Noradrenaline (NA) regulates cold-stimulated adipocyte thermogenesis1. Aside from cAMP signalling downstream of β-adrenergic receptor activation, how NA promotes thermogenic output is still not fully understood. Here, we show that coordinated α1-adrenergic receptor (AR) and β3-AR signalling induces the expression of thermogenic genes of the futile creatine cycle2,3, and that early B cell factors, oestrogen-related receptors and PGC1α are required for this response in vivo. NA triggers physical and functional coupling between the α1-AR subtype (ADRA1A) and Gαq to promote adipocyte thermogenesis in a manner that is dependent on the effector proteins of the futile creatine cycle, creatine kinase B and tissue-non-specific alkaline phosphatase. Combined Gαq and Gαs signalling selectively in adipocytes promotes a continual rise in whole-body energy expenditure, and creatine kinase B is required for this effect. Thus, the ADRA1A–Gαq–futile creatine cycle axis is a key regulator of facultative and adaptive thermogenesis.

Objectives Long-chain fatty acids (LCFAs) released from adipocytes inhibit lipolysis through an unclear mechanism. We hypothesized that the LCFA receptor, FFAR4 (GPR120), which is highly expressed in adipocytes, may be involved in this feedback regulation. Methods and results Liquid chromatography mass spectrometry (LC-MS) analysis of conditioned media from isoproterenol-stimulated primary cultures of murine and human adipocytes demonstrated that most of the released non-esterified free fatty acids (NEFAs) are known agonists for FFAR4. In agreement with this, conditioned medium from isoproterenol-treated adipocytes stimulated signaling strongly in FFAR4 transfected COS-7 cells as opposed to non-transfected control cells. In transfected 3T3-L1 cells, FFAR4 agonism stimulated Gi- and Go-mini G protein binding more strongly than Gq, effects which were blocked by the selective FFAR4 antagonist AH7614. In primary cultures of murine white adipocytes, the synthetic, selective FFAR4 agonist CpdA inhibited isoproterenol-induced intracellular cAMP accumulation in a manner similar to the antilipolytic control agent nicotinic acid acting through another receptor, HCAR2. In vivo , oral gavage with the synthetic, specific FFAR4 agonist CpdB decreased the level of circulating NEFAs in fasting lean mice to a similar degree as nicotinic acid. In agreement with the identified anti-lipolytic effect of FFAR4, plasma NEFAs and glycerol were increased in FFAR4-deficient mice as compared to littermate controls despite having elevated insulin levels, and cAMP accumulation in primary adipocyte cultures was augmented by treatment with the FFAR4 antagonist conceivably by blocking the stimulatory tone of endogenous NEFAs on FFAR4. Conclusions In white adipocytes, FFAR4 functions as an NEFA-activated, autocrine, negative feedback regulator of lipolysis by decreasing cAMP though Gi-mediated signaling.

Investigating the intricate mechanisms of G protein-coupled receptor (GPCR) signalling in living cells is far from trivial. Over the last 20 years, the rise of genetically encoded resonance energy transfer (RET) sensors has shed new light onto the mechanisms of GPCR signalling. Such findings have challenged classical views on GPCR signalling and enhanced our understanding of the spatiotemporal dimensions of GPCR activity, leading to the discovery of endosomal GPCR signalling. This review highlights the use of RET sensors to monitor GPCR signalling in real-time and in live cells, focusing on GPCR activation and trafficking, and second messenger activity. It explores the physiological relevance of illustrative cases of endosomal signalling and discusses potential avenues to improve RET approaches to further explore endogenous GPCR activity in physiologically relevant contexts.

No abstract

No abstract

Noradrenaline is the primary physiological regulator of adipocyte thermogenesis in response to decreased environmental temperature1. However, the molecular factors and effector pathways that lie downstream of noradrenaline-stimulated thermogenesis are still not fully understood but are purportedly driven by cAMP downstream of β-adrenergic receptor (βAR) activation. Furthermore, while the transcriptional mechanisms regulating Ucp1 are well-characterized2, the transcriptional regulation of UCP1-independent thermogenesis is largely unknown. Here, we show that brown adipose tissue (BAT) is primed to respond to environmental cold by triggering coordinated α-adrenergic receptor (αAR) and βAR signaling to induce the expression of thermogenic genes of the futile creatine cycle3,4. Using fat-specific loss-of-function models, we reveal that EBFs, ERRs, and PGC1α are required for the cold-stimulated transcriptional induction of the futile creatine cycle in vivo. Through the application of chemogenetics, we demonstrate that combined fat-selective Gαs (activated by βARs) and Gαq (activated by αARs) signaling elevates whole-body energy expenditure to a greater extent than either signaling pathway alone in a manner that is dependent on the key effector protein of the futile creatine cycle, CKB3. Moreover, genetic and pharmacological studies reveal that CKB is necessary for nearly all of the α1AR-stimulated component of brown adipocyte-intrinsic respiration and is thus critical for the full activation of noradrenaline-stimulated thermogenesis. Thus, the futile creatine cycle is integrated into facultative and adaptive thermogenesis through coordinated α1AR and β3AR signaling.