Anatomy and physiology of adipose tissue

Adipose tissue is a specialized tissue formed by several depots located below the skin (subcutaneous depots) or in the trunk (visceral depots). It provides the survival of the body by storing/dispensing energy for metabolism and regulating thermogenesis, immune responses, and lactation. Two major types of adipose tissue exist in mammals, the white and brown fats, which are mainly composed of white and brown adipocytes, respectively. White adipocytes primarily act as storage cells for triacylglycerols. They have endocrine functions including the secretion of adipokines such as leptin, resistin, and adiponectin. Brown adipocytes are characterized by a cytoplasm composed of several small lipid droplets and a high amount of mitochondria. They mediate non-shivering thermogenesis, which is the major physiological function of brown adipose tissue. Marrow adipose tissue (MAT) is a third type of adipose tissue, functionally distinct from both white and brown adipose tissues. The development of marrow adipose tissue depends on the stage of life and greatly increases in pathological conditions. Recently, a growing body of evidence has finally confirmed that fully differentiated adipocytes retain the physiological ability to transdifferentiate, undergoing the reprogram of genome and turning into a different cell type with different physiological roles. This peculiar plasticity of adipose tissue ensures that certain physiologic stimuli can induce change of cell phenotype and, consequently, their function. In future, increasingly in-depth analysis of the observed phenomenon of transdifferentiation will contribute to further understanding the plasticity of adipose cells, improving knowledge of their biology and encouraging novel therapeutic strategies.