title: Hypoxia inhibits hypertrophic differentiation and endochondral ossification in explanted tibiae.
abstract: OBJECTIVE
  Hypertrophic differentiation of growth plate chondrocytes induces angiogenesis which alleviates hypoxia normally present in cartilage. In the current study, we aim to determine whether alleviation of hypoxia is merely a downstream effect of hypertrophic differentiation as previously described or whether alleviation of hypoxia and consequent changes in oxygen tension mediated signaling events also plays an active role in regulating the hypertrophic differentiation process itself.
  
  
  METHODS
  Fetal mouse tibiae (E17.5) explants were cultured up to 21 days under normoxic or hypoxic conditions (21% and 2.5% oxygen respectively). Tibiae were analyzed on growth kinetics, histology, gene expression and protein secretion.
  
  
  RESULTS
  The oxygen level had a strong influence on the development of explanted fetal tibiae. Compared to hypoxia, normoxia increased the length of the tibiae, length of the hypertrophic zone, calcification of the cartilage and mRNA levels of hypertrophic differentiation-related genes e.g. MMP9, MMP13, RUNX2, COL10A1 and ALPL. Compared to normoxia, hypoxia increased the size of the cartilaginous epiphysis, length of the resting zone, calcification of the bone and mRNA levels of hyaline cartilage-related genes e.g. ACAN, COL2A1 and SOX9. Additionally, hypoxia enhanced the mRNA and protein expression of the secreted articular cartilage markers GREM1, FRZB and DKK1, which are able to inhibit hypertrophic differentiation.
  
  
  CONCLUSIONS
  Collectively our data suggests that oxygen levels play an active role in the regulation of hypertrophic differentiation of hyaline chondrocytes. Normoxia stimulates hypertrophic differentiation evidenced by the expression of hypertrophic differentiation related genes. In contrast, hypoxia suppresses hypertrophic differentiation of chondrocytes, which might be at least partially explained by the induction of GREM1, FRZB and DKK1 expression.
authors.affiliation: Department of Developmental BioEngineering, MIRA Institute for Biomedical Technology and Technical Medicine, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Jeroen C H
authors.initials: JC
authors.lastname: Leijten
authors.forename: Liliana S
authors.initials: LS
authors.lastname: Moreira Teixeira
authors.forename: Ellie B M
authors.initials: EB
authors.lastname: Landman
authors.forename: Clemens A
authors.initials: CA
authors.lastname: van Blitterswijk
authors.forename: Marcel
authors.initials: M
authors.lastname: Karperien
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006132:Growth Plate / Q000166:cytology / Q000254:growth & development; D006984:Hypertrophy / Q000378:metabolism / Q000473:pathology; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018919:Neovascularization, Physiologic / Q000235:genetics; D009924:Organ Culture Techniques; D010012:Osteogenesis / Q000235:genetics / Q000502:physiology; D010100:Oxygen / Q000378:metabolism*; D015398:Signal Transduction; D013977:Tibia / Q000254:growth & development / Q000378:metabolism
chemical_list: D010100:Oxygen