| Autor: |
Solanki AK; Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA., Kondkar AA; Glaucoma Research Chair, Department of Ophthalmology, College of Medicine, King Saud University, Riyadh 11411, Saudi Arabia., Fogerty J; Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, OH 44195, USA., Su Y; Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA., Kim SH; Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA., Lipschutz JH; Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.; Ralph H. Johnson VA Medical Center, Division of Research, Charleston, SC 29420, USA., Nihalani D; Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA., Perkins BD; Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, OH 44195, USA., Lobo GP; Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.; Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29425, USA. |
| Abstrakt: |
Dietary vitamin A/all- trans retinol/ROL plays a critical role in human vision. ROL circulates bound to the plasma retinol-binding protein (RBP4) as RBP4-ROL. In the eye, the STRA6 membrane receptor binds to circulatory RBP4 and internalizes ROL. STRA6 is, however, not expressed in systemic tissues, where there is high affinity RBP4 binding and ROL uptake. We tested the hypothesis that the second retinol binding protein 4 receptor 2 (Rbpr2), which is highly expressed in systemic tissues of zebrafish and mouse, contains a functional RBP4 binding domain, critical for ROL transport. As for STRA6, modeling and docking studies confirmed three conserved RBP4 binding residues in zebrafish Rbpr2. In cell culture studies, disruption of the RBP4 binding residues on Rbpr2 almost completely abolished uptake of exogenous vitamin A. CRISPR-generated rbpr2- RBP4 domain zebrafish mutants showed microphthalmia, shorter photoreceptor outer segments, and decreased opsins, which were attributed to impaired ocular retinoid content. Injection of WT-Rbpr2 mRNA into rbpr2 mutant or all- trans retinoic acid treatment rescued the mutant eye phenotypes. In conclusion, zebrafish Rbpr2 contains a putative extracellular RBP4-ROL ligand-binding domain, critical for yolk vitamin A transport to the eye for ocular retinoid production and homeostasis, for photoreceptor cell survival. |
