Overexpressed NLRC3 acts as an anti-inflammatory cytosolic protein

In vitro analysis of the expression of inflammasome, antiviral, and immune genes in an Oreochromis niloticus liver cell line following stimulation with bacterial ligands and infection with tilapia lake virus

The inflammasome is a multimeric protein complex that plays a vital role in the defence against pathogens and is therefore considered an essential component of the innate immune system. In this study, the expression patterns of inflammasome genes (NLRC3, ASC, and CAS-1), antiviral genes (IFNγ and MX), and immune genes (IL-1β and IL-18) were analysed in Oreochromis niloticus liver (ONIL) cells following stimulation with the bacterial ligands peptidoglycan (PGN) and lipopolysaccharide (LPS) and infection with TiLV. The cells were stimulated with PGN and LPS at concentrations of 10, 25, and 50 µg/ml. For viral infection, 106 TCID50 of TiLV per ml was used. After LPS stimulation, all seven genes were found to be expressed at specific time points at each of the three doses tested. However, at even higher doses of LPS, NLRC3 levels decreased. Following TiLV infection, all of the genes showed significant upregulation, especially at early time points. However, the gene expression pattern was found to be unique in PGN-treated cells. For instance, NLRC3 and ASC did not show any response to PGN stimulation, and the expression of IFNγ was downregulated at 25 and 50 µg of PGN per ml. CAS-1 and IL-18 expression was downregulated at 25 µg of PGN per ml. At a higher dose (50 µg/ml), IL-1β showed downregulation. Overall, our results indicate that these genes are involved in the immune response to viral and bacterial infection and that the degree of response is ligand- and dose-dependent.

Regulation of NF-κB signaling by NLRC (NLRC3-like) gene in the common carp (Cyprinus carpio)

Among teleost NLRs, NLR-C subfamily is a large group of proteins that were teleost-specific and evolution analysis showed that NLR-Cs are most likely to evolve from NLRC3 gene (thus also called as NLRC3Ls). Presently, although there have been rich studies investigating teleost NLRC3 and NLRC3L, the data on the regulatory mechanism was limited. In this study, immune regulation of inflammatory signaling pathway mediated by common carp NLRC3L gene (CcNLRC) has been investigated. Confocal microscopy analysis showed that CcNLRC was located in cytoplasm, and in HEK293T cells, dual-luciferase reporter assay showed the regulation of NF-κB signaling by CcNLRC, in which CcNLRC could alter/decrease RIPK2-induced activation of NF-κB. These results indicated that CcNLRC may function as a negative NLR in the regulation of inflammatory response in common carp. Our data will allow to gain more insights into the molecular mechanism of teleost specific NLR (NLRC3L).

Pyroptosis: a new insight into intestinal inflammation and cancer

Pyroptosis is an innate immune response triggered by the activation of inflammasomes by various influencing factors, characterized by cell destruction. It impacts the immune system and cancer immunotherapy. In recent years, the roles of pyroptosis and inflammasomes in intestinal inflammation and cancer have been continuously confirmed. This article reviews the latest progress in pyroptosis mechanisms, new discoveries of inflammasomes, mutual regulation between inflammasomes, and their applications in intestinal diseases. Additionally, potential synergistic treatment mechanisms of intestinal diseases with pyroptosis are summarized, and challenges and future directions are discussed, providing new ideas for pyroptosis therapy.

NLRC3 negatively regulates Pasteurella multocida-induced NF-κB signaling in rabbits

Pasteurella multocida (P. multocida) is a significant zoonotic pathogen that has the ability to infect various animals. The inflammatory response caused by P. multocida and the negative regulatory mechanism are not completely understood. NOD-like receptor family CARD-containing 3 (NLRC3), an intracellular member of the NLR family, has been reported as a negative regulator in human. In this study, we aimed to explore the role of rabbit NLRC3 (rNLRC3) in P. multocida infection. Our findings revealed a negative correlation between the expression of rNLRC3 and inflammatory cytokines during P. multocida infection. The expression of rNLRC3 was reduced at the initial stage of P. multocida infection and then recovered. Furthermore, rNLRC3 significantly inhibited the activation of NF-κB by reducing phosphorylation and nuclear import of p65 in response to P. multocida infection. Additionally, overexpression of rNLRC3 attenuated the expression of pro-inflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α. Moreover, we demonstrated that rNLRC3 diminished NF-κB activation by interacting with rTRAF4 and rTRAF6. Overexpression of rNLRC3 promoted P. multocida proliferation, while P. multocida proliferation decreased after knockdown of rNLRC3. We also found that the NACHT-LRR domain is a functional domain of rNLRC3 that regulates the NF-κB pathway. Our study suggests that rNLRC3 negatively regulates P. multocida-induced NF-κB signaling in rabbits. It can serve as a checkpoint to prevent dysfunctional inflammation.

The evolution of NLRC3 subfamily genes in Sebastidae teleost fishes

BACKGROUND

With more than 36,000 valid fish species, teleost fishes constitute the most species-rich vertebrate clade and exhibit extensive genetic and phenotypic variation, including diverse immune defense strategies. NLRC3 subfamily genes, which are specific to fishes, play vital roles in the immune system of teleosts. The evolution of teleosts has been impacted by several whole-genome duplication (WGD) events, which might be a key reason for the expansions of the NLRC3 subfamily, but detailed knowledge of NLRC3 subfamily evolution in the family Sebastidae is still limited.

RESULTS

Phylogenetic inference of NLRC3 subfamily protein sequences were conducted to evaluate the orthology of NLRC3 subfamily genes in black rockfish (Sebastes schlegilii), 13 other fish species from the families Sebastidae, Serranidae, Gasterosteidae and Cyclopteridae, and three species of high vertebrates (bird, reptile and amphibian). WGD analyses were used to estimate expansions and contractions of the NLRC3 subfamily, and patterns of expression of NLRC3 subfamily genes in black rockfish following bacterial infections were used to investigate the functional roles of these genes in the traditional and mucosal immune system of the Sebastidae. Different patterns of gene expansions and contractions were observed in 17 fish and other species examined, and one and two whole-genome duplication events were observed in two members of family Sebastidae (black rockfish and honeycomb rockfish, Sebastes umbrosus), respectively. Subsequently, 179 copy numbers of NLRC3 genes were found in black rockfish and 166 in honeycomb rockfish. Phylogenetic analyses corroborated the conservation and evolution of NLRC3 orthologues between Sebastidae and other fish species. Finally, differential expression analyses provided evidence of the immune roles of NLRC3 genes in black rockfish during bacterial infections and gene ontology analysis also indicated other functional roles.

CONCLUSIONS

We hypothesize that NLRC3 genes have evolved a variety of different functions, in addition to their role in the immune response, as a result of whole genome duplication events during teleost diversification. Importantly, this study had underscored the importance of sampling across taxonomic groups, to better understand the evolutionary patterns of the innate immunity system on which complex immunological novelties arose. Moreover, the results in this study could extend current knowledge of the plasticity of the immune system.

Genome-wide identification, phylogenetic relationships and expression patterns of the NOD-like receptor (NLR) gene family in flounder (Paralichthys olivaceus)

NOD-like receptors (NLRs) are one of the pattern recognition receptors which have been widely known for identifying pathogens and regulating innate immunity in mammals, but the functions of the NLR gene family in teleost fish remain poorly understood. In this study, we conducted a comprehensive identification and analysis of the flounder (Paralichthys olivaceus) NLR gene family, including bioinformatics information, evolutionary relationships, gene structures, conserved motifs, domain composition, expression patterns and protein-protein interaction (PPI). We identified 22 NLRs in flounder (flNLRs) which were clustered into three subfamilies according to their domain organizations and phylogenetic features, i.e., NLR-A (6 members) resembling mammalian NODs, NLR-B (1 member) resembling mammalian NLRPs, and NLR-C (15 members) unique to teleost fish. All flNLRs shared a conserved NACHT domain including an N-terminal nucleotide-binding domain, a middle helical domain 1, and a winged helix domain. Gene structure analysis displayed that flNLRs were significantly different, with exon numbers from 1 to 52. Conserved domain analysis showed that the N-terminus of flNLRs possessed different characteristics of the domains including CARD domain, PYRIN domain, RING domain, and fish-specific FISNA domain, and the C-terminus of seven NLR-C members contained an extra B30.2 domain, named NLRC-B30.2 group. Notably, flNLRs were expressed in all nine tested tissues, showing higher expressions in the systemic and mucosal immune tissues (e.g., kidney, spleen, hindgut, gills, skin, liver) in healthy flounder, and significant responses to intraperitoneal injection and immersion immunization of inactivated Vibrio anguillarum in mucosal tissues, especially the NLR-C members. In addition, PPI analysis demonstrated that some flNLRs of NLR-A and NLR-C shared the same interacting proteins such as RIPK2, TRAF6, MAVS, CASP, ASC, and ATG5, suggesting they might play crucial roles in host defense, antiviral innate immunity, inflammation, apoptosis and autophagy. This study for the first time characterized the NLR gene family of flounder at the genome-wide level, and the results provided a better understanding of the evolution of the NLR gene family and their immune functions in innate immunity in fish.

Divergent functions of NLRP3 inflammasomes in cancer: a review

The cancer is a serious health problem, which is The cancer death rate (cancer mortality) is 158.3 per 100,000 men and women per year (based on 2013-2017 deaths). Both clinical and translational studies have demonstrated that chronic inflammation is associated with Cancer progression. However, the precise mechanisms of inflammasome, and the pathways that mediate this phenomenon are not fully characterized. One of the most recently identified signaling pathways, whose activation seems to affect many metabolic disorders, is the "inflammasome" a multiprotein complex composed of NLRP3 (nucleotide-binding domain and leucine-rich repeat protein 3), ASC (apoptosis associated speck-like protein containing a CARD), and procaspase-1. NLRP3 inflammasome activation leads to the processing and secretion of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. The goal of this paper is to review new insights on the effects of the NLRP3 inflammasome activation in the complex mechanisms of crosstalk between different organs, for a better understanding of the role of chronic inflammation in cancer pathogenesis. We will provide here a perspective on the current research on NLRP3 inflammasome, which may represent an innovative therapeutic target to reverse the malignancy condition consequences of the inflammation. Video Abstract.

NLRC3 Participates in Inhibiting the Pulmonary Inflammatory Response of Sepsis-Induced Acute Lung Injury

Acute lung injury (ALI) progresses rapidly, is difficult to treat, and has a high fatality rate. The excessive inflammatory response is an important pathological mechanism of ALI. NLRC3 (NLR family CARD domain-containing 3), a non-inflammasome member of the NLR family, has been found that it could negatively regulates various biological pathways associated with inflammatory response, such as NF-κB (nuclear factor kappa B), PI3K (Phosphatidylinositol 3'-kinase)-Akt (protein kinase B)-mTOR (mammalian target of the rapamycin), and STING (stimulator of interferon genes) pathways, which are responsible for the progression of pulmonary inflammation and participate in regulating the pathological progression of ALI. However, the effects of NLRC3 in sepsis-induced pathological injury of lung tissue remain unclear. In this study, we aimed to investigate the potential effects of NLRC3 in the sepsis-induced ALI. To investigate whether NLRC3 participates in inhibiting the pulmonary inflammatory response of sepsis-induced ALI. Sepsis-induced ALI mice models were established by intrabronchial injection of lipopolysaccharide (LPS) or cecum ligation and puncture (CLP). The lentivirus with overexpression of NLRC3 (LV-NLRC3) and downregulation of NLRC3 (LV-NLRC3-RNAi) were transfected to LPS-induced ALI mice. The expression of NLRC3 was upregulated or downregulated in the lung tissue of sepsis-induced ALI mice. Transfection with NLRC3-overexpression lentivirus significantly decreased inflammatory response in the lung of LPS-induced ALI mice in contrast to the control group. By transfection with NLRC3-silencing lentivirus, the inflammatory response in LPS-induced ALI mice was aggravated. Our study provides evidence of the protective effect of NLRC3 in sepsis-induced ALI by inhibiting excessive inflammatory response of the lung tissue.AbbreviationsAcute lung injury: ALI; intensive care units: ICU; lipopolysaccharide: LPS; acute respiratory distress syndrome: ARDS; bronchoalveolar lavage fluid: BALF; nucleotide-binding oligomerization domain-like receptors: NLRs; NLR family CARD domain containing 3: NLRC3; nuclear factor kappa B: NF-κB; tumor necrosis factor receptor-associated factor 6: TRAF6; Phosphatidylinositol 3'-kinase: PI3K; protein kinase B: Akt; mammalian target of the rapamycin: mTOR; stimulator of interferon genes: STING; TANK-binding kinase 1: TBK1; type I interferon: IFN-I; toll-like receptors: TLRs; tumor necrosis factor: TNF; interleukin: IL; NOD-like receptor protein 3: NLRP3; enhanced green fluorescent protein: EGFP; lentivirus: LV; phosphate-buffered saline: PBS; intrabronchial: i.t.; cecum ligation and puncture: CLP; wet/dry: W/D; Real time polymerase chain reaction: RT-PCR; enzyme-linked immunosorbent assay: ELISA; hematoxylin and eosin: H&E; radio immunoprecipitation assay: RIPA; sodium dodecyl sulfate polyacrylamide gel electrophoresis: SDS-PAGE; polyvinylidene fluoride: PVDF; glyceraldehyde 3-phosphate dehydrogenase: GAPDH; bovine serum albumin: BSA; Tris buffered saline containing Tween 20: TBST; standard deviation: SD; one-way analysis of variance: ANOVA; janus kinase 2: JAK2; activators of transcription 3: STAT3; pathogen associated molecular patterns: PAMPs; danger associated molecular patterns: DAMPs.

NLRC3 is a potential prognostic biomarker that is correlated with immune cell infiltration in lung adenocarcinoma

The NLR family CARD domain containing 3 (NLRC3) gene has been reported to have a crucial effect on immunity, inflammation, and tumorigenesis. However, the clinical relevance of NLRC3 in lung adenocarcinoma (LUAD) remains unclear. This study analyzed both RNA sequencing data and corresponding clinical outcomes obtained from public databases to identify (i) NLRC3 as a tumor suppressor in LUAD and (ii) its predictive value for the likelihood of patient responsiveness to immunotherapy. The results showed that NLRC3 expression was reduced in LUAD and was lower in advanced-stage tumors. Additionally, reduced NLRC3 expression was correlated with worse patient prognosis. The protein level of NLRC3 was also observed to have prognostic significance. Moreover, downregulation of NLRC3 was found to suppress the chemotaxis and infiltration of antitumor lymphocyte subpopulations as well as natural killer cells. Mechanistic analysis indicated that NLRC3 may be involved in immune infiltration by regulating chemokines and their receptors in LUAD. Furthermore, NLRC3 functions as a molecular switch in macrophages, whereby it mediates the polarization of M1 macrophages. Patients with high NLRC3 expression were also found to exhibit a more promising response to immunotherapy. In conclusion, NLRC3 could serve as a potential prognostic biomarker for LUAD, help predict the immunotherapeutic response of patients, and guide personalized strategies for the treatment of LUAD.

Overview of the anti-inflammatory function of the innate immune sensor NLRC3

The innate immune system is the first line of defense for the host against any microbial attack. It can quickly identify microorganisms and produce an immune response, removing pathogenic microorganisms. However, a strong immune response might lead to excessive inflammation and even autoimmune diseases. NLRC3 is an important regulator of innate immune system homeostasis. It is a member of the anti-inflammatory NLR family and can inhibit excessive immune response in the body. In this review, we primarily focused on the current research progress on NLRC3 and its potential application. It can decrease the production of pro-inflammatory cytokines by inhibiting the NF-κB, MAK-ERK, PI3K-mTOR, IL-6/JAK2/STAT3, and cGAS-STING pathways. It also inhibits inflammatory responses by interfering with the assembly and activity of the NLRP3 inflammasome complexes. Additionally, NLRC3 can also reduce the functions of some antigen-presenting cells and their ability to activate and polarize CD4⁺ T cells into Th1 and Th17 subsets. NLRC3 is closely related to the development of tumors, infectious diseases, autoimmune diseases, and AD. These diseases might be treated effectively by regulating the expression of NLRC3.

Gene expression changes implicate specific peripheral immune responses to Deep and Lobar Intracerebral Hemorrhages in humans

The peripheral immune system response to Intracerebral Hemorrhage (ICH) may differ with ICH in different brain locations. Thus, we investigated peripheral blood mRNA expression of Deep ICH, Lobar ICH, and vascular risk factor-matched control subjects (n = 59). Deep ICH subjects usually had hypertension. Some Lobar ICH subjects had cerebral amyloid angiopathy (CAA). Genes and gene networks in Deep ICH and Lobar ICH were compared to controls. We found 774 differentially expressed genes (DEGs) and 2 co-expressed gene modules associated with Deep ICH, and 441 DEGs and 5 modules associated with Lobar ICH. Pathway enrichment showed some common immune/inflammatory responses between locations including Autophagy, T Cell Receptor, Inflammasome, and Neuroinflammation Signaling. Th2, Interferon, GP6, and BEX2 Signaling were unique to Deep ICH. Necroptosis Signaling, Protein Ubiquitination, Amyloid Processing, and various RNA Processing terms were unique to Lobar ICH. Finding amyloid processing pathways in blood of Lobar ICH patients suggests peripheral immune cells may participate in processes leading to perivascular/vascular amyloid in CAA vessels and/or are involved in its removal. This study identifies distinct peripheral blood transcriptome architectures in Deep and Lobar ICH, emphasizes the need for considering location in ICH studies/clinical trials, and presents potential location-specific treatment targets.

Negative regulator NLRC3: Its potential role and regulatory mechanism in immune response and immune-related diseases

NLRC3 is a member of the pattern recognition receptors nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) family, and plays a pivotal regulatory role in modulating the activation of immune cells. In macrophages, NLRC3 inhibits the activation of the NF-κB signaling pathway, the STING/TBK1 signaling pathway, and the formation of the inflammasome. In the context of T cells immune response, NLRC3 prevents the activation of T cells by regulating the function of dendritic cells and directly influencing the function of T cells. Different from other pattern recognition receptors, NLRC3 is more closely associated with regulatory activity than pathogens recognition, it influences the fates of cells, for example, prevents proliferation, promotes apoptosis and inhibits pyroptosis. These cellular functions regulated by NLRC3 are involved in the development processes of a variety of diseases, such as infectious disease, sterile inflammatory diseases, and cancer. However, its characteristics, function and regulatory mechanism in immune response and immune-related diseases have not been addressed fully. In this review, we elaborate the potential roles of NLRC3 from several different levels, include molecular mechanism, cellular functions in the immune-related diseases.

NLRC3 attenuates antiviral immunity and activates inflammasome responses in primary grouper brain cells following nervous necrosis virus infection

NLRC3 is identified as a unique regulatory NLR involved in the modulation of cellular processes and inflammatory responses. In this study, a novel Nod like receptor C3 (NLRC3) was functionally characterized from seven band grouper in the context of nervous necrosis virus infection. The grouper NLRC3 is highly conserved and homologous with other vertebrate proteins with a NACHT domain and a C-terminal leucine-rich repeat (LRR) domain and an N-terminal CARD domain. Quantitative gene expression analysis revealed the highest mRNA levels of NLRC3 were in the brain and gill followed by the spleen and kidney following NNV infection. Overexpression of NLRC3 augmented the NNV replication kinetics in primary grouper brain cells. NLRC3 attenuated the interferon responses in the cells following NNV infection by impacting the TRAF6/NF-κB activity and exhibited reduced IFN sensitivity, ISRE promoter activity, and IFN pathway gene expression. In contrast, NLRC3 expression positively regulated the inflammasome response and pro-inflammatory gene expression during NNV infection. NLRC3 negatively regulates the PI3K-mTOR axis and activated the cellular autophagic response. Delineating the complexity of NLRC3 regulation of immune response in the primary grouper brain cells following NNV infection suggests that the protein acts as a virally manipulated host factor that negatively regulated the antiviral immune response to augment the NNV replication.

Insights into inflammasome regulation: cellular, molecular, and pathogenic control of inflammasome activation

Maintenance of immune homeostasis is an intricate process wherein inflammasomes play a pivotal role by contributing to innate and adaptive immune responses. Inflammasomes are ensembles of adaptor proteins that can trigger a signal following innate sensing of pathogens or non-pathogens eventuating in the inductions of IL-1β and IL-18. These inflammatory cytokines substantially influence the antigen-presenting cell's costimulatory functions and T helper cell differentiation, contributing to adaptive immunity. As acute and chronic disease conditions may accompany parallel tissue damage, we analyze the critical role of extracellular factors such as cytokines, amyloids, cholesterol crystals, etc., intracellular metabolites, and signaling molecules regulating inflammasome activation/inhibition. We develop an operative framework for inflammasome function and regulation by host cell factors and pathogens. While inflammasomes influence the innate and adaptive immune components' interplay modulating the anti-pathogen adaptive immune response, pathogens may target inflammasome inhibition as a survival strategy. As trapped between health and diseases, inflammasomes serve as promising therapeutic targets and their modus operandi serves as a scientific rationale for devising better therapeutic strategies.

Brain immunity response of fish Eleginops maclovinus to infection with Francisella noatunensis

The brain's immune system is selective and hermetic in most species, including fish, favoring immune responses mediated by soluble immunomodulatory factors such as serotonin and the availability of nutrients against infectious processes. Francisella noatunensis coexist with fish such as Eleginops maclovinus, which raises questions about the susceptibility and immune response of the brain of E. maclovinus against Francisella. In this study, we inoculated fish with different doses of Francisella and took samples for 28 days. We detected bacteria in the brain of fish injected with a high concentration of Francisella at all time points. qPCR analysis of immune genes indicated a response mainly in the medium-dose and early expression of genes involved in iron metabolism. Finally, brain serotonin levels were higher than in uninfected fish in all conditions, suggesting possible immunomodulatory participation in an infectious process.

α‑rhamnrtin‑3‑α‑rhamnoside exerts anti‑inflammatory effects on lipopolysaccharide‑stimulated RAW264.7 cells by abrogating NF‑κB and activating the Nrf2 signaling pathway

α-rhamnrtin-3-α-rhamnoside (ARR) is the principal compound extracted from Loranthus tanakae Franch. & Sav. However, its underlying pharmacological properties remain undetermined. Inflammation is a defense mechanism of the body; however, the excessive activation of the inflammatory response can result in physical injury. The present study aimed to investigate the effects of ARR on lipopolysaccharide (LPS)-induced RAW264.7 macrophages and to determine the underlying molecular mechanism. A Cell Counting Kit-8 assay was performed to assess cytotoxicity. Nitric oxide (NO) production was measured via a NO colorimetric kit. Levels of prostaglandin E2 (PGE₂) and proinflammatory cytokines, IL-1β and IL-6, were detected using ELISAs. Reverse transcription-quantitative (RT-q)PCR analysis was performed to detect the mRNA expression levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), IL-6 and IL-1β in LPS-induced RAW246.7 cells. Western blotting, immunofluorescence and immunohistochemistry analyses were performed to measure the expression levels of NF-κB and nuclear factor-erythroid 2-related factor 2 (Nrf2) signaling pathway-related proteins to elucidate the molecular mechanisms of the inflammatory response. The results of the cytotoxicity assay revealed that doses of ARR ≤200 µg/ml exhibited no significant effect on the viability of RAW264.7 cells. The results of the Griess assay demonstrated that ARR inhibited the production of NO. In addition, the results of the ELISAs and RT-qPCR analysis discovered that ARR reduced the production of the proinflammatory cytokines, IL-1β and IL-6, as well as the proinflammatory mediators, PGE₂, iNOS and COX-2, in LPS-induced RAW264.7 cells. Immunohistochemical analysis demonstrated that ARR inhibited LPS-induced activation of TNF-associated factor 6 (TRAF6) and NF-κB p65 signaling molecules, while reversing the downregulation of the NOD-like receptor family CARD domain containing 3 (NLRC3) signaling molecule, which was consistent with the results of the western blotting analysis. Immunofluorescence results indicated that ARR reduced the increase of NF-κB p65 nuclear expression induced by LPS. Furthermore, the results of the western blotting experiments also revealed that ARR upregulated heme oxygenase-1, NAD(P)H quinone dehydrogenase 1 and Nrf2 pathway molecules. In conclusion, the results of the present study suggested that ARR may exert anti-inflammatory effects by downregulating NF-κB and activating Nrf2-mediated inflammatory responses, suggesting that ARR may be an attractive anti-inflammatory candidate drug.

Transcriptome analysis of the bursa of Fabricius and thymus of laying ducks reveals immune gene expression changes underlying the impacts of stocking densities

The thymus and bursa of Fabricius are important immune organs in poultry as they play essential roles in sustaining the normal immune function to maintain health. The following trial investigated whether the stocking density affected gene expressions in immune organs.Jinding ducklings were raised in either low or high density (4 or 8 birds/m²) conditions from four to 14 weeks of age, and were then slaughtered and tissues removed. Samples were subjected to high-throughput sequencing to sequence RNA extraction. After filtering calculations with R software, a total of 508 (thymus) and 1,356 (bursa of Fabricius) differentially expressed genes (DEGs) were identified, suggesting that stocking density has an effect on gene expression in duck immune organs.A total of 112 immune factor genes and 112 immune pattern receptor genes in ducks, of which four thymus genes and 18 bursa of Fabricius genes were differentially expressed in ducks, which indicated that the change of stocking density could affect the expression of immune genes in poultry.

Exploring genetic resistance to infectious salmon anaemia virus in Atlantic salmon by genome-wide association and RNA sequencing

Background

Infectious Salmonid Anaemia Virus (ISAV) causes a notifiable disease that poses a large threat for Atlantic salmon (Salmo salar) aquaculture worldwide. There is no fully effective treatment or vaccine, and therefore selective breeding to increase resistance to ISAV is a promising avenue for disease prevention. Genomic selection and potentially genome editing can be applied to enhance host resistance, and these approaches benefit from improved knowledge of the genetic and functional basis of the target trait. The aim of this study was to characterise the genetic architecture of resistance to ISAV in a commercial Atlantic salmon population and study its underlying functional genomic basis using RNA Sequencing.

Results

A total of 2833 Atlantic salmon parr belonging to 194 families were exposed to ISAV in a cohabitation challenge in which cumulative mortality reached 63% over 55 days. A total of 1353 animals were genotyped using a 55 K SNP array, and the estimate of heritability for the trait of binary survival was 0.13–0.33 (pedigree-genomic). A genome-wide association analysis confirmed that resistance to ISAV was a polygenic trait, albeit a genomic region in chromosome Ssa13 was significantly associated with resistance and explained 3% of the genetic variance. RNA sequencing of the heart of 16 infected (7 and 14 days post infection) and 8 control fish highlighted 4927 and 2437 differentially expressed genes at 7 and 14 days post infection respectively. The complement and coagulation pathway was down-regulated in infected fish, while several metabolic pathways were up-regulated. The interferon pathway showed little evidence of up-regulation at 7 days post infection but was mildly activated at 14 days, suggesting a potential crosstalk between host and virus. Comparison of the transcriptomic response of fish with high and low breeding values for resistance highlighted TRIM25 as being up-regulated in resistant fish.

Conclusions

ISAV resistance shows moderate heritability with a polygenic architecture, but a significant QTL was detected on chromosome 13. A mild up-regulation of the interferon pathway characterises the response to the virus in heart samples from this population of Atlantic salmon, and candidate genes showing differential expression between samples with high and low breeding values for resistance were identified.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07671-6.

