Effects of sex and gender on adaptations to space: reproductive health

Long-term space missions' effects on the human organism: what we do know and what requires further research

Space has always fascinated people. Many years have passed since the first spaceflight, and in addition to the enormous technological progress, the level of understanding of human physiology in space is also increasing. The presented paper aims to summarize the recent research findings on the influence of the space environment (microgravity, pressure differences, cosmic radiation, etc.) on the human body systems during short-term and long-term space missions. The review also presents the biggest challenges and problems that must be solved in order to extend safely the time of human stay in space. In the era of increasing engineering capabilities, plans to colonize other planets, and the growing interest in commercial space flights, the most topical issues of modern medicine seems to be understanding the effects of long-term stay in space, and finding solutions to minimize the harmful effects of the space environment on the human body.

The effect of space travel on human reproductive health: a systematic review

With increasing possibilities of multi-year missions in deep space, colonizing other planets, and space tourism, it is important to investigate the effects of space travel on human reproduction. This study aimed to systematically review and summarize the results of available literature on space travel, microgravity, and space radiation, or Earth-based spaceflight analogues impact on female and male reproductive functions in humans. This systematic review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and Space Biomedicine Systematic Review methods. The search was performed using three databases: PubMed, Web of Science, and Medline Complete. During the database search, 364 studies were identified. After the study selection process, 16 studies were included in the review. Five studies included female participants, and the findings show an increased risk of thromboembolism in combined oral contraceptive users, decreased decidualization, functional insufficiency of corpus luteum, and decreased progesterone and LH levels related to space travel or its simulation. Male participants were included in 13 studies. In males, reproductive health considerations focused on the decrease in testosterone and sex hormone-binding globulin levels, the ratio of male offspring, sperm motility, sperm vitality, and the increase in sperm DNA fragmentation related to space travel or its simulation. Results of this systematic review highlight the need to focus more on the astronaut's reproductive health in future research, as only 16 studies were found during the literature search, and many more research questions related to reproductive health in astronauts still need to be answered.

Venous Thromboembolism in Exploration Class Human Spaceflight

INTRODUCTION: A recent finding of a deep venous thrombosis during spaceflight has prompted the need to clarify mechanisms and risks of venous thromboembolism (VTE). In turn, mitigation countermeasures, diagnostic modalities, and treatment options must be explored. The objective of this review was to synthesize current evidence on VTE in spaceflight.METHODS: A literature review was performed from inception to April 2023 pertaining to VTE in the context of spaceflight or ground-based analogs with human participants. PubMed was searched for papers written in English using the terms "spaceflight" or "weightlessness" and "thrombotic" or "embolism" or "thromboembolism" in "venous" or "veins". Papers using cellular or animal models were excluded.RESULTS: There were 63 papers captured; 7 original scientific studies, 3 narrative reviews, 2 systematic reviews, and 3 commentaries discussed VTE in spaceflight. Reference lists were screened. Important themes included: altered venous hemodynamics, increased fibrinogen and coagulation markers, hypoalbuminemia, and immune dysfunction. Additional risk factors may be seen in women, such as the use of oral contraceptives.DISCUSSION: Venous stasis and decreased shear stress secondary to fluid shifts may induce inflammatory changes in the venous system, resulting in endothelial damage and upregulation of the coagulation cascade. Additionally, women in space are subject to physiological factors increasing their VTE risk, such as the use of oral contraceptives, inducing increased blood viscosity and hypoalbuminemia. Efforts should also be placed in optimizing sensitivity and specificity of imaging markers, payload, and training ability, notably the use of vector flow imaging, and improving point-of-testing biomarkers, such as albumin and p-selectin.Levasseur S, Purvis N, Trozzo S, Chung SH, Ades M, Drudi LM. Venous thromboembolism in exploration class human spaceflight. Aerosp Med Hum Perform. 2024; 95(1):45-53.

Space nutrition and the biochemical changes caused in Astronauts Health due to space flight: A review

Astronauts required food that is healthy, nutritious, and tasted good, while also meeting their dietary needs. To ensure the astronauts' nutritional needs are met, a Nutritional Status Assessment Supplemental Medical Objective (Nutrition SMO) is conducted. This involves collecting blood and urine samples from the astronauts, which are then tested and analysed. The assessment looks for indications of bone health, muscle loss, hormonal imbalances, gastrointestinal functions, cardiovascular health, iron metabolism, ophthalmic changes, and immune changes that occur during space flight under conditions of microgravity or weightlessness. It was discovered that iron levels in astronauts tend to increase due to the decrease in body volume during space flight. It requires skilful optimization considering nutrient delivery, shelf life, and packaging of space food, while minimizing resource usage and ensuring reliability, safety, and addressing the physiological and psychological effects on the crew members.

