Granulocyte-macrophage colony-stimulating factor delays neutrophil constitutive apoptosis through phosphoinositide 3-kinase and extracellular signal-regulated kinase pathways

Leptin inhibits neutrophil apoptosis in children via ERK/NF-κB-dependent pathways

Introduction and Rationale

Previous studies have shown that delayed neutrophil apoptosis is associated with chronic airway diseases. Leptin is an adipocyte-derived hormone that acts as a regulator of energy homeostasis and food intake. Emerging evidence suggests that leptin can regulate immune responses including the release of proinflammatory cytokines and protection of inflammatory cells from apoptosis. Serum leptin is increased during allergic reactions in the airways. However, the expression and function of leptin receptor in neutrophils isolated from children is not known.

Methods

Flow cytometry was used to detect leptin receptor expression in neutrophils isolated from allergic asthmatic (n = 14), allergic non asthmatic (n = 21), non allergic asthmatic (n = 7) and healthy children (n = 23); confocal laser scanning microscopy combined with immunofluorescence was performed to detect intracellular pool of leptin receptor; Annexin-V/PI staining and caspase 3 activity was used to determine neutrophil survival. Pharmacological inhibitors were utilized to understand the role of MAPK and NF-κB pathway in leptin-induced neutrophil survival.

Results and Conclusion

A heterogeneous leptin receptor expression was observed on neutrophils isolated from children. Neutrophils isolated from healthy children expressed more leptin receptor than those from allergic asthmatic (P<0.05) but not allergic non-asthmatic (P>0.05) or non-allergic asthmatic children (n = 7, P>0.05). Neutrophils isolated from children express an intracellular pool of leptin receptor that was mobilized to the cell surface upon GM-CSF stimulation. Finally, leptin exhibited anti-apoptotic properties on neutrophils via NF-κB and MEK1/2 MAPK pathway. Collectively, our data suggest that leptin may enhance airway inflammation by promoting neutrophil survival.

Bax/Mcl-1 balance affects neutrophil survival in intermittent hypoxia and obstructive sleep apnea: effects of p38MAPK and ERK1/2 signaling

BACKGROUND

Prolonged neutrophil survival is evident in various cardiovascular and respiratory morbidities, in hypoxic conditions in-vitro and in patients with obstructive sleep apnea (OSA) characterized by nightly intermittent hypoxia (IH). This may lead to persistent inflammation, tissue injury and dysfunction. We therefore investigated by a translational approach the potential contribution of the intrinsic stress-induced mitochondrial pathway in extending neutrophil survival under IH conditions. Thus, neutrophils of healthy individuals treated with IH in-vitro and neutrophils of OSA patients undergoing nightly IH episodes in-vivo were investigated. Specifically, the balance between pro-apoptotic Bax and anti-apoptotic Mcl-1 protein expression, and the potential involvement of p38MAPK and ERK1/2 signaling pathways in the control of Mcl-1 expression were investigated.

METHODS

Purified neutrophils were exposed to IH and compared to normoxia and to sustained hypoxia (SH) using a BioSpherix-OxyCycler C42 system. Bax and Mcl-1 levels, and p38MAPK and ERK1/2 phosphorylation were determined by western blotting. Also, Bax/Mcl-1 expression and Bax translocation to the mitochondria were assessed by confocal microscopy in pre-apoptotic neutrophils, before the appearance of apoptotic morphology. Co-localization of Bax and mitochondria was quantified by LSM 510 CarlZeiss MicroImaging using Manders Overlap Coefficient. A paired two-tailed t test, with Bonferroni correction for multiple comparisons, was used for statistical analysis.

RESULTS

Compared to normoxia, IH and SH up-regulated the anti-apoptotic Mcl-1 by about 2-fold, down-regulated the pro-apoptotic Bax by 41% and 27%, respectively, and inhibited Bax co-localization with mitochondria before visible morphological signs of apoptosis were noted. IH induced ERK1/2 and p38MAPKs phosphorylation, whereas SH induced only p38MAPK phosphorylation. Accordingly, both ERK and p38MAPK inhibitors attenuated the IH-induced Mcl-1 increase. In SH, only p38MAPK inhibition decreased Mcl-1 expression. Similar to neutrophils of healthy subjects exposed to IH (0.97± 0.2), in OSA neutrophils, Bax/Mcl-1 ratio was significantly lower compared to normoxic controls (1.0±0.5 vs.1.99±0.3, p=0.015), and Bax did not co-localize with mitochondria.

CONCLUSIONS

These findings suggest that decreased Bax/Mcl-1 balance promotes neutrophil survival in IH in-vitro as well as in OSA patients. Moreover, Bax/Mcl-1 protein function in IH and SH might be regulated by different signal transduction pathways, highlighting a novel regulatory function through ERK1/2 signaling in IH.

Infection with Anaplasma phagocytophilum activates the phosphatidylinositol 3-Kinase/Akt and NF-κB survival pathways in neutrophil granulocytes

Anaplasma phagocytophilum, a Gram-negative, obligate intracellular bacterium infects primarily neutrophil granulocytes. Infection with A. phagocytophilum leads to inhibition of neutrophil apoptosis and consequently contributes to the longevity of the host cells. Previous studies demonstrated that the infection inhibits the executionary apoptotic machinery in neutrophils. However, little attempt has been made to explore which survival signals are modulated by the pathogen. The aim of the present study was to clarify whether the phosphatidylinositol 3-kinase (PI3K)/Akt and NF-κB signaling pathways, which are considered as important survival pathways in neutrophils, are involved in A. phagocytophilum-induced apoptosis delay. Our data show that infection of neutrophils with A. phagocytophilum activates the PI3K/Akt pathway and suggest that this pathway, which in turn maintains the expression of the antiapoptotic protein Mcl-1, contributes to the infection-induced apoptosis delay. In addition, the PI3K/Akt pathway is involved in the activation of NF-κB in A. phagocytophilum-infected neutrophils. Activation of NF-κB leads to the release of interleukin-8 (IL-8) from infected neutrophils, which, in an autocrine manner, delays neutrophil apoptosis. In addition, enhanced expression of the antiapoptotic protein cIAP2 was observed in A. phagocytophilum-infected neutrophils. Taken together, the data indicate that upstream of the apoptotic cascade, signaling via the PI3K/Akt pathway plays a major role for apoptosis delay in A. phagocytophilum-infected neutrophils.

Activation pattern of neutrophils from blood of elderly individuals with Candida-related denture stomatitis

We have identified impaired neutrophils in elderly individuals which could be involved with Candida-related denture stomatitis (DS), an oral infection predominantly caused by Candida albicans, affecting especially elderly individuals using dental prosthesis. However, specific mechanisms performed by neutrophil contributing to the susceptibility of the elderly to DS are not fully understood. This study evaluated activation features of blood neutrophils from elderly and young individuals with DS. Blood neutrophils cultured with C. albicans from elderly subjects secreted decreased levels of CXCL8. However, C. albicans challenged-neutrophils from DS patients produced high IL-4 and IL-10, and low GM-CSF levels, regardless of age. Additional elastase activity of neutrophils from both elderly groups was detected after incubation with C. albicans, but only neutrophils from elderly DS demonstrated high myeloperoxidase activity. Therefore, DS patients have affected neutrophils, and the advance of age intensifies these damages. In summary, individuals with Candida-related denture stomatitis presented variation in the neutrophil phenotype and activation. Such alterations were more intense in neutrophils from infected elderly individuals.