Carvacrol, Thymol, and Garlic Essential Oil Promote Skin Innate Immunity in Gilthead Seabream (Sparus aurata) Through the Multifactorial Modulation of the Secretory Pathway and Enhancement of Mucus Protective Capacity

One of the main targets for the use of phytogenics in aquafeeds is the mucosal tissues as they constitute a physical and biochemical shield against environmental and pathogenic threats, comprising elements from both the innate and acquired immunity. In the present study, the modulation of the skin transcriptional immune response, the bacterial growth capacity in skin mucus, and the overall health condition of gilthead seabream (Sparus aurata) juveniles fed a dietary supplementation of garlic essential oil, carvacrol, and thymol were assessed. The enrichment analysis of the skin transcriptional profile of fish fed the phytogenic-supplemented diet revealed the regulation of genes associated to cellular components involved in the secretory pathway, suggesting the stimulation, and recruitment of phagocytic cells. Genes recognized by their involvement in non-specific immune response were also identified in the analysis. The promotion of the secretion of non-specific immune molecules into the skin mucus was proposed to be involved in the in vitro decreased growth capacity of pathogenic bacteria in the mucus of fish fed the phytogenic-supplemented diet. Although the mucus antioxidant capacity was not affected by the phytogenics supplementation, the regulation of genes coding for oxidative stress enzymes suggested the reduction of the skin oxidative stress. Additionally, the decreased levels of cortisol in mucus indicated a reduction in the fish allostatic load due to the properties of the tested additive. Altogether, the dietary garlic, carvacrol, and thymol appear to promote the gilthead seabream skin innate immunity and the mucus protective capacity, decreasing its susceptibility to be colonized by pathogenic bacteria.

The expanding and function of NLRC3 or NLRC3-like in teleost fish: Recent advances and novel insights

The nucleotide-binding domain and leucine-rich repeat-containing family (NLR) proteins are innate immune sensors which recognize highly conserved pathogen-associated molecular patterns (PAMPs). Mammals have small numbers of NLR proteins, whereas in some species such as in invertebrates and jawless vertebrates, NLRs have expanded into very large families. Nearly 400 NLR proteins are identified in the zebrafish genome. Members of the NLR family can be divided into two functional sub-groups based on their ability to either positively or negatively regulate host immune response or inflammatory signaling cascades. Mammalian NLRC3 has been identified as an inhibitory NLR, and serves as a negative regulator in the NF-κB-mediated inflammatory response, STING-mediated DNA sensing and PI3K-mTOR pathways. Different from mammalian NLRC3, the analysis from genomes or transcriptomes revealed that the expansions of NLRC3 existed in different species of fish. Furthermore, piscine NLRC3-like genes were confirmed to have a negative or positive regulatory function in response to different kinds of pathogen infections and in the production of proinflammatory cytokines. In this review, we summarize recent advances in our understanding of the expanding and function of NLRC3 or NLRC3-like genes in teleost fish, and give our view of important directions for future studies. The knowledge of piscine NLRC3 or expansive NLRC3-like genes-mediated biological functions in homeostasis and diseases will shed new light on the prevention and control of inflammatory and/or infectious diseases.

Characterization and expression analysis of Nod-like receptor 3 (NLRC3) against infection with Piscirickettsia salmonis in Atlantic salmon

The nucleotide binding oligomerization domain like receptors, or NOD like receptors (NLRs), are intracellular receptors responsible for recognizing pathogens in vertebrates. Several NLR mammalian models have been characterized and analyzed but few studies have been performed with teleost species. In this study, we analyzed the nucleotide sequence of six mRNA variants of NLRC3 in Atlantic salmon (SsNLRC3), and we deduced the amino acid sequence coding for two different isoforms with a total length of 1135 amino acids and 1093 amino acids. We analyzed the phylogeny of all variants, including a Piscirickettsia salmonis infection in Atlantic salmon. All variants and their expression pattern during infection were analyzed using real-time qPCR. One of the analyzed variants was over-expressed during the early stages of Piscirickettsia salmonis infection, and we were able to identify two different SsNLRC3 isoforms. Lastly, we observed that an alteration in the amino acid sequence of one of the isoforms can directly affect the pathogen recognition function.

NLRC3 Delays the Progression of AD in APP/PS1 Mice via Inhibiting PI3K Activation

NLRC3 inhibits inflammatory responses. Neuroinflammation induces and accelerates the onset of Alzheimer's disease (AD). This study is aimed at investigating whether NLRC3 plays a role in neuroinflammation, Aβ accumulation, and neuroprotection in AD mice. 12-month-old APP/PS1 transgenic and C57 mice were used for studies in vivo. In vitro, organotypic hippocampal slices were cultured. We found that the expression of NLRC3 was downregulated in the brain tissues of APP/PS1 mice. Mice in the APP/PS1 group had a significant attenuation of learning and memory ability compared to the control group, and the ability was improved in APP/PS1 + LV-NLRC3 mice. The expressions of 6E10, GFAP, Iba1, and PI3K in the hippocampus and brains of APP/PS1 mice were significantly higher than those of the control group, while the expressions of NeuN were lower than that of the control group. With the overexpression of NLRC3 in the APP/PS1 + LV-NLRC3 group, the expressions of 6e10, GFAP, Iba1, and PI3K were significantly lower, while the expression of NeuN was significantly higher compared to the APP/PS1 group. NLRC3 colocalized with NeuN. PI3K activation with 740YP increased the expression of GFAP and Iba-1 in the hippocampus with the exogenous NLRC3 protein. We conclude that NLRC3 may play an important role in the development and progression of AD. Downregulation of NLRC3 can lead to the activation of PI3K, resulting in abnormal plaque deposition, glial cell activation, and neuron loss during AD. NLRC3 delays the progression of AD in APP/PS1 mice via inhibiting PI3K activation.

NLRC3-like 1 inhibits NOD1-RIPK2 pathway via targeting RIPK2

Both NLRC3 and NOD1 belong to regulatory NLR subfamily based on their best-characterized function. In mammals, NLRC3 was reported to function by attenuating signaling cascades initiated by other families of PRRs. In teleosts, multiple NLRC3-like genes were identified through transcriptome sequencing. However, the functions of many NLRC3-like genes, especially the fish-specific NLRC3-like genes, remain unclear. In the present study, we report the functional characterization of a novel category of NLRC3-like proteins (named as NLRC3-like 1) from the zebrafish, which consists of a fish-specific FISNA, a conserved NACHT and five C-terminal LRRs domains. The expression of zebrafish NLRC3-like 1 was inducible in response to Edwardsiella piscicida infection. During bacterial infection, the in vitro and in vivo studies revealed that zebrafish NLRC3-like 1 overexpression facilitated bacterial growth and dissemination, together with the decreased survival rate of zebrafish larvae infected with E. piscicida. The attenuated response by zebrafish NLRC3-like 1 in response to bacterial infection were characterized by the impaired expression of antibacterial genes, proinflammatory cytokines and Nox genes. Furthermore, zebrafish NLRC3-like 1 interacted with the adaptor protein RIPK2 of NODs signaling via the FISNA (Fish-specific NACHT associated domain) and NACHT domains. However, the interaction between zebrafish NLRC3-like 1 and RIPK2 inhibited the assembly of the NOD1-RIPK2 complex. Importantly, zebrafish NLRC3-like 1 inhibited NOD1-mediated antibacterial activity, NF-κB and MAPK pathways and proinflammatory cytokine production. All together, these results firstly demonstrate that zebrafish NLRC3-like 1 inhibits NOD1-RIPK2 antibacterial pathway via targeting the adaptor protein RIPK2.

