NLRP1 variant M1184V decreases inflammasome activation in the context of DPP9 inhibition and asthma severity

Inflammasomes in epithelial innate immunity: front line warriors

Our epithelium represents a battle ground against a variety of insults including pathogens and danger signals. It encodes multiple sensors that detect and respond to such insults, playing an essential role in maintaining and defending tissue homeostasis. One key set of defense mechanisms is our inflammasomes which drive innate immune responses including, sensing and responding to pathogen attack, through the secretion of pro-inflammatory cytokines and cell death. Identification of physiologically relevant triggers for inflammasomes has greatly influenced our ability to decipher the mechanisms behind inflammasome activation. Furthermore, identification of patient mutations within inflammasome components implicates their involvement in a range of epithelial diseases. This review will focus on exploring the roles of inflammasomes in epithelial immunity and cover: the diversity and differential expression of inflammasome sensors amongst our epithelial barriers, their ability to sense local infection and damage and the contribution of the inflammasomes to epithelial homeostasis and disease.

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

NLRP1- A CINDERELLA STORY: a perspective of recent advances in NLRP1 and the questions they raise

NLRP1, while the first inflammasome described, has only recently begun to gain significant attention in disease pathology, inflammation research, and potentially, as a therapeutic target. Recently identified human variants provide key insights into NLRP1 biology while its unique expression in barrier cells such as keratinocytes and airway epithelial cells has aligned with new, human specific agonists. This differentiates NLRP1 from other inflammasomes such as NLRP3 and identifies it as a key therapeutic target in inflammatory diseases. Indeed, recent discoveries highlight that NLRP1 may be the predominant inflammasome in human barrier cells, its primary role akin to NLRP3, to respond to cellular stress. This review focuses on recent studies identifying new human-specific NLRP1 mechanisms of activation of, gain-of-function human variants and disease, its role in responding to cellular stress, and discuss potential advances and the therapeutic potential for NLRP1.

Expression and clinical value of NLRP1 and NLRC4 inflammasomes in prostate cancer

The present study explored the clinical value of the protein expression levels of nucleotide binding oligomerization-like receptor family pyrin domain containing 1 (NLRP1) and nucleotide-binding oligomerization domain leucine-rich repeat and caspase recruitment domain-containing 4 (NLRC4) inflammasomes in the diagnosis and treatment of prostate cancer. A total of 54 patients with prostatic hyperplasia and 58 patients with prostate cancer were recruited at The First People's Hospital of Pinghu between January and May 2022. Immunohistochemical staining was used to determine the protein expression levels of the NLRP1 and NLRC4 inflammasomes in addition to the proinflammatory cytokines IL-18 and IL-1β in the two groups of patients. The protein expression levels of NLRP1 and NLRC4 inflammasome were significantly increased in patients with prostate cancer compared with patients with prostate hyperplasia. The differences in expression of NLRP1 and NLRC4 inflammatory vesicles in prostate cancer of different stages were also compared based on data from The Cancer Genome Atlas. The protein expression level of NLRP1 demonstrated a significant positive correlation with IL-1β and IL-18 expression, and the protein expression level of the NLRC4 inflammasome was significantly positively correlated with IL-18 expression. The protein expression levels of both NLRP1 and NLRC4 demonstrated a significant positive correlation with the Gleason score of prostate cancer. The expression of NLRP1 in tumor (T)3/T4 was significantly higher compared with T1 and expression of the NLRC4 inflammasome in T2 and T3/T4 was significantly higher compared with T1. Expression of the NLRP1 and NLRC4 inflammasomes was significantly higher in patients with prostate cancer, compared with patients with prostatic hyperplasia. Therefore, expression of NLRP1 and NLRC4 may promote tumorigenesis by promoting the maturation and release of proinflammatory cytokines IL-1β and IL-18. Expression of the NLRP1 and NLRC4 inflammasomes demonstrated a significant positive correlation with the risk of prostate cancer. Expression of the NLRP1 and NLRC4 inflammasomes in middle- and advanced-stage tumors was higher compared with early-stage tumors. These results suggested that inflammasome expression may serve a significant role in the progression of tumors and could provide a fixed value for the risk assessment and prognosis prediction of prostate cancer.

The prognostic value of NLRP1/NLRP3 and its relationship with immune infiltration in human gastric cancer

BACKGROUND

Inflammasomes are related to tumorigenesis and immune-regulation. Here, we investigated the prognostic value of the NLR family pyrin domain containing (NLRP) 1/NLRP3 inflammasome and its potential mechanisms in immune-regulation in gastric cancer (GC).

METHODS

We analyzed the differential expression of NLRP1/NLRP3 between tumor and normal tissues using the Oncomine and Tumor Immune Estimate Resource (TIMER) databases. Immunohistochemistry and western blotting were used to detect NLRP1/NLRP3 protein expression in GC tissues. Correlations between NLRP1/NLRP3 expression levels and patient survival were analyzed using Kaplan-Meier survival curves. The relationships of NLRP1/NLRP3 expression and tumor-infiltrating immune cells/marker genes were assessed using the TIMER database. NLRP1/NLRP3 and immune checkpoint gene correlations were verified by single-gene co-expression analyses, and tumor immune-related pathways involving NLRP1/NLRP3 were analyzed using gene set enrichment analysis (GSEA).

