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Purpose: EphB4 receptors and their ephrinB2 ligands are essential for vascular development, but also play a role in pathological neovascularization (NV). We previously reported that soluble (s) forms of EphB4 and ephrinB2 significantly reduced retinal NV in a model of oxygen-induced retinopathy. This study investigates if these molecules suppress retinal NV by stimulation of endothelial cell (EC) apoptosis., Methods: C57BL/6 mice at postnatal day 7 (P7) were exposed to 75% oxygen for 5 days (P12) and allowed to recover in room air to induce retinal NV. One eye was injected intravitreally with 150 ng in 1.5 microL of sEphB4 or sEphrinB2 on P12 and P14, while contralateral eyes were injected with IgG antibody as control. Eyes were enucleated for histological analysis. At P16 TUNEL analysis and caspase-3 immunohistochemistry was performed on retinal sections to compare the apoptotic response between sEphB4 or sEphrinB2 injected eyes and controls. In vitro studies were performed with human retinal microvascular EC (HREC)., Results: Quantification of TUNEL positive vascular cells, located in areas of retinal NV, revealed approximately 2.5-fold increase in apoptosis in sEphrinB2 injected eyes compared to control eyes. Immunohistochemistry studies revealed co-localization of both TUNEL positive cells and caspase-3 positive cells with the endothelial marker, von Willebrand factor. Cultured HREC demonstrated significantly higher caspase-3 activity after a 3 h stimulation with sEphrinB2+/-VEGF compared to IgG control+/-VEGF (P<0.005). sEphB4 stimulation had no significant effect on caspase-3 activity in HREC cultures., Conclusions: These data suggest that modulation of the endogenous ephrin signaling mechanism by sEphrinB2 may induce suppression of retinal NV via induction of apoptosis. Results of the in vitro studies suggest that sEphrinB2 may directly induce apoptosis of EC during pathological neovascularization.

Purpose: Consistent with clinical observations that posterior uveitis frequently involves the retinal vasculature and recent recognition of vascular heterogeneity, the hypothesis for this study was that retinal vascular endothelium was a cell population of unique molecular phenotype., Methods: Donor-matched cultures of primary retinal and choroidal endothelial cells from six human cadavers were incubated with either Toxoplasma gondii tachyzoites (10:1, parasites per cell) or Escherichia coli lipopolysaccharide (100 ng/mL); control cultures were simultaneously incubated with medium. Gene expression profiling of endothelial cells was performed using oligonucleotide arrays containing probes designed to detect 8746 human transcripts. After normalization, differential gene expression was assessed by the significance analysis of microarrays, with the false-discovery rate set at 5%. For selected genes, differences in the level of expression between retinal and choroidal cells were evaluated by real-time RT-PCR., Results: Graphic descriptive analysis demonstrated a strong correlation between gene expression of unstimulated retinal and choroidal endothelial cells, but also highlighted distinctly different patterns of expression that were greater than differences noted between donors or between unstimulated and stimulated cells. Overall, 779 (8.9%) of 8746 transcripts were differentially represented. Of note, the 330 transcripts that were present at higher levels in retinal cells included a larger percentage of transcripts encoding molecules involved in the immune response. Differential gene expression was confirmed for 12 transcripts by RT-PCR., Conclusions: Retinal and choroidal vascular endothelial cells display distinctive gene expression profiles. The findings suggest the possibility of treating posterior uveitis by targeting specific interactions between the retinal endothelial cell and an infiltrating leukocyte.

Purpose: To develop a method to isolate human iris microvascular endothelial cells (HIECs) for exploring their constitutive and inflammatory agent-modulated expression of intercellular adhesion molecules (ICAM)-1 and -2, vascular cell adhesion molecule (VCAM)-1, and E-selectin., Methods: Endothelial cells from collagenase-digested irises were isolated on the basis of their expression of platelet endothelial cell adhesion molecule (PECAM)-1, using antibody-coupled magnetic beads. Cells were characterized as endothelial based on morphologic criteria, their expression of PECAM-1 and von Willebrand factor, their uptake of acetylated low-density lipoprotein, and their ability to form capillary-like networks on a synthetic basement membrane. Constitutive and inflammatory agent-modulated expression of ICAM-1 and -2, VCAM-1, and E-selectin was evaluated by the reverse transcription-polymerase chain reaction, enzyme-linked immunocellular assays (ELICAs), Western blot analysis, and functional studies of leukocyte adhesion to HIEC monolayers., Results: HIECs constitutively expressed mRNA and protein for ICAM-1 and -2, but only low to nondetectable levels of VCAM-1 or E-selectin. When stimulated with endotoxin- or tumor necrosis factor (TNF)-alpha, ICAM-1, VCAM-1, and E-selectin were potently and time- and dose-dependently upregulated at both the message and protein levels. By contrast, ICAM-2 message and protein were slowly downregulated by inflammatory agents over time, but nonetheless remained present and functional. Overall, cytokine- or endotoxin-activation of HIECs resulted in enhanced adhesiveness for leukocytes., Conclusions: ICAM-1, VCAM-1, and E-selectin have been previously implicated in mediating anterior ocular inflammation. This is a report of the selective isolation of HIECs, with a demonstration of differential expression and regulation of these adhesion molecules in them. In addition, this is the first demonstration of the regulated expression of ICAM-2 in any ocular microvascular cells.