NLRC3 alleviates hypoxia/reoxygenation induced inflammation in RAW264.7 cells by inhibiting K63-linked ubiquitination of TRAF6

BACKGROUND

NOD-like receptor family CARD domain containing 3 (NLRC3) plays an important role in both innate and adaptive immunity. This study was to explore the function and related mechanisms of NLRC3 in a hypoxia/reoxygenation (H/R)-induced inflammatory response in RAW264.7 cells.

METHODS

Liver ischemia-reperfusion (I/R) model in mice and H/R model in RAW264.7 cells were constructed. Western blotting was used to determine the protein expression level of NLRC3 in liver tissue and NLRC3, TRAF6, p-p65, p65, IκB-α, and the K63-linked ubiquitination level of TRAF6 in cells. The immunofluorescence assay was performed to evaluate the nuclear level of the NF-κB (p65). ELISA was conducted to measure the content of IL-1β in serum and cell supernatant. The interaction between NLRC3 and TRAF6 in cells was analyzed by the Co-IP assay.

RESULTS

The NLRC3 protein level in liver tissue was decreased with the prolongation of reperfusion time (P < 0.05). The expression of NLRC3 and IκB-α protein in RAW264.7 was decreased gradually, while the expression of p-p65 and TRAF6 proteins and K63-linked ubiquitination of TRAF6 were increased gradually with the prolongation of reoxgenation time (P < 0.05). The Co-IP assay revealed that NLRC3 and TRAF6 can bind to each other directly. However, NLRC3 had no effect on the expression of TRAF6 protein. The ubiquitination test results showed that the K63-linked ubiquitination level of TRAF6 in H/R + Lv-NLRC3 group was significantly lower than that in the H/R + negative control (NC) group (P < 0.05). Moreover, the activation of NF-κB in H/R + Lv-NLRC3 group was inhibited compared with that in the H/R + NC group, and the level of the inflammatory factor IL-1β in the cell culture supernatant was also decreased accordingly (P < 0.05).

CONCLUSIONS

NLRC3 might alleviate H/R-induced inflammation in RAW264.7 cells by inhibiting K63-linked ubiquitination of TRAF6.

Complement and human T cell metabolism: Location, location, location

The complement system represents one of the evolutionary oldest arms of our immune system and is commonly recognized as a liver-derived and serum-active system critical for providing protection against invading pathogens. Recent unexpected findings, however, have defined novel and rather "uncommon" locations and activities of complement. Specifically, the discovery of an intracellularly active complement system-the complosome-and its key role in the regulation of cell metabolic pathways that underly normal human T cell responses have taught us that there is still much to be discovered about this system. Here, we summarize the current knowledge about the emerging functions of the complosome in T cell metabolism. We further place complosome activities among the non-canonical roles of other intracellular innate danger sensing systems and argue that a "location-centric" view of complement evolution could logically justify its close connection with the regulation of basic cell physiology.

Promising key genes associated with tumor microenvironments and prognosis of hepatocellular carcinoma

BACKGROUND

Despite significant advances in multimodality treatments, hepatocellular carcinoma (HCC) remains one of the most common malignant tumors. Identification of novel prognostic biomarkers and molecular targets is urgently needed.

AIM

To identify potential key genes associated with tumor microenvironments and the prognosis of HCC.

METHODS

The infiltration levels of immune cells and stromal cells were calculated and quantified based on the ESTIMATE algorithm. Differentially expressed genes (DEGs) between high and low groups according to immune or stromal scores were screened using the gene expression profile of HCC patients in The Cancer Genome Atlas and were further linked to the prognosis of HCC. These genes were validated in four independent HCC cohorts. Survival-related key genes were identified by a LASSO Cox regression model.

RESULTS

HCC patients with a high immune/stromal score had better survival benefits than patients with a low score. A total of 899 DEGs were identified and found to be involved in immune responses and extracellular matrices, 147 of which were associated with overall survival. Subsequently, 52 of 147 survival-related DEGs were validated in additional cohorts. Finally, ten key genes (STSL2, TMC5, DOK5, RASGRP2, NLRC3, KLRB1, CD5L, CFHR3, ADH1C, and UGT2B15) were selected and used to construct a prognostic gene signature, which presented a good performance in predicting overall survival.

CONCLUSION

This study extracted a list of genes associated with tumor microenvironments and the prognosis of HCC, thereby providing several valuable directions for the prognostic prediction and molecular targeted therapy of HCC in the future.

NLRC3 inhibits MCT-induced pulmonary hypertension in rats via attenuating PI3K activation

Phosphoinositide 3-kinase (PI3K) activation plays a critical role in the pulmonary vascular remodeling of pulmonary hypertension (PH). The nucleotide-oligomerization domain (NOD)-like receptor subfamily C3 (NLRC3) inhibits proliferation and inflammation via PI3K signaling in cancer. We previously showed NLRC3 was significantly reduced in PH patients, but the mechanism of function remains unclear. This study aimed to determine the potential role of NLRC3 in PH. We found that NLRC3 was downregulated in the pulmonary arteries of PH animal models and platelet-derived growth factor-BB (PDGF-BB) stimulated pulmonary arterial smooth muscle cells (PASMCs). NLRC3 pretreatment reduced right ventricular systolic pressure, attenuated pulmonary vascular remodeling and RVHI, and ameliorated proliferation, migration, and inflammation. Monocrotaline (MCT)- and PDGF-BB-mediated PI3K activation were suppressed by NLRC3 pretreatment. 740Y-P decreased the effect of NLRC3. Collectively, NLRC3 protected against MCT-induced rat PH and PDGF-BB-induced PASMC proliferation, migration, and inflammation through a mechanism involving PI3K inhibition. NLRC3 may have a therapeutic effect on PH and provide a promising therapeutic strategy for PH.

High doses of Francisella noatunensis induces an immune response in Eleginops maclovinus

Francisella noatunensis subsp. noatunensis, the etiological agent of Francisellosis, affects a large number of farmed species such as Salmo salar. This species coexists with several native species in the same ecosystem, including Eleginops maclovinus. Our objective was to evaluate the susceptibility, presence of clinical symptoms, and the ability of Eleginops maclovinus to respond to Francisella infection. For this, healthy individuals were inoculated with 1.5 × 10¹, 1.5 × 10⁵, and 1.5 × 10¹⁰ bact/μL of Francisella by intraperitoneal injection, subsequently the fish were sampled on days 1, 3, 7, 14, 21, and 28 post injection (dpi). At the end of the experiment, no mortality, nor internal and external clinical signs were observed, although in the high dose anaemia was detected. Additionally, bacteria were detected in all three doses, however there was replication at day 28 only in the liver in the high dose. Analysis of gene expression by qPCR showed that the spleen generated an immune response against infection from day 1 dpi, however at day 7 dpi most of the genes suffered repressed expression; observing over expression of the genes C3, NLRC3, NLRC5, MHCI, IgM. In contrast, expression in the anterior kidney did not vary significantly during the challenge. IgM quantification showed the production of antibodies in the medium and high doses. This study provides new knowledge about Francisella infection and the long-lasting and specific immune response generated by Eleginops maclovinus. It also demonstrates its susceptibility to Francisellosis where there is a difference in the immune response according to the tissue.

