Apoptotic Cell-Directed Resolution of Lung Inflammation Requires Myeloid αv Integrin-Mediated Induction of Regulatory T Lymphocytes.

Intratracheal instillation of apoptotic cells enhances resolution of experimental lung inflammation by incompletely understood mechanisms. We report that this intervention induces functional regulatory T lymphocytes (Tregs) in mouse lung experimentally inflamed by intratracheal administration of lipopolysaccharide. Selective depletion demonstrated that Tregs were necessary for maximal apoptotic cell-directed enhancement of resolution, and adoptive transfer of additional Tregs was sufficient to promote resolution without administering apoptotic cells. After intratracheal instillation, labeled apoptotic cells were observed in most CD11c+CD103+ myeloid dendritic cells migrating to mediastinal draining lymph nodes and bearing migratory and immunoregulatory markers, including increased CCR7 and ß8 integrin (ITGB8) expression. In mice deleted for αv integrin in the myeloid line to reduce phagocytosis of dying cells by CD103+ dendritic cells, exogenous apoptotic cells failed to induce transforming growth factor-ß1 expression or Treg accumulation and failed to enhance resolution of lipopolysaccharide-induced lung inflammation. We conclude that in murine lung, myeloid phagocytes encountering apoptotic cells can deploy αv integrin-mediated mechanisms to induce Tregs and enhance resolution of acute inflammation.

Molecular detection of Gram-positive bacteria in the human lung through an optical fiber-based endoscope.

PURPOSE: The relentless rise in antimicrobial resistance is a major societal challenge and requires, as part of its solution, a better understanding of bacterial colonization and infection. To facilitate this, we developed a highly efficient no-wash red optical molecular imaging agent that enables the rapid, selective, and specific visualization of Gram-positive bacteria through a bespoke optical fiber-based delivery/imaging endoscopic device. METHODS: We rationally designed a no-wash, red, Gram-positive-specific molecular imaging agent (Merocy-Van) based on vancomycin and an environmental merocyanine dye. We demonstrated the specificity and utility of the imaging agent in escalating in vitro and ex vivo whole human lung models (n = 3), utilizing a bespoke fiber-based delivery and imaging device, coupled to a wide-field, two-color endomicroscopy system. RESULTS: The imaging agent (Merocy-Van) was specific to Gram-positive bacteria and enabled no-wash imaging of S. aureus within the alveolar space of whole ex vivo human lungs within 60 s of delivery into the field-of-view, using the novel imaging/delivery endomicroscopy device. CONCLUSION: This platform enables the rapid and specific detection of Gram-positive bacteria in the human lung.

Mcl-1 protects eosinophils from apoptosis and exacerbates allergic airway inflammation.

Eosinophils are key effector cells in allergic diseases. Here we investigated Mcl-1 (an anti-apoptotic protein) in experimental allergic airway inflammation using transgenic overexpressing human Mcl-1 mice (hMcl-1) and reducing Mcl-1 by a cyclin-dependent kinase inhibitor. Overexpression of Mcl-1 exacerbated allergic airway inflammation, with increased bronchoalveolar lavage fluid cellularity, eosinophil numbers and total protein, and an increase in airway mucus production. Eosinophil apoptosis was suppressed by Mcl-1 overexpression, with this resistance to apoptosis attenuated by cyclin-dependent kinase inhibition which also rescued Mcl-1-exacerbated allergic airway inflammation. We propose that targeting Mcl-1 may be beneficial in treatment of allergic airway disease.

Mer-mediated eosinophil efferocytosis regulates resolution of allergic airway inflammation.

