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Forced exercise-induced osteoarthritis is attenuated in mice lacking the small leucine-rich proteoglycan decorin
  1. Tobias Gronau1,2,
  2. Karsten Krüger3,
  3. Carina Prein4,
  4. Attila Aszodi5,
  5. Isabel Gronau2,
  6. Renato V Iozzo6,
  7. Frank C Mooren3,
  8. Hauke Clausen-Schaumann4,
  9. Jessica Bertrand1,7,
  10. Thomas Pap1,
  11. Peter Bruckner2,
  12. Rita Dreier2
  1. 1Institute of Experimental Musculoskeletal Medicine, University Hospital Münster, Münster, Germany
  2. 2Institute of Physiological Chemistry and Pathobiochemistry, University of Münster, Münster, Germany
  3. 3Institute of Sports Medicine, Justus-Liebig University Giessen, Giessen, Germany
  4. 4Center for Applied Tissue Engineering and Regenerative Medicine (CANTER), Munich University of Applied Sciences and Center for Nanoscience (CeNS), Munich, Germany
  5. 5Laboratory of Experimental Surgery and Regenerative Medicine, Department of General, Trauma and Reconstruction Surgery, Ludwig-Maximilians-University, Munich, Germany
  6. 6Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, USA
  7. 7Department of Orthopaedic Surgery, Otto-von-Guericke University, Magdeburg, Germany
  1. Correspondence to Dr Rita Dreier, Institute of Physiological Chemistry and Pathobiochemistry, Waldeyerstraße 15, Münster 49149, Germany; dreierr{at}uni-muenster.de

Abstract

Objective Interterritorial regions of articular cartilage matrix are rich in decorin, a small leucine-rich proteoglycan and important structural protein, also involved in many signalling events. Decorin sequesters transforming growth factor β (TGFβ), thereby regulating its activity. Here, we analysed whether increased bioavailability of TGFβ in decorin-deficient (Dcn/−) cartilage leads to changes in biomechanical properties and resistance to osteoarthritis (OA).

Methods Unchallenged knee cartilage was analysed by atomic force microscopy (AFM) and immunohistochemistry. Active transforming growth factor β-1 (TGFβ1) content within cultured chondrocyte supernatants was measured by ELISA. Quantitative real-time (RT)-PCR was used to analyse mRNA expression of glycosaminoglycan (GAG)-modifying enzymes in C28/I2 cells following TGFβ1 treatment. In addition, OA was induced in Dcn−/− and wild-type (WT) mice via forced exercise on a treadmill.

Results AFM analysis revealed a strikingly higher compressive stiffness in Dcn−/− than in WT cartilage. This was accompanied by increased negative charge and enhanced sulfation of GAG chains, but not by alterations in the levels of collagens or proteoglycan core proteins. In addition, decorin-deficient chondrocytes were shown to release more active TGFβ1. Increased TGFβ signalling led to enhanced Chst11 sulfotransferase expression inducing an increased negative charge density of cartilage matrix. These negative charges might attract more water resulting in augmented compressive stiffness of the tissue. Therefore, decorin-deficient mice developed significantly less OA after forced exercise than WT mice.

Conclusions Our study demonstrates that the disruption of decorin-restricted TGFβ signalling leads to higher stiffness of articular cartilage matrix, rendering joints more resistant to OA. Therefore, the loss of an important structural component can improve cartilage homeostasis.

  • Chondrocytes
  • Knee Osteoarthritis
  • Cytokines

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