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Jühlen R, Grauer L, Martinelli V, Rencurel C, Fahrenkrog B. Alteration of actin cytoskeletal organisation in fetal akinesia deformation sequence. Sci Rep 2024; 14:1742. [PMID: 38242956 PMCID: PMC10799014 DOI: 10.1038/s41598-023-50615-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Accepted: 12/22/2023] [Indexed: 01/21/2024] Open
Abstract
Fetal akinesia deformation sequence (FADS) represents the severest form of congenital myasthenic syndrome (CMS), a diverse group of inherited disorders characterised by impaired neuromuscular transmission. Most CMS originate from defects in the muscle nicotinic acetylcholine receptor, but the underlying molecular pathogenesis is only poorly understood. Here we show that RNAi-mediated silencing of FADS-related proteins rapsyn and NUP88 in foetal fibroblasts alters organisation of the actin cytoskeleton. We show that fibroblasts from two independent FADS individuals have enhanced and shorter actin stress fibre bundles, alongside with an increased number and size of focal adhesions, with an otherwise normal overall connectivity and integrity of the actin-myosin cytoskeleton network. By proximity ligation assays and bimolecular fluorescence complementation, we show that rapsyn and NUP88 localise nearby adhesion plaques and that they interact with the focal adhesion protein paxillin. Based on these findings we propose that a respective deficiency in rapsyn and NUP88 in FADS alters the regulation of actin dynamics at focal adhesions, and thereby may also plausibly dictate myofibril contraction in skeletal muscle of FADS individuals.
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Affiliation(s)
- Ramona Jühlen
- Laboratory Biology of the Cell Nucleus, Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium.
- Institute of Biochemistry and Molecular Cell Biology, Medical School, RWTH Aachen University, 52074, Aachen, Germany.
| | - Lukas Grauer
- Institute of Biochemistry and Molecular Cell Biology, Medical School, RWTH Aachen University, 52074, Aachen, Germany
| | - Valérie Martinelli
- Laboratory Biology of the Cell Nucleus, Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium
- Laboratory of Neurovascular Signaling, Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium
| | | | - Birthe Fahrenkrog
- Laboratory Biology of the Cell Nucleus, Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium.
- Biozentrum, University of Basel, 4056, Basel, Switzerland.
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2
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Liao X, Wang Y, Lai X, Wang S. The role of Rapsyn in neuromuscular junction and congenital myasthenic syndrome. BIOMOLECULES & BIOMEDICINE 2023; 23:772-784. [PMID: 36815443 PMCID: PMC10494853 DOI: 10.17305/bb.2022.8641] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 02/02/2023] [Accepted: 02/17/2023] [Indexed: 02/23/2023]
Abstract
Rapsyn, an intracellular scaffolding protein associated with the postsynaptic membranes in the neuromuscular junction (NMJ), is critical for nicotinic acetylcholine receptor clustering and maintenance. Therefore, Rapsyn is essential to the NMJ formation and maintenance, and Rapsyn mutant is one of the reasons causing the pathogenies of congenital myasthenic syndrome (CMS). In addition, there is little research on Rapsyn in the central nervous system (CNS). In this review, the role of Rapsyn in the NMJ formation and the mutation of Rapsyn leading to CMS will be reviewed separately and sequentially. Finally, the potential function of Rapsyn is prospected.
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Affiliation(s)
- Xufeng Liao
- Institute of Life Science and School of Life Sciences, Nanchang University, Nanchang, China
| | - Yingxing Wang
- Institute of Life Science and School of Life Sciences, Nanchang University, Nanchang, China
| | - Xinsheng Lai
- Institute of Life Science and School of Life Sciences, Nanchang University, Nanchang, China
- School of Basic Medical Sciences, Nanchang University, Nanchang, China
| | - Shunqi Wang
- Institute of Life Science and School of Life Sciences, Nanchang University, Nanchang, China
- School of Basic Medical Sciences, Nanchang University, Nanchang, China
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3
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Alvarez-Suarez P, Nowak N, Protasiuk-Filipunas A, Yamazaki H, Prószyński TJ, Gawor M. Drebrin Regulates Acetylcholine Receptor Clustering and Organization of Microtubules at the Postsynaptic Machinery. Int J Mol Sci 2021; 22:9387. [PMID: 34502296 PMCID: PMC8430516 DOI: 10.3390/ijms22179387] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 08/20/2021] [Accepted: 08/24/2021] [Indexed: 01/07/2023] Open
Abstract
Proper muscle function depends on the neuromuscular junctions (NMJs), which mature postnatally to complex "pretzel-like" structures, allowing for effective synaptic transmission. Postsynaptic acetylcholine receptors (AChRs) at NMJs are anchored in the actin cytoskeleton and clustered by the scaffold protein rapsyn, recruiting various actin-organizing proteins. Mechanisms driving the maturation of the postsynaptic machinery and regulating rapsyn interactions with the cytoskeleton are still poorly understood. Drebrin is an actin and microtubule cross-linker essential for the functioning of the synapses in the brain, but its role at NMJs remains elusive. We used immunohistochemistry, RNA interference, drebrin inhibitor 3,5-bis-trifluoromethyl pyrazole (BTP2) and co-immunopreciptation to explore the role of this protein at the postsynaptic machinery. We identify drebrin as a postsynaptic protein colocalizing with the AChRs both in vitro and in vivo. We also show that drebrin is enriched at synaptic podosomes. Downregulation of drebrin or blocking its interaction with actin in cultured myotubes impairs the organization of AChR clusters and the cluster-associated microtubule network. Finally, we demonstrate that drebrin interacts with rapsyn and a drebrin interactor, plus-end-tracking protein EB3. Our results reveal an interplay between drebrin and cluster-stabilizing machinery involving rapsyn, actin cytoskeleton, and microtubules.
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Affiliation(s)
- Paloma Alvarez-Suarez
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Natalia Nowak
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Anna Protasiuk-Filipunas
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Hiroyuki Yamazaki
- Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan;
| | - Tomasz J. Prószyński
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
| | - Marta Gawor
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warsaw, Poland; (P.A.-S.); (N.N.); (A.P.-F.); (T.J.P.)
