Inflammasomes : from regulation to auto inflammatory diseases

Les inflammasomes sont des complexes protéiques intracellulaires qui ont un rôle majeur dans l'immunité innée. Leur activation conduit à la mort de la cellule dans un contexte hyperinflammatoire. Compte-tenu des effets potentiellement délétères, tissulaires et systémiques, les inflammasomes sont strictement régulés. A l'heure actuelle, la compréhension des mécanismes conduisant à leur activation et leur régulation reste partielle. Dans une première partie de cette thèse, nous avons utilisé une technique de biotinylation proximale (BioID) pour identifier les protéines interagissant avec l'inflammasome. Nous avons identifié 111 protéines dont la relation étroite avec l'inflammasome était vraisemblable. Parmi ces 111 protéines, 25% avaient d'ailleurs déjà été décrites comme des protéines interagissant avec le complexe. L'identification d'un adaptateur majeur de l'autophagie, p62/sequestosome-1 (p62), nous a conduit à focaliser notre attention sur son rôle dans la régulation de l'inflammasome. Nous avons d'abord démontré que l'interaction entre p62 et l'inflammasome existait, sur le plan biochimique. Par la suite, nous avons prouvé que p62 était un substrat du complexe et que l'activation de ce dernier entrainait le clivage de p62 au niveau d'un résidu aspartique en position 329. Enfin, nous avons caractérisé les conséquences fonctionnelles de ce clivage, en montrant que les fragments protéiques générés entrainaient une régulation positive ou négative du complexe. Nous avons alors émis l'hypothèse que p62 pourrait réguler l'inflammasome de manière différente selon le signal activateur. Dans une seconde partie, translationnelle, nous nous sommes intéressés aux conséquences des mutations dans la séquence de gènes codant les constituants de l'inflammasome ou des protéines régulatrices du complexe. Celles-ci sont à l'origine des maladies auto-inflammatoires monogéniques. Ces maladies sont caractérisées par des épisodes récurrents de fièvre associés variablement à d'autres symptômes systémiques. La plus fréquente est la fièvre méditerranéenne familiale (FMF), avec une prévalence estimée entre 1 et 5 pour 10 000 habitants en France. Les mutations du gène MEFV, codant la pyrine, sont à l'origine de la FMF. La pyrine peut induire la formation d'un inflammasome spécifique. Récemment, le mécanisme d'activation de l'inflammasome pyrine a été mieux caractérisé : certaines toxines (comme la toxine B du Clostridium difficile, TcdB) induisent l'activation de l'inflammasome pyrine. Nous avons utilisé ces nouvelles connaissances afin d'explorer les conséquences de l'activation de l'inflammasome pyrine par la TcdB dans les monocytes des patients atteints de FMF, comparés aux monocytes de donneurs sains. Nos résultats indiquent que ces mutations induisent un abaissement du seuil d'activation de l'inflammasome pyrine. Par ailleurs, les corrélations génotype/phénotype indiquent qu'il existe un effet de dosage génétique, en lien avec le nombre d'allèles mutés. Ces résultats ouvrent de nouvelles perspectives pour les patients atteints de FMF, tant dans la compréhension de la physiopathologie que dans la possibilité de mise au point de tests fonctionnels pour le diagnostic de la maladieInflammasomes are intracellular multiprotein complexes that have a major role in innate immunity. Their activation leads to hyperinflammatory cell death. In view of potentially deleterious effects, the inflammasomes are strictly regulated. At present, the understanding of the mechanisms leading to their activation and regulation remains partial. In a first part of this thesis, we used a technique of proximity-dependent biotinylation (BioID) to identify the proteins interacting with the inflammasome. We identified 111 proteins with a close relationship to the inflammasome. Among these 111 proteins, 25% had already been described as proteins interacting with the complex. The identification of a major adaptor of autophagy, p62/sequestosome-1 (p62), led us to focus our attention on its role in the regulation of inflammasome. We first demonstrated that the interaction between p62 and inflammasome was real, at the biochemical level. Subsequently, we proved that p62 was a substrate of the complex and that the activation of the latter led to the cleavage of p62 at the aspartate 329. Finally, we characterized the functional consequences of this cleavage and showed that the protein fragments generated led to a positive or negative regulation of the complex. We thus hypothesized that p62 could regulate the inflammasome differently according to the activator signal. In a second translational part, we looked at the consequences of mutations in the sequence of genes coding components of the inflammasome or proteins regulating it. These are the cause of monogenic auto-inflammatory diseases. These diseases are characterized by recurrent episodes of fever associated with other systemic symptoms. The most frequent is Familial Mediterranean Fever (FMF), with prevalence estimated at between 1 and 5 per 10 000 inhabitants, in France. Mutations of the MEFV gene, encoding pyrin, cause FMF. Pyrine may trigger the formation of a specific inflammasome. Recently, the mechanism of activation of the pyrin inflammasome has been better characterized: toxins (such as toxin B of Clostridium difficile, TcdB) induce the activation of the pyrin inflammasome. We used this new knowledge to investigate the consequences of TcdB on pyrin inflammasome activation in monocytes from FMF patients compared to monocytes from healthy donors. Our results indicate that these mutations induce a decreased threshold of activation of the pyrin inflammasome. In addition, genotype / phenotype correlations indicate a gene-dosage effect, related to the number of mutated alleles. These results open new perspectives for patients with FMF, in understanding the pathophysiology of the diseass and in developing functional diagnostic test

