Selective up-regulation of LXR-regulated genes ABCA1, ABCG1, and APOE in macrophages through increased endogenous synthesis of 24(S),25-epoxycholesterol.
J Biol Chem
; 282(8): 5207-16, 2007 Feb 23.
Article
em En
| MEDLINE
| ID: mdl-17186944
ABSTRACT
Liver X receptor (LXR) activation represents a mechanism to prevent macrophage foam cell formation. Previously, we demonstrated that partial inhibition of oxidosqualenelanosterol cyclase (OSC) stimulated synthesis of the LXR agonist 24(S),25-epoxycholesterol (24(S),25-epoxy) and enhanced ABCA1-mediated cholesterol efflux. In contrast to a synthetic, nonsteroidal LXR activator, TO-901317, triglyceride accumulation was not observed. In the present study, we determined whether endogenous 24(S),25-epoxy synthesis selectively enhanced expression of macrophage LXR-regulated cholesterol efflux genes but not genes that regulate fatty acid metabolism. THP-1 human macrophages incubated with the OSC inhibitor (OSCi) RO0714565 (15 nM) significantly reduced cholesterol synthesis and maximized synthesis of 24(S),25-epoxy. Endogenous 24(S),25-epoxy increased ABCA1, ABCG1, and APOE mRNA abundance and consequently increased cholesterol efflux to apoAI. In contrast, OSCi had no effect on LXR-regulated genes LPL (lipoprotein lipase) and FAS (fatty acid synthase). TO-901317 (>or=10 nM) significantly enhanced expression of all genes examined. OSCi and TO-901317 increased the mRNA and precursor form of SREBP-1c, a major regulator of fatty acid and triglyceride synthesis. However, conversion of the precursor to the active form (nSREBP-1c) was blocked by OSCi-induced 24(S),25-epoxy but not by TO-901317 (>or=10 nm), which instead markedly increased nSREBP-1c. Disruption of nSREBP-1c formation by 24(S),25-epoxy accounted for diminished FAS and LPL expression. In summary, endogenous synthesis of 24(S),25-epoxy selectively up-regulates expression of macrophage LXR-regulated cholesterol efflux genes without stimulating genes linked to fatty acid and triglyceride synthesis.
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Base de dados:
MEDLINE
Assunto principal:
Apolipoproteínas E
/
Regulação para Cima
/
Colesterol
/
Receptores Citoplasmáticos e Nucleares
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Transportadores de Cassetes de Ligação de ATP
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Proteínas de Ligação a DNA
/
Células Espumosas
Limite:
Humans
Idioma:
En
Ano de publicação:
2007
Tipo de documento:
Article