Mutations of pyrin and mevalonate kinase (MVK) cause distinct interleukin-1β (IL-1β)-mediated autoinflammatory diseases, familial Mediterranean fever (FMF) and hyperimmunoglobulinemia D syndrome (HIDS). Pyrin forms an inflammasome when mutated or in response to bacterial modification of the GTPase RhoA. Here we show that RhoA activates the serine-threonine kinases PKN1 and PKN2 that bind and phosphorylate pyrin. Phosphorylated pyrin binds 14-3-3 proteins, which block the pyrin inflammasome. The binding of 14-3-3 and PKN proteins to FMF-associated mutant pyrin is substantially decreased, and the constitutive IL-1β release from FMF or HIDS patients’ peripheral blood mononuclear cells is attenuated by activating PKN1 and PKN2. Defects in prenylation, seen in HIDS, lead to RhoA inactivation and consequent pyrin inflammasome activation. These data indicate a previously unsuspected fundamental molecular connection between two seemingly distinct autoinflammatory disorders.
Deficiency of mevalonate kinase (MVK) causes systemic inflammation. However, the molecular mechanisms linking the mevalonate pathway to inflammation remain obscure. Geranylgeranyl pyrophosphate (GGPP), a non-sterol intermediate of the mevalonate pathway, is the substrate for protein geranylgeranylation, protein post-translational modification catalyzed by protein geranylgeranyl transferase I (GGTase I). Pyrin is an innate immune sensor that forms an active inflammasome in response to bacterial toxins. Mutations in MEFV (encoding human PYRIN) cause autoinflammatory Familial Mediterranean Fever (FMF) syndrome. Here, we show that protein geranylgeranylation enables Toll-like receptor (TLR)-induced phosphatidylinositol-3-OH kinase PI(3)K) activation by promoting the interaction between the small GTPase Kras and the PI(3)K catalytic subunit p110δ. Macrophages deficient for GGTase I or p110δ exhibited constitutive interleukin-1β release that was MEFV-dependent, but NLRP3-, AIM2- and NLRC4- inflammasome independent. In the absence of protein geranylgeranylation, compromised PI(3)K activity allows for an unchecked TLR-induced inflammatory responses and constitutive activation of the Pyrin inflammasome.
Endoplasmic reticulum aminopeptidase 1 (ERAP1) protein is highly polymorphic with numerous missense amino acid variants. We sought to determine the naturally occurring ERAP1 protein allotypes and their contribution to Behçet’s disease.
Genotypes of all reported missense ERAP1 gene variants with 1000 Genomes EUR super-population frequency greater than 1% were determined in 1,900 Behçet’s disease cases and 1,779 controls from Turkey. ERAP1 protein allotypes and their contributions to Behçet’s disease risk were determined by haplotype identification and disease association analyses.
One ERAP1 protein allotype with 5 non-ancestral amino acids was recessively associated with disease (P = 3.13 × 10−6, odds ratio 2.55, 95% CI 1.70 to 3.82). The ERAP1 association was absent in individuals who lacked HLA-B*51. Individuals who carry HLA-B*51 and who are also homozygous for the haplotype had an increased disease odds compared with those with neither risk factor (P = 4.80 × 10−20, odds ratio 10.96, 95% CI 5.91 to 20.32).
The Behçet’s disease-associated ERAP1 protein allotype was previously shown to have poor peptide trimming activity. Combined with its requirement for HLA-B*51, these data suggest that a hypoactive ERAP1 allotype contributes to Behçet’s disease risk by altering the peptides available for binding to HLA-B*51.
To identify the cause of disease in an adult patient presenting with recent onset fevers, chills, urticaria, fatigue, and profound myalgia, who was negative for cryopyrin-associated periodic syndrome (CAPS) NLRP3 mutations by conventional Sanger DNA sequencing.
We performed whole-exome sequencing and targeted deep sequencing using DNA from the patient’s whole blood to identify a possible NLRP3 somatic mutation. We then screened for this mutation in subcloned NLRP3 amplicons from fibroblasts, buccal cells, granulocytes, negatively-selected monocytes, and T and B lymphocytes and further confirmed the somatic mutation by targeted sequencing of exon 3.
