ABSTRACT
The rich and varied history of brown adipose tissue as an anatomically discreet tissue type includes early speculations in the 17th century that it was part of the thymus. The suggestive role for brown fat and thermogenesis in body weight regulation was strengthened further by the generation of mice lacking brown fat as a consequence of targeted expression of diptheria toxin in brown adipocytes. The uncoupling activity of uncoupling protein gene1 (UCP1) in brown adipocytes is inhibited by guanine nucleotides and stimulated by fatty acids, although there is debate over the exact molecular mechanism whereby fatty acids stimulate UCP1 proton passage across the inner membrane. At least at the mRNA level, the UCP2 gene is expressed in an enormous assortment of tissues and cell types. Some of these tissues, such as skeletal muscle, adipose tissue, and even certain brain regions such as hypothalamus, would be consistent with hypotheses that UCP2 has a role in energy expenditure and fuel metabolism.
