LIPOFUSCIN AND MELANIN OF HUMAN RETINAL-PIGMENT EPITHELIUM - FLUORESCENCE, ENZYME CYTOCHEMICAL, AND ULTRASTRUCTURAL STUDIES

  • 1 January 1978
    • journal article
    • research article
    • Vol. 17  (7) , 583-+
Abstract
The life history of melanin and lipofuscin granules of human retinal pigment epithelium (RPE) was studied in 30 human eyes spanning 9 decades of life. Autofluorescent granules in the cytoplasm of eyes over 30 yr old were shown ultrastructurally and through lipid solvent lipofuscin granule extraction. Sparse small fluorescent granules in infant eyes were secondary lysosomes containing small droplets of lipid. Fluorescent substances in RPE granules of eyes < 50 yr old were more readily extracted with lipid solvents than those in very old eyes (> 70). Lipofuscin granules were positive for acid phosphatase and aryl sulfatase activity. Fusions between primary lysosomes and lipofuscin granules were common in older eyes, suggesting that the over-all degradative process involves repeated injection of lysosomal enzymes, i.e., the initial fusion of lysosomes with phagosomes (phagocytized outer segment disks) is only one of several attempts to hydrolyze the membranous material. Some melanin granules showed hydrolytic enzyme reactions. By enzyme cytochemistry, fluorescence microscopy and lipid extraction, 2 types of melanin-containing complex granules were identified: melanin with a cortex of lipofuscin (melanolipofuscin) and melanin with a cortex of nonlipid, enzyme-reactive material (melanolysosomes). Apparently melanin commonly becomes incorporated into the lysosomal system of the RPE cell, and it may undergo modification or degradation there. There is a dynamic, complex interrelationship between the various components of the phagolysosomal system and the melanin granules in the RPE cytoplasm. The observed variation from one human eye to another in the content and lipid extractability of RPE lipofuscin granules suggests that there may be differences in lipid composition of phagocytized photoreceptor disks and/or differences in the degradation of these lipids in the phagolysosomal system of the RPE cell.