A knock‐in mouse model for KCNQ2‐related epileptic encephalopathy displays spontaneous generalized seizures and cognitive impairment

Abstract

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. AbstractObjective: Early onset epileptic encephalopathy with suppression-burst is one of the most severe epilepsy phenotypes in human patients. A significant proportion of cases have a genetic origin, and the most frequently mutated gene is KCNQ2, encoding Kv7.2, a voltage-dependent potassium channel subunit, leading to so-called KCNQ2related epileptic encephalopathy (KCNQ2-REE). To study the pathophysiology of KCNQ2-REE in detail and to provide a relevant preclinical model, we generated and described a knock-in mouse model carrying the recurrent p.(Thr274Met) variant. Methods: We introduced the p.(Thr274Met) variant by homologous recombination in embryonic stem cells, injected into C57Bl/6N blastocysts and implanted in pseudopregnant mice. Mice were then bred with 129Sv Cre-deleter to generate heterozygous mice carrying the p.(Thr274Met), and animals were maintained on the 129Sv genetic background. We studied the development of this new model and performed in vivo electroencephalographic (EEG) recordings, neuroanatomical studies at different time points, and multiple behavioral tests. Results: The Kcnq2 Thr274Met/+ mice are viable and display generalized spontaneous seizures first observed between postnatal day 20 (P20) and P30. In vivo EEG recordings show that the paroxysmal events observed macroscopically are epileptic seizures. The brain of the Kcnq2 Thr274Met/+ animals does not display major structural defects, similar to humans, and their body weight is normal. Kcnq2 Thr274Met/+ mice have a reduced life span, with a peak of unexpected death occurring for 25% of the animals by 3 months of age. Epileptic seizures were generally not observed when animals grew older. Behavioral characterization reveals important deficits in spatial learning and memory in adults but no gross abnormality during early neurosensory development. | 869 MILH et aL.

The Role of Kv7.2 in Neurodevelopment: Insights and Gaps in Our Understanding

“…These mice show learning and memory deficits when tested in the Morris water maze or the Barnes maze, as well as reduced exploratory behavior, suggesting that hippocampal dysfunction is involved in the disease pathology, although no abnormalities were observed upon morphological examination of the hippocampus. Furthermore, these mice present spontaneous clinical seizures starting from P20, which are rarely observed after P100 (Milh et al, 2020). This nicely mimics what is seen in patients, as most of them become seizure free a few months after seizure onset (Weckhuysen et al, 2012).…”

“…Very recently, the first KI mouse model of a recurrent KCNQ2-E variant, KCNQ2-T274M, has been published, reproducing several phenotypic traits of human KCNQ2-E (Weckhuysen et al, 2012;Milh et al, 2020). These mice show learning and memory deficits when tested in the Morris water maze or the Barnes maze, as well as reduced exploratory behavior, suggesting that hippocampal dysfunction is involved in the disease pathology, although no abnormalities were observed upon morphological examination of the hippocampus.…”

“…Regarding human disease related to Kv7.2 channel dysfunction, more specifically KCNQ2-E, it is clear that pathology goes beyond a simple increased open or closed state of the channel, but includes impact on temporo-spatial expression levels, binding partners, and widespread homeostatic network changes that are difficult to study in simplified models. The recent publication of a KCNQ2-E KI mouse model is certainly promising and will be an important tool for further in-depth studies (Milh et al, 2020). Another promising model that would contribute to our understanding of the role of Kv7.2 channels in neurodevelopment is neuronal cultures derived from human iPSCs, as they provide the neuronal environment which is lacking in heterologous cell systems.…”

The M-current works in tandem with the persistent sodium current to set the speed of locomotion

“…Kv7.2 mutation associated with Ohtahara syndrome [42]. Because this mutation is homozygous lethal, we studied I M on Kv7.2 Thr274Met/+ animals.…”

The Role of Kv7 Channels in Neural Plasticity and Behavior

“…Surprisingly, genetic inhibition or reduction of K v 7 currents induces an opposite effect on memory ( Figure 1B). Deficits in hippocampal-dependent spatial memory and spontaneous seizures are observed in mice with conditional transgenic expression of dominant-negative mutant K v 7.2-G279S (Peters et al, 2005) and heterozygous knock-in mice for K v 7.2 containing epileptic encephalopathy loss-of-function variant T274M (Milh et al, 2020). Considering that K v 7 channels are critical for development and inhibition of neonatal brain (Peters et al, 2005;Soh et al, 2014), the memory impairment in these genetic models could be attributed to abnormal hippocampal morphology and/or hyperexcitability (Peters et al, 2005;Milh et al, 2020).…”