A novel in vivo model to study endochondral bone formation; HIF-1alpha activation and BMP expression.
Numerous growth and transcription factors have been implicated in endochondral bone formation of the growth plate. Many of these factors are up-regulated during hypoxia and downstream of Hypoxia-Inducible Factor (HIF)-1alpha activation. However, the specific function of these factors, in the context of oxygenation and metabolic adaptation during adult periosteal endochondral bone formation, is largely unknown. Here, we studied HIF-1alpha and the possible roles of (HIF-1alpha related) growth and transcription factors in a recently developed in vivo model for adult periosteal endochondral bone formation. At different phases of periosteal endochondral bone formation, mRNA levels of Transforming Growth Factor (TGF)-beta1, Bone Morphogenetic Proteins (BMP)-2, -4, and -7, Indian Hedgehog (Ihh), Parathyroid Hormone-related Protein (PTHrP), Sox9, Runx2, HIF-1alpha, Vascular Endothelial Growth Factor (VEGF), periostin (POSTN), and Glyceraldehyde-3-Phophate Dehydrogenase (GAPDH) were evaluated with RT-real time-PCR. Also protein levels of TGF-beta1, BMP-2, -4, and -7, HIF-1alpha, and POSTN were examined. During the chondrogenic phase, the expression of Sox9, Ihh, and HIF-1alpha was significantly up-regulated. TGF-beta1 mRNA levels were rather constant, and the mRNA levels of BMPs were significantly lower. Immunohistochemical detection of corresponding gene products, however, revealed the presence of the proteins of TGF-beta1, BMP-2, -4, and -7, HIF-1alpha, and POSTN within the chondrocytes during chondrogenesis. This discrepancy in gene expression between mRNA and protein level for TGF-beta1 and the different BMPs is indicative of post-transcriptional regulation of protein synthesis. HIF-1alpha activation and up-regulation of GAPDH support a hypoxia-induced metabolic shift during periosteal chondrogenesis. Our model recapitulates essential steps in osteochondrogenesis and provides a new experimental system to study and ultimately control tissue regeneration in the adult organism.
Emans
Pieter J
PJ
Department of Orthopedic Surgery, University Hospital Maastricht, Maastricht, The Netherlands. pj.emans@orthop.unimaas.nl
Spaapen
Frank
F
Surtel
Don A M
DA
Reilly
Keryn M
KM
Cremers
Andy
A
van Rhijn
Lodewijk W
LW
Bulstra
Sjoerd K
SK
Voncken
Jan Willem
JW
Kuijer
Roel
R
D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis* / Q000235:genetics; D001842:Bone and Bones / Q000378:metabolism; D002356:Cartilage / Q000378:metabolism; D020219:Chondrogenesis; D005260:Female; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D010012:Osteogenesis; D010521:Periosteum / Q000166:cytology / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits
D019485:Bone Morphogenetic Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger