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Walker CL. Progress in perisynaptic Schwann cell and neuromuscular junction research. Neural Regen Res 2021; 17:1273-1274. [PMID: 34782570 PMCID: PMC8643052 DOI: 10.4103/1673-5374.327334] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Affiliation(s)
- Chandler L Walker
- Department of Biomedical Sciences and Comprehensive Care, Indiana University School of Dentistry, Neuromusculoskeletal Research Group, Richard L. Roudebush Veterans Affairs Medical Center, Indianapolis, IN, USA
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2
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The Neuromuscular Junction: Roles in Aging and Neuromuscular Disease. Int J Mol Sci 2021; 22:ijms22158058. [PMID: 34360831 PMCID: PMC8347593 DOI: 10.3390/ijms22158058] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 07/20/2021] [Accepted: 07/22/2021] [Indexed: 02/07/2023] Open
Abstract
The neuromuscular junction (NMJ) is a specialized synapse that bridges the motor neuron and the skeletal muscle fiber and is crucial for conversion of electrical impulses originating in the motor neuron to action potentials in the muscle fiber. The consideration of contributing factors to skeletal muscle injury, muscular dystrophy and sarcopenia cannot be restricted only to processes intrinsic to the muscle, as data show that these conditions incur denervation-like findings, such as fragmented NMJ morphology and corresponding functional changes in neuromuscular transmission. Primary defects in the NMJ also influence functional loss in motor neuron disease, congenital myasthenic syndromes and myasthenia gravis, resulting in skeletal muscle weakness and heightened fatigue. Such findings underscore the role that the NMJ plays in neuromuscular performance. Regardless of cause or effect, functional denervation is now an accepted consequence of sarcopenia and muscle disease. In this short review, we provide an overview of the pathologic etiology, symptoms, and therapeutic strategies related to the NMJ. In particular, we examine the role of the NMJ as a disease modifier and a potential therapeutic target in neuromuscular injury and disease.
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Castro R, Taetzsch T, Vaughan SK, Godbe K, Chappell J, Settlage RE, Valdez G. Specific labeling of synaptic schwann cells reveals unique cellular and molecular features. eLife 2020; 9:e56935. [PMID: 32584256 PMCID: PMC7316509 DOI: 10.7554/elife.56935] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 06/08/2020] [Indexed: 12/14/2022] Open
Abstract
Perisynaptic Schwann cells (PSCs) are specialized, non-myelinating, synaptic glia of the neuromuscular junction (NMJ), that participate in synapse development, function, maintenance, and repair. The study of PSCs has relied on an anatomy-based approach, as the identities of cell-specific PSC molecular markers have remained elusive. This limited approach has precluded our ability to isolate and genetically manipulate PSCs in a cell specific manner. We have identified neuron-glia antigen 2 (NG2) as a unique molecular marker of S100β+ PSCs in skeletal muscle. NG2 is expressed in Schwann cells already associated with the NMJ, indicating that it is a marker of differentiated PSCs. Using a newly generated transgenic mouse in which PSCs are specifically labeled, we show that PSCs have a unique molecular signature that includes genes known to play critical roles in PSCs and synapses. These findings will serve as a springboard for revealing drivers of PSC differentiation and function.
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Affiliation(s)
- Ryan Castro
- Department of Molecular Biology, Cellular Biology, and Biochemistry, Brown UniversityProvidenceUnited States
- Center for Translational Neuroscience, Robert J. and Nancy D. Carney Institute for Brain Science and Brown Institute for Translational Science, Brown UniversityProvidenceUnited States
- Neuroscience Graduate Program, Brown UniversityProvidenceUnited States
| | - Thomas Taetzsch
- Department of Molecular Biology, Cellular Biology, and Biochemistry, Brown UniversityProvidenceUnited States
- Center for Translational Neuroscience, Robert J. and Nancy D. Carney Institute for Brain Science and Brown Institute for Translational Science, Brown UniversityProvidenceUnited States
| | - Sydney K Vaughan
- Department of Molecular Biology, Cellular Biology, and Biochemistry, Brown UniversityProvidenceUnited States
- Center for Translational Neuroscience, Robert J. and Nancy D. Carney Institute for Brain Science and Brown Institute for Translational Science, Brown UniversityProvidenceUnited States
| | - Kerilyn Godbe
- Fralin Biomedical Research Institute at Virginia Tech CarilionRoanokeUnited States
| | - John Chappell
- Fralin Biomedical Research Institute at Virginia Tech CarilionRoanokeUnited States
| | - Robert E Settlage
- Department of Advanced Research Computing, Virginia TechBlacksburgUnited States
| | - Gregorio Valdez
- Department of Molecular Biology, Cellular Biology, and Biochemistry, Brown UniversityProvidenceUnited States
- Center for Translational Neuroscience, Robert J. and Nancy D. Carney Institute for Brain Science and Brown Institute for Translational Science, Brown UniversityProvidenceUnited States
- Department of Neurology, Warren Alpert Medical School of Brown UniversityProvidenceUnited States
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Bermedo-García F, Ojeda J, Méndez-Olivos EE, Marcellini S, Larraín J, Henríquez JP. The neuromuscular junction of Xenopus tadpoles: Revisiting a classical model of early synaptogenesis and regeneration. Mech Dev 2018; 154:91-97. [PMID: 29807117 DOI: 10.1016/j.mod.2018.05.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Revised: 05/22/2018] [Accepted: 05/23/2018] [Indexed: 11/17/2022]
Abstract
The frog neuromuscular junction (NMJ) has been extensively used as a model system to dissect the mechanisms involved in synapse formation, maturation, maintenance, regeneration, and function. Early NMJ synaptogenesis relies on a combination of cell-autonomous and interdependent pre/postsynaptic communication processes. Due to their transparency, comparatively easy manipulation, and remarkable regenerative abilities, frog tadpoles constitute an excellent model to study NMJ formation and regeneration. Here, we aimed to contribute new aspects on the characterization of the ontogeny of NMJ formation in Xenopus embryos and to explore the morphological changes occurring at the NMJ after spinal cord injury. Following analyses of X. tropicalis tadpoles during development we found that the early pathfinding of rostral motor axons is likely helped by previously formed postsynaptic specializations, whereas NMJ formation in recently differentiated ventral muscles in caudal segments seems to rely on presynaptic inputs. After spinal cord injury of X. laevis tadpoles our results suggest that rostral motor axon projections help caudal NMJ re-innervation before spinal cord connectivity is repaired.
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Affiliation(s)
- Francisca Bermedo-García
- Neuromuscular Studies Laboratory (NeSt Lab), Center for Advanced Microscopy, Faculty of Biological Sciences, Department of Cell Biology, Universidad de Concepción, Concepción, Chile
| | - Jorge Ojeda
- Neuromuscular Studies Laboratory (NeSt Lab), Center for Advanced Microscopy, Faculty of Biological Sciences, Department of Cell Biology, Universidad de Concepción, Concepción, Chile
| | - Emilio E Méndez-Olivos
- Center for Aging and Regeneration, Faculty of Biological Sciences, P. Universidad Católica de Chile, Avenida Libertador Bernardo O'Higgins 340, Santiago, Chile
| | - Sylvain Marcellini
- Laboratory of Development and Evolution (LADE), Department of Cell Biology, Faculty of Biological Sciences, Universidad de Concepción, Concepción, Chile
| | - Juan Larraín
- Center for Aging and Regeneration, Faculty of Biological Sciences, P. Universidad Católica de Chile, Avenida Libertador Bernardo O'Higgins 340, Santiago, Chile
| | - Juan Pablo Henríquez
- Neuromuscular Studies Laboratory (NeSt Lab), Center for Advanced Microscopy, Faculty of Biological Sciences, Department of Cell Biology, Universidad de Concepción, Concepción, Chile.
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5
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Ko CP, Robitaille R. Perisynaptic Schwann Cells at the Neuromuscular Synapse: Adaptable, Multitasking Glial Cells. Cold Spring Harb Perspect Biol 2015; 7:a020503. [PMID: 26430218 PMCID: PMC4588062 DOI: 10.1101/cshperspect.a020503] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The neuromuscular junction (NMJ) is engineered to be a highly reliable synapse to carry the control of the motor commands of the nervous system over the muscles. Its development, organization, and synaptic properties are highly structured and regulated to support such reliability and efficacy. Yet, the NMJ is also highly plastic, able to react to injury and adapt to changes. This balance between structural stability and synaptic efficacy on one hand and structural plasticity and repair on another hand is made possible by the intricate regulation of perisynaptic Schwann cells, glial cells at this synapse. They regulate both the efficacy and structural plasticity of the NMJ in a dynamic, bidirectional manner owing to their ability to decode synaptic transmission and by their interactions via trophic-related factors.
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Affiliation(s)
- Chien-Ping Ko
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520
| | - Richard Robitaille
- Département de Neurosciences, Université de Montréal, Montréal, Québec H3C 3J7, Canada Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec H3C 3J7, Canada
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6
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Motor nerve terminal destruction and regeneration following anti-ganglioside antibody and complement-mediated injury: An in and ex vivo imaging study in the mouse. Exp Neurol 2012; 233:836-48. [DOI: 10.1016/j.expneurol.2011.12.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Revised: 10/27/2011] [Accepted: 12/07/2011] [Indexed: 01/10/2023]
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Abstract
Glia are an indispensable structural and functional component of the synapse. They modulate synaptic transmission and also play important roles in synapse formation and maintenance. The vertebrate neuromuscular junction (NMJ) is a classic model synapse. Due to its large size, simplicity and accessibility, the NMJ has contributed greatly to our understanding of synapse development and organization. In the past decade, the NMJ has also emerged as an effective model for studying glia-synapse interactions, in part due to the development of various labeling techniques that permit NMJs and associated Schwann cells (the glia at NMJs) to be visualized in vitro and in vivo. These approaches have demonstrated that Schwann cells are actively involved in synapse remodeling both during early development and in post-injury reinnervation. In vivo imaging has also recently been combined with serial section transmission electron microscopic (ssTEM) reconstruction to directly examine the ultrastructural organization of remodeling NMJs. In this review, we focus on the anatomical studies of Schwann cell dynamics and their roles in formation, maturation and remodeling of vertebrate NMJs using the highest temporal and spatial resolution methods currently available.
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Abstract
The CNS contains relatively few unmyelinated nerve fibers, and thus benefits from the advantages that are conferred by myelination, including faster conduction velocities, lower energy consumption for impulse transmission, and greater stability of point-to-point connectivity. In the PNS many fibers or regions of fibers the Schwann do not form myelin. Examples include C fibers nociceptors, postganglionic sympathetic fibers, and the Schwann cells associated with motor nerve terminals at neuromuscular junctions. These examples retain a degree of plasticity and a capacity to sprout collaterally that is unusual in myelinated fibers. Nonmyelin-forming Schwann cells, including those associated with uninjured fibers, have the capacity to act as the "first responders" to injury or disease in their neighborhoods.
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Affiliation(s)
- John W Griffin
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
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Schwann cells promote synaptogenesis at the neuromuscular junction via transforming growth factor-beta1. J Neurosci 2008; 28:9599-609. [PMID: 18815246 DOI: 10.1523/jneurosci.2589-08.2008] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Recent studies suggest that glial cells actively participate in the formation, function, maintenance, and repair of the chemical synapse. However, the molecular mechanisms of glia-synapse interactions are largely unknown. We have shown previously that Schwann cell-conditioned medium (SC-CM) promotes synaptogenesis in Xenopus nerve-muscle cocultures. The present study aimed to identify the synaptogenic molecules in SC-CM. Combining biochemical approaches and in vitro bioassays, we found that SC-CM contains transforming growth factor (TGF)-beta1, which is expressed in Schwann cells both in vivo and in vitro. Similar to SC-CM, TGF-beta1 doubled the size of acetylcholine receptor (AChR) clusters at nerve-muscle contacts and significantly increased the percentage of nerve-muscle contacts that show AChR clusters to approximately 60%, compared with approximately 20% seen in control cultures. The synaptogenic effects of SC-CM were abolished if SC-CM was immunodepleted of TGF-beta1 or if the latency-associated protein or a TGF-beta1 receptor kinase inhibitor was added to block the bioactivity of TGF-beta1. Similar to frog SC-CM, mammalian SC-CM also showed synaptogenic effects, which were prevented by immunodepletion of TGF-beta1. TGF-beta1 upregulated agrin expression in spinal neurons, which could explain the increase in AChR clusters in cultures treated with SC-CM. These results suggest that Schwann cells express TGF-beta1, which is both sufficient and necessary for mediating the synapse-promoting effects of Schwann cells at the developing neuromuscular junction. Schwann cell-derived TGF-beta1 thus joins other astrocyte-derived synaptogenic factors in further strengthening the emerging concept that glial cells contribute to synaptogenesis in both the PNS and the CNS.
