Diabetic retinopathy is associated with a switch in splicing from anti- to pro-angiogenic isoforms of vascular endothelial growth factor

Abstract

Proliferative diabetic retinopathy results from excess blood vessel growth into the vitreous fluid of the eye. Retinal angiogenesis is regulated by expression of vascular endothelial growth factor (VEGF), and many studies have shown that VEGF is critically involved in proliferative diabetic retinopathy. VEGF is alternatively spliced to form the angiogenic (VEGF(xxx)) and potentially anti-angiogenic (VEGF(xxx)b) family of isoforms. The VEGF(xxx)b family is found in normal tissues, but down-regulated in renal and prostate cancer. Previous studies on endogenous expression of VEGF in the eye have not distinguished between the two families of isoforms. We measured VEGF(xxx)b isoform expression in normal human eye tissue (lens, sclera, retina and iris) and vitreous fluid using enzyme-linked immunosorbent assay and Western blotting with a VEGF(xxx)b-specific antibody. VEGF(xxx)b protein was expressed in lens, sclera, retina, iris and vitreous fluid. Multiple isoforms were seen, including VEGF(165)b, VEGF(121)b, VEGF(145)b, VEGF(183)b and VEGF(189)b. In non-diabetic patients, 64+/-7% of the VEGF in the vitreous was VEGF(xxx)b (n=18), whereas in diabetic patients only 12.5+/-3.6% of total VEGF was VEGF(xxx)b. Since VEGF(xxx)b inhibits VEGF(xxx)-induced angiogenesis in a one-to-one stoichiometric manner, these results show that in the eye of diabetic patients VEGF splicing was switched from an anti-angiogenic to a pro-angiogenic environment. This occurred through changes to the ratio of VEGF(xxx):VEGF(xxx)b. Alterations to splicing, and through that to the balance of VEGF isoforms, could therefore be a potential therapeutic strategy for diabetic retinopathy.