Inhibition of TNF-alpha-induced neutrophil apoptosis by crystals of calcium pyrophosphate dihydrate is mediated by the extracellular signal-regulated kinase and phosphatidylinositol 3-kinase/Akt pathways up-stream of caspase 3

Neutrophils and extracellular traps in crystal-associated diseases

Crystalline material can cause a multitude of acute and chronic inflammatory diseases, such as gouty arthritis, silicosis, kidney disease, and atherosclerosis. Crystals of various types are thought to cause similar inflammatory responses, including the release of proinflammatory mediators and formation of neutrophil extracellular traps (NETs), processes that further promote necroinflammation and tissue damage. It has become apparent that the intensity of inflammation and the related mechanisms of NET formation and neutrophil death in crystal-associated diseases can vary depending on the crystal type, amount, and site of deposition. This review details new mechanistic insights into crystal biology, highlights the differential effects of various crystals on neutrophils and extracellular trap (ET) formation, and discusses treatment strategies and potential future approaches for crystal-associated disorders.

Cytokine Production and NET Formation by Monosodium Urate-Activated Human Neutrophils Involves Early and Late Events, and Requires Upstream TAK1 and Syk

Gout is a prevalent and incapacitating disease triggered by the deposition of monosodium urate (MSU) crystals in joints, which are also massively infiltrated by neutrophils. The interaction of the latter with MSU crystals triggers several responses, including the generation of inflammatory mediators and of neutrophil extracellular traps (NETs). Though some of the signaling events mobilized by MSU in neutrophils have been described (e.g., Src family kinases, Syk, PKC, PI3K), the picture remains fragmentary. Likewise, the impact of these signaling events on cellular responses is incompletely understood. In this study, we examined transcriptomic changes triggered by MSU in neutrophils and their impact on the corresponding proteins, as well as the role of various signaling pathways in prominent functional responses. We report for the first time that neutrophils can secrete the monocyte chemoattractant, CCL4, in response to MSU. Accordingly, we found that transcription factors NF-κB, CREB, and C/EBP are belatedly activated by MSU crystals, and at least the former is involved in chemokine generation. Moreover, we show that MAPKs and Akt are activated by MSU in neutrophils, that they are under the control of TAK1 and Syk, and that they participate in cytokine generation and NETosis. In the latter instance, we found the phenomenon to be independent of endogenous ROS, but under the control of PAD4. We finally provide evidence that endogenous factors contribute to the belated phosphorylation of kinases and transcription factors in response to MSU. Collectively, our findings unveil potentially important therapeutic targets for gouty arthritis.

Arctium lappa Extract Suppresses Inflammation and Inhibits Melanoma Progression

Background: Arctium lappa has been used as popular medicinal herb and health supplement in Chinese societies. Bioactive components from A. lappa have attracted the attention of researchers due to their promising therapeutic effects. In this study, we investigated the effects of A. lappa hydroalcoholic extract (Alhe) during different models of inflammation, in vivo. Methods: The anti-inflammatory activity was evaluated through the air pouch model. For this, mice received an inflammatory stimulus with lipopolysaccharide (LPS) and were later injected with Alhe. To assess anti-tumoral activity, the animals were inoculated with B16F10 cells and injected with Alhe every 5 days, along the course of 30 days. Controls were submitted to the same conditions and injected with the vehicle. Peritoneal or air pouch fluids were collected to evaluate leukocyte counting or cellular activation via quantification of cytokines and nitric oxide. Results: Alhe injection reduced the neutrophil influx and production of inflammatory mediators in inflammatory foci after LPS or tumor challenges. Furthermore, Alhe injection reduced tumor growth and enhanced mice survival. Conclusions: Collectively, these data suggest that Alhe regulates immune cell migration and activation, which correlates with favorable outcome in mouse models of acute inflammation and melanoma progression.

Monosodium urate crystals induce oxidative stress in human synoviocytes

Background

Gout is the most common inflammatory arthropathy of metabolic origin and it is characterized by intense inflammation, the underlying mechanisms of which are unknown. The aim of this study was to evaluate the oxidative stress in human fibroblast-like synoviocytes (FLS) exposed to monosodium urate (MSU) crystals, which trigger an inflammatory process.

