Out-of-this-world impacts of spaceflight on the brain and body

August 6th, 2024

Written by: Julia Riley

Would you go to space if you had the chance?

Many factors would come into play when making that decision. There’s the living situation in a small pod with several roommates, the incredible views, the lack of running water, and how fun it looks to float around in zero gravity. There is also the thrill of knowing you were able to embark on an incredible journey that very few people get to experience. Every country has their own requirements and system for selecting space travelers- in the U.S. over 10,000 people apply when NASA is hiring new astronauts-in-training!

Something you might not consider when embarking on this hypothetical journey is the toll that spaceflight takes on your body. Among other body parts, the brain is altered by spaceflight in both easily noticeable and microscopic ways. Due to low levels of gravity, radiation, and the social challenges presented by spending all your time with a handful of people, stays in space are a grueling experience physically and psychologically. A previous PennNeuroKnow article explored some of the ways that these factors can impact brain function. Here, we explore some newer research on the impact that spaceflight has on the nervous system, why it might help us understand neurological phenomena here on earth, and how technological advances might benefit starry-eyed aspiring space travelers.

Changes in brain anatomy

Due to the small number of people who have gone to space, it’s quite difficult to accurately study how spaceflight impacts the body. This is because the amount of evidence we have to base predictions for the future on often determines the accuracy of these predictions. This is especially true of studies related to people because there are so many differences between human beings that we don’t have any control over. In science, we call this variability. The more variability that exists, the harder it is to attribute an effect to any particular cause, which makes it harder to draw conclusions.

Despite this barrier, several groups have studied the toll that space can take on the brain’s anatomy and function. In one study, scientists wondered whether brain structure would change after space flight. They were especially interested in whether the amount of changes in the brain increase with the amount of time that astronauts spend in space. The most notable change was the expansion of certain ventricles (ven-treh-kulls) in the brain¹. Ventricles are the vacant tunnels through brain tissue that allow the fluid your brain thrives in, cerebrospinal fluid, to reach parts of the brain it couldn’t otherwise access. This helps maintain a constant supply of oxygen, nutrients, and other things your brain needs. In a study of 30 astronauts, scientists found that two of the four ventricles in their brains, called the third ventricle and right ventricle, were especially likely to be enlarged. They also found that the ventricles seemed to stop expanding after about six months in space. This is interesting in that ventricles also expand with increasing age in non-astronauts here on Earth. However, astronauts show signs of ventricle expansion regardless of age. This suggests that existing in an environment with very little gravity accelerates the process of ventricle expansion. It also raises the question of whether other physical changes that we typically associate with age are accelerated by going to space.

Mitochondria don’t function normally in outer space

Spaceflight doesn’t just impact the brain and nervous system tissue; a host of other organs and systems are affected, especially the liver and skeletal system. To identify malfunctions that these tissues might have in common, one group performed a series of tests in what is called a multi-omics approach. Your body conducts many reactions every day intended to keep you functioning and ease any biological issues you encounter. Scientists figure out what those issues are by looking at what your body produces in response. You can think of this kind of like when doctors use the symptoms you experience to identify the underlying sickness, or when investigators use evidence to figure out who committed a crime.  The reason this approach is called multi-omics is that different types of tests are used to assess different biological materials, and each individual test name starts with the molecule it assesses and ends in “-omics”. For example, the building blocks of fats are called lipids, so if we wanted to assess all the lipids that cells were producing, we would use an approach called lipidomics; if we wanted to look at genes, we would do genomics, and so on. When you combine information from all these different approaches into a multi-omics approach, you end up with a comprehensive list of the biological molecules that are present in a sample. This means multi-omics entails taking a lot of different evidence into account to come to a conclusion, which makes it a powerful way to identify the ways in which cells or body parts are malfunctioning.

