Konstantinos Kambas

Neutrophil Extracellular Trap Formation Is Associated with IL-1β and Autophagy-Related Signaling in Gout

Background Gout is a prevalent inflammatory arthritis affecting 1–2% of adults characterized by activation of innate immune cells by monosodium urate (MSU) crystals resulting in the secretion of interleukin-1β (IL-1β). Since neutrophils play a major role in gout we sought to determine whether their activation may involve the formation of proinflammatory neutrophil extracellular traps (NETs) in relation to autophagy and IL-1β. Methodology/Principal Findings Synovial fluid neutrophils from six patients with gout crisis and peripheral blood neutrophils from six patients with acute gout and six control subjects were isolated. MSU crystals, as well as synovial fluid or serum obtained from patients with acute gout, were used for the treatment of control neutrophils. NET formation was assessed using immunofluorescence microscopy. MSU crystals or synovial fluid or serum from patients induced NET formation in control neutrophils. Importantly, NET production was observed in neutrophils isolated from synovial fluid or peripheral blood from patients with acute gout. NETs contained the alarmin high mobility group box 1 (HMGB1) supporting their pro-inflammatory potential. Inhibition of phosphatidylinositol 3-kinase signaling or phagolysosomal fusion prevented NET formation, implicating autophagy in this process. NET formation was driven at least in part by IL-1β as demonstrated by experiments involving IL-1β and its inhibitor anakinra. Conclusions/Significance These findings document for the first time that activation of neutrophils in gout is associated with the formation of proinflammatory NETs and links this process to both autophagy and IL-1β. Modulation of the autophagic machinery may represent an additional therapeutic study in crystalline arthritides.

Autophagy mediates the delivery of thrombogenic tissue factor to neutrophil extracellular traps in human sepsis.

Background Sepsis is associated with systemic inflammatory responses and induction of coagulation system. Neutrophil extracellular traps (NETs) constitute an antimicrobial mechanism, recently implicated in thrombosis via platelet entrapment and aggregation. Methodology/Principal Findings In this study, we demonstrate for the first time the localization of thrombogenic tissue factor (TF) in NETs released by neutrophils derived from patients with gram-negative sepsis and normal neutrophils treated with either serum from septic patients or inflammatory mediators involved in the pathogenesis of sepsis. Localization of TF in acidified autophagosomes was observed during this process, as indicated by positive LC3B and LysoTracker staining. Moreover, phosphatidylinositol 3-kinase inhibition with 3-MA or inhibition of endosomal acidification with bafilomycin A1 hindered the release of TF-bearing NETs. TF present in NETs induced thrombin generation in culture supernatants, which further resulted in protease activated receptor-1 signaling. Conclusions/Significance This study demonstrates the involvement of autophagic machinery in the extracellular delivery of TF in NETs and the subsequent activation of coagulation cascade, providing evidence for the implication of this process in coagulopathy and inflammatory response in sepsis.

Tissue factor expression in neutrophil extracellular traps and neutrophil derived microparticles in antineutrophil cytoplasmic antibody associated vasculitis may promote thromboinflammation and the thrombophilic state associated with the disease

Objectives Antineutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) is characterised by neutrophil activation. An elevated prevalence of venous thromboembolic events has been reported in AAV. Because of the critical role of neutrophils in inflammation associated thrombosis, we asked whether neutrophil tissue factor (TF) may be implicated in the thrombotic diathesis in AAV. Methods Neutrophils from four patients and sera from 17 patients with ANCA associated vasculitis with active disease and remission were studied. TF expression was assessed by immunoblotting and confocal microscopy. Circulating DNA levels were evaluated. TF expressing microparticles (MPs) were measured by flow cytometry and thrombin–antithrombin complex levels by ELISA. Results Peripheral blood neutrophils from four patients with active disease expressed elevated TF levels and released TF expressing neutrophil extracellular traps (NETs) and MPs. TF positive NETs were released by neutrophils isolated from the bronchoalveolar lavage and were detected in nasal and renal biopsy specimens. Elevated levels of circulating DNA and TF expressing neutrophil derived MPs were further observed in sera from patients with active disease. Induction of remission attenuated the aforementioned effects. Control neutrophils treated with sera from patients with active disease released TF bearing NETs and MPs which were abolished after IgG depletion. Treatment of control neutrophils with isolated IgG from sera from patients with active disease also resulted in the release of TF bearing NETs. TF implication in MP dependent thrombin generation was demonstrated by antibody neutralisation studies. Conclusions Expression of TF in NETs and neutrophil derived MPs proposes a novel mechanism for the induction of thrombosis and inflammation in active AAV.

