Caspase-11-Mediated Hepatocytic Pyroptosis Promotes the Progression of Nonalcoholic Steatohepatitis

Molecular mechanisms of pyroptosis in non-alcoholic steatohepatitis and feasible diagnosis and treatment strategies

Pyroptosis is a distinct form of cell death that plays a critical role in intensifying inflammatory responses. It primarily occurs via the classical pathway, non-classical pathway, caspase-3/6/7/8/9-mediated pathways, and granzyme-mediated pathways. Key effector proteins involved in the pyroptosis process include gasdermin family proteins and pannexin-1 protein. Pyroptosis is intricately linked to the onset and progression of non-alcoholic steatohepatitis (NASH). During the development of NASH, factors such as pyroptosis, innate immunity, lipotoxicity, endoplasmic reticulum stress, and gut microbiota imbalance interact and interweave, collectively driving disease progression. This review analyzes the molecular mechanisms of pyroptosis and its role in the pathogenesis of NASH. Furthermore, it explores potential diagnostic and therapeutic strategies targeting pyroptosis, offering new avenues for improving the diagnosis and treatment of NASH.

Cisplatin induces acute liver injury by triggering caspase-3/GSDME-mediated cell pyroptosis

BACKGROUND

Cisplatin triggers Gasdermin E (GSDME) cleavage, causing membrane bubble formation, content release, and inflammation. Caspase-3 activation initiates GSDME cleavage, and thus inhibiting this pathway mitigates cisplatin-induced pyroptosis in hepatocytes. This study aimed to delve into how cisplatin induces liver injury via pyroptosis.

METHODS

For animal experiments, C57BL/6J mice were divided into three groups: control, liver injury model group, and Ac-DMLD-CMK (caspase-3 inhibitor) intervention group. The liver histology was evaluated by hematoxylin and eosin staining, immunohistochemistry, immunofluorescence and TUNEL staining. The mRNA and protein levels were detected by real-time polymerase chain reaction (PCR) and Western blot analysis. For in vitro experiments, HL-7702 cells were treated with cisplatin or GSDME siRNA. Cell pyroptosis was determined via cellular morphology, cytotoxicity and viability detection, flow cytometric assay, and Western blot detection for the expression of pyroptosis-related proteins.

RESULTS

Cisplatin-induced distinct liver morphological changes, hepatocellular injury, and inflammation in mice, along with elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and increased pro-inflammatory cytokine expression. Heightened macrophage infiltration and hepatocellular death indicated cisplatin-induced hepatotoxicity. Cisplatin upregulated GSDME activation, along with Bax-mediated caspase-3 cleavage both in vivo and in vitro, implicating caspase-3/GSDME-dependent pyroptosis in liver injury. Treatment with Ac-DMLD-CMK ameliorated cisplatin-induced liver injury, reducing hepatocellular lesions, serum ALT and AST levels, cytokine expression, macrophage infiltration, and hepatocyte death. Ac-DMLD-CMK also attenuated GSDME-dependent pyroptosis post-cisplatin induction, as evidenced by decreased GSDME expression, Bax upregulation, and cleaved caspase-3 activation. For HL-7702 cells, GSDME siRNA transfection reduced GSDME expression, attenuated typical signs of cisplatin-induced pyroptosis, partially restored cell viability, and significantly inhibited cytotoxicity and a decrease in the proportion of propidium iodide-positive cells, indicating protection against cisplatin-induced hepatocyte pyroptosis.

CONCLUSIONS

Our study underscores the role of the caspase-3/GSDME signaling pathway in mediating cisplatin-induced hepatotoxicity, particularly in cases of excessive or cumulative cisplatin exposure. These findings suggest that targeting GSDME could represent a promising therapeutic approach to mitigate cisplatin-induced liver damage.

