Bone morphogenetic protein-2 induces the differentiation of a mesenchymal progenitor cell line, ROB-C26, into mature osteoblasts and adipocytes

Osteoblasts and adipocytes originate from common precursor cells. We examined the effects of bone morphogenetic protein-2 (BMP-2) on the molecular mechanisms governing the diametric actions of BMP-2 on simultaneous mature osteoblast and adipocyte differentiation in a clonal mesenchymal progenitor cell line, ROB-C26 (C26). The present study using RT-PCR, Western blotting and ELISA investigated the effects of BMP-2 on transcription factors for osteoblasts (Runx2, Dlx5, Osterix, Msx2 and AJ18) and adipocytes (PPARγ2), osteoblastic markers, alkaline phosphatase (ALP), bone sialoprotein (BSP) and osteocalcin (OC), and adipocyte differentiation-dependent protein, aP2 in C26 cells. BMP-2 increased not only mRNA and protein expressions of Dlx5 followed by inducing Osterix and BSP levels in a dose- and time-dependent manner with an increase in Runx2, Msx2, AJ18, ALP and OC levels, but also induced PPARγ2 and aP2 levels. At the light microscopic level, BMP-2 induced mature osteoblastic and adipogenic differentiation in the C26 cultures not only by an increase in the number of ALP-positive osteoblasts, in their staining intensity and in the number of mature adipocytes with Oil Red O-positive lipid droplets, but also mineralized matrix formation of the cultures assessed by detecting an increase in calcium concentration and the formation of Alizarin Red S-positive mineralization nodules. These results indicate that BMP-2 induces the differentiation of C26 mesenchymal progenitors into mature osteoblasts and adipocytes and the usefulness of this cell line for studying the regulatory mechanism of osteoblast and adipocyte differentiation from common mesenchymal progenitors.