Abstract
PurposeIn this study, we measured the effect of the removal of sulfated glycosaminoglycans (sGAGs) on the pressure-induced strains of the human lamina cribrosa (LC).MethodsWe applied an ex vivo inflation method to measure the three-dimensional (3D) deformation response of six human LCs to pressure, before and after the degradation of chondroitin and dermatan sulfates. The experiment used a laser-scanning microscope (LSM) to acquire the second harmonic generation (SHG) signal of the collagen structure in the LC. Digital volume correlation (DVC) was used to calculate the deformation in the LC after a change in pressure from 5 to 45 mm Hg.ResultsThe average strains between 5 and 45 mm Hg in the LC decreased significantly after sGAG degradation (P ≤ 0.03), with the greatest change occurring in regions of previously high strain (P ≤ 0.003) and the peripheral regions of the LC (P ≤ 0.02). The stiffening effect was greater in the LC of middle-aged (42–49 years) donors compared with those of older (64–88 years) donors (P < 0.0001).ConclusionsThe LC experienced less strain at the same pressures after most sGAGs were removed. These results suggest that the natural decrease in sGAGs within the LC with age may contribute to the stiffer inflation response of older LC to IOP. Likewise, the increase in the amount of sGAGs observed in the LC of glaucomatous eyes, may contribute to a more compliant LC, which may affect the susceptibility and progression of axon damage.
Highlights
The average strains between 5 and 45 mm Hg in the lamina cribrosa (LC) decreased significantly after sulfated glycosaminoglycans (sGAGs) degradation (P 0.03), with the greatest change occurring in regions of previously high strain (P 0.003) and the peripheral regions of the LC (P 0.02)
The LC experienced less strain at the same pressures after most sGAGs were removed. These results suggest that the natural decrease in sGAGs within the LC with age may contribute to the stiffer inflation response of older LC to IOP
The PGs in the LC contain sulfated glycosaminoglycans as a side chain, which occur in three varieties in the LC: chondroitin and dermatan sulfates, which are found near collagen fibrils, and heparan sulfate, which is found in the basal laminae of astrocytes and blood vessels.[4]
Summary
We applied an ex vivo inflation method to measure the three-dimensional (3D) deformation response of six human LCs to pressure, before and after the degradation of chondroitin and dermatan sulfates. Each sample was cut into two parts of size one-fourth and threefourths, creating two samples from each area. Both the large and the small samples from each area were weighed after blotting dry on Whatman paper, using a precision balance (XP26DR; Mettler-Toledo LLC, Columbus, OH, USA). SGAG content per wet tissue weight was assessed in the larger sample using the Blyscan assay (Accurate Chemical and Scientific Corporation, Westbury, NY, USA) and the protocol described by Boubriak et al.[41] The smaller samples were dehydrated at 608C for 48 hours and weighed in the same manner as before. The thickness at eight locations in the sclera before and after buffer and enzyme treatment was measured using a custom ultrasonic device, as described in Murienne et al.,[40] for the LE and RE specimens (Supplementary Material S4; Supplementary Table S4)
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