1
|
Song SH, Augustine GJ. A role for synapsin tetramerization in synaptic vesicle clustering. J Physiol 2024. [PMID: 38979871 DOI: 10.1113/jp286177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2024] [Accepted: 06/06/2024] [Indexed: 07/10/2024] Open
Abstract
Although synapsins have long been proposed to be key regulators of synaptic vesicle (SV) clustering, their mechanism of action has remained mysterious and somewhat controversial. Here, we review synapsins and their associations with each other and with SVs. We highlight the recent hypothesis that synapsin tetramerization is a mechanism for SV clustering. This hypothesis, which aligns with numerous experimental results, suggests that the larger size of synapsin tetramers, in comparison to dimers, allows tetramers to form optimal bridges between SVs that overcome the repulsive force associated with the negatively charged membrane of SVs and allow synapsins to form a reserve pool of SVs within presynaptic terminals.
Collapse
Affiliation(s)
| | - George J Augustine
- Temasek Life sciences Laboratory, Singapore
- Department of Physiology, National University of Singapore, Singapore
| |
Collapse
|
2
|
Mir S, Ashraf S, Saeed M, Rahman AU, Ul-Haq Z. Protonation states at different pH, conformational changes and impact of glycosylation in synapsin Ia. Phys Chem Chem Phys 2021; 23:16718-16729. [PMID: 34318818 DOI: 10.1039/d1cp00531f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Synapsin I (SynI) is the most abundant brain phosphoprotein present at presynaptic terminals that regulates neurotransmitter release, clustering of synaptic vesicles (SVs) at active zones, and stimulates synaptogenesis and neurite outgrowth. Earlier studies have established that SynI displays pH-dependent tethering of SVs to actin filaments and exhibits a maximum binding around neutral pH, however, the effect of pH shift from acidic to basic on the conformational stability of SynI has not been explored yet. Another important aspect of SynIa is its O-GlcNAcylation (O-GlcNac) at the Thr87 position, which is responsible for the positive regulation of synaptic plasticity linked to learning and memory in mice. Furthermore, reduced levels of O-GlcNAc have been observed in Alzheimer's disease, suggesting a possible link to deficits in synaptic plasticity. In this study, the effect of pH and glycosylation on the structure and functional stability of SynIa is determined through molecular dynamics (MD) simulation approach. The 3D structure of SynIa was established via threading-based homology modeling methods. It was observed that the structure of SynIa adopts extended conformational changes as the pH shifts from acidic to basic, resulting in a compact conformation at pH 8.0. Moreover, the results obtained by comparing the glycosylated and unglycosylated protein indicated that the glycan moiety imparts stability to the protein by forming intramolecular hydrogen bond interactions with the protein residues. The results indicate that although O-GlcNAc moieties do not induce a significant change in SynIa structure they minimize protein dynamics, likely leading to enhanced protein stability.
Collapse
Affiliation(s)
- Sonia Mir
- H.E.J., Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi 75270, Pakistan.
| | | | | | | | | |
Collapse
|
3
|
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.
Collapse
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.
| |
Collapse
|
4
|
Xiong J, Duan H, Chen S, Kessi M, He F, Deng X, Zhang C, Yang L, Peng J, Yin F. Familial SYN1 variants related neurodevelopmental disorders in Asian pediatric patients. BMC Med Genomics 2021; 14:182. [PMID: 34243774 PMCID: PMC8272254 DOI: 10.1186/s12920-021-01028-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 06/22/2021] [Indexed: 12/01/2022] Open
Abstract
Background SYN1 encodes synapsin I, which is a neuronal phosphoprotein involving in regulating axonogenesis and synaptogenesis. Variants in the gene have been associated with X-linked neurodevelopmental disorders in recent years. Methods In the study, we reported two male patients with familial SYN1 variants related neurodevelopmental disorders from Asian population. Previously published cases with significant SYN1 variants from the literature were also included to analyze the phenotype and genotype of the disorder. Results Two maternally inherited SYN1 variants, including c.C1076A, p.T359K in proband A and c.C1444T, p. Q482X in proband B (NM_133499) were found, which have never been described in detail. Combining with our research, all reported probands were male in the condition, whose significant SYN1 variants were inherited from their asymptomatic or mild affected mother. Although the disorder encompasses three main clinical presentations: mental deficiency, easily controlled reflex seizure and behavior problems, patients’ clinical manifestations vary in genders and individuals, even in the same pedigree. Conclusion We firstly reported two familial SYN1-related neurodevelopmental disorders in Asian pediatric patients. Gender and phenotype differences should be highly valued in the disorder.
