Coexpression of VEGF receptors VEGF-R2 and neuropilin-1 in proliferative diabetic retinopathy

PURPOSE. To elucidate vascular endothelial growth factor (VEGF)-mediated pathogenesis of fibrovascular proliferation in diabetic retinopathy. METHODS. Fibrovascular tissues were obtained at vitrectomy from 22 cases with proliferative diabetic retinopathy. The half-divided tissues were processed for reverse transcription-polymerase chain reaction (RT-PCR) analysis to examine the expression of VEGF isoforms and their receptors. Paraffin sections of the other half were used for immunohistochemistry for CD34, glial fibrillary acidic protein and VEGF, and in situ hybridization for VEGF. RESULTS. RT-PCR analysis demonstrated the expression of VEGF receptors VEGF- R1, VEGF-R2, and neuropilin-1 in 12, 14, and 14 of 22 cases, respectively. Notably, VEGF-R2 and neuropilin-1 were simultaneously expressed in the identical 14 tissues. The isoform VEGF₁₂₁ was constitutively expressed in all the tissues examined, whereas the expression of VEGF₁₆₅ was confined to the 7 tissues that also expressed VEGF-R2 and neuropilin-1. The vascular density of fibrovascular tissues evaluated by immunohistochemistry for CD34 was significantly higher in the cases with the expression of VEGF-R2 and neuropilin-1 than in those without their expression (P < 0.01), whereas VEGF- R1 expression had no such relationship with the vascular density. The fibrovascular tissues that expressed VEGF₁₆₅ together with VEGF-R2 and neuropilin-1 were found in significantly younger patients (P < 0.01). In situ hybridization and immunohistochemical studies demonstrated that glial cells in the fibrovascular tissues express and produce VEGF. CONCLUSIONS. Coexpression of VEGF-R2 and neuropilin-1 is suggested to facilitate fibrovascular proliferation in diabetic retinopathy.