Altered cytokine expression in tissues of mice subjected to simulated microgravity

Effects of spaceflight on the spleen and thymus of mice: Gene pathway analysis and immune infiltration analysis

During space flight, the immune system function of the body is disrupted due to continuous weightlessness, radiation and other factors, resulting in an increased incidence of infectious diseases in astronauts. However, the effect of space flight on the immune system at the molecular level is unknown. The aim of this study was to identify key genes and pathways of spatial environmental effects on the spleen and thymus using bioinformatics analysis of the GEO dataset. Differentially expressed genes (DEGs) in the spleen and thymus of mice preflight and postflight were screened by comprehensive analysis of gene expression profile data. Then, GO enrichment analysis of DEGs was performed to determine the biological role of DEGs. A protein-protein interaction network was used to identify hub genes. In addition, transcription factors in DEGs were screened, and a TF-target regulatory network was constructed. Finally, immune infiltration analysis was performed on spleen and thymus samples from mice. The results showed that DEGs in the spleen and thymus are mainly involved in immune responses and in biological processes related to platelets. Six hub genes were identified in the spleen and 13 in the thymus, of which Ttr, Aldob, Gc and Fabp1 were common to both tissues. In addition, 5 transcription factors were present in the DEGs of the spleen, and 9 transcription factors were present in the DEGs of the thymus. The spatial environment can influence the degree of immune cell infiltration in the spleen and thymus. Our study bioinformatically analyzed the GEO dataset of spacefaring mice to identify the effects of the space environment on the immune system and the genes that play key roles, providing insights for the treatment of spaceflight-induced immune system disorders.

Microgravity and immune cells

The microgravity environment experienced during spaceflight severely impaired immune system, making astronauts vulnerable to various diseases that seriously threaten the health of astronauts. Immune cells are exceptionally sensitive to changes in gravity and the microgravity environment can affect multiple aspects of immune cells through different mechanisms. Previous reports have mainly summarized the role of microgravity in the classification of innate and adaptive immune cells, lacking an overall grasp of the laws that microgravity effects on immune cells at different stages of their entire developmental process, such as differentiation, activation, metabolism, as well as function, which are discussed and concluded in this review. The possible molecular mechanisms are also analysed to provide a clear understanding of the specific role of microgravity in the whole development process of immune cells. Furthermore, the existing methods by which to reverse the damage of immune cells caused by microgravity, such as the use of polysaccharides, flavonoids, other natural immune cell activators etc. to target cell proliferation, apoptosis and impaired function are summarized. This review will provide not only new directions and ideas for the study of immune cell function in the microgravity environment, but also an important theoretical basis for the development of immunosuppression prevention and treatment drugs for spaceflight.

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.

Hindlimb unloading-induced reproductive suppression via Downregulation of hypothalamic Kiss-1 expression in adult male rats

BACKGROUND

Spaceflights-induced microgravity can alter various physiological processes in human's body including the functional status of the reproductive system. Rodent model of tail-suspension hindlimb unloading is extensively used to stimulate the organs responses to the microgravity condition. This study explores the potential effects of hindlimb unloading on testicular functions and spermatogenesis in adult male rats and the underlying mechanism/s.

METHODS

Twenty Sprague-Dawley rats were allotted into two groups: normally loaded group (control; all arms were in touch with the grid floor) and hindlimb unloaded group (HU; only the forearms were in contact with the grid floor).

RESULTS

Following 30 days of exposure, the HU group saw a decline in body weight, testicular and epidydimal weights, and all semen parameters. The circulating concentrations of gonadotropin-releasing hormone (GnRH), follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone significantly decreased, while levels of kisspeptin, corticosterone, inhibin, prolactin and estradiol (E2) increased in the HU group. Intratesticular levels of 5α-reductase enzyme and dihydrotestosterone (DHT) were suppressed, while the levels of aromatase and kisspeptin were significantly elevated in the HU group. Hypothalamic kisspeptin (Kiss1) mRNA expression levels were downregulated while its receptors (Kiss1R) were upregulated in the HU group. On the contrary, the mRNA expression levels of testicular Kiss1 were upregulated while Kiss1R were downregulated. The pituitary mRNA expression levels of FSHβ and LHβ decreased in the HU group. The levels of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and nitric oxide (NO) concentrations, and total antioxidant capacity (TAC) were elevated while malondialdehyde (MDA) concentrations declined in the testes of HU group. The testes of the HU rats showed positive immunostaining of caspase-3, heat shock protein 70 (HSP70) and Bcl2.

