51
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Mendonça PRF, Tagliatti E, Langley H, Kotzadimitriou D, Zamora-Chimal CG, Timofeeva Y, Volynski KE. Asynchronous glutamate release is enhanced in low release efficacy synapses and dispersed across the active zone. Nat Commun 2022; 13:3497. [PMID: 35715404 PMCID: PMC9206079 DOI: 10.1038/s41467-022-31070-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Accepted: 05/31/2022] [Indexed: 11/09/2022] Open
Abstract
The balance between fast synchronous and delayed asynchronous release of neurotransmitters has a major role in defining computational properties of neuronal synapses and regulation of neuronal network activity. However, how it is tuned at the single synapse level remains poorly understood. Here, using the fluorescent glutamate sensor SF-iGluSnFR, we image quantal vesicular release in tens to hundreds of individual synaptic outputs from single pyramidal cells with 4 millisecond temporal and 75 nm spatial resolution. We find that the ratio between synchronous and asynchronous synaptic vesicle exocytosis varies extensively among synapses supplied by the same axon, and that the synchronicity of release is reduced at low release probability synapses. We further demonstrate that asynchronous exocytosis sites are more widely distributed within the release area than synchronous sites. Together, our results reveal a universal relationship between the two major functional properties of synapses - the timing and the overall efficacy of neurotransmitter release.
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Affiliation(s)
- Philipe R F Mendonça
- University College London Institute of Neurology, London, UK. .,Department of Physiology and Biophysics, Federal University of Minas Gerais, Gerais, Brazil.
| | - Erica Tagliatti
- University College London Institute of Neurology, London, UK
| | - Helen Langley
- University College London Institute of Neurology, London, UK
| | | | | | - Yulia Timofeeva
- University College London Institute of Neurology, London, UK. .,Department of Computer Science, University of Warwick, Coventry, UK.
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52
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Rizo J, Sari L, Qi Y, Im W, Lin MM. All-atom molecular dynamics simulations of Synaptotagmin-SNARE-complexin complexes bridging a vesicle and a flat lipid bilayer. eLife 2022; 11:76356. [PMID: 35708237 PMCID: PMC9239685 DOI: 10.7554/elife.76356] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 06/15/2022] [Indexed: 12/14/2022] Open
Abstract
Synaptic vesicles are primed into a state that is ready for fast neurotransmitter release upon Ca2+-binding to Synaptotagmin-1. This state likely includes trans-SNARE complexes between the vesicle and plasma membranes that are bound to Synaptotagmin-1 and complexins. However, the nature of this state and the steps leading to membrane fusion are unclear, in part because of the difficulty of studying this dynamic process experimentally. To shed light into these questions, we performed all-atom molecular dynamics simulations of systems containing trans-SNARE complexes between two flat bilayers or a vesicle and a flat bilayer with or without fragments of Synaptotagmin-1 and/or complexin-1. Our results need to be interpreted with caution because of the limited simulation times and the absence of key components, but suggest mechanistic features that may control release and help visualize potential states of the primed Synaptotagmin-1-SNARE-complexin-1 complex. The simulations suggest that SNAREs alone induce formation of extended membrane-membrane contact interfaces that may fuse slowly, and that the primed state contains macromolecular assemblies of trans-SNARE complexes bound to the Synaptotagmin-1 C2B domain and complexin-1 in a spring-loaded configuration that prevents premature membrane merger and formation of extended interfaces, but keeps the system ready for fast fusion upon Ca2+ influx.
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Affiliation(s)
- Josep Rizo
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Levent Sari
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Green Center for Systems Biology, The University of Texas Southwestern Medical Center, Dallas, United States
| | - Yife Qi
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, Shanghai, China
| | - Wonpil Im
- Department of Biological Sciences, Lehigh University, Bethlehem, United States.,Department of Chemistry, Lehigh University, Bethlehem, United States.,Department of Bioengineering, Lehigh University, Bethlehem, United States.,Department of Computer Science and Engineering, Lehigh University, Bethlehem, United States
| | - Milo M Lin
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Green Center for Systems Biology, The University of Texas Southwestern Medical Center, Dallas, United States
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53
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Kusick GF, Ogunmowo TH, Watanabe S. Transient docking of synaptic vesicles: Implications and mechanisms. Curr Opin Neurobiol 2022; 74:102535. [PMID: 35398664 PMCID: PMC9167714 DOI: 10.1016/j.conb.2022.102535] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 02/19/2022] [Accepted: 03/06/2022] [Indexed: 02/03/2023]
Abstract
As synaptic vesicles fuse, they must continually be replaced with new docked, fusion-competent vesicles to sustain neurotransmission. It has long been appreciated that vesicles are recruited to docking sites in an activity-dependent manner. However, once entering the sites, vesicles were thought to be stably docked, awaiting calcium signals. Based on recent data from electrophysiology, electron microscopy, biochemistry, and computer simulations, a picture emerges in which vesicles can rapidly and reversibly transit between docking and undocking during activity. This "transient docking" can account for many aspects of synaptic physiology. In this review, we cover recent evidence for transient docking, physiological processes at the synapse that it may support, and progress on the underlying mechanisms. We also discuss an open question: what determines for how long and whether vesicles stay docked, or eventually undock?
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Affiliation(s)
- Grant F Kusick
- Department of Cell Biology, Johns Hopkins University, School of Medicine, 725 N Wolfe St., Baltimore, MD 21287, USA; Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University, School of Medicine, 1830 E. Monument St., Baltimore, MD 21287, USA. https://twitter.com/@ultrafastgrant
| | - Tyler H Ogunmowo
- Department of Cell Biology, Johns Hopkins University, School of Medicine, 725 N Wolfe St., Baltimore, MD 21287, USA; Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University, School of Medicine, 1830 E. Monument St., Baltimore, MD 21287, USA. https://twitter.com/@unculturedTy
| | - Shigeki Watanabe
- Department of Cell Biology, Johns Hopkins University, School of Medicine, 725 N Wolfe St., Baltimore, MD 21287, USA; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University, School of Medicine, 725 N Wolfe St., Baltimore, MD 21287, USA.
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54
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Xie D, Yin K, Yang ZJ, Huang H, Li X, Shu Z, Duan H, He J, Jiang J. Polarization-perceptual anisotropic two-dimensional ReS 2 neuro-transistor with reconfigurable neuromorphic vision. MATERIALS HORIZONS 2022; 9:1448-1459. [PMID: 35234765 DOI: 10.1039/d1mh02036f] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Polarization is a common and unique phenomenon in nature, which reveals more camouflage features of objects. However, current polarization-perceptual devices based on conventional physical architectures face enormous challenges for high-performance computation due to the traditional von Neumann bottleneck. In this work, a novel polarization-perceptual neuro-transistor with reconfigurable anisotropic vision is proposed based on a two-dimensional ReS2 phototransistor. The device exhibits excellent photodetection ability and superior polarization sensitivity due to its direct band gap semiconductor property and strong anisotropic crystal structure, respectively. The fascinating polarization-sensitive neuromorphic behavior, such as polarization memory consolidation and reconfigurable visual imaging, are successfully realized. In particular, the regulated polarization responsivity and dichroic ratio are successfully emulated through our artificial compound eyes. More importantly, two intriguing polarization-perceptual applications for polarized navigation with reconfigurable adaptive learning abilities and three-dimensional visual polarization imaging are also experimentally demonstrated. The proposed device may provide a promising opportunity for future polarization perception systems in intelligent humanoid robots and autonomous vehicles.
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Affiliation(s)
- Dingdong Xie
- Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China.
| | - Kai Yin
- Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China.
| | - Zhong-Jian Yang
- Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China.
| | - Han Huang
- Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China.
| | - Xiaohui Li
- School of Physics and Information Technology, Shanxi Normal University, Xi'an 710119, P. R. China
| | - Zhiwen Shu
- State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, P. R. China
| | - Huigao Duan
- State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, P. R. China
| | - Jun He
- Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China.
| | - Jie Jiang
- Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China.
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55
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Abstract
Major recent advances and previous data have led to a plausible model of how key proteins mediate neurotransmitter release. In this model, the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptor (SNARE) proteins syntaxin-1, SNAP-25, and synaptobrevin form tight complexes that bring the membranes together and are crucial for membrane fusion. NSF and SNAPs disassemble SNARE complexes and ensure that fusion occurs through an exquisitely regulated pathway that starts with Munc18-1 bound to a closed conformation of syntaxin-1. Munc18-1 also binds to synaptobrevin, forming a template to assemble the SNARE complex when Munc13-1 opens syntaxin-1 while bridging the vesicle and plasma membranes. Synaptotagmin-1 and complexin bind to partially assembled SNARE complexes, likely stabilizing them and preventing fusion until Ca2+ binding to synaptotagmin-1 causes dissociation from the SNARE complex and induces interactions with phospholipids that help trigger release. Although fundamental questions remain about the mechanism of membrane fusion, these advances provide a framework to investigate the mechanisms underlying presynaptic plasticity.
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Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry, and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA;
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56
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Qin N, Chen Z, Xue R. A two-subpopulation model that reflects heterogeneity of large dense core vesicles in exocytosis. Cell Cycle 2022; 21:531-546. [PMID: 35067177 PMCID: PMC8942488 DOI: 10.1080/15384101.2022.2026576] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Exocytosis of large dense core vesicles is responsible for hormone secretion in neuroendocrine cells. The population of primed vesicles ready to release upon cell excitation demonstrates large heterogeneity. However, there are currently no models that clearly reflect such heterogeneity. Here, we develop a novel model based on single vesicle release events from amperometry recordings of PC12 cells using carbon fiber microelectrode. In this model, releasable vesicles can be grouped into two subpopulations, namely, SP1 and SP2. SP1 vesicles replenish quickly, with kinetics of ~0.0368 s-1, but likely undergo slow fusion pore expansion (amperometric signals rise at ~2.5 pA/ms), while SP2 vesicles demonstrate slow replenishment (kinetics of ~0.0048 s-1) but prefer fast dilation of fusion pore, with an amperometric signal rising rate of ~9.1 pA/ms. Phorbol ester enlarges the size of SP2 partially via activation of protein kinase C and conveys SP1 vesicles into SP2. Inhibition of Rho GTPase-dependent actin rearrangement almost completely depletes SP2. We also propose that the phorbol ester-sensitive vesicle subpopulation (SP2) is analogous to the subset of superprimed synaptic vesicles in neurons. This model provides a meticulous description of the architecture of the readily releasable vesicle pool and elucidates the heterogeneity of the vesicle priming mechanism.
