No abstract

Brown adipose tissue (BAT) activation stimulates energy expenditure in human adults, which makes it an attractive target to combat obesity and related disorders. Recent studies demonstrated a role for G protein‐coupled receptor 120 (GPR120) in BAT thermogenesis. Here, we investigated the therapeutic potential of GPR120 agonism and addressed GPR120‐mediated signaling in BAT. We found that activation of GPR120 by the selective agonist TUG‐891 acutely increases fat oxidation and reduces body weight and fat mass in C57Bl/6J mice. These effects coincided with decreased brown adipocyte lipid content and increased nutrient uptake by BAT, confirming increased BAT activity. Consistent with these observations, GPR120 deficiency reduced expression of genes involved in nutrient handling in BAT. Stimulation of brown adipocytes in vitro with TUG‐891 acutely induced O2 consumption, through GPR120‐dependent and GPR120‐independent mechanisms. TUG‐891 not only stimulated GPR120 signaling resulting in intracellular calcium release, mitochondrial depolarization, and mitochondrial fission, but also activated UCP1. Collectively, these data suggest that activation of brown adipocytes with the GPR120 agonist TUG‐891 is a promising strategy to increase lipid combustion and reduce obesity.

Aims/hypothesisWhite adipose tissue (WAT) consists of various depots with different adipocyte functionality and immune cell composition. Knowledge of WAT-depot-specific differences in expandability and immune cell influx during the development of obesity is limited, therefore we aimed to characterise different WAT depots during the development of obesity in mice.MethodsGonadal WAT (gWAT), subcutaneous WAT (sWAT) and mesenteric WAT (mWAT) were isolated from male C57Bl/6J mice with different body weights (approximately 25–60 g) and analysed. Linear and non-linear regression models were used to describe the extent of WAT depot expandability and immune cell composition as a function of body weight.ResultsWhereas mouse sWAT and mWAT continued to expand with body weight, gWAT expanded mainly during the initial phase of body weight gain. The expansion diminished after the mice reached a body weight of around 40 g. From this point on, gWAT crown-like structure formation, liver steatosis and insulin resistance occurred. Mouse WAT depots showed major differences in immune cell composition: gWAT consisted mainly of macrophages, whereas sWAT and mWAT primarily contained lymphocytes.Conclusions/interpretationMarked inter-depot differences exist in WAT immune cell composition and expandability. The limited storage capacity of gWAT seems to direct the development of metabolic disorders in male C57Bl/6J mice.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-015-3594-8) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Obesity is a well-established risk factor for atherosclerosis. However, the mechanistic link between accumulation of adipose tissue and development of atherosclerosis is not clear. Adipose tissue comprises various depots including white adipose tissue (WAT), brown adipose tissue (BAT) and thoracic and abdominal perivascular adipose tissue (PVAT). The phenotype of thoracic PVAT resembles BAT, whereas abdominal PVAT is more like WAT. Here, we review the distinct roles of the adipose tissue depots in the development of atherosclerosis with the ultimate aim to understand how these can be targeted to reduce atherosclerosis. In obesity, increased fatty acid release by WAT and decreased lipid combustion by BAT and thoracic PVAT lead to hyperlipidaemia, which contributes to atherosclerosis development. Besides, obese WAT and abdominal PVAT release pro-inflammatory factors that further promote atherosclerosis. To discourage atherosclerosis development, strategies that reduce the release of pro-inflammatory factors and fatty acids from WAT and abdominal PVAT, or increase combustion of fatty acids by activation of BAT and thoracic PVAT and beiging of WAT are probably most efficient. Possible therapies could include anti-inflammatory compounds such as adiponectin and salicylates to lower inflammation, and β3-adrenergic receptor activators to increase fatty acid combustion. Additional and more specific strategies to promote fatty acid combustion are currently subject of investigation. In conclusion, different adipose depots differentially affect atherosclerosis development, in which atherosclerosis is promoted by energy-storing adipose depots and attenuated by energy-combusting adipose tissue. In obesity, combining therapies that reduce inflammation and increase combustion of lipids are most conceivable to restrain atherogenesis.

The endocannabinoid system is an important player in energy metabolism by regulating appetite, lipolysis, and energy expenditure. Chronic blockade of the cannabinoid 1 receptor (CB1R) leads to long-term maintenance of weight loss and reduction of dyslipidemia in experimental and human obesity. The molecular mechanism by which CB1R blockade reverses dyslipidemia in obesity has not yet been clarified. In this study, we showed that CB1R blockade with the systemic CB1R blocker rimonabant enhanced whole-body energy expenditure and activated brown adipose tissue (BAT), indicated by increased expression of genes involved in BAT thermogenesis and decreased lipid droplet size in BAT. This was accompanied by selectively increased triglyceride (TG) uptake by BAT and lower plasma TG levels. Interestingly, the effects on BAT activation were still present at thermoneutrality and could be recapitulated by using the strictly peripheral CB1R antagonist AM6545, indicating direct peripheral activation of BAT. Indeed, CB1R blockade directly activated T37i brown adipocytes, resulting in enhanced uncoupled respiration, most likely via enhancing cAMP/PKA signaling via the adrenergic receptor pathway. Our data indicate that selective targeting of the peripheral CB1R in BAT has therapeutic potential in attenuating dyslipidemia and obesity.