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PN Bishop, DF Holmes, KE Kadler, D McLeod, K Bos; Vitreous Collagen Fibrils Lose Type IX Collagen and Other Surface Macromolecules During Ageing, thus Predisposing to Fibrillar Aggregation and Vitreous Liquefaction . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2460.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Vitreous collagen fibrils are heterotypic and composed of cross-linked collagens, including types II, V/XI and IX. In addition, they possess a surface coating of non-covalently bound structural macromolecules including opticin. Type II collagen is sticky and if exposed on the fibril surfaces may allow the lateral aggregation of adjacent fibrils. Here we investigate the hypothesis that there is an age-related loss of surface components resulting in increasing exposure of type II collagen on the fibril surfaces. Methods: Vitreous collagen fibrils were isolated from the eyes of 24 subjects with an age-range of 3 to 90 years old. The collagen fibrils were analysed by (a) scanning transmission electron microscopy to determine mass per unit length, before and after the removal of non-covalently bound macromolecules (using 1.5 M guanidine hydrochloride), or by transmission electron microscopy after (b) staining with Cupromeronic Blue in 0.2 M MgCl2, (c) labelling with type IX collagen antibodies or (d) labelling with type II collagen antibodies. Results: With increasing age there is a progressive loss of type IX collagen and non-covalently bound macromolecules from the fibril surfaces. Concomitantly, there is increasing exposure of type II collagen on the fibril surfaces with age. Conclusion: Type IX collagen and/or non-collagenous structural macromolecules shield type II collagen from exposure on the fibril surfaces. This insulating layer is lost with age resulting in the exposure of type II collagen. The exposed type II collagen on adjacent fibrillar surfaces will, on contact between the fibrils, allow irreversible aggregation. Collagen fibrillar aggregation results in vitreous liquefaction and thereby predisposes to posterior vitreous detachment.
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