NLRP3 inflammasome assembly in neutrophils is supported by PAD4 and promotes NETosis under sterile conditions

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Muenzer, P., Negro, R., Fukui, S., di Meglio, L., Aymonnier, K., Chu, L., Cherpokova, D., Gutch, S., Sorvillo, N., Shi, L., Magupalli, V. G., Weber, A. N. R., Scharf, R. E., Waterman, C. M., Wu, H., & Wagner, D. D. NLRP3 inflammasome assembly in neutrophils is supported by PAD4 and promotes NETosis under sterile conditions. Frontiers in Immunology, 12, (2021): 683803, https://doi.org/10.3389/fimmu.2021.683803.Neutrophil extracellular trap formation (NETosis) and the NLR family pyrin domain containing 3 (NLRP3) inflammasome assembly are associated with a similar spectrum of human disorders. While NETosis is known to be regulated by peptidylarginine deiminase 4 (PAD4), the role of the NLRP3 inflammasome in NETosis was not addressed. Here, we establish that under sterile conditions the cannonical NLRP3 inflammasome participates in NETosis. We show apoptosis-associated speck-like protein containing a CARD (ASC) speck assembly and caspase-1 cleavage in stimulated mouse neutrophils without LPS priming. PAD4 was needed for optimal NLRP3 inflammasome assembly by regulating NLRP3 and ASC protein levels post-transcriptionally. Genetic ablation of NLRP3 signaling resulted in impaired NET formation, because NLRP3 supported both nuclear envelope and plasma membrane rupture. Pharmacological inhibition of NLRP3 in either mouse or human neutrophils also diminished NETosis. Finally, NLRP3 deficiency resulted in a lower density of NETs in thrombi produced by a stenosis-induced mouse model of deep vein thrombosis. Altogether, our results indicate a PAD4-dependent formation of the NLRP3 inflammasome in neutrophils and implicate NLRP3 in NETosis under noninfectious conditions in vitro and in vivo.This work was supported by a grant from National Heart, Lung, and Blood Institute of the National Institutes of Health (grant R35 HL135765) and a Steven Berzin family support to DDW, an Individual Erwin Deutsch fellowship by the German, Austrian and Swiss Society of Thrombosis and Hemostasis Research to RES, a Whitman fellowship (MBL) to DDW, and an Individual Marie Skłodowska-Curie Actions fellowship by the European Commission (796365 - COAGULANT) to PM. ANRW was funded by the Deutsche Forschungsgemeinschaft (TRR156/2 –246807620) and a research grant (We-4195/15-19). CMW was supported by the Division of Intramural Research, NHLBI, NIH

Extracellular DNA NET-Works With Dire Consequences for Health

Neutrophils play a central role in innate immune defense. Advances in neutrophil biology have brought to light the capacity of neutrophils to release their decondensed chromatin and form large extracellular DNA networks called neutrophil extracellular traps (NETs). NETs are produced in response to many infectious and noninfectious stimuli and, together with fibrin, block the invasion of pathogens. However, their formation in inflamed blood vessels produces a scaffold that supports thrombosis, generates neo-antigens favoring autoimmunity, and aggravates damage in ischemia/reperfusion injury. NET formation can also be induced by cancer and promotes tumor progression. Formation of NETs within organs can be immediately detrimental, such as in lung alveoli, where they affect respiration, or they can be harmful over longer periods of time. For example, NETs initiate excessive deposition of collagen, resulting in fibrosis, thus likely contributing to heart failure. Here, we summarize the latest knowledge on NET generation and discuss how excessive NET formation mediates propagation of thrombosis and inflammation and, thereby, contributes to various diseases. There are many ways in which NET formation could be averted or NETs neutralized to prevent their detrimental consequences, and we will provide an overview of these possibilities.status: publishe

Sirt3 deficiency does not affect venous thrombosis or NETosis despite mild elevation of intracellular ROS in platelets and neutrophils in mice

Inflammation is a common denominator in chronic diseases of aging. Yet, how inflammation fuels these diseases remains unknown. Neutrophils are the primary leukocytes involved in the early phase of innate immunity and inflammation. As part of their anti-microbial defense, neutrophils form extracellular traps (NETs) by releasing decondensed chromatin lined with cytotoxic proteins. NETs have been shown to induce tissue injury and thrombosis. Here, we demonstrated that Sirt3, a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase, an enzyme linked to human longevity, was expressed in mouse neutrophils and platelets. Using Sirt3-/- mice as a model of accelerated aging, we investigated the effects of Sirt3 deficiency on NETosis and platelet function, aiming to detect enhancement of thrombosis. More mitochondrial reactive oxygen species (ROS) were generated in neutrophils and platelets of Sirt3-/- mice compared to WT, when stimulated with a low concentration of phorbol 12-myristate 13-acetate (PMA) and a high concentration of thrombin, respectively. There were no differences in in vitro NETosis, with or without stimulation. Platelet aggregation was mildly augmented in Sirt3-/- mice compared to WT mice, when stimulated with a low concentration of collagen. The effect of Sirt3 deficiency on platelet and neutrophil activation in vivo was examined by the venous thrombosis model of inferior vena cava stenosis. Elevation of plasma DNA concentration was observed after stenosis in both genotypes, but no difference was shown between the two genotypes. The systemic response to thrombosis was enhanced in Sirt3-/- mice with significantly elevated neutrophil count and reduced platelet count. However, no differences were observed in incidence of thrombus formation, thrombus weight and thrombin-antithrombin complex generation between WT and Sirt3-/- mice. We conclude that Sirt3 does not considerably impact NET formation, platelet function, or venous thrombosis in healthy young mice

Peptidylarginine deiminase 4 promotes age-related organ fibrosis

Aging promotes inflammation, a process contributing to fibrosis and decline in organ function. The release of neutrophil extracellular traps (NETs [NETosis]), orchestrated by peptidylarginine deiminase 4 (PAD4), damages organs in acute inflammatory models. We determined that NETosis is more prevalent in aged mice and investigated the role of PAD4/NETs in age-related organ fibrosis. Reduction in fibrosis was seen in the hearts and lungs of aged PAD4−/− mice compared with wild-type (WT) mice. An increase in left ventricular interstitial collagen deposition and a decline in systolic and diastolic function were present only in WT mice, and not in PAD4−/− mice. In an experimental model of cardiac fibrosis, cardiac pressure overload induced NETosis and significant platelet recruitment in WT but not PAD4−/− myocardium. DNase 1 was given to assess the effects of extracellular chromatin. PAD4 deficiency or DNase 1 similarly protected hearts from fibrosis. We propose a role for NETs in cardiac fibrosis and conclude that PAD4 regulates age-related organ fibrosis and dysfunction

Sirt3 deficiency does not affect venous thrombosis or NETosis despite mild elevation of intracellular ROS in platelets and neutrophils in mice

Inflammation is a common denominator in chronic diseases of aging. Yet, how inflammation fuels these diseases remains unknown. Neutrophils are the primary leukocytes involved in the early phase of innate immunity and inflammation. As part of their anti-microbial defense, neutrophils form extracellular traps (NETs) by releasing decondensed chromatin lined with cytotoxic proteins. NETs have been shown to induce tissue injury and thrombosis. Here, we demonstrated that Sirt3, a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase, an enzyme linked to human longevity, was expressed in mouse neutrophils and platelets. Using Sirt3-/- mice as a model of accelerated aging, we investigated the effects of Sirt3 deficiency on NETosis and platelet function, aiming to detect enhancement of thrombosis. More mitochondrial reactive oxygen species (ROS) were generated in neutrophils and platelets of Sirt3-/- mice compared to WT, when stimulated with a low concentration of phorbol 12-myristate 13-acetate (PMA) and a high concentration of thrombin, respectively. There were no differences in in vitro NETosis, with or without stimulation. Platelet aggregation was mildly augmented in Sirt3-/- mice compared to WT mice, when stimulated with a low concentration of collagen. The effect of Sirt3 deficiency on platelet and neutrophil activation in vivo was examined by the venous thrombosis model of inferior vena cava stenosis. Elevation of plasma DNA concentration was observed after stenosis in both genotypes, but no difference was shown between the two genotypes. The systemic response to thrombosis was enhanced in Sirt3-/- mice with significantly elevated neutrophil count and reduced platelet count. However, no differences were observed in incidence of thrombus formation, thrombus weight and thrombin-antithrombin complex generation between WT and Sirt3-/- mice. We conclude that Sirt3 does not considerably impact NET formation, platelet function, or venous thrombosis in healthy young mice.status: publishe