Regulation of neutrophil survival/apoptosis by Mcl-1

Neutrophil granulocytes have the shortest lifespan among leukocytes in the circulation and die via apoptosis. At sites of infection or tissue injury, prolongation of neutrophil lifespan is critical for effective host defense. Apoptosis of inflammatory neutrophils and their clearance are critical control points for termination of the inflammatory response. Evasion of neutrophil apoptosis aggravates local injury and leads to persistent tissue damage. The short-lived prosurvival Bcl-2 family protein, Mcl-1 (myeloid cell leukemia-1), is instrumental in controlling apoptosis and consequently neutrophil lifespan in response to rapidly changing environmental cues during inflammation. This paper will focus on multiple levels of control of Mcl-1 expression and function and will discuss targeting Mcl-1 as a potential therapeutic strategy to enhance the resolution of inflammation through accelerating neutrophil apoptosis.

Peculiarities of cell death mechanisms in neutrophils

Analyses of neutrophil death mechanisms have revealed many similarities with other cell types; however, a few important molecular features make these cells unique executors of cell death mechanisms. For instance, in order to fight invading pathogens, neutrophils possess a potent machinery to produce reactive oxygen species (ROS), the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Evidence is emerging that these ROS are crucial in the execution of most neutrophil cell death mechanisms. Likewise, neutrophils exhibit many diverse granules that are packed with cytotoxic mediators. Of those, cathepsins were recently shown to activate pro-apoptotic B-cell lymphoma-2 (Bcl-2) family members and caspases, thus acting on apoptosis regulators. Moreover, neutrophils have few mitochondria, which hardly participate in ATP synthesis, as neutrophils gain energy from glycolysis. In spite of relatively low levels of cytochrome c in these cells, the mitochondrial death pathway is functional. In addition to these pecularities defining neutrophil death pathways, neutrophils are terminally differentiated cells, hence they do not divide but undergo apoptosis shortly after maturation. The initial trigger of this spontaneous apoptosis remains to be determined, but may result from low transcription and translation activities in mature neutrophils. Due to the unique biological characteristics of neutrophils, pharmacological intervention of inflammation has revealed unexpected and sometimes disappointing results when neutrophils were among the prime target cells during therapy. In this study, we review the current and emerging models of neutrophil cell death mechanisms with a focus on neutrophil peculiarities.

Granulocyte macrophage-colony stimulating factor shows anti-apoptotic activity in neural progenitor cells via JAK/STAT5-Bcl-2 pathway

Recently, many studies have shown that granulocyte macrophage-colony stimulating factor (GM-CSF) has anti-apoptotic activity and regulates the expression of anti-apoptotic genes including Bcl-2 family proteins in neuronal cells in vitro and in vivo. This study investigated detailed mechanism of GM-CSF involved in its anti-apoptotic activity and regulation of Bcl-2 expression in neural progenitor cells (NPCs) as a model. NPCs were cultured from the brain of E13 ICR mouse. When NPCs were treated with staurosporine at 1 μM, apoptosis occurred in more than 30% of cells in TUNEL assay. However, apoptosis was significantly inhibited by pre-treatment with GM-CSF at 10 ng/ml. Under the same experimental condition, the expression of both Bcl-2 and Bcl-xl was clearly induced by GM-CSF regardless of staurosporine treatment in RT-PCR and Western blot analyses. GM-CSF was shown to induce the expression of Bcl-2 and Bcl-xl via Janus tyrosine kinase (JAK) but not via phosphatidylinositol 3-kinase (PI3K) or RAS-mitogen activated protein kinase kinase-1 (MEK-1) using specific signal pathway inhibitors. Further analyses showed that the expression of Bcl-2 and Bcl-xl was induced by GM-CSF via signal transducers and activators of transcription 5 (STAT5) and STAT3, respectively. In addition, JAK/STAT5-Bcl-2 pathway but not JAK/STAT3-Bcl-xl pathway was responsible for the anti-apoptotic activity of GM-CSF in NPCs in TUNEL assay. To our knowledge, this study is the first report that shows differential roles of Bcl-2 and Bcl-xl, and their regulation mechanism involved in the anti-apoptotic activity of GM-CSF in NPCs.

The molecular mechanisms of glucocorticoids-mediated neutrophil survival

Neutrophil-dominated inflammation plays an important role in many airway diseases including asthma, chronic obstructive pulmonary disease (COPD), bronchiolitis and cystic fibrosis. In cases of asthma where neutrophil-dominated inflammation is a major contributing factor to the disease, treatment with corticosteroids can be problematic as corticosteroids have been shown to promote neutrophil survival which, in turn, accentuates neutrophilic inflammation. In light of such cases, novel targeted medications must be developed that could control neutrophilic inflammation while still maintaining their antibacterial/anti-fungal properties, thus allowing individuals to maintain effective innate immune responses to invading pathogens. The aim of this review is to describe the molecular mechanisms of neutrophil apoptosis and how these pathways are modulated by glucocorticoids. These new findings are of potential clinical value and provide further insight into treatment of neutrophilic inflammation in lung disease.

Granule exocytosis contributes to priming and activation of the human neutrophil respiratory burst

The role of exocytosis in the human neutrophil respiratory burst was determined using a fusion protein (TAT-SNAP-23) containing the HIV transactivator of transcription (TAT) cell-penetrating sequence and the N-terminal SNARE domain of synaptosome-associated protein-23 (SNAP-23). This agent inhibited stimulated exocytosis of secretory vesicles and gelatinase and specific granules but not azurophil granules. GST pulldown showed that TAT-SNAP-23 bound to the combination of vesicle-associated membrane protein-2 and syntaxin-4 but not to either individually. TAT-SNAP-23 reduced phagocytosis-stimulated hydrogen peroxide production by 60% without affecting phagocytosis or generation of HOCl within phagosomes. TAT-SNAP-23 had no effect on fMLF-stimulated superoxide release but significantly inhibited priming of this response by TNF-α and platelet-activating factor. Pretreatment with TAT-SNAP-23 inhibited the increase in plasma membrane expression of gp91(phox) in TNF-α-primed neutrophils, whereas TNF-α activation of ERK1/2 and p38 MAPK was not affected. The data demonstrate that neutrophil granule exocytosis contributes to phagocytosis-induced respiratory burst activity and plays a critical role in priming of the respiratory burst by increasing expression of membrane components of the NADPH oxidase.

Adenovirus-delivered angiopoietin 1 accelerates the resolution of inflammation of acute endotoxic lung injury in mice

BACKGROUND

The immune system plays a key role in protecting the organism from infection. Timely resolution of the inflammatory response to infection plays a vital role in returning homeostasis and maintaining normal organ function. Angiopoietin1 prevents endothelial activation, part of the inflammatory response to a pathogen, and has an anti-inflammatory effect in acute lung injury. We designed this study to investigate whether increasing serum production of angiopoietin1 by IV administration of adenoviral-delivered angiopoietin1 could accelerate the resolution of inflammation in endotoxin-induced acute lung injury in mice.

METHODS

Lipopolysaccharide was intratracheally instilled to induce acute lung injury in animals pretreated for 24 hours with adenoviral-GFP vector or adenoviral-GFP-angiopoietin1, respectively. An additional 6 mice in each pretreatment group were killed before lipopolysaccharide instillation to serve as controls. Indices of resolution of inflammation were analyzed. Apoptotic polymorphonuclear leukocytes and their phagocytosis by macrophages were determined by fluorescent activated cell sorter. The expression of angiopoietin1 in tissues and granulocyte macrophage colony-stimulating factor in the bronchoalveolar lavage fluid were measured.

