Abstract
Purpose :
The blood-retinal barrier (BRB) mediates movement of molecules from the blood to the inner retina, protecting the neural retina from potentially harmful molecules and maintaining retinal homeostasis. We previously demonstrated that retinoic acid (RA) signaling is necessary for BRB integrity in the zebrafish model. RA signaling is known to induce expression of RA-metabolizing enzyme Cyp26a1 in a sensitive feedback mechanism. The purpose of this study was to investigate the cellular mechanisms by which RA maintains the BRB by examining the expression patterns of cyp26a1 in the retina.
Methods :
To visualize the BRB in vivo, we utilized the transgenic Tg(l-fabp:DBP-EGFP) zebrafish model that expresses vitamin D binding protein (a member of the albumin gene family) tagged to GFP. This model displays the integrity of the BRB with GFP-tagged protein localized within the retinal vasculature by 3 days post-fertilization. Breakdown of the BRB is visualized as “leaking” of GFP outside the vasculature. To disrupt RA signaling, zebrafish embryos, larvae, and adults were treated with varying concentrations of DEAB and BMS493, antagonists of retinal dehydrogenase and the RA receptor, respectively. To visualize the Müller cells and endothelial cells, gfap:GFP and kdrl:GFP transgenic fish were used, respectively. RNAScope analysis was used to detect and quantify the expression of cyp26a1 in retinas of zebrafish at different developmental stages.
Results :
Treatment with DEAB or BMS493 resulted in a non-functional disrupted BRB in up to 95% of embryos and adults. In the retina, cyp26a1 was primarily detected in the Müller cells starting at 3 dpf, and treatment with pharmacological RA signaling inhibitors significantly decreased Müller cell cyp26a1 expression.
Conclusions :
The gene encoding RA-metabolizing enzyme Cyp26a1 is primarily expressed in the Müller cells of the retina, indicating that Müller cells may play a critical role in RA-mediated BRB maintenance.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.