51
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Abstract
Motor neurons regulate neuromuscular junction formation by using agrin to stimulate acetylcholine receptor clustering and using acetylcholine to disperse unnecessary receptor clusters on muscle fibers. Wang et al. (2014) now report in this issue of Developmental Cell a critical role for caspase-3 in intracellular mechanisms of acetylcholine-induced dispersal.
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Affiliation(s)
- Chengyong Shen
- Department of Neuroscience and Regenerative Medicine and Department of Neurology, Medical College of Georgia, Georgia Regents University, 1120 15(th) Street, Augusta, GA 30912, USA; Charlie Norwood VA Medical Center, Augusta, GA 30904, USA
| | - Wen C Xiong
- Department of Neuroscience and Regenerative Medicine and Department of Neurology, Medical College of Georgia, Georgia Regents University, 1120 15(th) Street, Augusta, GA 30912, USA; Charlie Norwood VA Medical Center, Augusta, GA 30904, USA
| | - Lin Mei
- Department of Neuroscience and Regenerative Medicine and Department of Neurology, Medical College of Georgia, Georgia Regents University, 1120 15(th) Street, Augusta, GA 30912, USA; Charlie Norwood VA Medical Center, Augusta, GA 30904, USA.
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52
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Wang JY, Chen F, Fu XQ, Ding CS, Zhou L, Zhang XH, Luo ZG. Caspase-3 cleavage of dishevelled induces elimination of postsynaptic structures. Dev Cell 2014; 28:670-84. [PMID: 24631402 DOI: 10.1016/j.devcel.2014.02.009] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2013] [Revised: 12/17/2013] [Accepted: 02/13/2014] [Indexed: 11/19/2022]
Abstract
During the development of vertebrate neuromuscular junction (NMJ), agrin stabilizes, whereas acetylcholine (ACh) destabilizes AChR clusters, leading to the refinement of synaptic connections. The intracellular mechanism underlying this counteractive interaction remains elusive. Here, we show that caspase-3, the effector protease involved in apoptosis, mediates elimination of AChR clusters. We found that caspase-3 was activated by cholinergic stimulation of cultured muscle cells without inducing cell apoptosis and that this activation was prevented by agrin. Interestingly, inhibition of caspase-3 attenuated ACh agonist-induced dispersion of AChR clusters. Furthermore, we identified Dishevelled1 (Dvl1), a Wnt signaling protein involved in AChR clustering, as the substrate of caspase-3. Blocking Dvl1 cleavage prevented induced dispersion of AChR clusters. Finally, inhibition or genetic ablation of caspase-3 or expression of a caspase-3-resistant form of Dvl1 caused stabilization of aneural AChR clusters. Thus, caspase-3 plays an important role in the elimination of postsynaptic structures during the development of NMJs.
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MESH Headings
- Acetylcholine/metabolism
- Adaptor Proteins, Signal Transducing/antagonists & inhibitors
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/metabolism
- Agrin/physiology
- Animals
- Caspase 3/metabolism
- Cells, Cultured
- Dishevelled Proteins
- Electrophysiology
- Embryo, Mammalian/cytology
- Embryo, Mammalian/metabolism
- Image Processing, Computer-Assisted
- Immunoenzyme Techniques
- Mice
- Mice, Knockout
- Motor Neurons/cytology
- Motor Neurons/metabolism
- Muscle, Skeletal/cytology
- Muscle, Skeletal/metabolism
- Neuromuscular Junction/physiology
- Phosphoproteins/antagonists & inhibitors
- Phosphoproteins/genetics
- Phosphoproteins/metabolism
- RNA, Small Interfering/genetics
- Rats
- Rats, Sprague-Dawley
- Receptors, Cholinergic/metabolism
- Signal Transduction
- Synaptic Potentials/physiology
- Synaptic Transmission
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Affiliation(s)
- Jin-Yuan Wang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; Graduate School, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Fei Chen
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Xiu-Qing Fu
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; Graduate School, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Chuang-Shi Ding
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; School of Life Science and Technology, ShanghaiTech University, 319 Yueyang Road, Shanghai 200031, China
| | - Li Zhou
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; Graduate School, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Xiao-Hui Zhang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Zhen-Ge Luo
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; Graduate School, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; School of Life Science and Technology, ShanghaiTech University, 319 Yueyang Road, Shanghai 200031, China.
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53
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Fontenele M, Lim B, Oliveira D, Buffolo M, Perlman DH, Schupbach T, Araujo H. Calpain A modulates Toll responses by limited Cactus/IκB proteolysis. Mol Biol Cell 2013; 24:2966-80. [PMID: 23864715 PMCID: PMC3771957 DOI: 10.1091/mbc.e13-02-0113] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Calcium-dependent cysteine proteases of the calpain family are modulatory proteases that cleave their substrates in a limited manner. Among their substrates, calpains target vertebrate and invertebrate IκB proteins. Because proteolysis by calpains potentially generates novel protein functions, it is important to understand how this affects NFκB activity. We investigate the action of Calpain A (CalpA) on the Drosophila melanogaster IκB homologue Cactus in vivo. CalpA alters the absolute amounts of Cactus protein. Our data indicate, however, that CalpA uses additional mechanisms to regulate NFκB function. We provide evidence that CalpA interacts physically with Cactus, recognizing a Cactus pool that is not bound to Dorsal, a fly NFκB/Rel homologue. We show that proteolytic cleavage by CalpA generates Cactus fragments lacking an N-terminal region required for Toll responsiveness. These fragments are generated in vivo and display properties distinct from those of full-length Cactus. We propose that CalpA targets free Cactus, which is incorporated into and modulates Toll-responsive complexes in the embryo and immune system.
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Affiliation(s)
- Marcio Fontenele
- Institute for Biomedical Sciences, Federal University of Rio de Janeiro, CEP 21941-902 Rio de Janeiro, Brazil Chemistry Institute, Federal University of Rio de Janeiro, CEP 21941-902 Rio de Janeiro, Brazil Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Rio de Janeiro, Brazil Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544 Princeton Collaborative Proteomics and Mass Spectrometry Center, Princeton University, Princeton, NJ 08544 Molecular Biology Department, Princeton University, Princeton, NJ 08544 Howard Hughes Medical Institute, Chevy Chase, MD 20815
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54
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Skeletal muscle calpain acts through nitric oxide and neural miRNAs to regulate acetylcholine release in motor nerve terminals. J Neurosci 2013; 33:7308-7324. [PMID: 23616539 DOI: 10.1523/jneurosci.0224-13.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Cholinergic overactivity in diseases of neuromuscular transmission elicits a retrograde signal resembling homeostatic synaptic plasticity that downregulates transmitter release. Understanding this compensatory pathway could provide insights into novel therapeutic avenues and molecular mechanisms underlying learning and memory. Here we identify nitric oxide as a possible source of this signal in pathological human and mouse muscle samples and link this signaling pathway to changes in synaptic function in the neuromuscular junction. We further show that neuronal nitric oxide synthase is regulated by cholinergic excess through activation of skeletal muscle calpain and its effect on Cdk5 and CaMKII, leading to direct modulation of presynaptic function. Finally, we show that this signaling pathway acts through specific miRNA control of presynaptic vesicle protein expression. The control of presynaptic miRNA levels by postsynaptic activity represents a novel mechanism for the modulation of synaptic activity in normal or pathological conditions.
