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Barbara Murienne, Harry Quigley, Thao Nguyen; The role of glycosaminoglycans in the mechanical behavior of the posterior sclera. Invest. Ophthalmol. Vis. Sci. 2013;54(15):52. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the role of glycosaminoglycans (GAGs) in the mechanical behavior of the posterior sclera.
The posterior sclera from 6-9 months old pig eyes was dissected within 72 hours of enucleation. Mechanical testing was performed through a series of pressure-controlled load-unload and ramp-hold tests (Myers et al., Acta Biomater., 2010). 3D digital image correlation was used to calculate the full-field surface displacements and analytical methods were developed to calculate circumferential and longitudinal strains. Each scleral cup was tested before and after overnight treatment at 37°C with Chondroitinase ABC at 2 units/ml in a modified Tris buffer at pH 8.0 (Sigma). Sulphated GAG (sGAG) removal was assessed quantitatively using the Blyscan assay (Biocolor) after sample digestion with Papain (Boubriak et al., Exp Eye Res., 2003). Student’s t-test was used for statistical analysis.
Preliminary results suggest that removing GAGs accelerates the creep and recovery rates (Fig. 1), increases tissue extensibility but has no noticeable effect on the stiffness of the loading curve. Assessment of sGAG removal showed a 57.7 ± 9.2% mean decrease in sGAG content after treatment with Chondroitinase ABC (n=4, p<0.01, Fig. 2). Experiments using DPBS instead of Tris buffer to rinse the samples showed a much higher decrease in sGAG content (94.6 ± 0.83%, n=4, p<0.01), suggesting that even if in average 57.7% sGAGs are extracted out of the tissue using Tris buffer, at least 94% are disconnected from their environment.
Changes in GAG levels may contribute to the observed myopia-related (Phillips et al., Invest Ophthalmol Vis Sci., 2000) or glaucoma-related (Coudrillier et al., Biomech Model Mechanobiol., 2012) changes in the viscoelastic behavior of the sclera.
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