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M.J. Radeke, K.E. Peterson, L.V. Johnson, D.H. Anderson; Differences in Macular and Extramacular Gene Expression in the Human RPE/Choroid . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4159.
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© ARVO (1962-2015); The Authors (2016-present)
Recently, several gene alterations have been identified that confer an increased risk for the development of age–related macular degeneration (AMD). However, the identification of these genetic variants has done little to explain why the degeneration is most pronounced in the macula. As a first step in addressing the macula’s inherent susceptibility to disease, we used a genome–scale expression profiling approach to identify differences in gene transcription between the macular and extramacular RPE/choroid.
RNA was isolated from trephine punches obtained from the mid–periphery and macular RPE/choroids of normal human donor eyes (45–87 yrs) and from eyes with a clinical diagnosis of early AMD (78–92 yrs). The gene expression profiles of the peripheral and macular RPE/choroids from the same eye were then compared using a two–color microarray platform (Agilent 22K and whole genome arrays). Finally, the results obtained by array analysis were confirmed using real–time quantitative PCR (qPCR).
From the array analysis of 5 normal donor eyes and 3 AMD eyes, we identified 70 candidate genes with > 2 fold differences in the ratio of macular to extramacular expression levels. From these 70 candidates, we selected 31 genes–of–interest for further analysis by qPCR using material obtained from ten normal and five AMD eyes. We confirmed that 6 of the 31 genes are consistently over–expressed in the macular RPE/choroids relative to the extramacular locations within the same eye; whereas, 16 genes are consistently under–expressed in the macula relative to the periphery. Seven of the differentially expressed genes are growth factors or chemokines, a number of which are involved in the inflammatory response and/or angiogenesis. Three genes are known components of the extracellular matrix. One gene is involved in amyloid beta precursor protein (APP) function, and another is a putative transcription factor. The expression levels of most of the differentially expressed genes remained constant irrespective of age or disease state. However, we did identify a few genes whose expression levels are altered as a function of age and/or AMD state. Finally, 5 of the genes validated by qPCR are located within or adjacent to established AMD chromosomal loci.
The documentation of regional differences in gene expression in the RPE/choroid is a first step in explaining the macula’s propensity for degeneration. The findings lay the groundwork for further studies into the functional roles of the proteins encoded by these genes in the normal, aged, and diseased macula.
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