Chungtaejeon (CTJ) inhibits adhesion and migration of VSMC through cytoskeletal remodeling pathway.

Introduction: Vascular remodeling is crucial for the progression of vascular disease such as atherosclerosis. We utilize the in vitro experimental model of atherosclerosis to elucidate the activity of Chungtaejeon (CTJ), a Korean fermented tea on adhesion and migration of human aortic vascular smooth muscle cells (HASMC). Materials and methods: Various in vitro assays such as cell viability, cell adhesion, Western blot, immunofluorescence, were carried out on HASMC to explore pathway associated with cytoskeletal remodeling during the progression of atherosclerosis. Results: In result, CTJ significantly inhibited adhesion of HASMC as revealed by collagen assay. Similarly, CTJ inhibited the ß1-integrin protein expression as well as FAK phosphorylation. Treatment of CTJ also inhibited stress fiber formation. Likewise, adherence of cells on collagen optimally increased the expression of both RhoA and Cdc42, however, treatment of CTJ dose dependently decreased their expression. The lysophosphatidic acid stimulation of HASMC rapidly increased the level of phosphorylated forms of MLC20 within 15 min, followed by an extended level of MLC20 phosphorylation. The treatment of CTJ at a dose of 50, 100 and 250 µg/ml remarkably reduced the diphosphorylated form while decreased the level of monophosphorylated form of MLC20. Conclusions: Our results suggests that, with further validation CTJ could be a promising herbal resource for prevention of atherosclerosis.

DNA sensors in metabolic and cardiovascular diseases: Molecular mechanisms and therapeutic prospects.

DNA sensors generally initiate innate immune responses through the production of type I interferons. While extensively studied for host defense against invading pathogens, emerging evidence highlights the involvement of DNA sensors in metabolic and cardiovascular diseases. Elevated levels of modified, damaged, or ectopically localized self-DNA and non-self-DNA have been observed in patients and animal models with obesity, diabetes, fatty liver disease, and cardiovascular disease. The accumulation of cytosolic DNA aberrantly activates DNA signaling pathways, driving the pathological progression of these disorders. This review highlights the roles of specific DNA sensors, such as cyclic AMP-GMP synthase and stimulator of interferon genes (cGAS-STING), absent in melanoma 2 (AIM2), toll-like receptor 9 (TLR9), interferon gamma-inducible protein 16 (IFI16), DNA-dependent protein kinase (DNA-PK), and DEAD-box helicase 41 (DDX41) in various metabolic disorders. We explore how DNA signaling pathways in both immune and non-immune cells contribute to the development of these diseases. Furthermore, we discuss the intricate interplay between metabolic stress and immune responses, offering insights into potential therapeutic targets for managing metabolic and cardiovascular disorders. Understanding the mechanisms of DNA sensor signaling in these contexts provides a foundation for developing novel interventions aimed at mitigating the impact of these pervasive health issues.

Implications of inflammatory cell death-PANoptosis in health and disease.

Regulated cell death (RCD) pathways, such as pyroptosis, apoptosis, and necroptosis, are essential for maintaining the body's balance, defending against pathogens, and eliminating abnormal cells that could lead to diseases like cancer. Although these pathways operate through distinct mechanisms, recent genetic and pharmacological studies have shown that they can interact and influence each other. The concept of "PANoptosis" has emerged, highlighting the interplay between pyroptosis, apoptosis, and necroptosis, especially during cellular responses to infections. This article provides a concise overview of PANoptosis and its molecular mechanisms, exploring its implications in various diseases. The review focuses on the extensive interactions among different RCD pathways, emphasizing the role of PANoptosis in infections, cytokine storms, inflammatory diseases, and cancer. Understanding PANoptosis is crucial for developing novel treatments for conditions involving infections, sterile inflammations, and cancer.

Inhibition of the RPS6KA1/FoxO1 signaling axis by hydroxycitric acid attenuates HFD-induced obesity through MCE suppression.

