The investigation of pathophysiological mechanisms underlying KV7-related epilepsy and neurodevelopmental delay
Affecting more than 65 million people worldwide, epilepsy is the fourth most common neurological disorder (Epilepsy Foundation). Neuronal Kv7 channels composed of Kv7.2/KCNQ2 and Kv7.3/KCNQ3 subunits are enriched at the axonal plasma membrane where their voltage-dependent potassium currents suppress neuronal excitability. Close to 400 variants in Kv7.2 subunit cause Benign Familial Neonatal Epilepsy (BFNE), Epileptic Encephalopathy (EE) and neurodevelopmental disorder (NDD). EE is often associated with poor response to antiepileptic drugs (AEDs), whereas both EE and NDD patients display progressive loss of cognitive and behavioral functions over time. While extensive studies have focused on BFNE mutations, the pathogenetic mechanism underlying EE and NDD variants in Kv7.2 remains unclear. The goal of this dissertation is to dissect the extent to which EE and NDD mutations in key functional domains affect the function, trafficking, expression, and regulation of Kv7.2 channels and how these changes impair their ability to control neuronal excitability and glutamate release. Chapter 2 presents our published study on the identification and characterization of EE mutation hotspots in Kv7.2 (Zhang, Kim, Chen et al., 2020, Scientific Reports). By combining statistical algorithm, electrophysiology, immunostaining and molecular dynamics simulation, our paper revealed that each EE mutation causes a unique combination of defects in Kv7 channel function, expression and regulation. Chapter 3 includes our submitted manuscript examining how PIP2 facilitates the voltage-dependent activation of Kv7.2 by strategically interacting with multiple clusters of basic residues in the voltage sensor, pore domain, and intracellular helices (Pant, Zhang, Kim et al., 2021, under revision at Communications Biology). Chapter 4 discusses my preliminary results and our lab’s future directions of a project investigating the underlying mechanism of EE and NDD variants in the S6 of Kv7.2. Chapter 5 covers part of our submitted manuscript investigating the murine model of a dominant EE mutation M546V from human patients, and how the M546V mutation affects Kv7.2 protein expression and regulation in mouse brains. The full manuscript is currently under revision at PNAS. The findings of this study will increase our understanding of pathophysiology of Kv7.2 variants associated with EE and NDD, which should facilitate new and effective therapy. In Appendix, I included my two projects that investigate how calmodulin binding and axonal surface enrichment of Kv7 channels in hippocampal neurons are affected by BFNE mutation as well as the phosphorylation in the Helix B of Kv7.2.
Epilepsy, Ion channel, Epileptic encephalopathy, Kv7
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign