Objective       To determine the  effect of phosphatase and tensin homolog deleted on chromosome ten (PTEN) on bone morphogenetic protein 9 (BMP9) induced osteogenic differentiation in mouse embryonic fibroblasts (MEFs) and investigate the possible molecular mechanism.       Methods        Real-time PCR was employed to detect the endogenous expression of PTEN in mesenchymal stem cells (MSCs)

and the effect of BMP9 on the expression of PTEN in the MEFs. Histochemical staining was used to assay the activity of alkaline phosphatase (ALP)

PCR to detect the expression of osteopontin (OPN) and osteocalcin (OCN) induced by BMP9 in MEFs

and Alizarin Red S staining to detect the effect of PTEN on BMP9 induced matrix mineralization. Finally

BMPR-Smad luciferase reporter and Western blot assay were employed to determine the effect of PTEN on BMPs/Smads signaling pathway.       Results      PTEN was expressed in MSCs

and BMP9 inhibited the expression of PTEN in MEFs. Exogenous expression of PTEN inhibited the enhanced ALP activity induced by BMP9

whereas over-expression of PTEN suppressed the induced activity enhancement. Inhibition of PTEN improved the BMP9-induced expression of OCN in MEFs and promoted matrix mineralization. PTEN inhibitor potentiated BMP9-induced activation of BMPs/Smads signaling and phosphorylation of Smad1/5/8 in MEFs.       Conclusion        Down-regulation of PTEN plays an important role in the promotion of osteogenic differentiation induced by BMP9 in MSCs

which may be mediated by enhancing BMPs/Smads signaling transduction initialized by BMP9.