Heat shock protein (HSP)90 involvement in the development of idiopathic epiretinal membranes

Purpose This work was aimed to further characterize cells of idiopathic epiretinal membranes (iERMs). In particular, we wanted to determine the contribution of 90-kDa heat shock protein (HSP90) to sustain the TGF-β-mediated signal transduction pathway in iERM. Methods Immunofluorescence and confocal microscopy were carried out on de-plasticized sections from 36 epiretinal membrane processed for electron microscopy and on frozen sections from 5 additional samples with antibodies against α-smooth muscle actin (αSMA), vimentin, GFAP, SMAD2, HSP90α, type-II transforming growth factor β (TGFβ)-1 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 labelling 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 cases these cells contained type-I collagen suggesting their involvement in matrix deposition. HSP90 over-expressing 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-over-expressing 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.