NOD-like receptors and the innate immune system: Coping with danger, damage and death

Mettl3‑mediated m6A RNA methylation regulates osteolysis induced by titanium particles

Peri‑prosthetic osteolysis (PPO) induced by wear particles is considered the primary cause of titanium prosthesis failure and revision surgery. The specific molecular mechanisms involve titanium particles inducing multiple intracellular pathways, which impact disease prevention and the targeted therapy of PPO. Notably, N6‑methyladenosine (m6A) serves critical roles in epigenetic regulation, particularly in bone metabolism and inflammatory responses. Thus, the present study aimed to determine the role of RNA methylation in titanium particle‑induced osteolysis. Results of reverse transcription‑quantitative PCR (RT‑qPCR), western blotting, ELISA and RNA dot blot assays revealed that titanium particles induced osteogenic inhibition and proinflammatory responses, accompanied by the reduced expression of methyltransferase‑like (Mettl) 3, a key component of m6A methyltransferase. Specific lentiviruses vectors were employed for Mettl3 knockdown and overexpression experiments. RT‑qPCR, western blotting and ELISA revealed that the knockdown of Mettl3 induced osteogenic inhibition and proinflammatory responses comparable with that induced by titanium particle, while Mettl3 overexpression attenuated titanium particle‑induced cellular reactions. Methylated RNA immunoprecipitation‑qPCR results revealed that titanium particles mediated the methylation of two inhibitory molecules, namely Smad7 and SMAD specific E3 ubiquitin protein ligase 1, via Mettl3 in bone morphogenetic protein signaling, leading to osteogenic inhibition. Furthermore, titanium particles induced activation of the nucleotide binding oligomerization domain 1 signaling pathway through methylation regulation, and the subsequent activation of the MAPK and NF‑κB pathways. Collectively, the results of the present study indicated that titanium particles utilized Mettl3 as an upstream regulatory molecule to induce osteogenic inhibition and inflammatory responses. Thus, the present study may provide novel insights into potential therapeutic targets for aseptic loosening in titanium prostheses.

Bridging the Gap: Investigating the Link between Inflammasomes and Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a cluster of cognitive problems that may arise after surgery. POCD symptoms include memory loss, focus inattention, and communication difficulties. Inflammasomes, intracellular multiprotein complexes that control inflammation, may have a significant role in the development of POCD. It has been postulated that the NLRP3 inflammasome promotes cognitive impairment by triggering the inflammatory response in the brain. Nevertheless, there are many gaps in the current literature to understand the underlying pathophysiological mechanisms and develop future therapy. This review article underlines the limits of our current knowledge about the NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome and POCD. We first discuss inflammasomes and their types, structures, and functions, then summarize recent evidence of the NLRP3 inflammasome's involvement in POCD. Next, we propose a hypothesis that suggests the involvement of inflammasomes in multiple organs, including local surgical sites, blood circulation, and other peripheral organs, leading to systemic inflammation and subsequent neuronal dysfunction in the brain, resulting in POCD. Research directions are then discussed, including analyses of inflammasomes in more clinical POCD animal models and clinical trials, studies of inflammasome types that are involved in POCD, and investigations into whether inflammasomes occur at the surgical site, in circulating blood, and in peripheral organs. Finally, we discuss the potential benefits of using new technologies and approaches to study inflammasomes in POCD. A thorough investigation of inflammasomes in POCD might substantially affect clinical practice.

Recent advances in pyroptosis, liver disease, and traditional Chinese medicine: A review

In recent years, the incidence of liver disease has increased, becoming a major cause of death. Various liver diseases are intricately linked to pyroptosis, which is one of the most common forms of programmed cell death. As a powerful weapon in the fight against liver diseases, traditional Chinese medicine (TCM) can affect pyroptosis via a number of routes, including the classical, nucleotide oligomerization domain-like receptors protein 3/caspase-1/gasdermin D (GSDMD) pathway, the nonclassical lipopolysaccharide/caspase-11/GSDMD pathway, the ROS/caspase-3/gasdermin E pathway, the caspase-9/caspase-3/GSDMD pathway, and the Apaf-1/caspase-11/caspase-3 pathway. In this review, we provide an overview of pyroptosis, the interplay between pyroptosis and liver diseases, and the mechanisms through which TCM regulates pyroptosis in liver diseases. The information used in the text was collected and compiled from the databases of PubMed, Web of Science, Scopus, CNKI, and Wanfang Data up to June 2023. The search was not limited with regard to the language and country of the articles. Research and review articles were included, and papers with duplicate results or unrelated content were excluded. We examined the current understanding of the relationship between pyroptosis and liver diseases as well as the advances in TCM interventions to provide a resource for the identification of potential targets for TCM in the treatment of liver diseases.

Crosstalk between alternative splicing and inflammatory bowel disease: Basic mechanisms, biotechnological progresses and future perspectives

BACKGROUND

Alternative splicing (AS) is an omnipresent regulatory mechanism of gene expression that enables the generation of diverse splice isoforms from a single gene. Recently, AS events have gained considerable momentum in the pathogenesis of inflammatory bowel disease (IBD).

METHODS

Our review has summarized the complex process of RNA splicing, and firstly highlighted the potential involved molecules that target aberrant splicing events in IBD. The quantitative transcriptome analyses such as microarrays, next-generation sequencing (NGS) for AS events in IBD have been also discussed.

RESULTS

Available evidence suggests that some abnormal splicing RNAs can lead to multiple intestinal disorders during the onset of IBD as well as the progression to colitis-associated cancer (CAC), including gut microbiota perturbations, intestinal barrier dysfunctions, innate/adaptive immune dysregulations, pro-fibrosis activation and some other risk factors. Moreover, current data show that the advanced technologies, including microarrays and NGS, have been pioneeringly employed to screen the AS candidates and elucidate the potential regulatory mechanisms of IBD. Besides, other biotechnological progresses such as the applications of third-generation sequencing (TGS), single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST), will be desired with great expectations.

CONCLUSIONS

To our knowledge, the current review is the first one to evaluate the potential regulatory mechanisms of AS events in IBD. The expanding list of aberrantly spliced genes in IBD along with the developed technologies provide us new clues to how IBD develops, and how these important AS events can be explored for future treatment.

Multifaceted roles and regulation of nucleotide-binding oligomerization domain containing proteins

Nucleotide-binding oligomerization domain-containing proteins, NOD1 and NOD2, are cytosolic receptors that recognize dipeptides and tripeptides derived from the bacterial cell wall component peptidoglycan (PGN). During the past two decades, studies have revealed several roles for NODs beyond detecting PGN fragments, including activation of an innate immune anti-viral response, NOD-mediated autophagy, and ER stress induced inflammation. Recent studies have also clarified the dynamic regulation of NODs at cellular membranes to generate specific and balanced immune responses. This review will describe how NOD1 and NOD2 detect microbes and cellular stress and detail the molecular mechanisms that regulate activation and signaling while highlighting new evidence and the impact on inflammatory disease pathogenesis.

