Involvement of transcription factors in plasma HDL protection against TNF-alpha-induced vascular cell adhesion molecule-1 expression.

Plasma HDL has been reported to protect against the initial development of inflammatory atherosclerosis. Although cellular and molecular mechanisms of this HDL protection are not fully understood, they may involve prevention of the endothelial trafficking of circulating leukocytes via its down-regulation of inflammatory genes. To test this hypothesis, HDL inhibition of monocyte adherence to the endothelium and of the expression of vascular cell adhesion molecule-1 (VCAM-1) and its transcriptional regulatory mechanism were elucidated in human umbilical vein endothelial cells (HUVECs) stimulated by pro-inflammatory TNF-alpha. Plasma HDL (1mg/ml apo A1) markedly prevented the monocyte adhesion to TNF-alpha-activated HUVECs with blunting the increased expression levels of VCAM-1 protein and its mRNA at a maximal TNF-alpha stimulation. Electrophoretic mobility shift assay showed that in the activated HUVECs HDL substantially inhibited DNA binding activities of transcription factors of nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) that have binding sites in the promoter region of the VCAM-1 gene. In addition, immunocytochemical staining analysis confirmed that HDL inhibited TNF-alpha-induced VCAM-1 expression via reduced nuclear translocation of NF-kappaB. These results suggest that HDL down-regulates the expression of VCAM-1 gene in TNF-alpha-activated HUVECs at transcriptional levels via blunted translocation and transactivation of NF-kappaB and AP-1 transcription factors. Plasma HDL may block the initial atherosclerotic process via inhibited monocyte adhesion to the endothelium, which is independent of modulating the cholesterol reverse transport of plasma HDL.