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Affiliation(s)
- Nan Qin
- Shanghai Key Laboratory of Maternal Fetal Medicine, Clinical and Translational Research Center of Shanghai First Maternity & Infant Hospital, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, China
| | - Zhixi Chen
- Shanghai Key Laboratory of Maternal Fetal Medicine, Clinical and Translational Research Center of Shanghai First Maternity & Infant Hospital, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, China
| | - Renhao Xue
- Shanghai Key Laboratory of Maternal Fetal Medicine, Clinical and Translational Research Center of Shanghai First Maternity & Infant Hospital, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, China,CONTACT Renhao Xue Shanghai Key Laboratory of Maternal Fetal Medicine, Clinical and Translational Research Center of Shanghai First Maternity & Infant Hospital, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, China
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57
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Munc13 structural transitions and oligomers that may choreograph successive stages in vesicle priming for neurotransmitter release. Proc Natl Acad Sci U S A 2022; 119:2121259119. [PMID: 35135883 PMCID: PMC8851502 DOI: 10.1073/pnas.2121259119] [Citation(s) in RCA: 30] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/21/2021] [Indexed: 12/24/2022] Open
Abstract
The speed of neural information processing in the human central nervous system is ultimately determined by the speed of chemical transmission at synapses, because action potentials have relatively short distances to traverse. The release of synaptic vesicles containing neurotransmitters must therefore be remarkably fast as compared to other forms of membrane fusion. Six separate SNARE complexes cooperate to achieve this. But how can exactly six copies be assembled under every vesicle? Here we report that six copies of the key molecular chaperone that assembles the SNAREs can arrange themselves into a closed hexagon, providing the likely answer. How can exactly six SNARE complexes be assembled under each synaptic vesicle? Here we report cryo-EM crystal structures of the core domain of Munc13, the key chaperone that initiates SNAREpin assembly. The functional core of Munc13, consisting of C1–C2B–MUN–C2C (Munc13C) spontaneously crystallizes between phosphatidylserine-rich bilayers in two distinct conformations, each in a radically different oligomeric state. In the open conformation (state 1), Munc13C forms upright trimers that link the two bilayers, separating them by ∼21 nm. In the closed conformation, six copies of Munc13C interact to form a lateral hexamer elevated ∼14 nm above the bilayer. Open and closed conformations differ only by a rigid body rotation around a flexible hinge, which when performed cooperatively assembles Munc13 into a lateral hexamer (state 2) in which the key SNARE assembly-activating site of Munc13 is autoinhibited by its neighbor. We propose that each Munc13 in the lateral hexamer ultimately assembles a single SNAREpin, explaining how only and exactly six SNARE complexes are templated. We suggest that state 1 and state 2 may represent two successive states in the synaptic vesicle supply chain leading to “primed” ready-release vesicles in which SNAREpins are clamped and ready to release (state 3).
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58
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Martínez-Valencia A, Ramírez-Santiago G, De-Miguel FF. Dynamics of Neuromuscular Transmission Reproduced by Calcium-Dependent and Reversible Serial Transitions in the Vesicle Fusion Complex. Front Synaptic Neurosci 2022; 13:785361. [PMID: 35242023 PMCID: PMC8885725 DOI: 10.3389/fnsyn.2021.785361] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 12/30/2021] [Indexed: 11/28/2022] Open
Abstract
Neuromuscular transmission, from spontaneous release to facilitation and depression, was accurately reproduced by a mechanistic kinetic model of sequential maturation transitions in the molecular fusion complex. The model incorporates three predictions. First, calcium-dependent forward transitions take vesicles from docked to preprimed to primed states, followed by fusion. Second, prepriming and priming are reversible. Third, fusion and recycling are unidirectional. The model was fed with experimental data from previous studies, whereas the backward (β) and recycling (ρ) rate constant values were fitted. Classical experiments were successfully reproduced with four transition states in the model when every forward (α) rate constant had the same value, and both backward rate constants were 50–100 times larger. Such disproportion originated an abruptly decreasing gradient of resting vesicles from docked to primed states. By contrast, a three-state version of the model failed to reproduce the dynamics of transmission by using the same set of parameters. Simulations predict the following: (1) Spontaneous release reflects primed to fusion spontaneous transitions. (2) Calcium elevations synchronize the series of forward transitions that lead to fusion. (3) Facilitation reflects a transient increase of priming following the calcium-dependent maturation transitions. (4) The calcium sensors that produce facilitation are those that evoke the transitions form docked to primed states. (5) Backward transitions and recycling restore the resting state. (6) Depression reflects backward transitions and slow recycling after intense release. Altogether, our results predict that fusion is produced by one calcium sensor, whereas the modulation of the number of vesicles that fuse depends on the calcium sensors that promote the early transition states. Such finely tuned kinetics offers a mechanism for collective non-linear transitional adaptations of a homogeneous vesicle pool to the ever-changing pattern of electrical activity in the neuromuscular junction.
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Affiliation(s)
- Alejandro Martínez-Valencia
- Posgrado en Ciencias Físicas, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
- Instituto de Fisiología Celular-Neurociencias, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
| | | | - Francisco F. De-Miguel
- Instituto de Fisiología Celular-Neurociencias, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
- *Correspondence: Francisco F. De-Miguel,
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59
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Holderith N, Aldahabi M, Nusser Z. Selective Enrichment of Munc13-2 in Presynaptic Active Zones of Hippocampal Pyramidal Cells That Innervate mGluR1α Expressing Interneurons. Front Synaptic Neurosci 2022; 13:773209. [PMID: 35221979 PMCID: PMC8866005 DOI: 10.3389/fnsyn.2021.773209] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/27/2021] [Indexed: 11/13/2022] Open
Abstract
Selective distribution of proteins in presynaptic active zones (AZs) is a prerequisite for generating postsynaptic target cell type-specific differences in presynaptic vesicle release probability (Pv) and short-term plasticity, a characteristic feature of cortical pyramidal cells (PCs). In the hippocampus of rodents, somatostatin and mGluR1α expressing interneurons (mGluR1α+ INs) receive small, facilitating excitatory postsynaptic currents (EPSCs) from PCs and express Elfn1 that trans-synaptically recruits mGluR7 into the presynaptic AZ of PC axons. Here we show that Elfn1 also has a role in the selective recruitment of Munc13-2, a synaptic vesicle priming and docking protein, to PC AZs that innervate mGluR1α+ INs. In Elfn1 knock-out mice, unitary EPSCs (uEPSCs) in mGluR1α+ INs have threefold larger amplitudes with less pronounced short-term facilitation, which might be the consequence of the loss of either mGluR7 or Munc13-2 or both. Conditional genetic deletion of Munc13-2 from CA1 PCs results in the loss of Munc13-2, but not mGluR7 from the AZs, and has no effect on the amplitude of uEPSCs and leaves the characteristic short-term facilitation intact at PC to mGluR1α+ IN connection. Our results demonstrate that Munc13-1 alone is capable of imposing low Pv at PC to mGluR1α+ IN synapses and Munc13-2 has yet an unknown role in this synapse.
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Affiliation(s)
- Noemi Holderith
- Institute of Experimental Medicine, Eotvos Lorand Research Network, Budapest, Hungary
| | - Mohammad Aldahabi
- Institute of Experimental Medicine, Eotvos Lorand Research Network, Budapest, Hungary
- János Szentágothai School of Neurosciences, Semmelweis University, Budapest, Hungary
| | - Zoltan Nusser
- Institute of Experimental Medicine, Eotvos Lorand Research Network, Budapest, Hungary
- *Correspondence: Zoltan Nusser,
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60
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Three small vesicular pools in sequence govern synaptic response dynamics during action potential trains. Proc Natl Acad Sci U S A 2022; 119:2114469119. [PMID: 35101920 PMCID: PMC8812539 DOI: 10.1073/pnas.2114469119] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/08/2021] [Indexed: 11/30/2022] Open
Abstract
Short-term changes in the strength of synaptic connections underlie many brain functions. The strength of a synapse in response to subsequent stimulation is largely determined by the remaining number of synaptic vesicles available for release. We developed a methodological approach to measure the dynamics of various vesicle pools following synaptic activity. We find that the readily releasable pool, which comprises vesicles that are docked or tethered to release sites, is fed by a small-sized pool containing approximately one to four vesicles per release site at rest. This upstream pool is significantly depleted even after a short stimulation train. Therefore, regulation of the size of the upstream pool emerges as a key factor in determining synaptic strength during and after sustained stimulation. During prolonged trains of presynaptic action potentials (APs), synaptic release reaches a stable level that reflects the speed of replenishment of the readily releasable pool (RRP). Determining the size and filling dynamics of vesicular pools upstream of the RRP has been hampered by a lack of precision of synaptic output measurements during trains. Using the recent technique of tracking vesicular release in single active zone synapses, we now developed a method that allows the sizes of the RRP and upstream pools to be followed in time. We find that the RRP is fed by a small-sized pool containing approximately one to four vesicles per docking site at rest. This upstream pool is significantly depleted by short AP trains, and reaches a steady, depleted state for trains of >10 APs. We conclude that a small, highly dynamic vesicular pool upstream of the RRP potently controls synaptic strength during sustained stimulation.
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61
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Wichmann C, Kuner T. Heterogeneity of glutamatergic synapses: cellular mechanisms and network consequences. Physiol Rev 2022; 102:269-318. [PMID: 34727002 DOI: 10.1152/physrev.00039.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Chemical synapses are commonly known as a structurally and functionally highly diverse class of cell-cell contacts specialized to mediate communication between neurons. They represent the smallest "computational" unit of the brain and are typically divided into excitatory and inhibitory as well as modulatory categories. These categories are subdivided into diverse types, each representing a different structure-function repertoire that in turn are thought to endow neuronal networks with distinct computational properties. The diversity of structure and function found among a given category of synapses is referred to as heterogeneity. The main building blocks for this heterogeneity are synaptic vesicles, the active zone, the synaptic cleft, the postsynaptic density, and glial processes associated with the synapse. Each of these five structural modules entails a distinct repertoire of functions, and their combination specifies the range of functional heterogeneity at mammalian excitatory synapses, which are the focus of this review. We describe synapse heterogeneity that is manifested on different levels of complexity ranging from the cellular morphology of the pre- and postsynaptic cells toward the expression of different protein isoforms at individual release sites. We attempt to define the range of structural building blocks that are used to vary the basic functional repertoire of excitatory synaptic contacts and discuss sources and general mechanisms of synapse heterogeneity. Finally, we explore the possible impact of synapse heterogeneity on neuronal network function.
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Affiliation(s)
- Carolin Wichmann
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Institute for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Thomas Kuner
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, Heidelberg, Germany
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62
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Abstract
Rapid and precise neuronal communication is enabled through a highly synchronous release of signaling molecules neurotransmitters within just milliseconds of the action potential. Yet neurotransmitter release lacks a theoretical framework that is both phenomenologically accurate and mechanistically realistic. Here, we present an analytic theory of the action-potential-triggered neurotransmitter release at the chemical synapse. The theory is demonstrated to be in detailed quantitative agreement with existing data on a wide variety of synapses from electrophysiological recordings in vivo and fluorescence experiments in vitro. Despite up to ten orders of magnitude of variation in the release rates among the synapses, the theory reveals that synaptic transmission obeys a simple, universal scaling law, which we confirm through a collapse of the data from strikingly diverse synapses onto a single master curve. This universality is complemented by the capacity of the theory to readily extract, through a fit to the data, the kinetic and energetic parameters that uniquely identify each synapse. The theory provides a means to detect cooperativity among the SNARE complexes that mediate vesicle fusion and reveals such cooperativity in several existing data sets. The theory is further applied to establish connections between molecular constituents of synapses and synaptic function. The theory allows competing hypotheses of short-term plasticity to be tested and identifies the regimes where particular mechanisms of synaptic facilitation dominate or, conversely, fail to account for the existing data for the paired-pulse ratio. The derived trade-off relation between the transmission rate and fidelity shows how transmission failure can be controlled by changing the microscopic properties of the vesicle pool and SNARE complexes. The established condition for the maximal synaptic efficacy reveals that no fine tuning is needed for certain synapses to maintain near-optimal transmission. We discuss the limitations of the theory and propose possible routes to extend it. These results provide a quantitative basis for the notion that the molecular-level properties of synapses are crucial determinants of the computational and information-processing functions in synaptic transmission.
