Loss of nuclear receptor SHP impairs but does not eliminate negative feedback regulation of bile acid synthesis |
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Authors: | Kerr Thomas A Saeki Shigeru Schneider Manfred Schaefer Karen Berdy Sara Redder Thadd Shan Bei Russell David W Schwarz Margrit |
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Institution: | Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75390, USA. |
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Abstract: | The in vivo role of the nuclear receptor SHP in feedback regulation of bile acid synthesis was examined. Loss of SHP in mice caused abnormal accumulation and increased synthesis of bile acids due to derepression of rate-limiting CYP7A1 and CYP8B1 hydroxylase enzymes in the biosynthetic pathway. Dietary bile acids induced liver damage and restored feedback regulation. A synthetic agonist of the nuclear receptor FXR was not hepatotoxic and had no regulatory effects. Reduction of the bile acid pool with cholestyramine enhanced CYP7A1 and CYP8B1 expression. We conclude that input from three negative regulatory pathways controls bile acid synthesis. One is mediated by SHP, and two are SHP independent and invoked by liver damage and changes in bile acid pool size. |
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