Critical roles of NLRP3 inflammasome in IL-1β secretion induced by Corynebacterium pseudotuberculosis in vitro

Inflammasome activation by Gram-positive bacteria: Mechanisms of activation and regulation

The inflammasomes are intracellular multimeric protein complexes consisting of an innate immune sensor, the adapter protein ASC and the inflammatory caspases-1 and/or -11 and are important for the host defense against pathogens. Activaton of the receptor leads to formation of the inflammasomes and subsequent processing and activation of caspase-1 that cleaves the proinflammatory cytokines IL-1β and IL-18. Active caspase-1, and in some instances caspase-11, cleaves gasdermin D that translocates to the cell membrane where it forms pores resulting in the cell death program called pyroptosis. Inflammasomes can detect a range of microbial ligands through direct interaction or indirectly through diverse cellular processes including changes in ion fluxes, production of reactive oxygen species and disruption of various host cell functions. In this review, we will focus on the NLRP3, NLRP6, NLRC4 and AIM2 inflammasomes and how they are activated and regulated during infections with Gram-positive bacteria, including Staphylococcus spp., Streptococcus spp. and Listeria monocytogenes.

Isolation and Molecular Characterization of Corynebacterium pseudotuberculosis: Association with Proinflammatory Cytokines in Caseous Lymphadenitis Pyogranulomas

Corynebacterium pseudotuberculosis (C. pseudotuberculosis) is a causative agent of numerous chronic diseases, including caseous lymphadenitis (CLA) in sheep and goats, which has a zoonotic potential in humans in addition to a poor therapeutic response. In this study, out of 120 collected samples, only 12 (10%) were positive for C. pseudotuberculosis by PCR and by intraperitoneal injection of male Guinea pigs and then characterized for antimicrobial susceptibility and its genetic-relatedness by enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR), which showed 2-4 bands ranging from 100 to 3000 bp that can be clustered into four clusters (C1-C4). Despite the serotype biovar 1 only infecting sheep and goats, ERIC-PCR reveals intra-subtyping variation. Examination of affected LNs and organs revealed marked enlargement with either thick creamy green pus or multiple abscesses of variable sizes with a central caseated core surrounded by dense fibrous capsule. A histopathological examination revealed a central necrotic core surrounded by a peripheral mantle of mononuclear cells and a fibrous capsule. Positive immune expression of nuclear factor kappa B (NF-κB/p65) and interleukin-1β (IL-1β) and negative expression of tumor necrosis factor (TNF) in CLA is the first report to our knowledge. Conclusion: In CLA pyogranulomas, IL1β is a more crucial proinflammatory cytokine than TNF in the regulation of C. pseudotuberculosis infection, which is accompanied by marked NF-κB immunoexpression. Therefore, the NF-κB/p65 signaling pathway is involved in the activation of IL1β, and additional immunohistochemical studies are required to determine the various roles of NF-κB/p65 in the inflammatory response within CLA pyogranulomas to control this pathogen.

Role of HMGB1/TLR4 and IL-1β/IL-1R1 Signaling Pathways in Epilepsy

Epilepsy is a chronic disorder of the nervous system characterized by recurrent seizures. Inflammation is one of the six major causes of epilepsy, and its role in the pathogenesis of epilepsy is gaining increasing attention. Two signaling pathways, the high mobility group box-1 (HMGB1)/toll-like receptor 4 (TLR4) and interleukin-1β (IL-1β)/interleukin-1 receptor 1 (IL-1R1) pathways, have become the focus of research in recent years. These two signaling pathways have potential as biomarkers in the prediction, prognosis, and targeted therapy of epilepsy. This review focuses on the association between epilepsy and the neuroinflammatory responses mediated by these two signaling pathways. We hope to contribute further in-depth studies on the role of HMGB1/TLR4 and IL-1β/IL-1R1 signaling in epileptogenesis and provide insights into the development of specific agents targeting these two pathways.

Cerebral Small Vessel Disease: Neuroimaging Features, Biochemical Markers, Influencing Factors, Pathological Mechanism and Treatment

Cerebral small vessel disease (CSVD) is the most common chronic vascular disease involving the whole brain. Great progress has been made in clinical imaging, pathological mechanism, and treatment of CSVD, but many problems remain. Clarifying the current research dilemmas and future development direction of CSVD can provide new ideas for both basic and clinical research. In this review, the risk factors, biological markers, pathological mechanisms, and the treatment of CSVD will be systematically illustrated to provide the current research status of CSVD. The future development direction of CSVD will be elucidated by summarizing the research difficulties.

