NLRC5 Mediates Cytokine Secretion in RAW264.7 Macrophages and Modulated by the JAK2/STAT3 Pathway

Adaptor molecules mediate negative regulation of macrophage inflammatory pathways: a closer look

Macrophages play a central role in initiating, maintaining, and terminating inflammation. For that, macrophages respond to various external stimuli in changing environments through signaling pathways that are tightly regulated and interconnected. This process involves, among others, autoregulatory loops that activate and deactivate macrophages through various cytokines, stimulants, and other chemical mediators. Adaptor proteins play an indispensable role in facilitating various inflammatory signals. These proteins are dynamic and flexible modulators of immune cell signaling and act as molecular bridges between cell surface receptors and intracellular effector molecules. They are involved in regulating physiological inflammation and also contribute significantly to the development of chronic inflammatory processes. This is at least partly due to their involvement in the activation and deactivation of macrophages, leading to changes in the macrophages' activation/phenotype. This review provides a comprehensive overview of the 20 adaptor molecules and proteins that act as negative regulators of inflammation in macrophages and effectively suppress inflammatory signaling pathways. We emphasize the functional role of adaptors in signal transduction in macrophages and their influence on the phenotypic transition of macrophages from pro-inflammatory M1-like states to anti-inflammatory M2-like phenotypes. This endeavor mainly aims at highlighting and orchestrating the intricate dynamics of adaptor molecules by elucidating the associated key roles along with respective domains and opening avenues for therapeutic and investigative purposes in clinical practice.

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.

Viola yedoensis Makino formula alleviates DNCB-induced atopic dermatitis by activating JAK2/STAT3 signaling pathway and promoting M2 macrophages polarization

BACKGROUND

Atopic dermatitis (AD), a common inflammatory skin disorder, severely affects the life quality of patients and renders heavy financial burden on patient's family. The Chinese medicine Viola yedoensis Makino formula (VYAC) has been widely used for treating various skin disorders. Previous studies have reported that VYAC is effective in relieving DNCB-induced AD and inflammation. However, the anti-inflammatory mechanism of VYAC is still ill-defined and poorly understood. This study aims to investigate the therapeutic effects of VYAC on DNCB-induced AD and to elucidate the underlying anti-inflammatory mechanisms.

METHODOLOGY

VYAC were extracted with 70% ethanol and lyophilized for use. AD mice were established by DNCB. The therapeutic effects of VYAC were evaluated by oral administration VYAC (150, 300 and 600 mg/kg) daily in vivo. The histopathological and immunohistochemistry were used to analyze skin lesion and macrophages infiltration, RT-qPCR and Elisa were used to analyze the inflammatory factors in skin tissues and serum. To explore the underlying mechanism of VYAC against AD in vitro. RAW264.7 cells and bone-marrow-derived macrophages (BMDMs) were employed for macrophage polarization analysis. Flow cytometer, immunofluorescence and western blot were used to analyze M2 macrophages markers. STAT3 siRNA were transfected into both cells to validate the effects of VYAC-induced macrophages M2 polarization via JAK2/STAT3 signaling pathway.

RESULTS

VYAC ameliorated skin lesion of DNCB-induced AD mice by decreased clinical scores and epidermal thickness, decreased the level of pro-inflammatory factors (IL-1β, TNF-α and IL-18) and enhanced IL-10 anti-inflammatory factor level, inhibited macrophages infiltration and promoted M2 macrophages polarization in vivo. VYAC significantly promoted M2 macrophages polarization in vitro. It is observed that VYAC not only inhibited the phosphorylation of JAK2 and STAT3 in RAW264.7 cells and BMDMs, but also accelerated the translocation to the nucleus. What's more, VYAC reduced the polarization of M2 macrophage by activating JAK2/STAT3 signaling pathway was observed in both cells.

CONCLUSIONS

Our findings demonstrate that VYAC significantly ameliorates skin lesion of DNCB-induced AD mice and reduces the levels of inflammatory factors by activating JAK2/STAT3 signaling pathway and promoting M2 macrophages polarization.

NLRC5 Deficiency Deregulates Hepatic Inflammatory Response but Does Not Aggravate Carbon Tetrachloride-Induced Liver Fibrosis

