Activity of caspase-8 determines plasticity between cell death pathways

Targeting TNF-α: The therapeutic potential of certolizumab pegol in the early period of cerebral ischemia reperfusion injury in mice

The neuroinflammatory response triggered by cerebral ischemia-reperfusion injury (CIRI) is characterized by the upsurge of pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6, which promote leukocyte infiltration and subsequent accumulation in the ischemic zone. This accumulation further intensifies inflammation and aggravates ischemic damage. Certolizumab pegol (CZP), a monoclonal antibody targeting TNF-α, is widely used in treating various inflammatory diseases. This study explored the therapeutic potential of CZP in a mouse model of CIRI, induced by middle cerebral artery occlusion (MCAO), focusing on its influence on the microglial inflammatory response. In vitro analyses revealed that CZP markedly inhibits TNF-α-stimulated inflammation in primary microglia with an EC50 of 1.743 ng/mL. In vivo, MCAO mice treated with CZP (10 μg/mouse, i.p.) for 3 days showed reduced infarct volume, partially improved neurological function, and diminished blood-brain barrierdisruption. Additionally, CZP treatment curtailed microglial activation and the release of pro-inflammatory mediators in the early stages of stroke. It also favorably modulated microglial M1/M2 polarization, rebalanced Th17/Treg cells dynamics, and inhibited Caspase-8-mediated GSDMD cleavage, preventing microglial pyroptosis. Collectively, this study described that the treatment with CZP reversed damaging process caused by CIRI, offering a promising therapeutic strategy for the treatment of ischemic stroke.

PLK-3-mediated phosphorylation of BAP1 prevents diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus, and its main clinical manifestation is retinal vascular dysfunction. DR causes blindness and is a problem with significant global health implications. However, treating DR is still challenging. In this study, we aimed to explore the role of polo-like kinase-3 (PLK-3) and the potential regulatory mechanism in DR. Sprague-Dawley rats were injected intraperitoneally with streptozotocin (STZ, 60 mg/kg) to induce a rat model of DR, and rat retinal microvascular endothelial cells (RRMECs) were treated with high glucose (HG, 25 mmol/L glucose) to develop a cell model of DR. We found that PLK-3 was significantly downregulated in the retinal tissues of STZ-induced diabetic rats and HG-induced RRMECs. Lentivirus-mediated PLK-3 overexpression alleviated the histological damages in DR rats. After HG stimulation, cell proliferation, migration, and angiogenesis in RRMECs were inhibited after PLK-3 upregulation. By using label-free proteomics, we identified 82 differentially expressed proteins downstream of PLK-3, including BRCA1-associated protein 1 (BAP1), which was significantly upregulated in PLK-3-overexpressed RRMECs compared to control cells under the HG condition. In vivo and in vitro assays indicated that the forced expression of PLK-3 increased the phosphorylation of BAP1 at serine 592 and caspase-8 expression. Detailed evidence showed that BAP1-shRNA-mediated knockdown restored the cell function in HG-treated RRMECs when PLK-3 was overexpressed. Collectively, this study shows that PLK-3 alleviates retinal vascular dysfunction in DR by inhibiting the phosphorylation of BAP1. Thus, PLK-3 may develop as a promising target for the therapy of DR.

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

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

Intranuclear Irradiation Inhibits Solid Tumor Growth by Upregulating Caspase8 and Activating Apoptosis

Radioimmunotherapy (RIT) is a novel and promising cancer treatment method, with ongoing research focusing on RIT antibody selection, radionuclides, treatment options, and benefited patient groups. As we dive into the mechanisms of tumor biology, a deeper exploration of how RIT affects tumor tissue is needed to provide new ways to improve clinical treatment outcome and patient prognosis. We labeled the anti-PD-L1 monoclonal antibody atezolizumab with iodine-131 (131I), separated and purified the labeled mAb with Sephadex G-25 medium gel filtration resin, and tested product stability. We detected the in vivo activity of 131I-PD-L1 mAb by analyzing its in vivo biodistribution and performing SPECT imaging and then set different treatment groups to study the effect of 131I-atezolizumab on the survival of tumor-bearing mice. Western blot, real-time quantitative PCR, and immunohistochemistry were used to detect the expression level of Caspase8 and Nlrp3 in tumor. TUNEL fluorescence staining was used to detect the apoptosis in the tumor. The radiopharmaceutical molecular probe 131I-atezolizumab showed high stability and in vivo biological activity. The treatment regimen adopted had a positive effect on the survival of tumor-bearing mice. 131I internal irradiation upregulated Caspase8 in tumor and ultimately inhibited solid tumor growth by activating apoptosis pathways. We also found a significant increase in the expression of NLRP3, which plays an important role in the pyroptosis pathway, in tumor. In summary, our data demonstrated that radiopharmaceuticals combined with immunotherapy affected tumor tissue by modulating relevant biological pathways, thereby achieving better antitumor effects compared with single therapy and providing new insights for promoting better patient prognosis and combination treatment strategies.

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

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

Inflammatory caspase substrate specificities

Caspases are a family of cysteine proteases that act as molecular scissors to cleave substrates and regulate biological processes such as programmed cell death and inflammation. Extensive efforts have been made to identify caspase substrates and to determine factors that dictate substrate specificity. Thousands of putative substrates have been identified for caspases that regulate an immunologically silent type of cell death known as apoptosis, but less is known about substrates of the inflammatory caspases that regulate an immunostimulatory type of cell death called pyroptosis. Furthermore, much of our understanding of caspase substrate specificities is derived from work done with peptide substrates, which do not often translate to native protein substrates. Our knowledge of inflammatory caspase biology and substrates has recently expanded and here, we discuss the recent advances in our understanding of caspase substrate specificities, with a focus on inflammatory caspases. We highlight new substrates that have been discovered and discuss the factors that engender specificity. Recent evidence suggests that inflammatory caspases likely utilize two binding interfaces to recognize and process substrates, the active site and a conserved exosite.

Initiator cell death event induced by SARS-CoV-2 in the human airway epithelium

Virus-induced cell death is a key contributor to COVID-19 pathology. Cell death induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is well studied in myeloid cells but less in its primary host cell type, angiotensin-converting enzyme 2 (ACE2)-expressing human airway epithelia (HAE). SARS-CoV-2 induces apoptosis, necroptosis, and pyroptosis in HAE organotypic cultures. Single-cell and limiting-dilution analysis revealed that necroptosis is the primary cell death event in infected cells, whereas uninfected bystanders undergo apoptosis, and pyroptosis occurs later during infection. Mechanistically, necroptosis is induced by viral Z-RNA binding to Z-DNA-binding protein 1 (ZBP1) in HAE and lung tissues from patients with COVID-19. The Delta (B.1.617.2) variant, which causes more severe disease than Omicron (B1.1.529) in humans, is associated with orders of magnitude-greater Z-RNA/ZBP1 interactions, necroptosis, and disease severity in animal models. Thus, Delta induces robust ZBP1-mediated necroptosis and more disease severity.