We identified a previously reported CAPS-associated mutation, p.Tyr570Cys, with a mutant allele frequency of 15% based on exome data. Targeted sequencing and subcloning of NLRP3 amplicons confirmed the presence of the somatic mutation in whole blood at a ratio similar to the exome data. The mutant allele frequency was in the range of 13.3%–16.8% in monocytes and 15.2%–18% in granulocytes; Notably, this mutation was either absent or present at a very low frequency in B and T lymphocytes, buccal cells, and in the patient’s cultured fibroblasts.
These data document the possibility of myeloid-restricted somatic mosaicism in the pathogenesis of CAPS, underscoring the emerging role of massively-parallel sequencing in clinical diagnosis.
Behçet’s disease is a chronic multisystem inflammatory disorder characterized mainly by recurrent oral ulcers, ocular involvement, genital ulcers, and skin lesions, presenting with remissions and exacerbations. It is thought that both environmental and genetic factors contribute to its onset and development. Although the etiology of Behçet’s disease remains unclear, recent immunogenetic findings are providing clues to its pathogenesis. In addition to the positive association of HLA-B*51, which was identified more than four decades ago, and which has since been confirmed in multiple populations, recent studies report additional independent associations in the major histocompatibility complex class I region. HLA-B*15, -B*27, -B*57, and -A*26 are independent risk factors for Behçet’s disease, while HLA-B*49 and – A*03 are independent class I alleles that are protective for Behçet’s disease. Genome-wide association studies have identified associations with genome-wide significance (P < 5 × 10−8) in the IL23R–IL12RB2, IL10, STAT4, CCR1-CCR3, KLRC4, ERAP1, TNFAIP3, and FUT2 loci. In addition, targeted next-generation sequencing has revealed the involvement of rare nonsynonymous variants of IL23R, TLR4, NOD2, and MEFV in Behçet’s disease pathogenesis. Significant differences in gene function or mRNA expression associated with the risk alleles of the disease susceptibility loci suggest which genes in a disease-associated locus influence disease pathogenesis. These genes encompass both innate and adaptive immunity and confirm the importance of the predominant polarization towards helper T cell (Th) 1 versus Th2 cells, and the involvement of Th17 cells. In addition, epistasis observed between HLA-B*51 and the risk coding haplotype of the endoplasmic reticulum-associated protease, ERAP1, provides a clue that an HLA class I-peptide presentation-based mechanism contributes to this complex disease.
Behçet’s disease; GWAS; HLA-B*51; ERAP1; disease-associated genetic variants
Patients with autosomal dominant vibratory urticaria have localized hives and systemic manifestations in response to dermal vibration, with coincident degranulation of mast cells and increased histamine levels in serum. We identified a previously unknown missense substitution in ADGRE2 (also known as EMR2), which was predicted to result in the replacement of cysteine with tyrosine at amino acid position 492 (p.C492Y), as the only nonsynonymous variant cosegregating with vibratory urticaria in two large kindreds. The ADGRE2 receptor undergoes autocatalytic cleavage, producing an extracellular subunit that noncovalently binds a transmembrane subunit. We showed that the variant probably destabilizes an autoinhibitory subunit interaction, sensitizing mast cells to IgE-independent vibration-induced degranulation. (Funded by the National Institutes of Health.)
Case reports have linked adult hypophosphatasia as a possible cause of atypical femur fractures (AFF) associated with bisphosphonate use. Adult hypophosphatasia is an asymptomatic genetic condition which results in low alkaline phosphatase and elevated pyridoxal phosphate. We conducted a case–control study to assess the role of hypophosphatasia and atypical femur fracture.
We recruited 13 control patients who took long term bisphosphonates without complication and 10 patients who sustained atypical femur fractures (mean bisphosphonate use, 9 years both cohorts). Patients underwent clinical exam and measurement of alkaline phosphatase and pyridoxal phosphate (PLP) levels. In addition, DNA was extracted and the ALPL gene was sequenced in both cohorts.
