title: Farnesoid X receptor represses hepatic human APOA gene expression.
abstract: High plasma concentrations of lipoprotein(a) [Lp(a), which is encoded by the APOA gene] increase an individual's risk of developing diseases, such as coronary artery diseases, restenosis, and stroke. Unfortunately, increased Lp(a) levels are minimally influenced by dietary changes or drug treatment. Further, the development of Lp(a)-specific medications has been hampered by limited knowledge of Lp(a) metabolism. In this study, we identified patients suffering from biliary obstructions with very low plasma Lp(a) concentrations that rise substantially after surgical intervention. Consistent with this, common bile duct ligation in mice transgenic for human APOA (tg-APOA mice) lowered plasma concentrations and hepatic expression of APOA. To test whether farnesoid X receptor (FXR), which is activated by bile acids, was responsible for the low plasma Lp(a) levels in cholestatic patients and mice, we treated tg-APOA and tg-APOA/Fxr-/- mice with cholic acid. FXR activation markedly reduced plasma concentrations and hepatic expression of human APOA in tg-APOA mice but not in tg-APOA/Fxr-/- mice. Incubation of primary hepatocytes from tg-APOA mice with bile acids dose dependently downregulated APOA expression. Further analysis determined that the direct repeat 1 element between nucleotides -826 and -814 of the APOA promoter functioned as a negative FXR response element. This motif is also bound by hepatocyte nuclear factor 4α (HNF4α), which promotes APOA transcription, and FXR was shown to compete with HNF4α for binding to this motif. These findings may have important implications in the development of Lp(a)-lowering medications.
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria.
authors.forename: Indumathi
authors.initials: I
authors.lastname: Chennamsetty
authors.forename: Thierry
authors.initials: T
authors.lastname: Claudel
authors.forename: Karam M
authors.initials: KM
authors.lastname: Kostner
authors.forename: Anna
authors.initials: A
authors.lastname: Baghdasaryan
authors.forename: Dagmar
authors.initials: D
authors.lastname: Kratky
authors.forename: Sanja
authors.initials: S
authors.lastname: Levak-Frank
authors.forename: Sasa
authors.initials: S
authors.lastname: Frank
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Gonzalez
authors.forename: Michael
authors.initials: M
authors.lastname: Trauner
authors.forename: Gert M
authors.initials: GM
authors.lastname: Kostner
mesh_terms: D000818:Animals; D001054:Apolipoproteins A / Q000235:genetics* / Q000378:metabolism*; D001647:Bile Acids and Salts / Q000008:administration & dosage / Q000097:blood; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D041781:Jaundice, Obstructive / Q000097:blood; D008099:Liver / Q000166:cytology / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D001054:Apolipoproteins A; D001647:Bile Acids and Salts; D051557:Hepatocyte Nuclear Factor 4; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D000099150:Receptor, Farnesoid X-Activated; C496592:HNF4A protein, human