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55
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Morsch M, Reddel SW, Ghazanfari N, Toyka KV, Phillips WD. Pyridostigmine but not 3,4-diaminopyridine exacerbates ACh receptor loss and myasthenia induced in mice by muscle-specific kinase autoantibody. J Physiol 2013; 591:2747-62. [PMID: 23440963 DOI: 10.1113/jphysiol.2013.251827] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In myasthenia gravis, the neuromuscular junction is impaired by the antibody-mediated loss of postsynaptic acetylcholine receptors (AChRs). Muscle weakness can be improved upon treatment with pyridostigmine, a cholinesterase inhibitor, or with 3,4-diaminopyridine, which increases the release of ACh quanta. The clinical efficacy of pyridostigmine is in doubt for certain forms of myasthenia. Here we formally examined the effects of these compounds in the antibody-induced mouse model of anti-muscle-specific kinase (MuSK) myasthenia gravis. Mice received 14 daily injections of IgG from patients with anti-MuSK myasthenia gravis. This caused reductions in postsynaptic AChR densities and in endplate potential amplitudes. Systemic delivery of pyridostigmine at therapeutically relevant levels from days 7 to 14 exacerbated the anti-MuSK-induced structural alterations and functional impairment at motor endplates in the diaphragm muscle. No such effect of pyridostigmine was found in mice receiving control human IgG. Mice receiving smaller amounts of MuSK autoantibodies did not display overt weakness, but 9 days of pyridostigmine treatment precipitated generalised muscle weakness. In contrast, one week of treatment with 3,4-diaminopyridine enhanced neuromuscular transmission in the diaphragm muscle. Both pyridostigmine and 3,4-diaminopyridine increase ACh in the synaptic cleft yet only pyridostigmine potentiated the anti-MuSK-induced decline in endplate ACh receptor density. These results thus suggest that ongoing pyridostigmine treatment potentiates anti-MuSK-induced AChR loss by prolonging the activity of ACh in the synaptic cleft.
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Affiliation(s)
- Marco Morsch
- School of Medical Sciences (Physiology) and Bosch Institute, Anderson Stuart Bldg (F13), University of Sydney, NSW 2006, Australia
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56
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Wang J, Luo ZG. The role of Wnt/beta-catenin signaling in postsynaptic differentiation. Commun Integr Biol 2012; 1:158-60. [PMID: 19704879 DOI: 10.4161/cib.1.2.7099] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2008] [Accepted: 09/30/2008] [Indexed: 01/05/2023] Open
Abstract
Synapses are basic units that mediate the communication between neurons and their target cells. The formation of synapse is regulated by secreted factors, receptors, adhesion molecules and intracellular signaling molecules. The interplay between positive and negative factors determines synapse assembling, remodeling and elimination, resulting in the formation of precise synaptic connections. However, compared to the abundant identified positive factors, negative factors are largely unknown. We have recently shown that Wnt3a acts as a negative factor that inhibits postsynaptic differentiation at the neuromuscular junction (NMJ), the synapse formed between motor neurons and skeletal muscle fibers. The clustering of acetylcholine receptor (AChR) guarantees efficient and accurate neurotransmission and is a hallmark for postsynaptic differentiation at the NMJ. We found that treatment with Wnt3a or upregulation of beta-catenin inhibited the formation of AChR clusters. Furthermore, we investigated the underlying mechanism and found that Wnt/beta-catenin signaling negatively regulated AChR clustering by downregulating the expression of Rapsyn, an AChR-associated protein required for formation and stabilization of AChR clusters.
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Affiliation(s)
- Jia Wang
- Institute of Neuroscience and Key Laboratory of Neurobiology; Chinese Academy of Sciences; Shanghai P.R. China
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57
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Acetylcholine receptors enable the transport of rapsyn from the Golgi complex to the plasma membrane. J Neurosci 2012; 32:7356-63. [PMID: 22623681 DOI: 10.1523/jneurosci.0397-12.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The accumulation of acetylcholine receptors (AChRs) at nerve terminals is critical for signal transmission at the neuromuscular junction, and rapsyn is essential for this process. Previous studies suggest that AChRs might direct rapsyn self-clusters to the synapse. In vivo experiments with fluorescently tagged AChR or rapsyn in zebrafish larvae revealed that rapsyn self-clusters separate from AChRs did not exist before synapse formation. Examination of rapsyn in the AChR-less mutant sofa potato revealed that rapsyn in the absence of AChR was localized in the Golgi complex. Expression of muscle-type AChR in sofa potato restored synaptic clustering of rapsyn, while neuronal type AChR had no effect. To determine whether this requirement of protein interaction is reciprocal, we examined the mutant twitch once, which has a missense mutation in rapsyn. While the AChRs distributed nonsynaptically on the plasma membrane in twitch once, mutant rapsyn was retained in the Golgi complex. We conclude that AChRs enable the transport of rapsyn from the Golgi complex to the plasma membrane through a molecule-specific interaction.
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58
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Singhal N, Martin PT. Role of extracellular matrix proteins and their receptors in the development of the vertebrate neuromuscular junction. Dev Neurobiol 2012; 71:982-1005. [PMID: 21766463 DOI: 10.1002/dneu.20953] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The vertebrate neuromuscular junction (NMJ) remains the best-studied model for understanding the mechanisms involved in synaptogenesis, due to its relatively large size, its simplicity of patterning, and its unparalleled experimental accessibility. During neuromuscular development, each skeletal myofiber secretes and deposits around its extracellular surface an assemblage of extracellular matrix (ECM) proteins that ultimately form a basal lamina. This is also the case at the NMJ, where the motor nerve contributes additional factors. Before most of the current molecular components were known, it was clear that the synaptic ECM of adult skeletal muscles was unique in composition and contained factors sufficient to induce the differentiation of both pre- and postsynaptic membranes. Biochemical, genetic, and microscopy studies have confirmed that agrin, laminin (221, 421, and 521), collagen IV (α3-α6), collagen XIII, perlecan, and the ColQ-bound form of acetylcholinesterase are all synaptic ECM proteins with important roles in neuromuscular development. The roles of their many potential receptors and/or binding proteins have been more difficult to assess at the genetic level due to the complexity of membrane interactions with these large proteins, but roles for MuSK-LRP4 in agrin signaling and for integrins, dystroglycan, and voltage-gated calcium channels in laminin-dependent phenotypes have been identified. Synaptic ECM proteins and their receptors are involved in almost all aspects of synaptic development, including synaptic initiation, topography, ultrastructure, maturation, stability, and transmission.
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Affiliation(s)
- Neha Singhal
- Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Department of Pediatrics, Ohio State University College of Medicine, Columbus, Ohio 43205, USA
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59
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Molecular mechanisms underlying maturation and maintenance of the vertebrate neuromuscular junction. Trends Neurosci 2012; 35:441-53. [PMID: 22633140 DOI: 10.1016/j.tins.2012.04.005] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 04/09/2012] [Accepted: 04/15/2012] [Indexed: 01/22/2023]
Abstract
The vertebrate neuromuscular junction (NMJ), a peripheral synapse formed between motoneuron and skeletal muscle, is characterized by a protracted postnatal period of maturation and life-long maintenance. In neuromuscular disorders such as congenital myasthenic syndromes (CMSs), disruptions of NMJ maturation and/or maintenance are frequently observed. In particular, defective neuromuscular transmission associated with structural and molecular abnormalities at the pre- and postsynaptic membranes, as well as at the synaptic cleft, has been reported in these patients. Here, we review recent advances in the understanding of molecular and cellular events that mediate NMJ maturation and maintenance. The underlying regulatory mechanisms, including key molecular regulators at the presynaptic nerve terminal, synaptic cleft, and postsynaptic muscle membrane, are discussed.
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60
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Wu H, Lu Y, Barik A, Joseph A, Taketo MM, Xiong WC, Mei L. β-Catenin gain of function in muscles impairs neuromuscular junction formation. Development 2012; 139:2392-404. [PMID: 22627288 DOI: 10.1242/dev.080705] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Neuromuscular junction (NMJ) formation requires proper interaction between motoneurons and muscle cells. β-Catenin is required in muscle cells for NMJ formation. To understand underlying mechanisms, we investigated the effect of β-catenin gain of function (GOF) on NMJ development. In HSA-β-cat(flox(ex3)/+) mice, which express stable β-catenin specifically in muscles, motor nerve terminals became extensively defasciculated and arborized. Ectopic muscles were observed in the diaphragm and were innervated by ectopic phrenic nerve branches. Moreover, extensive outgrowth and branching of spinal axons were evident in the GOF mice. These results indicate that increased β-catenin in muscles alters presynaptic differentiation. Postsynaptically, AChR clusters in HSA-β-cat(flox(ex3)/+) diaphragms were distributed in a wider region, suggesting that muscle β-catenin GOF disrupted the signal that restricts AChR clustering to the middle region of muscle fibers. Expression of stable β-catenin in motoneurons, however, had no effect on NMJ formation. These observations provide additional genetic evidence that pre- and postsynaptic development of the NMJ requires an intricate balance of β-catenin activity in muscles.