Collapse
Affiliation(s)
- Juan Xiong
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Haolin Duan
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Shimeng Chen
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Miriam Kessi
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Fang He
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Xiaolu Deng
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Ciliu Zhang
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Li Yang
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Jing Peng
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Fei Yin
- Department of Pediatrics, Xiangya Hospital, Central South University, No. 86, Xiangya Road, Kaifu District, Changsha, 410008, China. .,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China.
| |
Collapse
|
5
|
Affiliation(s)
- Massimo Vassalli
- James Watt School of Engineering, University of Glasgow, Center for the Cellular Microenvironment, 70 University Avenue, School of Engineering, G12 8LT, Glasgow, UK
| |
Collapse
|
6
|
Zhang M, Augustine GJ. Synapsins and the Synaptic Vesicle Reserve Pool: Floats or Anchors? Cells 2021; 10:cells10030658. [PMID: 33809712 PMCID: PMC8002314 DOI: 10.3390/cells10030658] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 03/08/2021] [Accepted: 03/11/2021] [Indexed: 11/24/2022] Open
Abstract
In presynaptic terminals, synaptic vesicles (SVs) are found in a discrete cluster that includes a reserve pool that is mobilized during synaptic activity. Synapsins serve as a key protein for maintaining SVs within this reserve pool, but the mechanism that allows synapsins to do this is unclear. This mechanism is likely to involve synapsins either cross-linking SVs, thereby anchoring SVs to each other, or creating a liquid phase that allows SVs to float within a synapsin droplet. Here, we summarize what is known about the role of synapsins in clustering of SVs and evaluate experimental evidence supporting these two models.
Collapse
|
7
|
Giving names to the actors of synaptic transmission: The long journey from synaptic vesicles to neural plasticity. ADVANCES IN PHARMACOLOGY 2021; 90:19-37. [PMID: 33706933 DOI: 10.1016/bs.apha.2020.09.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
Abstract
More than a scientific paper or a review article, this is a remembrance of a unique time of science and life that the authors spent in Paul Greengard's laboratory at the Rockefeller University in New York in the 1980s and 1990s, forming the so-called synaptic vesicle group. It was a time in which the molecular mechanisms of synaptic transmission and the nature of the organelles in charge of storing and releasing neurotransmitter were just beginning to be understood. It was an exciting time in which the protein composition of synaptic vesicles started to be identified. It turned out that the interactions of synaptic vesicle proteins with the cytoskeleton and the presynaptic membrane and their modulation by protein phosphorylation represented an essential network regulating the efficiency of neurotransmitter release and thereby synaptic strength and plasticity. This is also a description of the distinct scientific journeys that the three authors took on going back to Europe and how they were strongly influenced by the generous and outstanding mentorship of Paul Greengard, his genuine interest in their lives and careers and the life-long friendship with him.
Collapse
|
8
|
Ma M, Xiong W, Hu F, Deng MF, Huang X, Chen JG, Man HY, Lu Y, Liu D, Zhu LQ. A novel pathway regulates social hierarchy via lncRNA AtLAS and postsynaptic synapsin IIb. Cell Res 2020; 30:105-118. [PMID: 31959917 DOI: 10.1038/s41422-020-0273-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 12/30/2019] [Indexed: 12/16/2022] Open
Abstract
Dominance hierarchy is a fundamental phenomenon in grouped animals and human beings, however, the underlying regulatory mechanisms remain elusive. Here, we report that an antisense long non-coding RNA (lncRNA) of synapsin II, named as AtLAS, plays a crucial role in the regulation of social hierarchy. AtLAS is decreased in the prefrontal cortical excitatory pyramidal neurons of dominant mice; consistently, silencing or overexpression of AtLAS increases or decreases the social rank, respectively. Mechanistically, we show that AtLAS regulates alternative polyadenylation of synapsin II gene and increases synapsin 2b (syn2b) expression. Syn2b reduces AMPA receptor (AMPAR)-mediated excitatory synaptic transmission through a direct binding with AMPAR at the postsynaptic site via its unique C-terminal sequence. Moreover, a peptide disrupting the binding of syn2b with AMPARs enhances the synaptic strength and social ranks. These findings reveal a novel role for lncRNA AtLAS and its target syn2b in the regulation of social behaviors by controlling postsynaptic AMPAR trafficking.
Collapse
Affiliation(s)
- Mei Ma
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Wan Xiong
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Fan Hu
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Man-Fei Deng
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Xian Huang
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Jian-Guo Chen
- The Institute of Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Heng-Ye Man
- Department of Biology, Boston University, Boston, MA, 02215, USA
| | - Youming Lu
- The Institute of Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China
| | - Dan Liu
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China. .,The Institute of Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China.
| | - Ling-Qiang Zhu
- Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China. .,The Institute of Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, China.
