Search

The Stimulator of Interferon Genes (STING) is a major adaptor protein that is central to the initiation of type I interferon responses and proinflammatory signalling. STING-dependent signalling is triggered by the presence of cytosolic nucleic acids that are generated following pathogen infection or cellular stress. Beyond this central role in controlling immune responses through the production of cytokines and chemokines, recent reports have uncovered inflammation-independent STING functions. Amongst these, a rapidly growing body of evidence demonstrates a key role of STING in controlling metabolic pathways at several levels. Since immunity and metabolic homeostasis are tightly interconnected, these findings deepen our understanding of the involvement of STING in human pathologies. Here, we discuss these findings and reflect on their impact on our current understanding of how nucleic acid immunity controls homeostasis and promotes pathological outcomes.

International audience; Cytosolic DNA promotes inflammatory responses upon detection by the cyclic GMP-AMP (cGAMP) synthase (cGAS). It has been suggested that cGAS downregulation is an immune escape strategy harnessed by tumor cells. Here, we used glioblastoma cells that show undetectable cGAS levels to address if alternative DNA detection pathways can promote pro-inflammatory signaling. We show that the DNA-PK DNA repair complex (i) drives cGAS-independent IRF3-mediated type I Interferon responses and (ii) that its catalytic activity is required for cGAS-dependent cGAMP production and optimal downstream signaling. We further show that the cooperation between DNA-PK and cGAS favors the expression of chemokines that promote macrophage recruitment in the tumor microenvironment in a glioblastoma model, a process that impairs early tumorigenesis but correlates with poor outcome in glioblastoma patients. Thus, our study supports that cGAS-dependent signaling is acquired during tumorigenesis and that cGAS and DNA-PK activities should be analyzed concertedly to predict the impact of strategies aiming to boost tumor immunogenicity.

SUMMARYCytosolic DNAs promote inflammatory responses upon detection by the cyclic GMP-AMP (cGAMP) synthase (cGAS). It has been thus suggested that cGAS downregulation is an immune escape strategy harnessed by tumor cells. Here, we used glioblastoma cells that lack cGAS to question whether alternative DNA detection pathways can promote pro-inflammatory signaling. We show that the DNA-PK DNA repair complex drives cGAS independent inflammatory responses but that its catalytic activity is required for cGAS-dependent cGAMP production and optimal downstream signaling. We further show that the cooperation between DNA-PK and cGAS favors the expression of chemokines that promote macrophage recruitment in the tumor microenvironment, a process that impaired early tumorigenesis but correlated with poor outcome. Thus, our study supports that cGAS-dependent signaling is acquired during tumorigenesis and that cGAS and DNA-PK activities should be analyzed concertedly to predict the impact of strategies aiming to boost tumor immunogenicity.

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway plays a pivotal role in several cellular processes including pathogen recognition and inflammatory responses. We describe a protocol to activate the cGAS-STING pathway in murine cells using nucleic acids transfection. We describe how to prepare the nucleic acid probes and validate activation of the pathway by western blot and gene expression analysis. The protocol can be applied to investigate cGAS-STING signaling in both murine and human cell lines. For complete details on the use and execution of this protocol, please refer to Vila et al. (2022)

International audience; The maintenance of genomic stability in multicellular organisms relies on the DNA damage response (DDR). The DDR encompasses several interconnected pathways that cooperate to ensure the repair of genomic lesions. Besides their repair functions, several DDR proteins have emerged as involved in the onset of inflammatory responses. In particular, several actors of the DDR have been reported to elicit innate immune activation upon detection of cytosolic pathological nucleic acids. Conversely, pattern recognition receptors (PRRs), initially described as dedicated to the detection of cytosolic immune-stimulatory nucleic acids, have been found to regulate DDR. Thus, although initially described as operating in specific subcellular localizations, actors of the DDR and nucleic acid immune sensors may be involved in interconnected pathways, likely influencing the efficiency of one another. Within this mini review, we discuss evidences for the crosstalk between PRRs and actors of the DDR. For this purpose, we mainly focus on cyclic GMP-AMP (cGAMP) synthetase (cGAS) and Interferon Gamma Inducible Protein 16 (IFI16), as major PRRs involved in the detection of aberrant nucleic acid species, and components of the DNA-dependent protein kinase (DNA-PK) complex, involved in the repair of double strand breaks that were recently described to qualify as potential PRRs. Finally, we discuss how the crosstalk between DDR and nucleic acid-associated Interferon responses cooperate for the fine-tuning of innate immune activation, and therefore dictate pathological outcomes. Understanding the molecular determinants of such cooperation will be paramount to the design of future therapeutic approaches.

