1
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Wernert F, Moparthi SB, Pelletier F, Lainé J, Simons E, Moulay G, Rueda F, Jullien N, Benkhelifa-Ziyyat S, Papandréou MJ, Leterrier C, Vassilopoulos S. The actin-spectrin submembrane scaffold restricts endocytosis along proximal axons. Science 2024; 385:eado2032. [PMID: 39172837 DOI: 10.1126/science.ado2032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 06/24/2024] [Indexed: 08/24/2024]
Abstract
Clathrin-mediated endocytosis has characteristic features in neuronal dendrites and presynapses, but how membrane proteins are internalized along the axon shaft remains unclear. We focused on clathrin-coated structures and endocytosis along the axon initial segment (AIS) and their relationship to the periodic actin-spectrin scaffold that lines the axonal plasma membrane. A combination of super-resolution microscopy and platinum-replica electron microscopy on cultured neurons revealed that AIS clathrin-coated pits form within "clearings", circular areas devoid of actin-spectrin mesh. Actin-spectrin scaffold disorganization increased clathrin-coated pit formation. Cargo uptake and live-cell imaging showed that AIS clathrin-coated pits are particularly stable. Neuronal plasticity-inducing stimulation triggered internalization of the clathrin-coated pits through polymerization of branched actin around them. Thus, spectrin and actin regulate clathrin-coated pit formation and scission to control endocytosis at the AIS.
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Affiliation(s)
- Florian Wernert
- Aix Marseille Université, CNRS, INP UMR7051, NeuroCyto, 13005 Marseille, France
| | - Satish Babu Moparthi
- Sorbonne Université, INSERM, Institute of Myology, Centre of Research in Myology, UMRS 974, Paris, France
| | - Florence Pelletier
- Aix Marseille Université, CNRS, INP UMR7051, NeuroCyto, 13005 Marseille, France
| | - Jeanne Lainé
- Sorbonne Université, Department of Physiology, Faculty of Medicine Pitié-Salpêtrière, Paris, France
| | - Eline Simons
- Aix Marseille Université, CNRS, INP UMR7051, NeuroCyto, 13005 Marseille, France
| | - Gilles Moulay
- Sorbonne Université, INSERM, Institute of Myology, Centre of Research in Myology, UMRS 974, Paris, France
| | - Fanny Rueda
- Aix Marseille Université, CNRS, INP UMR7051, NeuroCyto, 13005 Marseille, France
| | - Nicolas Jullien
- Aix Marseille Université, CNRS, INP UMR7051, NeuroCyto, 13005 Marseille, France
| | - Sofia Benkhelifa-Ziyyat
- Sorbonne Université, INSERM, Institute of Myology, Centre of Research in Myology, UMRS 974, Paris, France
| | | | | | - Stéphane Vassilopoulos
- Sorbonne Université, INSERM, Institute of Myology, Centre of Research in Myology, UMRS 974, Paris, France
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2
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Hoffmann C, Ruff KM, Edu IA, Shinn MK, Tromm JV, King MR, Pant A, Ausserwöger H, Morgan JR, Knowles TPJ, Pappu RV, Milovanovic D. Driving forces for condensation of synapsin are governed by sequence-encoded molecular grammars. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.08.03.606464. [PMID: 39131319 PMCID: PMC11312526 DOI: 10.1101/2024.08.03.606464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 08/13/2024]
Abstract
Brain functioning relies on orchestrated synaptic vesicle dynamics and controlled neurotransmitter release. Multiple biomolecular condensates coexist at the pre- and post-synapse and they are driven by condensation that combines binding, phase separation, and percolation. In pre-synapses, intrinsically disordered regions (IDRs) of synaptic proteins are drivers of condensation that enable clustering of synaptic vesicles (SVs). Although sequences of IDRs are poorly conserved across evolution, our computational analysis reveals the existence of non-random compositional biases and sequence patterns (molecular grammars) in IDRs of pre-synaptic proteins. For example, synapsin-1, which is essential for condensation of SVs, contains a conserved valence of arginine residues and blocks of polar and proline residues that are segregated from one another along the linear sequence. We show that these conserved features are crucial for driving synapsin-1 condensation in vitro and in cells. Our results highlight how conserved molecular grammars drive the condensation of key proteins at the pre-synapse.
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Affiliation(s)
- Christian Hoffmann
- Laboratory of Molecular Neuroscience Berlin, German Center for Neurodegenerative Diseases (DZNE), 10117 Berlin, Germany
| | - Kiersten M. Ruff
- Department of Biomedical Engineering and Center for Biomolecular Condensates, James McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Irina A. Edu
- Centre for Misfolding Diseases, Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Min Kyung Shinn
- Department of Biomedical Engineering and Center for Biomolecular Condensates, James McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Johannes V. Tromm
- Laboratory of Molecular Neuroscience Berlin, German Center for Neurodegenerative Diseases (DZNE), 10117 Berlin, Germany
| | - Matthew R. King
- Department of Biomedical Engineering and Center for Biomolecular Condensates, James McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Avnika Pant
- Department of Biomedical Engineering and Center for Biomolecular Condensates, James McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Hannes Ausserwöger
- Centre for Misfolding Diseases, Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Jennifer R. Morgan
- Eugene Bell Center for Regenerative Biology and Tissue Engineering, Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Tuomas P. J. Knowles
- Centre for Misfolding Diseases, Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
- Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Road, Cambridge CB3 0HE, United Kingdom
| | - Rohit V. Pappu
- Department of Biomedical Engineering and Center for Biomolecular Condensates, James McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Dragomir Milovanovic
- Laboratory of Molecular Neuroscience Berlin, German Center for Neurodegenerative Diseases (DZNE), 10117 Berlin, Germany
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany
- Einstein Center for Neuroscience, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität Berlin, and Berlin Institute of Health, 10117 Berlin, Germany
- Whitman Center, Marine Biological Laboratory, 02543 Woods Hole, MA, USA
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3
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Sansevrino R, Hoffmann C, Milovanovic D. Condensate biology of synaptic vesicle clusters. Trends Neurosci 2023; 46:293-306. [PMID: 36725404 DOI: 10.1016/j.tins.2023.01.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 12/20/2022] [Accepted: 01/10/2023] [Indexed: 01/31/2023]
Abstract
Neuronal communication crucially relies on exocytosis of neurotransmitters from synaptic vesicles (SVs) which are clustered at synapses. To ensure reliable neurotransmitter release, synapses need to maintain an adequate pool of SVs at all times. Decades of research have established that SVs are clustered by synapsin 1, an abundant SV-associated phosphoprotein. The classical view postulates that SVs are crosslinked in a scaffold of protein-protein interactions between synapsins and their binding partners. Recent studies have shown that synapsins cluster SVs via liquid-liquid phase separation (LLPS), thus providing a new framework for the organization of the synapse. We discuss the evidence for phase separation of SVs, emphasizing emerging questions related to its regulation, specificity, and reversibility.
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Affiliation(s)
- Roberto Sansevrino
- Laboratory of Molecular Neuroscience, German Center for Neurodegenerative Diseases (DZNE), 10117 Berlin, Germany
| | - Christian Hoffmann
- Laboratory of Molecular Neuroscience, German Center for Neurodegenerative Diseases (DZNE), 10117 Berlin, Germany
| | - Dragomir Milovanovic
- Laboratory of Molecular Neuroscience, German Center for Neurodegenerative Diseases (DZNE), 10117 Berlin, Germany.
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4
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Jadiya P, Cohen HM, Kolmetzky DW, Kadam AA, Tomar D, Elrod JW. Neuronal loss of NCLX-dependent mitochondrial calcium efflux mediates age-associated cognitive decline. iScience 2023; 26:106296. [PMID: 36936788 PMCID: PMC10014305 DOI: 10.1016/j.isci.2023.106296] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 12/12/2022] [Accepted: 02/20/2023] [Indexed: 03/05/2023] Open
Abstract
Mitochondrial calcium overload contributes to neurodegenerative disease development and progression. We recently reported that loss of the mitochondrial sodium/calcium exchanger (NCLX), the primary mechanism of mCa2+ efflux, promotes mCa2+ overload, metabolic derangement, redox stress, and cognitive decline in models of Alzheimer's disease (AD). However, whether disrupted mCa2+ signaling contributes to neuronal pathology and cognitive decline independent of pre-existing amyloid or tau pathology remains unknown. Here, we generated mice with neuronal deletion of the mitochondrial sodium/calcium exchanger (NCLX, Slc8b1 gene), and evaluated age-associated changes in cognitive function and neuropathology. Neuronal loss of NCLX resulted in an age-dependent decline in spatial and cued recall memory, moderate amyloid deposition, mild tau pathology, synaptic remodeling, and indications of cell death. These results demonstrate that loss of NCLX-dependent mCa2+ efflux alone is sufficient to induce an Alzheimer's disease-like pathology and highlights the promise of therapies targeting mCa2+ exchange.
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Affiliation(s)
- Pooja Jadiya
- Cardiovascular Research Center, Department of Cardiovascular Sciences, Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA
- Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC, 27157, USA
| | - Henry M. Cohen
- Cardiovascular Research Center, Department of Cardiovascular Sciences, Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA
| | - Devin W. Kolmetzky
- Cardiovascular Research Center, Department of Cardiovascular Sciences, Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA
| | - Ashlesha A. Kadam
- Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC, 27157, USA
| | - Dhanendra Tomar
- Cardiovascular Research Center, Department of Cardiovascular Sciences, Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA
- Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC, 27157, USA
| | - John W. Elrod
- Cardiovascular Research Center, Department of Cardiovascular Sciences, Lewis Katz School of Medicine at Temple University, Philadelphia, PA 19140, USA
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5
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Synaptic vesicle proteins and ATG9A self-organize in distinct vesicle phases within synapsin condensates. Nat Commun 2023; 14:455. [PMID: 36709207 PMCID: PMC9884207 DOI: 10.1038/s41467-023-36081-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Accepted: 01/16/2023] [Indexed: 01/30/2023] Open
Abstract
Ectopic expression in fibroblasts of synapsin 1 and synaptophysin is sufficient to generate condensates of vesicles highly reminiscent of synaptic vesicle (SV) clusters and with liquid-like properties. Here we show that unlike synaptophysin, other major integral SV membrane proteins fail to form condensates with synapsin, but co-assemble into the clusters formed by synaptophysin and synapsin in this ectopic expression system. Another vesicle membrane protein, ATG9A, undergoes activity-dependent exo-endocytosis at synapses, raising questions about the relation of ATG9A traffic to the traffic of SVs. We find that both in fibroblasts and in nerve terminals ATG9A does not co-assemble into synaptophysin-positive vesicle condensates but localizes on a distinct class of vesicles that also assembles with synapsin but into a distinct phase. Our findings suggest that ATG9A undergoes differential sorting relative to SV proteins and also point to a dual role of synapsin in controlling clustering at synapses of SVs and ATG9A vesicles.
