β-Adrenergic Receptors and Regulation of Energy Expenditure: A Family Affair

The family of adrenergic receptors (ARs) expressed in adipocytes includes three sibling βARs and two αAR cousins. Together they profoundly influence the mobilization of stored fatty acids, secretion of fat-cell derived hormones, and the specialized process of nonshivering thermogenesis in brown adipose tissue. The two types of fat cells that compose adipose tissue, brown and white, are structurally and functionally distinct. Studies on the mechanisms by which individual βAR regulates these cell-specific functions have recently uncovered new signal transduction cascades involved in processes traditionally ascribed to adenylyl cyclase/cAMP/protein kinase A system. They illustrate how βAR signaling can orchestrate a coordinated set of intracellular responses for fine control of metabolic balance.