2020-P: ß3-Adrenergic Receptors Regulate Lipolysis and Thermogenesis in Human Brown/Beige Adipocytes

Activation of rodent brown adipose tissue (BAT) via pharmacological stimulation of β₃-adrenergic receptors (β₃-AR) leads to metabolic benefit, however in humans, the physiological relevance of BAT and β₃-AR remain controversial. To investigate the role of the β₃-AR in human brown adipocytes, first, we established a human primary supraclavicular adipocyte in vitro model that upon differentiation preserved the physiological properties brown adipose tissue with increased β-ARs, adipogenic, thermogenic and brown/beige markers. Next, we selective silenced β₃-AR expression in differentiated primary brown/beige adipocytes using a lipofectamine-based non-viral transfection. 48h of transfection of siRNA targeting ADRB3 (siRNA-ADRB3) resulted in a 90% reduction in ADRB3 mRNA levels, relative to control siRNA-transfected cells (siRNA-Ctrl). siRNA-ADRB3 also reduced genes of fatty acid metabolism, thermogenesis (UCP1, 90% decrease), and mitochondrial mass. Functionally, lower cAMP levels, lipolysis, oxygen consumption rates and higher glycolysis were caused by silencing β₃-AR receptor. Immortalized brown adipocyte (hBA’s), from a separate subject, displayed a similar decrease in lipolysis and cellular respiration. Mirabegron, the selective human β₃-AR agonist, stimulated BAT lipolysis and thermogenesis, that were lost after knockdown ADRB3. Similarly, selective subtype human β-AR agonists dobutamine (β₁-AR agonist) and terbutaline (β₂-AR agonist) treatment also increased lipolysis and thermogenesis, that were also attenuated when β₃-AR was silenced. Thus, the β₃-AR maintains multiple components of the human brown/beige adipocyte lipolytic and thermogenic cellular machinery. These findings indicate that ADRB3 and β₃-AR agonists could be used to achieve metabolic benefit in humans.