The CATERPILLER protein monarch-1 is an antagonist of toll-like receptor-, tumor necrosis factor alpha-, and Mycobacterium tuberculosis-induced pro-inflammatory signals

Innate Immunity Never "NODs" Off: NLRs Regulate the Host Anti-Viral Immune Response

A robust innate immune response is essential in combating viral pathogens. However, it is equally critical to quell overzealous immune signaling to limit collateral damage and enable inflammation resolution. Pattern recognition receptors are critical regulators of these processes. The cytosolic nucleotide-binding domain leucine-rich repeat (NLR; NOD-like receptor) family of pattern recognition receptors plays essential roles in the sensing of viral pathogen-associated molecular patterns and is best characterized for itsr pro-inflammatory biological functions. Specifically, these include the formation of multi-protein complexes, defined as inflammasomes or NODosomes that regulate the production of IL-1beta, IL-18, and pyroptosis, or the induction of NF-ΚB signaling. While these biological effects are inherently pro-inflammatory, it is also important to recognize that other NLR family members conversely function to negatively regulate inflammation through modulating signaling initiated by other families of pattern recognition receptors. Mechanistically, these unique NLRs also form multiprotein complexes that act to attenuate a variety of biological signaling pathways, such as the inhibition of NF-ΚB. This inhibition facilitates inflammation resolution and functions to restore cellular homeostasis. Despite extensive characterization of individual NLR family members, the mechanisms of immune system regulation are highly nuanced and remain enigmatic. This is especially true for non-inflammasome-forming, regulatory NLRs. Here, we discuss recent findings associated with NLR family members that play essential roles in the host immune response to viruses and mechanisms by which these pattern recognition receptors may function to regulate antiviral immunity.

Integrative Bioinformatics Analysis and Experimental Study of NLRP12 Reveal Its Prognostic Value and Potential Functions in Ovarian Cancer

NLRP12 plays a significant role in cellular functional behavior and immune homeostasis, influencing inflammation, tumorigenesis, and prognosis. This study aimed to explore its specific effects on the tumor microenvironment (TME) and its contribution to heterogeneity in ovarian cancer (OV) through bioinformatics analysis and experimental verification. Utilizing various bioinformatics databases and clinical specimens, we investigated NLRP12 expression and its relationship with OV prognosis and immune infiltration. In vitro assays were conducted to assess the impact of NLRP12 on the proliferation and invasion of OV cells. Our findings indicate that NLRP12 is upregulated in OV, with high expression correlating with a negative prognosis. Furthermore, NLRP12 expression demonstrated a positive correlation with the infiltration of various immune cells and the expression of immune checkpoint molecules in OV. Analysis of The Cancer Immunome Atlas (TCIA) database revealed that OV patients with lower NLRP12 expression may exhibit an enhanced response to immunotherapy, particularly CTLA4 blockers, a finding validated in animal experiments. Additionally, the study emphasized the role of NLRP12 in influencing the prognosis of OV patients by promoting epithelial-mesenchymal transition (EMT) in ovarian cancer cells. Finally, we identified a potential therapeutic compound, Schisandrin B (Schi B), which decreases NLRP12 expression in ovarian cancer cells by binding to the transcription factor SPI1 associated with NLRP12. Our findings suggest that NLRP12 serves as a crucial immune-related biomarker predicting poor outcomes in OV, and targeting NLRP12 may represent a promising therapeutic approach for OV patients in the future.

Molecular mechanisms of emerging inflammasome complexes and their activation and signaling in inflammation and pyroptosis

Inflammasomes are multi-protein complexes that assemble within the cytoplasm of mammalian cells in response to pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs), driving the secretion of the pro-inflammatory cytokines IL-1β and IL-18, and pyroptosis. The best-characterized inflammasome complexes are the NLRP3, NAIP-NLRC4, NLRP1, AIM2, and Pyrin canonical caspase-1-containing inflammasomes, and the caspase-11 non-canonical inflammasome. Newer inflammasome sensor proteins have been identified, including NLRP6, NLRP7, NLRP9, NLRP10, NLRP11, NLRP12, CARD8, and MxA. These inflammasome sensors can sense PAMPs from bacteria, viruses and protozoa, or DAMPs in the form of mitochondrial damage, ROS, stress and heme. The mechanisms of action, physiological relevance, consequences in human diseases, and avenues for therapeutic intervention for these novel inflammasomes are beginning to be realized. Here, we discuss these emerging inflammasome complexes and their putative activation mechanisms, molecular and signaling pathways, and physiological roles in health and disease.

NLRP12 c.1382dup promotes the development of Crohn's disease through the ERK/NLRP3/ IL-1β pathway

Whole-genome sequencing was used to identify a dominant inherited NLRP12 c.1382dup mutation in refractory familial Crohn's disease (CD) patients. Additionally, we observed a T insertion at position 1382 in the third exon of NLRP12, leading to a frameshift mutation. Isolation of peripheral blood from mutation carriers and subsequent experiments demonstrated increased interleukin (IL)-1β in CD patients with the NLRP12 c.1382dup mutation. However, the mechanisms by which the NLRP12 c.1382dup mutation mediates IL-1β remain unclear. Our research findings reveal a close correlation between elevated p-ERK levels and increased expression of NLRP3 and IL-1β in the presence of the NLRP12 c.1382dup mutation. Further experiments demonstrate that inhibiting p-ERK with PD98059 effectively reduces the production of NLRP3 and IL-1β. This discovery provides new insights into the pathogenesis of CD, highlighting the significant role of the ERK/NLRP3/IL-1β pathway in the progression of CD. Not only does this offer novel therapeutic targets for treating CD, but it also lays the groundwork for the development of treatment strategies targeting this pathway.

NLRP12-associated autoinflammatory disease: A novel causal mutation and bioinformatics analyses

Nucleotide-binding leucine-rich repeat-containing receptor 12-associated autoinflammatory disease (NLRP12-AID) is a rare autosomal dominant disorder. In this study, we reported a case of this rare disease with a novel NLRP12 mutation (A218V, rs749659859). The patient displayed typical symptoms, including recurrent fever, arthralgia, and skin allergies. Elevated serum IgE, decreased apolipoprotein A1, high-density lipoprotein cholesterol, and fluctuating levels of various leukocyte subtypes, procalcitonin, IL6, creatine kinase, and 25-hydroxyvitamin D were also detected. Inflammatory lesions were observed in multiple organs using 18F-FDG PET/CT. By mining single-cell transcriptome data, we identified relatively high expression of NLRP12 in monocytes compared to other human peripheral blood mononuclear cells. NLRP12-positive monocytes exhibited reduced expression of IL18, CCL3, and TNFA compared to NLRP12-negative monocytes. Structural analyses suggested that the A218V mutation, along with A218T and F402L, may reduce the ATP-binding affinity of the NLRP12 protein. These findings may provide new insights into the mechanisms of NLRP12-AID, and suggest the potential ATP-based therapy for further investigation.

Focus on negatively regulated NLRs in inflammation and cancer

Nucleotide-binding and oligomerization structural domain (NOD)-like receptors (NLRs) play an important role in innate immunity as cytoplasmic pattern recognition receptors (PRRs). Over the past decade, considerable progress has been made in understanding the mechanisms by which NLR family members regulate immune system function, particularly the formation of inflammasome and downstream inflammatory signals. However, recent studies have shown that some members of the NLRs, including Nlrp12, NLRX1, and NLRC3, are important in the negative regulation of inflammatory signaling and are involved in the development of various diseases, including inflammatory diseases and cancer. Based on this, in this review, we first summarize the interactions between canonical and non-canonical nuclear factor-κB (NF-κB) signaling pathways that are mainly involved in NLRs, then highlight the mechanisms by which the above NLRs negatively regulate inflammatory signaling responses as well as their roles in tumor progression, and finally summarize the synthetic and natural derivatives with therapeutic effects on these NLRs, which are considered as potential therapeutic agents for overcoming inflammatory diseases.

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.

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.

Sulforaphane inhibits the migration and invasion of BPDE-induced lung adenocarcinoma cells by regulating NLRP12

This study aims to explore the impact and underlying mechanism of sulforaphane (SFN) intervention on the migration and invasion of lung adenocarcinoma induced by 7, 8-dihydroxy-9, 10-epoxy-benzo (a) pyrene (BPDE). Human lung adenocarcinoma A549 cells were exposed to varying concentrations of BPDE (0.25, 0.50, and 1.00 μM) and subsequently treated with 5 μM SFN. Cell viability was determined using CCK8 assay, while migration and invasion were assessed using Transwell assays. Lentivirus transfection was employed to establish NLRP12 overexpressing A549 cells. ELISA was utilized to quantify IL-33, CXCL12, and CXCL13 levels in the supernatant, while quantitative real-time PCR (qRT-PCR) and Western Blot were used to analyze the expression of NLRP12 and key factors associated with canonical and non-canonical NF-κB pathways. Results indicated an increase in migratory and invasive capabilities, concurrent with heightened expression of IL-33, CXCL12, CXCL13, and factors associated with both canonical and non-canonical NF-κB pathways. Moreover, mRNA and protein levels of NLRP12 were decreased in BPDE-stimulated A549 cells. Subsequent SFN intervention attenuated BPDE-induced migration and invasion of A549 cells. Lentivirus-mediated NLRP12 overexpression not only reversed the observed phenotype in BPDE-induced cells but also led to a reduction in the expression of critical factors associated with both canonical and non-canonical NF-κB pathways. Collectively, we found that SFN could inhibit BPDE-induced migration and invasion of A549 cells by upregulating NLRP12, thereby influencing both canonical and non-canonical NF-κB pathways.

Identification of a Novel NLRP12 Frameshift Mutation (Val730Glyfs∗41) by Whole-Exome Sequencing in Patients with Crohn's Disease

NLRP12 encodes the nucleotide-binding leucine-rich repeat-containing receptor 12 protein and has been linked to familial cold autoinflammatory syndrome 2 (FCAS2). Previous studies have reported that NLRP12 protein can dampen inflammatory responses in DSS-induced mice colitis. To date, only four alterations in the NLRP12 gene have been associated with Crohn's disease (CD). Here, we reported a novel heterozygous NLRP12 frameshift mutation (c.2188dupG, p.Val730Glyfs∗41) identified by whole-exome sequencing in the proband with CD. The Sanger sequencing confirmed that his sister and father also carried this NLRP12 mutation, which cosegregated well with the CD phenotype. In silico analysis predicted this mutation to be disease-causing. Patients heterozygous for this mutation exhibited decreased NLRP12 protein levels in the peripheral blood and colon. Functional assays showed that mutant NLRP12 plasmid-transfected HEK293T cells exhibited significantly lower NLRP12 mRNA and protein levels than wild-type plasmid-transfected cells. The nonsense-mediated decay inhibitor NMDI14 significantly increased NLRP12 mRNA and protein levels in mutant plasmid-transfected cells. Overall, our results demonstrated that this heterozygous NLRP12 mutation (c.2188dupG) resulted in decreased NLRP12 expression, which might contribute to the mechanism underlying CD.

BLK positively regulates TLR/IL-1R signaling by catalyzing TOLLIP phosphorylation

TLR/IL-1R signaling plays a critical role in sensing various harmful foreign pathogens and mounting efficient innate and adaptive immune responses, and it is tightly controlled by intracellular regulators at multiple levels. In particular, TOLLIP forms a constitutive complex with IRAK1 and sequesters it in the cytosol to maintain the kinase in an inactive conformation under unstimulated conditions. However, the underlying mechanisms by which IRAK1 dissociates from TOLLIP to activate TLR/IL-1R signaling remain obscure. Herein, we show that BLK positively regulates TLR/IL-1R-mediated inflammatory response. BLK-deficient mice produce less inflammatory cytokines and are more resistant to death upon IL-1β challenge. Mechanistically, BLK is preassociated with IL1R1 and IL1RAcP in resting cells. IL-1β stimulation induces heterodimerization of IL1R1 and IL1RAcP, which further triggers BLK autophosphorylation at Y309. Activated BLK directly phosphorylates TOLLIP at Y76/86/152 and further promotes TOLLIP dissociation from IRAK1, thereby facilitating TLR/IL-1R-mediated signal transduction. Overall, these findings highlight the importance of BLK as an active regulatory component in TLR/IL-1R signaling.

Biomaterials Functionalized with Inflammasome Inhibitors-Premises and Perspectives

This review aimed at searching literature for data regarding the inflammasomes' involvement in the pathogenesis of oral diseases (mainly periodontitis) and general pathologies, including approaches to control inflammasome-related pathogenic mechanisms. The inflammasomes are part of the innate immune response that activates inflammatory caspases by canonical and noncanonical pathways, to control the activity of Gasdermin D. Once an inflammasome is activated, pro-inflammatory cytokines, such as interleukins, are released. Thus, inflammasomes are involved in inflammatory, autoimmune and autoinflammatory diseases. The review also investigated novel therapies based on the use of phytochemicals and pharmaceutical substances for inhibiting inflammasome activity. Pharmaceutical substances can control the inflammasomes by three mechanisms: inhibiting the intracellular signaling pathways (Allopurinol and SS-31), blocking inflammasome components (VX-765, Emricasan and VX-740), and inhibiting cytokines mediated by the inflammasomes (Canakinumab, Anakinra and Rilonacept). Moreover, phytochemicals inhibit the inflammasomes by neutralizing reactive oxygen species. Biomaterials functionalized by the adsorption of therapeutic agents onto different nanomaterials could represent future research directions to facilitate multimodal and sequential treatment in oral pathologies.

The role of NLRP12 in inflammatory diseases

Nucleotide-binding leucine-rich repeat-containing receptor 12 (NLRP12), a highly conserved protein containing an N-terminal pyrin domain (PYD), a nucleotide-binding domain and a C-terminal leucine-rich repeat region, belongs to the nucleotide-binding oligomerization domain-like receptor-containing PYD (NLRP) family and is a cytoplasmic sensor that plays a negative role in inflammation. NLRP12 is involved in multiple disease processes, including formation of inflammasomes and regulation of both canonical and noncanonical inflammatory signaling pathways. NLRP12 and pathogenic infections are closely linked, and alterations in NLRP12 expression and activity are associated with inflammatory diseases. In this review, we begin with a summary of the mechanisms of negative regulation by NLRP12. We then underscore the important roles of NLRP12 in the onset and progression of inflammation, infectious disease, host defense, carcinogenesis and COVID-19. Finally, we highlight factors that influence NLRP12 activity, including synthetic and naturally derived agonists, and are regarded as potential therapeutic agents to overcome inflammatory 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.

