The nuclear receptor REV-ERBA is a component of the core molecular clock, which exerts rhythmic control over numerous processes. REV-ERBA is furthermore considered a critical regulator of energy metabolism, particularly of lipogenesis. The glucocorticoid receptor, GR, has a rhythmic endogenous ligand which is a fundamental component of the stress response, mobilising energy stores. Glucocorticoids are one of the most widely-used agents in medicine and, in excess, promote lipid accumulation and glucose intolerance. The aim of this work was to investigate factors which influence GR and REV-ERBA action, with a particular focus on where these nuclear receptors bind the genome. We show that combining chromatin immunoprecipitation (ChIP) with digital PCR offers advantages when quantifying nuclear receptor-DNA binding. Using a new transgenic mouse model, we map the liver cistrome of REV-ERBA in an antibody-independent manner and combine this with gene expression data. We demonstrate that REV-ERBA action is context-dependent and REV-ERBA does not in fact regulate metabolism in the basal state. Moving to study GR, we find a time-of-day difference in the sensitivity of the GR cistrome to glucocorticoid treatment, but are unable to support previous findings that REV-ERBA regulates GR action. The GR cistrome is however remodelled by the lineage-determining factor HNF4A, with corresponding, albeit complex, changes in gene expression. Hepatocyte nuclear factor HNF6 also directs the glucocorticoid response. Taken together, our findings demonstrate that the actions of REV-ERBA and GR are not fixed, but are instead shaped by context. This has important implications for future studies, particularly of REV-ERBA, and for pharmacological targeting of these receptors.
- nuclear receptor
- circadian clock
Determinants of nuclear receptor action in circadian and metabolic regulation
Hunter, A. L. (Author). 31 Dec 2019
Student thesis: Phd