Study On The Response Of Osteoblasts To Overuse And Disuse In Vitro

The balance of bone resorption and bone formation keeps the bone mass level, while many factors including the mechanical loading can break it. Normally the balance is kept, even though the physical loading input on bone changes in a range due to the change of our activity. However, it is broken down when our activity and the loading exerted on bone and its cells are greatly changed, such as the obvious weight gain/loss, long-term bed rest, space flight. These phenomena were consistent with the hypothesis put forword by Burger in 1999 that overuse will profit bone formation, while disuse will profit bone resorption, from the point of signaling and nutrients supply among cells in bone. However, if it is true in cellular level remains unknown. In this study, the aim of our investigation is to make clear if the overuse increases bone formation and disuse increases bone resorption in vitro cellular level.We used Wistar primary cultured osteoblasts and studied its differentiation as bone formation index and the ratio of secreted RANKL and OPG as bone resorption index. Stepwise increased and decreased laminar shear stress was used to mimic the overuse and disuse. The flow chamber was to provide controlled shear stress. The main work and conclusions were as follows:Flow chamber was designed and used in our study. It provided laminar flowshear stress which can be adjusted via the flow rate. The assembly and disassembly were very easy. About 35 mL of flow fluid was used in our flow system.The primary Wistar rat's osteoblasts were cultured from the calvaria of new-born rats by the tissue piece culture method. The osteoblasts were identified by the morphology and Von Kossa staining. The third passage of osteoblasts cultured on glass slides was used in mechanical experiments after they reached confluence.Six processes of shear stress were designed here to validate the effect of overuse and disuse on the gene expression of osteoprotegerin ( OPG ) and osteoclast differentiation facto(rRANKL)and alkaline phosphatase(ALP)and mineralization. The results confirmed that the stepwise increased shear stress inhibited bone resorption; while the stepwise decreased shear stress gave rise to adverse response. The stepwise increased shear stress promoted the mineralization, while 30-20-10-5 dyn/cm2 stepwise decreased shear stress inhibited it, the other two stepwise decreased shear stresses promoted the mineralization. Our results confirmed that overuse can profit bone formation by increasing bone formation and inhibiting bone resorption; while disuse can profit bone resorption at least by increasing bone resorption.