Spaceflight results in a number of adaptations to skeletal muscle including atrophy and shifts towards faster muscle fiber types. To identify changes in gene expression that may underlie these adaptations microarray expression analysis was performed on gastrocnemius from mice flown on the STS-108 shuttle flight (11 days 19 hours) versus mice maintained on earth for the same period. Additionally to identify changes that were due to unloading and reloading microarray analyses were conducted on calf muscle from ground-based mice subjected to hindlimb suspension (12 days) and mice subjected to hindlimb suspension plus a brief period of reloading (3.5 hours) to simulate the time between landing and sacrifice of the spaceflight mice.

Microphysiological systems provide the opportunity to model accelerated changes at the human tissue level in the extreme space environment. Spaceflight-induced muscle atrophy experienced by astronauts shares similar physiological changes to muscle wasting in older adults, known as sarcopenia. These shared attributes provide a rationale for investigating molecular changes in muscle cells exposed to spaceflight that may mimic the underlying pathophysiology of sarcopenia. We report the results from three-dimensional myobundles derived from muscle biopsies from young and older adults, integrated into an autonomous CubeLab™, and flown to the International Space Station (ISS) aboard SpaceX CRS-21 as part of the NIH/NASA funded Tissue Chips in Space program. Global transcriptomic RNA-Seq analyses comparing the myobundles in space and on the ground revealed downregulation of shared transcripts related to myoblast proliferation and muscle differentiation. The analyses also revealed downregulated differentially expressed gene pathways related to muscle metabolism unique to myobundles derived from the older cohort exposed to the space environment compared to ground controls. Gene classes related to inflammatory pathways were downregulated in flight samples cultured from the younger cohort compared to ground controls. Our muscle tissue chip platform provides an approach to studying the cell autonomous effects of spaceflight on muscle cell biology that may not be appreciated on the whole organ or organism level and sets the stage for continued data collection from muscle tissue chip experimentation in microgravity. We also report on the challenges and opportunities for conducting autonomous tissue-on-chip CubeLab™ payloads on the ISS.

Exposure to weightlessness in microgravity and elevated space radiation are associated with rapid bone loss in mammals, but questions remain about their mechanisms of action and relative importance. In this study, we tested the hypothesis that bone loss during spaceflight in Low Earth Orbit is primarily associated with site-specific microgravity unloading of weight-bearing sites in the skeleton. Microcomputed tomography and histological analyses of bones from mice space flown on ISS for 37 days in the NASA Rodent Research-1 experiment show significant site-specific cancellous and cortical bone loss occurring in the femur, but not in L2 vertebrae. The lack of bone degenerative effects in the spine in combination with same-animal paired losses in the femur suggests that space radiation levels in Low Earth Orbit or other systemic stresses are not likely to significantly contribute to the observed bone loss. Remarkably, spaceflight is also associated with accelerated progression of femoral head endochondral ossification. This suggests the microgravity environment promotes premature progression of secondary ossification during late stages of skeletal maturation at 21 weeks. Furthermore, mice housed in the NASA ISS Rodent Habitat during 1g ground controls maintained or gained bone relative to mice housed in standard vivarium cages that showed significant bone mass declines. These findings suggest that housing in the Rodent Habitat with greater topological enrichment from 3D wire-mesh surfaces may promote increased mechanical loading of weight-bearing bones and maintenance of bone mass. In summary, our results indicate that in female mice approaching skeletal maturity, mechanical unloading of weight-bearing sites is the major cause of bone loss in microgravity, while sites loaded predominantly by muscle activity, such as the spine, appear unaffected. Additionally, we identified early-onset of femoral head epiphyseal plate secondary ossification as a novel spaceflight skeletal unloading effect that may lead to premature long bone growth arrest in microgravity. This study derives results from femur and vertebrae using the micro computed tomography assay.

Spaceflight results in a number of adaptations to skeletal muscle, including atrophy and shifts towards faster muscle fiber types. To identify changes in gene expression that may underlie these adaptations, microarray expression analysis was performed on gastrocnemius from mice flown on the STS-108 shuttle flight (11 days, 19 hours) versus mice maintained on earth for the same period. Additionally, to identify changes that were due to unloading and reloading, microarray analyses were conducted on calf muscle from ground-based mice subjected to hindlimb suspension (12 days) and mice subjected to hindlimb suspension plus a brief period of reloading (3.5 hours) to simulate the time between landing and sacrifice of the spaceflight mice.

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.