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Affiliation(s)
- Bin Wang
- Department of Physics, University of California, San DiegoLa JollaUnited States
| | - Olga K Dudko
- Department of Physics, University of California, San DiegoLa JollaUnited States
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63
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Camacho M, Quade B, Trimbuch T, Xu J, Sari L, Rizo J, Rosenmund C. Control of neurotransmitter release by two distinct membrane-binding faces of the Munc13-1 C 1C 2B region. eLife 2021; 10:e72030. [PMID: 34779770 PMCID: PMC8648301 DOI: 10.7554/elife.72030] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 11/14/2021] [Indexed: 11/23/2022] Open
Abstract
Munc13-1 plays a central role in neurotransmitter release through its conserved C-terminal region, which includes a diacyglycerol (DAG)-binding C1 domain, a Ca2+/PIP2-binding C2B domain, a MUN domain and a C2C domain. Munc13-1 was proposed to bridge synaptic vesicles to the plasma membrane through distinct interactions of the C1C2B region with the plasma membrane: (i) one involving a polybasic face that is expected to yield a perpendicular orientation of Munc13-1 and hinder release; and (ii) another involving the DAG-Ca2+-PIP2-binding face that is predicted to result in a slanted orientation and facilitate release. Here, we have tested this model and investigated the role of the C1C2B region in neurotransmitter release. We find that K603E or R769E point mutations in the polybasic face severely impair Ca2+-independent liposome bridging and fusion in in vitro reconstitution assays, and synaptic vesicle priming in primary murine hippocampal cultures. A K720E mutation in the polybasic face and a K706E mutation in the C2B domain Ca2+-binding loops have milder effects in reconstitution assays and do not affect vesicle priming, but enhance or impair Ca2+-evoked release, respectively. The phenotypes caused by combining these mutations are dominated by the K603E and R769E mutations. Our results show that the C1-C2B region of Munc13-1 plays a central role in vesicle priming and support the notion that two distinct faces of this region control neurotransmitter release and short-term presynaptic plasticity.
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Affiliation(s)
- Marcial Camacho
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of NeurophysiologyBerlinGermany
- NeuroCure Cluster of ExcellenceBerlinGermany
| | - Bradley Quade
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biochemistry, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Pharmacology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Thorsten Trimbuch
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of NeurophysiologyBerlinGermany
- NeuroCure Cluster of ExcellenceBerlinGermany
| | - Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biochemistry, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Pharmacology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Levent Sari
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Cecil H. and Ida Green Comprehensive Center for Molecular, Computational and Systems Biology, University of Texas Southwestern Medical CenterDallasUnited States
- Center for Alzheimer’s and Neurodegenerative Diseases, University of Texas Southwestern Medical CenterDallasUnited States
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biochemistry, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Pharmacology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Christian Rosenmund
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of NeurophysiologyBerlinGermany
- NeuroCure Cluster of ExcellenceBerlinGermany
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64
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Das B, Singh N, Yao AY, Zhou J, He W, Hu X, Yan R. BACE1 controls synaptic function through modulating release of synaptic vesicles. Mol Psychiatry 2021; 26:6394-6410. [PMID: 34158621 PMCID: PMC8760050 DOI: 10.1038/s41380-021-01166-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 04/27/2021] [Accepted: 05/06/2021] [Indexed: 01/20/2023]
Abstract
BACE1 initiates production of β-amyloid peptides (Aβ), which is associated with cognitive dysfunction in Alzheimer's disease (AD) due to abnormal oligomerization and aggregation. While BACE1 inhibitors show strong reduction in Aβ deposition, they fail to improve cognitive function in patients, largely due to its role in synaptic function. We show that BACE1 is required for optimal release of synaptic vesicles. BACE1 deficiency or inhibition decreases synaptic vesicle docking in the synaptic active zones. Consistently, BACE1-null mice or mice treated with clinically tested BACE1 inhibitors Verubecestat and Lanabecestat exhibit severe reduction in hippocampal LTP and learning behaviors. To counterbalance this synaptic deficit, we discovered that BACE1-null mice treated with positive allosteric modulators (PAMs) of metabotropic glutamate receptor 1 (mGluR1), whose levels were reduced in BACE1-null mice and significantly improved long-term potentiation and cognitive behaviors. Similarly, mice treated with mGluR1 PAM showed significantly mitigated synaptic deficits caused by BACE1 inhibitors. Together, our data suggest that a therapy combining BACE1 inhibitors for reducing amyloid deposition and an mGluR1 PAM for counteracting BACE1-mediated synaptic deficits appears to be an effective approach for treating AD patients.
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Affiliation(s)
- Brati Das
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - Neeraj Singh
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - Annie Y Yao
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - John Zhou
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - Wanxia He
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - Xiangyou Hu
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - Riqiang Yan
- Department of Neuroscience, UConn Health, Farmington, CT, USA.
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65
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Mochida S. Stable and Flexible Synaptic Transmission Controlled by the Active Zone Protein Interactions. Int J Mol Sci 2021; 22:ijms222111775. [PMID: 34769208 PMCID: PMC8583982 DOI: 10.3390/ijms222111775] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 10/24/2021] [Accepted: 10/25/2021] [Indexed: 12/28/2022] Open
Abstract
An action potential triggers neurotransmitter release from synaptic vesicles docking to a specialized release site of the presynaptic plasma membrane, the active zone. The active zone is a highly organized structure with proteins that serves as a platform for synaptic vesicle exocytosis, mediated by SNAREs complex and Ca2+ sensor proteins, within a sub-millisecond opening of nearby Ca2+ channels with the membrane depolarization. In response to incoming neuronal signals, each active zone protein plays a role in the release-ready site replenishment with synaptic vesicles for sustainable synaptic transmission. The active zone release apparatus provides a possible link between neuronal activity and plasticity. This review summarizes the mostly physiological role of active zone protein interactions that control synaptic strength, presynaptic short-term plasticity, and homeostatic synaptic plasticity.
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Affiliation(s)
- Sumiko Mochida
- Department of Physiology, Tokyo Medical University, Tokyo 160-8402, Japan
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66
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Grabner CP, Moser T. The mammalian rod synaptic ribbon is essential for Ca v channel facilitation and ultrafast synaptic vesicle fusion. eLife 2021; 10:63844. [PMID: 34617508 PMCID: PMC8594941 DOI: 10.7554/elife.63844] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 10/06/2021] [Indexed: 12/19/2022] Open
Abstract
Rod photoreceptors (PRs) use ribbon synapses to transmit visual information. To signal ‘no light detected’ they release glutamate continually to activate post-synaptic receptors. When light is detected glutamate release pauses. How a rod’s individual ribbon enables this process was studied here by recording evoked changes in whole-cell membrane capacitance from wild-type and ribbonless (Ribeye-ko) mice. Wild-type rods filled with high (10 mM) or low (0.5 mM) concentrations of the Ca2+-buffer EGTA created a readily releasable pool (RRP) of 87 synaptic vesicles (SVs) that emptied as a single kinetic phase with a τ<0.4 ms. The lower concentration of EGTA accelerated Cav channel opening and facilitated release kinetics. In contrast, ribbonless rods created a much smaller RRP of 22 SVs, and they lacked Cav channel facilitation; however, Ca2+ channel-release coupling remained tight. These release deficits caused a sharp attenuation of rod-driven scotopic light responses. We conclude that the synaptic ribbon facilitates Ca2+-influx and establishes a large RRP of SVs.
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Affiliation(s)
- Chad Paul Grabner
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 1286 'Quantitative Synaptology', University of Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 1286 'Quantitative Synaptology', University of Göttingen, Göttingen, Germany.,Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
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67
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Eshra A, Schmidt H, Eilers J, Hallermann S. Calcium dependence of neurotransmitter release at a high fidelity synapse. eLife 2021; 10:70408. [PMID: 34612812 PMCID: PMC8494478 DOI: 10.7554/elife.70408] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Accepted: 08/24/2021] [Indexed: 11/15/2022] Open
Abstract
The Ca2+-dependence of the priming, fusion, and replenishment of synaptic vesicles are fundamental parameters controlling neurotransmitter release and synaptic plasticity. Despite intense efforts, these important steps in the synaptic vesicles’ cycle remain poorly understood due to the technical challenge in disentangling vesicle priming, fusion, and replenishment. Here, we investigated the Ca2+-sensitivity of these steps at mossy fiber synapses in the rodent cerebellum, which are characterized by fast vesicle replenishment mediating high-frequency signaling. We found that the basal free Ca2+ concentration (<200 nM) critically controls action potential-evoked release, indicating a high-affinity Ca2+ sensor for vesicle priming. Ca2+ uncaging experiments revealed a surprisingly shallow and non-saturating relationship between release rate and intracellular Ca2+ concentration up to 50 μM. The rate of vesicle replenishment during sustained elevated intracellular Ca2+ concentration exhibited little Ca2+-dependence. Finally, quantitative mechanistic release schemes with five Ca2+ binding steps incorporating rapid vesicle replenishment via parallel or sequential vesicle pools could explain our data. We thus show that co-existing high- and low-affinity Ca2+ sensors mediate priming, fusion, and replenishment of synaptic vesicles at a high-fidelity synapse.
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Affiliation(s)
- Abdelmoneim Eshra
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Hartmut Schmidt
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Stefan Hallermann
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
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68
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Mrestani A, Pauli M, Kollmannsberger P, Repp F, Kittel RJ, Eilers J, Doose S, Sauer M, Sirén AL, Heckmann M, Paul MM. Active zone compaction correlates with presynaptic homeostatic potentiation. Cell Rep 2021; 37:109770. [PMID: 34610300 DOI: 10.1016/j.celrep.2021.109770] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 05/14/2021] [Accepted: 09/07/2021] [Indexed: 12/30/2022] Open
Abstract
Neurotransmitter release is stabilized by homeostatic plasticity. Presynaptic homeostatic potentiation (PHP) operates on timescales ranging from minute- to life-long adaptations and likely involves reorganization of presynaptic active zones (AZs). At Drosophila melanogaster neuromuscular junctions, earlier work ascribed AZ enlargement by incorporating more Bruchpilot (Brp) scaffold protein a role in PHP. We use localization microscopy (direct stochastic optical reconstruction microscopy [dSTORM]) and hierarchical density-based spatial clustering of applications with noise (HDBSCAN) to study AZ plasticity during PHP at the synaptic mesoscale. We find compaction of individual AZs in acute philanthotoxin-induced and chronic genetically induced PHP but unchanged copy numbers of AZ proteins. Compaction even occurs at the level of Brp subclusters, which move toward AZ centers, and in Rab3 interacting molecule (RIM)-binding protein (RBP) subclusters. Furthermore, correlative confocal and dSTORM imaging reveals how AZ compaction in PHP translates into apparent increases in AZ area and Brp protein content, as implied earlier.
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Affiliation(s)
- Achmed Mrestani
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Neurology, Leipzig University Medical Center, 04103 Leipzig, Germany
| | - Martin Pauli
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Neurosurgery, University Hospital of Würzburg, 97080 Würzburg, Germany
| | - Philip Kollmannsberger
- Center for Computational and Theoretical Biology, Julius Maximilians University Würzburg, 97074 Würzburg, Germany
| | - Felix Repp
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Center for Computational and Theoretical Biology, Julius Maximilians University Würzburg, 97074 Würzburg, Germany; Department of Neurosurgery, University Hospital of Würzburg, 97080 Würzburg, Germany
| | - Robert J Kittel
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Institute of Biology, Department of Animal Physiology, Leipzig University, 04103 Leipzig, Germany; Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - Sören Doose
- Department of Biotechnology and Biophysics, Julius Maximilians University Würzburg, 97074 Würzburg, Germany
| | - Markus Sauer
- Department of Biotechnology and Biophysics, Julius Maximilians University Würzburg, 97074 Würzburg, Germany
| | - Anna-Leena Sirén
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Neurosurgery, University Hospital of Würzburg, 97080 Würzburg, Germany
| | - Manfred Heckmann
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany.
| | - Mila M Paul
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Orthopaedic Trauma, Hand, Plastic and Reconstructive Surgery, University Hospital of Würzburg, 97080 Würzburg, Germany.