CONCLUSIONS

Altogether, these results revealed an inhibitory effect of hindlimb unloading on kisspeptin signaling in the hypothalamic-pituitary-testicular axis with impaired spermatogenesis and steroidogenesis.

Intermittent reloading does not prevent reduction in iron availability and hepcidin upregulation caused by hindlimb unloading

NEW FINDINGS

What is the central question of this study? Could skeletal muscle be involved in microgravity-induced iron misdistribution by modulating expression of hepcidin, the master regulator of iron metabolism? What is the main finding and its importance? We demonstrate, in rats, that hepcidin upregulation is not a transient adaptation associated with early exposure to microgravity and that intermittent reloading does not limit microgravity-induced iron misdistribution despite having a beneficial effect on soleus muscle wasting.

ABSTRACT

In humans, exposure to microgravity during spaceflight causes muscle atrophy, changes in iron storage and a reduction in iron availability. We previously observed that during 7 days of simulated microgravity in rats, hepcidin plays a key role in iron misdistribution, and we suggested that a crosstalk between skeletal muscle and liver could regulate hepcidin synthesis in this context. In the present study in rats, we investigated the medium-term effects of simulated microgravity on iron metabolism. We also tested whether intermittent reloading (IR) to target skeletal muscle atrophy limits iron misdistribution efficiently. For this purpose, Wistar rats underwent 14 days of hindlimb unloading (HU) combined or not combined with daily IR. At the end of this period, the serum iron concentration and transferrin saturation were significantly reduced, whereas hepatic hepcidin mRNA was upregulated. However, the main signalling pathways involved in hepcidin synthesis in the liver (BMP-small mothers against decapentaplegic (SMAD), interleukin-6-STAT3 and ERK1/2) were unaffected. Unlike what was observed after 7 days of HU, the iron concentration in the spleen, liver and skeletal muscle was comparable between control animals and those that underwent HU or HU plus IR for 14 days. Despite its beneficial effect on soleus muscle atrophy and slow-to-fast myosin heavy chain distribution, IR did not significantly prevent a reduction in iron availability and hepcidin upregulation. Altogether, these results highlight that iron availability is durably reduced during longer exposure to simulated microgravity and that the related hepcidin upregulation is not a transient adaptation to these conditions. The results also suggest that skeletal muscle does not necessarily play a key role in the iron misdistribution that occurs during simulated microgravity.

IL-6 and the dysregulation of immune, bone, muscle, and metabolic homeostasis during spaceflight

We have previously reported that exercise-related secretion of IL-6 by peripheral blood mononuclear cells is proportionate to body weight, suggesting that IL-6 is gravisensitive and that suboptimal production of this key cytokine may contribute to homeostatic dysregulations that occur during spaceflight. This review details what is known about the role of this key cytokine in innate and adaptive immunity, hematopoiesis, and in bone, muscle and metabolic homeostasis on Earth and in the microgravity of space and suggests an experimental approach to confirm or disavow the role of IL-6 in space-related dysregulations.