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6
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Wu X, Qiu H, Zhang M. Interactions between Membraneless Condensates and Membranous Organelles at the Presynapse: A Phase Separation View of Synaptic Vesicle Cycle. J Mol Biol 2023; 435:167629. [PMID: 35595170 DOI: 10.1016/j.jmb.2022.167629] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Revised: 05/03/2022] [Accepted: 05/04/2022] [Indexed: 02/04/2023]
Abstract
Action potential-induced neurotransmitter release in presynaptic boutons involves coordinated actions of a large list of proteins that are associated directly or indirectly with membrane structures including synaptic vesicles and plasma membranes. These proteins are often highly abundant in different synaptic bouton sub-compartments, and they rarely act alone. Instead, these proteins interact with each other forming intricate and distinct molecular complexes. Many of these complexes form condensed clusters on membrane surfaces. This review summarizes findings in recent years showing that many of presynaptic protein complex assemblies are formed via phase separation. These protein condensates extensively interact with lipid membranes via distinct modes, forming various mesoscale structures by different mode of organizations between membraneless condensates and membranous organelles. We discuss that such mesoscale interactions could have deep implications on mobilization, exocytosis, and retrieval of synaptic vesicles.
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Affiliation(s)
- Xiandeng Wu
- Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Hua Qiu
- Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Mingjie Zhang
- Greater Bay Biomedical Innocenter, Shenzhen Bay Laboratory, Shenzhen 518036, China; School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China.
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7
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Yeo XY, Lim YT, Chae WR, Park C, Park H, Jung S. Alterations of presynaptic proteins in autism spectrum disorder. Front Mol Neurosci 2022; 15:1062878. [DOI: 10.3389/fnmol.2022.1062878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Accepted: 10/31/2022] [Indexed: 11/19/2022] Open
Abstract
The expanded use of hypothesis-free gene analysis methods in autism research has significantly increased the number of genetic risk factors associated with the pathogenesis of autism. A further examination of the implicated genes directly revealed the involvement in processes pertinent to neuronal differentiation, development, and function, with a predominant contribution from the regulators of synaptic function. Despite the importance of presynaptic function in synaptic transmission, the regulation of neuronal network activity, and the final behavioral output, there is a relative lack of understanding of the presynaptic contribution to the pathology of autism. Here, we will review the close association among autism-related mutations, autism spectrum disorders (ASD) phenotypes, and the altered presynaptic protein functions through a systematic examination of the presynaptic risk genes relating to the critical stages of synaptogenesis and neurotransmission.
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8
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Shrestha AP, Saravanakumar A, Konadu B, Madireddy S, Gibert Y, Vaithianathan T. Embryonic Hyperglycemia Delays the Development of Retinal Synapses in a Zebrafish Model. Int J Mol Sci 2022; 23:ijms23179693. [PMID: 36077087 PMCID: PMC9456524 DOI: 10.3390/ijms23179693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Revised: 08/16/2022] [Accepted: 08/19/2022] [Indexed: 11/22/2022] Open
Abstract
Embryonic hyperglycemia negatively impacts retinal development, leading to abnormal visual behavior, altered timing of retinal progenitor differentiation, decreased numbers of retinal ganglion cells and Müller glia, and vascular leakage. Because synaptic disorganization is a prominent feature of many neurological diseases, the goal of the current work was to study the potential impact of hyperglycemia on retinal ribbon synapses during embryonic development. Our approach utilized reverse transcription quantitative PCR (RT-qPCR) and immunofluorescence labeling to compare the transcription of synaptic proteins and their localization in hyperglycemic zebrafish embryos, respectively. Our data revealed that the maturity of synaptic ribbons was compromised in hyperglycemic zebrafish larvae, where altered ribeye expression coincided with the delay in establishing retinal ribbon synapses and an increase in the immature synaptic ribbons. Our results suggested that embryonic hyperglycemia disrupts retinal synapses by altering the development of the synaptic ribbon, which can lead to visual defects. Future studies using zebrafish models of hyperglycemia will allow us to study the underlying mechanisms of retinal synapse development.
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Affiliation(s)
- Abhishek P. Shrestha
- Department of Pharmacology, Addiction Science, and Toxicology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA
| | - Ambalavanan Saravanakumar
- Department of Pharmacology, Addiction Science, and Toxicology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA
- Program in Biology, Rhodes College, Memphis, TN 38112, USA
| | - Bridget Konadu
- Department of Cell and Molecular Biology, University of Mississippi Medical Center, Jackson, MS 39216, USA
| | - Saivikram Madireddy
- Department of Pharmacology, Addiction Science, and Toxicology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA
| | - Yann Gibert
- Department of Cell and Molecular Biology, University of Mississippi Medical Center, Jackson, MS 39216, USA
| | - Thirumalini Vaithianathan
- Department of Pharmacology, Addiction Science, and Toxicology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA
- Department of Ophthalmology, Hamilton Eye Institute, University of Tennessee Health Science Center, Memphis, TN 38163, USA
- Correspondence: ; Tel.: +1-901-448-2786
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9
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Larocque G, Royle SJ. Integrating intracellular nanovesicles into integrin trafficking pathways and beyond. Cell Mol Life Sci 2022; 79:335. [PMID: 35657500 PMCID: PMC9166830 DOI: 10.1007/s00018-022-04371-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 04/28/2022] [Accepted: 05/11/2022] [Indexed: 12/24/2022]
Abstract
Membrane traffic controls the movement of proteins and lipids from one cellular compartment to another using a system of transport vesicles. Intracellular nanovesicles (INVs) are a newly described class of transport vesicles. These vesicles are small, carry diverse cargo, and are involved in multiple trafficking steps including anterograde traffic and endosomal recycling. An example of a biological process that they control is cell migration and invasion, due to their role in integrin recycling. In this review, we describe what is known so far about these vesicles. We discuss how INVs may integrate into established membrane trafficking pathways using integrin recycling as an example. We speculate where in the cell INVs have the potential to operate and we identify key questions for future investigation.
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Affiliation(s)
| | - Stephen J Royle
- Centre for Mechanochemical Cell Biology, Warwick Medical School, Gibbet Hill Road, Coventry, CV4 7AL, UK.
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10
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Lomoio S, Willen R, Kim W, Ho KZ, Robinson EK, Prokopenko D, Kennedy ME, Tanzi RE, Tesco G. Gga3 deletion and a GGA3 rare variant associated with late onset Alzheimer's disease trigger BACE1 accumulation in axonal swellings. Sci Transl Med 2021; 12:12/570/eaba1871. [PMID: 33208500 DOI: 10.1126/scitranslmed.aba1871] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Revised: 05/18/2020] [Accepted: 08/03/2020] [Indexed: 12/13/2022]
Abstract
Axonal dystrophy, indicative of perturbed axonal transport, occurs early during Alzheimer's disease (AD) pathogenesis. Little is known about the mechanisms underlying this initial sign of the pathology. This study proves that Golgi-localized γ-ear-containing ARF binding protein 3 (GGA3) loss of function, due to Gga3 genetic deletion or a GGA3 rare variant that cosegregates with late-onset AD, disrupts the axonal trafficking of the β-site APP-cleaving enzyme 1 (BACE1) resulting in its accumulation in axonal swellings in cultured neurons and in vivo. We show that BACE pharmacological inhibition ameliorates BACE1 axonal trafficking and diminishes axonal dystrophies in Gga3 null neurons in vitro and in vivo. These data indicate that axonal accumulation of BACE1 engendered by GGA3 loss of function results in local toxicity leading to axonopathy. Gga3 deletion exacerbates axonal dystrophies in a mouse model of AD before β-amyloid (Aβ) deposition. Our study strongly supports a role for GGA3 in AD pathogenesis, where GGA3 loss of function triggers BACE1 axonal accumulation independently of extracellular Aβ, and initiates a cascade of events leading to the axonal damage distinctive of the early stage of AD.
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Affiliation(s)
- Selene Lomoio
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - Rachel Willen
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - WonHee Kim
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - Kevin Z Ho
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - Edward K Robinson
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - Dmitry Prokopenko
- Genetics and Aging Research Unit, MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA
| | | | - Rudolph E Tanzi
- Genetics and Aging Research Unit, MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA
| | - Giuseppina Tesco
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA.
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11
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Park D, Wu Y, Lee SE, Kim G, Jeong S, Milovanovic D, De Camilli P, Chang S. Cooperative function of synaptophysin and synapsin in the generation of synaptic vesicle-like clusters in non-neuronal cells. Nat Commun 2021; 12:263. [PMID: 33431828 PMCID: PMC7801664 DOI: 10.1038/s41467-020-20462-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Accepted: 12/02/2020] [Indexed: 02/01/2023] Open
Abstract
Clusters of tightly packed synaptic vesicles (SVs) are a defining feature of nerve terminals. While SVs are mobile within the clusters, the clusters have no boundaries consistent with a liquid phase. We previously found that purified synapsin, a peripheral SV protein, can assemble into liquid condensates and trap liposomes into them. How this finding relates to the physiological formation of SV clusters in living cells remains unclear. Here, we report that synapsin alone, when expressed in fibroblasts, has a diffuse cytosolic distribution. However, when expressed together with synaptophysin, an integral SV membrane protein previously shown to be localized on small synaptic-like microvesicles when expressed in non-neuronal cells, is sufficient to organize such vesicles in clusters highly reminiscent of SV clusters and with liquid-like properties. This minimal reconstitution system can be a powerful model to gain mechanistic insight into the assembly of structures which are of fundamental importance in synaptic transmission. Synaptic vesicle clusters were proposed to represent phase separated condensates. Here, the authors show that only two proteins, synapsin and synaptophysin, are sufficient to make vesicle clusters in fibroblasts which are similar to those found at synapses in morphology and liquid-like properties.
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Affiliation(s)
- Daehun Park
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, 06510, USA
| | - Yumei Wu
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, 06510, USA
| | - Sang-Eun Lee
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul, 03080, South Korea
| | - Goeun Kim
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul, 03080, South Korea
| | - Seonyoung Jeong
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul, 03080, South Korea
| | - Dragomir Milovanovic
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, 06510, USA.,Laboratory of Molecular Neuroscience, German Center for Neurodegenerative Diseases (DZNE), Charitéplatz 1, 10117, Berlin, Germany
| | - Pietro De Camilli
- Departments of Neuroscience and Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, 06510, USA.
| | - Sunghoe Chang
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul, 03080, South Korea.
