The long-range goal of this research was to identify and characterize the omics and biochemical mechanisms that underlie the changes in cardiovascular and musculoskeletal function following prolonged space flight. It is well established that microgravity elicits central and peripheral decrements within the cardiovascular system. Traditional cardiovascular measurements have demonstrated significant decreases in left ventricular volume and mass within only a few weeks of exposure. Similarly, human and animal models suggest that microgravity exposure significantly alters vasomotor reactivity to various physiologic stressors. However, despite the recognition that cardiovascular function is decreased with prolonged microgravity exposure, the mechanistic underpinnings of these changes are not completely understood. In addition to changes within the cardiovascular system, significant decreases in bone health occur with prolonged microgravity. These changes are mediated, in part, due to general deconditioning and muscular/mechanical unloading that occurs with microgravity. As such, the average monthly rate of loss in areal bone mineral density can reach 1.0-1.5% when measured over a 14 month period. Given the significant and time-dependent changes in cardiovascular function and bone health associated with microgravity exposure, a continued evaluation of these systems is required, particularly within the genomic and biochemical sciences.
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Eleven participants (five women, six men) completed a 30 day head down bed rest (HDBR) period at the :envihab bed rest facility located at the institute for Aerospace Medicine in Cologne Germany. The bed rest consisted of three phases: (1) baseline control experiments pre bed rest; (2) a 30 day period of -6° head-down tilt bed rest without countermeasures with an ambient CO2 of 0.5% consistent with the average levels on the International Space Station; and (3) post bed rest experiments. Blood sampling for complete blood count and c-miRNA analysis was performed on BDC-3 and immediately upon completion of the bed rest period (R+0). All blood samples were obtained following an overnight fast with no exercise eight hours prior.
This work found significant alterations in cardiovascular-health related c-miRNAs following 30 days sedentary HDBR. Importantly, several of these c-miRNAs were significantly correlated with changes in stroke volume, cardiac output, and maximal aerobic exercise capacity. The investigators speculate that miRNA may play an epigenetic effect on modulating the cardiovascular responses associated with prolonged microgravity exposure. Future work will need to confirm these results in a larger bed rest cohort and in the true space flight environment. In addition, serum levels of miRNAs associated with bone and muscle function (miRNA-21, -100, -125b, -126) were analyzed using qPCR. Sclerostin and TRAP5b concentrations were assayed using commercial ELISA kits. TRAP 5b (p=0.001) and sclerostin (p=0.05) significantly increased post bed rest. miRNA-21 was significantly upregulated (p = 0.019) from pre to post bed rest. miRNA-125b showed a trend (p = 0.11) for upregulation with 10 participants showing increased expression and 1 showing decreased expression post bed rest.
Crew health and performance is critical to successful human exploration beyond low Earth orbit.
The Human Research Program (HRP) investigates and mitigates the highest risks to human health
and performance, providing essential countermeasures and technologies for human space exploration.
Risks include physiological and performance effects from hazards such as radiation, altered gravity,
and hostile environments, as well as unique challenges in medical support, human factors,
and behavioral health support. The HRP utilizes an Integrated Research Plan (IRP) to identify
the approach and research activities planned to address these risks, which are assigned to specific
Elements within the program. The Human Research Roadmap is the web-based tool for communicating the IRP content.
The Human Research Roadmap is located at: https://humanresearchroadmap.nasa.gov/
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for information of how this experiment is contributing to the HRP's path for risk reduction.