Antiphospholipid antibodies promote leukocyte-endothelial cell adhesion and thrombosis in mice by antagonizing eNOS via beta 2GPI and apoER2

In antiphospholipid syndrome (APS), antiphospholipid antibodies (aPL) binding to beta 2 glycoprotein I (beta 2GPI) induce endothelial cell-leukocyte adhesion and thrombus formation via unknown mechanisms Here we show that in mice both of these processes are caused by the inhibition of eNOS In studies of cultured human, bovine, and mouse endothelial cells, the promotion of monocyte adhesion by aPL entailed decreased bioavailable NO, and aPL fully antagonized eNOS activation by diverse agonists Similarly, NO-dependent, acetylcholine-induced increases in carotid vascular conductance were impaired in aPL-treated mice The inhibition of eNOS was caused by antibody recognition of domain I of beta 2GPI and beta 2GPI dimerization, and it was due to attenuated eNOS S1179 phosphorylation mediated by protein phosphatase 2A (PP2A) Furthermore, LDL receptor family member antagonism with receptor-associated protein (RAP) prevented aPL inhibition of eNOS in cell culture, and ApoER2(-/-) mice were protected from aPL inhibition of eNOS in vivo Moreover, both aPL-induced increases in leukocyte-endothelial cell adhesion and thrombus formation were absent m eNOS(-/-) and in ApoER2(-/-) mice Thus, aPL-induced leukocyte-endothelial cell adhesion and thrombosis are caused by eNOS antagonism, which is due to impaired S1179 phosphorylation mediated by beta 2GPI, apoER2, and PP2A Our results suggest that novel therapies for APS can now be developed targeting these mechanisms