DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis

The NLRP1 and CARD8 inflammasomes detect reductive stress

The danger signals that activate the related nucleotide-binding domain leucine-rich repeat pyrin domain-containing 1 (NLRP1) and caspase activation and recruitment domain-containing 8 (CARD8) inflammasomes have not been fully established. We recently reported that the oxidized form of TRX1 binds to NLRP1 and represses inflammasome activation. These findings suggested that intracellular reductive stress, which would reduce oxidized TRX1 and thereby abrogate the NLRP1-TRX1 interaction, is an NLRP1 inflammasome-activating danger signal. However, no agents that induce reductive stress were known to test this premise. Here, we identify and characterize several radical-trapping antioxidants, including JSH-23, that induce reductive stress. We show that these compounds accelerate the proteasome-mediated degradation of the repressive N-terminal fragments of both NLRP1 and CARD8, releasing the inflammasome-forming C-terminal fragments from autoinhibition. Overall, this work validates chemical probes that induce reductive stress and establishes reductive stress as a danger signal sensed by both the NLRP1 and CARD8 inflammasomes.

Pyroptosis Provides New Strategies for the Treatment of Cancer

Cancer is an important cause of death worldwide. The main types of cancer treatment are still surgery, chemotherapy and radiotherapy, and immunotherapy is becoming an important cancer treatment. Pyroptosis is a type of programmed cell death that accompanies an inflammatory response. This paper reviews the recent research progress in pyroptosis in tumors. Pyroptosis has been observed since 1986 and until recently has been recognized as programmed cell death mediated by GSDM family proteins. The molecular pathway of pyroptosis depends on the inflammasome-mediated caspase-1/GSDMD pathway, which is the canonical pathway, and the caspase-4/5/11/GSDMD pathway, which is the noncanonical pathway. Other pathways include caspase3/GSDME. Pyroptosis is a double-edged sword that is closely related to the tumor immune microenvironment. On the one hand, pyroptosis produces a chronic inflammatory environment, promotes the transition of normal cells to tumor cells, helps tumor cells achieve immune escape, and promotes tumor growth and metastasis. On the other hand, some tumor cell treatments can induce pyroptosis, which is a nonapoptotic form of cell death. Additionally, pyroptosis releases inflammatory molecules that promote lymphocyte recruitment and enhance the immune system's ability to kill tumor cells. With the advent of immunotherapy, pyroptosis has been shown to enhance the antitumor efficacy of immune checkpoint inhibitors. Some antineoplastic agents, such as chemotherapeutic agents, can also exert antineoplastic effects through the pyroptosis pathway. Pyroptosis, which is a programmed cell death mode, has been the focus of research in recent years, and the relationship between pyroptosis, tumors and tumor immunity has attracted attention, but there are still some questions to be answered regarding the specific mechanism. Further study of pyroptosis would aid in developing new antitumor therapies and has great clinical prospects.

CARD8 Inflammasome Activation by HIV-1 Protease

The pattern recognition receptor CARD8 is an inflammasome sensor for intracellular HIV-1 protease activity. Previously, the only method for studying the CARD8 inflammasome has been through utilizing DPP8/DPP9 inhibitors including Val-boroPro (VbP) to modestly and nonspecifically activate the CARD8 inflammasome. The identification of HIV-1 protease as a target for sensing by CARD8 has opened the door for a new method of studying the underlying mechanism of CARD8 inflammasome activation. Additionally, triggering the CARD8 inflammasome offers a promising strategy for reducing HIV-1 latent reservoirs. Here we describe the methods to study CARD8 sensing of HIV-1 protease activity through non-nucleoside reverse transcriptase inhibitor (NNRTI)-mediated pyroptosis of HIV-1-infected immune cells and through an HIV and CARD8 co-transfection model.

Uncoupled pyroptosis and IL-1β secretion downstream of inflammasome signaling

Inflammasomes are supramolecular platforms that organize in response to various damage-associated molecular patterns and pathogen-associated molecular patterns. Upon activation, inflammasome sensors (with or without the help of ASC) activate caspase-1 and other inflammatory caspases that cleave gasdermin D and pro-IL-1β/pro-IL-18, leading to pyroptosis and mature cytokine secretion. Pyroptosis enables intracellular pathogen niche disruption and intracellular content release at the cost of cell death, inducing pro-inflammatory responses in the neighboring cells. IL-1β is a potent pro-inflammatory regulator for neutrophil recruitment, macrophage activation, and T-cell expansion. Thus, pyroptosis and cytokine secretion are the two main mechanisms that occur downstream of inflammasome signaling; they maintain homeostasis, drive the innate immune response, and shape adaptive immunity. This review aims to discuss the possible mechanisms, timing, consequences, and significance of the two uncoupling preferences downstream of inflammasome signaling. While pyroptosis and cytokine secretion may be usually coupled, pyroptosis-predominant and cytokine-predominant uncoupling are also observed in a stimulus-, cell type-, or context-dependent manner, contributing to the pathogenesis and development of numerous pathological conditions such as cryopyrin-associated periodic syndromes, LPS-induced sepsis, and Salmonella enterica serovar Typhimurium infection. Hyperactive cells consistently release IL-1β without LDH leakage and pyroptotic death, thereby leading to prolonged inflammation, expanding the lifespans of pyroptosis-resistant neutrophils, and hyperactivating stimuli-challenged macrophages, dendritic cells, monocytes, and specific nonimmune cells. Death inflammasome activation also induces GSDMD-mediated pyroptosis with no IL-1β secretion, which may increase lethality in vivo. The sublytic GSDMD pore formation associated with lower expressions of pyroptotic components, GSDMD-mediated extracellular vesicles, or other GSDMD-independent pathways that involve unconventional secretion could contribute to the cytokine-predominant uncoupling; the regulation of caspase-1 dynamics, which may generate various active species with different activities in terms of GSDMD or pro-IL-1β, could lead to pyroptosis-predominant uncoupling. These uncoupling preferences enable precise reactions to different stimuli of different intensities under specific conditions at the single-cell level, promoting cooperative cell and host fate decisions and participating in the pathogen "game". Appropriate decisions in terms of coupling and uncoupling are required to heal tissues and eliminate threats, and further studies exploring the inflammasome tilt toward pyroptosis or cytokine secretion may be helpful.

Deciphering the Role of Pyroptosis Impact on Cardiovascular Diseases

Pyroptosis has become a noteworthy area of focus in recent years due to its association with inflammatory diseases. Pyroptosis is a type of programmed cell death accompanied by an inflammatory response, and the discovery of the gasdermin family has expanded the study of pyroptosis. The primary characteristics of pyroptosis include cell expansion, membrane penetration, and the ejection of cell contents. In healthy physiology, pyroptosis is an essential part of the host's defence against pathogen infection. Excessive Pyroptosis, however, can lead to unchecked and persistent inflammatory responses, including the emergence of inflammatory diseases. More precisely, gasdermin family members have a role in the creation of membrane holes during pyroptosis, which leads to cell lysis. It is also related to how pro-inflammatory intracellular substances, including IL-1, IL-18, and High mobility group box 1 (HMGB1), are used. Two different signalling pathways, one of which is regulated by caspase-1 and the other by caspase-4/5/11, are the primary causes of pyroptosis. Cardiovascular diseases are often associated with cell death and acute or chronic inflammation, making this area of research particularly relevant. In this review, we first systematically summarize recent findings related to Pyroptosis, exploring its characteristics and the signalling pathway mechanisms, as well as various treatment strategies based on its modulation that has emerged from the studies. Some of these strategies are currently undergoing clinical trials. Additionally, the article elaborates on the scientific evidence indicating the role of Pyroptosis in various cardiovascular diseases. As a whole, this should shed insight into future paths and present innovative ideas for employing Pyroptosis as a strong disease-fighting weapon.