Activation of Inflammasome complex in nasopharyngeal epithelial cells from patients with Coronavirus disease 2019 contributes to inflammatory state and worse disease outcomes

Pathogenesis of Coronavirus disease 2019 (COVID-19) has been associated with dysregulation of both adaptive and innate immune systems. Hence, we determined the contribution of inflammasome in the nasopharyngeal epithelial cells isolated from COVID-19 subjects to disease pathogenesis and outcomes. Epithelial cells from 150 COVID-19 patients and 150 healthy controls were yielded through nasopharyngeal swab sampling. Patients were categorized into three groups of those with clinical presentations/need hospitalization, with clinical presentations/no need hospitalization and cases without clinical symptoms/no need hospitalization. Finally, the transcriptional amount of inflammasome related genes were assessed in the nasopharyngeal epithelial cells using qPCR. There was a significant upregulation of nod-like receptor (NLR) family pyrin domain containing 1 (NLRP1), nod-like receptor (NLR) family pyrin domain containing 3 (NLRP3), Apoptosis-associated speck-like protein containing a CARD (ASC) and Caspase-1 mRNA expressions in patients compared to controls. NLRP1, NLRP3, ASC and Caspase-1 were upregulated in epithelial cells of patients with clinical symptoms/need hospitalization and cases with clinical symptoms/no need hospitalization when compared to controls. There was a correlation between expression of inflammasome-related genes and clinicopathological features. Abnormal expression of inflammasome-related genes in the nasopharyngeal epithelial cells obtained from COVID-19 patients may be of prognostic value to determine the intensity of the disease's outcomes and requirement for alternative supports in hospitals.

Inflammatory bowel disease increases the risk of hepatobiliary pancreatic cancer: A two-sample Mendelian randomization analysis of European and East Asian populations

BACKGROUND

Both inflammatory bowel disease (IBD) and hepato-pancreato-biliary cancers (HPBC) have been established to cause a huge socioeconomic burden. Epidemiological studies have revealed a close association between IBD and HPBC.

METHODS

Herein, we utilized inverse-variance weighting to conduct a two-sample Mendelian randomization analysis. We sought to investigate the link between various subtypes of IBD and HPBC. To ensure the accuracy and consistency of our findings, we conducted heterogeneity tests, gene pleiotropy tests, and sensitivity analyses.

RESULTS

Compared to the general population, IBD patients in Europe exhibited a 1.22-fold increased incidence of pancreatic cancer (PC) with a 95% confidence interval (CI) of 1.0022-1.4888 (p = 0.0475). We also found a 1.14-fold increased incidence of PC in Crohn's disease (CD) patients with (95% CI: 1.0017-1.3073, p = 0.0472). In the East Asian population, the incidence of hepatocellular carcinoma (HCC) was 1.28-fold higher (95% CI = 1.0709-1.5244, p = 0.0065) in IBD patients than in the general population. Additionally, ulcerative colitis (UC) patients displayed 1.12-fold (95% CI: 1.1466-1.3334, p < 0.0001) and 1.31-fold (95% CI: 1.0983-1.5641, p = 0.0027) increased incidences of HCC and cholangiocarcinoma (CCA), respectively. Finally, the incidence of PC was 1.19-fold higher in CD patients than in the general population (95% CI = 1.0741-1.3132, p = 0.0008).

CONCLUSION

Our study validated that IBD is a risk factor for HPBC. This causal relationship exhibited significant heterogeneity in different European and East Asian populations.

Inflammasomes: a rising star on the horizon of COVID-19 pathophysiology

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a contagious respiratory virus that is the cause of the coronavirus disease 2019 (COVID-19) pandemic which has posed a serious threat to public health. COVID-19 is characterized by a wide spectrum of clinical manifestations, ranging from asymptomatic infection to mild cold-like symptoms, severe pneumonia or even death. Inflammasomes are supramolecular signaling platforms that assemble in response to danger or microbial signals. Upon activation, inflammasomes mediate innate immune defense by favoring the release of proinflammatory cytokines and triggering pyroptotic cell death. Nevertheless, abnormalities in inflammasome functioning can result in a variety of human diseases such as autoimmune disorders and cancer. A growing body of evidence has showed that SARS-CoV-2 infection can induce inflammasome assembly. Dysregulated inflammasome activation and consequent cytokine burst have been associated with COVID-19 severity, alluding to the implication of inflammasomes in COVID-19 pathophysiology. Accordingly, an improved understanding of inflammasome-mediated inflammatory cascades in COVID-19 is essential to uncover the immunological mechanisms of COVID-19 pathology and identify effective therapeutic approaches for this devastating disease. In this review, we summarize the most recent findings on the interplay between SARS-CoV-2 and inflammasomes and the contribution of activated inflammasomes to COVID-19 progression. We dissect the mechanisms involving the inflammasome machinery in COVID-19 immunopathogenesis. In addition, we provide an overview of inflammasome-targeted therapies or antagonists that have potential clinical utility in COVID-19 treatment.

NPAS4 Exacerbates Pyroptosis via Transcriptionally Regulating NLRP6 in the Acute Phase of Intracerebral Hemorrhage in Mice

Intracerebral hemorrhage (ICH) is a severe cerebrovascular disease with a high disability rate and high mortality, and pyroptosis is a type of programmed cell death in the acute phase of ICH. Neuronal Per-Arnt-Sim domain protein 4 (Npas4) is a specific transcription factor highly expressed in the nervous system, yet the role of NPAS4 in ICH-induced pyroptosis is not fully understood. NLR family Pyrin-domain-containing 6 (NLRP6), a new member of the Nod-like receptor family, aggravates pyroptosis via activating cysteine protease-1 (Caspase-1) and Caspase-11. In this study, we found that NPAS4 was upregulated in human and mouse peri-hematoma brain tissues and peaked at approximately 24 h after ICH modeling. Additionally, NPAS4 knockdown improved neurologic dysfunction and brain damage induced by ICH in mice after 24 h. Meanwhile, inhibiting NPAS4 expression reduced the levels of myeloperoxidase (MPO)-positive cells and Caspase-1/TUNEL-double-positive cells and decreased cleaved Caspase-1, cleaved Caspase-11, and N-terminal GSDMD levels. Consistently, NPAS4 overexpression reversed the above alternations after ICH in the mice. Moreover, NPAS4 could interact with the Nlrp6 promoter region (-400--391 bp and -33--24 bp) and activate the transcription of Nlrp6. Altogether, our study demonstrated that NPAS4, as a transcription factor, can exacerbate pyroptosis and transcriptionally activate NLRP6 in the acute phase of intracerebral hemorrhage in mice.

Insights on Host-Parasite Immunomodulation Mediated by Extracellular Vesicles of Cutaneous Leishmania shawi and Leishmania guyanensis

Leishmaniasis is a parasitic disease caused by different species of Leishmania and transmitted through the bite of sand flies vector. Macrophages (MΦ), the target cells of Leishmania parasites, are phagocytes that play a crucial role in the innate immune microbial defense and are antigen-presenting cells driving the activation of the acquired immune response. Exploring parasite-host communication may be key in restraining parasite dissemination in the host. Extracellular vesicles (EVs) constitute a group of heterogenous cell-derived membranous structures, naturally produced by all cells and with immunomodulatory potential over target cells. This study examined the immunogenic potential of EVs shed by L. shawi and L. guyanensis in MΦ activation by analyzing the dynamics of major histocompatibility complex (MHC), innate immune receptors, and cytokine generation. L. shawi and L. guyanensis EVs were incorporated by MΦ and modulated innate immune receptors, indicating that EVs cargo can be recognized by MΦ sensors. Moreover, EVs induced MΦ to generate a mix of pro- and anti-inflammatory cytokines and favored the expression of MHCI molecules, suggesting that EVs antigens can be present to T cells, activating the acquired immune response of the host. Since nano-sized vesicles can be used as vehicles of immune mediators or immunomodulatory drugs, parasitic EVs can be exploited by bioengineering approaches for the development of efficient prophylactic or therapeutic tools for leishmaniasis.

