Cold-induced expression of a truncated adenylyl cyclase 3 acts as rheostat to brown fat function.

Promoting brown adipose tissue (BAT) activity innovatively targets obesity and metabolic disease. While thermogenic activation of BAT is well understood, the rheostatic regulation of BAT to avoid excessive energy dissipation remains ill-defined. Here, we demonstrate that adenylyl cyclase 3 (AC3) is key for BAT function. We identified a cold-inducible promoter that generates a 5' truncated AC3 mRNA isoform (Adcy3-at), whose expression is driven by a cold-induced, truncated isoform of PPARGC1A (PPARGC1A-AT). Male mice lacking Adcy3-at display increased energy expenditure and are resistant to obesity and ensuing metabolic imbalances. Mouse and human AC3-AT are retained in the endoplasmic reticulum, unable to translocate to the plasma membrane and lack enzymatic activity. AC3-AT interacts with AC3 and sequesters it in the endoplasmic reticulum, reducing the pool of adenylyl cyclases available for G-protein-mediated cAMP synthesis. Thus, AC3-AT acts as a cold-induced rheostat in BAT, limiting adverse consequences of cAMP activity during chronic BAT activation.

Apoptotic brown adipocytes enhance energy expenditure via extracellular inosine.

Brown adipose tissue (BAT) dissipates energy1,2 and promotes cardiometabolic health3. Loss of BAT during obesity and ageing is a principal hurdle for BAT-centred obesity therapies, but not much is known about BAT apoptosis. Here, untargeted metabolomics demonstrated that apoptotic brown adipocytes release a specific pattern of metabolites with purine metabolites being highly enriched. This apoptotic secretome enhances expression of the thermogenic programme in healthy adipocytes. This effect is mediated by the purine inosine that stimulates energy expenditure in brown adipocytes by the cyclic adenosine monophosphate-protein kinase A signalling pathway. Treatment of mice with inosine increased BAT-dependent energy expenditure and induced 'browning' of white adipose tissue. Mechanistically, the equilibrative nucleoside transporter 1 (ENT1, SLC29A1) regulates inosine levels in BAT: ENT1-deficiency increases extracellular inosine levels and consequently enhances thermogenic adipocyte differentiation. In mice, pharmacological inhibition of ENT1 as well as global and adipose-specific ablation enhanced BAT activity and counteracted diet-induced obesity, respectively. In human brown adipocytes, knockdown or blockade of ENT1 increased extracellular inosine, which enhanced thermogenic capacity. Conversely, high ENT1 levels correlated with lower expression of the thermogenic marker UCP1 in human adipose tissues. Finally, the Ile216Thr loss of function mutation in human ENT1 was associated with significantly lower body mass index and 59% lower odds of obesity for individuals carrying the Thr variant. Our data identify inosine as a metabolite released during apoptosis with a 'replace me' signalling function that regulates thermogenic fat and counteracts obesity.

Functional changes of the gastric bypass microbiota reactivate thermogenic adipose tissue and systemic glucose control via intestinal FXR-TGR5 crosstalk in diet-induced obesity.

BACKGROUND: Bariatric surgery remains the most effective therapy for adiposity reduction and remission of type 2 diabetes. Although different bariatric procedures associate with pronounced shifts in the gut microbiota, their functional role in the regulation of energetic and metabolic benefits achieved with the surgery are not clear. METHODS: To evaluate the causal as well as the inherent therapeutic character of the surgery-altered gut microbiome in improved energy and metabolic control in diet-induced obesity, an antibiotic cocktail was used to eliminate the gut microbiota in diet-induced obese rats after gastric bypass surgery, and gastric bypass-shaped gut microbiota was transplanted into obese littermates. Thorough metabolic profiling was combined with omics technologies on samples collected from cecum and plasma to identify adaptions in gut microbiota-host signaling, which control improved energy balance and metabolic profile after surgery. RESULTS: In this study, we first demonstrate that depletion of the gut microbiota largely reversed the beneficial effects of gastric bypass surgery on negative energy balance and improved glucolipid metabolism. Further, we show that the gastric bypass-shaped gut microbiota reduces adiposity in diet-induced obese recipients by re-activating energy expenditure from metabolic active brown adipose tissue. These beneficial effects were linked to improved glucose homeostasis, lipid control, and improved fatty liver disease. Mechanistically, these effects were triggered by modulation of taurine metabolism by the gastric bypass gut microbiota, fostering an increased abundance of intestinal and circulating taurine-conjugated bile acid species. In turn, these bile acids activated gut-restricted FXR and systemic TGR5 signaling to stimulate adaptive thermogenesis. CONCLUSION: Our results establish the role of the gut microbiome in the weight loss and metabolic success of gastric bypass surgery. We here identify a signaling cascade that entails altered bile acid receptor signaling resulting from a collective, hitherto undescribed change in the metabolic activity of a cluster of bacteria, thereby readjusting energy imbalance and metabolic disease in the obese host. These findings strengthen the rationale for microbiota-targeted strategies to improve and refine current therapies of obesity and metabolic syndrome. Video Abstract Bariatric Surgery (i.e. RYGB) or the repeated fecal microbiota transfer (FMT) from RYGB donors into DIO (diet-induced obesity) animals induces shifts in the intestinal microbiome, an effect that can be impaired by oral application of antibiotics (ABx). Our current study shows that RYGB-dependent alterations in the intestinal microbiome result in an increase in the luminal and systemic pool of Taurine-conjugated Bile acids (TCBAs) by various cellular mechanisms acting in the intestine and the liver. TCBAs induce signaling via two different receptors, farnesoid X receptor (FXR, specifically in the intestines) and the G-protein-coupled bile acid receptor TGR5 (systemically), finally resulting in metabolic improvement and advanced weight management. BSH, bile salt hydrolase; BAT brown adipose tissue.