The CARD8 inflammasome in HIV infection

The biggest challenge to immune control of HIV infection is the rapid within-host viral evolution, which allows selection of viral variants that escape from T cell and antibody recognition. Thus, it is impossible to clear HIV infection without targeting "immutable" components of the virus. Unlike the adaptive immune system that recognizes cognate epitopes, the CARD8 inflammasome senses the essential enzymatic activity of the HIV-1 protease, which is immutable for the virus. Hence, all subtypes of HIV clinical isolates can be recognized by CARD8. In HIV-infected cells, the viral protease is expressed as a subunit of the viral Gag-Pol polyprotein and remains functionally inactive prior to viral budding. A class of anti-HIV drugs, the non-nucleoside reverse transcriptase inhibitors (NNRTIs), can promote Gag-pol dimerization and subsequent premature intracellular activation of the viral protease. NNRTI treatment triggers CARD8 inflammasome activation, which leads to pyroptosis of HIV-infected CD4⁺ T cells and macrophages. Targeting the CARD8 inflammasome can be a potent and broadly effective strategy for HIV eradication.

High p62 expression suppresses the NLRP1 inflammasome and increases stress resistance in cutaneous SCC cells

NLRP1 is the primary inflammasome sensor in human keratinocytes. Sensing of UVB radiation by NLRP1 is believed to underlie the induction of sunburn. Although constitutive NLRP1 activation causes skin inflammation and predisposes patients to the development of cutaneous SCCs, the NLRP1 pathway is suppressed in established SCCs. Here, we identified high levels of the autophagy receptor p62 in SCC cells lines and SCC tumors. Increased NF-κB activity in SCC cells causes p62 up-regulation. Suppression of p62 expression rescues UVB-induced NLRP1 inflammasome activation in early-stage SCC cells. p62 expression protects SCC cells from cytotoxic drugs, whereas NLRP1 sensitizes them. In summary, we identify p62 as a novel negative regulator of the NLRP1 inflammasome in human cutaneous SCC cells, in which suppression of NLRP1 by increased levels of p62 supports stress resistance of skin cancer cells.

Gasdermins and pannexin-1 mediate pathways of chemotherapy-induced cell lysis in hematopoietic malignancies

Pyroptosis is a mechanism of programmed, necrotic cell death mediated by gasdermins, a family of pore-forming proteins. Caspase-1 activates gasdermin D (GSDMD) under inflammatory conditions, whereas caspase-3 activates GSDME under apoptotic conditions, such as those induced by chemotherapy. These pathways are thought to be separate. However, we found that they are part of an integrated network of gatekeepers that enables pyroptotic cell death. We observed that GSDMD was the primary pyroptotic mediator in cultured blood cells in response to doxorubicin and etoposide, two common chemotherapies for hematopoietic malignancies. Upon treatment, the channel protein pannexin-1 (PANX1), which is stimulated by the initiation of apoptosis, increased membrane permeability to induce K⁺ efflux-driven activation of the NLRP3 inflammasome and GSDMD. However, either PANX1 or GSDME could also be the primary mediator of chemotherapy-induced pyroptosis when present at higher amounts. The most abundant pore-forming protein in acute myeloid leukemias from patients predicted the cell death pathway in response to chemotherapy. This interconnected network, a multistep switch that converts apoptosis to pyroptosis, could be clinically titratated to modulate cell death with regard to antitumor immunity or tumor lysis syndrome in patients.

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.

The human inflammasomes

Two decades of inflammasome research has led to a vast body of knowledge on the complex regulatory mechanisms and pathological roles of canonical and non-canonical inflammasome activation in a plethora of research models of primarily rodent origin. More recently, the field has made notable progress in characterizing human-specific inflammasomes and their regulation mechanisms, including an expansion of inflammasome biology to adaptive immune cells. These exciting developments in basic research have been accompanied by potentially transformative results from large clinical trials and translational efforts to develop inflammasome-targeted small molecule inhibitors for therapeutic use. Here, we will discuss recent findings in the field with a specific emphasis on activation mechanisms of human inflammasomes and their potential role in auto-inflammatory, metabolic and neoplastic diseases.

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.

The Awesome Power of Human Genetics of Infectious Disease

Since the identification of sickle cell trait as a heritable form of resistance to malaria, candidate gene studies, linkage analysis paired with sequencing, and genome-wide association (GWA) studies have revealed many examples of genetic resistance and susceptibility to infectious diseases. GWA studies enabled the identification of many common variants associated with small shifts in susceptibility to infectious diseases. This is exemplified by multiple loci associated with leprosy, malaria, HIV, tuberculosis, and coronavirus disease 2019 (COVID-19), which illuminate genetic architecture and implicate pathways underlying pathophysiology. Despite these successes, most of the heritability of infectious diseases remains to be explained. As the field advances, current limitations may be overcome by applying methodological innovations such as cellular GWA studies and phenome-wide association (PheWA) studies as well as by improving methodological rigor with more precise case definitions, deeper phenotyping, increased cohort diversity, and functional validation of candidate loci in the laboratory or human challenge studies.

Chemoproteomics-Enabled Identification of 4-Oxo-β-Lactams as Inhibitors of Dipeptidyl Peptidases 8 and 9

Dipeptidyl peptidases 8 and 9 (DPP8/9) have gathered interest as drug targets due to their important roles in biological processes like immunity and tumorigenesis. Elucidation of their distinct individual functions remains an ongoing task and could benefit from the availability of novel, chemically diverse and selective chemical tools. Here, we report the activity-based protein profiling (ABPP)-mediated discovery of 4-oxo-β-lactams as potent, non-substrate-like nanomolar DPP8/9 inhibitors. X-ray crystallographic structures revealed different ligand binding modes for DPP8 and DPP9, including an unprecedented targeting of an extended S2' (eS2') subsite in DPP8. Biological assays confirmed inhibition at both target and cellular levels. Altogether, our integrated chemical proteomics and structure-guided small molecule design approach led to novel DPP8/9 inhibitors with alternative molecular inhibition mechanisms, delivering the highest selectivity index reported to date.

