PAN1/NALP2/PYPAF2, an inducible inflammatory mediator that regulates NF-kappaB and caspase-1 activation in macrophages

Genome editing of TXNIP in human pluripotent stem cells for the generation of hepatocyte-like cells and insulin-producing islet-like aggregates

BACKGROUND

Thioredoxin-interacting protein (TXNIP) plays a role in regulating endoplasmic reticulum (ER) and oxidative stress, which disrupt glucose homeostasis in diabetes. However, the impact of TXNIP deficiency on the differentiation and functionality of human stem cell-derived somatic metabolic cells remains unclear.

METHODS

We used CRISPR-Cas12a genome editing to generate TXNIP-deficient (TXNIP-/-) H1 human embryonic stem cells (H1-hESCs). These cells were differentiated into hepatocyte-like cells (HLCs) and stem-cell-derived insulin-producing islets (SC-islets). The maturation and functionality TXNIP-/- and TXNIP+/+ SC-islets were assessed by implantation under the kidney capsule of male or female NOD-SCID mice.

RESULTS

TXNIP deficiency significantly increased H1-hESC proliferation without affecting pluripotency, viability, or differentiation potential into HLCs and SC-islets. Bulk RNA-sequencing of thapsigargin-treated TXNIP-/- and TXNIP+/+ hESCs revealed differential expression of stress-responsive genes, with enriched apoptosis-related pathways in TXNIP+/+ cells, but minimal transcriptional changes specific to TXNIP deficiency. In HLCs, TXNIP deletion reduced albumin secretion and insulin signalling, as indicated by decreased AKT phosphorylation, while showing no differences in glycolytic activity or lipid metabolism markers. Under thapsigargin-induced ER stress, TXNIP-/- HLCs exhibited transiently reduced eIF2α phosphorylation and lower BiP expression, suggesting compromised adaptive responses to prolonged stress. SC-islets derived from TXNIP-/- hESCs showed comparable viability, endocrine cell composition, and cytokine responses to TXNIP+/+ islets. Following IFNα or IFNγ treatment, STAT1 phosphorylation was increased in TXNIP-/- SC-islets, indicating that IFN signalling remained intact despite TXNIP deficiency. Upon implantation into NOD-SCID mice, both TXNIP-/- and TXNIP+/+ SC-islets produced human C-peptide and responded to glucose stimulation. However, TXNIP-/- SC-islets did not demonstrate enhanced glycaemic control or glucose-stimulated insulin secretion compared to controls.

CONCLUSIONS

Our study demonstrates that TXNIP deficiency does not improve the differentiation or functionality of HLCs and SC-islets. We present the generation and characterisation of TXNIP-/- and TXNIP+/+ H1-hESCs, HLCs, and SC-islets as valuable models for future studies on the role of TXNIP in metabolic cell biology.

A novel homozygous mutation in the NLRP2 gene causes early embryonic arrest

PURPOSE

Successful reproduction in humans requires maturation and fertilization of gametes as well as early embryonic development. Any deviation from these processes leads to infertility. Early embryonic arrest (EEA) is common in female infertility and is primarily attributed to genetic factors. Mutations in the NLRP2 gene have been identified as the causative factors for EEA. In the present study, a novel mutation identified in NLRP2 underscored the novel homozygous variant and phenotypes that might contribute to its inclusion in the genetic counseling of infertile patients.

METHODS

We recruited a proband from a consanguineous family with a diagnosis of EEA. Peripheral blood samples were collected from the proband and family members for whole-exome sequencing to identify the genes and inheritance patterns associated with infertility; the results were substantiated by Sanger sequencing. All genetic variants and protein structures were analyzed based on computational predictions. Wild-type and mutant plasmids were constructed and transfected into HeLa cells. Subsequent in vitro analyses elucidated the functional impact of the variant.

RESULTS

A novel homozygous mutation in NLRP2 was identified in the proband. The patient harbored a frameshift deletion mutation (c.195delC: p.Tyr66Thrfs*32) in the pyrin structural domain. This genetic alteration resulted in the down-regulation of NLRP2 mRNA expression, truncation of the protein structure, and altered protein localization in cells.

CONCLUSIONS

The current findings broaden the spectra of NLRP2 variants, especially concerning EEA. Also, potential diagnostic markers for patients experiencing recurrent IVF/ICSI failure were identified, and a solid foundation was laid for genetic counseling for female infertility.

Early divergent modulation of NLRP2's and NLRP3's inflammasome sensors vs. AIM2's one by signals from Aβ·Calcium-sensing receptor complexes in human astrocytes

Alzheimer's disease (AD), the most prevalent human dementia, is driven by accruals of extracellular Aβ42 senile patches and intracellular neurofibrillary tangles of hyperphosphorylated Tau (p-Tau) proteins. AD's concurrent neuroinflammation is prompted by innate immunity-related cytosolic protein oligomers named inflammasomes. Upon proper "first" (priming) and "second" (activating) signals, inflammasomes overproduce proinflammatory Interleukin (IL)-1β, and IL-18 while cleaving pyroptosis-promoting Gasdermin D's N-terminal fragments. Our earlier studies highlighted that in pure monocultures, exogenous Aβ25-35-treated nonproliferating human cortical astrocytes (HCAs) made and released surpluses of endogenous Aβ42-oligomers (-os) and p-Tau-os, just as alike-treated human cortical neurons did. Aβ25-35-exposed HCAs also over-released NO, VEGFA, and IL-6. Aβ•CaSR (Aβ·Calcium-Sensing Receptor) complexes generated intracellular signals mediating all such neurotoxic effects since CaSR's negative allosteric modulators (aka NAMs or calcilytics, e.g., NPS2143) fully suppressed them. However, it had hitherto remained unexplored whether signals from Aβ·CaSR complexes also induced the early expression and/or activation of NOD-like 2 (NLRP2) and 3 (NLRP3) and of PYHIN absent in melanoma 2 (AIM2) inflammasomes in monocultured HCAs. To clarify this topic, we used in-situ-Proximity Ligation, qRT-PCR, double antibody arrays, immunoblots, and Caspase 1/4 enzymatic assays. Aβ·CaSR complexes quickly assembled on HCAs surface and issued intracellular signals activating Akt and JAK/STAT axes. In turn, the latter upregulated NLRP2 and NLRP3 PRRs (pattern recognition receptors) yet downregulated AIM2. These effects were specific, being significantly hindered by NPS2143 and inhibitors of PI3K (LY294002), AMPKα (Dorsomorphin), mTOR (Torin1), and JAK/TYK (Brepoticinib). A wide-spectrum inhibitor, Bay11-7082, intensified the Aβ·CaSR/Akt/JAK/STAT axis-driven opposite control of NLRP3's and AIM2's PRR proteins without affecting NLRP2 PRR upregulation. However, the said effects on the PRRs proteins vanished within 24-h. Moreover, Aβ·CaSR signals neither concurrently changed ASC, pro-IL-1β, and Gasdermin-D (holo- and fragments) protein levels and Caspases 1 and 4 enzymatic activities nor induced pyroptosis. Therefore, Aβ·CaSR cues acted as "first (priming) signals" temporarily increasing NLRP2 and NLRP3 PRRs expression without activating the corresponding inflammasomes. The neatly divergent modulation of NLRP3's vs. AIM2's PRR proteins by Aβ·CaSR cues and by Bay11-7082 suggests that, when bacterial or viral DNA fragments are absent, AIM2 might play "anti-inflammasomal" or other roles in HCAs. However, Bay11-7082's no effect on NLRP2 PRR overexpression also reveals that CaSR's downstream mechanisms controlling inflammasomes' sensors are quite complex in HCAs, and hence, given AD's impact on human health, well worth further studies.

The Neglected Sibling: NLRP2 Inflammasome in the Nervous System

While classical NOD-like receptor pyrin domain containing protein 1 (NLRP1) and NLRP3 inflammasomal proteins have been extensively investigated, the contribution of NLRP2 is still ill-defined in the nervous system. Given the putative significance of NLRP2 in orchestrating neuroinflammation, further inquiry is needed to gain a better understanding of its connectome, hence its specific targeting may hold a promising therapeutic implication. Therefore, bioinformatical approach for extracting information, specifically in the context of neuropathologies, is also undoubtedly preferred. To the best of our knowledge, there is no review study selectively targeting only NLRP2. Increasing, but still fragmentary evidence should encourage researchers to thoroughly investigate this inflammasome in various animal- and human models. Taken together, herein we aimed to review the current literature focusing on the role of NLRP2 inflammasome in the nervous system and more importantly, we provide an algorithm-based protein network of human NLRP2 for elucidating potentially valuable molecular partnerships that can be the beginning of a new discourse and future therapeutic considerations.

NLRP inflammasomes in health and disease

NLRP inflammasomes are a group of cytosolic multiprotein oligomer pattern recognition receptors (PRRs) involved in the recognition of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) produced by infected cells. They regulate innate immunity by triggering a protective inflammatory response. However, despite their protective role, aberrant NLPR inflammasome activation and gain-of-function mutations in NLRP sensor proteins are involved in occurrence and enhancement of non-communicating autoimmune, auto-inflammatory, and neurodegenerative diseases. In the last few years, significant advances have been achieved in the understanding of the NLRP inflammasome physiological functions and their molecular mechanisms of activation, as well as therapeutics that target NLRP inflammasome activity in inflammatory diseases. Here, we provide the latest research progress on NLRP inflammasomes, including NLRP1, CARD8, NLRP3, NLRP6, NLRP7, NLRP2, NLRP9, NLRP10, and NLRP12 regarding their structural and assembling features, signaling transduction and molecular activation mechanisms. Importantly, we highlight the mechanisms associated with NLRP inflammasome dysregulation involved in numerous human auto-inflammatory, autoimmune, and neurodegenerative diseases. Overall, we summarize the latest discoveries in NLRP biology, their forming inflammasomes, and their role in health and diseases, and provide therapeutic strategies and perspectives for future studies about NLRP inflammasomes.

NLRP2 in health and disease

NLR family pyrin domain containing 2 (NLRP2) is a novel member of the Nod-like receptor (NLR) family. However, our understanding of NLRP2 has long been ambiguous. NLRP2 may have a role in the innate immune response, but its 'specific' functions remain controversial. Although NLRP2 can initiate inflammasome and promote inflammation, it can also downregulate inflammatory signals. Additionally, NLRP2 has been reported to function in the reproductive system and shows high expression in the placenta. However, the exact role of NLRP2 in the reproductive system is unclear. Here, we highlight the most current progress on NLRP2 in inflammasome activation, effector function and regulation of nuclear factor-κB. And we discuss functions of NLRP2 in inflammatory diseases, reproductive disorders and the potential implication of NLRP2 in human diseases.

"Other Than NLRP3" Inflammasomes: Multiple Roles in Brain Disease

Human neuroinflammatory and neurodegenerative diseases, whose prevalence keeps rising, are still unsolved pathobiological/therapeutical problems. Among others, recent etiology hypotheses stressed as their main driver a chronic neuroinflammation, which is mediated by innate immunity-related protein oligomers: the inflammasomes. A panoply of exogenous and/or endogenous harmful agents activates inflammasomes' assembly, signaling, and IL-1β/IL-18 production and neural cells' pyroptotic death. The underlying concept is that inflammasomes' chronic activation advances neurodegeneration while their short-lasting operation restores tissue homeostasis. Hence, from a therapeutic standpoint, it is crucial to understand inflammasomes' regulatory mechanisms. About this, a deluge of recent studies focused on the NLRP3 inflammasome with suggestions that its pharmacologic block would hinder neurodegeneration. Yet hitherto no evidence proves this view. Moreover, known inflammasomes are numerous, and the mechanisms regulating their expression and function may vary with the involved animal species and strains, as well as organs and cells, and the harmful factors triggered as a result. Therefore, while presently leaving out some little-studied inflammasomes, this review focuses on the "other than NLRP3" inflammasomes that participate in neuroinflammation's complex mechanisms: NLRP1, NLRP2, NLRC4, and AIM2. Although human-specific data about them are relatively scant, we stress that only a holistic view including several human brain inflammasomes and other potential pathogenetic drivers will lead to successful therapies for neuroinflammatory and neurodegenerative diseases.

Derived myeloid lineage induced pluripotent stem as a platform to study human C-C chemokine receptor type 5Δ32 homozygotes

The C-C chemokine receptor type 5 (CCR5) expressed on immune cells supports inflammatory responses by directing cells to the inflammation site. CCR5 is also a major coreceptor for macrophage tropic human immunodeficiency viruses (R5-HIV-1) and its variants can confer protection from HIV infection, making it an ideal candidate to target for therapy. We developed a stepwise protocol that differentiates induced pluripotent stem cells (iPSCs) from individuals homozygous for the CCR5Δ32 variant and healthy volunteers into myeloid lineage induced monocytes (iMono) and macrophages (iMac). By characterizing iMono and iMac against their primary counterparts, we demonstrated that CCR5Δ32 homozygous cells are endowed with similar pluripotent potential for self-renewal and differentiation as iPSC lines generated from non-variant individuals while also showing resistance to HIV infection. In conclusion, these cells are a platform to investigate CCR5 pathophysiology in HIV-positive and negative individuals and to help develop novel therapies.

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.

Activation of NLRP2 in Triple-Negative Breast Cancer sensitizes chemotherapeutic therapy through facilitating hnRNPK function

Nucleotide-binding oligomerization domain (NOD)-like receptor type 2 protein (NLRP2) was reported to inhibit NF-κB in response to inflammatory stimuli, but its role in tumors remains elusive. We screened out NLRP2 from mouse models of breast cancer metastasis. Bioinformatics analysis showed NLRP2 expression was positively correlated with survival rate and negatively correlated with the potential of cancer metastasis. Its significance in Triple-Negative Breast Cancer (TNBC) was investigated by gain- and loss-of-function studies in vivo and vitro. Re-expression of NLRP2 dramatically inhibited the growth and metastasis of the xenograft model of MDA-MB-231 cells. Mechanically, NLRP2 confined hnRNPK within cytoplasm, which in turn blocked vimentin mRNA production. Not only that, NLRP2 further enhanced the H2O2-induced high level of p53&Bax and hence dramatically increased the apoptosis rate (fivefold). Likewise, carboplatin-treated cells showed decreased cell viability, suggesting that patients of TNBC with high level of NLRP2 respond well to chemotherapeutics. Under the stimulus of H2O2, NLRP2-hnRNPK no longer stayed in the cytoplasm, but entered the nucleus to increase the expression of p53 and hence enhanced corresponding apoptosis effect, increasing Bax expression. It suggested that NLRP2 helps p53 enter the nucleus to induce apoptosis. This study revealed a novel function of NLRP2 that modulated oncogenic and anti-oncogenic characteristics of hnRNPK, and provided a new biomarker for TNBC chemotherapy.

Identification of a novel fusion gene NLRC3-NLRP12 in miiuy croaker (Miichthys miiuy)

Fusion gene is a new gene formed by the fusion of all or part of the sequences of two genes, it is caused by chromosome translocation, middle deletion or chromosome inversion. Numerous studies in the past have continuously shown that gene fusions are tightly associated with the occurrence and development of various diseases, especially cancer. Many fusion genes have been identified in humans. However, few fusion genes have been identified in fish. In this study, a novel NLRC3-NLRP12 fusion gene was identified in the Miichthys miiuy (miiuy croaker) by quantitative real-time PCR (qRT-PCR), PCR, and Sanger sequencing. This fusion gene is fused by two genes related to NLRs (nucleotide binding domain and oligomerization domain like receptors). We found that the expression of the NLRC3-NLRP12 fusion gene was significantly upregulated after infection with Vibrio anguillarum (V. anguillarum) or stimulation with lipopolysaccharide (LPS). In addition, the NLRC3-NLRP12 fusion gene was strongly induced by V. anguillarum infection, peaking within the kidney and liver at 12 h post infection. Further functional experiments showed that overexpression of NLRC3-NLRP12 significantly inhibited nuclear factor kappa-B (NF-κB) activation. This study suggests that the newly discovered NLRC3-NLRP12 fusion genes may play an important role in innate immunity in miiuy croaker.

