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New insights into the early mechanisms of epileptogenesis in a zebrafish model of Dravet syndrome
Author(s) -
Tiraboschi Ettore,
Martina Silvia,
Ent Wietske,
Grzyb Kamil,
Gawel Kinga,
CorderoMaldonado Maria Lorena,
Poovathingal Suresh Kumar,
Heintz Sarah,
Satheesh Somisetty Venkata,
Brattespe Jarle,
Xu Ju,
Suster Maximiliano,
Skupin Alexander,
Esguerra Camila V.
Publication year - 2020
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/epi.16456
Subject(s) - dravet syndrome , biology , neuroscience , gabaergic , zebrafish , epileptogenesis , epilepsy , endocrinology , medicine , inhibitory postsynaptic potential , genetics , gene
Objective To pinpoint the earliest cellular defects underlying seizure onset (epileptogenic period) during perinatal brain development in a new zebrafish model of Dravet syndrome (DS) and to investigate potential disease‐modifying activity of the 5HT 2 receptor agonist fenfluramine. Methods We used CRISPR/Cas9 mutagenesis to introduce a missense mutation, designed to perturb ion transport function in all channel isoforms, into scn1lab , the zebrafish orthologue of SCN1A (encoding voltage‐gated sodium channel alpha subunit 1). We performed behavioral analysis and electroencephalographic recordings to measure convulsions and epileptiform discharges, followed by single‐cell RNA‐Seq, morphometric analysis of transgenic reporter‐labeled γ‐aminobutyric acidergic (GABAergic) neurons, and pharmacological profiling of mutant larvae. Results Homozygous mutant ( scn1lab mut/mut ) larvae displayed spontaneous seizures with interictal, preictal, and ictal discharges (mean = 7.5 per 20‐minute recording; P < .0001; one‐way analysis of variance). Drop‐Seq analysis revealed a 2:1 shift in the ratio of glutamatergic to GABAergic neurons in scn1lab mut/mut larval brains versus wild type (WT), with dynamic changes in neuronal, glial, and progenitor cell populations. To explore disease pathophysiology further, we quantified dendritic arborization in GABAergic neurons and observed a 40% reduction in arbor number compared to WT ( P < .001; n = 15 mutant, n = 16 WT). We postulate that the significant reduction in inhibitory arbors causes an inhibitory to excitatory neurotransmitter imbalance that contributes to seizures and enhanced electrical brain activity in scn1lab mut/mut larvae (high‐frequency range), with subsequent GABAergic neuronal loss and astrogliosis. Chronic fenfluramine administration completely restored dendritic arbor numbers to normal in scn1lab mut/mut larvae, whereas similar treatment with the benzodiazepine diazepam attenuated seizures, but was ineffective in restoring neuronal cytoarchitecture. BrdU labeling revealed cell overproliferation in scn1lab mut/mut larval brains that were rescued by fenfluramine but not diazepam. Significance Our findings provide novel insights into early mechanisms of DS pathogenesis, describe dynamic cell population changes in the scn1lab mut/mut brain, and present first‐time evidence for potential disease modification by fenfluramine.