GUT MICROBIOME DYNAMICS UNDER SIMULATED MICROGRAVITY - FIRST INFORMATION FROM THE SPACEFLIGHT-ASSOCIATED NEURO-OCULAR SYNDROME (SANS) - COUNTERMEASURES STUDIES

Abstract

In the area of space exploration, numerous factors are able to decrease the quality of health and recovery of space travelers. Among those, weightlessness comes with significant challenges. Besides the negative effect it has on bone density, muscle mass, and risk for space-associated neuro-ocular syndrome, it also has the ability to influence the composition of the gut microbiome. The human gut microbiome, as the largest endocrine organ in the human body, plays a central role in the modulation of human health and disease. Disruption to the microbiota composition, as through space conditions, leads to changes in functional composition, metabolic activities, or local distribution which all can lead to gut microbiome dysbiosis. A decrease in diversity is detrimental. Some beneficial microorganisms may decrease, while potentially harmful microorganisms may increase in abundance. These shifts in microbial composition can impact the overall health of the gut. This is important, as 70% of the immune system is built into the gut, manifesting as the gut-associated lymphoid tissue. The observed compromised immune system in astronauts could therefore find its origin in the alterations of the gut microbiome. To answer these questions, we investigated, whether individual space environment factors influence the gut microbiome. We therefore examined stool samples of participants from the four SANS campaigns spending 30 days in 6° head-down-tilt position (HDT) except for specific countermeasures: i.e., from a control group, exposure to a vacuum chamber (lower body negative pressure, LBNP) for a total of 6 hours per day, 7 times per week, maintaining an upright seated position for a total of 6 hours per day, 7 times per week , cycling in a 6° head-down tilt for 45 minutes, followed by wearing thigh cuffs with a pressure of 50 mmHg for 6 hours, 6 times per week. The HDT position enforces a fluid shift to the head simulating weightlessness. Stool samples were collected periodically during baseline, HDT, and recovery periods of the study investigating the compositional shifts in the gut microbiome. All subjects received identical meals to eliminate diet as a factor of influence in this study. Therefore, hypoactivity can also be seen as an outstanding factor in changing the composition of the gut microbiome. Using Illumina Sequencing, the bacterial composition and change over time of the gut microbiome was analyzed. Our results show that gut microbiome change over the period of the experiments are mainly individual. However, there are general trends that can be observed, such as a decrease in short-chain fatty acid (SCFA) producers, especially during the middle of the HDT phase. SCFAs are known to improve the gut health through a number of local effects, ranging from maintenance of intestinal barrier integrity, mucus production, and protection against inflammation to reduction of the risk of e.g., colorectal cancer. It also seems that subjects with a high volume of physical activity before the study are more resilient to negative changes. Our first data give directions to anticipate possible dysbiotic changes in the space environment, in general, and individually, and may even help to find different predispositions and lifestyles that are able to sustain a more rigid gut microbiome for space travel. Also, different suggestions for prebiotics, probiotics, or dietary decisions could be made to reduce a shift of the gut microbiome to a dysbiotic composition and therefore increase health and support fast recovery in case of sickness. To facilitate individual suggestions in the future, regular stool sample collection of astronauts could aid in increasing health and faster recovery from sickness. With regard to Earth-bound implications of this work – the gut microbiota, as a major human health factor, is influenced by physical activity (immobilization) and diet, and displays a functional cross-talk with skeletal muscle. Conversely, only few data are available on the impact of hypoactivity, although sedentary lifestyles are widespread and associated with negative health and socio-economic impacts, also here additional more personalized microbiome research is needed.