Phagocyte NADPH oxidase restrains the inflammasome in ANCA-induced GN

Transcription factor Nrf2 activation regulates NETosis, endothelial injury, and kidney disease in myeloperoxidase-positive antineutrophil cytoplasmic antibody-associated vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease pathologically characterized by vascular necrosis with inflammation. During AAV development, activated neutrophils produce reactive oxygen species (ROS), leading to the aberrant formation of neutrophil extracellular traps (NETs) via NETosis and subsequent fibrinoid vascular necrosis. Nuclear factor-erythroid 2-related factor 2 (Nrf2) functions as an intracellular defense system to counteract oxidative stress by providing antioxidant properties. Herein, we explored the role of Nrf2 in the pathogenesis of AAV. The role and mechanism of Nrf2 in ANCA-stimulated neutrophils and subsequent endothelial injury were evaluated in vitro using Nrf2 genetic deletion and Nrf2 activator treatment. In corresponding in vivo studies, the role of Nrf2 in ANCA-transfer AAV and spontaneous AAV murine models was examined. Pharmacological activation of Nrf2 in vitro suppressed ANCA-induced NET formation via the inhibition of ROS. In contrast, NET formation was enhanced in Nrf2-deficient neutrophils. Furthermore, Nrf2 activation protected endothelial cells from ANC-induced NETs-mediated injury. In vivo, Nrf2 activation ameliorated glomerulonephritis in two AAV models by upregulating antioxidants and inhibiting ROS-mediated NETs. Furthermore, Nrf2 activation restrained the expansion of splenic immune cells, including T lymphocytes and limited the infiltration of Th17 cells into the kidney. In contrast, Nrf2 genetic deficiency exacerbated vasculitis in a spontaneous AAV model. Thus, the pathophysiological process in AAV may be downregulated by Nrf2 activation, potentially leading to a new therapeutic strategy by regulating NETosis.

The neutrophil: A key resourceful agent in immune‐mediated vasculitis

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.

CSF2-dependent monocyte education in the pathogenesis of ANCA-induced glomerulonephritis

Objectives

Myeloid cell activation by antineutrophil cytoplasmic antibody (ANCA) is pivotal for necrotising vasculitis, including necrotising crescentic glomerulonephritis (NCGN). In contrast to neutrophils, the contribution of classical monocyte (CM) and non-classical monocyte (NCM) remains poorly defined. We tested the hypothesis that CMs contribute to antineutrophil cytoplasmic antibody-associated vasculitis (AAV) and that colony-stimulating factor-2 (CSF2, granulocyte-macrophage colony-stimulating factor (GM-CSF)) is an important monocyte-directed disease modifier.

Methods

Myeloperoxidase (MPO)-immunised MPO^−/− mice were transplanted with haematopoietic cells from wild-type (WT) mice, C–C chemokine receptor 2 (CCR2)^−/− mice to abrogate CM, or transcription factor CCAAT–enhancer-binding protein beta (C/EBPβ)^−/− mice to reduce NCM, respectively. Monocytes were stimulated with CSF2, and CSF2 receptor subunit beta (CSF2rb)-deficient mice were used. Urinary monocytes and CSF2 were quantified and kidney Csf2 expression was analysed. CSF2-blocking antibody was used in the nephrotoxic nephritis (NTN) model.

Results

Compared with WT mice, CCR2^−/− chimeric mice showed reduced circulating CM and were protected from NCGN. C/EBPβ^−/− chimeric mice lacked NCM but developed NCGN similar to WT chimeric mice. Kidney and urinary CSF2 were upregulated in AAV mice. CSF2 increased the ability of ANCA-stimulated monocytes to generate interleukin-1β and to promote T_H17 effector cell polarisation. CSF2rb^−/− chimeric mice harboured reduced numbers of kidney T_H17 cells and were protected from NCGN. CSF2 neutralisation reduced renal damage in the NTN model. Finally, patients with active AAV displayed increased urinary CM numbers, CSF2 levels and expression of GM-CSF in infiltrating renal cells.

Conclusions

CMs but not NCMs are important for inducing kidney damage in AAV. CSF2 is a crucial pathological factor by modulating monocyte proinflammatory functions and thereby T_H17 cell polarisation.

