Oh, how you've changed
NASA reported on the experiment with twin astronauts
Polina Loseva, "The Attic"
In 2015, NASA sent astronaut Scott Kelly (pictured on the right) into space for as much as 340 days – a record time for American cosmonautics to this day. Kelly became a record holder due to the fact that, among all other advantages, he has a twin brother - Mark Kelly.
When the "cosmic" brother returned to the "earthly" one, scientists compared them on a variety of grounds. Among the unexpected findings are changes in the work of genes, a decrease in cognitive functions and the fleeting cellular youth of the "cosmic" twin.
In the 2030s, NASA plans to send the first astronauts to Mars. Such a flight can take about three years, taking into account the round trip and experiments on the surface of the planet. At the same time, we still hardly imagine what exactly happens to the human body during its stay in space. Most of the previous studies that were conducted on astronauts were limited to only six months outside the Earth. Now NASA has received data on changes in the physiology of an astronaut who spent 340 days on the ISS – almost a whole year. The "control" was his twin brother, who remained on Earth at that time.
The "cosmic" effect on Kelly's body was studied by as many as 10 research groups. They presented their results in one general article in Science (Garrett-Bakelman et al., The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight).
At the beginning of the study, Mark and Scott were 50 years old. They are both astronauts, but with different flight experience: Scott has spent 180 days in space over the past 12 years and was not there for four years before the last expedition. Mark spent only 54 days there and has also not left Earth for the past four years. During the year of the experiment, the researchers (on Earth) and Scott (in orbit) collected a total of 317 samples of blood, feces and urine of both brothers. The latter had a harder time: as Brinda Rana, one of the authors of the study, told the press service of the University of California, "it was not easy to collect the right amount of biological fluids on board the ISS. In space, blood volume drops, and astronauts are constantly dehydrated." Despite this, the biomaterial turned out to be enough to assess the state of cells, the work of genes and the microbial composition in the organisms of the brothers. In addition, before and after the experiment, as well as six months after Scott's return to Earth, the twins were examined by doctors. Here is a short list of the differences in their condition.
Body weight. During his time on the ISS, Scott Kelly lost about 7% of his body weight, while his "earth twin", on the contrary, gained an extra 4%. This coincides with the data of previous studies: astronauts often lose body weight both due to fluid loss and due to a decrease in muscle mass.
Heart and blood vessels. As is often the case, Scott Kelly's blood pressure in space was slightly lowered. At the same time, in response to changes in pressure and load, the walls of his vessels became thicker. This is especially noticeable in the carotid artery. On Earth, the thickening of the walls of blood vessels is associated with increased pressure (as they become less elastic) and the risk of cardiovascular diseases such as heart attack and stroke. In addition, such changes resemble a pattern characteristic of atherosclerosis. And Scott really had elevated levels of cholesterol-transporting proteins in his blood. Despite the fact that after returning to Earth, all these indicators returned to their place, the researchers call changes in the walls of blood vessels one of the main problems that will face people going on a three-year flight to Mars.
Vision. Upon returning to Earth, many astronauts have vision problems. Perhaps the fact is that in the absence of gravity, the blood pressure in the thin eye vessels changes. In response to pressure drops, the vascular membrane of the eye forms folds, and the optic nerve becomes thicker. This phenomenon, interestingly, is characteristic only of men, but not for female astronauts, and it was also found in Scott. Mark's eyes, as expected, have not changed in any way this year.
The nervous system. Both on the Ground and during the flight, the brothers passed simple computer tests. Despite the fact that before the flight and at its beginning, the twins almost did not differ either in speed or accuracy of completing tasks, after returning to Earth, Scott began to cope with them worse. His results in speed, accuracy and overall efficiency were lower than Mark's for at least the first six months after landing. This could be another problem for the first people on Mars.
