The impact of microgravity and gravitational countermeasures on the gut microbiome of humans enrolled in the AGBRESA study

The Artificial Gravity Bed Rest Study – AGBRESA – was the first joint study conducted by DLR, ESA and NASA to simulate the effects of microgravity on healthy subjects. Moreover, the study included the use of artificial gravity protocols in a short-arm human centrifuge as a measure to counteract the negative effects of weightlessness. The health of the gut translates into the overall wellbeing since the disruption of the gut symbiotic networks – dysbiosis – could be due to either diet, antibiotic ingestion, sleep disturbance, physical activity or psychological stresses. In recent times, the gut microbiome has changed from being a complementary addition to our digestive tract to a potentially life-changing role by directly being the source of stimuli which revealed to impact neurochemistry, behavior and overall physiological status. Combined, microbial fluctuations could alter the intestinal microbiota composition and bacterial metabolite production, or more severely, in the disruption of host intestinal barrier integrity and the immune system activity, triggering intestinal inflammation syndromes and making the gut a very relevant organ to be studied in the context of spaceflight. Thus, 12 subjects, 8 males, were subjected to bed rest at negative 6-degree inclination for a period of 60 days with a preceding baseline of 15 days and posterior recovery period of 14 days. In other to characterize the gut microenvironment of healthy humans in simulated microgravity, fecal samples were collected during the baseline stage (once), during the head-down tilt treatment (at days 10, 30, and 50) and during the recovery period (once), and the samples were then processed for 16S rRNA sequencing and taxonomic analysis of the gut microenvironment. The characterization of the prokaryote flora was conducted 1) throughout time in contrast to the baseline reference and 2) in the context of the gravitational countermeasure vs the bed-rest-only control. The analysis revealed the detection of commensal microorganisms described to positively impact the gut such as Bifidobacterium spp., Lactobacillus spp., Akkermansia spp. and Enterococus spp.. Interestingly, we were able to detect pathogens like Campylobacter hominis which has been linked to severe bowel diseases ulcerative colitis and Crohn's disease. Also, opportunistic microorganisms such as Fusobacterium spp., Prevotella spp., Pseudomonas spp., Staphylococcus and Streptococcus spp., could potentially indicate an imbalance of the microbial networks and be a good an indicator of dysbiosis. Additionally, we set aside samples to undergo proteomic and metabolite analysis to improve the characterization of the gut microenvironment under microgravity simulation and the extent of the gravitational countermeasure recovery on bowel condition. Overall, the microgravity simulation performed on the AGBRESA study did not impact dramatically the fitness of the participants. Nonetheless, the analysis of the gut provides important insights on the triggers that occur during the adaptation of human physiology to long term exposure to spaceflight conditions and whether these relate to the described complications associated with gut disease

Analysis of bacterial profiles of AGBRESA participants – a study concerning terrestrial astronauts under simulated microgravity

Introduction: Long-term space missions are accompanied by harmful environmental conditions like microgravity. Due to the reduced gravity, astronauts adapt to their environment resulting in tissue fluidic shifts. Since the knowledge about microbiome data in space is sparse and conduction of experiments at the ISS is complex, suitable analogs are needed. Therefore, the first cooperative bed-rest study called Artificial Gravity Bed-Rest study with ESA (AGBRESA), by NASA, ESA and DLR offered optimal features to investigate possible correlations between microbial shifts and physiological microgravity by using -6° head-downtilt (HDT). The aim of this survey was to identify changes within the standardized conditions, such as diet and wrongly distributed tissue fluids to reveal causal connections among health state and microbial communities

Effects of 30days bed rest and exercise countermeasures on PBMC bioenergetics

Abstract Aim: Altered mitochondrial function across various tissues is a key determinant of spaceflight-induced physical deconditioning. In comparison to tissue biopsies, blood cell bioenergetics holds promise as a systemic and more readily accessible biomarker, which was evaluated during head-down tilt bed rest (HDTBR), an established ground-based analog for spaceflight-induced physiological changes in humans. More specifically, this study explored the effects of HDTBR and an exercise countermeasure on mitochondrial respiration in peripheral blood mononuclear cells (PBMCs). Methods: We subjected 24 healthy participants to a strict 30-day HDTBR protocol. The control group (n=12) underwent HDTBR only, while the countermeasure group (n=12) engaged in regular supine cycling exercise followed by veno-occlusive thigh cuffs post-exercise for 6h. We assessed routine blood parameters 14 days before bed rest, the respiratory capacity of PBMCs via highresolution respirometry, and citrate synthase activity 2days before and at day 30 of bed rest. We confirmed PBMC composition by flow cytometry. Results: The change of the PBMC maximal oxidative phosphorylation capacity (OXPHOS) amounted to an 11% increase in the countermeasure group, while it decreased by 10% in the control group (p=0.04). The limitation of OXPHOS increased in control only while other respiratory states were not affected by either intervention. Correlation analysis revealed positive associations between white blood cells, lymphocytes, and basophils with PBMC bioenergetics in both groups. Conclusion: This study reveals that a regular exercise countermeasure has a positive impact on PBMC mitochondrial function, confirming the potential application of blood cell bioenergetics for human spaceflight

The impact of bed rest on human skeletal muscle metabolism

Insulin sensitivity and metabolic flexibility decrease in response to bed rest, but the temporal and causal adaptations in human skeletal muscle metabolism are not fully defined. Here, we use an integrative approach to assess human skeletal muscle metabolism during bed rest and provide a multi-system analysis of how skeletal muscle and the circulatory system adapt to short- and long-term bed rest (German Clinical Trials: DRKS00015677). We uncover that intracellular glycogen accumulation after short-term bed rest accompanies a rapid reduction in systemic insulin sensitivity and less GLUT4 localization at the muscle cell membrane, preventing further intracellular glycogen deposition after long-term bed rest. We provide evidence of a temporal link between the accumulation of intracellular triglycerides, lipotoxic ceramides, and sphingomyelins and an altered skeletal muscle mitochondrial structure and function after long-term bed rest. An intracellular nutrient overload therefore represents a crucial determinant for rapid skeletal muscle insulin insensitivity and mitochondrial alterations after prolonged bed rest

High-Intensity Jump Training Is Tolerated during 60 Days of Bed Rest and Is Very Effective in Preserving Leg Power and Lean Body Mass: An Overview of the Cologne RSL Study

Purpose Space agencies are looking for effective and efficient countermeasures for the degrading effects of weightlessness on the human body. The aim of this study was to assess the effects of a novel jump exercise countermeasure during bed rest on vitals, body mass, body composition, and jump performance. Methods 23 male participants (29±6 years, 181±6 cm, 77±7 kg) were confined to a bed rest facility for 90 days: a 15-day ambulatory measurement phase, a 60-day six-degree head-down-tilt bed rest phase (HDT), and a 15-day ambulatory recovery phase. Participants were randomly allocated to the jump training group (JUMP, n = 12) or the control group (CTRL, n = 11). A typical training session consisted of 4x10 countermovement jumps and 2x10 hops in a sledge jump system. The training group had to complete 5–6 sessions per week. Results Peak force for the reactive hops (3.6±0.4 kN) as well as jump height (35±4 cm) and peak power (3.1±0.2 kW) for the countermovement jumps could be maintained over the 60 days of HDT. Lean body mass decreased in CTRL but not in JUMP (-1.6±1.9 kg and 0±1.0 kg, respectively, interaction effect p = 0.03). Resting heart rate during recovery was significantly increased for CTRL but not for JUMP (interaction effect p<0.001). Conclusion Participants tolerated the near-daily high-intensity jump training and maintained high peak forces and high power output during 60 days of bed rest. The countermeasure was effective in preserving lean body mass and partly preventing cardiac deconditioning with only several minutes of training per day

Fetuin-A as a Potential Biomarker of Metabolic Variability Following 60 Days of Bed Rest

Background: Fetuin-A is a hepatokine linked to the development of insulin resistance. The purpose of this study was to determine if 60 days head-down-tilt (HDT) bed rest increased circulating fetuin-A and if it was linked to whole body insulin sensitivity (IS). Additionally, we examined whether reactive jump training (RJT) could alleviate the metabolic changes associated with bed rest. Methods: 23 young men (29 ± 6 years, 181 ± 6 cm, 77 ± 7 kg) were randomized to a control (CTRL, n = 11) or RJT group (JUMP, n = 12) and exposed to 60 days of bed rest. Before and after bed rest, body composition and V . O 2peak V.O2⁢p⁢e⁢a⁢k were measured and an oral glucose tolerance test was performed to estimate IS. Circulating lipids and fetuin-A were measured in fasting serum. Results: Body weight, lean mass, and V . O 2peak V.O2⁢p⁢e⁢a⁢k decreased in both groups following bed rest, with greater reductions in CTRL (p < 0.05). There was a main effect of time, but not the RJT intervention, for the increase in fetuin-A, triglycerides (TG), area under the curve for glucose (AUCG) and insulin (AUCI), and the decrease in Matsuda and tissue-specific IS (p < 0.05). Fetuin-A increased in participants who became less insulin sensitive (p = 0.019). In this subgroup, liver IS and adipose IS decreased (p < 0.05), while muscle IS was unchanged. In a subgroup, where IS did not decrease, fetuin-A did not change. Liver IS increased (p = 0.012), while muscle and adipose tissue IS remained unchanged. Conclusions: In this study, we report an increase in circulating fetuin-A following 60 days of bed rest, concomitant with reduced IS, which could not be mitigated by RJT. The amount of fetuin-A released from the liver may be an important determinant of changes in whole body IS. In this regard, it may also be a useful biomarker of individual variation due to inactivity or lifestyle interventions

Early-life and parental predation risk shape fear acquisition in adult minnows

Crane AL, Meuthen D, Thapa H, Ferrari MCO, Brown GE. Early-life and parental predation risk shape fear acquisition in adult minnows. Animal Cognition. 2020.Exposure to predation risk can induce a fearful baseline state, as well as fear reactions toward novel situations (i.e., neophobia). Some research indicates that risk exposure during sensitive periods makes adults more prone to acquiring long-term fearful phenotypes. However, chronic risk can also lead to ignoring threats in order to maintain other activities. We sought to assess how a relatively long period of low risk, experienced either early in life or by the previous generation, influences fear behaviour acquired from a short period of high risk as adults. We used fathead minnows as study subjects and simulated predation risk with repeated exposures to conspecific chemical alarm cues. The period of high risk experienced by adults induced typical fear behaviour (baseline freezing and neophobia), whereas the early-life low-risk period 1 year prior caused only a reduction in baseline foraging. We found no evidence that the early-life risk significantly altered the fear acquired from the adult-risk period. However, in a second experiment, a low-risk period during the parental generation interacted with a high-risk period experienced by the adult offspring. The combination of both risk periods heightened baseline freezing despite parental risk having little effect independently. Hence, our study provides evidence that parental risk exposure can lead to an additive intergenerational effect on fear acquisition in minnows