Brucella abortus Infection Elicited Hepatic Stellate Cell-Mediated Fibrosis Through Inflammasome-Dependent IL-1β Production

New Insights on NLRP3 Inflammasome: Mechanisms of Activation, Inhibition, and Epigenetic Regulation

Inflammasomes are important modulators of inflammation. Dysregulation of inflammasomes can enhance vulnerability to conditions such as neurodegenerative diseases, autoinflammatory diseases, and metabolic disorders. Among various inflammasomes, Nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) is the best-characterized inflammasome related to inflammatory and neurodegenerative diseases. NLRP3 is an intracellular sensor that recognizes pathogen-associated molecular patterns and damage-associated patterns resulting in the assembly and activation of NLRP3 inflammasome. The NLRP3 inflammasome includes sensor NLRP3, adaptor apoptosis-associated speck-like protein (ASC), and effector cysteine protease procaspase-1 that plays an imperative role in caspase-1 stimulation which further initiates a secondary inflammatory response. Regulation of NLRP3 inflammasome ameliorates NLRP3-mediated diseases. Much effort has been invested in studying the activation, and exploration of specific inhibitors and epigenetic mechanisms controlling NLRP3 inflammasome. This review gives an overview of the established NLRP3 inflammasome assembly, its brief molecular mechanistic activations as well as a current update on specific and non-specific NLRP3 inhibitors that could be used in NLRP3-mediated diseases. We also focused on the recently discovered epigenetic mechanisms mediated by DNA methylation, histone alterations, and microRNAs in regulating the activation and expression of NLRP3 inflammasome, which has resulted in a novel method of gaining insight into the mechanisms that modulate NLRP3 inflammasome activity and introducing potential therapeutic strategies for CNS disorders.

The anti-liver fibrosis effect of Tibetan medicine (Qiwei Tiexie capsule) is related to the inhibition of NLRP3 inflammasome activation in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Qiwei Tiexie capsule (QWTX) is an improved form of a classical prescription of Tibetan medicine-Qiwei Tiexie pill. It has been employed in the treatment of a variety of chronic liver disorders, including liver fibrosis. Uncertainty still exists regarding the mechanism of QWTX action in liver fibrosis.

AIM OF THE STUDY

Confirm the anti-liver fibrosis effect of QWTX and reveal its mechanism from the perspective of NOD-like receptor protein 3 (NLRP3) inflammasome activation.

MATERIALS AND METHODS

In vivo experiment: A rat model of carbon tetrachloride -induced liver fibrosis was constructed. All rats were randomly divided into six groups: a control group, a model group, a group receiving the positive drug (Biejia Ruangan tablet), and three groups receiving QWTX at high, medium, and low doses. The contents of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin (TBil) were detected in serum. Hematoxylin and eosin staining and Masson's staining were used to assess the histomorphological alteration of the liver. The levels of glutathione peroxidase, hydroxyproline, tumor necrosis factor alpha (TNF-α), and interleukin 1 beta (IL-1β) in the liver were determined using the corresponding detection kits. Real-time polymerase chain reaction, immunofluorescence, and western blotting were used to determine the expression levels of NLRP3, adaptor protein (ASC), caspase-1, and alpha-smooth muscle actin (α-SMA). In vitro experiment: Four groups of rat hepatic stellate cell line (HSC-T6) cells were created: the control group, the low-dose QWTX group (0.05 mg/mL), the medium-dose QWTX group (0.1 mg/mL), and the high-dose QWTX group (0.2 mg/mL). Cell viability was assessed using a cell counting kit, and the amounts of collagen type I (Col I) and IL-1β in the cell lysate were measured using an enzyme-linked immunosorbent assay kit. The mRNA and protein expression of NLRP3, ASC, caspase-1, and α-SMA were also estimated.