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4
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Medina-Moreno A, Henríquez JP. Maturation of a postsynaptic domain: Role of small Rho GTPases in organising nicotinic acetylcholine receptor aggregates at the vertebrate neuromuscular junction. J Anat 2021; 241:1148-1156. [PMID: 34342888 DOI: 10.1111/joa.13526] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 07/15/2021] [Accepted: 07/20/2021] [Indexed: 12/13/2022] Open
Abstract
The neuromuscular junction (NMJ) is the peripheral synapse formed between a motor axon and a skeletal muscle fibre that allows muscle contraction and the coordinated movement in many species. A main hallmark of the mature NMJ is the assembly of nicotinic acetylcholine receptor (nAChR) aggregates in the muscle postsynaptic domain, that distributes in perfect apposition to presynaptic motor terminals. To assemble its unique functional architecture, initial embryonic NMJs undergo an early postnatal maturation process characterised by the transformation of homogenous nAChR-containing plaques to elaborate and branched pretzel-like structures. In spite of a detailed morphological characterisation, the molecular mechanisms controlling the intracellular scaffolding that organises a postsynaptic domain at the mature NMJ have not been fully elucidated. In this review, we integrate evidence of key processes and molecules that have shed light on our current understanding of the NMJ maturation process. On the one hand, we consider in vitro studies revealing the potential role of podosome-like structures to define discrete low nAChR-containing regions to consolidate a plaque-to-pretzel transition at the NMJ. On the other hand, we focus on in vitro and in vivo evidence demonstrating that members of the Ras homologous (Rho) protein family of small GTPases (small Rho GTPases) play indispensable roles on NMJ maturation by regulating the stability of nAChR aggregates. We combine this evidence to propose that small Rho GTPases are key players in the assembly of podosome-like structures that drive the postsynaptic maturation of vertebrate NMJs.
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Affiliation(s)
- Angelymar Medina-Moreno
- Laboratory of Neuromuscular Studies (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA BioBio), Universidad de Concepción, Concepción, Chile
| | - Juan Pablo Henríquez
- Laboratory of Neuromuscular Studies (NeSt Lab), Department of Cell Biology, Faculty of Biological Sciences, Center for Advanced Microscopy (CMA BioBio), Universidad de Concepción, Concepción, Chile
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5
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Luttrell SM, Smith AST, Mack DL. Creating stem cell-derived neuromuscular junctions in vitro. Muscle Nerve 2021; 64:388-403. [PMID: 34328673 PMCID: PMC9292444 DOI: 10.1002/mus.27360] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Revised: 05/28/2021] [Accepted: 06/21/2021] [Indexed: 12/14/2022]
Abstract
Recent development of novel therapies has improved mobility and quality of life for people suffering from inheritable neuromuscular disorders. Despite this progress, the majority of neuromuscular disorders are still incurable, in part due to a lack of predictive models of neuromuscular junction (NMJ) breakdown. Improvement of predictive models of a human NMJ would be transformative in terms of expanding our understanding of the mechanisms that underpin development, maintenance, and disease, and as a testbed with which to evaluate novel therapeutics. Induced pluripotent stem cells (iPSCs) are emerging as a clinically relevant and non‐invasive cell source to create human NMJs to study synaptic development and maturation, as well as disease modeling and drug discovery. This review will highlight the recent advances and remaining challenges to generating an NMJ capable of eliciting contraction of stem cell‐derived skeletal muscle in vitro. We explore the advantages and shortcomings of traditional NMJ culturing platforms, as well as the pioneering technologies and novel, biomimetic culturing systems currently in use to guide development and maturation of the neuromuscular synapse and extracellular microenvironment. Then, we will explore how this NMJ‐in‐a‐dish can be used to study normal assembly and function of the efferent portion of the neuromuscular arc, and how neuromuscular disease‐causing mutations disrupt structure, signaling, and function.
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Affiliation(s)
- Shawn M Luttrell
- Department of Rehabilitation Medicine, University of Washington, Seattle, Washington, USA.,Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, USA
| | - Alec S T Smith
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, USA.,Department of Physiology and Biophysics, University of Washington, Seattle, Washington, USA
| | - David L Mack
- Department of Rehabilitation Medicine, University of Washington, Seattle, Washington, USA.,Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, USA.,Department of Physiology and Biophysics, University of Washington, Seattle, Washington, USA
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6
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Tsai LK, Chen IH, Chao CC, Hsueh HW, Chen HH, Huang YH, Weng RW, Lai TY, Tsai YC, Tsao YP, Chen SL. Autoantibody of NRIP, a novel AChR-interacting protein, plays a detrimental role in myasthenia gravis. J Cachexia Sarcopenia Muscle 2021; 12:665-676. [PMID: 33773096 PMCID: PMC8200423 DOI: 10.1002/jcsm.12697] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 01/30/2021] [Accepted: 02/10/2021] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND Nuclear receptor interaction protein (NRIP) co-localizes with acetylcholine receptor (AChR) at the neuromuscular junction (NMJ), and NRIP deficiency causes aberrant NMJ architecture. However, the normal physiological and pathophysiological roles of NRIP in NMJ are still unclear. METHODS We investigated the co-localization and interaction of NRIP with AChR-associated proteins using immunofluorescence and immunoprecipitation assay, respectively. The binding affinity of AChR-associated proteins was analysed in muscle-restricted NRIP knockout mice and NRIP knockout muscle cells (C2C12). We further collected the sera from 43 patients with myasthenia gravis (MG), an NMJ disorder. The existence and features of anti-NRIP autoantibody in sera were studied using Western blot and epitope mapping. RESULTS NRIP co-localized with AChR, rapsyn and α-actinin 2 (ACTN2) in gastrocnemius muscles of mice; and α-bungarotoxin (BTX) pull-down assay revealed NRIP with rapsyn and ACTN2 in complexes from muscle tissues and cells. NRIP directly binds with α subunit of AChR (AChRα) in vitro and in vivo to affect the binding affinity of AChR with rapsyn and rapsyn with ACTN2. In 43 patients with MG (age, 58.4 ± 14.5 years; female, 55.8%), we detected six of them (14.0%) having anti-NRIP autoantibody. The presence of anti-NRIP autoantibody correlated with a more severe type of MG when AChR autoantibody existed (P = 0.011). The higher the titre of anti-NRIP autoantibody, the more severe MG severity (P = 0.032). The main immunogenic region is likely on the IQ motif of NRIP. We also showed the IgG subclass of anti-NRIP autoantibody mainly to be IgG1. CONCLUSIONS NRIP is a novel AChRα binding protein and involves structural NMJ formation, which acts as a scaffold to stabilize AChR-rapsyn-ACTN2 complexes. Anti-NRIP autoantibody is a novel autoantibody in MG and plays a detrimental role in MG with the coexistence of anti-AChR autoantibody.
