The retinal pigment epithelium (RPE) plays a pivotal role in the development and function of the outer retina. We are interested in RPE-specific mechanisms, at both the regulatory and functional levels. To this end we have been studying the function and regulation of RPE65, a gene whose expression is restricted to the RPE and mutations in which cause severe blindness in humans. Disruption of the RPE-based vitamin A visual cycle metabolism of all-trans-retinyl esters to 11-cis-retinal appears to underlie the phenotype of the Rpe65 knockout mouse. The function of RPE65 thus appears to be associated with that of the retinol isomerase, the crucial enzyme in visual pigment regeneration. We have also continued studies on beta-carotene 15,15'-dioxygenase (beta-CD). Beta-CD is closely related to RPE65 and both are members of a newly emerging diverse family of carotenoid-cleavage enzymes. We postulate that beta-CD and RPE65 may share a similar mechanism of action. In the past year we have made the following progress: a) One year-old Rpe65 knockout mice show a dramatically lowered accumulation of lipofuscin fluorophores (an irreversible by-product of vitamin A associated with age-related macular degeneration) compared to wildtype. This, in parallel with an over-accumulation of retinyl esters in the RPE, shows that a functioning visual cycle is required for the generation of lipofuscin fluorophores. b) A collaborative effort using double knockout mice (Rpe65 knockout crossed with rhodopsin-knockout (pure cone response) or cyclic nucleotide gated channel alpha 3 knockout (pure rod response)) was used to study the origin of the reduced electroretinogram (ERG) response seen in Rpe65-deficient mice. In contrast to the original conclusion, it was determined that the ERG is actually due to severely desensitized rod photoreceptors rather than to cone photoreceptors. The rods in Rpe65-deficient mice, because of extreme chromophore starvation, have so little rhodopsin that they perceive far less light than is administered and, masquerading as cones, respond to bright light stimuli that would suppress normal rods. These findings also explain features of RPE65-associated retinal dystrophy in human patients and may be useful in therapy. c) By immunofluorescence microscopy and RT-PCR, beta-CD was found to be expressed in the mouse inner retina and not in the mouse RPE. RT-PCR of various RPE cell lines revealed expression in a monkey RPE cell line but not in 3 human RPE cell lines. d) We have analyzed the genomic structure of the beta-CD gene and are beginning transient transfection in a variety of cell lines, including monkey RPE, COS-7 and Caco-2, of beta-CD gene promoter-reporter constructs to analyze promoter function of the beta-CD gene. e) Experimental autoimmune uveoretinitis (EAU) induced by retina-specific antigens (e.g., arrestin, IRBP and rhodopsin) is a model for human ocular inflammatory diseases such as uveitis. In collaboration with LI, we have found that a moderate immunopathogenic response is induced in Lewis rats immunized with the RPE-specific RPE65 antigen. The disease is more active in the posterior segment and does not affect the anterior segment to the same extent as arrestin-induced EAU. Adoptive transfer of the disease from immunized to naive animals indicates that the disease is cell-mediated, like other forms of EAU. f) Rescue of the Rpe65 knockout mouse phenotype by AAV-mediated gene transfer has resulted in increased sensitivity of electrophysiological and behavioral responses to light in treated mice.
| Huber, Gesine; Beck, Susanne C; Grimm, Christian et al. (2009) Spectral domain optical coherence tomography in mouse models of retinal degeneration. Invest Ophthalmol Vis Sci 50:5888-95 |
| Maguire, Albert M; Simonelli, Francesca; Pierce, Eric A et al. (2008) Safety and efficacy of gene transfer for Leber's congenital amaurosis. N Engl J Med 358:2240-8 |
| Cortes, Lizette M; Mattapallil, Mary J; Silver, Phyllis B et al. (2008) Repertoire analysis and new pathogenic epitopes of IRBP in C57BL/6 (H-2b) and B10.RIII (H-2r) mice. Invest Ophthalmol Vis Sci 49:1946-56 |
| Lu, Zhongjian; Poliakov, Eugenia; Redmond, T Michael (2006) Identification of a KRAB-zinc finger protein binding to the Rpe65 gene promoter. Curr Eye Res 31:457-66 |
| Moiseyev, Gennadiy; Takahashi, Yusuke; Chen, Ying et al. (2006) RPE65 is an iron(II)-dependent isomerohydrolase in the retinoid visual cycle. J Biol Chem 281:2835-40 |
| Fan, Jie; Wu, Bill X; Sarna, Tadeusz et al. (2006) 9-cis Retinal increased in retina of RPE65 knockout mice with decrease in coat pigmentationt. Photochem Photobiol 82:1461-7 |
| Stoddart, Chris W; Yu, Meaghan J T; Martin-Iverson, Matthew T et al. (2006) Assessing the efficacy of gene therapy in Rpe65-/- mice using photoentrainment of circadian rhythm. Adv Exp Med Biol 572:239-45 |
| Poliakov, Eugenia; Gentleman, Susan; Cunningham Jr, Francis X et al. (2005) Key role of conserved histidines in recombinant mouse beta-carotene 15,15'-monooxygenase-1 activity. J Biol Chem 280:29217-23 |
| Lyubarsky, Arkady L; Savchenko, Andrey B; Morocco, Sarah B et al. (2005) Mole quantity of RPE65 and its productivity in the generation of 11-cis-retinal from retinyl esters in the living mouse eye. Biochemistry 44:9880-8 |
| Redmond, T Michael; Poliakov, Eugenia; Yu, Shirley et al. (2005) Mutation of key residues of RPE65 abolishes its enzymatic role as isomerohydrolase in the visual cycle. Proc Natl Acad Sci U S A 102:13658-63 |
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