Australasian Science Magazine

Space is a harsh environment that presents several serious health risks to astronauts

By Elizabeth Blaber, Helder Marcal, John Foster & Brendan Burns

The altered gravity conditions of space can have serious detrimental effects on the health of astronauts. Understanding the cellular basis of this phenomenon could lead to better medical treatments on Earth.

Humans have gazed into the night sky for thousands of years and wondered what the billions of twinkling spots were that they could see. Different cultures have assigned their own meaning to the universe throughout the millennia, but rapid advances in research and technology are only just beginning to further our understanding of the nature and mysteries of the cosmos.

We recently celebrated the 40th anniversary of our first steps on the Moon, and within two decades it is hoped that humankind will have both the financial and technological means to establish a settlement on Mars. However, space is a harsh environment that presents several serious health risks to astronauts. Therefore, before space exploration can be pursued these health risks need to be identified and suitable countermeasures or preventative steps need to be taken to ensure the health and safety of our astronauts. The field of bioastronautics attempts to address these issues.

Our focus is to examine the way that microgravity influences cellular function. Microgravity in space is 1000 times less strong as the gravity we find here on Earth. It poses a serious health threat to astronauts, including loss of bone mass, skeletal and cardiac muscle wasting and muscular fatigue, decreased capacity of the immune system to fight infections, and a decreased ability of the body to repair itself.

Due to the isolation of astronauts travelling on a spacecraft and their inability to reach medical attention, these alterations in the ability of the body to function normally can be life-threatening. If a person on Earth catches a cold then generally we will recover within about a week due to the ability of our immune system to attack the virus causing this illness. However, in space an astronaut’s immune system is weakened to the point where a simple cold may endanger the astronaut’s life.

Similarly, if we cut ourselves here on Earth we can put a band-aid on the cut and within several days it has healed. In space, however, the body’s ability to repair itself is compromised to the point where a cut may not heal at all.

Such effects of space on an astronaut’s body are largely due to the lack of gravity in space. Therefore, before we can further pursue space exploration we need to be able to overcome these health issues.

The aim of our research was to investigate the influence of microgravity on the function of human stem cells. We aimed to identify specific proteins that were linked to particular functional pathways in cells kept under simulated microgravity conditions.

As proteins are the functional units of a cell, we hypothesised that any alterations occurring in the cells maintained in simulated microgravity conditions would be evident at this level. Once these changes were identified, they would be correlated with health problems encountered in microgravity conditions.

To look at the effects of microgravity on stem cells we used a system designed by NASA known as the Rotary Cell Culture System. This consists of a cylindrical vessel that is completely filled with a growth medium. The vessel and growth medium that it contains rotates along the horizontal axis, allowing the cell mass to remain in constant freefall. Due to this, the gravitational vectors cancel out to produce a microgravity environment within the vessel that can be used to simulate the microgravity that is encountered in space.

We have found that a number of proteins are expressed differently in microgravity. Within a cell, DNA is translated into a chain of amino acids that is then folded into a protein. The sequence of amino acids that forms the protein is determined by the DNA sequence from which it is made. A protein’s function is determined by this sequence as well as its structure.

Proteins are essential to all cells. Some may be enzymes that are involved in metabolism, while others may form the structure of the cell. Alternatively proteins may be signalling molecules such as hormones, or may help the cell to adhere to other cells.

In other words, proteins form the functional units of our bodies. Therefore, changes in the production of proteins due to microgravity may have significant impacts on the function of a cell and may be detrimental to an individual’s well-being.

We found that the expression of a number of proteins was altered under microgravity conditions. These proteins were involved in cell adhesion, cytoskeleton formation, cell death and the cell matrix maintenance.

However, some of these proteins are only found in specific systems within the human body. For example, a particular protein’s function may be to regulate cell death but it only does this in muscle cells. Therefore, if this protein’s production is decreased it is detrimental to the health of muscle cells and thus the overall ability of an individual to use his or her muscles.

Specifically our study found that a number of proteins that are important for the correct functioning of the skeleton, skeletal muscle, immune system and cardiovascular system are affected by microgravity.

The bones that make up an individual’s skeleton are constantly remodelled. Cells within the bone constantly break down bone material while other cells constantly remake bone material. A balance between these two cell types must be maintained to ensure the correct functioning of the bone.

But during spaceflight this balance is disturbed so that bone material is broken down faster than it can be made, resulting in a loss of bone mass and producing a condition known as spaceflight osteopenia. Although this effect of spaceflight has been well-documented, the precise mechanisms by which it occurs remains unknown.

Our study has identified proteins that may provide insights into the causes of osteopenia in astronauts. And since spaceflight osteopenia has many parallels with osteoporosis on Earth, determining the role of the proteins involved in spaceflight osteopenia could be of significant medical importance.

Our study also found a number of proteins that are involved in the degradation of other proteins. These types of proteins are important for cellular turnover, whereby old proteins are degraded to enable the production of new proteins. However, just like the degradation of bone, the degradation of proteins must be tightly coupled to the formation of new proteins to enable a balance to be maintained.

Our study identified proteins involved in the degradation of the cellular cytoskeleton, which maintains the structural integrity of the cell while also maintaining the cell’s shape. Previous research had found that the cytoskeleton is altered in microgravity conditions, causing a loss of cellular integrity and the death of the cell. Therefore, the degradation of these types of proteins in microgravity conditions may provide insights into the cause of structural alterations of cells observed in microgravity conditions. These proteins also have important implications for the movement of cells, and their ability to contract, divide and signal other cells.

These effects may occur at the cellular level, but changes that occur at the level of the cell can have implications for entire systems in the body. For example, cell motility is a critical function of cells within the immune system as immune cells need to be able to migrate towards foreign invaders such as bacteria.

Previous studies have shown that the ability of immune cells to respond to foreign bodies is decreased in conditions of microgravity. The inability of immune cells to migrate to foreign matter may therefore prevent successful and effective immune responses in space.

We also found that the number of antioxidants in microgravity samples was decreased. When a cell is exposed to oxygen during normal cellular metabolism it produces a molecule known as a reactive oxygen species or oxygen free radicals. These species can cause extensive damage to DNA and proteins within the cell, and thus antioxidants are needed to neutralise reactive oxygen species inside the cell.

But if antioxidants are present at low concentrations in microgravity conditions, then neutralisation of reactive oxygen species may not be effective and substantial cellular damage may occur.

Additionally, we found some proteins indicating that cells in microgravity conditions are under oxidative stress. As the functional units of a cell are proteins, these results suggest that simulated microgravity has a significant impact on cellular function.

Our study has the potential to impact not only on the effects of microgravity on human health in space but may also have vast impacts on ground-based medical problems. As many spaceflight-induced medical complications have parallels with medical problems here on Earth, any medical advances made in space or space-like conditions can have valuable applications here. Thus the potential benefits of this research are far-reaching, both in terms of advancing human knowledge and contributing to addressing medical issues faced in both a space environment and back on Earth.

Space science research in Australia is at a critical stage, particularly when the need to build the nation’s capacity and capability in space science and engineering has been highlighted by the government with the recent introduction of the Australian Space Research Program. There has never been a better time to be in this area of space science, and our research will help Australia to remain at the forefront of an exciting and rapidly developing field.