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Affiliation(s)
- Li-Kai Tsai
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan.,Department of Neurology, National Taiwan University Hospital, Hsinchu Branch, Hsinchu, Taiwan
| | - I-Hsin Chen
- Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Chi-Chao Chao
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
| | - Hsueh-Wen Hsueh
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
| | - Hsin-Hsiung Chen
- Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Yun-Hsin Huang
- Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Rong-Wei Weng
- Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Tzu-Yun Lai
- Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Yi-Chieh Tsai
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
| | - Yeou-Ping Tsao
- Department of Ophthalmology, Mackay Memorial Hospital, Taipei, Taiwan
| | - Show-Li Chen
- Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan
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Xing G, Jing H, Yu Z, Chen P, Wang H, Xiong WC, Mei L. Membraneless condensates by Rapsn phase separation as a platform for neuromuscular junction formation. Neuron 2021; 109:1963-1978.e5. [PMID: 34033754 DOI: 10.1016/j.neuron.2021.04.021] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 03/27/2021] [Accepted: 04/22/2021] [Indexed: 12/29/2022]
Abstract
Our daily life depends on muscle contraction, a process that is controlled by the neuromuscular junction (NMJ). However, the mechanisms of NMJ assembly remain unclear. Here we show that Rapsn, a protein critical for NMJ formation, undergoes liquid-liquid phase separation (LLPS) and condensates into liquid-like assemblies. Such assemblies can recruit acetylcholine receptors (AChRs), cytoskeletal proteins, and signaling proteins for postsynaptic differentiation. Rapsn LLPS requires multivalent binding of tetratricopeptide repeats (TPRs) and is increased by Musk signaling. The capacity of Rapsn to condensate and co-condensate with interaction proteins is compromised by mutations of congenital myasthenic syndromes (CMSs). NMJ formation is impaired in mutant mice carrying a CMS-associated, LLPS-deficient mutation. These results reveal a critical role of Rapsn LLPS in forming a synaptic semi-membraneless compartment for NMJ formation.
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Affiliation(s)
- Guanglin Xing
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Hongyang Jing
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Zheng Yu
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Peng Chen
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Hongsheng Wang
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Wen-Cheng Xiong
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, USA.
| | - Lin Mei
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, USA.
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An Inside Job: Molecular Determinants for Postsynaptic Localization of Nicotinic Acetylcholine Receptors. Molecules 2021; 26:molecules26113065. [PMID: 34063759 PMCID: PMC8196675 DOI: 10.3390/molecules26113065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/13/2021] [Accepted: 05/15/2021] [Indexed: 11/29/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission at neuromuscular and autonomic ganglionic synapses in the peripheral nervous system. The postsynaptic localization of muscle ((α1)2β1γδ) and neuronal ((α3β4)2β4) nicotinic receptors at these synapses is mediated by interactions between the nAChR intracellular domains and cytoplasmic scaffolding proteins. Recent high resolution structures and functional studies provide new insights into the molecular determinants that mediate these interactions. Surprisingly, they reveal that the muscle nAChR binds 1–3 rapsyn scaffolding molecules, which dimerize and thereby form an interconnected lattice between receptors. Moreover, rapsyn binds two distinct sites on the nAChR subunit cytoplasmic loops; the MA-helix on one or more subunits and a motif specific to the β subunit. Binding at the latter site is regulated by agrin-induced phosphorylation of βY390, and increases the stoichiometry of rapsyn/AChR complexes. Similarly, the neuronal nAChR may be localized at ganglionic synapses by phosphorylation-dependent interactions with 14-3-3 adaptor proteins which bind specific motifs in each of the α3 subunit cytoplasmic loops. Thus, postsynaptic localization of nAChRs is mediated by regulated interactions with multiple scaffolding molecules, and the stoichiometry of these complexes likely helps regulate the number, density, and stability of receptors at the synapse.
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Wu T, Wang Y, Shi W, Zhang BQ, Raelson J, Yao YM, Wu HD, Xu ZX, Marois-Blanchet FC, Ledoux J, Blunck R, Sheng JZ, Hu SJ, Luo H, Wu J. A Variant in the Nicotinic Acetylcholine Receptor Alpha 3 Subunit Gene Is Associated With Hypertension Risks in Hypogonadic Patients. Front Genet 2020; 11:539862. [PMID: 33329690 PMCID: PMC7728919 DOI: 10.3389/fgene.2020.539862] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 11/10/2020] [Indexed: 12/29/2022] Open
Abstract
Ephb6 gene knockout causes hypertension in castrated mice. EPHB6 controls catecholamine secretion by adrenal gland chromaffin cells (AGCCs) in a testosterone-dependent way. Nicotinic acetylcholine receptor (nAChR) is a ligand-gated Ca2+/Na+ channel, and its opening is the first signaling event leading to catecholamine secretion by AGCCs. There is a possibility that nAChR might be involved in EPHB6 signaling, and thus sequence variants of its subunit genes are associated with hypertension risks. CHRNA3 is the major subunit of nAChR used in human and mouse AGCCs. We conducted a human genetic study to assess the association of CHRNA3 variants with hypertension risks in hypogonadic males. The study cohort included 1,500 hypogonadic Chinese males with (750 patients) or without (750 patients) hypertension. The result revealed that SNV rs3743076 in the fourth intron of CHRNA3 was significantly associated with hypertension risks in the hypogonadic males. We further showed that EPHB6 physically interacted with CHRNA3 in AGCCs, providing a molecular basis for nAChR being in the EPHB6 signaling pathway.
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Affiliation(s)
- Tao Wu
- Institute of Cardiology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China
| | - Yujia Wang
- Research Centre, Centre Hospitalier de l'Université de Montréal (CHUM), Montreal, QC, Canada.,Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Wei Shi
- Research Centre, Centre Hospitalier de l'Université de Montréal (CHUM), Montreal, QC, Canada
| | - Bi-Qi Zhang
- Institute of Cardiology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China
| | - John Raelson
- Research Centre, Centre Hospitalier de l'Université de Montréal (CHUM), Montreal, QC, Canada
| | - Yu-Mei Yao
- Department of Cardiology, The Third Affiliated Hospital of Zhejiang Chinese Medical University, Hangzhou, China
| | - Huan-Dong Wu
- Institute of Cardiology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China
| | - Zao-Xian Xu
- Institute of Cardiology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China
| | | | - Jonathan Ledoux
- Montreal Heart Institute, Université de Montréal, Montreal, QC, Canada
| | - Rikard Blunck
- Department of Physics, University of Montreal, Montreal, QC, Canada
| | - Jian-Zhong Sheng
- Department of Pathology and Physiopathology, College of Medicine, Zhejiang University, Hangzhou, China
| | - Shen-Jiang Hu
- Institute of Cardiology, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China
| | - Hongyu Luo
- Research Centre, Centre Hospitalier de l'Université de Montréal (CHUM), Montreal, QC, Canada
| | - Jiangping Wu
- Research Centre, Centre Hospitalier de l'Université de Montréal (CHUM), Montreal, QC, Canada.,Nephrology Service, Centre Hospitalier de l'Université de Montréal (CHUM), Montreal, QC, Canada
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10
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Jühlen R, Martinelli V, Vinci C, Breckpot J, Fahrenkrog B. Centrosome and ciliary abnormalities in fetal akinesia deformation sequence human fibroblasts. Sci Rep 2020; 10:19301. [PMID: 33168876 PMCID: PMC7652866 DOI: 10.1038/s41598-020-76192-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 10/23/2020] [Indexed: 02/06/2023] Open
Abstract
Ciliopathies are clinical disorders of the primary cilium with widely recognised phenotypic and genetic heterogeneity. Here, we found impaired ciliogenesis in fibroblasts derived from individuals with fetal akinesia deformation sequence (FADS), a broad spectrum of neuromuscular disorders arising from compromised foetal movement. We show that cells derived from FADS individuals have shorter and less primary cilia (PC), in association with alterations in post-translational modifications in α-tubulin. Similarly, siRNA-mediated depletion of two known FADS proteins, the scaffold protein rapsyn and the nucleoporin NUP88, resulted in defective PC formation. Consistent with a role in ciliogenesis, rapsyn and NUP88 localised to centrosomes and PC. Furthermore, proximity-ligation assays confirm the respective vicinity of rapsyn and NUP88 to γ-tubulin. Proximity-ligation assays moreover show that rapsyn and NUP88 are adjacent to each other and that the rapsyn-NUP88 interface is perturbed in the examined FADS cells. We suggest that the perturbed rapsyn-NUP88 interface leads to defects in PC formation and that defective ciliogenesis contributes to the pleiotropic defects seen in FADS.