Exosomes derived from diabetic microenvironment-preconditioned mesenchymal stem cells ameliorate nonalcoholic fatty liver disease and inhibit pyroptosis of hepatocytes

AIM

Pyroptosis, a type of programmed cell death, is a key mechanism underlying non-alcoholic fatty liver disease (NAFLD). Mesenchymal stem cell (MSC)-derived exosomes (MSC-Exos) have the potential to ameliorate NAFLD, an effect that is enhanced by curcumin preconditioning. We previously reported that diabetic microenvironment preconditioning enhances the secretion capacity and anti-inflammatory activity of MSCs. Therefore, we hypothesized that MSC-Exos would inhibit hepatocyte pyroptosis and thereby ameliorate NAFLD, and that diabetic microenvironment preconditioning would enhance these effects.

METHODS

MSCs were preconditioned in a diabetic microenvironment (pMSCs). MSC-Exos and pMSC-Exos collected from MSCs or pMSCs were applied to methionine- and choline-deficient (MCD)-induced NAFLD mice and in vitro models involving induction with lipopolysaccharide or palmitic acid to mimic hepatic steatosis and injury. MCC950 treatment was used as a positive control. We analyzed the characteristics of NAFLD and pyroptosis markers. Protein profiles of MSC-Exos and pMSC-Exos were evaluated by label-free quantitative proteomics.

RESULTS

In vivo, MSC-Exos partially attenuated inflammation and fibrosis, but not lipid deposition and NAFLD progression in the livers of NAFLD mice. pMSC-Exos significantly improved lipid metabolism, hepatic steatosis, inflammation, and fibrosis but also retarded the progression of NAFLD. Pyroptosis was upregulated in the liver of NAFLD mice. MSC-Exos and pMSC-Exos inhibited pyroptosis, and the effect of the latter was greater than that of the former. In vitro, MSC-Exos and pMSC-Exos ameliorated hepatocyte steatosis, lipid metabolism disorder, and inflammation, and pMSC-Exos exerted a greater inhibitory effect on hepatocyte pyroptosis than MSC-Exos did, which were remitted after inhibition of peroxiredoxin-1 (PRDX-1).

CONCLUSION

MSC-Exos ameliorated NAFLD and inhibited hepatocyte pyroptosis by downregulating the NLRP3/Caspase-1/GSDMD pathway, effects enhanced by pMSC-Exos, partly due to PRDX-1 upregulation.

Bisphenol A induces non-alcoholic fatty liver disease by promoting the O-GlcNAcylation of NLRP3

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease. The mechanism by which bisphenol A (BPA) promots NAFLD remains unclear. Palmitic acid (PA) and lipopolysaccharide (LPS) were used to simulate NAFLD in HepG2 cells in vitro. Total cholesterol (TC), triglyceride (TG) content, and lipid accumulation were measured to evaluate lipid metabolism. The caspase-1-stained cells and NLRP3 inflammasome-associated proteins were evaluated for pyroptosis. Western blot analysis was used to detect protein levels and co-immunoprecipitation (Co-IP) was used to detect the association between the proteins. Cycloheximide (CHX) treatment combined with western blot was performed to access protein stability. This data have shown that BPA induces lipid metabolism dysfunction and pyroptosis by upregulating O-GlcNAc transferase (OGT) level. NLRP3 directly interacts with OGT, and elevated OGT enhanced the stability of NLRP3 protein. BPA promoted OGT-mediated O-GlcNAcylation to stabilised NLRP3, thus accelerating NAFLD progress in vitro. Our study reveals that BPA, as an environmental factor, may be involved in the promotion of NAFLD, and that targeting NLRP3 and OGT may inhibit BPA's induction of NAFLD.

Targeting cell death in NAFLD: mechanisms and targeted therapies

Nonalcoholic fatty liver disease (NAFLD) is a group of chronic liver disease which ranges from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) and is characterized by lipid accumulation, inflammation activation, fibrosis, and cell death. To date, a number of preclinical studies or clinical trials associated with therapies targeting fatty acid metabolism, inflammatory factors and liver fibrosis are performed to develop effective drugs for NAFLD/NASH. However, few therapies are cell death signaling-targeted even though the various cell death modes are present throughout the progression of NAFLD/NASH. Here we summarize the four types of cell death including apoptosis, necroptosis, pyroptosis, and ferroptosis in the NAFLD and the underlying molecular mechanisms by which the pathogenic factors such as free fatty acid and LPS induce cell death in the pathogenesis of NAFLD. In addition, we also review the effects of cell death-targeted therapies on NAFLD. In summary, our review provides comprehensive insight into the roles of various cell death modes in the progression of NAFLD, which we hope will open new avenues for therapeutic intervention.

Role of gasdermin D in inflammatory diseases: from mechanism to therapeutics

Inflammatory diseases compromise a clinically common and diverse group of conditions, causing detrimental effects on body functions. Gasdermins (GSDM) are pore-forming proteins, playing pivotal roles in modulating inflammation. Belonging to the GSDM family, gasdermin D (GSDMD) actively mediates the pathogenesis of inflammatory diseases by mechanistically regulating different forms of cell death, particularly pyroptosis, and cytokine release, in an inflammasome-dependent manner. Aberrant activation of GSDMD in different types of cells, such as immune cells, cardiovascular cells, pancreatic cells and hepatocytes, critically contributes to the persistent inflammation in different tissues and organs. The contributory role of GSDMD has been implicated in diabetes mellitus, liver diseases, cardiovascular diseases, neurodegenerative diseases, and inflammatory bowel disease (IBD). Clinically, alterations in GSDMD levels are potentially indicative to the occurrence and severity of diseases. GSDMD inhibition might represent an attractive therapeutic direction to counteract the progression of inflammatory diseases, whereas a number of GSDMD inhibitors have been shown to restrain GSDMD-mediated pyroptosis through different mechanisms. This review discusses the current understanding and future perspectives on the role of GSDMD in the development of inflammatory diseases, as well as the clinical insights of GSDMD alterations, and therapeutic potential of GSDMD inhibitors against inflammatory diseases. Further investigation on the comprehensive role of GSDM shall deepen our understanding towards inflammation, opening up more diagnostic and therapeutic opportunities against inflammatory diseases.

The role and mechanism of pyroptosis and potential therapeutic targets in non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is a clinical pathological syndrome characterized by the excessive accumulation of fat within liver cells, which can progress to end-stage liver disease in severe cases, posing a threat to life. Pyroptosis is a distinct, pro-inflammatory form of cell death, differing from traditional apoptosis. In recent years, there has been growing research interest in the association between pyroptosis and NAFLD, encompassing the mechanisms and functions of pyroptosis in the progression of NAFLD, as well as potential therapeutic targets. Controlled pyroptosis can activate immune cells, eliciting host immune responses to shield the body from harm. However, undue activation of pyroptosis may worsen inflammatory responses, induce cellular or tissue damage, disrupt immune responses, and potentially impact liver function. This review elucidates the involvement of pyroptosis and key molecular players, including NOD-like receptor thermal protein domain associated protein 3(NLRP3) inflammasome, gasdermin D (GSDMD), and the caspase family, in the pathogenesis and progression of NAFLD. It emphasizes the promising prospects of targeting pyroptosis as a therapeutic approach for NAFLD and offers valuable insights into future directions in the field of NAFLD treatment.

Vinpocetine represses the progression of nonalcoholic steatohepatitis in mice by mediating inflammasome components via NF-κB signaling

BACKGROUND

Inflammasome activation is known to be involved in nonalcoholic steatohepatitis (NASH). Vinpocetine is a derivative of vincamine and is reported to suppress the activation of inflammasome.

