August 7, 2014
What Can Grizzly Bears Tell Us About Diabetes And Obesity?
April Flowers for redOrbit.com - Your Universe Online
Diabetes rates are continuing to rise globally, affecting the lives of millions of people. With such high rates, it seems feasible to ask if the condition serves any biological purpose. A new study, published in Cell Metabolism, reveals that grizzly bears have a natural state of diabetes, which not only serves a biological purpose, it is also reversible.
The researchers note that grizzly bears are obese, but not diabetic, in the fall. During hibernation, however, they become diabetic. The condition seemingly cures itself when they wake up in the springtime. The findings demonstrate how much we still have to learn about how animals cope with conditions that would cause disease in humans from observing natural biology and evolutionary experimentation.
According to the Wall Street Journal, grizzly bears can take in as much as 58,000 calories a day and weigh over 1,000 pounds. They can lift a heavy tree trunk with one paw, and take on wolves and mountain lions — and win. But these aren't the qualities that the researchers were concerned with. Ursus arctos horribilis, or the grizzly bear, spend their entire lives obese, dealing with weight gain in a way that rats could never imitate.
A person has Type 2 diabetes when their cells lose the ability to respond to insulin. The research team, led by Dr. Kevin Corbit of Amgen, Inc., found that in grizzly bears, unlike in humans, insulin levels in the animals’ blood do not change. Instead, the bears' cells that communicate with insulin are able to turn off and on their ability to respond to the hormone. More surprising, when the grizzlies are at their most obese, they are also the most insulin sensitive, or least diabetic. They are able to do this by deactivating a protein called PTEN in fat cells.
"This is in contrast to the common notion that obesity leads to diabetes in humans," Corbit said in a Cell Press statement. Liver and muscle tissue are common places for fat to accumulate in other animals with obesity, but grizzlies store all of the fuel that they need during hibernation in fat tissue, instead.
The researchers say that their findings highlight how complex the relationship between obesity and diabetes really is. "Our results clearly and convincingly add to an emerging paradigm where diabetes and obesity—in contrast to the prevailing notion that the two always go hand-in-hand—may exist naturally on opposite ends of the metabolic spectrum," explained Dr. Corbit. "While care must be taken in extrapolating preclinical findings to the care of particular patients, we believe that these and other data do support a more comprehensive and perhaps holistic approach to caring for patients with diabetes and/or obesity," he added.
According to Corbin, the cellular mechanisms that lead to obesity in certain people could also be protecting them from diabetes, and the mechanisms that lead to diabetes in other people might protect them from becoming obese. For example, humans with low PTEN levels are exquisitely insulin sensitive, even if they are obese.
"Moving forward, this more sophisticated understanding of the relationship between diabetes and obesity should enable researchers not only to develop therapies targeting these mechanisms, but also to identify the appropriate patients to whom these therapies should be targeted."
Corbin intends to continue his research, over the next two years, exploring how the bears are able to maintain this balance between obesity and diabetes by sequencing the bears' genome.
"That would really accelerate the discovery research for bears," he concluded.