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Kaplan MM, Zeidler M, Knapp A, Hölzl M, Kress M, Fritsch H, Krogsdam A, Flucher BE. Spatial transcriptomics in embryonic mouse diaphragm muscle reveals regional gradients and subdomains of developmental gene expression. iScience 2024; 27:110018. [PMID: 38883818 PMCID: PMC11177202 DOI: 10.1016/j.isci.2024.110018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 03/22/2024] [Accepted: 05/14/2024] [Indexed: 06/18/2024] Open
Abstract
The murine embryonic diaphragm is a primary model for studying myogenesis and neuro-muscular synaptogenesis, both representing processes regulated by spatially organized genetic programs of myonuclei located in distinct myodomains. However, a spatial gene expression pattern of embryonic mouse diaphragm has not been reported. Here, we provide spatially resolved gene expression data for horizontally sectioned embryonic mouse diaphragms at embryonic days E14.5 and E18.5. These data reveal gene signatures for specific muscle regions with distinct maturity and fiber type composition, as well as for a central neuromuscular junction (NMJ) and a peripheral myotendinous junction (MTJ) compartment. Comparing spatial expression patterns of wild-type mice with those of transgenic mice lacking either the skeletal muscle calcium channel CaV1.1 or β-catenin, reveals curtailed muscle development and dysregulated expression of genes potentially involved in NMJ formation. Altogether, these datasets provide a powerful resource for further studies of muscle development and NMJ formation in the mouse.
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Affiliation(s)
| | - Maximilian Zeidler
- Institute of Physiology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Annabella Knapp
- Institute of Clinical and Functional Anatomy, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Martina Hölzl
- Deep Sequencing Core and Institute for Bioinformatics Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Michaela Kress
- Institute of Physiology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Helga Fritsch
- Institute of Clinical and Functional Anatomy, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Anne Krogsdam
- Deep Sequencing Core and Institute for Bioinformatics Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Bernhard E Flucher
- Institute of Physiology, Medical University Innsbruck, 6020 Innsbruck, Austria
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2
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Hart CC, Lee YI, Xie J, Gao G, Lin BL, Hammers DW, Sweeney HL. Potential limitations of microdystrophin gene therapy for Duchenne muscular dystrophy. JCI Insight 2024; 9:e165869. [PMID: 38713520 DOI: 10.1172/jci.insight.165869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Accepted: 05/01/2024] [Indexed: 05/09/2024] Open
Abstract
Clinical trials delivering high doses of adeno-associated viruses (AAVs) expressing truncated dystrophin molecules (microdystrophins) are underway for Duchenne muscular dystrophy (DMD). We examined the efficiency and efficacy of this strategy with 4 microdystrophin constructs (3 in clinical trials and a variant of the largest clinical construct), in a severe mouse model of DMD, using AAV doses comparable with those in clinical trials. We achieved high levels of microdystrophin expression in striated muscles with cardiac expression approximately 10-fold higher than that observed in skeletal muscle. Significant, albeit incomplete, correction of skeletal muscle disease was observed. Surprisingly, a lethal acceleration of cardiac disease occurred with 2 of the microdystrophins. The detrimental cardiac effect appears to be caused by variable competition (dependent on microdystrophin design and expression level) between microdystrophin and utrophin at the cardiomyocyte membrane. There may also be a contribution from an overloading of protein degradation. The significance of these observations for patients currently being treated with AAV-microdystrophin therapies is unclear since the levels of expression being achieved in the DMD hearts are unknown. However, these findings suggest that microdystrophin treatments need to avoid excessively high levels of expression in the heart and that cardiac function should be carefully monitored in these patients.
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Affiliation(s)
- Cora C Hart
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Young Il Lee
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Jun Xie
- Horae Gene Therapy Center, University of Massachusetts Medical School, Worchester, Massachusetts, USA
| | - Guangping Gao
- Horae Gene Therapy Center, University of Massachusetts Medical School, Worchester, Massachusetts, USA
| | - Brian L Lin
- Department of Cell Biology, Neurobiology, and Anatomy & Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - David W Hammers
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - H Lee Sweeney
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
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Rudolf R. Myosin Va: Capturing cAMP for synaptic plasticity. Front Physiol 2024; 14:1342994. [PMID: 38239886 PMCID: PMC10794446 DOI: 10.3389/fphys.2023.1342994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Accepted: 12/12/2023] [Indexed: 01/22/2024] Open
Abstract
The plus-end directed actin-dependent motor protein, myosin Va, is of particular relevance for outward vesicular protein trafficking and for restraining specific cargo vesicles within the actin cortex. The latter is a preferred site of cAMP production, and the specificity of cAMP signaling is largely mediated through the formation of microdomains that spatially couple localized metabotropic receptor activity and cAMP production to selected effectors and downstream targets. This review summarizes the core literature on the role of myosin Va for the creation of such a cAMP microdomain at the mammalian nerve-muscle synapse that serves the activity-dependent recycling of nicotinic acetylcholine receptors (nAChRs)-a principal ligand-gated ion channel which is imperative for voluntary muscle contraction. It is discussed that i) the nerve-muscle synapse is a site with a unique actin-dependent microstructure, ii) myosin Va and protein kinase A regulatory subunit Iα as well as nAChR and its constitutive binding partner, rapsyn, colocalize in endocytic/recycling vesicles near the postsynaptic membrane, and iii) impairment of myosin Va or displacement of protein kinase A regulatory subunit Iα leads to the loss of nAChR stability. Regulation of this signaling process and underlying basic pieces of machinery were covered in previous articles, to which the present review refers.
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Affiliation(s)
- Rüdiger Rudolf
- Center for Mass Spectrometry and Optical Spectroscopy (CeMOS), Mannheim University of Applied Sciences, Mannheim, Germany
- Interdisciplinary Center for Neurosciences, Heidelberg University, Heidelberg, Germany
- Mannheim Center for Translational Neurosciences, Heidelberg University, Mannheim, Germany
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Navarro-Martínez A, Vicente-García C, Carvajal JJ. NMJ-related diseases beyond the congenital myasthenic syndromes. Front Cell Dev Biol 2023; 11:1216726. [PMID: 37601107 PMCID: PMC10436495 DOI: 10.3389/fcell.2023.1216726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 07/21/2023] [Indexed: 08/22/2023] Open
Abstract
Neuromuscular junctions (NMJs) are a special type of chemical synapse that transmits electrical stimuli from motor neurons (MNs) to their innervating skeletal muscle to induce a motor response. They are an ideal model for the study of synapses, given their manageable size and easy accessibility. Alterations in their morphology or function lead to neuromuscular disorders, such as the congenital myasthenic syndromes, which are caused by mutations in proteins located in the NMJ. In this review, we highlight novel potential candidate genes that may cause or modify NMJs-related pathologies in humans by exploring the phenotypes of hundreds of mouse models available in the literature. We also underscore the fact that NMJs may differ between species, muscles or even sexes. Hence the importance of choosing a good model organism for the study of NMJ-related diseases: only taking into account the specific features of the mammalian NMJ, experimental results would be efficiently translated to the clinic.
