EXPRESSIONS OF INTEGRIN SUBUNITS IN OSTEOBLASTS DURING WEIGHTLESSNESS SIMULATION USING CLINOSTAT.  Z. Shu^{1, 2}, B. Wang², J.L. Nie¹, Y.H. Li¹. ¹Lab of Space Cellular and Molecular Biology, ISME, Beijing, 100094 and ²Dept of Aerospace Medicine, FMMU, Xi’an, 710032, P.R.China.

   Space flight experiments and studies carried out in altered gravity environments have revealed that exposure to altered gravity conditions results in (mal) adaptation of cellular function. In the present study, we used a clinostat to generate a vector-averaged gravity to simulate weightlessness environment. We then observed the responses of rat calvarial osteoblasts subsequent to rotation at 30 revolutions per minute (rpm) for 72 h. We found that the protein expressions of three integrin subunits started to change from 24 h of rotation in clinostat but not in stationary cultures. The decreased percent changes of integrin α₅ protein at 24, 48 and 72 h were 13.1 +/- 3.4%, 20.3 +/- 6.7% and 11.9 +/- 2.5%, respectively. The same tendency was saw in the expression of integrin α_v protein as 7.4 +/- 4.1%, 18.2 +/- 5.3% and 25.2 +/- 7.5%, respectively. Moreover, the expressions of integrin β₁ protein in different periods were also declined with the percent changes of 18.6 +/- 3.3%, 25.9 +/- 4.7% and 27.5 +/- 6.5%, respectively. We all know that most cell-matrix interactions are mainly mediated by receptors of the integrins family, heterodimeric molecules made of an extracellular domain connected through a transmembrane sequence to an intracyto- plasmic tail. Our results suggest that vector-averaged gravity causes alterations of signal transduction and integrin-mediated cell adhesion in osteoblasts by altering the protein expressions of several crucial integrin subunits. These alterations might contribute to the pathogenesis of osteoporotic bone loss as observed in actual space flights.