Localizations of visual cycle components in retinal pigment epithelium

[摘要] Purpose: We used immunocytochemistry andconfocal microscopy to determine whether enzymes of the rod visualcycle were uniformly distributed in retinal pigment epithelium (RPE)cells. The localizations of these enzymes were compared to knownlocalizations of retinoid-binding proteins and associated proteins. Methods: Antibodies to proteins andenzymes associated with the rod visual cycle were used for fluorescenceimmunocytochemistry with frozen sections of albino mouse and ratretina. Images were obtained with a laser scanning confocal microscope.Results: Components associated with therod visual cycle were distributed in three distinct patterns in mouseand rat RPE. Three visual cycle enzymes (RDH5, LRAT, and RPE65) wererestricted to the somata of RPE cells and were not detected withinapical processes. Ezrin, an actin-binding protein, and ERM-bindingphosphoprotein50/sodium-hydrogen exchanger regulatory factor1(EBP50/NHERF1), an ezrin-binding PDZ-domain protein, were largelyrestricted to RPE apical processes. The fluorescence intensity overMüller cell apical processes was less intense. Cellularretinaldehyde-binding protein (CRALBP), which binds to EBP50/NHERF1,and cellular retinol-binding protein type 1 (CRBP1) were foundthroughout RPE cells and Müller cells. Conclusions: Visual cycle enzymes wereconfined to the somata of RPE cells and did not occur within the longapical processes, either in dark- or light-adapted animals. Othercomponents previously linked to the visual cycle (EBP50/NHERF1 andezrin) were largely confined to the apical processes, where they couldbe associated with release of 11-cis-retinal or uptake of all-trans-retinol.CRALBP and CRBP1 were distributed throughout the RPE cell, where theycould mediate diffusion of retinoids between apical processes andsomata.

[学科分类] 生物化学/生物物理