Abstracts

Rationale: Mesial temporal lobe epilepsy (MTLE) is the most prevalent type of drug-resistant epilepsy. MTLE is often associated with structural abnormalities such as hippocampal sclerosis (HS) and cortical dysplasia (CD). The causes of the MTLE and, specifically, mechanisms of its drug resistance remain obscure. It has been proposed that epigenetic modifications play a critical role in the etiology and drug resistance of MTLE. Recent studies focus mainly on DNA methylation, while only a few articles have been published related to histone modifications. We have studied epigenetic modifications of histone H3 in brain tissue of patients with refractory MTLE. Methods: Tissue samples were collected during epilepsy surgery (hippocampal and temporal lobe resections) in drug-resistant patients. Three groups of samples were formed: hippocampus, temporal lobe and unspecified tissue. Modifications of histone H3 were analyzed using Western blotting. The following modifications of lysine residues (K) were studied: acetylation (ac) of H3K9, H3K14 and H3K18 and mono-, di-, di/tri- and trimethylation (me1, me2, me2,3, me3) of H3K4, H3K9 and H3K27. The study focused on associations between H3 modifications, differences in modification patterns between temporal lobe and hippocampus, epigenetic features of morphological pathologies and putative associations between histone modifications and antiepileptic drugs used by the patient (valproate, carbamazepine, levetiracetam and lamotrigine). Results: We found correlations between following methylation types (p < 0.005): me1 and me2 H3K4 (r=0.59), me2H3K9 and me1H3K4 (r=0.58), me2H3K4 and me3H3K27 (r=0.54), me2H3K27 and me2,3H3K9 (r=0.73). Acetylation and methylation also correlated with each other (p < 0.005): acH3K14 and me1H3K4 (r=0.55), acH3K14 and me3H3K4 (r=0.6), acH3K18 and me3H3K27 (r=0.94). Levels of acH3K14, me1 and me2H3K4, me2H3K9, me2 and me3H3K27 were higher in the temporal lobe than in the hippocampus (p < 0.05).Morphological pathologies included CD and HS. We did not find the connection between CD and changes in H3 modifications. In patients with HS the levels of me3H3K4 (p < 0.05), me2H3K9 and me2H3K27 (p < 0.01) were decreased, but the level of me3H3K27 (p < 0.01) was increased.Valproate and lamotrigine did not affect H3 modifications. In patients treated with carbamazepine the levels of me1H3K4 and me2H3K9 were decreased (p < 0.05). Levetiracetam intake was associated with the increase in me1H3K4 (p < 0.05). Conclusions: We have shown that different H3 modifications correlate with each other. Patterns of histone H3 modifications are structurally specific, related to specific antiepileptic drug intake and vary in patients with HS. In our further studies we will focus on specific genes regulated by these epigenetic modifications. Funding: The study was supported by RFBR grant ?16-04-01513.