Functional Assessment of Disease-Associated Pyrin Variants.

The pyrin inflammasome detects effectors and toxins that inhibit RhoA GTPases and triggers inflammatory cytokines release and a fast cell death termed pyroptosis. Ancient plague pandemics in the Mediterranean basin have selected in the human population pyrin variants that can trigger an autoinflammatory disease termed familial Mediterranean fever (FMF). In addition, distinct mutations in MEFV, the gene encoding pyrin, cause a different rare autoinflammatory disease termed pyrin-associated autoinflammation with neutrophilic dermatosis (PAAND). As of today, more than 385 MEFV variants have been described although for most of them, whether they are pathogenic variant or benign polymorphism is unknown.Here, we describe different methods using primary human monocytes or engineered monocytic cell lines to functionally characterize MEFV variants, determine their potential pathogenicity, and classify them as either FMF-like or PAAND-like variants.

Chirita D ，Jamilloux Y ，Henry T ，Magnotti F ... -  《-》

Familial Mediterranean fever mutations are hypermorphic mutations that specifically decrease the activation threshold of the Pyrin inflammasome.

FMF is the most frequent autoinflammatory disease and is associated in most patients with bi-allelic MEFV mutations. MEFV encodes Pyrin, an inflammasome sensor activated following RhoGTPase inhibition. The functional consequences of MEFV mutations on the ability of Pyrin variants to act as inflammasome sensors are largely unknown. The aim of this study was to assess whether MEFV mutations affect the ability of Pyrin to detect RhoGTPase inhibition and other inflammasome stimuli. IL-1β and IL-18 released by monocytes from healthy donors (HDs) and FMF patients were measured upon specific engagement of the Pyrin, NLRP3 and NLRC4 inflammasomes. Cell death kinetics following Pyrin activation was monitored in real time. Monocytes from FMF patients secreted significantly more IL-1β and IL-18 and died significantly faster than HD monocytes in response to low concentrations of Clostridium difficile toxin B (TcdB), a Pyrin-activating stimulus. Monocytes from patients bearing two MEFV exon 10 pathogenic variants displayed an increased Pyrin inflammasome response compared with monocytes from patients with a single exon 10 pathogenic variant indicating a gene-dosage effect. Using a short priming step, the response of monocytes from FMF patients to NLRP3- and NLRC4-activating stimuli was normal indicating that MEFV mutations trigger a specific hypersensitivity of monocytes to low doses of a Pyrin-engaging stimulus. Contrary to the NLRP3 mutations described in cryopyrin-associated periodic syndrome, FMF-associated MEFV mutations do not lead to a constitutive activation of Pyrin. Rather, FMF-associated mutations are hypermorphic mutations that specifically decrease the activation threshold of the Pyrin inflammasome without affecting other canonical inflammasomes.

Jamilloux Y ，Lefeuvre L ，Magnotti F ，Martin A ，Benezech S ，Allatif O ，Penel-Page M ，Hentgen V ，Sève P ，Gerfaud-Valentin M ，Duquesne A ，Desjonquères M ，Laurent A ，Rémy-Piccolo V ，Cimaz R ，Cantarini L ，Bourdonnay E ，Walzer T ，Py BF ，Belot A ，Henry T ... -  《-》

Fast diagnostic test for familial Mediterranean fever based on a kinase inhibitor.

Familial Mediterranean fever (FMF) is the most frequent hereditary autoinflammatory disease. Its diagnosis relies on a set of clinical criteria and a genetic confirmation on identification of biallelic pathogenic MEFV variants. MEFV encodes pyrin, an inflammasome sensor. Using a kinase inhibitor, UCN-01, we recently identified that dephosphorylation of FMF-associated pyrin mutants leads to inflammasome activation. The aim of this study was to assess whether quantifying UCN-01-mediated inflammasome activation could discriminate FMF patients from healthy donors (HD) and from patients with other inflammatory disorders (OID). Real-time pyroptosis and IL-1β secretion were monitored in response to UCN-01 in monocytes from FMF patients (n=67), HD (n=71) and OID patients (n=40). Sensitivity and specificity of the resulting diagnostic tests were determined by receiver operating characteristic curve analyses. Inflammasome monitoring in response to UCN-01 discriminates FMF patients from other individuals. Pyroptosis assessment leads to a fast FMF diagnosis while combining pyroptosis and IL-1β dosage renders UCN-01-based assays highly sensitive and specific. UCN-01-triggered monocytes responses were influenced by MEFV gene dosage and MEFV mutations in a similar way as clinical phenotypes are. UCN-01-based inflammasome assays could be used to rapidly diagnose FMF, with high sensitivity and specificity.

