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Chen J, Chen H, Dong X, Hui T, Yan M, Ren D, Zou S, Wang S, Fei E, Zhang W, Lai X. Deficiency of skeletal muscle Agrin contributes to the pathogenesis of age-related sarcopenia in mice. Cell Death Dis 2024; 15:201. [PMID: 38461287 PMCID: PMC10925061 DOI: 10.1038/s41419-024-06581-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 02/28/2024] [Accepted: 02/29/2024] [Indexed: 03/11/2024]
Abstract
Sarcopenia, a progressive and prevalent neuromuscular disorder, is characterized by age-related muscle wasting and weakening. Despite its widespread occurrence, the molecular underpinnings of this disease remain poorly understood. Herein, we report that levels of Agrin, an extracellular matrix (ECM) protein critical for neuromuscular formation, were decreased with age in the skeletal muscles of mice. The conditional loss of Agrin in myogenic progenitors and satellite cells (SCs) (Pax7 Cre:: Agrin flox/flox) causes premature muscle aging, manifesting a distinct sarcopenic phenotype in mice. Conversely, the elevation of a miniaturized form of Agrin in skeletal muscle through adenovirus-mediated gene transfer induces enhanced muscle capacity in aged mice. Mechanistic investigations suggest that Agrin-mediated improvement in muscle function occurs through the stimulation of Yap signaling and the concurrent upregulation of dystroglycan expression. Collectively, our findings underscore the pivotal role of Agrin in the aging process of skeletal muscles and propose Agrin as a potential therapeutic target for addressing sarcopenia.
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Affiliation(s)
- Jie Chen
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Hong Chen
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- School of Life Science, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Xia Dong
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Tiankun Hui
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- School of Life Science, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Min Yan
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Dongyan Ren
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- School of Life Science, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Suqi Zou
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Shunqi Wang
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Erkang Fei
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Wenhua Zhang
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China
| | - Xinsheng Lai
- School of Basic Medical Sciences, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China.
- Institute of Biomedical Innovation, Jiangxi Medical College, Nanchang University, Nanchang, 330031, Jiangxi, China.
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Volpe P, Bosutti A, Nori A, Filadi R, Gherardi G, Trautmann G, Furlan S, Massaria G, Sciancalepore M, Megighian A, Caccin P, Bernareggi A, Salanova M, Sacchetto R, Sandonà D, Pizzo P, Lorenzon P. Nerve-dependent distribution of subsynaptic type 1 inositol 1,4,5-trisphosphate receptor at the neuromuscular junction. J Gen Physiol 2022; 154:213498. [PMID: 36149386 PMCID: PMC9513380 DOI: 10.1085/jgp.202213128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 08/30/2022] [Accepted: 09/09/2022] [Indexed: 11/20/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3Rs) are enriched at postsynaptic membrane compartments of the neuromuscular junction (NMJ), surrounding the subsynaptic nuclei and close to nicotinic acetylcholine receptors (nAChRs) of the motor endplate. At the endplate level, it has been proposed that nerve-dependent electrical activity might trigger IP3-associated, local Ca2+ signals not only involved in excitation-transcription (ET) coupling but also crucial to the development and stabilization of the NMJ itself. The present study was undertaken to examine whether denervation affects the subsynaptic IP3R distribution in skeletal muscles and which are the underlying mechanisms. Fluorescence microscopy, carried out on in vivo denervated muscles (following sciatectomy) and in vitro denervated skeletal muscle fibers from flexor digitorum brevis (FDB), indicates that denervation causes a reduction in the subsynaptic IP3R1-stained region, and such a decrease appears to be determined by the lack of muscle electrical activity, as judged by partial reversal upon field electrical stimulation of in vitro denervated skeletal muscle fibers.
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Affiliation(s)
- Pompeo Volpe
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
- Correspondence to Pompeo Volpe:
| | | | - Alessandra Nori
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
| | - Riccardo Filadi
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
- National Research Council, Neuroscience Institute, Padova, Italy
| | - Gaia Gherardi
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
| | - Gabor Trautmann
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Institute of Integrative Neuroanatomy, Berlin, Germany
| | - Sandra Furlan
- National Research Council, Neuroscience Institute, Padova, Italy
| | | | | | - Aram Megighian
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
| | - Paola Caccin
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
| | | | - Michele Salanova
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Institute of Integrative Neuroanatomy, Berlin, Germany
- Neuromuscular Signaling, Center of Space Medicine Berlin, Berlin, Germany
| | - Roberta Sacchetto
- Department of Comparative Biomedicine and Food Science, University of Padova, Padova, Italy
| | - Dorianna Sandonà
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
| | - Paola Pizzo
- Department of Biomedical Sciences and Interdepartmental Research Center of Myology (cirMYO), University of Padova, Padova, Italy
- National Research Council, Neuroscience Institute, Padova, Italy
| | - Paola Lorenzon
- Department of Life Sciences, University of Trieste, Trieste, Italy
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Huang X, Jiang J, Xu J. Denervation-Related Neuromuscular Junction Changes: From Degeneration to Regeneration. Front Mol Neurosci 2022; 14:810919. [PMID: 35282655 PMCID: PMC8908450 DOI: 10.3389/fnmol.2021.810919] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 12/30/2021] [Indexed: 11/13/2022] Open
Abstract
Neuromuscular junctions (NMJs) are the key interface between terminal nerves and targeted muscle, which undergo degeneration during denervation periods. Denervation-related NMJs changes limits the recovery level of nerve repair strategies. Insights into mechanisms behind neuromuscular junction degeneration and regeneration, following denervation and reinnervation, are of clinical value. Developing some therapies to maintain or protect structures and functions of NMJs may contribute to a better prognosis. Here, we reviewed previous studies of NMJs focusing on the morphological, functional, and molecular changes after denervation, and if those changes can be reversed after reinnervation. Also, we reviewed about the present probable strategies that have been applied clinically or could still be studied in targeting the neuromuscular junction protection or regeneration improvement.
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Affiliation(s)
- Xinying Huang
- Department of Hand Surgery, Huashan Hospital, Fudan University, Shanghai, China
- Shanghai Medical College, Fudan University, Shanghai, China
- Key Laboratory of Hand Reconstruction, Ministry of Health, Shanghai, China
- Shanghai Key Laboratory of Peripheral Nerve and Microsurgery, Shanghai, China
| | - Junjian Jiang
- Department of Hand Surgery, Huashan Hospital, Fudan University, Shanghai, China
- Key Laboratory of Hand Reconstruction, Ministry of Health, Shanghai, China
- Shanghai Key Laboratory of Peripheral Nerve and Microsurgery, Shanghai, China
- *Correspondence: Junjian Jiang,
| | - Jianguang Xu
- Department of Hand Surgery, Huashan Hospital, Fudan University, Shanghai, China
- Key Laboratory of Hand Reconstruction, Ministry of Health, Shanghai, China
- Shanghai Key Laboratory of Peripheral Nerve and Microsurgery, Shanghai, China
- Jianguang Xu,
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Martinez-Pena y Valenzuela I, Akaaboune M. The Metabolic Stability of the Nicotinic Acetylcholine Receptor at the Neuromuscular Junction. Cells 2021; 10:cells10020358. [PMID: 33572348 PMCID: PMC7916148 DOI: 10.3390/cells10020358] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Revised: 02/03/2021] [Accepted: 02/04/2021] [Indexed: 11/16/2022] Open
Abstract
The clustering and maintenance of nicotinic acetylcholine receptors (AChRs) at high density in the postsynaptic membrane is a hallmark of the mammalian neuromuscular junction (NMJ). The regulation of receptor density/turnover rate at synapses is one of the main thrusts of neurobiology because it plays an important role in synaptic development and synaptic plasticity. The state-of-the-art imaging revealed that AChRs are highly dynamic despite the overall structural stability of the NMJ over the lifetime of the animal. This review highlights the work on the metabolic stability of AChRs at developing and mature NMJs and discusses the role of synaptic activity and the regulatory signaling pathways involved in the dynamics of AChRs.
