A critical region of A20 unveiled by missense TNFAIP3 variations that lead to autoinflammation.

A20 haploinsufficiency (HA20) is an autoinflammatory disease caused by heterozygous loss-of-function variations in TNFAIP3, the gene encoding the A20 protein. Diagnosis of HA20 is challenging due to its heterogeneous clinical presentation and the lack of pathognomonic symptoms. While the pathogenic effect of TNFAIP3 truncating variations is clearly established, that of missense variations is difficult to determine. Herein, we identified a novel TNFAIP3 variation, p.(Leu236Pro), located in the A20 ovarian tumor (OTU) domain and demonstrated its pathogenicity. In the patients' primary cells, we observed reduced A20 levels. Protein destabilization was predicted in silico for A20_Leu236Pro and enhanced proteasomal degradation was confirmed in vitro through a flow cytometry-based functional assay. By applying this approach to the study of another missense variant, A20_Leu275Pro, for which no functional characterization has been performed to date, we showed that this variant also undergoes enhanced proteasomal degradation. Moreover, we showed a disrupted ability of A20_Leu236Pro to inhibit the NF-κB pathway and to deubiquitinate its substrate TRAF6. Structural modeling revealed that two residues involved in OTU pathogenic missense variations (i.e. Glu192Lys and Cys243Tyr) establish common interactions with Leu236. Interpretation of newly identified missense variations is challenging, requiring, as illustrated here, functional demonstration of their pathogenicity. Together with functional studies, in silico structure analysis is a valuable approach that allowed us (i) to provide a mechanistic explanation for the haploinsufficiency resulting from missense variations and (ii) to unveil a region within the OTU domain critical for A20 function.

De Novo Gain-Of-Function Variations in LYN Associated With an Early-Onset Systemic Autoinflammatory Disorder.

OBJECTIVE: To identify the molecular basis of a severe systemic autoinflammatory disorder (SAID) and define its main phenotypic features, and to functionally assess the sequence variations identified in LYN, a gene encoding a nonreceptor tyrosine kinase. METHODS: We used targeted next-generation sequencing and in vitro functional studies of Lyn phosphorylation state and Lyn-dependent NF-κB activity after expression of recombinant Lyn isoforms carrying different sequence variations. RESULTS: We identified a de novo LYN variation (p.Tyr508His) in a patient presenting since birth with recurrent fever, chronic urticaria, atopic dermatitis, arthralgia, increased inflammatory biomarkers, and elevated plasma cytokine levels. We studied the consequences on Lyn phosphorylation state of the p.Tyr508His variation and of the 2 LYN variations reported so far (p.Tyr508Phe and p.Tyr508*), and found that all 3 variations prevent phosphorylation of residue 508 and lead to autophosphorylation of Tyr397. Additionally, these 3 LYN variations activate the NF-κB pathway. These results show a gain-of-function effect of the variations involving Tyr508 on Lyn activity. CONCLUSION: This study demonstrates the pathogenicity of the first 3 LYN variations identified in SAID patients and delineates the phenotypic spectrum of a disease entity characterized by severe, early-onset, systemic inflammatory disease affecting neonates with no family history of SAID. All 3 LYN variations affect the same tyrosine residue located in the C-terminus of Lyn, thereby demonstrating the critical role of this residue in the proper regulation of Lyn activity in humans.

RNF213-associated urticarial lesions with hypercytokinemia.

BACKGROUND: Urticarial lesions are observed in both cutaneous and systemic disorders. Familial forms of urticarial syndromes are rare and can be encountered in systemic autoinflammatory diseases. OBJECTIVE: We sought to investigate a large family with dominantly inherited chronic urticarial lesions associated with hypercytokinemia. METHODS: We performed a genetic linkage analysis in 14 patients from a 5-generation family, as well as whole-exome sequencing, cytokine profiling, and transcriptomic analyses on samples from 2 patients. The identified candidate protein was studied after in vitro expression of the corresponding normal and mutated recombinant proteins. An unsupervised proteomic approach was used to unveil the associated protein network. RESULTS: The disease phenotype of the most affected family members is characterized by chronic urticarial flares associated with extremely high plasma levels of proinflammatory (IL-1ß, IL-6, and TNF-α) and anti-inflammatory (IL-10 and IL-1 receptor antagonist [IL-1RA]) cytokines, with no secondary organ dysfunction, no susceptibility to infections, no fever, and normal C-reactive protein levels. Monocyte transcriptomic analyses identified an immunotolerant profile in the most affected patient. The affected family members carried a loss-of-function mutation in RNF213 that encodes mysterin, a protein with a poorly known physiologic role. We identified the deubiquitinase CYLD, a major regulator of inflammation, as an RNF213 partner and showed that CYLD expression is inhibited by wild-type but not mutant RNF213. CONCLUSION: We identified a new entity characterized by chronic urticarial lesions associated with a clinically blunted hypercytokinemia. This disease, which is due to loss of function of RNF213, reveals mysterin's key role in the complex molecular network of innate immunity.

