1
|
Alignment of Skeletal Muscle Cells Facilitates Acetylcholine Receptor Clustering and Neuromuscular Junction Formation with Co-Cultured Human iPSC-Derived Motor Neurons. Cells 2022; 11:cells11233760. [PMID: 36497020 PMCID: PMC9738074 DOI: 10.3390/cells11233760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 11/04/2022] [Accepted: 11/20/2022] [Indexed: 11/27/2022] Open
Abstract
In vitro neuromuscular junction (NMJ) models are powerful tools for studying neuromuscular disorders. Although linearly patterned culture surfaces have been reported to be useful for the formation of in vitro NMJ models using mouse motor neuron (MNs) and skeletal muscle (SkM) myotubes, it is unclear how the linearly patterned culture surface increases acetylcholine receptor (AChR) clustering, one of the steps in the process of NMJ formation, and whether this increases the in vitro NMJ formation efficiency of co-cultured human MNs and SkM myotubes. In this study, we investigated the effects of a linearly patterned culture surface on AChR clustering in myotubes and examined the possible mechanism of the increase in AChR clustering using gene expression analysis, as well as the effects of the patterned surface on the efficiency of NMJ formation between co-cultured human SkM myotubes and human iPSC-derived MNs. Our results suggest that better differentiation of myotubes on the patterned surface, compared to the flat surface, induced gene expression of integrin α7 and AChR ε-subunit, thereby increasing AChR clustering. Furthermore, we found that the number of NMJs between human SkM cells and MNs increased upon co-culture on the linearly patterned surface, suggesting the usefulness of the patterned surface for creating in vitro human NMJ models.
Collapse
|
2
|
Takahashi H, Oikawa F, Takeda N, Shimizu T. Contraction Control of Aligned Myofiber Sheet Tissue by Parallel Oriented iPS Cell-derived Neurons. Tissue Eng Part A 2022; 28:661-671. [PMID: 35057641 DOI: 10.1089/ten.tea.2021.0202] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Fabrication and application of engineered complex tissues composed of different types of cells is a crucial milestone in the next phase of tissue engineering. The delicate organization structure of each tissue component and their physiological connections enable all the functions in the human body. In this study, cell sheet-based engineering allowed us to fabricate a complex myofiber sheet tissue using motor neurons derived from human iPS cells. In contrast with previous studies of other groups, a myofiber sheet with a biomimetic aligned structure was produced from human myoblasts using a striped-patterned thermoresponsive dish, which enabled manipulation of the sheet tissue by simply lowering the culture temperature. The myofiber sheet was transferred onto a gel that promotes functional maturation of human myofibers, resulting in production of contractile human muscle tissue. Just by seeding motor neurons onto the sheet tissue, all the neurons physically contacted to the aligned myofibers, and autonomously elongated in parallel to the myofiber orientation. In addition, the neurite outgrowth was enlarged by co-culturing on the myofiber sheet. The presence of the neurons enhanced clustering of myofiber acetylcholine receptors (AChR), typically found at the neuromuscular junctions (NMJs). Consequently, contraction behaviors of the myofiber sheet were regulated by neuronal signal transduction through NMJs. Muscle contraction was induced when the motor neurons were stimulated by glutamic acid, and effectively blocked by administration of d-tubocurarine as an antagonistic inhibitor for the AChR. The fibrin-based gel was useful as a culture environment for tissue maturation and as a favorable substrate for unobstructed contractions. Our neuron-muscle sheet tissue will be scalable by simply enlarging the micropatterned substrate and manipulable three-dimensionally; fabrication of a thick tissue and a bundle-like structured tissue will be possible just by layering multiple sheets or rolling up the sheet. Simplified control over self-orientation of neurite elongation will be advantageous for fabrication of such a large and complex tissue. Therefore, our methodology, established in this study, will be instrumental in future applications of regenerative medicine for locomotion apparatus.
Collapse
Affiliation(s)
| | - Fumiko Oikawa
- Waseda University, 13148, Shinjuku-ku, Tokyo, Japan;
| | - Naoya Takeda
- Waseda University, 13148, Shinjuku-ku, Tokyo, Japan;
| | | |
Collapse
|
3
|
Rodríguez Cruz PM, Cossins J, Beeson D, Vincent A. The Neuromuscular Junction in Health and Disease: Molecular Mechanisms Governing Synaptic Formation and Homeostasis. Front Mol Neurosci 2020; 13:610964. [PMID: 33343299 PMCID: PMC7744297 DOI: 10.3389/fnmol.2020.610964] [Citation(s) in RCA: 87] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 10/30/2020] [Indexed: 12/28/2022] Open
Abstract
The neuromuscular junction (NMJ) is a highly specialized synapse between a motor neuron nerve terminal and its muscle fiber that are responsible for converting electrical impulses generated by the motor neuron into electrical activity in the muscle fibers. On arrival of the motor nerve action potential, calcium enters the presynaptic terminal, which leads to the release of the neurotransmitter acetylcholine (ACh). ACh crosses the synaptic gap and binds to ACh receptors (AChRs) tightly clustered on the surface of the muscle fiber; this leads to the endplate potential which initiates the muscle action potential that results in muscle contraction. This is a simplified version of the events in neuromuscular transmission that take place within milliseconds, and are dependent on a tiny but highly structured NMJ. Much of this review is devoted to describing in more detail the development, maturation, maintenance and regeneration of the NMJ, but first we describe briefly the most important molecules involved and the conditions that affect their numbers and function. Most important clinically worldwide, are myasthenia gravis (MG), the Lambert-Eaton myasthenic syndrome (LEMS) and congenital myasthenic syndromes (CMS), each of which causes specific molecular defects. In addition, we mention the neurotoxins from bacteria, snakes and many other species that interfere with neuromuscular transmission and cause potentially fatal diseases, but have also provided useful probes for investigating neuromuscular transmission. There are also changes in NMJ structure and function in motor neuron disease, spinal muscle atrophy and sarcopenia that are likely to be secondary but might provide treatment targets. The NMJ is one of the best studied and most disease-prone synapses in the nervous system and it is amenable to in vivo and ex vivo investigation and to systemic therapies that can help restore normal function.
Collapse
Affiliation(s)
- Pedro M. Rodríguez Cruz
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| | - Judith Cossins
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| | - David Beeson
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| | - Angela Vincent
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom
| |
Collapse
|
4
|
Pęziński M, Daszczuk P, Pradhan BS, Lochmüller H, Prószyński TJ. An improved method for culturing myotubes on laminins for the robust clustering of postsynaptic machinery. Sci Rep 2020; 10:4524. [PMID: 32161296 PMCID: PMC7066178 DOI: 10.1038/s41598-020-61347-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 02/20/2020] [Indexed: 01/03/2023] Open
Abstract
Motor neurons form specialized synapses with skeletal muscle fibers, called neuromuscular junctions (NMJs). Cultured myotubes are used as a simplified in vitro system to study the postsynaptic specialization of muscles. The stimulation of myotubes with the glycoprotein agrin or laminin-111 induces the clustering of postsynaptic machinery that contains acetylcholine receptors (AChRs). When myotubes are grown on laminin-coated surfaces, AChR clusters undergo developmental remodeling to form topologically complex structures that resemble mature NMJs. Needing further exploration are the molecular processes that govern AChR cluster assembly and its developmental maturation. Here, we describe an improved protocol for culturing muscle cells to promote the formation of complex AChR clusters. We screened various laminin isoforms and showed that laminin-221 was the most potent for inducing AChR clusters, whereas laminin-121, laminin-211, and laminin-221 afforded the highest percentages of topologically complex assemblies. Human primary myotubes that were formed by myoblasts obtained from patient biopsies also assembled AChR clusters that underwent remodeling in vitro. Collectively, these results demonstrate an advancement of culturing myotubes that can facilitate high-throughput screening for potential therapeutic targets for neuromuscular disorders.
Collapse
Affiliation(s)
- Marcin Pęziński
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Patrycja Daszczuk
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Bhola Shankar Pradhan
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland.,Łukasiewicz Research Network - PORT Polish Center for Technology Development, Wrocław, Poland
| | - Hanns Lochmüller
- Department of Neuropediatrics and Muscle Disorders, Faculty of Medicine, Medical Centre, University of Freiburg, Freiburg, Germany.,Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada.,Division of Neurology, Department of Medicine, The Ottawa Hospital, Ottawa, Canada
| | - Tomasz J Prószyński
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland. .,Łukasiewicz Research Network - PORT Polish Center for Technology Development, Wrocław, Poland.
| |
Collapse
|
5
|
The role of the dystrophin glycoprotein complex on the neuromuscular system. Neurosci Lett 2020; 722:134833. [DOI: 10.1016/j.neulet.2020.134833] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2019] [Revised: 02/07/2020] [Accepted: 02/09/2020] [Indexed: 12/26/2022]
|
6
|
MMP-mediated modulation of ECM environment during axonal growth and NMJ development. Neurosci Lett 2020; 724:134822. [PMID: 32061716 DOI: 10.1016/j.neulet.2020.134822] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Revised: 01/31/2020] [Accepted: 02/04/2020] [Indexed: 12/19/2022]
Abstract
Motor neurons, skeletal muscles, and perisynaptic Schwann cells interact with extracellular matrix (ECM) to form the tetrapartite synapse in the peripheral nervous system. Dynamic remodeling of ECM composition is essential to diversify its functions for distinct cellular processes during neuromuscular junction (NMJ) development. In this review, we give an overview of the proteolytic regulation of ECM proteins, particularly by secreted and membrane-type matrix metalloproteinases (MMPs), in axonal growth and NMJ development. It is suggested that MMP-2, MMP-9, and membrane type 1-MMP (MT1-MMP) promote axonal outgrowth and regeneration upon injury by clearing the glial scars at the lesion site. In addition, these MMPs also play roles in neuromuscular synaptogenesis, ranging from spontaneous formation of synaptic specializations to activity-dependent synaptic elimination, via proteolytic cleavage or degradation of growth factors, neurotrophic factors, and ECM molecules. For instance, secreted MMP-3 has been known to cleave agrin, the main postsynaptic differentiation inducer, further highlighting the importance of MMPs in NMJ formation and maintenance. Furthermore, the increased level of several MMPs in myasthenia gravis (MG) patient suggest the pathophysiological mechanisms of MMP-mediated proteolytic degradation in MG pathogenesis. Finally, we speculate on potential major future directions for studying the regulatory functions of MMP-mediated ECM remodeling in axonal growth and NMJ development.
