Objective To investigate the effect of all-trans retinoic acid (ATRA) on the osteogenesis induced by bone morphogenetic protein 9 (BMP9) in mesenchymal stem cells (MSCs). Methods Histochemical staining was used to test the alkaline phosphatase (ALP) activities when C3H10T1/2 cells were treated with BMP9 and/or ATRA for 5 or 7 d. Then
the protein level of osteopontin in the C3H10T1/2 cells after treatment of BMP9 and/or ATRA for 9 or 11 d was detected by Western blotting. The mineralization in the cells were tested with Alizarin red staining after the treatment for 14 or 20 d. Finally
the activation of BMP-Smad signaling was studied with BMPR-Smad binding site luciferase reporter assay and Western blotting to determine the phosphorylation level of Smad1/5/8. Results The activities of ALP were increased by BMP9 and/or ATRA
but the ALP activities in the cells treated by BMP9 and ATRA are more pronounced than that the cells by BMP9 or ATRA alone. ATRA potentiated the osteopontin expression and mineralization induced by BMP9 in C3H10T1/2 cells. ATRA promoted the phosphorylation level of Smad-1/5/8 and increased the luciferase activity of BMPR-Smad luciferase reporter. Conclusion ATRA potentiates the osteogenesis induced by BMP9 in MSCs
which may be mediated by increase of the BMP-Smad signaling transduction.