The Oxidative Phosphorylation and Cytoskeleton Proteins of Mouse Ovaries after 96 Hours of Hindlimb Suspension

The purpose of this study was to assess oxidative phosphorylation (OXPHOS) in mouse ovaries, determine the relative content of proteins that form the respiratory chain complexes and the main structures of the cytoskeleton, and determine the mRNA of the corresponding genes after hindlimb suspension for 96 h. After hindlimb suspension, the maximum rate of oxygen uptake increased by 133% (p < 0.05) compared to the control due to the complex I of the respiratory chain. The content of mRNA of genes encoding the main components of the respiratory chain increased (cyt c by 78%, cox IV by 56%, ATPase by 69%, p < 0.05 compared with the control). The relative content of cytoskeletal proteins that can participate in the processes of transport and localization of mitochondria does not change, with the exception of an increase in the content of alpha-tubulin by 25% (p < 0.05) and its acetylated isoform (by 36%, p < 0.05); however, the mRNA content of these cytoskeletal genes did not differ from the control. The content of GDF9 mRNA does not change after hindlimb suspension. The data obtained show that short-term exposure to simulated weightlessness leads to intensification of metabolism in the ovaries.

Space Environment Impacts Homeostasis: Exposure to Spaceflight Alters Mammary Gland Transportome Genes

Membrane transporters and ion channels that play an indispensable role in metabolite trafficking have evolved to operate in Earth's gravity. Dysregulation of the transportome expression profile at normogravity not only affects homeostasis along with drug uptake and distribution but also plays a key role in the pathogenesis of diverse localized to systemic diseases including cancer. The profound physiological and biochemical perturbations experienced by astronauts during space expeditions are well-documented. However, there is a paucity of information on the effect of the space environment on the transportome profile at an organ level. Thus, the goal of this study was to analyze the effect of spaceflight on ion channels and membrane substrate transporter genes in the periparturient rat mammary gland. Comparative gene expression analysis revealed an upregulation (p < 0.01) of amino acid, Ca²⁺, K⁺, Na⁺, Zn²⁺, Cl^-, PO₄^3-, glucose, citrate, pyruvate, succinate, cholesterol, and water transporter genes in rats exposed to spaceflight. Genes associated with the trafficking of proton-coupled amino acids, Mg²⁺, Fe²⁺, voltage-gated K⁺-Na⁺, cation-coupled chloride, as well as Na⁺/Ca²⁺ and ATP-Mg/Pi exchangers were suppressed (p < 0.01) in these spaceflight-exposed rats. These findings suggest that an altered transportome profile contributes to the metabolic modulations observed in the rats exposed to the space environment.

Occupational and Environmental Challenges for Women

ABSTRACT

The prevalence of women in the global workforce is increasing. Women increasingly participate in nontraditional employment settings in previously male-dominated industries and manually intensive professions, such as military service, emergency response, health care, aviation, space, agriculture, and technical trades. Limited occupational and environmental hazard data specific to women exist for these work environments. Physiologic and biomechanical differences between sexes create unique workplace challenges specific to women. This article will summarize challenges confronting women working in nontraditional employment and identify strategies to mitigate risk within these populations.

Human development and reproduction in space-a European perspective

This review summarises key aspects of the first reproductive and developmental systems Science Community White Paper, supported by the European Space Agency (ESA). Current knowledge regarding human development and reproduction in space is mapped to the roadmap. It acknowledges that sex and gender have implications on all physiological systems, however, gender identity falls outside the scope of the document included in the white paper collection supported by ESA. The ESA SciSpacE white papers on human developmental and reproductive functions in space aim to reflect on the implications of space travel on the male and female reproductive systems, including the hypothalamic-pituitary-gonadal (HPG) reproductive hormone axis, and considerations for conception, gestation and birth. Finally, parallels are drawn as to how this may impact society as a whole on Earth.

Addressing Spaceflight Biology through the Lens of a Histologist-Embryologist

Embryogenesis and fetal development are highly delicate and error-prone processes in their core physiology, let alone if stress-associated factors and conditions are involved. Space radiation and altered gravity are factors that could radically affect fertility and pregnancy and compromise a physiological organogenesis. Unfortunately, there is a dearth of information examining the effects of cosmic exposures on reproductive and proliferating outcomes with regard to mammalian embryonic development. However, explicit attention has been given to investigations exploring discrete structures and neural networks such as the vestibular system, an entity that is viewed as the sixth sense and organically controls gravity beginning with the prenatal period. The role of the gut microbiome, a newly acknowledged field of research in the space community, is also being challenged to be added in forthcoming experimental protocols. This review discusses the data that have surfaced from simulations or actual space expeditions and addresses developmental adaptations at the histological level induced by an extraterrestrial milieu.