BACKGROUND: Because obesity is associated with a hyperplasia-mediated increase in adipose tissue, inhibiting cell proliferation during mitotic clonal expansion (MCE) is a leading strategy for preventing obesity. Although (-)-hydroxycitric acid (HCA) is used to control obesity, the molecular mechanisms underlying its effects on MCE are poorly understood. PURPOSE: This study aimed to investigate the potential effects of HCA on MCE and underlying molecular mechanisms affecting adipogenesis and obesity improvements. METHODS: Preadipocyte cell line, 3T3-L1, were treated with HCA; oil red O, cell proliferation, cell cycle, and related alterations in signaling pathways were examined. High-fat diet (HFD)-fed mice were administered HCA for 12 weeks; body and adipose tissues weights were evaluated, and the regulation of signaling pathways in epidydimal white adipose tissue were examined in vivo. RESULTS: Here, we report that during MCE, HCA attenuates the proliferation of the preadipocyte cell line, 3T3-L1, by arresting the cell cycle at the G0/G1 phase. In addition, HCA markedly inhibits Forkhead Box O1 (FoxO1) phosphorylation, thereby inducing the expression of cyclin-dependent kinase inhibitor 1B and suppressing the levels of cyclin-dependent kinase 2, cyclin E1, proliferating cell nuclear antigen, and phosphorylated retinoblastoma. Importantly, we found that ribosomal protein S6 kinase A1 (RPS6KA1) influences HCA-mediated inactivation of FoxO1 and its nuclear exclusion. An animal model of obesity revealed that HCA reduced high-fat diet-induced obesity by suppressing adipocyte numbers as well as epididymal and mesenteric white adipose tissue mass, which is attributed to the regulation of RPS6KA1, FoxO1, CDKN1B and PCNA that had been consistently identified in vitro. CONCLUSIONS: These findings provide novel insights into the mechanism by which HCA regulates adipogenesis and highlight the RPS6KA1/FoxO1 signaling axis as a therapeutic target for obesity.

NINJ1 mediates inflammatory cell death, PANoptosis, and lethality during infection conditions and heat stress.

Innate immunity provides the first line of defense through multiple mechanisms, including pyrogen production and cell death. While elevated body temperature during infection is beneficial to clear pathogens, heat stress (HS) can lead to inflammation and pathology. Links between pathogen exposure, HS, cytokine release, and inflammation have been observed, but fundamental innate immune mechanisms driving pathology during pathogen exposure and HS remain unclear. Here, we use multiple genetic approaches to elucidate innate immune pathways in infection or LPS and HS models. Our results show that bacteria and LPS robustly increase inflammatory cell death during HS that is dependent on caspase-1, caspase-11, caspase-8, and RIPK3 through the PANoptosis pathway. Caspase-7 also contributes to PANoptosis in this context. Furthermore, NINJ1 is an important executioner of this cell death to release inflammatory molecules, independent of other pore-forming executioner proteins, gasdermin D, gasdermin E, and MLKL. In an in vivo HS model, mortality is reduced by deleting NINJ1 and fully rescued by deleting key PANoptosis molecules. Our findings suggest that therapeutic strategies blocking NINJ1 or its upstream regulators to prevent PANoptosis may reduce the release of inflammatory mediators and benefit patients.

A comparative study of apoptosis, pyroptosis, necroptosis, and PANoptosis components in mouse and human cells.

Regulated cell death is a key component of the innate immune response, which provides the first line of defense against infection and homeostatic perturbations. However, cell death can also drive pathogenesis. The most well-defined cell death pathways can be categorized as nonlytic (apoptosis) and lytic (pyroptosis, necroptosis, and PANoptosis). While specific triggers are known to induce each of these cell death pathways, it is unclear whether all cell types express the cell death proteins required to activate these pathways. Here, we assessed the protein expression and compared the responses of immune and non-immune cells of human and mouse origin to canonical pyroptotic (LPS plus ATP), apoptotic (staurosporine), necroptotic (TNF-α plus z-VAD), and PANoptotic (influenza A virus infection) stimuli. When compared to fibroblasts, both mouse and human innate immune cells, macrophages, expressed higher levels of cell death proteins and activated cell death effectors more robustly, including caspase-1, gasdermins, caspase-8, and RIPKs, in response to specific stimuli. Our findings highlight the importance of considering the cell type when examining the mechanisms regulating inflammation and cell death. Improved understanding of the cell types that contain the machinery to execute different forms of cell death and their link to innate immune responses is critical to identify new strategies to target these pathways in specific cellular populations for the treatment of infectious diseases, inflammatory disorders, and cancer.

Regulated cell death pathways and their roles in homeostasis, infection, inflammation, and tumorigenesis.

