The mechanism of NLRP3 inflammasome activation and its pharmacological inhibitors

NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) is a cytosolic pattern recognition receptor (PRR) that recognizes multiple pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Once activated, NLRP3 initiates the inflammasome assembly together with the adaptor ASC and the effector caspase-1, leading to caspase-1 activation and subsequent cleavage of IL-1β and IL-18. Aberrant NLRP3 inflammasome activation is linked with the pathogenesis of multiple inflammatory diseases, such as cryopyrin-associated periodic syndromes, type 2 diabetes, non-alcoholic steatohepatitis, gout, and neurodegenerative diseases. Thus, NLRP3 is an important therapeutic target, and researchers are putting a lot of effort into developing its inhibitors. The review summarizes the latest advances in the mechanism of NLRP3 inflammasome activation and its pharmacological inhibitors.

CASP4 can be a diagnostic biomarker and correlated with immune infiltrates in gliomas

Background

Gliomas are the most common and invasive malignant tumors that originate in the central nervous system. Currently, the primary treatment modality for gliomas is maximum surgical resection, supplemented by radiotherapy and chemotherapy. However, the long-term survival rate has not signifificantly increased. Pyroptosis is a new form of programmed lytic death that has been recently discovered. Caspase 4 (CASP4) plays a key role in pyroptosis. Many studies have shown that pyroptosis is not only related to inflflammation but is also closely related to the occurrence and development of most tumors. This study aimed to prove that CASP4 has a key role in the mechanism of gliomas.

Methods

We used expression data from The Cancer Genome Atlas and the Chinese Glioma Genome Atlas to explore the relationship between CASP4 expression and glioma prognosis. The differential expression of CASP4 in gliomas and normal tissues was fifirst tested, and then the connection between CASP4 and tumor prognosis was explored. The relationship between CASP4 expression and immune cell infifiltration was also investigated. Finally, the possible pathways were analyzed using Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Gene Set Enrichment Analysis.

Results

CASP4 was highly expressed and associated with a signifificantly lower survival rate in patients with glioma. It could also inflfluence immune cell infifiltration by releasing cytokines.

Conclusion

CASP4 can be a diagnostic biomarker and is a promising therapeutic target for gliomas.

The Therapeutic Potential of Pyroptosis in Melanoma

Pyroptosis is a programmed cell death characterized by the rupture of the plasma membranes and release of cellular content leading to inflammatory reaction. Four cellular mechanisms inducing pyroptosis have been reported thus far, including the (i) caspase 1-mediated canonical, (ii) caspase 4/5/11-mediated non-canonical, (iii) caspase 3/8-mediated and (iv) caspase-independent pathways. Although discovered as a defense mechanism protecting cells from infections of intracellular pathogens, pyroptosis plays roles in tumor initiation, progression and metastasis of tumors, as well as in treatment response to antitumor drugs and, consequently, patient outcome. Pyroptosis induction following antitumor therapies has been reported in several tumor types, including lung, colorectal and gastric cancer, hepatocellular carcinoma and melanoma. This review provides an overview of the cellular pathways of pyroptosis and discusses the therapeutic potential of pyroptosis induction in cancer, particularly in melanoma.

Korean Red Ginseng Saponins Play an Anti-Inflammatory Role by Targeting Caspase-11 Non-Canonical Inflammasome in Macrophages

We previously reported that Korean red ginseng (KRG) exerts an anti-inflammatory role through inhibiting caspase-11 non-canonical inflammasome in macrophages; however, the components responsible for the anti-inflammatory role remained unclear. This study explored the anti-inflammatory activity of the KRG saponin fraction (KRGSF) in caspase-11 non-canonical inflammasome-activated macrophages. KRGSF inhibited pyroptosis, pro-inflammatory cytokine secretion, and inflammatory mediator production in caspase-11 non-canonical inflammasome-activated J774A.1 cells. A mechanism study revealed that KRGSF-induced anti-inflammatory action was mediated via suppressing the proteolytic activation of caspase-11 and gasdermin D (GSDMD) in caspase-11 non-canonical inflammasome-activated J774A.1 cells. Moreover, KRGSF increased the survival of lethal septic mice. Taken together, these results reveal KRGSF-mediated anti-inflammatory action with a novel mechanism, by inhibiting caspase-11 non-canonical inflammasome in macrophages.

Targeting Noncanonical Pyroptosis With a Small Molecular Inhibitor Alleviates Inflammation in the LPS-Induced Keratitis Mouse Model

Purpose

Pyroptosis, a novel proinflammatory programmed cell death, has been implicated in some ocular diseases. Of special note is the noncanonical pyroptosis that has recently been recognized to play a critical role in microbial keratitis. We previously discovered a new potent small molecular pyroptosis inhibitor, J114. In this investigation, we will explore whether J114 is able to inhibit the noncanonical pyroptosis and the underlying mechanism. Then a lipopolysaccharide (LPS)-induced keratitis mouse model will be used to evaluate the therapeutic effect of J114 in vivo.

Methods

In vitro, macrophages originating from humans or mice were stimulated with intracellular LPS to induce noncanonical pyroptosis activation. in vivo, acute keratitis in mouse was induced by LPS intrastromal injection. We verified the protective effect of J114 on noncanonical pyroptosis. Clinical scoring, histological observation, macrophage localization, and quantification of pyroptotic markers in the cornea were used to characterize the therapeutic effects.

Results

J114 substantially inhibited the noncanonical pyroptosis and the release of inflammatory cytokines by suppressing the activation of caspase-4/5/11 and the noncanonical NLRP3 inflammasome through blocking the NLRP3-ASC interaction. in vivo, J114 protected against LPS-induced noncanonical pyroptosis of acute keratitis, as manifested by alleviated clinical manifestations and histological disorders, and relieved inflammatory reactions.

Conclusions

In this study, we found that J114 could efficiently inhibit LPS-induced noncanonical pyroptosis and revealed the underlying mechanism. This compound displayed significant anti-inflammatory activity in the LPS-induced keratitis mouse model. All the findings indicated that J114 could be a potential lead compound for drug development against inflammatory ocular surface diseases.

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.

Solid fuel derived PM2.5 induced oxidative stress and according cytotoxicity in A549 cells: The evidence and potential neutralization by green tea

PM_2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) is a well-known cytotoxic pollutant that capable to induce severe intracellular oxidative stress while the underlying mechanisms remain unclear. Herein, 4 types of PM_2.5 derived from solid fuel burning were selected as stimuli in A549 cells exposure model to evaluate their effects on oxidative stress and inflammatory responses. Although resulting in different responses in cell viability, all PM_2.5 exhibited over 50 % higher oxidative stress than control group, expression as intracellular reactive oxygen species, malondialdehyde and superoxide dismutase levels. The Pearson's correlation results indicated that cations (e.g., Ca²⁺), heavy metals (e.g., Cr and Pb), nPAHs (nitro-polycyclic aromatic hydrocarbons, e.g., 6-nitrochrysene) and oPAHs (oxygenated PAHs, e.g., 9-fluorenone) were the main functioning toxics (r > 0.6). A key finding was the dual-directional regulation function of ECG (epicatechin gallate), that is, it could either increase the low A549 cell viabilities in coal combustion PM_2.5 group or reduce them in charcoal PM_2.5 group (P < 0.05). The dual-directional effects were likely because ECG can activate Nrf2 oxidation signaling pathway then inhibit the inflammatory signaling pathway NF-κB accordingly. Therefore, evidences indicated cytotoxicity of solid fuel derived PM_2.5 were mainly caused by oxidative stress, which was proved to be reversed by green tea, providing a potential therapy method to PM_2.5 and other hazards.