| |
Collapse
|
9
|
Rocchi A, Sacchetti S, De Fusco A, Giovedi S, Parisi B, Cesca F, Höltje M, Ruprecht K, Ahnert-Hilger G, Benfenati F. Autoantibodies to synapsin I sequestrate synapsin I and alter synaptic function. Cell Death Dis 2019; 10:864. [PMID: 31727880 PMCID: PMC6856194 DOI: 10.1038/s41419-019-2106-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 10/25/2019] [Accepted: 10/31/2019] [Indexed: 12/18/2022]
Abstract
Synapsin I is a phosphoprotein that coats the cytoplasmic side of synaptic vesicles and regulates their trafficking within nerve terminals. Autoantibodies against Syn I have been described in sera and cerebrospinal fluids of patients with numerous neurological diseases, including limbic encephalitis and clinically isolated syndrome; however, the effects and fate of autoantibodies in neurons are still unexplored. We found that in vitro exposure of primary hippocampal neurons to patient’s autoantibodies to SynI decreased the density of excitatory and inhibitory synapses and impaired both glutamatergic and GABAergic synaptic transmission. These effects were reproduced with a purified SynI antibody and completely absent in SynI knockout neurons. Autoantibodies to SynI are internalized by FcγII/III-mediated endocytosis, interact with endogenous SynI, and promote its sequestration and intracellular aggregation. Neurons exposed to human autoantibodies to SynI display a reduced density of SVs, mimicking the SynI loss-of-function phenotype. Our data indicate that autoantibodies to intracellular antigens such as SynI can reach and inactivate their targets and suggest that an antibody-mediated synaptic dysfunction may contribute to the evolution and progression of autoimmune-mediated neurological diseases positive for SynI autoantibodies.
Collapse
Affiliation(s)
- Anna Rocchi
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy.,IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy
| | - Silvio Sacchetti
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy
| | - Antonio De Fusco
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132, Genova, Italy
| | - Silvia Giovedi
- IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132, Genova, Italy
| | - Barbara Parisi
- IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132, Genova, Italy
| | - Fabrizia Cesca
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy.,Department of Life Science, University of Trieste, via Giorgieri, 5, 34127, Trieste, Italy
| | - Markus Höltje
- Institute of Integrative Neuroanatomy, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Klemens Ruprecht
- Department of Neurology, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Gudrun Ahnert-Hilger
- Institute of Integrative Neuroanatomy, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, 16132, Genova, Italy. .,IRCSS, Ospedale Policlinico San Martino, Largo Rosanna Benzi 10, 16132, Genova, Italy.
| |
Collapse
|
10
|
Song SH, Augustine GJ. Synapsin Isoforms and Synaptic Vesicle Trafficking. Mol Cells 2015; 38:936-40. [PMID: 26627875 PMCID: PMC4673407 DOI: 10.14348/molcells.2015.0233] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 11/09/2015] [Accepted: 11/10/2015] [Indexed: 11/27/2022] Open
Abstract
Synapsins were the first presynaptic proteins identified and have served as the flagship of the presynaptic protein field. Here we review recent studies demonstrating that different members of the synapsin family play different roles at presynaptic terminals employing different types of synaptic vesicles. The structural underpinnings for these functions are just beginning to be understood and should provide a focus for future efforts.
Collapse
Affiliation(s)
- Sang-Ho Song
- Lee Kong Chian School of Medicine,
Singapore 637553,
Singapore
- Institute of Molecular and Cell Biology,
Singapore 138673,
Singapore
| | - George J. Augustine
- Lee Kong Chian School of Medicine,
Singapore 637553,
Singapore
- Institute of Molecular and Cell Biology,
Singapore 138673,
Singapore
| |
Collapse
|
11
|
Molinaro L, Hui P, Tan M, Mishra RK. Role of presynaptic phosphoprotein synapsin II in schizophrenia. World J Psychiatry 2015; 5:260-272. [PMID: 26425441 PMCID: PMC4582303 DOI: 10.5498/wjp.v5.i3.260] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Revised: 04/30/2015] [Accepted: 06/11/2015] [Indexed: 02/05/2023] Open
Abstract
Synapsin II is a member of the neuronal phosphoprotein family. These phosphoproteins are evolutionarily conserved across many organisms and are important in a variety of synaptic functions, including synaptogenesis and the regulation of neurotransmitter release. A number of genome-wide scans, meta-analyses, and genetic susceptibility studies have implicated the synapsin II gene (3p25) in the etiology of schizophrenia (SZ) and other psychiatric disorders. Further studies have found a reduction of synapsin II mRNA and protein in the prefrontal cortex in post-mortem samples from schizophrenic patients. Disruptions in the expression of this gene may cause synaptic dysfunction, which can result in neurotransmitter imbalances, likely contributing to the pathogenesis of SZ. SZ is a costly, debilitating psychiatric illness affecting approximately 1.1% of the world’s population, amounting to 51 million people today. The disorder is characterized by positive (hallucinations, paranoia), negative (social withdrawal, lack of motivation), and cognitive (memory impairments, attention deficits) symptoms. This review provides a comprehensive summary of the structure, function, and involvement of the synapsin family, specifically synapsin II, in the pathophysiology of SZ and possible target for therapeutic intervention/implications.
