Muscle loading is important for maintaining muscle mass; when load is removed, atrophy is inevitable. However, in clinical situations such as critical care myopathy, masticatory muscles do not lose mass. Thus, their properties may be harnessed to preserve mass. We compared masticatory and appendicular muscles responses to microgravity, using mice aboard the space shuttle Space Transportation System-135. Age- and sex-matched controls remained on the ground. After 13 days of space flight, 1 masseter (MA) and tibialis anterior (TA) were frozen rapidly for biochemical and functional measurements, and the contralateral MA was processed for morphologic measurements. Flight TA muscles exhibited 20 +/- 3% decreased muscle mass, 2-fold decreased phosphorylated (P)-Akt, and 4- to 12-fold increased atrogene expression. In contrast, MAs had no significant change in mass but a 3-fold increase in P-focal adhesion kinase, 1.5-fold increase in P-Akt, and 50-90% lower atrogene expression compared with limb muscles, which were unaltered in microgravity. Myofibril force measurements revealed that microgravity caused a 3-fold decrease in specific force and maximal shortening velocity in TA muscles. It is surprising that myofibril-specific force from both control and flight MAs were similar to flight TA muscles, yet power was compromised by 40% following flight. Continued loading in microgravity prevents atrophy, but masticatory muscles have a different set point that mimics disuse atrophy in the appendicular muscle.-Philippou, A., Minozzo, F. C., Spinazzola, J. M., Smith, L. R., Lei, H., Rassier, D. E., Barton, E. R. Masticatory muscles of mouse do not undergo atrophy in space.
Research Containing: Mice
Selected Contribution: Effects of spaceflight on immunity in the C57BL/6 mouse. I. Immune population distributions
There are several aspects of the spaceflight environment that may lead to changes in immunity: mission-related psychological stress, radiation, and changes in gravity. On December 5, 2001, the space shuttle Endeavor launched for a 12-day mission to examine these effects on C57BL/6 mice for the first time. On their return, assays were performed on the spleen, blood, and bone marrow. In response to flight, there were no significant differences in the general circulating leukocyte proportions. In contrast, there was an increase in splenic lymphocyte percentages, with a corresponding decrease in granulocytes. There was an overall shift in splenic lymphocytes away from T cells toward B cells, and a decrease in the CD4-to-CD8 ratios due to a decrease in T helpers. In contrast, there were proportional increases in bone marrow T cells, with decreases in B cells. Although the blast percentage and count were decreased in flight mice, the CD34+ population was increased. The data were more consistent with a shift in bone marrow populations rather than a response to changes in the periphery. Many of the results are similar to those using other models. Clearly, spaceflight can influence immune parameters ranging from hematopoiesis to mature leukocyte mechanisms.
Genetic models in applied physiology: selected contribution: effects of spaceflight on immunity in the C57BL/6 mouse. I. Immune population distributions
There are several aspects of the spaceflight environment that may lead to changes in immunity: mission-related psychological stress, radiation, and changes in gravity. On December 5, 2001, the space shuttle Endeavor launched for a 12-day mission to examine these effects on C57BL/6 mice for the first time. On their return, assays were performed on the spleen, blood, and bone marrow. In response to flight, there were no significant differences in the general circulating leukocyte proportions. In contrast, there was an increase in splenic lymphocyte percentages, with a corresponding decrease in granulocytes. There was an overall shift in splenic lymphocytes away from T cells toward B cells, and a decrease in the CD4-to-CD8 ratios due to a decrease in T helpers. In contrast, there were proportional increases in bone marrow T cells, with decreases in B cells. Although the blast percentage and count were decreased in flight mice, the CD34(+) population was increased. The data were more consistent with a shift in bone marrow populations rather than a response to changes in the periphery. Many of the results are similar to those using other models. Clearly, spaceflight can influence immune parameters ranging from hematopoiesis to mature leukocyte mechanisms.
A critical step of spermatogenesis is the entry of mitotic spermatogonia into meiosis. Progresses on these topics are hampered by the lack of an in vitro culture system allowing mouse spermatogonia differentiation and entry into meiosis. Previous studies have shown that mouse pachytene spermatocytes cultured in simulated microgravity (SM) undergo a spontaneous meiotic progression. Here we report that mouse mitotic spermatogonia cultured under SM with a rotary cell culture system (RCCS) enter into meiosis in the absence of any added exogenous factor or contact with somatic cells. We found that isolated Kit-positive spermatogonia under the RCCS condition enter into the prophase of the first meiotic division (leptotene stage), as monitored by chromosomal organization of the synaptonemal complex 3 protein (Scp3) and up-regulation of several pro-meiotic genes. SM was found to activate the phosphatidyl inositol 3 kinase (PI3K) pathway and to induce in Kit-positive spermatogonia the last round of DNA replication, typical of the preleptotene stage. A PI3K inhibitor abolished Scp3 induction and meiotic entry stimulated by RCCS conditions. A positive effect of SM on germ cell differentiation was also observed in undifferentiated (Kit-negative) spermatogonia, in which RCCS conditions stimulate the expression of Kit and Stra8. In conclusion, SM is an artificial environmental condition which promotes postnatal male germ cell differentiation and might provide a tool to study the molecular mechanisms underlying the switch from mitosis to meiosis in mammals.