Total Flavonoids of Drynariae Rhizoma Prevent Bone Loss Induced by Hindlimb Unloading in Rats

Drynariae Rhizoma is a kidney-tonifying herb that has a long history in clinical practice for the treatment of bone fractures and joint diseases in China. Flavonoids are considered to be its major active ingredients and are reported to ease bone loss in ovariectomized rats. However, the beneficial effects of the total flavonoids of Drynariae Rhizoma on osteoporosis caused by microgravity or mechanical inactivity remain unknown. This study assessed the effects of total Drynariae Rhizoma flavonoids (DRTF, Qihuang, Beijing, China, national medicine permit No. Z20030007, number of production: 04080081, content of DRTF ≥80%) against bone loss induced by simulated microgravity. A hindlimb unloading tail-suspended rat model was established to determine the effect of DRTF on bone mineral density (BMD), biomechanical strength and trabecular bone microarchitecture. Twenty-eight male Sprague-Dawley rats were divided into four groups: the baseline, control, hindlimb unloading with vehicle (HLU), and hindlimb unloading treated with DRTF (HLU-DRTF, 75 mg/kg/day) groups. Oral DRTF was administered for 4 weeks. The underlying mechanisms of the DRTF actions on disuse-induced osteoporosis are discussed. The results showed that DRTF treatment significantly increased the BMD and mechanical strength of tail-suspended rats. Enhanced bone turnover markers with HLU treatment were attenuated by DRTF administration. Deterioration of trabecular bone induced by HLU was prevented through elevated bone volume/tissue volume (BV/TV), trabecular number (Tb. N), trabecular thickness (Tb. Th) and decreased trabecular separation (Tb. Sp). The present study provides the first evidence that DRTF prevents bone loss induced by HLU treatment, indicating its potential application in the treatment of disuse-induced osteoporosis.

Effect of Long-Term Antiorthostatic Suspension in a Murine Model of Acute Lung Injury

Objectives

Antiorthostatic suspension (AOS) is ground-based model of simulated microgravity. There is still no study about the effect of long-term microgravity on the clinical course of acute lung injury. We evaluated the effect of simulated microgravity using AOS in a murine model of acute lung injury by lipopolysaccharide (LPS).

Methods

Thirty BALB/c mice were used. During 4 weeks, mice were equally allocated to control (free movement), restraint (tail suspended, but hindlimbs not unloaded), and AOS group (hindlimb unloaded). After then, mice got intranasal challenge with LPS (20 mg/kg, 50 μL). We measured: weight gain before and after AOS, the number of inflammatory cells and titers of cytokines (interleukin [IL]-1β, IL-6, IL-10, tumor necrosis factor-α, and interferon-γ) in bronchoalveolar lavage (BAL) fluid, titer of myeloperoxidase (MPO) in serum and lung homogenate, and histopathologic examination of lung tissue.

Results

AOS group had significant weight loss compared to control and restraint group (P<0.001). AOS group also showed significantly decreased lymphocytes (P=0.023) compared to control group. In AOS group, titer for IL-1β in BAL fluid was significantly lower than restraint group (P=0.049). Titer for serum MPO was significantly decreased in AOS group compared to restraint group (P=0.004). However, there was no significant difference of MPO titers in lung tissue between groups. Histopathologic examination of lung tissue revealed no significant difference in the degree of pulmonary infiltration between restraint and AOS group.

Conclusion

In spite of modest anti-inflammatory effect, prolonged AOS caused no significant change in LPS-induced pulmonary inflammation.

Effect of Prolonged Simulated Microgravity on Metabolic Proteins in Rat Hippocampus: Steps toward Safe Space Travel

Mitochondria are not only the main source of energy in cells but also produce reactive oxygen species (ROS), which result in oxidative stress when in space. This oxidative stress is responsible for energy imbalances and cellular damage. In this study, a rat tail suspension model was used in individual experiments for 7 and 21 days to explore the effect of simulated microgravity (SM) on metabolic proteins in the hippocampus, a vital brain region involved in learning, memory, and navigation. A comparative (18)O-labeled quantitative proteomic strategy was used to observe the differential expression of metabolic proteins. Forty-two and sixty-seven mitochondrial metabolic proteins were differentially expressed after 21 and 7 days of SM, respectively. Mitochondrial Complex I, III, and IV, isocitrate dehydrogenase and malate dehydrogenase were down-regulated. Moreover, DJ-1 and peroxiredoxin 6, which defend against oxidative damage, were up-regulated in the hippocampus. Western blot analysis of proteins DJ-1 and COX 5A confirmed the mass spectrometry results. Despite these changes in mitochondrial protein expression, no obvious cell apoptosis was observed after 21 days of SM. The results of this study indicate that the oxidative stress induced by SM has profound effects on metabolic proteins.