Low alkaline phosphatase levels (<55 U/L) were seen in 5/10 AFF patients and 5/13 control patients. Two control patients demonstrated low alkaline phosphatase levels and elevated PLP. The alkaline phosphatase (ALPL) gene exons and intron splice sites were sequenced in the atypical femur fracture and control cohorts and no coding mutations were identified in any subjects. Atypical femur fracture patients demonstrated more varus hip alignment (p < 0.048) with no significant difference in mechanical axis.
We found no evidence of hypophosphatasia as a risk factor for atypical femur fractures. Laboratory findings of mildly low alkaline phosphatase activity were equally common in atypical and control cohorts and may be due to long term bisphosphonate use.
Clinicaltrials.gov number NCT01360099. Prospectively registered May 20, 2011. First patient enrolled June 14, 2011.
Type I interferon (IFN-α/β or IFN-I) signals through two receptor subunits, IFNAR1 and IFNAR2, to orchestrate sterile and infectious immunity. Cellular pathways that regulate IFNAR1 are often targeted by viruses to suppress the antiviral effects of IFN-I. Here we report that encephalitic flaviviruses, including tick-borne encephalitis virus and West Nile virus, antagonize IFN-I signaling by inhibiting IFNAR1 surface expression. Loss of IFNAR1 was associated with binding of the viral IFN-I antagonist, NS5, to prolidase (PEPD), a cellular dipeptidase implicated in primary immune deficiencies in humans. Prolidase was required for IFNAR1 maturation and accumulation, activation of IFNβ-stimulated gene induction, and IFN-I-dependent viral control. Human fibroblasts derived from patients with genetic prolidase deficiency exhibited decreased IFNAR1 surface expression and reduced IFNβ-stimulated signaling. Thus, by understanding flavivirus IFN-I antagonism, prolidase is revealed as a central regulator of IFN-I responses.
Previously, we reported that a novel variant, p.Ser707Tyr, in phospholipase Cγ2 (PLCγ2) is the cause of a dominantly inherited autoinflammatory disease, APLAID. The hypermorphic mutation enhances the PLCγ2 activity and causes an increase in intracellular Ca2+ release from ER stores. As increased intracellular Ca2+ signaling has been associated with NLRP3 inflammasome activation, we studied the role of the NLRP3 inflammasome in the pathogenesis of this disease.
Human peripheral blood mononuclear cells (PBMCs) were isolated from healthy controls and two affected patients. Inflammasome activation was analyzed by Western blotting. Intracellular Ca2+ levels were measured with the FLIPR Calcium 4 assay kit.
Patients’ cells had elevated basal levels of intracellular Ca2+ and the intracellular Ca2+ flux triggered by extracellular CaCl2 was substantially enhanced. Patients’ PBMCs secreted IL-1β in response to LPS priming alone, and this effect was attenuated by use of a PLC inhibitor, intracellular Ca2+ blockers, or an adenylate cyclase activator.
Our findings suggest that the inflammation in patients with APLAID is partially driven by the activation of the NLRP3 inflammasome. These data link two seemingly distinct molecular pathways and provide new insights into the pathogenesis of APLAID and autoinflammation.
autoinflammatory disease; inflammasome; phospholipase Cγ2; IL-1β; pathogenesis
Purpose of review
This article will review the genetic evidence implicating ERAP1, which encodes the endoplasmic reticulum-associated amino-peptidase 1, in susceptibility to rheumatic disease.
Genetic variants and haplotypes of ERAP1 are associated with ankylosing spondylitis, psoriasis, and Behçet’s disease in people of varying ancestries. In each of these diseases, disease-associated variants of ERAP1 have been shown to interact with disease-associated class I Human Leukocyte Antigen (HLA) alleles to influence disease risk. Functionally, disease-associated missense variants of ERAP1 concertedly alter ERAP1 enzymatic function, both quantitatively and qualitatively, while other disease-associated variants influence ERAP1 expression. Therefore, ERAP1 haplotypes (or allotypes) should be examined as functional units. Biologically, this amounts to an examination of the gene regulation and function of the protein encoded by each allotype. Genetically, the relationship between disease risk and ERAP1 allotypes should be examined to determine whether allotypes or individual variants produce the most parsimonious risk models.
