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Carl Romano, Bibiana Iglesias, Jingtai Cao; Analysis of VEGF expression in a chronic model of retinal neovascularization.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5482.
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© ARVO (1962-2015); The Authors (2016-present)
Intravitreal injection of DL-alpha-aminoadipic acid (AAA) causes retinal degeneration and neovascularization in the rabbit retina. The pathological vasculature develops over 8 weeks and remains stable for up to 2 years. These new vessels are leaky and sensitive to VEGF inhibition. Here, we identified which cells remain in the degenerated retina, and which are the likely sources of VEGF supporting the pathological vessels and leak.
Male New Zealand White rabbits (2.0-2.5 kg) received AAA intravitreally, with follow-up examinations at weeks 1, 2, 4, 6 and 8 by fluorescein angiography and optical coherence tomography. Two animals were euthanized at each time point. The eyes were fixed and processed for immunostaining and in situ hybridization for VEGF mRNA. Retinal cells were identified using fluorescently labeled antibodies to: GFAP, vimentin, Fox3, beta-tubulin, rhodopsin, RPE65, CD18 and MBP.
In the first weeks after AAA administration, there was a disorganization of astrocytes with increased GFAP expression, shortening of Muller cells, rhodopsin distribution shift from the outer segments to the ONL and loss of order of axon bundles. We also noted a large number of macrophages/activated microglia over the surface of the retina. The medullary ray thinned over time as the ganglion cells died. By week 8, there was only a remnant retina remaining, composed of astrocytes, Muller cells, patches of neuronal somas and macrophages/activated microglia. Normal rabbit retinas showed expression of VEGF by RPE, photoreceptors, Muller cells, RGC and oligodendrocytes. In degenerated retinas, VEGF mRNA was expressed by RPE and stressed glia but surprisingly not by macrophages/activated microglia.
AAA-induced damage correlates with drastic changes in retinal cellular composition, including an increase in macrophages/activated microglia, a loss of almost all neurons, and gliosis. VEGF, a key mediator of pathological neovascularization, is expressed after AAA in RPE and stressed glia, but not macrophages. The role of macrophages in retinal pathological neovascularization is unclear. These results suggest that macrophages may play a role in neovascularization and vascular remodeling other than providing VEGF, and that the major sources of VEGF driving the pathology are RPE and glial cells.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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