Novel NLRP14 Mutations Induce Azoospermia

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

Diversification of PAR signaling through receptor crosstalk

Protease activated receptors (PARs) are among the first receptors shown to transactivate other receptors: noticeably, these interactions are not limited to members of the same family, but involve receptors as diverse as receptor kinases, prostanoid receptors, purinergic receptors and ionic channels among others. In this review, we will focus on the evidence for PAR interactions with members of their own family, as well as with other types of receptors. We will discuss recent evidence as well as what we consider as emerging areas to explore; from the signalling pathways triggered, to the physiological and pathological relevance of these interactions, since this additional level of molecular cross-talk between receptors and signaling pathways is only beginning to be explored and represents a novel mechanism providing diversity to receptor function and play important roles in physiology and disease.

Molecular characterization of NLRC3 and its interaction with other inflammasome components and regulation on the bacterial colonization in Qihe crucian carp Carassius auratus

The NLRC as a very unique subfamily of Nod like receptors (NLRs), is believed to play an important role in the bacterial recognition of animals. However, the molecular characterization and immunological role of NLRC3 in Carassius auratus is little known. In this study, we identified and achieved a complete cDNA sequence of NLRC3 gene in Qihe crucian carp Carassius auratus (named as CaNLRC3). The full-length cDNA sequence of CaNLRC3 was composed of 3823 bp, which contained a 5'-UTR of 251 bp, a 3'-UTR of 158 bp, and an open reading frame (ORF) of 3414 bp encoded 1137 amino acids with a predicted isoelectric point of 8.25 and a molecular mass of 124.1 kDa, characterized with a caspase recruitment domain (CARD) at N-terminus. The mRNA expression of CaNLRC3 was detected to be constitutive in all the examined tissues, with the high expression levels in spleen, skin and intestine. After challenges with bacteria or pathogenic analogue, expression levels of CaNLRC3 gene were strongly induced. Co-localization and co-immunoprecipitation results found that CaNLRC3 can assemble CaASC through CARD domain interaction, then CaASC associated with CaCaspase-1a, presumably to assemble the NLRC3 inflammasome complex. The overexpression of CaNLRC3 could significantly increase the mRNA expression of IL-1β, and promote the bacterial elimination and result in the decrease of bacterial loading in liver, spleen and kidney after bacterial infection. Vice versa, the knockdown of CaNLRC3 could obviously reduce IL-1β expression at mRNA level, and bacterial loading was significantly increased in tissue. Taken together, CaNLRC3 is proved to be a pivotal cytosolic innate immune receptor in this study, which is acted as the potential component of inflammasome to regulate inflammation reaction, and could modify bacterial loading in tissue and restrict bacterial infection in teleost.

Postbiotic muramyl dipeptide alleviates colitis via activating autophagy in intestinal epithelial cells

The pathogenesis of IBD is complicated and still unclear. Nucleotide-binding oligomerization domain 2 (NOD2) plays a significant role in regulating gut inflammation under the activation of muramyl dipeptide (MDP), which is used as a postbiotic. The study aimed to investigate the effect of MDP on the intestinal barrier in colitis and the mechanism involved. In this study, C57BL/6 mice were challenged with dextran sodium sulfate (DSS) for establishing a colitis model with the pre-treatment of MDP in vivo. Intestinal permeability was reflected by detecting the serum concentration of 4 kDa Fluorescein Isothiocyanate-Dextran. The expression of inflammation, barrier-related proteins, and autophagy was tested by Western Blotting. Proliferation and apoptosis in intestinal epithelial cells were detected by immunohistochemistry. Caco-2 cells were exposed to lipopolysaccharide for imitating inflammation in vitro. The findings showed that administration of MDP ameliorated losses of body weight loss, gross injury, and histology score of the colon in the DSS-induced colitis mice. MDP significantly ameliorated the condition of gut permeability, and promoted intestinal barrier repair by increasing the expression of Zonula occludens-1 and E-cadherin. Meanwhile, MDP promoted proliferation and reduced apoptosis of intestinal epithelial cells. In the experiment group treated with MDP, LC3 was upregulated, and p62 was downregulated, respectively. These results suggested that MDP stimulation attenuates intestinal inflammation both in vivo and in vitro. Potentially, MDP reduced the intestinal barrier damage by regulating autophagy in intestinal epithelial cells. Future trials investigating the effects of MDP-based postbiotics on IBD may be promising.

Expression of NLRP3 and AIM2 inflammasome in Peripheral blood in Chinese patients with acute and chronic brucellosis

Brucellosis is a zoonotic disease caused by Brucella abortus. An efficient immune response is crucial for curing brucellosis. The inflammasome plays a significant role in the immune response. It is unclear which inflammasome is active in acute and chronic brucellosis and how its levels relate to inflammatory cytokines. A total of 40 patients with acute or chronic brucellosis and 20 healthy volunteers had peripheral blood samples collected. The expression levels of AIM2, NLRP3, ASC, and Caspase-1 were determined by a real-time polymerase chain reaction from RNA and serum samples, and IL-1β, IL-18, and IFN-γ were measured by enzyme-linked immunosorbent assay. In the acute brucellosis group, AIM2 expression was significantly higher, while ACS expression was significantly lower than that of healthy volunteers. In patients with chronic brucellosis, AIM2 expression was significantly lower, while Caspase-1 expression was significantly higher than that of healthy volunteers. Serum IL-18 and IFN-γ levels were significantly higher in patients with acute brucellosis than in healthy controls. The IFN-γ level was also significantly higher in patients with chronic brucellosis than in healthy controls. The inflammasome responds differently in different stages of brucellosis. The inflammasome may be the site of action of immune escape in brucellosis.

Supramolecular organizing centers at the interface of inflammation and neurodegeneration

The pathogenesis of neurodegenerative diseases involves the accumulation of misfolded protein aggregates. These deposits are both directly toxic to neurons, invoking loss of cell connectivity and cell death, and recognized by innate sensors that upon activation release neurotoxic cytokines, chemokines, and various reactive species. This neuroinflammation is propagated through signaling cascades where activated sensors/receptors, adaptors, and effectors associate into multiprotein complexes known as supramolecular organizing centers (SMOCs). This review provides a comprehensive overview of the SMOCs, involved in neuroinflammation and neurotoxicity, such as myddosomes, inflammasomes, and necrosomes, their assembly, and evidence for their involvement in common neurodegenerative diseases. We discuss the multifaceted role of neuroinflammation in the progression of neurodegeneration. Recent progress in the understanding of particular SMOC participation in common neurodegenerative diseases such as Alzheimer's disease offers novel therapeutic strategies for currently absent disease-modifying treatments.

