AIM2 Facilitates the Apoptotic DNA-induced Systemic Lupus Erythematosus via Arbitrating Macrophage Functional Maturation

Cytoplasmic DNA and AIM2 inflammasome in RA: where they come from and where they go?

Rheumatoid arthritis is a chronic autoimmune disease of undetermined etiology characterized by symmetric synovitis with predominantly destructive and multiple joint inflammation. Cytoplasmic DNA sensors that recognize protein molecules that are not themselves or abnormal dsDNA fragments play an integral role in the generation and perpetuation of autoimmune diseases by activating different signaling pathways and triggering innate immune signaling pathways and host defenses. Among them, melanoma deficiency factor 2 (AIM2) recognizes damaged DNA and double-stranded DNA and binds to them to further assemble inflammasome, initiating the innate immune response and participating in the pathophysiological process of rheumatoid arthritis. In this article, we review the research progress on the source of cytoplasmic DNA, the mechanism of assembly and activation of AIM2 inflammasome, and the related roles of other cytoplasmic DNA sensors in rheumatoid arthritis.

The DNA sensor AIM2 mediates psoriasiform inflammation by inducing type 3 immunity

Psoriasis is a chronic and recurrent inflammatory skin disease characterized by abnormal proliferation and differentiation of keratinocytes and activation of immune cells. However, the molecular driver that triggers this immune response in psoriatic skin remains unclear. The inflammation-related gene absent in melanoma 2 (AIM2) was identified as a susceptibility gene/locus associated with psoriasis. In this study, we investigated the role of AIM2 in the pathophysiology of psoriasis. We found elevated levels of mitochondrial DNA in patients with psoriasis, along with high expression of AIM2 in both the human psoriatic epidermis and a mouse model of psoriasis induced by topical imiquimod (IMQ) application. Genetic ablation of AIM2 reduced the development of IMQ-induced psoriasis by decreasing the production of type 3 cytokines (such as IL-17A and IL-23) and infiltration of immune cells into the inflammatory site. Furthermore, we demonstrate that IL-17A induced AIM2 expression in keratinocytes. Finally, the genetic absence of inflammasome components downstream AIM2, ASC, and caspase-1 alleviated IMQ-induced skin inflammation. Collectively, our data show that AIM2 is involved in developing psoriasis through its canonical activation.

Inflammasome activity regulation by PUFA metabolites

Oxidative stress and the accompanying chronic inflammation constitute an important metabolic problem that may lead to pathology, especially when the body is exposed to physicochemical and biological factors, including UV radiation, pathogens, drugs, as well as endogenous metabolic disorders. The cellular response is associated, among others, with changes in lipid metabolism, mainly due to the oxidation and the action of lipolytic enzymes. Products of oxidative fragmentation/cyclization of polyunsaturated fatty acids (PUFAs) [4-HNE, MDA, 8-isoprostanes, neuroprostanes] and eicosanoids generated as a result of the enzymatic metabolism of PUFAs significantly modify cellular metabolism, including inflammation and the functioning of the immune system by interfering with intracellular molecular signaling. The key regulators of inflammation, the effectiveness of which can be regulated by interacting with the products of lipid metabolism under oxidative stress, are inflammasome complexes. An example is both negative or positive regulation of NLRP3 inflammasome activity by 4-HNE depending on the severity of oxidative stress. 4-HNE modifies NLRP3 activity by both direct interaction with NLRP3 and alteration of NF-κB signaling. Furthermore, prostaglandin E2 is known to be positively correlated with both NLRP3 and NLRC4 activity, while its potential interference with AIM2 or NLRP1 activity is unproven. Therefore, the influence of PUFA metabolites on the activity of well-characterized inflammasome complexes is reviewed.

Decoding the connection between SLE and DNA Sensors: A comprehensive review

Systemic lupus erythematosus (SLE) is recognized as a prevalent autoimmune disorder characterized by a multifaceted pathogenesis potentially influenced by a combination of environmental factors, genetic predisposition, and hormonal regulation. The continuous study of immune system activation is especially intriguing. Analysis of blood samples from individuals with SLE reveals an abnormal increase in interferon levels, along with the existence of anti-double-stranded DNA antibodies. This evidence suggests that the development of SLE may be initiated by innate immunity. The presence of abnormal dsDNA fragments can activate DNA sensors within cells, particularly immune cells, leading to the initiation of downstream signaling cascades that result in the upregulation of relevant cytokines and the subsequent initiation of adaptive immune responses, such as B cell differentiation and T cell activation. The intricate pathogenesis of SLE results in DNA sensors exhibiting a wide range of functions in innate immune responses that are subject to variation based on cell types, developmental processes, downstream effector signaling pathways and other factors. The review aims to reorganize how DNA sensors influence signaling pathways and contribute to the development of SLE according to current studies, with the aspiration of furnishing valuable insights for future investigations into the pathological mechanisms of SLE and potential treatment approaches.

Assessment of the role of high-density lipoproteins and their immunomodulatory activity in systemic lupus erythematosus immunopathology

OBJECTIVE

To explore the potential associations between high-density lipoprotein (HDL) levels and inflammasome components in the context of systemic lupus erythematosus (SLE).

METHODS

A cross-sectional study was conducted. A group of 50 patients with SLE and 50 healthy controls matched by sex and similar age ranges were enrolled. Serum HDL cholesterol (HDL-C) and C reactive protein (CRP) levels were quantified. Serum cytokine levels, including IL-1β and IL-6, were determined by ELISA. The gene expression of inflammasome-related genes in peripheral blood mononuclear cells was measured by quantitative real-time PCR.

RESULTS

HDL-C levels were lower in the patients with SLE (p<0.05), and on segregation according to disease activity, those with active SLE had the lowest HDL-C levels. Patients with SLE presented higher concentrations of the serum inflammatory cytokines IL-1β and IL-6 (p<0.0001) but similar levels of CRP to those in controls. A similar scenario was observed for the gene expression of inflammasome components, where all the evaluated markers were significantly upregulated in the SLE population. These results revealed significant negative correlations between HDL levels and disease activity, serum IL-6 and IL-1β levels and the mRNA expression of NLRP3, IL-1β and IL-18. In addition, significant positive correlations were found between disease activity and serum IL-1β and between disease activity and the mRNA expression of IL-18, and interestingly, significant positive correlations were also observed between active SLE and serum IL-1β and the mRNA expression of NLRP3.

CONCLUSION

Our results suggest that HDL is essential for SLE beyond atherosclerosis and is related to inflammation regulation, possibly mediated by inflammasome immunomodulation.

Pyroptosis and its role in autoimmune skin disease

Autoimmune skin disease is a kind of heterogeneous disease with complicated pathogenesis. Many factors such as genetic, infectious, environmental and even psychological factors may interact together to trigger a synergistic effect for the development of abnormal innate and adaptive immune responses. Although the exact mechanisms remain unclear, recent evidence suggests that pyroptosis plays a pivotal role in the development of autoimmune skin disease. The feature of pyroptosis is the first formation of pores in cellular membranes, then cell rupture and the release of intracellular substances and pro-inflammatory cytokines, such as interleukin-1 beta (IL-1β) and IL-18. This hyperactive inflammatory programmed cell death damages the homeostasis of the immune system and advances autoimmunity. This review briefly summarises the molecular regulatory mechanisms of pyrin domain-containing protein 3 (NLRP3) inflammasome and gasdermin family, as well as the molecular mechanisms of pyroptosis, highlights the latest progress of pyroptosis in autoimmune skin disease, including systemic lupus erythematosus, psoriasis, atopic dermatitis and systemic scleroderma and attempts to identify its potential advantages as a therapeutic target or prognostic biomarker for these diseases.

