Hypoxia activates a variety of intracellular signaling pathways and regulates target genes by the transcriptional factor, HIF (hypoxia-inducible factor). One of the three �- subunits [HIF1�, -2�, and -3�] and �-subunit (HIF1�, or ARNT) form HIF heterodimer . Many biochemical processes involve HIF target genes, such as anaerobic metabolism and angiogenesis. Wang et al. showed that activation of the HIF1� pathway increased blood vessel formation in bone and was involved in bone remodeling .