Correlation of Serum C-Peptide, Soluble Intercellular Adhesion Molecule-1, and NLRP3 Inflammasome-Related Inflammatory Factor Interleukin-1β after Brain Magnetic Resonance Imaging Examination with Cerebral Small Vessel Disease

Objective. To explore the correlation of serum c-peptide, soluble intercellular adhesion molecule-1 (sICAM-1), and NLRP3 inflammasome-related inflammatory factor interleukin-1β (IL-1β) after brain magnetic resonance imaging (MRI) examination with cerebral small vessel disease (CSVD). Methods. A total of 72 CSVD patients treated in our hospital from December 2018 to December 2019 were selected as the case group and another 72 patients who presented cerebrovascular risk factors but obtained normal brain MRI examination result in the same period were selected as the control group. The serum specimen of patients in the two groups were collected, their serum c-peptide levels were measured by radio immunoassay, and their serum sICAM-1 and NLRP3 inflammasome-related inflammatory factor IL-1β were measured by enzyme-linked immunosorbent assay (ELISA), so as to analyze the correlation between these indicators and CSVD. Results. Compared with the control group, the level values of serum c-peptide, sICAM-1, and IL-1β were significantly higher in the case group ( $P<0.001$ ), with CSVD being the dependent variable, and age, smoking, uric acid, history of stroke, serum c-peptide, sICAM-1, and IL-1β being the independent variables. A logistic regression analysis was conducted, and the result showed that age, smoking, serum c-peptide, sICAM-1, and IL-1β were the risk factors for CSVD, and by drawing the ROC curves, it could be concluded that the area under sICAM-1 curve was larger than that of other single indicator. Conclusion. Elevation of level values of serum c-peptide, sICAM-1, and NLRP3 inflammasome-related inflammatory factor IL-1β is correlative with CSVD, and age, smoking, serum c-peptide, sICAM-1, and IL-1β are the independent risk factors for CSVD.

Lactiplantibacillus plantarum Reduced Renal Calcium Oxalate Stones by Regulating Arginine Metabolism in Gut Microbiota

Renal calcium oxalate (CaOx) stones are a common kidney disease. There are few methods for reducing the formation of these stones. However, the potential of probiotics for reducing renal stones has received increasing interest. We previously isolated a strain of Lactiplantibacillus plantarum N-1 from traditional cheese in China. This study aimed to investigate the effects of N-1 on renal CaOx crystal deposition. Thirty rats were randomly allocated to three groups: control group (ddH2O by gavage), model group [ddH2O by gavage and 1% ethylene glycol (EG) in drinking water], and Lactiplantibacillus group (N-1 by gavage and 1% EG in drinking water). After 4 weeks, compared with the model group, the group treated with N-1 exhibited significantly reduced renal crystals (P < 0.05). In the ileum and caecum, the relative abundances of Lactobacillus and Eubacterium ventriosum were higher in the control group, and those of Ruminococcaceae UCG 007 and Rikenellaceae RC9 were higher in the N-1-supplemented group. In contrast, the relative abundances of Staphylococcus, Corynebacterium 1, Jeotgalicoccus, Psychrobacter, and Aerococcus were higher in the model group. We also predicted that the arginase level would be higher in the ileal microbiota of the model group than in the N-1-supplemented group with PICRUSt2. The arginase activity was higher, while the level of arginine was lower in the ileal contents of the model group than in the N-1-supplemented group. The arginine level in the blood was also higher in the N-1-supplemented group than in the model group. In vitro studies showed that exposure to arginine could reduce CaOx crystal adhesion to renal epithelial HK-2 cells. Our findings highlighted the important role of N-1 in reducing renal CaOx crystals by regulating arginine metabolism in the gut microbiota. Probiotics containing L. plantarum N-1 may be potential therapies for preventing renal CaOx stones.

TRIM21 negatively regulates Corynebacterium pseudotuberculosis-induced inflammation and is critical for the survival of C. pseudotuberculosis infected C57BL6 mice

Corynebacterium pseudotuberculosis, a facultative intracellular bacterium, is an important zoonotic pathogen responsible for chronic inflammatory diseases. TRIM21, an E3 ubiquitin-protein ligase, plays pivotal roles in inflammation regulation. However, its role during C. pseudotuberculosis infection is unclear. Here, we found that TRIM21 expression was significantly increased in C. pseudotuberculosis-infected macrophages. Following infection by C. pseudotuberculosis, we observed a significantly higher number of bacteria and a higher degree of LDH release from Trim21^-/- macrophages compared to wild-type (WT) macrophages, suggesting that TRIM21 limits C. pseudotuberculosis replication in macrophages and protects the infected cells from death. Further in vivo experiments showed a significantly higher mortality, higher bacterial load, much more severe abscess formation, and lesions in the organs of C. pseudotuberculosis-infected Trim21^-/- mice compared to those of the infected WT mice, suggesting that TRIM21 plays critical roles in protecting against C. pseudotuberculosis infection. Moreover, the secretory levels of IL-1α, IL-1β, IL-6, and TNF-α were significantly higher in C. pseudotuberculosis-infected Trim21^-/- macrophages compared to infected WT macrophages; the levels of these cytokines were also higher in the sera, organs, and ascites of C. pseudotuberculosis-infected Trim21^-/- mice compared to infected WT mice. These findings suggest that TRIM21 negatively regulates the secretion of pro-inflammatory cytokines in macrophages, sera, organs, and ascites of mice following C. pseudotuberculosis infection. Collectively, the present study demonstrates that TRIM21 plays a vital role in preventing C. pseudotuberculosis infection, which may be related to the negative regulation of pro-inflammatory cytokines production by TRIM21 during this pathogen infection.

