[Show abstract][Hide abstract] ABSTRACT: Previous work in our laboratory has shown that transglutaminase 2 (TG2) acting as a coreceptor for integrin β3 is required for proper phagocytosis of apoptotic cells. In the absence of TG2, systemic lupus erythematosus-like autoimmunity develops in mice, similarly to other mice characterized by a deficiency in the clearance of apoptotic cells. In this study, we demonstrate that increasing TG2 expression alone in wild-type macrophages is not sufficient to enhance engulfment. However, during engulfment, the lipid content of the apoptotic cells triggers the lipid-sensing receptor liver X receptor (LXR), which in response upregulates the expression of the phagocytic receptor Mer tyrosine kinase and the phagocytosis-related ABCA1, and that of retinaldehyde dehydrogenases leading to the synthesis of a nonclassical retinoid. Based on our retinoid analysis, this compound might be a dihydro-retinoic acid derivative. The novel retinoid then contributes to the upregulation of further phagocytic receptors including TG2 by ligating retinoic acid receptors. Inhibition of retinoid synthesis prevents the enhanced phagocytic uptake induced by LXR ligation. Our data indicate that stimulation of LXR enhances the engulfment of apoptotic cells via regulating directly and indirectly the expression of a range of phagocytosis-related molecules, and its signaling pathway involves the synthesis of a nonclassical retinoid. We propose that retinoids could be used for enhancing the phagocytic capacity of macrophages in diseases such as systemic lupus erythematosus, where impaired phagocytosis of apoptotic cells plays a role in the pathogenesis of the disease.
Full-text · Article · May 2014 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: During the cell-death program known as apoptosis, cells break up into membrane-bound fragments. It emerges that this process is controlled by the protein pannexin 1 and can be deregulated by an antibiotic. See Article p.329
[Show abstract][Hide abstract] ABSTRACT: Most cases of systemic lupus erythematosus (SLE) are characterized by an impaired clearance of apoptotic cells in various tissues. Not cleared apoptotic waste is considered an immunogen driving the autoimmune response in patients with SLE. During the execution of apoptosis, membrane blebs are formed and filled with cellular components. Here, we evaluate the cytoskeletal pathway(s) responsible for the loading of SLE prototypic nuclear autoantigens into the apoptotic cell-derived membranous vesicles (ACMV) generated during late phases of apoptosis.HeLa cells expressing a fusion protein of histone H2B with green fluorescent protein (GFP) were irradiated with UV-B to induce apoptosis. The appearance and trafficking of chromatin-derived material was monitored by fluorescence microscopy. Specific inhibitors of cytoskeletal pathways were employed to identify the motile elements involved in translocation and trafficking of the nuclear components.We observed that immediately after their appearance the ACMV did not contain histone H2BGFP; in this phase the fluorescence was contained in the nuclear remnants and the cytoplasm. Within the consecutive minutes the ACMV were loaded with chromatin-derived material whereas the loading of simultaneously created ACMV with histone H2BGFP was not uniform. Some ACMV were preferentially filled and, consequently, showed a remarkably higher histone H2BGFP accumulation. Inhibitors of the cytoskeleton revealed that functional microtubules and myosin light chain kinase are required for nuclear shrinkage and loading of nuclear material into the ACMV, respectively.
[Show abstract][Hide abstract] ABSTRACT: Small cell lung cancer (SCLC) is a highly aggressive malignancy with poor survival rates, with initial responses nearly invariably followed by rapid recurrence of therapy-resistant disease. Drug resistance in SCLC may be attributable to the persistence of a sub-population of cancer stem-like cells (CSC) that exhibit multiple drug resistance. In this study, we characterised the expression of CD133, one important marker of CSC in other cancers, in SCLC cancer cells. CD133 expression correlated with chemoresistance and increased tumorigenicity in vitro and in vivo accompanied by increased expression of Akt/PKB and Bcl-2. CD133 expression was increased in mouse and human SCLC after chemotherapy, an observation confirmed in clinical specimens isolated longitudinally from a patient receiving chemotherapy. We discovered in CD133+ SCLC cells an increased expression of the mitogenic neuropeptide receptors for gastrin releasing peptide and arginine vasopressin. Notably, these cells exhibited increased sensitivity to the growth inhibitory and pro-apoptotic effects of a novel broad spectrum neuropeptide antagonist (related to SP-G) which has completed a Phase I clinical trial for SCLC. Our results offer evidence that this agent can preferentially target chemoresistant CD133+ cells with CSC character in SCLC, emphasizing its potential utility for improving therapy in this setting.
