HBV inhibits LPS-induced NLRP3 inflammasome activation and IL-1β production via suppressing the NF-κB pathway and ROS production

Hepatic macrophages in liver homeostasis and diseases-diversity, plasticity and therapeutic opportunities

Macrophages, which are key cellular components of the liver, have emerged as essential players in the maintenance of hepatic homeostasis and in injury and repair processes in acute and chronic liver diseases. Upon liver injury, resident Kupffer cells (KCs) sense disturbances in homeostasis, interact with hepatic cell populations and release chemokines to recruit circulating leukocytes, including monocytes, which subsequently differentiate into monocyte-derived macrophages (MoMϕs) in the liver. Both KCs and MoMϕs contribute to both the progression and resolution of tissue inflammation and injury in various liver diseases. The diversity of hepatic macrophage subsets and their plasticity explain their different functional responses in distinct liver diseases. In this review, we highlight novel findings regarding the origins and functions of hepatic macrophages and discuss the potential of targeting macrophages as a therapeutic strategy for liver disease.

Glycyrrhetinic acid alleviates acute lung injury by PI3K/AKT suppressing macrophagic Nlrp3 inflammasome activation

Glycyrrhetinic acid (GA), a triterpene saponins, has been widely proven to have multiple medicinal properties. Our study aimed to figure out the protective effect of GA on acute lung injury (ALI) and the underlying mechanism. The LPS-induced ALI model mice were intratracheally administrated with 10 mg/kg LPS. Pretreatment with GA (10, 20, 40 mg/kg, i.g.) ameliorated acute lung injury pathological damage, macrophage infiltration and lung edema. In the lung tissue, immunofluorescence (IF) and Immunohistochemistry (IHC) were performed to detect macrophage Nod-like receptor 3 (Nlrp3) inflammasome activation and interleukin-1β (IL-1β) protein expression. In macrophages, the co-localization of Nlrp3 with caspase-1 and Nlrp3 with ASC were assessed by IF. The translational and transcriptional level of Nlrp3, cle-caspase-1 and apoptosis-associated speck-like protein containing CARD (ASC), were examined by Western blot and Real time PCR (RT-PCR). The protein expression of Cle-caspase-1 was remarkably suppressed via sh-Nlrp3 transfection compared with LPS groups. GA notably attenuated ALI by inhibiting Nlrp3 formation and activation. Furthermore, GA downregulated the production of reactive oxygen species (ROS) and the phosphorylation level of PI3K and AKT in macrophages. These findings indicate that GA ameliorated ALI in mice by suppressing the activation of Nlrp3 inflammasome which may be mediated by ROS-PI3K/AKT pathway. GA may serve as a promising agent for the attenuation of ALI-related inflammation and pathology.

Irisin alleviates LPS-induced liver injury and inflammation through inhibition of NLRP3 inflammasome and NF-κB signaling

Lipopolysaccharide (LPS) provokes severe inflammation and cell death in sepsis, with liver being the major affected organ. Up-to-date, neither the mechanism of action nor target treatment is readily available for LPS-induced liver injury. This study examined the effect of irisin, an endogenous hormonal peptide, on LPS-induced liver injury using animal and cell models, and the mechanism involved with a special focus on pyroptosis. Irisin is known to regulate glucose metabolism, inflammation, and immune response, while our earlier work denoted the anti-inflammatory and anti-apoptotic properties for irisin. Inflammatory factors and AST/ALT were also detected. Pyroptosis, apoptosis, and reactive oxygen species (ROS) were evaluated using PI staining, TUNEL staining, DCFH-DA fluorescence, and western blot, respectively. Our results indicated that irisin attenuated LPS-induced liver injury and release of inflammatory cytokines. Increased activity of NLRP3 inflammasome was discovered in LPS-challenged Raw264.7 cells, along with elevated levels of inflammation and apoptosis, the effects of which were mediated by activation of ROS and nuclear factor κB (NF-κB) signaling. These changes were reversed following irisin treatment. Our study demonstrated that irisin countered LPS-mediated liver injury via inhibiting apoptosis, NLRP3 inflammasome activation and NF-κB signaling. These findings revealed the role of irisin as a promising new anti-pyroptosis/apoptosis agent to reconcile the onset and progression of septic liver injury.

Exposure to environmental black carbon exacerbates nasal epithelial inflammation via the reactive oxygen species (ROS)-nucleotide-binding, oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3)-caspase-1-interleukin 1β (IL-1β) pathway

BACKGROUND

Allergic rhinitis(AR) is an increasing challenge to public health worldwide. Exposure to environmental black carbon (BC) is associated with increased risk of allergic rhinitis, but the molecular mechanisms underlying its toxicity have not been fully elucidated. The aims of the present study were therefore to determine the effect of BC on the expression of interleukin 1β (IL-1β) and to investigate the mechanism underlying BC-induced IL-1β production in pollen-sensitized human nasal epithelial cells (hNECs).

METHODS

Nasal mucosal samples collected from 10 patients undergoing nasal surgery were used to isolate and culture epithelial cells as air-liquid interface (ALI) cultures. Cultures exposed to BC ± pollen allergen for 24 hours were assessed for the presence of IL-1β, the production of reactive oxygen species (ROS), and activation of the nucleotide-binding, oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome. Furthermore, the mechanisms underlying BC ± pollen allergen-induced IL-1β in hNECs were evaluated.

RESULTS

Exposure to BC significantly increased the production of IL-1β and ROS and the expression of NLRP3 in hNECs, compared with control, all of which were significantly increased further by exposure to a combination of BC and pollen. Incubation of hNECs with N-acetyl-L-cysteine (NAC) significantly attenuated BC ± pollen-induced expression of ROS, NLRP3, and IL-1β. NLRP3 and Caspase-1 inhibitors (MCC950 and YVAD) significantly inhibited IL-1β expression and NLRP3 activation, but not NLRP3 expression following exposure to BC ± pollen.

CONCLUSION

These findings suggest that exposure to BC and pollen can exaggerate oxidative stress and significantly increase the expression of IL-1β in hNECs, and that this may involve a pathway integrating ROS-NLRP3-Caspase-1-IL-1β signaling.

Polysaccharides from Armillariella tabescens mycelia ameliorate renal damage in type 2 diabetic mice

Diabetic kidney disease (DKD), accompanied by chronic low-grade inflammation, is one of the most common complications of diabetes. Armillariella tabescens has potent anti-inflammatory and immunomodulatory properties. The purpose of the present study was to investigate the effects of polysaccharides from Armillariella tabescens mycelia (AT) on the kidney in type 2 diabetic mice and explore the underlying mechanism. The mice were randomized into 4 groups: normal control (NC), diabetic control (DC), DC + 200 mg/kg AT (LAT), and DC + 400 mg/kg AT (HAT). The results showed that compared with the NC group, the levels of fasting blood glucose, renal function-related indices, and serum pro-inflammatory mediators including lipopolysaccharide (LPS), interleukin (IL)-1β, and IL-18 were elevated; the renal morphopathological alterations, oxidative stress, and nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome-mediated inflammation and renal fibrosis were aggravated; the intestinal microbiota dysbiosis and colonic inflammation and barrier dysfunction were deteriorated in the DC group. After supplementation with AT, the aforementioned indices were ameliorated in the AT treatment groups, especially in the HAT group. In conclusion, these results demonstrated that modulating the intestinal microbiota and inflammatory reaction was implicated in the effects of AT against DKD in mice.

Role of NLRP3 inflammasome in liver disease

Inflammasomes have become an important natural sensor of host immunity, and can protect various organs against pathogenic infections, metabolic syndromes, cellular stress and cancer metastasis. Inflammasomes are intracellular multi-protein complexes found in both parenchymal and non-parenchymal cells, stimulating the initiation of caspase-1 and interleukin (IL)-1β and IL-18 in response to cell danger signals. Inflammasomes induce cell death mechanisms. The potential role of NOD-like receptor protein 3 (NLRP3) inflammasome in alcoholic and non-alcoholic steatohepatitis, hepatitis, nanoparticle-induced liver injury and other liver diseases has recently attracted widespread attention from clinicians and researchers. In this review we summarize the role played by the NLRP3 inflammasome in molecular and pathophysiological mechanisms in the pathogenesis and progression of liver disease. This article aims to establish that targeting the NLRP3 inflammasome and other inflammasome components may make a significant therapeutic approach to the treatment of liver disease.

