Mechanism of membrane pore formation by human gasdermin-D

Igniting hope: Harnessing NLRP3 inflammasome-GSDMD-mediated pyroptosis for cancer immunotherapy

In the contemporary landscape of oncology, immunotherapy, represented by immune checkpoint blockade (ICB) therapy, stands out as a beacon of innovation in cancer treatment. Despite its promise, the therapy's progression is hindered by suboptimal clinical response rates. Addressing this challenge, the modulation of the NLRP3 inflammasome-GSDMD-mediated pyroptosis pathway holds promise as a means to augment the efficacy of immunotherapy. In the pathway, the NLRP3 inflammasome serves as a pivotal molecular sensor that responds to inflammatory stimuli within the organism. Its activation leads to the release of cytokines interleukin 1β and interleukin 18 through the cleavage of GSDMD, thereby forming membrane pores and potentially resulting in pyroptosis. This cascade of processes exerts a profound impact on tumor development and progression, with its function and expression exhibiting variability across different tumor types and developmental stages. Consequently, understanding the specific roles of the NLRP3 inflammasome and GSDMD-mediated pyroptosis in diverse tumors is imperative for comprehending tumorigenesis and crafting precise therapeutic strategies. This review aims to elucidate the structure and activation mechanisms of the NLRP3 inflammasome, as well as the induction mechanisms of GSDMD-mediated pyroptosis. Additionally, we provide a comprehensive overview of the involvement of this pathway in various cancer types and its applications in tumor immunotherapy, nanotherapy, and other fields. Emphasis is placed on the feasibility of leveraging this approach to enhance ICB therapy within the field of immunotherapy. Furthermore, we discuss the potential applications of this pathway in other immunotherapy methods, such as chimeric antigen receptor T-cell (CAR-T) therapy and tumor vaccines.

Modulating the HSP90 control over NFκB/NLRP3/Caspase-1 axis is a new therapeutic target in the management of liver fibrosis: Insights into the role of TAS-116 (Pimitespib)

Aberrant activation of the NLRP3 inflammasome is recognized to induce a chronic inflammatory response in the liver, ultimately leading to hepatic fibrosis. HSP90 is suggested to regulate NLRP3 activation and its downstream signaling. This study is the first to explore the potential therapeutic role of pimitespib in mitigating liver fibrosis in rats. The results of the study revealed that pimitespib effectively suppressed hepatic inflammation and fibrogenesis by modulating HSP90's control over the NFκB/NLRP3/caspase-1 axis. In vitro experiments demonstrated that pimitespib reduced LDH levels and increased hepatocyte survival, whereas in vivo, it prolonged the survival of rats with hepatic fibrosis. Additionally, pimitespib exhibited improvements in the function and microscopic characteristics of rat livers. Pimitespib effectively inhibited NFκB, which serves as the priming signal for NLRP3 activation. Pimitespib's inhibitory effect on NLRP3, identified as an HSP90 client protein, plays a central role in the observed anti-fibrotic effect. The simultaneous inhibition of both priming and activation signals of NLRP3 by pimitespib led to a reduction in caspase-1 activity and subsequent suppression of the N-terminal fragment of gasdermin D, ultimately constraining hepatocyte pyroptotic cell death. These diverse effects were associated with a decrease in the transcription of inflammatory mediators IL-1β, IL-18, and TNF-α, as well as the fibrogenic mediators TGF-β, TIMP-1, PDGF-BB, and Col1a1. Moreover, pimitespib induced the expression of HSP70, which could further contribute to the repression of fibrosis development. In summary, our findings provide an evolutionary perspective on managing liver fibrosis, positioning pimitespib as a promising candidate for anti-inflammatory and antifibrotic therapy.

Gasdermins as evolutionarily conserved executors of inflammation and cell death

The gasdermins are a family of pore-forming proteins that have recently emerged as executors of pyroptosis, a lytic form of cell death that is induced by the innate immune system to eradicate infected or malignant cells. Mammalian gasdermins comprise a cytotoxic N-terminal domain, a flexible linker and a C-terminal repressor domain. Proteolytic cleavage in the linker releases the cytotoxic domain, thereby allowing it to form β-barrel membrane pores. Formation of gasdermin pores in the plasma membrane eventually leads to a loss of the electrochemical gradient, cell death and membrane rupture. Here we review recent work that has expanded our understanding of gasdermin biology and function in mammals by revealing their activation mechanism, their regulation and their roles in autoimmunity, host defence and cancer. We further highlight fungal and bacterial gasdermin pore formation pointing to a conserved mechanism of cell death induction.

Gasdermin D cysteine residues synergistically control its palmitoylation-mediated membrane targeting and assembly

Gasdermin D (GSDMD) executes the cell death program of pyroptosis by assembling into oligomers that permeabilize the plasma membrane. Here, by single-molecule imaging, we elucidate the yet unclear mechanism of Gasdermin D pore assembly and the role of cysteine residues in GSDMD oligomerization. We show that GSDMD preassembles at the membrane into dimeric and trimeric building blocks that can either be inserted into the membrane, or further assemble into higher-order oligomers prior to insertion into the membrane. The GSDMD residues Cys39, Cys57, and Cys192 are the only relevant cysteines involved in GSDMD oligomerization. S-palmitoylation of Cys192, combined with the presence of negatively-charged lipids, controls GSDMD membrane targeting. Simultaneous Cys39/57/192-to-alanine (Ala) mutations, but not Ala mutations of Cys192 or the Cys39/57 pair individually, completely abolish GSDMD insertion into artificial membranes as well as into the plasma membrane. Finally, either Cys192 or the Cys39/Cys57 pair are sufficient to enable formation of GSDMD dimers/trimers, but they are all required for functional higher-order oligomer formation. Overall, our study unveils a cooperative role of Cys192 palmitoylation-mediated membrane binding and Cys39/57/192-mediated oligomerization in GSDMD pore assembly. This study supports a model in which Gasdermin D oligomerization relies on a two-step mechanism mediated by specific cysteine residues.

Programmed cell death: NINJ1 and mechanisms of plasma membrane rupture

Lytic cell death culminates in cell swelling and plasma membrane rupture (PMR). The cellular contents released, including proteins, metabolites, and nucleic acids, can act as danger signals and induce inflammation. During regulated cell death (RCD), lysis is actively initiated and can be preceded by an initial loss of membrane integrity caused by pore-forming proteins, allowing small molecules and cytokines to exit the cell. A recent seminal discovery showed that ninjurin1 (NINJ1) is the common executioner of PMR downstream of RCD, resulting in the release of large proinflammatory molecules and representing a novel target of cell death-associated lysis. We summarize recent developments in understanding membrane integrity and rupture of the plasma membrane with a focus on NINJ1.

Multiple sclerosis: the NLRP3 inflammasome, gasdermin D, and therapeutics

Multiple sclerosis (MS) stands as a chronic inflammatory disease characterized by its neurodegenerative impacts on the central nervous system. The complexity of MS and the significant challenges it poses to patients have made the exploration of effective treatments a crucial area of research. Among the various mechanisms under investigation, the role of inflammation in MS progression is of particular interest. Inflammatory responses within the body are regulated by various cellular mechanisms, one of which involves the nucleotide-binding oligomerization domain (NOD)-, leucine-rich repeat (LRR)-, and pyrin domains (PYD)-containing protein 3 (NLRP3). NLRP3 acts as a sensor within cells, playing a pivotal role in controlling the inflammatory response. Its activation is a critical step leading to the assembly of the NLRP3 inflammasome complex, a process that has profound implications for inflammatory diseases like MS. The NLRP3 inflammasome's activation is intricately linked to the subsequent activation of caspase 1 and gasdermin D (GsdmD), signaling pathways that are central to the inflammatory process. GsdmD, a prominent member of the Gasdermin protein family, is particularly noteworthy for its role in pyroptotic cell death, a form of programmed cell death that is distinct from apoptosis and is characterized by its inflammatory nature. This pathway's activation contributes significantly to the pathology of MS by exacerbating inflammatory responses within the nervous system. Given the detrimental effects of unregulated inflammation in MS, therapeutics targeting these inflammatory processes offer a promising avenue for alleviating the symptoms experienced by patients. This review delves into the intricacies of the pyroptotic pathways, highlighting how the formation of the NLRP3 inflammasome induces such pathways and the potential intervention points for therapeutic agents. By inhibiting key steps within these pathways, it is possible to mitigate the inflammatory response, thereby offering relief to those suffering from MS. Understanding these mechanisms not only sheds light on the pathophysiology of MS but also paves the way for the development of novel therapeutic strategies aimed at controlling the disease's progression through the modulation of the body's inflammatory response.

