Epilepsy is the 4th most prevalent neurological disorder after stroke, Alzheimer?s and migraine with an incidence of 1 in 26 individuals. Though there are a number of anti-convulsant drugs available, there are no anti-epileptogenic drugs that mitigate the progression of the disease. Using novel bioinformatic approaches, we have identified an endogenous, protective program launched by the brain after a prolonged seizure that functions to mitigate pathological changes. Epileptogenesis is associated with a plethora of changes in the brain including alterations in plasticity, cell death, neurogenesis, inflammation and axonal sprouting. These changes occur over timescales ranging from many minutes to years, but the orchestrating mechanisms are virtually unknown. Long-term changes in gene expression that are associated with epileptogenesis imply that one or more master regulators of transcription may be coordinating the brain alterations. In order to uncover these transcriptional mechanisms, we turned to our recently published genome-wide expression datasets generated by the Epilepsy Microarray Consortium (EMC). The datasets consist of mRNA expression profiles of rat dentate granule cells assayed at various time points after Status Epilepticus (SE). Using a novel bioinformatic tool that integrates whole genome transcription factor binding data with gene expression profiles, we analyzed datasets derived from brains induced by 3 different convulsant stimuli, each in 2 independent labs, and at various time-points. This analysis projected that Polycomb target genes represent the majority of chronically altered genes during epileptogenesis. REST targets represent a second, overlapping, group of repressed genes. Polycomb is a well-known driver of life-long changes in gene expression that works by epigenetically silencing genes across the phyla. Our data shows an extremely robust induction of EZH2 protein (the catalytic methylase subunit of Polycomb) over a 20 day window post SE in neurons. Further, we find that antagonizing EZH2 shortly after SE robustly accelerates the onset of spontaneous recurrent seizures in mice, suggesting a protective rather than pathological role for EZH2. How antagonism of EZH2 later after SE remains to be determined. In this project, we will test the hypothesis that an alteration in Polycomb output is a principal modifier of epileptogenesis. We will ascertain whether EZH2 upregulation is always protective or whether its role evolves during the latent period. We will test the effect of an order-of-magnitude change in EZH2 levels on corepressor function to see whether such upregulation augments or hampers the repressive abilities of two major EZH2 containing complexes: Polycomb and REST. We anticipate that these studies will establish Polycomb as a major orchestrator of the long-term changes associated with epileptogenesis. If so, approaches that modulate Polycomb function may be of benefit to the 65 million people world-wide that live with epilepsy.
Epilepsy afflicts 1% of the population and is characterized by spontaneous seizures. About 30% of patients do not respond to current therapies. Thus, a deeper understanding of the mechanisms that drive the disease are required. By analyzing the expression level of every gene in the rat hippocampus in 3 different epilepsy models in 11 institutions and 3 time points after seizure induction, we have found a core driver of long term gene changes in the epileptic brain. This complex is called Polycomb. This project will study the role of Polycomb in the progression of epilepsy.
