The plaque-aortic ring assay: a new method to study human atherosclerosis-induced angiogenesis

Progression of atherosclerotic plaques into life-threatening lesions is associated with angiogenesis which contributes to intraplaque hemorrhages and plaque instability. The lack of adequate models for the study of human plaque-induced angiogenesis has limited progress in this field. We describe here a novel ex vivo model which fills this gap. Plaques obtained from 15 patients who underwent endarterectomy procedures were co-cultured in collagen gels with rat aorta rings which served as read-out of human plaque angiogenic activity. The majority of plaque fragments markedly stimulated angiogenic sprouting from the aortic rings while concurrently promoting the outgrowth of resident macrophages from the aortic adventitia. This stimulatory activity correlated with the presence of intraplaque macrophages. Proteomic analysis of plaque secretomes revealed heterogeneity of macrophage-stimulatory cytokine and angiogenic factor production by different plaques. VEGF was identified in some of the plaque secretomes. Antibody-mediated blockade of VEGF had significant but transient inhibitory effect on angiogenesis, which suggested redundancy of plaque-derived angiogenic stimuli. Pharmacologic ablation of adventitial macrophages permanently impaired the angiogenic response of aortic rings to plaque stimuli. Our results show that human plaque-induced angiogenesis can be reproduced ex vivo using rat aortic rings as read-out of plaque angiogenic activity. This model can be used to identify key cellular and molecular mechanisms responsible for the neovascularization of human plaques.