Artikel
As the bright light dims: loss of lipofuscin-attributable autofluorescence from RPE in aging and AMD
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Veröffentlicht: | 1. Oktober 2015 |
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Gliederung
Text
Background: In healthy persons, fundus autofluorescence (AF) intensity diminishes after age 70 [1], with the underlying mechanisms still unknown. In age-related macular degeneration (AMD), hypoautofluorescent areas in fundus AF-imaging are often referred to as retinal pigment epithelium (RPE) atrophy; however, how atrophy starts in individual cells is not known. This microscopy study uses human RPE-flatmounts to demonstrate possible mechanisms, which lead to the formation of hypoautofluorescent areas in the RPE cell layer.
Methods: From 35 human donor eyes (25 AMD (>69 years); 10 age-matched controls), RPE-flatmounts were prepared. RPE cells were systematically imaged at >1300 predefined locations twofold:
1) using a spinning-disk confocal fluorescence microscope, RPE lipofuscin/melanolipofuscin AF (exc. 488, em. >510nm) and RPE cytoskeleton (labeled with AlexaPhalloidin647);
2) using high-resolution structured illumination microscopy (SIM), RPE-AF granules were imaged at locations chosen by an unbiased sampling scheme.
Results: In normal aging, hypofluorescence is attributable to:
1) RPE cells densely packed with melanosomes, or
2) degranulation (loss of individual AF granules).
In AMD, hypofluorescence results from:
1) degranulation (as in normal aging), or
2) aggregation and shedding into the sub-RPE space. All these mechanisms lead to a diminished AF signal in the en face view.
Aggregates (5-20 µm in diameter) in AMD RPE-flatmounts comprise multiple AF granules, and multiple aggregates can be found in a single RPE cell.
Conclusion: For the first time, possible mechanisms leading to reduced RPE-AF in normal aging and AMD, are demonstrated on a histological basis. An overall reduced AF intensity in older adults might be explained by a slow but steady loss of individual granules (shed into the sub-retinal and sub-RPE space), while in AMD the shedding of aggregates of individual cells (shed basolaterally into basal laminar deposits) leads to circumscribed areas of reduced RPE-AF. These results can help to further interpret clinical fundus AF findings.
References
- 1.
- Delori FC, Goger DG, Dorey CK. Age-related accumulation and spatial distribution of lipofuscin in RPE of normal subjects. Invest Ophthalmol Vis Sci. 2001 Jul;42(8):1855-66.