Hepatic metabolic regulatory networks of Foxa2

The winged helix transcription factor Foxa2 is an important regulator that plays a critical role in many tissues. Our group has found that Foxa2 facilitates maximal induction of hepatic genes in response to fasting, but the role of this transcription factor in the fed state is not yet clear. To determine the role of Foxa2 in the adult liver I used a functional genomics approach and a conditional knockout model, the Foxa2loxP/loxP Alfp.Cre mouse, where Foxa2 is deleted in the hepatocyte. Global location analysis ( ChIP-on-Chip ) of Foxa2 in the liver indicates that a cluster of categories with genes involved in lipid and steroid metabolism is over-represented in the set of targets bound by Foxa2 in vivo. Bile acids are oxidized derivatives of cholesterol produced by the liver to facilitate absorption of dietary lipids. Dysregulation of bile acid homeostasis can cause cholestatic liver disease. As suggested by the location analysis, deletion of Foxa2 in the hepatocyte leads to decreased transcription of genes encoding bile acid transporters on both the basolateral and canalicular membranes, resulting in intrahepatic cholestasis. Feeding Foxa2 mutants a cholic acid enriched diet results in harmful accretion of bile salts, ER stress, and liver injury. In addition to showing that Foxa2 is required for normal bile acid homeostasis in mice, I demonstrate that FOXA2 expression is severely reduced in livers of patients suffering from several cholestatic syndromes, suggesting that decreased FOXA2 levels could worsen the injury. To investigate why Foxa2-deficient mice exhibit a more dramatic phenotype on a cholic acid diet than on normal chow, in the second part of my dissertation I examine how Foxa2 regulates its targets in a cholic acid-dependent manner. I focus on direct targets, genes which were bound and whose expression was downregulated in Foxa2 mutants. Multiple cell-to-cell signaling pathways crucial for response of the liver to acute injury are suppressed in Foxa2 loxP/loxPAlfp.Cre mice, suggesting that the deletion of Foxa2 in the hepatocyte affects the liver on a global scale. I demonstrate that distinct feed-forward regulatory loops regulate Foxa2-dependent targets in a cholic acid dependent or independent manner and show that Foxa2 interacts with different partners to attain gene expression responses suitable for each physiological state