OBJECTIVES:
The Rodent Research 4 (RR-4) science investigation was sponsored by the Center for Advancement of Science in Space (CASIS) and the US Department of Defense Space Test Program. The investigation was designed to examine bone healing and bone tissue regeneration, to study the impacts of microgravity on these processes, and to examine the ability of a bone healing drug (BMP-2) and a new drug (TPO) to improve bone healing in spaceflight.
Although reduced gravity induces cell proliferation and propagation, which is favorable for tissue regeneration, immunological responses are delayed in this environment. Therefore, microgravity presents a contrasting environment for the healing process. The results from this experiment may help scientists evaluate the practicality of growing complex bone tissues in spaceflight and examine molecular mechanisms underlying the negative effects of microgravity on bone density.
Specifically, this flight study had four aims:
1. To characterize the biological events associated with the healing and tissue regeneration process in spaceflight.
2. To gauge the therapeutic success of certain osteoinductive agents capable of inducing bone healing and regeneration in spaceflight.
3. To evaluate the transcriptomic, epigenomic, proteomic, metabolomic, and metagenomic (microbiome) aspects of the selected biomaterials critical for bone healing and regeneration, as well as sort and integrate the pan-omics results to discover regeneration mechanisms.
4. To use these methods to identify novel biomarkers of bone regeneration, loss, and healing.
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APPROACH:
The RR4 payload consisted of forty male C57BL/6J mice that were approximately nine to twelve weeks old. Prior to launch, at launch minus four days, the mice were segregated into four groups of ten. Three groups underwent a surgical procedure to create an artificial segmental femoral defect, after which a bone scaffold was inserted in the femur and filled with one of three substances to treat the defect: thrombopoietin (TPO), bone morphogenic protein-2 (BMP-2), and saline. The fourth group underwent a sham operation consisting of anesthesia and recovery, but received no treatment.
The mice were carried to ISS in two transporters aboard the SpaceX Commercial Resupply Mission 10 Dragon cargo spacecraft (SpaceX-10, CRS-10). After a canceled initial launch on February 18 and an aborted rendezvous with ISS on February 22, Dragon docked with the station on February 23, 2017. By February 25, 2017 the animals were transferred aboard the station. Once onboard, they were divided into four groups of ten and housed in four habitats. On-orbit operations were conducted between February 23, 2017 and March 17, 2017. Approximately one hour of video per day showing animal health and behavior was recorded in each habitat during the mission.
After about three weeks in the habitats, thirty-four of the forty animals remained. Those thirty-four animals were dissected over four days at launch plus twenty through launch plus twenty-three days. Eight mice were dissected on the first two days, and nine were dissected on the next two days. For all thirty-four mice, the dissection protocol consisted of anesthetization of the animals, exsanguination via closed chest cardiac puncture to collect blood, and cervical dislocation. For twenty of the thirty-four mice, one hind limb was removed after euthanasia and a fixative was added for tissue preservation. The remaining fourteen mice were euthanized with no dissection. All samples and carcasses were frozen on board for return to Earth. Samples and carcasses were returned on SpaceX-10 on March 19th, 2017.
Ground controls were conducted on a four-day delay at Kennedy Space Center in ISS environmental simulators (ISSESs) programmed with data from the Dragon capsule and the ISS cabin. Based on post-flight analysis of the Rodent Research 2 habitat telemetry data, the ISSESs were programmed to be two degrees Celsius higher than the ISS cabin data. The result of this temperature offset was that the internal temperatures of the ground control habitats matched the flight habitats closely for most of the experiment.
RESULTS:
Results for this experiment are not targeted for archiving.
Dadwal, U., Maupin, K., Zamarioli, A., Tucker, A., Harris J., Fischer, J., Rytlewski, J., Scofield, D., Wininger A., Ur Rehman Bhatti F., Alvarez, M., Childress P., Chakraborty N., Gautam, A., Hammamieh, R., Kacena, M. (2019). The efects of spacefight and fracture healing on distant skeletal sites. Scientific Reports, 9:11419. doi:10.1038/s41598-019-47695-3.
[DOI]
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