title: Impaired negative feedback suppression of bile acid synthesis in mice lacking betaKlotho.
abstract: We have generated a line of mutant mouse that lacks betaKlotho, a protein that structurally resembles Klotho. The synthesis and excretion of bile acids were found to be dramatically elevated in these mutants, and the expression of 2 key bile acid synthase genes, cholesterol 7alpha-hydroxylase (Cyp7a1) and sterol 12alpha-hydroxylase (Cyp8b1), was strongly upregulated. Nuclear receptor pathways and the enterohepatic circulation, which regulates bile acid synthesis, seemed to be largely intact; however, bile acid-dependent induction of the small heterodimer partner (SHP) NR0B2, a common negative regulator of Cyp7a1 and Cyp8b1, was significantly attenuated. The expression of Cyp7a1 and Cyp8b1 is known to be repressed by dietary bile acids via both SHP-dependent and -independent regulations. Interestingly, the suppression of Cyp7a1 expression by dietary bile acids was impaired, whereas that of Cyp8b1 expression was not substantially altered in betaklotho mice. Therefore, betaKlotho may stand as a novel contributor to Cyp7a1-selective regulation. Additionally, betaKlotho-knockout mice exhibit resistance to gallstone formation, which suggests the potential future clinical relevance of the betaKlotho system.
authors.affiliation: Department of Pathology and Tumor Biology, Graduate School of Medicine, and Horizontal Medical Research Organization, Faculty of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Ito
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Fujimori
authors.forename: Akiko
authors.initials: A
authors.lastname: Furuya
authors.forename: Junko
authors.initials: J
authors.lastname: Satoh
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nabeshima
authors.forename: Yo-Ichi
authors.initials: Y
authors.lastname: Nabeshima
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000096:biosynthesis; D004789:Enzyme Activation / Q000235:genetics; D042882:Gallstones / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D000090265:Klotho Proteins; D008102:Liver Circulation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D013253:Steroid 12-alpha-Hydroxylase / Q000096:biosynthesis
chemical_list: D001647:Bile Acids and Salts; C418622:Klb protein, mouse; D008565:Membrane Proteins; D018160:Receptors, Cytoplasmic and Nuclear; C099713:nuclear receptor subfamily 0, group B, member 2; D002790:Cholesterol 7-alpha-Hydroxylase; C502772:Cyp7a1 protein, mouse; D013253:Steroid 12-alpha-Hydroxylase; D000090265:Klotho Proteins