Disease relevance of Rpe65

• In Rpe65 knockout mice, photoreceptors show a drastically reduced light sensitivity and are subject to degeneration, the cone photoreceptors being lost at early stages of the disease [1].
• Mutations in Rpe65 disrupt synthesis of the opsin chromophore ligand 11-cis-retinal and cause Leber congenital amaurosis (LCA), a severe, early-onset retinal dystrophy [2].
• Retinal degeneration and RPE transplantation in Rpe65(-/-) mice [3].

High impact information on Rpe65

• The gene Rpe65 is specifically expressed in the PE and essential for the re-isomerization of all-trans retinol in the visual cycle and thus for the regeneration of rhodopsin after bleaching [4].
• Outer segment discs of rod photoreceptors in Rpe65-/- mice are disorganized compared with those of Rpe65+/+ and Rpe65+/- mice [5].
• RESTs accumulate in Rpe65-/- mice incapable of carrying out the enzymatic isomerization, and correspondingly, are absent in the eyes of Lrat-/- mice deficient in retinyl ester synthesis [6].
• Nonvisual light responses in the Rpe65 knockout mouse: rod loss restores sensitivity to the melanopsin system [7].
• Surprisingly, rod loss in Rpe65 knockout mice resulted in restoration of circadian photosensitivity [7].

Biological context of Rpe65

• Downregulation of cone-specific gene expression and degeneration of cone photoreceptors in the Rpe65-/- mouse at early ages [8].
• Our purpose was to investigate the physiological phenotype of albino mice with a variation in the Rpe65 gene encoding either methionine or leucine at amino acid #450 [9].
• F(1) hybrid mice, carrying one normal and one variant Rpe65 gene, had intermediate levels of the corresponding protein and showed intermediate rhodopsin regeneration kinetics and an intermediate LDS [10].
• Mass spectrometric analysis of opsin from Rpe65(-/-) mice revealed unusually high levels of phosphorylation in dark-adapted mice but no other structural alterations [11].
• Rpe65 is a retinyl ester binding protein that presents insoluble substrate to the isomerase in retinal pigment epithelial cells [12].

Anatomical context of Rpe65

• Rod photoreceptors in the RPE65-knockout (Rpe65(-/-)) mouse are known to degenerate slowly with age [8].
• This study was designed to examine cone photoreceptors and the expression of cone-specific genes in the Rpe65(-/-) mouse [8].
• Rpe65 Leu450Met variant is associated with reduced levels of the retinal pigment epithelium lipofuscin fluorophores A2E and iso-A2E [13].
• Using a novel fluorescent resonance energy transfer (FRET) binding assay in liposomes, we demonstrate that Rpe65 extracts all-trans-retinyl esters from phospholipid membranes [12].
• Assays of isomerase activity reveal that Rpe65 strongly stimulates the enzymatic conversion of all-trans-retinyl palmitate to 11-cis-retinol in microsomes from bovine RPE cells [12].

Associations of Rpe65 with chemical compounds

• Administration of 9- or 11-cis retinal to Rpe65(-/-) mice 2 weeks of age increased cone density by twofold in these areas [8].
• Retinyl esters in WT mice plateau at 8 weeks-of-age, but Rpe65(-/-) mice continue to accumulate retinyl esters with age (e.g., at 36 weeks, the levels are 20x that of WT) [14].
• Here we show that Rpe65 specifically binds all-trans-retinyl palmitate but not 11-cis-retinyl palmitate by a spectral-shift assay, by co-elution during gel filtration, and by co-immunoprecipitation [12].
• Rpe65 knockout mice (Rpe65-/-) are unable to synthesize the visual pigment chromophore 11-cis retinal; however, if these animals are reared in complete darkness, the rod photoreceptors accumulate a small amount of 9-cis retinal and its corresponding visual pigment isorhodopsin [15].
• CONCLUSIONS: Retinal degeneration in the Rpe65(-/-) mice is slowly progressive [3].

Other interactions of Rpe65

• We exposed to bright light two groups of genetically altered mice that lack the visual pigment rhodopsin (Rpe65-/- and Rho-/-) [4].
• Despite the loss of rods and cones, the RPE65(-/-) and rd/rd maintained a 24-h circadian rhythm entrained to light similar to controls and were capable of circadian reentrainment to a 12-h light reversal [16].

Analytical, diagnostic and therapeutic context of Rpe65

• Rod function, as measured by electroretinography, is abolished in Rpe65-/- mice, although cone function remains [5].
• Application (intraperitoneal injection) of 11-cis-retinal to Rpe65(-/-) mice increased the rod ERG signal, increased levels of rhodopsin, and decreased opsin phosphorylation [11].
• CONCLUSIONS: By demonstrating that lentivirus-mediated Rpe65 gene transfer protects and restores the function of cones in the Rpe65(-/-) mouse, this study reinforces the therapeutic value of gene therapy for RPE65 deficiencies, suggests a cone-preserving treatment for the retina, and evaluates a potentially effective viral vector for this purpose [1].
• Photoreceptor function can be transiently increased for several months and anatomic degeneration slightly reduced in Rpe65(-/-) mice by RPE cell transplantation [3].
• Sequence analysis of the coding region of the Rpe65 cDNA revealed no relevant sequence variations in the two strains [17].

References