Platelet-activating factor modulates endotoxin-induced macrophage procoagulant activity by a protein kinase C-dependent mechanism

Abstract

Macrophage procoagulant activity is an important mediator of extravascular fibrin deposition at sites of infection and appears to contribute to the pathogenesis of several infectious disease processes. Previous studies have shown that the inflammatory mediator platelet-activating factor was able to prime macrophages for induction of procoagulant activity by bacterial lipopolysaccharide. The present studies were designed to examine the mechanism of this priming effect. Platelet-activating factor (100 nM) primed macrophages for procoagulant activity generation in response to endotoxin at concentrations as low as 100 ng/ml and also following exposure to Escherichia coli, Bacteroides fragilis, and Staphylococcus aureus. The priming effect occurred following a pretreatment with platelet-activating factor for as short as 1 min, suggesting a rapid activation event. Two different doses of the calcium ionophore ionomycin were used to mimic the peak and sustained effects of platelet-activating factor on cytoplasmic calcium levels (1 microM and 100 nM, respectively). Neither dose was able to mimic the priming effect. However, extracellular calcium was necessary for induction of procoagulant activity and the priming effect. By contrast, the protein kinase C agonist phorbol myristate acetate reproduced the priming phenomenon observed for platelet-activating factor. In further support of the concept that protein kinase C activation mediated the effect of platelet-activating factor, the specific protein kinase C inhibitor staurosporine reversed the ability of platelet-activating factor to augment induction of macrophage procoagulant activity by endotoxin. These data suggest mechanisms by which inflammatory mediators within the microenvironment of infection might modulate the host response to bacterial pathogens.

The role of tyrosine phosphorylation in lipopolysaccharide- and zymosan-induced procoagulant activity and tissue factor expression in macrophages

“…This agent completely prevented the release of PGE 2 by LPS-stimulated cells. Consistent with our previous reports (40), indomethacin had no effect on LPS-stimulated PCA (Fig. 8B).…”

“…Brozna and Carson (8) demonstrated that phorbol myristate acetate, at concentrations sufficient to translocate PKC activity from the cytosolic to the particulate fraction in adherent human monocytes, blocked adherence-induced PCA expression and suppressed PCA expression in cells activated by adherence or LPS treatment. Our laboratory has previously shown that PMA alone had little direct effect on PCA in thioglycolate-elicited murine peritoneal macrophages, although it primed cells for increased PCA expression in response to LPS and live bacteria (40,41). The variability observed with respect to the role of PKC in LPSinduced PCA in monocytes/macrophages may be related to the source of the cell studied as well as the degree of cellular activation.…”

“…However, subsequent studies have indicated no significant increase in PKC activity following cell stimulation with LPS (22). Further, inhibitors of PKC have varied effects on the ability of LPS to stimulate the production of mediator molecules by macrophages or to effect macrophage priming (10,11,39,40,62), suggesting the existence of PKC-independent signalling pathways in these cells.…”

Inflammatory processes in a murine model of intra-abdominal abscess formation

“…As noted above, stimulated mast cells can release histamine, as well as neutral proteases and proteoglycans, TNF-␣ and other cytokines as preformed mediators, and arachidonic acid metabolites such as prostaglandin D 2 , leukotriene B 4 , and platelet activating factor as mediators synthesized de novo [49]. These mediators cause cellular and plasma protein influxes (including fibrinogen), and may have direct effects on resident and recruited cells relevant, e.g., to fibrin deposition (e.g., platelet-activating factor primes macrophages for LPS induction of PCA [50]). Mast cell lysates can induce macrophage PCA and TNF-␣ release [51].…”

Hypoxia primes endotoxin-induced tissue factor expression in human monocytes and endothelial cells by a PAF-dependent mechanism

“…Fibrin deposition is part of the pathological picture observed in each of these processes, suggesting that PAF contributes to the pathogenesis of these diseases by inducing local coagulation. In this regard, recent studies demonstrated the ability of PAF to augment the induction of procoagulant activity (PCA) in macrophages in response to LPS or tumor necrosis factor-a (Kucey et al, 1991a(Kucey et al, , 1992Maier et al, 1992). Moreover, several authors suggested that hypoxia, whose importance in the development of venous thrombosis has been acknowledged for a long time, induces the expression of PCA in cultured human umbilical vein endothelial cells (HUVEC) and mono-cytes Gertler et al, 1991;Kucey et al, 1991b).…”