Methods

Human FLS isolated from synovial tissue explants were stimulated with MSU crystals (75 μg/mL) for 24 h. Cellular viability was evaluated by crystal violet staining, apoptosis was assessed using Annexin V, and the cellular content of reactive oxygen species (ROS) and nitrogen species (RNS) (O₂^-, H₂O₂, NO) was assessed with image-based cytometry and fluorometric methods. In order to determine protein oxidation levels, protein carbonyls were detected through oxyblot analysis, and cell ultrastructural changes were assessed by transmission electron microscopy.

Results

The viability of FLS exposed to MSU crystals decreased by 30 % (P < 0.05), while apoptosis increased by 42 % (P = 0.01). FLS stimulated with MSU crystals exhibited a 2.1-fold increase in H₂O₂ content and a 1.5-fold increase in O₂^- and NO levels. Oxyblots revealed that the spots obtained from FLS protein lysates exposed to MSU crystals exhibited protein carbonyl immunoreactivity, which reflects the presence of oxidatively modified proteins. Concomitantly, MSU crystals triggered the induction of changes in the morphostructure of FLS, such as the thickening and discontinuity of the endoplasmic reticulum, and the formation of vacuoles and misfolded glycoproteins.

Conclusions

Our results prove that MSU crystals induce the release of ROS and RNS in FLS, subsequently oxidizing proteins and altering the cellular oxidative state of the endoplasmic reticulum, which results in FLS apoptosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1012-3) contains supplementary material, which is available to authorized users.

Neutrophils with protumor potential could efficiently suppress tumor growth after cytokine priming and in presence of normal NK cells

In tumor-bearing state, the function of neutrophils is converted from tumor-suppressing to tumor-promoting. Here we report that priming with IFN-γ and TNF-α could convert the potential of neutrophils from tumor-promoting to tumor-suppressing. The neutrophils with protumor potential have not lost their responsiveness to IFN-γ and TNF-α. After priming with IFN-γ and TNF-α, the potential of the neutrophils to express Bv8 and Mmp9 genes was reduced. Conversely, the tumor-promotional neutrophils recovered the expression of Rab27a and Trail, resumed the activation levels of PI3K and p38 MAPK pathways in response to stimuli, and expressed higher levels of IL-18 and NK-activating ligands such as RAE-1, MULT-1, and H60. Therefore, the anti-tumor function of the neutrophils was augmented, including the cytotoxicity to tumor cells, the capability of degranulation, and the capacity to activate NK cells. Since the function of NK cells is impaired in tumor-bearing state, the administration of normal NK cells could significantly augment the efficiency of tumor therapy based on neutrophil priming. These findings highlight the reversibility of neutrophil function in tumor-bearing state, and suggest that neutrophil priming by IFN-γ/TNF-α might be a potential approach to eliminate residual tumor cells in comprehensive strategy for tumor therapy.

Pathophysiology of articular chondrocalcinosis--role of ANKH

Calcium pyrophosphate (CPP) crystal deposition (CPPD) is associated with ageing and osteoarthritis, and with uncommon disorders such as hyperparathyroidism, hypomagnesemia, hemochromatosis and hypophosphatasia. Elevated levels of synovial fluid pyrophosphate promote CPP crystal formation. This extracellular pyrophosphate originates either from the breakdown of nucleotide triphosphates by plasma-cell membrane glycoprotein 1 (PC-1) or from pyrophosphate transport by the transmembrane protein progressive ankylosis protein homolog (ANK). Although the etiology of apparent sporadic CPPD is not well-established, mutations in the ANK human gene (ANKH) have been shown to cause familial CPPD. In this Review, the key regulators of pyrophosphate metabolism and factors that lead to high extracellular pyrophosphate levels are described. Particular emphasis is placed on the mechanisms by which mutations in ANKH cause CPPD and the clinical phenotype of these mutations is discussed. Cartilage factors predisposing to CPPD and CPP-crystal-induced inflammation and current treatment options for the management of CPPD are also described.

Calcium pyrophosphate dihydrate crystal-induced inhibition of neutrophil apoptosis: involvement of Bcl-2 family members

INTRODUCTION

The inflammation associated with calcium pyrophosphate dihydrate (CPPD) crystal-induced arthritis arises from the activation of neutrophils with crystals in the synovial joint. Furthermore, constitutive neutrophil apoptosis is inhibited by this interaction with CPPD so that the lifetime of the cells and the duration of the inflammatory response are extended. The objective of this study was to investigate the role of bcl-2 protein family members in the CPPD-induced prosurvival response.

