Abstract 2288: LOX-1 Mediates Renin-Angiotensin System-Dependent Redox-Sensitive and Ca2+ Signaling Pathways Induced in Endothelial Cells by Monocyte Adhesion
Background: Lectin-like oxidized-LDL receptor-1 (LOX-1) is a major receptor for oxidized LDL. NADPH oxidase closely associates with renin-angiotensin system (RAS) in the vasculature. We have reported that NADPH oxidase-dependent and Ca2+ signaling pathways are mediated via LOX-1 in endothelial cells (ECs) by monocyte adhesion independent of oxidized LDL.
Hypothesis: RAS plays an essential role in redox-sensitive and Ca2+ signaling pathways induced in ECs by monocyte adhesion, and LOX-1 mediates RAS-dependent events in monocyte-EC interaction.
Methods: A neutral antibody (TS92) was used for inhibition of LOX-1. Whole peripheral blood was pretreated with or without 10 μmol/L ACE inhibitor (temocaprilat) or AT1 receptor antagonist (olmesartan) for 3 hours, and monocytes were isolated and added to cultured human aortic ECs. Rac1 activity was determined by membrane translocarion, whereas NADPH oxidase activity was determined by lucigenin-enhanced chemiluminescence. Molecular expression and NF-κB phosphorylation were assessed by Western blotting. AT1 receptor activation in ECs was evaluated by epidermal growth factor receptor (EGFR) transactivation.
Results: RT-PCR of ACE revealed that monocyte adhesion upregulated endothelial RAS. Monocyte adhesion increased Rac1 activity, NADPH oxidase activity, and ROS generation within 30 minutes and NF-κB phosphorylation within 1 hour, resulting in upregulation of MCP-1, ICAM-1 and TF expression in ECs. Ca2+ signaling including intracellular Ca2+ mobilization and Ca2+ influx was induced in ECs just after adding monocytes. These redox-sensitive and Ca2+ signaling pathways were blocked by pretreatment of whole blood or ECs with temocaprilat and olmesartan, as well as by inhibition of endothelial LOX-1 by TS92. In addition, monocyte adhesion triggered EGFR transactivation within 30 minutes in ECs, which was blocked by inhibition of endothelial LOX-1 by TS92, indicating linkage beween LOX-1 and RAS in monocyte-EC interaction independent of oxidized LDL-LOX-1 axis.
Conclusions: We show new insights into the regulation of LOX-1/RAS axis in monocyte adhesion-triggered signaling pathways, which may be an attractive target for treatment of atherosclerosis.