As society becomes more geared towards space travel and looks towards establishing outer-space colonies, it is important to understand the mental health risks that would threaten astronauts on extended missions. Two main disorders that affect astronauts are anxiety, which is characterized by worry, and depression, which manifests in extreme sadness and loss of interest. In addition to possibly jeopardizing missions, these mental health implications may put astronauts at risk of permanent brain damage. Space flight was shown to deteriorate the brain, specifically the white matter, with longer durations of time in space (5). Although these changes might be due to the shifts in brain fluid from microgravity, they may also be a result of changes within the genome. We will focus on the genes associated with neuroticism, a personality trait linked with anxiety, loneliness, and depression (1). We plan to answer the question of whether or not the environment of space contributes to mental health issues in astronauts. We will focus on genes on chromosome 8, specifically CLDN23, XKR6, MSRA, and MTMR9, within neuron cells to see if there is a change in the SNPs as a result of being in space (1).
If the PC12 cell culture is exposed to microgravity and space radiation, then there will be a change in the genome within the cell culture that results in a predisposition towards depression, anxiety, and neuroticism (4) due to a deterioration in the CLDN23, XKR6, MSRA, and MTMR9 genes on chromosome 8 within the neuronal cells. The objective of our experiment is to use PCR to replicate and send those specific genes into space for up to a year, which is the maximum estimated time it would take to get to Mars. After a year has gone by, we would then sequence the genome in order to compare the SNPs with a control group on Earth. This would determine the correlation between space exposure and the expression of genes relating to depressive disorders. Hopefully, this data can then be applied to astronauts by providing more knowledge around why many of the depressive disorders arise within astronauts and open the door for new technologies that combat, if any, deterioration of these genes in space.
Since we are studying mental disorders, we have decided to use the PC12 cell line, a cell culture found in rat neuron cells (2). The advantages of using this line over primary neuronal cells is that in order to preserve the cells as extracted from rat brains, a supply of basic fibroblast growth factor (bFGF) is needed for long-term culture (8). However, since our experiment is long term and we intend to keep the experiment running for up to a year, it would be impractical and unnecessary to send a heavy supply of bFGF when the same end can be achieved by using a cell culture. We chose the PC12 cell culture over cultures because although it is a rat cell line, it contains the same genes we chose to study (CLDN23, XKR6, MSRA, and MTMR9) and this information is nearly identical to those found in humans.
The International Space Station (ISS) is necessary for our experiment because it has unique characteristics, like radiation and microgravity, that cannot be replicated on Earth. Cosmic radiation is composed of many different types of subatomic particles moving close to light speed. Exposure to these rays can cause risks towards the central nervous system (6). Since cosmic rays are already proven to be detrimental to the brain and mental health, this experiment would determine if these risks are associated with changes to the genome. To collect accurate results, it is important that the samples are exposed to actual cosmic radiation instead of Earthly substitutes. Next, microgravity is a very weak gravitational force. Magnetic fields separated PC12 cells containing magnetic nanoparticles, mimicking a different gravitational force, and showed no significant difference in gene expression between stretched and unstretched groups (7). Even though this study contradicts our hypothesis that microgravity would affect the genome, it shows the need for the experiment to be performed in the proper environment. Substitutes on Earth, such as stretching and parabolic flight are impractical and inaccurate for a long term study. The ISS will allow this experiment to be conducted in a more accurate and practical manner.
Our control group will be genes from the PC12 cell line subjected to normal Earth conditions (normal gravity, radiation) and the experimental group will be subjected to the conditions inside the ISS (microgravity, cosmic rays). Our independent variable is this change in the environment and the dependent variable is the genetic changes the PC12 cells go through. After one year, the target genes in both groups will be isolated with restriction enzymes. These genes will be duplicated through the use of PCR to create a large sample size, the purity of which will be tested by gel electrophoresis. The genes will be recombined through the process of ligation so that they can be properly sequenced. The genes of both groups will then be sequenced by the MinION, a DNA sequencing machine already aboard the ISS (3). The nitrogen bases, once read, would reveal the state of the genes after a year. A difference within the sequence of these bases between the experimental and control groups would signify deterioration. Any deterioration, which is expected in our hypothesis, would signify that space conditions such as radiation and microgravity are, in fact, responsible for activating genes related to depression and anxiety in astronauts.
Our experiment looks for mutations due to spaceflight in genes linked to anxiety, depression, and neuroticism in the PC12 cell culture.