High dose vitamin A supplementation reduces proangiogenic gene expression in a rat model of oxygen induced retinopathy (OIR).

Abstract

Purpose: Prematurity and high oxygen (O₂) therapy disrupt retinal vascular development and lead to retinal injury. Hypoxia in avascular retinal regions increases hypoxia inducible factor 1α (HIF-1α) signaling, leading to increased expression of proangiogenic genes, such as vascular endothelial growth factor (Vegf) and erythropoietin (Epo), which drive neovascularization. Retinoic acid (RA), a metabolite of vitamin A, acts as a trascriptional regulator of genes with RA response elements in their promoter regions, including proangiogenic HIF-1α and antiangiogenic pigment epithelial derived factor (Pedf). High dose vitamin A (HDVA) supplementation can preserve retinal vascular development and inner retinal function in a hyperoxic rat model of OIR. This study investigates the effects of HDVA on retinal gene expression in this model.

Methods: To induce OIR, albino Fisher 344 rats were exposed to 95-100% O₂ from postnatal day 1 (P1) to P7, then returned to room air. Control pups were raised in room air. All pups received daily intraperitoneal injections of either vehicle (corn oil, 33ml/kg), or vitamin A (2mg/kg) from P1 to P5. Total RNA was isolated from retinas harvested at P20-22, P25-28, P34-37. Quantitative RT PCR used TaqMan probes against Vegf, Epo, Pedf, two VEGF receptors (Flt-1, Kdr), normalized to acidic ribosomal phosphoprotein P0 (Rplp0). Cross group comparisons used a pair-wise fixed reallocation randomization test using REST-MCS software.

Results: Vegf was significantly up-regulated in vehicle treated OIR rats at P20-22 (>2 fold, p=0.001), and Epo was increased at all ages tested (>30 fold, p=0.001). Vegf expression in HDVA treated OIR (HDVA+O₂) rats was no different from control, and Epo was elevated only at P25-28 (13.7 fold, p=0.001). Pedf was significantly up-regulated in room air reared rats treated with HDVA at P20-22 (2.4 fold, p=0.001), and up-regulated in HDVA+O₂ rats at P25-28 (3 fold, p=0.011). There were no differences in VEGF receptor expression for any group at any age.

Conclusions: Postnatal hyperoxia leads to a sustained increase in proangiogenic gene expression (Vegf, Epo), which was reduced with HDVA supplementation. HDVA promoted the expression of the antiangiogenic and neuroprotective Pedf.

Keywords: 706 retinopathy of prematurity • 700 retinal neovascularization • 533 gene/expression