Scientists sent a human heart to space, but it came back broken

With space explorers gearing up for human missions to Mars, researchers took human heart tissue onboard a Space X mission to test how low gravity affects it.

Space missions have long been shrouded in mystery. Astronauts returning to Earth often exhibit age-related conditions such as weakened heart muscle function and irregular heartbeats. Some effects fade over time after their return, but not all.

To broaden scientists' understanding of how low gravity might impact astronauts' survival and health on extended space missions, scientists at Johns Hopkins Medicine in Baltimore have conducted an experiment to test heart tissue for 30 days at the International Space Station (ISS).

Bioengineered heart travels to space

The team took 48 bioengineered human heart tissue samples onboard the SpaceX CRS-20 mission, which launched in March 2020. Scientists developed the cardiac payload by prompting human stem cells to grow into heart muscle cells.

The tissues were placed in a miniaturized tissue chip that connected them between two posts to gather data on how they beat. The 3D structure was designed to simulate the environment of an adult human heart, fitting into a chamber half the size of a cell phone.

Astronaut Jessica Meir at the ISS changed the liquid nutrients around the tissues weekly and preserved samples for gene analysis and imaging. To compare results, the research team kept a set of cardiac tissues grown the same way on Earth in identical chambers.

The heart tissues didn’t fare well

After closely monitoring the heart tissue activity in space and on return, the scientists were confident enough to claim that the tissue “really doesn’t fare well in space.”

The results indicate that the low gravity conditions in space weakened the tissues and disrupted their normal rhythmic beating when compared to Earth-based samples from the same source.

Such a condition can cause human heart failure. Typically, the time between heartbeats is about one second. In the tissues aboard the space station, this interval became nearly five times longer than on Earth, but it returned close to normal once the tissues were back on our planet.

The scientists discovered that in the tissues sent to space, sarcomeres – protein bundles in muscle cells that aid contraction – became shorter and more disordered, which is a sign of heart disease.

Additionally, the energy-producing mitochondria in these cells grew larger, rounder, and lost their usual folds, which are important for energy use and production.

They also analyzed gene activity in the tissues from both space and Earth, finding that the space-based tissues had increased gene production linked to inflammation and oxidative damage, both indicators of heart disease.

“Many of these markers of oxidative damage and inflammation are consistently demonstrated in post flight checks of astronauts,” said assistant research professor Eun Hyun Ahn Mair.

The research has been published on 23rd of September in Proceedings of the National Academy of Sciences. Scientists believe, that the findings might not be only useful for astronauts missions, but it could also serve as models for studying heart muscle aging and therapeutics on Earth.