Functional differentiation of white and brown adipocytes

Adipose tissue plays an important role in mammalian energy equilibrium not only as a lipid-dissipating, i.e. energy-storing, tissue (white adipose tissue), but also as an energy-dissipating one (brown adipose tissue). Brown adipocytes have the ability of facultative heat production due to a unique mitochondrial protein, the uncoupling protein (UCP). Differentiation of white and (to a lesser extent) brown adipocytes has been studied in different cell culture systems, which has led to the identification of external inducers, second messenger pathways and transcription factors involved in adipocyte differentiation. Functional differentiation of white adipocytes implies adipose conversion, whereas in brown adipocytes it insinuates additionally the development of a thermogenic function. This review discusses recent advances in the elucidation of the pathways responsible for, and the molecular bases of, adipose conversion on the one hand and development of the thermogenic properties of brown adipocytes on the other.