Dyshomeostatic modulation of Ca2+-activated K+ channels in a human neuronal model of KCNQ2 encephalopathy.

Dina Simkin,Evangelos Kiskinis,Juan A Ortega,Steven J Lubbe,Linda C Laux,Carlos G Vanoye,Gabriella L Robertson,Brandon N Piyevsky,Marc Forrest,Alfred L George,Reshma R Desai,Bernabe I Bustos,John J Millichap,Peter Penzes,Kelly A Marshall

doi:10.7554/elife.64434

Abstract

Mutations in KCNQ2, which encodes a pore-forming K+ channel subunit responsible for neuronal M-current, cause neonatal epileptic encephalopathy, a complex disorder presenting with severe early-onset seizures and impaired neurodevelopment. The condition is exceptionally difficult to treat, partially because the effects of KCNQ2 mutations on the development and function of human neurons are unknown. Here, we used induced pluripotent stem cells (iPSCs) and gene editing to establish a disease model and measured the functional properties of differentiated excitatory neurons. We find that patient iPSC-derived neurons exhibit faster action potential repolarization, larger post-burst afterhyperpolarization and a functional enhancement of Ca2+-activated K+ channels. These properties, which can be recapitulated by chronic inhibition of M-current in control neurons, facilitate a burst-suppression firing pattern that is reminiscent of the interictal electroencephalography pattern in patients. Our findings suggest that dyshomeostatic mechanisms compound KCNQ2 loss-of-function leading to alterations in the neurodevelopmental trajectory of patient iPSC-derived neurons.

Highlights

The KCNQ2 gene encodes KV7.2, voltage-dependent potassium (K+) channels widely distributed in central and peripheral neurons
We developed and studied a patient-specific induced pluripotent stem cells (iPSCs)-based model of KCNQ2-developmental and epileptic encephalopathy (DEE) that provided novel insight into the pathogenic mechanisms evoked by dysfunction of this ion channel
Our study demonstrated that neurons derived from an iPSC line heterozygous for a loss-of-function KCNQ2 mutation exhibited progressive escalation of burst firing and developed intrinsic membrane properties that promoted phasic bursting as they matured over time in culture

Summary

Introduction

The KCNQ2 gene encodes KV7.2 (referred to here as KCNQ2), voltage-dependent potassium (K+) channels widely distributed in central and peripheral neurons. The earliest hypothesis to explain epilepsy associated with KCNQ2 mutations posited that loss of KCNQ2 channel function allows for sustained membrane depolarization after a single action potential leading to increased repetitive firing within bursts in excitatory neurons (Cooper and Jan, 2003). What remains elusive is how the defects in M-current affect the electrophysiological properties of human neurons leading to impaired neurodevelopment It is unclear whether KCNQ2-DEE pathogenesis results from altered M-channel function or from maladaptive cellular reorganization to compensate for chronic KCNQ2 channel dysfunction. We use KCNQ2-DEE patient-specific and isogenic control iPSC-derived excitatory neurons to elucidate the dynamic functional effects of a KCNQ2 mutation during differentiation and maturation in culture

Results

Discussion

Materials and methods