Common Angiogenic Signaling Pathways Induced by Monomeric C - reactive protein and FGF-2 through MAPK and PI3K

Excessive angiogenesis (i.e. neovascularization) in atherosclerotic lesions, sites of dissociation of the inflammatory biomarker pentameric C-reactive protein (pCRP) into monomeric CRP (mCRP), represents a focus of plaque instability with haemorrhagic complications. We previously demonstrated mCRP pro-angiogenic effects on cultured aortic endothelial cells. However, mCRP effects in combination with FGF-2, pro-angiogenic factor released by activated macrophages infiltrating developing lesions, have not yet been described. Here, we examined in vitro the angiogenic capabilities of mCRP combined with FGF-2 by performing endothelial cell proliferation, migration, and differentiation including tube formation and spheroid sprouting assays. The signaling pathways were also investigated by Western blotting and all the cell-based assays were used with or without pharmacological inhibitors of mitogen-activated protein kinase (MAPK), phosphatidylinositol-3 kinase (PI3K) and I³-secretase, considered as key regulators of angiogenesis. We showed that mCRP-induced endothelial cell proliferation and migration required activation of PI3K pathway. MAPK pathway was essential in mCRP-induced endothelial cell proliferation and spheroid sprouting while I³-secretase activity was indispensable for mCRP-induced tube formation only. MAPK pathway was required in all FGF-2-stimulated angiogenic assays whereas I³-secretase slightly inhibited FGF-2 angiogenic effects. PI3K pathway was necessary for FGF-2 angiogenic activities except for cell differentiation. In most of the assays, the additive pro-angiogenic effects of mCRP combined to FGF-2 were mainly attenuated by PI3K and MAPK inhibitors. Altogether, mCRP and FGF-2 have common angiogenic signaling pathways through PI3K and MAPK. Thus, the therapeutic use of PI3K and MAPK inhibitors may inhibit this increased vascularization whilst reducing the haemorrhagic complications from unstable plaques.