Shiga Toxin 2a Induces NETosis via NOX-Dependent Pathway

Targeting neutrophil extracellular trap accumulation under flow in patients with immune-mediated thrombotic thrombocytopenic purpura

ABSTRACT

Neutrophil NETosis is a unique form of cell death, characterized by the release of decondensed chromatin and antimicrobial contents to the extracellular space, which is involved in inflammation and thrombosis. However, the role of NETosis in the pathogenesis of immune-mediated thrombotic thrombocytopenic purpura (iTTP) and how a targeted therapy affects the accumulation of neutrophil extracellular traps (NETs) under flow remain unknown. Flow cytometry demonstrated that the percentage of neutrophils undergoing NETosis in whole blood from patients with iTTP on admission was significantly increased, with a concurrent decrease in the capacity of inducible NETosis by shigatoxin. After therapy, the percentage of H3Cit+MPO+ neutrophils was significantly reduced, with an improvement in inducible NETosis in these patients. Additionally, little to no NET and thrombus formation was detected underflow in the whole blood from patients with iTTP when platelet counts were very low, but the NET and thrombus formation was dramatically increased following therapy when platelet counts rose to ≥50 × 109/L or were restored to normal with donor platelets. Similarly, there was no thrombus or NET accumulation under flow in the whole blood from vwf-/- mice, but NET accumulation was significantly higher in Adamts13-/- mice than in wild-type mice. Finally, recombinant ADAMTS13 or caplacizumab (or anfibatide) prevented NET and thrombus formation under flow in whole blood from patients with iTTP or from Adamts13-/- mice. These results indicate that neutrophil NETosis and NET formation depend on platelets and von Willebrand factor (VWF) in iTTP, and a targeted therapy such as recombinant ADAMTS13 or caplacizumab may prevent NET and thrombus formation under flow in iTTP.

Anti-inflammatory and antiviral activities of flavone C-glycosides of Lophatherum gracile for COVID-19

Lophatherum gracile (L. gracile) has long been used as a functional food and herbal medicine. Previous studies have demonstrated that extracts of L. gracile attenuate inflammatory response and inhibit SARS-CoV-2 replication; however, the underlying active constituents have yet to be identified. This study investigated the bioactive components of L. gracile. Flavone C-glycosides of L. gracile were found to dominate both anti-inflammatory and antiviral effects. A simple chromatography-based method was developed to obtain flavone C-glycoside-enriched extract (FlavoLG) from L. gracile. FlavoLG and its major flavone C-glycoside isoorientin were shown to restrict respiratory bursts and the formation of neutrophil extracellular traps in activated human neutrophils. FlavoLG and isoorientin were also shown to inhibit SARS-CoV-2 pseudovirus infection by interfering with the binding of the SARS-CoV-2 spike on ACE2. These results provide scientific evidence indicating the efficacy of L. gracile as a potential supplement for treating neutrophil-associated COVID-19.

ROS and DNA repair in spontaneous versus agonist-induced NETosis: Context matters

Reactive oxygen species (ROS) is essential for neutrophil extracellular trap formation (NETosis). Nevertheless, how ROS induces NETosis at baseline and during neutrophil activation is unknown. Although neutrophils carry DNA transcription, replication and repair machineries, their relevance in the short-lived mature neutrophils that carry pre-synthesized proteins has remained a mystery for decades. Our recent studies show that (i) NETosis-inducing agonists promote NETosis-specific kinase activation, genome-wide transcription that helps to decondense chromatin, and (ii) excess ROS produced by NADPH oxidase activating agonists generate genome-wide 8-oxy-guanine (8-OG), and the initial steps of DNA repair are needed to decondense chromatin in these cells. These steps require DNA repair proteins necessary for the assembly and nicking at the damaged DNA sites (poly ADP ribose polymerase PARP, apurinic endonuclease APE1 and DNA ligase), but not the enzymes that mediate the repair DNA synthesis (Proliferating cell nuclear antigen (PCNA) and DNA Polymerases). In this study, we show that (i) similar to agonist-induced NETosis, inhibition of early steps of oxidative DNA damage repair proteins suppresses spontaneous NETosis, but (ii) the inhibition of late stage repair proteins DNA polymerases and PCNA drastically promotes baseline NETosis. Hence, in the absence of excessive ROS generation and neutrophil activation, DNA repair mediated by PCNA and DNA polymerases is essential to prevent chromatin decondensation and spontaneous NETosis. These findings indicate that ROS, oxidative DNA damage, transcription and DNA repair differentially regulate spontaneous and agonist-induced NETosis. Therefore, context matters.

Neutrophil Extracellular Traps Induced by Shiga Toxin and Lipopolysaccharide-Treated Platelets Exacerbate Endothelial Cell Damage

Hemolytic uremic syndrome (HUS) is the most common cause of acute renal failure in the pediatric population. The etiology of HUS is linked to Gram-negative, Shiga toxin (Stx)-producing enterohemorrhagic bacterial infections. While the effect of Stx is focused on endothelial damage of renal glomerulus, cytokines induced by Stx or bacterial lipopolysaccharide (LPS) and polymorphonuclear cells (PMNs) are involved in the development of the disease. PMN release neutrophil extracellular traps (NETs) to eliminate pathogens, although NETs favor platelets (Plts) adhesion/thrombus formation and can cause tissue damage within blood vessels. Since thrombus formation and occlusion of vessels are characteristic of HUS, PMN–Plts interaction in the context of Stx may promote netosis and contribute to the endothelial damage observed in HUS. The aim of this study was to determine the relevance of netosis induced by Stx in the context of LPS-sensitized Plts on endothelial damage. We observed that Stx2 induced a marked enhancement of netosis promoted by Plts after LPS stimulation. Several factors seemed to promote this phenomenon. Stx2 itself increased the expression of its receptor on Plts, increasing toxin binding. Stx2 also increased LPS binding to Plts. Moreover, Stx2 amplified LPS induced P-selectin expression on Plts and mixed PMN–Plts aggregates formation, which led to activation of PMN enhancing dramatically NETs formation. Finally, experiments revealed that endothelial cell damage mediated by PMN in the context of Plts treated with LPS and Stx2 was decreased when NETs were disrupted or when mixed aggregate formation was impeded using an anti-P-selectin antibody. Using a murine model of HUS, systemic endothelial damage/dysfunction was decreased when NETs were disrupted, or when Plts were depleted, indicating that the promotion of netosis by Plts in the context of LPS and Stx2 plays a fundamental role in endothelial toxicity. These results provide insights for the first time into the pivotal role of Plts as enhancers of endothelial damage through NETs promotion in the context of Stx and LPS. Consequently, therapies designed to reduce either the formation of PMN–Plts aggregates or NETs formation could lessen the consequences of endothelial damage in HUS.