Deficiency of NADPH oxidase components p47phox and gp91phox caused granulomatous synovitis and increased connective tissue destruction in experimental arthritis models

Reactive oxygen species (ROS), but not nitric oxide (NO), contribute to strain differences in the susceptibility to experimental arthritis in rats

There is extensive evidence for the critical role of reactive oxygen species (ROS) and nitric oxide (NO) produced by phagocytes in development of inflammatory processes and pathogenesis of numerous diseases, including rheumatoid arthritis (RA). Apart from their function as mediators of inflammation and tissue damage, recent research supports their role as signaling and regulatory molecules. In the present study we have investigated the production of ROS and NO over the course of adjuvant arthritis (AA) and oil-induced arthritis (OIA), by resident peritoneal macrophages of two rat strains: Dark Agouti (DA), susceptible, and Albino Oxford (AO), resistant to induction of AA and OIA. We have compared levels of ROS and NO produced by susceptible vs. resistant rat strain, and investigated their relevancy for arthritis development and severity. In addition, we have stimulated macrophages in vitro with Mycobacterium bovis BCG, and two heat shock proteins (HSP): endogenous HSP47 and mycobacterial HSP71 (mHSP71). Our results suggest a possible contribution of increased ROS production to arthritis resistance of AO rats. The ROS production in AO rats is potentiated by endogenous HSP47, but not with mycobacterial cell and mHSP71, suggesting HSP47 participates in AA control. We have found no fundamental relationship between the magnitude of NO production and AA and OIA susceptibility and severity, suggesting that NO has no effector role in AA and OIA. Our results advocate a regulatory type action of NO molecule might be more significant in arthritis development.

Acid aspiration-induced lung inflammation and injury are exacerbated in NADPH oxidase-deficient mice

Increased reactive oxidant intermediates (ROIs) from primed leukocytes have been implicated in the pathogenesis of acid aspiration lung injury. To evaluate the specific role of the phagocyte NADPH oxidase-derived ROIs in acid lung injury, the p47phox-/- knockout mouse model of chronic granulomatous disease was used. p47phox-/- mice developed a significantly greater alveolar neutrophilic leukocytosis compared with wild-type mice at all time points after acid injury, with the difference between genotypes being most marked at 48 h. In contrast, the p47phox-/- mice had a decreased number of macrophages in bronchoalveolar lavage (BAL) compared with wild-type at 48 h after acid or saline aspiration. Albumin concentration in BAL reflecting capillary leak was also greater in p47phox-/- compared with wild-type mice. BAL concentrations of proinflammatory cytokines and chemokines were greater in p47phox-/- compared with wild-type mice. These findings suggest that NADPH oxidase, directly or indirectly, plays a role in attenuating the acute neutrophilic response after acid lung injury. We speculate that this downmodulating effect may be mediated by promoting the transition from production of cytokines and chemokines involved in neutrophilic infiltration to a less injurious, chronic inflammatory response.

In the Absence of Reactive Oxygen Species, T Cells Default to a Th1 Phenotype and Mediate Protection against PulmonaryCryptococcus neoformansInfection

In recent years, the prevalence of invasive fungal infections has increased, attributed mostly to the rising population of immunocompromised individuals. Cryptococcus neoformans has been one of the most devastating, with an estimated 6-8% of AIDS-infected patients succumbing to Cryptococcus-associated meningitis. Reactive oxygen species (ROS) are potent antimicrobial agents but also play a significant role in regulating immune cell phenotype, but cause immunopathology when produced in excess. We now show that mice lacking phagocyte NADPH oxidase have heightened macrophage and Th1 responses and improved pathogen containment within pulmonary granulomatous lesions. Consequently, dissemination of this fungus to the brain is diminished, an effect that is independent of IL-12. Similar results are described using the metalloporphyrin antioxidant manganese(III) tetrakis(N-ethyl pyridinium-2-yl)porphyrin, which also promoted a protective Th1 response and reduced dissemination to the brain. These findings are in sharp contrast to the protective potential of ROS against other fungal pathogens, and highlight the pivotal role that ROS can fulfill in shaping the profile of the host's immune response.

Harmful waste products as novel immune modulators for treating inflammatory arthritis?

