Malondialdehyde-specific natural IgM inhibit toll-like receptor 4 and peptidyl-arginine deiminase 4-dependent NETosis triggered by coronary extracellular vesicles of myocardial infarction patients

Abstract Background Neutrophil extracellular traps (NETs) are critical mediators of thromboinflammation during acute myocardial infarction (AMI). However, triggers and signalling pathways of NETosis in AMI remain incompletely understood. Levels of extracellular vesicles (EV) carrying oxidation-specific epitopes (OSE) originating from lipid peroxidation are increased at the culprit site in AMI. Importantly, natural IgM antibodies with specificity for OSE, such as malondialdehyde (MDA), have been shown to modulate functional effects of EV, and are associated with reduced cardiovascular risk. Purpose We investigated the stimulatory capacity of EV on neutrophil effector functions and specifically targeted key mediators of NET formation using pharmacological inhibitors and atheroprotective natural IgM to inhibit this process. Methods Patients were included after diagnosis of ST-segment elevation myocardial infarction and blood was aspirated from the culprit site and peripheral arterial site (n=28) during primary percutaneous coronary intervention (pPCI). Myocardial function was documented by cardiac magnetic resonance imaging 4±2 days and 195±15 days after pPCI. EV were isolated from cell culture supernatants and culprit site plasma for neutrophil stimulation in vitro. Pharmacological inhibitors were used to map NET signalling pathways of EV. Isolated EV were used for neutrophil stimulation in a murine injection model in the presence of the MDA-specific IgM LR04 or an isotype control. NET formation and other neutrophil functions were assessed by flow cytometry, ELISA and fluorescence microscopy. Results Levels of NET surrogate markers and CD45+ MDA+ EV were higher at the culprit site than in the peripheral circulation. EV generated by LPS-activated THP-1 monocytic cells induced in vitro NET formation, release of neutrophil elastase and IL-8, and degranulation of MPO and NGAL in primary human neutrophils, but not reactive oxygen species. Toll-like receptor 4 (TLR4) and peptidyl-arginine deiminase 4 (PAD4) were identified as key mediators of NET formation induced by in vitro-generated EV and EV isolated from the culprit site of AMI patients. Functionally, the MDA-specific monoclonal IgM antibody LR04, but not an isotype control, inhibited the ability of patient-derived and in vitro-generated EV to trigger release of NETs in primary human neutrophils and in mice. Titres of MDA-specific IgM antibodies were inversely associated with the NET marker citH3 in blood of AMI patients. Finally, we found that the concentration of CD45+ MDA+ EV per protective MDA-specific IgM at the culprit site showed an inverse association with left ventricular ejection fraction 72 hours and 6 months after AMI. Conclusions We show that EV can trigger several neutrophil effector functions. EV-induced NET formation is TLR4- and PAD4-dependent and can be inhibited by OSE-specific natural IgM potentially influencing cardiovascular outcomes after an acute event.