ABSTRACT: Purpose: to evaluate changes in the transcriptome of hippocampal cells during the course of epileptogenesis, from the early events post status epilepticus (SE) to the onset of recurrent spontaneous seizures. Experimental Design: Gene expression profiling was analyzed in hippocampi of rats subjected to the pilocarpine model of epilepsy at different times during the course of epileptogenesis: 3 days post-SE (3D), 7 days post-SE (7D), and immediately (up to 12h) after the first spontaneous seizure (Chronic). All three pilocarpine subgroups had a corresponding age-matched control group (saline-treated rats), from which normal hippocampi samples were obtained at the same experimental time points. Independent microarray hybridizations were carried out for each sample (n = 5, per experimental group) with oligonucleotide microarrays covering 34,000 transcripts representing most of the known and predictive genes of the rat genome (CodeLink⢠Rat Whole Genome Bioarrays, GE Healthcare), following the manufacturerâs protocol. Results: differential expression of almost 1,400 genes was detected during the course of epileptogenesis, from the early events post status epilepticus (SE) to the onset of recurrent spontaneous seizures. Most of these genes are novel and displayed an up-regulation after SE. Noteworthy, a group of 128 genes functioning in neurogenesis, apoptosis, immune response, and intracellular signal transduction was found consistently hyper-expressed throughout epileptogenesis, indicating stable molecular alterations within the hippocampus. Those include modulation of the MAPK, Jak-STAT, PI3K, TGF-beta, and mTOR signaling pathways. Differential expression of genes from the p38 MAPK pathway, mediating inflammation and neurogenesis, was also confirmed by real-time PCR. These findings reveal dynamic molecular changes occurring in the hippocampus that may serve as a starting point for the generation of new hypothesis regarding the underlying mechanisms of epilepsy and for the designing of alternative therapeutic strategies. Keywords: gene expression changes during epileptogenesis. We performed a genome wide analysis of genes differentially expressed during epileptogenesis. Virtually, all possible changes in the rat transcriptome were monitored at distinct time points corresponding to the latent to chronic phase transition of the pilocarpine model of epilepsy, which is probably the most extensively studied chemically inductive model of TLE. Genes identified as being differentially expressed were classified based on their respective biological functions to envisage processes and pathways likely implicated in epileptogenesis, as well as their possible value as targets for therapy. Results were expressed as fold variation, and genes displaying greater than 2-fold changes in transcript abundance and p<0.01 were selected.
