Intracellular Pattern Recognition Receptors Research Articles

Beyond transcription, aryl hydrocarbon receptor plays a protective role in periodontitis by interacting with CaMKII.

The aryl hydrocarbon receptor (AhR) has been studied as an intracellular pattern recognition receptor that can identify bacterial pigments. To identify a potential therapeutic target for periodontitis, we investigated the expression of AhR in periodontitis and its role in the pathogenesis of periodontitis. First, we analyzed AhR expression in a single-cell dataset from human periodontal tissue. Quantitative polymerase chain reaction (qPCR), immunofluorescence, and immunohistochemistry were used to verify the AhR level. Later, we determined the phenotypes of ligature-induced periodontitis in myeloid-specific AhR-deficient mice (Lyz2-Cre+/- AhRfx/fx), after which RNA sequencing (RNA-seq), qPCR, Western blot, immunofluorescence, and immunohistochemistry were used to investigate the impacts of AhR on periodontitis and its mechanism. Finally, we determined the therapeutic effect of AhR agonist 6-Formylindolo[3,2-b]carbazole (FICZ) administration on murine periodontitis and verified the effects of FICZ on macrophage polarization in vitro. AhR expression was enhanced in macrophages from periodontitis patients. Deletion of AhR from macrophages aggravated ligature-induced periodontitis and promoted the inflammatory response. Calcium/calmodulin-stimulated protein kinase II (CaMKII) phosphorylation was accelerated in AhR-deficient macrophages. Inhibiting CaMKII phosphorylation ameliorated periodontitis in Lyz2-Cre+/- AhRfx/fx mice. FICZ treatment blocked alveolar bone loss and relieved periodontal inflammation. FICZ diminished M1 macrophage polarization and promoted M2 macrophage polarization upon M1 macrophage induction. AhR played a protective role in the pathogenesis of periodontitis by orchestrating macrophage polarization via interacting with the CaMKII signaling pathway.

Identification of Mycoplasma pneumoniae proteins interacting with NOD2 and their role in macrophage inflammatory response.

Mycoplasma pneumoniae (M. pneumoniae, Mp) is a cell wall-deficient microorganism known to cause chronic respiratory infections in both children and adults. Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) is an intracellular pattern recognition receptor primarily responsible for identifying muramyl dipeptide (MDP) found in bacterial cell walls. Previous experiments have demonstrated that Mycoplasma ovipneumoniae induces macrophage autophagy through NOD2. In this study, we conducted RNA-seq analysis on macrophages infected with M. pneumoniae and observed an up-regulation in the expression of genes associated with the NOD2 signaling pathway. Mechanistic investigations further revealed the involvement of the NOD2 signaling pathway in the inflammatory response of macrophages activated by M. pneumoniae. We utilized GST pull-down technology in conjunction with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to pinpoint the M. pneumoniae proteins that interact with NOD2. Additionally, co-immunoprecipitation (Co-IP) and immunofluorescence co-localization techniques were used to confirm the interaction between DUF16 protein and NOD2. We found that DUF16 protein can enter macrophages and induce macrophage inflammatory response through the NOD2/RIP2/NF-κB pathway. Notably, the region spanning amino acids 13-90 was identified as a critical region necessary for DUF16-induced inflammation. This research not only broadens our comprehension of the recognition process of the intracellular receptor NOD2, but also deepens our understanding of the development of M. pneumoniae infection.

Mitochondrial damage and activation of NLRP3 induced by Yersinia ruckeri infection play an important role in the occurrence of diffuse acute inflammation of channel catfish (Ictalurus punctatus)

