The advances in pyroptosis initiated by inflammasome in inflammatory and immune diseases

The regulation of pyroptosis by post-translational modifications: molecular mechanisms and therapeutic targets

Pyroptosis, a type of programmed cell death mediated by gasdermin family proteins, releases a large amount of immune stimulatory substances, which further contribute to inflammation and elicit an adaptive immune response against tumours and pathogens. And it occurs through multiple pathways that involve the activation of specific caspases and the cleavage of gasdermins. Post-translational modifications (PTMs) could influence the chemical properties of the modified residues and neighbouring regions, ultimately affecting the activity, stability, and functions of proteins to regulate pyroptosis. Many studies have been conducted to explore the influence of PTMs on the regulation of pyroptosis. In this review, we provide a comprehensive summary of different types of PTMs that influence pyroptosis, along with their corresponding modifying enzymes. Moreover, it elaborates on the specific contributions of different PTMs to pyroptosis and delves into how the regulation of these modifications can be leveraged for therapeutic interventions in cancer and inflammatory diseases.

Nanoparticle-mediated cell pyroptosis: a new therapeutic strategy for inflammatory diseases and cancer

Pyroptosis, a lytic form of cell death mediated by the gasdermin family, is characterized by cell swelling and membrane rupture. Inducing pyroptosis in cancer cells can enhance antitumor immune responses and is a promising strategy for cancer therapy. However, excessive pyroptosis may trigger the development of inflammatory diseases due to immoderate and continuous inflammatory reactions. Nanomaterials and nanobiotechnology, renowned for their unique advantages and diverse structures, have garnered increasing attention owing to their potential to induce pyroptosis in diseases such as cancer. A nano-delivery system for drug-induced pyroptosis in cancer cells can overcome the limitations of small molecules. Furthermore, nanomedicines can directly induce and manipulate pyroptosis. This review summarizes and discusses the latest advancements in nanoparticle-based treatments with pyroptosis among inflammatory diseases and cancer, focusing on their functions and mechanisms and providing valuable insights into selecting nanodrugs for pyroptosis. However, the clinical application of these strategies still faces challenges owing to a limited understanding of nanobiological interactions. Finally, future perspectives on the emerging field of pyroptotic nanomaterials are presented.

TREM-1 inhibition or ondansetron administration ameliorates NLRP3 inflammasome and pyroptosis in traumatic brain injury-induced acute lung injury

Introduction

Recently, NLR family pyrin domain containing 3 (NLRP3) and pyroptosis have been reported to be involved in traumatic brain injury-induced acute lung injury (TBI-ALI). Studies have shown that triggering receptor expressed on myeloid cells-1 (TREM-1) may be one of the upstream molecules regulating NLRP3/pyroptosis, and 5-hydroxytryptamine type 3-receptor (5-HT3R) antagonists can inhibit NLRP3/pyroptosis. However, the role of TRME-1 in TBI-ALI, the therapeutic effect of 5-HT3R inhibition on TBI-ALI and its mechanism are still unclear. Therefore, this study aimed to evaluate the protective effect of ondansetron, a 5-HT3 inhibitor, on TBI-ALI, and to explore whether the underlying mechanism is related to the regulation of TREM-1.

Material and methods

A TBI-ALI rat model was constructed via lateral fluid percussion (LFP) brain injury, and either TREM-1 inhibitor (LP17) or ondansetron was administered as needed.

Results

TBI induced NLRP3 inflammasome, pyroptosis, and TREM-1 activation in rat lung tissues in a time-dependent manner. Inhibition of TREM-1 activity attenuated TBI-ALI; this is evident from reduced pathological scores, wet/dry ratios, and bronchoalveolar lavage fluid protein levels and alleviated NLRP3 inflammasome/pyroptosis. In addition, ondansetron reduced NLRP3 inflammasome/pyroptosis and alleviated TBI-ALI. Moreover, ondansetron reduced TREM-1 activation in macrophages and lung tissue.

Conclusions

Ondansetron alleviated TBI-ALI. In terms of mechanism, TREM-1 promotes TBI-ALI via the NLRP3-related pyroptosis pathway, and the protective effect of ondansetron on TBI-ALI may be related to the inhibition of TREM-1.

Total paeony glycoside relieves neuroinflammation to exert antidepressant effect via the interplay between NLRP3 inflammasome, pyroptosis and autophagy

BACKGROUND

Depression is a common mental illness characterised by abnormal and depressed emotions. Total paeony glycoside (TPG) is a naturally active saponin extracted from the traditional Chinese medicine Radix Paeoniae rubra. However, the antidepressant and neuroinflammatory effects of TPG have not been thoroughly studied.

PURPOSE

To study the therapeutic potential of TGP in depression caused by neuronal injury and neuroinflammation and to explore the mechanism of TGP and the relationship between the NLRP3 inflammasome, pyroptosis, and autophagy.

STUDY DESIGN

A chronic unpredictable mild stress (CUMS)-induced depression model and a cell model of corticosterone (CORT)-induced hippocampal neuron injury were established to evaluate the therapeutic effects of TPG.

METHODS

The composition of TPG was analysed using high-performance liquid chromatography and mass spectrometry. The effects of TPG and fluoxetine on depression-like behaviour, neuronal injury, neuroinflammation, pyroptosis, and mitochondrial autophagy in the mice models were evaluated.

RESULTS

TGP alleviated depression-like behaviours in mice and inhibited hippocampal neuronal apoptosis. The secretion of inflammatory cytokines was significantly reduced in CORT-induced hippocampal neuron cells and in the serum of a mouse model of CUMS-induced depression. In addition, TGP treatment reduced the levels of NLRP3 family pyrin structural domains, including NLRP3, pro-caspase-1, caspase-1, and IL-1β, and the pyroptosis related proteins such as GSDMD-N. Importantly, TPG attenuated mitochondrial dysfunction, promoted the clearance of damaged mitochondria, and the activation of mitochondrial autophagy, which reduced ROS accumulation and NLRP3 inflammasome activation. An in-depth study observed that the regulatory effect of TPG on autophagy was attenuated by the autophagy inhibitor 3-methyladenine (3-MA) in vitro and in vivo. However, administration of the caspase-1 inhibitor Belnacasan (VX-765) successfully inhibited pyroptosis and showed a synergistic therapeutic effect with TPG.

CONCLUSION

These results indicate that TPG can repair neuronal damage by activating autophagy, restoring mitochondrial function, and reducing inflammation-mediated pyroptosis, thereby playing an important role in the alleviation of neuroinflammation and depression. This study suggests new potential drugs and treatment strategies for neuroinflammation-related diseases and depression.

New insights into Gasdermin D pore formation

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

GSDMD mediated pyroptosis induced inflammation of Graves' orbitopathy via the NF-κB/ AIM2/ Caspase-1 pathway

Gasdermin D (GSDMD) is a key executor which triggers pyroptosis as well as an attractive checkpoint in various inflammatory and autoimmune diseases but it has yet to prove its function in Graves'orbitopathy (GO). Our aim was to investigate GSDMD levels in orbital connective tissue and serum of GO patients and then assess the association between serum levels and patients' clinical activity score (CAS). Further, GSDMD-mediated pyroptosis and the underlying mechanism in inflammatory pathogenesis in the cultured orbital fibroblasts (OFs) of GO patients were examined. OFs were collected after tumor necrosis factor (TNF)-α or interferon (IFN)-γ treatment or combination treatment at different times, and the expression of GSDMD and related molecular mechanisms were analyzed. Then, we constructed the GSDMD knockout system with siRNA and the system was further exposed to the medium with or without IFN-γ and TNF-α for a specified time. Finally, we evaluated the production of interleukin (IL)-1β and IL-18. We found that serum GSDMD levels were elevated and positively correlated with the CAS in GO patients. Meanwhile, the expression of GSDMD and N-terminal domain (NT-GSDMD) in orbital connective tissue of GO patients was augmented. Also, increased expression of GSDMD and related pyroptosis factors was observed in vitro model of GO. We further demonstrated that GSDMD-mediated pyroptosis induced inflammation via the nuclear factor kB (NF-κB)/absent in melanoma-2 (AIM-2)/caspase-1 pathway. In addition, blocking GSDMD suppressed proinflammatory cytokine production in GO. We concluded that GSDMD may be a biomarker as well as a potential target for the evaluation and treatment of inflammation related with GO.