Negative regulatory NLRs mitigate inflammation via NF-κB pathway signaling in inflammatory bowel disease

A subset of Nucleotide-binding and leucine-rich repeat-containing receptors (NLRs) function to mitigate overzealous pro-inflammatory signaling produced by NF-κB activation. Under normal pathophysiologic conditions, proper signaling by these NLRs protect against potential autoimmune responses. These NLRs associate with several different proteins within both the canonical and noncanonical NF-κB signaling pathways to either prevent activation of the pathway or inhibit signal transduction. Inhibition of the NF-κB pathways ultimately dampens the production of pro-inflammatory cytokines and activation of other downstream pro-inflammatory signaling mechanisms. Dysregulation of these NLRs, including NLRC3, NLRX1, and NLRP12, have been reported in human inflammatory bowel disease (IBD) and colorectal cancer patients, suggesting the potential of these NLRs as biomarkers for disease detection. Mouse models deficient in these NLRs also have increased susceptibility to colitis and colitis-associated colorectal cancer. While current standard of care for IBD patients and FDA-approved therapeutics function to remedy symptoms associated with IBD and chronic inflammation, these negative regulatory NLRs have yet to be explored as potential drug targets. In this review, we describe a comprehensive overview of recent studies that have evaluated the role of NLRC3, NLRX1, and NLRP12 in IBD and colitis-associated colorectal cancer.

Copper induced intestinal inflammation response through oxidative stress induced endoplasmic reticulum stress in Takifugu fasciatus

Copper (Cu) pollution in aquaculture water has seriously threatened the healthy and sustainable development of the aquaculture industry. Recently, many researchers have studied the toxic effects of Cu exposure on fish. However, the relationship between endoplasmic reticulum stress (ERS) and the inflammatory response, as well as its possible mechanisms, remain unclear. Particularly, information related to fish intestines must be expanded. Our study initially investigated the mechanisms underlying intestinal toxicity and inflammation resulting from Cu-induced ERS in vivo and in vitro in Takifugu fasciatus. In vivo study, T. fasciatus were treated with different concentrations (control, 20, and 100 µg/L) of Cu exposure for 28 days, causing intestinal oxidative stress, ERS, inflammatory responses, and histopathological and ultrastructural damage. Transcriptomic data further showed that Cu exposure caused ERS, as well as inflammatory responses, in the intestinal tracts of T. fasciatus. In vitro experiments on the intestinal cells of T. fasciatus showed that Cu exposure treatment (7.5 µg/mL) for 24 h induced ERS and increased mitochondrial numbers and inflammatory responses. In contrast, the addition of 4-phenylbutyric acid (4-PBA) alleviated ERS and inflammatory response in the Cu-exposed group. Furthermore, the reactive oxygen species (ROS) inhibitor, N-Acetyl-l-cysteine (NAC), effectively alleviated Cu-induced ERS. In conclusion, our in vivo and in vitro studies have confirmed that oxidative stress triggers the ERS pathway, which is involved in the intestinal inflammatory response. Our study provides new insights into the relationship among Cu-induced oxidative stress, ERS, and inflammatory responses in fish, as well as for the healthy culture of fish in aqueous environments.

NLRP12 attenuates ozone-induced pulmonary inflammation by regulating canonical NF-κB Pathway

Ozone (O3) is an important urban air pollutant having strong correlations with respiratory diseases. Several lines of evidence suggest that O3 exposure causes airway hyperresponsiveness (AHR) and pulmonary inflammation. Inhibitory innate immune receptors, such as NLRP12, have been demonstrated to alleviate inflammation, but the functional role for NLRP12 in O3-induced lung inflammatory inflammation remains to be reported. Here, we determined whether NLRP12 took a protective role in O3-induced AHR and pulmonary inflammation via the suppression of canonical NF-κB. C57BL/6 J mice were exposed to filtered air (FA) or 0.25, 0.50 and 1.00 ppm (3 h/day for 5 consecutive days) followed by detection of airway resistance, white blood cells, total proteins, and cytokines. Meanwhile, NLRP12 in lung tissue were detected by real time PCR. Moreover, we also examined protein expression of NLRP12 and key biomarkers of NF-κB pathway. It was shown that 24 h post O3 exposure, AHR as wells as total cells, proteins, and cytokines contents in BALF of mice were increased compare to those of FA controls in a dose-dependent manner. Notably, O3-induced AHR and lung inflammation were associated with significant decrease in pulmonary NLRP12 and upregulation of phosphorylated IRAK1, p65 and IκBα in canonical NF-κB pathway. Intratracheal administration of NLRP12-overexpresing adenovirus 4 days prior to O3 exposure alleviated AHR and lung inflammation, and inhibited canonical NF-κB pathway activation. The findings from this study indicate that NLRP12 attenuates O3-induced AHR and pulmonary inflammation, possibly through regulating canonical NF-κB pathway. This provides a novel target for the prevention and treatment of lung diseases induced by O3 exposure.

Inflammasomes: Mechanisms of Action and Involvement in Human Diseases

Inflammasome complexes and their integral receptor proteins have essential roles in regulating the innate immune response and inflammation at the post-translational level. Yet despite their protective role, aberrant activation of inflammasome proteins and gain of function mutations in inflammasome component genes seem to contribute to the development and progression of human autoimmune and autoinflammatory diseases. In the past decade, our understanding of inflammasome biology and activation mechanisms has greatly progressed. We therefore provide an up-to-date overview of the various inflammasomes and their known mechanisms of action. In addition, we highlight the involvement of various inflammasomes and their pathogenic mechanisms in common autoinflammatory, autoimmune and neurodegenerative diseases, including atherosclerosis, rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, Alzheimer's disease, Parkinson's disease, and multiple sclerosis. We conclude by speculating on the future avenues of research needed to better understand the roles of inflammasomes in health and disease.

The regulation of self-tolerance and the role of inflammasome molecules

Inflammasome molecules make up a family of receptors that typically function to initiate a proinflammatory response upon infection by microbial pathogens. Dysregulation of inflammasome activity has been linked to unwanted chronic inflammation, which has also been implicated in certain autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, type 1 diabetes, systemic lupus erythematosus, and related animal models. Classical inflammasome activation-dependent events have intrinsic and extrinsic effects on both innate and adaptive immune effectors, as well as resident cells in the target tissue, which all can contribute to an autoimmune response. Recently, inflammasome molecules have also been found to regulate the differentiation and function of immune effector cells independent of classical inflammasome-activated inflammation. These alternative functions for inflammasome molecules shape the nature of the adaptive immune response, that in turn can either promote or suppress the progression of autoimmunity. In this review we will summarize the roles of inflammasome molecules in regulating self-tolerance and the development of autoimmunity.

NLRP12-expressing dendritic cells mediate both dissemination of infection and adaptive immune responses in visceral leishmaniasis

The NLR protein NLRP12 contributes to innate immunity, but the mechanism remains elusive. Infection of Nlrp12 -/- or wild-type mice with Leishmania infantum led to aberrant parasite tropism. Parasites replicated to higher levels in livers of Nlrp12 -/- mice than in the livers of WT mice and failed to disseminate to spleens. Most retained liver parasites resided in dendritic cells (DCs), with correspondingly fewer infected DCs in spleens. Furthermore, Nlrp12 -/- DCs expressed lower CCR7 than WT DCs, failed to migrate toward CCL19 or CCL21 in chemotaxis assays, and migrated poorly to draining lymph nodes after sterile inflammation. Leishmania-infected Nlpr12 -/- DCs were significantly less effective at transporting parasites to lymph nodes than WT DCs. Consistently, adaptive immune responses were also impaired in infected Nlrp12 -/- mice. We hypothesize that Nlrp12-expressing DCs are required for efficient dissemination and immune clearance of L. infantum from the site of initial infection. This is at least partly due to the defective expression of CCR7.

