Brown Adipose Tissue, Not Just a Heater

Adipose tissues are distributed in multiple depots in the body of animals including human beings and rodents.1 In the past decades, the biology of adipose tissues has been intensely studied. Currently, it is well accepted that the existence of adipose tissues is essential to maintain normal physiological activities and health. However, excessive accumulation of adipose tissues in their original depots and ectopic accumulation of lipids especially in the liver and skeletal muscles lead to obesity and insulin resistance, which will further cause lethal cardiovascular complications.2 Mechanistically, it has been established that macrophage infiltration and oxidative stress in adipose tissues cause malfunction of the adipose tissue, resulting in the secretion of numerous inflammatory factors and adipocyte-derived hormones that negatively regulate functions of the target organs such as heart and blood vessels and eventually lead to cardiac and vascular diseases.3 Notably, adipose tissue may be originally differentiated from cells in the vasculature or share the same precursors with vasculature cells.4 Also, adipogenesis always is companied by angiogenesis of blood vessels.5 Thus, the relationship between adipose tissue and blood vessels is drawing much attention on aspects relating to both physiology and shared origin.See accompanying article on page 455 One of the primary functions of adipose tissue is to store extra triglycerides in the form of lipid droplets. However, the sizes and distributions of lipid droplets are considerably different in different adipose tissue depots. Most adipose tissues in the human body comprise adipocytes containing a single large lipid droplet with fewer mitochondria, which is called white adipose tissue (WAT) and is distributed in visceral and subcutaneous regions. It is well accepted that visceral WAT is positively associated with development of cardiovascular diseases (CVDs) and related complications, whereas subcutaneous WAT …