Expression regulation and function of NLRC5

New insights into the structure domain and function of NLR family CARD domain containing 5

NOD-like receptor family CARD domain-containing 5 (NLRC5) is a major transcriptional coactivator of MHC class I genes. NLRC5 is the largest member of the NLR family and contains three domains: an untypical caspase recruitment domain (uCARD), a central nucleotide-binding and oligomerization domain (NOD or NACHT), and a leucine-rich repeat (LRR) domain. The functional variability of NLRC5 has been attributed to its different domain interactions with specific ligands in different cell types. In this review, we address the molecular mechanisms and their implications in multiple microenvironments based on the different functional domains of NLRC5.

Orientia tsutsugamushi Ank5 promotes NLRC5 cytoplasmic retention and degradation to inhibit MHC class I expression

How intracellular bacteria subvert the major histocompatibility complex (MHC) class I pathway is poorly understood. Here, we show that the obligate intracellular bacterium Orientia tsutsugamushi uses its effector protein, Ank5, to inhibit nuclear translocation of the MHC class I gene transactivator, NLRC5, and orchestrate its proteasomal degradation. Ank5 uses a tyrosine in its fourth ankyrin repeat to bind the NLRC5 N-terminus while its F-box directs host SCF complex ubiquitination of NLRC5 in the leucine-rich repeat region that dictates susceptibility to Orientia- and Ank5-mediated degradation. The ability of O. tsutsugamushi strains to degrade NLRC5 correlates with ank5 genomic carriage. Ectopically expressed Ank5 that can bind but not degrade NLRC5 protects the transactivator during Orientia infection. Thus, Ank5 is an immunoevasin that uses its bipartite architecture to rid host cells of NLRC5 and reduce surface MHC class I molecules. This study offers insight into how intracellular pathogens can impair MHC class I expression.

NLRC5 exerts anti-endometriosis effects through inhibiting ERβ-mediated inflammatory response

BACKGROUND

Endometriosis is well known as a chronic inflammatory disease. The development of endometriosis is heavily influenced by the estrogen receptor β (ERβ), while NOD-like receptors (NLRs) family CARD domain-containing 5 (NLRC5) exhibits anti-inflammatory properties during endometriosis. However, whether NLRC5-mediated anti-inflammation is involved in the ERβ-mediated endometriosis is still uncertain. This study aimed to assess that relation.

METHODS

Nine cases of eutopic endometrial tissue and ten cases of ectopic endometrial tissue were collected from patients with endometriosis, and endometrial samples from ten healthy fertile women were analyzed, and the expression levels of ERβ were quantified using immunohistochemistry (IHC). Subsequently, we constructed mouse model of endometriosis by intraperitoneal injection. We detected the expression of ERβ, NLRC5, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and IL-10 and measured the volume of ectopic lesions in mice with endometriosis. In vitro, human endometrial stromal cells (hESCs) were transfected respectively with ERβ-overexpressing and NLRC5-overexpressing plasmids. We then assessed the expression of ERβ and NLRC5 using quantitative real-time PCR (qRT-PCR) and western blot analysis. Furthermore, we measured the concentrations of TNF-α, IL-6, and IL-10 in the cell culture supernatant through enzyme-linked immunosorbent assay (ELISA). Additionally, we evaluated the migration and invasion ability of hESCs using transwell and wound healing assays.

RESULTS

Inhibition of NLRC5 expression promotes the development of ectopic lesions in mice with endometriosis, upregulates the expression of pro-inflammatory factors TNF-α and IL-6, and downregulates the expression of anti-inflammatory factor IL-10. The high expression of NLRC5 in endometriosis depended on the ERβ overexpression. And ERβ promoted the migration of hESCs partially depend on inflammatory microenvironment. Lastly, NLRC5 overexpression inhibited ERβ-mediated development and inflammatory response of endometriosis.

CONCLUSIONS

Our results suggest that the innate immune molecule NLRC5-mediated anti-inflammation participates in ERβ-mediated endometriosis development, and partly clarifies the pathological mechanism of endometriosis, expanding our knowledge of the specific molecules related to the inflammatory response involved in endometriosis and potentially providing a new therapeutic target for endometriosis.

NOD-like Receptors-Emerging Links to Obesity and Associated Morbidities

Obesity and its associated metabolic morbidities have been and still are on the rise, posing a major challenge to health care systems worldwide. It has become evident over the last decades that a low-grade inflammatory response, primarily proceeding from the adipose tissue (AT), essentially contributes to adiposity-associated comorbidities, most prominently insulin resistance (IR), atherosclerosis and liver diseases. In mouse models, the release of pro-inflammatory cytokines such as TNF-alpha (TNF-α) and interleukin (IL)-1β and the imprinting of immune cells to a pro-inflammatory phenotype in AT play an important role. However, the underlying genetic and molecular determinants are not yet understood in detail. Recent evidence demonstrates that nucleotide-binding and oligomerization domain (NOD)-like receptor (NLR) family proteins, a group of cytosolic pattern recognition receptors (PRR), contribute to the development and control of obesity and obesity-associated inflammatory responses. In this article, we review the current state of research on the role of NLR proteins in obesity and discuss the possible mechanisms leading to and the outcomes of NLR activation in the obesity-associated morbidities IR, type 2 diabetes mellitus (T2DM), atherosclerosis and non-alcoholic fatty liver disease (NAFLD) and discuss emerging ideas about possibilities for NLR-based therapeutic interventions of metabolic diseases.

NOD-like receptor NLRC5 promotes neuroinflammation and inhibits neuronal survival in Parkinson's disease models

Parkinson's disease (PD) is mainly characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and neuroinflammation mediated by overactivated microglia and astrocytes. NLRC5 (nucleotide-binding oligomerization domain-like receptor family caspase recruitment domain containing 5) has been reported to participate in various immune disorders, but its role in neurodegenerative diseases remains unclear. In the current study, we found that the expression of NLRC5 was increased in the nigrostriatal axis of mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-induced PD, as well as in primary astrocytes, microglia and neurons exposed to different neurotoxic stimuli. In an acute MPTP-induced PD model, NLRC5 deficiency significantly reduced dopaminergic system degeneration and ameliorated motor deficits and striatal inflammation. Furthermore, we found that NLRC5 deficiency decreased the expression of the proinflammatory genes IL-1β, IL-6, TNF-α and COX2 in primary microglia and primary astrocytes treated with neuroinflammatory stimuli and reduced the inflammatory response in mixed glial cells in response to LPS treatment. Moreover, NLRC5 deficiency suppressed activation of the NF-κB and MAPK signaling pathways and enhanced the activation of AKT-GSK-3β and AMPK signaling in mixed glial cells. Furthermore, NLRC5 deficiency increased the survival of primary neurons treated with MPP⁺ or conditioned medium from LPS-stimulated mixed glial cells and promoted activation of the NF-κB and AKT signaling pathways. Moreover, the mRNA expression of NLRC5 was decreased in the blood of PD patients compared to healthy subjects. Therefore, we suggest that NLRC5 promotes neuroinflammation and dopaminergic degeneration in PD and may serve as a marker of glial activation.

NLRC5 restricts dengue virus infection by promoting the autophagic degradation of viral NS3 through E3 ligase CUL2 (cullin 2)

NLRC5 has been reported to be involved in antiviral immunity; however, the underlying mechanism remains poorly understood. Here, we investigated the functional role of NLRC5 in the infection of a flavivirus, dengue virus (DENV). We found that the expression of NLRC5 was strongly induced by virus infection and IFNB or IFNG stimulation in different cell lines. Overexpression of NLRC5 remarkably suppressed DENV infection, whereas knockout of NLRC5 led to a significant increase in DENV infection. Mechanistic study revealed that NLRC5 interacted with the viral nonstructural protein 3 (NS3) protease domain and mediated degradation of NS3 through a ubiquitin-dependent selective macroautophagy/autophagy pathway. We demonstrated that NLRC5 recruited the E3 ubiquitin ligase CUL2 (cullin 2) to catalyze K48-linked poly-ubiquitination of the NS3 protease domain, which subsequently served as a recognition signal for cargo receptor TOLLIP-mediated selective autophagic degradation. Together, we have demonstrated that NLRC5 exerted an antiviral effect by mediating the degradation of a multifunctional protein of DENV, providing a novel antiviral signal axis of NLRC5-CUL2-NS3-TOLLIP. This study expands our understanding of the regulatory network of NLRC5 in the host defense against virus infection.

Transcriptome profiling of lung immune responses potentially related to acute respiratory distress syndrome in forest musk deer

Background

Forest musk deer is an endangered species globally. The death of captive forest musk deer can be caused by certain respiratory system diseases. Acute respiratory distress syndrome (ARDS) is a huge threat to the life of forest muck deer that breed in our department.

Methods

Lung histopathologic analysis was conducted by hematoxylin and eosin (HE) staining. The lung gene changes triggered by ARDS were examined by RNA sequencing and related bioinformatics analysis in forest musk deer. The potential functions of unigenes were investigated by NR, SwissProt KOG, GO, and KEGG annotation analyses. Vital biological processes or pathways in ARDS were examined by GO and KEGG enrichment analyses.

Results

A total of 3265 unigenes were differentially expressed (|log₂fold-change|> 2 and adjusted P value < 0.01) in lung tissues of 3 forest musk deer with ARDS compared with normal lung tissues of the non-ARDS group. These differentially expressed unigenes (DEGs) played crucial roles in immunity and defense responses to pathogens. Moreover, we identified the DEGs related to one or more of the following biological processes: lung development, immunity, and bacterial/viral/fungal infection. And six DEGs that might be involved in lung injury caused by immune dysregulation or viral/fungal infection were identified.

Conclusion

ARDS-mediated lung gene alterations were identified in forest musk deer. Moreover, multiple genes involved in lung development and lung defense responses to bacteria/viruses/fungi in ARDS were filtered out in forest musk deer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08917-7.

NOD-like receptors in asthma

Asthma is an extremely prevalent chronic inflammatory disease of the airway where innate and adaptive immune systems participate collectively with epithelial and other structural cells to cause airway hyperresponsiveness, mucus overproduction, airway narrowing, and remodeling. The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are a family of intracellular innate immune sensors that detect microbe-associated molecular patterns and damage-associated molecular patterns, well-recognized for their central roles in the maintenance of tissue homeostasis and host defense against bacteria, viruses and fungi. In recent times, NLRs have been increasingly acknowledged as much more than innate sensors and have emerged also as relevant players in diseases classically defined by their adaptive immune responses such as asthma. In this review article, we discuss the current knowledge and recent developments about NLR expression, activation and function in relation to asthma and examine the potential interventions in NLR signaling as asthma immunomodulatory therapies.

