Spaceflight changes gene expressionOne of the most intriguing results from the Twins Study came from investigating how gene expression (or epigenetics) changed over the duration of the mission. Led by Chris Mason of Weill Cornell Medicine, researchers carried out whole-genome sequencing to identify chemical changes that occurred in the twins' DNA and RNA. Though both Kellys were expected to experience epigenetic changes over the course of the study, the sheer number of transformations still took researchers by surprise.
"Some of the most exciting things that we've seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space," Mason said in a press release when the preliminary results first came out. "With this study, we've seen thousands and thousands of genes change how they are turned on and turned off. This happens as soon as an astronaut gets into space, and some of the activity persists temporarily upon return to Earth."
Overall, when Scott ventured to space, his body activated many previously dormant genes. Primarily, it turned on genes related to telomere growth, collagen production, immune system response, and DNA repair. And though such changes started soon after Scott got into space, they dramatically ramped up about halfway through his stay.
"Gene expression changed dramatically," Mason said in a press release. "In the last six months of the mission, there were six times more changes in gene expression than in the first half of the mission." However, more than 90 percent of Scott's genes were again expressing themselves normally within six months of his return.
The researchers point out that Earth-bound Mark also experienced a significant number of epigenetic changes. "The amount of difference that we saw in Scott was within the range of the fluctuation that we see in Mark," said Andy Feinberg of Johns Hopkins University in a press conference Tuesday, "so we don't see that as pathological."
"The Twins Study has been an important step toward understanding epigenetics and gene expression in human spaceflight," said J.D. Polk, NASA's Chief Health and Medical Officer, in a statement.
Chris Mason carried out research investigated how gene expression is affected by living in a microgravity environment. In this video from 2017, he discusses their preliminary results.
Chromosome shields grow longer in spaceAnother important aspect of the Twins Study focused on how spaceflight altered the length of Scott's telomeres, which are the protective caps on the ends of chromosomes that prevent DNA strands from degrading as we age. Led by professor Susan Bailey of Colorado State University, this study monitored the length of each twins' telomeres before, during, and after Scott's stay aboard the space station.
Telomeres "can serve as a biomarker of accelerated aging or some of the associated health risks like cardiovascular disease or cancer," Bailey said during the press conference. "We imagined going into the study that the unique kinds of stresses and extreme environmental exposures like space radiation and microgravity, all of these things would act to accelerate telomere loss."
Unexpectedly, Bailey and her team found the length of Scott's telomeres did not shrink while he was in space. Instead, they significantly increased in length. However, within just two days of Scott's return to Earth, his telomeres drastically shortened again.
Though Scott's telomeres are now, on average, about the same length as they were preflight, Bailey notes that Scott currently has more very short telomeres than he did at the start of the project, which could indicate his time in space negatively affected his telomeres over the long-term. Meanwhile, Mark's telomeres remained about the same throughout the study.
"For us Earthlings," Bailey explained in a press release, "We all worry about getting older, and everyone wants to avoid cardiovascular disease and cancer. If we can figure out what's going on, what's causing these changes in telomere length, perhaps we could slow it down. That's something that would be a benefit to everybody."
To do this, Bailey is already planning to carry out further telomere research as part of NASA's One-Year Mission Project, which is currently under development. In the project, Bailey will study 10 astronauts on full-year missions, 10 astronauts on half-year missions, and 10 more on short missions of only two to three months.
Unlike the Twins Study, which allowed Mark to go about his normal life, the One-Year Mission project will house control subjects in isolation during each astronaut's mission. According to Bailey, "We're trying to determine if it is indeed something specific about space flight that is causing the changes we've seen."