Extracellular matrix regulates apoptosis in human neutrophils

The extracellular matrix - immune microenvironment crosstalk in cancer therapy: Challenges and opportunities

Targeting the tumour immune microenvironment (TIME) by cancer immunotherapy has led to improved patient outcomes. However, response to these treatments is heterogeneous and cancer-type dependant. The therapeutic activity of classical cancer therapies such as chemotherapy, radiotherapy, and surgical oncology is modulated by alterations of the TIME. A major regulator of immune cell function and resistance to both immune and classical therapies is the extracellular matrix (ECM). Concurrently, cancer therapies reshape the TIME as well as the ECM, causing both pro- and anti-tumour responses. Accordingly, the TIME-ECM crosstalk presents attractive opportunities to improve therapy outcomes. Here, we review the molecular crosstalk between the TIME and the ECM in cancer and its implications in cancer progression and clinical intervention. Additionally, we discuss examples and future directions of ECM and TIME co-targeting in combination with oncological therapies including surgery, chemotherapy, and radiotherapy.

The cardiac wound healing response to myocardial infarction

Myocardial infarction (MI) is defined as evidence of myocardial necrosis consistent with prolonged ischemia. In response to MI, the myocardium undergoes a series of wound healing events that initiate inflammation and shift to anti-inflammation before transitioning to tissue repair that culminates in scar formation to replace the region of the necrotic myocardium. The overall response to MI is determined by two major steps, the first of which is the secretion of proteases by infiltrating leukocytes to breakdown extracellular matrix (ECM) components, a necessary step to remove necrotic cardiomyocytes. The second step is the generation of new ECM that comprises the scar; and this step is governed by the cardiac fibroblasts as the major source of new ECM synthesis. The leukocyte component resides in the middle of the two-step process, contributing to both sides as the leukocytes transition from pro-inflammatory to anti-inflammatory and reparative cell phenotypes. The balance between the two steps determines the final quantity and quality of scar formed, which in turn contributes to chronic outcomes following MI, including the progression to heart failure. This review will summarize our current knowledge regarding the cardiac wound healing response to MI, primarily focused on experimental models of MI in mice. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Immune System Diseases > Molecular and Cellular Physiology.

Endothelial inflammation and neutrophil transmigration are modulated by extracellular matrix composition in an inflammation-on-a-chip model

Inflammatory diseases are often characterised by excessive neutrophil infiltration from the blood stream to the site of inflammation, which damages healthy tissue and prevents resolution of inflammation. Development of anti-inflammatory drugs is hindered by lack of in vitro and in vivo models which accurately represent the disease microenvironment. In this study, we used the OrganoPlate to develop a humanized 3D in vitro inflammation-on-a-chip model to recapitulate neutrophil transmigration across the endothelium and subsequent migration through the extracellular matrix (ECM). Human umbilical vein endothelial cells formed confluent vessels against collagen I and geltrex mix, a mix of basement membrane extract and collagen I. TNF-α-stimulation of vessels upregulated inflammatory cytokine expression and promoted neutrophil transmigration. Intriguingly, major differences were found depending on the composition of the ECM. Neutrophils transmigrated in higher number and further in geltrex mix than collagen I, and did not require an N-formyl-methionyl-leucyl-phenylalanine (fMLP) gradient for transmigration. Inhibition of neutrophil proteases inhibited neutrophil transmigration on geltrex mix, but not collagen I. These findings highlight the important role of the ECM in determining cell phenotype and response to inhibitors. Future work could adapt the ECM composition for individual diseases, producing accurate models for drug development.

Overexpression of Neutrophil MMP-9 and HIF-1α May Contribute to the Finger-Like Projections Formation and Histo-Pathogenesis in Nasal Inverted Papilloma

Background

Nasal inverted papilloma (NIP) is defined based on its histological characteristic of inverted epithelium growth into the stroma. The inversion can result in epithelial growth in the underlying connective tissue stroma when the basement membrane completely separates from the epithelial layer. To date, such inversion mechanism underlying NIP's pathological phenomenon is unknown. Therefore, we hypothesized that mediators and soluble proteins released by neutrophils, the most predominant infiltrating cells in NIP, is vital in causing the epithelial changes and pathogenesis of NIP.