Pyroptosis in Antiviral Immunity

Pyroptosis is a form of lytic, programmed cell death that functions as an innate immune effector mechanism to facilitate host defense against pathogenic microorganisms, including viruses. This type of proinflammatory cell death is orchestrated by proteolytic activation of human or mouse caspase-1, mouse caspase-11 and human caspase-4 and caspase-5 in response to infectious and inflammatory stimuli. Induction of pyroptosis requires either a canonical inflammasome responsible for caspase-1 activation or a noncanonical complex composed of caspase-11 in mice or caspase-4 or caspase-5 in humans. Recent studies have identified the pore-forming protein gasdermin D, a substrate of these inflammatory caspases, as an executioner of pyroptosis. The membrane pores formed by gasdermin D facilitate release of proinflammatory cytokines IL-1β and IL-18 and consequent biologic effects of these cytokines together with other released components. Pyroptosis, like other forms of programmed cell death, helps eliminate infected cells and thereby restricts the replicative niche, undermining survival and proliferation of intracellular pathogens. This includes viruses as well as bacteria, where ample evidence supports a critical role for inflammasome effector functions and cell death in host defense. Viruses have evolved their own mechanisms to modulate inflammasome signaling and pyroptosis. Here, we review the current literature regarding the role of pyroptosis in antiviral immune responses.

Similarities and differences of chemical compositions and physical and functional properties of adjuvant system 01 and army liposome formulation with QS21

A vaccine adjuvant known as Adjuvant System 01 (AS01) consists of liposomes containing a mixture of natural congeners of monophosphoryl lipid A (MPL^®) obtained from bacterial lipopolysaccharide, and a tree saponin known as QS21. Two vaccines containing AS01 as the adjuvant have been licensed, including a malaria vaccine (Mosquirix^®) approved by World Health. Organization and European Medicines Agency for use in sub-Saharan Africa, and a shingles vaccine (Shingrix^®) approved by the U.S. Food and Drug Administration. The success of the AS01 vaccine adjuvant has led to the development of another liposomal vaccine adjuvant, referred to as Army Liposome Formulation with QS21 (ALFQ). Like AS01, ALFQ consists of liposomes containing monophosphoryl lipid A (as a synthetic molecule known as 3D-PHAD^®) and QS21 as adjuvant constituents, and the polar headgroups of the liposomes of AS01 and ALFQ are similar. We compare here AS01 with ALFQ with respect to their similar and different liposomal chemical structures and physical characteristics with a goal of projecting some of the likely mechanisms of safety, side effects, and mechanisms of adjuvanticity. We hypothesize that some of the side effects exhibited in humans after injection of liposome-based vaccines might be caused by free fatty acid and lysophospholipid released by enzymatic attack of liposomal phospholipid by phospholipase A₂ at the injection site or systemically after injection.

TLR4 activation by lysozyme induces pain without inflammation

Mostly, pain has been studied in association with inflammation, until recent studies which indicate that during bacterial infections, pain mechanisms could be independent of the inflammation. Chronic pain can sustain long after the healing from the injury, even in the absence of any visible inflammation. However, the mechanism behind this is not known. We tested inflammation in lysozyme-injected mice foot paw. Interestingly, we observed no inflammation in mice foot paw. Yet, lysozyme injections induced pain in these mice. Lysozyme induces pain in a TLR4-dependent manner and TLR4 activation by its ligands such as LPS leads to inflammatory response. We compared the intracellular signaling of MyD88 and TRIF pathways upon TLR4 activation by lysozyme and LPS to understand the underlying mechanism behind the absence of an inflammatory response upon lysozyme treatment. We observed a TLR4 induced selective TRIF and not MyD88 pathway activation upon lysozyme treatment. This is unlike any other previously known endogenous TLR4 activators. A selective activation of TRIF pathway by lysozyme induces weak inflammatory cytokine response devoid of inflammation. However, lysozyme activates glutamate oxaloacetate transaminase-2 (GOT2) in neurons in a TRIF-dependent manner, resulting in enhanced glutamate response. We propose that this enhanced glutaminergic response could lead to neuronal activation resulting in pain sensation upon lysozyme injections. Collectively we identify that TLR4 activation by lysozyme can induce pain in absence of a significant inflammation. Also, unlike other known TLR4 endogenous activators, lysozyme does not activate MyD88 signaling. These findings uncover a mechanism of selective activation of TRIF pathway by TLR4. This selective TRIF activation induces pain with negligible inflammation, constituting a chronic pain homeostatic mechanism.

Time-Lapse Imaging of Inflammasome-Dependent Cell Death and Extrusion in Enteroid-Derived Intestinal Epithelial Monolayers

Inflammasome-induced cell death is an epithelium-intrinsic innate immune response to pathogenic onslaught on epithelial barriers, caused by invasive microbes such as Salmonella Typhimurium (S.Tm). Pattern recognition receptors detect pathogen- or damage-associated ligands and elicit inflammasome formation. This ultimately restricts bacterial loads within the epithelium, limits breaching of the barrier, and prevents detrimental inflammatory tissue damage. Pathogen restriction is mediated via the specific extrusion of dying intestinal epithelial cells (IECs) from the epithelial tissue, accompanied by membrane permeabilization at some stage of the process. These inflammasome-dependent mechanisms can be studied in real time in intestinal epithelial organoids (enteroids), which allow imaging at high temporal and spatial resolution in a stable focal plane when seeded as 2D monolayers. The protocols described here involve the establishment of murine and human enteroid-derived monolayers, as well as time-lapse imaging of IEC extrusion and membrane permeabilization following inflammasome activation by S.Tm infection. The protocols can be adapted to also study other pathogenic insults or combined with genetic and pharmacological manipulation of the involved pathways.

Cancer-associated pyroptosis: A new license to kill tumor

Pyroptosis is a programmed necrotic cell death mediated by pore-forming Gasdermin (GSDM) proteins. After being unleashed from the C-terminal auto-inhibitory domains by proteolytic cleavage, the N-terminal domains of GSDMs oligomerize and perforate on the plasma membrane to induce cytolytic pyroptosis, releasing immune mediators and alarming the immune system. Upon infection or danger signal perception, GSDMD that functions downstream of the inflammasome, a supramolecular complex for inflammatory caspase activation, is cleaved and activated by inflammasome-activated caspase-1/4/5/11 in immune cells and epithelial cells to trigger pyroptosis and exert anti-infection protection. Unlike this inflammasome-activated pyroptosis (IAP), recent studies also suggest an emerging role of cancer-associated pyroptosis (CAP), mediated by other GSDMs in cancer cells, in provoking anti-tumor immunity. IAP and CAP share common features like cell membrane rupture but also differ in occurrence sites, activating mechanisms, secreting cytokines and biological outcomes. Here we review the most recent knowledge of cancer-associated pyroptosis and present a promising avenue for developing therapeutic interventions to enhance anti-tumor immunity for cancer treatment.

Emerging mechanisms and functions of inflammasome complexes in teleost fish

Inflammasomes are multiprotein complexes, which are assembled in response to a diverse range of exogenous pathogens and endogenous danger signals, leading to produce pro-inflammatory cytokines and induce pyroptotic cell death. Inflammasome components have been identified in teleost fish. Previous reviews have highlighted the conservation of inflammasome components in evolution, inflammasome function in zebrafish infectious and non-infectious models, and the mechanism that induce pyroptosis in fish. The activation of inflammasome involves the canonical and noncanonical pathways, which can play critical roles in the control of various inflammatory and metabolic diseases. The canonical inflammasomes activate caspase-1, and their signaling is initiated by cytosolic pattern recognition receptors. However the noncanonical inflammasomes activate inflammatory caspase upon sensing of cytosolic lipopolysaccharide from Gram-negative bacteria. In this review, we summarize the mechanisms of activation of canonical and noncanonical inflammasomes in teleost fish, with a particular focus on inflammasome complexes in response to bacterial infection. Furthermore, the functions of inflammasome-associated effectors, specific regulatory mechanisms of teleost inflammasomes and functional roles of inflammasomes in innate immune responses are also reviewed. The knowledge of inflammasome activation and pathogen clearance in teleost fish will shed new light on new molecular targets for treatment of inflammatory and infectious diseases.

Noncanonical NLRP3 Inflammasome Activation: Standard Protocols

The canonical activation of multimeric inflammasomes usually occurs through caspase-1 activation, and it is characterized by the presence of extracellular IL-1β and IL-18 or measuring danger signal proteins, such as HMGB1 using enzyme-linked immunosorbent assay (ELISA) or Western blots; these assays differentiate non-cleaved and cleaved forms of these two cytokines (the cleaved form is the mature and active form). Similar techniques can be used to assess noncanonical inflammasome activation. Real-time PCR can measure the relative mRNA expression for a specific gene, whereas Western blots or immunocytochemistry can detect the presence of proteins by binding of specific antibodies to their antigens in biological samples. Moreover, noncanonical inflammasome activation can be evaluated through the cleavage of the amino and the carboxy terminals of one important component, gasdermin D (GSDMD), whose cleavage induces its pyroptotic activity. Thus, the analysis of cleaved GSDMD is an ideal pathway to study the noncanonical inflammasome. ELISA and immunoblot can be performed on cell culture supernatants or cell extracts.

