Heat Shock Protein 90 Involvement in the Development of Idiopathic Epiretinal Membranes

PURPOSE: This work was aimed to further characterize cells of idiopathic epiretinal membranes (iERMs). We wanted to determine the contribution of 90-kDa heat shock protein (HSP90) to sustain the transforming growth factor-β (TGF-β)-mediated signal transduction pathway in iERM. METHODS: Immunofluorescence and confocal microscopy were carried out on deplasticized sections from 36 epiretinal membranes processed for electron microscopy and on frozen sections from five additional samples with antibodies against α-smooth muscle actin (αSMA), vimentin, glial fibrillary acidic protein (GFAP), SMAD2, HSP90α, type-II TGF-β1 receptor (TβRII), type-I collagen, and type-IV collagen. In addition, Müller MIO-M1 cells were transfected with HSP90 and challenged with TGF-β1. RESULTS: Double and triple labeling experiments showed that a variable number of TβRII(+) cells were present in 94.1% of tested iERMs and they were mostly GFAP(−)/αSMA(+)/vimentin(+)/HSP90α(+). In almost half of the cases these cells contained type-I collagen, suggesting their involvement in matrix deposition. HSP90 overexpressing MIO-M1 cells challenged with TGF-β1 showed increased levels of TβRII, SMAD2, SMAD3, and phosphor-SMAD2. Nuclear SMAD2 staining could be observed in HSP90α(+) cells on frozen sections of iERMs. CONCLUSIONS: Cells in iERMs that express TβRII are also HSP90α(+) and show the antigenic profile of myofibroblast-like cells as they are GFAP(−)/αSMA(+)/vimentin(+). HSP90α-overexpressing MIO-M1 cells challenged with TGF-β1 showed an increased activation of the SMAD pathway implying that HSP90α might play a role in sustaining the TGF-β1-induced fibrotic response of iERM cells.