Methods

We collected 37 NIP tissues from patients who underwent surgical removal of NIP and performed hematoxylin-eosin (HE), immunohistochemical, and immunofluorescence staining to analyze in-depth the basic characteristics of NIP, including detecting the expression and distribution of MMPs and associated factors in NIP. Western blotting and quantitative real-time PCR were further performed to analyze the protein and mRNA expression levels of specific factors including MMPs, HIF-1α, and tissue inhibitors of metalloproteinases (TIMPs).

Results

We observed finger-like projections that insert into the epithelium in NIP tissue as its main characteristics. The projections contain fibroblasts, extracellular matrix, capillaries, and infiltrating inflammatory cells. We found abundant neutrophils clustered at the finger-like projection of NIP, and also noted MMP-1 and MMP-9 were up-regulated in NIP (p<0.05), whereas TIMP-1/3 was decreased. The expression level of HIF-1α was also found to be increased in NIP tissue. We further showed that MMP-9 and HIF-1α were mainly expressed by neutrophils and were predominantly observed in the finger-like projections that contribute to the NIP pathology.

Conclusion

Upregulation and release of MMP-9 and HIF-1α from infiltrating neutrophils may cause damage to the epithelial basement membrane and epithelial clefts, forming finger-like projections with angiogenesis and fibroblasts insertion, resulting in epithelial growth in the tissue stroma, a typical histo-pathological characteristic in NIP.

Neutrophils: Many Ways to Die

Neutrophils or polymorphonuclear leukocytes (PMN) are key participants in the innate immune response for their ability to execute different effector functions. These cells express a vast array of membrane receptors that allow them to recognize and eliminate infectious agents effectively and respond appropriately to microenvironmental stimuli that regulate neutrophil functions, such as activation, migration, generation of reactive oxygen species, formation of neutrophil extracellular traps, and mediator secretion, among others. Currently, it has been realized that activated neutrophils can accomplish their effector functions and simultaneously activate mechanisms of cell death in response to different intracellular or extracellular factors. Although several studies have revealed similarities between the mechanisms of cell death of neutrophils and other cell types, neutrophils have distinctive properties, such as a high production of reactive oxygen species (ROS) and nitrogen species (RNS), that are important for their effector function in infections and pathologies such as cancer, autoimmune diseases, and immunodeficiencies, influencing their cell death mechanisms. The present work offers a synthesis of the conditions and molecules implicated in the regulation and activation of the processes of neutrophil death: apoptosis, autophagy, pyroptosis, necroptosis, NETosis, and necrosis. This information allows to understand the duality encountered by PMNs upon activation. The effector functions are carried out to eliminate invading pathogens, but in several instances, these functions involve activation of signaling cascades that culminate in the death of the neutrophil. This process guarantees the correct elimination of pathogenic agents, damaged or senescent cells, and the timely resolution of the inflammation that is essential for the maintenance of homeostasis in the organism. In addition, they alert the organism when the immunological system is being deregulated, promoting the activation of other cells of the immune system, such as B and T lymphocytes, which produce cytokines that potentiate the microbicide functions.

Cancer Extracellular Matrix Proteins Regulate Tumour Immunity

The extracellular matrix (ECM) plays an increasingly recognised role in the development and progression of cancer. Whilst significant progress has been made in targeting aspects of the tumour microenvironment such as tumour immunity and angiogenesis, there are no therapies that address the cancer ECM. Importantly, immune function relies heavily on the structure, physics and composition of the ECM, indicating that cancer ECM and immunity are mechanistically inseparable. In this review we highlight mechanisms by which the ECM shapes tumour immunity, identifying potential therapeutic targets within the ECM. These data indicate that to fully realise the potential of cancer immunotherapy, the cancer ECM requires simultaneous consideration.

Update on Neutrophil Function in Severe Inflammation

Neutrophils are main players in the effector phase of the host defense against micro-organisms and have a major role in the innate immune response. Neutrophils show phenotypic heterogeneity and functional flexibility, which highlight their importance in regulation of immune function. However, neutrophils can play a dual role and besides their antimicrobial function, deregulation of neutrophils and their hyperactivity can lead to tissue damage in severe inflammation or trauma. Neutrophils also have an important role in the modulation of the immune system in response to severe injury and trauma. In this review we will provide an overview of the current understanding of neutrophil subpopulations and their function during and post-infection and discuss the possible mechanisms of immune modulation by neutrophils in severe inflammation.

