Search

Neutrophil overstimulation plays a crucial role in tissue damage during severe infections. As pathogen-derived neuraminidase (NEU) stimulate neutrophils, we investigated whether host NEU can be targeted to regulate neutrophil dysregulation observed in severe infections.The effects of NEU inhibitors in lipopolysaccharide (LPS)-stimulated neutrophils from healthy donors or COVID-19 patients were determined by evaluating the shedding of surface sialic acids, cell activation, and reactive oxygen species (ROS) production. Re-analysis of single-cell RNA sequencing of respiratory tract samples from COVID-19 patients was also carried out. The effects of Oseltamivir on sepsis and betacoronavirus-induced acute lung injury were evaluated in murine models.Oseltamivir and Zanamivir constrain host NEU activity, surface sialic acid release, cell activation, and ROS production by LPS-activated human neutrophils. Mechanistically, LPS increased the interaction of NEU1 with the matrix metalloproteinase (MMP)-9. Inhibition of MMP-9 prevents LPS-induced NEU activity and neutrophil response. In vivo, treatment with Oseltamivir fine-tunes neutrophil migration and improves infection control and host survival in peritonitis and pneumonia sepsis. NEU1 is also highly expressed in neutrophils from COVID-19 patients and treatment of whole blood samples from these patients with Oseltamivir or Zanamivir reduces neutrophil overactivation. Oseltamivir treatment of intranasally infected mice with the mouse hepatitis coronavirus 3 (MHV-3) decreased lung neutrophil infiltration, viral load, and tissue damage.These findings suggest that NEU1-MMP-9 interplay induces neutrophil overactivation. In vivo, it was shown that NEU may serve as a host-directed target to dampen neutrophil dysfunction during severe infections.

The term "vasculitis" refers to a group of rare immune-mediated diseases characterized by the dysregulated immune system attacking blood vessels located in any organ of the body, including the skin, lungs, and kidneys. Vasculitides are classified according to the size of the vessel that is affected. Although this observation is not specific to small-, medium-, or large-vessel vasculitides, patients show a high circulating neutrophil-to-lymphocyte ratio, suggesting the direct or indirect involvement of neutrophils in these diseases. As first responders to infection or inflammation, neutrophils release cytotoxic mediators, including reactive oxygen species, proteases, and neutrophil extracellular traps. If not controlled, this dangerous arsenal can injure the vascular system, which acts as the main transport route for neutrophils, thereby amplifying the initial inflammatory stimulus and the recruitment of immune cells. This review highlights the ability of neutrophils to "set the tone" for immune cells and other cells in the vessel wall. Considering both their long-established and newly described roles, we extend their functions far beyond their direct host-damaging potential. We also review the roles of neutrophils in various types of primary vasculitis, including immune complex vasculitis, anti-neutrophil cytoplasmic antibody-associated vasculitis, polyarteritis nodosa, Kawasaki disease, giant cell arteritis, Takayasu arteritis, and Behçet's disease.

Neutrophil overstimulation plays a crucial role in tissue damage during severe infections. Neuraminidase (NEU)-mediated cleavage of surface sialic acid has been demonstrated to regulate leukocyte responses. Here, we report that antiviral NEU inhibitors constrain host NEU activity, surface sialic acid release, ROS production, and NETs released by microbial-activated human neutrophils.In vivo, treatment with Oseltamivir results in infection control and host survival in peritonitis and pneumonia models of sepsis. Single-cell RNA sequencing re-analysis of publicly data sets of respiratory tract samples from critical COVID-19 patients revealed an overexpression of NEU1 in infiltrated neutrophils. Moreover, Oseltamivir or Zanamivir treatment of whole blood cells from severe COVID-19 patients reduces host NEU-mediated shedding of cell surface sialic acid and neutrophil overactivation. These findings suggest that neuraminidase inhibitors can serve as host-directed interventions to dampen neutrophil dysfunction in severe infections.At a GlanceIn a severe systemic inflammatory response, such as sepsis and COVID-19, neutrophils play a central role in organ damage. Thus, finding new ways to inhibit the exacerbated response of these cells is greatly needed. Here, we demonstrate thatin vitrotreatment of whole blood with the viral neuraminidase inhibitors Oseltamivir or Zanamivir, inhibits the activity of human neuraminidases as well as the exacerbated response of neutrophils. In experimental models of severe sepsis, oseltamivir decreased neutrophil activation and increased the survival rate of mice. Moreover, Oseltamivir or Zanamivirex vivotreatment of whole blood cells from severe COVID-19 patients rewire neutrophil function.

Neutrophils are key players in the hyperinflammatory response upon SARS-CoV-2 infection. We have previously described that cytosolic proliferating cell nuclear antigen (PCNA) controls neutrophil survival and NADPH oxidase-dependent ROS production. We here show that both PCNA and S100A8 expression and interaction were elevated in neutrophils from patients with COVID-19 compared to healthy donors and this was correlated with disease severity. Increased PCNA expression was accompanied by a decreased apoptosis and increased NADPH-oxidase activity in neutrophils from COVID-19 patients compared to healthy donors. These effects, as well as the interaction between PCNA and S100A8, were potently counteracted by T2 amino alcohol (T2AA), a PCNA inhibitor, demonstrating that the PCNA scaffold orchestrated neutrophil activation. Notably, the interaction between PCNA-S100A8 was more intense in the CD16high-CD62Llowactivated neutrophil subset. We propose that PCNA-S100A8 complex acts as potential driver for neutrophil dysregulation in COVID-19 and show for the first time that the PCNA scaffold is a decisive component of both neutrophil activation and heterogeneity.

Objectives To characterize lymphocytes dysregulation in patients with granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). Methods Using flow cytometry, we analysed B- and T-cell subsets in peripheral blood from 37 untreated patients with active disease (29 GPA and 8 MPA) and 22 healthy controls (HCs). Results GPA patients had increased Th2 (1.8 vs 1.0%, P = 0.02), Th9 (1.1 vs 0.2%, P = 0.0007) and Th17 (1.4 vs 0.9%, P = 0.03) cells compared with HC. Patients with MPO-ANCAs had significantly more CD21– B cells than HC or PR3-ANCA patients (6.9 vs 3.3% and 4.4%, P = 0.01). CD69 expressing B cells were significantly higher in GPA and MPA (3.0 and 5.9 vs 1.4%, P = 0.02 and P = 0.03, respectively) compared with HC, whereas B-cell activating factor-receptor expression was decreased in GPA and MPA (median fluorescence intensity ratio 11.8 and 13.7 vs 45.1 in HC, P Conclusion Skewed T-cell polarization towards Th2, Th9 and Th17 responses characterizes GPA, whereas B-cell populations are dysregulated in both GPA and MPA with an activated phenotype and a decreased B-cell activating factor-receptor expression. Finally, inflammatory B cells producing IL-6 are dramatically increased in GPA, providing an additional mechanism by which rituximab could be effective.

