Plasmin Induces In Vivo Monocyte Recruitment through Protease-Activated Receptor-1–, MEK/ERK-, and CCR2-Mediated Signaling

Abstract

The plasminogen (Plg)/plasmin (Pla) system is associated with a variety of biological activities beyond the classical dissolution of fibrin clots, including cell migration, tissue repair, and inflammation. Although the capacity of Plg/Pla to induce cell migration is well defined, the mechanism underlying this process in vivo is elusive. In this study, we show that Pla induces in vitro migration of murine fibroblasts and macrophages (RAW 264.7) dependent on the MEK/ERK pathway and by requiring its proteolytic activity and lysine binding sites. Plasmin injection into the pleural cavity of BALB/c mice induced a time-dependent influx of mononuclear cells that was associated with augmented ERK1/2 and IκB-α phosphorylation and increased levels of CCL2 and IL-6 in pleural exudates. The inhibition of protease activity by using a serine protease inhibitor leupeptin or two structurally different protease-activated receptor-1 antagonists (SCH79797 and RWJ56110) abolished Pla-induced mononuclear recruitment and ERK1/2 and IκB-α phosphorylation. Interestingly, inhibition of the MEK/ERK pathway abolished Pla-induced CCL2 upregulation and mononuclear cell influx. In agreement with a requirement for the CCL2/CCR2 axis to Pla-induced cell migration, the use of a CCR2 antagonist (RS504393) prevented the Plg/Pla-induced recruitment of mononuclear cells to the pleural cavity and migration of macrophages at transwell plates. Therefore, Pla-induced mononuclear cell recruitment in vivo was dependent on protease-activated receptor-1 activation of the MEK/ERK/NF-κB pathway, which led to the release of CCL2 and activation of CCR2.

Tissue-type plasminogen activator neutralizes LPS but not protease-activated receptor-mediated inflammatory responses to plasmin

“…The predominant activity of plasmin, observed in different experimental model systems, may reflect the abundance of PARs on the cell surface and whether alternative PAR activators are present. It is also possible that activation of PARs by plasmin reflects selective presentation of PAR peptide bonds to plasmin that is bound to cell‐surface plasminogen receptors.…”

“…Plasminogen receptors, such as annexin A2/S100A10 complex, annexin A1, α‐enolase, and plasminogen‐R TK , play a critical role in mediating the effects of plasmin in inflammation . One function of plasminogen receptors may be to facilitate plasminogen activation and then deliver plasmin to cell‐signaling receptors in the protease‐activated receptor (PAR) family . Alternative pathways by which plasmin may induce inflammation also have been described, such as by proteolytic activation of the chemokine, monocyte chemoattractant protein‐1 (MCP‐1/CCL2) …”

“…15,[17][18][19][20] One function of plasminogen receptors may be to facilitate plasminogen activation and then deliver plasmin to cell-signaling receptors in the proteaseactivated receptor (PAR) family. 18,[21][22][23][24] Alternative pathways by which plasmin may induce inflammation also have been described, such as by proteolytic activation of the chemokine, monocyte chemoattractant protein-1 (MCP-1/CCL2). 24,25 In this study, we demonstrate that the activity of tPA as an inhibitor of the LPS response in BMDMs is apparently comprehensive; not only does tPA block expression of proinflammatory cytokines but also IL-10 and IL-1 receptor antagonist (IL-1ra), which demonstrate antiinflammatory activity.…”

“…18,[21][22][23][24] Alternative pathways by which plasmin may induce inflammation also have been described, such as by proteolytic activation of the chemokine, monocyte chemoattractant protein-1 (MCP-1/CCL2). 24,25 In this study, we demonstrate that the activity of tPA as an inhibitor of the LPS response in BMDMs is apparently comprehensive; not only does tPA block expression of proinflammatory cytokines but also IL-10 and IL-1 receptor antagonist (IL-1ra), which demonstrate antiinflammatory activity. 26,27 In the presence of plasminogen, the previously reported indistinguishable effects of EI-tPA and enzymatically active tPA on cytokine expression 6 are no longer observed because plasmin independently promotes expression of cytokines, including proinflammatory cytokines, by a pathway that is independent of the NMDA-R, and instead, dependent on PAR activation.…”

Plasmin improves oedematous blood-gas barrier by cleaving epithelial sodium channels

“…We could not completely rule out the involvement of protease-activated receptor-1, -2 and -4 (PAR) to fluid resolution in human and mouse lungs (Bock et al, 2015;Carmo et al, 2014;Mannaioni et al, 2008;Quinton, Kim, Derian, Jin & Kunapuli, 2004). However, activation of lung epithelial PAR isoforms by plasmin have not been reported.…”