METHODS

Apoptosis was measured using DNA fragmentation and Caspase 3 assays. The expression and activation levels of the bcl-2 protein family members A1, Mcl-1, Bcl-xl, Bim, Bad and Bax-alpha were measured using western blot analysis.

RESULTS

The prosurvival proteins Mcl-1 and Bcl-xl were both found to be strongly expressed but unaffected by CPPD-induced neutrophil activation over 3 h. The expression of proapoptotic proteins Bim and Bax-alpha was found to decrease over the time course of a 3 h incubation of neutrophils with CPPD crystals (but not the bacterial chemoattractant fMLP). Furthermore, expression of the unphosphorylated (active, proapoptotic) form of Bim was dominant in control cells at 0.5 h, whereas the status of this protein switched to the phosphorylated form following cell activation by both CPPD and fMLP. For CPPD (but not fMLP) this phosphorylation effect reversed over a 3 h incubation.

CONCLUSION

Upon stimulation by CPPD crystals, the expression of both Bim and Bax-alpha decreased after 3 h suggesting a reduced proapoptotic effect of these proteins so that the static expression of the prosurvival proteins Bcl-xl and Mcl-1 might allow for a temporary shift in the balance to a prosurvival state of the cells. Because a sudden (but transient) increase in the phosphorylated form of Bim was observed in CPPD-stimulated neutrophils it is possible that this species might act as a signaling intermediate, resulting in the observed downregulation of Bax-alpha.

Effects of HMGB1 on PMN apoptosis during LPS-induced acute lung injury

OBJECTIVE

To observe the effects of intravenous injection of HMGB1 inhibitor sodium butyrate on changes in apoptosis of PMN during LPS-induced acute lung injury in rats and HMGB1 in vitro on human circulating PMN apoptosis, in order to clarify the role of HMGB1 in the pathogenesis of acute lung injury.

METHODS

(1) LPS-induced acute lung injury rat model was developed by LPS infusion. At different time-points after LPS challenge in the presence or absence of sodium butyrate (SB), the rat tissue sample, peripheral blood PMNs and BALF were collected. RT-PCR was applied to examining rat lung tissue HMGB1 mRNA expression level, and Western blotting analysis was adopted to determine expression of rat lung tissue HMGB1 protein. PMN apoptotic changes were determined by flow cytometric (FCM) analysis, Giemsa staining and TdT-mediated dUTP nick end labeling (TUNEL) method. (2) Separated and purified human circulating PMN were coincubated for 24 h with different doses of HMGB1 (0, 10, 100, 1000 ng/ml, respectively) at 37 degrees C in 5% CO(2). PMN apoptosis rate was determined by flow cytometric (FCM) analysis and by TdT-mediated dUTP nick end labeling (TUNEL) method.

RESULTS

(1) The percentage of apoptosis of PMN in rat model of LPS-induced ALI was gradually decreased as compared with that of normal control. The PMN apoptosis-initiation time and non-survival time in rat BALF prolonged significantly as compared with that of normal control. The injured rat lung tissue HMGB1 mRNA and protein expression was upregulated 6-24 h after LPS exposure; SB intervention significantly ameliorated the upregulation. In addition, the morphologic examination indicated that the edema severity and pathological changes of lung tissues were excessively aggravated in rats after LPS administration. By comparison, SB treatment diminished the severity of lung damage. Combined with lung HMGB1 expression level, the above changes indicate that the pathological changes of lung tissue were related to the injured lung HMGB1 expression, as well as apoptotic changes in PMN. (2) After coincubation of HMGB1 with human circulating PMNs, TUNEL and flow cytometry were performed. The study revealed that PMN apoptosis ratios was (40.53+/-4.12) % in control group (PMNs+RPMI 1640 medium), (19.05+/-2.44) % in LPS group (PMNs+RPMI 1640 medium+10 microg/ml LPS), (40.52+/-2.73) % in HMGB1-1 group (PMNs+RPMI 1640 medium+10 ng/ml HMGB1), (34.89+/-1.15) % in HMGB1-2 group (PMNs+RPMI 1640 medium+100 ng/ml HMGB1), and (18.77+/-3.02) % in HMGB1-3 group (PMNs+RPMI 1640 medium+1 000 ng/ml HMGB1). There was statistical significance. Meanwhile, PMN TUNEL positive rate was (31.42+/-4.40) %, (31.39+/-3.80) %, (25.62+/-2.46) %, and (17.98+/-3.20) % in control group, HMGB1-1 group, HMGB1-2 group and HMGB1-3 group, respectively. The inhibitory effect was HMGB1 dose-depended as compared with that of control group.

