Essential role for platelet‐activating factor‐induced NF‐κB activation in macrophage‐derived angiogenesis

Abstract

Activated monocyte-macrophages have been implicated in tumor angiogenesis via their capacity to produce many potent angiogenic factors. However, the mechanisms leading to production of these angiogenic factors in macrophages remain to be elucidated. In this study, we demonstrated by use of a mouse Matrigel implantation model that mouse peritoneal macrophages induce angiogenesis. mRNA expression and protein synthesis of macrophage-derived crucial angiogenic factors such as IL-1, TNF- § , basic fibroblast growth factor, and vascular endothelial growth factor (VEGF) were blocked by platelet-activating factor (PAF) receptor antagonists. It was also observed that inhibitors of NF-‹ B blocked macrophage production of these angiogenic factors. Gene expression and protein synthesis of the angiogenic factors cited above were also inhibited in I ‹ B § -mutated macrophages. VEGF is the most potent angiogenic factor in macrophage-induced angiogenesis. PAF antagonists or NF-‹ B inhibitors also inhibit the capacity of conditioned medium from LPSstimulated human peripheral blood monocytes to induce sprouting of porcine pulmonary arterial endothelial cells. These data indicate that PAF-induced NF-‹ B activation is a common upstream pathway leading to the production of crucial macrophage-derived angiogenic factors. This will provide an important clue for a better understanding of mechanisms involved in tumor angiogenesis.

Monocyte/macrophage infiltration in tumors: modulators of angiogenesis

“…Among them are the chemotactic proteins M-CSF and MCP-1, which induce VEGF and IL-8; they have already been described previously in this manuscript. Furthermore, TAMs express urokinase-type plasminogen activator (uPA) and its receptor uPAR (CD87) [64,67,156], macrophage-inhibitory factor (MIF) [157,158], platelet activating factor (PAF) [159], TGF-␤ [82], heparin-binding epidermal growth factor (HB-EGF) [160], and platelet-derived growth factor (PDGF) [33,161], which are described further in Table 2. Although these angiogenic factors might be of equal importance, knowledge about them is limited compared with the ones described in this review.…”

Macrophages and tumor angiogenesis

“…28 Also VEGF is chemotactic for monocytes via VEGFR-1. 29,30 TAM expresses and releases epidermal growth factor (EGF), fibroblast growth factor-2 (FGF-2), 31,32 transforming growth factor-a and -b (TGF-a and -b), [33][34][35] VEGF, 36 TNF-a 37 IL-1, 38 IL-6, IL-8, 39 platelet-activating factor 40 platelet-derived growth factor (PDGF) 41 G-CSF and GM-CSF. 42 thymidine phosphorylase 43 and chemokines, such as CCL2.…”

Involvement of matrix metalloproteinase‐9 in platelet‐activating factor‐induced angiogenesis

“…ECV304 cells, an immortalized and transformed human vascular endothelial cell line [20], and PPAEC were prepared by collagenase digestion as described [21] were maintained in DulbeccoÕs modified Eagle medium (DMEM, GIBCO, Island, NY) supplemented with 10% (v/v) fetal bovine serum (CAMBREX Co., Walkersville, MD) at 37°C in a 5% CO 2 atmosphere. Porcine pulmonary arterial endothelial cells (PPAEC) used in the sprouting assay were between passages 2 and 4.…”

“…To investigate the effects of PAF on angiogenesis in vitro, endothelial sprouting was assessed, as previously described [21]. Briefly, microcarrier beads coated with denatured collagen (Cytodex 3; Sigma) were seeded with PPAEC and embedded in fibrin gels in 24-well plates.…”

“…We determined the in vitro effect of MMP-9 on the PAF-induced sprouting of PPAEC, given that the sprouting of the endothelial cell is the initial step in angiogenesis, requiring cell migration into the extracellular matrix beneath the basement membrane [21,23]. Addition of PAF into PPAEC grown on microcarrier beads in fibrin gel resulted in increases in sprout formation ( Fig.…”