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Emily Hughes, Neil Docherty, John Crean, Abbot Clark, Deborah Wallace, Colm O'Brien; The retinal pigmented epithelial cell and peripapillary atrophy: potential mediators of glaucomatous optic disc cupping?. Invest. Ophthalmol. Vis. Sci. 2013;54(15):764.
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There is a well established link between peripapillary atrophy (PPA) and glaucoma. Histologically the zone of PPA adjacent to the optic disc (beta zone), is bare of retinal pigment epithelial cells (RPEC) but the aetiology is unknown. Epithelial cells in other organs have been shown to differentiate to a myofibroblastic phenotype through the process of epithelial to mesenchymal transition (EMT) in response to a variety of stimuli. EMT has been shown to play a role in fibrotic disease. This work examines the possibility that glaucoma-like stimuli such as stretch and growth factor stimulation may induce EMT in the RPEC, causing it to have a migratory ability and myofibroblastic phenotype. This may infer a role for the RPEC, and therefore PPA, in glaucomatous optic disc cupping.
The human retinal pigment epithelial cell line, ARPE-19, was exposed to cyclical stretch (15% cell elongation, 1Hz cycles). As a positive control, cells were treated with recombinant human transforming growth factor beta-1 (TGFβ1, 10ng/ml) to induce EMT. Post-treatment analysis included real time polymerase chain reaction for gene expression of Zona Occludens 1 (ZO-1), alpha smooth muscle actin (αSMA), collagen type 1A1, and TGFβ1. The migratory capacity of ARPE-19 cells under the influence of growth factors was examined by scratch migration assay. Human optic nerve heads from normal and glaucomatous donors underwent immunohistochemical analysis for TGFβ1, and RPE65 (visual cycle protein found in RPEC).
Cyclical stretch of ARPE-19 cells resulted in a decrease in epithelial marker ZO-1, and an increase in myofibroblastic marker αSMA, as well as an increase in collagen type 1A1 and TGFβ1 expression (results significant, p<0.05). Growth factor treatment altered the migratory capacity of the cells as measured by scratch assay. Immunohistochemical analysis of human optic nerves demonstrated increased levels of RPE65 and TGFβ1 in the glaucomatous optic nerve compared to normal.
ARPE-19 cells were shown to change from an epithelial to a mesenchymal phenotype after exposure to glaucoma-like stimuli in-vitro. There is also immunohistochemical evidence suggesting the presence of RPEC within the glaucomatous optic nerve head from human eyes. This may indicate a role for the RPEC and PPA in glaucomatous cupping. Future work will examine the use of EMT inhibitors on the process.
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