Zero Genie

Epithelial cells that line our intestines serve as a robust barrier to invasion by viruses, bacteria and exposure to ingested agents. A new study, published in the journal Scientific Reports, shows that microgravity, such as that encountered in spaceflight, disrupts the functioning of this epithelial barrier even after removal from the microgravity environment.

The Expedition 20 crew members share a meal in the Unity node of the International Space Station. Image credit: NASA.

“Our study is the first to investigate if functional changes to epithelial cell barrier properties are sustained over time following removal from a simulated microgravity environment,” said study senior author Professor Declan McCole, a researcher at the University of California, Riverside.

“Our work can inform long-term space travel and colonization where exposure to a food-borne pathogen may result in a more severe pathology than on Earth.”

The microgravity environment has profound effects on human physiology, leading to clinical symptoms and illnesses including gastroenteritis.

Previous studies have shown microgravity weakens the human immune system and increases the intestinal disease-causing ability of food-borne bacteria such as salmonella.

“Our study shows for the first time that a microgravity environment makes epithelial cells less able to resist the effects of an agent that weakens the barrier properties of these cells,” Professor McCole said.

“Importantly, we observed that this defect was retained up to 14 days after removal from the microgravity environment.”

The permeability-inducing agent Professor McCole and colleagues chose to investigate was acetaldehyde, an alcohol metabolite.

“Alcohol compromises barrier function and increases gastrointestinal permeability in normal subjects and in patients with alcoholic liver disease,” Professor McCole explained.

“The barrier function of the intestinal epithelium is critical for maintaining a healthy intestine; when disrupted, it can lead to increased permeability or leakiness. This, in turn, can greatly increase the risk of infections and chronic inflammatory conditions such as inflammatory bowel disease, celiac disease, Type 1 diabetes, and liver disease.”

The scientists used a rotating wall vessel to examine the impact of simulated microgravity on cultured intestinal epithelial cells.

Following culture for 18 days in the vessel, they discovered intestinal epithelial cells showed delayed formation of ‘tight junctions,’ which are junctions that connect individual epithelial cells and are necessary for maintaining impermeability.

The rotating wall vessel also produces an altered pattern of tight junction assembly that is retained up to 14 days after the intestinal epithelial cells were removed from the vessel.

“Our findings have implications for our understanding of the effects of space travel on intestinal function of astronauts in space, as well as their capability to withstand the effects of agents that compromise intestinal epithelial barrier function following their return to Earth,” Professor McCole concluded.

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R. Alvarez et al. 2019. A Simulated Microgravity Environment Causes a Sustained Defect in Epithelial Barrier Function. Sci Rep 9, 17531; doi: 10.1038/s41598-019-53862-3