Induction of pyroptotic cell death as a potential tool for cancer treatment

Cancer is a complex pathological disease and the existing strategies for introducing chemotherapeutic agents have restricted potential due to a lack of cancer cell targeting specificity, cytotoxicity, bioavailability, and induction of multi-drug resistance. As a prospective strategy in tackling cancer, regulating the inflammatory pyroptosis cell death pathway has been shown to successfully inhibit the proliferation and metastasis of various cancer cell types. Activation of inflammasomes such as the NLRP3 results in pyroptosis through cleavage of gasdermins, which forms pores in the cell membranes, inducing membrane breakage, cell rupture, and death. Furthermore, pyroptotic cells release pro-inflammatory cytokines such as IL-1β and IL-18 along with various DAMPs that prime an auxiliary anti-tumor immune response. Thus, regulation of pyroptosis in cancer cells is a way to enhance their immunogenicity. However, immune escape involving myeloid-derived suppressor cells has limited the efficacy of most pyroptosis-based immunotherapy strategies. In this review, we comprehensively summarize the cellular and molecular mechanisms involved in the inflammasome-mediated pyroptosis pathways in cancer cells, exploring how it could modulate the tumor microenvironment and be beneficial in anti-cancer treatments. We discuss various existing therapeutic strategies against cancer, including immunotherapy, oncolytic virus therapy, and nanoparticle-based therapies that could be guided to trigger and regulate pyroptosis cell death in cancer cells, and reduce tumor growth and spread. These pyroptosis-based cancer therapies may open up fresh avenues for targeted cancer therapy approaches in the future and their translation into the clinic.

Oxidized thioredoxin-1 restrains the NLRP1 inflammasome

The danger signals that activate the NLRP1 inflammasome have not been established. Here, we report that the oxidized, but not the reduced, form of thioredoxin-1 (TRX1) binds to NLRP1. We found that oxidized TRX1 associates with the NACHT-LRR region of NLRP1 in an ATP-dependent process, forming a stable complex that restrains inflammasome activation. Consistent with these findings, patient-derived and ATPase-inactivating mutations in the NACHT-LRR region that cause hyperactive inflammasome formation interfere with TRX1 binding. Overall, this work strongly suggests that reductive stress, the cellular perturbation that will eliminate oxidized TRX1 and abrogate the TRX1-NLRP1 interaction, is a danger signal that activates the NLRP1 inflammasome.

Clinical Phenotypes and the Clinical Course of Bullous Pemphigoid Receiving Dipeptidyl Pepitidase-4 Inhibitor Treatment: An Analysis of Cases in a Single Japanese Center

Objective Several studies have shown an increased risk of bullous pemphigoid (BP) when receiving dipeptidyl pepitidase-4 inhibitor (DPP-4i) treatment. The present study explored the associations of DPP-4i treatment with the clinical phenotypes and clinical course of BP. Methods We analyzed data of 146 patients with BP at Tokai University School of Medicine from December 1, 2009, to December 31, 2021. We obtained data by a retrospective medical record review and compared the bullous pemphigoid disease area index (BPDAI) between diabetes patients receiving DPP-4i treatment and those not receiving DPP-4i treatment. We employed multivariable linear regression models to explore the association between the DPP-4i treatment and the BPDAI scores. Results Among 53 BP patients with diabetes, 33 had developed BP during treatment with DPP-4i agents, among which vildagliptin was the most frequently used. The urticaria/erythema scores of the BPDAI were significantly lower in patients who developed BP while receiving DPP-4i treatment than among others. Of note, 69.2% of the patients who stopped DPP-4i treatment experienced complete remission, and the clinical course was more favorable in patients with lower scores for urticaria/erythema than among others. Conclusion These findings suggest that, in patients who developed BP while receiving DPP-4i treatment, a noninflammatory phenotype may indicate a high likelihood that DPP-4i treatment contributes to the development of BP. The discontinuation of DPP-4i should be carefully considered in close consultation with dermatologists.

The emerging role of pyroptosis in pediatric cancers: from mechanism to therapy

Pediatric cancers are the driving cause of death for children and adolescents. Due to safety requirements and considerations, treatment strategies and drugs for pediatric cancers have been so far scarcely studied. It is well known that tumor cells tend to progressively evade cell death pathways, which is known as apoptosis resistance, one of the hallmarks of cancer, dominating tumor drug resistance. Recently, treatments targeting nonapoptotic cell death have drawn great attention. Pyroptosis, a newly specialized form of cell death, acts as a critical physiological regulator in inflammatory reaction, cell development, tissue homeostasis and stress response. The action in different forms of pyroptosis is of great significance in the therapy of pediatric cancers. Pyroptosis could be induced and consequently modulate tumorigenesis, progression, and metastasis if treated with local or systemic therapies. However, excessive or uncontrolled cell death might lead to tissue damage, acute inflammation, or even cytokine release syndrome, which facilitates tumor progression or recurrence. Herein, we aimed to describe the molecular mechanisms of pyroptosis, to highlight and discuss the challenges and opportunities for activating pyroptosis pathways through various oncologic therapies in multiple pediatric neoplasms, including osteosarcoma, neuroblastoma, leukemia, lymphoma, and brain tumors.

Dipeptidyl peptidase 9 triggers BRCA2 degradation and promotes DNA damage repair

N-terminal sequences are important sites for post-translational modifications that alter protein localization, activity, and stability. Dipeptidyl peptidase 9 (DPP9) is a serine aminopeptidase with the rare ability to cleave off N-terminal dipeptides with imino acid proline in the second position. Here, we identify the tumor-suppressor BRCA2 as a DPP9 substrate and show this interaction to be induced by DNA damage. We present crystallographic structures documenting intracrystalline enzymatic activity of DPP9, with the N-terminal Met1-Pro2 of a BRCA21-40 peptide captured in its active site. Intriguingly, DPP9-depleted cells are hypersensitive to genotoxic agents and are impaired in the repair of DNA double-strand breaks by homologous recombination. Mechanistically, DPP9 targets BRCA2 for degradation and promotes the formation of RAD51 foci, the downstream function of BRCA2. N-terminal truncation mutants of BRCA2 that mimic a DPP9 product phenocopy reduced BRCA2 stability and rescue RAD51 foci formation in DPP9-deficient cells. Taken together, we present DPP9 as a regulator of BRCA2 stability and propose that by fine-tuning the cellular concentrations of BRCA2, DPP9 alters the BRCA2 interactome, providing a possible explanation for DPP9's role in cancer.

Viral proteases activate the CARD8 inflammasome in the human cardiovascular system

Nucleotide-binding oligomerization domain (NBD), leucine-rich repeat (LRR) containing protein family (NLRs) are intracellular pattern recognition receptors that mediate innate immunity against infections. The endothelium is the first line of defense against blood-borne pathogens, but it is unclear which NLRs control endothelial cell (EC) intrinsic immunity. Here, we demonstrate that human ECs simultaneously activate NLRP1 and CARD8 inflammasomes in response to DPP8/9 inhibitor Val-boro-Pro (VbP). Enterovirus Coxsackie virus B3 (CVB3)-the most common cause of viral myocarditis-predominantly activates CARD8 in ECs in a manner that requires viral 2A and 3C protease cleavage at CARD8 p.G38 and proteasome function. Genetic deletion of CARD8 in ECs and human embryonic stem cell-derived cardiomyocytes (HCMs) attenuates CVB3-induced pyroptosis, inflammation, and viral propagation. Furthermore, using a stratified endothelial-cardiomyocyte co-culture system, we demonstrate that deleting CARD8 in ECs reduces CVB3 infection of the underlying cardiomyocytes. Our study uncovers the unique role of CARD8 inflammasome in endothelium-intrinsic anti-viral immunity.

