Abstract
Purpose::
Blue light induces apoptosis in human fetal retinal pigment epithelium (HFRPE) cells.The apoptosis rate depends on the age (number of passages) of cultured human fetal RPE cells and time of culturing the cells. In this study we examined the aging process of cultured HFRPE cells and find the evidence of melanogenesis in these cells.
Methods::
Retinal pigment epithelium cells were isolated from human fetal eyes and pure cultures were obtained. Purity of cells was confirmed with cytokeratin assay. HFRPE cells of the second to seventh passages were cultured beyond the point of confluence for 2 to 14 weeks and then they were analyzed by the EPR techniques for melanin content. Parallel cultures of HFRPE cells were illuminated by blue light (4.5 mW/cm2) for 7 days in an especially designed incubator. The rate of apoptosis induced by blue light irradiation was analyzed by Annexin V staining using the flow cytometry techniques. The cells cultured in dark served as a control.
Results::
Blue light induced apoptosis in human fetal RPE cells depends on the cells age and the time of culturing. Cells cultured for prolonged time demonstrate lower percentage of apoptosis as compared to the cells cultured only to the point of confluence (3 days).EPR experiments prove that melanin content increase in older cultured cells.
Conclusions::
Melanin is the photoprotective agent in human RPE cells against blue light induced apoptosis (PNAS, 2006, 103, 16644-48). Resistance to blue light induced apoptosis by aged cultured RPE cells which have higher content of melanin is consistent with the process of melanogenesis in HFRPE cells.
Keywords: apoptosis/cell death • protective mechanisms • age-related macular degeneration