Absence of Interphotoreceptor Retinoid-Binding Protein (IRBP, RBP3) in Transgenic Rats Causes Photoreceptor Degeneration and Myopia

Abstract

Purpose : IRBP is the major protein component of the interphotoreceptor matrix (IPM) separating the retina from the RPE. Recently, its presence in vitreous and aqueous has been appreciated. Early expression of IRBP in rats suggests a critical role of the IPM in ocular development (Gonzalez-Fernandez and Healy, J Cell Biol 111:2775-84,1990). Although IRBP promotes the trafficking and protection of visual cycle retinoids in the adult, its function in retinal and ocular development is yet to be understood. Here, we seek to determine the effect of the absence of IRBP on postnatal eye growth and retinal integrity.

Methods : We generated an IRBP CRISPER/Cas9 knockout in a Sprague Dawley background. IRBP(-/-) and wildtype (WT) animals were reared from birth through p103 under dim cyclic light. Body and eye weight were determined together with globe dimensions via laser micrometry. Outer and inner nuclear cell densities were characterized morphometrically by QuPath image analysis of digitized sagittal histological sections oriented through the optic nerve. This data was correlated with scotopic and photopic ERGs, immunohistochemistry, and electron microscopy.

Results : WT animals showed IRBP immunospecific staining in the IPM; IRBP(-/-) did not express IRBP. Beginning at ~1.5 months globe weight was noticeably greater for IRBP(-/-) rats compared to age-matched WT animals. The maximal size difference, which occurred at ~4.5 months, was 18% and 16% for males and females respectively. Beyond that age, the difference in eye size did not increase appreciably further. The differences between age-matched IRBP(-/-) and WT globe size were independent of sex and body mass. Laser micrometry showed a slight increase in the anterior-posterior dimension for IRBP (-/-) which remains to be further studied. The outer nuclear layer began to gradually thin after weaning. The inner nuclear layer was spared relative to the outer nuclear layer. The degeneration was associated with the reduction of ERG A and B waves. Ultrastructural studies showed that the rod outer segments were irregular in contour and often broken.

Conclusions : Knockout of IRBP resulted in a gradual photoreceptor degeneration with concomitant globe enlargement. Transgenic absence of IRBP may provide a useful system not only to study the role of IRBP in the photoreceptor function and survival but also in ocular development and myopia.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.