XIAP Restricts TNF- and RIP3-Dependent Cell Death and Inflammasome Activation

Current advances on RIPK2 and its inhibitors in pathological processes: a comprehensive review

Receptor-Interacting Protein Kinase 2 (RIPK2) is a critical component of the signaling pathways downstream of Nucleotide-binding oligomerization domain-like receptor (NOD-like receptor), playing a vital role in the immune response, particularly in the context of cellular transport, adaptive immunity, and tumorigenesis. Recent advances have further clarified the complex roles of RIPK2, offering insights into its structural and functional characteristics. In this review, we provide a comprehensive overview of RIPK2's involvement in signaling, examine the development of RIPK2 inhibitors, and discuss novel strategies for targeting RIPK2 in therapeutic applications. Additionally, we highlight the dynamic interactions between RIPK2 and NOD-like receptors and explore future directions for improving RIPK2-targeted therapies.

Late presentation of X-linked inhibitor of apoptosis (XIAP) deficiency in a young adult

BACKGROUND

X-linked inhibitor of apoptosis (XIAP) deficiency is a rare inborn error of immunity which occurs secondary to mutations in the XIAP/BIRC4 gene. Disease onset usually manifests within the first few years of life, and is associated with a spectrum of clinical features, secondary to immune dysregulation. Males typically present with refractory chronic colitis, hemophagocytic lymphohistiocytosis, and severe and/or recurrent infections. Laboratory analysis may reveal hypogammaglobulinemia and cytopenias. At present, the only curative treatment is allogenic hematopoietic stem cell transplantation.

CASE PRESENTATION

A 24-year-old gentleman, immigrant from the Democratic Republic of Congo, was referred to outpatient immunology for evaluation of an inborn error of immunity given a past medical history significant for refractory fistulizing Crohn's disease, arthritis, liver abscesses, prior disseminated tuberculosis, anemia, and recurrent infections. He had been asymptomatic throughout his childhood and adolescence, with no infections or symptoms of inflammatory disease until the age of 19, when he was diagnosed with Crohn's disease. He was soon after admitted to hospital and was diagnosed with hemophagocytic lymphohistiocytosis. Primary immunodeficiency gene panel testing revealed a nonsense variant XIAP c833C > G p.(Ser278*), which generates a premature stop codon at exon 2 (of total 7 exons). On flow cytometry analysis, XIAP protein expression was significantly reduced, confirming the diagnosis of XIAP deficiency.

CONCLUSION

This is one of the only documented reports of a patient with XIAP deficiency, presenting with symptom-onset in adulthood. This case highlights the need to maintain a high index of suspicion for XIAP deficiency in patients with the appropriate clinical presentation, despite advanced age of presentation.

Genetic Regulation of Cell Death: Insights from Autoinflammatory Diseases

Metazoans have evolved innate antimicrobial defenses that promote cellular survival and proliferation. Countering the inevitable molecular mechanisms by which microbes sabotage these pathways, multicellular organisms rely on an alternative, perhaps more ancient, strategy that is the immune equivalent of suicide bombing: Infection triggers cell death programs that summon localized or even systemic inflammation. The study of human genetics has now unveiled a level of complexity that refutes the naive view that cell death is merely a blunt instrument or an evolutionary afterthought. To the contrary, findings from patients with rare diseases teach us that cell death-induced inflammation is a sophisticated, tightly choreographed process. We herein review the emerging body of evidence describing a group of illnesses-inborn errors of cell death, which define many of the molecular building blocks and regulatory elements controlling cell death-induced inflammation in humans-and provide a possible road map to countering this process across the spectrum of rare and common illnesses.