NLRP7 Enhances Choriocarcinoma Cell Survival and Camouflage in an Inflammasome Independent Pathway

BACKGROUND

Gestational choriocarcinoma (GC) is a highly malignant trophoblastic tumor that often develops from a complete hydatidiform mole (HM). NLRP7 is the major gene responsible for recurrent HM and is involved in the innate immune response, inflammation and apoptosis. NLRP7 can function in an inflammasome-dependent or -independent pathway. Recently, we have demonstrated that NLRP7 is highly expressed in GC tumor cells and contributes to their tumorigenesis. However, the underlying mechanisms are still unknown. Here, we investigated the mechanism by which NLRP7 controls these processes in malignant (JEG-3) and non-tumor (HTR8/SVneo) trophoblastic cells. Cell survival, dedifferentiation, camouflage, and aggressiveness were compared between normal JEG-3 cells or knockdown for NLRP7, JEG-3 Sh NLRP7. In addition, HTR8/SVneo cells overexpressing NLRP7 were used to determine the impact of NLRP7 overexpression on non-tumor cells. NLRP7 involvement in tumor cell growth and tolerance was further characterized in vivo using the metastatic mouse model of GC.

RESULTS

We demonstrate that NLRP7 (i) functions in an inflammasome-dependent and -independent manners in HTR8/SVneo and JEG-3 cells, respectively; (ii) differentially regulates the activity of NF-κB in tumor and non-tumor cells; (iii) increases malignant cell survival, dedifferentiation, and camouflage; and (iv) facilitates tumor cells colonization of the lungs in the preclinical model of GC.

CONCLUSIONS

This study demonstrates for the first time the mechanism by which NLRP7, independently of its inflammasome machinery, contributes to GC growth and tumorigenesis. The clinical relevance of NLRP7 in this rare cancer highlights its potential therapeutic promise as a molecular target to treat resistant GC patients.

Activation and Pharmacological Regulation of Inflammasomes

Inflammasomes are intracellular signaling complexes of the innate immune system, which is part of the response to exogenous pathogens or physiological aberration. The multiprotein complexes mainly consist of sensor proteins, adaptors, and pro-caspase-1. The assembly of the inflammasome upon extracellular and intracellular cues drives the activation of caspase-1, which processes pro-inflammatory cytokines IL-1β and IL-18 to maturation and gasdermin-D for pore formation, leading to pyroptosis and cytokine release. Inflammasome signaling functions in numerous infectious or sterile inflammatory diseases, including inherited autoinflammatory diseases, metabolic disorders, cardiovascular diseases, cancers, neurodegenerative disorders, and COVID-19. In this review, we summarized current ideas on the organization and activation of inflammasomes, with details on the molecular mechanisms, regulations, and interventions. The recent developments of pharmacological strategies targeting inflammasomes as disease therapeutics were also covered.

Glial Cells and Brain Diseases: Inflammasomes as Relevant Pathological Entities

Inflammation mediated by the innate immune system is a physiopathological response to diverse detrimental circumstances such as microbe infections or tissular damage. The molecular events that underlie this response involve the assembly of multiprotein complexes known as inflammasomes. These assemblages are essentially formed by a stressor-sensing protein, an adapter protein and a non-apoptotic caspase (1 or 11). The coordinated aggregation of these components mediates the processing and release of pro-inflammatory interleukins (IL-β and IL-18) and cellular death by pyroptosis induction. The inflammatory response is essential for the defense of the organism; for example, it triggers tissue repair and the destruction of pathogen microbe infections. However, when inflammation is activated chronically, it promotes diverse pathologies in the lung, liver, brain and other organs. The nervous system is one of the main tissues where the inflammatory process has been characterized, and its implications in health and disease are starting to be understood. Thus, the regulation of inflammasomes in specific cellular types of the central nervous system needs to be thoroughly understood to innovate treatments for diverse pathologies. In this review, the presence and participation of inflammasomes in pathological conditions in different types of glial cells will be discussed.

NLRP2 inhibits cell proliferation and migration by regulating EMT in lung adenocarcinoma cells

Nucleotide-binding oligomerization domain-like receptors (NLRs) are crucial types of innate immune sensors and well known for their critical roles in the immune system. However, how NLRP2 functions in the progression of cancer is largely unknown. Here, we identified NLRP2 as an antioncogene in lung adenocarcinoma (LUAD) cells. Gain- and loss-of-function studies revealed that NLRP2 silencing promoted cell proliferation and migration by stimulating NF-kB signaling in the microenvironment, which induced epithelial-to-mesenchymal transition (EMT) phenotype and cytoskeleton reorganization in LUAD cells. The addition of the NF-kB inhibitor rescued the function of NLRP2 on EMT. Moreover, NLRP2 increased the level of cofilin phosphorylation and repressed subsequent F-actin reorganization. Consistently, the in vivo study showed that NLRP2 played an inhibitory role in forming metastasis foci. Taken together, NLRP2 inhibited cell proliferation and migration by regulating EMT in LUAD cells, demonstrating the essential function of NLRP2 in the development of LUAD.

Toll-Like Receptors (TLRs), NOD-Like Receptors (NLRs), and RIG-I-Like Receptors (RLRs) in Innate Immunity. TLRs, NLRs, and RLRs Ligands as Immunotherapeutic Agents for Hematopoietic Diseases

The innate immune system plays a pivotal role in the first line of host defense against infections and is equipped with patterns recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Several classes of PRRS, including Toll-like receptors (TLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs) recognize distinct microbial components and directly activate immune cells. TLRs are transmembrane receptors, while NLRs and RLRs are intracellular molecules. Exposure of immune cells to the ligands of these receptors activates intracellular signaling cascades that rapidly induce the expression of a variety of overlapping and unique genes involved in the inflammatory and immune responses. The innate immune system also influences pathways involved in cancer immunosurveillance. Natural and synthetic agonists of TLRs, NLRs, or RLRs can trigger cell death in malignant cells, recruit immune cells, such as DCs, CD8+ T cells, and NK cells, into the tumor microenvironment, and are being explored as promising adjuvants in cancer immunotherapies. In this review, we provide a concise overview of TLRs, NLRs, and RLRs: their structure, functions, signaling pathways, and regulation. We also describe various ligands for these receptors and their possible application in treatment of hematopoietic diseases.

Risk-focused differences in molecular processes implicated in SARS-CoV-2 infection: corollaries in DNA methylation and gene expression

BACKGROUND

Understanding the molecular basis of susceptibility factors to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a global health imperative. It is well-established that males are more likely to acquire SARS-CoV-2 infection and exhibit more severe outcomes. Similarly, exposure to air pollutants and pre-existing respiratory chronic conditions, such as asthma and chronic obstructive respiratory disease (COPD) confer an increased risk to coronavirus disease 2019 (COVID-19).

METHODS

We investigated molecular patterns associated with risk factors in 398 candidate genes relevant to COVID-19 biology. To accomplish this, we downloaded DNA methylation and gene expression data sets from publicly available repositories (GEO and GTEx Portal) and utilized data from an empirical controlled human exposure study conducted by our team.

RESULTS

First, we observed sex-biased DNA methylation patterns in autosomal immune genes, such as NLRP2, TLE1, GPX1, and ARRB2 (FDR < 0.05, magnitude of DNA methylation difference Δβ > 0.05). Second, our analysis on the X-linked genes identified sex associated DNA methylation profiles in genes, such as ACE2, CA5B, and HS6ST2 (FDR < 0.05, Δβ > 0.05). These associations were observed across multiple respiratory tissues (lung, nasal epithelia, airway epithelia, and bronchoalveolar lavage) and in whole blood. Some of these genes, such as NLRP2 and CA5B, also exhibited sex-biased gene expression patterns. In addition, we found differential DNA methylation patterns by COVID-19 status for genes, such as NLRP2 and ACE2 in an exploratory analysis of an empirical data set reporting on human COVID-9 infections. Third, we identified modest DNA methylation changes in CpGs associated with PRIM2 and TATDN1 (FDR < 0.1, Δβ > 0.05) in response to particle-depleted diesel exhaust in bronchoalveolar lavage. Finally, we captured a DNA methylation signature associated with COPD diagnosis in a gene involved in nicotine dependence (COMT) (FDR < 0.1, Δβ > 0.05).