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Affiliation(s)
| | - Cristina Vicente-García
- Centro Andaluz de Biología del Desarrollo, CSIC-UPO-JA, Universidad Pablo de Olavide, Sevilla, Spain
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Nimgampalle M, Chakravarthy H, Sharma S, Shree S, Bhat AR, Pradeepkiran JA, Devanathan V. Neurotransmitter systems in the etiology of major neurological disorders: Emerging insights and therapeutic implications. Ageing Res Rev 2023; 89:101994. [PMID: 37385351 DOI: 10.1016/j.arr.2023.101994] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Revised: 06/21/2023] [Accepted: 06/25/2023] [Indexed: 07/01/2023]
Abstract
Neurotransmitters serve as chemical messengers playing a crucial role in information processing throughout the nervous system, and are essential for healthy physiological and behavioural functions in the body. Neurotransmitter systems are classified as cholinergic, glutamatergic, GABAergic, dopaminergic, serotonergic, histaminergic, or aminergic systems, depending on the type of neurotransmitter secreted by the neuron, allowing effector organs to carry out specific functions by sending nerve impulses. Dysregulation of a neurotransmitter system is typically linked to a specific neurological disorder. However, more recent research points to a distinct pathogenic role for each neurotransmitter system in more than one neurological disorder of the central nervous system. In this context, the review provides recently updated information on each neurotransmitter system, including the pathways involved in their biochemical synthesis and regulation, their physiological functions, pathogenic roles in diseases, current diagnostics, new therapeutic targets, and the currently used drugs for associated neurological disorders. Finally, a brief overview of the recent developments in neurotransmitter-based therapeutics for selected neurological disorders is offered, followed by future perspectives in that area of research.
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Affiliation(s)
- Mallikarjuna Nimgampalle
- Department of Biology, Indian Institute of Science Education and Research Tirupati (IISER T), Transit campus, Karakambadi Road, Mangalam, Tirupati 517507, Andhra Pradesh, India
| | - Harshini Chakravarthy
- Department of Biology, Indian Institute of Science Education and Research Tirupati (IISER T), Transit campus, Karakambadi Road, Mangalam, Tirupati 517507, Andhra Pradesh, India.
| | - Sapana Sharma
- Department of Biology, Indian Institute of Science Education and Research Tirupati (IISER T), Transit campus, Karakambadi Road, Mangalam, Tirupati 517507, Andhra Pradesh, India
| | - Shruti Shree
- Department of Biology, Indian Institute of Science Education and Research Tirupati (IISER T), Transit campus, Karakambadi Road, Mangalam, Tirupati 517507, Andhra Pradesh, India
| | - Anoop Ramachandra Bhat
- Department of Biology, Indian Institute of Science Education and Research Tirupati (IISER T), Transit campus, Karakambadi Road, Mangalam, Tirupati 517507, Andhra Pradesh, India
| | | | - Vasudharani Devanathan
- Department of Biology, Indian Institute of Science Education and Research Tirupati (IISER T), Transit campus, Karakambadi Road, Mangalam, Tirupati 517507, Andhra Pradesh, India.
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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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McIntosh J, Mekrouda I, Dashti M, Giuraniuc CV, Banks RW, Miles GB, Bewick GS. Development of abnormalities at the neuromuscular junction in the SOD1-G93A mouse model of ALS: dysfunction then disruption of postsynaptic structure precede overt motor symptoms. Front Mol Neurosci 2023; 16:1169075. [PMID: 37273905 PMCID: PMC10237339 DOI: 10.3389/fnmol.2023.1169075] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2023] [Accepted: 04/12/2023] [Indexed: 06/06/2023] Open
Abstract
Introduction The ultimate deficit in amyotrophic lateral sclerosis (ALS) is neuromuscular junction (NMJ) loss, producing permanent paralysis, ultimately in respiratory muscles. However, understanding the functional and structural deficits at NMJs prior to this loss is crucial for therapeutic strategy design. Should early interventions focus on reversing denervation, or supporting largely intact NMJs that are functionally impaired? We therefore determined when functional and structural deficits appeared in diaphragmatic NMJs relative to the onset of hindlimb tremor (the first overt motor symptoms) in vivo in the SOD1-G93A mouse model of ALS. Materials and methods We employed electrophysiological recording of NMJ postsynaptic potentials for spontaneous and nerve stimulation-evoked responses. This was correlated with fluorescent imaging microscopy of the postsynaptic acetylcholine receptor (AChR) distribution throughout the postnatal developmental timecourse from 2 weeks to early symptomatic ages. Results Significant reduction in the amplitudes of spontaneous miniature endplate potentials (mEPPs) and evoked EPPs emerged only at early symptomatic ages (in our colony, 18-22 weeks). Reductions in mEPP frequency, number of vesicles per EPP, and EPP rise time were seen earlier, at 16weeks, but this reversed by early symptomatic ages. However, the earliest and most striking impairment was an inability to maintain EPP amplitude during a 20 Hz stimulus train, which appeared 6 weeks before overt in vivo motor symptoms. Despite this, fluorescent α-bungarotoxin labelling revealed no systematic, progressive changes in 11 comprehensive NMJ morphological parameters (area, shape, compactness, number of acetylcholine receptor, AChR, regions, etc.) with disease progression. Rather, while NMJs were largely normally-shaped, from 16 weeks there was a progressive and substantial disruption in AChR concentration and distribution within the NMJ footprint. Discussion Thus, NMJ functional deficits appear at least 6 weeks before motor symptoms in vivo, while structural deficits occur 4 weeks later, and predominantly within NMJs. These data suggest initial therapies focused on rectifying suboptimal NMJ function could produce effective relief of symptoms of weakness.
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Affiliation(s)
- Jayne McIntosh
- Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom
| | - Imane Mekrouda
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Maryam Dashti
- Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom
| | | | - Robert W. Banks
- Department of Biosciences, Durham University, Durham, United Kingdom
| | - Gareth B. Miles
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
| | - Guy S. Bewick
- Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom
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Lysenkov SP, Muzhenya DV, Tuguz AR, Urakova TU, Shumilov DS, Thakushinov IA, Thakushinov RA, Tatarkova EA, Urakova DM. Cholinergic deficiency in the cholinergic system as a pathogenetic link in the formation of various syndromes in COVID-19. CHINESE J PHYSIOL 2023; 66:1-13. [PMID: 36814151 DOI: 10.4103/cjop.cjop-d-22-00072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
According to recent data, several mechanisms of viral invasion of the central nervous system (CNS) have been proposed, one of which is both direct penetration of the virus through afferent nerve fibers and damage to the endothelium of cerebral vessels. It has been proven that the SARS-CoV-2 virus affects pathologically not only the human cardiorespiratory system but is also associated with a wide range of neurological diseases, cerebrovascular accidents, and neuromuscular pathologies. However, the observed post-COVID symptom complex in patients, manifested in the form of headache, "fog in the head," high temperature, muscle weakness, lowering blood pressure, does it make us think about the pathophysiological mechanisms that contribute to the development of this clinical picture? One possible explanation is a disruption in the signaling of the acetylcholine system (AChS) in the body. Viral invasions, and in particular COVID-19, can negatively affect the work of the AChS, disrupting its coordination activities. Therefore, the main goal of this literature review is to analyze the information and substantiate the possible mechanisms for the occurrence of post-COVID syndrome in people who have had COVID-19 from the standpoint of AChS dysfunctions.
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Affiliation(s)
- Sergey Petrovich Lysenkov
- FSBEI HE "Maikop State Technological University", Medical Institute, Maikop, Republic of Adygeya, Russia
| | | | - Aminat Ramazanovna Tuguz
- FSBEI HE "Adyghe State University", Immunogenetic Laboratory of the Research Institute of Complex Problems, Maikop, Republic of Adygeya, Russia
| | - Tamara Ur'evna Urakova
- FSBEI HE "Maikop State Technological University", Medical Institute, Maikop, Republic of Adygeya, Russia
| | - Dmitriy Sergeevich Shumilov
- FSBEI HE "Adyghe State University", Immunogenetic Laboratory of the Research Institute of Complex Problems, Maikop, Republic of Adygeya, Russia
| | | | | | - Elena Anatolevna Tatarkova
- FSBEI HE "Adyghe State University", Immunogenetic Laboratory of the Research Institute of Complex Problems, Maikop, Republic of Adygeya, Russia
| | - Diana Muratovna Urakova
- FSBEI HE "Maikop State Technological University", Medical Institute, Maikop, Republic of Adygeya, Russia
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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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Davis LA, Fogarty MJ, Brown A, Sieck GC. Structure and Function of the Mammalian Neuromuscular Junction. Compr Physiol 2022; 12:3731-3766. [PMID: 35950651 PMCID: PMC10461538 DOI: 10.1002/cphy.c210022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre- and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short-term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12:1-36, 2022.
