Activation of beta-catenin-LEF/TCF signal pathway in chondrocytes stimulates ectopic endochondral ossification.
OBJECTIVE
Members of the Wnt signaling protein family are expressed during cartilage development and skeletogenesis, but their roles and mechanisms of action in those processes remain unclear. Recently, we found that beta-catenin-LEF/TCF-dependent Wnt signaling stimulates chondrocyte maturation and hypertrophy and extracellular matrix calcification in vitro, events normally associated with cartilage-to-bone transition during skeletogenesis. Thus, we tested here whether activation of this pathway promotes endochondral ossification.


METHODS
Chick chondrocytes were infected with avian retroviral expression vectors encoding constitutive-active (CA) or dominant-negative (DN) forms of LEF, which activate or block beta-catenin-dependent Wnt signaling respectively. These cells and companion uninfected control cells were seeded into type I collagen gels and transplanted intramuscularly into nude mice. The resulting ectopic tissue masses forming over time in vivo were subjected to histological and molecular biological analyses.


RESULTS
Transplantation of chick chondrocytes induced de novo endochondral bone formation. In situ hybridization and RT-PCR using species-specific probes and primers showed that the ectopic cartilaginous tissue was avian and thus donor-derived, whereas the bone tissue was mouse and thus host-derived. CA-LEF-expressing ectopic tissue masses contained abundant bone and marrow, while DN-LEF-expressing masses contained little bone and lacked marrow.


CONCLUSIONS
Activation of beta-catenin-LEF/TCF-dependent Wnt signaling accelerates chondrocyte maturation and replacement of cartilage by bone.
Kitagaki
J
J
Department of Molecular, Cell and Tumor Biology, Osaka University Faculty of Dentistry, Osaka 565-0871, Japan.
Iwamoto
M
M
Liu
J-G
JG
Tamamura
Y
Y
Pacifci
M
M
Enomoto-Iwamoto
M
M
D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D019902:Chondrocytes / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D051821:Lymphoid Enhancer-Binding Factor 1; D051379:Mice; D009999:Ossification, Heterotopic / Q000209:etiology* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D051821:Lymphoid Enhancer-Binding Factor 1; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin