Project description:Dravet syndrome is a developmental and epileptic encephalopathy characterized by seizures, behavioral abnormalities, developmental deficits, and elevated risk of sudden unexpected death in epilepsy (SUDEP). Most patient cases are caused by de novo loss-of-function mutations in the gene SCN1A, causing a haploinsufficiency of the alpha subunit of the voltage-gated sodium channel NaV1.1. Within the brain, NaV1.1 is primarily localized to the axons of inhibitory neurons, and decreased NaV1.1 function is hypothesized to reduce GABAergic inhibitory neurotransmission within the brain, driving neuronal network hyperexcitability and subsequent pathology. We have developed a human in vitro model of Dravet syndrome using differentiated neurons derived from patient iPSC and enriched for GABA expressing neurons. Neurons were plated on high definition multielectrode arrays (HD-MEAs), permitting recordings from the same cultures over the 7-weeks duration of study at the network, single cell, and subcellular resolution. Using this capability, we characterized the features of axonal morphology and physiology. Neurons developed increased spiking activity and synchronous network bursting. Recordings were processed through a spike sorting pipeline for curation of single unit activity and to assess the effects of pharmacological treatments. At 7-weeks, the application of the GABAAR receptor agonist muscimol eliminated network bursting, indicating the presence of GABAergic neurotransmission. To identify the role of NaV1.1 on neuronal and network activity, cultures were treated with a dose-response of the NaV1.1 potentiator δ-theraphotoxin-Hm1a. This resulted in a strong increase in firing rates of putative GABAergic neurons, an increase in the intraburst firing rate, and eliminated network bursting. These results validate that potentiation of NaV1.1 in Dravet patient iPSC-derived neurons results in decreased firing synchrony in neuronal networks through increased GABAergic neuron activity and support the use of human neurons and HD-MEAs as viable high-throughput electrophysiological platform to enable therapeutic discovery.
Project description:Dravet syndrome (DS) is a devastating early onset refractory epilepsy syndrome caused by variants in the SCN1A gene. A disturbed GABAergic interneuron function is implicated in the progression to DS but the underlying developmental and pathophysiological mechanisms remain elusive, in particularly at the chromatin level. In this study, we utilized induced pluripotent stem cells (iPSCs) derived from DS cases and healthy donors to model disease-associated epigenetic abnormalities of GABAergic development. Employing the ATAC-Seq technique, we assessed chromatin accessibility at multiple time points (Day 0, Day 19, Day 35, and Day 65) of GABAergic differentiation. Additionally, we elucidated the effects of the commonly used anti-seizure drug valproic acid (VPA) on chromatin accessibility in GABAergic cells. The distinct dynamics in chromatin profile of DS iPSC predicted accelerated early GABAergic development, evident at D19, and diverged further from the pattern in control iPSC with continued differentiation, indicating a disrupted GABAergic maturation. Exposure to VPA at D65 reshaped the chromatin landscape at a variable extent in different iPSC-lines and rescued the observed dysfunctional development in some DS iPSC-GABA. This study provides the first comprehensive investigation on the chromatin landscape of GABAergic differentiation in DS-patient iPSC, offering valuable insights into the epigenetic dysregulations associated with interneuronal dysfunction in DS. Moreover, our detailed analysis of the chromatin changes induced by VPA in iPSC-GABA holds the potential to improve development of personalized and targeted anti-epileptic therapies.
Project description:Dravet syndrome (DS) is a severe epileptic encephalopathy caused by heterozygous loss-of-function mutations in the SCN1A gene, indicating a haploinsufficient genetic mechanism underlining this pathology. Here, we tested whether dCas9-mediated Scn1a gene activation could rescue Scn1a haploinsufficiency and restore physiological levels of its gene product, the Nav1.1 voltage-gated sodium channel. We screeened sgRNAs for their ability to stimulate Scn1a gene transcription in association with the dCas9 activation system. Interestingly, we identified one single sgRNA able to significantly increase Scn1a gene expression levels in cell lines as well as in primary neurons, with high specificity. Accordingly, levels of Nav1.1 protein were sufficiently augmented to potentiate firing ability of wild-type immature GABAergic interneurons. A similar effect in activating the Scn1a transcription was elicited in Dravet GABAergic interneurons rescuing their dysfunctional properties. To determine whether this approach could have therapeutic effect, we packaged adeno-associated viruses with the Scn1a-dCas9 activation system and showed their ability to ameliorate the febrile epileptic crises in DS mice. Our results pave the way for exploiting the dCas9-based gene activation as an effective and targeted approach to DS and other similar disorders resulting from altered gene dosage.
Project description:Transplantation of GABAergic interneurons (INs) can sustain long-standing benefits in animal models of epilepsy and other neurological disorders. In a therapeutic perspective, a renewable source of functional GABAergic INs is needed. Here, we identified five factors (Foxg1, Sox2, Ascl1, Dlx5 and Lhx6) able to convert fibroblasts directly into induced GABAergic INs (iGABA-INs), displaying the molecular signature of telencephalic INs. The selected factors recapitulate in fibroblasts the activation of transcriptional networks required for the specification of GABAergic fate during telencephalon development. iGABA-INs exhibited progressively maturing firing patterns comparable to those of cortical INs, had synaptic currents and released GABA. Importantly, upon grafting in the hippocampus, iGABA-INs survived, matured and their optogenetic stimulation triggered GABAergic transmission and inhibited the activity of connected granule cells. The five factors also converted human cells into functional GABAergic neurons. These properties define iGABA-INs as a promising tool for disease modeling and cell-based therapeutic approaches. Comparison of iGABA-INs transcriptional profile with those of starting fibroblasts and GAD67-GFP+ cortical interneurons.
Project description:Severe myoclonic epilepsy of infancy (SMEI), or Dravet syndrome (DS), is a catastrophic pediatric epilepsy with severe intellectual disability, impaired social development, and persistent drug-resistant seizures. One of its primary monogenic causes is a mutation in SCN1A (Nav1.1), a type I voltage-gated sodium channel. In mice, Nav1.1 mutation is associated with reduced sodium current, altered interneuron firing, cognitive deficits, autistic-like traits and seizures. Here we describe a larval zebrafish Nav1.1 mutant that recapitulates salient features of the human SCN1A mutation phenotype. Between three and seven days post-fertilization, Nav1.1 mutants exhibit spontaneous abnormal electrographic activity, hyperactivity and convulsive behaviors. Transcriptomic analysis of Nav1.1 mutants was remarkable for the relatively small fraction of genes that were differentially expressed (~2%) and the lack of compensatory changes in expression for other SCN subunits. Pharmacological studies confirmed an antiepileptic action for the ketogenic diet, benzodiazepine, valproate, potassium bromide and stiripentol in Nav1.1 mutants; acetazolamide, phenytoin, ethosuximide had no effect, carbamazepine and vigabatrin made seizures worse. Using this mutant, we screened a chemical library of 320 compounds and identified four compounds that reduced spontaneous seizure-like behavior and one compound (clemizole) that inhibited convulsive behavior and electrographic seizures. Drug-resistant scn1a zebrafish mutants described here represent a new direction in modeling pediatric epilepsy and could be used to identify novel lead compounds for DS patients 4 Control sibling samples (sample= 10 pooled larvae) and 4 Nav1.1 mutants (sample= 10 pooled larvae) were collected at 6 dpf (days post fertilization). The Nav1.1 mutants were selected based on phenotype (dark color).
Project description:Transplantation of GABAergic interneurons (INs) can sustain long-standing benefits in animal models of epilepsy and other neurological disorders. In a therapeutic perspective, a renewable source of functional GABAergic INs is needed. Here, we identified five factors (Foxg1, Sox2, Ascl1, Dlx5 and Lhx6) able to convert fibroblasts directly into induced GABAergic INs (iGABA-INs), displaying the molecular signature of telencephalic INs. The selected factors recapitulate in fibroblasts the activation of transcriptional networks required for the specification of GABAergic fate during telencephalon development. iGABA-INs exhibited progressively maturing firing patterns comparable to those of cortical INs, had synaptic currents and released GABA. Importantly, upon grafting in the hippocampus, iGABA-INs survived, matured and their optogenetic stimulation triggered GABAergic transmission and inhibited the activity of connected granule cells. The five factors also converted human cells into functional GABAergic neurons. These properties define iGABA-INs as a promising tool for disease modeling and cell-based therapeutic approaches.
Project description:Severe myoclonic epilepsy of infancy (SMEI), or Dravet syndrome (DS), is a catastrophic pediatric epilepsy with severe intellectual disability, impaired social development, and persistent drug-resistant seizures. One of its primary monogenic causes is a mutation in SCN1A (Nav1.1), a type I voltage-gated sodium channel. In mice, Nav1.1 mutation is associated with reduced sodium current, altered interneuron firing, cognitive deficits, autistic-like traits and seizures. Here we describe a larval zebrafish Nav1.1 mutant that recapitulates salient features of the human SCN1A mutation phenotype. Between three and seven days post-fertilization, Nav1.1 mutants exhibit spontaneous abnormal electrographic activity, hyperactivity and convulsive behaviors. Transcriptomic analysis of Nav1.1 mutants was remarkable for the relatively small fraction of genes that were differentially expressed (~2%) and the lack of compensatory changes in expression for other SCN subunits. Pharmacological studies confirmed an antiepileptic action for the ketogenic diet, benzodiazepine, valproate, potassium bromide and stiripentol in Nav1.1 mutants; acetazolamide, phenytoin, ethosuximide had no effect, carbamazepine and vigabatrin made seizures worse. Using this mutant, we screened a chemical library of 320 compounds and identified four compounds that reduced spontaneous seizure-like behavior and one compound (clemizole) that inhibited convulsive behavior and electrographic seizures. Drug-resistant scn1a zebrafish mutants described here represent a new direction in modeling pediatric epilepsy and could be used to identify novel lead compounds for DS patients
Project description:How early- and late-firing origins are selected on eukaryotic chromosomes is largely unknown. Here we show that Mrc1, a conserved factor required for stabilization of stalled replication forks, selectively binds to the early-firing origins in a manner independent of Cdc45 and Hsk1 kinase in fission yeast. In mrc1∆ (and in swi1∆ to some extent), efficiency of firing is stimulated and its timing is advanced selectively at those origins that are normally bound by Mrc1. In contrast, the late or inefficient origins which are not bound by Mrc1 are not activated in mrc1∆. The enhanced firing and precocious Cdc45 loading at Mrc1-bound early-firing origins are not observed in a checkpoint mutant of mrc1, suggesting that non-checkpoint function is involved in maintaining the normal program of early-firing origins. We propose that pre-firing binding of Mrc1 is an important marker of early-firing origins which are precociously activated by the absence this protein. Mrc1 binding profiles at G1/S boundary or early S-phase in wild type vs hsk1-89 mutant.