cFLIPL protects macrophages from LPS-induced pyroptosis via inhibition of complex II formation

GYY4137-induced p65 sulfhydration protects synovial macrophages against pyroptosis by improving mitochondrial function in osteoarthritis development

INTRODUCTION

Osteoarthritis (OA) is the most common arthritis that is characterized by the progressive synovial inflammation and loss of articular cartilage. Although GYY4137 is a novel and slow-releasing hydrogen sulfide (H2S) donor with potent anti-inflammatory properties that may modulate the progression of OA, its underlying mechanism remains unclear.

OBJECTIVES

In this study, we validated the protective role of GYY4137 against OA pathological courses and elucidated its underlying regulatory mechanisms.

METHODS

Cell transfection, immunofluorescence staining, EdU assay, transmission electron microscopy, mitochondrial membrane potential measurement, electrophoretic mobility shift assay, sulfhydration assay, qPCR and western blot assays were performed in the primary mouse chondrocytes or the mouse macrophage cell line raw 264.7 for in vitro study. DMM-induced OA mice model and Macrophage-specific p65 knockout (p65f/f LysM-CreERT2) mice on the C57BL/6 background were used for in vivo study.

RESULTS

We found that GYY4137 can alleviate OA progress by suppressing synovium pyroptosis in vivo. Moreover, our in vitro data revealed that GYY4137 attenuates inflammation-induced NLRP3 and caspase-1 activation and results in a decrease of IL-1β production in macrophages. Mechanistically, GYY4137 increased persulfidation of NF-kB p65 in response to inflammatory stimuli that results in a decrease of cellular reactive oxygen species (ROS) accumulation and ameliorates mitochondrial dysfunctions. Using site-directed mutagenesis, we showed that H2S persulfidates cysteine38 in p65 protein and hampers p65 transcriptional activity, and p65 mutant impaired macrophage responses to GYY4137.

CONCLUSION

These findings suggest a mechanism by which GYY4137 through redox modification of p65 participates in inhibiting NLRP3 activation by OA to regulate inflammatory responses. Thus, we propose that GYY4137 represents a promising novel therapeutic strategy for the treatment of OA.

Manipulation of cancer cell pyroptosis for therapeutic approaches: challenges and opportunities

Remarkable advances have been achieved following discoveries that gasdermins are the executioners of pyroptosis. The pyroptotic process consists a subcellular permeabilization phase and a cell lysis phase, the latter of which is irreversible. Besides immune cells, pyroptosis has also been observed in cancer cells, which exhibit distinct mechanisms compared to canonical immune cell pyroptosis. Although chronic cancer cell pyroptosis fuels tumor growth, intense pyroptotic cell death in tumor cells enhances anticancer immunity by promoting killer lymphocytes infiltration. Triggering pyroptosis in cancer cells is emerging as a promising strategy for cancer treatment. In this review, we introduce the process of cancer cell pyroptosis and its role in antitumor immunity, discuss the translation of these insights into therapies, and highlight current challenges and opportunities in the investigation of cancer cell pyroptosis.

Ghrelin alleviates inflammation and pyroptosis by inhibiting TNF-α /caspase-8/caspase-3/ GSDME signalling pathways in an in vitro model of high glucose induced liver injury

Diabetic liver injury (DLI) refers to liver injury resulting from prolonged chronic hyperglycemia and represents a significant complication associated with diabetes, The specific pathogenic mechanism of DLI remains incompletely understood. Tumor necrosis factor α (TNF-α) has been demonstrated to play a crucial role in diabetic complications through intricate signalling pathways, including pyroptosis. However, it remains uncertain whether TNF-α mediates pyroptosis in DLI, we initially established an in vitro model of DLI and confirmed the presence of an inflammatory state characterized by TNF-α in DLI. Furthermore, evidence of gasdermin E (GSDME)-mediated pyroptosis and the activation of cysteinyl aspartate specific proteinase (caspase)-8 was observed in AML-12 cell exposed to high glucose concentrations. We subsequently demonstrated that TNF-α can trigger caspase-8 activation, leading to GSDME-mediated cellular pyroptosis. Furthermore, treatment with ghrelin effectively suppressed hepatic cell pyroptosis induced by high glucose concentrations and provided protection against liver injury. Therefore, we propose that the TNF-α/caspase-8/caspase-3/GSDME pathway represents a novel mechanism underlying pyrodeath in DLI cells and to explore the protective role and molecular mechanisms underlying the effects of ghrelin on DLI by this special pathway, These findings may present potential therapeutic implications for the management of DLI.

The stems of Syringa oblata Lindl. exert cardioprotective effects against acute myocardial ischemia by inhibiting the TLR4/MyD88/NF-κB and NLRP3 inflammasome signaling pathways in mice

ETHNOPHARMACOLOGICAL RELEVANCE

The stripped roots and stems of Syringa oblata Lindl. (SO), a Mongolian and Tibetan folk medicinal plant, are renowned for their traditional use against "Khii", pain relief, and heat clearing. It is used to treat cardiovascular diseases (CVDs), upset, insomnia, and other symptoms and is commonly used as a substitute for another plant known as S. pinnatifolia, which is used in Mongolian folk medicine.

OBJECTIVE

This study analyzed the cardioprotective effect of SO against myocardial ischemia and the underlying mechanism through cardiac inflammation and the pyroptosis pathway.

MATERIALS AND METHODS

This study developed an acute myocardial infarction (AMI) model by ligating the left anterior descending coronary artery (LAD) in mice. Additionally, the cardioprotective effect was determined via echocardiography, detection of creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and cardiac troponin-I (cTnI) detection, and hematoxylin and eosin (HE) staining. Lipopolysaccharide (LPS) plus adenosine triphosphate (ATP) was used to stimulate RAW264.7 mouse monocyte macrophages to induce pyroptosis. The cell morphology was monitored by scanning electron microscopy. The underlying mechanisms were assessed via immunohistochemistry, immunofluorescence staining, and western blotting (WB).

RESULTS

SO (40-160 mg/kg) significantly decreased the values of left ventricular internal dimension diastole (LVID; d) and left ventricular internal dimension systole (LVID; s), increased the ejection fraction (EF) and fractional shortening (FS), reduced serum levels of CK-MB, LDH, and cTnI, and mitigated microstructural destruction of MI tissue. SO at concentrations of 1.25-10 μg/mL significantly inhibited nitrogen monoxide (NO) production. At 10 μg/mL, it strongly suppressed pyroptosis while maintaining the morphological features of RAW264.7 cells. These findings suggest that SO has significant anti-myocardial ischemic effects. Administration of SO (40-160 mg/kg) in mice significantly reduced interleukin-1β (IL-1β) and interleukin-18 (IL-18) levels, accompanied by decreased fluorescence intensities of the apoptosis speck-like protein containing a caspase recruitment domain (ASC), NOD-like receptor family pyrin domain-containing 3 (NLRP3), and cysteinyl aspartate-specific protease-1 (caspase-1) proteins. WB analysis revealed that SO (40-160 mg/kg) treatment reduced inflammatory protein levels, including toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88). Additionally, the phosphorylation levels of nuclear factor-kappa-B (NF-κB) and inhibitors of NF-kappa-Bα (IκBα) were suppressed. Moreover, levels of pyroptosis-related proteins, including ASC, caspase-1, NLRP3, and gasdermin D (GSDMD), were reduced.

CONCLUSIONS

SO may protect against myocardial ischemia through modulation of the TLR4/MyD88/NF-κB inflammatory pathway and suppression of NLRP3 inflammasome-mediated pyroptosis. This study demonstrates that SO alleviates AMI by mechanisms involving anti-inflammatory effects and pyroptosis inhibition, establishing an experimental basis for evaluating its therapeutic efficacy and clinical translation.

Chromosome Missegregation Triggers Tumor Cell Pyroptosis and Enhances Anti-Tumor Immunotherapy in Colorectal Cancer

Immune checkpoint inhibitor (ICI) therapy is a promising anti-tumor therapeutic strategy; however, its efficacy in solid tumors is limited. Chromosome missegregation is common in various solid tumors; however, its role in tumor progression remains poorly understood, and its correlation with ICI is yet to be explored. Here, it is found that increased chromosome missegregation promotes tumor immune microenvironment, and eventually immunotherapeutic efficacy, by triggering pyroptosis. yin yang 2 (YY2) is identified as a mitotic checkpoint regulator, which promotes chromosome missegregation by upregulating BUB1B transcription. Increased chromosome missegregation promoted the formation of micronuclei and release of double-stranded DNA (dsDNA) into the cytosol, triggering an AIM2-mediated cytosolic dsDNA response. The subsequent pyroptosis strengthened the tumor immune microenvironment, thereby enhancing immunoinfiltration and cytotoxicity of CD8+ T cells, while preventing their exhaustion. Finally, through in vitro and in vivo experiments, it is demonstrated that combining YY2 overexpression-induced chromosome missegregation/cytosolic dsDNA response and PD-1 inhibitor significantly enhanced the efficacy of ICI immunotherapy in microsatellite instable and microsatellite stable colorectal cancer cells. Together, these findings provide new insights on the role of chromosome missegregation in triggering cytosolic dsDNA response-mediated pyroptosis and modulating the tumor immune microenvironment, suggesting a novel strategy for improving ICI therapeutic efficacy in colorectal cancer.

