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SPACE travel wreaks havoc on the human body, a new study has revealed.
A paper published May 28 in Nature Communications examined the effects of space travel on the immune system.
Researchers collected data from the two men and two women who orbited Earth on the SpaceX Inspiration4 mission in 2021.
They that the immune system went awry, triggering inflammatory responses and creating chaos at the cellular level.
The team found evidence that a high elevation, three-day spaceflight induces the production of known cytokine signatures as well as previously undocumented cytokines.
Cytokines are substances secreted by the immune system. They play critical roles in immune response and the regulation of muscles.
The scientists noted that they are not normally associated with systemic inflammation, which is an immune response that affects the whole body.
Some of the cytokines were considered exerkines, a specific type of protein produced by the muscle and other tissues during exercise.
The scientists set out to determine whether muscle tissue could be the source of these immune markers.
They found significant increases in some myokines, or proteins produced by skeletal muscle cells.
The paper notes that this increase represented "a physiological response to microgravity" rather than a purely immune response.
Non-muscle tissues did not show changes in Interleukin 6, a protein that indicates inflammation, nor in Interleukin 10, an anti-inflammatory molecule.
However, a muscle along the back of the leg called the soleus showed a significant increase in a molecule associated with muscle exertion.
Furthermore, the tibialis anterior muscle, located in the front of the leg, showed an increase in interleukins, which play a key role in the activation of immune cells.
The largest increase upon landing was noted in the pro-inflammatory cytokine Interleukin 5, further implicating muscles as a potential source for the cytokines found in the I4 crew.
The researchers collected blood from the Inspiration4 crew before and after the trip into orbit.
Analysis revealed cell-specific and sex-specific responses to spaceflight.
Increases in Interleukin 6, Interleukin 10, and MCP-1, a pro-inflammatory molecule, were consistent with changes observed in other astronauts following long-duration missions.
Several other pro-inflammatory proteins were also significantly up-regulated.
However, proteins like fibrinogen, which is involved in forming blood clots, and hemoglobin, which carries oxygen through the bloodstream, did not significantly change.
To better understand spaceflight’s impact on different cell types, the scientists delved even deeper and examined changes happening at the cellular level.
One observation stood out. While other types of cells remained stable in terms of mutations, the total number of B-cell receptor mutations increased relative to pre-flight data.
These mutations are usually caused by inflammatory stimuli or exposure to antigens, which are substances that trigger an immune response.
The scientists also found evidence of possible up-regulation of BCR signaling pathway genes immediately post-flight.
While they fell short of spelling out a conclusion, the data indicates that B-cells are more active after a trip to space.
These cells produce antibodies to neutralize harmful substances and contribute to the body's immune response.
Cell differentiation is the process by which young cells take on specialized characteristics and reach their mature function.
Scientists found that this occurred less in CD4 T and CD8 T cells.
T cells are a type of white blood cell called lymphophytes. They develop from stem cells in the bone marrow and play a key role in protecting the body from infection.
These findings mirrored the T cell suppression previously observed in simulated irradiation and microgravity.
Upon return to Earth, the astronauts’ serum showed higher concentrations of cytokines associated with inflammation.
The scientists simultaneously noted an increase in cytokines with anti-inflammatory activity, "which likely balances the inflammation from returning to Earth."
The researchers observed significant changes in secreted proteins related to the migration of monocytes and neutrophils, which travel to the site of an injury.
Prior studies have indicated that women may be more resilient than men to the stresses of space, and may be able to recover more quickly once they return to Earth.
The scientists set out to test this theory. They looked at differentially expressed genes, or DEGs, which show different levels of activity under different conditions.
The team compared the ratio of up- and down-regulated DEGs between males and females, which showed a higher number of DEGs in males for almost all cell types.
The scientists also observed a higher number of altered gene expression pathways in males.
The scientists also observed a significant difference between males and females for levels of Interleukin 8 and fibrinogen.
Interleukin 8, or IL-8, plays a major role in the body's inflammatory response by triggering the movement of a type of white blood cell to the site of injury.
Ultimately, the scientists concluded that gene activity was more disrupted in men than in women, possibly indicating that women are more resistant to the stressors of space travel.
The researchers concluded that they found evidence of an immune response to space travel in the Inspiration4 data.
"We found that 18 cytokines/chemokines related to inflammation, aging, and muscle homeostasis changed after spaceflight," they wrote.
And while the findings may seem like they have implications for future crew selection, the scientists noted that they have a ways to go.
They noted that their sample size of four astronauts was small, even though they used data from previous missions and studies to bolster their findings.
The I4 mission was "not designed to determine the safety of spaceflight for all civilians," the team concluded.
However, the consistent cellular and molecular responses could help "narrow the targets for countermeasures and monitoring in future studies."
The Twins Study provided a much-needed window into the effect of space travel on the human body.
The NASA examined identical twin astronauts, Scott Kelly and Mark Kelly, who were in different environments for roughly a year. While Scott spent 340 days in space, Mark was on Earth.
Because identical twins share the same genetic makeup, they are physically very similar. This controls for other variables that could impact study results and gives scientists a way to study how the environment impacts health.
Samples taken before, during, and after Scott's trip to space showed changes in gene expression. This includes the process by which our DNA instructs cells to make components like proteins, which are used to build and repair tissue.
Mark experienced changes in gene expression on Earth, but not to the same extent as Scott in space.
One of the most striking discoveries was evidence of telomere shortening. Telomeres are the ends of each DNA strand, which protect them from becoming "frayed." Without telomeres, our chromosomes would become damaged and our cells would no longer work properly.
Scott was found to have experienced a change in telomere length dynamics during his flight. These findings may help evaluate general health and potential long-term risks of astronauts in space.
