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T. Nakajima, T. R. Shearer, M. Azuma; Involvement of Calpain in Ionomycin-Induced Cell Death in Cultured Mouse Lens Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2610.
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© ARVO (1962-2015); The Authors (2016-present)
Calpains are calcium-dependent, intracellular, nonlysosomal, cysteine proteases. Activation causes proteolysis of several lens proteins. In rodent lenses, two calpains exist with differing distributions: ubiquitous calpain 2 is highest in lens epithelium, while tissue-preferred Lp82 is located in cortical and nuclear fibers. Lp82 is a major cause of lens opacities in rodent models. However, only limited information exists concerning the role of calpains in lens epithelium. Thus, the purpose of present experiment was to determine role of calpain 2 in lens epithelial cell death.
Mouse lens α-TN4 epithelial cells were cultured with calcium ionophore ionomycin to promote calcium influx. Activation of calpains was detected by casein zymography, immunoblotting for calpain fragments, and proteolysis of the calpain substrate α-spectrin. LDH release into the culture medium measured cell death.
Calpain 2, and lower levels of calpain 1, were detected in mouse lens epithelial cells. Ionomycin induced leakage of LDH from mouse lens epithelial cells, indicating cell death due to calcium influx. Activation of calpain 2 and proteolysis of α-spectrin were associated with cell death. Calpain inhibitor SNJ1945 significantly inhibited the metabolic effects caused by ionomycin.
Ubiquitous calpain 2 was involved in lens epithelial cell death. Lens epithelial cells are important for maintaining lens transparency. Our data suggest that proteolysis by calpain 2 in lens epithelium could contribute to rodent cataract formation, in addition to the activation of Lp82 in nuclear fibers.
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