Novel NLRP14 Mutations Induce Azoospermia

Background. LR family pyrin domain-containing 14 (NLRP14 or NALP14) is one of the important members of the NLR family and was mainly expressed in testis. It is reported that deficiency in the NALP14 gene in mice can cause spermatogenic failure, and several NALP14 mutations have been found in oligospermia and infertile men. Case Presentation. This study reported two novel NALP14 mutations (c.2076delC: p.L697X and c.T2963C: p.F988S) in our patients with azoospermia. The exonic deletion mutation (c.2076delC) and one missense mutation (c.T2963C) were firstly screened out by whole-exome sequencing (WES) and further verified by amplifying and sequencing the specific exons 5 and 10. Histological analysis of testicular biopsy revealed that NALP14 expression was detected strongly in spermatogonia and weakly in early spermatocytes. Additionally, mutations in this gene caused meiotic arrest, and no postmeiotic round spermatids and mature spermatozoa were observed in the seminiferous tubules. Conclusions. This study and previous literatures showed that NLRP14 mutations are closely related to male infertility; we discovered two novel NALP14 mutations and summarized the kinds of literatures on NLRP14 mutations and male infertility. This is the first report that deletion mutation (c.2076delC) and one missense mutation (c.T2963C) in NALP14 all lead to azoospermia, which is still significant to the clinical auxiliary diagnosis of male infertility.

Inflammasome-Independent Roles of NLR and ALR Family Members

Pattern recognition receptors, including members of the NLR and ALR families, are essential for recognition of both pathogen- and host-derived danger signals. Several members of these families, including NLRP1, NLRP3, NLRC4, and AIM2, are capable of forming multiprotein complexes, called inflammasomes, that result in the activation of pro-inflammatory caspase-1. However, in addition to the formation of inflammasomes, a number of these family members exert inflammasome-independent functions. Here, we will discuss inflammasome-independent functions of NLRC4, NLRP12, and AIM2 and examine their roles in regulating innate and adaptive immune processes.

NLRX1 Deficiency Alters the Gut Microbiome and Is Further Exacerbated by Adherence to a Gluten-Free Diet

Patients with gluten sensitivities present with dysbiosis of the gut microbiome that is further exacerbated by a strict adherence to a gluten-free diet (GFD). A subtype of patients genetically susceptible to gluten sensitivities are Celiac Disease (CeD) patients, who are carriers of the HLA DR3/DQ2 or HLA DR4/DQ8 haplotypes. Although 85-95% of all CeD patients carry HLA DQ2, up to 25-50% of the world population carry this haplotype with only a minority developing CeD. This suggests that CeD and other gluten sensitivities are mediated by factors beyond genetics. The contribution of innate immune system signaling has been generally understudied in the context of gluten sensitivities. Thus, here we examined the role of NOD-like receptors (NLRs), a subtype of pattern recognition receptors, in maintaining the composition of the gut microbiome in animals maintained on a GFD. Human transcriptomics data revealed significant increases in the gene expression of multiple NLR family members, across functional groups, in patients with active CeD compared to control specimens. However, NLRX1 was uniquely down-regulated during active disease. NLRX1 is a negative regulatory NLR that functions to suppress inflammatory signaling and has been postulate to prevent inflammation-induced dysbiosis. Using Nlrx1^-/- mice maintained on either a normal or gluten-free diet, we show that loss of NLRX1 alters the microbiome composition, and a distinctive shift further ensues following adherence to a GFD, including a reciprocal loss of beneficial microbes and increase in opportunistic bacterial populations. Finally, we evaluated the functional impact of an altered gut microbiome by assessing short- and medium-chain fatty acid production. These studies revealed significant differences in a selection of metabolic markers that when paired with 16S rRNA sequencing data could reflect an overall imbalance and loss of immune system homeostasis in the gastrointestinal system.

NOD2 and reproduction-associated NOD-like receptors have been lost during the evolution of pangolins

NOD-like receptors (NLRs) are sensors of pathogen-associated molecular patterns with critical roles in the control of immune responses and programmed cell death. Recent studies have revealed inter-species differences in mammalian innate immune genes and a particular degeneration of nucleic acid sensing pathways in pangolins, which are currently investigated as potential hosts for zoonotic pathogens. Here, we used comparative genomics to determine which NLR genes are conserved or lost in pangolins and related mammals. We show that NOD2, which is implicated in sensing bacterial muramyl dipeptide and viral RNA, is a pseudogene in pangolins, but not in any other mammalian species investigated. NLRC4 and NAIP are absent in pangolins and canine carnivorans, suggesting convergent loss of cytoplasmic sensing of bacterial flagellin in these taxa. Among NLR family pyrin domain containing proteins (NLRPs), skin barrier-related NLRP10 has been lost in pangolins after the evolutionary divergence from Carnivora. Strikingly, pangolins lack all NLRPs associated with reproduction (germ cells and embryonic development) in other mammals, i.e., NLRP2, 4, 5, 7, 8, 9, 11, 13, and 14. Taken together, our study shows a massive degeneration of NLR genes in pangolins and suggests that these endangered mammals may have unique adaptations of innate immunity and reproductive cell biology.

The innate immune receptor Nlrp12 suppresses autoimmunity to the retina

Background

Nod-like receptors (NLRs) are critical to innate immune activation and induction of adaptive T cell responses. Yet, their role in autoinflammatory diseases of the central nervous system (CNS) remains incompletely defined. The NLR, Nlrp12, has been reported to both inhibit and promote neuroinflammation in an animal model of multiple sclerosis (experimental autoimmune encephalomyelitis, EAE), where its T cell-specific role has been investigated. Uveitis resulting from autoimmunity of the neuroretina, an extension of the CNS, involves a breach in immune privilege and entry of T cells into the eye. Here, we examined the contribution of Nlrp12 in a T cell-mediated model of uveitis, experimental autoimmune uveitis (EAU).

Methods

Mice were immunized with interphotoreceptor retinoid-binding protein peptide 1–20 (IRBP_1–20) emulsified in Complete Freund’s adjuvant, CFA. Uveitis was evaluated by clinical and histopathological scoring, and comparisons were made in WT vs. Nlrp12^−/− mice, lymphopenic Rag1^−/− mice reconstituted with WT vs. Nlrp12^−/− CD4⁺ T cells, or among bone marrow (BM) chimeric mice. Antigen-specific Th-effector responses were evaluated by ELISA and intracellular cytokine staining. Cellular composition of uveitic eyes from WT or Nlrp12^−/− mice was compared using flow cytometry. Expression of Nlrp12 and of cytokines/chemokines within the neuroretina was evaluated by immunoblotting and quantitative PCR.

Results

Nlrp12^−/− mice developed exacerbated uveitis characterized by extensive vasculitis, chorioretinal infiltrates and photoreceptor damage. Nlrp12 was dispensable for T cell priming and differentiation of peripheral Th1 or Th17 cells, and uveitis in immunodeficient mice reconstituted with either Nlrp12^−/− or WT T cells was similar. Collectively, this ruled out T cells as the source of Nlrp12-mediated protection to EAU. Uveitic Nlrp12^−/− eyes had more pronounced myeloid cell accumulation than uveitic WT eyes. Transplantation of Nlrp12^−/− BM resulted in increased susceptibility to EAU regardless of host genotype, but interestingly, a non-hematopoietic origin for Nlrp12 function was also observed. Indeed, Nlrp12 was found to be constitutively expressed in the neuroretina, where it suppressed chemokine/cytokine induction.