Les inflammasomes : de la régulation aux maladies auto-inflammatoires

Inflammasomes are intracellular multiprotein complexes that have a major role in innate immunity. Their activation leads to hyperinflammatory cell death. In view of potentially deleterious effects, the inflammasomes are strictly regulated. At present, the understanding of the mechanisms leading to their activation and regulation remains partial. In a first part of this thesis, we used a technique of proximity-dependent biotinylation (BioID) to identify the proteins interacting with the inflammasome. We identified 111 proteins with a close relationship to the inflammasome. Among these 111 proteins, 25% had already been described as proteins interacting with the complex. The identification of a major adaptor of autophagy, p62/sequestosome-1 (p62), led us to focus our attention on its role in the regulation of inflammasome. We first demonstrated that the interaction between p62 and inflammasome was real, at the biochemical level. Subsequently, we proved that p62 was a substrate of the complex and that the activation of the latter led to the cleavage of p62 at the aspartate 329. Finally, we characterized the functional consequences of this cleavage and showed that the protein fragments generated led to a positive or negative regulation of the complex. We thus hypothesized that p62 could regulate the inflammasome differently according to the activator signal. In a second translational part, we looked at the consequences of mutations in the sequence of genes coding components of the inflammasome or proteins regulating it. These are the cause of monogenic auto-inflammatory diseases. These diseases are characterized by recurrent episodes of fever associated with other systemic symptoms. The most frequent is Familial Mediterranean Fever (FMF), with prevalence estimated at between 1 and 5 per 10 000 inhabitants, in France. Mutations of the MEFV gene, encoding pyrin, cause FMF. Pyrine may trigger the formation of a specific inflammasome. Recently, the mechanism of activation of the pyrin inflammasome has been better characterized: toxins (such as toxin B of Clostridium difficile, TcdB) induce the activation of the pyrin inflammasome. We used this new knowledge to investigate the consequences of TcdB on pyrin inflammasome activation in monocytes from FMF patients compared to monocytes from healthy donors. Our results indicate that these mutations induce a decreased threshold of activation of the pyrin inflammasome. In addition, genotype / phenotype correlations indicate a gene-dosage effect, related to the number of mutated alleles. These results open new perspectives for patients with FMF, in understanding the pathophysiology of the diseass and in developing functional diagnostic testsLes inflammasomes sont des complexes protéiques intracellulaires qui ont un rôle majeur dans l'immunité innée. Leur activation conduit à la mort de la cellule dans un contexte hyperinflammatoire. Compte-tenu des effets potentiellement délétères, tissulaires et systémiques, les inflammasomes sont strictement régulés. A l'heure actuelle, la compréhension des mécanismes conduisant à leur activation et leur régulation reste partielle. Dans une première partie de cette thèse, nous avons utilisé une technique de biotinylation proximale (BioID) pour identifier les protéines interagissant avec l'inflammasome. Nous avons identifié 111 protéines dont la relation étroite avec l'inflammasome était vraisemblable. Parmi ces 111 protéines, 25% avaient d'ailleurs déjà été décrites comme des protéines interagissant avec le complexe. L'identification d'un adaptateur majeur de l'autophagie, p62/sequestosome-1 (p62), nous a conduit à focaliser notre attention sur son rôle dans la régulation de l'inflammasome. Nous avons d'abord démontré que l'interaction entre p62 et l'inflammasome existait, sur le plan biochimique. Par la suite, nous avons prouvé que p62 était un substrat du complexe et que l'activation de ce dernier entrainait le clivage de p62 au niveau d'un résidu aspartique en position 329. Enfin, nous avons caractérisé les conséquences fonctionnelles de ce clivage, en montrant que les fragments protéiques générés entrainaient une régulation positive ou négative du complexe. Nous avons alors émis l'hypothèse que p62 pourrait réguler l'inflammasome de manière différente selon le signal activateur. Dans une seconde partie, translationnelle, nous nous sommes intéressés aux conséquences des mutations dans la séquence de gènes codant les constituants de l'inflammasome ou des protéines régulatrices du complexe. Celles-ci sont à l'origine des maladies auto-inflammatoires monogéniques. Ces maladies sont caractérisées par des épisodes récurrents de fièvre associés variablement à d'autres symptômes systémiques. La plus fréquente est la fièvre méditerranéenne familiale (FMF), avec une prévalence estimée entre 1 et 5 pour 10 000 habitants en France. Les mutations du gène MEFV, codant la pyrine, sont à l'origine de la FMF. La pyrine peut induire la formation d'un inflammasome spécifique. Récemment, le mécanisme d'activation de l'inflammasome pyrine a été mieux caractérisé : certaines toxines (comme la toxine B du Clostridium difficile, TcdB) induisent l'activation de l'inflammasome pyrine. Nous avons utilisé ces nouvelles connaissances afin d'explorer les conséquences de l'activation de l'inflammasome pyrine par la TcdB dans les monocytes des patients atteints de FMF, comparés aux monocytes de donneurs sains. Nos résultats indiquent que ces mutations induisent un abaissement du seuil d'activation de l'inflammasome pyrine. Par ailleurs, les corrélations génotype/phénotype indiquent qu'il existe un effet de dosage génétique, en lien avec le nombre d'allèles mutés. Ces résultats ouvrent de nouvelles perspectives pour les patients atteints de FMF, tant dans la compréhension de la physiopathologie que dans la possibilité de mise au point de tests fonctionnels pour le diagnostic de la maladi

