Abstracts

This abstract is a recipient of the Young Investigator Award.
This abstract has been invited to present during the Basic Mechanisms platform session.
This abstract has been invited to present during the Broadening Representation Inclusion and Diversity by Growing Equity (BRIDGE) poster session.

Rationale: The dentate gyrus of the hippocampus undergoes pathological remodeling during temporal lobe epileptogenesis, including dentate granule neuron dispersion, decreased neurogenesis, increased migration and dendritic complexity. These pathological changes contribute to the pathogenesis of temporal lobe epilepsy, however, the underlying pathways responsible are unknown. Previously, we determined that Wnt signaling is dysregulated in the mouse kainate model of temporal lobe epilepsy, and Wnt antagonism exacerbated pro-epileptogenic pathological remodeling (PMID 31596871). We therefore hypothesize that Wnt agonism may prevent pathological remodeling._x000D_
Methods: Focal temporal lobe epilepsy was induced by unilateral CA3 kainate (KA) injection (19 nM) in 8 wk-old C57BL/6J and POMC-eGFP transgenic mice, controls received saline. For RNA-seq, bilateral dentate gyri were collected 3, 7 and 14-days post injection (dpi) and the dorsal portion processed for RNA extraction. _x000D_ _x000D_ To monitor electrographic seizures mice were implanted with bilateral hippocampal recording wires, seizures were quantified for 21-dpi; animals received intraperitoneal vehicle or Wnt agonist Chir99021 (12.5mg/kg) daily until sacrifice.  For immunohistochemistry, POMC-eGFP mice received I.P. vehicle or Wnt agonist Chir99021 daily until sacrifice at 14-dpi, GFP+ immature dentate granule cells were characterized by confocal microscopy (20x, 1.1 µm/step, 22 steps/stack). N=2-4/group._x000D_
Results: RNAseq analysis demonstrated early dysregulation of the whole transcriptome early in epileptogenesis (Figure 1A). This was more marked in the epileptogenic zone than in the peri-ictal regions. The canonical Wnt pathway was found to be dysregulated in the dentate gyrus, in both the ipsilateral epileptogenic zone (EZ) and in the contralateral peri-ictal seizure network (SN) as soon as 3-days after KA injection (Figure 1B). Having identified that the Wnt pathway plays a role in early epileptogenesis, we sought to determine whether exogenous canonical Wnt signaling can modulate epileptogenesis. Wnt agonist daily treatment reduced 24-hr electrographic seizure duration from 1879 secs to 33 secs 21-days after KA. In order to determine how Wnt agonist treatment might be affecting epileptogenesis, we characterized changes in immature dentate granule cell morphology. In untreated epileptic animals, immature dentate granule cell neurons showed decreased dendritic arborization in the EZ, consistent with neuronal injury (36±25 µm vs. 79±14 µm) and increased dendritic arborization in the SN (114±19 µm vs. 86±18 µm), consistent with expected pathological remodeling compared to saline injected controls. After treatment with Wnt agonist, dendritic length trended towards normalization in the EZ and SN (162±128 µm and 119±12 µm respectively).

Conclusions: The pathogenesis of TLE is characterized by remodeling of the hippocampal dentate gyrus. The Wnt pathway may play a role in pathological remodeling of the dentate gyrus and represents a potential therapeutic target in epileptogenesis._x000D_
Funding: NIH K12NS080223