title: Suppression of 2,3-oxidosqualene cyclase by high fat diet contributes to liver X receptor-alpha-mediated improvement of hepatic lipid profile.
abstract: The liver X receptors (LXRs) sense oxysterols and regulate genes involved in cholesterol metabolism. Synthetic agonists of LXRs are potent stimulators of fatty acid synthesis, which is mediated largely by sterol regulatory element-binding protein-1c (SREBP-1c). Paradoxically, an improved hepatic lipid profile by LXR was observed in mice fed a Western high fat (HF) diet. To explore the underlying mechanism, we administered mice normal chow or an HF diet and overexpressed LXRalpha in the liver. The HF diet with tail-vein injection of adenovirus of LXRalpha increased the expression of LXR-targeted genes involved in cholesterol reverse transport but not those involved in fatty acid synthesis. A similar effect was also observed with the use of 22R-hydroxycholesterol, an LXR ligand, in cultured hepatocytes. Consequently, SREBP-1c maturation was inhibited by the HF diet, which resulted from the induction of Insig-2a. Importantly, increased cholesterol level suppressed the expression of 2,3-oxidosqualene cyclase (OSC), which led to an increase in endogenous LXR ligand(s). Furthermore, siRNA-mediated knockdown of OSC expression enhanced LXR activity and selectively up-regulated LXR-targeted genes involved in cholesterol reverse transport. Thus, down-regulation of OSC may account for a novel mechanism underlying the LXR-mediated lipid metabolism in the liver of mice fed an HF diet.
authors.affiliation: Department of Physiology and Pathophysiology, Health Science Center, Institute of Cardiovascular Research, Peking University, Beijing, China.
authors.forename: Huaixin
authors.initials: H
authors.lastname: Dang
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Wei
authors.initials: W
authors.lastname: Pang
authors.forename: Chenghong
authors.initials: C
authors.lastname: Li
authors.forename: Nanping
authors.initials: N
authors.lastname: Wang
authors.forename: John Y-J
authors.initials: JY
authors.lastname: Shyy
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D000256:Adenoviridae; D000818:Animals; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004032:Diet; D004041:Dietary Fats / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D019751:Intramolecular Transferases / Q000096:biosynthesis* / Q000235:genetics; D050356:Lipid Metabolism / Q000187:drug effects / Q000502:physiology*; D008099:Liver / Q000201:enzymology*; D000071518:Liver X Receptors; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D057093:Orphan Nuclear Receptors; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D004041:Dietary Fats; C467727:INSIG2 protein, human; C506120:Insig2 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D000071518:Liver X Receptors; D008565:Membrane Proteins; C000605213:NR1H3 protein, human; C000605214:Nr1h3 protein, mouse; C000605215:Nr1h3 protein, rat; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; C497387:SREBF1 protein, human; C497388:Srebf1 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D019751:Intramolecular Transferases; C021924:lanosterol synthase