Collapse
|
7
|
Besser RR, Bowles AC, Alassaf A, Carbonero D, Claure I, Jones E, Reda J, Wubker L, Batchelor W, Ziebarth N, Silvera R, Khan A, Maciel R, Saporta M, Agarwal A. Enzymatically crosslinked gelatin-laminin hydrogels for applications in neuromuscular tissue engineering. Biomater Sci 2020; 8:591-606. [PMID: 31859298 PMCID: PMC7141910 DOI: 10.1039/c9bm01430f] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
We report a water-soluble and non-toxic method to incorporate additional extracellular matrix proteins into gelatin hydrogels, while obviating the use of chemical crosslinkers such as glutaraldehyde. Gelatin hydrogels were fabricated using a range of gelatin concentrations (4%-10%) that corresponded to elastic moduli of approximately 1 kPa-25 kPa, respectively, a substrate stiffness relevant for multiple cell types. Microbial transglutaminase was then used to enzymatically crosslink a layer of laminin on top of gelatin hydrogels, resulting in 2-component gelatin-laminin hydrogels. Human induced pluripotent stem cell derived spinal spheroids readily adhered and rapidly extended axons on GEL-LN hydrogels. Axons displayed a more mature morphology and superior electrophysiological properties on GEL-LN hydrogels compared to the controls. Schwann cells on GEL-LN hydrogels adhered and proliferated normally, displayed a healthy morphology, and maintained the expression of Schwann cell specific markers. Lastly, skeletal muscle cells on GEL-LN hydrogels achieved long-term culture for up to 28 days without delamination, while expressing higher levels of terminal genes including myosin heavy chain, MyoD, MuSK, and M-cadherin suggesting enhanced maturation potential and myotube formation compared to the controls. Future studies will employ the superior culture outcomes of this hybrid substrate for engineering functional neuromuscular junctions and related organ on a chip applications.
Collapse
Affiliation(s)
- Rachel R Besser
- Department of Biomedical Engineering, University of Miami, 1251 Memorial Dr, MEA 203, Coral Gables, FL 33146, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
8
|
Patel A, Vendrell-Gonzalez S, Haas G, Marcinczyk M, Ziemkiewicz N, Talovic M, Fisher JS, Garg K. Regulation of Myogenic Activity by Substrate and Electrical Stimulation In Vitro. Biores Open Access 2019; 8:129-138. [PMID: 31367477 PMCID: PMC6664826 DOI: 10.1089/biores.2019.0016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Skeletal muscle has a remarkable regenerative capacity in response to mild injury. However, when muscle is severely injured, muscle regeneration is impaired due to the loss of muscle-resident stem cells, known as satellite cells. Fibrotic tissue, primarily comprising collagen I (COL), is deposited with this critical loss of muscle. In recent studies, supplementation of laminin (LM)-111 has been shown to improve skeletal muscle regeneration in several models of disease and injury. Additionally, electrical stimulation (E-stim) has been investigated as a possible rehabilitation therapy to improve muscle's functional recovery. This study investigated the role of E-stim and substrate in regulating myogenic response. C2C12 myoblasts were allowed to differentiate into myotubes on COL- and LM-coated polydimethylsiloxane molds. The myotubes were subjected to E-stim and compared with nonstimulated controls. While E-stim resulted in increased myogenic activity, irrespective of substrate, LM supported increased proliferation and uniform distribution of C2C12 myoblasts. In addition, C2C12 myoblasts cultured on LM showed higher Sirtuin 1, mammalian target of rapamycin, desmin, nitric oxide, and vascular endothelial growth factor expression. Taken together, these results suggest that an LM substrate is more conducive to myoblast growth and differentiation in response to E-stim in vitro.
Collapse
Affiliation(s)
- Anjali Patel
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| | - Sara Vendrell-Gonzalez
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| | - Gabriel Haas
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| | - Madison Marcinczyk
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| | - Natalia Ziemkiewicz
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| | - Muhamed Talovic
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| | - Jonathan S Fisher
- Department of Biology, College of Arts and Sciences, Saint Louis University, St. Louis, Missouri
| | - Koyal Garg
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, St. Louis, Missouri
| |
Collapse
|
9
|
Mella J, Pérez V, Zelada D, Moreno N, Ionescu A, Perlson E, Henríquez JP. Efficient gene transfer into primary muscle cells to analyze nerve-independent postsynaptic organization in vitro. Neuromuscul Disord 2019; 29:533-542. [DOI: 10.1016/j.nmd.2019.05.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 04/23/2019] [Accepted: 05/17/2019] [Indexed: 01/08/2023]
|
10
|
Marcinczyk M, Dunn A, Haas G, Madsen J, Scheidt R, Patel K, Talovic M, Garg K. The Effect of Laminin-111 Hydrogels on Muscle Regeneration in a Murine Model of Injury. Tissue Eng Part A 2019; 25:1001-1012. [PMID: 30426851 PMCID: PMC9839345 DOI: 10.1089/ten.tea.2018.0200] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
IMPACT STATEMENT Extremity injuries make up the most common survivable injuries in vehicular accidents and modern military conflicts. A majority of these injuries involve volumetric muscle loss (VML). The potential for donor site morbidity may limit the clinical use of autologous muscle grafts for VML injuries. Treatments that can improve the regeneration of functional muscle tissue are critically needed to improve limb salvage and reduce the rate of delayed amputations. The development of a laminin-111-enriched fibrin hydrogel will offer a potentially transformative and "off-the-shelf" clinically relevant therapy for functional skeletal muscle regeneration.
Collapse
Affiliation(s)
- Madison Marcinczyk
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Andrew Dunn
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Gabriel Haas
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Josh Madsen
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Robert Scheidt
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Krishna Patel
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Muhamed Talovic
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri
| | - Koyal Garg
- Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, St. Louis, Missouri.,Address correspondence to: Koyal Garg, PhD, Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, 3507 Lindell Boulevard, St. Louis, MO 63103
| |
Collapse
|
11
|
Hunter DD, Manglapus MK, Bachay G, Claudepierre T, Dolan MW, Gesuelli KA, Brunken WJ. CNS synapses are stabilized trans-synaptically by laminins and laminin-interacting proteins. J Comp Neurol 2017; 527:67-86. [PMID: 29023785 DOI: 10.1002/cne.24338] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 09/21/2017] [Accepted: 09/29/2017] [Indexed: 01/05/2023]
Abstract
The retina expresses several laminins in the outer plexiform layer (OPL), where they may provide an extracellular scaffold for synapse stabilization. Mice with a targeted deletion of the laminin β2 gene (Lamb2) exhibit retinal disruptions: photoreceptor synapses in the OPL are disorganized and the retinal physiological response is attenuated. We hypothesize that laminins are required for proper trans-synaptic alignment. To test this, we compared the distribution, expression, association and modification of several pre- and post-synaptic elements in wild-type and Lamb2-null retinae. A potential laminin receptor, integrin α3, is at the presynaptic side of the wild-type OPL. Another potential laminin receptor, dystroglycan, is at the post-synaptic side of the wild-type OPL. Integrin α3 and dystroglycan can be co-immunoprecipitated with the laminin β2 chain, demonstrating that they may bind laminins. In the absence of the laminin β2 chain, the expression of many pre-synaptic components (bassoon, kinesin, among others) is relatively undisturbed although their spatial organization and anchoring to the membrane is disrupted. In contrast, in the Lamb2-null, β-dystroglycan (β-DG) expression is altered, co-localization of β-DG with dystrophin and the glutamate receptor mGluR6 is disrupted, and the post-synaptic bipolar cell components mGluR6 and GPR179 become dissociated, suggesting that laminins mediate scaffolding of post-synaptic components. In addition, although pikachurin remains associated with β-DG, pikachurin is no longer closely associated with mGluR6 or α-DG in the Lamb2-null. These data suggest that laminins act as links among pre- and post-synaptic laminin receptors and α-DG and pikachurin in the synaptic space to maintain proper trans-synaptic alignment.
