scholarly journals GABAB receptor deficiency causes failure of neuronal homeostasis in hippocampal networks

2015 ◽  
Vol 112 (25) ◽  
pp. E3291-E3299 ◽  
Author(s):  
Irena Vertkin ◽  
Boaz Styr ◽  
Edden Slomowitz ◽  
Nir Ofir ◽  
Ilana Shapira ◽  
...  
Keyword(s):  
Neural Circuits ◽  
Gabab Receptor ◽  
Snare Complex ◽  
Homeostatic Plasticity ◽  
Calcium Flux ◽  
Neuronal Homeostasis ◽  
Protein Receptor ◽  
Presynaptic Calcium ◽  
Hippocampal Networks ◽  
Synaptic Vesicle Release

Stabilization of neuronal activity by homeostatic control systems is fundamental for proper functioning of neural circuits. Failure in neuronal homeostasis has been hypothesized to underlie common pathophysiological mechanisms in a variety of brain disorders. However, the key molecules regulating homeostasis in central mammalian neural circuits remain obscure. Here, we show that selective inactivation of GABAB, but not GABAA, receptors impairs firing rate homeostasis by disrupting synaptic homeostatic plasticity in hippocampal networks. Pharmacological GABAB receptor (GABABR) blockade or genetic deletion of the GB1a receptor subunit disrupts homeostatic regulation of synaptic vesicle release. GABABRs mediate adaptive presynaptic enhancement to neuronal inactivity by two principle mechanisms: First, neuronal silencing promotes syntaxin-1 switch from a closed to an open conformation to accelerate soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex assembly, and second, it boosts spike-evoked presynaptic calcium flux. In both cases, neuronal inactivity removes tonic block imposed by the presynaptic, GB1a-containing receptors on syntaxin-1 opening and calcium entry to enhance probability of vesicle fusion. We identified the GB1a intracellular domain essential for the presynaptic homeostatic response by tuning intermolecular interactions among the receptor, syntaxin-1, and the CaV2.2 channel. The presynaptic adaptations were accompanied by scaling of excitatory quantal amplitude via the postsynaptic, GB1b-containing receptors. Thus, GABABRs sense chronic perturbations in GABA levels and transduce it to homeostatic changes in synaptic strength. Our results reveal a novel role for GABABR as a key regulator of population firing stability and propose that disruption of homeostatic synaptic plasticity may underlie seizure's persistence in the absence of functional GABABRs.

scholarly journals Control of synaptic vesicle release probability via VAMP4 targeting to endolysosomes

2021 ◽  
Vol 7 (18) ◽  
pp. eabf3873
Author(s):  
Daniela Ivanova ◽  
Katharine L. Dobson ◽  
Akshada Gajbhiye ◽  
Elizabeth C. Davenport ◽  
Daniela Hacker ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Snare Complex ◽  
Release Probability ◽  
Clearing System ◽  
Protein Receptor ◽  
Sensitive Factor ◽  
And Function ◽  
Synaptic Vesicle Release ◽  
And Control ◽  
Activity Dependent

Synaptic vesicle (SV) release probability (Pr), determines the steady state and plastic control of neurotransmitter release. However, how diversity in SV composition arises and regulates the Pr of individual SVs is not understood. We found that modulation of the copy number of the noncanonical vesicular SNARE (soluble N-ethylmaleimide–sensitive factor attachment protein receptor), vesicle-associated membrane protein 4 (VAMP4), on SVs is key for regulating Pr. Mechanistically, this is underpinned by its reduced ability to form an efficient SNARE complex with canonical plasma membrane SNAREs. VAMP4 has unusually high synaptic turnover and is selectively sorted to endolysosomes during activity-dependent bulk endocytosis. Disruption of endolysosomal trafficking and function markedly increased the abundance of VAMP4 in the SV pool and inhibited SV fusion. Together, our results unravel a new mechanism for generating SV heterogeneity and control of Pr through coupling of SV recycling to a major clearing system that regulates protein homeostasis.

scholarly journals Visualization of the exocyst complex dynamics at the plasma membrane of Arabidopsis thaliana

2013 ◽  
Vol 24 (4) ◽  
pp. 510-520 ◽  
Author(s):  
Matyáš Fendrych ◽  
Lukáš Synek ◽  
Tamara Pečenková ◽  
Edita Janková Drdová ◽  
Juraj Sekereš ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Fluorescent Protein ◽  
Complex Dynamics ◽  
Active Regions ◽  
Snare Complex ◽  
Epifluorescence Microscopy ◽  
Rab Gtpases ◽  
Exocyst Complex ◽  
Protein Receptor ◽  
Outer Domain