Conclusions

Our data identify a combinatorial role for Nlrp12 in dampening autoimmunity of the neuroretina. These findings could provide a pathway for development of therapies for uveitis and potentially other autoinflammatory/autoimmune diseases of the CNS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02425-x.

Inflammasome-independent functions of NAIPs and NLRs in the intestinal epithelium

The gut relies on the complex interaction between epithelial, stromal and immune cells to maintain gut health in the face of food particles and pathogens. Innate sensing by the intestinal epithelium is critical for maintaining epithelial barrier function and also orchestrating mucosal immune responses. Numerous innate pattern recognition receptors (PRRs) are involved in such sensing. In recent years, several Nucleotide-binding-domain and Leucine-rich repeat-containing receptors (NLRs) have been found to partake in pathogen or damage sensing while also being implicated in gut pathologies, such as colitis and colorectal cancer (CRC). Here, we discuss the current literature focusing on NLR family apoptosis inhibitory proteins (NAIPs) and other NLRs that have non-inflammasome roles in the gut. The mechanisms behind NLR-mediated protection often converges on similar signalling pathways, such as STAT3, MAPK and NFκB. Further understanding of how these NLRs contribute to the maintenance of gut homeostasis will be important for understanding gut pathologies and developing new therapies.

Nod-like Receptors: Critical Intracellular Sensors for Host Protection and Cell Death in Microbial and Parasitic Infections

Cell death is an essential immunological apparatus of host defense, but dysregulation of mutually inclusive cell deaths poses severe threats during microbial and parasitic infections leading to deleterious consequences in the pathological progression of infectious diseases. Nucleotide-binding oligomerization domain (NOD)-Leucine-rich repeats (LRR)-containing receptors (NLRs), also called nucleotide-binding oligomerization (NOD)-like receptors (NLRs), are major cytosolic pattern recognition receptors (PRRs), their involvement in the orchestration of innate immunity and host defense against bacteria, viruses, fungi and parasites, often results in the cleavage of gasdermin and the release of IL-1β and IL-18, should be tightly regulated. NLRs are functionally diverse and tissue-specific PRRs expressed by both immune and non-immune cells. Beyond the inflammasome activation, NLRs are also involved in NF-κB and MAPK activation signaling, the regulation of type I IFN (IFN-I) production and the inflammatory cell death during microbial infections. Recent advancements of NLRs biology revealed its possible interplay with pyroptotic cell death and inflammatory mediators, such as caspase 1, caspase 11, IFN-I and GSDMD. This review provides the most updated information that caspase 8 skews the NLRP3 inflammasome activation in PANoptosis during pathogen infection. We also update multidimensional roles of NLRP12 in regulating innate immunity in a content-dependent manner: novel interference of NLRP12 on TLRs and NOD derived-signaling cascade, and the recently unveiled regulatory property of NLRP12 in production of type I IFN. Future prospects of exploring NLRs in controlling cell death during parasitic and microbial infection were highlighted.

Negative Regulation of the Innate Immune Response through Proteasomal Degradation and Deubiquitination

The rapid and dynamic activation of the innate immune system is achieved through complex signaling networks regulated by post-translational modifications modulating the subcellular localization, activity, and abundance of signaling molecules. Many constitutively expressed signaling molecules are present in the cell in inactive forms, and become functionally activated once they are modified with ubiquitin, and, in turn, inactivated by removal of the same post-translational mark. Moreover, upon infection resolution a rapid remodeling of the proteome needs to occur, ensuring the removal of induced response proteins to prevent hyperactivation. This review discusses the current knowledge on the negative regulation of innate immune signaling pathways by deubiquitinating enzymes, and through degradative ubiquitination. It focusses on spatiotemporal regulation of deubiquitinase and E3 ligase activities, mechanisms for re-establishing proteostasis, and degradation through immune-specific feedback mechanisms vs. general protein quality control pathways.

Gut microbiota, NLR proteins, and intestinal homeostasis

The gastrointestinal tract harbors a highly complex microbial community, which is referred to as gut microbiota. With increasing evidence suggesting that the imbalance of gut microbiota plays a significant role in the pathogenesis of multiple diseases, interactions between the host immune system and the gut microbiota are now attracting emerging interest. Nucleotide-binding and leucine-rich repeat–containing receptors (NLRs) encompass a large number of innate immune sensors and receptors, which mediate the activation of Caspase-1 and the subsequent release of mature interleukin-1β and interleukin-18. Several family members have been found to restrain rather than activate inflammatory cytokines and immune signaling. NLR family members are central regulators of pathogen recognition, host immunity, and inflammation with utmost importance in human diseases. In this review, we focus on the potential roles played by NLRs in controlling and shaping the microbiota community and discuss how the functional axes interconnecting gut microbiota with NLRs impact the modulation of colitis, inflammatory bowel diseases, and colorectal cancer.

A rare case of an NLRP12-associated autoinflammatory disease

Pathogenic variants in nucleotide-binding oligomerization-like receptor protein 12 (NLRP12) have been recently suggested as possible causes of autoinflammatory syndromes and should be considered for the differential diagnosis in the patients presenting with symptoms of autoinflammatory diseases. Here we report a very rare case of NLRP12-associated autoinflammatory disease patient who initially presented with polyarthritis and was diagnosed as FMF. Later, the genetic analysis excluded many autoinflammatory conditions including FMF and revealed a c.1206C>G; p.(Phe402Leu) variant in the NLRP12 gene. Awareness of rare autoinflammatory conditions is important to have the best approach to the patients presenting with common symptoms of autoinflammatory diseases.

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.

The clinical phenotype and genotype of NLRP12-autoinflammatory disease: a Chinese case series with literature review

BACKGROUND

The nucleotide-binding oligomerization domain-like receptor protein 12 (NLRP12)-autoinflammatory disorder (NLRP12-AD) is a rare autoinflammatory disease characterized by recurrent fever, rash as well as musculoskeletal symptoms, which is rarely reported in Asian populations.

METHODS

Three cases of NLRP12-AD presented to our hospital were studied after parental consents were obtained. Clinical presentations were recorded on a standardized case report form. Mutations of NLRP12 were detected by primary immunodeficiency disease panels and further examined by Sanger sequencing. PubMed literature search for relevant studies of systemic autoinflammatory disorders, especially NLRP12-AD between January, 2000 and January, 2019 was carried and the clinical data were summarized. Comparisons were made between groups in terms of onset age and of ethnicity.

RESULTS

All our patients presented with fever, rash and arthritis/arthralgia, and sensorineural as well as sensorineural deafness (1/3), uveitis (1/3), abdominal pain (1/3), and myalgia (1/3). Two novel mutation variations, p.W581X and p.L558R, are reported here. In addition, we also found that two patients inherited the mutated alleles from their healthy parents, and this may be evidence of haploinsufficiency.

CONCLUSIONS

Although the genotypes are similar, the clinical manifestations between Chinese patients and Western patients vary thus highlighting the possible influence of ethnic and environmental factors. On the other hand, some genetic mutations may lead to specific phenotype, as we have found a high prevalence of sensorineural hearing loss among p.R284X patients.

