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Does Hypergravity Regulate Gene Expression of Integrins and other Focal Adhesion Components in the Matrix-Integrin Signaling Pathway?     J. Krishnakumar1,2,3, E. Almeida1 and W. Vercoutere1. 1NASA Ames Research Ctr,   2National Space Grant Foundation, and 3California State University, East Bay.

   Humans and other animals exposed to the decreased mechanical loading of microgravity during space exploration suffer from atrophy in mechanosensitive tissues including muscle and bone. For long-duration missions, a suitable countermeasure will be necessary. Artificially inducing gravity via rotation may provide the required countermeasure. One of the goals in our laboratory is to identify the molecular pathways involved in this cellular response to altered gravity, to help answer how and why artificial gravity may function as a countermeasure. Our early studies indicated that increased gravity-loading may stimulate bone cell (osteoblast) proliferation via extracellular matrix-integrin signaling pathways. We hypothesized that the origin of bone cell proliferative response to increased gravity may be at the gene expression level of the signaling components, including integrins and other focal adhesion components. ß1-integrin is known to be involved in both mechantransduction and proliferation, therefore may play a key role in bone cell response to increased gravity.   αv-integrin is known to be involved in cell motility and therefore may also be involved in mediating bone cell response to increased gravity. We use cell culture centrifugation (Incu-fuge) to provide increased gravity mechano-stimulation. The first step of this gene expression study was to find a standard housekeeping gene that remained constant in hypergravity. We found that 2 out of 12 standard housekeeping genes were altered by increased gravity. We identified cyclophilin as the most stable house-keeping gene to use as the control in our subsequent gene expression studies. Our second set of experiments was to test whether gene expression of subunits αv and ß1 integrin are altered by increased gravity. Our results show that αv integrin subunit was not significantly altered by increased gravity, but that ß1 integrin expression increased.