Collapse
Affiliation(s)
- Dale D Hunter
- Department of Anatomy and Cellular Biology, Tufts University and Tufts Center for Vision Research, Boston, Massachusetts.,Department of Ophthalmology and the SUNY Eye Institute, Upstate Medical University, Syracuse, New York
| | - Mary K Manglapus
- Department of Anatomy and Cellular Biology, Tufts University and Tufts Center for Vision Research, Boston, Massachusetts
| | - Galina Bachay
- Department of Ophthalmology and the SUNY Eye Institute, Upstate Medical University, Syracuse, New York
| | - Thomas Claudepierre
- Department of Anatomy and Cellular Biology, Tufts University and Tufts Center for Vision Research, Boston, Massachusetts
| | - Michael W Dolan
- Department of Ophthalmology and the SUNY Eye Institute, Upstate Medical University, Syracuse, New York
| | - Kelly-Ann Gesuelli
- Department of Ophthalmology and the SUNY Eye Institute, Upstate Medical University, Syracuse, New York
| | - William J Brunken
- Department of Anatomy and Cellular Biology, Tufts University and Tufts Center for Vision Research, Boston, Massachusetts.,Department of Ophthalmology and the SUNY Eye Institute, Upstate Medical University, Syracuse, New York
| |
Collapse
|
12
|
|
13
|
Vezina-Audette R, Tremblay M, Carbonetto S. Laminin is instructive and calmodulin dependent kinase II is non-permissive for the formation of complex aggregates of acetylcholine receptors on myotubes in culture. Matrix Biol 2016; 57-58:106-123. [PMID: 27964993 DOI: 10.1016/j.matbio.2016.11.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 11/16/2016] [Indexed: 12/11/2022]
Abstract
Previous work has shown that myotubes cultured on laminin-coated substrates form complex aggregates of synaptic proteins that are similar in shape and composition to neuromuscular junctions (NMJs). Here we show that laminin instructs the location of complex aggregates which form only on the lower surface when laminin is coated onto culture dishes but over the entire cell when laminin is added in solution. Silencing of myotubes by agents that block electrical activity (tetrodotoxin, verapamil) or by inhibitors of calmodulin dependent kinase (CaMKII) render the myotube permissive for the formation of complex aggregates. Treatment with laminin alone will facilitate the formation of complex aggregates hours later when myotubes are made permissive by inhibiting CaMKII. The AChR agonist carbachol disperses pre formed aggregates suggesting that non-permissiveness may involve active dispersal of AChRs. The permissive period requires ongoing protein synthesis. The latter may reflect a requirement for rapsyn, which turns over rapidly, and is necessary for aggregation. Consistent with this geldanamycin, an agent that increases rapsyn turnover disrupts complex aggregates. Agrin is well known to induce small clusters of AChRs but does not induce complex aggregates even though aggregate formation requires MuSK, a receptor tyrosine kinase activated by agrin. Dystroglycan (DG) is the major laminin receptor mediating complex aggregate formation with some contribution from β1 integrins. In addition, there is a pool of CaMKII associated with DG. We discuss how these permissive and instructive mechanisms bear on NMJ formation in vivo.
Collapse
Affiliation(s)
- Raphael Vezina-Audette
- Centre for Research in Neuroscience, and Dept. of Neurology, McGill University Health Centre, 1650, Cedar Ave., Montreal, Quebec, H3G 1A4, Canada
| | - Mathieu Tremblay
- Centre for Research in Neuroscience, and Dept. of Neurology, McGill University Health Centre, 1650, Cedar Ave., Montreal, Quebec, H3G 1A4, Canada
| | - Salvatore Carbonetto
- Centre for Research in Neuroscience, and Dept. of Neurology, McGill University Health Centre, 1650, Cedar Ave., Montreal, Quebec, H3G 1A4, Canada.
| |
Collapse
|
14
|
Jarosz J, White C, Grow WA. Sodium nitrate decreases agrin-induced acetylcholine receptor clustering. BMC Pharmacol Toxicol 2016; 17:20. [PMID: 27132129 PMCID: PMC4852099 DOI: 10.1186/s40360-016-0062-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 04/14/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Humans are exposed to nitrate predominantly through diet with peak plasma concentrations within an hour after ingestion, but additional exposure is obtained from the environment, and minimally through de novo synthesis. Higher nitrate consumption has been associated with methemoglobinemia, spontaneous abortions, atherosclerosis, myocardial ischemia, septic and distressed lung, inflammatory bowel disease, amyotrophic lateral sclerosis, and neural tube defects. However, skeletal muscle development has not been examined. METHODS C2C12 skeletal muscle cell cultures were maintained, myoblasts were fused into myotubes, and then cultures were exposed to motor neuron derived agrin to enhance acetylcholine receptor (AChR) clustering. Untreated cultures were compared with cultures exposed to sodium nitrate at concentrations ranging from 10 ng/mL-100 μg/mL. RESULTS The results reported here demonstrate that 1 μg/mL sodium nitrate was sufficient to decrease the frequency of agrin-induced AChR clustering without affecting myotube formation. In addition, concentrations of sodium nitrate of 1 μg/mL or 100 μg/mL decreased gene expression of the myogenic transcription factor myogenin and AChR in correlation with the agrin-induced AChR clustering data. CONCLUSIONS These results reveal that sodium nitrate decreases the frequency of agrin-induced AChR clustering by a mechanism that includes myogenin and AChR gene expression. As a consequence sodium nitrate may pose a risk for skeletal muscle development and subsequent neuromuscular synapse formation in humans.
Collapse
Affiliation(s)
- Jess Jarosz
- Department of Anatomy, Midwestern University, 19555 N. 59th Avenue, Glendale, AZ 85308 USA
| | - Cullen White
- Department of Anatomy, Midwestern University, 19555 N. 59th Avenue, Glendale, AZ 85308 USA
| | - Wade A. Grow
- Department of Anatomy, Midwestern University, 19555 N. 59th Avenue, Glendale, AZ 85308 USA
| |
Collapse
|
15
|
Zhang BGX, Quigley AF, Bourke JL, Nowell CJ, Myers DE, Choong PFM, Kapsa RMI. Combination of agrin and laminin increase acetylcholine receptor clustering and enhance functional neuromuscular junction formation In vitro. Dev Neurobiol 2015; 76:551-65. [PMID: 26251299 DOI: 10.1002/dneu.22331] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 06/23/2015] [Accepted: 08/01/2015] [Indexed: 01/07/2023]
Abstract
Clustering of acetylcholine receptors (AChR) at the postsynaptic membrane is a crucial step in the development of neuromuscular junctions (NMJ). During development and after denervation, aneural AChR clusters form on the sarcolemma. Recent studies suggest that these receptors are critical for guiding and initiating synaptogenesis. The aim of this study is to investigate the effect of agrin and laminin-1; agents with known AChR clustering activity; on NMJ formation and muscle maturation. Primary myoblasts were differentiated in vitro on collagen, laminin or collagen and laminin-coated surfaces in the presence or absence of agrin and laminin. The pretreated cells were then subject to innervation by PC12 cells. The number of neuromuscular junctions was assessed by immunocytochemical co-localization of AChR clusters and the presynaptic marker synaptophysin. Functional neuromuscular junctions were quantitated by analysis of the level of spontaneous as well as neuromuscular blocker responsive contractile activity and muscle maturation was assessed by the degree of myotube striation. Agrin alone did not prime muscle for innervation while a combination of agrin and laminin pretreatment increased the number of neuromuscular junctions formed and enhanced acetylcholine based neurotransmission and myotube striation. This study has direct clinical relevance for treatment of denervation injuries and creating functional neuromuscular constructs for muscle tissue repair.
Collapse
Affiliation(s)
- Bill G X Zhang
- Department of Orthopaedics, St. Vincent's Hospital Melbourne and the University of Melbourne, Fitzroy, VIC, 3065, Australia.,Department of Surgery, St. Vincent's Hospital Melbourne and the University of Melbourne, Fitzroy, VIC, 3065, Australia
| | - Anita F Quigley
- Department of Medicine, the University of Melbourne, St Vincent's Hospital Melbourne, Fitzroy, VIC, 3065, Australia.,ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Justin L Bourke
- Department of Medicine, the University of Melbourne, St Vincent's Hospital Melbourne, Fitzroy, VIC, 3065, Australia
| | - Cameron J Nowell
- Walter and Eliza Hall Institute, Parkville, VIC, 3052, Australia
| | - Damian E Myers
- Department of Orthopaedics, St. Vincent's Hospital Melbourne and the University of Melbourne, Fitzroy, VIC, 3065, Australia.,Department of Surgery, St. Vincent's Hospital Melbourne and the University of Melbourne, Fitzroy, VIC, 3065, Australia
| | - Peter F M Choong
- Department of Orthopaedics, St. Vincent's Hospital Melbourne and the University of Melbourne, Fitzroy, VIC, 3065, Australia.,Department of Surgery, St. Vincent's Hospital Melbourne and the University of Melbourne, Fitzroy, VIC, 3065, Australia
| | - Robert M I Kapsa
- ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong, Wollongong, NSW, 2522, Australia
| |
Collapse
|
16
|
Neufeld K, Ezell K, Grow WA. Plastic Additives Decrease Agrin-Induced Acetylcholine Receptor Clusters and Myotube Formation in C2C12 Skeletal Muscle Cell Culture. ACTA ACUST UNITED AC 2015. [DOI: 10.4236/cellbio.2015.41002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
17
|
Basu S, Sladecek S, Pemble H, Wittmann T, Slotman JA, van Cappellen W, Brenner HR, Galjart N. Acetylcholine receptor (AChR) clustering is regulated both by glycogen synthase kinase 3β (GSK3β)-dependent phosphorylation and the level of CLIP-associated protein 2 (CLASP2) mediating the capture of microtubule plus-ends. J Biol Chem 2014; 289:30857-30867. [PMID: 25231989 DOI: 10.1074/jbc.m114.589457] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The postsynaptic apparatus of the neuromuscular junction (NMJ) traps and anchors acetylcholine receptors (AChRs) at high density at the synapse. We have previously shown that microtubule (MT) capture by CLASP2, a MT plus-end-tracking protein (+TIP), increases the size and receptor density of AChR clusters at the NMJ through the delivery of AChRs and that this is regulated by a pathway involving neuronal agrin and several postsynaptic kinases, including GSK3. Phosphorylation by GSK3 has been shown to cause CLASP2 dissociation from MT ends, and nine potential phosphorylation sites for GSK3 have been mapped on CLASP2. How CLASP2 phosphorylation regulates MT capture at the NMJ and how this controls the size of AChR clusters are not yet understood. To examine this, we used myotubes cultured on agrin patches that induce AChR clustering in a two-dimensional manner. We show that expression of a CLASP2 mutant, in which the nine GSK3 target serines are mutated to alanine (CLASP2-9XS/9XA) and are resistant to GSK3β-dependent phosphorylation, promotes MT capture at clusters and increases AChR cluster size, compared with myotubes that express similar levels of wild type CLASP2 or that are noninfected. Conversely, myotubes expressing a phosphomimetic form of CLASP2 (CLASP2-8XS/D) show enrichment of immobile mutant CLASP2 in clusters, but MT capture and AChR cluster size are reduced. Taken together, our data suggest that both GSK3β-dependent phosphorylation and the level of CLASP2 play a role in the maintenance of AChR cluster size through the regulated capture and release of MT plus-ends.