Identification of Two Genetic Loci Associated with Leukopenia after Chemotherapy in Patients with Breast Cancer

PURPOSE

To identify molecular predictors of grade 3/4 neutropenic or leukopenic events (NLE) after chemotherapy using a genome-wide association study (GWAS).

EXPERIMENTAL DESIGN

A GWAS was performed on patients in the phase III chemotherapy study SUCCESS-A (n = 3,322). Genotyping was done using the Illumina HumanOmniExpress-12v1 array. Findings were functionally validated with cell culture models and the genotypes and gene expression of possible causative genes were correlated with clinical treatment response and prognostic outcomes.

RESULTS

One locus on chromosome 16 (rs4784750; NLRC5; P = 1.56E-8) and another locus on chromosome 13 (rs16972207; TNFSF13B; P = 3.42E-8) were identified at a genome-wide significance level. Functional validation revealed that expression of these two genes is altered by genotype-dependent and chemotherapy-dependent activity of two transcription factors. Genotypes also showed an association with disease-free survival in patients with an NLE.

CONCLUSIONS

Two loci in NLRC5 and TNFSF13B are associated with NLEs. The involvement of the MHC I regulator NLRC5 implies the possible involvement of immuno-oncological pathways.

NLR family CARD domain containing 5 promotes hypoxia-induced cancer progress and carboplatin resistance by activating PI3K/AKT via carcinoembryonic antigen related cell adhesion molecule 1 in non-small cell lung cancer

It is well known that non-small cell lung cancer (NSCLC) is a malignant tumor with high incidence in the world. We aimed to clarify a possible target and identify its precise molecular biological mechanism in NSCLC. NLR family CARD domain containing 5 (NLRC5) is widely expressed in tissues and exerts a vital role in anti-tumor immunity. We determined NLRC5 expression by RT-qPCR and western blot assay. The role of NLRC5 in the development of NSCLC was assessed by a loss-of-function assay. CCK-8, Annexin-V-FITC/PI Apoptosis Detection Kit, Transwell, and wound healing assays were used to determine the cell functions. Drug resistance-related proteins were analyzed by western blot assay. Furthermore, the modulation of NLRC5 on carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) expression and subsequent PI3K/AKT signaling was assessed. In this study, a hyper-expression of NLRC5 was found in NSCLC tissues and cell lines. Knockdown of NLRC5 suppressed cell viability, invasion, and migration, and furthermore promoted cell apoptosis in NSCLC cells. Moreover, under normoxia or hypoxia treatment, the upregulation of NLRC5 was related to carboplatin resistance. NLRC5 silencing increased carboplatin-resistant cell chemosensitivity, as evidenced by the increase in the cell inhibition rate and decrease in drug resistance-related protein expression. Mechanistically, NLRC5 knockdown inhibited the expression of CEACAM1 and subsequently blocked the PI3K/AKT signaling pathway. In conclusion, NLRC5 promotes the malignant biological behaviors of NSCLC cells by activating the PI3K/AKT signaling pathway via the regulation of CEACAM1 expression under normoxia and hypoxia.

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.

Inhibition of NLRC5 regulates cytokine expression in CD4+ T helper lymphocytes and prolongs murine islet and skin allograft survival

The purpose of this study was to study the effect of inhibiting NLRC5 expression and function on CD4 + T cells, and islet and skin transplantation in mice. A murine skin graft model and islet cell transplantation model were established, and the expression of NLRC5 was compared in rejection and immune tolerance groups. Mice spleen-derived CD4 + T cells were cultured, purified, and enriched in vitro, and transfected with the shRNA lentiviral vector NLRC5-RNAi-GFP. Changes in cytokine secretion were detected to understand changes in immunological function. Murine islet and skin transplantation models were injected with CD4 + T cells transfected with the lentivirus, and the survival time of the grafts and the levels of IFN-γ and IL-10 were compared between groups. The expression of NLRC5 mRNA in islet and skin grafts was significantly increased. In vitro experiments showed that the expression of IL-4 and IL-10 was up-regulated in CD4 + T cells, and T cells differentiation turned to Th2 after inhibition of NLRC5. In vivo experiments showed that inhibition of NLRC5 prolonged islet and skin graft survival. Pathological examination showed that the rejection of transplanted skin and islets in the NLRC5-RNAi group was mild, and there was a correlation between high expression of NLRC5 and rejection of mouse islet and skin grafts. In summary, inhibition of NLRC5 can prolong islet and skin graft survival induce transplant immune tolerance through induction of the secretion of Th2 cytokines by CD4 + T cells.

NLRC5: A Potential Target for Central Nervous System Disorders

Nucleotide oligomerization domain-like receptors (NLRs), a class of pattern recognition receptors, participate in the host’s first line of defense against invading pathogenic microorganisms. NLR family caspase recruitment domain containing 5 (NLRC5) is the largest member of the NLR family and has been shown to play an important role in inflammatory processes, angiogenesis, immunity, and apoptosis by regulating the nuclear factor-κB, type I interferon, and inflammasome signaling pathways, as well as the expression of major histocompatibility complex I genes. Recent studies have found that NLRC5 is also associated with neuronal development and central nervous system (CNS) diseases, such as CNS infection, cerebral ischemia/reperfusion injury, glioma, multiple sclerosis, and epilepsy. This review summarizes the research progress in the structure, expression, and biological characteristics of NLRC5 and its relationship with the CNS.

Update on the Mechanisms of Tubular Cell Injury in Diabetic Kidney Disease

Increasing evidence supports a role of proximal tubular (PT) injury in the progression of diabetic kidney disease (DKD), in patients with or without proteinuria. Research on the mechanisms of the PT injury in DKD could help us to identify potential new biomarkers and drug targets for DKD. A high glucose transport state and mismatched local hypoxia in the PT of diabetes patients may be the initiating factors causing PT injury. Other mechanism such as mitochondrial dysfunction, reactive oxygen species (ROS) overproduction, ER stress, and deficiency of autophagy interact with each other leading to more PT injury by forming a vicious circle. PT injury eventually leads to the development of tubulointerstitial inflammation and fibrosis in DKD. Many downstream signaling pathways have been demonstrated to mediate these diseased processes. This review focuses mostly on the novel mechanisms of proximal renal tubular injury in DKD and we believe such review could help us to better understand the pathogenesis of DKD and identify potential new therapies for this disease.

Relevance of the Pyroptosis-Related Inflammasome Pathway in the Pathogenesis of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a major cause of chronic kidney disease (CKD) in many developed and developing countries. Pyroptosis is a recently discovered form of programmed cell death (PCD). With progress in research on DKD, researchers have become increasingly interested in elucidating the role of pyroptosis in DKD pathogenesis. This review focuses on the three pathways of pyroptosis generation: the canonical inflammasome, non-canonical inflammasome, and caspase-3-mediated inflammasome pathways. The molecular and pathophysiological mechanisms of the pyroptosis-related inflammasome pathway in the development of DKD are summarized. Activation of the diabetes-mediated pyroptosis-related inflammasomes, such as nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), Toll-like receptor 4 (TLR4), caspase-1, interleukin (IL)-1β, and the IL-18 axis, plays an essential role in DKD lesions. By inhibiting activation of the TLR4 and NLRP3 inflammasomes, the production of caspase-1, IL-1β, and IL-18 is inhibited, thereby improving the pathological changes associated with DKD. Studies using high-glucose-induced cell models, high-fat diet/streptozotocin-induced DKD animal models, and human biopsies will help determine the spatial and temporal expression of DKD inflammatory components. Recent studies have confirmed the relationship between the pyroptosis-related inflammasome pathway and kidney disease. However, these studies are relatively superficial at present, and the mechanism needs further elucidation. Linking these findings with disease activity and prognosis would provide new ideas for DKD research.

The MHC Class-I Transactivator NLRC5: Implications to Cancer Immunology and Potential Applications to Cancer Immunotherapy

The immune system constantly monitors the emergence of cancerous cells and eliminates them. CD8⁺ cytotoxic T lymphocytes (CTLs), which kill tumor cells and provide antitumor immunity, select their targets by recognizing tumor antigenic peptides presented by MHC class-I (MHC-I) molecules. Cancer cells circumvent immune surveillance using diverse strategies. A key mechanism of cancer immune evasion is downregulation of MHC-I and key proteins of the antigen processing and presentation machinery (APM). Even though impaired MHC-I expression in cancers is well-known, reversing the MHC-I defects remains the least advanced area of tumor immunology. The discoveries that NLRC5 is the key transcriptional activator of MHC-I and APM genes, and genetic lesions and epigenetic modifications of NLRC5 are the most common cause of MHC-I defects in cancers, have raised the hopes for restoring MHC-I expression. Here, we provide an overview of cancer immunity mediated by CD8⁺ T cells and the functions of NLRC5 in MHC-I antigen presentation pathways. We describe the impressive advances made in understanding the regulation of NLRC5 expression, the data supporting the antitumor functions of NLRC5 and a few reports that argue for a pro-tumorigenic role. Finally, we explore the possible avenues of exploiting NLRC5 for cancer immunotherapy.

NLRC5 deficiency ameliorates cardiac fibrosis in diabetic cardiomyopathy by regulating EndMT through Smad2/3 signaling pathway

Diabetic cardiomyopathy (DCM) is one of the main causes of heart failure in patients with diabetes. Cardiac fibrosis caused by endothelial mesenchymal transformation (EndMT) plays an important role in the pathogenesis of DCM. NLRC5 is a recently discovered immune and inflammatory regulatory molecule in the NOD-like receptor family, and is involved in organ fibrosis. In this study, we found that the expression of NLRC5 was up-regulated in endothelial cells (ECs) and cardiac fibroblasts (CFs) in diabetes models both in vivo and in vitro. NLRC5 knockdown significantly inhibited high glucose-induced EndMT. In addition, NLRC5 deficiency inhibited the expression of phosphorylated Smad2/3 and the activation of EndMT-related transcription factors in ECs induced by high glucose. However, the effect of NLRC5 deficiency on CFs was not obvious. In summary, our results suggest that NLRC5 deficiency ameliorates cardiac fibrosis in DCM by inhibiting EndMT through Smad2/3 signaling pathway and related transcription factors. NLRC5 is likely to be a biomarker and therapeutic target of cardiac fibrosis in diabetic cardiomyopathy.

NLRC5: new cancer buster?

Recent decades, there is significant progress in understanding the mechanisms of tumor progression and immune evasion. The newly discovered protein NLRC5 is demonstrated to participate in regulating cancer immune escape through enhancing MHC class I genes expression in certain tumors. Nevertheless, increasing evidence has revealed that NLRC5 is up-regulated in some other tumors and promote tumor development and progression. The purpose of this review is to describe the role of NLRC5 in tumors and discuss whether NLRC5 can be a potential target in cancer treatment.

Emerging Roles for NLRC5 in Immune Diseases

Innate immunity activates the corresponding immune response relying on multiple pattern recognition receptors (PRRs) that includes pattern recognition receptors (PRRs), like NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs), which could accurately recognize invasive pathogens. In particular, NLRs belong to a large protein family of pattern recognition receptors in the cytoplasm, where they are highly correlated with activation of inflammatory response system followed by rapid clearance of invasive pathogens. Among the NLRs family, NLRC5, also known as NOD4 or NOD27, accounts for a large proportion and involves in immune responses far and wide. Notably, in the above response case of inflammation, the expression of NLRC5 remarkably increased in immune cells and immune-related tissues. However, the evidence for higher expression of NLRC5 in immune disease still remains controversial. It is noted that the growing evidence further accounts for the participation of NLRC5 in the innate immune response and inflammatory diseases. Moreover, NLRC5 has also been confirmed to exert a critical role in the control of regulatory diverse signaling pathways. Together with its broad participation in the occurrence and development of immune diseases, NLRC5 can be consequently treated as a potential therapeutic target. Nevertheless, the paucity of absolute understanding of intrinsic characteristics and underlying mechanisms of NLRC5 still make it hard to develop targeting drugs. Therefore, current summary about NLRC5 information is indispensable. Herein, current knowledge of NLRC5 is summarized, and research advances in terms of NLRC5 in characteristics, biological function, and regulatory mechanisms are reviewed.

NLRC5 inhibits neointima formation following vascular injury and directly interacts with PPARγ

NLR Family CARD Domain Containing 5 (NLRC5), an important immune regulator in innate immunity, is involved in regulating inflammation and antigen presentation. However, the role of NLRC5 in vascular remodeling remains unknown. Here we report the role of NLRC5 on vascular remodeling and provide a better understanding of its underlying mechanism. Nlrc5 knockout (Nlrc5^−/−) mice exhibit more severe intimal hyperplasia compared with wild-type mice after carotid ligation. Ex vivo data shows that NLRC5 deficiency leads to increased proliferation and migration of human aortic smooth muscle cells (HASMCs). NLRC5 binds to PPARγ and inhibits HASMC dedifferentiation. NACHT domain of NLRC5 is essential for the interaction with PPARγ and stimulation of PPARγ activity. Pioglitazone significantly rescues excessive intimal hyperplasia in Nlrc5^−/− mice and attenuates the increased proliferation and dedifferentiation in NLRC5-deficient HASMCs. Our study demonstrates that NLRC5 regulates vascular remodeling by directly inhibiting SMC dysfunction via its interaction with PPARγ.

NLRC5 is known for its role in inflammation and antigen presentation. Here Luan et al. find that NLRC5 protects mice from intimal hyperplasia following vascular injury, and regulates the response of vascular smooth muscle cells to injury through direct interaction with PPARγ.

NLRC5 mediates cell proliferation, migration, and invasion by regulating the Wnt/β-catenin signalling pathway in clear cell renal cell carcinoma

NLRC5, a newly discovered member of the NLR family, has been reported to regulate immune responses and promote cell proliferation, migration, and invasion in hepatocellular carcinoma. However, to date, the potential regulatory roles and molecular mechanisms by which NLRC5 affects the development and progression of clear cell renal cell carcinoma (ccRCC) remain largely unknown. In this study, human clinical data from The Cancer Genome Atlas database revealed that increased NLRC5 expression was associated with advanced stage and poor prognosis in ccRCC patients. Moreover, experimental results showed that NLRC5 is aberrantly overexpressed in human ccRCC tissues and cell lines. Depletion of NLRC5 attenuated ccRCC cell proliferation, migration, and invasion and suppressed ccRCC growth in a nude mouse model. By contrast, overexpression of NLRC5 promoted the proliferation, migration, and invasion of ccRCC cells in vitro. Additionally, NLRC5 expression is not only positively correlated with β-catenin but also coordinates the activation of the downstream Wnt/β-catenin signalling pathway. Together, our data suggest that NLRC5 may be a potential therapeutic target for ccRCC therapy.

Regulatory NLRs Control the RLR-Mediated Type I Interferon and Inflammatory Responses in Human Dendritic Cells

Unique members of the nucleotide-binding domain leucine-rich repeat (NLR) family have been found to regulate intracellular signaling pathways initiated by other families of pattern recognition receptors (PRR) such as Toll-like receptors (TLRs) and retinoic-acid inducible gene I (RIG-I)-like receptors (RLRs). Plasmacytoid dendritic cells (pDCs), the most powerful type I interferon (IFN) producing cells, preferentially employ endosomal TLRs to elicit antiviral IFN responses. By contrast, conventional DCs (cDCs) predominantly use cytosolic RLRs, which are constitutively expressed in them, to sense foreign nucleic acids. Previously we have reported that, though RIG-I is absent from resting pDCs, it is inducible upon TLR stimulation. In the recent study we investigated the regulatory ability of NLRs, namely NLRC5 and NLRX1 directly associated with the RLR-mediated signaling pathway in DC subtypes showing different RLR expression, particularly in pDCs, and monocyte-derived DCs (moDCs). Here we demonstrate that similarly to RLRs, NLRC5 is also inducible upon TLR9 stimulation, whereas NLRX1 is constitutively expressed in pDCs. Inhibition of NLRC5 and NLRX1 expression in pDCs augmented the RLR-stimulated expression of type I IFNs but did not affect the production of the pro-inflammatory cytokines TNF, IL-6, and the chemokine IL-8. Further we show that immature moDCs constantly express RLRs, NLRX1 and NLRC5 that are gradually upregulated during their differentiation. Similarly to pDCs, NLRX1 suppression increased the RLR-induced production of type I IFNs in moDCs. Interestingly, RLR stimulation of NLRX1-silenced moDCs leads to a significant increase in pro-inflammatory cytokine production and IκBα degradation, suggesting increased NF-κB activity. On the contrary, NLRC5 does not seem to have any effect on the RLR-mediated cytokine responses in moDCs. In summary, our results indicate that NLRX1 negatively regulates the RLR-mediated type I IFN production both in pDCs and moDCs. Further we show that NLRX1 inhibits pro-inflammatory cytokine secretion in moDCs but not in pDCs following RLR stimulation. Interestingly, NLRC5 suppresses the RLR-induced type I IFN secretion in pDCs but does not appear to have any regulatory function on the RLR pathway in moDCs. Collectively, our work demonstrates that RLR-mediated innate immune responses are primarily regulated by NLRX1 and partly controlled by NLRC5 in human DCs.