Development and Validation of a Bayesian Network for Supporting the Etiological Diagnosis of Uveitis

The etiological diagnosis of uveitis is complex. We aimed to implement and validate a Bayesian belief network algorithm for the differential diagnosis of the most relevant causes of uveitis. The training dataset (n = 897) and the test dataset (n = 154) were composed of all incident cases of uveitis admitted to two internal medicine departments, in two independent French centers (Lyon, 2003–2016 and Dijon, 2015–2017). The etiologies of uveitis were classified into eight groups. The algorithm was based on simple epidemiological characteristics (age, gender, and ethnicity) and anatomoclinical features of uveitis. The cross-validated estimate obtained in the training dataset concluded that the etiology of uveitis determined by the experts corresponded to one of the two most probable diagnoses in at least 77% of the cases. In the test dataset, this probability reached at least 83%. For the training and test datasets, when the most likely diagnosis was considered, the highest sensitivity was obtained for spondyloarthritis and HLA-B27-related uveitis (76% and 63%, respectively). The respective specificities were 93% and 54%. This algorithm could help junior and general ophthalmologists in the differential diagnosis of uveitis. It could guide the diagnostic work-up and help in the selection of further diagnostic investigations

Cell-Free Assay for Inflammasome Activation

International audienceInflammasomes are multiprotein complexes, which assembly results in caspase-1 activation and subsequent IL-1β and IL-18 activation and secretion. In a cell-free system, based on cytosols of normally growing cells, the disruption of the cell membrane spontaneously activates the inflammasome. Studying the activation of the inflammasome in cytosolic extracts provides multiple advantages, as it is synchronized, rapid, strong, and mostly plasma membrane-free. This protocol covers the methods required to prepare cell lysates and study inflammasome activation using different read-outs. General considerations are provided that may help in the design of modified methods. This assay can be useful to study potential inflammasome interactors and the signaling pathways involved in its activation

The inflammasomes: platforms of innate immunity

International audienceHuman beings are constantly exposed to pathogens. The innate immune system is the first line of defense against microbes. It has evolved to recognize conserved microbial motifs (PAMP or pathogen-associated molecular patterns) thanks to a limited array of receptors termed pattern recognition receptors (PRR). Upon activation, most PRR trigger a transcriptional response leading to neosynthesis of hundreds of genes. In contrast, engagement of various PRR in the recently identified inflammasome complexes lead to activation of a cysteine protease, caspase-1. This inflammatory caspase has a dual activity: it triggers the release of very potent proinflammatory cytokines IL-1β and IL-18 and, an hyperinflammatory cell death termed pyroptosis. In this review, we describe the inflammasome receptors and their ligands, the molecular mechanisms leading to the assembly of this innate immune platform and the role of the inflammasome during viral and bacterial infections

Inflammasomes, innate immunity platforms

Human beings are continuously exposed to pathogens and have developed a highly complex immune system to protect them. The first line of defence is the innate immune system. It has evolved to recognise conserved microbial patterns (PAMPs, or pathogen-associated molecular patterns) via a group of receptors known as pattern-recognition receptors (PRRs). Recognition of most PAMPs by PRRs triggers a transcriptional response which leads to the neosynthesis of hundreds of proteins. The inflammasome is a multiprotein complex which is activated in response to detection of microbial patterns or danger signals by certain PRRs and specifically activates the caspase-1, an inflammatory caspase. The activated caspase-1 triggers the activation and secretion of proinflammatory cytokines such as interleukin (IL)-1β and IL-18. Caspase-1 also initiates a form of programmed cell death known as pyroptosis. In this paper, we describe inflammasome receptors and their ligands, the way in which this protein complex assembles and the role of inflammasomes in bacterial and viral infections

