Plasminogen/plasmin induce macrophage reprogramming and promote resolution of acute inflammation.
Plasminogen/plasmin enhance the efferocytic capacity of macrophages and override the pro-survival effect of LPS on neutrophils via AnxA1.
Inflammation resolution is an active process that functions to restore tissue homeostasis. Participation of the plasminogen/plasmin (Plg/Pla) system in the productive phase of inflammation is well known, but its involvement in the resolution phase remains unclear. Therefore, we aimed to investigate the potential role of Plg/Pla in key events during the resolution of acute inflammation and its underlying mechanisms. Plg/Pla injection into the pleural cavity of BALB/c mice induced a time-dependent influx of mononuclear cells that were primarily macrophages of anti-inflammatory (M2 - F4/80high Gr1- CD11bhigh) and proresolving (Mres - F4/80med CD11blow) phenotypes, without changing the number of macrophages with a pro-inflammatory profile (M1 - F4/80low Gr1+ CD11bmed). Pleural injection of Plg/Pla also increased M2 markers (CD206 and Arginase-1) and secretory products (TGF-β and IL-6) and decreased the expression of iNOS (M1 marker). During the resolving phase of LPS-induced inflammation, when resolving macrophages predominate, we found increased Plg expression and Pla activity, further supporting a link between the Plg/Pla system and key cellular events in resolution. Indeed, Plg or Pla given at the peak of inflammation promoted resolution by decreasing neutrophil numbers and increasing neutrophil apoptosis and efferocytosis in a serine-protease inhibitor sensitive manner. Next, we confirmed the ability of Plg/Pla to both promote efferocytosis and override the pro-survival effect of LPS, via AnxA1. These findings suggest that Plg/Pla regulate several key steps in inflammation resolution, namely, neutrophil apoptosis, macrophage reprogramming and efferocytosis, which have a major impact on the establishment of an efficient resolution process.
- Submitted September 28, 2016.
- Accepted March 14, 2017.
- Copyright © 2017 American Society of Hematology
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