NLRC5 deficiency ameliorates diabetic nephropathy through alleviating inflammation

NOD-like receptor family caspase recruitment domain family domain containing 5 (NLRC5) has important roles in inflammation and innate immunity. NLRC5 was highly expressed in kidney from streptozotocin-induced diabetic mice, db/ db mice and patients with diabetes. Based on that evidence, the present study was designed to explore the roles of NLRC5 in the progression of diabetic nephropathy (DN). We examined kidney injury, including inflammation and fibrosis in Nlrc5 gene knockout ( Nlrc5^-/-) and wild-type (WT) diabetic mice. We found that Nlrc5^-/- mice developed less-severe diabetic kidney injury compared with WT mice, exhibiting lower albuminuria, less fibronectin and collagen IV expression, and reduced macrophage infiltration but greater levels of podocin and nephrin in the diabetic kidney. The underlying mechanisms were further investigated in vitro with peritoneal macrophages and mesangial cells treated with high glucose. Reduced proinflammatory effect was observed in peritoneal macrophages from Nlrc5^-/- mice, associated with NF-κB pathway suppression. Knocking down of NLRC5 in mesangial cells in high-glucose conditions was also associated with reduced NF-κB and TGF-β/Smad signaling. Taken together, NLRC5 promotes inflammation and fibrosis during DN progression partly through the effects on NF-κB and TGF-β/Smad pathways. NLRC5 may, therefore, be a promising therapeutic target for DN treatment.-Luan, P., Zhuang, J., Zou, J., Li, H., Shuai, P., Xu, X., Zhao, Y., Kou, W., Ji, S., Peng, A., Xu, Y., Su, Q., Jian, W., Peng, W. NLRC5 deficiency ameliorates diabetic nephropathy through alleviating inflammation.

NLRC5 promotes cell proliferation via regulating the NF-κB signaling pathway in Rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease and the pathogenesis remains unclear. Previous studies suggested that fibroblast-like synoviocytes (FLSs) play an important role in RA pathogenesis, including the injury of cartilage, the hyperplasia of the synovium and the release of inflammatory cytokines. We used complete Freund's adjuvant (CFA) induced rats as animal models for studying the RA pathogenesis. NLRC5 as the largest member of the NLR family has been reported to play a critical role in regulating immune responses. Increasing evidence suggests that NLRC5 is an pivotal negative modulator of inflammatory pathways. We investigated the mechanisms and signaling pathways of NLRC5 in RA progression. Significantly increased expression of NLRC5 was found in AA rats synovial tissues and cells. And high expression of inflammatory cytokine and cell proliferation of FLSs accompanied with NLRC5 overexpression, but inhibited in cells with NLRC5 silencing treatment. Interestingly, we found that overexpression of NLRC5 also coordinated the activation of NF-κB signaling pathway. These results suggested that NLRC5 promotes RA progression via the NF-κB signaling pathway potentially.

Negative regulation of HLA-DR expression on endothelial cells by anti-blood group A/B antibody ligation and mTOR inhibition

Donor-specific antibody (DSA), particularly against HLA class II, is a major cause of chronic antibody-mediated rejection (CAMR) after transplantation, although ABO-incompatible kidney transplantation has recently demonstrated favorable graft outcomes. The condition of no injury even in the presence of anti-donor antibody has been referred to as "accommodation", which would be one of the key factors for successful long-term graft survival. The purpose of this study was to analyze the beneficial effect of anti-blood group A/B antibody ligation on endothelial cells against HLA-DR antibody-mediated, complement-dependent cytotoxicity (CDC). Blood group A/B-expressing endothelial cells EA.hy926 or Human Umbilical Vein Endothelia Cells (HUVEC) were incubated with IFNγ in the presence or absence of anti-blood group A/B antibody or mTOR inhibitor (mTOR-i) for 48h. The effects on signaling pathway, HLA expression, complement regulatory factors, and CDC were investigated. Expression of HLA-DR on EA.hy926 or HUVEC were successfully elicited by IFNγ treatment, although little or no expression was observed in quiescent cells. Pre-incubation with anti-blood group A/B antibody had resistance to HLA-DR antibody-mediated CDC against IFNγ-treated cells in a concentration-dependent manner. This finding was ascribed to decreased expression of HLA-DR by post-translational regulation and increased expression of CD55/59, which was related to ERK and mTOR pathway inhibition. mTOR-i also inhibited HLA-DR expression by itself. Furthermore, the combination of mTOR-I and anti-blood group A/B ligation had an additive effect in preventing HLA-DR antibody-mediated CDC. Anti-blood group A/B antibody might play a preventive role in CAMR. Inhibition of the ERK and mTOR pathways may contribute to the development of a novel treatment in the maintenance period after transplantation.