SummaryInflammatory disorders are major health issues in which immune function and metabolic homeostasis are concertedly altered. Yet, the molecular mechanisms coordinating innate and metabolic pathways in homeostatic conditions are poorly understood. Here, we unveil a negative regulatory feedback loop involving the Stimulator of interferon genes (Sting) and the Fatty acid desaturase 2 (Fads2). At steady state, Sting regulates FA metabolism by repressing the activity of the Fads2 enzyme responsible for the desaturation of polyunsaturated FAs (PUFAs). Importantly, Sting activation increased Fads2 activity, while antagonizing Fads2 enhanced Sting activation, promoting the establishment of an anti-viral state. Remarkably, the cross-regulation between Sting and Fads2 is mediated by the cyclic GMP-AMP (cGAMP) Sting agonist and PUFAs. Indeed, we found that PUFAs inhibit Sting activation, while Sting agonists bind Fads2. Thus, our study identifies Sting as a master regulator of FA metabolism, and PUFAs as modulators of Sting-dependent inflammation. The interplay between Fads2 and Sting determines the fine-tuning of inflammatory responses, but comes at the expense of metabolic alterations, which are critical to consider in human pathologies associated with aberrant Sting activation.

Unresolved inflammation fosters and supports a wide range of human pathologies. There is growing evidence for a role played by cytosolicnucleic acidsin initiating and supporting pathological chronic inflammation. In particular, the cGAS-STING pathway has emerged as central to the mounting of nucleic acid-dependenttype I interferonresponses, leading to the identification of small-molecule modulators of STING that have raised clinical interest. However, several new challenges have emerged, representing potential obstacles to efficient clinical translation. Indeed, the current literature underscores that nucleic acid-induced inflammatory responses are subjected to several layers of regulation, further suggesting complex coordination at the cell-type, tissue or organism level. Untangling the underlying processes is paramount to the identification of specific therapeutic strategies targeting deleterious inflammation. Herein, we present an overview of human pathologies presenting with deregulated interferon levels and with accumulation of cytosolicnucleic acids. We focus on the central role of the STING adaptor protein in these pathologies and discuss howin vivomodels have forged our current understanding of nucleic acid immunity. We present our opinion on the advantages and limitations of zebrafish and mice models to highlight their complementarity for the study of inflammatory human pathologies and the development of therapeutics. Finally, we discuss high-throughput screening strategies that generate multi-parametric datasets that allow integrative analysis of heterogeneous information (imaging and omics approaches). These approaches are likely to structure the future of screening strategies for the treatment of human pathologies.

Summary Concerted alteration of immune and metabolic homeostasis underlies several inflammation-related pathologies, ranging from metabolic syndrome to infectious diseases. Here, we explored the coordination of nucleic acid-dependent inflammatory responses and metabolic homeostasis. We reveal that the STING (stimulator of interferon genes) protein regulates metabolic homeostasis through inhibition of the fatty acid desaturase 2 (FADS2) rate-limiting enzyme in polyunsaturated fatty acid (PUFA) desaturation. STING ablation and agonist-mediated degradation increased FADS2-associated desaturase activity and led to accumulation of PUFA derivatives that drive thermogenesis. STING agonists directly activated FADS2-dependent desaturation, promoting metabolic alterations. PUFAs in turn inhibited STING, thereby regulating antiviral responses and contributing to resolving STING-associated inflammation. Thus, we have unveiled a negative regulatory feedback loop between STING and FADS2 that fine-tunes inflammatory responses. Our results highlight the role of metabolic alterations in human pathologies associated with aberrant STING activation and STING-targeting therapies., Graphical abstract, Highlights • STING inhibits FADS2-dependent desaturation of PUFAs and LC-PUFAs • STING activation leads to upregulation of FADS2-associated desaturase activity • STING agonists activate FADS2-dependent PUFA and LC-PUFA desaturation • PUFAs inhibit STING-dependent inflammatory responses, The stimulator of interferon genes (STING) is a central regulator of nucleic acid-associated inflammatory responses. Here, Vila et al. discover that STING regulates polyunsaturated fatty acid (PUFA) metabolism, and in turn, PUFAs inhibit STING-dependent inflammation. This cross-regulation is central to the maintenance of metabolic homeostasis.

