One interesting and recent study on human embryonic stem cells experiencing net microgravity sheds some insight into what may be causing long lasting health problems for astronauts. Researchers at the University of New South Wales in Australia placed stem cells in a rotating machine developed by NASA that introduces a net gravity close to 0g. The stem cells were in the machine for 28 days, while the control group of stem cells was maintained in the exact same nourishing conditions while experiencing normal Earth gravity conditions. After the experiment, the cells showed several differences at the molecular layer. Nearly 64% of proteins in the microgravity group differed from those grown under normal gravity. In the microgravity treated stem cells, there was more expression of proteins that degrade bone and there was less expression of proteins with antioxidant effects. Additionally, proteins involved in cell division, the immune system, the muscle and skeletal systems, calcium levels within cells, and cell motility were also affected in this group.
These results suggest that microgravity conditions directly impact the development of stem cells in the human body. Human embryonic stem cells can develop into any cell type, and they play a role in repair of damaged tissue and in the maintenance of the normal regeneration of organs with the potential to regenerate. With this importance, if experiencing microgravity hinders their development, then long-term space travel poses serious threats to the health of astronauts. Research is currently being done on several differentiated cell types to determine if the molecular changes are more widespread, and these experiments will also take place on future missions into space in order to verify that these results are also seen in true microgravity, as opposed to net microgravity. Another implication of these results is that future research should be directed towards biomedical interventions that prevent these changes in protein expression.
Yet another implication of this study that concerns long-term survival during space travel is the complications that might arise during procreation. If cells do rely on gravity for some sort of mechanical feedback, then the development of an embryo in microgravity could prove to be impossible. Thus, if humans plan to make long distance trips to other planets in our solar system, the issue of genetically engineering human bodies for them to survive procreation in space might be a necessary step in future.