Platelet Activation by Polymorphonuclear Leukocytes: Role of Cathepsin G and P-Selectin

Abstract

The platelet-polymorphonuclear (PMN) leukocyte interaction may occur in vivo, as observed in animal models of inflammatory and thrombotic diseases. Mixed masses of PMN and platelets have been observed in the lungs of experimental animals subjected to hemorrhagic shock (1) or anaphylatoxin instillation (2) or following intradermal or intravenous infusion of n-formyl-Methionyl-Leucyl-Phenylalanine (fMLP) (3,4), or in rat glomeruli inamodel o f immune complex nephritis (5). Plateletaccumulation in experimental myocardial infarction was depressed by PMN depletion (6). Leukocyte accumulation at the site of platelet thrombus was reported (7) as well as platelet-leukocyte interaction after injection of oxidized lipoproteins in vivo (8). Thepathogenesis of the adult respiratory distress syndrome also appears to involve activation o f PMN and platelets (9). The broad range o f interactions between PMN and platelets in vitro includes reciprocal modulatory effects (10-13). In view of epidemiological evidence of a positive correlation between the number o f PMN and the development of ischemic disease (14), the observation that activated PMN induce platelet activation may be of great physiopathological relevance. We have focussed our attention on the stimulating effects ofPM N on platelets. Different pathways and mediators o f this cell-cell interaction have been suggested: several PMN-derived products, such as myeloperoxidase, hydrogen peroxide (H20 2) and superoxide anion (O2), may induce platelet activation (15-17). PAF, a lipid mediator produced by PMN, also has platelet stimulating activity. Though it seems to play a role in rabbitPMN-platelet cooperation (18), this mediator seems not to be implicated in PMN-dependent platelet activation with human cells (19). A direct role for PMN-derived proteinases was shown by the enhancement o f platelet serotonin release induced by thrombin or immune com plexes, using chym otrypsin-like cationic proteins (20). Bykowska et al. (21) provided evidence that a neutral-chymotrypsin-like-serine proteinase purified from human neutrophils, stimulated platelet function. Marked platelet activation, involving cytoplasmic Ca2+ increase, was also reported when mixed human platelet-PMN suspensions were challenged with fMLP (or other PMN agonists) in the presence of cytochalasin B, which allow s azurophilic granule discharge. Cell-free supernatants o f fMLP-activated PMN also induced platelet activation, suggesting a soluble factor was involved (19,22). Electron microscopic observation o f aggregates from mixed

Fibrin(ogen) and diabetes mellitus: don't forget fibrinolysis

“…Leukocytes increase fibrinogen synthesis by secreting interleukin-6 under stimulus from fibrinogen degradation products [2]. The pathogenetic role of inflammation in the development of atherosclerosis is supported by recent studies showing that interleukin-1 and tumour necrosis factor are able to reverse the functional non-thrombogenic properties of normal endothelium towards prothrombotic changes, enhancing the generation of thrombin at the endothelial surface [3][4][5][6]. Polymorphonuclear leukocytes can activate platelets [6], which stimulate the adherence of monocytes to surfaces [5] and the endothelial expression of leukocyte adhesion molecules [7].…”

“…Inflammation is associated with both hypercoagulability (increased fibrinogen, factor VIII, platelets) [1][2][3][4][5][6][7] and hypofibrinolysis (increased expression of plasminogen activator inhibitor-1, PAI-1) [10]. Plasma levels of fibrinogen were found to be associated with the severity of atheromatous involvement of the arterial walls [11].…”

Human Neutrophil Elastase Proteolytically Activates the Platelet Integrin αIIbβ3 through Cleavage of the Carboxyl Terminus of the αIIb Subunit Heavy Chain

“…Briefly, 20 g of 1 The abbreviations used are: PLC, phospholipase C; NE, neutrophil elastase; threshold of cathepsin G, threshold concentration of cathepsin G; PKC, protein kinase C; P47, pleckstrin; MALDI-TOF, matrix-assisted laser desorption/ionization-time of flight; LIBS, ligand-induced binding site; CHO, Chinese hamster ovary; PAGE, polyacrylamide gel electrophoresis; PMSF, phenylmethylsulfonyl fluoride; PGI 2 , prostaglandin I 2 ; PtdOH, phosphatidic acid; 5-HT, 5-hydroxytryptamine.…”

“…As part of such a cell cooperation network, polymorphonuclear neutrophils contribute to vessel injury not only by their own, but also through interactions with platelets. Thus, neutrophils are found admixed with platelets in the core of vascular occlusions in several experimental models (1,3), and more importantly, a neutrophil-dependent platelet deposition has been described in arterial injuries (4 -6). Neutrophil-mediated platelet activation can be demonstrated in vitro by adding specific neutrophil agonists such as the formyl-Met-Leu-Phe (fMLP) peptide, tumor necrosis factor-␣, or interleukin-8 to autologous neutrophil-platelet mixed suspensions (7)(8)(9)(10).…”

“…Acting similarly to ␣-thrombin, another serine proteinase agonist of platelets, cathepsin G-induced platelet activation results in massive exocytosis and aggregation reactions. The potent signal transduction triggered by this neutrophil proteinase includes the activation of an as yet unidentified proteinaseactivated membrane receptor, and the subsequent stimulation of the phospholipase C (PLC) 1 /protein kinase C (PKC) and Ca 2ϩ pathways (14 -16). Another important serine proteinase released from the azurophilic granules concomitantly with cathepsin G is neutrophil elastase (NE).…”