Objective      To determine the role of Smad7 (mothers against decapentaplegic homolog 7) in bone morphogengetic protein 2 (BMP2)-induced chondrogenic differentiation which was potentiated by Sox9 (sex determing region Y-related high mobility group-box gene 9) and investigate the underlying mechanism.       Methods      Mouse bone marrow mesenchymal stem cell line C3H10T1/2 was transfected with recombinant adenoviruses Ad-GFP (as control)

Ad-BMP2

Ad-Sox9 and Ad-BMP2+Ad-Sox9 respectively. The expression of Smad7 at mRNA and protein levels was measured by real-time PCR

immunocytochemical staining and Western blot analysis. Real-time PCR and Western blot analysis was also used to detect the expression of Smad7 related factors MMP13 and osteopontin (OPN).       Results      When the C3H10T1/2 cells were transfected with recombinant adenoviruses Ad-BMP2+Ad-Sox9 for 7 and 11 d

the mRNA and protein expression of Smad7 was significantly lower than in the cells transfected by Ad-BMP2 (P0.05)

and similar results were also found by immunocytochemical staining. What’s more

the over-expression of Sox9 also effectively reduced the expression of MMP13 and OPN at mRNA and protein levels than the Ad-BMP2-transfected cells (P0.05).       Conclusion      In the BMP2-induced chondrogenic differentiation of mouse mesenchymal stem cells

the over-expression of Smad7 is suppressed by Sox9

so is the expression of Smad7 related factors

MMP13 and OPN. Thus

the inhibitory effect of Smad7 on chondrogenic differentiation is relieved

which prevent the maturation of chondrocyts and then keep the normal status of chondrocyts in development.