Highlights d A therapeutic dose (50 mg) of mirabegron does not stimulate human BAT thermogenesis d Human brown adipocytes lack b 3 -AR and do not respond to mirabegron in vitro d Norepinephrine-induced respiration is driven by b 2 -AR, which co-localizes with UCP1 d b 2 -AR is the main target for pharmacological activation of human brown adipocytes

The retinoblastoma protein (RB) has previously been shown to facilitate adipocyte differentiation by inducing cell cycle arrest and enhancing the transactivation by the adipogenic CCAAT/enhancer binding proteins (C/EBP). We show here that the peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear receptor pivotal for adipogenesis, promotes adipocyte differentiation more efficiently in the absence of RB. PPARgamma and RB were shown to coimmunoprecipitate, and this PPARgamma-RB complex also contains the histone deacetylase HDAC3, thereby attenuating PPARgamma's capacity to drive gene expression and adipocyte differentiation. Dissociation of the PPARgamma-RB-HDAC3 complex by RB phosphorylation or by inhibition of HDAC activity stimulates adipocyte differentiation. These observations underscore an important function of both RB and HDAC3 in fine-tuning PPARgamma activity and adipocyte differentiation.