Loss of KCNQ2 or KCNQ3 Leads to Multifocal Time-Varying Activity in the Neonatal ForebrainEx Vivo

Abstract

Epileptic encephalopathies represent a group of disorders often characterized by refractory seizures, regression in cognitive development, and typically poor prognosis. Dysfunction of KCNQ2 and KCNQ3 channels has emerged as a major cause of neonatal epilepsy. However, our understanding of the cellular mechanisms that may both explain the origins of epilepsy and inform treatment strategies for KCNQ2 and KCNQ3 dysfunction is still lacking. Here, using mesoscale calcium imaging and pharmacology, we demonstrate that in mouse neonatal brain slices, conditional loss of Kcnq2 from forebrain excitatory neurons ( Pyr:Kcnq2 mice) or constitutive deletion of Kcnq3 leads to sprawling hyperactivity across the neocortex. Surprisingly, the generation of time-varying hypersynchrony in slices from Pyr:Kcnq2 mice does not require fast synaptic transmission. This is in contrast to control littermates and constitutive Kcnq3 knock-out mice where activity is primarily driven by fast synaptic transmission in the neocortex. Unlike in the neocortex, hypersynchronous activity in the hippocampal formation from Kcnq2 conditional and Kcnq3 constitutive knock-out mice persists in the presence of synaptic transmission blockers. Thus, we propose that loss of KCNQ2 or KCNQ3 function differentially leads to network hyperactivity across the forebrain in a region-specific and macro-circuit-specific manner.

Time‐limited alterations in cortical activity of a knock‐in mouse model of KCNQ2‐related developmental and epileptic encephalopathy

“…In addition, the resting membrane potential might be underestimated, particularly during the neonatal period, owing to the short-circuit effect of the leak through the contact between the electrode and the membrane in whole-cell recordings (Tyzio et al, 2003). Moreover, in a recent study aiming to analyse the electrophysiological consequences of the deletion of KCNQ2 or KCNQ3 at network level, Hou et al (2021) performed calcium imaging, and rare calcium activity was detected in the neocortex from neonates in control (wild-type conditions) with a physiological extracellular concentration of K + ([K + ] o ; some modest activity was observed only in the hippocampus and in the entorhinal cortex). It was necessary to increase [K + ] o from 2.5 to 8 mM to obtain calcium events in the neocortex and enhance the role of KCNQ2 or KCNQ3.…”

“…Our results also suggest that the Kv7.2 subunit might contribute strongly to the M current in layers II/III. A recent study performed in the somatosensory cortex showed that the conditional ablation of KCNQ2 or the transfection by electroporation of the pathogenic p.I205V variant related to DEE leads to a hyperexcitability of pyramidal cells of layers II/III, whereas conditional ablation of KCNQ3 did not have such an impact (Niday et al., 2017; but see Hou et al., 2021). In the present study, we cannot exclude the contribution of other subunits to Kv7 channels in these cells, and in particular Kv7.5, but if anything, this should be small regarding the large reduction of M current (∼85%) produced by the blocker at 20 μM, while homomeric Kv7.5 or heteromeric Kv7.3/Kv7.5 subunits display low sensitivity to XE‐991 (Schroeder et al., 2000).…”

“…This was also described in acutely dissociated pyramidal cells and paravalbumin‐like interneurons of layers II/III of the somatosensory cortex, CA1 and CA3 pyramidal cells of the hippocampus, and lumbar interneurons of the spinal cord from rodents aged 1 week (Guan et al., 2011; Marguet et al., 2015; Safiulina et al., 2008; Soh et al., 2018; Verneuil et al., 2020). Thus, Kv7/M channels already appear to be important modulators of firing properties of neurons from several regions at early developmental stage, and even if M current density is much lower at neonatal stage than at juvenile and adult stages, these channels are likely to play fundamental roles for proper brain development and for preventing hypersynchronicity of cellular activity (Hou et al., 2021; Marguet et al., 2015; Peters et al., 2005; Safiulina et al., 2008).…”

“…Although the functional role of Kv7 channels and their different subunits is now well documented (Brown & Passmore, 2009; Fidzinski et al., 2015; Greene & Hoshi, 2017; Hou et al., 2021; Peters et al., 2005; Soh et al., 2014, 2018), the relationship between Kv7.2 variants and DEE remains poorly understood. The functional consequences of variants in the KCNQ2 gene associated with DEE have been analysed widely in heterologous cells and, more recently, in patient induced pluripotent stem cell‐derived neurons (Dirkx et al., 2020; Simkin et al., 2021).…”

KCNQ2 and KCNQ5 form heteromeric channels independent of KCNQ3

“…Mice were generated and validated by the University of Rochester transgenic facility. Constitutive Kcnq3 knockout mice have been described before ( 29 , 50 ). Mice were housed in ventilated cages with controlled temperature (22–23 °C) and a 14 h:10 h light:dark cycle.…”