Platelet-Activating Factor Mediates CD40-Dependent Angiogenesis and Endothelial-Smooth Muscle Cell Interaction

Abstract

The aim of the present study was to investigate whether stimulation of CD40 expressed by endothelial or smooth muscle cells triggers the synthesis of platelet-activating factor (PAF), an inflammatory mediator with angiogenic properties, and whether PAF contributes to CD40-induced neoangiogenesis. The results obtained indicate that the interaction of CD40 with soluble CD154 or with CD154 expressed on the membrane of leukocytes (CD154-transfected J558 cells) or of activated platelets, stimulated the synthesis of PAF by endothelial cells but not by smooth cells. The synthesis of PAF triggered by activated platelets was inhibited by a soluble CD40-murine Ig fusion protein that prevents the interaction between membrane CD40 and CD154. Studies with specific inhibitors and evaluation of protein phosphorylation indicated the involvement in PAF synthesis of two intracellular signaling pathways leading to cytosolic phospholipase A2 activation: a phospholipase Cγ-protein kinase C-Raf-p42/p44-mitogen-activated protein kinase (MAPK) and a MAPK kinase-3/6-dependent activation of p38 MAPK. PAF synthesized by endothelial cells after CD40 stimulation was instrumental in the in vitro migration and vessel-like organization of endothelial cells, and in the interaction between endothelial cells and smooth muscle cells, as inferred by the inhibitory effect of two different PAF receptor antagonists, WEB2170 and CV3988. In vivo, blockade of PAF receptors prevented the angiogenic effect triggered by CD40 stimulation in a murine model of s.c. Matrigel implantation. In conclusion, these observations indicate that PAF synthesis induced by stimulation of endothelial CD40 contributes to the formation and organization of new vessels. This may be relevant in the vascular remodeling associated with tumor and inflammatory neoangiogenesis.

Expression of Platelet-Activating Factor Receptor: A Novel Prognosticator in Patients with Hepatocellular Carcinoma following Hepatectomy

“…On the other hand, inhibitory effects on cellular invasion and oncogenic transformation have also been reported for PAF [14,15,16,17]. PAF inhibited Src- and hepatocyte growth factor-dependent invasiveness of intestinal and kidney epithelial cells [16].…”

“…PAF has been shown to be involved in allergy, inflammation, infection and endotoxic shock [3]. Various functions of PAF have also been related to tumor activities [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Melanocytic tumorigenesis was observed in PAFR transgenic mice [4], and PAF demonstrated a metastasis-promoting effect in melanoma cells [5, 6].…”

Inhibitory effects of lipoteichoic acid from Staphylococcus aureus on platelet function and platelet–monocyte aggregation

“…Platelet-endothelial cell interactions increase expression of chemokines, cytokines and adhesion molecules, and enhance endothelial interaction with leukocytes [38]. Platelet-platelet interactions, as described above, play an important role in hemostasis as well as in the release of immunomodulatory factors [39]. In this study, plateletmonocyte aggregates were used to represent the effects of LTA on platelet-cell interactions.…”

CD40 Ligand and Its Receptors in Atherothrombosis

“…For instance, CD40 ligation on endothelial cells and macrophages was shown to upregulate the expression of potent angiogenic factors such as VEGF, fibroblast growth factor and plateletactivating factor, in addition to inducing the synthesis and proteinase activity of various MMPs such as MMP-1, MMP-2, MMP-3 and MMP-9. 18,[74][75][76] These responses are tightly linked to tubule formation and angiogenesis, essential elements of plaque support and growth. Interestingly, the 5 1 integrin is upregulated on angiogenesis-prone endothelial cells and could also provide a novel mechanism by which CD40L modulates pathological angiogenesis.…”