Neutrophils are vital for the innate immune system’s control of pathogens and neutrophil deficiency can render the host susceptible to life-threatening infections. Neutrophil responses must also be tightly regulated because excessive production, recruitment or activation of neutrophils can cause tissue damage in both acute and chronic inflammatory diseases. Granulocyte colony stimulating factor (G-CSF) is a key regulator of neutrophil biology, from production, differentiation, and release of neutrophil precursors in the bone marrow (BM) to modulating the function of mature neutrophils outside of the BM, particularly at sites of inflammation. G-CSF acts by binding to its cognate cell surface receptor on target cells, causing the activation of intracellular signalling pathways mediating the proliferation, differentiation, function, and survival of cells in the neutrophil lineage. Studies in humans and mice demonstrate that G-CSF contributes to protecting the host against infection, but conversely, it can play a deleterious role in inflammatory diseases. As such, neutrophils and the G-CSF pathway may provide novel therapeutic targets. This review will focus on understanding the role G-CSF plays in the balance between effective neutrophil mediated host defence versus neutrophil-mediated inflammation and tissue damage in various inflammatory and infectious diseases.

Neutrophils are the most abundant circulating white blood cells and are the central players of the innate immune response. During their lifecycle, neutrophils mainly evolve under low oxygen conditions (0.1–4% O2), to which they are well adapted. Neutrophils are atypical cells since they are highly glycolytic and susceptible to oxygen exposure, which induces their activation and death through mechanisms that remain currently elusive. Nevertheless, nearly all studies conducted on neutrophils are carried out under atmospheric oxygen (21%), corresponding to hyperoxia. Here, we investigated the impact of hyperoxia during neutrophil purification and culture on neutrophil viability, activation and cytosolic protein content. We demonstrate that neutrophil hyper‐activation (CD62L shedding) is induced during culture under hyperoxic conditions (24 h), compared with neutrophils cultured under anoxic conditions. Spontaneous neutrophil extracellular trap (NET) formation is observed when neutrophils face hyperoxia during purification or culture. In addition, we show that maintaining neutrophils in autologous plasma is the preferred strategy to maintain their basal state. Our results show that manipulating neutrophils under hyperoxic conditions leads to the loss of 57 cytosolic proteins during purification, while it does not lead to an immediate impact on neutrophil activation (CD11bhigh, CD54high, CD62Lneg) or viability (DAPI+). We identified two clusters of proteins belonging to cholesterol metabolism and to the complement and coagulation cascade pathways, which are highly susceptible to neutrophil oxygen exposure during neutrophil purification. In conclusion, protecting neutrophil from oxygen during their purification and culture is recommended to avoid activation and to prevent the alteration of cytosolic protein composition., In this study, we demonstrate that preserving neutrophils from oxygen exposure during their purification and culture is recommended to avoid their activation and to prevent formation of spontaneous neutrophil extracellular traps. Studying neutrophils in vitro under controlled oxygen levels similar to those encountered in vivo is essential for a better comprehension of their physiology.

Neutrophils are the most abundant circulating white blood cells and are central players of the innate immune response. During their lifecycle, neutrophils mainly evolve under low oxygen conditions (0.1 - 4% O2) to which they are well adapted. Neutrophils are atypical cells since they are mainly glycolytic, and highly susceptible to oxygen-exposure, which induces their activation and death, through mechanisms which remain currently elusive. Nevertheless, nearly all studies conducted on neutrophils are carried out under atmospheric oxygen (21%), corresponding to hyperoxic conditions. Here we investigated the impact of hyperoxia during neutrophil purification and culture on neutrophil viability, activation and cytosolic protein content. Neutrophil hyper-activation (CD62L shedding) is induced during culture under hyperoxic conditions (24h), compared to neutrophils cultured under anoxic conditions. In addition, we show that maintaining neutrophils in autologous plasma is the most suitable strategy to maintain their basal state.Our results show that manipulating neutrophils under hyperoxic conditions leads to the loss of ~100 cytosolic proteins during purification, while it does not lead to an immediate impact on neutrophils activation (CD11bhigh, CD54high, CD62Llow) or viability (DAPI+). We identified two clusters of proteins belonging to the cholesterol metabolism and to the complement and coagulation cascade pathways, which are highly susceptible to neutrophil oxygen-exposure during their purification.In conclusion, preserving neutrophil from oxygen-exposure during their manipulation – purification and culture- is recommended to avoid their experimental activation and for preserving a large set of cytosolic proteins from alteration.

International audience; Research into neutrophil biology in the last 10 years has uncovered a number of unexpected aspects of this still mysterious innate immune cell. Advances in technology have allowed visualisation of neutrophil trafficking to sites of inflammation, and, remarkably, neutrophils have been observed to depart from the scene in what has been termed reverse migration. There has also been increasing appreciation of the heterogeneity of neutrophils with ongoing categorisation of neutrophil subsets, including myeloid-derived suppressor cells and low-density granulocytes. Newly recognised neutrophil functions include the ability to release novel immune mediators such as extracellular DNA and microvesicles. Finally, studies of neutrophil cell death, both apoptotic and non-apoptotic, have revealed remarkable differences compared to other cell types. This review will highlight important discoveries in these facets of neutrophil biology and how the new findings will inform treatment of diseases where neutrophils are implicated.

Resume La granulomatose avec polyangeite (GPA, Wegener) est une vascularite systemique des vaisseaux de petit calibre (arteres, arterioles et capillaires) qui affecte particulierement les reins et les poumons. Dans cette pathologie auto-immune, la proteinase 3 (PR3) produite par les neutrophiles, est la cible des anti-neutrophil cytoplasmic antibodies (ANCA). Les travaux recents de notre equipe ont permis de decrypter comment la PR3 interfere avec les mecanismes de resolution de l’inflammation et deregule le systeme immunitaire. En conditions normales, l’elimination des neutrophiles actives enclenche un processus anti-inflammatoire et pro-resolutif. Chez les patients GPA, la phagocytose des neutrophiles apoptotiques exprimant PR3 par les macrophages est associee a une liberation massive de mediateurs pro-inflammatoires par ces derniers, en particulier l’interleukine-1, generant un microenvironnement pro-inflammatoire favorable a l’auto-immunite. Cette deregulation immunitaire s’accompagne d’une activation des cellules dendritiques plasmacytoides et d’une polarisation des lymphocytes T helper (Th)2 et Th9 et Th17. Ces donnees recentes mettent en lumiere le double role de la PR3, proteine auto-antigenique et auto-inflammatoire, ouvrant ainsi de potentielles pistes therapeutiques.

Neutrophils are critical in the defense against bacterial and fungal pathogens, and they also modulate the inflammatory process. The areas where neutrophils are studied have expanded from the restricted field of antibacterial defense to the modulation of inflammation and finally, to fine-tuning immune responses. As a result, recent studies have shown that neutrophils are implicated in several systemic autoimmune diseases, although exactly how neutrophils contribute to these diseases and the molecular mechanisms responsible are still under investigation. In a group of autoimmune vasculitides associated with anti-neutrophil cytoplasmic antibodies (AAVs), granulomatosis with polyangiitis (GPA) illustrates the concept that autoimmunity can develop against one specific neutrophil protein, namely, proteinase 3 (PR3), one of the four serine protease homologs contained within azurophilic granules. In this review, we will focus on recent molecular analyses combined with functional studies that provide clear evidence that the pathogenic properties of PR3 are not only a result of its enzymatic activity but also mediated by a particular structural element—the hydrophobic patch—which facilitates associations with various proteins and lipids and permits anchorage into the plasma membrane. Furthermore, these unique structural and functional characteristics of PR3 might be key contributors to the systemic inflammation and to the immune dysregulation observed in GPA.

Microbial infection elicits robust immune responses that initially depend on polymorphonuclear neutrophils (PMN), which ingest and kill invading bacteria. However, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) remain viable within PMN and prompt their lysis with concomitant release of damage-associated molecular patterns and proinflammatory cytokines that promote additional inflammation. Here, we show that ultrapure human PMN (>99.8% pure) that have ingested CA-MRSA released interleukin (IL)-1β but not IL-18. The ingested CA-MRSA needed to be viable, and phagocytosis alone was insufficient to stimulate IL-1β secretion from PMN fed CA-MRSA. In contrast to PMN response to the canonical NLRP3 inflammasome agonist nigericin, IL-1β secretion by PMN fed CA-MRSA occurred independently of NLRP3 inflammasome or caspase-1 activation and required instead active receptor-interacting protein kinase 3 (RIPK3) but not RIPK1. Furthermore, inhibition of neutrophil serine proteases blocked pro-IL-1β cleavage in PMN fed CA-MRSA. Taken together, our data suggest that with respect to secretion of IL-1β and IL-18, PMN differ from human macrophages and exhibit agonist-specific responses. After phagocytosis of CA-MRSA, human PMN secreted IL-1β through a previously unrecognized mechanism dependent on RIPK3 and serine proteases but independent of canonical NLRP3 inflammasome and caspase-1 activation.

Introduction La crise renale sclerodermique (CRS) est une complication vasculaire grave de la sclerodermie systemique, affectant 5 a 13 % des patients sclerodermiques. Les mecanismes mis en jeu au cours de la CRS sont imparfaitement compris, a l’exception de l’activation du systeme renine angiotensine aldosterone (SRAA) qui semble occuper un role central. Le complexe mTOR est implique dans differents phenomenes cellulaires, en particulier la croissance et la proliferation cellulaire. Les lesions histologiques vasculaires observees au cours de la CRS se caracterisant par une proliferation et une hyperplasie endotheliale, nous avons emis l’hypothese d’une implication de la voie mTOR au cours de la CRS. Materiels et methodes L’activation de la voie mTOR etait etudiee par immunomarquage de p-S6RP sur des biopsies renales de CRS et differents controles (reins sains, nephroangioscleroses et hypertension arterielle maligne). Le serum de patients ayant eu une CRS et des controles sains etait ensuite separe sur colonnes en immunoglobulines G (IgG) d’une part et serum deplete en IgG d’autre part. Nous avons evalue l’effet des differentes fractions de serums in vitro sur de cellules endotheliales immortalisees, les HMEC-1. L’activation de la voie mTOR a ete etudiee par quantification de la phosphorylation de la proteine S6RP et AKT en western blot. La croissance et proliferation cellulaire des HMEC-1 etait ensuite analysee en temps reel dans differentes conditions par technique xCELLigence. Enfin, nous avons evalue l’impact de l’angiotensine II sur l’activation de la voie mTOR et la proliferation des HMEC-1. Resultats L’etude en immunofluorescence a mis en evidence une activation de la voie mTOR au niveau de l’endothelium vasculaire chez la totalite des CRS (n = 7) et des HTA malignes (n = 4), alors qu’elle etait absente sur les reins sains (n = 5) et de nephroangiosclerose (n = 3). La voie mTOR etait activee dans un plus grand nombre de coupes vasculaires des biopsies de CRS (36 %) que d’HTA malignes (16 %). L’activation de la voie mTOR evaluee par western blot etait en revanche similaire apres incubation des HMEC-1 avec les IgG purifiees de patients avec CRS (n = 8) ou de controles sains (n = 7), suggerant l’absence d’effet « activateur » de la voie mTOR par les IgG de patients avec CRS. Le serum deplete en IgG n’induisait pas non plus d’activation de la voie mTOR differente chez les patients avec CRS et les sujets sains. Nous avons ensuite analyse la croissance et la proliferation cellulaire. Le serum deplete en IgG des patients avec CRS (n = 7) stimulait significativement plus la croissance et la proliferation des HMEC-1 que le serum deplete en IgG de sujets sains (n = 8). A l’inverse, aucune difference n’etait observee avec les IgG purifiees des malades ou des controles. Enfin, compte-tenu de l’efficacite des inhibiteurs de l’enzyme de conversion au cours de la CRS et du role de l’angiotensine II au cours de l’HTA maligne, nous avons evoque un role possible de l’angiotensine II sur l’activation de la voie mTOR au cours de la CRS. Par western blot, l’angiotensine II stimulait in vitro l’activation de la voie mTOR, mais pas la croissance et la proliferation des cellules endotheliales. Conclusion Nous avons mis en evidence une activation de la voie mTOR au niveau de l’endothelium vasculaire au cours de la CRS, qui semble etre independante des IgG. Cette activation pourrait etre induite par la production d’angiotensine II a la phase aigue de la CRS. La proliferation endotheliale observee sur les biopsies renales pourrait quant a elle etre induite par la production de facteurs de croissance presents dans le serum des patients, mais non encore caracterises. Ces elements suggerent ainsi un mecanisme au moins en deux etapes au cours de la crise renale, avec une activation precoce de la voie mTOR suivie d’un remodelage endothelial induit par des facteurs de croissance circulants.

The life span of a neutrophil is a tightly regulated process as extended survival is beneficial for pathogen elimination and cell death necessary to prevent cytotoxic content release from activated neutrophils at the inflammatory site. Therefore, the control between survival and death must be a dynamic process. We have previously described that proliferating cell nuclear antigen (PCNA) which is known as a nuclear protein pivotal in DNA synthesis, is a key element in controlling neutrophil survival through its association with procaspases. Contrary to the dogma which asserted that PCNA has a strictly nuclear function, in mature neutrophils, PCNA is present exclusively within the cytosol due to its nuclear export at the end of the granulocytic differentiation. More recent studies are consistent with the notion that the cytosolic scaffold of PCNA is aimed at modulating neutrophil fate rather than simply preventing death. Ultimately, targeting neutrophil survival might have important applications not just in the field of immunology and inflammation, but also in hematology and transfusion. The neutrophil emerges as a unique and powerful cellular model to unravel the basic mechanisms governing the cell cycle-independent functions of PCNA and should be considered as a leader of the pack.

