Abstracts

Rationale: Brain-derived neurotrophic factor (BDNF) has been identified as a possible molecular mediator in epileptogenesis and in memory formation. However, little is known about the regulation of the bdnf gene in the CNS. We hypothesize that aberrant expression of memory-related genes, such as bdnf, contribute to deficits in hippocampus-dependent long-term memory formation associated with prolonged seizure activity. The studies presented here expand on the idea that epigenetics, a new molecular mechanism for gene expression changes in the nervous system, may play a role in memory disorders associated with epilepsy. For our studies we focused on area CA1 of hippocampus, a brain region well-characterized in the process of contextual long-term memory storage. Methods: First, we determined the pattern of post-translationally modified histones (Chromatin Immunoprecipitation) and DNA methylation (Bisulfite Sequencing) at the bdnf gene in area CA1 of hippocampus after 1 h of kainate (KA)-induced status epilepticus (SE). We next determined the expression of exon-specific bdnf mRNA levels in hippocampus following KA-SE. Finally, using a contextual fear conditioning learning paradigm, we assessed the effect of histone deacetylase inhibition (HDACi) on long-term memory formation in epileptic animals (2-3 months post-SE). Results: Quantitative real-time PCR revealed significant increases in exons I, II, IV, VI and IX bdnf mRNA levels in area CA1 of hippocampus at 1 h of KA-SE. These results support previous findings that exon-specific bdnf gene regulation occurs in hippocampus following KA-SE. Interestingly, we found that alterations in hippocampal bdnf mRNA levels correlated with DNA methylation changes at the bdnf gene during SE. Specifically, we observed demethylation of the bdnf gene at a CpG island within bdnf promoter 4 in area CA1 after 1 h of KA-SE. Next, we examined whether histone modifications at bdnf promoters, another epigenetic mechanism directly implicated in bdnf gene regulation, was altered in area CA1 of hippocampus during SE. We found that both histone H3 acetylation and phosphoacetylation levels increased at bdnf promoter 4 in area CA1 of hippocampus after 1 h of KA-SE. Moreover, HDACi with sodium butyrate significantly altered SE-induced bdnf gene expression changes in area CA1 of hippocampus at 1 h or 24 h after KA-SE and HDACi significantly enhanced long-term memory formation in epileptic animals. Conclusions: Together our findings suggest that epigenetic regulation of the bdnf gene during epileptogenesis, mechanistically via histone modification and DNA methylation, may mediate long-lasting behavioral changes in epilepsy. Indeed, our present findings suggest that HDACi improves fear memory processing in animals that had experienced epilepsy. Additional studies are underway for assessment of altered DNA methylation patterns at the bdnf promoters in hippocampus during fear memory consolidation after KA-SE. Support:NINDS/NIMH