RESULTS

Lipopolysaccharide induced leukocyte infiltration into air spaces, with maximal infiltration 48 hours after lipopolysaccharide instillation. Pretreatment with adenovirus-GFP-angiopoietin1 markedly increased angiopoietin1 expression, reduced leukocyte, and neutrophil infiltration and shortened the duration of inflammation. Adenovirus-GFP-angiopoietin1 pretreatment augmented the magnitude without altering the time course of granulocyte macrophage colony-stimulating factor.

CONCLUSIONS

Our results suggest that angiopoietin1 pretreatment promotes resolution of inflammation in endotoxin-induced acute lung injury in mice by accelerating the apoptosis of neutrophils and their phagocytosis by macrophages.

Interleukin-18 delays neutrophil apoptosis following alcohol intoxication and burn injury

Studies have shown that burn patients who are intoxicated at the time of injury are more susceptible to infection and have a higher incidence of mortality. A major cause of death in burn and trauma patients regardless of their alcohol (EtOH) exposure is multiple organ dysfunction, which is driven in part by the systemic inflammatory response and activated neutrophils. Neutrophils are short lived and undergo apoptosis to maintain homeostasis and resolution of inflammation. A delay in apoptosis of neutrophils is one important mechanism which allows for their prolonged presence and the release of potentially harmful enzymes. The purpose of this study was to examine whether EtOH intoxication combined with burn injury influences neutrophil apoptosis and whether IL-18 plays any role in this setting. To accomplish this investigation, rats were gavaged with EtOH (3.2 g/kg) 4 h before being subjected to sham or burn injury of ~12.5% of the total body surface area, and then killed on d 1 after injury. Peripheral blood neutrophils were isolated and lysed. The lysates were analyzed for pro- and antiapoptotic proteins. We found that EtOH combined with burn injury prolonged neutrophil survival. This prolonged neutrophil survival was accompanied by a decrease in the levels of the neutrophil proapoptotic protein Bax, and an increase in antiapoptotic proteins Mcl-1 and Bcl-xl. Administration of IL-18 antibody following burn injury normalized the levels of Bax, Mcl-1 and Bcl-xl. The decrease in caspase-3 and DNA fragmentation observed following EtOH and burn injury was also normalized in rats treated with anti-IL-18 antibody. These findings suggest that IL-18 delays neutrophil apoptosis following EtOH and burn injury by modulating the pro- and antiapoptotic proteins.

Protein kinase B (AKT) mediates phospholipase D activation via ERK1/2 and promotes respiratory burst parameters in formylpeptide-stimulated neutrophil-like HL-60 cells

Phospholipase D (PLD), a major source of lipid second messengers (phosphatidic acid, diglycerides) in many cell types, is tightly regulated by protein kinases, but only a few of them have been identified. We show here that protein kinase B (AKT) is a novel major signaling effector of PLD activity induced by the formylpeptide f-Met-Leu-Phe (fMLP) in human neutrophil-like HL-60 cells (dHL-60 cells). AKT inhibition with the selective antagonist AKTib1/2 almost completely prevented fMLP-mediated activity of PLD, its upstream effector ERK1/2, but not p38 MAPK. Immunoprecipitation studies show that phosphorylated AKT, ERK, and PLD2 form a complex induced by fMLP, which can be prevented by AKTib1/2. In cell-free systems, AKT1 stimulated PLD activity via activation of ERK. AKT1 actually phosphorylated ERK2 as a substrate (K(m) 1 μm). Blocking AKT activation with AKTib1/2 also prevented fMLP- but not phorbol 12-myristate 13-acetate-mediated NADPH oxidase activation (respiratory burst, RB) of dHL-60 cells. Impaired RB was associated with defective membrane translocation of NADPH oxidase components p67(phox) and p47(phox), ERK, AKT1, AKT2, but not AKT3. Depletion of AKT1 or AKT2 with antisense oligonucleotides further indicates a partial contribution of both isoforms in fMLP-induced activation of ERK, PLD, and RB, with a predominant role of AKT1. Thus, formylpeptides induce sequential activation of AKT, ERK1/2, and PLD, which represents a novel signaling pathway. A major primarily role of this AKT signaling pathway also emerges in membrane recruitment of NOX2 components p47(phox), p67(phox), and ERK, which may contribute to assembly and activation of the RB motor system, NADPH oxidase.

TLR signaling and effector functions are intact in XLA neutrophils

Toll-like receptors (TLRs) are essential components of the innate immune system, and their ligands are important activators of neutrophils. Bruton's tyrosine kinase (Btk) has been reported to mediate signaling through toll-like receptors (TLRs) in many cell types, however, the role of Btk in TLR activation of neutrophils remains unclear. Impaired TLR-induced neutrophil function was found in mice with loss of Btk and in humans with TLR-signaling defects, but the integrity of TLR pathways in X-linked agammaglobulinemia (XLA) neutrophils has not been assessed. In this study LPS (TLR4) or an imidazoquinoline compound (TLR7/8) activated XLA neutrophil shedding of surface CD62L, and phosphorylated MAP kinases p38, JNK and ERK. TLR activation also induced normal respiratory burst and retarded apoptosis for XLA neutrophils, comparable to normal controls. These data demonstrate that the loss of Btk in XLA neutrophils does not impair functional responses to TLR signals.

Flagellin delays spontaneous human neutrophil apoptosis

Neutrophils are short-lived cells that rapidly undergo apoptosis. However, their survival can be regulated by signals from the environment. Flagellin, the primary component of the bacterial flagella, is known to induce neutrophil activation. In this study we examined the ability of flagellin to modulate neutrophil apoptosis. Neutrophils cultured for 12 and 24 h in the presence of flagellin from Salmonella typhimurium at concentrations found in pathological situations underwent a marked prevention of apoptosis. In contrast, Helicobacter pylori flagellin did not affect neutrophil survival, suggesting that Salmonella flagellin exerts the antiapoptotic effect by interacting with TLR5. The delaying in apoptosis mediated by Salmonella flagellin was coupled to higher expression levels of the antiapoptotic protein Mcl-1 and lower levels of activated caspase-3. Analysis of the signaling pathways indicated that Salmonella flagellin induced the activation of the p38 and ERK1/2 MAPK pathways as well as the PI3K/Akt pathway. Furthermore, it also stimulated IkappaBalpha degradation and the phosphorylation of the p65 subunit, suggesting that Salmonella flagellin also triggers NF-kappaB activation. Moreover, the pharmacological inhibition of ERK1/2 pathway and NF-kappaB activation partially prevented the antiapoptotic effects exerted by flagellin. Finally, the apoptotic delaying effect exerted by flagellin was also evidenced when neutrophils were cultured with whole heat-killed S. typhimurium. Both a wild-type and an aflagellate mutant S. typhimurium strain promoted neutrophil survival; however, when cultured in low bacteria/neutrophil ratios, the flagellate bacteria showed a higher capacity to inhibit neutrophil apoptosis, although both strains showed a similar ability to induce neutrophil activation. Taken together, our results indicate that flagellin delays neutrophil apoptosis by a mechanism partially dependent on the activation of ERK1/2 MAPK and NF-kappaB. The ability of flagellin to delay neutrophil apoptosis could contribute to perpetuate the inflammation during infections with flagellated bacteria.

