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W. J. Lukiw, Y. Zhao, P. K. Mukherjee, N. G. Bazan, J. G. Cui; Common Pathogenic Mechanism Involving Altered Beta-Amyloid Precursor Protein (ßAPP) Processing in Alzheimer's Disease (AD) and Age-Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2007;48(13):17.
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Alzheimer's disease (AD) and age-related macular degeneration (AMD) are respectively, the most common causes of senile dementia and central vision impairment in our aging population. Down-regulation of soluble amyloid precursor protein alpha (sAPPα), a monomeric, neuroprotective protein, coupled to up-regulation of neurotoxic amyloid-beta (Aß42) peptide, is characteristic of both AD and AMD. While pro-inflammatory Aß42-peptides are abundant in both AD amyloid and amyloid-like drusen of AMD, sAPPα abundance is significantly reduced. Elevated cholesterol, a known risk factor for the development of both AD and AMD appears to contribute to amyloid-triggered cellular pathology. These studies were undertaken to further our understanding of the molecular mechanisms involved in Aß peptide speciation, sAPPα and Aß42 abundance, and the α-, ß-, and γ-secretase activities that accompany human retinal epithelial, retinal endothelial and human neural cell degeneration.
Control or stressed (5% hypoxia or 20 ng/ml IL-1ß) retinal pigment epithelial (ARPE-19), retinal choroidal endothelial (RF/6A) or human neural (HN) cells in primary culture, AD and age-matched control temporal lobe and primary visual cortex, AMD-affected and control human retina, confocal microscopy, DNA array analysis (Affymetrix and Oligo GEArray), RT-PCR, Northern and Western immunoassay, ELISA, bioinformatics and statistical analysis.
Secretase-mediated cleavage of beta-amyloid precursor protein (ßAPP) generates a series of neurotrophic or neurotoxic amyloid-peptides while depleting plasma membranes of ßAPP holoprotein. Pathogenic stress factors such as hypoxia or IL-1ß were found to divert production of sAPPα into the more toxic, amyloidogenic Aß42-peptides in ARPE-19, RF/6A and in human neural cells. In vitro, cholesterol and the primary cholesterol oxide 24S-hydroxycholesterol, were found to intensify this potentially pathogenic signaling.
ßAPP holoprotein depletion, decreased sAPPα, and increases in γ-secretase-mediated Aß42-peptide abundance may contribute to common pathogenic mechanisms leading to age-related, inflammation-mediated degeneration not only in AD brain but also in human retinal disease.
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