Role of LL-37 in Oral Bacterial DNA Accumulation in Dental Plaque

Dental plaque, a highly structured polymicrobial biofilm, persistently forms in the oral cavity and is a common problem affecting oral health. The role of oral defense factors in either collaborating or disrupting host-microbiome interactions remains insufficiently elucidated. This study aims to explore the role of LL-37, a critical antimicrobial peptide in the oral cavity, in dental plaque formation. Through immunostaining dental plaque specimens, we observed that LL-37 and DNA colocalized in the samples, appearing as condensed clusters. In vitro experiments revealed that LL-37 binds rapidly to oral bacterial DNA, forming high molecular weight, DNase-resistant complexes. This interaction results in LL-37 losing its inherent antibacterial activity. Further, upon the addition of LL-37, we observed a visible increase in the precipitation of bacterial DNA. We also discovered a significant correlation between the levels of the DNA-LL-37 complex and LL-37 within dental plaque specimens, demonstrating the ubiquity of the complex within the biofilm. By using immunostaining on dental plaque specimens, we could determine that the DNA-LL-37 complex was present as condensed clusters and small bacterial cell-like structures. This suggests that LL-37 immediately associates with the released bacterial DNA to form complexes that subsequently diffuse. We also demonstrated that the complexes exhibited similar Toll-like receptor 9-stimulating activities across different bacterial species, including Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia, and Streptococcus salivarius. However, these complexes prompted dissimilar activities, such as the production of IL-1β in monocytic cells via both NLRP3 pathway-dependent and pathway-independent mechanisms. This study, therefore, reveals the adverse role of LL-37 in dental plaque, where it binds bacterial DNA to form complexes that may precipitate to behave like an extracellular matrix. Furthermore, the unveiled stimulating properties and species-dependent activities of the oral bacterial DNA-LL-37 complexes enrich our understanding of dental plaque pathogenicity and periodontal innate immune responses.

Pro-Inflammatory of PRDM1/SIRT2/NLRP3 Axis in Monosodium Urate-Induced Acute Gouty Arthritis

PR domain-containing 1 with zinc finger domain (PRDM1) has been reported as a promoter of inflammation, which is a critical process involved in the pathogenesis of acute gouty arthritis. Herein, we sought to ascertain the function of PRDM1 in the development of acute gouty arthritis and related mechanisms. At first, peripheral blood-derived monocytes from patients with acute gouty arthritis and healthy individuals were collected as experimental samples. Then, macrophages were induced from monocytes using phorbol myristate acetate (PMA). The expression patterns of PRDM1, sirtuin 2 (SIRT2), and NLR family, pyrin domain-containing 3 (NLRP3) were characterized by RT-qPCR and Western blot assay. PMA-induced macrophages were stimulated by monosodium urate (MSU) for in vitro experimentation. Meanwhile, a murine model of MSU-induced acute gouty arthritis was established for in vivo validation. PRDM1 was highly expressed while SIRT2 poorly expressed in patients with acute gouty arthritis. Loss of PRDM1 could reduce NLRP3 inflammasome and mature IL-1β levels and downregulate inflammatory cytokines in macrophages, which contributed to protection against acute gouty arthritis. Furthermore, results showed that PRDM1 could inhibit SIRT2 expression via binding to the deacetylase SIRT2 promoter. Finally, the in vivo experiments demonstrated that PRDM1 increased NLRP3 inflammasome and mature IL-1β through transcriptional inhibition of SIRT2, whereby aggravating MSU-induced acute gouty arthritis. To sum up, PRDM1 increased NLRP3 inflammasome through inhibiting SIRT2, consequently aggravating MSU-induced acute gouty arthritis.

Identification and expression profile of novel STAND gene Nwd2 in the mouse central nervous system

