Cholesterol dependent downregulation of mouse and human apical sodium dependent bile acid transporter (ASBT) gene expression: molecular mechanism and physiological consequences

• Published in: Gut Vol. 55; no. 9; pp. 1321 - 1331
• Main Authors: Thomas, C, Landrier, J-F, Gaillard, D, Grober, J, Monnot, M-C, Athias, A, Besnard, P
• Format: Journal Article
• Language: English
• Published: London BMJ Publishing Group Ltd and British Society of Gastroenterology 01.09.2006; BMJ; BMJ Publishing Group LTD; BMJ Publishing Group; BMJ Group
• Subjects: 25(OH)CS; 25-hydroxycholesterol; Acids; Animals; apical sodium dependent bile acid transporter; ASBT; Base Sequence; Bile; bile acids; Bile Acids and Salts - metabolism; Biological and medical sciences; Caco-2 Cells; CAT; Cells, Cultured; chloramphenicol acetyltransferase; Cholesterol; cholesterol 7α-hydroxylase; cholesterol homeostasis; Cholesterol, Dietary - pharmacology; Cognitive science; CYP7A1; Down-Regulation - drug effects; Electrophoretic Mobility Shift Assay; EMSA; Experiments; farnesoid-X receptor; FCS; fetal calf serum; Food and Nutrition; FXR; Gastroenterology. Liver. Pancreas. Abdomen; Gene expression; hepatocyte nuclear factor; Hepatocyte Nuclear Factor 1-alpha - genetics; Hepatocyte Nuclear Factor 1-alpha - metabolism; HMG-CoA reductase; HNF; HNF-1α; HNF-1α responsive element; HNFE; Homeostasis; Humans; hydroxymethylglutaryl-coenzyme A reductase; Ileum - metabolism; Intestinal Absorption - drug effects; Laboratory animals; LDL; Life Sciences; Liver Disease; liver X-receptor; low density lipoprotein; LXR; Male; Medical sciences; Mice; Mice, Inbred C57BL; Molecular Sequence Data; Mutagenesis, Site-Directed; Na+-taurocholate co-transporting polypeptide; National Collection of Type Cultures; NCTC; Neuroscience; NTCP; OATP; Organ Culture Techniques; organic anion transport protein; Organic Anion Transporters, Sodium-Dependent - biosynthesis; Organic Anion Transporters, Sodium-Dependent - genetics; Organic Anion Transporters, Sodium-Dependent - physiology; peroxisome proliferator activated receptor; PGC-1; Physiology; PPAR; PPAR γ co-activator 1; Promoter Regions, Genetic; Proteins; RNA, Messenger - genetics; Rodents; SHP; small heterodimer partner; SRE; SREBP; SREBP-2; sterol regulatory element binding protein; Sterol Regulatory Element Binding Protein 2 - physiology; sterol responsive element; Sterols; Symporters - biosynthesis; Symporters - genetics; Symporters - physiology; taurocholic acid; TCA; Transfection; France; Human; Vertebrata; Mammalia; Sodium; Mouse; Bile acid; Animal; Rodentia; Gastroenterology; Gene expression; Cholesterol; Mechanism
• ISSN: 0017-5749; 1468-3288
• DOI: 10.1136/gut.2005.085555

Background and aims: Faecal bile acid elimination greatly contributes to cholesterol homeostasis. Synthesised from cholesterol in the liver, bile acids are actively reclaimed in the ileum by the apical sodium dependent bile acid transporter (ASBT). Although the expression level of ASBT affects body cholesterol balance, the impact of cholesterol on ASBT gene expression remains unclear. In this study, the effect of cholesterol on ASBT expression and ileal bile acid uptake was explored in vivo and in vitro. Methods: ASBT gene expression was assessed by real time quantitative polymerase chain reaction and northern or western blotting, or both, in mice subjected to a 2% cholesterol diet for two weeks, in mouse ileal explants, or in human enterocyte-like Caco-2 cells cultured in sterol enriched or depleted media. Bile acid uptake was determined by measuring [3H]-taurocholic acid influx into in situ isolated ileal loops from mice or into differentiated Caco-2 cells. Molecular analysis of mouse and human ASBT promoters was undertaken with reporter assays, site directed mutagenesis, and electrophoretic mobility shift assays. Results: In mice, cholesterol enriched diet triggered a downregulation of ASBT expression (mRNA and protein), a fall in ileal bile acid uptake, and a rise in the faecal excretion of bile acids. This effect was direct as it was reproduced ex vivo using mouse ileal explants and in vitro in differentiated Caco-2 cells. Conclusions: This regulation, which involves an original partnership between SREBP-2 and HNF-1α transcription factors, affects ileal bile acid recycling and thus might participate in the maintenance of body cholesterol homeostasis.