Cope discusses a new study in rats suggesting that oxidative burst inducers might have a role to play in treating inflammatory arthritis.

NAD(P)H oxidase activity of Nox4 in chondrocytes is both inducible and involved in collagenase expression

Reactive oxygen species (ROS) are regulators of redox-sensitive cell signaling pathways. In osteoarthritis, human interleukin-1beta is implicated in cartilage destruction through an ROS-dependent matrix metalloproteinase production. To determine the molecular source of ROS production in the human IL-1beta (hIL-1beta)-sensitive chondrocyte immortalized cell line C-20/A4, transfected cells were constructed that overexpress NAD(P)H oxidases. First, RT-PCR analysis showed that the C-20/A4 cell line expressed Nox2, Nox4, p22( phox ), and p67( phox ), but not p47( phox ). It was found that ROS production by C-20/A4 chondrocytes does not depend on PMA and ionomycin activation. This indicates that Nox2 was not involved in the production of ROS. In C- 20/A4 cells that overexpress Nox4, hIL-1beta stimulated ROS production three times more than the normal production of C-20/A4 cells. Moreover, there was a fourfold increase in the production of collagenase (MMP-1) by chondrocytes that overexpress Nox4. Interestingly, MMP-1 production in cells that overexpress Nox2 was not sensitive to hIL-1beta. These data suggest that under hIL-1beta stimulation, C-20/A4 chondrocytes produce MMP-1 through a Nox4-mediated, ROS-dependent pathway.

Phagocyte-derived reactive species: salvation or suicide?

Activated phagocytes produce "reactive oxygen, halogen and nitrogen species" that help to kill some types of microorganism. How these species destroy microorganisms remains, however, an enigma: both direct oxidative damage and indirect damage (whereby reactive species promote the actions of other antibacterial agents) are involved, and no single mechanism is likely to account for the killing of all microorganisms. Phagocyte-derived reactive species are known to injure human tissues and to contribute to inflammation. Recently, however, we have learned that they can also be anti-inflammatory by modulating the immune response. These data have implications for the proposed use of antioxidants to treat inflammation.

The expanding role of NADPH oxidases in health and disease: no longer just agents of death and destruction

The NADPH oxidase was originally identified as a key component of human innate host defence. In phagocytes, this enzyme complex is activated to produce superoxide anion and other secondarily derived ROS (reactive oxygen species), which promote killing of invading micro-organisms. However, it is now well-established that NADPH oxidase and related enzymes also participate in important cellular processes not directly related to host defence, including signal transduction, cell proliferation and apoptosis. These enzymes are present in essentially every organ system in the body and contribute to a multitude of physiological events. Although essential for human health, excess NADPH-oxidase-generated ROS can promote numerous pathological conditions. Herein, we summarize our current understanding of NADPH oxidases and provide an overview of how they contribute to specific human diseases.

Bb2Bb3 regulation of murine Lyme arthritis is distinct from Ncf1 and independent of the phagocyte nicotinamide adenine dinucleotide phosphate oxidase

Several quantitative trait loci regulating murine Lyme arthritis severity have been mapped, including a highly significant linkage found on chromosome 5, termed Bb2Bb3. Within this region, the Ncf1 gene of the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has recently been identified as a major regulator of arthritis severity in rodent models of rheumatoid arthritis, an effect attributed to protective properties of reactive oxygen species. To assess the role of Ncf1 in Lyme arthritis, we introgressed Bb2Bb3 from severely arthritic C3H/He mice onto mildly arthritic C57BL/6 mice. This increased Lyme arthritis severity, whereas the reciprocal transfer conferred protection from disease. A single nucleotide polymorphism was identified in the Ncf1 gene that did not influence the protein sequence or expression of Ncf1. Although polymorphonuclear leukocytes from C57BL/6 mice generated a greater oxidative burst than polymorphonuclear leukocytes from C3H/He mice, studies with the Bb2Bb3 congenic mice demonstrated this difference was not linked to Ncf1 alleles. Furthermore, Lyme arthritis severity was not altered in mice lacking either the Ncf1 or Gp91phox subunits of the NADPH oxidase complex. Together, these results argue that Ncf1 is not a candidate gene for regulation of Lyme arthritis and reveal Lyme arthritis to be independent of NADPH oxidase activity, distinguishing it from other models of rheumatoid arthritis.

Point Mutations in the Proline-rich Region of p22 Are Dominant Inhibitors of Nox1- and Nox2-dependent Reactive Oxygen Generation

The integral membrane protein p22phox is an indispensable component of the superoxide-generating phagocyte NADPH oxidase, whose catalytic core is the membrane-associated gp91phox (also known as Nox2). p22phox associates with gp91phox and, through its proline-rich C terminus, provides a binding site for the tandem Src homology 3 domains of the activating subunit p47phox. Whereas p22phox is expressed ubiquitously, its participation in regulating the activity of other Nox enzymes is less clear. This study investigates the requirement of p22phox for Nox enzyme activity and explores the role of its proline-rich region (PRR) for regulating activity. Coexpression of specific Nox catalytic subunits (Nox1, Nox2, Nox3, Nox4, or Nox5) along with their corresponding regulatory subunits (NOXO1/NOXA1 for Nox1; p47phox/p67phox/Rac for Nox2; NOXO1 for Nox3; no subunits for Nox4 or Nox5) resulted in marked production of reactive oxygen. Small interfering RNAs decreased endogenous p22phox expression and inhibited reactive oxygen generation from Nox1, Nox2, Nox3, and Nox4 but not Nox5. Truncated forms of p22phox that disrupted the PRR-inhibited reactive oxygen generation from Nox1, Nox2, and Nox3 but not from Nox4 and Nox5. Similarly, p22phox (P156Q), a mutation that disrupts Src homology 3 binding by the PRR, potently inhibited reactive oxygen production from Nox1 and Nox2 but not from Nox4 and Nox5. Expression of p22phox (P156Q) inhibited NOXO1-stimulated Nox3 activity, but co-expression of NOXA1 overcame the inhibitory effect. The P157Q and P160Q mutations of p22phox showed selective inhibition of Nox2/p47phox/p67phox, and selectivity was specific for the organizing subunit (p47phox or NOXO1) rather than the Nox catalytic subunit. These studies stress the importance of p22phox for the function of Nox1, Nox2, Nox3, and Nox4, and emphasize the key role of the PRR for regulating Nox proteins whose activity is dependent upon p47phox or NOXO1.

NADPH oxidase restrains the matrix metalloproteinase activity of macrophages

Matrix metalloproteinases (MMPs) regulate numerous functions in normal and disease processes; thus, irreversibly blocking their activity is a key step in regulating MMP catalysis. We previously showed in vitro that oxidizing intermediates generated by phagocytes inactivate MMPs by modifying specific amino acids. To assess whether this mechanism operates in vivo, we focused on MMP-12, a macrophage-specific MMP known to mediate emphysema in mouse models. We found that mice lacking gp91(phox), a phagocyte-specific component of the NADPH oxidase, developed extensive, spontaneous emphysematous destruction of their peripheral air spaces, whereas mice deficient in both NADPH oxidase and MMP-12 were protected from spontaneous emphysema. Although gp91(phox)-null and wild-type macrophages produced equivalent levels of MMP-12 protein, the oxidant-deficient cells had greater MMP-12 activity than wild-type macrophages. These findings indicate that reactive intermediates provide a physiological mechanism to protect tissues from excessive macrophage-mediated damage during inflammation.

Conditional haploinsufficiency of NCF1 (encoding p47(phox)), a signaling gene with a heterozygous phenotype potentially subject to natural selection

Even a minor degree of haploinsufficiency could eventually reduce the frequency of an autosomal immunodeficiency disease. Searching for such a condition, we have re-examined the phenotype of mice +/- for the NCF1 gene encoding p47(phox) and humans +/- for NCF1 and NCF2 using a procedure that allowed the respiratory burst of granulocytes and macrophages to be measured simultaneously. The mice showed significant haploinsufficiency in granulocytes but not in macrophages (i.e. conditional haploinsufficiency). Our human data were obtained from blister cells, and were too scattered to allow a firm conclusion. In view of recent re-evaluation of the role of the respiratory burst these findings are compatible with the view that haploinsufficiency occurs particularly among rate-limiting genes that operate in regulatory/signaling pathways.

