title: Ectosomes of polymorphonuclear neutrophils activate multiple signaling pathways in macrophages.
abstract: Ectosomes are vesicles shed directly from the cell surface. Human polymorphonuclear neutrophils release ectosomes (PMN-Ect) upon their activation. PMN-Ect expose phosphatidylserine (PS) on the outer leaflet of the plasma membrane, and down-modulate the inflammatory response of human macrophages and dendritic cells exposed to TLR-2 and -4 ligands. This down-modulation is mediated by PS via the engagement and activation of the Mer receptor tyrosine kinase (MerTK). In the present study, we demonstrate that exposure of macrophages to PMN-Ect activates directly 2 additional pathways, an immediate Ca(2+) flux and a rapid release of TGF-β1. As expected, the Ca(2+) flux was necessary for the activation of TLR-2 pathway with the release of cytokines. However, MerTK blockade with antibodies did not modify the Ca(2+) flux, indicating an independent activation of Ca(2+) by PMN-Ect. Striking was that the rapid release of TGF-β1 was independent of the MerTK pathway and did not require a Ca(2+) flux. TGF-β1 was present in cytosolic storage pools, which were depleted after exposure of the macrophages to PMN-Ect, and no increase in TGF-β1 mRNA could be detected in the 3 first hours when maximal release had occurred. The release of TGF-β1 by macrophages was seen only for PMN-Ect and not for PS-liposomes or erythrocyte ectosomes, which express PS. However, blocking the PS of PMN-Ect inhibited TGF-β1 release, suggesting that PS expression was necessary although not sufficient for this release. Interestingly, the effects of PMN-Ect pre-exposure were lasting for 24h with the macrophages being less receptive to TLR-2 activation and TGF-β1 stores remaining low. In sum, PMN-Ect induce several signaling pathways in resting and stimulated macrophages, which include independently the MerTK pathway, Ca(2+) flux and the release of stored TGF-β1, and each might influence the immunomodulatory effects of macrophages.
authors: Immunonephrology Laboratory, Departments of Biomedicine and Medicine, University Hospital Basel, Basel, Switzerland. ceylan.eken@unibas.ch
authors: Ceylan
authors: C
authors: Eken
authors: Salima
authors: S
authors: Sadallah
authors: Perrine J
authors: PJ
authors: Martin
authors: Susan
authors: S
authors: Treves
authors: Jürg A
authors: JA
authors: Schifferli
mesh_terms: D020013:Calcium Signaling / Q000276:immunology; D055252:Cell-Derived Microparticles / Q000276:immunology*; D002478:Cells, Cultured; D006801:Humans; D056747:Immunomodulation; D008264:Macrophages / Q000276:immunology*; D018375:Neutrophil Activation; D009504:Neutrophils / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology; D010718:Phosphatidylserines / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020239:Receptor Cross-Talk; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D000076202:c-Mer Tyrosine Kinase
chemical_list: D010718:Phosphatidylserines; D011518:Proto-Oncogene Proteins; D051195:Toll-Like Receptor 2; D016212:Transforming Growth Factor beta; C097072:MERTK protein, human; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase