Modeling Dravet syndrome using induced pluripotent stem cells (iPSCs) and directly converted neurons

Abstract

Severe myoclonic epilepsy of infancy (SMEI, also known as Dravet syndrome) and genetic epilepsy with febrile seizures plus (mild febrile seizures) can both arise due to mutations of SCN1A, the gene encoding alpha 1 pore-forming subunit of the Nav1.1 voltage-gated sodium channel. Owing to the inaccessibility of patient brain neurons, the precise mechanism of mild febrile seizures and SMEI remains elusive, and there is no effective pharmacotherapy. Induced pluripotent stem cells (iPSCs) and induced neurons (iNs) have been successfully generated from patients and applied for modeling various neuronal diseases. In this study, we established iPSC lines from one SMEI patient and one mild febrile seizures patient, respectively. Functional glutamatergic neurons were subsequently differentiated from these iPSCs. Electrophysiological analysis of patient iPSC-derived glutamatergic neurons revealed a hyperexcitable state of enlarged and persistent sodium channel activation, more intensive evoked action potentials and typical epileptic spontaneous action potentials. In consistent with the severity of the symptoms, the hyperexcitability of the neurons derived from SMEI patient was more serious than that of mild febrile seizures patient. Furthermore, the hyperexcitability of the neurons can be alleviated by treatment with phenytoin, a conventional antiepileptic drug. In parallel, iNs were directly converted from patient fibroblasts which also showed a delayed inactivation of sodium channels. Our results demonstrate that both iPSC-derived neurons and iNs from mild febrile seizures and SMEI patients exhibited a hyperexcitable state. More importantly, patient iPSC-derived neurons can recapitulate the neuronal pathophysiology and respond to drug treatment, indicating that these neurons can be potentially used for screening appropriate drugs for personalized therapies.

Voltage-Gated Na+Channels: Not Just for Conduction

“…However, this has become controversial (Chopra and Isom, 2014; Isom, 2014). More recent studies of DS patient derived induced pluripotent stem cell (iPSC) neurons showed either that both inhibitory and excitatory (Liu et al, 2013) or excitatory neurons (Jiao et al, 2013) are hyperexcitable compared to non- epileptic controls (Mistry et al, 2014). These studies suggest that SCN1A haploinsufficiency may result in compensatory upregulation of other VGSC α subunits.…”

Reprogramming patient-derived cells to study the epilepsies

“…In contrast, two other groups found hyperexcitability of DS patient-derived neurons. Jiao et al generated glutamatergic neurons via iPSCs or directed reprogramming of fibroblasts to neurons in a DS subject, and showed increased evoked and spontaneous neuronal activity along with persistent sodium channel activation or delayed inactivation 65 . Liu and colleagues generated a mix of GABAergic and glutamatergic neurons, predominantly GABAergic, from two DS subject and three control iPSC lines 66 .…”

The potential of induced pluripotent stem cells in models of neurological disorders: implications on future therapy

“…By comparison, disease-specific iPSCs provide new prospects for disease-related R&D by enabling screening for genes and disease processes potentially modifiable by drugs identified through in vitro screening. Consequently, iPSCs have been successfully derived from patients with NDv disorders including schizophrenia [3][4][5][6][7][8][9][10][11], Down's syndrome [12][13][14][15][16][17][18][19][20][21], autism spectrum disorders (ASDs) including fragile X, Rett and Timothy syndromes [22][23][24][25][26][27][28][29][30][31][32][33][34][35], and epilepsy [36][37][38][39], as well as NDg disorders such as Alzheimer's disease [40][41][42][43][44][45][46][47][48], Parkinson's disease [49][50][51][52]…”