GSDMD-mediated pyroptosis: molecular mechanisms, diseases and therapeutic targets

Pyroptosis is a regulated form of inflammatory cell death in which Gasdermin D (GSDMD) plays a central role as the key effector molecule. GSDMD-mediated pyroptosis is characterized by complex biological features and considerable heterogeneity in its expression, mechanisms, and functional outcomes across various tissues, cell types, and pathological microenvironments. This heterogeneity is particularly pronounced in inflammation-related diseases and tumors. In the context of inflammatory diseases, GSDMD expression is typically upregulated, and its activation in macrophages, neutrophils, T cells, epithelial cells, and mitochondria triggers both pyroptotic and non-pyroptotic pathways, leading to the release of pro-inflammatory cytokines and exacerbation of tissue damage. However, under certain conditions, GSDMD-mediated pyroptosis may also serve a protective immune function. The expression of GSDMD in tumors is regulated in a more complex manner, where it can either promote immune evasion or, in some instances, induce tumor cell death. As our understanding of GSDMD's role continues to progress, there have been advancements in the development of inhibitors targeting GSDMD-mediated pyroptosis; however, these therapeutic interventions remain in the preclinical phase. This review systematically examines the cellular and molecular complexities of GSDMD-mediated pyroptosis, with a particular emphasis on its roles in inflammation-related diseases and cancer. Furthermore, it underscores the substantial therapeutic potential of GSDMD as a target for precision medicine, highlighting its promising clinical applications.

New insights into pulmonary arterial hypertension: interaction between PANoptosis and perivascular inflammatory responses

Pulmonary arterial hypertension (PAH) is a heterogeneous disease characterized by various etiologies, with pulmonary vascular remodeling recognized as a main pathological change. Currently, it is widely accepted that vascular remodeling is closely associated with abnormal pulmonary vascular cell death and perivascular inflammation. The simultaneous activation of various pulmonary vascular cell death leads to immune cell adhesion and inflammatory mediator releases; And in turn, the inflammatory response may also trigger cell death and jointly promote the progression of vascular remodeling. Recently, PANoptosis has been identified as a phenomenon that describes the simultaneous activation and interaction of multiple forms of programmed cell death (PCD). Therefore, the relationship between PANoptosis and inflammation in PAH warrants further investigation. This review examines the mechanisms underlying apoptosis, necroptosis, pyroptosis, and inflammatory responses in PAH, with a focus on PANoptosis and its interactions with inflammation. And it aims to elucidate the significance of this emerging form of cell death and inflammation in the pathophysiology of PAH and to explore its potential as a therapeutic target.

Raver1 links Ripk1 RNA splicing to caspase-8-mediated pyroptotic cell death, inflammation, and pathogen resistance

Multiple cell death and inflammatory signaling pathways converge on two critical factors: receptor-interacting serine/threonine kinase 1 (RIPK1) and caspase-8. Careful regulation of these molecules is critical to control apoptosis, pyroptosis, and inflammation. Here, we found a pivotal role of Raver1 as an essential regulator of Ripk1 pre-mRNA splicing, expression, and functionality and the subsequent caspase-8-dependent inflammatory cell death. We show that Raver1 influences mRNA diversity primarily by repressing alternative exon inclusion. Macrophages from Raver1-deficient mice exhibit altered splicing of Ripk1. As a result, Raver1-deficient primary macrophages display diminished cell death and decreased interleukin-18 and interleukin-1ß production, when infected with Yersinia bacteria, or by restraining TGF-ß-activated kinase 1 or IKKβ in the presence of lipopolysaccharide, tumor necrosis factor family members, or interferon-γ. These responses are accompanied by reduced activation of caspase-8, Gasdermin D and E, and caspase-1 in the absence of Raver1. Consequently, Raver1-deficient mice showed heightened susceptibility to Yersinia infection. Raver1 and RIPK1 also controlled the expression and function of the C-type lectin receptor Mincle. Our study underscores the critical regulatory role of Raver1 in modulating innate immune responses and highlights its significance in directing in vivo and in vitro inflammatory processes.

Dendritic cells activate pyroptosis and effector-triggered apoptosis to restrict Legionella infection

The innate immune system relies on pattern recognition receptors (PRRs) to detect pathogen-associated molecular patterns (PAMPs) and guard proteins to monitor pathogen disruption of host cell processes. How different immune cell types engage PRR- and guard protein-dependent defenses in response to infection is poorly understood. Here, we show that macrophages and dendritic cells (DCs) respond in distinct ways to bacterial virulence activities. In macrophages, the bacterial pathogen Legionella pneumophila deploys its Dot/Icm type IV secretion system (T4SS) to deliver effector proteins that facilitate its robust intracellular replication. In contrast, T4SS activity triggers rapid DC death that potently restricts Legionella replication within this cell type. Intriguingly, we found that infected DCs exhibit considerable heterogeneity at the single cell level. Initially, a subset of DCs activate caspase-11 and NLRP3 inflammasome-dependent pyroptosis and release IL-1 β early during infection. At later timepoints, a separate DC population undergoes apoptosis driven by T4SS effectors that block host protein synthesis, thereby depleting the levels of the pro-survival proteins Mcl-1 and cFLIP. Together, pyroptosis and effector-triggered apoptosis robustly restrict Legionella replication in DCs. Collectively, our work suggests a model where Mcl-1 and cFLIP guard host translation in DCs, and that macrophages and DCs distinctly employ innate immune sensors and guard proteins to mount divergent responses to Legionella infection.

Regulated cell death in acute myocardial infarction: Molecular mechanisms and therapeutic implications

Acute myocardial infarction (AMI), primarily caused by coronary atherosclerosis, initiates a series of events that culminate in the obstruction of coronary arteries, resulting in severe myocardial ischemia and hypoxia. The subsequent myocardial ischemia/reperfusion (I/R) injury further aggravates cardiac damage, leading to a decline in heart function and the risk of life-threatening complications. The complex interplay of multiple regulated cell death (RCD) pathways plays a pivotal role in the pathogenesis of AMI. Each RCD pathway is orchestrated by a symphony of molecular regulatory mechanisms, highlighting the dynamic changes and critical roles of key effector molecules. Strategic disruption or inhibition of these molecular targets offers a tantalizing prospect for mitigating or even averting the onset of RCD, thereby limiting the extensive loss of cardiomyocytes and the progression of detrimental myocardial fibrosis. This review systematically summarizes the mechanisms underlying various forms of RCD, provides an in-depth exploration of the pathogenesis of AMI through the lens of RCD, and highlights a range of promising therapeutic targets that hold the potential to revolutionize the management of AMI.

Plasticity of cell death pathways ensures GSDMD activation during Yersinia pseudotuberculosis infection

Macrophages express pattern recognition and cytokine receptors that mediate proinflammatory signal transduction pathways to combat microbial infection. To retaliate against such responses, pathogenic microorganisms have evolved multiple strategies to impede innate immune signaling. Recent studies demonstrated that YopJ suppression of TAK1 signaling during Yersinia pseudotuberculosis infection promotes the assembly of a RIPK1-dependent death-inducing complex that enables caspase-8 to directly cleave and activate gasdermin D (GSDMD). However, whether and how macrophages respond to Yersinia infection in the absence of YopJ or caspase-8 activity remains unclear. Here, we demonstrate that loss of YopJ or its catalytic activity triggers non-canonical inflammasome activation in macrophages and that caspase-11 is required to restrict the bacterial burden in vivo. Under conditions of low caspase-8 activity, wild-type Y. pseudotuberculosis invades macrophages and accesses the cytosol, leading to non-canonical inflammasome activation. Thus, our study highlights the plasticity of death pathways to ensure GSDMD activation during Yersinia infection.

Morphine Preconditioning Alleviates Ischemia/Reperfusion-induced Caspase-8-dependent Neuronal Apoptosis Through cPKCγ-NF-κB-cFLIP L Pathway

BACKGROUND

Perioperative cerebral ischemia/reperfusion injury is a major contributor to postoperative death and cognitive dysfunction in patients. It was reported that morphine preconditioning (MP) can mimic ischemia/hypoxia preconditioning to protect against ischemia/reperfusion injury. However, the mechanism of MP on the ischemia/reperfusion-induced neuronal apoptosis has not been fully clarified.

METHODS

The middle cerebral artery occlusion/reperfusion (MCAO/R) model of mice and the oxygen-glucose deprivation/reoxygenation (OGD/R) model in primary cortical neurons were used to mimic ischemic stroke. In vivo, the infarct size was measured by using TTC staining; NDSS, Longa score system, and beam balance test were performed to evaluate the neurological deficits of mice; the expression of the protein was detected by using a western blot. In vitro, the viability of neurons was determined by using CCK-8 assay; the expression of protein and mRNA were assessed by using western blot, RT-qPCR, and immunofluorescent staining; the level of apoptosis was detected by using TUNEL staining.

RESULTS

MP can improve the neurological functions of mice following MCAO/R ( P <0.001, n=10 per group). MP can decrease the infarct size ( P <0.001, n=10 per group) and the level of cleaved-caspase-3 of mice following MCAO/R ( P <0.01 or 0.001, n=6 p er group). MP can increase the levels of cPKCγ membrane translocation, p-p65, and cFLIP L , and decrease the levels of cleaved-caspase-8, 3 in neurons after OGD/R or MCAO/R 1 d ( P <0.05, 0.01 or 0.001, n=6 per group). In addition, MP could alleviate OGD/R-induced cell apoptosis ( P <0.001, n=6 per group).

CONCLUSION

MP alleviates ischemia/reperfusion-induced Caspase 8-dependent neuronal apoptosis through the cPKCγ-NF-κB-cFLIP L pathway.

Raver1 links Ripk1 RNA splicing to caspase-8-mediated pyroptotic cell death, inflammation, and pathogen resistance

Multiple cell death and inflammatory signaling pathways converge on two critical factors: receptor interacting serine/threonine kinase 1 (RIPK1) and caspase-8. Careful regulation of these molecules is critical to control apoptosis, pyroptosis and inflammation. Here we discovered a pivotal role of Raver1 as an essential regulator of Ripk1 pre-mRNA splicing, expression, and functionality, and the subsequent caspase-8-dependent inflammatory cell death. Macrophages from Raver1 -deficient mice exhibit altered splicing of Ripk1 , accompanied by diminished cell death and reduced activation of caspase-8, Gasdermin D and E, caspase-1, as well as decreased interleukin-18 (IL-18) and IL-1ß production. These effects were triggered by Yersinia bacteria, or by restraining TAK1 or IKKβ in the presence of LPS, TNF family members, or IFNγ. Consequently, animals lacking Raver1 showed heightened susceptibility to Yersinia infection. Raver1 and RIPK1 also controlled the expression and function of the C-type lectin receptor Mincle. Our study underscores the critical regulatory role of Raver1 in modulating innate immune responses and highlights its significance in directing in vivo and in vitro inflammatory processes.

Significance

Caspase-8 and the kinase RIPK1 are at focal points of several inflammation and cell death pathways. Thus, a careful regulation of their actions is needed. Our work identifies the RNA splicing factor Raver1 as a critical factor directing the splicing of Ripk1 in order to modulate RIPK1/caspase-8-driven pyroptosis, apoptosis and inflammation. Raver1 is central for macrophage responses to Yersinia bacteria, initiated after blockade of kinases TAK1 and IKK, measured as activation of RIPK1, caspase-8, Gasdermin D, caspase-3, IL-1ß and IL-18. Importantly, Raver1 is necessary for host resistance to Yersinia infection in vivo . We propose that Raver1 is key for correct tuning of RIPK1-caspase-8 dependent processes.

Targeting type I DED interactions at the DED filament serves as a sensitive switch for cell fate decisions

Activation of procaspase-8 in the death effector domain (DED) filaments of the death-inducing signaling complex (DISC) is a key step in apoptosis. In this study, a rationally designed cell-penetrating peptide, DEDid, was engineered to mimic the h2b helical region of procaspase-8-DED2 containing a highly conservative FL motif. Furthermore, mutations were introduced into the DEDid binding site of the procaspase-8 type I interface. Additionally, our data suggest that DEDid targets other type I DED interactions such as those of FADD. Both approaches of blocking type I DED interactions inhibited CD95L-induced DISC assembly, caspase activation and apoptosis. We showed that inhibition of procaspase-8 type I interactions by mutations not only diminished procaspase-8 recruitment to the DISC but also destabilized the FADD core of DED filaments. Taken together, this study offers insights to develop strategies to target DED proteins, which may be considered in diseases associated with cell death and inflammation.

Pyroptotic macrophages induce disruption of glutamate metabolism in periodontal ligament stem cells contributing to their compromised osteogenic potential

Macrophage pyroptosis is of key importance to host defence against pathogen infections and may participate in the progression and recovery of periodontitis. However, the role of pyroptotic macrophages in regulating periodontal ligament stem cells (PDLSCs), the main cell source for periodontium renewal, remains unclear. First, we found that macrophage pyroptosis were enriched in gingiva tissues from periodontitis patients compared with those of healthy people through immunofluorescence. Then the effects of pyroptotic macrophages on the PDLSC osteogenic differentiation were investigated in a conditioned medium (CM)-based coculture system in vitro. CM derived from pyroptotic macrophages inhibited the osteogenic differentiation-related gene and protein levels, ALP activity and mineralized nodule formation of PDLSCs. The osteogenic inhibition of CM was alleviated when pyroptosis was inhibited by VX765. Further, untargeted metabolomics showed that glutamate limitation may be the underlying mechanism. However, exogenous glutamate supplementation aggravated the CM-inhibited osteogenic differentiation of PDLSCs. Moreover, CM increased extracellular glutamate and decreased intracellular glutamate levels of PDLSCs, and enhanced the gene and protein expression levels of system xc - (a cystine/glutamate antiporter). After adding cystine to CM-based incubation, the compromised osteogenic potency of PDLSCs was rescued. Our data suggest that macrophage pyroptosis is related to the inflammatory lesions of periodontitis. Either pharmacological inhibition of macrophage pyroptosis or nutritional supplements to PDLSCs, can rescue the compromised osteogenic potency caused by pyroptotic macrophages.

CD14 is a decision-maker between Fas-mediated death and inflammation

Signaling through classical death receptor Fas was mainly appreciated as a pro-death pathway until recent reports characterized pro-inflammatory outcomes of Fas-mediated activation in pathological contexts. How Fas signaling can switch to pro-inflammatory activation is poorly understood. Herein, we report that in macrophages and neutrophils, the Toll-like receptor (TLR) adapter CD14 determines the inflammatory output of Fas-mediated signaling. Our findings propose CD14 as a crucial chaperone of Fas receptor internalization in macrophages and neutrophils, resulting in Cd14-/- myeloid cells that are protected from FasL-induced apoptosis, activate nuclear factor κB (NF-κB), and release cytokines in response. As in TLR signaling, CD14 is also required for Fas to signal through the adaptor TRIF (TIR-domain-containing adapter-inducing interferon-β) and induce a pro-death complex. Our findings demonstrate that CD14 availability can determine the switch between Fas-mediated pro-death and pro-inflammatory outcomes by internalizing the receptor.

Butyrate and propionate are microbial danger signals that activate the NLRP3 inflammasome in human macrophages upon TLR stimulation

Short-chain fatty acids (SCFAs) are immunomodulatory compounds produced by the microbiome through dietary fiber fermentation. Although generally considered beneficial for gut health, patients suffering from inflammatory bowel disease (IBD) display poor tolerance to fiber-rich diets, suggesting that SCFAs may have contrary effects under inflammatory conditions. To investigate this, we examined the effect of SCFAs on human macrophages in the presence of Toll-like receptor (TLR) agonists. In contrast to anti-inflammatory effects under steady-state conditions, we found that butyrate and propionate activated the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome in the presence of TLR agonists. Mechanistically, these SCFAs prevented transcription of FLICE-like inhibitory protein (cFLIP) and interleukin-10 (IL-10) through histone deacetylase (HDAC) inhibition, triggering caspase-8-dependent NLRP3 inflammasome activation. SCFA-driven NLRP3 activation was potassium efflux independent and did not result in cell death but rather triggered hyperactivation and IL-1β release. Our findings demonstrate that butyrate and propionate are bacterially derived danger signals that regulate NLRP3 inflammasome activation through epigenetic modulation of the inflammatory response.

Non-canonical autophosphorylation of RIPK1 drives timely pyroptosis to control Yersinia infection

Caspase-8-dependent pyroptosis has been shown to mediate host protection from Yersinia infection. For this mode of cell death, the kinase activity of receptor-interacting protein kinase 1 (RIPK1) is required, but the autophosphorylation sites required to drive caspase-8 activation have not been determined. Here, we show that non-canonical autophosphorylation of RIPK1 at threonine 169 (T169) is necessary for caspase-8-mediated pyroptosis. Mice with alanine in the T169 position are highly susceptible to Yersinia dissemination. Mechanistically, the delayed formation of a complex containing RIPK1, ZBP1, Fas-associated protein with death domain (FADD), and caspase-8 abrogates caspase-8 maturation in T169A mice and leads to the eventual activation of RIPK3-dependent necroptosis in vivo; however, this is insufficient to protect the host, suggesting that timely pyroptosis during early response is specifically required to control infection. These results position RIPK1 T169 phosphorylation as a driver of pyroptotic cell death critical for host defense.

Yersinia infection induces glucose depletion and AMPK-dependent inhibition of pyroptosis in mice

Nutritional status and pyroptosis are important for host defence against infections. However, the molecular link that integrates nutrient sensing into pyroptosis during microbial infection is unclear. Here, using metabolic profiling, we found that Yersinia pseudotuberculosis infection results in a significant decrease in intracellular glucose levels in macrophages. This leads to activation of the glucose and energy sensor AMPK, which phosphorylates the essential kinase RIPK1 at S321 during caspase-8-mediated pyroptosis. This phosphorylation inhibits RIPK1 activation and thereby restrains pyroptosis. Boosting the AMPK-RIPK1 cascade by glucose deprivation, AMPK agonists, or RIPK1-S321E knockin suppresses pyroptosis, leading to increased susceptibility to Y. pseudotuberculosis infection in mice. Ablation of AMPK in macrophages or glucose supplementation in mice is protective against infection. Thus, we reveal a molecular link between glucose sensing and pyroptosis, and unveil a mechanism by which Y. pseudotuberculosis reduces glucose levels to impact host AMPK activation and limit host pyroptosis to facilitate infection.

