MON-727 The Chromatin Landscape of Glucocorticoid Regulated Genes in Mouse Embryonic Neural Stem / Progenitor Cells

Abstract Stem/Progenitor Cells Antenatal administration of Dexamethasone (Dex), a synthetic glucocorticoid (GC), is a common clinical intervention for women at risk for preterm birth or in preterm labor that effectively reduces fetal risk of mortality and bronchopulmonary-related comorbidities. Despite the therapeutic potential of Dex, excess GC act adversely in the developing central nervous system to reprogram distinct neural circuits in the brain by acting through the glucocorticoid receptor (GR). For example, prenatal exposure to excess GCs can impact neural stem and progenitor cell (NSPC) proliferation leading to long-term alterations in prefrontal cortical neuronal complexity, which could contribute to behavioral and cognitive impairments later in life. The GR is a member of the nuclear receptor superfamily that, when bound by a ligand, translocates from the cytoplasm to the nucleus and associates indirectly or directly with DNA elements (e.g. glucocorticoid responsive elements or GREs) resulting in the activation and/or repression of target genes. While GR-regulated transcriptomes have been identified in many NSPC models, the mechanisms responsible for programming these cells for GC-responsiveness remain largely unknown. We therefore used transposase accessible chromatin followed by genome-wide sequencing (Omni ATAC-seq) to characterize the chromatin landscape of primary embryonic mouse NSPCs in response to an acute in vitro treatment with Dex. We identified a small, yet distinct fraction (0.002%, p<0.05) of open chromatin sites that were Dex-inducible. 95% of these Dex-induced changes in chromatin accessibility occur within intronic or intergenic regions, suggesting the presence of long-range enhancer-promoter contacts that mediate NSPC transcriptional responses to Dex. Motif enrichment analysis revealed putative GRE sites located in Dex-inducible open chromatin within -5kb/+2kb of a Dex-induced gene, providing possible DNA targets of GR for further validation. A number of other transcription factors implicated in neurodevelopmental processes were found to underlie both Dex-inducible and constitutively open chromatin regions. Characterization of the precise epigenetic and transcriptional response to excess GC in-utero, and its influence on acute and chronic neurological outcomes, will encourage the development of alternative GC treatment regimens that could protect the developing brain from insult while providing optimal health outcomes in neonates.