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12
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Solé L, Tamkun MM. Trafficking mechanisms underlying Na v channel subcellular localization in neurons. Channels (Austin) 2020; 14:1-17. [PMID: 31841065 PMCID: PMC7039628 DOI: 10.1080/19336950.2019.1700082] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Accepted: 11/13/2019] [Indexed: 01/06/2023] Open
Abstract
Voltage gated sodium channels (Nav) play a crucial role in action potential initiation and propagation. Although the discovery of Nav channels dates back more than 65 years, and great advances in understanding their localization, biophysical properties, and links to disease have been made, there are still many questions to be answered regarding the cellular and molecular mechanisms involved in Nav channel trafficking, localization and regulation. This review summarizes the different trafficking mechanisms underlying the polarized Nav channel localization in neurons, with an emphasis on the axon initial segment (AIS), as well as discussing the latest advances regarding how neurons regulate their excitability by modifying AIS length and location. The importance of Nav channel localization is emphasized by the relationship between mutations, impaired trafficking and disease. While this review focuses on Nav1.6, other Nav isoforms are also discussed.
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Affiliation(s)
- Laura Solé
- Molecular, Cellular and Integrative Neurosciences Graduate Program, Colorado State University, Fort Collins, CO, USA
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
| | - Michael M. Tamkun
- Molecular, Cellular and Integrative Neurosciences Graduate Program, Colorado State University, Fort Collins, CO, USA
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA
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13
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Land MA, Chapman HL, Davis-Reyes BD, Felsing DE, Allen JA, Moeller FG, Elferink LA, Cunningham KA, Anastasio NC. Serotonin 5-HT 2C Receptor Cys23Ser Single Nucleotide Polymorphism Associates with Receptor Function and Localization In Vitro. Sci Rep 2019; 9:16737. [PMID: 31723224 PMCID: PMC6853916 DOI: 10.1038/s41598-019-53124-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 10/21/2019] [Indexed: 11/09/2022] Open
Abstract
A non-synonymous single nucleotide polymorphism of the human serotonin 5-HT2C receptor (5-HT2CR) gene that converts a cysteine to a serine at amino acid codon 23 (Cys23Ser) appears to impact 5-HT2CR pharmacology at a cellular and systems level. We hypothesized that the Cys23Ser alters 5-HT2CR intracellular signaling via changes in subcellular localization in vitro. Using cell lines stably expressing the wild-type Cys23 or the Ser23 variant, we show that 5-HT evokes intracellular calcium release with decreased potency and peak response in the Ser23 versus the Cys23 cell lines. Biochemical analyses demonstrated lower Ser23 5-HT2CR plasma membrane localization versus the Cys23 5-HT2CR. Subcellular localization studies demonstrated O-linked glycosylation of the Ser23 variant, but not the wild-type Cys23, may be a post-translational mechanism which alters its localization within the Golgi apparatus. Further, both the Cys23 and Ser23 5-HT2CR are present in the recycling pathway with the Ser23 variant having decreased colocalization with the early endosome versus the Cys23 allele. Agonism of the 5-HT2CR causes the Ser23 variant to exit the recycling pathway with no effect on the Cys23 allele. Taken together, the Ser23 variant exhibits a distinct pharmacological and subcellular localization profile versus the wild-type Cys23 allele, which could impact aspects of receptor pharmacology in individuals expressing the Cys23Ser SNP.
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Affiliation(s)
| | - Holly L Chapman
- Center for Addiction Research, Galveston, TX, USA.,Department of Pharmacology and Toxicology, Galveston, TX, USA
| | | | - Daniel E Felsing
- Center for Addiction Research, Galveston, TX, USA.,Department of Pharmacology and Toxicology, Galveston, TX, USA
| | - John A Allen
- Center for Addiction Research, Galveston, TX, USA.,Department of Pharmacology and Toxicology, Galveston, TX, USA
| | - F Gerard Moeller
- Center for Addiction Research, Galveston, TX, USA.,Department of Psychiatry, Virginia Commonwealth University, Richmond, VA, USA
| | - Lisa A Elferink
- Center for Addiction Research, Galveston, TX, USA.,Department of Neuroscience, Cell Biology and Anatomy, University of Texas Medical Branch, Galveston, TX, USA
| | - Kathryn A Cunningham
- Center for Addiction Research, Galveston, TX, USA.,Department of Pharmacology and Toxicology, Galveston, TX, USA
| | - Noelle C Anastasio
- Center for Addiction Research, Galveston, TX, USA. .,Department of Pharmacology and Toxicology, Galveston, TX, USA.
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14
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Matsuda T, Oinuma I. Imaging endogenous synaptic proteins in primary neurons at single-cell resolution using CRISPR/Cas9. Mol Biol Cell 2019; 30:2838-2855. [PMID: 31509485 PMCID: PMC6789158 DOI: 10.1091/mbc.e19-04-0223] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Fluorescence imaging at single-cell resolution is a crucial approach to analyzing the spatiotemporal regulation of proteins within individual cells of complex neural networks. Here we present a nonviral strategy that enables the tagging of endogenous loci by CRISPR/Cas9-mediated genome editing combined with a nucleofection technique. The method allowed expression of fluorescently tagged proteins at endogenous levels, and we successfully achieved tagging of a presynaptic protein, synaptophysin (Syp), and a postsynaptic protein, PSD-95, in cultured postmitotic neurons. Superresolution fluorescence microscopy of fixed neurons confirmed the identical localization patterns of the tagged proteins to those of endogenous ones verified by immunohistochemistry. The system is also applicable for multiplexed labeling and live-cell imaging. Live imaging with total internal reflection fluorescence microscopy of a single dendritic process of a neuron double-labeled with Syp-mCherry and PSD-95-EGFP revealed the previously undescribed dynamic localization of the proteins synchronously moving along dendritic shafts. Our convenient and versatile strategy is potent for analysis of proteins whose ectopic expressions perturb cellular functions.
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Affiliation(s)
- Takahiko Matsuda
- Laboratory of Cell and Molecular Biology, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan
| | - Izumi Oinuma
- Laboratory of Cell and Molecular Biology, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan.,Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Kyoto 606-8501, Japan
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15
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Song X, He R, Han W, Li T, Xie L, Cheng L, Chen H, Xie M, Jiang L. Protective effects of the ROCK inhibitor fasudil against cognitive dysfunction following status epilepticus in male rats. J Neurosci Res 2018; 97:506-519. [PMID: 30421453 DOI: 10.1002/jnr.24355] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 09/30/2018] [Accepted: 10/17/2018] [Indexed: 12/26/2022]
Affiliation(s)
- Xiaojie Song
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
- Department of Neurology Children’s Hospital of Chongqing Medical University Chongqing China
| | - Rong He
- Pediatric department University‐Town Hospital of Chongqing Medical University Chongqing China
| | - Wei Han
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
| | - Tianyi Li
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
- Department of Neurology Children’s Hospital of Chongqing Medical University Chongqing China
| | - Lingling Xie
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
- Department of Neurology Children’s Hospital of Chongqing Medical University Chongqing China
| | - Li Cheng
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
| | - Hengsheng Chen
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
| | - Mingdan Xie
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
| | - Li Jiang
- Pediatric Research Institute Children’s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing Key Laboratory of Pediatrics Chongqing China
- Department of Neurology Children’s Hospital of Chongqing Medical University Chongqing China
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16
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Zhang N, Chin JS, Chew SY. Localised non-viral delivery of nucleic acids for nerve regeneration in injured nervous systems. Exp Neurol 2018; 319:112820. [PMID: 30195695 DOI: 10.1016/j.expneurol.2018.09.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 08/31/2018] [Accepted: 09/05/2018] [Indexed: 02/07/2023]
Abstract
Axons damaged by traumatic injuries are often unable to spontaneously regenerate in the adult central nervous system (CNS). Although the peripheral nervous system (PNS) has some regenerative capacity, its ability to regrow remains limited across large lesion gaps due to scar tissue formation. Nucleic acid therapy holds the potential of improving regeneration by enhancing the intrinsic growth ability of neurons and overcoming the inhibitory environment that prevents neurite outgrowth. Nucleic acids modulate gene expression by over-expression of neuronal growth factor or silencing growth-inhibitory molecules. Although in vitro outcomes appear promising, the lack of efficient non-viral nucleic acid delivery methods to the nervous system has limited the application of nucleic acid therapeutics to patients. Here, we review the recent development of efficient non-viral nucleic acid delivery platforms, as applied to the nervous system, including the transfection vectors and carriers used, as well as matrices and scaffolds that are currently used. Additionally, we will discuss possible improvements for localised nucleic acid delivery.
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Affiliation(s)
- Na Zhang
- School of Chemical and Biomedical Engineering, Nanyang Technological University, 637459, Singapore
| | - Jiah Shin Chin
- School of Chemical and Biomedical Engineering, Nanyang Technological University, 637459, Singapore; NTU Institute of Health Technologies, Interdisciplinary Graduate School, Nanyang Technological University, 639798, Singapore
| | - Sing Yian Chew
- School of Chemical and Biomedical Engineering, Nanyang Technological University, 637459, Singapore; Lee Kong Chian School of Medicine, Nanyang Technological University, 308232, Singapore.
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17
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Abstract
Flaviviruses are a globally important group of human viral pathogens. These viruses enter cells by hijacking an endocytic pathway, clathrin-mediated endocytosis, used by cells to take up growth factors and nutrients. While most cargo is small, virions are large, and we identified host factors specifically required for the internalization of large cargo including these viruses. These studies define a set of requirements for viral internalization and which may be amenable to therapeutic interventions. Flaviviruses enter host cells through the process of clathrin-mediated endocytosis, and the spectrum of host factors required for this process are incompletely understood. Here we found that lymphocyte antigen 6 locus E (LY6E) promotes the internalization of multiple flaviviruses, including West Nile virus, Zika virus, and dengue virus. Perhaps surprisingly, LY6E is dispensable for the internalization of the endogenous cargo transferrin, which is also dependent on clathrin-mediated endocytosis for uptake. Since viruses are substantially larger than transferrin, we reasoned that LY6E may be required for uptake of larger cargoes and tested this using transferrin-coated beads of similar size as flaviviruses. LY6E was indeed required for the internalization of transferrin-coated beads, suggesting that LY6E is selectively required for large cargo. Cell biological studies found that LY6E forms tubules upon viral infection and bead internalization, and we found that tubule formation was dependent on RNASEK, which is also required for flavivirus internalization, but not transferrin uptake. Indeed, we found that RNASEK is also required for the internalization of transferrin-coated beads, suggesting it functions upstream of LY6E. These LY6E tubules resembled microtubules, and we found that microtubule assembly was required for their formation and flavivirus uptake. Since microtubule end-binding proteins link microtubules to downstream activities, we screened the three end-binding proteins and found that EB3 promotes virus uptake and LY6E tubularization. Taken together, these results highlight a specialized pathway required for the uptake of large clathrin-dependent endocytosis cargoes, including flaviviruses.
