DNA Methylation Mediates Persistent Epileptiform Activity <i>In Vitro</i> and <i>In Vivo</i>

<div><p>Epilepsy is a chronic brain disorder involving recurring seizures often precipitated by an earlier neuronal insult. The mechanisms that link the transient neuronal insult to the lasting state of epilepsy are unknown. Here we tested the possible role of DNA methylation in mediating long-term induction of epileptiform activity by transient kainic acid exposure using <i>in vitro</i> and <i>in vivo</i> rodent models. We analyzed changes in the <i>gria2</i> gene, which encodes for the GluA2 subunit of the ionotropic glutamate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid receptor and is well documented to play a role in epilepsy. We show that kainic acid exposure for two hours to mouse hippocampal slices triggers methylation of a 5’ regulatory region of the <i>gria2</i> gene. Increase in methylation persists one week after removal of the drug, with concurrent suppression of <i>gria2</i> mRNA expression levels. The degree of kainic acid-induced hypermethylation of <i>gria2</i> 5’ region varies between individual slices and correlates with the changes in excitability induced by kainic acid. In a rat <i>in vivo</i> model of post kainic acid-induced epilepsy, we show similar hypermethylation of the 5’ region of <i>gria2</i>. Inter-individual variations in <i>gria2</i> methylation, correlate with the frequency and intensity of seizures among epileptic rats. Luciferase reporter assays support a regulatory role for methylation of <i>gria2</i> 5’ region. Inhibition of DNA methylation by RG108 blocked kainic acid-induced hypermethylation of <i>gria2</i> 5’ region in hippocampal slice cultures and bursting activity. Our results suggest that DNA methylation of such genes as <i>gria2</i> mediates persistent epileptiform activity and inter-individual differences in the epileptic response to neuronal insult and that pharmacological agents that block DNA methylation inhibit epileptiform activity raising the prospect of DNA methylation inhibitors in epilepsy therapeutics.</p>