B(a)P induces ovarian granulosa cell apoptosis via TRAF2-NFκB-Caspase1 axis during early pregnancy

Benzo(a)pyrene [B(a)P] is an environmental endocrine disruptor with reproductive toxicity. The corpus luteum (CL) of the ovary plays an important role in embryo implantation and pregnancy maintenance. Our previous studies have shown that B(a)P exposure affects embryo implantation and endometrial decidualization in mouse, but its effects and mechanisms on CL function remain unclear. In this study, we explore the mechanism of ovarian toxicity of B(a)P using a pregnant mouse model and an in vitro model of human ovarian granulosa cells (GCs) KGN. Pregnant mice were gavaged with corn oil or 0.2 mg/kg.bw B(a)P from pregnant day 1 (D1) to D7, while KGN cells were treated with DMSO, 1.0IU/mL hCG, or 1.0IU/mL hCG plus benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), a B(a)P metabolite. Our findings revealed that B(a)P exposure damaged embryo implantation and reduced estrogen and progesterone levels in early pregnant mice. Additionally, in vitro, BPDE impaired luteinization in KGN cells. We observed that B(a)P/BPDE promoted oxidative stress (OS) and inflammation, leading to apoptosis rather than pyroptosis in ovaries and luteinized KGN cells. This apoptotic response was mediated by the activation of inflammatory Caspase1 through the cleavage of BID. Furthermore, B(a)P/BPDE inhibited TRAF2 expression and suppressed NFκB signaling pathway activation. The administration of VX-765 to inhibit the Caspase1 activation, over-expression of TRAF2 using TRAF2-pcDNA3.1 (+) plasmid, and BetA-induced activation of NFκB signaling pathway successfully alleviated BPDE-induced apoptosis and cellular dysfunction in luteinized KGN cells. These findings were further confirmed in the KGN cell treated with H2O2 and NAC. In conclusion, this study elucidated that B(a)P/BPDE induces apoptosis rather than pyroptosis in GCs via TRAF2-NFκB-Caspase1 during early pregnancy, and highlighting OS as the primary contributor to B(a)P/BPDE-induced ovarian toxicity. Our results unveil a novel role of TRAF2-NFκB-Caspase1 in B(a)P-induced apoptosis and broaden the understanding of mechanisms underlying unexplained luteal phase deficiency.

Mechanistic insights from inflammasome structures

Inflammasomes are supramolecular complexes that form in the cytosol in response to pathogen-associated and damage-associated stimuli, as well as other danger signals that perturb cellular homoeostasis, resulting in host defence responses in the form of cytokine release and programmed cell death (pyroptosis). Inflammasome activity is closely associated with numerous human disorders, including rare genetic syndromes of autoinflammation, cardiovascular diseases, neurodegeneration and cancer. In recent years, a range of inflammasome components and their functions have been discovered, contributing to our knowledge of the overall machinery. Here, we review the latest advances in inflammasome biology from the perspective of structural and mechanistic studies. We focus on the most well-studied components of the canonical inflammasome - NAIP-NLRC4, NLRP3, NLRP1, CARD8 and caspase-1 - as well as caspase-4, caspase-5 and caspase-11 of the noncanonical inflammasome, and the inflammasome effectors GSDMD and NINJ1. These structural studies reveal important insights into how inflammasomes are assembled and regulated, and how they elicit the release of IL-1 family cytokines and induce membrane rupture in pyroptosis.

Targeting inflammasomes and pyroptosis in retinal diseases-molecular mechanisms and future perspectives

Retinal diseases encompass various conditions associated with sight-threatening immune responses and are leading causes of blindness worldwide. These diseases include age-related macular degeneration, diabetic retinopathy, glaucoma and uveitis. Emerging evidence underscores the vital role of the innate immune response in retinal diseases, beyond the previously emphasized T-cell-driven processes of the adaptive immune system. In particular, pyroptosis, a newly discovered programmed cell death process involving inflammasome formation, has been implicated in the loss of membrane integrity and the release of inflammatory cytokines. Several disease-relevant animal models have provided evidence that the formation of inflammasomes and the induction of pyroptosis in innate immune cells contribute to inflammation in various retinal diseases. In this review article, we summarize current knowledge about the innate immune system and pyroptosis in retinal diseases. We also provide insights into translational targeting approaches, including novel drugs countering pyroptosis, to improve the diagnosis and treatment of retinal diseases.

Gasdermin D deficiency aborts myeloid calcium influx to drive granulopoiesis in lupus nephritis

Gasdermin D (GSDMD) is emerging as an important player in autoimmune diseases, but its exact role in lupus nephritis (LN) remains controversial. Here, we identified markedly elevated GSDMD in human and mouse LN kidneys, predominantly in CD11b+ myeloid cells. Global or myeloid-conditional deletion of GSDMD was shown to exacerbate systemic autoimmunity and renal injury in lupus mice with both chronic graft-versus-host (cGVH) disease and nephrotoxic serum (NTS) nephritis. Interestingly, RNA sequencing and flow cytometry revealed that myeloid GSDMD deficiency enhanced granulopoiesis at the hematopoietic sites in LN mice, exhibiting remarkable enrichment of neutrophil-related genes, significant increases in total and immature neutrophils as well as granulocyte/macrophage progenitors (GMPs). GSDMD-deficient GMPs and all-trans-retinoic acid (ATRA)-stimulated human promyelocytes NB4 were further demonstrated to possess enhanced clonogenic and differentiation abilities compared with controls. Mechanistically, GSDMD knockdown promoted self-renewal and granulocyte differentiation by restricting calcium influx, contributing to granulopoiesis. Functionally, GSDMD deficiency led to increased pathogenic neutrophil extracellular traps (NETs) in lupus peripheral blood and bone marrow-derived neutrophils. Taken together, our data establish that GSDMD deletion accelerates LN development by promoting granulopoiesis in a calcium influx-regulated manner, unraveling its unrecognized critical role in LN pathogenesis.

Cleavage of gasdermin by apoptotic caspases triggers pyroptosis restricting bacterial colonization in Hydra

Gasdermin (GSDM) proteins, as the direct executors of pyroptosis, are structurally and functionally conserved among vertebrates and play crucial roles in host defense against infection, inflammation, and cancer. However, the origin of functional GSDMs remains elusive in the animal kingdom. Here, we found that functional GSDME homologs first appeared in the cnidarian. Moreover, these animal GSDME homologs share evolutionarily conserved apoptotic caspase cleavage sites. Thus, we verified the functional conservation of apoptotic caspase-GSDME cascade in Hydra, a representative species of cnidarian. Unlike vertebrate GSDME homologs, HyGSDME could be cleaved by four Hydra caspase homologs with caspase-3 activity at two sites. Furthermore, in vivo activation of Hydra caspases resulted in HyGSDME cleavage to induce pyroptosis, exacerbating injury and restricting bacterial burden, which protects Hydra from pathogen invasion. In conclusion, these results suggest that GSDME-dependent pyroptosis may be an ancient and conserved host defense mechanism, which may contribute to better understanding on the origin and evolution of GSDMs.

Targeting pyroptosis to treat ischemic stroke: From molecular pathways to treatment strategy

Ischemic stroke is the primary reason for human disability and death, but the available treatment options are limited. Hence, it is imperative to explore novel and efficient therapies. In recent years, pyroptosis (a pro-inflammatory cell death characterized by inflammation) has emerged as an important pathological mechanism in ischemic stroke that can cause cell death through plasma membrane rupture and release of inflammatory cytokines. Pyroptosis is closely associated with inflammation, which exacerbates the inflammatory response in ischemic stroke. The level of inflammasomes, GSDMD, Caspases, and inflammatory factors is increased after ischemic stroke, exacerbating brain injury by mediating pyroptosis. Hence, inhibition of pyroptosis can be a therapeutic strategy for ischemic stroke. In this review, we have summarized the relationship between pyroptosis and ischemic stroke, as well as a series of treatments to attenuate pyroptosis, intending to provide insights for new therapeutic targets on ischemic stroke.

