Growth factor modulation of TGF-beta (TGF-β)-induced epithelial-to-mesenchymal transition (EMT) in the eye lens

Abstract

The eye lens is a transparent organ dependent on growth factors within the ocular media (e.g. FGF) to regulate its normal functionality. During stress &/or inflammation, activation of cytokine TGF-β disrupts normal lens cell processes & the epithelial cell phenotype due to epithelial reorganisation of cytoskeletal proteins (e.g. Tpm). TGF-β promotes an epithelial-mesenchymal transition (EMT) leading to lens fibrosis (cataracts) namely ASC or secondary cataracts (PCO). In situ, ASC & PCO both present differential cell types (myofibroblastic or fibre-like) that are induced/maintained by ocular growth factors. This thesis examines the interactions between FGF-2 & TGF-β2 during rodent lens EMT & targets specific molecules involved in TGF-β downstream signalling that regulate lens cell behaviour during fibrosis. We investigate the role of Tpms in cataractogenesis using in vivo postnatal lenses from wild type & an overexpressing TGF-β1 transgenic mouse line that develops ASC postnatally. We established a potential model for ASC & PCO in vitro given FGF-2+TGF-β2 cotreated rat lens epithelial cell (LEC) explants led to a heterogenous lens cell population that were differentially regulated in a dose-dependent manner. We identified several Tpms as potential markers for lens fibre differentiation &/or TGF-β-induced EMT in LECs, fibre-like cells & myofibroblasts. We characterise Tpm3.1/3.2 & Tpm4.2 deficient mouse models and use pharmacological compounds targeting Tpm3.1/3.2 to further elucidate their role during TGF-β-induced lens EMT. We examine TGF-β-activated downstream signalling protein p38α MAPK & revisit its role during lens EMT. We showed inhibition of p38α impacted morphological changes during TGF-β-induced EMT. The present study demonstrates the importance of understanding how the lens is dysregulated during lens pathology. Targeting specific signalling molecules & cytoskeletal mechanisms in rodent lenses may lead to finding new treatments for fibrotic cataract.