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Affiliation(s)
- Leah A. Davis
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Matthew J. Fogarty
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Alyssa Brown
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Gary C. Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
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Nicole S, Lory P. New Challenges Resulting From the Loss of Function of Na v1.4 in Neuromuscular Diseases. Front Pharmacol 2021; 12:751095. [PMID: 34671263 PMCID: PMC8521073 DOI: 10.3389/fphar.2021.751095] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Accepted: 09/16/2021] [Indexed: 11/13/2022] Open
Abstract
The voltage-gated sodium channel Nav1.4 is a major actor in the excitability of skeletal myofibers, driving the muscle force in response to nerve stimulation. Supporting further this key role, mutations in SCN4A, the gene encoding the pore-forming α subunit of Nav1.4, are responsible for a clinical spectrum of human diseases ranging from muscle stiffness (sodium channel myotonia, SCM) to muscle weakness. For years, only dominantly-inherited diseases resulting from Nav1.4 gain of function (GoF) were known, i.e., non-dystrophic myotonia (delayed muscle relaxation due to myofiber hyperexcitability), paramyotonia congenita and hyperkalemic or hypokalemic periodic paralyses (episodic flaccid muscle weakness due to transient myofiber hypoexcitability). These last 5 years, SCN4A mutations inducing Nav1.4 loss of function (LoF) were identified as the cause of dominantly and recessively-inherited disorders with muscle weakness: periodic paralyses with hypokalemic attacks, congenital myasthenic syndromes and congenital myopathies. We propose to name this clinical spectrum sodium channel weakness (SCW) as the mirror of SCM. Nav1.4 LoF as a cause of permanent muscle weakness was quite unexpected as the Na+ current density in the sarcolemma is large, securing the ability to generate and propagate muscle action potentials. The properties of SCN4A LoF mutations are well documented at the channel level in cellular electrophysiological studies However, much less is known about the functional consequences of Nav1.4 LoF in skeletal myofibers with no available pertinent cell or animal models. Regarding the therapeutic issues for Nav1.4 channelopathies, former efforts were aimed at developing subtype-selective Nav channel antagonists to block myofiber hyperexcitability. Non-selective, Nav channel blockers are clinically efficient in SCM and paramyotonia congenita, whereas patient education and carbonic anhydrase inhibitors are helpful to prevent attacks in periodic paralyses. Developing therapeutic tools able to counteract Nav1.4 LoF in skeletal muscles is then a new challenge in the field of Nav channelopathies. Here, we review the current knowledge regarding Nav1.4 LoF and discuss the possible therapeutic strategies to be developed in order to improve muscle force in SCW.
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Affiliation(s)
- Sophie Nicole
- Institut de Génomique Fonctionnelle (IGF), Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics (ICST), Montpellier, France
| | - Philippe Lory
- Institut de Génomique Fonctionnelle (IGF), Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics (ICST), Montpellier, France
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12
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Petralia RS, Wang YX. Review of Post-embedding Immunogold Methods for the Study of Neuronal Structures. Front Neuroanat 2021; 15:763427. [PMID: 34720893 PMCID: PMC8551803 DOI: 10.3389/fnana.2021.763427] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 09/28/2021] [Indexed: 01/03/2023] Open
Abstract
The post-embedding immunogold (PI) technique for immunolabeling of neuronal tissues utilizing standard thin-section transmission electron microscopy (TEM) continues to be a prime method for understanding the functional localization of key proteins in neuronal function. Its main advantages over other immunolabeling methods for thin-section TEM are (1) fairly accurate and quantifiable localization of proteins in cells; (2) double-labeling of sections using two gold particle sizes; and (3) the ability to perform multiple labeling for different proteins by using adjacent sections. Here we first review in detail a common method for PI of neuronal tissues. This method has two major parts. First, we describe the freeze-substitution embedding method: cryoprotected tissue is frozen in liquid propane via plunge-freezing, and is placed in a freeze-substitution instrument in which the tissue is embedded in Lowicryl at low temperatures. We highlight important aspects of freeze-substitution embedding. Then we outline how thin sections of embedded tissue on grids are labeled with a primary antibody and a secondary gold particle-conjugated antibody, and the particular problems encountered in TEM of PI-labeled sections. In the Discussion, we compare our method both to earlier PI methods and to more recent PI methods used by other laboratories. We also compare TEM immunolabeling using PI vs. various pre-embedding immunolabeling methods, especially relating to neuronal tissue.
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Affiliation(s)
- Ronald S. Petralia
- Advanced Imaging Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, United States
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13
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Membrane excitability: Ankyrins keep neuromuscular junctions firing. Curr Biol 2021; 31:R1061-R1063. [PMID: 34520721 DOI: 10.1016/j.cub.2021.07.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage-gated sodium channels are clustered and immobilized at high densities in electrically excitable cells. A new study shows that ankyrins are essential to tether sodium channels and prevent synaptic fatigue at the neuromuscular junction.
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14
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An investigation on the effects of carbamazepine and sodium valproate on neuromuscular transmission. Acta Neurol Belg 2020; 120:545-548. [PMID: 28940165 DOI: 10.1007/s13760-017-0839-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 09/18/2017] [Indexed: 10/18/2022]
Abstract
The aim of this study was to investigate the effects of sodium valproate (SV) and carbamazepine (CBZ) on neuromuscular transmission using single-fibre electromyography (SFEMG) in patients with epilepsy. We performed SFEMG during the voluntary contraction of extensor digitorum communis muscle. 30 epileptic patients taking SV, 25 epileptic patients taking CBZ, and 25 age-matched healthy volunteers were included in the study. Mean jitter values (MCD) of subjects taking SV and CBZ were compared with normal controls. MCD values of subjects taking SV and CBZ were statistically significantly higher than those of control group. Review of the correlation between disease duration and MCD values of patients showed that MCD values were increased with the prolonged use of drugs, and thus, indicated a positive relationship between these two parameters. These results suggest that both SV and CBZ reduce neuromuscular transmission in patients without a neuromuscular junction disease.
