsynaptic folding than other extraocular fibers.
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Affiliation(s)
- Alessandro Serra
- Mellen Center for Multiple Sclerosis, Department of Neurology, Cleveland Clinic Foundation, Cleveland, Ohio, USA.
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35
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Volkov ME, Volkov EM, Nurullin LF. Immunocytochemical identification of synaptotagmin 1, syntaxin 1, Ca2+ channel of the N-type, and nicotinic cholinoreceptor in motor neuromuscular junctions of somatic muscle of the earthworm Lumbricus terrestris. ACTA ACUST UNITED AC 2013. [DOI: 10.1134/s1990519x13010148] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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36
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Tarr TB, Dittrich M, Meriney SD. Are unreliable release mechanisms conserved from NMJ to CNS? Trends Neurosci 2012; 36:14-22. [PMID: 23102681 DOI: 10.1016/j.tins.2012.09.009] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Revised: 05/19/2012] [Accepted: 09/24/2012] [Indexed: 01/15/2023]
Abstract
The frog neuromuscular junction (NMJ) is a strong and reliable synapse because, during activation, sufficient neurotransmitter is released to trigger a postsynaptic action potential (AP). Recent evidence supports the hypothesis that this reliability emerges from the assembly of thousands of unreliable single vesicle release sites. The mechanisms that govern this unreliability include a paucity of voltage-gated calcium channels, a low probability of calcium channel opening during an AP, and the rare triggering of synaptic vesicle fusion even when a calcium channel does open and allows calcium flux. Here, we discuss the evidence that these unreliable single vesicle release sites may be the fundamental building blocks of many types of synapses in both the peripheral and central nervous system (PNS and CNS, respectively).
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Affiliation(s)
- Tyler B Tarr
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
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37
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Kusner LL, Halperin JA, Kaminski HJ. Cell surface complement regulators moderate experimental myasthenia gravis pathology. Muscle Nerve 2012; 47:33-40. [PMID: 23042232 DOI: 10.1002/mus.23448] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/01/2012] [Indexed: 01/01/2023]
Abstract
INTRODUCTION Intrinsic mouse complement regulators influence the severity of passively induced experimental acquired myasthenia gravis (EAMG). To assess the potential influence of CD59b in the absence of CD59a background, we used the mCD59ab(-/-) mouse model to re-evaluate mCD59 in protecting the neuromuscular junction (NMJ). METHODS EAMG was induced with monoclonal antibody to the acetylcholine receptor (AChR) in Daf1(-/-) , CD59ab(-/-) , Daf1(-/-) CD59ab(-/-) , and wild-type C57Bl/6 mice. Animals were monitored throughout the experiment. Diaphragms were analyzed for NMJ injury. RESULTS Daf1(-/-) CD59ab(-/-) mice required euthanasia 24 hours after disease induction because of severe weakness. Histological assessment demonstrated reduced AChR density, simplification of synaptic folds, and disrupted mitochondria. CD59ab-deficient mice demonstrated mild weakness and reduction in weight after 24 hours. In contrast, Daf1(-/-) had more severe weakness at 60 hours. The NMJ of EAMG-induced Daf1(-/-) and CD59ab(-/-) mice demonstrated similar AChR density. CONCLUSION NMJs of CD59 and DAF mice are protected from complement-mediated injury of passive EAMG.
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Affiliation(s)
- Linda L Kusner
- Department of Pharmacology and Physiology, George Washington University, Washington, DC, USA.
