title: Central and peripheral region tibial plateau chondrocytes respond differently to in vitro dynamic compression.
abstract: OBJECTIVE
  The objective of this study was to test the hypotheses that chondrocytes from distinct regions of the porcine tibial plateau: (1) display region-specific baseline gene expression, and (2) respond differently to in vitro mechanical loading.
  
  
  METHODS
  Articular cartilage explants were obtained from central (not covered by meniscus) and peripheral (covered by meniscus) regions of porcine tibial plateaus. For baseline gene expression analysis, samples were snap frozen. To determine the effect of mechanical loading, central and peripheral region explants were exposed to equivalent dynamic compression (0-100 kPa) and compared to site-matched free-swelling controls (FSCs). mRNA levels for type II collagen (CII), aggrecan (AGGR), matrix metalloproteinase 1 (MMP-1), MMP-3, MMP-13, A disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAM-TS4), ADAM-TS5, tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, and tumor necrosis factor alpha (TNFalpha) were quantified using real time polymerase chain reaction (RT-PCR).
  
  
  RESULTS
  At baseline, mRNA levels for the structural proteins CII and AGGR were approximately twofold greater in the central region compared with peripheral region explants. In vitro dynamic compression strongly affected expression levels for CII, AGGR, MMP-3, and TIMP-2 relative to FSCs. Response differed significantly by region, with greater upregulation of CII, AGGR, and MMP-3 in central region explants.
  
  
  CONCLUSIONS
  Chondrocytes from different regions of the porcine tibial plateau express mRNA for structural proteins at different levels and respond to equivalent in vitro mechanical loading with distinctive changes in gene expression. These regional biological variations appear to be related to the local mechanical environment in the normal joint, and thus may indicate a sensitivity of the joint to conditions that alter joint loading such as anterior cruciate ligament (ACL) injury, meniscectomy, or joint instability.
authors.affiliation: Biomechanical Engineering, Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, United States. sbevill@stanford.edu
authors.forename: S L
authors.initials: SL
authors.lastname: Bevill
authors.forename: P L
authors.initials: PL
authors.lastname: Briant
authors.forename: M E
authors.initials: ME
authors.lastname: Levenston
authors.forename: T P
authors.initials: TP
authors.lastname: Andriacchi
mesh_terms: D053674:Aggrecans / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism* / Q000503:physiopathology; D019902:Chondrocytes / Q000378:metabolism*; D019245:Compressive Strength / Q000502:physiology; D015870:Gene Expression; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013314:Stress, Mechanical; D013552:Swine; D013977:Tibia / Q000378:metabolism* / Q000502:physiology
chemical_list: D053674:Aggrecans; D012333:RNA, Messenger