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Andrew Scott, Michael B. Powner, Kristis Vevis, Jenny McKenzie, Marcus Fruttiger; Quantification Of Vascular Tortuosity As An Early Outcome Measure Of Hypoxia In Ischaemic Retinopathies. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3973.
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© ARVO (1962-2015); The Authors (2016-present)
Hypoxia is a driving force for angiogenesis. The degree of hypoxia determines whether this angiogenesis is pathological or physiological but as yet cannot be quantified. Insight into the pathogenesis of human ischaemic retinopathies can be gained with a mouse model based on oxygen-induced retinopathy (OIR). In this model, 7 day old (P7) mouse pups are exposed to 75% oxygen for 5 days resulting in capillary obliteration in the central retina. Upon return to room air this central vasobliterated zone turns hypoxic and drives an angiogenic response. Currently we can only demonstrate an angiogenic response 5 days later, at P17 when neovascularization occurs. In order to quantify the vascular response earlier, we quantified vascular tortuosity which is an early response of arterioles to hypoxia.Our aim is to investigate a novel outcome measure of hypoxia in the mouse OIR model based on quantification of vascular tortuosity at P14.
Pups from two mouse strains (C57Bl6 and C3H) were put through the OIR model and retinal wholemounts were retrieved at P14 - 2 days after coming out of hyperoxia. The level of hypoxia was assessed in both strains with a chemical hypoxia marker (EF5) and qPCR measurement of Vegf mRNA. Furthermore, whole mount retinas were stained with lectin and collagen IV (vessel markers). The tortuosity of radial arterioles was assessed in digital images using Image J software with a normalized measurement of the integrated curvature (nIC) and the tortuosity index (TI).
In comparison to the C57Bl6 strain, the C3H strain showed reduced EF5 staining and lower Vegf mRNA expression, indicating less pronounce hypoxia. This correlated clearly with reduced vessel tortuosity in the C3H strain (as assessed by nIC and TI values).
Measuring vascular tortuosity with our computer-based analysis system of digital retinal images is an effective way of obtaining an indirect quantification of early hypoxia in the OIR model. This would be particularly useful in experiments testing cellular and molecular reversal of hypoxia and in experiments where an early outcome measure of vascular pathology is desirable.
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