[Pathogenesis of osteoporosis--overview]

Pathogenesis of osteoporosis was overviewed from standpoints of individual level, organ level and cellular level, respectively. As for the individual level, it is important to discriminate the pathogenetic factors related to low BMD or fractures. Independent from BMD, age, previous fractures, bone geometry, microstructure of the bone are related to fractures by influencing the bone quality. As for the organ level, pathogenesis of osteoporosis should be discussed from the view point of bone remodeling and its controlling factors. However, details of this process are still unclear. As for the cellular level, clarification of the roles of osteoblast, osteoclast and their interactions are essential in understanding the pathogenesis of osteoporosis. Recent discovery of Cbfa1, RANK/RANKL signaling and osteoprotegerin may open the new insight in the pathogenesis of osteoporosis.