RESULTS

QWTX had an inhibitory effect on liver fibrosis and a negative effect on HSC activation, while it improved liver histopathological injury and abnormal liver function and increased hydroxyproline content and glutathione peroxidase activity in vivo. QWTX decreased the expression of α-SMA, NLRP3, caspase-1, ASC, and IL-1β both in vitro and in vivo.

CONCLUSIONS

Tibetan medicine QWTX had a significant anti-liver fibrosis effect that was related to the inhibition of NLRP3 inflammasome activation in vivo and in vitro.

Recent advances in pyroptosis, liver disease, and traditional Chinese medicine: A review

In recent years, the incidence of liver disease has increased, becoming a major cause of death. Various liver diseases are intricately linked to pyroptosis, which is one of the most common forms of programmed cell death. As a powerful weapon in the fight against liver diseases, traditional Chinese medicine (TCM) can affect pyroptosis via a number of routes, including the classical, nucleotide oligomerization domain-like receptors protein 3/caspase-1/gasdermin D (GSDMD) pathway, the nonclassical lipopolysaccharide/caspase-11/GSDMD pathway, the ROS/caspase-3/gasdermin E pathway, the caspase-9/caspase-3/GSDMD pathway, and the Apaf-1/caspase-11/caspase-3 pathway. In this review, we provide an overview of pyroptosis, the interplay between pyroptosis and liver diseases, and the mechanisms through which TCM regulates pyroptosis in liver diseases. The information used in the text was collected and compiled from the databases of PubMed, Web of Science, Scopus, CNKI, and Wanfang Data up to June 2023. The search was not limited with regard to the language and country of the articles. Research and review articles were included, and papers with duplicate results or unrelated content were excluded. We examined the current understanding of the relationship between pyroptosis and liver diseases as well as the advances in TCM interventions to provide a resource for the identification of potential targets for TCM in the treatment of liver diseases.

Simultaneous intervention against oxidative stress and inflammation by targeting Nrf2/ARE and NLRP3 inflammasome pathway mitigates thioacetamide-induced liver fibrosis in rat

Liver fibrosis is a typical pathological state/stage involved in most chronic liver diseases and its persistence results in cirrhosis. Inflammasomes are cytoplasmic sensors that induce inflammation in response to stress. Glibenclamide (GLB) is an USFDA-approved drug for type 2 diabetes and is reported to possess anti-inflammatory activity by inhibiting inflammatory cytokines. Dimethyl fumarate (DMF) is an USFDA-approved drug for multiple sclerosis and has been reported to activate the Nrf2/ARE pathway to maintain the cellular antioxidant balance. A total of 36 rats were randomized into six groups (n = 6 each). The rats were injected with thioacetamide (TAA) 200 mg/kg, intraperitoneally every third day for eight consecutive weeks to induce liver fibrosis and oral treatment of GLB 0.5 mg/kg/day and DMF 25 mg/kg/day, and their combinations were provided for the last four consecutive weeks. Treatment with GLB, DMF, and GLB+DMF significantly protected against TAA-mediated oxidative stress and inflammatory conditions by improving hepatic function test, triglycerides, hydroxyproline, and histopathological alterations, by inhibiting the NLRP3 inflammasome signaling and fibrogenic markers, and by activating Nrf2/ARE pathway in Wistar rats. The present results suggest that simultaneous Nrf2/ARE activation and NLRP3 inflammasome inhibition could significantly contribute to developing a novel therapy for patients with liver fibrosis.

The role of IL-1β during human immunodeficiency virus type 1 infection

Interleukin (IL)-1β is a key innate cytokine that is essential for immune activation and promoting the inflammatory process. However, abnormal elevation in IL-1β levels has been associated with unwanted clinical outcomes. IL-1β is the most extensively studied cytokine among the IL-1 family of cytokines and its role in pathology is well established. During the course of human immunodeficiency virus type 1 (HIV-1) infection, the level of this proinflammatory cytokine is increased in different anatomical compartments, particularly in lymphatic tissues, and this elevation is associated with disease progression. The aim of this review is to address the pathological roles play by IL-1β in the light of enhancing HIV-1 replication, driving immune cell depletion, and chronic immune activation. The role of IL-1β in HIV-1 transmission (sexually or vertically 'from mother-to-child') will also be discussed. Additionally, the impact of the available antiretroviral therapy regimens on the levels of IL-1β in HIV-1 treated patients is also discussed. Finally, we will provide a glance on how IL-1β could be targeted as a therapeutic strategy.