PANoptosis: a novel target for cardiovascular diseases

PANoptosis is a unique innate immune inflammatory lytic cell death pathway initiated by an innate immune sensor and driven by caspases and RIPKs. As a distinct pathway, the execution of PANoptosis cannot be hindered by targeting other cell death pathways, such as pyroptosis, apoptosis, or necroptosis. Instead, targeting key PANoptosome components can serve as a strategy to prevent this form of cell death. Given the physiological relevance in several diseases, PANoptosis is a pivotal therapeutic target. Notably, previous research has primarily focused on the role of PANoptosis in cancer and infectious and inflammatory diseases. By contrast, its role in cardiovascular diseases has not been comprehensively discussed. Here, we review the available evidence on PANoptosis in cardiovascular diseases, including cardiomyopathy, atherosclerosis, myocardial infarction, myocarditis, and aortic aneurysm and dissection, and explore a variety of agents that target PANoptosis, with the overarching goal of providing a novel complementary approach to combatting cardiovascular diseases.

The protease caspase-1: Activation pathways and functions

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

The crosstalk between immune cells and tumor pyroptosis: advancing cancer immunotherapy strategies

Pyroptosis is a cell death process characterized by cell swelling until membrane rupture and release of intracellular contents. As an effective tumor treatment strategy, inducing tumor cell pyroptosis has received widespread attention. In this process, the immune components within the tumor microenvironment play a key regulatory role. By regulating and altering the functions of immune cells such as cytotoxic T lymphocytes, natural killer cells, tumor-associated macrophages, and neutrophils, tumor cell pyroptosis can be induced. This article provides a comprehensive review of the molecular mechanisms of cell pyroptosis, the impact of the tumor immune microenvironment on tumor cell pyroptosis, and its mechanisms. It aims to gain an in-depth understanding of the communication between the tumor immune microenvironment and tumor cells, and to provide theoretical support for the development of new tumor immunotherapies.

PANoptosis: bridging apoptosis, pyroptosis, and necroptosis in cancer progression and treatment

This comprehensive review explores the intricate mechanisms of PANoptosis and its implications in cancer. PANoptosis, a convergence of apoptosis, pyroptosis, and necroptosis, plays a crucial role in cell death and immune response regulation. The study delves into the molecular pathways of each cell death mechanism and their crosstalk within PANoptosis, emphasizing the shared components like caspases and the PANoptosome complex. It highlights the significant role of PANoptosis in various cancers, including respiratory, digestive, genitourinary, gliomas, and breast cancers, showing its impact on tumorigenesis and patient survival rates. We further discuss the interwoven relationship between PANoptosis and the tumor microenvironment (TME), illustrating how PANoptosis influences immune cell behavior and tumor progression. It underscores the dynamic interplay between tumors and their microenvironments, focusing on the roles of different immune cells and their interactions with cancer cells. Moreover, the review presents new breakthroughs in cancer therapy, emphasizing the potential of targeting PANoptosis to enhance anti-tumor immunity. It outlines various strategies to manipulate PANoptosis pathways for therapeutic purposes, such as targeting key signaling molecules like caspases, NLRP3, RIPK1, and RIPK3. The potential of novel treatments like immunogenic PANoptosis-initiated therapies and nanoparticle-based strategies is also explored.

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

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

ROS induced pyroptosis in inflammatory disease and cancer

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

Homer1a reduces inflammatory response after retinal ischemia/reperfusion injury

JOURNAL/nrgr/04.03/01300535-202407000-00042/figure1/v/2023-11-20T171125Z/r/image-tiff

Elevated intraocular pressure (IOP) is one of the causes of retinal ischemia/reperfusion injury, which results in NLRP3 inflammasome activation and leads to visual damage. Homer1a is reported to play a protective role in neuroinflammation in the cerebrum. However, the effects of Homer1a on NLRP3 inflammasomes in retinal ischemia/reperfusion injury caused by elevated IOP remain unknown. In our study, animal models were constructed using C57BL/6J and Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice with elevated IOP-induced retinal ischemia/reperfusion injury. For in vitro experiments, the oxygen-glucose deprivation/reperfusion injury model was constructed with Müller cells. We found that Homer1a overexpression ameliorated the decreases in retinal thickness and Müller cell viability after ischemia/reperfusion injury. Furthermore, Homer1a knockdown promoted NF-κB P65Ser536 activation via caspase-8, NF-κB P65 nuclear translocation, NLRP3 inflammasome formation, and the production and processing of interleukin-1β and interleukin-18. The opposite results were observed with Homer1a overexpression. Finally, the combined administration of Homer1a protein and JSH-23 significantly inhibited the reduction in retinal thickness in Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice and apoptosis in Müller cells after ischemia/reperfusion injury. Taken together, these studies demonstrate that Homer1a exerts protective effects on retinal tissue and Müller cells via the caspase-8/NF-κB P65/NLRP3 pathway after I/R injury.

The interaction between RIPK1 and FADD controls perinatal lethality and inflammation

Perturbation of the apoptosis and necroptosis pathways critically influences embryogenesis. Receptor-associated protein kinase-1 (RIPK1) interacts with Fas-associated via death domain (FADD)-caspase-8-cellular Flice-like inhibitory protein long (cFLIPL) to regulate both extrinsic apoptosis and necroptosis. Here, we describe Ripk1-mutant animals (Ripk1R588E [RE]) in which the interaction between FADD and RIPK1 is disrupted, leading to embryonic lethality. This lethality is not prevented by further removal of the kinase activity of Ripk1 (Ripk1R588E K45A [REKA]). Both Ripk1RE and Ripk1REKA animals survive to adulthood upon ablation of Ripk3. While embryonic lethality of Ripk1RE mice is prevented by ablation of the necroptosis effector mixed lineage kinase-like (MLKL), animals succumb to inflammation after birth. In contrast, Mlkl ablation does not prevent the death of Ripk1REKA embryos, but animals reach adulthood when both MLKL and caspase-8 are removed. Ablation of the nucleic acid sensor Zbp1 largely prevents lethality in both Ripk1RE and Ripk1REKA embryos. Thus, the RIPK1-FADD interaction prevents Z-DNA binding protein-1 (ZBP1)-induced, RIPK3-caspase-8-mediated embryonic lethality, affected by the kinase activity of RIPK1.

Mitochondria and cell death

Mitochondria are cellular factories for energy production, calcium homeostasis and iron metabolism, but they also have an unequivocal and central role in intrinsic apoptosis through the release of cytochrome c. While the subsequent activation of proteolytic caspases ensures that cell death proceeds in the absence of collateral inflammation, other phlogistic cell death pathways have been implicated in using, or engaging, mitochondria. Here we discuss the emerging complexities of intrinsic apoptosis controlled by the BCL-2 family of proteins. We highlight the emerging theory that non-lethal mitochondrial apoptotic signalling has diverse biological roles that impact cancer, innate immunity and ageing. Finally, we delineate the role of mitochondria in other forms of cell death, such as pyroptosis, ferroptosis and necroptosis, and discuss mitochondria as central hubs for the intersection and coordination of cell death signalling pathways, underscoring their potential for therapeutic manipulation.

Pyroptosis: A spoiler of peaceful coexistence between cells in degenerative bone and joint diseases

BACKGROUND

As people age, degenerative bone and joint diseases (DBJDs) become more prevalent. When middle-aged and elderly people are diagnosed with one or more disorders such as osteoporosis (OP), osteoarthritis (OA), and intervertebral disc degeneration (IVDD), it often signals the onset of prolonged pain and reduced functionality. Chronic inflammation has been identified as the underlying cause of various degenerative diseases, including DBJDs. Recently, excessive activation of pyroptosis, a form of programed cell death (PCD) mediated by inflammasomes, has emerged as a primary driver of harmful chronic inflammation. Consequently, pyroptosis has become a potential target for preventing and treating DBJDs.

AIM OF REVIEW

This review explored the physiological and pathological roles of the pyroptosis pathway in bone and joint development and its relation to DBJDs. Meanwhile, it elaborated the molecular mechanisms of pyroptosis within individual cell types in the bone marrow and joints, as well as the interplay among different cell types in the context of DBJDs. Furthermore, this review presented the latest compelling evidence supporting the idea of regulating the pyroptosis pathway for DBJDs treatment, and discussed the potential, limitations, and challenges of various therapeutic strategies involving pyroptosis regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In summary, an interesting identity for the unregulated pyroptosis pathway in the context of DBJDs was proposed in this review, which was undertaken as a spoiler of peaceful coexistence between cells in a degenerative environment. Over the extended course of DBJDs, pyroptosis pathway perpetuated its activity through crosstalk among pyroptosis cascades in different cell types, thus exacerbating the inflammatory environment throughout the entire bone marrow and joint degeneration environment. Correspondingly, pyroptosis regulation therapy emerged as a promising option for clinical treatment of DBJDs.

Pyroptosis mediates osteoporosis via the inflammation immune microenvironment

Osteoporosis represents a systemic imbalance in bone metabolism, augmenting the susceptibility to fractures among patients and emerging as a notable mortality determinant in the elderly population. It has evolved into a worldwide concern impacting the physical well-being of the elderly, imposing a substantial burden on both human society and the economy. Presently, the precise pathogenesis of osteoporosis remains inadequately characterized and necessitates further exploration. The advancement of osteoporosis is typically linked to the initiation of an inflammatory response. Cells in an inflammatory environment can cause inflammatory death including pyroptosis. Pyroptosis is a recently identified form of programmed cell death with inflammatory properties, mediated by the caspase and gasdermin families. It is regarded as the most inflammatory form of cell death in contemporary medical research. Under the influence of diverse cytokines, macrophages, and other immune cells may undergo pyroptosis, releasing inflammatory factors, such as IL-1β and IL-18. Numerous lines of evidence highlight the pivotal role of pyroptosis in the pathogenesis of inflammatory diseases, including cancer, intestinal disorders, hepatic conditions, and cutaneous ailments. Osteoporosis progression is frequently associated with inflammation; hence, pyroptosis may also play a role in the pathogenesis of osteoporosis to a certain extent, making it a potential target for treatment. This paper has provided a comprehensive summary of pertinent research concerning pyroptosis and its impact on osteoporosis. The notion proposing that pyroptosis mediates osteoporosis via the inflammatory immune microenvironment is advanced, and we subsequently investigate potential targets for treating osteoporosis through the modulation of pyroptosis.

The protein phosphatase PP6 promotes RIPK1-dependent PANoptosis

BACKGROUND

The innate immune system serves as the first line of host defense. Transforming growth factor-β-activated kinase 1 (TAK1) is a key regulator of innate immunity, cell survival, and cellular homeostasis. Because of its importance in immunity, several pathogens have evolved to carry TAK1 inhibitors. In response, hosts have evolved to sense TAK1 inhibition and induce robust lytic cell death, PANoptosis, mediated by the RIPK1-PANoptosome. PANoptosis is a unique innate immune inflammatory lytic cell death pathway initiated by an innate immune sensor and driven by caspases and RIPKs. While PANoptosis can be beneficial to clear pathogens, excess activation is linked to pathology. Therefore, understanding the molecular mechanisms regulating TAK1 inhibitor (TAK1i)-induced PANoptosis is central to our understanding of RIPK1 in health and disease.

RESULTS

In this study, by analyzing results from a cell death-based CRISPR screen, we identified protein phosphatase 6 (PP6) holoenzyme components as regulators of TAK1i-induced PANoptosis. Loss of the PP6 enzymatic component, PPP6C, significantly reduced TAK1i-induced PANoptosis. Additionally, the PP6 regulatory subunits PPP6R1, PPP6R2, and PPP6R3 had redundant roles in regulating TAK1i-induced PANoptosis, and their combined depletion was required to block TAK1i-induced cell death. Mechanistically, PPP6C and its regulatory subunits promoted the pro-death S166 auto-phosphorylation of RIPK1 and led to a reduction in the pro-survival S321 phosphorylation.

CONCLUSIONS

Overall, our findings demonstrate a key requirement for the phosphatase PP6 complex in the activation of TAK1i-induced, RIPK1-dependent PANoptosis, suggesting this complex could be therapeutically targeted in inflammatory conditions.

Histone deacetylase-mediated silencing of PSTPIP2 expression contributes to aristolochic acid nephropathy-induced PANoptosis

BACKGROUND AND PURPOSE

Aristolochic acid nephropathy (AAN) is a progressive kidney disease caused by using herbal medicines. Currently, no therapies are available to treat or prevent aristolochic acid nephropathy. Histone deacetylase (HDAC) plays a crucial role in the development and progression of renal disease. We tested whether HDAC inhibitors could prevent aristolochic acid nephropathy and determined the underlying mechanism.

EXPERIMENTAL APPROACH

HDACs expression in the aristolochic acid nephropathy model was examined. The activation of PANoptosis of mouse kidney and renal tubular epithelial cell were assessed after exposure to HDAC1 and HDAC2 blockade. Kidney-specific knock-in of proline-serine-threonine-phosphatase-interacting protein 2 (PSTPIP2) mice were used to investigate whether PSTPIP2 affected the production of PANoptosome.

KEY RESULTS

Aristolochic acid upregulated the expression of HDAC1 and HDAC2 in the kidneys. Notably, the HDAC1 and HDAC2 specific inhibitor, romidepsin (FK228, depsipeptide), suppressed aristolochic acid-induced kidney injury, epithelial cell pyroptosis, apoptosis and necroptosis (PANoptosis). Moreover, romidepsin upregulated PSTPIP2 in renal tubular epithelial cells, which was enhanced by aristolochic acid treatment. Conditional knock-in of PSTPIP2 in the kidney protected against aristolochic acid nephropathy. In contrast, the knockdown of PSTPIP2 expression in PSTPIP2-knock-in mice restored kidney damage and PANoptosis. PSTPIP2 function was determined in vitro using PSTPIP2 knockdown or overexpression in mouse renal tubular epithelial cells (mTECs). Additionally, PSTPIP2 was found to regulate caspase 8 in aristolochic acid nephropathy.

CONCLUSION AND IMPLICATIONS

HDAC-mediated silencing of PSTPIP2 may contribute to aristolochic acid nephropathy. Hence, HDAC1 and HDAC2 specific inhibitors or PSTPIP2 could be valuable therapeutic agents for preventing aristolochic acid nephropathy.

ZBP1 and TRIF trigger lethal necroptosis in mice lacking caspase-8 and TNFR1

Necroptosis is a lytic form of cell death that is mediated by the kinase RIPK3 and the pseudokinase MLKL when caspase-8 is inhibited downstream of death receptors, toll-like receptor 3 (TLR3), TLR4, and the intracellular Z-form nucleic acid sensor ZBP1. Oligomerization and activation of RIPK3 is driven by interactions with the kinase RIPK1, the TLR adaptor TRIF, or ZBP1. In this study, we use immunohistochemistry (IHC) and in situ hybridization (ISH) assays to generate a tissue atlas characterizing RIPK1, RIPK3, Mlkl, and ZBP1 expression in mouse tissues. RIPK1, RIPK3, and Mlkl were co-expressed in most immune cell populations, endothelial cells, and many barrier epithelia. ZBP1 was expressed in many immune populations, but had more variable expression in epithelia compared to RIPK1, RIPK3, and Mlkl. Intriguingly, expression of ZBP1 was elevated in Casp8-/- Tnfr1-/- embryos prior to their succumbing to aberrant necroptosis around embryonic day 15 (E15). ZBP1 contributed to this embryonic lethality because rare Casp8-/- Tnfr1-/- Zbp1-/- mice survived until after birth. Necroptosis mediated by TRIF contributed to the demise of Casp8-/- Tnfr1-/- Zbp1-/- pups in the perinatal period. Of note, Casp8-/- Tnfr1-/- Trif-/- Zbp1-/- mice exhibited autoinflammation and morbidity, typically within 5-7 weeks of being born, which is not seen in Casp8-/- Ripk1-/- Trif-/- Zbp1-/-, Casp8-/- Ripk3-/-, or Casp8-/- Mlkl-/- mice. Therefore, after birth, loss of caspase-8 probably unleashes RIPK1-dependent necroptosis driven by death receptors other than TNFR1.

RIPK3 cleavage is dispensable for necroptosis inhibition but restricts NLRP3 inflammasome activation

Caspase-8 activity is required to inhibit necroptosis during embryogenesis in mice. In vitro studies have suggested that caspase-8 directly cleaves RIPK1, CYLD and the key necroptotic effector kinase RIPK3 to repress necroptosis. However, recent studies have shown that mice expressing uncleavable RIPK1 die during embryogenesis due to excessive apoptosis, while uncleavable CYLD mice are viable. Therefore, these results raise important questions about the role of RIPK3 cleavage. To evaluate the physiological significance of RIPK3 cleavage, we generated Ripk3D333A/D333A mice harbouring a point mutation in the conserved caspase-8 cleavage site. These mice are viable, demonstrating that RIPK3 cleavage is not essential for blocking necroptosis during development. Furthermore, unlike RIPK1 cleavage-resistant cells, Ripk3D333A/D333A cells were not significantly more sensitive to necroptotic stimuli. Instead, we found that the cleavage of RIPK3 by caspase-8 restricts NLRP3 inflammasome activation-dependent pyroptosis and IL-1β secretion when Inhibitors of APoptosis (IAP) are limited. These results demonstrate that caspase-8 does not inhibit necroptosis by directly cleaving RIPK3 and further underscore a role for RIPK3 in regulating the NLRP3 inflammasome.

CRABP2 reduces the sensitivity of Olaparib in ovarian cancer by downregulating Caspase-8 and decreasing the production of reactive oxygen species

Poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors, such as Olaparib, have been pivotal in treating BRCA-deficient ovarian cancer. However, their efficacy is limited in over 40% of BRCA-deficient patients, with acquired resistance posing new clinical challenges. To address this, we employed bioinformatics methods to identify key genes impacting Olaparib sensitivity in ovarian cancer. Through comprehensive analysis of public databases including GEO, CPTAC, Kaplan Meier Plotter, and CCLE, we identified CRABP2 as significantly upregulated at both mRNA and protein levels in ovarian cancer, correlating with poor prognosis and decreased Olaparib sensitivity. Using colony formation and CCK-8 assays, we confirmed that CRABP2 knockdown in OVCAR3 and TOV112D cells enhanced sensitivity to Olaparib. Additionally, 4D label-free quantitative proteomics analysis, GSEA, and GO/KEGG analysis revealed CRABP2's involvement in regulating oxidation signals. Flow cytometry, colony formation assays, and western blotting demonstrated that CRABP2 knockdown promoted ROS production by activating Caspase-8, thereby augmenting Olaparib sensitivity and inhibiting ovarian cancer cell proliferation. Moreover, in xenograft models, CRABP2 knockdown significantly suppressed tumorigenesis and enhanced Olaparib sensitivity, with the effect being reversed upon Caspase-8 knockdown. These findings suggest that CRABP2 may modulate Olaparib sensitivity in ovarian cancer through the Caspase-8/ROS axis, highlighting its potential as a target for Olaparib sensitization.

Cell death as an architect of adult skin stem cell niches

Our skin provides a physical and immunological barrier against dehydration and environmental insults ranging from microbial attacks, toxins and UV irradiation to wounding. Proper functioning of the skin barrier largely depends on the interplay between keratinocytes- the epithelial cells of the skin- and immune cells. Two spatially distinct populations of keratinocyte stem cells (SCs) maintain the epidermal barrier function and the hair follicle. These SCs are inherently long-lived, but cell death can occur within their niches and impacts their functionality. The default cell death programme in skin is apoptosis, an orderly and non-inflammatory suicide programme. However, recent findings are shedding light on the significance of various modes of regulated necrotic cell death, which are lytic and can provoke inflammation within the local skin environment. While the presence of dying cells was generally regarded as a mere consequence of inflammation, findings in various human dermatological conditions and experimental mouse models of aberrant cell death control demonstrated that cell death programmes in keratinocytes (KCs) can drive skin inflammation and even tumour initiation. When cells die, they need to be removed by phagocytosis and KCs can function as non-professional phagocytes of apoptotic cells with important implications for their SC capacities. It is becoming apparent that in conditions of heightened SC activity, distinct cell death modalities differentially impact the different skin SC populations in their local niches. Here, we describe how regulated cell death modalities functionally affect epidermal SC niches along with their relevance to injury repair, inflammatory skin disorders and cancer.