Mosaic variants in TNFRSF1A: an emerging cause of tumour necrosis factor receptor-associated periodic syndrome.

OBJECTIVE: To identify the molecular basis of a systemic autoinflammatory disorder (SAID) evocative of TNF receptor-associated periodic syndrome (TRAPS). METHODS: (i) Deep next generation sequencing (NGS) through a SAID gene panel; (ii) variant allele distribution in peripheral blood subpopulations; (iii) in silico analyses of mosaic variants using TNF receptor superfamily 1A (TNFRSF1A) crystal structure; (iv) review of the very rare TNFRSF1A mosaic variants reported previously. RESULTS: In a 36-year-old man suffering from recurrent fever for 12 years, high-depth NGS revealed a TNFRSF1A mosaic variant, c.176G>A p.(Cys59Tyr), which Sanger sequencing failed to detect. This mosaic variant displayed a variant allele fraction of 14% in whole blood; it affects both myeloid and lymphoid lineages. p.(Cys59Tyr), a recurrent germline pathogenic variant, affects a crucial cysteine located in the first cysteine-rich domain (CRD1) and involved in a disulphide bridge. Introduction of a tyrosine at this position is expected to disrupt the CRD1 structure. Review of the three previously reported TNFRSF1A mosaic variants revealed that they are all located in a small region of CRD2 and that germinal cells can be affected. CONCLUSION: This study expands the localization of TNFRSF1A mosaic variants to the CRD1 domain. Noticeably, residues involved in germline TNFRSF1A mutational hot spots can also be involved in post-zygotic mutational events. Including our study, only four patients have been thus far reported with TNFRSF1A mosaicism, highlighting the need for a high-depth NGS-based approach to avoid the misdiagnosis of TRAPS. Genetic counselling has to consider the potential occurrence of TNFRSF1A mosaic variants in germinal cells.

Somatic Mosaic NLRP3 Mutations and Inflammasome Activation in Late-Onset Chronic Urticaria.

Chronic urticaria is a common skin disorder with heterogeneous causes. In the absence of physical triggers, chronic urticarial rash is called idiopathic or spontaneous. The objective of this study was to identify the molecular and cellular bases of a disease condition displayed by two unrelated patients aged over 60 years who presented for two decades with a chronic urticaria resistant to standard therapy that occurred in the context of systemic inflammation not triggered by cold. In both patients, a targeted sequencing approach using a next generation technology identified somatic mosaic mutations in NLRP3, a gene encoding a key inflammasome component. The study of several of both patients' cell types showed that, despite the late onset of the disease, NLRP3 mutations were not found to be restricted to myelomonocytic cells. Rather, the data obtained strongly suggested that the mutational event occurred very early, during embryonic development. As shown by functional studies, the identified mutations-an in-frame deletion and a recurrent NLRP3 missense mutation-have a gain-of-function effect on NLRP3-inflammasome activation. Consistently, a complete remission was obtained in both patients with anti-IL-1 receptor antagonists. This study unveils that in late-onset chronic urticaria, the search for autoinflammatory markers and somatic mosaic NLRP3 mutations may have important diagnostic and therapeutic consequences.

NLRP3-associated autoinflammatory diseases: Phenotypic and molecular characteristics of germline versus somatic mutations.

BACKGROUND: NLRP3-associated autoinflammatory diseases (NLRP3-AIDs) include conditions of various severities, due to germline or somatic mosaic NLRP3 mutations. OBJECTIVE: To identify mosaic- versus germline-specific NLRP3 mutations' characteristics, we reinterpreted all the mutations reported in NLRP3-AIDs and performed an in-depth study of 3 novel patients. METHODS: The pathogenicity of all reported mosaic/germline mutations was reassessed according to international recommendations and their location on the NLRP3 3-dimensional structure. Deep-targeted sequencing and NLRP3-inflammasome-activation assays were used to identify the disease-causing mutation in 3 patients. RESULTS: We identified, in 3 patients, mosaic mutations affecting the same NLRP3 amino acid (Glu569). This residue belongs to 1 of the 2 mosaic mutational hot spots that face each other in the core of the NLRP3 ATPase domain. The review of the 90 NLRP3 mutations identified in 277 patients revealed that those hot spots account for 68.5% of patients (37 of 54) with mosaic mutations. Glu569 is affected in 22% of the patients (12 of 54) with mosaic mutations and in 0.4% of patients (1 of 223) with germline mutations. Only 8 of 90 mutations were found in mosaic and germinal states. All of the germline mutations were associated with a severe phenotype. These data suggest that mutations found only in mosaic state could be incompatible with life if present in germinal state. None of the 5 most frequent germline mutations was identified in mosaic state. Mutations found only in germinal state could, therefore, be asymptomatic in mosaic state. CONCLUSIONS: The phenotypic spectrum of NLRP3-AIDs appears to be related to the germinal/mosaic status and localization of the underlying mutations.

