Cold-induced changes in gene expression in brown adipose tissue: implications for the activation of thermogenesis.

Brown adipose tissue (BAT) is the site of heat production (thermogenesis). This unique function is performed by uncoupling protein 1 (UCP1) specifically expressed in mitochondria of BAT. UCP1 dissipates the driving force of ATP synthesis, and thus causes heat production followed by energy expenditure. The thermogenic function of BAT has the role of maintaining body temperature under cold conditions. When animals are exposed to cold, the expression of UCP1 gene is increased to activate thermogenesis. To date, functional analysis of BAT has been focused on UCP1, because it plays an indispensable role in thermogenesis. However, the gene expression of not only UCP1 but also that of other genes in BAT is expected to be regulated to achieve effective thermogenesis. Our previous investigations showed increased expression of genes that encode several energy metabolic enzymes in the BAT of rats kept in the cold. These changes in gene expression imply that the enhancement of energy metabolism is needed to activate thermogenesis. Furthermore, various reports from studies focused on genes whose expression is changed in response to cold stimulation have provided new insights into the function of BAT. In this review, to understand the thermogenic function of BAT systematically, we have provided an overview of previous findings on changes in the expression of genes thought to be related to the activation of thermogenesis in BAT.