Yin and Yang: A disrupted skin microbiome and an aberrant host immune response in hidradenitis suppurativa

The skin microbiome plays an important role in maintaining skin homeostasis by controlling inflammation, providing immune education and maintaining host defense. However, in many inflammatory skin disorders the skin microbiome is disrupted. This dysbiotic community may contribute to disease initiation or exacerbation through the induction of aberrant immune responses in the absence of infection. Hidradenitis suppurativa (HS) is a complex, multifaceted disease involving the skin, innate and adaptive immunity, microbiota and environmental stimuli. Herein, we discuss the current state of HS skin microbiome research and how microbiome components may activate pattern recognition receptor (PRR) pathways, metabolite sensing pathways and antigenic receptors to drive antimicrobial peptide, cytokine, miRNA and adaptive immune cell responses in HS. We highlight the major open questions that remain to be addressed and how antibiotic therapies for HS likely influence both microbial burden and inflammation. Ultimately, we hypothesize that the two-way communication between the skin microbiome and host immune response in HS skin generates a chronic positive feed-forward loop that perpetuates chronic inflammation, tissue destruction and disease exacerbation.

Expression profiles of NOD-like receptors and regulation of NLRP3 inflammasome activation in Toxoplasma gondii-infected human small intestinal epithelial cells

BACKGROUND

Toxoplasma gondii is a parasite that primarily infects through the oral route. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) play crucial roles in the immune responses generated during parasitic infection and also drive the inflammatory response against invading parasites. However, little is known about the regulation of NLRs and inflammasome activation in T. gondii-infected human small intestinal epithelial (FHs 74 Int) cells.

METHODS

FHs 74 Int cells infected with T. gondii were subsequently evaluated for morphological changes, cytotoxicity, expression profiles of NLRs, inflammasome components, caspase-cleaved interleukins (ILs), and the mechanisms of NLRP3 and NLRP6 inflammasome activation. Immunocytochemistry, lactate dehydrogenase assay, reverse transcription polymerase chain reaction (RT-PCR), real-time quantitative RT-PCR, and western blotting techniques were utilized for analysis.

RESULTS

Under normal and T. gondii-infected conditions, members of the NLRs, inflammasome components and caspase-cleaved ILs were expressed in the FHs Int 74 cells, except for NLRC3, NLRP5, and NLRP9. Among the NLRs, mRNA expression of NOD2, NLRP3, NLRP6, and NAIP1 was significantly increased in T. gondii-infected cells, whereas that of NLRP2, NLRP7, and CIITA mRNAs decreased significantly in a time-dependent manner. In addition, T. gondii infection induced NLRP3, NLRP6 and NLRC4 inflammasome activation and production of IL-1β, IL-18, and IL-33 in FHs 74 Int cells. T. gondii-induced NLRP3 inflammasome activation was strongly associated with the phosphorylation of p38 MAPK; however, JNK1/2 had a weak effect. NLRP6 inflammasome activation was not related to the MAPK pathway in FHs 74 Int cells.

CONCLUSIONS

This study highlighted the expression profiles of NLRs and unraveled the underlying mechanisms of NLRP3 inflammasome activation in T. gondii-infected FHs 74 Int cells. These findings may contribute to understanding of the mucosal and innate immune responses induced by the NLRs and inflammasomes during T. gondii infection in FHs 74 Int cells.

Toxic Shock Syndrome Toxin 1 Induces Immune Response via the Activation of NLRP3 Inflammasome

Staphylococcus aureus is a Gram-positive opportunistic pathogen which causes infections in a variety of vertebrates. Virulence factors are the main pathogenesis of S. aureus as a pathogen, which induce the host’s innate and adaptive immune responses. Toxic shock syndrome toxin 1 (TSST-1) is one of the most important virulence factors of S. aureus. However, the role of nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) in TSST-1-induced innate immune response is still unclear. Here, purified recombinant TSST-1 (rTSST-1) was prepared and used to stimulate mouse peritoneal macrophages. The results showed that under the action of adenosine-triphosphate (ATP), rTSST-1 significantly induced interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) production in mouse macrophages and the production was dose-dependent. In addition, rTSST-1+ATP-stimulated cytokine production in macrophage depends on the activation of toll like receptor 4 (TLR4), but not TLR2 on the cells. Furthermore, the macrophages of NLRP3^−/− mice stimulated with rTSST-1+ATP showed significantly low levels of IL-1β production compared to that of wild-type mice. These results demonstrated that TSST-1 can induce the expression of inflammatory cytokines in macrophages via the activation of the TLR4 and NLRP3 signaling pathways. Our study provides new information about the mechanism of the TSST-1-inducing host’s innate immune responses.