Human Immune Responses to Epstein-Barr Virus Highlighted by Immunodeficiencies

Inborn errors of immunity (IEIs) represent unique in natura models that uncover key components of immunity in humans, in particular those that predispose to infections. Epstein-Barr virus (EBV) is one of the most common opportunistic infectious agents in humans and is responsible for several diseases, including infectious mononucleosis, nonmalignant and malignant lymphoproliferative disorders, hemophagocytic lymphohistiocytosis, and smooth muscle and epithelial tumors. For most individuals, EBV infection persists for life without pathological consequences. IEIs that do not predispose to EBV infection suggest that innate and humoral responses are not necessary or redundant for the immune response to EBV. IEIs associated with high susceptibility to EBV infection provide unequivocal genetic proof of the central role of CD8+ T cell responses in immunity to EBV. They also highlight the distinct steps and pathways required for, on the one hand, the effector cytotoxic functions of CD8+ T cells and, on the other hand, the expansion and maturation of cytotoxic CD8+ T cells.

Effects of a Western Diet on Colonic Dysbiosis, Bile Acid Dysmetabolism and Intestinal Inflammation in Clinically Healthy Dogs

BACKGROUND

Consumption of a high-fat, high-carbohydrate Western-style diet (WD) associated with obesity and inflammation in humans has not been investigated in dogs.

AIMS

To determine the effects of WD on inflammatory indices, microbiome, and fecal bile acids (BAs) in dogs.

ANIMALS

Ten adult clinically healthy dogs.

METHODS

A dietary trial compared the effects of two home-prepared diets: a high-fiber, low-fat control diet (CD) to a diet containing the macronutrient composition of WD (low-fiber, high fat). Dietary treatments were given sequentially for three feeding periods, each lasting 1 month. Outcome measures included molecular/microbiologic testing of colonic biopsies, histopathology, inflammatory biomarkers, and quantification of fecal BA following each feeding period.

RESULTS

Cell markers of apoptosis (TUNEL-positive cells: CD1, 0.36% ± 0.2%; WD, 0.79% ± 0.5%; CD2, 0.42% ± 0.3%; 95% CI) and inflammation (NF-ĸB area: CD1, 8.09% ± 3.3%; WD, 11.58% ± 3.4%; CD2 7.25% ± 3.8%; 95% CI), as well as serum high-sensitivity C-reactive protein (CD1, 2.0 ± 0.4 ng/mL; WD, 2.76 ± 0.23 ng/mL; CD2, 2.29 ± 0.25 ng/mL; 95% CI), were increased (p < 0.05) in dogs fed WD versus CD. Other perturbations seen with WD ingestion included altered (p < 0.05) colonic mucosal bacteria (bacterial counts: CD1, 301.5 ± 188.5; WD, 769.8 ± 431.9; CD2, 542.1 ± 273.9; 95% CI) and increased (p < 0.05) fecal cholic acid (median and interquartile range/IQR: CD1, 9505 [2384-33 788] peak heights; WD, 34 131 [10 113-175 909] peak heights) and serum myeloperoxidase (CD1, 46.98 ± 16.6 ng/mL; WD, 82.93 ± 33.6 ng/mL; CD2, 63.52 ± 29.5 ng/mL; 95% CI).

CONCLUSIONS AND CLINICAL IMPORTANCE

WD fed to clinically healthy dogs promotes colonic dysbiosis, altered fecal BA, and low-grade inflammation independent of obesity.

[Autoinflammatory diseases associated with IL-18]

Autoinflammatory diseases (AIDs) are conditions characterized by dysfunction of innate immunity, causing systemic inflammation and various clinical symptoms. The field of AIDs has expanded due to improved comprehension of pathophysiological mechanisms and advancements in genomics techniques. A new emerging category of AIDs is characterized by a significant increase in interleukin 18 (IL-18), a pro-inflammatory cytokine synthesized in macrophages and activated by caspase 1 via various inflammasomes. IL-18 plays a role in the regulation of innate and adaptive immunity. IL-18 is involved in various functions, such as the proliferation, survival, and differentiation of immune cells, tissue infiltration of immune cells, polarization of immune responses, and production of other pro-inflammatory cytokines. This review analyzes the literature on IL-18 regarding its functions and its implications in the diagnosis and treatment of AIDs. IL-18-associated AIDs comprise Still's disease and diseases associated with mutations in NLRC4, XIAP, CDC42, and PSTPIP1, as well as IL-18BP deficiencies. With the exception of PSTPIP1-associated diseases, these conditions all carry a risk of macrophagic activation syndrome. Measuring IL-18 levels in serum can aid in the diagnosis, prognosis, and monitoring of these diseases. Therapies targeting IL-18 and its signaling pathways are currently under investigation.

