PURPOSE. Amyloid-beta (Ab) is an endogenous peptide that becomes dysregulated in AMD and Alzheimer disease. Both of these disorders are marked by extracellular deposits that contain Ab, highly branched capillary networks, and neurodegeneration. Although Ab has been implicated in AMD and Alzheimer pathology for decades, its nonpathological function has remained unclear. We recently showed that high levels of monomeric Ab induce blood vessel branching in embryonic zebrafish brain, and here we report that a similar mechanism may contribute to aberrant blood vessel branching in the retina of adult zebrafish. METHODS.Transgenic zebrafish expressing enhanced green fluorescence protein (EGFP) in their endothelial cells were sedated and small intraocular injections of PBS were made into one eye and either Ab or c-secretase inhibitor were injected into their opposite eye. A week later, the eyes were enucleated and high resolution maps of the retina vasculature were created using confocal microscopy. Comparisons were made between the treatment groups using the general linear model ANOVA. RESULTS.We found that Ab significantly affects capillary blood vessels in the retina. Small volumes of Ab injected into the eyes of adult zebrafish induced the formation of significantly more endothelial tip cells and capillary bridges-some with loopsnear the circumferential vein. These effects were dosedependent and increased capillary bed density, though there was no effect on larger arterial vessels.CONCLUSIONS. This study reveals a previously unknown role for Ab in regulating capillary bed density, providing new insight into the normal biological function. Ab will help in the development of therapeutic interventions for AMD and Alzheimer disease. (Invest Ophthalmol Vis Sci. 2013; 54:1516-1521) DOI:10.1167/iovs.12-10821 A myloid-beta (Ab) is produced by the proteolytic cleavage of amyloid precursor protein (APP) through a two-step process involving b-and c-secretases. Zebrafish have all of the necessary proteins to produce Ab, including APP and band c-secretases, and APP knockdown effects in zebrafish can be rescued by human APP mRNA. 1,2 Ab production from APP proceeds by the same two-step process in neurons and RPE. Initially, a portion of the extracellular region is shed by a bsecretase metalloproteinase (BACE1/2) to produce a C99 intermediate, which is then cleaved by c-secretase to release Ab from the cell's plasma membrane. 3 The c-secretase complex is also critical to the processing of other substrates including cadherins and Notch. Notably, c-secretase inhibitors induce angiogenesis through their disruption of Notch signaling. 4 We previously proposed that the development of aberrant blood vessels that occurs between Alzheimer disease (AD) plaques involves the disruption of Notch signaling by high levels of Ab. 5 That hypothesis has been supported by recent studies showing that excessive APP leads to cerebral hypervascularization in mice and young zebrafish. 6,7 AD is the leading cause of dementia in the elderly, affecting more...
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