New insights into Gasdermin D pore formation

Gasdermin D (GSDMD) is a pore-forming protein that perforates the plasma membrane (PM) during pyroptosis, a pro-inflammatory form of cell death, to induce the unconventional secretion of inflammatory cytokines and, ultimately, cell lysis. GSDMD is activated by protease-mediated cleavage of its active N-terminal domain from the autoinhibitory C-terminal domain. Inflammatory caspase-1, -4/5 are the main activators of GSDMD via either the canonical or non-canonical pathways of inflammasome activation, but under certain stimuli, caspase-8 and other proteases can also activate GSDMD. Activated GSDMD can oligomerize and assemble into various nanostructures of different sizes and shapes that perforate cellular membranes, suggesting plasticity in pore formation. Although the exact mechanism of pore formation has not yet been deciphered, cysteine residues are emerging as crucial modulators of the oligomerization process. GSDMD pores and thus the outcome of pyroptosis can be modulated by various regulatory mechanisms. These include availability of activated GSDMD at the PM, control of the number of GSDMD pores by PM repair mechanisms, modulation of the lipid environment and post-translational modifications. Here, we review the latest findings on the mechanisms that induce GSDMD to form membrane pores and how they can be tightly regulated for cell content release and cell fate modulation.

The gasdermin family: emerging therapeutic targets in diseases

The gasdermin (GSDM) family has garnered significant attention for its pivotal role in immunity and disease as a key player in pyroptosis. This recently characterized class of pore-forming effector proteins is pivotal in orchestrating processes such as membrane permeabilization, pyroptosis, and the follow-up inflammatory response, which are crucial self-defense mechanisms against irritants and infections. GSDMs have been implicated in a range of diseases including, but not limited to, sepsis, viral infections, and cancer, either through involvement in pyroptosis or independently of this process. The regulation of GSDM-mediated pyroptosis is gaining recognition as a promising therapeutic strategy for the treatment of various diseases. Current strategies for inhibiting GSDMD primarily involve binding to GSDMD, blocking GSDMD cleavage or inhibiting GSDMD-N-terminal (NT) oligomerization, albeit with some off-target effects. In this review, we delve into the cutting-edge understanding of the interplay between GSDMs and pyroptosis, elucidate the activation mechanisms of GSDMs, explore their associations with a range of diseases, and discuss recent advancements and potential strategies for developing GSDMD inhibitors.

Gasdermin D promotes influenza virus-induced mortality through neutrophil amplification of inflammation

Influenza virus activates cellular inflammasome pathways, which can be both beneficial and detrimental to infection outcomes. Here, we investigate the function of the inflammasome-activated, pore-forming protein gasdermin D (GSDMD) during infection. Ablation of GSDMD in knockout (KO) mice (Gsdmd-/-) significantly attenuates influenza virus-induced weight loss, lung dysfunction, lung histopathology, and mortality compared with wild type (WT) mice, despite similar viral loads. Infected Gsdmd-/- mice exhibit decreased inflammatory gene signatures shown by lung transcriptomics. Among these, diminished neutrophil gene activation signatures are corroborated by decreased detection of neutrophil elastase and myeloperoxidase in KO mouse lungs. Indeed, directly infected neutrophils are observed in vivo and infection of neutrophils in vitro induces release of DNA and tissue-damaging enzymes that is largely dependent on GSDMD. Neutrophil depletion in infected WT mice recapitulates the reductions in mortality, lung inflammation, and lung dysfunction observed in Gsdmd-/- animals, while depletion does not have additive protective effects in Gsdmd-/- mice. These findings implicate a function for GSDMD in promoting lung neutrophil responses that amplify influenza virus-induced inflammation and pathogenesis. Targeting the GSDMD/neutrophil axis may provide a therapeutic avenue for treating severe influenza.

GSDMD induces hepatocyte pyroptosis to trigger alcoholic hepatitis through modulating mitochondrial dysfunction

BACKGROUND

Mechanisms and consequences of Gasdermin D (GSDMD) activation in alcoholic hepatitis (AH) are unclear. In the present study, we investigated whether GSDMD induces hepatocyte pyroptosis by regulating mitochondrial dysfunction in AH.

RESULTS

Liver damage in AH mice was assessed by HE staining, serum levels of AST, ALT, TC, and TG. The levels of IL-1β, IL-18, LDH, inflammasome-associated proteins and hepatocyte death were assessed to determine pyroptosis. Mitochondrial dysfunction was assessed through various parameters including mitochondrial DNA (mtDNA) levels, ROS generation, mitochondrial membrane potential, ATP contents, levels of mitochondrial function-related proteins and morphological changes of mitochondria. AH induced gasdermin D (GSDMD) activation, leading to increased protein expression of N-terminal GSDMD (GSDMD-N), NLRP3, and Caspase 11 in liver tissues. Downregulation of GSDMD alleviated alcohol-induced hepatocyte pyroptosis. Alcohol also causes mitochondrial dysfunction in hepatocytes in AH, which was improved by inhibiting GSDMD. Furthermore, enhancing mitochondrial function suppressed alcohol-induced hepatocyte pyroptosis. Further, knockdown of GSDMD or dynamin-related protein 1 (Drp1) improved AH-induced liver injury, accompanied by a decrease in hepatocyte pyroptosis.

CONCLUSION

GSDMD induces hepatocyte pyroptosis by modulating mitochondrial dysfunction during AH-induced inflammation and liver injury. These findings may pave the way to develop new therapeutic treatments for AH.

Phosphoinositide switches in cell physiology - From molecular mechanisms to disease

Phosphoinositides are amphipathic lipid molecules derived from phosphatidylinositol that represent low abundance components of biological membranes. Rather than serving as mere structural elements of lipid bilayers, they represent molecular switches for a broad range of biological processes, including cell signaling, membrane dynamics and remodeling, and many other functions. Here, we focus on the molecular mechanisms that turn phosphoinositides into molecular switches and how the dysregulation of these processes can lead to disease.

Pathological and Therapeutical Implications of Pyroptosis in Psoriasis and Hidradenitis Suppurativa: A Narrative Review

This manuscript explores the role of pyroptosis, an inflammatory programmed cell death, in the pathogenesis of two chronic dermatoses, psoriasis and hidradenitis suppurativa (HS). The diseases, though clinically diverse, share common pathogenetic pathways involving the unbalanced interaction between the adaptive and innate immune systems. This review focuses on the molecular changes in psoriatic and HS skin, emphasizing the activation of dendritic cells, secretion of interleukins (IL-17, IL-22, and TNF-α), and the involvement of inflammasomes, particularly NLRP3. This manuscript discusses the role of caspases, especially caspase-1, in driving pyroptosis and highlights the family of gasdermins (GSDMs) as key players in the formation of pores leading to cell rupture and the release of proinflammatory signals. This study delves into the potential therapeutic implications of targeting pyroptosis in psoriasis and HS, examining existing medications like biologics and Janus kinase inhibitors. It also reviews the current limitations and challenges in developing therapies that selectively target pyroptosis. Additionally, the manuscript explores the role of pyroptosis in various inflammatory disorders associated with psoriasis and HS, such as inflammatory bowel disease, diabetes mellitus, and cardiovascular disorders. The review concludes by emphasizing the need for further research to fully elucidate the pathomechanisms of these dermatoses and develop effective, targeted therapies.