Caspase 8 deletion causes infection/inflammation-induced bone marrow failure and MDS-like disease in mice

Myelodysplastic syndromes (MDS) are a heterogeneous group of pre-leukemic hematopoietic disorders characterized by cytopenia in peripheral blood due to ineffective hematopoiesis and normo- or hypercellularity and morphologic dysplasia in bone marrow (BM). An inflammatory BM microenvironment and programmed cell death of hematopoietic stem/progenitor cells (HSPCs) are thought to be the major causes of ineffective hematopoiesis in MDS. Pyroptosis, apoptosis and necroptosis (collectively, PANoptosis) are observed in BM tissues of MDS patients, suggesting an important role of PANoptosis in MDS pathogenesis. Caspase 8 (Casp8) is a master regulator of PANoptosis, which is downregulated in HSPCs from most MDS patients and abnormally spliced in HSPCs from MDS patients with SRSF2 mutation. To study the role of PANoptosis in hematopoiesis, we generated inducible Casp8 knockout mice (Casp8-/-). Mx1-Cre-Casp8-/- mice died of BM failure within 10 days of polyI:C injections due to depletion of HSPCs. Rosa-ERT2Cre-Casp8-/- mice are healthy without significant changes in BM hematopoiesis within the first 1.5 months after Casp8 deletion. Such mice developed BM failure upon infection or low dose polyI:C/LPS injections due to the hypersensitivity of Casp8-/- HSPCs to infection or inflammation-induced necroptosis which can be prevented by Ripk3 deletion. However, impaired self-renewal capacity of Casp8-/- HSPCs cannot be rescued by Ripk3 deletion due to activation of Ripk1-Tbk1 signaling. Most importantly, mice transplanted with Casp8-/- BM cells developed MDS-like disease within 4 months of transplantation as demonstrated by anemia, thrombocytopenia and myelodysplasia. Our study suggests an essential role for a balance in Casp8, Ripk3-Mlkl and Ripk1-Tbk1 activities in the regulation of survival and self-renewal of HSPCs, the disruption of which induces inflammation and BM failure, resulting in MDS-like disease.

Understanding the Role of Connexins in Hepatocellular Carcinoma: Molecular and Prognostic Implications

Connexins, a family of tetraspan membrane proteins forming intercellular channels localized in gap junctions, play a pivotal role at the different stages of tumor progression presenting both pro- and anti-tumorigenic effects. Considering the potential role of connexins as tumor suppressors through multiple channel-independent mechanisms, their loss of expression may be associated with tumorigenic activity, while it is hypothesized that connexins favor the clonal expansion of tumor cells and promote cell migration, invasion, and proliferation, affecting metastasis and chemoresistance in some cases. Hepatocellular carcinoma (HCC), characterized by unfavorable prognosis and limited responsiveness to current therapeutic strategies, has been linked to gap junction proteins as tumorigenic factors with prognostic value. Notably, several members of connexins have emerged as promising markers for assessing the progression and aggressiveness of HCC, as well as the chemosensitivity and radiosensitivity of hepatocellular tumor cells. Our review sheds light on the multifaceted role of connexins in HCC pathogenesis, offering valuable insights on recent advances in determining their prognostic and therapeutic potential.

NcRNA Regulated Pyroptosis in Liver Diseases and Traditional Chinese Medicine Intervention: A Narrative Review

Pyroptosis is a novel pro-inflammatory mode of programmed cell death that differs from ferroptosis, necrosis, and apoptosis in terms of its onset and regulatory mechanisms. Pyroptosis is dependent on cysteine aspartate protein hydrolase (caspase)-mediated activation of GSDMD, NLRP3, and the release of pro-inflammatory cytokines, interleukin-1 (IL-1β), and interleukin-18 (IL-18), ultimately leading to cell death. Non-coding RNA (ncRNA) is a type of RNA that does not encode proteins in gene transcription but plays an important regulatory role in other post-transcriptional links. NcRNA mediates pyroptosis by regulating various related pyroptosis factors, which we termed the pyroptosis signaling pathway. Previous researches have manifested that pyroptosis is closely related to the development of liver diseases, and is essential for liver injury, alcoholic fatty liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), liver fibrosis, and liver cancer. In this review, we attempt to address the role of the ncRNA-mediated pyroptosis pathway in the above liver diseases and their pathogenesis in recent years, and briefly outline that TCM (Traditional Chinese Medicine) intervene in liver diseases by modulating ncRNA-mediated pyroptosis, which will provide a strategy to find new therapeutic targets for the prevention and treatment of liver diseases in the future.

NK-cell-elicited gasdermin-D-dependent hepatocyte pyroptosis induces neutrophil extracellular traps that facilitate HBV-related acute-on-chronic liver failure

BACKGROUND AND AIMS

HBV infection is a major etiology of acute-on-chronic liver failure (ACLF). At present, the pattern and regulation of hepatocyte death during HBV-ACLF progression are still undefined. Evaluating the mode of cell death and its inducers will provide new insights for developing therapeutic strategies targeting cell death. In this study, we aimed to elucidate whether and how immune landscapes trigger hepatocyte death and lead to the progression of HBV-related ACLF.

APPROACH AND RESULTS

We identified that pyroptosis represented the main cell death pattern in the liver of patients with HBV-related ACLF. Deficiency of MHC-I in HBV-reactivated hepatocytes activated cytotoxic NK cells, which in turn operated in a perforin/granzyme-dependent manner to trigger GSDMD/caspase-8-dependent pyroptosis of hepatocytes. Neutrophils selectively accumulated in the pyroptotic liver, and HMGB1 derived from the pyroptotic liver constituted an important factor triggering the generation of pathogenic extracellular traps in neutrophils (NETs). Clinically, elevated plasma levels of myeloperoxidase-DNA complexes were a promising prognostic biomarker for HBV-related ACLF. More importantly, targeting GSDMD pyroptosis-HMGB1 release in the liver abrogates NETs that intercept the development of HBV-related ACLF.

CONCLUSIONS

Studying the mechanisms that selectively modulate GSDMD-dependent pyroptosis, as well as its immune landscapes, will provide a novel strategy for restoring the liver function of patients with HBV-related ACLF.

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

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

Selective induction of programmed cell death using synthetic biology tools

Regulated cell death (RCD) controls the removal of dispensable, infected or malignant cells, and is thus essential for development, homeostasis and immunity of multicellular organisms. Over the last years different forms of RCD have been described (among them apoptosis, necroptosis, pyroptosis and ferroptosis), and the cellular signaling pathways that control their induction and execution have been characterized at the molecular level. It has also become apparent that different forms of RCD differ in their capacity to elicit inflammation or an immune response, and that RCD pathways show a remarkable plasticity. Biochemical and genetic studies revealed that inhibition of a given pathway often results in the activation of back-up cell death mechanisms, highlighting close interconnectivity based on shared signaling components and the assembly of multivalent signaling platforms that can initiate different forms of RCD. Due to this interconnectivity and the pleiotropic effects of 'classical' cell death inducers, it is challenging to study RCD pathways in isolation. This has led to the development of tools based on synthetic biology that allow the targeted induction of RCD using chemogenetic or optogenetic methods. Here we discuss recent advances in the development of such toolset, highlighting their advantages and limitations, and their application for the study of RCD in cells and animals.