Regulation of the macrophage-hepatic stellate cell interaction by targeting macrophage peroxisome proliferator-activated receptor gamma to prevent non-alcoholic steatohepatitis progression in mice

BACKGROUND & AIMS

Macrophages display remarkable plasticity and can interact with surrounding cells to affect hepatic immunity and tissue remodelling during the progression of liver diseases. Peroxisome proliferator-activated receptor gamma (PPARγ) plays a critical role in macrophage maturation, polarization and metabolism. In this study, we investigated the role of PPARγ in macrophage-hepatic stellate cell (HSC) interaction during non-alcoholic steatohepatitis (NASH) development.

METHODS

Wild-type, Pparg^fl/fl and Pparg^ΔLyz2 mice were fed a methionine- and choline-deficient (MCD) diet to induce NASH. Depletion of macrophages was performed using an injection of gadolinium chloride intraperitoneally. PPARγ-overexpressing or PPARγ-knockout macrophages were stimulated with saturated fatty acid (SFA) and cocultured with HSCs in a conditioned medium or the transwell coculture system.

RESULTS

Depletion of macrophages inhibited HSC activation and ameliorated NASH progression in MCD diet-fed mice. Coculturing HSCs with macrophages or culturing HSCs in a macrophage-conditioned medium-facilitated HSC activation, and this effect was magnified when macrophages were metabolically activated by SFA. Moreover, the absence of PPARγ in macrophages enhanced metabolic activation, promoting the migration and activation of HSCs through IL-1β and CCL2. In contrast, overexpression of PPARγ in macrophages obtained the opposite effects. In vivo, macrophage-specific PPARγ knockout affected the phenotype of hepatic macrophages and HSCs, involving the MAPK and NLRP3/caspase-1/IL-1β signalling pathways. Infiltrating hepatic monocyte-derived macrophages became the predominant macrophages in NASH liver, especially in Pparg^ΔLyz2 mice, paralleling with aggravated inflammation and fibrosis.

CONCLUSIONS

Regulating macrophage PPARγ affected the metabolic activation of macrophages and their interaction with HSCs. Macrophage-specific PPARγ may be an attractive therapeutic target for protecting against NASH-associated inflammation and fibrosis.

Targeted activation of HNF4α/HGF1/FOXA2 reverses hepatic fibrosis via exosome-mediated delivery of CRISPR/dCas9-SAM system

Aim: Hepatic fibrosis is one of the most common conditions worldwide, and yet no effective antifibrotic therapy is available. This study aimed to reverse hepatic fibrosis via exosome-mediated delivery of the CRISPR/dCas9-SAM system. Materials & methods: The authors constructed a modified-exosome delivery system targeting hepatic stellate cells (HSCs), and constructed the CRISPR/dCas9-SAM system inducing HSCs convert into hepatocyte-like cells in vitro and in vivo. Results: RBP4-modified exosomes could efficiently load and deliver the CRISPR/dCas9 system to HSCs. The in vitro CRISPR/dCas9 system induced the conversion from HSCs to hepatocyte-like cells via targeted activation of HNF4α/HGF1/FOXA2 genes. Importantly, in vivo targeted delivery of this system significantly attenuated CCl₄-induced hepatic fibrosis. Conclusion: Targeted activation of HNF4α/HGF1/FOXA2 reverses hepatic fibrosis via exosome-mediated delivery of the CRISPR/dCas9-SAM system, which provides a feasible antifibrotic strategy.

