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Longhena F, Faustini G, Brembati V, Pizzi M, Benfenati F, Bellucci A. An updated reappraisal of synapsins: structure, function and role in neurological and psychiatric disorders. Neurosci Biobehav Rev 2021; 130:33-60. [PMID: 34407457 DOI: 10.1016/j.neubiorev.2021.08.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 07/29/2021] [Accepted: 08/09/2021] [Indexed: 01/02/2023]
Abstract
Synapsins (Syns) are phosphoproteins strongly involved in neuronal development and neurotransmitter release. Three distinct genes SYN1, SYN2 and SYN3, with elevated evolutionary conservation, have been described to encode for Synapsin I, Synapsin II and Synapsin III, respectively. Syns display a series of common features, but also exhibit distinctive localization, expression pattern, post-translational modifications (PTM). These characteristics enable their interaction with other synaptic proteins, membranes and cytoskeletal components, which is essential for the proper execution of their multiple functions in neuronal cells. These include the control of synapse formation and growth, neuron maturation and renewal, as well as synaptic vesicle mobilization, docking, fusion, recycling. Perturbations in the balanced expression of Syns, alterations of their PTM, mutations and polymorphisms of their encoding genes induce severe dysregulations in brain networks functions leading to the onset of psychiatric or neurological disorders. This review presents what we have learned since the discovery of Syn I in 1977, providing the state of the art on Syns structure, function, physiology and involvement in central nervous system disorders.
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Affiliation(s)
- Francesca Longhena
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Gaia Faustini
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Viviana Brembati
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Marina Pizzi
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
| | - Fabio Benfenati
- Italian Institute of Technology, Via Morego 30, Genova, Italy; IRCSS Policlinico San Martino Hospital, Largo Rosanna Benzi 10, 16132, Genova, Italy.
| | - Arianna Bellucci
- Division of Pharmacology, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy; Laboratory for Preventive and Personalized Medicine, Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy.
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Chouchane M, Melo de Farias AR, Moura DMDS, Hilscher MM, Schroeder T, Leão RN, Costa MR. Lineage Reprogramming of Astroglial Cells from Different Origins into Distinct Neuronal Subtypes. Stem Cell Reports 2017; 9:162-176. [PMID: 28602612 PMCID: PMC5511102 DOI: 10.1016/j.stemcr.2017.05.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 05/08/2017] [Accepted: 05/09/2017] [Indexed: 12/20/2022] Open
Abstract
Astroglial cells isolated from the rodent postnatal cerebral cortex are particularly susceptible to lineage reprogramming into neurons. However, it remains unknown whether other astroglial populations retain the same potential. Likewise, little is known about the fate of induced neurons (iNs) in vivo. In this study we addressed these questions using two different astroglial populations isolated from the postnatal brain reprogrammed either with Neurogenin-2 (Neurog2) or Achaete scute homolog-1 (Ascl1). We show that cerebellum (CerebAstro) and cerebral cortex astroglia (CtxAstro) generates iNs with distinctive neurochemical and morphological properties. Both astroglial populations contribute iNs to the olfactory bulb following transplantation in the postnatal and adult mouse subventricular zone. However, only CtxAstro transfected with Neurog2 differentiate into pyramidal-like iNs after transplantation in the postnatal cerebral cortex. Altogether, our data indicate that the origin of the astroglial population and transcription factors used for reprogramming, as well as the region of integration, affect the fate of iNs.
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Affiliation(s)
- Malek Chouchane
- Brain Institute, Federal University of Rio Grande do Norte, Natal 59056-450, Brazil
| | | | | | | | - Timm Schroeder
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, 4058 Basel, Switzerland
| | | | - Marcos Romualdo Costa
- Brain Institute, Federal University of Rio Grande do Norte, Natal 59056-450, Brazil.
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Mackenzie KD, Lumsden AL, Guo F, Duffield MD, Chataway T, Lim Y, Zhou XF, Keating DJ. Huntingtin-associated protein-1 is a synapsin I-binding protein regulating synaptic vesicle exocytosis and synapsin I trafficking. J Neurochem 2016; 138:710-21. [PMID: 27315547 DOI: 10.1111/jnc.13703] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 06/14/2016] [Accepted: 06/15/2016] [Indexed: 12/27/2022]
Abstract
Huntingtin-associated protein-1 (HAP1) is involved in intracellular trafficking, vesicle transport, and membrane receptor endocytosis. However, despite such diverse functions, the role of HAP1 in the synaptic vesicle (SV) cycle in nerve terminals remains unclear. Here, we report that HAP1 functions in SV exocytosis, controls total SV turnover and the speed of vesicle fusion in nerve terminals and regulates glutamate release in cortical brain slices. We found that HAP1 interacts with synapsin I, an abundant neuronal phosphoprotein that associates with SVs during neurotransmitter release and regulates synaptic plasticity and neuronal development. The interaction between HAP1 with synapsin I was confirmed by reciprocal co-immunoprecipitation of the endogenous proteins. Furthermore, HAP1 co-localizes with synapsin I in cortical neurons as discrete puncta. Interestingly, we find that synapsin I localization is specifically altered in Hap1(-/-) cortical neurons without an effect on the localization of other SV proteins. This effect on synapsin I localization was not because of changes in the levels of synapsin I or its phosphorylation status in Hap1(-/-) brains. Furthermore, fluorescence recovery after photobleaching in transfected neurons expressing enhanced green fluorescent protein-synapsin Ia demonstrates that loss of HAP1 protein inhibits synapsin I transport. Thus, we demonstrate that HAP1 regulates SV exocytosis and may do so through binding to synapsin I. The Proposed mechanism of synapsin I transport mediated by HAP1 in neurons. HAP1 interacts with synapsin I, regulating the trafficking of synapsin I containing vesicles and/or transport packets, possibly through its engagement of microtubule motors. The absence of HAP1 reduces synapsin I transport and neuronal exocytosis. These findings provide insights into the processes of neuronal trafficking and synaptic signaling.
