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.
Highlights
Astronauts experience several environmental changes during space flight such as hypergravity during launching, microgravity, psychological stress, and high-dose space radiation
To elucidate the impact of spaceflight on thymus homeostasis and the effect of 1 × g exposure on spaceflight-induced changes in the thymus, we analysed the thymi of mice housed in Multiple Artificial-gravity Research System (MARS) on board the International Space Station (ISS)
A further six mice on the same genetic background were housed on earth in identical cages to those used in MHU-1 as ground control (GC)
Summary
Astronauts experience several environmental changes during space flight such as hypergravity during launching, microgravity, psychological stress, and high-dose space radiation. Analysis of blood samples from astronauts suggested that spaceflight influences the distribution of leukocytes[7,8], and natural killer cell[9], granulocyte and monocyte function[7,10], along with plasma cytokine levels[11,12]. These studies suggested that spaceflight impacts on the immune system. JAXA executed several missions to perform mouse experiments using MARS on board the ISS14,26,27 In these missions, groups of mice were exposed to 1 × g during spaceflight to help clarify the effect of artificial 1 × g exposure on adverse events induced by spaceflight. The spaceflight-induced atrophy and changes in gene expression in the thymus were significantly rescued by exposure to 1 × g during spaceflight
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