Telomere length, telomerase activity, and structural variants as biomarkers of extreme environments
Date
2017
Authors
McKenna, Miles J., author
Bailey, Susan M., advisor
Dow, Steven, committee member
Kato, Takamitsu, committee member
Simon, Steven, committee member
Thamm, Douglas, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Mammals, and in particular humans, are masterful at overcoming and adapting to extreme environments. Whether astronauts in low earth orbit aboard the International Space Station (ISS) or U.S. military veterans exposed to nuclear fallout from atomic weapons testing, humans can persist through a wide range of physical, psychological, and environmental stressors. The overall goal of the studies presented here was to evaluate the biological influences of extreme environments not commonly experienced by the general population. Whether spaceflight or exposure to nuclear fallout, results improve our understanding of short- and long-term effects of low gravity environments, exposure to ionizing radiation (IR) of mixed qualities, as well as low dose and low dose effects of IR. We explored these scenarios by evaluating biomarkers of stress, specifically telomere length dynamics, and biomarkers of DNA damage, specifically transmissible structural rearrangements. Telomeres are not only regarded as valuable biomarkers of aging and age-related degenerative pathologies like cardiovascular disease and cancer, and so are reflective of overall health status, they also serve as "hallmarks" of radiosensitivity. Stable chromosomal structural rearrangements (translocations and inversions) persist with time and so provide informative signatures of IR exposure as well. During the 1950's United States military personnel and weathermen, collectively known as the atomic veterans, were unintentionally exposed to nuclear fallout during atomic bomb testing following WWII. Here, directional Genomic Hybridization (dGH) for high-resolution detection of IR-induced chromosomal inversions and translocations was assessed as a more sensitive, quantitative retrospective biodosimetry approach. The influence of IR exposure on telomere length dynamics was also evaluated to determine the long-term influence of such exposures. Our results illustrate that even for nuclear events that occurred six decades in the past, evidence of exposure is still present. We find that although translocations and inversions are reliable biodosimeters independently, a combined approach provides a more sensitive measurement of past radiation exposure. We also report, for the first time, the influence of age and smoking on background inversion frequencies. Furthermore, telomere length was inversely related to IR dose, suggesting that a single acute exposure to nuclear fallout may lead to persistent long-term effects on overall health. Telomere length dynamics and structural rearrangements were also monitored longitudinally in monozygotic twin and unrelated astronauts. NASA astronauts are a unique group of individuals who experience an extreme environment that the human body is not adapted for. Little is known about the biological health effects of a low gravity environment with increased IR exposure including galactic cosmic rays (GCRs), solar particle events, and secondary neutrons. Not only do astronauts have shorter telomeres than age-/gender-matched controls at baseline (pre-flight), but a transient increase in telomere length during space flight was also observed. Results suggest this unexpected finding may be due to an upregulation of telomerase, the enzyme responsible for maintaining telomere length. Moreover, telomerase activity also increased post-flight in both twins, Scott and Mark Kelly. Although not spaceflight specific, this is the first report of telomerase upregulation in humans due to a psychologically traumatic event. A dose dependent increase in inversions, and to a lesser extent, translocations, as a consequence of IR exposure on the ISS was also seen in Scott Kelly. Collectively, the studies presented here demonstrate a profound influence of extreme environments, particularly those involving low dose IR, on human biological responses. Telomere length dynamics and chromosome aberration frequencies (e.g. translocations and inversions) provide insight into the long-term health effects and implications of spaceflight and exposure to nuclear events.