CONCLUSION

Our findings on sex differences might be of clinical relevance given that they revealed molecular associations of sex-biased differences in COVID-19. Specifically, our results hinted at a potentially exaggerated immune response in males linked to autosomal genes, such as NLRP2. In contrast, our findings at X-linked loci such as ACE2 suggested a potentially distinct DNA methylation pattern in females that may interact with its mRNA expression and inactivation status. We also found tissue-specific DNA methylation differences in response to particulate exposure potentially capturing a nitrogen dioxide (NO2) effect-a contributor to COVID-19 susceptibility. While we identified a molecular signature associated with COPD, all COPD-affected individuals were smokers, which may either reflect an association with the disease, smoking, or may highlight a compounded effect of these two risk factors in COVID-19. Overall, our findings point towards a molecular basis of variation in susceptibility factors that may partly explain disparities in the risk for SARS-CoV-2 infection.

Oxysterols Modify NLRP2 in Epithelial Cells, Identifying a Mediator of Ozone-induced Inflammation

Ozone (O3) is a prevalent air pollutant causing lung inflammation. Previous studies demonstrate that O3 oxidizes lipids, such as cholesterol, in the airway to produce oxysterols, such as secosterol A (SecoA), which are electrophiles that are capable of forming covalent linkages preferentially with lysine residues and that consequently modify protein function. The breadth of proteins modified by this oxysterol as well as the biological consequences in the lung are unknown. By using an alkynyl-tagged form of SecoA and shotgun proteomics, we identified 135 proteins as being modified in bronchial epithelial cells. Among them was NLRP2 (NLR family pyrin domain-containing protein 2), which forms an alkynyl-tagged SecoA-protein adduct at lysine residue 1019 (K1019) in the terminal leucine-rich repeat region, a known regulatory region for NLR proteins. NLRP2 expression in airway epithelial cells was characterized, and CRISPR-Cas9 knockout (KO) and shRNA knockdown of NLRP2 were used to determine its function in O3-induced inflammation. No evidence for NLPR2 inflammasome formation or an NLRP2-dependent increase in caspase-1 activity in response to O3 was observed. O3-induced proinflammatory gene expression for CXCL2 and CXCL8/IL8 was further enhanced in NLRP2-KO cells, suggesting a negative regulatory role. Reconstitution of NLRP2-KO cells with the NLRP2 K1019 mutated to arginine partially blocked SecoA adduction and enhanced O3-induced IL-8 release as compared with wild-type NLRP2. Together, our findings uncover NLRP2 as a highly abundant, key component of proinflammatory signaling pathways in airway epithelial cells and as a novel mediator of O3-induced inflammation.

NLRP2 Is Overexpressed in Spinal Astrocytes at the Peak of Mechanical Pain Sensitivity during Complete Freund Adjuvant-Induced Persistent Pain

Our earlier findings revealed that interleukin-1 receptor type-1 (IL-1R1) was overexpressed in spinal neurons, and IL-1R1-deficient mice showed significant attenuation of thermal and mechanical allodynia during the course of the Complete Freund adjuvant (CFA)-induced persistent pain model. In the present study, we found that a ligand of IL-1R1, termed interleukin-1β (IL-1β), is also significantly overexpressed at the peak of mechanical pain sensitivity in the CFA-evoked pain model. Analysis of cellular distribution and modeling using IMARIS software showed that in the lumbar spinal dorsal horn, IL-1β is significantly elevated by astrocytic expression. Maturation of IL-1β to its active form is facilitated by the formation of the multiprotein complex called inflammasome; thus, we tested the expression of NOD-like receptor proteins (NLRPs) in astrocytes. At the peak of mechanical allodynia, we found expression of the NLRP2 inflammasome sensor and its significantly elevated co-localization with the GFAP astrocytic marker, while NLRP3 was moderately present and NLRP1 showed total segregation from the astrocytic profiles. Our results indicate that peripheral CFA injection induces NLRP2 inflammasome and IL-1β expression in spinal astrocytes. The release of mature IL-1β can contribute to the maintenance of persistent pain by acting on its neuronally expressed receptor, which can lead to altered neuronal excitability.

Molecular biology of autoinflammatory diseases

The long battle between humans and various physical, chemical, and biological insults that cause cell injury (e.g., products of tissue damage, metabolites, and/or infections) have led to the evolution of various adaptive responses. These responses are triggered by recognition of damage-associated molecular patterns (DAMPs) and/or pathogen-associated molecular patterns (PAMPs), usually by cells of the innate immune system. DAMPs and PAMPs are recognized by pattern recognition receptors (PRRs) expressed by innate immune cells; this recognition triggers inflammation. Autoinflammatory diseases are strongly associated with dysregulation of PRR interactomes, which include inflammasomes, NF-κB-activating signalosomes, type I interferon-inducing signalosomes, and immuno-proteasome; disruptions of regulation of these interactomes leads to inflammasomopathies, relopathies, interferonopathies, and proteasome-associated autoinflammatory syndromes, respectively. In this review, we discuss the currently accepted molecular mechanisms underlying several autoinflammatory diseases.

Nod-Like Receptors in Host Defence and Disease at the Epidermal Barrier

The nucleotide-binding domain and leucine-rich-repeat-containing family (NLRs) (sometimes called the NOD-like receptors, though the family contains few bona fide receptors) are a superfamily of multidomain-containing proteins that detect cellular stress and microbial infection. They constitute a critical arm of the innate immune response, though their functions are not restricted to pathogen recognition and members engage in controlling inflammasome activation, antigen-presentation, transcriptional regulation, cell death and also embryogenesis. NLRs are found from basal metazoans to plants, to zebrafish, mice and humans though functions of individual members can vary from species to species. NLRs also display highly wide-ranging tissue expression. Here, we discuss the importance of NLRs to the immune response at the epidermal barrier and summarise the known role of individual family members in the pathogenesis of skin disease.

microRNA in inflammatory bowel disease at a glance

Inflammatory bowel disease (IBD) as a chronic inflammation in colon and small intestine has two subtypes: ulcerative colitis (UC) and Crohn's disease (CD). Genome studies have shown that UC and CD are related to microRNAs (miRNAs) expression in addition to environmental factors. This article reviews important researches that have recently been done on miRNAs roles in CD and UC disease. First, miRNA is introduced and its biogenesis and function are discussed. Afterward, roles of miRNAs in inflammatory processes involved in IBD are showed. Finally, this review proposes some circulating and tissue-specific miRNAs, which are useful for CD and UC fast diagnosis and grade prediction. As a conclusion, miRNAs are efficient diagnostic molecules especially in IBD subtypes discrimination and can be used by microarray and real time PCR methods for disease detection and classification.

The emerging roles of NOD-like receptors in antiviral innate immune signaling pathways

Viral infection triggers host pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns or danger-associated molecular patterns to initiate antiviral innate immune responses. NOD-like receptors (NLRs) are a subgroup of cytosolic PRRs. While substantial advances have been made over the past decade, recent studies have unveiled NLRs' emerging roles in the antiviral innate immune signaling pathways. However, the underlying mechanisms have not been fully understood. Here we present a detailed updated overview and novel insights into NLRs' functions in the antiviral innate immune signaling pathways, including TLR, RLR, and cyclic GMP-AMP synthase-stimulator of interferon genes signaling pathways, and highlight discrepancies in the reported findings and current challenges to future studies. A better understanding of this interplay's underlying molecular mechanisms is very important to provide scientific and theoretical bases for regulating antiviral innate immunity.