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15
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The role of the dystrophin glycoprotein complex on the neuromuscular system. Neurosci Lett 2020; 722:134833. [DOI: 10.1016/j.neulet.2020.134833] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2019] [Revised: 02/07/2020] [Accepted: 02/09/2020] [Indexed: 12/26/2022]
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16
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Mukund K, Subramaniam S. Skeletal muscle: A review of molecular structure and function, in health and disease. WILEY INTERDISCIPLINARY REVIEWS. SYSTEMS BIOLOGY AND MEDICINE 2020; 12:e1462. [PMID: 31407867 PMCID: PMC6916202 DOI: 10.1002/wsbm.1462] [Citation(s) in RCA: 210] [Impact Index Per Article: 52.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 07/03/2019] [Accepted: 07/03/2019] [Indexed: 12/11/2022]
Abstract
Decades of research in skeletal muscle physiology have provided multiscale insights into the structural and functional complexity of this important anatomical tissue, designed to accomplish the task of generating contraction, force and movement. Skeletal muscle can be viewed as a biomechanical device with various interacting components including the autonomic nerves for impulse transmission, vasculature for efficient oxygenation, and embedded regulatory and metabolic machinery for maintaining cellular homeostasis. The "omics" revolution has propelled a new era in muscle research, allowing us to discern minute details of molecular cross-talk required for effective coordination between the myriad interacting components for efficient muscle function. The objective of this review is to provide a systems-level, comprehensive mapping the molecular mechanisms underlying skeletal muscle structure and function, in health and disease. We begin this review with a focus on molecular mechanisms underlying muscle tissue development (myogenesis), with an emphasis on satellite cells and muscle regeneration. We next review the molecular structure and mechanisms underlying the many structural components of the muscle: neuromuscular junction, sarcomere, cytoskeleton, extracellular matrix, and vasculature surrounding muscle. We highlight aberrant molecular mechanisms and their possible clinical or pathophysiological relevance. We particularly emphasize the impact of environmental stressors (inflammation and oxidative stress) in contributing to muscle pathophysiology including atrophy, hypertrophy, and fibrosis. This article is categorized under: Physiology > Mammalian Physiology in Health and Disease Developmental Biology > Developmental Processes in Health and Disease Models of Systems Properties and Processes > Cellular Models.
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Affiliation(s)
- Kavitha Mukund
- Department of BioengineeringUniversity of CaliforniaSan DiegoCalifornia
| | - Shankar Subramaniam
- Department of Bioengineering, Bioinformatics & Systems BiologyUniversity of CaliforniaSan DiegoCalifornia
- Department of Computer Science and EngineeringUniversity of CaliforniaSan DiegoCalifornia
- Department of Cellular and Molecular Medicine and NanoengineeringUniversity of CaliforniaSan DiegoCalifornia
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17
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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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18
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Ayvazyan NM, O'Leary VB, Dolly JO, Ovsepian SV. Neurobiology and therapeutic utility of neurotoxins targeting postsynaptic mechanisms of neuromuscular transmission. Drug Discov Today 2019; 24:1968-1984. [PMID: 31247153 DOI: 10.1016/j.drudis.2019.06.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2019] [Revised: 05/15/2019] [Accepted: 06/17/2019] [Indexed: 11/28/2022]
Abstract
The neuromuscular junction (NMJ) is the principal site for the translation of motor neurochemical signals to muscle activity. Therefore, the release and sensing machinery of acetylcholine (ACh) along with muscle contraction are two of the main targets of natural toxins and pathogens, causing paralysis. Given pharmacology and medical advances, the active ingredients of toxins that target postsynaptic mechanisms have become of major interest, showing promise as drug leads. Herein, we review key facets of prevalent toxins modulating the mechanisms of ACh sensing and generation of the postsynaptic response, with muscle contraction. We consider the correlation between their outstanding selectivity and potency plus effects on motor function, and discuss emerging data advocating their usage for the development of therapies alleviating neuromuscular dysfunction.
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Affiliation(s)
- Naira M Ayvazyan
- Orbeli Institute of Physiology, National Academy of Sciences of the Republic of Armenia, Yerevan, Armenia.
| | - Valerie B O'Leary
- Department of Medical Genetics, Third Faculty of Medicine, Charles University, Ruská 87, 100 00, Praha 10, Czech Republic
| | - J Oliver Dolly
- International Centre for Neurotherapeutics, Dublin City University, Dublin, Ireland
| | - Saak V Ovsepian
- International Centre for Neurotherapeutics, Dublin City University, Dublin, Ireland; The National Institute of Mental Health, Topolová 748, Klecany, Czech Republic; Department of Psychiatry and Medical Psychology, Third Faculty of Medicine, Charles University, Ruská 87, 100 00, Praha 10, Czech Republic.
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19
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20
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Smith KR, Penzes P. Ankyrins: Roles in synaptic biology and pathology. Mol Cell Neurosci 2018; 91:131-139. [PMID: 29730177 DOI: 10.1016/j.mcn.2018.04.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Revised: 04/23/2018] [Accepted: 04/24/2018] [Indexed: 12/27/2022] Open
Abstract
Ankyrins are broadly expressed adaptors that organize diverse membrane proteins into specialized domains and link them to the sub-membranous cytoskeleton. In neurons, ankyrins are known to have essential roles in organizing the axon initial segment and nodes of Ranvier. However, recent studies have revealed novel functions for ankyrins at synapses, where they organize and stabilize neurotransmitter receptors, modulate dendritic spine morphology and control adhesion to the presynaptic site. Ankyrin genes have also been highly associated with a range of neurodevelopmental and psychiatric diseases, including bipolar disorder, schizophrenia and autism, which all demonstrate overlap in their genetics, mechanisms and phenotypes. This review discusses the novel synaptic functions of ankyrin proteins in neurons, and places these exciting findings in the context of ANK genes as key neuropsychiatric disorder risk-factors.
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Affiliation(s)
- Katharine R Smith
- Department of Pharmacology, University of Colorado Denver, 12800 East 19th Avenue, Aurora, CO 80045, USA.
| | - Peter Penzes
- Department of Physiology, Northwestern University Feinberg School of Medicine, 303 E. Chicago Avenue, Chicago, IL 60611, USA; Psychiatry and Behavioral Sciences, Northwestern University Feinberg School of Medicine, 303 E. Chicago Avenue, Chicago, IL 60611, USA.
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21
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Blotnick-Rubin E, Anglister L. Fine Localization of Acetylcholinesterase in the Synaptic Cleft of the Vertebrate Neuromuscular Junction. Front Mol Neurosci 2018; 11:123. [PMID: 29725289 PMCID: PMC5917012 DOI: 10.3389/fnmol.2018.00123] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2018] [Accepted: 03/29/2018] [Indexed: 11/13/2022] Open
Abstract
Acetylcholinesterase (AChE) is concentrated at cholinergic synapses, where it is a major factor in controlling the duration of transmitter action. The concentration and localization of AChE within the synaptic cleft are in keeping with the functional requirements of the particular type of synapse. The densities of synaptic AChE at various neuromuscular junctions (NMJs) had been evaluated by quantitative EM-autoradiography using radiolabeled probes. Yet, fundamental issues concerning the precise distribution and location of the enzyme in the cleft remained open: whether and to what extent synaptic AChE is associated with pre- or postsynaptic membranes, or with synaptic basal lamina (BL), and whether it occurs only in the primary cleft (PC) or also in postjunctional folds (PJFs). Nanogold-conjugates of fasciculin, an anticholinesterase polypeptide toxin, were prepared and used to label AChE at NMJs of mouse and frog muscles. Selective intense labeling was obtained at the NMJs, with gold-labeled AChE sites distributed over the BL in the PC and the PJFs. Quantitative analysis demonstrated that AChE sites are almost exclusively located on the BL rather than on pre- or postsynaptic membranes and are distributed in the PC and down the PJFs, with a defined pattern. This localization pattern of AChE is suggested to ensure full hydrolysis of acetylcholine (ACh) bouncing off receptors, thus eliminating its unnecessary detrimental reattachment.