The Role of Inflammasomes in Glomerulonephritis

The inflammasome is an immune multiprotein complex that activates pro-caspase 1 in response to inflammation-inducing stimuli and it leads to IL-1β and IL-18 proinflammatory cytokine production. NLRP1 and NLRP3 inflammasomes are the best characterized and they have been related to several autoimmune diseases. It is well known that the kidney expresses inflammasome genes, which can influence the development of some glomerulonephritis, such as lupus nephritis, ANCA glomerulonephritis, IgA nephropathy and anti-GBM nephropathy. Polymorphisms of these genes have also been described to play a role in autoimmune and kidney diseases. In this review, we describe the main characteristics, activation mechanisms, regulation and functions of the different inflammasomes. Moreover, we discuss the latest findings about the role of the inflammasome in several glomerulonephritis from three different points of view: in vitro, animal and human studies.

Genetic Background but Not Intestinal Microbiota After Co-Housing Determines Hyperoxaluria-Related Nephrocalcinosis in Common Inbred Mouse Strains

Calcium oxalate (CaOx) crystal formation, aggregation and growth is a common cause of kidney stone disease and nephrocalcinosis-related chronic kidney disease (CKD). Genetically modified mouse strains are frequently used as an experimental tool in this context but observed phenotypes may also relate to the genetic background or intestinal microbiota. We hypothesized that the genetic background or intestinal microbiota of mice determine CaOx crystal deposition and thus the outcome of nephrocalcinosis. Indeed, Casp1^-/-, Cybb^-/- or Casp1^-/-/Cybb^-/- knockout mice on a 129/C57BL/6J (B6J) background that were fed an oxalate-rich diet for 14 days did neither encounter intrarenal CaOx crystal deposits nor nephrocalcinosis-related CKD. To test our assumption, we fed C57BL/6N (B6N), 129, B6J and Balb/c mice an oxalate-rich diet for 14 days. Only B6N mice displayed CaOx crystal deposits and developed CKD associated with tubular injury, inflammation and interstitial fibrosis. Intrarenal mRNA expression profiling of 64 known nephrocalcinosis-related genes revealed that healthy B6N mice had lower mRNA levels of uromodulin (Umod) compared to the other three strains. Feeding an oxalate-rich diet caused an increase in uromodulin protein expression and CaOx crystal deposition in the kidney as well as in urinary uromodulin excretion in B6N mice but not 129, B6J and Balb/c mice. However, backcrossing 129 mice on a B6N background resulted in a gradual increase in CaOx crystal deposits from F2 to F7, of which all B6N/129 mice from the 7^th generation developed CaOx-related nephropathy similar to B6N mice. Co-housing experiments tested for a putative role of the intestinal microbiota but B6N co-housed with 129 mice or B6N/129 (3^rd and 6^th generation) mice did not affect nephrocalcinosis. In summary, genetic background but not the intestinal microbiome account for strain-specific crystal formation and, the levels of uromodulin secretion may contribute to this phenomenon. Our results imply that only littermate controls of the identical genetic background strain are appropriate when performing knockout mouse studies in this context, while co-housing is optional.

Neutrophil Gelatinase-Associated Lipocalin Protects from ANCA-Induced GN by Inhibiting TH17 Immunity

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is a diagnostic marker of intrinsic kidney injury produced by damaged renal cells and by neutrophils. ANCA-associated vasculitis features necrotizing crescentic GN (NCGN), and ANCA-activated neutrophils contribute to NCGN. Whether NGAL plays a mechanistic role in ANCA-associated vasculitis is unknown.

METHODS

We measured NGAL in patients with ANCA-associated vasculitis and mice with anti-myeloperoxidase (anti-MPO) antibody-induced NCGN. We compared kidney histology, neutrophil functions, T cell proliferation and polarization, renal infiltrating cells, and cytokines in wild-type and NGAL-deficient chimeric mice with anti-MPO antibody-induced NCGN. To assess the role of T_H17 immunity, we transplanted irradiated MPO-immunized MPO-deficient mice with bone marrow from either wild-type or NGAL-deficient mice; we also transplanted irradiated MPO-immunized MPO/IL-17A double-deficient mice with bone marrow from either IL-17A-deficient or NGAL/IL-17A double-deficient mice.