Adenosine/A2B Receptor Signaling Ameliorates the Effects of Aging and Counteracts Obesity.

The combination of aging populations with the obesity pandemic results in an alarming rise in non-communicable diseases. Here, we show that the enigmatic adenosine A2B receptor (A2B) is abundantly expressed in skeletal muscle (SKM) as well as brown adipose tissue (BAT) and might be targeted to counteract age-related muscle atrophy (sarcopenia) as well as obesity. Mice with SKM-specific deletion of A2B exhibited sarcopenia, diminished muscle strength, and reduced energy expenditure (EE), whereas pharmacological A2B activation counteracted these processes. Adipose tissue-specific ablation of A2B exacerbated age-related processes and reduced BAT EE, whereas A2B stimulation ameliorated obesity. In humans, A2B expression correlated with EE in SKM, BAT activity, and abundance of thermogenic adipocytes in white fat. Moreover, A2B agonist treatment increased EE from human adipocytes, myocytes, and muscle explants. Mechanistically, A2B forms heterodimers required for adenosine signaling. Overall, adenosine/A2B signaling links muscle and BAT and has both anti-aging and anti-obesity potential.

A2A R-induced transcriptional deregulation in astrocytes: An in vitro study.

Adenosine A2A receptors (A2A R) are modulators of various physiological processes essential for brain homeostasis and fine synaptic tuning. In certain neurodegenerative conditions, notably Alzheimer's disease (AD), A2A Rs are pathologically upregulated in neurons but also in astrocytes. In that context, the use of A2A Rs inhibitors, normalizing impaired receptor function, is seen as a potential therapeutic strategy. However, the impact of A2A R alterations, particularly in astrocytes, is not fully understood. Here, we investigated the effect of A2A R overexpression on transcriptional deregulation in primary astrocytic cultures. By performing whole transcriptome analysis, we found that A2A R overexpression promotes robust transcriptional changes, mostly affecting immune response, angiogenesis, and cell activation-related genes. Importantly, we observed that treatment with SCH58261, a selective A2A R antagonist, restored the expression levels of several inflammatory and astrocytic activation-related genes, such as Interleukin-1beta and vimentin. This supports the notion that A2A R blockade could restore some astrocytic dysfunctions associated with abnormal A2A R expression, further arguing for a potential beneficial impact of receptor antagonists in A2A R-induced transcriptional deregulation, inflammation, and astrogliosis. Overall, our findings provide novel insights into the putative impact of A2A R overexpression on transcriptional deregulation in astrocytes, thereby opening novel avenues for the use of A2A R antagonists as potential therapeutic strategy in neurodegenerative diseases.

Adenosine activates brown adipose tissue and recruits beige adipocytes via A2A receptors.

Brown adipose tissue (BAT) is specialized in energy expenditure, making it a potential target for anti-obesity therapies. Following exposure to cold, BAT is activated by the sympathetic nervous system with concomitant release of catecholamines and activation of ß-adrenergic receptors. Because BAT therapies based on cold exposure or ß-adrenergic agonists are clinically not feasible, alternative strategies must be explored. Purinergic co-transmission might be involved in sympathetic control of BAT and previous studies reported inhibitory effects of the purinergic transmitter adenosine in BAT from hamster or rat. However, the role of adenosine in human BAT is unknown. Here we show that adenosine activates human and murine brown adipocytes at low nanomolar concentrations. Adenosine is released in BAT during stimulation of sympathetic nerves as well as from brown adipocytes. The adenosine A2A receptor is the most abundant adenosine receptor in human and murine BAT. Pharmacological blockade or genetic loss of A2A receptors in mice causes a decrease in BAT-dependent thermogenesis, whereas treatment with A2A agonists significantly increases energy expenditure. Moreover, pharmacological stimulation of A2A receptors or injection of lentiviral vectors expressing the A2A receptor into white fat induces brown-like cells-so-called beige adipocytes. Importantly, mice fed a high-fat diet and treated with an A2A agonist are leaner with improved glucose tolerance. Taken together, our results demonstrate that adenosine-A2A signalling plays an unexpected physiological role in sympathetic BAT activation and protects mice from diet-induced obesity. Those findings reveal new possibilities for developing novel obesity therapies.

