Overexpressing wild-type γ2 subunits rescued the seizure phenotype in Gabrg2 Dravet syndrome mice.

Huang X, Zhou C, Tian M, Kang JQ, Shen W, Verdier K, Pimenta A, MacDonald RL
Epilepsia. 2017 58 (8): 1451-1461

PMID: 28586508 · PMCID: PMC5554098 · DOI:10.1111/epi.13810

OBJECTIVE - The mutant γ-aminobutyric acid type A (GABA ) receptor γ2(Q390X) subunit (Q351X in the mature peptide) has been associated with the epileptic encephalopathy, Dravet syndrome, and the epilepsy syndrome genetic epilepsy with febrile seizures plus (GEFS+). The mutation generates a premature stop codon that results in translation of a stable truncated and misfolded γ2 subunit that accumulates in neurons, forms intracellular aggregates, disrupts incorporation of γ2 subunits into GABA receptors, and affects trafficking of partnering α and β subunits. Heterozygous Gabrg2 knock-in (KI) mice had reduced cortical inhibition, spike wave discharges on electroencephalography (EEG), a lower seizure threshold to the convulsant drug pentylenetetrazol (PTZ), and spontaneous generalized tonic-clonic seizures. In this proof-of-principal study, we attempted to rescue these deficits in KI mice using a γ2 subunit gene (GABRG2) replacement therapy.

METHODS - We introduced the GABRG2 allele by crossing Gabrg2 KI mice with bacterial artificial chromosome (BAC) transgenic mice overexpressing HA (hemagglutinin)-tagged human γ2 subunits, and compared GABA receptor subunit expression by Western blot and immunohistochemical staining, seizure threshold by monitoring mouse behavior after PTZ-injection, and thalamocortical inhibition and network oscillation by slice recording.

RESULTS - Compared to KI mice, adult mice carrying both mutant allele and transgene had increased wild-type γ2 and partnering α1 and β2/3 subunits, increased miniature inhibitory postsynaptic current (mIPSC) amplitudes recorded from layer VI cortical neurons, reduced thalamocortical network oscillations, and higher PTZ seizure threshold.

SIGNIFICANCE - Based on these results we suggest that seizures in a genetic epilepsy syndrome caused by epilepsy mutant γ2(Q390X) subunits with dominant negative effects could be rescued potentially by overexpression of wild-type γ2 subunits.

Wiley Periodicals, Inc. © 2017 International League Against Epilepsy.

MeSH Terms (21)

Action Potentials Animals Convulsants Electric Stimulation Epilepsies, Myoclonic Humans Inhibitory Postsynaptic Potentials In Vitro Techniques Male Mice Mice, Inbred C57BL Mice, Transgenic Mutation Neural Pathways Patch-Clamp Techniques Pentylenetetrazole Protein Subunits Pyramidal Cells Receptors, GABA-A Somatosensory Cortex Thalamus

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