The incredible ability of bears to hibernate for months at a time has inspired some interesting lines of research around how their secrets might benefit human health, and among them is a focus on muscle wasting. Scientists in Japan have made a fascinating discovery in this space, demonstrating how human muscle cells can be infused with serum from hibernating black bears to not just prevent atrophy, but actively promote an increase in mass.
Where humans can begin losing muscle mass within weeks of inactivity, hibernating bears can stay still for up to seven months without eating or drinking and without severe impacts on their health. They do this after gorging on food in the summer and autumn to build up fat stores and then endure the winter without doing much at all, all the while resisting ailments like heart disease, diabetes and cancer.
Scientists have studied this phenomenon in hopes of unlocking new treatments for obesity and muscle atrophy, while studies into other hibernating creatures like zebrafish have hinted at ways we might be able to endure inhospitable environments. This could be pivotal when it comes to deep space travel, with the high levels of radiation known to pose a range of risks to human health.
This new study focused on skeletal muscle, which is susceptible to wasting caused by immobility. Led by scientists at Hiroshima University and Hokkaido University, the research team took cultured human skeletal muscle cells and infused them with serum drawn from the blood of hibernating black bears, which led to significant protein growth after 24 hours. Importantly, serum collected during the bears' active summer season did not induce these same effects.
The scientists believe this is due to a factor in the hibernating bear serum that suppresses a "destruction mechanism" behind muscle degradation, which normally kicks into action when we don't use them. Bears are able to resist this "use it or lose it" phenomenon with regard to their muscle mass, which the scientists attribute to the suppression of a protein called MuRF1 that activates the shredding of unused muscles. Their next steps involve identifying the hormones and pathways that suppress this key protein.
“We have indicated that ‘some factor’ present in hibernating bear serum may regulate protein metabolism in cultured human skeletal muscle cells and contribute to the maintenance of muscle mass," said study first-author Mitsunori Miyazaki. "However, the identification of this 'factor' has not yet been achieved."
Doing so could open up some exciting possibilities around protecting humans during deep space travel, or preventing muscle wastage in people who are immobile due to aging or disease.
“By identifying this ‘factor’ in hibernating bear serum and clarifying the unexplored mechanism behind ‘muscles that do not weaken even without use’ in hibernating animals, it is possible to develop effective rehabilitation strategies in humans and prevent becoming bedridden in the future," said Miyazaki.
The research was published in the journal PLOS One.
Source: Hiroshima University
