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Lana Pollock, Jing Xie, Brent A. Bell, Bela Anand-Apte; Retinoic acid signaling maintains the blood-retinal barrier through potential crosstalk with the mTOR pathway. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2368.
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The blood-retinal barrier (BRB) mediates movement of molecules from the blood to the inner retina, protecting the retinal neural tissue from potentially harmful molecules and maintaining retinal homeostasis. We have previously demonstrated that retinoic acid (RA) signaling is necessary for integrity of the blood-retinal barrier (BRB). The purpose of this study was to investigate the molecular mechanisms by which RA maintains the BRB.
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, transgenic embryos and adults were treated with varying concentrations of DEAB and BMS493, antagonists of retinal dehydrogenase and the RA receptor, respectively. Leakage from the retinal vasculature was visualized under a fluorescent microscope. To identify molecular pathways that potentially regulate RA-mediated BRB maintenance, we conducted RNA-seq comparing gene expression in retinas of adult DEAB-treated zebrafish with control (DMSO)-treated fish.
Treatment with DEAB or BMS493 resulted in a non-functional disrupted BRB in up to 95% of embryos and adults. Co-treatment with 0.05 µM all-trans retinoic acid effectively rescued BRB integrity. Pathway analysis of differentially expressed genes indicated that the mTOR pathway is significantly upregulated in retinas of DEAB-treated fish. Inhibition of mTOR signaling in BMS493 or DEAB-treated larvae by co-treatment with rapamycin prevented BRB breakdown.
The mTOR signaling pathway is significantly upregulated in the retinas of RA-inhibitor-treated fish and inhibition of mTOR signaling prevents RA-inhibitor-mediated BRB breakdown. Thus, RA signaling may maintain BRB integrity via crosstalk with the mTOR pathway.
This is a 2020 ARVO Annual Meeting abstract.
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