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Affiliation(s)
- Edna Blotnick-Rubin
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada (IMRIC), Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Lili Anglister
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada (IMRIC), Hebrew University-Hadassah Medical School, Jerusalem, Israel
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22
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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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23
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The Structure of Human Neuromuscular Junctions: Some Unanswered Molecular Questions. Int J Mol Sci 2017; 18:ijms18102183. [PMID: 29048368 PMCID: PMC5666864 DOI: 10.3390/ijms18102183] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 09/25/2017] [Accepted: 10/13/2017] [Indexed: 12/21/2022] Open
Abstract
The commands that control animal movement are transmitted from motor neurons to their target muscle cells at the neuromuscular junctions (NMJs). The NMJs contain many protein species whose role in transmission depends not only on their inherent properties, but also on how they are distributed within the complex structure of the motor nerve terminal and the postsynaptic muscle membrane. These molecules mediate evoked chemical transmitter release from the nerve and the action of that transmitter on the muscle. Human NMJs are among the smallest known and release the smallest number of transmitter "quanta". By contrast, they have the most deeply infolded postsynaptic membranes, which help to amplify transmitter action. The same structural features that distinguish human NMJs make them particularly susceptible to pathological processes. While much has been learned about the molecules which mediate transmitter release and action, little is known about the molecular processes that control the growth of the cellular and subcellular components of the NMJ so as to give rise to its mature form. A major challenge for molecular biologists is to understand the molecular basis for the development and maintenance of functionally important aspects of NMJ structure, and thereby to point to new directions for treatment of diseases in which neuromuscular transmission is impaired.
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24
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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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25
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Castro PATDS, Faccioni LC, Boer PA, Carvalho RF, Matheus SMM, Dal-Pai-Silva M. Neuromuscular junctions (NMJs): ultrastructural analysis and nicotinic acetylcholine receptor (nAChR) subunit mRNA expression in offspring subjected to protein restriction throughout pregnancy. Int J Exp Pathol 2017; 98:109-116. [PMID: 28543723 DOI: 10.1111/iep.12229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 02/17/2017] [Indexed: 11/29/2022] Open
Abstract
Protein restriction during gestation can alter the skeletal muscle phenotype of offspring; however, little is known with regard to whether this also affects the neuromuscular junction (NMJ), as muscle phenotype maintenance depends upon NMJ functional integrity. This study aimed to evaluate the effects of a low protein (6%) intake by dams throughout gestation on male offspring NMJ morphology and nicotinic acetylcholine receptor (nAChR) α1, γ and ε subunit expression in the soleus (SOL) and extensor digitorum longus (EDL) muscles. Four groups of male Wistar offspring rats were studied. The offspring of dams fed low-protein (6% protein, LP) and normal protein (17% protein, NP) diets were evaluated at 30 and 120 days of age, and the SOL and EDL muscles were collected for analysis. Morphological studies using transmission electron microscopy revealed that only SOL NMJs were affected in 30-day-old offspring in the LP group compared with the NP group. SOL NMJs exhibited fewer synaptic folds, the postsynaptic membranes were smooth and myelin figures were also frequently observed in the terminal axons. With regard to the expression of mRNAs encoding nAChR subunits, only 30-day-old LP offspring EDL muscles exhibited reduced α, γ and ε subunit expression compared with the NP group. In conclusion, our results demonstrate that a low-protein diet (6%) imposed throughout pregnancy impairs the expression of mRNAs encoding the nAChR α, γ and ε subunits in EDL NMJs and promotes morphological changes in SOL NMJs of 30-day-old offspring, indicating specific differences among muscle types following long-term maternal protein restriction.
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Affiliation(s)
| | | | - Patrícia Aline Boer
- Department of Internal Medicine, State University of Campinas, Campinas, São Paulo, Brazil
| | | | | | - Maeli Dal-Pai-Silva
- Department of Morphology, UNESP Institute of Biosciences, Botucatu, São Paulo, Brazil
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26
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Campanari ML, García-Ayllón MS, Ciura S, Sáez-Valero J, Kabashi E. Neuromuscular Junction Impairment in Amyotrophic Lateral Sclerosis: Reassessing the Role of Acetylcholinesterase. Front Mol Neurosci 2016; 9:160. [PMID: 28082868 PMCID: PMC5187284 DOI: 10.3389/fnmol.2016.00160] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 12/12/2016] [Indexed: 01/13/2023] Open
Abstract
Amyotrophic Lateral Sclerosis (ALS) is a highly debilitating disease caused by progressive degeneration of motorneurons (MNs). Due to the wide variety of genes and mutations identified in ALS, a highly varied etiology could ultimately converge to produce similar clinical symptoms. A major hypothesis in ALS research is the “distal axonopathy” with pathological changes occurring at the neuromuscular junction (NMJ), at very early stages of the disease, prior to MNs degeneration and onset of clinical symptoms. The NMJ is a highly specialized cholinergic synapse, allowing signaling between muscle and nerve necessary for skeletal muscle function. This nerve-muscle contact is characterized by the clustering of the collagen-tailed form of acetylcholinesterase (ColQ-AChE), together with other components of the extracellular matrix (ECM) and specific key molecules in the NMJ formation. Interestingly, in addition to their cholinergic role AChE is thought to play several “non-classical” roles that do not require catalytic function, most prominent among these is the facilitation of neurite growth, NMJ formation and survival. In all this context, abnormalities of AChE content have been found in plasma of ALS patients, in which AChE changes may reflect the neuromuscular disruption. We review these findings and particularly the evidences of changes of AChE at neuromuscular synapse in the pre-symptomatic stages of ALS.
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Affiliation(s)
- Maria-Letizia Campanari
- Sorbonne Université, Université Pierre et Marie Curie (UPMC), Université de Paris 06, Unité Mixte 75, Institut National de la Santé et de la Recherche Médicale (INSERM) Unité 1127, Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche 7225 Institut du Cerveau et de la Moelle Épinière (ICM) Paris, France
| | - María-Salud García-Ayllón
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'AlacantSpain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)Madrid, Spain; Unidad de Investigación, Hospital General Universitario de Elche, FISABIOElche, Spain
| | - Sorana Ciura
- Sorbonne Université, Université Pierre et Marie Curie (UPMC), Université de Paris 06, Unité Mixte 75, Institut National de la Santé et de la Recherche Médicale (INSERM) Unité 1127, Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche 7225 Institut du Cerveau et de la Moelle Épinière (ICM) Paris, France
| | - Javier Sáez-Valero
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'AlacantSpain; Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)Madrid, Spain
| | - Edor Kabashi
- Sorbonne Université, Université Pierre et Marie Curie (UPMC), Université de Paris 06, Unité Mixte 75, Institut National de la Santé et de la Recherche Médicale (INSERM) Unité 1127, Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche 7225 Institut du Cerveau et de la Moelle Épinière (ICM) Paris, France
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27
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Poort JE, Rheuben MB, Breedlove SM, Jordan CL. Neuromuscular junctions are pathological but not denervated in two mouse models of spinal bulbar muscular atrophy. Hum Mol Genet 2016; 25:3768-3783. [PMID: 27493028 DOI: 10.1093/hmg/ddw222] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 06/15/2016] [Accepted: 07/04/2016] [Indexed: 12/21/2022] Open
Abstract
Spinal bulbar muscular atrophy (SBMA) is a progressive, late onset neuromuscular disease causing motor dysfunction in men. While the morphology of the neuromuscular junction (NMJ) is typically affected by neuromuscular disease, whether NMJs in SBMA are similarly affected by disease is not known. Such information will shed light on whether defective NMJs might contribute to the loss of motor function and represent a potential therapeutic target for treating symptoms of SBMA. To address this gap in information, the morphology of NMJs was examined in two mouse models of SBMA, a myogenic model that overexpresses wildtype androgen receptor (AR) exclusively in muscle fibres and a knockin (KI) model expressing a humanized mutant AR gene. The tripartite motor synapse consisting of motor nerve terminal, terminal Schwann cells (tSCs) and postsynaptic specialization were visualized and analysed using confocal microscopy. Counter to expectation, we found no evidence of denervation in either model, but junctions in both models show pathological fragmentation and an abnormal synaptophysin distribution consistent with functionally weak synapses. Neurofilament accumulations were observed only in the myogenic model, even though axonal transport dysfunction is characteristic of both models. The ultrastructure of NMJs revealed additional pathology, including deficits in docked vesicles presynaptically, wider synaptic clefts, and simpler secondary folds postsynaptically. The observed pathology of NMJs in diseased SBMA mice is likely the morphological correlates of defects in synaptic function which may underlie motor impairments associated with SBMA.
