27-Hydroxycholesterol up-regulates CD14 and predisposes monocytic cells to superproduction of CCL2 in response to lipopolysaccharide

• Consumption of high-cholesterol diet induces CD14 expression in the aortas of ApoE−/− mice.
• 27OHChol up-regulates the expression of CD14 in monocytic cells.
• Addition of LPS to the 27OHChol-treated monocytic cells leads to superproduction of CCL2.
• We propose a mechanism underlying aggravated atherosclerosis after bacterial infection.

We investigated the possibility that a cholesterol-rich milieu can accelerate response to pathogen-associated molecular patterns in order to elucidate mechanisms underlying aggravation of atherosclerosis after bacterial infection. The consumption of a high-cholesterol diet resulted in enhanced the expression of CD14 in arteries of ApoE−/− mice. 27-Hydroxycholesterol (27OHChol), the most abundant cholesterol oxide in atherosclerotic lesions, induced the significant expression of CD14 by THP-1 monocytic cells, but not by vascular smooth muscle cells or Jurkat T cells. Additions of lipopolysaccharide (LPS) to 27OHChol-treated THP-1 monocytic cells resulted in superinduction in terms of the gene transcription of CCL2 and the secretion of its gene product. In contrast, cholesterol did not cause increased the expression of CD14 in the aforementioned cells, and the addition of LPS to cholesterol-treated monocytic cells did not result in enhanced the expression of CCL2. The conditioned medium isolated from THP-1 cells exposed to 27OHChol plus LPS further induced the migration of monocytic cells in comparison with conditioned media obtained from THP-1 cells treated with 27OHChol or LPS alone. Treatment with 27OHChol also resulted in the enhanced secretion of MMP-9 and soluble CD14 (sCD14), and the secretion of sCD14 was blocked by a selective MMP-9 inhibitor. The inhibition of the ERK pathway resulted in significantly attenuated the secretion of sCD14 via mechanisms that were distinct from those by PI3K inhibition. We propose that 27OHChol can prime monocytes/macrophages by up-regulation of CD14 such that LPS-mediated inflammatory reaction is accelerated, thereby contributing to aggravated development of atherosclerotic lesions by enhancing recruitment of monocytic cells after infection with Gram-negative bacteria.

We attempted to determine whether a cholesterol-rich milieu can accelerate inflammatory response to pathogen-associated molecular patterns in order to elucidate mechanisms underlying aggravated atherosclerosis after bacterial infection. Based on the results of the current study and previous findings, we propose a model for accelerated inflammation by LPS in the presence of 27OHChol in atherosclerotic lesions. Macrophages release CCL2 and MMP-9 and up-regulate CD14 in response to 27OHChol. CCL2 will direct the migration of monocytes attached on the endothelium whose expression of cell adhesion molecules was induced by oxidized LDL, and MMP-9 will enhance the secretion of sCD14 by conversion of mCD14 to sCD14 (A). Upon exposure of 27OHChol-activated macrophages to LPS, the elevated levels of mCD14 and sCD14 enable transfer of much more LPS from LPS-CD14 complex to TLR4, which leads to the superproduction of CCL2 and migration of more monocytes (B). In addition, sCD may induce inflammatory responses of CD14-negative endothelial cells to LPS. We propose that 27OHChol can prime monocytes/macrophages by up-regulation of CD14 such that LPS-mediated inflammatory reaction is accelerated, thereby contributing to aggravated development of atherosclerotic lesions after infection with Gram-negative bacteria.Figure optionsDownload high-quality image (68 K)Download as PowerPoint slide