Differential regulation of functional responses by β-adrenergic receptor subtypes in brown adipocytes.

Brown adipose tissue contains both β1- and β3-adrenergic receptors (β-ARs), and whereas both receptor subtypes can activate adenylyl cyclase, recent studies suggest that these subtypes have different pharmacological properties and may serve different signaling functions. In this study, primary brown adipocyte cultures were used to determine the role of β-AR subtypes in mediating lipolysis and uncoupling protein-1 (UCP1) gene expression, elicited by the physiological neurohormone norepinephrine (NE). NE increased both lipolysis and UCP1 mRNA levels in brown adipocyte cultures; the β1-receptor-selective antagonist CGP-20712A strongly antagonized the increase in UCP1 gene expression but had little effect on lipolysis. The β3-receptor-selective agonist CL-316243 (CL) also increased lipolysis and UCP1 mRNA levels, yet CL was more potent in stimulating lipolysis than UCP1 gene expression. NE also increased the phosphorylation of cAMP response element-binding protein (CREB) and perilipin (PL), both of which are protein kinase A substrates that are differentially targeted to the nucleus and lipid droplets, respectively. β1-receptor blockade inhibited NE-stimulated phosphorylation of CREB but not PL. The results suggest that β-AR subtypes regulate different physiological responses stimulated by NE in brown adipocyte cultures in part by differentially transducing signals to subcellular compartments.