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69
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Sauvola CW, Littleton JT. SNARE Regulatory Proteins in Synaptic Vesicle Fusion and Recycling. Front Mol Neurosci 2021; 14:733138. [PMID: 34421538 PMCID: PMC8377282 DOI: 10.3389/fnmol.2021.733138] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 07/20/2021] [Indexed: 01/01/2023] Open
Abstract
Membrane fusion is a universal feature of eukaryotic protein trafficking and is mediated by the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) family. SNARE proteins embedded in opposing membranes spontaneously assemble to drive membrane fusion and cargo exchange in vitro. Evolution has generated a diverse complement of SNARE regulatory proteins (SRPs) that ensure membrane fusion occurs at the right time and place in vivo. While a core set of SNAREs and SRPs are common to all eukaryotic cells, a specialized set of SRPs within neurons confer additional regulation to synaptic vesicle (SV) fusion. Neuronal communication is characterized by precise spatial and temporal control of SNARE dynamics within presynaptic subdomains specialized for neurotransmitter release. Action potential-elicited Ca2+ influx at these release sites triggers zippering of SNAREs embedded in the SV and plasma membrane to drive bilayer fusion and release of neurotransmitters that activate downstream targets. Here we discuss current models for how SRPs regulate SNARE dynamics and presynaptic output, emphasizing invertebrate genetic findings that advanced our understanding of SRP regulation of SV cycling.
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Affiliation(s)
- Chad W Sauvola
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States
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70
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Rapid Ca 2+ channel accumulation contributes to cAMP-mediated increase in transmission at hippocampal mossy fiber synapses. Proc Natl Acad Sci U S A 2021; 118:2016754118. [PMID: 33622791 DOI: 10.1073/pnas.2016754118] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The cyclic adenosine monophosphate (cAMP)-dependent potentiation of neurotransmitter release is important for higher brain functions such as learning and memory. To reveal the underlying mechanisms, we applied paired pre- and postsynaptic recordings from hippocampal mossy fiber-CA3 synapses. Ca2+ uncaging experiments did not reveal changes in the intracellular Ca2+ sensitivity for transmitter release by cAMP, but suggested an increase in the local Ca2+ concentration at the release site, which was much lower than that of other synapses before potentiation. Total internal reflection fluorescence (TIRF) microscopy indicated a clear increase in the local Ca2+ concentration at the release site within 5 to 10 min, suggesting that the increase in local Ca2+ is explained by the simple mechanism of rapid Ca2+ channel accumulation. Consistently, two-dimensional time-gated stimulated emission depletion microscopy (gSTED) microscopy showed an increase in the P/Q-type Ca2+ channel cluster size near the release sites. Taken together, this study suggests a potential mechanism for the cAMP-dependent increase in transmission at hippocampal mossy fiber-CA3 synapses, namely an accumulation of active zone Ca2+ channels.
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71
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Ma R, Hanse E, Gustafsson B. Homosynaptic frequency-dependent depression by release site inactivation at neonatal hippocampal synapses in the stratum lacunosum-moleculare. Eur J Neurosci 2021; 54:4838-4862. [PMID: 34137082 DOI: 10.1111/ejn.15357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Accepted: 05/31/2021] [Indexed: 11/27/2022]
Abstract
When activated at low frequencies (0.1-1 Hz), second postnatal week synapses onto the most distal part of the apical dendritic tree (stratum lacunosum-moleculare) of rat hippocampal CA1 pyramidal cells display a frequency-dependent synaptic depression not observed for the more proximal (stratum radiatum) synapses. Depression in this frequency range is thought of as a possible contributor to behavioural habituation. In fact, in contrast to the proximal synapses, the distal synapses provide more direct sensory information from the entorhinal cortex as well as from thalamic nuclei. The use of antagonists showed that the activation of GABAA , GABAB , NMDA, mGlu, kainate, adenosine, or endocannabinoid receptors was not directly involved in the depression, indicating it to be intrinsic to the synapses themselves. While the depression affected paired-pulse plasticity in a manner indicating a decrease in vesicle release probability, the depression could not be explained by a stimulus-dependent decrease in calcium influx. Despite affecting the synaptic response evoked by brief high-frequency stimulation (10 impulses, 20 Hz) in a manner indicating vesicle depletion, the depression was unaffected by large variations in release probability. The depression was found not only to affect the synaptic transmission at low frequencies (0.1-1 Hz) but also to contribute to the depression evolving during brief high-frequency stimulation (10 impulses, 20 Hz). We propose that a release-independent process directly inactivating release sites with a fast onset (ms) and long duration (up to 20 s) underlies this synaptic depression.
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Affiliation(s)
- Rong Ma
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Eric Hanse
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Bengt Gustafsson
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
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72
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Cross-platform validation of neurotransmitter release impairments in schizophrenia patient-derived NRXN1-mutant neurons. Proc Natl Acad Sci U S A 2021; 118:2025598118. [PMID: 34035170 DOI: 10.1073/pnas.2025598118] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Heterozygous NRXN1 deletions constitute the most prevalent currently known single-gene mutation associated with schizophrenia, and additionally predispose to multiple other neurodevelopmental disorders. Engineered heterozygous NRXN1 deletions impaired neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. Utilizing this observation for drug discovery, however, requires confidence in its robustness and validity. Here, we describe a multicenter effort to test the generality of this pivotal observation, using independent analyses at two laboratories of patient-derived and newly engineered human neurons with heterozygous NRXN1 deletions. Using neurons transdifferentiated from induced pluripotent stem cells that were derived from schizophrenia patients carrying heterozygous NRXN1 deletions, we observed the same synaptic impairment as in engineered NRXN1-deficient neurons. This impairment manifested as a large decrease in spontaneous synaptic events, in evoked synaptic responses, and in synaptic paired-pulse depression. Nrxn1-deficient mouse neurons generated from embryonic stem cells by the same method as human neurons did not exhibit impaired neurotransmitter release, suggesting a human-specific phenotype. Human NRXN1 deletions produced a reproducible increase in the levels of CASK, an intracellular NRXN1-binding protein, and were associated with characteristic gene-expression changes. Thus, heterozygous NRXN1 deletions robustly impair synaptic function in human neurons regardless of genetic background, enabling future drug discovery efforts.
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73
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Silva M, Tran V, Marty A. Calcium-dependent docking of synaptic vesicles. Trends Neurosci 2021; 44:579-592. [PMID: 34049722 DOI: 10.1016/j.tins.2021.04.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 02/23/2021] [Accepted: 04/09/2021] [Indexed: 10/21/2022]
Abstract
The concentration of calcium ions in presynaptic terminals regulates transmitter release, but underlying mechanisms have remained unclear. Here we review recent studies that shed new light on this issue. Fast-freezing electron microscopy and total internal reflection fluorescence microscopy studies reveal complex calcium-dependent vesicle movements including docking on a millisecond time scale. Recordings from so-called 'simple synapses' indicate that calcium not only triggers exocytosis, but also modifies synaptic strength by controlling a final, rapid vesicle maturation step before release. Molecular studies identify several calcium-sensitive domains on Munc13 and on synaptotagmin-1 that are likely involved in bringing the vesicular and plasma membranes closer together in response to calcium elevation. Together, these results suggest that calcium-dependent vesicle docking occurs in a wide range of time domains and plays a crucial role in several phenomena including synaptic facilitation, post-tetanic potentiation, and neuromodulator-induced potentiation.
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Affiliation(s)
- Melissa Silva
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRS, F-75006 Paris, France
| | - Van Tran
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRS, F-75006 Paris, France
| | - Alain Marty
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRS, F-75006 Paris, France.
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74
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CAPS1 is involved in hippocampal synaptic plasticity and hippocampus-associated learning. Sci Rep 2021; 11:8656. [PMID: 33883618 PMCID: PMC8060421 DOI: 10.1038/s41598-021-88009-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 04/07/2021] [Indexed: 12/14/2022] Open
Abstract
Calcium-dependent activator protein for secretion 1 (CAPS1) is a key molecule in vesicular exocytosis, probably in the priming step. However, CAPS1's role in synaptic plasticity and brain function is elusive. Herein, we showed that synaptic plasticity and learning behavior were impaired in forebrain and/or hippocampus-specific Caps1 conditional knockout (cKO) mice by means of molecular, physiological, and behavioral analyses. Neonatal Caps1 cKO mice showed a decrease in the number of docked vesicles in the hippocampal CA3 region, with no detectable changes in the distribution of other major exocytosis-related molecules. Additionally, long-term potentiation (LTP) was partially and severely impaired in the CA1 and CA3 regions, respectively. CA1 LTP was reinforced by repeated high-frequency stimuli, whereas CA3 LTP was completely abolished. Accordingly, hippocampus-associated learning was severely impaired in adeno-associated virus (AAV) infection-mediated postnatal Caps1 cKO mice. Collectively, our findings suggest that CAPS1 is a key protein involved in the cellular mechanisms underlying hippocampal synaptic release and plasticity, which is crucial for hippocampus-associated learning.
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75
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Shortened tethering filaments stabilize presynaptic vesicles in support of elevated release probability during LTP in rat hippocampus. Proc Natl Acad Sci U S A 2021; 118:2018653118. [PMID: 33875591 DOI: 10.1073/pnas.2018653118] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Long-term potentiation (LTP) is a cellular mechanism of learning and memory that results in a sustained increase in the probability of vesicular release of neurotransmitter. However, previous work in hippocampal area CA1 of the adult rat revealed that the total number of vesicles per synapse decreases following LTP, seemingly inconsistent with the elevated release probability. Here, electron-microscopic tomography (EMT) was used to assess whether changes in vesicle density or structure of vesicle tethering filaments at the active zone might explain the enhanced release probability following LTP. The spatial relationship of vesicles to the active zone varies with functional status. Tightly docked vesicles contact the presynaptic membrane, have partially formed SNARE complexes, and are primed for release of neurotransmitter upon the next action potential. Loosely docked vesicles are located within 8 nm of the presynaptic membrane where SNARE complexes begin to form. Nondocked vesicles comprise recycling and reserve pools. Vesicles are tethered to the active zone via filaments composed of molecules engaged in docking and release processes. The density of tightly docked vesicles was increased 2 h following LTP compared to control stimulation, whereas the densities of loosely docked or nondocked vesicles congregating within 45 nm above the active zones were unchanged. The tethering filaments on all vesicles were shorter and their attachment sites shifted closer to the active zone. These findings suggest that tethering filaments stabilize more vesicles in the primed state. Such changes would facilitate the long-lasting increase in release probability following LTP.
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76
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Xu YF, Chen X, Yang Z, Xiao P, Liu CH, Li KS, Yang XZ, Wang YJ, Zhu ZL, Xu ZG, Zhang S, Wang C, Song YC, Zhao WD, Wang CH, Ji ZL, Zhang ZY, Cui M, Sun JP, Yu X. PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates. EMBO Rep 2021; 22:e52141. [PMID: 33764618 DOI: 10.15252/embr.202052141] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/26/2021] [Accepted: 02/18/2021] [Indexed: 02/02/2023] Open
Abstract
Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrate that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses reveal key residues that govern the interaction between PTP-MEG2 and its substrate, a peptide containing the phosphorylated NSF-pY83 site, specify PTP-MEG2 substrate selectivity, and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface reveals that PTP-MEG2 controls the fusion pore opening through NSF independent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we uncover that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY125 and MUNC18-1-pY145 sites. Further structural and biochemical analyses confirmed the interaction of PTP-MEG2 with MUNC18-1-pY145 or DYNAMIN2-pY125 through a distinct structural basis compared with that of the NSF-pY83 site. Our studies thus provide mechanistic insights in complex exocytosis processes.
