Vascular Patterning as Integrative Readout of Complex Molecular and Physiological Signaling by VESsel GENeration Analysis.

The molecular signaling cascades that regulate angiogenesis and microvascular remodeling are fundamental to normal development, healthy physiology, and pathologies such as inflammation and cancer. Yet quantifying such complex, fractally branching vascular patterns remains difficult. We review application of NASA's globally available, freely downloadable VESsel GENeration (VESGEN) Analysis software to numerous examples of 2D vascular trees, networks, and tree-network composites. Upon input of a binary vascular image, automated output includes informative vascular maps and quantification of parameters such as tortuosity, fractal dimension, vessel diameter, area, length, number, and branch point. Previous research has demonstrated that cytokines and therapeutics such as vascular endothelial growth factor, basic fibroblast growth factor (fibroblast growth factor-2), transforming growth factor-beta-1, and steroid triamcinolone acetonide specify unique "fingerprint" or "biomarker" vascular patterns that integrate dominant signaling with physiological response. In vivo experimental examples described here include vascular response to keratinocyte growth factor, a novel vessel tortuosity factor; angiogenic inhibition in humanized tumor xenografts by the anti-angiogenesis drug leronlimab; intestinal vascular inflammation with probiotic protection by Saccharomyces boulardii, and a workflow programming of vascular architecture for 3D bioprinting of regenerative tissues from 2D images. Microvascular remodeling in the human retina is described for astronaut risks in microgravity, vessel tortuosity in diabetic retinopathy, and venous occlusive disease.

Selective inhibition of angiogenesis in small blood vessels and decrease in vessel diameter throughout the vascular tree by triamcinolone acetonide.

PURPOSE: To quantify the effects of the steroid triamcinolone acetonide (TA) on branching morphology within the angiogenic microvascular tree of the chorioallantoic membrane (CAM) of quail embryos. METHODS: Increasing concentrations of TA (0-16 ng/mL) were applied topically on embryonic day (E) 7 to the chorioallantoic membrane (CAM) of quail embryos cultured in petri dishes and incubated for an additional 24 or 48 hours until fixation. Binary (black/white) microscopic images of arterial end points were quantified by generational analysis of vessel branching (VESGEN) software to obtain major vascular parameters that include vessel diameter (D(v)), fractal dimension (D(f)), tortuosity (T(v)), and densities of vessel area, length, number, and branch point (A(v), L(v), N(v), and Br(v)). For assessment of specific changes in vascular morphology induced by TA, the VESGEN software automatically segmented the vascular tree into branching generations (G(1)... G(10)) according to changes in vessel diameter and branching. RESULTS: Vessel density decreased significantly up to 34% as the function of increasing concentration of TA according to A(v), L(v), Br(v), N(v), and D(f). TA selectively inhibited the growth of new, small vessels because L(v) decreased from 13.14 +/- 0.61 cm/cm(2) for controls to 8.012 +/- 0.82 cm/cm(2) at 16 ng TA/mL in smaller branching generations (G(7)-G(10)) and for N(v) from 473.83 +/- 29.85 cm(-2) to 302.32 +/- 33.09 cm(-2). In contrast, vessel diameter (D(v)) decreased throughout the vascular tree (G(1)-G(10)). CONCLUSIONS: By VESGEN analysis, TA selectively inhibited the angiogenesis of smaller blood vessels, but decreased the vessel diameter of all vessels within the vascular tree.

Lymphangiogenesis by blind-ended vessel sprouting is concurrent with hemangiogenesis by vascular splitting.

Development of effective vascular therapies requires the understanding of all modes of vessel formation involved in angiogenesis (here termed "hemangiogenesis") and lymphangiogenesis. Two major modes of vessel morphogenesis include sprouting of a new vessel from a preexisting vessel and splitting of a preexisting parent vessel into two offspring vessels. In the quail chorioallantoic membrane (CAM) during mid-development (embryonic days E6-E9), lymphangiogenesis progressed primarily via blind-ended vessel sprouting. Isolated lymphatic endothelial progenitor cells were recruited to the tips of growing vessels. During concurrent hemangiogenesis, parent blood vessels expanded from the capillary network and split into offspring vessels, accompanied by transient capillary expression of alpha smooth muscle actin (alphaSMA) and recruitment of polarized mural progenitor cells. Lymphatics and blood vessels were identified by confocal/fluorescence microscopy of vascular endothelial growth factor (VEGF) receptor VEGFR-2, alphaSMA (specific to CAM blood vessels), homeobox transcription factor Prox1 (specific to lymphatics), and the quail hematopoetic marker, QH-1. VEGFR-2 was expressed intensely in isolated cells and lymphatics, and moderately in blood vessels. Prox1 was absent from isolated progenitor cells prior to lymphatic recruitment. Exogenous vascular endothelial growth factor-165 (VEGF165) increased blood vessel density and anastomotic frequency without changing endogenous modes of vascular/lymphatic vessel formation or marker expression. Although VEGF165 is a key cellular regulator of hemangiogenesis and vasculogenesis, the role of VEGF165 in lymphangiogenesis is less clear. Interestingly, VEGF165 increased lymphatic vessel diameter and density as measured by novel Euclidean distance mapping, and the antimaturational dissociation of lymphatics from blood vessels, accompanied by lymphatic reassociation into homogeneous networks.