Blockade of IKK signaling induces RIPK1-independent apoptosis in human macrophages

Regulated cell death in response to microbial infection plays an important role in immune defense and is triggered by pathogen disruption of essential cellular pathways. Gram-negative bacterial pathogens in the Yersinia genus disrupt NF-κB signaling via translocated effectors injected by a type III secretion system, thereby preventing induction of cytokine production and antimicrobial defense. In murine models of infection, Yersinia blockade of NF-κB signaling triggers cell-extrinsic apoptosis through Receptor Interacting Serine-Threonine Protein Kinase 1 (RIPK1) and caspase-8, which is required for bacterial clearance and host survival. Unexpectedly, we find that human macrophages undergo apoptosis independently of RIPK1 in response to Yersinia or chemical blockade of IKKβ. Instead, IKK blockade led to decreased cFLIP expression, and overexpression of cFLIP contributed to protection from IKK blockade-induced apoptosis in human macrophages. We found that IKK blockade also induces RIPK1 kinase activity-independent apoptosis in human T cells and human pancreatic cells. Altogether, our data indicate that, in contrast to murine cells, blockade of IKK activity in human cells triggers a distinct apoptosis pathway that is independent of RIPK1 kinase activity. These findings have implications for the contribution of RIPK1 to cell death in human cells and the efficacy of RIPK1 inhibition in human diseases.

The TRIF-RIPK1-Caspase-8 signalling in the regulation of TLR4-driven gene expression

The inflammatory response is tightly regulated to eliminate invading pathogens and avoid excessive production of inflammatory mediators and tissue damage. Caspase-8 is a cysteine protease that is involved in programmed cell death. Here we show the TRIF-RIPK1-Caspase-8 is required for LPS-induced CYLD degradation in macrophages. TRIF functions in the upstream of RIPK1. The homotypic interaction motif of TRIF and the death domain of RIPK1 are essential for Caspase-8 activation. Caspase-8 cleaves CYLD and the D235A mutant is resistant to the protease activity of Caspase-8. TRIF and RIPK1 serve as substrates of Capase-8 in vitro. cFLIP interacts with Caspase-8 to modulate its protease activity on CYLD and cell death. Deficiency in TRIF, Caspase-8 or CYLD can lead to a decrease or increase in the expression of genes encoding inflammatory cytokines. Together, the TRIF-Caspase-8 and CYLD play opposite roles in the regulation of TLR4 signalling.

The protease caspase-1: Activation pathways and functions

Caspase-1 is one of the main mediators of inflammatory caspases and has become a correspondent with inflammation, cell death, and several inflammatory diseases. In this review, we systematically summarize both original and recent advances in caspase-1 to provide references for a better understanding of the molecular mechanisms in its activation and functions. This study investigates and summarizes the published articles concerning caspase-1, inflammation, pyroptosis, apoptosis, and cell death by searching academic search systems, including the PubMed, Web of Science, and Google Scholar. Caspase-1 is one of the main mediators of inflammatory caspases and has become a correspondent with inflammation and cell death. In cell death, caspase-1 was originally found to cause apoptosis in fibroblasts. Importantly, caspase-1 was later reported to execute programmed cell death, including pyroptosis and apoptosis, in many immune cells in response to diverse stimuli. It is widely established that different pathways can activate caspase-1 and subsequently mediate cell death and inflammation. It has become increasingly clear that caspase-1 is responsible for the initiation and control of pyroptosis, apoptosis, and inflammation in addition to its well-known function in cleaving IL-1β. The significant advancement in the understanding of caspase-1-controlled cell death and novel substrates inspires new therapeutic approaches in the future.

c-FLIP facilitates ZIKV infection by mediating caspase-8/3-dependent apoptosis

c-FLIP functions as a dual regulator of apoptosis and inflammation, yet its implications in Zika virus (ZIKV) infection remain partially understood, especially in the context of ZIKV-induced congenital Zika syndrome (CZS) where both apoptosis and inflammation play pivotal roles. Our findings demonstrate that c-FLIP promotes ZIKV infection in placental cells and myeloid-derived macrophages, involving inflammation and caspase-8/3-mediated apoptosis. Moreover, our observations reveal that c-FLIP augments ZIKV infection in multiple tissues, including blood cell, spleen, uterus, testis, and the brain of mice. Notably, the partial deficiency of c-FLIP provides protection to embryos against ZIKV-induced CZS, accompanied by a reduction in caspase-3-mediated apoptosis. Additionally, we have found a distinctive parental effect of c-FLIP influencing ZIKV replication in fetal heads. In summary, our study reveals the critical role of c-FLIP as a positive regulator in caspase-8/3-mediated apoptosis during ZIKV infection, significantly contributing to the development of CZS.

ROS induced pyroptosis in inflammatory disease and cancer

Pyroptosis, a form of caspase-1-dependent cell death, also known as inflammation-dependent death, plays a crucial role in diseases such as stroke, heart disease, or tumors. Since its elucidation, pyroptosis has attracted widespread attention from various sectors. Reactive oxygen species (ROS) can regulate numerous cellular signaling pathways. Through further research on ROS and pyroptosis, the level of ROS has been revealed to be pivotal for the occurrence of pyroptosis, establishing a close relationship between the two. This review primarily focuses on the molecular mechanisms of ROS and pyroptosis in tumors and inflammatory diseases, exploring key proteins that may serve as drug targets linking ROS and pyroptosis and emerging fields targeting pyroptosis. Additionally, the potential future development of compounds and proteins that influence ROS-regulated cell pyroptosis is anticipated, aiming to provide insights for the development of anti-tumor and anti-inflammatory drugs.

Inflammasome-independent pyroptosis

Gasdermins are membrane pore-forming proteins that cause pyroptosis, an inflammatory cell death in which cells burst and release cytokines, chemokines, and other host alarm signals, such as ATP and HMGB1, which recruit and activate immune cells at sites of infection and danger. There are five gasdermins in humans - gasdermins A to E. Pyroptosis was first described in myeloid cells and mucosal epithelia, which express gasdermin D and activate it when cytosolic sensors of invasive infection or tissue damage assemble into large macromolecular structures, called inflammasomes. Inflammasomes recruit and activate inflammatory caspases (caspase 1, 4, 5, and 11), which cut gasdermin D to remove an inhibitory C-terminal domain, allowing the N-terminal domain to bind to membrane acidic lipids and oligomerize into pores. Recent studies have identified inflammasome-independent proteolytic pathways that activate gasdermin D and the other gasdermins. Here, we review inflammasome-independent pyroptosis pathways and what is known about their role in normal physiology and disease.

cFLIP in the molecular regulation of astroglia-driven neuroinflammation in experimental glaucoma

BACKGROUND

Recent experimental studies of neuroinflammation in glaucoma pointed to cFLIP as a molecular switch for cell fate decisions, mainly regulating cell type-specific caspase-8 functions in cell death and inflammation. This study aimed to determine the importance of cFLIP for regulating astroglia-driven neuroinflammation in experimental glaucoma by analyzing the outcomes of astroglia-targeted transgenic deletion of cFLIP or cFLIPL.

METHODS

Glaucoma was modeled by anterior chamber microbead injections to induce ocular hypertension in mouse lines with or without conditional deletion of cFLIP or cFLIPL in astroglia. Morphological analysis of astroglia responses assessed quantitative parameters in retinal whole mounts immunolabeled for GFAP and inflammatory molecules or assayed for TUNEL. The molecular analysis included 36-plexed immunoassays of the retina and optic nerve cytokines and chemokines, NanoString-based profiling of inflammation-related gene expression, and Western blot analysis of selected proteins in freshly isolated samples of astroglia.

RESULTS

Immunoassays and immunolabeling of retina and optic nerve tissues presented reduced production of various proinflammatory cytokines, including TNFα, in GFAP/cFLIP and GFAP/cFLIPL relative to controls at 12 weeks of ocular hypertension with no detectable alteration in TUNEL. Besides presenting a similar trend of the proinflammatory versus anti-inflammatory molecules displayed by immunoassays, NanoString-based molecular profiling detected downregulated NF-κB/RelA and upregulated RelB expression of astroglia in ocular hypertensive samples of GFAP/cFLIP compared to ocular hypertensive controls. Analysis of protein expression also revealed decreased phospho-RelA and increased phospho-RelB in parallel with an increase in caspase-8 cleavage products.

CONCLUSIONS

A prominent response limiting neuroinflammation in ocular hypertensive eyes with cFLIP-deletion in astroglia values the role of cFLIP in the molecular regulation of glia-driven neuroinflammation during glaucomatous neurodegeneration. The molecular responses accompanying the lessening of neurodegenerative inflammation also seem to maintain astroglia survival despite increased caspase-8 cleavage with cFLIP deletion. A transcriptional autoregulatory response, dampening RelA but boosting RelB for selective expression of NF-κB target genes, might reinforce cell survival in cFLIP-deleted astroglia.