The role of pyroptosis in incomplete immune reconstitution among people living with HIV：Potential therapeutic targets

Globally, HIV infection causes significant morbidity and mortality, and is a major public health problem. Despite the fact that widespread use of antiretroviral therapy (ART) has substantially altered the natural history of HIV infection from originally being a universally lethal disease to now being a chronic medical condition for those taking appropriate treatment, approximately 10-40% of people living with HIV (PLWH) who take effective ART and maintain long-term viral suppression fail to achieve normalization of CD4 + T-cell counts. This phenomenon is referred to as incomplete immune reconstitution or immunological non-response. Although the precise mechanisms underlying this outcome have not been elucidated, recent evidence indicates that excessive pyroptosis may play a crucial role in the development of incomplete immune reconstitution. Pyroptosis is characterized by the formation of pores in the cell membrane, cell rupture, and secretion of intracellular contents and pro-inflammatory cytokines, including IL-1β and IL-18. This excessive inflammation-induced programmed cell death leads to a massive loss of CD4 + T-cells, and inflammatory consequences that may promote and sustain incomplete immune reconstitution. Herein, we review the possible pathways activated in HIV infection by inflammasomes that act as switches of pyroptosis, and the role of pyroptosis in HIV, as well as the relevance of CD4 + T-cells in incomplete immune reconstitution. We also highlight the possible mechanisms of pyroptosis involved in incomplete immune reconstitution, thus paving the way for the development of potential targets for the treatment of incomplete immune reconstitution.

Establishment of a novel indicator of pyroptosis regulated gene transcription level and its application in pan-cancer

Pyroptosis is a type of programmed cell death and plays a dual role in distinct cancers. It is elusive to evaluate the activation level of pyroptosis and to appraise the involvement of pyroptosis in the occurrence and development of diverse tumors. Accordingly, we herein established an indicator to evaluate pyroptosis related gene transcription levels based on the expression level of genes involved in pyroptosis and tried to elaborated on the association between pyroptosis and tumors across diverse tumor types. We found that pyroptosis related gene transcription levels could predict the prognosis of patients, which could act as either a favorable or a dreadful factor in diverse cancers. According to signaling pathway analyses we observed that pyroptosis played a significant role in immune regulation and tumorigenesis and had strong links with other forms of cell death. We also performed analysis on the crosstalk between pyroptosis and immune status and further investigated the predictive potential of pyroptosis level for the efficacy of immunotherapy. Lastly, we manifested that pyroptosis status could serve as a biomarker to the efficacy of chemotherapy across various cancers. In summary, this study established a quantitative indicator to evaluate pyroptosis related gene transcription levels, systematically explored the role of pyroptosis in pan-cancer. These results could provide potential research directions targeting pyroptosis, and highlighted that pyroptosis may be used to develop a novel strategy for the treatment of cancer.

Ursolic Acid Promotes Autophagy by Inhibiting Akt/mTOR and TNF-α/TNFR1 Signaling Pathways to Alleviate Pyroptosis and Necroptosis in Mycobacterium tuberculosis-Infected Macrophages

As a lethal infectious disease, tuberculosis (TB) is caused by Mycobacterium tuberculosis (Mtb). Its complex pathophysiological process limits the effectiveness of many clinical treatments. By regulating host cell death, Mtb manipulates macrophages, the first line of defense against invading pathogens, to evade host immunity and promote the spread of bacteria and intracellular inflammatory substances to neighboring cells, resulting in widespread chronic inflammation and persistent lung damage. Autophagy, a metabolic pathway by which cells protect themselves, has been shown to fight intracellular microorganisms, such as Mtb, and they also play a crucial role in regulating cell survival and death. Therefore, host-directed therapy (HDT) based on antimicrobial and anti-inflammatory interventions is a pivotal adjunct to current TB treatment, enhancing anti-TB efficacy. In the present study, we showed that a secondary plant metabolite, ursolic acid (UA), inhibited Mtb-induced pyroptosis and necroptosis of macrophages. In addition, UA induced macrophage autophagy and enhanced intracellular killing of Mtb. To investigate the underlying molecular mechanisms, we explored the signaling pathways associated with autophagy as well as cell death. The results showed that UA could synergistically inhibit the Akt/mTOR and TNF-α/TNFR1 signaling pathways and promote autophagy, thus achieving its regulatory effects on pyroptosis and necroptosis of macrophages. Collectively, UA could be a potential adjuvant drug for host-targeted anti-TB therapy, as it could effectively inhibit pyroptosis and necroptosis of macrophages and counteract the excessive inflammatory response caused by Mtb-infected macrophages via modulating the host immune response, potentially improving clinical outcomes.

Identification of a novel pyroptosis-related gene signature in human spermatogenic dysfunction

PURPOSE

To reveal the underlying roles that pyroptosis-related genes (PRGs) played in human spermatogenic dysfunction.

METHODS

One discovery set and three validation sets were employed to inspect the previously reported 33 PRGs in the human testis with different status of spermatogenesis. PRGs that differentially expressed in all sets were considered as key differentially expressed pyroptosis-related genes (PR-DEGs). The relationships between key PR-DEGs and samples' clinicopathological, therapeutic, and immune patterns were respectively studied. Single-cell RNA sequencing (scRNS-seq) analyses were conducted to show the expression changes and related mechanisms of key PR-DEGs at a single-cell resolution.

RESULTS

CASP4 and GPX4 were identified as two key PR-DEGs. These two genes were significantly dysregulated in spermatogenic dysfunctional samples, but with opposite tendency. CASP4 was negatively correlated with Johnsen scores but positively correlated with follicle-stimulating hormone (FSH) levels (all p < 0.05), while GPX4 exhibited significant positive correlations with Johnsen scores and negative relevance with FSH. For treatments, both molecules showed a prospective value of being predictors for sperm retrieval surgeries. Moreover, CASP4 and GPX4 were potential immunoregulators in the testicular immune microenvironment and showed significant correlations to testicular macrophages and mast cell infiltration. In scRNA-seq analyses, GPX4 was highly expressed in germ cells, which therefore suffered a sharp reduction with the loss of germ cells in spermatogenic dysfunction. On the other hand, CASP4 were basically somatic cell-derived, and the proportion of CASP4-positive Leydig cells significantly increased in disease testes (p = 0.0001).

CONCLUSION

In all, we revealed two key PRGs of human testes that might be functional in spermatogenic dysfunction.

Resistance of hypervirulent Klebsiella pneumoniae to cathepsin B-mediated pyroptosis in murine macrophages

Introduction

Hypervirulent Klebsiella pneumoniae (hvKp) has emerged as a clinically significant global pathogen in the last decade. However, the host immune responses of the macrophages during hvKp infection are largely unknown. In the present study, we aimed to compare the cytotoxic effects of hvKp and classical K. pneumoniae (cKp) in murine macrophages.

Results

We found that the activation of caspase-1 -dependent pyroptosis was higher in cKp-infected macrophages compared with that in hvKp-infected macrophages. In Caspase-1 deficiency macrophages, pyroptosis diminished during infection. Both hvKp and cKp strains led to nucleotide-binding and oligomerization domain-like receptor protein 3 (NLRP3) inflammasome formation and lysosomal cathepsin B activation, thus resulting in pyroptosis. Compared with the cKp strain, the hvKp strain inhibited these phenomena in murine macrophages.

Conclusion

HvKp infection resulted in different levels of pyroptosis via the activation of cathepsin B-NLRP3-caspase-1 in murine macrophages. Therefore, the manipulation of pyroptotic cell death is a potential target for host response during hvKp infection in macrophages.

Role of inflammasome in severe, steroid-resistant asthma

Purpose of review

Asthma is a common heterogeneous group of chronic inflammatory diseases with different pathological phenotypes classified based on the various clinical, physiological and immunobiological profiles of patients. Despite similar clinical symptoms, asthmatic patients may respond differently to treatment. Hence, asthma research is becoming more focused on deciphering the molecular and cellular pathways driving the different asthma endotypes. This review focuses on the role of inflammasome activation as one important mechanism reported in the pathogenesis of severe steroid resistant asthma (SSRA), a Th2-low asthma endotype. Although SSRA represents around 5-10% of asthmatic patients, it is responsible for the majority of asthma morbidity and more than 50% of asthma associated healthcare costs with clear unmet need. Therefore, deciphering the role of the inflammasome in SSRA pathogenesis, particularly in relation to neutrophil chemotaxis to the lungs, provides a novel target for therapy.