Diverging inflammasome signals in tumorigenesis and potential targeting

Inflammasomes are molecular platforms that assemble upon sensing various intracellular stimuli. Inflammasome assembly leads to activation of caspase 1, thereby promoting the secretion of bioactive interleukin-1β (IL-1β) and IL-18 and inducing an inflammatory cell death called pyroptosis. Effectors of the inflammasome efficiently drive an immune response, primarily providing protection against microbial infections and mediating control over sterile insults. However, aberrant inflammasome signalling is associated with pathogenesis of inflammatory and metabolic diseases, neurodegeneration and malignancies. Chronic inflammation perpetuated by inflammasome activation plays a central role in all stages of tumorigenesis, including immunosuppression, proliferation, angiogenesis and metastasis. Conversely, inflammasome signalling also contributes to tumour suppression by maintaining intestinal barrier integrity, which portrays the diverse roles of inflammasomes in tumorigenesis. Studies have underscored the importance of environmental factors, such as diet and gut microbiota, in inflammasome signalling, which in turn influences tumorigenesis. In this Review, we deliver an overview of the interplay between inflammasomes and tumorigenesis and discuss their potential as therapeutic targets.

Acting locally - affecting globally: RNA sequencing of gilthead sea bream with a mild Sparicotyle chrysophrii infection reveals effects on apoptosis, immune and hypoxia related genes

BACKGROUND

Monogenean flatworms are the main fish ectoparasites inflicting serious economic losses in aquaculture. The polyopisthocotylean Sparicotyle chrysophrii parasitizes the gills of gilthead sea bream (GSB, Sparus aurata) causing anaemia, lamellae fusion and sloughing of epithelial cells, with the consequent hypoxia, emaciation, lethargy and mortality. Currently no preventive or curative measures against this disease exist and therefore information on the host-parasite interaction is crucial to find mitigation solutions for sparicotylosis. The knowledge about gene regulation in monogenean-host models mostly comes from freshwater monopysthocotyleans and almost nothing is known about polyopisthocotyleans. The current study aims to decipher the host response at local (gills) and systemic (spleen, liver) levels in farmed GSB with a mild natural S. chrysophrii infection by transcriptomic analysis.

RESULTS

Using Illumina RNA sequencing and transcriptomic analysis, a total of 2581 differentially expressed transcripts were identified in infected fish when compared to uninfected controls. Gill tissues in contact with the parasite (P gills) displayed regulation of fewer genes (700) than gill portions not in contact with the parasite (NP gills) (1235), most likely due to a local silencing effect of the parasite. The systemic reaction in the spleen was much higher than that at the parasite attachment site (local) (1240), and higher than in liver (334). NP gills displayed a strong enrichment of genes mainly related to immune response and apoptosis. Processes such as apoptosis, inflammation and cell proliferation dominated gills, whereas inhibition of apoptosis, autophagy, platelet activation, signalling and aggregation, and inflammasome were observed in spleen. Proteasome markers were increased in all tissues, whereas hypoxia-related genes were down-regulated in gills and spleen.

CONCLUSIONS

Contrasting forces seem to be acting at local and systemic levels. The splenic down-regulation could be part of a hypometabolic response, to counteract the hypoxia induced by the parasite damage to the gills and to concentrate the energy on defence and repair responses. Alternatively, it can be also interpreted as the often observed action of helminths to modify host immunity in its own interest. These results provide the first toolkit for future studies towards understanding and management of this parasitosis.

The correlation of NLRC3 expression with the progression and prognosis of hepatocellular carcinoma

NLRC3 is a member of the nucleotide-binding domain and leucine-rich repeat (NLR) family protein that plays a role in inflammation and immunity. Although chronic inflammation has been identified as a hallmark of cancer, NLRC3 expression correlation with the development and prognosis of hepatocellular carcinoma (HCC) is unclear. In the present study, we first used Oncomine and OncoLnc database to determine the clinical significance of NLRC3 in HCC. Then we performed quantitative real-time polymerase chain reaction, Western blot, and immunohistochemical staining (IHC) and analyzed the correlation between NLRC3 expression and clinicopathological features of HCC in a Chinese population. We found that high levels of NLRC3 messenger RNA (mRNA) correlated with a favorable clinical outcome; furthermore, expression of NLRC3 was significantly reduced in the cancer tissue in patients compared with noncancerous hepatic tissues. NLRC3 reduction was correlated with Edmondson grade and metastasis. Kaplan-Meier survival analysis revealed that HCC patients with high expression of NLRC3 have a more favorable prognosis compared with those with low expression of NLRC3. We then used short hairpin RNA to knock down NLRC3 expression in HCC cell lines and evaluated its effect on cell proliferation and apoptosis. Suppression of NLRC3 expression promoted cell proliferation and inhibited apoptosis in vitro. Genomic analysis of the OncoLnc database also showed that NLRC3 mRNA level was directly correlated with mRNA levels of inflammasome components caspase-1, IL-1β, and IL-18. Based on our present study, down-regulated expression of NLRC3 may play an important role in cancer progression and prognosis of HCC by acting as a tumor suppressor.

Basal polarization of the immune responses to Streptococcus agalactiae susceptible and resistant tilapia (Oreochromis niloticus)

One of the highest priority areas for improvement is the development of effective strategies for decreasing disease mortality levels in aquaculture production, a better understanding of the components of the fish immune system and their functions in the context of pathogen invasion is needed. Tilapia is the most common fish in South China, and Streptococcus agalactiae has become the most serious disease problem for tilapia industry in China. Here, we profiled gene expression differences between tilapia differing in their susceptibility to S. agalactiae both basally (before infection) and at three early timepoints post-infection (5 h, 50 h, and 7 d). Between group comparisons revealed 5756 unique genes differentially expressed greater than 2-fold at one or more timepoints. And the resistant fish showed much more strong ability in pathogen recognition, antigen presentation, immune activation, while the susceptible fish showed fast activation of apoptosis. Taken together, the immune profiles expand our knowledge for molecular mechanisms for disease resistance, as well as provide solid molecular resources for further identification of the candidate markers for disease-resistant selection and evaluation of disease prevention and treatment options for tilapia industry.

Characterization and functional assessment of the NLRC3-like molecule of the goldfish (Carassius auratus L.)

The NLRC3-like (NLRC3L) molecule from the goldfish transcriptome database was identified and characterized. Quantitative gene expression analysis revealed the highest mRNA levels of NLRC3L were in the spleen and intestine, with lower mRNA levels observed in muscle and liver. Goldfish NLRC3L was differentially expressed in goldfish immune cell populations with highest mRNA levels measured in PBLs and macrophages. We generated a recombinant form of the molecule (rgfNLRC3L) and an anti-CT-NLRC3L IgG. Treatment of goldfish primary kidney macrophages in vitro with ATP, LPS and heat-killed Aeromonas salmonicida up-regulated the NLRC3L mRNA and protein. Confocal microscopy and co-immunoprecipitation assays indicated that goldfish rgfNLRC3L interacted with apoptosis-associated spec-like protein (ASC) in eukaryotic cells, indicating that NLRC3L may participate in the regulation of the inflammasome responses. The dual-luciferase reporter assay showed that NLRC3L over-expression did not cause the activation of NF-κB, but that it cooperated with RIP2 to down-regulate NF-κB activation. Our results indicate that the NLRC3L may function as a regulator of NLR pathways in teleosts.