The nucleotide-binding leucine-rich repeat-containing receptor (NLR) family protein-5 (NLRC5) controls NF-κB activation and production of inflammatory cytokines in certain cell types. NLRC5 is considered a potential regulator of hepatic fibrogenic response due to its ability to inhibit hepatic stellate activation in vitro. To test whether NLRC5 is critical to control liver fibrosis, we treated wildtype and NLRC5-deficient mice with carbon tetrachloride (CCl4) and assessed pathological changes in the liver. Serum alanine transaminase levels and histopathology examination of liver sections revealed that NLRC5 deficiency did not exacerbate CCl4-induced liver damage or inflammatory cell infiltration. Sirius red staining of collagen fibers and hydroxyproline content showed comparable levels of liver fibrosis in CCl4-treated NLRC5-deficient and control mice. Myofibroblast differentiation and induction of collagen genes were similarly increased in both groups. Strikingly, the fibrotic livers of NLRC5-deficient mice showed reduced expression of matrix metalloproteinase-3 (Mmp3) and tissue inhibitor of MMPs-1 (Timp1) but not Mmp2 or Timp2. Fibrotic livers of NLRC5-deficient mice had increased expression of TNF but similar induction of TGFβ compared to wildtype mice. CCl4-treated control and NLRC5-deficient mice displayed similar upregulation of Cx3cr1, a monocyte chemoattractant receptor gene, and the Cd68 macrophage marker. However, the fibrotic livers of NLRC5-deficient mice showed increased expression of F4/80 (Adgre1), a marker of tissue-resident macrophages. NLRC5-deficient livers showed increased phosphorylation of the NF-κB subunit p65 that remained elevated following fibrosis induction. Taken together, NLRC5 deficiency deregulates hepatic inflammatory response following chemical injury but does not significantly aggravate the fibrogenic response, showing that NLRC5 is not a critical regulator of liver fibrosis pathogenesis.

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.

MHC class I transactivator NLRC5 in host immunity, cancer and beyond

The presentation of antigenic peptides by major histocompatibility complex (MHC) class I and class II molecules is crucial for activation of the adaptive immune system. The nucleotide-binding domain and leucine-rich repeat receptor family members CIITA and NLRC5 function as the major transcriptional activators of MHC class II and class I gene expression, respectively. Since the identification of NLRC5 as the master regulator of MHC class I and class-I-related genes, there have been major advances in understanding the function of NLRC5 in infectious diseases and cancer. Here, we discuss the biological significance and mechanism of NLRC5-dependent MHC class I expression.

NLRC5 negatively regulates inflammatory responses in LPS-induced acute lung injury through NF-κB and p38 MAPK signal pathways

Acute lung injury is an acute inflammatory disease with high morbidity rate and high mortality rate. However, there is still no effective clinical treatment to date. Our previous studies found that NLRC5 was significantly increased in acute liver injury model induced by LPS to reduce the secretion of IL-6 and TNF-α. Nevertheless, there is no report on the role of NLRC5 in regulating the development of acute lung injury. In this study we successfully established a model of acute lung injury induced by tracheal instillation of LPS in mice, and found NLRC5 expression was apparently elevated in mouse lung tissue and primary alveolar macrophages. NLRC5 overexpression negatively regulated secretion of inflammatory cytokines in murine alveolar macrophage cells through NF-κB and p38 MAPK pathway inhibition. There is a positively feedback between NLRC5 and NF-κB or p38 MAPK pathway. This study may provide some new ideas for clinical prevention of lung injury.

NLRC5 Serves as a Pro-viral Factor During Influenza Virus Infection in Chicken Macrophages

Avian influenza viruses (AIVs) cause major economic losses to the global poultry industry. Many host factors have been identified that act as regulators of the inflammatory response and virus replication in influenza A virus (IAV) infected cells including nucleotide-binding oligomerization domain (NOD) like receptor (NLR) family proteins. Evidence is emerging that NLRC5, the largest NLR member, is a regulator of host immune responses against invading pathogens including viruses; however, its role in the avian immune system and AIV pathogenesis has not been fully explored. In this study, we found that NLRC5 is activated by a range of low and highly pathogenic AIVs in primary chicken lung cells and a chicken macrophage cell line. Further, siRNA mediated NLRC5 knockdown in chicken macrophages resulted in a significant reduction in AIV replication which was associated with the upregulation of genes associated with activated NFκB signaling pathway. The knockdown of NLRC5 enhanced the expression of genes known to be associated with viral defense and decreased innate cytokine gene expression following AIV infection. Overall, our investigation strongly suggests that NLRC5 is a pro-viral factor during IAV infection in chicken and may contribute to pathogenesis through innate cytokine regulation. Further studies are warranted to investigate the IAV protein(s) that may regulate activation of NLRC5.

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.

