Inflammasome Priming in Sterile Inflammatory Disease

Ozone protects the rat lung from ischemia-reperfusion injury by attenuating NLRP3-mediated inflammation, enhancing Nrf2 antioxidant activity and inhibiting apoptosis

Ischemia-reperfusion injury (IRI) is a major cause of lung dysfunction during cardiovascular surgery, heart transplantation and cardiopulmonary bypass procedures, and the inflammatory response, oxidative stress, and apoptosis play key and allegedly maladaptive roles in its pathogenesis. The aim of this study was to initially elucidate whether ozone induces oxidative preconditioning by activating nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and secondly to determine whether ozone oxidative preconditioning (OzoneOP) protects the lung from IRI by attenuating nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3)-mediated inflammation, enhancing the antioxidant activity of Nrf2 and inhibiting apoptosis. Rats treated with or without OzoneOP (2 ml containing 100 µg/kg/day) were subjected to 1 h of lung ischemia followed by 2 h of reperfusion for 10 days. Lung damage, antioxidant capacity, inflammation and apoptosis were evaluated and compared among different groups after reperfusion. OzoneOP significantly ameliorated changes in lung morphology and protected the lung from IRI by attenuating oxidative stress, inflammation-induced injury and lung apoptosis. Moreover, OzoneOP increased the expression of Nrf2 and decreased the levels of NLRP3, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), un-cleavable cysteine-requiring aspartate protease-1 (procaspase-1), cysteine-requiring aspartate protease-1 (caspase-1) and interleukin-1β (IL-1β) in the rat lungs. In summary, these results provide new insights into the molecular events modulated by ozone and suggest that ozone therapy may be an integrative support for patients with lung IRI.

NLRP3 Inflammasome Participates in Host Response to Neospora caninum Infection

Neospora caninum is an intracellular protozoan parasite closely related to Toxoplasma gondii that mainly infects canids as the definitive host and cattle as the intermediate host, resulting in abortion in cattle and leading to financial losses worldwide. Commercial vaccines or drugs are not available for the prevention and treatment of bovine neosporosis. Knowledge about the hallmarks of the immune response to this infection could form the basis of important prevention strategies. The innate immune system first responds to invading parasite and subsequently initiates the appropriate adaptive immune response against this parasite. Upon infection, activation of host pattern-recognition receptors expressed by immune cells triggers the innate immune response. Toll-like receptors, NOD-like receptors, and C-type lectin receptors play key roles in recognizing protozoan parasite. Therefore, we aimed to explore the role of the NLRP3 inflammasome during the acute period of N. caninum infection. In vitro results showed that N. caninum infection of murine bone marrow-derived macrophages activated the NLRP3 inflammasome, accompanied by the release of IL-1β and IL-18, cleavage of caspase-1, and induction of cell death. K⁺ efflux induced by N. caninum infection participated in the activation of the inflammasome. Infection of mice deficient in NLRP3, ASC, and caspase-1/11 resulted in decreased production of IL-18 and reduced IFN-γ in serum. Elevated numbers of monocytes/macrophages and neutrophils were found at the initial infection site, but they failed to limit N. caninum replication. These findings suggest that the NLRP3 inflammasome is involved in the host response to N. caninum infection at the acute stage and plays an important role in limiting parasite growth, and it may enhance Th1 response by inducing production of IFN-γ. These findings may help devise protocols for controlling neosporosis.

Alcohol accumulation promotes esophagitis via pyroptosis activation

Gastroesophageal reflux impairs the mucosal barrier in the distal esophagus, allowing chronic exposure of the squamous epithelium to multitudinous stimulations and inducing chronic inflammation. Esophagitis is a response to inflammation of the esophageal squamous mucosa. Our study clarified that alcohol accumulation could aggravate the progress of esophagitis by inducing pyroptosis; however, Ac-YVAD-CMK, an inhibitor of caspase-1, could effectively suppress the expression of IL-1β and IL-18 both in vivo and in vitro, reducing the inflammatory response, which is promised to be an agent to inhibit the progression of esophagitis. Additionally, caspase-1-derived pyroptosis is involved in esophageal cancer.

High-density lipoprotein inhibits serum amyloid A-mediated reactive oxygen species generation and NLRP3 inflammasome activation

Serum amyloid A (SAA) is a high-density apolipoprotein whose plasma levels can increase more than 1000-fold during a severe acute-phase inflammatory response and are more modestly elevated in chronic inflammation. SAA is thought to play important roles in innate immunity, but its biological activities have not been completely delineated. We previously reported that SAA deficiency protects mice from developing abdominal aortic aneurysms (AAAs) induced by chronic angiotensin II (AngII) infusion. Here, we report that SAA is required for AngII-induced increases in interleukin-1β (IL-1β), a potent proinflammatory cytokine that is tightly controlled by the Nod-like receptor protein 3 (NLRP3) inflammasome and caspase-1 and has been implicated in both human and mouse AAAs. We determined that purified SAA stimulates IL-1β secretion in murine J774 and bone marrow-derived macrophages through a mechanism that depends on NLRP3 expression and caspase-1 activity, but is independent of P2X7 nucleotide receptor (P2X7R) activation. Inhibiting reactive oxygen species (ROS) by N-acetyl-l-cysteine or mito-TEMPO and inhibiting activation of cathepsin B by CA-074 blocked SAA-mediated inflammasome activation and IL-1β secretion. Moreover, inhibiting cellular potassium efflux with glyburide or increasing extracellular potassium also significantly reduced SAA-mediated IL-1β secretion. Of note, incorporating SAA into high-density lipoprotein (HDL) prior to its use in cell treatments completely abolished its ability to stimulate ROS generation and inflammasome activation. These results provide detailed insights into SAA-mediated IL-1β production and highlight HDL's role in regulating SAA's proinflammatory effects.