Future investigations of ERAP1 should focus on comprehensively characterizing naturally-occurring ERAP1 allotypes, examining the enzymatic function and gene expression of each allotype, and identifying specific allotypes that influence disease susceptibility.
major histocompatibility complex; antigen processing; epistasis
Systemic autoinflammatory diseases are driven by abnormal activation of innate immunity1. Herein we describe a new syndrome caused by high penetrance heterozygous germline mutations in the NFκB regulatory protein TNFAIP3 (A20) in six unrelated families with early onset systemic inflammation. The syndrome resembles Behçet’s disease (BD), which is typically considered a polygenic disorder with onset in early adulthood2. A20 is a potent inhibitor of the NFκB signaling pathway3. TNFAIP3 mutant truncated proteins are likely to act by haploinsufficiency since they do not exert a dominant-negative effect in overexpression experiments. Patients’ cells show increased degradation of IκBα and nuclear translocation of NFκB p65, and increased expression of NFκB-mediated proinflammatory cytokines. A20 restricts NFκB signals via deubiquitinating (DUB) activity. In cells expressing the mutant A20 protein, there is defective removal of K63-linked ubiquitin from TRAF6, NEMO, and RIP1 after TNF stimulation. NFκB-dependent pro-inflammatory cytokines are potential therapeutic targets for these patients.
Prostaglandin E2 (PGE2) is a potent lipid mediator involved in maintaining homeostasis but also promotion of acute inflammation or immune suppression in chronic inflammation and cancer. NLRP3 inflammasome plays an important role in host defense. Uncontrolled activation of NLRP3 inflammasome, due to mutations in the NLRP3 gene causes cryopyrin-associated periodic syndromes (CAPS). Here, we showed that NLRP3 inflammasome activation is inhibited by PGE2 in human primary monocyte-derived macrophages. This effect was mediated through prostaglandin E receptor 4 (EP4) and an increase in intracellular cAMP, independently of protein kinase A (PKA) or exchange protein directly activated by cAMP (Epac). A specific agonist of EP4 mimicked, while its antagonist or EP4 knockdown reversed PGE2-mediated NLRP3 inhibition. PGE2 caused an increase in intracellular cAMP. Blockade of adenylate cyclase by its inhibitor reversed PGE2-mediated NLRP3 inhibition. Increase of intracellular cAMP by an activator of adenylate cyclase or an analog of cAMP, or a blockade of cAMP degradation by phosphodiesterase inhibitor decreased NLRP3 activation. PKA or Epac agonists did not mimic and their antagonists did not reverse PGE2-mediated NLRP3 inhibition. In addition, constitutive IL-1β secretion from LPS-primed PBMCs of CAPS patients was substantially reduced by high doses of PGE2. Moreover, blocking cytosolic phospholipase A2α by its inhibitor or siRNA or inhibiting cyclooxygenase 2, resulting in inhibition of endogenous PGE2 production, caused an increase in NLRP3 inflammasome activation. Our results suggest that PGE2 might play a role in maintaining homeostasis during the resolution phase of inflammation and might serve as an autocrine and paracrine regulator.
inflammasome; prostaglandin; PGE2; phospholipase; cAMP; macrophage; COX2; cPLA2
Behçet's disease (BD) is a multi-system inflammatory disorder of unknown etiology. Two recent genome-wide association studies (GWASs) of BD confirmed a strong association with the MHC class I region and identified two non-HLA common genetic variations. In complex diseases, multiple factors may target different sets of genes in the same pathway and thus may cause the same disease phenotype. We therefore hypothesized that identification of disease-associated pathways is critical to elucidate mechanisms underlying BD, and those pathways may be conserved within and across populations. To identify the disease-associated pathways, we developed a novel methodology that combines nominally significant evidence of genetic association with current knowledge of biochemical pathways, protein–protein interaction networks, and functional information of selected SNPs. Using this methodology, we searched for the disease-related pathways in two BD GWASs in Turkish and Japanese case–control groups. We found that 6 of the top 10 identified pathways in both populations were overlapping, even though there were few significantly conserved SNPs/genes within and between populations. The probability of random occurrence of such an event was 2.24E−39. These shared pathways were focal adhesion, MAPK signaling, TGF-β signaling, ECM–receptor interaction, complement and coagulation cascades, and proteasome pathways. Even though each individual has a unique combination of factors involved in their disease development, the targeted pathways are expected to be mostly the same. Hence, the identification of shared pathways between the Turkish and the Japanese patients using GWAS data may help further elucidate the inflammatory mechanisms in BD pathogenesis.
