Papers by Author: Satoru Toyosawa

Abstract: Bone microstructure and its functions are maintained by the activity of bone cells such as osteoclast for bone resorption and osteoblast for bone formation. In this study, we examined the role of osteoclast on the formation of the preferential orientation of biological apatite (BAp) as a bone quality parameter using OPG-KO and op/op mouse models in which the expression of osteoclast increases for osteoporosis and decreases for osteopetrosis. The orientation degree of the BAp c-axis was analyzed by a microbeam X-ray diffraction system. We found more decrease in the preferential alignment of the BAp c-axis along the longitudinal direction of bone in the femoral bones of both OPG-KO and op/op mice at 12 weeks compared with normal control mice. We concluded that changes in the amount and activity of osteoclast affect BAp alignment, resulting in the degradation of bone microstructure in osteoporosis and osteopetrosis.

Abstract: Absorption and formation of hard tissues are repeated in vivo by the activity of osteoclast and osteoblast, respectively. The preferential alignment of BAp or collagen fibril is thought to be closely related to the activity of the bone cells. In this study, changes in bone mineral density (BMD) and preferential alignment of biological apatite (BAp) were examined focusing on the role of osteoblast using the model of osteopetrotic (op/op) mice in which osteoblast activity was normal but the expression of osteoclast was reduced. Osteopetrotic (op/op) mice and their normal littermates aged 5, 12 and 24 weeks were analyzed. The BMD and BAp texture of femoral diaphysis were measured using peripheral quantitative computed tomography (pQCT) and a microbeam X-ray diffractometer system with a 50 µmφ diameter beam spot respectively. The decrease in osteoclast expression induced both the reduction of the skeletal system and calcification of the medullary cavity, which are typical features of osteopetrosis. As a result, the shape, BMD and preferential BAp alignment of the femur in the op/op mice were remarkably different from those in the control group. At the center of the femoral diaphysis, BMD in the cortical area showed no significant difference between the two groups, but preferential alignment of the BAp c-axis in the op/op mice group had a lower value than that in the control group. This suggests that the decrease in the number of osteoclasts suppresses normal remodeling, resulting in a decrease in bone quality, especially the preferential alignment of the BAp c-axis.