Coupling between osteogenesis and angiogenesis

Abstract

Recent progresses clear show that osteogenesis, which requires a coupling between angiogenesis and osteogenesis, is not a cell autonomous process. The new findings suggest that pericytes, arising from a vessel‐associated stem cell progenitor, represent an osteoprogenitor capable of bone formation in a “right” microenvironment. Second, hypoxia environment where bone cells are located greatly affect osteogenesis. Recent studies showed that hypoxia‐inducible factor 1α (HIF‐1α), a transcriptional regulator of vascular endothelial growth factor (VEGF) expression, represents rate‐limiting components of osteogenic‐angiogenic coupling and trabecular bone formation. Last but not the least, the bone does not have a lymphatic system to transport the excessive fluid back to the circulation system. Our studies using a scanning electronic microscope combining with a resin‐casted‐acid etching method reveal that the entire blood vessel system in bone, including arterioles, venules and capillaries are connected with dendritic osteocytes. We propose that osteo‐canalicular system, in addition to its mechanical function, may play a role in facilitating fluid flow back to circulation system. (This work is partially supported by NIH grants: AR51587 and DE 016977).