Systematic identification of a synthetic lethal interaction in brain-metastatic lung adenocarcinoma

Metastatic lung adenocarcinoma (LuAC) presents a significant clinical challenge due to the short latency and the lack of efficient treatment options. Therefore, identification of molecular vulnerabilities in metastatic LuAC holds great importance in the development of therapeutic drugs against this disease. In this study, we performed a genome-wide siRNA screening using poorly and highly brain-metastatic LuAC cell lines. Using this approach, we discovered that compared to poorly metastatic LuAC (LuAC-Par) cells, brain-metastatic LuAC (LuAC-BrM) cells exhibited a significantly higher vulnerability to c-FLIP (an inhibitor of caspase-8)-depletion-induced apoptosis. Furthermore, in vivo studies demonstrated that c-FLIP knockdown specifically inhibited growth of LuAC-BrM, but not the LuAC-Par, tumors, suggesting the addiction of LuAC-BrM to the function of c-FLIP for their survival. Our in vitro and in vivo analyses also demonstrated that LuAC-BrM is more sensitive to c-FLIP-depletion due to ER stress-induced activation of the c-JUN and subsequent induction of stress genes including ATF4 and DDIT3. Finally, we found that c-JUN not only sensitized LuAC-BrM to c-FLIP-depletion-induced cell death but also promoted brain metastasis in vivo, providing strong evidence for c-JUN's function as a double-edged sword in LuAC-BrM. Collectively, our findings not only reveal a novel link between c-JUN, brain metastasis, and c-FLIP addiction in LuAC-BrM but also present an opportunity for potential therapeutic intervention.

CFLAR: A novel diagnostic and prognostic biomarker in soft tissue sarcoma, which positively modulates the immune response in the tumor microenvironment

Anoikis is highly associated with tumor cell apoptosis and tumor prognosis; however, the specific role of anoikis-related genes (ARGs) in soft tissue sarcoma (STS) remains to be fully elucidated. The present study aimed to use a variety of bioinformatics methods to determine differentially expressed anoikis-related genes in STS and healthy tissues. Subsequently, three machine learning algorithms, Least Absolute Shrinkage and Selection Operator, Support Vector Machine and Random Forest, were used to screen genes with the highest importance score. The results of the bioinformatics analyses demonstrated that CASP8 and FADD-like apoptosis regulator (CFLAR) exhibited the highest importance score. Subsequently, the diagnostic and prognostic value of CFLAR in STS development was determined using multiple public and in-house cohorts. The results of the present study demonstrated that CFLAR may be considered a diagnostic and prognostic marker of STS, which acts as an independent prognostic factor of STS development. The present study also aimed to explore the potential role of CFLAR in the STS tumor microenvironment, and the results demonstrated that CFLAR significantly enhanced the immune response of STS, and exerted a positive effect on the infiltration of CD8+ T cells and M1 macrophages in the STS immune microenvironment. Notably, the aforementioned results were verified using multiplex immunofluorescence analysis. Collectively, the results of the present study demonstrated that CFLAR may act as a novel diagnostic and prognostic marker for STS, and may positively regulate the immune response of STS. Thus, the present study provided a novel theoretical basis for the use of CFLAR in STS diagnosis, in predicting clinical outcomes and in tailoring individualized treatment options.

The dance of macrophage death: the interplay between the inevitable and the microenvironment

Macrophages are highly plastic cells ubiquitous in various tissues, where they perform diverse functions. They participate in the response to pathogen invasion and inflammation resolution following the immune response, as well as the maintenance of homeostasis and proper tissue functions. Macrophages are generally considered long-lived cells with relatively strong resistance to numerous cytotoxic factors. On the other hand, their death seems to be one of the principal mechanisms by which macrophages perform their physiological functions or can contribute to the development of certain diseases. In this review, we scrutinize three distinct pro-inflammatory programmed cell death pathways - pyroptosis, necroptosis, and ferroptosis - occurring in macrophages under specific circumstances, and explain how these cells appear to undergo dynamic yet not always final changes before ultimately dying. We achieve that by examining the interconnectivity of these cell death types, which in macrophages seem to create a coordinated and flexible system responding to the microenvironment. Finally, we discuss the complexity and consequences of pyroptotic, necroptotic, and ferroptotic pathway induction in macrophages under two pathological conditions - atherosclerosis and cancer. We summarize damage-associated molecular patterns (DAMPs) along with other microenvironmental factors, macrophage polarization states, associated mechanisms as well as general outcomes, as such a comprehensive look at these correlations may point out the proper methodologies and potential therapeutic approaches.

Identification and Validation of the Pyroptosis-Related Hub Gene Signature and the Associated Regulation Axis in Diabetic Keratopathy

Background

Diabetic keratopathy (DK) poses a significant challenge in diabetes mellitus, yet its molecular pathways and effective treatments remain elusive. The aim of our research was to explore the pyroptosis-related genes in the corneal epithelium of the streptozocin-induced diabetic rats.

Methods

After sixteen weeks of streptozocin intraperitoneal injection, corneal epithelium from three diabetic rats and three normal groups underwent whole-transcriptome sequencing. An integrated bioinformatics pipeline, including differentially expressed gene (DEG) identification, enrichment analysis, protein-protein interaction (PPI) network, coexpression, drug prediction, and immune deconvolution analyses, identified hub genes and key drivers in DK pathogenesis. These hub genes were subsequently validated in vivo through RT-qPCR.

Results

A total of 459 DEGs were screened out from the diabetic group and nondiabetic controls. Gene Set Enrichment Analysis highlighted significant enrichment of the NOD-like receptor, Toll-like receptor, and NF-kappa B signaling pathways. Intersection of DEGs and pyroptosis-related datasets showed 33 differentially expressed pyroptosis-related genes (DEPRGs) associated with pathways such as IL-17, NOD-like receptor, TNF, and Toll-like receptor signaling. A competing endogenous RNA network comprising 16 DEPRGs, 22 lncRNAs, 13 miRNAs, and 3 circRNAs was constructed. After PPI network, five hub genes (Nfkb1, Casp8, Traf6, Ptgs2, and Il18) were identified as upregulated in the diabetic group, and their expression was validated by RT-qPCR in streptozocin-induced rats. Immune infiltration characterization showed that diabetic corneas owned a higher proportion of resting mast cells, activated NK cells, and memory-resting CD4 T cells. Finally, several small compounds including all-trans-retinoic acid, Chaihu Shugan San, dexamethasone, and resveratrol were suggested as potential therapies targeting these hub genes for DK.

Conclusions

The identified and validated hub genes, Nfkb1, Casp8, Traf6, Ptgs2, and Il18, may play crucial roles in DK pathogenesis and serve as therapeutic targets.

Pyroptosis in health and disease

The field of cell death has witnessed significant advancements since the initial discovery of apoptosis in the 1970s. This review delves into the intricacies of pyroptosis, a more recently identified form of regulated, lytic cell death, and explores the roles of pyroptotic effector molecules, with a strong emphasis on their mechanisms and relevance in various diseases. Pyroptosis, characterized by its proinflammatory nature, is driven by the accumulation of large plasma membrane pores comprised of gasdermin family protein subunits. In different contexts of cellular homeostatic perturbations, infections, and tissue damage, proteases, such as caspase-1 and caspase-4/5, play pivotal roles in pyroptosis by cleaving gasdermins. Gasdermin-D (GSDMD), the most extensively studied member of the gasdermin protein family, is expressed in various immune cells and certain epithelial cells. Upon cleavage by caspases, GSDMD oligomerizes and forms transmembrane pores in the cell membrane, leading to the release of proinflammatory cytokines. GSDMD-N, the NH2-terminal fragment, displays an affinity for specific lipids, contributing to its role in pore formation in pyroptosis. While GSDMD is the primary focus, other gasdermin family members are also discussed in detail. These proteins exhibit distinct tissue-specific functions and contribute to different facets of cell death regulation. Additionally, genetic variations in some gasdermins have been linked to diseases, underscoring their clinical relevance. Furthermore, the interplay between GSDM pores and the activation of other effectors, such as ninjurin-1, is elucidated, providing insights into the complexity of pyroptosis regulation. The findings underscore the molecular mechanisms that govern pyroptosis and its implications for various physiological and pathological processes.

Pyroptosis in Osteoarthritis: Molecular Mechanisms and Therapeutic Implications

Osteoarthritis (OA) is a chronic disease that causes pain and functional impairment by affecting joint tissue. Its global impact is noteworthy, causing significant economic losses and property damage. Despite extensive research, the underlying pathogenesis of OA remain an area of ongoing investigation. It has recently been discovered that the OA progression is significantly influenced by pyroptosis. Pyroptosis is a complex process that involves three pathways culminating in the assembly of Gasdermin-D (GSDMD)-N-terminal (GSDMD-NT) into pores through aggregation on the plasma membrane. The aggregation of GSDMD-NT proteins stimulates the release of inflammatory mediators, such as Interleukin-1β (IL-1β), Interleukin-18 (IL-18), and Matrix Metallopeptidase 13 (MMP13), ultimately leading to cellular lysis. The pyroptosis process in specific cells, including synovial macrophages, fibroblast-like synoviocytes (FLS), chondrocytes, and subchondral osteoblasts, contributs factor to the development of OA. Currently, the specific cells that undergo pyroptosis first are not yet fully understood, and it remains unknown whether pyroptosis in one cell can trigger the same process in other cells. Therefore, targeting pyroptosis could potentially offer a novel treatment approach for OA patients. We present a comprehensive analysis of the molecular mechanisms and key features of pyroptosis. We also outline the current research progress on various aspects, including synovial tissue, articular cartilage, extracellular matrix (ECM), and subchondral bone, with a focus on pyroptosis. The aim is to provide theoretical references for the effective management of OA.

