Abstract 5537: Toll-Like 2 Receptor Mediates Apolipoprotein CIII-Induced Monocyte Activation
Plasma apolipoprotein CIII (apoCIII) independently predicts risk for coronary heart disease. We recently reported that apoCIII directly activates human monocytes adhesion to vascular endothelial cells. Recent evidences identified toll-like receptors (TLRs) as a direct contributor to atherogenesis through inflammatory processes via unknown endogenous agonists. This study tested a hypothesis that apoCIII activates human monocytoid THP-1 cells through TLRs. ApoCIII activated NF-κB in THP-1 cells and increased their adhesion to human umbilical vein endothelial cells (HUVECs). ApoCIII induced association of TLR2 with MyD88 in THP-1 cells. Anti-TLR2 blocking antibody, but not anti-TLR4 blocking antibody inhibited these processes. Anti-TLR2 antibody also inhibited apoCIII-induced human peripheral blood monocyte activation. ApoCIII bound to recombinant TLR2 protein, but not to recombinant TLR4 protein or albumin. Moreover, apoCIII showed a significantly higher and saturable binding to human TLR2 overexpressed-293 cells, compared with parental 293 cells. Overexpression of TLR2 in 293 cells augmented apoCIII-induced NF-κB activation and β1-integrin expression, which are inhibited by anti-apoCIII antibody as well as by anti-TLR2 antibody. Stimulation with apoCIII of peripheral blood monocytes from C57BL/6 mice activated NF-κB, and increased their adhesion to HUVECs. In contrast, apoCIII did not activate monocytes from TLR2−/− mice. Finally we assessed a role of physiologically relevant apoCIII such as those contained in VLDL. Intravenous administration of apoCIII-rich VLDL, but not VLDL lacking apoCIII, into C57BL/6 mice activated peripheral blood monocytes and increased their adhesion to HUVECs. Anti-TLR2 antibody as well as anti-apoCIII antibody attenuated these effects. ApoCIII-rich VLDL failed to activate monocytes from TLR2−/− mice. ApoCIII activated monocytes at least partly through a TLR2-dependent pathway. The present study identifies a novel mechanism for pro-inflammatory and pro-atherogenic effects of apoCIII, and a role for TLR2 in atherosclerosis induced by atherogenic lipoproteins.