STIMULATION OF BONE-MATRIX APPOSITION INVITRO BY LOCAL GROWTH-FACTORS - A COMPARISON BETWEEN INSULIN-LIKE GROWTH FACTOR-I, PLATELET-DERIVED GROWTH-FACTOR, AND TRANSFORMING GROWTH-FACTOR-BETA

Many recent in vitro studies have shown effects of insulin-like growth factor I (IGF I), platelet-derived growth factor (PDGF), and transforming growth factor-β (TGFβ) on the proliferation and differential functions of bone-forming os-teoblasts; however, the question whether these factors might ultimately lead to a net increase or decrease in bone formation has been difficult to assess. In this study, we have used an autoradiographic method based on the incorporation of [3H] proline into freshly synthesized bone matrix to determine the overall effects of these factors on bone matrix apposition in 21- day-old fetal rat calvariae. IGF I, PDGF, and TGFβ increased bone matrix apposition in a dose-dependent manner up to 2-fold within 48 h. In addition, they partially or completely reversed the inhibition of bone matrix apposition observed with PTH. Exogenously added TGFβ was significantly more potent than equimolar concentra-tions of PDGF or IGF I in stimulating bone formation. Matrix apposition was greatest when IGF I, PDGF, and TGFβ were added simultaneously to the culture medium, indicating that these factors can enhance each other in stimulating bone for-mation. In conclusion, our results provide direct evidence that IGF I, PDGF, and TGFβ are capable of stimulating bone formation in vitro. © 1990 by The Endocrine Society.