title: TGF-ß1 enhances the BMP-2-induced chondrogenesis of bovine synovial explants and arrests downstream differentiation at an early stage of hypertrophy.
abstract: BACKGROUND
  Synovial explants furnish an in-situ population of mesenchymal stem cells for the repair of articular cartilage. Although bone morphogenetic protein 2 (BMP-2) induces the chondrogenesis of bovine synovial explants, the cartilage formed is neither homogeneously distributed nor of an exclusively hyaline type. Furthermore, the downstream differentiation of chondrocytes proceeds to the stage of terminal hypertrophy, which is inextricably coupled with undesired matrix mineralization. With a view to optimizing BMP-2-induced chondrogenesis, the modulating influences of fibroblast growth factor 2 (FGF-2) and transforming growth factor beta 1 (TGF-ß1) were investigated.
  
  
  RESULTS
  Explants of bovine calf metacarpal synovium were exposed to BMP-2 (200 ng/ml) for 4 (or 6) weeks. FGF-2 (10 ng/ml) or TGF-ß1 (10 ng/ml) was introduced at the onset of incubation and was present either during the first week of culturing alone or throughout its entire course. FGF-2 enhanced the BMP-2-induced increase in metachromatic staining for glycosaminoglycans (GAGs) only when it was present during the first week of culturing alone. TGF-ß1 enhanced not only the BMP-2-induced increase in metachromasia (to a greater degree than FGF-2), but also the biochemically-assayed accumulation of GAGs, when it was present throughout the entire culturing period; in addition, it arrested the downstream differentiation of cells at an early stage of hypertrophy. These findings were corroborated by an analysis of the gene- and protein-expression levels of key cartilaginous markers and by an estimation of individual cell volume.
  
  
  CONCLUSIONS
  TGF-ß1 enhances the BMP-2-induced chondrogenesis of bovine synovial explants, improves the hyaline-like properties of the neocartilage, and arrests the downstream differentiation of cells at an early stage of hypertrophy. With the prospect of engineering a mature, truly articular type of cartilage in the context of clinical repair, our findings will be of importance in fine-tuning the stimulation protocol for the optimal chondrogenic differentiation of synovial explants.
authors.affiliation: Departments of Orthopaedic Surgery and Clinical Research, Center of Regenerative Medicine for Skeletal Tissues, University of Bern, Bern, Switzerland.
authors.forename: Nahoko
authors.initials: N
authors.lastname: Shintani
authors.forename: Klaus A
authors.initials: KA
authors.lastname: Siebenrock
authors.forename: Ernst B
authors.initials: EB
authors.lastname: Hunziker
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology*; D002358:Cartilage, Articular / Q000254:growth & development; D002417:Cattle; D019902:Chondrocytes / Q000166:cytology; D020219:Chondrogenesis / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D005786:Gene Expression Regulation; D006025:Glycosaminoglycans / Q000378:metabolism; D006984:Hypertrophy; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D012313:RNA / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013583:Synovial Membrane / Q000166:cytology*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
chemical_list: D055396:Bone Morphogenetic Protein 2; D006025:Glycosaminoglycans; D053773:Transforming Growth Factor beta1; D016222:Fibroblast Growth Factor 2; D012313:RNA