Regulation of KCNQ Genes as a Mechanism Underlying Epileptogenesis

Epilepsy can develop in response to a brain insult, such as an initial seizure, stroke or traumatic brain injury. This insult induces a variety of cellular and molecular changes, observed in the clinic as a latent period, leading to a state of chronic spontaneous seizures. KCNQ/Kv7 channels are voltage-gated potassium channels which regulate neuronal excitability and protect against hyperexcitability through the Kv7 current. The transcriptional expression of KCNQ/Kv7 channels has previously been shown to be regulated by the transcription factors REST/NRSF, Sp1 and NFAT in peripheral neurons, but the presence of these mechanisms in the brain has not been examined. In this project, organotypic hippocampal slice cultures were used to investigate changes in Kcnq/Kv7 expression changes in epileptic conditions and in response to REST modulation. Adenovirus was used to deliver REST overexpression or a dominant negative REST to the slice cultures, with a novel delivery technique enabling up to 41% infection of total cells, including neurons and microglia, without observable toxicity. REST modulation had no effect on Kcnq2/3 expression, but inhibition of HDACs, which are recruited by REST to repress its target genes, caused de-repression of Kcnq2, suggesting Kcnq2 is regulated by HDACs. The chemoconvulsants kainate and 4-aminopyridine both caused a large upregulation of the epileptic marker BDNF. Kainate exposure caused a downregulation of Kcnq2, associated with a reduction of the Kv7.2 protein it encodes, specific to the CA1 hippocampal region. Expression patterns suggest that in contrast to REST’s known direct repression of BDNF, it may indirectly contribute to Bdnf upregulation following seizure through its pro-epileptic effects. Furthermore, Bdnf levels were correlated with Kcnq2 and Kcnq3, and Bdnf appears to help to maintain Kcnq2/3 expression in epileptic conditions. The downregulation of Kcnq2 after kainate exposure may contribute to epileptogenesis and could provide an area for therapeutic targeting.