Functional studies of human neutrophils and their transfusion for clinical purposes have been hampered by their short life span after isolation. Here, we demonstrate that neutrophil viability is maintained for 20 hours in culture media at 37°C under anoxic conditions with 3 mM glucose and 32 μg/mL dimethyloxalylglycine supplementation, as evidenced by stabilization of Mcl-1, proliferating cell nuclear antigen (PCNA), and pro-caspase-3. Notably, neutrophil morphology (nucleus shape and cell-surface markers) and functions (phagocytosis, degranulation, calcium release, chemotaxis, and reactive oxygen species production) were comparable to blood circulating neutrophils. The observed extension in neutrophil viability was reversed upon exposure to oxygen. Extending neutrophil life span allowed efficient transfection of plasmids (40% transfection efficiency) and short interfering RNA (interleukin-8, PCNA, and Bax), as a validation of effective and functional genetic manipulation of neutrophils both in vitro and in vivo. In vivo, transfusion of conditioned neutrophils in a neutropenic guinea pig model increased bacterial clearance of Shigella flexneri upon colonic infection, strongly suggesting that these conditioned neutrophils might be suitable for transfusion purposes. In summary, such conditioning of neutrophils in vitro should facilitate their study and offer new opportunities for genetic manipulation and therapeutic use.

Neutrophil-associated inflammation during Pseudomonas aeruginosa lung infection is a determinant of morbidity in cystic fibrosis (CF). Neutrophil apoptosis is a key factor in inflammation resolution and is controlled by cytosolic proliferating cell nuclear antigen (PCNA). p21/Waf1, a cyclin-dependent kinase inhibitor, is a partner of PCNA, and its mRNA is up-regulated in human neutrophils during LPS challenge. We show here that, after 7 days of persistent infection with P. aeruginosa, neutrophilic inflammation was more prominent in p21(-/-) compared with wild-type (WT) mice. Notably, no intrinsic defect in the phagocytosis of apoptotic cells by macrophages was found in p21(-/-) compared with WT mice. Inflammatory cell analysis in peritoneal lavages after zymosan-induced peritonitis showed a significantly increased number of neutrophils at 48 hours in p21(-/-) compared with WT mice. In vitro analysis was consistent with delayed neutrophil apoptosis in p21(-/-) compared with WT mice. Ectopic expression of p21/waf1 in neutrophil-differentiated PLB985 cells potentiated apoptosis and reversed the prosurvival effect of PCNA. In human neutrophils, p21 messenger RNA was induced by TNF-α, granulocyte colony-stimulating factor, and LPS. Neutrophils isolated from patients with CF showed enhanced survival, which was reduced after treatment with a carboxy-peptide derived from the sequence of p21/waf1. Notably, p21/waf1 was detected by immunohistochemistry in neutrophils within lungs from patients with CF. Our data reveal a novel role for p21/waf1 in the resolution of inflammation via its ability to control neutrophil apoptosis. This mechanism may be relevant in the neutrophil-dominated inflammation observed in CF and other chronic inflammatory lung conditions.

International audience; Granulomatosis with polyangiitis (GPA, Wegener granulomatosis) is a systemic autoimmune vasculitis that affects small arteries, arterioles, and capillaries, most notably in the kidneys and lungs. In this disease, proteinase-3 (PR3), produced by neutrophils, is targeted by antineutrophil cytoplasmic antibodies (ANCA). Recent work by our group has shown how PR3 impairs the resolution of inflammation and deregulates the immune system. Normally, the clearance of activated neutrophils triggers an anti-inflammatory, pro-resolution process. In patients with GPA, however, macrophages phagocytose apoptotic neutrophils then release massive amounts of pro-inflammatory mediators, notably interleukin-1, thereby generating a pro-inflammatory microenvironment conducive to autoimmunity. This deregulation of immune processes is accompanied with activation of plasmacytoid dendritic cells and with polarization of T-helper-2 (Th2), Th9, and Th17 cells. These recent data highlight the dual role of PR3, both auto-antigenic and auto-inflammatory, thus potentially opening up new therapeutic avenues.

International audience; Neutrophils are critically involved in host defence and they also modulate the inflammatory process. Turning the inflammatory response towards a resolutive outcome requires a dialogue between apoptotic neutrophils and proresolving macrophages through complex key molecular interactions controlling efferocytosis, anti-inflammatory reprogramming and ultimately immune regulation. In this review, we will first focus on recent molecular analyses aiming at characterizing the role of proteins expressed on apoptotic neutrophils and their cognate partners expressed on macrophages in the resolution of inflammation. These will include chemokine receptors and their ligands and annexin A1 and its receptor FPR2. We will next depict how the structural and enzymatic properties of proteinase 3 (PR3), the autoantigen in vasculitis, allow its expression on apoptotic neutrophils, which in turn affects efferocytosis and immune response associated with the clearance of apoptotic cells. This example illustrates that the fate of apoptotic neutrophils directly influences the resolution of inflammation and immune responses thereby potentially contributing to systemic and nonresolving inflammation as well as autoimmunity.

finity chromatography purification method combined with a simple kinase assay to search for potential pharmacological inhibitors, and this led to the discovery of roscovitine in Roscoff [4] . This molecule has been used extensively as a pharmacological tool to investigate the cell cycle, synchronize cells, and trigger cell cycle arrest or apoptosis, in order to evaluate its effects on numerous diseases ranging from cancers, viral infections, or neurodegeneration to polycystic kidney disease. While originally roscovitine was believed to exert its effects mainly on proliferating cells, Adriano Rossi and his colleagues (University of Edinburgh) reported that roscovitine also affected neutrophils, key cells in innate immunity deprived of proliferative capacities [5–10] . They discovered that roscovitine could trigger apoptosis of neutrophils, thereby favoring their phagocytosis by macrophages to promote the resolution of inflammation [11] . Notably, this activity was due to the inhibition of CDK7 and CDK9 involved in the regulation of RNA transcription [12] . These observations opened novel perspectives in the field of anti-inflammatory drugs and especially in chronic lung inflammation like that observed in CF patients. CF is indeed a complex genetic disease [13] that involves the mutation of the chloride channel CFTR gene, where the deletion of F508 is the most frequent mutation. Discoveries can take unpredictable paths! In a review presented in the current issue of the Journal of Innate Immunity , Meijer et al. [1] describe the rationale for evaluating roscovitine for the treatment of cystic fibrosis (CF) patients chronically infected with Pseudomonas aeruginosa . Roscovitine is a low-molecular-weight inhibitor of cyclin-dependent kinase (CDK) discovered over 20 years ago during studies on the regulation of cell division using a rather unlikely research subject, starfish oocytes [2] . Marine invertebrate oocytes and eggs have been used for decades to investigate cellular and molecular mechanisms involved in the regulation of the cell division cycle as these cells have a natural break at specific stages in the cell cycle [3] . In parallel to Xenopus oocytes and genetic models such as yeast and Drosophila , they have allowed the identification of the CDK1/cyclin B protein kinase as the major regulator in G2/M cell cycle transition. In fact, this discovery eventually led to the awarding of the Nobel Prize in Physiology or Medicine to Paul Nurse, Tim Hunt, and Leland H. Hartwell in 2001. CDK1/cyclin B is the archetype of CDKs that were found not only to be major players in all steps of the cell cycle but also to display other functions including a role in the central nervous system (CDK5/p25). Given that active CDK1/cyclin B is present in huge quantities in starfish M-phase oocytes, the group of Laurent Meijer at the CNRS (France) developed an afPublished online: April 26, 2016 Journal of Innate Immunity