METHODS

This study explored the therapeutical potential of Vinpocetine on NASH. Mice were fed with a choline-deficient (MCD) or chow diet in the presence or absence of Vinpocetine for 8 weeks. H&E staining and biochemical assays were determined to evaluate the hepatic steatosis and fibrosis symptoms. In addition, primary hepatocytes and Kupffer cells were isolated and induced by MCD or lipopolysaccharides/cholesterol crystals with or without Vinpocetine. ELISAs, qPCR, and Western blotting were applied to determine the levels of NASH-related biomarkers in both in vivo mouse model and in vitro cell models.

RESULTS

Treatment of Vinpocetine did not cause observable side effects against and MCD-induced cells and mouse NASH model. However, treatment of Vinpocetine ameliorated hepatic steatosis and fibrosis and suppressed the levels of alanine transaminase and aspartate transferase in the mouse NASH model. In addition, treatment of Vinpocetine suppressed the mRNA and protein levels of inflammasome components both in vitro and in vivo.

CONCLUSION

Vinpocetine suppressed NASH in mice by mediating inflammasome components via nuclear factor κB signaling.

Research Progress of Pyroptosis in Fatty Liver Disease

Fatty liver disease (FLD) is a clinical and pathological syndrome characterized by excessive fat deposition and even steatosis in hepatocytes. It has been proven that liver inflammation induced by fat and its derivatives are involved in the pathogenesis of FLD, while the precise mechanism still remains poorly understood. Pyroptosis is programmed inflammatory cell death driving cell swelling and membrane rupture. Pyroptosis is initiated by the activation of inflammasomes and caspases, which further cleaves and activates various gasdermins, leading to pores forming on the cell membrane and the release of pro-inflammatory factors such as interleukin (IL)-1β and IL-18. Recent studies demonstrate that pyroptosis occurs in hepatocytes, and inhibiting pyroptosis could effectively reduce fat deposition in the liver and could ameliorate inflammation from FLD, attracting our prime focus on the role of pyroptosis in FLD. In this manuscript, we reviewed the current understanding of pyroptosis in FLD development, aiming to provide new insights and potential research targets for the clinical diagnosis and intervention of FLD.

Treatment of liver fibrosis: Past, current, and future

Liver fibrosis accompanies the progression of chronic liver diseases independent of etiologies, such as hepatitis viral infection, alcohol consumption, and metabolic-associated fatty liver disease. It is commonly associated with liver injury, inflammation, and cell death. Liver fibrosis is characterized by abnormal accumulation of extracellular matrix components that are expressed by liver myofibroblasts such as collagens and alpha-smooth actin proteins. Activated hepatic stellate cells contribute to the major population of myofibroblasts. Many treatments for liver fibrosis have been investigated in clinical trials, including dietary supplementation (e.g., vitamin C), biological treatment (e.g., simtuzumab), drug (e.g., pegbelfermin and natural herbs), genetic regulation (e.g., non-coding RNAs), and transplantation of stem cells (e.g., hematopoietic stem cells). However, none of these treatments has been approved by Food and Drug Administration. The treatment efficacy can be evaluated by histological staining methods, imaging methods, and serum biomarkers, as well as fibrosis scoring systems, such as fibrosis-4 index, aspartate aminotransferase to platelet ratio, and non-alcoholic fatty liver disease fibrosis score. Furthermore, the reverse of liver fibrosis is slowly and frequently impossible for advanced fibrosis or cirrhosis. To avoid the life-threatening stage of liver fibrosis, anti-fibrotic treatments, especially for combined behavior prevention, biological treatment, drugs or herb medicines, and dietary regulation are needed. This review summarizes the past studies and current and future treatments for liver fibrosis.