Collapse
Affiliation(s)
- Sreya Basu
- Institute of Physiology, Department of Biomedicine, University of Basel, CH-4056 Basel, Switzerland,; Department of Cell Biology, Erasmus Medical Center, 3015 GE, Rotterdam, Netherlands
| | - Stefan Sladecek
- Institute of Physiology, Department of Biomedicine, University of Basel, CH-4056 Basel, Switzerland
| | - Hayley Pemble
- Department of Cell and Tissue Biology, University of California at San Francisco, San Francisco, California 94143, and
| | - Torsten Wittmann
- Department of Cell and Tissue Biology, University of California at San Francisco, San Francisco, California 94143, and
| | - Johan A Slotman
- Optical Imaging Center, Erasmus Medical Center, 3015 GE Rotterdam, Netherlands
| | | | - Hans-Rudolf Brenner
- Institute of Physiology, Department of Biomedicine, University of Basel, CH-4056 Basel, Switzerland,.
| | - Niels Galjart
- Department of Cell Biology, Erasmus Medical Center, 3015 GE, Rotterdam, Netherlands,.
| |
Collapse
|
18
|
Talaga ML, Fan N, Fueri AL, Brown RK, Chabre YM, Bandyopadhyay P, Roy R, Dam TK. Significant Other Half of a Glycoconjugate: Contributions of Scaffolds to Lectin–Glycoconjugate Interactions. Biochemistry 2014; 53:4445-54. [DOI: 10.1021/bi5001307] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
| | | | | | | | - Yoann M. Chabre
- Department
of Chemistry, Université du Québec à Montréal, Montréal, QC, Canada H3C 3P8
| | | | - René Roy
- Department
of Chemistry, Université du Québec à Montréal, Montréal, QC, Canada H3C 3P8
| | | |
Collapse
|
19
|
Ghazanfari N, Morsch M, Reddel SW, Liang SX, Phillips WD. Muscle-specific kinase (MuSK) autoantibodies suppress the MuSK pathway and ACh receptor retention at the mouse neuromuscular junction. J Physiol 2014; 592:2881-97. [PMID: 24860174 DOI: 10.1113/jphysiol.2013.270207] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Muscle-specific kinase (MuSK) autoantibodies from myasthenia gravis patients can block the activation of MuSK in vitro and/or reduce the postsynaptic localization of MuSK. Here we use a mouse model to examine the effects of MuSK autoantibodies upon some key components of the postsynaptic MuSK pathway and upon the regulation of junctional ACh receptor (AChR) numbers. Mice became weak after 14 daily injections of anti-MuSK-positive patient IgG. The intensity and area of AChR staining at the motor endplate was markedly reduced. Pulse-labelling of AChRs revealed an accelerated loss of pre-existing AChRs from postsynaptic AChR clusters without a compensatory increase in incorporation of (newly synthesized) replacement AChRs. Large, postsynaptic AChR clusters were replaced by a constellation of tiny AChR microaggregates. Puncta of AChR staining also appeared in the cytoplasm beneath the endplate. Endplate staining for MuSK, activated Src, rapsyn and AChR were all reduced in intensity. In the tibialis anterior muscle there was also evidence that phosphorylation of the AChR β-subunit-Y390 was reduced at endplates. In contrast, endplate staining for β-dystroglycan (through which rapsyn couples AChR to the synaptic basement membrane) remained intense. The results suggest that anti-MuSK IgG suppresses the endplate density of MuSK, thereby down-regulating MuSK signalling activity and the retention of junctional AChRs locally within the postsynaptic membrane scaffold.
Collapse
Affiliation(s)
- Nazanin Ghazanfari
- Physiology and Bosch Institute, University of Sydney, Sydney, New South Wales, 2006, Australia
| | - Marco Morsch
- Physiology and Bosch Institute, University of Sydney, Sydney, New South Wales, 2006, Australia
| | - Stephen W Reddel
- Department of Molecular Medicine, Concord Hospital, Concord, New South Wales, 2139, Australia
| | - Simon X Liang
- Department of Biochemistry and Molecular Biology, College of Basic Medical Sciences, Liaoning Medical University, China
| | - William D Phillips
- Physiology and Bosch Institute, University of Sydney, Sydney, New South Wales, 2006, Australia
| |
Collapse
|
20
|
Abstract
The function of muscle is to contract, which means to exert force on a substrate. The adaptations required for skeletal muscle differentiation, from a prototypic cell, involve specialization of housekeeping cytoskeletal contracting and supporting systems into crystalline arrays of proteins. Here I discuss the changes that all three cytoskeletal systems (microfilaments, intermediate filaments, and microtubules) undergo through myogenesis. I also discuss their interaction, through the membrane, to extracellular matrix and to other cells, where force will be exerted during contraction. The three cytoskeletal systems are necessary for the muscle cell and must exert complementary roles in the cell. Muscle is a responsive system, where structure and function are integrated: the structural adaptations it undergoes depend on force production. In this way, the muscle cytoskeleton is a portrait of its physiology. I review the cytoskeletal proteins and structures involved in muscle function and focus particularly on their role in myogenesis, the process by which this incredible muscle machine is made. Although the focus is on skeletal muscle, some of the discussion is applicable to cardiac and smooth muscle.
Collapse
|
21
|
K. Ball M, H. Campbell D, Ezell K, B. Henley J, R. Standley P, A. Grow W. Antibody to MyoD or Myogenin Decreases Acetylcholine Receptor Clustering in C2C12 Myotube Culture. Cell 2013. [DOI: 10.4236/cellbio.2013.23016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
22
|
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: 2.2] [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.
Collapse
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
Collapse
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
| |
Collapse
|
23
|
Owen DB, Chamberlain KT, Shishido S, Grow WA. Ethanol decreases agrin-induced acetylcholine receptor clustering in C2C12 myotube culture. Toxicol In Vitro 2009; 24:645-51. [PMID: 19800963 DOI: 10.1016/j.tiv.2009.09.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2009] [Revised: 09/11/2009] [Accepted: 09/26/2009] [Indexed: 11/16/2022]
Abstract
We investigated the effect of ethanol on skeletal muscle development using C2C12 cell culture. The ethanol concentrations of 10mM, 25mM, and 100mM, were tested because plasma samples of alcohol-dependent individuals fall within this range. We assessed two specific events in skeletal muscle development, the fusion of myoblasts to form myotubes and the acetylcholine receptor (AChR) clustering associated with neuromuscular synapse formation. We report that ethanol does not effect myotube formation or the viability of myoblasts or myotubes in C2C12 cell culture. However, ethanol does effect AChR clustering on C2C12 myotubes. As motor neurons approach skeletal muscle during development, agrin is released by motor neurons and induces AChR clustering on muscle fibers. In our experiments, agrin was applied to cell cultures during the period when myoblasts fuse to form myotubes. In cell cultures exposed to ethanol during myotube formation, agrin-induced AChR clustering was decreased compared to untreated cultures. In cell cultures exposed to ethanol during myoblast proliferation, with ethanol removed during myotube formation, agrin-induced AChR clustering was unaffected. We conclude that exposure to a physiologically relevant concentration of ethanol during the specific period of myotube formation decreases agrin-induced AChR clustering.
