Keratoendotheliitis Fugax Hereditaria: A Novel Cryopyrin-Associated Periodic Syndrome Caused by a Mutation in the Nucleotide-Binding Domain, Leucine-Rich Repeat Family, Pyrin Domain-Containing 3 (NLRP3) Gene

The NLR family of innate immune and cell death sensors

Nucleotide-binding oligomerization domain (NOD)-like receptors, also known as nucleotide-binding leucine-rich repeat receptors (NLRs), are a family of cytosolic pattern recognition receptors that detect a wide variety of pathogenic and sterile triggers. Activation of specific NLRs initiates pro- or anti-inflammatory signaling cascades and the formation of inflammasomes-multi-protein complexes that induce caspase-1 activation to drive inflammatory cytokine maturation and lytic cell death, pyroptosis. Certain NLRs and inflammasomes act as integral components of larger cell death complexes-PANoptosomes-driving another form of lytic cell death, PANoptosis. Here, we review the current understanding of the evolution, structure, and function of NLRs in health and disease. We discuss the concept of NLR networks and their roles in driving cell death and immunity. An improved mechanistic understanding of NLRs may provide therapeutic strategies applicable across infectious and inflammatory diseases and in cancer.

Update on ocular manifestations of the main monogenic and polygenic autoinflammatory diseases

Autoinflammatory diseases include disorders with a genetic cause and also complex syndromes associated to polygenic or multifactorial factors. Eye involvement is present in many of them, with different extent and severity. The present review covers ophthalmological lesions in the most prevalent monogenic autoinflammatory diseases, including FMF (familial Mediterranean fever), TRAPS (TNF receptor-associated periodic syndrome), CAPS (cryopyrin-associated periodic syndromes), Blau syndrome, DADA2 (deficiency of adenosine deaminase 2), DITRA (deficiency of the interleukin-36 receptor antagonist), other monogenic disorders, including several ubiquitinopathies, interferonopathies, and the recently described ROSAH (retinal dystrophy, optic nerve edema, splenomegaly, anhidrosis, and headache) syndrome, and VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome. Among polygenic autoinflammatory diseases, ocular manifestations have been reviewed in Behçet's disease, PFAPA (periodic fever, aphthous stomatitis, pharyngitis and cervical adenitis) syndrome, Still's disease and autoinflammatory bone diseases, which encompass CRMO (chronic recurrent multifocal osteomyelitis) and SAPHO (synovitis, acne, pustulosis, hyperostosis and osteitis) syndrome.

Keratitis Fugax Hereditaria Associated With a Novel NLRP3 Mutation in a Non-Finnish Patient

PURPOSE

The aim of this study was to report a novel heterozygous variant c.1712G>T (p.Gly571Val) in the nucleotide-binding domain, leucine-rich repeat family, pyrin domain-containing 3 gene ( NLRP3 ) in a previously unreported non-Finnish individual with keratitis fugax hereditaria (KFH).

METHODS

Ophthalmologic examination of the proband was performed with slit-lamp biomicroscopy and anterior segment optical coherence tomography. Saliva was collected as a source of DNA, after which targeted exome sequencing of candidate genes was performed using a commercially available panel. Identified presumed pathogenic variants were confirmed by Sanger sequencing.

RESULTS

Slit-lamp examination of the 52-year-old female proband revealed peripheral arcus-like degeneration and bilateral central corneal opacification, observed on anterior segment optical coherence tomography to involve the anterior half of the corneal stroma. Examination of the proband's parents revealed clear corneas in each eye. Genetic testing of the proband identified the presence of a novel heterozygous NLRP3 missense mutation (c.1712G>T, p.Gly571Val), which was confirmed by Sanger sequencing. This mutation was absent in the proband's parents.

CONCLUSIONS

Although KFH has been reported only in individuals of Finnish descent and only in association with a missense mutation in exon 1 of NLRP3 , we report an individual of non-Finnish descent with KFH associated with a novel heterozygous variant in exon 2 of NLRP3 . Thus, ophthalmologists should be aware of the ethnic and genetic heterogeneity associated with KFH.

