Synaptic recruitment of gephyrin regulates surface GABAA receptor dynamics for the expression of inhibitory LTP

Abstract

Postsynaptic long-term potentiation of inhibition (iLTP) can rely on increased GABAA receptors (GABAARs) at synapses by promoted exocytosis. However, the molecular mechanisms that enhance the clustering of postsynaptic GABAARs during iLTP remain obscure. Here we demonstrate that during chemically induced iLTP (chem-iLTP), GABAARs are immobilized and confined at synapses, as revealed by single-particle tracking of individual GABAARs in cultured hippocampal neurons. Chem-iLTP expression requires synaptic recruitment of the scaffold protein gephyrin from extrasynaptic areas, which in turn is promoted by CaMKII-dependent phosphorylation of GABAAR-β3-Ser383. Impairment of gephyrin assembly prevents chem-iLTP and, in parallel, blocks the accumulation and immobilization of GABAARs at synapses. Importantly, an increase of gephyrin and GABAAR similar to those observed during chem-iLTP in cultures were found in the rat visual cortex following an experience-dependent plasticity protocol that potentiates inhibitory transmission in vivo. Thus, phospho-GABAAR-β3-dependent accumulation of gephyrin at synapses and receptor immobilization are crucial for iLTP expression and are likely to modulate network excitability.

Activity-dependent inhibitory synapse remodeling through gephyrin phosphorylation

“…Several forms of plasticity have been described at inhibitory synapses. Changes in strength of GABAergic transmission have been reported at many inhibitory synapses (3,4,24) and shown to involve different molecular events (25,26). The notion that inhibitory synapses could also be structurally plastic and undergo continuous rearrangements is, however, much less understood.…”

“…Similar mechanisms are also expected to finely tune the level of inhibition in response to activity in individual neurons, but the mechanisms remain poorly understood. Different forms of plasticity at GABAergic synapses have been reported based on either presynaptic or postsynaptic mechanisms (3,4). Similar to receptors at excitatory synapses, GABA A receptors (GABA A Rs), which mediate the fast component of inhibitory transmission, display complex trafficking mechanisms that affect the surface localization and diffusion of receptors (5).…”

Gephyrin: a central GABAergic synapse organizer

“…6 Indeed, CaMKII-dependent phosphorylation of the GABA A receptor β3-subunit promotes the recruitment of gephyrin from extrasynaptic sites during postsynaptic LTP of inhibition. 6 Impairment of gephyrin assembly blocks chemically induced postsynaptic LTP of inhibition and the accumulation/confinement of GABA A receptors at inhibitory synapses. These results strongly indicate that the immobilization (or clustering) of gephyrin at synapses and the subsequent immobilization of receptors are crucial for postsynaptic LTP of inhibition.…”

“…Gephyrin is the most extensively studied scaffold responsible for organizing the inhibitory postsynaptic density, which is essential for clustering of glycine and γ-aminobutyric acid type A (GABA A ) receptors, inhibitory synaptic transmission and long-term potentiation (reviewed in refs [4][5][6]. Since the discovery of gephyrin in 1982 by Heinrich Betz's group, 7 its biochemical and cellular properties have been extensively studied.…”

CaMKIIα Expression Defines Two Functionally Distinct Populations of Granule Cells Involved in Different Types of Odor Behavior

“…Indeed, CaMKIIa plays an essential role in decoding Ca 2+ signals in excitatory neurons and modulates the synaptic remodeling and plasticity of these cells [40][41][42][43]. CaMKIIa is also involved in the remodeling and plasticity of inhibitory synapses via trafficking of different GABA A receptor subunits as well as gephyrin, the main scaffolding protein of inhibitory synapses [44][45][46][47]. Several GABA A receptor subunits are highly expressed in the OB [48], and differences in subunit composition determine the functional characteristics of GABA A receptors [49].…”