RESULTS

Elevated NLRP1/NLRP3 expression was significantly correlated with lymph node metastasis, poor survival, immune-infiltrating cell abundances, and immune cell markers. NLRP3 showed stronger correlations with immune infiltration and the prognosis of gastric cancer. NLRP1 and NLRP3 might be involved in the same tumor immune-related pathways. Thus, high NLRP1/NLRP3 expression promotes immune cell infiltration and poor prognosis in GC. NLRP1/NLRP3, particularly NLRP3, may have important roles in immune infiltration and may serve as a prognostic biomarker for GC.

CONCLUSIONS

NLRP1/NLRP3, particularly NLRP3, may have important roles in immune infiltration and may serve as a prognostic biomarker for GC.

Inflammasome sensor NLRP1 disease variant M1184V promotes autoproteolysis and DPP9 complex formation by stabilizing the FIIND domain

The inflammasome sensor NLRP1 (nucleotide-binding oligomerization domain-like receptor containing a pyrin domain 1) detects a variety of pathogen-derived molecular patterns to induce an inflammatory immune response by triggering pyroptosis and cytokine release. A number of mutations and polymorphisms of NLRP1 are known to cause autoinflammatory diseases, the functional characterization of which contributes to a better understanding of NLRP1 regulation. Here, we assessed the effect of the common NLRP1 variant M1184V, associated with asthma, inflammatory bowel disease, and diabetes, on the protein level. Our size-exclusion chromatography experiments show that M1184V stabilizes the "function-to-find" domain (FIIND) in a monomeric conformation. This effect is independent of autoproteolysis. In addition, molecular dynamics simulations reveal that the methionine residue increases flexibility within the ZU5 domain, whereas valine decreases flexibility, potentially indirectly stabilizing the catalytic triad responsible for autocleavage. By keeping the FIIND domain monomeric, formation of a multimer of full-length NLRP1 is promoted. We found that the stabilizing effect of the valine further leads to improved dipeptidyl peptidase 9 (DPP9)-binding capacities for the FIIND domain as well as the full-length protein as determined by surface plasmon resonance. Moreover, our immunoprecipitation experiments confirmed increased DPP9 binding for the M1184V protein in cells, consistent with improved formation of an autoinhibited complex with DPP9 in activity assays. Collectively, our study establishes a molecular rationale for the dichotomous involvement of the NLRP1 variant M1184V in autoimmune syndromes.

NOD-like receptors in asthma

Asthma is an extremely prevalent chronic inflammatory disease of the airway where innate and adaptive immune systems participate collectively with epithelial and other structural cells to cause airway hyperresponsiveness, mucus overproduction, airway narrowing, and remodeling. The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are a family of intracellular innate immune sensors that detect microbe-associated molecular patterns and damage-associated molecular patterns, well-recognized for their central roles in the maintenance of tissue homeostasis and host defense against bacteria, viruses and fungi. In recent times, NLRs have been increasingly acknowledged as much more than innate sensors and have emerged also as relevant players in diseases classically defined by their adaptive immune responses such as asthma. In this review article, we discuss the current knowledge and recent developments about NLR expression, activation and function in relation to asthma and examine the potential interventions in NLR signaling as asthma immunomodulatory therapies.

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

Inflammasome activation: from molecular mechanisms to autoinflammation

Inflammasomes are assembled by innate immune sensors that cells employ to detect a range of danger signals and respond with pro-inflammatory signalling. Inflammasomes activate inflammatory caspases, which trigger a cascade of molecular events with the potential to compromise cellular integrity and release the IL-1β and IL-18 pro-inflammatory cytokines. Several molecular mechanisms, working in concert, ensure that inflammasome activation is tightly regulated; these include NLRP3 post-translational modifications, ubiquitination and phosphorylation, as well as single-domain proteins that competitively bind to key inflammasome components, such as the CARD-only proteins (COPs) and PYD-only proteins (POPs). These diverse regulatory systems ensure that a suitable level of inflammation is initiated to counteract any cellular insult, while simultaneously preserving tissue architecture. When inflammasomes are aberrantly activated can drive excessive production of pro-inflammatory cytokines and cell death, leading to tissue damage. In several autoinflammatory conditions, inflammasomes are aberrantly activated with subsequent development of clinical features that reflect the degree of underlying tissue and organ damage. Several of the resulting disease complications may be successfully controlled by anti-inflammatory drugs and/or specific cytokine inhibitors, in addition to more recently developed small-molecule inhibitors. In this review, we will explore the molecular processes underlying the activation of several inflammasomes and highlight their role during health and disease. We also describe the detrimental effects of these inflammasome complexes, in some pathological conditions, and review current therapeutic approaches as well as future prospective treatments.

NLRP1 Inflammasome Activation in Keratinocytes: Increasing Evidence of Important Roles in Inflammatory Skin Diseases and Immunity

In 2007, it was shown that DNA sequence variants of the human NLRP1 gene are associated with autoimmune and autoinflammatory diseases affecting mainly the skin. However, at that time, the underlying cellular and molecular mechanisms were poorly characterized. Meanwhile, increasing evidence suggests that the NLRP1 inflammasome expressed by keratinocytes not only plays a part in the pathology of common inflammatory skin diseases and cancer development but also contributes to skin immunity. Understanding the mechanisms regulating NLRP1 activation in keratinocytes and the downstream events in human skin might pave the way for developing novel strategies for treating patients suffering from NLRP1-mediated skin diseases.