Autosomal recessive mutations in proteasome subunit β 8 (PSMB8), which encodes the inducible proteasome subunit β5i, cause the immune-dysregulatory disease chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE), which is classified as a proteasome-associated autoinflammatory syndrome (PRAAS). Here, we identified 8 mutations in 4 proteasome genes, PSMA3 (encodes α7), PSMB4 (encodes β7), PSMB9 (encodes β1i), and proteasome maturation protein (POMP), that have not been previously associated with disease and 1 mutation in PSMB8 that has not been previously reported. One patient was compound heterozygous for PSMB4 mutations, 6 patients from 4 families were heterozygous for a missense mutation in 1 inducible proteasome subunit and a mutation in a constitutive proteasome subunit, and 1 patient was heterozygous for a POMP mutation, thus establishing a digenic and autosomal dominant inheritance pattern of PRAAS. Function evaluation revealed that these mutations variably affect transcription, protein expression, protein folding, proteasome assembly, and, ultimately, proteasome activity. Moreover, defects in proteasome formation and function were recapitulated by siRNA-mediated knockdown of the respective subunits in primary fibroblasts from healthy individuals. Patient-isolated hematopoietic and nonhematopoietic cells exhibited a strong IFN gene-expression signature, irrespective of genotype. Additionally, chemical proteasome inhibition or progressive depletion of proteasome subunit gene transcription with siRNA induced transcription of type I IFN genes in healthy control cells. Our results provide further insight into CANDLE genetics and link global proteasome dysfunction to increased type I IFN production.
Kim et al. identify an autoinflammatory disease in mice that is driven by IL-18, resulting from an inactivating mutation in the actin-depolymerizing cofactor Wdr1. This alteration in actin dynamics is recognized by the pyrin inflammasome and results in exaggerated monocyte IL-18 production, whereas inflammasome activation in mature macrophages is unaltered.
Gain-of-function mutations that activate the innate immune system can cause systemic autoinflammatory diseases associated with increased IL-1β production. This cytokine is activated identically to IL-18 by an intracellular protein complex known as the inflammasome; however, IL-18 has not yet been specifically implicated in the pathogenesis of hereditary autoinflammatory disorders. We have now identified an autoinflammatory disease in mice driven by IL-18, but not IL-1β, resulting from an inactivating mutation of the actin-depolymerizing cofactor Wdr1. This perturbation of actin polymerization leads to systemic autoinflammation that is reduced when IL-18 is deleted but not when IL-1 signaling is removed. Remarkably, inflammasome activation in mature macrophages is unaltered, but IL-18 production from monocytes is greatly exaggerated, and depletion of monocytes in vivo prevents the disease. Small-molecule inhibition of actin polymerization can remove potential danger signals from the system and prevents monocyte IL-18 production. Finally, we show that the inflammasome sensor of actin dynamics in this system requires caspase-1, apoptosis-associated speck-like protein containing a caspase recruitment domain, and the innate immune receptor pyrin. Previously, perturbation of actin polymerization by pathogens was shown to activate the pyrin inflammasome, so our data now extend this guard hypothesis to host-regulated actin-dependent processes and autoinflammatory disease.
To describe the pregnancy course and outcome, and use of anakinra, a recombinant selective IL-1 receptor blocker, during pregnancy in patients with cryopyrin-associated periodic syndromes (CAPS), including familial cold auto-inflammatory syndrome (FCAS), Muckle-Wells syndrome (MWS) and neonatal onset multi-system inflammatory disease (NOMID).
Women currently enrolled in natural history protocols (NCT00059748, and/or NCT00069329 under IND) who have been pregnant were included. Subjects underwent a structured, standardized interview with regards to maternal health, pregnancy and fetal outcomes. Medical records were reviewed.
