Abstracts

Rationale: Epigenetic mechanisms, such as 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) DNA methylation, have been implicated in the pathogenesis of temporal lobe epilepsy (TLE). However, the role of DNA methylation in the development of TLE is unclear. Recently, a new role has been described for O-linked N-acetylglucosamine (GlcNAc) transferase (OGT) in the regulation of 5hmC. OGT co-localizes with the Ten-Eleven Translocation (TET) proteins that catalyze the conversion of 5mC to 5hmC, thus linking protein O-GlcNAcylation to chromatin structure. Whether OGT and TET interact to mediate 5hmC DNA methylation changes in the epileptic hippocampus is currently unknown.Methods: Here, we assessed protein O-GlcNAcylation, OGT, and DNA methylation levels in hippocampal tissue from TLE patients compared to aged-matched controls (Average age: 39.6yrs). Using the kainate rodent model of TLE we determined protein O-GlcNAcylation, DNA methylation (5mc and 5hmC), and OGT levels in the epileptic hippocampus. To artificially increase O-GlcNAcylation levels we employed the OGA inhibitor Thiamet-G (TMG) and determined effects on DNA methylation (5hmc) and epileptiform activity.Results: We found a dramatic decrease in protein O-GlcNAcylation, OGT, and 5hmC levels in human hippocampal TLE tissue relative to controls, which we recapitulated in the kainate-induced TLE rat model. Further analysis of cell-type specific effects after treatment with glutamine, a substrate involved in the O-GlcNAc pathway, revealed OGT and TET expression changes in primary cultured pyramidal neurons but not in astrocytes. Next, we hypothesized that elevating O-GlcNAcylation levels in the rat epileptic hippocampus might be sufficient to affect 5hmC levels. We found that TMG treatment reduced epileptiform activity and frequency oscillations in our TLE rodent model, while 5hmC levels in the epileptic hippocampus returned to similar levels as non-epileptic controls.Conclusions: Collectively, these findings demonstrate the therapeutic potential of TMG, and identify a novel epigenetic role for protein O-GlcNAcylation in TLE.