Transforming growth factor-beta1 modulates insulin-like growth factor binding protein-4 expression and proteolysis in cultured periosteal explants.

Objective: Periosteum is involved in bone growth and fracture healing and has been used as a cell source and tissue graft for tissue engineering and orthopedic reconstruction including joint resurfacing. Periosteum can be induced by transforming growth factor beta (TGF-beta) or insulin-like growth factor-I (IGF-I) alone or in combination to form cartilage. However, little is known about the interaction between IGF and TGF-beta signaling during periosteal chondrogenesis. The purpose of this study was to determine the effect of TGF-beta1 on IGF binding protein-4 (IGFBP-4) and the IGFBP-4 protease pregnancy-associated plasma protein-A (PAPP-A) expression in cultured periosteal explants.
Design: Periosteal explants from rabbits were cultured with or without TGF-beta1. IGFBP-4 and PAPP-A mRNA levels were determined by real-time quantitative PCR. Conditioned medium was analyzed for IGFBP-4 and PAPP-A protein levels and IGFBP-4 protease activity.
Results: TGF-beta1-treated explants contained lower IGFBP-4 mRNA levels throughout the culture period with a maximum reduction of 70% on day 5 of culture. Lower levels of IGFBP-4 protein were also detected in the conditioned medium from TGF-beta1-treated explants. PAPP-A mRNA levels were increased 1.6-fold, PAPP-A protein levels were increased threefold, and IGFBP-4 protease activity was increased 8.5-fold between 7 and 10days of culture (the onset of cartilage formation in this model) in conditioned medium from TGF-beta1-treated explants.
Conclusions: This study demonstrates that TGF-beta1 modulates the expression of IGFBP-4 and PAPP-A in cultured periosteal explants.
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