Cell cycling determines integrin-mediated adhesion in osteoblastic ROS 17/2.8 cells exposed to space-related conditions

Six days of microgravity (Bion10 mission) induced dramatic shape changes in ROS 17/2.8 osteoblasts (7). During the Foton 11 and 12 space flights, we s tudied the kinetics (0-4 days) of ROS 17/2.8 morphology and adhesion, the r elationships between adhesion and cell cycle progression after 4 days in sp ace, and osteoblastic growth and activity after 6 days in space. Quantitati ve analysis of high-resolution adhesion [focal adhesion area imaged by tota l interference reflection fluorescent microscopy (TIRFM)] and integrin-depe ndent adhesion (imaged on confocal microscope by vinculin and phosphotyrosi ne staining) as well as cell cycle phase classification [Ki-67 staining, S- G2, mitotic cells and G1 (postmitotic cells)] were performed using programs validated in parabolic flight and clinostat. We observed disorganization o f the cytoskeleton associated with disassembling of vinculin spots and phos phorylated proteins within focal contacts with no major change in TIRFM adh esion after 2 and 4 days of microgravity. Postmitotic cells, alone, account ed for the differences observed in the whole population. They are character ized by immature peripheral contacts with complete loss of central spots an d decreased spreading. Osteocalcin, P1CP and alkaline phosphatase, and prol iferation were similar in flight cells and 1 g centrifuge and ground contro ls after 6 days. In conclusion, microgravity substantially affected osteobl astic integrin-mediated cell adhesion. ROS17/2.8 cells responded differentl y, whether or not they were cycling by reorganizing adhesion plaque topogra phy or morphology. In ROS 17/2.8, this reorganization did not impair osteob lastic phenotype.