Pyroptosis, apoptosis, necroptosis, and ferroptosis, which are the most well-studied regulated cell death (RCD) pathways, contribute to the clearance of infected or potentially neoplastic cells, highlighting their importance in homeostasis, host defense against pathogens, cancer, and a wide range of other pathologies. Although these four RCD pathways employ distinct molecular and cellular processes, emerging genetic and biochemical studies have suggested remarkable flexibility and crosstalk among them. The crosstalk among pyroptosis, apoptosis and necroptosis pathways is more evident in cellular responses to infection, which has led to the conceptualization of PANoptosis. In this review, we provide a brief overview of the molecular mechanisms of pyroptosis, apoptosis, necroptosis, and ferroptosis and their importance in maintaining homeostasis. We discuss the intricate crosstalk among these RCD pathways and the current evidence supporting PANoptosis, focusing on infectious diseases and cancer. Understanding the fundamental processes of various cell death pathways is crucial to inform the development of new therapeutics against many diseases, including infection, sterile inflammation, and cancer.

Immune regulator IRF1 contributes to ZBP1-, AIM2-, RIPK1-, and NLRP12-PANoptosome activation and inflammatory cell death (PANoptosis).

The innate immune system provides the first line of defense against pathogens and cellular insults and is activated by pattern recognition receptors sensing pathogen- or damage-associated molecular patterns. This activation can result in inflammation via cytokine release as well as the induction of lytic regulated cell death (RCD). Innate immune signaling can also induce the expression of interferon regulatory factor 1 (IRF1), an important molecule in regulating downstream inflammation and cell death. While IRF1 has been shown to modulate some RCD pathways, a comprehensive evaluation of its role in inflammatory cell death pathways is lacking. Here, we examined the role of IRF1 in cell death during inflammasome and PANoptosome activation using live cell imaging, Western blotting, and ELISA in primary murine macrophages. IRF1 contributed to the induction of ZBP1- (Z-DNA binding protein 1), AIM2- (absent in melanoma-2), RIPK1- (receptor interacting protein kinase 1), and NLRP12 (NOD-like receptor family, pyrin domain-containing 12)-PANoptosome activation and PANoptosis. Furthermore, IRF1 regulated the cell death under conditions where inflammasomes, along with caspase-8 and RIPK3, act as integral components of PANoptosomes to drive PANoptosis. However, it was dispensable for other inflammasomes that form independent of the PANoptosome to drive pyroptosis. Overall, these findings define IRF1 as an upstream regulator of PANoptosis and suggest that modulating the activation of molecules in the IRF1 pathway could be used as a strategy to treat inflammatory and infectious diseases associated with aberrant inflammatory cell death.

PANoptosome signaling and therapeutic implications in infection: central role for ZBP1 to activate the inflammasome and PANoptosis.

The innate immune response provides the first line of defense against infection and disease. Regulated cell death (RCD) is a key component of innate immune activation, and RCD must be tightly controlled to clear pathogens while preventing excess inflammation. Recent studies have highlighted a central role for the innate immune sensor Z-DNA-binding protein 1 (ZBP1) as an activator of a form of inflammatory RCD called PANoptosis, which is regulated by a multifaceted cell death complex called the PANoptosome. In response to influenza A virus infection, ZBP1 activates the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome, which then acts as an integral component of the ZBP1-PANoptosome to drive inflammatory cell death, PANoptosis. In this context, the NLRP3 inflammasome is critical for caspase-1 activation and proinflammatory cytokine interleukin (IL)-1ß and IL-18 maturation, but dispensable for cell death due to functional redundancies between PANoptosome molecules. Similarly, ZBP1 is also central to the absent in melanoma 2 (AIM2)-PANoptosome; this PANoptosome forms in response to Francisella novicida and herpes simplex virus 1 infection and incorporates the AIM2 inflammasome as an integral component. In this review, we will discuss the critical roles of ZBP1 in mediating innate immune responses through inflammasomes, PANoptosomes, and PANoptosis during infection. An improved understanding of the molecular mechanisms of innate immunity and cell death will be essential for the development of targeted modalities that can improve patient outcomes by mitigating severe disease.

NLRP12-PANoptosome activates PANoptosis and pathology in response to heme and PAMPs.

Cytosolic innate immune sensors are critical for host defense and form complexes, such as inflammasomes and PANoptosomes, that induce inflammatory cell death. The sensor NLRP12 is associated with infectious and inflammatory diseases, but its activating triggers and roles in cell death and inflammation remain unclear. Here, we discovered that NLRP12 drives inflammasome and PANoptosome activation, cell death, and inflammation in response to heme plus PAMPs or TNF. TLR2/4-mediated signaling through IRF1 induced Nlrp12 expression, which led to inflammasome formation to induce maturation of IL-1ß and IL-18. The inflammasome also served as an integral component of a larger NLRP12-PANoptosome that drove inflammatory cell death through caspase-8/RIPK3. Deletion of Nlrp12 protected mice from acute kidney injury and lethality in a hemolytic model. Overall, we identified NLRP12 as an essential cytosolic sensor for heme plus PAMPs-mediated PANoptosis, inflammation, and pathology, suggesting that NLRP12 and molecules in this pathway are potential drug targets for hemolytic and inflammatory diseases.