Functional Assessment of Disease-Associated Pyrin Variants

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The pyrin inflammasome: from sensing RhoA GTPases-inhibiting toxins to triggering autoinflammatory syndromes

International audienceNumerous pathogens including Clostridium difficile and Yersinia pestis have evolved toxins or effectors targeting GTPases from the RhoA subfamily (RhoA/B/C) to inhibit or hijack the host cytoskeleton dynamics. The resulting impairment of RhoA GTPases activity is sensed by the host via an innate immune complex termed the pyrin inflammasome in which caspase-1 is activated. The cascade leading to activation of the pyrin inflammasome has been recently uncovered. In this review, following a brief presentation of RhoA GTPases-modulating toxins, we present the pyrin inflammasome and its regulatory mechanisms. Furthermore, we discuss how some pathogens have developed strategies to escape detection by the pyrin inflammasome. Finally, we present five monogenic autoinflammatory diseases associated with pyrin inflammasome deregulation. The molecular insights provided by the study of these diseases and the corresponding mutations on pyrin inflammasome regulation and activation are presented

Diagnostic value of lymphopaenia and elevated serum ACE in patients with uveitis

Aim To evaluate the diagnostic worth of elevated serum ACE (sACE) and lymphopaenia, singly or combined, in diagnosing sarcoid uveitis. Methods Monocentric retrospective study, on a cohort of 996 adult patients referred to our department between March 2001 and December 2018 for a diagnostic work-up of uveitis. The sensitivity (SE), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV) of the two biomarkers were calculated in different contexts. Results Eight hundred and sixty-eight patient cases were reviewed. The mean age at uveitis onset was 49.4 (±18.6) years. Of them, 144 patients had a diagnosis of sarcoid uveitis. An elevated sACE had SE of 45.8%, Sp of 88.8%, PPV of 44.9% and NPV of 89.2% in diagnosing sarcoid uveitis. For lymphopaenia, SE was 15.3%, Sp was 96.7%, PPV was 47.8% and NPV was 85.2%. For the combination of elevated sACE and lymphopaenia, SE was 18.9%, Sp was 99.0%, PPV was 73.9% and NPV was 89.5%. The value of this combination varied according to patient age at diagnosis plus anatomoclinical entities: for patients aged ≤50 years, SE was 31.3%, Sp was 99.7%, PPV was 90.9% and NPV was 94.3%. For granulomatous uveitis, SE was 26.2%, Sp was 97.3%, PPV was 73.3% and NPV was 82.5%. Conclusion A combination of elevated serum ACE and lymphopaenia more convincingly suggests sarcoid uveitis than these investigational tests used alone, especially in patients with granulomatous uveitis, while a lack of these markers corresponds to a high NPV. Trial registration number NCT03863782

Adult-onset Still's disease

International audienceFirst described in 1971, adult-onset Still's disease (AOSD) is a rare multisystemic disorder considered as a complex (multigenic) autoinflammatory syndrome. A genetic background would confer susceptibility to the development of autoinflammatory reactions to environmental triggers. Macrophage and neutrophil activation is a hallmark of AOSD which can lead to a reactive hemophagocytic lymphohistiocytosis. As in the latter disease, the cytotoxic function of natural killer cells is decreased in patients with active AOSD. IL-18 and IL-1β, two proinflammatory cytokines processed through the inflammasome machinery, are key factors in the pathogenesis of AOSD; they cause IL-6 and Th1 cytokine secretion as well as NK cell dysregulation leading to macrophage activation. The clinico-biological picture of AOSD usually includes high spiking fever with joint symptoms, evanescent skin rash, sore throat, striking neutrophilic leukocytosis, hyperferritinemia with collapsed glycosylated ferritin (\textless20%), and abnormal liver function tests. According to the clinical presentation of the disease at diagnosis, two AOSD phenotypes may be distinguished: i) a highly symptomatic, systemic and feverish one, which would evolve into a systemic (mono- or polycyclic) pattern; ii) a more indolent one with arthritis in the foreground and poor systemic symptomatology, which would evolve into a chronic articular pattern. Steroid- and methotrexate-refractory AOSD cases benefit now from recent insights into autoinflammatory disorders: anakinra seems to be an efficient, well tolerated, steroid-sparing treatment in systemic patterns; tocilizumab seems efficient in AOSD with active arthritis and systemic symptoms while TNFα-blockers could be interesting in chronic polyarticular refractory AOSD