title: IGF-1 does not moderate the time-dependent transcriptional patterns of key homeostatic genes induced by sustained compression of bovine cartilage.
abstract: OBJECTIVE
  To determine changes in chondrocyte transcription of a range of anabolic, catabolic and signaling genes following simultaneous treatment of cartilage with Insulin-like growth factor-1 (IGF-1) and ramp-and-hold mechanical compression, and compare with effects on biosynthesis.
  
  
  METHODS
  Explant disks of bovine calf cartilage were slowly compressed (unconfined) over 3-min to their 1mm cut-thickness (0%-compression) or to 50%-compression with or without 300 ng/ml IGF-1. Expression of 24 genes involved in cartilage homeostasis was measured using qPCR at 2, 8, 24, 32, 48 h after compression +/-IGF-1. Clustering analysis was used to identify groups of co-expressed genes to further elucidate mechanistic pathways.
  
  
  RESULTS
  IGF-1 alone stimulated gene expression of aggrecan and collagen II, but simultaneous 24h compression suppressed this effect. Compression alone up-regulated expression of matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-5 and transforming growth factor (TGF)-beta, an effect not reversed by simultaneous IGF-1 treatment. Temporal changes in expression following IGF-1 treatment were generally slower than that following compression. Clustering analysis revealed five distinct groups within which the pairings, tissue inhibitor of metalloproteinase (TIMP)-3 and ADAMTS-5, MMP-1 and IGF-2, and IGF-1 and Collagen II, were all robustly co-expressed, suggesting inherent regulation and feedback in chondrocyte gene expression. While aggrecan synthesis was transcriptionally regulated by IGF-1, inhibition of aggrecan synthesis by sustained compression appeared post-transcriptionally regulated.
  
  
  CONCLUSIONS
  Sustained compression markedly altered the effects of IGF-1 on expression of genes involved in cartilage homeostasis, while IGF-1 was largely unable to moderate the transcriptional effects of compression alone. The demonstrated co-expressed gene pairings suggest a balance of anabolic and catabolic activity following simultaneous mechanical and growth factor stimuli.
authors.affiliation: Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Wheeler
authors.forename: S R
authors.initials: SR
authors.lastname: Jafarzadeh
authors.forename: D M
authors.initials: DM
authors.lastname: Rocke
authors.forename: A J
authors.initials: AJ
authors.lastname: Grodzinsky
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000502:physiology; D002417:Cattle; D019902:Chondrocytes / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects* / Q000502:physiology; D006706:Homeostasis / Q000235:genetics*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D013314:Stress, Mechanical; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D007334:Insulin-Like Growth Factor I