Abstract 1950: Cd40ligand+ Microparticles from Human Atherosclerotic Plaques Stimulate Angiogenesis : A Potential Mechanism For Intra-Plaque Neovascularization.
Atherosclerotic plaques prone to rupture are characterized by increased number of vasa vasorum and frequent intraplaque haemorrhage, but mechanisms of plaque neovascularization remain unknown. We have shown that human plaques contain submicron membrane-shed microparticles (MPs) of different cellular origin, which promote CD40-dependent endothelial proliferation in vitro. We hypothesized that plaque MPs are the endogenous signal for neovessel formation in atherosclerotic lesions. MPs isolated by mincing and sequential centrifugation of 26 human endarterectomy specimens were characterized by electron microscopy, phosphatidylserine exposure and specific markers of cellular origin. This procedure did not yield MPs from healthy arteries. Plaque MPs express CD40L and 93% of CD40L+ MPs derived from macrophage. In vitro MP-induced endothelial proliferation was mimicked by recombinant CD40L and inhibited by endothelial CD40 silencing (p=0.05; n=6), Wortmanin (1μM; p=0.02; n=4), LY294002 (1μM; p=0.005; n=6) or an anti-VEGF-R2 (p=0.04; n=6). Mice received a subcutaneous Matrigel plug with 3x106 plaque MPs or vehicle and presence of endothelial cells and erythrocytes was investigated after 7 days. Plaque MPs stimulated in vivo angiogenesis in C57BL/6 mice (p=0.001; n=10), as well as in athymic BALB/c (nu/nu) mice (p=0.04; n=8), ruling out the possibility that MPs pro-angiogenic effects were due to allogenic immune responses in immunocompetent mice. MPs pro-angiogenic effect was not different from that of recombinant CD40L (p=0.47; n=6) and was abolished by a CD40L neutralizing antibody (p=0.003; n=6) or in CD40-deficient mice (p=0.007; n=6). Microparticles isolated from human atherosclerotic lesions promote in vivo angiogenesis and stimulate endothelial cell proliferation following CD40 ligation and activation of VEGF-R2 PI3k/Akt pathways. Therefore, microparticles could represent a major determinant of plaque neovascularization and vulnerability.