title: Hypoxia paradoxically inhibits the angiogenic response of isolated vessel explants while inducing overexpression of vascular endothelial growth factor.
abstract: This study was designed to investigate how changes in O2 levels affected angiogenesis in vascular organ culture. Although hypoxia is a potent inducer of angiogenesis, aortic rings cultured in collagen paradoxically failed to produce an angiogenic response in 1-4 % O2. Additionally, aortic neovessels preformed in atmospheric O2 lost pericytes and regressed at a faster rate than control when exposed to hypoxia. Aortic explants remained viable in hypoxia and produced an angiogenic response when returned to atmospheric O2. Hypoxic aortic rings were unresponsive to VEGF, while increased oxygenation of the system dose-dependently enhanced VEGF-induced angiogenesis. Hypoxia-induced refractoriness to angiogenic stimulation was not restricted to the aorta because similar results were obtained with vena cava explants or isolated endothelial cells. Unlike endothelial cells, aorta-derived mural cells were unaffected by hypoxia. Hypoxia downregulated expression in aortic explants of key signaling molecules including VEGFR2, NRP1 and Prkc-beta while upregulating expression of VEGFR1. Medium conditioned by hypoxic cultures exhibited angiostatic and anti-VEGF activities likely mediated by sVEGFr1. Hypoxia reduced expression of VEGFR1 and VEGFR2 in endothelial cells while upregulating VEGFR1 in macrophages and VEGF in both macrophages and mural cells. Thus, changes in O2 levels profoundly affect the endothelial response to angiogenic stimuli. These results suggest that hypoxia-induced angiogenesis is fine-tuned by complex regulatory mechanisms involving not only production of angiogenic factors including VEGF but also differential regulation of VEGFR expression in different cell types and production of inhibitors of VEGF function such as sVEGFR1.
authors.affiliation: Department of Pathology, University of Washington, Seattle, WA, USA.
authors.forename: Alfred C
authors.initials: AC
authors.lastname: Aplin
authors.affiliation: Department of Pathology, University of Washington, Seattle, WA, USA. Roberto.Nicosia@va.gov.|Pathology and Laboratory Medicine Service (S-113-Lab), VA Puget Sound Health Care System, Seattle, WA, USA. Roberto.Nicosia@va.gov.
authors.forename: Roberto F
authors.initials: RF
authors.lastname: Nicosia
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001011:Aorta / Q000187:drug effects; D000077214:Becaplermin; D001808:Blood Vessels / Q000187:drug effects / Q000502:physiology*; D015687:Cell Hypoxia / Q000187:drug effects; D002469:Cell Separation; D002470:Cell Survival / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000494:pharmacology; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D008297:Male; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D010100:Oxygen / Q000494:pharmacology; D020286:Pericytes / Q000187:drug effects / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis / Q000494:pharmacology; D011916:Rats, Inbred F344; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D046509:Tissue Culture Techniques; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology*; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000378:metabolism
chemical_list: D000975:Antioxidants; D017077:Culture Media, Conditioned; D020574:Proto-Oncogene Proteins c-sis; D042461:Vascular Endothelial Growth Factor A; D000077214:Becaplermin; D040281:Vascular Endothelial Growth Factor Receptor-1; D010100:Oxygen
keywords: Aorta; Collagen; Endothelial cells; Neovascularization; Neovessels; Pericytes; Vascular endothelial growth factor; Vein