Abstract
Purpose: :
Epithelial-mesenchymal transition (EMT) is characterized by loss of epithelial phenotype and the gain of mesenchymal characteristics in epithelial cells and occurs during embryogenesis, wound healing, and inflammatory fibrotic diseases including proliferative vitreoretinopathy (PVR). Recent studies suggest that EMT induced in retinal pigment epithelial cells (RPE) promotes excess extracellulat matrix (ECM) production and cell-cell contact abnormality, which is associated with pathological status of PVR. This study was conducted to establish a model of EMT in RPE cells (ARPE-19), using proinflammatory cytokine TNF-α and TGF-β2 and to evaluate the contribution of Hyaluronan (HA)/ CD44/ ERM proteins complex to EMT.
Methods: :
ARPE-19 cells were cultured and stimulated with TNF-α or TGF-β2. Morphological changes were photographed by phase-contrast microscopy and the expression of mesenchymal markers (α-SMA and fibronectin) and epithelial marker (cytokerain18) were examined by Western blot analysis. Status of adherens junctions were observed by immunofluorescence. Wound healing assays were performed to assess migration.
Results: :
We show that TNF-α stimulation induces EMT in ARPE-19 cells. TNF-α-stimulated ARPE-19 cells accelerate to produce ECM including HA and fibrous proteins and cell migration. Mesenchymal markers are upregulated and epithelial marker is decreased in the presence of TNF-α. TNF-α treatment elicited phosphorylation of ERM proteins through PKC activation. Activated ERM proteins, especially Moesin interacts with CD44, leading to actin cytoskeleton remodeling and disruption of cell-cell contact, which are earlier events during process of EMT. Moreover, the formation of HA-CD44-ERM complex is associated with continuous ERK activation, which is essential for maintenance of EMT.
Conclusions: :
Elucidation of underlying mechanisms of TNF-α-induced EMT may allow us to identify new strategies for treatment of PVR and other inflammatory eye diseases.
Keywords: EMT (epithelial mesenchymal transition) • extracellular matrix • inflammation