Molecular Docking of Lactoferrin with Apoptosis-Related Proteins Insights into Its Anticancer Mechanism

Human Lactoferrin (hLf), a multifunctional glycoprotein, has been analyzed through molecular docking to evaluate its role in apoptosis regulation and its potential as an anticancer agent. The docking results highlight XIAP (X-linked Inhibitor of Apoptosis Protein) and Caspase-3 as the most reliable targets, where hLf disrupts XIAP's inhibition of Caspase-3 and Caspase-9, potentially restoring apoptotic signaling; hLf also stabilizes Caspase-3, enhancing its activation in intrinsic and extrinsic pathways. Weaker interactions were observed with Fas, Bcl-2, and Akt. hLf's role in Fas signaling is likely due to expression upregulation rather than direct binding. In contrast, its binding to Bcl-2 may disrupt anti-apoptotic function, and its interaction with Akt suggests interference with pro-survival signaling. These findings suggest that hLf may promote apoptosis by enhancing caspase activation and modulating key apoptotic regulators, supporting its potential use in cancer treatment. However, further experimental validation is needed to confirm these interactions and their therapeutic implications.

Identification of Acanthopanax trifoliatus (L.) Merr as a Novel Potential Therapeutic Agent Against COVID-19 and Pharyngitis

Individuals infected with COVID-19 often experience the distressing discomfort of pharyngitis. Thus, it is crucial to develop novel drugs to improve therapeutic options. In this study, we investigated the interaction between bioactive compounds isolated from Acanthopanax trifoliatus (L.) Merr and proteins associated with COVID-19 and pharyngitis through in silico analysis. Several molecules demonstrated high affinities to multiple targets, indicating significant potential for alleviating pharyngitis and other COVID-19-related symptoms. Among them, rutin and isochlorogenic acid C, two major components in Acanthopanax trifoliatus (L.) Merr ethanol extracts, were further experimentally demonstrated to exhibit strong inhibitory effects against SARS-CoV-2 and to possess significant anti-inflammatory activities. Inhibition of over 50% in several key genes was observed, demonstrating the efficacy of in silico methods in identifying high-affinity target binders. Our findings provide a theoretical foundation for the development of Acanthopanax trifoliatus (L.) Merr as a novel multi-target therapeutic agent for both COVID-19 and pharyngitis.

Divergent roles of RIPK3 and MLKL in high-fat diet-induced obesity and MAFLD in mice

Cell death frequently occurs in the pathogenesis of obesity and metabolic dysfunction-associated fatty liver disease (MAFLD). However, the exact contribution of core cell death machinery to disease manifestations remains ill-defined. Here, we show via the direct comparison of mice genetically deficient in the essential necroptotic regulators, receptor-interacting protein kinase-3 (RIPK3) and mixed lineage kinase domain-like (MLKL), as well as mice lacking apoptotic caspase-8 in myeloid cells combined with RIPK3 loss, that RIPK3/caspase-8 signaling regulates macrophage inflammatory responses and drives adipose tissue inflammation and MAFLD upon high-fat diet feeding. In contrast, MLKL, divergent to RIPK3, contributes to both obesity and MAFLD in a manner largely independent of inflammation. We also uncover that MLKL regulates the expression of molecules involved in lipid uptake, transport, and metabolism, and congruent with this, we discover a shift in the hepatic lipidome upon MLKL deletion. Collectively, these findings highlight MLKL as an attractive therapeutic target to combat the growing obesity pandemic and metabolic disease.

