Astronauts have a change of heart in space: Experts find heart cells are altered in space - but return to normal within 10 days on Earth

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The thought of spaceflight may make the heart skip a beat, but actually travelling beyond Earth could alter the organ's cells.

With extended stays aboard the International Space Station (ISS) commonplace, and the likelihood of humans spending longer periods in space increasing, there is a need to better understand the effects of micro-gravity on cardiac function.

New research suggests heart muscle cells derived from stem cells have a remarkable ability to adapt to their environment during and after spaceflight.

Scientists examined cell-level cardiac function and gene expression in human heart cells cultured aboard the International Space Station for five-and-a-half weeks.

Exposure to micro-gravity changed the expression of thousands of genes - most notably those related to mitochondrial function

They found that exposure to micro-gravity changed the expression of thousands of genes, but largely normal patterns reappeared within 10 days after returning to Earth.

Senior study author, Joseph Wu, of Stanford University School of Medicine, said: "Our study is novel because it is the first to use human induced pluripotent stem cells to study the effects of spaceflight on human heart function.

"Micro-gravity is an environment that is not very well understood, in terms of its overall effect on the human body, and studies like this could help shed light on how the cells of the body behave in space, especially as the world embarks on more and longer space missions such as going to the moon and Mars."

Until now, most studies on how the heart reacts to micro-gravity have been conducted in either non-human models or at tissue, organ or systemic level.

To address this, the beating cells were launched to the ISS aboard a SpaceX spacecraft as part of a commercial resupply service mission.

Simultaneously, they were also cultured on Earth for comparison purposes.

Human heart cells were cultured aboard the International Space Station for five-and-a-half weeks before being brought back to Earth for analysis

When they returned to the planet, the cells showed normal structure and morphology.

However, they did adapt by modifying their beating pattern and calcium recycling patterns.

Researchers sequenced the cells harvested at four-and-a-half weeks aboard the ISS, and 10 days after returning to Earth.

Results showed that 2,635 genes were differentially expressed among flight, post-flight, and ground control samples.

The study could help shed light on how the cells of the body behave in space - which is vital as the world embarks on more and longer space missions such as going to the moon and Mars 

Most notably, gene pathways related to mitochondrial function were expressed more in the space-flown cells, according to the research published in the Stem Cells Reports journal.

A comparison of the samples revealed the space cells adopted a unique gene expression pattern during spaceflight, which reverted to one that is similar to ground-side controls upon return to normal gravity.

Dr Wu added: "We're surprised about how quickly human heart muscle cells are able to adapt to the environment in which they are placed, including micro-gravity.

"These studies may provide insight into cellular mechanisms that could benefit astronaut health during long-duration spaceflight, or potentially lay the foundation for new insights into improving heart health on Earth."

The study was published in the journal Stem Cell Reports. 

HOW DID SCOTT KELLY'S DNA CHANGE IN SPACE?

After 340 days aboard the International Space Station, American astronaut Scott Kelly returned to Earth in March 2016.

Nasa has since undertaken tests to study the effects living in orbit had on Kelly using his identical twin brother Mark - who remained on Earth - as a control subject.

The Kelly brothers have nearly identical genomes, allowing for an unprecedented look at the physical effects of long-term spaceflight.

While astronaut Scott Kelly (right) lived aboard the International Space Station for 340 days, his identical twin brother Mark (left) remained on Earth – and researchers have now found a number of differences between the two

Blood and other biological samples were collected from the pair before, during, and after Scott Kelly's mission.

The agency found that Kelly came home 5 cm (2 inches) taller than his twin - a change had resolved itself within two days of his return.

The height difference was caused by the ISS' microgravity conditions which elongate the spine – but the effect was only temporary. 

Nasa found that while 93 per cent of Kelly's genes returned to normal shortly after returning home, seven per cent were permanently altered.

These long-term changes hit genes related to the immune system, DNA repair, bone formation and the ways his tissues take up oxygen and carbon dioxide.

Kelly's telomeres – the caps at the end of each chromosome – lengthened while in space.

Telomeres are key to protecting DNA from damage and tend to shorten with age. Kelly's telomeres shortened again once he was back on Earth.

Scientists reported their preliminary results at a meeting for Nasa's Human Research Program in January 2017. Pictured are some of the areas studied by the team

Nasa says that Kelly's lengthening telomeres are linked with his diet and exercise routine on the station.

The ratio of two groups of gut bacteria shifted while Kelly was in space, likely due to his change in diet. This also returned to normal shortly after his return. 

Nasa research has spotted hundreds of diverging genetic mutations in Kelly and Mark's genomes.

The research team speculate that a 'space gene' could have been activated while Kelly was in orbit.