CONCLUSION

After LPS challenge, high expression of rats' lung HMGB1 mRNA occurs at a later phase, but keeps for a long time. Sodium butyrate (SB) treatment attenuated LPS-induced PMN apoptosis delay and inhibition, and down-regulated HMGB1 mRNA expression of injured lung. HMGB1 in vitro inhibited human circulating PMN apoptosis markedly, and the inhibitory effect was HMGB1 dose-depended. The results demonstrated that HMGB1 may play an important role as a modulator in apoptotic changes in PMN during LPS-induced ALI. It concludes that HMGB1 may contribute to the development of PMN apoptotic changes during LPS-induced acute lung injury.

Constitutive neutrophil apoptosis: mechanisms and regulation

Neutrophil constitutive death is a critical cellular process for modulating neutrophil number and function, and it plays an essential role in neutrophil homeostasis and the resolution of inflammation. Neutrophils die due to programmed cell death or apoptosis. In this article, we review recent studies on the mechanism of neutrophil apoptosis. The involvement of caspase, calpain, reactive oxygen species, cellular survival/death signaling pathways, mitochondria, and BCL-2 family member proteins are discussed. The fate of neutrophils can be influenced within the inflammatory microenvironment. We summarize the current understanding regarding the modulation of neutrophil apoptotic death by various extracellular stimuli such as proinflammatory cytokines, cell adhesion, phagocytosis, red blood cells, and platelets. The involvement of neutrophil apoptosis in infectious and inflammatory diseases is also addressed.

Calcium crystal deposition diseases: update on pathogenesis and manifestations

Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate crystals are the most common types of pathologic calcium-containing crystals. Although these crystals long have been associated with a variety of rheumatic syndromes, recent evidence implicates BCP crystals in the pathogenesis of breast cancer and atherosclerosis. Although understanding of molecular mechanisms involved in generating these pathologic effects has been advanced significantly in recent years, they still are understood incompletely. Such advances are essential to the ongoing search for effective therapies for crystal-associated diseases.

Role of phosphatidylinositol 3-kinase/protein kinase B signal transduction pathway in activation of neutrophils during severe acute pancreatitis

AIM: To investigate the role of phosphatidy-linositol 3-kinase/protein kinase B (PI3K/PKB) signal transduction pathway in the activation of neutrophils during severe acute pancreatitis (SAP).

METHODS: Thirty male health adult Sprague Dawley rats were averagely randomized into group A, B and C. SAP model was established in group B and C by retrograde injection of 50 g/L sodium taurocholate into the pancreatic and biliary duct. The rats in group C were treated with wortmannin 4 h before modeling, and those in group A served as the controls. All the rats were killed 6 h after modeling, and the neutrophils were isolated by density gradient centrifugation. The serum levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were analyzed by enzyme-linked immunosorbent assay (ELISA). The expression of TNF-α and IL-1β mRNA were detected by RT-PCR and the activity of phosphorylated PKB (p-PKB) was examined by Western blot.

RESULTS: The serum levels of TNF-α and IL-1β were significantly higher in group B than those in group A (150.8 ± 31.7 ng/L vs22.4 ± 5.2 ng/L, P < 0.01; 217.5 ± 38.4 ng/L vs 43.7 ± 9.6 ng/L, P < 0.01), and mRNA levels of TNF-α and IL-1β were also markedly increased (0.72 ± 0.06 vs 0.19 ± 0.03, P < 0.01; 0.84 ± 0.11 vs 0.14 ± 0.04, P < 0.01). However, the serum and mRNA levels of TNF-α and IL-1β were all significantly decreased in group C in comparison with those in group B (TNF-α: 70.9 ± 11.3 ng/L, 0.32 ± 0.04; IL-1β: 93.0 ± 11.5 ng/L, 0.22 ± 0.04; all P < 0.01). Western blot showed that the activity of p-PKB was increased in group B as compared with that in group A (0.63 ± 0.08 vs 0.34 ± 0.03, P < 0.01), but it was markedly down-regulated in group C (0.38 ± 0.06, P < 0.01).

CONCLUSION: PI3K/PKB signal transduction pathway is activated in the neutrophils during severe acute pancreatitis, which mediates the production of pro-inflammatory cytokines TNF-α and IL-1β.