A functional interplay between 5-lipoxygenase and μ-calpain affects survival and cytokine profile of human Jurkat T lymphocyte exposed to simulated microgravity

A growing body of evidence strongly indicates that both simulated and authentic weightlessness exert a broad range of effects on mammalian tissues and cells, including impairment of immune cell function and increased apoptotic death. We previously reported that microgravity-dependent activation of 5-lipoxygenase (5-LOX) might play a central role in the initiation of apoptosis in human T lymphocytes, suggesting that the upregulation of this enzyme might be (at least in part) responsible for immunodepression observed in astronauts during space flights. Herein, we supplement novel information about the molecular mechanisms underlying microgravity-triggered apoptotic cell death and immune system deregulation, demonstrating that under simulated microgravity human Jurkat T cells increase the content of cytosolic DNA fragments and cytochrome c (typical hallmarks of apoptosis) and have an upregulated expression and activity of µ-calpain. These events were paralleled by the unbalance of interleukin- (IL-) 2 and interferon- (INF-) γ, anti- and proapoptotic cytokines, respectively, that seemed to be dependent on the functional interplay between 5-LOX and µ-calpain. Indeed, we report unprecedented evidence that 5-LOX inhibition reduced apoptotic death, restored the initial IL-2/INF-γ ratio, and more importantly reverted µ-calpain activation induced by simulated microgravity.

Terrestrial stress analogs for spaceflight associated immune system dysregulation

Recent data indicates that dysregulation of the immune system occurs and persists during spaceflight. Impairment of immunity, especially in conjunction with elevated radiation exposure and limited clinical care, may increase certain health risks during exploration-class deep space missions (i.e. to an asteroid or Mars). Research must thoroughly characterize immune dysregulation in astronauts to enable development of a monitoring strategy and validate any necessary countermeasures. Although the International Space Station affords an excellent platform for on-orbit research, access may be constrained by technical, logistical vehicle or funding limitations. Therefore, terrestrial spaceflight analogs will continue to serve as lower cost, easier access platforms to enable basic human physiology studies. Analog work can triage potential in-flight experiments and thus result in more focused on-orbit studies, enhancing overall research efficiency. Terrestrial space analogs generally replicate some of the physiological or psychological stress responses associated with spaceflight. These include the use of human test subjects in a laboratory setting (i.e. exercise, bed rest, confinement, circadian misalignment) and human remote deployment analogs (Antarctica winterover, undersea, etc.) that incorporate confinement, isolation, extreme environment, physiological mission stress and disrupted circadian rhythms. While bed rest has been used to examine the effects of physical deconditioning, radiation and microgravity may only be simulated in animal or microgravity cell culture (clinorotation) analogs. This article will characterize the array of terrestrial analogs for spaceflight immune dysregulation, the current evidence base for each, and interpret the analog catalog in the context of acute and chronic stress.

Differential expression of specific cellular defense proteins in rat hypothalamus under simulated microgravity induced conditions: comparative proteomics

Microgravity severely halts the structural and functional cerebral capacity of astronauts especially affecting their brains due to the stress produced by cephalic fluid shift. We employed a rat tail suspension model to substantiate simulated microgravity (SM) in brain. In this study, comparative mass spectrometry was applied in order to demonstrate the differential expression of 17 specific cellular defense proteins. Gamma-enolase, peptidyl-prolyl cis-trans isomerase A, glial fibrillary acidic protein, heat shock protein HSP 90-alpha, 10 kDa heat shock protein, mitochondrial, heat shock cognate 71 kDa protein, superoxide dismutase 1 and dihydropyrimidinase-related protein 2 were found to be upregulated by HPLC/ESI-TOF. Furthermore, five differentially expressed proteins including 60 kDa heat shock protein, mitochondrial, heat shock protein HSP 90-beta, peroxiredoxin-2, stress-induced-phosphoprotein, and UCHL-1 were found to be upregulated by HPLC/ESI-Q-TOF MS. In addition, downregulated proteins include cytochrome C, superoxide dismutase 2, somatic, and excitatory amino acid transporter 1 and protein DJ-1. Validity of MS results was successfully performed by Western blot analysis of DJ-1 protein. This study will not only help to understand the neurochemical responses produced under microgravity but also will give future direction to cure the proteomic losses and their after effects in astronauts.