Inflammasomes and Pyroptosis of Liver Cells in Liver Fibrosis

Inflammasomes are multiprotein complexes that can sense danger signals and activate caspase-1 to mediate pro-inflammatory cytokines release and pyroptotic cell death. There are two main canonical and non-canonical signaling pathways that trigger inflammasome activation. Inflammasomes are expressed and assembled in parenchymal and nonparenchymal cells in response to liver injury in the liver. Additionally, the hepatocytes, biliary epithelial cells (cholangiocytes), hepatic stellate cells (HSCs), hepatic macrophages, and liver sinusoidal endothelial cells (LSECs) contribute to liver fibrosis via different mechanisms. However, the underlying mechanism of the inflammasome and pyroptosis in these liver cells in liver fibrosis remains elusive. This review summarizes the activation and function of inflammasome complexes and then discusses the association between inflammasomes, pyroptosis, and liver fibrosis. Unlike other similar reviewers, we will focus on the effect of inflammasome activation and pyroptosis in the various liver cells during the development of liver fibrosis. We will also highlight the latest progress of pharmacological intervention in inflammasome-mediated liver fibrosis.

The Mechanism and Regulation of the NLRP3 Inflammasome during Fibrosis

Fibrosis is often the end result of chronic inflammation. It is characterized by the excessive deposition of extracellular matrix. This leads to structural alterations in the tissue, causing permanent damage and organ dysfunction. Depending on the organ it effects, fibrosis can be a serious threat to human life. The molecular mechanism of fibrosis is still not fully understood, but the NLRP3 (NOD-, LRR- and pyrin–domain–containing protein 3) inflammasome appears to play a significant role in the pathogenesis of fibrotic disease. The NLRP3 inflammasome has been the most extensively studied inflammatory pathway to date. It is a crucial component of the innate immune system, and its activation mediates the secretion of interleukin (IL)-1β and IL-18. NLRP3 activation has been strongly linked with fibrosis and drives the differentiation of fibroblasts into myofibroblasts by the chronic upregulation of IL-1β and IL-18 and subsequent autocrine signaling that maintains an activated inflammasome. Both IL-1β and IL-18 are profibrotic, however IL-1β can have antifibrotic capabilities. NLRP3 responds to a plethora of different signals that have a common but unidentified unifying trigger. Even after 20 years of extensive investigation, regulation of the NLRP3 inflammasome is still not completely understood. However, what is known about NLRP3 is that its regulation and activation is complex and not only driven by various activators but controlled by numerous post-translational modifications. More recently, there has been an intensive attempt to discover NLRP3 inhibitors to treat chronic diseases. This review addresses the role of the NLRP3 inflammasome in fibrotic disorders across many different tissues. It discusses the relationships of various NLRP3 activators to fibrosis and covers different therapeutics that have been developed, or are currently in development, that directly target NLRP3 or its downstream products as treatments for fibrotic disorders.

Hepatic Stellate Cell: A Double-Edged Sword in the Liver

Hepatic stellate cells (HSCs) are located in the space of Disse, between liver sinusoidal endothelia cells (LSECs) and hepatocytes. They have surprised and excited hepatologists for their biological characteristics. Under physiological quiescent conditions, HSCs are the major vitamin A-storing cells of the liver, playing crucial roles in the liver development, regeneration, and tissue homeostasis. Upon injury-induced activation, HSCs convert to a pro-fibrotic state, producing the excessive extracellular matrix (ECM) and promoting angiogenesis in the liver fibrogenesis. Activated HSCs significantly contribute to liver fibrosis progression and inactivated HSCs are key to liver fibrosis regression. In this review, we summarize the comprehensive understanding of HSCs features, including their roles in normal liver and liver fibrosis in hopes of advancing the development of emerging diagnosis and treatment for hepatic fibrosis.

