Gasdermin D plays a key role as a pyroptosis executor of non-alcoholic steatohepatitis in humans and mice

Liraglutide ameliorates non-alcoholic steatohepatitis by inhibiting NLRP3 inflammasome and pyroptosis activation via mitophagy

Non-alcoholic steatohepatitis (NASH) is a key step in the progression of non-alcoholic fatty liver disease (NAFLD), which causes serious health problems worldwide. The nucleotide-binding oligomerization domain, leucine-rich repeat-containing receptor-containing pyrin domain 3 (NLRP3) inflammasome and pyroptosis play crucial roles in the progression of NASH. Our team has provided clinical evidence of the effects of glucagon-like peptide-1 (GLP-1) on the improvement in liver function and histological resolution of NAFLD. Preliminary work has demonstrated that GLP-1 inhibited NLRP3 inflammasome activation in a mouse model of NAFLD. We further explored the potential molecular mechanisms underlying the anti-inflammatory effect of liraglutide, a long-acting GLP-1 analog, in the treatment of NASH. We established a HepG2 cell model of NASH using double stimulation with palmitic acid and lipopolysaccharide to assess NLRP3 inflammasome and pyroptotic cell activity and to evaluate mitochondrial function and mitophagy. Liraglutide reduced lipid accumulation, inhibited NLRP3 inflammasome and pyroptosis activation, attenuated mitochondrial dysfunction and reactive oxygen species generation, augmented mitophagy in hepatocytes. Mitophagy inhibition with 3-methyladenine/PINK1-directed siRNA weakened the liraglutide-mediated suppression of inflammatory injury. We propose that liraglutide suppresses NLRP3 inflammasome-induced hepatocyte pyroptosis via mitophagy to slow the progression of NASH.

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.

Gasdermins and their role in immunity and inflammation

Pyroptosis is an important component of the innate immune system. Gasdermin D, the mediator of pyroptosis, has been shown to be crucial for optimal defense against microbial infection. In this review, the authors discuss gasdermin D and its role in disease.

The gasdermins are a family of pore-forming proteins recently implicated in the immune response. One of these proteins, gasdermin D (GSDMD), has been identified as the executioner of pyroptosis, an inflammatory form of lytic cell death that is induced upon formation of caspase-1–activating inflammasomes. The related proteins GSDME and GSDMA have also been implicated in autoimmune diseases and certain cancers. Most gasdermin proteins are believed to have pore-forming capabilities. The best-studied member, GSDMD, controls the release of the proinflammatory cytokines IL-1ß and IL-18 and pyroptotic cell death. Because of its potential as a driver of inflammation in septic shock and autoimmune diseases, GSDMD represents an attractive drug target. In this review, we discuss the gasdermin proteins with particular emphasis on GSDMD and its mechanism of action and biological significance.

Sodium butyrate alleviates high-glucose-induced renal glomerular endothelial cells damage via inhibiting pyroptosis

We recently found that Sodium butyrate (NaB) possesses anti-inflammatory effects in diabetic nephropathy (DN) mouse model and in high-glucose induced mouse glomerular mesangial cells. Pyroptosis is a programmed cell death accompanied with the release of pro-inflammatory factors. Gasdermin D (GSDMD) is a novel discovered pivotal executive protein of pyroptosis, which can be cleaved by inflammatory caspases. The aim of our study is to verify if NaB have some effects against high-glucose induces pyroptosis in renal Glomerular endothelial cells (GECs). For this aim, human GECs were cultured and exposed to high-glucose. Exogenous NaB, caspase 1 inhibitor Ac-YVAD-CMK (A-Y-C) or knockdown GSDMD by siRNA were used. We found high glucose could increase Propidium Iodide (PI) positive cells and elevate release of lactate dehydrogenase (LDH), Interleukin 1 beta (IL-1β) and Interleukin 18 (IL-18); protein levels of GSDMD, GSDMD N-terminal domain (GSDMD-N) and cleaved-caspase-1 were also elevated. Effect of NaB on LDH release and PI positive cells was further enhanced by inhibiting caspase 1-GSDMD. In addition, high glucose-induced nuclear factor kappa-B (NF-κB)/NF-κB inhibitor α (IκB-α) signaling pathway was reversed by NaB or A-Y-C administration. In conclusion, NaB could ameliorate high-glucose induced GECs via caspase1-GSDMD canonical pyroptosis pathway; and NF-κB/IκB-α signaling pathway was involved in it.