Mesenchymal Stromal Cells as Active Regulators of Lymphocyte Recruitment to Blood Vascular Endothelial Cells

Methods are described for analyzing adhesion and migration of isolated lymphocytes on endothelial cell monolayers which have been cocultured with different mesenchymal stromal cells, with or without additional cytokine treatment. The different cells types are grown on opposite sides of 3.0 or 0.4 μm pore filters, depending on whether migration through the whole construct is to be analyzed, or adhesion to the endothelial cells alone. Migration away from the sub-endothelial space and through the stromal layer can also be assessed by culturing mesenchymal stromal cells within a 3-D collagen gel overlaid with endothelial cells. Assays may be "static" or the filter-based constructs can be incorporated into flow chambers so that cell behavior can be directly observed under conditions simulating those in vivo. In general, by choice of method, one can evaluate efficiency of attachment, and ability of cells to migrate across the endothelial monolayer, through the filter and through the stromal cell layer in 2-D or 3-D. Fluorescence microscopic examination of fixed filters can be used, e.g., to ascertain whether lymphocytes are retained by stromal cells. In general, static assays have the higher throughput and greatest ease of use, while the flow-based assays are more physiologically relevant and allow detailed recording of cell behavior in real time.

Influence of stromal cells on lymphocyte adhesion and migration on endothelial cells

Methods are described for analysing adhesion and migration of isolated lymphocytes on endothelial cell monolayers which have been co-cultured with different stromal cells, with or without additional cytokine treatment. The different cells types are grown on opposite sides of 3.0- or 0.4-mum pore filters depending on whether migration through the whole construct is to be analysed or adhesion to the endothelial cells alone. Assays may be "static" or filters can be incorporated into flow chambers so that cell behaviour can be directly observed under conditions simulating those in vivo. In general, by choice of method, one can evaluate efficiency of attachment and ability of cells to migrate across the endothelial monolayer, through the filter and through the stromal cell layer. Fluorescence microscopic examination of fixed filters can be used, e.g. to ascertain whether lymphocytes are retained by stromal cells. In general, static assays have the higher throughput and greatest ease of use, while the flow-based assays are more physiologically relevant and allow detailed recording of cell behaviour in real time.

The role of complement opsonization in interactions between F. tularensis subsp. novicida and human neutrophils

The remarkable infectiousness of Francisella tularensis suggests that the bacterium efficiently evades innate immune responses that typically protect the host during its continuous exposure to environmental and commensal microbes. In our studies of the innate immune response to F. tularensis, we have observed that, unlike the live vaccine strain (LVS) of F. tularensis subsp. holarctica, F. tularensis subsp. novicida U112 opsonized in pooled human serum activated the NADPH oxidase when incubated with human neutrophils. Given previous observations that F. tularensis fixes relatively small quantities of complement component C3 during incubation in human serum and the importance of C3 to neutrophil phagocytosis, we hypothesized that F. tularensis subsp. novicida may fix C3 in human serum more readily than would LVS. We now report that F. tularensis subsp. novicida fixed approximately six-fold more C3 than did LVS when incubated in 50% pooled human serum and that this complement opsonization was antibody-mediated. Furthermore, antibody-mediated C3 deposition enhanced bacterial uptake and was indispensable for the neutrophil oxidative response to F. tularensis subsp. novicida. Taken together, our results reveal important differences between these two strains of F. tularensis and may, in part, explain the low virulence of F. tularensis subsp. novicida for humans.

Vascular cells contribute to atherosclerosis by cytokine- and innate-immunity-related inflammatory mechanisms

Cardiovascular diseases are the human diseases with the highest death rate and atherosclerosis is one of the major underlying causes of cardiovascular diseases. Inflammatory and innate immune mechanisms, employing monocytes, innate receptors, innate cytokines, or chemokines are suggested to be involved in atherogenesis. Among the inflammatory pathways the cytokines are central players. Plasma levels of cytokines and related proteins, such as CRP, have been investigated in cardiovascular patients, tissue mRNA expression was analyzed and correlations to vascular diseases established. Consistent with these findings the generation of cytokine-deficient animals has provided direct evidence for a role of cytokines in atherosclerosis. In vitro cell culture experiments further support the suggestion that cytokines and other innate mechanisms contribute to atherogenesis. Among the initiation pathways of atherogenesis are innate mechanisms, such as toll-like-receptors (TLRs), including the endotoxin receptor TLR4. On the other hand, innate cytokines, such as IL-1 or TNF, or even autoimmune triggers may activate the cells. Cytokines potently activate multiple functions relevant to maintain or spoil homeostasis within the vessel wall. Vascular cells, not least smooth muscle cells, can actively contribute to the inflammatory cytokine-dependent network in the blood vessel wall by: (i) production of cytokines; (ii) response to these potent cell activators; and (iii) cytokine-mediated interaction with invading cells, such as monocytes, T-cells, or mast cells. Activation of these pathways results in accumulation of cells and increased LDL- and ECM-deposition which may serve as an 'immunovascular memory' resulting in an ever-growing response to subsequent invasions. Thus, vascular cells may potently contribute to the inflammatory pathways involved in development and acceleration of atherosclerosis.