Three weeks of murine hindlimb unloading induces shifts from B to T and from th to tc splenic lymphocytes in absence of stress and differentially reduces cell-specific mitogenic responses

Extended space missions are known to induce stress and immune dysregulation. Hindlimb unloading is a ground-based model used to reproduce most spaceflight conditions. The aim of this study was to better characterize the consequences of prolonged exposure to hindlimb unloading on murine splenic lymphocyte sub-populations. To ensure that the observed changes were not due to tail restraint but to the antiorthostatic position, three groups of mice were used: control (C), orthostatic restrained (R) and hindlimb unloaded (HU). After 21 days of exposure, no difference in serum corticosterone levels nor in thymus and spleen weights were observed between HU mice and their counterparts, revealing a low state of stress. Interestingly, flow cytometric analyses showed that B cells were drastically reduced in HU mouse spleens by 59% and, while the T cells number did not change, the Th/Tc ratio was decreased. Finally, the use of a fluorescent dye monitoring lymphoproliferation demonstrated that lymphocyte response to mitogen was reduced in Th and Tc populations and to a greater extent in B cells. Thus, we showed for the first time that, even if restraint has its own effects on the animals and their splenic lymphocytes, the prolonged antiorthostatic position leads, despite the absence of stress, to an inversion of the B/T ratio in the spleen. Furthermore, the lymphoproliferative response was impaired with a strong impact on B cells. Altogether, these results suggest that B cells are more affected by hindlimb unloading than T cells which may explain the high susceptibility to pathogens, such as gram-negative bacteria, described in animal models and astronauts.

Spaceflight influences both mucosal and peripheral cytokine production in PTN-Tg and wild type mice

Spaceflight is associated with several health issues including diminished immune efficiency. Effects of long-term spaceflight on selected immune parameters of wild type (Wt) and transgenic mice over-expressing pleiotrophin under the human bone-specific osteocalcin promoter (PTN-Tg) were examined using the novel Mouse Drawer System (MDS) aboard the International Space Station (ISS) over a 91 day period. Effects of this long duration flight on PTN-Tg and Wt mice were determined in comparison to ground controls and vivarium-housed PTN-Tg and Wt mice. Levels of interleukin-2 (IL-2) and transforming growth factor-beta1 (TGF-β1) were measured in mucosal and systemic tissues of Wt and PTN-Tg mice. Colonic contents were also analyzed to assess potential effects on the gut microbiota, although no firm conclusions could be made due to constraints imposed by the MDS payload and the time of sampling. Spaceflight-associated differences were observed in colonic tissue and systemic lymph node levels of IL-2 and TGF-β1 relative to ground controls. Total colonic TGF-β1 levels were lower in Wt and PTN-Tg flight mice in comparison to ground controls. The Wt flight mouse had lower levels of IL-2 and TGF-β1 compared to the Wt ground control in both the inguinal and brachial lymph nodes, however this pattern was not consistently observed in PTN-Tg mice. Vivarium-housed Wt controls had higher levels of active TGF-β1 and IL-2 in inguinal lymph nodes relative to PTN-Tg mice. The results of this study suggest compartmentalized effects of spaceflight and on immune parameters in mice.