Monosodium urate and calcium pyrophosphate dihydrate (CPPD) crystals, inflammation, and cellular signaling

Monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals are responsible for acute synovial inflammation but also contribute to cartilage degradation and bone lesions within the joint. They activate multiple signal transduction pathways leading to cell activation and recruitment. Some signalling pathways are activated by both types of crystals, and other pathways may only be activated by one type depending on cell type, namely neutrophils, monocytes, macrophages, synovial fibroblasts, endothelial cells and chondrocytes. Cascades of activated proteins involve cytoplasmic membrane related proteins (FAK complex, Src family tyrosine kinases), but also MAPK and NF-kB pathways, leading to NO, prostanoid and cytokine production, and protease activation. This review will also focus on potential therapeutic targets related to cellular signalling in MSU and CPPD crystal-induced inflammation.

IFN-γ prevents TNF-α-induced apoptosis in C2C12 myotubes through down-regulation of TNF-R2 and increased NF-κB activity

Wasting of skeletal muscle (cachexia) is associated with a variety of chronic or inflammatory disorders and has long been recognized as a poor prognostic sign. It is currently accepted that the cytokine tumor necrosis factor alpha (TNF-alpha; cachectin) plays a key role in the development of this condition. TNF-alpha-induced apoptotic cell death represents a potential mechanism by which muscle wasting can occur. Evidence has accumulated that the cytokine interferon gamma (IFN-gamma) may act as a modulator of TNF-alpha signalling. Thus, the present study was designed to elucidate if TNF-alpha can directly induce apoptosis in differentiated myotubes, to assess the potential anti-apoptotic properties of IFN-gamma and to get insight into the signalling pathways implicated in the modulatory effects of IFN-gamma. Myoblasts of the murine cell line C2C12 were allowed to differentiate in a low serum containing media and myogenesis assessed by muscle specific protein expression. Non-proliferating, polynucleated, fully differentiated myotubes were obtained after seven days in differentiation media. Exposure of C2C12 myotubes to TNF-alpha for 48 h induced apoptosis characterized by enhanced caspase-3 activity, which resulted in poly(ADP-ribose) polymerase (PARP) cleavage and increased histone-associated-DNA fragmentation. These effects were fully reverted in the presence of IFN-gamma. This cytokine induced down-regulation of the subtype 2 of TNF-alpha receptors (TNF-R2), enhanced TNF-alpha-induced NF-kappaB translocation to the nucleus and binding to DNA and increased the immunoreactivity of the protein c-IAP1, a member of the inhibitor of apoptosis (IAP) gene family whose synthesis is stimulated by NF-kappaB at the transcriptional level. Together, these results demonstrate that TNF-alpha directly induces apoptosis in differentiated myotubes and suggest that the cytokine IFN-gamma, might represent a new immunoadjuvant therapeutic tool for managing cachexia.

Biologic effects of calcium-containing crystals

PURPOSE OF REVIEW

Calcium-containing crystals can cause the degeneration of articular tissues in two separate pathways. In the direct pathway, crystals directly induce synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other pathway, the paracrine pathway, involves the interaction between crystals and macrophages/monocytes, which leads to the synthesis and release of cytokines, which can reinforce the action of crystals on synoviocytes and/or induce chondrocytes to secrete enzymes and which eventually causes the degeneration of articular tissues. The purpose of this review is to highlight the recent findings of the biologic effect of these crystals.

RECENT FINDINGS

In the past few years, major advances in the understanding of the biologic effect of crystals and the signal transduction pathway of crystal-induced cell activation offer a unique opportunity to examine the role of crystal in osteoarthritis and cartilage degeneration.

SUMMARY

Evidence for a causal role of crystals in cartilage degeneration in osteoarthritis is primarily inferential and is based on correlative data. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. Studies have shown two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that subject these crystals to phagocytosis. New information on how crystals form and how they exert their biologic effects will help in the design of an effective therapeutic approach.

