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      Trypsin-mediated enzymatic degradation of type II collagen in the human vitreous

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          Abstract

          Purpose

          Aging of the vitreous body can result in sight-threatening pathology. One aspect of vitreous aging is liquefaction, which results from the vanishing of collagen fibrils. We investigated the possibility that trypsins are involved in vitreous type II collagen degradation.

          Methods

          Immunohistochemistry and western blotting were used for detecting and locating trypsin isoforms in the vitreous and retina of human donor eyes. The capability of the retina to produce these trypsins was analyzed with polymerase chain reaction. Whether the different trypsins degraded type II collagen was tested in vitro. The sizes of the in vitro induced type II collagen degradation products were compared to those present in the vitreous of human eyes of different ages.

          Results

          Trypsin-1 and trypsin-2 were detected in the vitreous. In the retina, messenger ribonucleic acid (mRNA) coding for trypsin-2, -3, and -4 was present. Using immunohistochemistry, trypsin-2 was detected in microglial cells located in the vitreous and the retina. All trypsin isoforms degraded type II collagen and produced degradation products of similar sizes as those present in the vitreous.

          Conclusions

          Trypsin-1 and trypsin-2 appear to have a function in the degradation of vitreous type II collagen. They could therefore have a role in the development of vitreous liquefaction.

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          Structural macromolecules and supramolecular organisation of the vitreous gel.

          Paul Bishop (2000)
          The vitreous gel is a transparent extracellular matrix that fills the cavity behind the lens of the eye and is surrounded by and attached to the retina. This gel liquefies during ageing and in 25-30% of the oppulation the residual gel structure eventually collapses away from the posterior retina in a process called posterior retina in a process called posterior vitreous detachment. This process plays a pivotal role in a number of common blinding conditions including rhegmatogenous retinal detachment, proliferative diabetic retinopathy and macular hole formation. In order to understand the molecular events underlying vitreous liquefaction and posterior vitreous detachment and to develop new therapies it is important to understand the molecular basis of normal vitreous gel structure and how this is altered during ageing. It has previously been established that a dilute dispersion of thin (heterotypic) collagen fibrils is essential to the gel structure and that age-related vitreous liquefaction is intimately related to a process whereby these collagen fibrils aggregate. Collagen fibrils have a natural tendency to aggregate so a key question that has to be addressed is: what normally maintains the spacing of the collagen fibrils? In mammalian vitreous a network of hyaluronan normally fills the spaces between these collagen fibrils. This hyaluronan network can be removed without destroying the gel structure, so the hyaluronan is not essential for maintaining the spacing of the collagen fibrils although it probably does increase the mechanical resilience of the gel. The thin heterotypic collagen fibrils have a coating of non-covalently bound macromolecules which, along with the surface features of the collagen fibrils themselves, probably play a fundamental role in maintaining gel stability. They are likely to both maintain the short-range spacing of vitreous collagen fibrils and to link the fibrils together to form a contiguous network. A collagen fibril-associated macromolecule that may contribute to the maintenance of short-range spacing is opticin, a newly discovered extracellular matrix leucine-rich repeat protein. In addition, surface features of the collagen fibrils such as the chondroitin sulphate glycosaminoglycan chains of type IX collagen proteoglycan may also play an important role in maintaining fibril spacing. Furthering our knowledge of these and other components related to the surface of the heterotypic collagen fibrils will allow us to make important strides in understanding the macromolecular organisation of this unique and fascinating tissue. In addition, it will open up new therapeutic opportunities as it will allow the development of therapeutic reagents that can be used to modulate vitreous gel structure and thus treat a number of common, potentially blinding, ocular conditions.
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            Anomalous posterior vitreous detachment: a unifying concept in vitreo-retinal disease.