Nine women (four with FCAS, one with MWS and four with NOMID) reported one to four pregnancies, each resulting in a total of fifteen FCAS, three MWS, and six NOMID pregnancies. Six births from FCAS mothers and three births from NOMID mothers occurred while patients were receiving anakinra. If a woman became pregnant while taking anakinra, the pre-pregnancy anakinra dose was continued. Anakinra dose was increased during one twin pregnancy. No preterm births or serious complications of pregnancy were observed. One fetus of the twin pregnancy had renal agenesis and suffered fetal demise. Genetic testing showed the deceased twin carried the same NLRP3 c.785T>C, p.V262A mutation as the mother. The other twin is healthy and mutation negative.
Anakinra was continued during pregnancy in women with CAPS and provided significant, persistent CAPS symptom relief while continuing to prevent the long-term sequelae of CAPS. Anakinra was well tolerated. Although a causal relation between anakinra and renal agenesis seems unlikely, further safety data are needed.
Neonatal-onset multisystem inflammatory disease (NOMID; also known as chronic infantile neurologic, cutaneous, articular [CINCA] syndrome) is characterized by fever, chronic meningitis, uveitis, sensorineural hearing loss, urticarial skin rash, and a characteristic deforming arthropathy. We investigated whether patients with this disorder have mutations in CIAS1, the gene which causes Muckle-Wells syndrome and familial cold autoinflammatory syndrome, two dominantly inherited disorders with some similarities to NOMID/CINCA syndrome.
Genomic DNA from 13 patients with classic manifestations of NOMID/CINCA syndrome and their available parents was screened for CIAS1 mutations by automated DNA sequencing. Cytokine messenger RNA (mRNA) levels were assessed by real-time polymerase chain reaction on peripheral blood leukocyte mRNA, and serum cytokine levels were assayed by enzyme-linked immunosorbent assay. Protein expression was assessed by Western blotting of lysates from plastic-adherent peripheral blood mononuclear cells.
In 6 of the 13 patients, we found 6 heterozygous missense substitutions in CIAS1. Five of the 6 mutations are novel. None of these sequence changes was observed in a panel of >900 chromosomes from healthy controls. Two distinct nucleotide changes in a single codon in unrelated patients resulted in the same amino acid change. In 4 mutation-positive children whose parental DNA was available, no mutation was found in the parental DNA, supporting the conclusion that the mutations arose de novo. Consistent with the recently discovered role of CIAS1 in the regulation of interleukin-1 (IL-1), we found evidence of increased IL-1β, as well as tumor necrosis factor, IL-3, IL-5, and IL-6, but not transforming growth factor β, in a mutation-positive patient compared with normal controls.
Our data increase the total number of known germline mutations in CIAS1 to 20, causing a spectrum of diseases ranging from familial cold autoinflammatory syndrome to Muckle-Wells syndrome to NOMID/CINCA syndrome. Mutations in CIAS1 were only found in ~50% of the cases identified clinically as NOMID/CINCA syndrome, which raises the possibility of genetic heterogeneity. IL-1 regulation by CIAS1 suggests that IL-1 receptor blockade may constitute a rational approach to the treatment of NOMID/CINCA syndrome.
The NLRP3 inflammasome is a component of the inflammatory process and its aberrant activation is pathogenic in inherited disorders such as the cryopyrin associated periodic syndromes (CAPS) and complex diseases such as multiple sclerosis, type 2 diabetes and atherosclerosis. We describe the development of MCC950, a potent, selective, small molecule inhibitor of NLRP3. MCC950 blocks canonical and non-canonical NLRP3 activation at nanomolar concentrations. MCC950 specifically inhibits NLRP3 but not AIM2, NLRC4 or NLRP1 activation. MCC950 reduces Interleukin-1p (IL-1β) production in vivo and attenuates the severity of experimental autoimmune encephalomyelitis (EAE), a disease model of multiple sclerosis. Furthermore, MCC950 treatment rescues neonatal lethality in a mouse model of CAPS and is active in ex vivo samples from individuals with Muckle-Wells syndrome. MCC950 is thus a potential therapeutic for NLRP3-associated syndromes, including autoinflammatory and autoimmune diseases, and a tool for the further study of the NLRP3 inflammasome in human health and disease.
