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H Yan, YN Hui, MY Li, JJ Harding; Comparative Study of Chaperone Activity of A-crystallin with Different Assays in Human Age-related Cataract . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3559.
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Purpose: A decrease in molecular chaperone activity of a-crystallin has been implicated in possible mechanisms of cataract formation. We investigated the effects of ageing and the different grade opacity on chaperone activity of a-crystallin in human age-related cataractous lenses by using four different assays. Methods: a-Crystallin was isolated from human age-related cataractous lenses (45-64 and 65-85 years, nuclei only; Grade II or IV Pirie Scale) and clear human lenses (25-35 years) by size-exclusion chromatography on Sephacryl S-300 HR respectively. The chaperone activity of a-crystallin was assessed spectrophotometrically by using the aggregation assays of catalase and bL-crystallin, and the inactivation of catalase assays by glycation and heat. Results: The protective ability in the cortex was greatly higher than in the nucleus of clear lenses, and that of aH-crystallin was less than that of aL-crystallin in both cortex and nucleus. Both aH- and aL-crystallin from cataractous lenses have a markedly reduced chaperone ability compared to those from clear lenses by four methods. There was a remarkable decrease of chaperone activity of aL-crystallin in cataractous lenses with significant differences between under 65 years and over 65 years old group in grade IV, and between grade II and grade IV in over 65 years group, whereas aL-crystallin showed no statistically change in the under 65 years group between grade II and grade IV, and between under 65 years and over 65 years old group in grade II. However, the preventive ability of both aH- and aL-crystallin from the over 65 years group in grade IV was diminished as shown by aggregation assays and glycation-induced inactivation of catalase assay. The inactivation by heat assay did not provide statistically differences in chaperone activity with ageing and the grade of opacity in two groups although the protection by a-crystallin presented a parallel type of activity with four different methods. The thermal aggregation of catalase was much more effective than its thermally and glycation-induced inactivation. Conclusion: Chaperone activity of aL-crystallin in human cataractous lenses decreased with age and opacity, whereas the protective effect of aH-crystallin showed no such a fashion. Post-translational modification may result in the formation of aggregated proteins with ageing. Present: Nuffield Lab.of Ophthalmology, University of Oxford, UK.
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