The State of the Organs of the Female Reproductive System after a 5-Day "Dry" Immersion

The impact of weightlessness on the female reproductive system remains poorly understood, although deep space exploration is impossible without the development of effective measures to protect women's health. The purpose of this work was to study the effect of a 5-day "dry" immersion on the state of the reproductive system of female subjects. On the fourth day of the menstrual cycle after immersion, we observed an increase in inhibin B of 35% (p < 0.05) and a decrease in luteinizing hormone of 12% (p < 0.05) and progesterone of 52% (p < 0.05) compared with the same day before immersion. The size of the uterus and the thickness of the endometrium did not change. On the ninth day of the menstrual cycle after immersion, the average diameters of the antral follicles and the dominant follicle were, respectively, 14% and 22% (p < 0.05) higher than before. The duration of the menstrual cycle did not change. The obtained results may indicate that the stay in the 5-day "dry" immersion, on the one hand, can stimulate the growth of the dominant follicle, but, on the other hand, can cause functional insufficiency of the corpus lutea.

The Case for Space Sexology

Space poses significant challenges for human intimacy and sexuality. Life in space habitats during long-term travel, exploration, or settlement may: detrimentally impact the sexual and reproductive functions of astronauts, restrict privacy and access to intimate partners, impose hygiene protocols and abstinence policies, and heighten risks of interpersonal conflicts and sexual violence. Together, this may jeopardize the health and well-being of space inhabitants, crew performance, and mission success. Yet, little attention has been given to the sexological issues of human life in space. This situation is untenable considering our upcoming space missions and expansion. It is time for space organizations to embrace a new discipline, space sexology: the scientific study of extraterrestrial intimacy and sexuality. To make this case, we draw attention to the lack of research on space intimacy and sexuality; discuss the risks and benefits of extraterrestrial eroticism; and propose an initial biopsychosocial framework to envision a broad, collaborative scientific agenda on space sexology. We also underline key anticipated challenges faced by this innovative field and suggest paths to solutions. We conclude that space programs and exploration require a new perspective - one that holistically addresses the intimate and sexual needs of humans - in our pursuit of a spacefaring civilization.

Simulated microgravity reduces quality of ovarian follicles and oocytes by disrupting communications of follicle cells

Ovarian follicles are the fundamental structures that support oocyte development, and communications between oocytes and follicle somatic cells are crucial for oogenesis. However, it is unknown that whether exposure to microgravity influences cellular communications and ovarian follicle development, which might be harmful for female fertility. By 3D culturing of ovarian follicles under simulated microgravity (SMG) conditions in a rotating cell culture system, we found that SMG treatment did not affect the survival or general growth of follicles but decreased the quality of cultured follicles released oocytes. Ultrastructure detections by high-resolution imaging showed that the development of cellular communicating structures, including granulosa cell transzonal projections and oocyte microvilli, were markedly disrupted. These abnormalities caused chaotic polarity of granulosa cells (GCs) and a decrease in oocyte-secreted factors, such as Growth Differentiation Factor 9 (GDF9), which led to decreased quality of oocytes in these follicles. Therefore, the quality of oocytes was dramatically improved by the supplementations of GDF9 and NADPH-oxidase inhibitor apocynin. Together, our results suggest that exposure to simulated microgravity impairs the ultrastructure of ovarian follicles. Such impairment may affect female fertility in space environment.

Are Skeletal Muscle Changes during Prolonged Space Flights Similar to Those Experienced by Frail and Sarcopenic Older Adults?

Microgravity exposure causes several physiological and psychosocial alterations that challenge astronauts' health during space flight. Notably, many of these changes are mostly related to physical inactivity influencing different functional systems and organ biology, in particular the musculoskeletal system, dramatically resulting in aging-like phenotypes, such as those occurring in older persons on Earth. In this sense, sarcopenia, a syndrome characterized by the loss in muscle mass and strength due to skeletal muscle unloading, is undoubtedly one of the most critical aging-like adverse effects of microgravity and a prevalent problem in the geriatric population, still awaiting effective countermeasures. Therefore, there is an urgent demand to identify clinically relevant biological markers and to underline molecular mechanisms behind these effects that are still poorly understood. From this perspective, a lesson from Geroscience may help tailor interventions to counteract the adverse effects of microgravity. For instance, decades of studies in the field have demonstrated that in the older people, the clinical picture of sarcopenia remarkably overlaps (from a clinical and biological point of view) with that of frailty, primarily when referred to the physical function domain. Based on this premise, here we provide a deeper understanding of the biological mechanisms of sarcopenia and frailty, which in aging are often considered together, and how these converge with those observed in astronauts after space flight.

Drosophila melanogaster Oocytes after Space Flight: The Early Period of Adaptation to the Force of Gravity

The effect of space flight factors and the subsequent adaptation to the Earth's gravity on oocytes is still poorly understood. Studies of mammalian oocytes in space present significant technical difficulties; therefore, the fruit fly Drosophila melanogaster is a convenient test subject. In this study, we analyzed the structure of the oocytes of the fruit fly Drosophila melanogaster, the maturation of which took place under space flight conditions (the "Cytomehanarium" experiment on the Russian Segment of the ISS during the ISS-67 expedition). The collection of the oocytes began immediately after landing and continued for 12 h. The flies were then transferred onto fresh agar plates and oocyte collection continued for the subsequent 12 h. The stiffness of oocytes was determined by atomic force microscopy and the content of the cytoskeletal proteins by Western blotting. The results demonstrated a significant decrease in the stiffness of oocytes in the flight group compared to the control (26.5 ± 1.1 pN/nm vs. 31.0 ± 1.8 pN/nm) against the background of a decrease in the content of some cytoskeletal proteins involved in the formation of microtubules and microfilaments. This pattern of oocyte structure leads to the disruption of cytokinesis during the cleavage of early embryos.

