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N. Kato, S. Shimmura, T. Kawakita, H. Miyashita, S. Yoshida, K. Tsubota; Ultraviolet-A Exposure Induces Epithelial-Mesenchymal Transition-Like Changes in Cultured Corneal Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6312.
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We previously reported epithelial cells at the leading edge of pterygial head showed epithelial-mesenchymal transition (EMT) (Kato et al, IOVS 2007), a well-known phenomenon that epithelial cells loose their epithelial characteristics and simultaneously upregulate mesenchymal markers. Since pteryium is known to correlate with cumulative ultraviolet exposure on the corneal limbus, we speculated that oxidative stress generated by ultraviolet exposure may induce EMT in the pterygial epithelium. Furthermore, we showed cultured corneal epithelial cells expressed the characteristics of EMT when exposed to extrinsic oxidative stress, hydrogen peroxide or buthionine sulfoxide (Kato et al, 2008 ARVO meeting). In the present study, we assessed the characteristical changes of the corneal epithelial cells after UVA irradiation.
TKE2 cells (mouse corneal epithelial cell line) were cultured in 5% CO2 at 37oC using the defined KSFM medium. When the cells grew semi-confluent, cells were irradiated with 25 mJ of UVA (370 nm). The elevation of EMT-related factors was assessed by RT-PCR and immunofluorescence.
UVA exposed cells revealed dissociated interceller junctions and elongated cell contour. RT-PCR showed upregulation of a transcription factor, snail in the cells exposed to UVA. mRMA of vimentin, a representative mesenchymal marker, and matrix metalloproteinase (MMP)-9 was also upregulated. Immunofluorescence showed decline of membrane staining and increase of cytoplasmic staining of β-catenin, and upregulation of MMP-9 in the UVA-exposed cells.
UVA irradiation induced EMT-like changes in cultured corneal epithelial cells, which were similar to that seen by the oxidative stress. The present results may indicate that intracellular oxidative stress generated by ultraviolet irradiation may cause EMT in the pathogenesis of pterygium.
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