Role of NLRs in the Regulation of Type I Interferon Signaling, Host Defense and Tolerance to Inflammation

Type I interferon signaling contributes to the development of innate and adaptive immune responses to either viruses, fungi, or bacteria. However, amplitude and timing of the interferon response is of utmost importance for preventing an underwhelming outcome, or tissue damage. While several pathogens evolved strategies for disturbing the quality of interferon signaling, there is growing evidence that this pathway can be regulated by several members of the Nod-like receptor (NLR) family, although the precise mechanism for most of these remains elusive. NLRs consist of a family of about 20 proteins in mammals, which are capable of sensing microbial products as well as endogenous signals related to tissue injury. Here we provide an overview of our current understanding of the function of those NLRs in type I interferon responses with a focus on viral infections. We discuss how NLR-mediated type I interferon regulation can influence the development of auto-immunity and the immune response to infection.

Understanding Inflammasomes and PD-1/PD-L1 Crosstalk to Improve Cancer Treatment Efficiency

Inflammasomes and immune checkpoints have been shown to participate in carcinogenesis, cancer growth and response to treatment. Thus, targeting cytokines resulting from inflammasome activation, such as interleukin (IL)-1β, has emerged as a new tool in the therapeutic arsenal. Moreover, the use of checkpoint inhibitors such as anti-PD-1 or anti-PD-L1 has revolutionized the treatment of some cancer patients. However, inflammasome activation and consecutive cytokine release only occurs in some chemotherapeutic treatments and immune checkpoint inhibitors only work for a restricted number of patients, thus limiting the use of therapies targeting these pathways. Expanding knowledge about the inefficiency of these therapies recently brought forward the hypothesis of targeting both pathways. In this review, we provide an overview of the crosstalk between inflammasomes and programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) that might explain how these two pathways are mutually dependent, and perhaps why targeting only one of them leads to inefficiency of cancer treatment in some patients.

Danger-Sensing/Patten Recognition Receptors and Neuroinflammation in Alzheimer's Disease

Fibrillar aggregates and soluble oligomers of both Amyloid-β peptides (Aβs) and hyperphosphorylated Tau proteins (p-Tau-es), as well as a chronic neuroinflammation are the main drivers causing progressive neuronal losses and dementia in Alzheimer’s disease (AD). However, the underlying pathogenetic mechanisms are still much disputed. Several endogenous neurotoxic ligands, including Aβs, and/or p-Tau-es activate innate immunity-related danger-sensing/pattern recognition receptors (PPRs) thereby advancing AD’s neuroinflammation and progression. The major PRR families involved include scavenger, Toll-like, NOD-like, AIM2-like, RIG-like, and CLEC-2 receptors, plus the calcium-sensing receptor (CaSR). This quite intricate picture stresses the need to identify the pathogenetically topmost Aβ-activated PRR, whose signaling would trigger AD’s three main drivers and their intra-brain spread. In theory, the candidate might belong to any PRR family. However, results of preclinical studies using in vitro nontumorigenic human cortical neurons and astrocytes and in vivo AD-model animals have started converging on the CaSR as the pathogenetically upmost PRR candidate. In fact, the CaSR binds both Ca²⁺ and Aβs and promotes the spread of both Ca²⁺ dyshomeostasis and AD’s three main drivers, causing a progressive neurons’ death. Since CaSR’s negative allosteric modulators block all these effects, CaSR’s candidacy for topmost pathogenetic PRR has assumed a growing therapeutic potential worth clinical testing.

ATP-Binding and Hydrolysis in Inflammasome Activation

The prototypical model for NOD-like receptor (NLR) inflammasome assembly includes nucleotide-dependent activation of the NLR downstream of pathogen- or danger-associated molecular pattern (PAMP or DAMP) recognition, followed by nucleation of hetero-oligomeric platforms that lie upstream of inflammatory responses associated with innate immunity. As members of the STAND ATPases, the NLRs are generally thought to share a similar model of ATP-dependent activation and effect. However, recent observations have challenged this paradigm to reveal novel and complex biochemical processes to discern NLRs from other STAND proteins. In this review, we highlight past findings that identify the regulatory importance of conserved ATP-binding and hydrolysis motifs within the nucleotide-binding NACHT domain of NLRs and explore recent breakthroughs that generate connections between NLR protein structure and function. Indeed, newly deposited NLR structures for NLRC4 and NLRP3 have provided unique perspectives on the ATP-dependency of inflammasome activation. Novel molecular dynamic simulations of NLRP3 examined the active site of ADP- and ATP-bound models. The findings support distinctions in nucleotide-binding domain topology with occupancy of ATP or ADP that are in turn disseminated on to the global protein structure. Ultimately, studies continue to reveal how the ATP-binding and hydrolysis properties of NACHT domains in different NLRs integrate with signaling modules and binding partners to control innate immune responses at the molecular level.

NLRP3 Sensing of Diverse Inflammatory Stimuli Requires Distinct Structural Features

The NLRP3 inflammasome is central to host defense and implicated in various inflammatory diseases and conditions. While the favored paradigm of NLRP3 inflammasome activation stipulates a unifying signal intermediate that de-represses NLRP3, this view has not been tested. Further, structures within NLRP3 required for inflammasome activation are poorly defined. Here we demonstrate that while the NLRP3 LRRs are not auto-repressive and are not required for inflammasome activation by all agonists, distinct sequences within the NLRP3 LRRs positively and negatively modulate inflammasome activation by specific ligands. In addition, elements within the HD1/HD2 “hinge” of NLRP3 and the nucleotide-binding domain have contrasting functions depending upon the specific agonists. Further, while NLRP3 1–432 is minimally sufficient for inflammasome activation by all agonists tested, the pyrin, and linker domains (1–134) function cooperatively and are sufficient for inflammasome activation by certain agonists. Conserved cysteines 8 and 108 appear important for inflammasome activation by sterile, but not infectious insults. Our results define common and agonist-specific regions of NLRP3 that likely mediate ligand-specific responses, discount the hypothesis that NLRP3 inflammasome activation has a unified mechanism, and implicate NLRP3 as an integrator of agonist-specific, inflammasome activating signals.

Kynurenine regulates NLRP2 inflammasome in astrocytes and its implications in depression

Increased kynurenine (Kyn) metabolized from tryptophan (Try) is a biomarker in the immune dysfunction of depression. However, the mechanism by which Kyn change promotes depression is poorly defined. Astrocytes are involved in the neuroinflammation of depression. Among the numerous inflammatory cytokines, interleukin-1β (IL-1β) produced by astrocytic Nod-like receptor protein (NLRP) inflammasome is crucial in the pathogenesis of depression. In the present study, Kyn was shown to be a proinflammatory metabolite in the neuroimmune signaling network mediating depressive-like behavior. First, in chronic mild stress (CMS)-induced depressive mice, the level of Kyn notably increased in the hippocampus, accompanied by the activation of astrocytic NLRP2 inflammasome. Kyn treatment specifically upregulated Nod-like receptor protein 2 (NLPR2) expression in primary mouse astrocytes. Kyn + ATP activated NLRP2 inflammasome, evidenced by increased caspase-1 expression and IL-1β release. After Kyn treatment, nuclear factor kappa-B (NF-κB) could translocate to the nucleus and bind the promoter of NLRP2, subsequently increased NLRP2 transcription in cultured astrocytes in vitro. Intraperitoneal injection of Kyn activated NLRP2 inflammasome in astrocytes of hippocampus in mice, while NLRP2 knockdown in astrocytes abolished depressive-like behaviors in mice induced by Kyn, suggesting the critical role of NLRP2 in Kyn-induced depression. These findings demonstrate a novel mechanism that Kyn upregulates NLRP2 in an NF-κB-dependent pathway and provide a new strategy for treatment of depression.

Genetics and Epigenetics of Atopic Dermatitis: An Updated Systematic Review

BACKGROUND

Atopic dermatitis is a common inflammatory skin disorder that affects up to 15-20% of the population and is characterized by recurrent eczematous lesions with intense itching. As a heterogeneous disease, multiple factors have been suggested to explain the nature of atopic dermatitis (AD), and its high prevalence makes it necessary to periodically compile and update the new information available. In this systematic review, the focus is set at the genetic and epigenetic studies carried out in the last years.

