Involvement of IRAKs and TRAFs in anti-β2GPI/β2GPI-induced tissue factor expression in THP-1 cells

Elevated plasma level of soluble triggering receptor expressed on myeloid cells-1 is associated with inflammation activity and is a potential biomarker of thrombosis in primary antiphospholipid syndrome

Background

Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is an innate-immune receptor found in blood. Its presence reflects innate immune cell activation. We sought to investigate plasma sTREM-1 levels in patients with primary antiphospholipid syndrome (PAPS).

Methods

A cross-sectional, case-control design was used. Plasma sTREM-1 levels were analyzed by enzyme-linked immunosorbent assay (ELISA) in consecutive patients diagnosed with PAPS or asymptomatic antiphospholipid antibody (APLA) carriers and controls.

Results

The study cohort included 33 patients with PAPS, 10 asymptomatic APLA carriers, and 73 controls. Mean plasma sTREM-1 levels were significantly higher in patients with PAPS (299.2 ± 146.7 pg/ml) and thrombotic PAPS-ever (current and past thrombotic event) (327.2 ± 151.3 pg/ml) compared with controls (230.2 ± 85.5 pg/ml; p = 0.006 and p = 0.003, respectively), patients with thrombotic PAPS compared with patients with past obstetric APS (195.12 ± 58.52 pg/ml, p = 0.01) and APLA carriers (215.8 ± 51.6 pg/ml, p = 0.02), patients with current thrombotic PAPS (429.5 ± 227.5 pg/ml) compared with patients with past thrombotic PAPS (289.5 ± 94.65 pg/ml, p = 0.01), and patients with PAPS who had ever had a stroke or venous thromboembolic event compared with patients who had not (p = 0.007 and p = 0.02, respectively). On receiver operator characteristic curve analysis, plasma sTREM-1 levels differentiated patients with current thrombotic PAPS from asymptomatic APLA carriers and controls, with an area under the curve of 0.7292 (p = 0.0014) and 0.88 (p < 0.0001), respectively. Multivariate regression analysis to identify sTREM-1 predictors (thrombotic PAPS-ever, age, and sex) yielded an independent association of sTREM-1 levels with thrombotic PAPS (p < 0.0001).

Conclusions

Plasma sTREM-1 levels are significantly elevated in patients with thrombotic PAPS. Levels of sTREM-1 might serve as a biomarker for thrombosis in patients with PAPS.

oxLDL/β2GPI/anti-β2GPI complex induced macrophage differentiation to foam cell involving TLR4/NF-kappa B signal transduction pathway

Macrophage-derived foam cell formation is a hallmark of atherosclerosis. It has been reported that oxidized low density lipoprotein (oxLDL) inducing formation of foam cells and expression of inflammatory molecules are partly mediated by toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) pathway. However, whether oxLDL/β2-glycoprotein I/anti-β2-glycoprotein I (oxLDL/β2GPI/anti-β2GPI) complex enhanced formation of foam cells involving TLR4/NF-κB pathway or not has never been explored. In the current study, we focused on investigating the transformation of peritoneal macrophages from BALB/c mice into foam cells induced by the three complexes, and the involvement of TLR4 as well as its downstream signal molecule NF-κB. The results showed that treatment of macrophages with oxLDL/β2GPI/anti-β2GPI complex could markedly increase intracellular lipid loading and expression of TLR4, phosphorylated NF-κB p65 (p-NF-κB p65), monocyte chemoattractant protein-1 (MCP-1), as well as tissue factor (TF). The oxLDL and oxLDL/β2GPI/anti-β2GPI complex induced formation of foam cells and expression of p-NF-κB p65 were significantly reduced, while macrophages were pre-treated with TLR4 inhibitor TAK-242. Meanwhile, both TAK-242 and NF-κB inhibitor PDTC could remarkably inhibit oxLDL, oxLDL/β2GPI/anti-β2GPI complex, as well as LPS increased MCP-1 and TF levels. Nevertheless, β2GPI/anti-β2GPI complex-induced MCP-1 and TF mRNA expression were inhibited by TAK-242 rather than PDTC, although TF activity was significantly reduced by both of the inhibitors. In conclusion, our results indicate that oxLDL/β2GPI/anti-β2GPI complex could enhance the conversion of macrophages into foam cells and the process may be at least partly mediated by TLR4/NF-κB pathway, which may contribute to the accelerated development of atherosclerosis in APS.

NF-κB is activated from endosomal compartments in antiphospholipid antibodies-treated human monocytes

BACKGROUND

The antiphospholipid antibody syndrome (APS) is an autoimmune disease associated with arterial or venous thrombosis and/or recurrent fetal loss and is caused by pathogenic antiphospholipid antibodies (aPLA). We recently demonstrated that Toll-like receptor 2 (TLR2) and CD14 contribute to monocyte activation of aPLA.