Cryptotanshinone Inhibits Bladder Cancer Cell Malignant Progression in a Lipopolysaccharide-Induced Inflammatory Microenvironment through NLRP3 Inhibition

Background

Bladder cancer (BC) is one of the most common malignancies of the urogenital system. This study assessed the nucleotide-binding oligomerization domain and leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) in BC as well as the effects of cryptotanshinone on changes in BC malignant behaviors and NLRP3 expression under a lipopolysaccharide (LPS)-induced inflammatory microenvironment.

Methods

BC tissue specimens from 62 patients were collected for immunohistochemical detection of NLRP3 protein. BC and normal urothelial cell lines were cultured for the detection of NLRP3 mRNA and protein. Then, BC cells were pretreated with LPS to mimic the inflammatory tumor microenvironment. Next, these cells were incubated with a low or high dose of cryptotanshinone to assess its effects on tumor cell malignant behaviors as well as transfected with NLRP3 cDNA to confirm the role of NLRP3 in BC cells in vitro.

Results

High NLRP3 expression was associated with larger tumor diameters (>2 cm), muscle invasion, and metastasis. The levels of NLRP3 mRNA and protein were greater in BC cells than in normal urothelial cells. LPS pretreatment significantly promoted NLRP3 and inflammatory cytokine expression in BC cells, and induced cell viability, migration, and invasion. However, cryptotanshinone was able to reduce the LPS-induced increase of NLRP3 and inflammatory cytokine expression as well as the BC cell malignant progression. NLRP3 overexpression using NLRP3 cDNA further promoted BC cell malignant progression after LPS stimulation and reversed cryptotanshinone-reduced LPS-induced BC cell malignant behaviors.

Conclusion

NLRP3 might possess oncogenic activity in BC, and the antitumor activity of cryptotanshinone in BC in vitro might be related to its inhibition of NLRP3 expression.

Functional consequences of pathogenic variant c.61G>C in the inflammasome gene NLRP3 underlying keratitis fugax hereditaria

AIMS

To elucidate the effect of NLRP3 variant c.61G>C on interleukin-1β (IL-1β) secretion in keratitis fugax hereditaria (KFH), a cryopyrin-associated periodic syndrome limited to the eye, and to probe the potential modifying role of prednisolone.

METHODS

Peripheral blood mononuclear cells (PBMCs) isolated from whole blood of patients with KFH and healthy controls were grown under steady-state conditions or primed with lipopolysaccharide (LPS) with or without prednisolone, and subsequently activated with ATP. Cell lysates and proteins precipitated from the cell culture media were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. NLRP3, procaspase-1, and IL-1β were visualised by western blotting. The concentration of secreted IL-1β in the culture media was quantified by ELISA.

RESULTS

Following priming of the NLRP3 inflammasome with LPS, a lower threshold for IL-1β secretion was observed in patient-derived PBMCs, compared with healthy controls (median, 124 vs 10 pg/mL, respectively). Interestingly, in PBMCs derived from patients with frequent KFH symptoms, LPS priming alone was able to trigger substantial IL-1β secretion (median, 522 pg/mL), whereas those of patients experiencing occasional KFH attacks showed a subtler release of IL-1β (median, 85 pg/mL). NLRP3 expression was significantly enhanced with LPS stimulation (p=0.03) whereas procaspase-1 expression was not affected. LPS and ATP treated PBMCs from patients with KFH showed significantly diminished IL-1β secretion with prednisolone treatment (p=0.04).

CONCLUSIONS

PBMCs from patients with KFH are more prone to secrete IL-1β, confirming the presumption that the c.61G>C is a gain-of-function variant. Furthermore, prednisolone is confirmed as a potent drug to reduce IL-1β secretion in KFH.

How to Build a Fire: The Genetics of Autoinflammatory Diseases

Systemic autoinflammatory diseases (SAIDs) are a heterogeneous group of disorders caused by excess activation of the innate immune system in an antigen-independent manner. Starting with the discovery of the causal gene for familial Mediterranean fever, more than 50 monogenic SAIDs have been described. These discoveries, paired with advances in immunology and genomics, have allowed our understanding of these diseases to improve drastically in the last decade. The genetic causes of SAIDs are complex and include both germline and somatic pathogenic variants that affect various inflammatory signaling pathways. We provide an overview of the acquired SAIDs from a genetic perspective and summarize the clinical phenotypes and mechanism(s) of inflammation, aiming to provide a comprehensive understanding of the pathogenesis of autoinflammatory diseases.

