Upregulation of endothelial receptor for oxidized low-density lipoprotein (LOX-1) in cultured human coronary artery endothelial cells by angiotensin II type 1 receptor activation

Cross talk between oxidized LDL (ox-LDL) and angiotensin II (Ang II) may be relevant in atherosclerosis. In this study, we examined the presence of a specific endothelial receptor for ox-LDL (LOX-1) and Ang II receptors in human coronary artery endothelial cells (HCAECs). In addition, we studied the effect of Ang II on LOX-1 gene and protein expression. LOX-1 was consistently identified in HCAECs by reverse transcriptase-polymerase chain reaction (RT-PCR), cDNA sequence, Western blot, and I-125-labeled ox-LDL binding assay (B-max, 29.7 ng/mg protein). The HCAECs also exhibited Ang II receptors (AT(1)>AT(2)), as determined by RT-PCR and I-125-labeled Ang II binding assay (B-max, 2.21 and 1.19 fmol/mg protein, respectively). Incubation of HCAECs with Ang II markedly increased LOX-1 mRNA (RT-PCR) and protein (Western blot) expression. The increase in LOX-1 expression was dependent on Ang II concentration (10(-12) to 10(-6) mol/L). Ang IT caused a concentration-dependent increase in I-125-labeled ox-LDL uptake by HCAECs and enhanced ox-LDL-mediated cell injury, as evident from an increase in LDH release and a decrease in cell viability. These effects of Ang II were completely blocked by pretreatment of HCAECs with losartan, a specific AT(1) blocker, but not by PD123319, a specific AT(2) blocker. These observations indicate the following: (1) HCAECs possess abundant LOX-1 as well as Ang II (AT(1)>AT(2)) receptors, (2) Ang II upregulates LOX-1 receptor and ox-LDL uptake, (3) the effects of Ang II are mediated by AT(1) activation, and (4) Ang II enhances ox-LDL-mediated injury to HCAECs.