Abstracts

Rationale: Dravet syndrome (DS) is a monogenic epilepsy resultant from haploinsufficiency of the SCN1A voltage-gated sodium channel gene. Seizures in DS are often resistant to conventional antiepileptic drugs and are in fact exacerbated by some. A novel therapeutic target in DS that is not addressed by any conventional antiepileptic drug and can be engaged in isolation or as adjunctive therapy is desirable. Reduced expression of the rodent astrocytic glutamate transporter type 1 (GLT-1; in humans termed excitatory amino acid transporter type 2, EAAT2)—the major determinant of glutamate clearance from excitatory synapses—is a contributor to a range of epilepsy syndromes, both in rodents and humans. Its reduction corresponds to excess to excitotoxic injury of vulnerable inhibitory interneuron populations, which are already compromised by the SCN1A haploinsufficiency in DS. We, therefore, tested whether GLT-1 is depressed in an epileptic mouse DS model. Further, given that the SCN1A+/- genotype results in seizures only in some mouse backgrounds (e.g., F1 hybrid C57x129S6), but not others (e.g., 129S6), we hypothesize that the amount of astrocytic GLT-1 expression varies among background mouse strains and that the magnitude of GLT-1 background expression contributes to strain-specific seizure susceptibility. Notably, GLT-1 expression may be augmented by FDA-cleared medications (e.g., β-lactam antibiotics such as ceftriaxone).

Methods: Cortical tissue was obtained from young adult (p > 90) SCN1A+/- mice on 129S6 and F1 hybrid C57x129S6 backgrounds and age-matched, wild-type littermate controls (N = 6-7/group). Cortical GLT-1 protein expression was averaged across technical and biological replicates on repeat western blots. Additionally, continuous wireless video-EEG was acquired from F1 hybrid SCN1A+/- mice (p > 90) to monitor for convulsive seizures. Statistical comparisons were performed using unpaired t-tests.

Results: Convulsive seizures were confirmed in F1 mice (average ~1 seizure/40h). Cortical GLT-1 protein was depressed in F1 SCN1A+/- mice compared to littermate controls. GLT-1 protein expression was also decreased in the cortex of non-epileptic 129S6 SCN1A+/- mice compared to wild-type littermate controls, but not by as much as in F1 mice (F1 SCN1A+/-: 72% of wild-type, p < 0.05; 129S6 SCN1A+/-: 88.4% of wild-type, p < 0.05; F1 SCN1A+/- vs. 129S6 SCN1A+/-, p < 0.05).