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Affiliation(s)
| | - Mohammed Akaaboune
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA;
- Program in Neuroscience, University of Michigan, Ann Arbor, MI 48109, USA
- Correspondence: ; Tel.: +1-73-(46)-478512; Fax: +1-73-(46)-470884
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Zelada D, Bermedo-García F, Collao N, Henríquez JP. Motor function recovery: deciphering a regenerative niche at the neuromuscular synapse. Biol Rev Camb Philos Soc 2020; 96:752-766. [PMID: 33336525 PMCID: PMC7986695 DOI: 10.1111/brv.12675] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 11/20/2020] [Accepted: 11/25/2020] [Indexed: 12/13/2022]
Abstract
The coordinated movement of many organisms relies on efficient nerve–muscle communication at the neuromuscular junction (NMJ), a peripheral synapse composed of a presynaptic motor axon terminal, a postsynaptic muscle specialization, and non‐myelinating terminal Schwann cells. NMJ dysfunctions are caused by traumatic spinal cord or peripheral nerve injuries as well as by severe motor pathologies. Compared to the central nervous system, the peripheral nervous system displays remarkable regenerating abilities; however, this capacity is limited by the denervation time frame and depends on the establishment of permissive regenerative niches. At the injury site, detailed information is available regarding the cells, molecules, and mechanisms involved in nerve regeneration and repair. However, a regenerative niche at the final functional step of peripheral motor innervation, i.e. at the mature neuromuscular synapse, has not been deciphered. In this review, we integrate classic and recent evidence describing the cells and molecules that could orchestrate a dynamic ecosystem to accomplish successful NMJ regeneration. We propose that such a regenerative niche must ensure at least two fundamental steps for successful NMJ regeneration: the proper arrival of incoming regenerating axons to denervated postsynaptic muscle domains, and the resilience of those postsynaptic domains, in morphological and functional terms. We here describe and combine the main cellular and molecular responses involved in each of these steps as potential targets to help successful NMJ regeneration.
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Affiliation(s)
- Diego Zelada
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
| | - Francisca Bermedo-García
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
| | - Nicolás Collao
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
| | - Juan P Henríquez
- Neuromuscular Studies Laboratory (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA Bio-Bio), Universidad de Concepción, Casilla 160-C, Concepción, Chile
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Grönholdt‐Klein M, Altun M, Becklén M, Dickman Kahm E, Fahlström A, Rullman E, Ulfhake B. Muscle atrophy and regeneration associated with behavioural loss and recovery of function after sciatic nerve crush. Acta Physiol (Oxf) 2019; 227:e13335. [PMID: 31199566 DOI: 10.1111/apha.13335] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2019] [Revised: 05/31/2019] [Accepted: 06/11/2019] [Indexed: 12/22/2022]
Abstract
AIM To resolve timing and coordination of denervation atrophy and the re-innervation recovery process to discern correlations indicative of common programs governing these processes. METHODS Female Sprague-Dawley (SD) rats had a unilateral sciatic nerve crush. Based on longitudinal behavioural observations, the triceps surae muscle was analysed at different time points post-lesion. RESULTS Crush results in a loss of muscle function and mass (-30%) followed by a recovery to almost pre-lesion status at 30 days post-crush (dpc). There was no loss of fibres nor any significant change in the number of nuclei per fibre but a shift in fibres expressing myosins I and II that reverted back to control levels at 30 dpc. A residual was the persistence of hybrid fibres. Early on a CHNR -ε to -γ switch and a re-expression of embryonic MyHC showed as signs of denervation. Foxo1, Smad3, Fbxo32 and Trim63 transcripts were upregulated but not Myostatin, InhibinA and ActivinR2B. Combined this suggests that the mechanism instigating atrophy provides a selectivity of pathway(s) activated. The myogenic differentiation factors (MDFs: Myog, Myod1 and Myf6) were upregulated early on suggesting a role also in the initial atrophy. The regulation of these transcripts returned towards baseline at 30 dpc. The examined genes showed a strong baseline covariance in transcript levels which dissolved in the response to crush driven mainly by the MDFs. At 30 dpc the naïve expression pattern was re-established. CONCLUSION Peripheral nerve crush offers an excellent model to assess and interfere with muscle adaptions to denervation and re-innervation.
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Affiliation(s)
| | - Mikael Altun
- Department of Laboratory Medicine Karolinska Institutet Huddinge Sweden
| | - Meneca Becklén
- Department of Neuroscience Karolinska Institutet Stockholm Sweden
| | | | - Andreas Fahlström
- Department of Neuroscience Karolinska Institutet Stockholm Sweden
- Department of Neuroscience, Neurosurgery Uppsala University Uppsala Sweden
| | - Eric Rullman
- Department of Laboratory Medicine Karolinska Institutet Huddinge Sweden
| | - Brun Ulfhake
- Department of Neuroscience Karolinska Institutet Stockholm Sweden
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Scherbakov N, Knops M, Ebner N, Valentova M, Sandek A, Grittner U, Dahinden P, Hettwer S, Schefold JC, von Haehling S, Anker SD, Joebges M, Doehner W. Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation. J Cachexia Sarcopenia Muscle 2016; 7:60-7. [PMID: 27066319 PMCID: PMC4799857 DOI: 10.1002/jcsm.12068] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 07/15/2015] [Accepted: 07/31/2015] [Indexed: 01/15/2023] Open
Abstract
BACKGROUND C-terminal Agrin Fragment (CAF) has been proposed as a novel biomarker for sarcopenia originating from the degeneration of the neuromuscular junctions. In patients with stroke muscle wasting is a common observation that predicts functional outcome. We aimed to evaluate agrin sub-fragment CAF22 as a marker of decreased muscle mass and physical performance in the early phase after acute stroke. METHODS Patients with acute ischaemic or haemorrhagic stroke (n = 123, mean age 70 ± 11 y, body mass index BMI 27.0 ± 4.9 kg/m(2)) admitted to inpatient rehabilitation were studied in comparison to 26 healthy controls of similar age and BMI. Functional assessments were performed at begin (23 ± 17 days post stroke) and at the end of the structured rehabilitation programme (49 ± 18 days post stroke) that included physical assessment, maximum hand grip strength, Rivermead motor assessment, and Barthel index. Body composition was assessed by bioelectrical impedance analysis (BIA). Serum levels of CAF22 were measured by ELISA. RESULTS CAF22 levels were elevated in stroke patients at admission (134.3 ± 52.3 pM) and showed incomplete recovery until discharge (118.2 ± 42.7 pM) compared to healthy controls (95.7 ± 31.8 pM, p < 0.001). Simple regression analyses revealed an association between CAF22 levels and parameters of physical performance, hand grip strength, and phase angle, a BIA derived measure of the muscle cellular integrity. Improvement of the handgrip strength of the paretic arm during rehabilitation was independently related to the recovery of CAF22 serum levels only in those patients who showed increased lean mass during the rehabilitation. CONCLUSIONS CAF22 serum profiles showed a dynamic elevation and recovery in the subacute phase after acute stroke. Further studies are needed to explore the potential of CAF22 as a serum marker to monitor the muscle status in patients after stroke.
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Affiliation(s)
- Nadja Scherbakov
- Center for Stroke Research CSB Charite Universitätsmedizin Berlin Germany; German Centre for Cardiovascular Research (DZHK), partner site Berlin Germany
| | - Michael Knops
- Center for Stroke Research CSB Charite Universitätsmedizin Berlin Germany
| | - Nicole Ebner
- Innovative Clinical Trials, Department of Cardiology and Pneumology University Medicine Göttingen Germany
| | - Miroslava Valentova
- Innovative Clinical Trials, Department of Cardiology and Pneumology University Medicine Göttingen Germany; 1st Department of Internal Medicine Comenius University Bratislava Slovak Republic
| | - Anja Sandek
- Innovative Clinical Trials, Department of Cardiology and Pneumology University Medicine Göttingen Germany
| | - Ulrike Grittner
- Center for Stroke Research CSB Charite Universitätsmedizin Berlin Germany
| | | | | | - Jörg C Schefold
- Department of Intensive Care Medicine Inselspital, University Hospital of Bern Switzerland
| | - Stephan von Haehling
- Innovative Clinical Trials, Department of Cardiology and Pneumology University Medicine Göttingen Germany
| | - Stefan D Anker
- Innovative Clinical Trials, Department of Cardiology and Pneumology University Medicine Göttingen Germany
| | | | - Wolfram Doehner
- Center for Stroke Research CSB Charite Universitätsmedizin Berlin Germany; German Centre for Cardiovascular Research (DZHK), partner site Berlin Germany; Department of Cardiology Charite Universitätsmedizin Berlin Germany
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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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Yampolsky P, Pacifici PG, Witzemann V. Differential muscle-driven synaptic remodeling in the neuromuscular junction after denervation. Eur J Neurosci 2010; 31:646-58. [DOI: 10.1111/j.1460-9568.2010.07096.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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10
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Glutamatergic Reinnervation and Assembly of Glutamatergic Synapses in Adult Rat Skeletal Muscle Occurs at Cholinergic Endplates. J Neuropathol Exp Neurol 2009; 68:1103-15. [PMID: 19918122 DOI: 10.1097/nen.0b013e3181b7bfc8] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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11
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Röder IV, Petersen Y, Choi KR, Witzemann V, Hammer JA, Rudolf R. Role of Myosin Va in the plasticity of the vertebrate neuromuscular junction in vivo. PLoS One 2008; 3:e3871. [PMID: 19057648 PMCID: PMC2587709 DOI: 10.1371/journal.pone.0003871] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2008] [Accepted: 11/10/2008] [Indexed: 01/07/2023] Open
Abstract
Background Myosin Va is a motor protein involved in vesicular transport and its absence leads to movement disorders in humans (Griscelli and Elejalde syndromes) and rodents (e.g. dilute lethal phenotype in mice). We examined the role of myosin Va in the postsynaptic plasticity of the vertebrate neuromuscular junction (NMJ). Methodology/Principal Findings Dilute lethal mice showed a good correlation between the propensity for seizures, and fragmentation and size reduction of NMJs. In an aneural C2C12 myoblast cell culture, expression of a dominant-negative fragment of myosin Va led to the accumulation of punctate structures containing the NMJ marker protein, rapsyn-GFP, in perinuclear clusters. In mouse hindlimb muscle, endogenous myosin Va co-precipitated with surface-exposed or internalised acetylcholine receptors and was markedly enriched in close proximity to the NMJ upon immunofluorescence. In vivo microscopy of exogenous full length myosin Va as well as a cargo-binding fragment of myosin Va showed localisation to the NMJ in wildtype mouse muscles. Furthermore, local interference with myosin Va function in live wildtype mouse muscles led to fragmentation and size reduction of NMJs, exclusion of rapsyn-GFP from NMJs, reduced persistence of acetylcholine receptors in NMJs and an increased amount of punctate structures bearing internalised NMJ proteins. Conclusions/Significance In summary, our data show a crucial role of myosin Va for the plasticity of live vertebrate neuromuscular junctions and suggest its involvement in the recycling of internalised acetylcholine receptors back to the postsynaptic membrane.
