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Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1.

ABSTRACT: Architecturally defective, leaky blood vessels typify pathologic angiogenesis induced by vascular endothelial growth factor-A (VEGF-A). Such neovascular defects aggravate disease pathology and seriously compromise the therapeutic utility of VEGF. Endothelial cell (EC) transduction with active L61Rac1 strongly improved VEGF-driven angiogenesis in vivo as measured by increased neovascular density, enhanced lumen formation, and reduced vessel leakiness. Conversely, transduction with dominant-negative N17Rac1 strongly inhibited neovascularization. In vitro, active L61Rac1 promoted organization of cortical actin filaments and vascular cords and improved EC-EC junctions, indicating that improved cytoskeletal dynamics are important to the mechanism by which active L61Rac1 rectifies VEGF-driven angiogenesis. SEW2871, a sphingosine 1-phosphate receptor-1 agonist that activates Rac1 in ECs, improved cord formation and EC-EC junctions in vitro similarly to active L61Rac. Moreover, SEW2871 administration in vivo markedly improved VEGF neovessel architecture and reduced neovascular leak. Angiopoietin-1, a cytokine that "normalizes" VEGF neovessels in vivo, activated Rac1 and improved cord formation and EC-EC junctions in vitro comparably to active L61Rac1, and a specific Rac1 inhibitor blocked these effects. These studies distinguish augmentation of Rac1 activity as a means to rectify the pathologic angioarchitecture and dysfunctionality of VEGF neovessels, and they identify a rational pharmacologic strategy for improving VEGF angiogenesis.

SUBMITTER: Hoang MV

PROVIDER: S-EPMC3056599 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

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Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1.

Hoang Mien V MV Nagy Janice A JA Senger Donald R DR

Blood 20101028 5

Architecturally defective, leaky blood vessels typify pathologic angiogenesis induced by vascular endothelial growth factor-A (VEGF-A). Such neovascular defects aggravate disease pathology and seriously compromise the therapeutic utility of VEGF. Endothelial cell (EC) transduction with active L61Rac1 strongly improved VEGF-driven angiogenesis in vivo as measured by increased neovascular density, enhanced lumen formation, and reduced vessel leakiness. Conversely, transduction with dominant-negati ...[more]

PMID: 21030561

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Project description:Specific Aims ; To identify novel transcriptional events associated with angiogenesis in VEGF and Ang-1 stimulated rat aortic rings. Our studies take advantage of the capacity of rat aortic rings to generate new vessels in collagen gels. Rat aortic rings embedded in collagen gel immediately after excision from the animal produce a self-limited angiogenic response under serum-free conditions and in the absence of exogenous stimuli. This angiogenic response can be dose-dependently promoted by vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), which are critical regulators of the angiogenic process during embryonal development and postnatal angiogenesis. Aortic rings lose their capacity to spontaneously generate new vessels if embedded in collagen gels 10-14 days after excision. VEGF has the capacity to turn back âonâ these quiescent rings producing florid angiogenesis. Conversely, Ang-1 potentiates an existing angiogenic response, but is unable to turn the quiescent system âonâ. Since VEGF-mediated induction of angiogenic sprouting occurs 1-2 days of treatment, we hypothesize that this process is regulated by a unique set of âangiogenesis inducer genesâ that are activated by VEGF and not by Ang-1. Identification of the proteins encoded by these genes may advance our understanding of the molecular mechanisms that regulate the earliest stages of the angiogenic cascade. Experiment Overall Design: Rat thoracic aortic rings will be excised from 1 month old Fisher 344 rats and placed into suspension culture. 15-20 individual rings will be isolated from each animal and cultured in suspension in serum free medium. The rings will be divided into three groups as described below. (Assay is described in; Nicosia et al., 1997 Am.J.Pathol, 151). Experiment Overall Design: All individual aortic rings isolated from a single animal will be split into three groups, VEGF treated, Ang-1 treated, and untreated controls. Rings dissected from proximal and distal portions of the aorta will be mixed so that positional bias will not be carried through to the RNA preparation. Experiment Overall Design: 13 days post isolation, one set of aortic rings will be treated with 10ng/ml of recombinant human VEGF in serum free EBM media, a second set of rings will be treated with 100ng/ml of human recombinant Ang-1 (R&D Systems 923-AN) in conjunction with 5ug/ml poly-His antibody (R&D Systems MAB050), and a third set of rings will be incubated in serum free medium alone. Experiment Overall Design: All samples were incubated for 18 hours post VEGF and Ang-1 treatment and then RNA was harvested. Experiment Overall Design: With the number of aortic rings typically obtained, we anticipate having 4-6 individual rings from each animal for each experimental condition. Furthermore, 10-100ng of total RNA will be collected per aortic ring, corresponding to 400-600ng of total RNA for each experimental condition per animal. Experiment Overall Design: In order to have a minimum of three independent samples from each experimental condition, three animals were sacrificed, each of which gave rise to three individual RNA samples. The resulting 9 individual RNA samples to be compared with respect to transcriptional profiles. Experiment Overall Design: Total RNA will be extracted from each aortic ring using the Trizol reagent (Invitrogen) protocol. RNA will be stored at â80C until all 9 individual samples have been prepared. Trizol extracted total RNA will be further purified/concentrated using the MicroRNAEasy Kit (Qiagen) with DNAseI digestion.

Dataset Information

Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1.

Publications

Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1.

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