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Affiliation(s)
- Haitao Wu
- Institute of Molecular Medicine and Genetics, Georgia Health Sciences University, Augusta, Georgia 30912, USA
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61
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Barik A, Xiong WC, Mei L. MuSK: A Kinase Critical for the Formation and Maintenance of the Neuromuscular Junction. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/978-1-61779-824-5_11] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
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62
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Ngo ST, Cole RN, Sunn N, Phillips WD, Noakes PG. Neuregulin-1 potentiates agrin-induced acetylcholine receptor clustering through muscle-specific kinase phosphorylation. J Cell Sci 2012; 125:1531-43. [PMID: 22328506 DOI: 10.1242/jcs.095109] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
At neuromuscular synapses, neural agrin (n-agrin) stabilizes embryonic postsynaptic acetylcholine receptor (AChR) clusters by signalling through the muscle-specific kinase (MuSK) complex. Live imaging of cultured myotubes showed that the formation and disassembly of primitive AChR clusters is a dynamic and reversible process favoured by n-agrin, and possibly other synaptic signals. Neuregulin-1 is a growth factor that can act through muscle ErbB receptor kinases to enhance synaptic gene transcription. Recent studies suggest that neuregulin-1-ErbB signalling can modulate n-agrin-induced AChR clustering independently of its effects on transcription. Here we report that neuregulin-1 increased the size of developing AChR clusters when injected into muscles of embryonic mice. We investigated this phenomenon using cultured myotubes, and found that in the ongoing presence of n-agrin, neuregulin-1 potentiates AChR clustering by increasing the tyrosine phosphorylation of MuSK. This potentiation could be blocked by inhibiting Shp2, a postsynaptic tyrosine phosphatase known to modulate the activity of MuSK. Our results provide new evidence that neuregulin-1 modulates the signaling activity of MuSK and hence might function as a second-order regulator of postsynaptic AChR clustering at the neuromuscular synapse. Thus two classic synaptic signalling systems (neuregulin-1 and n-agrin) converge upon MuSK to regulate postsynaptic differentiation.
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Affiliation(s)
- Shyuan T Ngo
- School of Biomedical Sciences, University of Queensland, St. Lucia, 4072, Queensland, Australia
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63
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Zhu H, Bhattacharyya BJ, Lin H, Gomez CM. Skeletal muscle IP3R1 receptors amplify physiological and pathological synaptic calcium signals. J Neurosci 2011; 31:15269-83. [PMID: 22031873 PMCID: PMC3237715 DOI: 10.1523/jneurosci.3766-11.2011] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2011] [Revised: 08/24/2011] [Accepted: 09/01/2011] [Indexed: 01/11/2023] Open
Abstract
Ca(2+) release from internal stores is critical for mediating both normal and pathological intracellular Ca(2+) signaling. Recent studies suggest that the inositol 1,4,5-triphosphate (IP(3)) receptor mediates Ca(2+) release from internal stores upon cholinergic activation of the neuromuscular junction (NMJ) in both physiological and pathological conditions. Here, we report that the type I IP(3) receptor (IP(3)R(1))-mediated Ca(2+) release plays a crucial role in synaptic gene expression, development, and neuromuscular transmission, as well as mediating degeneration during excessive cholinergic activation. We found that IP(3)R(1)-mediated Ca(2+) release plays a key role in early development of the NMJ, homeostatic regulation of neuromuscular transmission, and synaptic gene expression. Reducing IP(3)R(1)-mediated Ca(2+) release via siRNA knockdown or IP(3)R blockers in C2C12 cells decreased calpain activity and prevented agonist-induced acetylcholine receptor (AChR) cluster dispersal. In fully developed NMJ in adult muscle, IP(3)R(1) knockdown or blockade effectively increased synaptic strength at presynaptic and postsynaptic sites by increasing both quantal release and expression of AChR subunits and other NMJ-specific genes in a pattern resembling muscle denervation. Moreover, in two mouse models of cholinergic overactivity and NMJ Ca(2+) overload, anti-cholinesterase toxicity and the slow-channel myasthenic syndrome (SCS), IP(3)R(1) knockdown eliminated NMJ Ca(2+) overload, pathological activation of calpain and caspase proteases, and markers of DNA damage at subsynaptic nuclei, and improved both neuromuscular transmission and clinical measures of motor function. Thus, blockade or genetic silencing of muscle IP(3)R(1) may be an effective and well tolerated therapeutic strategy in SCS and other conditions of excitotoxicity or Ca(2+) overload.
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MESH Headings
- Action Potentials/drug effects
- Action Potentials/genetics
- Animals
- Boron Compounds/pharmacology
- Calcium/metabolism
- Calcium Signaling/genetics
- Calcium Signaling/physiology
- Calpain/metabolism
- Carbachol/pharmacology
- Caspase 3/metabolism
- Caspase 9/metabolism
- Cell Line, Transformed
- Cholinergic Agonists/pharmacology
- Cholinesterase Inhibitors/toxicity
- Disease Models, Animal
- Electromyography
- Electroporation/methods
- Exercise Test
- Gene Expression Regulation/drug effects
- Gene Expression Regulation/genetics
- Green Fluorescent Proteins/genetics
- Histone Deacetylases/metabolism
- Histones/genetics
- Histones/metabolism
- In Vitro Techniques
- Inositol 1,4,5-Trisphosphate Receptors/deficiency
- Inositol 1,4,5-Trisphosphate Receptors/physiology
- Male
- Membrane Potentials/drug effects
- Membrane Potentials/genetics
- Mice
- Mice, Transgenic
- Muscle, Skeletal/metabolism
- Myasthenic Syndromes, Congenital/genetics
- Myasthenic Syndromes, Congenital/pathology
- Myasthenic Syndromes, Congenital/therapy
- Neostigmine/toxicity
- Nerve Tissue Proteins/metabolism
- Neuromuscular Junction/metabolism
- Neuromuscular Junction/physiology
- Neurotoxicity Syndromes/etiology
- Neurotoxicity Syndromes/pathology
- Neurotoxicity Syndromes/therapy
- Patch-Clamp Techniques
- RNA, Small Interfering/pharmacology
- Receptors, Cholinergic/classification
- Receptors, Cholinergic/genetics
- Receptors, Cholinergic/metabolism
- Sciatic Nerve/physiopathology
- Time Factors
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Affiliation(s)
- Haipeng Zhu
- Department of Neurology, University of Chicago Medical Center, Chicago, Illinois 60637
| | - Bula J. Bhattacharyya
- Department of Molecular Pharmacology and Biological Chemistry, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, and
| | - Hong Lin
- Departments of Neurology and Pediatrics, the Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104-4318
| | - Christopher M. Gomez
- Department of Neurology, University of Chicago Medical Center, Chicago, Illinois 60637
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64
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Yang J, Dominguez B, de Winter F, Gould TW, Eriksson JE, Lee KF. Nestin negatively regulates postsynaptic differentiation of the neuromuscular synapse. Nat Neurosci 2011; 14:324-30. [PMID: 21278733 PMCID: PMC3069133 DOI: 10.1038/nn.2747] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Accepted: 12/22/2010] [Indexed: 01/14/2023]
Abstract
Positive and negative regulation of neurotransmitter receptor aggregation on the postsynaptic membrane is a critical event during synapse formation. Acetylcholine (ACh) and agrin are two opposing signals that regulate ACh receptor (AChR) clustering during neuromuscular junction (NMJ) development. ACh induces dispersion of AChR clusters that are not stabilized by agrin via a cyclin-dependent kinase 5 (Cdk5)-mediated mechanism, but regulation of Cdk5 activation is poorly understood. We found that the intermediate filament protein nestin physically interacts with Cdk5 and is required for ACh-induced association of p35, the co-activator of Cdk5, with the muscle membrane. Blockade of nestin-dependent signaling inhibited ACh-induced Cdk5 activation and the dispersion of AChR clusters in cultured myotubes. Similar to the effects of Cdk5 gene inactivation, knockdown of nestin in agrin-deficient mouse embryos substantially restored AChR clusters. These results suggest that nestin is required for ACh-induced, Cdk5-dependent dispersion of AChR clusters during NMJ development.