Stress response and humoral immune system alterations related to chronic hypergravity in mice

Spaceflights are known to induce stress and immune dysregulation. Centrifugation, as hindlimb unloading, is a good ground based-model to simulate altered gravity which occurs during space missions. The aim of this study was to investigate the consequences of a long-term exposure to different levels of hypergravity on the stress response and the humoral immunity in a mouse model. For this purpose, adult C57Bl/6J male mice were subjected for 21 days either to control conditions or to 2G or 3G acceleration gravity forces. Corticosterone level and anxiety behavior revealed a stress response which was associated with a decrease of body weight, after 21-day of centrifugation at 3G but not at 2G. Spleen lymphocyte lipopolysaccharide (LPS) responsiveness was diminished by 40% in the 2G group only, whereas a decrease was noted when cells were stimulated with concanavalin A for both 2G and 3G groups (about 25% and 20%, respectively) compared to controls. Pro-inflammatory chemokines (MCP-1 and IP-10) and Th1 cytokines (IFNγ and IL2) were slightly decreased in the 2G group and strongly decreased in the 3G mouse group. Regarding Th2 cytokines (IL4, IL5) no further significant modification was observed, whereas the immunosuppressive cytokine IL10 was slightly increased in the 3G mice. Finally, serum IgG concentration was twice higher whereas IgA concentration was slightly increased (about 30%) and IgM were unchanged in 2G mice compared to controls. No difference was observed in the 3G group with these isotypes. Consequently, functional immune dysregulations and stress responses were dependent of the gravity level.

Proteomic analysis of mouse hypothalamus under simulated microgravity

Exposure to altered microgravity during space travel induces changes in the brain and these are reflected in many of the physical behavior seen in the astronauts. The vulnerability of the brain to microgravity stress has been reviewed and reported. Identifying microgravity-induced changes in the brain proteome may aid in understanding the impact of the microgravity environment on brain function. In our previous study we have reported changes in specific proteins under simulated microgravity in the hippocampus using proteomics approach. In the present study the profiling of the hypothalamus region in the brain was studied as a step towards exploring the effect of microgravity in this region of the brain. Hypothalamus is the critical region in the brain that strictly controls the pituitary gland that in turn is responsible for the secretion of important hormones. Here we report a 2-dimensional gel electrophoretic analysis of the mouse hypothalamus in response to simulated microgravity. Lowered glutathione and differences in abundance expression of seven proteins were detected in the hypothalamus of mice exposed to microgravity. These changes included decreased superoxide dismutase-2 (SOD-2) and increased malate dehydrogenase and peroxiredoxin-6, reflecting reduction of the antioxidant system in the hypothalamus. Taken together the results reported here indicate that oxidative imbalance occurred in the hypothalamus in response to simulated microgravity.

Modeled gravitational unloading induced downregulation of endothelin-1 in human endothelial cells

Many space missions have shown that prolonged space flights may increase the risk of cardiovascular problems. Using a three-dimensional clinostat, we investigated human endothelial EA.hy926 cells up to 10 days under conditions of simulated microgravity (microg) to distinguish transient from long-term effects of microg and 1g. Maximum expression of all selected genes occurred after 10 min of clinorotation. Gene expression (osteopontin, Fas, TGF-beta(1)) declined to slightly upregulated levels or rose again (caspase-3) after the fourth day of clinorotation. Caspase-3, Bax, and Bcl-2 protein content was enhanced for 10 days of microgravity. In addition, long-term accumulation of collagen type I and III and alterations of the cytoskeletal alpha- and beta-tubulins and F-actin were detectable. A significantly reduced release of soluble factors in simulated microgravity was measured for brain-derived neurotrophic factor, tissue factor, vascular endothelial growth factor (VEGF), and interestingly for endothelin-1, which is important in keeping cardiovascular balances. The gene expression of endothelin-1 was suppressed under microg conditions at days 7 and 10. Alterations of the vascular endothelium together with a decreased release of endothelin-1 may entail post-flight health hazards for astronauts.

Proteomic analysis of mice hippocampus in simulated microgravity environment

Space travel induces many deleterious effects on the flight crew due to the '0' g environment. The brain experiences a tremendous fluid shift, which is responsible for many of the detrimental changes in physical behavior seen in astronauts. It therefore indicates that the brain may undergo major changes in its protein levels in a '0' g environment to counteract the stress. Analysis of these global changes in proteins may explain to better understand the functioning of brain in a '0' g condition. Toward such an effort, we have screened proteins in the hippocampus of mice kept in simulated microgravity environment for 7 days and have observed a few changes in major proteins as compared to control mice. Essentially, the results show a major loss of proteins in the hippocampus of mice subjected to simulated microgravity. These changes occur in structural proteins such as tubulin, coupled with the loss of proteins involved in metabolism. This preliminary investigation leads to an understanding of the alteration of proteins in the hippocampus in response to the microgravity environment.

