The neurovascular relation in oxygen-induced retinopathy

Longitudinal studies in rat models of retinopathy of prematurity (ROP) have demonstrated that abnormalities of retinal vasculature and function change hand-in-hand. In the developing retina, vascular and neural structures are under cooperative molecular control. In this study of rats with oxygen-induced retinopathy (OIR) models of ROP, mRNA expression of vascular endothelial growth factor (VEGF), semaphorin (Sema), and their neuropilin receptor (NRP) were examined during the course of retinopathy to evaluate their roles in the observed neurovascular congruency.

Oxygen exposures designed to induce retinopathy were delivered to Sprague-Dawley rat pups (n=36) from postnatal day (P) 0 to P14 or from P7 to P14. Room-air-reared controls (n=18) were also studied. Sensitivities of the rod photoreceptors (S(rod)) and the postreceptor cells (Sm) were derived from electroretinographic (ERG) records. Arteriolar tortuosity, T(A), was derived from digital fundus images using Retinal Image multi-Scale Analysis (RISA) image analysis software. mRNA expression of VEGF(164), semaphorin IIIA (Sema3A), and neuropilin-1 (NRP-1) was evaluated by RT-PCR of retinal extracts. Tests were performed at P15-P16, P18-P19, and P25-P26. Relations among ERG, RISA, and PCR parameters were evaluated using linear regression on log transformed data.

Sm was low and T(A) was high at young ages, then both resolved by P25-P26. VEGF(164) and Sema3A mRNA expression were also elevated early and decreased with age. Low Sm was significantly associated with high VEGF(164) and Sema3A expression. Low S(rod) was also significantly associated with high VEGF(164). S(rod) and Sm were both correlated with T(A). NRP-1 expression was little affected by OIR.

The postreceptor retina appears to mediate the vascular abnormalities that characterize OIR. Because of the relationships revealed by these data, early treatment that targets the neural retina may mitigate the effects of ROP.