New discovery: a single month in space is enough for human cardiac tissue to age significantly

Scientists sent bioengineering samples of heart tissue to the International Space Station to study how to keep astronauts safe during future long-term space travel.

Heart tissues ISS
Heart tissue in one of the chambers. Credit: Jonathan Tsui

Biomedical scientist Jonathan Tsui provided NASA's Kennedy Space Center with small compact cameras that contained 48 fragments of human heart tissue. These were loaded into a SpaceX spacecraft and sent to the International Space Station (ISS) for a month, with the aim of studying the effects of low gravity conditions on the human heart in preparation for long-term space travel.

After only 30 days in space, the cardiac tissue samples not only weakened, but showed irregular heartbeat patterns and characteristic symptoms of aging.

The results of the study were published on Tuesday in the journal Proceedings of the National Academy of Sciences. "With the current plans for manned missions to Mars and beyond, the need to better understand, prevent and counteract the harmful effects of long-term space flights on the body is increasingly important," the researchers wrote in the article.

The use of human-induced pluripotent stem cells

Scientists have long known that low and zero severity conditions have adverse effects on the human body. Muscle atrophy, bone loss, decreased heart function and irregular heartbeats are just some of the symptoms that can affect astronauts who spend a lot of time in space.

Most of these conditions, although not all, resolve with time after returning to Earth. But to better understand these health problems, scientists wanted to study them at the molecular level, something difficult to achieve so far.

Tissue chambers
Tissue chambers loaded in a plate enclosure designed for research aboard the International Space Station. Credit: Deok-Ho Kim and Devin Mair / Johns Hopkins Medicine

The team used induced human pluripotent stem cells (which can become different types of cells) and induced them to become human cardiac muscle cells. Then, they connected the individual samples, each of them mounted between a pair of pillars. One pillar per tissue sample was rigid, while the other was flexible, allowing the fabric to contract like a beating heart. The flexible pillar contained a magnet that transmitted tissue contraction data to a sensor.

The whole system is called "heart on a chip" and was housed in a small gadget that imitated the camera of an adult human heart, with which Tsui traveled to Florida, where he had to continue taking care of it for a month before the launch. On the ISS, astronaut Jessica U. Meir took care of the tissues, which involved changing the liquid nutrients weekly.

As the heart tissues contracted on the ISS, the ground investigation team received real-time data. They compared the figures received with the measurements of a set of identical samples still on Earth. When the heart on a chip returned from the ISS, the team continued its analysis and the results were surprising.

What did they find?

The tissues of the heart had grown to beat at half the strength of the ground samples, and the beat-up period was five times longer. Irregular heartbeat, known as arrhythmia, can cause heart failure, but tissue contractions regained a normal cadence after returning to Earth.

At the molecular level, sarcomers - proteins that help contraction - were shorter and more disordered after spatial exposure, and the mitochondria of the cells, responsible for energy production, had been deformed

Last year, scientists sent another group of samples to the ISS, this time to test drugs that could counteract the effects of low severity. The study is ongoing and, given that the impact of low gravity on cardiac tissue is similar to that of advanced age, the results could have implications for the treatment of age-related heart problems.

News reference:

Devin Mair et.al, Spaceflight-induced contractile and mitochondrial dysfunction in an automated heart-on-a-chip platform. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.240464412