Activation of activator protein-1 in mouse brain regions exposed to simulated microgravity

Microgravity induces stress, and the brain is one of the targets that is more influenced in this environment. Alteration in transcription factors can have enormous effect because of discrepancy in the signaling process of the cells. Activator protein-1 (AP-1) is a stress-regulated transcription factor and is involved in the regulation of physiological and pathological stimuli that include cytokines, growth factors, and stress signals. In the present study, an attempt has been made to observe the effect of a microgravity environment on the activation of AP-1 in the mouse brain. Our results show that AP-1 transcription factor is activated in simulated microgravity conditions in different regions of the brain. The activation of the AP-1 is dependent upon the increased kinase activity of c-Jun NH-terminal2 kinase-1. These results suggest that microgravity stress in the brain can elicit AP-1 activity.

Impact of simulated microgravity on cell cycle control and cytokine release by U937 cells

Previous experiments from flight- and ground-based model systems indicate unexpected alterations of human leukocytes, leading to growth retardation and depression of mitogenic activation. The response of myelomonocytic U937 cells to simulated microgravity was therefore investigated. To this purpose, U937 cells were cultured in the NASA-developed bioreactor Rotating Wall Vessel (RWV) as a device to simulate microgravity on earth. No apoptosis was detected, in part because of the up-regulation of hsp70. In agreement with results obtained in space-flown U937 cells, the cells grew more slowly in the RWV than under normal conditions and this correlated with the down-modulation of cdc25B. Marked alterations of the cytokine secretion profile and, in particular, of inflammatory chemokines, as well as a decrease of the proteasome activity, were also observed in response to microgravity.

Proteomics and genomics of microgravity

Many serious adverse physiological changes occur during spaceflight. In the search for underlying mechanisms and possible new countermeasures, many experimental tools and methods have been developed to study microgravity caused physiological changes, ranging from in vitro bioreactor studies to spaceflight investigations. Recently, genomic and proteomic approaches have gained a lot of attention; after major scientific breakthroughs in the fields of genomics and proteomics, they are now widely accepted and used to understand biological processes. Understanding gene and/or protein expression is the key to unfolding the mechanisms behind microgravity-induced problems and, ultimately, finding effective countermeasures to spaceflight-induced alterations. Significant progress has been made in identifying the genes/proteins responsible for these changes. Although many of these genes and/or proteins were observed to be either upregulated or downregulated, however, no large-scale genomics and proteomics studies have been published so far. This review aims at summarizing the current status of microgravity-related genomics and proteomics studies and stimulating large-scale proteomics and genomics research activities.

Activation of nuclear transcription factor-kappaB in mouse brain induced by a simulated microgravity environment

Microgravity induces inflammatory responses and modulates immune functions that may increase oxidative stress. Exposure to a microgravity environment induces adverse neurological effects; however, there is little research exploring the etiology of these effects resulting from exposure to such an environment. It is also known that spaceflight is associated with increase in oxidative stress; however, this phenomenon has not been reproduced in land-based simulated microgravity models. In this study, an attempt has been made to show the induction of reactive oxygen species (ROS) in mice brain, using ground-based microgravity simulator. Increased ROS was observed in brain stem and frontal cortex with concomitant decrease in glutathione, on exposing mice to simulated microgravity for 7 d. Oxidative stress-induced activation of nuclear factor-kappaB was observed in all the regions of the brain. Moreover, mitogen-activated protein kinase kinase was phosphorylated equally in all regions of the brain exposed to simulated microgravity. These results suggest that exposure of brain to simulated microgravity can induce expression of certain transcription factors, and these have been earlier argued to be oxidative stress dependent.