Purpose: To improve our understanding of how retinal pigment epithelial (RPE) cells behave in vivo and to establish similarities with dedifferentiation and adaptive events observed in RPE cells cultured under simulated intraocular pathologic conditions. At the same time, to examine the origin of epithelioid-shaped and fibroblast/fusiform-shaped cells in epiretinal membranes (ERM) from proliferative vitreoretinopathy (PVR).
Methods: Cells of ERM were studied by electron-immunocytochemical techniques, using simple, double, and triple immunostaining for cytokeratins (CK), vimentin (Vim), and glial fibrillary acidic protein (GFAP). Ultrastructural morphology analysis was also carried out. Adult human RPE cells were obtained and cultured with normal and pathologic vitreous from proliferative vitreoretinal disorders, subretinal fluid aspirates from retinal detachment, and normal human serum. Their cytoskeleton was fractionated at 7 (early cultures) and 24 (late cultures) days of culture, electrophoresed, immunoblotted for intermediate filament proteins, and quantified by densitometric analysis for each condition. Changes in phenotype characteristics were also evaluated.
Results: Epithelioid-shaped and fibroblast/fusiform-shaped cells, resembling 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/fusiform-shaped phenotype in the presence of subretinal fluid aspirates and pathologic vitreous from proliferative intraocular disorders. In simulated cultures of proliferative intraocular disorders, cells decreased or retained their CK7, CK8, and CK18, retained Vim, and increased CK19 and GFAP, while their 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 may be responsible for epithelioid-like and fibroblast/fusiform-like cells. Furthermore, changes in intermediate filament protein levels were observed in RPE cells in simulated cultures of proliferative intraocular disorders. These changes were linked to cells acquiring a mesenchymal migratory, phenotype. Results indicate that the dedifferentiation of RPE cells occurs both in vivo and in vitro and that it can be explained as an epithelial-mesenchymal transition.