Resistance of Corneal RFUVA–Cross-Linked Collagens and Small Leucine-Rich Proteoglycans to Degradation by Matrix Metalloproteinases

Abstract

PURPOSE. Extracellular matrix metalloproteinases (MMPs) are thought to play a crucial role in corneal degradation associated with the pathological progression of keratoconus. Currently, corneal cross-linking by riboflavin and ultraviolet A (RFUVA) has received significant attention for treatment of keratoconus. However, the extent to which MMPs digest cross-linked collagen and small leucine-rich proteoglycans (SLRPs) remains unknown. In this study, the resistance of RFUVA-cross-linked collagens and SLRPs to MMPs has been investigated. METHODS.To investigate the ability of MMPs to digest crosslinked collagen and SLRPs, a model reaction system using purified collagen type I, type IV, and nonglycosylated, commercially available recombinant SLRPs, keratocan, lumican, mimecan, decorin, and biglycan in solution in vitro has been compared using reactions inside an intact bovine cornea, ex vivo.RESULTS. Our data demonstrate that corneal cross-linked collagen type I and type IV are resistant to cleavage by MMP-1, MMP-2, MMP-9, and MMP-13, whereas non-cross-linked collagen I, IV, and natively glycosylated SLRPs are susceptible to degradation by MMPs. In addition, both cross-linked SLRPs themselves and cross-linked polymers of SLRPs and collagen appear able to resist degradation. These results suggest that the interactions between SLRPs and collagen caused by RFUVA protect both SLRPs and collagen fibrils from cleavage by MMPs. CONCLUSIONS.A novel approach for understanding the biochemical mechanism whereby RFUVA cross-linking stops keratoconus progression has been achieved. (Invest Ophthalmol Vis Sci.

Spatially heterogeneous corneal mechanical responses before and after riboflavin–ultraviolet-A crosslinking

“…1–4 Corneal collagen crosslinking (CXL) has the potential to be a treatment option not only for keratoconus but also for ocular conditions such as corneal ectasia after laser in situ keratomileusis, alkali burns of the cornea, and infectious keratitis. 5–8 However, a better understanding of the biomechanical effects of CXL is required to optimize this treatment.…”

“…11 The increased chemical bonding between corneal microstructural components is believed to strengthen the tissue mechanically and reduce its susceptibility to enzymatic degradations. 4,12–15 …”

Corneal Collagen Cross-linking for Terrien Marginal Degeneration

“…8,9 Corneal homeostasis of the stromal extracellular matrix is determined by a delicate balance between collagen synthesis via corneal keratocytes and collagen catalysis, mediated by digestive enzymes such as matrix metalloproteinases. 10 Corneal cross-linked collagen types I and IV are resistant to cleavage by matrix metallopeptidases (MMP-1, MMP-2, MMP-9, and MMP-13), whereas non-cross-linked collagens I and IV and natively glycosylated, small leucine-rich proteoglycans are susceptible to degradation by matrix metallopeptidases. 10 An increased resistance of the corneal stroma to enzymatic digestion might downregulate the catalytic activity with a subsequent net increase in collagen production and a resulting augmentation of corneal stroma.…”

Ultraviolet Corneal Crosslinking

“…Богатые лей-цином протеогликаны, сшитые с коллагеном в системе in vitro, способны к защите от катаболизма матриксных металлопротеиназ (ММП). Показано, что коллагены I и IV типа, обработанные рибофлавин-УФ-А, становятся устойчивыми к действию ММП-1, ММП-2, ММП-9 и ММП-13 [24].…”