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65
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Fuentes JL, Strayer MS, Matera AG. Molecular determinants of survival motor neuron (SMN) protein cleavage by the calcium-activated protease, calpain. PLoS One 2010; 5:e15769. [PMID: 21209906 PMCID: PMC3012718 DOI: 10.1371/journal.pone.0015769] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Accepted: 11/28/2010] [Indexed: 01/13/2023] Open
Abstract
Spinal muscular atrophy (SMA) is a leading genetic cause of childhood mortality, caused by reduced levels of survival motor neuron (SMN) protein. SMN functions as part of a large complex in the biogenesis of small nuclear ribonucleoproteins (snRNPs). It is not clear if defects in snRNP biogenesis cause SMA or if loss of some tissue-specific function causes disease. We recently demonstrated that the SMN complex localizes to the Z-discs of skeletal and cardiac muscle sarcomeres, and that SMN is a proteolytic target of calpain. Calpains are implicated in muscle and neurodegenerative disorders, although their relationship to SMA is unclear. Using mass spectrometry, we identified two adjacent calpain cleavage sites in SMN, S192 and F193. Deletion of small motifs in the region surrounding these sites inhibited cleavage. Patient-derived SMA mutations within SMN reduced calpain cleavage. SMN(D44V), reported to impair Gemin2 binding and amino-terminal SMN association, drastically inhibited cleavage, suggesting a role for these interactions in regulating calpain cleavage. Deletion of A188, a residue mutated in SMA type I (A188S), abrogated calpain cleavage, highlighting the importance of this region. Conversely, SMA mutations that interfere with self-oligomerization of SMN, Y272C and SMNΔ7, had no effect on cleavage. Removal of the recently-identified SMN degron (Δ268-294) resulted in increased calpain sensitivity, suggesting that the C-terminus of SMN is important in dictating availability of the cleavage site. Investigation into the spatial determinants of SMN cleavage revealed that endogenous calpains can cleave cytosolic, but not nuclear, SMN. Collectively, the results provide insight into a novel aspect of the post-translation regulation of SMN.
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Affiliation(s)
- Jennifer L. Fuentes
- Program in Molecular Biology and Biotechnology, Departments of Biology and Genetics, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Molly S. Strayer
- Program in Molecular Biology and Biotechnology, Departments of Biology and Genetics, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - A. Gregory Matera
- Program in Molecular Biology and Biotechnology, Departments of Biology and Genetics, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, United States of America
- * E-mail:
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66
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Piguet J, Schreiter C, Segura JM, Vogel H, Hovius R. Acetylcholine receptor organization in membrane domains in muscle cells: evidence for rapsyn-independent and rapsyn-dependent mechanisms. J Biol Chem 2010; 286:363-9. [PMID: 20978122 DOI: 10.1074/jbc.m110.139782] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChR) in muscle fibers are densely packed in the postsynaptic region at the neuromuscular junction. Rapsyn plays a central role in directing and clustering nAChR during cellular differentiation and neuromuscular junction formation; however, it has not been demonstrated whether rapsyn is the only cause of receptor immobilization. Here, we used single-molecule tracking methods to investigate nAChR mobility in plasma membranes of myoblast cells during their differentiation to myotubes in the presence and absence of rapsyn. We found that in myoblasts the majority of nAChR were immobile and that ∼20% of the receptors showed restricted diffusion in small domains of ∼50 nm. In myoblasts devoid of rapsyn, the fraction of mobile nAChR was considerably increased, accompanied by a 3-fold decrease in the immobile population of nAChR with respect to rapsyn-expressing cells. Half of the mobile receptors were confined to domains of ∼120 nm. Measurements performed in heterologously transfected HEK cells confirmed the direct immobilization of nAChR by rapsyn. However, irrespective of the presence of rapsyn, about one-third of nAChR were confined in 300-nm domains. Our results show (i) that rapsyn efficiently immobilizes nAChR independently of other postsynaptic scaffold components; (ii) nAChR is constrained in confined membrane domains independently of rapsyn; and (iii) in the presence of rapsyn, the size of these domains is strongly reduced.
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Affiliation(s)
- Joachim Piguet
- Laboratoire de Chimie Physique des Polymères et Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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Ghazanfari N, Fernandez KJ, Murata Y, Morsch M, Ngo ST, Reddel SW, Noakes PG, Phillips WD. Muscle specific kinase: organiser of synaptic membrane domains. Int J Biochem Cell Biol 2010; 43:295-8. [PMID: 20974278 DOI: 10.1016/j.biocel.2010.10.008] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Revised: 10/15/2010] [Accepted: 10/15/2010] [Indexed: 11/19/2022]
Abstract
Muscle Specific Kinase (MuSK) is a transmembrane tyrosine kinase vital for forming and maintaining the mammalian neuromuscular junction (NMJ: the synapse between motor nerve and skeletal muscle). MuSK expression switches on during skeletal muscle differentiation. MuSK then becomes restricted to the postsynaptic membrane of the NMJ, where it functions to cluster acetylcholine receptors (AChRs). The expression, activation and turnover of MuSK are each regulated by signals from the motor nerve terminal. MuSK forms the core of an emerging signalling complex that can be acutely activated by neural agrin (N-agrin), a heparin sulfate proteoglycan secreted from the nerve terminal. MuSK activation initiates complex intracellular signalling events that coordinate the local synthesis and assembly of synaptic proteins. The importance of MuSK as a synapse organiser is highlighted by cases of autoimmune myasthenia gravis in which MuSK autoantibodies can deplete MuSK from the postsynaptic membrane, leading to complete disassembly of the adult NMJ.
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Affiliation(s)
- Nazanin Ghazanfari
- Physiology and Bosch Institute, Anderson Stuart Bldg (F13), The University of Sydney, Sydney, NSW 2006, Australia.
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68
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Liang B, Duan BY, Zhou XP, Gong JX, Luo ZG. Calpain activation promotes BACE1 expression, amyloid precursor protein processing, and amyloid plaque formation in a transgenic mouse model of Alzheimer disease. J Biol Chem 2010; 285:27737-44. [PMID: 20595388 PMCID: PMC2934641 DOI: 10.1074/jbc.m110.117960] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2010] [Revised: 06/27/2010] [Indexed: 12/17/2022] Open
Abstract
Abnormal activation of calpain is implicated in synaptic dysfunction and participates in neuronal death in Alzheimer disease (AD) and other neurological disorders. Pharmacological inhibition of calpain has been shown to improve memory and synaptic transmission in the mouse model of AD. However, the role and mechanism of calpain in AD progression remain elusive. Here we demonstrate a role of calpain in the neuropathology in amyloid precursor protein (APP) and presenilin 1 (PS1) double-transgenic mice, an established mouse model of AD. We found that overexpression of endogenous calpain inhibitor calpastatin (CAST) under the control of the calcium/calmodulin-dependent protein kinase II promoter in APP/PS1 mice caused a remarkable decrease of amyloid plaque burdens and prevented Tau phosphorylation and the loss of synapses. Furthermore, CAST overexpression prevented the decrease in the phosphorylation of the memory-related molecules CREB and ERK in the brain of APP/PS1 mice and improved spatial learning and memory. Interestingly, treatment of cultured primary neurons with amyloid-beta (Abeta) peptides caused an increase in the level of beta-site APP-cleaving enzyme 1 (BACE1), the key enzyme responsible for APP processing and Abeta production. This effect was inhibited by CAST overexpression. Consistently, overexpression of calpain in heterologous APP expressing cells up-regulated the level of BACE1 and increased Abeta production. Finally, CAST transgene prevented the increase of BACE1 in APP/PS1 mice. Thus, calpain activation plays an important role in APP processing and plaque formation, probably by regulating the expression of BACE1.