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Feng Z, Ko CP. The Role of Glial Cells in the Formation and Maintenance of the Neuromuscular Junction. Ann N Y Acad Sci 2008; 1132:19-28. [DOI: 10.1196/annals.1405.016] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Cao G, Ko CP. Schwann cell-derived factors modulate synaptic activities at developing neuromuscular synapses. J Neurosci 2007; 27:6712-22. [PMID: 17581958 PMCID: PMC6672697 DOI: 10.1523/jneurosci.1329-07.2007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Glial cells are active participants in the function, formation, and maintenance of the chemical synapse. To investigate the molecular basis of neuron-glia interactions at the peripheral synapse, we examined whether and how Schwann cell-derived factors modulate synaptic function at developing neuromuscular junctions (NMJs). Schwann cell-conditioned medium (SC-CM) from Xenopus Schwann cell cultures was collected and applied to Xenopus nerve-muscle cocultures. We found that SC-CM increased the frequency of spontaneous synaptic currents (SSCs) within 3-15 min by an average of approximately 150-fold at developing neuromuscular synapses. The increase in SSC frequency by SC-CM is a presynaptic effect independent of neuronal excitability and requires the influx of Ca2+. In contrast to its potentiating effect on spontaneous transmitter release, SC-CM suppressed the evoked transmitter release. The SC-CM effect required the presence of motoneuron soma but not protein synthesis. Using molecular weight cutoff filters and dialysis membranes, we found that the molecular weight of functional factor(s) in SC-CM was within 500 and 5000 Da. The SC-CM effect was not attributable to currently known factors that modulate synaptic efficacy, including neurotrophins, glutamate, and ATP. SC-CM also enhanced spontaneous synaptic release at developing NMJs in Xenopus tadpoles in situ. Our results suggest that Schwann cells release small molecules that enhance spontaneous synaptic activities acutely and potently at developing neuromuscular synapses, and the glial cell-enhanced spontaneous neurotransmission may contribute to synaptogenesis.
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Affiliation(s)
- Guan Cao
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520
| | - Chien-Ping Ko
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520
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12
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VanSaun M, Humburg BC, Arnett MG, Pence M, Werle MJ. Activation of matrix metalloproteinase-3 is altered at the frog neuromuscular junction following changes in synaptic activity. Dev Neurobiol 2007; 67:1488-97. [PMID: 17525979 DOI: 10.1002/dneu.20523] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The extracellular matrix surrounding the neuromuscular junction is a highly specialized and dynamic structure. Matrix Metalloproteinases are enzymes that sculpt the extracellular matrix. Since synaptic activity is critical to the structure and function of this synapse, we investigated whether changes in synaptic activity levels could alter the activity of Matrix Metalloproteinases at the neuromuscular junction. In particular, we focused on Matrix Metalloproteinase 3 (MMP3), since antibodies to MMP3 recognize molecules at the frog neuromuscular junction, and MMP3 cleaves a number of synaptic basal lamina molecules, including agrin. Here we show that the fluorogenic compound (M2300) can be used to perform in vivo proteolytic imaging of the frog neuromuscular junction to directly measure the activity state of MMP3. Application of this compound reveals that active MMP3 is concentrated at the normal frog neuromuscular junction, and is tightly associated with the terminal Schwann cell. Blocking presynaptic activity via denervation, or TTX nerve blockade, results in a decreased level of active MMP3 at the neuromuscular junction. The loss of active MMP3 at the neuromuscular junction in denervated muscles can result from decreased activation of pro-MMP3, or it could result from increased inhibition of MMP3. These results support the hypothesis that changes in synaptic activity can alter the level of active MMP3 at the neuromuscular junction.
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Affiliation(s)
- M VanSaun
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
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Abstract
Glial cells are widely distributed throughout the nervous system, including at the chemical synapse. However, our knowledge of the role of glial cells at the synapse is rudimentary. Recent studies using a model synapse, the vertebrate neuromuscular junction (NMJ), have demonstrated that perisynaptic Schwann cells (PSCs), which are the glia juxtaposed to the nerve terminal at the NMJ, play active and essential roles in synaptic function, maintenance, and development. PSCs can respond to nerve activity by increasing intracellular calcium and are capable of modulating synaptic function in response to pharmacological manipulations. Studies using PSC ablation in vivo have shown that PSCs are essential for the long-term maintenance of synaptic structure and function at the adult NMJ. In vivo observations have also shown that PSCs guide presynaptic nerve terminal extension and dictate the pattern of innervation during synaptic regeneration and remodeling at adult NMJs. PSCs may also induce postsynaptic acetylcholine receptor aggregation. Furthermore, PSCs play an essential role in synaptic growth and maintenance during development of NMJs in vivo, and Schwann cell-derived factors can promote synaptogenesis and enhance synaptic transmission in tissue culture. These recent findings advance the emerging concept that glial cells help make bigger, stronger, and more stable synapses.
