Changes in mouse thymus and spleen after return from the STS-135 mission in space

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.

Figure 1. Thymus and spleen mass alone and relative to body mass (RTM, RSM).

Bars represent mean ± SEM. For thymus mass and RTM, n = 7 (AEM group) and n = 4 (FLT group). For spleen mass and RSM, n = 8 (AEM group) and n = 5 (FLT group). AEM, animal enclosure module (control mice housed on ground); FLT, flight mice. *P<0.05 vs. AEM. For FLT vs. AEM thymus mass, P=0.101.

Figure 2. DNA fragmentation in thymus.

The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used. The top panel shows two representative examples from each of the groups. AEM (A34 and A42): control mice housed on ground in animal enclosure modules; FLT (F64 and F74): flight mice. The bottom panel shows the results after quantification; bars represent mean ± SEM for 6 AEM and 3 FLT mice. *P<0.01 vs. AEM.

Figure 3. Impact of space flight on Myc-mediated apoptosis signaling in the thymus.

Pathways are modified versions of the canonical pathways generated with IPA software. The up-down-regulated genes are from the cancer gene array. Red = Up-regulated. Green = Down-regulated. White = Not measured. Further description of the legend can be found at the IPA website indicated in the Materials and Methods. This analysis was based on gene expression levels in thymuses obtained from 4 AEM and 3 FLT mice.

Figure 4. Impact of space flight on G1/S checkpoint regulation in the thymus.

Pathways are modified versions of the canonical pathways generated with IPA software. The up-down-regulated genes are from the cancer gene array. Red = Up-regulated. Green = Down-regulated. White = Not measured. Further description of the legend can be found at the IPA website indicated in the Materials and Methods. This analysis was based on gene expression levels in thymuses obtained from 4 AEM and 3 FLT mice.

Figure 5. Impact of space flight on Myc-mediated apoptosis signaling in the spleen.

Pathways are modified versions of the canonical pathways generated with IPA software. The up-down-regulated genes are from the cancer gene array. Red = Up-regulated. Green = Down-regulated. White = Not measured. Further description of the legend can be found at the IPA website indicated in the Materials and Methods. This analysis was based on gene expression levels in spleens obtained from 5 AEM and 4 FLT mice.

Figure 6. Impact of space flight on G1/S checkpoint regulation in the spleen.

Pathways are modified versions of the canonical pathways generated with IPA software. The up-down-regulated genes are from the cancer gene array. Red = Up-regulated. Green = Down-regulated. White = Not measured. Further description of the legend can be found at the IPA website indicated in the Materials and Methods. This analysis was based on gene expression levels in spleens obtained from 5 AEM and 4 FLT mice.