Targeting NF-κB pathway for the therapy of diseases: mechanism and clinical study

NF-κB pathway consists of canonical and non-canonical pathways. The canonical NF-κB is activated by various stimuli, transducing a quick but transient transcriptional activity, to regulate the expression of various proinflammatory genes and also serve as the critical mediator for inflammatory response. Meanwhile, the activation of the non-canonical NF-κB pathway occurs through a handful of TNF receptor superfamily members. Since the activation of this pathway involves protein synthesis, the kinetics of non-canonical NF-κB activation is slow but persistent, in concordance with its biological functions in the development of immune cell and lymphoid organ, immune homeostasis and immune response. The activation of the canonical and non-canonical NF-κB pathway is tightly controlled, highlighting the vital roles of ubiquitination in these pathways. Emerging studies indicate that dysregulated NF-κB activity causes inflammation-related diseases as well as cancers, and NF-κB has been long proposed as the potential target for therapy of diseases. This review attempts to summarize our current knowledge and updates on the mechanisms of NF-κB pathway regulation and the potential therapeutic application of inhibition of NF-κB signaling in cancer and inflammatory diseases.

APOL1 renal risk variants exacerbate podocyte injury by increasing inflammatory stress

Background

Apolipoprotein L1, APOL1, is a trypanosome lytic factor present in human and certain other primates. APOL1 gene variants, present in individuals of recent sub-Saharan African descent, increase risk for glomerular disease and associate with the disease progression, but the molecular mechanisms have not been defined.

Objectives

We focus on the mechanism how APOL1 variant proteins enhance podocyte injury in the stressed kidney.

Methods

First, we investigated the expression of APOL1 protein isoform and the localization of APOL1 protein in the kidney. Next, we examined the role of APOL1 in the podocyte stress and the inflammatory signaling in the kidney after hemi-nephrectomy.

Results

We identified a novel RNA variant that lacks a secretory pathway signal sequence and we found that the predicted APOL1-B3 protein isoform was expressed in human podocytes in vivo and by BAC-APOL1 transgenic mice. APOL1-B3-G2 transgenic mice, carrying a renal risk variant, manifested podocyte injury and increased pro-IL-1β mRNA in isolated glomeruli and increased IL-1β production in the remnant kidney after uninephrectomy. APOL1-B3 interacted with NLRP12, a key regulator of Toll-like receptor signaling.

Conclusions

These results suggest a possible mechanism for podocyte injury by which one of the APOL1 protein isoforms, APOL1-B3 and its renal risk variants, enhances inflammatory signaling.

NLRP12 in innate immunity and inflammation

Nucleotide-binding leucine-rich repeat-containing proteins, or NOD-like receptors (NLRs), are intracellular innate immune sensors that can regulate several signaling pathways, including MyD88- and TRIF-dependent pathways. In addition to these regulatory roles, some NLRs can assemble into multimeric protein complexes known as inflammasomes. NLRP12 is a member of the NLR family that contains an N-terminal pyrin domain, a central nucleotide-binding domain, and a C-terminal leucine-rich repeat. It has been shown to play a role in forming an inflammasome in response to specific infections, and it can also function as a regulator of inflammatory signaling. During Yersinia pestis or Plasmodium chabaudi infection, NLRP12 induces the release of the inflammasome-dependent cytokines IL-1β and IL-18. These NLRP12-dependent cytokines confer protection against severe infections caused by these pathogens. Conversely, during infection with Salmonella enterica serovar Typhimurium, vesicular stomatitis virus, Klebsiella pneumoniae, or Mycobacterium tuberculosis, and in colonic tumorigenesis, NLRP12 acts as a negative regulator of the NFκB and MAPK signaling pathways. NLRP12 also negatively regulates canonical and non-canonical signaling in T cells and causes exacerbated autoimmune diseases. Furthermore, NLRP12 acts as a central component in maintaining intestinal inflammation and gut homeostasis. Therefore, the ability of NLRP12 to function as an inflammasome or as a negative regulator is context-dependent. In this review, we provide an overview of the NLR family members and summarize recent insights into the roles of NLRP12 as an inflammasome and as a negative regulator.

NLR and Intestinal Dysbiosis-Associated Inflammatory Illness: Drivers or Dampers?

The intestinal microbiome maintains a close relationship with the host immunity. This connection fosters a health state by direct and indirect mechanisms. Direct influences occur mainly through the production of short-chain fatty acids (SCFAs), gastrointestinal hormones and precursors of bioactive molecules. Indirect mechanisms comprise the crosstalk between bacterial products and the host's innate immune system. Conversely, intestinal dysbiosis is a condition found in a large number of chronic intestinal inflammatory diseases, such as ulcerative colitis and Crohn's disease, as well as in diseases associated with low-grade inflammation, such as obesity, type 1 and 2 diabetes mellitus and cardiovascular diseases. NOD-Like receptors (NLRs) are cytoplasmic receptors expressed by adaptive and innate immune cells that form a multiprotein complex, termed the inflammasome, responsible for the release of mature interleukin (IL)-1β and IL-18. NLRs are also involved in the recognition of bacterial components and production of antimicrobial molecules that shape the gut microbiota and maintain the intestinal homeostasis. Recent novel findings show that NLRs may act as positive or negative regulators of inflammation by modulating NF-κB activation. This mini-review presents current and updated evidence on the interplay between NLRs and gut microbiota and their dual role, contributing to progression or conferring protection, in diabetes and other inflammatory diseases.

The microbiome and cytosolic innate immune receptors

The discovery of innate immune sensors (pattern recognition receptors, PRRs) has profoundly transformed the notion of innate immunity, in providing a mechanistic basis for host immune interactions with a wealth of environmental signals, leading to a variety of immune-mediated outcomes including instruction and activation of the adaptive immune arm. As part of this growing understanding of host-environmental cross talk, an intimate connection has been unveiled between innate immune sensors and signals perceived from the commensal microbiota, which may be regarded as a hub integrating a variety of environmental cues. Among cytosolic PRRs impacting on host homeostasis by interacting with the commensal microbiota are nucleotide-binding domain, leucine-rich repeat-containing protein receptors (NLRs), together with a number of cytosolic DNA sensors and the family of absent in melanoma (AIM)-like receptors (ALRs). NLR sensors have been a particular focus of research, and some NLRs have emerged as key orchestrators of inflammatory responses and host homeostasis. Some NLRs achieve this through the formation of cytoplasmic multiprotein complexes termed inflammasomes. More recently discovered PRRs include retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), cyclic GMP-AMP synthase (cGAS), and STING. In the present review, they summarize recent advancements in knowledge on structure and function of cytosolic PRRs and their roles in host-microbiota cross talk and immune surveillance. In addition, we discuss their relevance for human health and disease and future therapeutic applications involving modulation of their activation and signaling.

