Each fall, grizzly bears pack on the pounds for hibernation. In humans, this extreme weight gain would probably lead to diabetes or other metabolic diseases, but the bears manage to stay healthy year after year. Their ability to remain free diabetes, researchers have now discovered, can be chalked up to the closure of a protein found in fat cells. The discovery could lead to new drugs against diabetes that off the same way in humans.
The results are "provocative and interesting," said Sandy Martin biologist at the University of Colorado, Denver, who was not involved in the new work. "They found a natural solution to a problem we have not been able to solve."
As people gain weight, fat, liver and muscle cells generally become less sensitive to the hormone insulin, which normally help-levels and sugar levels of insulin control blood increase . In turn, the increase in insulin prevents the breakdown of fat cells, which causes a vicious cycle which can lead to insulin resistance in its own right, or diabetes.
The development of new drugs against diabetes has been hampered by the fact that the results of many diabetes mouse models are not translated to humans. So Kevin Corbit, senior researcher at the company's California-based drug Thousand Oaks, Amgen, decided to start looking at obesity and metabolic diseases in other animals. "When I thought of things that are very large, one of the first things I thought the bear was, and what they do to prepare to go into hibernation," he said. "But of course you do not see the bear run with diabetes and heart disease."
Corbit and scientists from Washington State University Bear Center in Pullman measured blood sugar levels, insulin levels, body weight, and other markers of metabolism in six captive grizzly bears before, during and after hibernation in October, January and May. Surprisingly, even that each bear has won over a hundred books in the fall, their cells remained sensitive to insulin, and insulin levels and blood sugar remained constant. In people, such a huge weight gain might cause insulin resistance. It was not until well after they had started hibernating bears that have experienced a temporary seasonal episode of insulin resistance, but even that was completely reversed come spring. "This type of physiology has never been described before and was completely opposite to what is seen in humans," said Corbit.
When he and his colleagues analyzed the levels of several molecules blood cells, liver and fat bears, they discovered that controlled the insulin sensitivity and resistance independent of weight gain or loss: a protein called PTEN in the fall. bears have versions of PTEN has switched off in their fat cells, the team reports today in Corbit cell Metabolism . As a result, the cells continue to respond to the insulin- and signals to store the sugar itself that the bears are gaining weight. for the bears, the stop protein helps maximize the storage of sugar in their bodies for the long winter ahead.
discovery could also help humans, said Corbit. Because PTEN cut aid obese bears maintain insulin sensitivity, the deactivation pathway in overweight people could prevent or treat diabetes, he suggests. Interestingly, he noted, a previous study showed that missing a gene for the production of PTEN are less likely to develop metabolic cardiovascular disease or even they gain weight. These people develop other conditions, including cancer, but Corbit suspect that is because PTEN levels are the body to the diminished scale. If scientists were able to extinguish only in fat cells are like bears, these side effects can be reduced.
specialist in metabolic diseases Abhimanyu Garg at the University of Texas Southwestern Medical Center in Dallas said that more evidence is needed to support any link between the finding of the bear and human diabetes. And you have to be careful with a drug that deactivates PTEN, even if it is only in fat cells, he said. Even if we could treat diabetes, it could also lead to increased weight gain. After all, it helps the bears store up their winter fat, Garg notes. "You can create a situation where patients are metabolically healthy but you are shopping for joint problems and back problems and arthritis."
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