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Unlocking the secrets of brown fat



Brown fat, or thermogenic adipose tissue, appears to act as a “nutrient sink,” consuming glucose and lactate, among other metabolites, say U.S. researchers in a mouse study that supports its potential role in tackling obesity and even cancer.

The research, published recently in Nature Metabolism, was led by David A. Guertin, PhD, of the program in molecular medicine, University of Massachusetts, Worcester.

To find out more about the study, its clinical implications, and whether the results are translatable to humans, this news organization interviewed Dr. Guertin, asking him to explain some of the concepts behind the research.

What is adaptive thermogenesis, and why is it important in temperature regulation?

Adaptive thermogenesis is a physiologic process that occurs in a special type of fat cell, called a brown adipocyte, in which intracellular stored lipids and nutrients taken up from the blood are catabolized to generate heat.

The heat generated by these thermogenic adipocytes is critical for warming the blood and maintaining body temperature in cold environments, and is especially critical in human infants and small mammals, which are more sensitive to low temperatures.

The process is stimulated by the sympathetic nervous system, especially in response to feeling cold, but it can be activated by other stresses as well.

While adaptative thermogenesis is also called nonshivering thermogenesis to distinguish it from muscle shivering, both means of generating heat can work together to maintain body temperature.

Why is it considered a potential target for obesity?

Adult humans have brown adipocytes in specific locations in the body called brown adipose tissues (BAT) or, more simply, “brown fat.”

Intriguingly, clinical data show that the more BAT you have, the more likely you are to be protected against cardiometabolic disorders associated with obesity.

Since obesity results from an imbalance between energy intake and energy expenditure, one model proposes that brown adipocytes rebalance this formula by expending the excess energy (calories) as heat rather than storing it.

This has been referred to as the “nutrient sink” model, and the ability to activate this process therapeutically is a very attractive antiobesity strategy.

Why was it important to understand which circulating metabolites BAT uses for thermogenesis?

It is still not clear why brown fat is so beneficial for human health, and thus there is strong rationale for understanding its metabolism and how it cooperates with other tissues in the body.

For example, prior to our work, the field lacked a broad quantitative picture of how much any individual nutrient from the blood was used by brown fat, or which specific nutrients brown fat prefers to use to make heat – such as lipids, glucose, amino acids, etc. Knowing this information helps us identify more precise strategies to activate brown fat.

In addition, circulating metabolites sometimes also have messenger functions, similar to those of hormones, that stimulate physiologic processes such as adaptative thermogenesis. Highly metabolic tissues also put metabolites back into the blood, which can send messages to the brain and other tissues.

We don’t have a lot of information yet on how brown fat might engage in these processes, and so our study also aimed at finding these special metabolite messengers.


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