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Affiliation(s)
- Bin Liang
- From the Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Bao-Yu Duan
- From the Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiu-Ping Zhou
- From the Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Jia-Xin Gong
- From the Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Zhen-Ge Luo
- From the Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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69
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Wang J, Fu XQ, Lei WL, Wang T, Sheng AL, Luo ZG. Nuclear factor kappaB controls acetylcholine receptor clustering at the neuromuscular junction. J Neurosci 2010; 30:11104-13. [PMID: 20720118 PMCID: PMC6633475 DOI: 10.1523/jneurosci.2118-10.2010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 06/29/2010] [Accepted: 07/02/2010] [Indexed: 11/21/2022] Open
Abstract
At the vertebrate neuromuscular junction (NMJ), acetylcholine receptor (AChR) clustering is stimulated by motor neuron-derived glycoprotein Agrin and requires a number of intracellular signal or structural proteins, including AChR-associated scaffold protein Rapsyn. Here, we report a role of nuclear factor kappaB (NF-kappaB), a well known transcription factor involved in a variety of immune responses, in regulating AChR clustering at the NMJ. We found that downregulating the expression of RelA/p65 subunit of NF-kappaB or inhibiting NF-kappaB activity by overexpression of mutated form of IkappaB (inhibitor kappaB), which is resistant to proteolytic degradation and thus constitutively keeps NF-kappaB inactive in the cytoplasma, impeded the formation of AChR clusters in cultured C2C12 muscle cells stimulated by Agrin. In contrast, overexpression of RelA/p65 promoted AChR clustering. Furthermore, we investigated the mechanism by which NF-kappaB regulates AChR clustering. Interestingly, we found that downregulating the expression of RelA/p65 caused a marked reduction in the protein and mRNA level of Rapsyn and upregulation of RelA/p65 enhanced Rapsyn promoter activity. Mutation of NF-kappaB binding site on Rapsyn promoter prevented responsiveness to RelA/p65 regulation. Moreover, forced expression of Rapsyn in RelA/p65 downregulated muscle cells partially rescued AChR clusters, suggesting that NF-kappaB regulates AChR clustering, at least partially through the transcriptional regulation of Rapsyn. In line with this notion, genetic ablation of RelA/p65 selectively in the skeletal muscle caused a reduction of AChR density at the NMJ and a decrease in the level of Rapsyn. Thus, NF-kappaB signaling controls AChR clustering through transcriptional regulation of synaptic protein Rapsyn.
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Affiliation(s)
- Jia Wang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiu-Qing Fu
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Wen-Liang Lei
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Tong Wang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Ai-Li Sheng
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Zhen-Ge Luo
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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70
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Guo L, Xu J, Liu J. Electroacupuncture, Calpain I Expression, and Survival of Hippocampal Neurons in Cerebral Ischemia Reperfusion Rats. Med Acupunct 2010. [DOI: 10.1089/acu.2009.0728] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Lin Guo
- Mailman Research Center 311, Belmont, MA
- Molecular Biology Laboratory, Acupuncture and Moxibustion Research Institute, The First Hospital Affiliated to Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - J.F. Xu
- Molecular Biology Laboratory, Acupuncture and Moxibustion Research Institute, The First Hospital Affiliated to Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - Jian Liu
- Molecular Biology Laboratory, Acupuncture and Moxibustion Research Institute, The First Hospital Affiliated to Tianjin University of Traditional Chinese Medicine, Tianjin, China
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71
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Jang YC, Lustgarten MS, Liu Y, Muller FL, Bhattacharya A, Liang H, Salmon AB, Brooks SV, Larkin L, Hayworth CR, Richardson A, Van Remmen H. Increased superoxide in vivo accelerates age-associated muscle atrophy through mitochondrial dysfunction and neuromuscular junction degeneration. FASEB J 2010; 24:1376-90. [PMID: 20040516 PMCID: PMC2987499 DOI: 10.1096/fj.09-146308] [Citation(s) in RCA: 239] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Accepted: 12/03/2009] [Indexed: 11/11/2022]
Abstract
Oxidative stress has been implicated in the etiology of age-related muscle loss (sarcopenia). However, the underlying mechanisms by which oxidative stress contributes to sarcopenia have not been thoroughly investigated. To directly examine the role of chronic oxidative stress in vivo, we used a mouse model that lacks the antioxidant enzyme CuZnSOD (Sod1). Sod1(-/-) mice are characterized by high levels of oxidative damage and an acceleration of sarcopenia. In the present study, we demonstrate that muscle atrophy in Sod1(-/-) mice is accompanied by a progressive decline in mitochondrial bioenergetic function and an elevation of mitochondrial generation of reactive oxygen species. In addition, Sod1(-/-) muscle exhibits a more rapid induction of mitochondrial-mediated apoptosis and loss of myonuclei. Furthermore, aged Sod1(-/-) mice show a striking increase in muscle mitochondrial content near the neuromuscular junctions (NMJs). Despite the increase in content, the function of mitochondria is significantly impaired, with increased denervated NMJs and fragmentation of acetylcholine receptors. As a consequence, contractile force in aged Sod1(-/-) muscles is greatly diminished. Collectively, we show that Sod1(-/-) mice display characteristics of normal aging muscle in an accelerated manner and propose that the superoxide-induced NMJ degeneration and mitochondrial dysfunction are potential mechanisms of sarcopenia.
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Affiliation(s)
- Youngmok C Jang
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78245, USA
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72
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Luo Z. Synapse formation and remodeling. SCIENCE CHINA-LIFE SCIENCES 2010; 53:315-321. [PMID: 20596925 DOI: 10.1007/s11427-010-0069-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2009] [Accepted: 01/19/2010] [Indexed: 10/19/2022]
Abstract
Synapses are specialized structures that mediate information flow between neurons and target cells, and thus are the basis for neuronal system to execute various functions, including learning and memory. There are around 10(11) neurons in the human brain, with each neuron receiving thousands of synaptic inputs, either excitatory or inhibitory. A synapse is an asymmetric structure that is composed of pre-synaptic axon terminals, synaptic cleft, and postsynaptic compartments. Synapse formation involves a number of cell adhesion molecules, extracellular factors, and intracellular signaling or structural proteins. After the establishment of synaptic connections, synapses undergo structural or functional changes, known as synaptic plasticity which is believed to be regulated by neuronal activity and a variety of secreted factors. This review summarizes recent progress in the field of synapse development, with particular emphasis on the work carried out in China during the past 10 years (1999-2009).
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Affiliation(s)
- ZhenGe Luo
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200031, China.
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73
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Wu H, Xiong WC, Mei L. To build a synapse: signaling pathways in neuromuscular junction assembly. Development 2010; 137:1017-33. [PMID: 20215342 DOI: 10.1242/dev.038711] [Citation(s) in RCA: 389] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Synapses, as fundamental units of the neural circuitry, enable complex behaviors. The neuromuscular junction (NMJ) is a synapse type that forms between motoneurons and skeletal muscle fibers and that exhibits a high degree of subcellular specialization. Aided by genetic techniques and suitable animal models, studies in the past decade have brought significant progress in identifying NMJ components and assembly mechanisms. This review highlights recent advances in the study of NMJ development, focusing on signaling pathways that are activated by diffusible cues, which shed light on synaptogenesis in the brain and contribute to a better understanding of muscular dystrophy.