Collapse
|
12
|
SUMOylation of synapsin Ia maintains synaptic vesicle availability and is reduced in an autism mutation. Nat Commun 2015; 6:7728. [PMID: 26173895 PMCID: PMC4504226 DOI: 10.1038/ncomms8728] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Accepted: 06/04/2015] [Indexed: 11/08/2022] Open
Abstract
Synapsins are key components of the presynaptic neurotransmitter release machinery. Their main role is to cluster synaptic vesicles (SVs) to each other and anchor them to the actin cytoskeleton to establish the reserve vesicle pool, and then release them in response to appropriate membrane depolarization. Here we demonstrate that SUMOylation of synapsin Ia (SynIa) at K687 is necessary for SynIa function. Replacement of endogenous SynIa with a non-SUMOylatable mutant decreases the size of the releasable vesicle pool and impairs stimulated SV exocytosis. SUMOylation enhances SynIa association with SVs to promote the efficient reclustering of SynIa following neuronal stimulation and maintain its presynaptic localization. The A548T mutation in SynIa is strongly associated with autism and epilepsy and we show that it leads to defective SynIa SUMOylation. These results identify SUMOylation as a fundamental regulator of SynIa function and reveal a novel link between reduced SUMOylation of SynIa and neurological disorders.
Collapse
|
13
|
Functional role of ATP binding to synapsin I in synaptic vesicle trafficking and release dynamics. J Neurosci 2015; 34:14752-68. [PMID: 25355227 DOI: 10.1523/jneurosci.1093-14.2014] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Synapsins (Syns) are synaptic vesicle (SV)-associated proteins involved in the regulation of synaptic transmission and plasticity, which display a highly conserved ATP binding site in the central C-domain, whose functional role is unknown. Using molecular dynamics simulations, we demonstrated that ATP binding to SynI is mediated by a conformational transition of a flexible loop that opens to make the binding site accessible; such transition, prevented in the K269Q mutant, is not significantly affected in the absence of Ca(2+) or by the E373K mutation that abolishes Ca(2+)-binding. Indeed, the ATP binding to SynI also occurred under Ca(2+)-free conditions and increased its association with purified rat SVs regardless of the presence of Ca(2+) and promoted SynI oligomerization. However, although under Ca(2+)-free conditions, SynI dimerization and SV clustering were enhanced, Ca(2+) favored the formation of tetramers at the expense of dimers and did not affect SV clustering, indicating a role of Ca(2+)-dependent dimer/tetramer transitions in the regulation of ATP-dependent SV clustering. To elucidate the role of ATP/SynI binding in synaptic physiology, mouse SynI knock-out hippocampal neurons were transduced with either wild-type or K269Q mutant SynI and inhibitory transmission was studied by patch-clamp and electron microscopy. K269Q-SynI expressing inhibitory synapses showed increased synaptic strength due to an increase in the release probability, an increased vulnerability to synaptic depression and a dysregulation of SV trafficking, when compared with wild-type SynI-expressing terminals. The results suggest that the ATP-SynI binding plays predocking and postdocking roles in the modulation of SV clustering and plasticity of inhibitory synapses.
Collapse
|
14
|
Effects of Oxidation of Membrane Cholesterol on the Vesicle Cycle in Motor Nerve Terminals in the Frog Rana Ridibunda. ACTA ACUST UNITED AC 2014. [DOI: 10.1007/s11055-014-0019-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
|
15
|
Giovedí S, Corradi A, Fassio A, Benfenati F. Involvement of synaptic genes in the pathogenesis of autism spectrum disorders: the case of synapsins. Front Pediatr 2014; 2:94. [PMID: 25237665 PMCID: PMC4154395 DOI: 10.3389/fped.2014.00094] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 08/21/2014] [Indexed: 12/03/2022] Open
Abstract
Autism spectrum disorders (ASDs) are heterogeneous neurodevelopmental disorders characterized by deficits in social interaction and social communication, restricted interests, and repetitive behaviors. Many synaptic protein genes are linked to the pathogenesis of ASDs, making them prototypical synaptopathies. An array of mutations in the synapsin (Syn) genes in humans has been recently associated with ASD and epilepsy, diseases that display a frequent comorbidity. Syns are pre-synaptic proteins regulating synaptic vesicle traffic, neurotransmitter release, and short-term synaptic plasticity. In doing so, Syn isoforms control the tone of activity of neural circuits and the balance between excitation and inhibition. As ASD pathogenesis is believed to result from dysfunctions in the balance between excitatory and inhibitory transmissions in neocortical areas, Syns are novel ASD candidate genes. Accordingly, deletion of single Syn genes in mice, in addition to epilepsy, causes core symptoms of ASD by affecting social behavior, social communication, and repetitive behaviors. Thus, Syn knockout mice represent a good experimental model to define synaptic alterations involved in the pathogenesis of ASD and epilepsy.