The NLR gene family: from discovery to present day

The mammalian NLR gene family was first reported over 20 years ago, although several genes that were later grouped into the family were already known at that time. Although it is widely known that NLRs include inflammasome receptors and/or sensors that promote the maturation of caspase 1, IL-1β, IL-18 and gasdermin D to drive inflammation and cell death, the other functions of NLR family members are less well appreciated by the scientific community. Examples include MHC class II transactivator (CIITA), a master transcriptional activator of MHC class II genes, which was the first mammalian NBD-LRR-containing protein to be identified, and NLRC5, which regulates the expression of MHC class I genes. Other NLRs govern key inflammatory signalling pathways or interferon responses, and several NLR family members serve as negative regulators of innate immune responses. Multiple NLRs regulate the balance of cell death, cell survival, autophagy, mitophagy and even cellular metabolism. Perhaps the least discussed group of NLRs are those with functions in the mammalian reproductive system. The focus of this Review is to provide a synopsis of the NLR family, including both the intensively studied and the underappreciated members. We focus on the function, structure and disease relevance of NLRs and highlight issues that have received less attention in the NLR field. We hope this may serve as an impetus for future research on the conventional and non-conventional roles of NLRs within and beyond the immune system.

S-palmitoylation regulates innate immune signaling pathways: molecular mechanisms and targeted therapies

S-palmitoylation is a reversible posttranslational lipid modification that targets cysteine residues of proteins and plays critical roles in regulating the biological processes of substrate proteins. The innate immune system serves as the first line of defense against pathogenic invaders and participates in the maintenance of tissue homeostasis. Emerging studies have uncovered the functions of S-palmitoylation in modulating innate immune responses. In this review, we focus on the reversible palmitoylation of innate immune signaling proteins, with particular emphasis on its roles in the regulation of protein localization, protein stability, and protein-protein interactions. We also highlight the potential and challenge of developing therapies that target S-palmitoylation or de-palmitoylation for various diseases.

Differential Binding of NLRP3 to non-oxidized and Ox-mtDNA mediates NLRP3 Inflammasome Activation

The NLRP3 inflammasome is a key mediator of the innate immune response to sterile tissue injury and is involved in many chronic and acute diseases. Physically and chemically diverse agents activate the NLRP3 inflammasome. Here, we show that NLRP3 binds non-oxidized and Ox-mtDNA differentially, with a half maximum inhibitory concentration (IC50) for non-oxidized and Ox-mtDNA of 4 nM and 247.2 nM, respectively. The NLRP3 Neonatal-Onset Multisystem Inflammatory Disease (NOMIDFCAS) gain of function mutant could bind non-oxidized mtDNA but had higher affinity for Ox-mtDNA compared to WT with an IC50 of 8.1 nM. NLRP3 lacking the pyrin domain can bind both oxidized and non-oxidized mtDNA. Isolated pyrin domain prefers Ox-mtDNA. The NLRP3 pyrin domain shares a protein fold with DNA glycosylases and generate a model for DNA binding based on the structure and sequence alignment to Clostridium acetobutylicum and human OGG1, an inhibitor of Ox-mtDNA generation, 8-oxoguanine DNA glycosylases. We provide a new model for how NLRP3 interacts with Ox-mtDNA supported by DNA binding in the presence of a monoclonal antibody against the pyrin domain. These results give new insights into the mechanism of inflammasome assembly, and into the function of reactive oxygen species in establishing a robust immune response.

Palmitoylation prevents sustained inflammation by limiting NLRP3 inflammasome activation through chaperone-mediated autophagy

As a key component of the inflammasome, NLRP3 is a critical intracellular danger sensor emerging as an important clinical target in inflammatory diseases. However, little is known about the mechanisms that determine the kinetics of NLRP3 inflammasome stability and activity to ensure effective and controllable inflammatory responses. Here, we show that S-palmitoylation acts as a brake to turn NLRP3 inflammasome off. zDHHC12 is identified as the S-acyltransferase for NLRP3 palmitoylation, which promotes its degradation through the chaperone-mediated autophagy pathway. Zdhhc12 deficiency in mice enhances inflammatory symptoms and lethality following alum-induced peritonitis and LPS-induced endotoxic shock. Notably, several disease-associated mutations in NLRP3 are associated with defective palmitoylation, resulting in overt NLRP3 inflammasome activation. Thus, our findings identify zDHHC12 as a repressor of NLRP3 inflammasome activation and uncover a previously unknown regulatory mechanism by which the inflammasome pathway is tightly controlled by the dynamic palmitoylation of NLRP3.