Helicobacter pylori promotes eukaryotic protein translation by activating phosphatidylinositol 3 kinase/mTOR.

The innate immune response elicited by Helicobacter pylori in the human gastric mucosa involves a range of cellular signalling pathways, including those implicated in metabolism regulation. In this study, we analysed H. pylori-induced PI3K/Akt/mTOR signalling, which regulates glycolysis and protein synthesis and associates thereby with cellular energy- and nutrients-consuming processes such as growth and proliferation. The immunohistochemical analysis demonstrated that Akt kinase phosphorylation is abundant in gastric biopsies obtained from gastritis, gastric adenoma and adenocarcinoma patients. Infection with H. pylori led to the phosphorylation of Akt effectors mTOR and S6 in a type 4 secretion system (T4SS)-independent manner in AGS cells. We observed that the activation of these molecules was dependent on PI3K and the Src family tyrosine kinases. Furthermore, H. pylori induced the phosphorylation of 4E-BP1 and eIF4E and suppressed the phosphorylation of eEF2, which are important regulators of protein synthesis. Inhibition of PI3K and Akt kinase prevented the phosphorylation of 4E-BP1, suggesting that PI3K signalling is involved in the regulation of translation initiation during H. pylori infection. Metabolic labelling showed that infected cells had higher rates of [(35)S]methionine/cysteine incorporation, and this effect could be prevented using LY294002, an PI3K inhibitor. Thus, H. pylori activates PI3K/Akt signalling, mTOR, eIFs and protein translation, which might impact H. pylori-related gastric pathophysiology.

Helicobacter pylori-induced activation of beta-catenin involves low density lipoprotein receptor-related protein 6 and Dishevelled.

BACKGROUND: The human microbial pathogen Helicobacter pylori resides in the stomach of about fifty percent of the world's population and represents a risk factor for chronic gastritis, peptic ulcers and, in rare cases, gastric cancer. Alterations of the Wnt/beta-catenin signaling pathway have been described in almost every human cancer disease, due to the regulation of target genes being involved in cell cycle control, differentiation, cell migration or stem cell control. Our study aimed to elucidate the role of proximal Wnt signaling components low density lipoprotein receptor-related protein 6 (LRP6) and Dishevelled (Dvl) in the activation of beta-catenin early after infection of gastric epithelial cells with H. pylori. RESULTS: Infection of gastric epithelial NCI-N87 cells with H. pylori induces rapid phosphorylation of the Wnt/beta-catenin pathway co-receptor LRP6 independent of the cytotoxin-associated gene A (CagA) or vacuolating cytotoxin A (VacA). However, bacteria lacking a functional type 4 secretion system (T4SS) failed to induce LRP6 phosphorylation. Further, we identified proteins of the Dvl family, namely Dvl2 and Dvl3, which are involved in LRP6 phosphorylation. H. pylori-induced nuclear accumulation of beta-catenin and its transcriptional activation, and expression of Wnt target genes are strongly reduced in stable knockdown cell lines deficient for LRP6, Dvl2 or Dvl3. CONCLUSION: We analysed the H. pylori-induced activation of Wnt-signaling factors and demonstrate for the first time that the canonical Wnt-signaling proteins LRP6 and Dvl2 and Dvl3 are involved in the regulation of beta-catenin.

Ectodomain shedding of E-cadherin and c-Met is induced by Helicobacter pylori infection.

Helicobacter pylori, a microaerophilic gram-negative bacterium, colonizes the human stomach. About 50% of the world's population is infected, and this infection is considered as the major risk factor for the development of gastric adenocarcinomas in 1% of infected subjects. Carcinogenesis is characterized by the process of epithelial-to-mesenchymal transition (EMT), in the course of which fully differentiated epithelial cells turn into depolarized and migratory cells. Concomitant disruption of adherence junctions (AJ) is facilitated by growth factors like hepatocyte growth factor 1 (HGF-1), but has been also shown to depend on ectodomain shedding of E-cadherin. The aim of this study was to investigate the impact of infection with H. pylori of NCI-N87 gastric epithelial cells on the shedding of E-cadherin and HGF-receptor c-Met. Our results show that infection with H. pylori provokes shedding of the surface proteins c-Met and E-cadherin. Evidence is provided that ADAM10 contributes to the shedding of c-Met and E-cadherin.