The exocyst complex, an effector of Rho and Rab GTPases, is believed to function as an exocytotic vesicle tether at the plasma membrane before soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complex formation. Exocyst subunits localize to secretory-active regions of the plasma membrane, exemplified by the outer domain of Arabidopsis root epidermal cells. Using variable-angle epifluorescence microscopy, we visualized the dynamics of exocyst subunits at this domain. The subunits colocalized in defined foci at the plasma membrane, distinct from endocytic sites. Exocyst foci were independent of cytoskeleton, although prolonged actin disruption led to changes in exocyst localization. Exocyst foci partially overlapped with vesicles visualized by VAMP721 v-SNARE, but the majority of the foci represent sites without vesicles, as indicated by electron microscopy and drug treatments, supporting the concept of the exocyst functioning as a dynamic particle. We observed a decrease of SEC6–green fluorescent protein foci in an exo70A1 exocyst mutant. Finally, we documented decreased VAMP721 trafficking to the plasma membrane in exo70A1 and exo84b mutants. Our data support the concept that the exocyst-complex subunits dynamically dock and undock at the plasma membrane to create sites primed for vesicle tethering.

scholarly journals Sec1p and Mso1p C-terminal tails cooperate with the SNAREs and Sec4p in polarized exocytosis

2011 ◽  
Vol 22 (2) ◽  
pp. 230-244 ◽  
Author(s):  
Marion Weber-Boyvat ◽  
Nina Aro ◽  
Konstantin G. Chernov ◽  
Tuula Nyman ◽  
Jussi Jäntti
Keyword(s):  
Close Association ◽  
Adaptor Protein ◽  
Binding Mode ◽  
Snare Complex ◽  
Bimolecular Fluorescence Complementation ◽  
Rab Gtpase ◽  
Temperature Sensitive ◽  
Nucleotide Exchange ◽  
Protein Receptor

The Sec1/Munc18 protein family members perform an essential, albeit poorly understood, function in association with soluble n-ethylmaleimide sensitive factor adaptor protein receptor (SNARE) complexes in membrane fusion. The Saccharomyces cerevisiae Sec1p has a C-terminal tail that is missing in its mammalian homologues. Here we show that deletion of the Sec1p tail (amino acids 658–724) renders cells temperature sensitive for growth, reduces sporulation efficiency, causes a secretion defect, and abolishes Sec1p-SNARE component coimmunoprecipitation. The results show that the Sec1p tail binds preferentially ternary Sso1p-Sec9p-Snc2p complexes and it enhances ternary SNARE complex formation in vitro. The bimolecular fluorescence complementation (BiFC) assay results suggest that, in the SNARE-deficient sso2–1 Δsso1 cells, Mso1p, a Sec1p binding protein, helps to target Sec1p(1–657) lacking the C-terminal tail to the sites of secretion. The results suggest that the Mso1p C terminus is important for Sec1p(1–657) targeting. We show that, in addition to Sec1p, Mso1p can bind the Rab-GTPase Sec4p in vitro. The BiFC results suggest that Mso1p acts in close association with Sec4p on intracellular membranes in the bud. This association depends on the Sec4p guanine nucleotide exchange factor Sec2p. Our results reveal a novel binding mode between the Sec1p C-terminal tail and the SNARE complex, and suggest a role for Mso1p as an effector of Sec4p.

S-nitrosylation of syntaxin 1 at Cys145 is a regulatory switch controlling Munc18-1 binding

2008 ◽  
Vol 413 (3) ◽  
pp. 479-491 ◽  
Author(s):  
Zoë J. Palmer ◽  
Rory R. Duncan ◽  
James R. Johnson ◽  
Lu-Yun Lian ◽  
Luciane V. Mello ◽  
...  
Keyword(s):  
Release Kinetics ◽  
Cell Types ◽  
Snare Complex ◽  
Syntaxin 1A ◽  
Dynamic Simulations ◽  
Closed Conformation ◽  
Quantal Size ◽  
Protein Receptor ◽  
Protein Attachment

