Objective      To determine the effect of hypoxia inducible factor-1α (HIF-1α) on bone morphogenetic protein 2 (BMP2)-induced chondrogenic and osteogenic diff

erentiation in stem cells.       Methods      Recombinant adenoviruses AdBMP2

AdHIF-1α and AdGFP were generated to transfect mouse stem cell line C3H10T1/2. We detected the protein levels of Sox9 and Runx2 (chondrogenic and osteogenic differentiation critical regulatory factors) by Western blotting and the mRNA levels of COL2A1

aggrecan

COL1A1 and ALP (chondrogenic and osteogenic differentiation markers) by real-time PCR. Alcian blue staining

ALP staining and Alizarin red S staining were used to detect the secretion of cartilaginous matrix

ALP activity and bone matrix mineralization

respectively. We further demonstrated the role of HIF-1α in BMP2-induced chondrogenic and osteogenic differentiation by subcutaneous stem cell implantation in nude mice.       Results      On day 1 and day 3

the BMP2+HIF-1α group (stem cells treated with AdBMP2 and AdHIF-1α) showed significantly higher protein level of Sox9 and significantly lower protein level of Runx2 than the BMP2 group (stem cells treated with AdBMP2). On day 7 and day 9

the BMP2+HIF-1α group showed significantly higher mRNA level of COL2A1 and aggrecan (

P

0.05) and significantly lower mRNA levels of COL1A1 and ALP (

P

0.05) than the BMP2 group. We also found that the secretion of cartilaginous matrix in the BMP2+HIF-1α group was more than that in the BMP2 group

proven by Alcian blue staining. Bone matrix mineralization was not obvious in the BMP2+HIF-1α group as compared to the BMP2 group. In vivo

the BMP2+HIF-1α group formed more cartilage structures

but the BMP2 group formed more bone structures.       Conclusion      HIF-1α promotes BMP2-induced stem cell chondrogenic differentiation but inhibits osteogenic differentiation and endochondral ossification and maintains chondrogenic phenotype.