Among the physiological consequences of extended spaceflight are loss of skeletal muscle and bone mass. One signaling pathway that plays an important role in maintaining muscle and bone homeostasis is that regulated by the secreted signaling proteins, myostatin (MSTN) and activin A. Here, we used both genetic and pharmacological approaches to investigate the effect of targeting MSTN/activin A signaling in mice that were sent to the International Space Station. Wild type mice lost significant muscle and bone mass during the 33 d spent in microgravity. Muscle weights of Mstn -/- mice, which are about twice those of wild type mice, were largely maintained during spaceflight. Systemic inhibition of MSTN/activin A signaling using a soluble form of the activin type IIB receptor (ACVR2B), which can bind each of these ligands, led to dramatic increases in both muscle and bone mass, with effects being comparable in ground and flight mice. Exposure to microgravity and treatment with the soluble receptor each led to alterations in numerous signaling pathways, which were reflected in changes in levels of key signaling components in the blood as well as their RNA expression levels in muscle and bone. These findings have implications for therapeutic strategies to combat the concomitant muscle and bone loss occurring in people afflicted with disuse atrophy on Earth as well as in astronauts in space, especially during prolonged missions.

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.

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.

Spaceflight imposes the risk of skeletal muscle atrophy for astronauts. The understanding of muscle atrophy because of spaceflight is limited but continued efforts are essential for developing countermeasures of this effect. A distinct difference between spaceflight-induced muscle atrophy and other forms of atrophy is the additional effect of cosmic rays in outer space. To study spaceflight-induced muscle atrophy we performed two ground-based models of microgravity in a low dose radiation environment and studied transcriptional changes in rat soleus muscle using microarray technology.

Bone loss is one of the major health problems for astronauts during long-term spaceflight and for patients during prolonged bed rest or paralysis. Growing evidence suggests that osteocytes, the most abundant cells in the mineralized bone matrix, play a key role in sensing mechanical forces applied to the skeleton and in transducing them into subcellular biochemical signals to modulate bone homeostasis. However, the precise molecular mechanisms underlying both mechanosensation and mechanotransduction in osteocytes under the real microgravity (µG) condition are poorly understood. To unravel the mechanisms by which osteocyte, sense and responds to mechanical unloading, we exposed murine osteocytic cell line, Ocy454, seeded on a highly porous polystyrene 3D scaffold, to 2, 4, or 6 days of µG on board the International Space Station (ISS) and compared their gene expression with cells at 1G on Earth. Bioinformatics analysis of cells exposed to µG revealed several pathways differentially regulated upon exposure to microgravity.

We examined the effects of ~30 days of spaceflight on glycogen synthase kinase 3 (GSK3) content and inhibitory serine phosphorylation in murine muscle and bone samples from four separate missions (BION-M1, rodent research [RR]1, RR9, and RR18). Spaceflight reduced GSK3b content across all missions, whereas its serine phosphorylation was elevated with RR18 and BION-M1. The reduction in GSK3b was linked to the reduction in type IIA fibers commonly observed with spaceflight as these fibers are particularly enriched with GSK3. We then tested the effects of inhibiting GSK3 before this fiber type shift, and we demonstrate that muscle-specific Gsk3 knockdown increased muscle mass, preserved muscle strength, and promoted the oxidative fiber type with Earth-based hindlimb unloading. In bone, GSK3 activation was enhanced after spaceflight; and strikingly, muscle-specific Gsk3 deletion increased bone mineral density in response to hindlimb unloading. Thus, future studies should test the effects of GSK3 inhibition during spaceflight. This study derives results from the Western blot assay using tibialis anterior tissue from the RR9 mission. The tibialis anterior data in this study are related to other studies using tissues from the same experiment; OSD-654 (tibia), OSD-661 (lumbar spine), OSD-662 (soleus), OSD-663 (femur), and OSD-664 (extensor digitorum longus).

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.

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. Abbreviation Key: Sham surgical procedure done (Sh); non-surgical control (NS); Ground Control group (G); Flight Group (F); Whole Body frozen as sample on ISS (W).

During space flight bone mineral density is decreased by the influence of osteoclast activation which molecular mechanism is expectantly investigated. In the study of medaka bone development we investigated the system of vertebra formation and firstly identified the presence of osteoclasts in medaka. Moreover osteoclast rsorbing activity was affected by hypergravity indicating the possibility that we can investigate the effect of microgravity on osteoclasts in space. To find this effect we examine the alteration of osteoclast activity under microgravity with the histological analysis or the expression analysis by RNA in-situ hybridization. Furthermore since we have succeeded the establishment of the medaka osteoclast-specific transgenic lines we perform the in-vivo imaging analyses for gene expression and cell mobility. Finally to examine the gravity sensing system we employ tooth and bone as the high density organs which are highly sensitive to gravity and perform the histological analysis and the gene expression analysis of such gravity-sensitive tissues at surrounding pharyngeal teeth and supporting bone.

During space flight bone mineral density is decreased by the influence of osteoclast activation which molecular mechanism is expectantly investigated. In the study of medaka bone development we investigated the system of vertebra formation and firstly identified the presence of osteoclasts in medaka. Moreover osteoclast rsorbing activity was affected by hypergravity indicating the possibility that we can investigate the effect of microgravity on osteoclasts in space. To find this effect we examine the alteration of osteoclast activity under microgravity with the histological analysis or the expression analysis by RNA in-situ hybridization. Furthermore since we have succeeded the establishment of the medaka osteoclast-specific transgenic lines we perform the in-vivo imaging analyses for gene expression and cell mobility. Finally to examine the gravity sensing system we employ tooth and bone as the high density organs which are highly sensitive to gravity and perform the histological analysis and the gene expression analysis of such gravity-sensitive tissues at surrounding pharyngeal teeth and supporting bone.