Activation of GABAA receptors controls mesiotemporal lobe epilepsy despite changes in chloride transporters expression: In vivo and in silico approach

Séverine Stamboulian-Platel; Arnaud Legendre; Tanguy Chabrol; Jean-Claude Platel; Fabien Pernot; Venceslas Duveau; Corinne Roucard; Michel Baudry; Antoine Depaulis

doi:10.1016/j.expneurol.2016.07.009

Activation of GABA_A receptors controls mesiotemporal lobe epilepsy despite changes in chloride transporters expression: In vivo and in silico approach

Exp Neurol. 2016 Oct;284(Pt A):11-28. doi: 10.1016/j.expneurol.2016.07.009. Epub 2016 Jul 19.

Authors

Séverine Stamboulian-Platel¹, Arnaud Legendre², Tanguy Chabrol¹, Jean-Claude Platel¹, Fabien Pernot³, Venceslas Duveau⁴, Corinne Roucard⁴, Michel Baudry⁵, Antoine Depaulis⁶

Affiliations

¹ INSERM, U1216, F-3800 Grenoble, France; Univ. Grenoble Alpes, Grenoble Institut des Neurosciences, F-38000 Grenoble, France.
² Rhenovia Pharma SAS, F-68200 Mulhouse, France; Laboratoire MIPS EA2332, Université de Haute Alsace, F-68200 Mulhouse, France.
³ Rhenovia Pharma SAS, F-68200 Mulhouse, France.
⁴ SynapCell SAS, F-38700 La Tronche, France.
⁵ Rhenovia Pharma SAS, F-68200 Mulhouse, France; GCBS, Western University of Health Sciences, Pomona, CA 91766, USA.
⁶ INSERM, U1216, F-3800 Grenoble, France; Univ. Grenoble Alpes, Grenoble Institut des Neurosciences, F-38000 Grenoble, France. Electronic address: antoine.depaulis@ujf-grenoble.fr.

PMID: 27443630
DOI: 10.1016/j.expneurol.2016.07.009

Abstract

Mesiotemporal lobe Epilepsy (MTLE), the most frequent form of focal epilepsy, is often drug-resistant. Enriching the epileptic focus with GABA-releasing engineered cells has been proposed as a strategy to prevent seizures. However, ex vivo data from animal models and MTLE patients suggest that, due to changes in chloride homeostasis, GABA_A receptor activation is depolarizing and partly responsible for focal interictal discharges and seizure initiation. To understand how these two contradictory aspects of GABAergic neurotransmission coexist in MTLE, we used an established mouse model of MTLE presenting hippocampal sclerosis and recurrent hippocampal paroxysmal discharges (HPDs) 30-40days after a unilateral injection of kainate in the dorsal hippocampus. We first showed that injections of GABA_A receptor agonists either systemically or directly into hippocampus suppressed HPDs. Western-blotting and immunostaining revealed that levels of α1, α3 and γ2 GABA_A receptor subunits were increased in epileptic mice, compared to saline controls, while levels of R1 and R2 GABA_B receptor subunits but also NR1, NR2A and NR2B NMDA receptor subunits and GluR1 and GluR2 AMPA receptor subunits were decreased. In addition, we showed that the expression of the transporter NKCC1, which load neurons with chloride, was increased, whereas KCC2, a chloride extruder, was decreased and that HPDs were suppressed by injection of blockers of NKCC1. These different changes were integrated in a numerical model, and in silico simulations supported the notion that chloride imbalance impair local inhibitory control of pyramidal neurons' activity in this model of MTLE. However, our numerical model also suggested that lasting activation of these receptors restore physiological intracellular chloride concentrations and suppress HPDs. Overall, our study suggests that activation of GABA_A receptor remains an effective antiepileptic strategy to suppress focal seizures in MTLE, and demonstrates that modeling and simulation studies provide new insights about the cellular and synaptic mechanisms of this disease.

Keywords: MTLE; Mouse; Numerical model; Protein expression; Synaptic transmission.