Simultaneous Modulation of NLRP3 Inflammasome and Nrf2/ARE Pathway Rescues Thioacetamide-Induced Hepatic Damage in Mice: Role of Oxidative Stress and Inflammation

Chronic tissue injury resulting in fibrosis of multiple organs, responsible for one-third of the death globally. Liver fibrosis is a common pathway/condition involved in all chronic liver diseases. Thioacetamide (TAA), a hepatotoxicant, was used to induce hepatic fibrosis. Anti-diabetic drug glibenclamide (GLB) possesses anti-inflammatory properties and inhibits NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation. Dimethyl fumarate (DMF), a multiple sclerosis drug, activates the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway and maintains the antioxidant status in the cell. The present study was designed to investigate (i) role of NLRP3 inflammasome and Nrf2/ARE pathway in TAA-induced hepatotoxicity and liver fibrosis, (ii) mechanism involved in GLB and DMF mediated hepatoprotection against TAA-induced hepatotoxicity, and (iii) additional/synergistic hepatoprotective effect of combination treatment with NLRP3 inhibition + Nrf2 activation or GLB + DMF or MCC950 + 4OI to reverse/ameliorate the experimental liver fibrosis completely. TAA was administered intraperitoneally to mice for seven consecutive weeks, and treatments of GLB, DMF, GLB + DMF, MCC950, 4OI, and MCC950 + 4OI were provided for the last three consecutive weeks. The intervention with GLB, DMF, GLB + DMF, MCC950, 4OI, and MCC950 + 4OI significantly protected TAA-induced oxidative stress and inflammatory conditions by improving biochemical, histological, and immunoexpression changes in mice. The GLB, DMF, and GLB + DMF intervention exhibited a better protective effect compared with MCC950, 4OI, and MCC950 + 4OI, which revealed that this specific inhibitor/activator possesses only NLRP3 inflammasome inhibitory/Nrf2 activatory properties. In contrast, the clinical drug GLB and DMF have several other beneficial effects, which are independent of NLRP3 inhibition and Nrf2 activation.

Reversal of Endothelial Extracellular Vesicle-Induced Smooth Muscle Phenotype Transition by Hypercholesterolemia Stimulation: Role of NLRP3 Inflammasome Activation

Recent studies reported that vascular endothelial cells (ECs) secrete NLR family pyrin domain-containing 3 (NLRP3) inflammasome products such as interleukin-1β (IL-1β) via extracellular vesicles (EVs) under various pathological conditions. EVs represent one of the critical mechanisms mediating the cell-to-cell communication between ECs and vascular smooth muscle cells (VSMCs). However, whether or not the inflammasome-dependent EVs directly participate in the regulation of VSMC function remains unknown. In the present study, we found that in cultured carotid ECs, atherogenic stimulation by oxysterol 7-ketocholesterol (7-Ket) induced NLRP3 inflammasome formation and activation, reduced lysosome-multivesicular bodies (MVBs) fusion, and increased secretion of EVs that contain inflammasome product IL-1β. These EC-derived IL-1β-containing EVs promoted synthetic phenotype transition of co-cultured VSMCs, whereas EVs from unstimulated ECs have the opposite effects. Moreover, acid ceramidase (AC) deficiency or lysosome inhibition further exaggerated the 7-Ket-induced release of IL-1β-containing EVs in ECs. Using a Western diet (WD)-induced hypercholesterolemia mouse model, we found that endothelial-specific AC gene knockout mice (Asah1^fl/fl/EC^Cre) exhibited augmented WD-induced EV secretion with IL-1β and more significantly decreased the interaction of MVBs with lysosomes in the carotid arterial wall compared to their wild-type littermates (WT/WT). The endothelial AC deficiency in Asah1^fl/fl/EC^Cre mice also resulted in enhanced VSMC phenotype transition and accelerated neointima formation. Together, these results suggest that NLRP3 inflammasome-dependent IL-1β production during hypercholesterolemia promotes VSMC phenotype transition to synthetic status via EV machinery, which is controlled by lysosomal AC activity. Our findings provide novel mechanistic insights into understanding the pathogenic role of endothelial NLRP3 inflammasome in vascular injury through EV-mediated EC-to-VSMC regulation.

