Characterization of beta amyloid assemblies in drusen: the deposits associated with aging and age-related macular degeneration.
OBJECTIVE
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 beta (Abeta), a major pro-inflammatory component of Alzheimer's disease plaques. We characterized the ultrastructural organization and histochemical staining properties of these Abeta-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 Abeta-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 Abeta-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 Abeta 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 Abeta as well as activated complement components. The presence of Abeta 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.
Anderson
Don H
DH
Center for the Study of Macular Degeneration, Neuroscience Research Institute, University of California, Santa Barbara, CA 93106, USA. d_anders@lifesci.ucsb.edu
Talaga
Kevin C
KC
Rivest
Alexander J
AJ
Barron
Ernesto
E
Hageman
Gregory S
GS
Johnson
Lincoln V
LV
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism* / Q000473:pathology; D016229:Amyloid beta-Peptides / Q000032:analysis* / Q000378:metabolism / Q000648:ultrastructure; D002648:Child; D005136:Eye Proteins / Q000032:analysis / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D046911:Macromolecular Substances; D008268:Macular Degeneration / Q000378:metabolism* / Q000473:pathology; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000737:chemistry; D015593:Retinal Drusen / Q000378:metabolism* / Q000473:pathology
D016229:Amyloid beta-Peptides; D005136:Eye Proteins; D046911:Macromolecular Substances