Cone outer segment morphology and cone function in the Rpe65-/-Nrl-/- mouse retina are amenable to retinoid replacement

Abstract

PURPOSE. RPE65, a major retinal pigment epithelium protein, is essential in generating 11-cis retinal, the chromophore for all opsins. Without chromophore, cone opsins are mislocalized and cones degenerate rapidly (e.g., Rpe65-/- mouse). Function, survival, and correct targeting of opsins is increased in Rpe65-/- cones on supplying 11-cis retinal. Here, we determine the consequences of 11-cis retinal withdrawal and supplementation on cone development in the all-cone Nrl-/- retina. METHODS. Rpe65-/- Nrl-/-, Nrl-/-, and wild-type mice were examined. Cone structure was analyzed by using TUNEL assay, electron microscopy, and cone-specific antibodies. Cone function was assessed with light-adapted single-flash ERGs. RESULTS. Rpe65-/- Nrl-/- mice had an increased number of TUNEL-positive photoreceptors during programmed cell death compared with Nrl-/- mice, in addition to accelerated agerelated degeneration. Cone function in Rpe65-/- Nrl-/- mice was minimal, and opsins were mislocalized. Treatment with 11-cis retinal restored cone function, promoted outer segment formation, and enabled opsin trafficking to outer segments. Eliminating Rpe65 prevented rosette formation in Nrl-/- retinas; supplementation of Rpe65-/- Nrl-/- mice with 11-cis retinal resulted in their reoccurrence. CONCLUSIONS. Taken together, function and opsin trafficking in Nrl-/- and wild-type cones are comparable, confirming and extending our findings that cone maturation and outer segment development are dependent on the presence of chromophore. The data on age-related cone death in Rpe65 -/- Nrl-/- mice and the reintroduction of rosettes after 11-cis retinal injections confirm that outer segments, which for steric reasons appear to introduce rosettes in an all-cone retina, are essential for cell survival. These results are important for understanding and treating chromophorerelated cone dystrophies. © Association for Research in Vision and Ophthalmology.