Using this multi-omics approach, scientists looked at data from many different samples ranging from single layers of cells grown in a dish all the way to samples collected from astronauts and mice that had travelled to space². One astronaut in the study had an identical twin who stayed on earth while he went to the International Space Station, which made it possible to compare samples between two people with identical DNA. By looking at all of this information from so many different kinds of samples, the scientists doing this study were hoping to find patterns that might indicate a common and consistent cause for changes induced by spaceflight.

Excitingly, evidence from this study suggested that there is at least one common culprit for the biological issues resulting from spaceflight. The multi-omics results suggested that spaceflight impairs the function of cellular components called mitochondria . Mitochondria, affectionately nicknamed “powerhouses of the cell” in biology classes across the U.S., are best known for “fueling” cells by producing a molecule that is used to power reactions. However, mitochondria perform a host of other functions. This includes helping each cell respond to stress appropriately and convey to other cells when it’s in trouble. In the identical twin that was an astronaut and in biological samples that endured spaceflight, there were indicators of an initial increase in the components of mitochondria that actually produce energy. Each cell has an energy quota that is has to meet to work properly, so this increase in energy-producing structures could mean that cells needed to meet a higher energy quota because of the extreme environment in space. It could also mean that these energy-producing structures were not working as efficiently as normal, so more of them were required to produce enough energy to meet the cell’s normal quota.

An increase in the energy-producing structures in mitochondria appears to come at a cost. Following spaceflight, scientists detected higher levels of reactive oxygen species, a type of damaging chemical that can be released from mitochondria. Normally, the body has built-in safeguards against reactive oxygen species. This includes  antioxidants, which you may have heard of in the context of their abundance in some healthy foods.  However, the astronaut twin that was in space for an extended period of time had less antioxidants than his brother. This means that the astronaut’s body was less prepared to fight an increase in reactive oxygen species. Although these changes occur throughout the body and not specifically in nervous system, nervous tissue is especially vulnerable to damaging agents like reactive oxygen species because of the cell types (like neurons) that make up this tissue. You can’t just make new neurons; the only option is to fix the ones that are already there. This means that damage to the nervous system is more difficult to reverse than damage to most other organ systems.

This is also interesting because much like ventricle expansion, mitochondrial dysfunction is closely associated with ageing and ageing-related diseases, such as Alzheimer’s Disease and Parkinson’s disease. As we continue to send people to space and develop technology and nutritional regimens to aid in maintaining mitochondrial health, it is possible we might be able to apply that same technology to see whether it aids patients with diseases like these where mitochondrial function is known to be impaired. Similarly, studying the ventricle expansion that occurs in space might help us better understand why ventricles expand in ageing, and the relevance this has for human health.

Technological developments to counteract the physical impacts of spaceflight

So what do these studies recommend to counteract the side effects of space flight? Ventricle expansion seems to eventually reverse on its own after returning to Earth. However, this does take a while- it’s hard to pinpoint exactly how long, but the scientists who performed the study believe it is somewhere over three years before ventricles return to their typical size. To address issues with mitochondrial function, authors recommend continuing a strict exercise and nutritional regimen. There are several dietary supplements being developed that might be able to decrease the amount of reactive oxygen species roaming free in astronaut’s bodies and brains. In addition to allowing for safer spaceflight, this is exciting because these supplements could potentially be repurposed to help counteract some of the mitochondrial malfunction associated with the ageing brain. Our ability to perform longer-duration missions in space will depend on our ability to keep the astronauts manning those missions healthy and happy.

References

1. McGregor, H. R., Hupfeld, K. E., Pasternak, O., Beltran, N. E., De Dios, Y. E., Bloomberg, J. J., … & Seidler, R. D. (2023). Impacts of spaceflight experience on human brain structure. Scientific Reports, 13(1), 7878.

2. da Silveira, W. A., Fazelinia, H., Rosenthal, S. B., Laiakis, E. C., Kim, M. S., Meydan, C., … & Beheshti, A. (2020). Comprehensive multi-omics analysis reveals mitochondrial stress as a central biological hub for spaceflight impact. Cell, 183(5), 1185-1201.

Cover photo generated with DeepAI.