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The inflammatory response induced by Pseudomonas aeruginosa in macrophages enhances apoptotic cell removal.

ABSTRACT: Pathogens phagocytosis and the uptake of apoptotic cells (efferocytosis) are essential macrophages tasks, classically considered as mutually exclusive. Macrophages have been observed to polarize into either pro-inflammatory/microbicidal or anti-inflammatory/efferocytic phenotypes. However, macrophage functions have shown to be more complex. Furthermore, little is known about the regulation of efferocytosis under inflammatory conditions. In this study, we elucidate the modulation of the macrophage efferocytic function during an inflammatory stimulus. We find that bone marrow-derived macrophages (BMDM) are very efficient in engulfing both the bacterial pathogen Pseudomonas aeruginosa and apoptotic cells. BMDM showed a high bactericidal capacity unaffected by the concomitant presence of apoptotic material. Plasticity in macrophage programming, in response to changing environmental cues, may modulate efferocytic capability. In this work, we further show that, after phagocyting and processing Pseudomonas aeruginosa, macrophages highly increase their efferocytic capacity without affecting their phagocytic function. Moreover, we demonstrate that Pseudomonas aeruginosa enhances efferocytosis of these phagocytes through the IL-6 signaling pathway. Our results show that the inflammatory response generated by the bacterial processing enhances these macrophages' capacity to control inflammation through an increased efferocytosis.

SUBMITTER: Jager AV

PROVIDER: S-EPMC7841155 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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The inflammatory response induced by Pseudomonas aeruginosa in macrophages enhances apoptotic cell removal.

Jäger Adriana Valeria AV Arias Paula P Tribulatti Maria Virginia MV Brocco Marcela Adriana MA Pepe Maria Victoria MV Kierbel Arlinet A

Scientific reports 20210127 1

Pathogens phagocytosis and the uptake of apoptotic cells (efferocytosis) are essential macrophages tasks, classically considered as mutually exclusive. Macrophages have been observed to polarize into either pro-inflammatory/microbicidal or anti-inflammatory/efferocytic phenotypes. However, macrophage functions have shown to be more complex. Furthermore, little is known about the regulation of efferocytosis under inflammatory conditions. In this study, we elucidate the modulation of the macrophag ...[more]

PMID: 33504816

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Project description:Pseudomonas aeruginosa is an opportunistic pathogen that can cause severe infections at compromised epithelial surfaces, such those found in burns, wounds, and in lungs damaged by mechanical ventilation or recurrent infections, particularly in cystic fibrosis (CF) patients. CF patients have been proposed to have a Th2 and Th17-biased immune response suggesting that the lack of Th1 and/or over exuberant Th17 responses could contribute to the establishment of chronic P. aeruginosa infection and deterioration of lung function. Accordingly, we have observed that interferon (IFN)-? production by peripheral blood mononuclear cells from CF patients positively correlated with lung function, particularly in patients chronically infected with P. aeruginosa. In contrast, IL-17A levels tended to correlate negatively with lung function with this trend becoming significant in patients chronically infected with P. aeruginosa. These results are in agreement with IFN-? and IL-17A playing protective and detrimental roles, respectively, in CF. In order to explore the protective effect of IFN-? in CF, the effect of IFN-? alone or in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF), on the ability of human macrophages to control P. aeruginosa growth, resist the cytotoxicity induced by this bacterium or promote inflammation was investigated. Treatment of macrophages with IFN-?, in the presence and absence of GM-CSF, failed to alter bacterial growth or macrophage survival upon P. aeruginosa infection, but changed the inflammatory potential of macrophages. IFN-? caused up-regulation of monocyte chemoattractant protein-1 (MCP-1) and TNF-? and down-regulation of IL-10 expression by infected macrophages. GM-CSF in combination with IFN-? promoted IL-6 production and further reduction of IL-10 synthesis. Comparison of TNF-? vs. IL-10 and IL-6 vs. IL-10 ratios revealed the following hierarchy in regard to the pro-inflammatory potential of human macrophages infected with P. aeruginosa: untreated < treated with GM-CSF < treated with IFN-? < treated with GM-CSF and IFN-?.

Project description:RationaleCystic fibrosis lung disease is characterized by accumulation of apoptotic neutrophils, indicating impaired clearance of dying cells. Pseudomonas aeruginosa, the principal microbial pathogen in cystic fibrosis, manipulates apoptosis induction via production of toxic metabolites. Whether these metabolites, particularly pyocyanin, can also modulate apoptotic cell engulfment is unknown.ObjectivesTo assess the effects of pyocyanin on apoptotic cell engulfment by macrophages in vitro and in vivo and to investigate potential mechanisms of the observed effects.MethodsHuman monocyte-derived macrophages were treated with pyocyanin before challenge with apoptotic neutrophils, apoptotic Jurkat cells, or latex beads, and phagocytosis was assessed by light microscopy and flow cytometry. Effects of pyocyanin production on apoptotic cell clearance in vivo were assessed in a murine model, comparing infection by wild-type or pyocyanin-deficient P. aeruginosa. Oxidant production was investigated using fluorescent probes and pharmacologic inhibition and Rho GTPase signaling by immunoblotting and inhibitor studies.Measurements and main resultsPyocyanin treatment impaired macrophage engulfment of apoptotic cells in vitro, without inducing significant macrophage apoptosis, whereas latex bead uptake was preserved. Macrophage ingestion of apoptotic cells was reduced and late apoptotic/necrotic cells were increased in mice infected with pyocyanin-producing P. aeruginosa compared with the pyocyanin-deficient strain. Inhibition of apoptotic cell uptake involved intracellular generation of reactive oxygen species (ROS) and effects on Rho GTPase signaling. Antioxidants or blockade of Rho signaling substantially restored apoptotic cell engulfment.ConclusionsThese studies demonstrate that P. aeruginosa can manipulate the inflammatory microenvironment through inhibition of apoptotic cell engulfment, and suggest potential strategies to limit pulmonary inflammation in cystic fibrosis.

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The inflammatory response induced by Pseudomonas aeruginosa in macrophages enhances apoptotic cell removal.

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The inflammatory response induced by Pseudomonas aeruginosa in macrophages enhances apoptotic cell removal.

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