NOD-like receptor(s) and host immune responses with Pseudomonas aeruginosa infection

INTRODUCTION

Molecular mechanisms underlying the interactions between Pseudomonas aeruginosa, the common opportunistic pathogen in cystic fibrosis individuals, and host induce a number of marked inflammatory responses and associate with complex therapeutic problems due to bacterial resistance to antibiotics in chronic stage of infection.

METHODS

Pseudomonas aeruginosa is recognized by number of pattern recognition receptors (PRRs); NOD-like receptors (NLRs) are a class of PRRs, which can recognize a variety of endogenous and exogenous ligands, thereby playing a critical role in innate immunity.

RESULTS

NLR activation initiates forming of a multi-protein complex called inflammasome that induces activation of caspase-1 and resulted in cleavage of pro-inflammatory cytokines interleukin (IL)-1β and IL-18. When the IL-1β is secreted excessively, this causes tissue damage and extensive inflammatory responses that are potentially hazardous for the host.

CONCLUSIONS

Recent evidence has laid out inflammasome-forming NLR far beyond inflammation. This review summarizes current knowledge regarding the various roles played by different NLRs and associated down-signals, either in recognition of P. aeruginosa or may be associated with such bacterial pathogen infection, which may relate to for the complexity of lung diseases caused by P. aeruginosa.

Host Genotype and Microbiota Contribute Asymmetrically to Transcriptional Variation in the Threespine Stickleback Gut

Recent studies of interactions between hosts and their resident microbes have revealed important ecological and evolutionary consequences that emerge from these complex interspecies relationships, including diseases that occur when the interactions go awry. Given the preponderance of these interactions, we hypothesized that effects of the microbiota on gene expression in the developing gut—an important aspect of host biology—would be pervasive, and that these effects would be both comparable in magnitude to and contingent on effects of the host genetic background. To evaluate the effects of the microbiota, host genotype, and their interaction on gene expression in the gut of a genetically diverse, gnotobiotic host model, the threespine stickleback (Gasterosteus aculeatus), we compared RNA-seq data among 84 larval fish. Surprisingly, we found that stickleback population and family differences explained substantially more gene expression variation than the presence of microbes. Expression levels of 72 genes, however, were affected by our microbiota treatment. These genes, including many associated with innate immunity, comprise a tractable subset of host genetic factors for precise, systems-level study of host–microbe interactions in the future. Importantly, our data also suggest subtle signatures of a statistical interaction between host genotype and the microbiota on expression patterns of genetic pathways associated with innate immunity, coagulation and complement cascades, focal adhesion, cancer, and peroxisomes. These genotype-by-environment interactions may prove to be important leads to the understanding of host genetic mechanisms commonly at the root of sometimes complex molecular relationships between hosts and their resident microbes.

NLRC3 protein inhibits inflammation by disrupting NALP3 inflammasome assembly via competition with the adaptor protein ASC for pro-caspase-1 binding

Inflammasomes are multiprotein complexes that sense pathogen-associated and danger-associated molecular patterns and induce inflammation in cells. The NALP3 inflammasome is tightly regulated by recently discovered control mechanisms, but other modulators still remain to be characterized. NLR family CARD-containing 3 (NLRC3) protein, a caspase recruitment domain (CARD)-containing member of the nucleotide oligomerization domain-like receptor (NLR) family, was found to down-regulate the NF-κB pathway and stimulator of interferon genes (STING)-dependent cytokine secretion. However, the effect of NLRC3 on the NALP3 inflammasome or other inflammasomes is still unknown. We hypothesized that NLRC3 might inhibit NALP3 inflammasome complex assembly. Toward this end, we tested whether NLRC3 overexpression or knockdown influences NALP3 activity in human monocyte and HEK293FT cells when the complex is ectopically reconstituted. We found that NLRC3 indeed decreases NALP3-induced IL-1β maturation and secretion, pro-caspase-1 cleavage, and speck formation by apoptosis-associated speck-like protein containing a CARD (ASC) protein in response to NALP3 activators. We also show that endogenous NLRC3 interacts with both ASC and pro-caspase-1 but not with NALP3, disrupts ASC speck formation through its CARD, and impairs the ASC and pro-caspase-1 interaction. Moreover, the NLRC3 CARD alone could dampen IL-1β secretion and ASC speck formation induced by NALP3 mutants associated with autoinflammatory diseases. In conclusion, we show here that, besides its role in the inhibition of the NF-κB pathway, NLRC3 interferes with the assembly and activity of the NALP3 inflammasome complex by competing with ASC for pro-caspase-1 binding.

Identification and characterization of a novel NOD-like receptor family CARD domain containing 3 gene in response to extracellular ATP stimulation and its role in regulating LPS-induced innate immune response in Japanese flounder (Paralichthys olivaceus) head kidney macrophages

Nucleotide oligomerization domain (NOD)-like receptor (NLR) family with a caspase activation and recruitment domain (CARD) containing 3 (NLRC3) protein is an important cytosolic pattern recognition receptor that negatively regulates innate immune response in mammals. Hitherto, the immunological significance of NLRC3 protein in fish remains largely uncharacterized. Here we identified and characterized a novel NLRC3 gene (named poNLRC3) implicated in regulation of fish innate immunity from Japanese flounder Paralichthys olivaceus. The poNLRC3 protein is a cytoplasmic protein with an undefined N-terminal domain, a NACHT domain, a fish-specific NACHT associated domain, six LRR motifs, and a C-terminal fish-specific PYR/SPYR (B30.2) domain but only shares less than 40% sequence identities with the known Japanese flounder NLRC proteins. poNLRC3 gene is ubiquitously expressed in all tested tissues and is dominantly expressed in the Japanese flounder head kidney macrophages (HKMs). We for the first time showed that poNLRC3 expression was significantly modulated by the stimulation of extracellular ATP, an important danger/damage-associated molecular pattern in activating innate immunity in P. olivaceus. Importantly, we revealed that poNLRC3 plays an important role in positively regulating ATP-induced IL-1beta and IL-6 gene expression, suggesting the involvement of poNLRC3 in extracellular ATP-mediated immune signaling. In addition, we showed that poNLRC3 mRNA expression was up-regulated in response to LPS and Edwardsiella tarda immune challenges. Finally, we showed that down-regulating the endogenous poNLRC3 expression with small interfering RNA significantly reduced LPS-induced proinflammatory cytokine gene expression in the Japanese flounder HKM cells. Altogether, we have identified a novel inducible fish NLR member, poNLRC3, which is involved in extracellular ATP-mediated immune signaling and may positively regulate the LPS-induced innate immune response in the Japanese flounder HKM cells.