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Affiliation(s)
| | - Mary B Rheuben
- Neuroscience Program, Michigan State University, MI, USA
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28
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Abstract
Ticks are important vectors of pathogens and secreted neurotoxins with approximately 69 out of 692 tick species having the ability to induce severe toxicoses in their hosts. The Australian paralysis tick (Ixodes holocyclus) is known to be one of the most virulent tick species producing a flaccid paralysis and fatalities caused by a family of neurotoxins known as holocyclotoxins (HTs). The paralysis mechanism of these toxins is temperature dependent and is thought to involve inhibition of acetylcholine levels at the neuromuscular junction. However, the target and mechanism of this inhibition remain uncharacterised. Here, we report that three members of the holocyclotoxin family; HT-1 (GenBank AY766147), HT-3 (GenBank KP096303) and HT-12 (GenBank KP963967) induce muscle paralysis by inhibiting the dependence of transmitter release on extracellular calcium. Previous study was conducted using extracts from tick salivary glands, while the present study is the first to use pure toxins from I. holocyclus. Our findings provide greater insight into the mechanisms by which these toxins act to induce paralysis.
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29
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Chand KK, Lee KM, Lavidis NA, Rodriguez-Valle M, Ijaz H, Koehbach J, Clark RJ, Lew-Tabor A, Noakes PG. Tick holocyclotoxins trigger host paralysis by presynaptic inhibition. Sci Rep 2016; 6:29446. [PMID: 27389875 PMCID: PMC4937380 DOI: 10.1038/srep29446] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 06/20/2016] [Indexed: 11/25/2022] Open
Abstract
Ticks are important vectors of pathogens and secreted neurotoxins with approximately 69 out of 692 tick species having the ability to induce severe toxicoses in their hosts. The Australian paralysis tick (Ixodes holocyclus) is known to be one of the most virulent tick species producing a flaccid paralysis and fatalities caused by a family of neurotoxins known as holocyclotoxins (HTs). The paralysis mechanism of these toxins is temperature dependent and is thought to involve inhibition of acetylcholine levels at the neuromuscular junction. However, the target and mechanism of this inhibition remain uncharacterised. Here, we report that three members of the holocyclotoxin family; HT-1 (GenBank AY766147), HT-3 (GenBank KP096303) and HT-12 (GenBank KP963967) induce muscle paralysis by inhibiting the dependence of transmitter release on extracellular calcium. Previous study was conducted using extracts from tick salivary glands, while the present study is the first to use pure toxins from I. holocyclus. Our findings provide greater insight into the mechanisms by which these toxins act to induce paralysis.
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Affiliation(s)
- Kirat K Chand
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
| | - Kah Meng Lee
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
| | - Nickolas A Lavidis
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
| | - Manuel Rodriguez-Valle
- Queensland Alliance for Agriculture &Food Innovation, The University of Queensland, QLD, Australia
| | - Hina Ijaz
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
| | - Johannes Koehbach
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
| | - Richard J Clark
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
| | - Ala Lew-Tabor
- Queensland Alliance for Agriculture &Food Innovation, The University of Queensland, QLD, Australia.,Centre for Comparative Genomics, Murdoch University, Perth, WA 6150, Australia
| | - Peter G Noakes
- School of Biomedical Sciences, The University of Queensland, St Lucia, 4067, Australia
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30
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Insight into the Mode of Action of Haedoxan A from Phryma leptostachya. Toxins (Basel) 2016; 8:53. [PMID: 26907348 PMCID: PMC4773806 DOI: 10.3390/toxins8020053] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2015] [Revised: 02/14/2016] [Accepted: 02/15/2016] [Indexed: 11/26/2022] Open
Abstract
Haedoxan A (HA) is a major active ingredient in the herbaceous perennial plant lopseed (Phryma leptostachya L.), which is used as a natural insecticide against insect pests in East Asia. Here, we report that HA delayed the decay rate of evoked excitatory junctional potentials (EJPs) and increased the frequency of miniature EJPs (mEJPs) on the Drosophila neuromuscular junction. HA also caused a significant hyperpolarizing shift of the voltage dependence of fast inactivation of insect sodium channels expressed in Xenopus oocytes. Our results suggest that HA acts on both axonal conduction and synaptic transmission, which can serve as a basis for elucidating the mode of action of HA for further designing and developing new effective insecticides.
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31
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An Adaptable Spectrin/Ankyrin-Based Mechanism for Long-Range Organization of Plasma Membranes in Vertebrate Tissues. CURRENT TOPICS IN MEMBRANES 2015; 77:143-84. [PMID: 26781832 DOI: 10.1016/bs.ctm.2015.10.001] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Ankyrins are membrane-associated proteins that together with their spectrin partners are responsible for micron-scale organization of vertebrate plasma membranes, including those of erythrocytes, excitable membranes of neurons and heart, lateral membrane domains of columnar epithelial cells, and striated muscle. Ankyrins coordinate functionally related membrane transporters and cell adhesion proteins (15 protein families identified so far) within plasma membrane compartments through independently evolved interactions of intrinsically disordered sequences with a highly conserved peptide-binding groove formed by the ANK repeat solenoid. Ankyrins are coupled to spectrins, which are elongated organelle-sized proteins that form mechanically resilient arrays through cross-linking by specialized actin filaments. In addition to protein interactions, cellular targeting and assembly of spectrin/ankyrin domains also critically depend on palmitoylation of ankyrin-G by aspartate-histidine-histidine-cysteine 5/8 palmitoyltransferases, as well as interaction of beta-2 spectrin with phosphoinositide lipids. These lipid-dependent spectrin/ankyrin domains are not static but are locally dynamic and determine membrane identity through opposing endocytosis of bulk lipids as well as specific proteins. A partnership between spectrin, ankyrin, and cell adhesion molecules first emerged in bilaterians over 500 million years ago. Ankyrin and spectrin may have been recruited to plasma membranes from more ancient roles in organelle transport. The basic bilaterian spectrin-ankyrin toolkit markedly expanded in vertebrates through gene duplications combined with variation in unstructured intramolecular regulatory sequences as well as independent evolution of ankyrin-binding activity by ion transporters involved in action potentials and calcium homeostasis. In addition, giant vertebrate ankyrins with specialized roles in axons acquired new coding sequences by exon shuffling. We speculate that early axon initial segments and epithelial lateral membranes initially were based on spectrin-ankyrin-cell adhesion molecule assemblies and subsequently served as "incubators," where ion transporters independently acquired ankyrin-binding activity through positive selection.