Lipid and Non-lipid Factors Affecting Macrophage Dysfunction and Inflammation in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease and a leading cause of human mortality. The lesional microenvironment contains a complex accumulation of variably oxidized lipids and cytokines. Infiltrating monocytes become polarized in response to these stimuli, resulting in a broad spectrum of macrophage phenotypes. The extent of lipid loading in macrophages influences their phenotype and consequently their inflammatory status. In response to excess atherogenic ligands, many normal cell processes become aberrant following a loss of homeostasis. This can have a direct impact upon the inflammatory response, and conversely inflammation can lead to cell dysfunction. Clear evidence for this exists in the lysosomes, endoplasmic reticulum and mitochondria of atherosclerotic macrophages, the principal lesional cell type. Furthermore, several intrinsic cell processes become dysregulated under lipidotic conditions. Therapeutic strategies aimed at restoring cell function under disease conditions are an ongoing coveted aim. Macrophages play a central role in promoting lesional inflammation, with plaque progression and stability being directly proportional to macrophage abundance. Understanding how mixtures or individual lipid species regulate macrophage biology is therefore a major area of atherosclerosis research. In this review, we will discuss how the myriad of lipid and lipoprotein classes and products used to model atherogenic, proinflammatory immune responses has facilitated a greater understanding of some of the intricacies of chronic inflammation and cell function. Despite this, lipid oxidation produces a complex mixture of products and with no single or standard method of derivatization, there exists some variation in the reported effects of certain oxidized lipids. Likewise, differences in the methods used to generate macrophages in vitro may also lead to variable responses when apparently identical lipid ligands are used. Consequently, the complexity of reported macrophage phenotypes has implications for our understanding of the metabolic pathways, processes and shifts underpinning their activation and inflammatory status. Using oxidized low density lipoproteins and its oxidized cholesteryl esters and phospholipid constituents to stimulate macrophage has been hugely valuable, however there is now an argument that only working with low complexity lipid species can deliver the most useful information to guide therapies aimed at controlling atherosclerosis and cardiovascular complications.

NLRP3 in somatic non-immune cells of rodent and primate testes

NLRP3 is part of the NLRP3 inflammasome and a global sensor of cellular damage. It was recently discovered in rodent Sertoli cells. We investigated NLRP3 in mouse, human and non-human primate (marmoset and rhesus macaque) testes, employing immunohistochemistry. Sertoli cells of all species expressed NLRP3, and the expression preceded puberty. In addition, peritubular cells of the adult human testes expressed NLRP3. NLRP3 and associated genes (PYCARD, CASP1, IL1B) were also found in isolated human testicular peritubular cells and the mouse Sertoli cell line TM4. Male infertility due to impairments of spermatogenesis may be related to sterile inflammatory events. We observed that the expression of NLRP3 was altered in the testes of patients suffering from mixed atrophy syndrome, in which tubules with impairments of spermatogenesis showed prominent NLRP3 staining. In order to explore a possible role of NLRP3 in male infertility, associated with sterile testicular inflammation, we studied a mouse model of male infertility. These human aromatase-expressing transgenic mice (AROM+) develop testicular inflammation and impaired spermatogenesis during aging, and the present data show that this is associated with strikingly elevated Nlrp3 expression in the testes compared to WT controls. Interference by aromatase inhibitor treatment significantly reduced increased Nlrp3 levels. Thus, throughout species NLRP3 is expressed by somatic cells of the testis, which are involved in testicular immune surveillance. We conclude that NLRP3 may be a novel player in testicular immune regulation.

Insights From Pre-Clinical and Clinical Studies on the Role of Innate Inflammation in Atherosclerosis Regression

Atherosclerosis, the underlying cause of coronary artery (CAD) and other cardiovascular diseases, is initiated by macrophage-mediated immune responses to lipoprotein and cholesterol accumulation in artery walls, which result in the formation of plaques. Unlike at other sites of inflammation, the immune response becomes maladaptive and inflammation fails to resolve. The most common treatment for reducing the risk from atherosclerosis is low density lipoprotein cholesterol (LDL-C) lowering. Studies have shown, however, that while significant lowering of LDL-C reduces the risk of heart attacks to some degree, there is still residual risk for the majority of the population. We and others have observed “residual inflammatory risk” of atherosclerosis after plasma cholesterol lowering in pre-clinical studies, and that this phenomenon is clinically relevant has been dramatically reinforced by the recent Canakinumab Anti-inflammatory Thrombosis Outcomes Study (CANTOS) trial. This review will summarize the role of the innate immune system, specifically macrophages, in atherosclerosis progression and regression, as well as the pre-clinical and clinical models that have provided significant insights into molecular pathways involved in the resolution of plaque inflammation and plaque regression. Partnered with clinical studies that can be envisioned in the post-CANTOS period, including progress in developing targeted plaque therapies, we expect that pre-clinical studies advancing on the path summarized in this review, already revealing key mechanisms, will continue to be essential contributors to achieve the goals of dampening plaque inflammation and inducing its resolution in order to maximize the therapeutic benefits of conventional risk factor modifications, such as LDL-C lowering.

Mitochondrial Damage-Associated Molecular Patterns: From Inflammatory Signaling to Human Diseases

Over the recent years, much has been unraveled about the pro-inflammatory properties of various mitochondrial molecules once they are leaving the mitochondrial compartment. On entering the cytoplasm or the extracellular space, mitochondrial DAMPs (also known as mitochondrial alarmins) can become pro-inflammatory and initiate innate and adaptive immune responses by activating cell surface and intracellular receptors. Current evidence indicates that uncontrolled and excessive release of mitochondrial DAMPs is associated with severity, has prognosis value in human diseases, and contributes to the dysregulated process observed in numerous inflammatory and autoimmune conditions, as well as in ischemic heart disease and cancer. Herein, we review that the expanding research field of mitochondrial DAMPs in innate immune responses and the current knowledge on the association between mitochondrial DAMPs and human diseases.

Huanglian-Wendan Decoction Inhibits NF-κB/NLRP3 Inflammasome Activation in Liver and Brain of Rats Exposed to Chronic Unpredictable Mild Stress

Depression is a common mental disorder in modern society. A traditional Chinese medicine Huanglian-Wendan decoction with potential anti-inflammation is used as a clinical antidepressant. Our previous study showed central and peripheral inflammatory responses in a rat model of depression developed by chronic unpredictable mild stress (CUMS). Here, we investigated the anti-inflammatory activity and mechanism of Huanglian-Wendan decoction in CUMS rats. LC-MS/MS and HPLC were performed to determine the major compounds in water extract of this decoction. This study showed that Huanglian-Wendan decoction significantly increased sucrose consumption and reduced serum levels of interleukin-1 beta (IL-1β), IL-6, and alanine aminotransferase (ALT) in CUMS rats. Moreover, this decoction inhibited nuclear entry of nuclear factor-kappa B (NF-κB) with the reduction of phosphorylated protein of NF-κB (p-NF-κB) and inhibitor of NF-κB alpha (p-IκBα) and downregulated protein of nod-like receptor family pyrin domain-containing 3 (NLRP3), apoptosis-associated speck-like protein containing CARD (ASC), cysteinyl aspartate-specific proteinase-1 (Caspase-1), and IL-1β in liver and brain regions of CUMS rats. These findings demonstrated that Huanglian-Wendan decoction had antidepressant activity with hepatoprotection in CUMS rats coinciding with its anti-inflammation in both periphery and central. The inhibitory modulation of NF-κB and NLRP3 inflammasome activation by Huanglian-Wendan decoction may mediate its antidepressant action.

Placental inflammation in pre-eclampsia by Nod-like receptor protein (NLRP)3 inflammasome activation in trophoblasts

Pre-eclampsia is associated with increased levels of cholesterol and uric acid and an inflamed placenta expressing danger-sensing pattern recognition receptors (PRRs). Crystalline cholesterol and uric acid activate the PRR Nod-like receptor protein (NLRP)3 inflammasome to release interleukin (IL)-1β and result in vigorous inflammation. We aimed to characterize crystal-induced NLRP3 activation in placental inflammation and examine its role in pre-eclampsia. We confirmed that serum total cholesterol and uric acid were elevated in pre-eclamptic compared to healthy pregnancies and correlated positively to high sensitivity C-reactive protein (hsCRP) and the pre-eclampsia marker soluble fms-like tyrosine kinase-1 (sFlt-1). The NLRP3 inflammasome pathway components (NLRP3, caspase-1, IL-1β) and priming factors [complement component 5a (C5a) and terminal complement complex (TCC)] were co-expressed by the syncytiotrophoblast layer which covers the placental surface and interacts with maternal blood. The expression of IL-1β and TCC was increased significantly and C5a-positive regions in the syncytiotrophoblast layer appeared more frequent in pre-eclamptic compared to normal pregnancies. In-vitro activation of placental explants and trophoblasts confirmed NLRP3 inflammasome pathway functionality by complement-primed crystal-induced release of IL-1β. This study confirms crystal-induced NLRP3 inflammasome activation located at the syncytiotrophoblast layer as a mechanism of placental inflammation and suggests contribution of enhanced NLRP3 activation to the harmful placental inflammation in pre-eclampsia.

Cardiovascular diseases, NLRP3 inflammasome, and western dietary patterns

Cardiovascular diseases (CVD) are the leading cause of death worldwide, with high prevalence in industrialized countries. Cardiovascular risk factors are mainly influenced by diet, which like other lifestyle factors can be modified to either reduce or increase cardiovascular risk. Other metabolic diseases such as metabolic syndrome, type II diabetes mellitus, and obesity are associated to CVD and highly influenced by the diet. Inflammation has demonstrated to be a key factor in the biological progress of these diseases. Interestingly, IL-1β which is associated to several steps in the development of atherosclerosis, heart disease, and the association of obesity and type II diabetes with CVD, is activated by the inflammasome complex, a multiprotein complex composed of an intracellular sensor, typically a Nod-like receptor (NLR), the precursor procaspase-1, and the adaptor ASC (apoptosis-associated speck-like protein containing a CARD. In the last years, inflammasome complex has been studied in depth and has been associated with the effect of unhealthy diets both from a clinical and experimental view point. We have reviewed the evidences supporting the role of the inflammasome complex in the development of cardiovascular pathology by unhealthy diets and the therapeutic perspectives.

Calcium-sensing receptor activates the NLRP3 inflammasome in LS14 preadipocytes mediated by ERK1/2 signaling

The study of the mechanisms that trigger inflammation in adipose tissue is key to understanding and preventing the cardiometabolic consequences of obesity. We have proposed a model where activation of the G protein-coupled calcium sensing receptor (CaSR) leads to inflammation and dysfunction in adipose cells. Upon activation, CaSR can mediate the expression and secretion of proinflammatory factors in human preadipocytes, adipocytes, and adipose tissue explants. One possible pathway involved in CaSR-induced inflammation is the activation of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome, that promotes maturation and secretion of interleukin (IL)-1β. The present work aimed to study whether CaSR mediates the activation of NLRP3 inflammasome in the human adipose cell model LS14. We assessed NLRP3 inflammasome priming and assembly after cinacalcet-induced CaSR activation and evaluated if this activation is mediated by downstream ERK1/2 signaling in LS14 preadipocytes. Exposure to 2 μM cinacalcet elevated mRNA expression of NLRP3, CASP-1, and IL-1β, as well as an increase in pro-IL-1β protein. In addition, CaSR activation triggered NLRP3 inflammasome assembly, as evidenced by a 25% increase in caspase-1 activity and 63% IL-1β secretion. CaSR silencing (siRNA) abolished the effect. Upstream ERK pathway inhibition decreased cinacalcet-dependent activation of NLRP3 inflammasome. We propose CaSR-dependent NLRP3 inflammasome activation in preadipocytes through ERK signaling as a novel mechanism for the development of adipose dysfunction, that may favor the cardiovascular and metabolic consequences of obesity. To the best of our knowledge, this is the first report linking the inflammatory effect of CaSR to NLRP3 inflammasome induction in adipose cells.

Melatonin prevents endothelial cell pyroptosis via regulation of long noncoding RNA MEG3/miR-223/NLRP3 axis

Atherosclerosis (AS) is an inflammatory disease linked to endothelial dysfunction. Melatonin is reported to possess substantial anti-inflammatory properties, which has proven to be effective in AS. Emerging literature suggests that pyroptosis plays a critical role during AS progression. However, whether pyroptosis contributes to endothelial dysfunction and the underlying molecular mechanisms remained unexploited. This study was designed to investigate the antipyroptotic effects of melatonin in atherosclerotic endothelium and to elucidate the potential mechanisms. In this study, high-fat diet (HFD)-treated ApoE^-/- mice were used as an atherosclerotic animal model. We found intragastric administration of melatonin for 12 weeks markedly reduced the atherosclerotic plaque in aorta. Meanwhile, melatonin also attenuated the expression of pyroptosis-related genes, including NLRP3, ASC, cleaved caspase1, NF-κB/GSDMD, GSDMD N-termini, IL-1β, and IL-18 in aortic endothelium of melatonin-treated animals. Consistent antipyroptotic effects were also observed in ox-LDL-treated human aortic endothelial cells (HAECs). We found that lncRNA MEG3 enhanced pyroptosis in HAECs. Moreover, MEG3 acted as an endogenous sponge by sequence complementarity to suppress the function of miR-223 and to increase NLRP3 expression and enhance endothelial cell pyroptosis. Furthermore, knockdown of miR-223 blocked the antipyroptotic actions of melatonin in ox-LDL-treated HAECs. Together, our results suggest that melatonin prevents endothelial cell pyroptosis via MEG3/miR-223/NLRP3 axis in atherosclerosis, and therefore, melatonin replacement might be considered a new strategy for protecting endothelium against pyroptosis, thereby for the treatment of atherosclerosis associated with pyroptosis.

Sulforaphane Inhibits Lipopolysaccharide-Induced Inflammation, Cytotoxicity, Oxidative Stress, and miR-155 Expression and Switches to Mox Phenotype through Activating Extracellular Signal-Regulated Kinase 1/2-Nuclear Factor Erythroid 2-Related Factor 2/Antioxidant Response Element Pathway in Murine Microglial Cells

Sulforaphane (SFN) is a natural product with cytoprotective, anti-inflammatory, and antioxidant effects. In this study, we evaluated the mechanisms of its effects on lipopolysaccharide (LPS)-induced cell death, inflammation, oxidative stress, and polarization in murine microglia. We found that SFN protects N9 microglial cells upon LPS-induced cell death and suppresses LPS-induced levels of secreted pro-inflammatory cytokines, tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6. SFN is also a potent inducer of redox sensitive transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), which is responsible for the transcription of antioxidant, cytoprotective, and anti-inflammatory genes. SFN induced translocation of Nrf2 to the nucleus via extracellular signal-regulated kinase 1/2 (ERK1/2) pathway activation. siRNA-mediated knockdown study showed that the effects of SFN on LPS-induced reactive oxygen species, reactive nitrogen species, and pro-inflammatory cytokine production and cell death are partly Nrf2 dependent. Mox phenotype is a novel microglial phenotype that has roles in oxidative stress responses. Our results suggested that SFN induced the Mox phenotype in murine microglia through Nrf2 pathway. SFN also alleviated LPS-induced expression of inflammatory microRNA, miR-155. Finally, SFN inhibits microglia-mediated neurotoxicity as demonstrated by conditioned medium and co-culture experiments. In conclusion, SFN exerts protective effects on microglia and modulates the microglial activation state.

Microglia and CNS Interleukin-1: Beyond Immunological Concepts

Activation of microglia and expression of the inflammatory cytokine interleukin-1 (IL-1) in the CNS have become almost synonymous with neuroinflammation. In numerous studies, increased CNS IL-1 expression and altered microglial morphology have been used as hallmarks of CNS inflammation. A central concept of how CNS IL-1 and microglia influence functions of the nervous system was derived from the notion initially generated in the peripheral immune system: IL-1 stimulates monocyte/macrophage (the peripheral counterparts of microglia) to amplify inflammation. It is increasingly clear, however, CNS IL-1 acts on other targets in the CNS and microglia participates in many neural functions that are not related to immunological activities. Further, CNS exhibits immunological privilege (although not as absolute as previously thought), rendering amplification of inflammation within CNS under stringent control. This review will analyze current literature to evaluate the contribution of immunological and non-immunological aspects of microglia/IL-1 interaction in the CNS to gain insights for how these aspects might affect health and disease in the nervous tissue.

Expression of inflammasome proteins and inflammasome activation occurs in human, but not in murine keratinocytes

Inflammasomes are multimeric protein complexes that assemble upon sensing of a variety of stress factors. Their formation results in caspase-1-mediated activation and secretion of the pro-inflammatory cytokines pro-interleukin(IL)-1β and -18, which induce an inflammatory response. Inflammation is supported by a lytic form of cell death, termed pyroptosis. Innate immune cells, such as macrophages or dendritic cells, express and activate inflammasomes. However, it has also been demonstrated that human primary keratinocytes activate different types of inflammasomes in vitro, for example, upon UVB irradiation or viral infection. Keratinocytes are the main cell type of the epidermis, the outermost layer of the body, and form a protective barrier consisting of a stratified multi-layered epithelium. In human, gain-of-function mutations of the NLRP1 gene cause syndromes mediated by inflammasome activation in keratinocytes that are characterised by skin inflammation and skin cancer susceptibility. Here we demonstrate that murine keratinocytes do not activate inflammasomes in response to stimuli, which induce IL-1β and -18 secretion by human keratinocytes. Whereas murine keratinocytes produced caspase-1 and proIL-18, expression of the inflammasome proteins Nlrp1, Nlrp3, Aim2, Asc, and proIL-1β was, compared to human keratinocytes or murine dendritic cells, very low or even undetectable. Priming of murine keratinocytes with cytokines commonly used for induction of proIL-1β and inflammasome protein expression did not rescue inflammasome activation. Nevertheless, UVB-induced inflammation and neutrophil recruitment in murine skin was dependent on IL-1β and caspase-1. However, also under these conditions, we did not detect expression of proIL-1β by keratinocytes in murine skin, but by immune cells. These results demonstrate a higher immunological competence of human compared to murine keratinocytes, which is reflected by stress-induced IL-1β secretion that is mediated by inflammasomes. Therefore, keratinocytes in human skin can exert immune functions, which are carried out by professional immune cells in murine skin.

The NLRP3 inflammasome: Role in metabolic disorders and regulation by metabolic pathways

Inflammasomes are large multimolecular complexes present in the cytosol of stimulated immune cells; they mediate the activation of caspase-1, leading to cellular pyroptosis. So far, a variety of studies on inflammasomes have emerged, and the best-studied is the NLRP3 inflammasome that is involved in many inflammatory responses. Furthermore, its relationship with metabolism is gaining increasing attention in this field. In this review, we discuss the importance of the NLRP3 inflammasome in metabolic disorders and its close association with metabolic pathways.

Sweet Taste Receptors Mediated ROS-NLRP3 Inflammasome Signaling Activation: Implications for Diabetic Nephropathy

Previous studies demonstrated that ROS-NLRP3 inflammasome signaling activation was involved in the pathogenesis of diabetic nephropathy (DN). Recent research has shown that sweet taste receptors (STRs) are important sentinels of innate immunity. Whether high glucose primes ROS-NLRP3 inflammasome signaling via STRs is unclear. In this study, diabetic mouse model was induced by streptozotocin (STZ) in vivo; mouse glomerular mesangial cells (GMCs) and human proximal tubular cells were stimulated by high glucose (10, 20, and 30 mmol/L) in vitro; STR inhibitor lactisole was used as an intervention reagent to evaluate the role and mechanism of the STRs in the pathogenesis of DN. Our results showed that the expression of STRs and associated signaling components (Gα-gustducin, PLCβ2, and TRPM5) was obviously downregulated under the condition of diabetes in vivo and in vitro. Furthermore, lactisole significantly mitigated the production of intracellular ROS and reversed the high glucose-induced decrease of Ca²⁺ and the activation of NLRP3 inflammasome signaling in vitro (p < 0.05). These combined results support the hypothesis that STRs could be involved in the activation of ROS-NLRP3 inflammasome signaling in the pathogenesis of DN, suggesting that STRs may act as new therapeutic targets of DN.

Inflammasome and Oral Diseases

One of the main steps in the development of the life in the earth is multicellularity. It enables cell differentiation and the development of morphological structures within an organism and is an essential factor in how to recognize friendly cells that are part of the multicellular organism and which foreign organisms can be harmful. Recognition includes devices such as the major histocompatibility complex (MHC), and the pattern recognition receptors (PRRs). PRRs are a group of proteins expressed by cells of the innate immune system that identify two classes of products: pathogen-associated molecular patterns (PAMPs), related to microbial pathogens, and damage-associated molecular patterns (DAMPs), associated with cell components that are released during cell damage or death. All these activate the inflammasome, which is a multiprotein oligomer that includes caspase 1, PYCARD, NALP, and caspase 5 (also known as caspase 11 or ICH-3). It is responsible for activation of inflammatory processes and has been shown to induce cell pyroptosis, a programmed cell death distinct from apoptosis, and promotes the maturation of the inflammatory cytokines interleukin 1β (IL-1β) and interleukin 18 (IL-18). We review whether inflammasome is related to diseases that can occur in the oral cavity. The mouth is always a possible environment for the development of pathological conditions because of the wide variety of microorganisms. Small variations in the equilibrium of the oral flora can cause disorders that could affect the organism in a systemic form. We provide data on periodontal disease, candidiasis, herpes virus, oral cancer, caries, and other oral diseases. There are very few papers that study this issue; therefore, we need more investigation and publications about inflammatory molecular processes, and more specifically, related to the inflammasome complex.

The Emerging Role of Inflammasomes as Central Mediators in Inflammatory Bladder Pathology

Irritative voiding symptoms (e.g. increased frequency and urgency) occur in many common pathologic conditions such as urinary tract infections and bladder outlet obstruction, and these conditions are well-established to have underlying inflammation that directly triggers these symptoms. However, it remains unclear as to how such diverse stimuli individually generate a common inflammatory process. Jürg Tschopp provided substantial insight into this conundrum when, working with extracts from THP-1 cells, he reported the existence of the inflammasome. He described it as a structure that senses multiple diverse signals from intracellular/extracellular sources and pathogens and triggers inflammation by the maturation and release of the pro-inflammatory cytokines interleukin-1β and interleukin-18. Recently, many of these sensors were found in the bladder and the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3, has been shown to be a central mediator of inflammation in several urological diseases. In this review, we introduce the nucleotide-binding domain, leucine-rich-containing family, pyrin domaincontaining-3 inflammasome, highlight its emerging role in several common urologic conditions, and speculate on the potential involvement of other inflammasomes in bladder pathology.

Role of immune cells in crystal-induced kidney fibrosis

Chronic kidney diseases can lead to kidney fibrosis, which can be considered a futile attempt of tissue healing to replaces functional kidney tissue with connective tissue, basically forming a scar. Chronic inflammation is a frequent cause of kidney fibrosis. Classical as well as recently discovered immune cell subsets and their molecular mediators have been intensively investigated for their contribution to kidney fibrosis and their potential as therapeutic targets. Here we review the current knowledge about the role of immune cells in crystal-induced renal fibrosis.

Role of Perinatal Inflammation in Neonatal Arterial Ischemic Stroke

Based on the review of the literature, perinatal inflammation often induced by infection is the only consistent independent risk factor of neonatal arterial ischemic stroke (NAIS). Preclinical studies show that acute inflammatory processes take place in placenta, cerebral arterial wall of NAIS-susceptible arteries and neonatal brain. A top research priority in NAIS is to further characterize the nature and spatiotemporal features of the inflammatory processes involved in multiple levels of the pathophysiology of NAIS, to adequately design randomized control trials using targeted anti-inflammatory vasculo- and neuroprotective agents.

Interleukin-1 Beta as a Target for Atherosclerosis Therapy: Biological Basis of CANTOS and Beyond

Inflammatory pathways drive atherogenesis and link conventional risk factors to atherosclerosis and its complications. One inflammatory mediator has come to the fore as a therapeutic target in cardiovascular disease. The experimental and clinical evidence reviewed here support interleukin-1 beta (IL-1β) as both a local vascular and systemic contributor in this regard. Intrinsic vascular wall cells and lesional leukocytes alike can produce this cytokine. Local stimuli in the plaque favor the generation of active IL-1β through the action of a molecular assembly known as the inflammasome. Clinically applicable interventions that interfere with IL-1 action can improve cardiovascular outcomes, ushering in a new era of anti-inflammatory therapies for atherosclerosis. The translational path described here illustrates how advances in basic vascular biology may transform therapy. Biomarker-directed application of anti-inflammatory interventions promises to help us achieve a more precise and personalized allocation of therapy for our cardiovascular patients.

Antimycobacterial and Anti-inflammatory Mechanisms of Baicalin via Induced Autophagy in Macrophages Infected with Mycobacterium tuberculosis

Tuberculosis (TB) remains a leading killer worldwide among infectious diseases and the effective control of TB is still challenging. Autophagy is an intracellular self-digestion process which has been increasingly recognized as a major host immune defense mechanism against intracellular microorganisms like Mycobacterium tuberculosis (Mtb) and serves as a key negative regulator of inflammation. Clinically, chronic inflammation surrounding Mtb can persist for decades leading to lung injury that can remain even after successful treatment. Adjunct host-directed therapy (HDT) based on both antimycobacterial and anti-inflammatory interventions could be exploited to improve treatment efficacy and outcome. Autophagy occurring in the host macrophages represents a logical host target. Here, we show that herbal medicine, baicalin, could induce autophagy in macrophage cell line Raw264.7 and caused increased killing of intracellular Mtb. Further, baicalin inhibited Mtb-induced NLRP3 inflammasome activation and subsequent inflammasome-derived IL-1β. To investigate the molecular mechanisms of baicalin, the signaling pathways associated with autophagy were examined. Results indicated that baicalin decreased the levels of phosphorylated protein kinase B (p-Akt) and phosphorylated mammalian target of rapamycin (p-mTOR) at Ser473 and Ser2448, respectively, but did not alter the phosphorylation of p38, JNK, or ERK both in Raw264.7 and primary peritoneal macrophages. Moreover, baicalin exerted an obvious inhibitory effect on nuclear factor-kappa B (NF-κB) activity. Finally, immunofluorescence studies demonstrated that baicalin promoted the co-localization of inflammasome with autophagosome may serve as the underlying mechanism of autophagic degradative effect on reducing inflammasome activation. Together, baicalin definitely induces the activation of autophagy on the Mtb-infected macrophages through PI3K/Akt/mTOR pathway instead of MAPK pathway. Furthermore, baicalin inhibited the PI3K/Akt/NF-κB signal pathway, and both autophagy induction and NF-κB inhibition contribute to limiting the NLRP3 inflammasome as well as subsequent production of pro-inflammatory cytokine IL-1β. Based on these results, we conclude that baicalin is a promising antimycobacterial and anti-inflammatory agent which can be a novel candidate for the development of new adjunct drugs targeting HDT for possible improved treatment.

COPs and POPs Patrol Inflammasome Activation

Sensing and responding to pathogens and tissue damage is a core mechanism of innate immune host defense, and inflammasomes represent a central cytosolic pattern recognition receptor pathway leading to the generation of the pro-inflammatory cytokines interleukin-1β and interleukin-18 and pyroptotic cell death that causes the subsequent release of danger signals to propagate and perpetuate inflammatory responses. While inflammasome activation is essential for host defense, deregulated inflammasome responses and excessive release of inflammatory cytokines and danger signals are linked to an increasing spectrum of inflammatory diseases. In this review, we will discuss recent developments in elucidating the role of PYRIN domain-only proteins (POPs) and the related CARD-only proteins (COPs) in regulating inflammasome responses and their impact on inflammatory disease.

Conditional, Genetically Encoded, Small Molecule-Regulated Inhibition of NFκB Signaling in RPE Cells

Purpose

Nuclear factor κB (NFκB) is a ubiquitously expressed, proinflammatory transcription factor that controls the expression of genes involved in cell survival, angiogenesis, complement activation, and inflammation. Studies have implicated NFκB-dependent cytokines or complement-related factors as being detrimentally involved in retinal diseases, thus making inhibition of NFκB signaling a potential therapeutic target. We sought to develop a conditional and reversible method that could regulate pathogenic NFκB signaling by the addition of a small molecule.

Methods

We developed a genetically based, trimethoprim (TMP)-regulated approach that conditionally inhibits NFκB signaling by fusing a destabilized dihydrofolate reductase (DHFR) domain to an inhibitor of NFκB, IκBα, in ARPE-19 cells. We then challenged ARPE-19 cells with a number of stimuli that have been demonstrated to trigger NFκB signaling, including LPS, TNFα, IL-1α, and A2E. Western blotting, electrophoretic mobility shift assay, quantitative PCR, ELISA, and NFκB reporter assays were used to evaluate the effectiveness of this DHFR-IκBα approach.

Results

This destabilized domain approach, coupled with doxycycline-inducibility, allowed for accurate control over the abundance of DHFR-IκBα. Stabilization of DHFR-IκBα with TMP prevented IL-1α-, A2E-, LPS-, and TNFα-induced NFκB-mediated upregulation and release of the proinflammatory cytokines IL-1β and IL-6 from ARPE-19 cells (by as much as 93%). This strategy is dosable, completely reversible, and can be cycled “on” or “off” within the same cell population repeatedly to confer protection at desired time points.

Conclusions

These studies lay the groundwork for the use of destabilized domains in retinal pigment epithelium (RPE) cells in vivo and in this context, demonstrate their utility for preventing inflammatory signaling.

The P2X7 Receptor Primes IL-1β and the NLRP3 Inflammasome in Astrocytes Exposed to Mechanical Strain

Inflammatory responses play a key role in many neural pathologies, with localized signaling from the non-immune cells making critical contributions. The NLRP3 inflammasome is an important component of innate immune signaling and can link neural insult to chronic inflammation. The NLRP3 inflammasome requires two stages to contribute: priming and activation. The priming stage involves upregulation of inflammasome components while the activation stage results in the assembly and activation of the inflammasome complex. The priming step can be rate limiting and can connect insult to chronic inflammation, but our knowledge of the signals that regulate NLRP3 inflammasome priming in sterile inflammation is limited. This study examined the link between mechanical strain and inflammasome priming in neural systems. Transient non-ischemic elevation of intraocular pressure increased mRNA for inflammasome components IL-1β, NLRP3, ASC, and CASP1 in rat and mouse retinas. The elevation was greater 1 day after the insult, with the rise in IL-1β most pronounced. The P2X7 receptor was implicated in the mechanosensitive priming of IL-1β mRNA in vivo, as the antagonist Brilliant Blue G (BBG) blocked the increased expression, the agonist BzATP mimicked the pressure-dependent rise in IL-1β, and the rise was absent in P2X7 knockout mice. In vitro measurements from optic nerve head astrocytes demonstrated an increased expression of IL-1β following stretch or swelling. This increase in IL-1β was eliminated by degradation of extracellular ATP with apyrase, or by the block of pannexin hemichannels with carbenoxolone, probenecid, or 10panx1 peptide. The rise in IL-1β expression was also blocked by P2X7 receptor antagonists BBG, A839977 or A740003. The rise in IL-1β was prevented by blocking transcription factor NFκB with Bay 11-7082, while the swelling-dependent fall in NFκB inhibitor IκB-α was reduced by A839977 and in P2X7 knockout mice. In summary, mechanical trauma to the retina primed NLRP3 inflammasome components, but only if there was ATP release through pannexin hemichannels, and autostimulation of the P2X7 receptor. As the P2X7 receptor can also trigger stage two of inflammasome assembly and activation, the P2X7 receptor may have a central role in linking mechanical strain to neuroinflammation.

Human periodontal ligament stem cells secretome from multiple sclerosis patients suppresses NALP3 inflammasome activation in experimental autoimmune encephalomyelitis

Research in recent years has largely explored the immunomodulatory effects of mesenchymal stem cells (MSCs) and their secretory products, called “secretome,” in the treatment of neuroinflammatory diseases. Here, we examined whether such immunosuppressive effects might be elicited due to inflammasome inactivation. To this end, we treated experimental autoimmune encephalomyelitis (EAE) mice model of multiple sclerosis (MS) with the conditioned medium or purified exosomes/microvesicles (EMVs) obtained from relapsing-remitting-MS patients human periodontal ligament stem cells (hPDLSCs) and investigated the regulation of NALP3 inflammasome. We noticed enhanced expression of NALP3, Cleaved Caspase 1, interleukin (IL)-1β, and IL-18 in EAE mouse spinal cord. Conversely, hPDLSCs-conditioned medium and EMVs significantly blocked NALP3 inflammasome activation and provided protection from EAE. Reduction in NALP3, Cleaved Caspase 1, IL-1β, and IL-18 level was noticed in conditioned medium and EMVs-treated EAE mice. Pro-inflammatory Toll-like receptor (TLR)-4 and nuclear factor (NF)-κB were elevated in EAE, while hPDLSCs-conditioned medium and EMVs treatment reduced their expression and increased IκB-α expression. Characterization of hPDLSCs-conditioned medium showed substantial level of anti-inflammatory IL-10, transforming growth factor (TGF)-β, and stromal cell–derived factor 1α (SDF-1α). We propose that the immunosuppressive role of hPDLSCs-derived conditioned medium and EMVs in EAE mice may partly attribute to the presence of soluble immunomodulatory factors, NALP3 inflammasome inactivation, and NF-κB reduction.