A New ex vivo Model to Study Venous Angiogenesis and Arterio-Venous Anastomosis Formation

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Abstract
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. Medium conditioned by untreated vena cava cultures contained endogenous VEGF, and a blocking antibody against VEGF significantly reduced the spontaneous angiogenic response of the explants. Vena cava explants exhibited a greater capacity to form neovessels than aortic rings when tested in parallel cultures from the same animal. When compared with aorta-derived microvessels, neovessels of vena cava origin were longer and had fewer pericytes. Vena cava-aorta cocultures produced extensive anastomosing networks of microvessels, which were primarily contributed by the venous explants. Because of its florid angiogenesis and exquisite sensitivity to angiogenic factor stimulation, the vena cava model may provide novel insights into the regulation of the angiogenic process, which typically initiates from the venous side of the vascular bed. Combined with the aortic ring model, this new assay may also enhance our understanding of the mechanisms of anastomosis formation between the arterial and the venous circulations.