NLRP3 inflammasome and NLRP3-related autoinflammatory diseases: From cryopyrin function to targeted therapies

The NLRP3 inflammasome is one of the NOD-like receptor family members with the most functional characterization and acts as a key player in innate immune system, participating in several physiological processes including, among others, the modulation of the immune system response and the coordination of host defences. Activation of the inflammasome is a crucial signaling mechanism that promotes both an acute and a chronic inflammatory response, which can accelerate the production of pro-inflammatory cytokines, mainly Interleukin (IL)-1β and IL-18, leading to an exacerbated inflammatory network. Cryopyrin associated periodic syndrome (CAPS) is a rare inherited autoinflammatory disorder, clinically characterized by cutaneous and systemic, musculoskeletal, and central nervous system inflammation. Gain-of-function mutations in NLRP3 gene are causative of signs and inflammatory symptoms in CAPS patients, in which an abnormal activation of the NLRP3 inflammasome, resulting in an inappropriate release of IL-1β and gasdermin-D-dependent pyroptosis, has been demonstrated both in in vitro and in ex vivo studies. During recent years, two new hereditary NLRP3-related disorders have been described, deafness autosomal dominant 34 (DFN34) and keratitis fugax hereditaria (KFH), with an exclusive cochlear- and anterior eye- restricted autoinflammation, respectively, and caused by mutations in NLRP3 gene, thus expanding the clinical and genetic spectrum of NLRP3-associated autoinflammatory diseases. Several crucial mechanisms involved in the control of activation and regulation of the NLRP3 inflammasome have been identified and researchers took advantage of this to develop novel target therapies with a significant improvement of clinical signs and symptoms of NLRP3-associated diseases. This review provides a broad overview of NLRP3 inflammasome biology with particular emphasis on CAPS, whose clinical, genetic, and therapeutic aspects will be explored in depth. The latest evidence on two “new” diseases, DFN34 and KFH, caused by mutations in NLRP3 is also described.

Directionality of PYD filament growth determined by the transition of NLRP3 nucleation seeds to ASC elongation

Inflammasomes sense intrinsic and extrinsic danger signals to trigger inflammatory responses and pyroptotic cell death. Homotypic pyrin domain (PYD) interactions of inflammasome forming nucleotide-binding oligomerization domain (NOD)-like receptors with the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD) mediate oligomerization into filamentous assemblies. We describe the cryo-electron microscopy (cryo-EM) structure of the human NLRP3^PYD filament and identify a pattern of highly polar interface residues that form the homomeric interactions leading to characteristic filament ends designated as A- and B-ends. Coupling a titration polymerization assay to cryo-EM, we demonstrate that ASC adaptor protein elongation on NLRP3^PYD nucleation seeds is unidirectional, associating exclusively to the B-end of the filament. Notably, NLRP3 and ASC PYD filaments exhibit the same symmetry in rotation and axial rise per subunit, allowing a continuous transition between NLRP3 and ASC. Integrating the directionality of filament growth, we present a molecular model of the ASC speck consisting of active NLRP3, ASC, and Caspase-1 proteins.

Clinical Spectrum and Geographic Distribution of Keratitis Fugax Hereditaria Caused by the Pathogenic Variant c.61G>C in NLRP3

PURPOSE

To chart clinical findings in individuals with keratitis fugax hereditaria (KFH) and the geographic distribution of their ancestors.

DESIGN

A prospective cross-sectional study.

METHODS

This study took place in a tertiary referral center with a cohort of 84 Finnish patients (55% female) from 25 families with the pathogenic nucleotide-binding domain, leucine-rich repeat (NLR) family pyrin domain containing 3 (NLRP3) variant c.61G>C. Observation procedures and main outcome measures were Sanger sequencing, clinical examination, corneal imaging, and a questionnaire regarding symptoms, quality of life, treatment, and comorbidities.