Abrogation of NF-κB signaling in human neutrophils induces neutrophil survival through sustained p38-MAPK activation

NF-κB, an important transcription factor in the regulation of cellular inflammation, is one of the prime targets for novel anti-inflammatory therapeutics. Nowadays, anti-inflammatory therapies rely mostly on steroids, which among other effects, inhibit NF-κB activity. However, steroids have only limited efficacy in the treatment on neutrophil-driven diseases, such as COPD. Human neutrophils play an important role in the pathogenesis of COPD, and clearance of these cells by apoptosis is an effective pathway for resolution of inflammation. In this study, we tested the hypothesis that modulation of the NF-κB pathway in human neutrophils affects survival. Importantly, the pharmacological NF-κB inhibitor Bay 11-7082 inhibited NF-κB signaling in human neutrophils as expected. However, we found that complete inhibition of NF-κB activity with 10 μM Bay 11-7082 prolonged neutrophil survival significantly, which was not observed with inhibitors for other signaling pathways. Bay 11-7082-induced neutrophil survival was dependent on p38-MAPK kinase activity, as the p38 kinase activity inhibitor SB203580 abrogated this response completely. Bay 11-7082 induced rapid and sustained p38 activation that correlated with inhibited NF-κB signaling and prolonged neutrophil survival. The precise role of NF-κB in regulation of p38-MAPK activation remains to be established. Under these conditions of survival, the stability of Bcl-xL but not Mcl-1 was enhanced. Although inhibition of NF-κB leads to down-regulation of inflammatory genes in many cell types, our results illustrate that interference with basal NF-κB signaling in neutrophils as a drug target should be used with caution.

Mcl-1-mediated impairment of the intrinsic apoptosis pathway in circulating neutrophils from critically ill patients can be overcome by Fas stimulation

The systemic inflammatory response syndrome and subsequent organ failure are mainly driven by activated neutrophils with prolonged life span, which is believed to be due to apoptosis resistance. However, detailed underlying mechanisms leading to neutrophil apoptosis resistance are largely unknown, and possible therapeutic options to overcome this resistance do not exist. Here we report that activated neutrophils from severely injured patients exhibit cell death resistance due to impaired activation of the intrinsic apoptosis pathway, as evidenced by limited staurosporine-induced mitochondrial membrane depolarization and decreased caspase-9 activity. Moreover, we found that these neutrophils express high levels of antiapoptotic Mcl-1 and low levels of proapoptotic Bax protein. Mcl-1 up-regulation was dependent on elevated concentrations of GM-CSF in patient serum. Accordingly, increased Mcl-1 protein stability and GM-CSF serum concentrations were shown to correlate with staurosporine-induced apoptosis resistance. However, cross-linking of neutrophil Fas by immobilized agonistic anti-Fas IgM resulted in caspase-dependent mitochondrial membrane depolarization and apoptosis induction. In conclusion, the observed impairment of the intrinsic pathway and the resulting apoptosis resistance may be overcome by immobilized agonistic anti-Fas IgM. Targeting of neutrophil Fas by immobilized agonistic effector molecules may represent a new therapeutic tool to limit neutrophil hyperactivation and its sequelae in patients with severe immune disorders.

Secondary necrosis of apoptotic neutrophils induced by the human cathelicidin LL-37 is not proinflammatory to phagocytosing macrophages

Cathelicidins are CHDP with essential roles in innate host defense but also more recently associated with the pathogenesis of certain chronic diseases. These peptides have microbicidal potential and the capacity to modulate innate immunity and inflammatory processes. PMN are key innate immune effector cells with pivotal roles in defense against infection. The appropriate regulation of PMN function, death, and clearance is critical to innate immunity, and dysregulation is implicated in disease pathogenesis. The efferocytosis of apoptotic PMN, in contrast to necrotic cells, is proposed to promote the resolution of inflammation. We demonstrate that the human cathelicidin LL-37 induced rapid secondary necrosis of apoptotic human PMN and identify an essential minimal region of LL-37 required for this activity. Using these LL-37-induced secondary necrotic PMN, we characterize the consequence for macrophage inflammatory responses. LL-37-induced secondary necrosis did not inhibit PMN ingestion by monocyte-derived macrophages and in contrast to expectation, was not proinflammatory. Furthermore, the anti-inflammatory effects of apoptotic PMN on activated macrophages were retained and even potentiated after LL-37-induced secondary necrosis. However, this process of secondary necrosis did induce the release of potentially harmful PMN granule contents. Thus, we suggest that LL-37 can be a potent inducer of PMN secondary necrosis during inflammation without promoting macrophage inflammation but may mediate host damage through PMN granule content release under chronic or dysregulated conditions.

Siglec-9 and SHP-1 are differentially expressed in neonatal and adult neutrophils

Neonatal PMN (polymorphonuclear neutrophils) exhibit altered inflammatory responsiveness and greater longevity compared with adult PMN; however, the involved mechanisms are incompletely defined. Receptors containing immunoreceptor tyrosine-based inhibitory motif (ITIM) domains promote apoptosis by activating inhibitory phosphatases, such as Src homology domain 2-containing tyrosine phosphatase-1 (SHP-1), that block survival signals. Sialic acid-binding immunoglobulin-like lectin (Siglec)-9, an immune inhibitory receptor with an ITIM domain, has been shown to induce cell death in adult PMN in association with SHP-1. To test our hypothesis that neonatal PMN inflammatory function may be modulated by unique Siglec-9 and SHP-1 interactions, we compared expression of these proteins in adult and neonatal PMN. Neonatal PMN exhibited diminished cellular expression of Siglec-9, which was phosphorylated in the basal state. Granulocyte-macrophage colony-stimulating factor (GM-CSF) treatment decreased Siglec-9 phosphorylation levels in neonatal PMN but promoted its phosphorylation in adult PMN, observations associated with altered survival signaling. Although SHP-1 expression was also diminished in neonatal PMN, GM-CSF treatment had minimal effect on phosphorylation status. Further analysis revealed that Siglec-9 and SHP-1 physically interact, as has been observed in other immune cells. Our data suggest that age-specific interactions between Siglec-9 and SHP-1 may influence the altered inflammatory responsiveness and longevity of neonatal PMN.

Ageing exacerbates damage of systemic and salivary neutrophils from patients presenting Candida-related denture stomatitis

Background

Ageing leads to a decline in the function of the immune system, increasing the body's susceptibility to infections through the impairment of T-cells, macrophages, neutrophils and dendritic cells Denture stomatitis is a primary oral disease affecting elderly denture wearers. The major etiologic factor involved in this pathology is the infection by Candida albicans, an opportunistic pathogen that causes local and disseminated diseases in immunosuppressed humans. Neutrophils play a critical role in the immune response against C. albicans and are continually present in the salivary fluid and in the blood. The aim of this study was to determine ageing-related changes in salivary and blood neutrophils and their potential implications in Candida-related denture stomatitis.

Results

Our results showed a lower number of neutrophils in the saliva from patients presenting Candida-related denture stomatitis in comparison to their matched controls. Furthermore, fewer neutrophils were isolated from the saliva of aged control individuals in comparison to matched younger subjects. CXCR1, CD62L and CD11b expression were significantly greater on systemic neutrophils from younger control individuals. Elderly individuals showed more apoptotic salivary neutrophils and lower GM-CSF levels than younger ones, regardless of the occurrence of Candida infection. On the other hand, CXCL-8 concentrations were higher in the saliva from elderly individuals. Besides, TNF-α was detected at elevated levels in the saliva from infected elderly subjects. Salivary neutrophils from elderly and young patients presented impaired phagocytic activity against C. albicans. However, just systemic neutrophils from elderly showed decreased phagocytosis when compared to the younger ones, regardless of the occurrence of infection. In addition, neutrophils from aged individuals and young patients presented low fungicidal activity.