NADPH-oxidase-driven oxygen radical production determines chondrocyte death and partly regulates metalloproteinase-mediated cartilage matrix degradation during interferon-gamma-stimulated immune complex arthritis

In previous studies we have found that FcγRI determines chondrocyte death and matrix metalloproteinase (MMP)-mediated cartilage destruction during IFN-γ-regulated immune complex arthritis (ICA). Binding of immune complexes (ICs) to FcγRI leads to the prominent production of oxygen radicals. In the present study we investigated the contribution of NADPH-oxidase-driven oxygen radicals to cartilage destruction by using p47phox^-/- mice lacking a functional NADPH oxidase complex. Induction of a passive ICA in the knee joints of p47phox^-/- mice resulted in a significant elevation of joint inflammation at day 3 when compared with wild-type (WT) controls as studied by histology. However, when IFN-γ was overexpressed by injection of adenoviral IFN-γ in the knee joint before ICA induction, a similar influx of inflammatory cells was found at days 3 and 7, comprising mainly macrophages in both mouse strains. Proteoglycan depletion from the cartilage layers of the knee joints in both groups was similar at days 3 and 7. Aggrecan breakdown in cartilage caused by MMPs was further studied by immunolocalisation of MMP-mediated neoepitopes (VDIPEN). VDIPEN expression in the cartilage layers of arthritic knee joints was markedly lower (between 30 and 60%) in IFN-γ-stimulated arthritic p47phox^-/- mice at day 7 than in WT controls, despite significant upregulation of mRNA levels of various MMPs such as MMP-3, MMP-9, MMP-12 and MMP-13 in synovia and MMP-13 in cartilage layers as measured with quantitative RT-PCR. The latter observation suggests that oxygen radicals are involved in the activation of latent MMPs. Chondrocyte death, determined as the percentage of empty lacunae in articular cartilage, ranged between 20 and 60% at day 3 and between 30 and 80% at day 7 in WT mice, and was completely blocked in p47phox^-/- mice at both time points. FcγRI mRNA expression was significantly lower, and FcγRII and FcγRIII were higher, in p47phox^-/- mice than in controls. NADPH-oxidase-driven oxygen radical production determines chondrocyte death and aggravates MMP-mediated cartilage destruction during IFN-γ-stimulated IC-mediated arthritis. Upregulation of FcγRI by oxygen radicals may contribute to cartilage destruction.

Null mutation of myeloperoxidase in mice prevents mechanical activation of neutrophil lysis of muscle cell membranes in vitro and in vivo

Membrane lysis is a common and early defect in muscles experiencing acute injuries or inflammation. Although increased mechanical loading of muscles can induce inflammation and membrane lysis, whether mechanical loads applied to muscle can promote the activation and cytolytic capacity of inflammatory cells and thereby increase muscle damage is unknown. We tested whether mechanical loads applied to mouse muscle cells in vitro can increase membrane lysis, and whether neutrophil-mediated lysis of muscle cells is promoted by mechanical loads applied in vitro and in vivo. Cyclic loads applied to muscle cells for 24 h in vitro produced little muscle cell lysis. Similarly, the addition of neutrophils to muscle cell cultures in the presence of superoxide dismutase (SOD) produced little muscle cell lysis. However, when cyclic mechanical loads were applied to neutrophil-muscle co-cultures in the presence of SOD, there was a synergistic effect on muscle cell lysis, suggesting that mechanical loading activates neutrophil cytotoxicity. However, application of mechanical loads to co-cultures of muscle cells and neutrophils that are null mutants for myeloperoxidase (MPO) showed no mechanical activation of neutrophil cytotoxicity. This indicates that loading promotes neutrophil cytotoxicity via MPO. Activity assays confirmed that mechanical loading of neutrophil-muscle co-cultures significantly increased MPO activity. We further tested whether muscle membrane lysis in vivo was mediated by neutrophils when muscle was subjected to modified loading by using a mouse model of muscle reloading following a period of unloading. We observed that MPO-/-soleus muscles showed a significant 52% reduction in membrane lysis compared to wild-type mice, although the mutation did not decrease inflammatory cell extravasation. Together, these in vitro and in vivo findings show that mechanical loading activates neutrophil-mediated lysis of muscle cells through an MPO-dependent pathway.

