Abstracts

Rationale: Wnt signaling has significant roles in brain development, neuron growth and guidance. Wnt signaling is active in specific regions of the adult brain, including the hippocampus, cortex and other regions. Wnt signaling is required for maintenance of neuronal stem cells. In status epilepticus (SE) and the post-SE epileptogenic period, there is significant expansion of resident stem cells and neuronal remodeling. We reasoned that Wnt signaling might be altered in the epileptogenic period and then investigated Wnt signaling activity in multiple experimental models to establish general principles. We conclude that Wnt signaling is robustly activated in the post-SE, epileptogenic period. Methods: 7-week-old mice of appropriate background strains were treated with kainate (KA)/(C57bl6) or pilocarpine (PILO)/(FVBN). The brain regions were dissected between 1 hr. and 7 days following SE. Wnt signaling pathway activity was measured by a combination of qRT-PCR and quantitative western blots. Statistical significance was assessed with Instat software. In vivo KA-induced Wnt activation in forebrain neurons was assessed using the Wnt pathway reporter transgenic mouse line BAT-GAL (in C57bl6).Results: Using the KA/C57bl6 mouse model, Wnt signaling was activated in the hippocampus rapidly and transiently with SE (1-2 hr.) then maximally at 5 days in the post-SE epileptogenic period. At day 5, we observed maximal induction of -catenin levels, of the Wnt-target gene MYC, and of MYC targets LDHA and PK-M2. A detailed qRT-PCR analysis with a Wnt pathway specific gene array revealed that 23 known Wnt target genes were significantly induced, including LEF1, TCF4 and TCF7. In vivo analysis of Wnt signaling in BAT-GAL mice corroborated the biochemical analyses and further refined the location of highest Wnt signaling to the dentate gyrus and CA1 region. Using the PILO/FVBN mouse model, a similar analysis showed identical Wnt signaling and target gene activation patterns. Lastly, similar results were additionally obtained in equivalent rat SE models. Together, these data underscore that activated Wnt signaling is a general feature of SE and of epileptogenesis. Conclusions: Molecular and in vivo analyses demonstrate that Wnt signaling is induced in the hippocampus in the post-SE epileptogenic period in multiple models. Furthermore, the induction of Wnt signaling in the dentate gyrus suggests that Wnt signaling may play a role in the neuronal reorganization that occurs in the epileptogenic period. These results establish Wnt signaling as a general feature of epileptogenesis in multiple experimental models. Our findings further suggest that the attenuation of Wnt signaling (by numerous drugs under development for cancer) may have unexpected efficacy for disease modification in the complex process of epileptogenesis. Elaboration of a molecular framework for investigating Wnt signaling should expedite the testing of new therapeutic strategies for epilepsy. Supported by grants from CURE (Citizens United for Research in Epilepsy) and the Dept. of Defense to ASY and ASY.