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Affiliation(s)
- Ira Verena Röder
- Institute of Toxicology and Genetics, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Germany
| | - Yvonne Petersen
- Institute of Toxicology and Genetics, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Germany
| | - Kyeong Rok Choi
- Institute of Toxicology and Genetics, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Germany
| | - Veit Witzemann
- Max-Planck-Institute for Medical Research, Heidelberg, Germany
| | - John A. Hammer
- Laboratory of Cell Biology, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Rüdiger Rudolf
- Institute of Toxicology and Genetics, Research Center Karlsruhe, Eggenstein-Leopoldshafen, Germany
- * E-mail:
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12
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Brockhausen J, Cole RN, Gervásio OL, Ngo ST, Noakes PG, Phillips WD. Neural agrin increases postsynaptic ACh receptor packing by elevating rapsyn protein at the mouse neuromuscular synapse. Dev Neurobiol 2008; 68:1153-69. [PMID: 18506821 DOI: 10.1002/dneu.20654] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Fluorescence resonance energy transfer (FRET) experiments at neuromuscular junctions in the mouse tibialis anterior muscle show that postsynaptic acetylcholine receptors (AChRs) become more tightly packed during the first month of postnatal development. Here, we report that the packing of AChRs into postsynaptic aggregates was reduced in 4-week postnatal mice that had reduced amounts of the AChR-associated protein, rapsyn, in the postsynaptic membrane (rapsyn(+/-) mice). We hypothesize that nerve-derived agrin increases postsynaptic expression and targeting of rapsyn, which then drives the developmental increase in AChR packing. Neural agrin treatment elevated the expression of rapsyn in C2 myotubes by a mechanism that involved slowing of rapsyn protein degradation. Similarly, exposure of synapses in postnatal muscle to exogenous agrin increased rapsyn protein levels and elevated the intensity of anti-rapsyn immunofluorescence, relative to AChR, in the postsynaptic membrane. This increase in the rapsyn-to-AChR immunofluorescence ratio was associated with tighter postsynaptic AChR packing and slowed AChR turnover. Acute blockade of synaptic AChRs with alpha-bungarotoxin lowered the rapsyn-to-AChR immunofluorescence ratio, suggesting that AChR signaling also helps regulate the assembly of extra rapsyn in the postsynaptic membrane. The results suggest that at the postnatal neuromuscular synapse agrin signaling elevates the expression and targeting of rapsyn to the postsynaptic membrane, thereby packing more AChRs into stable, functionally-important AChR aggregates.
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Affiliation(s)
- Jennifer Brockhausen
- School of Medical Sciences (Physiology), Bosch Institute, University of Sydney, Sydney, Australia
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Wu X, Gao H, Xiao D, Luo S, Zhao Z. Effects of tensile stress on the α1 nicotinic acetylcholine receptor expression in maxillofacial skeletal myocytes. Mol Cell Biochem 2007; 311:51-6. [DOI: 10.1007/s11010-007-9693-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2007] [Accepted: 12/17/2007] [Indexed: 01/15/2023]
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Santos HR, Ribeiro HS, Setti-Perdigão P, Albuquerque EX, Castro NG. The Magnitude of α7 Nicotinic Receptor Currents in Rat Hippocampal Neurons Is Dependent upon GABAergic Activity and Depolarization. J Pharmacol Exp Ther 2006; 319:376-85. [PMID: 16837558 DOI: 10.1124/jpet.106.106385] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hippocampal alpha7(*) nicotinic acetylcholine receptors modulate the release of GABA and glutamate. The control of functional receptor pools by cell firing or synaptic activity could therefore allow for a local adjustment of the sensitivity to cholinergic input upon changes in neuronal activity. We first investigated whether tonic depolarization or cell firing affected the function of alpha7(*). The amplitude of alpha7(*)-gated whole-cell currents in cultured rat hippocampal neurons exposed to high-extracellular K(+) (40 mM KCl) for 24 to 48 h increased 1.3 to 5.5 times. The proportion of alpha7(*)-responsive neurons (99%), the potency of acetylcholine, and the sensitivity to nicotinic antagonists were all unaffected. In contrast, block of spontaneous cell firing with tetrodotoxin for 24 h led to a 37% reduction in mean current amplitude. Reduced alpha7(*) responses were seen after a 24-h blockade of N-type calcium channels but not of L-type calcium channels, N-methyl-d-aspartate (NMDA), or non-NMDA receptor channels, protein kinase C, or calcium-calmodulin kinases II and IV. The N-type or L-type calcium channel antagonists omega-conotoxin GVIA and nifedipine did not prevent the current-potentiating effect of KCl. The GABA(A) antagonist picrotoxin led to a 44% reduction of the currents, despite increasing action potential firing, and also reversed the potentiating effect of KCl. Treatment with GABA, midazolam, or a GABA uptake blocker led to increased currents. These data indicate that alpha7(*)-gated currents in hippocampal neurons are regulated by GABAergic activity and suggest that depolarization-induced GABA release may underlie the effect of increased extracellular KCl.
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Affiliation(s)
- Hélio R Santos
- Departmento de Farmacologia Básica e Clínica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Rio de Janeiro, Brazil
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15
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Szabo M, Salpeter EE, Randall W, Salpeter MM. Transients in acetylcholine receptor site density and degradation during reinnervation of mouse sternomastoid muscle. J Neurochem 2003; 84:180-8. [PMID: 12485414 DOI: 10.1046/j.1471-4159.2003.01542.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The degradation rates of acetylcholine receptors (AchRs) were evaluated at the neuromuscular junction during and just after reinnervation of denervated muscles. When mouse sternomastoid muscles are denervated by multiple nerve crush, reinnervation begins 2-4 days later and is complete by day 7-9 after the last crush. In fully innervated muscles, the AChR degradation rate is stable and slow (t1/2 approximately 10 days), whereas after denervation the newly inserted receptors degrade rapidly (t1/2 approximately 1.2 days). The composite profile of degradation, which a mixture of the stable and the rapid receptors would give, is not observed during reinnervation. Instead, the receptors inserted between 2.5 and 7.5 days after the last crush all have an intermediate degradation rate of t1/2 approximately 3.7 days with standard error +/- 0.3 days. The total receptor site density at the endplate was evaluated during denervation and during reinnervation. As predicted theoretically, the site density increased substantially, but temporarily, after denervation. An analogous deleterious substantial decrease in density would be expected during reinnervation, without the intermediate receptor. This decrease is not observed, however, because of a large insertion rate at intermediate times (3000 +/- 700 receptor complexes per micro m2 per day). The endplate density of receptors thus remains relatively constant.