Inflammasome Molecular Insights in Autoimmune Diseases

Autoimmune diseases (AIDs) emerge due to an irregular immune response towards self- and non-self-antigens. Inflammation commonly accompanies these conditions, with inflammatory factors and inflammasomes playing pivotal roles in their progression. Key concepts in molecular biology, inflammation, and molecular mimicry are crucial to understanding AID development. Exposure to foreign antigens can cause inflammation, potentially leading to AIDs through molecular mimicry triggered by cross-reactive epitopes. Molecular mimicry emerges as a key mechanism by which infectious or chemical agents trigger autoimmunity. In certain susceptible individuals, autoreactive T or B cells may be activated by a foreign antigen due to resemblances between foreign and self-peptides. Chronic inflammation, typically driven by abnormal immune responses, is strongly associated with AID pathogenesis. Inflammasomes, which are vital cytosolic multiprotein complexes assembled in response to infections and stress, are crucial to activating inflammatory processes in macrophages. Chronic inflammation, characterized by prolonged tissue injury and repair cycles, can significantly damage tissues, thereby increasing the risk of AIDs. Inhibiting inflammasomes, particularly in autoinflammatory disorders, has garnered significant interest, with pharmaceutical advancements targeting cytokines and inflammasomes showing promise in AID management.

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.

Mesenchymal stem cells attenuate systemic lupus erythematosus by inhibiting NLRP3 inflammasome activation through Pim-1 kinase

The inflammatory response runs through the whole pathogenesis of systemic lupus erythematosus (SLE). Mesenchymal stem cells (MSC) have exhibited a positive therapeutic effect on SLE. This study aimed to ascertain the pathogenic role of inflammasome activation in SLE and whether MSC alleviate SLE by suppressing it. The results showed that the nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome was activated in macrophages from MRL/lpr mice and patients with SLE, correlating with disease activity. After MSC transplantation, the disease severity in MRL/lpr mice was alleviated, and NLRP3 inflammasome activation was inhibited with decreased levels of NLRP3 and caspase-1 in macrophages. Furthermore, lower serum levels of interleukin (IL)-1β and IL-18 were observed in patients with SLE who underwent MSC transplantation. In vitro and in vivo studies indicated that MSC suppressed NLRP3 inflammasome activation by inhibiting Pim-1 expression. The findings provide an updated view of inflammasome signaling in SLE. Additionally, MSC ameliorated SLE by inhibiting NLRP3 inflammasome activation, implying a possible molecular mechanism for the clinical application of MSC and a potential therapeutic target in patients with SLE.

Research Progress of Pyroptosis in Renal Diseases

Kidney diseases, particularly Acute Kidney Injury (AKI) and Chronic Kidney Disease (CKD), are identified as global public health issues affecting millions of individuals. In addition, the frequency of renal diseases in the population has increased dramatically and rapidly in recent years. Renal disorders have become a significant public health burden. The pathophysiology of renal diseases is significantly connected with renal cell death, including apoptosis, necrosis, necroptosis, ferroptosis, pyroptosis, and autophagy, as is now recognized. Unlike other forms of cell death, pyroptosis is a unique planned cell death (PCD). Scientists have proven that pyroptosis is crucial in developing various disorders, and this phenomenon is gaining increasing attention. It is considered a novel method of inflammatory cell death. Intriguingly, inflammation is among the most significant pathological characteristics of renal disease. This study investigates the effects of pyroptosis on Acute Kidney Injury (AKI), Chronic Kidney Disease (CKD), Diabetic Nephropathy (DN), Immunoglobulin A (IgA) Nephropathy, and Lupus Nephritis (LN) to identify novel therapeutic targets for kidney diseases.

C/EBPβ isoform-specific regulation of podocyte pyroptosis in lupus nephritis-induced renal injury

As an essential factor in the prognosis of systemic lupus erythematosus (SLE), lupus nephritis (LN) can accelerate the rate at which patients with SLE can transition to chronic kidney disease or even end-stage renal disease. Podocytes now appear to be a possible direct target in LN in addition to being prone to collateral damage from glomerular capillary lesions induces by immune complexes and inflammatory processes. The NLRP3 inflammasome is regulated by CCAAT/enhancer-binding protein β (C/EBPβ), which is involved in the pathogenesis of SLE. However, the role and mechanism of C/EBPβ in LN remain unclear. In this investigation, glomerular podocytes treated with LN serum and MRL/lpr mice were employed as in vivo and in vitro models of LN, respectively. In vivo, the expression of C/EBPβ isoforms was detected in kidney specimens of humans and mice with LN. Then we assessed the effect of C/EBPβ inhibition on renal structure and function by injecting RNAi adeno-associated virus of C/EBPβ shRNA into MRL/lpr mice. In vitro, glomerular podocytes were treated with LN serum and C/EBPβ siRNA to explore the role of C/EBPβ in the activation of the AIM2 inflammasome and podocyte injury. C/EBPβ-LAP and C/EBPβ-LIP were significantly overexpressed in kidney tissue samples from LN patients and mice, and C/EBPβ inhibition significantly alleviated renal function damage and ameliorated renal structural deficiencies. Inflammatory pathways downstream from the AIM2 inflammasome could be suppressed by C/EBPβ knockdown. Furthermore, the upregulation of C/EBPβ-LAP could activate the AIM2 inflammasome and podocyte pyroptosis by binding to the promoters of AIM2 and CASPASE1 to enhance their expression, and the knockdown of AIM2 or (and) caspase-1 reversed the effects of C/EBPβ-LAP overexpression. Interestingly, C/EBPβ-LIP overexpression could transcriptionally inhibit IRAG and promote Ca2+ release-mediated activation of the AIM2 inflammasome. This finding suggests that C/EBPβ is not only involved in the regulation of the expression of key proteins of the AIM2 inflammasome but also affects the polymerization of key proteins of the AIM2 inflammasome through the regulation of Ca2+ release. In conclusion, this study provides a new idea for studying the regulatory mechanism of C/EBPβ and provides a theoretical basis for the early diagnosis and treatment of LN in the future. © 2023 The Pathological Society of Great Britain and Ireland.

Exploring the anti-inflammatory activity of sulforaphane

Dysregulation of innate immune responses can result in chronic inflammatory conditions. Glucocorticoids, the current frontline therapy, are effective immunosuppressive drugs but come with a trade-off of cumulative and serious side effects. Therefore, alternative drug options with improved safety profiles are urgently needed. Sulforaphane, a phytochemical derived from plants of the brassica family, is a potent inducer of phase II detoxification enzymes via nuclear factor-erythroid factor 2-related factor 2 (NRF2) signaling. Moreover, a growing body of evidence suggests additional diverse anti-inflammatory properties of sulforaphane through interactions with mediators of key signaling pathways and inflammatory cytokines. Multiple studies support a role for sulforaphane as a negative regulator of nuclear factor kappa-light chain enhancer of activated B cells (NF-κB) activation and subsequent cytokine release, inflammasome activation and direct regulation of the activity of macrophage migration inhibitory factor. Significantly, studies have also highlighted potential steroid-sparing activity for sulforaphane, suggesting that it may have potential as an adjunctive therapy for some inflammatory conditions. This review discusses published research on sulforaphane, including proposed mechanisms of action, and poses questions for future studies that might help progress our understanding of the potential clinical applications of this intriguing molecule.

SGLT-2 Inhibitors and the Inflammasome: What's Next in the 21st Century?

The nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome in the kidney and the heart is increasingly being suggested to play a key role in mediating inflammation. In the kidney, NLRP3 activation was associated with the progression of diabetic kidney disease. In the heart, activation of the NLRP3 inflammasome was related to the enhanced release of interleukin-1β (IL-1β) and the subsequent induction of atherosclerosis and heart failure. Apart from their glucose-lowering effects, SGLT-2 inhibitors were documented to attenuate activation of the NLRP3, thus resulting in the constellation of an anti-inflammatory milieu. In this review, we focus on the interplay between SGLT-2 inhibitors and the inflammasome in the kidney, the heart and the neurons in the context of diabetes mellitus and its complications.

PYHIN protein IFI207 regulates cytokine transcription and IRF7 and contributes to the establishment of K. pneumoniae infection

PYHIN proteins AIM2 and IFI204 sense pathogen DNA, while other PYHINs have been shown to regulate host gene expression through as-yet unclear mechanisms. We characterize mouse PYHIN IFI207, which we find is not involved in DNA sensing but rather is required for cytokine promoter induction in macrophages. IFI207 co-localizes with both active RNA polymerase II (RNA Pol II) and IRF7 in the nucleus and enhances IRF7-dependent gene promoter induction. Generation of Ifi207-/- mice shows no role for IFI207 in autoimmunity. Rather, IFI207 is required for the establishment of a Klebsiella pneumoniae lung infection and for Klebsiella macrophage phagocytosis. These insights into IFI207 function illustrate that PYHINs can have distinct roles in innate immunity independent of DNA sensing and highlight the need to better characterize the whole mouse locus, one gene at a time.

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.

cGAS deficiency enhances inflammasome activation in macrophages and inflammatory pathology in pristane-induced lupus

Introduction

Type I interferon (IFN) plays a vital role in the pathogenesis of systemic lupus erythematosus. Cyclic GMP AMP synthase (cGAS) is a cytosolic DNA sensor that recognizes dsDNA and creates cGAMP to activate STING-mediated type I IFN production. The activation of STING induces lupus disease in Fcgr2b deficient mice through the differentiation of dendritic cells. In contrast, Cgas-deficient mice could be generated more autoantibody production and proteinuria in pristane-induced lupus (PIL). These data suggested that the other dsDNA sensors could be involved in lupus development mechanisms.

Methods

This study aimed to identify the cGAS-mediated mechanisms contributing to lupus pathogenesis in PIL. The Cgas-deficient and WT mice were induced lupus disease with pristane and subsequently analyzed autoantibody, histopathology, and immunophenotypes. The lung tissues were analyzed with the expression profiles by RT-PCR and western blot. The bone marrow-derived macrophages were stimulated with inflammasome activators and observed pyroptosis.

Results

The Cgas-/- mice developed more severe pulmonary hemorrhage and autoantibody production than WT mice. The activated dendritic cells, IFN-g-, and IL-17a-producing T helper cells, and infiltrated macrophages in the lung were detected in Cgas-/- mice higher than in WT mice. We observed an increase in expression of Aim2, Casp11, and Ifi16 in the lung and serum IL-1a but IL-1b in pristane-injected Cgas-/- mice. The rise of Caspase-11 in the lung of pristane-injected Cgas-/- mice suggested noncanonical inflammasome activation. The activation of AIM2 and NLRP3 inflammasomes in bone marrow-derived macrophages (BMDMs) enhanced the number of dead cells in Cgas-/- mice compared with WT mice. Activation of the inflammasome significantly induced pyroptosis in Cgas-/- BMDMs. The dsDNA level, but not mitochondrial DNA, increased dramatically in pristane-injected Cgas-/- mice suggesting the dsDNA could be a ligand activating inflammasomes. The cGAS agonist-induced BMDM activation in the Cgas-/- mice indicated that the activation of DNA sensors other than cGAS enhanced activated macrophages.

Conclusion

These findings suggested that cGAS hampers the unusual noncanonical inflammasome activation through other DNA sensors.

GBP2 acts as a member of the interferon signalling pathway in lupus nephritis

Lupus nephritis (LN) is a common and serious clinical manifestation of systemic lupus erythematosus. However, the pathogenesis of LN is not fully understood. The currently available treatments do not cure the disease and appear to have a variety of side effects in the long term. The purpose of this study was to search for key molecules involved in the LN immune response through bioinformatics techniques to provide a reference for LN-specific targeted therapy. The GSE112943 dataset was downloaded from the Gene Expression Omnibus database, and 20 of the samples were selected for analysis. In total, 2330 differentially expressed genes were screened. These genes were intersected with a list of immune genes obtained from the IMMPORT immune database to obtain 128 differentially expressed immune-related genes. Enrichment analysis showed that most of these genes were enriched in the interferon signalling pathway. Gene set enrichment analysis revealed that the sample was significantly enriched for expression of the interferon signalling pathway. Further analysis of the core gene cluster showed that nine genes, GBP2, VCAM1, ADAR, IFITM1, BST2, MX2, IRF5, OAS1 and TRIM22, were involved in the interferon signalling pathway. According to our analysis, the guanylate binding protein 2 (GBP2), interferon regulatory factor 5 and 2′-5′-oligoadenylate synthetase 1 (OAS1) genes are involved in three interferon signalling pathways. At present, we do not know whether GBP2 is associated with LN. Therefore, this study focused on the relationship between GBP2 and LN pathogenesis. We speculate that GBP2 may play a role in the pathogenesis of LN as a member of the interferon signalling pathway. Further immunohistochemical results showed that the expression of GBP2 was increased in the renal tissues of LN patients compared with the control group, confirming this conjecture. In conclusion, GBP2 is a member of the interferon signalling pathway that may have implications for the pathogenesis of LN and serves as a potential biomarker for LN.

Does Pyroptosis Play a Role in Inflammasome-Related Disorders?

Inflammasomes are multiprotein complexes orchestrating intracellular recognition of endogenous and exogenous stimuli, cellular homeostasis, and cell death. Upon sensing of certain stimuli, inflammasomes typically activate inflammatory caspases that promote the production and release of the proinflammatory cytokines IL-1β, IL-1α, and IL-18 and induce a type of inflammatory cell death known as “pyroptosis”. Pyroptosis is an important form of regulated cell death executed by gasdermin proteins, which is largely different from apoptosis and necrosis. Recently, several signaling pathways driving pyroptotic cell death, including canonical and noncanonical inflammasome activation, as well as caspase-3-dependent pathways, have been reported. While much evidence exists that pyroptosis is involved in the development of several inflammatory diseases, its contribution to inflammasome-related disorders (IRDs) has not been fully clarified. This article reviews molecular mechanisms leading to pyroptosis, and attempts to provide evidence for its possible role in inflammasome-related disorders, including NLR pyrin domain containing 3 (NLRP3) inflammasome disease, NLR containing a caspase recruitment domain 4 (NLRC4) inflammasome disease, and pyrin inflammasome disease. Although the specific mechanism needs further investigations, these studies have uncovered the role of pyroptosis in inflammasome-related disorders and may open new avenues for future therapeutic interventions.

Disulfiram alleviates pristane-induced lupus via inhibiting GSDMD-mediated pyroptosis

Activation of multiple inflammasomes in monocytes/macrophages is associated with the pathogenesis of systemic lupus erythematosus (SLE). Gasdermin D (GSDMD)-mediated pyroptosis, a common consequence of multiple activated inflammasomes, is a programmed cell death with strong inflammatory responses. This suggested that targeting monocyte/macrophage pyroptosis might provide an opportunity to cure SLE. Here, we aimed to investigate the effect of disulfiram (DSF), a small molecule inhibitor of pyroptosis, and its potential therapeutic mechanism for SLE. The mRNA expression of GSDMD and IL-1β were significantly increased in peripheral blood mononuclear cells (PBMCs) from SLE patients. Importantly, we found serum from SLE patients rather than healthy controls induced GSDMD-mediated pyroptosis in THP-1 cells, as evidenced by enhanced LDH release, increased number of PI-positive cells, and high expression of full-length GSDMD and N-terminal GSDMD. Interestingly, treatment with DSF obviously inhibited pyroptosis of THP-1 cells induced by serum from SLE patients. Of note, DSF administration reduced proteinuria, serum anti-dsDNA level, and renal immune complex. It also attenuated renal damage in PIL mice. Further research found that the high level of serum IL-β and GSDMD-mediated pyroptosis of glomerular macrophages in PIL mice were rescued with DSF treatment. These data implied that GSDMD-mediated monocytes/macrophages pyroptosis played an important role in the pathogenesis of SLE and DSF might be a potential alternative therapeutic agent for SLE.