Ubiquitin-conjugating enzyme E2O (UBE2O) is expressed preferentially in metabolic tissues, but its role in regulating energy homeostasis has yet to be defined. Here we find that UBE2O is markedly upregulated in obese subjects with type 2 diabetes and show that whole-body disruption of Ube2o in mouse models in vivo results in improved metabolic profiles and resistance to high-fat diet–induced (HFD-induced) obesity and metabolic syndrome. With no difference in nutrient intake, Ube2o(–/–) mice were leaner and expended more energy than WT mice. In addition, hyperinsulinemic-euglycemic clamp studies revealed that Ube2o(–/–) mice were profoundly insulin sensitive. Through phenotype analysis of HFD mice with muscle-, fat-, or liver–specific knockout of Ube2o, we further identified UBE2O as an essential regulator of glucose and lipid metabolism programs in skeletal muscle, but not in adipose or liver tissue. Mechanistically, UBE2O acted as a ubiquitin ligase and targeted AMPKα2 for ubiquitin-dependent degradation in skeletal muscle; further, muscle-specific heterozygous knockout of Prkaa2 ablated UBE2O-controlled metabolic processes. These results identify the UBE2O/AMPKα2 axis as both a potent regulator of metabolic homeostasis in skeletal muscle and a therapeutic target in the treatment of diabetes and metabolic disorders.

Activation of macrophages by fatty acids (FAs) is a potential mechanism linking obesity to adipose tissue (AT) inflammation and insulin resistance. Here, we investigated the effects of FAs released during adipocyte lipolysis on AT macrophages (ATMs).Human THP-1 macrophages were treated with media from human multipotent adipose-derived stem (hMADS) adipocytes stimulated with lipolytic drugs. Macrophages were also treated with mixtures of FAs and an inhibitor of Toll-like receptor 4, since this receptor is activated by saturated FAs. Levels of mRNA and the secretion of inflammation-related molecules were measured in macrophages. FA composition was determined in adipocytes, conditioned media and macrophages. The effect of chronic inhibition or acute activation of fat cell lipolysis on ATM response was investigated in vivo in mice.Whereas palmitic acid alone activates THP-1, conditioned media from hMADS adipocyte lipolysis had no effect on IL, chemokine and cytokine gene expression, and secretion by macrophages. Mixtures of FAs representing de novo lipogenesis or habitual dietary conditions also had no effect. FAs derived from adipocyte lipolysis were taken up by macrophages and stored as triacylglycerol droplets. In vivo, chronic treatment with an antilipolytic drug did not modify gene expression and number of ATMs in mice with intact or defective Tlr4. Stimulation of adipocyte lipolysis increased storage of neutral lipids by macrophages without change in number and phenotype.Our data suggest that adipocyte lipolysis does not activate inflammatory pathways in ATMs, which instead may act as scavengers of FAs.

Skeletal muscle wasting is prevalent in many chronic diseases, necessitating inquiries into molecular regulation of muscle mass. Nuclear receptor co-activator peroxisome proliferator-activated receptor co-activator 1 alpha (PGC1α) and its splice variant PGC1α4 increase skeletal muscle mass. However, the effect of the other PGC1 sub-type, PGC1β, on muscle size is unclear. In transgenic mice selectively over-expressing PGC1β in the skeletal muscle, we have found that PGC1β progressively decreases skeletal muscle mass predominantly associated with loss of type 2b fast-twitch myofibers. Paradoxically, PGC1β represses the ubiquitin-proteolysis degradation pathway genes resulting in ubiquitinated protein accumulation in muscle. However, PGC1β overexpression triggers up-regulation of apoptosis and autophagy genes, resulting in robust activation of these cell degenerative processes, and a concomitant increase in muscle protein oxidation. Concurrently, PGC1β up-regulates apoptosis and/or autophagy transcriptional factors such as E2f1, Atf3, Stat1, and Stat3, which may be facilitating myopathy. Therefore, PGC1β activation negatively affects muscle mass over time, particularly fast-twitch muscles, which should be taken into consideration along with its known aerobic effects in the skeletal muscle.