Drugging the NLRP3 inflammasome: from signalling mechanisms to therapeutic targets

Diseases associated with chronic inflammation constitute a major health burden across the world. As central instigators of the inflammatory response to infection and tissue damage, inflammasomes - and the NACHT, LRR and PYD domain-containing protein 3 (NLRP3) inflammasome in particular - have emerged as key regulators in diverse rheumatic, metabolic and neurodegenerative diseases. Similarly to other inflammasome sensors, NLRP3 assembles a cytosolic innate immune complex that activates the cysteine protease caspase-1, which in turn cleaves gasdermin D (GSDMD) to induce pyroptosis, a regulated mode of lytic cell death. Pyroptosis is highly inflammatory, partly because of the concomitant extracellular release of the inflammasome-dependent cytokines IL-1β and IL-18 along with a myriad of additional danger signals and intracellular antigens. Here, we discuss how NLRP3 and downstream inflammasome effectors such as GSDMD, apoptosis-associated speck-like protein containing a CARD (ASC) and nerve injury-induced protein 1 (NINJ1) have gained significant traction as therapeutic targets. We highlight the recent progress in developing small-molecule and biologic inhibitors that are advancing into the clinic and serving to harness the broad therapeutic potential of modulating the NLRP3 inflammasome.

Cryo-electron tomography of NLRP3-activated ASC complexes reveals organelle co-localization

NLRP3 induces caspase-1-dependent pyroptotic cell death to drive inflammation. Aberrant activity of NLRP3 occurs in many human diseases. NLRP3 activation induces ASC polymerization into a single, micron-scale perinuclear punctum. Higher resolution imaging of this signaling platform is needed to understand how it induces pyroptosis. Here, we apply correlative cryo-light microscopy and cryo-electron tomography to visualize ASC/caspase-1 in NLRP3-activated cells. The puncta are composed of branched ASC filaments, with a tubular core formed by the pyrin domain. Ribosomes and Golgi-like or endosomal vesicles permeate the filament network, consistent with roles for these organelles in NLRP3 activation. Mitochondria are not associated with ASC but have outer-membrane discontinuities the same size as gasdermin D pores, consistent with our data showing gasdermin D associates with mitochondria and contributes to mitochondrial depolarization.

Inflammasome pathway in kidney transplantation

Kidney transplantation is the best available renal replacement therapy for patients with end-stage kidney disease and is associated with better quality of life and patient survival compared with dialysis. However, despite the significant technical and pharmaceutical advances in this field, kidney transplant recipients are still characterized by reduced long-term graft survival. In fact, almost half of the patients lose their allograft after 15-20 years. Most of the conditions leading to graft loss are triggered by the activation of a large immune-inflammatory machinery. In this context, several inflammatory markers have been identified, and the deregulation of the inflammasome (NLRP3, NLRP1, NLRC4, AIM2), a multiprotein complex activated by either whole pathogens (including fungi, bacteria, and viruses) or host-derived molecules, seems to play a pivotal pathogenetic role. However, the biological mechanisms leading to inflammasome activation in patients developing post-transplant complications (including, ischemia-reperfusion injury, rejections, infections) are still largely unrecognized, and only a few research reports, reviewed in this manuscript, have addressed the association between abnormal activation of this pathway and the onset/development of major clinical effects. Finally, the regulation of the inflammasome machinery could represent in future a valuable therapeutic target in kidney transplantation.

The insertase YidC chaperones the polytopic membrane protein MelB inserting and folding simultaneously from both termini

The insertion and folding of proteins into membranes is crucial for cell viability. Yet, the detailed contributions of insertases remain elusive. Here, we monitor how the insertase YidC guides the folding of the polytopic melibiose permease MelB into membranes. In vivo experiments using conditionally depleted E. coli strains show that MelB can insert in the absence of SecYEG if YidC resides in the cytoplasmic membrane. In vitro single-molecule force spectroscopy reveals that the MelB substrate itself forms two folding cores from which structural segments insert stepwise into the membrane. However, misfolding dominates, particularly in structural regions that interface the pseudo-symmetric α-helical domains of MelB. Here, YidC takes an important role in accelerating and chaperoning the stepwise insertion and folding process of both MelB folding cores. Our findings reveal a great flexibility of the chaperoning and insertase activity of YidC in the multifaceted folding processes of complex polytopic membrane proteins.

DNase based therapeutic approaches for the treatment of NETosis related inflammatory diseases

Neutrophils are the primary host innate immune cells defending against pathogens. One proposed mechanism by which neutrophils limit pathogen transmission is NETosis, which includes releasing the nuclear content into the cytosol by forming pores in the plasma membrane. The extrusion of cellular deoxyribonucleic acid (DNA) results in neutrophil extracellular traps (NETs) composed of nuclear DNA associated with histones and granule proteins. NETosis is driven by the enzyme PAD-4 (Peptidylarginine deiminase-4), which converts arginine into citrulline, leading to decondensation of chromatin, separation of DNA, and eventual extrusion. DNase is responsible for the breakdown of NETs. On the one hand, the release of DNase may interfere with the antibacterial effects of NETs; further, DNase may protect tissues from self-destruction caused by the increased release of NET under septic conditions. NETs in physiological quantities are expected to have a role in anti-infectious innate immune responses. In contrast, abnormally high concentrations of NETs in the body that are not adequately cleared by DNases can damage tissues and cause inflammation. Through several novel approaches, it is now possible to avoid the adverse effects caused by the continued release of NETs into the extracellular environment. In this review we have highlighted the basic mechanisms of NETosis, its significance in the pathogenesis of various inflammatory disorders, and the role of DNase enzyme with a focus on the possible function of nanotechnology in its management.

Effects of toxicants on endoplasmic reticulum stress and hepatic cell fate determination

Toxicant-induced injury is a significant global health issue. However, the mechanisms through which toxicants such as carbon tetrachloride, acetaminophen, dimethylformamide, cocaine, and morphine induce the death of multiple cell types and contribute to liver toxicity are highly complex. This phenomenon involves intricate signaling pathways in association with oxidative stress, inflammation, and activation of death receptors, which are closely linked to endoplasmic reticulum (ER) stress. ER stress initially triggers the unfolded protein response, which either promotes cell survival or causes cell death at later times, depending on the severity and duration of the stress. Thus, comprehending the molecular basis governing cell fate determination in the context of ER stress may provide key insights into the prevention and treatment of toxicant-induced injury. This review summarizes our current understanding of agents that trigger different forms of ER stress-mediated cell death, necroptosis, ferroptosis, pyroptosis, and apoptosis, and covers the underlying molecular basis of toxicant-induced ER stress, as well as potential target molecules.

Pyroptosis and inflammasomes in cancer and inflammation

Nonprogrammed cell death (NPCD) and programmed cell death (PCD) are two types of cell death. Cell death is significantly linked to tumor development, medication resistance, cancer recurrence, and metastatic dissemination. Therefore, a comprehensive understanding of cell death is essential for the treatment of cancer. Pyroptosis is a kind of PCD distinct from autophagy and apoptosis in terms of the structure and function of cells. The defining features of pyroptosis include the release of an inflammatory cascade reaction and the expulsion of lysosomes, inflammatory mediators, and other cellular substances from within the cell. Additionally, it displays variations in osmotic pressure both within and outside the cell. Pyroptosis, as evidenced by a growing body of research, is critical for controlling the development of inflammatory diseases and cancer. In this paper, we reviewed the current level of knowledge on the mechanism of pyroptosis and inflammasomes and their connection to cancer and inflammatory diseases. This article presents a theoretical framework for investigating the potential of therapeutic targets in cancer and inflammatory diseases, overcoming medication resistance, establishing nanomedicines associated with pyroptosis, and developing risk prediction models in refractory cancer. Given the link between pyroptosis and the emergence of cancer and inflammatory diseases, pyroptosis-targeted treatments may be a cutting-edge treatment strategy.