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Affiliation(s)
- Haitao Wu
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Department of Neurology, Medical College of Georgia, Augusta, GA 30912, USA
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74
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Abstract
Cholesterol is an essential partner of the nicotinic acetylcholine receptor (AChR). It is not only an abundant component of the postsynaptic membrane but also affects the stability of the receptor protein in the membrane, its supramolecular organization and function. In the absence of innervation, early on in ontogenetic development of the muscle cell, embryonic AChRs occur in the form of diffusely dispersed molecules. At embryonic day 13, receptors organize in the form of small aggregates. This organization can be mimicked in mammalian cells in culture.Trafficking to the plasmalemma is a cholesterol-dependent process. Receptors acquire association with the sterol as early as the endoplasmic reticulum and the Golgi apparatus. Once AChRs reach the cell surface, their stability is also highly dependent on cholesterol levels. Acute cholesterol depletion reduces the number of receptor domains by accelerating the rate of endocytosis. In muscle cells, AChRs are internalized via a recently discovered dynamin- and clathrin-independent, cytoskeleton-dependent endocytic mechanism. Unlike other endocytic pathways, cholesterol depletion accelerates internalization and re-routes AChR endocytosis to an Arf6-dependent pathway. Cholesterol depletion also results in ion channel gain-of-function of the remaining cell-surface AChRs, whereas cholesterol enrichment has the opposite effect.Wide-field microscopy shows AChR clusters as diffraction-limited puncta of approximately 200 nm diameter. Stimulated emission depletion (STED) fluorescence microscopy resolves these puncta into nanoclusters with an average diameter of approximately 55 nm. Exploiting the enhanced resolution, the effect of acute cholesterol depletion can be shown to alter the short- and long-range organization of AChR nanoclusters. In the short range, AChRs form bigger nanoclusters. On larger scales (0.5-3.5 mum) nanocluster distribution becomes non-random, attributable to the cholesterol-related abolition of cytoskeletal physical barriers normally preventing the lateral diffusion of AChR nanoclusters. The dependence of AChR numbers at the cell surface on membrane cholesterol raises the possibility that cholesterol depletion leads to AChR conformational changes that alter its stability and its long-range dynamic association with other AChR nanoclusters, accelerate its endocytosis, and transiently affect the channel kinetics of those receptors remaining at the surface. Cholesterol content at the plasmalemma may thus homeostatically modulate AChR dynamics, cell-surface organization and lifetime of receptor nanodomains, and fine tune the ion permeation process.
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75
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Abstract
The assembly of specific synaptic connections during development of the nervous system represents a remarkable example of cellular recognition and differentiation. Neurons employ several different cellular signaling strategies to solve this puzzle, which successively limit unwanted interactions and reduce the number of direct recognition events that are required to result in a specific connectivity pattern. Specificity mechanisms include the action of contact-mediated and long-range signals that support or inhibit synapse formation, which can take place directly between synaptic partners or with transient partners and transient cell populations. The molecular signals that drive the synaptic differentiation process at individual synapses in the central nervous system are similarly diverse and act through multiple, parallel differentiation pathways. This molecular complexity balances the need for central circuits to be assembled with high accuracy during development while retaining plasticity for local and dynamic regulation.
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Affiliation(s)
- Kang Shen
- Howard Hughes Medical Institute, Department of Biology and Pathology, Stanford University, Stanford, California 94305;
| | - Peter Scheiffele
- Department of Cell Biology, Biozentrum of the University of Basel, Basel 4056, Switzerland;
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76
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Lee CW, Han J, Bamburg JR, Han L, Lynn R, Zheng JQ. Regulation of acetylcholine receptor clustering by ADF/cofilin-directed vesicular trafficking. Nat Neurosci 2009; 12:848-56. [PMID: 19483689 PMCID: PMC2714269 DOI: 10.1038/nn.2322] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Accepted: 03/23/2009] [Indexed: 01/23/2023]
Abstract
Postsynaptic receptor localization is crucial for synapse development and function, but the underlying cytoskeletal mechanisms remain elusive. Using Xenopus neuromuscular junctions as a model, we found that actin depolymerizing factor (ADF)/cofilin regulated actin-dependent vesicular trafficking of acetylcholine receptors (AChRs) to the postsynaptic membrane. Active ADF/cofilin was concentrated in small puncta adjacent to AChR clusters and was spatiotemporally correlated with the formation and maintenance of surface AChR clusters. Notably, increased actin dynamics, vesicular markers and intracellular AChRs were all enriched at the sites of ADF/cofilin localization. Furthermore, a substantial amount of new AChRs was detected at these ADF/cofilin-enriched sites. Manipulation of either ADF/cofilin activity through its serine-3 phosphorylation or ADF/cofilin localization via 14-3-3 proteins markedly attenuated AChR insertion and clustering. These results suggest that spatiotemporally restricted ADF/cofilin-mediated actin dynamics regulate AChR trafficking during the development of neuromuscular synapses.
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Affiliation(s)
- Chi Wai Lee
- Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia, USA
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77
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Martínez-Martínez P, Phernambucq M, Steinbusch L, Schaeffer L, Berrih-Aknin S, Duimel H, Frederik P, Molenaar P, De Baets MH, Losen M. Silencing rapsyn in vivo decreases acetylcholine receptors and augments sodium channels and secondary postsynaptic membrane folding. Neurobiol Dis 2009; 35:14-23. [PMID: 19344765 DOI: 10.1016/j.nbd.2009.03.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Revised: 02/23/2009] [Accepted: 03/18/2009] [Indexed: 10/21/2022] Open
Abstract
The receptor-associated protein of the synapse (rapsyn) is required for anchoring and stabilizing the nicotinic acetylcholine receptor (AChR) in the postsynaptic membrane of the neuromuscular junction (NMJ) during development. Here we studied the role of rapsyn in the maintenance of the adult NMJ by reducing rapsyn expression levels with short hairpin RNA (shRNA). Silencing rapsyn led to the average reduction of the protein levels of rapsyn (31% loss) and AChR (36% loss) at the NMJ within 2 weeks, corresponding to previously reported half life of these proteins. On the other hand, the sodium channel protein expression was augmented (66%) in rapsyn-silenced muscles. Unexpectedly, at the ultrastructural level a significant increase in the amount of secondary folds of the postsynaptic membrane in silenced muscles was observed. The neuromuscular transmission in rapsyn-silenced muscles was mildly impaired. The results suggest that the adult NMJ can rapidly produce postsynaptic folds to compensate for AChR and rapsyn loss.
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Affiliation(s)
- Pilar Martínez-Martínez
- Department of Neuroscience, School of Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands, Maastricht, The Netherlands.
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Nam S, Min K, Hwang H, Lee HO, Lee JH, Yoon J, Lee H, Park S, Lee J. Control of rapsyn stability by the CUL-3-containing E3 ligase complex. J Biol Chem 2009; 284:8195-206. [PMID: 19158078 PMCID: PMC3282941 DOI: 10.1074/jbc.m808230200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Revised: 01/13/2009] [Indexed: 11/06/2022] Open
Abstract
Rapsyn is a postsynaptic protein required for clustering of nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction. Here we report the mechanism for posttranslational control of rapsyn protein stability. We confirmed that C18H9.7-encoded RPY-1 is a rapsyn homolog in Caenorhabditis elegans by showing that human rapsyn rescued rpy-1 mutant phenotypes in nematodes, as determined by levamisole assays and micropost array behavioral assays. We found that RPY-1 was degraded in the absence of functional UNC-29, a non-alpha subunit of the receptor, in an allele-specific manner, but not in the absence of other receptor subunits. The cytoplasmic loop of UNC-29 was found to be critical for RPY-1 stability. Through RNA interference screening, we found that UBC-1, UBC-12, NEDD-8, and RBX-1 were required for degradation of RPY-1. We identified cullin (CUL)-3 as a component of E3 ligase and KEL-8 as the substrate adaptor of RPY-1. Mammalian rapsyn was ubiquitinated by the CUL3/KLHL8-containing E3 ligase in vitro, and the knockdown of KLHL-8, a mammalian KEL-8 homolog, inhibited rapsyn ubiquitination in vivo, implying evolutionary conservation of the rapsyn stability control machinery. kel-8 suppression and rpy-1 overexpression in C. elegans produced a phenotype similar to that of a loss-of-function mutation of rpy-1, suggesting that control of rapsyn abundance is important for proper function of the receptor. Our results suggest a link between the control of rapsyn abundance and congenital myasthenic syndromes.
