Impact of spaceflight on the murine thymus and mitigation by exposure to artificial gravity during spaceflight

Abstract

The environment experienced during spaceflight may impact the immune system and the thymus appears to undergo atrophy during spaceflight. However, molecular aspects of this thymic atrophy remain to be elucidated. In this study, we analysed the thymi of mice on board the international space station (ISS) for approximately 1 month. Thymic size was significantly reduced after spaceflight. Notably, exposure of mice to 1 × g using centrifugation cages in the ISS significantly mitigated the reduction in thymic size. Although spaceflight caused thymic atrophy, the global thymic structure was not largely changed. However, RNA sequencing analysis of the thymus showed significantly reduced expression of cell cycle-regulating genes in two independent spaceflight samples. These reductions were partially countered by 1 × g exposure during the space flights. Thus, our data suggest that spaceflight leads to reduced proliferation of thymic cells, thereby reducing the size of the thymus, and exposure to 1 × g might alleviate the impairment of thymus homeostasis induced by spaceflight.

In Pursuit of Adult Progenitors of Thymic Epithelial Cells

“…The thymus is extremely sensitive to damage and exposure to acute or chronic insults results in a pronounced decline in cellularity, a phenomenon known as thymic atrophy ( 41 , 42 ). For example, we recently demonstrated thymic atrophy displayed by mice under microgravity (0 g) conditions during spaceflight, which was partially mitigated by exposure to 1 g during spaceflight ( 43 ). After resolution of acute insults such as infections, cytoreductive therapies, and emotional and physical discomfort, the thymus is able to regenerate, although its capacity declines with age ( 41 , 42 ).…”

How the Immune System Deploys Creativity: Why We Can Learn From Astronauts and Cosmonauts

“…Intriguingly, space travel was shown to adversely affect T cell development in the thymus of astronauts ( Benjamin et al, 2016 ). Complementary studies involving mice aboard the International Space Station identified that the stress of microgravity led to defects in T cell development and generation in the thymus ( Horie et al, 2019 ). How space travel ultimately affects the creative process by which T cells generate their antigen recognition repertoire–the combined capacity of all individual T cell clones have in recognizing antigens–remains incompletely understood.…”

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

“…The study revealed that a short-term mission in space resulted in significant impact in both organs: Altered expression of genes related to T cells (e.g., Il10 , Il18bp , Il18r1 , Spp1 , Ccl7 , and IL6 ) and cancer cells (e.g., Casp8 , Fgfr2 , Figf , Hgf , Igf1 , Itga4 , Ncam1 , Pdgfa , Pik3r1 , Serpinb2 , Sykb , Cdc25a , E2f1 , Mmp9 , and Myc ). During a recent spaceflight study (35-day exposure on the ISS), researchers investigated the microgravity effects on the thymus of mice [ 72 ]. There were significant changes in gene expression, DNA fragmentation, as well as in thymus size compared with control mice, which encountered artificial 1 g acceleration by centrifugation on the ISS [ 72 ].…”

“…During a recent spaceflight study (35-day exposure on the ISS), researchers investigated the microgravity effects on the thymus of mice [ 72 ]. There were significant changes in gene expression, DNA fragmentation, as well as in thymus size compared with control mice, which encountered artificial 1 g acceleration by centrifugation on the ISS [ 72 ]. The authors found a strong reduction in genes involved in the regulation of the cell cycle.…”