Yersinia ruckeri, as a facultative intracellular pathogen, can cause two different infection phenotypes of fish. An important phenotype is diffuse acute inflammation (DAI), which is mainly characterized by systemic hemorrhage and multiple tissues damage. Another phenotype is enteric redmouth symptom (EM) with predominantly digestive system damage, while slight damage to other tissues and organs. At present, the causes and mechanisms of heterogeneity of Y. ruckeri infection are not clear. According to our previous research and related bioinformatics analysis, it is suggested that the heterogeneity of infection of Y. ruckeri may be related to the activation of intracellular pattern recognition receptor (NLRP3). Furthermore, combined with the transmission electron microscope observation and ultrastructural pathological analysis of DAI and EM phenotypes, it is hypothesized that Y. ruckeri infection may mediate the occurrence of DAI by inducing mitochondrial damage and activation of NLRP3. In this study, we established DAI and EM phenotypes of channel catfish (Ictalurus punctatus) through the artificial infection experiment. Subsequently, we observed the pathological changes and characteristics of different tissues in DAI and EM phenotypes, such as liver, spleen, kidney, intestine and gill. In addition, the mitochondrial damage of head kidney mediated by Y. ruckeri infection was confirmed by transmission electron microscope observation. Furthermore, by detecting the expression of proinflammatory factors and related pattern recognition receptors in various tissues, we preliminarily clarified the molecular characteristics of immune response in DAI and EM phenotype fish. Moreover, the head kidney macrophages isolated from DAI and EM were observed through transmission electron microscope, and the expression levels of NLRP3, Caspase-1 and IL-1β were detected. Finally, the correlation between mitochondrial damage induced by Y. ruckeri infection and NLRP3 signal transduction was preliminary revealed. Taken together, our results showed that the inflammatory DAI phenotype of fish mediated by Y. ruckeri infection is closely related to mitochondrial damage and NLRP3 activation, which will provide theoretical basis for further study on the pathogenic mechanism of Y. ruckeri infection and clinical diagnosis of the disease, and also provide some insights into the role of NLRP3 in the natural immunity of aquatic animals.

MURAMYL DIPEPTIDE CAUSES MITOCHONDRIAL DYSFUNCTION AND INTESTINAL INFLAMMATORY CYTOKINE RESPONSES IN RATS.

Introduction: Intestinal flora and the translocation of its products, such as muramyl dipeptide (MDP), are common causes of sepsis. MDP is a common activator of the intracellular pattern recognition receptor NOD2, and MDP translocation can cause inflammatory damage to the small intestine and systemic inflammatory responses in rats. Therefore, this study investigated the effects of MDP on the intestinal mucosa and distant organs during sepsis and the role of the NOD2/AMPK/LC3 pathway in MDP-induced mitochondrial dysfunction in the intestinal epithelium. Methods: Fifty male Sprague Dawley rats were randomly divided into five treatment groups: lipopolysaccharide (LPS) only, 1.5 and 15 mg/kg MDP+LPS, and 1.5 and 15 mg/kg MDP+short-peptide enteral nutrition (SPEN)+LPS. The total caloric intake was the same per group. The rats were euthanized 24 h after establishing the model, and peripheral blood and small intestinal mucosal and lung tissues were collected. Results: Compared to the LPS group, both MDP+LPS groups had aggravated inflammatory damage to the intestinal mucosal and lung tissues, increased IL-6 and MDP production, increased NOD2 expression, decreased AMPK and LC3 expression, increased mitochondrial reactive oxygen species production, and decreased mitochondrial membrane potential. Compared to the MDP+LPS groups, the MDP+SPEN+LPS groups had decreased IL-6 and MDP production, increased AMPK and LC3 protein expression, and protected mitochondrial and organ functions. Conclusions: MDP translocation reduced mitochondrial autophagy by regulating the NOD2/AMPK/LC3 pathway, causing mitochondrial dysfunction. SPEN protected against MDP-induced impairment of intestinal epithelial mitochondrial function during sepsis.