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Affiliation(s)
- Kimberly D Mackenzie
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia
| | - Amanda L Lumsden
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia
| | - Feng Guo
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia
| | - Michael D Duffield
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia
| | - Timothy Chataway
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia
| | - Yoon Lim
- Sansom Institute, University of South Australia, Adelaide, South Australia, Australia
| | - Xin-Fu Zhou
- Sansom Institute, University of South Australia, Adelaide, South Australia, Australia
| | - Damien J Keating
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia.,South Australian Health and Medical Research Institute, Adelaide, South Australia, Australia
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Bonifacino T, Musazzi L, Milanese M, Seguini M, Marte A, Gallia E, Cattaneo L, Onofri F, Popoli M, Bonanno G. Altered mechanisms underlying the abnormal glutamate release in amyotrophic lateral sclerosis at a pre-symptomatic stage of the disease. Neurobiol Dis 2016; 95:122-33. [PMID: 27425885 DOI: 10.1016/j.nbd.2016.07.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 07/08/2016] [Accepted: 07/13/2016] [Indexed: 01/29/2023] Open
Abstract
Abnormal Glu release occurs in the spinal cord of SOD1(G93A) mice, a transgenic animal model for human ALS. Here we studied the mechanisms underlying Glu release in spinal cord nerve terminals of SOD1(G93A) mice at a pre-symptomatic disease stage (30days) and found that the basal release of Glu was more elevated in SOD1(G93A) with respect to SOD1 mice, and that the surplus of release relies on synaptic vesicle exocytosis. Exposure to high KCl or ionomycin provoked Ca(2+)-dependent Glu release that was likewise augmented in SOD1(G93A) mice. Equally, the Ca(2+)-independent hypertonic sucrose-induced Glu release was abnormally elevated in SOD1(G93A) mice. Also in this case, the surplus of Glu release was exocytotic in nature. We could determine elevated cytosolic Ca(2+) levels, increased phosphorylation of Synapsin-I, which was causally related to the abnormal Glu release measured in spinal cord synaptosomes of pre-symptomatic SOD1(G93A) mice, and increased phosphorylation of glycogen synthase kinase-3 at the inhibitory sites, an event that favours SNARE protein assembly. Western blot experiments revealed an increased number of SNARE protein complexes at the nerve terminal membrane, with no changes of the three SNARE proteins and increased expression of synaptotagmin-1 and β-Actin, but not of an array of other release-related presynaptic proteins. These results indicate that the abnormal exocytotic Glu release in spinal cord of pre-symptomatic SOD1(G93A) mice is mainly based on the increased size of the readily releasable pool of vesicles and release facilitation, supported by plastic changes of specific presynaptic mechanisms.
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Affiliation(s)
- Tiziana Bonifacino
- Department of Pharmacy, Unit of Pharmacology and Toxicology, and Center of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy.
| | - Laura Musazzi
- Department of Pharmacological and Biomolecular Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, 20133 Milan, Italy.
| | - Marco Milanese
- Department of Pharmacy, Unit of Pharmacology and Toxicology, and Center of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy.
| | - Mara Seguini
- Department of Pharmacological and Biomolecular Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, 20133 Milan, Italy.
| | - Antonella Marte
- Department of Experimental Medicine, Unit of Human Physiology, University of Genoa, Viale Benedetto XV, 16132 Genoa, Italy.
| | - Elena Gallia
- Department of Pharmacy, Unit of Pharmacology and Toxicology, and Center of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy.
| | - Luca Cattaneo
- Department of Pharmacy, Unit of Pharmacology and Toxicology, and Center of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy.
| | - Franco Onofri
- Department of Experimental Medicine, Unit of Human Physiology, University of Genoa, Viale Benedetto XV, 16132 Genoa, Italy.
| | - Maurizio Popoli
- Department of Pharmacological and Biomolecular Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, 20133 Milan, Italy.
| | - Giambattista Bonanno
- Department of Pharmacy, Unit of Pharmacology and Toxicology, and Center of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy.
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Zheng BW, Yang L, Dai XL, Jiang ZF, Huang HC. Roles of O-GlcNAcylation on amyloid-β precursor protein processing, tau phosphorylation, and hippocampal synapses dysfunction in Alzheimer’s disease. Neurol Res 2016; 38:177-86. [DOI: 10.1080/01616412.2015.1133485] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Nikolaev M, Heggelund P. Functions of synapsins in corticothalamic facilitation: important roles of synapsin I. J Physiol 2015; 593:4499-510. [PMID: 26256545 DOI: 10.1113/jp270553] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 08/04/2015] [Indexed: 12/15/2022] Open
Abstract
KEY POINTS The synaptic vesicle associated proteins synapsin I and synapsin II have important functions in synaptic short-term plasticity. We investigated their functions in cortical facilitatory feedback to neurons in dorsal lateral geniculate nucleus (dLGN), feedback that has important functions in state-dependent regulation of thalamic transmission of visual input to cortex. We compared results from normal wild-type (WT) mice and synapsin knockout (KO) mice in several types of synaptic plasticity, and found clear differences between the responses of neurons in the synapsin I KO and the WT, but no significant differences between the synapsin II KO and the WT. These results are in contrast to the important role of synapsin II previously demonstrated in similar types of synaptic plasticity in other brain regions, indicating that the synapsins can have different roles in similar types of STP in different parts of the brain. ABSTRACT The synaptic vesicle associated proteins synapsin I (SynI) and synapsin II (SynII) have important functions in several types of synaptic short-term plasticity in the brain, but their separate functions in different types of synapses are not well known. We investigated possible distinct functions of the two synapsins in synaptic short-term plasticity at corticothalamic synapses on relay neurons in the dorsal lateral geniculate nucleus. These synapses provide excitatory feedback from visual cortex to the relay cells, feedback that can facilitate transmission of signals from retina to cortex. We compared results from normal wild-type (WT), SynI knockout (KO) and SynII KO mice, in three types of synaptic plasticity mainly linked to presynaptic mechanism. In SynI KO mice, paired-pulse stimulation elicited increased facilitation at short interpulse intervals compared to the WT. Pulse-train stimulation elicited weaker facilitation than in the WT, and also post-tetanic potentiation was weaker in SynI KO than in the WT. Between SynII KO and the WT we found no significant differences. Thus, SynI has important functions in these types of synaptic plasticity at corticothalamic synapses. Interestingly, our data are in contrast to the important role of SynII previously shown for sustained synaptic transmission during intense stimulation in excitatory synapses in other parts of the brain, and our results suggest that SynI and SynII may have different roles in similar types of STP in different parts of the brain.