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Affiliation(s)
- Ramona Jühlen
- Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium.,Institute of Biochemistry and Molecular Cell Biology, Medical School, RWTH Aachen University, 52074, Aachen, Germany
| | - Valérie Martinelli
- Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium
| | - Chiara Vinci
- Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium
| | - Jeroen Breckpot
- Center for Human Genetics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium
| | - Birthe Fahrenkrog
- Institute of Molecular Biology and Medicine, Université Libre de Bruxelles, 6041, Gosselies, Belgium. .,Biozentrum, University of Basel, 4056, Basel, Switzerland.
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11
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Grp94 Regulates the Recruitment of Aneural AChR Clusters for the Assembly of Postsynaptic Specializations by Modulating ADF/Cofilin Activity and Turnover. eNeuro 2020; 7:ENEURO.0025-20.2020. [PMID: 32747457 PMCID: PMC7540925 DOI: 10.1523/eneuro.0025-20.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2020] [Revised: 07/27/2020] [Accepted: 07/27/2020] [Indexed: 11/21/2022] Open
Abstract
Temperature is a physiological factor that affects neuronal growth and synaptic homeostasis at the invertebrate neuromuscular junctions (NMJs); however, whether temperature stress could also regulate the structure and function of the vertebrate NMJs remains unclear. In this study, we use Xenopus laevis primary cultures as a vertebrate model system for investigating the involvement of heat shock protein 90 (HSP90) family of stress proteins in NMJ development. First, cold temperature treatment or HSP90 inhibition attenuates the formation of aneural acetylcholine receptor (AChR) clusters, but increases their stability after they are formed, in cultured muscles. HSP90 inhibition specifically affects the stability of aneural AChR clusters and their associated intracellular scaffolding protein rapsyn, instead of causing a global change in cell metabolism and protein expression in Xenopus muscle cultures. Upon synaptogenic stimulation, a specific HSP90 family member, glucose-regulated protein 94 (Grp94), modulates the phosphorylation and dynamic turnover of actin depolymerizing factor (ADF)/cofilin at aneural AChR clusters, leading to the recruitment of AChR molecules from aneural clusters to the assembly of agrin-induced postsynaptic specializations. Finally, postsynaptic Grp94 knock-down significantly inhibits nerve-induced AChR clustering and postsynaptic activity in nerve-muscle co-cultures as demonstrated by live-cell imaging and electrophysiological recording, respectively. Collectively, this study suggests that temperature-dependent alteration in Grp94 expression and activity inhibits the assembly of postsynaptic specializations through modulating ADF/cofilin phosphorylation and activity at aneural AChR clusters, which prevents AChR molecules from being recruited to the postsynaptic sites via actin-dependent vesicular trafficking, at developing vertebrate NMJs.
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12
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Xing G, Xiong WC, Mei L. Rapsyn as a signaling and scaffolding molecule in neuromuscular junction formation and maintenance. Neurosci Lett 2020; 731:135013. [DOI: 10.1016/j.neulet.2020.135013] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 04/23/2020] [Indexed: 12/20/2022]
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13
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Koppel N, Friese MB, Cardasis HL, Neubert TA, Burden SJ. Vezatin is required for the maturation of the neuromuscular synapse. Mol Biol Cell 2019; 30:2571-2583. [PMID: 31411944 PMCID: PMC6740198 DOI: 10.1091/mbc.e19-06-0313] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Key genes, such as Agrin, Lrp4, and MuSK, are required for the initial formation, subsequent maturation, and long-term stabilization of mammalian neuromuscular synapses. Additional molecules are thought to function selectively during the evolution and stabilization of these synapses, but these molecular players are largely unknown. Here, we used mass spectrometry to identify vezatin, a two-pass transmembrane protein, as an acetylcholine receptor (AChR)–associated protein, and we provide evidence that vezatin binds directly to AChRs. We show that vezatin is dispensable for the formation of synapses but plays a later role in the emergence of a topologically complex and branched shape of the synapse, as well as the stabilization of AChRs. In addition, neuromuscular synapses in vezatin mutant mice display premature signs of deterioration, normally found only during aging. Thus, vezatin has a selective role in the structural elaboration and postnatal maturation of murine neuromuscular synapses.
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Affiliation(s)
- Natasha Koppel
- Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016
| | - Matthew B Friese
- Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016
| | - Helene L Cardasis
- Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016
| | - Thomas A Neubert
- Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016
| | - Steven J Burden
- Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016
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14
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Blondelle J, Tallapaka K, Seto JT, Ghassemian M, Clark M, Laitila JM, Bournazos A, Singer JD, Lange S. Cullin-3 dependent deregulation of ACTN1 represents a new pathogenic mechanism in nemaline myopathy. JCI Insight 2019; 5:125665. [PMID: 30990797 PMCID: PMC6542616 DOI: 10.1172/jci.insight.125665] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Accepted: 04/11/2019] [Indexed: 12/11/2022] Open
Abstract
Nemaline myopathy is a congenital neuromuscular disorder characterized by muscle weakness, fiber atrophy and presence of nemaline bodies within myofibers. However, the understanding of underlying pathomechanisms is lacking. Recently, mutations in KBTBD13, KLHL40 and KLHL41, three substrate adaptors for the E3-ubiquitin ligase Cullin-3, have been associated with early-onset nemaline myopathies. We hypothesized that deregulation of Cullin-3 and its muscle protein substrates may be responsible for the disease development. Using Cullin-3 knockout mice, we identified accumulation of non-muscle alpha-Actinins (ACTN1 and ACTN4) in muscles of these mice, which we also observed in KBTBD13 patients. Our data reveal that proper regulation of Cullin-3 activity and ACTN1 levels is essential for normal muscle and neuromuscular junction development. While ACTN1 is naturally downregulated during myogenesis, its overexpression in C2C12 myoblasts triggered defects in fusion, myogenesis and acetylcholine receptor clustering; features that we characterized in Cullin-3 deficient mice. Taken together, our data highlight the importance for Cullin-3 mediated degradation of ACTN1 for muscle development, and indicate a new pathomechanism for the etiology of myopathies seen in Cullin-3 knockout mice and nemaline myopathy patients.
