Activated Platelets Autocrine 5-Hydroxytryptophan Aggravates Sepsis-Induced Acute Lung Injury by Promoting Neutrophils Extracellular Traps Formation
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ABSTRACT:
SUBMITTER: Huang Y
PROVIDER: S-EPMC8801939 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Equilibrium within the immune system can often determine the fate of its host. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the pathogen responsible for the coronavirus disease 2019 (COVID-19) pandemic. Immune dysregulation remains one of the main pathophysiological components of SARS-CoV-2-associated organ injury, with over-activation of the innate immune system, and induced apoptosis of adaptive immune cells. Here, we provide an overview of the innate immune system, both in general and relating to COVID-19. We specifically discuss "NETosis," the process of neutrophil release of their extracellular traps, which may be a more recently described form of cell death that is different from apoptosis, and how this may propagate organ dysfunction in COVID-19. We complete this review by discussing Stem Cell Therapies in COVID-19 and emerging COVID-19 phenotypes, which may allow for more targeted therapy in the future. Finally, we consider the array of potential therapeutic targets in COVID-19, and associated therapeutics.
| S-EPMC8416266 | biostudies-literature
Project description:Venous thromboembolic (VTE) disease, often manifesting as deep vein thrombosis or pulmonary embolism, involves clot formation consisting of blood cells and platelets locked in plasma protein and chromatin networks. The latter derives from neutrophil extracellular traps released by dying neutrophils; however, the molecular mechanisms of neutrophil death in VTE remains unknown. We speculated that mixed lineage kinase-like (MLKL)-driven neutrophil necroptosis contributes to VTE. Indeed, human inferior venous cava thrombus material stained positive for phosphorylated MLKL, the activated version of MLKL that executes necroptotic cell death. In mice, MLKL immunostaining showed co-localization of MLKL with citrullinated histone H3, a marker of neutrophil extracellular trap (NET) formation. These data provide indirect support for a role of MLKL-mediated necroptosis. As a functional proof, both the stabilizer of receptor-interacting protein kinase-1 (RIPK1) and necroptosis inhibitor necrostatin-1s as well as genetic deficiency of MLKL partially prevented clot formation upon inferior vena cava ligation in mice. In both experiments terminal deoxynucleotidyl transferase dUTP nick-end labeling, RIPK3, and citrullinated histone H3+ areas were markedly reduced within the remnant thrombus. In vitro, thrombin-activated platelets induced cell death and NET formation in human neutrophils, which was inhibited by necrostatin-1s treatment. Necrostatin-1s and necrosulfonamide also inhibited neutrophil-platelet aggregate formation induced by tumor necrosis factor-? but had no effect on platelet activation itself. We conclude that in VTE, activated platelets, and possibly other triggers, induce neutrophil necroptosis, a process contributing to clot formation by releasing chromatin in the extracellular space.
| S-EPMC6060161 | biostudies-literature
Project description:ObjectiveNeonates with necrotizing enterocolitis (NEC) have higher calprotectin levels in stool than do healthy neonates. However, it is not known whether high stool calprotectin at the onset of bowel symptoms identifies neonates who truly have NEC vs other bowel disorders.Study designNeonates were eligible for this study when an x-ray was ordered to 'rule-out NEC'. Stool calprotectin was quantified at that time and in a follow-up stool. Each episode was later categorized as NEC or not NEC. The location of calprotectin in the bowel was determined by immunohistochemistry.ResultsNeonates with NEC had higher initial and follow-up stool calprotectin levels than did neonates without NEC. Calprotectin in bowel from neonates with NEC was within neutrophil extracellular traps (NETs).ConclusionAt the onset of signs concerning for NEC, fecal calprotectin is likely to be higher in neonates with NEC. Calprotectin in their stools is exported from neutrophils via NETs.