METHODS

A systematic literature review was conducted in three scientific publication databases (PubMed, Cochrane Library, and Scopus). The search was restricted to publications indexed from July 2016 to December 2019, and keywords related to atopic dermatitis genetics and epigenetics were used.

RESULTS

A total of 73 original papers met the inclusion criteria established, including 9 epigenetic studies. A total of 62 genes and 5 intergenic regions were described as associated with AD.

CONCLUSION

Filaggrin (FLG) polymorphisms are confirmed as key genetic determinants for AD development, but also epigenetic regulation and other genes with functions mainly related to the immune system and extracellular matrix, reinforcing the notion of skin homeostasis breakage in AD.

NLRP2 Regulates Proinflammatory and Antiapoptotic Responses in Proximal Tubular Epithelial Cells

Nod-like Receptor Pyrin domain containing proteins (NLRPs) expressed by resident renal cells may contribute to the pathogenesis of multiple renal diseases. Cystinosis is a genetic disorder that affects kidney and particularly proximal tubular epithelial cells (PTEC). Here, we investigated the expression of NLRP family members in human control and cystinotic conditionally immortalized PTEC. Among all the NLRPs tested, we found that NLRP2 is highly expressed in cystinostic PTEC, but not in PTEC from healthy subjects. The NLRP2 overexpression was confirmed in primary PTEC and in kidney biopsies from cystinotic patients. In order to elucidate the role of NLRP2 in PTEC, we stably transfected control PTEC with an NLRP2-containing plasmid. We showed that NLRP2 markedly increases the production of several NF-κB regulated cytokines and chemokines. Accordingly, we demonstrated that NLRP2 interacts with IKKa and positively regulates the DNA-binding activity of p50 and p65 NF-κB, by modulating the p65 NF-κB phosphorylation status in Serine 536. Transcriptome analysis revealed that NLRP2 also upregulates the expression of profibrotic mediators and reduces that of several interferon-inducible genes. Finally, NLRP2 overexpression decreased the apoptotic cell rate. Consistently, silencing of NLRP2 by small-interfering RNA in cystinotic PTEC resulted in a significant decrease in cytokine and chemokine production as well as in an increase in the apoptosis rate. Altogether, our data reveals a previously unrecognized role for NLRP2 in regulating proinflammatory, profibrotic and antiapoptotic responses in PTEC, through NF-κB activation. Moreover, our findings unveil a novel potential mechanism involving NLRP2 overexpression in the pathogenesis of cystinosis.

The Innate Immune Sensor NLRC3 Acts as a Rheostat that Fine-Tunes T Cell Responses in Infection and Autoimmunity

Appropriate immune responses require a fine balance between immune activation and attenuation. NLRC3, a non-inflammasome-forming member of the NLR innate immune receptor family, attenuates inflammation in myeloid cells and proliferation in epithelial cells. T lymphocytes express the highest amounts of Nlrc3 transcript where its physiologic relevance is unknown. We show that NLRC3 attenuated interferon-γ and TNF expression by CD4⁺ T cells and reduced T helper 1 (Th1) and Th17 cell proliferation. Nlrc3^-/- mice exhibited increased and prolonged CD4⁺ T cell responses to lymphocytic choriomeningitis virus infection and worsened experimental autoimmune encephalomyelitis (EAE). These functions of NLRC3 were executed in a T-cell-intrinsic fashion: NLRC3 reduced K63-linked ubiquitination of TNF-receptor-associated factor 6 (TRAF6) to limit NF-κB activation, lowered phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), and diminished glycolysis and oxidative phosphorylation. This study reveals an unappreciated role for NLRC3 in attenuating CD4⁺ T cell signaling and metabolism.

Suppressing NLRP2 expression accelerates hepatic steatosis: A mechanism involving inflammation and oxidative stress

Nonalcoholic fatty liver disease (NAFLD) is characterized by lipid accumulation and inflammation in the liver, contributing to a broad spectrum of severe pathologies, such as metabolic syndrome and hepatocellular carcinoma. Presently, the pathogenesis that attributes to NAFLD has not been fully understood. NLRP2 has been shown to inhibit the NF-κB signaling, and thus may contribute to regulate the inflammatory response. However, its role in NAFLD is largely unclear. In the study, we found that NLRP2 was markedly decreased in liver tissues of individuals with severe steatosis, or in a genetic deficiency (ob/ob) mice. High fat diet (HFD) feeding also led to a significant reduction of NLRP2 in liver of mice. Then, the wild type (WT) and NLRP2 knockout (KO) mice were used to further explore the role of NLRP2 in the NAFLD progression. NLRP2 knockout mice exhibited severer metabolic syndrome and hepatic steatosis after HFD administration, as evidenced by the increased body weight, liver histological changes and lipid accumulation. Moreover, HFD feeding-induced inflammation was significantly accelerated by the loss of NLRP2, as evidenced by the increased expression of pro-inflammatory cytokines and activation of nuclear factor κB (NF-κB) pathway. In addition, oxidative stress triggered by HFD was further promoted by NLRP2 deletion through repressing NF-E2-related factor 2 (Nrf2) pathway. In vitro, we surprisingly found that promoting Nrf2 activation could attenuate NLRP2 knockout-accelerated inflammation and reactive oxygen species (ROS) generation. Therefore, our study indicated that NLRP2 might be a potential target for developing effective therapeutic strategy to prevent NAFLD progression.

Negative Regulation of Cytosolic Sensing of DNA

In mammals, cytosolic detection of nucleic acids is critical in initiating innate antiviral responses against invading pathogens (like bacteria, viruses, fungi and parasites). These programs are mediated by multiple cytosolic and endosomal sensors and adaptor molecules (c-GAS/STING axis and TLR9/MyD88 axis, respectively) and lead to the production of type I interferons (IFNs), pro-inflammatory cytokines, and chemokines. While the identity and role of multiple pattern recognition receptors (PRRs) have been elucidated, such immune surveillance systems must be tightly regulated to limit collateral damage and prevent aberrant responses to self- and non-self-nucleic acids. In this review, we discuss recent advances in our understanding of how cytosolic sensing of DNA is controlled during inflammatory immune responses.

NLRP2 negatively regulates antiviral immunity by interacting with TBK1

Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are intracellular pattern recognition receptors (PRRs) that regulate a variety of inflammatory and host defense responses. Unlike the well-established NLRs, the roles of NLRP2 are controversial and poorly defined. Here, we report that NLRP2 acts as a negative regulator of TANK-binding kinase 1 (TBK1)-mediated type I interferon (IFN) signaling. Mechanistically, NLRP2 interacted directly with TBK1, and this binding disrupted the interaction of TBK1 and interferon regulatory factor 3 (IRF3), which interfered with TBK1-induced IRF3 phosphorylation. IFNs induce a series of proteins that have well-known antiviral or immune-regulatory functions, and tight control of the IFN signaling cascade is critical for limiting tissue damage and preventing autoimmunity. Our studies indicate that the NLRP2-TBK1 axis may serve as an additional signaling cascade to maintain immune homeostasis in response to viral infection.

Rare coding variant analysis in a large cohort of Ashkenazi Jewish families with inflammatory bowel disease

Rare variants are thought to contribute to the genetics of inflammatory bowel disease (IBD), which is more common amongst the Ashkenazi Jewish (AJ) population. A family-based approach using exome sequencing of AJ individuals with IBD was employed with a view to identify novel rare genetic variants for this disease. Exome sequencing was performed on 960 Jewish individuals including 513 from 199 multiplex families with up to eight cases. Rare, damaging variants in loci prioritized by linkage analysis and those shared by multiple affected individuals within the same family were identified. Independent evidence of association of each variant with disease was assessed. A number of candidate variants were identified, including in genes involved in the immune system. The ability to achieve statistical significance in independent case/control replication data was limited by power and was only achieved for variants in the well-established Crohn's disease gene, NOD2. This work demonstrates the challenges of identifying disease-associated rare damaging variants from exome data, even amongst a favorable cohort of familial cases from a genetic isolate. Further research of the prioritized rare candidate variants is required to confirm their association with the disease.

