Low gravity conditions in space cause heart damage
The low gravity conditions of space may cause significant damage to heart tissue, according to a new study. Cardiac tissues exposed to a low-gravity environment showed signs of mitochondrial impairment and oxidative stress, which are key features of heart failure.
For the investigation, experts at Johns Hopkins University arranged for 48 human bioengineered heart tissue samples to spend 30 days aboard the International Space Station.
Heart tissue in a low-gravity environment
Upon analysis, the experts observed that the low-gravity environment weakened the heart tissues and disrupted their normal rhythmic beats compared to control samples kept on Earth.
According to the scientists, the heart tissues “really don’t fare well in space.” Over time, the tissues on the space station beat with only about half the strength of their Earth-bound counterparts.
Impacts of long-duration spaceflight
“With current plans for manned missions to Mars and beyond, the need to better understand, prevent, and counteract the harmful effects of long-duration spaceflight on the body is becoming increasingly important,” noted the study authors.
Previous research has shown that astronauts returning to Earth often experience age-related conditions such as reduced heart muscle function and arrhythmias (irregular heartbeats), some of which dissipate after their return.
However, scientists have been seeking ways to study these effects at a cellular and molecular level in order to develop strategies to keep astronauts safe on long-duration space flights, explained project leader Professor Deok-Ho Kim.
Bioengineered heart tissues
The project used heart muscle cells (cardiomyocytes) derived from human induced pluripotent stem cells (iPSCs) – a process developed by Jonathan Tsui, a former PhD student in Kim’s lab at the University of Washington.
Tsui later continued the space biology research with Professor Kim at Johns Hopkins University.
The bioengineered heart tissues were placed in a miniaturized tissue chip that mimicked the environment of an adult human heart.
The tissue chip was designed to string the cells between two posts, allowing the researchers to collect data on how the tissues contracted.
Sending heart tissues to space
To send the cardiac tissues aboard the SpaceX CRS-20 mission, which launched in March 2020, Tsui personally hand-carried the tissue chambers to Florida, where he cared for them for a month at the Kennedy Space Center.
Once aboard the space station, real-time data was collected every 30 minutes for 10 seconds, measuring the strength of the tissue contractions, known as twitch forces, and detecting any irregular beating patterns.
Astronaut Jessica Meir helped maintain the experiment by changing the liquid nutrients surrounding the tissues weekly and preserving samples at specific intervals for later gene and imaging analysis.
Protecting the viability of the tissues
On Earth, a second set of heart tissues (developed the same way) was housed in identical chambers to serve as a control. When the space-bound tissue chambers returned to Earth, Tsui resumed collecting data from the tissues.
“An incredible amount of cutting-edge technology in the areas of stem cell and tissue engineering, biosensors and bioelectronics, and microfabrication went into ensuring the viability of these tissues in space,” said Professor Kim, whose team developed the tissue chip used for this project and future studies.
Devin Mair, a former PhD student in Kim’s lab and now a postdoctoral fellow at Johns Hopkins, analyzed the tissues’ ability to contract.
Weakened tissues and potential heart disease
The heart muscle tissues in space not only lost strength but also developed irregular beating patterns, known as arrhythmias – disruptions that could potentially lead to heart failure.
Typically, the time between one beat and the next is about one second, but in the space-bound tissues, this time increased nearly fivefold. However, when the tissues were returned to Earth, their beating rhythm gradually returned to near-normal levels.
The researchers also discovered that sarcomeres – the protein bundles in muscle cells that facilitate contraction – became shorter and more disordered in the space-bound tissues, a hallmark of heart disease.
Additionally, the mitochondria, which are responsible for producing energy in cells, became larger, rounder, and lost their characteristic folds, further indicating impaired energy production.
Inflammation and oxidative damage
Finally, Mair, along with assistant research professor Eun Hyun Ahn, and PhD student Zhipeng Dong, analyzed gene activity in the tissues.
The heart tissues that had spent time in space showed increased expression of genes associated with inflammation and oxidative damage, both of which are common markers of heart disease and are consistently observed in post-flight health checks of astronauts.
Shielding the heart from damage in space
Professor Kim’s team sent a second batch of 3D-engineered heart tissues to the space station in 2023 to screen for drugs that might protect the cells from the harmful effects of low gravity.
This ongoing research may lead to therapies that not only help astronauts maintain heart function during spaceflight but could also benefit people on Earth as they age.
The team is also continuing to refine their “tissue on a chip” system while exploring the effects of radiation on heart tissues at the NASA Space Radiation Laboratory.
The space station orbits within the Earth’s magnetic field, which shields its occupants from most space radiation, but further research is needed to understand the impact of cosmic radiation on astronauts’ cardiovascular health during longer missions outside this protective zone.
The study is published in the journal Proceedings of the National Academy of Sciences.
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