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J Zurdel, V Zubaty, RM Nitsch, G Richard; Immunohistochemical Analysis of Cystatin C in Age-related Macular Degeneration . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2783.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To compare the expression pattern of cystatin C in RPE cells in early ARMD and in CNV membranes of late ARMD. Cystatin C is a protease inhibitor mainly localized to the RPE and is involved in the regulation of cathepsins in RPE cells. A polymorphism of the cystatin C gene CST3 is associated with exudative ARMD. Methods:10 macular sections were obtained from donor eyes. 17 CNV membranes were removed using a standard three port vitrectomy. Tissues were fixated, embedded in parrafin, and dissected into 4µm layers. Sections then deparrafinized, stained in diluted (1:400) cystatin C primary antibody and were subsequently visualized using a labelled streptavidine-biotine secondary antibody. Results were evaluated using a semiquantitative scale to compare cystatin C immunostaining of RPE cells. A-cells of pancreas served as positive controls. Negative controls included omission of the primary antibody and preabsorption of the primary antibody with an excess of recombinant cystatin C. Results:Cystatin C was present in macular sections and in all CNV membranes. No negative control showed any immunostaining. Assessment of cystatin C distribution in CNV membranes showed the strongest immunostaining in the vicinity of included RPE cells which were surrounded by intense amounts of secreted cystatin C. Semiquantitative evaluation of macular sections in early ARMD revealed high concentrations of cystatin C in the RPE layer but staining was confined to the RPE layer and no secretory mechanism could be detected. No traces of cystatin C deposits were found in drusen. Significant amounts of cystatin C were also detected in the layer of the photoreceptor outer and inner segments and in the nerve fiber layer. Macular sections of young control patients were similar to early ARMD. Conclusion:Our results support other studies demonstrating that cystatin C is mainly localized to the RPE in macular sections. It does not accumulate in drusen. In CNV membranes, RPE cells actively secrete high amounts of cystatin C into the matrix tissue suggesting activation of these cells. Our results therefore support the idea that an altered balance between proteases and protease inhibitors may contribute to the progression of ARMD. Further investigation on cultured RPE cells is under way to obtain quantitative data on cystatin C secretion depending on donor age, diagnosis of ARMD and polymorphism of the cystatin C gene CST3.
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