The OIR model results in characteristic loss of central retinal vessels by P12, followed by hypoxia-induced regeneration of the central vascular plexus and development of preretinal neovascularization.
15 EphrinB2
lacZ/+ mice were exposed to the OIR to test the hypothesis that ephrinB2 reverse signaling contributes to hypoxia-induced revascularization of the central retina. To investigate the vasoregressive response in the OIR model, we measured the avascular central retinal zones at P12 in ephrinB2
lacZ/+ and WT mice, immediately after the hyperoxic period when the mice had been returned to normoxia. Importantly, despite the ephrinB2
lacZ/+ mice retinal vasculature developing more slowly than WT as measured at P5, the avascular area to total area ratio at P12 for the retinas of ephrinB2
lacZ/+ and WT mice were comparable (0.166 for ephrinB2
lacZ/+; 0.164 for WT,
P = 0.84). Attenuated ephrinB2 reverse signaling resulted in decreased central revascularization at P18 following exposure to OIR, as indicated by the larger area of avascular retinal tissue space remaining at P18 as compared with WT controls (
Fig. 2A). A substantial central avascular area remains in the ephrinB2
lacZ/+mice, whereas in WT retinas much of the avascular area has already been invaded by new vessels (
Fig. 2A). Quantification of avascular retinal area at P18 and P21 indicated that attenuated ephrinB2 reverse signaling resulted in a significant decrease in the amount of intraretinal revascularization in ephrinB2
lacZ/+ mice as compared with WT controls (
P = 0.003) (
Fig. 2B). A significant reduction in intraretinal avascular area (60%) occurred in WT retinas between P18 and P21 (
Fig. 2B). However, in ephrinB2
lacZ/+ mice, there was no statistically significant change in intraretinal avascular area between P12 and P18, and only a moderate trend (38%) toward reduced avascular area between P18 and P21.