An investigation into the genomic actions of glucocorticoid binding receptors in the rat brain following acute stress and circadian influences

Abstract

Glucocorticoid (GC) hormones secreted upon activation of the HPA axis following stress or circadian input are vital regulators of many important physiological processes. In the brain, genomically acting mineralocorticoid receptors (MRs) and glucocorticoid receptor (GRs), orchestrate the cellular and molecular effects of GCs. Upon receptor occupancy, MRs and GRs translocate to the nucleus where they bind the DNA to transactivate or transrepress GC-target gene expression. Here, we conducted hippocampal ChIP- and RNA-seq to investigate the genome-wide binding of MRs and GRs and the transcriptomic response following elevations in corticosterone, the primary GC in the rat, in response to an acute stressor (Forced swimming – FS) or the circadian rise of GC secretion. ChIP-seq revealed a strikingly distinct profile of MR- and/or GR-binding to over 1,000 loci, while RNA-seq identified transcriptional responses in over 1,000 genes. Cross-correlation of both datasets was carried out for the first time, while extensive pathway analysis highlighted many promising novel targets for further exploration. Of these targets, we further investigated the Krüppel-like factors (KLFs) in a separate cohort of rats while validating findings of ChIP- and RNA-seq. We extended our examination to other brain regions such as the amygdala, PFC and neocortex which showed substantial MR DNA-binding in these regions despite previous reports describing a localised expression of this receptor primarily in the hippocampus. Subsequently, we investigated whether the increases in binding were in fact the underlying events responsible for the observed transcriptional responses by blocking the actions of genomically acting MRs and GRs, using receptor antagonists, inhibitors of corticosterone synthesis and surgical adrenalectomy. This thesis has provided novel insights into the genomic actions of MRs and GRs under physiological conditions of relevance for GC secretion, while providing the groundwork for future experiments aiming to elucidate further the genomic mechanisms underlying GC hormone action in the brain.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	J M H M Reul (Supervisor)