[Show abstract][Hide abstract] ABSTRACT: Exosomes are vesicles that are released from the kidney into urine. They contain protein and RNA from the glomerulus and all sections of the nephron and represent a reservoir for biomarker discovery. Current methods for identifying and quantifying urinary exosomes are time-consuming and only semi-quantitative. Nanoparticle tracking analysis (NTA) counts and sizes particles by measuring their Brownian motion in solution. In this study we applied NTA to human urine and identified particles with a range of sizes. Using antibodies against the exosomal proteins CD24 and aquaporin 2 (AQP2), conjugated to a fluorophore, we could identify a sub-population of CD24 and AQP2 positive particles of characteristic exosomal size. Extensive pre-NTA processing of urine was not necessary. However, the intra-assay variability in the measurement of exosome concentration was significantly reduced when an ultra-centrifugation step preceded NTA. Without any sample processing, NTA tracked exosomal AQP2 upregulation induced by desmopressin stimulation of kidney collecting duct cells. NTA was also able to track changes in exosomal AQP2 concentration that followed desmopressin treatment of mice and a patient with central diabetes insipidus. When urine was stored at room temperature, 4 C or frozen, nanoparticle concentration was reduced; freezing at -80 C with the addition of protease inhibitors produced the least reduction. In conclusion, with appropriate sample storage, NTA has potential as a tool for characterising and quantifying extra-cellular vesicles in human urine.
Full-text · Article · Sep 2013 · The Journal of Physiology
[Show abstract][Hide abstract] ABSTRACT: Biopsies taken from individual tumours exhibit extensive differences in their cellular composition due to the inherent heterogeneity of cancers and vagaries of sample collection. As a result genes expressed in specific cell types, or associated with certain biological processes are detected at widely variable levels across samples in transcriptomic analyses. This heterogeneity also means that the level of expression of genes expressed specifically in a given cell type or process, will vary in line with the number of those cells within samples or activity of the pathway, and will therefore be correlated in their expression.
Using a novel 3D network-based approach we have analysed six large human cancer microarray datasets derived from more than 1,000 individuals. Based upon this analysis, and without needing to isolate the individual cells, we have defined a broad spectrum of cell-type and pathway-specific gene signatures present in cancer expression data which were also found to be largely conserved in a number of independent datasets.
The conserved signature of the tumour-associated macrophage is shown to be largely-independent of tumour cell type. All stromal cell signatures have some degree of correlation with each other, since they must all be inversely correlated with the tumour component. However, viewed in the context of established tumours, the interactions between stromal components appear to be multifactorial given the level of one component e.g. vasculature, does not correlate tightly with another, such as the macrophage.
[Show abstract][Hide abstract] ABSTRACT: Cells dying by apoptosis are normally cleared by phagocytes through mechanisms that can suppress inflammation and immunity. Molecules of the innate immune system, the pattern recognition receptors (PRRs), are able to interact not only with conserved structures on microbes (pathogen-associated molecular patterns, PAMPs) but also with ligands displayed by apoptotic cells. We reasoned that PRRs might therefore interact with structures on apoptotic cells - apoptotic cell-associated molecular patterns (ACAMPs) - that are analogous to PAMPs. Here we show that certain monoclonal antibodies raised against the prototypic PAMP, lipopolysaccharide (LPS), can crossreact with apoptotic cells. We demonstrate that one such antibody interacts with a constitutively expressed intracellular protein, laminin-binding protein, which translocates to the cell surface during apoptosis and can interact with cells expressing the prototypic PRR, mCD14 as well as with CD14-negative cells. Anti-LPS cross reactive epitopes on apoptotic cells colocalised with annexin V- and C1q-binding sites on vesicular regions of apoptotic cell surfaces and were released associated with apoptotic cell-derived microvesicles (MVs). These results confirm that apoptotic cells and microbes can interact with the immune system through common elements and suggest that anti-PAMP antibodies could be used strategically to characterise novel ACAMPs associated not only with apoptotic cells but also with derived MVs.Cell Death and Differentiation advance online publication, 8 February 2013; doi:10.1038/cdd.2012.165.
Preview · Article · Feb 2013 · Cell death and differentiation
[Show abstract][Hide abstract] ABSTRACT: It is well known that an important property of apoptosis is the prevention of cancer. However, it is becoming increasingly clear that apoptotic cells have the capacity to activate reparative and regenerative responses, which have the potential to make significant impact on pathological processes underlying autoimmune disease and cancer. Those properties of apoptotic cells that influence their immediate microenvironment are reviewed here in the context of cancer progression and treatment.
[Show abstract][Hide abstract] ABSTRACT: Embryonic stem cells provide a potentially convenient source of macrophages in the laboratory. Given the propensity of macrophages for plasticity in phenotype and function, standardised culture and differentiation protocols are required to ensure consistency in population output and activity in functional assays. Here we detail the development of an optimised culture protocol for the production of murine embryonic stem cell-derived macrophages (ESDM). This protocol provides improved yields of ESDM and we demonstrate that the cells are suitable for application to the study of macrophage responses to apoptotic cells. ESDM so produced were of higher purity than commonly used primary macrophage preparations and were functional in chemotaxis assays and in phagocytosis of apoptotic cells. Maturation of ESDM was found to be associated with reduced capacity for directed migration and increased capacity for phagocytic clearance of apoptotic cells. These results show ESDM to be functionally active in sequential phases of interaction with apoptotic cells and establish these macrophage populations as useful models for further study of molecular mechanisms underlying the recognition and removal of apoptotic cells.
No preview · Article · Jun 2012 · Journal of immunological methods
[Show abstract][Hide abstract] ABSTRACT: An expanding body of evidence demonstrates that cells undergoing apoptosis send out a selection of molecular navigational signals including proteins, lipids and nucleotides that serve to recruit phagocytes to the dying targets which are subsequently engulfed and removed. This homeostatic process is essentially non-phlogistic, contrasting markedly with the acute inflammatory responses elicited in phagocytes by damaging or infectious agents. The "professional" scavengers of apoptotic cells are mononuclear phagocytes-the macrophages-and sites of high-rate apoptosis are clearly characterized by macrophages associated with the apoptotic cells. By contrast, members of the other class of professional phagocytes-the granulocytes-are not recruited to sites of apoptosis as a direct consequence of the cell-death program. Indeed, recent work indicates that apoptotic cells release a mixture of migratory cues to leukocytes in order to selectively attract mononuclear phagocytes but not granulocytes through functional balancing of positive and negative signals. Here we discuss these molecular mechanisms which not only serve as migratory cues but also may activate responding phagocytes to engulf apoptotic cells effectively. Finally, we speculate upon new therapeutic opportunities these mechanisms offer for a range of pathological conditions, including inflammatory disorders and cancer.
[Show abstract][Hide abstract] ABSTRACT: Here we consider the impact of the physiological cell-death programme on normal tissue homeostasis and on disease pathogenesis, with particular reference to evolution and progression of neoplasia. We seek to describe the direct contributions played by apoptosis in creating the microenvironments of normal and malignant tissues and to discuss the molecular mechanisms underlying the elements of the '3Rs' that define the meaning of apoptosis: recognition, response, and removal. Apoptotic cells elicit responses in other cell types-both phagocytic and non-phagocytic-through short- and long-range signalling modes that range from direct contact to intercellular communication via membrane-bound microparticles. Such cellular responses include migration, proliferation, and differentiation, as well as production of immunomodulatory and anti-inflammatory mediators together with, in the case of phagocytes, engulfment, and breakdown of apoptotic cells. In normal tissues, the removal of apoptotic cells is rapid and typically non-phlogistic. We discuss the importance of this clearance process in tissue homeostasis and the consequences of its failure in disease pathogenesis. Using the typical cell culture environment in vitro as an illustrative example in which apoptosis occurs commonly in the absence of the removal mechanisms, we also discuss the inhibitory effects of persistent apoptotic cells on their otherwise viable neighbours. Since apoptosis is a common and sustained event in high-grade malignancies, we hypothesize on its purposeful role in conditioning the tumour microenvironment. We propose that apoptosis subserves several pro-tumour functions-trophic, anti-inflammatory, and immunomodulatory-and we identify strategies targeting host responses to apoptotic cells as promising modes of future therapies that could be applied to multiple cancer types in which tumour-cell apoptosis is active.
Preview · Article · Jan 2011 · The Journal of Pathology
[Show abstract][Hide abstract] ABSTRACT: The apoptosis program of physiological cell death elicits a range of non-phlogistic homeostatic mechanisms-"recognition, response and removal"-that regulate the microenvironments of normal and diseased tissues via multiple modalities operating over short and long distances. The molecular mechanisms mediate intercellular signaling through direct contact with neighboring cells, release of soluble factors and production of membrane-delimited fragments (apoptotic bodies, blebs and microparticles) that allow for interaction with host cells over long distances. These processes effect the selective recruitment of mononuclear phagocytes and the specific activation of both phagocytic and non-phagocytic cells. While much evidence is available concerning the mechanisms underlying the recognition and responses of phagocytes that culminate in the engulfment and removal of apoptotic cell bodies, relatively little is yet known about the non-phagocytic cellular responses to the apoptosis program. These responses regulate inflammatory and immune cell activation as well as cell fate decisions of proliferation, differentiation and death. Here, we review current knowledge of these processes, considering especially how apoptotic cells condition the microenvironments of normal and malignant tissues. We also discuss how apoptotic cells that persist in the absence of phagocytic clearance exert inhibitory effects over their viable neighbors, paying particular attention to the specific case of cell cultures and highlighting how new cell-corpse-clearance devices-Dead-Cert Nanoparticles-can significantly improve the efficacy of cell cultures through effective removal of non-viable cells in the absence of phagocytes in vitro.
