Abstracts

Rationale: A number of receptors (e.g., GluR2), ion channels (e.g., HCN1) and transporters (e.g., Kcc2) regulated by the transcriptional repressor NRSF have recently been found to be altered in the epileptic hippocampus. This suggests that repression by NRSF may define a general mechanism by which expression of gene clusters crucial to normal neuronal function might be deranged after insults that promote hyperexcitability and spontaneous seizures. Methods: Genome-wide expression analysis was performed using Illumina RatRef-12 Expression Beadchips. Experimental groups included controls and rats that experienced kainic-acid-induced status epilepticus (KA-SE). Control and KA-SE groups were treated with oligodeoxynucleotides (ODNs) comprising either the NRSE sequence (as a decoy preventing NRSF binding to its cognate DNA-binding sequence) or a scrambled sequence. In all cases, the CA1 region of the hippocampus was resected two days after KA-SE and mRNA recovered. Results: 470 genes were repressed by kainic-acid-induced status epilepticus (KA-SE). Of these, 39 contained an NRSE, including, KCC2, TAP1, Kv3.2, NELL1, Grik5, GluR2, NMDA receptor type 2A, SCN3B, GLRA2, KCNIP2, and HCN1. In total 49 ion channels were reduced, of which 22 have a functional NRSE. Treatment with NRSE ODNs left 347 genes repressed, but only 2% contain putative NRSE binding sites. Pathway and cluster analyses showed that ion channels were commonly reduced by KA-SE and rescued by the ODNs. Another major cluster of these NRSF dependent genes is that of calcium binding proteins. NRSF independent gene changes were manifest after KA-SE. These included gene clusters related to stress response and inflammation. Functionally, administration of NRSE ODNs to KA-SE attenuated subsequent hippocampal hyperexcitability and the severity of the resulting epilepsy. Conclusions: (1) NRSF dependent and independent changes in the expression of gene clusters are provoked by insults resulting in epilepsy. (2) Rescue from repression, using NRSE ODNs is relatively selective for NRSE-containing genes. (3) This rescue attenuated the conversion of the hippocampal network into a hyperexcitable one, and the generation of epilepsy, suggesting that NRSF might be a master switch in the coordinated program that promotes hyperexcitability after KA-SE and similar insults. Therefore, the selective suppression of the function of specific transcription factors, followed by genome-wide analysis provides a powerful tool to uncover genes that are crucial for epileptogenesis and might be therapeutic or preventive targets.