AUTHOR=Satta Valentina , Alonso Cristina , Díez Paula , Martín-Suárez Soraya , Rubio Marta , Encinas Juan M. , Fernández-Ruiz Javier , Sagredo Onintza 

TITLE=Neuropathological Characterization of a Dravet Syndrome Knock-In Mouse Model Useful for Investigating Cannabinoid Treatments

JOURNAL=Frontiers in Molecular Neuroscience

VOLUME=Volume 13 - 2020

YEAR=2021

URL=https://www.frontiersin.org/journals/molecular-neuroscience/articles/10.3389/fnmol.2020.602801

DOI=10.3389/fnmol.2020.602801

ISSN=1662-5099

ABSTRACT=Dravet Syndrome (DS) is an epileptic syndrome caused by mutations in the Scn1a gene encoding the 1 subunit of the sodium channel Nav1.1, which is associated with febrile seizures that progress to severe tonic-clonic seizures and associated comorbidities. Treatment with cannabidiol has been approved to reduce seizures in DS, but it may be also active against these comorbidities. This study was aimed at validating a new model of DS having lower mortality, which may serve to evaluate therapies for the long-term comorbidities. It consists of heterozygous conditional knock-in mice carrying a missense mutation in Scn1a gene expressed exclusively in CNS neurons (Syn-Cre/Scn1aWT/A1783V). These mice were used to determine the persistence of the behavioural deterioration in postnatal days (PND), as well as to investigate the alterations that the disease produces in the endocannabinoid system and the contribution of inflammation and impaired neurogenesis in the pathology. Syn-Cre/Scn1aWT/A1783V mice showed a reduction in hindlimb grasp reflex at PND10, whereas at PND25 they presented spontaneous convulsions and a greater susceptibility to pentylenetetrazole-induced seizures, marked hyperactivity, deficient spatial working memory, lower levels of anxiety, and altered social interaction behaviour. These differences disappeared at PND40 and PND60, except the changes in social interaction and anxiety. The analysis of CNS structures associated with behavioural alterations revealed an elevated glial reactivity in the prefrontal cortex and the dentate gyrus. This was associated in the dentate gyrus with a greater cell proliferation detected with Ki67 immunostaining, whereas double-labelling analyses identified that proliferating cells were GFAP-positive suggesting failed neurogenesis but astrocyte proliferation. The analysis of the endocannabinoid system confirmed reductions in CB1 receptors and MAGL and FAAH enzyme, mainly in the cerebellum but also in other areas, whereas CB2 receptors became upregulated in the hippocampus. In conclusion, Syn-Cre/Scn1aWT/A1783V mice showed seizuring susceptibility and several comorbidities (hyperactivity, memory impairment, less anxiety and altered social behaviour), which exhibited a pattern of age expression similar to DS patients. Syn-Cre/Scn1aWT/A1783V mice also exhibited greater glial reactivity and a reactive response in the neurogenic niche, and regional changes in the status of the endocannabinoid signaling, events that could contribute in the behavioural impairment.