ABSTRACT
The bony skeleton, an essential component of the skeletal system, enables locomotive activity, the storage of calcium, and the harboring of hematopoietic stem cells. This multifunctional organ is characterized by the calci—ed hard tissue composed of type I collagen and highly organized deposits of calcium phosphate (hydroxyapatite) (Seeman and Delmas, 2006). Although bone seems to be metabolically inert, it is restructured at such a high speed that approximately 10% of the total bone content is replaced per year in adult vertebrates. This process, called bone remodeling, is dependent on the dynamic balance of bone formation and resorption, which are mediated by osteoblasts and osteoclasts, respectively. A delicate regulation of this process is a prerequisite for normal bone homeostasis, and an imbalance is often related to metabolic bone diseases in humans (Takayanagi, 2007).