Crosstalk between ER stress, NLRP3 inflammasome, and inflammation

Endoplasmic reticulum stress (ERS) is a protective response to restore protein homeostasis by activating the unfolded protein response (UPR). However, UPR can trigger cell death under severe and/or persistently high ERS. The NLRP3 inflammasome is a complex of multiple proteins that activates the secretion of the proinflammatory cytokine IL-1β in a caspase-1-dependent manner to participate in the regulation of inflammation. The NLRP3 inflammasome involvement in ERS-induced inflammation has not been completely described. The intersection of ERS with multiple inflammatory pathways can initiate and aggravate chronic diseases. Accumulating evidence suggests that ERS-induced activation of NLRP3 inflammasome is the pathological basis of various inflammatory diseases. In this review, we have discussed the networks between ERS and NLRP3 inflammasome, with the view to identifying novel therapeutic targets in inflammatory diseases. KEY POINTS: • Endoplasmic reticulum stress (ERS) is an important factor for the activation of the NLRP3 inflammasomes that results in pathological processes. • ERS can activate the NLRP3 inflammasome to induce inflammatory responses via oxidative stress, calcium homeostasis, and NF-κB activation. • The interactions between ERS and NLRP3 inflammasome are associated with inflammation, which represent a potential therapeutic opportunity of inflammatory diseases.

Macrophage Sphingosine 1-Phosphate Receptor 2 Blockade Attenuates Liver Inflammation and Fibrogenesis Triggered by NLRP3 Inflammasome

NLR family pyrin domain containing 3 (NLRP3) inflammasome accompanies chronic liver injury and is a critical mediator of inflammation-driven liver fibrosis. Sphingosine 1-phosphate (S1P)/S1P Receptor (S1PR) signaling participates in liver fibrogenesis by affecting bone marrow (BM)-derived monocytes/macrophage (BMM) activation. However, the relationship between S1P/S1PR signaling and NLRP3 inflammasome in BMMs remains unclear. Here, we found significantly elevated gene expression of NLRP3 inflammasome components (NLRP3, pro-interleukin-1β, and pro-interleukin-18) and the activation of NLRP3 inflammasome significantly elevated during murine chronic liver injury induced by a bile duct ligation operation, a methionine-choline–deficient and high-fat diet, or carbon tetrachloride intraperitoneal injection. Moreover, the increased expression of sphingosine kinase 1 (SphK1), the rate-limiting synthetic enzyme of S1P, was positively correlated with NLRP3 inflammasome components in both patients and mouse model livers. Flow cytometry analysis and immunofluorescence staining showed BMMs contributed to the significant proportion of NLRP3⁺ cells in murine inflammatory livers, but not Kupffer cells, dendritic cells, endothelial cells, T cells, and hepatocytes. Focusing on macrophages, S1P promoted NLRP3 inflammasome priming and activation in a dose-dependent manner. Blockade of S1PR₂ by JTE-013 (antagonist of S1PR₂) or S1PR₂-siRNA inhibited S1P-induced NLRP3 inflammasome priming and inflammatory cytokine (interleukin-1β and interleukin-18) secretion, whereas blockade of S1PR₁ or S1PR₃ had no such effect. in vivo, a β1,3-d-glucan-encapsulated siRNA particle (GeRP) delivery system is capable of silencing genes in macrophages specifically. Treatment with S1PR₂ siRNA-GeRPs markedly reduced NLRP3 inflammasome priming and activation and attenuated liver inflammation and fibrosis. Together, the conclusions indicated that targeting macrophage S1PR₂ retarded liver inflammation and fibrogenesis via downregulating NLRP3 inflammasome, which may represent an effective therapeutic strategy for chronic liver injury.

Hepatitis B e Antigen Induces NKG2A+ Natural Killer Cell Dysfunction via Regulatory T Cell-Derived Interleukin 10 in Chronic Hepatitis B Virus Infection

Although persistent hepatitis B virus (HBV) infection is associated with natural killer (NK) cell dysfunction, it remains obscure whether HBV viral antigens are responsible for NK cell dysfunction in patients with chronic hepatitis B (CHB) infection. In this study, we found that the percentage of NK cells expressing the inhibitory receptor, NKG2A, was increased in CHB patients, and NKG2A blockade restored NK cell function. Furthermore, in CHB patients, the frequency of NK cells expressing NKG2A positively correlated with the number of regulatory T cells (Tregs) and production of interleukin-10 (IL-10) in these Tregs. Moreover, exposure of peripheral blood mononuclear cells (PBMCs) isolated from healthy controls to sera from CHB patients resulted in increased proportion of NKG2A⁺ NK cells; IL-10 blockade reduced the frequency of NKG2A⁺ NK cells while increasing the percentage of IFN-γ⁺ NK cells. In addition, stimulation of NK cells and Tregs from healthy controls with CHB sera together with anti-IL-10 antibody increased IFN-γ production in the culture supernatant. The frequencies of NKG2A⁺ NK cells and IL-10⁺ Tregs, along with serum levels of alanine transferase and HBV DNA, were significantly increased in CHB patients positive for the Hepatitis B e antigen (HBeAg, a marker of viral replication) when compared to HBeAg-negative CHB patients. Importantly, exposure of PBMCs from healthy controls to HBeAg resulted in increased IL-10 production but reduced levels of TNF and IFN-γ, and IL-10 blockade rescued the generation of TNF and IFN-γ in this assay. The reduced production of TNF and IFN-γ was also observed in NK cells and Tregs from healthy controls that were stimulated with HBeAg, while IL-10 blockade increased the secretion of these two cytokines. We conclude that HBeAg induces IL-10 production in Tregs, thereby leading to increased expression of NKG2A on NK cells, which contributes to NK cell dysfunction during CHB infection. These data suggest that HBeAg is associated with NK cell dysfunction in CHB.

Mechanisms of HBV immune evasion

The concept of immune evasion is a longstanding topic of debate during chronic Hepatitis B Virus infection. The 292 million individuals chronically infected by HBV are clear evidence that the virus avoids elimination by the immune system. The exact mechanisms of immune evasion remain undefined and are distinct, but likely interconnected, between innate and adaptive immunity. There is a significant body of evidence that supports peripheral tolerance and exhaustion of adaptive immunity but our understanding of the role that central tolerance plays is still developing. Innate immunity instructs the adaptive immune response and subversion of its functionality will impact both T and B cell responses. However, literature around the interaction of HBV with innate immunity is inconsistent, with reports suggesting that HBV avoids innate recognition, suppresses innate recognition, or activates innate immunity. This complexity has led to confusion and controversy. This review will discuss the mechanisms of central and peripheral tolerance/exhaustion of adaptive immunity in the context of chronic HBV infection. We also cover the interaction of HBV with cells of the innate immune system and propose concepts for the heterogeneity of responses in chronically infected patients.

Hepatitis B virus X protein promotes liver cell pyroptosis under oxidative stress through NLRP3 inflammasome activation

Objective

Hepatitis B virus X protein (HBx) is a pivotal factor for HBV-induced hepatitis. Herein, we sought to investigate HBx-mediated NLR pyrin domain containing 3 (NLRP3) inflammasome activation and pyroptosis under oxidative stress.

Methods

The effect of HBx on the NLRP3 inflammasome was analyzed by enzyme-linked immunosorbent assays, quantitative reverse transcription-polymerase chain reaction, western blotting, and immunofluorescence in hepatic HL7702 cells. Pyroptosis was evaluated by western blotting, lactate dehydrogenase release, propidium iodide staining, and transmission electron microscopy. NLRP3 expression in the inflammasome from liver tissues was assessed by immunohistochemistry.

Results

In hydrogen peroxide (H₂O₂)-stimulated HL7702 cells, HBx triggered the release of pro-inflammatory mediators apoptosis-associated speck-like protein containing a CARD (ASC), interleukin (IL)-1β, IL-18, and high-mobility group box 1 (HMGB1); activated NLRP3; and initiated pro-inflammatory cell death (pyroptosis). HBx localized to the mitochondria, where it induced mitochondrial damage and production of mitochondrial reactive oxygen species (mitoROS). Treatment of HL7702 cells with a mitoROS scavenger attenuated HBx-induced NLRP3 activation and pyroptosis. Expression levels of NLRP3, ASC, and IL-1β in liver tissues from patients were positively correlated with HBV DNA concentration.

Conclusions

The NLRP3 inflammasome was activated by elevated mitoROS levels and mediated HBx-induced liver inflammation and hepatocellular pyroptosis under H₂O₂-stress conditions.

Electronic supplementary material

The online version of this article (10.1007/s00011-020-01351-z) contains supplementary material, which is available to authorized users.

