High-Density Lipoproteins Differentially Modulate Cytokine-Induced Expression of E-Selectin and Cyclooxygenase-2

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Abstract
—Atherogenesis is a multifactorial chronic inflammatory disease in which low plasma levels of HDLs are a strong predictor of the condition. Although the mechanism of protection by HDLs is not precisely known, HDLs have been shown to influence many of the events involved in the development of atherosclerosis. Previously we have shown that HDLs inhibited the cytokine-induced expression of adhesion molecules (E-selectin, VCAM-1, and ICAM-1) by endothelial cells (ECs). As the complete transcriptional regulation of all 3 genes requires the NF-κB family of transcription factors, we examined the effect of HDLs on activation of NF-κB. We also investigated the effect of HDLs on 2 other cytokine-induced genes, granulocyte-macrophage colony-stimulating factor (GM-CSF) and cyclooxygenase (Cox-2; prostaglandin H2synthase, EC0.1.14.99.1). E-selectin expression in response to tumor necrosis factor-α (TNFα) was, as expected, inhibited in ECs that had been preincubated with HDLs. However, the level of secretion of GM-CSF in the same cultures was no different from control. In a similar manner, although HDLs had no effect on steady-state mRNA levels of GM-CSF, the levels of E-selectin were significantly inhibited by HDLs. In transient cotransfection experiments we found that HDLs inhibited the cytokine-induced expression of a reporter gene driven by the E-selectin proximal promoter (−383 to 80) but had no effect on the expression of a reporter gene driven under the control of the proximal promoter of GM-CSF (−627 to 28). As would be predicted from this differential response, HDLs did not influence the nuclear translocation or DNA binding of NF-κB, or alter the kinetics of degradation and resynthesis of the inhibitory protein IκBα. We found that HDLs synergized with cytokine to enhance the expression of Cox-2 and induce the synthesis of its main EC product, prostacyclin (PGI2), a potent inhibitor of platelet and leukocyte functions. In conclusion, HDL induces an antiinflammatory phenotype in cytokine-induced ECs, synergizing with cytokine to induce elevation of Cox-2 in addition to inhibiting adhesion molecule expression. Our studies show that these differential effects are mediated in a manner that is likely to be independent of NF-κB per se.