RESULTS

The oldest members in each family were born in Ostrobothnia in Western Finland or in Southwestern Finland with historical ties to Sweden. One carrier was asymptomatic. Most (77%, 46/60) experienced their first attack between age 6 and 20 years. Three-quarters had unilateral attacks 3 to 5 times annually, primarily triggered by cold wind or air, or stress. Eighty percent (48/60) reported ocular pain (median, 7 on scale 1-10), conjunctival injection, photophobia, foreign body sensation, and tearing during attacks. Visual blur occurred in 75% (45/60) and 91% (55/60) during and after the attack, respectively, for a median of 10 days (range, 1 day-2 months). Forty-seven percent (39/60) had corneal oval opacities with irregular tomography patterns and mild to moderate decrease (20/60 or better) in best-corrected visual acuity that improved with scleral contact lenses. Except for headache in 40%, systemic symptoms were absent during the attacks.

CONCLUSIONS

Symptoms and signs of KFH are restricted to the anterior segment of the eye and vary widely between individuals. We recommend scleral contact lenses as the first-line treatment for reduced vision. Allele frequencies suggest that KFH goes unrecognized in Sweden and populations with Scandinavian heritage.

Pathogenic insights from genetic causes of autoinflammatory inflammasomopathies and interferonopathies

A number of systemic autoinflammatory diseases arise from gain-of-function mutations in genes encoding IL-1-activating inflammasomes or cytoplasmic nucleic acid sensors including the receptor and sensor STING and result in increased IL-1 and type I interferon production, respectively. Blocking these pathways in human diseases has provided proof-of-concept, confirming the prominent roles of these cytokines in disease pathogenesis. Recent insights into the multilayered regulation of these sensor pathways and insights into their role in amplifying the disease pathogenesis of monogenic and complex genetic diseases spurred new drug development targeting the sensors. This review provides insights into the pathogenesis and genetic causes of these "prototypic" diseases caused by gain-of function mutations in IL-1-activating inflammasomes (inflammasomopathies) and in interferon-activating pathways (interferonopathies) including STING-associated vasculopathy with onset in infancy, Aicardi-Goutieres syndrome, and proteasome-associated autoinflammatory syndromes that link activation of the viral sensors STING, "self" nucleic acid metabolism, and the ubiquitin-proteasome system to "type I interferon production" and human diseases. Clinical responses and biomarker changes to Janus kinase inhibitors confirm a role of interferons, and a growing number of diseases with "interferon signatures" unveil extensive cross-talk between major inflammatory pathways. Understanding these interactions promises new tools in tackling the significant clinical challenges in treating patients with these conditions.

Ocular involvement in monogenic autoinflammatory disease

OBJECTIVE

Monogenic Autoinflammatory diseases (AIDs) are a broad spectrum of rare hereditary diseases whose ocular involvement has not been well characterized yet. This systematic review aims to provide an overview of the current knowledge about ocular findings in AIDs.

METHODS

A systematic literature review was conducted using 2 electronic databases, according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. A combination of AIDs and ophthalmology-related search terms were used. All articles were screened by 2 independent reviewers for title, abstract and full text level. We included solely studies that investigated ocular findings in AIDs.

RESULTS

198 papers of 4268 records were retained. Data about 1353 patients with a diagnosis of autoinflammatory disease and ocular involvement were collected (680 CAPS, 211 FMF, 138 TRAPS, 238 Blau, 32 MKD, 21 SIFD, 7 Aicardi Goutières, 3 CANDLE, 8 DADA2, 9 HA20, 6 APLAID). Conjunctivitis was significantly more frequent in CAPS (p < 0.00001), uveitis in Blau, MKD, HA20 and CANDLE (p < 0.00001), papillitis/papilledema in CAPS (p < 0.00001), optic neuritis in Aicardi and DADA2 (p < 0.008), retinal vasculitis in FMF (p < 0.00001), progressive reduction in choroidal thickness in FMF and DADA2 (p < 0.00001), periorbital oedema in TRAPS (p < 0.00001) and retinitis in SIFD (p < 0.00001). Among AIDs with uveitis, granulomatous inflammation was more common in Blau syndrome (p < 0.00001).

CONCLUSION

This systematic literature review characterized the ocular involvement of several AIDs, and the present data may encourage to consider a timely ophthalmological screening program for these rare diseases.