Mitochondrial P-JNK target, SAB (SH3BP5), in regulation of cell death

Cell death occurs in various circumstances, such as homeostasis, stress response, and defense, via specific pathways and mechanisms that are regulated by specific activator-induced signal transductions. Among them, Jun N-terminal kinases (JNKs) participate in various aspects, and the recent discovery of JNKs and mitochondrial protein SAB interaction in signal regulation of cell death completes our understanding of the mechanism of sustained activation of JNK (P-JNK), which leads to triggering of the machinery of cell death. This understanding will lead the investigators to discover the modulators facilitating or preventing cell death for therapeutic application in acute or chronic diseases and cancer. We discuss here the mechanism and modulators of the JNK-SAB-ROS activation loop, which is the core component of mitochondria-dependent cell death, specifically apoptosis and mitochondrial permeability transition (MPT)-driven necrosis, and which may also contribute to cell death mechanisms of ferroptosis and pyroptosis. The discussion here is based on the results and evidence discovered from liver disease models, but the JNK-SAB-ROS activation loop to sustain JNK activation is universally applicable to various disease models where mitochondria and reactive oxygen species contribute to the mechanism of disease.

New prospects of cancer therapy based on pyroptosis and pyroptosis inducers

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

Caspase cleavage of RIPK3 after Asp333 is dispensable for mouse embryogenesis

The proteolytic activity of caspase-8 suppresses lethal RIPK1-, RIPK3- and MLKL-dependent necroptosis during mouse embryogenesis. Caspase-8 is reported to cleave RIPK3 in addition to the RIPK3-interacting kinase RIPK1, but whether cleavage of RIPK3 is crucial for necroptosis suppression is unclear. Here we show that caspase-8-driven cleavage of endogenous mouse RIPK3 after Asp333 is dependent on downstream caspase-3. Consistent with RIPK3 cleavage being a consequence of apoptosis rather than a critical brake on necroptosis, Ripk3D333A/D333A knock-in mice lacking the Asp333 cleavage site are viable and develop normally. Moreover, in contrast to mice lacking caspase-8 in their intestinal epithelial cells, Ripk3D333A/D333A mice do not exhibit increased sensitivity to high dose tumor necrosis factor (TNF). Ripk3D333A/D333A macrophages died at the same rate as wild-type (WT) macrophages in response to TNF plus cycloheximide, TNF plus emricasan, or infection with murine cytomegalovirus (MCMV) lacking M36 and M45 to inhibit caspase-8 and RIPK3 activation, respectively. We conclude that caspase cleavage of RIPK3 is dispensable for mouse development, and that cleavage of caspase-8 substrates, including RIPK1, is sufficient to prevent necroptosis.

Control of Cell Death in Health and Disease

Apoptosis, necroptosis, and pyroptosis are genetically programmed cell death mechanisms that eliminate obsolete, damaged, infected, and self-reactive cells. Apoptosis fragments cells in a manner that limits immune cell activation, whereas the lytic death programs of necroptosis and pyroptosis release proinflammatory intracellular contents. Apoptosis fine-tunes tissue architecture during mammalian development, promotes tissue homeostasis, and is crucial for averting cancer and autoimmunity. All three cell death mechanisms are deployed to thwart the spread of pathogens. Disabling regulators of cell death signaling in mice has revealed how excessive cell death can fuel acute or chronic inflammation. Here we review strategies for modulating cell death in the context of disease. For example, BCL-2 inhibitor venetoclax, an inducer of apoptosis, is approved for the treatment of certain hematologic malignancies. By contrast, inhibition of RIPK1, NLRP3, GSDMD, or NINJ1 to limit proinflammatory cell death and/or the release of large proinflammatory molecules from dying cells may benefit patients with inflammatory diseases.

Cell death

Cell death supports morphogenesis during development and homeostasis after birth by removing damaged or obsolete cells. It also curtails the spread of pathogens by eliminating infected cells. Cell death can be induced by the genetically programmed suicide mechanisms of apoptosis, necroptosis, and pyroptosis, or it can be a consequence of dysregulated metabolism, as in ferroptosis. Here, we review the signaling mechanisms underlying each cell-death pathway, discuss how impaired or excessive activation of the distinct cell-death processes can promote disease, and highlight existing and potential therapies for redressing imbalances in cell death in cancer and other diseases.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Association Between Diverse Cell Death Patterns Related Gene Signature and Prognosis, Drug Sensitivity, and Immune Microenvironment in Glioblastoma

Glioblastoma (GBM) is the most invasive type of glioma and is difficult to treat. Diverse programmed cell death (PCD) patterns have a significant association with tumor initiation and progression. A novel prognostic model based on PCD genes may serve as an effective tool to predict the prognosis of GBM. The study incorporated 11 PCD patterns, namely apoptosis, necroptosis, pyroptosis, ferroptosis, cuproptosis, entotic cell death, netotic cell death, parthanatos, lysosome-dependent cell death, autophagy-dependent cell death, alkaliptosis, and oxeiptosis, to develop the model. To construct and validate the model, both bulk and single-cell transcriptome data, along with corresponding clinical data from GBM cases, were obtained from the TCGA-GBM, REMBRANDT, CGGA, and GSE162631 datasets. A cell death-related signature containing 14 genes was constructed with the TCGA-GBM cohort and validated in the REMBRANDT and CGGA datasets. GBM patients with a higher cell death index (CDI) were significantly associated with poorer survival outcomes. Two separate clusters associated with clinical outcomes emerged from unsupervised analysis. A multivariate Cox regression analysis was conducted to examine the association of CDI with clinical characteristics, and a prognostic nomogram was developed. Drug sensitivity analysis revealed high-CDI GBM patients might be resistant to carmustine while sensitive to 5-fluorouracil. Less abundance of natural killer cells was found in GBM cases with high CDI and bulk transcriptome data. A cell death-related prognostic model that could predict the prognosis of GBM patients with good performance was established, which could discriminate between the prognosis and drug sensitivity of GBM.

Mechanisms of immune response and cell death in ischemic stroke and their regulation by natural compounds

Ischemic stroke (IS), which is the third foremost cause of disability and death worldwide, has inflammation and cell death as its main pathological features. IS can lead to neuronal cell death and release factors such as damage-related molecular patterns, stimulating the immune system to release inflammatory mediators, thereby resulting in inflammation and exacerbating brain damage. Currently, there are a limited number of treatment methods for IS, which is a fact necessitating the discovery of new treatment targets. For this review, current research on inflammation and cell death in ischemic stroke was summarized. The complex roles and pathways of the principal immune cells (microglia, astrocyte, neutrophils, T lymphocytes, and monocytes/macrophage) in the immune system after IS in inflammation are discussed. The mechanisms of immune cell interactions and the cytokines involved in these interactions are summarized. Moreover, the cell death mechanisms (pyroptosis, apoptosis, necroptosis, PANoptosis, and ferroptosis) and pathways after IS are explored. Finally, a summary is provided of the mechanism of action of natural pharmacological active ingredients in the treatment of IS. Despite significant recent progress in research on IS, there remain many challenges that need to be overcome.

