Neutrophil extracellular traps (NETs) production is a major strategy employed by polymorphonuclear neutrophils (PMNs) to fight against microbes. NETs have been implicated in the pathogenesis of various lung injuries, although few studies have explored NETs in sepsis-associated acute lung injury (SI-ALI). Here, we demonstrate a major contribution of NETs to the pathology of sepsis-associated ALI by inducing ferroptosis of alveolar epithelial cells. Using both in vitro and in vivo studies, our findings show enhanced NETs accumulation in sepsis-associated ALI patients and mice, as well as the closely related upregulation of ferroptosis, the induction of which depends on METTL3-induced m6A modification of GPX4. Using a CLP-induced sepsis-associated ALI mouse model established with METTL3 -/- versus WT mice, in addition to METTL3 knockout and overexpression in vitro , we elucidated and confirmed the critical role of ferroptosis in NETs-induced ALI. These findings support a role for NETs-induced METTL3 modification and the subsequent induction of ferroptosis in the pathogenesis of sepsis-associated ALI.

Patients with sepsis commonly suffer from coagulation dysfunction and lead to the formation of thrombus. During the development of sepsis, neutrophils migrate from the circulating blood to infected tissues and mediate the formation of neutrophil extracellular traps (NETs) that kill pathogens. However, the overactivation of neutrophils can promote the formation of immunothrombosis and even cause disseminated intravascular coagulation (DIC), which damages microcirculation. The outcome of sepsis depends on early recognition and intervention, so clinical evaluation of NETs function may be a valuable biomarker for early diagnosis of sepsis. The interaction of NETs with platelets, complement, and endothelium mediates the formation of immunothrombosis in sepsis. Inhibiting the formation of NETs is also considered to be one of the potential treatments for sepsis. In this review, we will discuss the key role of neutrophils and NETs in sepsis and septic thrombosis, in order to reveal new mechanisms for thrombosis treatment of sepsis.

BackgroundPatients with sepsis may progress to acute respiratory distress syndrome (ARDS). Evidence of neutrophil extracellular traps (NETs) in sepsis-induced lung injury has been reported. However, the role of circulating NETs in the progression and thrombotic tendency of sepsis-induced lung injury remains elusive. The aim of this study was to investigate the role of tissue factor-enriched NETs in the progression and immunothrombosis of sepsis-induced lung injury.MethodsHuman blood samples and an animal model of sepsis-induced lung injury were used to detect and evaluate NET formation in ARDS patients. Immunofluorescence imaging, ELISA, Western blotting, and qPCR were performed to evaluate in vitro NET formation and tissue factor (TF) delivery ability. DNase, an anti-TF antibody, and thrombin inhibitors were applied to evaluate the contribution of thrombin to TF-enriched NET formation and the contribution of TF-enriched NETs to immunothrombosis in ARDS patients.ResultsSignificantly increased levels of TF-enriched NETs were observed in ARDS patients and mice. Blockade of NETs in ARDS mice alleviated disease progression, indicating a reduced lung wet/dry ratio and PaO2 level. In vitro data demonstrated that thrombin-activated platelets were responsible for increased NET formation and related TF exposure and subsequent immunothrombosis in ARDS patients.ConclusionThe interaction of thrombin-activated platelets with PMNs in ARDS patients results in local NET formation and delivery of active TF. The notion that NETs represent a mechanism by which PMNs release thrombogenic signals during thrombosis may offer novel therapeutic targets.