Satoko Uchida

Microgravity promotes osteoclast activity in medaka fish reared at the international space station

The bone mineral density (BMD) of astronauts decreases specifically in the weight-bearing sites during spaceflight. It seems that osteoclasts would be affected by a change in gravity; however, the molecular mechanism involved remains unclear. Here, we show that the mineral density of the pharyngeal bone and teeth region of TRAP-GFP/Osterix-DsRed double transgenic medaka fish was decreased and that osteoclasts were activated when the fish were reared for 56 days at the international space station. In addition, electron microscopy observation revealed a low degree of roundness of mitochondria in osteoclasts. In the whole transcriptome analysis, fkbp5 and ddit4 genes were strongly up-regulated in the flight group. The fish were filmed for abnormal behavior; and, interestingly, the medaka tended to become motionless in the late stage of exposure. These results reveal impaired physiological function with a change in mechanical force under microgravity, which impairment was accompanied by osteoclast activation.

NASDA aquatic animal experiment facilities for space shuttle and ISS

National Space Development Agency of Japan (NASDA) has developed aquatic animal experiment facilities for NASA Space Shuttle use. Vestibular Function Experiment Unit (VFEU) was firstly designed and developed for physiological research using carp in Spacelab-J (SL-J, STS-47) mission. It was modified as Aquatic Animal Experiment Unit (AAEU) to accommodate small aquatic animals, such as medaka and newt, for second International Microgravity Laboratory (IML-2, STS-65) mission. Then, VFEU was improved to accommodate marine fish and to perform neurobiological experiment for Neurolab (STS-90) and STS-95 missions. We have also developed and used water purification system which was adapted to each facility. Based on these experiences of Space Shuttle missions, we are studying to develop advanced aquatic animal experiment facility for both Space Shuttle and International Space Station (ISS).

Involvement of splenic iron accumulation in the development of nonalcoholic steatohepatitis in Tsumura Suzuki Obese Diabetes mice.

Nonalcoholic steatohepatitis (NASH) is a common hepatic manifestation of metabolic syndrome and can lead to hepatic cirrhosis and cancer. It is considered that NASH is caused by multiple parallel events, including abnormal lipid metabolism, gut-derived-endotoxin-induced inflammation, and adipocytokines derived from adipose tissue, suggesting that other tissues are involved in NASH development. Previous studies demonstrated that spleen enlargement is observed during the course of NASH pathogenesis. However, the involvement of splenic status in the progression of NASH remains unclear. In this study, we examined hepatic and splenic histopathological findings in the early stage of NASH using the Tsumura Suzuki Obese Diabetes (TSOD) mouse model established for assessing NASH. We found that 12-week-old TSOD mice clearly exhibited the histopathological features of NASH in the early stage. At this age, the spleen of TSOD mice showed markedly higher iron level than that of control Tsumura Suzuki Non Obesity (TSNO) mice. The level of accumulated iron was significantly decreased by feeding a diet with glucosyl hesperidin, a bioactive flavonoid, accompanied with alleviation of hepatic lesions. Furthermore, we found that splenic iron level was positively correlated with the severity of NASH manifestations, suggesting that abnormalities in the spleen are involved in the development of NASH.

Acute transcriptional up-regulation specific to osteoblasts/osteoclasts in medaka fish immediately after exposure to microgravity

Bone loss is a serious problem in spaceflight; however, the initial action of microgravity has not been identified. To examine this action, we performed live-imaging of animals during a space mission followed by transcriptome analysis using medaka transgenic lines expressing osteoblast and osteoclast-specific promoter-driven GFP and DsRed. In live-imaging for osteoblasts, the intensity of osterix- or osteocalcin-DsRed fluorescence in pharyngeal bones was significantly enhanced 1 day after launch; and this enhancement continued for 8 or 5 days. In osteoclasts, the signals of TRAP-GFP and MMP9-DsRed were highly increased at days 4 and 6 after launch in flight. HiSeq from pharyngeal bones of juvenile fish at day 2 after launch showed up-regulation of 2 osteoblast- and 3 osteoclast- related genes. Gene ontology analysis for the whole-body showed that transcription of genes in the category “nucleus” was significantly enhanced; particularly, transcription-regulators were more up-regulated at day 2 than at day 6. Lastly, we identified 5 genes, c-fos, jun-B-like, pai-1, ddit4 and tsc22d3, which were up-regulated commonly in the whole-body at days 2 and 6, and in the pharyngeal bone at day 2. Our results suggested that exposure to microgravity immediately induced dynamic alteration of gene expression levels in osteoblasts and osteoclasts.

Histological and Transcriptomic Analysis of Adult Japanese Medaka Sampled Onboard the International Space Station

To understand how humans adapt to the space environment, many experiments can be conducted on astronauts as they work aboard the Space Shuttle or the International Space Station (ISS). We also need animal experiments that can apply to human models and help prevent or solve the health issues we face in space travel. The Japanese medaka (Oryzias latipes) is a suitable model fish for studying space adaptation as evidenced by adults of the species having mated successfully in space during 15 days of flight during the second International Microgravity Laboratory mission in 1994. The eggs laid by the fish developed normally and hatched as juveniles in space. In 2012, another space experiment (“Medaka Osteoclast”) was conducted. Six-week-old male and female Japanese medaka (Cab strain osteoblast transgenic fish) were maintained in the Aquatic Habitat system for two months in the ISS. Fish of the same strain and age were used as the ground controls. Six fish were fixed with paraformaldehyde or kept in RNA stabilization reagent (n = 4) and dissected for tissue sampling after being returned to the ground, so that several principal investigators working on the project could share samples. Histology indicated no significant changes except in the ovary. However, the RNA-seq analysis of 5345 genes from six tissues revealed highly tissue-specific space responsiveness after a two-month stay in the ISS. Similar responsiveness was observed among the brain and eye, ovary and testis, and the liver and intestine. Among these six tissues, the intestine showed the highest space response with 10 genes categorized as oxidation–reduction processes (gene ontogeny term GO:0055114), and the expression levels of choriogenin precursor genes were suppressed in the ovary. Eleven genes including klf9, klf13, odc1, hsp70 and hif3a were upregulated in more than four of the tissues examined, thus suggesting common immunoregulatory and stress responses during space adaptation.