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

TLDR

Spaceflight may impair the immune system, with the thymus undergoing atrophy whose molecular mechanisms remain unclear. The study aimed to analyze the thymi of mice aboard the ISS over approximately one month. The authors examined thymic tissue from mice flown on the ISS, assessing size and gene expression after about a month in space. Spaceflight reduced thymic size and expression of cell‑cycle genes, but exposure to 1 × g during flight partially mitigated these effects without altering overall thymic architecture.

Abstract

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.