Extraterrestrial Gynecology: Could Spaceflight Increase the Risk of Developing Cancer in Female Astronauts? An Updated Review

Outer space is an extremely hostile environment for human life, with ionizing radiation from galactic cosmic rays and microgravity posing the most significant hazards to the health of astronauts. Spaceflight has also been shown to have an impact on established cancer hallmarks, possibly increasing carcinogenic risk. Terrestrially, women have a higher incidence of radiation-induced cancers, largely driven by lung, thyroid, breast, and ovarian cancers, and therefore, historically, they have been permitted to spend significantly less time in space than men. In the present review, we focus on the effects of microgravity and radiation on the female reproductive system, particularly gynecological cancer. The aim is to provide a summary of the research that has been carried out related to the risk of gynecological cancer, highlighting what further studies are needed to pave the way for safer exploration class missions, as well as postflight screening and management of women astronauts following long-duration spaceflight.

Assessment of Sex-Dependent Medical Outcomes During Spaceflight

Introduction: In this study sex-differences in medical outcomes during spaceflight are reviewed and probabilistic risk assessment (PRA) is used to assess the impact on spaceflight missions of varying lengths. Materials and Methods: We use PRA to simulate missions of 42 days, 6 months, and 2.5 years. We model medical outcomes using three crews: two men and two women, four women, or four men. Total medical events (TME), crew health index (CHI), probability (0-1) of medical evacuation (pEVAC), probability of loss of crew life (pLOCL), and influential medical conditions were determined. Results: No differences were seen in any metric for the 42-day mission. There were no differences seen for any mission length, in any crew, for TME, CHI, pLOCL, or environmental causes of pEVAC. Sex-dependent differences are seen for rates of nonemergent pEVAC during the 6 month and 2.5-year missions, where women have a higher pEVAC in the 182-day (0.0388 vs. 0.0354) and 2.5-year missions (0.350 vs. 0.228). These differences were driven by higher incidence of partially treated urinary tract infection (UTI). In the 2.5 year mission, with resupply of medical resources, the influence of UTI in women on pEVAC decreases (0.35-0.11). Discussion: Although resupply is unlikely for deep space missions, modeled results suggest that sex-specific medical needs can be readily managed through preventive measures and inclusion of appropriate medical capabilities. Within its many limitations, PRA is a useful tool to estimate medical risks in unique environments where only expert opinion was previously available.

Female astronauts: Impact of space radiation on menopause

Space travel has different effects on the reproductive capacity of women compared to men. The radiation exposure intrinsic to deep space travel causes destruction of some of a woman's primordial follicles. Data suggests that a typical Mars mission may reduce a women's ovarian reserve by about 50%. This has consequences to a woman's reproductive capacity and, more significantly, decreases the time interval to her menopause. A reduced time interval to menopause is associated with earlier mortality. Estrogen replacement therapy and cryopreservation of a female astronaut's oocytes may be used to address these issues. However, cortical tissue freezing provides advantages to more directly compensate for these workplace complications. Cortical tissue freezing especially provides advantages if there are plans to reproduce in an extraterrestrial location.

Simulated Microgravity Induces the Proliferative Inhibition and Morphological Changes in Porcine Granulosa Cells

Astronauts are always faced with serious health problems during prolonged spaceflights. Previous studies have shown that weightlessness significantly affects the physiological function of female astronauts, including a change in reproductive hormones and ovarian cells, such as granulosa and theca cells. However, the effects of microgravity on these cells have not been well characterized, especially in granulosa cells. This study aimed to investigate the effects of simulated microgravity (SMG) on the proliferation and morphology of porcine granulosa cells (pGCs). pGC proliferation from the SMG group was inhibited, demonstrated by the reduced O.D. value and cell density in the WST-1 assay and cell number counting. SMG-induced pGCs exhibited an increased ratio of cells in the G0/G1 phase and a decreased ratio of cells in the S and G2/M phase. Western blot analysis indicated a down-regulation of cyclin D1, cyclin-dependent kinase 4 (cdk4), and cyclin-dependent kinase 6 (cdk6), leading to the prevention of the G1-S transition and inducing the arrest phase. pGCs under the SMG condition showed an increase in nuclear area. This caused a reduction in nuclear shape value in pGCs under the SMG condition. SMG-induced pGCs exhibited different morphologies, including fibroblast-like shape, rhomboid shape, and pebble-like shape. These results revealed that SMG inhibited proliferation and induced morphological changes in pGCs.

What can biofabrication do for space and what can space do for biofabrication?

