title: In vitro expansion affects the response of chondrocytes to mechanical stimulation.
abstract: OBJECTIVE
  Expansion of autologous chondrocytes is a common step in procedures for cartilage defect repair. Subsequent dedifferentiation can alter cellular response to mechanical loading, having major consequences for the cell's behavior in vivo after reimplantation. Therefore, we examined the response of primary and expanded human articular chondrocytes to mechanical loading.
  
  
  METHODS
  Primary and expanded chondrocytes were stretched at either 0.5% or 3.0% at 0.5Hz, 2h per day, for 3 days. Gene expression levels of matrix components (aggrecan (AGC1), lubricin (PRG4), collagen type I (COL1), type II (COL2) and type X (COL10)) as well as matrix enzymes (matrix metalloproteinase 1 (MMP1), MMP3, MMP13) and SOX9 were compared to unstretched controls. To evaluate the effect of a chondrogenic environment on cellular response to stretch, redifferentiation medium was used on expanded cells.
  
  
  RESULTS
  In primary chondrocytes, stretch led to mild decreases in AGC1, COL1 and COL10 gene expression (maximum of 3.8-fold) and an up-regulation of PRG4 (2.0-fold). In expanded chondrocytes, expression was down-regulated for AGC1 (up to 21-fold), PRG4 (up to 5.0-fold), COL1 (10-fold) and COL2 (2.9-fold). Also, expression was up-regulated for MMP1 (20-fold) and MMP3 (up to 4-fold), while MMP13 was down-regulated (2.8-fold). A chondrogenic environment appeared to temper effects of stretch.
  
  
  CONCLUSIONS
  Our results show that expansion alters the response of human chondrocytes to stretch. Expanded chondrocytes greatly decrease gene expression of matrix constituents and increase expression of MMPs, whereas primary chondrocytes hardly respond. Our data could be a reference for optimization of cell sources or expansion protocols for reimplanted chondrocytes.
authors.affiliation: Department of Orthopaedics, Erasmus MC, University Medical Center Rotterdam, PO Box 2040, 3000 CA, The Netherlands.
authors.forename: R H J
authors.initials: RH
authors.lastname: Das
authors.forename: H
authors.initials: H
authors.lastname: Jahr
authors.forename: J A N
authors.initials: JA
authors.lastname: Verhaar
authors.forename: J C
authors.initials: JC
authors.lastname: van der Linden
authors.forename: G J V M
authors.initials: GJ
authors.lastname: van Osch
authors.forename: H
authors.initials: H
authors.lastname: Weinans
mesh_terms: D053674:Aggrecans / Q000235:genetics; D002358:Cartilage, Articular / Q000473:pathology* / Q000637:transplantation; D002454:Cell Differentiation; D048429:Cell Size; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000502:physiology* / Q000637:transplantation; D024121:Collagen Type X / Q000235:genetics; D017077:Culture Media, Conditioned; D015536:Down-Regulation; D005109:Extracellular Matrix / Q000201:enzymology / Q000235:genetics*; D024022:Fibrillar Collagens / Q000235:genetics; D015870:Gene Expression; D006023:Glycoproteins / Q000235:genetics; D006609:High Mobility Group Proteins / Q000235:genetics; D006801:Humans; D020782:Matrix Metalloproteinases / Q000235:genetics; D010641:Phenotype; D012038:Regeneration / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055758:SOX9 Transcription Factor; D013314:Stress, Mechanical; D023822:Tissue Engineering / Q000379:methods*; D014157:Transcription Factors / Q000235:genetics; D015854:Up-Regulation; D000099158:Proteoglycan 4
chemical_list: D053674:Aggrecans; D024121:Collagen Type X; D017077:Culture Media, Conditioned; D024022:Fibrillar Collagens; D006023:Glycoproteins; D006609:High Mobility Group Proteins; D020782:Matrix Metalloproteinases; D055758:SOX9 Transcription Factor; D014157:Transcription Factors; D000099158:Proteoglycan 4; C527932:SOX9 protein, human