NLRP6 deficiency aggravates liver injury after allogeneic hematopoietic stem cell transplantation

This study aims to observe the expression and role of NLRP6 in liver injury after allogeneic hematopoietic stem cell transplantation (Allo-HSCT). Allo-HSCT model was established through infusion of 5 × 10⁶ bone marrow mononuclear cells into whole body irradiated mice. On days 7, 14, 21 and 28 after transplantation, the peripheral blood was collected to detect liver function. The liver of the mice was obtained to assess the pathological changes of liver tissues after allo-HSCT by H&E staining and Mason staining. Meanwhile, expression of NLRP6, phosphorylated p38-MAPK and IκBα, caspase-1 and NLRP3 in liver were detected by Western blot. ELISA was used for detection of the level of interleukin (IL)-1β, IL-18, tumor necrosis factor (TNF)-α, IL-6, myeloperoxidase (MPO) and tumor growth factor (TGF)-β1. Increased expression of NLRP6, phosphorylated Iκbα, phosphorylated p38-MAPK, pro-caspase-1, and p20, in liver tissue with injury and fibrosis in mice after allo-HSCT were observed. Meanwhile, the level of IL-1β, IL-18, IL-6 and TNF-α was also increased. However, NLRP6^-/- mice showed more severe liver damage and liver fibrosis after transplantation together with higher level of phosphorylated Iκbα, phosphorylated p38-MAPK, Pro-caspase-1, p20 expression as well as IL-1β, IL-18, IL-6, and TNF-α secretion compared with wide-type. Interestingly, the expression of NLRP3 in the liver of NLRP6^-/- mice was significantly higher than that of wild-type. In conclusion, the expression of NLRP6 in host's liver is associated with liver injury after allo-HSCT. NLRP6 deficiency in host's liver leads to more severe liver damage, indicating a protective role of NLRP6 in host's liver to liver damage after allo-HSCT.

Hepatic ferroptosis plays an important role as the trigger for initiating inflammation in nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a metabolic liver disease that progresses from simple steatosis to the disease state of inflammation and fibrosis. Previous studies suggest that apoptosis and necroptosis may contribute to the pathogenesis of NASH, based on several murine models. However, the mechanisms underlying the transition of simple steatosis to steatohepatitis remain unclear, because it is difficult to identify when and where such cell deaths begin to occur in the pathophysiological process of NASH. In the present study, our aim is to investigate which type of cell death plays a role as the trigger for initiating inflammation in fatty liver. By establishing a simple method of discriminating between apoptosis and necrosis in the liver, we found that necrosis occurred prior to apoptosis at the onset of steatohepatitis in the choline-deficient, ethionine-supplemented (CDE) diet model. To further investigate what type of necrosis is involved in the initial necrotic cell death, we examined the effect of necroptosis and ferroptosis inhibition by administering inhibitors to wild-type mice in the CDE diet model. In addition, necroptosis was evaluated using mixed lineage kinase domain-like protein (MLKL) knockout mice, which is lacking in a terminal executor of necroptosis. Consequently, necroptosis inhibition failed to block the onset of necrotic cell death, while ferroptosis inhibition protected hepatocytes from necrotic death almost completely, and suppressed the subsequent infiltration of immune cells and inflammatory reaction. Furthermore, the amount of oxidized phosphatidylethanolamine, which is involved in ferroptosis pathway, was increased in the liver sample of the CDE diet-fed mice. These findings suggest that hepatic ferroptosis plays an important role as the trigger for initiating inflammation in steatohepatitis and may be a therapeutic target for preventing the onset of steatohepatitis.

The cleavage of gasdermin D by caspase-11 promotes tubular epithelial cell pyroptosis and urinary IL-18 excretion in acute kidney injury

Inflammation and tubular cell death are the hallmarks of acute kidney injury. However, the precise mechanism underlying these effects has not been fully elucidated. Here we tested whether caspase-11, an inflammatory member of the caspase family, was increased in cisplatin or ischemia-reperfusion-induced acute kidney injury. Caspase-11 knockout mice after cisplatin treatment exhibited attenuated deterioration of renal functional, reduced tubular damage, reduced macrophage and neutrophil infiltration, and decreased urinary IL-18 excretion. Mechanistically, the upregulation of caspase-11 by either cisplatin or ischemia-reperfusion cleaved gasdermin D (GSDMD) into GSDMD-N, which translocated onto the plasma membrane, thus triggering cell pyroptosis and facilitated IL-18 release in primary cultured renal tubular cells. These results were further confirmed in GSDMD knockout mice that cisplatin-induced renal morphological and functional deterioration as well as urinary IL-18 excretion were alleviated. Furthermore, deficiency of GSDMD significantly suppressed cisplatin-induced IL-18 release but not the transcription and maturation level of IL-18 in tubular cells. Thus, our study indicates that caspase-11/GSDMD dependent tubule cell pyroptosis plays a significant role in initiating tubular cell damage, urinary IL-18 excretion and renal functional deterioration in acute kidney injury.