Increased toll-like receptors and p53 levels regulate apoptosis and angiogenesis in non-muscle invasive bladder cancer: mechanism of action of P-MAPA biological response modifier

BACKGROUND

The new modalities for treating patients with non-muscle invasive bladder cancer (NMIBC) for whom BCG (Bacillus Calmette-Guerin) has failed or is contraindicated are recently increasing due to the development of new drugs. Although agents like mitomycin C and BCG are routinely used, there is a need for more potent and/or less-toxic agents. In this scenario, a new perspective is represented by P-MAPA (Protein Aggregate Magnesium-Ammonium Phospholinoleate-Palmitoleate Anhydride), developed by Farmabrasilis (non-profit research network). This study detailed and characterized the mechanisms of action of P-MAPA based on activation of mediators of Toll-like Receptors (TLRs) 2 and 4 signaling pathways and p53 in regulating angiogenesis and apoptosis in an animal model of NMIBC, as well as, compared these mechanisms with BCG treatment.

RESULTS

Our results demonstrated the activation of the immune system by BCG (MyD88-dependent pathway) resulted in increased inflammatory cytokines. However, P-MAPA intravesical immunotherapy led to distinct activation of TLRs 2 and 4-mediated innate immune system, resulting in increased interferons signaling pathway (TRIF-dependent pathway), which was more effective in the NMIBC treatment. Interferon signaling pathway activation induced by P-MAPA led to increase of iNOS protein levels, resulting in apoptosis and histopathological recovery. Additionally, P-MAPA immunotherapy increased wild-type p53 protein levels. The increased wild-type p53 protein levels were fundamental to NO-induced apoptosis and the up-regulation of BAX. Furthermore, interferon signaling pathway induction and increased p53 protein levels by P-MAPA led to important antitumor effects, not only suppressing abnormal cell proliferation, but also by preventing continuous expansion of tumor mass through suppression of angiogenesis, which was characterized by decreased VEGF and increased endostatin protein levels.

CONCLUSIONS

Thus, P-MAPA immunotherapy could be considered an important therapeutic strategy for NMIBC, as well as, opens a new perspective for treatment of patients that are refractory or resistant to BCG intravesical therapy.

NLRC5 Mediates IL-6 and IL-1β Secretion in LX-2 Cells and Modulated by the NF-κB/Smad3 Pathway

Recent data have shown that nucleotide-binding domain leucine-rich repeat proteins (NLRs), a class of innate immune receptors that respond to pathogen attack or cellular stress, have gained increasing attention. NLRC5 (NLR family, CARD domain containing 5) is the largest member of the NLR family, which has recently been identified as a critical regulator of immune responses. Until recently, the function of NLRC5 has been a matter of debate. In this study, we explore the role of NLRC5 in cytokine secretion and the role of the nuclear factor-κB (NF-κB) signaling pathway in tumor necrosis factor-alpha (TNF-α)-induced NLRC5 expression in LX-2 cells. We demonstrated that overexpression of NLRC5 results in an upregulation of IL-6 and IL-1β secretion. On the other hand, knockdown of NLRC5 by transfecting siRNA decreased IL-6 and IL-1β secretion in LX-2 cells. Meanwhile, the results showed that pyrrolidine dithiocarbamate (PDTC) (a specific inhibitor of the NF-κB signaling pathway) inhibited NLRC5 expression and NLRC5 silencing could increase the expression levels of p65 in cell nucleus accompanied with upregulated phosphorylation of Smad3 protein levels in response to TNF-α. These results indicated that NLRC5 plays a significant role in TNF-α-enhanced cytokine (IL-6 and IL-1β) secretion of LX-2 cells and the NF-κB/Smad3 signal pathway is involved in its induction of expression.

Atypical Inflammasomes

Pattern recognition receptors, including members of the NLR and PYHIN families, are essential for recognition of both pathogen- and host-derived danger signals. A number of molecules in these families are capable of forming multiprotein complexes termed inflammasomes that result in the activation of caspase-1. In addition to NLRP1, NLRP3, NLRC4, and AIM2, which form well-described inflammasome complexes, IFI16, NLRP6, NLRP7, NLRP12, and NLRC5 have also been proposed to form inflammasomes under specific conditions. The structure and function of these atypical inflammasomes will be highlighted here.

Exploring transcriptomic diversity in muscle revealed that cellular signaling pathways mainly differentiate five Western porcine breeds

Background

Among transcriptomic studies, those comparing species or populations can increase our understanding of the impact of the evolutionary forces on the differentiation of populations. A particular situation is the one of short evolution time with breeds of a domesticated species that underwent strong selective pressures. In this study, the gene expression diversity across five pig breeds has been explored in muscle. Samples came from: 24 Duroc, 33 Landrace, 41 Large White dam line, 10 Large White sire line and 39 Piétrain. From these animals, 147 muscle samples obtained at slaughter were analyzed using the porcine Agilent 44 K v1 microarray.