Conclusion

The data suggests that the Candida related-denture stomatitis is associated to neutrophils function deficiency, and ageing drastically appears to alter important characteristics of such cells, facilitating the establishment of this infection.

Granulocyte-colony stimulating factor inhibits neuronal apoptosis in a rat model of diabetic cerebral ischemia

Incidence of cerebral vascular disease (CVD) is higher in patients with diabetes mellitus (DM) than that in individuals without DM, and neuronal apoptosis determines the severity of cerebral infarction. However, there is no effective therapy for CVD. Granulocyte-colony stimulating factor (G-CSF), a potent hematopoietic factor, could inhibit apoptosis of hematopoietic progenitor cells. However, its effect on neuronal cells is still unclear. In this study, we investigated the anti-apoptosis properties of G-CSF in neurons following focal cerebral ischemia in diabetic rats. The diabetic condition was generated in rats by intravenous injection of streptozotocin. After 6 weeks, diabetic rats underwent middle cerebral artery occlusion (MCAO) and received subcutaneous administration of G-CSF (50 microg/kg) daily for 7, 14 or 21 days. We analyzed the changes in neurological severity scores, infarct volume, number of apoptotic neurons, and the expression of G-CSF receptor, phosphorylated signal transducer and activator of transcription 3 (pSTAT3), cellular inhibitor of apoptosis protein 2 (cIAP2), Bcl-2, and Bax in the brain tissue. Bax is a pro-apoptotic member of the Bcl-2 protein family. The DM rats treated with G-CSF not only showed the reduced infarct volume and decreased apoptosis cell number, but also presented improved neurological scores. The G-CSF also increased the expression of pSTAT3, Bcl-2, and cIAP2 proteins as well as Bcl-2 mRNA, but inhibited Bax protein expression in the brain. These results indicate that G-CSF partially increases neuronal survival by affecting apoptosis pathways. G-CSF provides a potential treatment for stroke and other neurological dysfunction accompanied by neuronal apoptosis.

Angiotensin II in apoptotic lung injury: potential role in meconium aspiration syndrome

Meconium aspiration injures a number of cell types in the lung, most notably airway and alveolar epithelial lining cells. Recent data show that at least some of the cell death induced by meconium occurs by apoptosis, and therefore has the potential for pharmacologic inhibition through the use of apoptosis blockers or other strategies. Related work in adult animal models of lung injury has shown that apoptosis of lung epithelial cells induces a local (that is, entirely lung tissue specific) renin-angiotensin system (RAS(L)). Furthermore, this inducible RAS(L) is required for the apoptotic response and affects other adjacent cell types through the release of angiotensin II and related peptides. This manuscript reviews the published data supporting this viewpoint as well as more recent works that suggest the involvement of a RAS(L) in the perinatal lung damage associated with meconium aspiration syndrome (MAS). The implications of these findings regarding their potential for the clinical management of MAS are also discussed.

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.

Distinct role of c-Jun N-terminal kinase isoforms in human neutrophil apoptosis regulated by tumor necrosis factor-alpha and granulocyte-macrophage colony-stimulating factor

We studied the role of c-Jun N-terminal kinase (JNK) in human neutrophils stimulated by tumor necrosis factor-alpha (TNF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Stimulation of neutrophils with TNF-alpha and GM-CSF caused phosphorylation of p54 or p46 JNK or both. The phosphorylated p46 JNK band in TNF-alpha-stimulated neutrophils mobilized faster than that in GM-CSF-stimulated cells. The JNK isoform transcripts expressed in neutrophils were JNK1beta1, JNK1beta2, JNK2alpha1, and JNK2alpha2. The JNK isoforms phosphorylated by TNF-alpha and GM-CSF stimulation were found to be JNK1 and JNK2, respectively, on the basis of the molecular mass and the capture assay. TNF-alpha-induced JNK phosphorylation was sustained in the presence of cycloheximide, which was accompanied by accelerated neutrophil apoptosis. The JNK inhibitors (SP600125 and TAT-TI-JIP(153163)) suppressed neutrophil apoptosis induced by TNF-alpha plus cycloheximide, whereas they attenuated the GM-CSF-mediated antiapoptotic effect on neutrophils. The JNK inhibitor did not affect the levels of Mcl-1 and XIAP (antiapoptotic molecules), which were regulated by TNF-alpha plus cycloheximide and GM-CSF. The JNK inhibitor markedly suppressed TNF-alpha-induced and GM-CSF-induced superoxide release. These findings suggest that JNK1 and JNK2 are involved in TNF-alpha-induced neutrophil apoptosis and GM-CSF-mediated antiapoptotic effect on neutrophils, respectively, and both JNK isoforms are involved in TNF-alpha-induced and GM-CSF-induced superoxide release.

Neutrophil apoptosis: selective regulation by different ligands of integrin alphaMbeta2

Neutrophils undergo spontaneous apoptosis, but their survival can be extended during inflammatory responses. alpha(M)beta(2) is reported either to delay or accelerate neutrophil apoptosis, but the mechanisms by which this integrin can support such diametrically opposed responses are poorly understood. The abilities of closely related alpha(M)beta(2) ligands, plasminogen and angiostatin, derived from plasminogen, as well as fibrinogen and its two derivative alpha(M)beta(2) recognition peptides, P1 and P2-C, differed markedly in their effects on neutrophil apoptosis. Plasminogen, fibrinogen, and P2-C suppressed apoptosis via activation of Akt and ERK1/2 kinases, while angiostatin and P1 failed to activate these prosurvival pathways and did not prevent neutrophil apoptosis. Using cells transfected with alpha(M)beta(2) or its individual alpha(M) or beta(2) subunits, and purified receptors and its constituent chains, we show that engagement of both subunits with prosurvival ligands is essential for induction of the prosurvival response. Hence, engagement of a single integrin by closely related ligands can induce distinct signaling pathways, which can elicit distinct cellular responses.

IL-3 induces a Pim1-dependent antiapoptotic pathway in primary human basophils

The contribution of basophils in allergic disease and other Th2-type immune responses depends on their persistence at sites of inflammation, but the ligands and molecular pathways supporting basophil survival are largely unknown. The comparison of rates of apoptosis and of the expression of antiapoptotic proteins in different human granulocyte types revealed that basophils have a considerably longer spontaneous life span than neutrophils and eosinophils consistent with high levels of constitutive Bcl-2 expression. Interleukin-3 (IL-3) is the only ligand that efficiently protects basophils from apoptosis as evidenced by screening a large number of stimuli. IL-3 up-regulates the expression of the antiapoptotic proteins cIAP2, Mcl-1, and Bcl-X(L) and induces a rapid and sustained de novo expression of the serine/threonine kinase Pim1 that closely correlates with cytokine-enhanced survival. Inhibitor studies and protein transduction of primary basophils using wild-type and kinase-dead Pim1-Tat fusion-proteins demonstrate the functional importance of Pim1 induction in the IL-3-enhanced survival. Our data further indicate that the antiapoptotic Pim1-mediated pathway operates independently of PI3-kinase but involves the activation of p38 MAPK. The induction of Pim1 leading to PI3-kinase-independent survival as described here for basophils may also be a relevant antiapoptotic mechanism in other terminally differentiated leukocyte types.

