Lipofuscin Accumulation in Iris Pigment Epithelial Cells Exposed to Photoreceptor Outer Segments

• Published in: Experimental eye research Vol. 69; no. 5; pp. 539 - 546
• Main Authors: GENG, LIJUN, WIHLMARK, ULF, ALGVERE, PEEP V
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01-11-1999; Elsevier
• Subjects: Animals; autofluorescence; Biological and medical sciences; Cattle; Cell Culture Techniques; Eye and associated structures. Visual pathways and centers. Vision; Fluorescence; Fundamental and applied biological sciences. Psychology; Iris - metabolism; Iris - ultrastructure; iris pigment epithelium; lipofuscin; Lipofuscin - metabolism; MEDICIN; MEDICINE; Phagocytosis; photoreceptor outer segments; Pigment Epithelium of Eye - metabolism; Pigment Epithelium of Eye - ultrastructure; retinal pigment epithelium; Rod Cell Outer Segment - physiology; Vertebrates: nervous system and sense organs; iris pigment epithelium; phagocytosis; lipofuscin; autofluorescence; retinal pigment epithelium; photoreceptor outer segments; Photoreceptor; Retina; Ox; Lipofuscin; Eye; Visual system; Vertebrata; Mammalia; Outer segment; Iris(eye); Epithelial cell; Artiodactyla; Biological accumulation; Ungulata; Phagocytosis
• ISSN: 0014-4835; 1096-0007; 1096-0007
• DOI: 10.1006/exer.1999.0735

Lipofuscin accumulates in retinal pigment epithelial (RPE) cells with increasing age in response to phagocytotic degradation of worn-out disks of photoreceptor outer segments (POS). This study investigates the ability of iris pigment epithelial (IPE) cells to ingest POS and compares the phagocytotic capacity of RPE and IPE cells by measuring their amounts of lipofuscin-specific autofluorescence.
IPE and RPE cells were isolated from the same calf eyes. After growing to confluence, primary cultures from 15 eyes (69 wells) were exposed to bovine POS daily, or kept as controls. After 1, 2 and 3 weeks, respectively, the cellular amounts of lipofuscin were quantified by a computerized static cytofluorometer system (Nikon Microphot SA with a Nikon p102 photometer). Lipofuscin-specific fluorescence (550 nm barrier filter eliminating nonspecific autofluorescence) of 100 randomly selected individual cells from each well was measured.
Electron microscopy revealed phagosomes (containing POS disk membranes) and lipofuscin-like inclusions in the cytoplasm of RPE and IPE cells. In both IPE and RPE cultures, the POS-challenged cells had significantly higher (P<0.01) lipofuscin-specific fluorescence than the control cells. The fluorescence levels were higher in POS-challenged RPE cells as compared to IPE cells after 1 (P< 0.001), 2 (P<0.01) and 3 (P<0.001) weeks, respectively. The fluorescence level of POS-fed IPE cells at 3 weeks was 56% of that of RPE cells.
IPE cells have the ability to phagocytose POS, resulting in an accumulation of lipofuscin intracellularly. The amount of lipofuscin was lower in IPE cells compared to RPE cells, probably reflecting the lower phagocytotic capacity of IPE.