Protection of Cone Photoreceptor M-Opsin Degradation with 9-Cis-β-Carotene-Rich AlgaDunaliella bardawilinRpe65−/−Mouse Retinal Explant Culture

RPE65, a retinal pigment epithelium-specific 65-kDa protein, plays a critical role in the visual cycle of the eye. Rpe65(-/-) mice develop vision loss due to a lack of 11-cis-retinal, degradation of M-opsin and mislocalization of S-opsin. Several studies have suggested that 9-cis-β-carotene, a precursor of 9-cis-retinal and all-trans-retinal, could have therapeutic applications in vision loss. We therefore examined whether Dunaliella bardawil, a 9-cis-β-carotene-rich alga, protects against the degradation of M-opsin using Rpe65(-/-) mouse retinal explant cultures.The eyes of three-week-old Rpe65(-/-) and C57BL/6 J mice were enucleated, and the corneas were removed. The eyecups were incubated with culture medium in the absence or presence of D. bardawil for 6 h to 4 days. Localizations of M-opsin proteins in the retina were observed immunohistochemically. Expression levels of M-opsin, S-opsin and rhodopsin proteins were evaluated by Western blot analysis.In C57BL/6 J mouse retina, no change was observed in localization and expression levels of M-opsin in the explant culture system. In Rpe65(-/-) mouse retina, the amount of M-opsin protein was decreased in the photoreceptor outer segment after 6 h to 4 days of culture. However, the presence of D. bardawil significantly ameliorated this decrease. In contrast, expression levels of S-opsin and rhodopsin were unchanged in the presence of the explant culture.These results demonstrate that D. bardawil treatment protects against M-opsin degradation in Rpe65(-/-) mouse retina and suggest that D. bardawil has therapeutic potential for retinal degeneration caused by Rpe65 gene mutation, such as Leber congenital amaurosis and retinitis pigmentosa.