American twin astronauts provided NASA scientists with rare data on how long-term spaceflight affects the human body. While one brother spent a record-setting 340 days in outer space, the other was stranded on Earth. They spent years under a medical microscope. A comparative study on their genetic profiles showed differences in length of telomeres and gene expression, which seemed to diminish slowly over time.

It seems we are finally getting a clearer picture of what microgravity, radiation, and the space environment do to an astronaut’s body after prolonged time in space. After three years and hard work of dozens of researchers from around the globe, first results on the effects of zero gravity on Scott’s body were published in Science. Scott experienced several genetic changes while he was in space, but most of them reversed once he landed back on Earth.

“It is predominantly very good news for spaceflight and those interested in joining the ranks of astronauts,” Cornell professor Chris Mason, principal investigator for the NASA Twins Study, said for MIT Technology Review. “While the body has an extraordinary number of changes, it also exhibits extraordinary plasticity in reverting back to a normal terrestrial state.”

Many test results correlated with previously gained knowledge (Scott’s retinal nerve thickened) or assumptions; however, two of them stood out after a closer look at the DNA level and gene expression. Susan Bailey from Colorado State University focused on the length of Scott Kelly’s telomeres and its “custodian”, the telomerase. Telomeres are located on the ends of DNA, they protect chromosomes, and their length generally signifies the age and health of an individual. Stress and radiation can cause them to shrink additionally, and spaceflight exposes people to both.

Researchers expected Scott’s telomeres had shrunk during his prolonged time in space. “It was exactly the opposite,” said Bailey. “As soon as our earliest samples [were taken] in flight, which was within about two weeks after him being up there, we saw significantly longer telomeres in Scott than he had before he went”.

By the end of Scott’s time on the space station, his telomeres lengthened by about 14.5%. The changes were shortlived, though.  Within a week after his return, his telomeres shortened substantially. After half a year from his return to Earth, his lengthened telomeres returned to normal. Unfortunately for Scott, some new, shorter telomeres that formed upon his return persisted.

“They’re very, very spaceflight-specific and very rapid kinds of changes, which really left us scratching our head as to what in the world could be causing such a thing,” said Bailey.

A key piece of data is missing to explain such changes. Telomerase did not make it back to the lab. The environment on the track to the lab was not controlled well enough to prevent the telomerase activity from being lost.

The other major change was found in Scott Kelly’s gene expression. Many genes have turned off and on again during flight, especially ones related to circulation and the immune system. The researchers could get a hint at how the body attempts to adapt to space from the data obtained. In the first half of the mission, almost 1,500 genes changed their expression. In the latter half of the mission, six times as many genes changed. Mason said that the human body changes throughout its time in space.

Although most of the gene expression changes reversed themselves after Scott came home, several hundred persisted. The researchers cannot determine is that a lot and what the direct effects on health are. They have no data to compare with.

“It’s analogous to the very first time that we measured someone’s blood pressure,” said Mason. “We didn’t know what the actual reference numbers were until we started to measure more people.”

Scott Kelly does not notice much of a difference in his health now and hopefully he will not have negative consequences from high radiation exposure.

“I feel different than when I launched a little bit, but that’s probably because, you know, I’m four years older,” Scott said.

The next step is to upgrade technology. Bailey and her team will try to create better testing methods for observing telomerase activity. Mason is going to deal with removing the time pressure on the sample transportation step. His team has already performed the first DNA sequencing onboard the ISS.

Even though the new findings reveal that changes in the immune system are largely temporary and that astronauts recover quickly, one person is not enough to draw definitive conclusions. Researchers will study additional astronauts during two-month, six-month, and year-long tests. Space agencies want to gain knowledge and prepare their astronauts for longer and deeper missions into space.

Learn more about this one-of-a-kind research in the video below:

By Andreja Gregoric, MSc