Compromising the phosphodependent regulation of the GABA _A R β3 subunit reproduces the core phenotypes of autism spectrum disorders

Abstract

Alterations in the efficacy of neuronal inhibition mediated by GABA A receptors (GABA A Rs) containing β3 subunits are continually implicated in autism spectrum disorders (ASDs). In vitro, the plasma membrane stability of GABA A Rs is potentiated via phosphorylation of serine residues 408 and 409 (S408/9) in the β3 subunit, an effect that is mimicked by their mutation to alanines. To assess if modifications in β3 subunit expression contribute to ASDs, we have created a mouse in which S408/9 have been mutated to alanines (S408/9A). S408/9A homozygotes exhibited increased phasic, but decreased tonic, inhibition, events that correlated with alterations in the membrane stability and synaptic accumulation of the receptor subtypes that mediate these distinct forms of inhibition. S408/9A mice exhibited alterations in dendritic spine structure, increased repetitive behavior, and decreased social interaction, hallmarks of ASDs. ASDs are frequently comorbid with epilepsy, and consistent with this comorbidity, S408/9A mice exhibited a marked increase in sensitivity to seizures induced by the convulsant kainic acid. To assess the relevance of our studies using S408/9A mice for the pathophysiology of ASDs, we measured S408/9 phosphorylation in Fmr1 KO mice, a model of fragile X syndrome, the most common monogenetic cause of ASDs. Phosphorylation of S408/9 was selectively and significantly enhanced in Fmr1 KO mice. Collectively, our results suggest that alterations in phosphorylation and/or activity of β3-containing GABA A Rs may directly contribute to the pathophysiology of ASDs.GABA receptor | phosphorylation | autism spectrum disorder | tonic inhibition | phasic inhibition

Endogenous and synthetic neuroactive steroids evoke sustained increases in the efficacy of GABAergic inhibition via a protein kinase C-dependent mechanism

“…However, in our metabotropic studies only SGE-516 significantly altered sIPSC properties, with an increase in sIPSC amplitude. Our previous data has demonstrated the link between PKC-mediated phosphorylation of β3 subunits with a subsequent reduction in GABA A R endocytosis and an increase in IPSC amplitude (Jovanovic et al, 2004; Kittler et al, 2005; Vien et al, 2015). …”

“…We have previously shown that the naturally occurring NAS, THDOC, increased tonic current in part through phosphorylation of S408/409 of the β3 subunit (Abramian et al, 2014; Vien et al, 2015). To further our understanding of the NAS-mediated increase in tonic current we measured the effects of ALLO, SGE-516, on the phosphorylation and membrane expression of β3 subunits in hippocampal slices.…”

“…Antibodies against the β3 subunit and the phospho- β3 antibody were generated and verified by the laboratory of S.J.M. (Vien et al, 2015). …”

Decreased surface expression of the δ subunit of the GABA A receptor contributes to reduced tonic inhibition in dentate granule cells in a mouse model of fragile X syndrome

“…While the basic mechanisms could be related directly to the δ subunit, alterations in associated subunits, such as altered phosphorylation of the β3 subunit, as observed in Fmr1 KO mice (Vien et al, 2015), could also play a role. The possibility of identifying the underlying mechanisms and finding ways to increase surface expression of δ subunit-containing GABA A Rs is particularly intriguing since the current findings indicate that a substantial amount of δ subunit protein is present in the neurons but fails to reach its normal localization at the dendritic surface.…”

Regulating the Efficacy of Inhibition Through Trafficking of γ-Aminobutyric Acid Type A Receptors

“…Furthermore, when S408/9 of β3 subunits have been mutated to alanines (S408/409A), the increase in α4 PKC-mediated phosphorylation is abolished and THDOC fails to increase the cell surface expression of the α4 subunit (104). …”