Pro-atherogenic activation of A7r5 cells induced by the oxLDL/β(2)GPI/anti-β(2)GPI complex

A previous study has revealed that oxidized low-density lipoprotein (oxLDL)/β(2)-glycoprotein I (β(2)GPI)/anti-β(2)-glycoprotein I (anti-β(2)GPI), an immune complex, is able to activate the Toll-like receptor 4 (TLR4)/nuclear factor κβ (NF-κβ) inflammatory signaling pathway in macrophages, and consequently enhance foam cell formation and the secretion of prothrombin activators. However, the effects of the oxLDL/β(2)GPI/anti-β(2)GPI complex on vascular smooth muscle cells have yet to be investigated. The present study investigated whether the oxLDL/β(2)GPI/anti-β(2)GPI complex was able to reinforce the pro-atherogenic activities of a rat thoracic aorta smooth muscle cell line (A7r5) and examined the underlying molecular mechanisms. The results revealed that the oxLDL/β(2)GPI/anti-β(2)GPI complex treatment significantly (P<0.05 vs. the media, oxLDL, oxLDL/β(2)GPI and β(2)GPI/anti-β(2)GPI groups) enhanced the pro-atherogenic activation of A7r5 cells, including intracellular lipid loading, Acyl-coenzyme A cholesterol acyltransferase mRNA expression, migration, matrix metalloproteinase-9 and monocyte chemoattractant protein 1 secretion, all via TLR4. In addition, the expression of TLR4 and the phosphorylation of NF-κβ p65, p38 and ERK1/2 were also upregulated in oxLDL/β(2)GPI/anti-β(2)GPI complex-treated A7r5 cells. Pre-treatment with TAK-242, a TLR4 inhibitor, was able to partly attenuate the oxLDL/β(2)GPI/anti-β(2)GPI complex-induced phosphorylation of NF-κβ p65; however, it had no effect on the phosphorylation of extracellular regulated kinase 1/2 (ERK1/2) and p38. Meanwhile, the NF-κβ p65 inhibitor ammonium pyrrolidinedithiocarbamate and the ERK1/2 inhibitor U0126, but not the p38 inhibitor SB203580, were able to block oxLDL/β(2)GPI/anti-β(2)GPI complex-induced foam cell formation and migration in A7r5 cells. Hence, it was demonstrated that the oxLDL/β(2)GPI/anti-β(2)GPI complex is able to enhance the lipid uptake, migration and active molecule secretion of A7r5 cells via TLR4, and finally deteriorate atherosclerosis plaques. Additionally, it was demonstrated that oxLDL/β(2)GPI/anti-β(2)GPI complex-induced foam cell formation and migration may be partly mediated by the TLR4/NF-κβ signaling pathway and that ERK1/2 may also participate in the process.