The gasdermins: a pore-forming protein family expressed in the epidermis

Gasdermins comprise a family of pore-forming proteins, which play critical roles in (auto)inflammatory diseases and cancer. They are expressed as self-inhibited precursor proteins consisting of an aminoterminal cytotoxic effector domain (NT-GSDM) and a carboxyterminal inhibitor domain (GSDM-CT) separated by an unstructured linker region. Proteolytic processing in the linker region liberates NT-GSDM, which translocates to membranes, forms oligomers, and induces membrane permeabilization, which can disturb the cellular equilibrium that can lead to cell death. Gasdermin activation and pore formation are associated with inflammation, particularly when induced by the inflammatory protease caspase-1 upon inflammasome activation. These gasdermin pores allow the release of the pro-inflammatory cytokines interleukin(IL)-1β and IL-18 and induce a lytic type of cell death, termed pyroptosis that supports inflammation, immunity, and tissue repair. However, even at the cellular level, the consequences of gasdermin activation are diverse and range from induction of programmed cell death - pyroptosis or apoptosis - to poorly characterized protective mechanisms. The specific effects of gasdermin activation can vary between species, cell types, the membrane that is being permeabilized (plasma membrane, mitochondrial membrane, etc.), and the overall biological state of the local tissue/cells. In epithelia, gasdermins seem to play crucial roles. Keratinocytes represent the main cell type of the epidermis, which is the outermost skin layer with an essential barrier function. Compared to other tissues, keratinocytes express all members of the gasdermin family, in part in a differentiation-specific manner. That raises questions regarding the specific roles of individual GSDM family members in the skin, the mechanisms and consequences of their activation, and the potential crosstalk between them. In this review, we summarize the current knowledge about gasdermins with a focus on keratinocytes and the skin and discuss the possible roles of the different family members in immunity and disease.

Gasdermins gone wild: new roles for GSDMs in regulating cellular homeostasis

Since their discovery, members of the gasdermin (GSDM) family of proteins have been firmly established as executors of pyroptosis, with the N-terminal fragment of most GSDMs capable of forming pores in the plasma membrane. More recent findings suggest that some GSDMs can drive additional cell death pathways, such as apoptosis and necroptosis, through mechanisms independent of plasma membrane perforation. There is also emerging evidence that by associating with cellular compartments such as mitochondria, peroxisomes, endosomes, and the nucleus, GSDMs regulate cell death-independent aspects of cellular homeostasis. Here, we review the diversity of GSDM function across several cell types and explore how various cellular stresses can promote relocalization - and thus refunctionalization - of GSDMs.

Pyroptosis and the cellular consequences of gasdermin pores

The family of gasdermin proteins plays a key role in the host response against external and internal pathogenic signals by mediating the form of inflammatory regulated cell death known as pyroptosis. One of the most well-studied gasdermins within innate immunity is gasdermin D, which is cleaved, oligomerizes, and forms plasma membrane pores. Gasdermin D pores lead to a number of downstream cellular consequences including plasma membrane rupture, or cell lysis. In this review, we describe mechanisms of activation for each of the gasdermins, their cell type specificity and some disease associations. We then discuss downstream consequences of gasdermin pore formation, including cellular mechanisms of membrane repair. Finally, we present some important next steps to better understand pyroptosis and the cellular consequences of gasdermin pore formation.

S100A4 Promotes BCG-Induced Pyroptosis of Macrophages by Activating the NF-κB/NLRP3 Inflammasome Signaling Pathway

Pyroptosis is a host immune strategy to defend against Mycobacterium tuberculosis (Mtb) infection. S100A4, a calcium-binding protein that plays an important role in promoting cancer progression as well as the pathophysiological development of various non-tumor diseases, has not been explored in Mtb-infected hosts. In this study, transcriptome analysis of the peripheral blood of patients with pulmonary tuberculosis (PTB) revealed that S100A4 and GSDMD were significantly up-regulated in PTB patients' peripheral blood. Furthermore, there was a positive correlation between the expression of GSDMD and S100A4. KEGG pathway enrichment analysis showed that differentially expressed genes between PTB patients and healthy controls were significantly related to inflammation, such as the NOD-like receptor signaling pathway and NF-κB signaling pathway. To investigate the regulatory effects of S100A4 on macrophage pyroptosis, THP-1 macrophages infected with Bacillus Calmette-Guérin (BCG) were pre-treated with exogenous S100A4, S100A4 inhibitor or si-S100A4. This research study has shown that S100A4 promotes the pyroptosis of THP-1 macrophages caused by BCG infection and activates NLRP3 inflammasome and NF-κB signaling pathways, which can be inhibited by knockdown or inhibition of S100A4. In addition, inhibition of NF-κB or NLRP3 blocks the promotion effect of S100A4 on BCG-induced pyroptosis of THP-1 macrophages. In conclusion, S100A4 activates the NF-κB/NLRP3 inflammasome signaling pathway to promote macrophage pyroptosis induced by Mtb infection. These data provide new insights into how S100A4 affects Mtb-induced macrophage pyroptosis.

Pyroptosis Modulators: New Insights of Gasdermins in Health and Disease

Pyroptosis is an inflammation-dependent type of cell death that has been in the spotlight for the scientific community in the last few years. Crucial players in the process of pyroptosis are the members of the gasdermin family of proteins, which have been parallelly studied. Upon induction of pyroptosis, gasdermins suffer from structural changes leading to the formation of pores in the membrane that subsequently cause the release of pro-inflammatory contents. Recently, it has been discovered that oxidation plays a key role in the activation of certain gasdermins. Here, we review the current knowledge on pyroptosis and human gasdermins, focusing on the description of the different members of the family, their molecular structures, and their influence on health and disease directly or non-directly related to inflammation. Noteworthy, we have focused on the existing understanding of the role of this family of proteins in cancer, which could translate into novel promising strategies aimed at benefiting human health. In conclusion, the modulation of pyroptosis and gasdermins by natural and synthetic compounds through different mechanisms, including modification of the redox state of cells, has been proven effective and sets precedents for future therapeutic strategies.

Inhibitory effect of Portulaca oleracea L. aqueous extract and juice on NLRP3 inflammasome activation in an ulcerative colitis mouse model

Portulaca oleracea L. (PO) is an edible and medicinal plant used for treating gastrointestinal diseases. However, the effects of PO on ulcerative colitis (UC) and underlying mechanisms remain unclear. This study investigated the effects of PO aqueous extract (POE) and PO juice (PJ) on dextran sulfate sodium (DSS)-induced UC in a mouse model and attempted to unravel their underlying mechanisms. The results revealed that PJ contains more bioactive compounds and has more overlapping targets with UC than POE. Both POE and PJ effectively reduced Disease Activity Index scores and inflammatory cell infiltration in the UC mouse model, but PJ had a better effect than POE. Furthermore, PJ inhibited pyroptosis by decreasing the expression of the NLRP3 inflammasome, while also repairing the dysfunction of the intestinal barrier by upregulating the expression of tight junction proteins. Therefore, based on the study findings, we concluded that PJ can improve DSS-induced UC and may suppress pyroptosis by interfering with the activation of the NLRP3 inflammasome.

Molecular mechanisms of gasdermin D pore-forming activity

The regulated disruption of the plasma membrane, which can promote cell death, cytokine secretion or both is central to organismal health. The protein gasdermin D (GSDMD) is a key player in this process. GSDMD forms membrane pores that can promote cytolysis and the release of interleukin-1 family cytokines into the extracellular space. Recent discoveries have revealed biochemical and cell biological mechanisms that control GSDMD pore-forming activity and its diverse downstream immunological effects. Here, we review these multifaceted regulatory activities, including mechanisms of GSDMD activation by proteolytic cleavage, dynamics of pore assembly, regulation of GSDMD activities by posttranslational modifications, membrane repair and the interplay of GSDMD and mitochondria. We also address recent insights into the evolution of the gasdermin family and their activities in species across the kingdoms of life. In doing so, we hope to condense recent progress and inform future studies in this rapidly moving field in immunology.

Peptide-Based Nanoparticles for Systemic Extrahepatic Delivery of Therapeutic Nucleotides

Peptide-based nanoparticles (PBN) for nucleotide complexation and targeting of extrahepatic diseases are gaining recognition as potent pharmaceutical vehicles for fine-tuned control of protein production (up- and/or down-regulation) and for gene delivery. Herein, we review the principles and mechanisms underpinning self-assembled formation of PBN, cellular uptake, endosomal release, and delivery to extrahepatic disease sites after systemic administration. Selected examples of PBN that have demonstrated recent proof of concept in disease models in vivo are summarized to offer the reader a comparative view of the field and the possibilities for clinical application.

Pharmacological Inhibition of Gasdermin D Suppresses Angiotensin II-Induced Experimental Abdominal Aortic Aneurysms

BACKGROUND

Gasdermin D, a molecule downstream of the nucleotide-binding oligomerization domain-like receptor family pyrin domain containing inflammasome, forms the membrane pore for the secretion of interleukin (IL)-1β and IL-18, and also mediates pyroptosis. This study was to explore the influence of treatment with disulfiram, a small molecule inhibitor to gasdermin D, on the formation and progression of experimental abdominal aortic aneurysms (AAA).

METHODS

AAAs were induced in 10-week-old male apolipoprotein E deficient mice by subcutaneous infusion of angiotensin II (1000 ng/min/kg body weight) for 28 days via osmotic minipumps. Three days prior to angiotensin II infusion, disulfiram (50 mg/kg) or an equal volume of saline as the vehicle control was administered daily via oral gavage. The influence on experimental AAAs was analyzed by serial measurements of aortic diameters via ultrasonography, grading AAA severity and histopathology at sacrifice. Serum IL-1β and IL-18 levels, systolic blood pressure, total cholesterol, and triglyceride were also measured. Additional experiments assayed the influences on the cell viability and IL-1β secretion of in vitro activated macrophages.

RESULTS

Disulfiram significantly reduced the enlargement, incidence, and severity of angiotensin II-induced experimental AAAs with attenuation of medial elastin breaks, mural macrophage accumulation, and systolic blood pressure. The AAA suppression was also associated with reduced systemic levels of IL-1β but not IL-18. However, disulfiram treatment had no impact on body weight gain and lipid levels in aneurysmal mice. Additionally, disulfiram treatment also markedly reduced the secretion of IL-1β from activated macrophages with a limited effect on cell viability in vitro.

CONCLUSIONS

Gasdermin D inhibition by disulfiram attenuated angiotensin II-induced experimental AAAs with reduced systemic IL-1β levels and in vitro activated macrophage IL-1β secretion. Our study suggests that pharmacological gasdermin D inhibition may have translational potential for limiting clinical AAA progression.

Determining the Functional Oligomeric State of Membrane-Associated Protein Oligomers Forming Membrane Pores on Giant Lipid Vesicles

Several peripheral membrane proteins are known to form membrane pores through multimerization. In many cases, in biochemical reconstitution experiments, a complex distribution of oligomeric states has been observed that may, in part, be irrelevant to their physiological functions. This phenomenon makes it difficult to identify the functional oligomeric states of membrane lipid interacting proteins, for example, during the formation of transient membrane pores. Using fibroblast growth factor 2 (FGF2) as an example, we present a methodology applicable to giant lipid vesicles by which functional oligomers can be distinguished from nonspecifically aggregated proteins without functionality. Two distinct populations of fibroblast growth factor 2 were identified with (i) dimers to hexamers and (ii) a broad population of higher oligomeric states of membrane-associated FGF2 oligomers significantly distorting the original unfiltered histogram of all detectable oligomeric species of FGF2. The presented statistical approach is relevant for various techniques for characterizing membrane-dependent protein oligomerization.

Human gasdermin D and MLKL disrupt mitochondria, endocytic traffic and TORC1 signalling in budding yeast

Gasdermin D (GSDMD) and mixed lineage kinase domain-like protein (MLKL) are the pore-forming effectors of pyroptosis and necroptosis, respectively, with the capacity to disturb plasma membrane selective permeability and induce regulated cell death. The budding yeast Saccharomyces cerevisiae has long been used as a simple eukaryotic model for the study of proteins associated with human diseases by heterologous expression. In this work, we expressed in yeast both GSDMD and its N-terminal domain (GSDMD(NT)) to characterize their cellular effects and compare them to those of MLKL. GSDMD(NT) and MLKL inhibited yeast growth, formed cytoplasmic aggregates and fragmented mitochondria. Loss-of-function point mutants of GSDMD(NT) showed affinity for this organelle. Besides, GSDMD(NT) and MLKL caused an irreversible cell cycle arrest through TORC1 inhibition and disrupted endosomal and autophagic vesicular traffic. Our results provide a basis for a humanized yeast platform to study GSDMD and MLKL, a useful tool for structure-function assays and drug discovery.

Alternative splicing of GSDMB modulates killer lymphocyte-triggered pyroptosis

Granzyme A from killer lymphocytes cleaves gasdermin B (GSDMB) and triggers pyroptosis in targeted human tumor cells, eliciting antitumor immunity. However, GSDMB has a controversial role in pyroptosis and has been linked to both anti- and protumor functions. Here, we found that GSDMB splicing variants are functionally distinct. Cleaved N-terminal (NT) fragments of GSDMB isoforms 3 and 4 caused pyroptosis, but isoforms 1, 2, and 5 did not. The nonfunctional isoforms have a deleted or modified exon 6 and therefore lack a stable belt motif. The belt likely contributes to the insertion of oligomeric GSDMB-NTs into the membrane. Consistently, noncytotoxic GSDMB-NTs blocked pyroptosis caused by cytotoxic GSDMB-NTs in a dominant-negative manner. Upon natural killer (NK) cell attack, GSDMB3-expressing cells died by pyroptosis, whereas GSDMB4-expressing cells died by mixed pyroptosis and apoptosis, and GSDMB1/2-expressing cells died only by apoptosis. GSDMB4 partially resisted NK cell-triggered cleavage, suggesting that only GSDMB3 is fully functional. GSDMB1-3 were the most abundant isoforms in the tested tumor cell lines and were similarly induced by interferon-γ and the chemotherapy drug methotrexate. Expression of cytotoxic GSDMB3/4 isoforms, but not GSDMB1/2 isoforms that are frequently up-regulated in tumors, was associated with better outcomes in bladder and cervical cancers, suggesting that GSDMB3/4-mediated pyroptosis was protective in those tumors. Our study indicates that tumors may block and evade killer cell-triggered pyroptosis by generating noncytotoxic GSDMB isoforms. Therefore, therapeutics that favor the production of cytotoxic GSDMB isoforms by alternative splicing may improve antitumor immunity.

A Lipid Perspective on Regulated Pyroptosis

Pyroptosis is a novel pro-inflammatory cell programmed death dependent on Gasdermin (GSMD) family-mediated membrane pore formation and subsequent cell lysis, accompanied by the release of inflammatory factors and expanding inflammation in multiple tissues. All of these processes have impacts on a variety of metabolic disorders. Dysregulation of lipid metabolism is one of the most prominent metabolic alterations in many diseases, including the liver, cardiovascular system, and autoimmune diseases. Lipid metabolism produces many bioactive lipid molecules, which are important triggers and endogenous regulators of pyroptosis. Bioactive lipid molecules promote pyroptosis through intrinsic pathways involving reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, mitochondrial dysfunction, lysosomal disruption, and the expression of related molecules. Pyroptosis can also be regulated during the processes of lipid metabolism, including lipid uptake and transport, de novo synthesis, lipid storage, and lipid peroxidation. Taken together, understanding the correlation between lipid molecules such as cholesterol and fatty acids and pyroptosis during metabolic processes can help to gain insight into the pathogenesis of many diseases and develop effective strategies from the perspective of pyroptosis.

Gasdermin D promotes influenza virus-induced mortality through neutrophil amplification of inflammation

Influenza virus activates cellular inflammasome pathways, which can be either beneficial or detrimental to infection outcomes. Here, we investigated the role of the inflammasome-activated pore-forming protein gasdermin D (GSDMD) during infection. Ablation of GSDMD in knockout (KO) mice significantly attenuated virus-induced weight loss, lung dysfunction, lung histopathology, and mortality compared with wild type (WT) mice, despite similar viral loads. Infected GSDMD KO mice exhibited decreased inflammatory gene signatures revealed by lung transcriptomics, which also implicated a diminished neutrophil response. Importantly, neutrophil depletion in infected WT mice recapitulated the reduced mortality and lung inflammation observed in GSDMD KO animals, while having no additional protective effects in GSDMD KOs. These findings reveal a new function for GSDMD in promoting lung neutrophil responses that amplify influenza virus-induced inflammation and pathogenesis. Targeting the GSDMD/neutrophil axis may provide a new therapeutic avenue for treating severe influenza.