RESULTS

Mice and patients with active ANCA-associated vasculitis demonstrated strongly increased serum and urinary NGAL levels. ANCA-stimulated neutrophils released NGAL. Mice with NGAL-deficient bone marrow developed worsened MPO-ANCA-induced NCGN. Intrinsic neutrophil functions were similar in NGAL-deficient and wild-type neutrophils, whereas T cell immunity was increased in chimeric mice with NGAL-deficient neutrophils with more renal infiltrating T_H17 cells. NGAL-expressing neutrophils and CD3⁺ T cells were in close proximity in kidney and spleen. CD4⁺ T cells showed no intrinsic difference in proliferation and polarization in vitro, whereas iron siderophore-loaded NGAL suppressed T_H17 polarization. We found significantly attenuated NCGN in IL-17A-deficient chimeras compared with MPO-deficient mice receiving wild-type bone marrow, as well as in NGAL/IL-17A-deficient chimeras compared with NGAL-deficient chimeras.

CONCLUSIONS

Our findings support that bone marrow-derived, presumably neutrophil, NGAL protects from ANCA-induced NCGN by downregulating T_H17 immunity.

Therapeutic targeting of neutrophil exocytosis

Dysregulation of neutrophil activation causes disease in humans. Neither global inhibition of neutrophil functions nor neutrophil depletion provides safe and/or effective therapeutic approaches. The role of neutrophil granule exocytosis in multiple steps leading to recruitment and cell injury led each of our laboratories to develop molecular inhibitors that interfere with specific molecular regulators of secretion. This review summarizes neutrophil granule formation and contents, the role granule cargo plays in neutrophil functional responses and neutrophil-mediated diseases, and the mechanisms of granule release that provide the rationale for development of our exocytosis inhibitors. We present evidence for the inhibition of granule exocytosis in vitro and in vivo by those inhibitors and summarize animal data indicating that inhibition of neutrophil exocytosis is a viable therapeutic strategy.

Endothelium structure and function in kidney health and disease

The kidney harbours different types of endothelia, each with specific structural and functional characteristics. The glomerular endothelium, which is highly fenestrated and covered by a rich glycocalyx, participates in the sieving properties of the glomerular filtration barrier and in the maintenance of podocyte structure. The microvascular endothelium in peritubular capillaries, which is also fenestrated, transports reabsorbed components and participates in epithelial cell function. The endothelium of large and small vessels supports the renal vasculature. These renal endothelia are protected by regulators of thrombosis, inflammation and complement, but endothelial injury (for example, induced by toxins, antibodies, immune cells or inflammatory cytokines) or defects in factors that provide endothelial protection (for example, regulators of complement or angiogenesis) can lead to acute or chronic renal injury. Moreover, renal endothelial cells can transition towards a mesenchymal phenotype, favouring renal fibrosis and the development of chronic kidney disease. Thus, the renal endothelium is both a target and a driver of kidney and systemic cardiovascular complications. Emerging therapeutic strategies that target the renal endothelium may lead to improved outcomes for both rare and common renal diseases.

Inflammasomes and autoimmune and rheumatic diseases: A comprehensive review

Inflammasomes are a multi-protein platform forming a part of the innate immune system. Inflammasomes are at standby status and can be activated when needed. Inflammasome activation is an important mechanism for the production of active interleukin (IL)-1β and IL-18, which have important roles to instruct adaptive immunity. Active forms of inflammasomes trigger a series of inflammatory cascades and lead to the differentiation and polarization of naïve T cells and secretion of various cytokines, which can induce various kinds of autoimmune and rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), gout, Sjögren's syndrome, Behçet's disease, anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and IgA vasculitis (former Henoch-Schönlein purpura ). In this review, we summarize studies published on inflammasomes and review their roles in various autoimmune diseases. Understanding of the role of inflammasomes may facilitate the diagnosis of autoimmune diseases and the development of tailored therapies in the future.