Objectives Takayasu arteritis (TA) and GCA are large-vessel vasculitides characterized by vascular remodelling involving endothelial cells (ECs) and vascular smooth muscle cells. Mammalian target of rapamycin (mTOR) pathway has been involved in vascular remodelling. We hypothesized that the mTOR pathway was involved in the pathogenesis of large-vessel vasculitis. Methods We used IF analysis on aortic and temporal artery biopsies from patients with TA and GCA to assess the involvement of the mTOR pathway and searched for antibodies targeting ECs in serum by IIF and cellular ELISA. We evaluated in vitro the effect of purified IgG from patients on mTOR pathway activation and cell proliferation. Results IF analyses on tissues revealed that both mTORC1 and mTORC2 are activated specifically in ECs from TA patients but not in ECs from GCA patients and healthy controls (HCs). Using IIF and ELISA, we observed higher levels of antibodies binding to ECs in TA patients compared with GCA patients and HCs. Using western blot, we demonstrated that purified IgG from TA patients caused mTORC1 activation in ECs, whereas this effect was not observed with purified IgG from GCA patients or HCs. Purified IgG from TA patients induced a significant EC proliferation compared with to GCA and HC IgG, and this effect was decreased after EC exposure with sirolimus, a specific mTOR inhibitor and PI3K inhibitor. Conclusion Our results suggest that antibodies targeting ECs drive endothelial remodelling in TA through activation of the mTOR pathway, but not in GCA. Inhibition of the mTOR pathway could represent a therapeutic option in TA.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides are a heterogeneous group of diseases corresponding to necrotising inflammation of small vessels with a wide range of clinical presentations. At least two of the diseases are believed to exhibit a common ground of pathophysiological mechanisms. These are granulomatosis with polyangiitis (GPA, formerly known as Wegener’s granulomatosis) and microscopic polyangiitis (MPA). ANCA directed against proteinase 3 (PR3) are preferentially associated with GPA, and anti-myeloperoxidase (MPO) ANCA are associated mainly with MPA and eosinophilic GPA (formerly known as Churg-Strauss syndrome). Anti-MPO and anti-PR3 antibodies can activate neutrophils in vitro. In vivo data are available for humans and mice on the pathogenicity of anti-MPO but it is more controversial for PR3-ANCA. A recent genome-wide association study of patients with ANCA-associated vasculitides confirmed the genetic contribution to the pathogenesis of these conditions, with significant association of PR3-ANCA and human leukocyte antigen-DP and the genes encoding α1-antitrypsin and PR3. MPO-ANCA were significantly associated with human leukocyte antigen-DQ. Thus, recent results from epidemiological studies, genome-wide association study and therapeutic trials have suggested that these entities are, in fact, distinct. We have summarised these results and discuss the idea that these two entities should be studied separately as the nature of the two auto-antigens suggests at a molecular level despite shared ANCA involvement.

Resume Les vascularites a anticorps anti-cytoplasme de polynucleaire neutrophile (ANCA) regroupent trois entites distinctes : la granulomatose avec polyangeite (GPA) anciennement maladie de Wegener, la polyangeite microscopique (PAM) et la granulomatose eosinophilique avec polyangeite (GEPA) (anciennement syndrome de Churg et Strauss). Ces trois pathologies ont comme point commun d’etre des vascularites impliquant des vaisseaux de petit calibre et d’etre associees a une auto-immunite dirigee contre des proteines contenues dans les granules cytoplasmiques des neutrophiles. Dans cet article, nous avons resume les elements cles qui interviennent dans la physiopathologie de ces maladies et souligne les nouveaux concepts qui ont recemment emerge. De multiples travaux portant sur la physiopathologie de ces maladies se sont concentres sur le role eventuellement pathogene des ANCA dans l’activation des neutrophiles. Cependant, la distinction entre GPA et PAM n’etait pas clairement enoncee et les schemas physiopathologiques proposes insistaient principalement sur les mecanismes communs a ces pathologies. Il existe de reelles differences entre GPA et PAM, probablement liees au fait que les proteines autoantigenes cibles des ANCA, la proteinase 3 (PR3) et la myeloperoxydase (MPO), respectivement, ont des fonctions tres differentes dans le neutrophile mais egalement dans la regulation de la reaction inflammatoire. En particulier, l’existence de granulome associee a une auto-immunite specifique dirigee contre la proteinase 3 pourrait resulter de mecanismes propres a la GPA, comme sembleraient le montrer des travaux recents de notre equipe.

Objective The pathophysiology of giant cell arteritis (GCA) and the mechanisms underlying vascular remodeling, are poorly understood. We aimed to compare vascular smooth muscle cells (VSMCs) from patients with GCA and controls by a proteomic and gene expression profile approach and to identify the signaling pathways involved in proliferation. Methods VSMCs were cultured from temporal artery biopsies (TABs) from patients with biopsy-proven GCA (TAB+-GCA), biopsy-negative GCA (TAB−-GCA), and diagnosis other than GCA (GCA-control). VSMCs from normal human aorta (HAoSMC) were used as controls. 2D-differential in-gel electrophoresis and Affymetrix chips were used to compare proteomes and gene expression profiles of VSMCs. Proliferation was assessed by BrdU incorporation assay. TAB+-GCA and GCA-control TABs underwent immunohistochemistry staining for endothelin-1 (ET-1) and receptors ETAR and ETBR. Results We identified 16, 30 and 2 protein spots differentially expressed between TAB+-GCA and GCA-control VSMCs, TAB+-GCA and TAB−-GCA VSMCs and TAB−-GCA and GCA-control VSMCs, respectively (fold change ≥ 1.5 and p ≤ 0.05). Among the 153 proteins differentially expressed between TAB+-GCA and HAoSMC VSMCs, many were linked with ET-1. Genes differentially expressed between TAB+-GCA and GCA-control VSMCs were involved in proliferation. ET-1 was identified as a link between genes of interest. Proliferation was reduced for TAB+-GCA VSMCs on treatment with the endothelin antagonist macitentan and its active metabolite. Patients showing transmural expression of ET-1 in temporal artery lesions received a significantly higher glucocorticoid daily dose after 6-month follow-up. Conclusion Inhibiting the proliferation with macitentan, combined with glucocorticoids, might be a promising therapeutic approach for patients with GCA.

