Urokinase-Type Plasminogen Activator Promotes Paracellular Transmigration of Neutrophils Via Mac-1, But Independently of Urokinase-Type Plasminogen Activator Receptor

Abstract

Background-Urokinase-type plasminogen activator (uPA) has recently been implicated in the pathogenesis of ischemia-reperfusion (I/R) injury. The underlying mechanisms remain largely unclear. Methods and Results-Using in vivo microscopy on the mouse cremaster muscle, I/R-elicited firm adherence and transmigration of neutrophils were found to be significantly diminished in uPA-deficient mice and in mice treated with the uPA inhibitor WX-340, but not in uPA receptor (uPAR)-deficient mice. Interestingly, postischemic leukocyte responses were significantly reduced on blockade of the integrin CD11b/Mac-1, which also serves as uPAR receptor. Using a cell transfer technique, postischemic adherence and transmigration of wild-type leukocytes were significantly decreased in uPA-deficient animals, whereas uPA-deficient leukocytes exhibited a selectively reduced transmigration in wild-type animals. On I/R or stimulation with recombinant uPA, Ͼ90% of firmly adherent leukocytes colocalized with CD31-immunoreactive endothelial junctions as detected by in vivo fluorescence microscopy. In a model of hepatic I/R, treatment with WX-340 significantly attenuated postischemic neutrophil infiltration and tissue injury. Conclusions-Our data suggest that endothelial uPA promotes intravascular adherence, whereas leukocyte uPA facilitates the subsequent paracellular transmigration of neutrophils during I/R. This process is regulated via CD11b/Mac-1, and does not require uPAR. Pharmacological blockade of uPA interferes with these events and effectively attenuates postischemic tissue injury. (Circulation. 2011;124:1848-1859.)Key Words: ischemia Ⅲ leukocytes Ⅲ plasminogen activators Ⅲ reperfusion Ⅲ urokinase I schemia-reperfusion (I/R) injury is considered to be the most common cause of organ dysfunction and failure after myocardial infarction, hemorrhagic shock, and transplantation. Leukocyte infiltration of postischemic tissue is a key event in the pathogenesis of I/R injury. In this multistep cascade, a diversity of adhesion molecules, chemoattractants, and proteases are involved, regulating intravascular rolling and firm adherence as well as transendothelial migration of leukocytes to the reperfused tissue. [1][2][3][4] Clinical Perspective on p 1859Urokinase-type plasminogen activator (uPA) is a serine protease that has been implicated in a variety of physiological and pathophysiological processes. In this context, uPA is known to activate extracellular matrix-degrading enzymes and, through interaction with the urokinase receptor (uPAR; CD87), uPA is thought to induce intracellular signaling pathways, ultimately regulating cell adhesion and migration. 5 Moreover, uPA mediates the conversion of plasminogen to plasmin, which, in addition to its fibrinolytic properties, is also able to degrade components of the ECM as well as to activate intracellular signaling mechanisms. 6 Plasminogen activators, such as recombinant uPA, are therapeutically used for the activation of the fibrinolytic system during thrombembolic events. 7 Interestingl...

Critical Role of Platelet Glycoprotein Ibα in Arterial Remodeling

“…Furthermore, in GPIbα-deficient animals, collateral vessel walls displayed a reduction in urokinase-type plasminogen activator expression, which is linked to decreased leukocyte extravasation. 8,56 Our results are in line with recent observations in other inflammatory processes, such as venous thrombosis or myocardial infarction, demonstrating that the absence of platelet GPIbα results in reduced leukocyte accumulation and transmigration. 14,57 Hence, GPIbα-dependent interactions of platelets with leukocytes and the endothelium exert a dual function during collateral development, (1) supporting leukocyte recruitment and (2) facilitating leukocyte transmigration into the perivascular space.…”

Matrix metalloproteinases modulate ameboid-like migration of neutrophils through inflamed interstitial tissue

“…by guest www.bloodjournal.org From relevance of proteases in particular is still an issue of controversial debate. [11][12][13][14][15][16][17][18] In the present study, we sought to define whether and how serine proteases, which represent over one third of all known proteolytic enzymes, as well as MMPs, which form a class of enzymes specialized on the degradation of the extracellular matrix, 22 are involved in leukocyte migration to the site of inflammation. Using a model of sterile peritonitis, we found that migration of neutrophils to the inflamed peritoneal cavity was effectively prevented by the broad-spectrum serine protease inhibitor aprotinin as well as by the broad-spectrum MMP inhibitor GM-6001.…”

“…In this regard, the role of proteases in particular for leukocyte migration remains an issue of controversial debate. [11][12][13][14][15][16][17][18] Over one third of all known proteolytic enzymes are serine proteases, which are characterized by the ability to hydrolyze the peptide bond of their substrates via a nucleophilic serine residue in the active site. Among these enzymes, plasmin is one of the most prominent members regarding its elementary function in the fibrinolytic system.…”

“…20,21 Moreover, plasmin is able to activate various matrix metalloproteinases (MMPs), a class of proteolytic enzymes specialized on the degradation of the extracellular matrix, which is also supposed to contribute to the interstitial locomotion of cells. 22 Using genetically altered mice or specific inhibitors, serine proteases, including plasmin [14][15][16] as well as MMPs, 12,17,18 have previously been implicated in leukocyte extravasation to the perivascular tissue by regulating interactions of these inflammatory cells with endothelial cells and the perivascular basement membrane. The online version of this article contains a data supplement.…”

Tissue Plasminogen Activator Promotes Postischemic Neutrophil Recruitment via Its Proteolytic and Nonproteolytic Properties

“…5,[8][9][10][11][12] In the context of I/R, the single components of the fibrinolytic system are increasingly recognized as individual and autonomous mediators: Plasmin has been demonstrated to contribute to leukocyte infiltration of reperfused tissue largely via its proteolytic properties, 14 whereas the serine protease urokinase-type plasminogen activator has been shown to regulate postischemic leukocyte responses independently of its proteolytic properties via receptor-mediated processes. 15 Recently, it has been reported that also tPA is critically involved in the pathogenesis of I/R injury. [16][17][18][19] The underlying mechanisms remained largely unclear.…”