DNA Methylation Mediates Persistent Epileptiform Activity In Vitro and In Vivo

Abstract

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 in vitro and in vivo rodent models. We analyzed changes in the gria2 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 gria2 gene. Increase in methylation persists one week after removal of the drug, with concurrent suppression of gria2 mRNA expression levels. The degree of kainic acid-induced hypermethylation of gria2 5’ region varies between individual slices and correlates with the changes in excitability induced by kainic acid. In a rat in vivo model of post kainic acid-induced epilepsy, we show similar hypermethylation of the 5’ region of gria2. Inter-individual variations in gria2 methylation, correlate with the frequency and intensity of seizures among epileptic rats. Luciferase reporter assays support a regulatory role for methylation of gria2 5’ region. Inhibition of DNA methylation by RG108 blocked kainic acid-induced hypermethylation of gria2 5’ region in hippocampal slice cultures and bursting activity. Our results suggest that DNA methylation of such genes as gria2 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.

Association of RASgrf1 methylation with epileptic seizures

“…It has been shown that mouse hippocampal slices treated with 2 h of KA exposure exhibit hypermethylation of the gria2 gene, and this effect persisted one week after the removal of the drug. RG108 was able to completely block the bursting activity and the persistent hypermethylation induced by KA [9]. In our study, the inhibition of increased methylation started on the 1st day after acute epileptic seizures, and this inhibition was significant by the 10th day when compared to the SE group.…”

Sex, epilepsy, and epigenetics

“…Third, several lines of evidence support the conclusion that epigenetic factors and mechanisms are functionally deregulated in epilepsy, including analyses performed utilizing human specimens as well as many different animal models (Crowe et al, 2011; Huang et al, 2012; Hwang et al, 2013; Kobow and Blumcke, 2012; Kobow et al, 2009; Kobow et al, 2013; Machnes et al, 2013; Miller-Delaney et al, 2012; Park et al, 2014; Ryley Parrish et al, 2013; Sng et al, 2006; Taniura et al, 2006; Tsankova et al, 2004; Williams-Karnesky et al, 2013; Zhu et al, 2012). One of the most persuasive studies found that, in a rat model of TLE, increased levels of DNA methylation in the hippocampus are associated with epileptogenesis and that adenosine, an endogenous anticonvulsant and anti-epileptogenic factor, exerts these effects via inhibition of DNA methylation (Williams-Karnesky et al, 2013).…”

Epigenetic interventions for epileptogenesis: A new frontier for curing epilepsy

“…DNMTs also play a key role in the development of epilepsy as evidenced by studies of DNMT inhibitors. Inhibiting DNA methylation via DNMT inhibitor RG108 resulted in Gria2 upregulation and blocked the seizure inducing effects of kainic acid in the hippocampus (Machnes et al, 2013). …”