In the central nervous system (CNS), neurons need synaptic neurotransmitter release and cellular response for various cellular stress or environmental stimuli. To achieve these highly orchestrated cellular processes, neurons should drive the molecular mechanisms that govern and integrate complex signaling pathways. The signal transduction ATPases with numerous domains (STAND) family of proteins has been shown to play essential roles in diverse signal transduction mechanisms, including apoptosis and innate immunity. However, a comprehensive understanding of STAND genes remains lacking. Previously, we identified the NACHT and WD repeat domain-containing protein 1 (NWD1), a member of STAND family, in the regulation of the assembly of a giant multi-enzyme complex that enables efficient de novo purine biosynthesis during brain development. Here we identified the mouse Nwd2 gene, which is a paralog of Nwd1. A molecular phylogenetic analysis suggested that Nwd1 emerged during the early evolution of the animal kingdom, and that Nwd2 diverged in the process of Nwd1 duplication. RT-PCR and in situ hybridization analyses revealed the unique expression profile of Nwd2 in the developing and adult CNS. Unlike Nwd1, Nwd2 expression was primarily confined to neurons in the medial habenular nucleus, an essential modulating center for diverse psychological states, such as fear, anxiety, and drug addiction. In the adult brain, Nwd2 expression, albeit at a lower level, was also observed in some neuronal populations in the piriform cortex, hippocampus, and substantia nigra pars compacta. NWD2 might play a unique role in the signal transduction required for specific neuronal circuits, especially for cholinergic neurons in the habenula.

Effect of Er Miao San on peritoneal macrophage polarisation through the miRNA-33/NLRP3 signalling pathway in a rat model of adjuvant arthritis

CONTEXT

Er Miao San (EMS) is a formulation that contains Atractylodis Rhizoma and Phellodendri Cortex in 1:1 ratio, and is commonly used to treat rheumatoid arthritis (RA) and other inflammatory diseases.

OBJECTIVE

We investigated the mechanism of action and effects of EMS on peritoneal macrophage differentiation in a rat model of adjuvant arthritis (AA).

MATERIALS AND METHODS

EMS (3, 1.5 and 0.75 g/kg; once daily) and methotrexate (0.5 mg/kg; once every 3 days) were administered orally from days 21 to 35 after immunisation. Paw swelling and arthritis index were measured; pathological changes in the ankle joint were observed using x-ray and haematoxylin eosin staining. The ratio of CD86/CD206 in macrophages was detected by flow cytometry. Examination of the miRNA-33/NLRP3 signalling pathway was examined by RT-qPCR and western blotting. The levels of cytokines in the serum and cell supernatants were tested by ELISA.

RESULTS

EMS significantly reduced the AA index in rats (from 11.0 to 9.3) and pathological changes in the ankle joint (from 3.8 to 1.4). The ratio of CD86/CD206 was reduced, and polarisation to M1 improved (from 0.9 to 0.6) in macrophages of EMS-treated rats. EMS downregulated the miRNA-33/NLRP3 pathway. Furthermore, EMS treatment increased IL-10 and TGF-β levels in the serum and supernatant of macrophages of AA rats and simultaneously decreased the levels of IL-1β and TNF-α.

DISCUSSION AND CONCLUSIONS

Our results suggest that EMS may reduce macrophage polarisation to the M1 inflammatory phenotype by downregulating the miRNA-33/NLRP3 pathway in AA rats. These findings may provide new insights into the treatment of RA.

Treadmill training attenuates pyroptosis in rats with cerebral ischemia/reperfusion injury

OBJECTIVES

Few studies have investigated the mechanism by which exercise training promotes neural repair during rehabilitation after stroke. In this study, we evaluated the neuroprotective effects of exercise training and pyroptosis-associated factors in the penumbra and elucidated the possible mechanisms.

MATERIALS AND METHODS

Neurological deficits, body weight, and the infarct size were evaluated, and haematoxylin-eosin (HE) staining was performed. Western blotting and immunofluorescence staining were used to assess NOD-like receptor family pyrin domain-containing 3 (NLRP3) and caspase-1 levels. Interleukin-1β (IL-1β) and interleukin-18 (IL-18) levels were assessed by enzyme-linked immunosorbent assay (ELISA). B-cell lymphoma 2 (bcl-2) and bax protein levels were measured by Western blotting, and terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining was used to evaluate apoptotic cells.

RESULTS

Exercise training decreased neurological deficits and the infarct size in MCAO rats Moreover, NLRP3 inflammasome-associated protein levels in the peri-infarct cortex were decreased by exercise training. Exercise training decreased the serum concentrations of IL1β and IL18, upregulated bcl-2, downregulated bax, and reduced the TUNEL index.

CONCLUSION

Exercise training suppresses NLRP3 inflammasome activity and inhibits pyroptosis to protect against cerebral ischaemic injury. Exercise training can also suppress apoptosis, which may be the target of exercise-induced neuroprotection, thereby reducing brain injury.

