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Zeev Dvashi, Mordechai Goldberg, Ayala Pollack, ; TGF-β1 Induced Epithelial-Mesenchymal Transition in RPE cell is Mediated by TAK-1 Activation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1093.
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Proliferative vitreoretinopathy (PVR) is a scarring process that develops as a complication during retinal detachment (RD), accompanied by formation of fibrotic tissue and it is the most common cause of RD failure. Retinal pigment epithelial (RPE) cells regulates the development of the fibrotic tissue during PVR. RPE cells are quiescent and differentiated cells, however upon RD and the break of the blood-retina barrier, RPE cells are exposed to a variety of cytokines and growth factors. Upon this exposure the RPE cells undergo epithelial-mesenchymal transition (EMT) characterized by enhanced expression of α-smooth muscle actin, secretion of chemokines and cytokines, increased cell motility and production of extracellular matrix components. Transforming growth factor-β1 (TGF-β1) plays a key role in EMT of RPE cells. In this study we examined the effect of inhibition of the canonical and non-canonical pathways of TGF-β1 on EMT of RPE cells.
ARPE-19 Cells were treated with 5Z-7 oxozeaenol [transforming growth factor beta-activated kinase 1 (TAK-1) inhibitor] or SB431542 (TGF-β1 receptor kinase inhibitor) followed by TGF-β1 (5 ng/ml) stimulation for all experiments. Immunofluorescence assays examined: phospho-p38, α-SMA, E-cadherin and stress fiber assembly and subcellular distribution. Cell migration was determined using scratch assay. Cell contractility was examined using collagen contraction assay. Real time PCR assessed the transcription of pro inflammatory factors.
Stimulation of RPE cells with TGF-β1 increase α-SMA expression, cell migration, contractility and the transcription of CTGF (connective tissue growth factor) and collagen type 1, all are EMT features. However, addition of TAK-1 inhibitor abolishes all these processes. Moreover, while TGF-β1 treatment reduced E-cadherin expression during the EMT process addition of TAK-1 inhibitor halt this process and maintains the naive form of the cells.
This study demonstrates TAK-1, the non-canonical pathway of TGF-β1, as a key player in the EMT process and in the homeostasis of RPE cells. The ability to halt the process of EMT in RPE cells may reduce the severity of the fibrotic response that occurs upon PVR, leading to a better prognosis and increase the probability of success in RD
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