OxLDL/β2GPI/anti-β2GPI Ab complex induces inflammatory activation via the TLR4/NF-κB pathway in HUVECs

Patients with antiphospholipid syndrome have been identified to have higher incidence rates of atherosclerosis (AS) due to the elevated levels of anti-β2-glycoprotein I (β2GPI) antibody (Ab). Our previous studies revealed that the anti-β2GPI Ab formed a stable oxidized low-density lipoprotein (oxLDL)/β2GPI/anti-β2GPI Ab complex, which accelerated AS development by promoting the accumulation of lipids in macrophages and vascular smooth muscle cell. However, the effects of the complex on endothelial cells, which drive the initiation and development of AS, remain unknown. Thus, the present study aimed to determine the proinflammatory roles of the oxLDL/β2GPI/anti-β2GPI Ab complex in human umbilical vein endothelial cells (HUVECs) in an attempt to determine the underlying mechanism. Reverse transcription-quantitative PCR, enzymy-linked immunosorbent assay, western blotting and immunofluorescence staining were performed to detect the expressions of inflammation related factors and adhesion molecules. Monocyte-binding assay was used to investigate the effects of oxLDL/β2GPI/anti-β2GPI Ab complex on monocyte adhesion to endothelial cells. The results demonstrated that the oxLDL/β2GPI/anti-β2GPI Ab complex upregulated the expression of Toll-like receptor (TLR)4 and the levels of NF-κB phosphorylation in HUVECs, and subsequently enhanced the expression levels of inflammatory cytokines, including TNF-α, IL-1β and IL-6, as well as those of adhesion molecules, such as intercellular adhesion molecule 1 and vascular adhesion molecule 1. In addition, the complex facilitated the recruitment of monocytes by promoting the secretion of monocyte chemotactic protein 1 in HUVECs. Notably, the described effects of the oxLDL/β2GPI/anti-β2GPI Ab complex in HUVECs were abolished by either TLR4 or NF-κB blockade. In conclusion, these findings suggested that the oxLDL/β2GPI/anti-β2GPI Ab complex may induce a hyper-inflammatory state in endothelial cells by promoting the secretion of proinflammatory cytokines and monocyte recruitment, which was discovered to be largely dependent on the TLR4/NK-κB signaling pathway.