Human heart ‘aged’ after just one month in space, says study

Space travel is often seen as a frontier of human exploration, but it comes with hidden dangers — even for the human heart. A recent study has revealed that just one month in space can weaken engineered human heart tissue, make its ‘beating’ patterns irregular, and trigger molecular and genetic changes similar to ageing. These findings, published in the Proceedings of the National Academy of Sciences, shed light on how spaceflight affects the cardiovascular system.

Microgravity can take a toll on the human body, causing cardiovascular changes like irregular heartbeats in astronauts. However, understanding how extended space missions impact the heart at a molecular level has been challenging. “It’s not possible to do the different molecular and functional studies in human astronauts,” explains study co-author Deok-Ho Kim, a biomedical engineer at Johns Hopkins University.

To tackle this challenge, Kim and his team engineered heart tissue and sent it to the International Space Station (ISS) for 30 days. They used human induced pluripotent stem cells, which can transform into any cell type, to develop heart muscle cells. These cells were arranged in a ‘heart-on-a-chip’ system — a tiny structure that mimics the beating function of a heart.

While in space, sensors monitored the tissue’s strength and beating patterns in real time, and the results were striking. After just 12 days on the ISS, the heart tissue's contraction strength had nearly halved, while the samples that remained on Earth stayed relatively stable. The tissues’ beats also became increasingly irregular, with the time between each beat stretching over five times by day 19. Interestingly, these irregularities resolved after the tissue returned to Earth, suggesting that astronauts, like Sunita Williams and Butch Wilmore, currently stationed on the ISS, may experience similar cardiovascular stress that could subside upon returning to Earth.

Further analysis revealed that spaceflight caused significant structural changes in the heart tissue. Protein bundles responsible for muscle contractions, called sarcomeres, became shorter and more disordered. The mitochondria, cells' energy producers, also appeared swollen and fragmented. Additionally, genes linked to inflammation and heart disorders were more active in the tissues from space, while those crucial for heart contraction and energy production had reduced expression.

While this heart-on-a-chip model doesn’t capture all cardiovascular changes, it offers a valuable tool for studying the effects of microgravity on the human body. Joseph Wu, a cardiologist at Stanford University, believes this approach could help explore how other organs fare in space. Kim and his team now plan to send more tissues into space for longer periods to deepen their understanding and test potential drugs to counteract microgravity's effects on the heart.