No abstract

No abstract

27-Hydroxycholesterol (27OHChol) exhibits agonistic activity for liver X receptors (LXRs). To determine roles of the LXR agonistic activity in macrophage gene expression, we investigated the effects of LXR inhibition on the 27OHChol-induced genes. Treatment of human THP-1 cells with GSK 2033, a potent cell-active LXR antagonist, results in complete inhibition in the transcription of LXR target genes (such as LXRα and ABCA1) induced by 27OHChol or a synthetic LXR ligand TO 901317. Whereas expression of CCL2 and CCL4 remains unaffected by GSK 2033, TNF-α expression is further induced and 27OHChol-induced CCL3 and CXCL8 genes are suppressed at both the transcriptional and protein translation levels in the presence of GSK 2033. This LXR antagonist downregulates transcript levels and surface expression of CD163 and CD206 and suppresses the transcription of CD14, CD80, and CD86 genes without downregulating their surface levels. GSK 2033 alone had no effect on the basal expression levels of the aforementioned genes. Collectively, these results indicate that LXR inhibition leads to differential regulation of 27-hydroxycholesterol-induced genes in macrophages. We propose that 27OHChol induces gene expression and modulates macrophage functions via LXR-dependent and -independent mechanisms.

We investigated effects of 7-oxygenated cholesterol derivatives present in atherosclerotic lesions, 7α-hydroxycholesterol (7αOHChol), 7β-hydroxycholesterol (7βOHChol), and 7-ketocholesterol (7K), on IL-8 expression. Transcript levels of IL-8 and secretion of its corresponding gene product by monocytes/macrophages were enhanced by treatment with 7αOHChol and, to a lesser extent, 7K, but not by 7βOHChol. The 7-oxygenated cholesterol derivatives, however, did not change transcription of the IL-8 gene in vascular smooth muscle cells. 7αOHChol-induced IL-8 gene transcription was inhibited by cycloheximide and Akt1 downregulation, but not by OxPAPC. Expression of C5a receptor was upregulated after stimulation with 7αOHChol, but not with 7K and 7βOHChol, and a specific antagonist of C5a receptor inhibited 7αOHChol-induced IL-8 gene expression in a dose dependent manner. Pharmacological inhibitors of PI3K and MEK almost completely inhibited expression of both IL-8 and cell-surface C5a receptor induced by 7αOHChol. These results indicate that 7-oxygenated cholesterol derivatives have differential effects on monocyte/macrophage expression of IL-8 and C5a receptor and that C5a receptor is involved in 7αOHChol-induced IL-8 expression via PI3K and MEK.

No abstract