Epileptogenesis has been predominantly studied in the context of neuronal dysfunction, but emerging studies indicate that dysregulation of glia, such as astrocytes, oligodendrocytes, and microglia, contributes to the pathogenesis and maintenance of an epileptic scar. Under physiological conditions, astrocytes are essential for the maintenance of synaptic function and neuronal survival. Reactive astrocytes in epilepsy display several phenotypic changes, including dys-expression of ion channels and glutamate transporters, as well as aberrant activation of signaling pathways for cell proliferation. Oligodendrocyte progenitors (OPCs) are also present in greater numbers in epileptic foci. Using fresh cortical samples from patients with temporal lobe epilepsy, our laboratory has recently characterized a subpopulation of re-activated glia, which overexpress EGFR and are capable of generating neurospheres in vitro. This has lead to our hypothesis that pathological remodeling of mature glia towards a more primitive, immature state, contributes to abnormal activity in an epileptic scar, by turning on transcriptional networks for proliferation while repressing homeostatic mechanisms of ion balance, glutamate transport, and myelin support. The transcriptional changes driving glial re-activation in primary human samples have been challenging to study, however, due to the difficulty of accessing such material fresh, and the inherent cellular heterogeneity present within the tissues in vivo. To this effect, our laboratory has developed a unique strategy for the successful isolation of astrocytic, OPC, and neuronal nuclei, giving us a unique tool to study the cell-type specific molecular dynamics in human lesional tissue. Specifically, here we will profile the epilepsy-associated changes within the nuclear transcriptome (by RNA-seq) and associated open chromatin landscape (by ATAC-seq) of acutely isolated astrocytes, OPCs, and neurons. This analysis will allow us to define, for each cell type, the epilepsy-associated remodeling of transcriptionally accessible loci, and to derive a blueprint for specific transcription factor (TF) binding sites. We will disseminate this data to the scientific community as an open database using the Synapse gateway platform (project Glia in Epilepsy). Furthermore, we will use this data to analyze bioinformatically the TF motifs and binding occupancy present specifically within epileptic astrocytes, in an effort to define better the transcriptional mechanisms driving their altered phenotype in epileptic human tissue. Defining the specific epigenetic landscape and associated transcriptional phenotype in different cell types derived from epileptic human tissue will advance deeply our understanding of the lasting molecular adaptations present in drug-resistant epilepsy. By depositing our data in an open access platform, we will maximize data dissemination and facilitate further investigation into the role of glial pathology in epilepsy, hoping to uncover new avenues for antiepileptic therapy aimed at restoring glial-neuronal homeostasis.
The goal of this study is to define the transcriptional changes leading to glial pathology in drug-resistant human epilepsy. To do this, we will isolate distinct populations of astrocytes, oligodendroglial progenitors, and neurons directly from freshly frozen human epilepsy vs. control tissues, and will define the cell-type specific changes in open chromatin architecture, transcriptome dynamics, and transcription factor binding activity induced by epilepsy in these distinct human populations.