Immunogenetics of the Ocular Anterior Segment: Lessons from Inherited Disorders

Autoimmune and autoinflammatory diseases cause morbidity in multiple organ systems including the ocular anterior segment. Genetic disorders of the innate and adaptive immune system present an avenue to study more common inflammatory disorders and host-pathogen interactions. Many of these Mendelian disorders have ophthalmic manifestations. In this review, we highlight the ophthalmic and molecular features of disorders of the innate immune system. A comprehensive literature review was performed using PubMed and the Online Mendelian Inheritance in Man databases spanning 1973-2020 with a focus on three specific categories of genetic disorders: RIG-I-like receptors and downstream signaling, inflammasomes, and RNA processing disorders. Tissue expression, clinical associations, and animal and functional studies were reviewed for each of these genes. These genes have broad roles in cellular physiology and may be implicated in more common conditions with interferon upregulation including systemic lupus erythematosus and type 1 diabetes. This review contributes to our understanding of rare inherited conditions with ocular involvement and has implications for further characterizing the effect of perturbations in integral molecular pathways.

Molecular mechanisms of phenotypic variability in monogenic autoinflammatory diseases

Monogenic autoinflammatory diseases are a group of rheumatologic disorders caused by dysregulation in the innate immune system. The molecular mechanisms of these disorders are linked to defects in inflammasome-mediated, NF-κB-mediated or interferon-mediated inflammatory signalling pathways, cytokine receptors, the actin cytoskeleton, proteasome complexes and various enzymes. As with other human disorders, disease-causing variants in a single gene can present with variable expressivity and incomplete penetrance. In some cases, pathogenic variants in the same gene can be inherited either in a recessive or dominant manner and can cause distinct and seemingly unrelated phenotypes, although they have a unifying biochemical mechanism. With an enhanced understanding of protein structure and functionality of protein domains, genotype-phenotype correlations are beginning to be unravelled. Many of the mutated proteins are primarily expressed in haematopoietic cells, and their malfunction leads to systemic inflammation. Disease presentation is also defined by a specific effect of the mutant protein in a particular cell type and, therefore, the resulting phenotype might be more deleterious in one tissue than in another. Many patients present with the expanded immunological disease continuum that includes autoinflammation, immunodeficiency, autoimmunity and atopy, which necessitate genetic testing.

A novel missense TGFBI variant p.(Ser591Phe) in a Finnish family with variant lattice corneal dystrophy

INTRODUCTION

We describe the phenotype of a variant lattice corneal dystrophy (LCD) potentially caused by a novel variant c.1772C>T p.(Ser591Phe) in exon 13 of the transforming growth factor beta-induced (TGFBI) gene.

CASE REPORT

The proband, a 71-year-old woman referred because of bilateral LCD, first seen at the age of 65 years, with recent progressive symptoms, underwent a clinical ophthalmological examination, anterior segment optical coherence tomography and confocal microscopy. Additionally, three siblings and three children were examined. The identified TGFBI variant was screened in six family members using Sanger sequencing. A corneal dystrophy gene screen was performed for the proband. Translucent subepithelial irregularities and central to midperipheral stubby branching corneal stromal lattice lines, asymmetric between the right and the left eye, were visible and resulted in mild deterioration of vision in one eye. Genetic testing revealed a novel variant c.1772C>T in TGFBI, leading to the amino acid change p.(Ser591Phe). One daughter carried the same variant but had only thick stromal nerve fibres at the age of 49 years. The other family members neither had corneal abnormalities nor carried the variant. No keratoplasty is yet planned for the proband.

CONCLUSIONS

We classify the novel variant in TGFBI as possibly pathogenic, potentially causing the late-onset, asymmetric variant LCD. Our findings add to the growing number of TGFBI variants associated with a spectrum of phenotypes of variant LCD.

Computational Modeling of NLRP3 Identifies Enhanced ATP Binding and Multimerization in Cryopyrin-Associated Periodic Syndromes

