Task Progress:
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Spaceflight exposes physiologic systems to multiple stressors, including radiation, confinement, and lack of gravitational loading. Artificial gravity by centrifugation has been proposed as a potential countermeasure to mitigate physiologic changes due to lack of gravitational loading. Indeed, Shiba et al. (Sci Report 2017) reported that exposure of male mice to artificial gravity (at 1G) by centrifugation for 35 days on the ISS prevented deleterious musculoskeletal changes associated with microgravity. Yet, the physiologic responses to lesser magnitudes of artificial gravity are not well established. Thus, the aim of this multi-Principal Investigator (PI), multi-national collaborative study is to determine how different physiologic systems respond to various levels of partial gravity. Using the JAXA Multiple Artificial-gravity research system (MARS), adult male C57Bl/6 mice (age 12 weeks) will be exposed to either 0G, 0.33G, 0.67G, or 1G (6 mice per group) during a 30-day missing to the International Space Station. Two groups of ground controls will be utilized: one group (n=12) will be housed in identical environment as the artificial gravity cages and a second group (n=12) will be housed in normal cages in the NASA vivarium. All mice will be returned to Earth alive. Prior to launch, mice will undergo implantation of an intraperitoneal datalogger that continuously records body temperature for evaluation of circadian rhythms. Mice will also undergo a series of preflight testing, including muscle function (via grip strength), neuromotor function via gait analysis and rotarod testing, and assessment of bone mass and body composition via DXA. Fecal pellets will be collected for microbiome analyses. During flight, mice will be weighed and fecal pellets collected weekly in coordination with cage maintenance activities. Injection of fluorochromes towards the end of the flight period will facilitate assessment of bone formation rate via histomorphometry. Upon return, mice will repeat muscle function and neuromotor testing, and then tissues will be collected by each principal investigator for a variety of histologic, transcriptomic and proteomic analyses. It is expected the flight for this experiment will occur in Feb 2023.
Project Accomplishments
Study Protocol & Administrative Tasks. We have worked with the multi-PI team to create a harmonized protocol that is able to complete the scientific aims of each individual PI. The PI team has met monthly. We reviewed, edited, and approved the Science Requirements Document. We attended a kick-off meeting with the service provider, Leidos.
Ground-based Test of Fluorochrome Labels. The primary aim of this technical experiment was to determine if the fluorophores would be stable and taken up in the bone if prepared and frozen for 5 weeks and then injected into the animals. We also tested different combinations of fluorophores (Calcein green, Calcein Blue, Alizarin red, and Xylenol orange). In addition, we collected fecal samples and soleus muscle tissue for Mouse Habitat Unit (MHU) MHU-8 co-principal investigators M. Vitaterna and S. Takahashi, respectively, to determine whether the fluorochrome injections impacted their proposed outcomes.
Reference: Shiba D, Mizuno H, Yumoto A, Shimomura M, Kobayashi H, Morita H, Shimbo M, Hamada M, Kudo T, Shinohara M, Asahara H, Shirakawa M, Takahashi S. Development of new experimental platform 'MARS'-Multiple Artificial-gravity Research System-to elucidate the impacts of micro/partial gravity on mice. Sci Rep. 2017 Sep 7;7(1):10837.
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