The expression of NOD2, NLRP3 and NLRC5 and renal injury in anti-neutrophil cytoplasmic antibody-associated vasculitis

Background

Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are intracellular sensors of pathogens and molecules from damaged cells to regulate the inflammatory response in the innate immune system. Emerging evidences suggested a potential role of NLRs in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This study aimed to investigate the expression of nucleotide-binding oligomerization domain containing protein 2 (NOD2), NOD-like receptor family pyrin domain containing 3 (NLRP3) and NOD-like receptor family CARD domain containing 5 (NLRC5) in kidneys of AAV patients, and further explored their associations with clinical and pathological parameters.

Methods

Thirty-four AAV patients in active stage were recruited. Their renal specimens were processed with immunohistochemistry to assess the expression of three NLRs, and with double immunofluorescence to detect NLRs on intrinsic and infiltrating cells. Analysis of gene expression was also adopted in cultured human podocytes. The associations between expression of NLRs and clinicopathological parameters were analyzed.

Results

The expression of NOD2, NLRP3 and NLRC5 was significantly higher in kidneys from AAV patients than those from normal controls, minimal change disease or class IV lupus nephritis. These NLRs co-localized with podocytes and infiltrating inflammatory cells. The mean optical density of NOD2 in glomeruli was significantly higher in crescentic class than non-crescentic class, and correlated with levels of proteinuria and serum creatinine at renal biopsy. The mean optical density of NLRC5 in glomeruli was significantly higher in crescentic class than non-crescentic class, and correlated with proteinuria level, Birmingham Vasculitis Activity Score and the proportion of crescents in the renal specimen.

Conclusions

The expression of three NLRs was upregulated in kidneys of AAV patients. The expression of NOD2 and NLRC5 was associated with the severity of renal lesions in AAV.

Endothelium structure and function in kidney health and disease

The kidney harbours different types of endothelia, each with specific structural and functional characteristics. The glomerular endothelium, which is highly fenestrated and covered by a rich glycocalyx, participates in the sieving properties of the glomerular filtration barrier and in the maintenance of podocyte structure. The microvascular endothelium in peritubular capillaries, which is also fenestrated, transports reabsorbed components and participates in epithelial cell function. The endothelium of large and small vessels supports the renal vasculature. These renal endothelia are protected by regulators of thrombosis, inflammation and complement, but endothelial injury (for example, induced by toxins, antibodies, immune cells or inflammatory cytokines) or defects in factors that provide endothelial protection (for example, regulators of complement or angiogenesis) can lead to acute or chronic renal injury. Moreover, renal endothelial cells can transition towards a mesenchymal phenotype, favouring renal fibrosis and the development of chronic kidney disease. Thus, the renal endothelium is both a target and a driver of kidney and systemic cardiovascular complications. Emerging therapeutic strategies that target the renal endothelium may lead to improved outcomes for both rare and common renal diseases.

Thioredoxin-interacting protein deficiency ameliorates kidney inflammation and fibrosis in mice with unilateral ureteral obstruction

Thioredoxin-interacting protein (TXNIP) is associated with inflammation, tubulointerstitial fibrosis, and oxidative stress in diabetic kidney disease, yet the potential role of TXNIP in nondiabetic renal injury is not well known. This study aimed to investigate the effect of TXNIP on renal injury by creating a unilateral ureteral obstruction (UUO) model in TXNIP knockout (TKO) mice. We performed sham or UUO surgery in 8-week-old TXNIP KO male mice and age and sex-matched wild-type (WT) mice. Animals were killed at 3, 5, 7, or 14 days after surgery, and renal tissues were obtained for RNA, protein, and other analysis. Our results show that the expression of TXNIP was increased in a time-dependent manner in the ligated kidneys. TXNIP deletion reduced renal fibrosis, apoptosis, α-SMA, TGF-β1 and CTGF expression, and activation of Smad3, p38 MAPK, and ERK1/2 in UUO kidneys. We also found UUO-induced renal F4/80+ macrophage infiltration, MCP-1 expression and activation of NF-κB and NLRP3 inflammasome were attenuated in TKO mice. Furthermore, our study revealed that TXNIP deficiency inhibited the expression of 8-OHdG, heme oxygenase-1 (HO-1) and NADPH oxidase 4 (Nox4) in UUO kidney. In summary, our study suggests that TXNIP plays a key role in the renal inflammation and fibrosis induced by UUO. Inhibition of TXNIP may be a strategy to slow the progression of chronic kidney diseases.