Regulatory Roles of Flavonoids in Caspase-11 Non-Canonical Inflammasome-Mediated Inflammatory Responses and Diseases

Inflammasomes are multiprotein complexes that activate inflammatory responses by inducing pyroptosis and secretion of pro-inflammatory cytokines. Along with many previous studies on inflammatory responses and diseases induced by canonical inflammasomes, an increasing number of studies have demonstrated that non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 inflammasomes, are emerging key players in inflammatory responses and various diseases. Flavonoids are natural bioactive compounds found in plants, fruits, vegetables, and teas and have pharmacological properties in a wide range of human diseases. Many studies have successfully demonstrated that flavonoids play an anti-inflammatory role and ameliorate many inflammatory diseases by inhibiting canonical inflammasomes. Others have demonstrated the anti-inflammatory roles of flavonoids in inflammatory responses and various diseases, with a new mechanism by which flavonoids inhibit non-canonical inflammasomes. This review discusses recent studies that have investigated the anti-inflammatory roles and pharmacological properties of flavonoids in inflammatory responses and diseases induced by non-canonical inflammasomes and further provides insight into developing flavonoid-based therapeutics as potential nutraceuticals against human inflammatory diseases.

The role of pyroptosis in inflammatory diseases

Programmed cell death has crucial roles in the physiological maturation of an organism, the maintenance of metabolism, and disease progression. Pyroptosis, a form of programmed cell death which has recently received much attention, is closely related to inflammation and occurs via canonical, non-canonical, caspase-3-dependent, and unclassified pathways. The pore-forming gasdermin proteins mediate pyroptosis by promoting cell lysis, contributing to the outflow of large amounts of inflammatory cytokines and cellular contents. Although the inflammatory response is critical for the body's defense against pathogens, uncontrolled inflammation can cause tissue damage and is a vital factor in the occurrence and progression of various diseases. In this review, we briefly summarize the major signaling pathways of pyroptosis and discuss current research on the pathological function of pyroptosis in autoinflammatory diseases and sterile inflammatory diseases.

Caspase-11 promotes high-fat diet-induced NAFLD by increasing glycolysis, OXPHOS, and pyroptosis in macrophages

Introduction

Non-alcoholic fatty liver disease (NAFLD) has a global prevalence of 25% of the population and is a leading cause of cirrhosis and hepatocellular carcinoma. NAFLD ranges from simple steatosis (non-alcoholic fatty liver) to non-alcoholic steatohepatitis (NASH). Hepatic macrophages, specifically Kupffer cells (KCs) and monocyte-derived macrophages, act as key players in the progression of NAFLD. Caspases are a family of endoproteases that provide critical connections to cell regulatory networks that sense disease risk factors, control inflammation, and mediate inflammatory cell death (pyroptosis). Caspase-11 can cleave gasdermin D (GSDMD) to induce pyroptosis and specifically defends against bacterial pathogens that invade the cytosol. However, it's still unknown whether high fat diet (HFD)-facilitated gut microbiota-generated cytoplasmic lipopolysaccharides (LPS) activate caspase-11 and promote NAFLD.

Methods

To examine this hypothesis, we performed liver pathological analysis, RNA-seq, FACS, Western blots, Seahorse mitochondrial stress analyses of macrophages and bone marrow transplantation on HFD-induced NAFLD in WT and Casp11-/- mice.

Results and Discussion

Our results showed that 1) HFD increases body wight, liver wight, plasma cholesterol levels, liver fat deposition, and NAFLD activity score (NAS score) in wild-type (WT) mice; 2) HFD increases the expression of caspase-11, GSDMD, interleukin-1β, and guanylate-binding proteins in WT mice; 3) Caspase-11 deficiency decreases fat liver deposition and NAS score; 4) Caspase-11 deficiency decreases bone marrow monocyte-derived macrophage (MDM) pyroptosis (inflammatory cell death) and inflammatory monocyte (IM) surface GSDMD expression; 5) Caspase-11 deficiency re-programs liver transcriptomes and reduces HFD-induced NAFLD; 6) Caspase-11 deficiency decreases extracellular acidification rates (glycolysis) and oxidative phosphorylation (OXPHOS) in inflammatory fatty acid palmitic acid-stimulated macrophages, indicating that caspase-11 significantly contributes to maintain dual fuel bioenergetics-glycolysis and OXPHOS for promoting pyroptosis in macrophages. These results provide novel insights on the roles of the caspase-11-GSDMD pathway in promoting hepatic macrophage inflammation and pyroptosis and novel targets for future therapeutic interventions involving the transition of NAFLD to NASH, hyperlipidemia, type II diabetes, metabolic syndrome, metabolically healthy obesity, atherosclerotic cardiovascular diseases, autoimmune diseases, liver transplantation, and hepatic cancers.

