Vertebrate opsins in photoreceptors and the retinal pigment epithelium (RPE) have fundamental roles in the visual process. The visual pigments in photoreceptors are bound to 11 -cis-retinal and are responsible for the initiation of visual excitation. Retinochrome-like opsins in the RPE are bound to all-trans-retinal and may play an important role in chromophore metabolism. The retinal G protein-coupled receptor (RGR) in the RPE and Muller cells is an opsin that is necessary for normal synthesis of 11 -cis-retinal and regeneration of rhodopsin during light adaptation. It is hypothesized that RGR has a central role in light-dependent synthesis of 11-cis-retinal and the regeneration of rhodopsin, hence RGR is involved in the visual cycle. The objective of this grant application is to prove this hypothesis by demonstration of a detailed mechanistic model for the function of RGR at the molecular and physiological levels. ? ? The study of RGR opsin is impeded by limitations in accessibility, low abundance, biochemical properties, and the lack of an appropriate cell culture model. To be able to study the RGR opsin, three experimental approaches to this research problem have been created. A functional RGR opsin from bovine RPE has been isolated. Second, a cell culture model of RPE cells that stably express RGR and remain able to process retinoids has been established. Third, the RGR opsin knockout mouse with an informative phenotype has been produced. These experimental approaches will be used in this grant proposal to further investigate the function of RGR and its role in retinoid metabolism and regulation in the RPE. ? ? By preserving rhodopsin levels and retinal sensitivity, the RGR opsin gene helps to prevent night blindness and provides a selective advantage for species subject to wide variation in environmental luminance. Further understanding of RGR at the biochemical level will be important in learning how RPE cells work, and characterization of defects in RGR function may show how human RPE cells undergo dysfunction and deteriorate leading to disease. Since RGR is involved in a fundamental visual process, defects in RGR are likely to impair the health of the RPE and retina. The importance of RGR opsin to the health and viability of the neuroretina is shown by mutations in the human RGR gene that segregate with retinitis pigmentosa (RP) in patients with autosomal dominant or recessive RP. Errors in retinoid metabolism in either the photoreceptors or RPE cells may lead to abnormal levels of A2E, a major compound of lipofuscin that accumulates in the RPE during aging and age-related macular degeneration.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY008364-16
Application #
7101727
Study Section
Special Emphasis Panel (ZRG1-VISC (01))
Program Officer
Mariani, Andrew P
Project Start
1990-08-01
Project End
2008-07-31
Budget Start
2006-08-01
Budget End
2008-07-31
Support Year
16
Fiscal Year
2006
Total Cost
$373,512
Indirect Cost
Name
Doheny Eye Institute
Department
Type
DUNS #
020738787
City
Los Angeles
State
CA
Country
United States
Zip Code
90033
Zhang, Zhaoxia; Fong, Henry K W (2018) Coexpression of nonvisual opsin, retinal G protein-coupled receptor, and visual pigments in human and bovine cone photoreceptors. Mol Vis 24:434-442
Kochounian, Harold; Zhang, Zhaoxia; Spee, Christine et al. (2016) Targeting of exon VI-skipping human RGR-opsin to the plasma membrane of pigment epithelium and co-localization with terminal complement complex C5b-9. Mol Vis 22:213-23
Kochounian, Harold; Johnson, Lincoln V; Fong, Henry K W (2009) Accumulation of extracellular RGR-d in Bruch's membrane and close association with drusen at intercapillary regions. Exp Eye Res 88:1129-36
Lin, Meng-Yin; Kochounian, Harold; Moore, Roger E et al. (2007) Deposition of exon-skipping splice isoform of human retinal G protein-coupled receptor from retinal pigment epithelium into Bruch's membrane. Mol Vis 13:1203-14
Fong, Henry K W; Lin, Meng-Yin; Pandey, Sujay (2006) Exon-skipping variant of RGR opsin in human retina and pigment epithelium. Exp Eye Res 83:133-40
Yang, Mao; Fong, Henry K W (2002) Synthesis of the all-trans-retinal chromophore of retinal G protein-coupled receptor opsin in cultured pigment epithelial cells. J Biol Chem 277:3318-24
Chen, P; Lee, T D; Fong, H K (2001) Interaction of 11-cis-retinol dehydrogenase with the chromophore of retinal g protein-coupled receptor opsin. J Biol Chem 276:21098-104
Chen, P; Hao, W; Rife, L et al. (2001) A photic visual cycle of rhodopsin regeneration is dependent on Rgr. Nat Genet 28:256-60
Yang, M; Wang, X G; Stout, J T et al. (2000) Expression of a recombinant human RGR opsin in Lentivirus-transduced cultured cells. Mol Vis 6:237-42
Hao, W; Fong, H K (1999) The endogenous chromophore of retinal G protein-coupled receptor opsin from the pigment epithelium. J Biol Chem 274:6085-90

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