The NLRP3 p.A441V Mutation in NLRP3-AID Pathogenesis: Functional Consequences, Phenotype-Genotype Correlations and Evidence for a Recurrent Mutational Event.

OBJECTIVE: To determine the molecular and cellular bases of autoinflammatory syndromes in a multigenerational French family with Muckle-Wells syndrome and in a patient originating from Portugal with familial cold autoinflammatory syndrome. METHODS: Sequencing of NLRP3 exon 3 was performed in all accessible patients. Microsatellite and whole-genome single nucleotide polymorphism genotyping was used i) to test the intrafamilial segregation of the identified variant and ii) to look for a founder effect. Functional analyses included the study of i) apoptosis-associated speck-like protein containing a CARD (ASC) speck formation in HEK293T cells (stably expressing ASC-green fluorescent protein and pro-caspase 1-FLAG) transiently expressing the wild-type or mutated NLRP3 protein, ii) levels of IL-1ß secreted from transfected THP-1 cells, and iii) inflammasome-related gene expression and cytokine secretion from monocytes isolated from patients in crisis (probands from the two families), related patients out of crisis, and from controls. RESULTS: The same heterozygous mutation (c.1322C>T, p.A441V) located in the NACHT domain, segregating with the disease within the first family, was identified in the two families. This mutation was found to be associated with different core haplotypes. NLRP3-A441V led to increased ASC speck formation and high levels of secreted IL-1ß. Monocyte inflammasome-related gene expression and cytokine secretion, which were within the normal range in patients out of crisis, were found to be differentially regulated between the two probands, correlating with their phenotypic status. CONCLUSION: These molecular and cellular findings, which indicate a recurrent mutational event, clearly demonstrate the pathogenicity of the p.A441V missense mutation in NLRP3-associated autoinflammatory disease and point to the interest of studying patients' primary cells to assess disease activity.

Expression of SAA1, SAA2 and SAA4 genes in human primary monocytes and monocyte-derived macrophages.

Circulating serum amyloid A (SAA) is increased in various inflammatory conditions. The human SAA protein family comprises the acute phase SAA1/SAA2, known to activate a large set of innate and adaptive immune cells, and the constitutive SAA4. The liver synthesis of SAA1/SAA2 is well-established but there is still an open debate on extrahepatic SAA expression especially in macrophages. We aimed to investigate the ability of human primary monocytes and monocyte-derived macrophages to express SAA1, SAA2 and SAA4 at both the transcriptional and protein levels, as previous studies almost exclusively dealt with monocytic cell lines. Monocytes and derived macrophages from healthy donors were stimulated under various conditions. In parallel with SAA, pro-inflammatory IL1A, IL1B and IL6 cytokine expression was assessed. While LPS alone was non-effective, a combined LPS/dexamethasone treatment induced SAA1 and to a lesser extent SAA2 transcription in human monocytes and macrophages. In contrast, as expected, pro-inflammatory cytokine expression was strongly induced following stimulation with LPS, an effect which was dampened in the presence of dexamethasone. Furthermore, in monocytes polarized towards a pro-inflammatory M1 phenotype, SAA expression in response to LPS/dexamethasone was potentiated; a result mainly seen for SAA1. However, a major discrepancy was observed between SAA mRNA and intracellular protein levels under the experimental conditions used. Our results demonstrate that human monocytes and macrophages can express SAA genes, mainly SAA1 in response to an inflammatory environment. While SAA is considered as a member of a large cytokine network, its expression in the monocytes-macrophages in response to LPS-dexamethasone is strikingly different from that observed for classic pro-inflammatory cytokines. As monocytes-macrophages are major players in chronic inflammatory diseases, it may be hypothesized that SAA production from macrophages may contribute to the local inflammatory microenvironment, especially when macrophages are compactly organized in granulomas as in sarcoidosis.

