The Ordering of Corneal Collagen Fibrils with Increasing Ionic Strength

Regini, Justyn Wiktor; Elliott, G.F.; Hodson, Stuart

doi:10.1016/j.jmb.2003.12.001

Cited by 16 publications

(14 citation statements)

References 19 publications

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“…3 3-D electron microscope reconstruction of the arrangement of proteoglycans stained with Cuprolinic blue dye (yellow) and collagen fibrils in cross-section (blue) in the bovine cornea (courtesy of Dr. C. Knupp and Dr. P. Booth) maintenance of fibrillar order. Transparency of the corneal stroma has been shown to be crucially dependent on the concentration of the ambient ion (Kostyuk et al 2002), and Regini et al (2004) showed that increasing the ionic strength (up to physiological levels) improves fibril ordering significantly, in agreement with the transparency data. It is believed that as the NaCl concentration is increased, chloride ions increasingly bind to the collagen fibrils (Elliott and Hodson 1998) and the fibrils become more and more electronegative, giving rise to extra repulsion between fibrils and leading to a higher level of ordering.…”

Section: Regulators Of Fibril Diameter and Spacingsupporting

confidence: 64%

Corneal collagen—its role in maintaining corneal shape and transparency

2009

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Corneal collagen has a number of properties that allow it to fulfil its role as the main structural component within the tissue. Fibrils are narrow, uniform in diameter and precisely organised. These properties are vital to maintain transparency and to provide the biomechanical prerequisites necessary to sustain shape and provide strength. This review describes the structure and arrangement of corneal collagen from the nanoscopic to the macroscopic level, and how this relates to the maintenance of the form and transparency of the cornea.

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Section: Regulators Of Fibril Diameter and Spacingsupporting

confidence: 64%

Corneal collagen—its role in maintaining corneal shape and transparency

2009

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“…The average center-to-center collagen interfibrillar Bragg spacing and average collagen fibril diameter were calculated, respectively, from the positions of the firstorder equatorial x-ray reflection and the position of the first subsidiary maximum as described by Meek and Quantock (25). The angular width of the first-order equatorial (i.e., interfibrillar) reflection was used to obtain an appreciation of the degree of local order in the fibrillar array by calculating the coherence distance as described by Regini and associates (26).…”

Section: Methodsmentioning

confidence: 99%

Matrix morphogenesis in cornea is mediated by the modification of keratan sulfate by GlcNAc 6- O -sulfotransferase

Hayashida

Akama

Beecher

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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Matrix assembly and homeostasis in collagen-rich tissues are mediated by interactions with proteoglycans (PGs) substituted with sulfated glycosaminoglycans (GAGs). The major GAG in cornea is keratan sulfate (KS), which is N-linked to one of three PG core proteins. To ascertain the importance of the carbohydrate chain sulfation step in KS functionality, we generated a strain of mice with a targeted gene deletion in Chst5, which encodes an N-acetylglucosamine-6-O-sulfotransferase that is integral to the sulfation of KS chains. Corneas of homozygous mutants were significantly thinner than those of WT or heterozygous mice. They lacked high-sulfated KS, but contained the core protein of the major corneal KSPG, lumican. Histochemically stained KSPGs coassociated with fibrillar collagen in WT corneas, but were not identified in the Chst5-null tissue. Conversely, abnormally large chondroitin sulfate͞dermatan sulfate PG complexes were abundant throughout the Chst5-deficient cornea, indicating an alteration of controlled PG production in the mutant cornea. The corneal stroma of the Chst5-null mouse exhibited widespread structural alterations in collagen fibrillar architecture, including decreased interfibrillar spacing and a more spatially disorganized collagen array. The enzymatic sulfation of KS GAG chains is thus identified as a key requirement for PG biosynthesis and collagen matrix organization.collagen ͉ glycosaminoglycans ͉ proteoglycans G lycosaminoglycans (GAGs) substituted on proteoglycans (PGs) are influential in defining collagen fibrillar architecture in a wide range of connective tissue matrices. Keratan sulfate (KS) is an important constituent of several collagen-rich tissues and is the major GAG in cornea where it is N-linked to asparagine residues in one of three PG core proteins: lumican (1), keratocan (2), and mimecan͞osteoglycin (3). Human corneal GlcNAc 6-O-sulfotransferase (also known as human GlcNAc6ST-5 and GST4␤) is the responsible enzyme for the synthesis of high-sulfated KS via the transfer of sulfate onto the GlcNAc 6-O position of the KS backbone (4).Fairly compelling evidence exists for a regulatory role for KSPGs in the maintenance of corneal matrix structure in a number of species. The avian cornea in ovo, for example, synthesizes an unsulfated form of KS midway through development when it is structurally disorganized and transmits relatively little light, but switches to produce a sulfated KS GAG as it becomes transparent and attains a more well ordered collagen fibrillar ultrastructure (5, 6). KS sulfation patterns are also altered in opaque, structurally disorganized corneal scar tissue in rabbits (7,8) and in cloudy human corneas with the inherited disease, macular corneal dystrophy (9), which is caused by mutations in CHST6, a gene encoding human corneal GlcNAc 6-O-sulfotransferase (10).Hybrid type I͞V collagen fibrils are the cornea's main nonspecular light-scattering elements and are formed into wide, interweaving belts or lamellae that lie approximately in the tissue plane (11). Wit...

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“…Theories have been proposed that any array of equal-sized filaments whose diameter is smaller than l/4 will be transparent provided they are in a pseudoparallel array and that there are no substantial voids in the disordered lattice, which are comparable in dimension to the wavelength of light. 27 Because the collagen spacing in our postoperative patches was also smaller than l/4, our results could be interpreted by this theory. Therefore, although the collagen fibrils were disorganized and had different spacings, the corneal tissue retained its transparency after almost 1 year.…”

Section: How Are Transparency and Spacial Structures Maintained In Acm?mentioning

confidence: 65%