TLR2 Signaling in Chondrocytes Drives Calcium Pyrophosphate Dihydrate and Monosodium Urate Crystal-Induced Nitric Oxide Generation

Microcrystals of calcium pyrophosphate dihydrate (CPPD) and monosodium urate (MSU) deposited in synovium and articular cartilage initiate joint inflammation and cartilage degradation in large part by binding and directly activating resident cells. TLRs trigger innate host defense responses to infectious pathogens, and the expression of certain TLRs by synovial fibroblasts has revealed the potential for innate immune responses to be triggered by mesenchymally derived resident cells in the joint. In this study we tested the hypothesis that chondrocytes also express TLRs and that one or more TLRs centrally mediate chondrocyte responsiveness to CPPD and MSU crystals in vitro. We detected TLR2 expression in normal articular chondrocytes and up-regulation of TLR2 in osteoarthritic cartilage chondrocytes in situ. We demonstrated that transient transfection of TLR2 signaling-negative regulator Toll-interacting protein or treatment with TLR2-blocking Ab suppressed CPPD and MSU crystal-induced chondrocyte release of NO, an inflammatory mediator that promotes cartilage degeneration. Conversely, gain-of-function of TLR2 in normal chondrocytes via transfection was associated with increased CPPD and MSU crystal-induced NO release. Canonical TLR signaling by parallel pathways involving MyD88, IL-1R-associated kinase 1, TNF receptor-associated factor 6, and IkappaB kinase and Rac1, PI3K, and Akt critically mediated NO release in chondrocytes stimulated by both CPPD and MSU crystals. We conclude that CPPD and MSU crystals critically use TLR2-mediated signaling in chondrocytes to trigger NO generation. Our results indicate the potential for innate immunity at the level of the articular chondrocyte to directly contribute to inflammatory and degenerative tissue reactions associated with both gout and pseudogout.

Activation of extracellular signal-regulated kinase couples platelet-activating factor-induced adhesion and delayed apoptosis of human neutrophils

Platelet-activating factor (PAF) promotes adhesion of neutrophil granulocytes to the endothelium, which is also linked to neutrophil survival. Here we report that PAF can prolong neutrophil survival by suppressing spontaneous apoptosis. PAF induced concurrent activation of the Ras/Raf-1/mitogen-activated protein kinase kinase (MAPKK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt pathways. ERK activation tightly correlated with up-regulation of CD11b/CD18 expression and beta(2)-integrin-dependent homotypic adhesion. These actions of PAF were markedly attenuated by the MAPKK/ERK inhibitor PD98059, but not by the phosphatidylinositol 3-kinase inhibitor wortmannin. By contrast, concurrent activation of ERK and Akt was required to inhibit caspase-3 activation and consequently to delay apoptosis. Consistently, pharmacological inhibition of either ERK or Akt partially reversed the anti-apoptotic action of PAF; however, they did not produce additive inhibition. These results indicate that PAF-induced activation of ERK contributes to both the expression of the pro-adhesive phenotype and repression of neutrophil apoptosis, thereby amplifying the inflammatory response.

Calcium pyrophosphate dihydrate crystal associated induction of neutrophil activation and repression of TNF-alpha-induced apoptosis is mediated by the p38 MAP kinase

The role of p38 mitogen-activated protein (MAP) kinase in the activation of human neutrophils and repression of TNF-alpha-induced apoptosis in response to plasma opsonized crystals of calcium pyrophosphate dihydrate (CPPD) was investigated. We monitored the endogenous phosphotransferase activity of p38 kinase in neutrophils stimulated with CPPD crystals (25 mg/ml) alone or in the presence of TNF-alpha (10 ng/ml), and with TNF-alpha alone. CPPD crystals induced a 2-fold activation of p38 kinase activity over the basal activity that was observed in untreated neutrophils. Furthermore, CPPD crystals repressed the TNF-alpha associated 6-fold induction of p38 kinase phosphotransferase activity to levels associated with CPPD crystal incubation alone in a PD98059 (20 ng/ml) and Wortmannin (100 nM) sensitive manner. Inhibition of CPPD crystal-induced activation of the neutrophil inflammatory response as measured by chemiluminescence, superoxide anion generation and degranulation as determined by myeloperoxidase and lysozyme release was observed in the presence of the specific p38 MAP kinase inhibitor SB203580 (5 microM). CPPD crystal associated repression of TNF-alpha-induced activation of neutrophil apoptosis as determined by DNA fragmentation correlated with the CPPD crystal mediated inhibition of p38 kinase activity, probably through crystal inhibition of caspase 3. Together, our results indicate that the CPPD crystal associated inflammatory response is regulated through the activation of p38 kinase to sub-apoptotic levels, and that the repression of the TNF-alpha-induced apoptosis program in neutrophils is mediated via the repression of caspase 3 mediated apoptosis-associated p38 kinase activity.

