Scientists have discovered that astronauts' bone density decreases in space.Now, scientists at the International Space Station have found that changes in the space traveler's gut microbiota may be linked to bone loss.The study was recently published in the Cell Report.
U.S. scientists have found that rodent communities that have been on the ISS for a month or more have changed and become more diverse, while breeding in space may help increase the production of molecules known to affect bone remodeling.
"This is another vivid example of dynamic interaction between microbial groups and mammalian hosts.The gut microbiota is constantly monitoring and responding, even when you are exposed to microgravity.Shi Wenyuan, the paper's correspondent and chief executive officer of the Forsyth Institute, said.
Although no causal relationship has been found between microbial changes and bone loss observed under microgravity, and this is only a positive compensation, the data are encouraging and open new avenues for exploration, he said.
Human bones are not static, and even when adults are fully developed, matter is being added, removed, and moved in the process called bone remodeling.Recent studies suggest that gut microorganisms may influence bone remodeling through a variety of mechanisms, including interactions with immune and hormonal systems.Microorganisms also produce molecules through their own metabolism, some of which interact indirectly with cells responsible for bone remodeling.
First author of the paper, Joseph K. of the Forsyth Institute and UCLA. Bedree says research suggests that microbial groups are affected by space travel for a number of reasons.First, there are physical forces at work, such as microgravity and cosmic radiation exposure that affect not only bacterial cells but also human cells.At the same time, microgravity exposure can have many effects on host biological systems – immune system irregularities, musculoskeletal changes, circadian rhythms, stress, and microbial communities can be destroyed when these systems become unbalanced.
To explore how microbial communities change when exposed to microgravity for extended periods of time and to investigate possible links between these changes and bone density, researchers sent 20 rodents to the International Space Station.Ten of the rodents returned to Earth alive after four and a half weeks, and they tracked the recovery of the microbiota in the mice.The remaining 10 space rodents stayed in orbit for a total of nine weeks.Then 20 "ground-controlled" rodents were placed on Earth under the same conditions—though without microgravity.The team characterized groups of rodent microbial communities and compared them over time: before launch, after return to Earth and at the end of the study.They also assessed changes in serum metabolites in space rodents exposed to microgravity for a full nine weeks.
"This is the first time in NASA's history that a rodent has been returned alive to Earth.That means we can collect information about changes in space and then monitor the recovery of the microbiota when they return.The good news is that, despite changes in the microbiota in space, these changes do not seem to continue after returning to Earth.”
When the team characterized and compared the intestinal microbiota of space rodents with those of "ground-controlled" rodents, they found that the intestinal microbiota of space rodents were more diverse.Two species of bacteria—lactic acid bacteria and Doraea—are higher in rodents exposed to microgravity, and are found in rodents that stay in space for nine weeks even higher than those that stay in space for four and a half weeks.The metabolism of these two bacteria may also contribute to the detected elevation of metabolites associated with microgravity exposure.
When we mapped the genetic pathways of lactobacillus and Doraea, they seemed to be consistent with metabolites that rose during microgravity exposure."When a person is in microgravity and experiences bone loss, their body tries to compensate, and so does the biological system, which makes sense, but we need to do more mechanical research to really test these hypotheses," Bedree said.”
Researchers say a potential non-microgravity factor affecting rodent microbial changes in space is their inability to eat their own feces, a normal behavior that reintroduces microbes into the gut.However, rodents returning from space four and a half weeks later were able to eat feces on their return, which may help their microbial communities recover.
While the study sheds light on how microbiome changes during space travel, Swinyon says more needs to be done to understand the possible link between microbiome and bone density.They plan to continue their research on Earth.Knowing which microbes maintain bone density could help astronauts stay healthy in space.The researchers said the information could also help people on Earth with osteoporosis caused by gravity.
"This could lead to new tools for treating diseases such as osteopenia or osteoporosis, so it's not just an isolated story in space." said Shi Wenyuan.