Biofabrication in space is one of the novel promising and prospective research directions in the rapidly emerging field of space STEM. There are several advantages of biofabrication in space. Under microgravity, it is possible to engineer constructs using more fluidic channels and thus more biocompatible bioinks. Microgravity enables biofabrication of tissue and organ constructs of more complex geometries, thus facilitating novel scaffold-, label-, and nozzle-free technologies based on multi-levitation principles. However, when exposed to microgravity and cosmic radiation, biofabricated tissues could be used to study pathophysiological phenomena that will be useful on Earth and for deep space manned missions. Here, we provide leading concepts about the potential mutual benefits of the application of biofabrication technologies in space.

The First Female Dry Immersion (NAIAD-2020): Design and Specifics of a 3-Day Study

This article describes procedures and some results of the first study of females undergoing 3-day Dry Immersion. The experiment “NAIAD-2020” was carried out at the Institute of Biomedical Problems (Moscow, Russia) with the participation of six healthy women volunteers (age 30.17 ± 5.5 years, height 1.66 ± 0.1 m, weight 62.05 ± 8.4 kg, BMI 22.39 ± 2.2 kg/m²) with a natural menstrual cycle. During the study, a standard protocol was used, the same as for men, with a minimum period of time spent outside the immersion bath. Before, during and after Immersion, 22 experiments were carried out aimed at studying the neurophysiological, functional, metabolic and psychophysiological functions of the body, the results of which will be presented in future publications. The total time outside the bath for women did not exceed that for men. Systolic and diastolic pressure did not significantly change during the immersion. In the first 24 h after the end of the immersion, heart rate was significantly higher than the background values [F(4,20) = 14.67; P < 0.0001]. Changes in body temperature and water balance were consistent with the patterns found in men. No significant changes in height and weight were found during immersion. All women reported general discomfort and pain in the abdomen and back. The results of this study did not find significant risks to women’s health and showed the feasibility of using this model of the effects of space flight in women of reproductive age.

Effects of spaceflight aboard the International Space Station on mouse estrous cycle and ovarian gene expression

Ovarian steroids dramatically impact normal homeostatic and metabolic processes of most tissues within the body, including muscle, bone, neural, immune, cardiovascular, and reproductive systems. Determining the effects of spaceflight on the ovary and estrous cycle is, therefore, critical to our understanding of all spaceflight experiments using female mice. Adult female mice (n = 10) were exposed to and sacrificed on-orbit after 37 days of spaceflight in microgravity. Contemporary control (preflight baseline, vivarium, and habitat; n = 10/group) groups were maintained at the Kennedy Space Center, prior to sacrifice and similar tissue collection at the NASA Ames Research Center. Ovarian tissues were collected and processed for RNA and steroid analyses at initial carcass thaw. Vaginal wall tissue collected from twice frozen/thawed carcasses was fixed for estrous cycle stage determinations. The proportion of animals in each phase of the estrous cycle (i.e., proestrus, estrus, metestrus, and diestrus) did not appreciably differ between baseline, vivarium, and flight mice, while habitat control mice exhibited greater numbers in diestrus. Ovarian tissue steroid concentrations indicated no differences in estradiol across groups, while progesterone levels were lower (p < 0.05) in habitat and flight compared to baseline females. Genes involved in ovarian steroidogenic function were not differentially expressed across groups. As ovarian estrogen can dramatically impact multiple non-reproductive tissues, these data support vaginal wall estrous cycle classification of all female mice flown in space. Additionally, since females exposed to long-term spaceflight were observed at different estrous cycle stages, this indicates females are likely undergoing ovarian cyclicity and may yet be fertile.

Oral Estradiol Impact on Mitigating Unloading-Induced Bone Loss in Ovary-Intact Rats

BACKGROUND: The impact of the spaceflight environment on endogenous estrogen production in female crewmembers and the resulting impact on other adaptations, like bone loss, is an under-investigated topic. Hence, we investigated the interaction of exogenous 17- estradiol (E2) treatment and disuse to test the hypothesis that E2 treatment would mitigate disuse-induced bone loss.METHODS: There were 40 virgin female Sprague-Dawley rats (5 mo old) randomized to placebo (PL; 0 ppm E2) or estrogen (E2; 10 ppm E2) treatments, delivered via custom-made rodent diets; half of each group was randomized to either weightbearing (WB) or hindlimb unloading (HU) for 39 d.RESULTS: We observed expected lower values after HU (615%) in volumetric BMD and cross-sectional areas at the proximal tibia metaphysis (PTM, by pQCT), 20% lower %BV/TV (nonsignificant) at the PTM, and 11% lower femoral neck maximal load; none of these HU-induced impacts were modified by E2. Impaired PTM periosteal expansion was observed in all E2-treated rats, with smaller (13 to 18%) cross-sectional areas. Midshaft tibial geometry was unaffected by E2 treatment, but large reductions (73 to 81%) in periosteal bone formation indices were observed in E2-treated rats.DISCUSSION: In summary, modest supplementation of exogenous E2 did not mitigate decrements in volumetric BMD, PTM cross-sectional geometry, or femoral neck strength observed with HU. However, numerous independent impacts of E2 treatment were observed, with significant suppression of periosteal bone formation indices. If maintained over time, this might impact negatively on cortical bone integrity during prolonged nonweightbearing.Mantri AV, Allaway HCM, Brezicha JE, Hogan HA, Bloomfield SA. Oral estradiol impact on mitigating unloading-induced bone loss in ovary-intact rats. Aerosp Med Hum Perform. 2021; 92(2):6574.