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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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The formation of complex acetylcholine receptor clusters requires MuSK kinase activity and structural information from the MuSK extracellular domain. Mol Cell Neurosci 2011; 49:475-86. [PMID: 22210232 PMCID: PMC3359500 DOI: 10.1016/j.mcn.2011.12.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Revised: 12/12/2011] [Accepted: 12/15/2011] [Indexed: 01/05/2023] Open
Abstract
Efficient synaptic transmission at the neuromuscular junction (NMJ) requires the topological maturation of the postsynaptic apparatus from an oval acetylcholine receptor (AChR)-rich plaque into a complex pretzel-shaped array of branches. However, compared to NMJ formation very little is known about the mechanisms that regulate NMJ maturation. Recently the process of in vivo transformation from plaque into pretzel has been reproduced in vitro by culturing myotubes aneurally on laminin-coated substrate. It was proposed that the formation of complex AChR clusters is regulated by a MuSK-dependent muscle intrinsic program. To elucidate the structure–function role of MuSK in the aneural maturation of AChR pretzels, we used muscle cell lines expressing MuSK mutant and chimeric proteins. Here we report, that besides its role during agrin-induced AChR clustering, MuSK kinase activity is also necessary for substrate-dependent cluster formation. Constitutive-active MuSK induces larger AChR clusters, a faster cluster maturation on laminin and increases the anchorage of AChRs to the cytoskeleton compared to MuSK wild-type. In addition, we find that the juxtamembrane region of MuSK, which has previously been shown to regulate agrin-induced AChR clustering, is unable to induce complex AChR clusters on laminin substrate. Most interestingly, MuSK kinase activity is not sufficient for laminin-dependent AChR cluster formation since the MuSK ectodomain is also required suggesting a so far undiscovered instructive role for the extracellular domain of MuSK.
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Schmidt N, Akaaboune M, Gajendran N, Martinez-Pena y Valenzuela I, Wakefield S, Thurnheer R, Brenner HR. Neuregulin/ErbB regulate neuromuscular junction development by phosphorylation of α-dystrobrevin. ACTA ACUST UNITED AC 2011; 195:1171-84. [PMID: 22184199 PMCID: PMC3246897 DOI: 10.1083/jcb.201107083] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neuregulin/ErbB signaling maintains high efficacy of synaptic transmission by stabilizing the postsynaptic apparatus via phosphorylation of α-dystrobrevin1. Neuregulin (NRG)/ErbB signaling is involved in numerous developmental processes in the nervous system, including synapse formation and function in the central nervous system. Although intensively investigated, its role at the neuromuscular synapse has remained elusive. Here, we demonstrate that loss of neuromuscular NRG/ErbB signaling destabilized anchoring of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane and that this effect was caused by dephosphorylation of α-dystrobrevin1, a component of the postsynaptic scaffold. Specifically, in mice in which NRG signaling to muscle was genetically or pharmacologically abolished, postsynaptic AChRs moved rapidly from the synaptic to the perisynaptic membrane, and the subsynaptic scaffold that anchors the AChRs was impaired. These defects combined compromised synaptic transmission. We further show that blockade of NRG/ErbB signaling abolished tyrosine phosphorylation of α-dystrobrevin1, which reduced the stability of receptors in agrin-induced AChR clusters in cultured myotubes. Our data indicate that NRG/ErbB signaling maintains high efficacy of synaptic transmission by stabilizing the postsynaptic apparatus via phosphorylation of α-dystrobrevin1.