Myeloperoxidase Delays Neutrophil Apoptosis Through CD11b/CD18 Integrins and Prolongs Inflammation

Polymorphonuclear neutrophil granulocytes have a central role in innate immunity and their programmed cell death and removal are critical for efficient resolution of acute inflammation. Myeloperoxidase (MPO), a heme protein abundantly expressed in neutrophils, is generally associated with killing of bacteria and oxidative tissue injury. Because MPO also binds to neutrophils, we investigated whether MPO could affect the lifespan of neutrophils. Here, we report that MPO independent of its catalytic activity through signaling via the adhesion molecule CD11b/CD18 rescued human neutrophils from constitutive apoptosis and prolonged their life span. MPO evoked a transient concurrent activation of extracellular signal-regulated kinase and Akt, leading to phosphorylation of Bad at both Ser112 and Ser136, prevention of mitochondrial dysfunction, and subsequent activation of caspase-3. Consistently, pharmacological inhibition of extracellular signal-regulated kinase, Akt, or caspase-3 reversed the antiapoptosis action of MPO. Acute increases in plasma MPO delayed murine neutrophil apoptosis assayed ex vivo. In a mouse model of self-resolving inflammation, MPO also prolonged the duration of carrageenan-induced acute lung injury, as evidenced by enhanced alveolar permeability and accumulation of neutrophils parallel with suppression of neutrophil apoptosis. Our results indicate that MPO functions as a survival signal for neutrophils and thereby contribute to prolongation of inflammation.

Acrolein inhalation suppresses lipopolysaccharide-induced inflammatory cytokine production but does not affect acute airways neutrophilia

Acrolein is a reactive unsaturated aldehyde that is produced during endogenous oxidative processes and is a major bioactive component of environmental pollutants such as cigarette smoke. Because in vitro studies demonstrate that acrolein can inhibit neutrophil apoptosis, we evaluated the effects of in vivo acrolein exposure on acute lung inflammation induced by LPS. Male C57BL/6J mice received 300 microg/kg intratracheal LPS and were exposed to acrolein (5 parts per million, 6 h/day), either before or after LPS challenge. Exposure to acrolein either before or after LPS challenge did not significantly affect the overall extent of LPS-induced lung inflammation, or the duration of the inflammatory response, as observed from recovered lung lavage leukocytes and histology. However, exposure to acrolein after LPS instillation markedly diminished the LPS-induced production of several inflammatory cytokines, specifically TNF-alpha, IL-12, and the Th1 cytokine IFN-gamma, which was associated with reduction in NF-kappaB activation. Our data demonstrate that acrolein exposure suppresses LPS-induced Th1 cytokine responses without affecting acute neutrophilia. Disruption of cytokine signaling by acrolein may represent a mechanism by which smoking contributes to chronic disease in chronic obstructive pulmonary disease and asthma.

Opposing regulation of neutrophil apoptosis through the formyl peptide receptor-like 1/lipoxin A4 receptor: implications for resolution of inflammation

Neutrophils have a central role in innate immunity, and their programmed cell death and removal are critical to the optimal expression as well as to efficient resolution of inflammation. Human neutrophils express the pleiotropic receptor formyl peptide receptor-like 1/lipoxin A4 (LXA(4)) receptor that binds a variety of ligands, including the acute-phase reactant serum amyloid A (SAA), the anti-inflammatory lipids LXA(4) and aspirin-triggered 15-epi-LXA(4) (ATL), and the glucocorticoid-inducible protein annexin 1. In addition to regulation of neutrophil activation and recruitment, these ligands have a profound influence on neutrophil survival and apoptosis with contrasting actions, mediating aggravation or resolution of the inflammatory response. Thus, annexin 1 accelerates, whereas SAA rescues human neutrophils from constitutive apoptosis by preventing mitochondrial dysfunction and subsequent activation of caspase-3. Furthermore, ATL overcomes the antiapoptosis signal from SAA and redirects neutrophils to caspase-mediated cell death. We review recent developments about the molecular basis of these actions and suggest a novel mechanism by which aspirin promotes resolution of acute inflammation and tissue injury.

A neuroprotective function for the hematopoietic protein granulocyte-macrophage colony stimulating factor (GM-CSF)

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine responsible for the proliferation, differentiation, and maturation of cells of the myeloid lineage, which was cloned more than 20 years ago. Here we uncovered a novel function of GM-CSF in the central nervous system (CNS). We identified the GM-CSF alpha-receptor as an upregulated gene in a screen for ischemia-induced genes in the cortex. This receptor is broadly expressed on neurons throughout the brain together with its ligand and induced by ischemic insults. In primary cortical neurons and human neuroblastoma cells, GM-CSF counteracts programmed cell death and induces BCL-2 and BCL-Xl expression in a dose- and time-dependent manner. Of the signaling pathways studied, GM-CSF most prominently induced the PI3K-Akt pathway, and inhibition of Akt strongly decreased antiapoptotic activity. Intravenously given GM-CSF passes the blood-brain barrier, and decreases infarct damage in two different experimental stroke models (middle cerebral artery occlusion (MCAO), and combined common carotid/distal MCA occlusion) concomitant with induction of BCL-Xl expression. Thus, GM-CSF acts as a neuroprotective protein in the CNS. This finding is remarkably reminiscent of the recently discovered functionality of two other hematopoietic factors, erythropoietin and granulocyte colony-stimulating factor in the CNS. The identification of a third hematopoietic factor acting as a neurotrophic factor in the CNS suggests a common principle in the functional evolution of these factors. Clinically, GM-CSF now broadens the repertoire of hematopoietic factors available as novel drug candidates for stroke and neurodegenerative diseases.

Akt in the pathogenesis of COPD

In this review we consider the therapeutic potential of targeting Akt for the treatment of COPD. Akt is a serine/threonine protein kinase that functions as a signaling intermediate linked to multiple signaling programs involved in survival, inflammation, and growth. Akt is closely associated with key membrane-bound receptors and represents a convergent integration point for multiple stimuli implicated in COPD pathogenesis. Persistent activation of Akt secondary to somatic mutations in regulatory oncogenes, such as PTEN, may explain why inflammation in COPD does not resolve when smoking is ceased. Akt is also implicated in the systemic manifestations of COPD such as skeletal muscle wasting and metabolic disturbances. Furthermore, targeting Akt may provide a useful means of limiting the severity and duration of disease exacerbations in COPD. As such, Akt represents a particularly attractive therapeutic target for the treatment of COPD. Interestingly, current knowledge suggests that both inhibitors and activators of Akt may be useful for treating different clinical subpopulations of COPD patients.

Phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase regulate induction of Mcl-1 and survival in glucocorticoid-treated human neutrophils

BACKGROUND

Glucocorticoids have been shown to inhibit human neutrophil apoptosis, with implications that this might help accentuate neutrophilic inflammation.

OBJECTIVE

The aim of this study was to investigate the molecular mechanisms involved in glucocorticoid-mediated inhibition of primary human neutrophil apoptosis.

METHODS

Primary human neutrophils were isolated from peripheral blood of healthy volunteers and cultured in vitro with dexamethasone.

RESULTS

Here we confirm that dexamethasone, a classical glucocorticoid, significantly inhibited apoptosis of primary human neutrophils. This inhibition was not dependent on transrepression of proapoptotic molecules but was associated with induction of antiapoptotic Mcl-1. Remarkably, glucocorticoid-mediated enhancement of Mcl-1 and survival were significantly suppressed by pharmacologic inhibition of p38 mitogen-activated protein kinase or phosphatidylinositol 3-kinase. Inhibition of the above kinases also blocked glucocorticoid-induced maintenance of mitochondrial transmembrane potential and suppression of caspases.

CONCLUSION

Phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase are protein kinases that regulate the prosurvival effect of glucocorticoids on human neutrophils.