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Affiliation(s)
- Maria Szabo
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853, USA
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16
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Sava A, Barisone I, Di Mauro D, Fumagalli G, Sala C. Modulation of nicotinic acetylcholine receptor turnover by tyrosine phosphorylation in rat myotubes. Neurosci Lett 2001; 313:37-40. [PMID: 11684334 DOI: 10.1016/s0304-3940(01)02244-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The muscle nicotinic acetylcholine receptor (AChR) turns over at different rates depending on stage of synaptogenesis and innervation. Tyrosine phosphorylation modulates desensitization, interaction with cytoskeleton and lateral mobility in the membrane of AChR. To determine whether tyrosine phosphorylation also modulates the turnover of AChR, myotubes in vitro were exposed to the tyrosine phosphatase inhibitor pervanadate. Our data indicate that a transient increase of phosphotyrosine levels stabilized a fraction of AChRs. The effects were limited to the non-epsilon subunit-containing AChRs already present in the membrane. Tyrosine phosphorylation of the receptor occurred on the beta subunit, was transient and stable molecules were not selectively tyrosine phosphorylated. The data indicate that modulation of phosphotyrosine levels in muscle cells provides signals to control AChR metabolic stability.
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Affiliation(s)
- A Sava
- Department of Medicine & Public Health, Section of Pharmacology, School of Medicine, University of Verona, Policlinico Borgo Roma, 37134 Verona, Italy
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17
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Bezakova G, Rabben I, Sefland I, Fumagalli G, Lømo T. Neural agrin controls acetylcholine receptor stability in skeletal muscle fibers. Proc Natl Acad Sci U S A 2001; 98:9924-9. [PMID: 11493710 PMCID: PMC55554 DOI: 10.1073/pnas.171539698] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2000] [Indexed: 11/18/2022] Open
Abstract
At mammalian neuromuscular junctions (NMJs), innervation induces and maintains the metabolic stability of acetylcholine receptors (AChRs). To explore whether neural agrin may cause similar receptor stabilization, we injected neural agrin cDNA of increasing transfection efficiencies into denervated adult rat soleus (SOL) muscles. As the efficiency increased, the amount of recombinant neural agrin expressed in the muscles also increased. This agrin aggregated AChRs on muscle fibers, whose half-life increased in a dose-dependent way from 1 to 10 days. Electrical muscle stimulation enhanced the stability of AChRs with short half-lives. Therefore, neural agrin can stabilize aggregated AChRs in a concentration- and activity-dependent way. However, there was no effect of stimulation on AChRs with a long half-life (10 days). Thus, at sufficiently high concentrations, neural agrin alone can stabilize AChRs to levels characteristic of innervated NMJs.
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Affiliation(s)
- G Bezakova
- Department of Physiology, University of Oslo, Norway
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18
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Bezakova G, Lømo T. Muscle activity and muscle agrin regulate the organization of cytoskeletal proteins and attached acetylcholine receptor (AchR) aggregates in skeletal muscle fibers. J Cell Biol 2001; 153:1453-63. [PMID: 11425875 PMCID: PMC2150728 DOI: 10.1083/jcb.153.7.1453] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
In innervated skeletal muscle fibers, dystrophin and beta-dystroglycan form rib-like structures (costameres) that appear as predominantly transverse stripes over Z and M lines. Here, we show that the orientation of these stripes becomes longitudinal in denervated muscles and transverse again in denervated electrically stimulated muscles. Skeletal muscle fibers express nonneural (muscle) agrin whose function is not well understood. In this work, a single application of > or = 10 nM purified recombinant muscle agrin into denervated muscles preserved the transverse orientation of costameric proteins that is typical for innervated muscles, as did a single application of > or = 1 microM neural agrin. At lower concentration, neural agrin induced acetylcholine receptor aggregates, which colocalized with longitudinally oriented beta-dystroglycan, dystrophin, utrophin, syntrophin, rapsyn, and beta 2-laminin in denervated unstimulated fibers and with the same but transversely oriented proteins in innervated or denervated stimulated fibers. The results indicate that costameres are plastic structures whose organization depends on electrical muscle activity and/or muscle agrin.
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Affiliation(s)
- G Bezakova
- Department of Physiology, University of Oslo, 0317 Oslo, Norway.
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19
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Abstract
After nerve injury, denervated synaptic sites in skeletal muscle commonly become reinnervated by sprouts that grow from nerve terminals on nearby muscle fibers. These terminal sprouts grow along a glial cell guide or "bridge" formed by Schwann cell (SC) processes that extend from denervated synaptic sites. Data presented here show that most bridges connect innervated and denervated synaptic sites rather than pairs of denervated sites even when most sites in the muscle are denervated. Furthermore, bridges are inhibited by presynaptic or postsynaptic blockade of synaptic transmission, manipulations that do not alter the extent of SC growth. These results show that an activity-dependent postsynaptic signal promotes the formation and/or maintenance of glial bridges and thus muscle reinnervation.
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20
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Mathiesen I, Rimer M, Ashtari O, Cohen I, McMahan UJ, Lømo T. Regulation of the size and distribution of agrin-induced postsynaptic-like apparatus in adult skeletal muscle by electrical muscle activity. Mol Cell Neurosci 1999; 13:207-17. [PMID: 10328882 DOI: 10.1006/mcne.1999.0744] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
We compared actylcholine receptor (AChR) aggregates induced by neural agrin released from transfected muscle fibers with AChR aggregates induced by transplanted axons in extrajunctional regions of denervated rat soleus muscles. Both neural agrin and transplanted axons induced multiple, irregularly distributed AChR aggregates on muscle fibers. Direct electrical muscle stimulation of transfected muscles for up to 10 weeks removed all agrin-induced AChR aggregates (the losers) except one (the winner) on many fibers. Axon-induced AChR aggregates underwent comparable selection of winners and losers. The results suggest that agrin and acetylcholine-driven muscle activity provided by transplanted axons are sufficient to elicit in a denervated adult muscle fiber processes that regulate the size and distribution of ectopic neuromuscular junctions.
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Affiliation(s)
- I Mathiesen
- Department of Physiology, University of Oslo, Norway
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21
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Horikawa HP, Nawa H. Turnover rates of the AMPA-type glutamate receptor GluR1 measured by transient gene expression. J Neurosci Methods 1998; 84:173-9. [PMID: 9821649 DOI: 10.1016/s0165-0270(98)00109-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Protein turnover rates have until now been measured by pulse chasing of the target protein after labeling it with radioactive amino acids. This procedure, however, requires severe amino acid depletion followed by specific immunoprecipitation of the target protein. In the present study, we assessed the turnover rates of an AMPA-type glutamate receptor, GluR1 (or GluRA), with the conventional method and a novel one using gene transfer, and compared both of them. GluR1 cDNA was introduced into PC12 cells and cultured rat hippocampal neurons by electroporation and lipofection, respectively. Expression of its mRNA was transient and had almost ceased 2 days in PC12 cells after transfection, while the receptor protein continued to be detectable by Western blotting for a week. When the levels of the receptor protein in PC12 cells were plotted on a semi-logarithmic scale, the decay curve appeared linear after 2 days: Its decay half time (tau 1/2) was calculated as 41 h. In contrast, the pulse chase experiment revealed that the decay half time was 2-4 h in PC12 cells although cell damage was seen during this procedure. The receptor decay speed was also measured in cultured hippocampal neurons using GluR1 cDNA attached to a tag sequence. Decay of the receptor protein was monitored by Western blotting probed by an anti-tag antibody: tau 1/2 was 52 h in hippocampal neurons, similar to that in PC12. These observations suggest that the transfection procedure is more sensitive and beneficial than the conventional pulse chasing method when measuring protein turnover rates in fragile neural cells.
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Affiliation(s)
- H P Horikawa
- Department of Molecular Neurobiology, Niigata University, Japan
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22
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Lévi S, Vannier C, Triller A. Strychnine-sensitive stabilization of postsynaptic glycine receptor clusters. J Cell Sci 1998; 111 ( Pt 3):335-45. [PMID: 9427682 DOI: 10.1242/jcs.111.3.335] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cellular and molecular mechanisms underlying the postsynaptic aggregation of ionotropic receptors in the central nervous system are not understood. The glycine receptor (GlyR) and its cytoplasmic domain-associated protein, gephyrin, are clustered at the postsynaptic membrane and constitute a good model for addressing these questions. The glycine receptor is inhibited by strychnine. The effects of chronic strychnine treatment on the expression and cellular distribution of gephyrin and glycine receptor were therefore tested using primary cultures of spinal cord neurons. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that the glycine receptor alpha1, alpha2, beta subunits and gephyrin mRNAs were expressed at comparable levels in strychnine-treated and untreated cultures. The number of immunoreactive cells and the subcellular distribution of gephyrin and GlyR subunits was determined with standard and confocal immunofluorescence. The proportion of gephyrin and glycine receptor-immunoreactive (IR) cells was unaffected by strychnine treatment. Confocal microscopy revealed that the glycine receptor was mainly localized intracellularly near the nucleus. This cytoplasmic glycine receptor was not associated with the Golgi apparatus nor with the rough endoplasmic reticulum and therefore is not likely to correspond to neosynthesized proteins. The number of GlyR clusters on the somato-dendritic membrane was dramatically reduced on neurons displaying intracellular staining. In contrast, the subcellular distribution and the number of gephyrin clusters was not modified by the treatment. The fact that gephyrin postsynaptic localization was not modified by strychnine suggests that the aggregation of glycine receptor and gephyrin is governed by different mechanisms. The distribution of other cell surface molecules such as NCAM or GABAA receptor beta2/3 subunits was not modified by strychnine treatment. Chronic exposure of the cultures to tetrodotoxin did not affect gephyrin or glycine receptor cluster formation. Taken together, these results indicate that functional glycine receptor, but not electrical synaptic activity, is required for the formation of glycine receptor clusters.
