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L. Z. Chen, L. Tong, K. C. Yoon, H. Qi, D.-Q. Li, S. C. Pflugfelder; Hyperosmolarity Induced Cornification in Human Corneal Epithelial Cells is Regulated by JNK MAPK. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3491.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effects of hyperosmolar stress on expression of cornified envelope precursors (CE) and transglutaminases (TG) by primary cultured human corneal epithelial cells (PCHCE) and the regulatory effects of JNK MAPK on this process.
Expression of CE precursors (involucrin, SPRR 1 and 2), and TG 1 and 2 were evaluated in PCHCE exposed to media of increasing osmolarity (350 - 450 mOsm), generated by addition of sodium chloride, for 24, 48 and 72 hours. JNK 1 and 2 MAPK was inhibited by addition of short interfering RNA (siRNA). Relative levels of mRNA transcripts were compared by real-time PCR. Levels of CE precursor proteins were evaluated by immunofluorescent laser scanning confocal microscopy and western blot. An immunobead assay measured total levels of JNK. TG activity was detected by fluorescein cadaverine. Cell viability was assessed by an MTT assay and apoptosis was detected by TUNEL and annexin A5 staining and flow cytometry.
Exposure of PCHCE to hyperosmolar media increased TG activity by 3 hours, levels of CE precursors SPRR1b and 2a and TG1 mRNA by 6 hours and TG2 mRNA by 24 hours. Levels of SPRR2 protein in 24 hour cultures positively correlated with media NaCl concentration. Osmotic stress decreased corneal epithelial cell viability, which was due in part to stimulation of apoptosis. Inhibition of JNK production by siRNA in osmotically stressed corneal epithelial cells prevented the stimulation of SPRR and TG1 production and TG activity and improved cell viability; however, it did not inhibit apoptosis.
Osmotic stress promotes production of certain CE proteins and cross-linking TG 1, and decreases cell viability via JNK MAPK mediated pathways. Strategies that inhibit JNK production blunt the cornification response of the corneal epithelium to osmotic stress. These findings have potential therapeutic implications for preventing cornification of the corneal epithelium in response to the hyperosmolar tear film in dry eye disease.
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