Astronauts live and work in an extreme environment fraught with extraordinary hazards and combined stressors, including space radiation exposure, microgravity and/or altered gravity, confinement and isolation (psychologically stressful), altered atmospheres and closed environment (biologically hostile), changed nutrition and microbiome – all in addition to intermittent bouts of acute stress; e.g., extravehicular activities (EVAs), and endurance/aerobic exercise to maintain bone and muscle mass. Considering the combination of unique stressors and chronic space radiation exposures associated with long-duration spaceflight, as well as the adverse health effects experienced by multiple physiological systems (e.g., dysregulated immunity, inflammation, infection), we proposed that monitoring telomere length dynamics and persistent DDRs (genomic instability) would be of particular relevance for astronauts because these informative biomarkers provide insight into individual health status during a mission, as well as potential implications and predictions for aging and disease risk later in life.

The successful mission of Artemis 1 carried with it the hopes and dreams of humankind returning to the Moon and venturing beyond to Mars. As such missions and even space tourism become realities in the coming years, the number and diversity of space travelers will likewise increase. Thus, a better understanding of how long-duration spaceflight impacts human health is essential to maintaining individual astronaut performance during, and improving disease and aging trajectories following, future exploration missions.

Findings from our previous NASA Twins Study and Telomeres investigations provided vital clues suggestive of potential mechanistic roles for chronic space radiation exposure underlying changes in telomere length dynamics and persistent DNA damage responses associated with long- (and short)-duration human spaceflight. Chronic exposure to the space radiation environment contributes to a number of fundamental biological features of spaceflight, including mitochondrial dysregulation and elevated oxidative stress, increased DNA damage, and dramatic shifts in telomere length dynamics.

We proposed that in the context of chronic exposure to the space radiation environment, persistent DDRs to increased reactive oxygen species (ROS) production by dysfunctional mitochondria, elevated levels of oxidative damage and replication stress, and low dose, low dose rate high LET space radiations, conspire at continuously damaged telomeres, acting to either enhance telomerase activity, or perhaps more likely, particularly in blood lymphocytes with very low levels of telomerase activity, transiently activate telomerase-independent Alternative Lengthening of Telomeres (ALT) or ALT-like recombinational pathways that are at least partially responsible for the striking shifts in telomere length dynamics observed.

Chronic exposure to the complex and changing space radiation environment is one of the primary hazards of long-duration spaceflight, particularly as astronauts venture deeper into space and completely outside of the protection the Earth provides. The mechanistic links between chronic exposure to space radiation and the telomeric and DNA damage responses we observed, as well as radiation dose-dependent decreases in white blood cell (WBC) counts post-spaceflight, provide support for the development of effective radiation mitigators and individualized countermeasures for upcoming deep space exploration missions. Furthermore, a major conclusion from our previous studies is that inter-individual differences in response to the combined stressors and extreme exposures associated with spaceflight predominates over general trends of individual factors, and highlights the critical need for personalized monitoring and precision space medicine strategies for current and future astronauts.

While the definitive mechanisms involved in these processes remain elusive, we are testing a model based on our foundational findings: chronic exposure to the space radiation environment results in on-going genomic and telomeric DNA damage and instability, as well as transient activation of telomerase-dependent and/or independent pathways that occur in response to on-going chronic oxidative damage specifically to telomeres, which together with lymphocyte radiosensitivity, particularly those with short telomeres, and the resulting redistribution of leukocyte subsets, contribute to the telomere elongation observed during spaceflight. The goal of our current Telomeres 2 investigation as part of CIPHER is to assess a larger, more diverse cohort of astronauts, on various duration missions (ranging from several months to >one year), and thereby further elucidate and confirm underlying mechanisms of the dramatic changes in telomere length dynamics associated with spaceflight, as well as to provide additional insight into individual differences in response and outcomes (accelerated aging, increased disease risk), and guide future development of effective countermeasures and mitigation strategies. Our efforts are ongoing, with sample collection and data analyses working well for currently consented participants.

The rate at which telomeres shorten or change over time (telomere length dynamics) provides an informative biomarker of aging that can also be linked to risk of age-related degenerative pathologies, ranging from reduced immune function [including increased risk of the common cold], loss of fertility, idiopathic pulmonary fibrosis, and dementias, to cardiovascular disease (CVD) and cancer. Importantly, recent evidence supports telomere length not only as an informative biomarker, but even a determinant of CVD and cancer, thereby suggesting a telomere length trade-off of sorts; on the one hand, shorter telomeres, senescence, and cancer resistance in exchange for increased risk of age-related (degenerative) CVD, and on the other, longer telomeres and increased cancer risk (proliferative pathology) for reduced CVD risk. Such health effects relevant to spaceflight are largely unknown and controversial, yet they have very real potential for influencing performance during long-duration missions. Longitudinal changes in telomere length maintenance in human populations are also not well understood, particularly as associated with long-duration spaceflight, with its unique lifestyle factors and environmental exposures.

