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M. H. Davies, K. E. Hubert, A. J. Stempel, M. R. Powers; EphrinB2 and EphB4 Expression in Pathologic Neovascularization in a Model of Oxygen-Induced Retinopathy. Invest. Ophthalmol. Vis. Sci. 2008;49(13):531.
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EphrinB2 (B2) ligands and their EphB4 (B4) receptors are expressed on endothelial cells (EC) from arteries and veins respectively, and are essential for vascular development. We previously reported that soluble B2 or B4 significantly reduced retinal neovascularization (NV) in a model of oxygen-induced retinopathy (OIR), suggesting a role in pathologic angiogenesis (Zamora, IOVS 2005;46). The current study examines the expression patterns of B2 and B4 using mice with a taulacZ reporter targeted to the ephrinB2 and EphB4 locus respectively in the model of OIR.
EphrinB2taulacZ/+ and EphB4taulacZ/+ neonatal mice were exposed to hyperoxic conditions (75% O2) from postnatal day (P)7 until P12 and then returned to room air. Eyes were enucleated from hyperoxia-exposed and room air control mice at P12 and P17 and prepared for retinal whole mounts (n=4-6) or cryo-sections (n=4-6). B2 and B4 expression was analyzed histochemically by X-Gal staining or using a primary antibody against β-galactosidase. To confirm B2 and B4 expression on EC, retinal whole mounts and cryo-sections were also double labeled for either B2 or B4 and Alexa Fluor® 594 labeled GS-isolectin, an EC marker. In addition, B2 and B4 expression was evaluated in cryo-sections double labeled with an antibody to GFAP, a marker for activated Müller cells.
As expected, B2 and B4 expression are localized to arteries and veins respectively, on P12 and P17 room air mice in retinal whole mounts. However, B4 expression is reduced on P12O2, while B2 expression remains unaltered. In addition to being expressed on major arteries and veins, both B2 and B4 are expressed on a subset of neovascular tufts in P17O2 retinal whole mounts. Double labeling of whole mounts and cryo-sections for β-galactosidase and GS-isolectin reveals that only a subset of the neovascular tufts, as well as a portion of the intra-retinal vessels express B2 or B4. Additionally, double labeling of cryo-sections for β-galactosidase and GFAP demonstrate some co-localization suggesting a subset of Müller cells express B2, but not B4.
These data demonstrate the presence and localization of B2 and B4 within the neovascular tufts, suggesting that intravitreally injected soluble B2 and B4 interacts directly with tuft ECs, thereby modulating retinal NV. Furthermore, these data confirm the contribution of both venual and arterial derived ECs to the neovascular response in this model. This study provides a foundation for understanding the mechanistic role these molecules play during pathologic retinal NV.
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