title: Farnesoid X Receptor Activation Promotes Hepatic Amino Acid Catabolism and Ammonium Clearance in Mice.
abstract: The nuclear receptor subfamily 1 group H member 4 (NR1H4 or farnesoid X receptor [FXR]) regulates bile acid synthesis, transport, and catabolism. FXR also regulates postprandial lipid and glucose metabolism. We performed quantitative proteomic analyses of liver tissues from mice to evaluate these functions and investigate whether FXR regulates amino acid metabolism.
  
  
  
  To study the role of FXR in mouse liver, we used mice with a disruption of Nr1h4 (FXR-knockout mice) and compared them with floxed control mice. Mice were gavaged with the FXR agonist obeticholic acid or vehicle for 11 days. Proteome analyses, as well as targeted metabolomics and chromatin immunoprecipitation, were performed on the livers of these mice. Primary rat hepatocytes were used to validate the role of FXR in amino acid catabolism by gene expression and metabolomics studies. Finally, control mice and mice with liver-specific disruption of Nr1h4 (liver FXR-knockout mice) were re-fed with a high-protein diet after 6 hours fasting and gavaged a15NH4Cl tracer. Gene expression and the metabolome were studied in the livers and plasma from these mice.
  
  
  
  In livers of control mice and primary rat hepatocytes, activation of FXR with obeticholic acid increased expression of proteins that regulate amino acid degradation, ureagenesis, and glutamine synthesis. We found FXR to bind to regulatory sites of genes encoding these proteins in control livers. Liver tissues from FXR-knockout mice had reduced expression of urea cycle proteins, and accumulated precursors of ureagenesis, compared with control mice. In liver FXR-knockout mice on a high-protein diet, the plasma concentration of newly formed urea was significantly decreased compared with controls. In addition, liver FXR-knockout mice had reduced hepatic expression of enzymes that regulate ammonium detoxification compared with controls. In contrast, obeticholic acid increased expression of genes encoding enzymes involved in ureagenesis compared with vehicle in C57Bl/6 mice.
  
  
  
  In livers of mice, FXR regulates amino acid catabolism and detoxification of ammonium via ureagenesis and glutamine synthesis. Failure of the urea cycle and hyperammonemia are common in patients with acute and chronic liver diseases; compounds that activate FXR might promote ammonium clearance in these patients.
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Vittoria
authors.initials: V
authors.lastname: Massafra
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Milona
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Harmjan R
authors.initials: HR
authors.lastname: Vos
authors.affiliation: Department of Genetics, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Rúben J J
authors.initials: RJJ
authors.lastname: Ramos
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands; Department of Genetics, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Johan
authors.initials: J
authors.lastname: Gerrits
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Ellen C L
authors.initials: ECL
authors.lastname: Willemsen
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: José M
authors.initials: JM
authors.lastname: Ramos Pittol
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Noortje
authors.initials: N
authors.lastname: Ijssennagger
authors.affiliation: Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
authors.forename: Martin
authors.initials: M
authors.lastname: Houweling
authors.affiliation: Department of Genetics, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Hubertus C M T
authors.initials: HCMT
authors.lastname: Prinsen
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands; Department of Genetics, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Nanda M
authors.initials: NM
authors.lastname: Verhoeven-Duif
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands.
authors.forename: Boudewijn M T
authors.initials: BMT
authors.lastname: Burgering
authors.affiliation: Center for Molecular Medicine, Universitair Medisch Centrum Utrecht, Utrecht, The Netherlands. Electronic address: S.W.C.vanMil@umcutrecht.nl.
authors.forename: Saskia W C
authors.initials: SWC
authors.lastname: van Mil
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism; D002635:Chenodeoxycholic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004044:Dietary Proteins / Q000008:administration & dosage; D015870:Gene Expression; D005973:Glutamine / Q000096:biosynthesis*; D022781:Hepatocytes; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D055442:Metabolome; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020543:Proteome; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D014508:Urea / Q000378:metabolism*; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D000641:Ammonia; D001647:Bile Acids and Salts; D002635:Chenodeoxycholic Acid; D004044:Dietary Proteins; D005973:Glutamine; D020543:Proteome; D018160:Receptors, Cytoplasmic and Nuclear; D014508:Urea; D000099150:Receptor, Farnesoid X-Activated; C464660:obeticholic acid
keywords: Cps1; Glutamine Synthetase; INT-747; Liver Proteome