Characterization of a Dehydrogenase Activity Responsible for Oxidation of 11-cis-Retinol in the Retinal Pigment Epithelium of Mice with a Disrupted RDH5 Gene

Abstract

In the vertebrate retina, the final step of visual chromophore production is the oxidation of 11-cis-retinol to 11-cis-retinal. This reaction is catalyzed by 11-cis-retinol dehydrogenases (11-cis-RDHs), prior to the chromophore rejoining with the visual pigment apo-proteins. The RDH5 gene encodes a dehydrogenase that is responsible for the majority of RDH activity. In humans, mutations in this gene are associated with fundus albipunctatus, a disease expressed by delayed dark adaptation of both cones and rods. In this report, an animal model for this disease, 11-cis-rdh؊/؊ mice, was used to investigate the flow of retinoids after a bleach, and microsomal membranes from the retinal pigment epithelium of these mice were employed to characterize remaining enzymatic activities oxidizing 11-cis-retinol. Lack of 11-cis-RDH leads to an accumulation of cis-retinoids, particularly 13-cis-isomers. The analysis of 11-cisrdh؊/؊ mice showed that the RDH(s) responsible for the production of 11-cis-retinal displays NADP-dependent specificity toward 9-cis-and 11-cis-retinal but not 13-cisretinal. The lack of 13-cis-RDH activity could be a reason why 13-cis-isomers accumulate in the retinal pigment epithelium of 11-cis-rdh؊/؊ mice. Furthermore, our results provide detailed characterization of a mouse model for the human disease fundus albipunctatus and emphasize the importance of 11-cis-RDH in keeping the balance between different components of the retinoid cycle.

Dual-substrate Specificity Short Chain Retinol Dehydrogenases from the Vertebrate Retina

“…However, disabling mutations in men and mice produce no embryonic developmental abnormalities (16)(17)(18)(19). In this report, we provide unequivocal evidence that RDH11-14 display high activity toward 9-cis-and all-trans-retinol.…”

“…6E). These properties resemble those of the photoreceptor dehydrogenase, prRDH (24,31), and not those of the RPE enzyme RDH5 (16,24), which is active toward the pro-S position of both substrates. The results also suggest that these enzymes catalyze the reaction in both directions, NADPH/retinals ↔ NADP/retinols.…”

“…These studies indicate that another enzyme is responsible for the production of 11-cis-retinal under bleaching conditions (16). The RDH(s) responsible for the production of 11-cis-retinal in RPE membrane from rdh5−/− mice display pro-S hydrogen specificity for NADPH and utilize 9-cis-and 11-cis-retinal but not 13-cis-retinal (16). Furthermore, pro-R stereospecificity toward 11-cis-retinol with NADP was observed in bovine RPE (24).…”

“…Detailed analyses of rdh5−/− mice have identified only a minor phenotype manifested by the accumulation of 13-cis-retinoids. These studies indicate that another enzyme is responsible for the production of 11-cis-retinal under bleaching conditions (16). The RDH(s) responsible for the production of 11-cis-retinal in RPE membrane from rdh5−/− mice display pro-S hydrogen specificity for NADPH and utilize 9-cis-and 11-cis-retinal but not 13-cis-retinal (16).…”

“…An enzyme encoded by the RDH5 gene (10,11), 11-cis-RDH, was proposed to be responsible for both 11-cis-retinal and 9-cis-retinal production due to its relaxed substrate specificity (12)(13)(14)(15). However, the disruption of this gene in a mouse model led to uninterrupted production of 11-cis-retinal (16,17) and a lack of any embryonic abnormalities. Furthermore, patients with fundus albipunctatus who also have a disabling mutation in the RDH5 gene still show efficient production of the chromophore, albeit with slower kinetics (18,19).…”