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GLENN Prazere LOBO, Gayle Pauer, Stephanie A Hagstrom, Joshua Lipschutz; The Retinol Binding Protein Receptor 2 (Rbpr2) is required for Photoreceptor Health and Visual Function in Zebrafish. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3585.
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Short-term dietary Vitamin A deficiency (VAD) manifests as night blindness, while prolonged VAD causes RPE and photoreceptor degeneration. Therefore, a sustained uptake and supply of dietary Vitamin A, for ocular retinoid production, is essential for visual function. However, mechanisms influencing the uptake of dietary vitamin A, for ocular retinoid production, are not fully understood. We investigated the physiological role of the retinol binding protein receptor 2 (rbpr2), in zebrafish, for uptake of dietary Vitamin A/ Retinol/ROL, for vision.
ROL-binding capabilities of zebrafish Rbpr2 receptor was tested in stable NIH3T3 cells expressing Rbpr2. In-vivo Rbpr2 mRNA expression patterns were visualized using whole-mount in-situ hybridization (WISH) in staged zebrafish larvae. TALEN genomic editing technologies were used to generate rbpr2 mutant zebrafish alleles. Consequences, of the loss of rbpr2 for ROL uptake, and subsequent retinoid production were measured in rbpr2-mutants by, immunohistochemistry, HPLC analysis and Optokintetic Reflex (OKR) tests, for visual function.
Zebrafish Rbpr2 localized predominantly to the plasma membrane in NIH3T3 cells, and were capable of ROL uptake from its bound form. In staged zebrafish, Rbpr2 expression was evident in the intestine, liver and pancreas. In retinal cross-sections, rbpr2-/- larvae showed smaller eyes, retinal lamination layer disruption and thinner RPE layer, as compared to wild-type sibling controls. Immunostaining for cones (PNA-568) and rods (Rho-488) at 5.5 days post fertilization, showed shorter OS lengths and loss of cone and rod staining in rbpr2-/- larvae, when compared to wild-type siblings. Finally, no consistent OKR was detected in rbpr2-/- larvae, which resulted in a flat contrast response function.
rbpr2-/- zebrafish larvae, showed significant eye phenotypes and loss of visual function. The loss of visual function correlated significantly with reduced cone and rod photoreceptor staining, likely due to low ocular retinoid levels. Therefore, based on our in-vitro and in-vivo analysis, Rbpr2 functions as a transporter for dietary ROL, and loss of this receptor significantly impacts photoreceptor health and visual function, in zebrafish.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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