Immunity. Scott was subjected to more severe stress than his brother, so the concentration of stress (pro-inflammatory) markers in his blood was higher. Nevertheless, the overall activity of the immune system turned out to be approximately the same. To test this, both twins – one on the ISS, the other on Earth – received a seasonal flu shot. The number of T-lymphocytes that learned to recognize a new pathogen after vaccination did not differ among the brothers.
Microflora. Despite the fact that intestinal microbes have recently been credited with many important functions in the human body, significant differences between microscopic cohabitants of twins could not be found. During the flight, Scott changed the ratio between the number of representatives of the Firmicutes and Bacteroidetes groups, to which most of the inhabitants of our intestines belong, but these changes are no stronger than those of a stressed person on Earth. And soon after the end of the experiment, the balance in the intestine was restored.
Cells and genes. In previous studies, scientists have found an increased frequency of DNA mutations in astronauts. And Scott was no exception. Basically, these were major rearrangements in chromosomes: the exchange of sections, double-strand breaks. Probably, the mutagen in this case was cosmic radiation.
In addition, during the experiment, the researchers found 9317 genes whose activity differed in Mark and Scott. They suggested that this may be due to epigenetic changes – DNA methylation, "closing" genes for reading. However, despite the fact that the brothers had methylated different regions of the genome, the total number of these differences was small – no more than 5% of the regions.
It is also interesting that most of the discrepancies in gene activity (8564) appeared only in the second half of the experiment, from the 6th to the 12th month of Scott's stay on the ISS. This suggests that changes continue to occur in the body throughout the time in space and short-term studies are unable to detect them.
After returning to Earth, 90% of these changes disappeared. However, about 800 genes continued to work with a different force (compared to Mark's genes) even after six months on Earth.
In particular, these are genes associated with immunity (probably due to the stress experienced) and DNA repair (repair). Perhaps these are the genetic traces of being in space, which remain in the human body for a long time.
Cellular youth. One of the most common markers of cellular age are telomeres – the end sections of chromosomes. During the life of the cell, they gradually shorten, and the cell ages. Other factors, such as inflammation or other types of stress, can also affect the rate of telomere loss. Researchers were surprised to find that while working on the ISS, Scott Kelly suddenly looked younger compared to his earthly brother. His telomeres have become 14.5% longer. However, when he returned to Earth, literally in the first 48 hours they shortened back – perhaps due to the stress associated with landing. And now the length of Scott's telomeres is even less than it was before his expedition to the ISS. However, it is hardly possible to talk about the "rejuvenating effect of the cosmos" here. Firstly, we still don't fully know what caused the elongation of the ends of the chromosomes. Secondly, other parameters of Scott's body (weight loss, vision problems, thickening of the walls of blood vessels) do not indicate an improvement in his health. Therefore, the fluctuation in the length of telomeres remains only a curious phenomenon.
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Thus, the cosmos affects human physiology at different levels, although it does not change it entirely – for example, immunity works about the same as on Earth. Most of the features of the cosmic mode of the body's work quickly disappear upon returning home: genes begin to work the same way as before, vision is restored, telomeres are shortened, and pressure increases. However, scientists are concerned about the long-term consequences of living in space. Since many genes have changed their work only after six months in orbit, who knows what will happen in a year or two? In addition, some changes in physiology, such as cognitive decline or thickening of the vascular wall, can lead to serious complications. And so far we cannot predict whether they will be reversible after several years of living in zero gravity.
However, numerous authors of the article do not draw far-reaching conclusions from their research. A sample of two people does not allow accurate comparison of their physiological characteristics, so the work is rather observational. Its purpose was to create a multi-sided portrait of a person in space and to identify individual changes in his health that may pose a danger to participants of longer expeditions. Rather, it is a pilot project that demonstrates how efficiently it is possible to collect and store biomaterial in the conditions of the ISS and how much information from it can then be obtained on Earth. Before sending the first humans to Mars, NASA will, of course, have to conduct much larger and carefully controlled experiments.
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