Ncf1 (p47phox) polymorphism determines oxidative burst and the severity of arthritis in rats and mice

Identifying genes that regulate polygenic diseases influenced by the environment such as rheumatoid arthritis (RA), has so far proven to be difficult. By using an alternative approach, i.e., linkage analysis using relevant animal models we succeeded in finding the Ncf1 gene residing in the Pia4 quantitative trait locus to be responsible for the severity of pristane induced arthritis in rats. The influence of another mutation in the mouse Ncf1 gene showed the same association between decreased oxidative burst and enhanced arthritis. In this case the mutation affected a splice site giving a non-detectable oxidative burst response and enhanced collagen induced arthritis as well as myelin oligodendrocyte protein induced experimental autoimmune encephalomyelitis. These findings open up new possibilities for new treatments for autoimmune diseases, i.e., RA, targeting the NADPH oxidase pathway.

Chronic Granulomatous Disease and Other Disorders of Phagocyte Function

The analysis of specific gene defects in disorders of phagocyte function has shed light on important aspects of the innate immune response. Each disorder has distinctive features in the clinical presentation and characteristic microbial pathogens. Chronic granulomatous disease has been extensively studied both in patient series and in mouse models. New insights continue to be obtained regarding the role of the nicotinamide dinucleotide phosphate (NADPH) oxidase and related enzymes in host defense and other aspects of the inflammatory response, as well as optimal management of this disorder. Approaches based on hematopoietic stem cell transplantation and gene therapy offer promise for the future, but are still under investigation. Also briefly summarized are updates on newly described leukocyte adhesion defects and on inherited susceptibility to mycobacterial infection due to defects in interleukin (IL)-12 and interferon-γ pathways.

Enhancement of collagen-induced arthritis in mice genetically deficient in extracellular superoxide dismutase

OBJECTIVE

To examine the influence of superoxide on the severity of collagen-induced arthritis (CIA) in mice.

METHODS

CIA was induced in DBA/1J mice lacking the extracellular superoxide dismutase (EC-SOD) gene (knockout [KO]) and in normal DBA/1J mice (wild-type [WT]).

RESULTS

The clinical disease activity score was significantly higher in EC-SOD-KO mice than in WT mice between days 36 and 53, and the histologic scores for joint damage on day 53 increased 2-fold or more in the EC-SOD-KO mice. There were no significant differences between the 2 groups of mice in proliferation indices of spleen or lymph node cells in vitro after stimulation with type II collagen. Although both IgG1 and IgG2a anticollagen antibody levels increased in both groups of mice between days 21 and 53, there were no significant differences between the 2 groups. Lipopolysaccharide-stimulated spleen cells from EC-SOD-KO mice produced greater levels of tumor necrosis factor alpha (TNFalpha) over 48 hours in culture compared with cells from WT mice. Increased steady-state levels of messenger RNA (mRNA) for interferon-gamma (IFNgamma), TNFalpha, and interleukin-1beta (IL-1beta), and lower levels of IL-1 receptor antagonist (IL-1Ra) mRNA were present in the joints of the EC-SOD-KO mice compared with the WT mice.

CONCLUSION

The absence of EC-SOD leads to more severe CIA, which may be accompanied by enhanced production of the proinflammatory cytokines IFNgamma, TNFalpha, and IL-1beta, and decreased production of the antiinflammatory cytokine IL-1Ra in the joints.

Oxidation in rheumatoid arthritis

Oxygen metabolism has an important role in the pathogenesis of rheumatoid arthritis. Reactive oxygen species (ROS) produced in the course of cellular oxidative phosphorylation, and by activated phagocytic cells during oxidative bursts, exceed the physiological buffering capacity and result in oxidative stress. The excessive production of ROS can damage protein, lipids, nucleic acids, and matrix components. They also serve as important intracellular signaling molecules that amplify the synovial inflammatory-proliferative response. Repetitive cycles of hypoxia and reoxygenation associated with changes in synovial perfusion are postulated to activate hypoxia-inducible factor-1alpha and nuclear factor-kappaB, two key transcription factors that are regulated by changes in cellular oxygenation and cytokine stimulation, and that in turn orchestrate the expression of a spectrum of genes critical to the persistence of synovitis. An understanding of the complex interactions involved in these pathways might allow the development of novel therapeutic strategies for rheumatoid arthritis.

