Effect of centrifugal force on growth of mouse osteoblastic MC3T3-E1 cells in vitro

The effect of biomechanical force on growth of skeletal tissue was studied in monolayer cultures of mouse osteoblastic MC3T3-E1 cells which were centrifuged at 320 g for 15 min to 72 h in a CO2 incubator. Centrifugation of the cells for 30 min in low concentrations (0.3 or 1%) of fetal bovine serum (FBS) caused a two-fold increase of [3H]thymidine incorporation at 20 h from the start of centrifugation. However, centrifugation under 10% FBS caused no increase in [3H]thymidine incorporation into DNA. Under 0.3% FBS, [3H]thymidine incorporation increased in a manner dependent on the period of centrifugation and reached a maximum when the cells were centrifuged for 3 h. Stimulation of DNA synthesis by centrifugation was abolished in the presence of H-7, an inhibitor of protein kinase C. Moreover, conditioned medium collected from the centrifuged cultures increased [3H]thymidine incorporation by two-fold over the basal when added to a quiescent culture of MC3T3-E1 cells. These results suggest that centrifugal force stimulates growth of osteoblastic cells through autocrine secretion of some diffusible growth-promoting activity. On the other hand, centrifugation of the cells inhibited induction by FBS of alkaline phosphatase activity and calcium-uptake, two indices of the differentiated phenotype of osteoblasts.