Reproduction and the Early Development of Vertebrates in Space: Problems, Results, Opportunities

Humans and animals adapt to space flight conditions. However, the adaptive changes of fully formed organisms differ radically from the responses of vertebrate embryos, foetuses, and larvae to space flight. Development is associated with active cell proliferation and the formation of organs and systems. The instability of these processes is well known. Over 20 years has passed since the last systematic experiments on vertebrate reproduction and development in space flight. At the same time, programs are being prepared for the exploration of Mars and the Moon, which justifies further investigations into space flight's impact on vertebrate development. This review focuses on various aspects of reproduction and early development of vertebrates in space flights. The results of various experiments on fishes, amphibians, reptiles, birds and mammals are described. The experiments in which our team took part and ontogeny of the vertebrate nervous and special sensory systems are considered in more detail. Possible causes of morphological changes are also discussed. Research on evolutionarily and taxonomically different models can advance the understanding of reproduction in microgravity. Reptiles, in particular, geckos, due to their special features, can be a promising object of space developmental biology.

Reproductive hazards of space travel in women and men

Extended travel in deep space poses potential hazards to the reproductive function of female and male astronauts, including exposure to cosmic radiation, microgravity, increased gravity (hypergravity), psychological stress, physical stress and circadian rhythm disruptions. This Review focuses on the effects of microgravity, hypergravity and cosmic radiation. Cosmic radiation contains protons, helium nuclei and high charge and energy (HZE) particles. Studies performed on Earth in which rodents were exposed to experimentally generated HZE particles have demonstrated a high sensitivity of ovarian follicles and spermatogenic cells to HZE particles. Exposure to microgravity during space flight and to simulated microgravity on Earth disrupts spermatogenesis and testicular testosterone synthesis in rodents, whereas the male reproductive system seems to adapt to exposure to moderate hypergravity. A few studies have investigated the effects of microgravity on female reproduction, with findings of disrupted oestrous cycling and in vitro follicle development being cause for concern. Many remaining data gaps need to be addressed, including the effects of microgravity, hypergravity and space radiation on the male and female reproductive tracts, hypothalamic-pituitary regulation of reproduction and prenatal development of the reproductive system as well as the combined effects of the multiple reproductive hazards encountered in space.

Oxidative Stress as Cause, Consequence, or Biomarker of Altered Female Reproduction and Development in the Space Environment

Oxidative stress has been implicated in the pathophysiology of numerous terrestrial disease processes and associated with morbidity following spaceflight. Furthermore, oxidative stress has long been considered a causative agent in adverse reproductive outcomes. The purpose of this review is to summarize the pathogenesis of oxidative stress caused by cosmic radiation and microgravity, review the relationship between oxidative stress and reproductive outcomes in females, and explore what role spaceflight-induced oxidative damage may have on female reproductive and developmental outcomes.

Charged-Iron-Particles Found in Galactic Cosmic Rays are Potent Inducers of Epithelial Ovarian Tumors

Astronauts traveling in deep space are exposed to high-charge and energy (HZE) particles from galactic cosmic rays. We have previously determined that irradiation of adult female mice with iron HZE particles induces DNA double-strand breaks, oxidative damage and apoptosis in ovarian follicles, causing premature ovarian failure. These effects occur at lower doses than with conventional photon irradiation. Ovarian failure with resultant loss of negative feedback and elevated levels of gonadotropin hormones is thought to play a role in the pathophysiology of ovarian cancer. Therefore, we hypothesized that charged-iron-particle irradiation induces ovarian tumorigenesis in mice. In this study, three-month-old female mice were exposed to 0 cGy (sham) or 50 cGy iron ions and aged to 18 months. The 50 cGy irradiated mice had increased weight gain with age and lack of estrous cycling, consistent with ovarian failure. A total of 47% and 7% of mice irradiated with 50 cGy had unilateral and bilateral ovarian tumors, respectively, whereas 14% of mice in the 0 cGy group had unilateral tumors. The tumors contained multiple tubular structures, which were lined with cells positive for the epithelial marker cytokeratin, and had few proliferating cells. In some tumors, packets of cells between the tubular structures were immunopositive for the granulosa cell marker FOXL2. Based on these findings, tumors were diagnosed as tubular adenomas or mixed tubular adenoma/granulosa cell tumors. In conclusion, charged-iron-particle-radiation induces ovarian tumors in mice, raising concerns about ovarian tumors as late sequelae of deep space travel in female astronauts.