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Affiliation(s)
- Jordan Blondelle
- Division of Cardiology, School of Medicine, UCSD, La Jolla, California, USA
| | - Kavya Tallapaka
- Division of Cardiology, School of Medicine, UCSD, La Jolla, California, USA
| | - Jane T. Seto
- Neuromuscular Research, Murdoch Children’s Research Institute, Royal Children’s Hospital, Parkville, Victoria, Australia
- Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia
| | - Majid Ghassemian
- Department of Chemistry and Biochemistry. UCSD, La Jolla, California, USA
| | - Madison Clark
- Division of Cardiology, School of Medicine, UCSD, La Jolla, California, USA
| | - Jenni M. Laitila
- Folkhälsan Research Center and Medicum, University of Helsinki, Helsinki, Finland
| | - Adam Bournazos
- Kids Neuroscience Centre, Kids Research, Children’s Hospital at Westmead, Sydney, New South Wales, Australia
- Discipline of Child and Adolescent Health, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Jeffrey D. Singer
- Department of Biology, Portland State University, Portland, Oregon, USA
| | - Stephan Lange
- Division of Cardiology, School of Medicine, UCSD, La Jolla, California, USA
- Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Institute of Medicine, University of Gothenburg, Gothenburg, Sweden
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15
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Oury J, Liu Y, Töpf A, Todorovic S, Hoedt E, Preethish-Kumar V, Neubert TA, Lin W, Lochmüller H, Burden SJ. MACF1 links Rapsyn to microtubule- and actin-binding proteins to maintain neuromuscular synapses. J Cell Biol 2019; 218:1686-1705. [PMID: 30842214 PMCID: PMC6504910 DOI: 10.1083/jcb.201810023] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 01/07/2019] [Accepted: 02/07/2019] [Indexed: 12/20/2022] Open
Abstract
Oury et al. show that the scaffolding protein MACF1 links Rapsyn, which binds acetylcholine receptors, to the microtubule- and actin-network at neuromuscular synapses. MACF1 thereby plays a role in synaptic maturation in mice, and mutations of MACF1 are associated with congenital myasthenia in humans. Complex mechanisms are required to form neuromuscular synapses, direct their subsequent maturation, and maintain the synapse throughout life. Transcriptional and post-translational pathways play important roles in synaptic differentiation and direct the accumulation of the neurotransmitter receptors, acetylcholine receptors (AChRs), to the postsynaptic membrane, ensuring for reliable synaptic transmission. Rapsyn, an intracellular peripheral membrane protein that binds AChRs, is essential for synaptic differentiation, but how Rapsyn acts is poorly understood. We screened for proteins that coisolate with AChRs in a Rapsyn-dependent manner and show that microtubule actin cross linking factor 1 (MACF1), a scaffolding protein with binding sites for microtubules (MT) and actin, is concentrated at neuromuscular synapses, where it binds Rapsyn and serves as a synaptic organizer for MT-associated proteins, EB1 and MAP1b, and the actin-associated protein, Vinculin. MACF1 plays an important role in maintaining synaptic differentiation and efficient synaptic transmission in mice, and variants in MACF1 are associated with congenital myasthenia in humans.
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Affiliation(s)
- Julien Oury
- Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, NY
| | - Yun Liu
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX
| | - Ana Töpf
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Slobodanka Todorovic
- Clinic for Neurology and Psychiatry for Children and Youth, Belgrade, Serbia and Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Esthelle Hoedt
- Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, NY
| | | | - Thomas A Neubert
- Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, NY
| | - Weichun Lin
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX
| | - Hanns Lochmüller
- Department of Neuropediatrics and Muscle Disorders, Medical Center, University of Freiburg, Faculty of Medicine, Freiburg, Germany.,Centro Nacional de Análisis Genómico, Center for Genomic Regulation, Barcelona Institute of Science and Technology, Barcelona, Spain.,Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada.,Division of Neurology, Department of Medicine, The Ottawa Hospital, Ottawa, Canada
| | - Steven J Burden
- Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, NY
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16
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Fundamental Molecules and Mechanisms for Forming and Maintaining Neuromuscular Synapses. Int J Mol Sci 2018; 19:ijms19020490. [PMID: 29415504 PMCID: PMC5855712 DOI: 10.3390/ijms19020490] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 01/24/2018] [Accepted: 01/29/2018] [Indexed: 02/08/2023] Open
Abstract
The neuromuscular synapse is a relatively large synapse with hundreds of active zones in presynaptic motor nerve terminals and more than ten million acetylcholine receptors (AChRs) in the postsynaptic membrane. The enrichment of proteins in presynaptic and postsynaptic membranes ensures a rapid, robust, and reliable synaptic transmission. Over fifty years ago, classic studies of the neuromuscular synapse led to a comprehensive understanding of how a synapse looks and works, but these landmark studies did not reveal the molecular mechanisms responsible for building and maintaining a synapse. During the past two-dozen years, the critical molecular players, responsible for assembling the specialized postsynaptic membrane and regulating nerve terminal differentiation, have begun to be identified and their mechanism of action better understood. Here, we describe and discuss five of these key molecular players, paying heed to their discovery as well as describing their currently understood mechanisms of action. In addition, we discuss the important gaps that remain to better understand how these proteins act to control synaptic differentiation and maintenance.
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17
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Legay C, Mei L. Moving forward with the neuromuscular junction. J Neurochem 2017; 142 Suppl 2:59-63. [PMID: 28449366 PMCID: PMC6029705 DOI: 10.1111/jnc.14028] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 03/13/2017] [Accepted: 03/17/2017] [Indexed: 11/30/2022]
Abstract
The neuromuscular junction (NMJ) is indispensable for survival. This synapse between motoneurons and skeletal muscle fibers allows posture, movement and respiration. Therefore, its dysfunction creates pathologies than can be lethal. The molecular mechanisms of NMJ development and maintenance are the subject of intensive studies. This mini-review focuses on some of the most recent discoveries. An unexpected role for a protein, rapsyn, which has been known for 40 years to aggregate acetylcholine receptors has emerged. A new cell partner at NMJ has been unmasked and is challenging our understanding of the functioning of this synapse. Toxins are now used as new tools to study degeneration/regeneration. The possibility of creating human NMJ in vitro is within reach with major consequences for drug screening. Wnts are secreted neurogenic factors that have been involved in vitro in acetylcholine receptor clustering, but their precise role in vivo remains to be clarified. All these data are raising new and exciting perspectives in the field and are discussed in this Review. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.