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Affiliation(s)
- Seunghee Nam
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Kyoengwoo Min
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Hyejin Hwang
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Hae-ock Lee
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Jung Hwa Lee
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Jongbok Yoon
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Hyunsook Lee
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Sungsu Park
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
| | - Junho Lee
- Research Center for
Cellulomics, Institute of Molecular Biology and Genetics, School of Biological
Sciences, Seoul National University, 151-742 Seoul, Korea, the
Division of Nano Sciences (BK21),
Ewha Womans University, 120-750 Seoul, Korea,
Protein Network Research Center,
Department of Biochemistry, Yonsei University, 134 Shinchon, 120-749 Seoul,
Korea
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79
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Abstract
The heparan sulfate proteoglycan agrin is best known for its essential role during formation, maintenance and regeneration of the neuromuscular junction. Mutations in agrin-interacting proteins are the genetic basis for a number of neuromuscular disorders. However, agrin is widely expressed in many tissues including neurons and glial cells of the brain, where its precise function is much less understood. Fewer synapses develop in brains that lack agrin, consistent with a function of agrin during CNS synaptogenesis. Recently, a specific transmembrane form of agrin (TM-agrin) was identified that is concentrated at that interneuronal synapses in the brain. Clustering or overexpression of TM-agrin leads to the formation of filopodia-like processes, which might be precursors for CNS synapses. Agrin is subject to defined and activity-dependent proteolytic cleavage by neurotrypsin at synapses and dysregulation of agrin processing might contribute to the development of mental retardation. This review summarizes what is known about the role of agrin during synapse formation at the neuromuscular junction and in the developing CNS and will discuss additional functions of agrin in the adult CNS, in particular during BBB formation, during recovery after traumatic brain injury and in the etiology of diseases, including Alzheimer’s disease and mental retardation.
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Affiliation(s)
- Stephan Kröger
- Department of Physiological Genomics, Ludwig-Maximilians University, Schillerstrasse 46, D-80336 Munich, Germany
| | - Heike Pfister
- Department of Physiological Genomics, Ludwig-Maximilians University, Schillerstrasse 46, D-80336 Munich, Germany
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80
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Dobbins GC, Luo S, Yang Z, Xiong WC, Mei L. alpha-Actinin interacts with rapsyn in agrin-stimulated AChR clustering. Mol Brain 2008; 1:18. [PMID: 19055765 PMCID: PMC2621155 DOI: 10.1186/1756-6606-1-18] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2008] [Accepted: 12/03/2008] [Indexed: 11/10/2022] Open
Abstract
AChR is concentrated at the postjunctional membrane at the neuromuscular junction. However, the underlying mechanism is unclear. We show that α-actinin, a protein known to cross-link F-actin, interacts with rapsyn, a scaffold protein essential for neuromuscular junction formation. α-Actinin, rapsyn, and surface AChR form a ternary complex. Moreover, the rapsyn-α-actinin interaction is increased by agrin, a factor known to stimulate AChR clustering. Downregulation of α-actinin expression inhibits agrin-mediated AChR clustering. Furthermore, the rapsyn-α-actinin interaction can be disrupted by inhibiting Abl and by cholinergic stimulation. Together these results indicate a role for α-actinin in AChR clustering.
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Affiliation(s)
- G Clement Dobbins
- Institute of Molecular Medicine and Genetics, Department of Neurobiology, Medical College of Georgia, Augusta, Georgia 30912, USA.
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81
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Bruneau EG, Esteban JA, Akaaboune M. Receptor-associated proteins and synaptic plasticity. FASEB J 2008; 23:679-88. [PMID: 18978155 DOI: 10.1096/fj.08-107946] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Changes in synaptic strength are important for synaptic development and synaptic plasticity. Most directly responsible for these synaptic changes are alterations in synaptic receptor number and density. Although alterations in receptor density mediated by the insertion, lateral mobility, removal, and recycling of receptors have been extensively studied, the dynamics and regulators of intracellular scaffolding proteins have only recently begun to be illuminated. In particular, a closer look at the receptor-associated proteins, which bind to receptors and are necessary for their synaptic localization and clustering, has revealed broader functions than previously thought and some rather unexpected thematic similarities. More than just "placeholders" or members of a passive protein "scaffold," receptor-associated proteins in every synapse studied have been shown to provide a number of signaling roles. In addition, the most recent state-of-the-art imaging has revealed that receptor-associated proteins are highly dynamic and are involved in regulating synaptic receptor density. Together, these results challenge the view that receptor-associated proteins are members of a static and stable scaffold and argue that their dynamic mobility may be essential for regulating activity-dependent changes in synaptic strength.
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Affiliation(s)
- Emile G Bruneau
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
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82
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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: 1.6] [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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83
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Luo S, Zhang B, Dong XP, Tao Y, Ting A, Zhou Z, Meixiong J, Luo J, Chiu FA, Xiong WC, Mei L. HSP90 beta regulates rapsyn turnover and subsequent AChR cluster formation and maintenance. Neuron 2008; 60:97-110. [PMID: 18940591 PMCID: PMC2586976 DOI: 10.1016/j.neuron.2008.08.013] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 06/06/2008] [Accepted: 08/10/2008] [Indexed: 10/21/2022]
Abstract
Rapsyn, an acetylcholine receptor (AChR)-interacting protein, is essential for synapse formation at the neuromuscular junction (NMJ). Like many synaptic proteins, rapsyn turns over rapidly at synapses. However, little is known about molecular mechanisms that govern rapsyn stability. Using a differential mass-spectrometry approach, we identified heat-shock protein 90beta (HSP90beta) as a component in surface AChR clusters. The HSP90beta-AChR interaction required rapsyn and was stimulated by agrin. Inhibition of HSP90beta activity or expression, or disruption of its interaction with rapsyn attenuated agrin-induced formation of AChR clusters in vitro and impaired the development and maintenance of the NMJ in vivo. Finally, we showed that HSP90beta was necessary for rapsyn stabilization and regulated its proteasome-dependent degradation. Together, these results indicate a role of HSP90beta in NMJ development by regulating rapsyn turnover and subsequent AChR cluster formation and maintenance.
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Affiliation(s)
- Shiwen Luo
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Bin Zhang
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Xian-ping Dong
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Yanmei Tao
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Annie Ting
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Zheng Zhou
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - James Meixiong
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Junjie Luo
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - F.C. Alex Chiu
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Wen C. Xiong
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
| | - Lin Mei
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Georgia 30912
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84
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Qian YK, Chan AWS, Madhavan R, Peng HB. The function of Shp2 tyrosine phosphatase in the dispersal of acetylcholine receptor clusters. BMC Neurosci 2008; 9:70. [PMID: 18647419 PMCID: PMC2490698 DOI: 10.1186/1471-2202-9-70] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Accepted: 07/23/2008] [Indexed: 11/25/2022] Open
Abstract
Background A crucial event in the development of the vertebrate neuromuscular junction (NMJ) is the postsynaptic enrichment of muscle acetylcholine (ACh) receptors (AChRs). This process involves two distinct steps: the local clustering of AChRs at synapses, which depends on the activation of the muscle-specific receptor tyrosine kinase MuSK by neural agrin, and the global dispersal of aneural or "pre-patterned" AChR aggregates, which is triggered by ACh or by synaptogenic stimuli. We and others have previously shown that tyrosine phosphatases, such as the SH2 domain-containing phosphatase Shp2, regulate AChR cluster formation in muscle cells, and that tyrosine phosphatases also mediate the dispersal of pre-patterned AChR clusters by synaptogenic stimuli, although the specific phosphatases involved in this latter step remain unknown. Results Using an assay system that allows AChR cluster assembly and disassembly to be studied separately and quantitatively, we describe a previously unrecognized role of the tyrosine phosphatase Shp2 in AChR cluster disassembly. Shp2 was robustly expressed in embryonic Xenopus muscle in vivo and in cultured myotomal muscle cells, and treatment of the muscle cultures with an inhibitor of Shp2 (NSC-87877) blocked the dispersal of pre-patterned AChR clusters by synaptogenic stimuli. In contrast, over-expression in muscle cells of either wild-type or constitutively active Shp2 accelerated cluster dispersal. Significantly, forced expression in muscle of the Shp2-activator SIRPα1 (signal regulatory protein α1) also enhanced the disassembly of AChR clusters, whereas the expression of a truncated SIRPα1 mutant that suppresses Shp2 signaling inhibited cluster disassembly. Conclusion Our results suggest that Shp2 activation by synaptogenic stimuli, through signaling intermediates such as SIRPα1, promotes the dispersal of pre-patterned AChR clusters to facilitate the selective accumulation of AChRs at developing NMJs.