Transient increases in intracellular calcium and reactive oxygen species levels in TCam-2 cells exposed to microgravity

The effects of microgravity on functions of the human body are well described, including alterations in the male and female reproductive systems. In the present study, TCam-2 cells, which are considered a good model of mitotically active male germ cells, were used to investigate intracellular signalling and cell metabolism during exposure to simulated microgravity, a condition that affects cell shape and cytoskeletal architecture. After a 24 hour exposure to simulated microgravity, TCam-2 cells showed 1) a decreased proliferation rate and a delay in cell cycle progression, 2) increased anaerobic metabolism accompanied by increased levels of intracellular Ca²⁺, reactive oxygen species and superoxide anion and modifications in mitochondrial morphology. Interestingly, all these events were transient and were no longer evident after 48 hours of exposure. The presence of antioxidants prevented not only the effects described above but also the modifications in cytoskeletal architecture and the activation of the autophagy process induced by simulated microgravity. In conclusion, in the TCam-2 cell model, simulated microgravity activated the oxidative machinery, triggering transient macroscopic cell events, such as a reduction in the proliferation rate, changes in cytoskeleton-driven shape and autophagy activation.

Very low doses of heavy oxygen ion radiation induce premature ovarian failure

Astronauts are exposed to charged particles during space travel, and charged particles are also used for cancer radiotherapy. Premature ovarian failure is a well-known side effect of conventional, low linear energy transfer (LET) cancer radiotherapy, but little is known about the effects of high LET charged particles on the ovary. We hypothesized that lower LET (16.5 keV/µm) oxygen particles would be less damaging to the ovary than we previously found for iron (LET = 179 keV/µm). Adult female mice were irradiated with 0, 5, 30 or 50 cGy oxygen ions or 50 cGy oxygen plus dietary supplementation with the antioxidant alpha lipoic acid (ALA). Six-hour after irradiation, percentages of ovarian follicles immunopositive for γH2AX, a marker of DNA double strand breaks, 4-HNE, a marker of oxidative lipid damage and BBC3 (PUMA), a proapoptotic BCL-2 family protein, were dose dependently increased in irradiated mice compared to controls. One week after irradiation, numbers of primordial, primary and secondary follicles per ovary were dose dependently decreased, with complete absence of follicles in the 50 cGy groups. The ED₅₀ for primordial follicle destruction was 4.6 cGy for oxygen compared to 27.5 cGy for iron in our previous study. Serum FSH and LH concentrations were significantly elevated in 50 cGy groups at 8 week. Supplementation with ALA mitigated the early effects, but not the ultimate depletion of ovarian follicles. In conclusion, oxygen charged particles are even more potent inducers of ovarian follicle depletion than charged iron particles, raising concern for premature ovarian failure in astronauts exposed to both particles during space travel.

Beyond astronaut's capabilities: The current state of the art

Space agencies have developed extensive expertise with sustaining human presence in low earth orbits and microgravity. Prolonged human presence in space beyond EarthâĂŹs orbit presents additional, some still unsolved issues. These are linked to the distance to Earth (impossibility of effective tele-operation, psychological effects linked to remoteness from Earth, required autonomy, the handling of emergencies, long mission durations), and to the environments beyond the Earth magnetosphere (radiation levels, local environments including atmospheres, dust, gravity, day-night cycles). These issues have impacts on the spacecraft design, the mission operations, astronaut selection and preparation and required supporting/ enabling technologies. This paper builds upon previous work by Rossini et al. , in critically reviewing and updating the current state of scientific research on enhancing astronaut's capabilities to face some of these challenges. In particular, it discusses the pertinence and feasibility of two approaches aiming at enhancing the chances of success of human missions: induced hibernation state and brain-machine interfaces.

Charged iron particles, components of space radiation, destroy ovarian follicles

STUDY QUESTION

Do charged iron particles, components of space radiation, cause premature ovarian failure?

SUMMARY ANSWER

Exposure to charged iron particles causes ovarian DNA damage, oxidative damage and apoptosis, resulting in premature ovarian failure.

WHAT IS KNOWN ALREADY

The ovary is very sensitive to follicle destruction by low linear energy transfer (LET) radiation, such as X-rays and γ-rays. However, it is completely unknown whether high-LET radiation, such as charged iron particles, also destroys ovarian follicles.

STUDY DESIGN, SIZE, DURATION

Twelve week old C57BL/6J female mice were exposed to single doses of 0, 5, 30 or 50 cGy (n = 8/group) charged iron particles (LET = 179 keV/µm) at energy of 600 MeV/u. Two groups were irradiated at the highest dose, one fed AIN-93M chow and the other fed AIN-93M chow supplemented with 150 mg/kg diet alpha lipoic acid (ALA).

PARTICIPANTS/MATERIALS, SETTING, METHODS

We quantified the numbers of ovarian follicles, measured serum follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations, and analyzed histone H2AX phosphorylation, oxidative damage and apoptosis markers in the ovarian follicles.

