Characterisation of a Dravet syndrome knock-in mouse model useful for investigating cannabinoid-based treatments

Dravet syndrome (DS) is a rare pediatric epileptic encephalopathy which, in approximately 60-80% of patients, is caused by mutations in the gene SCN1A that encodes the α1 subunit of the voltage-gated sodium channel Na V 1.1 [1]. Clinically, DS patients present different types of epileptic seizures, which are normally accompanied by cognitive impairment and behavioral disturbances such as hyperactivity and autistic traits [2]. These patients are typically resistant to most antiepileptic drugs, but recent preliminary data suggest that a promising therapy for DS may be based on the use of cannabidiol (CBD) [3]. However, this issue has not been investigated in DS mouse models, therefore existing a wide field of research focused on finding biochemical evidences that could justify the beneficial effects of CBD shown in DS patients. The aim of the present study was to characterize a new DS condicional knock-in mouse model, which may be useful for investigate the effects of CBD in DS. This characterization was focused on behavioral and biochemical/histological terms, specifically on postnatal day 25, stage corresponding to early ages in humans, when main features of the disease are presented. Heterozygous conditional knock-in mice (B6(Cg)-Scn1atm1.1Dsf/J) carrying a missense mutation in SCN1A gene, A1783V, were crossed to Cre recombinase mice (Cre B6.Cg-Tg (Syn1-cre)671Jxm/J) generating offspring with A1783V mutation in cre-expressing tissues. At postnatal day 25, behavioural tests were conducted to analyze motor activity (spontaneous activity test), autistic-like traits (social interaction test) and cognitive deficits (Y-maze test). At this age, mice were euthanized and brains collected for biochemical and histopathological analysis. Data are expressed as mean ± SEM (10/15 animals per group in behavioural analysis and 6 animals per group in biochemical and histopathological analysis) and the statistical analysis used was one-way ANOVA followed by Bonferroni test. Behavioral analyses showed that DS mice exhibit hyperactivity in the actimeter reduced social behaviors in the social interaction test and cognitive impairment in the Y-maze test. Biochemical analysis revealed the existence of a partial dysregulation of the endocannabinoid system (ECS), with a decrease in mRNA (measured by qRT-PCR) levels for the CB 1 receptor in cerebellum and MAGL hydrolyzing enzyme in prefrontal cortex and cerebellum. We also found an increase of microglia and astrocyte cells in cerebral cortex, striatum and hippocampus of DS mice, revealed by elevated Iba-1 and GFAP immunolabeling, respectively, which suggests that neuroinflammation might be part of DS pathogenesis. Our results reveal that DS mice present behavioral disturbances, a dysregulation of ECS and neuroinflammation events. We hypothesize whether CBD efficay may be associated with the direct or indirect correction of the dysregulation in the ECS, which contains targets for CBD, and also associated with the potent anti-inflammatory effect of CBD. We are currently engaged in pharmacological experiments to investigate if CBD treatment is able to normalize the changes in the ECS, neuroinflammation and behavioral impairment in DS mice.