Effect of a continuously applied compressive pressure on mouse osteoblast‐like cells (MC3T3‐E1) in vitro

Bone metabolism is often affected by a variety of mechanical forces, but the cytological basis of their action is not known. In this study, we examined the effect of a continuously applied compressive pressure (CCP) on the growth and differentiation of clonal mouse osteoblast‐like cells (MC3T3‐E1) cultured in a specifically devised culture chamber. The gas phase of the chamber was maintained at a pressure of 2 atmospheres (atm) above ambient (3 atm total, 3.1 kg/cm 2 ; 3.0 × 10 5 Pa) by continuously infusing a compressed mixed gas (O 2 : N 2 :CO 2 = 7.0%:91.3%:1.7%). The pO 2 , pCO 2 , and pH in the culture medium at 37°C under 3 atm were maintained at the same levels as those under 1 atm. MC3T3‐E1 cells were cultured in α minimal essential medium containing 10% fetal bovine serum under either 3 atm in the CCP culture chamber or 1 atm in an ordinary CO 2 incubator. Alkaline phosphatase activity, a marker of osteoblasts, was greatly suppressed by the CCP treatment. The inhibition of alkaline phosphatase activity was rapidly restored when the cells were transferred to an ordinary CO 2 , incubator under 1 atm, indicating that the inhibition of alkaline phosphatase activity by CCP is reversible. Cell growth was not altered under CCP. The CCP treatment greatly increased the production and secretion of prostaglandin E 2 (PGE 2 ). Adding either conditioned medium from the CCP culture or exogenous PGE 2 to the control culture under 1 atm suppressed alkaline phosphatase activity dose‐dependently. The CCP treatment also suppressed collagen synthesis and calcification. These results suggest that CCP causes the cells to produce and secrete PGE 2 which, in turn, inhibits differentiation of osteoblasts and the concomitant calcification.