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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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Tintignac LA, Brenner HR, Rüegg MA. Mechanisms Regulating Neuromuscular Junction Development and Function and Causes of Muscle Wasting. Physiol Rev 2015; 95:809-52. [DOI: 10.1152/physrev.00033.2014] [Citation(s) in RCA: 224] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The neuromuscular junction is the chemical synapse between motor neurons and skeletal muscle fibers. It is designed to reliably convert the action potential from the presynaptic motor neuron into the contraction of the postsynaptic muscle fiber. Diseases that affect the neuromuscular junction may cause failure of this conversion and result in loss of ambulation and respiration. The loss of motor input also causes muscle wasting as muscle mass is constantly adapted to contractile needs by the balancing of protein synthesis and protein degradation. Finally, neuromuscular activity and muscle mass have a major impact on metabolic properties of the organisms. This review discusses the mechanisms involved in the development and maintenance of the neuromuscular junction, the consequences of and the mechanisms involved in its dysfunction, and its role in maintaining muscle mass during aging. As life expectancy is increasing, loss of muscle mass during aging, called sarcopenia, has emerged as a field of high medical need. Interestingly, aging is also accompanied by structural changes at the neuromuscular junction, suggesting that the mechanisms involved in neuromuscular junction maintenance might be disturbed during aging. In addition, there is now evidence that behavioral paradigms and signaling pathways that are involved in longevity also affect neuromuscular junction stability and sarcopenia.
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Affiliation(s)
- Lionel A. Tintignac
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Hans-Rudolf Brenner
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Markus A. Rüegg
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
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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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Auditory neuroplasticity, hearing loss and cochlear implants. Cell Tissue Res 2014; 361:251-69. [DOI: 10.1007/s00441-014-2004-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/04/2014] [Indexed: 10/24/2022]
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Brenner HR, Akaaboune M. Recycling of acetylcholine receptors at ectopic postsynaptic clusters induced by exogenous agrin in living rats. Dev Biol 2014; 394:122-8. [PMID: 25093969 DOI: 10.1016/j.ydbio.2014.07.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Revised: 06/16/2014] [Accepted: 07/18/2014] [Indexed: 10/24/2022]
Abstract
During the development of the neuromuscular junction, motor axons induce the clustering of acetylcholine receptors (AChRs) and increase their metabolic stability in the muscle membrane. Here, we asked whether the synaptic organizer agrin might regulate the metabolic stability and density of AChRs by promoting the recycling of internalized AChRs, which would otherwise be destined for degradation, into synaptic sites. We show that at nerve-free AChR clusters induced by agrin in extrasynaptic membrane, internalized AChRs are driven back into the ectopic synaptic clusters where they intermingle with pre-existing and new receptors. The extent of AChR recycling depended on the strength of the agrin stimulus, but not on the development of junctional folds, another hallmark of mature postsynaptic membranes. In chronically denervated muscles, in which both AChR stability and recycling are significantly decreased by muscle inactivity, agrin maintained the amount of recycled AChRs at agrin-induced clusters at a level similar to that at denervated original endplates. In contrast, AChRs did not recycle at agrin-induced clusters in C2C12 or primary myotubes. Thus, in muscles in vivo, but not in cultured myotubes, neural agrin promotes the recycling of AChRs and thereby increases their metabolic stability.
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Affiliation(s)
- Hans Rudolf Brenner
- Department of Biomedicine, University of Basel, Pharmazentrum, Klingelbergstrasse 50, CH-4056 Basel, Switzerland.
| | - Mohammed Akaaboune
- Department of Molecular, Cellular, and Developmental Biology and Program in Neuroscience, University of Michigan, Ann Arbor, MI 48109, USA.
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Ankyrin-3 is a novel binding partner of the voltage-gated potassium channel Kv1.1 implicated in renal magnesium handling. Kidney Int 2013; 85:94-102. [PMID: 23903368 DOI: 10.1038/ki.2013.280] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 05/16/2013] [Accepted: 05/23/2013] [Indexed: 11/08/2022]
Abstract
The voltage-gated potassium channel, Kv1.1, was recently identified as a causative gene in isolated dominant hypomagnesemia. The channel is situated in the distal convoluted tubule, where it participates in maintaining a favorable electrical gradient for driving magnesium ion into the cell through the transient receptor potential melastatin 6 channel. Pull-down experiments coupled to mass spectrometry using the carboxy-terminal domain of Kv1.1 as bait were used in mouse kidney lysates. Ankyrin-3 (ANK3) was identified as a binding partner of Kv1.1 and was enriched in isolated distal convoluted tubules as compared to whole kidney. Electrophysiology studies performed in HEK293 cells expressing Kv1.1 showed that ANK3 significantly inhibited Kv1.1-mediated currents (267 compared to 125 pA/pF) for control and ANK3, respectively. Finally, to evaluate a potential role of ANK3 in magnesium handling, the intrarenal abundance of ANK3 was measured in mice fed a low-, normal-, or high-magnesium diet for 10 days. Mice maintained on high dietary magnesium significantly doubled their fractional urinary excretion of magnesium, which coincided with a 1.8-fold increase in the renal expression of ANK3 compared to mice on a normal- or low-magnesium diet. Thus, our observations demonstrate a novel role for ANK3 in modulating the biophysical properties of Kv1.1. Such regulation appears to be particularly important in conditions of high dietary magnesium.
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Kline CF, Mohler PJ. Defective interactions of protein partner with ion channels and transporters as alternative mechanisms of membrane channelopathies. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:723-30. [PMID: 23732236 DOI: 10.1016/j.bbamem.2013.05.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 05/15/2013] [Accepted: 05/21/2013] [Indexed: 01/27/2023]
Abstract
The past twenty years have revealed the existence of numerous ion channel mutations resulting in human pathology. Ion channels provide the basis of diverse cellular functions, ranging from hormone secretion, excitation-contraction coupling, cell signaling, immune response, and trans-epithelial transport. Therefore, the regulation of biophysical properties of channels is vital in human physiology. Only within the last decade has the role of non-ion channel components come to light in regard to ion channel spatial, temporal, and biophysical regulation in physiology. A growing number of auxiliary components have been determined to play elemental roles in excitable cell physiology, with dysfunction resulting in disorders and related manifestations. This review focuses on the broad implications of such dysfunction, focusing on disease-causing mutations that alter interactions between ion channels and auxiliary ion channel components in a diverse set of human excitable cell disease. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé
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Affiliation(s)
- Crystal F Kline
- The Dorothy M. Davis Heart and Lung Research Institute, Department of Internal Medicine, Division of Cardiovascular Medicine, Department of Physiology & Cell Biology, The Ohio State University Wexner Medical Center, USA
| | - Peter J Mohler
- The Dorothy M. Davis Heart and Lung Research Institute, Department of Internal Medicine, Division of Cardiovascular Medicine, Department of Physiology & Cell Biology, The Ohio State University Wexner Medical Center, USA.
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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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Savio-Galimberti E, Gollob MH, Darbar D. Voltage-gated sodium channels: biophysics, pharmacology, and related channelopathies. Front Pharmacol 2012; 3:124. [PMID: 22798951 PMCID: PMC3394224 DOI: 10.3389/fphar.2012.00124] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Accepted: 06/11/2012] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated sodium channels (VGSC) are multi-molecular protein complexes expressed in both excitable and non-excitable cells. They are primarily formed by a pore-forming multi-spanning integral membrane glycoprotein (α-subunit) that can be associated with one or more regulatory β-subunits. The latter are single-span integral membrane proteins that modulate the sodium current (INa) and can also function as cell adhesion molecules. In vitro some of the cell-adhesive functions of the β-subunits may play important physiological roles independently of the α-subunits. Other endogenous regulatory proteins named “channel partners” or “channel interacting proteins” (ChiPs) like caveolin-3 and calmodulin/calmodulin kinase II (CaMKII) can also interact and modulate the expression and/or function of VGSC. In addition to their physiological roles in cell excitability and cell adhesion, VGSC are the site of action of toxins (like tetrodotoxin and saxitoxin), and pharmacologic agents (like antiarrhythmic drugs, local anesthetics, antiepileptic drugs, and newly developed analgesics). Mutations in genes that encode α- and/or β-subunits as well as the ChiPs can affect the structure and biophysical properties of VGSC, leading to the development of diseases termed sodium “channelopathies”. This review will outline the structure, function, and biophysical properties of VGSC as well as their pharmacology and associated channelopathies and highlight some of the recent advances in this field.
