Forschungsgruppe: Epileptogenese von genetischen Epilepsien (FOR 2715) Projekt: „Mechanismen der Epileptogenese in KCNA2-/SCN2A induzierten Epilepsien“

01/10/2021 to 30/09/2024

Although causes of genetic epilepsy have been identified as ion channel defects and functional studies have revealed important first insights into protein dysfunction, the exact mechanisms underlying seizure generation and disease progression including intellectual disability and other neurodevelopmental impairment are still unknown. During the 1st funding period we, therefore, studied the pathophysiology of loss- and gain-of-function (LOF/GOF) variants in the KCNA2 gene, encoding the voltage-gated K+ channel KV1.2 as well as a GOF variant in the SCN2A gene, encoding the voltage-gated Na+ channel NaV1.2. Using in utero electroporation or transduction to overexpress KV1.2-WT, -R297Q (GOF) or P405L (LOF) variants in cortical layer 2/3 neurons, cortical inhibitory neurons and adult-born neurons of the olfactory bulb, we could identify a profound impairment of cell morphogenesis as a robust consequence of the increased K+ channel function. In addition, we could show that this increase in channel function caused a reduction in the firing rate, whereas overexpression of mutant KV1.2-LOF subunits but not, as expected, for overexpression of KV1.2-WT or -GOF subunits, resulted in an increased after-hyperpolarization amplitude of action potentials within a train.
Based on our data and data of our collaboration partners (P7, P8), we hypothesize that abnormal migration, differentiation and morphogenesis of principal cells and interneurons and thus also miswiring of the developing neural networks are the key mechanisms of epileptogenesis in genetic epilepsies. Here, we will test this hypothesis in knock-in (KI) and inducible mouse models of genetic epilepsies. We will investigate the pathophysiology of both loss- and gain-of-function (LOF/GOF) variants in the KCNA2 gene, and, in collaboration with P4, P5, P7 and P8, a GOF variant in the SCN2A, and a LOF variants in the HCN1 gene, encoding the hyperpolarization-activated cyclic nucleotide-gated channel 1. Doxycycline-inducible Kcna2-GOF and -LOF mouse models and a Scn2a KI mouse model will be used to identify (i) the critical time frame for epileptogenesis, (ii) changes in migration, differentiation and morphogenesis of the developing neurons caused by SCN2A and KCNA2 variants, (iii) characterize the network dysfunction in Scna2, Kcna2 and Hcn1 mouse models and (iv) test new therapeutic strategies based on early pharmacological treatments, RNA-targeting antisense therapy and targeting genes/pathways involved in migration, differentiation, morphogenesis. Besides, we will use our know-how to assist P7 in characterization of a LOF variant in the HCN1 gene.