Studies on epigenetic mechanisms and corticosteroid receptor action in the rat hippocampus

  • Emily Price

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Following a stressful event or during circadian changes glucocorticoid (GC) hormones are secreted into the blood and bind to their cognate receptors; mineralocorticoid (MRs) and glucocorticoid receptors (GRs). In the hippocampus, an important brain region involved in learning, memory and stress regulation, MRs and GRs are known to influence gene transcription by binding to their recognition elements within the DNA. The chromatin accessibility of these interaction sites is a determinant factor of receptor binding and could be influenced by remodelling factors, e.g. BRG1, and epigenetic marks, e.g. histone modifications. To date, however, the involvement of histone modifications has been largely unexplored. This thesis therefore initially utilised recently obtained MR and GR ChIP-seq data, RiboZero-RNA-seq data as well as pharmacological blockade of both receptors to determine important transcriptional regulatory regions across a specific gene implicated in GC regulation and psychiatric disorders called Fkbp5. At the majority of MR and GR binding sites, stress- and circadian-induced increases in histone 3 acetylation at lysine 9 and phosphorylation at serine 10 (H3K9acS10p) and BRG1 recruitment were identified. Furthermore, antagonism of the GR resulted in a reduction of stress-induced H3K9acS10p formation across Fkbp5 suggestive that non-genomic GR action influences the accessibility of itself binding to the genome. Due to the apparent involvement of H3K9acS10p in Fkbp5 regulation, investigation of H3K9acS10p was taken to the genome-wide level which led to the identification of >44,000 loci enriched for this histone modification under baseline and stress conditions. Further integrative ChIP-seq analysis defined a strong overlap between sites of corticosteroid receptor binding and H3K9acS10p with the pattern and level of H3K9acS10p correlating with the degree of MR and GR enrichment at many stress- and circadian-inducible genes genome-wide. To investigate whether the H3K9acS10p modification was directly responsible for MR and GR binding permissibility, pharmacological agents directed to the pathway previously implicated in the stress-induced formation of this histone mark were used. These interventions failed to determine the causal link between H3K9acS10p and MR/GR binding due to an apparent off-target effect on GC secretion and therefore further work should be conducted using different experimental approaches. Overall, this thesis has further defined the molecular underpinnings of Fkbp5 regulation in vivo as well as providing a strong novel link between H3K9acS10p, sites of corticosteroid binding, and gene transcription under physiological conditions. This provides a basis to which further investigations can evaluate how these (epi-)genomic factors are altered in pathophysiological conditions e.g. major depression and anxiety.
Date of Award25 Jan 2022
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorJ M H M Reul (Supervisor) & Oscar Cordero Llana (Supervisor)

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