Oscillation of angiogenesis with vascular dropout in diabetic retinopathy by VESsel GENeration analysis (VESGEN).

PURPOSE: Vascular dropout and angiogenesis are hallmarks of the progression of diabetic retinopathy (DR). However, current evaluation of DR relies on grading of secondary vascular effects, such as microaneurysms and hemorrhages, by clinical examination instead of by evaluation of actual vascular changes. The purpose of this study was to map and quantify vascular changes during progression of DR by VESsel GENeration Analysis (VESGEN). METHODS: In this prospective cross-sectional study, 15 eyes with DR were evaluated with fluorescein angiography (FA) and color fundus photography, and were graded using modified Early Treatment Diabetic Retinopathy Study criteria. FA images were separated by semiautomatic image processing into arterial and venous trees. Vessel length density (L(v)), number density (N(v)), and diameter (D(v)) were analyzed in a masked fashion with VESGEN software. Each vascular tree was automatically segmented into branching generations (G(1)...G(8) or G(9)) by vessel diameter and branching. Vascular remodeling status (VRS) for N(v) and L(v) was graded 1 to 4 for increasing severity of vascular change. RESULTS: By N(v) and L(v), VRS correlated significantly with the independent clinical diagnosis of mild to proliferative DR (13/15 eyes). N(v) and L(v) of smaller vessels (G(> or =6)) increased from VRS1 to VRS2 by 2.4 x and 1.6 x, decreased from VRS2 to VRS3 by 0.4 x and 0.6 x, and increased from VRS3 to VRS4 by 1.7 x and 1.5 x (P < 0.01). Throughout DR progression, the density of larger vessels (G(1-5)) remained essentially unchanged, and D(v1-5) increased slightly. CONCLUSIONS: Vessel density oscillated with the progression of DR. Alternating phases of angiogenesis/neovascularization and vascular dropout were dominated first by remodeling of arteries and subsequently by veins.

VESGEN 2D: automated, user-interactive software for quantification and mapping of angiogenic and lymphangiogenic trees and networks.

Quantification of microvascular remodeling as a meaningful discovery tool requires mapping and measurement of site-specific changes within vascular trees and networks. Vessel density and other critical vascular parameters are often modulated by molecular regulators as determined by local vascular architecture. For example, enlargement of vessel diameter by vascular endothelial growth factor (VEGF) is restricted to specific generations of vessel branching (Parsons-Wingerter et al., Microvascular Research72: 91, 2006). The averaging of vessel diameter over many successively smaller generations is therefore not particularly useful. The newly automated, user-interactive software VESsel GENeration Analysis (VESGEN) quantifies major vessel parameters within two-dimensional (2D) vascular trees, networks, and tree-network composites. This report reviews application of VESGEN 2D to angiogenic and lymphangiogenic tissues that includes the human and murine retina, embryonic coronary vessels, and avian chorioallantoic membrane. Software output includes colorized image maps with quantification of local vessel diameter, fractal dimension, tortuosity, and avascular spacing. The density of parameters such as vessel area, length, number, and branch point are quantified according to site-specific generational branching within vascular trees. The sole user input requirement is a binary (black/white) vascular image. Future applications of VESGEN will include analysis of 3D vascular architecture and bioinformatic dimensions such as blood flow and receptor localization. Branching analysis by VESGEN has demonstrated that numerous regulators including VEGF(165), basic fibroblast growth factor, transforming growth factor beta-1, angiostatin and the clinical steroid triamcinolone acetonide induce 'fingerprint' or 'signature' changes in vascular patterning that provide unique readouts of dominant molecular signaling.