Results

A total of 12,358 genes were identified as expressed in muscle after normalization and 1,703 genes were declared differential for at least one breed (FDR < 0.001). The functional analysis highlighted that gene expression diversity is mainly linked to cellular signaling pathways such as the PI3K (phosphoinositide 3-kinase) pathway. The PI3K pathway is known to be involved in the control of development of the skeletal muscle mass by affecting extracellular matrix - receptor interactions, regulation of actin cytoskeleton pathways and some metabolic functions. This study also highlighted 228 spots (171 unique genes) that differentiate the breeds from each other. A common subgroup of 15 genes selected by three statistical methods was able to differentiate Duroc, Large White and Piétrain breeds.

Conclusions

This study on transcriptomic differentiation across Western pig breeds highlighted a global picture: mainly signaling pathways were affected. This result is consistent with the selection objective of increasing muscle mass. These transcriptional changes may indicate selection pressure or simply breed differences which may be driven by human selection. Further work aiming at comparing genetic and transcriptomic diversities would further increase our understanding of the consequences of human impact on livestock species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2259-9) contains supplementary material, which is available to authorized users.

NLRC5 regulates TGF-β1-induced proliferation and activation of hepatic stellate cells during hepatic fibrosis

Therapeutic management of liver fibrosis remains an unsolved clinical problem. Hepatic accumulation of extracellular matrix, mainly collagen, is mediated by the production of transforming growth factor-β1 (TGF-β1) in hepatic stellate cells (HSCs). NLRC5, the largest member of the NLR protein family, has recently been identified as a critical regulator of immune responses. Novel evidence shows that NLRC5 is an important negative modulator of inflammatory pathways. Herein, we determined the regulation of NLRC5 in liver fibrogenesis and its underlying mechanisms. We have shown that NLRC5 was upregulated in human liver fibrotic tissues. Overexpression of NLRC5 resulted in an upregulation of collagen 1 and α-smooth muscle actin expression in HSC LX-2 cells, which was inhibited by NLRC5 knockdown with its siRNA. Furthermore, NLRC5 deficiency significantly suppressed TGF-β1-induced proliferation but increased apoptosis (i.e., increased caspases-3, DR4 and DR5) in LX-2 cells. In addition, knockdown of NLRC5 promoted the activation of NF-κB signaling pathways but abrogated phosphorylation of Smad2 and Smad3 proteins in response to TGF-β1. These results indicate that NLRC5 is a potent pro-fibrogenic molecule for HSC activation through TGF-β1/Smad and NF-κB signaling pathways. NLRC5 inhibition would be a promising therapeutic avenue for treating hepatic fibrosis.

NLRC5 expression in tumors and its role as a negative prognostic indicator in stage III non-small-cell lung cancer patients

Major histocompatibility complex (MHC) class I molecules have a crucial role in tumor immune evasion; however, the association of MHC class I molecules with outcomes in cancer patients remains controversial. Nucleotide-binding oligomerization-like receptor family caspase recruitment domain-containing 5 (NLRC5) has been reported to be a MHC class I transactivator. However, the expression and function of NLRC5 in cancer remains to be elucidated. The present study aimed to retrospectively examine NLRC5 expression in human tumor tissues and its association with clinical outcomes of non-small-cell lung cancer (NSCLC) stage III patients. The expression of MHC class I and NLRC5 in NSCLC were detected using immunohistochemistry (IHC). The association between their expression levels was assessed using the Pearson's χ² test and their association with survival was assessed using Kaplan-Meier analysis and the log-rank test. In addition, the expression of NLRC5 and MHC class I were examined in 323 cases of seven other types of tumors and their correlations were studied. The results revealed that the expression of NLRC5 was correlated with that of MHC class I in NSCLC patients (P=0.008). MHC class I-positive and nuclear NLRC5-positive NSCLC patients were found to have shorter overall survival (OS) rates (log-rank, P=0.032 and P=0.039, respectively). In addition, in the seven different tumor types, there was a significant correlation between MHC class I and NLRC5 nuclear expression (P<0.001) as well as MHC class I and NLRC5 cytoplasmic expression (P=0.003). In conclusion, NLRC5 was demonstrated to be widely expressed in eight tumor tissues and its expression was correlated with that of MHC class I. Of note, nuclear NLRC5-negative and MHC class I-negative stage III NSCLC patients had improved OS rates compared to those with positive expression. Therefore, NLRC5 and MHC class I may be negative prognostic indicators in NSCLC stage III patients.

NLRC5 interacts with RIG-I to induce a robust antiviral response against influenza virus infection

The NLR protein, NLRC5 is an important regulator of MHC class I gene expression, however, the role of NLRC5 in other innate immune responses is less well defined. In the present study, we report that NLRC5 binds RIG-I and that this interaction is critical for robust antiviral responses against influenza virus. Overexpression of NLRC5 in the human lung epithelial cell line, A549, and normal human bronchial epithelial cells resulted in impaired replication of influenza virus A/Puerto Rico/8/34 virus (PR8) and enhanced IFN-β expression. Influenza virus leads to induction of IFN-β that drives RIG-I and NLRC5 expression in host cells. Our results suggest that NLRC5 extends and stabilizes influenza virus induced RIG-I expression and delays expression of the viral inhibitor protein NS1. We show that NS1 binds to NLRC5 to suppress its function. Interaction domain mapping revealed that NLRC5 interacts with RIG-I via its N-terminal death domain and that NLRC5 enhanced antiviral activity in an leucine-rich repeat domain independent manner. Taken together, our findings identify a novel role for NLRC5 in RIG-I-mediated antiviral host responses against influenza virus infection, distinguished from the role of NLRC5 in MHC class I gene regulation.