NLRP12 controls arthritis severity by acting as a checkpoint inhibitor of Th17 cell differentiation

Nucleotide oligomerization domain (NOD)-like receptor-12 (NLRP12) has emerged as a negative regulator of inflammation. It is well described that the Th17 cell population increases in patients with early Rheumatoid Arthritis (RA), which correlates with the disease activity. Here, we investigated the role of NLRP12 in the differentiation of Th17 cells and the development of experimental arthritis, using the antigen-induced arthritis (AIA) murine model. We found that Nlrp12^{-/ -} mice develop severe arthritis characterized by an exacerbated Th17-mediated inflammatory response with increases in the articular hyperalgesia, knee joint swelling, and neutrophil infiltration. Adoptive transfer of Nlrp12^{-/ -} cells into WT mice recapitulated the hyperinflammatory response seen in Nlrp12^{-/ -} mice and the treatment with anti-IL-17A neutralizing antibody abrogated arthritis development in Nlrp12^{-/ -} mice, suggesting that NLRP12 works as an inhibitor of Th17 cell differentiation. Indeed, Th17 cell differentiation markedly increases in Nlrp12^-/- T cells cultured under the Th17-skewing condition. Mechanistically, we found that NLRP12 negatively regulates IL-6-induced phosphorylation of STAT3 in T cells. Finally, pharmacological inhibition of STAT3 reduced Th17 cell differentiation and abrogated hyperinflammatory arthritis observed in Nlrp12^{-/ -} mice. Thus, we described a novel role for NLRP12 as a checkpoint inhibitor of Th17 cell differentiation, which controls the severity of experimental arthritis.

Nucleotide binding domain and leucine-rich repeat pyrin domain-containing protein 12: characterization of its binding to hematopoietic cell kinase

Protein-protein interactions are key to define the function of nucleotide binding domain (NBD) and leucine-rich repeat (LRR) family, pyrin domain (PYD)-containing protein 12 (NLRP12). cDNA encoding the human PYD + NBD of NLRP12 was used as bait in a yeast two-hybrid screen with a human leukocyte cDNA library as prey. Hematopoiesis cell kinase (HCK), a member of the c-SRC family of non-receptor tyrosine kinases, was among the top hits. The C-terminal 40 amino acids of HCK selectively bound to NLRP12's PYD + NBD, but not to that of NLRP3 and NLRP8. Amino acids F503, I506, Q507, L510, and D511 of HCK are critical for the binding of HCK's C-terminal 40 amino acids to NLRP12's PYD + NBD. Additionally, the C-terminal 30 amino acids of HCK are sufficient to bind to NLRP12's PYD + NBD, but not to its PYD alone nor to its NBD alone. In cell lines that express HCK endogenously, it was co- immunoprecipitated with stably expressed exogenous NLRP12. Also, NLRP12 co-immunoprecipitated and co-localized with HCK when both were overexpressed in 293T cells. In addition, in this overexpression system, steady-state NLRP12 protein expression levels significantly decreased when HCK was co-expressed. Bioinformatic analysis showed that HCK mRNA co-occurred with NLRP12 mRNA, but not with other NLRP mRNAs, in blood and marrow samples from acute myeloid leukemia (AML) patients. The mRNA of NLRP12 is also co-expressed with HCK in AML patient samples, and the levels of mRNA expression of each are correlated. Together these data suggest that NLRP12, through its binding to HCK, may have an effect on the pathogenesis of AML.

Inflammasomes and their regulation in periodontal disease: A review

Interleukin-1β (IL-1β), which is secreted by host tissues leading to periodontal tissue inflammation, is a major pro-inflammatory cytokine in the pathogenesis of periodontal disease. The conversion of pro-IL-1β into its biologically active form is controlled by multiprotein complexes named as inflammasomes, which are key regulator of host defense mechanisms and inflammasome involved diseases, including the periodontal diseases. Inflammasomes are regulated by different proteins and processes, including pyrin domain (PYD)-only proteins (POPs), CARD-only proteins (COPs), tripartite motif family proteins (TRIMs), autophagy, and interferons. A review of in vitro, in vivo, and clinical data from these publications revealed that several inflammasomes including (NOD)-like receptor (NLR) pyrin domain-containing 3 (NLRP3) and absent in melanoma 2 (AIM2) have been found to be involved in periodontal disease pathogenesis. To the best of our knowledge, the current article provides the first review of the literature focusing on studies that evaluated both inflammasomes and their regulators in periodontal disease. An upregulation for inflammasomes and a downregulation of inflammasome regulator proteins including POPs, COPs, and TRIMs have been reported in periodontal disease. Although interferons (types I and II) and autophagy have been found to be involved in periodontal disease, their possible role in inflammasome activation has not evaluated yet. Modulating the excessive inflammatory response by the use of inflammasome regulators may have potential in the management of periodontal disease.

Pattern Recognition Receptors in Multiple Sclerosis and Its Animal Models

Pattern recognition receptors (PRRs) coordinate the innate immune response and have a significant role in the development of multiple sclerosis (MS). Accumulating evidence has identified both pathogenic and protective functions of PRR signaling in MS and its animal model, experimental autoimmune encephalomyelitis (EAE). Additionally, evidence for PRR signaling in non-immune cells and PRR responses to host-derived endogenous ligands has also revealed new pathways controlling the development of CNS autoimmunity. Many PRRs remain uncharacterized in MS and EAE, and understanding the distinct triggers and functions of PRR signaling in CNS autoimmunity requires further investigation. In this brief review, we discuss the diverse pathogenic and protective functions of PRRs in MS and EAE, and highlight major avenues for future research.

Canonical and noncanonical inflammasomes in intestinal epithelial cells

Inflammasomes are cytosolic, multimeric protein complexes capable of activating pro-inflammatory cytokines such as IL-1β and IL-18, which play a key role in host defence. Inflammasome components are highly expressed in the intestinal epithelium. In recent years, studies have begun to demonstrate that epithelial-intrinsic inflammasomes play a critical role in regulating epithelial homeostasis, both by defending the epithelium from pathogenic insult and through the regulation of the mucosal environment. However, the majority of research regarding inflammasome activation has focused on professional immune cells, such as macrophages. Here, we present an overview of the current understanding of inflammasome function in epithelial cells and at mucosal surfaces and, in particular, in the intestine.

NLRP3, NLRP12, and IFI16 Inflammasomes Induction and Caspase-1 Activation Triggered by Virulent HSV-1 Strains Are Associated With Severe Corneal Inflammatory Herpetic Disease

The crosstalk between the host's inflammasome system and the invading virulent/less-virulent viruses determines the outcome of the ensuing inflammatory response. An appropriate activation of inflammasomes triggers antiviral inflammatory responses that clear the virus and heal the inflamed tissue. However, an aberrant activation of inflammasomes can result in a harmful and overwhelming inflammation that could damage the infected tissue. The underlying host's immune mechanisms and the viral virulent factors that impact severe clinical inflammatory disease remain to be fully elucidated. In this study, we used herpes simplex virus type 1 (HSV-1), the causative agent of corneal inflammatory herpetic disease, as a model pathogen to determine: (i) Whether and how the virulence of a virus affects the type and the activation level of the inflammasomes; and (ii) How triggering specific inflammasomes translates into protective or damaging inflammatory response. We showed that, in contrast to the less-virulent HSV-1 strains (RE, F, KOS, and KOS63), corneal infection of B6 mice with the virulent HSV-1 strains (McKrae, 17 or KOS79): (i) Induced simultaneous expression of the NLRP3, NLRP12, and IFI16 inflammasomes; (ii) Increased production of the biologically active Caspase-1 and pro-inflammatory cytokines IL-1β and IL-18; (iii) Heightened recruitment into the inflamed cornea of CD45highLy6C+Ly6G-F4/80+CD11b+CD11c- inflammatory monocytes and CD45highCD11b+F4/80-Ly6GhiLy6Cmed neutrophils; and (iv) This intensified inflammatory response was associated with a severe corneal herpetic disease, irrespective of the level of virus replication in the cornea. Similarly, in vitro infection of human corneal epithelial cells and human monocytic THP-1 cells with the virulent HSV-1 strains triggered a synchronized early expression of NLRP3, NLRP12 and IFI16, 2 h post-infection, associated with formation of single and dense specks of the adapter molecule ASC in HSV(+) cells, but not in the neighboring bystander HSV(-) cells. This was associated with increased cleavages of Caspase-1, IL-1β, and IL-18. These findings suggest a previously unappreciated role of viral virulence in a synchronized early induction of the NLRP3, NLRP12, and IFI16 inflammasomes that lead to a damaging inflammatory response. A potential role of common virus virulent factors that stimulate this harmful inflammatory corneal disease is currently under investigation.