Unraveling the role of RIPKs in diabetic kidney disease and its therapeutic perspectives

Nephropathy is the microvascular complication of diabetes mellitus and is the leading cause of chronic kidney disease. This review discusses the implications of receptor-interacting protein kinase (RIPK) family members and their regulation of inflammation and cell death pathways in the initiation and progression of diabetic kidney disease. Hyperglycemia leads to reactive oxygen species (ROS) generation and RIPK1 overexpression, the first regulator of necroptosis. Further, RIPK1 can form complex I to promote nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) pathway activation or complex II to cause programmed cell death in the kidneys. The rise in RIPK1 level upon ROS generation declines the apoptosis regulators' level while the necroptosis regulators' level is boosted. Necroptosis is a programmed or controlled necrosis-type cell death pathway executed by RIPK1, RIPK3, and mixed lineage kinase domain-like (MLKL) proteins, and recent research suggests its importance in diabetic nephropathy. In necroptosis, RIPK1 and RIPK3 interrelate with their RIP homotypic interaction motif (RHIM) domains and cause the recruitment of MLKL. Next, MLKL gets oligomerized, migrate towards the plasma membrane, and causes its rupture. We emphasized different research studies on drugs highlighting the nephroprotective effects via regulating the RIPKs. We hope that the conclusions of this review may provide new strategies for diabetic kidney disease treatment and promising targets for drug development based on necroptosis.

BIRC3 induces the phosphoinositide 3-kinase-Akt pathway activation to promote trastuzumab resistance in human epidermal growth factor receptor 2-positive gastric cancer

BACKGROUND

Trastuzumab-targeted therapy is currently the standard of care for advanced human epidermal growth factor receptor 2 (HER2)-positive gastric cancer. However, the emergence of resistance to trastuzumab poses significant challenges.

AIM

To identify the key genes associated with trastuzumab resistance. These results provide a basis for the development of interventions to address drug resistance and improve patient outcomes.

METHODS

High-throughput sequencing and bioinformatics were used to identify the differentially expressed pivotal gene BIRC3 and delineate its potential function and pathway regulation. Tumor samples were collected from patients with HER2-positive gastric cancer to evaluate the correlation between BIRC3 expression and trastuzumab resistance. We established gastric cancer cell lines with both highly expressed and suppressed levels of BIRC3, followed by comprehensive in vitro and in vivo experiments to confirm the involvement of BIRC3 in trastuzumab resistance and to elucidate its underlying mechanisms.

RESULTS

In patients with HER2-positive gastric cancer, there is a significant correlation between elevated BIRC3 expression in tumor tissues and higher T stage, tumor node metastasis stage, as well as poor overall survival and progression-free survival. BIRC3 is highly expressed in trastuzumab-resistant gastric cancer cell lines, where it inhibits tumor cell apoptosis and enhances trastuzumab resistance by promoting the phosphorylation and activation of the phosphoinositide 3-kinase-Akt (PI3K-AKT) pathway in HER2-positive gastric cancer cells, both in vivo and in vitro.

CONCLUSION

This study revealed a robust association between high BIRC3 expression and an unfavorable prognosis in patients with HER2-positive gastric cancer. Thus, the high expression of BIRC3 stimulated PI3K-AKT phosphorylation and activation, stimulating the proliferation of HER2-positive tumor cells and suppressing apoptosis, ultimately leading to trastuzumab resistance.