| S-EPMC5045760 | biostudies-literature
Project description:Host innate immunity is fundamental to the resistance against Candida albicans and Candida glabrata infection, two of the most important agents contributing to human fungal infections. Phagocytic cells, such as neutrophils, constitute the first line of host defense mechanisms, and the release of neutrophil extracellular traps (NETs) represent an important strategy to immobilize and to kill invading microorganisms, arresting the establishment of infection. The purinergic system operates an important role in the homeostasis of immunity and inflammation, and ectophosphatase and ectonucleotidase activities are recognized as essential for survival strategies and infectious potential of several pathogens. The expression and unique activity of a 3'-nucleotidase/nuclease (3'NT/NU), able to hydrolyze not only AMP but also nucleic acids, has been considered as part of a possible mechanism of microbes to escape from NETs. The aim of the present study was to evaluate if yeasts escape from the NET-mediated killing through their 3'NT/NU enzymatic activity contributing to NET-hydrolysis. After demonstrating the presence of 3'NT/NU activity in C. albicans, C. glabrata, and Saccharomyces cerevisiae, we show that, during neutrophils-Candida interaction, when NETs formation and release are triggered, NETs digestion occurs and this process of NETs disruption promoted by yeast cells was prevented by ammonium tetrathiomolybdate (TTM), a 3'NT/NU inhibitor. In conclusion, although the exact nature and specificity of yeasts ectonucleotidases are not completely unraveled, we highlight the importance of these enzymes in the context of infection, helping yeasts to overcome host defenses, whereby C. albicans and C. glabrata can escape NET-mediate killing through their 3'NT/NU activity.
| S-EPMC8313894 | biostudies-literature
Project description:BackgroundThe role of neutrophil extracellular traps (NETs) in procoagulant activity (PCA) in stroke patients caused by thromboembolic occlusion of the internal carotid artery (ICA) remains unclear. Our objectives were to evaluate the critical role of NETs in the induction of hypercoagulability in stroke and to identify the functional significance of NETs during atherothrombosis.MethodsThe levels of NETs, activated platelets (PLTs), and PLT-derived microparticles (PMPs) were detected in the plasma of 55 stroke patients and 35 healthy controls. NET formation and thrombi were analysed using immunofluorescence. Exposed phosphatidylserine (PS) was evaluated with flow cytometry and confocal microscopy. PCA was analysed using purified coagulation complex, thrombin, and fibrin formation assays.FindingsThe plasma levels of NETs, activated PLTs, and PMP markers in the carotid lesion site (CLS) were significantly higher than those in the aortic blood. NETs were decorated with PS in thrombi and the CLS plasma of ICA occlusion patients. Notably, the complementary roles of CLS plasma and thrombin-activated PLTs were required for NET formation and subsequent PS exposure. PS-bearing NETs provided functional platforms for PMPs and coagulation factor deposition and thus increased thrombin and fibrin formation. DNase I and lactadherin markedly inhibited these effects. In addition, NETs were cytotoxic to endothelial cells, converting these cells to a procoagulant phenotype. Sivelestat, anti-MMP9 antibody, and activated protein C (APC) blocked this cytotoxicity by 25%, 39%, or 52%, respectively.InterpretationNETs played a pivotal role in the hypercoagulability of stroke patients. Strategies that prevent NET formation may offer a potential therapeutic strategy for thromboembolism interventions.FundingThis study was supported by grants from the National Natural Science Foundation of China (61575058, 81873433 and 81670128) and Graduate Innovation Fund of Harbin Medical University (YJSKYCX2018-58HYD).