Bone marrow cells were isolated from the humeri of C57BL/6 mice after a 13-day flight on the space shuttle Space Transportation System (STS)-118 to determine how spaceflight affects differentiation of cells in the granulocytic lineage. We used flow cytometry to assess the expression of molecules that define the maturation/activation state of cells in the granulocytic lineage on three bone marrow cell subpopulations. These molecules included Ly6C, CD11b, CD31 (platelet endothelial cell adhesion molecule-1), Ly6G (Gr-1), F4/80, CD44, and c-Fos. The three subpopulations were small agranular cells [region (R)1], larger granular cells (R2), which were mostly neutrophils, and very large, very granular cells (R3), which had properties of macrophages. Although there were no composite phenotypic differences between total bone marrow cells isolated from spaceflight and ground-control mice, there were subpopulation differences in Ly6C (R1 and R3), CD11b (R2), CD31 (R1, R2, and R3), Ly6G (R3), F4/80 (R3), CD44(high) (R3), and c-Fos (R1, R2, and R3). In particular, the elevation of CD11b in the R2 subpopulation suggests neutrophil activation in response to landing. In addition, decreases in Ly6C, c-Fos, CD44(high), and Ly6G and an increase in F4/80 suggest that the cells in the bone marrow R3 subpopulation of spaceflight mice were more differentiated compared with ground-control mice. The presence of more differentiated cells may not pose an immediate risk to immune resistance. However, the reduction in less differentiated cells may forebode future consequences for macrophage production and host defenses. This is of particular importance to considerations of future long-term spaceflights.
Simulated microgravity using the Random Positioning Machine inhibits differentiation and alters gene expression profiles of 2T3 preosteoblasts
Exposure to microgravity causes bone loss in humans, and the underlying mechanism is thought to be at least partially due to a decrease in bone formation by osteoblasts. In the present study, we examined the hypothesis that microgravity changes osteoblast gene expression profiles, resulting in bone loss. For this study, we developed an in vitro system that simulates microgravity using the Random Positioning Machine (RPM) to study the effects of microgravity on 2T3 preosteoblast cells grown in gas-permeable culture disks. Exposure of 2T3 cells to simulated microgravity using the RPM for up to 9 days significantly inhibited alkaline phosphatase activity, recapitulating a bone loss response that occurs in real microgravity conditions without altering cell proliferation and shape. Next, we performed DNA microarray analysis to determine the gene expression profile of 2T3 cells exposed to 3 days of simulated microgravity. Among 10,000 genes examined using the microarray, 88 were downregulated and 52 were upregulated significantly more than twofold using simulated microgravity compared with the static 1-g condition. We then verified the microarray data for some of the genes relevant in bone biology using real-time PCR assays and immunoblotting. We confirmed that microgravity downregulated levels of alkaline phosphatase, runt-related transcription factor 2, osteomodulin, and parathyroid hormone receptor 1 mRNA; upregulated cathepsin K mRNA; and did not significantly affect bone morphogenic protein 4 and cystatin C protein levels. The identification of gravisensitive genes provides useful insight that may lead to further hypotheses regarding their roles in not only microgravity-induced bone loss but also the general patient population with similar pathological conditions, such as osteoporosis.
Skin physiology in microgravity: a 3-month stay aboard ISS induces dermal atrophy and affects cutaneous muscle and hair follicles cycling in mice
Aims: The Mice Drawer System (MDS) Tissue Sharing program was the longest rodent space mission ever performed. It provided 20 research teams with organs and tissues collected from mice having spent 3 months on the International Space Station (ISS). Our participation to this experiment aimed at investigating the impact of such prolonged exposure to extreme space conditions on mouse skin physiology. Methods: Mice were maintained in the MDS for 91 days aboard ISS (space group (S)). Skin specimens were collected shortly after landing for morphometric, biochemical, and transcriptomic analyses. An exact replicate of the experiment in the MDS was performed on ground (ground group (G)). Results: A significant reduction of dermal thickness (−15%, P=0.05) was observed in S mice accompanied by an increased newly synthetized procollagen (+42%, P=0.03), likely reflecting an increased collagen turnover. Transcriptomic data suggested that the dermal atrophy might be related to an early degradation of defective newly formed procollagen molecules. Interestingly, numerous hair follicles in growing anagen phase were observed in the three S mice, validated by a high expression of specific hair follicles genes, while only one mouse in the G controls showed growing hairs. By microarray analysis of whole thickness skin, we observed a significant modulation of 434 genes in S versus G mice. A large proportion of the upregulated transcripts encoded proteins related to striated muscle homeostasis. Conclusions: These data suggest that a prolonged exposure to space conditions may induce skin atrophy, deregulate hair follicle cycle, and markedly affect the transcriptomic repertoire of the cutaneous striated muscle panniculus carnosus.