Recent findings

The literature highlighted several activators of inflammasomes that are elevated during SSRA and result in the release of proinflammatory mediators, mainly IL-1β and IL-18, through different signaling pathways. Consequently, the expression of NLRP3 and IL-1β is shown to be positively correlated with neutrophil recruitment and negatively correlated with airflow obstruction. Furthermore, exaggerated NLRP3 inflammasome/IL-1β activation is reported to be associated with glucocorticoid resistance.

Summary

In this review, we summarized the reported literature on the activators of the inflammasome during SSRA, the role of IL-1β and IL-18 in SSRA pathogenesis, and the pathways by which inflammasome activation contributes to steroid resistance. Finally, our review shed light on the different levels to target inflammasome involvement in an attempt to ameliorate the serious outcomes of SSRA.

Beneficial effects of flavonoids on cardiovascular diseases by influencing NLRP3 inflammasome

Cardiovascular diseases (CVDs) are a leading cause of global mortality and have a high incidence rate worldwide. The function of inflammasomes in CVDs has received a lot of attention recently, and the nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome may be a new target for the prevention and treatment of CVDs. Flavonoids, which are found in food and plant extracts, inhibited inflammation in CVDs by regulating the NLRP3 inflammasome. CB-Dock was used to investigate whether 34 flavonoids from natural products acted on NLRP3 inflammasome. In brief, the PDB format of NLRP3 was selected as a protein file, and 34 flavonoids in SDF format were selected as the ligand file, and then input to CB-Dock for molecular docking. The docking results showed that epigallocatechin-3-gallate (EGCG), amentoflavone, baicalin, scutellarin, vitexin, silibinin, and puerarin had good binding affinities to NLRP3, which could be used as NLRP3 inhibitors, and aid in the discovery of lead compounds for the design and development of CVDs.

Jinyinqingre Oral Liquid alleviates LPS-induced acute lung injury by inhibiting the NF-κB/NLRP3/GSDMD pathway

Acute lung injury (ALI) is a prevalent and severe clinical condition characterized by inflammatory damage to the lung endothelial and epithelial barriers, resulting in high incidence and mortality rates. Currently, there is a lack of safe and effective drugs for the treatment of ALI. In a previous clinical study, we observed that Jinyinqingre oral liquid (JYQR), a Traditional Chinese Medicine formulation prepared by the Taihe Hospital, Affiliated Hospital of Hubei University of Medicine, exhibited notable efficacy in treating inflammation-related hepatitis and cholecystitis in clinical settings. However, the potential role of JYQR in ALI/acute respiratory distress syndrome (ARDS) and its anti-inflammatory mechanism remains unexplored. Thus, the present study aimed to investigate the therapeutic effects and underlying molecular mechanisms of JYQR in ALI using a mouse model of lipopolysaccharide (LPS)-induced ALI and an in vitro RAW264.7 cell model. JYQR yielded substantial improvements in LPS-induced histological alterations in lung tissues. Additionally, JYQR administration led to a noteworthy reduction in total protein levels within the BALF, a decrease in MPAP, and attenuation of pleural thickness. These findings collectively highlight the remarkable efficacy of JYQR in mitigating the deleterious effects of LPS-induced ALI. Mechanistic investigations revealed that JYQR pretreatment significantly inhibited NF-κB activation and downregulated the expressions of the downstream proteins, namely NLRP3 and GSDMD, as well as proinflammatory cytokine levels in mice and RAW2647 cells. Consequently, JYQR alleviated LPS-induced ALI by inhibiting the NF-κB/NLRP3/GSDMD pathway. JYQR exerts a protective effect against LPS-induced ALI in mice, and its mechanism of action involves the downregulation of the NF-κB/NLRP3/GSDMD inflammatory pathway.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

PPAR-γ Activation Alleviates Osteoarthritis through Both the Nrf2/NLRP3 and PGC-1α/Δψm Pathways by Inhibiting Pyroptosis

Osteoarthritis (OA) is a common degenerative joint disease with a gradually increasing morbidity in the aging and obese population. Emerging evidence has implicated pyroptosis in the etiology of OA and it may be recognized as a therapeutic target in OA. We have previously reported regarding another disease that peroxisome proliferator-activated receptor gamma (PPAR-γ) activation exerts an anti-inflammatory effect by suppressing the nucleotide-binding and oligomerization domain-like receptor containing protein (NLRP) 3 inflammasome. However, the relationship between PPAR-γ and NLRP3-mediated pyroptosis in OA cartilage and its underlying mechanisms is fully unclear. In this study, we found that the level of NLRP3-mediated pyroptosis in severe lateral femoral condyle cartilage wear in the knee of an OA patient was significantly higher than that in the mild lateral femoral condyle cartilage wear areas. Moreover, in lipopolysaccharide (LPS)/adenosine triphosphate (ATP)-induced primary chondrocytes and knee OA rat models, we demonstrated that activation of PPAR-γ by pioglitazone (Piog) attenuated LPS/ATP-induced chondrocyte pyroptosis and arthritis. These effects were partially counteracted by either blocking the nuclear factor erythroid-2-related factor (Nrf2)/NLRP3 or PGC1-α/Δψm signaling pathway. Simultaneous depression of these two signaling pathways can completely abrogate the protective effects of Piog on OA and chondrocytes. Taken together, Piog protects OA cartilage against pyroptosis-induced damage by simultaneously activating both the Nrf2/NLRP3 and PGC-1α/Δψm pathways, which enhances antioxidative and anti-inflammatory responses as well as mitochondrial biogenesis. Therefore, Piog may be a promising agent for human OA cartilage damage in future clinical treatments.

The Role of Regulated Programmed Cell Death in Osteoarthritis: From Pathogenesis to Therapy

Osteoarthritis (OA) is a worldwide chronic disease that can cause severe inflammation to damage the surrounding tissue and cartilage. There are many different factors that can lead to osteoarthritis, but abnormally progressed programmed cell death is one of the most important risk factors that can induce osteoarthritis. Prior studies have demonstrated that programmed cell death, including apoptosis, pyroptosis, necroptosis, ferroptosis, autophagy, and cuproptosis, has a great connection with osteoarthritis. In this paper, we review the role of different types of programmed cell death in the generation and development of OA and how the different signal pathways modulate the different cell death to regulate the development of OA. Additionally, this review provides new insights into the radical treatment of osteoarthritis rather than conservative treatment, such as anti-inflammation drugs or surgical operation.

The role of selenoprotein M in nickel-induced pyroptosis in mice spleen tissue via oxidative stress

Nickel (Ni) is a heavy metal element and a pollutant that threatens the organism's health. Melatonin (Mel) is an antioxidant substance that can be secreted by the organism and has a protective effect against heavy metals. Selenoprotein M (SelM) is a selenoprotein widely distributed of the body, and its role is to protect these tissues from oxidative damage. To study the mechanism of Ni, Mel, and SelM in mouse spleen, 80 SelM^+/+ wild-type and 80 SelM^-/- homozygous mice were divided into 8 groups with 20 mice in each group. The Ni group was intragastric at a concentration of 10 mg/kg, while the Mel group was intragastric at 2 mg/kg. Mice were injected with 0.1 mL/10 g body weight for 21 days. Histopathological and ultrastructural observations showed the changes in Ni, such as the destruction of white and red pulp and the appearance of pyroptosomes. SelM knockout showed more severe injury, while Mel could effectively interfere with Ni-induced spleen toxicity. The results of antioxidant capacity determination showed that Ni could cause oxidative stress in the spleen, and Mel could also effectively reduce oxidative stress. Finally, Ni exposure increased the expression levels of the pyroptotic genes, including apoptosis-associated speck protein (ASC), absent in melanoma-2 (AIM2), NOD-like receptor thermal protein domain-associated protein 3 (NLRP3), Caspase-1, interleukin- (IL-) 18, and IL-1β (p < 0.05). Loss of SelM significantly increased these (p < 0.05), while Mel decreased the alleviated impact of Ni. In conclusion, the loss of SelM aggravated Ni-induced pyroptosis of the spleen via activating oxidative stress, which was alleviated by Mel, but the effect of Mel was not obvious in the absence of SelM, which reflected the important role of SelM in Ni-induced pyroptosis.

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.