| S-EPMC7047181 | biostudies-literature
Project description:Background: Cases of excessive neutrophil counts in the blood in severe coronavirus disease (COVID-19) patients have drawn significant attention. Neutrophil infiltration was also noted on the pathological findings from autopsies. It is urgent to clarify the pathogenesis of neutrophils leading to severe pneumonia in COVID-19. Methods: A retrospective analysis was performed on 55 COVID-19 patients classified as mild (n = 22), moderate (n = 25), and severe (n = 8) according to the Guidelines released by the National Health Commission of China. Trends relating leukocyte counts and lungs examined by chest CT scan were quantified by Bayesian inference. Transcriptional signatures of host immune cells of four COVID19 patients were analyzed by RNA sequencing of lung specimens and BALF. Results: Neutrophilia occurred in 6 of 8 severe patients at 7-19 days after symptom onset, coinciding with lesion progression. Increasing neutrophil counts paralleled lesion CT values (slope: 0.8 and 0.3-1.2), reflecting neutrophilia-induced lung injury in severe patients. Transcriptome analysis revealed that neutrophil activation was correlated with 17 neutrophil extracellular trap (NET)-associated genes in COVID-19 patients, which was related to innate immunity and interacted with T/NK/B cells, as supported by a protein-protein interaction network analysis. Conclusion: Excessive neutrophils and associated NETs could explain the pathogenesis of lung injury in COVID-19 pneumonia.
| S-EPMC7461898 | biostudies-literature
Project description:Neutrophil extracellular traps (NETs) consist of decondensed nuclear chromatin that is associated with proteins and are released by neutrophils during an inflammatory response. Released NETs are able to capture pathogens, prevent their dissemination and potentially kill them via antimicrobial peptides and proteins that are associated with the decondensed chromatin. In addition to their antimicrobial functions, NETs have also been shown to exert immunomodulatory effects by activation and differentiation of macrophages, dendritic cells and T cells. However, the effect of NETs on neutrophil functions is poorly understood. Here we report the first comprehensive study regarding the effects of NETs on human primary neutrophils in vitro. NETs were isolated from cultures of PMA-exposed neutrophils. Exposure of neutrophils to isolated NETs resulted in the activation of several neutrophil functions in a concentration-dependent manner. NETs induced exocytosis of granules, the production of reactive oxygen species (ROS) by the NADPH oxidase NOX2, NOX2-dependent NET formation, increased the phagocytosis and killing of microbial pathogens. Furthermore, NETs induced the secretion of the proinflammatory chemokine IL-8 and the B-cell-activating cytokine BAFF. We could show that the NET-induced activation of neutrophils occurs by pathways that involve the phosphorylation of Akt, ERK1/2 and p38. Taken together our results provide further insights into the proinflammatory role of NETs by activating neutrophil effector function and further supports the view that NETs can amplify inflammatory events. On the one hand the amplified functions enhance the antimicrobial defense. On the other hand, NET-amplified neutrophil functions can be involved in the pathophysiology of NET-associated diseases. In addition, NETs can connect the innate and adaptive immune system by inducing the secretion of the B-cell-activating cytokine BAFF.
| S-EPMC8217666 | biostudies-literature
Project description:BackgroundNeutrophil extracellular traps (NETs) are innate defense mechanisms that are also implicated in the pathogenesis of organ dysfunction. However, the role of NETs in pediatric sepsis is unknown.MethodsInfant (2 weeks old) and adult (6 weeks old) mice were submitted to sepsis by intraperitoneal (i.p.) injection of bacteria suspension or lipopolysaccharide (LPS). Neutrophil infiltration, bacteremia, organ injury, and concentrations of cytokine, NETs, and DNase in the plasma were measured. Production of reactive oxygen and nitrogen species and release of NETs by neutrophils were also evaluated. To investigate the functional role of NETs, mice undergoing sepsis were treated with antibiotic plus rhDNase and the survival, organ injury, and levels of inflammatory markers and NETs were determined. Blood samples from pediatric and adult sepsis patients were collected and the concentrations of NETs measured.ResultsInfant C57BL/6 mice subjected to sepsis or LPS-induced endotoxemia produced significantly higher levels of NETs than the adult mice. Moreover, compared to that of the adult mice, this outcome was accompanied by increased organ injury and production of inflammatory cytokines. The increased NETs were associated with elevated expression of Padi4 and histone H3 citrullination in the neutrophils. Furthermore, treatment of infant septic mice with rhDNase or a PAD-4 inhibitor markedly attenuated sepsis. Importantly, pediatric septic patients had high levels of NETs, and the severity of pediatric sepsis was positively correlated with the level of NETs.ConclusionThis study reveals a hitherto unrecognized mechanism of pediatric sepsis susceptibility and suggests that NETs represents a potential target to improve clinical outcomes of sepsis.