DPP9 deficiency: An inflammasomopathy that can be rescued by lowering NLRP1/IL-1 signaling

Dipeptidyl peptidase 9 (DPP9) is a direct inhibitor of NLRP1, but how it affects inflammasome regulation in vivo is not yet established. Here, we report three families with immune-associated defects, poor growth, pancytopenia, and skin pigmentation abnormalities that segregate with biallelic DPP9 rare variants. Using patient-derived primary cells and biochemical assays, these variants were shown to behave as hypomorphic or knockout alleles that failed to repress NLRP1. The removal of a single copy of Nlrp1a/b/c, Asc, Gsdmd, or Il-1r, but not Il-18, was sufficient to rescue the lethality of Dpp9 mutant neonates in mice. Similarly, dpp9 deficiency was partially rescued by the inactivation of asc, an obligate downstream adapter of the NLRP1 inflammasome, in zebrafish. These experiments suggest that the deleterious consequences of DPP9 deficiency were mostly driven by the aberrant activation of the canonical NLRP1 inflammasome and IL-1β signaling. Collectively, our results delineate a Mendelian disorder of DPP9 deficiency driven by increased NLRP1 activity as demonstrated in patient cells and in two animal models of the disease.

A Phenotypic Screen Identifies Potent DPP9 Inhibitors Capable of Killing HIV-1 Infected Cells

Although current antiretroviral therapy can control HIV-1 replication and prevent disease progression, it is not curative. Identifying mechanisms that can lead to eradication of persistent viral reservoirs in people living with HIV-1 (PLWH) remains an outstanding challenge to achieving cure. Utilizing a phenotypic screen, we identified a novel chemical class capable of killing HIV-1 infected peripheral blood mononuclear cells. Tool compounds ICeD-1 and ICeD-2 ("inducer of cell death-1 and 2"), optimized for potency and selectivity from screening hits, were used to deconvolute the mechanism of action using a combination of chemoproteomic, biochemical, pharmacological, and genetic approaches. We determined that these compounds function by modulating dipeptidyl peptidase 9 (DPP9) and activating the caspase recruitment domain family member 8 (CARD8) inflammasome. Efficacy of ICeD-1 and ICeD-2 was dependent on HIV-1 protease activity and synergistic with efavirenz, which promotes premature activation of HIV-1 protease at high concentrations in infected cells. This in vitro synergy lowers the efficacious cell kill concentration of efavirenz to a clinically relevant dose at concentrations of ICeD-1 or ICeD-2 that do not result in complete DPP9 inhibition. These results suggest engagement of the pyroptotic pathway as a potential approach to eliminate HIV-1 infected cells.

Activation and regulation mechanisms of NOD-like receptors based on structural biology

Innate immunity is a primary defense system against microbial infections. Innate immune pattern recognition receptors (PRRs) play pivotal roles in detection of invading pathogens. When pathogens, such as bacteria and viruses, invade our bodies, their components are recognized by PRRs as pathogen-associated molecular patterns (PAMPs), activating the innate immune system. Cellular components such as DNA and RNA, acting as damage-associated molecular patterns (DAMPs), also activate innate immunity through PRRs under certain conditions. Activation of PRRs triggers inflammatory responses, interferon-mediated antiviral responses, and the activation of acquired immunity. Research on innate immune receptors is progressing rapidly. A variety of these receptors has been identified, and their regulatory mechanisms have been elucidated. Nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) constitute a major family of intracellular PRRs and are involved in not only combating pathogen invasion but also maintaining normal homeostasis. Some NLRs are known to form multi-protein complexes called inflammasomes, a process that ultimately leads to the production of inflammatory cytokines and induces pyroptosis through the proteolytic cascade. The aberrant activation of NLRs has been found to be associated with autoimmune diseases. Therefore, NLRs are considered targets for drug discovery, such as for antiviral drugs, immunostimulants, antiallergic drugs, and autoimmune disease drugs. This review summarizes our recent understanding of the activation and regulation mechanisms of NLRs, with a particular focus on their structural biology. These include NOD2, neuronal apoptosis inhibitory protein (NAIP)/NLRC4, NLR family pyrin domain containing 1 (NLRP1), NLRP3, NLRP6, and NLRP9. NLRs are involved in a variety of diseases, and their detailed activation mechanisms based on structural biology can aid in developing therapeutic agents in the future.

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

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.

Defining resistance and tolerance traits in Covid-19: towards a stratified medicine approach

Successful host defence against infectious disease involves resistance (reduce pathogen load) and tolerance (reduce tissue damage associated with pathogen presence). Integration of clinical, immunologic, genetic and therapeutic discoveries has identified defects in both of these responses in the progression from SARS-CoV-2 infection to life-threatening coronavirus disease 2019 (Covid-19) lung injury. Early after infection with SARS-CoV-2, resistance can be compromised by a failed type 1 interferon (IFN-I) response, due to direct viral antagonism of induction and signalling, deleterious host genetic variants (IFNAR2, IFNA10, TYK2 and PLSCR1), and neutralizing auto-antibodies directed against IFN-I (predominantly IFN-α). Later in the disease, after pathogen sensing has activated a pro-inflammatory response, a failure to appropriately regulate this response compromises tolerance resulting in virus-independent immunopathology involving the lung and reticuloendothelial system. Monocytes are activated in the periphery (involving M-CSF, GM-CSF, IL-6, NLRP1 inflammasomes, TYK2 and afucosylated anti-spike IgG) then recruited to the lung (involving CCR2::MCP-3/MCP-1 and C5a::C5aR1 axes) as pro-inflammatory monocyte-derived macrophages, resulting in inflammatory lung injury. Phenotypic and genotypic heterogeneity is apparent in all these responses, identifying 'treatable traits' (therapeutically relevant components of inter-individual variation) which could be exploited to achieve a stratified medicine approach to Covid-19. Overall, Covid-19 pathogenesis re-affirms the importance of resistance in surviving an infectious disease and highlights that tolerance is also a central pillar of host defence in humans and can be beneficially modified using host-directed therapies.

LDC7559 Exerts Neuroprotective Effects by Inhibiting GSDMD-dependent Pyroptosis of Microglia in Mice with Traumatic Brain Injury

Pyroptosis is considered one of a critical factor in the recovery of neurological function following traumatic brain injury. Brain injury activates a molecular signaling cascade associated with pyroptosis and inflammation, including NLRP3, inflammatory cytokines, caspase-1, gasdermin D (GSDMD), and other pyroptosis-related proteins. In this study, we explored the neuroprotective effects of LDC7559, a GSDMD inhibitor. Briefly, LDC7559, siRNA-GSDMD (si-GSDMD), or equal solvent was administrated to mice with a lipopolysaccharide + nigericin (LPS + Nig) model in vitro or with controlled cortical impact brain injury. The findings revealed that inflammation and pyroptosis levels were decreased by LDC7559 or si-GSDMD treatment both in vitro and in vivo. Immunofluorescence staining, brain water content, hematoxylin and eosin staining, and behavioral investigations suggested that LDC7559 or si-GSDMD inhibited microglial proliferation, ameliorated cerebral edema, reduced brain tissue loss, and promoted brain function recovery. Taken together, LDC7559 may inhibit pyroptosis and reduce inflammation by inhibiting GSDMD, thereby promoting the recovery of neurological function.

Supramolecular organizing centers at the interface of inflammation and neurodegeneration

The pathogenesis of neurodegenerative diseases involves the accumulation of misfolded protein aggregates. These deposits are both directly toxic to neurons, invoking loss of cell connectivity and cell death, and recognized by innate sensors that upon activation release neurotoxic cytokines, chemokines, and various reactive species. This neuroinflammation is propagated through signaling cascades where activated sensors/receptors, adaptors, and effectors associate into multiprotein complexes known as supramolecular organizing centers (SMOCs). This review provides a comprehensive overview of the SMOCs, involved in neuroinflammation and neurotoxicity, such as myddosomes, inflammasomes, and necrosomes, their assembly, and evidence for their involvement in common neurodegenerative diseases. We discuss the multifaceted role of neuroinflammation in the progression of neurodegeneration. Recent progress in the understanding of particular SMOC participation in common neurodegenerative diseases such as Alzheimer's disease offers novel therapeutic strategies for currently absent disease-modifying treatments.

Activation and Pharmacological Regulation of Inflammasomes

Inflammasomes are intracellular signaling complexes of the innate immune system, which is part of the response to exogenous pathogens or physiological aberration. The multiprotein complexes mainly consist of sensor proteins, adaptors, and pro-caspase-1. The assembly of the inflammasome upon extracellular and intracellular cues drives the activation of caspase-1, which processes pro-inflammatory cytokines IL-1β and IL-18 to maturation and gasdermin-D for pore formation, leading to pyroptosis and cytokine release. Inflammasome signaling functions in numerous infectious or sterile inflammatory diseases, including inherited autoinflammatory diseases, metabolic disorders, cardiovascular diseases, cancers, neurodegenerative disorders, and COVID-19. In this review, we summarized current ideas on the organization and activation of inflammasomes, with details on the molecular mechanisms, regulations, and interventions. The recent developments of pharmacological strategies targeting inflammasomes as disease therapeutics were also covered.

Constructing novel molecular subtypes and an 11-gene signature based on pyroptosis signaling for lung adenocarcinoma

Pyroptosis plays important roles in various cancers. In this study, we focused on lung adenocarcinoma (LUAD) and aimed to develop new molecular subtypes based on pyroptosis signaling. Pyroptosis-related genes were used as a basis to classify molecular subtypes through unsupervised consensus clustering. Gene set enrichment analysis was performed to characterize tumor microenvironment (TME) and functional pathways. Univariate Cox regression and least absolute shrinkage and selection operator (LASSO) analysis were conducted to identify prognostic genes for establishing a prognostic model. Three molecular subtypes were established with distinct overall survival, TME and enriched pathways. C3 subtype had the longest survival and the highest immune infiltration. 11 prognostic genes were screened to build a prognostic signature for predicting LUAD prognosis. This study emphasized the important role of pyroptosis in LUAD development. Pyroptosis was considered to play critical roles in regulating TME. Moreover, the 11-gene signature could serve as an indicator for predicting LUAD prognosis, and was potential targets for developing targeted drugs.

Identification of pyroptosis related subtypes and tumor microenvironment infiltration characteristics in breast cancer

Understanding the association of pyroptosis with tumor progression, prognosis and effect on immunotherapeutic response in breast cancer (BC) is limited. This study analysed forty pyroptosis-related genes to construct the pyroptosis score. Association of the pyroptosis score with the overall survival, clinical features, tumor mutation load, immune cell infiltration, and treatment sensitivity of patients with BC was analysed. Out of 983 BC samples, 304 (30.93%) had genetic alterations with the highest TP53 frequency. We identified three separate subtypes associated with pyroptosis action. These subtypes correlate with the clinicopathological characteristics, TME immune cell infiltration, and disease prognosis. Based on the expression levels of the pyroptosis genes, we divided the pyroptosis score into a high group and a low group. The immune-activated pyroptosis subtype had a higher score with a better prognosis. We also observed that the pyroptosis score correlates with the tumor mutation burden. The pyroptosis score and disease prognosis were directly proportional. A higher pyroptosis score indicated a better prognosis. Results suggest that the pyroptosis-related gene prognosis model is closely related to the immune cell infiltration of BC. The three pyroptosis subtypes associated with BC assist in accurately identifying the tumor subtype, the prognosis of immunotherapy drugs and the patient’s therapeutic response.

UVB-Induced Skin Autoinflammation Due to Nlrp1b Mutation and Its Inhibition by Anti-IL-1β Antibody

NLRP1 (NACHT and leucine-rich repeat-containing protein family, pyrin domain-containing protein 1) is an innate immune sensor that is involved in the formation of inflammasome complexes. NLRP1 hyperactivity has been reported to cause inherited autoinflammatory diseases including familial keratosis lichenoides chronica and NLRP1-associated autoinflammation with arthritis and dyskeratosis. We generated Nlrp1b (the mouse homologue of human NLRP1) gain-of-function knock-in (Nlrp1b KI) mice with UVB irradiation-induced autoinflammatory skin lesions. We demonstrated that UVB irradiation induces IL-1β upregulation and IL-1β-dependent inflammation via caspase-1 activation in these Nlrp1b KI mice. RNA sequencing revealed the upregulation of inflammasome pathway-related genes, keratinocyte stress marker genes, and keratinocyte differentiation marker genes in the Nlrp1b KI mice after UVB irradiation. The skin inflammation and hyperkeratosis from UVB irradiation in the Nlrp1b KI mice were inhibited by both intraperitoneal and subcutaneous administration of anti-IL-1β antibodies before UVB irradiation. UVB irradiation and the IL-1β pathway are important in the pathogenesis of NLRP1-associated autoinflammatory skin lesions.

The Regulation and Modification of GSDMD Signaling in Diseases

Gasdermin D (GSDMD) serves as a key executor to trigger pyroptosis and is emerging as an attractive checkpoint in host defense, inflammatory, autoimmune diseases, and many other systemic diseases. Although canonical and non-canonical inflammasome-mediated classic GSDMD cleavage, GSDMD-NT migration to cell membrane, GSDMD-NT oligomerization, and pore forming have been well recognized, a few unique features of GSDMD in specific condition beyond its classic function, including non-lytic function of GSDMD, the modification and regulating mechanism of GSDMD signaling have also come to great attention and played a crucial role in biological processes and diseases. In the current review, we emphasized the GSDMD protein expression, stabilization, modification, activation, pore formation, and repair during pyroptosis, especially the regulation and modification of GSDMD signaling, such as GSDMD complex in polyubiquitination and non-pyroptosis release of IL-1β, ADP-riboxanation, NINJ1 in pore forming, GSDMD binding protein TRIM21, GSDMD succination, and Regulator-Rag-mTOR-ROS regulation of GSDMD. We also discussed the novel therapeutic strategies of targeting GSDMD and summarized recently identified inhibitors with great prospect.