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Affiliation(s)
- Claire Legay
- Université Paris Descartes, CNRS UMR 8119, Sorbonne Paris Cité, Paris, France
| | - Lin Mei
- Department of Neurosciences and Regenerative medicine, Charlie Norwood VA Medical Center, Augusta, Georgia, USA
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18
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Axonal degeneration, distal collateral branching and neuromuscular junction architecture alterations occur prior to symptom onset in the SOD1G93A mouse model of amyotrophic lateral sclerosis. J Chem Neuroanat 2016; 76:35-47. [DOI: 10.1016/j.jchemneu.2016.03.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 01/29/2016] [Accepted: 03/19/2016] [Indexed: 12/11/2022]
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Aittaleb M, Chen PJ, Akaaboune M. Failure of lysosome clustering and positioning in the juxtanuclear region in cells deficient in rapsyn. J Cell Sci 2015; 128:3744-56. [PMID: 26330529 DOI: 10.1242/jcs.172536] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 08/23/2015] [Indexed: 01/06/2023] Open
Abstract
Rapsyn, a scaffold protein, is required for the clustering of acetylcholine receptors (AChRs) at contacts between motor neurons and differentiating muscle cells. Rapsyn is also expressed in cells that do not express AChRs. However, its function in these cells remains unknown. Here, we show that rapsyn plays an AChR-independent role in organizing the distribution and mobility of lysosomes. In cells devoid of AChRs, rapsyn selectively induces the clustering of lysosomes at high density in the juxtanuclear region without affecting the distribution of other intracellular organelles. However, when the same cells overexpress AChRs, rapsyn is recruited away from lysosomes to colocalize with AChR clusters on the cell surface. In rapsyn-deficient (Rapsn(-/-)) myoblasts or cells overexpressing rapsyn mutants, lysosomes are scattered within the cell and highly dynamic. The increased mobility of lysosomes in Rapsn(-/-) cells is associated with a significant increase in lysosomal exocytosis, as evidenced by increased release of lysosomal enzymes and plasma membrane damage when cells were challenged with the bacterial pore-forming toxin streptolysin-O. These findings uncover a new link between rapsyn, lysosome positioning, exocytosis and plasma membrane integrity.
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Affiliation(s)
- Mohamed Aittaleb
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Po-Ju Chen
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Mohammed Akaaboune
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA Program in Neuroscience, University of Michigan, Ann Arbor, MI 48109, USA
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20
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Ostrovidov S, Hosseini V, Ahadian S, Fujie T, Parthiban SP, Ramalingam M, Bae H, Kaji H, Khademhosseini A. Skeletal muscle tissue engineering: methods to form skeletal myotubes and their applications. TISSUE ENGINEERING. PART B, REVIEWS 2014; 20:403-36. [PMID: 24320971 PMCID: PMC4193686 DOI: 10.1089/ten.teb.2013.0534] [Citation(s) in RCA: 163] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Accepted: 12/05/2013] [Indexed: 12/25/2022]
Abstract
Skeletal muscle tissue engineering (SMTE) aims to repair or regenerate defective skeletal muscle tissue lost by traumatic injury, tumor ablation, or muscular disease. However, two decades after the introduction of SMTE, the engineering of functional skeletal muscle in the laboratory still remains a great challenge, and numerous techniques for growing functional muscle tissues are constantly being developed. This article reviews the recent findings regarding the methodology and various technical aspects of SMTE, including cell alignment and differentiation. We describe the structure and organization of muscle and discuss the methods for myoblast alignment cultured in vitro. To better understand muscle formation and to enhance the engineering of skeletal muscle, we also address the molecular basics of myogenesis and discuss different methods to induce myoblast differentiation into myotubes. We then provide an overview of different coculture systems involving skeletal muscle cells, and highlight major applications of engineered skeletal muscle tissues. Finally, potential challenges and future research directions for SMTE are outlined.
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Affiliation(s)
- Serge Ostrovidov
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan
| | - Vahid Hosseini
- Laboratory of Applied Mechanobiology, Department of Health Sciences and Technology, ETH, Zurich, Switzerland
| | - Samad Ahadian
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan
| | - Toshinori Fujie
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan
- Department of Life Science and Medical Bioscience, Graduate School of Advanced Science and Engineering, Waseda University, Tokyo, Japan
| | | | - Murugan Ramalingam
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan
- Faculté de Chirurgie Dentaire, Université de Strasbourg, Strasbourg Cedex, France
- Centre for Stem Cell Research, Christian Medical College Campus, Vellore, India
| | - Hojae Bae
- College of Animal Bioscience and Technology, Department of Bioindustrial Technologies, Konkuk University, Hwayang-dong, Kwangjin-gu, Seoul, Republic of Korea
| | - Hirokazu Kaji
- Department of Bioengineering and Robotics, Graduate School of Engineering, Tohoku University, Sendai, Japan
| | - Ali Khademhosseini
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Japan
- Department of Maxillofacial Biomedical Engineering, Institute of Oral Biology, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea
- Center for Biomedical Engineering, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Cambridge, Massachusetts, United States
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States
- Department of Physics, King Abdulaziz University, Jeddah, Saudi Arabia
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21
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Barik A, Zhang B, Sohal GS, Xiong WC, Mei L. Crosstalk between Agrin and Wnt signaling pathways in development of vertebrate neuromuscular junction. Dev Neurobiol 2014; 74:828-38. [PMID: 24838312 DOI: 10.1002/dneu.22190] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 05/01/2014] [Accepted: 05/14/2014] [Indexed: 11/08/2022]
Abstract
Neuromuscular junction (NMJ) is a cholinergic synapse where motor neurons elicit muscle contraction. Agrin and its coreceptors LRP4 and MuSK are critical for vertebrate NMJ formation. This paper reviews recent evidence for Wnts and Wnt signaling molecules in NMJ formation including a possible retrograde mechanism by muscle β-catenin. We also present data that Wnt3a, 7a, 8a and 10b could inhibit agrin-mediated AChR clustering. Together with the stimulating effect of Wnt9a, 9b, 10b, 11 and 16 on AChR clustering in the absence of agrin, these results suggest diverse roles for Wnt ligands in NMJ development.