BACKGROUND: Eosinophils play a central role in propagation of allergic diseases, including asthma. Both recruitment and retention of eosinophils regulate pulmonary eosinophilia, but the question of whether alterations in apoptotic cell clearance by phagocytes contributes directly to resolution of allergic airway inflammation remains unexplored. OBJECTIVES: In this study we investigated the role of the receptor tyrosine kinase Mer in mediating apoptotic eosinophil clearance and allergic airway inflammation resolution in vivo to establish whether apoptotic cell clearance directly affects the resolution of allergic airway inflammation. METHODS: Alveolar and bone marrow macrophages were used to study Mer-mediated phagocytosis of apoptotic eosinophils. Allergic airway inflammation resolution was modeled in mice by using ovalbumin. Fluorescently labeled apoptotic cells were administered intratracheally or eosinophil apoptosis was driven by administration of dexamethasone to determine apoptotic cell clearance in vivo. RESULTS: Inhibition or absence of Mer impaired phagocytosis of apoptotic human and mouse eosinophils by macrophages. Mer-deficient mice showed delayed resolution of ovalbumin-induced allergic airway inflammation, together with increased airway responsiveness to aerosolized methacholine, increased bronchoalveolar lavage fluid protein levels, altered cytokine production, and an excess of uncleared dying eosinophils after dexamethasone treatment. Alveolar macrophage phagocytosis was significantly Mer dependent, with the absence of Mer attenuating apoptotic cell clearance in vivo to enhance inflammation in response to apoptotic cells. CONCLUSIONS: We demonstrate that Mer-mediated apoptotic cell clearance by phagocytes contributes to resolution of allergic airway inflammation, suggesting that augmenting apoptotic cell clearance is a potential therapeutic strategy for treating allergic airway inflammation.

Delayed neutrophil apoptosis enhances NET formation in cystic fibrosis.

BACKGROUND: Cystic fibrosis (CF) lung disease is defined by large numbers of neutrophils and associated damaging products in the airway. Delayed neutrophil apoptosis is described in CF although it is unclear whether this is a primary neutrophil defect or a response to chronic inflammation. Increased levels of neutrophil extracellular traps (NETs) have been measured in CF and we aimed to investigate the causal relationship between these phenomena and their potential to serve as a driver of inflammation. We hypothesised that the delay in apoptosis in CF is a primary defect and preferentially allows CF neutrophils to form NETs, contributing to inflammation. METHODS: Blood neutrophils were isolated from patients with CF, CF pigs and appropriate controls. Neutrophils were also obtained from patients with CF before and after commencing ivacaftor. Apoptosis was assessed by morphology and flow cytometry. NET formation was determined by fluorescent microscopy and DNA release assays. NET interaction with macrophages was examined by measuring cytokine generation with ELISA and qRT-PCR. RESULTS: CF neutrophils live longer due to decreased apoptosis. This was observed in both cystic fibrosis transmembrane conductance regulator (CFTR) null piglets and patients with CF, and furthermore was reversed by ivacaftor (CFTR potentiator) in patients with gating (G551D) mutations. CF neutrophils formed more NETs and this was reversed by cyclin-dependent kinase inhibitor exposure. NETs provided a proinflammatory stimulus to macrophages, which was enhanced in CF. CONCLUSIONS: CF neutrophils have a prosurvival phenotype that is associated with an absence of CFTR function and allows increased NET production, which can in turn induce inflammation. Augmenting neutrophil apoptosis in CF may allow more appropriate neutrophil disposal, decreasing NET formation and thus inflammation.

Cerebral Concussion Primes the Lungs for Subsequent Neutrophil-Mediated Injury.