Activation of Nervous System Development Genes in Bone Marrow Derived Mesenchymal Stem Cells Following Spaceflight Exposure
Stalled cell division in precursor bone cells and reduced osteoblast function are considered responsible for the microgravity-induced bone loss observed during spaceflight. However, underlying molecular mechanisms remain unraveled. Having overcome technological difficulties associated with flying cells in a space mission, we present the first report on the behavior of the potentially osteogenic murine bone marrow stromal cells (BMSC) in a 3D culture system, flown inside the KUBIK aboard space mission ISS 12S (Soyuz TMA-8+Increment 13) from March 30 to April 8, 2006 (experiment "Stroma-2''). Flight 1g control cultures were performed in a centrifuge located within the payload. Ground controls were maintained on Earth in another KUBIK payload and in Petri dishes. Half of the cultures were stimulated with osteo-inductive medium. Differences in total RNA extracted suggested that cell proliferation was inhibited in flight samples. Affymetrix technology revealed that 1,599 genes changed expression after spaceflight exposure. A decreased expression of cell-cycle genes confirmed the inhibition of cell proliferation in space. Unexpectedly, most of the modulated expression was found in genes related to various processes of neural development, neuron morphogenesis, transmission of nerve impulse and synapse, raising the question on the lineage restriction in BMSC. J. Cell. Biochem. 111: 442-452, 2010. (C) 2010 Wiley-Liss, Inc.
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A recent report shows that more than 30% of the astronauts returning from Space Shuttle missions or the International Space Station (ISS) were diagnosed with eye problems that can cause reduced visual acuity. We investigate here whether spaceflight environment-associated retinal damage might be related to oxidative stress-induced mitochondrial apoptosis. Female C57BL/6 mice were flown in the space shuttle Atlantis (STS-135), and within 35 h of landing, the spaceflight and ground-control mice, similarly housed in animal enclosure modules (AEMs) were euthanized and their eyes were removed for analysis. Changes in expression of genes involved in oxidative stress, mitochondrial and endothelial cell biology were examined. Apoptosis in the retina was analyzed by caspase-3 immunocytochemical analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. Levels of 4-hydroxynonenal (4-HNE) protein, an oxidative specific marker for lipid peroxidation were also measured. Evaluation of spaceflight mice and AEM ground-control mice showed that expression of several genes playing central roles in regulating the mitochondria-associated apoptotic pathway were significantly altered in mouse ocular tissue after spaceflight compared to AEM ground-control mice. In addition, the mRNA levels of several genes, which are responsible for regulating the production of reactive oxygen species were also significantly up-regulated in spaceflight samples compared to AEM ground-control mice. Further more, the level of HNE protein was significantly elevated in the retina after spaceflight compared to controls. Our results also revealed that spaceflight conditions induced significant apoptosis in the retina especially inner nuclear layer (INL) and ganglion cell layer (GCL) compared to AEM ground controls. The data provided the first evidence that spaceflight conditions induce oxidative damage that results in mitochondrial apoptosis in the retina. This data suggest that astronauts may be at increased risk for late retinal degeneration.
There is evidence that space flight condition-induced biological damage is associated with increased oxidative stress and extracellular matrix (ECM) remodeling. To explore possible mechanisms, changes in gene expression profiles implicated in oxidative stress and in ECM remodeling in mouse skin were examined after space flight. The metabolic effects of space flight in skin tissues were also characterized. Space Shuttle Atlantis (STS-135) was launched at the Kennedy Space Center on a 13-day mission. Female C57BL/6 mice were flown in the STS-135 using animal enclosure modules (AEMs). Within 3-5 h after landing, the mice were euthanized and skin samples were harvested for gene array analysis and metabolic biochemical assays. Many genes responsible for regulating production and metabolism of reactive oxygen species (ROS) were significantly (p < 0.05) altered in the flight group, with fold changes >1.5 compared to AEM control. For ECM profile, several genes encoding matrix and metalloproteinases involved in ECM remodeling were significantly up-/down-regulated following space flight. To characterize the metabolic effects of space flight, global biochemical profiles were evaluated. Of 332 named biochemicals, 19 differed significantly (p < 0.05) between space flight skin samples and AEM ground controls, with 12 up-regulated and 7 down-regulated including altered amino acid, carbohydrate metabolism, cell signaling, and transmethylation pathways. Collectively, the data demonstrated that space flight condition leads to a shift in biological and metabolic homeostasis as the consequence of increased regulation in cellular antioxidants, ROS production, and tissue remodeling. This indicates that astronauts may be at increased risk for pathophysiologic damage or carcinogenesis in cutaneous tissue.