Ubiquitin-conjugating enzyme E2O (UBE2O) is upregulated in human cancers. We have demonstrated that genetic deletion or pharmacological blockade of UBE2O reduces tumorigenesis through inhibiting the mammalian target of rapamycin complex 1-hypoxia-inducible factor 1-α pathway. Critically, UBE2O targets adenosine monophosphate (AMP)-activated protein kinase-α 2 (AMPKα2) for ubiquitination and degradation. We thus suggest the UBE2O-AMPKα2 axis as a potential therapeutic target for cancer.

International audience; Adipose tissue fibrosis development blocks adipocyte hypertrophy and favors ectopic lipid accumulation. Here, we show that adipose tissue fibrosis is associated with obesity and insulin resistance in humans and mice. Kinetic studies in C3H mice fed a high-fat diet show activation of macrophages and progression of fibrosis along with adipocyte metabolic dysfunction and death. Adipose tissue fibrosis is attenuated by macrophage depletion. Impairment of Toll-like receptor 4 signaling protects mice from obesity-induced fibrosis. The presence of a functional Toll-like receptor 4 on adipose tissue hematopoietic cells is necessary for the initiation of adipose tissue fibrosis. Continuous low-dose infusion of the Toll-like receptor 4 ligand, lipopolysaccharide, promotes adipose tissue fibrosis. Ex vivo, lipopolysaccharide-mediated induction of fibrosis is prevented by antibodies against the profibrotic factor TGFβ1. Together, these results indicate that obesity and endotoxemia favor the development of adipose tissue fibrosis, a condition associated with insulin resistance, through immune cell Toll-like receptor 4.

Dissecting exercise-mimicking pathways that can replicate the benefits of exercise in obesity and diabetes may lead to promising treatments for metabolic disorders. Muscle estrogen-related receptor gamma (ERRγ) is induced by exercise, and when over-expressed in the skeletal muscle mimics exercise by stimulating glycolytic-to-oxidative myofiber switch, mitochondrial biogenesis and angiogenesis in lean mice. The objective of this study was to test whether muscle ERRγ in obese mice mitigates weight gain and insulin resistance. To do so, ERRγ was selectively over-expressed in the skeletal muscle of obese and diabetic db/db mice. Muscle ERRγ over-expression successfully triggered glycolytic-to-oxidative myofiber switch, increased functional mitochondrial content and boosted vascular supply in the db/db mice. Despite aerobic remodeling, ERRγ surprisingly failed to improve whole-body energy expenditure, block muscle accumulation of triglycerides, toxic diacylglycerols (DAG) and ceramides or suppress muscle PKCε sarcolemmal translocation in db/db mice. Consequently, muscle ERRγ did not mitigate impaired muscle insulin signaling or insulin resistance in these mice. In conclusion, obesity and diabetes in db/db mice are not amenable to selective ERRγ-directed programming of classic exercise-like effects in the skeletal muscle. Other biochemical pathways or integrated whole-body effects of exercise may be critical for resisting diabetes and obesity.

UBE2O is localized in the 17q25 locus, which is known to be amplified in human cancers, but its role in tumorigenesis remains undefined. Here we show that Ube2o deletion in MMTV-PyVT or TRAMP mice profoundly impairs tumor initiation, growth, and metastasis, while switching off the metabolic reprogramming of tumor cells. Mechanistically, UBE2O specifically targets AMPKα2 for ubiquitination and degradation, and thereby promotes activation of the mTOR-HIF1α pathway. Notably, inactivation of AMPKα2, but not AMPKα1, abrogates the tumor attenuation caused by UBE2O loss, while treatment with rapamycin or inhibition of HIF1α ablates UBE2O-dependent tumor biology. Finally, pharmacological blockade of UBE2O inhibits tumorigenesis through the restoration of AMPKα2, suggesting the UBE2O-AMPKα2 axis as a potential cancer therapeutic target.

