Abstract
Our previous results with flight (FLT) mice showed abnormalities in thymuses and spleens that have potential to compromise immune defense mechanisms. In this study, the organs were further evaluated in C57BL/6 mice after Space Shuttle Atlantis returned from a 13-day mission. Thymuses and spleens were harvested from FLT mice and ground controls housed in similar animal enclosure modules (AEM). Organ and body mass, DNA fragmentation and expression of genes related to T cells and cancer were determined. Although significance was not obtained for thymus mass, DNA fragmentation was greater in the FLT group (P<0.01). Spleen mass alone and relative to body mass was significantly decreased in FLT mice (P<0.05). In FLT thymuses, 6/84 T cell-related genes were affected versus the AEM control group (P<0.05; up: IL10, Il18bp, Il18r1, Spp1; down: Ccl7, IL6); 15/84 cancer-related genes had altered expression (P<0.05; up: Casp8, FGFR2, Figf, Hgf, IGF1, Itga4, Ncam1, Pdgfa, Pik3r1, Serpinb2, Sykb; down: Cdc25a, E2F1, Mmp9, Myc). In the spleen, 8/84 cancer-related genes were affected in FLT mice compared to AEM controls (P<0.05; up: Cdkn2a; down: Birc5, Casp8, Ctnnb1, Map2k1, Mdm2, NFkB1, Pdgfa). Pathway analysis (apoptosis signaling and checkpoint regulation) was used to map relationships among the cancer–related genes. The results showed that a relatively short mission in space had a significant impact on both organs. The findings also indicate that immune system aberrations due to stressors associated with space travel should be included when estimating risk for pathologies such as cancer and infection and in designing appropriate countermeasures. Although this was the historic last flight of NASA’s Space Shuttle Program, exploration of space will undoubtedly continue.
Highlights
Astronaut health and safety are of key importance to the success of long-term missions in space
The immune system consists of a complex network of organs, tissues and cells that are essential for both maintenance of homeostasis in the body and for defense against infectious microbes and aberrant cell types with potential to progress to cancer
The thymus mass and RTM values were relatively low for the FLT group compared to the animal enclosure modules (AEM) group, statistical significance was not obtained possibly due to low sample size
Summary
Astronaut health and safety are of key importance to the success of long-term missions in space. Understanding of the underlying mechanisms remains limited, there are numerous reports that stressors in the space flight environment, e.g., microgravity, radiation and psychological stress of confinement, can have a profound impact on immune system status [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. A better understanding of space flight-related health issues is needed, when missions proceed beyond Earth’s protective geomagnetic field. Knowledge gained on the biological effects of factors in the space flight environment is relevant to the general public as high altitude commercial airline flights and space tourism will undoubtedly continue to increase
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