Long-lasting astrocyte remodeling in Dravet Syndrome Scn1a +/– mouse model

Background Dravet syndrome (DS) is a prototypical developmental and epileptic encephalopathy caused by SCN1A gene mutations leading to NaV1.1 loss of function. The latter causes early-onset drug-resistant seizures and enduring cognitive and behavioral deficits. In this pathological context, the implication of astrocytes remains insufficiently explored. Methods Using a heterozygous Scn1a knock-out ( Scn1a ⁺/⁻ ) mouse model that recapitulates the DS-human phenotype, we examine astrocyte remodeling at landmark disease stages, as defined by video-EEG and behavioral read-outs. Results From initial disease aggravation (PN20-35) to long-term stabilization (up to PN90), Scn1a ⁺/⁻ mice showed increased hippocampal and cortical GFAP transcript and protein levels, compared to age-matched control littermates and to an earlier presymptomatic (<PN20) time point. During the aggravation phase in Scn1a ⁺/⁻ mice, astrocyte branching, revealed by GFAP histological analysis and by intracellular delivery of Alexa Fluor 488 in hippocampal slices was increased but not sustained long-term. These disease-stage-dependent astrocyte modifications were not associated with macroscopic hippocampal sclerosis or cortical atrophy. To further study astrocyte remodeling during disease progression, we used biocytin diffusion following single-astrocyte loading to reveal an expanded astrocyte–astrocyte network in Scn1a ⁺/⁻ mice long-term, along with increased Cx30 and Cx43 protein levels. An ethidium bromide uptake assay indicated impaired astrocytic hemichannel function in Scn1a ⁺/⁻ mice long-term. Regionally, these long-term cellular and network astrocyte modifications coincided with augmented post-tetanic synaptic potentiation. Discussion In DS, astrocytes undergo a long-lasting network remodeling. We discuss how this astrocyte remodeling may be related to seizures as well as synaptic and cognitive deficits.