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18
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Transferrin Receptor Controls AMPA Receptor Trafficking Efficiency and Synaptic Plasticity. Sci Rep 2016; 6:21019. [PMID: 26880306 PMCID: PMC4754636 DOI: 10.1038/srep21019] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 01/14/2016] [Indexed: 02/05/2023] Open
Abstract
Transferrin receptor (TFR) is an important iron transporter regulating iron homeostasis and has long been used as a marker for clathrin mediated endocytosis. However, little is known about its additional function other than iron transport in the development of central nervous system (CNS). Here we demonstrate that TFR functions as a regulator to control AMPA receptor trafficking efficiency and synaptic plasticity. The conditional knockout (KO) of TFR in neural progenitor cells causes mice to develop progressive epileptic seizure, and dramatically reduces basal synaptic transmission and long-term potentiation (LTP). We further demonstrate that TFR KO remarkably reduces the binding efficiency of GluR2 to AP2 and subsequently decreases AMPA receptor endocytosis and recycling. Thus, our study reveals that TFR functions as a novel regulator to control AMPA trafficking efficiency and synaptic plasticity.
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19
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Farías GG, Guardia CM, Britt DJ, Guo X, Bonifacino JS. Sorting of Dendritic and Axonal Vesicles at the Pre-axonal Exclusion Zone. Cell Rep 2015; 13:1221-1232. [PMID: 26527003 PMCID: PMC5410646 DOI: 10.1016/j.celrep.2015.09.074] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Revised: 08/19/2015] [Accepted: 09/24/2015] [Indexed: 02/03/2023] Open
Abstract
Polarized sorting of newly synthesized proteins to the somatodendritic and axonal domains of neurons occurs by selective incorporation into distinct populations of vesicular transport carriers. An unresolved issue is how the vesicles themselves are sorted to their corresponding neuronal domains. Previous studies concluded that the axon initial segment (AIS) is an actin-based filter that selectively prevents passage of somatodendritic vesicles into the axon. We find, however, that most somatodendritic vesicles fail to enter the axon at a more proximal region in the axon hillock, herein referred to as the pre-axonal exclusion zone (PAEZ). Forced coupling of a somatodendritic cargo protein to an axonally directed kinesin is sufficient to drive transport of whole somatodendritic vesicles through the PAEZ toward the distal axon. Based on these findings, we propose that polarized sorting of transport vesicles occurs at the PAEZ and depends on the ability of the vesicles to acquire an appropriately directed microtubule motor.
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Affiliation(s)
- Ginny G Farías
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD 20892, USA
| | - Carlos M Guardia
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD 20892, USA
| | - Dylan J Britt
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD 20892, USA
| | - Xiaoli Guo
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD 20892, USA
| | - Juan S Bonifacino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD 20892, USA.
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20
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Sands SA, Tsau S, LeVine SM. The habenula and iron metabolism in cerebral mouse models of multiple sclerosis. Neurosci Lett 2015; 606:204-8. [PMID: 26362814 DOI: 10.1016/j.neulet.2015.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 09/03/2015] [Accepted: 09/04/2015] [Indexed: 12/25/2022]
Abstract
Iron accumulates in the CNS of patients with multiple sclerosis, but our understanding of the mechanism accounting for this accumulation is unclear. Mouse models of cerebral experimental autoimmune encephalomyelitis (EAE) in C57BL/6 and SJL mice were used together with a histochemical stain for iron and immunohistochemical stains for transferrin receptor, synaptophysin, iron regulatory protein 1 (IRP1) and/or IRP2 to investigate the role of disease activity on CNS iron metabolism. The expression of transferrin receptor, but not IRP1 or IRP2, increased in the medial habenula, which is adjacent to the third ventricle, in response to both types of cerebral EAE. In the habenula, the elevated expression of transferrin receptor in C57BL/6 mice with cerebral EAE was generally restricted to the medial habenula while the expression in SJL mice with cerebral EAE was more diffusely expressed. Iron levels were increased in all regions of the habenula in C57BL/6 mice with cerebral EAE, and in the medial and medial lateral but not the lateral habenula in SJL mice with cerebral EAE. Synaptophysin, which has been observed previously in endocytic vesicles together with the transferrin receptor, was concentrated at the medial habenula, but its levels did not increase with disease in C57BL/6 mice with cerebral EAE. Our results support the model that the medial habenula responds to disease activity by upregulating transferrin receptor to facilitate the movement of iron into the brain from the third ventricle, raising the possibility that a similar mechanism accounts for iron accumulation in deep gray matter structures in patients with multiple sclerosis.
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Affiliation(s)
- Scott A Sands
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Sheila Tsau
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Steven M LeVine
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
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21
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The structure and function of presynaptic endosomes. Exp Cell Res 2015; 335:172-9. [DOI: 10.1016/j.yexcr.2015.04.017] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 04/23/2015] [Indexed: 11/19/2022]
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22
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Roman-Vendrell C, Chevalier M, Acevedo-Canabal AM, Delgado-Peraza F, Flores-Otero J, Yudowski GA. Imaging of kiss-and-run exocytosis of surface receptors in neuronal cultures. Front Cell Neurosci 2014; 8:363. [PMID: 25404895 PMCID: PMC4217495 DOI: 10.3389/fncel.2014.00363] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2014] [Accepted: 10/14/2014] [Indexed: 02/01/2023] Open
Abstract
Transmembrane proteins are continuously shuttled from the endosomal compartment to the neuronal plasma membrane by highly regulated and complex trafficking steps. These events are involved in many homeostatic and physiological processes such as neuronal growth, signaling, learning and memory among others. We have previously shown that endosomal exocytosis of the B2 adrenergic receptor (B2AR) and the GluR1-containing AMPA receptor to the neuronal plasma membrane is mediated by two different types of vesicular fusion. A rapid type of exocytosis in which receptors are delivered to the plasma membrane in a single kinetic step, and a persistent mode in which receptors remain clustered at the insertion site for a variable period of time before delivery to the cell surface. Here, by comparing the exocytosis of multiple receptors in dissociated hippocampal and striatal cultures, we show that persistent events are a general mechanism of vesicular delivery. Persistent events were only observed after 10 days in vitro, and their frequency increased with use of the calcium ionophore A23187 and with depolarization induced by KCl. Finally, we determined that vesicles producing persistent events remain at the plasma membrane, closing and reopening their fusion pore for a consecutive release of cargo in a mechanism reminiscent of synaptic kiss-and-run. These results indicate that the delivery of transmembrane receptors to the cell surface can be dynamically regulated by kiss-and-run exocytosis.
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Affiliation(s)
- Cristina Roman-Vendrell
- Institute of Neurobiology, University of Puerto Rico Medical Sciences Campus San Juan, PR, USA ; Department of Physiology, School of Medicine, University of Puerto Rico San Juan, PR, USA
| | - Michael Chevalier
- Department of Biochemistry and Biophysics, California Institute for Quantitative Biosciences, University of California San Francisco San Francisco, CA, USA
| | - Agnes M Acevedo-Canabal
- Institute of Neurobiology, University of Puerto Rico Medical Sciences Campus San Juan, PR, USA ; Department of Anatomy and Neurobiology, School of Medicine, University of Puerto Rico San Juan, PR, USA
| | - Francheska Delgado-Peraza
- Institute of Neurobiology, University of Puerto Rico Medical Sciences Campus San Juan, PR, USA ; Department of Anatomy and Neurobiology, School of Medicine, University of Puerto Rico San Juan, PR, USA
| | - Jacqueline Flores-Otero
- Department of Anatomy and Neurobiology, School of Medicine, University of Puerto Rico San Juan, PR, USA
| | - Guillermo A Yudowski
- Institute of Neurobiology, University of Puerto Rico Medical Sciences Campus San Juan, PR, USA ; Department of Anatomy and Neurobiology, School of Medicine, University of Puerto Rico San Juan, PR, USA
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23
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Romero AM, Renau-Piqueras J, Marín MP, Esteban-Pretel G. Chronic alcohol exposure affects the cell components involved in membrane traffic in neuronal dendrites. Neurotox Res 2014; 27:43-54. [PMID: 25022897 DOI: 10.1007/s12640-014-9484-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Revised: 06/13/2014] [Accepted: 07/01/2014] [Indexed: 01/09/2023]
Abstract
The specific traffic of the membrane components in neurons is a major requirement to establish and maintain neuronal domains-the axonal and the somatodendritic domains-and their polarized morphology. Unlike axons, dendrites contain membranous organelles, which are involved in the secretory pathway, including the endoplasmic reticulum, the Golgi apparatus and post-Golgi apparatus carriers, the cytoskeleton, and plasma membrane. A variety of molecules and factors are also involved in this process. Previous studies have shown that chronic alcohol exposure negatively affects several of these cell components, such as the Golgi apparatus or cytoskeleton in neurons. Yet very little information is available on the possible effects of this exposure on the remaining cell elements involved in intracellular trafficking in neurons, particularly in dendrites. By qualitative and quantitative electron microscopy, immunofluorescence and immunoblotting, we herein show that chronic exposure to moderate levels (30 mM) of ethanol in cultured neurons reduces the volume and surface density of the rough endoplasmic reticulum, and increases the levels of GRP78, a chaperone involved in endoplasmic reticulum stress. Ethanol also significantly diminishes the proportion of neurons that show an extension of Golgi into dendrites and dendritic Golgi outposts, a structure present exclusively in longer, thicker apical dendrites. Both Golgi apparatus types were also fragmented into a large number of cells. We also investigated the effect of alcohol on the levels of microtubule-based motor proteins KIF5, KIF17, KIFC2, dynein, and myosin IIb, responsible for transporting different cargoes in dendrites. Of these, alcohol differently affects several of them by lowering dynein and raising KIF5, KIFC2, and myosin IIb. These results, together with other previously published ones, suggest that practically all the protein trafficking steps in dendrites are altered to a greater or lesser extent by chronic alcohol exposure in neuronal cells, which may have negative repercussions for the development and maintenance of their polarized morphology and function.