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Affiliation(s)
- Zhihua Feng
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520, USA
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14
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Zuo Y, Lubischer JL, Kang H, Tian L, Mikesh M, Marks A, Scofield VL, Maika S, Newman C, Krieg P, Thompson WJ. Fluorescent proteins expressed in mouse transgenic lines mark subsets of glia, neurons, macrophages, and dendritic cells for vital examination. J Neurosci 2005; 24:10999-1009. [PMID: 15590915 PMCID: PMC6730273 DOI: 10.1523/jneurosci.3934-04.2004] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
To enable vital observation of glia at the neuromuscular junction, transgenic mice were generated that express proteins of the green fluorescent protein family under control of transcriptional regulatory sequences of the human S100B gene. Terminal Schwann cells were imaged repetitively in living animals of one of the transgenic lines to show that, except for extension and retraction of short processes, the glial coverings of the adult neuromuscular synapse are stable. In other lines, subsets of Schwann cells were labeled. The distribution of label suggests that Schwann cells at individual synapses are clonally related, a finding with implications for how these cells might be sorted during postnatal development. Other labeling patterns, some present in unique lines, included astrocytes, microglia, and subsets of cerebellar Bergmann glia, spinal motor neurons, macrophages, and dendritic cells. We show that lines with labeled macrophages can be used to follow the accumulation of these cells at sites of injury.
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Affiliation(s)
- Yi Zuo
- Section of Neurobiology, Institute for Neuroscience, University of Texas, Austin, Texas 78712, USA
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Corfas G, Velardez MO, Ko CP, Ratner N, Peles E. Mechanisms and roles of axon-Schwann cell interactions. J Neurosci 2005; 24:9250-60. [PMID: 15496660 PMCID: PMC6730082 DOI: 10.1523/jneurosci.3649-04.2004] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Gabriel Corfas
- Division of Neuroscience, Children's Hospital, Boston, Massachusetts 02115, USA
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Pinard A, Lévesque S, Vallée J, Robitaille R. Glutamatergic modulation of synaptic plasticity at a PNS vertebrate cholinergic synapse. Eur J Neurosci 2004; 18:3241-50. [PMID: 14686898 DOI: 10.1111/j.1460-9568.2003.03028.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The presence and the functionality of a glutamatergic regulation was studied at the frog neuromuscular junction (NMJ), a singly innervated cholinergic synapse. Bath application of glutamate reduced transmitter release without affecting nerve-evoked presynaptic Ca2+ entry and handling. (1S,3R)-aminocyclopentanedicarboxylic acid (ACPD), a metabotropic glutamate receptor (mGluR) agonist, mimicked the effects of glutamate while (S)-alpha-methyl-4-carboxyphenylglycine (MCPG), a mGluR antagonist, blocked glutamate effects. MCPG had no effect on transmitter release evoked at low frequency (0.2 Hz) but significantly reduced synaptic depression (10 Hz, 80 s). This suggests that a frequency-dependent endogenous glutamatergic modulation is present at the frog NMJ and is mediated through mGluRs. Immunohistochemical labelling revealed the presence of mGluRs at the end plate area, primarily on muscle fibers. Functional glutamate uptake machinery was also found at the NMJ as blockade of glutamate transport by the inhibitor dl-threo-beta-benzyloxyaspartate (DL-TBOA) increased high frequency-induced depression, suggesting that the transporters system is used to eliminate glutamate from the extracellular space. Moreover, immunohistochemical labelling revealed that glutamate-aspartate transporters (GLASTs) are predominantly present on perisynaptic Schwann cells (PSCs). However, local application of glutamate on PSCs unreliability evoked small Ca2+ responses. Hence, these data suggest that functional glutamatergic interactions at a purely cholinergic synapse, shape synaptic efficacy and short-term plasticity in a frequency-dependent fashion.
