The effect of space flight on individual cells continues to fascinate and confound scientists. Physicists originally predicted that gravitational changes would have no effect at the sub-cellular level because gravity is insignificantly weak compared with other physical forces acting on cells. Yet cells undergo profound changes in space including alterations in shape, metabolism, intracellular organization, and gene expression. The question facing researchers now is not if but how cells are affected by altered gravity.
Cellular experiments in space have focused primarily on understanding the underlying mechanisms of physiological changes that affect astronaut health. These changes include loss of bone density, muscle atrophy, and suppression of the immune system. Bone, muscle, and immune cells all show alterations in microgravity. Investigations of complete signaling pathways are also a focus of research. These studies seek to connect mechano-sensitive receptors on the surface of cells all the way through to the control of gene expression in the cell nucleus and will enhance our understanding of the indirect effects of altered gravity on cells. Indirect effects include changes in mechanical stimulation and cytoskeletal organization. Changes in convection and sedimentation alter the physical environment of cells and are also likely to impact cell activity. Ultimately, this research will contribute to the development of effective countermeasures as well as benefiting biological and medical research on Earth.