Adipose tissue and fat cell biology

Abstract

Adipose tissue is present in most vertebrates, including mammals, birds, reptiles, amphibians and most of the fish. This tissue is formed from mesoderm during embryonic development and is comprised of several fat depots around the body. It is composed from adipocytes, the cells forming the majority of the tissue when studied in histological sections, as well as several other cell types, namely preadipocytes, endothelial cells, pericytes and innate immune cells. In all mammals including humans, two types of adipose tissue are recognized, white and brown adipose tissue (WAT and BAT, respectively), which are engaged in two major distinct and opposite functions: energy storage (in WAT) and energy dissipation (in BAT). White adipocytes are spherical unilocular cells, filled by a large lipid droplet, with all cellular organelles packed in a thin cytoplasmic rim in the vicinity of plasma membrane. Brown adipocytes are polygonal multilocular cells, with cytoplasmic space filled with typical mitochondria containing many cristae. Brown adipocytes are marked by the presence of mitochondrial uncoupling protein-1 (UCP1), which mediates cold- and diet-inducible non-shivering thermogenesis that is adrenergically regulated.