Characterization of β amyloid assemblies in drusen: the deposits associated with aging and age-related macular degeneration

• Published in: Experimental eye research 2004-02, Vol.78 (2), p.243-256
• Main Authors: Anderson, Don H., Talaga, Kevin C., Rivest, Alexander J., Barron, Ernesto, Hageman, Gregory S., Johnson, Lincoln V.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Age Distribution; age-related macular degeneration; Aged; Aged, 80 and over; Aging - metabolism; Aging - pathology; Alzheimer's disease; Amyloid beta-Peptides - analysis; Amyloid beta-Peptides - metabolism; Amyloid beta-Peptides - ultrastructure; Bruch's membrane; Child; Eye Proteins - analysis; Eye Proteins - metabolism; Eye Proteins - ultrastructure; Humans; Macromolecular Substances; Macular Degeneration - metabolism; Macular Degeneration - pathology; Microscopy, Confocal; Microscopy, Immunoelectron; Middle Aged; Pigment Epithelium of Eye - chemistry; Retinal Drusen - metabolism; Retinal Drusen - pathology
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2003.10.011

Purpose. Recent studies strongly suggest that drusen, the extracellular deposits associated with age-related macular degeneration (AMD), are a manifestation of local inflammatory events. New evidence indicates that substructural elements within drusen contain activated complement components as well as amyloid β (Aβ), a major pro-inflammatory component of Alzheimer's disease plaques. We characterized the ultrastructural organization and histochemical staining properties of these Aβ-containing elements in order to further assess their significance in drusen formation and AMD pathogenesis. Methods. We used differential interference contrast optics, laser scanning confocal immunofluorescence, and immunogold electron microscopy to characterize the structural properties and molecular composition of Aβ-containing elements in drusen. We obtained estimates of their frequency from montages of electron micrographs gathered from 152 human donor eyes ranging from 9 to 91 years of age. Results. Spherical Aβ-containing elements, which are typically organized as concentric ring-like structures, are common substructural components of drusen. They stain with thioflavin T, but are not stained by Congo red; nor do they bind cationic, lipophilic, or nucleic acid-binding fluorescent dyes. Ultrastructurally, they are composed of a central core, one or more concentric inner rings with intervening electron lucent layers, and an electron dense outer shell. Immunogold labeling indicates that most Aβ immunoreactivity is associated with the outer layers that consist of densely-packed spherical subunits. No longitudinally-oriented fibril arrays, characteristic of aggregated amyloid fibrils in the brain, are evident. Other prominent drusen-associated proteins including the terminal complement complex C5b-9, vitronectin, apolipoprotein E, serum amyloid P component, and ubiquitin are excluded from the spheres. Conclusions. These structures embedded in drusen appear to represent a new type of macromolecular assembly that contains Aβ as well as activated complement components. The presence of Aβ in these extracellular deposits is an additional indication that some of the pathogenic pathways that give rise to drusen and AMD may be shared with other neurodegenerative diseases characterized by misfolded protein deposition and aggregation.