Abstract
Purpose: :
To test whether the amount of retinyl esters in the Retinal Pigment Epithelium (RPE) increases in the absence of light. In the light, retinyl esters are mobilized as substrates for regeneration of the visual chromophore, 11-cis retinal. In mice lacking Rpe65, a protein required for regeneration of 11-cis retinal, large quantities of retinyl esters accumulate in the RPE.
Methods: :
Wild-type mice (129/sv) were age matched and reared in the dark for various lengths of time over the course of one month. Whole eyecups were collected and retinyl esters were extracted and quantified using normal phase HPLC coupled to UV/Vis spectroscopy. The quantity of retinyl esters found in dark reared wild-type mice was compared to that in cyclic light reared and Rpe65-deficient mice.
Results: :
The amounts of esters in the RPE of mice kept in the dark for up to 29 days was not significantly different from those in cyclic-light reared mice. Ester levels stayed relatively stable at ~50 pmol per eye in both dark- and cyclic-light reared mice. Quantities of retinyl esters in both groups of wild-type mice were much lower than in age-matched Rpe65-deficient mice, which were ~460 pmol/eye on Day 1 and ~1140 pmol/eye on Day 28.
Conclusions: :
The stability of retinyl ester content over one month suggests that formation and storage of retinyl esters is tightly regulated in the RPE. The data suggest that Rpe65 is not simply involved in the generation of 11-cis retinal, but also in the regulation of the size of the retinyl ester pool.
Keywords: retinoids/retinoid binding proteins • retinal pigment epithelium • lipids