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Affiliation(s)
- Yueping K Qian
- Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, PR China.
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85
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Wang J, Ruan NJ, Qian L, Lei WL, Chen F, Luo ZG. Wnt/beta-catenin signaling suppresses Rapsyn expression and inhibits acetylcholine receptor clustering at the neuromuscular junction. J Biol Chem 2008; 283:21668-75. [PMID: 18541538 DOI: 10.1074/jbc.m709939200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The dynamic interaction between positive and negative signals is necessary for remodeling of postsynaptic structures at the neuromuscular junction. Here we report that Wnt3a negatively regulates acetylcholine receptor (AChR) clustering by repressing the expression of Rapsyn, an AChR-associated protein essential for AChR clustering. In cultured myotubes, treatment with Wnt3a or overexpression of beta-catenin, the condition mimicking the activation of the Wnt canonical pathway, inhibited Agrin-induced formation of AChR clusters. Moreover, Wnt3a treatment promoted dispersion of AChR clusters, and this effect was prevented by DKK1, an antagonist of the Wnt canonical pathway. Next, we investigated possible mechanisms underlying Wnt3a regulation of AChR clustering in cultured muscle cells. Interestingly, we found that Wnt3a treatment caused a decrease in the protein level of Rapsyn. In addition, Rapsyn promoter activity in cultured muscle cells was inhibited by the treatment with Wnt3a or beta-catenin overexpression. Forced expression of Rapsyn driven by a promoter that is not responsive to Wnt3a prevented the dispersing effect of Wnt3a on AChR clusters, suggesting that Wnt3a indeed acts to disperse AChR clusters by down-regulating the expression of Rapsyn. The role of Wnt/beta-catenin signaling in dispersing AChR clusters was also investigated in vivo by electroporation of Wnt3a or beta-catenin into mouse limb muscles, where ectopic Wnt3a or beta-catenin caused disassembly of postsynaptic apparatus. Together, these results suggest that Wnt/beta-catenin signaling plays a negative role for postsynaptic differentiation at the neuromuscular junction, probably by regulating the expression of synaptic proteins, such as Rapsyn.
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Affiliation(s)
- Jia Wang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai, China
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86
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Michalk A, Stricker S, Becker J, Rupps R, Pantzar T, Miertus J, Botta G, Naretto VG, Janetzki C, Yaqoob N, Ott CE, Seelow D, Wieczorek D, Fiebig B, Wirth B, Hoopmann M, Walther M, Körber F, Blankenburg M, Mundlos S, Heller R, Hoffmann K. Acetylcholine receptor pathway mutations explain various fetal akinesia deformation sequence disorders. Am J Hum Genet 2008; 82:464-76. [PMID: 18252226 DOI: 10.1016/j.ajhg.2007.11.006] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Revised: 11/21/2007] [Accepted: 11/21/2007] [Indexed: 01/21/2023] Open
Abstract
Impaired fetal movement causes malformations, summarized as fetal akinesia deformation sequence (FADS), and is triggered by environmental and genetic factors. Acetylcholine receptor (AChR) components are suspects because mutations in the fetally expressed gamma subunit (CHRNG) of AChR were found in two FADS disorders, lethal multiple pterygium syndrome (LMPS) and Escobar syndrome. Other AChR subunits alpha1, beta1, and delta (CHRNA1, CHRNB1, CHRND) as well as receptor-associated protein of the synapse (RAPSN) previously revealed missense or compound nonsense-missense mutations in viable congenital myasthenic syndrome; lethality of homozygous null mutations was predicted but never shown. We provide the first report to our knowledge of homozygous nonsense mutations in CHRNA1 and CHRND and show that they were lethal, whereas novel recessive missense mutations in RAPSN caused a severe but not necessarily lethal phenotype. To elucidate disease-associated malformations such as frequent abortions, fetal edema, cystic hygroma, or cardiac defects, we studied Chrna1, Chrnb1, Chrnd, Chrng, and Rapsn in mouse embryos and found expression in skeletal muscles but also in early somite development. This indicates that early developmental defects might be due to somite expression in addition to solely muscle-specific effects. We conclude that complete or severe functional disruption of fetal AChR causes lethal multiple pterygium syndrome whereas milder alterations result in fetal hypokinesia with inborn contractures or a myasthenic syndrome later in life.
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87
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Abstract
The neuromuscular junction (NMJ) is a well-studied chemical synapse and has served as a tractable model system to clarify how synapse formation occurs. Proteins on both the presynaptic and postsynaptic sides collaborate to induce the high-density accumulation of acetylcholine receptors (AChRs) at the NMJ. Two opposing pathways work in this process: A dispersing pathway works through acetylcholine and the AChR, and a clustering pathway works through agrin and the transmembrane tyrosine kinase MuSK. The molecular mechanisms underlying these two signaling cascades are beginning to be understood.
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Affiliation(s)
- Fumihito Ono
- Laboratory of Molecular Physiology, National Institute on Alcohol Abuse and Alcoholism, Bethesda, MD 20892, USA.
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88
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Groshong JS, Spencer MJ, Bhattacharyya BJ, Kudryashova E, Vohra BP, Zayas R, Wollmann RL, Miller RJ, Gomez CM. Calpain activation impairs neuromuscular transmission in a mouse model of the slow-channel myasthenic syndrome. J Clin Invest 2007; 117:2903-12. [PMID: 17853947 PMCID: PMC1974862 DOI: 10.1172/jci30383] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Accepted: 06/26/2007] [Indexed: 11/17/2022] Open
Abstract
The slow-channel myasthenic syndrome (SCS) is a hereditary disorder of the acetylcholine receptor (AChR) of the neuromuscular junction (NMJ) that leads to prolonged AChR channel opening, Ca(2+) overload, and degeneration of the NMJ. We used an SCS transgenic mouse model to investigate the role of the calcium-activated protease calpain in the pathogenesis of synaptic dysfunction in SCS. Cleavage of a fluorogenic calpain substrate was increased at the NMJ of dissociated muscle fibers. Inhibition of calpain using a calpastatin (CS) transgene improved strength and neuromuscular transmission. CS caused a 2-fold increase in the frequency of miniature endplate currents (MEPCs) and an increase in NMJ size, but MEPC amplitudes remained reduced. Persistent degeneration of the NMJ was associated with localized activation of the non-calpain protease caspase-3. This study suggests that calpain may act presynaptically to impair NMJ function in SCS but further reveals a role for other cysteine proteases whose inhibition may be of additional therapeutic benefit in SCS and other excitotoxic disorders.
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Affiliation(s)
- Jason S. Groshong
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Melissa J. Spencer
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Bula J. Bhattacharyya
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Elena Kudryashova
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Bhupinder P.S. Vohra
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Roberto Zayas
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Robert L. Wollmann
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Richard J. Miller
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
| | - Christopher M. Gomez
- Department of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
UCLA, Los Angeles, California, USA.
Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Neurology, The University of Chicago, Chicago, Illinois, USA
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