SHAPE CHANGES OF OSTEOBLASTIC CELLS UNDER GRAVITATIONAL VARIATIONS DURING PARABOLIC FLIGHT - RELATIONSHIP WITH PGE(2) SYNTHESIS

The relationship existing between cell morphofogy and cell metabolism, and the role of mechanical load in bone remodelling are well-known. I n osteoblasts, PGE(2) mediates part of the response to mechanical stre ss and induce cell shape changes. We studied the influence of gravity variations on osteoblast morphology and its relationship with PGE(2) s ynthesis during a parabolic flight. ROS 17/2.8 osteosarcoma cells flew 15 or 30 parabolae. We measured cell area and shape factor after fluo rescein staining with a semi-automatic image analyser and PGE(2) level s by RIA. Significant flight-induced shape changes consisted in a decr ease in cell area and an increase in shape factor (cell irregularity), in some cells, as compared to ground controls. This heterogeneity in cell response might be explained by a cell-cycle sensitivity to mechan ical stress. A 45 min pretreatment with indomethacin inhibited the fli ght-induced increase in cell irregularity whereas cell area remained d ecreased. PGE(2) levels were higher in flight than in ground controls. Linear regression analysis showed a significant negative relationship between cell area and PGE(2) synthesis. We concluded that ROS 17/2.8 are highly sensitive to gravitational variations and that PGE(2) is pa rtly implicated in cell shape changes observed during parabolic flight . However, other mechanisms than PGE(2) synthesis condition ROS 17/2.8 morphology in response to mechanical changes.