Lipopolysaccharide restricts murine norovirus infection in macrophages mainly through NF-kB and JAK-STAT signaling pathway

The inflammasome machinery has recently been recognized as an emerging pillar of innate immunity. However, little is known regarding the interaction between the classical interferon (IFN) response and inflammasome activation in response to norovirus infection. We found that murine norovirus (MNV-1) infection induces the transcription of IL-1β, a hallmark of inflammasome activation, which is further increased by inhibition of IFN response, but fails to trigger the release of mature IL-1β. Interestingly, pharmacological inflammasome inhibitors do not affect viral replication, but slightly reverse the inflammasome activator lipopolysaccharide (LPS)-mediated inhibition of MNV replication. LPS efficiently stimulates the transcription of IFN-β through NF-ĸB, which requires the transcription factors IRF3 and IRF7. This activates downstream antiviral IFN-stimulated genes (ISGs) via the JAK-STAT pathway. Moreover, inhibition of NF-ĸB and JAK-STAT signaling partially reverse LPS-mediated anti-MNV activity, suggesting additional antiviral mechanisms activated by NF-ĸB. This study reveals additional insight in host defense against MNV infection.

NLRP3 inflammasome and related cytokines reflect the immune status of patients with HBV-ACLF

BACKGROUND

The NLRP3 inflammasome has been suggested to play a crucial role in host antiviral defense, including against hepatitis B virus (HBV) infection. In the present study, we measured expression of NLRP3 and its related cytokines in patients with different stages of HBV-related acute-on-chronic liver failure (HBV-ACLF), a pattern of end-stage liver disease that occurs frequently in patients with chronic HBV (CHB) infection or HBV-related cirrhosis.

METHODS

A total of 75 subjects including 30 HBV-ACLF patients, 30 CHB patients, and 15 healthy controls (HCs) were enrolled. The NLRP3 inflammasome and its components (caspase-1, interleukin (IL)-1β, and IL-18) were measured in peripheral blood mononuclear cells (PBMCs), macrophages, and liver using flow cytometry, quantitative real-time polymerase chain reaction (RT-PCR), western blot, and immunohistochemistry. The LPS was used to evaluate changes in NLRP3 and its related cytokines in CD14⁺ monocytes which may reflect immune status. Cytokine expression was measured using RT-PCR.

RESULTS

Patients with HBV-ACLF had lower NLRP3 inflammasome expression in peripheral CD14⁺ monocytes, particularly in the middle-to-late stage, but higher expression in liver macrophages compared to CHB and HCs. Compared with H-LPS or L-LPS alone, L-LPS sequential H-LPS can significantly inhibit the expression of NLRP3 and its related cytokines.

CONCLUSION

Differential expression patterns of the NLRP3 inflammasome in the periphery and liver might be related to immune dysfunction and recruitment of monocytes to the injured liver during disease progression. Persistent systemic inflammation is likely a cause of compromised immune status in patients with HBV-ACLF.

NLRP3 Inflammasome-A Key Player in Antiviral Responses

The NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome is an oligomeric complex comprised of the NOD-like receptor NLRP3, the adaptor ASC, and caspase-1. This complex is crucial to the host's defense against microbes as it promotes IL-1β and IL-18 secretion and induces pyroptosis. NLRP3 recognizes variety of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) generated during viral replication that triggers the NLRP3 inflammasome-dependent antiviral immune responses and facilitates viral eradication. Meanwhile, several viruses have evolved elaborate strategies to evade the immune system by targeting the NLRP3 inflammasome. In this review, we will focus on the crosstalk between the NLRP3 inflammasome and viruses, provide an overview of viral infection-induced NLRP3 inflammasome activation, and the immune escape strategies of viruses through their modulation of the NLRP3 inflammasome activity.

Melatonin alleviates intervertebral disc degeneration by disrupting the IL-1β/NF-κB-NLRP3 inflammasome positive feedback loop

The inflammatory response is induced by the overexpression of inflammatory cytokines, mainly interleukin (IL)-1β, and is one of the main causes of intervertebral disc degeneration (IVDD). NLR pyrin domain containing 3 (NLRP3) inflammasome activation is an important source of IL-1β. As an anti-inflammatory neuroendocrine hormone, melatonin plays various roles in different pathophysiological conditions. However, its roles in IVDD are still not well understood and require more examination. First, we demonstrated that melatonin delayed the progression of IVDD and relieved IVDD-related low back pain in a rat needle puncture IVDD model; moreover, NLRP3 inflammasome activation (NLRP3, p20, and IL-1β levels) was significantly upregulated in severely degenerated human discs and a rat IVDD model. Subsequently, an IL-1β/NF-κB-NLRP3 inflammasome activation positive feedback loop was found in nucleus pulposus (NP) cells that were treated with IL-1β. In these cells, expression of NLRP3 and p20 was significantly increased, NF-κB signaling was involved in this regulation, and mitochondrial reactive oxygen species (mtROS) production increased. Furthermore, we found that melatonin disrupted the IL-1β/NF-κB-NLRP3 inflammasome activation positive feedback loop in vitro and in vivo. Melatonin treatment decreased NLRP3, p20, and IL-1β levels by inhibiting NF-κB signaling and downregulating mtROS production. Finally, we showed that melatonin mediated the disruption of the positive feedback loop of IL-1β in vivo. In this study, we showed for the first time that IL-1β promotes its own expression by upregulating NLRP3 inflammasome activation. Furthermore, melatonin disrupts the IL-1β positive feedback loop and may be a potential therapeutic agent for IVDD.

NLRP3 Inflammasome and Inflammatory Diseases

Almost all human diseases are strongly associated with inflammation, and a deep understanding of the exact mechanism is helpful for treatment. The NLRP3 inflammasome composed of the NLRP3 protein, procaspase-1, and ASC plays a vital role in regulating inflammation. In this review, NLRP3 regulation and activation, its proinflammatory role in inflammatory diseases, interactions with autophagy, and targeted therapeutic approaches in inflammatory diseases will be summarized.

The rOX-stars of inflammation: links between the inflammasome and mitochondrial meltdown

The nod‐like receptor protein 3 (NLRP3) inflammasome drives inflammation in response to mitochondrial dysfunction. As metabolic powerhouses with prokaryotic ancestry, mitochondria are a cache for danger‐associated molecular patterns and pathogen‐associated molecular pattern‐like molecules that elicit potent innate immune responses. Persistent mitochondrial damage caused by infection, or genetic or environmental factors, can lead to inappropriate or sustained inflammasome signalling. Here, we review the features of mitochondria that drive inflammatory signalling, with a particular focus on mitochondrial activation of the NLRP3 inflammasome. Given that mitochondrial network dynamics, metabolic activity and redox state are all intricately linked to each other and to NLRP3 inflammasome activity, we highlight the importance of a holistic approach to investigations of NLRP3 activation by dysfunctional mitochondria.

Spirulina maxima extract prevents activation of the NLRP3 inflammasome by inhibiting ERK signaling

The blue-green alga Spirulina maxima is a microscopic filamentous cyanobacterium. Spirulina was recently reported to elicit beneficial effects such as reducing cholesterol and inducing weight loss; however, its effects on inflammation are unknown. To determine the effect of S. maxima extract (SME) on innate immunity, we investigated the NLRP3 inflammasome activation, which is a multiprotein scaffolding complex that plays important roles in innate immune responses to many pathogenic infections in macrophages. SME suppressed lipopolysaccharide (LPS)-induced upregulation of the pro-inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-12, IL-1β, and IL-18 in RAW264.7 cells. In addition, SME attenuated LPS-induced NLRP3 inflammasome activation, and thus pro-IL-1β could not be cleaved to IL-1β by activated caspase-1, which is activated by the NLRP3 inflammasome in RAW264.7 cells. Moreover, SME inhibited LPS-induced phosphorylation of extracellular signal-regulated kinase (ERK) in RAW264.7 cells, and attenuated the generation of ERK1 induced-reactive oxygen species (ROS), resulting in decreased expression of NF-κB. These findings suggest that SME suppresses the effects of the NLRP3 inflammasome via regulation of extracellular signal-regulated kinase (ERK). In summary, we demonstrated that SME prevents activation of the NLRP3 inflammasome by inhibiting ERK signaling.

Identification of Aberrantly Methylated Differentially CpG Sites in Hepatocellular Carcinoma and Their Association With Patient Survival

This study aimed to identify aberrantly methylated differentially methylated CpG sites (DMCs) and investigate their prognostic value in hepatocellular carcinoma (HCC). A total of 2,404 DMCs were selected from Gene Expression Omnibus (GEO) and validated by The Cancer Genome Atlas (TCGA). The TCGA cohort was divided into a training cohort and a validating cohort. First, the prognostic model based on six DMCs, including cg08351331, cg02910574, cg09947274, cg17589341, cg24652919, and cg26545968, was constructed based on the least absolute shrinkage and selection operator (LASSO) regression Cox analysis. The area under the curve (AUC) of the DMC-based model was 0.765 in the training cohort and 0.734 in the validating cohort. The accuracy of a model combining the DMC signature and American Joint Committee on Cancer (AJCC) stage, with an AUC of 0.795, was better than that of the DMCs or AJCC stage alone. Second, further analysis revealed that the methylation rate of cg08351331 was negatively associated with the expression of its relative gene, lipopolysaccharide-binding protein (LBP). Besides, the gene expression of LBP was significantly associated with poor overall survival in patients with hepatitis B virus (HBV) infection. Finally, these findings were confirmed by GSE57956 data and our own cohort. In conclusion, we established an accurate DMC-based prognostic model that could be combined with AJCC stage to improve the accuracy of prognostic prediction in HCC. Moreover, our preliminary data indicate that LBP may be a new key factor in HBV-induced HCC initiation through the regulation of its methylation.

