Spaceflight Speeds Up Cellular Aging in Human Stem Cells

What happens to human cells when they leave Earth?

Scientists at the University of California, San Diego (UC San Diego), have found that space travel accelerates aging in human hematopoietic stem and progenitor cells (HSPCs), which are essential for maintaining blood and immune health.

In research published in Cell Stem Cell, the team deployed automated, artificial intelligence (AI)-driven nanobioreactor systems aboard four SpaceX resupply missions to the International Space Station (ISS).

Results revealed that after spaceflight, the cells showed a reduced ability to generate healthy new cells, an increased vulnerability to DNA damage and faster aging at chromosome ends – clear indicators of accelerated cellular aging.

Building on The NASA Twins Study

“Space is the ultimate stress test for the human body,” said Catriona Jamieson, MD, PhD, director of the Sanford Stem Cell Institute (SSCI) and a professor of medicine in the UC San Diego School of Medicine. “These findings are critically important because they show that the stressors of space – like microgravity and cosmic galactic radiation – can accelerate the molecular aging of blood stem cells.”

She added, “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. This is essential knowledge as we enter a new era of commercial space travel and research in low Earth orbit.”

Previous National Aeronautics and Space Administration (NASA) research has already shown that spaceflight impacts the body. The NASA Twins Study, for example, tracked astronaut Scott Kelly during his 340-day mission aboard the ISS while his identical twin, Mark Kelly, remained on Earth.

Conducted between 2015 and 2016, the study revealed shifts in gene expression, telomere length, immune function and the gut microbiome. Many of these changes reversed once Kelly returned to Earth, though some persisted, including disrupted gene expression and an increase in short telomeres – factors with potential implications for longer missions.

The new UC San Diego-led study builds on those findings as well as the extensive work of the Space Omics and Medical Atlas group, which has published 44 papers in Nature on aerospace medicine and space biology. By focusing on HSPCs, the researchers provided a deeper, mechanistic view of how space conditions drive molecular aging – insights that the Twins Study suggested but could not fully capture at the cellular level.

Human HSPCs display hallmarks of aging during spaceflight

To carry out the study, researchers – including the biotech company Space Tango – developed a novel nanobioreactor platform. These miniaturized three-dimensional biosensing systems made it possible to culture human stem cells in space and track their behavior using AI-powered imaging tools.

When human HSPCs were exposed to 32 to 45 days of spaceflight, they began to display hallmark features of aging. The cells became unusually active, quickly exhausting their reserves and losing the ability to rest and recover – a crucial trait that allows stem cells to regenerate over time. Their capacity to generate healthy new cells declined, while molecular signs of wear, including DNA damage and shortened telomeres, grew more evident.

The study also revealed that the cells showed inflammation and stress in their mitochondria. At the same time, normally silent sections of the genome were activated, destabilizing the cells and potentially impairing immune function. Such stress responses could heighten the risk of disease.

Importantly, when the space-exposed stem cells were later placed into a young, healthy environment, some of this damage began to reverse. The finding suggests that with the right interventions, it may be possible to rejuvenate aging cells.

These results carry implications far beyond astronaut health. They shed new light on the molecular mechanisms of aging and age-related diseases here on Earth, while also highlighting the need for countermeasures to safeguard stem cell function during long-term space missions.

“We're excited this breakthrough work is being published to the wider scientific and space communities,” said Twyman Clements, president and co-founder of Space Tango. “Like many accomplishments, this one was a team effort bringing together the Integrated Space Stem Cell Orbital Research Center within SSCI, Space Tango and others. Coupling Space Tango's CubeLab capabilities, specifically the persistent microscopy, has enabled this work and will continue to do so in the future.”

Expanding space-based stem cell research to safeguard health on Earth

The research team now plans to expand this work through additional missions aboard the ISS and astronaut-based studies. Future efforts will focus on the real-time monitoring of molecular changes in stem cells and testing potential pharmaceutical or genetic countermeasures to safeguard human health, both in space and on Earth.

“Space experiments are so complex that they force you to do better science on the ground,” said Jamieson. “Space research has accelerated technological advancements on Earth, making ground-based research easier and more relevant to human health. What we have learned about cancer from our studies in space is absolutely remarkable.”

Reference: Pham J, Isquith J, Balaian L, et al. Nanobioreactor detection of space-associated hematopoietic stem and progenitor cell aging. Cell Stem Cell. 2025;32(9):1403-1420.e8. doi: 10.1016/j.stem.2025.07.013

This article is a rework of a press release issued by the University of California, San Diego. Material has been edited for length and content.