Exocytosis is regulated by NO in many cell types, including neurons. In the present study we show that syntaxin 1a is a substrate for S-nitrosylation and that NO disrupts the binding of Munc18-1 to the closed conformation of syntaxin 1a in vitro. In contrast, NO does not inhibit SNARE {SNAP [soluble NSF (N-ethylmaleimide-sensitive fusion protein) attachment protein] receptor} complex formation or binding of Munc18-1 to the SNARE complex. Cys145 of syntaxin 1a is the target of NO, as a non-nitrosylatable C145S mutant is resistant to NO and novel nitrosomimetic Cys145 mutants mimic the effect of NO on Munc18-1 binding in vitro. Furthermore, expression of nitrosomimetic syntaxin 1a in living cells affects Munc18-1 localization and alters exocytosis release kinetics and quantal size. Molecular dynamic simulations suggest that NO regulates the syntaxin–Munc18 interaction by local rearrangement of the syntaxin linker and H3c regions. Thus S-nitrosylation of Cys145 may be a molecular switch to disrupt Munc18-1 binding to the closed conformation of syntaxin 1a, thereby facilitating its engagement with the membrane fusion machinery.

scholarly journals Differentially poised vesicles underlie fast and slow components of release at single synapses

2020 ◽  
Vol 152 (5) ◽  
Author(s):  
Kris Blanchard ◽  
Javier Zorrilla de San Martín ◽  
Alain Marty ◽  
Isabel Llano ◽  
Federico F. Trigo
Keyword(s):  
Action Potential ◽  
Laser Pulses ◽  
Presynaptic Receptors ◽  
Vesicular Release ◽  
Strong Stimulation ◽  
Subthreshold Laser ◽  
Presynaptic Calcium ◽  
Two Phases ◽  
Synaptic Vesicle Release ◽  
Selective Enhancement

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.

scholarly journals Dual inhibition of SNARE complex formation by tomosyn ensures controlled neurotransmitter release

2008 ◽  
Vol 183 (2) ◽  
pp. 323-337 ◽  
Author(s):  
Toshiaki Sakisaka ◽  
Yasunori Yamamoto ◽  
Sumiko Mochida ◽  
Michiko Nakamura ◽  
Kouki Nishikawa ◽  
...  
Keyword(s):  
Complex Formation ◽  
Neurotransmitter Release ◽  
Snare Complex ◽  
Protein Receptor ◽  
Repeat Domain ◽  
Dual Inhibition ◽  
Presynaptic Nerve Terminals ◽  
Synaptic Vesicle Fusion ◽  
Deficient Mice ◽  
Snare Complex Formation

Neurotransmitter release from presynaptic nerve terminals is regulated by soluble NSF attachment protein receptor (SNARE) complex–mediated synaptic vesicle fusion. Tomosyn inhibits SNARE complex formation and neurotransmitter release by sequestering syntaxin-1 through its C-terminal vesicle-associated membrane protein (VAMP)–like domain (VLD). However, in tomosyn-deficient mice, the SNARE complex formation is unexpectedly decreased. In this study, we demonstrate that the N-terminal WD-40 repeat domain of tomosyn catalyzes the oligomerization of the SNARE complex. Microinjection of the tomosyn N-terminal WD-40 repeat domain into neurons prevented stimulated acetylcholine release. Thus, tomosyn inhibits neurotransmitter release by catalyzing oligomerization of the SNARE complex through the N-terminal WD-40 repeat domain in addition to the inhibitory activity of the C-terminal VLD.

scholarly journals Synapse-Specific Homeostatic Mechanisms in the Hippocampus

2009 ◽  
Vol 101 (2) ◽  
pp. 503-506 ◽  
Author(s):  
Katherine E. Deeg
Keyword(s):  
Neural Circuits ◽  
Epileptic Seizures ◽  
Homeostatic Plasticity ◽  
Excitatory Synapses ◽  
Network Stability ◽  
Homeostatic Synaptic Plasticity ◽  
New Type ◽  
Hippocampal Network ◽  
Synaptic Gain ◽  
Different Populations

Homeostatic synaptic plasticity allows neural circuits to function stably despite fluctuations to their inputs. Previous work has shown that excitatory synaptic strength increases globally when neuronal inputs are chronically silenced. A recent paper by Kim and Tsien describes a new type of synapse-specific homeostatic plasticity in which input silencing causes simultaneous strengthening and weakening of different populations of excitatory synapses within a hippocampal network. These seemingly antagonistic homeostatic adaptations maintain synaptic gain and preserve overall network stability by limiting harmful reverberatory bursting, which may underlie epileptic seizures.