Rhein attenuates lipopolysaccharide-primed inflammation through NF-κB inhibition in RAW264.7 cells: targeting the PPAR-γ signal pathway

Inflammation is a common inducer of numerous severe diseases such as sepsis. The NF-κB signaling pathway plays a key role in the inflammatory process. Its activation promotes the release of pro-inflammatory mediators like inducible nitric oxide synthase and tumor necrosis factor alpha. Peroxisome proliferator-activated receptor gamma (PPAR-γ) inactivates nuclear factor kappa B (NF-κB) and subsequently attenuates inflammation. Rhein, an agent isolated from rhubarb, has been known to have anti-inflammatory effects. However, its influence on PPAR-γ remains largely unknown. In this study, an inflammation model was constructed by stimulating RAW264.7 cells with lipopolysaccharide. Rhein was used as a therapeutic agent, while rosiglitazone (PPAR-γ activator) and GW9662 (PPAR-γ inhibitor) were used as disrupters for in depth studies. The results demonstrated that rhein inhibits NF-κB activation and inflammatory factor release. However, GW9662 significantly reduced this effect, indicating that PPAR-γ is a critical mediator in the rhein-mediated anti-inflammatory process. Additionally, positive modulation of PPAR-γ expression and activity by rosiglitazone correspondingly influenced the effects of rhein on inflammatory factors and NF-κB expression. We also found that rhein could enhance PPAR-γ, NF-κB, and histone deacetylase 3 (HDAC3) binding. These results indicate that rhein exerts its anti-inflammation function by regulating the PPAR-γ-NF-κB-HDAC3 axis.

Hepatitis B virus-induced modulation of liver macrophage function promotes hepatocyte infection

BACKGROUND & AIMS

Liver macrophages can be involved in both pathogen clearance and/or pathogenesis. To get further insight on their role during chronic hepatitis B virus (HBV) infections, our aim was to phenotypically and functionally characterize in vivo and ex vivo the interplay between HBV, primary human liver macrophages (PLMs) and primary blood monocytes differentiated into pro-inflammatory or anti-inflammatory macrophages (M1-MDMs or M2-MDMs, respectively).

METHODS

PLMs or primary blood monocytes, either ex vivo differentiated into M1-MDMs or M2-MDMs, were exposed to HBV and their activation followed by ELISA or quantitative reverse transcription PCR (RT-qPCR). Liver biopsies from HBV-infected patients were analysed by RT-qPCR or immunohistochemistry. Viral parameters in HBV-infected primary human hepatocytes and differentiated HepaRG cells were followed by ELISA, qPCR and RT-qPCR analyses.

RESULTS

HBc protein was present within the macrophages of liver biopsies taken from HBV-infected patients. Macrophages from HBV-infected patients also expressed higher levels of anti-inflammatory macrophage markers than those from non-infected patients. Ex vivo exposure of naive PLMs to HBV led to reduced secretion of pro-inflammatory cytokines. Upon exposure to HBV or HBV-producing cells during differentiation and activation, M1-MDMs secreted less IL-6 and IL-1β, whereas M2-MDMs secreted more IL-10 when exposed to HBV during activation. Finally, cytokines produced by M1-MDMs, but not those produced by HBV-exposed M1-MDMs, decreased HBV infection of hepatocytes.

CONCLUSIONS

Altogether, our data strongly suggest that HBV modulates liver macrophage functions to favour the establishment of infection.

LAY SUMMARY

Hepatitis B virus modulates liver macrophage function in order to favour the establishment and likely maintenance of infection. It impairs the production of the antiviral cytokine IL-1β, while promoting that of IL-10 in the microenvironment. This phenotype can be recapitulated in naive liver macrophages or monocyte-derived-macrophages ex vivo by short exposure to the virus or cells replicating the virus, thus suggesting an "easy to implement" mechanism of inhibition.

HBV-Pol is crucial for HBV-mediated inhibition of inflammasome activation and IL-1β production

BACKGROUND & AIMS

Hepatitis B virus (HBV) infection is the most critical factor underlying liver cirrhosis and hepatocellular carcinoma worldwide. IL-1β and IL-18, generated by activation of the inflammasome/caspase-1 signaling pathway, play important roles in the control and clearance of HBV. However, the specific relationship between the inflammasome response and IFN-α resistance or viral persistence is yet to be established.

METHODS

Blood samples of patients and supernatant fractions of HBV cell lines were collected for analysis and the effects on inflammasome activation and IL-1β production evaluated via enzyme-linked immunosorbent assay (ELISA), western blot, quantitative RT-PCR and immunofluorescence.

RESULTS

IL-1β and IL-18 levels produced in sera of IFN-α non-responders were significantly lower than those of responders and normal donors. Additionally, expression of IL-1β and inflammasome components was decreased in peripheral blood mononuclear cells (PBMC) of non-responders, compared with those of responders. In vitro experiments on HepG2, HepG2.2.15 and HepAD38 cell lines showed that HBV induces a significant decrease in IL-1β production through inhibiting activation of the NF-κB signaling and inflammasome/caspase-1 pathways. And hepatitis B virus polymerase (HBV-Pol) appeared crucial for these inhibitory effects of HBV.

CONCLUSION

IL-1β production is suppressed in HBV carriers and IFN-α non-responders. HBV induces a significant decrease in IL-1β production through inhibiting the NF-κB signaling and inflammasome pathways, for which HBV-Pol is a crucial requirement. Trial approval number: 20 173 402.

Novel biphenyl diester derivative AB-38b inhibits NLRP3 inflammasome through Nrf2 activation in diabetic nephropathy

Inflammation reaction mediated by NLRP3 inflammasome and Nrf2-related oxidative stress are vital participants in the development of diabetic nephropathy (DN) and closely associated to kidney fibrosis. Nrf2, a known antioxidative transcription factor, has been reported to activate NLRP3 inflammasome through its downstream factors (HO-1, NQO1, etc.) recently. AB38b is a newly synthesized biphenyl diester derivative with a Nrf2 activation property. This research aims to evaluate the renal protective effects of AB-38b and to elucidate the anti-inflammation mechanisms involved. Type 2 diabetic mice induced by high fat diet with streptozocin (STZ) and high glucose-cultured mouse glomerular mesangial cells (GMCs) were used in current study. Results showed that administration of AB-38b improved the kidney function while attenuated renal fibrosis progression in diabetic mice together with reducing the extracellular matrix (ECM) accumulation of GMCs cultured in high glucose. Mechanistically, treatment with AB-38b significantly decreased the high level of NLRP3 inflammasome in diabetic condition by inhibiting the ROS/TXNIP/NLRP3 signaling pathway. And meanwhile, AB-38b treatment effectively improved Nrf2 signaling during diabetic condition. Furthermore, knocking down the gene expression of Nrf2 by siRNA in GMCs abolished the inhibition effect of AB-38b on NLRP3 inflammasome activation and ECM accumulation. Taken together, our data suggest that AB-38b was able to improve the renal function of diabetic mice, and the NLRP3 inflammasome inhibition effect of AB-38b was responsible for the renal protective effect. Further exploration indicate that Nrf2 plays pivotal role in AB-38b's attenuation of DN progression through inhibiting NLRP3 inflammasome activation.

TAF and TDF attenuate liver fibrosis through NS5ATP9, TGFβ1/Smad3, and NF-κB/NLRP3 inflammasome signaling pathways

BACKGROUND

This study aimed to investigate the roles and mechanisms of tenofovir alafenamide fumarate (TAF)/tenofovir disoproxil fumarate (TDF) in treating liver fibrosis.

METHODS

The effects of TAF/TDF on carbon tetrachloride (CCl₄)-induced liver fibrosis in C57BL/6 wild-type or nonstructural protein 5A transactivated protein 9 (NS5ATP9) knockout mice were studied. The differentiation, activation, and proliferation of LX-2 cells after TAF/TDF treatment were tested in vitro. The expression of NS5ATP9 and activities of transforming growth factor-β1 (TGFβ1)/Sekelsky mothers against decapentaplegic homolog 3 (Smad3) and NF-κB/NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome signaling pathways were detected in TAF/TDF-treated mice and LX-2 cells. The genes related to extracellular matrix accumulation were detected in vivo and in vitro after NS5ATP9 silencing or knockout.

