The aortic ring model of angiogenesis: a quarter century of search and discovery

Abstract

The aortic ring model has become one of the most widely used methods to study angiogenesis and its mechanisms. Many factors have contributed to its popularity including reproducibility, cost effectiveness, ease of use and good correlation with in vivo studies. In this system aortic rings embedded in biomatrix gels and cultured under chemically defined conditions generate arborizing vascular outgrowths which can be stimulated or inhibited with angiogenic regulators. Originally based on the rat aorta, the aortic ring model was later adapted to the mouse for the evaluation of specific molecular alterations in genetically modified animals. Viral transduction of the aortic rings has enabled investigators to overexpress genes of interest in the aortic cultures. Experiments on angiogenic mechanisms have demonstrated that formation of neovessels in aortic cultures is regulated by macrophages, pericytes and fibroblasts through a complex molecular cascade involving growth factors, inflammatory cytokines, axonal guidance cues, extracellular matrix (ECM) molecules and matrix-degrading proteolytic enzymes. These studies have shown that endothelial sprouting can be effectively blocked by depleting the aortic explants of macrophages or by interfering with the angiogenic cascade at multiple levels including growth factor signalling, cell adhesion and proteolytic degradation of the ECM. In this paper, we review the literature in this field and retrace the journey from our first morphological descriptions of the aortic outgrowths to the latest breakthroughs in the cellular and molecular regulation of aortic vessel growth and regression.

MULTIMERIN2 impairs tumor angiogenesis and growth by interfering with VEGF-A/VEGFR2 pathway

“…The negative effect of MMRN2 in regulating angiogenesis may likely depend on the endogenous VEGF-A released by ECs when not added directly in the various tests (Roccaro et al, 2006), for instance the sprouting of novel vessels in aortic ring assays is highly dependent on endogenously released VEGF-A (Ligresti et al, 2011). Although the inhibition of EC motility was directly linked to MMRN2, it cannot be excluded that the striking effects in halting angiogenesis in vivo may also depend on its influence on other cell types that may be responsible for an amplification of the anti-angiogenic effects of this molecule (Anghelina et al, 2006;Nicosia, 2009).…”

Paracrine regulation of angiogenesis by different cell types in the aorta ring model

“…The angioformative properties of the intimal endothelium can be further demonstrated by embedding isolated aortic endothelial cells in collagen gel or by treating them with angiogenic factors (Nicosia et al, 1994b). In addition rat carotid explants fail to generate an angiogenic response when completely de-endothelialized with a balloon catheter whereas control carotid arteries with an intact intimal endothelium produce microvessels from their ends of resection (Nicosia, 2009). These findings indicate that the intimal layer of the aortic wall plays a central role in the sprouting of the aortic explants.…”

“…bFGF, VEGF (Fig. 2) and many of the growth factors, cytokines and chemokines upregulated in aortic ring cultures stimulate the angiogenic response of the aortic rings when added as exogenous molecules to the system (Gelati et al, 2008;Aplin et al, 2010;Salcedo et al, 1999;Nicosia et al, 1994a;Nicosia, 2009).…”

“…Aortic outgrowths are composed of a mixed population of endothelial cells, pericytes, fibroblasts, and macrophages. Angiogenesis in aortic cultures is mediated by paracrine interactions between cells of the vessel wall and can be modulated by incorporating into the system exogenous cells or by supplementing the culture medium with molecular regulators of angiogenesis (Nicosia, 2009). In this paper we describe how the aortic ring model can be used to study paracrine mechanisms of angiogenesis regulation and the role of different cell types in the induction, maturation, and resolution of the angiogenic process.…”

Procedure for the Development of Multi-depth Circular Cross-sectional Endothelialized Microchannels-on-a-chip

“…Recapitulation of functional microvessels in vitro could provide a platform for the study of complex vascular phenomena. However, conventional in vitro microvessel assays, such as endothelial cell migration assays, endothelial tube formation assays, and rat and mouse aortic ring assays, are unable to recreate the in vivo microvessels with respect to three-dimensional (3D) geometry and continuous flow control [1][2][3][4][5][6][7][8] . Studies of microvessels using animal models and in vivo assays, such as corneal angiogenesis assay, chick chorioallantoic membrane angiogenesis assay, and Matrigel plug assay, are more time-consuming, high in cost, challenging with respect to observation and quantifications, and raise ethical issues 1,[9][10][11][12][13] .…”