Analysis of esterification of retinoids in the retinal pigmented epithelium of the Mitf-vit (vitiligo) mutant mouse.
OBJECTIVE
Mice homozygous for the vitiligo mutation of the microphthalmia (Mitf) gene have a retinal degeneration characterized by slow loss of photoreceptor cells and compromised retinal pigment epithelial (RPE) structure and function. The levels of retinyl esters, which are essential for generation of 11-cis-retinaldehyde for the formation of rhodopsin, were reported previously to be elevated by 6 weeks postnatally in the RPE of vitiligo mutant mice. The purpose of the present study was to determine whether this elevation was due to increased activity of lecithin:retinol acyl transferase (LRAT) the enzyme that converts all-trans-retinol to retinyl esters.


METHODS
Retinoids extracted from the RPE and neural retina of mutant and normal mice ages 2, 4, 6 and 8 weeks were analyzed by reversed-phase HPLC. The esterification capacity of the RPE to convert 3H-retinol to 3H-retinyl ester was determined by HPLC in mutant and normal mice at 3 and 9 weeks.


RESULTS
Retinyl ester levels were elevated significantly in the mutant RPE as early as postnatal week 2 and were four-fold greater by 8 weeks. The esterification assay indicated no significant differences between mutants and controls at 3 weeks. At 9 weeks, the esterification activity of the mutant RPE was significantly reduced compared to controls rather than elevated.


CONCLUSIONS
The data suggest that the accumulation of retinyl esters is not due to increased LRAT activity. Alternative explanations for the retinyl ester accumulation are discussed.
Evans
B L
BL
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, Georgia 30912-2000, USA.
Smith
S B
SB
D000217:Acyltransferases / Q000378:metabolism*; D000375:Aging; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004268:DNA-Binding Proteins / Q000235:genetics*; D004224:Diterpenes; D004951:Esterification; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D051739:Microphthalmia-Associated Transcription Factor; D008855:Microscopy, Electron, Scanning; D008862:Microsomes, Liver / Q000378:metabolism; D009154:Mutation; D010857:Pigment Epithelium of Eye / Q000737:chemistry / Q000201:enzymology* / Q000648:ultrastructure; D000084562:Retinyl Esters; D013997:Time Factors; D014157:Transcription Factors; D014212:Tretinoin / Q000378:metabolism*; D014801:Vitamin A / Q000031:analogs & derivatives / Q000378:metabolism; D014820:Vitiligo / Q000378:metabolism
D004268:DNA-Binding Proteins; D004224:Diterpenes; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D000084562:Retinyl Esters; D014157:Transcription Factors; D014801:Vitamin A; C014794:retinol palmitate; D014212:Tretinoin; D000217:Acyltransferases; C056942:lecithin-retinol acyltransferase