The inflammasome as a target for pain therapy

The interleukin-1 family of cytokines are potent inducers of inflammation and pain. Proteolytic activation of this family of cytokines is under the control of several innate immune receptors that coordinate to form large multiprotein signalling platforms, termed inflammasomes. Recent evidence suggests that a wide range of inflammatory diseases, cancers, and metabolic and autoimmune disorders, in which pain is a common complaint, may be coordinated by inflammasomes. Activation of inflammasomes results in cleavage of caspase-1, which subsequently induces downstream initiation of several potent pro-inflammatory cascades. Therefore, it has been proposed that targeting inflammasome activity may be a novel and effective therapeutic strategy for these pain-related diseases. The purpose of this narrative review article is to provide the reader with an overview of the activation and regulation of inflammasomes and to investigate the potential therapeutic role of inflammasome inhibition in the treatment of diseases characterized by pain, including the following: complex regional pain syndrome, gout, rheumatoid arthritis, inflammatory pain, neuropathic pain, chronic prostatitis, chronic pelvic pain syndrome, and fibromyalgia. We conclude that the role of the inflammasome in pain-associated diseases is likely to be inflammasome subtype and disease specific. The currently available evidence suggests that disease-specific targeting of the assembly and activity of the inflammasome complex may be a novel therapeutic opportunity for the treatment of refractory pain in many settings.

NLRP2 is a suppressor of NF-ƙB signaling and HLA-C expression in human trophoblasts†,‡

During pregnancy, fetal extravillous trophoblasts (EVT) play a key role in the regulation of maternal T cell and NK cell responses. EVT display a unique combination of human leukocyte antigens (HLA); EVT do not express HLA-A and HLA-B, but do express HLA-C, HLA-E, and HLA-G. The mechanisms establishing this unique HLA expression pattern have not been fully elucidated. The major histocompatibility complex (MHC) class I and class II transcriptional activators NLRC5 and CIITA are expressed neither by EVT nor by the EVT model cell line JEG3, which has an MHC expression pattern identical to that of EVT. Therefore, other MHC regulators must be present to control HLA-C, HLA-E, and HLA-G expression in these cells. CIITA and NLRC5 are both members of the nucleotide-binding domain, leucine-rich repeat (NLR) family of proteins. Another member of this family, NLRP2, is highly expressed by EVT and JEG3, but not in maternal decidual stromal cells. In this study, transcription activator-like effector nuclease technology was used to delete NLRP2 in JEG3. Furthermore, lentiviral delivery of shRNA was used to knockdown NLRP2 in JEG3 and primary EVT. Upon NLRP2 deletion, Tumor Necrosis Factor-α (TNFα)-induced phosphorylation of NF-KB p65 increased in JEG3 and EVT, and more surprisingly a significant increase in constitutive HLA-C expression was observed in JEG3. These data suggest a broader role for NLR family members in the regulation of MHC expression during inflammation, thus forming a bridge between innate and adaptive immune responses. As suppressor of proinflammatory responses, NLRP2 may contribute to preventing unwanted antifetal responses.

From the Psychiatrist's Couch to Induced Pluripotent Stem Cells: Bipolar Disease in a Dish

Bipolar disease (BD) is one of the major public health burdens worldwide and more people are affected every year. Comprehensive genetic studies have associated thousands of single nucleotide polymorphisms (SNPs) with BD risk; yet, very little is known about their functional roles. Induced pluripotent stem cells (iPSCs) are powerful tools for investigating the relationship between genotype and phenotype in disease-relevant tissues and cell types. Neural cells generated from BD-specific iPSCs are thought to capture associated genetic risk factors, known and unknown, and to allow the analysis of their effects on cellular and molecular phenotypes. Interestingly, an increasing number of studies on BD-derived iPSCs report distinct alterations in neural patterning, postmitotic calcium signaling, and neuronal excitability. Importantly, these alterations are partly normalized by lithium, a first line treatment in BD. In light of these exciting findings, we discuss current challenges to the field of iPSC-based disease modelling and future steps to be taken in order to fully exploit the potential of this approach for the investigation of BD and the development of new therapies.

Human parvovirus B19 nonstructural protein NS1 activates NLRP3 inflammasome signaling in adult‑onset Still's disease

Dysregulation of inflammasomes serves a pathogenic role in autoinflammatory diseases (AIDs) and adult-onset Still's disease (AOSD) has been categorized as an AID. The present study investigated the expression of NLR family pyrin domain containing proteins (NLRPs) inflammasome in patients with AOSD, the effect of inflammasome inhibitors on NLRP3 signaling and whether human parvovirus B19‑associated antigens can activate NLRP3 in patients with AOSD. mRNA expression levels of NLRPs in peripheral blood mononuclear cells (PBMCs) from 34 patients with AOSD and 14 healthy individuals were determined using reverse transcription‑quantitative polymerase chain reaction. Protein expression of NLRP3 was evaluated by western blotting. Supernatant cytokine levels were measured by ELISA. Among the NLRPs investigated in the present study, NLRP3 transcripts were markedly elevated and expression of NLRP2, NLRP7 and NLRP12 was decreased in patients with AOSD compared with the controls. Treatment with NLRP3 inhibitors significantly reduced downstream NLRP3 signaling in PBMCs form patients with AOSD. B19‑nonstructural protein (NS)1 stimulation of PBMCs from patients with AOSD induced significant upregulation of transcript levels of NLRP3, caspase‑1 and interleukin (IL)‑1β compared with PBMCs from healthy controls. B19‑NS1 stimulation of PBMCs from patients with AOSD induced significant increase in supernatant levels of IL‑1β and protein expression of NLRP3, caspase‑1, IL‑1β, and IL‑18 compared with healthy controls. Elevated expression of NLRP3 and its downstream inflammasome signaling components in patients with AOSD indicated a potential pathogenic role of B19‑NS1. Thus, B19‑NS1 may induce expression of IL‑1β and IL‑18 through activation of caspase‑1‑associated NLRP3‑inflammasome in AOSD.

CRISPR/Cas9-Correctable mutation-related molecular and physiological phenotypes in iPSC-derived Alzheimer's PSEN2 N141I neurons

Basal forebrain cholinergic neurons (BFCNs) are believed to be one of the first cell types to be affected in all forms of AD, and their dysfunction is clinically correlated with impaired short-term memory formation and retrieval. We present an optimized in vitro protocol to generate human BFCNs from iPSCs, using cell lines from presenilin 2 (PSEN2) mutation carriers and controls. As expected, cell lines harboring the PSEN2^N141I mutation displayed an increase in the Aβ42/40 in iPSC-derived BFCNs. Neurons derived from PSEN2^N141I lines generated fewer maximum number of spikes in response to a square depolarizing current injection. The height of the first action potential at rheobase current injection was also significantly decreased in PSEN2^N141I BFCNs. CRISPR/Cas9 correction of the PSEN2 point mutation abolished the electrophysiological deficit, restoring both the maximal number of spikes and spike height to the levels recorded in controls. Increased Aβ42/40 was also normalized following CRISPR/Cas-mediated correction of the PSEN2^N141I mutation. The genome editing data confirms the robust consistency of mutation-related changes in Aβ42/40 ratio while also showing a PSEN2-mutation-related alteration in electrophysiology.

