Hibernation + human spaceflight

Astronauts in hibernation-like states have long been a fixture of sci-fi. While this is usually more fiction than science, the reality is that certain hibernation-related metabolic traits have the potential to mitigate major logistical and biological challenges of human spaceflight*. For this reason, some of the world’s leading space administrations, including CSA, NASA and ESA, are pursuing the translation of these traits as potential countermeasures, and the Regan Lab is involved in some of this work.

 

Logistically, inducing states of metabolic depression in crewmembers would reduce rates at which they use consumables such as food, water, O2, and CO2 scrubbers. This would reduce demands on spacecraft mass, volume and power capacities, which, due to the constraints these capacities place on launch limits, could make long-duration missions more cost-effective and thus feasible.

 

Biologically, hibernation metabolism may benefit spaceflight in multiple ways. For example, a major biological challenge of the deep space environment is chronic radiation exposure. Any object outside of Earth’s protective Van Allen belts is bathed in ionizing radiation from the sun and cosmos generally, a major hazard to humans in deep space due to the damage this causes biologically important molecules such as DNA. Amazingly, torpid ground squirrels are remarkably resistant to lethal doses of space-type radiation. Active ground squirrels are not, suggesting torpor per se confers radioprotection. Thus, inducing states of metabolic depression in crewmembers may help protect them from space radiation.

 

Another major biological challenge of the spaceflight environment is chronic exposure to micro- (or zero-) gravity, which reduces load on muscles and bones and leads to rapid muscle atrophy and bone density loss. As we’ve discussed, hibernating mammals are remarkably resistant to muscle atrophy and bone density loss over their hibernation seasons, which is an analogous situation to microgravity because the many months of inactivity during winter similarly reduce load on muscles and bones. A contributing factor to this muscle atrophy resistance is the gut microbially dependent urea nitrogen salvage process that we study in the Regan Lab. Translating this process to crewmembers – or more specifically, enhancing this process, as humans are capable of modest degrees of urea nitrogen salvage – could help preserve crewmember muscle mass and performance. We are currently investigating this potential countermeasure in the lab.

 

*Hibernation’s benefits to spaceflight would not necessarily require that all aspects of the complex hibernation phenotype be recapitulated in astronauts/crewmembers – the limits of human physiology would probably make this impossible. Rather, certain metabolic processes related to hibernation could be harnessed to mitigate specific challenges of spaceflight that have analogous challenges of hibernation. One example is microbe-dependent nitrogen recycling to sustain tissue protein balance amid long periods of inactivity, but there are other examples too. The upshot is that astronauts could benefit from hibernation metabolism without the complexity of inducing, sustaining and recovering from states of deep torpor in the austere spacecraft environment. We feel that this is a critically important point to make when discussing hibernation applications to spaceflight and biomedicine.

 

Key publications:

Regan MD, Flynn-Evans EE, Griko YV, Kilduff TS, Rittenberger JC, Ruskin K, Buck CL. 2020. Shallow metabolic depression and human spaceflight: a feasible first step. Journal Applied Physiology 128, 637-647.

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Griko Y, Regan MD. 2018. Synthetic torpor: A method for safely and practically transporting experimental animals aboard spaceflight missions to deep space. Life Sciences in Space Research 16, 101-107.

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