Mechanisms of neutrophil death in human immunodeficiency virus-infected patients: role of reactive oxygen species, caspases and map kinase pathways

Neutrophils from human immunodeficiency virus-positive (HIV+) patients have an increased susceptibility to undergo programmed cell death (PCD), which could explain neutropenia during advanced disease. In this work, key steps of PCD have been evaluated in neutrophils from HIV+ patients. The role of caspase-3, caspase-8, mitogen activated protein kinase (MAPK) and reactive oxygen species (ROS) was analysed. Spontaneous neutrophil death is dependent upon caspase-3 but independent of caspase-8, suggesting that the intrinsic pathway is involved as a pathogenic mechanism of PCD. Inhibition of ROS decreased spontaneous PCD and caspase-3 hydrolysis, connecting oxidative stress and caspase-3 activation with neutrophil PCD in HIV-infected patients. Additionally, an increased neutrophil death was observed in HIV+ patients, following inhibition of p38 MAPK, suggesting a role for p38 MAPK in cell survival during the disease. We conclude that oxidative stress secondary to HIV infection can accelerate neutrophil death.

Inhibition of caspase-dependent spontaneous apoptosis via a cAMP-protein kinase A dependent pathway in neutrophils from sickle cell disease patients

Sickle cell disease (SCD) is a chronic inflammatory condition characterized by high leucocyte counts, altered cytokine levels and endothelial cell injury. As the removal of inflammatory cells by apoptosis is fundamental for the resolution of inflammation, we aimed to determine whether the leucocyte apoptotic process is altered in SCD. Neutrophils from SCD individuals showed an inhibition of spontaneous apoptosis when cultured in vitro, in the presence of autologous serum for 20 h. Intracellular cyclic adenosine monophosphate (cAMP) levels were approximately twofold increased in SCD neutrophils; possible cAMP-upregulating factors present in SCD serum include interleukin-8, granulocyte-macrophage colony-stimulating factor and prostaglandin. Accordingly, co-incubation of SCD neutrophils with KT5720, a cAMP-dependent protein kinase (PKA) inhibitor, abrogated increased SCD neutrophil survival. Caspase-3 activity was also significantly diminished in SCD neutrophils cultured for 16 h and this activity was restored when cells were co-incubated with KT5720. BIRC2 (encoding cellular inhibitor of apoptosis protein 1, cIAP(1)), MCL1 and BAX expression were unaltered in SCD neutrophils; however, BIRC3 (encoding the caspase inhibitor, cIAP(2)), was expressed at significantly higher levels. Thus, we report an inhibition of spontaneous SCD neutrophil apoptosis that appears to be mediated by upregulated cAMP-PKA signalling and decreased caspase activity. Increased neutrophil survival may have significant consequences in SCD; contributing to leucocytosis, tissue damage and exacerbation of the chronic inflammatory state.

Apoptosis of human neutrophils induced by protein phosphatase 1/2A inhibition is caspase-independent and serine protease-dependent

Protein phosphatase (PP) activity is associated with the regulation of apoptosis in neutrophils. However, the underlying regulatory mechanism(s) in apoptosis remain unclear. The type of cell death induced by okadaic acid (OA), the inhibitor of PP1 and PP2A, is characterized by apoptotic morphological changes of the cells and annexin V-positive staining without DNA fragmentation. The apoptotic effects of OA and calyculin A on neutrophils were observed at concentrations ranging from 50 to 200 nM, or 10 to 50 nM, respectively. Cyclosporine A (a PP2B specific inhibitor), however, did not exhibit any pro-apoptotic effects. OA and calyculin A, but not cyclosporine A, exhibited significant effects on protein levels and on the electrophoretic mobility of Mcl-1. zVAD-fmk, a pancaspase inhibitor, failed to inhibit the effect of OA on the caspase-3 activity, procaspase-3 processing, and the apoptotic rate of neutrophils. However, 4-(2-aminoethyl) benzenesulfonylfluoride (AEBSF), a general serine protease inhibitor, significantly abrogated the OA-induced mobility shift in procaspase-3, caspase-3 activation, and the apoptotic morphological changes in neutrophils. Moreover, OA enhanced the serine protease activity of the neutrophils. The addition of the proteinase-3 protein increased the rate of neutrophil apoptosis, which was also blocked by AEBSF but not by zVAD-fmk. These results suggest that OA induces procaspase-3 processing but that OA-induced apoptosis is caspase-independent and serine protease-dependent.

Age-related impairment of GM-CSF-induced signalling in neutrophils: role of SHP-1 and SOCS proteins

Functional activities of mature human neutrophils are strongly influenced by the pro-inflammatory cytokine granulocyte macrophage-colony stimulating factor (GM-CSF). Accordingly, a defective response to GM-CSF might have dramatic consequences for neutrophil functions and the host defence against infections. Such an event is most likely to occur in senescence. A number of studies have, in fact, reported an impairment of the GM-CSF capacity to prime and/or to activate respiratory burst, as well as to delay apoptotic events, in neutrophils from elderly individuals. In the last 2 decades many efforts have been made to explore at molecular levels the mechanism underlying these defects. Recent studies let us depict a scenario in which an increased activity of inhibitory molecules, such as Src homology domain-containing protein tyrosine phosphatase-1 (SHP-1) and suppressors of cytokine signalling (SOCS), is responsible for the age-related failure of GM-CSF to stimulate neutrophil functions via inhibition of Lyn-, phosphoinositide 3-kinase (PI3-K)/extracellular signal-regulated kinase (ERK)- and signal transducers and activators of transcription (STAT)-dependent pathways. The control of SHP-1 and/or SOCS activity might therefore be an important therapeutic target for the restoration of normal immune responses during senescence.

The role of Toll-like receptors in the regulation of neutrophil migration, activation, and apoptosis

Toll-like receptors (TLRs) play an essential role in the detection of invading pathogens and in the induction of host antimicrobial defenses. TLR4, the major endotoxin receptor, and TLR2, with agonists derived principally from gram-positive organisms, are likely to be important in the pathogenesis of sepsis. Both TLR2 and TLR4 agonists regulate important neutrophil functions, including adhesion, generation of reactive oxygen species, and release of chemokines, and activate major proinflammatory signaling pathways, including the nuclear factor- kappa B pathway. TLR stimulation produces only a modest direct inhibition of neutrophil apoptosis, although this signal is greatly amplified by the presence of monocytes, suggesting that regulation of the life span of neutrophils by TLR agonists may be principally mediated by responses of other endotoxin-responsive cells. We suggest that activation of neutrophils by TLRs is highly regulated, permitting acute neutrophil antimicrobial responses to TLR activation while providing a "brake" on inflammation by requiring the presence of mononuclear cells to significantly extend neutrophil survival.

