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ORIGINAL RESEARCH ARTICLE

Apoptotic and Necrotic Mechanisms of Stress-Induced Human Lens Epithelial Cell Death

Amy C. Long^*, Carmen M. H. Colitz and Joshua A. Bomser^*,,1

^* OSU Interdisciplinary PhD Program in Nutrition, College of Veterinary Medicine, and Department of Human Nutrition, The Ohio State University, Columbus, Ohio 43210

To whom requests for reprints should be addressed at ¹ 325 Campbell Hall, 1787 Neil Avenue, The Ohio State University, Columbus, OH 43210. E-mail: bomser.1{at}osu.edu

Exposure to ultraviolet radiation (UVR) and reactive oxygen species (ROS) can damage the human lens and contribute to cataract formation. Recent evidence suggests that apoptosis in lens epithelial cells (LEC) is an initiating event in noncongenital cataract formation in humans and animals. The present study examines the cellular and molecular mechanisms by which environmental (ultraviolet B [UVB]) and chemical (hydrogen peroxide [H₂O₂], t-butyl hydroperoxide [TBHP]) stress induces cell death in an SV-40 immortalized human lens epithelial (HLE) cell line. Treatment of HLE cells with UVB, H₂O₂, and TBHP significantly decreased cell density with LD50 values of 350 J/m², 500 µM, and 200 µM, respectively. Cellular morphology, DNA fragmentation, and annexin/propidium iodide staining consistent with apoptosis was observed only in UVB-treated cells, whereas lactate dehydrogenase (LDH) release was significantly higher in H₂0₂- and TBHP-treated cells. In addition, activation of apoptotic stress-signaling proteins, including c-Jun NH2-terminal kinase (JNK), caspase-3, and DNA fragmentation factor 45 (DFF45) was observed only in UVB-treated cells. Inhibition of JNK activity increased UVB-induced cell death, suggesting that this pathway may serve a prosurvival role in HLE cells. These findings suggest UVB predominantly induces apoptosis in HLE cells, whereas H₂O₂ and TBHP induce necrosis.

Key Words: ultraviolet radiation • human lens epithelial cells • apoptosis • necrosis • mitogen-activated protein kinases