Function of TREM1 and TREM2 in Liver-Related Diseases

TREM1 and TREM2 are members of the triggering receptors expressed on myeloid cells (TREM) family. Both TREM1 and TREM2 are immunoglobulin superfamily receptors. Their main function is to identify foreign antigens and toxic substances, thereby adjusting the inflammatory response. In the liver, TREM1 and TREM2 are expressed on non-parenchymal cells, such as liver sinusoidal endothelial cells, Kupffer cells, and hepatic stellate cells, and cells which infiltrate the liver in response to injury including monocyte-derived macrophages and neutrophils. The function of TREM1 and TREM2 in inflammatory response depends on Toll-like receptor 4. TREM1 mainly augments inflammation during acute inflammation, while TREM2 mainly inhibits chronic inflammation to protect the liver from pathological changes. Chronic inflammation often induces metabolic abnormalities, fibrosis, and tumorigenesis. The above physiological changes lead to liver-related diseases, such as liver injury, nonalcoholic steatohepatitis, hepatic fibrosis, and hepatocellular carcinoma. Here, we review the function of TREM1 and TREM2 in different liver diseases based on inflammation, providing a more comprehensive perspective for the treatment of liver-related diseases.

The Emerging Relevance of AIM2 in Liver Disease

Absent in melanoma 2 (AIM2) is a cytosolic receptor that recognizes double-stranded DNA (dsDNA) and triggers the activation of the inflammasome cascade. Activation of the inflammasome results in the maturation of inflammatory cytokines, such as interleukin (IL)-1 β and IL-18, and a form of cell death known as pyroptosis. Owing to the conserved nature of its ligand, AIM2 is important during immune recognition of multiple pathogens. Additionally, AIM2 is also capable of recognizing host DNA during cellular damage or stress, thereby contributing to sterile inflammatory diseases. Inflammation, either in response to pathogens or due to sterile cellular damage, is at the center of the most prevalent and life-threatening liver diseases. Therefore, during the last 15 years, the study of inflammasome activation in the liver has emerged as a new research area in hepatology. Here, we discuss the known functions of AIM2 in the pathogenesis of different hepatic diseases, including non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH), hepatitis B, liver fibrosis, and hepatocellular carcinoma (HCC).

Hepatic Stellate Cells and Hepatocytes as Liver Antigen-Presenting Cells during B. abortus Infection

In Brucellosis, the role of hepatic stellate cells (HSCs) in the induction of liver fibrosis has been elucidated recently. Here, we study how the infection modulates the antigen-presenting capacity of LX-2 cells. Brucella abortus infection induces the upregulation of class II transactivator protein (CIITA) with concomitant MHC-I and -II expression in LX-2 cells in a manner that is independent from the expression of the type 4 secretion system (T4SS). In concordance, B. abortus infection increases the phagocytic ability of LX-2 cells and induces MHC-II-restricted antigen processing and presentation. In view of the ability of B. abortus-infected LX-2 cells to produce monocyte-attracting factors, we tested the capacity of culture supernatants from B. abortus-infected monocytes on MHC-I and -II expression in LX-2 cells. Culture supernatants from B. abortus-infected monocytes do not induce MHC-I and -II expression. However, these supernatants inhibit MHC-II expression induced by IFN-γ in an IL-10 dependent mechanism. Since hepatocytes constitute the most abundant epithelial cell in the liver, experiments were conducted to determine the contribution of these cells in antigen presentation in the context of B. abortus infection. Our results indicated that B. abortus-infected hepatocytes have an increased MHC-I expression, but MHC-II levels remain at basal levels. Overall, B. abortus infection induces MHC-I and -II expression in LX-2 cells, increasing the antigen presentation. Nevertheless, this response could be modulated by resident or infiltrating monocytes/macrophages.