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Theo G. Gorgels, Judith C. Booij, Sovann Kaing, Imre Lengyel, Arthur A. Bergen; On the Origin of Proteins in Human Bruch’s Membrane and Drusen. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6484.
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© ARVO (1962-2015); The Authors (2016-present)
To identify the cellular origin of proteins in the acellular human Bruch's membrane (BM) and in drusen.
Gene expression profiling of laser micro dissected RPE, photoreceptor and choroidal cells from selected human donor eyes was carried out using Agilent microarrays. This provided detailed information of the transcriptomes of these three cell layers: Information 1) on level of gene expression, by comparing with the expression of other genes in the same cell layer, and, 2) on cell-layer specificity of expression by comparing between cell layers. Expression data were confirmed by RT-PCR and WWW database searches. Functional annotation was carried out using DAVID and the Ingenuity knowledge database. A list of proteins present in the BM and in drusen was compiled from the literature. In order to identify the origin of these proteins, we then checked the presence or absence of the corresponding genes in the transcriptomes of the adjacent RPE, choroidal and photoreceptors cells and in the serum proteome.
Most of the genes of Bruch’s membrane proteins, e.g. collagen, laminin and fibronectin, are expressed both in the RPE and in the choroid. Yet, for most of these proteins the RNA expression in the choroid is much higher than in the RPE. We also found that 28 (22 %) out of 129 known drusen proteins are likely to have a choroidal cell origin, 7 (5%) were primarily derived from the RPE and 2 (2%) originated primarily from photoreceptor cells. Nine (7%) proteins occur both in serum and drusen, but are low or not expressed in photoreceptor, RPE or choroidal cells. For the other drusen proteins, the specific cellular origin(s) remained undetermined, e.g. because their mRNA was detected in more than one cell layer.
We found that, in humans, choroidal cells and/or serum are important suppliers of BM and drusen proteins. Since some of the drusen proteins are nuclear, cytoplasmic of membrane proteins of RPE and choroidal cells, our study suggests that drusen contain the remains of dead RPE and choroidal cells. The data may be useful in the search for a (systemic) treatment for retinal disorders, such as age-related macular degeneration (AMD).
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