Preparation for mice spaceflight: Indications for training C57BL/6J mice to adapt to microgravity effect with three-dimensional clinostat on the ground

Abstract

Like astronauts, animals need to undergo training and screening before entering space. At present, pre-launch training for mice mainly focuses on adaptation to habitat system. Training for the weightless environment of space in mice has not received much attention. Three-dimensional (3D) clinostat is a method to simulate the effects of microgravity on Earth. However, few studies have used a 3D clinostat apparatus to simulate the effects of microgravity on animal models. Therefore, we conducted a study to evaluate the feasibility and effects of long-term treatment with three-dimensional clinostat in C57BL/6 J mice. Thirty 8-week-old male C57BL/6 J mice were randomly assigned to three groups: mice in individually ventilated cages (MC group, n = 6), mice in survival boxes (SB group, n = 12), and mice in survival boxes receiving 3D clinostat treatment (CS group, n = 12). The mice showed good tolerance after 12 weeks of alternate day training. To evaluate the biological effects of simulated microgravity, the changes in serum metabolites were monitored using untargeted metabolomics, whereas bone loss was assessed using microcomputed tomography of the left femur. Compared with the metabolome of the SB group, the metabolome of the CS group showed significant differences during the first three weeks and the last three weeks. The KEGG pathways in the late stages were mainly related to the nervous system, indicating the influence of long-term microgravity on the central nervous system. Besides, a marked reduction in the trabecular number (P < 0.05) and an increasing trend of trabecular spacing (P < 0.1) were observed to occur in a time-dependent manner in the CS group compared with the SB group. These results showed that mice tolerated well in a 3D clinostat and may provide a new strategy in pre-launch training for mice and conducting relevant ground-based modeling experiments.

Keywords: Animal model; Bone loss; Microgravity; Random positioning machine (RPM); Serum metabolomics; Three-dimensional clinostat (3D clinostat).

Fig. 1

(a) Three-dimensional clinostat and (b) the controller. (c) Mouse survival box (SB) pattern; 1: Activity area. 2: Rest area. 3: Food and water areas; (d) Adaptive training of the clinostat (CS) group on the 3D clinostat; (e) Mice in the CS group on the 3D clinostat during the study.

Fig. 2

Effects of 3D clinostat on body weight and bone parameters in mice. (a) Weekly body weight chart of the mice. (b) NMDS analysis of metabolic pattern in mouse cage (MC) and survival box (SB) group. (c) R² of permanova between 3D clinostat (CS) group and SB group mice metabolic patterns in different time regions. (d) NMDS analysis of differences characteristics of CS and SB group mice metabolic patterns in different time regions. Ⅰ: 1–3 weeks, Ⅱ: 4–6 weeks, Ⅲ: 7–9 weeks, Ⅳ: 10–12 weeks. *P < 0.05 (CS versus MC), #P < 0.00.05 (CS versus SB), $ P < 0.05 (SB versus MC).

Fig. 3

Differential metabolites involved in enrichment analysis of signaling pathways in the stage Ⅰ.

Fig. 4

Venn of the differential metabolites. (a) Total differential metabolites (known). (b) Up-regulated differential metabolites (known). (c) Down-regulated differential metabolites (known). Ⅰ: 1–3 weeks, Ⅱ: 4–6 weeks, Ⅲ: 7–9 weeks, Ⅳ: 10–12 weeks.

Fig. 5

KEGG pathway enriched with differential metabolites at all stages. Ⅰ: 1–3 weeks, Ⅱ: 4–6 weeks, Ⅲ: 7–9 weeks, Ⅳ: 10–12 weeks.

Fig. 6

Effects of 3D clinostat on bone parameters in mice. (a) Representative micro-CT images at stage Ⅳ. (b) Trabecular numbers. (c) Trabecular spacing. (d) Trabecular thickness. (e) Bone surface area/bone volume. (f) Bone volume/total volume. Ⅰ: 1–3 weeks, Ⅱ: 4–6 weeks, Ⅲ: 7–9 weeks, Ⅳ: 10–12 weeks. *P < 0.05, #P < 0.1.