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Affiliation(s)
- Nadine Schmidt
- Institute of Physiology, Department of Biomedicine, University of Basel, CH-4056, Basel, Switzerland
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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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42
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Ruff RL. Endplate contributions to the safety factor for neuromuscular transmission. Muscle Nerve 2011; 44:854-61. [DOI: 10.1002/mus.22177] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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43
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Serra A, Ruff R, Kaminski H, Leigh RJ. Factors contributing to failure of neuromuscular transmission in myasthenia gravis and the special case of the extraocular muscles. Ann N Y Acad Sci 2011; 1233:26-33. [DOI: 10.1111/j.1749-6632.2011.06123.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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44
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Gaffield MA, Romberg CF, Betz WJ. Live imaging of bulk endocytosis in frog motor nerve terminals using FM dyes. J Neurophysiol 2011; 106:599-607. [PMID: 21543750 DOI: 10.1152/jn.00123.2011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We observed endocytosis in real time in stimulated frog motor nerve terminals by imaging the growth of large membrane infoldings labeled with a low concentration of FM dye. The spatial and temporal information made available by these experiments allowed us to image several new aspects of this synaptic vesicle recycling pathway. Membrane infoldings appeared near synaptic vesicle clusters and grew rapidly during long-duration, high-frequency stimulation. In some cases, we observed large, elongated infoldings growing laterally into the terminal. We used these observations to calculate infolding growth rates. A decrease in stimulation frequency caused a decrease in growth rates, but the overall length of these structures was unaffected by frequency changes. Attempts to wash the dye from these infoldings after stimulation were unsuccessful, demonstrating that the fluorescent structures had been endocytosed. We also used this technique to trigger and image infoldings during repeated, short trains. We found that membrane uptake occurred repeatedly at individual endocytosis sites, but only during a portion of the total number of trains delivered to the terminal. Finally, we showed that phosphatidylinositol 3-kinase, but not actin, was involved in this endocytosis pathway. The ability to monitor many individual bulk endocytosis sites in real time should allow for new types of endocytosis measurements and could reveal novel and unexpected mechanisms for coordinating membrane recovery during synaptic activity.
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Affiliation(s)
- Michael A Gaffield
- Department of Physiology and Biophysics, University of Colorado-Denver, Anshutz Medical Campus, Aurora, CO 80045, USA
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45
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Johnson AM, Connor NP. Effects of electrical stimulation on neuromuscular junction morphology in the aging rat tongue. Muscle Nerve 2011; 43:203-11. [PMID: 21254085 DOI: 10.1002/mus.21819] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Alterations in neuromuscular junction (NMJ) structure in cranial muscles may contribute to age-related deficits in critical sensorimotor actions such as swallowing. Neuromuscular electrical stimulation (NMES) is used in swallowing therapy, but it is unclear how NMJ structure is affected or if NMJ morphology is best measured in two or three dimensions. Two- and three-dimensional measurements of NMJ morphology in the genioglossus muscle were compared in rats that had undergone 8 weeks of hypoglossal nerve stimulation vs. untreated controls. The relationship between motor endplate volume and nerve terminal volume had a mean positive slope in 90% of the young adult controls, but it was positive in only 50% of the old controls; 89% of NMES old rats had a positive slope. NMJ measurements were more accurate when measured in three dimensions. In the NMJ, aging and NMES are associated with changes in the pre- and post-synaptic relationship.
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Affiliation(s)
- Aaron M Johnson
- Department of Surgery, University of Wisconsin-Madison, Madison, WI 53792, USA
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46
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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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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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Synapse-glia interactions are governed by synaptic and intrinsic glial properties. Neuroscience 2010; 167:621-32. [PMID: 20188148 DOI: 10.1016/j.neuroscience.2010.02.036] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2009] [Revised: 01/30/2010] [Accepted: 02/16/2010] [Indexed: 11/24/2022]
Abstract
It is believed that glial cell activation and their interactions with synapses are predominantly dependent upon the characteristics of synaptic activity and the level of transmitter release. Because synaptic properties vary from one type of synapse to another, synapse-glia interactions should differ accordingly. The goal of this work was to examine how glial cell activation is dependent upon the properties of their respective synapses as well as the level of synaptic activity. We contrasted Ca(2+) responses of perisynaptic Schwann cells (PSCs) at neuromuscular junctions (NMJs) with different synaptic properties; the slow-twitch soleus (SOL) and the fast-twitch levator auris longus (LAL) muscles. Amplitude of PSC Ca(2+) responses elicited by repeated motor nerve stimulation at 40, 50 and 100 Hz were larger and their kinetics faster at LAL NMJs and this, at all frequencies examined. In addition, a greater number of PSCs per NMJ was activated by sustained synaptic transmission at NMJs of LAL in comparison to SOL. Differences in PSC activation could not be explained solely by differences in levels of transmitter release but also by intrinsic PSC properties since increasing transmitter release with tetraethylammonium chloride (TEA) did not increase their responsiveness. As a whole, these results indicate that PSC responsiveness at NMJs of slow- and fast-twitch muscles differ not only according to the level of activity of their synaptic partner but also in accordance with inherent glial properties.
