Knockout of the cholesterol 24-hydroxylase gene in mice reveals a brain-specific mechanism of cholesterol turnover

Erik G. Lund, Chonglun Xie, Tiina Kotti, Stephen D. Turley, John M. Dietschy, David W. Russell

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Abstract

Most cholesterol turnover takes place in the liver and involves the conversion of cholesterol into soluble and readily excreted bile acids. The synthesis of bile acids is limited to the liver, but several enzymes in the bile acid biosynthetic pathway are expressed in extra-hepatic tissues and there also may contribute to cholesterol turnover. An example of the latter type of enzyme is cholesterol 24-hydroxylase, a cytochrome P450 (CYP46A1) that is expressed at 100-fold higher levels in the brain than in the liver. Cholesterol 24-hydroxylase catalyzes the synthesis of the oxysterol 24(S)-hydroxycholesterol. To assess the relative contribution of the 24-hydroxylation pathway to cholesterol turnover, we performed balance studies in mice lacking the cholesterol 24-hydroxylase gene (Cyp46a1-/- mice). Parameters of hepatic cholesterol and bile acid metabolism in the mutant mice remained unchanged relative to wild type controls. In contrast to the liver, the synthesis of new cholesterol was reduced by ∼40% in the brain, despite steady-state levels of cholesterol being similar in the knockout mice. These data suggest that the synthesis of new cholesterol and the secretion of 24(S)-hydroxycholesterol are closely coupled and that at least 40% of cholesterol turnover in the brain is dependent on the action of cholesterol 24-hydroxylase. We conclude that cholesterol 24-hydroxylase constitutes a major tissue-specific pathway for cholesterol turnover in the brain.

Original languageEnglish (US)
Pages (from-to)22980-22988
Number of pages9
JournalJournal of Biological Chemistry
Volume278
Issue number25
DOIs
StatePublished - Jun 20 2003

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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