Background: Oxidized low-density lipoprotein (oxLDL) promotes expression and secretion of endothelin-1 (ET-1), however, the precise mechanism involved is unclear. This study was designed to identify the regulatory mechanism of oxLDL-induced ET-1 expression in endothelial cells.
Methods: ET-1 mRNA expression, secretion and promoter activity were evaluated by reverse transcriptase-PCR (RT-PCR), enzyme immunometric and luciferase assays, respectively.
Results: oxLDL (35 microg/ml) significantly enhanced reactive oxygen species (ROS), mRNA expression, secretion and promoter activity of ET-1 in human umbilical vein endothelial cells (HUVECs), all of which were nullified by the antioxidant N-acetyl cysteine (NAC). oxLDL stimulated the extracellular signal-regulated kinase (ERK) phosphorylation in HUVECs, which was blocked by NAC and the mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitor PD98059. NAC and PD98059 stopped oxLDL-elicited increase in mRNA expression, secretion and promoter activity of ET-1. Fusion plasmids with decreasing length of 5'-flanking sequence of ET-1 from -566 bpLuc to -250 bpLuc displayed increased luciferase activity after 24 h of oxLDL treatment. Interestingly, fusion plasmid from -233 and -185 bpLuc significantly reduced the luciferase activity in control and oxLDL-treated HUVECs. In addition, transfection of the reporter construct -250Luc, which contains a 2 bp mutation at activator protein-1 site, abolished both basal and oxLDL-stimulated ET-1 promoter activities.
Conclusion: Collectively, our data favor the notion that oxLDL stimulates ERK phosphorylation via ROS accumulation, which in turn stimulates vascular endothelial transcriptional factor activator protein-1 and ET-1 expression as well as secretion.