Abstracts

Rationale: Mutations in KCNQ2, which encodes a pore-forming K+ channel subunit responsible for neuronal M-current, have been associated with neonatal epileptic encephalopathy (NEE). This complex disorder manifests as severe early-onset seizures and impaired neurodevelopment due to an imbalance in neuronal circuit activity in the brain. While the effects of KCNQ2 mutations have been studied extensively in heterologous expression systems, their effects on the inherent properties of human neurons have not. Specifically, what remains unclear is how the likely defects in M-current affect the electrophysiological properties of human neurons during a critical period of neuronal maturation. Methods: Here, we used induced pluripotent stem cells (iPSCs) and CRISPR/Cas9 gene editing to establish a disease model, and measured the functional properties of patient-derived neurons using electrophysiological and optical approaches. Results: We find that while NEE patient-derived excitatory neurons exhibit a ~60% smaller M-current early, they develop intrinsic and network hyperexcitability progressively over time in culture. This hyperexcitability is associated with faster action potential repolarization, larger post-burst afterhyperpolarization, and a functional enhancement of Ca2+-dependent K+ (BK and SK) channels. These properties facilitate a burst-suppression firing pattern that is reminiscent of the interictal electroencephalography pattern in patients. Importantly, we were able to phenocopy these excitability features in control neurons only by chronic but not acute pharmacological inhibition of M-current. Conclusions: Our findings suggest that dyshomeostatic mechanisms compound KCNQ2 loss-of-function and lead to alterations in the neurodevelopmental trajectory of patient-derived neurons. Our work has therapeutic implications in explaining why KCNQ2 agonists may not be beneficial once maladaptive compensatory features arise at later stages of the disease. Funding: NIH U54 NS108874; NIH grant NS032387; Northwestern University Dixon Translational Award and Dravet foundation award (EK)