Abstracts

Rationale: Epilepsy is a highly prevalent neurological disorder defined by the emergence of recurring, spontaneous seizures. Current anticonvulsant medications are not disease modifying and do not prevent epileptogenesis. We previously identified the histone methylase EZH2 as a principal regulator of gene expression changes in rodent dentate granule cells after status epilepticus (SE). Pharmacological inhibition of EZH2 suggested that its upregulation post-SE was an endogenous protective measure launched by the brain after SE.  We wished to discern the mechanism by which EZH2 upregulation might confer protection in epilepsy._x000D_
Methods: We utilized novel bioinformatic approaches and algorithms to mine RNAseq profiles of hippocampi from naïve or epileptic, wildtype and EZH2 neuronal conditional knockout (EZH2nKO) mice.  Epilepsy was induced with either pilocarpine or repeated low dose kainic acid. Gene clusters were generated to define blocks of genes that were differentially expressed in response to SE in WT and EZH2nKO brains. Clusters were subjected to MAGIC analysis to define transcription factor/cofactor networks recruited after SE. Ontological analysis was performed to obtain heuristics describing global gene changes in epilepsy.  Predictions were tested in vivo using biochemical, molecular biological, and physiological techniques to assess gene changes, alterations in protein levels and seizure threshold in mouse models of status epilepticus and epileptogenesis._x000D_
Results: We report here that EZH2 protein is expressed in approximately half of hippocampal neurons and is  strongly induced after seizures induced by pilocarpine or kainate. Upon conditional knockout of EZH2 in neurons, we observe a robust reduction in the flurothyl seizure threshold of mice after SE. This occurs in the absence of threshold changes in naïve mice and in the absence of changes in seizure severity during induction of SE. This suggests that EZH2 induction post-SE is a protective mechanism invoked during seizures._x000D_ _x000D_ Whole hippocampus RNAseq analysis suggests that EZH2 targets a number of pro-epileptogenic signal transduction pathways, including the JAK/STAT pathway. Consistent with this, we report that whereas wildtype mice exhibit a transient induction of the JAK/STAT pathway post-SE, loss of EZH2 results in sustained induction of this pathway. Pharmacological blockade of the JAK/STAT pathway suppresses the seizure threshold phenotype in EZH2nKO mice._x000D_
Conclusions: EZH2 induction post-SE is a protective mechanism invoked to temper activation of pro-epileptic signal transduction pathways including the Jak/STAT pathway. _x000D_
Funding: This work was supported by CURE, NIH, and Lily’s Fund. NIH grant number: NS108756 to AR and RD.