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

Interleukin-1-mediated hyperinflammation in XIAP deficiency is associated with defective autophagy

ABSTRACT

Deficiency of X-linked inhibitor of apoptosis protein (XIAP) is a rare genetic condition that can present with recurrent episodes of hemophagocytic lymphohistiocytosis (HLH), though the exact mechanisms leading to this hyperinflammatory disorder are unclear. Understanding its biology is critical to developing targeted therapies for this potentially fatal disease. Here, we report on a novel multiexonic intragenic duplication leading to XIAP deficiency with recurrent HLH that demonstrated complete response to interleukin (IL)-1β blockade. We further demonstrate using both primary patient cells and genetically modified THP-1 monocyte cell lines that, contrary to what has previously been shown in mouse cells, XIAP-deficient human macrophages do not produce excess IL-1β when stimulated under standard conditions. Instead, nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated hyperproduction of IL-1β is observed only when the XIAP-deficient cells are stimulated under autophagy-promoting conditions and this correlates with defective autophagic flux as measured by decreased accumulation of the early autophagy marker LC3-II. This work, therefore, highlights IL-1β blockade as a therapeutic option for patients with XIAP deficiency experiencing recurrent HLH and identifies a critical role for XIAP in promoting autophagy as a means of limiting IL-1β-mediated hyperinflammation during periods of cellular stress.

Implications of neonatal absence of innate immune mediated NFκB/AP1 signaling in the murine liver

BACKGROUND

The developmental immaturity of the innate immune system helps explains the increased risk of infection in the neonatal period. Importantly, innate immune signaling pathways such as p65/NFκB and c-Jun/AP1 are responsible for the prevention of hepatocyte apoptosis in adult animals, yet whether developmental immaturity of these pathways increases the risk of hepatic injury in the neonatal period is unknown.

METHODS

Using a murine model of endotoxemia (LPS 5 mg/kg IP x 1) in neonatal (P3) and adult mice, we evaluated histologic evidence of hepatic injury and apoptosis, presence of p65/NFκB and c-Jun/AP1 activation and associated transcriptional regulation of apoptotic genes.

RESULTS

We demonstrate that in contrast to adults, endotoxemic neonatal (P3) mice exhibit a significant increase in hepatic apoptosis. This is associated with absent hepatic p65/NFκB signaling and impaired expression of anti-apoptotic target genes. Hepatic c-Jun/AP1 activity was attenuated in endotoxemic P3 mice, with resulting upregulation of pro-apoptotic factors.

CONCLUSIONS

These results demonstrate that developmental absence of innate immune p65/NFκB and c-Jun/AP1 signaling, and target gene expression is associated with apoptotic injury in neonatal mice. More work is needed to determine if this contributes to long-term hepatic dysfunction, and whether immunomodulatory approaches can prevent this injury.

IMPACT

Various aspects of developmental immaturity of the innate immune system may help explain the increased risk of infection in the neonatal period. In adult models of inflammation and infection, innate immune signaling pathways such as p65/NFκB and c-Jun/AP1 are responsible for a protective, pro-inflammatory transcriptome and regulation of apoptosis. We demonstrate that in contrast to adults, endotoxemic neonatal (P3) mice exhibit a significant increase in hepatic apoptosis associated with absent hepatic p65/NFκB signaling and c-Jun/AP1 activity. We believe that these results may explain in part hepatic dysfunction with neonatal sepsis, and that there may be unrecognized developmental and long-term hepatic implications of early life exposure to systemic inflammatory stress.

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.

Sterigmatocystin induces autophagic and apoptotic cell death of liver cancer cells via downregulation of XIAP

XIAP, or the X-linked Inhibitor of Apoptosis Protein, is the most extensively studied member within the IAP gene family. It possesses the capability to impede apoptosis through direct inhibition of caspase activity. Various kinds of cancers overexpress XIAP to enable cancer cells to avoid apoptosis. Consequently, the inhibition of XIAP holds significant clinical implications for the development of anti-tumor medications and the treatment of cancer. In this study, sterigmatocystin, a natural compound obtained from the genus asperigillus, was demonstrated to be able to induce apoptotic and autophagic cell death in liver cancer cells. Mechanistically, sterigmatocystin induces apoptosis by downregulation of XIAP expression. Additionally, sterigmatocystin treatment induces cell cycle arrest, blocks cell proliferation, and slows down colony formation in liver cancer cells. Importantly, sterigmatocystin exhibits a remarkable therapeutic effect in a nude mice model. Our findings revealed a novel mechanism through which sterigmatocystin induces apoptotic and autophagic cell death of liver cancer cells by suppressing XIAP expression, this offers a promising therapeutic approach for treating liver cancer patients.