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Affiliation(s)
- Maxim Nikolaev
- Institute of Basic Medical Sciences, University of Oslo, N-0317, Oslo, Norway.,I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry RAS, 194223, 44 Thorez pr., St Petersburg, Russia
| | - Paul Heggelund
- Institute of Basic Medical Sciences, University of Oslo, N-0317, Oslo, Norway
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Ketzef M, Gitler D. Epileptic synapsin triple knockout mice exhibit progressive long-term aberrant plasticity in the entorhinal cortex. ACTA ACUST UNITED AC 2012; 24:996-1008. [PMID: 23236212 DOI: 10.1093/cercor/bhs384] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Studying epileptogenesis in a genetic model can facilitate the identification of factors that promote the conversion of a normal brain into one chronically prone to seizures. Synapsin triple-knockout (TKO) mice exhibit adult-onset epilepsy, thus allowing the characterization of events as preceding or following seizure onset. Although it has been proposed that a congenital reduction in inhibitory transmission is the underlying cause for epilepsy in these mice, young TKO mice are asymptomatic. We report that the genetic lesion exerts long-term progressive effects that extend well into adulthood. Although inhibitory transmission is initially reduced, it is subsequently strengthened relative to its magnitude in control mice, so that the excitation to inhibition balance in adult TKOs is inverted in favor of inhibition. In parallel, we observed long-term alterations in synaptic depression kinetics of excitatory transmission and in the extent of tonic inhibition, illustrating adaptations in synaptic properties. Moreover, age-dependent acceleration of the action potential did not occur in TKO cortical pyramidal neurons, suggesting wide-ranging secondary changes in brain excitability. In conclusion, although congenital impairments in inhibitory transmission may initiate epileptogenesis in the synapsin TKO mice, we suggest that secondary adaptations are crucial for the establishment of this epileptic network.
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Affiliation(s)
- Maya Ketzef
- Department of Physiology and Cell Biology, Faculty of Health Sciences and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
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Synapsins contribute to the dynamic spatial organization of synaptic vesicles in an activity-dependent manner. J Neurosci 2012; 32:12214-27. [PMID: 22933803 DOI: 10.1523/jneurosci.1554-12.2012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The precise subcellular organization of synaptic vesicles (SVs) at presynaptic sites allows for rapid and spatially restricted exocytotic release of neurotransmitter. The synapsins (Syns) are a family of presynaptic proteins that control the availability of SVs for exocytosis by reversibly tethering them to each other and to the actin cytoskeleton in a phosphorylation-dependent manner. Syn ablation leads to reduction in the density of SV proteins in nerve terminals and increased synaptic fatigue under high-frequency stimulation, accompanied by the development of an epileptic phenotype. We analyzed cultured neurons from wild-type and Syn I,II,III(-/-) triple knock-out (TKO) mice and found that SVs were severely dispersed in the absence of Syns. Vesicle dispersion did not affect the readily releasable pool of SVs, whereas the total number of SVs was considerably reduced at synapses of TKO mice. Interestingly, dispersion apparently involved exocytosis-competent SVs as well; it was not affected by stimulation but was reversed by chronic neuronal activity blockade. Altogether, these findings indicate that Syns are essential to maintain the dynamic structural organization of synapses and the size of the reserve pool of SVs during intense SV recycling, whereas an additional Syn-independent mechanism, whose molecular substrate remains to be clarified, targets SVs to synaptic boutons at rest and might be outpaced by activity.
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Wendt A, Speidel D, Danielsson A, Esguerra JLS, Bogen IL, Walaas SI, Salehi A, Eliasson L. Synapsins I and II are not required for insulin secretion from mouse pancreatic β-cells. Endocrinology 2012; 153:2112-9. [PMID: 22334712 DOI: 10.1210/en.2011-1702] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Synapsins are a family of phosphoproteins that modulate the release of neurotransmitters from synaptic vesicles. The release of insulin from pancreatic β-cells has also been suggested to be regulated by synapsins. In this study, we have utilized a knock out mouse model with general disruptions of the synapsin I and II genes [synapsin double knockout (DKO)]. Stimulation with 20 mm glucose increased insulin secretion 9-fold in both wild-type (WT) and synapsin DKO islets, whereas secretion in the presence of 70 mm K(+) and 1 mm glucose was significantly enhanced in the synapsin DKO mice compared to WT. Exocytosis in single β-cells was investigated using patch clamp. The exocytotic response, measured by capacitance measurements and elicited by a depolarization protocol designed to visualize exocytosis of vesicles from the readily releasable pool and from the reserve pool, was of the same size in synapsin DKO and WT β-cells. The increase in membrane capacitance corresponding to readily releasable pool was approximately 50fF in both genotypes. We next investigated the voltage-dependent Ca(2+) influx. In both WT and synapsin DKO β-cells the Ca(2+) current peaked at 0 mV and measured peak current (I(p)) and net charge (Q) were of similar magnitude. Finally, ultrastructural data showed no variation in total number of granules (N(v)) or number of docked granules (N(s)) between the β-cells from synapsin DKO mice and WT control. We conclude that neither synapsin I nor synapsin II are directly involved in the regulation of glucose-stimulated insulin secretion and Ca(2)-dependent exocytosis in mouse pancreatic β-cells.