[Show abstract][Hide abstract] ABSTRACT: Eosinophilic granulocytes are innate effector cells that are important in immune responses against helminth parasitic infections and contribute towards the pathology associated with allergic inflammatory conditions, including allergic rhinitis and asthma. Their recruitment to inflammatory sites occurs in response to chemotactic and activation signals, such as eotaxin and interleukin-5, and is a tightly controlled process. However, the mechanisms that counterbalance these positive chemoattractive processes, thereby preventing excessive eosinophil infiltration, have received little attention. Here, we show that, lactoferrin (LTF), a pleiotropic 80-kDa glycoprotein with iron-binding properties, acts as a powerful inhibitor of eosinophil migration. Irrespective of its source (milk or neutrophil derived), LTF inhibits eotaxin-stimulated eosinophil migration with no effects on eosinophil viability. Transferrin, a closely related cationic glycoprotein, failed to produce an analogous effect. Furthermore, the iron-saturation status of LTF did not influence the observed inhibitory effect on migration, proving that LTF exerts its effect on eosinophil chemotaxis independent of its iron-chelating activity. These results highlight LTF as one of the few molecules reported to negatively regulate eosinophil migration. Thus, through its ability to inhibit eosinophil migration, LTF has potential as an effective therapeutic in the control of eosinophil infiltration in atopic inflammatory conditions.
Preview · Article · Nov 2009 · Immunology and Cell Biology
[Show abstract][Hide abstract] ABSTRACT: Dying cells release 'find-me' factors that attract professional scavenger cells to engulf and digest them. These cellular invitations to dine can take unexpected forms.
[Show abstract][Hide abstract] ABSTRACT: Cells undergoing apoptosis in vivo are rapidly detected and cleared by phagocytes. Swift recognition and removal of apoptotic cells is important for normal tissue homeostasis and failure in the underlying clearance mechanisms has pathological consequences associated with inflammatory and auto-immune diseases. Cell cultures in vitro usually lack the capacity for removal of non-viable cells because of the absence of phagocytes and, as such, fail to emulate the healthy in vivo micro-environment from which dead cells are absent. While a key objective in cell culture is to maintain viability at maximal levels, cell death is unavoidable and non-viable cells frequently contaminate cultures in significant numbers. Here we show that the presence of apoptotic cells in monoclonal antibody-producing hybridoma cultures has markedly detrimental effects on antibody productivity. Removal of apoptotic hybridoma cells by macrophages at the time of seeding resulted in 100% improved antibody productivity that was, surprisingly to us, most pronounced late on in the cultures. Furthermore, we were able to recapitulate this effect using novel super-paramagnetic Dead-Cert Nanoparticles to remove non-viable cells simply and effectively at culture seeding. These results (1) provide direct evidence that apoptotic cells have a profound influence on their non-phagocytic neighbors in culture and (2) demonstrate the effectiveness of a simple dead-cell removal strategy for improving antibody manufacture in vitro.
[Show abstract][Hide abstract] ABSTRACT: Microaspiration of Pseudomonas aeruginosa contributes to the pathogenesis of nosocomial pneumonia. Trappin-2 is a host defense peptide that assists with the clearance of P. aeruginosa through undefined mechanisms. A model of macrophage interactions with replicating P. aeruginosa (strain PA01) in serum-free conditions was developed, and the influence of subantimicrobial concentrations of trappin-2 was subsequently studied. PA01 that was pre-incubated with trappin-2 (at concentrations that have no direct antimicrobial effects), but not control PA01, was cleared by alveolar and bone marrow-derived macrophages. However, trappin-2-enhanced clearance of PA01 was completely abrogated by CD14- null macrophages. Fluorescence microscopy demonstrated the presence of trappin-2 on the bacterial cell surface of trappin-2-treated PA01. In a murine model of early lung infection, trappin-2-treated PA01 was cleared more efficiently than control PA01 2 hours of intratracheal instillation. Furthermore, trappin-2-treated PA01 up-regulated the murine chemokine CXCL1/KC after 2 hours with a corresponding increase in neutrophil recruitment 1 hour later. These in vivo trappin-2-treated PA01 effects were absent in CD14-deficient mice. Trappin-2 appears to opsonize P. aeruginosa for more efficient, CD14-dependent clearance by macrophages and contributes to the induction of chemokines that promote neutrophil recruitment. Trappin-2 may therefore play an important role in innate recognition and clearance of pathogens during the very earliest stages of pulmonary infection.
Full-text · Article · May 2009 · American Journal Of Pathology