Oxidants inhibit ERK/MAPK and prevent its ability to delay neutrophil apoptosis downstream of mitochondrial changes and at the level of XIAP

Normal spontaneous apoptosis in neutrophils is enhanced by "stress" stimuli such as tumor necrosis factor-alpha, Fas ligand, and oxidants, and this effect is inhibited by anti-apoptotic stimuli including granulocyte-macrophage colony-stimulating factor, lipopolysaccharide, and formylmethionine-leucine-phenylalanine. In this report we demonstrate that anti-apoptotic stimuli protect neutrophils from stress-induced apoptosis via activation of the ERK/MAPK pathway. The protection occurs downstream of mitochondrial alterations assessed as a decrease in membrane potential concomitant with enhanced cytochrome c release. ERK activation was shown to inhibit apoptosis by maintaining levels of XIAP, which is normally decreased in the presence of the pro-apoptotic/stress stimuli. This report also demonstrates that potent intra- and extracellular oxidants inhibit the protective effect of ERK. Oxidant-dependent inhibition of ERK was because of activation of p38 MAPK and activation of the protein phosphatases PP1 and PP2A. Our data suggest that ERK suppresses stress-induced apoptosis downstream of mitochondrial alterations by maintaining XIAP levels and that oxidants block this effect through activation of p38 and protein phosphatases.

How crystals damage tissue

Basic calcium phosphate, calcium pyrophosphate dihydrate, and monosodium urate crystals are the most common types of crystals associated with human disease. Although there is a well-established association between these crystals and various forms of joint disease, recent evidence points to an association of basic calcium phosphate crystals with breast cancer and atherosclerosis. Crystal-induced tissue damage is affected by degradative proteases, cytokines, chemokines, and prostanoids produced by cells stimulated by crystals. In the case of basic calcium phosphate and calcium pyrophosphate dihydrate crystals, these responses are augmented by the cellular proliferation that results from their induction of mitogenesis. The understanding of the molecular mechanisms involved in generating these pathologic effects has been significantly advanced in recent years. Such advances are essential to the ongoing search for more effective therapies for crystal-associated diseases.

×Phosphorylation of Bax Ser184 by Akt Regulates Its Activity and Apoptosis in Neutrophils

Although important for apoptosis, the mechanism of Bax regulation is poorly understood. This study demonstrates that phosphorylation of Ser(184) regulates Bax activity. The phosphorylation required phosphatidylinositol 3-kinase/Akt activation and appeared to be mediated by Akt itself. In the serine-phosphorylated form, Bax was detected in the cytoplasm, could not be immunoprecipitated with the activation-specific antibody 6A7, and promoted heterodimerization with Mcl-1, Bcl-x(L), and A1. Apoptotic neutrophils possessed reduced levels of serine-phosphorylated Bax correlating with an increase in activated Bax as well as an increase in the amount of Bax found translocated to the mitochondria. We suggest that Bax is regulated by phosphorylation of Ser(184) in an Akt-dependent manner and that phosphorylation inhibits Bax effects on the mitochondria by maintaining the protein in the cytoplasm, heterodimerized with antiapoptotic Bcl-2 family members.

Loss of pentameric symmetry of C-reactive protein is associated with delayed apoptosis of human neutrophils

Human neutrophil granulocytes die rapidly, and their survival is contingent upon rescue from programmed cell death by signals from the environment. Here we report that a novel signal for delaying neutrophil apoptosis is the classic acute phase reactant, C-reactive protein (CRP). However, this anti-apoptotic activity is expressed only when the cyclic pentameric structure of CRP is lost, resulting in formation of modified or monomeric CRP (mCRP), which may be formed in inflamed tissues. By contrast, native pentameric CRP and CRP peptides 77-82, 174-185, and 201-206 failed to affect neutrophil apoptosis. The apoptosis delaying action of mCRP was markedly attenuated by an antibody against the low affinity IgG immune complex receptor (CD16) but not by an anti-CD32 antibody. mCRP evoked a transient concurrent activation of the extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt signaling pathways, leading to inhibition of caspase-3 and consequently to delaying apoptosis. Consistently, pharmacological inhibition of either ERK or Akt reversed the anti-apoptotic action of mCRP; however, they did not produce additive inhibition. Thus, mCRP, but not pentameric CRP or peptides derived from CRP, promotes neutrophil survival and may therefore contribute to amplification of the inflammatory response.