Collapse
Affiliation(s)
- Silvia Giovedí
- Department of Experimental Medicine, University of Genova , Genova , Italy
| | - Anna Corradi
- Department of Experimental Medicine, University of Genova , Genova , Italy
| | - Anna Fassio
- Department of Experimental Medicine, University of Genova , Genova , Italy ; Department of Neuroscience and Brain Technologies, Fondazione Istituto Italiano di Tecnologia , Genova , Italy
| | - Fabio Benfenati
- Department of Experimental Medicine, University of Genova , Genova , Italy ; Department of Neuroscience and Brain Technologies, Fondazione Istituto Italiano di Tecnologia , Genova , Italy
| |
Collapse
|
16
|
Giannandrea M, Guarnieri FC, Gehring NH, Monzani E, Benfenati F, Kulozik AE, Valtorta F. Nonsense-mediated mRNA decay and loss-of-function of the protein underlie the X-linked epilepsy associated with the W356× mutation in synapsin I. PLoS One 2013; 8:e67724. [PMID: 23818987 PMCID: PMC3688603 DOI: 10.1371/journal.pone.0067724] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 05/21/2013] [Indexed: 11/22/2022] Open
Abstract
Synapsins are a family of neuronal phosphoproteins associated with the cytosolic surface of synaptic vesicles. Experimental evidence suggests a role for synapsins in synaptic vesicle clustering and recycling at the presynaptic terminal, as well as in neuronal development and synaptogenesis. Synapsin knock-out (Syn1(-/-) ) mice display an epileptic phenotype and mutations in the SYN1 gene have been identified in individuals affected by epilepsy and/or autism spectrum disorder. We investigated the impact of the c.1067G>A nonsense transition, the first mutation described in a family affected by X-linked syndromic epilepsy, on the expression and functional properties of the synapsin I protein. We found that the presence of a premature termination codon in the human SYN1 transcript renders it susceptible to nonsense-mediated mRNA decay (NMD). Given that the NMD efficiency is highly variable among individuals and cell types, we investigated also the effects of expression of the mutant protein and found that it is expressed at lower levels compared to wild-type synapsin I, forms perinuclear aggregates and is unable to reach presynaptic terminals in mature hippocampal neurons grown in culture. Taken together, these data indicate that in patients carrying the W356× mutation the function of synapsin I is markedly impaired, due to both the strongly decreased translation and the altered function of the NMD-escaped protein, and support the value of Syn1(-/-) mice as an experimental model mimicking the human pathology.
Collapse
MESH Headings
- Animals
- Blotting, Northern
- Cells, Cultured
- Codon, Nonsense
- Epilepsy/genetics
- Epilepsy/metabolism
- Female
- Gene Expression
- Genetic Diseases, X-Linked/genetics
- Genetic Diseases, X-Linked/metabolism
- HeLa Cells
- Hippocampus/cytology
- Hippocampus/metabolism
- Humans
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Microscopy, Fluorescence
- Microtubule-Associated Proteins/metabolism
- Neurons/metabolism
- Nonsense Mediated mRNA Decay
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Synapsins/genetics
- Synapsins/metabolism
Collapse
Affiliation(s)
- Maila Giannandrea
- Division of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
| | - Fabrizia C. Guarnieri
- Division of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
| | | | - Elena Monzani
- Division of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
| | - Fabio Benfenati
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Genoa, Italy
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
| | - Andreas E. Kulozik
- Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg Medical Center and Molecular Medicine Partnership Unit, EMBL and University of Heidelberg, Heidelberg, Germany
| | - Flavia Valtorta
- Division of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
| |
Collapse
|
17
|
Ahmed S, Wittenmayer N, Kremer T, Hoeber J, Kiran Akula A, Urlaub H, Islinger M, Kirsch J, Dean C, Dresbach T. Mover is a homomeric phospho-protein present on synaptic vesicles. PLoS One 2013; 8:e63474. [PMID: 23723986 PMCID: PMC3665746 DOI: 10.1371/journal.pone.0063474] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2012] [Accepted: 04/03/2013] [Indexed: 01/13/2023] Open
Abstract
With remarkably few exceptions, the molecules mediating synaptic vesicle exocytosis at active zones are structurally and functionally conserved between vertebrates and invertebrates. Mover was found in a yeast-2-hybrid assay using the vertebrate-specific active zone scaffolding protein bassoon as a bait. Peptides of Mover have been reported in proteomics screens for self-interacting proteins, phosphorylated proteins, and synaptic vesicle proteins, respectively. Here, we tested the predictions arising from these screens. Using flotation assays, carbonate stripping of peripheral membrane proteins, mass spectrometry, immunogold labelling of purified synaptic vesicles, and immuno-organelle isolation, we found that Mover is indeed a peripheral synaptic vesicle membrane protein. In addition, by generating an antibody against phosphorylated Mover and Western blot analysis of fractionated rat brain, we found that Mover is a bona fide phospho-protein. The localization of Mover to synaptic vesicles is phosphorylation dependent; treatment with a phosphatase caused Mover to dissociate from synaptic vesicles. A yeast-2-hybrid screen, co-immunoprecipitation and cell-based optical assays of homomerization revealed that Mover undergoes homophilic interaction, and regions within both the N- and C- terminus of the protein are required for this interaction. Deleting a region required for homomeric interaction abolished presynaptic targeting of recombinant Mover in cultured neurons. Together, these data prove that Mover is associated with synaptic vesicles, and implicate phosphorylation and multimerization in targeting of Mover to synaptic vesicles and presynaptic sites.
