High mobility group box-1 contributes to anti-myeloperoxidase antibody-induced glomerular endothelial cell injury through a moesin-dependent route

BACKGROUND Our previous study found that circulating and urinary levels of high mobility group box-1 (HMGB1) were closely associated with disease activity in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Moreover, HMGB1 participates in ANCA-induced neutrophil activation. Cross-reactivity between moesin and anti-myeloperoxidase (MPO) antibody has been reported in both human and mouse. The current study investigated whether HMGB1 participated in MPO-ANCA-induced glomerular endothelial cell (GEnC) injury, which is one of the most important aspects in the pathogenesis of AAV. METHODS The effects of HMGB1 on expression of moesin on GEnCs and anti-MPO antibody binding to GEnCs were measured. MPO expression on GEnCs was explored. The effects of HMGB1 in MPO-ANCA induced GEnC injury were measured, during which the role of moesin was explored. Antagonists for various relevant receptors were employed. RESULTS Sera from AAV patients at the active stage could mediate GEnC injury, while this effect could be attenuated by preblocking HMGB1. HMGB1 could increase the expression of moesin on GEnCs and the binding of anti-MPO antibody to moesin. The colocalization of moesin expression and anti-MPO antibody binding can be detected. Little, if any, MPO was expressed in GEnCs. HMGB1 increased GEnC activation and injury in the presence of patient-derived MPO-ANCA-positive IgGs through moesin. The effects of HMGB1 on expression of moesin on GEnCs, anti-MPO antibody binding to GEnCs, GEnC activation and injury were mainly toll like receptor 4 (TLR4) dependent. CONCLUSIONS HMGB1 can increase the expression of moesin but not MPO on GEnCs, and can further participate in MPO-ANCA-induced GEnC activation and injury by cross-reactivity between moesin and anti-MPO antibody.