Enhanced autoimmunity, arthritis, and encephalomyelitis in mice with a reduced oxidative burst due to a mutation in the Ncf1 gene

The Ncf1 gene was recently identified as a strong regulator of severe arthritis in rat. This finding was surprising, because the disease-promoting allele mediated a lower level of reactive oxygen species in NADPH oxidase-expressing cells. We have now investigated a splice mutation of the Ncf1 gene in B10.Q mice, causing a truncated and nonfunctional Ncf1 protein. We found that the mutated Ncf1 led to a more severe and chronic relapsing collagen-induced arthritis. Enhanced IgG and delayed-type hypersensitivity responses against type II collagen were seen, indicating increased activity of autoreactive T cells. Interestingly, female Ncf1-mutated mice spontaneously developed severe arthritis during the postpartum period. The arthritis was accompanied by an increased antibody response to type II collagen, with the same fine specificity as in collagen-induced arthritis. The enhancing effect of the mutated Ncf1 could also be shown to be more general in that it enhanced myelin oligodendrocyte glycoprotein protein-induced experimental autoimmune encephalomyelitis, a model for multiple sclerosis. These results show that Ncf1, a gene important for oxidative burst, regulates the susceptibility and severity of both arthritis and encephalomyelitis and modulates, directly or indirectly, the level of T cell-dependent autoimmune responses.

Local activation of STAT-1 and STAT-3 in the inflamed synovium during zymosan-induced arthritis: exacerbation of joint inflammation in STAT-1 gene-knockout mice

OBJECTIVE

STAT proteins play an important role in cytokine signaling. Some investigators have reported preferential activation of STAT-1, and others have reported preferential activation of STAT-3, in response to endogenous interleukin-6 (IL-6), in patients with rheumatoid arthritis. The present study was undertaken to investigate synovial STAT-1 and STAT-3 activation in an experimental animal model of arthritis.

METHODS

Zymosan was injected intraarticularly into naive wild-type (WT), IL-6(-/-), and STAT-1(-/-) mice to induce arthritis. Western blots of synovial lysates were probed with phosphospecific antibodies to detect STAT-1/STAT-3 activation. Inflammation was assessed histologically. Synovial gene expression of the STAT-induced feedback inhibitors suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 in WT and STAT-1(-/-) mice was investigated by reverse transcriptase-polymerase chain reaction.

RESULTS

STAT-3 was activated in inflamed synovium of WT mice throughout the course of disease, whereas activated STAT-1 was observed only during the chronic phase. In IL-6(-/-) mice, STAT activation was limited to STAT-3 on day 1. Although macrophage influx was not inhibited, disease went into remission after day 7 in IL-6(-/-) mice. STAT-1 deficiency resulted in exacerbation of chronic joint inflammation and granuloma formation. In STAT-1(-/-) mice, STAT-3 activation in the inflamed joints was unaltered as compared with WT mice. However, synovial SOCS-1, but not SOCS-3, gene expression was markedly reduced in STAT-1(-/-) mice.

CONCLUSION

The results in the IL-6(-/-) mice suggest that STAT-3 is involved in the chronicity of ZIA. Exacerbation of arthritis in STAT-1(-/-) mice suggests an opposing effect of STAT-1, i.e., suppression of joint inflammation. The expression of SOCS-1 could be the underlying mechanism by which STAT-1 controls joint inflammation.

Anaplasma phagocytophilum infection induces protracted neutrophil degranulation

Anaplasma phagocytophilum-infected neutrophil degranulation could exacerbate inflammation. Thus, the degranulation of infected neutrophils was assayed. Infected neutrophils expressed CD11b and CD66b, and supernatants of infected neutrophils showed more proMMP-9 and MMP-9 activity than controls and continued to do so for > or =18 h. Degranulation-related inflammatory tissue injury may account for some clinical manifestations in human granulocytic anaplasmosis.