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Affiliation(s)
- Audrée Pinard
- Centre de Recherche en Sciences Neurologiques and Département de physiologie, Université de Montréal, Montréal, Canada,H3C 3J7
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Reddy LV, Koirala S, Sugiura Y, Herrera AA, Ko CP. Glial cells maintain synaptic structure and function and promote development of the neuromuscular junction in vivo. Neuron 2004; 40:563-80. [PMID: 14642280 DOI: 10.1016/s0896-6273(03)00682-2] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To investigate the in vivo role of glial cells in synaptic function, maintenance, and development, we have developed an approach to selectively ablate perisynaptic Schwann cells (PSCs), the glial cells at the neuromuscular junction (NMJ), en masse from live frog muscles. In adults, following acute PSC ablation, synaptic structure and function were not altered. However, 1 week after PSC ablation, presynaptic function decreased by approximately half, while postsynaptic function was unchanged. Retraction of nerve terminals increased over 10-fold at PSC-ablated NMJs. Furthermore, nerve-evoked muscle twitch tension was reduced. In tadpoles, repeated in vivo observations revealed that PSC processes lead nerve terminal growth. In the absence of PSCs, growth and addition of synapses was dramatically reduced, and existing synapses underwent widespread retraction. Our findings provide in vivo evidence that glial cells maintain presynaptic structure and function at adult synapses and are vital for the growth and stability of developing synapses.
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Affiliation(s)
- Linga V Reddy
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA
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Auld DS, Robitaille R. Perisynaptic Schwann cells at the neuromuscular junction: nerve- and activity-dependent contributions to synaptic efficacy, plasticity, and reinnervation. Neuroscientist 2003; 9:144-57. [PMID: 12708618 DOI: 10.1177/1073858403252229] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Glial cells are increasingly recognized for their important contributions to CNS and PNS synaptic function. Perisynaptic Schwann cells, which are glial cells at the neuromuscular junction, have proven to be an exceptionally useful model for studying these roles. Recent studies have shown that they detect and reciprocally modulate synaptic efficacy in an activity-dependent manner in the short term. In addition, perisynaptic Schwann cells guide reinnervating nerve sprouts after deinnervation, and many important parameters of this are dependent on synapse activity. Thus, it is hypothesized that perisynaptic Schwann cells are key integrators in a continuum of synaptic efficacy, stability, and plasticity at the neuromuscular junction, which is important for maintaining and restoring synaptic efficacy.
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Affiliation(s)
- Daniel S Auld
- Centre de Recherche en Sciences Neurologiques, Université de Montréal, Québec, Canada
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Abstract
The specificity of action of Xestospongin C (XeC) towards the inositol 1,4,5-trisphosphate (IP3) receptor has been studied using the frog neuromuscular junction. In perisynaptic Schwann cells (PSCs), glial cells at this synapse, Ca2+ stores are dependent upon IP3 activation. Bath application of XeC (700 nM) caused a transient calcium elevation and blocked Ca2+ responses evoked in PSCs by synaptic activity or various agonists (ATP, muscarine, adenosine) only when Ca2+ stores had previously been challenged with local application of agonists. Moreover, XeC occluded the effects of thapsigargin (tg; 2 microM), a blocker of the Ca2+ ATPase pump of internal stores, which failed to evoke Ca2+ transients following 20 min of exposure to XeC. In nerve terminals, where the Ca2+ stores are ryanodine-sensitive, application of XeC (700 nM) prolonged the recovery phase of Ca2+ transients evoked by single action potentials, due to a prolonged Ca2+ clearance in the nerve terminal. No effects of tg (2 microM) were observed on Ca2+ response evoked by nerve stimulation when applied on the preparation after XeC (700 nM). Conversely, XeC (700 nM) had no effect on the shape and duration of Ca2+ entry in nerve terminals when tg was applied before XeC. These results indicate that XeC acts as an inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) pump of internal stores.
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Affiliation(s)
- A Castonguay
- Centre de Recherche en Sciences Neurologiques, Université de Montréal, Que., H3C 3J7, Montréal, Canada.
