Intestinal FXR-mediated FGF15 production contributes to diurnal control of hepatic bile acid synthesis in mice.
Hepatic bile acid synthesis is subject to complex modes of transcriptional control, in which the bile acid-activated nuclear receptor farnesoid X receptor (FXR) in liver and intestine-derived, FXR-controlled fibroblast growth factor 15 (Fgf15) are involved. The Fgf15 pathway is assumed to contribute significantly to control of hepatic bile acid synthesis. However, scientific evidence supporting this assumption is primarily based on gene expression data. Using intestine-selective FXR knockout mice (iFXR-KO), we show that contribution of intestinal FXR-Fgf15 signalling in regulation of hepatic cholesterol 7α-hydroxylase (Cyp7A1) expression depends on time of the day with increased hepatic Cyp7A1 expression in iFXR-KO mice compared with controls exclusively during the dark phase. To assess the physiological relevance hereof, we determined effects of intestine-selective deletion of FXR on physiological parameters such as bile formation and kinetics of the enterohepatic circulation of bile acids. It appeared that intestinal FXR deficiency leads to a modest but significant increase in cholic acid pool size, without changes in fractional turnover rate. As a consequence, bile flow and biliary bile acid secretion rates were increased in iFXR-KO mice compared with controls. Feeding a bile acid-containing diet or treatment with a bile acid sequestrant similarly affected bile formation in iFXR-KO and control mice and induced similar changes in Cyp7A1 and Cyp8B1 expression patterns. In conclusion, this study is the first to demonstrate the physiological relevance of the contribution of the intestinal FXR-Fgf15 signalling pathway in control of hepatic bile acid synthesis. Fgf15 contributes to the regulation of hepatic bile acid synthesis in mice mainly during the dark phase. Expansion of the circulating bile acid pool as well as bile acid sequestration diminishes the contribution of intestinal FXR-Fgf15 signalling in control of hepatic bile acid synthesis and bile formation.
Stroeve
Johanna H M
JH
Department of Pediatrics, Center for Liver, Digestive and Metabolic Diseases, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. J.H.M.Stroeve@med.umcg.nl
Brufau
Gemma
G
Stellaard
Frans
F
Gonzalez
Frank J
FJ
Staels
Bart
B
Kuipers
Folkert
F
D000818:Animals; D001647:Bile Acids and Salts / Q000096:biosynthesis*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism; D019826:Cholic Acid / Q000378:metabolism; D004764:Enterohepatic Circulation / Q000502:physiology; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D017440:Photoperiod; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction; D013253:Steroid 12-alpha-Hydroxylase / Q000378:metabolism; D000099150:Receptor, Farnesoid X-Activated
D001647:Bile Acids and Salts; D002790:Cholesterol 7-alpha-Hydroxylase; D019826:Cholic Acid; D005346:Fibroblast Growth Factors; D018160:Receptors, Cytoplasmic and Nuclear; D013253:Steroid 12-alpha-Hydroxylase; D000099150:Receptor, Farnesoid X-Activated; C108526:fibroblast growth factor 15, mouse