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Affiliation(s)
- Anna Wendt
- Lund University Diabetes Centre, Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University, 20502 Malmö, Sweden.
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Orenbuch A, Ayelet O, Shulman Y, Yoav S, Lipstein N, Noa L, Bechar A, Amit B, Lavy Y, Yotam L, Brumer E, Eliaz B, Vasileva M, Mariya V, Kahn J, Joy K, Barki-Harrington L, Liza BH, Kuner T, Thomas K, Gitler D, Daniel G. Inhibition of exocytosis or endocytosis blocks activity-dependent redistribution of synapsin. J Neurochem 2011; 120:248-58. [PMID: 22066784 DOI: 10.1111/j.1471-4159.2011.07579.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The synaptic vesicle cycle encompasses the pre-synaptic events that drive neurotransmission. Influx of calcium leads to the fusion of synaptic vesicles with the plasma membrane and the release of neurotransmitter, closely followed by endocytosis. Vacated release sites are repopulated with vesicles which are then primed for release. When activity is intense, reserve vesicles may be mobilized to counteract an eventual decline in transmission. Recently, interplay between endocytosis and repopulation of the readily releasable pool of vesicles has been identified. In this study, we show that exo-endocytosis is necessary to enable detachment of synapsin from reserve pool vesicles during synaptic activity. We report that blockage of exocytosis in cultured mouse hippocampal neurons, either by tetanus toxin or by the deletion of munc13, inhibits the activity-dependent redistribution of synapsin from the pre-synaptic terminal into the axon. Likewise, perturbation of endocytosis with dynasore or by a dynamin dominant-negative mutant fully prevents synapsin redistribution. Such inhibition of synapsin redistribution occurred despite the efficient phosphorylation of synapsin at its protein kinase A/CaMKI site, indicating that disengagement of synapsin from the vesicles requires exocytosis and endocytosis in addition to phosphorylation. Our results therefore reveal hitherto unidentified feedback within the synaptic vesicle cycle involving the synapsin-managed reserve pool.
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Affiliation(s)
- Ayelet Orenbuch
- Department of Physiology and Neurobiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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Fassio A, Raimondi A, Lignani G, Benfenati F, Baldelli P. Synapsins: from synapse to network hyperexcitability and epilepsy. Semin Cell Dev Biol 2011; 22:408-15. [PMID: 21816229 DOI: 10.1016/j.semcdb.2011.07.005] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Accepted: 07/13/2011] [Indexed: 01/31/2023]
Abstract
The synapsin family in mammals consists of at least 10 isoforms encoded by three distinct genes and composed by a mosaic of conserved and variable domains. Synapsins, although not essential for the basic development and functioning of neuronal networks, are extremely important for the fine-tuning of SV cycling and neuronal plasticity. Single, double and triple synapsin knockout mice, with the notable exception of the synapsin III knockout mice, show a severe epileptic phenotype without gross alterations in brain morphology and connectivity. However, the molecular and physiological mechanisms underlying the pathogenesis of the epileptic phenotype observed in synapsin deficient mice are still far from being elucidated. In this review, we summarize the current knowledge about the role of synapsins in the regulation of network excitability and about the molecular mechanism leading to epileptic phenotype in mouse lines lacking one or more synapsin isoforms. The current evidences indicate that synapsins exert distinct roles in excitatory versus inhibitory synapses by differentially affecting crucial steps of presynaptic physiology and by this mean participate in the determination of network hyperexcitability.
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Affiliation(s)
- Anna Fassio
- Department of Experimental Medicine, Section of Physiology and National Institute of Neuroscience, University of Genova, Genova, Italy
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Bogen IL, Jensen V, Hvalby Ø, Walaas SI. Glutamatergic neurotransmission in the synapsin I and II double knock-out mouse. Semin Cell Dev Biol 2011; 22:400-7. [DOI: 10.1016/j.semcdb.2011.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Accepted: 07/13/2011] [Indexed: 01/19/2023]
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Etholm L, Lindén H, Eken T, Heggelund P. Electroencephalographic characterization of seizure activity in the synapsin I/II double knockout mouse. Brain Res 2011; 1383:270-88. [DOI: 10.1016/j.brainres.2011.01.070] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2010] [Revised: 01/20/2011] [Accepted: 01/20/2011] [Indexed: 10/18/2022]
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Milanese M, Zappettini S, Onofri F, Musazzi L, Tardito D, Bonifacino T, Messa M, Racagni G, Usai C, Benfenati F, Popoli M, Bonanno G. Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis. J Neurochem 2011; 116:1028-42. [PMID: 21175617 DOI: 10.1111/j.1471-4159.2010.07155.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Glutamate-mediated excitotoxicity plays a major role in the degeneration of motor neurons in amyotrophic lateral sclerosis and reduced astrocytary glutamate transport, which in turn increases the synaptic availability of the amino acid neurotransmitter, was suggested as a cause. Alternatively, here we report our studies on the exocytotic release of glutamate as a possible source of excessive glutamate transmission. The basal glutamate efflux from spinal cord nerve terminals of mice-expressing human soluble superoxide dismutase (SOD1) with the G93A mutation [SOD1/G93A(+)], a transgenic model of amyotrophic lateral sclerosis, was elevated when compared with transgenic mice expressing the wild-type human SOD1 or to non-transgenic controls. Exposure to 15 mM KCl or 0.3 μM ionomycin provoked Ca(2+)-dependent glutamate release that was dramatically increased in late symptomatic and in pre-symptomatic SOD1/G93A(+) mice. Increased Ca(2+) levels were detected in SOD1/G93A(+) mouse spinal cord nerve terminals, accompanied by increased activation of Ca(2+)/calmodulin-dependent kinase II and increased phosphorylation of synapsin I. In line with these findings, release experiments suggested that the glutamate release augmentation involves the readily releasable pool of vesicles and a greater capability of these vesicles to fuse upon stimulation in SOD1/G93A(+) mice.