Programmed Necrosis in Host Defense

Host control over infectious disease relies on the ability of cells in multicellular organisms to detect and defend against pathogens to prevent disease. Evolution affords mammals with a wide variety of independent immune mechanisms to control or eliminate invading infectious agents. Many pathogens acquire functions to deflect these immune mechanisms and promote infection. Following successful invasion of a host, cell autonomous signaling pathways drive the production of inflammatory cytokines, deployment of restriction factors and induction of cell death. Combined, these innate immune mechanisms attract dendritic cells, neutrophils and macrophages as well as innate lymphoid cells such as natural killer cells that all help control infection. Eventually, the development of adaptive pathogen-specific immunity clears infection and provides immune memory of the encounter. For obligate intracellular pathogens such as viruses, diverse cell death pathways make a pivotal contribution to early control by eliminating host cells before progeny are produced. Pro-apoptotic caspase-8 activity (along with caspase-10 in humans) executes extrinsic apoptosis, a nonlytic form of cell death triggered by TNF family death receptors (DRs). Over the past two decades, alternate extrinsic apoptosis and necroptosis outcomes have been described. Programmed necrosis, or necroptosis, occurs when receptor interacting protein kinase 3 (RIPK3) activates mixed lineage kinase-like (MLKL), causing cell leakage. Thus, activation of DRs, toll-like receptors (TLRs) or pathogen sensor Z-nucleic acid binding protein 1 (ZBP1) initiates apoptosis as well as necroptosis if not blocked by virus-encoded inhibitors. Mammalian cell death pathways are blocked by herpesvirus- and poxvirus-encoded cell death suppressors. Growing evidence has revealed the importance of Z-nucleic acid sensor, ZBP1, in the cell autonomous recognition of both DNA and RNA virus infection. This volume will explore the detente between viruses and cells to manage death machinery and avoid elimination to support dissemination within the host animal.

Molecular Mechanisms of Pyroptosis

Pyroptosis is a regulated form of cell death that leads to inflammation and plays a role in many different diseases. Pyroptosis was initially defined by the dependence on caspase-1, a protease which is activated by innate immune signaling complexes called inflammasomes. Caspase-1 cleaves the protein gasdermin D, releasing the N-terminal pore-forming domain, which inserts into the plasma membrane. Recent studies have revealed that other gasdermin family members form plasma membrane pores, leading to lytic cell death, and the definition of pyroptosis was revised to gasdermin-dependent cell death. In this review, we discuss how the use of the term pyroptosis has changed over time, as well as currently understood molecular mechanisms leading to pyroptosis and functional consequences of this form of regulated cell death.

Therapeutic Targeting of TLR4 for Inflammation, Infection, and Cancer: A Perspective for Disaccharide Lipid A Mimetics

The Toll-like receptor 4 (TLR4) signaling pathway plays a central role in the prompt defense against infectious challenge and provides immediate response to Gram-negative bacterial infection. The TLR4/MD-2 complex can sense and respond to various pathogen-associated molecular patterns (PAMPs) with bacterial lipopolysaccharide (LPS) being the most potent and the most frequently occurring activator of the TLR4-mediated inflammation. TLR4 is believed to be both a friend and foe since improperly regulated TLR4 signaling can result in the overactivation of immune responses leading to sepsis, acute lung injury, or pathologic chronic inflammation involved in cancer and autoimmune disease. TLR4 is also considered a legitimate target for vaccine adjuvant development since its activation can boost the adaptive immune responses. The dual action of the TLR4 complex justifies the efforts in the development of both TLR4 antagonists as antisepsis drug candidates or remedies for chronic inflammatory diseases and TLR4 agonists as vaccine adjuvants or immunotherapeutics. In this review, we provide a brief overview of the biochemical evidences for possible pharmacologic applications of TLR4 ligands as therapeutics and report our systematic studies on the design, synthesis, and immunobiological evaluation of carbohydrate-based TLR4 antagonists with nanomolar affinity for MD-2 as well as disaccharide-based TLR4 agonists with picomolar affinity for the TLR4/MD-2 complex.

An Elemental Diet Enriched in Amino Acids Alters the Gut Microbial Community and Prevents Colonic Mucus Degradation in Mice with Colitis

The role of dietary amino acids or intact proteins in the progression of colitis remains controversial, and the mechanism involving gut microbes is unclear. Here, we investigated the effects of an elemental diet (ED) enriched in amino acids and a polymeric diet enriched in intact protein on the pathogenesis of dextran sulfate sodium (DSS)-induced colitis in mice. Our results showed that the ED induced remission of colitis in mice. Notably, ED treatment reduced the abundance of the mucolytic bacteria Akkermansia and Bacteroides, which was attributed to decreased colonic protein fermentation. Consistently, the activities of mucolytic enzymes were decreased, leading to protection against mucus layer degradation and microbial invasion. Fecal microbiota transplantation from ED-fed mice reshaped microbial ecology and alleviated intestinal inflammation in recipient mice. The ED failed to induce remission of colitis in pseudogermfree mice. Together, our results demonstrate the critical role of the gut microbiota in the prevention of colitis by an ED. IMPORTANCE The prevalence of inflammatory bowel disease is rapidly increasing and has become a global burden. Several specific amino acids have been shown to benefit mucosal healing and colitis remission. However, the role of amino acids or intact proteins in diets and enteral nutrition formulas is controversial, and the mechanisms involving gut microbes remain unclear. In this study, we investigated the effects of an elemental diet (ED) enriched in amino acids and a polymeric diet enriched in intact protein on the pathogenesis of colitis in mice. The underlying mechanisms were explored by utilizing fecal microbiota transplantation and pseudogermfree mice. ED treatment reduced the abundance of mucolytic bacteria, thereby protecting the mucus layer from microbial invasion and degradation. For the first time, we convincingly demonstrated the critical role of gut microbiota in the effects of the ED. This study may provide new insights into the gut microbiota-diet interaction and its role in human health.

Molecular mechanisms of neuronal death in brain injury after subarachnoid hemorrhage

Subarachnoid haemorrhage (SAH) is a common cerebrovascular disease with high disability and mortality rates worldwide. The pathophysiological mechanisms involved in an aneurysm rupture in SAH are complex and can be divided into early brain injury and delayed brain injury. The initial mechanical insult results in brain tissue and vascular disruption with hemorrhages and neuronal necrosis. Following this, the secondary injury results in diffused cerebral damage in the peri-core area. However, the molecular mechanisms of neuronal death following an aneurysmal SAH are complex and currently unclear. Furthermore, multiple cell death pathways are stimulated during the pathogenesis of brain damage. Notably, particular attention should be devoted to necrosis, apoptosis, autophagy, necroptosis, pyroptosis and ferroptosis. Thus, this review discussed the mechanism of neuronal death and its influence on brain injury after SAH.

Targeting cell death pathways for cancer therapy: recent developments in necroptosis, pyroptosis, ferroptosis, and cuproptosis research

Many types of human cells self-destruct to maintain biological homeostasis and defend the body against pathogenic substances. This process, called regulated cell death (RCD), is important for various biological activities, including the clearance of aberrant cells. Thus, RCD pathways represented by apoptosis have increased in importance as a target for the development of cancer medications in recent years. However, because tumor cells show avoidance to apoptosis, which causes treatment resistance and recurrence, numerous studies have been devoted to alternative cancer cell mortality processes, namely necroptosis, pyroptosis, ferroptosis, and cuproptosis; these RCD modalities have been extensively studied and shown to be crucial to cancer therapy effectiveness. Furthermore, evidence suggests that tumor cells undergoing regulated death may alter the immunogenicity of the tumor microenvironment (TME) to some extent, rendering it more suitable for inhibiting cancer progression and metastasis. In addition, other types of cells and components in the TME undergo the abovementioned forms of death and induce immune attacks on tumor cells, resulting in enhanced antitumor responses. Hence, this review discusses the molecular processes and features of necroptosis, pyroptosis, ferroptosis, and cuproptosis and the effects of these novel RCD modalities on tumor cell proliferation and cancer metastasis. Importantly, it introduces the complex effects of novel forms of tumor cell death on the TME and the regulated death of other cells in the TME that affect tumor biology. It also summarizes the potential agents and nanoparticles that induce or inhibit novel RCD pathways and their therapeutic effects on cancer based on evidence from in vivo and in vitro studies and reports clinical trials in which RCD inducers have been evaluated as treatments for cancer patients. Lastly, we also summarized the impact of modulating the RCD processes on cancer drug resistance and the advantages of adding RCD modulators to cancer treatment over conventional treatments.

