Brown adipose tissue (BAT) is an organ recently discovered to be functional in adults. In mammals, BAT contributes to the heat generated during standard physiological non-shivering thermogenesis and may also play a role in protection from weight gain and insulin resistance in both rodents and humans. At the cellular level, brown adipocytes regulate energy expenditure through their numerous, large mitochondria. In the inner mitochondrial membrane is the BAT-specific uncoupling protein 1 (UCP1), which when activated dissipates the intermembrane proton-motive force and generates heat instead of ATP.
The thermogenic capacity of BAT is impressive. In a cold-acclimatized animal models, oxygen consumption by BAT is approximately twice the normal whole-body basal metabolic rate. Until recently BAT was thought to be nonexistent and metabolically irrelevant in adult humans, in part because there were no methods to localize and quantify BAT mass and measure its activity.
Using a combination of molecular techniques and whole-body imaging, we have shown that BAT is present in adult humans in defined regions; more frequently found in women than men, and has an activity that correlates inversely with age and obesity, suggesting a potential role of brown adipose tissue in adult human metabolism.
Current translational research projects in the lab focus on brown and white adipose tissue function, energy balance, clinical physiology, and imaging in collaboration with multiple groups within the Intramural Research Program and Harvard Medical School.
BAT may contribute to three different facets of human physiology - energy balance, fuel utilization, and the regulation of metabolism. Answering the following three questions is the ultimate goal of our research:
- To what extent does adult human BAT contribute to increased energy expenditure?
- What is the intracellular response of human brown adipocytes to adrenergic stimulation, and how could this impact whole-body glucose and triglyceride metabolism?
- How does activated human BAT interact with other tissues as an endorince organ?