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Affiliation(s)
- Marco Milanese
- Department of Experimental Medicine, University of Genova, Genova, Italy
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Hvalby O, Jensen V, Kao HT, Walaas SI. Synapsin-dependent vesicle recruitment modulated by forskolin, phorbol ester and ca in mouse excitatory hippocampal synapses. Front Synaptic Neurosci 2010; 2:152. [PMID: 21423538 PMCID: PMC3059703 DOI: 10.3389/fnsyn.2010.00152] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2010] [Accepted: 12/09/2010] [Indexed: 12/03/2022] Open
Abstract
Repeated release of transmitter from presynaptic elements depends on stimulus-induced Ca2+ influx together with recruitment and priming of synaptic vesicles from different vesicle pools. We have compared three different manipulations of synaptic strength, all of which are known to increase short-term synaptic efficacy through presynaptic mechanisms, in the glutamatergic CA3-to-CA1 stratum radiatum synapse in the mouse hippocampal slice preparation. Synaptic responses elicited from the readily releasable vesicle pool during low-frequency synaptic activation (0.1 Hz) were significantly enhanced by both the adenylate cyclase activator forskolin, the priming activator β-phorbol-12,13-dibutyrate (PDBu) and 4 mM [Ca2+]o′ whereas during 20 Hz stimulation, the same manipulations reduced the time needed to reach the peak and increased the magnitude of the resulting frequency facilitation. In contrast, paired-pulse facilitations were unchanged in the presence of forskolin, decreased by 4 mM [Ca2+]o and essentially abolished by PDBu. The subsequent delayed response enhancement (DRE) responses, elicited during continuous 20 Hz stimulations and mediated by recruited vesicles, were enhanced by forskolin, essentially unchanged by PDBu and slightly decreased by 4 mM [Ca2+]o· Similar experiments done on slices devoid of the vesicle-associated synapsin I and II proteins indicated that synapsin I/II-induced enhancements of vesicle recruitment were restricted to Ca2+-induced frequency facilitations and forskolin-induced enhancements of the early DRE phase, whereas the proteins had minor effects during PDBu-treatment and represented constraints on late Ca2+-induced responses. The data indicate that in these glutamatergic synapses, the comparable enhancements of single synaptic responses induced by these biochemical mechanisms can be transformed during prolonged synaptic stimulation into highly distinct short-term plasticity patterns, which are partly dependent on synapsins I/II.
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Affiliation(s)
- Oivind Hvalby
- Institute of Basic Medical Sciences, University of Oslo Oslo, Norway
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Bogen IL, Risa Ø, Haug KH, Sonnewald U, Fonnum F, Walaas SI. Distinct changes in neuronal and astrocytic amino acid neurotransmitter metabolism in mice with reduced numbers of synaptic vesicles. J Neurochem 2010; 105:2524-34. [PMID: 18346203 DOI: 10.1111/j.1471-4159.2008.05344.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The relations between glutamate and GABA concentrations and synaptic vesicle density in nerve terminals were examined in an animal model with 40-50% reduction in synaptic vesicle numbers caused by inactivation of the genes encoding synapsin I and II. Concentrations and synthesis of amino acids were measured in extracts from cerebrum and a crude synaptosomal fraction by HPLC and (13)C nuclear magnetic resonance spectroscopy (NMRS), respectively. Analysis of cerebrum extracts, comprising both neurotransmitter and metabolic pools, showed decreased concentration of GABA, increased concentration of glutamine and unchanged concentration of glutamate in synapsin I and II double knockout (DKO) mice. In contrast, both glutamate and GABA concentrations were decreased in crude synaptosomes isolated from synapsin DKO mice, suggesting that the large metabolic pool of glutamate in the cerebral extracts may overshadow minor changes in the transmitter pool. (13)C NMRS studies showed that the changes in amino acid concentrations in the synapsin DKO mice were caused by decreased synthesis of GABA (20-24%) in cerebral neurons and increased synthesis of glutamine (36%) in astrocytes. In a crude synaptosomal fraction, the glutamate synthesis was reduced (24%), but this reduction could not be detected in cerebrum extracts. We suggest that lack of synaptic vesicles causes down-regulation of neuronal GABA and glutamate synthesis, with a concomitant increase in astrocytic synthesis of glutamine, in order to maintain normal neurotransmitter concentrations in the nerve terminal cytosol.
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Affiliation(s)
- Inger Lise Bogen
- Department of Biochemistry, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Oslo, Norway.
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17
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Cao D, Kevala K, Kim J, Moon HS, Jun SB, Lovinger D, Kim HY. Docosahexaenoic acid promotes hippocampal neuronal development and synaptic function. J Neurochem 2009; 111:510-21. [PMID: 19682204 DOI: 10.1111/j.1471-4159.2009.06335.x] [Citation(s) in RCA: 251] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Docosahexaenoic acid (DHA, 22:6n-3), the major polyunsaturated fatty acid accumulated in the brain during development, has been implicated in learning and memory, but underlying cellular mechanisms are not clearly understood. Here, we demonstrate that DHA significantly affects hippocampal neuronal development and synaptic function in developing hippocampi. In embryonic neuronal cultures, DHA supplementation uniquely promoted neurite growth, synapsin puncta formation and synaptic protein expression, particularly synapsins and glutamate receptors. In DHA-supplemented neurons, spontaneous synaptic activity was significantly increased, mostly because of enhanced glutamatergic synaptic activity. Conversely, hippocampal neurons from DHA-depleted fetuses showed inhibited neurite growth and synaptogenesis. Furthermore, n-3 fatty acid deprivation during development resulted in marked decreases of synapsins and glutamate receptor subunits in the hippocampi of 18-day-old pups with concomitant impairment of long-term potentiation, a cellular mechanism underlying learning and memory. While levels of synapsins and NMDA receptor subunit NR2A were decreased in most hippocampal regions, NR2A expression was particularly reduced in CA3, suggesting possible role of DHA in CA3-NMDA receptor-dependent learning and memory processes. The DHA-induced neurite growth, synaptogenesis, synapsin, and glutamate receptor expression, and glutamatergic synaptic function may represent important cellular aspects supporting the hippocampus-related cognitive function improved by DHA.