Drugging the NLRP3 inflammasome: from signalling mechanisms to therapeutic targets

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

Therapeutic potential of PANoptosis: innate sensors, inflammasomes, and RIPKs in PANoptosomes

The innate immune system initiates cell death pathways in response to pathogens and cellular stress. Cell death can be either non-lytic (apoptosis) or lytic (PANoptosis, pyroptosis, and necroptosis). PANoptosis has been identified as an inflammatory, lytic cell death pathway driven by caspases and RIPKs that is regulated by PANoptosome complexes, making it distinct from other cell death pathways. Several PANoptosome complexes (including ZBP1-, AIM2-, RIPK1-, and NLRP12-PANoptosomes) have been characterized to date. Furthermore, PANoptosis is implicated in infectious and inflammatory diseases, cancers, and homeostatic perturbations. Therefore, targeting its molecular components offers significant potential for therapeutic development. This review covers PANoptosomes and their assembly, PANoptosome-mediated cell death mechanisms, and ongoing progress in developing therapeutics that target PANoptosis.

Quercetin is a Potential Therapy for Rheumatoid Arthritis via Targeting Caspase-8 Through Ferroptosis and Pyroptosis

Background

Rheumatoid arthritis (RA) is one of the most common chronic inflammatory autoimmune diseases. However, the underlying molecular mechanisms of its pathogenesis are unknown. This study aimed to identify the common biomarkers of ferroptosis and pyroptosis in RA and screen potential drugs.

Methods

The RA-related differentially expressed genes (DEGs) in GSE55235 were screened by R software and intersected with ferroptosis and pyroptosis gene libraries to obtain differentially expressed ferroptosis-related genes (DEFRGs) and differentially expressed pyroptosis-related genes (DEPRGs). We performed Gene Ontology (GO), Kyoto Encyclopedia of the Genome (KEGG), ClueGO, and Protein-Protein Interaction (PPI) analysis for DEFRGs and DEPRGs and validated them by machine learning. The microRNA/transcription factor (TF)-hub genes regulatory network was further constructed. The key gene was validated using the GSE77298 validation set, cellular validation was performed in in vitro experiments, and immune infiltration analysis was performed using CIBERSORT. Network pharmacology was used to find key gene-targeting drugs, followed by molecular docking and molecular dynamics simulations to analyze the binding stability between small-molecule drugs and large-molecule proteins.

Results

Three hub genes (CASP8, PTGS2, and JUN) were screened via bioinformatics, and the key gene (CASP8) was validated and obtained through the validation set, and the diagnostic efficacy was verified to be excellent through the receiver operating characteristic (ROC) curves. The ferroptosis and pyroptosis phenotypes were constructed by fibroblast-like synoviocytes (FLS), and caspase-8 was detected and validated as a common biomarker for ferroptosis and pyroptosis in RA, and quercetin can reduce caspase-8 levels. Quercetin was found to be a potential target drug for caspase-8 by network pharmacology, and the stability of their binding was further verified using molecular docking and molecular dynamics simulations.

Conclusion

Caspase-8 is an important biomarker for ferroptosis and pyroptosis in RA, and quercetin is a potential therapy for RA via targeting caspase-8 through ferroptosis and pyroptosis.

PANoptosis in cancer, the triangle of cell death

BACKGROUND

PANoptosis is a novel form of programmed cell death (PCD) found in 2019 that is regulated by the PANoptosome. PANoptosis combines essential features of pyroptosis, apoptosis, and necroptosis, forming a "death triangle" of cells. While apoptosis, pyroptosis, and necroptosis have been extensively studied for their roles in human inflammatory diseases and many other clinical conditions, historically they were considered as independent processes. However, emerging evidence indicates that these PCDs exhibit cross talk and interactions, resulting in the development of the concept of PANoptosis.

METHODS

In this review, we offer a concise summary of the fundamental mechanisms of apoptosis, pyroptosis, and necroptosis. We subsequently introduce the notion of PANoptosis and detail the assembly mechanism of the PANoptosome complex which is responsible for inducing cell death. We also describe some regulatory networks of PANoptosis.

RESULTS

PANoptosis now has been associated with various human diseases including cancer. Although the exact function of PANoptosis in each tumor is not fully understood, it represents a prospective avenue for cancer therapy, offering promise for advancements in cancer therapy.

CONCLUSIONS

In the future, in-depth study of PANoptosis will continue to help us in understanding the fundamental processes underlying cell death and provide scientific support for cancer research.

Integrated NLRP3, AIM2, NLRC4, Pyrin inflammasome activation and assembly drive PANoptosis

Inflammasomes are important sentinels of innate immune defense; they sense pathogens and induce the cell death of infected cells, playing key roles in inflammation, development, and cancer. Several inflammasome sensors detect and respond to specific pathogen- and damage-associated molecular patterns (PAMPs and DAMPs, respectively) by forming a multiprotein complex with the adapters ASC and caspase-1. During disease, cells are exposed to several PAMPs and DAMPs, leading to the concerted activation of multiple inflammasomes. However, the molecular mechanisms that integrate multiple inflammasome sensors to facilitate optimal host defense remain unknown. Here, we discovered that simultaneous inflammasome activation by multiple ligands triggered multiple types of programmed inflammatory cell death, and these effects could not be mimicked by treatment with a pure ligand of any single inflammasome. Furthermore, NLRP3, AIM2, NLRC4, and Pyrin were determined to be members of a large multiprotein complex, along with ASC, caspase-1, caspase-8, and RIPK3, and this complex drove PANoptosis. Furthermore, this multiprotein complex was released into the extracellular space and retained as multiple inflammasomes. Multiple extracellular inflammasome particles could induce inflammation after their engulfment by neighboring macrophages. Collectively, our findings define a previously unknown regulatory connection and molecular interaction between inflammasome sensors, which drives the assembly of a multiprotein complex that includes multiple inflammasome sensors and cell death regulators. The discovery of critical interactions among NLRP3, AIM2, NLRC4, and Pyrin represents a new paradigm in understanding the functions of these molecules in innate immunity and inflammasome biology as well as identifying new therapeutic targets for NLRP3-, AIM2-, NLRC4- and Pyrin-mediated diseases.

A1 is induced by pathogen ligands to limit myeloid cell death and NLRP3 inflammasome activation

Programmed cell death pathways play an important role in innate immune responses to infection. Activation of intrinsic apoptosis promotes infected cell clearance; however, comparatively little is known about how this mode of cell death is regulated during infections and whether it can induce inflammation. Here, we identify that the pro-survival BCL-2 family member, A1, controls activation of the essential intrinsic apoptotic effectors BAX/BAK in macrophages and monocytes following bacterial lipopolysaccharide (LPS) sensing. We show that, due to its tight transcriptional and post-translational regulation, A1 acts as a molecular rheostat to regulate BAX/BAK-dependent apoptosis and the subsequent NLRP3 inflammasome-dependent and inflammasome-independent maturation of the inflammatory cytokine IL-1β. Furthermore, induction of A1 expression in inflammatory monocytes limits cell death modalities and IL-1β activation triggered by Neisseria gonorrhoeae-derived outer membrane vesicles (NOMVs). Consequently, A1-deficient mice exhibit heightened IL-1β production in response to NOMV injection. These findings reveal that bacteria can induce A1 expression to delay myeloid cell death and inflammatory responses, which has implications for the development of host-directed antimicrobial therapeutics.