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Affiliation(s)
- Ana M Romero
- Sección de Biología y Patología Celular, Centro de Investigación, Hospital Universitario ''La Fe'', Avenida Campanar 21, 46009, Valencia, Spain
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24
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Abstract
Synaptic vesicle recycling is one of the best-studied cellular pathways. Many of the proteins involved are known, and their interactions are becoming increasingly clear. However, as for many other pathways, it is still difficult to understand synaptic vesicle recycling as a whole. While it is generally possible to point out how synaptic reactions take place, it is not always easy to understand what triggers or controls them. Also, it is often difficult to understand how the availability of the reaction partners is controlled: how the reaction partners manage to find each other in the right place, at the right time. I present here an overview of synaptic vesicle recycling, discussing the mechanisms that trigger different reactions, and those that ensure the availability of reaction partners. A central argument is that synaptic vesicles bind soluble cofactor proteins, with low affinity, and thus control their availability in the synapse, forming a buffer for cofactor proteins. The availability of cofactor proteins, in turn, regulates the different synaptic reactions. Similar mechanisms, in which one of the reaction partners buffers another, may apply to many other processes, from the biogenesis to the degradation of the synaptic vesicle.
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Affiliation(s)
- Silvio O Rizzoli
- Department of Neuro- and Sensory Physiology, University Medical Center Göttingen European Neuroscience Institute, Göttingen, Germany
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25
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Enhanced recruitment of endosomal Na+/H+ exchanger NHE6 into Dendritic spines of hippocampal pyramidal neurons during NMDA receptor-dependent long-term potentiation. J Neurosci 2013; 33:595-610. [PMID: 23303939 DOI: 10.1523/jneurosci.2583-12.2013] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Postsynaptic endosomal trafficking has emerged as a principal regulatory mechanism of structural and functional plasticity of glutamatergic synapses. Recycling endosomes perform activity-dependent transport of AMPA receptors (AMPARs) and lipids to the postsynaptic membrane, activities that are known to contribute to long-term synaptic potentiation and hypothesized to subserve learning and memory processes in the brain. Recently, genetic defects in a widely expressed vesicular pH-regulating transporter, the Na(+)/H(+) exchanger NHE6 isoform, have been implicated in neurodevelopmental disorders including severe X-linked mental retardation and autism. However, little information is available regarding the cellular properties of this transporter in the CNS. Here, we show by quantitative light microscopy that the protein abundance of NHE6 is developmentally regulated in area CA1 of the mouse hippocampus. Within pyramidal neurons, NHE6 was found to localize to discrete puncta throughout the soma and neurites, with noticeable accumulation at dendritic spines and presynaptic terminals. Dual immunolabeling of dendritic spines revealed that NHE6 partially colocalizes with typical markers of early and recycling endosomes as well as with the AMPAR subunit GluA1. Significantly, NHE6-containing vesicles exhibited enhanced translocation to dendritic spine heads during NMDA receptor (NMDAR)-dependent long-term potentiation. These data suggest that NHE6 may play a unique, previously unrecognized, role at glutamatergic synapses that are important for learning and memory.
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26
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Lukashova V, Jinadasa T, Ilie A, Verbich D, Cooper E, Orlowski J. The Na(+)/H (+) exchanger NHE5 is sorted to discrete intracellular vesicles in the central and peripheral nervous systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:397-410. [PMID: 23224898 DOI: 10.1007/978-1-4614-4756-6_34] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The pH milieu of the central and peripheral nervous systems is an important determinant of neuronal excitability, function, and survival. In mammals, neural acid-base homeostasis is coordinately regulated by ion transporters belonging to the Na(+)/H(+) exchanger (NHE) and bicarbonate transporter gene families. However, the relative contributions of individual isoforms within the respective families are not fully understood. This report focuses on the NHE family, specifically the plasma membrane-type NHE5 which is preferentially transcribed in brain, but the distribution of the native protein has not been extensively characterized. To this end, we generated a rabbit polyclonal antibody that specifically recognizes NHE5. In both central (cortex, hippocampus) and peripheral (superior cervical ganglia, SCG) nervous tissue of mice, NHE5 immunostaining was punctate and highly concentrated in the somas and to lesser amounts in the dendrites of neurons. Very little signal was detected in axons. Similarly, in primary cultures of differentiated SCG neurons, NHE5 localized predominantly to vesicles in the somatodendritic compartment, though some immunostaining was also evident in punctate vesicles along the axons. NHE5 was also detected predominantly in intracellular vesicles of cultured SCG glial cells. Dual immunolabeling of SCG neurons showed that NHE5 did not colocalize with markers for early endosomes (EEA1) or synaptic vesicles (synaptophysin), but did partially colocalize with the transferrin receptor, a marker of recycling endosomes. Collectively, these data suggest that NHE5 partitions into a unique vesicular pool in neurons that shares some characteristics of recycling endosomes where it may serve as an important regulated store of functional transporters required to maintain cytoplasmic pH homeostasis.
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27
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Morelli S, Piscioneri A, Messina A, Salerno S, Al-Fageeh MB, Drioli E, Bartolo LD. Neuronal growth and differentiation on biodegradable membranes. J Tissue Eng Regen Med 2012; 9:106-17. [DOI: 10.1002/term.1618] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 07/11/2012] [Accepted: 08/25/2012] [Indexed: 12/13/2022]
Affiliation(s)
- Sabrina Morelli
- Institute of Membrane Technology, National Research Council of Italy, ITM-CNR; c/o University of Calabria; Rende CS Italy
| | - Antonella Piscioneri
- Institute of Membrane Technology, National Research Council of Italy, ITM-CNR; c/o University of Calabria; Rende CS Italy
| | - Antonietta Messina
- Institute of Membrane Technology, National Research Council of Italy, ITM-CNR; c/o University of Calabria; Rende CS Italy
- Department of Chemical Engineering and Materials; University of Calabria; Rende CS Italy
| | - Simona Salerno
- Institute of Membrane Technology, National Research Council of Italy, ITM-CNR; c/o University of Calabria; Rende CS Italy
| | - Mohamed B. Al-Fageeh
- National Centre for Biotechnology; King Abdulaziz City for Science and Technology; Riyadh Saudi Arabia
| | - Enrico Drioli
- Institute of Membrane Technology, National Research Council of Italy, ITM-CNR; c/o University of Calabria; Rende CS Italy
- Department of Chemical Engineering and Materials; University of Calabria; Rende CS Italy
- Hanyang University; WCU Energy Engineering Department; Seoul South Korea
| | - Loredana De Bartolo
- Institute of Membrane Technology, National Research Council of Italy, ITM-CNR; c/o University of Calabria; Rende CS Italy
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Farías GG, Cuitino L, Guo X, Ren X, Jarnik M, Mattera R, Bonifacino JS. Signal-mediated, AP-1/clathrin-dependent sorting of transmembrane receptors to the somatodendritic domain of hippocampal neurons. Neuron 2012; 75:810-23. [PMID: 22958822 PMCID: PMC3439821 DOI: 10.1016/j.neuron.2012.07.007] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/03/2012] [Indexed: 11/22/2022]
Abstract
Plasma membranes of the somatodendritic and axonal domains of neurons are known to have different protein compositions, but the molecular mechanisms that determine this polarized protein distribution remain poorly understood. Herein we show that somatodendritic sorting of various transmembrane receptors in rat hippocampal neurons is mediated by recognition of signals within the cytosolic domains of the proteins by the μ1A subunit of the adaptor protein-1 (AP-1) complex. This complex, in conjunction with clathrin, functions in the neuronal soma to exclude somatodendritic proteins from axonal transport carriers. Perturbation of this process affects dendritic spine morphology and decreases the number of synapses. These findings highlight the primary recognition event that underlies somatodendritic sorting and contribute to the evolving view of AP-1 as a global regulator of cell polarity.
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Affiliation(s)
- Ginny G. Farías
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Loreto Cuitino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Xiaoli Guo
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Xuefeng Ren
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Michal Jarnik
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Rafael Mattera
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
| | - Juan S. Bonifacino
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, MD 20892, USA
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29
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Russell CL, Semerdjieva S, Empson RM, Austen BM, Beesley PW, Alifragis P. Amyloid-β acts as a regulator of neurotransmitter release disrupting the interaction between synaptophysin and VAMP2. PLoS One 2012; 7:e43201. [PMID: 22905234 PMCID: PMC3419646 DOI: 10.1371/journal.pone.0043201] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 07/18/2012] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND It is becoming increasingly evident that deficits in the cortex and hippocampus at early stages of dementia in Alzheimer's disease (AD) are associated with synaptic damage caused by oligomers of the toxic amyloid-β peptide (Aβ42). However, the underlying molecular and cellular mechanisms behind these deficits are not fully understood. Here we provide evidence of a mechanism by which Aβ42 affects synaptic transmission regulating neurotransmitter release. METHODOLOGY/FINDINGS We first showed that application of 50 nM Aβ42 in cultured neurones is followed by its internalisation and translocation to synaptic contacts. Interestingly, our results demonstrate that with time, Aβ42 can be detected at the presynaptic terminals where it interacts with Synaptophysin. Furthermore, data from dissociated hippocampal neurons as well as biochemical data provide evidence that Aβ42 disrupts the complex formed between Synaptophysin and VAMP2 increasing the amount of primed vesicles and exocytosis. Finally, electrophysiology recordings in brain slices confirmed that Aβ42 affects baseline transmission. CONCLUSIONS/SIGNIFICANCE Our observations provide a necessary and timely insight into cellular mechanisms that underlie the initial pathological events that lead to synaptic dysfunction in Alzheimer's disease. Our results demonstrate a new mechanism by which Aβ42 affects synaptic activity.