CCN1/Integrin α5β1 Instigates Free Fatty Acid-Induced Hepatocyte Lipid Accumulation and Pyroptosis through NLRP3 Inflammasome Activation

Hyperlipidemia with high blood levels of free fatty acids (FFA) is the leading cause of non-alcoholic steatohepatitis. CCN1 is a secreted matricellular protein that drives various cellular functions, including proliferation, migration, and differentiation. However, its role in mediating FFA-induced pro-inflammatory cell death and its underlying molecular mechanisms have not been characterized. In this study, we demonstrated that CCN1 was upregulated in the livers of obese mice. The increase in FFA-induced CCN1 was evaluated in vitro by treating hepatocytes with a combination of oleic acid and palmitic acid (2:1). Gene silencing using specific small interfering RNAs (siRNA) revealed that CCN1 participated in FFA-induced intracellular lipid accumulation, caspase-1 activation, and hepatocyte pyroptosis. Next, we identified integrin α₅β₁ as a potential receptor of CCN1. Co-immunoprecipitation demonstrated that the binding between CCN1 and integrin α₅β₁ increased in hepatocytes upon FFA stimulation in the livers of obese mice. Similarly, the protein levels of integrin α₅ and β₁ were increased in vitro and in vivo. Experiments with specific siRNAs confirmed that integrin α₅β₁ played a part in FFA-induced intracellular lipid accumulation, NLRP3 inflammasome activation, and pyroptosis in hepatocytes. In conclusion, these results provide novel evidence that the CCN1/integrin α₅β₁ is a novel mediator that drives hepatic lipotoxicity via NLRP3-dependent pyroptosis.

FOSL2 deficiency delays nonalcoholic steatohepatitis progression by regulating LY6D-mediated NLRP3 activation

Lymphocyte antigen 6 family member D (LY6D) was enhanced specifically in senescent cells, while its effects on pyroptosis, a programmed cell death, remains unknown. The goal of this study was to assess the role of LY6D in the mediation of pyroptosis during nonalcoholic steatohepatitis (NASH). After screening out LY6D as a specific liver fibrosis-associated gene using the GSE55747 dataset from the GEO database, we established a NASH mouse model using methionine and choline deficient-diet feeding and an in vitro model using lipopolysaccharide (LPS)-treated hepatocytes. LY6D was overexpressed in NASH livers as well as in LPS-treated hepatocytes. Silencing of LY6D inhibited NASH-associated hepatocyte pyroptosis. With the aid of bioinformatics analysis, promoter-luciferase reporter and ChIP-qPCR assays, we identified FOSL2 as an upstream transcription factor of LY6D. FOSL2, which was highly expressed in NASH, promoted LY6D transcription by binding to the promoter of LY6D. Depletion of FOSL2 significantly inhibited NASH-associated hepatocyte pyroptosis, which was significantly reversed after overexpression of LY6D. Moreover, the promotion of hepatocyte pyroptosis by the FOSL2/LY6D axis was significantly attenuated by specific inhibition of NLRP3. These findings suggesting that FOSL2/LY6D axis may be a key molecular axis and a potential target for NASH therapeutics.

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.