ADAR1 and ZBP1 in innate immunity, cell death, and disease.

ADAR1 and ZBP1 are the only two mammalian proteins that contain Zα domains, which are thought to bind to nucleic acids in the Z-conformation. These two molecules are crucial in regulating diverse biological processes. While ADAR1-mediated RNA editing supports host survival and development, ZBP1-mediated immune responses provide host defense against infection and disease. Recent studies have expanded our understanding of the functions of ADAR1 and ZBP1 beyond their classical roles and established their fundamental regulation of innate immune responses, including NLRP3 inflammasome activation, inflammation, and cell death. Their roles in these processes have physiological impacts across development, infectious and inflammatory diseases, and cancer. In this review, we discuss the functions of ADAR1 and ZBP1 in regulating innate immune responses in development and disease.

Pancancer transcriptomic profiling identifies key PANoptosis markers as therapeutic targets for oncology.

Resistance to programmed cell death (PCD) is a hallmark of cancer. While some PCD components are prognostic in cancer, the roles of many molecules can be masked by redundancies and crosstalks between PCD pathways, impeding the development of targeted therapeutics. Recent studies characterizing these redundancies have identified PANoptosis, a unique innate immune-mediated inflammatory PCD pathway that integrates components from other PCD pathways. Here, we designed a systematic computational framework to determine the pancancer clinical significance of PANoptosis and identify targetable biomarkers. We found that high expression of PANoptosis genes was detrimental in low grade glioma (LGG) and kidney renal cell carcinoma (KIRC). ZBP1, ADAR, CASP2, CASP3, CASP4, CASP8 and GSDMD expression consistently had negative effects on prognosis in LGG across multiple survival models, while AIM2, CASP3, CASP4 and TNFRSF10 expression had negative effects for KIRC. Conversely, high expression of PANoptosis genes was beneficial in skin cutaneous melanoma (SKCM), with ZBP1, NLRP1, CASP8 and GSDMD expression consistently having positive prognostic effects. As a therapeutic proof-of-concept, we treated melanoma cells with combination therapy that activates ZBP1 and showed that this treatment induced PANoptosis. Overall, through our systematic framework, we identified and validated key innate immune biomarkers from PANoptosis which can be targeted to improve patient outcomes in cancers.

Innate immunity, cytokine storm, and inflammatory cell death in COVID-19.

The innate immune system serves as the first line of defense against invading pathogens; however, dysregulated innate immune responses can induce aberrant inflammation that is detrimental to the host. Therefore, careful innate immune regulation is critical during infections. The coronavirus disease 2019 (COVID-19) pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has resulted in global morbidity and mortality as well as socio-economic stresses. Innate immune sensing of SARS-CoV-2 by multiple host cell pattern recognition receptors leads to the production of various pro-inflammatory cytokines and the induction of inflammatory cell death. These processes can contribute to cytokine storm, tissue damage, and acute respiratory distress syndrome. Here, we discuss the sensing of SARS-CoV-2 to induce innate immune activation and the contribution of this innate immune signaling in the development and severity of COVID-19. In addition, we provide a conceptual framework for innate immunity driving cytokine storm and organ damage in patients with severe COVID-19. A better understanding of the molecular mechanisms regulated by innate immunity is needed for the development of targeted modalities that can improve patient outcomes by mitigating severe disease.

Molecular mechanism of RIPK1 and caspase-8 in homeostatic type I interferon production and regulation.

Type I interferons (IFNs) are essential innate immune proteins that maintain tissue homeostasis through tonic expression and can be upregulated to drive antiviral resistance and inflammation upon stimulation. However, the mechanisms that inhibit aberrant IFN upregulation in homeostasis and the impacts of tonic IFN production on health and disease remain enigmatic. Here, we report that caspase-8 negatively regulates type I IFN production by inhibiting the RIPK1-TBK1 axis during homeostasis across multiple cell types and tissues. When caspase-8 is deleted or inhibited, RIPK1 interacts with TBK1 to drive elevated IFN production, leading to heightened resistance to norovirus infection in macrophages but also early onset lymphadenopathy in mice. Combined deletion of caspase-8 and RIPK1 reduces the type I IFN signaling and lymphadenopathy, highlighting the critical role of RIPK1 in this process. Overall, our study identifies a mechanism to constrain tonic type I IFN during homeostasis which could be targeted for infectious and inflammatory diseases.