Identification and characterization of infiltrating macrophages in acetaminophen-induced liver injury

The role of macrophages in the pathogenesis of acetaminophen (APAP)-induced liver injury remains controversial, as it has been demonstrated that these cells display pro-toxicant and hepato-protective functions. This controversy may stem from the heterogeneity and/or plasticity of macrophages and the difficulty in distinguishing and differentially studying subpopulations of macrophages in the liver. In the present study, using flow cytometric analysis and fluorescence-labeled antibodies against specific cell surface macrophage markers, we were able to, for the first time, identify an APAP-induced macrophage (IM) population distinct from resident Kupffer cells. The data demonstrated that the IMs were derived from circulating monocytes that infiltrated the liver following APAP-induced liver injury. The IMs exhibited a phenotype consistent with that of alternatively activated macrophages and demonstrated the ability to phagocytize apoptotic cells and induce apoptosis of neutrophils. Furthermore, in the absence of the IMs, the resolution of hepatic damage following APAP-induced hepatotoxicity was delayed in CCR2(-/-) mice compared with wild-type mice. These findings likely contribute to the role of the IMs in the processes of tissue repair, including counteracting inflammation and promoting angiogenesis. The present study also demonstrated the ability of separating populations of macrophages and delineating distinct functions of each group in future studies of inflammatory disease in the liver and other tissues.

Apoptosis and Bax, Bcl-2, Mcl-1 expression in neutrophils of Crohn's disease patients

BACKGROUND

The etiology of Crohn's disease (CD) remains unknown, and the defective function of neutrophils appears to be associated with this pathology. Neutrophils undergo spontaneous apoptosis which, if not tightly regulated, can induce the development of chronic inflammatory disease. The Bcl-2 protein family is also involved in the regulation of neutrophil apoptosis.

METHODS

This study investigated the apoptosis and expression of some regulatory factors in CD patient and control polymorphonuclear neutrophils (PMN) in suspension and in adhesion on fibronectin, an extracellular matrix protein. These 2 conditions mimic circulating neutrophils before they are recruited at the intestinal levels, and their adhesion to tissue.

RESULTS

Apoptosis in CD patient PMN was delayed in suspension and accelerated in adhesion, which is the opposite of what happens in controls. Higher levels of Bax, Bcl-2, and Mcl-1 proteins were registered in freshly isolated CD patient PMN, in contrast to controls, in which Bcl-2 protein was undetectable. Among the studied pro- and antiapoptotic factors, Bax levels seem to be mainly related to the difference in apoptosis between PMN of CD patients and controls.

CONCLUSIONS

For the first time it has been demonstrated by direct experimental evidence that apoptosis in CD patient PMN is regulated differently from that of control PMN. Abnormal expression of regulating apoptosis proteins is shown in CD patient PMN. These data suggest that the defective functionality of neutrophils can be the early event responsible for the altered mucosal immune response in CD, and that neutrophil apoptosis may offer a new target for specific drugs and therapy tools.

Analysis of leukocyte migration through monolayers of cultured endothelial cells

In this chapter methods are described for analyzing the adhesion and migration of isolated leukocytes on endothelial cell monolayers that have been cultured on different substrates and treated with cytokines. When endothelial cells are grown on porous filters inserted in wells, the levels of leukocyte adhesion and migration are calculated from the number added and the numbers retrieved from the upper and lower chambers. Fluorescence microscopic examination of the fixed filters can be used to ascertain whether leukocytes are retained above or below the filter. Direct observations of the time course of migration can be made when endothelial cells are cultured in six-well plates after leukocytes are allowed to settle onto them for a short period. In a more specialized assay, leukocytes are perfused through glass capillaries coated with endothelial cells, and again, direct video-microscopic observations are made. In this assay all stages of capture, immobilization, and migration can be followed. In general, the filter-based assay has the highest throughput and greatest ease of use but yields less detailed information, whereas the flow-based assay is most difficult to set up but is most physiologically relevant.