Regulatory Roles of Caspase-11 Non-Canonical Inflammasome in Inflammatory Liver Diseases

An inflammatory response consists of two consecutive steps: priming and triggering, to prepare and activate inflammatory responses, respectively. The cardinal feature of the triggering step is the activation of intracellular protein complexes called inflammasomes, which provide a platform for the activation of inflammatory signaling pathways. Despite many studies demonstrating the regulatory roles of canonical inflammasomes in inflammatory liver diseases, the roles of newly discovered non-canonical inflammasomes in inflammatory liver diseases are still largely unknown. Recent studies have reported the regulatory roles of the caspase-11 non-canonical inflammasome in inflammatory liver diseases, providing strong evidence that the caspase-11 non-canonical inflammasome may play key roles in the pathogenesis of inflammatory liver diseases. This review comprehensively discusses the emerging roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory liver diseases, focusing on non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and inflammatory liver injuries and its underlying mechanisms. This review highlights the current knowledge on the regulatory roles of the caspase-11 non-canonical inflammasome in inflammatory liver diseases, providing new insights into the development of potential therapeutics to prevent and treat inflammatory liver diseases by targeting the caspase-11 non-canonical inflammasome.

Long noncoding RNA X-inactive specific transcript regulates NLR family pyrin domain containing 3/caspase-1-mediated pyroptosis in diabetic nephropathy

BACKGROUND

NLRP3-mediated pyroptosis is recognized as an essential modulator of renal disease pathology. Long noncoding RNAs (lncRNAs) are active participators of diabetic nephropathy (DN). X inactive specific transcript (XIST) expression has been reported to be elevated in the serum of DN patients.

AIM

To evaluate the mechanism of lncRNA XIST in renal tubular epithelial cell (RTEC) pyroptosis in DN.

METHODS

A DN rat model was established through streptozotocin injection, and XIST was knocked down by tail vein injection of the lentivirus LV sh-XIST. Renal metabolic and biochemical indices were detected, and pathological changes in the renal tissue were assessed. The expression of indicators related to inflammation and pyroptosis was also detected. High glucose (HG) was used to treat HK2 cells, and cell viability and lactate dehydrogenase (LDH) activity were detected after silencing XIST. The subcellular localization and downstream mechanism of XIST were investigated. Finally, a rescue experiment was carried out to verify that XIST regulates NLR family pyrin domain containing 3 (NLRP3)/caspase-1-mediated RTEC pyroptosis through the microRNA-15-5p (miR-15b-5p)/Toll-like receptor 4 (TLR4) axis.

RESULTS

XIST was highly expressed in the DN models. XIST silencing improved renal metabolism and biochemical indices and mitigated renal injury. The expression of inflammation and pyroptosis indicators was significantly increased in DN rats and HG-treated HK2 cells; cell viability was decreased and LDH activity was increased after HG treatment. Silencing XIST inhibited RTEC pyroptosis by inhibiting NLRP3/caspase-1. Mechanistically, XIST sponged miR-15b-5p to regulate TLR4. Silencing XIST inhibited TLR4 by promoting miR-15b-5p. miR-15b-5p inhibition or TLR4 overexpression averted the inhibitory effect of silencing XIST on HG-induced RTEC pyroptosis.

CONCLUSION

Silencing XIST inhibits TLR4 by upregulating miR-15b-5p and ultimately inhibits renal injury in DN by inhibiting NLRP3/caspase-1-mediated RTEC pyroptosis.

Multi-faceted role of pyroptosis mediated by inflammasome in liver fibrosis

Liver fibrosis is a reversible pathological overreaction during the self-repair of liver injuries, and it is the common period of chronic liver diseases induced by different pathogenesis progress into cirrhosis and even hepatocellular carcinoma. Pyroptosis, a novel form of programmed cell death, is reported to take part in the pathogenesis and progression of acute or chronic liver diseases and liver fibrosis. Caspase-1 dependent canonical pathway and caspase-4/-5/-11 mediated noncanonical pathway are the two signalling pathways to induce pyroptosis. The activation of inflammasomes under the stimulation of pathogenic microorganisms and danger signals can initiate the pyroptotic pathway and release large amounts of proinflammatory and profibrotic cytokines. This article comprehensively summarizes recent researches focused on the mechanism of pyroptosis and its role in major hepatic cells, which can provide potential therapeutic strategies for liver fibrosis.