Prolonged residence of mice in spaceflight is a scientifically robust and ethically ratified model of muscle atrophy caused by continued unloading. Under the Rodent Research Program of NASA we assayed the genomic and metabolomics perturbations in the quadriceps of C57BL/6j male mice that lived on the spaceflight (FLT) or at Ground Control (CTR) for approximately four weeks. Wet weight of quadriceps were significantly reduced in FLT mice. Deep next generation sequencing and untargeted mass spectroscopic assay interrogated the gene-metabolite landscape of same tissues. A majority of top ranked differentially suppressed genes in FLT encode proteins from myosin or troponin family suggesting a sarcomere alteration in space. Significantly enriched gene-metabolite networks were found linked to saromeric integrity immune fitness and oxidative stress response; all inhibited in space as per in silico prediction. A significant loss of FLT mitochondrial DNA copy numbers underlined the energy deprivation associated with spaceflight induced stress and this hypothesis was reinforced by the omics analysis that showed inhibited networks related to protein lipid and carbohydrate metabolism and ATP synthesis and hydrolysis. Finally we reported a list of upstream regulators which could be targeted for next generation therapeutic intervention for the betterment of the musculoskeletal system in male mice subjected to chronic disuse.

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.

Reduced skeletal loading leads to marked bone loss. Animal models of hindlimb suspension are widely used to assess alterations in skeleton during the course of complete unloading. More recently, the effects of partial unloading on the musculoskeletal system have been interrogated in mice and rats, revealing dose-dependent effects of partial weight bearing (PWB) on the skeleton and skeletal muscle. Here, we extended these studies to determine the structural and functional skeletal alterations in 14-week-old male Wister rats exposed to 20%, 40%, 70%, or 100% of body weight for 1, 2, or 4 weeks (n  equals 11–12/group). Using in vivo pQCT, we found that trabecular bone density at the proximal tibia declined in proportion to the degree of unloading and continued progressively with time, without evidence of a plateau by 4 weeks. Ex vivo measurements of trabecular microarchitecture in the distal femur by microcomputed tomography revealed deficits in bone volume fraction, 2 and 4 weeks after unloading. Histologic analyses of trabecular bone in the distal femur revealed the decreased osteoblast number and mineralizing surface in unloaded rats. Three-point bending of the femoral diaphysis indicated modest or no reductions in femoral stiffness and estimated modulus due to PWB. Our results suggest that this rat model of PWB leads to trabecular bone deterioration that is progressive and generally proportional to the degree of PWB, with minimal effects on cortical bone. This study derives results from the Mechanical Testing, Bone Microstructure (microCT), and bone histomorphometry assays using femur tissue.

Objective of this study was to further validate bone degradation in microgravity as site-specific and preferential to weight bearing bone. An objective of this study was to further understand the role of the mechanical environment in controlling the process of bone remodeling, namely local formation and resorption to maintain a healthy structure. These data from the lumbar 4 bones of Rodent Research-1 mission aboard the International Space Station, are unpublished, and were presented at the 2016 meeting of the American Society for Gravitational Space Research. This dataset derives results from the micro–computed tomography (mCT) assay.

The JAXA MHU-2 mission had two objectives: 1) To increase understanding of effects of spaceflight on the gut environment (microbiota and metabolites) and immune system using multi-omics based analysis; 2) To evaluate whether fructo-oligosaccharides added to the diet as prebiotics improve the gut environment and immune function during spaceflight. Twelve 16-18 week old male C57BL/6J mice were singly housed in the JAXA Habitat Cage Units (HCUs) on the ISS for 30 days. Six flight mice were housed in microgravity while six were exposed to simulated 1g by centrifugation. These two flight groups were further divided in half so that three mice in each group received standard JAXA chow while the other three were fed chow supplemented with fructooligosaccharides (FOS). Mice were returned live and euthanized and dissected <1 day after splashdown. Ground controls (n=6) were asynchronous and housed in HCUs. Vivarium controls (n=6) were asynchronous and housed in standard habitats. Three ground control and three vivarium animals received standard chow while the other three each ground control and vivarium animals received FOS-supplemented chow. Ground and vivarium samples were dissected by a separate dissection team than flight samples. Femoral skin was dissected 30 minutes after euthanasia and snap frozen in liquid nitrogen. Total RNA was extracted and sequenced at a target depth of 60 M clusters per sample (ribodepleted paired end 150). Study Factor Levels: 1)Spaceflight ug Std. Chow: 3; 2)Spaceflight ug FOS: 3; 3) Spaceflight Artificial 1g Std. Chow: 3; 4)Spaceflight Artificial 1g FOS: 3; 5)Ground 1g Std. Chow: 3; 6)Ground 1g FOS: 3; 7)Vivarium 1g Std. Chow: 3; 8)Vivarium 1g FOS: 3