“Space is the ultimate stress test for the human body,” said Catriona Jamieson, director of the Sanford Stem Cell Institute at UC San Diego. That stress, new research demonstrates, extends all the way into the bone marrow, where the stem cells that keep blood and immunity going start to weaken after weeks in space.
The research, reported in Cell Stem Cell, followed human hematopoietic stem and progenitor cells (HSPCs) on the International Space Station with AI-controlled nanobioreactors that could fit inside a CubeLab. The autonomous platforms, which were designed in collaboration with Space Tango, cultured the cells in microgravity for 45 days, tracking their division cycle in real-time with a fluorescent FUCCI2BL reporter system. Control counterparts were kept on Earth. The findings were dramatic: microgravity and cosmic radiation interfered with the cells’ usual quiescent cycle, thrusting them into persistent activity that drained their energy stores and resulted in functional exhaustion.
HSPCs give rise to all blood lineages red cells, platelets, and immune cells. On the ground, they lie dormant for about 80 percent of the time, and dormancy maintains their potential for regeneration. In orbit, that dormancy broke down. “The stem cells woke up, and they didn’t go back to sleep, and they became functionally exhausted,” Jamieson said. Returned to Earth, the space-exposed cells replated less frequently than ground controls, a marker of reduced self-renewal. Recovery was better when cultured on a youthful, healthy stromal layer but continued to be poor on their initial aged stroma, highlighting the microenvironment’s role in repair.
Molecular characterization uncovered several hallmarks of premature aging. Telomeres the caps protecting chromosome ends shortened. Mitochondria lost gene expression and copy number, lowering cellular energy reserves. The self-renewal gene ADAR1 p150 was decreased, while inflammatory cytokines skyrocketed. Whole-genome sequencing indicated elevated clonal hematopoietic mutations and deregulation of APOBEC3 family of base deaminases, enzymes capable of inducing DNA mutations. Even more alarming was the triggering of supposedly inactive repetitive DNA elements, so-called “dark genome,” which comprise more than half of human DNA and can act like remnants of ancient viruses when activated. Jamieson compared this cascade to a “death spiral” she has witnessed in preleukemic cells.
The results are consistent with trends in NASA’s Twins Study, which found telomere alterations, immune changes, and clonal hematopoiesis for astronaut Scott Kelly over the course of a year in space. But by targeting HSPCs directly, the new research reveals a cellular origin for these systemic changes. It also ties in with larger studies on microgravity-induced cellular aging, where mitochondrial stress and chronic inflammation push stem cells out of quiescence and speed wear and tear.
The orbital tests relied on accurate engineering. Each nanobioreactor mimicked certain properties of the bone marrow niche, employing an autoclaved sponge matrix that was seeded with human cells derived from hip replacement donors. The integrated imaging and environmental controls enabled the CubeLabs to run without crew intervention, a requirement considering ISS resource limits. This practice duplicates other in‑orbit biomedical platforms, including heart‑on‑a‑chip systems, which merge miniaturized bioreactors with sustained sensing to monitor physiological changes in real time.
The research also underscores the value of the stromal microenvironment. Under microgravity, mesenchymal stromal cells that nurture HSPCs can themselves experience lineage changes toward fat formation and away from bone formation changing secretion of essential factors such as CXCL12 that maintain stemness. These shifts can add to direct radiation and microgravity injury to HSPCs, constraining immune regeneration on long missions.
Some damage is reversible. Early data indicate that once astronauts return home, HSPC function can recover within a year. In the laboratory, culturing space‑exposed cells on young stroma downregulated inflammatory genes and reactivated protective pathways. This offers the prospect of countermeasures, from pharmacologic inhibitors of toxic genome activity to engineered stromal scaffolds that maintain quiescence in flight.
The stakes are high for missions to the Moon or Mars. Without healthy blood stem cell function, crews might experience compromised immunity, delayed wound healing, and increased cancer risk. The identical stress signatures telomere shortening, mitochondrial impairment, activation of repetitive elements occur in cancer patients and aging immune disorders on Earth. By leveraging space as a model system for intense physiological stress, scientists aim to create interventions that can safeguard both spacefaring astronauts and patients in earthly clinics.