New prospects of cancer therapy based on pyroptosis and pyroptosis inducers

Pyroptosis is a gasdermin-mediated programmed cell death (PCD) pathway. It differs from apoptosis because of the secretion of inflammatory molecules. Pyroptosis is closely associated with various malignant tumors. Recent studies have demonstrated that pyroptosis can either inhibit or promote the development of malignant tumors, depending on the cell type (immune or cancer cells) and duration and severity of the process. This review summarizes the molecular mechanisms of pyroptosis, its relationship with malignancies, and focuses on current pyroptosis inducers and their significance in cancer treatment. The molecules involved in the pyroptosis signaling pathway could serve as therapeutic targets for the development of novel drugs for cancer therapy. In addition, we analyzed the potential of combining pyroptosis with conventional anticancer techniques as a promising strategy for cancer treatment.

Multiomics characterization of pyroptosis in the tumor microenvironment and therapeutic relevance in metastatic melanoma

BACKGROUND

Pyroptosis, mediated by gasdermins with the release of multiple inflammatory cytokines, has emerged as playing an important role in targeted therapy and immunotherapy due to its effectiveness at inhibiting tumor growth. Melanoma is one of the most commonly used models for immunotherapy development, though an inadequate immune response can occur. Moreover, the development of pyroptosis-related therapy and combinations with other therapeutic strategies is limited due to insufficient understanding of the role of pyroptosis in the context of different tumor immune microenvironments (TMEs).

METHODS

Here, we present a computational model (pyroptosis-related gene score, PScore) to assess the pyroptosis status. We applied PScore to 1388 melanoma samples in our in-house cohort and eight other publicly available independent cohorts and then calculated its prognostic power of and potential as a predictive marker of immunotherapy efficacy. Furthermore, we performed association analysis for PScore and the characteristics of the TME by using bulk, single-cell, and spatial transcriptomics and assessed the association of PScore with mutation status, which contributes to targeted therapy.

RESULTS

Pyroptosis-related genes (PRGs) showed distinct expression patterns and prognostic predictive ability in melanoma. Most PRGs were associated with better survival in metastatic melanoma. Our PScore model based on genes associated with prognosis exhibits robust performance in survival prediction in multiple metastatic melanoma cohorts. We also found PScore to be associated with BRAF mutation and correlate positively with multiple molecular signatures, such as KRAS signaling and the IFN gamma response pathway. Based on our data, melanoma with an immune-enriched TME had a higher PScore than melanoma with an immune-depleted or fibrotic TME. Additionally, monocytes had the highest PScore and malignant cells and fibroblasts the lowest PScore based on single-cell and spatial transcriptome analyses. Finally, a higher PScore was associated with better therapeutic efficacy of immune checkpoint blockade, suggesting the potential of pyroptosis to serve as a marker of immunotherapy response.

CONCLUSIONS

Collectively, our findings indicate that pyroptosis is a prognostic factor and is associated with the immune response in metastatic melanoma, as based on multiomics data. Our results provide a theoretical basis for drug combination and reveal potential immunotherapy response markers.

cFLIPL alleviates myocardial ischemia-reperfusion injury by regulating pyroptosis

Alleviating myocardial ischemia-reperfusion injury (MIRI) plays a critical role in the prognosis and improvement of cardiac function following acute myocardial infarction. Pyroptosis is a newly identified form of cell death that has been implicated in the regulation of MIRI. In our study, H9c2 cells and SD rats were transfected using a recombinant adenovirus vector carrying cFLIPL , and the transfection was conducted for 3 days. Subsequently, H9c2 cells were subjected to 4 h of hypoxia followed by 12 h of reoxygenation to simulate an in vitro ischemia-reperfusion model. SD rats underwent 30 min of ischemia followed by 2 h of reperfusion to establish an MIRI model. Our findings revealed a notable decrease in cFLIPL expression in response to ischemia/reperfusion (I/R) and hypoxia/reoxygenation (H/R) injuries. Overexpression of cFLIPL can inhibit pyroptosis, reducing myocardial infarction area in vivo, and enhancing H9c2 cell viability in vitro. I/R and H/R injuries induced the upregulation of ASC, cleaved Caspase 1, NLRP3, GSDMD-N, IL-1β, and IL-18 proteins, promoting cell apoptosis. Our research indicates that cFLIPL may suppress pyroptosis by strategically binding with Caspase 1, inhibiting the release of inflammatory cytokines and preventing cell membrane rupture. Therefore, cFLIPL could potentially serve as a promising target for alleviating MIRI by suppressing the pyroptotic pathway.

cFLIPL acts as a suppressor of TRAIL- and Fas-initiated inflammation by inhibiting assembly of caspase-8/FADD/RIPK1 NF-κB-activating complexes

TRAIL and FasL are potent inducers of apoptosis but can also promote inflammation through assembly of cytoplasmic caspase-8/FADD/RIPK1 (FADDosome) complexes, wherein caspase-8 acts as a scaffold to drive FADD/RIPK1-mediated nuclear factor κB (NF-κB) activation. cFLIP is also recruited to FADDosomes and restricts caspase-8 activity and apoptosis, but whether cFLIP also regulates death receptor-initiated inflammation is unclear. Here, we show that silencing or deletion of cFLIP leads to robustly enhanced Fas-, TRAIL-, or TLR3-induced inflammatory cytokine production, which can be uncoupled from the effects of cFLIP on caspase-8 activation and apoptosis. Mechanistically, cFLIPL suppresses Fas- or TRAIL-initiated NF-κB activation through inhibiting the assembly of caspase-8/FADD/RIPK1 FADDosome complexes, due to the low affinity of cFLIPL for FADD. Consequently, increased cFLIPL occupancy of FADDosomes diminishes recruitment of FADD/RIPK1 to caspase-8, thereby suppressing NF-κB activation and inflammatory cytokine production downstream. Thus, cFLIP acts as a dual suppressor of apoptosis and inflammation via distinct modes of action.

Caspase-8 activation by cigarette smoke induces pro-inflammatory cell death of human macrophages exposed to lipopolysaccharide

Cigarette smoking impairs the lung innate immune response making smokers more susceptible to infections and severe symptoms. Dysregulation of cell death is emerging as a key player in chronic inflammatory conditions. We have recently reported that short exposure of human monocyte-derived macrophages (hMDMs) to cigarette smoke extract (CSE) altered the TLR4-dependent response to lipopolysaccharide (LPS). CSE caused inhibition of the MyD88-dependent inflammatory response and activation of TRIF/caspase-8/caspase-1 pathway leading to Gasdermin D (GSDMD) cleavage and increased cell permeability. Herein, we tested the hypothesis that activation of caspase-8 by CSE increased pro-inflammatory cell death of LPS-stimulated macrophages. To this purpose, we measured apoptotic and pyroptotic markers as well as the expression/release of pro-inflammatory mediators in hMDMs exposed to LPS and CSE, alone or in combination, for 6 and 24 h. We show that LPS/CSE-treated hMDMs, but not cells treated with CSE or LPS alone, underwent lytic cell death (LDH release) and displayed apoptotic features (activation of caspase-8 and -3/7, nuclear condensation, and mitochondrial membrane depolarization). Moreover, the negative regulator of caspase-8, coded by CFLAR gene, was downregulated by CSE. Activation of caspase-3 led to Gasdermin E (GSDME) cleavage. Notably, lytic cell death caused the release of the damage-associated molecular patterns (DAMPs) heat shock protein-60 (HSP60) and S100A8/A9. This was accompanied by an impaired inflammatory response resulting in inhibited and delayed release of IL6 and TNF. Of note, increased cleaved caspase-3, higher levels of GSDME and altered expression of cell death-associated genes were found in alveolar macrophages of smoker subjects compared to non-smoking controls. Overall, our findings show that CSE sensitizes human macrophages to cell death by promoting pyroptotic and apoptotic pathways upon encountering LPS. We propose that while the delayed inflammatory response may result in ineffective defenses against infections, the observed cell death associated with DAMP release may contribute to establish chronic inflammation. CS exposure sensitizes human macrophages to pro-inflammatory cell death. Upon exposure to LPS, CS inhibits the TLR4/MyD88 inflammatory response, downregulating the pro-inflammatory genes TNF and IL6 and the anti-apoptotic gene CFLAR, known to counteract caspase-8 activity. CS enhances caspase-8 activation through TLR4/TRIF, with a partial involvement of RIPK1, resulting on the activation of caspase-1/GSDMD axis leading to increased cell permeability and DAMP release through gasdermin pores [19]. At later timepoints caspase-3 becomes strongly activated by caspase-8 triggering apoptotic events which are associated with mitochondrial membrane depolarization, gasdermin E cleavage and secondary necrosis with consequent massive DAMP release.

