Evidence indicates that cerebral blood flow is both increased and diminished in astronauts on return to Earth. Data from ground-based animal models simulating the effects of microgravity have shown that decrements in cerebral perfusion are associated with enhanced vasoconstriction and structural remodeling of cerebral arteries. Based on these results, the purpose of this study was to test the hypothesis that 13 d of spaceflight [Space Transportation System (STS)-135 shuttle mission] enhances myogenic vasoconstriction, increases medial wall thickness, and elicits no change in the mechanical properties of mouse cerebral arteries. Basilar and posterior communicating arteries (PCAs) were isolated from 9-wk-old female C57BL/6 mice for in vitro vascular and mechanical testing. Contrary to that hypothesized, myogenic vasoconstrictor responses were lower and vascular distensibility greater in arteries from spaceflight group (SF) mice (n=7) relative to ground-based control group (GC) mice (n=12). Basilar artery maximal diameter was greater in SF mice (SF: 236+/-9 mum and GC: 215+/-5 mum) with no difference in medial wall thickness (SF: 12.4+/-1.6 mum; GC: 12.2+/-1.2 mum). Stiffness of the PCA, as characterized via nanoindentation, was lower in SF mice (SF: 3.4+/-0.3 N/m; GC: 5.4+/-0.8 N/m). Collectively, spaceflight-induced reductions in myogenic vasoconstriction and stiffness and increases in maximal diameter of cerebral arteries signify that elevations in brain blood flow may occur during spaceflight. Such changes in cerebral vascular control of perfusion could contribute to increases in intracranial pressure and an associated impairment of visual acuity in astronauts during spaceflight.
Research Containing: Mice
Exposure to long-duration microgravity leads to ocular changes in astronauts, manifested by a variety of signs and symptoms during spaceflight that in some cases persist after return to Earth. These morphological and functional changes are only partly understood and are of occupational health relevance. To investigate further into the molecular basis of the changes occurring in ocular tissue upon exposure to spaceflight, eyes were collected from female C57BL/6 mice flown on STS-135 (FLT) on landing day or from their ground control counterparts maintained at similar conditions within the Animal Enclosure Module (AEM). One eye was fixed for histological sectioning while the contralateral eye was dissected to isolate the retina for gene expression profiling. 8-hydroxy-deoxyguanosine (8OHdG) staining showed a statistically significant increase in the inner nuclear layer of FLT samples compared to AEM. Gene expression analysis in isolated retina identified 139 differentially expressed genes in FLT compared to AEM control samples. The genes affected were mainly involved in pathways and processes of endoplasmic reticulum (ER) stress, inflammation, neuronal and glial cell loss, axonal degeneration, and herpes virus activation. These results suggest a concerted change in gene expression in the retina of mice flown in space, possibly leading to retinal damage, degeneration, and remodeling.
Spaceflight modulates expression of extracellular matrix, adhesion, and profibrotic molecules in mouse lung
NASA has reported pulmonary abnormalities in astronauts on space missions, but the molecular changes in lung tissue remain unknown. The goal of the present study was to explore the effects of spaceflight on expression of extracellular matrix (ECM), cell adhesion, and pro-fibrotic molecules in lungs of mice flown on Space Shuttle Endeavour (STS-118). C57BL/6Ntac mice housed in animal enclosure modules during a 13-day mission in space (FLT) were killed within hours after return; ground controls were treated similarly for comparison (GRD). Analysis of genes associated with ECM and adhesion molecules was performed according to quantitative RT-PCR. The data revealed that FLT lung samples had statistically significant transcriptional changes, i.e., at least 1.5-fold, in 25 out of 84 examined genes (P < 0.05); 15 genes were upregulated and 10 were downregulated. The genes that were upregulated by more than twofold were Ctgf, Mmp2, Ncam1, Sparc, Spock1, and Timp3, whereas the most downregulated genes were Lama1, Mmp3, Mmp7, vcam-1, and Sele. Histology showed profibrosis-like changes occurred in FLT mice, more abundant collagen accumulation around blood vessels, and thicker walls compared with lung samples from GRD mice. Immunohistochemistry was used to compare expression of six selected proteins associated with fibrosis. Immunoreactivity of four proteins (MMP-2, CTGF, TGF-β1, and NCAM) was enhanced by spaceflight, whereas, no difference was detected in expression of MMP-7 and MMP-9 proteins between the FLT and GRD groups. Taken together, the data demonstrate that significant changes can be readily detected shortly after return from spaceflight in the expression of factors that can adversely influence lung function.
