The β2GPI/aβ2GPI inhibits phagocytosis of oxidized low-density lipoprotein in THP-1 macrophages via activating TLR4

Objective To investigate the effects of β2 glycoprotein I/anti-β2 glycoprotein I antibody complex (β2GPI/aβ2GPI) on lipid phagocytosis and class B scavenger receptor CD36 expression of macrophages, and the role of Toll-like receptor 4 (TLR4) during the process. Methods THP-1 macrophages were induced from THP-1 cells treated by 100 ng/mL phorbol ester (PMA), and then identified by morphological observation and DiI-oxLDL uptake assay. THP-1 macrophages were treated with RPMI1640 medium, β2GPI, aβ2GPI or β2GPI/aβ2GPI. The protein and mRNA expression of TLR4 were detected by Western blot analysis and real-time fluorescent quantitative PCR (qRT-PCR), respectively. After that, THP-1 macrophages were treated with RPMI1640 medium, oxidized low-density lipoprotein (oxLDL), oxLDL combined with β2GPI/aβ2GPI or oxLDL combined with LPS. Intracellular lipid deposition was observed by oil red O staining; the mRNA and protein expression of CD36 were detected by qRT-PCR, immunofluorescence and Western blot analysis. To unveil the role of TLR4 in this process, THP-1 macrophages were pre-treated with or without TLR4 inhibitor TAK-242 (1 μg/mL). Results After PMA treatment, THP-1 cells showed macrophage-like morphology and were able to engulf DiI-oxLDL. Compared with RPMI1640 medium, β2GPI/aβ2GPI treatment significantly increased TLR4 expression in THP-1 macrophages. Compared with oxLDL alone, oxLDL combined with β2GPI/aβ2GPI inhibited lipid deposition and CD36 expression in THP-1 macrophages, which could be partly reversed by TLR4 blockage. Conclusion The β2GPI/aβ2GPI can inhibit the phagocytosis of oxLDL and CD36 expression in macrophages, which is linked to the function of TLR4.