Identification, characterization and the inflammatory regulating effect of NOD1/2 in sturgeon

As an ancient species with both conservation and commercial value, Sturgeon's inflammatory regulation mechanism is a research point. Nucleotide-binding and oligomerization domain-containing proteins 1 and 2 (NOD1/2) are classical intracellular pattern recognition receptors (PRRs) in immunity of anti-bacterial infection. However, the characterization and function of NOD1/2 in Sturgeon are still unclear. In this study, we analyzed the synteny relationship of NOD1/2 genes between Acipenser ruthenus and representative fishes at the genome-level. Results showed that the ArNOD2 collinear genes pair was present in all representative fishes. The duplicated ArNOD1/2 genes were under purifying selection during evolution as indicated by their Ka/Ks values. To explore the function of NOD1/2, we further investigated their expression patterns and the effects of pathogenic infection, PAMPs treatment, and siRNA interference in Acipenser baerii, the sibling species of A. ruthenus. Results showed that both AbNOD1/2 were expressed at early developmental stages and in different tissues. Pathogenic infection in vivo and PAMPs treatment in vitro demonstrated that AbNOD1/2 could respond to pathogen stimulation. siRNA interference with AbNOD1/2 inhibited expression levels of RIPK2 and inflammatory cytokines compared to the control group after iE-DAP or MDP treatment. This study hinted that the AbNOD1/2 could stimulate the inflammatory cytokines response during evolutionary processes.

Sexual dimorphism in NLR transcripts and its downstream signaling protein IL-1ꞵ in teleost Channa punctata (Bloch, 1793)

Nucleotide-binding oligomerization domain-like receptors (NOD-like receptors or NLRs) are a family of intracellular pattern recognition receptors (PRRs) that initiates as well as regulate inflammatory responses. NLRs are characterized by a centrally located nucleotide binding domain and a leucine rich repeat domain at the C-terminal responsible for the recognition of intracellular microbe-associated molecular patterns (MAMPs) and danger-associated molecular patterns (DAMPs). In the present study in adult spotted snakehead we have investigated the sex-dependent tissue distribution of NLRs known to be associated with inflammation in teleost namely NOD1, NOD2, NLRC3, NLRC5, and NLRX1. Further, the sexual dimorphism in the expression of NLR transcript as well as the pro-inflammatory protein IL-1β was explored in fish under normal conditions, and in fish exposed to bacterial lipopolysaccharide (LPS). The NLRs show ubiquitous and constitutive expression in all the tissues. Moreover, a prominent disparity between males and females was observed in the basal expression of these genes in various tissues. The sexual dimorphism in NLR expression was also prominent when fish were exposed to LPS. Similarly, IL-1β exhibited sexual dimorphism in both normal as well as LPS-exposed fish.

LUBAC is required for RIG-I sensing of RNA viruses.

The ability of cells to mount an interferon response to virus infections depends on intracellular nucleic acid sensing pattern recognition receptors (PRRs). RIG-I is an intracellular PRR that binds short double-stranded viral RNAs to trigger MAVS-dependent signalling. The RIG-I/MAVS signalling complex requires the coordinated activity of multiple kinases and E3 ubiquitin ligases to activate the transcription factors that drive type I and type III interferon production from infected cells. The linear ubiquitin chain assembly complex (LUBAC) regulates the activity of multiple receptor signalling pathways in both ligase-dependent and -independent ways. Here, we show that the three proteins that constitute LUBAC have separate functions in regulating RIG-I signalling. Both HOIP, the E3 ligase capable of generating M1-ubiquitin chains, and LUBAC accessory protein HOIL-1 are required for viral RNA sensing by RIG-I. The third LUBAC component, SHARPIN, is not required for RIG-I signalling. These data cement the role of LUBAC as a positive regulator of RIG-I signalling and as an important component of antiviral innate immune responses.

Molecular Activation of NLRP3 Inflammasome by Particles and Crystals: A Continuing Challenge of Immunology and Toxicology.

Particles and crystals constitute a unique class of toxic agents that humans are constantly exposed to both endogenously and from the environment. Deposition of particulates in the body is associated with a range of diseases and toxicity. The mechanism by which particulates cause disease remains poorly understood due to the lack of mechanistic insights into particle-biological interactions. Recent research has revealed that many particles and crystals activate the NLRP3 inflammasome, an intracellular pattern-recognition receptor. Activated NLRP3 forms a supramolecular complex with an adaptor protein to activate caspase 1, which in turn activates IL-1β and IL-18 to instigate inflammation. Genetic ablation and pharmacological inhibition of the NLRP3 inflammasome dampen inflammatory responses to particulates. Nonetheless, how particulates activate NLRP3 remains a challenging question. From this perspective, we discuss our current understanding of and progress on revealing the function and mode of action of the NLRP3 inflammasome in mediating adaptive and pathologic responses to particulates in health and disease.

Surface toll-like receptor 9 on immune cells and its immunomodulatory effect.

Toll like receptor 9 (TLR9) has been considered as a crucial intracellular pattern recognition receptor in the immune system, which can directly or indirectly mediate innate and adaptive immune responses by recognizing CpG DNA in endosomes to initiate its downstream signaling. However, TLR9 can also be expressed on the membrane surface of some immune and non-immune cells, called surface TLR9 (sTLR9), which covers the TLR9 and its immunomodulatory role with a mysterious veil. In this review, we mainly focus on the sTLR9 expressed on neutrophils, B cells and erythrocytes, and its immunomodulatory roles displayed alone or in coordination with endosomal TLR9 (eTLR9), providing a theoretical reference for the application of its modulators.

Intracellular replication of Pseudomonas aeruginosa in epithelial cells requires suppression of the caspase-4 inflammasome.

Pathogenesis of Pseudomonas aeruginosa infections can include bacterial survival inside epithelial cells. Previously, we showed that this involves multiple roles played by the type three secretion system (T3SS), and specifically the effector ExoS. This includes ExoS-dependent inhibition of a lytic host cell response that subsequently enables intracellular replication. Here, we studied the underlying cell death response to intracellular P. aeruginosa, comparing wild-type to T3SS mutants varying in capacity to induce cell death and that localize to different intracellular compartments. Results showed that corneal epithelial cell death induced by intracellular P. aeruginosa lacking the T3SS, which remains in vacuoles, correlated with the activation of nuclear factor-κB as measured by p65 relocalization and tumor necrosis factor alpha transcription and secretion. Deletion of caspase-4 through CRISPR-Cas9 mutagenesis delayed cell death caused by these intracellular T3SS mutants. Caspase-4 deletion also countered more rapid cell death caused by T3SS effector-null mutants still expressing the T3SS apparatus that traffic to the host cell cytoplasm, and in doing so rescued intracellular replication normally dependent on ExoS. While HeLa cells lacked a lytic death response to T3SS mutants, it was found to be enabled by interferon gamma treatment. Together, these results show that epithelial cells can activate the noncanonical inflammasome pathway to limit proliferation of intracellular P. aeruginosa, not fully dependent on bacterially driven vacuole escape. Since ExoS inhibits the lytic response, the data implicate targeting of caspase-4, an intracellular pattern recognition receptor, as another contributor to the role of ExoS in the intracellular lifestyle of P. aeruginosa. IMPORTANCE Pseudomonas aeruginosa can exhibit an intracellular lifestyle within epithelial cells in vivo and in vitro. The type three secretion system (T3SS) effector ExoS contributes via multiple mechanisms, including extending the life of invaded host cells. Here, we aimed to understand the underlying cell death inhibited by ExoS when P. aeruginosa is intracellular. Results showed that intracellular P. aeruginosa lacking T3SS effectors could elicit rapid cell lysis via the noncanonical inflammasome pathway. Caspase-4 contributed to cell lysis even when the intracellular bacteria lacked the entire T33S and were consequently unable to escape vacuoles, representing a naturally occurring subpopulation during wild-type infection. Together, the data show the caspase-4 inflammasome as an epithelial cell defense against intracellular P. aeruginosa, and implicate its targeting as another mechanism by which ExoS preserves the host cell replicative niche.

Hypoxia dampens innate immune signalling at early time points and increases Zika virus RNA levels in iPSC-derived macrophages.

Type I interferons (IFNs) are the major host defence against viral infection and are induced following activation of cell surface or intracellular pattern recognition receptors, including retinoic-acid-inducible gene I (RIG-I)-like receptors (RLRs). All cellular processes are shaped by the microenvironment and one important factor is the local oxygen tension. The majority of published studies on IFN signalling are conducted under laboratory conditions of 18% oxygen (O2), that do not reflect the oxygen levels in most organs (1-5 % O2). We studied the effect of low oxygen on IFN induction and signalling in induced Pluripotent Stem Cell (iPSC)-derived macrophages as a model for tissue-resident macrophages and assessed the consequence for Zika virus (ZIKV) infection. Hypoxic conditions dampened the expression of interferon-stimulated genes (ISGs) following RLR stimulation or IFN treatment at early time points. RNA-sequencing and bio-informatic analysis uncovered several pathways including changes in transcription factor availability, the presence of HIF binding sites in promoter regions, and CpG content that may contribute to the reduced ISG expression. Hypoxic conditions increased the abundance of ZIKV RNA highlighting the importance of understanding how low oxygen conditions in the local microenvironment affect pathogen sensing and host defences.

Activation of inflammasomes and mechanisms for intracellular recognition of Listeria monocytogenes.

The high mortality rate associated with Listeria monocytogenes can be attributed to its ability to invade the body systemically and to activate inflammasomes. Both of these processes are facilitated by expressing a major virulence factor known as listeriolysin O, a 56 kDa pore-forming protein encoded by the hly gene. Listeriolysin O plays a crucial role in the pathogenesis of the bacterium by facilitating the escape of the pathogen from the phagosome into the cytosol. This process is essential for the successful establishment of infection. In addition, listeriolysin O is known as an immunomodulator that activates host signal transduction. In addition to listeriolysin O, Listeria expresses a variety of bacterial ligands, such as lipoteichoic acid, nucleotide, and flagellin, that are recognized by host intracellular pattern-recognition receptors including Nod-like receptors, AIM2-like receptors, and RIG-I-like receptors. This review introduces intracellular recognition of Listeria monocytogenes since recent studies have revealed that the activation of inflammasome exacerbates Gram-positive bacteria infection.

Neuroprotective Effects of Vinpocetine Against Ischemia-Reperfusion Injury Via Inhibiting NLRP3 Inflammasome Signaling Pathway

Ischemic stroke is one of the main causes of serious disability and death worldwide. NLRP3 inflammasome is an intracellular pattern recognition receptor composed of polyprotein complex, which participates in mediating a series of inflammatory responses and is considered as a potential target for the treatment of ischemic stroke. Vinpocetine, a derivative of vincamine, has been widely used in the prevention and treatment of ischemic stroke. However, the therapeutic mechanism of vinpocetine is not clear, and its effect on NLRP3 inflammasome remains to be determined. In this study, we used the mouse model of transient middle cerebral artery occlusion (tMCAO) to simulate the occurrence of ischemic stroke. Different doses of vinpocetine (5, 10, 15 mg/kg/d) were injected intraperitoneally for 3 days after ischemia–reperfusion in mice. The effects of different doses of vinpocetine on the degree of ischemia–reperfusion injury in mice were observed by TTC staining and modified neurological severity score scale, and the optimal dose was determined. Then, based on this optimal dose, we observed the effects of vinpocetine on apoptosis, microglial proliferation and NLRP3 inflammasome. In addition, we compared the effects of vinpocetine and MCC950 (a specific inhibitor of NLRP3 inflammasome) on NLRP3 inflammasome. Our results show that vinpocetine can effectively reduce the infarct volume and promote the recovery of behavioral function in stroke mice, and the maximal beneficial effects were observed at the dose of 10 mg/kg/d. Vinpocetine can effectively inhibit the apoptosis of peri-infarct neurons, promote the expression of Bcl-2, inhibit the expression of Bax and Cleaved Caspase-3, and reduce the proliferation of peri-infarct microglia. In addition, vinpocetine, like MCC950, can reduce the expression of NLRP3 inflammasome. Therefore, vinpocetine can effectively alleviate the ischemia–reperfusion injury in mice, and the inhibition of NLRP3 inflammasome may be an important therapeutic mechanism of vinpocetine.

Clinical characteristics of patients with NOD2 high risk allele variants

The nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular pattern recognition receptor. NOD2 gene variants are associated with inflammatory bowel disease (IBD) as well as Blau and Yao syndromes. IBD is associated with extraintestinal manifestations, including autoinflammation, which may be the presenting symptoms. The clinical symptoms may depend on the specific gene variants. This retrospective study was undertaken to examine the clinical manifestations of patients with pathogenic NOD2 variants in our institution. This study was approved by our Institutional Review Board.From January 2020 to February 2022, we identified 203 patients that had genetic testing that included the NOD2 gene. Forty-one had high risk alleles variants (HRA) that segregated in three mutations: HRA1 c.2104C>T (n = 24); HRA2 c.3019dup (n = 11); and HRA3 c.2722G > C (n = 6).The reported age of initial symptoms ranged from 21 days to 62 years, with most patients being < 12 years of age. All three variants had clinical evidence of immune dysregulation. Common manifestations (listed respectively for the three variants) included asthma (HRA1 = 21%, HRA2 = 9%, HRA3 = 33%), reflux/gastritis (29%, 18%, 33%), irritable bowel syndrome (21%, 18%, 7%), chronic diarrhea (8%, 18%, 0%), IBD (13%, 27%, 50%), recurrent fevers (38%, 45%, 0%), cytokine storm (4%, 9%, 17%), arthralgia/arthritis (33%, 45%, 17%), skin rashes (42%, 36%, 0%), malignancy (13%, 0%, 17%), bacterial infections (38%, 36%, 67%), fungal infections (4%, 18%, 0%), other autoimmune (21%, 9%, 0%), autoinflammatory syndromes (13%, 45%, 0%). Autoinflammatory/autoimmune disorders diagnosed within the cohort included PFAPA (HRA1 = 0, HRA2 = 1, HRA3 = 0), Yao syndrome (1, 0, 0), juvenile idiopathic arthritis (1, 1, 0), SAPHO syndrome (0, 1, 0), relapsing polychondritis (0,1,0), lupus (0,1,0), Sjogren’s syndrome (0,1,0), Raynaud’s syndrome (1, 0, 0), vitiligo (0, 1, 0), type I diabetes (2, 0, 0) and hypothyroidism (2, 1, 0). Detailed information is in table 1.Our chart review demonstrates a broad spectrum of extraintestinal clinical manifestations of patients with NOD2 variants which do not always include IBD. NOD2 is important in the protection of infection and autoinflammation and its role in human disease needs to be examined further.

Unexpected Need of the Epidermal Growth Factor Receptor Tyrosine Kinase Activity for Signaling by Intracellular Pattern Recognition Receptors of Nucleic Acids.

Many pattern recognition receptors in mammalian cells initiate signaling processes that culminate in mounting an innate protective response mediated by induced synthesis of a large number of proteins including type I interferons and other cytokines. Many of these receptors are not located on the plasma membrane but on the membranes of intracellular organelles such as endosomes, mitochondria, and the endoplasmic reticulum; they primarily recognize microbial or cellular nucleic acids. In the course of biochemical analyses of the signaling pathways triggered by these receptors, we discovered that they require tyrosine phosphorylation by the protein kinase activity of the epidermal growth factor receptor (EGFR), which is located not only on the plasma membrane but also on the intracellular membranes. Here, we discuss how specific members of this family of receptors, such as TLR3, TLR9, or STING, interact with EGFR and other protein tyrosine kinases and what are the functional consequences of their post-translational modifications. The article highlights an unexpected functional link between a growth factor receptor and cellular innate immune response.

Pattern-recognition receptors in endometriosis: A narrative review.

Endometriosis is closely associated with ectopic focal inflammation and immunosuppressive microenvironment. Multiple types of pattern recognition receptors (PRRs) are present in the innate immune system, which are able to detect pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) in both intracellular and external environments. However, the exact role of PRRs in endometriosis and the underlying molecular mechanism are unclear. PRRs are necessary for the innate immune system to identify and destroy invasive foreign infectious agents. Mammals mainly have two types of microbial recognition systems. The first one consists of the membrane-bound receptors, such as toll-like receptors (TLRs), which recognize extracellular microorganisms and activate intracellular signals to stimulate immune responses. The second one consists of the intracellular PRRs, including nod-like receptors (NLRs) and antiviral proteins retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5) with helix enzyme domain. In this review, we mainly focus on the key role of PRRs in the pathological processes associated with endometriosis. PRRs recognize PAMPs and can distinguish pathogenic microorganisms from self, triggering receptor ligand reaction followed by the stimulation of host immune response. Activated immune response promotes the transmission of microbial infection signals to the cells. As endometriosis is characterized by dysregulated inflammation and immune response, PRRs may potentially be involved in the activation of endometriosis-associated inflammation and immune disorders. Toll-like receptor 2 (TLR2), toll-like receptor 3 (TLR3), toll-like receptor 4 (TLR4), nod-like receptor family caspase activation and recruitment domain (CARD) domain containing 5 (NLRC5), nod-like receptor family pyrin domain containing 3 (NLRP3), and c-type lectin receptors (CLRs) play essential roles in endometriosis development by regulating immune and inflammatory responses. Absent in melanoma 2 (AIM2)-like receptors (ALRs) and retinoic acid-inducible gene I-like receptors (RLRs) may be involved in the activation of endometriosis-associated immune and inflammation disorders. PRRs, especially TLRs, may serve as potential therapeutic targets for alleviating pain in endometriosis patients. PRRs and their ligands interact with the innate immune system to enhance inflammation in the stromal cells during endometriosis. Thus, targeting PRRs and their new synthetic ligands may provide new therapeutic options for treating endometriosis.

Cytosolic DNA sensors and glial responses to endogenous DNA.

Genomic instability is a key driving force for the development and progression of many neurodegenerative diseases and central nervous system (CNS) cancers. The initiation of DNA damage responses is a critical step in maintaining genomic integrity and preventing such diseases. However, the absence of these responses or their inability to repair genomic or mitochondrial DNA damage resulting from insults, including ionizing radiation or oxidative stress, can lead to an accumulation of self-DNA in the cytoplasm. Resident CNS cells, such as astrocytes and microglia, are known to produce critical immune mediators following CNS infection due to the recognition of pathogen and damage-associated molecular patterns by specialized pattern recognition receptors (PRRs). Recently, multiple intracellular PRRs, including cyclic GMP-AMP synthase, interferon gamma-inducible 16, absent in melanoma 2, and Z-DNA binding protein, have been identified as cytosolic DNA sensors and to play critical roles in glial immune responses to infectious agents. Intriguingly, these nucleic acid sensors have recently been shown to recognize endogenous DNA and trigger immune responses in peripheral cell types. In the present review, we discuss the available evidence that cytosolic DNA sensors are expressed by resident CNS cells and can mediate their responses to the presence of self-DNA. Furthermore, we discuss the potential for glial DNA sensor-mediated responses to provide protection against tumorigenesis versus the initiation of potentially detrimental neuroinflammation that could initiate or foster the development of neurodegenerative disorders. Determining the mechanisms that underlie the detection of cytosolic DNA by glia and the relative role of each pathway in the context of specific CNS disorders and their stages may prove pivotal in our understanding of the pathogenesis of such conditions and might be leveraged to develop new treatment modalities.

The microbiome in HLA-B27-associated disease: implications for acute anterior uveitis and recommendations for future studies.

The pathogenesis of human leukocyte antigen (HLA)-B27-associated diseases such as acute anterior uveitis (AAU) and ankylosing spondylitis (AS) remains poorly understood, though Gram-negative bacteria and subclinical bowel inflammation are strongly implicated. Accumulating evidence from animal models and clinical studies supports several hypotheses, including HLA-B27-dependent dysbiosis, altered intestinal permeability, and molecular mimicry. However, the existing literature is hampered by inadequate studies designed to establish causation or uncover the role of viruses and fungi. Moreover, the unique disease model afforded by AAU to study the gut microbiota has been neglected. This review critically evaluates the current literature and prevailing hypotheses on the link between the gut microbiota and HLA-B27-associated disease. We propose a new potential role for HLA-B27-driven altered antibody responses to gut microbiota in disease pathogenesis and outline recommendations for future well-controlled human studies, focusing on AAU.

The role of NOD2 in intestinal immune response and microbiota modulation: A therapeutic target in inflammatory bowel disease.

As an intracellular pattern recognition receptor (PPR), the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) triggers a cascade of immune responses. Previous studies of NOD2 regarding inflammatory bowel disease (IBD) mainly focused on the relevance of NOD2 mutations and loss within the disease onset and progression. With increasing research, more studies are exploring other functional roles and clinical applications of NOD2. In this review, we discuss the role of NOD2 in intestinal immune response and microbiota modulation in IBD and explore its clinical potential as a therapeutic target for IBD.

Novel Evidence That NADPH Oxidase 2 (Nox-2) Enhances Trafficking of Hematopoietic Stem Progenitor Cells (HSPCs) By Involving ROS Mediated Activation of Nlrp3 Inflammasome

Background. NADPH oxidase 2 (Nox-2) is a superoxide-generating enzyme that forms reactive oxygen species (ROS) to regulate the redox state involved in the self-renewal of hematopoietic stem/progenitor cells (HSPCs). Moreover, ROS are released from Nox-2 expressed by cell surface and mitochondria membranes and are potent activators of intracellular pattern recognition receptor Nlrp3 inflammasome, which regulates several aspects of HSPCs biology, including their trafficking, proliferation, and metabolism. Our previous research demonstrated a novel role of Nlrp3 inflammasome in the migration, mobilization, homing, and engraftment of HSPCs (Leukemia 2022;36(1):23-32;Stem Cell Rev Rep. 2020 16(5):954-967). The role of ROS was extensively studied in the proliferation of hematopoietic cells; however, its role in the migration of HSPCs is not very well understood. Aim of the study.Based on the role of Nox-2 in activating Nlrp3 inflammasome, we hypothesized that activation of Nox-2-ROS-Nlrp3 inflammasome axis in both HSPCs and BM microenvironment orchestrates trafficking of HSPCs.Materials and Methods. First, we studied in Transwells chemotaxis of Nox-2 deficient cells to bone marrow (BM) chemoattractants, including SDF-1, S1P, and eATP. Next, to shed more light on the role of Nox2 in the trafficking of HSPCs, we performed in Nox-2-KO animals G-CSF- and AMD3100-induced pharmacological mobilization. We also studied homing and engraftment of Nox-2-KO cells in BM of wild-type (WT) animals and homing and engraftment o WT BM cells in Nox-2-KO recipients. Nox-2-KO mice were also sublethal irradiated, and we followed the recovery of peripheral blood counts in these animals. Activation of Nlrp3 inflammasome in Nox-2-KO murine Sca-1+c-kit+lineage- HSPCs was evaluated by Glow assay. To ''bypass'' Nox-2-ROS activation in control experiments, nigericin has been employed as a direct activator of Nlrp3 inflammasome. Since membrane lipid rafts (MLRs) play a crucial role optimal migration of HSPCs, we evaluated the formation of membrane lipid rafts by employing confocal analysis in Nox-2-KO cells stimulated with SDF-1. We also studied the expression of enzymes (SREBP2, HMGCs, and HMGCR) involved in providing lipid components for MLRs assemble in activated Nox-2-KO cells. Results. We noticed that Nox-2-KO animals have a profound defect in the trafficking of HSPCs as evidenced by impaired chemotaxis to BM chemoattractants, decrease in pharmacological mobilization, and defect in homing and engraftment after transplantation. Nox-2-KO mice have also defect in recovery from sublethal irradiation. At the molecular level, HSPCs from Nox-2-KO mice displayed a defect in activation of Nlrp3 inflammasome and in cholesterol and sphingolipids synthesizing enzymes, which provide lipid components required for optimal assemble of MLRs. These defects were partially ameliorated by using direct activator of Nlrp3 inflammasome that is nigericin. Conclusions. We provide for the first time evidence that Nox-2-ROS-Nlrp3 inflammasome axis operates in normal HSPCs and is crucial for regulating trafficking and post-irradiation recovery of these cells. These effects are mediated by providing components for MLRs required for optimal migration and signaling in HSPCs