OBJECTIVES: Mild traumatic brain injury in the form of concussion is extremely common, and the potential effects on pulmonary priming have been underestimated. The aim of this study was to characterize the pulmonary response following mild traumatic brain injury and assess the pulmonary susceptibility to lung injury after a subsequent innocuous pulmonary insult. DESIGN: Experimental in vivo study. SETTING: University research laboratory. SUBJECTS: Male CD1 mice. INTERVENTIONS: We developed a model of concussive traumatic brain injury in mice followed by pulmonary acid microaspiration. To assess the dependent role of neutrophils in mediating pulmonary injury, we specifically depleted neutrophils. MEASUREMENTS AND MAIN RESULTS: Lateral fluid percussion to the brain resulted in neuronal damage and neutrophil infiltration as well as extensive pulmonary interstitial neutrophil accumulation but no alveolar injury. Following subsequent innocuous acid microaspiration, augmented alveolar neutrophil influx led to the development of pulmonary hemorrhage that was reduced following neutrophil depletion. CONCLUSIONS: This model shows for the first time that innocuous acid microaspiration is sufficient to induce neutrophil-mediated lung injury following mild concussion and that the extracranial effects of mild traumatic brain injury have been underestimated.

The cyclin-dependent kinase inhibitor AT7519 accelerates neutrophil apoptosis in sepsis-related acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is a neutrophil-dominant disorder with no effective pharmacological therapies. While the cyclin-dependent kinase inhibitor AT7519 induces neutrophil apoptosis to promote inflammation resolution in preclinical models of lung inflammation, its potential efficacy in ARDS has not been examined. Untreated peripheral blood sepsis-related ARDS neutrophils demonstrated prolonged survival after 20 hours in vitro culture. AT7519 was able to override this phenotype to induce apoptosis in ARDS neutrophils with reduced expression of the pro-survival protein Mcl-1. We demonstrate the first pharmacological compound to induce neutrophil apoptosis in sepsis-related ARDS, highlighting cyclin-dependent kinase inhibitors as potential novel therapeutic agents.

Novel role for endogenous mitochondrial formylated peptide-driven formyl peptide receptor 1 signalling in acute respiratory distress syndrome.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is an often fatal neutrophil-dominant lung disease. Although influenced by multiple proinflammatory mediators, identification of suitable therapeutic candidates remains elusive. We aimed to delineate the presence of mitochondrial formylated peptides in ARDS and characterise the functional importance of formyl peptide receptor 1 (FPR1) signalling in sterile lung inflammation. METHODS: Mitochondrial formylated peptides were identified in bronchoalveolar lavage fluid (BALF) and serum of patients with ARDS by liquid chromatography-tandem mass spectrometry. In vitro, human neutrophils were stimulated with mitochondrial formylated peptides and their effects assessed by flow cytometry and chemotaxis assay. Mouse lung injury was induced by mitochondrial formylated peptides or hydrochloric acid. Bone marrow chimeras determined the contribution of myeloid and parenchymal FPR1 to sterile lung inflammation. RESULTS: Mitochondrial formylated peptides were elevated in BALF and serum from patients with ARDS. These peptides drove neutrophil activation and chemotaxis through FPR1-dependent mechanisms in vitro and in vivo. In mouse lung injury, inflammation was attenuated in Fpr1-/- mice, effects recapitulated by a pharmacological FPR1 antagonist even when administered after the onset of injury. FPR1 expression was present in alveolar epithelium and chimeric mice demonstrated that both myeloid and parenchymal FPR1 contributed to lung inflammation. CONCLUSIONS: We provide the first definitive evidence of mitochondrial formylated peptides in human disease and demonstrate them to be elevated in ARDS and important in a mouse model of lung injury. This work reveals mitochondrial formylated peptide FPR1 signalling as a key driver of sterile acute lung injury and a potential therapeutic target in ARDS.

The role of formylated peptides and formyl peptide receptor 1 in governing neutrophil function during acute inflammation.