Mitochondrial pores at the crossroad between cell death and inflammatory signaling

Mitochondria are cellular organelles with a major role in many cellular processes, including not only energy production, metabolism, and calcium homeostasis but also regulated cell death and innate immunity. Their proteobacterial origin makes them a rich source of potent immune agonists, normally hidden within the mitochondrial membrane barriers. Alteration of mitochondrial permeability through mitochondrial pores thus provides efficient mechanisms not only to communicate mitochondrial stress to the cell but also as a key event in the integration of cellular responses. In this regard, eukaryotic cells have developed diverse signaling networks that sense and respond to the release of mitochondrial components into the cytosol and play a key role in controlling cell death and inflammatory pathways. Modulating pore formation at mitochondria through direct or indirect mechanisms may thus open new opportunities for therapy. In this review, we discuss the current understanding of the structure and molecular mechanisms of mitochondrial pores and how they function at the interface between cell death and inflammatory signaling to regulate cellular outcomes.

Microglial pyroptosis in hippocampus mediates sevolfurane-induced cognitive impairment in aged mice via ROS-NLRP3 inflammasome pathway

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common complication with its pathophysiological mechanisms not been fully elucidated. Pyroptosis is a novel type of pro-inflammatory cell death and considered to be associated with cognitive dysfunction. Therefore, our study aimed to examine the effect of pyroptosis on sevoflurane-induced cognitive impairment in aged mice as well as its underlying mechanism.

METHODS

A mice model of cognitive impairment was established by sevoflurane exposure and the levels of reactive oxygen species (ROS), N-GSDMD, cleaved caspase-1, ASC, IL-1β and IL-18, and NLRP3 in hippocampus was determined. To explore the underlying mechanism, a pyroptosis inhibitor, necrosulfonamide (NSA), and a ROS scavenger, N-acetylcysteine (NAC), were administrated before sevoflurane exposure both in vitro and in vivo. Neurobehavioral tests, western blot, transmission electron microscope (TEM) observation, and immunofluorescence staining were performed.

RESULTS

Sevoflurane induced hippocampal pyroptosis in the cognitive impairment model. NSA effectively inhibited the pyroptosis and improved cognitive function. Co-labeled immunofluorescence staining suggested sevoflurane induces microglial pyroptosis. Sevoflurane induced pyroptosis accompanied with ROS accumulation in a dose-independent manner in BV2 cells, and NAC effectively reduce the levels of ROS and pyroptosis through NLRP3 inflammasome pathway in both vitro and vivo. Furthermore, NAC could also alleviate sevoflurane-induced cognitive dysfunction.

CONCLUSIONS

Microglial pyroptosis in hippocampus mediates sevolfurane-induced cognitive impairment in aged mice via ROS-NLRP3 inflammasome pathway. Both pyroptosis inhibition and ROS scavenging might be potential approaches to ameliorate sevoflurane-induced neurocognitive dysfunction.

Pore-Forming Proteins: From Pore Assembly to Structure by Quantitative Single-Molecule Imaging

Pore-forming proteins (PFPs) play a central role in many biological processes related to infection, immunity, cancer, and neurodegeneration. A common feature of PFPs is their ability to form pores that disrupt the membrane permeability barrier and ion homeostasis and generally induce cell death. Some PFPs are part of the genetically encoded machinery of eukaryotic cells that are activated against infection by pathogens or in physiological programs to carry out regulated cell death. PFPs organize into supramolecular transmembrane complexes that perforate membranes through a multistep process involving membrane insertion, protein oligomerization, and finally pore formation. However, the exact mechanism of pore formation varies from PFP to PFP, resulting in different pore structures with different functionalities. Here, we review recent insights into the molecular mechanisms by which PFPs permeabilize membranes and recent methodological advances in their characterization in artificial and cellular membranes. In particular, we focus on single-molecule imaging techniques as powerful tools to unravel the molecular mechanistic details of pore assembly that are often obscured by ensemble measurements, and to determine pore structure and functionality. Uncovering the mechanistic elements of pore formation is critical for understanding the physiological role of PFPs and developing therapeutic approaches.

Membrane damage and repair: a thin line between life and death

Bilayered membranes separate cells from their surroundings and form boundaries between intracellular organelles and the cytosol. Gated transport of solutes across membranes enables cells to establish vital ion gradients and a sophisticated metabolic network. However, an advanced compartmentalization of biochemical reactions makes cells also particularly vulnerable to membrane damage inflicted by pathogens, chemicals, inflammatory responses or mechanical stress. To avoid potentially lethal consequences of membrane injuries, cells continuously monitor the structural integrity of their membranes and readily activate appropriate pathways to plug, patch, engulf or shed the damaged membrane area. Here, we review recent insights into the cellular mechanisms that underly an effective maintenance of membrane integrity. We discuss how cells respond to membrane lesions caused by bacterial toxins and endogenous pore-forming proteins, with a primary focus on the intimate crosstalk between membrane proteins and lipids during wound formation, detection and elimination. We also discuss how a delicate balance between membrane damage and repair determines cell fate upon bacterial infection or activation of pro-inflammatory cell death pathways.

Pentoxifylline and thiamine ameliorate rhabdomyolysis-induced acute kidney injury in rats via suppressing TLR4/NF-κB and NLRP-3/caspase-1/gasdermin mediated-pyroptosis

Acute kidney injury (AKI) is a common complication of rhabdomyolysis (RM), a syndrome characterized by skeletal muscle damage resulting in renal tubular oxidative stress, inflammation, and activated toll like receptor-4 (TLR-4) and NOD-like receptor protein-3 (NLRP-3) inflammasome. Pyroptosis is a programmed cell death mediated by NLRP-3 leading to the activation of caspase-1 and gasdermin D (GSDMD), the hallmark of pyroptosis. This study aims to investigate the renoprotective effects of two antioxidants; pentoxifylline (PTX) and thiamine (TM) via targeting the aforementioned pathways. RM-AKI was induced in male Albino Wistar rats by intramuscular injection of glycerol (50% v/v, 10 ml/kg). PTX (100 mg/kg, oral) and TM (25 mg/kg, i.p) were administered for 12 days prior glycerol injection and continued for 3 days following induction of RM-AKI. Serum creatinine, blood urea nitrogen (BUN), creatin kinase, lipid peroxides, total antioxidant activity, inflammatory markers (tumor necrosis factor-α, interleukin-1β, and nuclear factor kappa B), TLR4, NLRP-3, caspase-1, GSDMD and c-myc (an apoptotic marker) were estimated. Compared to AKI model, co-administered drugs revealed a significant improvement in renal function and pathology as indicated by the reduction in serum creatinine, BUN and protein cast accumulation. The elevations of oxidative stress, and inflammatory markers as well as the over-expression of c-myc were alleviated. Protein levels of TLR4, NLRP3, cleaved caspase-1, and GSDMD were significantly elevated in RM-AKI model, and this elevation was attenuated by the tested drugs. In conclusion, PTX and TM could be a potential renoprotective approach for patients with RM through targeting TLR4/NF-κB and NLRP-3/caspase-1/gasdermin mediated-pyroptosis pathways.

Identification of a pyroptosis-based model for predicting clinical outcomes from immunotherapy in patients with metastatic melanoma

Immunotherapy has greatly improved outcomes for patients with advanced melanoma, but good predictive biomarkers remain lacking in clinical practice. Although increasing evidence has revealed a vital role of pyroptosis in the tumor microenvironment (TME), it remains unclear for pyroptosis as a predictive biomarker for immunotherapy in melanoma. RNA sequencing data and annotated clinical information of melanoma patients were obtained from four published immunotherapy datasets. LASSO regression analysis was conducted to develop a pyroptosis-based model for quantifying a pyroptosis score in each tumor. Based on four clinical cohorts, we evaluated the predictive capability of the model using multiple immunotherapeutic outcomes, including clinical benefits, overall survival (OS), and progression-free survival (PFS). Furthermore, we depicted the distinctive TME features associated with pyroptosis. Compared with the group with low pyroptosis scores, the group with high pyroptosis scores consistently achieved better durable clinical benefits in four independent cohorts and the meta-cohort. ROC analysis validated that the pyroptosis-based model was a reliable biomarker for predicting clinical benefits from immunotherapy in melanoma. Survival analyses showed that the group with high pyroptosis scores harbored more favorable OS and PFS than those with low pyroptosis scores. Molecular analysis revealed that tumors with high pyroptosis scores displayed a typical immune-inflamed phenotype in TME, including enrichment of immunostimulatory pathways, increased level of tumor-infiltrating lymphocytes, upregulation of immune effectors, and activation of the antitumor immune response. Our findings suggested that the pyroptosis-related model associated with multiple immune-inflamed characteristics might be a reliable tool for predicting clinical benefit and survival outcomes from immunotherapy in melanoma.