RESULTS

TAF/TDF significantly inhibited CCl₄-induced liver fibrosis in mice, and regulated the differentiation, activation, and proliferation of hepatic stellate cells (HSCs). Furthermore, TAF/TDF suppressed the activities of TGFβ1/Smad3 and NF-κB/NLRP3 inflammasome signaling pathways in vivo and in vitro. NS5ATP9 inhibited liver fibrosis through TGFβ1/Smad3 and NF-κB signaling pathways. TAF/TDF upregulated the expression of NS5ATP9 in vivo and in vitro. Finally, TAF/TDF could only show marginal therapeutic effects when NS5ATP9 was silenced and knocked out in vivo and in vitro.

CONCLUSIONS

TAF/TDF prevented progression and promoted reversion of liver fibrosis through assembling TGFβ1/Smad3 and NF-κB/NLRP3 inflammasome signaling pathways via upregulating the expression of NS5ATP9. TAF/TDF also regulated the differentiation, activation, and proliferation of HSCs. The findings provided strong evidence for the role of TAF/TDF as a new promising therapeutic strategy in liver fibrosis.

Baicalin relieves inflammation stimulated by lipopolysaccharide via upregulating TUG1 in liver cells

Hepatitis has become a major social, health, and economic problem worldwide. Herein, we tested the beneficial influence of baicalin, a flavonoid extracted from the roots of Scutellaria baicalensis, on human normal liver L-02 and THLE2 cell apoptosis and inflammatory reaction stimulated by lipopolysaccharide (LPS) and possible molecular mechanisms. L-02 and THLE2 cell viability and apoptosis after LPS and/or baicalin treatment were tested using CCK-8 assay and Annexin V-FITC/PI apoptosis kit, respectively. qRT-PCR was used to measure the MCP-1, IL-6, TNF-α, and lncRNA taurine upregulated gene 1 (TUG1) expressions in L-02 and THLE2 cells. sh-TUG1 was transfected to knockdown TUG1. SB203580 was used as inhibitor of p38MAPK pathway, while SP600125 was used as inhibitor of JNK pathway. We discovered that LPS stimulation caused L-02 and THLE2 cell apoptosis and inflammatory reaction. Baicalin relieved the L-02 and THLE2 cell apoptosis and inflammatory reaction stimulated by LPS. Moreover, LPS lowered the TUG1 expression in L-02 cells, while baicalin promoted the TUG1 expression in L-02 and L-02 and THLE2 cells, as well as inactivated p38MAPK and JNK pathways in LPS-stimulated L-02 cells. Besides, knockdown of TUG1 activated p38MAPK and JNK pathways and promoted inflammatory cytokine expression in L-02 cells. In conclusion, this study further affirmed the beneficial influences of baicalin on LPS-stimulated human normal liver cell apoptosis and inflammatory reaction. Baicalin relived liver cell inflammation stimulated by LPS might be via upregulating TUG1 and then inactivating p38MAPK and JNK pathways.

Using high-throughput sequencing to explore the anti-inflammatory effects of α-mangostin

Lipopolysaccharide (LPS) causes an inflammatory response, and α-mangostin (α-MG) is an ingredient of a Chinese herbal medicine with anti-inflammatory effects. We investigated the mechanism by which α-MG reduces LPS-stimulated IEC-6 cells inflammation. A genome-wide examination of control, LPS-stimulated, and α-MG-pretreated cells was performed with the Illumina Hiseq sequencing platform, and gene expression was verified with quantitative real-time PCR (qPCR). Among the 37,199 genes profiled, 2014 genes were regulated in the LPS group, and 475 genes were regulated in the α-MG group. GO enrichment and KEGG pathway analyses of the differentially expressed genes (DEGs) showed that they were mainly related to inflammation and oxidative stress. Based on the transcriptomic results, we constructed a rat model of inflammatory bowel disease (IBD) with LPS and investigated the effects of α-MG on NLRP3 inflammasomes. After LPS stimulation, the rat intestinal villi were significantly detached, with congestion and hemorrhage; the intestinal epithelial cell nuclei were deformed; and the mitochondria were swollen. However, after pretreatment with α-MG, the intestinal villus congestion and hemorrhage were reduced, the epithelial nuclei were rounded, and the mitochondrial morphology was intact. qPCR and western blotting were used to detect NLRP3, caspase 1, interleukin (IL)-18, and IL-1β expression at the gene and protein levels. Their expression increased at both the transcript and protein levels after LPS stimulation, whereas it decreased after pretreatment with α-MG. This study provides new methods and ideas for the treatment of inflammation. α-MG may have utility as a drug for intestinal inflammation.

Pyroptosis in Liver Disease: New Insights into Disease Mechanisms

There has been increasing interest in pyroptosis as a novel form of pro-inflammatory programmed cell death. The mechanism of pyroptosis is significantly different from other forms of cell death in its morphological and biochemical features. Pyroptosis is characterized by the activation of two different types of caspase enzymes-caspase-1 and caspase-4/5/11, and by the occurrence of a proinflammatory cytokine cascade and an immune response. Pyroptosis participates in the immune defense mechanisms against intracellular bacterial infections. On the other hand, excessive inflammasome activation can induce sterile inflammation and eventually cause some diseases, such as acute or chronic hepatitis and liver fibrosis. The mechanism and biological significance of this novel form of cell death in different liver diseases will be evaluated in this review. Specifically, we will focus on the role of pyroptosis in alcoholic and non-alcoholic fatty liver disease, as well as in liver failure. Finally, the therapeutic implications of pyroptosis in liver diseases will be discussed.

Curcumin relieves paraquat‑induced lung injury through inhibiting the thioredoxin interacting protein/NLR pyrin domain containing 3‑mediated inflammatory pathway

When paraquat (PQ) enters the human body, it increases oxidative stress and inflammation, ultimately resulting in acute lung injury (ALI). Curcumin, a naturally occurring compound, has been reported to ameliorate PQ-induced ALI; however, the underlying molecular mechanisms remain unclear. In the present study, normal lung fibroblasts (WI-38VA13) were treated with 10 µmol/l PQ for 48 h, followed by a further 48 h incubation with 300 µmol/l curcumin. Cells were then harvested to determine their viability. Flow cytometry was performed to analyze the levels of reactive oxygen species (ROS) and the rate of apoptosis. The levels of apoptotic proteins and activation of the thioredoxin interacting protein/NLR pyrin domain containing 3 (TXNIP/NLRP3) axis were measured via reverse transcription-quantitative polymerase chain reaction and western blot analyses. Proinflammatory cytokine levels were examined using enzyme-linked immunosorbent assays. Finally, the expression levels of Notch1, extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylated-ERK1/2 were evaluated via western blotting. Following treatment with curcumin, PQ-induced increases in ROS levels and apoptosis were significantly attenuated, and Bcl-2 expression levels were upregulated, whereas those of Bax were downregulated. It was also observed that curcumin treatment downregulated the expression levels of TXNIP, NLRP3, interleukin (IL)-1β and IL-18, and downstream caspase-1 compared with PQ treatment alone. Curcumin significantly attenuated the upregulation of Notch1 without affecting ERK1/2 phosphorylation. The present findings suggested that the inhibitory effects of curcumin on TXINP1 may inhibit activation of the NLRP3 inflammasome, subsequently suppressing the upregulation of proinflammatory cytokines and ultimately improving PQ-induced ALI.

Salidroside Suppresses IL-1β-Induced Apoptosis in Chondrocytes via Phosphatidylinositol 3-Kinases (PI3K)/Akt Signaling Inhibition

Background

Salidroside, a natural dietary isothiocyanate, has been widely studied for its multiple effects, including promoting proliferation, anti-inflammation, and anti-apoptosis. In the present study, these effects of Salidroside were explored to assess whether it could prevent osteoarthritis (OA) in vitro.

Material/Methods

The cytotoxic and proliferating effects of Salidroside on chondrocytes were detected by use of the Cell Counting Kit 8 assay. The expression levels of proteins were detected by Western blot. The cell apoptosis level was assessed by flow cytometry, and the levels of ROS, NO, caspase 3, and caspase 9 were assessed to evaluate the level of apoptosis. The expression level of pro-inflammatory factors was detected by ELISA.

Results

Our results demonstrated that Salidroside promotes chondrocytes proliferation, inhibits IL-1β-induced apoptosis and inflammation, and scavenges reactive oxygen species (ROS) and NO of chondrocytes. Salidroside upregulates the level of Bcl-2 and downregulates the level of Bax. Salidroside also inhibits the production of caspase 3/9 and suppresses the phosphorylation of PI3K and AKT.

