Effects of bone morphogenetic protein-2 and transforming growth factor-β1 on gene expression of decorin and biglycan by cultured osteoblastic cells

The influence of bone morphogenetic protein-2 (BMP-2) and transforming growth factor beta (TGF-beta) on the expression of small proteoglycans, decorin and biglycan was investigated in a clonal rat osteoblastic cell line, ROS-C26 (C26) cells, which is a potential osteoblast precursor cell line and capable of differentiating into mature osteoblasts after treatment with recombinant BMP-2 (rhBMP-2). Following the culture of C26 cells for 3, 6, and 9 days in the presence or absence of rhBMP-2, alkaline phosphatase activity increased in the rhBMP-2 treated cells in direct proportion to their differentiation into more mature osteoblastic cells, whereas decorin mRNA decreased in the cells, when compared to control cells without rhBMP-2 treatment. These results were evident 6 days after treatment. However, rhBMP-2 treatment had no effect on biglycan mRNA expression in the cells. Subsequently, after removal of rhBMP-2 from the culture media, the cells were further cultured for 24 h with graded concentrations of TGF-beta 1 (0, 0.1, 1.0, 5.0, and 10 ng/ml). TGF-beta 1 decreased decorin mRNA expression in the cells dose dependently, but did not affect their biglycan mRNA expression. Furthermore, either removal of rhBMP-2 from the culture media or addition of TGF-beta 1 significantly decreased alkaline phosphatase activity of rhBMP-2-induced cells. These results indicate that osteoblastic differentiation is accompanied by increased alkaline phosphatase activity and decreased expression of decorin mRNA, but continuous expression of biglycan mRNA. Both rhBMP-2 and TGF-beta 1 inhibit decorin mRNA expression in osteoblasts at varying stages of differentiation, but their effects on biglycan mRNA expression and alkaline phosphatase are different.