Collapse
Affiliation(s)
- David B Owen
- Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ, United States
| | | | | | | |
Collapse
|
24
|
Herbst R, Iskratsch T, Unger E, Bittner RE. Aberrant development of neuromuscular junctions in glycosylation-defective Large(myd) mice. Neuromuscul Disord 2009; 19:366-78. [PMID: 19346129 DOI: 10.1016/j.nmd.2009.02.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2007] [Revised: 02/17/2009] [Accepted: 02/27/2009] [Indexed: 01/13/2023]
Abstract
Mice deficient in the glycosyltransferase Large are characterized by severe muscle and central nervous system abnormalities. In this study, we show that the formation and maintenance of neuromuscular junctions in Large(myd) mice are greatly compromised. Neuromuscular junctions are not confined to the muscle endplate zone but are widely spread and are frequently accompanied by exuberant nerve sprouting. Nerve terminals are highly fragmented and binding of alpha-bungarotoxin to postsynaptic acetylcholine receptors (AChRs) is greatly reduced. In vitro, Large(myd) myotubes are responsive to agrin but produce aberrant AChR clusters, which are larger in area and less densely packed with AChRs. In addition, AChR expression on the cell surface is diminished suggesting that AChR assembly or transport is defective. These results together with the finding that O-linked glycosylation at neuromuscular junctions of Large(myd) mice is compromised indicate that the action of Large is necessary for proper neuromuscular junction development.
Collapse
Affiliation(s)
- Ruth Herbst
- Center for Brain Research, Medical University of Vienna, Vienna, Austria.
| | | | | | | |
Collapse
|
25
|
Linnoila J, Wang Y, Yao Y, Wang ZZ. A mammalian homolog of Drosophila tumorous imaginal discs, Tid1, mediates agrin signaling at the neuromuscular junction. Neuron 2009; 60:625-41. [PMID: 19038220 DOI: 10.1016/j.neuron.2008.09.025] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2007] [Revised: 05/14/2008] [Accepted: 09/12/2008] [Indexed: 11/29/2022]
Abstract
Motoneuron-derived agrin clusters nicotinic acetylcholine receptors (AChRs) in mammalian muscle cells. We used two-hybrid screens to identify a protein, tumorous imaginal discs (Tid1), that binds to the cytoplasmic domain of muscle-specific kinase (MuSK), a major component of the agrin receptor. Like MuSK, Tid1 colocalizes with AChRs at developing, adult, and denervated motor endplates. Knockdown of Tid1 by short hairpin RNA (shRNA) in skeletal muscle fibers dispersed synaptic AChR clusters and impaired neuromuscular transmission. In cultured myotubes, Tid1 knockdown inhibited AChR clustering, as well as agrin-induced activation of the Rac and Rho small GTPases and tyrosine phosphorylation of the AChR, without affecting MuSK activation. Tid1 knockdown also decreased Dok-7-induced clustering of AChRs. Overexpression of the N-terminal half of Tid1 induced agrin- and MuSK-independent phosphorylation and clustering of AChRs. These results demonstrate that Tid1 is an essential component of the agrin signaling pathway, crucial for synaptic development.
Collapse
Affiliation(s)
- Jenny Linnoila
- Molecular Pharmacology Graduate Training Program, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
| | | | | | | |
Collapse
|
26
|
Nishimune H, Valdez G, Jarad G, Moulson CL, Müller U, Miner JH, Sanes JR. Laminins promote postsynaptic maturation by an autocrine mechanism at the neuromuscular junction. ACTA ACUST UNITED AC 2008; 182:1201-15. [PMID: 18794334 PMCID: PMC2542479 DOI: 10.1083/jcb.200805095] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
A prominent feature of synaptic maturation at the neuromuscular junction (NMJ) is the topological transformation of the acetylcholine receptor (AChR)-rich postsynaptic membrane from an ovoid plaque into a complex array of branches. We show here that laminins play an autocrine role in promoting this transformation. Laminins containing the alpha4, alpha5, and beta2 subunits are synthesized by muscle fibers and concentrated in the small portion of the basal lamina that passes through the synaptic cleft at the NMJ. Topological maturation of AChR clusters was delayed in targeted mutant mice lacking laminin alpha5 and arrested in mutants lacking both alpha4 and alpha5. Analysis of chimeric laminins in vivo and of mutant myotubes cultured aneurally demonstrated that the laminins act directly on muscle cells to promote postsynaptic maturation. Immunohistochemical studies in vivo and in vitro along with analysis of targeted mutants provide evidence that laminin-dependent aggregation of dystroglycan in the postsynaptic membrane is a key step in synaptic maturation. Another synaptically concentrated laminin receptor, Bcam, is dispensable. Together with previous studies implicating laminins as organizers of presynaptic differentiation, these results show that laminins coordinate post- with presynaptic maturation.
Collapse
Affiliation(s)
- Hiroshi Nishimune
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
| | | | | | | | | | | | | |
Collapse
|
27
|
Shigemoto K, Kubo S, Jie C, Hato N, Abe Y, Ueda N, Kobayashi N, Kameda K, Mominoki K, Miyazawa A, Ishigami A, Matsuda S, Maruyama N. Myasthenia Gravis Experimentally Induced with Muscle-specific Kinase. Ann N Y Acad Sci 2008; 1132:93-8. [DOI: 10.1196/annals.1405.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
|
28
|
Teressa G, Prives J. Cell culture-based analysis of postsynaptic membrane assembly in muscle cells. Biol Proced Online 2008; 10:58-65. [PMID: 19461953 PMCID: PMC2683546 DOI: 10.1251/bpo143] [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: 12/19/2007] [Revised: 03/28/2008] [Accepted: 04/01/2008] [Indexed: 11/25/2022] Open
Abstract
We report a method for studying postsynaptic membrane assembly utilizing the replating of aneural cultures of
differentiated skeletal muscle cells onto laminin-coated surfaces. A significant limitation to the current cell culturebased
approaches has been their inability to recapitulate the multistage surface acetylcholine receptor (AChR)
redistribution events that produce complex AChR clusters found at the intact neuromuscular junction (NMJ). By taking
advantage of the ability of substrate laminin to induce advanced maturation of AChR aggregates on the surface of
myotubes, we have developed a secondary-plating method that allows more precise analysis of the signaling events
connecting substrate laminin stimulation to complex AChR cluster formation. We validate the utility of this method for
biochemical and microscopy studies by demonstrating the roles of RhoGTPases in substrate laminin-induced complex
cluster assembly.
Collapse
Affiliation(s)
- Getu Teressa
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794, USA
| | | |
Collapse
|
29
|
Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
| |
Collapse
|
30
|
Weston CA, Teressa G, Weeks BS, Prives J. Agrin and laminin induce acetylcholine receptor clustering by convergent, Rho GTPase-dependent signaling pathways. J Cell Sci 2007; 120:868-75. [PMID: 17298982 DOI: 10.1242/jcs.03367] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
During neuromuscular junction formation, extracellular matrix-mediated signals cause muscle surface acetylcholine receptors (AChRs) to aggregate at synaptic sites. Two extracellular matrix proteins, agrin and laminin, have each been shown to initiate signaling pathways that culminate in AChR clustering in cultured muscle cells. Here we present evidence that laminin-induced AChR clustering is mediated by the activation of the Rho GTPases Cdc42, Rac and Rho. Clustering in response to laminin is blocked by the dominant negative mutants Cdc42N17, RacN17 and RhoN19, as well as by the Rho inhibitor C3 transferase. Moreover, laminin-induced AChR clustering is impaired by the Rho kinase inhibitor Y-27632. Agrin-induced AChR clustering has previously been shown to require activation of Cdc42, Rac and Rho. Therefore, although agrin and laminin use distinct transmembrane receptors to initiate AChR clustering, their signaling pathways converge at the level of Rho GTPase activation.
Collapse
Affiliation(s)
- Christi A Weston
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794, USA
| | | | | | | |
Collapse
|
31
|
Saito F, Masaki T, Saito Y, Nakamura A, Takeda S, Shimizu T, Toda T, Matsumura K. Defective peripheral nerve myelination and neuromuscular junction formation in fukutin-deficient chimeric mice. J Neurochem 2007; 101:1712-22. [PMID: 17326765 DOI: 10.1111/j.1471-4159.2007.04462.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Dystroglycan is a central component of the dystrophin-glycoprotein complex that links the extracellular matrix with cytoskeleton. Recently, mutations of the genes encoding putative glycosyltransferases were identified in several forms of congenital muscular dystrophies accompanied by brain anomalies and eye abnormalities, and aberrant glycosylation of alpha-dystroglycan has been implicated in their pathogeneses. These diseases are now collectively called alpha-dystroglycanopathy. In this study, we demonstrate that peripheral nerve myelination is defective in the fukutin-deficient chimeric mice, a mouse model of Fukuyama-type congenital muscular dystrophy, which is the most common alpha-dystroglycanopathy in Japan. In the peripheral nerve of these mice, the density of myelinated nerve fibers was significantly decreased and clusters of abnormally large non-myelinated axons were ensheathed by a single Schwann cell, indicating a defect of the radial sorting mechanism. The sugar chain moiety and laminin-binding activity of alpha-dystroglycan were severely reduced, while the expression of beta1-integrin was not altered in the peripheral nerve of the chimeric mice. We also show that the clustering of acetylcholine receptor is defective and neuromuscular junctions are fragmented in appearance in these mice. Expression of agrin and laminin as well as the binding activity of alpha-dystroglycan to these ligands was severely reduced at the neuromuscular junction. These results demonstrate that fukutin plays crucial roles in the myelination of peripheral nerve and formation of neuromuscular junction. They also suggest that defective glycosylation of alpha-dystroglycan may play a role in the impairment of these processes in the deficiency of fukutin.