Neisseria gonorrhoeae delays the onset of apoptosis in polymorphonuclear leukocytes

Neisseria gonorrhoeae (gonococcus) infection results in recruitment of polymorphonuclear leukocytes (PMNs) to the urethral lumen. Recent work from our laboratory demonstrated that N. gonorrhoeae resists killing and replicates within PMNs. In this study, we examined the effect of gonococci on PMN viability. Using both transmission electron microscopy and light microscopy, we observed nuclear condensation after 6 h in PMNs that were resting or challenged with opsonized zymosan particles (OPZ). In contrast, N. gonorrhoeae delayed nuclear condensation in PMNs for 12 h (13% apoptotic PMNs vs. 90% for resting and 94% for OPZ-stimulated PMNs). Additionally, DNA fragmentation was reduced in PMNs challenged with gonococci for 12 h (28% apoptosis vs. 52% for resting and 98% for OPZ-stimulated PMNs). However, 74% of PMNs challenged with gonococci had condensed nuclei and 67% had fragmented DNA after 24 h. Caspase activity (total caspase, caspase-3/7, caspase-9) was reduced at 4 h and mitochondrial integrity was preserved at 2 h in PMNs challenged with N. gonorrhoeae. Quantitative reverse transcription polymerase chain reaction demonstrated that mRNA levels of X-IAP and cIAP-2 remained high after challenge with gonococci, but were downregulated in OPZ-stimulated PMNs. Collectively, these findings demonstrate that N. gonorrhoeae delayed apoptosis in PMNs, perhaps as a strategy to allow intracellular replication.

Chemokine- and adhesion-dependent survival of neutrophils after transmigration through cytokine-stimulated endothelium

We examined the fate of neutrophils following transmigration through an endothelial monolayer cultured on "Transwell" membrane filters. Treatment of human umbilical vein endothelial cells (HUVEC) with increasing doses of tumor necrosis factor-alpha increased the efficiency of transmigration and markedly reduced apoptosis among the transmigrated neutrophils in a dose-dependent manner. Apoptosis was also inhibited after transmigration of neutrophils through HUVEC stimulated with interleukin (IL)-1beta but not so effectively after chemotaxis through unstimulated HUVEC driven by IL-8 added below the filter. Inhibition of beta2-integrin binding after transmigration or coating the lower chamber with a nonadhesive polymer (polyhydroxyl-ethyl-methacrylate) abrogated neutrophil survival. Although integrin engagement during migration itself was not essential to inhibit apoptosis, activation of neutrophils through CXC chemokine receptors was necessary. Quite brief exposure to the HUVEC (30-120 min) was effective in reducing subsequent apoptosis, although if coincubation with the HUVEC were prolonged, neutrophil apoptosis was reduced further. Neutralization of granulocyte macrophage-colony stimulating factor inhibited this additional effect. Thus, a complex interplay between migration- and activation-dependent signals and adhesive interaction in tissue may combine to effectively prolong the survival of neutrophils recruited during inflammation.

The effect of fever‐like temperatures on neutrophil signaling

The effect of fever on neutrophils has not been explored. We tested the hypothesis that fever-like temperature spikes affect neutrophil signaling and function. Prior 60 min, 42 degrees C heat exposure inhibited p38 MAPK, ERK, PI3-Kinase/Akt, and NF-kappaB activation in TNF-alpha-challenged suspended neutrophils. Using pharmacological inhibitors and an inhibitory peptide transduced into neutrophils by a HIV-TAT sequence, we found that p38 MAPK and NF-kappaB mediate TNF-alpha-mediated delayed apoptosis in suspended neutrophils. Heat exposure (39-42 degrees C) did not affect constitutive apoptosis but abrogated TNF-alpha-delayed apoptosis in these suspended cells. In contrast, adhesion-dependent functions were not inhibited. Furthermore, we found that heat exposure neither blocked p38 MAPK, ERK, and NF-kappaB activation in neutrophils on fibronectin nor prevented delayed apoptosis by TNF-alpha when cells interacted with fibronectin. Above and beyond apoptosis, TNF-alpha initiated NF-kappaB-dependent gene transcription. Heat exposure blocked this effect in suspended neutrophils but not in neutrophils on fibronectin. Finally, we show that beta2-integrins, which are not necessary for TNF-alpha-induced NF-kappaB activation at 37 degrees C, transduce costimulatory signals allowing NF-kappaB activation after heat exposure. The effect could protect circulating neutrophils from TNF-alpha activation, while not interfering with activation of adherent neutrophils. Fever could make neutrophils more parsimonious.