Genetic and genomic investigations are a starting point for the study of human disease, seeking to discover causative variants relevant to disease pathophysiology. Over the past 5 years, massively parallel, high-throughput, next-generation sequencing techniques have revolutionized genetics and genomics, identifying the causes of many mendelian diseases. The application of whole genome sequencing and whole exome sequencing to large populations has produced several publicly-available sequence datasets that have revealed the scope of human genetic variation, and have contributed to important methodological advances in the study of both common and rare genetic variants in genetically-complex diseases. The importance of noncoding genetic variation has been highlighted by the Encyclopedia of DNA Elements (ENCODE) project and NIH Roadmap Epigenomics Program, and integrated analyses of these datasets, together with disease-specific datasets, will provide an important and powerful tool for determining the mechanisms through which disease-associated, noncoding variation influence disease risk.
pediatric rheumatology; somatic mosaicism; genomewide association study; targeted deep resequencing; miRNA; lncRNA
The cryopyrinopathies are a group of rare autoinflammatory disorders that are caused by mutations in CIAS1, encoding the cryopyrin protein. However, cryopyrin mutations are found only in 50% of patients with clinically diagnosed cryopyrinopathies. This study was undertaken to investigate the structural effect of disease-causing mutations on cryopyrin, in order to gain better understanding of the impact of disease-associated mutations on protein function.
We tested for CIAS1 mutations in 22 patients with neonatal-onset multisystem inflammatory disease/chronic infantile neurologic, cutaneous, articular syndrome, 12 with Muckle-Wells syndrome (MWS), 18 with familial cold-induced autoinflammatory syndrome (FCAS), and 3 probands with MWS/FCAS. In a subset of mutation-negative patients, we screened for mutations in proteins that are either homologous to cryopyrin or involved in the caspase 1/interleukin-1β signaling pathway. CIAS1 and other candidate genes were sequenced, models of cryopyrin domains were constructed using structurally homologous proteins as templates, and disease-causing mutations were mapped.
Forty patients were mutation positive, and 7 novel mutations, V262A, C259W, L264F, V351L, F443L, F523C, and Y563N, were found in 9 patients. No mutations in any candidate genes were identified. Most mutations mapped to an inner surface of the hexameric ring in the cryopyrin model, consistent with the hypothesis that the mutations disrupt a closed form of cryopyrin, thus potentiating inflammasome assembly. Disease-causing mutations correlated with disease severity only for a subset of known mutations.
Our modeling provides insight into potential molecular mechanisms by which cryopyrin mutations can inappropriately activate an inflammatory response. A significant number of patients who are clinically diagnosed as having cryopyrinopathies do not have identifiable disease-associated mutations.
Cytopenias are key prognostic indicators of life-threatening infection, contributing to immunosuppression and mortality. Here we define a role for Caspase-1-dependent death, known as pyroptosis, in infection-induced cytopenias by studying inflammasome activation in hematopoietic progenitor cells. The NLRP1a inflammasome is expressed in hematopoietic progenitor cells and its activation triggers their pyroptotic death. Active NLRP1a induced a lethal systemic inflammatory disease that was driven by Caspase-1 and IL-1β but was independent of apoptosis-associated speck-like protein containing a CARD (ASC) and ameliorated by IL-18. Surprisingly, in the absence of IL-1β-driven inflammation, active NLRP1a triggered pyroptosis of hematopoietic progenitor cells resulting in leukopenia in the steady state. During periods of hematopoietic stress induced by chemotherapy or lymphocytic choriomeningitis virus (LCMV) infection, active NLRP1a caused prolonged cytopenia, bone marrow hypoplasia and immunosuppression. Conversely, NLRP1-deficient mice showed enhanced recovery from chemotherapy and LCMV infection, demonstrating that NLRP1 acts as a cellular sentinel to alert Caspase-1 to hematopoietic and infectious stress.
inflammasome; NLRP1; IL-18; IL-1β; progenitor cells; pyroptosis; cytopenia; sepsis