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Affiliation(s)
- Arnab Barik
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, 30912
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22
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Abstract
α-Actinins are a major class of actin filament cross-linking proteins expressed in virtually all cells. In muscle, actinins cross-link thin filaments from adjacent sarcomeres. In non-muscle cells, different actinin isoforms play analogous roles in cross-linking actin filaments and anchoring them to structures such as cell-cell and cell-matrix junctions. Although actinins have long been known to play roles in cytokinesis, cell adhesion and cell migration, recent studies have provided further mechanistic insights into these functions. Roles for actinins in synaptic plasticity and membrane trafficking events have emerged more recently, as has a 'non-canonical' function for actinins in transcriptional regulation in the nucleus. In the present paper we review recent advances in our understanding of these diverse cell biological functions of actinins in non-muscle cells, as well as their roles in cancer and in genetic disorders affecting platelet and kidney physiology. We also make two proposals with regard to the actinin nomenclature. First, we argue that naming actinin isoforms according to their expression patterns is problematic and we suggest a more precise nomenclature system. Secondly, we suggest that the α in α-actinin is superfluous and can be omitted.
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23
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Lee CW, Zhang H, Geng L, Peng HB. Crosslinking-induced endocytosis of acetylcholine receptors by quantum dots. PLoS One 2014; 9:e90187. [PMID: 24587270 PMCID: PMC3934987 DOI: 10.1371/journal.pone.0090187] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Accepted: 01/31/2014] [Indexed: 12/22/2022] Open
Abstract
In a majority of patients with myasthenia gravis (MG), anti-acetylcholine receptor (AChR) antibodies target postsynaptic AChR clusters and thus compromise the membrane integrity of neuromuscular junctions (NMJs) and lead to muscle weakness. Antibody-induced endocytosis of AChRs in the postsynaptic membrane represents the initial step in the pathogenesis of MG; however, the molecular mechanisms underlying AChR endocytosis remain largely unknown. Here, we developed an approach to mimic the pathogenic antibodies for inducing the crosslinking and internalization of AChRs from the postsynaptic membrane. Using biotin-α-bungarotoxin and quantum dot (QD)-streptavidin, cell-surface and internalized AChRs could be readily distinguished by comparing the size, fluorescence intensity, trajectory, and subcellular localization of the QD signals. QD-induced AChR endocytosis was mediated by clathrin-dependent and caveolin-independent mechanisms, and the trafficking of internalized AChRs in the early endosomes required the integrity of microtubule structures. Furthermore, activation of the agrin/MuSK (muscle-specific kinase) signaling pathway strongly suppressed QD-induced internalization of AChRs. Lastly, QD-induced AChR crosslinking potentiated the dispersal of aneural AChR clusters upon synaptic induction. Taken together, our results identify a novel approach to study the mechanisms of AChR trafficking upon receptor crosslinking and endocytosis, and demonstrate that agrin-MuSK signaling pathways protect against crosslinking-induced endocytosis of AChRs.
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Affiliation(s)
- Chi Wai Lee
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science & Technology, Clear Water Bay, Hong Kong, China
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- * E-mail: (CWL); (HBP)
| | - Hailong Zhang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science & Technology, Clear Water Bay, Hong Kong, China
| | - Lin Geng
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science & Technology, Clear Water Bay, Hong Kong, China
- Department of Physiology, Faculty of Medicine, The University of Hong Kong, Pok Fu Lam, Hong Kong, China
| | - H. Benjamin Peng
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science & Technology, Clear Water Bay, Hong Kong, China
- * E-mail: (CWL); (HBP)
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24
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Rudell JB, Ferns MJ. Regulation of muscle acetylcholine receptor turnover by β subunit tyrosine phosphorylation. Dev Neurobiol 2013; 73:399-410. [PMID: 23325468 DOI: 10.1002/dneu.22070] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 11/17/2012] [Accepted: 12/29/2012] [Indexed: 12/21/2022]
Abstract
At the neuromuscular junction (NMJ), the postsynaptic localization of muscle acetylcholine receptor (AChR) is regulated by neural signals and occurs via several processes including metabolic stabilization of the receptor. However, the molecular mechanisms that influence receptor stability remain poorly defined. Here, we show that neural agrin and the tyrosine phosphatase inhibitor, pervanadate slow the degradation of surface receptor in cultured muscle cells. Their action is mediated by tyrosine phosphorylation of the AChR β subunit, as agrin and pervandate had no effect on receptor half-life in AChR-β(3F/3F) muscle cells, which have targeted mutations of the β subunit cytoplasmic tyrosines. Moreover, in wild type AChR-β(3Y) muscle cells, we found a linear relationship between average receptor half-life and the percentage of AChR with phosphorylated β subunit, with half-lives of 12.7 and 23 h for nonphosphorylated and phosphorylated receptor, respectively. Surprisingly, pervanadate increased receptor half-life in AChR-β(3Y) myotubes in the absence of clustering, and agrin failed to increase receptor half-life in AChR-β(3F/3F) myotubes even in the presence of clustering. The metabolic stabilization of the AChR was mediated specifically by phosphorylation of βY390 as mutation of this residue abolished β subunit phosphorylation but did not affect δ subunit phosphorylation. Receptor stabilization also led to higher receptor levels, as agrin increased surface AChR by 30% in AChR-β(3Y) but not AChR-β(3F/3F) myotubes. Together, these findings identify an unexpected role for agrin-induced phosphorylation of β(Y390) in downregulating AChR turnover. This likely stabilizes AChR at developing synapses, and contributes to the extended half-life of AChR at adult NMJs.
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Affiliation(s)
- John B Rudell
- Department of Physiology and Membrane Biology, University of California Davis, Davis, CA, USA
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25
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Molecular mechanisms underlying maturation and maintenance of the vertebrate neuromuscular junction. Trends Neurosci 2012; 35:441-53. [PMID: 22633140 DOI: 10.1016/j.tins.2012.04.005] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 04/09/2012] [Accepted: 04/15/2012] [Indexed: 01/22/2023]
Abstract
The vertebrate neuromuscular junction (NMJ), a peripheral synapse formed between motoneuron and skeletal muscle, is characterized by a protracted postnatal period of maturation and life-long maintenance. In neuromuscular disorders such as congenital myasthenic syndromes (CMSs), disruptions of NMJ maturation and/or maintenance are frequently observed. In particular, defective neuromuscular transmission associated with structural and molecular abnormalities at the pre- and postsynaptic membranes, as well as at the synaptic cleft, has been reported in these patients. Here, we review recent advances in the understanding of molecular and cellular events that mediate NMJ maturation and maintenance. The underlying regulatory mechanisms, including key molecular regulators at the presynaptic nerve terminal, synaptic cleft, and postsynaptic muscle membrane, are discussed.