The CD11/CD18 (beta2) integrins modulate neutrophil caspase activation and survival following TNF-alpha or endotoxin induced transendothelial migration

Neutrophils (PMN) are short-lived cells but their survival is often prolonged in inflammation. The beta2 (CD11/CD18) integrins are involved in PMN migration into inflammation but their role in PMN survival is not well understood. We investigated the role of beta2 integrins in PMN caspase activation, a key enzyme cascade in apoptosis. After 20 h, caspase activation (Western blotting) was markedly decreased in PMN cultured on fibrinogen, a ligand for Mac-1 (CD11b/CD18), but not on fibronectin or albumin. In the presence of TNF-alpha or endotoxin (LPS), blockade of CD18 (beta2 chain) with mAb markedly increased caspase activation in PMN on fibrinogen. PMN which migrated through endothelium in vitro in response to TNF-alpha, LPS, IL-1alpha, IL-8 or C5a contained 58% fewer active caspase positive PMN after 20 h than non-migrated PMN remaining on the endothelium. When beta2 (CD18) integrin or lymphocyte function antigen (LFA)-1 (CD11a) plus Mac1 (CD11b) were blocked by mAb (intact or Fab'), the proportion of migrated PMN (but not of non-migrated PMN) with active caspases was significantly increased (2-4-fold) and this was associated with accelerated PMN apoptosis and death. Thus, engagement of ligands on extracellular matrix and endothelium by the beta2 integrins Mac-1 and LFA-1 plays a role in delaying apoptosis in PMN recruited in response to LPS and TNF-alpha. Inhibition of beta2 integrin function may not only inhibit PMN infiltration, but also accelerate PMN clearance from inflamed tissue.

Effect of carotenoid oxidation products on neutrophil viability and function

Human neutrophils are short-lived cells that play important roles in host defense and acute inflammation by releasing hydrolytic and cytotoxic proteins and reactive oxygen derivatives. Apoptosis, a physiological mechanism for cell death, regulates both production and survival of neutrophils, representing a basic biological mechanism for this type of cells. Carotenoids may react with toxic oxygen metabolites released by neutrophils to form a multitude of carotenoid cleavage products that exert, in turn, relevant prooxidative biological effects. Recent data suggest that carotenoid oxidation products may affect neutrophil viability and function by exerting proapoptotic activity and interfering with superoxide production by activated cells. The prooxidant and proapoptotic activities of carotenoid oxidation products could account, at least in some cases, for the procancerogenic properties of carotenoid rich diet.

C5a delays apoptosis of human neutrophils by a phosphatidylinositol 3-kinase-signaling pathway

BACKGROUND

Studies have shown that survival factors including cytokines and growth factors delay apoptosis of human neutrophils via induction of the phosphatidylinositol-3 kinase (PI 3-K)/Akt pathway. In the present study, we explored whether complement fragment C5a has a modulatory effect on neutrophil apoptosis through this signaling pathway.

METHODS

Human neutrophils were isolated and treated with C5a for up to 24 hours, with or without wortmannin, a PI 3-K inhibitor, and staurosporine, a caspase-9 activator. Apoptosis was quantified by flow cytometry, using propidium iodide nuclear staining, and confirmed by the detection of DNA fragmentation on gel electrophoresis. PI 3-K downstream signaling events were evaluated by measuring the expression of cytosolic total and phosphorylated Akt and Bad proteins by Western blot analyses, and caspase-9 activity.

RESULTS

C5a inhibited neutrophil apoptosis in a dose- and time-dependent manner. The anti-apoptotic effects of C5a were markedly abrogated in the presence of wortmannin. Brief stimulation of neutrophils with C5a induced phosphorylation of Akt and Bad proteins through a PI 3-K-dependent pathway. Caspase-9 activity was minimal in C5a-treated cells, but markedly increased following PI 3-K inhibition by wortmannin. Finally, C5a reduced caspase-9 activity in staurosporine-treated cells.

CONCLUSIONS

This study demonstrates that C5a inhibits neutrophil apoptosis via a PI 3-K signaling pathway. This effect may be an important mechanism that improves cell survival and function in the inflammatory milieu.

