Microgravity causes changes in gene expression rhythms

Astronauts exposed to microgravity experience changes to physiology, including immune suppression, increased inflammation, and reduced muscle mass and bone density, according to research conducted by the University of Surrey and published in the journal iScience. Given the current increase in human spaceflight, it is important to understand changes in the molecular mechanisms underlying these changes.

In a study coordinated by the European Space Agency at the MEDES Space Clinic in Toulouse, 20 men completed a 90-day protocol consisting of two weeks of baseline before 60 days of constant bedrest at a -6°, head-down tilt angle to simulate the effects of microgravity experienced by astronauts. The protocol concluded with two weeks of recovery.

The research team analysed gene expression over a 24-hour time series during two days in baseline, three days in bed rest, and once in recovery. The results showed that 91% of gene expression was affected by the protocol, with major disruption to the number, timing and amplitude of rhythmic genes, which display changes in their mRNA every 24 hours. Disrupted gene expression is associated with protein translation, immune and inflammatory processes, and decreased muscle function. During the recovery period, disruption to muscle function was restored; however, lasting effects were identified with protein translation.

“This unique study represents the largest longitudinal dataset of time series gene expression in humans,” said lead author Professor Simon Archer. “Human gene expression varies rhythmically over the 24-hour day, and it is important to collect time series data rather than from just single time points to get a full picture of what occurs in the body when exposed to simulated microgravity. It also raises questions about the impact of constant bed rest on our bodies, as we have identified a dramatic effect on the temporal organisation of human gene expression.”

Senior author Professor Derk-Jan Dijk, Director of the Surrey Sleep Research Centre, said a lot remains unknown about the impact of microgravity on the body, and it is important we know more about this before we start ‘holidaying’ in space. Indeed, human spaceflight is very much on the agenda right now, with astronauts soon returning to the moon via NASA’s Artemis project, new plans in place for a UK astronaut going to the ISS in 2025 via the UKSA Axiom program, and the growth of space tourism.

“Building on what we have found, the second part of our study, using the same cohort of men, will investigate the impact microgravity has on sleep, circadian rhythms and hormones of individuals,” Dijk said.

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