Hibernation — A Bear’s Secret To Good Health
December 2, 2019 at 7:29 p.m.
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There has been a remarkable increase in hibernation research in the past few years, much directed to scientists studying obesity, which has become epidemic in the United States. Obesity in humans is associated with resistance to insulin, a hormone that regulates glucose in the blood, and Type 2 diabetes. According to one study, the bear’s handling of insulin appears to vary with the seasons, with resistance increasing during hibernation and sensitivity increasing in the summer. Strangely, obese bears are healthier and more reproductively fit than expected, and have advantages counterintuitive to human biology. In one study, researchers took samples from the liver, fat and muscle of six captive grizzly bears at three times during the year. In the lab, they analyzed the DNA to understand the changes that occur in the cells over the course of a year. They found that the effect of hibernation on each tissue is different which means that hibernation is not just as simple as hibernating and not hibernating, as there are transitional events happening throughout the year. Fatty tissue changed the most, whereas muscle tissue barely changed. The muscle cells remained active through the hibernation period, which might help explain why those tissues do not atrophy (decrease in size).
The most recent more sophisticated study published in Communication Biology from Washington State University used RNA sequencing to reveal tissue and seasonal changes occurring in grizzly bears. Comparing hibernation to other seasons, bear adipose tissue has a greater number of expressed genes than liver or skeletal muscle. Hibernation is characterized by reduced expression of genes associated with insulin signaling, muscle protein degradation, and urea production. Across all tissues there is a subset of shared differentially expressed genes, some of which are uncharacterized, that together may reflect a common regulatory mechanism. The gene families could be useful for developing novel therapeutics to treat human and animal diseases.
Other animals hibernate, too, like mountain pygmy possums in Australia, ground squirrels in North America grasslands and various species of bats. Hibernating ground squirrels use melatonin, a potent antioxidant, to protect the cells when blood flow increases after months of inactivity. This information may be used to treat hemorrhagic shock to reduce damage to tissues when blood supply returns. A team of scientists has recently identified a potential drug to use in humans to treat brain damage caused by strokes using information derived from studying hibernating ground squirrels. Nearly 800,000 Americans experience a stroke every year.
Final Thoughts
According to Bill Bryson in his new book, The Body, bears, the most famous of wintry slumberers, don’t actually hibernate. Real hibernation involves profound unconsciousness, and a dramatic fall in body temperature— to around 32 degrees. By this definition bears don’t hibernate because their body temperature is near normal and they are easily aroused. Their winter sleeps are more accurately called a state of torpor.
Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, touches on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at [email protected].
There has been a remarkable increase in hibernation research in the past few years, much directed to scientists studying obesity, which has become epidemic in the United States. Obesity in humans is associated with resistance to insulin, a hormone that regulates glucose in the blood, and Type 2 diabetes. According to one study, the bear’s handling of insulin appears to vary with the seasons, with resistance increasing during hibernation and sensitivity increasing in the summer. Strangely, obese bears are healthier and more reproductively fit than expected, and have advantages counterintuitive to human biology. In one study, researchers took samples from the liver, fat and muscle of six captive grizzly bears at three times during the year. In the lab, they analyzed the DNA to understand the changes that occur in the cells over the course of a year. They found that the effect of hibernation on each tissue is different which means that hibernation is not just as simple as hibernating and not hibernating, as there are transitional events happening throughout the year. Fatty tissue changed the most, whereas muscle tissue barely changed. The muscle cells remained active through the hibernation period, which might help explain why those tissues do not atrophy (decrease in size).
The most recent more sophisticated study published in Communication Biology from Washington State University used RNA sequencing to reveal tissue and seasonal changes occurring in grizzly bears. Comparing hibernation to other seasons, bear adipose tissue has a greater number of expressed genes than liver or skeletal muscle. Hibernation is characterized by reduced expression of genes associated with insulin signaling, muscle protein degradation, and urea production. Across all tissues there is a subset of shared differentially expressed genes, some of which are uncharacterized, that together may reflect a common regulatory mechanism. The gene families could be useful for developing novel therapeutics to treat human and animal diseases.
Other animals hibernate, too, like mountain pygmy possums in Australia, ground squirrels in North America grasslands and various species of bats. Hibernating ground squirrels use melatonin, a potent antioxidant, to protect the cells when blood flow increases after months of inactivity. This information may be used to treat hemorrhagic shock to reduce damage to tissues when blood supply returns. A team of scientists has recently identified a potential drug to use in humans to treat brain damage caused by strokes using information derived from studying hibernating ground squirrels. Nearly 800,000 Americans experience a stroke every year.
Final Thoughts
According to Bill Bryson in his new book, The Body, bears, the most famous of wintry slumberers, don’t actually hibernate. Real hibernation involves profound unconsciousness, and a dramatic fall in body temperature— to around 32 degrees. By this definition bears don’t hibernate because their body temperature is near normal and they are easily aroused. Their winter sleeps are more accurately called a state of torpor.
Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, touches on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at [email protected].
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