Phosphatidylinositol 3-kinase controls antineutrophil cytoplasmic antibodies-induced respiratory burst in human neutrophils

Antineutrophil cytoplasmic antibodies (ANCA) activate human polymorphonuclear neutrophils (PMN) primed with tumor necrosis factor alpha (TNF-alpha) in vitro. Phosphatidylinositol 3-kinase (PI3-K) and the protein-serine/threonine kinase Akt have been implicated in the control of the phagocyte respiratory burst. The hypothesis that PI3-K controls the ANCA-induced respiratory burst was tested. TNF-alpha-primed PMN were stimulated with a monoclonal antibody to myeloperoxidase (MPO) and with PR3- and MPO-ANCA, respectively. Akt activation was assessed with phospho-specific antibodies. Superoxide release was measured with ferricytochrome. ANCA antigen translocation was assessed by fluorescence-activated cell sorter. The effect of TNF-alpha and MPO-ANCA on Akt signaling was studied with immunoprecipitation and glutathione S-transferase pull-down assays. Western blotting revealed rapid transient Akt phosphorylation during TNF-alpha priming and a second phosphorylation after ANCA. PI3-K inhibition by LY294002 blocked both Akt phosphorylation and superoxide generation. A total of 20 +/- 3 nmol O(2)(-)/0.75 x 10(6) PMN/45 min was released after stimulation with PR3-ANCA. LY294002 (5 microM) decreased this amount to 0.3 +/- 2.6 nmol (n = 10, P < 0.05); the MPO-ANCA values were 23 +/- 3 versus 1.6 +/- 3.6 (n = 10, P < 0.05). p38 MAPK inhibition with 10 microM SB202190 that also decreased ANCA-induced superoxide generation prevented S473 phosphorylation of Akt in response to TNF-alpha and to ANCA. However, SB202190 but not LY294002 abrogated TNF-alpha-mediated ANCA antigen surface translocation, demonstrating that superoxide generation and ANCA antigen translocation proceed by separate mechanisms. Akt, PAK1, and Rac1 existed as cytosolic complex in resting PMN. TNF-alpha stimulation increased association of PAK1 with Akt. An MPO monoclonal antibody did not alter the Akt signaling complex further. The data demonstrate the importance of PI3-K for the ANCA-induced PMN oxidant production.

Signaling mechanisms involved in crystal-induced tissue damage

The association of crystal deposition with osteoarthritis and joint destruction is well established. Recent advances in understanding the mechanisms whereby calcium crystals contribute to cartilage damage are highlighted in this review. In vitro studies have shown that when calcium-containing crystals come in contact with cells they cause an influx in Ca 2+ concentration and activation of p42/44 mitogen-activated protein kinases. This is followed by induction of proto-oncogenes (c- fos, c- jun ) and induction of the nuclear transcription factors activator protein-1 and nuclear factor-kappaB, which in turn lead to crystal-induced modulation of normal gene expression. Some of the downstream effects known to date include increased mitogenesis, up-regulation of members of the matrix metalloproteinase family, down-regulation of tissue inhibitor of metalloproteinase-1 and -2 in fibroblasts, induction of neutrophil chemotactic chemokines such as interleukin-8, activation and degranulation of neutrophils, and inhibition of neutrophil apoptosis. Because no known drug prevents or treats the consequences of basic calcium phosphate crystal deposition, an improved understanding of the molecular mechanisms leading to crystal-induced joint degeneration is essential to the development of a rational approach to target the consequences of crystal deposition.

Activation of SHIP by NADPH oxidase-stimulated Lyn leads to enhanced apoptosis in neutrophils

Neutrophils undergo rapid spontaneous apoptosis. Multiple antiapoptotic stimuli can inhibit this process via activation of the Akt pathway. However, despite no such effect singly, combined anti- and proapoptotic stimuli inhibit Akt activity, leaving the cells susceptible to accelerated apoptosis. The blockade of Akt activation depended on reduced phosphoinositide 3,4,5-trisphosphate levels but not decreased phosphatidylinositol 3-kinase activity, thus implicating the involvement of an inositol phosphatase. Evidence for SHIP involvement was provided by SHIP localization to membrane receptors and subsequent activation along with the observed inability of SHIP -/- neutrophils to exhibit enhanced apoptosis with the stimulus combination. Activation of SHIP was found to depend on Lyn activation, and this, in turn, required NADPH oxidase. Neutrophils from chronic granulomatous disease patients and Lyn -/- mice no longer responded to the combined stimuli. Thus, we propose a role for oxidants and Lyn in SHIP regulation and suggest a novel mechanism for regulating neutrophil apoptosis.