Research Article

The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight

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Science  12 Apr 2019:
Vol. 364, Issue 6436, eaau8650
DOI: 10.1126/science.aau8650

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  • Comments on "The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight"
    • SMJ Mortazavi, Visiting Scientist, Fox Chase Cancer Center
    • Other Contributors:
      • Joseph Bevelacqua, Health Physicist, Bevelacqua Resources
      • James Welsh, Professor of Radiation Oncology, Edward Hines Jr VA Hospital

    This letter addresses “The NASA Twins Study” by Garrett-Bakelman et al. (1) which studied the biological effects of a 340-day mission onboard the International Space Station in a male astronaut compared to those in his monozygotic twin. This study showed that the majority of measured biological variables remained stable, or returned to baseline, after a nearly year-long human spaceflight. However, the authors assert that persistence of certain molecular changes (e.g., gene expression) should be considered in longer duration missions.

    Despite its undeniable strengths, the authors have not fully addressed the following issues:
    1. The authors rightly claimed that metabolic and nutritional status, physical activity, and weight loss may affect telomere length. However, space radiation (in particular, HZE or high (H) atomic number (Z) and energy (E) particles) also plays a key role in telomeric change. Might the elongation of telomeres during space flight be interpreted as an adaptive (positive) response to multiple changes in the environment (such as higher levels of radiation, microgravity, etc.)? Different aspects of this issue were initially raised in 2003 (2) and are discussed in recent publications (3, 4). Although elongation of telomeres in space is possibly a natural, protective adaptive response, telomerase activity is also a hallmark of cancer which grants immortality to malignant cells. Might telomerase activity, coupled with immune system dysregulation...

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    Competing Interests: None declared.
  • RE: Telomeres lengthened during spaceflight and the potential “fragile” effect
    • Virginia Boccardi, Geriatrician, Geriatric Unit, Santa Maria della Misericordia Hospital Perugia
    • Other Contributors:
      • Luigi Cari, PhD, Department of Medicine, Section of Pharmacology, University of Perugia
      • Giuseppe Nocentini, Associate Professor, Department of Medicine, Section of Pharmacology, University of Perugia
      • Patrizia Mecocci, Professor, Department of Medicine,Section of Gerontology and Geriatric, University of Perugia.

    We read with great interest the article by Garrett-Bakelman and collaborators (1) providing a unique multidimensional analysis of a yearlong human spaceflight. We want to congratulate the authors for their impressive results. It seems that astronauts could experience an “accelerated ageing syndrome,” which includes mitochondrial dysfunction, immunological defects, vascular changes and cognitive deficits associated with increased oxidative stress, inflammation, and insulin resistance. Data related to alterations in telomere length have caught our attention. It is well established that telomeres progressively shorten with age and that critically short and dysfunctional telomeres may contribute to ageing and ageing-associated diseases in humans (2). We recently demonstrated that, along with ageing, telomeres increasingly display accumulation of aberrant structures such as fragile sites characterized by the presence of multiple or diffuse telomeric signals on the chromatid arm. These sites seem to represent areas of de-condensed telomeric chromatin due to stalled DNA replication forks, which suggested that telomeric replication defects contribute to ageing associated-telomere erosion in humans (3). Fragile telomeres may appear as telomeric elongation when assessed by a quantitative real-time polymerase chain reaction (qRT-PCR) method. Authors showed a transient telomere elongation associated with a rapid shortening of astronaut’s telomeres upon return to Earth. Although th...

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    Competing Interests: None declared.
  • RE: Discussion about Cognition Performance Results

    As reported in the cognition performance section and subsequent discussion, there was some decline in TW's cognition measures such as speed, processing, and emotion recognition. To what extend can these declines be attributed to lack of social interaction? A lack of social interaction, with the condition being in-person interactions, has been associated with structural changes and processing. Humans are social creatures and need this interaction. I've also heard isolation can shrink cortex density. I'm curious to know how this could relate to the cognition performance results and partially explain any piece?

    Competing Interests: None declared.
  • RE: Diet

    Did the twins consume the same diet throughout the study?

    Ideally, TW and HR both consumed the same. Diet affects microbiome. Microbiome is the third brain.

    Competing Interests: None declared.