NLRP1 Inflammasomes: A Potential Target for the Treatment of Several Types of Brain Injury

NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) is a member of the NLR family. The NLRP1 inflammasome consists of the NLRP1 protein, the adaptor protein apoptosis-associated speck-like protein containing a CARD domain, and the effector molecule pro-caspase-1. When stimulated, the inflammasome initiates the cleavage of pro-caspase-1 and converts it into its active form, caspase-1; then, caspase-1 facilitates the cleavage of the proinflammatory cytokines interleukin-1β and interleukin-18 into their active and secreted forms. In addition, caspase-1 also mediates the cleavage of gasdermin D, which leads to pyroptosis, an inflammatory form of cell death. Pathological events that damage the brain and result in neuropathological conditions can generally be described as brain injury. Neuroinflammation, especially that driven by NLRP1, plays a considerable role in the pathophysiology of brain injury, such as early brain injury (EBI) of subarachnoid hemorrhage, ischemic brain injury during stroke, and traumatic brain injury (TBI). In this article, a thorough overview of NLRP1 is presented, including its structure, mechanism of activation, and role in neuroinflammation. We also present recent studies on NLRP1 as a target for the treatment of EBI, ischemic brain injury, TBI, and other types of brain injury, thus highlighting the perspective of NLRP1 as an effective mediator of catastrophic brain injury.

The Role of Inflammasomes in Osteoarthritis and Secondary Joint Degeneration Diseases

Osteoarthritis is age-related and the most common form of arthritis. The main characteristics of the disease are progressive loss of cartilage and secondary synovial inflammation, which finally result in pain, joint stiffness, and functional disability. Similarly, joint degeneration is characteristic of systemic inflammatory diseases such as rheumatoid arthritis and gout, with the associated secondary type of osteoarthritis. Studies suggest that inflammation importantly contributes to the progression of the disease. Particularly, cytokines TNFα and IL-1β drive catabolic signaling in affected joints. IL-1β is a product of inflammasome activation. Inflammasomes are inflammatory multiprotein complexes that propagate inflammation in various autoimmune and autoinflammatory conditions through cell death and the release of inflammatory cytokines and damage-associated molecule patterns. In this article, we review genetic, marker, and animal studies that establish inflammasomes as important drivers of secondary arthritis and discuss the current evidence for inflammasome involvement in primary osteoarthritis. The NLRP3 inflammasome has a significant role in the development of secondary osteoarthritis, and several studies have provided evidence of its role in the development of primary osteoarthritis, while other inflammasomes cannot be excluded. Inflammasome-targeted therapeutic options might thus provide a promising strategy to tackle these debilitating diseases.

NLRP1 Inflammasome Activation in Keratinocytes: Increasing Evidence of Important Roles in Inflammatory Skin Diseases and Immunity

In 2007, it was shown that DNA sequence variants of the human NLRP1 gene are associated with autoimmune and autoinflammatory diseases affecting mainly the skin. However, at that time, the underlying cellular and molecular mechanisms were poorly characterized. Meanwhile, increasing evidence suggests that the NLRP1 inflammasome expressed by keratinocytes not only plays a part in the pathology of common inflammatory skin diseases and cancer development but also contributes to skin immunity. Understanding the mechanisms regulating NLRP1 activation in keratinocytes and the downstream events in human skin might pave the way for developing novel strategies for treating patients suffering from NLRP1-mediated skin diseases.

The NLRP1 Inflammasome Induces Pyroptosis in Human Corneal Epithelial Cells

PURPOSE

Inflammasomes are multiprotein complexes that detect danger-associated signals and trigger an immunostimulatory form of cell death called pyroptosis. NLRP1 is an innate immune receptor that assembles into an inflammasome, but the primary cell types in which NLRP1 is functional have not yet been fully established. Mutations in NLRP1 are associated with diseases of barrier epithelial tissues, including skin lesions and corneal intraepithelial dyskeratosis, suggesting that NLRP1 functions within the eye. Here, we investigated the expression and activity of the NLRP1 inflammasome in primary human corneal epithelial (pHCE) cells.

METHODS

The small molecule Val-boroPro (VbP) activates the NLRP1 inflammasome. Proteasome (bortezomib, MG132) and caspase-1 (VX-765, Z-VAD-FMK) inhibitors block NLRP1 activation and downstream pyroptosis, respectively. Here, we treated pHCE cells with VbP alone or in combination proteasome inhibitors and caspase-1 inhibitors. We assessed NLRP1 expression and hallmarks of pyroptosis, including lytic cell rupture, cytokine processing and release, and gasdermin D (GSDMD) processing.

RESULTS

VbP triggered pyroptosis in pHCE cells, as determined by cytokine secretion, GSDMD processing, and lactate dehydrogenase (LDH) release. Proteasome and caspase-1 inhibitors completely blocked this pyroptotic cell death. In contrast, other primary ocular epithelial cells did not undergo NLRP1-dependent pyroptosis.

CONCLUSIONS

Our findings demonstrate that NLRP1 forms a functional inflammasome in pHCE cells. Importantly, these data reveal that NLRP1 is a key innate immune sensor of the corneal epithelium, and moreover indicate how aberrant inflammasome activation causes corneal damage. Blockade of NLRP1 signaling may benefit patients with hyperactive NLRP1 mutations and warrants further investigation.

CCR2 and DPP9 expression in the peripheral blood of COVID-19 patients: Influences of the disease severity and gender

Introduction

Hyper-inflammatory reactions play a crucial role in the pathogenesis of the severe forms of COVID-19. However, clarification of the molecular basis of the inflammatory-related factors needs more consideration. The aim was to evaluate the gene expression of two fundamental molecules contributing to the induction of inflammatory like CCR2 and DPP9 in cells from peripheral blood samples from patients with various patterns of COVID-19.

Methods

Peripheral blood samples were collected from 470 patients (235 male and 235 female) with RT-qPCR-confirmed COVID-19 test exhibiting moderate, severe, and critical symptoms based on WHO criteria. 100 healthy subjects (50 male and 50 female) were also enrolled in the study as a control group. The gene expression of DPP-9 and CCR-2 was assessed in the blood samples using real-time PCR method.

Results

The COVID-19 patients in severe stage expressed higher levels of CCR2 and DPP9 compared with healthy controls. In male and female patients, the levels of CCR2 and DDP9 expression significantly differed between moderate, severe, and critical patterns (p < 0.0001) as well as between each COVID-19 form and control group (p < 0.0001). The male patients with severe COVID-19 expressed greater levels of CCR2 and DPP-9 than female with same disease form. The female patients with moderate and critical COVID-19 expressed greater levels of CCR2 and DPP-9 than male patients with same disease stage.

Conclusion

We demonstrated that the expression of DPP-9 and CCR-2 was substantially increased in COVID-19 patients with different forms of disease. Considerable differences were also demonstrated between male and female with different patterns of disease. Therefore, we suggest to consider the gender of patients and disease severity for management of COVID-19.

Chemical Modulation of Gasdermin-Mediated Pyroptosis and Therapeutic Potential

Pyroptosis, a lytic form of programmed cell death, both stimulates effective immune responses and causes tissue damage. Gasdermin (GSDM) proteins are a family of pore-forming executors of pyroptosis. While the most-studied member, GSDMD, exerts critical functions in inflammasome biology, emerging evidence demonstrates potential broad relevance for GSDM-mediated pyroptosis across diverse pathologies. In this review, we describe GSDM biology, outline conditions where inflammasomes and GSDM-mediated pyroptosis represent rational therapeutic targets, and delineate strategies to manipulate these central immunologic processes for the treatment of human disease.