Neutrophil migration to sites of inflammation and the subsequent execution of multiple functions are designed to contain and kill invading pathogens. These highly regulated and orchestrated processes are controlled by interactions between numerous receptors and their cognate ligands. Unraveling and identifying those that are central to inflammatory processes may represent novel therapeutic targets for the treatment of neutrophil-dominant inflammatory disorders in which dysregulated neutrophil recruitment, function, and elimination serve to potentiate rather than resolve an initial inflammatory insult. The first G protein-coupled receptor to be described on human neutrophils, formyl peptide receptor 1 (FPR1), is one such receptor that plays a significant role in the execution of these functions through multiple intracellular signaling pathways. Recent work has highlighted important observations with regard to both receptor function and the importance and functional relevance of FPR1 in the pathogenesis of a range of both sterile and infective inflammatory conditions. In this review, we explore the multiple components of neutrophil migration and function in both health and disease, with a focus on the role of FPR1 in these processes. The current understanding of FPR1 structure, function, and signaling is examined, alongside discussion of the potential importance of FPR1 in inflammatory diseases suggesting that FPR1 is a key regulator of the inflammatory environment.

Wogonin induces eosinophil apoptosis and attenuates allergic airway inflammation.

RATIONALE: Eosinophils are key effector cells in allergic diseases, including allergic rhinitis, eczema, and asthma. Their tissue presence is regulated by both recruitment and increased longevity at inflamed sites. OBJECTIVES: To investigate the ability of the flavone wogonin to induce eosinophil apoptosis in vitro and attenuate eosinophil-dominant allergic inflammation in vivo in mice. METHODS: Human and mouse eosinophil apoptosis in response to wogonin was investigated by cellular morphology, flow cytometry, mitochondrial membrane permeability, and pharmacological caspase inhibition. Allergic lung inflammation was modeled in mice sensitized and challenged with ovalbumin. Bronchoalveolar lavage (BAL) and lung tissue were examined for inflammation, mucus production, and inflammatory mediator production. Airway hyperresponsiveness to aerosolized methacholine was measured. MEASUREMENTS AND MAIN RESULTS: Wogonin induced time- and concentration-dependent human and mouse eosinophil apoptosis in vitro. Wogonin-induced eosinophil apoptosis occurred with activation of caspase-3 and was inhibited by pharmacological caspase inhibition. Wogonin administration attenuated allergic airway inflammation in vivo with reductions in BAL and interstitial eosinophil numbers, increased eosinophil apoptosis, reduced airway mucus production, and attenuated airway hyperresponsiveness. This wogonin-induced reduction in allergic airway inflammation was prevented by concurrent caspase inhibition in vivo. CONCLUSIONS: Wogonin induces eosinophil apoptosis and attenuates allergic airway inflammation, suggesting that it has therapeutic potential for the treatment of allergic inflammation in humans.

Flavones induce neutrophil apoptosis by down-regulation of Mcl-1 via a proteasomal-dependent pathway.

Neutrophil apoptosis and subsequent nonphlogistic clearance by surrounding phagocytes are key to the successful resolution of neutrophilic inflammation, with dysregulated apoptosis reported in multiple human inflammatory diseases. Enhancing neutrophil apoptosis has proresolution and anti-inflammatory effects in preclinical models of inflammation. Here we investigate the ability of the flavones apigenin, luteolin, and wogonin to induce neutrophil apoptosis in vitro and resolve neutrophilic inflammation in vivo. Human neutrophil apoptosis was assessed morphologically and by flow cytometry following incubation with apigenin, luteolin, and wogonin. All three flavones induced time- and concentration-dependent neutrophil apoptosis (apigenin, EC=12.2 µM; luteolin, EC=14.6 µM; and wogonin, EC=28.9 µM). Induction of apoptosis was caspase dependent, as it was blocked by the broad-spectrum caspase inhibitor Q-VD-OPh and was associated with both caspase-3 and caspase-9 activation. Flavone-induced apoptosis was preceded by down-regulation of the prosurvival protein Mcl-1, with proteasomal inhibition preventing flavone-induced Mcl-1 down-regulation and apoptosis. The flavones abrogated the survival effects of mediators that prolong neutrophil life span, including lipoteichoic acid, peptidoglycan, dexamethasone, and granulocyte-macrophage colony stimulating factor, by driving apoptosis. Furthermore, wogonin enhanced resolution of established neutrophilic inflammation in a zebrafish model of sterile tissue injury. Wogonin-induced resolution was dependent on apoptosis in vivo as it was blocked by caspase inhibition. Our data show that the flavones induce neutrophil apoptosis and have potential as neutrophil apoptosis-inducing anti-inflammatory, proresolution agents.