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Affiliation(s)
- S Lévi
- Laboratoire de Biologie Cellulaire de la Synapse (INSERM U 497), Ecole Normale Supérieure, Paris, France
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23
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Missias AC, Mudd J, Cunningham JM, Steinbach JH, Merlie JP, Sanes JR. Deficient development and maintenance of postsynaptic specializations in mutant mice lacking an ‘adult’ acetylcholine receptor subunit. Development 1997; 124:5075-86. [PMID: 9362465 DOI: 10.1242/dev.124.24.5075] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
At many synapses, ‘fetal’ neurotransmitter receptor subunits are replaced by ‘adult’ subunits as development proceeds. To assess the significance of such transitions, we deleted the gene encoding the adult acetylcholine receptor (AChR) epsilon subunit, which replaces its fetal counterpart, the gamma subunit, at the skeletal neuromuscular junction during early postnatal life. Several aspects of postnatal maturation, including synapse elimination, proceeded normally in the absence of the adult AChR, but structural development of the endplate was compromised. Later, inadequate compensation by the gamma subunit led to severely reduced AChR density in mutant endplates relative to controls. This decreased density led to a profound reorganization of AChR-associated components of the postsynaptic membrane and cytoskeleton. Together, these results suggest novel roles for AChRs in assembly of the postsynaptic apparatus.
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Affiliation(s)
- A C Missias
- Department of Molecular Biology, Washington University School of Medicine, St. Louis, MO 63110, USA
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24
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Epsilon subunit-containing acetylcholine receptors in myotubes belong to the slowly degrading population. J Neurosci 1997. [PMID: 9364041 DOI: 10.1523/jneurosci.17-23-08937.1997] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Two types of muscle acetylcholine receptors (AChRs) can be distinguished on the basis of their degradation rates and sensitivities to innervation, muscle activity, and agents elevating intracellular cAMP. The first type (Rs), is present in a stable form (degradation t1/2 = approximately 10 d) at the adult innervated neuromuscular junctions (NMJs). Rs can also exist in a less stable form (called accelerated Rs; t1/2 = approximately 3-5 d) at denervated NMJs and in aneurally cultured myotubes; agents that increase intracellular cAMP reversibly modulate Rs stability. The second type of AChR is a rapidly degrading receptor (Rr) expressed only in embryonic and noninnervated muscles. Rr can be stabilized by ATP and not by cAMP. This study tested the hypothesis that the degradation properties unique to the Rs are attributable to the presence of the epsilon subunit. Immunoprecipitation and Western blot analysis of AChRs extracted from rat muscle cells in tissue culture showed that AChRs recognized by antibodies against the epsilon subunit degraded as a single population with a half-life similar to that of the slow component, Rs, in these cells. In addition, as for Rs receptors in denervated NMJs and cultured muscle cell, the degradation rate of these epsilon-containing AChRs was stabilized by dibutyryl-cAMP. The data indicate that the epsilon-containing AChRs behave like Rs. Thus, the presence of the epsilon subunit is sufficient for selecting an AChR molecule to the Rs pool.
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25
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Abstract
Acetylcholine receptors (AChRs) are present at the top of the postsynaptic membrane of the neuromuscular junction (NMJ) at very high density, possibly anchored to cytoskeletal elements. The present study investigated whether AChR degradation is affected in animals lacking dystrophin, a protein that is an integral part of the cytoskeletal complex and is missing in Duchenne muscular dystrophy. The animal model for Duchenne muscular dystrophy, the mutant mdx mouse, was used to determine whether disruption of the cytoskeleton, caused by the absence of dystrophin, affects AChR degradation. Of the two populations of junctional AChRs, Rs (expressed in innervated adult muscles) and Rr (expressed in embryonic or denervated muscles), only Rs are affected in mdx animals. In innervated mdx soleus, diaphragm, and sternomastoid muscles, the AChRs have an accelerated degradation rate (t1/2 of approximately 3-5 d), similar to that acquired by Rs in control muscles after denervation. The Rs in mdx NMJs do not accelerate further when the muscles are denervated. The absence of dystrophin does not affect the degradation rate of the Rr AChRs (t1/2 of 1 d), which are expressed after denervation in mdx as in control muscles. These results suggest that dystrophin or an intact cytoskeletal complex may be required for neuronal stabilization of Rs receptors at the adult neuromuscular junctions.
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26
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Cohen I, Rimer M, Lømo T, McMahan UJ. Agrin-induced postsynaptic-like apparatus in skeletal muscle fibers in vivo. Mol Cell Neurosci 1997; 9:237-53. [PMID: 9268503 DOI: 10.1006/mcne.1997.0623] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We find that when extrajunctional regions of denervated soleus muscles in adult rats are transfected with cDNA encoding rat agrin isoform Y4Z8, which is normally secreted by motor neurons at adult neuromuscular junctions, the myofibers express and secrete the neural agrin. Muscle fibers in the vicinity of transfection form at their surface specialized areas having extracellular, plasma membrane, and cytoplasmic protein aggregates, narrow and deep plasma membrane infoldings, and an accumulation of myonuclei, all of which are characteristic of the postsynaptic apparatus at neuromuscular junctions. We conclude that at ectopic neuromuscular junctions that form in the extrajunctional region of denervated adult soleus muscles after implantation of a foreign nerve, a single neural-derived factor, agrin, is sufficient not only to cause protein aggregation in the early stages of postsynaptic apparatus formation, as predicted by the agrin hypothesis, but also to bring about changes in conformation of the muscle fiber surface and distribution of organelles which appear as the apparatus reaches maturity.
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Affiliation(s)
- I Cohen
- Department of Neurobiology, Stanford University School of Medicine, California 94305, USA
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27
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el-Bizri H, Rigdon MG, Clarke PB. Intraneuronal accumulation and persistence of radiolabel in rat brain following in vivo administration of [3H]-chlorisondamine. Br J Pharmacol 1995; 116:2503-9. [PMID: 8581291 PMCID: PMC1909043 DOI: 10.1111/j.1476-5381.1995.tb15102.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. Chlorisondamine (CHL), a bisquaternary amine, produces a remarkably long-lasting blockade of central responses to nicotine. The mechanism underlying this blockade is not known. The main aim of this study was to test for possible accumulation of [3H]-CHL in rat brain during the period of chronic blockade. 2. Rats received CHL, either systemically (10 mg kg-1) or centrally (10 micrograms i.c.v.). Seven days later, striatal synaptosomes prepared from these animals were tested for nicotine-induced [3H]-dopamine release. This experiment showed that i.c.v. administration of CHL was as effective as systemic administration in producing ex vivo blockade of central nicotinic receptors. 3. Rats received bilateral i.c.v. infusions of [3H]-CHL (10 micrograms) and radioactivity was subsequently quantified in dissected cerebral cortex, striatum, hippocampus, midbrain and cerebellum. Radiolabel was detected at all three survival times (1, 7, and 21 days). Regional heterogeneity was apparent at 7 and 21 days survival. Radiolabel was almost exclusively confined to the insoluble subcellular fraction in all areas sampled. 4. The anatomical distribution of radiolabel was also visualized in brain sections. Rats received bilateral i.c.v. infusions of [3H]-CHL (10 micrograms) and were killed at 1, 7, 21 or 84 days. Immediately before they were killed, all rats were tested behaviourally, and central nicotinic blockade was demonstrated at 1, 7 and 21 days; partial recovery was observed at 84 days. Particularly at longer survival times, tritium was found to be heavily concentrated in the substantia nigra pars compacta, ventral tegmental area, dorsal raphé nucleus, and the granular layer of the cerebellum. 5. The possibility of retrograde axonal transport of radiolabel was then examined. Rats received a unilateral intrastriatal infusion of [3H]-CHL (0.34 or 0.034 micrograms) one week before they were killed. Autoradiographic labelling was largely confined to the site of infusion and to the ipsilateral substantia nigra pars compacta and dorsal raphé nucleus. 6. Thus, after i.c.v. administration, CHL (and/or centrally-formed derivatives) is initially widely distributed within the brain and is then selectively retained within a few brain areas. A persistent accumulation occurs within putative dopaminergic and 5-hydroxytryptaminergic neurones, at least partly through uptake by terminals and/or axons followed by retrograde transport. This persistent and anatomically-selective intraneuronal accumulation possibly underlies the long-term central nicotinic blockade associated with chlorisondamine.