Nucleotide-Binding Oligomerization Domain 1 (NOD1) Positively Regulates Neuroinflammation during Japanese Encephalitis Virus Infection

Japanese encephalitis virus (JEV) is a neurotropic flavivirus that invades the central nervous system and causes neuroinflammation and extensive neuronal cell death. Nucleotide-binding oligomerization domain 1 (NOD1) is a type of pattern recognition receptor that plays a regulatory role in both bacterial and nonbacterial infections. However, the role of NOD1 in JEV-induced neuroinflammation remains undisclosed. In this study, we evaluated the effect of NOD1 activation on the progression of JEV-induced neuroinflammation using a human astrocytic cell line and NOD1 knockout mice. The results showed that JEV infection upregulated the mRNA and protein expression of NOD1, ultimately leading to an enhanced neuroinflammatory response in vivo and in vitro. Inhibition of NOD1 in cultured cells or mice significantly abrogated the inflammatory response triggered by JEV infection. Moreover, compared to the wild-type mice, the NOD1 knockout mice showed resistance to JEV infection. Mechanistically, the NOD1-mediated neuroinflammatory response was found to be associated with increased expression or activation/phosphorylation of downstream receptor-interacting protein 2 (RIPK2), mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), Jun N-terminal protein kinase (JNK), and NF-κB signaling molecules. Thus, NOD1 targeting could be a therapeutic approach to treat Japanese encephalitis. IMPORTANCE Neuroinflammation is the main pathological manifestation of Japanese encephalitis (JE) and the most important factor leading to morbidity and death in humans and animals infected by JEV. An in-depth understanding of the basic mechanisms of neuroinflammation will contribute to research on JE treatment. This study proved that JEV infection can activate the NOD1-RIPK2 signal cascade to induce neuroinflammation through the proven downstream MAPK, ERK, JNK, and NF-κB signal pathway. Thus, our study unveiled NOD1 as a potential target for therapeutic intervention for JE.

NLRP1 Inflammasomes: A Potential Target for the Treatment of Several Types of Brain Injury

NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) is a member of the NLR family. The NLRP1 inflammasome consists of the NLRP1 protein, the adaptor protein apoptosis-associated speck-like protein containing a CARD domain, and the effector molecule pro-caspase-1. When stimulated, the inflammasome initiates the cleavage of pro-caspase-1 and converts it into its active form, caspase-1; then, caspase-1 facilitates the cleavage of the proinflammatory cytokines interleukin-1β and interleukin-18 into their active and secreted forms. In addition, caspase-1 also mediates the cleavage of gasdermin D, which leads to pyroptosis, an inflammatory form of cell death. Pathological events that damage the brain and result in neuropathological conditions can generally be described as brain injury. Neuroinflammation, especially that driven by NLRP1, plays a considerable role in the pathophysiology of brain injury, such as early brain injury (EBI) of subarachnoid hemorrhage, ischemic brain injury during stroke, and traumatic brain injury (TBI). In this article, a thorough overview of NLRP1 is presented, including its structure, mechanism of activation, and role in neuroinflammation. We also present recent studies on NLRP1 as a target for the treatment of EBI, ischemic brain injury, TBI, and other types of brain injury, thus highlighting the perspective of NLRP1 as an effective mediator of catastrophic brain injury.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

A unique NLRC4 receptor from echinoderms mediates Vibrio phagocytosis via rearrangement of the cytoskeleton and polymerization of F-actin

Many members of the nucleotide-binding and oligomerization domain (NACHT)- and leucine-rich-repeat-containing protein (NLR) family play crucial roles in pathogen recognition and innate immune response regulation. In our previous work, a unique and Vibrio splendidus-inducible NLRC4 receptor comprising Ig and NACHT domains was identified from the sea cucumber Apostichopus japonicus, and this receptor lacked the CARD and LRR domains that are typical of common cytoplasmic NLRs. To better understand the functional role of AjNLRC4, we confirmed that AjNLRC4 was a bona fide membrane PRR with two transmembrane structures. AjNLRC4 was able to directly bind microbes and polysaccharides via its extracellular Ig domain and agglutinate a variety of microbes in a Ca²⁺-dependent manner. Knockdown of AjNLRC4 by RNA interference and blockade of AjNLRC4 by antibodies in coelomocytes both could significantly inhibit the phagocytic activity and elimination of V. splendidus. Conversely, overexpression of AjNLRC4 enhanced the phagocytic activity of V. splendidus, and this effect could be specifically blocked by treatment with the actin-mediated endocytosis inhibitor cytochalasin D but not other endocytosis inhibitors. Moreover, AjNLRC4-mediated phagocytic activity was dependent on the interaction between the intracellular domain of AjNLRC4 and the β-actin protein and further regulated the Arp2/3 complex to mediate the rearrangement of the cytoskeleton and the polymerization of F-actin. V. splendidus was found to be colocalized with lysosomes in coelomocytes, and the bacterial quantities were increased after injection of chloroquine, a lysosome inhibitor. Collectively, these results suggested that AjNLRC4 served as a novel membrane PRR in mediating coelomocyte phagocytosis and further clearing intracellular Vibrio through the AjNLRC4-β-actin-Arp2/3 complex-lysosome pathway.

Vibrio splendidus is ubiquitously present in marine environments and in or on many aquaculture species and is considered to be an important opportunistic pathogen that has caused serious economic losses to the aquaculture industry worldwide. Phagocytosis is the first step of pathogen clearance and is triggered by specific interactions between host pattern recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) from invasive bacteria. However, the mechanism that underlies receptor-mediated V. splendidus phagocytosis is poorly understood. In this study, an atypical AjNLRC4 receptor without LRR and CARD domains was found to serve as the membrane receptor for V. splendidus, not the common cytoplasmic NLRs. The Ig domain of AjNLRC4 is replaced with a conventional LRR domain to bind V. splendidus, and the intracellular domain of AjNLRC4 specifically interacts with β-actin to mediate V. splendidus endocytosis in an actin-dependent manner. Endocytic V. splendidus is ultimately degraded in phagolysosomes. Our findings will contribute to the development of novel strategies for treating V. splendidus infection by modulating the actin-dependent endocytosis pathway.

DNA methyltransferase inhibitors increase NOD-like receptor activity and expression in a monocytic cell line

Background: The intracellular NOD-like receptor (NLR) family of pathogen recognition receptors (PRRa) is involved in initiating the innate immune response of which NOD1 and NOD2 are the best-characterized members. Aberrant expression of NOD1 and NOD2 has been uncovered in a number of chronic inflammatory diseases, such as inflammatory bowel disease and rheumatoid arthritis. However, the mechanism underlying NOD1/NOD2 gene expression regulation is still in its infancy. Epigenetic modifications such as DNA methylation and histone acetylation regulate the expression of genes and alterations in their patterns have been linked to many inflammatory diseases. This study investigated whether epigenetic modifying drugs affect the regulation of NOD1/NOD2 activity and expression. DNA methyltransferase inhibitors have recently been used in the treatment of myelodysplastic syndrome and as combination therapy in cancer but the full extent of their effects has not been quantified.Methods: Pharmacological inhibition of epigenetic enzymes in a human monocytic THP-1 cell line was carried out and NOD1/NOD2 expression and pro-inflammatory responses were quantified.Results: Cells primed with a DNA methyltransferase inhibitor (but not a histone deacetylase [HDAC] inhibitor) were found to be consistently more responsive to NOD1/NOD2 stimulation and had increased basal expression.Conclusion: The novel experimentation carried out here suggests for the first time that NOD1/NOD2 receptor activity and expression in monocytes are possibly regulated directly by DNA methylation.

