A novel pathway of cellular activation mediated by antiphospholipid antibody‐induced extracellular vesicles

Summary Background Elevated levels of endothelial cell ( EC )‐derived extracellular vesicles ( EV s) circulate in patients with antiphospholipid antibodies ( APLA s), and APLA s, particularly those against β 2 ‐glycoprotein I (β 2 GPI ), stimulate EV release from EC s. However, the effects of EC ‐derived EV s have not been characterized. Objective To determine the mechanism by which EV s released from EC s by anti‐β 2 GPI antibodies activate unstimulated EC s. Patients/methods We used interleukin ( IL )‐1 receptor inhibitors, small interfering RNA (si RNA ) against Toll‐like receptors ( TLR s) and micro RNA (mi RNA ) profiling to assess the mechanism(s) by which EV s released from EC s exposed to anti‐β 2 GPI antibodies activated unstimulated EC s. Results and conclusions Anti‐β 2 GPI antibodies caused formation of an EC inflammasome and the release of EV s that were enriched in mature IL ‐1β, had a distinct mi RNA profile, and caused endothelial activation. However, activation was not inhibited by an IL ‐1β antibody, an IL ‐1 receptor antagonist, or IL ‐1 receptor si RNA . EC activation by EV s required IL ‐1 receptor‐associated kinase 4 phosphorylation, and was inhibited by pretreatment of cells with TLR 7 si RNA or RN ase A, which degrades ss RNA . Profiling of mi RNA in EV s released from EC s incubated with β 2 GPI and either control IgG or anti‐β 2 GPI antibodies revealed numerous differences in the content of specific mi RNA s, including a significant decrease in mIR 126. These observations demonstrate that, although anti‐β 2 GPI ‐derived endothelial EV s contain IL ‐1β, they activate unstimulated EC s through a TLR 7‐dependent and ss RNA ‐dependent pathway. Alterations in mi RNA content may contribute to the ability of EV s derived from EC s exposed to anti‐β 2 GPI antibodies to activate unstimulated EC s in an autocrine or paracrine manner.