Modulation of vascular endothelial inflammatory response by proprotein convertase subtilisin-kexin type 9

BACKGROUND AND AIMS

Endotoxins carried within LDL are cleared from the circulation via hepatic LDL receptor (LDLR)-mediated endocytosis. Proprotein convertase subtilisin-kexin type 9 (PCSK9) reduces this clearance by down-regulating LDLR density on hepatocytes. In addition to hepatocytes, vascular endothelial cells also express receptor targets of PCSK9, including LDLR. Therefore, we hypothesized that PCSK9 may regulate vascular endothelial cell uptake of lipopolysaccharide (LPS) and alter the vascular endothelial cell inflammatory response.

METHODS AND RESULTS

We found that LPS is internalized by human umbilical vein vascular endothelial cells (HUVECs) and LPS uptake dose-dependently increased with increasing LDL concentration. Intracellular LPS co-localized with LDL. PCSK9 and, separately, blocking antibodies against LDLR, dose-dependently decreased the vascular endothelial cell uptake of LPS and, furthermore, inhibition of endocytosis using Dynasore blocked LPS uptake. In contrast, blocking antibodies against TLR4 did not alter LPS uptake. PCSK9 decreased the LPS-induced proinflammatory response (IL-6 and IL-8 gene expression and protein secretion, and VCAM-1/ICAM-1 expression) in vascular endothelial cells. In addition, a decrease in PCSK9 and increase in LDLR, mediated by triciribine or siPCSK9, increased LPS uptake and the LPS-induced proinflammatory response. Similar results were also found in aortic vascular tissue from Pcsk9^-/- mice after LPS injection.

CONCLUSIONS

Our data suggest that, similar to PCSK9 treatment in hepatocytes, PCSK9 reduces vascular endothelial cell uptake of LPS via LDLR-mediated endocytosis. Consequently, PCSK9 decreases the LPS-induced proinflammatory response in vascular endothelial cells. These results raise the possibility that PCSK9 inhibition may have additional effects on vascular endothelial inflammation via this alternative pathway, beyond the known effects of PCSK9 inhibition on LDL lowering and hepatic endotoxin clearance.

Research and development of Chinese anti-COVID-19 drugs

The outbreak and spread of coronavirus disease 2019 (COVID-19) highlighted the importance and urgency of the research and development of therapeutic drugs. Very early into the COVID-19 pandemic, China has begun developing drugs, with some notable progress. Herein, we summarizes the anti-COVID-19 drugs and promising drug candidates originally developed and researched in China. Furthermore, we discussed the developmental prospects, mechanisms of action, and advantages and disadvantages of the anti-COVID-19 drugs in development, with the aim to contribute to the rational use of drugs in COVID-19 treatment and more effective development of new drugs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the variants. Neutralizing antibody is an effective approach to overcome COVID-19. However, drug resistance induced by rapid virus mutation will likely to challenge neutralizing antibodies. Taking into account current epidemic trends, small molecule drugs have a crucial role in fighting COVID-19 due to their significant advantage of convenient administration and affordable and broad-spectrum. Traditional Chinese medicines, including natural products and traditional Chinese medicine prescriptions, contribute to the treatment of COVID-19 due to their unique mechanism of action. Currently, the research and development of Chinese anti-COVID-19 drugs have led to some promising achievements, thus prompting us to expect even more rapidly available solutions.

Caspase mechanisms in the regulation of inflammation

Regulated cell death is defined as genetically encoded pathways that lead towards the demise of cells. In mammals, cell demise can be either inflammatory or non-inflammatory, depending on whether the mechanism of death results in cell rupture or not. Inflammatory cell death can lead towards acute and chronic disease. Therefore, it becomes important to distinguish the mechanisms that result in these different inflammatory cell death outcomes. Apoptosis is a non-inflammatory form of cell death where cells resist rupture. In contrast, pyroptosis and necroptosis are inflammatory forms of cell death principally because of release of pro-inflammatory mediators from cells undergoing lysis. This review focusses on the mechanisms of these different cell death outcomes with specific emphasis on the caspase family of proteolytic enzymes.

Protective effects of S100A8 on sepsis mortality: Links to sepsis risk in obesity and diabetes

Obesity and diabetes are independent risk factors for death during sepsis. S100A8, an alarmin, is related to inflammation, obesity, and diabetes. Here, we examine the role of S100A8 in sepsis of obesity and diabetes models. Injection of S100A8 prolongs the survival of septic mice induced by lethal endotoxemia, Escherichia coli injection, or cecal ligation and puncture. S100A8 decrease the LPS-induced expression of proinflammatory cytokines in peritoneal macrophages by inhibiting TLR4-mediated signals in an autocrine manner. db/db, ob/ob, and western diet-fed mice demonstrate reduced upregulation of S100A8 induced by LPS treatment in both serum and peritoneal cells. These mice also show shorter survival after LPS injection, and S100A8 supplementation prolonged the survival. While myelomonocytic cells-specific S100A8-deficient mice (Lyz2 ^cre :S100A8 ^{floxed/floxed} ) exhibit shorter survival after LPS treatment, S100A8 supplementation prolonged the survival. Thus, myelomonocytic cell-derived S100A8 is crucial for protection from sepsis, and S100A8 supplementation improves sepsis, particularly in mice with obesity and diabetes.

Activation of IL1 signaling molecules by Kaposi's sarcoma-associated herpesvirus

Objective

Kaposi's Sarcoma-associated Herpesvirus (KSHV) is the etiologic agent of several human cancers, including Kaposi's sarcoma (KS) and Primary effusion lymphoma (PEL), which are usually seen in immunocompromised patients while lack of effective therapeutic options. Interleukin1 (IL1) family is a major mediator for inflammation response and has functional role in both innate and adaptive immunity. In contrast to the well-studied IL1 molecules, the activation and functional role of IL1 receptor/co-receptor and other related ligands, such as the IL1 receptor accessory protein (IL1RAP), in KSHV pathogenesis and tumorigenesis remain almost unknown.

Methods

In the current study, a series of KSHV negative and positive primary or tumor cells, as well as AIDS-KS tumor samples from cohort HIV+ patients were used to compare and determine the activation status of IL1 signaling molecules, and their functional roles in KSHV pathogenesis.

Results

We reported the high activation of multiple IL1 signaling molecules, including IL1, IL36, IL1R1, IL1RAP and IRAKs, during KSHV latent and lytic stages, as well as in clinical samples from patients with KSHV-related malignancies. Directly targeting these molecules especially IL1R1 and IL1RAP significantly impaired the survival and growth of KSHV+ tumor cells, as well as their colony formation on 3-D culture.

Conclusion

Our data indicate the importance of IL1 signaling molecules in KSHV pathogenesis and tumorigenesis, which may represent attractive therapeutic targets against these virus-associated diseases.

The role of NLRP3 inflammasome in inflammation-related skeletal muscle atrophy

Skeletal muscle atrophy is a common complication in survivors of sepsis, which affects the respiratory and motor functions of patients, thus severely impacting their quality of life and long-term survival. Although several advances have been made in investigations on the pathogenetic mechanism of sepsis-induced skeletal muscle atrophy, the underlying mechanisms remain unclear. Findings from recent studies suggest that the nucleotide-binding and oligomerisation domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, a regulator of inflammation, may be crucial in the development of skeletal muscle atrophy. NLRP3 inhibitors contribute to the inhibition of catabolic processes, skeletal muscle atrophy and cachexia-induced inflammation. Here, we review the mechanisms by which NLRP3 mediates these responses and analyse how NLRP3 affects muscle wasting during inflammation.