Conclusions

Our results suggest that Salidroside prevents OA by its powerful pro-proliferating, anti-phlogistic, and anti-apoptotic effects by inhibiting PI3K/AKT.

Porcine transmissible gastroenteritis virus inhibits NF-κB activity via nonstructural protein 3 to evade host immune system

Background

Transmissible gastroenteritis virus (TGEV), a member of the family Coronaviridae, causes lethal watery diarrhea in piglets. Previous studies have revealed that the coronaviruses develop various strategies to evade the host innate immunity through the inhibition of nuclear factor kappa B (NF-κB) signaling pathway. However, the ability of TGEV to inhibit the host innate immune response by modulating the NF-κB signaling pathway is not clear.

Methods

In this study, a dual luciferase reporter assay was used to confirm the inhibition of NF-κB by TGEV infection and to identify the major viral proteins involved in the inhibition of NF-κB signaling. Real-time quantitative PCR was used to quantify the mRNA expression of inflammatory factors. The deubiquitination of Nsp3 domains and its effect on IκBα and p65 were analyzed by western blotting. The ubiquitination level of IκBα was analyzed by immunoprecipitation.

Results

In ST and IPEC-J2 cells, TGEV exhibited a dose-dependent inhibition of NF-κB activity. Individual TGEV protein screening revealed the high potential of non-structural protein 3 (Nsp3) to inhibit NF-κB signaling, and leading to the downregulation of the NF-κB-induced cytokine production. We demonstrated that the inhibitory effect of Nsp3 was mainly mediated through the suppression of IκBα degradation as well as the inhibition of p65 phosphorylation and nuclear translocation. Furthermore, the amino acid residues at positions 590–1,215 in Nsp3 were demonstrated to inhibit the degradation of IκBα by inhibiting the IκBα ubiquitination.

Conclusion

TGEV infection can inhibit the activation of the NF-κB signaling pathway, which is mainly mediated by Nsp3 through the canonical pathway. The amino acid residues at positions 590–1,215 in Nsp3 compose the critical domain that mediates NF-κB inhibition. We speculate that this inhibitory effect is likely to be related to the structure of PLP2 with deubiquitinating enzyme activity of the amino acid residues at positions 590–1,215 in Nsp3. Our study provides a better understanding of the TGEV-mediated innate immune modulation and lays the basis for studies on the pathogenesis of coronavirus.

Aspirin alleviates endothelial gap junction dysfunction through inhibition of NLRP3 inflammasome activation in LPS-induced vascular injury

The loss of endothelial connective integrity and endothelial barrier dysfunction can lead to increased vascular injury, which is related to the activation of endothelial inflammasomes. There are evidences that low concentrations of aspirin can effectively prevent cardiovascular diseases. We hypothesized that low-dose aspirin could ameliorate endothelial injury by inhibiting the activation of NLRP3 inflammasomes and ultimately prevent cardiovascular diseases. Microvascular endothelial cells were stimulated by lipopolysaccharide (2 μg/mL) and administrated by 0.1–2 mmol/L aspirin. The wild type mice were stimulated with LPS (100 μg/kg/day), and 1 h later treated with aspirin (12.5, 62.5, or 125 mg/kg/day) and dexamethasone (0.0182 mg/kg/day) for 7 days. Plasma and heart were harvested for measurement of ELISA and immunofluorescence analyses. We found that aspirin could inhibit NLRP3 inflammasome formation and activation in vitro in dose-dependent manner and has correlation between the NLRP3 inflammasome and the ROS/TXNIP pathway. We also found that low-concentration aspirin could inhibit the formation and activation of NLRP3 inflammasome and restore the expression of the endothelial tight junction protein zonula occludens-1/2 (ZO1/2). We assume that aspirin can ameliorate the endothelial layer dysfunction by suppressing the activation of NLRP3 inflammasome.

Serum apolipoprotein C3 levels are negatively associated with hepatitis B virus DNA in HBeAg-negative chronic hepatitis B patients

Background

Hepatitis B virus (HBV) infection remains a global health issue associated with substantial morbidity and mortality. Serum apolipoprotein C3 (ApoC3) and apolipoprotein A5 (ApoA5) levels were decreased in chronic hepatitis B (CHB) patients, however the relationship between ApoC3 or ApoA5 and HBV DNA load remains elusive.

Methods

A total of 384 CHB patients including 194 HBsAg(+) HBeAg(−) and 190 HBsAg(+) HBeAg(+) and 154 healthy individuals were recruited in our study. Serum levels of alanine aminotransferase (ALT), aspartate transaminase (AST), total cholesterol (Chol), triglycerides (TG), apolipoprotein A1 (ApoA1), apolipoprotein B (ApoB), high-density lipoproteins cholesterol (HDL-C), low-density lipoproteins cholesterol (LDL-C) and lipoprotein a (Lpa) were examined in an automatic biochemical analyzer. Apolipoprotein A5 (ApoA5) and apolipoprotein C3 (ApoC3) were detected via ELISA.

Results

Serum ApoA1, ApoB, ApoC3 and ApoA5 levels were reduced in CHB patients. In HBeAg(−) CHB patients, plasma ApoC3 levels were negatively associated with HBV DNA load (r = 0.219, P < 0.001). But no correlation between ApoA5 and HBV DNA load was observed in CHB patients.

Conclusions

These data showed that HBV infection inhibits lipid metabolism and ApoC3 is negatively associated with HBV DNA load in HBeAg (−) CHB patients. These findings provided new evidence about the link between ApoC3-related lipid metabolism and immune response.

Dihydroartemisinin, an antimalarial drug, induces absent in melanoma 2 inflammasome activation and autophagy in human hepatocellular carcinoma HepG2215 cells

As an effective antimalarial drug, Dihydroartemisinin (DHA) is readily isolated from the traditional Chinese medicine of Artemisia annua. DHA is not only an autophagy promoter but also a substance with strong antitumor efficiency. The relationship between autophagy and inflammasomes has been suggested in hepatocellular carcinoma (HCC). However, there are few reports describing relationships between inflammasomes and autophagy in HCC therapy. The present study demonstrated that DHA suppressed cell proliferation in HepG2215 cells in a dose- and time-dependent manner. The inhibitory activity is mediated by autophagy, in which reactive oxygen species (ROS) production induced nuclear and mitochondrial DNA damage. Then, DHA were first shown to promote AIM2/caspase-1 inflammasome. Compared with the DHA group, the autophagy inhibitor 3-MA significantly inhibited the expressions of activated Caspase-1, a pyroptotic marker proteins. Meanwhile, repression of mTOR by rapamycin promoted autophagy and AIM2/caspase-1 activation. The caspase-1 inhibitor Z-YVAD-FMK also notably blocked autophagy cell death characterized by the downexpression of Beclin-1 and LC3-II. Additionally, the study demonstrated that DHA suppressed pseudopodium formation and cell mobility. Therefore, we first reveal a novel mechanism that DHA promotes AIM2/caspase-1 inflammasome, which contributes to autophagy in HepG2215 cells. Moreover, nuclear and mitochondrial DNA damage was also involved in this process via ROS production.

The relevance of pyroptosis in the pathogenesis of liver diseases

Pyroptosis is a novel programmed cell death form which is distinct from other types of cell death. As an inherently inflammatory process, it plays a vital role in cellular lysis and release of pro-inflammatory cytokines when hosts defend against infections. Recent studies have reported that pyroptosis was involved in liver diseases and had important functions in the progress and development of liver diseases. Here, we addressed the potential role of pyroptosis in liver diseases on the basis of brief introduction of the morphological characteristics, molecular and pathophysiological mechanisms of pyroptosis.

Inflammasomes and their roles in the pathogenesis of viral hepatitis and their related complications: An updated systematic review

Inflammasomes are a set of innate receptors which are the responsible molecules for activation of pro-interleukin (IL)-1β and IL-18 and induction of inflammation. Due to the key roles of the inflammasomes in the induction of inflammation, it has been hypothesized that the molecules may be the main parts of immune responses against viral infections and the tissue damage. Because some cases of viral hepatitis infections, including hepatitis B and C, are diagnosed as chronic and may be associated with various complications such as liver cirrhosis and hepatocellular carcinoma (HCC), several studies focused on the roles played by the inflammation on the pathogenesis of viral hepatitis. Based on the roles played by inflammasomes in induction of inflammation, it has been hypothesized that inflammasomes may be the main parts of the puzzle of the viral hepatitis complications. This article reviews the roles of the inflammasomes in the pathogenesis of hepatitis B and C viral infections and their complications, liver cirrhosis, and HCC.