M24B aminopeptidase inhibitors selectively activate the CARD8 inflammasome

Inflammasomes are multiprotein complexes that sense intracellular danger signals and induce pyroptosis. CARD8 and NLRP1 are related inflammasomes that are repressed by the enzymatic activities and protein structures of the dipeptidyl peptidases 8 and 9 (DPP8/9). Potent DPP8/9 inhibitors such as Val-boroPro (VbP) activate both NLRP1 and CARD8, but chemical probes that selectively activate only one have not been identified. Here we report a small molecule called CQ31 that selectively activates CARD8. CQ31 inhibits the M24B aminopeptidases prolidase (PEPD) and Xaa-Pro aminopeptidase 1 (XPNPEP1), leading to the accumulation of proline-containing peptides that inhibit DPP8/9 and thereby activate CARD8. NLRP1 is distinct from CARD8 in that it directly contacts DPP8/9's active site; these proline-containing peptides, unlike VbP, do not disrupt this repressive interaction and thus do not activate NLRP1. We expect that CQ31 will now become a valuable tool to study CARD8 biology.

Innate Sensors Trigger Regulated Cell Death to Combat Intracellular Infection

Intracellular pathogens pose a significant threat to animals. In defense, innate immune sensors attempt to detect these pathogens using pattern recognition receptors that either directly detect microbial molecules or indirectly detect their pathogenic activity. These sensors trigger different forms of regulated cell death, including pyroptosis, apoptosis, and necroptosis, which eliminate the infected host cell niche while simultaneously promoting beneficial immune responses. These defenses force intracellular pathogens to evolve strategies to minimize or completely evade the sensors. In this review, we discuss recent advances in our understanding of the cytosolic pattern recognition receptors that drive cell death, including NLRP1, NLRP3, NLRP6, NLRP9, NLRC4, AIM2, IFI16, and ZBP1. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Trimetazidine affects pyroptosis by targeting GSDMD in myocardial ischemia/reperfusion injury

OBJECTIVE

Trimetazidine (TMZ) exerts a strong inhibitory effect on ischemia/reperfusion (I/R) injury. Inflammation plays a key role in I/R injury. We hypothesized that TMZ may protect cardiomyocytes from I/R injury by inhibiting inflammation.

METHODS

The left anterior descending coronary artery was ligated for 30 min followed by 6 h of reperfusion to establish a model of I/R injury. H9c2 cardiomyocytes were subjected to 2 h of hypoxia and 3 h of normoxic conditions to establish a model of hypoxia/reoxygenation (H/R) injury. We monitored the change in pyroptosis by performing Western blot analysis, microscopy and ELISA.

RESULTS

I/R and H/R treatment stimulated gasdermin D-N domain (GSDMD-N) expression in cardiomyocytes (sham onefold vs. I/R 2.5-fold; control onefold vs. H/R 2.0-fold). Moreover, TMZ increased the viability of H9c2 cardiomyocytes subjected to H/R treatment (H/R 65.0% vs. H/R + TMZ 85.3%) and reduced the infarct size in vivo (I/R 47.0% vs. I/R + TMZ 28.3%). H/R and I/R treatment increased the levels of TLR4, MyD88, phospho-NF-κB p65 and the NLRP3 inflammasome; however, TMZ reduced the expression of these proteins. Additionally, TMZ inhibited noncanonical inflammasome signaling induced by I/R injury.

CONCLUSIONS

In summary, TMZ alleviated pyroptosis induced by myocardial I/R injury through the TLR4/MyD88/NF-κB/NLRP3 inflammasome pathway. Therefore, TMZ represents an alternative treatment for myocardial I/R injury.

Human NLRP1: From the shadows to center stage

In response to infection or cell damage, inflammasomes form intracellular multimeric protein complexes that play an essential role in host defense. Activation results in the maturation and subsequent secretion of pro-inflammatory cytokines of the IL-1 family and a specific cell death coined pyroptosis. Human NLRP1 was the first inflammasome-forming sensor identified at the beginning of the millennium. However, its functional relevance and its mechanism of activation have remained obscure for many years. Recent discoveries in the NLRP1 field have propelled our understanding of the functional relevance and molecular mode of action of this unique inflammasome sensor, which we will discuss in this perspective.

VX-765 ameliorates renal injury and fibrosis in diabetes by regulating caspase-1-mediated pyroptosis and inflammation

INTRODUCTION

As a lytic inflammatory cell death, pyroptosis has been recently described but has not been unequivocally elucidated in diabetic nephropathy (DN). VX-765 is a safe and effective inhibitor of caspase-1, that was well tolerated in a phase II clinical trial in patients with epilepsy, but its application in DN is still undefined.

MATERIALS AND METHODS

Immunoblot, co-immunoprecipitation, confocal microscope and flow cytometry were used to analyze the effects of glucose on pyroptosis in renal tubular epithelia (HK-2). In vitro, selective caspase-1 inhibitors VX-765 and Z-YVAD-FMK were administered. Pyroptosis and fibrogenesis were determined by immunoblot, ELISA, cytotoxicity assay and flow cytometry. In vivo, diabetic mice were administered with 100 mg/kg VX-765. Renal function, pathological changes, and the expressions of NLRC4, GSDMD, IL-1β, collagen I, fibronectin and CD45 in renal cortex were evaluated.

RESULTS

We identified NLRC4 as a sensor for caspase-1 activation. Moreover, we provided morphological and molecular evidence for pyroptosis in glucose-stressed tubular cells, including ballooned cell membrane, caspase-1 immunoreactivity, GSDMD cleavage, and the release of inflammatory cytokine and cellular contents. All these effects were prevented by treatment with VX-765 or Z-YVAD-FMK, confirming that caspase-1 effectively regulates the occurrence of pyroptosis in HK-2 cells. In vivo, treatment of diabetic animals with VX-765 ameliorated renal function, suppressed inflammatory cell infiltration and pyroptosis-associated protein expression, and mitigated tubulointerstitial fibrosis.

CONCLUSIONS

This work revealed that caspase-1-mediated pyroptosis drives renal inflammation and fibrosis in diabetes. Our results are the first demonstration of VX-765 representing a promising therapeutic opportunity for alleviating the progression of DN.

Inflammasome activation as a link between obesity and thyroid disorders: Implications for an integrated clinical management

Obesity is strongly associated with chronic low-grade inflammation. Obese patients have an increased risk to develop thyroid autoimmunity and to became hypothyroid, suggesting a pathogenetic link between obesity, inflammation and autoimmunity. Moreover, type 2 diabetes and dyslipidemia, also characterized by low-grade inflammation, were recently associated with more aggressive forms of Graves' ophthalmopathy. The association between obesity and autoimmune thyroid disorders may also go in the opposite direction, as treating autoimmune hyper and hypothyroidism can lead to weight gain. In addition, restoration of euthyroidism by L-T4 replacement therapy is more challenging in obese athyreotic patients, as it is difficult to maintain thyrotropin stimulation hormone (TSH) values within the normal range. Intriguingly, pro-inflammatory cytokines decrease in obese patients after bariatric surgery along with TSH levels. Moreover, the risk of thyroid cancer is increased in patients with thyroid autoimmune disorders, and is also related to the degree of obesity and inflammation. Molecular studies have shown a relationship between the low-grade inflammation of obesity and the activity of intracellular multiprotein complexes typical of immune cells (inflammasomes). We will now highlight some clinical implications of inflammasome activation in the relationship between obesity and thyroid disease.