Potential of gut microbiota for lipopolysaccharide biosynthesis in European women with type 2 diabetes based on metagenome

The abnormal accumulation of lipopolysaccharide (LPS) plays a crucial role in promoting type 2 diabetes (T2D). However, the capability of the gut microbiota to produce LPS in patients with T2D is still unclear, and evidence characterizing the patterns of gut microbiota with LPS productivity remains rare. This study aimed to uncover the profiles of LPS-biosynthesis-related enzymes and pathways, and explore the potential of LPS-producing gut microbiota in T2D. The gut metagenomic sequencing data from a European female cohort with normal glucose tolerance or untreated T2D were analyzed in this study. The sequence search revealed that the relative abundance of the critical enzymes responsible for LPS biosynthesis was significantly high in patients with T2D, especially for N-acetylglucosamine deacetylase, 3-deoxy-D-manno-octulosonic-acid transferase, and lauroyl-Kdo2-lipid IVA myristoyltransferase. The functional analysis indicated that a majority of pathways involved in LPS biosynthesis were augmented in patients with T2D. A total of 1,173 species from 335 genera containing the gene sequences of LPS enzymes, including LpxA/B/C/D/H/K/L/M and/or WaaA, coexisted in controls and patients with T2D. Critical taxonomies with discriminative fecal abundance between groups were revealed, which exhibited different associations with enzymes. Moreover, the identified gut microbial markers had correlations with LPS enzymes and were subsequently associated with microbial pathways. The present findings delineated the potential capability of gut microbiota toward LPS biosynthesis in European women and highlighted a gut microbiota−based mechanistic link between the disturbance in LPS biosynthesis and T2D. The restoration of LPS levels through gut microbiota manipulation might offer potential approaches for preventing and treating T2D.

Lipopolysaccharide detection by the innate immune system may be an uncommon defence strategy used in nature

Since the publication of the Janeway's Pattern Recognition hypothesis in 1989, study of pathogen-associated molecular patterns (PAMPs) and their immuno-stimulatory activities has accelerated. Most studies in this area have been conducted in model organisms, which leaves many open questions about the universality of PAMP biology across living systems. Mammals have evolved multiple proteins that operate as receptors for the PAMP lipopolysaccharide (LPS) from Gram-negative bacteria, but LPS is not immuno-stimulatory in all eukaryotes. In this review, we examine the history of LPS as a PAMP in mammals, recent data on LPS structure and its ability to activate mammalian innate immune receptors, and how these activities compare across commonly studied eukaryotes. We discuss why LPS may have evolved to be immuno-stimulatory in some eukaryotes but not others and propose two hypotheses about the evolution of PAMP structure based on the ecology and environmental context of the organism in question. Understanding PAMP structures and stimulatory mechanisms across multi-cellular life will provide insights into the evolutionary origins of innate immunity and may lead to the discovery of new PAMP variations of scientific and therapeutic interest.

A neutrophil-B-cell axis impacts tissue damage control in a mouse model of intraabdominal bacterial infection via Cxcr4

Sepsis is a life-threatening condition characterized by uncontrolled systemic inflammation and coagulation, leading to multiorgan failure. Therapeutic options to prevent sepsis-associated immunopathology remain scarce. Here, we established a mouse model of long-lasting disease tolerance during severe sepsis, manifested by diminished immunothrombosis and organ damage in spite of a high pathogen burden. We found that both neutrophils and B cells emerged as key regulators of tissue integrity. Enduring changes in the transcriptional profile of neutrophils include upregulated Cxcr4 expression in protected, tolerant hosts. Neutrophil Cxcr4 upregulation required the presence of B cells, suggesting that B cells promoted disease tolerance by improving tissue damage control via the suppression of neutrophils' tissue-damaging properties. Finally, therapeutic administration of a Cxcr4 agonist successfully promoted tissue damage control and prevented liver damage during sepsis. Our findings highlight the importance of a critical B-cell/neutrophil interaction during sepsis and establish neutrophil Cxcr4 activation as a potential means to promote disease tolerance during sepsis.

p38MAPK guards the integrity of endosomal compartments through regulating necrotic death

Pathogens trigger activation of sensors of the innate immune system that initiate molecular signaling enabling appropriate host defense programs. Although recognition of pathogen-specific moieties or PAMPs by specialized receptors of the immune system is well defined for a great number of pathogens, the mechanisms of sensing of pathogen-induced functional perturbations to the host cell remain poorly understood. Here we show that the disruption of endosomal compartments in macrophages by a bacterium or fully synthetic nanoparticles activates stress-response p38MAPK kinase, which triggers execution of cell death of a necrotic type. p38MAPK-mediated necrosis occurs in cells with a compound homozygous deletion of pyroptosis-inducing caspases-1 and -11, apoptotic caspase-8, and necroptosis-inducing receptor-interacting protein kinase-3 (RIPK3), indicating that all of these principal cell death mediators are dispensable for p38MAPK-induced necrosis in response to endosome rupture. p38MAPK-mediated necrosis is suppressed by the receptor-interacting protein kinase 1, RIPK1, and degradation of RIPK1 sensitizes macrophages to necrotic death. Since pathogen-induced cell death of necrotic types is implicated in host defense against infection, our results indicate that functional perturbations in host cells are sensed as a component of the innate immune system.

Identification of immunomodulatory drugs that inhibit multiple inflammasomes and impair SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) induces mild or asymptomatic COVID-19 in most cases, but some patients develop an excessive inflammatory process that can be fatal. As the NLRP3 inflammasome and additional inflammasomes are implicated in disease aggravation, drug repositioning to target inflammasomes emerges as a strategy to treat COVID-19. Here, we performed a high-throughput screening using a 2560 small-molecule compound library and identified FDA-approved drugs that function as pan-inflammasome inhibitors. Our best hit, niclosamide (NIC), effectively inhibits both inflammasome activation and SARS-CoV-2 replication. Mechanistically, induction of autophagy by NIC partially accounts for inhibition of NLRP3 and AIM2 inflammasomes, but NIC-mediated inhibition of NAIP/NLRC4 inflammasome are autophagy independent. NIC potently inhibited inflammasome activation in human monocytes infected in vitro, in PBMCs from patients with COVID-19, and in vivo in a mouse model of SARS-CoV-2 infection. This study provides relevant information regarding the immunomodulatory functions of this promising drug for COVID-19 treatment.

Retrovirus-derived RTL5 and RTL6 genes are novel constituents of the innate immune system in the eutherian brain

Retrotransposon Gag-like 5 [RTL5, also known as sushi-ichi-related retrotransposon homolog 8 (SIRH8)] and RTL6 (also known as SIRH3) are eutherian-specific genes presumably derived from a retrovirus and phylogenetically related to each other. They, respectively, encode a strongly acidic and extremely basic protein, and are well conserved among the eutherians. Here, we report that RTL5 and RTL6 are microglial genes with roles in the front line of innate brain immune response. Venus and mCherry knock-in mice exhibited expression of RTL5-mCherry and RTL6-Venus fusion proteins in microglia and appeared as extracellular dots and granules in the central nervous system. These proteins display a rapid response to pathogens such as lipopolysaccharide (LPS), double-stranded (ds) RNA analog and non-methylated CpG DNA, acting both cooperatively and/or independently. Experiments using Rtl6 or Rtl5 knockout mice provided additional evidence that RTL6 and RTL5 act as factors against LPS and dsRNA, respectively, in the brain, providing the first demonstration that retrovirus-derived genes play a role in the eutherian innate immune system. Finally, we propose a model emphasizing the importance of extra-embryonic tissues as the origin site of retrovirus-derived genes. This article has an associated 'The people behind the papers' interview.

