title: BMP activation and Wnt-signalling affect biochemistry and functional biomechanical properties of cartilage tissue engineering constructs.
abstract: OBJECTIVE
  Bone morphogenetic protein (BMP-) and Wnt-signalling play crucial roles in cartilage homeostasis. Our objective was to investigate whether activation of the BMP-pathway or stimulation of Wnt-signalling cascades effectively enhances cartilage-specific extracellular matrix (ECM) accumulation and functional biomechanical parameters of chondrocyte-seeded tissue engineering (TE)-constructs.
  
  
  METHODS
  Articular chondrocytes were cultured in collagen-type-I/III-matrices over 6 weeks to create a biomechanical standard curve. Effects of stimulation with 100 ng/mL BMP-4/-7 heterodimer or 10 mM lithium chloride (LiCl) on ECM-deposition was quantified and characterized histologically. Biomechanical parameters were determined by the Very Low Rubber Hardness (VLRH) method and under confined compression stress relaxation.
  
  
  RESULTS
  BMP-4/-7 treatment resulted in stronger collagen type-II staining and significantly enhanced glycosaminoglycan (GAG) deposition (3.2-fold; *P < 0.01) correlating with improved hardness (∼1.7-fold; *P = 0.001) reaching 83% of native cartilage values after 28 days, a value not reached before 9 weeks without stimulation. LiCl treatment enhanced VLRH slightly, but significantly (∼1.3-fold; *P = 0.016) with a trend to more ECM-deposition. BMP-4/-7 treatment significantly enhanced the E Modulus (105.7 ± 34.1 kPa; *P = 0.000001) compared to controls (8.0 ± 4.2 kPa). Poisson's ratio was significantly improved by BMP-4/-7 treatment (0.0703 ± 0.0409; *P = 0.013) vs controls (0.0432 ± 0.0284) and a significantly lower permeability (5.8 ± 2.1056 × 10(-14) m4/N.s; *P = 0.00001) was detected compared to untreated scaffolds (4.4 ± 3.1289 × 10(-13) m4/N.s).
  
  
  CONCLUSIONS
  While Wnt-activation is less effective, BMP-4/-7 heterodimer stimulation approximated native cartilage features in less than 50% of standard culture time representing a promising strategy for functional cartilage TE to improve biomechanical parameters of engineered cartilage.
authors.affiliation: Research Center for Experimental Orthopaedics, Department of Orthopaedics, Trauma Surgery and Paraplegiology, Heidelberg University Hospital, Heidelberg, Germany. Electronic address: Anika.Krase@med.uni-heidelberg.de.
authors.forename: A
authors.initials: A
authors.lastname: Krase
authors.affiliation: Laboratory for Biomechanics and Biomaterials, Orthopaedic Department, Hannover Medical School of Hannover, Hannover, Germany. Electronic address: Abediyan@gmail.com.
authors.forename: R
authors.initials: R
authors.lastname: Abedian
authors.affiliation: Research Center for Experimental Orthopaedics, Department of Orthopaedics, Trauma Surgery and Paraplegiology, Heidelberg University Hospital, Heidelberg, Germany. Electronic address: E.Steck@web.de.
authors.forename: E
authors.initials: E
authors.lastname: Steck
authors.affiliation: Laboratory for Biomechanics and Biomaterials, Orthopaedic Department, Hannover Medical School of Hannover, Hannover, Germany. Electronic address: Christof.Hurschler@ddh-gruppe.de.
authors.forename: C
authors.initials: C
authors.lastname: Hurschler
authors.affiliation: Research Center for Experimental Orthopaedics, Department of Orthopaedics, Trauma Surgery and Paraplegiology, Heidelberg University Hospital, Heidelberg, Germany. Electronic address: Wiltrud.Richter@med.uni-heidelberg.de.
authors.forename: W
authors.initials: W
authors.lastname: Richter
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D055415:Bone Morphogenetic Protein 4 / Q000494:pharmacology; D055419:Bone Morphogenetic Protein 7 / Q000494:pharmacology; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism; D024043:Collagen Type II / Q000378:metabolism; D005109:Extracellular Matrix / Q000502:physiology; D006025:Glycosaminoglycans / Q000378:metabolism; D006244:Hardness; D018021:Lithium Chloride / Q000494:pharmacology; D034421:Sus scrofa; D023822:Tissue Engineering / Q000379:methods*; D060449:Wnt Signaling Pathway / Q000502:physiology*
chemical_list: D055415:Bone Morphogenetic Protein 4; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D024043:Collagen Type II; D006025:Glycosaminoglycans; D018021:Lithium Chloride
keywords: BMP-4/-7 heterodimer; Biomechanical properties; Cartilage tissue engineering; Extracellular matrix proteins; Lithium chloride