C5a-mediated neutrophil dysfunction is RhoA-dependent and predicts infection in critically ill patients.

Critically ill patients are at heightened risk for nosocomial infections. The anaphylatoxin C5a impairs phagocytosis by neutrophils. However, the mechanisms by which this occurs and the relevance for acquisition of nosocomial infection remain undetermined. We aimed to characterize mechanisms by which C5a inhibits phagocytosis in vitro and in critically ill patients, and to define the relationship between C5a-mediated dysfunction and acquisition of nosocomial infection. In healthy human neutrophils, C5a significantly inhibited RhoA activation, preventing actin polymerization and phagocytosis. RhoA inhibition was mediated by PI3Kδ. The effects on RhoA, actin, and phagocytosis were fully reversed by GM-CSF. Parallel observations were made in neutrophils from critically ill patients, that is, impaired phagocytosis was associated with inhibition of RhoA and actin polymerization, and reversed by GM-CSF. Among a cohort of 60 critically ill patients, C5a-mediated neutrophil dysfunction (as determined by reduced CD88 expression) was a strong predictor for subsequent acquisition of nosocomial infection (relative risk, 5.8; 95% confidence interval, 1.5-22; P = .0007), and remained independent of time effects as assessed by survival analysis (hazard ratio, 5.0; 95% confidence interval, 1.3-8.3; P = .01). In conclusion, this study provides new insight into the mechanisms underlying immunocompromise in critical illness and suggests novel avenues for therapy and prevention of nosocomial infection.

Cyclin-dependent kinase inhibitors enhance the resolution of inflammation by promoting inflammatory cell apoptosis.

Apoptosis is essential for clearance of potentially injurious inflammatory cells and subsequent efficient resolution of inflammation. Here we report that human neutrophils contain functionally active cyclin-dependent kinases (CDKs), and that structurally diverse CDK inhibitors induce caspase-dependent apoptosis and override powerful anti-apoptosis signals from survival factors such as granulocyte-macrophage colony-stimulating factor (GM-CSF). We show that the CDK inhibitor R-roscovitine (Seliciclib or CYC202) markedly enhances resolution of established neutrophil-dependent inflammation in carrageenan-elicited acute pleurisy, bleomycin-induced lung injury, and passively induced arthritis in mice. In the pleurisy model, the caspase inhibitor zVAD-fmk prevents R-roscovitine-enhanced resolution of inflammation, indicating that this CDK inhibitor augments inflammatory cell apoptosis. We also provide evidence that R-roscovitine promotes apoptosis by reducing concentrations of the anti-apoptotic protein Mcl-1. Thus, CDK inhibitors enhance the resolution of established inflammation by promoting apoptosis of inflammatory cells, thereby demonstrating a hitherto unrecognized potential for the treatment of inflammatory disorders.

Integrin activation by Fam38A uses a novel mechanism of R-Ras targeting to the endoplasmic reticulum.

The integrin family of heterodimeric cell-surface receptors are fundamental in cell-cell and cell-matrix adhesion. Changes to either integrin-ligand affinity or integrin gene expression are central to a variety of disease processes, including inflammation, cardiovascular disease and cancer. In screening for novel activators of integrin-ligand affinity we identified the previously uncharacterised multi-transmembrane domain protein Fam38A, located at the endoplasmic reticulum (ER). siRNA knockdown of Fam38A in epithelial cells inactivates endogenous beta1 integrin, reducing cell adhesion. Fam38A mediates integrin activation by recruiting the small GTPase R-Ras to the ER, which activates the calcium-activated protease calpain by increasing Ca(2+) release from cytoplasmic stores. Fam38A-induced integrin activation is blocked by inhibition of either R-Ras or calpain activity, or by siRNA knockdown of talin, a well-described calpain substrate. This highlights a novel mechanism for integrin activation by Fam38A, utilising calpain and R-Ras signalling from the ER. These data represent the first description of a novel spatial regulator of R-Ras, of an alternative integrin activation-suppression pathway based on direct relocalisation of R-Ras to the ER, and of a mechanism linking R-Ras and calpain signalling from the ER with modulation of integrin-ligand affinity.

