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Knatokie M. Ford, Magali Saint-Geniez, Tony Walshe, Alisar Zahr, Patricia A. D'Amore; Expression and Role of VEGF in the Retinal Pigment Epithelium. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3358.
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Despite the lack of active angiogenesis, VEGF is expressed in nearly every adult tissue, and recent evidence suggests that VEGF may serve as a survival factor for both vascular and non-vascular cells. VEGF blockade is a widely used treatment for neovascular diseases such as age-related macular degeneration (AMD). Therefore, we sought to evaluate the expression of VEGF and its primary receptor VEGFR2 by RPE, as well as a role for endogenous VEGF in RPE.
Swiss-Webster albino mice (wild type and VEGF-LacZ) were used to determine the time course of VEGF and VEGFR2 expression during development. To assess the effect of systemic VEGF neutralization on RPE, CD1 mice were injected with an adenovirus expressing soluble VEGFR1 (sFlt). TEM analysis was performed to analyze RPE ultrastructure following systemic VEGF blockade, and quantitative real-time PCR was used to evaluate gene expression changes in the RPE-choroid complex. ARPE-19 cells, a line of human RPE cells, were used for in vitro studies. Constitutively phosphorylated VEGFR2 in ARPE-19 cells grown in the absence of added VEGF suggests an autocrine role for VEGF. To assess this possibility, differentiated ARPE-19 cells were incubated in the presence of a VEGF-neutralizing antibody (Avastin) for up to 4 weeks. The effects of Avastin treatment were evaluated using TUNEL to assess apoptosis and SEM was used to determine the effect on apical microvilli distribution and appearance.
VEGF expression was detected in the developing RPE as early as embryonic day 9.5. VEGFR2 expression was first detected between postnatal days 6.5 and P8.5. Systemic VEGF neutralization in vivo led to degenerative changes in the RPE-choroid complex. At day 4 and 7 following sFlt injection, RPE contained numerous vacuoles and showed signs of separation from photoreceptor outer segments, and choriocapillaris fenestrations were decreased. These changes appeared to be transient as RPE morphology and fenestration density were normalized by day 14 and day 28. Preliminary evidence suggests that RPE upregulate VEGF in response to VEGF blockade. Inhibition of VEGF signaling in vitro led to increased RPE apoptosis, and a reduction in microvilli density and length following 4 weeks of VEGF neutralization.
Our results indicate an autocrine role for VEGF in the adult that mediates RPE survival and integrity. Thus, chronic intraocular VEGF neutralization may have undesirable off-target effects.
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