Japan is participating in the International Space Station (ISS) Program conducted by the world’s largest international cooperation of 15 countries, including the United States of America, Russia, Canada, and several European countries. The ISS is a human-tended laboratory flying approximately 400 km above the Earth’s surface.
Japan launched and attached the Japanese Experiment Module (named “Kibo”) to the ISS in 2008. It is used as a laboratory to conduct experiments involving the unique space environment which is exposed to long-term microgravity and the various types of space radiation which cannot be recreated on Earth.
JAXA has promoted life science research using the “Kibo” space laboratory to contribute to studies relevant to human health, aging and disease on Earth. After lengthy periods living in space, even healthy astronauts experience detremental symptoms as a result of their living and working environment. These symptoms include weakened bones and muscles, and a degraded sense of balance. This is similar to those associated with aging on Earth except that they progress over 10 times faster in space.
In this context, since 2013 we have developed a new rodent (mouse) research capability on Kibo. In particular, we have developed a mouse habitation system that can rear mice under an artificial gravity environment using an on-orbit centrifuge, as a unique research facility aboard the ISS. This enables us to evaluate gravitational effects on mammals in space precisely by allowing a comparison between microgravity (µG) and artificial gravity (AG) conditions. We can rear mice over extended terms under partial gravity (lower gravity than 1 g) conditions, including simulated lunar (1⁄6 g) and Martian gravity (3⁄8 g) conditions which will contribute to studies for future human exploration in space.
Fig 1. Newly developed mouse cages for the space experiment. (a) Habitat Cage Unit (HCU). The HCU accommodates one mouse per cage. 1: Water tank, 2: Camera/LED, 3: Temperature sensor, 4: Washer water inlet, 5: Water nozzles, 6: Wiper for camera, 7: Food cartridge, 8: Polycarbonate floor/walls. A 7-day supply of food and water is provided inside the HCU. (b) Transportation Cage Unit (TCU). The TCU contains 12 cylindrical cages in one unit. Each cylindrical cage accommodates one mouse. The TCU supports up to a 10-day supply of food and water during the launch and landing phases. 1: Housing area with food, 2: Water tank, 3: Food, 4: Water nozzle, 5: Polycarbonate floor/walls. © Centrifuge-equipped Biological Experiment Facility (CBEF). The CBEF has two compartments: the micro-g section and the artificial-g section with a centrifuge. (d) AG section. The centrifuge accommodates six HCUs and has a rotation radius of 0.15 m where it contacts the floor
In August 2016, we accomplished the first mission titled “Transcriptome analysis and germ cell development analysis of mice in the space” (Principal Investigator: Satoru Takahashi, Univ. of Tsukuba) which included the world’s first long term (35 days) rearing of mice in both microgravity and artificial gravity conditions. Twelve live mice were successfully returned to Earth after habitation on the ISS.
JAXA plans to further promote and investigate research in the area of osteoporosis and muscle atrophy, leading to research of ageing and the gravity sensing mechanism related to these symptoms, as well as the genetic and epigenetic changes caused by aging and environmental factors.
Given that JAXA’s mouse habitation system is the world’s only existing research platform able to provide partial gravity environments for mammals in space, we also promote its use as a research testbed for international human space flight exploration activities to the Moon, Mars and beyond.
Fig 2. Effects of microgravity on vestibular function, skeletal muscle and bone. (a) Mid-air righting reflex test. AG (n = 5), MG (n = 6) and GC (n = 6). (b) Rotarod performance test. AG (n = 6), MG (n = 6) and GC (n = 5). *P < 0.05. © Body-weight-normalized skeletal muscle masses from AG (n = 5), MG (n = 4) and GC (n = 6) mice. *P < 0.05. (d) Representative vertical (upper) and horizontal (lower) sectional microCT photos of the proximal region of the femur. Scale bars = 1 mm. (e) The calculated cancellous bone volume/tissue volume (BV/TV, %) of the femurs of AG (n = 6), MG (n = 5) and GC (n = 6) mice. *P < 0.05.
Development of new experimental platform ‘MARS’—Multiple Artificial-gravity Research System—to elucidate the impacts of micro/partial gravity on mice, Scientific Reports, 7:10837, doi: 10.1038/ s41598-017-10998-4, 2017.
Professor Masaki Shirakawa (教授 白川正輝)
Japan Aerospace Exploration Agency (JAXA)