NOD1 Is Associated With the Susceptibility of Pekin Duck Flock to Duck Hepatitis A Virus Genotype 3

Duck viral hepatitis (DVH) is an acute, highly lethal infectious disease of ducklings that causes huge losses in the duck industry. Duck hepatitis A virus genotype 3 (DHAV-3) has been one of the most prevalent DVH pathogen in the Asian duck industry in recent years. Here, we investigated the genetic basis of the resistance and susceptibility of ducks to DVH by comparing the genomes and transcriptomes of a resistant Pekin duck flock (Z8) and a susceptible Pekin duck flock (SZ7). Our comparative genomic and transcriptomic analyses suggested that NOD1 showed a strong signal of association with DVH susceptibility in ducks. Then, we found that NOD1 showed a significant expression difference between the livers of susceptible and resistant individuals after infection with DHAV-3, with higher expression in the SZ7 flock. Furthermore, suppression and overexpression experiments showed that the number of DHAV-3 genomic copies in primary duck hepatocytes was influenced by the expression level of NOD1. In addition, in situ RNAscope analysis showed that the localization of NOD1 and DHAV-3 in liver cells was consistent. Altogether, our data suggested that NOD1 was likely associated with DHAV-3 susceptibility in ducks, which provides a target for future investigations of the pathogenesis of DVH.

SARS-CoV-2 Spike Glycoprotein S1 Induces Neuroinflammation in BV-2 Microglia

In addition to respiratory complications produced by SARS‐CoV‐2, accumulating evidence suggests that some neurological symptoms are associated with the disease caused by this coronavirus. In this study, we investigated the effects of the SARS‐CoV‐2 spike protein S1 stimulation on neuroinflammation in BV-2 microglia. Analyses of culture supernatants revealed an increase in the production of TNF-α, IL-6, IL-1β and iNOS/NO. S1 also increased protein levels of phospho-p65 and phospho-IκBα, as well as enhanced DNA binding and transcriptional activity of NF-κB. These effects of the protein were blocked in the presence of BAY11-7082 (1 µM). Exposure of S1 to BV-2 microglia also increased the protein levels of NLRP3 inflammasome and enhanced caspase-1 activity. Increased protein levels of p38 MAPK was observed in BV-2 microglia stimulated with the spike protein S1 (100 ng/ml), an action that was reduced in the presence of SKF 86,002 (1 µM). Results of immunofluorescence microscopy showed an increase in TLR4 protein expression in S1-stimulated BV-2 microglia. Furthermore, pharmacological inhibition with TAK 242 (1 µM) and transfection with TLR4 small interfering RNA resulted in significant reduction in TNF-α and IL-6 production in S1-stimulated BV-2 microglia. These results have provided the first evidence demonstrating S1-induced neuroinflammation in BV-2 microglia. We propose that induction of neuroinflammation by this protein in the microglia is mediated through activation of NF-κB and p38 MAPK, possibly as a result of TLR4 activation. These results contribute to our understanding of some of the mechanisms involved in CNS pathologies of SARS-CoV-2.

The Influence of Bifidobacterium bifidum and Bacteroides fragilis on Enteric Glial Cell-Derived Neurotrophic Factors and Inflammasome

Enteric glial cells (EGCs) and enteric glial-derived neurotrophic factor (GDNF) are directly involved in intestinal inflammation. In this study, we sought to examine the possible mechanisms for how Bifidobacterium bifidum (B.b.) and Bacteroides fragilis (B.f.) influence EGC regulation. In this study, lipopolysaccharide (LPS) and interferon-γ (IFN-γ) were used as exogenous stimuli of EGCs to establish an intestinal inflammation model. After stimulation with LPS and IFN-γ, B.b. and B.f. supernatants were used to activate EGCs and to examine EGC immune mechanisms. For this purpose, qRT-PCR, western blotting, and laser scanning confocal microscopy (LSCM) were used to detect the expression of NLRP3, NLRP6, NGF, NT-3, IL-18, IL-1β, and caspase-1. We found that EGCs, after stimulation with LPS and IFN-γ, could express NLRP3, NLRP6, NT-3, NGF, IL-18, IL-1β, and caspase-1 through LSCM. In intestinal inflammation, B.b. and B.f. could trigger an increase in NGF and NT-3 expression in EGCs in order to protect the intestine. Furthermore, B.b. and B.f. could upregulate NLRP3 expression in EGCs and promote an inflammatory response. B.b. had a dual regulatory role in EGC NLRP6 expression, while B.f. inhibited NLRP6 protein expression. Moreover, B.b. could decrease the expression of IL-18, IL-1β, and caspase-1 in EGCs in order to inhibit the inflammatory response. Contrary to this, B.f. could upregulate IL-18, IL-1β, and caspase-1 expression in EGCs in order to promote the inflammatory response. B.b. and B.f. can influence the expression of NGF, NT-3, NLRP3, NLRP6, IL-18, IL-1β, and caspase-1 in EGCs in order to inhibit or promote intestinal inflammation.

Inborn Errors in the LRR Domain of Nod2 and Their Potential Consequences on the Function of the Receptor

The innate immune system plays a critical role in the early detection of pathogens, primarily by relying on pattern-recognition receptor (PRR) signaling molecules. Nucleotide-binding oligomerization domain 2 (NOD2) is a cytoplasmic receptor that recognizes invading molecules and danger signals inside the cells. Recent studies highlight the importance of NOD2′s function in maintaining the homeostasis of human body microbiota and innate immune responses, including induction of proinflammatory cytokines, regulation of autophagy, modulation of endoplasmic reticulum (ER) stress, etc. In addition, there is extensive cross-talk between NOD2 and the Toll-like receptors that are so important in the induction and tuning of adaptive immunity. Polymorphisms of NOD2′s encoding gene are associated with several pathological conditions, highlighting NOD2′s functional importance. In this study, we summarize NOD2′s role in cellular signaling pathways and take a look at the possible consequences of common NOD2 polymorphisms on the structure and function of this receptor.

The role of inflammation in diabetic kidney disease

Diabetic kidney disease (DKD) has been the leading cause of chronic kidney disease for over 20 years. Yet, over these two decades, the clinical approach to this condition has not much improved beyond the administration of glucose-lowering agents, renin-angiotensin-aldosterone system blockers for blood pressure control, and lipid-lowering agents. The proportion of diabetic patients who develop DKD and progress to end-stage renal disease has remained nearly the same. This unmet need for DKD treatment is caused by the complex pathophysiology of DKD, and the difficulty of translating treatment from bench to bed, which further adds to the growing argument that DKD is not a homogeneous disease. To better capture the full spectrum of DKD in our design of treatment regimens, we need improved diagnostic tools that can better distinguish the subgroups within the condition. For instance, DKD is typically placed in the broad category of a non-inflammatory kidney disease. However, genome-wide transcriptome analysis studies consistently indicate the inflammatory signaling pathway activation in DKD. This review will utilize human data in discussing the potential for redefining the role of inflammation in DKD. We also comment on the therapeutic potential of targeted anti-inflammatory therapy for DKD.

Transcriptomic analysis of human brain microvascular endothelial cells exposed to laminin binding protein (adhesion lipoprotein) and Streptococcus pneumoniae

Streptococcus pneumoniae invades the CNS and triggers a strong cellular response. To date, signaling events that occur in the human brain microvascular endothelial cells (hBMECs), in response to pneumococci or its surface adhesins are not mapped comprehensively. We evaluated the response of hBMECs to the adhesion lipoprotein (a laminin binding protein—Lbp) or live pneumococci. Lbp is a surface adhesin recently identified as a potential ligand, which binds to the hBMECs. Transcriptomic analysis was performed by RNA-seq of three independent biological replicates and validated with qRT-PCR using 11 genes. In total 350 differentially expressed genes (DEGs) were identified after infection with S. pneumoniae, whereas 443 DEGs when challenged with Lbp. Total 231 DEGs were common in both treatments. Integrative functional analysis revealed participation of DEGs in cytokine, chemokine, TNF signaling pathways and phagosome formation. Moreover, Lbp induced cell senescence and breakdown, and remodeling of ECM. This is the first report which maps complete picture of cell signaling events in the hBMECs triggered against S. pneumoniae and Lbp. The data obtained here could contribute in a better understanding of the invasion of pneumococci across BBB and underscores role of Lbp adhesin in evoking the gene expression in neurovascular unit.

NLRC4 gene silencing-dependent blockade of NOD-like receptor pathway inhibits inflammation, reduces proliferation and increases apoptosis of dendritic cells in mice with septic shock

Septic shock is one of the most significant health concerns across the world, involving hypo-perfusion and defects in tissue energy. The current study investigates the role of NLR family CARD domain containing protein 4 (NLRC4) in septic shock-induced inflammatory reactions, lung tissue injuries, and dendritic cell (DC) apoptosis. Septic shock mice models were established by modified cecal ligation and puncture and injected with retroviral vector expressing siRNA-NLRC4. DCs were then isolated and transfected with siRNA-NLRC4. The degree of lung tissue injury, cell cycle distribution, cell apoptosis and cell viability of DCs were assessed. NLRC4 was found to be expressed at high levels in mice with septic shock. NLRC4 silencing inhibited the activation of the NOD-like receptor (NLR) pathway as evidenced by the decreased levels of NOD1, NOD2, RIP2, and NF-κB. In addition, NLRC4 silencing reduced the inflammatory reaction as attributed by reduced levels of IL-1β, TNF-α and IL-6. Suppressed NLRC4 levels inhibited cell viability and promoted cell apoptosis evidenced by inhibited induction of DC surface markers (CD80, CD86, and MHC II), along with alleviated lung tissue injury. In conclusion, NLRC4 silencing ameliorates lung injury and inflammation induced by septic shock by negatively regulating the NLR pathway.

A Nuclear Export Signal Is Required for cGAS to Sense Cytosolic DNA

The cyclic GMP-AMP (cGAMP) synthase (cGAS) is a key DNA sensor that initiates STING-dependent signaling to produce type I interferons through synthesizing the secondary messenger 2'3'-cGAMP. In this study, we confirm previous studies showing that cGAS is located both in the cytoplasm and in the nucleus. Nuclear accumulation is observed when leptomycin B is used to block the exportin, CRM1 protein. As a result, leptomycin B impairs the production of interferons in response to DNA stimulation. We further identify a functional nuclear export signal (NES) in cGAS, 169LEKLKL174. Mutating this NES leads to the sequestration of cGAS within the nucleus and the loss of interferon response to cytosolic DNA treatment, and it further determines the key amino acid to L172. Collectively, our data demonstrate that the cytosolic DNA-sensing function of cGAS depends on its presence within the cytoplasm, which is warranted by a functional NES.

Zanthoxylum zanthoxyloides inhibits lipopolysaccharide- and synthetic hemozoin-induced neuroinflammation in BV-2 microglia: roles of NF-κB transcription factor and NLRP3 inflammasome activation

OBJECTIVES

The effects of a root extract of Zanthoxylum zanthoxyloides on neuroinflammation in BV-2 microglia stimulated with LPS and hemozoin were investigated.

METHODS

ELISA, enzyme immunoassay and Griess assay were used to evaluate levels of cytokines, PGE2 and NO in culture supernatants, respectively. Microglia-mediated neurotoxicity was evaluated using a BV-2 microglia-HT-22 neuron transwell co-culture.

KEY FINDINGS

Treatment with Z. zanthoxyloides caused reduced elevated levels of TNFα, IL-6, IL-1β, NO and PGE2, while increasing the levels of IL-10. In addition, there were reduced levels of iNOS and COX-2 proteins. This was accompanied by a prevention of microglia-mediated damage to HT-22 mouse hippocampal neurons. Z. zanthoxyloides reduced elevated levels of phospho-IκB and phospho-p65, while preventing degradation of IκB protein and DNA binding of p65. Further mechanistic studies revealed that Z. zanthoxyloides reduced the levels of pro-IL-1β and IL-1β in hemozoin-activated BV-2 microglia. This was accompanied by a reduction in caspase-1 activity and NLRP3 protein expression. Bioassay-guided fractionation resulted in the isolation of skimmianine as an anti-inflammatory compound in Z. zanthoxyloides.

CONCLUSION

This is the first report showing the inhibition of neuroinflammation in LPS- and hemozoin-activated BV-2 microglia by the root extract of Z. zanthoxyloides by targeting the activation of both NF-κB and NLRP3 inflammasome.

Cyclic helix B peptide alleviates sepsis-induced acute lung injury by downregulating NLRP3 inflammasome activation in alveolar macrophages

Acute lung injury (ALI) exhibits high clinical morbidity and mortality rates. Our previous study has indicated that the novel proteolysis-resistant cyclic helix B peptide (CHBP) exerts an anti-inflammatory effect in mice with AKI. In the present study, we evaluated the effect of CHBP in an in vivo sepsis-induced ALI model and in vitro using lipopolysaccharide (LPS) and ATP stimulated bone marrow-derived macrophages (BMDMs). For in vivo experiments, mice were randomly divided into three groups: 1) sham; 2) LPS; and 3) LPS + CHBP (n = 6). All relevant data were collected after 18 h. Following CHBP treatment, the lung function of the mice was significantly improved compared to the LPS group. CHBP administration inhibited interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α production at both the protein and mRNA levels. Additionally, following CHBP treatment, the population of pulmonary macrophages decreased. Simultaneously, the proportion of caspase-1-activated alveolar macrophages was also decreased after CHBP treatment. The protein levels of NLRP3 and cleaved caspase-1 were attenuated in the lung tissue following CHBP treatment. In in vitro experiments, CHBP treatment decreased NLRP3 inflammasome expression and downstream IL-1β secretion, consistent with the in vivo results. In addition, CHBP reversed nuclear factor (NF)-κB and I-κB phosphorylation with a significant dose-dependent effect. Therefore, these findings suggest the potential of CHBP as a therapeutic agent in sepsis-induced ALI owing to inhibition of the NLRP3 inflammasome via the NF-κB pathway in macrophages.

The microbiome and cytosolic innate immune receptors

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

Pattern Recognition Receptor-reactivity Screening of Liver Transplant Patients: Potential for Personalized and Precise Organ Matching to Reduce Risks of Ischemia-reperfusion Injury

OBJECTIVE AND BACKGROUND

Pattern recognition receptors (PRRs) on immune and parenchymal cells can detect danger-associated molecular patterns (DAMPs) released from cells damaged during ischemia-reperfusion injury (IRI), in heart attack or stroke settings, but also as an unavoidable consequence of solid organ transplantation. Despite IRI being a significant clinical problem across all solid organ transplants, there are limited therapeutics and patient-specific diagnostics currently available.

METHODS

We screened portal blood samples obtained from 67 human liver transplant recipients both pre- [portal vein (PV) sample] and post-(liver flush; LF) reperfusion for their ability to activate a panel of PRRs, and analyzed this reactivity in relation to biopsy-proven IRI.

RESULTS

PV samples from IRI+ orthotopic liver transplantation (OLT) patients (n = 35) decreased activation of hTLR4- and hTLR9-transfected cells, whereas PV from IRI- patients (n = 32) primarily increased hTLR7 and hNOD2 activation. LF samples from OLT-IRI patients significantly increased activation of hTLR4 and hTLR9 over IRI- LF. In addition, the change from baseline reactivity to hTLR4/9/NOD2 was significantly higher in IRI+ than IRI- OLT patients.

