EVOLUTION OF NEOVASCULARIZATION IN MICE WITH OVEREXPRESSION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR IN PHOTORECEPTORS

PURPOSE. TO determine the earliest changes that occur in the retina af ter the onset of ectopic expression of vascular endothelial growth fac tor (VEGF) by photoreceptors in transgenic mice, to characterize the d evelopment of neovascularization (NV). and to determine the feasibilit y of using these mice to test the efficacy of antiangiogenic agents. M ETHODS. The time course of expression of VEGF transgene mRNA was deter mined by reverse transcription-polymerase chain reaction (RT-PCR). His topathologic changes in the retina were investigated by light and elec tron microscopy and immunocytochemistry. Standard and confocal fluores cence microscopy and image analysis were used to evaluate NV in retina l whole mounts. RESULTS. VEGF transgene mRNA was first detected in the retina by RT-PCR on postnatal day 6 (PG) and increased over the next several days to reach a constant steady-state level between P14 and P2 1. Abnormal cells were seen in the outer nuclear layer on P10 and amon g photoreccptors on P14; by P18 there were cell aggregates in the subr etinal space with evidence of lumen formation. The invading cells were demonstrated to be endothelial cells by staining with an endothelial cell-specific lectin. Whole mounts of retinas perfused with fluorescei n-labeled dextran showed a similar sequence of events, with sprouts fr om retinal vessels in the deep capillary bed seen on P14 and vessels r eaching the subretinal space by P18. Confocal and standard fluorescenc e microscopy and changes in the number and area of neovascular lesions in the subretinal space over time measured by image analysis suggest gradual enlargement and coalescence of vascular complexes. The subreti nal NV was progressively engulfed by the retinal pigmented epithelium. invasion of blood vessels from the choroid was not identified in and specimen. CONCLUSIONS. These data support the feasibility of using rho dopsin-VEGF transgenic mice to study tissue-specific aspects of NV in the retina and to test antiangiogenic agents for inhibition of intrare tinal and subretinal NV.