Magnotti F ，Malsot T ，Georgin-Lavialle S ，Abbas F ，Martin A ，Belot A ，Fauter M ，Rabilloud M ，Gerfaud-Valentin M ，Sève P ，Duquesne A ，Hot A ，Durupt S ，Savey L ，Giurgea I ，Grateau G ，Henry T ，Jamilloux Y ... -  《-》

Rapid Flow Cytometry-Based Assay for the Functional Classification of MEFV Variants.

Pathogenic MEFV variants cause pyrin-associated autoinflammatory diseases (PAADs), which include familial Mediterranean fever (FMF), FMF-like disease, and pyrin-associated autoinflammation with neutrophilic dermatosis (PAAND). The diagnosis of PAADs is established by clinical phenotypic and genetic analyses. However, the pathogenicity of most MEFV variants remains controversial, as they have not been functionally evaluated. This study aimed to establish and validate a new functional assay to evaluate the pathogenicity of MEFV variants. We transfected THP-1 monocytes with 32 MEFV variants and analyzed their effects on cell death with or without stimulation with Clostridium difficile toxin A (TcdA) or UCN-01. These variants were classified using hierarchical cluster analysis. Macrophages were obtained from three healthy controls and two patients with a novel homozygous MEFVP257L variant, for comparison of IL-1β secretion using a cell-based assay and a novel THP-1-based assay. Disease-associated MEFV variants induced variable degrees of spontaneous or TcdA/UCN-01-induced cell death in THP-1. Cell death was caspase-1 dependent and was accompanied by ASC speck formation and IL-1β secretion, indicating that pathogenic MEFV variants induced abnormal pyrin inflammasome activation and subsequent pyroptotic cell deaths in this assay. The MEFV variants (n = 32) exhibiting distinct response signatures were classified into 6 clusters, which showed a good correlation with the clinical phenotypes. Regarding the pathogenicity of MEFVP257L variants, the results were consistent between the cell-based assay and the THP-1-based assay. Our assay facilitates a rapid and comprehensive assessment of the pathogenicity of MEFV variants and contributes to a refined definition of PAAD subtypes.

Honda Y ，Maeda Y ，Izawa K ，Shiba T ，Tanaka T ，Nakaseko H ，Nishimura K ，Mukoyama H ，Isa-Nishitani M ，Miyamoto T ，Nihira H ，Shibata H ，Hiejima E ，Ohara O ，Takita J ，Yasumi T ，Nishikomori R ... -  《-》

A novel Pyrin-Associated Autoinflammation with Neutrophilic Dermatosis mutation further defines 14-3-3 binding of pyrin and distinction to Familial Mediterranean Fever.

Pyrin-Associated Autoinflammation with Neutrophilic Dermatosis (PAAND) is a recently described monogenic autoinflammatory disease. The causal p.S242R MEFV mutation disrupts a binding motif of the regulatory 14-3-3 proteins within pyrin. Here, we investigate a family with clinical features consistent with PAAND in whom the novel p.E244K MEFV mutation, located in the +2 site of the 14-3-3 binding motif in pyrin, has been found. Multiplex cytokine analyses were performed on p.E244K patient and control serum. Peripheral blood mononuclear cells were stimulated ex vivo with lipopolysaccharide (LPS). In vitro, inflammasome complex formation was evaluated by flow cytometry of Apoptosis-associated Speck-like protein containing a Caspase recruitment domain (ASC) specks. Interleukin-1β (IL-1β) and IL-18 production was quantified by ELISA. The ability of the p.E244K pyrin mutation to interact with 14-3-3 was assessed by immunoprecipitation. PAAND p.E244K patient serum displayed a different cytokine profile compared with patients with Familial Mediterranean Fever (FMF). In overexpression models, p.E244K pyrin was associated with decreased 14-3-3 binding and increased ASC speck formation. THP-1 monocytes expressing PAAND pyrin mutations demonstrated spontaneous caspase-1-dependent IL-1β and IL-18 secretion, as well as cell death, which were significantly greater than those of wild-type and the FMF-associated mutation p.M694V. In PAAND, disruption of the +2 position of a 14-3-3 binding motif in pyrin results in its constitutive activation, with spontaneous production of IL-1β and IL-18, associated with inflammatory cell death. The altered serum cytokine profile may explain the different clinical features exhibited by PAAND patients compared with those with FMF.

Moghaddas F ，Llamas R ，De Nardo D ，Martinez-Banaclocha H ，Martinez-Garcia JJ ，Mesa-Del-Castillo P ，Baker PJ ，Gargallo V ，Mensa-Vilaro A ，Canna S ，Wicks IP ，Pelegrin P ，Arostegui JI ，Masters SL ... -  《-》