Significance of pyroptosis-related gene in the diagnosis and classification of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA), a chronic autoimmune inflammatory disease, is often characterized by persistent morning stiffness, joint pain, and swelling. Early diagnosis and timely treatment of RA can effectively delay the progression of the condition and significantly reduce the incidence of disability. In the study, we explored the function of pyroptosis-related genes (PRGs) in the diagnosis and classification of rheumatoid arthritis based on Gene Expression Omnibus (GEO) datasets.

METHOD

We downloaded the GSE93272 dataset from the GEO database, which contains 35 healthy controls and 67 RA patients. Firstly, the GSE93272 was normalized by the R software "limma" package. Then, we screened PRGs by SVM-RFE, LASSO, and RF algorithms. To further investigate the prevalence of RA, we established a nomogram model. Besides, we grouped gene expression profiles into two clusters and explored their relationship with infiltrating immune cells. Finally, we analyzed the relationship between the two clusters and the cytokines.

RESULT

CHMP3, TP53, AIM2, NLRP1, and PLCG1 were identified as PRGs. The nomogram model revealed that decision-making based on established model might be beneficial for RA patients, and the predictive power of the nomogram model was significant. In addition, we identified two different pyroptosis patterns (pyroptosis clusters A and B) based on the 5 PRGs. We found that eosinophil, gamma delta T cell, macrophage, natural killer cell, regulatory T cell, type 17 T helper cell, and type 2 T helper cell were significant high expressed in cluster B. And, we identified gene clusters A and B based on 56 differentially expressed genes (DEGs) between pyroptosis cluster A and B. And we calculated the pyroptosis score for each sample to quantify the different patterns. The patients in pyroptosis cluster B or gene cluster B had higher pyroptosis scores than those in pyroptosis cluster A or gene cluster A.

CONCLUSION

In summary, PRGs play vital roles in the development and occurrence of RA. Our findings might provide novel views for the immunotherapy strategies with RA.

METTL3 contributes to slow transit constipation by regulating miR-30b-5p/PIK3R2/Akt/mTOR signaling cascade through DGCR8

BACKGROUND

N6-methyladenosine (m6A) is the most prevalent methylation modification of eukaryotic RNA, and methyltransferase-like 3 (METTL3) plays a vital role in multiple cell functions. This study aimed to investigate the role of m6A methylase METTL3 in slow transit constipation (STC).

MATERIAL AND METHOD

The expression of METTL3 and DGCR8 was measured in STC tissues and glutamic acid-induced interstitial cells of Cajal (ICCs). The effects of METTL3, miR-30b-5p, and DGCR8 on the biological characteristics of ICCs were investigated on the basis of loss-of-function analyses. Luciferase reporter assay was used to identify the direct binding sites of miR-30b-5p with PIK3R2.

RESULTS

The results showed that the METTL3, DGCR8, miR-30b-5p, and the methylation level of m6A were significantly increased in STC tissues and glutamic acid-induced ICCs. Silencing of METTL3 and miR-30b-5p inhibited apoptosis, autophagy, and pyroptosis of glutamic acid-induced ICCs. Moreover, overexpression of miR-30b-5p reversed the cytoprotection of METTL3 knockdown in glutamic acid-induced ICCs. Besides, DGCR8 knockdown could facilitate cell growth and decrease apoptotic glutamic acid-induced ICCs. Mechanically, we illustrated that METTL3 in glutamic acid-induced ICCs significantly accelerated the maturation of pri-miR-30b-5p by m6A methylation modification, resulting in the reduction of PIK3R2, which results in the inhibition of PI3K/Akt/mTOR pathway and ultimately leads to the cell death of STC.

CONCLUSIONS

Collectively, these data demonstrated that METTL3 promoted the apoptosis, autophagy, and pyroptosis of glutamic acid-induced ICCs by interacting with the DGCR8 and successively modulating the miR-30b-5p/PIK3R2 axis in an m6A-dependent manner, and METTL3 may be a potential therapeutic target for STC.

Targeting NLRP3 Inflammasome Alleviates Synovitis by Reducing Pyroptosis in Rats with Experimental Temporomandibular Joint Osteoarthritis

The mechanism of temporomandibular joint osteoarthritis (TMJOA), which leads to the final erosion of cartilage and subchondral bone, has been widely demonstrated, but still not clearly elucidated. Many studies have pointed that NLRP3-mediated inflammation played a vital role in degenerative diseases. However, its interaction with synovitis of TMJOA has remained poorly investigated. In our study, we explored the role of NLRP3 inflammasome in TMJOA synovitis and the therapeutic potential of caspase-1 and NLRP3 inhibitors. By establishing a rat TMJOA model, we found that NLRP3 was upregulated in synovial tissue of TMJOA. It was involved in the progress of a programmed cell death called pyroptosis, which was caspase-1 dependent and ultimately triggered inflammatory mediator interleukin IL-1β release. Treatment with Ac-YVAD-cmk and MCC950, inhibitors targeting caspase-1 and NLRP3, respectively, significantly suppressed pyroptosis in TMJOA synovial tissue. Then, a macrophage- and fibroblast-like synoviocyte (FLS) cocultured model further verified the above results. Macrophage somehow promoted FLS pyroptosis in this study. Our results suggested that the NLRP3 inflammasome-mediated pyroptosis participated in synovial inflammation of TMJOA. Interfering with the progress could be a potential option for controlling TMJOA development.

S100A8-Mediated NLRP3 Inflammasome-Dependent Pyroptosis in Macrophages Facilitates Liver Fibrosis Progression

NLRP3 inflammasome-dependent pyroptosis has been implicated in liver fibrosis progression. However, the definite intrahepatic cell types that undergo pyroptosis and the underlying mechanism as well as the clinical importance remain unclear. Here, augmented levels of pyroptosis-related indicators GSDMD, IL-1β, and IL-18 were verified in both liver fibrosis patients and CCl4-induced fibrotic mouse model. Confocal imaging of NLRP3 with albumin, F4/80 or α-SMA revealed that enhanced NLRP3 was mainly localized to kupffer cells (KCs), indicating that KCs are major cell types that undergo pyroptosis. Targeting pyroptosis by inhibitor MCC950 attenuated the severity and ameliorated liver function in fibrosis models. In addition, elevated S100A8 in liver fibrosis patients was correlated with pyroptosis-related indicators. S100A8 stimulated pyroptotic death of macrophages, which resulted in activation of human hepatic stellate cell line LX-2 cells and increased collagen deposition. Mechanistically, S100A8 activated TLR4/NF-κB signaling and upregulated its target genes NLRP3, pro-IL-1β, and pro-IL-18 expression, and induced reactive oxygen (ROS) abundance to activate NLRP3 inflammasome, finally leading to pyroptotic cell death in macrophages. More importantly, circulating GSDMD had the optimal predicting value for liver fibrosis progression. In conclusion, S100A8-mediated NLRP3 inflammasome-dependent pyroptosis by TLR4/NF-κB activation and ROS production in macrophages facilitates liver fibrosis progression. The identified GSDMD has the potential to be a biomarker for liver fibrosis evaluation.

GSDME deficiency leads to the aggravation of UVB-induced skin inflammation through enhancing recruitment and activation of neutrophils

Gasdermin E (GSDME)-mediated pyroptosis is induced in keratinocytes of UVB-challenged skin. The role of GSDME in UVB-caused skin damage remains unknown. To explore the role of GSDME in UVB-induced skin inflammation. We compared differences in skin appearance, histological features, keratinocyte death modalities, infiltration of immune cells, and levels of some inflammatory cytokines between Gsdme^-/- mice and wild type (WT) mice after UVB exposure. We explored whether keratinocytes contribute to GSDME deficiency-caused aggravation of UVB-induced skin inflammation in GSDME knockdown keratinocyte cultured in vitro and keratinocyte-specific Gsdme conditional knockout mice. We used anti-Ly6G antibody to deplete neutrophils and explore their role in UVB-caused skin damage. Skin damage and neutrophils infiltration were aggravated in UVB-challenged Gsdme^-/- mice, compared with UVB-challenged WT mice. Apoptosis and necroptosis, which were initiated together with GSDME-mediated pyroptosis in UVB-challenged WT mice, were not enhanced in UVB-challenged Gsdme^-/- mice. Neutrophils activation indicators and its recruiting cytokines were increased in skin tissue of UVB-challenged Gsdme^-/- mice. However, GSDME knockdown did not lead to the further increase of mRNA and secretion of TNF-α and IL-6 in UVB-challenged keratinocytes. Skin damage was not aggravated in UVB-challenged Gsdme cKO mice. Neutrophils depletion alleviated UVB-caused skin damage in WT mice and Gsdme^-/- mice, and eliminated its aggravation in Gsdme^-/- mice. This study demonstrates that GSDME plays a restrictive role in UVB-induced skin damage through inhibiting excessive recruitment and activation of neutrophils in the immune microenvironment in UVB-caused skin inflammation. However, keratinocytes might not contribute to this restrictive function.

