Washington: Researchers have tried to explain how body temperature rhythms are synchronized while maintaining the ability to adapt to changes in environmental temperature no matter the time of day or night.
Mitchell A. Lazar, MD, PhD, director of the Institute for Diabetes, Obesity, and Metabolism at the Perelman School of Medicine, University of Pennsylvania said that food is plentiful in our present day society, and his team, including lead author Zachary Gerhart-Hines , Ph.D., found that the ability of mice to withstand a cold-temperature challenge was greater at 5:00 AM, when the mice are awake, compared to 5:00 PM when they are normally sleeping.
This previously unrecognized circadian susceptibility to cold was found to be controlled by a protein called Rev-erb alpha, which is a molecular component of the body's biological clock mechanism.
Indeed, mice engineered to lack the Rev-erb alpha protein had similar cold tolerance throughout the 24-hour day and also lost the physiological circadian rhythm of body temperature.
Rev-erb alpha's effects were produced mainly by circadian regulation in brown adipose tissue, commonly called brown fat, the body's furnace. Brown fat cells, as opposed to white fat cells, make heat for the body and are thought to have evolved to help mammals cope with the cold.
But, their role in generating warmth might also be applied to coping with obesity and diabetes.
Brown fat cells are thought to counteract obesity by burning off excess energy stored in lipid, but white fat cells store energy. Indeed, brown fat cells contain many smaller droplets of lipids and the most mitochondria (containing pigmented cytochromes that bind iron) of any cell type, which make them brown. Mitochondria are the cells' energy factories in the form of the molecule ATP.
The study has been published in the journal Nature.