Aspirin-Triggered Lipoxins Override the Apoptosis-Delaying Action of Serum Amyloid A in Human Neutrophils: A Novel Mechanism for Resolution of Inflammation

Elevated plasma levels of the acute-phase reactant serum amyloid A (SAA) have been used as a marker and predictor of inflammatory diseases. SAA regulates leukocyte activation; however, it is not known whether it also modulates neutrophil apoptosis, which is critical to the optimal expression and resolution of inflammation. Culture of human neutrophils with SAA (0.1-20 microg/ml) markedly prolonged neutrophil longevity by delaying constitutive apoptosis. SAA evoked concurrent activation of the ERK and PI3K/Akt signaling pathways, leading to phosphorylation of BAD at Ser(112) and Ser(136), respectively, and to prevention of collapse of mitochondrial transmembrane potential, cytochrome c release, and caspase-3 activation. These actions were abrogated by pharmacological inhibition of the formyl peptide receptor, ERK or PI3K. Furthermore, aspirin-triggered 15-epi-lipoxin A(4) (15-epi-LXA(4)) and its stable analog 15-epi-16-p-fluorophenoxy-LXA(4), which binds to the same receptor as SAA, effectively overrode the antiapoptosis signal from SAA even when neutrophils were treated with 15-epi-LXA(4) at either 1 or 4 h postculture with SAA. 15-Epi-LXA(4) itself did not affect neutrophil survival and apoptosis. Our results indicate that SAA at clinically relevant concentrations promotes neutrophil survival by suppressing the apoptotic machinery, an effect that can be opposed by 15-epi-LXA(4). The opposing actions of SAA and aspirin-triggered 15-epi-LXA(4) may contribute to the local regulation of exacerbation and resolution of inflammation, respectively.

The phosphatidylinositol 3-kinase signaling pathway exerts protective effects during sepsis by controlling C5a-mediated activation of innate immune functions

The PI3K/Akt signaling pathway has been recently suggested to have controversial functions in models of acute and chronic inflammation. Our group and others have reported previously that the complement split product C5a alters neutrophil innate immunity and cell signaling during the onset of sepsis and is involved in PI3K activation. We report in this study that in vivo inhibition of the PI3K pathway resulted in increased mortality in septic mice accompanied by strongly elevated serum levels of TNF-alpha, IL-6, MCP-1, and IL-10 during sepsis as well as decreased oxidative burst activity in blood phagocytes. PI3K inhibition in vitro resulted in significant increases in TLR-4-mediated generation of various proinflammatory cytokines in neutrophils, whereas the opposite effect was observed in PBMC. Oxidative burst and phagocytosis activity was significantly attenuated in both neutrophils and monocytes when PI3K activation was blocked. In addition, PI3K inhibition resulted in strongly elevated TLR-4-mediated generation of IL-1beta and IL-8 in neutrophils when these cells were co-stimulated with C5a. C5a-induced priming effects on neutrophil and monocyte oxidative burst activity as well as C5a-induced phagocytosis in neutrophils were strongly reduced when PI3K activation was blocked. Our data suggest that the PI3K/Akt signaling pathway controls various C5a-mediated effects on neutrophil and monocyte innate immunity and exerts an overall protective effect during experimental sepsis.

Dual effect of AMD3100, a CXCR4 antagonist, on bleomycin-induced lung inflammation

The chemokine receptor CXCR4, which binds the chemokine stromal cell-derived factor 1, has been reported to be involved in the chemotaxis of inflammatory cells. In addition, AMD3100, an antagonist of CXCR4, has been reported to be an attractive drug candidate for therapeutic intervention in several disorders in which CXCR4 is critically involved. However, little is known about the therapeutic value of AMD3100 in the treatment of pulmonary fibrosis. In this study, we examined the effects of AMD3100 on a murine bleomycin-induced pulmonary fibrosis model. Concurrent administration of AMD3100 and bleomycin apparently attenuated bleomycin-induced pulmonary inflammation. In this process, an inhibition of neutrophil recruitment at early stage followed by the decrease of other inflammatory cell recruitment in the lung were observed. In addition, it also inhibited the expression of cytokines, including MCP-1, MIP-2, MIP-1alpha, and TGF-beta. In contrast, when AMD3100 was administered following bleomycin treatment, the bleomycin-induced lung inflammation progressed and resulted in severe pulmonary fibrosis. In this process, an increase of inflammatory cell recruitment, an up-regulation of lung MCP-1 and TGF-beta, and a remarkable activation of p44/42 MAPK in neutrophils were observed. U0126, an inhibitor of p44/42 MAPK, significantly abolished these effects. Thus, AMD3100 has dual effect on bleomycin-induced pulmonary fibrosis. Difference of inflammatory cell recruitment and activation might be associated with the dual effect of AMD3100 on bleomycin-induced pulmonary fibrosis.

Hsp27 regulates Akt activation and polymorphonuclear leukocyte apoptosis by scaffolding MK2 to Akt signal complex

We have shown previously that Akt exists in a signal complex with p38 MAPK, MAPK-activated protein kinase-2 (MK2), and heat shock protein 27 (Hsp27) and MK2 phosphorylates Akt on Ser-473. Additionally, dissociation of Hsp27 from Akt, prior to Akt activation, induced polymorphonuclear leukocyte (PMN) apoptosis. However, the role of Hsp27 in regulating Akt activation was not examined. This study tested the hypothesis that Hsp27 regulates Akt activation and promotes cell survival by scaffolding MK2 to the Akt signal complex. Here we show that loss of Akt/Hsp27 interaction by anti-Hsp27 antibody treatment resulted in loss of Akt/MK2 interaction, loss of Akt-Ser-473 phosphorylation, and induced PMN apoptosis. Transfection of myristoylated Akt (AktCA) in HK-11 cells induced Akt-Ser-473 phosphorylation, activation, and Hsp27-Ser-82 phosphorylation. Cotransfection of AktCA with Hsp27 short interfering RNA, but not scrambled short interfering RNA, silenced Hsp27 expression, without altering Akt expression in HK-11 cells. Silencing Hsp27 expression inhibited Akt/MK2 interaction, inhibited Akt phosphorylation and Akt activation, and induced HK-11 cell death. Deletion mutagenesis studies identified acidic linker region (amino acids 117-128) on Akt as an Hsp27 binding region. Deletion of amino acids 117-128 on Akt resulted in loss of its interaction with Hsp27 and MK2 but not with Hsp90 as demonstrated by immunoprecipitation and glutathione S-transferase pulldown studies. Co-transfection studies demonstrated that constitutively active MK2 (MK2EE) phosphorylated Aktwt (wild type) on Ser-473 but failed to phosphorylate Akt(Delta117-128) mutant in transfixed cells. These studies collectively define a novel role of Hsp27 in regulating Akt activation and cellular apoptosis by mediating interaction between Akt and its upstream activator MK2.

Role of phosphoinositide 3-kinase and extracellular signal-regulated kinase pathways in granulocyte macrophage-colony-stimulating factor failure to delay fas-induced neutrophil apoptosis in elderly humans

Fas-stimulated neutrophils from elderly individuals show impaired granulocyte macrophage-colony-stimulating factor (GM-CSF)-induced apoptosis cell rescue. Herein, this defect was found to be associated with a significant reduction in GM-CSF-mediated Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Using Akt and ERK1/2 inhibitors, we demonstrated that both kinases were critical for GM-CSF antiapoptotic effects. Whereas Akt inhibition also affected GM-CSF-dependent ERK1/2 phosphorylation, ERK1/2 inhibition did not affect GM-CSF-induced Akt phosphorylation, suggesting that phosphoinositide 3-kinase (PI3-K)/Akt and ERK1/2 are activated in series and that PI3-K is located upstream of ERK1/2 along the GM-CSF-dependent signaling pathway. No age-associated changes in GM-CSF receptor expression were observed. Interestingly, both suppressors of cytokine signaling (SOCS)1 and SOCS3 proteins were significantly higher in unstimulated neutrophils from elderly individuals and, unlike in young individuals, did not further increase following GM-CSF cell triggering. These results indicate that defective PI3-K/Akt/ERK1/2 activation, likely dependent on elevated SOCS1 and SOCS3 levels, may affect the GM-CSF capacity to delay neutrophil apoptosis in elderly persons.