Receptor for Advanced Glycation End-Products Promotes Activation of Alveolar Macrophages through the NLRP3 Inflammasome/TXNIP Axis in Acute Lung Injury

The roles of thioredoxin-interacting protein (TXNIP) and receptor for advanced glycation end-products (RAGE)-dependent mechanisms of NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome-driven macrophage activation during acute lung injury are underinvestigated. Cultured THP-1 macrophages were treated with a RAGE agonist (S100A12), with or without a RAGE antagonist; cytokine release and intracytoplasmic production of reactive oxygen species (ROS) were assessed in response to small interfering RNA knockdowns of TXNIP and NLRP3. Lung expressions of TXNIP and NLRP3 and alveolar levels of IL-1β and S100A12 were measured in mice after acid-induced lung injury, with or without administration of RAGE inhibitors. Alveolar macrophages from patients with acute respiratory distress syndrome and from mechanically ventilated controls were analyzed using fluorescence-activated cell sorting. In vitro, RAGE promoted cytokine release and ROS production in macrophages and upregulated NLRP3 and TXNIP mRNA expression in response to S100A12. TXNIP inhibition downregulated NLRP3 gene expression and RAGE-mediated release of IL-1β by macrophages in vitro. In vivo, RAGE, NLRP3 and TXNIP lung expressions were upregulated during experimental acute lung injury, a phenomenon being reversed by RAGE inhibition. The numbers of cells expressing RAGE, NLRP3 and TXNIP among a specific subpopulation of CD16+CD14+CD206- (“pro-inflammatory”) alveolar macrophages were higher in patients with lung injury. This study provides a novel proof-of-concept of complex RAGE–TXNIP–NLRP3 interactions during macrophage activation in acute lung injury.

Understanding the Role of Inflammasomes in Rheumatoid Arthritis

Inflammasomes are the molecular pathways that activate upon conditions of infection or stress and trigger the activation and maturation of inflammatory cytokines. Immune reactions in conjugation with inflammatory processes play a pivotal role in developing innumerable diseases. An over reactive immune system fabricates many allergic and hypersensitive reactions in response to autoantibodies activated against modified self-epitopes and similar molecules. Rheumatoid arthritis (RA) is a complex autoimmune inflammatory disorder commencing with inflammation in small joints like hands, knees, and wrist eventually entrapping larger joints such as spine. The formation of autoantibodies called rheumatoid factor (RF) and citrullinated proteins against immunoglobulin G symbolizes autoimmune nature of the disease. The presence of autoantibodies embarks principal diagnostic hallmark of the disease. With the advancement of technology, the therapeutic approach is also advancing. A new era of molecules, namely inflammasomes, are activated upon infection or in response to stress and trigger the activation of various proinflammatory cytokines such interleukins which engage in the defense mechanism of the innate immunity. Robust linking among the activity of dysregulated inflammasomes and the heritable acquired inflammatory diseases and disorders emphasizes the significance of this pathway in altering the immune responses. The current review highlights the functioning of inflammasomes and their possible role in disease dysregulation.

The APC10 subunit of the anaphase-promoting complex/cyclosome orchestrates NLRP3 inflammasome activation during the cell cycle

The activation of the NLRP3 inflammasome plays a crucial role in the innate immune response. During cell division, NLRP3 inflammasome activation must be strictly controlled. In this study, we discover that the anaphase-promoting complex subunit 10 (APC10), a substrate recognition protein of the anaphase-promoting complex/cyclosome (APC/C), is a critical mediator of NLRP3 inflammasome activation. During interphase, APC10 interacts with NLRP3 to promote NLRP3 inflammasome activation, whereas during mitosis, APC10 disassociates from the NLRP3 inflammasome to repress inflammatory responses. This study reveals a distinct mechanism by which APC10 serves as a switch for NLRP3 inflammasome activation during the cell cycle.

Piezo1 activates the NLRP3 inflammasome in nucleus pulposus cell-mediated by Ca2+/NF-κB pathway