We speculated that telomere length dynamics (changes over time) represent an especially relevant and informative biomarker of health risk for astronauts, as it reflects the combined exposures and experiences encountered during spaceflight. That is, an astronaut’s individual genetic susceptibilities, unique lifestyle stressors (e.g., nutritional, physical, and psychological) and environmental exposures [e.g., microgravity and the space radiation environment, which includes galactic cosmic rays (GCR), solar particle events (SPEs), as well as secondary particles that arise from interactions with spacecraft shielding], are all integrated and captured as changes in telomere length over time. We had the remarkable opportunity to assess telomere length and telomerase activity in twin (~1year mission duration) and unrelated (~6-month mission duration) astronauts, and age/sex-matched ground control subjects: pre-flight (to establish baseline); during flight (to evaluate short-term/temporary changes); and post-flight (to evaluate long-term/permanent changes).

Our ongoing work is demonstrating changes in human telomere length dynamics specifically associated with spaceflight, supporting telomeres as integrative biomarkers that encompass the extraordinary life stressors and environmental exposures encountered. Thus, telomeres are being established as informative biomarkers of astronaut health, disease risk, and aging. Individual differences are also being observed, therefore determining responses in a larger more diverse population of astronauts as proposed as part of CIPHER represents a critical next step. Importantly, our previous results have uniquely poised and informed our current approaches aimed at improving understanding of the mechanisms underlying such dramatic changes in telomere length associated with spaceflight and exposure to the space radiation environment; specifically, preliminary evidence suggests and we are currently monitoring changes in cell population dynamics (e.g., stem/progenitor cells), and/or transient activation of the telomerase independent, recombination-mediated Alternative Lengthening of Telomeres/ALT pathway of telomere maintenance. Together with evidence of radiation-induced chromosomal/genome instability, such vital mechanistic insight will provide potential targets for the development of countermeasures, thereby benefiting and helping to enable success of future missions, as well as informing development of novel anti-aging strategies on Earth. Moreover, as Telomeres 2 and other CIPHER projects mature and complete (e.g., Vascular Aging) and more data becomes available, improved precision space medicine strategies will better inform health and aging trajectories for individual astronauts, and the view of space as a model for accelerated aging will be rigorously tested.

The successful mission of Artemis 1 carried with it the hopes and dreams of returning to the Moon and venturing beyond to Mars. As the number and diversity of space travelers increase in the coming years, a better understanding of how long-duration spaceflight affects human health is essential to maintaining individual astronaut performance during and improving disease and aging trajectories following, future exploration missions. Findings from our NASA Twins Study and Telomeres investigations provided clues suggestive of potential mechanistic roles for chronic space radiation exposure underlying changes in telomere length dynamics and persistent DNA damage responses associated with long-duration spaceflight (see publications below).

Exposure to the space radiation environment contributes to a number of fundamental biological features of spaceflight, including mitochondrial dysregulation and elevated oxidative stress, increased DNA damage, and dramatic shifts in telomere length dynamics. Spaceflight-specific telomere elongation was confirmed in three unrelated astronauts during one-year and six-month missions onboard the International Space Station (ISS) using multiple assays (including sequencing), and in all samples and cell types evaluated (including urine). Rapid and significant telomere shortening after return to Earth was also observed in the vast majority of crewmembers. Interestingly, a mutational analysis of C. elegans flown on the ISS for 11 days found no significant differences in mutation rates but did report slightly elongated telomeres in the worms.

We proposed that in the context of chronic exposure to the space radiation environment, persistent DDRs to increased reactive oxygen species (ROS) production by dysfunctional mitochondria, elevated levels of oxidative damage and replication stress, and low dose rate high linear energy transfer (LET) space radiations, conspire at damaged telomeres, acting to either enhance telomerase activity, or perhaps more likely, particularly in blood lymphocytes with very low levels of telomerase activity, transiently activate telomerase-independent alternative lengthening of telomeres (ALT) or ALT-like recombinational pathways that are at least partially responsible for the striking shifts in telomere length dynamics observed. Interestingly and in support of such a view, we also found longer telomeres in a cohort of prostate cancer patients immediately following fractionated exposures associated with radiation therapy. Individual differences in response were observed in both cohorts, underscoring the importance of developing personalized approaches for evaluating human health effects and long-term outcomes associated with radiation exposure scenarios, whether on Earth or living in the extreme environment of space.

Ionizing radiations are exquisite in their ability to induce DNA damage in the form of prompt double-strand breaks (DSBs), which when mis-repaired can result in a variety of well-described chromosome rearrangements. Utilizing the strand-specific methodology of directional genomic hybridization (dGH), and for the first time in astronauts, we detected increased frequencies of intra-chromosomal inversions during spaceflight, which persisted after spaceflight, potentially suggestive of stem-cell damage, clonal hematopoiesis, and/or genome instability. Also consistent with exposure to the space radiation environment, strong relationships between post-spaceflight chromosome aberration frequencies, specifically inversions, and lifetime radiation dose estimates were identified, providing additional evidence of their persistence after exposure, and further support of inversions as informative biomarkers of radiation exposure associated with spaceflight.