The emerging roles of inflammasome-dependent cytokines in cancer development

In addition to the genomic alterations that occur in malignant cells, the immune system is increasingly appreciated as a critical axis that regulates the rise of neoplasms and the development of primary tumours and metastases. The interaction between inflammatory cell infiltrates and stromal cells in the tumour microenvironment is complex, with inflammation playing both pro- and anti-tumorigenic roles. Inflammasomes are intracellular multi-protein complexes that act as key signalling hubs of the innate immune system. They respond to cellular stress and trauma by promoting activation of caspase-1, a protease that induces a pro-inflammatory cell death mode termed pyroptosis along with the maturation and secretion of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. Here, we will briefly introduce inflammasome biology with a focus on the dual roles of inflammasome-produced cytokines in cancer development. Despite emerging insight that inflammasomes may promote and suppress cancer development according to the tumour stage and the tumour microenvironment, much remains to be uncovered. Further exploration of inflammasome biology in tumorigenesis should enable the development of novel immunotherapies for cancer patients.

Mechanisms protecting host cells against bacterial pore-forming toxins

Pore-forming toxins (PFTs) are key virulence determinants produced and secreted by a variety of human bacterial pathogens. They disrupt the plasma membrane (PM) by generating stable protein pores, which allow uncontrolled exchanges between the extracellular and intracellular milieus, dramatically disturbing cellular homeostasis. In recent years, many advances were made regarding the characterization of conserved repair mechanisms that allow eukaryotic cells to recover from mechanical disruption of the PM membrane. However, the specificities of the cell recovery pathways that protect host cells against PFT-induced damage remain remarkably elusive. During bacterial infections, the coordinated action of such cell recovery processes defines the outcome of infected cells and is, thus, critical for our understanding of bacterial pathogenesis. Here, we review the cellular pathways reported to be involved in the response to bacterial PFTs and discuss their impact in single-cell recovery and infection.

Emodin alleviates myocardial ischemia/reperfusion injury by inhibiting gasdermin D-mediated pyroptosis in cardiomyocytes

Background

Emodin has recently been reported to have a powerful antiinflammatory effect, protecting the myocardium against ischemia/reperfusion (I/R) injury. Pyroptosis is a proinflammatory programmed cell death that is related to many diseases. The present study investigated the effect of emodin on pyroptosis in cardiomyocytes.

Materials and methods

Sprague Dawley rats were randomly divided into sham, I/R, and I/R+Emodin groups. I/R model was subjected to 30 minutes' ligation of left anterior descending coronary artery, followed by 2 hours of reperfusion. Cardiomyocytes were exposed to hypoxic conditions for 1 hour and normoxic conditions for 2 hours. The level of the pyroptosis was detected by Western blot, real-time PCR analysis, and ELISA.

Results

The level of gasdermin D-N domains was upregulated in cardiomyocytes during I/R or hypoxia/reoxygenation (H/R) treatment. Moreover, emodin increased the rate of cell survival in vitro and decreased the myocardial infarct size in vivo via suppressing the levels of I/R-induced pyroptosis. Additionally, the expression of TLR4, MyD88, phospho-IκBα, phospho-NF-κB, and the NLRP3 inflammasome was significantly upregulated in cardiomyocytes subjected to H/R treatment, while emodin suppressed the expression of these proteins.

Conclusion

This study confirms that emodin treatment was able to alleviate myocardial I/R injury and inhibit pyroptosis in vivo and in vitro. The inhibitory effect of emodin on pyroptosis was mediated by suppressing the TLR4/MyD88/NF-κB/NLRP3 inflammasome pathway. Therefore, emodin may provide an alternative treatment for myocardial I/R injury.

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.

Compound C Protects Mice from HFD-Induced Obesity and Nonalcoholic Fatty Liver Disease

OBJECTIVES

The aim of this study was to investigate the effects of compound C on an in vivo mouse model of high-fat diet- (HFD-) induced obesity and hepatosteatosis.

METHODS

C57BL/6 mice were fed with a standard diet (n = 5) for 16 weeks and then injected saline once a day for 4 weeks as the normal chow group. Mice (n = 10) were fed with HFD for 16 weeks to induce obesity and hepatosteatosis and then divided into two groups: HFD + vehicle group injected with the vehicle solution (saline) and HFD + compound C group injected with compound C in saline (5 mg/kg i.p., once a day) for 4 weeks. Liver histology was observed. The expression levels of genes related to lipid metabolism and proinflammation in liver tissue were examined. NLRP3 inflammasome expression in liver tissue was detected by the western blot assay. HepG2 cells were pretreated with compound C and/or AICAR for 1 h and then treated with palmitic acid (PA) for 3 h. The cells were collected, and mRNA levels were determined.

