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(Investigative Ophthalmology and Visual Science. 2008;49:539-549.)
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.07-0569
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Hyperosmolarity-Induced Cornification of Human Corneal Epithelial Cells Is Regulated by JNK MAPK

Zhuo Chen,1 Louis Tong,1,2 Zhijie Li,3 Kyung-Chul Yoon,1,4 Hong Qi,1,5 William Farley,1 De-Quan Li,1 and Stephen C. Pflugfelder1

1From the Department of Ophthalmology, The Ocular Surface Center, Cullen Eye Institute, and the 3Leukocyte Biology Section, Department of Pediatrics, Baylor College of Medicine, Houston, Texas; the 4Department of Ophthalmology, Chonnam National University Medical School, Gwangju, Korea; the 2Singapore National Eye Center; Singapore Eye Research Institute, Singapore; and the 5Peking University Eye Center, Peking University Third Hospital, Beijing, China.

PURPOSE. To evaluate the effects of hyperosmolar stress on expression of cornified envelope (CE) precursors and transglutaminases (TGs) by primary cultured human corneal epithelial (PCHCE) cells and the regulatory effects of JNK MAPK on this process.

METHODS. Expression of CE precursors and TGs were evaluated in PCHCE cells exposed to media of increasing osmolarity (350–450 mOsM) for 24, 48, and 72 hours. JNK1 and -2 MAPKs were inhibited by addition of short interfering (si)RNA. Relative levels of mRNA transcripts and proteins were evaluated. TG activity, cell viability, and apoptosis were detected in PCHCE cells, with or without siRNA-JNKs.

RESULTS. Exposure of PCHCE cells to hyperosmolar medium increased TG activity at 3 hours, levels of the CE precursors SPRR1b and -2a and membrane-associated TG1 mRNA at 6 hours, and tissue-type TG2 mRNA at 24 hours. Osmotic stress decreased corneal epithelial cell viability, which was due in part to stimulation of apoptosis and cornification death. Inhibiting JNK2 production by siRNA in osmotically stressed PCHCE cells prevented the stimulation of SPRR and membrane-associated TG1 production and TG activity, and improved cell viability, whereas inhibition of JNK1 prevented early apoptosis.

CONCLUSIONS. Osmotic stress promotes production of certain CE proteins and cross-linking membrane-associated TG1 and decreases cell viability via JNK MAPK-mediated pathways. Strategies that inhibit JNK production downregulate the cornification response of PCHCE cells 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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