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Abstract

Objective

GABA_A receptor subunit gene mutations are major causes of various epilepsy syndromes, including severe kinds such as Dravet syndrome. Although the GABA_A receptor is a major target for antiseizure medications, treating GABA_A receptor mutations with the receptor channel modulators is ineffective. Here we determined the effect of a novel treatment with 4-phenylbutyrate (PBA) in the Gabrg2
^+/Q390X
knockin mice associated with Dravet syndrome.

Methods

We used biochemistry in conjunction with differential tagging of the wildtype and the mutant alleles, live brain slice surface biotinylation, microsome isolation, patch-clamp whole-cell recordings, and video-monitoring synchronized EEG recordings in a Gabrg2
^+/Q390X
mice to determine the effect of PBA in vitro with recombinant GABA_A receptors and in vivo with knockin mice.

Results

We found that PBA reduced the mutant γ2(Q390X) subunit protein aggregates, enhanced the wildtype GABA_A receptor subunits’ trafficking and increased the membrane expression of the wildtype receptors. PBA increased the current amplitude of GABA evoked current in HEK293T cells and the neurons bearing the γ2(Q390X) subunit protein. PBA also proved to reduce ER stress caused by the mutant γ2(Q390X) subunit protein, as well as mitigating seizures and EEG abnormalities in the Gabrg2
^+/Q390X
mice.

Significance

This research has unveiled a promising and innovative approach for treating epilepsy linked to GABA_A receptor mutations through an unconventional antiseizure mechanism. Rather than directly modulating the affected mutant channel, PBA facilitates the folding and transportation of wildtype receptor subunits to the cell membrane and synapse. Combining these findings with our previous study, which demonstrated PBA’s efficacy in restoring GABA transporter 1 (encoded by SLC6A1) function, we propose that PBA holds significant potential for a wide range of genetic epilepsies. Its ability to target shared molecular pathways involving mutant protein ER retention and impaired protein membrane trafficking suggests a broad application in treating such conditions.