Expression of functional tissue factor by neutrophil extracellular traps in culprit artery of acute myocardial infarction

Neutrophils are involved in the pathophysiology of infracted coronary arteries in STEMI via NET structures. Platelets, activated by thrombin, are required for NET formation, while the integrity of NET scaffold contributes to the functionality of NET-bound TF. The blockage of NET formation or local neutralization of NET-mediated TF signalling constitutes candidate therapeutic targets.

Regulation of the autophagic machinery in human neutrophils

The induction of the autophagy machinery, a process for the catabolism of cytosolic proteins and organelles, constitutes a crucial mechanism in innate immunity. However, the involvement of autophagy in human neutrophils and the possible inducers of this process have not been completely elucidated. In this study, the induction of autophagy was examined in human neutrophils treated with various activators and detected by the formation of acidified autophagosomes through monodansylcadaverine staining and via LC‐3B conversion screened by immunoblotting and immunofluorescence confocal microscopy. In addition, the expression of the ATG genes was assessed by real‐time RT‐PCR. We provide evidence that autophagy is implicated in human neutrophils in both a phagocytosis‐independent (rapamycin, TLR agonists, PMA) and phagocytosis (Escherichia coli)‐dependent initiation manner. ROS activation is a positive mechanism for autophagy induction in the case of PMA, TLR activation and phagocytosis. Furthermore, LC3B gene expression was uniformly upregulated, indicating a transcriptional level of regulation for the autophagic machinery. This study provides a stepping stone toward further investigation of autophagy in neutrophil‐driven inflammatory disorders.

C5a and TNF-α Up-Regulate the Expression of Tissue Factor in Intra-Alveolar Neutrophils of Patients with the Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is characterized by the presence of fibrin-rich inflammatory exudates in the intra-alveolar spaces and the extensive migration of neutrophils into alveoli of the lungs. Tissue factor (TF)-dependent procoagulant properties of bronchoalveaolar lavage fluid (BALF) obtained from ARDS patients favor fibrin deposition, and are likely the result of cross-talk between inflammatory mediators and hemostatic mechanisms. However, the regulation of these interactions remains elusive. Prompted by previous findings suggesting that neutrophils, under certain inflammatory conditions, can express functional TF, we investigated the contribution of intra-alveolar neutrophils to the procoagulant properties of BALF from patients with ARDS. Our results confirm that the procoagulant properties of BALF from ARDS patients are the result of TF induction, and further indicate that BALF neutrophils are a main source of TF in intra-alveolar fluid. We also found that BALF neutrophils in these patients express significantly higher levels of TF than peripheral blood neutrophils. These results suggest that the alveolar microenvironment contributes to TF induction in ARDS. Additional experiments indicated that the ability of BALF to induce TF expression in neutrophils from healthy donors can be abolished by inhibiting C5a or TNF-α signaling, suggesting a primary role for these inflammatory mediators in the up-regulation of TF in alveolar neutrophils in ARDS. This cross-talk between inflammatory mediators and the induction of TF expression in intra-alveolar neutrophils may be a potential target for novel therapeutic strategies to limit ARDS-associated disturbances of coagulation.

Neutrophil extracellular traps promote differentiation and function of fibroblasts.

Neutrophil activation by inflammatory stimuli and the release of extracellular chromatin structures (neutrophil extracellular traps – NETs) have been implicated in inflammatory disorders. Herein, we demonstrate that NETs released by neutrophils treated either with fibrosis‐related agents, such as cigarette smoke, magnesium silicate, bleomycin, or with generic NET inducers, such as phorbol 12‐myristate 13‐acetate, induced activation of lung fibroblasts (LFs) and differentiation into myofibroblast (MF) phenotype. Interestingly, the aforementioned agents or IL‐17 (a primary initiator of inflammation/fibrosis) had no direct effect on LF activation and differentiation. MFs treated with NETs demonstrated increased connective tissue growth factor expression, collagen production, and proliferation/migration. These fibrotic effects were significantly decreased after degradation of NETs with DNase1, heparin or myeloperoxidase inhibitor, indicating the key role of NET‐derived components in LF differentiation and function. Furthermore, IL‐17 was expressed in NETs and promoted the fibrotic activity of differentiated LFs but not their differentiation, suggesting that priming by DNA and histones is essential for IL‐17‐driven fibrosis. Additionally, autophagy was identified as the orchestrator of NET formation, as shown by inhibition studies using bafilomycin A1 or wortmannin. The above findings were further supported by the detection of NETs in close proximity to alpha‐smooth muscle actin (α‐SMA)‐expressing fibroblasts in biopsies from patients with fibrotic interstitial lung disease or from skin scar tissue. Together, these data suggest that both autophagy and NETs are involved not only in inflammation but also in the ensuing fibrosis and thus may represent potential therapeutic targets in human fibrotic diseases. Copyright

MEFV alterations and population genetics analysis in a large cohort of Greek patients with familial Mediterranean fever

Familial Mediterranean fever (FMF) is a disease characterized by recurrent, self‐limiting bouts of fever and serositis and caused by altered pyrin due to mutated MEFV gene. FMF is common in the Mediterranean Basin populations, although with varying genetic patterns. The spectrum and clinical significance of MEFV alterations in Greece has yet not been elucidated. The aim of this study was to analyze the spectrum of MEFV alterations in FMF patients and healthy individuals in Greece. A cohort of 152 Greek FMF patients along with 140 Greek healthy controls was enrolled. Non‐isotopic RNase cleavage assay (NIRCA) and sequencing allowed mutational and haplotypic analysis of the entire coding sequence of MEFV. The arlequin 2.0, dnasp 4.0 and phylip software were used for population genetics analysis. Among patients, 127 (83.6%) carried at least one known mutation. The most common mutations identified were M694V (38.1%), M680I (19.7%), V726A (12.2%), E148Q (10.9%) and E230K (6.1%). The total carrier rate among healthy individuals was 0.7%. The presence of R202Q homozygosity in 12 of the remaining 25 MEFV negative FMF patients might be considered as disease related in Greeks. Population genetics analysis revealed that Greeks rely closer to the eastern rather than western populations of the Mediterranean Basin.

The emerging role of neutrophils in thrombosis-the journey of TF through NETs.

The production of TF by neutrophils and their contribution in thrombosis was until recently a matter of scientific debate. Experimental data suggested the de novo TF production by neutrophils under inflammatory stimuli, while others proposed that these cells acquired microparticle-derived TF. Recent experimental evidence revealed the critical role of neutrophils in thrombotic events. Neutrophil derived TF has been implicated in this process in several human and animal models. Additionally, neutrophil extracellular trap (NET) release has emerged as a major contributor in neutrophil-driven thrombogenicity in disease models including sepsis, deep venous thrombosis, and malignancy. It is suggested that NETs provide the scaffold for fibrin deposition and platelet entrapment and subsequent activation. The recently reported autophagy-dependent extracellular delivery of TF in NETs further supports the involvement of neutrophils in thrombosis. Herein, we seek to review novel data regarding the role of neutrophils in thrombosis, emphasizing the implication of TF and NETs.

Leptin induces the expression of functional tissue factor in human neutrophils and peripheral blood mononuclear cells through JAK2-dependent mechanisms and TNFα involvement

INTRODUCTION Leptin is an adipocyte-derived cytokine primarily involved in the regulation of body weight and energy balance. In vivo studies suggest that leptin promotes platelet aggregation and thrombosis. Neutrophils are involved in the crosstalk between inflammation and thrombosis in clinical disorders. Leptin is also involved in the regulation of inflammation. AIM We examined the in vitro effects of leptin on the expression of tissue factor (TF), the primary initiator of coagulation, in healthy neutrophils. MATERIALS AND METHODS/RESULTS The effects on TF expression were assayed functionally using a modified prothrombin time (mPT), as well as at mRNA and protein levels. The same experiments were performed in parallel with PBMC. Leptin induced functional TF and increased TF mRNA and protein expression in both cell types, as determined by mPT, real-time RT-PCR, western blot, flow cytometry, immunocytochemistry. Inhibition studies revealed that the effect of leptin on TF expression is mediated, at least in part, by JAK2 and PI3K. Our findings, after neutralising TNFalpha in supernatants of leptin-treated cells, also suggest the involvement of TNFalpha in the leptin-induced TF expression in leukocytes. CONCLUSIONS This study indicates a novel link between inflammation, obesity and thrombosis by showing that leptin is able to trigger the extrinsic coagulation cascade. This work suggests a possible mechanism of the thrombotic effects of hyperleptinemic-associated clinical disorders.