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J. Qu, W. Huang, C. L. Grosskreutz; Calpain is Activated in Retinal Ganglion Cells in Experimental Glaucoma. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6097.
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© ARVO (1962-2015); The Authors (2016-present)
Calpain is a calcium-activated cystein protease that is involved in many neurodegenerative diseases. We previously demonstrated that calpain was activated in glaucomatous eyes, but it is still unknown in which retinal cell type calpain is activated. We hypothesize that calpain is activated in retinal ganglion cells (RGCs) in experimental glaucoma. Spectrin is a cytoskeletal protein located on the intracellular side of the plasma membrane. It can be cleaved by both calpain and caspase-3. Using antibodies that recognize specific spectrin cleavage products, we performed Western blot analysis and immunohistochemistry to study the activation and localization of calpain in a rat experimental glaucoma model.
Ocular hypertension was induced by injecting hypertonic saline into rat episcleral veins. Some animals were retrograde-labeled with Fluorogold to identify RGCs. Retinal protein was collected for Western blot. Eye cups were sectioned for immunohistochemistry. Two antibodies against different spectrin cleavage products were used. One recognized both the calpain-cleaved 145 kDa fragment and the caspase-cleaved 120 kDa fragment; the other antibody was specific to the calpain-cleaved 150 kDa fragment.
By Western blot, comparing to the control eyes, eight of eleven glaucomatous eyes had increases in calpain-cleaved 145 kDa band (Fisher’s exact test: p < 0.05) and seven had increases in caspase-cleaved 120 kDa band (not significant). In immunohistochemistry, the calpain-cleaved 150 kDa fragment was more abundant in the glaucomatous eyes than in the control eyes in three of four animals. The increase was mainly seen in the ganglion cell layer, but was also present in the inner plexiform layer and in the inner nuclear layer. Fluorogold retrograde labeling indentified the calpain-cleaved 150 kDa fragment in the RGC cytoplasm and primary dendrites.
Spectrin was cleaved by both calpain and caspase-3 in glaucomatous eyes. Using an antibody that selectively recognizes the calpain-cleaved spectrin fragment, we showed that calpain was activated specifically in RGCs in experimental glaucoma.
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