            J. Sebag (2004)
            Posterior vitreous detachment (PVD) is the consequence of changes in the macromolecular structure of gel vitreous that result in liquefaction, concurrent with alterations in the extracellular matrix at the vitro-retinal interface that allow the posterior vitreous cortex to detach from the internal limiting lamina of the retina. Gel liquefaction that exceeds the degree of vitro-retinal dehiscence results in anomalous PVD (APVD). APVD varies in its clinical manifestations depending upon where in the fundus vitreo-retinal adhesion is strongest. At the periphery, APVD results in retinal tears and detachments. In the macula, APVD causes vitreo-macular traction syndrome, results in vitreoeschisis with macular pucker or macular holes, or contributes to some cases of diabetic macular edema. At the optic disc and retina, APVD causes vitreo-papillary traction and promotes retinal and optic disc neovascularization. Unifying the spectrum of vitreo-retinal diseases into the conceptual frame-work of APVD underscores that to more effectively treat, and ultimately prevent, these disorders it is necessary to replicate the two components of an innocuous PVD, i.e., gel liquefaction and vitreo-retinal dehiscence. Pharmacologic vitreolysis is designed to mitigate against APVD by chemically breaking down vitreous macromolecules and weakening vitro-retinal adhesion to safely detach the posterior vitreous cortex. This would not only facilitate surgery, but if performed early in the natural history of disease, it should prevent progressive disease.
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              Characterization of the vitreous proteome in diabetes without diabetic retinopathy and diabetes with proliferative diabetic retinopathy.

              Edward Feener, Bo Gao, N Timothy … (2008)
              An understanding of the diabetes-induced alterations in vitreous protein composition in the absence and in the presence of proliferative diabetic retinopathy (PDR) may provide insights into factors and mechanisms responsible for this disease. We have performed a comprehensive proteomic analysis and comparison of vitreous samples from individuals with diabetes but without diabetic retinopathy (noDR) or with PDR and nondiabetic individuals (NDM). Using preparative one-dimensional SDS-PAGE and nano-LC/MS/MS of 17 independent vitreous samples, we identified 252 proteins from human vitreous. Fifty-six proteins were differentially abundant in noDR and PDR vitreous compared with NDM vitreous, including 32 proteins increased and 10 proteins decreased in PDR vitreous compared with NDM vitreous. Comparison of noDR and PDR groups revealed increased levels of angiotensinogen and decreased levels of calsyntenin-1, interphotoreceptor retinoid-binding protein, and neuroserpin in PDR vitreous. Biological pathway analysis revealed that vitreous contains 30 proteins associated with the kallikrein-kinin, coagulation, and complement systems. Five of them (complement C3, complement factor I, prothrombin, alpha-1-antitrypsin, and antithrombin III) were increased in PDR vitreous compared with NDM vitreous. Factor XII was detected in PDR vitreous but not observed in either NDM or noDR vitreous. PDR vitreous also had increased levels of peroxiredoxin-1 and decreased levels of extracellular superoxide dismutase, compared with noDR or NDM vitreous. These data provide an in depth analysis of the human vitreous proteome and reveal protein alterations that are associated with PDR.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Mol Vis
                Journal ID (iso-abbrev): Mol. Vis
                Journal ID (publisher-id): MV
                Title: Molecular Vision
                Publisher: Molecular Vision
                ISSN (Electronic): 1090-0535
                Publication date Collection: 2013
                Publication date (Electronic): 20 July 2013
                Volume: 19
                Pages: 1591-1599
                Affiliations
                [1 ]Department of Ophthalmology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
                [2 ]Department of Biomedical Engineering, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
                [3 ]Department of Dermatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
                [4 ]W.J. Kolff institute, Graduate School of Medical Sciences, Groningen, The Netherlands
                Author notes
                Correspondence to: Leonoor Inge Los, University Medical Center Groningen, Department of Ophthalmology, P.O. Box 30.001, 9700 RB Groningen, The Netherlands; Phone: +31 50 3612510; FAX: +31 50 3611709; email: l.i.los@ 123456umcg.nl
                Article
                Publisher ID: 163 Publisher-manuscript ID: 2012MOLVIS0222
                PMC ID: 3718489
                PubMed ID: 23882137
                SO-VID: f6032a80-d4db-4d30-9938-2949d7ece4ea
                Copyright © Copyright © 2013 Molecular Vision.
                License:

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 07 May 2012
                Date accepted : 15 July 2013
                Categories
                Subject: Research Article
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                ScienceOpen disciplines: Vision sciences
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                ScienceOpen disciplines: Vision sciences

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