Single cell analysis of PANoptosome cell death complexes through an expansion microscopy method.

In response to infection or sterile insults, inflammatory programmed cell death is an essential component of the innate immune response to remove infected or damaged cells. PANoptosis is a unique innate immune inflammatory cell death pathway regulated by multifaceted macromolecular complexes called PANoptosomes, which integrate components from other cell death pathways. Growing evidence shows that PANoptosis can be triggered in many physiological conditions, including viral and bacterial infections, cytokine storms, and cancers. However, PANoptosomes at the single cell level have not yet been fully characterized. Initial investigations have suggested that key pyroptotic, apoptotic, and necroptotic molecules including the inflammasome adaptor protein ASC, apoptotic caspase-8 (CASP8), and necroptotic RIPK3 are conserved components of PANoptosomes. Here, we optimized an immunofluorescence procedure to probe the highly dynamic multiprotein PANoptosome complexes across various innate immune cell death-inducing conditions. We first identified and validated antibodies to stain endogenous mouse ASC, CASP8, and RIPK3, without residual staining in the respective knockout cells. We then assessed the formation of PANoptosomes across innate immune cell death-inducing conditions by monitoring the colocalization of ASC with CASP8 and/or RIPK3. Finally, we established an expansion microscopy procedure using these validated antibodies to image the organization of ASC, CASP8, and RIPK3 within the PANoptosome. This optimized protocol, which can be easily adapted to study other multiprotein complexes and other cell death triggers, provides confirmation of PANoptosome assembly in individual cells and forms the foundation for a deeper molecular understanding of the PANoptosome complex and PANoptosis to facilitate therapeutic targeting.

ZBP1-dependent inflammatory cell death, PANoptosis, and cytokine storm disrupt IFN therapeutic efficacy during coronavirus infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease 2019 (COVID-19), continues to cause substantial morbidity and mortality in the ongoing global pandemic. Understanding the fundamental mechanisms that govern innate immune and inflammatory responses during SARS-CoV-2 infection is critical for developing effective therapeutic strategies. Whereas interferon (IFN)-based therapies are generally expected to be beneficial during viral infection, clinical trials in COVID-19 have shown limited efficacy and potential detrimental effects of IFN treatment during SARS-CoV-2 infection. However, the underlying mechanisms responsible for this failure remain unknown. In this study, we found that IFN induced Z-DNA-binding protein 1 (ZBP1)-mediated inflammatory cell death, PANoptosis, in human and murine macrophages and in the lungs of mice infected with ß-coronaviruses, including SARS-CoV-2 and mouse hepatitis virus (MHV). In patients with COVID-19, expression of the innate immune sensor ZBP1 was increased in immune cells from those who succumbed to the disease compared with those who recovered, further suggesting a link between ZBP1 and pathology. In mice, IFN-ß treatment after ß-coronavirus infection increased lethality, and genetic deletion of Zbp1 or its Zα domain suppressed cell death and protected the mice from IFN-mediated lethality during ß-coronavirus infection. Overall, our results identify that ZBP1 induced during coronavirus infection limits the efficacy of IFN therapy by driving inflammatory cell death and lethality. Therefore, inhibiting ZBP1 activity may improve the efficacy of IFN therapy, paving the way for the development of new and critically needed therapeutics for COVID-19 as well as other infections and inflammatory conditions where IFN-mediated cell death and pathology occur.

NLRC4 Deficiency Leads to Enhanced Phosphorylation of MLKL and Necroptosis.

Hosts rely on the innate immune system to clear pathogens in response to infection. Pathogen-associated molecular patterns bind to innate immune receptors and engage activation of downstream signaling to initiate a host immune response to fight infection. A key component of this innate response is programmed cell death. Recent work has highlighted significant cross-talk and functional redundancy between cell death pathways, leading to the discovery of PANoptosis, an inflammatory programmed cell death pathway dependent on PANoptosomes, which are innate immune danger-sensing complexes that activate inflammatory cell death and contain caspases with or without inflammasome components and receptor interacting protein homotypic interaction motif-containing proteins. Although PANoptosis has been characterized in response to a growing number of pathogens, inflammatory diseases, and cancer, its role and the functional consequences of PANoptotic component modulation during NLR family CARD domain-containing protein 4 (NLRC4) activation by Pseudomonas aeruginosa infection remain unknown. In this study, we show that P. aeruginosa can induce PANoptosis in mouse bone marrow-derived macrophages (BMDMs). Only the combined deletion of caspase-1, -11, -8, and RIPK3 protected mouse BMDMs from cell death. Moreover, we showed that PANoptotic components act in a compensatory manner; in the absence of NAIP5 and NLRC4 during P. aeruginosa challenge, activation of caspase-1, -3, -7, and -8 was reduced, whereas alternative cell death molecules such as RIPK1 and MLKL were activated in mouse BMDMs. Taken together, these data highlight the extensive cross-talk between cell death signaling molecules and showcase the plasticity of the system.