Cytosolic proliferating cell nuclear antigen (PCNA), a scaffolding protein involved in DNA replication, has been described as a key element in survival of mature neutrophil granulocytes, which are non-proliferating cells. Herein, we demonstrated an active export of PCNA involved in cell survival and chemotherapy resistance. Notably, daunorubicin-resistant HL-60 cells (HL-60R) have a prominent cytosolic PCNA localization due to increased nuclear export compared to daunorubicin-sensitive HL-60 cells (HL-60S). By interacting with nicotinamide phosphoribosyltransferase (NAMPT), a protein involved in NAD biosynthesis, PCNA coordinates glycolysis and survival, especially in HL-60R cells. These cells showed a dramatic increase in intracellular NAD+ concentration as well as glycolysis including increased expression and activity of hexokinase 1 and increased lactate production. Furthermore, this functional activity of cytoplasmic PCNA was also demonstrated in patients with acute myeloid leukemia (AML). Our data uncover a novel pathway of nuclear export of PCNA that drives cell survival by increasing metabolism flux.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides are a heterogeneous group of diseases corresponding to necrotising inflammation of small vessels with a wide range of clinical presentations. At least two of the diseases are believed to exhibit a common ground of pathophysiological mechanisms. These are granulomatosis with polyangiitis (GPA, formerly known as Wegener's granulomatosis) and microscopic polyangiitis (MPA). ANCA directed against proteinase 3 (PR3) are preferentially associated with GPA, and anti-myeloperoxidase (MPO) ANCA are associated mainly with MPA and eosinophilic GPA (formerly known as Churg-Strauss syndrome). Anti-MPO and anti-PR3 antibodies can activate neutrophils in vitro. In vivo data are available for humans and mice on the pathogenicity of anti-MPO but it is more controversial for PR3-ANCA. A recent genome-wide association study of patients with ANCA-associated vasculitides confirmed the genetic contribution to the pathogenesis of these conditions, with significant association of PR3-ANCA and human leukocyte antigen-DP and the genes encoding α1-antitrypsin and PR3. MPO-ANCA were significantly associated with human leukocyte antigen-DQ. Thus, recent results from epidemiological studies, genome-wide association study and therapeutic trials have suggested that these entities are, in fact, distinct. We have summarised these results and discuss the idea that these two entities should be studied separately as the nature of the two auto-antigens suggests at a molecular level despite shared ANCA involvement.

ANCA-associated vasculitides comprise granulomatosis with polyangiitis (GPA) (formerly names Wegener's granulomatosis), Churg-Strauss syndrome (SCS) (which will be renamed GPA and eosinophilia) and microscopic polyangiitis (MPA). Immune cells (dendritic and non dendritic cells) and inflammatory cells (neutrophils, monocytes, macrophages) and resident cells (endothelial cells, fibroblasts) are implicated in the pathophysiology of ANCA-associated vasculitides. One of the targets of ANCA, myeloperoxydase, is only present in the azurophil granules of neutrophils, whereas the other target of these antibodies, proteinase 3, is also present at the internal face of cytoplasmic membrane of neutrophils, as well as at their surface. Anti-myeloperoxydase ANCA are pathogenicin vitroandin vivo, whereas the pathogenicity of anti-proteinase 3 ANCA has only been demonstrated in vitro and recent studies suggest a pathogenic role of ANCA anti-PR3 in mouse model. Two phenotypes of GPA can be distinguished: a granulomatous form, localized to the respiratory tract with Th1 immune response features, and a vasculitic form with Th2 immune response features. Recently, an increase in TH17 lymphocytes at the acute phase and a defect in T regulatory cells at the chronic phase have been identified in GPA. The role of B-lymphocytes in the pathogenesis of ANCA-associated vasculitides is now well documented by the effectiveness of rituximab in the treatment of this condition.

Proteinase 3 (PR3) is a myeloid serine protease expressed in neutrophils, monocytes, and macrophages. PR3 has a number of well-characterized proinflammatory functions, including cleaving and activating chemokines and controlling cell survival and proliferation. When presented on the surface of apoptotic neutrophils, PR3 can disrupt the normal anti-inflammatory reprogramming of macrophages following the phagocytosis of apoptotic cells. To better understand the function of PR3 in vivo, we generated a human PR3 transgenic mouse (hPR3Tg). During zymosan-induced peritonitis, hPR3Tg displayed an increased accumulation of neutrophils within the peritoneal cavity compared with wild-type control mice, with no difference in the recruitment of macrophages or B or T lymphocytes. Mice were also subjected to cecum ligation and puncture, a model used to induce peritoneal inflammation through infection. hPR3Tg displayed decreased survival rates in acute sepsis, associated with increased neutrophil extravasation. The decreased survival and increased neutrophil accumulation were associated with the cleavage of annexin A1, a powerful anti-inflammatory protein known to facilitate the resolution of inflammation. Additionally, neutrophils from hPR3Tg displayed enhanced survival during apoptosis compared with controls, and this may also contribute to the increased accumulation observed during the later stages of inflammation. Taken together, our data suggest that human PR3 plays a proinflammatory role during acute inflammatory responses by affecting neutrophil accumulation, survival, and the resolution of inflammation.

International audience; Proteinase 3 (PR3), the autoantigen in granulomatosis with polyangiitis, is expressed at the plasma membrane of resting neutrophils, and this membrane expression increases during both activation and apoptosis. Using surface plasmon resonance and protein-lipid overlay assays, this study demonstrates that PR3 is a phosphatidylserine-binding protein and this interaction is dependent on the hydrophobic patch responsible for membrane anchorage. Molecular simulations suggest that PR3 interacts with phosphatidylserine via a small number of amino acids, which engage in long lasting interactions with the lipid heads. As phosphatidylserine is a major component of microvesicles (MVs), this study also examined the consequences of this interaction on MV production and function. PR3-expressing cells produced significantly fewer MVs during both activation and apoptosis, and this reduction was dependent on the ability of PR3 to associate with the membrane as mutating the hydrophobic patch restored MV production. Functionally, activation-evoked MVs from PR3-expressing cells induced a significantly larger respiratory burst in human neutrophils compared with control MVs. Conversely, MVs generated during apoptosis inhibited the basal respiratory burst in human neutrophils, and those generated from PR3-expressing cells hampered this inhibition. Given that membrane expression of PR3 is increased in patients with granulomatosis with polyangiitis, MVs generated from neutrophils expressing membrane PR3 may potentiate oxidative damage of endothelial cells and promote the systemic inflammation observed in this disease.