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Affiliation(s)
- Yun-Fei Xu
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China.,Department of General Surgery, Qilu Hospital of Shandong University, Jinan, China
| | - Xu Chen
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Physiology, Shandong University School of Medicine, Jinan, China
| | - Zhao Yang
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Peng Xiao
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Chun-Hua Liu
- Department of Physiology, Shandong First Medical University, Taian, China
| | - Kang-Shuai Li
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China.,Department of General Surgery, Qilu Hospital of Shandong University, Jinan, China
| | - Xiao-Zhen Yang
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen, China
| | - Yi-Jing Wang
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Zhong-Liang Zhu
- School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Zhi-Gang Xu
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, China
| | - Sheng Zhang
- Departments of Medicinal Chemistry and Molecular Pharmacology and of Chemistry, Center for Cancer Research, and Institute for Drug Discovery, Purdue University, West Lafayette, IN, USA
| | - Chuan Wang
- Department of Pharmacology, Hebei Medical University, Shijiazhuang, China
| | - You-Chen Song
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
| | - Wei-Dong Zhao
- Department of Developmental Cell Biology, China Medical University, Shenyang, China
| | - Chang-He Wang
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China
| | - Zhi-Liang Ji
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen, China
| | - Zhong-Yin Zhang
- Departments of Medicinal Chemistry and Molecular Pharmacology and of Chemistry, Center for Cancer Research, and Institute for Drug Discovery, Purdue University, West Lafayette, IN, USA
| | - Min Cui
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Physiology, Shandong University School of Medicine, Jinan, China
| | - Jin-Peng Sun
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Xiao Yu
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Physiology, Shandong University School of Medicine, Jinan, China
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Nestvogel DB, Merino RM, Leon-Pinzon C, Schottdorf M, Lee C, Imig C, Brose N, Rhee JS. The Synaptic Vesicle Priming Protein CAPS-1 Shapes the Adaptation of Sensory Evoked Responses in Mouse Visual Cortex. Cell Rep 2021; 30:3261-3269.e4. [PMID: 32160535 DOI: 10.1016/j.celrep.2020.02.045] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 10/22/2019] [Accepted: 02/10/2020] [Indexed: 10/24/2022] Open
Abstract
Short-term plasticity gates information transfer across neuronal synapses and is thought to be involved in fundamental brain processes, such as cortical gain control and sensory adaptation. Neurons employ synaptic vesicle priming proteins of the CAPS and Munc13 families to shape short-term plasticity in vitro, but the relevance of this phenomenon for information processing in the intact brain is unknown. By combining sensory stimulation with in vivo patch-clamp recordings in anesthetized mice, we show that genetic deletion of CAPS-1 in thalamic neurons results in more rapid adaptation of sensory-evoked subthreshold responses in layer 4 neurons of the primary visual cortex. Optogenetic experiments in acute brain slices further reveal that the enhanced adaptation is caused by more pronounced short-term synaptic depression. Our data indicate that neurons engage CAPS-family priming proteins to shape short-term plasticity for optimal sensory information transfer between thalamic and cortical neurons in the intact brain in vivo.
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Affiliation(s)
- Dennis B Nestvogel
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; International Max Planck Research School for Neuroscience at the University of Göttingen, 37075 Göttingen, Germany.
| | - Ricardo Martins Merino
- International Max Planck Research School for Neuroscience at the University of Göttingen, 37075 Göttingen, Germany; Theoretical Neurophysics Group, Max Planck Institute for Dynamics and Self Organization, 37077 Göttingen, Germany; Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Carolina Leon-Pinzon
- Theoretical Neurophysics Group, Max Planck Institute for Dynamics and Self Organization, 37077 Göttingen, Germany; Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Campus Institute for Dynamics of Biological Networks, 37075 Göttingen, Germany
| | - Manuel Schottdorf
- Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA
| | - ChoongKu Lee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Jeong-Seop Rhee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
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78
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Maus L, Lee C, Altas B, Sertel SM, Weyand K, Rizzoli SO, Rhee J, Brose N, Imig C, Cooper BH. Ultrastructural Correlates of Presynaptic Functional Heterogeneity in Hippocampal Synapses. Cell Rep 2021; 30:3632-3643.e8. [PMID: 32187536 PMCID: PMC7090384 DOI: 10.1016/j.celrep.2020.02.083] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 12/15/2019] [Accepted: 02/21/2020] [Indexed: 02/06/2023] Open
Abstract
Although similar in molecular composition, synapses can exhibit strikingly distinct functional transmitter release and plasticity characteristics. To determine whether ultrastructural differences co-define this functional heterogeneity, we combine hippocampal organotypic slice cultures, high-pressure freezing, freeze substitution, and 3D-electron tomography to compare two functionally distinct synapses: hippocampal Schaffer collateral and mossy fiber synapses. We find that mossy fiber synapses, which exhibit a lower release probability and stronger short-term facilitation than Schaffer collateral synapses, harbor lower numbers of docked synaptic vesicles at active zones and a second pool of possibly tethered vesicles in their vicinity. Our data indicate that differences in the ratio of docked versus tethered vesicles at active zones contribute to distinct functional characteristics of synapses. Electron tomography enables the dissection of vesicle pools at synaptic active zones Docked and primed vesicle availability contributes to initial release probability The ratio of docked and tethered vesicles may co-determine short-term plasticity Hippocampal mossy fibers contain three morphological types of docked vesicles
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Affiliation(s)
- Lydia Maus
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Georg August University, School of Science, 37073 Göttingen, Germany
| | - ChoongKu Lee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Bekir Altas
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Sinem M Sertel
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Kirsten Weyand
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Silvio O Rizzoli
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - JeongSeop Rhee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
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Chen Y, Wang YH, Zheng Y, Li M, Wang B, Wang QW, Fu CL, Liu YN, Li X, Yao J. Synaptotagmin-1 interacts with PI(4,5)P2 to initiate synaptic vesicle docking in hippocampal neurons. Cell Rep 2021; 34:108842. [PMID: 33730593 DOI: 10.1016/j.celrep.2021.108842] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 01/24/2021] [Accepted: 02/17/2021] [Indexed: 01/19/2023] Open
Abstract
Synaptic vesicle (SV) docking is a dynamic multi-stage process that is required for efficient neurotransmitter release in response to nerve impulses. Although the steady-state SV docking likely involves the cooperation of Synaptotagmin-1 (Syt1) and soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), where and how the docking process initiates remains unknown. Phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) can interact with Syt1 and SNAREs to contribute to vesicle exocytosis. In the present study, using the CRISPRi-mediated multiplex gene knockdown and 3D electron tomography approaches, we show that in mouse hippocampal synapses, SV docking initiates at ∼12 nm to the active zone (AZ) by Syt1. Furthermore, we demonstrate that PI(4,5)P2 is the membrane partner of Syt1 to initiate SV docking, and disrupting their interaction could abolish the docking initiation. In contrast, the SNARE complex contributes only to the tight SV docking within 0-2 nm. Therefore, Syt1 interacts with PI(4,5)P2 to loosely dock SVs within 2-12 nm to the AZ in hippocampal neurons.
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Affiliation(s)
- Yun Chen
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Ying-Han Wang
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yi Zheng
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Meijing Li
- Max Planck Institute of Biochemistry, Department of Molecular Structural Biology, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Bing Wang
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Qiu-Wen Wang
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Chong-Lei Fu
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yao-Nan Liu
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Xueming Li
- MOE Key Laboratory of Protein Science, Advanced Innovation Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Jun Yao
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, IDG/McGovern Institute for Brain Research, School of Life Sciences, Tsinghua University, Beijing 100084, China.
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80
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Abstract
Neurotransmitter release occurs by regulated exocytosis from synaptic vesicles (SVs). Evolutionarily conserved proteins mediate the essential aspects of this process, including the membrane fusion step and priming steps that make SVs release-competent. Unlike the proteins constituting the core fusion machinery, the SV protein Mover does not occur in all species and all synapses. Its restricted expression suggests that Mover may modulate basic aspects of transmitter release and short-term plasticity. To test this hypothesis, we analyzed synaptic transmission electrophysiologically at the mouse calyx of Held synapse in slices obtained from wild-type mice and mice lacking Mover. Spontaneous transmission was unaffected, indicating that the basic release machinery works in the absence of Mover. Evoked release and vesicular release probability were slightly reduced, and the paired pulse ratio was increased in Mover knockout mice. To explore whether Mover's role is restricted to certain subpools of SVs, we analyzed our data in terms of two models of priming. A model assuming two SV pools in parallel showed a reduced release probability of so-called "superprimed vesicles" while "normally primed" ones were unaffected. For the second model, which holds that vesicles transit sequentially from a loosely docked state to a tightly docked state before exocytosis, we found that knocking out Mover selectively decreased the release probability of tight state vesicles. These results indicate that Mover regulates a subclass of primed SVs in the mouse calyx of Held.
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81
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Pauli M, Heckmann M. Distinguishing between Synaptic Vesicles in Different Functional States. Neuroscience 2021; 458:180-181. [PMID: 33465415 DOI: 10.1016/j.neuroscience.2020.12.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Accepted: 12/27/2020] [Indexed: 10/22/2022]
Abstract
Editorial on Non-negative matrix factorization as a tool to distinguish between synaptic vesicles in different functional states.
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Affiliation(s)
- Martin Pauli
- Institute for Physiology, Department of Neurophysiology, Julius-Maximilians-University Würzburg, D-97070 Würzburg, Germany
| | - Manfred Heckmann
- Institute for Physiology, Department of Neurophysiology, Julius-Maximilians-University Würzburg, D-97070 Würzburg, Germany.
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82
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Neher E, Taschenberger H. Non-negative Matrix Factorization as a Tool to Distinguish Between Synaptic Vesicles in Different Functional States. Neuroscience 2021; 458:182-202. [PMID: 33454165 DOI: 10.1016/j.neuroscience.2020.10.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Revised: 10/06/2020] [Accepted: 10/07/2020] [Indexed: 10/22/2022]
Abstract
Synaptic vesicles (SVs) undergo multiple steps of functional maturation (priming) before being fusion competent. We present an analysis technique, which decomposes the time course of quantal release during repetitive stimulation as a sum of contributions of SVs, which existed in distinct functional states prior to stimulation. Such states may represent different degrees of maturation in priming or relate to different molecular composition of the release apparatus. We apply the method to rat calyx of Held synapses. These synapses display a high degree of variability, both with respect to synaptic strength and short-term plasticity during high-frequency stimulus trains. The method successfully describes time courses of quantal release at individual synapses as linear combinations of three components, representing contributions from functionally distinct SV subpools, with variability among synapses largely covered by differences in subpool sizes. Assuming that SVs transit in sequence through at least two priming steps before being released by an action potential (AP) we interpret the components as representing SVs which had been 'fully primed', 'incompletely primed' or undocked prior to stimulation. Given these assumptions, the analysis reports an initial release probability of 0.43 for SVs that were fully primed prior to stimulation. Release probability of that component was found to increase during high-frequency stimulation, leading to rapid depletion of that subpool. SVs that were incompletely primed at rest rapidly obtain fusion-competence during repetitive stimulation and contribute the majority of release after 3-5 stimuli.