The Transcription Factor IRF9 Promotes Colorectal Cancer via Modulating the IL-6/STAT3 Signaling Axis.

Colorectal cancer (CRC) is a leading cause of cancer-related deaths worldwide, and innate immune responses and inflammation are known to affect the course of disease. Interferon (IFN) signaling in particular is critical for modulating inflammation-associated diseases including CRC. While the effects of IFN signaling in CRC have been studied, results have been conflicting. Furthermore, individual molecules in the IFN pathway that could be therapeutically targeted have distinct functions, with many of their diverse roles in CRC remaining unclear. Here, we found that IRF9 had an oncogenic effect in CRC; loss of IRF9 reduced tumorigenesis in both azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced and spontaneous CRC models. IRF9 also reduced DSS-induced colitis and inflammation in the colon, but it had no effect on the NF-κB and MAPK signaling activation. Instead, IRF9 enhanced the transcription and production of the inflammatory cytokine IL-6. By promoting IL-6 release, IRF9 drove the activation of pro-oncogenic STAT3 signaling in the colon. Overall, our study found that IRF9 promoted the development of CRC via modulation of the IL-6/STAT3 signaling axis, identifying multiple potential targets and suggesting new therapeutic strategies for the treatment of CRC.

Caspase-6 promotes activation of the caspase-11-NLRP3 inflammasome during gram-negative bacterial infections.

The innate immune system acts as the first line of defense against infection. One key component of the innate immune response to gram-negative bacterial infections is inflammasome activation. The caspase-11 (CASP11)-nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome is activated by cytosolic lipopolysaccharide, a gram-negative bacterial cell wall component, to trigger pyroptosis and host defense during infection. Although several cellular signaling pathways have been shown to regulate CASP11-NLRP3 inflammasome activation in response to lipopolysaccharide, the upstream molecules regulating CASP11 activation during infection with live pathogens remain unclear. Here, we report that the understudied caspase-6 (CASP6) contributes to the activation of the CASP11-NLRP3 inflammasome in response to infections with gram-negative bacteria. Using in vitro cellular systems with bone marrow-derived macrophages and 293T cells, we found that CASP6 can directly process CASP11 by cleaving at Asp59 and Asp285, the CASP11 auto-cleavage sites, which could contribute to the activation of CASP11 during gram-negative bacterial infection. Thus, the loss of CASP6 led to impaired CASP11-NLRP3 inflammasome activation in response to gram-negative bacteria. These results demonstrate that CASP6 potentiates activation of the CASP11-NLRP3 inflammasome to produce inflammatory cytokines during gram-negative bacterial infections.

Cutting Edge: Caspase-8 Is a Linchpin in Caspase-3 and Gasdermin D Activation to Control Cell Death, Cytokine Release, and Host Defense during Influenza A Virus Infection.

Programmed cell death (PCD) is essential for the innate immune response, which serves as the first line of defense against pathogens. Caspases regulate PCD, immune responses, and homeostasis. Caspase-8 specifically plays multifaceted roles in PCD pathways including pyroptosis, apoptosis, and necroptosis. However, because caspase-8-deficient mice are embryonically lethal, little is known about how caspase-8 coordinates different PCD pathways under physiological conditions. Here, we report an anti-inflammatory role of caspase-8 during influenza A virus infection. We generated viable mice carrying an uncleavable version of caspase-8 (Casp8 DA/DA). We demonstrated that caspase-8 autoprocessing was responsible for activating caspase-3, thereby suppressing gasdermin D-mediated pyroptosis and inflammatory cytokine release. We also found that apoptotic and pyroptotic pathways were activated at the same time during influenza A virus infection, which enabled the cell-intrinsic anti-inflammatory function of the caspase-8-caspase-3 axis. Our findings provide new insight into the immunological consequences of caspase-8-coordinated PCD cross-talk under physiological conditions.