How do mammals keep two biologically crucial metabolites in balance during times when they are feeding, sleeping, and fasting? The answer may require rewriting some textbooks. In a study published online on March 17, 2017 in Science, University of Texas (UT) Southwestern Medical Center researchers report that fat cells “have the liver’s back,” so to speak, to maintain tight regulation of glucose (blood sugar) and uridine, a metabolite the body uses in a range of fundamental processes such as building RNA molecules, properly making proteins, and storing glucose as energy reserves. The article is titled “An Adipo-Biliary-Uridine Axis That Regulates Energy Homeostasis.” The scientists’ study may have implications for several diseases, including diabetes, cancer, and neurological disorders. Metabolites are substances produced by a metabolic process, such as glucose generated in the metabolism of complex sugars and starches, or amino acids used in the biosynthesis of proteins. “Like glucose, every cell in the body needs uridine to stay alive. Glucose is needed for energy, particularly in the brain’s neurons. Uridine is a basic building block for a lot of things inside the cell,” said Dr. Philipp Scherer, senior author of the study and Director of UT Southwestern’s Touchstone Center for Diabetes Research. “Biology textbooks indicate that the liver produces uridine for the circulatory system,” said Dr. Scherer, also Professor of Internal Medicine and Cell Biology. “But what we found is that the liver serves as the primary producer of this metabolite only in the fed state. In the fasted state, the body’s fat cells take over the production of uridine.” Basically, this method of uridine production can be viewed as a division of labor.
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