FGF-2 Differentially Regulates Lens Epithelial Cell Behaviour during TGF-β-Induced EMT

Fibroblast growth factor (FGF) and transforming growth factor-beta (TGF-beta) can regulate and/or dysregulate lens epithelial cell (LEC) behaviour, including proliferation, fibre differentiation, and epithelial-mesenchymal transition (EMT). Earlier studies have investigated the crosstalk between FGF and TGF-beta in dictating lens cell fate, that appears to be dose dependent. Here, we tested the hypothesis that a fibre-differentiating dose of FGF differentially regulates the behaviour of lens epithelial cells undergoing TGF-beta-induced EMT. Postnatal 21-day-old rat lens epithelial explants were treated with a fibre-differentiating dose of FGF-2 (200 ng/mL) and/or TGF-beta 2 (50 pg/mL) over a 7-day culture period. We compared central LECs (CLECs) and peripheral LECs (PLECs) using immunolabelling for changes in markers for EMT (alpha-SMA), lens fibre differentiation (beta-crystallin), epithelial cell adhesion (beta-catenin), and the cytoskeleton (alpha-tropomyosin), as well as Smad2/3- and MAPK/ERK1/2-signalling. Lens epithelial explants cotreated with FGF-2 and TGF-beta 2 exhibited a differential response, with CLECs undergoing EMT while PLECs favoured more of a lens fibre differentiation response, compared to the TGF-beta-only-treated explants where all cells in the explants underwent EMT. The CLECs cotreated with FGF and TGF-beta immunolabelled for alpha-SMA, with minimal beta-crystallin, whereas the PLECs demonstrated strong beta-crystallin reactivity and little alpha-SMA. Interestingly, compared to the TGF-beta-only-treated explants, alpha-SMA was significantly decreased in the CLECs cotreated with FGF/TGF-beta. Smad-dependent and independent signalling was increased in the FGF-2/TGF-beta 2 co-treated CLECs, that had a heightened number of cells with nuclear localisation of Smad2/3 compared to the PLECs, that in contrast had more pronounced ERK1/2-signalling over Smad2/3 activation. The current study has confirmed that FGF-2 is influential in differentially regulating the behaviour of LECs during TGF-beta-induced EMT, leading to a heterogenous cell population, typical of that observed in the development of post-surgical, posterior capsular opacification (PCO). This highlights the cooperative relationship between FGF and TGF-beta leading to lens pathology, providing a different perspective when considering preventative measures for controlling PCO.