Effect of bone morphogenetic protein-2 (BMP-2) or troglitazone, as an inducer of osteogenic cells or adipocytes, on differentiation of a bone marrow mesenchymal progenitor cell line established from temperature-sensitive (ts) simian virus (SV) 40 T-antigen gene transgenic mice.

TBR31-2 is one of the bone marrow stromal cell lines. Differentiation toward osteogenic cells and calcification was observed when TBR31-2 cells were cultured for 4 weeks. Bone morphogenetic protein-2 (BMP-2) stimulated alkaline phosphatase (ALP) activity in a dose- and time-dependent manner. On the other hand, troglitazone increased oil droplet accumulation in a dose-dependent manner. In the presence of BMP-2, an increase of expression in osteogenic cell differentiation marker genes and a decrease of expression in adipocyte differentiation marker genes were observed with the exception of the induced expression of peroxisome proliferator-activated receptor gamma (PPARgamma), however, troglitazone, a ligand of PPARgamma treatment exhibited the opposite tendency. Interestingly, treatment with both BMP-2 and troglitazone resulted in a decrease of ALP activity and an increase of oil droplet accumulation. Reverse tanscription-polymerase chain reaction (RT-PCR) analysis also indicated that osteogenic differentiation markers decreased and that adipocyte differentiation markers increased. Thus, when the cells were cultured with BMP-2, osteogenic differentiation was enhanced while the expression of PPARgamma was maintained, and the addition of troglitazone caused a significant number of differentiated cells into adipocytes. These findings indicate that BMP-2 enhanced osteogenic differentiation and the expression of adipogenic transcription factor (PPARgamma) followed by osteogenic differentiation without activation of PPARgamma by its ligand.