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Affiliation(s)
- H el-Bizri
- Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada
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28
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Xu R, Salpeter MM. Protein kinase A regulates the degradation rate of Rs acetylcholine receptors. J Cell Physiol 1995; 165:30-9. [PMID: 7559804 DOI: 10.1002/jcp.1041650105] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Acetylcholine receptors at the neuromuscular junction of innervated vertebrate muscle (called Rs AChRs) have a stable degradation rate (t1/2 approximately 8-12 days) which accelerates after denervation to a half-life of approximately 3 days, but can be restabilized by reinnervation or by cAMP. We examined the mechanism by which cAMP regulates the Rs degradation rate. When dibutyryl cAMP (DB-cAMP) was applied to denervated mouse diaphragms in organ culture, it stabilized the accelerated degradation rate of the Rs. We found that this stabilization is reversible upon removal of the DB-cAMP, is cAMP specific and is mediated by intracellular cAMP. A major observation of this study is that the cAMP-induced stabilization of Rs AChRs is via protein kinase A (PKA), since H89, a PKA inhibitor, blocked the DB-cAMP induced stabilization of Rs, and H85, an analog of H89, which does not inhibit PKA but does inhibit other kinases as efficiently as H89, did not prevent the DB-cAMP-induced stabilization of Rs degradation. These results suggest that the cAMP messenger system via a PKA-dependent pathway could be among the mechanisms whereby the nerve regulates AChR degradation.
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Affiliation(s)
- R Xu
- Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853-2702, USA
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29
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Broadie K, Bate M. The Drosophila NMJ: a genetic model system for synapse formation and function. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s1044-5781(06)80031-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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30
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Dodson BA, Kelly BJ, Braswell LM, Cohen NH. Changes in acetylcholine receptor number in muscle from critically ill patients receiving muscle relaxants: an investigation of the molecular mechanism of prolonged paralysis. Crit Care Med 1995; 23:815-21. [PMID: 7736737 DOI: 10.1097/00003246-199505000-00007] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
OBJECTIVE Previous reports have described prolonged paralysis after the administration of muscle relaxants in critically ill patients. The purpose of this study was to examine possible pathophysiologic causes for this paralysis by measuring muscle-type, nicotinic acetylcholine receptor number in necropsy muscle specimens from patients who had received muscle relaxants to facilitate mechanical ventilation before death. DESIGN Prospective laboratory study of human muscle collected at autopsy. SETTING Medical and surgical intensive care units (ICUs) at a university hospital and a research laboratory. PATIENTS Fourteen critically ill patients, with a variety of diagnoses, all of whom required mechanical ventilatory support before their deaths in the ICU and who underwent post mortem examination. Patients were arbitrarily divided into three groups, according to their total vecuronium dose and number of days mechanically ventilated before death. Three patients were in the control group (defined as dying within 72 hrs of initiation of ventilatory support and receiving a total dose of < 5 mg of vecuronium). Six patients were in the low-dose group (defined as requiring ventilatory support for > 3 days before death and receiving a total vecuronium dose of < or = 200 mg). Five patients were in the high-dose group (defined as requiring ventilatory support for > 3 days before death and receiving a total vecuronium dose of > 200 mg). INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Nicotinic acetylcholine receptor numbers as measured by specific 125I-alpha-bungarotoxin binding to human rectus abdominis muscle obtained at autopsy were determined. In general, receptor number reflected the clinical requirements for the muscle relaxants of each patient. Patients who had increasing requirements for muscle relaxants before death had increases in receptor number, as compared with control values. CONCLUSIONS The increase in nicotinic acetylcholine receptor number in muscle from patients with an increasing requirement for muscle relaxants before death suggests that nicotinic acetylcholine receptor up-regulation may underlie the increased requirements for muscle relaxants seen in some patients. Furthermore, these findings suggest that muscle relaxant-induced, denervation-like changes may at least be partially responsible for prolonged muscle paralysis after the long-term administration of muscle relaxants. This study may provide the first information into the molecular mechanisms underlying prolonged paralysis.
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Affiliation(s)
- B A Dodson
- Department of Anesthesia, University of California at San Francisco 94143-0648, USA
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31
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Lupa MT, Krzemien DM, Schaller KL, Caldwell JH. Expression and distribution of sodium channels in short- and long-term denervated rodent skeletal muscles. J Physiol 1995; 483 ( Pt 1):109-18. [PMID: 7776226 PMCID: PMC1157875 DOI: 10.1113/jphysiol.1995.sp020571] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
1. Loose-patch voltage-clamp recordings were made from rat and mouse skeletal muscle fibres denervated for up to 6 weeks. Innervated muscles possessed a Na+ current density of 107 +/- 3.3 mA cm-2 in endplate membrane, and 6.3 +/- 0.6 mA cm-2 in extrajunctional membrane. This high concentration of Na+ channels at the endplate was gradually reduced following denervation. After 6 weeks of denervation, the endplate Na+ channel concentration was reduced by 40-50%, and the density of Na+ channels in extrajunctional membrane was increased by about 30%. 2. The tetrodotoxin (TTX)-resistant form of the Na+ channel appeared after 3 days of denervation and comprised approximately 43% of the endplate Na+ channels 5-6 days after denervation. Subsequently, TTX-resistant Na+ channels were reduced in density to approximately 25% of the postjunctional Na+ channels and remained at this level up to 6 weeks after denervation. 3. RNase protection analysis showed that mRNA encoding the TTX-resistant Na+ channel was virtually absent in innervated muscle, rose > 50-fold after 3 days of denervation, then decreased by 95% 6 weeks after denervation. The density of TTX-resistant Na+ channels correlated qualitatively with changes in mRNA levels. 4. These results suggest that the density of Na+ channels at neuromuscular junctions is maintained by two mechanisms, one influenced by the nerve terminal and the other independent of innervation.
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Affiliation(s)
- M T Lupa
- University of Colorado Health Sciences Center, Department of Cellular and Structural Biology, Denver 80262, USA
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32
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Weldon P, Bachoo M, Polosa C. The role of tonic preganglionic neuron firing in the turnover of the large dense-cored vesicle store in sympathetic preganglionic nerve terminals. Neuroscience 1994; 62:531-8. [PMID: 7830896 DOI: 10.1016/0306-4522(94)90386-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Large dense-cored vesicles are transported centrifugally in the cervical sympathetic trunk and are depleted in a calcium-dependent manner from synaptic boutons of the cat superior cervical ganglion during orthodromic stimulation at 20-40 Hz [P. Weldon et al. (1993) Neuroscience 55, 1045-1054]. In the present study, we tested in awake cats whether the normal tonic firing of the sympathetic preganglionic neuron contributes to the turnover of large dense-cored vesicles in synaptic boutons of the superior cervical ganglion. Tetrodotoxin was applied with a mini-osmotic pump to one cervical sympathetic trunk, while vehicle alone was applied to the contralateral cervical sympathetic trunk, for two, four or seven days. The appearance of Horner syndrome ipsilateral to the tetrodotoxin application demonstrated block of action potential propagation. Both superior cervical ganglia were excised and processed for electron microscopy. The number of large dense-cored vesicles per bouton cross-section was higher in the ganglion with tetrodotoxin-treated input than in the control. The content at four days was higher than at two days; the content at seven days was similar to that at four days. The number of lysosomes per bouton profile also increased in the ganglion with tetrodotoxin-treated input. No changes were observed in size of bouton profiles, number of boutons or of synapses per grid square and length of the presynaptic densities in the ganglion with tetrodotoxin-treated input.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P Weldon
- Department of Physiology, McGill University, Montreal, Quebec, Canada
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33
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Godinho RO, Souccar C, Lapa AJ. Testosterone control of endplate and non-endplate acetylcholinesterase in the rat levator ani muscle. Neurochem Res 1994; 19:657-63. [PMID: 8065522 DOI: 10.1007/bf00967703] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The time course of effects of castration (5-60 days) and testosterone treatment (15-60 days) of adult male rats were examined on the endplate (+EP) and non-endplate (-EP) acetylcholinesterase (AChE) of the androgen-dependent levator ani (LA) muscle. The thiocholine method was used to determine the enzyme activity. Castration caused LA muscle atrophy within 5 days but reduced the -EP and +EP AChE after 10 and 20 days, respectively. Following 30 days castration -EP and +EP AChE reached respectively 41% and 35% of control activity. Testosterone retrieval restored the control values of both muscle weight and total AChE after 15 and 60 days, respectively. Recovery of the +EP AChE preceded that of -EP AChE by 30 days. The results showed that in the rat LA muscle, +EP and -EP AChE depend on a continuous testosterone regulation that predominates at +EP region spreading thereafter to -EP region. Those data suggest a hormone regulation of AChE exerted indirectly through the synthesis and release of neurotrophic substances.
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Affiliation(s)
- R O Godinho
- Department of Pharmacology, Escola Paulista de Medicina, São Paulo, Brazil
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34
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Deschenes MR, Covault J, Kraemer WJ, Maresh CM. The neuromuscular junction. Muscle fibre type differences, plasticity and adaptability to increased and decreased activity. Sports Med 1994; 17:358-72. [PMID: 8091046 DOI: 10.2165/00007256-199417060-00003] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The neuromuscular junction (NMJ) of adult mammalian muscle is the site of the transduction of electrical stimuli, generated by the nervous system, to the underlying muscle fibres, resulting in muscle action. It has been demonstrated that, in some ways, the morphology of the NMJ is specific to muscle fibre type. It is also known that while the structure of the NMJ generally remains stable in young, healthy adults, a subtle form of remodelling continuously occurs at this synapse. The morphology and physiology of the NMJ have been shown to adapt to both increased, and decreased use. Indeed, morphological changes of the NMJ are associated with functional alterations in neuromuscular transmission. Increased activity of the myoneural synapse results in adaptations that enhance neuromuscular transmission and, thus, muscle performance. Similarly to increased usage, decreased neuromuscular activity results in structural alterations of the NMJ. However, unlike those responses observed with enhanced activity, decreased recruitment of the myoneural synapse can impair neuromuscular transmission and muscle performance. Thus, the NMJ demonstrates both anatomical and physiological adaptations following substantial changes in its pattern of activity. These NMJ adaptations can affect the functional capacity of skeletal muscle in vivo.
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Affiliation(s)
- M R Deschenes
- Department of Physiology and Neurobiology, University of Connecticut, Storrs
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35
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el-Bizri H, Clarke PB. Blockade of nicotinic receptor-mediated release of dopamine from striatal synaptosomes by chlorisondamine administered in vivo. Br J Pharmacol 1994; 111:414-8. [PMID: 8004385 PMCID: PMC1909959 DOI: 10.1111/j.1476-5381.1994.tb14750.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
1. The chronic nicotinic blockade produced following in vivo administration of chlorisondamine was investigated in vitro. Nicotine-induced [3H]-dopamine release from striatal synaptosomes was used as a measure of central nicotinic receptor function. 2. In synaptosomal preparations from rats pretreated with a single administration of chlorisondamine (10 mg kg-1, s.c.), 1, 7, 21, 42, 63 or 84 days before they were killed, responses to (-)-nicotine (10(-6) M) were blocked. 3. In vivo administration of chlorisondamine (10 mg kg-1, s.c.), 7 days before rats were killed, produced a nicotinic blockade in vitro that was insurmountable even with a high concentration of (-)-nicotine (10(-4) M). 4. Both in vitro and in vivo administration of chlorisondamine blocked nicotinic responses to acetylcholine (10(-4) M). In contrast, neither in vitro nor in vivo administration of chlorisondamine reduced [3H]-dopamine release induced by high K+ (20 x 10(-3) M) or (+)-amphetamine (10(-6) M). 5. Nicotinic blockade resulting from in vitro administration of chlorisondamine (10(-5) M) recovered partially after 60 min wash-out, and completely by 90 min. In contrast, no recovery was seen in synaptosomes prepared from rats pretreated with chlorisondamine (10 mg kg-1, s.c.) in vivo. 6. Thus, in vivo treatment with chlorisondamine results in a quasi-irreversible, insurmountable block of CNS nicotinic receptors. The persistence of this block ex vivo indicates that physical trapping by the blood brain barrier is not solely responsible for the persistent blockade seen in vivo. The resistance of this blockade to prolonged in vitro wash-out suggests that the underlying mechanism differs from that associated with in vitro administration.
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Affiliation(s)
- H el-Bizri
- Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada
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36
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Mamalaki A, Tzartos SJ. Nicotinic acetylcholine receptor: structure, function and main immunogenic region. ADVANCES IN NEUROIMMUNOLOGY 1994; 4:339-54. [PMID: 7719615 DOI: 10.1016/0960-5428(94)00032-j] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- A Mamalaki
- Department of Biochemistry, Hellenic Pasteur Institute, Athens, Greece
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37
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Broadie KS. Synaptogenesis in Drosophila: coupling genetics and electrophysiology. JOURNAL OF PHYSIOLOGY, PARIS 1994; 88:123-39. [PMID: 7833856 DOI: 10.1016/0928-4257(94)90023-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Drosophila is one of the most fully described eukaryotic organisms and, as a system, offers the most advanced genetic and molecular techniques. In particular, Drosophila embryonic development has been subject to intensive genetic and molecular examination. Drosophila is also one of the few genetically malleable organisms to permit electrophysiological investigation and so allow detailed physiological characterization of specific molecular lesions. These two fields, the developmental and electrophysiological, are being coupled for the first time to examine a key aspect of neural development, synaptogenesis. Here, I describe synaptogenesis in the Drosophila embryo at the identified neuromuscular junction. I focus particular attention on the use of known genetic mutations to dissect the mechanisms of synapse formation. This simple, well-characterized synapse is already proving valuable in describing the defects of mutations in genes essential for synaptic development and function. In the long term, this system will allow us to systematically mutate the Drosophila genome to identify and describe the genetic and molecular pathways directing the construction of a synapse.
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Affiliation(s)
- K S Broadie
- Department of Zoology, University of Cambridge, United Kingdom
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38
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ORAL COMMUNICATIONS. Br J Pharmacol 1994. [DOI: 10.1111/j.1476-5381.1994.tb16294.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
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39
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Salpeter MM, Andreose J, O'Malley JP, Xu R, Fumagalli G, Lomo T. Degradation of acetylcholine receptors at vertebrate neuromuscular junctions. Ann N Y Acad Sci 1993; 681:155-64. [PMID: 8357161 DOI: 10.1111/j.1749-6632.1993.tb22881.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- M M Salpeter
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853
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40
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Kennel PF, Poindron P, Warter JM, Fonteneau P. alpha-Bungarotoxin sensitization in experimental autoimmune myasthenia gravis. Muscle Nerve 1993; 16:461-5. [PMID: 8390605 DOI: 10.1002/mus.880160505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A mouse model of MG, termed experimental autoimmune myasthenia gravis (EAMG), can be obtained after immunization with Torpedo acetylcholine receptor (AChR). Although many studies have detailed the consequence of AChR antibodies binding at the neuromuscular junction and the difficulty in obtaining obvious clinical signs, less attention has been focused on the possibility of amplifying the muscular block in order to discriminate between immunized and healthy animals. In the present studies we observe that a single inoculation of alpha-bungarotoxin (alpha-bgt) can amplify the neuromuscular block revealed by repetitive nerve stimulation, and induce in EAMG mice a stable muscular weakness state lasting for at least 169 hours instead of 95 hours in normal mice. This model could provide an excellent tool for evaluating drugs active on neuromuscular transmission.
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Affiliation(s)
- P F Kennel
- Université Louis Pasteur, Département d'Immunologie, Immunopharmacologie, et Pathologie [Equipe de pathologie expérimentale et de neurologie clinique], Illkirch, France
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41
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Cartaud J, Changeux JP. Post-transcriptional compartmentalization of acetylcholine receptor biosynthesis in the subneural domain of muscle and electrocyte junctions. Eur J Neurosci 1993; 5:191-202. [PMID: 8261100 DOI: 10.1111/j.1460-9568.1993.tb00485.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- J Cartaud
- Biologie Cellulaire des Membranes, Institut Jacques Monod, CNRS, Université Paris VII, France
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42
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Affiliation(s)
- Z W Hall
- Department of Physiology, University of California, San Francisco 94143
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43
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Arancio O, Buffelli M, Cangiano A, Pasino E. Nerve stump effects in muscle are independent of synaptic connections and are temporally correlated with nerve degeneration phenomena. Neurosci Lett 1992; 146:1-4. [PMID: 1475041 DOI: 10.1016/0304-3940(92)90157-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Close or distant denervation of the rat soleus muscle indicated that (1) longer soleus nerve stumps delay the onset of axon terminal degeneration and of muscle membrane changes (spike resistance to TTX) by strictly comparable times, and (2) the stump-induced delay of the muscle effect is independent of synaptic connections, because it is also obtained (RMP fall and TTX-resistance development) when sectioning a foreign nerve previously transplanted on the soleus surface but not making synaptic contacts. Both lines of evidence are consistent with the interpretation that, as far as the extrajunctional membrane properties are concerned, the effect of the length of the nerve stump on muscle is mediated by nerve terminal breakdown.
