Regulation of angiogenesis, mural cell recruitment and adventitial macrophage behavior by Toll-like receptors.

The angiogenic response to injury can be studied by culturing rat or mouse aortic explants in collagen gels. Gene expression studies show that aortic angiogenesis is preceded by an immune reaction with overexpression of Toll-like receptors (TLRs) and TLR-inducible genes. TLR1, 3, and 6 are transiently upregulated at 24 h whereas TLR2, 4, and 8 expression peaks at 24 h but remains elevated during angiogenesis and vascular regression.

MCP-1 promotes mural cell recruitment during angiogenesis in the aortic ring model.

Rings of rat or mouse aorta embedded in collagen gels produce angiogenic outgrowths in response to the injury of the dissection procedure. Aortic outgrowths are composed of branching endothelial tubes and surrounding mural cells. Mural cells emerge following endothelial sprouting and gradually increase during the maturation of the neovessels.

The angiogenic response of the aorta to injury and inflammatory cytokines requires macrophages.

The purpose of this study was to define early events during the angiogenic response of the aortic wall to injury. Rat aortic rings produced neovessels in collagen culture but lost this capacity over time. These quiescent rings responded to vascular endothelial growth factor but not to a mixture of macrophage-stimulatory cytokines and chemokines that was angiogenically active on fresh rings.

The aortic ring model of angiogenesis.

Angiogenesis is regulated by a complex cascade of cellular and molecular events. The entire process can be reproduced in vitro by culturing rat or mouse aortic explants in three-dimensional biomatrices under chemically defined conditions. Angiogenesis in this system is driven by endogenous growth factors released by the aorta and its outgrowth.

Aortic rings stimulate inflammatory angiogenesis in a subcutaneous implant in vivo model.

Rat or mouse aortic rings produce angiogenic outgrowths in vitro through endogenous production of growth factors and inflammatory cytokines. To further investigate this process in vivo, collagen-Gelfoam constructs containing aortic rings were implanted subcutaneously in syngeneic animals. Aortic rings stimulated a prominent angiogenic response characterized by peri- and intra-aortic accumulation of florid granulation tissue.

Regulation of postangiogenic neovessel survival by beta1 and beta3 integrins in collagen and fibrin matrices.

We used the aortic ring model of angiogenesis to investigate the role of beta(1) and beta(3) integrins in postangiogenic vascular survival in collagen and fibrin matrices. Confocal microscopy studies showed that both beta(1) and beta(3) integrins were expressed in endothelial cells and pericytes of sprouting neovessels. Antibody blocking experiments demonstrated that beta(1) integrins but not beta(3) integrins were required for angiogenic sprouting in collagen.

Angiopoietin-1 and vascular endothelial growth factor induce expression of inflammatory cytokines before angiogenesis.

The purpose of this study was to identify novel transcriptional events occurring in the aortic wall before angiogenesis. We used a defined tissue culture system that takes advantage of the capacity of rat aortic rings to generate neovessels ex vivo in response to angiogenic factor stimulation. Total RNA isolated from aortic rings 18 h posttreatment with angiopoietin (Ang)-1 or vascular endothelial growth factor (VEGF) was used to probe oligonucleotide microarrays.

A new ex vivo model to study venous angiogenesis and arterio-venous anastomosis formation.

Explants of rat inferior vena cava embedded in collagen gel and cultured under serum-free conditions produced microvascular outgrowths composed of endothelial cells and pericytes. Exogenous vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) dose-dependently stimulated angiogenesis and induced the formation of complex networks of highly branched microvessels. VEGF and the VEGF/bFGF combination also promoted pericyte recruitment.

The mouse aorta model: influence of genetic background and aging on bFGF- and VEGF-induced angiogenic sprouting.

Angiogenesis can be studied ex vivo by culturing rat or mouse aortic rings in collagen gels. Unlike rat aorta explants, unstimulated mouse aortic rings were unable to spontaneously produce an angiogenic response under serum-free conditions. They, however, responded to bFGF and VEGF, generating networks of branching neovessels.

Rat aorta-derived mural precursor cells express the Tie2 receptor and respond directly to stimulation by angiopoietins.

Recent studies have implicated the Tie2 tyrosine-kinase receptor and its main ligands--angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2)--as crucial regulators of mural cell recruitment during angiogenesis. Angiopoietin-mediated activation of Tie2 promotes perivascular mural cell assembly, but the mechanisms regulating this process are poorly understood because differentiated mural cells do not have the Tie2 receptor, which is reportedly expressed only in endothelial cells. There is also no direct evidence that Tie2 activation results in production of mural cell chemoattractants by the endothelium.