Identification of 5α,6α-Epoxycholesterol as a Novel Modulator of Liver X Receptor Activity

Abstract

The liver X receptors (LXR␣ and LXR␤) are members of the nuclear receptor superfamily that function as key transcriptional regulators of a number of biological processes, including cholesterol homeostasis, lipid metabolism, and keratinocyte differentiation. Natural ligands that activate LXRs include oxysterol derivatives such as 25-hydroxycholesterol, 27-hydroxycholesterol, 22(R)-hydroxycholesterol, 20(S)-hydroxycholesterol, and 24(S),25-epoxycholesterol. Related oxysterols, such as 5␣,6␣-epoxycholesterol (5,6-EC) are present in a number of foods and have been shown to induce atherosclerosis in animal models. Intriguingly, these oxysterols have also been detected in atherosclerotic plaques. Using a variety of biochemical and cellular assays, we demonstrate that 5,6-EC is the first dietary modulator and an endogenous LXR ligand with cell and gene context-dependent antagonist, agonist, and inverse agonist activities. In a multiplexed LXR-cofactor peptide interaction assay, 5,6-EC induced the recruitment of a number of cofactor peptides onto both LXR␣ and LXR␤ and showed an EC 50 of approximately 2 M in peptide recruitment. Furthermore, 5,6-EC bound to LXR␣ in a radiolabeled ligand displacement assay (EC 50 ϭ 76 nM), thus demonstrating it to be one of the most potent natural LXR␣ ligands known to date. Analysis of endogenous gene expression in various cell-based systems indicated the potential of 5,6-EC to antagonize LXR-mediated gene expression. Furthermore, it also induced the expression of some LXR-responsive genes in keratinocytes. These results clearly demonstrate that 5,6-EC is an LXR modulator that may play a role in the development of lipid disorders, such as atherosclerosis, by antagonizing the agonistic action of endogenous LXR ligands.

Surprising unreactivity of cholesterol-5,6-epoxides towards nucleophiles

“…They are extensively transformed into CT by ChEH, and they can be esterifi ed with fatty acids acyl ester by acylcoA:cholesterol acyl transferases (ACAT1 and ACAT2) ( 17 ) into fatty acyl-cholesteryl esters, and with sulfate by cholesterol sulfotransferase (SULT2B1b) into the 3 ␤ -sulfate of 5,6-EC ( 18 ). The 3 ␤ -sulfate of 5,6 ␣ -EC has been shown to antagonize the liver X receptor (LXR) signaling pathway ( 19,20 ), and recently 5,6 ␣ -EC was found to be a direct modulator of LXR, suggesting a physiological role for this 5,6-EC diastereoisomer ( 21 ). Interestingly 5,6 ␣ -EC has been shown to be a better substrate than 5,6 ␤ -EC for ACATs and SULT2B1b and the sole 5,6-EC substrate for glutathione transferase B ( 22,23 ).…”

Dendrogenin A arises from cholesterol and histamine metabolism and shows cell differentiation and anti-tumour properties

“…Stereo-selective biosynthesis of 5,6α-EC occurs in the adrenal cortex by a currently unidentified cytochrome p45016. 5,6α-EC and its sulfated derivative 5,6α-epoxy-5α-cholestestan-3β-sulphate are modulators of the liver-X-receptor (LXR)91718. 5,6α-EC can also be metabolized into 3β,5α-dihydroxycholestan-6β-yl-S-glutathione1920.…”

The Influence of an Obesogenic Diet on Oxysterol Metabolism in C57BL/6J Mice

“…Similar to 7 α -hydroxycholesterol, 5,6 α -epoxycholesterol and 5,6 β -epoxycholesterol are produced by the peroxidation and autooxidation of cholesterol [49]. In addition, 5,6 α -epoxycholesterol has been shown in vitro to be an antagonist of LXR [50]. LXR α and LXR β are oxysterol dependent transcription factors that induce the expression of genes involved with cholesterol efflux and transport and decrease the expression of inflammatory mediators such as nuclear factor- κ B [51, 52].…”