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Abstract
To explore novel roles of glial cells in synaptic function and formation, we examined the expression of agrin in frog Schwann cells and tested their role in the aggregation of acetylcholine receptors (AChRs). Using reverse transcription-PCR, we found that Schwann cells along nerve fibers in tadpoles expressed only the inactive agrin isoform B0 but began to also express active agrin isoforms B11 and B19 at approximately metamorphosis. During nerve regeneration in the adult, the expression of these active agrin isoforms in Schwann cells was upregulated, including the appearance of the most potent isoform, B8. This upregulation was induced by regenerating axons but not by nerve injury per se. In muscle cultures, the presence of adult Schwann cells enhanced the number and the total area of AChR aggregates 2.2- and 4.5-fold, respectively, and this enhancement was eliminated by heparin treatment. Furthermore, adult Schwann cells in culture expressed active agrin isoforms and produced agrin protein. Using a novel technique to selectively ablate perisynaptic Schwann cells (PSCs) at the neuromuscular junction, we found that PSCs also expressed active agrin isoforms B11 and B19, and these active isoforms were upregulated, including the appearance of B8, during reinnervation. Observation in vivo showed that extrajunctional AChR aggregates were associated with PSC sprouts after nerve injury and subsequent reinnervation. These results suggest that, contrary to the prevailing view that only neurons express active agrin, glial cells also express active agrin and play a role in the aggregation of AChRs both in vitro and in vivo.
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Formation and function of synapses with respect to Schwann cells at the end of motor nerve terminal branches on mature amphibian (Bufo marinus) muscle. J Neurosci 2001. [PMID: 11264312 DOI: 10.1523/jneurosci.21-07-02380.2001] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A study has been made of the formation and regression of synapses with respect to Schwann cells at the ends of motor nerve terminal branches in mature toad (Bufo marinus) muscle. Synapse formation and regression, as inferred from the appearance and loss of N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM1-43)-stained vesicle clusters, occurred at the ends of terminal branches over a 16 hr period. Multiple microelectrodes placed in an array about FM1-43 blobs at the ends of terminal branches detected the electrical signs of neurotransmitter being released onto receptors. Injection of a calcium indicator (Oregon Green 488 BAPTA-1) into the motor nerve with subsequent imaging of the calcium transients, in response to stimulation, often showed a reduced calcium influx in the ends of terminal branches. Injection of a fluorescent dye into motor nerves revealed the full extent of their terminal branches and growing processes. Injection of the terminal Schwann cells (TSCs) often revealed pseudopodial TSC processes up to 10-microm-long. Imaging of these TSC processes over minutes or hours showed that they were highly labile and capable of extending several micrometers in a few minutes. Injection of motor nerve terminals with a different dye to that injected into their TSCs revealed that terminal processes sometimes followed the TSC processes over a few hours. It is suggested that the ends of motor nerve terminals in vivo are in a constant state of remodeling through the formation and regression of processes, that TSC processes guide the remodeling, and that it can occur over a relatively short period of time.
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Herrera AA, Qiang H, Ko CP. The role of perisynaptic Schwann cells in development of neuromuscular junctions in the frog (Xenopus laevis). JOURNAL OF NEUROBIOLOGY 2000; 45:237-54. [PMID: 11077428 DOI: 10.1002/1097-4695(200012)45:4<237::aid-neu5>3.0.co;2-j] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Fluorescence microscopy was used to study the behavior of perisynaptic Schwann cells (PSCs) in relation to motor nerve terminals and postsynaptic clusters of acetylcholine receptors, during the development of the neuromuscular junction (NMJ) in the frog Xenopus laevis. Pectoral (supracoracoideus) muscles were labeled with monoclonal antibody 2A12 for Schwann cells, the dye FM4-64 for nerve terminals (NTs), alpha-bungarotoxin for acetylcholine receptors (AChRs), and Hoechst 33258 for cellular nuclei, in animals from tadpole stage 57 to fully grown adults. When muscle fibers first appeared in stage 57, NMJs consisted of tightly apposed NTs and AChRs and were only partially covered with PSCs or their processes. Within a few stages, PSCs fully occupied and overgrew the NMJs, extending fine sprouts between a few micrometers and hundreds of micrometers beyond the borders of the junction. Sprouts of PSCs were most abundant during the time when secondary myogenesis, synaptogenesis, and synaptic growth occurred at their highest rates. PSCs were recruited to NMJs during synaptic growth, at rates between 1.3 PSCs/100 microm junctional length early on and 0.4 PSCs/100 microm later. Shortly after metamorphosis, PSC sprouts disappeared and NMJs acquired the adult appearance, in which PSCs, NTs, and AChRs were mostly congruent. The results suggest that, although PSCs may not be required for initial nerve-muscle contacts, PSCs sprouts lead synaptic growth and play a role in the extension and maturation of developing NMJs.