Associations of interactions between NLRP3 SNPs and HLA mismatch with acute and extensive chronic graft-versus-host diseases

HLA matching is a well-known genetic requirement for successful bone marrow transplantation (BMT). However, the importance of non-HLA single-nucleotide polymorphisms (SNPs) remains poorly understood. The NLR family pyrin domain-containing 3 (NLRP3) inflammasome, a key regulator of innate immunity, is associated with multiple diseases. We retrospectively genotyped SNPs of NLRP1-3 and caspase recruitment domain family member 8 (CARD8), which are implicated in the interleukin 1β (IL-1β) signaling, in 999 unrelated BMT donor-recipient pairs. We identified an association of the interaction between the recipient NLRP3 SNP CC genotype and total HLA mismatches with grade 2-4 acute graft-versus-host disease (AGVHD), and an association of the interaction between the donor NLRP3 SNP T allele and HLA-C mismatch with extensive chronic GVHD (ECGVHD), in both adjusted and unadjusted regressions (P < 0.005). Importantly, the ECGVHD risk associated with HLA-C mismatch was not elevated when the donor NLRP3 genotype was CC. We also identified an association of the interaction between recipient NLRP3 SNP and donor cytomegalovirus seropositivity with overall survival in adjusted regressions (P < 0.005). These results suggest the importance of certain SNP-covariate interactions in unrelated BMT. The three identified interactions may be useful for donor selection or outcome prediction.

Posttranslational Modification as a Critical Determinant of Cytoplasmic Innate Immune Recognition

Cell surface innate immune receptors can directly detect a variety of extracellular pathogens to which cytoplasmic innate immune sensors are rarely exposed. Instead, within the cytoplasm, the environment is rife with cellular machinery and signaling pathways that are indirectly perturbed by pathogenic microbes to activate intracellular sensors, such as pyrin, NLRP1, NLRP3, or NLRC4. Therefore, subtle changes in key intracellular processes such as phosphorylation, ubiquitination, and other pathways leading to posttranslational protein modification are key determinants of innate immune recognition in the cytoplasm. This concept is critical to establish the “guard hypothesis” whereby otherwise homeostatic pathways that keep innate immune sensors at bay are released in response to alterations in their posttranslational modification status. Originally identified in plants, evidence that a similar guardlike mechanism exists in humans has recently been identified, whereby a mutation that prevents phosphorylation of the innate immune sensor pyrin triggers a dominantly inherited autoinflammatory disease. It is also noteworthy that even when a cytoplasmic innate immune sensor has a direct ligand, such as bacterial peptidoglycan (NOD1 or NOD2), RNA (RIG-I or MDA5), or DNA (cGAS or IFI16), it can still be influenced by posttranslational modification to dramatically alter its response. Therefore, due to their existence in the cytoplasmic milieu, posttranslational modification is a key determinant of intracellular innate immune receptor functionality.

Expression analysis of inflammasome sensors and implication of NLRP12 inflammasome in prostate cancer

Inflammasomes are multi-proteins complex regulating inflammation-associated signaling. While inflammation plays a critical role in cancer cell growth, studies remain uncharacterized on the role of inflammasomes in prostate cancer. Using Gene Expression Omnibus (GEO) public datasets, we screened the expression profiles of inflammasome sensors NLRP3, NLRC4, NLRP6, NRLP12, and AIM2 in prostate tumor tissues, and verified their mRNA level in a panel of prostate cancer cell lines. The selected expression of NLRP3 and NLRP12 inflammasomes was validated, and the clinical association was evaluated in human prostate archival tumor tissues. We observed that the expression of inflammasome sensors was dysregulated at the mRNA level except for the NLRP12. The intensity of NLRP12 immunostaining was significantly higher in malignant prostate as compared to their adjacent benign tissues. In contrast, the NLRP3 immunostaining in prostate tissues was heterogeneous. The inflammasome complex proteins ASC (apoptosis-associated speck-like protein containing a CARD) and pro-caspase-1, as well as its downstream targets IL-1β and IL-18 were confined to aggressive prostate cancer cells. These data suggest an increased expression of NLRP12 in association with prostate cancer and support the role of NLRP12 inflammasome complex regulating inflammatory cytokines in understanding the role of inflammation in the prostate cancer.

Danger of frustrated sensors: Role of Toll-like receptors and NOD-like receptors in aseptic and septic inflammations around total hip replacements

The innate immune sensors, Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs), can recognize not only exogenous pathogen-associated molecular patterns (PAMPs), but also endogenous molecules created upon tissue injury, sterile inflammation, and degeneration. Endogenous ligands are called damage-associated molecular patterns (DAMPs), and include endogenous molecules released from activated and necrotic cells as well as damaged extracellular matrix. TLRs and NLRs can interact with various ligands derived from PAMPs and DAMPs, leading to activation and/or modulation of intracellular signalling pathways. Intensive research on the innate immune sensors, TLRs and NLRs, has brought new insights into the pathogenesis of not only various infectious and rheumatic diseases, but also aseptic foreign body granuloma and septic inflammation of failed total hip replacements (THRs). In this review, recent knowledge is summarized on the innate immune system, including TLRs and NLRs and their danger signals, with special reference to their possible role in the adverse local host response to THRs.

Translational potential of this article: A clear understanding of the roles of Toll-like receptors and NOD-like receptors in aseptic and septic loosening of joint replacements will facilitate potential strategies to mitigate these events, thereby extending the longevity of implants in humans.

Pyrin-only protein 2 limits inflammation but improves protection against bacteria

Pyrin domain-only proteins (POPs) are recently evolved, primate-specific proteins demonstrated in vitro as negative regulators of inflammatory responses. However, their in vivo function is not understood. Of the four known POPs, only POP2 is reported to regulate NF-κB-dependent transcription and multiple inflammasomes. Here we use a transgenic mouse-expressing POP2 controlled by its endogenous human promotor to study the immunological functions of POP2. Despite having significantly reduced inflammatory cytokine responses to LPS and bacterial infection, POP2 transgenic mice are more resistant to bacterial infection than wild-type mice. In a pulmonary tularaemia model, POP2 enhances IFN-γ production, modulates neutrophil numbers, improves macrophage functions, increases bacterial control and diminishes lung pathology. Thus, unlike other POPs thought to diminish innate protection, POP2 reduces detrimental inflammation while preserving and enhancing protective immunity. Our findings suggest that POP2 acts as a high-order regulator balancing cellular function and inflammation with broad implications for inflammation-associated diseases and therapeutic intervention.

Pyrin-only proteins (POPs) are primate-specific negative regulators of inflammasome activation. Here the authors generate transgenic mice expressing POP2 under the control of the human promoter, and show that POP2 is important for balancing antibacterial inflammatory responses in vivo.

A NLRC3-like gene from blunt snout bream (Megalobrama amblycephala): Molecular characterization, expression and association with resistance to Aeromonas hydrophila infection

NLRC (the nucleotide-oligomerization domain (NOD)-like receptor subfamily C) consists of teleost-specific NLRs (NOD-like receptors) and plays pivotal roles in microbial recognition and regulation of innate immune response. In this study, we cloned and characterized a NLRC3-like gene (MamNLRC3-like) from blunt snout bream (Megalobrama amblycephala) by using the quantitative real-time PCR method, and analyzed the correlation between its polymorphisms and resistance to Aeromonas hydrophila infection. The full length cDNA of MamNLRC3-like was 2863 bp, with a 5'-UTR of 169 bp, ORF of 2301 bp and 3'-UTR of 393 bp, encoding 766 amino acid residues. MamNLRC3-like consisted of a conserved NACHT domain, a fish-specific NACHT associated domain (FISNA) and a PYRIN effective domain. During early developmental stages, MamNLRC3-like was most highly expressed at 39.4 hpf (hours post fertilization, hatching stage) and constitutively detected in various healthy tissues. The expression of MamNLRC3-like was strongly induced by A. hydrophila infection and peaked in the head kidney, liver, intestine, and trunk kidney at 12 h post infection. Six SNPs (single nucleotide polymorphisms) from MamNLRC3-like, with 2 in introns and 4 in exons, were identified by direct sequencing, in which 6515C/T was a novel non-synonymous mutation. HRM (high resolution melting) genotyping of the 6 loci showed that locus 6515C/T SNP was associated with the resistance/susceptibility of blunt snout bream to A. hydrophila infection (P < 0.01). The CC genotype fish were more resistant than CT carriers (P < 0.01). This study suggests that the MamNLRC3-like gene might play an important role in the innate immunity of blunt snout bream and could be used as a candidate marker for genetic selection of A. hydrophila-resistant blunt snout bream.