Understanding the brown adipocyte as a contributor to energy homeostasis

• Brown adipocytes express UCP1, which is capable of uncoupling fatty acid oxidation from ATP synthesis, leading to heat production upon stimulation.
• The presence of active brown adipocytes has been demonstrated in adult humans.
• Outdoor temperatures, age, and body fat mass affect the detection and activity of brown adipocytes in humans.
• Metabolic activity of brown adipocytes has been shown to increase energy expenditure in humans.
• Environmental, biological, or pharmacological means capable of stimulating brown adipose tissue selectively may serve to counteract obesity and diabetes.

Brown adipocytes are specialized cells capable of undergoing thermogenesis, a phenomenon regulated by the sympathetic nervous system, due to the presence of uncoupling protein 1 (UCP1). The recent demonstrations of their presence in adult humans, and the discovery that brown adipocytes can be derived from distinct precursors and express specific genes depending on their anatomic location, have sparked intense interest in enhancing the current understanding of their biology and relevance to human energy homeostasis. We provide an overview of the latest advances related to the developmental origins of brown adipocytes, discuss their regulation and function in both rodents and humans, and offer a critical perspective on the relevance of brown adipocyte-mediated thermogenesis in human physiology.