Spaceflight pushes the human body to its limits, exposing astronauts to microgravity, high levels of radiation, and extended periods of isolation. These stressors affect their health in various ways, many of which scientists are still working to fully understand. But if we are ever to boldly go where no human has gone before, we need to know all the risks before we take the leap.

And now new research published Thursday, September 4 in the journal Cell Stem Cell offers clues to another facet of health in space. Researchers discovered that spaceflight can accelerate the molecular aging of blood stem cells, specifically human hematopoietic stem and progenitor cells (HSPCs). These cells play a critical role in blood and immune system health, serving as the foundation for all the body’s different blood cells. The findings suggest that HSPCs lose some of their ability to re-regenerate and make healthy new cells after spaceflight.

“Understanding these changes not only informs how we protect astronauts during long-duration missions but also helps us model human aging and diseases like cancer here on Earth,” co-author Catriona Jamieson, director of the Sanford Stem Cell Institute and professor of medicine at UC San Diego School of Medicine, said in a press release.

Tracking cellular shifts in space

NASA has been hard at work at understanding what space does to the body for years. The landmark Twins Study involving Scott Kelly and (now Senator) Mark Kelly, for example, showed that spaceflight can lead to changes in gene expression, telomere length, and the gut microbiome. But few studies have investigated how the extremes of space affect processes at the level of HSPCs, according to Jamieson and her colleagues.

They sought to fill that gap by looking at how these cells change during and after a trip to space. Partnering with NASA and Space Tango, a company that facilitates research and manufacturing in microgravity, the researchers developed a “nanobioreactor” platform made up of miniature 3D biosensing systems. This novel tool cultures human stem cells in space and monitors them using AI-powered imaging. The team sent their system to the International Space Station via a SpaceX resupply mission.

Microscopic changes, big health impacts

After as few as 32 and as many as 45 days of spaceflight, HSPCs showed clear signs of aging. For one, the cells became more active than typical, quickly burning through their energy reserves and losing their ability to rest and recover. This hindered their ability to regenerate over time. Their ability to make new, healthy cells also declined, and they showed signs of DNA damage, shortened telomeres, and inflammation inside their mitochondria. They even activated hidden sections of their genome that usually remain dormant in what appeared to be a desperate bid to maintain stability.

These changes can impair immune function, in turn increasing the risk of disease, according to the researchers. Notably, only some of the damage reversed when the cells were placed in a non-space environment. This suggests it may be possible to recover aged HSPCs after spaceflight, but there may be limits.

As humans aim to travel farther from our home planet than ever before, understanding the health risks associated with long-term spaceflight is becoming increasingly important. Jamieson and her colleagues plan to dive deeper into the cellular impacts with additional ISS missions and astronaut-based studies. “This is essential knowledge as we enter a new era of commercial space travel and research in low earth orbit,” she said.