How the phagocyte NADPH oxidase regulates innate immunity

The phagocyte NADPH oxidase is a multi subunit protein complex that generates reactive oxygen species at cell membranes and within phagosomes. It is essential for host defence as evidenced by the severe immunodeficiency syndrome caused by a loss of one of the subunits. This is known as chronic granulomatous disease (CGD). However, the phagocyte NADPH oxidase also has a key role to play in regulating immunity and it is notable that chronic granulomatous disease is also characterised by autoimmune and autoinflammatory manifestations. This is because reactive oxygen species play a role in regulating signalling through their ability to post-translationally modify amino acid residues such as cysteine and methionine. In this review, I will outline the major aspects of innate immunity that are regulated by the phagocyte NADPH oxidase, including control of transcription, autophagy, the inflammasome and type 1 interferon signalling.

Inflammasomes in the Kidney

Inflammasomes influence a diverse range of kidney disease, including acute and chronic kidney diseases, and those mediated by innate and adaptive immunity. Both IL-18 and in particular IL-1β are validated therapeutic targets in several kidney diseases. In addition to leukocyte-derived inflammasomes, renal tissue cells express functional inflammasome components. Furthermore, a range of endogenous substances that directly activate inflammasomes also mediate kidney injury. Many of the functional studies have focussed on the NLRP3 inflammasome, and there is also evidence for the involvement of other inflammasomes in some conditions. While, at least in some disease, the mechanistic details of the involvement of the inflammasome remain to be elucidated, therapies focussed on inflammasomes and their products have potential in treating kidney disease in the future.

The phagocyte respiratory burst: Historical perspectives and recent advances

When exposed to certain stimuli, phagocytes (including neutrophils, macrophages and eosinophils) undergo marked changes in the way they handle oxygen. Firstly, their rate of oxygen uptake increases greatly. This is accompanied by (i) the production of large amounts of superoxide and hydrogen peroxide and (ii) the metabolism of large quantities of glucose through the hexose monophosphate shunt. We now know that the oxygen used is not for respiration but for the production of powerful microbiocidal agents downstream of the initial production of superoxide. Concomitantly, glucose is oxidised through the hexose monophosphate shunt to re-generate the NADPH that has been consumed through the reduction of molecular oxygen to generate superoxide. This phagocyte respiratory burst is generated by an NADPH oxidase multi-protein complex that has a catalytic core consisting of membrane-bound gp91phox (CYBB) and p22phox (CYBA) sub-units and cytosolic components p47phox (NCF1), p67phox (NCF2) and p40phox (NCF4). Finally, another cytosolic component, the small G-protein Rac (Rac2 in neutrophils and Rac1 in macrophages) is also required for full activation. The importance of the complex in host defence is underlined by chronic granulomatous disease, a severe life-limiting immunodeficiency caused by mutations in the genes encoding the individual subunits. In this review, I will discuss the experimental evidence that underlies our knowledge of the respiratory burst, outlining how elegant biochemical analysis, coupled with study of patients deficient in the various subunits has helped elucidate the function of this essential part of innate immunity. I will also discuss some exciting recent studies that shed new light on how the abundance of the various components is controlled. Finally, I will explore the emerging role of reactive oxygen species such as superoxide and hydrogen peroxide in the pathogenesis of major human diseases including auto-inflammatory diseases.

