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Identification of Mechanosensitive Genes in Osteoblasts by Comparative Microarray Studies Using the Rotating Wall Vessel and the Random Positioning Machine.  Patel, MJ^1,2, Liu, W³, Sykes, MC¹, Ward, NE², Risin, SA⁴, Risin, D², Jo, H^1,5.  ¹Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University,  ²Space Life Sciences Directorate, Human Adaptation and Countermeasures Office, NASA/Johnson Space Center,  ³Department of Molecular and Human Genetics and Microarray Core Facility, Baylor College of Medicine, ⁴Department of Pathology and Laboratory Medicine, University of Texas-Houston Medical School, ⁵Division of Cardiology, Emory University School of Medicine

   Microgravity of spaceflight induces bone loss due in part to decreased bone formation by osteoblasts.  Recently we have shown that simulated microgravity changes gene expression profiles in 2T3 preosteoblasts using the Random Positioning Machine (RPM).  Here, we hypothesized that exposure of preosteoblasts to an independent microgravity simulator, the Rotating Wall Vessel (RWV) bioreactor, induces similar changes in differentiation and gene transcript profiles, resulting in a more confined list of mechanosensitive genes that may play a role in bone formation.  In comparison to static 1g controls, exposure of 2T3 cells to the RWV for 3 days inhibited alkaline phosphatase activity, a marker of differentiation, and downregulated 61 and upregulated 45 genes by more than two-fold as shown by microarray analysis.  The microarray results were confirmed by real-time PCR for downregulated genes osteomodulin, bone morphogenic protein 4 (BMP4), runx2, and parathyroid hormone receptor 1 and by Western blots for 3 downregulated genes, BMP4, peroxiredoxin IV, and osteoglycin, and 1 upregulated gene peroxiredoxin I. Comparison of the microarrays from the RPM and RWV studies identified 14 mechanosensitive genes that changed in the same direction.  Further comparison of our results to a published microarray data with mechanically loaded mouse tibias revealed 16 genes upregulated by the loading that were downregulated by RWV and RPM.