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Plomp JJ, Willison HJ. Pathophysiological actions of neuropathy-related anti-ganglioside antibodies at the neuromuscular junction. J Physiol 2009; 587:3979-99. [PMID: 19564393 PMCID: PMC2756433 DOI: 10.1113/jphysiol.2009.171702] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2009] [Accepted: 06/24/2009] [Indexed: 12/17/2022] Open
Abstract
The outer leaflet of neuronal membranes is highly enriched in gangliosides. Therefore, specific neuronal roles have been attributed to this family of sialylated glycosphingolipids, e.g. in modulation of ion channels and transporters, neuronal interaction and recognition, temperature adaptation, Ca(2+) homeostasis, axonal growth, (para)node of Ranvier stability and synaptic transmission. Recent developmental, ageing and injury studies on transgenic mice lacking subsets of gangliosides indicate that gangliosides are involved in maintenance rather than development of the nervous system and that ganglioside family members are able to act in a mutually compensatory manner. Besides having physiological functions, gangliosides are the likely antigenic targets of autoantibodies present in Guillain-Barré syndrome (GBS), a group of neuropathies with clinical symptoms of motor- and/or sensory peripheral nerve dysfunction. Antibody binding to peripheral nerves is thought to either interfere with ganglioside function or activate complement, causing axonal damage and thereby disturbed action potential conduction. The presynaptic motor nerve terminal at the neuromuscular junction (NMJ) may be a prominent target because it is highly enriched in gangliosides and lies outside the blood-nerve barrier, allowing antibody access. The ensuing neuromuscular synaptopathy might contribute to the muscle weakness in GBS patients. Several groups, including our own, have studied the effects of anti-ganglioside antibodies in ex vivo and in vivo experimental settings at mouse NMJs. Here, after providing a background overview on ganglioside synthesis, localization and physiology, we will review those studies, which clearly show that anti-ganglioside antibodies are capable of binding to NMJs and thereby can exert a variety of pathophysiological effects. Furthermore, we will discuss the human clinical electrophysiological and histological evidence produced so far of the existence of a neuromuscular synaptopathy contributing to muscle weakness in GBS patients.
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Affiliation(s)
- Jaap J Plomp
- Glasgow Biomedical Research Centre, Room B330, 120 University Place, University of Glasgow, Glasgow G12 8TA, UK
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50
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Herbst R, Iskratsch T, Unger E, Bittner RE. Aberrant development of neuromuscular junctions in glycosylation-defective Large(myd) mice. Neuromuscul Disord 2009; 19:366-78. [PMID: 19346129 DOI: 10.1016/j.nmd.2009.02.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2007] [Revised: 02/17/2009] [Accepted: 02/27/2009] [Indexed: 01/13/2023]
Abstract
Mice deficient in the glycosyltransferase Large are characterized by severe muscle and central nervous system abnormalities. In this study, we show that the formation and maintenance of neuromuscular junctions in Large(myd) mice are greatly compromised. Neuromuscular junctions are not confined to the muscle endplate zone but are widely spread and are frequently accompanied by exuberant nerve sprouting. Nerve terminals are highly fragmented and binding of alpha-bungarotoxin to postsynaptic acetylcholine receptors (AChRs) is greatly reduced. In vitro, Large(myd) myotubes are responsive to agrin but produce aberrant AChR clusters, which are larger in area and less densely packed with AChRs. In addition, AChR expression on the cell surface is diminished suggesting that AChR assembly or transport is defective. These results together with the finding that O-linked glycosylation at neuromuscular junctions of Large(myd) mice is compromised indicate that the action of Large is necessary for proper neuromuscular junction development.
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Affiliation(s)
- Ruth Herbst
- Center for Brain Research, Medical University of Vienna, Vienna, Austria.
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