By Kaylie Shaver, WSU veterinary student, research scholar and summer research fellow
During their active season, bears’ fat cells are sensitive to a hormone called insulin which helps them to convert glucose in their food into fat that will fuel them during winter hibernation. During hibernation, the fat cells lose this sensitivity to insulin, allowing them to utilize their fat stores for energy.
When they finish hibernation, they regain that insulin sensitivity. The bears do not seem to exhibit any ill effects during this period of insulin resistance. However, if a human or a pet were to become insulin resistant, they would be considered diabetic and would experience symptoms such as extreme hunger and thirst, frequent urination and blurred vision to name a few.
Without treatment for diabetes, they may even die from complications. This phenomenon has led researchers to ask: how do bears tolerate their insulin resistance without negative side effects? And how do they reverse their essentially diabetic state every spring?
The body’s internal clock, or circadian rhythm, plays an important role in regulating metabolism and preventing the development of metabolic diseases like obesity and diabetes. Circadian rhythms are an evolutionary adaptation that help to coordinate physiological processes (hormone production, immune function, fat storage, etc.) with external environmental cues such as daylight.
These rhythms are generated in various tissues throughout the body by a group of genes aptly named ‘clock’ genes. It has become abundantly clear that disruption to circadian rhythms can alter metabolism and lead to weight gain and related health problems.
These health problems are commonly seen in people who are awake and functioning during the time their body’s clock would prefer them to be asleep, like shift workers. However, nighttime exposure to light (phones, computers, tvs, etc.), late bedtimes, and midnight snacks can be just as detrimental to a body’s circadian rhythm. Interestingly, veterinarians are seeing an increase in obesity and diabetes in pets as well, likely because a pet’s lifestyle mirrors that of its owner.
Our research at the WSU Bear Center this summer will investigate whether the grizzlies’ fat cells exhibit a circadian rhythm of glucose uptake and how this rhythm differs between cells from the active season versus hibernation. Fat and serum samples are collected from the bears during their active season as well as during hibernation, and then processed in the lab and cultured for experiments.
By investigating the role of circadian rhythms in grizzly bear metabolism, we hope to better understand how bears avoid developing diabetes and other metabolic diseases despite their unique lifestyle. This may lead to new and improved methods for treating or preventing these diseases in humans and companion animals.