Studying and understanding the mechanism of inflammation in nucleus pulposus is the key to understand and prevent intervertebral disc degeneration. We propose a model of mechanical sensitive ion channel Piezo1 mediated inflammation of nucleus pulposus cells. Piezo1 can up-regulate the level of interleukin-1β (IL-1β) in nucleus pulposus cells once it is activated. It is suggested that Piezo1 may mediate inflammation by activating Nod-like receptor protein 3 (NLRP3) inflammasome to accelerate the production and maturation of IL-1β. The primary objective of this study was to explore whether Piezo1 activates NLRP3 inflammasome in nucleus pulposus cells. Piezo1 sensitization was induced by mechanical stretch following which we analyzed the priming and assembly of NLRP3 inflammasome and also studied if the downstream Ca²⁺/NF-κB pathway mediated this activation in nucleus pulposus cells. The expression of Piezo1 and NLRP3 inflammasome increased in a time-dependent manner upon mechanical stretch. Piezo1 activation promoted NLRP3 inflammasome assembly, which was demonstrated by the upregulation of caspase-1 activation and IL-1β production. Transfection of Piezo1-siRNA reversed this process. The inhibition of Ca²⁺/NF-κB pathway reduced Piezo1-dependent activation of NLRP3 inflammasome. Thus, we propose that activation of NLRP3 inflammasome in nucleus pulposus cells mediated by Piezo1 through the Ca²⁺/NF-κB pathway is a novel pathogenesis for the progress of intervertebral disc degeneration. As per our knowledge this is the first study which has provided evidence linking Piezo1-mediated inflammation in nucleus pulposus cells with the production of NLRP3 inflammasome.

The Impact of Acute Ingestion of a Ketone Monoester Drink on LPS-Stimulated NLRP3 Activation in Humans with Obesity

Activation of the NOD-like receptor pyrin-domain containing 3 (NLRP3) inflammasome is associated with chronic low-grade inflammation in metabolic diseases such as obesity. Mechanistic studies have shown that β-hydroxybutyrate (OHB) attenuates activation of NLRP3, but human data are limited. In a randomized, double-blind, placebo-controlled crossover trial (n = 11) we tested the hypothesis that acutely raising β-OHB by ingestion of exogenous ketones would attenuate NLRP3 activation in humans with obesity. Blood was sampled before and 30 min post-ingestion of a ketone monoester drink ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate, 482 mg/kg body mass) or placebo. A 75 g oral glucose load was then ingested, and a third blood sample was obtained 60 min following glucose ingestion. NLRP3 activation was quantified by assessing monocyte caspase-1 activation and interleukin (IL)-1β secretion in ex vivo lipopolysaccharide (LPS)-stimulated whole-blood cultures. LPS-stimulated caspase-1 activation increased following glucose ingestion (main effect of time; p = 0.032), with no differences between conditions. IL-1β secretion did not differ between conditions but was lower 60 min post-glucose ingestion compared to the fasting baseline (main effect of time, p = 0.014). Plasma IL-1β was detectable in ~80% of samples and showed a decrease from fasting baseline to 60 min in the ketone condition only (condition × time interaction, p = 0.01). In individuals with obesity, an excursion into hyperglycemia following ingestion of a glucose load augments LPS-induced activation of caspase-1 in monocytes with no apparent impact of raising circulating β-OHB concentration via ingestion of exogenous ketones. Exogenous ketone supplementation may impact plasma IL-1β, but these findings require confirmation in studies with larger sample sizes.

Gain-of-function CEBPE mutation causes noncanonical autoinflammatory inflammasomopathy

BACKGROUND

CCAAT enhancer-binding protein epsilon (C/EBPε) is a transcription factor involved in late myeloid lineage differentiation and cellular function. The only previously known disorder linked to C/EBPε is autosomal recessive neutrophil-specific granule deficiency leading to severely impaired neutrophil function and early mortality.

OBJECTIVE

The aim of this study was to molecularly characterize the effects of C/EBPε transcription factor Arg219His mutation identified in a Finnish family with previously genetically uncharacterized autoinflammatory and immunodeficiency syndrome.

METHODS

Genetic analysis, proteomics, genome-wide transcriptional profiling by means of RNA-sequencing, chromatin immunoprecipitation (ChIP) sequencing, and assessment of the inflammasome function of primary macrophages were performed.

RESULTS

Studies revealed a novel mechanism of genome-wide gain-of-function that dysregulated transcription of 464 genes. Mechanisms involved dysregulated noncanonical inflammasome activation caused by decreased association with transcriptional repressors, leading to increased chromatin occupancy and considerable changes in transcriptional activity, including increased expression of NLR family, pyrin domain-containing 3 protein (NLRP3) and constitutively expressed caspase-5 in macrophages.

CONCLUSION

We describe a novel autoinflammatory disease with defective neutrophil function caused by a homozygous Arg219His mutation in the transcription factor C/EBPε. Mutated C/EBPε acts as a regulator of both the inflammasome and interferome, and the Arg219His mutation causes the first human monogenic neomorphic and noncanonical inflammasomopathy/immunodeficiency. The mechanism, including widely dysregulated transcription, is likely not unique for C/EBPε. Similar multiomics approaches should also be used in studying other transcription factor-associated diseases.

