| 20042656 |
Tamiya S, Liu L, Kaplan HJ: Loss of cell-cell contact initiates epithelial-mesenchymal transition and proliferation of retinal pigment epithelial cells. Invest Ophthalmol Vis Sci. 2009 Dec 30.
Purpose. Molecular mechanisms that initiate epithelial-mesenchymal transition (EMT) involved in ocular fibrotic complications remain elusive. Studies were conducted to examine the role of cell-cell contact in regulating EMT and proliferation of retinal pigment epithelial (RPE) cells. Methods. Porcine RPE cells were isolated as sheets and cultured in vitro on lens capsule. Cell morphology was examined by microscopy. Western blotting and immunostaining were used to follow protein expression. Cell proliferation and RPE function were assessed by BrdU incorporation and a phagocytosis assay, respectively. Results. RPE cells in the center of the sheet maintained cell-cell contacts and retained a differentiated phenotype. Disruption of cadherin function in these cells resulted in loss of cell-cell contact and concomitant induction of mesenchymal marker protein expression and cell proliferation. RPE cells at the edge of the sheet migrated away from the sheet, underwent EMT and initiated proliferation which was accompanied by a switch in cadherin expression from P-cadherin to N-cadherin. While TGF-beta is thought to be a classic inducer of EMT, it was unable to initiate EMT in RPE cells maintaining cell-cell contact. However, change to alpha-SMA positive myofibroblasts was induced by TGF-beta in cells that had already undergone EMT. Conclusions. EMT and the onset of proliferation in RPE cells is initiated by loss of cell-cell contact. TGF-beta cannot initiate EMT or proliferation of RPE cells maintaining cell-cell contact but appears to play an important secondary role downstream of EMT in inducing transition to a myofibroblast phenotype--a phenotype linked to the development of fibrotic complications. |
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