| Epilepsy is one of the most common neurological disorders characterized by recurrent seizures. Currently, the underlying mechanisms are not well understood and therapies only serve to relieve the symptoms. A single episode of seizure can trigger epileptogenesis, a process in which the brain undergoes network reorganization including neurodegeneration and sprouting of axons. The mechanisms linking the first seizure to development of epilepsy are currently unknown. Interestingly, changes in neuronal circuitry in epilepsy are accompanied by chronic alterations in the normal brain gene expression profile. Epigenetic mechanisms, including DNA methylation and covalent histone modifications stably program the genome during gestation. However, recent studies suggest also that epigenetic mechanisms might be involved in modifying genome function in response to environmental stimuli. We therefore hypothesize that a single seizure can disrupt normal epigenetic programming in the brain, which results in altered gene expression profiles that drive the network reorganization events.;In this study, we used in vitro and in vivo models of temporal lobe epilepsy (TLE) by kainic acid treatment to test whether DNA methylation changes are associated with epileptogenesis. DNA methylation is a covalent modification of DNA by adding a methyl group on the 5' position of cytosine by DNA methyltransferases. We focused our analysis on DNA methylation because of its importance role in gene regulation. Indeed there is an overall inverse correlation between DNA methylation of regulatory regions of genes and gene expression. We closely examined the DNA methylation changes associated with the promoters of the GRIA2 gene (codes for glutamate receptor ionotropic AMPA 2 subunit), which has been demonstrated to be down-regulated in epilepsy and to be highly implicated in hyper-excitable neuronal circuitries. We detected rapid hypermethylation in GRIA2 after a 2-hour period of epileptiform activity in the in vitro model. Similar changes in GRIA2 DNA methylation were also observed in our in vivo model 10 weeks post-kainic acid injection. We also observed a significant positive correlation between the number of seizures recorded by video-EEG and severity assessed by Racine scale and the average GRIA2 DNA methylation.;Epileptogenic insults induced by kainic acid treatment led to rapid DNA methylation changes in GRIA2 gene. This result suggests that alterations in DNA methylation may serve as a molecular memory of the insult, which can lead to the progressive changes in gene expressions, thus contributing to the development of epilepsy as well as the maintenance of an epileptic neuronal circuitry. |