Chronic radiation exposure is one of the primary hazards of long-duration space travel, particularly as astronauts venture deeper into space and outside of the protection the Earth provides. The mechanistic links between chronic exposure to the space radiation environment and the telomeric and DNA damage responses we observed, as well as radiation dose-dependent decreases in white blood cell (WBC) counts post-spaceflight, provide support for the development of effective radiation mitigators and individualized countermeasures for upcoming deep space exploration missions. Furthermore, a major conclusion from our previous studies is that inter-individual differences in response to the combined stressors and exposures associated with spaceflight predominate over general trends of individual factors and highlight the critical need for personalized monitoring and precision medicine strategies for future astronauts.

While the definitive mechanisms involved in these processes remain elusive, we propose a testable model based on our foundational findings: chronic exposure to the space radiation environment results in genomic DNA damage and instability, as well as transient activation of telomerase-dependent and/or independent pathways in response to chronic oxidative damage specifically to telomeres, which together with lymphocyte radiosensitivity, particularly those with short telomeres (55), and the resulting redistribution of leukocyte subsets (56), contribute to the telomere elongation observed during spaceflight. Our current studies as part of the Complement of Integrated Protocols for Human Exploration Research (CIPHER) will assess a larger, more diverse cohort of astronauts, on various duration missions (ranging from several months to one year), will serve to further elucidate and confirm underlying mechanisms of the dramatic changes in telomere length dynamics associated with spaceflight, and provide additional insight into individual differences in response and outcomes, and guide future development of effective mitigation strategies. Data collection and analysis is progressing successfully, with many sample collections (pre-flights, in-flights, and post-flights) completed and/or planned.

The recent launch of Artemis 1 carried with it the hopes and dreams of returning to the Moon and venturing beyond to Mars. As the number and diversity of space travelers increase in the coming years, a better understanding of how long-duration spaceflight affects human health is essential to maintaining individual astronaut performance during and improving disease and aging trajectories following future exploration missions. Findings from our NASA Twins Study and Telomeres investigations provided clues suggestive of potential mechanistic roles for chronic space radiation exposure underlying changes in telomere length dynamics and persistent DNA damage responses associated with long-duration spaceflight.

Chronic radiation exposure is one of the primary hazards of long-duration space travel, particularly as astronauts venture deeper into space and outside of the protection the Earth provides. The mechanistic links between chronic exposure to the space radiation environment and the telomeric and DNA damage responses we observed, as well as radiation dose-dependent decreases in WBC (white blood cell) counts post-spaceflight, provide support for the development of effective radiation mitigators and individualized countermeasures for upcoming deep space exploration missions. Furthermore, a major conclusion from our previous studies is that inter-individual differences in response to the combined stressors and exposures associated with spaceflight predominate over general trends of individual factors and highlight the critical need for personalized monitoring and precision medicine strategies for future astronauts.

While the definitive mechanisms involved in these processes remain elusive, we propose a testable model based on our foundational findings: in the space radiation environment, and in addition to genomic DNA damage and instability, transient activation of telomerase-dependent and/or independent pathways occurs in response to chronic oxidative damage specifically to telomeres, which together with lymphocyte radiosensitivity, particularly those with short telomeres, and the resulting redistribution of leukocyte subsets, contribute to the telomere elongation observed during spaceflight. Our current studies as part of the Complement of Integrated Protocols for Human Exploration Research (CIPHER) will assess a larger, more diverse cohort of astronauts on various duration missions (ranging from several months to one year), will serve to elucidate further and confirm underlying mechanisms of the dramatic changes in telomere length dynamics associated with spaceflight, as well as provide additional insight into individual differences in response and outcomes, and guide future development of effective mitigation strategies and/or strategies for extending healthspan. Informed Consent Briefings are ongoing, and recruitment of crewmembers into CIPHER has begun, as has baseline data collection.

Together with cell-by-cell analyses, approaches for more high throughput analyses (e.g., ddPCR) are being tested and optimized.

We are developing machine learning strategies for predicting telomere length outcomes, which will become more and more reliable/informative as the models see more data. We are also seeking ways to test mechanisms; e.g., to assess the influence of chronic oxidative stress on telomere length. We evaluated telomere length in blood samples from humans climbing Mt. Everest, and matched twin non-climbing controls.

Established Telomeres 2 stem/progenitor cell evaluation as part of Standard Measures; collaborating with Brian Crucian.

Established NASA and home institution (Colorado State University-CSU) Institutional Review Boards (IRBs) – continuing process. Awaiting crew selection and recruitment into the Telomeres 2 study.