RESULTS

There was a significant reduction in body-weight gain and daily food intake in the HFD + compound C group compared with the HFD + vehicle group (p < 0.05). The glucose tolerance test (GTT) and insulin tolerance test (ITT) showed that compound C alleviated insulin resistance. Histology analysis showed a significant reduction of hepatic steatosis by compound C. Compound C also significantly decreased fatty acid synthesis genes, while increased fatty acid oxidation genes. Furthermore, compound C significantly reduced the expression of proinflammatory markers and NLRP3 inflammasome (p < 0.05). Compound C enhanced mRNA levels of SOD1, SOD2, catalase, GPx1, and GPx4 and reduced the p-AMPK/AMPK ratio, which were stimulated by palmitic acid (PA). The effect was enhanced by AICAR.

CONCLUSION

Our data suggest that compound C is a potent NAFLD suppressor and an attractive therapeutic target for hepatic steatosis and related metabolic disorders.

Non-parenchymal hepatic cell lipotoxicity and the coordinated progression of non-alcoholic fatty liver disease and atherosclerosis

PURPOSE OF REVIEW

Non-alcoholic fatty liver disease (NAFLD) appears to be independently associated with the development of atherosclerosis. The biological mechanisms underlying this association are complex, and likely involve liver-resident cell types other than hepatocytes. Thus, we review recent evidence that non-parenchymal hepatic cell responses to lipid excess contribute to the pathogenesis of both NAFLD and atherosclerosis.

RECENT FINDINGS

Significant independent associations between NAFLD and atherosclerosis have been identified through cross-sectional studies and meta-analyses. Mechanistic studies in cell cultures and in rodent models suggest that liver-resident macrophages, activated hepatic stellate cells (HSC) and liver sinusoidal endothelial cells (LSEC) mount lipotoxic responses under NAFLD conditions which can contribute to the progression of both NAFLD and atherosclerosis.

SUMMARY

Non-parenchymal hepatic cell types exhibit some similarity in their responses to lipid excess, and in their pathogenic mechanisms, which likely contribute to the coordinated progression of NAFLD and atherosclerosis. In response to lipotoxic conditions, macrophages, Kupffer cells and HSC initiate robust inflammatory responses, whereas LSEC generate excess reactive oxygen species (ROS). The extent to which inflammatory cytokines and ROS produced by non-parenchymal cells contribute to the progression of both NAFLD and atherosclerosis warrants further investigation.

Inflammasome: A Double-Edged Sword in Liver Diseases

Inflammasomes have emerged as critical innate sensors of host immune that defense against pathogen infection, metabolism syndrome, cellular stress and cancer metastasis in the liver. The assembly of inflammasome activates caspase-1, which promotes the maturation of interleukin-1β (IL-1β) and interleukin-18 (IL-18), and initiates pyroptotic cell death (pyroptosis). IL-18 exerts pleiotropic effects on hepatic NK cells, priming FasL-mediated cytotoxicity, and interferon-γ (IFN-γ)-dependent responses to prevent the development of liver diseases. However, considerable attention has been attracted to the pathogenic role of inflammasomes in various acute and chronic liver diseases, including viral hepatitis, nanoparticle-induced liver injury, alcoholic and non-alcoholic steatohepatitis. In this review, we summarize the latest advances on the physiological and pathological roles of inflammasomes for further development of inflammasome-based therapeutic strategies for human liver diseases.

The clinical relevance of necroinflammation-highlighting the importance of acute kidney injury and the adrenal glands

Necroinflammation is defined as the inflammatory response to necrotic cell death. Different necrotic cell death pathways exhibit different immune reponses, despite a comparable level of intracellular content release (referred to as damage associated molecular patterns or DAMPs). In addition to DAMP release, which is inevitably associated with necrotic cell death, the active production of pro/anti-inflammatory cytokines characterizes certain necrotic pathways. Necroptosis, ferroptosis and pyroptosis, therefore, are immunogenic to a different extent. In this review, we discuss the clinical relevance of necroinflammation highlighting potential human serum markers. We focus on the role of the adrenal glands and the lungs as central organs affected by systemic and/or local DAMP release and underline their role in intensive care medicine. In addition, data from models of acute kidney injury (AKI) and kidney transplantation have significantly shaped the field of necroinflammation and may be helpful for the understanding of the potential role of dialysis and plasma exchange to treat ongoing necroinflammation upon intensive care unit (ICU) conditions. In conclusion, we are only beginning to understand the importance of necroinflammation in diseases and transplantation, including xenotransplantation. However, given the existing efforts to develop inhibitors of necrotic cell death (ferrostatins, necrostatins, etc), we consider it likely that interference with necroinflammation reaches clinical routine in the near future.

Acetylation regulation and pyroptosis in the process of liver failure

In recent years, many studies have confirmed that acetylation regulation and pyroptosis play important roles in the pathogenesis of liver failure. This paper systematically introduces the roles and possible mechanisms of acetylation regulation and pyroptosis signal pathways in the pathogenesis of liver failure, which may provide a potential novel strategy for the therapy of liver failure.