MAIN RESULTS AND THE ROLE OF CHANCE

H2AX phosphorylation, lipid peroxidation, protein nitration and apoptosis were highly induced in ovarian follicles at 6 h and remained increased 1 week after irradiation. As a result, numbers of healthy ovarian follicles were significantly and dose-dependently depleted at 1 and 8 weeks post-irradiation, with 57, 84 and 99% decreases in primordial follicles at 8 weeks at the 5, 30 and 50 cGy doses, respectively (P < 0.05 versus 0 cGy). Consistent with near-total depletion of ovarian follicles in the 50 cGy group, serum concentrations of FSH and LH were significantly elevated at 8 weeks. Dietary supplementation with ALA partially prevented the adverse ovarian effects of 50 cGy iron particles.

LIMITATIONS, REASONS FOR CAUTION

About 21% of the estimated radiation dose from exposure to galactic cosmic rays during a multi-year Mars mission will be due to high-LET particles, of which iron is only one. The effects of galactic cosmic rays, which contain a mixture of multiple charged particles, as well as protons, neutrons, and helium ions, may differ from the effects of iron alone.

WIDER IMPLICATIONS OF THE FINDINGS

We show for the first time that charged high-LET ions are highly damaging to the ovary even at low doses, causing premature ovarian failure. In addition to raising concerns for female astronauts, these findings raise concerns for ovarian damage due to clinical uses of high-LET particles for cancer treatment. In addition to causing infertility, premature ovarian failure has adverse implications for the functions of heart, brain, bone and muscle later in life.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by a National Aeronautics and Space Administration grant NNX14AC50G to U.L. B.M. was partially supported by a National Space Biomedical Research Institute First Award, PF04302. Additional support was received from the University of California Irvine Center for Occupational and Environmental Health. The authors have no conflicts of interests.

Spaceflight-induced vertebral bone loss in ovariectomized rats is associated with increased bone marrow adiposity and no change in bone formation

There is often a reciprocal relationship between bone marrow adipocytes and osteoblasts, suggesting that marrow adipose tissue (MAT) antagonizes osteoblast differentiation. MAT is increased in rodents during spaceflight but a causal relationship between MAT and bone loss remains unclear. In the present study, we evaluated the effects of a 14-day spaceflight on bone mass, bone resorption, bone formation, and MAT in lumbar vertebrae of ovariectomized (OVX) rats. Twelve-week-old OVX Fischer 344 rats were randomly assigned to a ground control or flight group. Following flight, histological sections of the second lumbar vertebrae (n=11/group) were stained using a technique that allowed simultaneous quantification of cells and preflight fluorochrome label. Compared with ground controls, rats flown in space had 32% lower cancellous bone area and 306% higher MAT. The increased adiposity was due to an increase in adipocyte number (224%) and size (26%). Mineral apposition rate and osteoblast turnover were unchanged during spaceflight. In contrast, resorption of a preflight fluorochrome and osteoclast-lined bone perimeter were increased (16% and 229%, respectively). The present findings indicate that cancellous bone loss in rat lumbar vertebrae during spaceflight is accompanied by increased bone resorption and MAT but no change in bone formation. These findings do not support the hypothesis that increased MAT during spaceflight reduces osteoblast activity or lifespan. However, in the context of ovarian hormone deficiency, bone formation during spaceflight was insufficient to balance increased resorption, indicating defective coupling. The results are therefore consistent with the hypothesis that during spaceflight mesenchymal stem cells are diverted to adipocytes at the expense of forming osteoblasts.

Effects of Spaceflight on Bone Microarchitecture in the Axial and Appendicular Skeleton in Growing Ovariectomized Rats

This study investigated the effects of a 14-day spaceflight on bone mass, density and microarchitecture in weight bearing (femur and humerus) and non-weight bearing (2^nd lumbar vertebra and calvarium) bones in the context of ovarian hormone insufficiency. 12-week-old Fisher 344 rats were ovariectomized 2 weeks before flight and randomized into one of three groups: 1) baseline (n = 6), 2) ground control (n = 12) or 3) spaceflight (n = 12). Additional ground-based ovary-intact rats provided age-matched reference values at baseline (n = 8) and landing (n = 10). Ovariectomy resulted in bone- and bone compartment-specific deficits in cancellous bone volume fraction. Spaceflight resulted in lower cortical bone accrual in the femur but had no effect on cortical bone in the humerus or calvarium. Cancellous bone volume fraction was lower in flight animals compared to ground control animals in lumbar vertebra and distal femur metaphysis and epiphysis; significant differences were not detected in the distal humerus. Bone loss (compared to baseline controls) in the femur metaphysis was associated with lower trabecular number, whereas trabecular thickness and number were lower in the epiphysis. In summary, the effect of spaceflight on bone microarchitecture in ovariectomized rats was bone-and bone compartment-specific but not strictly related to weight bearing.