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L.M. Tong, R. Corrales, Z. Chen, C.S. de Paiva, D.Q. Li, S.C. Pflugfelder; UVB Reduces Cornified Envelope Proteins and Barrier Function Through Transglutaminase and C–Jun N–Terminal Kinase Pathways in Human Corneal Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2112.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Stratified squamous epithelial cells assemble a specialized protective barrier structure on their periphery termed the cornified cell envelope (CE). This study evaluated the expression and regulatory signaling pathways of CE precusors (loricrin, involucrin and small proline–rich proteins [SPRR1A, 1B, 2A, 2B, 3 and 4]) and later envelope proteins (LEP1, 6, 16 and filaggrin) by human corneal epithelial cells in response to ultraviolet radiation (UVB). Methods: Primary epithelial cell cultures were grown from human cadaveric limbal explants. A uniform single dose (20 mJ/cm2) of UVB was employed. Gene expression was evaluated by semi–quantitative RT–PCR. Western blotting was performed using antibodies against transglutaminase (TG)–1 and phospho–c–Jun N–terminal kinase (p–JNK). The incorporation of fluorescein–cadaverine (FC), a TG substrate, was used to assess TG activity. The trans–epithelial electrical resistance (TER) was measured to evaluate the barrier function of corneal epithelial cells. Results: Among 12 CE proteins studied, 9 genes including involucrin, SPRR (1A, 1B, 2A, 2B and 3), LEP (1, 16) and filaggrin were expressed by human corneal epithelial cells. A single dose of UVB down–regulated SPRR (1A, 2A, 2B), LEP (1, 16) and filaggrin at 6 hours with reduced TER observed after 24 hours. UVB stimulated TG–1 production, which was detected only in the insoluble fraction of cell lysate, and FC incorporation in the cell membrane as early as 3 hours, as well as p–JNK within 1 hour. Monodansyl–cadaverine (MDC), a competititve TG inhibitor, reversed the UVB induced changes in mRNA expression of certain CE components (LEP1 and 16) and production of TG–1 protein. SP600125, a JNK inhibitor, opposed the stimulated TG–1 production and FC incorporation, as well as the reduced expression of SPRR1B and filaggrin by UVB. Either MDC or SP600125 restored the UVB reduced TER. Conclusions: These findings demonstrate for the first time that acute UVB stress reduces expression of cornified envelope proteins, such as SPRR1A, 2A, 2B, LEP1, 16 and filaggrin, and barrier function in human corneal epithelial cells. This effect is mediated by stimulated TG–1 and activated JNK signaling pathways, which could be potential therapeutic targets for ocular surface diseases.
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