Plasminogen and plasmin induce specialized proresolving mediators and promote efferocytosis via 5-lipoxygenase.

BACKGROUND: The plasminogen (Plg)/plasmin (Pla) system has been recognized for its proresolving actions, such as promoting efferocytosis. However, the role of specialized proresolving mediators (SPMs) in these Plg/Pla effects remains unexplored. OBJECTIVES: To investigate whether Plg/Pla promotes SPMs production in macrophages and to elucidate the role of the 5-lipoxygenase (5-LO) pathway in Pla-induced efferocytosis. METHODS: Bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Plg knockout (KO) mice were treated or not with Plg/Pla, with or without leupeptin (protease inhibitor) and tranexamic acid (lysine analog), for 24 hours. SPMs and leukotriene B4 production and the messenger RNA expression of 5-, 12-, and 15-LO (SPMs biosynthetic enzymes) were assessed in WT-BMDMs. Additionally, 12/15-LO expression was analyzed in pleural macrophages from Pla-injected mice. Efferocytosis of apoptotic neutrophils was examined in Pla-injected WT and 5-LO KO mice and by using the 5-LO inhibitor MK886 in Pla-stimulated BMDMs. RESULTS: Plg/Pla enhanced the production of lipoxin A(4), maresin 1, and resolvin D1, as well as the mRNA expression of 5-, 12-, and 15-LO in macrophages, a process dependent on proteolytic activity and lysine binding sites. Macrophages from Plg KO mice produced lower lipoxin A(4) levels, while leukotriene B(4) levels remained comparable to WT cells. Pla injection promoted macrophage recruitment to the pleural cavity alongside 12/15-LO protein upregulation. Furthermore, Pla increased the efferocytosis of apoptotic neutrophils in WT mice but not in 5-LO KO mice, and pharmacologic inhibition of 5-LO reduced Pla-induced efferocytosis in vitro. CONCLUSION: In summary, Plg/Pla proresolving actions are associated with SPMs production in macrophages and a 5-LO-dependent pro-efferocytosis mechanism.