LONG-RANGE OBJECTIVES: In the next 3 decades, nearly 8 million people will experience serious visual loss due to age-related macular degeneration (AMD) unless major advancements are made in our understanding of the disease process. Currently our research focuses on elucidating mechanisms modulating the onset of AMD. The progressive degeneration of the Retinal Pigment Epithelium (RPE) and Bruch's membrane, which characterizes AMD, may result from lipofuscin accumulation in RPE lysosomes, just as tissue dysfunction follows lysosomal engorgement in lysosomal storage diseases. Recent advances in the biology of lysosomes makes the lipofuscin hypothesis for AMD particularly timely and attractive. It is our belief that understanding the early cellular events leading to vision loss will greatly improve the possibility of slowing, or ultimately preventing the disease.
SPECIFIC AIMS : To test the hypothesis that accumulated lipofuscin disrupts essential RPE functions, a two-pronged approach is proposed to evaluate the histopathology of the aging macula and to examine cell functions in human RPE in vitro. The five Specific Aims are:
Aims 1 and 2 - Examine the macula of donors who are white (aged 60-80 years) to determine (a) whether individuals at greater risk for macular degeneration (i.e., whites with blue eyes) have greater lipofuscin concentrations than those with brown eyes of the same age and (b) the relationship between number of surviving photoreceptors and amount of RPE lipofuscin;
Aims 3 and 4 - Determine whether lipofuscin inhibits key events in phagosome digestion or nutrient uptake (e.g. acidification, lysosome fusion, action of acid hydrolases);
Aim 5 - Distinguish effects due to lysosomal expansion and to cumulative effects of oxidative damage. METHODS:These include microscopic examination of fixed sections of donor eyes and videomicroscopy with computer-assisted image analysis to measure lipofuscin concentration. Human RPE cells of the same age but varying lipofuscin content will be cultured from the macular and equatorial regions of donor eyes, and functions related to nutrient uptake and the formation and function of the phagolysosome will be assayed. Porcine RPE cells fed varying amounts of latex beads will be used as another model of vastly expanded lysosomal volume. Endocytosis and acidification of endosomes will be assayed as uptake of (125)I transferrin and (59)Fe. The kinetics of phagolysosome formation will be examined, and effects of lipofuscin, age, and retinal site on this and all RPE functions will be analyzed. SIGNIFICANCE AND HEALTH-RELATEDNESS: These experiments will systematically explore possible relationships between lipofuscin accumulation and RPE functions. If we find further evidence that lipofuscin accumulation may be an early event in AMD then noninvasive methods for its measurement (currently in development) could provide an additional index in assessing risk for AMD, a multifactorial condition. Finally these studies will extend our knowledge of essential RPE cell functions involved in phagosome processing.
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