CONCLUSIONS

These results demonstrate that TLR4/7/9 and NOD2 are involved in either promoting or attenuating hepatic IRI, and suggest a diagnostic screening of portal blood for reactivity to these PRRs might prove useful for prediction and/or therapeutic intervention in OLT patients before transplantation.

Metformin ameliorates the NLPP3 inflammasome mediated pyroptosis by inhibiting the expression of NEK7 in diabetic periodontitis

OBJECTIVES

To investigate the underlying mechanism between diabetic periodontitis and NLR family pyrin domain containing 3 (NLRP3) inflammasome associated pyroptosis.

DESIGN

Experimental models of diabetes-associated periodontitis were implemented in db/db mice. We detected NLRP3 inflammasome related cytokines and gasdermin D (GSDMD) both in vitro and in vivo. We performed bioinformatics predictions based on microarray analysis using bone marrow derived macrophages (BMDMs).

RESULTS

Diabetes-associated periodontitis mice exhibited the worst fasting glucose and alveolar bone destruction. GSDMD positive cells and NLRP3 inflammasome expression were augmented in gingival tissue, which were partly reversed by metformin. In vitro data suggested NLRP3 inflammasomes stimuli induced cell pyroptotic death and deletion of NLRP3 decreased GSDMD expression. We found a profile of differential lncRNAs expression and three co-expressed lncRNAs of nlrp3 and gsdmd in BMDMs.

CONCLUSIONS

Our data show that NLRP3 mediated pyroptosis has a significant role in diabetes-associated periodontitis. The pyroptotic cell death may be the pivot reason of the deteriorated inflammation in this disease, which is ameliorated by metformin treatment. Moreover, the role of both NLRP3 and GSDMD may be regulated by lncRNA_1810058I24Rik, lncRNA_Gm12474 and lncRNA_Gm41514.

Tripartite motif 31 alleviates IL-1ß secretion via promoting the ubiquitination of pyrin domain domains-containing protein 3 in human periodontal ligament fibroblasts

Apical periodontitis (AP) is an inflammatory disease caused by bacteria infection and is regarded as a common disease in the world. In the progression of AP, the function of nucleotide-binding oligomerization, leucine-rich repeat and pyrin domain domains-containing protein 3 (NLRP3) inflammasome has been revealed. Although tripartite motif 31 (TRIM31) has been suggested to regulate many chronic inflammations by mediating NLRP3 inflammasome, such mechanism in AP remains unclear. In this study, co-treatment of human periodontal ligament fibroblasts (HPDLFs) with lipopolysaccharides (LPS) and adenosine triphosphate (ATP) were conducted to establish AP cell model. ELISA assay was used to measure the concentration of secretive interleukin 1 beta (IL-1β). In addition, the expression levels of NLRP3 after TRIM31 up- or down-regulation were detected by real-time PCR and western blot. Immunoprecipitation was used to explore the interaction between TRIM31 and NLRP3. We found that co-treatment with LPS and ATP increased the secretion of IL-1β and expression of NLRP3 in HPDLFs, while TRIM31 overexpression could reverse these effects caused by LPS and ATP. Furthermore, the interaction between TRIM31 and NLRP3 was observed, and TRIM31 was found to promote the ubiquitination of NLRP3. TRIM31 may alleviate IL-1ß secretion caused by LPS and ATP via promoting the ubiquitination of NLRP3 and may exert an influence on the development of AP.

Consensus guidelines for the definition, detection and interpretation of immunogenic cell death

Cells succumbing to stress via regulated cell death (RCD) can initiate an adaptive immune response associated with immunological memory, provided they display sufficient antigenicity and adjuvanticity. Moreover, multiple intracellular and microenvironmental features determine the propensity of RCD to drive adaptive immunity. Here, we provide an updated operational definition of immunogenic cell death (ICD), discuss the key factors that dictate the ability of dying cells to drive an adaptive immune response, summarize experimental assays that are currently available for the assessment of ICD in vitro and in vivo, and formulate guidelines for their interpretation.

Tle1 attenuates hepatic ischemia/reperfusion injury by suppressing NOD2/NF-κB signaling

Liver damage induced by ischemia/reperfusion (I/R) remains a primary issue in multiple hepatic surgeries. Innate immune-mediated inflammatory responses during the reperfusion stage aggravate the injury. Nevertheless, the detailed mechanism of hepatic I/R has not been fully clarified yet. Our research focuses on the role of Transducin-like enhancer of split-1 (Tle1) in the liver I/R injury and the relation between Tle1 and Nucleotide-binding oligomerization domain 2 (NOD2). To answer these questions, we constructed mouse models of I/R and cell models of hypoxia/reoxygenation (H/R). We found decreased Tle1 accompanied by increased NOD2 during reperfusion. Mice pro-injected with Tle1-siRNA emerged aggravated liver dysfunction. Repression of Tle1 had a significant impact on NOD2 and downstream NF-κB signaling in vitro. However, alteration of NOD2 failed to affect the expression of Tle1. To conclude, our study demonstrates that Tle1 shelters the liver from I/R injury through suppression of NOD2-dependent NF-κB activation and subsequent inflammatory responses.

Ligustrazine ameliorates acute kidney injury through downregulation of NOD2‑mediated inflammation

Ligustrazine has been used to alleviate clinical acute kidney injury (AKI); however, the underlying molecular mechanisms are poorly understood. In order to further elucidate the molecular mechanism underlying its occurrence, the role of nucleotide-binding oligomerization domain-containing 2 (NOD2) in AKI was investigated in the present study, and the results indicated that ligustrazine exerts an important protective effect against AKI in vivo by inhibiting the upregulation of NOD2 expression and reducing apoptosis of kidney cells following ischemia/reperfusion injury in rat models. Furthermore, the inhibitory role of ligustrazine on the upregulation of NOD2 and apoptosis of kidney cells induced by CoCl₂ and oxygen and glucose deprivation followed by reoxygenation was investigated in in vitro experiments. The effect of ligustrazine on NOD2 downregulation was partially blocked by inhibiting autophagy. To the best of our knowledge, the results of the present study are the first to provide evidence that ligustrazine can inhibit NOD2-mediated inflammation to protect against renal injury, which may be in part attributed to the induction of autophagy. These findings may help design and develop new approaches and therapeutic strategies for AKI to prevent the deterioration of renal function.

Salt-Responsive Metabolite, β-Hydroxybutyrate, Attenuates Hypertension

Dietary salt reduction and exercise are lifestyle modifications for salt-sensitive hypertensives. While exercise has prominent metabolic effects, salt has an adverse effect on metabolic syndrome, of which hypertension is a hallmark. We hypothesized that dietary salt impacts metabolism in a salt-sensitive model of hypertension. An untargeted metabolomic approach demonstrates lower circulating levels of the ketone body, beta-hydroxybutyrate (βOHB), in high salt-fed hypertensive rats. Despite the high salt intake, specific rescue of βOHB levels by nutritional supplementation of its precursor, 1,3-butanediol, attenuates hypertension and protects kidney function. This beneficial effect of βOHB was likely independent of gut-microbiotal and Th17-mediated effects of salt and instead facilitated by βOHB inhibiting the renal Nlrp3 inflammasome. The juxtaposed effects of dietary salt and exercise on salt-sensitive hypertension, which decrease and increase βOHB respectively, indicate that nutritional supplementation of a precursor of βOHB provides a similar benefit to salt-sensitive hypertension as exercise.