Neutrophils are deprived of proliferative capacity and have a tightly controlled lifespan to avoid their persistence at the site of injury. We have recently described that the proliferating cell nuclear antigen (PCNA), a nuclear factor involved in DNA replication and repair of proliferating cells, is a key regulator of neutrophil survival. In neutrophils, PCNA was localized exclusively in the cytoplasm due to its nuclear-to-cytoplasmic relocalization during granulocytic differentiation. We showed here that leptomycin B, an inhibitor of the chromosome region maintenance 1 (CRM1) exportin, inhibited PCNA relocalization during granulocytic differentiation of HL-60 and NB4 promyelocytic cell lines and of human CD34(+) primary cells. Using enhanced green fluorescent protein fusion constructs, we have demonstrated that PCNA relocalization involved a nuclear export signal (NES) located from Ile-11 to Ile-23 in the PCNA sequence. However, this NES, located at the inner face of the PCNA trimer, was not functional in wild-type PCNA, but instead, was fully active and leptomycin B-sensitive in the monomeric PCNAY114A mutant. To test whether a defect in PCNA cytoplasmic relocalization would affect its antiapoptotic activity in mature neutrophils, a chimeric PCNA fused with the SV40 nuclear localization sequence (NLS) was generated to preclude its cytoplasmic localization. As expected, neutrophil-differentiated PLB985 cells expressing ectopic SV40NLS-PCNA had an increased nuclear PCNA as compared with cells expressing wild-type PCNA. Accordingly, the nuclear PCNA mutant did not show any antiapoptotic activity as compared with wild-type PCNA. Nuclear-to-cytoplasmic relocalization that occurred during myeloid differentiation is essential for PCNA antiapoptotic activity in mature neutrophils and is dependent on the newly identified monomerization-dependent PCNA NES.

Proteinase 3 (PR3) is the target of anti-neutrophil cytoplasm Abs in granulomatosis with polyangiitis, a form of systemic vasculitis. Upon neutrophil apoptosis, PR3 is coexternalized with phosphatidylserine and impaired macrophage phagocytosis. Calreticulin (CRT), a protein involved in apoptotic cell recognition, was found to be a new PR3 partner coexpressed with PR3 on the neutrophil plasma membrane during apoptosis, but not after degranulation. The association between PR3 and CRT was demonstrated in neutrophils by confocal microscopy and coimmunoprecipitation. Evidence for a direct interaction between PR3 and the globular domain of CRT, but not with its P domain, was provided by surface plasmon resonance spectroscopy. Phagocytosis of apoptotic neutrophils from healthy donors was decreased after blocking lipoprotein receptor-related protein (LRP), a CRT receptor on macrophages. In contrast, neutrophils from patients with granulomatosis with polyangiitis expressing high membrane PR3 levels showed a lower rate of phagocytosis than those from healthy controls not affected by anti-LRP, suggesting that the LRP-CRT pathway was disturbed by PR3-CRT association. Moreover, phagocytosis of apoptotic PR3-expressing cells potentiated proinflammatory cytokine in vitro by human monocyte-derived macrophages and in vivo by resident murine peritoneal macrophages, and diverted the anti-inflammatory response triggered by the phagocytosis of apoptotic cells after LPS challenge in thioglycolate-elicited murine macrophages. Therefore, membrane PR3 expressed on apoptotic neutrophils might amplify inflammation and promote autoimmunity by affecting the anti-inflammatory “reprogramming” of macrophages.

International audience; (R)-Roscovitine, a pharmacological inhibitor of kinases, is currently in phase II clinical trial as a drug candidate for the treatment of cancers, Cushing's disease and rheumatoid arthritis. We here review the data that support the investigation of (R)-roscovitine as a potential therapeutic agent for the treatment of cystic fibrosis (CF). (R)-Roscovitine displays four independent properties that may favorably combine against CF: (1) it partially protects F508del-CFTR from proteolytic degradation and favors its trafficking to the plasma membrane; (2) by increasing membrane targeting of the TRPC6 ion channel, it rescues acidification in phagolysosomes of CF alveolar macrophages (which show abnormally high pH) and consequently restores their bactericidal activity; (3) its effects on neutrophils (induction of apoptosis), eosinophils (inhibition of degranulation/induction of apoptosis) and lymphocytes (modification of the Th17/Treg balance in favor of the differentiation of anti-inflammatory lymphocytes and reduced production of various interleukins, notably IL-17A) contribute to the resolution of inflammation and restoration of innate immunity, and (4) roscovitine displays analgesic properties in animal pain models. The fact that (R)-roscovitine has undergone extensive preclinical safety/pharmacology studies, and phase I and II clinical trials in cancer patients, encourages its repurposing as a CF drug candidate.

Recently, unexpected biological features of polymorphonuclear neutrophils have been revealed. In addition to their pivotal role in the defence against pathogens, neutrophils display a high degree of plasticity and contribute to control of adaptive immune responses. An emerging aspect of neutrophils is their ability to modulate their survival in response to both intrinsic and extrinsic factors. This review focuses on recent advances that have uncovered proliferating cell nuclear antigen (PCNA) and other cell cycle regulatory proteins as novel players regulating neutrophil survival. A better understanding of the mechanisms involved in neutrophil fate might pave the way for the identification of new anti-inflammatory molecules.

Cytosolic proliferating cell nuclear antigen (PCNA) binds to procaspases and protects human neutrophils from apoptosis., Neutrophil apoptosis is a highly regulated process essential for inflammation resolution, the molecular mechanisms of which are only partially elucidated. In this study, we describe a survival pathway controlled by proliferating cell nuclear antigen (PCNA), a nuclear factor involved in DNA replication and repairing of proliferating cells. We show that mature neutrophils, despite their inability to proliferate, express high levels of PCNA exclusively in their cytosol and constitutively associated with procaspases, presumably to prevent their activation. Notably, cytosolic PCNA abundance decreased during apoptosis, and increased during in vitro and in vivo exposure to the survival factor granulocyte colony-stimulating factor (G-CSF). Peptides derived from the cyclin-dependent kinase inhibitor p21, which compete with procaspases to bind PCNA, triggered neutrophil apoptosis thus demonstrating that specific modification of PCNA protein interactions affects neutrophil survival. Furthermore, PCNA overexpression rendered neutrophil-differentiated PLB985 myeloid cells significantly more resistant to TNF-related apoptosis-inducing ligand– or gliotoxin-induced apoptosis. Conversely, a decrease in PCNA expression after PCNA small interfering RNA transfection sensitized these cells to apoptosis. Finally, a mutation in the PCNA interdomain-connecting loop, the binding site for many partners, significantly decreased the PCNA-mediated antiapoptotic effect. These results identify PCNA as a regulator of neutrophil lifespan, thereby highlighting a novel target to potentially modulate pathological inflammation.