Myeloid OTULIN deficiency couples RIPK3-dependent cell death to Nlrp3 inflammasome activation and IL-1β secretion

Loss-of-function mutations in the deubiquitinase OTULIN result in an inflammatory pathology termed "OTULIN-related autoinflammatory syndrome" (ORAS). Genetic mouse models revealed essential roles for OTULIN in inflammatory and cell death signaling, but the mechanisms by which OTULIN deficiency connects cell death to inflammation remain unclear. Here, we identify OTULIN deficiency as a cellular condition that licenses RIPK3-mediated cell death in murine macrophages, leading to Nlrp3 inflammasome activation and subsequent IL-1β secretion. OTULIN deficiency uncoupled Nlrp3 inflammasome activation from gasdermin D-mediated pyroptosis, instead allowing RIPK3-dependent cell death to act as an Nlrp3 inflammasome activator and mechanism for IL-1β release. Accordingly, elevated serum IL-1β levels in myeloid-specific OTULIN-deficient mice were diminished by deleting either Ripk3 or Nlrp3. These findings identify OTULIN as an inhibitor of RIPK3-mediated IL-1β release in mice.

Inhibition of Caspase-1-mediated pyroptosis promotes osteogenic differentiation, offering a therapeutic target for osteoporosis

BACKGROUND

Pyroptosis, an emerging inflammatory form of cell death, has been previously demonstrated to stimulate a massive inflammatory response, thus hindering the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Nevertheless, the impact of pyroptosis in thwarting osteogenic differentiation and exacerbating the advancement of osteoporosis (OP) remains enigmatic.

METHODS

We evaluated the expression levels of pyroptosis-associated indicators, including NOD-like receptor family pyrin domain-containing protein 3 (NLRP3), CASPASE-1, IL-1β, and IL-18, in specimens obtained from femoral heads of OP patients, as well as in an ovariectomy-induced mouse model of OP. Subsequently, the precise roles of pyroptosis in osteogenic differentiation were investigated using bioinformatics analysis, alongside morphological and biochemical assessments.

RESULTS

The pivotal pyroptotic proteins, including NLRP3, Caspase-1, IL-1β, and IL-18, exhibited significant upregulation within the bone tissue samples of clinical OP cases, as well as in the femoral tissues of ovariectomy (OVX)-induced mouse OP model, displaying a negatively associated with compromised osteogenic capacity, as represented by lessened bone mass, suppressed expression of osteogenic proteins such as Runt-related transcription factor 2 (RUNX2), Alkaline phosphatase (ALP), Osterix (OSX), and Osteopontin (OPN), and increased lipid droplets. Moreover, bioinformatics analysis substantiated shared gene expression patterns between pyroptosis and OP pathology, encompassing NLRP3, Caspase-1, IL-1β, IL-18, etc. Furthermore, our in vitro investigation using ST2 cells revealed that dexamethasone treatment prominently induced pyroptosis while impeding osteogenic differentiation. Notably, gene silencing of Caspase-1 effectively counteracted the inhibitory effects of dexamethasone on osteogenic differentiation, as manifested by increased ALP activity and enhanced expression of RUNX2, ALP, OSX, and OPN.

CONCLUSION

Our findings unequivocally underscore that inhibition of Caspase-1-mediated pyroptosis promotes osteogenic differentiation, providing a promising therapeutic target for managing OP.

The role of caspase-8 in inflammatory signalling and pyroptotic cell death

The programmed cell death machinery exhibits surprising flexibility, capable of crosstalk and non-apoptotic roles. Much of this complexity arises from the diverse functions of caspase-8, a cysteine-aspartic acid protease typically associated with activating caspase-3 and - 7 to induce apoptosis. However, recent research has revealed that caspase-8 also plays a role in regulating the lytic gasdermin cell death machinery, contributing to pyroptosis and immune responses in contexts such as infection, autoinflammation, and T-cell signalling. In mice, loss of caspase-8 results in embryonic lethality from unrestrained necroptotic killing, while in humans caspase-8 deficiency can lead to an autoimmune lymphoproliferative syndrome, immunodeficiency, inflammatory bowel disease or, when it can't cleave its substrate RIPK1, early onset periodic fevers. This review focuses on non-canonical caspase-8 signalling that drives immune responses, including its regulation of inflammatory gene transcription, activation within inflammasome complexes, and roles in pyroptotic cell death. Ultimately, a deeper understanding of caspase-8 function will aid in determining whether, and when, targeting caspase-8 pathways could be therapeutically beneficial in human diseases.

MgCl2 Attenuates ox-LDL-Induced Vascular Smooth Muscle-Derived Foam Cells Pyroptosis by Downregulating the TLR4/NF-κB Signaling Pathway

Pyroptosis is a type of programmed cell death that is generally upregulated during atherosclerosis (AS). Magnesium, an important cation in the body, has exhibited an antiatherosclerotic effect. We collected AS model datasets from the Gene Expression Omnibus (GEO) and explored the correlation between pyroptosis and AS through a series of bioinformatics methods. We next investigated the impact of oxidized low-density lipoprotein (ox-LDL) on primary cultured vascular smooth muscle cells (VSMCs) foaminess and pyroptosis. Finally, foam cells were preconditioned with different concentrations of MgCl2 to explore its influence on ox-LDL-induced VSMCs pyroptosis. NLRP3-mediated pyroptosis plays a core role in regulating AS progression as shown by bioinformatic analysis. Ox-LDL (50/75/100 mg/L) increased CE/TE ratio (> 50%) in VSMCs and prompted VSMC-derived foam cell formation, and (75/100 mg/L) ox-LDL-induced pyroptosis. Compared to 1 mmol/L MgCl2, 10 mmol/L MgCl2 significantly downregulated the expression of pyroptosis related molecules in VSMCs induced by 75 mg/L ox-LDL, including NLRP3, ASC, caspase-1, and GSDMD. The secretion of IL-1β, IL-18, and LDH was also inhibited by MgCl2. According to CCK-8 and Hoechst 33,342/PI staining, the damage to VSMCs viability induced by ox-LDL was ameliorated by MgCl2. In addition, MgCl2 attenuated the upregulation of TLR4, IKKβ, and p65 and the downregulation of IκBα in VSMCs induced by ox-LDL. The present study demonstrated that pyroptosis-related genes were the core genes in AS. We also revealed the effect and underlying mechanism of MgCl2 on ox-LDL-induced VSMCs pyroptosis, suggesting that MgCl2 has promising clinical applications for AS pyroptosis prevention and treatment.

CGRP-Loaded Porous Microspheres Protect BMSCs for Alveolar Bone Regeneration in the Periodontitis Microenvironment

Periodontitis is a prevalent dental disease marked by progressive destruction of tooth-supporting tissues, and the recovery of bone defects after periodontitis remains challenging. Although stem cell-based therapy is a promising treatment for periodontal tissue regeneration, the function of mesenchymal stem cells is constantly impaired by the inflammatory microenvironment, leading to compromised treatment outcomes. Herein, calcitonin gene-related peptide (CGRP)-loaded porous microspheres (PMs) are prepared to protect bone marrow mesenchymal stem cells (BMSCs) against inflammatory mediators in periodontitis. The released CGRP can effectively ameliorate the inflammation-induced dysfunction of BMSCs, which may involve suppressing the ROS (reactive oxygen species)/NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3)/Caspase-1 (CASP1) pathway. Moreover, the porous architecture of PMs provides effective cell-carrying capacity and physical protection for BMSCs during transplantation. In vivo experiments demonstrate that CGRP/BMSC-loaded PMs can effectively inhibit inflammation and improve osteogenic activity, resulting in better periodontal bone regeneration. This study focuses on the protection of stem cell function in the inflammatory microenvironment, which is important for stem cell-mediated tissue regeneration and repair under inflammatory conditions.

cFLIPS regulates alternative NLRP3 inflammasome activation in human monocytes

The innate immune responses, including inflammasome activation, are paramount for host defense against pathogen infection. In contrast to canonical and noncanonical inflammasome activation, in this study, heat-killed gram-negative bacteria (HK bacteria) were identified as single-step stimulators of the NLRP3 inflammasome in human monocytes, and they caused a moderate amount of IL-1β to be released from cells. Time course experiments showed that this alternative inflammasome response was finished within a few hours. Further analysis showed that the intrinsically limited NLRP3 inflammasome activation response was due to the negative regulation of caspase-8 by the short isoform of cFLIP (cFLIPs), which was activated by NF-κB. In contrast, overexpressed cFLIPS, but not overexpressed cFLIPL, inhibited the activation of caspase-8 and the release of IL-1β in response to HK bacteria infection in human monocytes. Furthermore, we demonstrated that TAK1 activity mediated the expression of cFLIPs and was upstream and essential for the caspase-8 cleavage induced by HK bacteria in human monocytes. The functional specificity of cFLIPs and TAK1 revealed unique responses of human monocytes to a noninvasive pathogen, providing novel insights into an alternative regulatory pathway of NLRP3 inflammasome activation.

