Plasminogen and the Plasminogen Receptor, Plg-RKT, Regulate Macrophage Phenotypic, and Functional Changes.

Graziele L Negreiros-Lima,Juliana P Vago,Lirlândia P Sousa,Kátia M Lima,Mauro M Teixeira,Robert J Parmer,Michelle A Sugimoto,Lindsey A Miles,Nagyung Baik,Mauro Perretti

doi:10.3389/fimmu.2019.01458

Abstract

Inflammation resolution is an active process that functions to restore tissue homeostasis. Clearance of apoptotic leukocytes by efferocytosis at inflammatory sites plays an important role in inflammation resolution and induces remarkable macrophage phenotypic and functional changes. Here, we investigated the effects of deletion of either plasminogen (Plg) or the Plg receptor, Plg-RKT, on the resolution of inflammation. In a murine model of pleurisy, the numbers of total mononuclear cells recruited to the pleural cavity were significantly decreased in both Plg−/− and Plg-RKT−/− mice, a response associated with decreased levels of the chemokine CCL2 in pleural exudates. Increased percentages of M1-like macrophages were determined in pleural lavages of Plg−/− and Plg-RKT−/− mice without significant changes in M2-like macrophage percentages. In vitro, Plg and plasmin (Pla) increased CD206/Arginase-1 expression and the levels of IL-10/TGF-β (M2 markers) while decreasing IFN/LPS-induced M1 markers in murine bone-marrow-derived macrophages (BMDMs) and human macrophages. Furthermore, IL4-induced M2-like polarization was defective in BMDMs from both Plg−/− and Plg-RKT−/− mice. Mechanistically, Plg and Pla induced transient STAT3 phosphorylation, which was decreased in Plg−/− and Plg-RKT−/− BMDMs after IL-4 or IL-10 stimulation. The extents of expression of CD206 and Annexin A1 (important for clearance of apoptotic cells) were reduced in Plg−/− and Plg-RKT−/− macrophage populations, which exhibited decreased phagocytosis of apoptotic neutrophils (efferocytosis) in vivo and in vitro. Taken together, these results suggest that Plg and its receptor, Plg-RKT, regulate macrophage polarization and efferocytosis, as key contributors to the resolution of inflammation.

Highlights

Inflammation is the physiological response of the host to infectious or sterile injurious stimuli that ensures rapid and successful restoration of the tissue, and requires production of mediators and activation of signaling pathways [1]
The in vitro efferocytosis assay was performed by coculturing bone-marrow-derived macrophages (BMDMs) with human or mouse apoptotic neutrophils labeled with CFSE in a proportion of 3 apoptotic neutrophils: 1 macrophage
MPlg-RKT−/− mice in which Plg-RKT was deleted in myeloid cells (Figure S1), did not differ in the number of mononuclear cells recruited into the pleural cavity or in levels of CCL2 compared with PlgRKTflox/flox controls (Figures S2A,B)

Summary

Introduction

Inflammation is the physiological response of the host to infectious or sterile injurious stimuli that ensures rapid and successful restoration of the tissue, and requires production of mediators and activation of signaling pathways [1]. Antiinflammatory/proresolving mechanisms are driven by a complex set of mediators that regulate cellular events required to clear inflammatory cells from sites of injury as a prerequisite for restoration of homeostasis [1,2,3,4]. Activated macrophages, M1 macrophages, are pro-inflammatory and enable host defense against infection, while M2 macrophages (alternatively activated macrophages) display anti-inflammatory and tissue remodeling properties, and play a key role in the resolution of inflammation [6, 7]. PlgRKT accounts for the majority of the Plg binding capacity of macrophages [17] and regulates macrophage recruitment in a model of sterile peritonitis [16]

Methods

Results

Conclusion