“Space is the ultimate stress test for the human body,” Catriona Jamieson, director of UC San Diego’s Sanford Stem Cell Institute, said. That stress, as new research reveals, imparts a molecular signature onto the very cells that maintain blood and immune systems hematopoietic stem and progenitor cells (HSPCs) hastening their aging and disabling their regenerative ability.
In four NASA-sponsored missions, AI-based nanobioreactor systems cultured human HSPCs on the International Space Station for 32 to 45 days. The biosensing platforms, which were mounted in Space Tango CubeLabs, preserved physiologic conditions and recorded daily confocal microscopy of fluorescent cell-cycle reporters. The results showed a remarkable transformation: space-flown HSPCs cycled more quickly, lost quiescence, and exhibited reduced self-renewal in post-flight colony assays versus paired ground controls.
Whole-genome sequencing to 90× coverage identified telomere erosion the gradual loss of chromosome ends signaling cellular aging in flight samples. This result is consistent with the NASA Twins Study, which saw lengthening of telomeres in space followed by hectic shortening upon return, but where here the net result was a quantifiable loss. Gene set enrichment analysis revealed downregulation of telomere-maintenance pathways, further endorsing the genomic instability signal.
Mitochondrial stress was a defining feature. RNA sequencing indicated extensive upregulation of mitochondrial pathways, and copy number for mitochondrial DNA was increased in space-exposed cells. These alterations are concordant with oxidative stress reactions observed in peripheral blood from astronauts and are established factors in stem cell senescence. In the distinct radiation environment of low Earth orbit where galactic cosmic rays and trapped protons provide 0.3–0.4 mSv/day on the ISS, several hundred times Earth’s background ionizing particles produce reactive oxygen and nitrogen species that cause DNA, protein, and lipid damage. The combined influence of radiation and microgravity has the potential to augment oxidative stress, a process defined as Oxidative Stress and Damage.
One of the most insightful molecular signatures was a single-base C-to-T substitution increase, the mutational signature of APOBEC3 cytidine deaminases. Spaceflight samples overexpressed APOBEC3A and APOBEC3C, enzymes whose deregulation can cause pre-leukemic mutations. In parallel, the RNA-editing p150 isoform of the ADAR1 enzyme essential for HSPC self-renewal was decreased, as was global A-to-I RNA editing levels. This base deaminase imbalance has been involved in immune evasion and malignant transformation in ground-based cancers.
The genomic disruptions also extended to repetitive DNA elements. Long interspersed nuclear elements (LINEs), specifically L1ME3A, were downregulated in post-flight cells, consistent with APOBEC-mediated restriction. These retrotransposon regulation changes have previously been associated with aging and tumorigenesis.
Mechanistically, these results overlap with decades of space biology demonstrating that microgravity disrupts cytoskeletal structure, chromatin organization, and gene expression. In HSPCs, loss of dormancy and augmented proliferation in orbit replicate stress-induced “fight or flight” responses within the bone marrow niche, possibly mediated by neuronal regulatory genes additionally mutated within the flight cohort.
Notably, some of the damage was reversible. When space-flown HSPCs were transferred into a youthful, healthy niche, some of their function started to come back, indicating that specific interventions pharmacologic, genetic, or environmental can restore aged stem cells. This bodes not only for astronaut health on long-duration missions but also for the treatment of age-related decline in hematologic function on Earth.
The work builds on the NASA Twins Study’s multi-omic portrait of a year-long mission, which cataloged shifts in gene expression, immune function, and telomere dynamics, some of which persisted months after return. By focusing on a single, clinically critical stem cell population and integrating real-time AI monitoring with deep genomic analysis, the UC San Diego-led team has provided a mechanistic bridge between systemic astronaut physiology and molecular aging pathways.
As commercial spaceflight grows and flights extend beyond the magnetosphere where the rate of cosmic ray dose may be 0.4–1.1 mSv/day, depending on solar activity knowing and countering these cellular risks will be critical. The ISSCOR program’s nanobioreactor strategy presents both a risk prediction platform and an in-orbit countermeasure testing venue, from radioprotective drugs to gene expression modifiers, for maintaining stem cell fitness in the most hostile lab in existence: space.