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Affiliation(s)
- O Arancio
- Istituto di Fisiologia Umana, Medical School, University of Verona, Italy
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44
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Hill JA. Nicotinic receptor-associated 43K protein and progressive stabilization of the postsynaptic membrane. Mol Neurobiol 1992; 6:1-17. [PMID: 1463586 DOI: 10.1007/bf02935564] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
An extrinsic membrane protein of apparent molecular mass 43 kDa is specifically localized in postsynaptic membranes closely associated with the nicotinic acetylcholine receptor (AChR). Since its discovery in 1977, biochemical and morphological studies have combined to provide relatively clear pictures of 43K protein structure and subcellular compartmentalization. Nevertheless, despite these advances, the precise function of this synapse-specific protein remains unclear. Data gathered in recent years indicate that the postsynaptic apparatus develops through the incremental agglomeration of receptor microaggregates; evidence derived from a number of sources points to a role for 43K protein in certain underlying reactions. In this paper, I review 43K protein structural and anatomical data and analyze evidence for its role in the organization and maintenance of the postsynaptic membrane. Finally, I offer a model presenting a view of the role of 43K protein in the ontogeny of the motor endplate.
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Affiliation(s)
- J A Hill
- URA CNRS D1284, Neurobiologie Moléculaire, Institut Pasteur, Paris, France
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45
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Lukas RJ, Bencherif M. Heterogeneity and regulation of nicotinic acetylcholine receptors. INTERNATIONAL REVIEW OF NEUROBIOLOGY 1992; 34:25-131. [PMID: 1587717 DOI: 10.1016/s0074-7742(08)60097-5] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- R J Lukas
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013
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46
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Yang JS, Sladky JT, Kallen RG, Barchi RL. TTX-sensitive and TTX-insensitive sodium channel mRNA transcripts are independently regulated in adult skeletal muscle after denervation. Neuron 1991; 7:421-7. [PMID: 1654949 DOI: 10.1016/0896-6273(91)90294-a] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The expression of mRNA encoding the TTX-sensitive (SkM1) and TTX-insensitive (SkM2) voltage-dependent sodium channels in adult skeletal muscle is independently regulated. In normal skeletal muscle, only the SkM1 message is expressed and the level varies with muscle fiber type. After surgical denervation, the steady-state SkM1 mRNA level declines transiently, but returns to control levels within 5 days. Expression of SkM2 transcripts is markedly activated, reaching a peak 3 days after axotomy and then declining to a maintained level at approximately 30% of peak. Chemical denervation with botulinum toxin results in higher levels of SkM2 mRNA, which by 7 days posttreatment are 7-fold greater than levels in paired axotomized muscles. SkM2 expression subsequently declines as functional reinnervation appears. Quantal acetylcholine release appears to play a major role in suppression of SkM2 expression in adult innervated or reinnervated muscle, whereas nonquantal factors in toxin-treated, but not axotomized, muscle may sustain high level SkM2 mRNA expression.
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Affiliation(s)
- J S Yang
- Mahoney Institute of Neurological Sciences, University of Pennsylvania School of Medicine, Philadelphia 19104
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47
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Held IR, Sayers ST, McLane JA. Acetylcholine receptor gene expression in skeletal muscle of chronic ethanol-fed rats. Alcohol 1991; 8:173-7. [PMID: 2069731 DOI: 10.1016/0741-8329(91)90742-f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The expression of the neuromuscular acetylcholine receptor (AChR) alpha-subunit gene was evaluated in soleus muscles from an animal model of chronic alcoholism. At 8 weeks of age, test rats were placed on a nutritionally complete liquid diet containing 6.7% ethanol (v/v). Age- and weight-matched control rats were pair-fed an isocaloric liquid diet. After a 16-week diet period, soleus muscles were obtained and total RNA and poly(A)+ RNA were isolated. Muscle RNA levels from ethanol-fed and control rats were comparable. AChR alpha-subunit mRNA was detected by hybridization of muscle poly(A)+ RNA with a 32P-labeled, complementary riboprobe. The steady-state level of AChR alpha-subunit mRNA was reduced by 39% (p less than 0.001) in soleus muscles from the ethanol-fed rats as compared to pair-fed controls. These results suggest that the expression of the AChR alpha-subunit gene is down-regulated after chronic ethanol exposure at a transcriptional or posttranscriptional level.
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Affiliation(s)
- I R Held
- Neuroscience Research Laboratory, VA Hospital, Hines, IL 60141
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48
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Rotzler S, Schramek H, Brenner HR. Metabolic stabilization of endplate acetylcholine receptors regulated by Ca2+ influx associated with muscle activity. Nature 1991; 349:337-9. [PMID: 1846230 DOI: 10.1038/349337a0] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
During formation of the neuromuscular junction, acetylcholine receptors in the endplate membrane become metabolically stabilized under neural control, their half-life increasing from about 1 day to about 10 days. The metabolic stability of the receptors is regulated by the electrical activity induced in the muscle by innervation. We report here that metabolic stabilization of endplate receptors but not of extrajunctional receptors can be induced in the absence of muscle activity if muscles are treated with the calcium ionophore A23187. Acetylcholine receptor stabilization was also induced by culturing non-stimulated muscle in elevated K+ with the Ca2+ channel activator (+)-SDZ202-791. Conversely, activity-dependent receptor stabilization is prevented in muscle stimulated in the presence of the Ca2+ channel blockers (+)-PN200-110 or D-600. Treatment of muscles with ryanodine, which induces Ca2+ release from the sarcoplasmic reticulum in the absence of activity, does not cause stabilization of junctional receptors. Evidently, muscle activity induces metabolic acetylcholine receptor stabilization by way of an influx of Ca2+ ions through dihydropyridine-sensitive Ca2+ channels in the endplate membrane, whereas Ca2+ released from the sarcoplasmic reticulum is ineffective in this developmental process.
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Affiliation(s)
- S Rotzler
- Department of Physiology, University of Basel, Switzerland
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49
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Abstract
1. The impulse activity in the sciatic nerve of rats was blocked for 30-59 days by a chronic infusion of tetrodotoxin (TTX) into a cuff around the nerve from an external mechanical pump. After this treatment the extensor digitorum longus muscle was isolated and the electrical activity at the endplates was recorded by intracellular electrodes. Endplates in the paralysed muscles were still functional as the muscle contracted briskly upon stimulation of the nerve distal to the block. 2. The spontaneous miniature endplate potentials (MEPPs) differed from those in normal muscles in having a more variable amplitude; 24% of the events were more than twice as large as the modal amplitude. In 30% of the fibres the largest of these 'giant' MEPPs (GMEPPs) triggered muscle action potentials. The amplitude distributions often had suggestive peaks indicating that the GMEPPs might consist of multiple quanta of the same size as those constituting the nerve impulse-evoked endplate potentials (EPPs). 3. The GMEPPs were more prolonged, but were similar in shape to MEPPs from normal muscles, with a smooth, relatively fast rising phase and a more prolonged decay. The mean time-to-peak was higher than for impulse-evoked EPPs of the same size, suggesting that the spontaneous release was more distant or less synchronized than after a nerve impulse. The half-decay time of the GMEPPs showed no large increase with increasing amplitude suggesting that the release of transmitter was not focal. The half-decay times were, however, longer than for impulse-evoked EPPs of the same size, suggesting that the spontaneous release might be less distributed than impulse-evoked release. 4. GMEPPs were not influenced by TTX, they were larger than the impulse-evoked EPPs in solutions containing high Mg2+ and low Ca2+, and they were not increased by high extracellular Ca2+ concentrations. Thus, the GMEPPs were not caused by spontaneous action potentials and probably not by Ca2+ influx. 5. In most cases the frequency of large and small MEPPs in paralysed muscles was influenced in the same way as those in normal muscles. It was increased by an increase in the extracellular K+ concentration or osmolarity, and reduced by a decrease in Ca2+ or an increase in Mg2+. The frequency was increased by Ruthenium Red. Also, like MEPPs in normal muscles, the frequency of small MEPPs in paralysed muscles was increased by increasing the extracellular Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K Gundersen
- Institute of Physiology and Neurophysiology, University of Oslo, Norway
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