In vivo imaging of farnesoid X receptor activity reveals the ileum as the primary bile acid signaling tissue

We generated and characterized a firefly luciferase reporter mouse for the nuclear receptor farnesoid X receptor (FXR). This FXR reporter mouse has basal luciferase expression in the terminal ileum, an organ with well-characterized FXRα signaling. In vivo luciferase activity reflected the diurnal activity pattern of the mouse, and is regulated by both natural (bile acids, chenodeoxycholic acid) and synthetic (GW4064) FXRα ligands. Moreover, in vivo and in vitro analysis showed luciferase activity after GW4064 administration in the liver, kidney, and adrenal gland, indicating that FXRα signaling is functional in these tissues. Hepatic luciferase activity was robustly induced in cholestatic mice, showing that FXRα signaling pathways are activated in this disease. In conclusion, we have developed an FXR reporter mouse that is useful to monitor FXRα signaling in vivo in health and disease. The use of this animal could facilitate the development of new therapeutic compounds that target FXRα in a tissue-specific manner.