title: GDF5 reduces MMP13 expression in human chondrocytes via DKK1 mediated canonical Wnt signaling inhibition.
abstract: OBJECTIVE
  Growth differentiation factor 5 (GDF5) is important for joint formation and associated with osteoarthritis (OA). Its role for the homeostasis of cartilage extracellular matrix (ECM) is, however, unknown. The canonical Wnt signaling pathway is also implemented in OA and activation of the pathway has detrimental effects on the cartilage ECM. The objective of this study was to investigate the effect of GDF5 stimulation on the Wnt signaling pathway and on the expression of known modulators of cartilage ECM.
  
  
  METHODS
  Human chondrocytes were cultured in the pellet mass system and stimulated with increasing concentrations of GDF5. Expression of matrix modulating enzymes and canonical Wnt inhibitors dickkopf 1 (DKK1) and frizzled related protein (FRZB) were measured with quantitative PCR (qPCR). Protein levels of matrix metalloprotease 13 (MMP13), DKK1 and β-catenin were measured with enzyme-linked immunosorbent assay (ELISA). Canonical Wnt signaling was stimulated with Wnt3a and small molecule CHIR-99021 and DKK1 was blocked with small molecule WAY-262611.
  
  
  RESULTS
  In this study, we show that GDF5 stimulation of human chondrocytes inhibits expression of the cartilage ECM degrading enzymes MMP13 and ADAMTS4 and stimulates the expression of cartilage anabolic genes ACAN and SOX9. We further show that the stimulation inhibits the canonical Wnt signaling pathway through expression of the canonical Wnt inhibitors DKK1 and FRZB. Finally we show that inhibition of MMP13 expression through GDF5 stimulation is mediated by DKK1.
  
  
  CONCLUSIONS
  Herein, we provide evidence of a previously unknown link between GDF5 signaling and canonical Wnt signaling that may contribute to the understanding of the molecular mechanisms of OA.
authors.affiliation: Department of Clinical Chemistry and Transfusion Medicine, The Sahlgrenska Academy at Gothenburg University, Gothenburg, Sweden. Electronic address: lars.enochson@gu.se.
authors.forename: L
authors.initials: L
authors.lastname: Enochson
authors.affiliation: Department of Clinical Chemistry and Transfusion Medicine, The Sahlgrenska Academy at Gothenburg University, Gothenburg, Sweden. Electronic address: johan.stenberg@gu.se.
authors.forename: J
authors.initials: J
authors.lastname: Stenberg
authors.affiliation: Cartilage Research Unit, Gothenburg University, Department of Orthopaedics, Kungsbacka Hospital, Kungsbacka, Sweden. Electronic address: mats.brittberg@regionhalland.se.
authors.forename: M
authors.initials: M
authors.lastname: Brittberg
authors.affiliation: Department of Clinical Chemistry and Transfusion Medicine, The Sahlgrenska Academy at Gothenburg University, Gothenburg, Sweden. Electronic address: anders.lindahl@clinchem.gu.se.
authors.forename: A
authors.initials: A
authors.lastname: Lindahl
mesh_terms: D051722:ADAM Proteins / Q000378:metabolism; D000071116:ADAMTS5 Protein; D000328:Adult; D053674:Aggrecans / Q000378:metabolism; D002358:Cartilage, Articular / Q000378:metabolism*; D019902:Chondrocytes / Q000378:metabolism*; D024082:Collagen Type XII / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006023:Glycoproteins / Q000378:metabolism; D055428:Growth Differentiation Factor 5 / Q000494:pharmacology*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism*; D010003:Osteoarthritis / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D055758:SOX9 Transcription Factor / Q000378:metabolism; D019714:Tissue Inhibitor of Metalloproteinases / Q000378:metabolism; D060449:Wnt Signaling Pathway / Q000502:physiology*; D051176:beta Catenin / Q000378:metabolism; D000099274:Frizzled-Related Proteins
chemical_list: D051722:ADAM Proteins; D000071116:ADAMTS5 Protein; D053674:Aggrecans; D024082:Collagen Type XII; D006023:Glycoproteins; D055428:Growth Differentiation Factor 5; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D053509:Matrix Metalloproteinase 13; D055758:SOX9 Transcription Factor; D019714:Tissue Inhibitor of Metalloproteinases; D051176:beta Catenin; D000099274:Frizzled-Related Proteins; C508319:ACAN protein, human; C501126:DKK1 protein, human; C527932:SOX9 protein, human; C121532:ADAMTS5 protein, human
keywords: Canonical Wnt signaling; Chondrocytes; Growth and differentiation factor 5; Matrix metalloprotease 13; Osteoarthritis