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Affiliation(s)
- Erwin Neher
- Emeritus Laboratory of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Germany.
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
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83
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Mochida S. Neurotransmitter Release Site Replenishment and Presynaptic Plasticity. Int J Mol Sci 2020; 22:ijms22010327. [PMID: 33396919 PMCID: PMC7794938 DOI: 10.3390/ijms22010327] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 12/23/2020] [Accepted: 12/27/2020] [Indexed: 12/19/2022] Open
Abstract
An action potential (AP) triggers neurotransmitter release from synaptic vesicles (SVs) docking to a specialized release site of presynaptic plasma membrane, the active zone (AZ). The AP simultaneously controls the release site replenishment with SV for sustainable synaptic transmission in response to incoming neuronal signals. Although many studies have suggested that the replenishment time is relatively slow, recent studies exploring high speed resolution have revealed SV dynamics with milliseconds timescale after an AP. Accurate regulation is conferred by proteins sensing Ca2+ entering through voltage-gated Ca2+ channels opened by an AP. This review summarizes how millisecond Ca2+ dynamics activate multiple protein cascades for control of the release site replenishment with release-ready SVs that underlie presynaptic short-term plasticity.
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Affiliation(s)
- Sumiko Mochida
- Department of Physiology, Tokyo Medical University, Tokyo 160-8402, Japan
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84
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Madhurantakam S, Karnam JB, Brabazon D, Takai M, Ahad IU, Balaguru Rayappan JB, Krishnan UM. "Nano": An Emerging Avenue in Electrochemical Detection of Neurotransmitters. ACS Chem Neurosci 2020; 11:4024-4047. [PMID: 33285063 DOI: 10.1021/acschemneuro.0c00355] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The growing importance of nanomaterials toward the detection of neurotransmitter molecules has been chronicled in this review. Neurotransmitters (NTs) are chemicals that serve as messengers in synaptic transmission and are key players in brain functions. Abnormal levels of NTs are associated with numerous psychotic and neurodegenerative diseases. Therefore, their sensitive and robust detection is of great significance in clinical diagnostics. For more than three decades, electrochemical sensors have made a mark toward clinical detection of NTs. The superiority of these electrochemical sensors lies in their ability to enable sensitive, simple, rapid, and selective determination of analyte molecules while remaining relatively inexpensive. Additionally, these sensors are capable of being integrated in robust, portable, and miniaturized devices to establish point-of-care diagnostic platforms. Nanomaterials have emerged as promising materials with significant implications for electrochemical sensing due to their inherent capability to achieve high surface coverage, superior sensitivity, and rapid response in addition to simple device architecture and miniaturization. Considering the enormous significance of the levels of NTs in biological systems and the advances in sensing ushered in with the integration of nanotechnology in electrochemistry, the analysis of NTs by employing nanomaterials as interface materials in various matrices has emerged as an active area of research. This review explores the advancements made in the field of electrochemical sensors for the sensitive and selective determination of NTs which have been described in the past two decades with a distinctive focus on extremely innovative attributes introduced by nanotechnology.
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Affiliation(s)
- Sasya Madhurantakam
- Department of Molecular Physiology, Niigata University School of Medicine, Niigata 951-8510, Japan
| | - Jayanth Babu Karnam
- School of Electrical and Electronics Engineering, SASTRA Deemed University, Thanjavur 613401, India
- Centre for Nanotechnology and Advanced Biomaterials (CeNTAB), SASTRA Deemed University, Thanjavur 613401, India
| | - Dermot Brabazon
- I-Form, Advanced Manufacturing Research Centre, Advanced Processing Technology Research Centre, Dublin City University, Dublin, Ireland
| | - Madoka Takai
- Department of Bioengineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Inam Ul Ahad
- I-Form, Advanced Manufacturing Research Centre, Advanced Processing Technology Research Centre, Dublin City University, Dublin, Ireland
| | | | - Uma Maheswari Krishnan
- Centre for Nanotechnology and Advanced Biomaterials (CeNTAB), SASTRA Deemed University, Thanjavur 613401, India
- School of Arts, Science & Humanities, SASTRA Deemed University, Thanjavur 613401, India
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85
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Imig C, López-Murcia FJ, Maus L, García-Plaza IH, Mortensen LS, Schwark M, Schwarze V, Angibaud J, Nägerl UV, Taschenberger H, Brose N, Cooper BH. Ultrastructural Imaging of Activity-Dependent Synaptic Membrane-Trafficking Events in Cultured Brain Slices. Neuron 2020; 108:843-860.e8. [PMID: 32991831 PMCID: PMC7736621 DOI: 10.1016/j.neuron.2020.09.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 07/03/2020] [Accepted: 09/01/2020] [Indexed: 12/15/2022]
Abstract
Electron microscopy can resolve synapse ultrastructure with nanometer precision, but the capture of time-resolved, activity-dependent synaptic membrane-trafficking events has remained challenging, particularly in functionally distinct synapses in a tissue context. We present a method that combines optogenetic stimulation-coupled cryofixation ("flash-and-freeze") and electron microscopy to visualize membrane trafficking events and synapse-state-specific changes in presynaptic vesicle organization with high spatiotemporal resolution in synapses of cultured mouse brain tissue. With our experimental workflow, electrophysiological and "flash-and-freeze" electron microscopy experiments can be performed under identical conditions in artificial cerebrospinal fluid alone, without the addition of external cryoprotectants, which are otherwise needed to allow adequate tissue preservation upon freezing. Using this approach, we reveal depletion of docked vesicles and resolve compensatory membrane recycling events at individual presynaptic active zones at hippocampal mossy fiber synapses upon sustained stimulation.
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Affiliation(s)
- Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
| | - Francisco José López-Murcia
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Lydia Maus
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Georg August University School of Science, Georg August University Göttingen, 37073 Göttingen, Germany
| | - Inés Hojas García-Plaza
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences, 37077 Göttingen, Germany
| | - Lena Sünke Mortensen
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Manuela Schwark
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Valentin Schwarze
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Julie Angibaud
- University of Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, IINS, UMR 5297, F-33000 Bordeaux, France
| | - U Valentin Nägerl
- University of Bordeaux, CNRS, Interdisciplinary Institute for Neuroscience, IINS, UMR 5297, F-33000 Bordeaux, France
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" University of Göttingen, 37073 Göttingen, Germany.
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
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86
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β-Adrenergic Receptors/Epac Signaling Increases the Size of the Readily Releasable Pool of Synaptic Vesicles Required for Parallel Fiber LTP. J Neurosci 2020; 40:8604-8617. [PMID: 33046543 DOI: 10.1523/jneurosci.0716-20.2020] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 09/25/2020] [Accepted: 10/01/2020] [Indexed: 01/10/2023] Open
Abstract
The second messenger cAMP is an important determinant of synaptic plasticity that is associated with enhanced neurotransmitter release. Long-term potentiation (LTP) at parallel fiber (PF)-Purkinje cell (PC) synapses depends on a Ca2+-induced increase in presynaptic cAMP that is mediated by Ca2+-sensitive adenylyl cyclases. However, the upstream signaling and the downstream targets of cAMP involved in these events remain poorly understood. It is unclear whether cAMP generated by β-adrenergic receptors (βARs) is required for PF-PC LTP, although noradrenergic varicosities are apposed in PF-PC contacts. Guanine nucleotide exchange proteins directly activated by cAMP [Epac proteins (Epac 1-2)] are alternative cAMP targets to protein kinase A (PKA) and Epac2 is abundant in the cerebellum. However, whether Epac proteins participate in PF-PC LTP is not known. Immunoelectron microscopy demonstrated that βARs are expressed in PF boutons. Moreover, activation of these receptors through their agonist isoproterenol potentiated synaptic transmission in cerebellar slices from mice of either sex, an effect that was insensitive to the PKA inhibitors (H-89, KT270) but that was blocked by the Epac inhibitor ESI 05. Interestingly, prior activation of these βARs occluded PF-PC LTP, while the β1AR antagonist metoprolol blocked PF-PC LTP, which was also absent in Epac2 -/- mice. PF-PC LTP is associated with an increase in the size of the readily releasable pool (RRP) of synaptic vesicles, consistent with the isoproterenol-induced increase in vesicle docking in cerebellar slices. Thus, the βAR-mediated modulation of the release machinery and the subsequent increase in the size of the RRP contributes to PF-PC LTP.SIGNIFICANCE STATEMENT G-protein-coupled receptors modulate the release machinery, causing long-lasting changes in synaptic transmission that influence synaptic plasticity. Nevertheless, the mechanisms underlying synaptic responses to β-adrenergic receptor (βAR) activation remain poorly understood. An increase in the number of synaptic vesicles primed for exocytosis accounts for the potentiation of neurotransmitter release driven by βARs. This effect is not mediated by the canonical protein kinase A pathway but rather, through direct activation of the guanine nucleotide exchange protein Epac by cAMP. Interestingly, this βAR signaling via Epac is involved in long term potentiation at cerebellar granule cell-to-Purkinje cell synapses. Thus, the pharmacological activation of βARs modulates synaptic plasticity and opens therapeutic opportunities to control this phenomenon.
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87
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Synaptic vesicles transiently dock to refill release sites. Nat Neurosci 2020; 23:1329-1338. [PMID: 32989294 PMCID: PMC8054220 DOI: 10.1038/s41593-020-00716-1] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 09/01/2020] [Indexed: 11/18/2022]
Abstract
Synaptic vesicles fuse with the plasma membrane to release neurotransmitter following an action potential, after which new vesicles must ‘dock’ to refill vacated release sites. To capture synaptic vesicle exocytosis at cultured mouse hippocampal synapses, we induced single action potentials by electrical field stimulation then subjected neurons to high-pressure freezing to examine their morphology by electron microscopy. During synchronous release, multiple vesicles can fuse at a single active zone. Fusions during synchronous release are distributed throughout the active zone, whereas fusions during asynchronous release are biased toward the center of the active zone. After stimulation, the total number of docked vesicles across all synapses decreases by ~40%. Within 14 ms, new vesicles are recruited and fully replenish the docked pool, but this docking is transient and they either undock or fuse within 100 ms. These results demonstrate that recruitment of synaptic vesicles to release sites is rapid and reversible.
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88
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Huson V, Meijer M, Dekker R, Ter Veer M, Ruiter M, van Weering JR, Verhage M, Cornelisse LN. Post-tetanic potentiation lowers the energy barrier for synaptic vesicle fusion independently of Synaptotagmin-1. eLife 2020; 9:55713. [PMID: 32831174 PMCID: PMC7500951 DOI: 10.7554/elife.55713] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 08/23/2020] [Indexed: 11/13/2022] Open
Abstract
Previously, we showed that modulation of the energy barrier for synaptic vesicle fusion boosts release rates supralinearly (Schotten, 2015). Here we show that mouse hippocampal synapses employ this principle to trigger Ca2+-dependent vesicle release and post-tetanic potentiation (PTP). We assess energy barrier changes by fitting release kinetics in response to hypertonic sucrose. Mimicking activation of the C2A domain of the Ca2+-sensor Synaptotagmin-1 (Syt1), by adding a positive charge (Syt1D232N) or increasing its hydrophobicity (Syt14W), lowers the energy barrier. Removing Syt1 or impairing its release inhibitory function (Syt19Pro) increases spontaneous release without affecting the fusion barrier. Both phorbol esters and tetanic stimulation potentiate synaptic strength, and lower the energy barrier equally well in the presence and absence of Syt1. We propose a model where tetanic stimulation activates Syt1-independent mechanisms that lower the energy barrier and act additively with Syt1-dependent mechanisms to produce PTP by exerting multiplicative effects on release rates.