Cardiovascular adaptations to microgravity undermine the physiological capacity to respond to orthostatic challenges upon return to terrestrial gravity. The purpose of the present study was to investigate the influence of spaceflight on vasoconstrictor and myogenic contractile properties of mouse gastrocnemius muscle resistance arteries. We hypothesized that vasoconstrictor responses acting through adrenergic receptors [norepinephrine (NE)], voltage-gated Ca2+ channels (KCl), and stretch-activated (myogenic) mechanisms would be diminished following spaceflight. Feed arteries were isolated from gastrocnemius muscles, cannulated on glass micropipettes, and physiologically pressurized for in vitro experimentation. Vasoconstrictor responses to intraluminal pressure changes (0–140 cmH2O), KCl (10–100 mM), and NE (10−9-10−4 M) were measured in spaceflown (SF; n = 11) and ground control (GC; n = 11) female C57BL/6 mice. Spaceflight reduced vasoconstrictor responses to KCl and NE; myogenic vasoconstriction was unaffected. The diminished vasoconstrictor responses were associated with lower ryanodine receptor-2 (RyR-2) and ryanodine receptor-3 (RyR-3) mRNA expression, with no difference in sarcoplasmic/endoplasmic Ca2+ ATPase 2 mRNA expression. Vessel wall thickness and maximal intraluminal diameter were unaffected by spaceflight. The data indicate a deficit in intracellular calcium release via RyR-2 and RyR-3 in smooth muscle cells as the mechanism of reduced contractile activity in skeletal muscle after spaceflight. Furthermore, the results suggest that impaired end-organ vasoconstrictor responsiveness of skeletal muscle resistance arteries contributes to lower peripheral vascular resistance and less tolerance of orthostatic stress in humans after spaceflight.
Spaceflight and hind limb unloading induce similar changes in electrical impedance characteristics of mouse gastrocnemius muscle
OBJECTIVE: To assess the potential of electrical impedance myography (EIM) to serve as a marker of muscle fiber atrophy and secondarily as an indicator of bone deterioration by assessing the effects of spaceflight or hind limb unloading. METHODS: In the first experiment, 6 mice were flown aboard the space shuttle (STS-135) for 13 days and 8 earthbound mice served as controls. In the second experiment, 14 mice underwent hind limb unloading (HLU) for 13 days; 13 additional mice served as controls. EIM measurements were made on ex vivo gastrocnemius muscle. Quantitative microscopy and areal bone mineral density (aBMD) measurements of the hindlimb were also performed. RESULTS: Reductions in the multifrequency phase-slope parameter were observed for both the space flight and HLU cohorts compared to their respective controls. For ground control and spaceflight groups, the values were 24.7+/-1.3 degrees /MHz and 14.1+/-1.6 degrees /MHz, respectively (p=0.0013); for control and HLU groups, the values were 23.9+/-1.6 degrees /MHz and 19.0+/-1.0 degrees /MHz, respectively (p=0.014). This parameter also correlated with muscle fiber size (rho=0.65, p=0.011) for spaceflight and hind limb aBMD (rho=0.65, p=0.0063) for both groups. CONCLUSIONS: These data support the concept that EIM may serve as a useful tool for assessment of muscle disuse secondary to immobilization or microgravity.
This paper summarizes experimental data on the erythropoiesis of rats flown on Cosmos biosatellites for 18-22 days. The histogenesis of the hemopoietic tissue is investigated at the level of stem cells, dividing-maturing pool and mature blood cells (erythrocytes). In weightlessness inhibition of the erythropoiesis in various skeletal sites occurs. Flight data are compared with hemopoietic findings in hypokinetic rats. Possible mechanisms underlying red blood disorders in humans during space flight are discussed. [References: 17]
Development of a Novel Three-Dimensional, Automatable and Integrated Bioprocess for the Differentiation of Embryonic Stem Cells into Pulmonary Alveolar Cells in a Rotating Vessel Bioreactor System
Application of stem cells for cell therapy of respiratory diseases is a developing field. We have previously established several protocols for the differentiation of embryonic stem cells (ESC) into alveolar epithelial cells, which require a high degree of operator interference and result in a low yield of target cells. Herein, we have shown that, by provision of a medium conditioned using A549 cells and by integration of classic steps of ESC differentiation into a single step through encapsulation in hydrogels (three-dimensional) and culture in a rotary bioreactor, murine ESC (mESC) could be directed to differentiate into distal respiratory epithelial cells. Type I and II pneumocytes (with a yield of 50% for type II) and Clara cells were demonstrated by the expression of aquaporin 5, surfactant protein C, and Clara cell secretory protein, respectively. We identified target cells as early as day 5 of culture and stably maintained our differentiated cells in vitro for 100 days. Electron microscopy demonstrated microvilli and intracellular lamellar bodies (LB), and fluorescent staining confirmed the active process of exocytosis of these LB in differentiated type II cells. When these cells were decapsulated and cultured in static conditions in flask cultures (two-dimensional), they retained their characteristic type II phenotype and morphology. In conclusion, our protocol offers integrated bioprocessing, shorter time of differentiation, lower cost, no use of growth factors, high reproducibility, and high phenotypic and functional stability, as well as being amenable to automation and being scalable, which would move this field closer to future clinical applications.
