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Activated platelets induce MLKL-driven neutrophil necroptosis and release of neutrophil extracellular traps in venous thrombosis.

ABSTRACT: 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.

SUBMITTER: Nakazawa D

PROVIDER: S-EPMC6060161 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Activated platelets induce MLKL-driven neutrophil necroptosis and release of neutrophil extracellular traps in venous thrombosis.

Nakazawa Daigo D Desai Jyaysi J Steiger Stefanie S Müller Susanne S Devarapu Satish Kumar SK Mulay Shrikant R SR Iwakura Takamasa T Anders Hans-Joachim HJ

Cell death discovery 20180628

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 infer ...[more]

PMID: 30062055

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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.

Project description:Upon activation, neutrophils release their content through different mechanisms like degranulation and NETosis, thus prompting thrombosis. The natural anticoagulant activated protein C (APC) inhibits neutrophil NETosis and, consequently, this may lower the levels of neutrophil activation markers in plasma, further diminishing the thrombotic risk exerted by this anticoagulant. We aimed to describe the status of markers of neutrophil activation in plasma of patients with venous thrombosis, their association with the thrombotic risk and the potential contribution of APC. We quantified three markers of neutrophil activation (cell-free DNA, calprotectin, and myeloperoxidase) in 253 patients with venous thromboembolism (VTE) in a stable phase (192 lower extremity VTE and 61 splanchnic vein thrombosis) and in 249 healthy controls. In them, we also quantified plasma APC, soluble endothelial protein C receptor (EPCR), and soluble thrombomodulin (TM), and we genotyped two genetic regulators of APC: the EPCR gene (PROCR) haplotypes (H) and the TM gene (THBD) c.1418C>T polymorphism. We found a significant increase in plasma cell-free DNA (p < 0.0001), calprotectin (p = 0.0001) and myeloperoxidase (p = 0.005) in VTE patients compared to controls. Furthermore, all three neutrophil activation markers were associated with an increase in the thrombotic risk. Cell-free DNA and calprotectin plasma levels were significantly correlated (Spearman r = 0.28; p < 0.0001). As expected, the natural anticoagulant APC was significantly decreased in VTE patients (p < 0.0001) compared to controls, what was mediated by its genetic regulators PROCR-H1, PROCR-H3, and THBD-c.1418T, and inversely correlated with cell-free DNA levels. This is the largest case-control study that demonstrates the increase in markers of neutrophil activation in vivo in VTE patients and their association with an increased thrombotic risk. This increase could be mediated by low APC levels and its genetic regulators, which could also increase NETosis, further enhancing thrombosis and inflammation.

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Activated platelets induce MLKL-driven neutrophil necroptosis and release of neutrophil extracellular traps in venous thrombosis.

Publications

Activated platelets induce MLKL-driven neutrophil necroptosis and release of neutrophil extracellular traps in venous thrombosis.

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