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Affiliation(s)
- Vincent Huson
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Marieke Meijer
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Rien Dekker
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Mirelle Ter Veer
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, Amsterdam, Netherlands
| | - Marvin Ruiter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, Amsterdam, Netherlands
| | - Jan Rt van Weering
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Matthijs Verhage
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands.,Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, Amsterdam, Netherlands
| | - Lennart Niels Cornelisse
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
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89
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The Synaptic Vesicle Cycle Revisited: New Insights into the Modes and Mechanisms. J Neurosci 2020; 39:8209-8216. [PMID: 31619489 DOI: 10.1523/jneurosci.1158-19.2019] [Citation(s) in RCA: 100] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Revised: 07/31/2019] [Accepted: 08/03/2019] [Indexed: 02/01/2023] Open
Abstract
Neurotransmission is sustained by endocytosis and refilling of synaptic vesicles (SVs) locally within the presynapse. Until recently, a consensus formed that after exocytosis, SVs are recovered by either fusion pore closure (kiss-and-run) or clathrin-mediated endocytosis directly from the plasma membrane. However, recent data have revealed that SV formation is more complex than previously envisaged. For example, two additional recycling pathways have been discovered, ultrafast endocytosis and activity-dependent bulk endocytosis, in which SVs are regenerated from the internalized membrane and synaptic endosomes. Furthermore, these diverse modes of endocytosis appear to influence both the molecular composition and subsequent physiological role of individual SVs. In addition, previously unknown complexity in SV refilling and reclustering has been revealed. This review presents a modern view of the SV life cycle and discusses how neuronal subtype, physiological temperature, and individual activity patterns can recruit different endocytic modes to generate new SVs and sculpt subsequent presynaptic performance.
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90
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Direct imaging of rapid tethering of synaptic vesicles accompanying exocytosis at a fast central synapse. Proc Natl Acad Sci U S A 2020; 117:14493-14502. [PMID: 32513685 DOI: 10.1073/pnas.2000265117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
A high rate of synaptic vesicle (SV) release is required at cerebellar mossy fiber terminals for rapid information processing. As the number of release sites is limited, fast SV reloading is necessary to achieve sustained release. However, rapid reloading has not been observed directly. Here, we visualize SV movements near presynaptic membrane using total internal reflection fluorescence (TIRF) microscopy. Upon stimulation, SVs appeared in the TIRF-field and became tethered to the presynaptic membrane with unexpectedly rapid time course, almost as fast as SVs disappeared due to release. However, such stimulus-induced tethering was abolished by inhibiting exocytosis, suggesting that the tethering is tightly coupled to preceding exocytosis. The newly tethered vesicles became fusion competent not immediately but only 300 ms to 400 ms after tethering. Together with model simulations, we propose that rapid tethering leads to an immediate filling of vacated spaces and release sites within <100 nm of the active zone by SVs, which serve as precursors of readily releasable vesicles, thereby shortening delays during sustained activity.
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91
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Satake S, Konishi S. Roscovitine differentially facilitates cerebellar glutamatergic and GABAergic neurotransmission by enhancing Ca v 2.1 channel-mediated multivesicular release. Eur J Neurosci 2020; 52:3002-3021. [PMID: 32383214 DOI: 10.1111/ejn.14771] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2019] [Revised: 04/22/2020] [Accepted: 05/01/2020] [Indexed: 11/29/2022]
Abstract
Synaptic vesicle exocytosis is triggered by Ca2+ influx through several subtypes of voltage-gated calcium channels in the presynaptic terminal. We previously reported that paired-pulse stimulation at brief intervals increases Cav 2.1 (P/Q-type) channel-mediated multivesicular release (MVR) at glutamatergic synapses between granule cells (GCs) and molecular layer interneurons (MLIs) in rat cerebellar slices. However, it has yet to be determined how Cav 2 channel subtypes take part in MVR in single axon terminal. This study therefore aimed at examining the effects of roscovitine on different types of cerebellar synapses that make contacts with Purkinje cells (PCs), because this compound has been shown to enhance Cav 2.1 channel-mediated MVR at GC-MLI synapses. Bath application of roscovitine profoundly increased the amplitude of excitatory postsynaptic currents (EPSCs) at GC-PC synapses by a presynaptic mechanism as previously observed at GC-MLI synapses, whereas it caused a marginal effect on climbing fiber-mediated EPSCs in PCs. At MLI-PC synapses, roscovitine increased both the amplitude and decay time of inhibitory postsynaptic currents (IPSCs) by enhancing multivesicular GABA release. When extracellular Ca2+ concentration ([Ca2+ ]e ) decreased, roscovitine became less effective in increasing GC-PC EPSCs. By contrast, roscovitine was able to augment MLI-PC IPSCs in the low [Ca2+ ]e . The Cav 2.1 channel blocker ω-agatoxin IVA suppressed the roscovitine-induced facilitatory actions on both GC-PC EPSCs and MLI-PC IPSCs. These results demonstrate that roscovitine enhances MVR at the GC-PC excitatory synapses in a manner dependent on the driving force of Cav 2.1 channel-mediated Ca2+ influx into the nerve terminal, while it also facilitates MLI-PC inhibitory transmission via Ca2+ -insensitive mechanisms.
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Affiliation(s)
- Shin'Ichiro Satake
- Department of Fundamental Neuroscience, National Institute for Physiological Sciences (NIPS), Okazaki, Japan.,School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Japan
| | - Shiro Konishi
- Department of Neurophysiology, Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, Sanuki, Japan
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92
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Blanchard K, Zorrilla de San Martín J, Marty A, Llano I, Trigo FF. Differentially poised vesicles underlie fast and slow components of release at single synapses. J Gen Physiol 2020; 152:e201912523. [PMID: 32243497 PMCID: PMC7201884 DOI: 10.1085/jgp.201912523] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 03/12/2020] [Indexed: 12/25/2022] Open
Abstract
In several types of central mammalian synapses, sustained presynaptic stimulation leads to a sequence of two components of synaptic vesicle release, reflecting the consecutive contributions of a fast-releasing pool (FRP) and of a slow-releasing pool (SRP). Previous work has shown that following common depletion by a strong stimulation, FRP and SRP recover with different kinetics. However, it has remained unclear whether any manipulation could lead to a selective enhancement of either FRP or SRP. To address this question, we have performed local presynaptic calcium uncaging in single presynaptic varicosities of cerebellar interneurons. These varicosities typically form "simple synapses" onto postsynaptic interneurons, involving several (one to six) docking/release sites within a single active zone. We find that strong uncaging laser pulses elicit two phases of release with time constants of ∼1 ms (FRP release) and ∼20 ms (SRP release). When uncaging was preceded by action potential-evoked vesicular release, the extent of SRP release was specifically enhanced. We interpret this effect as reflecting an increased likelihood of two-step release (docking then release) following the elimination of docked synaptic vesicles by action potential-evoked release. In contrast, a subthreshold laser-evoked calcium elevation in the presynaptic varicosity resulted in an enhancement of the FRP release. We interpret this latter effect as reflecting an increased probability of occupancy of docking sites following subthreshold calcium increase. In conclusion, both fast and slow components of release can be specifically enhanced by certain presynaptic manipulations. Our results have implications for the mechanism of docking site replenishment and the regulation of synaptic responses, in particular following activation of ionotropic presynaptic receptors.
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Affiliation(s)
- Kris Blanchard
- Université de Paris, SPPIN - Saints-Pères Paris Institute for the Neurosciences, Centre National de la Recherche Scientifique, UMR 8003, Paris, France
| | - Javier Zorrilla de San Martín
- Université de Paris, SPPIN - Saints-Pères Paris Institute for the Neurosciences, Centre National de la Recherche Scientifique, UMR 8003, Paris, France
| | - Alain Marty
- Université de Paris, SPPIN - Saints-Pères Paris Institute for the Neurosciences, Centre National de la Recherche Scientifique, UMR 8003, Paris, France
| | - Isabel Llano
- Université de Paris, SPPIN - Saints-Pères Paris Institute for the Neurosciences, Centre National de la Recherche Scientifique, UMR 8003, Paris, France
| | - Federico F Trigo
- Université de Paris, SPPIN - Saints-Pères Paris Institute for the Neurosciences, Centre National de la Recherche Scientifique, UMR 8003, Paris, France
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93
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Guan Z, Quiñones-Frías MC, Akbergenova Y, Littleton JT. Drosophila Synaptotagmin 7 negatively regulates synaptic vesicle release and replenishment in a dosage-dependent manner. eLife 2020; 9:e55443. [PMID: 32343229 PMCID: PMC7224696 DOI: 10.7554/elife.55443] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Accepted: 04/28/2020] [Indexed: 01/03/2023] Open
Abstract
Synchronous neurotransmitter release is triggered by Ca2+ binding to the synaptic vesicle protein Synaptotagmin 1, while asynchronous fusion and short-term facilitation is hypothesized to be mediated by plasma membrane-localized Synaptotagmin 7 (SYT7). We generated mutations in Drosophila Syt7 to determine if it plays a conserved role as the Ca2+ sensor for these processes. Electrophysiology and quantal imaging revealed evoked release was elevated 2-fold. Syt7 mutants also had a larger pool of readily-releasable vesicles, faster recovery following stimulation, and intact facilitation. Syt1/Syt7 double mutants displayed more release than Syt1 mutants alone, indicating SYT7 does not mediate the residual asynchronous release remaining in the absence of SYT1. SYT7 localizes to an internal membrane tubular network within the peri-active zone, but does not enrich at active zones. These findings indicate the two Ca2+ sensor model of SYT1 and SYT7 mediating all phases of neurotransmitter release and facilitation is not applicable at Drosophila synapses.
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Affiliation(s)
- Zhuo Guan
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Monica C Quiñones-Frías
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of TechnologyCambridgeUnited States
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94
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Malagon G, Miki T, Tran V, Gomez LC, Marty A. Incomplete vesicular docking limits synaptic strength under high release probability conditions. eLife 2020; 9:e52137. [PMID: 32228859 PMCID: PMC7136020 DOI: 10.7554/elife.52137] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 03/23/2020] [Indexed: 01/17/2023] Open
Abstract
Central mammalian synapses release synaptic vesicles in dedicated structures called docking/release sites. It has been assumed that when voltage-dependent calcium entry is sufficiently large, synaptic output attains a maximum value of one synaptic vesicle per action potential and per site. Here we use deconvolution to count synaptic vesicle output at single sites (mean site number per synapse: 3.6). When increasing calcium entry with tetraethylammonium in 1.5 mM external calcium concentration, we find that synaptic output saturates at 0.22 vesicle per site, not at 1 vesicle per site. Fitting the results with current models of calcium-dependent exocytosis indicates that the 0.22 vesicle limit reflects the probability of docking sites to be occupied by synaptic vesicles at rest, as only docked vesicles can be released. With 3 mM external calcium, the maximum output per site increases to 0.47, indicating an increase in docking site occupancy as a function of external calcium concentration.