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Affiliation(s)
- Claire L. Russell
- School of Biological Sciences, Royal Holloway University London, Surrey, United Kingdom
| | - Sophia Semerdjieva
- School of Biological Sciences, Royal Holloway University London, Surrey, United Kingdom
| | - Ruth M. Empson
- School of Biological Sciences, Royal Holloway University London, Surrey, United Kingdom
- Department of Physiology, University of Otago School of Medical Sciences, Dunedin, New Zealand
| | - Brian M. Austen
- Neurodegeneration Unit, Basic Medical Sciences, St George’s, University of London, Cranmer Terrace, London, United Kingdom
| | - Philip W. Beesley
- School of Biological Sciences, Royal Holloway University London, Surrey, United Kingdom
| | - Pavlos Alifragis
- School of Biological Sciences, Royal Holloway University London, Surrey, United Kingdom
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30
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Leitner DF, Connor JR. Functional roles of transferrin in the brain. Biochim Biophys Acta Gen Subj 2011; 1820:393-402. [PMID: 22138408 DOI: 10.1016/j.bbagen.2011.10.016] [Citation(s) in RCA: 111] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2011] [Revised: 10/13/2011] [Accepted: 10/24/2011] [Indexed: 12/11/2022]
Abstract
BACKGROUND Transferrin is synthesized in the brain by choroid plexus and oligodendrocytes, but only that in the choroid plexus is secreted. Transferrin is a major iron delivery protein to the brain, but the amount transcytosed across the brain microvasculature is minimal. Transferrin is the major source of iron delivery to neurons. It may deliver iron to immature oligodendrocytes but this trophic effect declines over time while iron requirements for maintaining myelination continue. Finally, transferrin may play an important role in neurodegenerative diseases through its ability to mobilize iron. SCOPE OF REVIEW The role of transferrin in maintaining brain iron homeostasis and the mechanism by which it enters the brain and delivers iron will be discussed. Its relevance to neurological disorders will also be addressed. MAJOR CONCLUSIONS Transferrin is the major iron delivery protein for neurons and the microvasculature, but has a limited role for glial cells. The main source of transferrin in the brain is likely from the choroid plexus although the concentration of transferrin at any given time in the brain includes that synthesized in oligodendrocytes. Little is known about brain iron egress or the role of transferrin in this process. GENERAL SIGNIFICANCE Neuron survival requires iron, which is predominantly delivered by transferrin. The concentration of transferrin in the cerebrospinal fluid is reflective of brain iron availability and can function as a biomarker in disease. Accumulation of iron in the brain contributes to neurodegenerative processes, thus an understanding of the role that transferrin plays in regulating brain iron homeostasis is essential. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.
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Affiliation(s)
- Dominique F Leitner
- Department of Neurosurgery, Penn State University, M.S. Hershey Medical Center, 500 University Dr., Hershey, PA 17033-0850, USA
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31
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Abstract
The formation of axon/dendrite polarity is critical for the neuron to perform its signaling function in the brain. Recent advance in our understanding of cellular and molecular mechanisms underlying the development and maintenance of neuronal polarity has been greatly facilitated by the use of the culture system of dissociated hippocampal neurons. Among many polarization-related proteins, we here focus on the mammalian LKB1, the counterpart of the C. elegans Par-4, which is an upstream regulator among six Par (partitioning-defective) genes that act as master regulators of cell polarity in different cell types across evolutionary distant species. Recent studies have identified LKB1 and its downstream targets SAD/MARK kinases (mammalian homologs of Par-1) as key regulators of neuronal polarization and axon development in cultured neurons and in developing cortical neurons in vivo. We will review the properties of and interactions among proteins in this LKB1-SAD/MARK pathway, drawing upon information obtained from both neuronal and non-neuronal systems. Due to central role of the protein kinase A-dependent phosphorylation of LKB1 in the activation of this pathway, we will review recent findings on how cAMP and cGMP signaling may serve as antagonistic second messengers for axon/dendrite development, and how these cyclic nucleotides may mediate the action of extracellular polarizing factors by modulating the activity of the LKB1-SAD/MARK pathway.
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Affiliation(s)
- Maya Shelly
- Department of Neurobiology and Behavior, State University of New York, Stony Brook, NY 11794-5230, USA.
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32
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Kwon SE, Chapman ER. Synaptophysin regulates the kinetics of synaptic vesicle endocytosis in central neurons. Neuron 2011; 70:847-54. [PMID: 21658579 DOI: 10.1016/j.neuron.2011.04.001] [Citation(s) in RCA: 320] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/01/2011] [Indexed: 01/27/2023]
Abstract
Despite being the most abundant synaptic vesicle membrane protein, the function of synaptophysin remains enigmatic. For example, synaptic transmission was reported to be completely normal in synaptophysin knockout mice; however, direct experiments to monitor the synaptic vesicle cycle have not been carried out. Here, using optical imaging and electrophysiological experiments, we demonstrate that synaptophysin is required for kinetically efficient endocytosis of synaptic vesicles in cultured hippocampal neurons. Truncation analysis revealed that distinct structural elements of synaptophysin differentially regulate vesicle retrieval during and after stimulation. Thus, synaptophysin regulates at least two phases of endocytosis to ensure vesicle availability during and after sustained neuronal activity.
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Affiliation(s)
- Sung E Kwon
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, WI 53706, USA
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33
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Nakajima K, Wu G, Sakudo A, Onodera T, Takeyama N. Distinct subcellular localization of three isoforms of insulinoma-associated protein 2β in neuroendocrine tissues. Life Sci 2011; 88:798-802. [PMID: 21362430 DOI: 10.1016/j.lfs.2011.02.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 02/10/2011] [Accepted: 02/17/2011] [Indexed: 11/29/2022]
Abstract
AIMS Insulinoma-associated protein 2β (IA-2β) is considered to play a significant role in regulated secretion. Recent studies have shown that the mouse brain expresses three major isoforms of IA-2β, named IA-2β60, IA-2β64, and IA-2β71. In this study, we analyzed the tissue-, cell- and organelle-specific distributions of IA-2β isoforms in mice. MAIN METHODS To localize IA-2β expression in mouse tissues and cells, western blot and immunohistochemical analyses were carried out. The subcellular distribution of IA-2β isoforms was assessed by sedimentation of mouse brain homogenates in a discontinuous sucrose density gradient. KEY FINDINGS IA-2β60 was abundant in the cerebrum, cerebellum, medulla oblongata, pancreas, adrenal gland, and pituitary, and in the muscular and mucosal layers of the digestive organs. In contrast, the expression of IA-2β64 and IA-2β71 was restricted to the cerebrum, cerebellum, medulla oblongata, and pituitary, and the muscular layers of the digestive organs. Immunohistochemical analysis of mouse pancreatic islets revealed that pancreatic beta cells expressed IA-2β60 exclusively, whereas alpha and delta cells expressed all three isoforms. By the sedimentation of mouse brain homogenates, it was shown that IA-2β64 and IA-2β71 were co-localized with IA-2 on secretory granules, but were absent from synaptic vesicles (SVs). On the other hand, IA-2β60 was co-localized with synaptophisin on SVs, but was absent from secretory granules. SIGNIFICANCE The tissue-, cell- and organelle-specific distributions of IA-2β isoforms suggest that IA-2β60 has a role in secretion from SVs, whereas IA-2β64 and IA-2β71 are involved in secretion from secretory granules.
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Affiliation(s)
- Kenta Nakajima
- Department of Molecular Immunology, School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo, Japan
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34
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Beug ST, Parks RJ, McBride HM, Wallace VA. Processing-dependent trafficking of Sonic hedgehog to the regulated secretory pathway in neurons. Mol Cell Neurosci 2010; 46:583-96. [PMID: 21182949 DOI: 10.1016/j.mcn.2010.12.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Revised: 11/25/2010] [Accepted: 12/09/2010] [Indexed: 01/22/2023] Open
Abstract
Neurons are an important source of the secreted morphogen Sonic hedgehog (Shh), however, little is known about neuron-specific regulation of Shh transport and secretion. To study this process, we investigated the subcellular distribution of Shh in primary neurons and differentiated cells of a neuroendocrine cell line by fluorescence microscopy and biochemical fractionation. In retinal ganglion cells, endogenous Shh was distributed as intra- and extracellular puncta at the soma, dendrites, axons and neurite terminals. Shh(+) puncta move bidirectionally and colocalize with markers of synaptic vesicles (SVs) and dense core granules. Lipid modification and proteolysis were required for Shh sorting to SVs and cell surface association. Finally, consistent with its association with regulated secretory vesicles, Shh secretion could be induced under depolarizing conditions. Taken together, these observations suggest that long-range Shh transport and signalling in neurons involves trafficking to the regulated secretory pathway and cell surface accumulation of Shh on axons and suggests a link between neuronal activity and Shh release.
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Affiliation(s)
- Shawn T Beug
- Vision Program, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, Ontario, Canada
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35
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The association of dynamin with synaptophysin regulates quantal size and duration of exocytotic events in chromaffin cells. J Neurosci 2010; 30:10683-91. [PMID: 20702699 DOI: 10.1523/jneurosci.5210-09.2010] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although synaptophysin is one of the most abundant integral proteins of synaptic vesicle membranes, its contribution to neurotransmitter release remains unclear. One possibility is that through its association with dynamin it controls the fine tuning of transmitter release. To test this hypothesis, we took advantage of amperometric measurements of quantal catecholamine release from chromaffin cells. First, we showed that synaptophysin and dynamin interact in chromaffin granule-rich fractions and that this interaction relies on the C terminal of synaptophysin. Experimental maneuvers that are predicted to disrupt the association between these two proteins, such as injection of antibodies against dynamin or synaptophysin, or peptides homologous to the C terminal of synaptophysin, increased the quantal size and duration of amperometric spikes. In contrast, the amperometric current that precedes the spike remained unchanged, indicating that synaptophysin/dynamin association does not regulate the initial fusion pore, but it appears to target a later step of exocytosis to control the amount of catecholamines released during a single vesicle fusion event.
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36
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Abstract
The norepinephrine transporter (NET) is a presynaptic plasma membrane protein that mediates reuptake of synaptically released norepinephrine. NET is also a major target for medications used for the treatment of depression, attention deficit/hyperactivity disorder, narcolepsy, and obesity. NET is regulated by numerous mechanisms, including catalytic activation and membrane trafficking. Amphetamine (AMPH), a psychostimulant and NET substrate, has also been shown to induce NET trafficking. However, neither the molecular basis nor the nature of the relevant membrane compartments of AMPH-modulated NET trafficking has been defined. Indeed, direct visualization of drug-modulated NET trafficking in neurons has yet to be demonstrated. In this study, we used a recently developed NET antibody and the presence of large presynaptic boutons in sympathetic neurons to examine basal and AMPH-modulated NET trafficking. Specifically, we establish a role for Rab11 in AMPH-induced NET trafficking. First, we found that, in cortical slices, AMPH induces a reduction in surface NET. Next, we observed AMPH-induced accumulation and colocalization of NET with Rab11a and Rab4 in presynaptic boutons of cultured neurons. Using tagged proteins, we demonstrated that NET and a truncated Rab11 effector (FIP2DeltaC2) do not redistribute in synchrony, whereas NET and wild-type Rab11a do. Analysis of various Rab11a/b mutants further demonstrates that Rab11 regulates NET trafficking. Expression of the truncated Rab11a effector (FIP2DeltaC2) attenuates endogenous Rab11 function and prevented AMPH-induced NET internalization as does GDP-locked Rab4 S22N. Our data demonstrate that AMPH leads to an increase of NET in endosomes of single boutons and varicosities in a Rab11-dependent manner.