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Affiliation(s)
- Dehua Cao
- Laboratory of Molecular Signaling, DICBR, NIAAA, NIH, Bethesda, Maryland 20892-9410, USA
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18
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The importance of synapsin I and II for neurotransmitter levels and vesicular storage in cholinergic, glutamatergic and GABAergic nerve terminals. Neurochem Int 2009; 55:13-21. [DOI: 10.1016/j.neuint.2009.02.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Revised: 02/14/2009] [Accepted: 02/16/2009] [Indexed: 11/20/2022]
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Abstract
Synapsins regulate synaptic transmission by controlling the reserve pool of synaptic vesicles. Each of the three mammalian synapsin genes is subject to alternative splicing, yielding several isoforms whose roles are unknown. To investigate the function of these isoforms, we examined the synaptic effects of introducing each isoform into glutamatergic cultured hippocampal neurons from synapsin triple knock-out mice. Remarkably, we found that synapsin IIa was the only isoform that could rescue the synaptic depression phenotype of the triple knock-out mice; other isoforms examined, including the well-studied synapsin Ia isoform, had no significant effect on the kinetics of synaptic depression. The slowing of synaptic depression by synapsin IIa was quantitatively paralleled by an increase in the density of reserve pool synaptic vesicles, as measured either by fluorescent tagging of the vesicle protein synaptobrevin-2 or by staining with the styryl dye FM4-64 [N-(3-triethylammoniumpropyl)-4-(6-(4-diethylamino)phenyl)-hexatrienyl)pyridinium dibromide]. Our results provide further support for the hypothesis that synapsins define the kinetics of synaptic depression at glutamatergic synapses by controlling the size of the vesicular reserve pool and identify synapsin IIa as the isoform primarily responsible for this task.
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Chiappalone M, Casagrande S, Tedesco M, Valtorta F, Baldelli P, Martinoia S, Benfenati F. Opposite Changes in Glutamatergic and GABAergic Transmission Underlie the Diffuse Hyperexcitability of Synapsin I–Deficient Cortical Networks. Cereb Cortex 2008; 19:1422-39. [DOI: 10.1093/cercor/bhn182] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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21
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Tallent MK, Varghis N, Skorobogatko Y, Hernandez-Cuebas L, Whelan K, Vocadlo DJ, Vosseller K. In vivo modulation of O-GlcNAc levels regulates hippocampal synaptic plasticity through interplay with phosphorylation. J Biol Chem 2008; 284:174-181. [PMID: 19004831 DOI: 10.1074/jbc.m807431200] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
O-Linked N-acetylglucosamine (O-GlcNAc) is a cytosolic and nuclear carbohydrate post-translational modification most abundant in brain. We recently reported uniquely extensive O-GlcNAc modification of proteins that function in synaptic vesicle release and post-synaptic signal transduction. Here we examined potential roles for O-GlcNAc in mouse hippocampal synaptic transmission and plasticity. O-GlcNAc modifications and the enzyme catalyzing their addition (O-GlcNAc transferase) were enriched in hippocampal synaptosomes. Pharmacological elevation or reduction of O-GlcNAc levels had no effect on Schaffer collateral CA1 basal hippocampal synaptic transmission. However, in vivo elevation of O-GlcNAc levels enhanced long term potentiation (LTP), an electrophysiological correlate to some forms of learning/memory. Reciprocally, pharmacological reduction of O-GlcNAc levels blocked LTP. Additionally, elevated O-GlcNAc led to reduced paired-pulse facilitation, a form of short term plasticity attributed to presynaptic mechanisms. Synapsin I and II are presynaptic proteins that increase synaptic vesicle availability for release when phosphorylated, thus contributing to hippocampal synaptic plasticity. Synapsins are among the most extensively O-GlcNAc-modified proteins known. Elevating O-GlcNAc levels increased phosphorylation of Synapsin I/II at serine 9 (cAMP-dependent protein kinase substrate site), serine 62/67 (Erk 1/2 (MAPK 1/2) substrate site), and serine 603 (calmodulin kinase II site). Activation-specific phosphorylation events on Erk 1/2 and calmodulin kinase II, two proteins required for CA1 hippocampal LTP establishment, were increased in response to elevation of O-GlcNAc levels. Thus, O-GlcNAc is a novel regulatory signaling component of excitatory synapses, with specific roles in synaptic plasticity that involve interplay with phosphorylation.
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Affiliation(s)
- Melanie K Tallent
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Neal Varghis
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Yuliya Skorobogatko
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Lisa Hernandez-Cuebas
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Kelly Whelan
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - David J Vocadlo
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Keith Vosseller
- Department of Biochemistry and Molecular Biology and Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102 and the Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
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Corradi A, Zanardi A, Giacomini C, Onofri F, Valtorta F, Zoli M, Benfenati F. Synapsin-I- and synapsin-II-null mice display an increased age-dependent cognitive impairment. J Cell Sci 2008; 121:3042-51. [DOI: 10.1242/jcs.035063] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Synapsin I (SynI) and synapsin II (SynII) are major synaptic vesicle (SV) proteins that function in the regulation of the availability of SVs for release in mature neurons. SynI and SynII show a high level of sequence similarity and share many functions in vivo, although distinct physiological roles for the two proteins have been proposed. Both SynI–/– and SynII–/– mice have a normal lifespan, but exhibit a decreased number of SVs and synaptic depression upon high-frequency stimulation. Because of the role of the synapsin proteins in synaptic organization and plasticity, we studied the long-lasting effects of synapsin deletion on the phenotype of SynI–/– and SynII–/– mice during aging. Both SynI–/– and SynII–/– mice displayed behavioural defects that emerged during aging and involved emotional memory in both mutants, and spatial memory in SynII–/– mice. These abnormalities, which were more pronounced in SynII–/– mice, were associated with neuronal loss and gliosis in the cerebral cortex and hippocampus. The data indicate that SynI and SynII have specific and non-redundant functions, and that synaptic dysfunctions associated with synapsin mutations negatively modulate cognitive performances and neuronal survival during senescence.
