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Unexpected cause of bone loss in astronauts revealed by mice sent to space

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Experiments with mice sent to the International Space Station (ISS) have shown that changes in the gut bacteria of space travelers may be associated with bone loss.

The study found that mice that spent a month or more on the International Space Station experienced more changes and diversity in their gut microbiome.

The findings suggest that bacterial species that thrive in space may have contributed to the increased production of molecules known to influence bone changes.

Senior author Wanyuan Shi, a microbiologist and CEO of the Foresight Institute in the US, said: “This is just another prime example showing the dynamic interactions between the microbiome and the mammalian host. The gut microbiome is constantly observing and interacting, and it is also the case when it is exposed to microgravity. Whether there is a causal relationship between changes in the microbiome and the bone loss observed in microgravity, and whether this is simply a consequence or an effective bone compensation, the data is inspiring and opens up new research opportunities.”

If scientists can identify the microbes that support maintaining bone density, the researchers said, it could help astronauts stay healthier in space and could also help people on Earth who suffer from bone loss, such as people with osteoporosis.

To study how the microbiome changes with prolonged exposure to microgravity and explore possible links between these changes and bone density, the researchers sent 20 mice to the International Space Station.

Ten of these mice returned alive to the ground after 4.5 weeks, and the researchers tracked how the rodents recovered.

The remaining 10 mice remained in orbit for nine weeks.

Twenty other mice were kept in identical conditions, except for microgravity, on the floor.

The researchers compared the microbial communities of different groups over time – before launch, after returning to Earth, and at the end of the study.

They found that space mice had more diverse gut microbes, with microgravity-exposed rodents having more than two specific types of bacteria.

Bacteria levels were higher in rodents that were in space for nine weeks rather than 4.5 weeks.

Dr Shi said: “This is the first time in NASA history that a rodent has been returned to Earth alive. This means that we were able to collect information about the change in space and then follow the recovery of the microbiome after its return.” The good news is that while the microbiome has changed in space, those changes do not appear to persist after returning to Earth.”

Bones are not static, and even when a person is fully grown, material is constantly being added, removed, and reshaped in a process called bone remodeling.

Recent studies have shown that the gut microbiota may influence this process through various mechanisms, including interactions with the immune and hormonal systems.

Microbes also produce various molecules through their metabolism, and some of them interact indirectly with the cells responsible for bone remodeling.

First author and microbiologist Joseph Pedre, who began at UCLA and continued at the Forsyth Institute, said experts expect space travel to impact the microbiome for a number of reasons.

He explains: “First of all, physical forces such as microgravity and exposure to cosmic radiation play a role, which affect not only bacterial cells, but also human cells. Similarly, the impact has many effects on the biological systems of the host. , Microgravity, dysregulation of the immune systems, musculoskeletal changes, altered circadian rhythm and stress, and when these systems are out of balance, microbial communities can also be disrupted.”

The researchers suggest that another factor, besides microgravity, that may have altered the microbiome of rodents in space is the fact that they were unable to participate in mating.

This is normal behavior for rodents, as they eat their own feces, bringing the microbes back into the intestines.

However, mice returning from space after 4.5 weeks were able to participate in mating upon their return, and this may have contributed to the recovery of their microbiomes.

While this study sheds light on how the microbiome changes during space travel, the researchers say more work needs to be done to understand the potential link between the microbiome and bone density.

“If we can identify which microbes support bone density, it could help astronauts stay healthier in space,” Dr. Shi explained.

The researchers say this information could also help people with bone loss from causes unrelated to Earth’s gravity.

“This is likely to lead to new tools for treating conditions like osteoporosis or osteoporosis, so it’s not just another story in space,” Dr. Shi said.

The results are published in the journal Cell Reports.

Source: Independent

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