[Coupling of bone resorption and formation.]

Preceding bone resorption is a prerequisite for the initiation of subsequent bone formation during adulthood and the quantity as well as the quality of bone is maintained by which newly formed bone by osteoblasts replaces precisely the amount removed by osteoclastic bone resorption at the same level. This process is namely " bone remodeling " and the rely of bone formation in response to resorption is termed " coupling " . Importantly, bone formation is induced by osteoclastic bone resorption or the presence of osteoclasts themselves in the bone remodeling. Recently, emerging evidence points to the involvement of factors secreted or presented by osteoclasts themselves in the coupling process. Thus, coupling mechanisms involved in the bone remodeling are critical for understanding of bone physiology and metabolic bone diseases such as osteoporosis.