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26
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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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27
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Zhang B, Liang C, Bates R, Yin Y, Xiong WC, Mei L. Wnt proteins regulate acetylcholine receptor clustering in muscle cells. Mol Brain 2012; 5:7. [PMID: 22309736 PMCID: PMC3296622 DOI: 10.1186/1756-6606-5-7] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Accepted: 02/06/2012] [Indexed: 01/08/2023] Open
Abstract
Background The neuromuscular junction (NMJ) is a cholinergic synapse that rapidly conveys signals from motoneurons to muscle cells and exhibits a high degree of subcellular specialization characteristic of chemical synapses. NMJ formation requires agrin and its coreceptors LRP4 and MuSK. Increasing evidence indicates that Wnt signaling regulates NMJ formation in Drosophila, C. elegans and zebrafish. Results In the study we systematically studied the effect of all 19 different Wnts in mammals on acetylcholine receptor (AChR) cluster formation. We identified five Wnts (Wnt9a, Wnt9b, Wnt10b, Wnt11, and Wnt16) that are able to stimulate AChR clustering, of which Wnt9a and Wnt11 are expressed abundantly in developing muscles. Using Wnt9a and Wnt11 as example, we demonstrated that Wnt induction of AChR clusters was dose-dependent and non-additive to that of agrin, suggesting that Wnts may act via similar pathways to induce AChR clusters. We provide evidence that Wnt9a and Wnt11 bind directly to the extracellular domain of MuSK, to induce MuSK dimerization and subsequent tyrosine phosphorylation of the kinase. In addition, Wnt-induced AChR clustering requires LRP4. Conclusions These results identify Wnts as new players in AChR cluster formation, which act in a manner that requires both MuSK and LRP4, revealing a novel function of LRP4.
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Affiliation(s)
- Bin Zhang
- Department of Neurology and Institute of Molecular Medicine and Genetics, Georgia Health Sciences University, Augusta, Georgia 30912, USA
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Onset of cholinergic efferent synaptic function in sensory hair cells of the rat cochlea. J Neurosci 2011; 31:15092-101. [PMID: 22016543 DOI: 10.1523/jneurosci.2743-11.2011] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In the developing mammalian cochlea, the sensory hair cells receive efferent innervation originating in the superior olivary complex. This input is mediated by α9/α10 nicotinic acetylcholine receptors (nAChRs) and is inhibitory due to the subsequent activation of calcium-dependent SK2 potassium channels. We examined the acquisition of this cholinergic efferent input using whole-cell voltage-clamp recordings from inner hair cells (IHCs) in acutely excised apical turns of the rat cochlea from embryonic day 21 to postnatal day 8 (P8). Responses to 1 mm acetylcholine (ACh) were detected from P0 on in almost every IHC. The ACh-activated current amplitude increased with age and demonstrated the same pharmacology as α9-containing nAChRs. Interestingly, at P0, the ACh response was not coupled to SK2 channels, so that the initial cholinergic response was excitatory and could trigger action potentials in IHCs. Coupling to SK current was detected earliest at P1 in a subset of IHCs and by P3 in every IHC studied. Clustered nAChRs and SK2 channels were found on IHCs from P1 on using Alexa Fluor 488 conjugated α-bungarotoxin and SK2 immunohistochemistry. The number of nAChRs clusters increased with age to 16 per IHC at P8. Cholinergic efferent synaptic currents first appeared in a subset of IHCs at P1 and by P3 in every IHC studied, contemporaneously with ACh-evoked SK currents, suggesting that SK2 channels may be necessary at onset of synaptic function. An analogous pattern of development was observed for the efferent synapses that form later (P6-P8) on outer hair cells in the basal cochlea.
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Comparison of muscle ultrastructure in myasthenia gravis with anti-MuSK and anti-AChR antibodies. J Neurol 2010; 258:746-52. [DOI: 10.1007/s00415-010-5823-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 10/22/2010] [Accepted: 10/29/2010] [Indexed: 10/18/2022]
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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: 0.8] [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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31
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Tseng CN, Zhang L, Wu SL, Wang WF, Wang ZZ, Cascio M. Asparagine of z8 insert is critical for the affinity, conformation, and acetylcholine receptor-clustering activity of neural agrin. J Biol Chem 2010; 285:27641-51. [PMID: 20566625 DOI: 10.1074/jbc.m110.130625] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Agrin isoforms with different bioactivities are synthesized by the nerve and the muscle. Neural agrin containing an 8-amino acid insert (z8) introduced by alternative splicing is the active form that induces synaptic differentiation at the neuromuscular junction. In addition to alternative splicing, extracellular calcium is also required for the activity of neural agrin. To understand better how the activity of agrin is regulated by alternative splicing, we have applied alanine substitution mutagenesis to the z8 insert and the calcium binding site in the minimally functional AgG3z8 fragment. Single alanine substitutions in the 4th through the 7th amino acid of the z8 splice insert significantly reduced the function of agrin, in terms of acetylcholine receptor clustering activity and the affinity for binding to the muscle surface. Mutation of the asparagine at the 4th position drastically reduces bioactivity such that it is equivalent to that of muscle form AgG3z0. These reduced activity mutants also show reduced magnitudes of the calcium-induced CD spectrum change from that observed in AgG3z8 fragments, indicating that cross-talk between calcium and the z8 insert is critical for the normal activity of agrin. However, removal of Ca(2+) binding via mutation of both aspartic acids in the calcium binding site did not totally eliminate the activity of AgG3z8. These results suggest a model wherein the z8 insert is a Ca(2+)-responsive allosteric element that is essential in forming an active conformation in neuronal agrin.
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Affiliation(s)
- Chao-Neng Tseng
- Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung City 807, Taiwan
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32
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Lek M, North KN. Are biological sensors modulated by their structural scaffolds? The role of the structural muscle proteins alpha-actinin-2 and alpha-actinin-3 as modulators of biological sensors. FEBS Lett 2010; 584:2974-80. [PMID: 20515688 DOI: 10.1016/j.febslet.2010.05.059] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2010] [Revised: 05/26/2010] [Accepted: 05/26/2010] [Indexed: 02/01/2023]
Abstract
Biological sensors and their ability to detect and respond to change in the cellular environment can be modulated by protein scaffolds acting within their interaction network. The skeletal muscle alpha-actinins have been considered as primarily structural scaffold proteins. However, deficiency of alpha-actinin-3 due to a common null polymorphism results in predominantly metabolic changes in skeletal muscle function. In this review, we explore the range of phenotypes associated with alpha-actinin-3 deficiency, and draw supporting evidence from known interaction partners for its role as a scaffold which acts to modulate biological sensors that result in changes in muscle metabolism and structure.
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Affiliation(s)
- Monkol Lek
- Institute for Neuroscience and Muscle Research, The Children's Hospital at Westmead, Sydney, NSW, Australia
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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: 379] [Impact Index Per Article: 27.1] [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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Yampolsky P, Pacifici PG, Witzemann V. Differential muscle-driven synaptic remodeling in the neuromuscular junction after denervation. Eur J Neurosci 2010; 31:646-58. [DOI: 10.1111/j.1460-9568.2010.07096.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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