A potential new pathway for heparin treatment of sepsis-induced lung injury: inhibition of pulmonary endothelial cell pyroptosis by blocking hMGB1-LPS-induced caspase-11 activation

Sepsis is a significant cause of mortality in critically ill patients. Acute lung injury (ALI) is a leading cause of death in these patients. Endothelial cells exposed to the bacterial endotoxin lipopolysaccharide (LPS) can progress into pyroptosis, a programmed lysis of cell death triggered by inflammatory caspases. It is characterized by lytic cell death induced by the binding of intracellular LPS to caspases 4/5 in human cells and caspase-11 in mouse cells. In mice,caspase-11-dependent pyroptosis plays an important role in endotoxemia. HMGB1 released into the plasma binds to LPS and is internalized into lysosomes in endothelial cells via the advanced glycation end product receptor. In the acidic lysosomal environment, HMGB1 permeates the phospholipid bilayer, which is followed by the leakage of LPS into the cytoplasm and the activation of caspase-11. Heparin is an anticoagulant widely applied in the treatment of thrombotic disease. Previous studies have found that heparin could block caspase-11-dependent inflammatory reactions, decrease sepsis-related mortality, and reduce ALI, independent of its anticoagulant activity. Heparin or modified heparin with no anticoagulant property could inhibit the alarmin HMGB1-LPS interactions, minimize LPS entry into the cytoplasm, and thus blocking caspase-11 activation. Heparin has been studied in septic ALI, but the regulatory mechanism of pulmonary endothelial cell pyroptosis is still unclear. In this paper, we discuss the potential novel role of heparin in the treatment of septic ALI from the unique mechanism of pulmonary endothelial cell pyroptosis.

Pyroptosis and Its Role in the Modulation of Cancer Progression and Antitumor Immunity

Pyroptosis is a type of programmed cell death (PCD) accompanied by an inflammatory reaction and the rupture of a membrane. Pyroptosis is divided into a canonical pathway triggered by caspase-1, and a non-canonical pathway independent of caspase-1. More and more pyroptosis-related participants, pathways, and regulatory mechanisms have been exploited in recent years. Pyroptosis plays crucial roles in the initiation, progression, and metastasis of cancer and it affects the immunotherapeutic outcome by influencing immune cell infiltration as well. Extensive studies are required to elucidate the molecular mechanisms between pyroptosis and cancer. In this review, we introduce the discovery history of pyroptosis, delineate the signaling pathways of pyroptosis, and then make comparisons between pyroptosis and other types of PCD. Finally, we provide an overview of pyroptosis in different cancer types. With the progression in the field of pyroptosis, new therapeutic targets and strategies can be explored to combat cancer.

Microglial pyroptosis: Therapeutic target in secondary brain injury following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a major cerebrovascular illness that causes substantial neurological sequelae and dysfunction caused by secondary brain injury (SBI), and there are no effective therapies to mitigate the disability. Microglia, the brain-resident macrophage, participates in the primary inflammatory response, and activation of microglia to an M1-like phenotype largely takes place in the acute phase following ICH. A growing body of research suggests that the pathophysiology of SBI after ICH is mediated by an inflammatory response mediated by microglial-pyroptotic inflammasomes, while inhibiting the activation of microglial pyroptosis could suppress the inflammatory cascade reaction, thus attenuating the brain injury after ICH. Pyroptosis is characterized by rapid plasma membrane disruption, followed by the release of cellular contents and pro-inflammatory mediators. In this review, we outline the molecular mechanism of microglial pyroptosis and summarize the up-to-date evidence of its involvement in the pathological process of ICH, and highlight microglial pyroptosis-targeted strategies that have the potential to cure intracerebral hemorrhage. This review contributes to a better understanding of the function of microglial pyroptosis in ICH and assesses it as a possible therapeutic target.

Does Pyroptosis Play a Role in Inflammasome-Related Disorders?

Inflammasomes are multiprotein complexes orchestrating intracellular recognition of endogenous and exogenous stimuli, cellular homeostasis, and cell death. Upon sensing of certain stimuli, inflammasomes typically activate inflammatory caspases that promote the production and release of the proinflammatory cytokines IL-1β, IL-1α, and IL-18 and induce a type of inflammatory cell death known as “pyroptosis”. Pyroptosis is an important form of regulated cell death executed by gasdermin proteins, which is largely different from apoptosis and necrosis. Recently, several signaling pathways driving pyroptotic cell death, including canonical and noncanonical inflammasome activation, as well as caspase-3-dependent pathways, have been reported. While much evidence exists that pyroptosis is involved in the development of several inflammatory diseases, its contribution to inflammasome-related disorders (IRDs) has not been fully clarified. This article reviews molecular mechanisms leading to pyroptosis, and attempts to provide evidence for its possible role in inflammasome-related disorders, including NLR pyrin domain containing 3 (NLRP3) inflammasome disease, NLR containing a caspase recruitment domain 4 (NLRC4) inflammasome disease, and pyrin inflammasome disease. Although the specific mechanism needs further investigations, these studies have uncovered the role of pyroptosis in inflammasome-related disorders and may open new avenues for future therapeutic interventions.

GSDMD-mediated pyroptosis in retinal vascular inflammatory diseases: a review

PURPOSE

Pyroptosis is a newly discovered form of programmed pro-inflammatory cell death. The main signaling pathways include the classical scorch death pathway that depends on NLRP3 inflammatory vesicles and other activation caspase-1 and the non-classical scorch death pathway that depends on caspase-4 /5/11. The substrate of all inflammatory caspases is GSDMD; a large number of studies have confirmed that pyroptosis is associated with certain infectious diseases, atherosclerotic diseases, metabolic diseases, and aseptic inflammatory diseases of important organs. In recent years, pyroptosis has been studied partially in the ocular field. So, this article reviews the recent literature intending to help readers understand the main mechanisms of cellular scorch death and the progress of GSDMD-mediated cellular scorch death in retinal vascular inflammatory diseases.

METHOD

A detailed review of the literature related to pyroptosis and inflammatory diseases of the retinal vasculature is presented. The following 6 electronic databases were searched: CNKI, Wanfang, VIP, PubMed, The Cochrane Library, and Embase Databases, and the search period was from the database to May 2022. The main search keywords include "Pyroptosis," " GSDMD," "Retinal Vascular Inflammatory Disease," "Diabetic retinopathy," "Retinal vasculitis." The discovery of pyroptosis, the main molecular mechanisms, key proteins, and their pathogenesis and therapeutic prospects in retinal vasculitis diseases are extensively studied and summarized.

RESULT

The mechanisms of gasdermin D-mediated pyroptosis are elaborated and analyzed, with particular emphasis on their key role and potential in the pathogenesis and treatment of inflammatory retinal vascular lesions.

CONCLUSION

Gasdermin D-mediated pyroptosis is a well-studied form of programmed pro-inflammatory cell death, which has a bidirectional regulatory effect on a variety of immune and inflammatory diseases. The literature reveals that pyroptosis is closely related to the pathogenesis of retinal vascular inflammatory diseases, and it may be an important therapeutic target for diabetic retinopathy and other retinal vasculitis eye diseases in the future.

Targeting innate immunity-driven inflammation in CKD and cardiovascular disease

Mortality among patients with chronic kidney disease (CKD) is largely a consequence of cardiovascular disease (CVD) and is a particular concern given the increasing prevalence of CKD. Sterile inflammation triggered by activation of the innate immune system is an important driver of both CKD and associated CVD. Several endogenous mediators, including lipoproteins, crystals such as silica, urate and cholesterol crystals, or compounds released from dying cells interact with pattern recognition receptors expressed on a variety of different cell types, leading to the release of pro-inflammatory cytokines. Disturbed regulation of the haematopoietic system by damage-associated molecular patterns, or as a consequence of clonal haematopoiesis or trained innate immunity, also contributes to the development of inflammation. In observational and genetic association studies, inflammation is linked to the progression of CKD and cardiovascular events. In 2017, the CANTOS trial of canakinumab provided evidence that inhibiting inflammation driven by NLRP3-IL-1-IL-6-mediated signalling significantly reduced cardiovascular event rates in individuals with and without CKD. Other approaches to target innate immune pathways are now under investigation for their ability to reduce cardiovascular events and slow disease progression among patients with atherosclerosis and stage 3 and 4 CKD. This Review summarizes current understanding of the role of inflammation in the pathogenesis of CKD and its associated CVD, and how this knowledge may translate into novel therapeutics.

