Chuck Bednar for redOrbit.com – Your Universe Online
Researchers from the Stanford University School of Medicine have for the first time discovered evidence of the existence of limostatin, a long-suspected hormone that decreases insulin in both flies and humans, according to research published Tuesday in the journal Cell Metabolism.
That hormone, which was named for the Greek goddess of starvation, Limos, lessens insulin levels during recovery from fasting or starvation, according to the study authors. By doing so, it ensures that essential nutrients remain in the blood stream long enough to rebuild injured tissues instead of being quickly ferried into fat cells where it is far less accessible.
Senior author Dr. Seung Kim, a professor of developmental biology at Stanford, lead author and graduate student Ronald Alfa, and their colleagues initially discovered limostatin in fruit flies. Shortly thereafter, however, they found a protein in humans which performed a similar function.
“Starvation or famine is an ancient, ever-present specter faced by all living organisms,” Dr. Kim explained. “The ways to deal with it metabolically are likely to be ancient and conserved. This research clearly connects the dots between flies and humans, and identifies a new potential way to regulate insulin output in humans.”
Specifically, a family whose members possess an inherited mutation in the human version of the hormone exhibited many of the same physiological characteristics as flies that had been modified to be unable to produce limostatin. Among those traits were elevated levels of circulating insulin, low levels of blood sugar and a tendency towards early onset obesity, the authors explained.
Limostatin
Limostatin is part of a class of hormones known as decretins, which scientists have speculated about for the past 150 years. In 1932, a class of hormones known as incretins (which were expressed in the gut following a meal and stimulated the secretion of insulin) were identified for the first time. Other metabolic studies suggested that there might be another hormone that might suppress insulin production during times of famine or starvation.
Furthermore, the discovery of the decretin limostatin helps validate the use of fruit flies as a model to study diabetes in humans, Dr. Kim added. It could also help explain a phenomenon that sometimes occurs following bariatric surgery, in which the removal of a portion of the stomach to enable weight loss rapidly reverses signs of diabetes before any weight loss is observed.
“Your body has multiple checks and balances to control insulin production,” explained Dr. Kim. “We believe it’s likely that the decretin pathway acts as a sensing and regulatory method in many other situations in addition to starvation. Perhaps this is one possible explanation for the effect of bariatric surgery.”
The hormone was identified by virtue of its response to fasting. The researchers withheld food from laboratory fruit flies for 24-28 hours, then checked to see which types of genes were highly expressed during this period. They then narrowed down the list to those that encoded proteins resembling hormones, and found one that caused characteristics of insulin deficiency when overexpressed in flies.
“This work has critical ramifications for our understanding of metabolism, and has the potential to transform our approach to treating diseases like diabetes,” said Dr. Domenico Accili, director of the Columbia University Diabetes and Endocrinology Research Center who was not involved in the research.
“The discovery of limostatin, a new hormone that can act to decrease insulin release, is an important advance,” he added. “The notion that mammals express a related family of intestinal hormones that can affect insulin secretion may inform new efforts to find drugs that combat diabetes in humans.”
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