A novel subpopulation of monocyte-like cells in the human lung after lipopolysaccharide inhalation.

The co-ordinated recruitment of monocyte subpopulations, neutrophils and regulatory T-cells (Tregs) during the early stages of human acute lung inflammation remains poorly understood. We therefore performed a detailed characterisation of these lineages in the blood and lungs in a model of human acute lung inflammation. Healthy volunteers inhaled lipopolysaccharide (LPS) or saline (n=6 for each group). Blood was collected at 0, 2, 4, 6 and 8 h and bronchoscopy with bronchoalveolar lavage (BAL) performed at 8 h. Multiparameter flow cytometry was used to characterise monocyte subpopulations, neutrophils and Tregs in the blood and lung. Inhalation of LPS was associated with significant blood and BAL fluid neutrophilia. Blood populations of monocyte subpopulations and Tregs were unaltered by LPS. In contrast, LPS induced an accumulation of a pulmonary monocyte-like cell (PMLC) population, which was further subdivided into "inducible" CD14(++)CD16(-) and "resident" CD14(++)CD16(+) subsets. Inducible PMLCs were significantly increased following LPS inhalation (p=0.0046), whereas resident PMLCs were unchanged. In addition, we noted a significant decrease in Tregs in BAL fluid with LPS inhalation (p=0.027). The early stages of LPS-induced inflammation in humans is characterised by pulmonary accumulation of a novel inducible monocyte-like subpopulation, accompanied by significant changes in both neutrophil and Treg numbers.

A randomized controlled trial of nebulized gentamicin in non-cystic fibrosis bronchiectasis.

RATIONALE: Bronchiectasis is a chronic debilitating disease with few evidence-based long-term treatments. OBJECTIVES: A randomized controlled trial assessing the efficacy of nebulized gentamicin therapy over 1 year in patients with non-cystic fibrosis bronchiectasis. METHODS: Sixty-five patients were randomized to either twice-daily nebulized gentamicin, 80 mg, or nebulized 0.9% saline, for 12 months. All were reviewed at three-monthly intervals during treatment and at 3 months' follow-up. MEASUREMENTS AND MAIN RESULTS: At each review the following were assessed: quantitative and qualitative sputum bacteriology; sputum purulence and 24-hour volume; FEV(1), FVC, and forced expiratory flow, midexpiratory phase; exercise capacity; Leicester Cough Questionnaire and St. George's Respiratory Questionnaire; and exacerbation frequency. Fifty-seven patients completed the study. At the end of 12 months' treatment, compared with the saline group, in the gentamicin group there was reduced sputum bacterial density with 30.8% eradication in those infected with Pseudomonas aeruginosa and 92.8% eradication in those infected with other pathogens; less sputum purulence (8.7% vs. 38.5%; P < 0.0001); greater exercise capacity (510 [350-690] m vs. 415 [267.5-530] m; P = 0.03); and fewer exacerbations (0 [0-1] vs. 1.5 [1-2]; P < 0.0001) with increased time to first exacerbation (120 [87-161.5] d vs. 61.5 [20.7-122.7] d; P = 0.02). The gentamicin group had greater improvements in Leicester Cough Questionnaire (81.4% vs. 20%; P < 0.01) and St. George's Respiratory Questionnaire (87.5% vs. 19.2%; P < 0.004) score. No differences were seen in 24-hour sputum volume, FEV(1), FVC, or forced expiratory flow, midexpiratory phase. No P. aeruginosa isolates developed resistance to gentamicin. At follow-up, all outcome measures were similar to baseline. CONCLUSIONS: Regular, long-term nebulized gentamicin is of significant benefit in non-cystic fibrosis bronchiectasis but treatment needs to be continuous for its ongoing efficacy. Clinical trial registered with www.clinicaltrials.gov (NCT 00749866).

