Anti-β2-GPI Antibodies Induce Endothelial Cell Expression of Tissue Factor by LRP6 Signal Transduction Pathway Involving Lipid Rafts

In this study we analyzed whether anti-beta 2-GPI antibodies from patients with APS induce the endothelial cell expression of Tissue Factor (TF) by a LRP6 signal transduction pathway involving lipid rafts. HUVEC were stimulated with affinity purified anti-beta 2-GPI antibodies. Both LRP6 and beta-catenin phosphorylation, as well as TF expression, were evaluated by western blot. Results demonstrated that triggering with affinity purified anti-beta 2-GPI antibodies induced LRP6 phosphorylation with consequent beta-catenin activation, leading to TF expression on the cell surface. Interestingly, the lipid rafts affecting agent methyl-beta-cyclodextrin as well as the LRP6 inhibitor Dickkopf 1 (DKK1) partially reduced the anti-beta 2-GPI antibodies effect, indicating that the anti-beta 2-GPI effects on TF expression may depend on a signalling transduction pathway involving both lipid rafts and LRP6. An interaction between beta 2-GPI, LRP6 and PAR-2 within these microdomains was demonstrated by gradient fractionation and coimmunoprecipitation experiments. Thus, anti-beta 2-GPI antibodies react with their target antigen likely associated to LRP6 and PAR-2 within plasma membrane lipid rafts of the endothelial cell. Anti-beta 2-GPI binding triggers beta-catenin phosphorylation, leading to a procoagulant phenotype characterized by TF expression. These findings deal with a novel signal transduction pathway which provides new insight in the APS pathogenesis, improving the knowledge of valuable therapeutic target(s).

Automated summary

This study analyzed the induction of Tissue Factor (TF) expression in endothelial cells by anti-beta 2-GPI antibodies from patients with APS through a LRP6 signal transduction pathway involving lipid rafts. The results showed that the anti-beta 2-GPI antibodies triggered LRP6 phosphorylation and subsequent activation of beta-catenin, leading to TF expression on the cell surface.