Sphk1 promotes ulcerative colitis via activating JAK2/STAT3 signaling pathway

Ulcerative colitis (UC) is a chronic non-specific inflammatory disease of the colon and rectum. The cause of ulcerative colitis is still unclear, although there may be a hereditary factor. SphK1 has been reported to exhibit an inhibitory effect on the occurrence and development of inflammation; however, the association between SphK1 and the progression of UC remains unclear. The aim of the present study was to investigate the effect of Sphk1 on the progression of UC. The proliferation of RAW264.7 cells was determined using a Cell Counting Kit-8 assay and apoptosis was measured using flow cytometry. The levels of pro-inflammatory cytokines secreted by RAW264.7 cells were investigated using ELISA kits and the protein expression levels in RAW264.7 cells were examined by western blotting. A dextran sulfate sodium (DSS)-induced mouse model was established to investigate the effect of SphK1 on the progression of UC in vivo. Overexpression of Sphk1 significantly increased the proliferation and inhibited the apoptosis of RAW264.7 cells. Additionally, overexpression of Sphk1 increased the secretion of pro-inflammatory cytokines and activated the JAK2/STAT3 signaling pathway in RAW264.7 cells, and JSI-124 partially suppressed these effects. Furthermore, SphK1-small interfering RNA or JSI-124 partially rescued lipopolysaccharide-induced proliferation and pro-inflammatory effects on RAW264.7 cells. The SphK1 inhibitor (PF-543) had an inhibitory effect on DSS-induced UC mice. Sphk1 had significant pro-inflammatory effects on the progression of UC, and may thus be a potential novel therapeutic target for the treatment of UC.

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 and autophagy combined as possible predictors in patients with endometriosis

OBJECTIVE

To investigate the levels of NLRC5 and autophagy in women with leiomyoma and endometriosis and the correlation between NLRC5 level and autophagy level.

DESIGN

Case-control study.

SETTING

Clinics.

PATIENT(S)

Sixty-five patients were recruited: 30 women with endometriosis were compared with 35 women with leiomyoma.

INTERVENTION(S)

Endometriosis was definitively diagnosed during surgery by laparoscopy or laparotomy and was confirmed by histopathological evaluation (n=30). Secretory phase ectopic endometrium tissues and eutopic endometrium tissues were obtained from 30 women with endometriosis. Control endometrium tissues were collected at hysterectomy from 35 women with leiomyoma. Immunohistochemical staining of NLRC5, LC3, Beclin1 and P62 were performed.

MAIN OUTCOME MEASURE(S)

A semiquantitative analysis was performed. Correlations between NLRC5 level and LC3, Beclin1, P62 levels were compared.

RESULT(S)

The expressions of NLRC5 and P62 in the ectopic and eutopic endometrium of endometriosis groups were significantly higher than that in the endometrium of leiomyoma group. And their expressions in ectopic endometrium were significantly up-regulated compared to the eutopic endometrium. The expressions of LC3 and Beclin1 were down-regulated in the ectopic and eutopic endometrium of endometriosis groups compared to the leiomyoma group. LC3 and Beclin1 levels were lower in ectopic endometrium than in the eutopic endometrium. There is a negative correlation between NLRC5 level and LC3, Beclin1 levels. There is a positive correlation between NLRC5 level and P62 level.

CONCLUSION(S)

There is a negative correlation between NLRC5 level and autophagy level. NLRC5 and autophagy combined may as promising predictors in patients with endometriosis.

Ginsenoside Rk1 suppresses pro-inflammatory responses in lipopolysaccharide-stimulated RAW264.7 cells by inhibiting the Jak2/Stat3 pathway

The saponin ginsenoside Rk1 is a major compound isolated from ginseng. Ginsenoside Rk1 has been reported to have anti-inflammatory and anti-tumor properties and to be involved in the regulation of metabolism. However, the effect and mechanism of anti-inflammatory action of ginsenoside Rk1 has not been fully clarified. We investigated whether ginsenoside Rk1 could suppress the inflammatory response in lipopolysaccharide-stimulated RAW264.7 macrophages and to explore its mechanism of the action. RAW264.7 cells were treated with LPS (1 μg·mL^-1) in the absence or the presence of Ginsenoside Rk1 (10, 20, and 40 μmol·L^-1). Then the inflammatory factors were tested with Griess reagents, ELISA, and RT-PCR. The proteins were analyzed by Western blotting. Ginsenoside Rk1 inhibited lipopolysaccharide-induced expression of nitric oxide (NO), interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, and monocyte chemotactic protein (MCP)-1. Ginsenoside Rk1 inhibited the lipopolysaccharide-stimulated phosphorylation of NF-κB and janus kinase (Jak)2 and signal transducer and activator of transcription (Stat)3 at Ser727 and Tyr705. These data suggested that ginsenoside Rk1 could inhibit expression of inflammatory mediators and suppress inflammation further by blocking activation of NF-κB and the Jak2/Stat3 pathway in LPS-stimulated RAW264.7 cells.