Gβγ Interferes with Ca2+-Dependent Binding of Synaptotagmin to the Soluble N-Ethylmaleimide-Sensitive Factor Attachment Protein Receptor (SNARE) Complex

2007 ◽  
Vol 72 (5) ◽  
pp. 1210-1219 ◽  
Author(s):  
Eun-Ja Yoon ◽  
Tatyana Gerachshenko ◽  
Bryan D. Spiegelberg ◽  
Simon Alford ◽  
Heidi E. Hamm
Keyword(s):  
Snare Complex ◽  
Attachment Protein ◽  
Protein Receptor ◽  
Sensitive Factor ◽  
Factor Attachment Protein Receptor

scholarly journals Syntaxin 16’s Newly Deciphered Roles in Autophagy

Cells ◽  
2019 ◽  
Vol 8 (12) ◽  
pp. 1655 ◽  
Author(s):  
Bor Luen Tang
Keyword(s):  
Membrane Trafficking ◽  
Functional Redundancy ◽  
Transport Processes ◽  
Snare Complex ◽  
Dual Roles ◽  
Trans Golgi Network ◽  
Protein Receptor ◽  
Sensitive Factor ◽  
Golgi Network

Syntaxin 16, a Qa-SNARE (soluble N-ethylmaleimide-sensitive factor activating protein receptor), is involved in a number of membrane-trafficking activities, particularly transport processes at the trans-Golgi network (TGN). Recent works have now implicated syntaxin 16 in the autophagy process. In fact, syntaxin 16 appears to have dual roles, firstly in facilitating the transport of ATG9a-containing vesicles to growing autophagosomes, and secondly in autolysosome formation. The former involves a putative SNARE complex between syntaxin 16, VAMP7 and SNAP-47. The latter occurs via syntaxin 16’s recruitment by Atg8/LC3/GABARAP family proteins to autophagosomes and endo-lysosomes, where syntaxin 16 may act in a manner that bears functional redundancy with the canonical autophagosome Qa-SNARE syntaxin 17. Here, I discuss these recent findings and speculate on the mechanistic aspects of syntaxin 16’s newly found role in autophagy.

VAMP-8 segregates mast cell–preformed mediator exocytosis from cytokine trafficking pathways

Blood ◽  
2008 ◽  
Vol 111 (7) ◽  
pp. 3665-3674 ◽  
Author(s):  
Neeraj Tiwari ◽  
Cheng-Chun Wang ◽  
Cristiana Brochetta ◽  
Gou Ke ◽  
Francesca Vita ◽  
...  
Keyword(s):  
Mast Cells ◽  
Inflammatory Responses ◽  
Secretory Granules ◽  
Snare Complex ◽  
Protein Receptor ◽  
Sensitive Factor ◽  
Syntaxin 4 ◽  
Deficient Mice ◽  
Snare Complex Formation ◽  
Vesicular Compartment

Abstract Inflammatory responses by mast cells are characterized by massive exocytosis of prestored granular mediators followed by cytokine/chemokine release. The vesicular trafficking mechanisms involved remain poorly understood. Vesicular-associated membrane protein-8 (VAMP-8), a member of the soluble N-ethylmaleimide–sensitive factor (NSF) attachment protein receptor (SNARE) family of fusion proteins initially characterized in endosomal and endosomal-lysosomal fusion, may also function in regulated exocytosis. Here we show that in bone marrow–derived mast cells (BMMCs) VAMP-8 partially colocalized with secretory granules and redistributed upon stimulation. This was associated with increased SNARE complex formation with the target t-SNAREs, SNAP-23 and syntaxin-4. VAMP-8–deficient BMMCs exhibited a markedly reduced degranulation response after IgE+ antigen-, thapsigargin-, or ionomycin-induced stimulation. VAMP-8–deficient mice also showed reduced plasma histamine levels in passive systemic anaphylaxis experiments, while cytokine/chemokine release was not affected. Unprocessed TNF accumulated at the plasma membrane where it colocalized with a VAMP-3–positive vesicular compartment but not with VAMP-8. The findings demonstrate that VAMP-8 segregates secretory lysosomal granule exocytosis in mast cells from cytokine/chemokine molecular trafficking pathways.

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