Intranasal Application of Budesonide Attenuates Lipopolysaccharide-Induced Acute Lung Injury by Suppressing Nucleotide-Binding Oligomerization Domain-Like Receptor Family, Pyrin Domain-Containing 3 Inflammasome Activation in Mice

Aim

To investigate the protective effects of budesonide against lipopolysaccharide- (LPS-) induced acute lung injury (ALI) in a murine model and its underlying mechanism.

Methods

Adult male C57BL/6 mice were divided into three groups: control, ALI, and ALI + budesonide groups. LPS (5 mg/kg) was intratracheally injected to induce ALI in mice. Budesonide (0.5 mg/kg) was intranasally given 1 h before LPS administration in the ALI + budesonide group. Twelve hours after LPS administration, all mice were sacrificed. Hematoxylin-eosin staining and pathological scores were used to evaluate pathological injury. Bronchoalveolar lavage was performed. The numbers of total cells, neutrophils, and macrophages in the bronchoalveolar lavage fluid (BALF) were counted. Enzyme-linked immunosorbent assay was employed to detect the proinflammatory cytokines in BALF and serum, including tumor necrosis factor- (TNF-) α, monocyte chemoattractant protein- (MCP-) 1, and interleukin- (IL-) 1β. The expression of the nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome was detected by western blotting. A lethal dose of LPS (40 mg/kg, intraperitoneally) was injected to evaluate the effects of budesonide on survival rates.

Results

Budesonide pretreatment dramatically attenuated pathological injury and reduced pathological scores in mice with ALI. Budesonide pretreatment obviously reduced the numbers of total cells, neutrophils, and macrophages in the BALF of mice with ALI. Additionally, budesonide dramatically reduced TNF-α and MCP-1 expression in the BALF and serum of mice with ALI. Budesonide significantly suppressed NLRP3 and pro-caspase-1 expression in the lung and reduced IL-1β content in the BALF, indicating that budesonide inhibited the activation of the NLRP3 inflammasome. Furthermore, we found that budesonide improved the survival rates of mice with ALI receiving a lethal dose of LPS.

Conclusion

Suppression of NLRP3 inflammasome activation in mice via budesonide attenuated lung injury induced by LPS in mice with ALI.

NLRP3 inflammasome activation from Kupffer cells is involved in liver fibrosis of Schistosoma japonicum-infected mice via NF-κB

BACKGROUND

NOD-like receptor protein 3 (NLRP3) inflammasome was reported as expressed in schistosomiasis-induced liver fibrosis (SSLF). We used an NLRP3 inflammasome inhibitor, MCC950, to investigate whether it inhibited liver fibrosis, and explored the preliminary molecular mechanism.

METHODS

BALB/c mice were infected with 15 cercariae through the abdominal skin. They received intraperitoneal injections of MCC950 on the day of infection and at day 22 post-infection. We examined their SSLF phenotype and the effect on liver fibrosis, primary Kupffer cells (KCs), and HSCs. Human hepatic stellate cell lines (human LX-2 cells) were treated with soluble egg antigen (SEA) released from the eggs. We then determined the expression of NLRP3 inflammasome and liver fibrosis-associated markers, liver granuloma and ALT/AST.

RESULTS

NLRP3 inflammasome expression in the liver was significantly increased, and eosinophilic granuloma and collagen deposition were found around the eggs in mice infected for 56 days. Additionally, IL-1β, ALT/AST in plasma, and NF-κB in liver tissue and in KCs were all greatly significantly increased. The above-mentioned indicators were largely reduced in mice treated with MCC950 on the day of infection. In vitro, lipopolysaccharide (LPS)/SEA could induce LX-2 cells to express NLRP3 and fibrosis markers, and the SEA-treated group was reversed by MCC950. Furthermore, NLRP3 inflammasome and liver fibrosis-associated markers were both increased in the primary KCs and HSCs isolated from infected mice. However, this effect was not observed in the same cells from the mice treated with MCC950 on the day of infection. Contrary to the aforementioned results, MCC950 treatment at day 22 post-infection aggravated this process. Surprisingly, NLRP3 inflammasome was involved in liver fibrosis mostly from KCs.

CONCLUSIONS

MCC950 acts dually on SSLF pathology and fibrosis in infected mice. Although MCC950 treatment improved SSLF on the day of infection, it exacerbated the pathological effects at day 22 post-infection. These dual effects were mediated via NF-κB. Moreover, NLRP3 inflammasome mainly came from KCs. Our results suggest that blocking NLRP3 on the day of infection may prove to be a promising direction in preventing SSLF.

Hepatitis B e Antigen Inhibits NF-κB Activity by Interrupting K63-Linked Ubiquitination of NEMO

Viruses have adopted diverse strategies to suppress antiviral responses. Hepatitis B virus (HBV), a virus that is prevalent worldwide, manipulates the host's innate immune system to evade scavenging. It is reported that the hepatitis B e antigen (HBeAg) can interfere with NF-κB activity, which then leads to high viral loads, while HBV with the G1896A mutation remains infectious without the production of HBeAg but can induce more severe proinflammatory response and liver damage. The aim of current work was to study the molecular mechanism by which HBeAg suppresses interleukin-1β (IL-1β)-stimulated NF-κB activity, which leads to the suppression of the innate immune responses to HBV infection. Our study revealed that HBeAg could interact with NEMO, a regulatory subunit associated with IκB kinase, which regulates the activation of NF-κB. HBeAg suppressed the IL-1β-induced tumor necrosis factor (TNF)-associated factor 6 (TRAF6)-dependent K63-linked ubiquitination of NEMO, thereby downregulating NF-κB activity and promoting virus replication. We further demonstrated the inhibitory effect of HBeAg on the NF-κB signaling pathway using primary human hepatocytes, HBV-infected HepG2-NTCP cells, and clinical liver samples. Our study reveals a molecular mechanism whereby HBeAg suppresses IL-1β-induced NF-κB activation by decreasing the TRAF6-dependent K63-linked ubiquitination of NEMO, which may thereby enhance HBV replication and promote a persistent infection.IMPORTANCE The role of HBeAg in inflammatory responses during the infection of hepatitis B virus (HBV) is not fully understood, and several previous reports with regard to the NF-κB pathway are controversial. In this study, we showed that HBeAg could suppress both Toll-like receptor 2 (TLR2)- and IL-1β-induced activation of NF-κB in cells and clinical samples, and we further revealed novel molecular mechanisms. We found that HBeAg can associate with NEMO, the regulatory subunit for IκB kinase (IKK) that controls the NF-κB signaling pathway, and thereby inhibits TRAF6-mediated K63-linked ubiquitination of NEMO, resulting in downregulation of NF-κB activity and promotion of virus replication. In contrast, the HBeAg-negative HBV mutant can induce higher levels of NF-κB activity. These results are important for understanding the HBV-induced pathogenesis of chronic hepatitis and indicate that different clinical measures should be considered to treat HBeAg-positive and HBeAg-negative infections. Our findings represent a conceptual advance in HBV-related suppression of NF-κB signaling.

Lipopolysaccharide (LPS) Aggravates High Glucose- and Hypoxia/Reoxygenation-Induced Injury through Activating ROS-Dependent NLRP3 Inflammasome-Mediated Pyroptosis in H9C2 Cardiomyocytes

Diabetes aggravates myocardial ischemia-reperfusion (I/R) injury because of the combination effects of changes in glucose and lipid energy metabolism, oxidative stress, and systemic inflammatory response. Studies have indicated that myocardial I/R may coincide and interact with sepsis and inflammation. However, the role of LPS in hypoxia/reoxygenation (H/R) injury in cardiomyocytes under high glucose conditions is still unclear. Our objective was to examine whether lipopolysaccharide (LPS) could aggravate high glucose- (HG-) and hypoxia/reoxygenation- (H/R-) induced injury by upregulating ROS production to activate NLRP3 inflammasome-mediated pyroptosis in H9C2 cardiomyocytes. H9C2 cardiomyocytes were exposed to HG (30 mM) condition with or without LPS, along with caspase-1 inhibitor (Ac-YVAD-CMK), inflammasome inhibitor (BAY11-7082), ROS scavenger N-acetylcysteine (NAC), or not for 24 h, then subjected to 4 h of hypoxia followed by 2 h of reoxygenation (H/R). The cell viability, lactate dehydrogenase (LDH) release, caspase-1 activity, and intracellular ROS production were detected by using assay kits. The incidence of pyroptosis was detected by calcein-AM/propidium iodide (PI) double staining kit. The concentrations of IL-1β and IL-18 in the supernatants were assessed by ELISA. The mRNA levels of NLRP3, ASC, and caspase-1 were detected by qRT-PCR. The protein levels of NF-κB p65, NLRP3, ASC, cleaved caspase-1 (p10), IL-1β, and IL-18 were detected by western blot. The results indicated that pretreatment LPS with 1 μg/ml not 0.1 μg/ml could efficiently aggravate HG and H/R injury by activating NLRP3 inflammasome to mediate pyroptosis in H9C2 cells, as evidenced by increased LDH release and decreased cell viability in the cells, and increased expression of NLRP3, ASC, cleaved caspase-1 (p10), IL-1β, and IL-18. Meanwhile, Ac-YVAD-CMK, BAY11-7082, or NAC attenuated HG- and H/R-induced H9C2 cell injury with LPS stimulated by reversing the activation of NLRP3 inflammasome-mediated pyroptosis. In conclusion, LPS could increase the sensitivity of H9C2 cells to HG and H/R and aggravated HG- and H/R-induced H9C2 cell injury by promoting ROS production to induce NLRP3 inflammasome-mediated pyroptosis.