Re-Examining Neutrophil Participation in GN

Significant advances in understanding the pathogenesis of GN have occurred in recent decades. Among those advances is the finding that both innate and adaptive immune cells contribute to the development of GN. Neutrophils were recognized as key contributors in early animal models of GN, at a time when the prevailing view considered neutrophils to function as nonspecific effector cells that die quickly after performing antimicrobial functions. However, advances over the past two decades have shown that neutrophil functions are more complex and sophisticated. Specifically, research has revealed that neutrophil survival is regulated by the inflammatory milieu and that neutrophils demonstrate plasticity, mediate microbial killing through previously unrecognized mechanisms, demonstrate transcriptional activity leading to the release of cytokines and chemokines, interact with and regulate cells of the innate and adaptive immune systems, and contribute to the resolution of inflammation. Therefore, neutrophil participation in glomerular diseases deserves re-evaluation. In this review, we describe advances in understanding classic neutrophil functions, review the expanded roles of neutrophils in innate and adaptive immune responses, and summarize current knowledge of neutrophil contributions to GN.

Of Inflammasomes and Alarmins: IL-1β and IL-1α in Kidney Disease

Kidney injury implies danger signaling and a response by the immune system. The inflammasome is a central danger recognition platform that triggers local and systemic inflammation. In immune cells, inflammasome activation causes the release of mature IL-1β and of the alarmin IL-1α Dying cells release IL-1α also, independently of the inflammasome. Both IL-1α and IL-1β ligate the same IL-1 receptor (IL-1R) that is present on nearly all cells inside and outside the kidney, further amplifying cytokine and chemokine release. Thus, the inflammasome-IL-1α/IL-β-IL-1R system is a central element of kidney inflammation and the systemic consequences. Seminal discoveries of recent years have expanded this central paradigm of inflammation. This review gives an overview of arising concepts of inflammasome and IL-1α/β regulation in renal cells and in experimental kidney disease models. There is a pipeline of compounds that can interfere with the inflammasome-IL-1α/IL-β-IL-1R system, ranging from recently described small molecule inhibitors of NLRP3, a component of the inflammasome complex, to regulatory agency-approved IL-1-neutralizing biologic drugs. Based on strong theoretic and experimental rationale, the potential therapeutic benefits of using such compounds to block the inflammasome-IL-1α/IL-β-IL-1R system in kidney disease should be further explored.

The role of monocytes in ANCA-associated vasculitides

The anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) are a heterogeneous group of diseases causing inflammation in small blood vessels and linked by the presence of circulating ANCA specific for proteinase 3 (PR3) or myeloperoxidase (MPO). These antigens are present both in the cytoplasmic granules and on the surface of neutrophils, and the effect of ANCA on neutrophil biology has been extensively studied. In contrast, less attention has been paid to the role of monocytes in AAV. These cells contain PR3 and MPO in lysosomes and can also express them at the cell surface. Monocytes respond to ANCA by producing pro-inflammatory and chemotactic cytokines, reactive-oxygen-species and by up-regulating CD14. Moreover, soluble and cell surface markers of monocyte activation are raised in AAV patients, suggesting an activated phenotype that may persist even during disease remission. The presence of monocyte-derived macrophages and giant cells within damaged renal and vascular tissue in AAV also attests to their role in pathogenesis. In particular, their presence in the tertiary lymphoid organ-like granulomas of AAV patients may generate an environment predisposed to maintaining autoimmunity. Here we discuss the evidence for a pathogenic role of monocytes in AAV, their role in granuloma formation and tissue damage, and their potential to both direct and maintain autoimmunity. ANCA-activation of monocytes may therefore provide an explanation for the relapsing-remitting course of disease and its links with infections. Monocytes may thus represent a promising target for the treatment of this group of life-threatening diseases.

Lessons from a double-transgenic neutrophil approach to induce antiproteinase 3 antibody-mediated vasculitis in mice