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Affiliation(s)
- A A Herrera
- Neurobiology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520, USA.
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Koirala S, Qiang H, Ko CP. Reciprocal interactions between perisynaptic Schwann cells and regenerating nerve terminals at the frog neuromuscular junction. JOURNAL OF NEUROBIOLOGY 2000; 44:343-60. [PMID: 10942887 DOI: 10.1002/1097-4695(20000905)44:3<343::aid-neu5>3.0.co;2-o] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The perisynaptic Schwann cell (PSC) has gained recent attention with respect to its roles in synaptic function, remodeling, and regeneration at the vertebrate neuromuscular junction (NMJ). Here we test the hypothesis that, following nerve injury, processes extended by PSCs guide regenerating nerve terminals (NTs) in vivo, and that the extension of sprouts by PSCs is triggered by the arrival of regenerating NTs. Frog NMJs were double-stained with a fluorescent dye, FM4-64, for NTs, and fluorescein isothiocyanate (FITC)-tagged peanut agglutinin (PNA) for PSCs. Identified NMJs were imaged in vivo repeatedly for several months after nerve injury. PSCs sprouted profusely beginning 3-4 weeks after nerve transection and, as reinnervation progressed, regenerating NTs closely followed the preceding PSC sprouts, which could extend tens to hundreds of microns beyond the original synaptic site. The pattern of reinnervation was dictated by PSC sprouts, which could form novel routes joining neighboring junctions or develop into new myelinated axonal pathways. In contrast to mammals, profuse PSC sprouting in frog muscles was not seen in response to axotomy alone, and did not occur at chronically denervated NMJs. Instead, sprouting coincided with the arrival of regenerating NTs. Immunofluorescent staining revealed that in muscle undergoing reinnervation 4 weeks after axotomy, 91% of NMJs bore PSC sprouts, compared to only 6% of NMJs in muscle that was chronically denervated for 4 weeks. These results suggest that reciprocal interactions between regenerating NTs and PSCs govern the process of reinnervation at frog NMJs: regenerating NTs induce PSCs to sprout, and PSC sprouts, in turn, lead and guide the elaboration of NTs.
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Affiliation(s)
- S Koirala
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520, USA
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Abstract
To gain insight into the role of F-actin in the organization of synaptic vesicles at release sites, we examined the synaptic distribution of F-actin by using a unique synaptic preparation of frog target-deprived nerve terminals. In this preparation, imaging of the synaptic site was unobstructed by the muscle fiber cytoskeleton, allowing for the examination of hundreds of synaptic sites in their entirety in whole mounts. At target-deprived synaptic sites F-actin was distributed in a ladder-like pattern and was colocalized with beta-fodrin. Surprisingly, F-actin stain, which we localized to the nerve terminal itself, did not overlap a synaptic vesicle marker, suggesting that it was concentrated in nonrelease domains of nerve terminals between clusters of synaptic vesicles. These findings suggest that the majority of the presynaptic F-actin is not involved in tethering synaptic vesicles. Instead, the strategic presynaptic positioning of this cytoskeletal meshwork in nonrelease domains of the nerve terminal suggests alternate functions such as restricting synaptic vesicles to release domains, recycling synaptic vesicles, or stabilizing the nerve terminal.
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Abstract
Active zones are the sites along nerve terminals where synaptic vesicles dock and undergo calcium-dependent exocytosis during synaptic transmission. Here we show, by immunofluorescent staining with antibodies generated against Xenopus laevis integrins, that alpha3beta1 integrin is concentrated at the active zones of Xenopus motor nerve terminals. Because integrins can link extracellular matrix molecules to cytoskeletal elements and participate in the formation of signaling complexes, the localization of integrin at active zones suggests that it may play a role in the adhesion of the nerve terminals to the synaptic basal lamina, in the formation and maintenance of active zones, and in some of the events associated with calcium-dependent exocytosis of neurotransmitter. Our findings also indicate that the integrin composition of the terminal Schwann cells differs from that of the motor nerve terminals, and this may account at least in part for differences in their adhesiveness to the synaptic basal lamina.
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