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Yuntao Zhang, Abigail H. Conrad, Gary W. Conrad; Effects Of Ultraviolet-a And Riboflavin On The Interaction Of Collagen And Proteoglycans During Corneal Cross-linking. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2525.
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Corneal cross-linking using riboflavin and ultraviolet-A (RFUVA) is a new clinical treatment strategy that directly targets the stroma in progressive keratoconus. In the corneal stroma, keratocan, lumican, mimecan and decorin are the core proteins of the major proteoglycans (PGs). They bind collagen fibrils and play important biological roles in maintaining the structure and function of the stroma. In this work, an in vitro model reaction system has been employed to investigate the effects of RFUVA on interactions that may occur between PGs and collagen during corneal cross-linking.
Purified collagen types I, core proteins and glycosaminoglycans (GAGs) were used to assess the mechanisms of cross-linking induced by the RFUVA under conditions which resemble those for the clinical treatment of progressive keratoconus
Irradiation with UVA in the presence of riboflavin cross-links collagen α and β chains into higher molecular weight (MW) polymers. In addition, RFUVA induces PG core proteins to cross-link to form higher MW polymers. When collagen type I is mixed with individual PG core proteins and subjected to RFUVA, both keratocan and lumican strongly inhibit collagen cross-linking. However, mimican and decorin do not interfere with collagen cross-linking, but instead form cross-links with collagen, to form new bands in high MW regions of SDS-polyacrylamide gels. In contrast, the corneal GAGs, keratan sulfate (KS) and chondroitin sulfate (CS), when studied in isolation from their core proteins, are not induced by RFUVA to crosslink among themselves or to form cross-links with collagen. Thus, RFUVA mainly appears to involve crosslinking of collagen molecules among themselves and PG core proteins among themselves, together with limited linkages between collagen and mimecan, and between collagen and decorin.
The data presented here reveal a new class of molecular interactions between PGs and collagen type I.
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