Chakraborty et al. report a link between dietary salt, a ketone, and experimental hypertension. Intake of a high salt diet lowers the ketone body betahydroxybutyrate (βOHB), produced by the liver, which functions to prevent Nlrp3-mediated kidney inflammation. Rescuing βOHB by nutritional supplementation of its precursor attenuates hypertension.

Pattern recognition receptors as potential drug targets in inflammatory disorders

Pattern recognition receptors (PRRs) are a key part of the innate immune system, the body's first line of defense against infection and tissue damage. This superfamily of receptors including Toll-like receptors (TLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs) and RIG-like receptors (RLRs) are responsible for initiation of the inflammatory response by their recognition of molecular patterns present in invading microorganisms (such as bacteria, viruses or fungi) during infection or in molecules released following tissue damage during acute or chronic disease states (such as sepsis or arthritis). These receptors are widely expressed and located on the cell surface, in intracellular compartments or in the cytoplasm can detect a single or subset of molecules including lipoproteins, carbohydrates or nucleic acids. In response, they initiate an intracellular signaling cascade that culminates in the synthesis and release of cytokines, chemokines and vasoactive molecules. These steps are necessary to maintain tissue homeostasis and remove potentially dangerous pathogens. However, during extreme or acute responses or during chronic disease, this can be damaging and even lead to death. Therefore, it is thought that targeting such receptors may offer a therapeutic approach in chronic inflammatory diseases or in cases of acute infection leading to sepsis. Herein, the current knowledge on the molecular biology of PRRs is reviewed along with their association with inflammatory and infectious diseases. Finally, the testing of therapeutic compounds and their future merit as targets is discussed.

PKR-dependent cytosolic cGAS foci are necessary for intracellular DNA sensing

Cyclic GMP-AMP synthase (cGAS) is a major sensor of cytosolic DNA from invading pathogens and damaged cellular organelles. Activation of cGAS promotes liquid-like phase separation and formation of membraneless cytoplasmic structures. Here, we found that cGAS bound G3BP1, a double-stranded nucleic acid helicase involved in the formation of stress granules. Loss of G3BP1 blocked subcellular cGAS condensation and suppressed the interferon response to intracellular DNA and DNA virus particles in cells. Furthermore, an RNA-dependent association with PKR promoted G3BP1 foci formation and cGAS-dependent interferon responses. Together, these results indicate that PKR promotes the formation of G3BP1-dependent, membraneless cytoplasmic structures necessary for the DNA-sensing function of cGAS in human cells. These data suggest that there is a previously unappreciated link between nucleic acid sensing pathways, which requires the formation of specialized subcellular structures.

Post-translational Control of Innate Immune Signaling Pathways by Herpesviruses

Herpesviruses constitute a large family of disease-causing DNA viruses. Each herpesvirus strain is capable of infecting particular organisms with a specific cell tropism. Upon infection, pattern recognition receptors (PRRs) recognize conserved viral features to trigger signaling cascades that culminate in the production of interferons and pro-inflammatory cytokines. To invoke a proper immune response while avoiding collateral tissue damage, signaling proteins involved in these cascades are tightly regulated by post-translational modifications (PTMs). Herpesviruses have developed strategies to subvert innate immune signaling pathways in order to ensure efficient viral replication and achieve persistent infection. The ability of these viruses to control the proteins involved in these signaling cascades post-translationally, either directly via virus-encoded enzymes or indirectly through the deregulation of cellular enzymes, has been widely reported. This ability provides herpesviruses with a powerful tool to shut off or restrict host antiviral and inflammatory responses. In this review, we highlight recent findings on the herpesvirus-mediated post-translational control along PRR-mediated signaling pathways.

Heat Shock Proteins and Inflammasomes

Heat shock proteins (HSP) regulate inflammation in many physiological contexts. However, inflammation is a broad process, involving numerous cytokines produced by different molecular pathways with multiple functions. In this review, we focused on the particular role of HSP on the inflammasomes intracellular platforms activated by danger signals and that enable activation of inflammatory caspases, mainly caspase-1, leading to the production of the pro-inflammatory cytokine IL-1β. Interestingly, some members of the HSP family favor inflammasomes activation whereas others inhibit it, suggesting that HSP modulators for therapeutic purposes, must be carefully chosen.

Induction of Neuroinflammation and Neurotoxicity by Synthetic Hemozoin

Hemozoin produced by Plasmodium falciparum during malaria infection has been linked to the neurological dysfunction in cerebral malaria. In this study, we determined whether a synthetic form of hemozoin (sHZ) produces neuroinflammation and neurotoxicity in cellular models. Incubation of BV-2 microglia with sHZ (200 and 400 µg/ml) induced significant elevation in the levels of TNFα, IL-6, IL-1β, NO/iNOS, phospho-p65, accompanied by an increase in DNA binding of NF-κB. Treatment of BV-2 microglia with sHZ increased protein levels of NLRP3 with accompanying increase in caspase-1 activity. In the presence of NF-κB inhibitor BAY11-7082 (10 µM), there was attenuation of sHZ-induced release of pro-inflammatory cytokines, NO/iNOS. In addition, increase in caspase-1/NLRP3 inflammasome activation was blocked by BAY11-7082. Pre-treatment with BAY11-7082 also reduced both phosphorylation and DNA binding of the p65 sub-unit. The NLRP3 inhibitor CRID3 (100 µM) did not prevent sHZ-induced release of TNFα and IL-6. However, production of IL-1β, NO/iNOS as well as caspase-1/NLRP3 activity was significantly reduced in the presence of CRID3. Incubation of differentiated neural progenitor (ReNcell VM) cells with sHZ resulted in a reduction in cell viability, accompanied by significant generation of cellular ROS and increased activity of caspase-6, while sHZ-induced neurotoxicity was prevented by N-acetylcysteine and Z-VEID-FMK. Taken together, this study shows that the synthetic form of hemozoin induces neuroinflammation through the activation of NF-κB and NLRP3 inflammasome. It is also proposed that sHZ induces ROS- and caspase-6-mediated neurotoxicity. These results have thrown more light on the actions of malarial hemozoin in the neurobiology of cerebral malaria.

The Role of Neuronal NLRP1 Inflammasome in Alzheimer's Disease: Bringing Neurons into the Neuroinflammation Game

The innate immune system and inflammatory response in the brain have critical impacts on the pathogenesis of many neurodegenerative diseases including Alzheimer's disease (AD). In the central nervous system (CNS), the innate immune response is primarily mediated by microglia. However, non-glial cells such as neurons could also partake in inflammatory response independently through inflammasome signalling. The NLR family pyrin domain-containing 1 (NLRP1) inflammasome in the CNS is primarily expressed by pyramidal neurons and oligodendrocytes. NLRP1 is activated in response to amyloid-β (Aβ) aggregates, and its activation subsequently cleaves caspase-1 into its active subunits. The activated caspase-1 proteolytically processes interleukin-1β (IL-1β) and interleukin-18 (IL-18) into maturation whilst co-ordinately triggers caspase-6 which is responsible for apoptosis and axonal degeneration. In addition, caspase-1 activation induces pyroptosis, an inflammatory form of programmed cell death. Studies in murine AD models indicate that the Nlrp1 inflammasome is indeed upregulated in AD and neuronal death is observed leading to cognitive decline. However, the mechanism of NLRP1 inflammasome activation in AD is particularly elusive, given its structural and functional complexities. In this review, we examine the implications of the human NLRP1 inflammasome and its signalling pathways in driving neuroinflammation in AD.