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Affiliation(s)
- Anna Corradi
- Department of Experimental Medicine, Section of Physiology, University of Genova and Istituto Nazionale di Neuroscienze, Viale Benedetto XV, 3 16132 Genova, Italy
| | - Alessio Zanardi
- Department of Biomedical Sciences, Section of Physiology, University of Modena, Via Campi 287, 41100 Modena, Italy
| | - Caterina Giacomini
- Department of Experimental Medicine, Section of Physiology, University of Genova and Istituto Nazionale di Neuroscienze, Viale Benedetto XV, 3 16132 Genova, Italy
| | - Franco Onofri
- Department of Experimental Medicine, Section of Physiology, University of Genova and Istituto Nazionale di Neuroscienze, Viale Benedetto XV, 3 16132 Genova, Italy
| | - Flavia Valtorta
- San Raffaele Scientific Institute/Vita-Salute University, IIT Unit of Molecular Neuroscience and Istituto Nazionale di Neuroscienze, via Olgettina 58, 20132 Milano, Italy
| | - Michele Zoli
- Department of Biomedical Sciences, Section of Physiology, University of Modena, Via Campi 287, 41100 Modena, Italy
| | - Fabio Benfenati
- Department of Experimental Medicine, Section of Physiology, University of Genova and Istituto Nazionale di Neuroscienze, Viale Benedetto XV, 3 16132 Genova, Italy
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy
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Bogen IL, Jensen V, Hvalby O, Walaas SI. Synapsin-dependent development of glutamatergic synaptic vesicles and presynaptic plasticity in postnatal mouse brain. Neuroscience 2008; 158:231-41. [PMID: 18606212 DOI: 10.1016/j.neuroscience.2008.05.055] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Revised: 05/08/2008] [Accepted: 05/21/2008] [Indexed: 10/21/2022]
Abstract
Inactivation of the genes encoding the neuronal, synaptic vesicle-associated proteins synapsin I and II leads to severe reductions in the number of synaptic vesicles in the CNS. We here define the postnatal developmental period during which the synapsin I and/or II proteins modulate synaptic vesicle number and function in excitatory glutamatergic synapses in mouse brain. In wild-type mice, brain levels of both synapsin I and synapsin IIb showed developmental increases during synaptogenesis from postnatal days 5-20, while synapsin IIa showed a protracted increase during postnatal days 20-30. The vesicular glutamate transporters (VGLUT) 1 and VGLUT2 showed synapsin-independent development during postnatal days 5-10, following which significant reductions were seen when synapsin-deficient brains were compared with wild-type brains following postnatal day 20. A similar, synapsin-dependent developmental profile of vesicular glutamate uptake occurred during the same age periods. Physiological analysis of the development of excitatory glutamatergic synapses, performed in the CA1 stratum radiatum of the hippocampus from the two genotypes, showed that both the synapsin-dependent part of the frequency facilitation and the synapsin-dependent delayed response enhancement were restricted to the period after postnatal day 10. Our data demonstrate that while both synaptic vesicle number and presynaptic short-term plasticity are essentially independent of synapsin I and II prior to postnatal day 10, maturation and function of excitatory synapses appear to be strongly dependent on synapsin I and II from postnatal day 20.
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Affiliation(s)
- I L Bogen
- Department of Biochemistry, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, P.O. Box 1112 Blindern, NO-0317 Oslo, Norway
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Owe SG, Jensen V, Evergren E, Ruiz A, Shupliakov O, Kullmann DM, Storm-Mathisen J, Walaas SI, Hvalby Ø, Bergersen LH. Synapsin- and actin-dependent frequency enhancement in mouse hippocampal mossy fiber synapses. Cereb Cortex 2008; 19:511-23. [PMID: 18550596 PMCID: PMC2638812 DOI: 10.1093/cercor/bhn101] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The synapsin proteins have different roles in excitatory and inhibitory synaptic terminals. We demonstrate a differential role between types of excitatory terminals. Structural and functional aspects of the hippocampal mossy fiber (MF) synapses were studied in wild-type (WT) mice and in synapsin double-knockout mice (DKO). A severe reduction in the number of synaptic vesicles situated more than 100 nm away from the presynaptic membrane active zone was found in the synapsin DKO animals. The ultrastructural level gave concomitant reduction in F-actin immunoreactivity observed at the periactive endocytic zone of the MF terminals. Frequency facilitation was normal in synapsin DKO mice at low firing rates (approximately 0.1 Hz) but was impaired at firing rates within the physiological range (approximately 2 Hz). Synapses made by associational/commissural fibers showed comparatively small frequency facilitation at the same frequencies. Synapsin-dependent facilitation in MF synapses of WT mice was attenuated by blocking F-actin polymerization with cytochalasin B in hippocampal slices. Synapsin III, selectively seen in MF synapses, is enriched specifically in the area adjacent to the synaptic cleft. This may underlie the ability of synapsin III to promote synaptic depression, contributing to the reduced frequency facilitation observed in the absence of synapsins I and II.
