Backgroundhe circadian clock extensively regulates physiology and behavior. In space, the astronauts encounter many environmental factors that are dramatically different from those on earth, however, the effects of these factors on circadian rhythms and the mechanisms remain largely unknown. The present study aimed to investigate the changes in the mouse circadian rhythm and gut microbiome under simulated space capsule conditions, including microgravity, noise and low atmospheric pressure.ResultsNoise and low atmospheric pressure were loaded in the capsule while the conditions in the animal room remained constant. The mice in the capsule showed disturbed locomotor rhythms and faster adaptation to a 6-h phase advance. RNA sequencing of hypothalamus samples revealed that microgravity simulated by hind limb unloading (HU) and exposure to noise and low atmospheric pressure led to decreases in the quantities of differentially expressed genes (DEGs), including circadian clock genes. Changes in the rhythmicity of genes implicated in pathways of cardiovascular deconditioning and more concentrated circadian phases were found under HU or noise and low atmospheric pressure. Furthermore, 16S rRNA sequencing revealed dysbiosis in the gut microbiome, and noise and low atmospheric pressure may repress the temporal discrepancy in the microbiome community structure induced by microgravity. Changes in diel oscillation were observed in a number of gut bacteria with critical physiological consequences in metabolism and immunodefense.ConclusionsOur data demonstrate that in addition to microgravity, exposure to noise and low atmospheric pressure affect the robustness of circadian rhythms and the community structure of the gut microbiome, and these factors may interfere with each other in their adaptation to respective conditions. These findings are important to further our understanding of the alteration of circadian rhythms in the space complex environment.

Background: Circadian clock plays a critical role in synchronizing the inner molecular, metabolic and physiological processes to the environmental cues which cycle with a period of 24 h. Misalignment in the circadian rhythms leads to decrease in adaptation, performance and increased risk of associated disorders. The non-24-h schedules and shift schedules are commonly used in maritime operations, both of which could result in disturbance in circadian rhythms. The comprehensive effects of these schedules remain to be further elucidated.Methods: In this study, we firstly conducted an experiment in which the volunteers followed a 3-d rotary schedule with consecutive shift in sleep time (rotatory schedule), and analyzed the changes in salivary cortisol rhythms and blood variables. Next we conducted another experiment in which the volunteers followed an 8 h on and 4 h off schedule (non-24-h schedule) to compare the changes in blood/serum variables. Furthermore, the plasma miRNAs from the volunteers following the rotatory schedule were subject for miRNA sequencing. Results: The rotatory schedule led to elevated levels of serum cortisol during the early stage, and the phase became delayed during the early and stages. The results show both of the schedules caused comprehensive changes in blood/serum biochemical variable, and consistently, the increase in phosphate levels. In addition, a subset of serum miRNAs targeting genes involved in circadian rhythms, sleep homeostasis and multiple important physiological processes or pathways were identified in the experiment with rotatory schedule.Conclusions: This study revealed an increased stress during the rotatory schedule. Circadian misalignment caused by either non-24-h or rotatory schedule lead to extensive changes in blood/serum variables. As to the rotatory schedule, altered expression of serum miRNAs may account for the consequences of circadian misalignment. These findings would help understand the deleterious effects of shift schedules and optimize to enhance performance and welfare of the personnel working with similar schedules.

cardio-vascular system, endocrine system, and so on, and decreases the performance of astronauts.Circadian clock will be a critical factor in future space life research and in study of astronaut health and performance.

Background: Circadian clock plays a critical role in synchronizing the inner molecular, metabolic and physiological processes to the environmental cues with a period of 24 h. Misalignment in the circadian rhythms leads to decreased adaptation and performance and increased risk of associated disorders. The non-24-h schedules and shift schedules are commonly used in maritime operations, both of which could result in disturbance of circadian rhythms.Methods: In this study, we recruited volunteers and conducted two experiments: in one experiment 15 subjects followed an 8-h on and 4-h off schedule (non-24-h schedule), and in the second experiment 12 subjects followed a 3-d rotary schedule with consecutive shift in sleep time (phase-changing schedule). The serum/blood biochemical variables were measured and the serum miRNAs of the volunteers in the second experiment were subjected to transcriptomic miRNA sequencing.Results: The results show both of the schedules caused comprehensive changes in the blood/serum biochemical variables. Notably, significant elevation in serum phosphate was observed in both experiments: 1.210 ± 0.141 in control and 1.330 ± 0.117 in recovery (P = 0.014) in the first experiment and 1.193 ± 0.152 in control and 1.343 ± 0.099 in recovery (P = 0.007) in the second experiment. In addition, a subset of serum miRNAs targeting genes involved in circadian rhythms, sleep homeostasis, phosphate metabolism and multiple critical physiological processes or pathways were identified in the second experiments.Conclusions: This study reveals that non-24-h and shift schedules lead to changes in a large spectrum of blood/serum biochemical variables due to circadian misalignment. Schedules with frequent shift may cause remarkable changes in serum miRNAs which are involved in multiple physiological pathways. These findings would help understand the deleterious effects of shift schedules and develop optimized strategy to enhance welfare and performance of the shift workers.