Differential Expression Profile of NLRs and AIM2 in Glioma and Implications for NLRP12 in Glioblastoma

Gliomas are the most prevalent primary brain tumors with immense clinical heterogeneity, poor prognosis and survival. The nucleotide-binding domain, and leucine-rich repeat containing receptors (NLRs) and absent-in-melanoma 2 (AIM2) are innate immune receptors crucial for initiation and progression of several cancers. There is a dearth of reports linking NLRs and AIM2 to glioma pathology. NLRs are expressed by cells of innate immunity, including monocytes, macrophages, dendritic cells, endothelial cells, and neutrophils, as well as cells of the adaptive immune system. NLRs are critical regulators of major inflammation, cell death, immune and cancer-associated pathways. We used a data-driven approach to identify NLRs, AIM2 and NLR-associated gene expression and methylation patterns in low grade glioma and glioblastoma, using The Cancer Genome Atlas (TCGA) patient datasets. Since TCGA data is obtained from tumor tissue, comprising of multiple cell populations including glioma cells, endothelial cells and tumor-associated microglia/macrophages we have used multiple cell lines and human brain tissues to identify cell-specific effects. TCGA data mining showed significant differential NLR regulation and strong correlation with survival in different grades of glioma. We report differential expression and methylation of NLRs in glioma, followed by NLRP12 identification as a candidate prognostic marker for glioma progression. We found that Nlrp12 deficient microglia show increased colony formation while Nlrp12 deficient glioma cells show decreased cellular proliferation. Immunohistochemistry of human glioma tissue shows increased NLRP12 expression. Interestingly, microglia show reduced migration towards Nlrp12 deficient glioma cells.

Association between genotypes of rs34436714 of NLRP12 and serum tumor necrosis factor-alpha in inflammatory bowel disease: A case-control study

We aimed to investigate the impact of the single nucleotide polymorphisms of rs34436714 of the NOD-like receptor protein 12 gene on the production of tumor necrosis factor-alpha (TNFα) in patients with inflammatory bowel disease (IBD)In a matched case-control study 90 patients with IBD, 56 with Crohn disease (CD) and 34 with ulcerative colitis, were genotyped and compared to 98 healthy comparators matched for age and gender. Expression level of TNFα, interleukin (IL)-6, IL-12, and soluble triggering receptor expressed on myeloid cells were measured in patients' sera. Peripheral blood mononuclear cells (PBMCs) were isolated and stimulated for TNFα production.Serum TNFα was greater among carriers of GT/TT genotypes than GG genotypes of rs34436714. Stimulated TNFα production was also higher in carriers of GT/TT genotypes. The frequency of CD with fistulizing behavior and with CD involving the small intestine was greater among carriers of GT/TT genotypes than of the GG genotype. Distribution of the GG, GT, and TT genotypes of rs34436714 were in Hardy-Weinberg equilibrium in both groups. The genotype distribution was the same in both groups.Carriage of minor frequency alleles of rs34436714 was accompanied by greater circulating levels of TNFα and by greater capacity for stimulated TNFα production by PBMCs. These alleles had an impact on the phenotype of patients with CD.

Inflammatory caspase regulation: maintaining balance between inflammation and cell death in health and disease

Members of the mammalian inflammatory caspase family, including caspase-1, caspase-4, caspase-5, caspase-11, and caspase-12, are key regulators of the innate immune response. Most studies to date have focused on the role of caspase-1 in the maturation of the proinflammatory cytokine interleukin-1β and its upstream regulation by the inflammasome signaling complexes. However, an emerging body of research has supported a role for caspase-4, caspase-5, and caspase-11 in both regulating caspase-1 activation and inducing the inflammatory form of cell death called pyroptosis. This inflammatory caspase pathway appears essential for the regulation of cytokine processing. Consequently, insight into this noncanonical pathway may reveal important and, to date, understudied targets for the treatment of autoinflammatory disorders where the inflammasome pathway is dysregulated. Here, we will discuss the mechanisms of inflammasome and inflammatory caspase activation and how these pathways intersect to promote pathogen clearance.

MicroRNA Post-transcriptional Regulation of the NLRP3 Inflammasome in Immunopathologies

Inflammation has a crucial role in protection against various pathogens. The inflammasome is an intracellular multiprotein signaling complex that is linked to pathogen sensing and initiation of the inflammatory response in physiological and pathological conditions. The most characterized inflammasome is the NLRP3 inflammasome, which is a known sensor of cell stress and is tightly regulated in resting cells. However, altered regulation of the NLRP3 inflammasome is found in several pathological conditions, including autoimmune disease and cancer. NLRP3 expression was shown to be post-transcriptionally regulated and multiple miRNA have been implicated in post-transcriptional regulation of the inflammasome. Therefore, in recent years, miRNA based post-transcriptional control of NLRP3 has become a focus of much research, especially as a potential therapeutic approach. In this review, we provide a summary of the recent investigations on the role of miRNA in the post-transcriptional control of the NLRP3 inflammasome, a key regulator of pro-inflammatory IL-1β and IL-18 cytokine production. Current approaches to targeting the inflammasome product were shown to be an effective treatment for diseases linked to NLRP3 overexpression. Although utilizing NLRP3 targeting miRNAs was shown to be a successful therapeutic approach in several animal models, their therapeutic application in patients remains to be determined.

Transcriptome analysis of normal-appearing white matter reveals cortisol- and disease-associated gene expression profiles in multiple sclerosis

Inter-individual differences in cortisol production by the hypothalamus–pituitary–adrenal (HPA) axis are thought to contribute to clinical and pathological heterogeneity of multiple sclerosis (MS). At the same time, accumulating evidence indicates that MS pathogenesis may originate in the normal-appearing white matter (NAWM). Therefore, we performed a genome-wide transcriptional analysis, by Agilent microarray, of post-mortem NAWM of 9 control subjects and 18 MS patients to investigate to what extent gene expression reflects disease heterogeneity and HPA-axis activity. Activity of the HPA axis was determined by cortisol levels in cerebrospinal fluid and by numbers of corticotropin-releasing neurons in the hypothalamus, while duration of MS and time to EDSS6 served as indicator of disease severity. Applying weighted gene co-expression network analysis led to the identification of a range of gene modules with highly similar co-expression patterns that strongly correlated with various indicators of HPA-axis activity and/or severity of MS. Interestingly, molecular profiles associated with relatively mild MS and high HPA-axis activity were characterized by increased expression of genes that actively regulate inflammation and by molecules involved in myelination, anti-oxidative mechanism, and neuroprotection. Additionally, group-wise comparisons of gene expression in white matter from control subjects and NAWM from (subpopulations of) MS patients uncovered disease-associated gene expression as well as strongly up- or downregulated genes in patients with relatively benign MS and/or high HPA-axis activity, with many differentially expressed genes being previously undescribed in the context of MS. Overall, the data suggest that HPA-axis activity strongly impacts on molecular mechanisms in NAWM of MS patients, but partly also independently of disease severity.