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.
De novo variants in the KCNQ2 gene encoding the Kv7.2 subunit of the voltage-gated potassium Kv7/M channel are the main cause of Early Onset Epileptic Encephalopathy (EOEE) with suppression burst suggesting that this channel plays an important role for proper brain development. Functional analysis of these variants in heterologous cells has shown that most of them are loss of function leading to a reduction of M current. However the cellular mechanism of the neuronal network dysfunctionning is still not known. Here we characterized the electrophysiological properties of developing pyramidal cells of the layer II/III and V and analyzed spontaneous synaptic activity in these layers in motor cortical slices obtained from a recently generated heterozygous knock-in mouse harboring the loss-of-function pathogenic p.T274M variant. Experiments were performed on animals aged one week, three weeks and four-five weeks, and the results were compared with those of pyramidal cells recorded in slices from wild-type mice untreated or treated with the Kv7 channel blocker XE-991. We showed that the variant led to a hyperexcitability of pyramidal cells of layer II/III in cortical slices from animal aged 1 week and 3 weeks and to a level that was similar to the effect of XE-911. In layer V the impact of the variant was observed in slices from animal aged 3 weeks but not earlier and to a level that was lower to the effect of XE-991. However, in cortical slices from animal aged 4-5 weeks electrophysiological properties of pyramidal cells of layers II/III and V were no more affected by the variant but still sensitive to XE-991. The recovery of the electrophysiological responses in knock-in animals was associated with a slight but significant distal shift of the axonal initial segment (AIS) from the soma of pyramidal cells of layer II/III and V. Recordings of spontaneous synaptic activity in these layers revealed the presence of recurrent GABAergic network activities (RGNA) that were mainly observed during the three first postnatal weeks of life and which occurrence and frequency were increased in pyramidal cells of the layer II/III but not of the layer V of the knock-in mouse. There were no significant differences in synaptic activities mediated by GABA and glutamate receptors in cortical slices from animal aged 4-5 weeks. Together our data provided evidences that the heterozygous p.T274M variant impacts the activity of pyramidal cells and probably of Gabaergic interneurons during a limited period of development. Our data also indicated that neurons of the layer II/III are more sensitive to the variant than those located in the layer V in terms of age of onset, neuronal firing and spontaneous synaptic activities. Moreover our data suggest that a compensatory mechanism might take place in the knock-in mice aged 4-5 weeks allowing the recovery of control activity at cellular and network levels and which is associated with a slight displacement of the AIS. Thus, the effect of the variant on neuronal activity is developmentally regulated a...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.