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37
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Muretta JM, Mastick CC. How insulin regulates glucose transport in adipocytes. VITAMINS AND HORMONES 2009; 80:245-86. [PMID: 19251041 DOI: 10.1016/s0083-6729(08)00610-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Insulin stimulates glucose storage and metabolism by the tissues of the body, predominantly liver, muscle and fat. Storage in muscle and fat is controlled to a large extent by the rate of facilitative glucose transport across the plasma membrane of the muscle and fat cells. Insulin controls this transport. Exactly how remains debated. Work presented in this review focuses on the pathways responsible for the regulation of glucose transport by insulin. We present some historical work to show how the prevailing model for regulation of glucose transport by insulin was originally developed, then some more recent data challenging this model. We finish describing a unifying model for the control of glucose transport, and some very recent data illustrating potential molecular machinery underlying this regulation. This review is meant to give an overview of our current understanding of the regulation of glucose transport through the regulation of the trafficking of Glut4, highlighting important questions that remain to be answered. A more detailed treatment of specific aspects of this pathway can be found in several excellent recent reviews (Brozinick et al., 2007 Hou and Pessin, 2007; Huang and Czech, 2007;Larance et al., 2008 Sakamoto and Holman, 2008; Watson and Pessin, 2007; Zaid et al., 2008)One of the main objectives of this review is to discuss the results of the experiments measuring the kinetics of Glut4 movement between subcellular compartments in the context of our emerging model of the Glut4 trafficking pathway.
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Affiliation(s)
- Joseph M Muretta
- Department of Biochemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
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38
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Cerebellar neurons possess a vesicular compartment structurally and functionally similar to Glut4-storage vesicles from peripheral insulin-sensitive tissues. J Neurosci 2009; 29:5193-201. [PMID: 19386915 DOI: 10.1523/jneurosci.0858-09.2009] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The insulin-sensitive isoform of the glucose transporting protein, Glut4, is expressed in fat as well as in skeletal and cardiac muscle and is responsible for the effect of insulin on blood glucose clearance. Recent studies have revealed that Glut4 is also expressed in the brain, although the intracellular compartmentalization and regulation of Glut4 in neurons remains unknown. Using sucrose gradient centrifugation, immunoadsorption and immunofluorescence staining, we have shown that Glut4 in the cerebellum is localized in intracellular vesicles that have the sedimentation coefficient, the buoyant density, and the protein composition similar to the insulin-responsive Glut4-storage vesicles from fat and skeletal muscle cells. In cultured cerebellar neurons, insulin stimulates glucose uptake and causes translocation of Glut4 to the cell surface. Using 18FDG (18fluoro-2-deoxyglucose) positron emission tomography, we found that physical exercise acutely increases glucose uptake in the cerebellum in vivo. Prolonged physical exercise increases expression of the Glut4 protein in the cerebellum. Our results suggest that neurons have a novel type of translocation-competent vesicular compartment which is regulated by insulin and physical exercise similar to Glut4-storage vesicles in peripheral insulin target tissues.
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39
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Donoso M, Cancino J, Lee J, van Kerkhof P, Retamal C, Bu G, Gonzalez A, Cáceres A, Marzolo MP. Polarized traffic of LRP1 involves AP1B and SNX17 operating on Y-dependent sorting motifs in different pathways. Mol Biol Cell 2008; 20:481-97. [PMID: 19005208 DOI: 10.1091/mbc.e08-08-0805] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Low-density lipoprotein receptor-related protein 1 (LRP1) is an endocytic recycling receptor with two cytoplasmic tyrosine-based basolateral sorting signals. Here we show that during biosynthetic trafficking LRP1 uses AP1B adaptor complex to move from a post-TGN recycling endosome (RE) to the basolateral membrane. Then it recycles basolaterally from the basolateral sorting endosome (BSE) involving recognition by sorting nexin 17 (SNX17). In the biosynthetic pathway, Y(29) but not N(26) from a proximal NPXY directs LRP1 basolateral sorting from the TGN. A N(26)A mutant revealed that this NPXY motif recognized by SNX17 is required for the receptor's exit from BSE. An endocytic Y(63)ATL(66) motif also functions in basolateral recycling, in concert with an additional endocytic motif (LL(86,87)), by preventing LRP1 entry into the transcytotic apical pathway. All this sorting information operates similarly in hippocampal neurons to mediate LRP1 somatodendritic distribution regardless of the absence of AP1B in neurons. LRP1 basolateral distribution results then from spatially and temporally segregation steps mediated by recognition of distinct tyrosine-based motifs. We also demonstrate a novel function of SNX17 in basolateral/somatodendritic recycling from a different compartment than AP1B endosomes.
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Affiliation(s)
- Maribel Donoso
- Centro de Regulación Celular y Patología , Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile and the Millenium Institute for Fundamental and Applied Biology, Santiago, Chile
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40
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Abstract
ClC-3 is an intracellular chloride transport protein known to reside on endosomes and synaptic vesicles. The endogenous protein has been notoriously difficult to detect in immunohistological experiments because of the lack of reliable antibodies. Using newly generated antibodies, we now examine its expression pattern at the cellular and subcellular level. In all tissues examined, immunostaining indicated that ClC-3 is a vesicular protein, with a prominent expression in endocrine cells like adrenal chromaffin cells and pancreatic islet cells. In line with a possible function of ClC-3 in regulating vesicle trafficking or exocytosis in those secretory cells, capacitance measurements and amperometry indicated that exocytosis of large dense-core vesicles (LDCVs) was decreased in chromaffin cells from ClC-3 knock-out mice. However, immunohistochemistry complemented with subcellular fractionation showed that ClC-3 is not detectable on LDCVs of endocrine cells, but localizes to endosomes and synaptic-like microvesicles in both adrenal chromaffin and pancreatic beta cells. This observation points to an indirect influence of ClC-3 on LDCV exocytosis in chromaffin cells, possibly by affecting an intracellular trafficking step.
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41
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Santos MS, Li H, Voglmaier SM. Synaptic vesicle protein trafficking at the glutamate synapse. Neuroscience 2008; 158:189-203. [PMID: 18472224 DOI: 10.1016/j.neuroscience.2008.03.029] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 02/25/2008] [Accepted: 03/08/2008] [Indexed: 11/27/2022]
Abstract
Expression of the integral and associated proteins of synaptic vesicles is subject to regulation over time, by region, and in response to activity. The process by which changes in protein levels and isoforms result in different properties of neurotransmitter release involves protein trafficking to the synaptic vesicle. How newly synthesized proteins are incorporated into synaptic vesicles at the presynaptic bouton is poorly understood. During synaptogenesis, synaptic vesicle proteins sort through the secretory pathway and are transported down the axon in precursor vesicles that undergo maturation to form synaptic vesicles. Changes in protein content of synaptic vesicles could involve the formation of new vesicles that either mix with the previous complement of vesicles or replace them, presumably by their degradation or inactivation. Alternatively, new proteins could individually incorporate into existing synaptic vesicles, changing their functional properties. Glutamatergic vesicles likely express many of the same integral membrane proteins and share certain common mechanisms of biogenesis, recycling, and degradation with other synaptic vesicles. However, glutamatergic vesicles are defined by their ability to package glutamate for release, a property conferred by the expression of a vesicular glutamate transporter (VGLUT). VGLUTs are subject to regional, developmental, and activity-dependent changes in expression. In addition, VGLUT isoforms differ in their trafficking, which may target them to different pathways during biogenesis or after recycling, which may in turn sort them to different vesicle pools. Emerging data indicate that differences in the association of VGLUTs and other synaptic vesicle proteins with endocytic adaptors may influence their trafficking. These observations indicate that independent regulation of synaptic vesicle protein trafficking has the potential to influence synaptic vesicle protein composition, the maintenance of synaptic vesicle pools, and the release of glutamate in response to changing physiological requirements.
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Affiliation(s)
- M S Santos
- Department of Psychiatry, University of California School of Medicine, 401 Parnassus Avenue, LPPI-A101, San Francisco, CA 94143-0984, USA
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42
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Lasiecka ZM, Yap CC, Vakulenko M, Winckler B. Chapter 7 Compartmentalizing the Neuronal Plasma Membrane. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 272:303-89. [DOI: 10.1016/s1937-6448(08)01607-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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43
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Bergen JM, Park IK, Horner PJ, Pun SH. Nonviral approaches for neuronal delivery of nucleic acids. Pharm Res 2007; 25:983-98. [PMID: 17932730 PMCID: PMC2292496 DOI: 10.1007/s11095-007-9439-5] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Accepted: 08/20/2007] [Indexed: 12/23/2022]
Abstract
The delivery of therapeutic nucleic acids to neurons has the potential to treat neurological disease and spinal cord injury. While select viral vectors have shown promise as gene carriers to neurons, their potential as therapeutic agents is limited by their toxicity and immunogenicity, their broad tropism, and the cost of large-scale formulation. Nonviral vectors are an attractive alternative in that they offer improved safety profiles compared to viruses, are less expensive to produce, and can be targeted to specific neuronal subpopulations. However, most nonviral vectors suffer from significantly lower transfection efficiencies than neurotropic viruses, severely limiting their utility in neuron-targeted delivery applications. To realize the potential of nonviral delivery technology in neurons, vectors must be designed to overcome a series of extra- and intracellular barriers. In this article, we describe the challenges preventing successful nonviral delivery of nucleic acids to neurons and review strategies aimed at overcoming these challenges.