Promotion of neutrophil apoptosis by TNF-alpha

We examined the ability of TNF-alpha to modulate human neutrophil apoptosis. Neutrophils cultured with TNF-alpha alone undergo a low but significant increase in the number of apoptotic cells. More interestingly, when neutrophils were pretreated with TNF-alpha for 1-2 min at 37 degrees C and then were exposed to a variety of agents such as immobilized IgG, IgG-coated erythrocytes, complement-treated erythrocytes, zymosan, PMA, zymosan-activated serum, fMLP, Escherichia coli, and GM-CSF for 3 h at 37 degrees C, a marked stimulation of apoptosis was observed. Similar results were obtained in neutrophils pretreated with TNF-alpha for 30 min, 1 h, 3 h, and 18 h. Dose-dependent studies showed that TNF-alpha enhances neutrophil apoptosis at concentrations ranging from 1 to 100 ng/ml. In contrast to the observations made in neutrophils pretreated with TNF-alpha, there was no stimulation of apoptosis when TNF-alpha was added to neutrophils previously activated by conventional agonists. Experiments performed to establish the mechanism through which TNF-alpha promotes neutrophil apoptosis showed that neither reactive oxygen intermediates nor the Fas/Fas ligand system appear to be involved. Our results suggest that TNF-alpha plays a critical role in the control of neutrophil survival by virtue of its ability to induce an apoptotic death program which could be triggered by a variety of conventional agonists.

Uremic toxins modulate the spontaneous apoptotic cell death and essential functions of neutrophils

Clearance of neutrophils via apoptosis from the site of infection is crucial for the coordinated resolution of inflammation. The balance between stimulating and attenuating as well as between pro- and anti-apoptotic factors is necessary for maintenance of an effective immune response without the harmful side effects of neutrophil action. This article describes the effect of glucose-modified serum proteins and of free immunoglobulin light chains (IgLCs) on neutrophil functions and apoptosis. Both groups of proteins are found at elevated levels in sera of uremic patients. Glucose-modified proteins increase both the chemotactic movement of neutrophils and the activation of glucose uptake. Spontaneous neutrophil apoptosis is increased in the presence of these modified serum proteins. On the other hand, the presence of free IgLCs, previously shown to diminish neutrophil chemotaxis and the activation of glucose uptake, increase the percentage of viable neutrophils by inhibiting spontaneous apoptotic cell death. We conclude that both glucose-modified proteins and free IgLCs can be considered to be uremic toxins and both contribute to the disturbed immune function in uremic patients. Their concentrations as well as the microenvironment in which they are acting seem to be important for their actual effects.

Differential roles for alpha(M)beta(2) integrin clustering or activation in the control of apoptosis via regulation of akt and ERK survival mechanisms

The role of integrins in leukocyte apoptosis is unclear, some studies suggest enhancement, others inhibition. We have found that beta(2)-integrin engagement on neutrophils can either inhibit or enhance apoptosis depending on the activation state of the integrin and the presence of proapoptotic stimuli. Both clustering and activation of alpha(M)beta(2) delays spontaneous, or unstimulated, apoptosis, maintains mitochondrial membrane potential, and prevents cytochrome c release. In contrast, in the presence of proapoptotic stimuli, such as Fas ligation, TNFalpha, or UV irradiation, ligation of active alpha(M)beta(2) resulted in enhanced mitochondrial changes and apoptosis. Clustering of inactive integrins did not show this proapoptotic effect and continued to inhibit apoptosis. This discrepancy was attributed to differential signaling in response to integrin clustering versus activation. Clustered, inactive alpha(M)beta(2) was capable of stimulating the kinases ERK and Akt. Activated alpha(M)beta(2) stimulated Akt, but not ERK. When proapoptotic stimuli were combined with either alpha(M)beta(2) clustering or activation, Akt activity was blocked, allowing integrin activation to enhance apoptosis. Clustered, inactive alpha(M)beta(2) continued to inhibit stimulated apoptosis due to maintained ERK activity. Therefore, beta(2)-integrin engagement can both delay and enhance apoptosis in the same cell, suggesting that integrins can play a dual role in the apoptotic progression of leukocytes.