Oncogenic KEAP1 mutations activate TRAF2-NFκB signaling to prevent apoptosis in lung cancer cells

The Kelch-like ECH-associated protein 1 (KEAP1) - Nuclear factor erythroid 2 -related factor 2 (NRF2) pathway is the major transcriptional stress response system in cells against oxidative and electrophilic stress. NRF2 is frequently constitutively active in many cancers, rendering the cells resistant to chemo- and radiotherapy. Loss-of-function (LOF) mutations in the repressor protein KEAP1 are common in non-small cell lung cancer, particularly adenocarcinoma. While the mutations can occur throughout the gene, they are enriched in certain areas, indicating that these may have unique functional importance. In this study, we show that in the GSEA analysis of TCGA lung adenocarcinoma RNA-seq data, the KEAP1 mutations in R320 and R470 were associated with enhanced Tumor Necrosis Factor alpha (TNFα) - Nuclear Factor kappa subunit B (NFκB) signaling as well as MYC and MTORC1 pathways. To address the functional role of these hotspot mutations, affinity purification and mass spectrometry (AP-MS) analysis of wild type (wt) KEAP1 and its mutation forms, R320Q and R470C were employed to interrogate differences in the protein interactome. We identified TNF receptor associated factor 2 (TRAF2) as a putative protein interaction partner. Both mutant KEAP1 forms showed increased interaction with TRAF2 and other anti-apoptotic proteins, suggesting that apoptosis signalling could be affected by the protein interactions. A549 lung adenocarcinoma cells overexpressing mutant KEAP1 showed high TRAF2-mediated NFκB activity and increased protection against apoptosis, XIAP being one of the key proteins involved in anti-apoptotic signalling. To conclude, KEAP1 R320Q and R470C and its interaction with TRAF2 leads to activation of NFκB pathway, thereby protecting against apoptosis.

Salvage Therapy and Allogeneic Hematopoietic Cell Transplantation for the Severe Cytokine Storm Syndrome of Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) can be considered as a severe cytokine storm syndrome disorder. HLH typically manifests as a life-threatening inflammatory syndrome characterized by fevers, cytopenias, hepatosplenomegaly, and various other accompanying manifestations such as coagulopathy, hepatitis or liver failure, seizures or altered mental status, and even multi-organ failure. Standard up-front treatments do not always bring HLH into remission or maintain adequate response, and salvage or alternative therapies are often needed. For patients with genetic diseases that cause HLH, curative allogeneic hematopoietic cell transplantation is usually offered to prevent future episodes of life-threatening HLH. Here, we will discuss the options and approaches for salvage therapy and hematopoietic cell transplantation for patients with HLH.

Autoinflammatory Contributors to Cytokine Storm

Cytokine Storm is a complex and heterogeneous state of life-threatening systemic inflammation and immunopathology. Autoinflammation is a mechanistic category of immune dysregulation wherein immunopathology originates due to poor regulation of innate immunity. The growing family of monogenic Systemic Autoinflammatory Diseases (SAIDs) has been a wellspring for pathogenic insights and proof-of-principle targeted therapeutic interventions. There is surprisingly little overlap between SAID and Cytokine Storm Syndromes, and there is a great deal to be inferred from those SAID that do, and do not, consistently lead to Cytokine Storm. This chapter will summarize how illustrations of the autoinflammatory paradigm have advanced the understanding of human inflammation, including the role of autoinflammation in familial HLH. Next, it will draw from monogenic SAID, both those with strong associations with cytokine storm and those without, to illustrate how the cytokine IL-18 links innate immune dysregulation and cytokine storm.