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.

Identification of a predictive gene signature related to pyroptosis for the prognosis of cutaneous melanoma

Pyroptosis is a form of inflammatory programmed cell death. However, because of no specific molecular biomarker, pyroptosis has not been considered as a novel therapeutic method to treat cutaneous melanoma (CM). Here, we identified pyroptosis genes that associate with the prognosis of CM patients and constructed an effective model for the prognostic prediction of CM patients. To identify genes related to pyroptosis that are differentially expressed in CM, we obtained gene expression data of CM patients and normal skin tissues from the Cancer Genome Atlas and the Genotype-Tissue Expression databases, and used another cohort obtained from Gene Expression Omnibus database for validation. Three genes (BST2, GBP5, and AIM2) that were associated with prognosis were found and incorporated into our prognostic model. Furthermore, we divided the patients into 2 groups: a high-risk group and a low-risk group. Functional analyses indicated that our model was correlated with patient survival and cancer growth. Multivariate and univariate Cox regressions revealed that the constructed model could serve as an independent prognostic factor for CM patients. Meanwhile, compared with other clinical characteristics, our model significantly improved the diagnostic accuracy. Gene function analysis revealed that pyroptosis genes BST2, GBP5, and AIM2 were differentially expressed in CM patients and positively associated with patient prognosis. Finally, a risk score was used to generate nomograms that displayed favorable discriminatory abilities for CM. In summary, our model could significantly predict the prognosis of CM patients and be used for the development of CM therapy.

Perspectives on the mechanism of pyroptosis after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a highly harmful neurological disorder with high rates of mortality, disability, and recurrence. However, effective therapies are not currently available. Secondary immune injury and cell death are the leading causes of brain injury and a poor prognosis. Pyroptosis is a recently discovered form of programmed cell death that differs from apoptosis and necrosis and is mediated by gasdermin proteins. Pyroptosis is caused by multiple pathways that eventually form pores in the cell membrane, facilitating the release of inflammatory substances and causing the cell to rupture and die. Pyroptosis occurs in neurons, glial cells, and endothelial cells after ICH. Furthermore, pyroptosis causes cell death and releases inflammatory factors such as interleukin (IL)-1β and IL-18, leading to a secondary immune-inflammatory response and further brain damage. The NOD-like receptor protein 3 (NLRP3)/caspase-1/gasdermin D (GSDMD) pathway plays the most critical role in pyroptosis after ICH. Pyroptosis can be inhibited by directly targeting NLRP3 or its upstream molecules, or directly interfering with caspase-1 expression and GSDMD formation, thus significantly improving the prognosis of ICH. The present review discusses key pathological pathways and regulatory mechanisms of pyroptosis after ICH and suggests possible intervention strategies to mitigate pyroptosis and brain dysfunction after ICH.

Aprepitant attenuates NLRC4-dependent neuronal pyroptosis via NK1R/PKCδ pathway in a mouse model of intracerebral hemorrhage

BACKGROUND

Pyroptosis is a programmed cell death mediated by inflammasomes. Previous studies have reported that inhibition of neurokinin receptor 1 (NK1R) exerted neuroprotection in several neurological diseases. Herein, we have investigated the role of NK1R receptor inhibition using Aprepitant to attenuate NLRC4-dependent neuronal pyroptosis after intracerebral hemorrhage (ICH), as well as the underlying mechanism.

METHODS

A total of 182 CD-1 mice were used. ICH was induced by injection of autologous blood into the right basal ganglia. Aprepitant, a selective antagonist of NK1R, was injected intraperitoneally at 1 h after ICH. To explore the underlying mechanism, NK1R agonist, GR73632, and protein kinase C delta (PKCδ) agonist, phorbol 12-myristate 13-acetate (PMA), were injected intracerebroventricularly at 1 h after ICH induction, and small interfering ribonucleic acid (siRNA) for NLRC4 was administered via intracerebroventricular injection at 48 h before ICH induction, respectively. Neurobehavioral tests, western blot, and immunofluorescence staining were performed.

RESULTS

The expression of endogenous NK1R and NLRC 4 were gradually increased after ICH. NK1R was expressed on neurons. Aprepitant significantly improved the short- and long-term neurobehavioral deficits after ICH, which was accompanied with decreased neuronal pyroptosis, as well as decreased expression of NLRC4, Cleaved-caspase-1, GSDMD (gasdermin D), IL-1β, and IL-18. Activation of NK1R or PKCδ abolished these neuroprotective effects of Aprepitant after ICH. Similarly, knocking down NLRC4 using siRNA produced similar neuroprotective effects.

CONCLUSION

Aprepitant suppressed NLRC4-dependent neuronal pyroptosis and improved neurological function, possibly mediated by inhibition of NK1R/PKCδ signaling pathways after ICH. The NK1R may be a promising therapeutic target for the treatment of ICH.

Ejiao ameliorates lipopolysaccharide-induced pulmonary inflammation via inhibition of NFκB regulating NLRP3 inflammasome and mitochondrial ROS

There is no effective treatment for acute lung injury (ALI) at present. Some studies have reported the anti-inflammatory effect of Ejiao, but no study has addressed the underlying action mechanism. In this study, the CCK8 assay displayed Ejiao had a protective effect against LPS-elicited inflammatory lung epithelial Beas 2B cells (LILEB 2B cells). Beas 2B cells treated with LPS and Ejiao were challenged with NFκB inhibitor Bay11-7082 and ROS scavenger N-acetyl cysteine (NAC) alone and in combination. The results of qRT-PCR, Western blotting and fluorescence labeling experiments using Bay11-7082 and NAC demonstrated Ejiao could significantly decrease the expression of p-p65 and p-IκBα in NFκB signaling pathway and its downstream NLRP3, ASC, Caspase-1 and IL-1β related to pyroptosis of LILEB 2B cells. Moreover, Ejiao reduced the production of mitochondrial ROS and reversed the change of mitochondrial membrane potential of LILEB 2B cells. Then, HE staining demonstrated Ejiao had a protective effect against the LPS-elicited ALI mouse model (LAMM). Ejiao also dramatically decreased the cell amount and the overall protein concentration of bronchoalveolar lavage fluid in LAMM. Immunohistochemical staining showed Ejiao remarkably reduced the expression of p-p65 and p-IκBα in NFκB signaling pathway and its downstream NLRP3, ASC, Caspase-1 and IL-1β. The ELISA of IL-1β revealed Ejiao could dose-dependably decrease the concentration of IL-1β in lung tissues, serum and BALF of LAMM. Finally, fluorescence labeling demonstrated Ejiao significantly reduced the mitochondrial ROS generation in the lung tissue of LAMM. This finding may afford a novel strategy for the precaution and therapy of ALI.

Nucleic Acid Sensing Pathways in DNA Repair Targeted Cancer Therapy

The repair of DNA damage is a complex process, which helps to maintain genome fidelity, and the ability of cancer cells to repair therapeutically DNA damage induced by clinical treatments will affect the therapeutic efficacy. In the past decade, great success has been achieved by targeting the DNA repair network in tumors. Recent studies suggest that DNA damage impacts cellular innate and adaptive immune responses through nucleic acid-sensing pathways, which play essential roles in the efficacy of DNA repair targeted therapy. In this review, we summarize the current understanding of the molecular mechanism of innate immune response triggered by DNA damage through nucleic acid-sensing pathways, including DNA sensing via the cyclic GMP-AMP synthase (cGAS), Toll-like receptor 9 (TLR9), absent in melanoma 2 (AIM2), DNA-dependent protein kinase (DNA-PK), and Mre11-Rad50-Nbs1 complex (MRN) complex, and RNA sensing via the TLR3/7/8 and retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs). Furthermore, we will focus on the recent developments in the impacts of nucleic acid-sensing pathways on the DNA damage response (DDR). Elucidating the DDR-immune response interplay will be critical to harness immunomodulatory effects to improve the efficacy of antitumor immunity therapeutic strategies and build future therapeutic approaches.