ANCA to either PR3 or MPO are found in patients with necrotizing vasculitis and glomerulonephritis. ANCA binding to their target antigens on neutrophils and subsequent neutrophil activation are pivotal disease mechanisms that lead to vascular inflammation and necrosis. ANCA interaction with PR3 is more complex than with MPO as the neutrophil-specific CD177 receptor is involved in PR3 surface expression and PR3-ANCA-induced neutrophil activation. Modeling human disease is important to clinical research. Highly successful mouse models of MPO-ANCA vasculitis exist; however, recapitulating PR3-ANCA vasculitis has not been successful. We generated double-transgenic (DT) mice that expressed human PR3 and CD177 under a myeloid-specific huMRP8 promoter in an attempt to model PR3-ANCA vasculitis. DT mice strongly expressed the human transgenes in and on murine neutrophils and bound murine and human anti-PR3 antibodies. Nevertheless, passive transfer of these antibodies into LPS-primed DT mice or immunization of C57BL/6 mice with human PR3 followed by irradiation and transplantation of DT bone marrow failed to induce glomerulonephritis. Further analyses revealed that anti-PR3 antibodies did not activate DT neutrophils as shown by superoxide generation. Moreover, we found that mice did not properly process human pro-PR3 into mature PR3 and, consequently, the signaling complex between PR3, CD177, and CD11b, which promotes neutrophil activation by anti-PR3 antibodies, failed to form. We conclude that important species differences in PR3 and CD177 exist between men and mice that prevented successful generation of a murine anti-PR3 antibody model.

Impaired phagocytosis and reactive oxygen species production in phagocytes is associated with systemic vasculitis

Background

Anti-neutrophil cytoplasmic antibodies associated vasculitides (AAV) is a group of autoimmune diseases, characterized by small vessel inflammation. Phagocytes such as neutrophils and monocytes are the main effector cells found around the inflamed vessel wall. Therefore, we wanted to investigate aspects of function and activation of these cells in patients with AAV.

Methods

Flow cytometry was used to evaluate: the expression of activation markers (CD11c, CD62L, CD177 and C5aR); the number of recently released neutrophils from bone marrow, defined as CD10^-D16^low cells in peripheral blood; and the capacity of peripheral blood monocytes and polymorphonuclear leukocytes (PMN) to produce reactive oxygen species and to phagocytose opsonized bacteria.

Results

AAV patients (n = 104) showed an increase of CD10^-CD16^low neutrophils and total PMN in peripheral blood, suggesting a combination of increased bone marrow release and prolonged survival. An increased percentage of AAV PMN expressed CD177 but no other signs of activation were seen. A decreased production of reactive oxygen species was observed in AAV phagocytes, which was associated with disease activity. Moreover, granulocytes from patients with microscopic polyangiitis showed lower oxidative burst capacity compared to patients with granulomatosis with polyangiitis or eosinophilic granulomatosis with polyangiitis. In addition, decreased phagocytosis capacity was seen in PMN and monocytes.

Conclusion

Our results indicate that phagocytes from AAV patients have impaired function, are easily mobilized from bone marrow but are not particularly activated. The association between low reactive oxygen species formation in PMN and disease severity is consistent with findings in other autoimmune diseases and might be considered as a risk factor.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-0994-1) contains supplementary material, which is available to authorized users.

Neutrophils in animal models of autoimmune disease

Neutrophils have traditionally been thought to play only a peripheral role in the genesis of many autoimmune and inflammatory diseases. However, recent studies in a variety of animal models suggest that these cells are central to the initiation and propagation of autoimmunity. The use of mouse models, which allow either deletion of neutrophils or the targeting of specific neutrophil functions, has revealed the many complex ways these cells contribute to autoimmune/inflammatory processes. This includes generation of self antigens through the process of NETosis, regulation of T-cell and dendritic cell activation, production of cytokines such as BAFF that stimulate self-reactive B-cells, as well as indirect effects on epithelial cell stability. In comparing the many different autoimmune models in which neutrophils have been examined, a number of common underlying themes emerge - such as a role for neutrophils in stimulating vascular permeability in arthritis, encephalitis and colitis. The use of animal models has also stimulated the development of new therapeutics that target neutrophil functions, such as NETosis, that may prove beneficial in human disease. This review will summarize neutrophil contributions in a number of murine autoimmune/inflammatory disease models.