Collapse
Affiliation(s)
- Saheeb Ahmed
- European Neuroscience Institute, Goettingen, Germany
| | - Nina Wittenmayer
- Center of Anatomy, University of Goettingen Medical School Goettingen, Germany
| | - Thomas Kremer
- Institute for Anatomy & Cell Biology, University of Heidelberg Medical School, Heidelberg, Germany
| | - Jan Hoeber
- Center of Anatomy, University of Goettingen Medical School Goettingen, Germany
| | - Asha Kiran Akula
- Center of Anatomy, University of Goettingen Medical School Goettingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Goettingen, Germany
| | - Markus Islinger
- Department of Neuroanatomy, Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany
| | - Joachim Kirsch
- Institute for Anatomy & Cell Biology, University of Heidelberg Medical School, Heidelberg, Germany
| | - Camin Dean
- European Neuroscience Institute, Goettingen, Germany
- * E-mail: (CD); (TD)
| | - Thomas Dresbach
- Center of Anatomy, University of Goettingen Medical School Goettingen, Germany
- * E-mail: (CD); (TD)
| |
Collapse
|
18
|
Marasini C, Jacchetti E, Moretti M, Canale C, Moran O, Vassalli M. Visualization of single proteins from stripped native cell membranes: A protocol for high-resolution atomic force microscopy. Microsc Res Tech 2013; 76:723-32. [DOI: 10.1002/jemt.22223] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Accepted: 04/08/2013] [Indexed: 11/09/2022]
Affiliation(s)
- Carlotta Marasini
- Istituto di Biofisica; Consiglio Nazionale delle Ricerche; Genova; 16149; Italy
| | | | - Manola Moretti
- Nanophysics Dipartimento; Istituto Italiano di Tecnologia; Morego; Genova; 16163; Italy
| | - Claudio Canale
- Nanophysics Dipartimento; Istituto Italiano di Tecnologia; Morego; Genova; 16163; Italy
| | - Oscar Moran
- Istituto di Biofisica; Consiglio Nazionale delle Ricerche; Genova; 16149; Italy
| | - Massimo Vassalli
- Istituto di Biofisica; Consiglio Nazionale delle Ricerche; Genova; 16149; Italy
| |
Collapse
|
19
|
Lignani G, Raimondi A, Ferrea E, Rocchi A, Paonessa F, Cesca F, Orlando M, Tkatch T, Valtorta F, Cossette P, Baldelli P, Benfenati F. Epileptogenic Q555X SYN1 mutant triggers imbalances in release dynamics and short-term plasticity. Hum Mol Genet 2013; 22:2186-99. [PMID: 23406870 PMCID: PMC3652419 DOI: 10.1093/hmg/ddt071] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Synapsin I (SynI) is a synaptic vesicle (SV) phosphoprotein playing multiple roles in synaptic transmission and plasticity by differentially affecting crucial steps of SV trafficking in excitatory and inhibitory synapses. SynI knockout (KO) mice are epileptic, and nonsense and missense mutations in the human SYN1 gene have a causal role in idiopathic epilepsy and autism. To get insights into the mechanisms of epileptogenesis linked to SYN1 mutations, we analyzed the effects of the recently identified Q555X mutation on neurotransmitter release dynamics and short-term plasticity (STP) in excitatory and inhibitory synapses. We used patch-clamp electrophysiology coupled to electron microscopy and multi-electrode arrays to dissect synaptic transmission of primary SynI KO hippocampal neurons in which the human wild-type and mutant SynI were expressed by lentiviral transduction. A parallel decrease in the SV readily releasable pool in inhibitory synapses and in the release probability in excitatory synapses caused a marked reduction in the evoked synchronous release. This effect was accompanied by an increase in asynchronous release that was much more intense in excitatory synapses and associated with an increased total charge transfer. Q555X-hSynI induced larger facilitation and post-tetanic potentiation in excitatory synapses and stronger depression after long trains in inhibitory synapses. These changes were associated with higher network excitability and firing/bursting activity. Our data indicate that imbalances in STP and release dynamics of inhibitory and excitatory synapses trigger network hyperexcitability potentially leading to epilepsy/autism manifestations.
Collapse
Affiliation(s)
- Gabriele Lignani
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
20
|
Abstract
Sustained neurotransmitter release at synapses during high-frequency synaptic activity involves the mobilization of synaptic vesicles (SVs) from the tightly clustered reserve pool (RP). Synapsin I (Syn I), a brain-specific peripheral membrane protein that undergoes activity-dependent cycles of SV association and dissociation, is implicated in RP organization via its ability to cluster SVs. Although Syn I has affinity for phospholipids, the mechanism for the reversible association of synapsin with SV membranes remains enigmatic. Here, we show that rat Syn I is able to sense membrane curvature via an evolutionary conserved amphipathic lipid packing sensor motif (ALPS). Deletion or mutational inactivation of the ALPS impairs the ability of Syn I to associate with highly curved membranes and with SVs. Furthermore, a Syn I mutant lacking ALPS displays defects in its ability to undergo activity-induced cycles of dispersion and reclustering in neurons and fails to induce vesicle clustering in vitro. Our data suggest a crucial role for ALPS-mediated sensing of membrane curvature in regulating synapsin function.
