Abstracts

Rationale: Temporal lobe epilepsy (TLE) is generally characterized by recurrent spontaneous seizures that emerge from a hyperexcitable hippocampal formation. In many patients, TLE develops after transient brain insults including status epilepticus (SE). The mechanisms that convert a normal into a chronically hyperexcitable hippocampus, i.e. epileptogenesis, are only incompletely understood. Our goal was to characterize transcription factor controlled expression signatures in early epileptogenesis. Methods: We induced SE by systemic application of pilocarpine to mice and sacrificed them at 2h, 6h, 12h, 24h and 36h after SE. Next we micro-dissected the CA1 region and isolated mRNA for Next Generation Sequencing. Results: To identify relevant signaling cascades during early epileptogenesis we first performed bioinformatic analysis of this mRNA-Sequencing data set. Using BioLayout3D, genes were clustered in co-expression networks revealing such with similar expression changes at different time points after SE. To identify clustered genes with substantial expression in neurons we filtered our data set against a published database of gene expression levels in glia, neurons, and vascular cells of the cerebral cortex by a homemade perl script. We identified 11015 genes that were clustered in a neuronal co-expression network and five clusters showed up-regulation of gene expression at distinct time points after SE. We then searched for transcription factor (TF) binding sites that are present in the promoters of most of the clustered genes using Cytoscape. Also here, TFs were filtered for significant neuronal expression. We then focused on one expression cluster, which shows a striking up-regulation already two hours after SE and consists of 170 genes. A gene ontology analysis revealed this cluster to contain 25 TFs. The Cytoscape prediction showed that the promoters of these 25 TFs are enriched in potential TF binding sites for six TFs. Of these, three have already been linked to epilepsy (Egr1, Jun, and NPAS4), whereas Sox11, Zbtb14 and Fezf2 have not. Functional verification experiments are currently ongoing and will be presented. Conclusions: Distinct gene expression signatures controlled by particular sets of TFs including Jun and Egr1 relate to key aspects of epileptogenesis. Transient antagonism of respective TFs after potentially epileptogenic brain insults may be effective in blocking epileptogenic gene expression dynamics and attenuate or retard spontaneous seizure emergence. Funding: Supported by European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n602102 (EPITARGET)