Collapse
Affiliation(s)
- Fumiaki Saito
- Department of Neurology and Neuroscience, Teikyo University, Tokyo, Japan
| | | | | | | | | | | | | | | |
Collapse
|
32
|
Wang Q, Zhang B, Xiong WC, Mei L. MuSK signaling at the neuromuscular junction. J Mol Neurosci 2007; 30:223-6. [PMID: 17192681 DOI: 10.1385/jmn:30:1:223] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 11/11/2022]
Abstract
The neuromuscular junction (NMJ) is a peripheral cholinergic synapse that conveys signals from motor neurons to muscle cells (Sanes and Lichtman, 1999; Sanes and Lichtman, 2001). The formation of the NMJ requires communication between motoneurons and muscle fibers. Three molecules are essential for NMJ formation: agrin, MuSK, and rapsyn. MuSK appears to be involved in every aspect of NMJ development and maintenance. The paper reviews agrin-MuSK cascades and its potential cross talk with Wnt signaling pathways.
Collapse
Affiliation(s)
- Qiang Wang
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Department of Neurology, Medical College of Georgia, Augusta, GA, USA
| | | | | | | |
Collapse
|
33
|
Milholland RBR, Dulla C, Gordon H. L-type calcium channels mediate acetylcholine receptor aggregation on cultured muscle. Dev Neurobiol 2007; 67:987-98. [PMID: 17565707 DOI: 10.1002/dneu.20397] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Agrin activation of muscle specific kinase (MuSK) initiates postsynaptic development on skeletal muscle that includes the aggregation of acetylcholine receptors (AChRs; Glass et al. [1996]: Cell 85: 513-523; Gautam et al. [1996]: Cell 85: 525-535). Although the agrin/MuSK signaling pathway remains largely unknown, changes in intracellular calcium levels are required for agrin-induced AChR aggregation (Megeath and Fallon [1998]: J Neurosci 18: 672-678). Here, we show that L-type calcium channels (L-CaChs) are required for full agrin-induced aggregation of AChRs and sufficient to induce agrin-independent AChR aggregation. Blockade of L-CaChs in muscle cultures inhibited agrin-induced AChR aggregation but not tyrosine phosphorylation of MuSK or AChR beta subunits. Activation of L-CaChs in the absence of agrin induced AChR aggregation but not tyrosine phosphorylation of MuSK or AChR beta subunits. Agrin responsiveness was significantly reduced in primary muscle cultures from the muscular dysgenesis mouse, a natural mutant, which does not express the L-CaCh. Our results establish a novel role for L-CaChs as important sources of the intracellular calcium necessary for the aggregation of AChRs.
Collapse
Affiliation(s)
- Rebecca B R Milholland
- Department of Cell Biology and Anatomy, University of Arizona Health Sciences Center, Tucson, Arizona 85724-5044, USA
| | | | | |
Collapse
|
34
|
Okada K, Inoue A, Okada M, Murata Y, Kakuta S, Jigami T, Kubo S, Shiraishi H, Eguchi K, Motomura M, Akiyama T, Iwakura Y, Higuchi O, Yamanashi Y. The muscle protein Dok-7 is essential for neuromuscular synaptogenesis. Science 2006; 312:1802-5. [PMID: 16794080 DOI: 10.1126/science.1127142] [Citation(s) in RCA: 309] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The formation of the neuromuscular synapse requires muscle-specific receptor kinase (MuSK) to orchestrate postsynaptic differentiation, including the clustering of receptors for the neurotransmitter acetylcholine. Upon innervation, neural agrin activates MuSK to establish the postsynaptic apparatus, although agrin-independent formation of neuromuscular synapses can also occur experimentally in the absence of neurotransmission. Dok-7, a MuSK-interacting cytoplasmic protein, is essential for MuSK activation in cultured myotubes; in particular, the Dok-7 phosphotyrosine-binding domain and its target in MuSK are indispensable. Mice lacking Dok-7 formed neither acetylcholine receptor clusters nor neuromuscular synapses. Thus, Dok-7 is essential for neuromuscular synaptogenesis through its interaction with MuSK.
Collapse
Affiliation(s)
- Kumiko Okada
- Department of Cell Regulation, Medical Research Institute, Tokyo Medical and Dental University, Tokyo 113-8510, Japan
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Tremblay MR, Carbonetto S. An Extracellular Pathway for Dystroglycan Function in Acetylcholine Receptor Aggregation and Laminin Deposition in Skeletal Myotubes. J Biol Chem 2006; 281:13365-13373. [PMID: 16531403 DOI: 10.1074/jbc.m600912200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The dystroglycan (DG) complex is involved in agrin-induced acetylcholine receptor clustering downstream of muscle-specific kinase where it regulates the stability of acetylcholine receptor aggregates as well as assembly of the synaptic basement membrane. We have previously proposed that this entails coordinate extracellular and intracellular interactions of its two subunits, alpha- and beta-DG. To assess the contribution of the extracellular and intracellular portions of DG, we have used adenoviruses to express full-length and deletion mutants of beta-DG in myotubes derived from wild-type embryonic stem cells or from cells null for DG. We show that alpha-DG is properly glycosylated and targeted to the myotube surface in the absence of beta-DG. Extracellular interactions of DG modulate the size and the microcluster density of agrin-induced acetylcholine receptor aggregates and are responsible for targeting laminin to these clusters. Thus, the association of alpha- and beta-DG in skeletal muscle may coordinate independent roles in signaling. We discuss how DG may regulate synapses through extracellular signaling functions of its alpha subunit.
Collapse
Affiliation(s)
- Mathieu R Tremblay
- Department of Biology, McGill University, Montréal General Hospital Research Institute, Montréal, Québec H3G 1A4, Canada
| | - Salvatore Carbonetto
- Department of Biology, McGill University, Montréal General Hospital Research Institute, Montréal, Québec H3G 1A4, Canada; Center for Research in Neuroscience, McGill University, Montréal General Hospital Research Institute, Montréal, Québec H3G 1A4, Canada.
| |
Collapse
|
36
|
Kumar P, Ferns MJ, Meizel S. Identification of agrinSN isoform and muscle-specific receptor tyrosine kinase in sperm. Biochem Biophys Res Commun 2006; 342:522-8. [PMID: 16487930 DOI: 10.1016/j.bbrc.2006.01.161] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2006] [Accepted: 01/28/2006] [Indexed: 10/25/2022]
Abstract
We previously demonstrated several nicotinic acetylcholine receptor (nAChR) subunits and associated proteins in human sperm. Here, we identified in sperm for the first time two additional nAChR-associated molecules: (1) agrin(SN)Z(+) in human sperm localized in the posterior post-acrosomal, neck, and flagellar mid-piece regions; (2) a low-molecular weight isoform of muscle-specific receptor tyrosine kinase in human and mouse sperm localized in the flagellar mid-piece of human sperm.
Collapse
Affiliation(s)
- Priyadarsini Kumar
- Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, CA 95616, USA.
| | | | | |
Collapse
|
37
|
Shigemoto K, Kubo S, Maruyama N, Hato N, Yamada H, Jie C, Kobayashi N, Mominoki K, Abe Y, Ueda N, Matsuda S. Induction of myasthenia by immunization against muscle-specific kinase. J Clin Invest 2006; 116:1016-24. [PMID: 16557298 PMCID: PMC1409737 DOI: 10.1172/jci21545] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Accepted: 02/07/2006] [Indexed: 11/17/2022] Open
Abstract
Muscle-specific kinase (MuSK) is critical for the synaptic clustering of nicotinic acetylcholine receptors (AChRs) and plays multiple roles in the organization and maintenance of neuromuscular junctions (NMJs). MuSK is activated by agrin, which is released from motoneurons, and induces AChR clustering at the postsynaptic membrane. Although autoantibodies against the ectodomain of MuSK have been found in a proportion of patients with generalized myasthenia gravis (MG), it is unclear whether MuSK autoantibodies are the causative agent of generalized MG. In the present study, rabbits immunized with MuSK ectodomain protein manifested MG-like muscle weakness with a reduction of AChR clustering at the NMJs. The autoantibodies activated MuSK and blocked AChR clustering induced by agrin or by mediators that do not activate MuSK. Thus MuSK autoantibodies rigorously inhibit AChR clustering mediated by multiple pathways, an outcome that broadens our general comprehension of the pathogenesis of MG.
Collapse
Affiliation(s)
- Kazuhiro Shigemoto
- Department of Preventive Medicine, Ehime University School of Medicine, Ehime, Japan.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
38
|
Abstract
The neuromuscular junction (NMJ) is a complex structure that serves to efficiently communicate the electrical impulse from the motor neuron to the skeletal muscle to signal contraction. Over the last 200 years, technological advances in microscopy allowed visualization of the existence of a gap between the motor neuron and skeletal muscle that necessitated the existence of a messenger, which proved to be acetylcholine. Ultrastructural analysis identified vesicles in the presynaptic nerve terminal, which provided a beautiful structural correlate for the quantal nature of neuromuscular transmission, and the imaging of synaptic folds on the muscle surface demonstrated that specializations of the underlying protein scaffold were required. Molecular analysis in the last 20 years has confirmed the preferential expression of synaptic proteins, which is guided by a precise developmental program and maintained by signals from nerve. Although often overlooked, the Schwann cell that caps the NMJ and the basal lamina is proving to be critical in maintenance of the junction. Genetic and autoimmune disorders are known that compromise neuromuscular transmission and provide further insights into the complexities of NMJ function as well as the subtle differences that exist among NMJ that may underlie the differential susceptibility of muscle groups to neuromuscular transmission diseases. In this review we summarize the synaptic physiology, architecture, and variations in synaptic structure among muscle types. The important roles of specific signaling pathways involved in NMJ development and acetylcholine receptor (AChR) clustering are reviewed. Finally, genetic and autoimmune disorders and their effects on NMJ architecture and neuromuscular transmission are examined.
