Additional pathways of sterol metabolism: Evidence from analysis of Cyp27a1-/- mouse brain and plasma

Biochim Biophys Acta Mol Cell Biol Lipids. 2019 Feb;1864(2):191-211. doi: 10.1016/j.bbalip.2018.11.006. Epub 2018 Nov 22.


Cytochrome P450 (CYP) 27A1 is a key enzyme in both the acidic and neutral pathways of bile acid biosynthesis accepting cholesterol and ring-hydroxylated sterols as substrates introducing a (25R)26-hydroxy and ultimately a (25R)26-acid group to the sterol side-chain. In human, mutations in the CYP27A1 gene are the cause of the autosomal recessive disease cerebrotendinous xanthomatosis (CTX). Surprisingly, Cyp27a1 knockout mice (Cyp27a1-/-) do not present a CTX phenotype despite generating a similar global pattern of sterols. Using liquid chromatography - mass spectrometry and exploiting a charge-tagging approach for oxysterol analysis we identified over 50 cholesterol metabolites and precursors in the brain and circulation of Cyp27a1-/- mice. Notably, we identified (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids, indicating the presence of an additional sterol 26-hydroxylase in mouse. Importantly, our analysis also revealed elevated levels of 7α-hydroxycholest-4-en-3-one, which we found increased the number of oculomotor neurons in primary mouse brain cultures. 7α-Hydroxycholest-4-en-3-one is a ligand for the pregnane X receptor (PXR), activation of which is known to up-regulate the expression of CYP3A11, which we confirm has sterol 26-hydroxylase activity. This can explain the formation of (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids; the acid with the former stereochemistry is a liver X receptor (LXR) ligand that increases the number of oculomotor neurons in primary brain cultures. We hereby suggest that a lack of a motor neuron phenotype in some CTX patients and Cyp27a1-/- mice may involve increased levels of 7α-hydroxycholest-4-en-3-one and activation PXR, as well as increased levels of sterol 26-hydroxylase and the production of neuroprotective sterols capable of activating LXR.

Keywords: Brain; CYP27A1; Cerebrotendinous xanthomatosis; Cholestenoic acid; Mass spectrometry; Oxysterol.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bile Acids and Salts / biosynthesis
  • Brain / metabolism
  • Cholestanetriol 26-Monooxygenase / genetics
  • Cholestanetriol 26-Monooxygenase / physiology*
  • Cholestenes / metabolism
  • Cholesterol / metabolism*
  • Chromatography, Liquid
  • Cytochrome P-450 Enzyme System / metabolism
  • Hydroxylation
  • Lipid Metabolism / physiology
  • Liver X Receptors / metabolism
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Oxysterols / metabolism
  • Pregnane X Receptor / metabolism
  • Sterols / metabolism*
  • Tandem Mass Spectrometry
  • Xanthomatosis, Cerebrotendinous


  • Bile Acids and Salts
  • Cholestenes
  • Liver X Receptors
  • Oxysterols
  • Pregnane X Receptor
  • Sterols
  • cholestenoic acid
  • Cytochrome P-450 Enzyme System
  • Cholesterol
  • Cholestanetriol 26-Monooxygenase
  • Cyp27a1 protein, mouse