Hypoxia Induces Osteogenesis-Related Activities and Expression of Core Binding Factor α1 in Mesenchymal Stem Cells

Mesenchymal stem sells (MSCs) have received much attention in the field of bone tissue engineering due to their biological capability to differentiate into osteogenic lineage cells. Hypoxia-inducible factor 1alpha (HIF-1 alpha) plays an important role in the MSC-related bone regeneration during hypoxia, while core binding factor alpha 1 (Cbf alpha 1) is a transcription regulator that is involved in the chondrocyte differentiation and ossification. In the present study, we investigated the effects of hypoxia on biological capability of MSCs. MSCs were isolated from adult rabbit bone marrow, and were cultured in vitro under normoxia (air with 5% CO2) or hypoxia (5% CO2 and 95% N-2). The proliferation of MSCs, alkaline phosphatase (ALP) activity, and production of collagens type I and type III (Col I/III) were examined. The expression levels of HIF-1 alpha and Cbf alpha 1 were measured by real-time PCR and western blot analyses. We found that hypoxia significantly induced the proliferation of MSCs and increased ALP activity and the production of Col I/III. Moreover, hypoxia increased the expression of Cbf alpha 1 mRNA after 12 h, whereas the expression of HIF-1 alpha mRNA was increased after 1 h of hypoxia. Knockdown of HIF-1 alpha expression with a small interfering RNA significantly increased the expression levels of Cbf alpha 1 protein either under the normoxia or hypoxia condition. Our results indicate that hypoxia enhances MSCs to differentiate into osteogenic lineage cells and suggest that Cbf alpha 1 may be negatively regulated by HIF-1 alpha.