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The effects of space travel are relatively unexplored in regard to the female reproductive system. An important step in determining possible adverse effects on the human female reproductive system is the analysis of test animal data. This study analyzed the ovarian tissue of mice flown aboard space shuttle Endeavour on NASA mission STS-118. The experiment consisted of three groups of animals: two sets of control animals and a single set of flight animals. Each set consisted of twelve individual mice. The flight animals were housed in the Animal Enclosure Module (AEM) of the Commercial Biomedical Testing Module-2 (CBTM-2) over the 13 day flight. One set of control animals (baseline) were housed in standard cages at room temperature. The other set of control animals (ground control) were housed in ground based AEMs which were environmentally controlled to match the conditions aboard the shuttle Endeavour with a delay of 48 hours and subject to normal gravity. The ovarian tissue samples were fixed in 4% paraformaldehyde, paraffin embedded, sectioned, mounted, and stained using standard Hematoxylin and Eosin staining procedures, and cover-slipped. The gross morphology of the tissue was then qualitatively analyzed. The flight animals were compared to the baseline and ground control sets. The presence of developing follicles of all stages as well as the presence of corpora lutea in all three treatment groups indicates no significant gross morphological changes occur within ovarian tissue when exposed to spaceflight for 13 days or less.
Simulated spaceflight produces a rapid and sustained loss of osteoprogenitors and an acute but transitory rise of osteoclast precursors in two genetic strains of mice
Shahnazari M, Kurimoto P, Boudignon BM, Orwoll BE, Bikle DD, Halloran BP. Simulated spaceflight produces a rapid and sustained loss of osteoprogenitors and an acute but transitory rise of osteoclast precursors in two genetic strains of mice. Am J Physiol Endocrinol Metab 303: E1354-E1362, 2012. First published October 9, 2012; doi:10.1152/ajpendo.00330.2012.-Loss of skeletal weight bearing or skeletal unloading as occurs during spaceflight inhibits bone formation and stimulates bone resorption. These are associated with a decline in the osteoblast (Ob.S/BS) and an increase in the osteoclast (Oc.S/BS) bone surfaces. To determine the temporal relationship between changes in the bone cells and their marrow precursor pools during sustained unloading, and whether genetic background influences these relationships, we used the hindlimb unloading model to induce bone loss in two strains of mice known to respond to load and having significantly different cancellous bone volumes (C57BL/6 and DBA/2 male mice). Skeletal unloading caused a progressive decline in bone volume that was accompanied by strain-specific changes in Ob.S/BS and Oc.S/BS. These were associated with a sustained reduction in the osteoprogenitor population and a dramatic but transient increase in the osteoclast precursor pool size in both strains. The results reveal that bone adaptation to skeletal unloading involves similar rapid changes in the osteoblast and osteoclast progenitor populations in both strains of mice but striking differences in Oc.S/BS dynamics, BFR, and cancellous bone structure. These strain-specific differences suggest that genetics plays an important role in determining the osteoblast and osteoclast populations on the bone surface and the dynamics of bone loss in response to skeletal unloading.
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Modeled Microgravity Sensitizes Osteoclast Precursors to RANKL Mediated Osteoclastogenesis by Increasing DAP12
Mechanical forces are essential to maintain skeletal integrity, and microgravity exposure leads to bone loss. The underlying molecular mechanisms leading to the changes in osteoblasts and osteoclast differentiation and function remain to be fully elucidated. Because of the infrequency of spaceflights and payload constraints, establishing in vitro and in vivo systems that mimic microgravity conditions becomes necessary. We have established a simulated microgravity (modeled microgravity, MMG) system to study the changes induced in osteoclast precursors. We observed that MMG, on its own, was unable to induce osteoclastogenesis of osteoclast precursors; however, 24 h of MMG activates osteoclastogenesis-related signaling molecules ERK, p38, PLCgamma2, and NFATc1. Receptor activator of NFkB ligand (RANKL) (with or without M-CSF) stimulation for 3-4 days in gravity of cells that had been exposed to MMG for 24 h enhanced the formation of very large tartrate-resistant acid phosphatase (TRAP)-positive multinucleated (>30 nuclei) osteoclasts accompanied by an upregulation of the osteoclast marker genes TRAP and cathepsin K. To validate the in vitro system, we studied the hindlimb unloading (HLU) system using BALB/c mice and observed a decrease in BMD of femurs and a loss of 3D microstructure of both cortical and trabecular bone as determined by micro-CT. There was a marked stimulation of osteoclastogenesis as determined by the total number of TRAP-positive multinucleated osteoclasts formed and also an increase in RANKL-stimulated osteoclastogenesis from precursors removed from the tibias of mice after 28 days of HLU. In contrast to earlier reported findings, we did not observe any histomorphometric changes in the bone formation parameters. Thus, the foregoing observations indicate that microgravity sensitizes osteoclast precursors for increased differentiation. The in vitro model system described here is potentially a valid system for testing drugs for preventing microgravity-induced bone loss by targeting the molecular events occurring in microgravity-induced enhanced osteoclastogenesis.
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