Epithelial-mesenchymal transition in proliferative vitreoretinopathy: Intermediate filament protein expression in retinal pigment epithelial cells

PURPOSE. To improve our understanding of how retinal pigment epithelial (RP E) cells behave in vivo and to establish similarities with dedifferentiatio n and adaptive events observed in RPE cells cultured under simulated intrao cular pathologic conditions. At the same time, to examine the origin of epi thelioid-shaped and fibroblast/fusiform-shaped cells in epiretinal membrane s (ERM) from proliferative vitreoretinopathy (PVR). METHODS. Cells of ERM were studied by electron-immunocytochemical technique s, using simple, double, and triple immunostaining for cytokeratins (CK) vi mentin (Vim), and glial fibrillary acidic protein (GFAP). Ultrastructural m orphology analysis was also carried out. Adult human RPE cells were obtaine d and cultured with normal and pathologic vitreous from proliferative vitre oretinal disorders, subretinal fluid aspirates from retinal detachment, and normal human serum. Their cytoskeleton was fractionated at 7 (early cultur es) and 21 (late cultures) days of culture, electrophoresed, immunoblotted for intermediate filament proteins, and quantified by densitometric analysi s for each condition. Changes in phenotype characteristics were also evalua ted. RESULTS. Epithelioid-shaped and fibroblast/fusiform-shaped cells, resemblin g RPE cells, expressed CK-Vim-GFAP simultaneously as intermediate filament proteins in their cytoskeleton. RPE cells in culture also expressed CK-Vim- GFAP and changed from an epithelial shape to a migratory fibroblast/fusifor m-shaped phenotype in the presence of subretinal fluid aspirates and pathol ogic vitreous from proliferative intraocular disorders. In simulated cultur es of proliferative intraocular disorders, cells decreased or retained thei r CK7, CK8, and CK18, retained Vim, and increased CK19 and GFAP, while thei r mesenchymal morphology became clearer over time. CONCLUSIONS. Studies of intermediate filament proteins in vivo suggest that dedifferentiation occurs in RPE cells in ERM. Dedifferentiated RPE cells m ay be responsible for epithelioid-like and fibroblast/fusiform-like cells. Furthermore, changes in intermediate filament protein levels a cre observed in RPE cells in simulated cultures of proliferative intraocular disorders. These changes were linked to cells acquiring a mesenchymal migratory pheno type. Results indicate that the dedifferentiation of RPE cells occurs both in vivo and in vitro and that it can be explained as an epithelial-mesenchy mal transition.