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Cholic acid mediates negative feedback regulation of bile acid synthesis in mice

Jia Li-Hawkins1, Mats Gåfvels, Maria Olin

  • 1Department of Molecular Genetics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9046, USA.

The Journal of Clinical Investigation
|October 24, 2002
PubMed

Insights

Cholesterol metabolism involves bile acid synthesis regulated by feedback mechanisms. Disrupting cholate synthesis in mice revealed its crucial role in regulating cholesterol 7alpha-hydroxylase (CYP7A1) and bile acid production.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Genetics

Background:

  • Bile acids are synthesized from cholesterol through complex pathways.
  • These pathways are regulated by feedback mechanisms involving nuclear receptors like the farnesoid X receptor (FXR).
  • The sterol 12alpha-hydroxylase gene (Cyp8b1) is essential for synthesizing cholate, a primary bile acid.

Purpose of the Study:

  • To investigate the role of cholate in bile acid synthesis regulation.
  • To understand the impact of disrupted cholate synthesis on cholesterol metabolism.
  • To examine the relationship between cholate, CYP7A1, and FXR signaling.

Main Methods:

  • Generation and analysis of Cyp8b1-deficient (Cyp8b1(-/-)) mice.
  • Measurement of bile acid pool composition and cholesterol metabolism.
  • In vivo and in vitro experiments to assess CYP7A1 regulation.
  • Analysis of FXR target gene expression.

Main Results:

  • Cyp8b1(-/-) mice showed a complete absence of cholate and its metabolites.
  • These mice exhibited loss of feedback regulation on cholesterol 7alpha-hydroxylase (CYP7A1), leading to an expanded bile acid pool.
  • Cholesterol metabolism was altered in Cyp8b1(-/-) mice.
  • Expression of other FXR target genes remained unaffected.
  • Administration of cholate restored CYP7A1 regulation in vivo and in vitro.

Conclusions:

  • Cholate is a critical negative regulator of bile acid synthesis.
  • The absence of cholate disrupts the feedback loop controlling CYP7A1.
  • These findings suggest ligand-specific gene activation by nuclear receptors, with cholate playing a key role.

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