Long-duration space travel has been shown to seriously harm the human body.
The goal of long-duration space travel is becoming increasingly important for humanity, especially as missions to the Moon, Mars, and beyond are being planned by space agencies worldwide. However, alongside the scientific and technological benefits that space exploration offers, scientists must also confront a series of physiological challenges. One of the biggest issues is the negative impact of the microgravity environment on the human body, including cardiovascular health.
Previously, studies have indicated that when humans live in a prolonged microgravity environment, their organs can undergo significant changes. From muscle atrophy and loss of bone density to vision changes and psychological issues, all have been documented in astronauts returning from the International Space Station (ISS). Now, a new study led by scientists at Johns Hopkins University has revealed a concerning finding: the human heart also weakens when living in space.
In a prolonged microgravity environment, the human body experiences numerous changes.
Special Experiments on the ISS
This research was conducted on human engineered heart tissue samples. In the experiment, 48 tissue samples were sent to the International Space Station for 30 days to examine how microgravity affects cardiac cells. This could help scientists better understand how the heart functions in a microgravity environment and what changes might occur at the cellular and molecular levels.
The results showed that in a microgravity environment, cardiac cells not only become weaker, but also struggle to maintain a rhythmic beat. The heart cells developed arrhythmias—a common symptom often seen in individuals with age-related cardiovascular issues. Notably, these changes occurred after only a short period of exposure to the space environment, indicating that microgravity can have a profound impact on cardiovascular health beyond what we previously thought.
“Heart-on-a-chip” and Technological Foundation
“Heart-on-a-chip” used for the experiment. (Illustrative image).
The research team, led by Deok-Ho Kim, a professor in the Department of Biomedical Engineering at Johns Hopkins University, developed the “heart-on-a-chip” platform for this experiment. This platform utilizes human-induced pluripotent stem cells, which can differentiate into various types of cells, including cardiac cells. These cells were placed onto a miniaturized bioengineering chip that simulates how an adult human heart functions.
Subsequently, these heart tissue chips were sent to the ISS on a SpaceX flight in March 2020. There, astronaut Jessica Meir took care of the experiment on behalf of the research team, maintaining living conditions for the heart tissues by changing the surrounding nutrients weekly. The tissue samples were also preserved for genetic analysis and imaging upon their return to Earth, allowing the team to gather comprehensive data on how microgravity affects the contraction and rhythmic function of the heart.
This experiment represents a significant advancement in cardiovascular health research in space. Unlike previous experiments that focused solely on the physiological effects of microgravity on astronaut bodies, this time the research team concentrated on cellular and molecular levels, providing deeper insights into how the space environment impacts heart function.
In a microgravity environment, cardiac cells lose their ability to contract powerfully.
Surprising Results
Data from the “heart-on-a-chip” experiment show that in a microgravity environment, cardiac cells lose their ability to contract strongly like they do on Earth. The tissue samples exhibited signs of arrhythmia, with the time between beats extending nearly five times longer than the normal rhythm of a healthy heart. This is particularly concerning as it indicates that not only is the strength of the heart compromised, but its rhythmic function is also severely affected.
Another important finding is that the protein bundles within cardiac cells, known as sarcomeres—responsible for heart contraction—became shorter and less organized compared to control cells. This is a sign of cardiac damage, similar to what is often observed in patients with age-related cardiovascular diseases.
Additionally, the mitochondria—the powerhouses of the cell—in the heart tissue samples became larger, rounder, and lost their characteristic folds, disrupting energy production. This reduction in energy production capability may explain why cardiac cells are significantly weakened in a microgravity environment.
Furthermore, the heart tissue samples showed increased signs of inflammation and oxidative stress, particularly an imbalance between free radicals and antioxidants. These signs not only reflect the impact of microgravity but also align with what we know about aging and heart disease on Earth.
Mitochondria became larger, rounder, and lost their characteristic folds. (Illustrative image).
Applications and the Future
The findings from this experiment are significant for both astronaut health and medical research on Earth. First, they expand our understanding of how microgravity affects the human body, particularly cardiovascular health. This will assist space agencies like NASA in developing health protection measures for astronauts during long-term missions in the future.
In 2023, Kim’s lab sent another batch of heart tissue samples to the ISS to test drugs that may protect the heart from the negative effects of microgravity. This is an important step, not only to maintain cardiovascular health for astronauts but also potentially to open new therapies for heart disease for those on Earth.
Moreover, Kim’s research team is collaborating with NASA to study the effects of space radiation on cardiovascular health. Radiation from cosmic rays and the Sun is one of the significant risks astronauts will face when moving beyond Earth’s orbit, where the planet’s magnetic field protects them from most cosmic radiation. Understanding the effects of this radiation will help scientists develop preventive measures and protections for astronauts’ cardiovascular health during space missions.
Radiation from cosmic rays and the Sun is also one of the significant risks for astronauts.
The new research on the effects of microgravity on cardiovascular health indicates that long-term living in space not only affects the body externally but also has profound impacts at the cellular level. The changes in cardiac function and structure in the space environment pose significant challenges for extraterrestrial exploration missions, but they also open new opportunities for research and the development of new therapies for cardiovascular disease on Earth.
Advancements in biotechnology, tissue engineering, and space medicine will not only help safeguard the health of astronauts but could also lead to major advancements in medicine for all humanity. With these important discoveries, the future of space travel will become increasingly safe and efficient, bringing humanity closer to conquering distant planets.
