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Amanda Bednar, Mayur Choudhary, Peter Saloupis, Alan Proia, Goldis Malek; Osteopontin (OPN) is Present in Drusen and Basal Deposits in Human Eyes with Age-Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2013;54(15):4606.
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AMD is the most common cause of irreversible vision loss. Chronic inflammation has been proposed to contribute to formation of diffuse basal deposits and lipid-protein rich focal deposits called drusen, characteristic phenotypes of the early dry form of AMD. OPN is a secreted phosphoprotein, which has been shown to play a regulatory role in inflammation in Alzheimer’s disease, atherosclerosis and fatty liver disease. Given that these diseases share common pathogenic pathways with AMD, we sought to investigate the localization of OPN in eyes from normal and AMD donors. Further, to identify potential inducers of OPN, we tested the effect of constituents of cigarette smoke and lipids, on OPN expression in human retinal pigment epithelial (RPE) cells in vitro.
OPN was localized via indirect immunofluorescence in ten micron thick paraffin sections cut from normal and diagnosed AMD human donor eyes (N=5). AMD eyes contained drusen, basal deposits and RPE changes. ARPE19 cells grown to post-confluence were exposed to cigarette smoke components (dioxin, hydroquinone) and lipids (OXLDL) for 24 hours prior to RNA and protein extraction. mRNA and protein expression of OPN relative to a housekeeping gene or protein were measured with qPCR and Western blot analysis respectively (n=3).
In normal eyes OPN immunolocalized to the retinal ganglion cell layer. In AMD eyes staining was also seen throughout diffuse deposits and as vesicles or spherical particulates within drusen. In vitro experiments confirmed RPE cells as a potential source of OPN as they express both RNA and protein. A significant increase in OPN mRNA in ARPE19 cells was seen following treatment with dioxin (2 fold), hydroquinone (15 fold) and oxLDL (3 fold). OPN protein expression also increased following treatment with these drugs.
These findings demonstrate the novel observation that OPN accumulates in drusen and basal deposits in human dry AMD. RPE cells express OPN and may be a local source. Drugs associated with initiation and progression of AMD were shown to stimulate and induce OPN expression in RPE cells. It is plausible that OPN serves as a signal for promoting AMD progression through its proposed functions in recruitment and retention of macrophages and inflammation. This potential aspect of OPN biology in AMD is currently under investigation.
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