Dual roles of the caspase-11 non-canonical inflammasome in inflammatory bowel disease

Inflammation is a two-step process comprising the first priming step that prepares inflammatory responses and the second triggering step that activates inflammatory responses. The key feature of the triggering step is the activation of inflammasomes and intracellular inflammatory protein complexes that provide molecular platforms to activate inflammatory signal transduction cascades. Although canonical inflammasomes have been well demonstrated to be actively involved in numerous human diseases, the roles of the recently identified non-canonical inflammasomes are largely unknown. However, recent studies have demonstrated the emerging roles of the caspase-11 non-canonical inflammasome in various human inflammatory diseases, ultimately providing strong evidence that the caspase-11 non-canonical inflammasome is a key player in the pathogenesis of various human diseases. Here, we comprehensively reviewed the regulatory roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory bowel disease (IBD) and its underlying mechanisms. Overall, this review highlights the current understanding of the regulatory roles of the caspase-11 non-canonical inflammasome in IBD and may provide insight into new strategies for preventing and treating IBD and caspase-11 non-canonical inflammasome-driven diseases.

Hyperlipidemia May Synergize with Hypomethylation in Establishing Trained Immunity and Promoting Inflammation in NASH and NAFLD

We performed a panoramic analysis on both human nonalcoholic steatohepatitis (NASH) microarray data and microarray/RNA-seq data from various mouse models of nonalcoholic fatty liver disease NASH/NAFLD with total 4249 genes examined and made the following findings: (i) human NASH and NAFLD mouse models upregulate both cytokines and chemokines; (ii) pathway analysis indicated that human NASH can be classified into metabolic and immune NASH; methionine- and choline-deficient (MCD)+high-fat diet (HFD), glycine N-methyltransferase deficient (GNMT-KO), methionine adenosyltransferase 1A deficient (MAT1A-KO), and HFCD (high-fat-cholesterol diet) can be classified into inflammatory, SAM accumulation, cholesterol/mevalonate, and LXR/RXR-fatty acid β-oxidation NAFLD, respectively; (iii) canonical and noncanonical inflammasomes play differential roles in the pathogenesis of NASH/NAFLD; (iv) trained immunity (TI) enzymes are significantly upregulated in NASH/NAFLD; HFCD upregulates TI enzymes more than cytokines, chemokines, and inflammasome regulators; (v) the MCD+HFD is a model with the upregulation of proinflammatory cytokines and canonical and noncanonical inflammasomes; however, the HFCD is a model with upregulation of TI enzymes and lipid peroxidation enzymes; and (vi) caspase-11 and caspase-1 act as upstream master regulators, which partially upregulate the expressions of cytokines, chemokines, canonical and noncanonical inflammasome pathway regulators, TI enzymes, and lipid peroxidation enzymes. Our findings provide novel insights on the synergies between hyperlipidemia and hypomethylation in establishing TI and promoting inflammation in NASH and NAFLD progression and novel targets for future therapeutic interventions for NASH and NAFLD, metabolic diseases, transplantation, and cancers.

Pyroptosis in Steatohepatitis and Liver Diseases

Pyroptosis is an inflammatory form of regulated cell death, which functions in the clearance of intracellularly replicating pathogens by cell lysis in order to induce further immune response. Since the discovery of the gasdermin (GSDM) family, pyroptosis has attracted attention in a wide range of inflammatory diseases such as nonalcoholic steatohepatitis and other liver diseases. Due to the cleavage of GSDMs by different caspases, the amino-terminal GSDM fragments form membrane pores essential for pyroptosis that facilitate the release of inflammatory cytokines by loss of ionic gradient and membrane rupture. In this review, we address the key molecular and cellular processes that induce pyroptosis in the liver and its significance in the pathogenesis of common liver diseases in different human and experimental mice studies.