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Affiliation(s)
- Gerardo Malagon
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRSParisFrance
- Department of Cell Biology and Physiology, Washington UniversitySt. LouisUnited States
| | - Takafumi Miki
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRSParisFrance
- Graduate School of Brain Science, Doshisha UniversityKyotoJapan
| | - Van Tran
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRSParisFrance
| | - Laura C Gomez
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRSParisFrance
| | - Alain Marty
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRSParisFrance
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95
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Yang L, Fomina AF. Ca 2+ influx and clearance at hyperpolarized membrane potentials modulate spontaneous and stimulated exocytosis in neuroendocrine cells. Cell Calcium 2020; 87:102184. [PMID: 32151786 DOI: 10.1016/j.ceca.2020.102184] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 02/10/2020] [Accepted: 02/21/2020] [Indexed: 01/09/2023]
Abstract
Neuroendocrine adrenal chromaffin cells release neurohormones catecholamines in response to Ca2+ entry via voltage-gated Ca2+ channels (VGCCs). Adrenal chromaffin cells also express non-voltage-gated channels, which may conduct Ca2+ at negative membrane potentials, whose role in regulation of exocytosis is poorly understood. We explored how modulation of Ca2+ influx at negative membrane potentials affects basal cytosolic Ca2+ concentration ([Ca2+]i) and exocytosis in metabolically intact voltage-clamped bovine adrenal chromaffin cells. We found that in these cells, Ca2+ entry at negative membrane potentials is balanced by Ca2+ extrusion by the Na+/Ca2+ exchanger and that this balance can be altered by membrane hyperpolarization or stimulation with an inflammatory hormone bradykinin. Membrane hyperpolarization or application of bradykinin augmented Ca2+-carrying current at negative membrane potentials, elevated basal [Ca2+]i, and facilitated synchronous exocytosis evoked by the small amounts of Ca2+ injected into the cell via VGCCs (up to 20 pC). Exocytotic responses evoked by the injections of the larger amounts of Ca2+ via VGCCs (> 20 pC) were suppressed by preceding hyperpolarization. In the absence of Ca2+ entry via VGCCs and Ca2+ extrusion via the Na+/Ca2+ exchanger, membrane hyperpolarization induced a significant elevation in [Ca2+]i and asynchronous exocytosis. Our results indicate that physiological interferences, such as membrane hyperpolarization and/or activation of non-voltage-gated Ca2+ channels, modulate basal [Ca2+]i and, consequently, segregation of exocytotic vesicles and their readiness to be released spontaneously and in response to Ca2+ entry via VGCCs. These mechanisms may play role in homeostatic plasticity of neuronal and endocrine cells.
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Affiliation(s)
- Lukun Yang
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, 95616, USA; Department of Anesthesiology, The 5th Affiliated Hospital of SUN YAT-SEN University, Zhuhai, 519000, China.
| | - Alla F Fomina
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, 95616, USA.
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96
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Heine M, Holcman D. Asymmetry Between Pre- and Postsynaptic Transient Nanodomains Shapes Neuronal Communication. Trends Neurosci 2020; 43:182-196. [DOI: 10.1016/j.tins.2020.01.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 01/12/2020] [Accepted: 01/13/2020] [Indexed: 10/25/2022]
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97
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Proportional Downscaling of Glutamatergic Release Sites by the General Anesthetic Propofol at Drosophila Motor Nerve Terminals. eNeuro 2020; 7:ENEURO.0422-19.2020. [PMID: 32019872 PMCID: PMC7053172 DOI: 10.1523/eneuro.0422-19.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 01/21/2020] [Accepted: 01/24/2020] [Indexed: 01/12/2023] Open
Abstract
Propofol is the most common general anesthetic used for surgery in humans, yet its complete mechanism of action remains elusive. In addition to potentiating inhibitory synapses in the brain, propofol also impairs excitatory neurotransmission. We use electrophysiological recordings from individual glutamatergic boutons in male and female larval Drosophila melanogaster motor nerve terminals to characterize this effect. We recorded from two bouton types, which have distinct presynaptic physiology and different average numbers of release sites or active zones. We show that a clinically relevant dose of propofol (3 μm) impairs neurotransmitter release similarly at both bouton types by decreasing the number of active release sites by half, without affecting release probability. In contrast, an analog of propofol has no effect on glutamate release. Coexpressing a truncated syntaxin1A protein in presynaptic boutons completely blocked this effect of propofol. Overexpressing wild-type syntaxin1A in boutons also conferred a level of resistance by increasing the number of active release sites to a physiological ceiling set by the number of active zones or T-bars, and in this way counteracting the effect of propofol. These results point to the presynaptic release machinery as a target for the general anesthetic. Proportionally equivalent effects of propofol on the number of active release sites across the different bouton types suggests that glutamatergic circuits that involve smaller boutons with fewer release sites may be more vulnerable to the presynaptic effects of the drug.
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98
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Kobbersmed JR, Grasskamp AT, Jusyte M, Böhme MA, Ditlevsen S, Sørensen JB, Walter AM. Rapid regulation of vesicle priming explains synaptic facilitation despite heterogeneous vesicle:Ca 2+ channel distances. eLife 2020; 9:51032. [PMID: 32077852 PMCID: PMC7145420 DOI: 10.7554/elife.51032] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Accepted: 02/14/2020] [Indexed: 12/27/2022] Open
Abstract
Chemical synaptic transmission relies on the Ca2+-induced fusion of transmitter-laden vesicles whose coupling distance to Ca2+ channels determines synaptic release probability and short-term plasticity, the facilitation or depression of repetitive responses. Here, using electron- and super-resolution microscopy at the Drosophila neuromuscular junction we quantitatively map vesicle:Ca2+ channel coupling distances. These are very heterogeneous, resulting in a broad spectrum of vesicular release probabilities within synapses. Stochastic simulations of transmitter release from vesicles placed according to this distribution revealed strong constraints on short-term plasticity; particularly facilitation was difficult to achieve. We show that postulated facilitation mechanisms operating via activity-dependent changes of vesicular release probability (e.g. by a facilitation fusion sensor) generate too little facilitation and too much variance. In contrast, Ca2+-dependent mechanisms rapidly increasing the number of releasable vesicles reliably reproduce short-term plasticity and variance of synaptic responses. We propose activity-dependent inhibition of vesicle un-priming or release site activation as novel facilitation mechanisms. Cells in the nervous system of all animals communicate by releasing and sensing chemicals at contact points named synapses. The ‘talking’ (or pre-synaptic) cell stores the chemicals close to the synapse, in small spheres called vesicles. When the cell is activated, calcium ions flow in and interact with the release-ready vesicles, which then spill the chemicals into the synapse. In turn, the ‘listening’ (or post-synaptic) cell can detect the chemicals and react accordingly. When the pre-synaptic cell is activated many times in a short period, it can release a greater quantity of chemicals, allowing a bigger reaction in the post-synaptic cell. This phenomenon is known as facilitation, but it is still unclear how exactly it can take place. This is especially the case when many of the vesicles are not ready to respond, for example when they are too far from where calcium flows into the cell. Computer simulations have been created to model facilitation but they have assumed that all vesicles are placed at the same distance to the calcium entry point: Kobbersmed et al. now provide evidence that this assumption is incorrect. Two high-resolution imaging techniques were used to measure the actual distances between the vesicles and the calcium source in the pre-synaptic cells of fruit flies: this showed that these distances are quite variable – some vesicles sit much closer to the source than others. This information was then used to create a new computer model to simulate facilitation. The results from this computing work led Kobbersmed et al. to suggest that facilitation may take place because a calcium-based mechanism in the cell increases the number of vesicles ready to release their chemicals. This new model may help researchers to better understand how the cells in the nervous system work. Ultimately, this can guide experiments to investigate what happens when information processing at synapses breaks down, for example in diseases such as epilepsy.
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Affiliation(s)
- Janus Rl Kobbersmed
- Department of Mathematical Sciences, University of Copenhagen, København, Denmark.,Department of Neuroscience, University of Copenhagen, København, Denmark
| | - Andreas T Grasskamp
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, FMP im CharitéCrossOver, Berlin, Germany
| | - Meida Jusyte
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, FMP im CharitéCrossOver, Berlin, Germany.,Einstein Center for Neuroscience, Berlin, Germany
| | - Mathias A Böhme
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, FMP im CharitéCrossOver, Berlin, Germany
| | - Susanne Ditlevsen
- Department of Mathematical Sciences, University of Copenhagen, København, Denmark
| | | | - Alexander M Walter
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, FMP im CharitéCrossOver, Berlin, Germany.,Einstein Center for Neuroscience, Berlin, Germany
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99
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Bornschein G, Brachtendorf S, Schmidt H. Developmental Increase of Neocortical Presynaptic Efficacy via Maturation of Vesicle Replenishment. Front Synaptic Neurosci 2020; 11:36. [PMID: 32009937 PMCID: PMC6974464 DOI: 10.3389/fnsyn.2019.00036] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 12/16/2019] [Indexed: 01/11/2023] Open
Abstract
The efficacy of neocortical synapses to transmit during bursts of action potentials (APs) increases during development but the underlying mechanisms are largely unclear. We investigated synaptic efficacy at synapses between layer 5 pyramidal neurons (L5PNs) during development, using paired recordings, presynaptic two-photon Ca2+ imaging, and numerical simulations. Our data confirm a developmental increase in paired-pulse ratios (PPRs). Independent of age, Ca2+ imaging revealed no AP invasion failures and linear summation of presynaptic Ca2+ transients, making differences in Ca2+ signaling an unlikely reason for developmental changes in PPR. Cumulative excitatory postsynaptic current (EPSC) amplitudes indicate that neither the size of the readily-releasable pool (RRP) nor replenishment rates were different between age groups, while the time-courses of depression differed significantly. At young synapses, EPSCs depressed rapidly to near steady-state during the first four APs, and synaptic failures (Fsyn) increased from 0 to 30%. At mature synapses this drop was significantly slower and strongly biphasic, such that near steady-state depression was reached not before 18 APs with Fsyn remaining between 0 and 5%. While young synapses reliably transmitted during pairs of APs, albeit with strong depression, mature synapses maintained near 100% transfer efficacy with significantly less depression during high-frequency bursts of APs. Our analysis indicates that at mature synapses a replenishment pool (RepP) is responsible for their high efficacy during bursting activity, while this RepP is functionally immature at young synapses. Hence, our data provide evidence that the functional maturation of a RepP underlies increasing synaptic efficacy during the development of an excitatory cortical synapse.
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Affiliation(s)
- Grit Bornschein
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Simone Brachtendorf
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Hartmut Schmidt
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
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100
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Doc2b Ca 2+ binding site mutants enhance synaptic release at rest at the expense of sustained synaptic strength. Sci Rep 2019; 9:14408. [PMID: 31594980 PMCID: PMC6783474 DOI: 10.1038/s41598-019-50684-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2019] [Accepted: 09/11/2019] [Indexed: 12/01/2022] Open
Abstract
Communication between neurons involves presynaptic neurotransmitter release which can be evoked by action potentials or occur spontaneously as a result of stochastic vesicle fusion. The Ca2+-binding double C2 proteins Doc2a and –b were implicated in spontaneous and asynchronous evoked release, but the mechanism remains unclear. Here, we compared wildtype Doc2b with two Ca2+ binding site mutants named DN and 6A, previously classified as gain- and loss-of-function mutants. They carry the substitutions D218,220N or D163,218,220,303,357,359A respectively. We found that both mutants bound phospholipids at low Ca2+ concentrations and were membrane-associated in resting neurons, thus mimicking a Ca2+-activated state. Their overexpression in hippocampal primary cultured neurons had similar effects on spontaneous and evoked release, inducing high mEPSC frequencies and increased short-term depression. Together, these data suggest that the DN and 6A mutants both act as gain-of-function mutants at resting conditions.
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