Bone sialoprotein (BSP) is a crucial factor for the expression of osteoblastic phenotypes of bone marrow cells cultured on type I collagen matrix

In this study, we demonstrated that type I collagen matrix induced the expr ession of osteoblastic phenotypes of bone marrow cells, and that antibone s ialoprotein (BSP) monoclonal antibody suppressed the expression of these ph enotypes. On the other hand, BSP accelerated the expression of osteoblastic phenotypes of bone marrow cells. The adherent bone marrow cells were harve sted from rat femur and cultured on type I collagen matrix gels in medium c ontaining 15% fetal calf serum, neither beta-glycerophosphate nor glucocort icoid. Cells showed osteoblastic phenotypes (high alkaline phosphatase acti vity, osteocalcin synthesis, and responsiveness against parathyroid hormone ) on collagen matrix gels at week 3 after the inoculation, and simultaneous ly, BSP was detected in the conditioned medium by Western blotting using an anti-BSP monoclonal antibody. However, cells in the conventional culture d ishes did not show osteoblastic phenotypes during the experimental period. To investigate the physiological function of BSP in osteoblastic differenti ation, bone marrow cells were cultured on collagen matrix with an anti-BSP monoclonal antibody for 3 weeks. This treatment suppressed the expression o f the osteoblastic phenotypes, and the effect of the antibody was abolished by the addition of bovine bone BSP. Furthermore, bovine bone BSP stimulate d the expression of osteoblastic phenotypes of bone marrow cells. Our resul ts indicate that BSP plays a crucial role in the expression of osteoblastic phenotypes of bone marrow cells.