Collapse
Affiliation(s)
- Benjamin W Hughes
- Department of Neurology, Case Western University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | | | | |
Collapse
|
39
|
Smirnov SP, Barzaghi P, McKee KK, Ruegg MA, Yurchenco PD. Conjugation of LG Domains of Agrins and Perlecan to Polymerizing Laminin-2 Promotes Acetylcholine Receptor Clustering. J Biol Chem 2005; 280:41449-57. [PMID: 16219760 DOI: 10.1074/jbc.m508939200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Neuromuscular junction (NMJ) assembly is characterized by the clustering and neuronal alignment of acetylcholine receptors (AChRs). In this study we have addressed post-synaptic contributions to assembly that may arise from the NMJ basement membrane with cultured myotubes. We show that the cell surface-binding LG domains of non-neural (muscle) agrin and perlecan promote AChR clustering in the presence of laminin-2. This type of AChR clustering occurs with a several hour lag, requires muscle-specific kinase (MuSK), and is accompanied by tyrosine phosphorylation of MuSK and betaAChR. It also requires conjugation of the agrin or perlecan to laminin together with laminin polymerization. Furthermore, AChR clustering can be mimicked with antibody binding to non-neural agrin, supporting a mechanism of ligand aggregation. Neural agrin, in addition to its unique ability to cluster AChRs through its B/z sequence insert, also exhibits laminin-dependent AChR clustering, the latter enhancing and stabilizing its activity. Finally, we show that type IV collagen, which lacks clustering activity on its own, stabilizes laminin-dependent AChR clusters. These findings provide evidence for cooperative and partially redundant MuSK-dependent functions of basement membrane in AChR assembly that can enhance neural agrin activity yet operate in its absence. Such interactions may contribute to the assembly of aneural AChR clusters that precede neural agrin release as well as affect later NMJ development.
Collapse
Affiliation(s)
- Sergei P Smirnov
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
| | | | | | | | | |
Collapse
|
40
|
Bruneau EG, Macpherson PC, Goldman D, Hume RI, Akaaboune M. The effect of agrin and laminin on acetylcholine receptor dynamics in vitro. Dev Biol 2005; 288:248-58. [PMID: 16256100 DOI: 10.1016/j.ydbio.2005.09.041] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2005] [Revised: 08/11/2005] [Accepted: 09/27/2005] [Indexed: 10/25/2022]
Abstract
Using optical imaging assays, we investigated the dynamics of acetylcholine receptors (AChRs) at laminin-associated clusters on cultured myotubes in the absence or presence of the nerve-derived clustering factor, agrin. Using fluorescence recovery after photobleaching (FRAP) on fluorescent bungarotoxin-labeled receptors, we found that approximately 9% of original fluorescence was recovered after 8 h as surface AChRs were recruited into clusters. By quantifying the loss of labeled receptors and the recovery of fluorescence after photobleaching, we estimated that the half-life of clustered receptors was approximately 4.5 h. Despite the rapid removal of receptors, the accumulation of new receptors at clusters was robust enough to maintain receptor density over time. We also found that the AChR half-life was not affected by agrin despite its role in inducing the aggregation of AChRs. Interestingly, when agrin was added to myotubes grown on laminin-coated substrates, most new receptors were not directed into preexisting laminin-induced clusters but instead formed numerous small aggregates on the entire muscle surface. Time-lapse imaging revealed that the agrin-induced clusters could be seen as early as 1 h, and agrin treatment resulted in the complete dissipation of laminin-associated clusters by 24 h. These results reveal that while laminin and agrin are involved in the clustering of receptors they are not critical to the regulation of receptor metabolic stability at these clusters, and further argue that agrin is able to rapidly and fully negate the laminin substrate clustering effect while inducing the rapid formation of new clusters.
Collapse
Affiliation(s)
- Emile G Bruneau
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, 830 N. University Ave., Ann Arbor, MI 48109, USA.
| | | | | | | | | |
Collapse
|
41
|
Gong Y, Zhang Z. Alternative signaling pathways: when, where and why? FEBS Lett 2005; 579:5265-74. [PMID: 16194539 DOI: 10.1016/j.febslet.2005.08.062] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Revised: 08/29/2005] [Accepted: 08/30/2005] [Indexed: 11/24/2022]
Abstract
Alternative cell signal transduction pathways have been demonstrated in some experimental systems. The importance of their existence has not been completely appreciated. In this review we present the cases of alternative pathways resulted from a survey of the available experimental data. The alternative pathways could show different relationships, i.e., synergistic, redundant, additive, opposite and competitive effects. They could have distinct time courses and cell, organ, sex or species specification. Further, they could happen during physiological or pathological situations, and display differentiated sensitivity. These case studies together imply that alternative signal pathways could be involved in the regulation of cell functions at the pathway level. In-depth understanding of the importance of the alternative pathways will rely on building and exploration of mathematical models.
Collapse
Affiliation(s)
- Yunchen Gong
- Banting and Best Department of Medical Research, University of Toronto 112 College, Canada.
| | | |
Collapse
|
42
|
Madhavan R, Peng HB. Molecular regulation of postsynaptic differentiation at the neuromuscular junction. IUBMB Life 2005; 57:719-30. [PMID: 16511964 DOI: 10.1080/15216540500338739] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The neuromuscular junction (NMJ) is a synapse that develops between a motor neuron and a muscle fiber. A defining feature of NMJ development in vertebrates is the re-distribution of muscle acetylcholine (ACh) receptors (AChRs) following innervation, which generates high-density AChR clusters at the postsynaptic membrane and disperses aneural AChR clusters formed in muscle before innervation. This process in vivo requires MuSK, a muscle-specific receptor tyrosine kinase that triggers AChR re-distribution when activated; rapsyn, a muscle protein that binds and clusters AChRs; agrin, a nerve-secreted heparan-sulfate proteoglycan that activates MuSK; and ACh, a neurotransmitter that stimulates muscle and also disperses aneural AChR clusters. Moreover, in cultured muscle cells, several additional muscle- and nerve-derived molecules induce, mediate or participate in AChR clustering and dispersal. In this review we discuss how regulation of AChR re-distribution by multiple factors ensures aggregation of AChRs exclusively at NMJs.
Collapse
Affiliation(s)
- Raghavan Madhavan
- Department of Biology, Hong Kong University of Science and Technology, Kowloon, Hong Kong, China
| | | |
Collapse
|
43
|
Sugie K, Noguchi S, Kozuka Y, Arikawa-Hirasawa E, Tanaka M, Yan C, Saftig P, von Figura K, Hirano M, Ueno S, Nonaka I, Nishino I. Autophagic vacuoles with sarcolemmal features delineate Danon disease and related myopathies. J Neuropathol Exp Neurol 2005; 64:513-22. [PMID: 15977643 DOI: 10.1093/jnen/64.6.513] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Among the autophagic vacuolar myopathies (AVMs), a subgroup is characterized pathologically by unusual autophagic vacuoles with sarcolemmal features (AVSF) and includes Danon disease and X-linked myopathy with excessive autophagy. The diagnostic importance and detailed morphologic features of AVSF in different AVMs have not been well established, and the mechanism of AVSF formation is not known. To address these issues, we have performed detailed histologic studies of myopathies with AVSF and other AVMs. In Danon disease and related AVMs, at the light microscopic level, autophagic vacuoles appeared to be accumulations of lysosomes, which, by electron microscopy consisted of clusters of autophagic vacuoles, indicative of autolysosomes. Some autolysosomes were surrounded by membranes with sarcolemmal proteins, acetylcholinesterase activity, and basal lamina. In Danon disease, the number of fibers with AVSF increased linearly with age while the number with autolysosomal accumulations decreased slightly, suggesting that AVSF are produced secondarily in response to autolysosomes. Most of the AVSF form enclosed spaces, indicating that the vacuolar membranes may be formed in situ rather than through sarcolemmal indentation. This unique intracytoplasmic membrane structure was not found in other AVMs. In conclusion, AVSF with acetylcholinesterase activity are autolysosomes surrounded by secondarily generated intracytoplasmic sarcolemma-like structure and delineates a subgroup of AVMs.
Collapse
Affiliation(s)
- Kazuma Sugie
- Department of Neuromuscular Research, National Institute of Neuroscience, National Hospital for Mental Nervous and Muscular Disorders, National Center of Neurology and Psychiatry, Kodaira, Tokyo, Japan
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
44
|
Schwander M, Shirasaki R, Pfaff SL, Müller U. Beta1 integrins in muscle, but not in motor neurons, are required for skeletal muscle innervation. J Neurosci 2005; 24:8181-91. [PMID: 15371519 PMCID: PMC6729792 DOI: 10.1523/jneurosci.1345-04.2004] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
In vitro studies have provided evidence that beta1 integrins in motor neurons promote neurite outgrowth, whereas beta1 integrins in myotubes regulate acetylcholine receptor (AChR) clustering. Surprisingly, using genetic studies in mice, we show here that motor axon outgrowth and neuromuscular junction (NMJ) formation in large part are unaffected when the integrin beta1 gene (Itgb1) is inactivated in motor neurons. In the absence of Itgb1 expression in skeletal muscle, interactions between motor neurons and muscle are defective, preventing normal presynaptic differentiation. Motor neurons fail to terminate their growth at the muscle midline, branch excessively, and develop abnormal nerve terminals. These defects resemble the phenotype of agrin-null mice, suggesting that signaling molecules such as agrin, which coordinate presynaptic and postsynaptic differentiation, are not presented properly to nerve terminals. We conclude that Itgb1 expression in muscle, but not in motor neurons, is critical for NMJ development.