Aconitate decarboxylase 1 is a mediator of polymicrobial sepsis

Sepsis is a challenging clinical syndrome caused by a dysregulated host response to infection. Here, we identified an unexpected proseptic activity of aconitate decarboxylase 1 (ACOD1) in monocytes and macrophages. Previous studies have suggested that ACOD1, also known as immune-responsive gene 1, is an immunometabolic regulator that favors itaconate production to inhibit bacterial lipopolysaccharide-induced innate immunity. We used next-generation sequencing of lipopolysaccharide-activated THP1 cells to demonstrate that ACOD1 accumulation confers a robust proinflammation response by activating a cytokine storm, predominantly through the tumor necrosis factor signaling pathway. We further revealed that the phosphorylation of cyclin-dependent kinase 2 (CDK2) on threonine-160 mediates the activation of mitogen-activated protein kinase 8 through receptor for activated C kinase 1, leading to JUN-dependent transcription of ACOD1 in human and mouse macrophages or monocytes. Genetic deletion of CDK2 or ACOD1 in myeloid cells, or the administration of the CDK inhibitor dinaciclib, protected mice against polymicrobial sepsis and was associated with improved survival and decreased cytokine storm. The expression of the CDK2-ACOD1 axis also correlated with severity of illness in a cohort of 40 patients with bacterial sepsis. Thus, our findings provide evidence for a previously unrecognized function of ACOD1 in innate immunity and suggest it as a potential therapeutic target for the treatment of sepsis.

Lipid A Variants Activate Human TLR4 and the Noncanonical Inflammasome Differently and Require the Core Oligosaccharide for Inflammasome Activation

Detection of Gram-negative bacterial lipid A by the extracellular sensor, myeloid differentiation 2 (MD2)/Toll-like receptor 4 (TLR4), or the intracellular inflammasome sensors, CASP4 and CASP5, induces robust inflammatory responses. The chemical structure of lipid A, specifically its phosphorylation and acylation state, varies across and within bacterial species, potentially allowing pathogens to evade or suppress host immunity. Currently, it is not clear how distinct alterations in the phosphorylation or acylation state of lipid A affect both human TLR4 and CASP4/5 activation. Using a panel of engineered lipooligosaccharides (LOS) derived from Yersinia pestis with defined lipid A structures that vary in their acylation or phosphorylation state, we identified that differences in phosphorylation state did not affect TLR4 or CASP4/5 activation. However, the acylation state differentially impacted TLR4 and CASP4/5 activation. Specifically, all tetra-, penta-, and hexa-acylated LOS variants examined activated CASP4/5-dependent responses, whereas TLR4 responded to penta- and hexa-acylated LOS but did not respond to tetra-acylated LOS or penta-acylated LOS lacking the secondary acyl chain at the 3' position. As expected, lipid A alone was sufficient for TLR4 activation. In contrast, both core oligosaccharide and lipid A were required for robust CASP4/5 inflammasome activation in human macrophages, whereas core oligosaccharide was not required to activate mouse macrophages expressing CASP4. Our findings show that human TLR4 and CASP4/5 detect both shared and nonoverlapping LOS/lipid A structures, which enables the innate immune system to recognize a wider range of bacterial LOS/lipid A and would thereby be expected to constrain the ability of pathogens to evade innate immune detection.

Position-Specific Secondary Acylation Determines Detection of Lipid A by Murine TLR4 and Caspase-11

Immune sensing of the Gram-negative bacterial membrane glycolipid lipopolysaccharide (LPS) is both a critical component of host defense against bacterial infection and a contributor to the hyperinflammatory response, potentially leading to sepsis and death. Innate immune activation by LPS is due to the lipid A moiety, an acylated di-glucosamine molecule that can activate inflammatory responses via the extracellular sensor Toll-like receptor 4 (TLR4)/myeloid differentiation 2 (MD2) or the cytosolic sensor caspase-11 (Casp11). The number and length of acyl chains present on bacterial lipid A structures vary across bacterial species and strains, which affects the magnitude of TLR4 and Casp11 activation. TLR4 and Casp11 are thought to respond similarly to various lipid A structures, as tetra-acylated lipid A structures do not activate either sensor, whereas hexa-acylated structures activate both sensors. However, the precise features of lipid A that determine the differential activation of each receptor remain poorly defined, as direct analysis of extracellular and cytosolic responses to the same sources and preparations of LPS/lipid A structures have been limited. To address this question, we used rationally engineered lipid A isolated from a series of bacterial acyl-transferase mutants that produce novel, structurally defined molecules. Intriguingly, we found that the location of specific secondary acyl chains on lipid A resulted in differential recognition by TLR4 or Casp11, providing new insight into the structural features of lipid A required to activate either TLR4 or Casp11. Our findings indicate that TLR4 and Casp11 sense nonoverlapping areas of lipid A chemical space, thereby constraining the ability of Gram-negative pathogens to evade innate immunity.

Novel 1-hydroxy phenothiazinium-based derivative protects against bacterial sepsis by inhibiting AAK1-mediated LPS internalization and caspase-11 signaling

Sepsis is a life-threatening syndrome with disturbed host responses to severe infections, accounting for the majority of death in hospitalized patients. However, effective medicines are currently scant in clinics due to the poor understanding of the exact underlying mechanism. We previously found that blocking caspase-11 pathway (human orthologs caspase-4/5) is effective to rescue coagulation-induced organ dysfunction and lethality in sepsis models. Herein, we screened our existing chemical pools established in our lab using bacterial outer membrane vesicle (OMV)-challenged macrophages, and found 7-(diethylamino)-1-hydroxy-phenothiazin-3-ylidene-diethylazanium chloride (PHZ-OH), a novel phenothiazinium-based derivative, was capable of robustly dampening caspase-11-dependent pyroptosis. The in-vitro study both in physics and physiology showed that PHZ-OH targeted AP2-associated protein kinase 1 (AAK1) and thus prevented AAK1-mediated LPS internalization for caspase-11 activation. By using a series of gene-modified mice, our in-vivo study further demonstrated that administration of PHZ-OH significantly protected mice against sepsis-associated coagulation, multiple organ dysfunction, and death. Besides, PHZ-OH showed additional protection on Nlrp3^-/- and Casp1^-/- mice but not on Casp11^-/-, Casp1/11^-/-, Msr1^-/-, and AAK1 inhibitor-treated mice. These results suggest the critical role of AAK1 on caspase-11 signaling and may provide a new avenue that targeting AAK1-mediated LPS internalization would be a promising therapeutic strategy for sepsis. In particular, PHZ-OH may serve as a favorable molecule and an attractive scaffold in future medicine development for efficient treatment of bacterial sepsis.

Role of pyroptosis in inflammation and cancer

Pyroptosis is a form of programmed cell death mediated by gasdermin and is a product of continuous cell expansion until the cytomembrane ruptures, resulting in the release of cellular contents that can activate strong inflammatory and immune responses. Pyroptosis, an innate immune response, can be triggered by the activation of inflammasomes by various influencing factors. Activation of these inflammasomes can induce the maturation of caspase-1 or caspase-4/5/11, both of which cleave gasdermin D to release its N-terminal domain, which can bind membrane lipids and perforate the cell membrane. Here, we review the latest advancements in research on the mechanisms of pyroptosis, newly discovered influencing factors, antitumoral properties, and applications in various diseases. Moreover, this review also provides updates on potential targeted therapies for inflammation and cancers, methods for clinical prevention, and finally challenges and future directions in the field.

Targeted therapeutics and novel signaling pathways in non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH)

Non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH) has become the leading cause of liver disease worldwide. NASH, an advanced form of NAFL, can be progressive and more susceptible to developing cirrhosis and hepatocellular carcinoma. Currently, lifestyle interventions are the most essential and effective strategies for preventing and controlling NAFL without the development of fibrosis. While there are still limited appropriate drugs specifically to treat NAFL/NASH, growing progress is being seen in elucidating the pathogenesis and identifying therapeutic targets. In this review, we discussed recent developments in etiology and prospective therapeutic targets, as well as pharmacological candidates in pre/clinical trials and patents, with a focus on diabetes, hepatic lipid metabolism, inflammation, and fibrosis. Importantly, growing evidence elucidates that the disruption of the gut-liver axis and microbe-derived metabolites drive the pathogenesis of NAFL/NASH. Extracellular vesicles (EVs) act as a signaling mediator, resulting in lipid accumulation, macrophage and hepatic stellate cell activation, further promoting inflammation and liver fibrosis progression during the development of NAFL/NASH. Targeting gut microbiota or EVs may serve as new strategies for the treatment of NAFL/NASH. Finally, other mechanisms, such as cell therapy and genetic approaches, also have enormous therapeutic potential. Incorporating drugs with different mechanisms and personalized medicine may improve the efficacy to better benefit patients with NAFL/NASH.