Roles of RIPK1 as a stress sentinel coordinating cell survival and immunogenic cell death

Cell death and inflammation are closely linked arms of the innate immune response to combat infection and tissue malfunction. Recent advancements in our understanding of the intricate signals originating from dying cells have revealed that cell death serves as more than just an end point. It facilitates the exchange of information between the dying cell and cells of the tissue microenvironment, particularly immune cells, alerting and recruiting them to the site of disturbance. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is emerging as a critical stress sentinel that functions as a molecular switch, governing cellular survival, inflammatory responses and immunogenic cell death signalling. Its tight regulation involves multiple layers of post-translational modifications. In this Review, we discuss the molecular mechanisms that regulate RIPK1 to maintain homeostasis and cellular survival in healthy cells, yet drive cell death in a context-dependent manner. We address how RIPK1 mutations or aberrant regulation is associated with inflammatory and autoimmune disorders and cancer. Moreover, we tease apart what is known about catalytic and non-catalytic roles of RIPK1 and discuss the successes and pitfalls of current strategies that aim to target RIPK1 in the clinic.

Innate immune inflammatory cell death: PANoptosis and PANoptosomes in host defense and disease

Regulated cell death (RCD) triggered by innate immune activation is an important strategy for host survival during pathogen invasion and perturbations of cellular homeostasis. There are two main categories of RCD, including nonlytic and lytic pathways. Apoptosis is the most well-characterized nonlytic RCD, and the inflammatory pyroptosis and necroptosis pathways are among the best known lytic forms. While these were historically viewed as independent RCD pathways, extensive evidence of cross-talk among their molecular components created a knowledge gap in our mechanistic understanding of RCD and innate immune pathway components, which led to the identification of PANoptosis. PANoptosis is a unique innate immune inflammatory RCD pathway that is regulated by PANoptosome complexes upon sensing pathogens, pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs) or the cytokines produced downstream. Cytosolic innate immune sensors and regulators, such as ZBP1, AIM2 and RIPK1, promote the assembly of PANoptosomes to drive PANoptosis. In this review, we discuss the molecular components of the known PANoptosomes and highlight the mechanisms of PANoptosome assembly, activation and regulation identified to date. We also discuss how PANoptosomes and mutations in PANoptosome components are linked to diseases. Given the impact of RCD, and PANoptosis specifically, across the disease spectrum, improved understanding of PANoptosomes and their regulation will be critical for identifying new therapeutic targets and strategies.

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

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

Role of toll-like receptor-mediated pyroptosis in sepsis-induced cardiomyopathy

Sepsis, a life-threatening dysregulated status of the host response to infection, can cause multiorgan dysfunction and mortality. Sepsis places a heavy burden on the cardiovascular system due to the pathological imbalance of hyperinflammation and immune suppression. Myocardial injury and cardiac dysfunction caused by the aberrant host responses to pathogens can lead to cardiomyopathy, one of the most critical complications of sepsis. However, many questions about the specific mechanisms and characteristics of this complication remain to be answered. The causes of sepsis-induced cardiac dysfunction include abnormal cardiac perfusion, myocardial inhibitory substances, autonomic dysfunction, mitochondrial dysfunction, and calcium homeostasis dysregulation. The fight between the host and pathogens acts as the trigger for sepsis-induced cardiomyopathy. Pyroptosis, a form of programmed cell death, plays a critical role in the progress of sepsis. Toll-like receptors (TLRs) act as pattern recognition receptors and participate in innate immune pathways that recognize damage-associated molecular patterns as well as pathogen-associated molecular patterns to mediate pyroptosis. Notably, pyroptosis is tightly associated with cardiac dysfunction in sepsis and septic shock. In line with these observations, induction of TLR-mediated pyroptosis may be a promising therapeutic approach to treat sepsis-induced cardiomyopathy. This review focuses on the potential roles of TLR-mediated pyroptosis in sepsis-induced cardiomyopathy, to shed light on this promising therapeutic approach, thus helping to prevent and control septic shock caused by cardiovascular disorders and improve the prognosis of sepsis patients.

Inflammasome: structure, biological functions, and therapeutic targets

Inflammasomes are a group of protein complex located in cytoplasm and assemble in response to a wide variety of pathogen-associated molecule patterns, damage-associated molecule patterns, and cellular stress. Generally, the activation of inflammasomes will lead to maturation of proinflammatory cytokines and pyroptotic cell death, both associated with inflammatory cascade amplification. A sensor protein, an adaptor, and a procaspase protein interact through their functional domains and compose one subunit of inflammasome complex. Under physiological conditions, inflammasome functions against pathogen infection and endogenous dangers including mtROS, mtDNA, and so on, while dysregulation of its activation can lead to unwanted results. In recent years, advances have been made to clarify the mechanisms of inflammasome activation, the structural details of them and their functions (negative/positive) in multiple disease models in both animal models and human. The wide range of the stimuli makes the function of inflammasome diverse and complex. Here, we review the structure, biological functions, and therapeutic targets of inflammasomes, while highlight NLRP3, NLRC4, and AIM2 inflammasomes, which are the most well studied. In conclusion, this review focuses on the activation process, biological functions, and structure of the most well-studied inflammasomes, summarizing and predicting approaches for disease treatment and prevention with inflammasome as a target. We aim to provide fresh insight into new solutions to the challenges in this field.

Pyroptosis burden is associated with anti-TNF treatment outcome in inflammatory bowel disease: new insights from bioinformatics analysis

Biological agents known as anti-tumor necrosis factor (TNF) drugs are frequently utilized in the treatment of inflammatory bowel disease (IBD). In this study, we analyzed the shared processes of pyroptosis in Ulcerative colitis (UC) and Crohn's disease (CD), as well as explored the correlation between the burden of pyroptosis and the results of anti-TNF treatment based on bioinformatics analyses. We identified CAPS1, CASP5, GSDMD, AIM2, and NLRP3 as the hub genes, with AIM2 being the most effective indicator for predicting the response to anti-TNF therapy. We also noticed that non-responders received anti-TNF therapy exhibited elevated AIM2 protein expression. Subsequently, we conducted a cluster analysis based on AIM2-inflammasome-related genes and discovered that patients with a higher burden of AIM2 inflammasome displayed stronger immune function and a poor response to anti-TNF therapy. Overall, our study elucidates the pathway of pyroptosis in IBD and reveals AIM2 expression level as a potential biomarker for predicting the effectiveness of anti-TNF therapy.