Collapse
Affiliation(s)
- Martin Schwander
- Department of Cell Biology and Institute for Childhood and Neglected Disease, The Scripps Research Institute, La Jolla, California 92037, USA
| | | | | | | |
Collapse
|
45
|
McDonnell KMW, Grow WA. Reduced Glycosaminoglycan Sulfation Diminishes the Agrin Signal Transduction Pathway. Dev Neurosci 2004; 26:1-10. [PMID: 15509893 DOI: 10.1159/000080706] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2003] [Accepted: 11/04/2003] [Indexed: 12/13/2022] Open
Abstract
Proteoglycans consist of a protein core complexed to glycosaminoglycan (GAG) side chains, are abundant in skeletal muscle cell membranes and basal lamina, and have important functions in neuromuscular synapse development. Treatment with chlorate results in the undersulfation of heparan sulfate and chondroitin sulfate GAGs in cell culture. In addition, chlorate treatment decreases the frequency of spontaneous acetylcholine receptor (AChR) clustering in skeletal muscle cell culture. AChRs and other molecules cluster to form the postsynaptic component of neuromuscular synapses. Chlorate treatment is shown here to decrease the frequency of agrin-induced AChR clustering and agrin-induced tyrosine phosphorylation of the AChR beta-subunit. These data suggest that reduced GAG chain sulfation decreases the frequency of AChR clustering by diminishing the agrin signal transduction pathway.
Collapse
Affiliation(s)
- Kelly M W McDonnell
- Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, Ariz. 85308, USA
| | | |
Collapse
|
46
|
Almqvist N, Bhatia R, Primbs G, Desai N, Banerjee S, Lal R. Elasticity and adhesion force mapping reveals real-time clustering of growth factor receptors and associated changes in local cellular rheological properties. Biophys J 2004; 86:1753-62. [PMID: 14990502 PMCID: PMC1304010 DOI: 10.1016/s0006-3495(04)74243-5] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Cell surface macromolecules such as receptors and ion channels serve as the interface link between the cytoplasm and the extracellular region. Their density, distribution, and clustering are key spatial features influencing effective and proper physical and biochemical cellular responses to many regulatory signals. In this study, the effect of plasma-membrane receptor clustering on local cell mechanics was obtained from maps of interaction forces between antibody-conjugated atomic force microscope tips and a specific receptor, a vascular endothelial growth factor (VEGF) receptor. The technique allows simultaneous measurement of the real-time motion of specific macromolecules and their effect on local rheological properties like elasticity. The clustering was stimulated by online additions of VEGF, or antibody against VEGF receptors. VEGF receptors are found to concentrate toward the cell boundaries and cluster rapidly after the online additions commence. Elasticity of regions under the clusters is found to change remarkably, with order-of-magnitude stiffness reductions and fluidity increases. The local stiffness reductions are nearly proportional to receptor density and, being concentrated near the cell edges, provide a mechanism for cell growth and angiogenesis.
Collapse
Affiliation(s)
- N Almqvist
- Department of Applied Physics & Mechanical Engineering, Luleå University of Technology, Luleå, Sweden
| | | | | | | | | | | |
Collapse
|
47
|
Ferayorni AJ, Gunville CF, Grow WA. Nicotine decreases agrin signaling and acetylcholine receptor clustering in C2C12 myotube culture. ACTA ACUST UNITED AC 2004; 60:51-60. [PMID: 15188272 DOI: 10.1002/neu.20012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The clustering of acetylcholine receptors (AChRs) in skeletal muscle fibers is a critical event in neuromuscular synaptogenesis. AChRs in concert with other molecules form postsynaptic scaffolds in response to agrin released from motor neurons as motor neurons near skeletal muscle fibers in development. Agrin drives an intracellular signaling pathway that precedes AChR clustering and includes the tyrosine phosphorylation of AChRs. In C2C12 myotube culture, agrin application stimulates the agrin signaling pathway and AChR clustering. Previous studies have determined that the frequency of spontaneous AChR clustering is decreased and AChRs are partially inactivated when bound by the acetylcholine agonist nicotine. We hypothesized that nicotine interferes with AChR clustering and consequent postsynaptic scaffold formation. In the present study, C2C12 myoblasts were cultured with growth medium to stimulate proliferation and then differentiation medium to stimulate fusion into myotubes. They were bathed in a physiologically relevant concentration of nicotine and then subject to agrin treatment after myotube formation. Our results demonstrate that nicotine decreases agrin-induced tyrosine phosphorylation of AChRs and decreases the frequency of spontaneous as well as agrin-induced AChR clustering. We conclude that nicotine interferes with postsynaptic scaffold formation by preventing the tyrosine phosphorylation of AChRs, an agrin signaling event that precedes AChR clustering.
Collapse
Affiliation(s)
- Angelique J Ferayorni
- Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, 85308, USA
| | | | | |
Collapse
|
48
|
Jones MA, Werle MJ. Agrin-induced AChR aggregate formation requires cGMP and aggregate maturation requires activation of cGMP-dependent protein kinase. Mol Cell Neurosci 2004; 25:195-204. [PMID: 15019937 DOI: 10.1016/j.mcn.2003.10.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2002] [Revised: 09/24/2003] [Accepted: 10/21/2003] [Indexed: 10/26/2022] Open
Abstract
Previously, it was demonstrated that agrin acting through the gaseous, signaling molecule, nitric oxide (NO), induces the formation of AChR aggregates on myotubes in culture. Soluble guanylyl cyclase (sGC), which is present at the neuromuscular junction, is a common target of NO. Therefore, we hypothesized that sGC and cGMP are involved in the agrin signaling cascade. Inhibition of sGC hindered AChR aggregation in both agrin- and NO donor-treated cultured myotubes; whereas, a cGMP analogue was able to induce the formation of AChR aggregates on naïve muscle cells. Due to the presence of cyclic GMP-dependent protein kinase (PKG) at the neuromuscular junction, we tested the ability of a PKG inhibitor to alter the agrin signaling cascade. PKG inhibition did not prevent nascent AChR aggregate formation; however, these aggregates were diffuse and composed of numerous microaggregates consistent with incomplete maturation. Thus, we conclude that cGMP is important for the initiation of AChR aggregation, while PKG is involved in the maturation of AChR aggregates.
Collapse
Affiliation(s)
- Melissa A Jones
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | | |
Collapse
|
49
|
Kummer TT, Misgeld T, Lichtman JW, Sanes JR. Nerve-independent formation of a topologically complex postsynaptic apparatus. ACTA ACUST UNITED AC 2004; 164:1077-87. [PMID: 15037598 PMCID: PMC2172060 DOI: 10.1083/jcb.200401115] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
As the mammalian neuromuscular junction matures, its acetylcholine receptor (AChR)–rich postsynaptic apparatus is transformed from an oval plaque into a pretzel-shaped array of branches that precisely mirrors the branching pattern of the motor nerve terminal. Although the nerve has been believed to direct postsynaptic maturation, we report here that myotubes cultured aneurally on matrix-coated substrates form elaborately branched AChR-rich domains remarkably similar to those seen in vivo. These domains share several characteristics with the mature postsynaptic apparatus, including colocalization of multiple postsynaptic markers, clustering of subjacent myonuclei, and dependence on the muscle-specific kinase and rapsyn for their formation. Time-lapse imaging showed that branched structures arise from plaques by formation and fusion of AChR-poor perforations through a series of steps mirroring that seen in vivo. Multiple fluorophore imaging showed that growth occurs by circumferential, asymmetric addition of AChRs. Analysis in vivo revealed similar patterns of AChR addition during normal development. These results reveal the sequence of steps by which a topologically complex domain forms on a cell and suggest an unexpected nerve-independent role for the postsynaptic cell in generating this topological complexity.
Collapse
Affiliation(s)
- Terrance T Kummer
- Dept. of Anatomy and Neurobiology, Washington University School of Medicine, 660 South Euclid Ave., St. Louis, MO 63110, USA
| | | | | | | |
Collapse
|
50
|
Abstract
Integrins are a family of transmembrane receptors that mediate interactions of cells with extracellular matrix (ECM) constituents and cell surface counter receptors. Each integrin mediates interactions with specific sets of ligands and regulates distinct aspects of cellular function including attachment to and organization of ECM assemblies, cell migration, proliferation and survival, and mechanical force transmission. Integrins exert their versatile functions by establishing a transmembrane link between the cell exterior and the cytoskeleton, and by activating intracellular second messenger systems. In addition, cellular signals can modulate integrin activity and ligand interactions, enabling transduction of information from the inside of the cell to the outside. Many of the basic functions of integrins and their ECM ligands have been uncovered by studying them biochemically or with cells in culture. Integrin and ECM functions have also been determined genetically, defining their essential roles in the organism. The ongoing challenge is to integrate cell biological, biochemical, and genetical evidence into a coherent picture. I will discuss here genetic findings, focusing on the murine system, that have shed light on the developmental functions of integrins and their ECM ligands. Where suitable information is available, I will relate the genetical finding to results obtained with cell biological and biochemical approaches.
Collapse
Affiliation(s)
- U Müller
- Department of Cell Biology, Institute for Childhood and Neglected Disease, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA, 92037, USA,
| |
Collapse
|