Circulating natriuretic peptide (NP) levels are reduced in obesity and predict the risk of type 2 diabetes (T2D). Since skeletal muscle was recently shown as a key target tissue of NP, we aimed to investigate muscle NP receptor (NPR) expression in the context of obesity and T2D. Muscle NPRA correlated positively with whole-body insulin sensitivity in humans and was strikingly downregulated in obese subjects and recovered in response to diet-induced weight loss. In addition, muscle NP clearance receptor (NPRC) increased in individuals with impaired glucose tolerance and T2D. Similar results were found in obese diabetic mice. Although no acute effect of brain NP (BNP) on insulin sensitivity was observed in lean mice, chronic BNP infusion improved blood glucose control and insulin sensitivity in skeletal muscle of obese and diabetic mice. This occurred in parallel with a reduced lipotoxic pressure in skeletal muscle due to an upregulation of lipid oxidative capacity. In addition, chronic NP treatment in human primary myotubes increased lipid oxidation in a PGC1α-dependent manner and reduced palmitate-induced lipotoxicity. Collectively, our data show that activation of NPRA signaling in skeletal muscle is important for the maintenance of long-term insulin sensitivity and has the potential to treat obesity-related metabolic disorders.

Introduction L'obesite et le diabete de type 2 (DT2) se caracterisent par une diminution des niveaux circulants de peptides natriuretiques (PN) chez l'homme. Nous avons recemment demontre une signalisation fonctionnelle des PN dans le muscle squelettique. L'objectif de ce travail est d'etudier l'influence de l'obesite et du DT2 sur la signalisation aux PN chez l'homme et la souris. Materiels et methodes Nous avons mesure l'expression proteique des recepteurs aux PN, biologiquement actif (NPRA) et de clairance (NPRC) dans des biopsies musculaires issues de patients normoponderes ou obeses et dans un modele murin d'obesite/diabete (souris db/db et db/+). Nous avons ensuite etudie l'influence d'une perfusion continue de Brain-NP (BNP) par mini-pompe osmotique pendant 4 semaines chez des souris engraissees pendant 16 semaines. Des mesures de poids, composition corporelle et tolerance au glucose ont ete realisees. Resultats Nos resultats demontrent une correlation positive entre l'expression proteique du NPRA musculaire et la sensibilite a l'insuline ( r =0,51, p p Conclusion Nous demontrons pour la premiere fois que la signalisation musculaire aux PN est associee a la sensibilite a l'insuline et que l'obesite et le DT2 se caracterisent par une diminution de la signalisation musculaire aux PN chez l'homme et la souris. Declaration d’interet Les auteurs declarent ne pas avoir d'interet direct ou indirect (financier ou en nature) avec un organisme prive, industriel ou commercial en relation avec le sujet presente.

Introduction L’obesite et le diabete de type 2 (DT2) se caracterisent par une diminution des niveaux circulants de peptides natriuretiques (PN) chez l’homme. Les PN jouent un role important dans la regulation de differentes voies metaboliques. L’objectif de ce travail est d’etudier le lien entre deficit en PN, obesite et DT2 dans differents modeles murins. Materiels et methodes Nous avons mesure le niveau d’expression proteique des recepteurs aux PN (NPRA et C) par Western blot dans un modele murin d’obesite/diabete genetique (souris db/db et db/+). Nous avons ensuite etudie l’influence d’une perfusion continue de brain-NP (BNP) par mini-pompe alzet pendant 4 semaines chez des souris db/db a 10 ng/kg/min et chez des souris engraissees par un regime hyperlipidique pendant 16 semaines a 50 ng/kg/min. Des mesures de poids, de composition corporelle, et de tolerances a l’insuline et au glucose ont ete realisees. Resultats Nos resultats montrent une diminution tres nette du ratio NPRA/NPRC (recepteur biologiquement actif/recepteur de clairance) dans les muscles, le foie, et les tissus adipeux blancs et bruns des souris db/db par rapport aux db/+. De plus, le BNP a faible dose diminue significativement la glycemie a jeun, l’hemoglobine glyquee (HbA1c) et ameliore l’insulinosensibilite chez les souris db/db independamment du poids corporel. A plus forte dose, le BNP previent la prise de poids et la degradation de la tolerance au glucose en regime hyperlipidique. Conclusion Nos donnees suggerent que l’obesite est associee a une perte de sensibilite des principaux organes metaboliques aux PN, ce qui pourrait contribuer au developpement du DT2. Une elevation des taux circulant de PN ameliore le controle glycemique et la tolerance au glucose chez des souris obeses et diabetiques.