NLRP3 inflammasome in neurodegenerative disease

Neurodegenerative diseases are characterized by a dysregulated neuro-glial microenvironment, culminating in functional deficits resulting from neuronal cell death. Inflammation is a hallmark of the neurodegenerative microenvironment and despite a critical role in tissue homeostasis, increasing evidence suggests that chronic inflammatory insult can contribute to progressive neuronal loss. Inflammation has been studied in the context of neurodegenerative disorders for decades but few anti-inflammatory treatments have advanced to clinical use. This is likely due to the related challenges of predicting and mitigating off-target effects impacting the normal immune response while detecting inflammatory signatures that are specific to the progression of neurological disorders. Inflammasomes are pro-inflammatory cytosolic pattern recognition receptors functioning in the innate immune system. Compelling pre-clinical data has prompted an intense interest in the role of the NLR family pyrin domain containing 3 (NLRP3) inflammasome in neurodegenerative disease. NLRP3 is typically inactive but can respond to sterile triggers commonly associated with neurodegenerative disorders including protein misfolding and aggregation, mitochondrial and oxidative stress, and exposure to disease-associated environmental toxicants. Clear evidence of enhanced NLRP3 inflammasome activity in common neurodegenerative diseases has coincided with rapid advancement of novel small molecule therapeutics making the NLRP3 inflammasome an attractive target for near-term interventional studies. In this review, we highlight evidence from model systems and patients indicating inflammasome activity in neurodegenerative disease associated with the NLRP3 inflammasome's ability to recognize pathologic forms of amyloid-β, tau, and α-synuclein. We discuss inflammasome-driven pyroptotic processes highlighting the potential utility of evaluating extracellular inflammasome-related proteins in the context of biomarker discovery. We complete the report by pointing out gaps in our understanding of intracellular modifiers of inflammasome activity and mechanisms regulating the resolution of inflammasome activation. The literature review and perspectives provide a conceptual platform for continued analysis of inflammation in neurodegenerative diseases through the study of inflammasomes and pyroptosis, mechanisms of inflammation and cell death now recognized to function in multiple highly prevalent neurological disorders.

Gasdermins and pyroptosis in the kidney

Pyroptosis is a form of regulated cell death that is mediated by the membrane-targeting, pore-forming gasdermin family of proteins. Pyroptosis was initially described as a caspase 1- and inflammasome-dependent cell death pathway typified by the loss of membrane integrity and the secretion of cytokines such as IL-1β. However, gasdermins are now recognized as the principal effectors of this form of regulated cell death; activated gasdermins insert into cell membranes, where they form pores that result in the secretion of cytokines, alarmins and damage-associated molecular patterns and cause cell membrane rupture. It is now evident that gasdermins can be activated by inflammasome- and caspase-independent mechanisms in multiple cell types and that crosstalk occurs between pyroptosis and other cell death pathways. Although they are important for host antimicrobial defence, a growing body of evidence supports the notion that pyroptosis and gasdermins have pathological roles in cancer and several non-microbial diseases involving the gut, liver and skin. The well-documented roles of inflammasome activity and apoptosis pathways in kidney diseases suggests that gasdermins and pyroptosis may also be involved to some extent. However, despite some evidence for involvement of pyroptosis in the context of acute kidney injury and chronic kidney disease, our understanding of gasdermin biology and pyroptosis in the kidney remains limited.

Development of synthetic lipoxin-A4 mimetics (sLXms): New avenues in the treatment of cardio-metabolic diseases

Resolution of inflammation is a complex, dynamic process consisting of several distinct processes, including inhibition of endothelial activation and leukocyte trafficking; promotion of inflammatory cell apoptosis and subsequent non-phlogistic scavenging and degradation; augmentation of pathogen phagocytosis; modulation of stromal cell phenotype coupled to the promotion of tissue regeneration and repair. Among these tightly regulated processes, the clearance and degradation of apoptotic cells without eliciting an inflammatory response is a crucial allostatic mechanism vital to developmental processes, host defence, and the effective resolution of inflammation. These efferocytic and subsequent effero-metabolism processes can be carried out by professional and non-professional phagocytes. Defective removal or inadequate processing of apoptotic cells leads to persistent unresolved inflammation, which may promote insidious pathologies including scarring, fibrosis, and eventual organ failure. In this manuscript, the well-established role of endothelial activation and leukocyte extravasation, as classical vascular targets of the 'inflammation pharmacology', will be briefly reviewed. The main focus of this work is to bring attention to a less explored aspect of the 'resolution pharmacology', aimed at tackling defective efferocytosis and inefficient effero-metabolism, as key targeted mechanisms to prevent or pre-empt vascular complications in cardio-metabolic diseases. Despite the use of gold standard lipid-lowering drugs or glucose-lowering drugs, none of them are able to tackle the so called residual inflammatory risk and/or the metabolic memory. In this review, the development of synthetic mimetics of endogenous mediators of inflammation is highlighted. Such molecules finely tune key components across the whole inflammatory process, amongst various other novel therapeutic paradigms that have emerged over the past decade, including anti-inflammatory therapy. More specifically, FPR2-agonists in general, and Lipoxin analogues in particular, greatly enhance the reprogramming and cross-talk between classical and non-classical innate immune cells, thus inducing both termination of the pro-inflammatory state as well as promoting the subsequent resolving phase, which represent pivotal mechanisms in inflammatory cardio-metabolic diseases.

Molecular Characteristics of Cell Pyroptosis and Its Inhibitors: A Review of Activation, Regulation, and Inhibitors

Pyroptosis is an active and ordered form of programmed cell death. The signaling pathways of pyroptosis are mainly divided into canonical pathways mediated by caspase-1 and noncanonical pathways mediated by caspase-11. Cell pyroptosis is characterized by the activation of inflammatory caspases (mainly caspase-1, 4, 5, 11) and cleavage of various members of the Gasdermin family to form membrane perforation components, leading to cell membrane rupture, inflammatory mediators release, and cell death. Moderate pyroptosis is an innate immune response that fights against infection and plays an important role in the occurrence and development of the normal function of the immune system. However, excessive pyroptosis occurs and leads to immune disorders in many pathological conditions. Based on canonical pathways, research on pyroptosis regulation has demonstrated several pyroptotic inhibitors, including small-molecule drugs, natural products, and formulations of traditional Chinese medicines. In this paper, we review the characteristics and molecular mechanisms of pyroptosis, summarize inhibitors of pyroptosis, and propound that herbal medicines should be a focus on the research and development for pyroptosis blockers.

Cryo-EM structures of perforin-2 in isolation and assembled on a membrane suggest a mechanism for pore formation

Perforin-2 (PFN2, MPEG1) is a key pore-forming protein in mammalian innate immunity restricting intracellular bacteria proliferation. It forms a membrane-bound pre-pore complex that converts to a pore-forming structure upon acidification; but its mechanism of conformational transition has been debated. Here we used cryo-electron microscopy, tomography and subtomogram averaging to determine structures of PFN2 in pre-pore and pore conformations in isolation and bound to liposomes. In isolation and upon acidification, the pre-assembled complete pre-pore rings convert to pores in both flat ring and twisted conformations. On membranes, in situ assembled PFN2 pre-pores display various degrees of completeness; whereas PFN2 pores are mainly incomplete arc structures that follow the same subunit packing arrangements as found in isolation. Both assemblies on membranes use their P2 β-hairpin for binding to the lipid membrane surface. Overall, these structural snapshots suggest a molecular mechanism for PFN2 pre-pore to pore transition on a targeted membrane, potentially using the twisted pore as an intermediate or alternative state to the flat conformation, with the capacity to cause bilayer distortion during membrane insertion.