Functional genomics is an emerging approach used for understanding the role of gene regulation in
polygenic disease development. One disease that belongs to this category is type II diabetes and its
precursor, the metabolic syndrome. A morbid and, in some cases, life-threatening aspect of these
pathological states is an inability of the body to cope with fluctuating nutrient levels after a meal. While the
role of the liver in regulating postprandial homeostasis is well established, there are still open questions
regarding the key players that regulate the gene and enhancer activity during a feeding response in the
liver. More specifically, only few studies have addressed the acute transition from a fasted to a fed state in
a genome-wide scale, and there is lack of research that would address the problem through a circadian relevant approach.
The aim of this thesis is to examine mechanisms involved in hepatic feeding-regulated gene expression and
the chromatin landscape by using genomics-based approaches. This includes a special focus on finding the
points of crosstalk between insulin signalling and glucocorticoid signalling pathways, which are relevant to
hepatic circadian and feeding regulated gene expression and enhancer activity.
We first characterized gene expression and chromatin remodelling during an acute hepatic feeding
response by using functional genomics approaches such as RNA-seq, DNase-seq and ChIP-seq in an in vivo
setting (Section 2). We found that in mice which are entrained to a circadian-integrated feeding regime, the
postprandial decrease in corticosterone in coordination with the acute postprandial hyperinsulinemia
cooperatively regulates hepatic transcriptional output. Through characterising the chromatin landscape
dynamics in the transition from a fasted to a fed state, we identified and further investigated the
involvement of FoxO1 and GR in the coordination of feeding-repressed gene expression. We showed that
pharmacological manipulation of GR and insulin receptor activity can fully reactivate feeding repressed
genes in the liver, and that discordance in both signalling pathways explains certain gene expression
profiles in mice harbouring genetic disruption of GR and IRS, as well as in diet induced obese mice.
We then focused on finding the crosstalk points between glucocorticoid and insulin signalling pathways in a
cell culture model (H4IIE rat hepatoma cells) - a setting which is independent of systemic signals other than
insulin and glucocorticoid input (Section 3). We observed that GR binding to chromatin and the majority of
glucocorticoid induced gene expression is reduced in the presence of insulin. By overexpressing a
constantly active FoxO1 mutant in these cells, we observed that GR activity is likely affected both by FoxO1
and by kinases downstream of the insulin signalling pathway.
Together, these results elucidate regulatory complexity between glucocorticoid and insulin signalling
pathways in coordinating the transcriptional networks when the liver switches from a fasted state to a fed
state. These results also encourage finding drug strategies which target the crosstalk between GR and
insulin signalling to improve glycemic control.