Validation of a New Rodent Experimental System to Investigate Consequences of Long Duration Space Habitation

Abstract

Animal models are useful for exploring the health consequences of prolonged spaceflight. Capabilities were developed to perform experiments in low earth orbit with on-board sample recovery, thereby avoiding complications caused by return to Earth. For NASA's Rodent Research-1 mission, female mice (ten 32 wk C57BL/6NTac; ten 16 wk C57BL/6J) were launched on an unmanned vehicle, then resided on the International Space Station for 21/22d or 37d in microgravity. Mice were euthanized on-orbit, livers and spleens dissected, and remaining tissues frozen in situ for later analyses. Mice appeared healthy by daily video health checks and body, adrenal, and spleen weights of 37d-flight (FLT) mice did not differ from ground controls housed in flight hardware (GC), while thymus weights were 35% greater in FLT than GC. Mice exposed to 37d of spaceflight displayed elevated liver mass (33%) and select enzyme activities compared to GC, whereas 21/22d-FLT mice did not. FLT mice appeared more physically active than respective Gc while soleus muscle showed expected atrophy. RnA and enzyme activity levels in tissues recovered on-orbit were of acceptable quality. thus, this system establishes a new capability for conducting long-duration experiments in space, enables sample recovery on-orbit, and avoids triggering standard indices of chronic stress.

Integrated RNA-seq Analysis Indicates Asynchrony in Clock Genes between Tissues under Spaceflight

“…Indeed, previous mice studies during spaceflight have implemented carefully controlled 12 h light–dark cycles but still observed circadian rhythm-related disruptions at both the behavioral and molecular biological levels. For instance, studies have reported that the FLT group showed significant increases in behavior activity during the dark cycle and in food intake throughout the mission compared to the GC group [ 3 , 38 ]. Likewise, other studies reported that clock-related gene expressions were changed in the liver and eyes of mice that underwent spaceflight for about one month [ 10 , 30 , 39 ].…”

“…While the fold change of Arntl was consistently up-regulated across all tissues, Per2 did not show significant changes in the adrenal glands and liver, and only showed significant changes at less conservative thresholds in the kidneys compared to the muscle tissues ( Figure 4 B). Given that the data we used came from studies that reported treating GC mice as similarly as possible to FLT mice by implementing controlled light–dark cycles and food resources within the same housing devices [ 3 , 38 ], we predicted that clock genes under spaceflight would show gene expression patterns that were in synchrony between peripheral tissues. However, our results suggested that other factors besides the environmental light–dark cycle (such as gravity, radiation, and rearing environment) may be driving asynchrony of the circadian rhythm between certain peripheral tissues during spaceflight.…”

“…Since the dawn of human spaceflight, basic life science experiments have been actively conducted in space to learn more about disease processes here on Earth from a new and unique perspective. Rodent models are often used as analogs for estimating biological mechanisms inside human tissues [ 3 , 4 ]. Mice studies under spaceflight conditions have been successfully conducted to elicit molecular mechanisms at the tissue and cellular levels [ 3 , 5 , 6 , 7 , 8 ].…”

A New Era for Space Life Science: International Standards for Space Omics Processing

“…Unfortunately, NASA Rodent Research-1 (RR-1) missions revealed that space mouse gene expression analysis may not be reliable with slow freezing. 14 Indeed, slow freezing of mouse carcasses on orbit for eventual dissection on Earth (ISS terminal frozen return samples) showed large gene expression changes when compared with mice dissected by astronauts in orbit (ISS terminal dissected return samples). This appeared to be exacerbated by the use of poly(A) enrichment-based RNA sequencing (RNA-seq) protocol, and could be alleviated by the use of a ribodepletion-based approach and by snap-freezing carcasses in liquid nitrogen.…”

“…Animal models are used to infer how spaceflight affects humans; plant models are used to elicit how crops can be cultivated in space for food and renewed oxygen sources; and microbes are studied to understand how space affects human microbiomes, plant-microbe interactions, and environmental cleanliness, while also advancing the fields of space biotechnology, planetary protection, and astrobiology. 12 , 13 Specifically, the NASA Rodent Research (RR) 14 and Japan Aerospace Exploration Agency (JAXA) Mouse Habitat Unit (MHU) 15 , 16 series are part of a long heritage of rodent experiments in space; the zebrafish, medaka fish, fruit fly, and worm have all been valuable models for studying the effects of microgravity (μ g ), hypergravity, and space stressors using much larger sample size 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 and proper 1 g controls in space via centrifuges and on ground via microgravity simulators; 25 plant models are consistently flown to investigate gravitropism 26 and now food production; 27 and microbial models have been guests on Apollo, 28 Space Lab 1, 29 the Space Shuttle, 30 and the International Space Station (ISS), 31 with recent interest turning toward understanding the natural microbiomes of spaceships 32 , 33 and astronauts. 34

Figure 1 Example Uses, Pros, and Cons of Various Model Organisms Used in Space Omics Experiments

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