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Affiliation(s)
- Simen G Owe
- Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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Jensen V, Rinholm JE, Johansen TJ, Medin T, Storm-Mathisen J, Sagvolden T, Hvalby O, Bergersen LH. N-methyl-D-aspartate receptor subunit dysfunction at hippocampal glutamatergic synapses in an animal model of attention-deficit/hyperactivity disorder. Neuroscience 2008; 158:353-64. [PMID: 18571865 DOI: 10.1016/j.neuroscience.2008.05.016] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Revised: 05/13/2008] [Accepted: 05/15/2008] [Indexed: 11/15/2022]
Abstract
Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioural disorder among children. ADHD children are hyperactive, impulsive and have problems with sustained attention. These cardinal features are also present in the best validated animal model of ADHD, the spontaneously hypertensive rat (SHR), which is derived from the Wistar Kyoto rat (WKY). Current theories of ADHD relate symptom development to factors that alter learning. N-methyl-D-aspartate receptor (NMDAR) dependent long term changes in synaptic efficacy in the mammalian CNS are thought to represent underlying cellular mechanisms for some forms of learning. We therefore hypothesized that synaptic abnormality in excitatory, glutamatergic synaptic transmission might contribute to the altered behavior in SHRs. We studied physiological and anatomical aspects of hippocampal CA3-to-CA1 synapses in age-matched SHR and WKY (controls). Electrophysiological analysis of these synapses showed reduced synaptic transmission (reduced field excitatory postsynaptic potential for a defined fiber volley size) in SHR, whereas short-term forms of synaptic plasticity, like paired-pulse facilitation, frequency facilitation, and delayed response enhancement were comparable in the two genotypes, and long-term potentiation (LTP) of synaptic transmission was of similar magnitude. However, LTP in SHR was significantly reduced (by 50%) by the NR2B specific blocker CP-101,606 (10 microM), whereas the blocker had no effect on LTP magnitude in the control rats. This indicates that the SHR has a functional predominance of NR2B, a feature characteristic of early developmental stages in these synapses. Quantitative immunofluorescence and electron microscopic postembedding immunogold cytochemistry of the three major NMDAR subunits (NR1, NR2A; and NR2B) in stratum radiatum spine synapses revealed no differences between SHR and WKY. The results indicate that functional impairments in glutamatergic synaptic transmission may be one of the underlying mechanisms leading to the abnormal behavior in SHR, and possibly in human ADHD.
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Affiliation(s)
- V Jensen
- Molecular Neurobiology Research Group, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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Liu XY, Yang JL, Chen LJ, Zhang Y, Yang ML, Wu YY, Li FQ, Tang MH, Liang SF, Wei YQ. Comparative proteomics and correlated signaling network of rat hippocampus in the pilocarpine model of temporal lobe epilepsy. Proteomics 2008; 8:582-603. [DOI: 10.1002/pmic.200700514] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Lack of synapsin I reduces the readily releasable pool of synaptic vesicles at central inhibitory synapses. J Neurosci 2007; 27:13520-31. [PMID: 18057210 DOI: 10.1523/jneurosci.3151-07.2007] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synapsins (Syns) are synaptic vesicle (SV) phosphoproteins that play a role in neurotransmitter release and synaptic plasticity by acting at multiple steps of exocytosis. Mutation of SYN genes results in an epileptic phenotype in mouse and man suggesting a role of Syns in the control of network excitability. We have studied the effects of the genetic ablation of the SYN1 gene on inhibitory synaptic transmission in primary hippocampal neurons. Inhibitory neurons lacking SynI showed reduced amplitude of IPSCs evoked by isolated action potentials. The impairment in inhibitory transmission was caused by a decrease in the size of the SV readily releasable pool, rather than by changes in release probability or quantal size. The reduction of the readily releasable pool was caused by a decrease in the number of SVs released by single synaptic boutons in response to the action potential, in the absence of variations in the number of synaptic contacts between couples of monosynaptically connected neurons. The deletion of SYN1 did not affect paired-pulse depression or post-tetanic potentiation, but was associated with a moderate increase of synaptic depression evoked by trains of action potentials, which became apparent at high stimulation frequencies and was accompanied by a slow down of recovery from depression. The decreased size of the SV readily releasable pool, coupled with a decreased SV recycling rate and refilling by the SV reserve pool, may contribute to the epileptic phenotype of SynI knock-out mice.
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Jensen V, Walaas SI, Hilfiker S, Ruiz A, Hvalby Ø. A delayed response enhancement during hippocampal presynaptic plasticity in mice. J Physiol 2007; 583:129-43. [PMID: 17569738 PMCID: PMC2277251 DOI: 10.1113/jphysiol.2007.131300] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
High frequency afferent stimulation of chemical synapses often induces short-term increases in synaptic efficacy, due to increased release probability and/or increased supply of readily releasable synaptic vesicles. This may be followed by synaptic depression, often caused by vesicle depletion. We here describe an additional, novel type of delayed and transient response enhancement phase which occurred during prolonged stimulation at 5-20 Hz frequency of excitatory glutamatergic synapses in slices from the adult mouse CA1 hippocampal region. This second enhancement phase, which was most clearly defined at physiological temperatures and essentially absent at 24 degrees C, was dependent on the presence of F-actin filaments and synapsins I and/or II, and could not be ascribed to changes in presynaptic action potentials, inhibitory neurotransmission or glutamate receptor desensitization. Time course studies showed that the delayed response phase interrupted the synaptic decay 3-4 s after stimulus train initiation and continued, when examined at 5-10 Hz frequencies, for approximately 75 stimuli before decay. The novel response enhancement, probably deriving from a restricted pool of synaptic vesicles, may allow maintenance of synaptic efficacy during prolonged periods of excitatory synaptic activity.
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Affiliation(s)
- Vidar Jensen
- Molecular Neurobiology Research Group (MONERG), PO Box 1104, Faculty of Medicine, University of Oslo, N-0317 Blindern, Oslo, Norway
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