Ly6Chi monocytes direct alternatively activated profibrotic macrophage regulation of lung fibrosis.

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a devastating disease. Antiinflammatory therapies, including corticosteroids, are of no benefit. The role of monocytes and macrophages is therefore controversial. OBJECTIVES: To define the role of monocytes and macrophages during lung fibrogenesis and resolution, and explore the phenotype of the cells involved. METHODS: We used multiple in vivo depletional strategies, backed up by adoptive transfer techniques. Further studies were performed on samples from patients with IPF. MEASUREMENTS AND MAIN RESULTS: Depletion of lung macrophages during fibrogenesis reduced pulmonary fibrosis as measured by lung collagen (P = 0.0079); fibrosis score (P = 0.0051); and quantitative polymerase chain reaction for surrogate markers of fibrosis Col1 (P = 0.0083) and a-smooth muscle actin (P = 0.0349). There was an associated reduction in markers of the profibrotic alternative macrophage activation phenotype, Ym1 (P = 0.0179), and Arginase 1. The alternative macrophage marker CD163 was expressed on lung macrophages from patients with IPF. Depletion of Ly6Chi circulating monocytes reduced pulmonary fibrosis (P = 0.0052) and the number of Ym1- positive alternatively activated lung macrophages (P = 0.0310). Their adoptive transfer during fibrogenesis exacerbated fibrosis (P = 0.0304); however, adoptively transferred CD45.1 Ly6Chi cells were not found in the lungs of recipient CD45.2 mice. CONCLUSIONS: We demonstrate the importance of circulating monocytes and lung macrophages during pulmonary fibrosis, and emphasize the importance of the alternatively activated macrophage phenotype. We show that Ly6Chi monocytes facilitate the progression of pulmonary fibrosis, but are not obviously engrafted into lungs thereafter. Finally, we provide empirical data to suggest that macrophages may have a resolution-promoting role during the reversible phase of bleomycin-induced pulmonary fibrosis.

Inhibition of Cyclin-Dependent Kinase 9 Downregulates Cytokine Production Without Detrimentally Affecting Human Monocyte-Derived Macrophage Viability.

Cyclin-dependent kinase (CDK) inhibitor drugs (CDKi), such as R-roscovitine and AT7519, induce neutrophil apoptosis in vitro and enhance the resolution of inflammation in a number of in vivo models. This class of compounds are potential novel therapeutic agents that could promote the resolution of acute and chronic inflammatory conditions where neutrophil activation contributes to tissue damage and aberrant tissue repair. In this study we investigated CDKi effects on macrophage pro-inflammatory mediator production and viability. Treatment of human monocyte-derived macrophages (MDMs) with the CDKi AT7519 and R-roscovitine at concentrations that induce neutrophil apoptosis had no significant effect on control or LPS-activated MDM apoptosis and viability, and did not detrimentally affect MDM efferocytosis of apoptotic cells. In addition, enhanced efferocytosis, induced by the glucocorticoid dexamethasone, was also unaffected after a short time treatment with R-roscovitine. Macrophage cytokine responses to inflammatory stimuli are also of importance during inflammation and resolution. As a key target of CDKi, CDK9, is involved in protein transcription via the RNA polymerase II complex, we investigated the effect of CDKi drugs on cytokine production. Our data show that treatment with AT7519 significantly downregulated expression and release of key MDM cytokines IL-6, TNF, IL-10 and IL-1ß, as well as markers of pro-inflammatory macrophage polarisation. R-Roscovitine was also able to downregulate inflammatory cytokine protein secretion from MDMs. Using siRNA transfection, we demonstrate that genetic knock-down of CDK9 replicates these findings, reducing expression and release of pro-inflammatory cytokines. Furthermore, overexpression of CDK9 in THP-1 cells can promote a pro-inflammatory phenotype in these cells, suggesting that CDK9 plays an important role in the inflammatory phenotype of macrophages. Overall, this study demonstrates that pharmacological and genetic targeting of CDK9 inhibits an inflammatory phenotype in human MDMs. As such these data indicate that CDK9 may be key to therapeutically targeting pro-inflammatory macrophage functions during chronic inflammation.