Knockdown of NLRC5 inhibits renal fibroblast activation via modulating TGF-β1/Smad signaling pathway

NLRC5, the largest member of the Nucleotide-binding domain and leucine-rich repeat (NLR) protein family, is recently proven to be a critical modulator in fibrogenesis. However, the role of NLRC5 in renal fibrosis remains unknown. In the present study, we investigated the effects of NLRC5 on transforming growth factor β1 (TGF-β1)-stimulated rat renal fibroblasts in vitro. Our results showed that the expression of NLRC5 was also obviously upregulated in renal fibrosis tissues and TGF-β1-treated NRK-49F cells. Knockdown of NLRC5 inhibited the proliferation of NRK-49F cells induced by TGF-β1, as well as suppressed the accumulation of extracellular matrix (ECM) in NRK-49F cells induced by TGF-β1. Furthermore, knockdown of NLRC5 inhibited the expression of phosphorylated Smad3 in TGF-β1-treated NRK-49F cells. In conclusion, our results show that knockdown of NLRC5 inhibits renal fibroblast activation via modulating TGF-β1/Smad signaling pathway. Therefore, NLRC5 may act as a key mediator in renal fibroblast activation and fibrogenesis.

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.

NLRC5 Functions beyond MHC I Regulation-What Do We Know So Far?

NLRC5 is a member of the NLR family that acts as a transcriptional activator of MHC class I genes. In line with the function of several related NLR proteins in innate immune responses, there is, however, also ample evidence that NLRC5 contributes to innate and adaptive immune responses beyond the regulation of MHC class I genes. In human and murine cells, for example, NLRC5 was proposed to contribute to inflammatory and type I interferon responses. The role of NLRC5 in these and other cellular processes is hitherto still not well understood and blurred by discrepancies in the reported data. Here, we provide a detailed and critical discussion of the available experimental data on the emerging biological functions of NLRC5 in innate immune responses in men and mice. Better awareness of the multiple roles of NLRC5 will help to define its overall contribution to immune responses and cancer.

Characterization of the NLRC5 promoter in chicken: SNPs, regulatory elements and CpG islands

NLRC5 plays an important role in the innate immunity and cellular immunity in many species, but the regulatory mechanism of NLRC5 expression in chickens remains unclear. In this study, a series of deletion fragments of the NLRC5 promoter region were constructed and dual-luciferase assay was performed. Then, we detected the SNP in the core region and its function. Important transcriptional regulatory elements were predicted and identified. Methylation of CpG islands was measured. The results revealed that the two core regions of -4372 to -3756 and -2925 to -2265 in the NLRC5 promoter were essential for NLRC5 mRNA expression in which a SNP (A/G), located at -2470, was found to have an effect on the transcriptional activity. Also, the STAT1 element in the second core region of the NLRC5 promoter was identified to bind with the STAT1 transcription factor, which was necessary for the transcriptional activity. In addition, many other elements in the NLRC5 promoter, including YY1 and CEBP, may contribute significantly to the expression activity of NLRC5. Moreover, two CpG islands were searched. Part of one was located in the first core region, which suggests that epigenetic modification may regulate the activity of the first promoter region, and the other was mostly in an unmethylated state. Collectively, these results suggest the complex regulation of NLRC5 expression includes SNPs, transcription factors and methylation.

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.

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.

Transcriptional regulation of pattern recognition receptors by Jak/STAT signaling, and the implications for disease pathogenesis

Cytokines are well known for their pleiotropism, affecting a large number of cellular responses, including proliferation, survival, functional maturation, and immunomodulation. It is, therefore, not surprising that both the deregulated expression of cytokines and the subsequent activation of their downstream signaling pathways is a common feature of many cancers, as well as chronic inflammatory, autoimmune, metabolic, and cardiovascular diseases. In this regard, activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is the predominant intracellular signaling event triggered by cytokines, with STAT1 and STAT3 having the greatest diversity of biological functions among the 7 known members of the STAT family of latent transcription factors. Notably, over recent years, it has emerged that STAT1 and STAT3 are employed by various cytokines to manipulate the signal output of heterologous receptors of the innate immune system, namely pattern recognition receptors (PRRs), with both immune and nonimmune (eg, oncogenic, metabolic) cellular processes being affected. This review highlights these pivotal advancements in our understanding of how a cross talk between cytokine and PRR signaling networks can impact on a variety of cellular responses during disease pathogenesis, and the potential therapeutic implications of targeting these networks.

Advances in Nod-like receptors (NLR) biology

The innate immune system is composed of a wide repertoire of conserved pattern recognition receptors (PRRs) able to trigger inflammation and host defense mechanisms in response to endogenous or exogenous pathogenic insults. Among these, nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) are intracellular sentinels of cytosolic sanctity capable of orchestrating innate immunity and inflammatory responses following the perception of noxious signals within the cell. In this review, we elaborate on recent advances in the signaling mechanisms of NLRs, operating within inflammasomes or through alternative inflammatory pathways, and discuss the spectrum of their effector functions in innate immunity. We describe the progressive characterization of each NLR with associated controversies and cutting edge discoveries.