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Affiliation(s)
- Jamie M Bergen
- Bioengineering, University of Washington, Seattle, WA 98195, USA
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44
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Bonanomi D, Rusconi L, Colombo C, Benfenati F, Valtorta F. Synaptophysin I selectively specifies the exocytic pathway of synaptobrevin 2/VAMP2. Biochem J 2007; 404:525-34. [PMID: 17331077 PMCID: PMC1896278 DOI: 10.1042/bj20061907] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Biogenesis and recycling of synaptic vesicles are accompanied by sorting processes that preserve the molecular composition of the compartments involved. In the present study, we have addressed the targeting of synaptobrevin 2/VAMP2 (vesicle-associated membrane protein 2), a critical component of the synaptic vesicle--fusion machinery, in a heterotypic context where its sorting is not confounded by the presence of other neuron-specific molecules. Ectopically expressed synaptophysin I interacts with VAMP2 and alters its default surface targeting to a prominent vesicular distribution, with no effect on the targeting of other membrane proteins. Protein-protein interaction is not sufficient for the control of VAMP2 sorting, which is mediated by the C-terminal domain of synaptophysin I. Synaptophysin I directs the sorting of VAMP2 to vesicles before surface delivery, without influencing VAMP2 endocytosis. Consistent with this, dynamin and alpha-SNAP (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein) mutants which block trafficking at the plasma membrane do not abrogate the effect of synaptophysin I on VAMP2 sorting. These results indicate that the sorting determinants of synaptic vesicle proteins can operate independently of a neuronal context and implicate the association of VAMP2 with synaptophysin I in the specification of the pathway of synaptic vesicle biogenesis.
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Affiliation(s)
- Dario Bonanomi
- *San Raffaele Scientific Institute and “Vita-Salute” University, Via Olgettina 58, 20132 Milan, Italy
| | - Laura Rusconi
- *San Raffaele Scientific Institute and “Vita-Salute” University, Via Olgettina 58, 20132 Milan, Italy
| | - Chiara Agnese Colombo
- *San Raffaele Scientific Institute and “Vita-Salute” University, Via Olgettina 58, 20132 Milan, Italy
| | - Fabio Benfenati
- †Department of Neuroscience, The Italian Institute of Technology, Genova, Italy
- ‡Department of Experimental Medicine, University of Genova, Via Benedetto XV 3, 16132 Genova, Italy
| | - Flavia Valtorta
- *San Raffaele Scientific Institute and “Vita-Salute” University, Via Olgettina 58, 20132 Milan, Italy
- §The Italian Institute of Technology, Research Unit of Molecular Neuroscience, via Olgettina 58, 20132 Milan, Italy
- To whom correspondence should be addressed (email )
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45
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Nakata A, Kamiguchi H. Serine phosphorylation by casein kinase II controls endocytic L1 trafficking and axon growth. J Neurosci Res 2007; 85:723-34. [PMID: 17253643 DOI: 10.1002/jnr.21185] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The cell adhesion molecule L1 plays crucial roles in axon tract development. In vitro, L1 presented as a culture substrate stimulates axon elongation by binding to L1 expressed on the growth cone. In migrating growth cones, L1 is endocytosed via the AP-2/clathrin-mediated pathway at the central domain, followed by anterograde vesicular transport and recycling to the plasma membrane of the leading front. It has previously been shown that this endocytic trafficking of L1 is critical for axon elongation (Kamiguchi and Yoshihara [2001] J. Neurosci. 21:9194-9203). Adjacent to the AP-2 recognition site, the L1 cytoplasmic domain has a cluster of acidic amino acids containing Ser1181 that can be phosphorylated by casein kinase II (CKII; Wong et al. [1996a] J. Neurochem. 66:779-786). In this paper, we demonstrate that Ser1181 phosphorylation by CKII is implicated in both normal endocytic trafficking of L1 and L1-stimulated axon growth. Whereas L1 is sorted into transferrin-positive endosomes after endocytosis, pharmacological inhibition of CKII caused some population of L1 to be internalized into transferrin-negative compartments. Single-amino-acid mutations at Ser1181, which either prevent or mimic phosphorylation by CKII, caused similar missorting of internalized L1. Furthermore, dorsal root ganglion neurons that had been treated with a CKII inhibitor or transfected with the L1 mutants showed impaired ability to extend axons on an L1 substrate but not on other control substrates. These results demonstrate the novel role of CKII in L1-mediated axon elongation and stress the importance of functional linkage between L1 phosphorylation and L1 trafficking in migrating growth cones.
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Affiliation(s)
- Asuka Nakata
- Laboratory for Neuronal Growth Mechanisms, RIKEN Brain Science Institute, Wako, Saitama, Japan
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Voglmaier SM, Edwards RH. Do different endocytic pathways make different synaptic vesicles? Curr Opin Neurobiol 2007; 17:374-80. [PMID: 17449236 DOI: 10.1016/j.conb.2007.04.002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 04/11/2007] [Indexed: 11/23/2022]
Abstract
At a wide range of synapses, synaptic vesicles reside in distinct pools that respond to different stimuli. The recycling pool supplies the vesicles required for release in response to modest stimulation, whereas the reserve pool is mobilized only by strong stimulation. Multiple pathways have been proposed for the recycling of synaptic vesicles after exocytosis, but the relationship of these pathways to the different synaptic vesicle pools has remained unclear. Synaptic vesicle proteins have also been assumed to undergo recycling as a unit. However, emerging data indicate that differences in the association with distinct endocytic adaptors such as the heterotetrameric adaptor AP3 influence the trafficking of individual synaptic vesicle proteins, affecting the composition of synaptic vesicles and hence their functional characteristics. These observations might begin to account for differences in the properties of different vesicle pools.
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Affiliation(s)
- Susan M Voglmaier
- Department of Psychiatry, UCSF School of Medicine, 600 16th Street, San Francisco, CA 94158-2517, USA
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Rizzoli SO, Bethani I, Zwilling D, Wenzel D, Siddiqui TJ, Brandhorst D, Jahn R. Evidence for early endosome-like fusion of recently endocytosed synaptic vesicles. Traffic 2007; 7:1163-76. [PMID: 17004320 DOI: 10.1111/j.1600-0854.2006.00466.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Early endosomes are well-established acceptor compartments of endocytic vesicles in many cell types. Little evidence of their existence or function has been obtained in synapses, and it is generally believed that synaptic vesicles recycle without passing through an endosomal intermediate. We show here that the early endosomal SNARE proteins are enriched in synaptic vesicles. To investigate their function in the synapse, we isolated synaptic nerve terminals (synaptosomes), stimulated them in presence of different fluorescent markers to label the recycling vesicles and used these vesicles in in vitro fusion assays. The recently endocytosed vesicles underwent homotypic fusion. They also fused with endosomes from PC12 and BHK cells. The fusion process was dependent upon NSF activity. Moreover, fusion was dependent upon the early endosomal SNAREs but not upon the SNAREs involved in exocytosis. Our results thus show that at least a fraction of the vesicles endocytosed during synaptic activity are capable of fusing with early endosomes and lend support to an involvement of endosomal intermediates during recycling of synaptic vesicles.
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Affiliation(s)
- Silvio O Rizzoli
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg, 37077 Göttingen, Germany
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48
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Bonanomi D, Benfenati F, Valtorta F. Protein sorting in the synaptic vesicle life cycle. Prog Neurobiol 2006; 80:177-217. [PMID: 17074429 DOI: 10.1016/j.pneurobio.2006.09.002] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Revised: 09/14/2006] [Accepted: 09/18/2006] [Indexed: 01/06/2023]
Abstract
At early stages of differentiation neurons already contain many of the components necessary for synaptic transmission. However, in order to establish fully functional synapses, both the pre- and postsynaptic partners must undergo a process of maturation. At the presynaptic level, synaptic vesicles (SVs) must acquire the highly specialized complement of proteins, which make them competent for efficient neurotransmitter release. Although several of these proteins have been characterized and linked to precise functions in the regulation of the SV life cycle, a systematic and unifying view of the mechanisms underlying selective protein sorting during SV biogenesis remains elusive. Since SV components do not share common sorting motifs, their targeting to SVs likely relies on a complex network of protein-protein and protein-lipid interactions, as well as on post-translational modifications. Pleiomorphic carriers containing SV proteins travel and recycle along the axon in developing neurons. Nevertheless, SV components appear to eventually undertake separate trafficking routes including recycling through the neuronal endomembrane system and the plasmalemma. Importantly, SV biogenesis does not appear to be limited to a precise stage during neuronal differentiation, but it rather continues throughout the entire neuronal lifespan and within synapses. At nerve terminals, remodeling of the SV membrane results from the use of alternative exocytotic pathways and possible passage through as yet poorly characterized vacuolar/endosomal compartments. As a result of both processes, SVs with heterogeneous molecular make-up, and hence displaying variable competence for exocytosis, may be generated and coexist within the same nerve terminal.
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Affiliation(s)
- Dario Bonanomi
- Department of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
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Liang YJ, Wu DF, Yang LQ, Höllt V, Koch T. Interaction of the mu-opioid receptor with synaptophysin influences receptor trafficking and signaling. Mol Pharmacol 2006; 71:123-31. [PMID: 17005904 DOI: 10.1124/mol.106.026062] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
There is increasing evidence that the signal transduction of opioid receptors is modulated by receptor-associated proteins. In the search for proteins regulating mu-opioid receptor (MOPr) endocytosis, synaptophysin was found to bind to the rat micro-opioid receptor in yeast two-hybrid assay. Coimmunoprecipitation experiments and bioluminescence resonance energy transfer assays confirmed that the micro-opioid receptor constitutively interacts with synaptophysin in human embryonic kidney 293 cells overexpressing MOPr and synaptophysin. In this study, we show that overexpression of synaptophysin enhances the micro-opioid receptor endocytosis. One explanation for the observed effects is that synaptophysin recruits dynamin to the plasma membrane, facilitating fission of clathrin-coated vesicles. This suggestion is supported by our finding that overexpression of a synaptophysin truncation mutant, which breaks the interaction between synaptophysin and dynamin, prevents agonist-mediated micro-opioid receptor endocytosis. In addition, the synaptophysin-augmented micro-opioid receptor trafficking leads to attenuated agonist-induced receptor desensitization and faster receptor resensitization. Taken together, our findings strongly suggest that synaptophysin plays an important role in the regulation of micro-opioid receptor trafficking and signaling.
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Affiliation(s)
- Ying-Jian Liang
- Department of Pharmacology and Toxicology, Otto-von-Guericke University, Leipziger Str. 44, 39120 Magdeburg, Germany
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Abstract
Neurons are among the largest and most complex cells in the body. Their immense size and intricate geometry pose many unique cell-biological problems. How is dendritic architecture established and maintained? How do neurons traffic newly synthesized integral membrane proteins over such long distances to synapses? Functionally, protein trafficking to and from the postsynaptic membrane has emerged as a key mechanism underlying various forms of synaptic plasticity. Which organelles are involved in postsynaptic trafficking, and how do they integrate and respond to activity at individual synapses? Here we review what is currently known about long-range trafficking of newly synthesized postsynaptic proteins as well as the local rules that govern postsynaptic trafficking at individual synapses.
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Affiliation(s)
- Matthew J Kennedy
- Howard Hughes Medical Institute, Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
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