Pathological mechanisms and crosstalk among different forms of cell death in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder characterized by a profound immune dysregulation and the presence of a variety of autoantibodies. Aberrant activation of programmed cell death (PCD) signaling and accelerated cell death is critical in the immunopathogenesis of SLE. Accumulating cellular components from the dead cells and ineffective clearance of the dead cell debris, in particular the nucleic acids and nucleic acids-protein complexes, provide a stable source of self-antigens, which potently activate auto-reactive B cells and promote IFN-I responses in SLE. Different cell types display distinct susceptibility and characteristics to a certain type of cell death, while different PCDs in various cells have mutual and intricate connections to promote immune dysregulation and contribute to the development of SLE. In this review, we discuss the role of various cell death pathways and their interactions in the pathogenesis of SLE. An in depth understanding of the interconnections among various forms cell death in SLE will lead to a better understanding of disease pathogenesis, shedding light on the development of novel therapeutic targets.

AIM2-inflammasome role in systemic lupus erythematous and rheumatoid arthritis

The inflammasome AIM2 regulates multiple aspects of innate immune functions and serves as a critical mediator of inflammatory responses. AIM2 inflammasome activation leads to the production of pro-inflammatory cytokines, IL-1β and IL-18 and participates triggering a pyroptosis response needed to counteract excessive cell proliferation. In addition, AIM2 expression and activation is wide regulated since alteration in its activity may derived in pathological consequences. Consequently, deregulated AIM2 activation contributes to the pathogenic processes of various inflammatory diseases. In this review, we will discuss the activation and function of AIM2 inflammasome, as well as its contribution in rheumatoid arthritis and systemic lupus erythematous pathology. Finally, we highlight the participation of the AIM2-inflammasome at the level of joint in rheumatoid arthritis and at kidney in systemic lupus erythematous. The development of therapeutic strategies based on modulation of AIM2-inflammasome activity should have a tissue-specific focus.

A Glimpse of Inflammation and Anti-Inflammation Therapy in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common complication of diabetes mellitus and a major cause of end-stage kidney disease (ESKD). The pathogenesis of DKD is very complex and not completely understood. Recently, accumulated evidence from in vitro and in vivo studies has demonstrated that inflammation plays an important role in the pathogenesis and the development of DKD. It has been well known that a variety of pro-inflammatory cytokines and related signaling pathways are involved in the procession of DKD. Additionally, some anti-hyperglycemic agents and mineralocorticoid receptor antagonists (MRAs) that are effective in alleviating the progression of DKD have anti-inflammatory properties, which might have beneficial effects on delaying the progression of DKD. However, there is currently a lack of systematic overviews. In this review, we focus on the novel pro-inflammatory signaling pathways in the development of DKD, including the nuclear factor kappa B (NF-κB) signaling pathway, toll-like receptors (TLRs) and myeloid differentiation primary response 88 (TLRs/MyD88) signaling pathway, adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling pathways, inflammasome activation, mitochondrial DNA (mtDNA) release as well as hypoxia-inducible factor-1(HIF-1) signaling pathway. We also discuss the related anti-inflammation mechanisms of metformin, finerenone, sodium-dependent glucose transporters 2 (SGLT2) inhibitors, Dipeptidyl peptidase-4 (DPP-4) inhibitors, Glucagon-like peptide-1 (GLP-1) receptor agonist and traditional Chinese medicines (TCM).

Strategies of Targeting Inflammasome in the Treatment of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple organ dysfunction resulting from the production of multiple autoantibodies and adaptive immune system abnormalities involving T and B lymphocytes. In recent years, inflammasomes have been recognized as an important component of innate immunity and have attracted increasing attention because of their pathogenic role in SLE. In short, inflammasomes regulate the abnormal differentiation of immune cells, modulate pathogenic autoantibodies, and participate in organ damage. However, due to the clinical heterogeneity of SLE, the pathogenic roles of inflammasomes are variable, and thus, the efficacy of inflammasome-targeting therapies is uncertain. To provide a foundation for the development of such therapeutic strategies, in this paper, we review the role of different inflammasomes in the pathogenesis of SLE and their correlation with clinical phenotypes and propose some corresponding treatment strategies.

The IL-18/IL-18R1 signalling axis: Diagnostic and therapeutic potential in hypertension and chronic kidney disease

Chronic kidney disease (CKD) is inherently an inflammatory condition, which ultimately results in the development of end stage renal disease or cardiovascular events. Low-grade inflammatory diseases such as hypertension and diabetes are leading causes of CKD. Declines in renal function correlate with elevated circulating pro-inflammatory cytokines in patients with these conditions. The inflammasome is an important inflammatory signalling platform that has been associated with low-grade chronic inflammatory diseases. Notably, activation and assembly of the inflammasome causes the auto cleavage of pro-caspase-1 into its active form, which then processes the pro-inflammatory cytokines pro-interleukin (IL)-1β and pro-IL-18 into their active forms. Currently, the nod-like receptor protein 3 (NLRP3) inflammasome has been implicated in the development of CKD in pre-clinical and clinical settings, and the ablation or inhibition of inflammasome components have been shown to be reno-protective in models of CKD. While clinical trials have demonstrated that neutralisation of IL-1β signalling by the drug anakinra lowers inflammation markers in haemodialysis patients, ongoing preclinical studies are showing that this ability to attenuate disease is limited in progressive models of kidney disease. These results suggest a potential predominant role for IL-18 in the development of CKD. This review will discuss the role of the inflammasome and its pro-inflammatory product IL-18 in the development of renal fibrosis and inflammation that contribute to the pathophysiology of CKD. Furthermore, we will examine the potential of the IL-18 signalling axis as an anti-inflammatory target in CKD and its usefulness as diagnostic biomarker to predict acute kidney injury.

The Role of Inflammasomes in Glomerulonephritis

The inflammasome is an immune multiprotein complex that activates pro-caspase 1 in response to inflammation-inducing stimuli and it leads to IL-1β and IL-18 proinflammatory cytokine production. NLRP1 and NLRP3 inflammasomes are the best characterized and they have been related to several autoimmune diseases. It is well known that the kidney expresses inflammasome genes, which can influence the development of some glomerulonephritis, such as lupus nephritis, ANCA glomerulonephritis, IgA nephropathy and anti-GBM nephropathy. Polymorphisms of these genes have also been described to play a role in autoimmune and kidney diseases. In this review, we describe the main characteristics, activation mechanisms, regulation and functions of the different inflammasomes. Moreover, we discuss the latest findings about the role of the inflammasome in several glomerulonephritis from three different points of view: in vitro, animal and human studies.

The IL-21-TET2-AIM2-c-MAF pathway drives the T follicular helper cell response in lupus-like disease

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that involves T follicular helper (TFH ) cell-mediated humoral immune responses. Absent in melanoma 2 (human AIM2 and murine Aim2) is a well-known component of the inflammasome in the innate immune system. Surprisingly, we observed that in SLE patients, upregulated levels of AIM2 expression were found in peripheral blood and skin lesions, with the highest levels detected in TFH -like cells. In the CD4cre Aim2fl/fl conditional knockout mice, a markedly reduced TFH cell response was observed, with significantly lower levels of serum autoantibodies and proteinuria, as well as profoundly reduced renal IgG deposition in pristane-induced lupus mice. Mechanistically, IL-21 was found to recruit hydroxymethyltransferase ten-eleven translocation 2 (TET2) to the AIM2 promoter, resulting in DNA demethylation and increased transcription of AIM2. In addition, AIM2 could regulate c-MAF expression to enhance IL-21 production, which consequently promoted TFH cell differentiation. Our results have identified a role of AIM2 in promoting the TFH cell response and further revealed that the IL-21-TET2-AIM2-c-MAF signalling pathway is dysregulated in lupus pathogenesis, which provides a potential therapeutic target for SLE.

Focus on the Mechanisms and Functions of Pyroptosis, Inflammasomes, and Inflammatory Caspases in Infectious Diseases

Eukaryotic cells can initiate several distinct self-destruction mechanisms to display essential roles for the homeostasis maintenance, development, and survival of an organism. Pyroptosis, a key response mode in innate immunity, also referred to as caspase-1-dependent proinflammatory programmed necrotic cell death activated by human caspase-1/4/5, or mouse caspase-1/11, plays indispensable roles in response to cytoplasmic insults and immune defense against infectious diseases. These inflammatory caspases are employed by the host to eliminate pathogen infections such as bacteria, viruses, protozoans, and fungi. Gasdermin D requires to be cleaved and activated by these inflammatory caspases to trigger the pyroptosis process. Physiological rupture of cells results in the release of proinflammatory cytokines, the alarmins IL-1β and IL-18, symbolizing the inflammatory potential of pyroptosis. Moreover, long noncoding RNAs play direct or indirect roles in the upstream of the pyroptosis trigger pathway. Here, we review in detail recently acquired insights into the central roles of inflammatory caspases, inflammasomes, and pyroptosis, as well as the crosstalk between pyroptosis and long noncoding RNAs in mediating infection immunity and pathogen clearance.

Calpain Inhibitor Calpeptin Alleviates Ischemia/Reperfusion-Induced Acute Kidney Injury via Suppressing AIM2 Inflammasome and Upregulating Klotho Protein

Renal ischemia/reperfusion injury is a major contributor of acute kidney injury (AKI), leading to renal cell necrosis, apoptosis, and inflammation. Calpains, a family of Ca²⁺-dependent cysteine proteases, play a pivotal role in the pathogenesis of renal diseases. Several studies have reported calpain inhibitors showing remarkable reno-protective effects against proteinuria and α-klotho deficiency-induced renal aging symptoms, particularly against glomerulus injury. However, little is known about the role of the calpain inhibitor calpeptin in acute kidney injury. The present study aims to investigate the potential mechanism of downregulation of Calpain 1 and 2 activity by calpeptin in the ischemia/reperfusion (IR)-induced AKI model. Firstly, we observed that the contents of Calpain 1 and 2 were significantly increased in the renal biopsy of clinical AKI patients, especially in the diseased tubules space. To investigate the impacts of calpain activity inhibition, we further pretreated with calpeptin in both the IR mouse model and in the HK-2 cells hypoxia model. We found that the calpain inhibitor calpeptin improved renal functional deterioration, attenuated pathological structure damage, and decreased tubular cell apoptosis in the IR injury-induced AKI mice model. Mechanistically, calpeptin significantly suppressed the AIM2 (absent in melanoma 2) and NLRP3 (NOD-like receptor protein 3) inflammasome signaling pathways and increased Klotho protein levels. Furthermore, immunofluorescence assays demonstrated that the application of calpeptin effectively inhibited Calpain 1 activation and gasdermin D (GSDMD) cleavage in the renal tubules of IR mice. Taken together, our both in vivo and in vitro experiments suggest that calpeptin conveyed reno-protection in AKI might be mediated by the inhibition of AIM2 inflammasome activation and upregulation of Klotho protein. As such, we provide new evidence that Calpain 1 and 2 activation may be closely associated with the pathogenesis of clinical AKI. The calpain-mediated AIM2 inflammasome signaling pathway and distinct interaction between calpain and Klotho may provide a potential novel preventative and therapeutic target for acute kidney injury.

AIM2 inflammasome contributes to aldosterone-induced renal injury via endoplasmic reticulum stress

Inflammatory response and renal fibrosis are the hallmarks of chronic kidney disease (CKD). However, the specific mechanism of aldosterone-induced renal injury in the progress of CKD requires elucidation. Emerging evidence has demonstrated that absent in melanoma 2 (AIM2)-mediated inflammasome activation and endoplasmic reticulum stress (ERS) play a pivotal role in the renal fibrosis. Here, we investigated whether overexpression or deficiency of AIM2 affects ERS and fibrosis in aldosterone-infused renal injury. Interestingly, we found that AIM2 was markedly expressed in the diseased proximal tubules from human and experimental CKD. Mechanically, overactivation of AIM2 aggravated aldosterone-induced ERS and fibrotic changes in vitro while knockdown of AIM2 blunted these effects in vivo and in vitro. By contrast, AIM2 deficiency ameliorated renal structure and function deterioration, decreased proteinuria levels and lowered systolic blood pressure in vivo; silencing of AIM2 blocked inflammasome-mediated signaling pathway, relieved ERS and fibrotic changes in vivo. Furthermore, mineralocorticoid receptor (MR) antagonist eplerenone and ERS inhibitor tauroursodeoxycholic acid (TUDCA) had nephroprotective effects on the basis of AIM2 overactivation in vitro, while they failed to produce a more remarkable renoprotective effect on the treatment of AIM2 silence in vitro. Notably, the combination of TUDCA with AIM2 knockdown significantly reduced proteinuria levels in vivo. Additionally, immunofluorescence assay identified that apoptosis-associated speck-like protein (ASC) recruitment and Gasdermin-D (GSDMD) cleavage respectively occurred in the glomeruli and tubules in vivo. These findings establish a crucial role for AIM2 inflammasome in aldosterone-induced renal injury, which may provide a novel therapeutic target for the pathogenesis of CKD.

The complex role of AIM2 in autoimmune diseases and cancers

Absent in melanoma 2 (AIM2) is a novel member of interferon (IFN)-inducible PYHIN proteins. In innate immune cells, AIM2 servers as a cytoplasmic double-stranded DNA sensor, playing a crucial role in the initiation of the innate immune response as a component of the inflammasome. AIM2 expression is increased in patients with systemic lupus erythematosus (SLE), psoriasis, and primary Sjogren's syndrome, indicating that AIM2 might be involved in the pathogenesis of autoimmune diseases. Meanwhile, AIM2 also plays an antitumorigenesis role in an inflammasome independent-manner. In melanoma, AIM2 is initially identified as a tumor suppressor factor. However, AIM2 is also found to contribute to lung tumorigenesis via the inflammasome-dependent release of interleukin 1β and regulation of mitochondrial dynamics. Additionally, AIM2 reciprocally dampening the cGAS-STING pathway causes immunosuppression of macrophages and evasion of antitumor immunity during antibody treatment. To summarize the complicated effect and role of AIM2 in autoimmune diseases and cancers, herein, we provide an overview of the emerging research progress on the function and regulatory pathway of AIM2 in innate and adaptive immune cells, as well as tumor cells, and discuss its pathogenic role in autoimmune diseases, such as SLE, psoriasis, primary Sjogren's syndrome, and cancers, such as melanomas, non-small-cell lung cancer, colon cancer, hepatocellular carcinoma, renal carcinoma, and so on, hopefully providing potential therapeutic and diagnostic strategies for clinical use.

Inflammation drives alternative first exon usage to regulate immune genes including a novel iron-regulated isoform of Aim2

Determining the layers of gene regulation within the innate immune response is critical to our understanding of the cellular responses to infection and dysregulation in disease. We identified a conserved mechanism of gene regulation in human and mouse via changes in alternative first exon (AFE) usage following inflammation, resulting in changes to the isoforms produced. Of these AFE events, we identified 95 unannotated transcription start sites in mice using a de novo transcriptome generated by long-read native RNA-sequencing, one of which is in the cytosolic receptor for dsDNA and known inflammatory inducible gene, Aim2. We show that this unannotated AFE isoform of Aim2 is the predominant isoform expressed during inflammation and contains an iron-responsive element in its 5′UTR enabling mRNA translation to be regulated by iron levels. This work highlights the importance of examining alternative isoform changes and translational regulation in the innate immune response and uncovers novel regulatory mechanisms of Aim2.

Pyroptosis and inflammasomes in obstetrical and gynecological diseases

Pyroptosis, an inflammatory form of programmed cell death, takes an essential part in a wide variety of physiological activities, for instance, implantation, placentation and the body's defense against infection. However, once excessively activated, pyroptosis mediated by the activation of inflammasomes can be highly pathological. It can cause inflammatory and autoimmune diseases including a variety of obstetrical and gynecological diseases, such as endometriosis, gestational diabetes mellitus, insulin resistance in polycystic ovary syndrome, and multiple obstetric complications including preeclampsia. Although the role of pyroptosis in the pathogenesis of the above mentioned diseases has not been fully elucidated, we try to tap its therapeutic potential by targeting pyroptosis signaling and inflammasome formation. Pyroptosis and inflammasomes are confirmed to be involved in endometriosis and gynecological malignant tumors, therefore, medical approachs inducing pyroptosis of the ectopic endometrium and tumor cells can be feasible treatments for endometriosis and gynecological cancers. On the maternal-fetal interface, although a certain level of the innate immune response activation is required for a successful implantation and placentation, maternal and fetal injury may occur once the inflammasomes are over-activated. Besides, since gestational diabetes mellitus and insulin resistance in polycystic ovary syndrome share common pathogenesis with metabolic diseases, this domain research sheds light on future study of some obstetrical and gynecological diseases.

Absent in melanoma 2-mediating M1 macrophages facilitate tumor rejection in renal carcinoma

Absent in melanoma 2 (AIM2) as an immune regulator for the regulation of tumor-associated macrophages (TAMs) function is unclear in tumor development. Here, the AIM2 function was investigated in TAMs-mediated malignant behaviors of renal carcinoma. The correlation analysis result showed that the AIM2 expression in TAMs was negatively correlated with the percentages of M2-like polarization phenotype in human or murine renal cancer specimens. By the cocultured assay with bone marrow-derived macrophages (BMDMs) and Renca cells, overexpression of AIM2 in macrophages enhanced the inflammasome activation and reversed the phenotype from M2 to M1. Compared with BMDMs-Ctrl cocultured group, BMDMs-AIM2 cocultured group showed reduced tumor cell proliferation and migration. The blockade of inflammasome activation by the inhibitor Ac-YVAD-CMK abrogated AIM2-mediated M1 polarization and the inhibition of tumor cell growth. To evaluate the therapeutic efficacy of AIM2-mediated M1 macrophages in vivo, BMDMs-AIM2 were intravenously injected into subcutaneous Renca-tumor mice. The results showed that the infiltration of M1 TAMs was increased and tumor growth was suppressed in BMDMs-AIM2-treated mice when compared with BMDMs-Ctrl-treat mice. Accordingly, the blockade of inflammasome activation reduced the anti-tumor activities of BMDMs-AIM2. Moreover, the lung metastases of renal carcinoma were suppressed by the administration of BMDMs-AIM2 accompanied with the reduced tumor foci. These results demonstrated that AIM2 enhanced TAMs polarization switch from anti-inflammatory M2 phenotypy to pro-inflammatory M1 through inflammasome signaling activation, thus exerting therapeutic intervention in renal carcinoma models. Our results provide a possible molecular mechanism for the modulation of TAMs polarization in tumor microenvironment and open a new potential therapeutic approach for renal cancer.

DNA Sensing in the Innate Immune Response

The innate immune system recognizes conserved pathogen-associated molecular patterns and produces inflammatory cytokines that direct downstream immune responses. The inappropriate localization of DNA within the cell cytosol or endosomal compartments indicates that a cell may either be infected by a DNA virus or bacterium, or has problems with its own nuclear integrity. This DNA is sensed by certain receptors that mediate cytokine production and, in some cases, initiate an inflammatory and lytic form of cell death called pyroptosis. Dysregulation of these DNA-sensing pathways is thought to contribute to autoimmune diseases and the development of cancer. In this review, we will discuss the DNA sensors Toll-like receptor 9 (TLR9), cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), absent in melanoma 2 (AIM2), and interferon gamma-inducible 16 (IFI16), their ligands, and their physiological significance. We will also examine the less-well-understood DEAH- and DEAD-box helicases DHX9, DHX36, DDX41, and RNA polymerase III, each of which may play an important role in DNA-mediated innate immunity.

Cannabinoids as Key Regulators of Inflammasome Signaling: A Current Perspective

Inflammasomes are cytoplasmic inflammatory signaling protein complexes that detect microbial materials, sterile inflammatory insults, and certain host-derived elements. Inflammasomes, once activated, promote caspase-1–mediated maturation and secretion of pro-inflammatory cytokines, interleukin (IL)-1β and IL-18, leading to pyroptosis. Current advances in inflammasome research support their involvement in the development of chronic inflammatory disorders in contrast to their role in regulating innate immunity. Cannabis (marijuana) is a natural product obtained from the Cannabis sativa plant, and pharmacologically active ingredients of the plant are referred to as cannabinoids. Cannabinoids and cannabis extracts have recently emerged as promising novel drugs for chronic medical conditions. Growing evidence indicates the potent anti-inflammatory potential of cannabinoids, especially Δ⁹-tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD), and synthetic cannabinoids; however, the mechanisms remain unclear. Several attempts have been made to decipher the role of cannabinoids in modulating inflammasome signaling in the etiology of chronic inflammatory diseases. In this review, we discuss recently published evidence on the effect of cannabinoids on inflammasome signaling. We also discuss the contribution of various cannabinoids in human diseases concerning inflammasome regulation. Lastly, in the milieu of coronavirus disease-2019 (COVID-19) pandemic, we confer available evidence linking inflammasome activation to the pathophysiology of COVID-19 suggesting overall, the importance of cannabinoids as possible drugs to target inflammasome activation in or to support the treatment of a variety of human disorders including COVID-19.

Genetics and Pathogenetic Role of Inflammasomes in Philadelphia Negative Chronic Myeloproliferative Neoplasms: A Narrative Review

The last decade has been very important for the quantity of preclinical information obtained regarding chronic myeloproliferative neoplasms (MPNs) and the following will be dedicated to the translational implications of the new biological acquisitions. The overcoming of the mechanistic model of clonal evolution and the entry of chronic inflammation and dysimmunity into the new model are the elements on which to base a part of future therapeutic strategies. The innate immune system plays a major role in this context. Protagonists of the initiation and regulation of many pathological aspects, from cytokine storms to fibrosis, the NLRP3 and AIM2 inflammasomes guide and condition the natural history of the disease. For this reason, MPNs share many biological and clinical aspects with non-neoplastic diseases, such as autoimmune disorders. Finally, cardiovascular risk and disturbances in iron metabolism and myelopoiesis are also closely linked to the role of inflammasomes. Although targeted therapies are already being tested, an increase in knowledge on the subject is desirable and potentially translates into better care for patients with MPNs.

Emerging roles of absent in melanoma 2 in cardiovascular diseases

Absent in melanoma 2 (AIM2) is a member of the PYHIN (pyrin and HIN domain-containing protein) family with important roles in sensing double-stranded DNA (dsDNA) and assembling the AIM2 inflammasome, which has wide-ranging, pro-inflammatory and pro-pyroptotic properties. The AIM2 inflammasome can become activated in atherosclerotic plaque, abdominal aortic aneurysm wall and injured myocardium, and its activation is tightly regulated by a variety of atherogenic factors. Activation of the AIM2 inflammasome has close links to the progression of several cardiovascular diseases. This review will summarize the current knowledge of AIM2 biology, providing the latest insights into the mechanisms and contributions of atherogenic factors to AIM2 inflammasome activation. In addition, we will also explore crosstalk between AIM2 and the pathologies of atherosclerosis, abdominal aortic aneurysm, myocardial infarction and heart failure. A better understanding of the pathological roles of AIM2 in these disorders will be helpful in developing novel therapeutic approaches.

Jieduquyuziyin Prescription Suppresses Inflammatory Activity of MRL/lpr Mice and Their Bone Marrow-Derived Macrophages via Inhibiting Expression of IRAK1-NF-κB Signaling Pathway

Jieduquyuziyin prescription (JP) has been used to treat systemic lupus erythematosus (SLE). Although the effectiveness of JP in the treatment of SLE has been clinically proven, the underlying mechanisms have yet to be completely understood. We observed the therapeutic actions of JP in MRL/lpr mice and their bone marrow-derived macrophages (BMDMs) and the potential mechanism of their inhibition of inflammatory activity. To estimate the effect of JP on suppressing inflammatory activity, BMDMs of MRL/lpr and MRL/MP mice were treated with JP-treated serum, and MRL/lpr mice were treated by JP for 8 weeks. Among them, JP and its treated serum were subjected to quality control, and BMDMs were separated and identified. The results showed that in the JP group of BMDMs stimulated by Lipopolysaccharide (LPS) in MRL/lpr mice, the secretion of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) reduced, and the expressions of Interleukin-1 receptor-associated kinase 1 (IRAK1) and its downstream nuclear factor κB (NF-κB) pathway decreased. Meanwhile, the alleviation of renal pathological damage, the decrease of urinary protein and serum anti-dsDNA contents, the inhibition of TNF-α level, and then the suppression of the IRAK1-NF-κB inflammatory signaling in the spleen and kidney, confirmed that the therapeutic effect of JP. These results demonstrated that JP could inhibit the inflammatory activity of MRL/lpr mice and their BMDMs by suppressing the activation of IRAK1-NF-κB signaling and was supposed to be a good choice for the treatment of SLE.

Inflammasomes in Common Immune-Related Skin Diseases

The inflammasome is an important protein complex that cleaves the proinflammatory cytokines pro-IL-1β and pro-IL-18 into their active forms. Owing to its critical role in eliciting innate immune responses, IL-1β has been suggested to contribute to various skin diseases, including psoriasis, vitiligo, systemic lupus erythematosus (SLE), and atopic dermatitis (AD). Recently, several types of activators and inhibitors of different inflammasomes, as well as inflammasome-related genes and genetic susceptibility loci, have been identified in these immune-related common skin diseases. In particular, inflammasome activators and inhibitors presented highly cell-type-specific activity, suggesting that the inflammasome might perform different functions in different cell types. Moreover, most of these findings were based on experimental disease models, and the clinical features of the models partly resemble the typical symptoms of the diseases. In this review, from the perspective of activators and inhibitors, we collected evidence from the widely-studied inflammasomes, NLRP3, AIM2, and NLRP1, in psoriasis, vitiligo, SLE, and AD. Importantly, some small-molecule inhibitors hold therapeutic promise for the treatment of these diseases.

The DNA Sensor AIM2 Protects against Streptozotocin-Induced Type 1 Diabetes by Regulating Intestinal Homeostasis via the IL-18 Pathway

Pattern recognition receptors (PRRs), such as Nod2, Nlrp3, Tlr2, Trl4, and Tlr9, are directly involved in type 1 diabetes (T1D) susceptibility. However, the role of the cytosolic DNA sensor, AIM2, in T1D pathogenesis is still unknown. Here, we demonstrate that C57BL/6 mice lacking AIM2 (AIM2^−/−) are prone to streptozotocin (STZ)-induced T1D, compared to WT C57BL/6 mice. The AIM2^−/− mice phenotype is associated with a greater proinflammatory response in pancreatic tissues, alterations in gut microbiota and bacterial translocation to pancreatic lymph nodes (PLNs). These alterations are related to an increased intestinal permeability mediated by tight-junction disruption. Notably, AIM2^−/− mice treated with broad-spectrum antibiotics (ABX) are protected from STZ-induced T1D and display a lower pancreatic proinflammatory response. Mechanistically, the AIM2 inflammasome is activated in vivo, leading to an IL-18 release in the ileum at 15 days after an STZ injection. IL-18 favors RegIIIγ production, thus mitigating gut microbiota alterations and reinforcing the intestinal barrier function. Together, our findings show a regulatory role of AIM2, mediated by IL-18, in shaping gut microbiota and reducing bacterial translocation and proinflammatory response against insulin-producing β cells, which ultimately results in protection against T1D onset in an STZ-induced diabetes model.

High salt diet accelerates the progression of murine lupus through dendritic cells via the p38 MAPK and STAT1 signaling pathways

The increased incidence of systemic lupus erythematosus (SLE) in recent decades might be related to changes in modern dietary habits. Since sodium chloride (NaCl) promotes pathogenic T cell responses, we hypothesize that excessive salt intake contributes to the increased incidence of autoimmune diseases, including SLE. Given the importance of dendritic cells (DCs) in the pathogenesis of SLE, we explored the influence of an excessive sodium chloride diet on DCs in a murine SLE model. We used an induced lupus model in which bone marrow-derived dendritic cells (BMDCs) were incubated with activated lymphocyte-derived DNA (ALD-DNA) and transferred into C57BL/6 recipient mice. We observed that a high-salt diet (HSD) markedly exacerbated lupus progression, which was accompanied by increased DC activation. NaCl treatment also stimulated the maturation, activation and antigen-presenting ability of DCs in vitro. Pretreatment of BMDCs with NaCl also exacerbated BMDC-ALD-DNA-induced lupus. These mice had increased production of autoantibodies and proinflammatory cytokines, more pronounced splenomegaly and lymphadenopathy, and enhanced pathological renal lesions. The p38 MAPK–STAT1 pathway played an important role in NaCl-induced DC immune activities. Taken together, our results demonstrate that HSD intake promotes immune activation of DCs through the p38 MAPK–STAT1 signaling pathway and exacerbates the features of SLE. Thus, changes in diet may provide a novel strategy for the prevention or amelioration of lupus or other autoimmune diseases.

The role of inflammasomes in kidney disease

Inflammasomes are multiprotein innate immune complexes that regulate caspase-dependent inflammation and cell death. Pattern recognition receptors, such as nucleotide-binding oligomerization domain (NOD)-like receptors and absent in melanoma 2 (AIM2)-like receptors, sense danger signals or cellular events to activate canonical inflammasomes, resulting in caspase 1 activation, pyroptosis and the secretion of IL-1β and IL-18. Non-canonical inflammasomes can be activated by intracellular lipopolysaccharides, toxins and some cell signalling pathways. These inflammasomes regulate the activation of alternative caspases (caspase 4, caspase 5, caspase 11 and caspase 8) that lead to pyroptosis, apoptosis and the regulation of other cellular pathways. Many inflammasome-related genes and proteins have been implicated in animal models of kidney disease. In particular, the NLRP3 (NOD-, LRR- and pyrin domain-containing 3) inflammasome has been shown to contribute to a wide range of acute and chronic microbial and non-microbial kidney diseases via canonical and non-canonical mechanisms that regulate inflammation, pyroptosis, apoptosis and fibrosis. In patients with chronic kidney disease, immunomodulation therapies targeting IL-1β such as canakinumab have been shown to prevent cardiovascular events. Moreover, findings in experimental models of kidney disease suggest that small-molecule inhibitors targeting NLRP3 and other inflammasome components are promising therapeutic agents.

Research Progress on the Role of Inflammasomes in Kidney Disease

Inflammasomes are multimeric complexes composed of cytoplasmic sensors, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC or PYCARD), and procaspase-1 and play roles in regulating caspase-dependent inflammation and cell death. Inflammasomes are assembled by sensing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) and initiate inflammatory responses by activating caspase-1. Activated caspase-1 promotes the release of the inflammatory cytokines interleukin-1β (IL-1β) and IL-18 and eventually induces pyroptosis. Inflammasomes are closely related to kidney diseases. In particular, the NLRP3 (NACHT, LRR, and PYD domain-containing protein 3) inflammasome has been shown to cause acute and chronic kidney diseases by regulating canonical and noncanonical mechanisms of inflammation. Small-molecule inhibitors that target NLRP3 and other components of the inflammasome are potential options for the treatment of kidney-related diseases such as diabetic nephropathy. This article will focus on the research progress on inflammasomes and the key pathogenic roles of inflammasomes in the development and progression of kidney diseases and explore the potential of this intracellular inflammation to further prevent or block the development of the kidney disease.

Effect and Regulation of the NLRP3 Inflammasome During Renal Fibrosis

Renal fibrosis is a common pathological process where certain primary or secondary kidney diseases can continue to progress to the end-stage of the kidney disease; however, the molecular mechanisms underlying renal fibrosis remain unclear. Recently, research focusing on examining the function of inflammasomes has attracted a great deal of attention, and data derived from these research projects have increased our understanding of the effects and regulation of inflammasomes during renal fibrosis. Based on this, the present review summarizes recent findings in regard to NLRP3 inflammasome functions during various kidney diseases, and these findings indicate that the NLRP3 inflammasome not only mediates the inflammatory response but is also associated with pyroptosis, mitochondrial regulation, and myofibroblast differentiation during renal fibrosis. These novel findings provide us with a more in-depth understanding of the pathogenesis of renal fibrosis and will aid in the identification of new targets that can be used for the prevention and treatment of this disease.

Advances in Disease Mechanisms and Translational Technologies: Clinicopathologic Significance of Inflammasome Activation in Autoimmune Diseases

Autoimmune diseases are characterized by dysregulated immune tolerance to self and inflammatory damage to tissues and organs. The development of inflammation involves multiple innate and adaptive immune pathways. Inflammasomes are multimeric cytosolic protein complexes that form to mediate host immune responses upon recognizing pathogen- or damage-associated molecular patterns via pattern-recognition receptors (PRRs). The accelerating pace of inflammasome research has demonstrated important roles for inflammasome activation in many pathologic conditions, including infectious, metabolic, autoinflammatory, and autoimmune diseases. The inflammasome generally comprises a PRR, procaspase 1, and an adaptor molecule connecting the PRR and procaspase 1. Upon inflammasome activation, procaspase 1 becomes active caspase 1 that converts pro-interleukin-1β (proIL-1β) and proIL-18 into mature and active IL-1β and IL-18, respectively. The cytokines IL-1β and IL-18 have multipotent effects on immune and nonimmune cells and induce and promote systemic and local inflammatory responses. Human studies have shown increased levels of these cytokines, altered activation of inflammasome-related molecules, and/or the presence of inflammasome activators in rheumatic diseases, including systemic lupus erythematosus, rheumatoid arthritis, crystal-induced arthropathies, and Sjögren's syndrome. Such changes are found in the primary target organs, such as the kidneys, joints, and salivary glands, as well as in the cardiovascular system. In animal models of rheumatic diseases, inflammation and tissue damage improve upon genetic or pharmacologic targeting of the inflammasome, supporting its pathogenic role. Herein, we review the clinicopathologic significance and therapeutic targeting of inflammasome activation in rheumatic diseases and related conditions based on recent findings.

Programmed Cell Death Pathways in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease characterized by excessive inflammatory and immune responses and tissue damage. Increasing evidence has demonstrated the important role of programmed cell death in SLE pathogenesis. When apoptosis encounters with defective clearance, accumulated apoptotic cells lead to secondary necrosis. Different forms of lytic cell death, including secondary necrosis after apoptosis, NETosis, necroptosis, and pyroptosis, contribute to the release of damage-associated molecular patterns (DAMPs) and autoantigens, resulting in triggering immunity and tissue damage in SLE. However, the role of autophagy in SLE pathogenesis is in dispute. This review briefly discusses different forms of programmed cell death pathways and lay particular emphasis on inflammatory cell death pathways such as NETosis, pyroptosis, and necroptosis and their roles in the inflammatory and immune responses in SLE.

Jieduquyuziyin Prescription-Treated Rat Serum Suppresses Activation of Peritoneal Macrophages in MRL/Lpr Lupus Mice by Inhibiting IRAK1 Signaling Pathway

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease, and Jieduquyuziyin prescription (JP) is a traditional Chinese medicine (TCM) formula that has been testified to be effective for SLE treatment as an approved hospital prescription for many years in China. However, its mechanism of action in the treatment of this disease is largely unknown. The purpose of this study was to determine whether JP-treated rat serum can inhibit the activation of peritoneal macrophages in MRL/lpr mice by downregulating the IRAK1 signaling pathway, thereby achieving the effect of improving SLE. The JP-treated rat serum was prepared, and the peritoneal macrophages of MRL/lpr lupus mice were isolated in vitro, and the effect of JP on cell viability was detected by the CCK8 method. After LPS induction and shRNA lentiviral transfection, the effect of JP on the expression of IRAK1 in cells was detected by immunofluorescence staining. The content of TNF-α and IL-6 in the cell supernatant was determined by ELISA. The expression of IRAK1, NF-κB, TNF-α, and IL-6 mRNA was detected by RT-PCR, and the expression levels of IRAK1, p-IRAK1, TRAF6, IKBα, p-IKBα, IKK + IKK, NF-κB, and p-NF-κB proteins was detected by western blot method. We investigated the role of JP in peritoneal macrophages of the MRL/lpr mouse and identified the possible mechanisms of action. The results showed that JP could reduce the phosphorylation of IRAK1 and its downstream proteins induced by LPS and inhibit the expression of inflammatory cytokines, including TNF-α and IL-6. In addition, after the transfection of cells with shRNA lentiviral, the results of JP tended to be consistent. In conclusion, JP may inhibit the activation of peritoneal macrophages in MRL/lpr mice by downregulating the IRAK1-NF-κB signaling pathway, and IRAK1 may be a potential target for JP treatment of SLE.

Inflammasomes in the pathophysiology of autoinflammatory syndromes

Inflammasomes are a specialized group of intracellular sensors that are key components of the host innate immune system. Autoinflammatory diseases are disorders of the innate immune system that are characterized by recurrent inflammation and serious complications. Dysregulation of the inflammasome is associated with the onset and progression of several autoinflammatory and autoimmune diseases, including cryopyrin-associated periodic fever syndrome, familial Mediterranean fever, rheumatoid arthritis, and systemic lupus erythematosus. In this review, we discuss the involvement of various inflammasome components in the regulation of autoinflammatory disorders and describe the manifestations of these autoinflammatory diseases caused by inflammasome activation.