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

Nicosia RF - J. Cell. Mol. Med. (2009)

Bottom Line: Many factors have contributed to its popularity including reproducibility, cost effectiveness, ease of use and good correlation with in vivo studies.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.

View Article: PubMed Central - PubMed

Affiliation: Pathology and Laboratory Medicine Services, Veterans Administration Puget Sound Health Care System, Seattle, WA 98108, USA. roberto.nicosia@va.gov

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.

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Standard and modified aortic ring model of angiogenesis with quiescent aortic rings. Freshly cut rings of rat aorta embedded in collagen gel generate outgrowths of branching microvessels. Aortic rings lose their spontaneous angioformative properties and become angiogenically quiescent if kept in serum-free growth medium for ∼2 weeks prior to collagen embedding. The medium is changed three times a week during this time to deplete the cultures of endogenous growth factors. Quiescent aortic rings remain viable and produce an angiogenic response comparable to that of freshly cut rings when they are re-injured or treated with exogenous angiogenic factors.
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fig04: Standard and modified aortic ring model of angiogenesis with quiescent aortic rings. Freshly cut rings of rat aorta embedded in collagen gel generate outgrowths of branching microvessels. Aortic rings lose their spontaneous angioformative properties and become angiogenically quiescent if kept in serum-free growth medium for ∼2 weeks prior to collagen embedding. The medium is changed three times a week during this time to deplete the cultures of endogenous growth factors. Quiescent aortic rings remain viable and produce an angiogenic response comparable to that of freshly cut rings when they are re-injured or treated with exogenous angiogenic factors.

Mentions: In 2004, the Rat genome Sequencing Project Consortium completed a decade long study aimed at deciphering the rat genome [74]. Meanwhile microarray analysis of cDNA had become a powerful method to detect genes dysregulated in physiological or pathological conditions [202]. To further define genetic events occurring in the aortic wall prior to angiogenic sprouting, we applied the microarray analysis method to rat aortic rings treated with angiogenic factors. For this study, aortic explants were made quiescent by a 14-day pre-incubation step in serum-free medium prior to collagen embedding. This procedure abrogated the spontaneous angiogenic activity of the rings while preserving their capacity to sprout in response to angiogenic factors or re-injury of the vessel wall. This approach produced angiogenic ‘on’ and ‘off’ conditions that enabled us to identify transcriptional events induced by angiogenic factors prior to endothelial sprouting (Fig. 4). We stimulated quiescent aortic rings with VEGF or angiopoietin-1 (Ang-1). Ang-1 had been identified by Yancopoulos’ group as the ligand of the tyrosine kinase receptor Tie2 and a key regulator of angiogenic sprouting, vessel branching and vessel maturation [44, 119, 219, 220]. Microarray analysis of quiescent aortic rings treated with VEGF or Ang-1 were confirmed by real time polymerase chain reaction and ELISA for selected genes.


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

Nicosia RF - J. Cell. Mol. Med. (2009)

Standard and modified aortic ring model of angiogenesis with quiescent aortic rings. Freshly cut rings of rat aorta embedded in collagen gel generate outgrowths of branching microvessels. Aortic rings lose their spontaneous angioformative properties and become angiogenically quiescent if kept in serum-free growth medium for ∼2 weeks prior to collagen embedding. The medium is changed three times a week during this time to deplete the cultures of endogenous growth factors. Quiescent aortic rings remain viable and produce an angiogenic response comparable to that of freshly cut rings when they are re-injured or treated with exogenous angiogenic factors.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4496118&req=5

fig04: Standard and modified aortic ring model of angiogenesis with quiescent aortic rings. Freshly cut rings of rat aorta embedded in collagen gel generate outgrowths of branching microvessels. Aortic rings lose their spontaneous angioformative properties and become angiogenically quiescent if kept in serum-free growth medium for ∼2 weeks prior to collagen embedding. The medium is changed three times a week during this time to deplete the cultures of endogenous growth factors. Quiescent aortic rings remain viable and produce an angiogenic response comparable to that of freshly cut rings when they are re-injured or treated with exogenous angiogenic factors.
Mentions: In 2004, the Rat genome Sequencing Project Consortium completed a decade long study aimed at deciphering the rat genome [74]. Meanwhile microarray analysis of cDNA had become a powerful method to detect genes dysregulated in physiological or pathological conditions [202]. To further define genetic events occurring in the aortic wall prior to angiogenic sprouting, we applied the microarray analysis method to rat aortic rings treated with angiogenic factors. For this study, aortic explants were made quiescent by a 14-day pre-incubation step in serum-free medium prior to collagen embedding. This procedure abrogated the spontaneous angiogenic activity of the rings while preserving their capacity to sprout in response to angiogenic factors or re-injury of the vessel wall. This approach produced angiogenic ‘on’ and ‘off’ conditions that enabled us to identify transcriptional events induced by angiogenic factors prior to endothelial sprouting (Fig. 4). We stimulated quiescent aortic rings with VEGF or angiopoietin-1 (Ang-1). Ang-1 had been identified by Yancopoulos’ group as the ligand of the tyrosine kinase receptor Tie2 and a key regulator of angiogenic sprouting, vessel branching and vessel maturation [44, 119, 219, 220]. Microarray analysis of quiescent aortic rings treated with VEGF or Ang-1 were confirmed by real time polymerase chain reaction and ELISA for selected genes.

Bottom Line: Many factors have contributed to its popularity including reproducibility, cost effectiveness, ease of use and good correlation with in vivo studies.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.

View Article: PubMed Central - PubMed

Affiliation: Pathology and Laboratory Medicine Services, Veterans Administration Puget Sound Health Care System, Seattle, WA 98108, USA. roberto.nicosia@va.gov

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.

Show MeSH
Related in: MedlinePlus