The cyclin-dependent kinase inhibitor R-roscovitine down-regulates Mcl-1 to override pro-inflammatory signalling and drive neutrophil apoptosis.

Successful resolution of inflammation requires inflammatory cells such as neutrophils to undergo apoptosis prior to non-inflammatory phagocytosis by professional phagocytes. Recently, cyclin-dependent kinase (CDK) inhibitors (e.g. R-roscovitine) have been shown to induce neutrophil apoptosis and enhance the resolution of inflammation. Interestingly, NF-kappaB and MAPK pathways and key endogenous survival proteins (typified by Mcl-1) are involved in the regulation of neutrophil apoptosis and, in cancer-cell lines, have been implicated as possible targets of CDK inhibitors. Here, we demonstrate that R-roscovitine over-rides TNF-alpha and LPS-induced survival (determined by morphological examination and binding of fluorescently labelled annexin-V) of isolated peripheral blood neutrophils. This effect did not appear to be mediated via effects on early markers of neutrophil activation (e.g. surface marker expression, shape change, aggregation and superoxide anion generation), by direct inhibition of NF-kappaB activation (assessed by cytoplasmic IkappaBalpha proteolysis and NF-kappaB p65 subunit translocation) and ERK activation (determined by specific ERK phosphorylation) but due to down-regulation (at protein and mRNA level) of the survival protein Mcl-1 but not the pro-apoptotic bcl-2 homologue Bim. These findings suggest that key endogenous survival proteins may be the targets of CDK inhibitors and consequently may be of critical importance in the resolution of inflammation.

Glucocorticoids induce protein S-dependent phagocytosis of apoptotic neutrophils by human macrophages.

During resolution of an inflammatory response, recruited neutrophil granulocytes undergo apoptosis and are removed by tissue phagocytes before induction of secondary necrosis without provoking proinflammatory cytokine production and release. Promotion of physiological neutrophil clearance mechanisms may represent a viable therapeutic strategy for the treatment of inflammatory or autoimmune diseases in which removal of apoptotic cells is impaired. The mechanism underlying enhancement of macrophage capacity for phagocytosis of apoptotic cells by the powerful anti-inflammatory drugs of the glucocorticoid family has remained elusive. In this study, we report that human monocyte-derived macrophages cultured in the presence of dexamethasone exhibit augmented capacity for phagocytosis of membrane-intact, early apoptotic cells only in the presence of a serum factor. Our results eliminate a role for a number of potential opsonins, including complement, pentraxin-3, and fibronectin. Using ion-exchange and gel filtration chromatography, we identified a high molecular mass serum fraction containing C4-binding protein and protein S responsible for the augmentation of phagocytosis of apoptotic neutrophils. Because the apoptotic neutrophils used in this study specifically bind protein S, we suggest that glucocorticoid treatment of macrophages induces a switch to a protein S-dependent apoptotic cell recognition mechanism. Consistent with this suggestion, pretreatment of macrophages with Abs to Mer tyrosine kinase, a member of the Tyro3/Axl/Mer family of receptor tyrosine kinases, prevented glucocorticoid augmentation of phagocytosis. Induction of a protein S/Mer tyrosine kinase-dependent apoptotic cell clearance pathway may contribute to the potent anti-inflammatory effects of glucocorticoids, representing a potential target for promoting resolution of inflammatory responses.