Pyroptosis in sepsis: Comprehensive analysis of research hotspots and core genes in 2022

Sepsis, a life-threatening disease caused by dysregulated host response to infection, is a major public health problem with a high mortality and morbidity rate. Pyroptosis is a new type of programmed cell death discovered in recent years, which has been proved to play an important role in sepsis. Nevertheless, there is no comprehensive report, which can help researchers get a quick overview and find research hotspots. Thus, we aimed to identify the study status and knowledge structures of pyroptosis in sepsis and summarize the key mechanism of pyroptosis in sepsis. The data were retrieved and downloaded from the WOS database. Software such as VOSviewer was used to analyze these publications. Key genes were picked out by using (https://www.genecards.org) and (http://www.bioinformatics.com). Then, Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were used to performed these key genes. From 2011 to 2021, a total of 299 papers met the search criteria, and the global interest in pyroptosis in sepsis measured by the value of (RRI) has started to increase since 2016. China ranked first in the number of publications, followed by the USA. The journal Frontiers in Immunology published the most relevant articles. Through keyword co-occurrence analysis, the high-frequency subject terms were divided into three clusters like “animal research”, “cell research,” and “molecular research” clusters. “mir,” “aki,” “monocyte,” and “neutrophil” were the newest keywords that may be the hotspot. In addition, a total of 15 genes were identified as hub genes. TNF, IL-1β, AKT1, CASP1, and STAT3 were highly expressed in lung tissues, thymus tissues, and lymphocytes. KEGG analysis indicated that pyroptosis may play a vital role in sepsis via the NOD, PI3K/AKT, and MAPK/JNK pathways. Through the quantitative analysis of the literature on pyroptosis in sepsis, we revealed the current status and hotspots of research in this field and provided some guidance for further studies.

Non-coding RNAs in necroptosis, pyroptosis, and ferroptosis in cardiovascular diseases

Accumulating evidence has proved that non-coding RNAs (ncRNAs) play a critical role in the genetic programming and gene regulation of cardiovascular diseases (CVDs). Cardiovascular disease morbidity and mortality are rising and have become a primary public health issue that requires immediate resolution through effective intervention. Numerous studies have revealed that new types of cell death, such as pyroptosis, necroptosis, and ferroptosis, play critical cellular roles in CVD progression. It is worth noting that ncRNAs are critical novel regulators of cardiovascular risk factors and cell functions by mediating pyroptosis, necroptosis, and ferroptosis. Thus, ncRNAs can be regarded as promising therapeutic targets for treating and diagnosing cardiovascular diseases. Recently, there has been a surge of interest in the mediation of ncRNAs on three types of cell death in regulating tissue homeostasis and pathophysiological conditions in CVDs. Although our understanding of ncRNAs remains in its infancy, the studies reviewed here may provide important new insights into how ncRNAs interact with CVDs. This review summarizes what is known about the functions of ncRNAs in modulating cell death-associated CVDs and their role in CVDs, as well as their current limitations and future prospects.

The Role of Inflammasomes in Mediating Urological Disease: A Short Literature Review

Inflammasome dysfunction may be responsible for underlying inflammatory diseases, which include renal and urological pathologies. Five inflammasomes have been described, including nucleotide-binding domain leucine-rich repeat (NLR), NL pyrin domain containing receptor 1(NLPR1), NLRP3, NLR and caspase recruitment domain containing receptor 4 (NLRC4), and the AIM2-like receptor. The purpose of this study was to review literature sources regarding how innate immunity and inflammasomes contribute to urologic disease and infection. A literature search of PubMed/MEDLINE, EMBASE and Google Scholar articles. Articles were selected for review if their content included (1) inflammasomes and (2) urology in the adult population. The initiation of specific cytokine cascades, which include IL-1β and IL-18, appear responsible for a repertoire of urologic pathologies. Inflammation mediates a wide range of uropathies (urologic disorders and infections) which are found in the bladder, prostate, or kidney and inflammasomes appear to be particularly responsible for urological and renal pathologies. Understanding the role of inflammasomes in urologic disorders can help improve treatment and overall quality of life in patients with these disorders.

Secreted fungal virulence effector triggers allergic inflammation via TLR4

Invasive fungal pathogens are major causes of human mortality and morbidity^1,2. Although numerous secreted effector proteins that reprogram innate immunity to promote virulence have been identified in pathogenic bacteria, so far, there are no examples of analogous secreted effector proteins produced by human fungal pathogens. Cryptococcus neoformans, the most common cause of fungal meningitis and a major pathogen in AIDS, induces a pathogenic type 2 response characterized by pulmonary eosinophilia and alternatively activated macrophages^3-8. Here, we identify CPL1 as an effector protein secreted by C. neoformans that drives alternative activation (also known as M2 polarization) of macrophages to enable pulmonary infection in mice. We observed that CPL1-enhanced macrophage polarization requires Toll-like receptor 4, which is best known as a receptor for bacterial endotoxin but is also a poorly understood mediator of allergen-induced type 2 responses^9-12. We show that this effect is caused by CPL1 itself and not by contaminating lipopolysaccharide. CPL1 is essential for virulence, drives polarization of interstitial macrophages in vivo, and requires type 2 cytokine signalling for its effect on infectivity. Notably, C. neoformans associates selectively with polarized interstitial macrophages during infection, suggesting a mechanism by which C. neoformans generates its own intracellular replication niche within the host. This work identifies a circuit whereby a secreted effector protein produced by a human fungal pathogen reprograms innate immunity, revealing an unexpected role for Toll-like receptor 4 in promoting the pathogenesis of infectious disease.

Honokiol alleviates ulcerative colitis by targeting PPAR-γ-TLR4-NF-κB signaling and suppressing gasdermin-D-mediated pyroptosis in vivo and in vitro

Ulcerative colitis (UC) is a chronic, idiopathic relapsing inflammatory bowel disease. Honokiol is a major active component of the traditional Chinese medicinal herb Magnolia officinalis, which has been widely used in traditional prescriptions to treat tumors, inflammation, and gastrointestinal disorders. In this study, we investigated the ability of this polyphenolic compound to suppress UC in mice and the possible regulatory mechanism. A mouse model of UC induced with dextran sulfate sodium (DSS) in 40 male C57BL/6J mice was used for the in vivo study, and in vitro experiments were performed in mouse RAW264.7 macrophages. Lipopolysaccharide was used to induce the inflammatory response. The mouse bodyweights, stool consistency, and bleeding were determined and the disease activity indices calculated. RAW264.7 macrophages were cultured with or without either honokiol or lipopolysaccharide. Gene and protein expression was analyzed with RT-PCR and western blotting, respectively. GW6471 and GW9662 were used to interrupt the transcription of peroxisome proliferator activated receptor alpha (PPAR-α) and peroxisome proliferator activated receptor gamma (PPAR-γ). Both the in vivo and in vitro experimental results showed that the oral administration of honokiol markedly attenuated the severity of UC by reducing the inflammatory signals and restoring the integrity of the colon. Honokiol dramatically reduced the proinflammatory cytokines TNF-α, IL6, IL1β, and IFN-γ in mice with DSS-induced UC. It also upregulated PPAR-γ expression, and downregulated the TLR4-NF-κB signaling pathway. Moreover, honokiol inhibited gasdermin-D-mediated cell pyroptosis. These findings demonstrate for the first time that honokiol exerts a strong anti-inflammatory effect in a mouse model of UC, and that its underlying mechanism is associated with the activation of the PPAR-γ-TLR4-NF-κB signaling pathway and gasdermin-D-mediated macrophage pyroptosis. Therefore, honokiol may be a promising new drug for the clinical management of UC.