Enhancement of TNF-alpha-induced apoptosis by immobilized arginine-glycine-aspartate: involvement of a tyrosine kinase-dependent, MAP kinase-independent mechanism

Extracellular matrix facilitates anchorage-dependent cell survival via interaction of its arginine-glycine-aspartate (RGD) motif with integrins. In this report, we describe an unexpected, apoptosis-promoting the effect of immobilized RGD (iRGD) on tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. Mesangial cells cultured on RGD-coated plates showed enhanced susceptibility to TNF-alpha-induced apoptosis. iRGD alone did not affect cell survival. In contrast, iRGD did not facilitate but inhibited apoptosis induced by H(2)O(2). Mitogen-activated protein (MAP) kinases and tyrosine kinases are important mediators for the RGD-integrin signaling. Pretreatment with MAP kinase kinase inhibitor PD098059, c-Jun N-terminal kinase (JNK)-c-Jun/AP-1 inhibitor curcumin or p38 MAP kinase inhibitor SB203580 did not attenuate the apoptosis-promoting effect of iRGD. Consistently, transfection with dominant-negative mutants of extracellular signal-regulated kinases, JNK or p38 MAP kinase did not inhibit the effect of iRGD. In contrast, protein tyrosine kinase inhibitors, genistein, and herbimycin A, abrogated the apoptosis-promoting effect of iRGD. Of note, TNF-alpha-induced apoptosis on uncoated plates was not attenuated by tyrosine kinase inhibitors. These data provide the first evidence that iRGD accelerates certain apoptosis. We identified that the effect was mediated by the tyrosine kinase-dependent, MAP kinase-independent mechanism.

Macrophage-induced neutrophil apoptosis

Macrophages (Mphi) contribute to the resolution of early inflammation by recognizing and ingesting apoptotic polymorphonuclear neutrophils (PMN). In addition, experiments reported here demonstrated that Mphi can actively induce PMN apoptosis. Coculture of cells from 2- or 5-day-old wounds in rats, or of Mphi purified from such preparations, with PMN-rich wound cell populations obtained 1 day after wounding increased PMN apoptosis by >3-fold. Neither resident- nor Proprionibacterium acnes-elicited peritoneal Mphi-induced PMN apoptosis. Apoptosis was not mediated by a soluble factor and required E:T contact. Fixed wound-Mphi and membrane isolates from viable Mphi were as effective as intact cells in inducing PMN apoptosis. Mphi-induced apoptosis was inhibited by peptide Arg-Gly-Asp-Ser, anti-beta3 (CD61) Ab, CD36 peptide, or anti-TNF-alpha Ab. Soluble TNF-alpha did not induce PMN apoptosis. In additional studies, K562 cells (negative for beta3, TNF-alpha, and Fas ligand) transfected to express either alphavbeta3 integrin, an uncleavable membrane form of TNF-alpha, or both were used in cocultures with wound PMN. Only the double transfectants were able to induce PMN apoptosis, an effect inhibited by anti-beta3 (CD61) or anti-TNF-alpha Abs. These results demonstrate that wound Mphi induce PMN apoptosis through a constitutive effector mechanism requiring both intercellular binding through integrin-ligand interactions and membrane-bound TNF-alpha.

Shear stress-induced apoptosis of adherent neutrophils: a mechanism for persistence of cardiovascular device infections

The mechanisms underlying problematic cardiovascular device-associated infections are not understood. Because the outcome of the acute response to infection is largely dependent on the function of neutrophils, the persistence of these infections suggests that neutrophil function may be compromised because of cellular responses to shear stress. A rotating disk system was used to generate physiologically relevant shear stress levels (0-18 dynes/cm(2); 1 dyne = 10 microN) at the surface of a polyetherurethane urea film. We demonstrate that shear stress diminishes phagocytic ability in neutrophils adherent to a cardiovascular device material, and causes morphological and biochemical alterations that are consistent with those described for apoptosis. Complete neutrophil apoptosis occurred at shear stress levels above 6 dynes/cm(2) after only 1 h. Morphologically, these cells displayed irreversible cytoplasmic and nuclear condensation while maintaining intact membranes. Analysis of neutrophil area and filamentous actin content demonstrated concomitant decreases in both cell area and actin content with increasing levels of shear stress. Neutrophil phagocytosis of adherent bacteria decreased with increasing shear stress. Biochemical alterations included membrane phosphatidylserine exposure and DNA fragmentation, as evaluated by in situ annexin V and terminal deoxynucleotidyltransferase-mediated dUTP end labeling (TUNEL) assays, respectively. The potency of the shear-stress effect was emphasized by comparative inductive studies with adherent neutrophils under static conditions. The combination of tumor necrosis factor-alpha and cycloheximide was ineffective in inducing >21% apoptosis after 3 h. These findings suggest a mechanism through which shear stress plays an important role in the development of bacterial infections at the sites of cardiovascular device implantation.