Regulation of Pyroptosis by ncRNA: A Novel Research Direction

Pyroptosis is a novel form of programmed cell death (PCD), which is characterized by DNA fragmentation, chromatin condensation, cell swelling and leakage of cell contents. The process of pyroptosis is performed by certain inflammasome and executor gasdermin family member. Previous researches have manifested that pyroptosis is closely related to human diseases (such as inflammatory diseases) and malignant tumors, while the regulation mechanism of pyroptosis is not yet clear. Non-coding RNA (ncRNA) such as microRNA (miRNA), long non-coding RNA (lncRNA) and circular RNA (circRNA) have been widely identified in the genome of eukaryotes and played a paramount role in the development of cell function and fate after transcription. Accumulating evidences support the importance of ncRNA biology in the hallmarks of pyroptosis. However, the associations between ncRNA and pyroptosis are rarely reviewed. In this review, we are trying to summarize the regulation and function of ncRNA in cell pyroptosis, which provides a new research direction and ideas for the study of pyroptosis in different diseases.

Salidroside Ameliorates Depression by Suppressing NLRP3-Mediated Pyroptosis via P2X7/NF-κB/NLRP3 Signaling Pathway

Depression is a common and serious mental disorder. Data on its pathogenesis remain unclear and the options of drug treatments are limited. Here, we explored the role of pyroptosis, a novel pro-inflammatory programmed cell death process, in depression as well as the anti-depression effects and mechanisms of salidroside (Sal), a bioactive extract from Rhodiola rosea L. We established a corticosterone (CORT)-induced or lipopolysaccharide (LPS)-induced mice in vivo, and CORT, or nigericin (NLRP3 agonist)-induced PC12 cells in vitro. Our findings demonstrated that Sal profoundly mediated CORT or LPS-induced depressive behavior and improved synaptic plasticity by upregulating the expression of brain-derived neurotrophic factor (BDNF) gene. The data showed upregulation of proteins associated with NLRP3-mediated pyroptosis, including NLRP3, cleaved Caspase-1, IL-1β, IL-18, and cleaved GSDMD. The molecular docking simulation predicted that Sal would interact with P2X7 of the P2X7/NF-κB/NLRP3 signaling pathway. In addition, our findings showed that the NLRP3-mediated pyroptosis was regulated by P2X7/NF-κB/NLRP3 signaling pathway. Interestingly, Sal was shown to ameliorate depression via suppression of the P2X7/NF-κB/NLRP3 mediated pyroptosis, and rescued nigericin-induced pyroptosis in the PC12 cells. Besides, knock down of the NLRP3 gene by siRNA markedly increased the inhibitory effects of Sal on pyroptosis and proinflammatory responses. Taken together, our findings demonstrated that pyroptosis plays a crucial role in depression, and Sal ameliorates depression by suppressing the P2X7/NF-κB/NLRP3-mediated pyroptosis. Thus, our study provides new insights into the potential treatment options for depression.

Multi-faceted role of pyroptosis mediated by inflammasome in liver fibrosis

Liver fibrosis is a reversible pathological overreaction during the self-repair of liver injuries, and it is the common period of chronic liver diseases induced by different pathogenesis progress into cirrhosis and even hepatocellular carcinoma. Pyroptosis, a novel form of programmed cell death, is reported to take part in the pathogenesis and progression of acute or chronic liver diseases and liver fibrosis. Caspase-1 dependent canonical pathway and caspase-4/-5/-11 mediated noncanonical pathway are the two signalling pathways to induce pyroptosis. The activation of inflammasomes under the stimulation of pathogenic microorganisms and danger signals can initiate the pyroptotic pathway and release large amounts of proinflammatory and profibrotic cytokines. This article comprehensively summarizes recent researches focused on the mechanism of pyroptosis and its role in major hepatic cells, which can provide potential therapeutic strategies for liver fibrosis.

Inhibition of gasdermin D-dependent pyroptosis attenuates the progression of silica-induced pulmonary inflammation and fibrosis

Silicosis is a leading cause of occupational disease-related morbidity and mortality worldwide, but the molecular basis underlying its development remains unclear. An accumulating body of evidence supports gasdermin D (GSDMD)-mediated pyroptosis as a key component in the development of various pulmonary diseases. However, there is little experimental evidence connecting silicosis and GSDMD-driven pyroptosis. In this work, we investigated the role of GSDMD-mediated pyroptosis in silicosis. Single-cell RNA sequencing of healthy and silicosis human and murine lung tissues indicated that GSDMD-induced pyroptosis in macrophages was relevant to silicosis progression. Through microscopy we then observed morphological alterations of pyroptosis in macrophages treated with silica. Measurement of interleukin-1β release, lactic dehydrogenase activity, and real-time propidium iodide staining further revealed that silica induced pyroptosis of macrophages. Additionally, we verified that both canonical (caspase-1-mediated) and non-canonical (caspase-4/5/11-mediated) signaling pathways mediated silica-induced pyroptosis activation, in vivo and in vitro. Notably, Gsdmd knockout mice exhibited dramatically alleviated silicosis phenotypes, which highlighted the pivotal role of pyroptosis in this disease. Taken together, our results demonstrated that macrophages underwent GSDMD-dependent pyroptosis in silicosis and inhibition of this process could serve as a viable clinical strategy for mitigating silicosis.

Melatonin ameliorates trimethyltin chloride-induced cardiotoxicity: The role of nuclear xenobiotic metabolism and Keap1-Nrf2/ARE axis-mediated pyroptosis

Trimethyltin chloride (TMT) is a stabilizer for polyvinyl chloride plastics that causes serious health hazards in nontarget organisms. Melatonin (MT) exhibits powerful protective effects in cardiac diseases. As a new environmental pollutant, TMT-induced cardiotoxicity and the protective effects of MT remain unclear. To explore this, the mice were treated with TMT (2.8 mg/kg) and/or MT (10 mg/kg) for 7 days. Firstly, the histopathological and ultrastructural evaluation showed that TMT induced cardiac damage, tumescent rupture and nuclear pyknosis. Moreover, TMT elevated the expressions of pyroptosis genes NLRP3, ASC and Cas1 and inflammation factors IL-6, IL-17 and TNFα. Secondly, TMT reduced antioxidant enzymes (GSH, CAT and T-AOC) via decreasing the expression of genes associated with the Keap1-Nrf2/ARE pathway to increase oxidative stress. Thirdly, TMT decreased the expression of genes associated with the ARE-driven drug metabolizing enzymes (DMEs), including Akr7a3, Akr1b8, and Akr1b10. Besides, TMT upregulated the mRNA expression of nuclear Xenobiotic metabolism on cytochrome P450s enzymes via increasing the expression of CAR, PXP, and AHR genes. Furthermore, MT treatment mitigated the aforementioned adverse changes induced by TMT. Overall, these results demonstrated that TMT caused pyroptosis and inflammation to aggravate cardiac damage via inducing excessive oxidative stress, imbalance of DMEs homeostasis, and nuclear Xenobiotic metabolism disorder, which could be alleviated by MT.

The ambiguous role of obesity in oncology by promoting cancer but boosting antitumor immunotherapy

Obesity is nowadays considered a pandemic which prevalence's has been steadily increasingly in western countries. It is a dynamic, complex, and multifactorial disease which propitiates the development of several metabolic and cardiovascular diseases, as well as cancer. Excessive adipose tissue has been causally related to cancer progression and is a preventable risk factor for overall and cancer-specific survival, associated with poor prognosis in cancer patients. The onset of obesity features a state of chronic low-grade inflammation and secretion of a diversity of adipocyte-derived molecules (adipokines, cytokines, hormones), responsible for altering the metabolic, inflammatory, and immune landscape. The crosstalk between adipocytes and tumor cells fuels the tumor microenvironment with pro-inflammatory factors, promoting tissue injury, mutagenesis, invasion, and metastasis. Although classically established as a risk factor for cancer and treatment toxicity, recent evidence suggests mild obesity is related to better outcomes, with obese cancer patients showing better responses to treatment when compared to lean cancer patients. This phenomenon is termed obesity paradox and has been reported in different types and stages of cancer. The mechanisms underlying this paradoxical relationship between obesity and cancer are still not fully described but point to systemic alterations in metabolic fitness and modulation of the tumor microenvironment by obesity-associated molecules. Obesity impacts the response to cancer treatments, such as chemotherapy and immunotherapy, and has been reported as having a positive association with immune checkpoint therapy. In this review, we discuss obesity's association to inflammation and cancer, also highlighting potential physiological and biological mechanisms underlying this association, hoping to clarify the existence and impact of obesity paradox in cancer development and treatment.

