Objective    To study the role of Notch signaling pathway in bone morphogenetic protein 9 (BMP9)  induced osteogenic differentiation of multipotent stem cells and its mechanism.     Methods     Adenovirus vectors (AdBMP9/AdGFP

AdHey1/AdRFP) and C2C12 cells treated with BMP9/GFP were stained with cell chemistry. Alkaline phosphatase (ALP)

an osteogenesis marker

was detected with a quantitative method. Target gene Hey1 of Notch signaling pathway was detected by quantitative RT-PCR in order to study its role in BMP9-induced osteogenic differentiation of multipotent stem cells. Effect of Notch signaling pathway on osteogenesis was detected by cell-density assay and Notch signaling pathway inhibitor (DAPT). After treatment with AdBMP9/AdGFP

ligands of Notch receptor and its expression were detected.     Results    AdBMP9 increased the activity of ALP on days 1

3

5 and 7

while transiently increased the Hey1 expression level in a dose-dependent manner. Although Hey1 itself could not increase ALP

it could help BMP9 to enhance ALP (P0.05). The expression level of ALP and Hey1 was higher in 40% and 80% cell density groups than in 20% cell density group (P0.05). The ALP activity was lower in DAPT group than in control group (P0.05). The number of Notch receptors and ligands was greater in BMP9 group than in GFP group

in which the receptor (Notch 4) and the ligand (Jag-1) increased by 11.3 and 5.1 times

respectively.     Conclusion      Notch signaling pathway can enhance BMP9-induced osteogenic differentiation of multipotent stem cells possibly by up-regulating the expression of its ligands and receptors through BMP9，thus leading to osteogenesis.