Molecular cloning and functional characterisation of NLRX1 in grass carp (Ctenopharyngodon idella)

The nucleotide-binding domain and leucine-rich-repeat-containing (NLR) proteins regulate innate immunity. Although the positive regulatory impact of NLRs is clear, their inhibitory roles are not well defined. In the present study, the NLR family gene NLRX1 from grass carp (Ctenopharyngodon idella) was cloned and characterised. NLRX1 was widely expressed in all tissues examined, albeit at varying levels. After exposure to the grass carp reovirus (GCRV), NLRX1 mRNA expression levels were altered in immune organs, and dramatically altered in liver. Subcellular localisation indicated that NLRX1 protein co-localised with the mitochondria in the transfected cells. Additionally, the bimolecular fluorescence complementation (BiFC) system was introduced to detect the interaction between tumour necrosis factor (TNF) receptor associated factor 6 (TRAF6) and NLRX1. Moreover, deficient of NLRX1 in CIK cells with small interference RNA (siRNA) promoted polyinosinic:polycytidylic acid (poly (I:C))-induced IFN-related genes production, including IRF3, IRF7, and IFN-I, which reveals that NLRX1 is a negative regulator of IFN. Taken together, our results demonstrate that NLRX1 gene plays an important role in innate immune regulation and provide new insights into understanding the functional characteristics of the NLRX1 in teleosts.

Effect of interleukin-31 on septic shock through regulating inflammasomes and interleukin-1β

Sepsis with severe systemic inflammation remains a great challenge for the intensive care unit in clinics. Although biomarkers have been identified to diagnose, monitor and predict these syndromes, novel therapeutic approaches are required for the amelioration of symptoms of sepsis and septic shock. The present study demonstrated that interleukin (IL)-31 was able reduce the mortality rate of lipopolysaccharide (LPS)-induced sepsis with the reduction of inflammatory cytokines in the sera. IL-31 also inhibited IL-1β production in the peritoneal lavage fluid in LPS-induced or cecal ligation and puncture-induced sepsis. The in vitro mechanism responsible for IL-31 regulation on peritoneal IL-1β activation following LPS challenge was explored. It was demonstrated that IL-1β secretion was suppressed by IL-31 treatment from LPS-challenged peritoneal macrophages following adenosine triphosphate stimulation, which is an activator of NLR family, pyrin domain-containing 3 (NLRP3). Furthermore, IL-31 inhibited the expression of NLRP3 at the transcriptional level. In human THP-1 cells, anti-IL-31/anti-IL-31 receptor (R) neutralizing antibody enhanced NLRP3 expression as well as IL-1β activation, suggesting a role of the IL-31-IL-31R-NLRP3-IL-1β signaling axis in the physiological status of sepsis. On the other hand, IL-31 displayed a negative effect on the NLRP1 inflammasome, but not on NLRP3 on the LPS-primed human peripheral blood monocytes, resulting in reduction of the inflammatory cytokine, tumor necrosis factor (TNF)-α, in the supernatant. Taken together, the present data implied that T helper 2-type cytokine, IL-31, may be a promising therapeutic option for treatment of sepsis and septic shock in clinics.

Expression Levels of Proinflammatory Cytokines and NLRP3 Inflammasome in an Experimental Model of Oxazolone-induced Colitis

IL-1β and IL-17A are two cytokines with strong proinflammatory activities and are now known to be involved in a number of chronic inflammatory disorders. High-mobility group box 1 (HMGB1) is a nuclear protein regulating the expression of these proinflammatory cytokines. The NLRP3 inflammasome promotes the maturation of the IL-1β and its activation has been shown as a critical mechanism in the pathogenesis of inflammatory bowel disease (IBD). However, underlying mechanisms to modulate their production in IBD are still unclear. The aim of this study was to investigate the expression levels of mRNA for the NLRP3 inflammasome, HMGB1 and proinflammatory cytokines, IL-1β, IL-17A in the inflamed colon of rats with experimental oxazolone-induced colitis. Experiments were carried out on male wistar rats. IL-1β, IL-17A, HMGB1 and NLRP3 inflammasome mRNA expression were analyzed by real-time reverse transcriptase-polymerase chain reaction. Our results indicated that the expression levels of IL-1β, IL-17A, NLRP3 and HMGB1 were elevated in the inflamed colon of rats with oxazolone-induced colitis.