The ROS/GRK2/HIF-1α/NLRP3 Pathway Mediates Pyroptosis of Fibroblast-Like Synoviocytes and the Regulation of Monomer Derivatives of Paeoniflorin

Hypoxia is an important factor in the development of synovitis in rheumatoid arthritis (RA). The previous study of the research group found that monomeric derivatives of paeoniflorin (MDP) can alleviate joint inflammation in adjuvant-induced arthritis (AA) rats by inhibiting macrophage pyroptosis. This study revealed increased levels of hypoxia-inducible factor- (HIF-) 1α and N-terminal p30 fragment of GSDMD (GSDMD-N) in fibroblast-like synoviocytes (FLS) of RA patients and AA rats, while MDP significantly inhibited their expression. Subsequently, FLS were exposed to a hypoxic environment or treated with cobalt ion in vitro. Western blot and immunofluorescence analysis showed increased expression of G protein-coupled receptor kinase 2 (GRK2), HIF-1α, nucleotide-binding oligomerization segment-like receptor family 3 (NLRP3), ASC, caspase-1, cleaved-caspase-1, and GSDMD-N. Electron microscopy revealed FLS pyroptosis after exposure in hypoxia. Next, corresponding shRNAs were transferred into FLS to knock down hypoxia-inducible factor- (HIF-) 1α, and in turn, NLRP3 and western blot results confirmed the same. The enhanced level of GSDMD was reversed under hypoxia by inhibiting NLRP3 expression. Knockdown and overexpression of GRK2 in FLS revealed GRK2 to be a positive regulator of HIF-1α. Levels of GRK2 and HIF-1α were inhibited by eliminating excess reactive oxygen species (ROS). Furthermore, MDP reduced FLS pyroptosis through targeted inhibition of GRK2 phosphorylation. According to these findings, hypoxia induces FLS pyroptosis through the ROS/GRK2/HIF-1α/NLRP3 pathway, while MDP regulates this pathway to reduce FLS pyroptosis.

HMGB1 plays an important role in pyroptosis induced blood brain barrier breakdown in diabetes-associated cognitive decline

Diabetes mellitus increases the risk of dementia, and evidence suggests hyperglycemia is a key contributor to neurodegeneration. However, our understanding of diabetes-associated cognitive decline, an important complication of diabetes mellitus, is lacking and the underlying mechanism is unclear. Blood brain barrier (BBB) breakdown is a possible cause of dementia in diabetes mellitus and Alzheimer's disease. Accumulating evidence shows BBB dysfunction caused by hyperglycemia contributes to cognitive decline. A specific type of inflammatory programmed cell death, called pyroptosis, has potential as a therapeutic target for BBB-associated diseases. Potential inducers of pyroptosis include inflammasomes such as NLRP3, whose activation relies on damage-associated molecular patterns. High mobility group box 1 (HMGB1) is a highly conserved, ubiquitous protein found in most cell types, and acts as a damage-associated molecular pattern when released from the nucleus. We propose that HMGB1 influences vascular inflammation by activating the NLRP3 inflammasome and thereby initiating pyroptosis in vascular cells. Moreover, HMGB1 plays a pivotal role in the pathogenesis of diabetes mellitus and diabetic complications. Here, we review the role of HMGB1 in BBB dysfunction induced by hyperglycemia and propose that HMGB1 is a promising therapeutic target for countering diabetes-associated cognitive decline.

Pyroptosis in the Retinal Neurovascular Unit: New Insights Into Diabetic Retinopathy

Diabetic retinopathy (DR) is prevalent among people with long-term diabetes mellitus (DM) and remains the leading cause of visual impairment in working-aged people. DR is related to chronic low-level inflammatory reactions. Pyroptosis is an emerging type of inflammatory cell death mediated by gasdermin D (GSDMD), NOD-like receptors and inflammatory caspases that promote interleukin-1β (IL-1β) and IL-18 release. In addition, the retinal neurovascular unit (NVU) is the functional basis of the retina. Recent studies have shown that pyroptosis may participate in the destruction of retinal NVU cells in simulated hyperglycemic DR environments. In this review, we will clarify the importance of pyroptosis in the retinal NVU during the development of DR.

Molecular Characteristics, Clinical Implication, and Cancer Immunity Interactions of Pyroptosis-Related Genes in Breast Cancer

Objective: Pyroptosis represents an emerging inflammatory form of programmed cell death. Herein, specific functions and clinical implications of pyroptosis-related genes were systematically characterized in breast cancer.

Methods: Expression, somatic mutation and copy number variation of 33 pyroptosis-related genes were assessed in breast cancer from TCGA dataset. Their interactions, biological functions and prognostic values were then observed. By stepwise Cox regression analysis, a pyroptosis-related gene signature was generated. The predictive efficacy in survival was examined by survival analyses, ROCs, univariate and multivariate analyses and subgroup analyses. Associations between risk score (RS) and cancer immunity cycle, HLA, immune cell infiltrations, and immune checkpoints were analyzed.

Results: Most of pyroptosis-related genes were abnormally expressed in breast cancer. CASP8, NLRC4, NLRP3, NLRP2, PLCG1, NLRP1, NLRP7, SCAF11, GSDMC, and NOD1 occurred somatic mutations as well as most of them had high frequency of CNV. There were closely interactions between them. These genes were distinctly enriched in immune-related processes. A three-gene signature was generated, containing IL-18, GSDMC, and TIRAP. High RS predicted poorer overall survival, progression, and recurrence. After verification, this RS was an independent and sensitive predictive index. This RS was negatively correlated to cancer immunity cycle. Also, low RS was characterized by high HLA, immune cell infiltrations and immune checkpoints. A nomogram including age and RS was generated for accurately predicting 5-, 8-, and 10-year survival probabilities.

Conclusion: Pyroptosis-related genes exert key roles in cancer immunity and might be applied as a prognostic factor of breast cancer.

Pyroptosis and Redox Balance in Kidney Diseases

Significance: Kidney diseases remain a worldwide public health problem resulting in millions of deaths each year; they are characterized by progressive destruction of renal function by sustained inflammation. Pyroptosis is a lytic type of programmed cell death involved in inflammation, as well as a key fibrotic mechanism that is critical in the development of kidney pathology. Pyroptosis is induced by the cleavage of Gasdermins by various caspases and is executed by the insertion of the N-terminal fragment of cleaved Gasdermins into the plasma membrane, creating oligomeric pores and allowing the release of diverse proinflammatory products into the extracellular space. Inflammasomes are multiprotein complexes leading to the activation of caspase-1, which will cleave Gasdermin D, releasing several proinflammatory cytokines; this results in the initiation and amplification of the inflammatory response. Recent Advances: The efficacy of Gasdermin D cleavage is reduced by a change in the redox balance. Recently, several studies have shown that the attenuation of reactive oxygen species (ROS) production induced by antioxidant pathways results in a reduction of renal pyroptosis. In this review, we discuss the role of pyroptosis in the pathogenesis of chronic kidney disease (CKD) and acute kidney disease; summarize the clinical outcomes and different molecular mechanisms leading to Gasdermin activation; and examine studies about the capacity of antioxidants, particularly Nrf2 activators, to ameliorate Gasdermin activity. Future Directions: We illustrate the potential influence of the deregulation of redox balance on inflammasome activity and pyroptosis as a novel therapeutic approach for the treatment of kidney diseases. Antioxid. Redox Signal. 35, 40-60.

Luteolin prevents THP-1 macrophage pyroptosis by suppressing ROS production via Nrf2 activation

Pyroptosis plays an important role in the pathogenesis of numerous infectious, autoimmune, and inflammatory diseases, which makes it a promising target for intervention. In this study, the effect of luteolin on pyroptosis and the underlying mechanism were investigated using the canonical NLRP3 inflammasome in THP-1 macrophages induced by LPS/ATP. The results showed that luteolin exhibited a potent preventive effect on THP-1 macrophage pyroptosis, as evidenced by the increase in cell viability and the decrease in LDH release. Moreover, luteolin was found to significantly reduce the expression of NLRP3, pro-CASP-1 and CASP-1, which are the key components of NLRP3 inflammasome, as well as the expression of N-GSDMD and IL-1β, and we proved that the inhibition of luteolin on NLRP3 inflammasome activation is ROS-dependent. Furthermore, it was demonstrated that luteolin promoted Nrf2 nuclear translocation, thereby increasing the expression of HO-1 that reduces ROS production, while the anti-pyroptotic effect of luteolin was reversed by a specific Nrf2 inhibitor. Additionally, luteolin inhibited NF-κB p65 phosphorylation and nuclear translocation. In summary, we conclude that luteolin prevents THP-1 macrophage pyroptosis by suppressing ROS production via Nrf2 activation as well as NF-κB inactivation. These results support luteolin as a potential bioactive chemical against pyroptosis-related inflammatory diseases.