Potential therapeutic role of pyroptosis mediated by the NLRP3 inflammasome in type 2 diabetes and its complications

As a new way of programmed cell death, pyroptosis plays a vital role in many diseases. In recent years, the relationship between pyroptosis and type 2 diabetes (T2D) has received increasing attention. Although the current treatment options for T2D are abundant, the occurrence and development of T2D appear to continue, and the poor prognosis and high mortality of patients with T2D remain a considerable burden in the global health system. Numerous studies have shown that pyroptosis mediated by the NLRP3 inflammasome can affect the progression of T2D and its complications; targeting the NLRP3 inflammasome has potential therapeutic effects. In this review, we described the molecular mechanism of pyroptosis more comprehensively, discussed the most updated progress of pyroptosis mediated by NLRP3 inflammasome in T2D and its complications, and listed some drugs and agents with potential anti-pyroptosis effects. Based on the available evidence, exploring more mechanisms of the NLRP3 inflammasome pathway may bring more options and benefits for preventing and treating T2D and drug development.

Merging the Versatile Functionalities of Boronic Acid with Peptides

Peptides inherently feature the favorable properties of being easily synthesized, water-soluble, biocompatible, and typically non-toxic. Thus, boronic acid has been widely integrated with peptides with the goal of discovering peptide ligands with novel biological activities, and this effort has led to broad applications. Taking the integration between boronic acid and peptide as a starting point, we provide an overview of the latest research advances and highlight the versatile and robust functionalities of boronic acid. In this review, we summarize the diverse applications of peptide boronic acids in medicinal chemistry and chemical biology, including the identification of covalent reversible enzyme inhibitors, recognition, and detection of glycans on proteins or cancer cell surface, delivery of siRNAs, development of pH responsive devices, and recognition of RNA or bacterial surfaces. Additionally, we discuss boronic acid-mediated peptide cyclization and peptide modifications, as well as the facile chemical synthesis of peptide boronic acids, which paved the way for developing a growing number of peptide boronic acids.

DPP inhibition alters the CXCR3 axis and enhances NK and CD8+ T cell infiltration to improve anti-PD1 efficacy in murine models of pancreatic ductal adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is projected to be the second leading cause of cancer death in the USA by 2030. Immune checkpoint inhibitors fail to control most PDAC tumors because of PDAC’s extensive immunosuppressive microenvironment and poor immune infiltration, a phenotype also seen in other non-inflamed (ie, ‘cold’) tumors. Identifying novel ways to enhance immunotherapy efficacy in PDAC is critical. Dipeptidyl peptidase (DPP) inhibition can enhance immunotherapy efficacy in other cancer types; however, the impact of DPP inhibition on PDAC tumors remains unexplored.

Methods

We examined the effects of an oral small molecule DPP inhibitor (BXCL701) on PDAC tumor growth using mT3-2D and Pan02 subcutaneous syngeneic murine models in C57BL/6 mice. We explored the effects of DPP inhibition on the tumor immune landscape using RNAseq, immunohistochemistry, cytokine evaluation and flow cytometry. We then tested if BXCL701 enhanced anti-programmed cell death protein 1 (anti-PD1) efficacy and performed immune cell depletion and rechallenged studies to explore the relevance of cytotoxic immune cells to combination treatment efficacy.

Results

In both murine models of PDAC, DPP inhibition enhanced NK and T cell immune infiltration and reduced tumor growth. DPP inhibition also enhanced the efficacy of anti-PD1. The efficacy of dual anti-PD1 and BXCL701 therapy was dependent on both CD8+ T cells and NK cells. Mice treated with this combination therapy developed antitumor immune memory that cleared some tumors after re-exposure. Lastly, we used The Cancer Genome Atlas (TCGA) to demonstrate that increased NK cell content, but not T cell content, in human PDAC tumors is correlated with longer overall survival. We propose that broad DPP inhibition enhances antitumor immune response via two mechanisms: (1) DPP4 inhibition increases tumor content of CXCL9/10, which recruits CXCR3+ NK and T cells, and (2) DPP8/9 inhibition activates the inflammasome, resulting in proinflammatory cytokine release and Th1 response, further enhancing the CXCL9/10-CXCR3 axis.

Conclusions

These findings show that DPP inhibition with BXCL701 represents a pharmacologic strategy to increase the tumor microenvironment immune cell content to improve anti-PD1 efficacy in PDAC, suggesting BXCL701 can enhance immunotherapy efficacy in ‘cold’ tumor types. These findings also highlight the potential importance of NK cells along with T cells in regulating PDAC tumor growth.

Dipeptidyl Peptidase Inhibition Enhances CD8 T Cell Recruitment and Activates Intrahepatic Inflammasome in a Murine Model of Hepatocellular Carcinoma

Simple Summary

This study reported, for the first time, on the expression and activity of the dipeptidyl peptidase 4 (DPP4) family during the development of hepatocellular carcinoma (HCC). We also demonstrated that the pan-DPP inhibitory compound ARI-4175 significantly reduced the number of macroscopic liver nodules in a mouse HCC model. ARI-4175 increased intrahepatic inflammatory cell infiltration, CD8⁺ T cell numbers and caspase-1-mediated inflammasome activation in the HCC-bearing liver. Thus, this study provides promising data on the efficacy of ARI-4175 in the treatment of early-stage HCC. Targeting the DPP4 family may be a novel and effective approach to promote anti-tumour immunity in HCC via caspase-1 activation.

Abstract

The mRNA expression of the dipeptidyl peptidase 4 (DPP4) gene family is highly upregulated in human hepatocellular carcinoma (HCC) and is associated with poor survival in HCC patients. Compounds that inhibit the DPP4 enzyme family, such as talabostat and ARI-4175, can mediate tumour regression by immune-mediated mechanisms that are believed to include NLRP1 activation. This study investigated the expression and activity of the DPP4 family during the development of HCC and evaluated the efficacy of ARI-4175 in the treatment of early HCC in mice. This first report on this enzyme family in HCC-bearing mice showed DPP9 upregulation in HCC, whereas intrahepatic DPP8/9 and DPP4 enzyme activity levels decreased with age. We demonstrated that ARI-4175 significantly lowered the total number of macroscopic liver nodules in these mice. In addition, ARI-4175 increased intrahepatic inflammatory cell infiltration, including CD8⁺ T cell numbers, into the HCC-bearing livers. Furthermore, ARI-4175 activated a critical component of the inflammasome pathway, caspase-1, in these HCC-bearing livers. This is the first evidence of caspase-1 activation by a pan-DPP inhibitor in the liver. Our data suggest that targeting the DPP4 enzyme family may be a novel and effective approach to promote anti-tumour immunity in HCC via caspase-1 activation.