[The regulatory mechanisms of bone metabolism by semaphorin].

Bone is continuously remodeled by osteoclastic bone resorption and osteoblastic bone formation to maintain the structural integrity and mineral homeostasis. This process is called "bone remodeling" . These bone cells are regulated by mechanical stimulation and systemic (hormonal) factors in addition to autocrine, paracrine factors and cell-cell interactions. Recently, we reported that two semaphorin molecules Sema4D and Sema3A have a crucial role in the regulation of bone remodeling. Sema4D derived from osteoclasts inhibits osteoblast differentiation not to hamper osteoclastic bone resorption. Sema3A derived from osteoblast lineage cells inhibits osteoclast differentiation and promotes osteoblast differentiation synchronously to increase bone mass. These studies provide a scientific basis for future therapeutic approaches to bone diseases.