Effect of tumor-associated macrophages on the pyroptosis of breast cancer tumor cells

Macrophages are immune cells with high plasticity that are widely distributed in all tissues and organs of the body. Under the influence of the immune microenvironment of breast tumors, macrophages differentiate into various germline lineages. They exert pro-tumor or tumor-suppressive effects by secreting various cytokines. Pyroptosis is mediated by Gasdermin family proteins, which form holes in cell membranes and cause a violent inflammatory response and cell death. This is an important way for the body to fight off infections. Tumor cell pyroptosis can activate anti-tumor immunity and inhibit tumor growth. At the same time, it releases inflammatory mediators and recruits tumor-associated macrophages (TAMs) for accumulation. Macrophages act as "mediators" of cytokine interactions and indirectly influence the pyroptosis pathway. This paper describes the mechanism of action on the part of TAM in affecting the pyroptosis process of breast tumor cells, as well as its key role in the tumor microenvironment. Additionally, it provides the basis for in-depth research on how to use immune cells to affect breast tumors and guide anti-tumor trends, with important implications for the prevention and treatment of breast tumors. Video Abstract.

Cleavage of cFLIP restrains cell death during viral infection and tissue injury and favors tissue repair

Cell death coordinates repair programs following pathogen attack and tissue injury. However, aberrant cell death can interfere with such programs and cause organ failure. Cellular FLICE-like inhibitory protein (cFLIP) is a crucial regulator of cell death and a substrate of Caspase-8. However, the physiological role of cFLIP cleavage by Caspase-8 remains elusive. Here, we found an essential role for cFLIP cleavage in restraining cell death in different pathophysiological scenarios. Mice expressing a cleavage-resistant cFLIP mutant, CflipD377A, exhibited increased sensitivity to severe acute respiratory syndrome coronavirus (SARS-CoV)-induced lethality, impaired skin wound healing, and increased tissue damage caused by Sharpin deficiency. In vitro, abrogation of cFLIP cleavage sensitizes cells to tumor necrosis factor(TNF)-induced necroptosis and apoptosis by favoring complex-II formation. Mechanistically, the cell death-sensitizing effect of the D377A mutation depends on glutamine-469. These results reveal a crucial role for cFLIP cleavage in controlling the amplitude of cell death responses occurring upon tissue stress to ensure the execution of repair programs.

Gasdermin D-mediated pyroptosis: mechanisms, diseases, and inhibitors

Gasdermin D (GSDMD)-mediated pyroptosis and downstream inflammation are important self-protection mechanisms against stimuli and infections. Hosts can defend against intracellular bacterial infections by inducing cell pyroptosis, which triggers the clearance of pathogens. However, pyroptosis is a double-edged sword. Numerous studies have revealed the relationship between abnormal GSDMD activation and various inflammatory diseases, including sepsis, coronavirus disease 2019 (COVID-19), neurodegenerative diseases, nonalcoholic steatohepatitis (NASH), inflammatory bowel disease (IBD), and malignant tumors. GSDMD, a key pyroptosis-executing protein, is linked to inflammatory signal transduction, activation of various inflammasomes, and the release of downstream inflammatory cytokines. Thus, inhibiting GSDMD activation is considered an effective strategy for treating related inflammatory diseases. The study of the mechanism of GSDMD activation, the formation of GSDMD membrane pores, and the regulatory strategy of GSDMD-mediated pyroptosis is currently a hot topic. Moreover, studies of the structure of caspase-GSDMD complexes and more in-depth molecular mechanisms provide multiple strategies for the development of GSDMD inhibitors. This review will mainly discuss the structures of GSDMD and GSDMD pores, activation pathways, GSDMD-mediated diseases, and the development of GSDMD inhibitors.

cFLIPL Alleviates Myocardial Ischemia-Reperfusion Injury by Inhibiting Endoplasmic Reticulum Stress

PURPOSE

Endoplasmic reticulum stress (ERS) plays a crucial role in myocardial ischemia-reperfusion injury (MIRI). Cellular FLICE-inhibitory protein (cFLIP) is an essential regulator of apoptosis and plays a major role in regulating ERS. The present study aimed to investigate the effects of long isoform cFLIP (cFLIPL) on endogenous apoptosis and the mechanism of ERS in MIRI.

METHODS

The cFLIPL recombinant adenovirus vector was used to infect H9c2 cells and Sprague-Dawley (SD) rats. After infection for 72 h, ischemia was induced for 30 min, and reperfusion was then performed for 2 h to establish the MIRI model in SD rats. H9c2 cells were hypoxic for 4 h and then reoxygenated for 12 h to simulate ischemia/reperfusion (I/R) injury. Model parameters were evaluated by assessing cardiomyocyte viability, cell death (apoptosis), and ERS-related protein expression. In addition, tunicamycin (TM), an ERS agonist, was also added to the medium for pretreatment. Coimmunoprecipitation (Co-IP) of cFLIPL and p38 MAPK protein was performed.

RESULTS

cFLIPL expression was decreased in I/R injury and hypoxia/reoxygenation (H/R) injury, and cFLIPL overexpression reduced myocardial infarction in vivo and increased the viability of H9c2 cells in vitro. I/R and H/R upregulated the protein expression of GRP78, IRE-1, and PERK to induce ERS and apoptosis. Interestingly, overexpression of cFLIPL significantly inhibited ERS and subsequent apoptosis, which was reversed by an agonist of ERS. Moreover, Co-IP showed that cFLIPL attenuated ERS and was associated with inhibiting the activation of p38 protein.

CONCLUSION

The expression of cFLIPL is significantly downregulated in MIRI, and it is accompanied by excessive ERS and apoptosis. Upregulated cFLIPL suppresses ERS to reduce myocardial apoptosis, which is associated with inhibiting the activity of p38 MAPK. Therefore, cFLIPL may be a potential intervention target for MIRI.

Citrulline inhibits LPS-induced pyroptosis of RAW264.7 macrophages through NF-κB signaling pathway

BACKGROUND

The aim of this study was to investigate the effect of citrulline on the pyroptosis of mouse macrophage RAW264.7 and the mechanism. We investigated the effect of citrulline on pyroptosis of RAW264.7 cell induced by lipopolysaccharide (LPS), and the modulation of nuclear factor-kappaB (NF-κB) signaling.

METHODS

Pyroptosis was evaluated using flow cytometry and caspase-1/sytox double staining. Cell counting kit-8 assay was performed to evaluate cell viability.

RESULTS

Citrulline promoted cell viability and inhibited the pyroptosis of RAW264.7 cell stimulated by LPS. Furthermore, citrulline inactivated NF-κb/p65 signaling pathway by suppressing p65 nuclear translocation induced by LPS. An NF-κb signaling pathway activator, betulinic acid, reversed the inhibition of pyroptosis induced by citrulline.

CONCLUSION

Citrulline inhibited LPS-induced pyrophosis, which may be closely related to the inactivation of NF-κB/p65 signaling pathway.

Caspase-8-driven apoptotic and pyroptotic crosstalk causes cell death and IL-1β release in X-linked inhibitor of apoptosis (XIAP) deficiency

Genetic lesions in X-linked inhibitor of apoptosis (XIAP) pre-dispose humans to cell death-associated inflammatory diseases, although the underlying mechanisms remain unclear. Here, we report that two patients with XIAP deficiency-associated inflammatory bowel disease display increased inflammatory IL-1β maturation as well as cell death-associated caspase-8 and Gasdermin D (GSDMD) processing in diseased tissue, which is reduced upon patient treatment. Loss of XIAP leads to caspase-8-driven cell death and bioactive IL-1β release that is only abrogated by combined deletion of the apoptotic and pyroptotic cell death machinery. Namely, extrinsic apoptotic caspase-8 promotes pyroptotic GSDMD processing that kills macrophages lacking both inflammasome and apoptosis signalling components (caspase-1, -3, -7, -11 and BID), while caspase-8 can still cause cell death in the absence of both GSDMD and GSDME when caspase-3 and caspase-7 are present. Neither caspase-3 and caspase-7-mediated activation of the pannexin-1 channel, or GSDMD loss, prevented NLRP3 inflammasome assembly and consequent caspase-1 and IL-1β maturation downstream of XIAP inhibition and caspase-8 activation, even though the pannexin-1 channel was required for NLRP3 triggering upon mitochondrial apoptosis. These findings uncouple the mechanisms of cell death and NLRP3 activation resulting from extrinsic and intrinsic apoptosis signalling, reveal how XIAP loss can co-opt dual cell death programs, and uncover strategies for targeting the cell death and inflammatory pathways that result from XIAP deficiency.

Yersinia interactions with regulated cell death pathways

Cell death in response to infection is conserved across all kingdoms of life. In metazoans, cell death upon bacterial infection is primarily carried out by the cysteine and aspartate protease and receptor-interacting serine/threonine protein kinase families. The Gram-negative bacterial genus Yersinia includes pathogens that cause disease in humans and other animals ranging from plague to gastrointestinal infections. Pathogenic Yersiniae express a type-III secretion system (T3SS), which translocates effectors that disrupt phagocytosis and innate immune signaling to evade immune defenses and replicate extracellularly in infected tissues. Blockade of innate immune signaling, disruption of the actin cytoskeleton, and the membrane-disrupting activity of the T3SS translocon pore, are all sensed by innate immune cells. Here, we discuss recent advances in understanding the pathways that regulate Yersinia-induced cell death, and how manipulation of these cell death pathways over the course of infection promotes bacterial dissemination or host defense.