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Eiji Tomoyori, Yuko Udaka, Mayumi Tsuji, Akiko Sasaki, Junichiro Kizaki, Katsuji Oguchi; Apoptosis-induced compensatory proliferation in the UV-irradiated human conjunctival epithelium cells. Invest. Ophthalmol. Vis. Sci. 2014;55(13):387.
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© ARVO (1962-2015); The Authors (2016-present)
Pterygium is a common eye disease characterized by the degeneration of fibrous connective tissue of the ocular surface with epithelial hyperplasia. Pterygum is usually not troublesome unless it grows large enough to cover cornea to interfere with vision. The exact cause of pterygium is not known. Possible causes of pterygium include too much exposure to ultraviolet (UV) light that can lead to these growths. UV irradiation generates the reactive oxygen species (ROS) and activates c-jun N- terminal kinase in the cells, both of which are known to induce apoptosis. We hypothesized that UV-induced apoptosis may trigger compensatory proliferation in surrounding cells to maintain tissue homeostasis. Therefore, we investigated into how activation of apoptosis is linked to the process of compensatory proliferation in the UV-irradiated human conjunctival epithelial (HCE) cells.
In this study, HCE cells were irradiated under UV (312 nm)-emitting lamps (4.94 mW/cm2, 100 mJ/cm2). After irradiation, HCE cells were analyzed to determine cell viability, apoptotic cells and cell cycle by Muse™ Cell Analyzer. We used CM-H2DCFDA, a cell-permeant indicator for ROS for the detection of ROS generated by UV irradiation. To determine compensatory proliferation, interleukin-11 (IL-11) was determined using an ELISA kit. To investigate the distribution of β-catenin in nuclei, β-catenin content in nuclear fraction was detected by ELISA and immunostaining for β-catenin was performed.
UV-irradiated cells that underwent apoptosis generated significantly higher levels of ROS, IL-11 and β-catenin after irradiation, compared with non-irradiated cells. After UV irradiation, the percentages of cells occupying the different phases of the cell cycle changed: cells in S and G2/M phases increased rather than cells in G0/G1 phase that are expected to result from apoptosis. In UV-irradiated cells, nuclear translocation of β-catenin levels increased. Staining for β-catenin showed negative results in non-irradiated cells, while high-level nuclear β-catenin staining was observed in UV-irradiated HCE cells.
These findings suggested that UV-induced apoptotic cells may have stimulated the compensatory proliferation of surrounding healthy cells to maintain homeostasis.
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