EXPRESSION OF BMP-2 AND TGF-BETA-1 MESSENGER-RNA DURING HEALING OF THE RABBIT MANDIBLE

To identify the cell types which produce BMP and TGF-beta during fract ure healing and to elucidate the interactions between BMP and TGF-beta in regulating cell proliferation and differentiation at various stage s, an experimental model of fracture healing in the rabbit mandible wa s established and the expression of BMP-2 and TGF-beta 1 mRNA was stud ied at different healing stages by in situ hybridization. The results showed that undifferentiated mesenchymal cells, differentiating osteob lasts and chondroblasts, had higher levels of BMP-2 mRNA at the stage of intramembranous bone formation and early chondrogenesis, while the level of TGF-beta 1 mRNA was higher in chondrocytes and active differe ntiated osteoblasts during chondrogenesis and endochondral ossificatio n, respectively. We conclude that BMP-2 expression was correlated with the differentiation of mesenchymal cells into osteoblasts and chondro cytes. TGF-beta 1 mRNA expression was closely associated with the acti ve synthetic stage of osteoblasts and chondrocytes. These observations suggest that both BMP and TGF-beta are involved in the regulation of fracture healing. BMP may play an important role in bone induction and early chondrogenesis, while TGF-beta regulates the proliferation and active synthetic ability of chondrocytes and osteoblasts.