Abundant lipid and protein components of drusen.
BACKGROUND
Drusen are extracellular lesions characteristic of aging and age-related maculopathy, a major retinal disease of the elderly. We determined the relative proportions of lipids and proteins in drusen capped with retinal pigment epithelium (RPE) and in RPE isolated from non-macular regions of 36 human retinas with grossly normal maculas obtained <6 hr after death.


RESULTS
Druse pellets were examined by light and electron microscopy. Component proteins were extracted using novel methods for preserved tissues, separated, subjected to tryptic digestion and LC-MS(MS)(2) analysis using an ion trap mass spectrometer, and identified with reference to databases. Lipid classes were separated using thin layer chromatography and quantified by densitometry. Major druse components were esterified cholesterol (EC), phosphatidylcholine (PC), and protein (37.5+/-13.7, 36.9+/-12.9, and 43.0+/-11.5 ng/druse, respectively). Lipid-containing particles (median diameter, 77 nm) occupied 37-44% of druse volume. Major proteins include vitronectin, complement component 9, apoE, and clusterin, previously seen in drusen, and ATP synthase subunit beta, scavenger receptor B2, and retinol dehydrogenase 5, previously seen in RPE. Drusen and RPE had similar protein profiles, with higher intensities and greater variability in drusen. C8, part of the complement membrane attack complex, was localized in drusen by immunofluorescence.


CONCLUSIONS
At least 40% of druse content is comprised by lipids dominated by EC and PC, 2 components that are potentially accounted for by just one pathway, the secretion of lipoproteins by RPE. Manipulating genes encoding apolipoprotein pathways would be a fruitful approach to producing drusen with high EC content in laboratory animals. Therapies that directly mitigate drusen should prepare for the substantial volume of neutral lipids. The catalog of major druse proteins is nearing completion.
Wang
Lan
L
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America.
Clark
Mark E
ME
Crossman
David K
DK
Kojima
Kyoko
K
Messinger
Jeffrey D
JD
Mobley
James A
JA
Curcio
Christine A
CA
D000368:Aged; D000369:Aged, 80 and over; D001053:Apolipoproteins / Q000032:analysis; D005136:Eye Proteins / Q000032:analysis*; D005260:Female; D006801:Humans; D008055:Lipids / Q000032:analysis*; D008268:Macular Degeneration; D008297:Male; D012160:Retina / Q000737:chemistry*; D015593:Retinal Drusen / Q000473:pathology*; D055213:Retinal Pigment Epithelium
D001053:Apolipoproteins; D005136:Eye Proteins; D008055:Lipids