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* Istituto Nazionale per la Ricerca sul Cancro, Centro di Biotecnologie Avanzate and During endochondral bone formation, avascular cartilage differentiates to hypertrophic cartilage
that then undergoes erosion and vascularization leading to bone deposition. Resting cartilage produces inhibitors of angiogenesis, shifting to production of angiogenic stimulators in hypertrophic cartilage. A major
protein synthesized by hypertrophic cartilage both in
vivo and in vitro is transferrin. Here we show that transferrin is a major angiogenic molecule released by hypertrophic cartilage. Endothelial cell migration and invasion is stimulated by transferrins from a number of
different sources, including hypertrophic cartilage.
Checkerboard analysis demonstrates that transferrin is
a chemotactic and chemokinetic molecule. Chondrocyte-conditioned media show similar properties. Polyclonal anti-transferrin antibodies completely block endothelial cell migration and invasion induced by
purified transferrin and inhibit the activity produced by
hypertrophic chondrocytes by 50-70% as compared
with controls. Function-blocking mAbs directed against
the transferrin receptor similarly reduce the endothelial migratory response. Chondrocytes differentiating in the
presence of serum produce transferrin, whereas those
that differentiate in the absence of serum do not. Conditioned media from differentiated chondrocytes not
producing transferrin have only 30% of the endothelial cell migratory activity of parallel cultures that synthesize transferrin.
The angiogenic activity of transferrins was confirmed
by in vivo assays on chicken egg chorioallantoic membrane, showing promotion of neovascularization by
transferrins purified from different sources including
conditioned culture medium.
Based on the above results, we suggest that transferrin
is a major angiogenic molecule produced by hypertrophic chondrocytes during endochondral bone formation.
Dipartimento di Oncologia Clinica e
Sperimentale, Università di Genova, Genova, Italy; § Istituto Internazionale di Genetica e Biofisica, Consiglio Nazionale delle
Ricerche, Napoli, Italy; and
Istituto di Anatomia Umana Normale, Istologia ed Embriologia, Università di Bari, Bari, Italy
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