Collapse
|
21
|
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.
Collapse
Affiliation(s)
- Ayelet Orenbuch
- Department of Physiology and Neurobiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Bykhovskaia M. Synapsin regulation of vesicle organization and functional pools. Semin Cell Dev Biol 2011; 22:387-92. [PMID: 21827866 DOI: 10.1016/j.semcdb.2011.07.003] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Accepted: 07/13/2011] [Indexed: 11/18/2022]
Abstract
Synaptic vesicles are organized in clusters, and synapsin maintains vesicle organization and abundance in nerve terminals. At the functional level, vesicles can be subdivided into three pools: the releasable pool, the recycling pool, and the reserve pool, and synapsin mediates transitions between these pools. Synapsin directs vesicles into the reserve pool, and synapsin II isoform has a primary role in this function. In addition, synapsin actively delivers vesicles to active zones. Finally, synapsin I isoform mediates coupling release events to action potentials at the latest stages of exocytosis. Thus, synapsin is involved in multiple stages of the vesicle cycle, including vesicle clustering, maintaining the reserve pool, vesicle delivery to active zones, and synchronizing release events. These processes are regulated via a dynamic synapsin phosphorylation/dephosphorylation cycle which involves multiple phosphorylation sites and several pathways. Different synapsin isoforms have unique and non-redundant roles in the multifaceted synapsin function.
Collapse
Affiliation(s)
- Maria Bykhovskaia
- Universidad Central del Caribe, Neuroscience Department, 2U6 Ave Laurel, Bayamon, PR 00956, USA.
| |
Collapse
|
23
|
Shupliakov O, Haucke V, Pechstein A. How synapsin I may cluster synaptic vesicles. Semin Cell Dev Biol 2011; 22:393-9. [DOI: 10.1016/j.semcdb.2011.07.006] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Accepted: 07/13/2011] [Indexed: 12/14/2022]
|
24
|
Fassio A, Patry L, Congia S, Onofri F, Piton A, Gauthier J, Pozzi D, Messa M, Defranchi E, Fadda M, Corradi A, Baldelli P, Lapointe L, St-Onge J, Meloche C, Mottron L, Valtorta F, Khoa Nguyen D, Rouleau GA, Benfenati F, Cossette P. SYN1 loss-of-function mutations in autism and partial epilepsy cause impaired synaptic function. Hum Mol Genet 2011; 20:2297-307. [PMID: 21441247 DOI: 10.1093/hmg/ddr122] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Several genes predisposing to autism spectrum disorders (ASDs) with or without epilepsy have been identified, many of which are implicated in synaptic function. Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis. This nonsense mutation was found in all affected individuals from a large French-Canadian family segregating epilepsy and ASDs. Additional mutations in SYN1 (A51G, A550T and T567A) were found in 1.0 and 3.5% of French-Canadian individuals with autism and epilepsy, respectively. The majority of these SYN1 mutations were clustered in the proline-rich D-domain which is substrate of multiple protein kinases. When expressed in synapsin I (SynI) knockout (KO) neurons, all the D-domain mutants failed in rescuing the impairment in the size and trafficking of synaptic vesicle pools, whereas the wild-type human SynI fully reverted the KO phenotype. Moreover, the nonsense Q555X mutation had a dramatic impact on phosphorylation by MAPK/Erk and neurite outgrowth, whereas the missense A550T and T567A mutants displayed impaired targeting to nerve terminals. These results demonstrate that SYN1 is a novel predisposing gene to ASDs, in addition to epilepsy, and strengthen the hypothesis that a disturbance of synaptic homeostasis underlies the pathogenesis of both diseases.
Collapse
Affiliation(s)
- Anna Fassio
- Department of Experimental Medicine, National Institute of Neuroscience, University of Genova, Viale Benedetto XV 3, 16132 Genova, Italy
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
25
|
Pechstein A, Shupliakov O. Taking a back seat: synaptic vesicle clustering in presynaptic terminals. Front Synaptic Neurosci 2010; 2:143. [PMID: 21423529 PMCID: PMC3059686 DOI: 10.3389/fnsyn.2010.00143] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Accepted: 08/23/2010] [Indexed: 11/13/2022] Open
Abstract
Central inter-neuronal synapses employ various molecular mechanisms to sustain neurotransmitter release during phases of high-frequency synaptic activity. One of the features ensuring this property is the presence of a pool of synaptic vesicles (SVs) in the presynaptic terminal. At rest and low rates of stimulation, most of the vesicles composing this pool remain in a tight cluster. They are actively utilized when neurons fire action potentials at higher rates and the capability of the recycling machinery is limited. In addition, SV clusters are capable of migrating between release sites and reassemble into clusters at neighboring active zones (AZs). Within the cluster, thin "tethers" interconnect SVs. These dynamic filamentous structures are reorganized during stimulation thereby releasing SVs from the cluster. So far, one protein family, the synapsins, which bind actin filaments and vesicles in a phosphorylation-dependent manner, has been implicated in SV clustering in vertebrate synapses. As evident from recent studies, many endocytic proteins reside in the SV cluster in addition to synapsin. Here we discuss alternative possible mechanisms involved in the organization of this population of SVs. We propose a model in which synapsins together with other synaptic proteins, a large proportion of which is involved in SV recycling, form a dynamic proteinaceous "matrix" which limits the mobility of SVs. Actin filaments, however, do not seem to contribute to SV crosslinking within the SV cluster, but instead they are present peripherally to it, at sites of neurotransmitter release, and at sites of SV recycling.
Collapse
Affiliation(s)
- Arndt Pechstein
- Department of Neuroscience, Developmental Biology for Regenerative Medicine, Karolinska Institutet Stockholm, Sweden
| | | |
Collapse
|
26
|
Messa M, Congia S, Defranchi E, Valtorta F, Fassio A, Onofri F, Benfenati F. Tyrosine phosphorylation of synapsin I by Src regulates synaptic-vesicle trafficking. J Cell Sci 2010; 123:2256-65. [PMID: 20530578 DOI: 10.1242/jcs.068445] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Synapsins are synaptic vesicle (SV)-associated phosphoproteins involved in the regulation of neurotransmitter release. Synapsins reversibly tether SVs to the cytoskeleton and their phosphorylation by serine/threonine kinases increases SV availability for exocytosis by impairing their association with SVs and/or actin. We recently showed that synapsin I, through SH3- or SH2-mediated interactions, activates Src and is phosphorylated by the same kinase at Tyr301. Here, we demonstrate that, in contrast to serine phosphorylation, Src-mediated tyrosine phosphorylation of synapsin I increases its binding to SVs and actin, and increases the formation of synapsin dimers, which are both potentially involved in SV clustering. Synapsin I phosphorylation by Src affected SV dynamics and was physiologically regulated in brain slices in response to depolarization. Expression of the non-phosphorylatable (Y301F) synapsin I mutant in synapsin-I-knockout neurons increased the sizes of the readily releasable and recycling pools of SVs with respect to the wild-type form, which is consistent with an increased availability of recycled SVs for exocytosis. The data provide a mechanism for the effects of Src on SV trafficking and indicate that tyrosine phosphorylation of synapsins, unlike serine phosphorylation, stimulates the reclustering of recycled SVs and their recruitment to the reserve pool.
Collapse
Affiliation(s)
- Mirko Messa
- Department of Experimental Medicine, University of Genova and Istituto Nazionale di Neuroscienze, Viale Benedetto XV 3, 161632 Genova, Italy
| | | | | | | | | | | | | |
Collapse
|
27
|
Fornasiero EF, Bonanomi D, Benfenati F, Valtorta F. The role of synapsins in neuronal development. Cell Mol Life Sci 2010; 67:1383-96. [PMID: 20035364 PMCID: PMC11115787 DOI: 10.1007/s00018-009-0227-8] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2009] [Revised: 11/22/2009] [Accepted: 12/04/2009] [Indexed: 12/23/2022]
Abstract
The synapsins, the first identified synaptic vesicle-specific proteins, are phosphorylated on multiple sites by a number of protein kinases and are involved in neurite outgrowth and synapse formation as well as in synaptic transmission. In mammals, the synapsin family consists of at least 10 isoforms encoded by 3 distinct genes and composed by a mosaic of conserved and variable domains. The synapsins are highly conserved evolutionarily, and orthologues have been found in invertebrates and lower vertebrates. Within nerve terminals, synapsins are implicated in multiple interactions with presynaptic proteins and the actin cytoskeleton. Via these interactions, synapsins control several mechanisms important for neuronal homeostasis. In this review, we describe the main functional features of the synapsins, in relation to the complex role played by these phosphoproteins in neuronal development.
Collapse
Affiliation(s)
- Eugenio F. Fornasiero
- San Raffaele Scientific Institute, Vita-Salute University, Via Olgettina 58, 20132 Milan, Italy
- Unit of Molecular Neuroscience, The Italian Institute of Technology, Via Olgettina 58, 20132 Milan, Italy
| | - Dario Bonanomi
- San Raffaele Scientific Institute, Vita-Salute University, Via Olgettina 58, 20132 Milan, Italy
- Present Address: Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA 92037 USA
- Unit of Molecular Neuroscience, The Italian Institute of Technology, Via Olgettina 58, 20132 Milan, Italy
| | - Fabio Benfenati
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Via Morego 30, 16163 Genoa, Italy
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV, 3, 16132 Genoa, Italy
| | - Flavia Valtorta
- San Raffaele Scientific Institute, Vita-Salute University, Via Olgettina 58, 20132 Milan, Italy
- Unit of Molecular Neuroscience, The Italian Institute of Technology, Via Olgettina 58, 20132 Milan, Italy
| |
Collapse
|