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

Abstract

Objective— Neutrophil infiltration of the postischemic tissue considerably contributes to organ dysfunction on ischemia/reperfusion injury. Beyond its established role in fibrinolysis, tissue-type plasminogen activator (tPA) has recently been implicated in nonfibrinolytic processes. The role of this serine protease in the recruitment process of neutrophils remains largely obscure. Approach and Results— Using in vivo microscopy on the postischemic cremaster muscle, neutrophil recruitment and microvascular leakage, but not fibrinogen deposition at the vessel wall, were significantly diminished in tPA −/− mice. Using cell transfer techniques, leukocyte and nonleukocyte tPA were found to mediate ischemia/reperfusion-elicited neutrophil responses. Intrascrotal but not intra-arterial application of recombinant tPA induced a dose-dependent increase in the recruitment of neutrophils, which was significantly higher compared with stimulation with a tPA mutant lacking catalytic activity. Whereas tPA-dependent transmigration of neutrophils was selectively reduced on the inhibition of plasmin or gelatinases, neutrophil intravascular adherence was significantly diminished on the blockade of mast cell activation or lipid mediator synthesis. Moreover, stimulation with tPA caused a significant elevation in the leakage of fluorescein isothiocyanate dextran to the perivascular tissue, which was completely abolished on neutrophil depletion. In vitro, tPA-elicited macromolecular leakage of endothelial cell layers was abrogated on the inhibition of its proteolytic activity. Conclusions— Endogenously released tPA promotes neutrophil transmigration to reperfused tissue via proteolytic activation of plasmin and gelatinases. As a consequence, tPA on transmigrating neutrophils disrupts endothelial junctions allowing circulating tPA to extravasate to the perivascular tissue, which, in turn, amplifies neutrophil recruitment through the activation of mast cells and release of lipid mediators.

Components of the Plasminogen Activation System Promote Engraftment of Porous Polyethylene Biomaterial via Common and Distinct Effects

“…In addition to its non-fibrinolytic effects on endothelial cells, uPA, tPA, and PAI-1 have been reported to contribute to the regulation of leukocyte recruitment under severe inflammatory conditions including ischemia-reperfusion injury [ 37 , 45 – 47 ] or sepsis [ 48 ]. Upon biomaterial implantation, however, only a ‘moderate’ inflammatory response arises which might explain that deficiency of the major components of the plasminogen activation system did not substantially alter leukocyte-endothelial cell interactions within the implant or in the surrounding host tissue in our experiments.…”

The role of tissue resident cells in neutrophil recruitment

“…36 Tissue plasminogen activator, a naturally occurring serine protease capable of converting plasminogen to plasmin, also has this same effect upon perivascular mast cells and resultant neutrophil recruitment. 37 …”

Plasmin: A Modulator of Immune Function

“…Moreover, plasmin indirectly promotes neutrophil recruitment by binding to mast cells and stimulating release of leukotrienes. 27,28 Also, t-PA was reported to support neutrophil trafficking by modulating endothelial tight junctions, 28 although in this study, the effect of t-PA was only partially due to its capacity to act as a (plasmin generating) protease.…”