Plasma Peptidylarginine Deiminase IV Promotes VWF-Platelet String Formation and Accelerates Thrombosis After Vessel Injury

RATIONALE: PAD4 (peptidylarginine deiminase type IV), an enzyme essential for neutrophil extracellular trap formation (NETosis), is released together with neutrophil extracellular traps into the extracellular milieu. It citrullinates histones and holds the potential to citrullinate other protein targets. While NETosis is implicated in thrombosis, the impact of the released PAD4 is unknown. OBJECTIVE: This study tests the hypothesis that extracellular PAD4, released during inflammatory responses, citrullinates plasma proteins, thus affecting thrombus formation. METHODS AND RESULTS: Here, we show that injection of r-huPAD4 in vivo induces the formation of VWF (von Willebrand factor)-platelet strings in mesenteric venules and that this is dependent on PAD4 enzymatic activity. VWF-platelet strings are naturally cleaved by ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type-1 motif-13). We detected a reduction of endogenous ADAMTS13 activity in the plasma of wild-type mice injected with r-huPAD4. Using mass spectrometry and in vitro studies, we found that r-huPAD4 citrullinates ADAMTS13 on specific arginine residues and that this modification dramatically inhibits ADAMTS13 enzymatic activity. Elevated citrullination of ADAMTS13 was observed in plasma samples of patients with sepsis or noninfected patients who were elderly (eg, age \u3e 65 years) and had underlying comorbidities (eg, diabetes mellitus and hypertension) as compared with healthy donors. This shows that ADAMTS13 is citrullinated in vivo. VWF-platelet strings that form on venules of Adamts13(-/-) mice were immediately cleared after injection of r-huADAMTS13, while they persisted in vessels of mice injected with citrullinated r-huADAMTS13. Next, we assessed the effect of extracellular PAD4 on platelet-plug formation after ferric chloride-induced injury of mesenteric venules. Administration of r-huPAD4 decreased time to vessel occlusion and significantly reduced thrombus embolization. CONCLUSIONS: Our data indicate that PAD4 in circulation reduces VWF-platelet string clearance and accelerates the formation of a stable platelet plug after vessel injury. We propose that this effect is, at least in part, due to ADAMTS13 inhibition

Deficiency of Sirt3 did not affect venous thrombosis <i>in vivo</i>.

<p>Sirt3-/- mice and WT mice underwent inferior vena cava (IVC) stenosis for 3 hrs. (A) Incidence of thrombus formation, (B) weight and (C) length are presented. (D) Thrombin anti-thrombin (TAT) complex, (E) plasma DNA concentration or (F) plasma soluble P-selectin concentration were determined. Circulating (G) platelet and (H) neutrophil counts were evaluated before (0 hr) and after (3 hrs) IVC stenosis. n = 11–12, *<i>P</i><0.05, **<i>P</i><0.01 vs WT or corresponding group (Student’s t tests). Thrombus frequencies were analyzed using χ2 tests of contingency tables.</p

Sirt3 deficiency had a minor impact on platelet functions.

<p>Platelet aggregation was induced by (A) collagen, (B) thrombin and (C) ADP at the concentration described using (A), (B) washed platelets or (C) platelet-rich plasma (PRP) from Sirt3-/- mice and WT mice. Representative aggregation traces are on the right. n = 7–10. (D) Washed platelets from Sirt3-/- mice and WT mice were incubated with thrombin 25 or 100 mU/mL for 20 min at 37°C. Percentage of JON/A and P-selectin double positive cells were quantified by flow cytometry. n = 4.*<i>P</i><0.05 vs WT (Student’s t tests).</p