AlCl3 inhibits LPS-induced NLRP3 inflammasome activation and IL-1β production through suppressing NF-κB signaling pathway in murine peritoneal macrophages

Aluminum (Al), a common environmental pollutant, has been reported to inhibit the immune functions of macrophage. However, the mechanisms involved remain unclear. In this study, murine peritoneal macrophages were exposed to 0, 0.27, 0.54, and 1.08 mg/mL of aluminium chloride (AlCl₃) for 24 h, and then treated with 1 μg/mL lipopolysaccharide (LPS) for another 6 h. No addition of both AlCl₃ and LPS serviced as control group. We observed that AlCl₃ has cytotoxicity in murine peritoneal macrophages, showing a decrease in cell viability and an increase in lactate dehydrogenase release. Besides, AlCl₃ exposure restrained the LPS-induced NLR pyrin domain containing 3 (NLRP3) inflammasome activation presented as NLRP3 expressions reduction, caspase-1 cleavage inhibition and interleukin 1 beta (IL-1β) maturation lessened. Meanwhile, AlCl₃ exposure decreased LPS-induced IKKβ activity, IκBα phosphorylation, the phosphorylation and mRNA expression of NF-κB p65, as well the genes expression and concentration in medium supernatant of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). The results suggested that AlCl₃ inhibited the activation of NF-κB signaling pathway induced by LPS, which maybe one of the upstream signals involved in the inhibition of NLRP3 inflammasome activation by AlCl₃. This research can provide theoretical basis for understanding the immune toxicity of Al, and deepening the cognition of Al exposure hazards to immune response.

Liver macrophages: Friend or foe during hepatitis B infection?

The Hepatitis B virus chronically infects the liver of 250 million people worldwide. Over the past decades, major advances have been made in the understanding of Hepatitis B virus life cycle in hepatocytes. Beside these parenchymal cells, the liver also contains resident and infiltrating myeloid cells involved in immune responses to pathogens and much less is known about their interplay with Hepatitis B virus. In this review, we summarized and discussed the current knowledge of the role of liver macrophages (including Kupffer cells and liver monocyte-derived macrophages), in HBV infection. While it is still unclear if liver macrophages play a role in the establishment and persistence of HBV infection, several studies disclosed data suggesting that HBV would favour liver macrophage anti-inflammatory phenotypes and thereby increase liver tolerance. In addition, alternatively activated liver macrophages might also play in the long term a key role in hepatitis B-associated pathogenesis, especially through the activation of hepatic stellate cells. Therapies aiming at a transient activation of pro-inflammatory liver macrophages should therefore be considered for the treatment of chronic HBV infection.

Differential Activation of NLRP3, AIM2, and IFI16 Inflammasomes in Humans with Acute and Chronic Hepatitis B

Nod-like receptor protein 3 (NLRP3), absent in melanoma 2 (AIM2), and interferon gamma inducible protein 16 (IFI16) are innate immune sensors for intracellular microbes, which can be activated by various dangerous signals and subsequently lead to caspase-1 (CASP1) activation and the maturation cleavage of effector molecules pro-IL-1β and pro-IL-18. Their roles in immunopathology of acute and chronic hepatitis B virus (HBV) infection are still unclear. In this study, we first investigated the activation of NLRP3, AIM2, and IFI16 inflammasomes in peripheral blood mononuclear cells (PBMCs) from patients infected with acute hepatitis B (AHB) and chronic hepatitis B (CHB) by quantitative real-time PCR and enzyme-linked immunosorbent assay. We next analyzed the impact of hepatitis B e antigen (HBeAg) on activation of AIM2 and IFI16 inflammasomes in PBMCs of CHB patients stimulated in vitro with AIM2 and IFI16 agonist ligands, poly (dA:dT) and VACA-70mer, respectively. The results showed that the mRNA expression levels of AIM2, IFI16, and CASP1 in PBMCs from AHB and CHB patients were both upregulated. Furthermore, the mRNA levels of AIM2 and IFI16 in CHB patients were significantly positively correlated with serum HBV loads. However, only in patients with AHB there was elevation of serum IL-1β and IL-18. There was no activation of NLRP3, AIM2, and IFI16 inflammasomes in CHB patients. Stimulation of PBMCs of CHB patients in vitro with poly (dA:dT) and VACA-70mer induced the activation of AIM2 and IFI16 inflammasomes, respectively. This ligand-induced activation was suppressed by HBeAg. Our results suggest that there exists activation of the AIM2 and IFI16 inflammasomes, but not the NLRP3 inflammasome, in AHB, and the activation of the AIM2 and IFI16 inflammasomes can be inhibited by HBeAg in CHB, which may contribute to HBV-induced immunotolerance.

AMSC-derived exosomes alleviate lipopolysaccharide/d-galactosamine-induced acute liver failure by miR-17-mediated reduction of TXNIP/NLRP3 inflammasome activation in macrophages

Background

Mesenchymal stem cell (MSC)-derived exosome administration has been considered as a novel cell-free therapy for liver diseases through cell-cell communication. This study was aimed to determine the effects and mechanisms of AMSC-derived exosomes (AMSC-Exo) for acute liver failure (ALF) treatment.

Methods

AMSC-Exo were intravenously administrated into the mice immediately after lipopolysaccharide and D-galactosamine (LPS/GalN)-exposure and their effects were evaluated by liver histological and serum biochemical analysis. To elucidate its mechanisms in ALF therapy, the expression levels of miRNAs and inflammasome-related genes in macrophages were evaluated by qPCR and Western blot analysis, respectively. The exosomes from miR-17-knockdowned AMSCs (AMSC-Exo^miR-17-KD) were used for further determine the role of miR-17 in AMSC-Exo-based therapy.

Findings

AMSC-Exo administration significantly ameliorated ALF as determined by reduced serum alanine aminotransferase and aspartate aminotransferase levels and hepatic inflammasome activation. Further experiments revealed that AMSC-Exo were colocalized with hepatic macrophages and could reduce inflammatory factor secretion by suppressing inflammasome activation in macrophages. Moreover, miR-17, which can suppress NLRP3 inflammasome activation by targeting TXNIP, was abundant in AMSC-Exo cargo. While, the therapeutic effects of AMSC-Exo^miR-17-KD on ALF were significantly abolished as they could not effectively suppress TXNIP expression and consequent inflammasome activation in vitro and in vivo.

Interpretation: Exosome-shuttled miR-17 plays an essential role in AMSC-Exo therapy for ALF by targeting TXNIP and suppressing inflammasome activation in hepatic macrophages. AMSC-Exo-based therapy may present as a promising approach for TXNIP/NLRP3 inflammasome-related inflammatory liver diseases.

Fund

Key R&D projects of Zhejiang province (2018C03019) and National Natural Science Fund (81470851 and 81500616).

The Potential Therapeutic Role of miR-223 in Bovine Endometritis by Targeting the NLRP3 Inflammasome

Bovine endometritis affects milk production and reproductive performance in dairy cows and causes serious economic loss. The underlying molecular mechanisms or signaling pathways of bovine endometritis remain unclear. In this study, we attempted to determine the expression mechanism of mir-223 in endometritis of dairy cows and evaluate its potential therapeutic value. We first confirmed that there was an increased level of miR-223 in endometritis, and then, an LPS-induced bovine endometrial epithelial cell (BEND) line was used to mimic the inflammatory model in vitro. Our data showed that activation of NF-κB promoted the transcription of miR-223, thus inhibiting activation of the inflammatory mediator NLRP3 and its mediation of IL-1β production to protect against inflammatory damage. Meanwhile, in vivo studies showed that inhibition of mir-223 resulted in an enhanced pathology of mice during LPS-induced endometritis, while overexpression of mir-223 attenuated the inflammatory conditions in the uterus. In summary, our study highlights that miR-223 serves both to constrain the level of NLRP3 activation and to act as a protective factor in the inflammatory response and thus provides a future novel therapeutic modality for active flares in cow endometritis and other inflammatory diseases.