Pyroptosis in stroke-new insights into disease mechanisms and therapeutic strategies

Stroke is a common disease with high mortality and disability worldwide. Different forms of cell deaths, including apoptosis and necrosis, occur in ischemic or hemorrhagic brain tissue, among which pyroptosis, a newly discovered inflammation-related programmed cell death, is generally divided into two main pathways, the canonical inflammasome pathway and the non-canonical inflammasome pathway. Caspase-mediated pyroptosis requires the assembly of inflammasomes such as NLRP3, which leads to the release of inflammatory cytokines IL-1β and IL-18 through the pores formed in the plasma membrane by GSDMD followed by neuroinflammation. Recently, pyroptosis and its relationship with inflammation have attracted more and more attention in the study of cerebral ischemia or hemorrhage. In addition, many inhibitors of pyroptosis targeting caspase, NLRP3, and the upstream pathway have been found to reduce brain tissue damage after stroke. In this review, we mainly introduce the pathology of stroke, the molecular mechanism, and process of pyroptosis, as well as the pivotal roles of pyroptosis in stroke, in order to provide new insights for the treatment of stroke.

CLEC5A knockdown protects against the cardiac dysfunction after Myocardial infarction by suppressing macrophage polarization, NLRP3 inflammasome activation and pyroptosis

Increasing evidence has shown that NOD-like receptor protein 3 (NLRP3) inflammasome and pyroptotic cell death play vital roles in the pathophysiology of myocardial infarction (MI), a common cardiovascular disease characterized with cardiac dysfunction. C-type lectin member 5A (CLEC5A) is reported to strongly associate with activation of NLRP3 inflammasome and pyroptosis. In this study, in vivo MI model was established by the ligation of left anterior descending coronary artery on male C57BL/6 mice, and CLEC5A knockdown was further achieved by intra-myocardial injection of adenovirus delivering shRNA-CLEC5A. CLEC5A was found to be highly expressed in left ventricular of MI mice, while CLEC5A knockdown conversely alleviated the cardiac dysfunction in MI mice. Besides, MI-induced classical activation of macrophages was significantly inhibited after CLEC5A silencing. Additionally, CLEC5A knockdown dramatically inhibited MI-triggered activation of NLRP3 inflammasome, pyroptosis and NF-κB signaling in left ventricular of mice. In vitro experiment further validated that CLEC5A knockdown suppressed M1 polarization in LPS/IFNγ-stimulated RAW264.7 cells, and inhibited the polarized RAW264.7-induced activation of NLRP3 inflammasome/pyroptosis signaling in co-cultured cardiomyocytes. In conclusion, CLEC5A knockdown protects against the MI-induced cardiac dysfunction by regulating macrophage polarization, NLRP3 inflammasome and cell pyroptosis.

Agnuside Alleviates Synovitis and Fibrosis in Knee Osteoarthritis through the Inhibition of HIF-1α and NLRP3 Inflammasome

Increasing evidence has shown that NLRP3 inflammasome activation participates in chronic aseptic inflammation and is related to tissue fibrosis. Our last study also revealed the vital role of NLRP3 inflammasome, highly associated with tissue hypoxia, in the onset and development of knee osteoarthritis (KOA). In this study, we tried to find a possible benign intervention for that pathological process. Agnuside (AGN), a nontoxic, natural small molecule isolated from the extract of Vitex negundo L. (Verbenaceae), has been demonstrated to have antioxidation, anti-inflammatory, analgesia, and many other properties as an iridoid glycoside, although its specific target is still unclear. Therefore, we established MIA-induced KOA model rats and investigated the effects of AGN oral gavage on oxygen-containing state, NLRP3 inflammasome, synovitis, and fibrosis in KOA. Pimonidazole staining and HIF-1α immunohistochemical assay both showed that AGN at the oral dose of 6.25 mg/kg can effectively relieve local hypoxia in synovial tissue. Besides, we observed a decrease of HIF-1α, caspase-1, ASC, and NLRP3 after AGN intervention, both in the mRNA and protein levels. In addition, rats treated with the AGN showed less inflammatory reaction and fibrosis, not only in the expression of NLRP3, inflammasome downstream factors IL-1β and IL-18, and fibrosis markers TGF-β, TIMP1, and VEGF but also in the observation of HE staining, anatomical characteristics, Sirius Red staining, and type I collagen immunohistochemistry. Subsequently, we established LPS-induced models of fibroblast-like synoviocytes (FLSs) mimicking the inflammatory environment of KOA and activating NLRP3 inflammasome. FLSs treated with AGN (3 μM) resulted in a downregulation of HIF-1α and the components required for NLRP3 inflammasome activation. Meanwhile, the content of proinflammatory factors IL-1β and IL-18 in FLS supernatant was also reduced by AGN. In addition, both mRNA and protein levels of the fibrotic markers were significantly decreased after AGN management. To conclude, this study demonstrates that AGN alleviates synovitis and fibrosis in experimental KOA through the inhibition of HIF-1α accumulation and NLRP3 inflammasome activation. Additionally, not only does it reveal some novel targets for anti-inflammatory and antioxidant effects of AGN but also announces its potential value in treating KOA in humans.

Suppression of NLRP3 Inflammasome, Pyroptosis, and Cell Death by NIM811 in Rotenone-Exposed Cells as an in vitro Model of Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is characterized by the selective death of dopaminergic neurons in the substantia nigra. Recently, NLRP3 inflammasome and pyroptosis were found to be associated with PD. Cyclosporine A (CsA), an immunosuppressant, reduces neuronal death in PD. However, CsA could hardly pass through the blood-brain barrier (BBB) and high dose is associated with severe side effects and toxicity. N-methyl-4-isoleucine-cyclosporine (NIM811) is a CsA derivate that can pass through the BBB. However, little is known about its effect on PD.

OBJECTIVE

The objectives of this study were to explore the mechanism of rotenone-induced cell damage and to examine the protective effects of NIM811 on the neurotoxicity of a Parkinson-like in vitro model induced by rotenone.

METHODS

Murine hippocampal HT22 cells were cultured with the mitochondrial complex I inhibitor rotenone, a widely used pesticide that has been used for many years as a tool to induce a PD model in vitro and in vivo and proven to be reproducible. NIM811 was added to the culture media 3 h prior to the rotenone incubation. Cell viability was determined by resazurin assay, reactive oxygen species (ROS) production by dihydroethidine (DHE), and mitochondrial membrane potential by tetramethyl rhodamine methyl ester (TMRM). TUNEL and caspase-1 immunofluorescent double staining was used to detect pyroptosis. NLRP3, caspase-1, pro-caspase-1, GSDMD, and interleukin-18 (IL-18) were measured using Western blotting after 24 h of rotenone incubation. The reactivity of interleukin-1β (IL-1β) was determined by ELISA.

RESULTS

Our results demonstrated that rotenone caused more than 40% of cell death, increased ROS production, and reduced mitochondrial membrane potential, while NIM811 reversed these alterations. Immunofluorescent double staining showed that rotenone increased the percentage of caspase-1 and TUNEL double-labelled cells, an indication of pyroptosis, after 24 h of incubation. The protein expression of NLRP3, caspase-1, pro-caspase-1, GSDMD, IL-18, and IL-1β was significantly increased after 24 h of rotenone incubation. NIM811 suppressed rotenone-induced pyroptosis and downregulated the protein expression of NLRP3, caspase-1, pro-caspase-1, GSDMD, IL-1β, and IL-18.

CONCLUSION

These results provide evidence that rotenone activates the NLRP3 inflammomere and induces pyroptosis. NIM811 protects the cell from rotenone-induced damage and inhibits NLRP3 inflammasome and pyroptosis. NIM811 might serve as a potential therapeutic drug in the treatment of PD.