Liprin-α2 promotes the presynaptic recruitment and turnover of RIM1/CASK to facilitate synaptic transmission

The presynaptic active zone mediates synaptic vesicle exocytosis, and modulation of its molecular composition is important for many types of synaptic plasticity. Here, we identify synaptic scaffold protein liprin-α2 as a key organizer in this process. We show that liprin-α2 levels were regulated by synaptic activity and the ubiquitin–proteasome system. Furthermore, liprin-α2 organized presynaptic ultrastructure and controlled synaptic output by regulating synaptic vesicle pool size. The presence of liprin-α2 at presynaptic sites did not depend on other active zone scaffolding proteins but was critical for recruitment of several components of the release machinery, including RIM1 and CASK. Fluorescence recovery after photobleaching showed that depletion of liprin-α2 resulted in reduced turnover of RIM1 and CASK at presynaptic terminals, suggesting that liprin-α2 promotes dynamic scaffolding for molecular complexes that facilitate synaptic vesicle release. Therefore, liprin-α2 plays an important role in maintaining active zone dynamics to modulate synaptic efficacy in response to changes in network activity.

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Piccolo modulation of Synapsin1a dynamics regulates synaptic vesicle exocytosis

The Journal of Cell Biology ◽

10.1083/jcb.200711167 ◽

2008 ◽

Vol 181 (5) ◽

pp. 831-846 ◽

Cited By ~ 86

Author(s):

Sergio Leal-Ortiz ◽

Clarissa L. Waites ◽

Ryan Terry-Lorenzo ◽

Pedro Zamorano ◽

Eckart D. Gundelfinger ◽

...

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Hippocampal Neurons ◽

Synapse Formation ◽

Zone Formation ◽

Homologous Protein ◽

Synaptic Vesicle Exocytosis ◽

Vesicle Exocytosis ◽

Presynaptic Plasma Membrane ◽

And Function

Active zones are specialized regions of the presynaptic plasma membrane designed for the efficient and repetitive release of neurotransmitter via synaptic vesicle (SV) exocytosis. Piccolo is a high molecular weight component of the active zone that is hypothesized to participate both in active zone formation and the scaffolding of key molecules involved in SV recycling. In this study, we use interference RNAs to eliminate Piccolo expression from cultured hippocampal neurons to assess its involvement in synapse formation and function. Our data show that Piccolo is not required for glutamatergic synapse formation but does influence presynaptic function by negatively regulating SV exocytosis. Mechanistically, this regulation appears to be calmodulin kinase II–dependent and mediated through the modulation of Synapsin1a dynamics. This function is not shared by the highly homologous protein Bassoon, which indicates that Piccolo has a unique role in coupling the mobilization of SVs in the reserve pool to events within the active zone.

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Liprin-α3 controls vesicle docking and exocytosis at the active zone of hippocampal synapses

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1719012115 ◽

2018 ◽

Vol 115 (9) ◽

pp. 2234-2239 ◽

Cited By ~ 22

Author(s):

Man Yan Wong ◽

Changliang Liu ◽

Shan Shan H. Wang ◽

Aram C. F. Roquas ◽

Stephen C. Fowler ◽

...

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Hippocampal Neurons ◽

Stimulated Emission ◽

Loss Of Function ◽

Zone Structure ◽

Vesicle Docking ◽

Synaptic Vesicle Exocytosis ◽

Vesicle Exocytosis ◽

And Function

The presynaptic active zone provides sites for vesicle docking and release at central nervous synapses and is essential for speed and accuracy of synaptic transmission. Liprin-α binds to several active zone proteins, and loss-of-function studies in invertebrates established important roles for Liprin-α in neurodevelopment and active zone assembly. However, Liprin-α localization and functions in vertebrates have remained unclear. We used stimulated emission depletion superresolution microscopy to systematically determine the localization of Liprin-α2 and Liprin-α3, the two predominant Liprin-α proteins in the vertebrate brain, relative to other active-zone proteins. Both proteins were widely distributed in hippocampal nerve terminals, and Liprin-α3, but not Liprin-α2, had a prominent component that colocalized with the active-zone proteins Bassoon, RIM, Munc13, RIM-BP, and ELKS. To assess Liprin-α3 functions, we generated Liprin-α3–KO mice by using CRISPR/Cas9 gene editing. We found reduced synaptic vesicle tethering and docking in hippocampal neurons of Liprin-α3–KO mice, and synaptic vesicle exocytosis was impaired. Liprin-α3 KO also led to mild alterations in active zone structure, accompanied by translocation of Liprin-α2 to active zones. These findings establish important roles for Liprin-α3 in active-zone assembly and function, and suggest that interplay between various Liprin-α proteins controls their active-zone localization.

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Intracellular Acidification Suppresses Synaptic Vesicle Mobilization in the Motor Nerve Terminals

Acta Naturae ◽

10.32607/actanaturae.11054 ◽

2020 ◽

Vol 12 (4) ◽

pp. 105-113

Author(s):

A. L. Zefirov ◽

R. D. Mukhametzyanov ◽

A. V. Zakharov ◽

K. A. Mukhutdinova ◽

U. O. Odnoshivkina ◽

...

Keyword(s):

Synaptic Vesicle ◽

Neurotransmitter Release ◽

Neuromuscular Junctions ◽

Motor Nerve ◽

Synaptic Activity ◽

Special Role ◽

Intracellular Acidification ◽

Synaptic Vesicle Exocytosis ◽

Vesicle Exocytosis ◽

Cytoplasmic Acidification

Intracellular protons play a special role in the regulation of presynaptic processes, since the functioning of synaptic vesicles and endosomes depends on their acidification by the H+-pump. Furthermore, transient acidification of the intraterminal space occurs during synaptic activity. Using microelectrode recording of postsynaptic responses (an indicator of neurotransmitter release) and exo-endocytic marker FM1-43, we studied the effects of intracellular acidification with propionate on the presynaptic events underlying neurotransmitter release. Cytoplasmic acidification led to a marked decrease in neurotransmitter release during the first minute of a 20-Hz stimulation in the neuromuscular junctions of mouse diaphragm and frog cutaneous pectoris muscle. This was accompanied by a reduction in the FM1-43 loss during synaptic vesicle exocytosis in response to the stimulation. Estimation of the endocytic uptake of FM1-43 showed no disruption in synaptic vesicle endocytosis. Acidification completely prevented the action of the cell-membrane permeable compound 24-hydroxycholesterol, which can enhance synaptic vesicle mobilization. Thus, the obtained results suggest that an increase in [H+]in negatively regulates neurotransmission due to the suppression of synaptic vesicle delivery to the sites of exocytosis at high activity. This mechanism can be a part of the negative feedback loop in regulating neurotransmitter release.

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