Endocrine Abstracts

Adipose tissue can be subdivided into two distinct categories of fat cells: white adipocytes are specialized for the storage of chemical energy such as triglycerides, and under conditions of obesity white adipose tissue is characterized by tissue inflammation and energy overload.

In contrast, brown adipocytes dissipate energy in the form of heat (thermogenesis) by uncoupling of the mitochondrial electron transport chain from ATP formation through the specific expression of so-called uncoupling protein (UCP)-1. Lineage tracking studies in mice have demonstrated that white adipocytes are distinct from brown adipocytes during normal embryonic development. Indeed, progenitors of the brown adipocyte lineage have been shown to share a common precursor with the myogenic lineage.

In addition, a third distinct brown adipocyte-like cell type has been identified (brown-in-white, BRITE). In response to cold exposure, many WAT depots develop an increased number of BRITE cells, which seems to be mediated – at least in part – through sympathetic beta3-adrenoceptor agonist action. Despite typical BAT-like functional properties, such as UCP-1 expression, the BRITE adipocytes are developmentally distinct from the ‘classical’ brown cells and their functional contribution to systemic energy metabolism has only recently been documented.

Here, new developments and findings from animal models with respect to white versus brown versus BRITE adipocyte determination as well as its implication for the control of systemic energy homeostasis will be discussed.