Hypoxia decreases Runx2/Cbfa1 expression in human osteoblast-like cells

To elucidate the molecular mechanism in relation to vascular supply and osteoporosis, we investigated the effect of hypoxia on Runx2 expression in MG63 cells. Also investigated was expression of type I collagen and osteocalcin, which are regulated by Runx2, alkaline phosphatase (ALPase) to see if they are affected by hypoxia. Quiescent cultures of MG63 cells were exposed to hypoxia (2% O₂) and normoxia (18% O₂) for 24, 48, 72 and 96 h. In cells exposed to hypoxia, reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that mRNA expression of Runx2, type I collagen, osteocalcin, and ALPase were decreased in a time dependent manner to 96 h. Activity of ALPase was also reduced in the same manner. Western blotting showed a marked decrease in Runx2 protein at 96 h in cells under hypoxia compared to normoxia. These data indicate that Runx2 expression in osteoblasts is reduced by hypoxia, and may be a mechanism of osteoporosis by decreased vascular supply.