Abstracts

Rationale: Acquired epilepsy is a debilitating condition that can require neurosurgical intervention to achieve sustained remission and cure. Therapies targeting neuronal-network remodeling after head injuries and other predisposing factors may prevent the occurrence or recurrence epilepsy in high-risk patients. Mouse epilepsy models recapitulate many aspects of human epilepsy, most importantly, delayed neuronal-network remodeling and spontaneous recurrent seizures. We demonstrate Wnt pathway dysregulation in a mouse epilepsy model, and modulation of post-ictal neuronal-network remodeling in the hippocampus by the novel Wnt antagonist, XAV939. Methods: Seizures were induced by intrahippocampal kainate injection in 3-4-month-old POMC-GFP transgenic mice; in these mice, adult-born dentate granule neurons express GFP for approximately 2-weeks. Animals received BRDU to label mitotic cells 48h-72h after injection. Tissue was analyzed using immunohistochemistry and confocal microscopy, and compared to saline-injected controls. Transcriptome analysis was performed using RNA extracted from anatomically micro-dissected dentate gyri 3-days post-seizure. N=4 per experimental arm. Results: Data demonstrate increased neurogenesis (1.9-fold, p<0.05) and dendrite arbor length (2.4-fold, p<0.05) in newborn hippocampal dentate granule cells in peri-ictal regions, and decreased neurogenesis in the ictal zone 2-weeks after kainate injection (88% decrease p<0.05). To investigate the role of the Wnt pathway in neuronal network remodeling, we administered XAV939, a canonical Wnt antagonist, daily for 2-weeks after kainate injection. With XAV939 administration, dendritic arborization in peri-ictal regions increased further after seizure (1.6-fold, p<0.05); neurogenesis remained unchanged (1.2-fold, p>0.05). We also examined newborn dentate granule cell migration, as Wnts have been implicated in neuronal migration; however, we saw no significant change in migration attributable to XAV939 in peri-ictal regions. We investigated which Wnt genes might contribute to the alterations in post-ictal neurogenesis using RT-PCR. Transcriptional analysis of micro-dissected dentate gyri demonstrated canonical Wnt gene dysregulation, specifically Wnts 5A, 7A, 9A (p<0.005) and DKK1 (p<0.05) in peri-ictal regions. Intriguingly, certain Wnt genes demonstrated differential patterns of dysregulation between the ictal and peri-ictal zones, most notably Wnt5B and 7B. These transcriptional changes might underpin the development of delayed epilepsy in this model. Conclusions: Neuronal-network remodeling occurs after seizures and is critical in the development and maintenance of epilepsy. We demonstrate that the Wnt pathway is critical to changes in neuronal behavior in the dentate gyrus and is dysregulated early in the post-ictal period. These changes are especially marked in the peri-ictal zones and may underlie the formation of epileptic foci away from the primary ictal zone. Therapies targeting Wnt activity and network remodeling may prevent the acquisition of delayed epilepsy in high-risk patients. Funding: NREF