Secondary amyloidosis in autoinflammatory diseases and the role of inflammation in renal damage

The release of proinflammatory cytokines during inflammation represents an attempt to respond to injury, but it may produce detrimental effects. The inflammasome is a large, multiprotein complex that drives proinflammatory cytokine production in response to infection and tissue injury; the best-characterized inflammasome is the nod-like receptor protein-3 (NLRP3). Once activated, inflammasome leads to the active form of caspase-1, the enzyme required for the maturation of interleukin-1beta. Additional mechanisms bringing to renal inflammatory, systemic diseases and fibrotic processes were recently reported, via the activation of the inflammasome that consists of NLRP3, apoptosis associated speck-like protein and caspase-1. Several manuscripts seem to identify NLRP3 inflammasome as a possible therapeutic target in the treatment of progressive chronic kidney disease. Serum amyloid A (SAA), as acute-phase protein with also proinflammatory properties, has been shown to induce the secretion of cathepsin B and inflammasome components from human macrophages. SAA is a well recognised potent activator of the NLRP3. Here we will address our description on the involvement of the kidney in autoinflammatory diseases driven mainly by secondary, or reactive, AA amyloidosis with a particular attention on novel therapeutic approach which has to be addressed in suppressing underlying inflammatory disease and reducing the SAA concentration.

Neutrophil serine proteases exert proteolytic activity on endothelial cells

Neutrophil serine proteases (NSPs) are released from activated neutrophils during inflammation. Here we studied the transfer of the three major NSPs, namely proteinase 3, human neutrophil elastase, and cathepsin G, from neutrophils to endothelial cells and used an unbiased approach to identify novel endothelial NSP substrates. Enzymatically active NSPs were released from stimulated neutrophils and internalized by endothelial cells in a dose- and time-dependent manner as shown by immunoblotting, flow cytometry, and the Boc-Ala substrate assay. Using terminal-amine isotopic labeling of substrates in endothelial cells, we identified 121 peptides from 82 different proteins consisting of 36 substrates for proteinase 3, 30 for neutrophil elastase, and 28 for cathepsin G, respectively. We characterized the extended cleavage pattern and provide corresponding IceLogos. Gene ontology analysis showed significant cytoskeletal substrate enrichment and confirmed several cytoskeletal protein substrates by immunoblotting. Finally, ANCA-stimulated neutrophils released all three active NSPs into the supernatant. Supernatants increased endothelial albumin flux and disturbed the endothelial cell cytoskeletal architecture. Serine protease inhibition abrogated this effect. Longer exposure to NSPs reduced endothelial cell viability and increased apoptosis. Thus, we identified novel NSP substrates and suggest NSP inhibition as a therapeutic measure to inhibit neutrophil-mediated inflammatory vascular diseases.

NLRP3 inflammasome activation in dialyzed chronic kidney disease patients

To assess whether NLR pyrin domain-containing protein 3 (NLRP3) inflammasome, a multiprotein complex that mediates the activation of caspase-1 (CASP-1) and pro-inflammatory cytokines IL-18 and IL-1β, could be involved in the chronic inflammatory state observed in chronic kidney disease patients undergoing hemodialysis treatment (CKD-HD), we employed several biomolecular techniques including RT-PCR, western blot, FACS analysis, confocal microscopy and microarray. Interestingly, peripheral blood mononuclear cells from 15 CKD-HD patients showed higher mRNA levels of NLRP3, CASP-1, ASC, IL-1β, IL-18 and P2X7receptor compared to 15 healthy subjects. Western blotting analysis confirmed the above results. In particular, active forms of CASP-1, IL1-β and IL-18 resulted significantly up-regulated in CKD-HD versus controls. Additionally, elevated mitochondrial ROS level, colocalization of NLRP3/ASC/mitochondria in peripheral blood mononuclear cells from CKD-HD patients and down-regulation of CASP-1, IL1-β and IL-18 protein levels in immune-cells of CKD-HD patients stimulated with LPS/ATP in presence of mitoTEMPO, inhibitor of mitochondrial ROS production, suggested a possible role of this organelle in the aforementioned CKD-associated inflammasome activation. Then, microarray analysis confirmed, in an independent microarray study cohort, that NLRP3 and CASP-1, along with other inflammasome-related genes, were up-regulated in 17 CKD-HD patients and they were able to clearly discriminate these patients from 5 healthy subjects. All together these data showed, for the first time, that NLRP3 inflammasome was activated in uremic patients undergoing dialysis treatment and they suggested that this unphysiological condition could be possibly induced by mitochondrial dysfunction.