Proteinase 3 and neutrophil elastase are serine proteinases of the polymorphonuclear neutrophils, which are considered to have both similar localization and ligand specificity because of their high sequence similarity. However, recent studies indicate that they might have different and yet complementary physiologic roles. Specifically, proteinase 3 has intracellular specific protein substrates resulting in its involvement in the regulation of intracellular functions such as proliferation or apoptosis. It behaves as a peripheral membrane protein and its membrane expression is a risk factor in chronic inflammatory diseases. Moreover, in contrast to human neutrophil elastase, proteinase 3 is the preferred target antigen in Wegener's granulomatosis, a particular type of vasculitis. We review the structural basis for the different ligand specificities and membrane binding mechanisms of both enzymes, as well as the putative anti-neutrophil cytoplasm autoantibody epitopes on human neutrophil elastase 3. We also address the differences existing between murine and human enzymes, and their consequences with respect to the development of animal models for the study of human proteinase 3-related pathologies. By integrating the functional and the structural data, we assemble many pieces of a complicated puzzle to provide a new perspective on the structure-function relationship of human proteinase 3 and its interaction with membrane, partner proteins or cleavable substrates. Hence, precise and meticulous structural studies are essential tools for the rational design of specific proteinase 3 substrates or competitive ligands that modulate its activities.

Cystic fibrosis (CF) is a chronic inflammatory lung disease characterized by polymorphonuclear neutrophil (PMN)-dominated airway inflammation. Defective apoptosis might explain PMN persistence at these inflammation sites. We previously reported that in CF patients PMN underwent delayed apoptosis, which was not always related to their infectious state and independent of the type of CF transmembrane regulator (CFTR) mutation. To understand the role of infection and PMN apoptosis in CF, PMN apoptosis was investigated in CF parents who are obligate heterozygotes for the CFTR mutation but without chronic bacterial infection. They also demonstrated delayed PMN apoptosis compared with healthy controls, as assessed by annexin-V labeling and caspase-3 cleavage. Diamide, a direct thiol-oxidizing agent, potentiated PMN apoptosis in controls and CF patients, resulting in similar levels of constitutive and Fas-potentiated apoptosis. The cyclin-dependent kinase inhibitor roscovitine provided another approach to restore normal PMN apoptosis. However, the selective CFTR inhibitor CFTRInh172 did not affect PMN apoptosis in control subjects. Apparently, the dysregulation of CF PMN is not only a consequence of the chronic infectious state in CF children but might also be related to CF ‘intrinsic’ factors. Restoration of normal PMN apoptosis by cellular redox modulation or roscovitine opens new research avenues to decrease PMN-mediated inflammation in CF.

This review focuses on proteinase 3 (PR3), the preferred target of antineutrophil cytoplasmic antibodies (ANCAs) in Wegener's granulomatosis. Deciphering the molecular associations that PR3 can make with its cognate partners might help to understand its pathophysiological significance in Wegener's granulomatosis and the potential role of ANCA as modulator of PR3 functions.In neutrophils, PR3 is mainly localized within azurophilic granules but is also detected at the plasma membrane. Among PR3 partners (CD16, CD11b/CD18), CD177, a glycosylphosphatidylinositol (GPI)-anchored membrane protein is a potential receptor for PR3. In addition, PR3 can be externalized at the plasma membrane at a very early stage of neutrophil apoptosis, in the absence of degranulation. In these conditions, PR3 is associated with specific partners including phospholipidscramblase-1 and calreticulin. Interestingly, apoptosis-induced PR3 membrane expression significantly impaired macrophage phagocytosis. This new role of PR3 acting as a 'don't eat me signal' that delays neutrophil clearance might potentiate inflammation and autoimmunity.Since PR3 membrane expression seems to represent a key element in the inflammatory and autoimmunity process, elucidation of the molecular basis of PR3 interaction with the plasma membrane or with receptor proteins led to the possibility of targeted therapy.

Proteinase 3 (PR3) is a neutrophil-derived serine proteinase localized within cytoplasmic granules which can be released upon activation. PR3 is exposed at the neutrophil plasma membrane where it can mediate proinflammatory effects. Moreover, PR3 membrane expression is of special relevance in patients with Wegener's granulomatosis, a systemic vasculitis presenting anticytoplasmic neutrophil autoantibodies (ANCA) against PR3, which can bind to PR3 expressed at the surface of neutrophils and amplify their activation state. Therefore, it is of special relevance to unravel the molecular mechanisms governing its association with the membrane to be able to modulate it. To this end, we performed molecular dynamics (MD) simulations of PR3 with the implicit membrane model IMM1-GC to identify its interfacial binding site (IBS). Both the energies and structures resulting from the MD suggest that PR3 associates strongly with anionic membranes. We observe a unique IBS consisting of five basic (R177, R186A, R186B, K187, R222) and six hydrophobic (F165, F166, F224, L223, F184, W218) amino acids. The basic residues provide the driving force to orient PR3 at the membrane surface, so that the hydrophobic residues can anchor into the hydrocarbon region. Energy decomposition and in silico mutations show that only a few residues account for the membrane association. Similar calculations with HNE suggest a different membrane-binding mechanism. Our results agree with previous experimental observations and this work predicts, for the first time, the structural determinants of the binding of PR3 to membranes.

Proteinase 3 (PR3), a serine proteinase contained in neutrophil azurophilic granules, is considered a risk factor for vasculitides and rheumatoid arthritis when expressed on the outer leaflet of neutrophil plasma membrane and is the preferred target of antineutrophil cytoplasm autoantibodies (ANCA) in Wegener granulomatosis. ANCA binding to PR3 expressed at the surface of neutrophils activates them. Evidence is provided that neutrophil apoptosis induced significantly more membrane PR3 expression without degranulation (but no enhanced membrane CD35, CD66b, CD63, myeloperoxidase, or elastase expression). This observation was confirmed on cytoplasts, a model of granule-free neutrophils. We hypothesized that PR3 could interact with proteins involved in membrane flip-flop (eg, phospholipid scramblase 1 [PLSCR1]). PR3-PLSCR1 interaction in neutrophils was demonstrated by confocal microscopy and coimmunoprecipitation. In the RBL-2H3 rat mast-cell line stably transfected with PR3 or its inactive mutant (PR3S203A), PR3 externalization depended on PLSCR1, as shown by less PR3 externalization in the presence of rPLSCR1 siRNA, but independently of its serine-proteinase activity. Finally, apoptosis-externalized PR3 decreased the human macrophage-phagocytosis rate of apoptotic PR3 transfectants. Therefore, in addition to ANCA binding in vasculitis, the proinflammatory role of membrane PR3 expression may involve interference with macrophage clearance of apoptotic neutrophils.