Cyropyrin-associated periodic syndromes (CAPS) are clinically distinct syndromes that encompass a phenotypic spectrum yet are caused by alterations in the same gene, NLRP3. Many CAPS cases and other NLRP3-autoinflammatory diseases (NLRP3-AIDs) are directly attributed to protein-coding alterations in NLRP3 and the subsequent dysregulation of the NLRP3 inflammasome leading to IL-1β-mediated inflammatory states. Here, we used bioinformatics tools, computational modeling, and computational assessments to explore the proteomic consequences of NLRP3 mutations, which potentially drive NLRP3 inflammasome dysregulation. We analyzed 177 mutations derived from familial cold autoinflammatory syndrome (FCAS), Muckle-Wells Syndrome (MWS), and the non-hereditary chronic infantile neurologic cutaneous and articular syndrome, also known as neonatal-onset multisystem inflammatory disease (CINCA/NOMID), as well as other NLRP3-AIDs. We found an inverse relationship between clinical severity and the severity of predicted structure changes resulting from mutations in NLRP3. Bioinformatics tools and computational modeling revealed that NLRP3 mutations that are predicted to be structurally severely-disruptive localize around the ATP binding pocket and that specific proteo-structural changes to the ATP binding pocket lead to enhanced ATP binding affinity by altering hydrogen-bond and charge interactions. Furthermore, we demonstrated that NLRP3 mutations that are predicted to be structurally mildly- or moderately-disruptive affect protein-protein interactions, such as NLRP3-ASC binding and NLRP3-NLRP3 multimerization, enhancing inflammasome formation and complex stability. Taken together, we provide evidence that proteo-structural mechanisms can explain multiple mechanisms of inflammasome activation in NLRP3-AID.

Immunomodulatory Effects of Diterpenes and Their Derivatives Through NLRP3 Inflammasome Pathway: A Review

Nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing protein (NLRP) inflammasomes are involved in the molecular pathogenesis of many diseases and disorders. Among NLRPs, the NLRP3 (in humans encoded by the NLRP3 gene) is expressed predominantly in macrophages as a component of the inflammasome and is associated with many diseases, including gout, type 2 diabetes, multiple sclerosis, atherosclerosis, and neurological diseases and disorders. Diterpenes containing repeated isoprenoid units in their structure are a member of some essential oils that possess diverse biological activities and are becoming a landmark in the field of drug discovery and development. This review sketches a current scenario of diterpenes or their derivatives acting through NLRPs, especially NLRP3-associated pathways with anti-inflammatory effects. For this, a literature survey on the subject has been undertaken using a number of known databases with specific keywords. Findings from the aforementioned databases suggest that diterpenes and their derivatives can exert anti-inflammatory effects via NLRPs-related pathways. Andrographolide, triptolide, kaurenoic acid, carnosic acid, oridonin, teuvincenone F, and some derivatives of tanshinone IIA and phorbol have been found to act through NLRP3 inflammasome pathways. In conclusion, diterpenes and their derivatives could be one of the promising compounds for the treatment of NLRP3-mediated inflammatory diseases and disorders.

In Vivo Corneal Confocal Microscopy and Histopathology of Keratitis Fugax Hereditaria From a Pathogenic Variant in NLRP3

PURPOSE

To apply in vivo corneal confocal microscopy (IVCM) to study the pathogenesis of keratitis (keratoendotheliitis) fugax hereditaria, an autosomal dominant cryopyrin-associated periodic keratitis, associated with the c.61G>C pathogenic variant in the NLRP3 gene, in its acute and chronic phase, and to report histopathologic findings after penetrating keratoplasty.

DESIGN

This was an observational case series.

METHODS

The study population included 6 patients during an acute attack, 18 patients in the chronic phase, and 1 patient who underwent penetrating keratoplasty. Interventions included Sanger sequencing for the NLRP3 variant c.61C>G, a clinical examination, corneal photography, IVCM, light microscopy, and immunohistochemistry. Our primary outcome measures included IVCM and histopathologic findings.

RESULTS

During the acute attack, hyperreflective cellular structures consistent with inflammatory cells transiently occupied the anterior to middle layers of the corneal stroma. Other corneal layers were unremarkable. With recurring attacks, central oval stromal opacities accumulated. IVCM revealed that they contained long, hyperreflective, needle-shaped structures in the extracellular matrix. Using light microscopy, the anterior half of the stroma displayed thin and finely vacuolated lamellae, and keratocytes throughout the stroma were immunopositive for syndecan.

CONCLUSIONS

The acute attacks and chronic stromal deposits mainly involve the anterior to middle layers of the corneal stroma, and the disease is primarily a keratitis rather than a keratoendotheliitis. IVCM shows that inflammatory cells invade only the stroma during an acute attack. IVCM and light microscopic findings suggest that the central corneal opacities represent gradual deposition of extracellular lipids. The disease could make a good in vivo model to study activation of the NLRP3 inflammasome in cryopyrin-associated periodic syndromes.