Heart Tissue Shows Signs of Aging After Just One Month in Space, Study Finds

A few years ago, biomedical scientist Jonathan Tsui flew to Florida with unique baggage. He toted compact chambers—smaller than a cell phone—containing 48 bits of human heart tissue.

Tsui brought the samples to NASA’s Kennedy Space Center, where in March 2020 they were loaded onto a SpaceX craft and sent to the International Space Station for a month. The goal? To study the effects of low gravity conditions on the human heart in preparation for long-term space travel.

After just 30 days in space, the heart tissue samples not only weakened, but also demonstrated irregular beating patterns and hallmark symptoms of aging. The results of the study were published in the journal Proceedings of the National Academy of Sciences on Tuesday.

“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,” the researchers write in the paper.

Scientists have known that low and zero gravity conditions have an adverse effect on human bodies for a while. Muscle atrophy, bone loss, reduced heart function and irregular heartbeat are just some of the symptoms that can impact astronauts who spend a long time in space.

Most, but not all, of these conditions are resolved over time after returning to Earth, which is good news for NASA astronauts Sunita Williams and Butch Wilmore, who currently have to spend an extra eight months on the ISS because of technical issues with their spacecraft.

But to more deeply understand these health problems, scientists wanted to study them on a molecular level—something that has been difficult to achieve in the past.

“It’s not possible to do the different molecular and functional studies in human astronauts,” Deok-Ho Kim, biomedical engineer and co-author of the study, tells Nature News’ Gemma Conroy.

Heart Tissue Heads to Space | Johns Hopkins Medicine

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Instead, Kim, Tsui and the rest of their team used human induced pluripotent stem cells—which can develop into different types of cells—and coaxed them to turn into human heart muscle cells, per a statement from Johns Hopkins University. Then, they strung the individual samples together, with each one mounted between a pair of posts. One post per tissue sample was stiff, while the other was flexible, which allowed the tissue to contract like a beating heart. The flexible post contained a magnet that passed on tissue contraction data to a sensor.

The entire system is called a heart-on-a-chip, and it was housed in a small contraption meant to mimic an adult human heart chamber—the one that Tsui traveled with to Florida, where he had to continue caring for it for a month before launch. At the ISS, astronaut Jessica U. Meir cared for the tissues, which involved changing their liquid nutrients weekly.

“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,” says Kim in the statement.

As the heart tissues contracted on the ISS, the research team, 250 miles below, received bursts of real-time data. They compared the incoming numbers to measurements from a set of identical samples still on Earth. When the heart-on-a-chip returned from the ISS, the team continued their analysis, and the results were striking.

The heart tissues had grown to beat half as strongly as the Earth-bound samples, and the period between beats stretched to five times longer. Heartbeat irregularity, known as arrhythmia, can cause heart failure, but the tissue’s contractions regained a normal cadence after returning to Earth. On a molecular level, sarcomeres—proteins that aid contraction—were shorter and disordered after space exposure, and cells’ mitochondria, responsible for energy production, had become deformed.

Last year, scientists sent another set of samples to the ISS, this time to test drugs that could potentially counteract the effects of low gravity. The study is ongoing, and since the impact of low gravity on heart tissue is similar to that of advancing age, the results could also hold implications for the treatment of age-related cardiac problems.

And with future tissue-on-a-chip experiments, researchers could study how other organs respond to spaceflight, Joseph Wu, a Stanford University cardiologist who was not involved in the research, tells Nature News. “The platform’s ability to function in a microgravity setting whilst maintaining tissue viability is a major advantage,” he adds.

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Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.