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Affiliation(s)
- Eleonora Savio-Galimberti
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Nashville, TN, 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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Malomouzh AI, Nurullin LF, Arkhipova SS, Nikolsky EE. NMDA receptors at the endplate of rat skeletal muscles: Precise postsynaptic localization. Muscle Nerve 2011; 44:987-9. [DOI: 10.1002/mus.22250] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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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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Abstract
Mammalian skeletal muscle comprises different fiber types, whose identity is first established during embryonic development by intrinsic myogenic control mechanisms and is later modulated by neural and hormonal factors. The relative proportion of the different fiber types varies strikingly between species, and in humans shows significant variability between individuals. Myosin heavy chain isoforms, whose complete inventory and expression pattern are now available, provide a useful marker for fiber types, both for the four major forms present in trunk and limb muscles and the minor forms present in head and neck muscles. However, muscle fiber diversity involves all functional muscle cell compartments, including membrane excitation, excitation-contraction coupling, contractile machinery, cytoskeleton scaffold, and energy supply systems. Variations within each compartment are limited by the need of matching fiber type properties between different compartments. Nerve activity is a major control mechanism of the fiber type profile, and multiple signaling pathways are implicated in activity-dependent changes of muscle fibers. The characterization of these pathways is raising increasing interest in clinical medicine, given the potentially beneficial effects of muscle fiber type switching in the prevention and treatment of metabolic diseases.
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Affiliation(s)
- Stefano Schiaffino
- Venetian Institute of Molecular Medicine, Department of Biomedical Sciences, University of Padova, Consiglio Nazionale delle Ricerche Institute of Neurosciences, and Department of Human Anatomy and Physiology, University of Padova, Padova, Italy
| | - Carlo Reggiani
- Venetian Institute of Molecular Medicine, Department of Biomedical Sciences, University of Padova, Consiglio Nazionale delle Ricerche Institute of Neurosciences, and Department of Human Anatomy and Physiology, University of Padova, Padova, Italy
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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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Martin AR. Amplification of neuromuscular transmission by postjunctional folds. Proc Biol Sci 2011; 258:321-6. [PMID: 21710792 DOI: 10.1098/rspb.1994.0180] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Previously, suggestions have been made that postjunctional folds at the vertebrate motor end plate might, in some way, serve to enhance neuromuscular transmission. This suggestion was examined quantitatively using a model junction with geometry similar to that seen in mammalian 'fast twitch' muscles. It was found that the depolarization produced at the top of an interfold by a quantum of acetylcholine is significantly greater than that produced in the absence of folds because of the series resistance of the interfold myoplasm. As a result, voltage-sensitive sodium channels in the postsynaptic membrane are activated more readily. In the model, activation of as few as four interfolds by eight quanta is sufficient for excitation to spread to the remainder of the muscle. With no folds, 19 quanta are required.
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Affiliation(s)
- A R Martin
- Department of Physiology C240, University of Colorado School of Medicine, Denver, Colorado 80262, U.S.A
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Selcen D, Juel VC, Hobson-Webb LD, Smith EC, Stickler DE, Bite AV, Ohno K, Engel AG. Myasthenic syndrome caused by plectinopathy. Neurology 2011; 76:327-36. [PMID: 21263134 DOI: 10.1212/wnl.0b013e31820882bd] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Plectin crosslinks intermediate filaments to their targets in different tissues. Defects in plectin cause epidermolysis bullosa simplex (EBS), muscular dystrophy (MD), and sometimes pyloric atresia. Association of EBS with a myasthenic syndrome (MyS) was documented in a single patient in 1999. OBJECTIVES To analyze the clinical, structural, and genetic aspects of a second and fatal case of EBS associated with a MyS and search for the genetic basis of the disease in a previously reported patient with EBS-MD-MyS. METHODS Clinical observations; histochemical, immunocytochemical, and electron microscopy studies of skeletal muscle and neuromuscular junction; and mutation analysis. RESULTS An African American man had EBS since early infancy, and progressive muscle weakness, hyperCKemia, and myasthenic symptoms refractory to therapy since age 3 years. Eventually he became motionless and died at age 42 years. At age 15 years, he had a marked EMG decrement, and a reduced miniature endplate potential amplitude. The myopathy was associated with dislocated muscle fiber organelles, structurally abnormal nuclei, focal plasmalemmal defects, and focal calcium ingress into muscle fibers. The neuromuscular junctions showed destruction of the junctional folds, and remodeling. Mutation analysis demonstrated a known p.Arg2319X and a novel c.12043dupG mutation in PLEC1. The EBS-MD-MyS patient reported in 1999 also carried c.12043dupG and a novel p.Gln2057X mutation. The novel mutations were absent in 200 Caucasian and 100 African American subjects. CONCLUSIONS The MyS in plectinopathy is attributed to destruction of the junctional folds and the myopathy to defective anchoring of muscle fiber organelles and defects in sarcolemmal integrity.
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Affiliation(s)
- D Selcen
- Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA
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Piitulainen H, Botter A, Merletti R, Avela J. Muscle fiber conduction velocity is more affected after eccentric than concentric exercise. Eur J Appl Physiol 2010; 111:261-73. [PMID: 20865423 DOI: 10.1007/s00421-010-1652-y] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/08/2010] [Indexed: 11/30/2022]
Affiliation(s)
- Harri Piitulainen
- Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä, P.O. Box 35, 40014, Jyväskylä, Finland.
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Modla S, Mendonca J, Czymmek KJ, Akins RE. Identification of neuromuscular junctions by correlative confocal and transmission electron microscopy. J Neurosci Methods 2010; 191:158-65. [PMID: 20600319 DOI: 10.1016/j.jneumeth.2010.06.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 06/07/2010] [Accepted: 06/16/2010] [Indexed: 11/16/2022]
Abstract
The physiological processes regulating neuromuscular transmission are highly dependent on the structural features of the motor neuron and motor endplate, and detailing the structure of neuromuscular junctions (NMJs) in muscle biopsies is a powerful method for research and diagnostics. The observation of NMJ ultrastructure, however, is complicated by the difficulty in locating NMJs for analysis by electron microscopy. Consequently, a correlative confocal-transmission electron microscopy method was developed. Fixed muscle samples were cryo-protected in sucrose, sectioned on a cryostat, and stained with fluorescent alpha-bungarotoxin for confocal microscopy. Sections containing junctions were mapped and then processed for transmission electron microscopy (TEM). Cryostat sections allowed large expanses of muscle tissue to be rapidly screened and enabled specific junctions to be targeted for TEM. The morphology of the junctions was well preserved with all essential features of the pre- and postsynaptic elements readily identifiable without freeze damage. Unlike NMJ correlative methods using histochemical stains and DAB photo-oxidation, no electron dense precipitate was deposited over the NMJ, enabling an unobstructed view of the pre- and postsynaptic structures.
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Affiliation(s)
- Shannon Modla
- Delaware Biotechnology Institute Bio-Imaging Center, University of Delaware, 15 Innovation Way, Suite 117, Newark, DE 19711, USA
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Understanding the in vitro neuromuscular activity of snake venom Lys49 phospholipase A2 homologues. Toxicon 2010; 55:1-11. [DOI: 10.1016/j.toxicon.2009.10.025] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Revised: 07/22/2009] [Accepted: 10/01/2009] [Indexed: 11/24/2022]
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