Photoaging and skin cancer: Is the inflammasome the missing link?

Photoaging and epithelial skin tumorigenesis are complex processes triggered mainly by UV radiation from chronic sun exposure. This leads to DNA damage and reactive oxygen species (ROS) production, which initiate an inflammatory response that alters cell structure and function. Changes in cell homeostasis and ROS production activate intracellular multiprotein platforms called inflammasomes. Inflammasomes nucleate around cytoplasmic receptors mainly of the NLR (nucleotide-binding domain and leucine-rich repeat) family and regulate caspase-1-dependant secretion of pro-inflammatory interleukin (IL)1ß and IL18 cytokines, and an inflammatory form of death named pyroptosis. NLRP1 inflammasomes have taken centre stage in skin biology, as mutations in NLRP1 underlie the genetic etiology of dermatological diseases and increase the susceptibility to skin cancer. Targeting inflammasome(s) might be an important approach to improve skin inflammation, photoaging and reduce the risk of epithelial skin tumorigenesis. In this context, we discuss the potential implication of NLRP1 and NLRP3 inflammasomes.

Inflammasome biology, molecular pathology and therapeutic implications.

Inflammasomes are intracellular multiprotein signaling complexes, mainly present in myeloid cells. They commonly assemble around a cytoplasmic receptor of the nucleotide-binding leucine-rich repeat containing receptor (NLR) family, although other cytoplasmic receptors like pyrin have been shown to form inflammasomes. The nucleation of the multiprotein scaffolding platform occurs upon detection of a microbial, a danger or a homeostasis pattern by the receptor that will, most commonly, associate with the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD) through homotypic domain interactions resulting in recruitment of procaspase-1. This will lead to the autoproteolytic activation of caspase-1, which regulates the secretion of proinflammatory IL1ß and IL18 cytokines and pyroptosis, a caspase-1-mediated form of cell death. Pyroptosis occurs through cleavage of Gasdermin D, a membrane pore forming protein. Recently, non-canonical inflammasomes have been described, which directly sense intracellular pathogens through caspase-4 and -5 in humans, leading to pyroptosis. Inflammasomes are important in host defense; however, a deregulated activity is associated with a number of inflammatory, immune and metabolic disorders. Furthermore, mutations in inflammasome receptor coding genes are causal for an increasing number of rare autoinflammatory diseases. Biotherapies targeting the products of inflammasome activation as well as molecules that directly or indirectly inhibit inflammasome nucleation and activation are promising therapeutic areas. This review discusses recent advances in inflammasome biology, the molecular pathology of several inflammasomes, and current therapeutic approaches in autoinflammatory diseases and in selected common multifactorial inflammasome-mediated disorders.

Impact of human monocyte and macrophage polarization on NLR expression and NLRP3 inflammasome activation.

Inflammasomes are multiprotein complexes nucleating around an NLR (Nucleotide-binding domain and Leucine-rich Repeat containing protein), which regulate the secretion of the pro-inflammatory interleukin (IL)-1ß and IL-18 cytokines. Monocytes and macrophages, the main cells expressing the inflammasome genes, adapt to their surrounding microenvironment by a phenotypic polarization towards a pro-inflammatory M1 phenotype that promotes inflammation or an anti-inflammatory M2 phenotype important for resolution of inflammation. Despite the importance of inflammasomes in health and disease, little is known about inflammasome gene expression in relevant human cells and the impact of monocyte and macrophage polarization in inflammasome gene expression. We examined the expression of several members of the NLR, caspase and cytokine family, and we studied the activation of the well-described NLRP3 inflammasome in an experimental model of polarized human primary monocytes and monocyte-derived macrophages (M1/M2 phenotypes) before and after activation with LPS, a well-characterized microbial pattern used in inflammasome activation studies. Our results show that the differentiation of monocytes to macrophages alters NLR expression. Polarization using IFN-γ (M1 phenotype), induces among the NLRs studied, only the expression of NOD2. One of the key results of our study is that the induction of NLRP3 expression by LPS is inhibited in the presence of IL-4+IL-13 (M2 phenotype) at both mRNA and protein level in monocytes and macrophages. Unlike caspase-3, the expression of inflammasome-related CASP1 (encodes caspase-1) and CASP4 (encodes caspase-4) is up-regulated in M1 but not in M2 cells. Interestingly, the presence of LPS marginally influenced IL18 mRNA expression and secretion, unlike its impact on IL1B. Our data provide the basis for a better understanding of the role of different inflammasomes within a given environment (M1 and M2) in human cells and their impact in the pathophysiology of several important inflammatory disorders.