Space accelerates cellular aging in astronauts

Spaceflight isn’t just tough on muscles and bones. It appears to age the very cells that keep blood and the immune system functioning.

Researchers at the University of California San Diego’s Sanford Stem Cell Institute report that human hematopoietic stem and progenitor cells (HSPCs) show clear signs of accelerated aging after weeks aboard the International Space Station.

The cells lost some of their capacity to produce healthy new blood cells, accumulated DNA damage, and displayed shortening at the ends of their chromosomes – classic markers of cellular aging.

“Space is the ultimate stress test for the human body,” said senior author Catriona Jamieson, the institute’s director. “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.”

New focus on stem cells

NASA’s landmark Twins Study, which followed astronaut Scott Kelly during his year in orbit while his twin, Mark, remained on Earth, hinted that spaceflight can alter immune function and telomere length.

Many changes reversed after landing, but some persisted, raising concerns for longer missions. The scientists took that story deeper, homing in on the cells that seed the blood and immune systems.

The research dovetails with the Space Omics and Medical Atlas effort, which mapped wide-ranging biological changes in space, but goes further by uncovering the mechanisms of stem cell aging at the cellular and molecular levels.

Space labs track cellular aging

To watch HSPCs respond in real time, the team flew automated, AI-guided “nanobioreactor” systems on four SpaceX resupply missions.

These miniaturized platforms – developed with Space Tango – kept human stem cells alive and dividing in microgravity while persistent microscopy and onboard analytics tracked their behavior.

In some cases, cells spent 32 to 45 days in orbit, long enough to reveal how space conditions reshape their biology.

Microgravity accelerates cellular stress

The picture that emerged is one of overdrive and wear. Blood-forming stem and progenitor cells typically cycle between bursts of work and periods of rest that protect their long-term potential.

In microgravity, the cells became hyperactive, burning through their reserves and losing that restful “quiescent” state that preserves regenerative capacity.

Their ability to generate healthy progeny declined. Molecular scars piled up in several ways: DNA damage increased, telomeres trended shorter, and mitochondria sent stress signals. Together, these signs suggested the cells’ energy systems were under strain.

The team also saw signs that normally silent stretches of the genome flickered on under stress – a loss of stability that can disrupt immune function and raise the risk of disease.

As Jamieson put it, 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.”

Echoes of space cellular aging on Earth

HSPCs sit at the root of the blood and immune tree. If they falter, the branches above – red cells, platelets, multiple layers of immune defenders – grow weaker.

For crews headed to the Moon, Mars, or extended stays in commercial space stations, the risks include greater vulnerability to infection. They may also face slower wound healing and long-term health problems after returning home.

The findings also feed a broader scientific question: what exactly pushes cells to age? Microgravity, radiation, circadian disruption, and isolation are an extreme blend of stressors not easily reproduced on Earth.

As a result, space becomes a powerful testbed for uncovering which stress pathways push stem cells toward decline. The insights gained could guide therapies for age-related disorders and cancers linked to malfunctioning stem and progenitor cells.

Some damage can be undone

One encouraging result stands out. When space-exposed HSPCs were returned to a young, healthy environment on Earth, some of the damage began to unwind.

Telomere dynamics stabilized, stress markers ebbed, and functional capacity improved.

That rebound suggests the changes aren’t a one-way street. With the right countermeasures – drugs, gene-based strategies, metabolic supports, or tailored exercise and sleep regimens – stem cells might stay healthier during flight and recover more effectively afterward.

Aging linked to stress signals

The team’s real-time imaging and biosensing pointed to a chain reaction familiar in aging biology. Mitochondrial distress can flood cells with reactive molecules, which in turn damage DNA and trigger repair responses.

To compensate, cells sometimes activate normally quiet genomic elements and pivot into pro-inflammatory states that accelerate wear and tear.

In the confined world of a stem cell, where balance is everything, that cascade appears to push HSPCs to churn rather than conserve – a costly strategy if it continues for months.

Scaling up stem cell research

Space Tango’s CubeLab hardware made the experiments possible by pairing persistent microscopy with a controlled microenvironment in orbit.

“Coupling Space Tango’s CubeLab capabilities, specifically the persistent microscopy, has enabled this work and will continue to do so in the future,” said company co-founder Twyman Clements.

The Sanford Stem Cell Institute has already flown 17 missions to the ISS and plans more, including astronaut-based studies that can align cellular readouts with clinical changes.

Earth research benefits from orbit

“Space experiments are so complex that they force you to do better science on the ground,” Jamieson said.

Paradoxically, the hard constraints of orbital research – limited sample sizes, no second chances, strict automation – drive innovations in imaging, analytics, and experimental design that later simplify Earth-bound studies.

As commercial spaceflight expands and long-duration missions move from concept to countdown, this kind of precision biology will be essential. If we want humanity to go farther, we’ll need our stem cells to stay younger, longer – and studies like this one are showing how.

The study is published in the journal Cell Stem Cell.

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