OBJECTIVE

To study the mechanisms of cell activation by aPLA, leading to pro-coagulant and pro-inflammatory responses.

METHODS AND RESULTS

For this study, we used purified antibodies from the plasmas of 10 different patients with APS and healthy donors. We demonstrate that aPLA, but not control IgG, co-localizes with TLR2 and TLR1 or TLR6 on human monocytes. Blocking antibodies to TLR2, TLR1 or TLR6, but not to TLR4, decreased TNF and tissue factor (TF) responses to aPLA. Pharmacological and siRNA approaches revealed the importance of the clathrin/dynamin-dependent endocytic pathway in cell activation by aPLA. In addition, soluble aPLA induced NF-κB activation, while bead-immobilized aPLA beads, which cannot be internalized, were unable to activate NF-κB. Internalization of aPLA in monocytes and NF-κB activation were dependent on the presence of CD14.

CONCLUSION

We show that TLR2 and its co-receptors, TLR1 and TLR6, contribute to the pathogenicity of aPLA, that aPLA are internalized via clathrin- and CD14-dependent endocytosis and that endocytosis is required for NF-κB activation. Our results contribute to a better understanding of the APS and provide a possible therapeutic approach.

Both NF-κB and c-Jun/AP-1 involved in anti-β2GPI/β2GPI-induced tissue factor expression in monocytes

Our previous data has demonstrated that Toll-like receptor 4 (TLR4) and its signalling pathway can contribute to anti-β2-glycoprotein I/β2-glycoprotein I (anti-β2GPI/β2GPI) -induced tissue factor (TF) expression in human blood monocytes and acute monocytic leukaemia cell line THP-1. However, its downstream nuclear transcription factors have not been well explored. In the current study, we further investigated whether nuclear factor kappa B (NF-κB) and activator protein (AP-1) were activated and their roles in anti-β2GPI/β2GPI complex stimulating TF expression. The results showed that treatment of the cells with anti-β2GPI (10μg/ml)/β2GPI (100 mg/ml) complex could markedly increase the levels of phosphorylated NF-κB (p-NF-κB p65) and c-Jun/AP-1 (p-c-Jun), as well as TF expression. Both NF-κB inhibitor PDTC (20 μM) and AP-1 inhibitor curcumin (25 mM) could attenuate TF expression induced by anti-β2GPI/β2GPI or APS-IgG/β2GPI complex. Combination of any two inhibitors of MAPKs (SB203580/U0126 or SB203580/SP600125 or U0126/SP600125) could decrease activation of NF-κB. SB203580/SP600125 or U0126/SP600125, but not SB203580/U0126, could reduce the phosphorylation of c-Jun/AP-1. Neither NF-κB nor c-Jun/AP-1 activation caused by anti-β2GPI/β2GPI complex could be affected by TLR4 inhibitor TAK-242. In conclusion, our results indicate that both NF-κB and c-Jun/AP-1 can be activated and play important roles in the process of anti-β2GPI/β2GPI-induced TF expression in monocytes, thereby contributing to the pathological processes of antiphospholipid syndrome.

Anti-β(2)GPI/β(2)GPI induced TF and TNF-α expression in monocytes involving both TLR4/MyD88 and TLR4/TRIF signaling pathways

Our previous study demonstrated that Toll-like receptor 4 (TLR4) could act as a co-receptor with annexin A2 (ANX2) mediating anti-β2-glycoprotein I/β2-glycoprotein I (anti-β(2)GPI/β(2)GPI)-induced tissue factor (TF) expression in human acute monocytic leukemia cell line THP-1. In the current study, we further explored the roles of TLR4 and its adaptors, MyD88 and TRIF, in anti-β(2)GPI/β(2)GPI-induced the activation of human blood monocytes and THP-1 cells and the relationship among TLR4, β(2)GPI and ANX2 in this process. The results showed that treatment of monocytes or THP-1 cells with anti-β(2)GPI/β(2)GPI complex could increase TF, MyD88, TRIF as well as TNF-α (tumor necrosis factor alpha) expression. These effects were blocked by addition of TAK-242, a blocker of signaling transduction mediated by the intracellular domain of TLR4. Moreover, TLR4/β(2)GPI/ANX2 complex could be detected in THP-1 cell lysates. Overall, our results indicate that anti-β(2)GPI/β(2)GPI complex induced TF and TNF-α expression involving both TLR4/MyD88 and TLR4/TRIF signaling pathways and TLR4 and its adaptors might be molecular targets for therapy of antiphospholipid syndrome (APS).