| S-EPMC6454713 | biostudies-literature
Project description:BackgroundThe release of neutrophil extracellular traps (NETs), a mesh of DNA, histones and neutrophil proteases from neutrophils, was first demonstrated as a host defence against pathogens. Recently it became clear that NETs are also released in pathological conditions. NETs released in the blood can activate thrombosis and initiate a cascade of platelet responses. However, it is not well understood if these responses are mediated through direct or indirect interactions. We investigated whether cell-free NETs can induce aggregation of washed human platelets in vitro and the contribution of NET-derived extracellular DNA and histones to platelet activation response.MethodsIsolated human neutrophils were stimulated with PMA to produce robust and consistent NETs. Cell-free NETs were isolated and characterised by examining DNA-histone complexes and quantification of neutrophil elastase with ELISA. NETs were incubated with washed human platelets to assess several platelet activation responses. Using pharmacological inhibitors, we explored the role of different NET components, as well as main platelet receptors, and downstream signalling pathways involved in NET-induced platelet aggregation.ResultsCell-free NETs directly induced dose-dependent platelet aggregation, dense granule secretion and procoagulant phosphatidyl serine exposure on platelets. Surprisingly, we found that inhibition of NET-derived DNA and histones did not affect NET-induced platelet aggregation or activation. We further identified the molecular pathways involved in NET-activated platelets. The most potent single modulator of NET-induced platelet responses included NET-bound cathepsin G, platelet Syk kinase, and P2Y12 and ?IIb?3 receptors.ConclusionsIn vitro-generated NETs can directly induce marked aggregation of washed human platelets. Pre-treatment of NETs with DNase or heparin did not reduce NET-induced activation or aggregation of human washed platelets. We further identified the molecular pathways activated in platelets in response to NETs. Taken together, we conclude that targeting certain platelet activation pathways, rather than the NET scaffold, has a more profound reduction on NET-induced platelet aggregation.
| S-EPMC5975482 | biostudies-literature
Project description:A growing body of evidence suggests that neutrophil extracellular traps (NETs) critically contribute to the development of atherosclerosis. However, the detailed mechanism of how NETs promote atherogenesis remains unknown. In this study, we explored the role of NETs for promoting atherosclerosis by modulating the activity of autophagy in macrophages. NETs were effectively induced by a nicotine administration to the HL-60 cell-derived neutrophil-like cells. Treatment with NETs markedly suppressed both autophagosome formation and autophagosome-lysosome fusion in 7-ketocholesterol-treated macrophages, which are accompanied by the enhancement of inflammasome activity. NETs upregulate epidermal growth factor receptor (EGFR) activity, which enhances Beclin-1 phosphorylation of the tyrosine residues of Beclin-1 by EGFR, inhibits the PI3 kinase activity of the Beclin1-Vps34 complex, and suppresses autophagosome formation in macrophages. Furthermore, NET-induced activation of EGFR allows Rubicon to increase its expression, thereby suppressing autophagosome-lysosome fusion. In vivo experiments revealed that the suppression of NET formation by ablating peptidyl arginine deiminase-4 in neutrophil leukocytes resulted in the attenuation of atherosclerotic plaques in a nicotine-administered HFD-fed ApoE -/- mice. Taken together, these results suggest that NET-mediated EGFR-Beclin-1 signaling in the macrophages promotes atherogenesis by autophagy inhibition-mediated inflammasome activation.
| S-EPMC9340257 | biostudies-literature