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Local depletion of proteoglycans mediates cartilage tissue repair in an ex vivo integration model

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Eileen Gentleman, Nicholas Merrild, Viktoria Holzmann, Yoanna Ariosa-Morejon, Peter A. Faull, Jen Coleman, Wills Barrell, Gloria Young, Roman Fischer, Daniel Kelly, Owen Addison, Tonia Vincent, Agamemnon Grigoriadis

Original languageEnglish
Pages (from-to)179-188
Number of pages10
JournalActa Biomaterialia
Volume149
DOIs
Accepted/In press17 Jun 2022
Published1 Sep 2022

Bibliographical note

Funding Information: This study was supported by the UK Medical Research Council (MRC) Doctoral Training Partnership in Biomedical Sciences at King's College London (award to NGM) and the MRC Flexible Supplement Fund. EG acknowledges funding support from the Rosetrees Trust. The funder played no role in the design or analysis of the data in this study. Funding Information: We are grateful for support from Dermot Daly of Trinity College Dublin and the Advanced Microscopy Laboratory, Graham Haggar of the Royal Veterinary College, and Mahmoud Ardakani at Imperial College London Department of Materials for assistance with electron microscopy. Publisher Copyright: © 2022

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Abstract

Successfully replacing damaged cartilage with tissue-engineered constructs requires integration with the host tissue and could benefit from leveraging the native tissue's intrinsic healing capacity; however, efforts are limited by a poor understanding of how cartilage repairs minor defects. Here, we investigated the conditions that foster natural cartilage tissue repair to identify strategies that might be exploited to enhance the integration of engineered/grafted cartilage with host tissue. We damaged porcine articular cartilage explants and using a combination of pulsed SILAC-based proteomics, ultrastructural imaging, and catabolic enzyme blocking strategies reveal that integration of damaged cartilage surfaces is not driven by neo-matrix synthesis, but rather local depletion of proteoglycans. ADAMTS4 expression and activity are upregulated in injured cartilage explants, but integration could be reduced by inhibiting metalloproteinase activity with TIMP3. These observations suggest that catabolic enzyme-mediated proteoglycan depletion likely allows existing collagen fibrils to undergo cross-linking, fibrillogenesis, or entanglement, driving integration. Catabolic enzymes are often considered pathophysiological markers of osteoarthritis. Our findings suggest that damage-induced upregulation of metalloproteinase activity may be a part of a healing response that tips towards tissue destruction under pathological conditions and in osteoarthritis, but could also be harnessed in tissue engineering strategies to mediate repair. Statement of significance: Cartilage tissue engineering strategies require graft integration with the surrounding tissue; however, how the native tissue repairs minor injuries is poorly understood. We applied pulsed SILAC-based proteomics, ultrastructural imaging, and catabolic enzyme blocking strategies to a porcine cartilage explant model and found that integration of damaged cartilage surfaces is driven by catabolic enzyme-mediated local depletion of proteoglycans. Although catabolic enzymes have been implicated in cartilage destruction in osteoarthritis, our findings suggest that damage-induced upregulation of metalloproteinase activity may be a part of a healing response that tips towards tissue destruction under pathological conditions. They also suggest that this natural cartilage tissue repair process could be harnessed in tissue engineering strategies to enhance the integration of engineered cartilage with host tissue.

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