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Y. Tamada, T.R. Shearer, M. Azuma; Contribution of Calpain to Retinal Pigment Epithelial Cell Damage in Age–Related Macular Degeneration . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1373.
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© ARVO (1962-2015); The Authors (2016-present)
Age–related macular degeneration (AMD) is one of the leading causes for loss of vision. AMD showed dysfunction of the retinal pigment epithelium (RPE). However, the mechanism for dysfunction in RPE has not been clarified. The purposes of the present studies were to determine 1) if calpain activation occurred in RPE from AMD patients and 2) if calpain activation contributed to damage of human RPE in a cell culture model of AMD.
Calpain activities in soluble proteins from the RPE in AMD patients were analyzed by casein zymography. Human primary RPE cells were also cultured with zinc chelator TPEN since zinc deficiency is a suspected risk factor for AMD. TUNEL staining was performed to detect apoptosis, and leakage of LDH into the medium was measured as a marker for RPE cell damage. Activation of calpains and proteolysis of the known calpain substrate α–spectrin were assessed by immunoblotting. To confirm contribution of calpain, calpain inhibitor SJA6017 was also tested.
Casein zymography showed that activity of calpain 2 in RPE was lower in AMD patients compared to control. Decreased calpain activity has been interpreted as indirect evidence of calpain activation due to autodegradation. Calpain 2 activity did not change during aging in normal adults. TPEN caused RPE cell damage with positive TUNEL staining. TPEN also caused leakage of LDH into the medium from RPE cells, and calpain inhibitor SJA6017 inhibited the leakage. Immunoblotting for calpain and α–spectrin showed activation of calpain in RPE cells cultured with TPEN.
These results suggest that activation of calpain could possibly contribute to cellular damage in RPE cells from AMD patients, and calpain inhibitor is a possible candidate for testing as part of drug therapy for AMD.
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