Murine Models of Familial Cytokine Storm Syndromes

Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disease caused by mutations in effectors and regulators of cytotoxicity in cytotoxic T cells (CTL) and natural killer (NK) cells. The complexity of the immune system means that in vivo models are needed to efficiently study diseases like HLH. Mice with defects in the genes known to cause primary HLH (pHLH) are available. However, these mice only develop the characteristic features of HLH after the induction of an immune response (typically through infection with lymphocytic choriomeningitis virus). Nevertheless, murine models have been invaluable for understanding the mechanisms that lead to HLH. For example, the cytotoxic machinery (e.g., the transport of cytotoxic vesicles and the release of granzymes and perforin after membrane fusion) was first characterized in the mouse. Experiments in murine models of pHLH have emphasized the importance of cytotoxic cells, antigen-presenting cells (APC), and cytokines in hyperinflammatory positive feedback loops (e.g., cytokine storms). This knowledge has facilitated the development of treatments for human HLH, some of which are now being tested in the clinic.

Targeting necroptosis in fibrosis

Necroptosis, a type of programmed cell death that resembles necrosis, is now known to depend on a different molecular mechanism from apoptosis, according to several recent studies. Many efforts have reported the possible influence of necroptosis in human disorders and concluded the crucial role in the pathophysiology of various diseases, including liver diseases, renal injuries, cancers, and others. Fibrosis is the most common end-stage pathological cascade of several chronic inflammatory disorders. In this review, we explain the impact of necroptosis and fibrosis, for which necroptosis has been demonstrated to be a contributing factor. We also go over the inhibitors of necroptosis and how they have been applied to fibrosis models. This review helps to clarify the role of necroptosis in fibrosis and will encourage clinical efforts to target this pathway of programmed cell death.

The pathological mechanisms of circRNAs in mediating intervertebral disc degeneration

Lower back pain (LBP) is a worldwide health problem associated with significant economic and social burden. Intervertebral disc degeneration (IVDD) is a leading cause of LBP. Several studies show that the death of nucleus pulposus cells (NPCs), abnormal metabolism of the extracellular matrix (ECM), and inflammatory response are the key mechanisms behind the pathogenesis of IVDD. Circular RNAs (circRNAs) are key regulators of gene expression and play a significant role in regulating NPCs death, ECM homeostasis, and inflammatory response by acting as microRNAs (miRNAs) sponges in IVDD. However, the regulatory role of circRNAs in mediating IVDD remains unknown. This review comprehensively describes the normal anatomic structure and function of IVD, the pathogenesis of IVDD, the characteristics, synthesis, mechanisms, and function of circRNAs. Moreover, we highlighted the 23 circRNAs that mediate ECM metabolism, 16 circRNAs that mediate NPCs apoptosis, circ_0004354 and circ_0040039 that mediate NPCs pyroptosis, and 5 circRNAs that mediate inflammatory response in IVDD. In addition, this review presents suggestions for future studies, such as the need for further investigation on ferroptosis-related circRNAs in IVDD. This review could provide novel insights into the pathogenesis and treatment of IVDD.

Myeloid OTULIN deficiency couples RIPK3-dependent cell death to Nlrp3 inflammasome activation and IL-1β secretion

Loss-of-function mutations in the deubiquitinase OTULIN result in an inflammatory pathology termed "OTULIN-related autoinflammatory syndrome" (ORAS). Genetic mouse models revealed essential roles for OTULIN in inflammatory and cell death signaling, but the mechanisms by which OTULIN deficiency connects cell death to inflammation remain unclear. Here, we identify OTULIN deficiency as a cellular condition that licenses RIPK3-mediated cell death in murine macrophages, leading to Nlrp3 inflammasome activation and subsequent IL-1β secretion. OTULIN deficiency uncoupled Nlrp3 inflammasome activation from gasdermin D-mediated pyroptosis, instead allowing RIPK3-dependent cell death to act as an Nlrp3 inflammasome activator and mechanism for IL-1β release. Accordingly, elevated serum IL-1β levels in myeloid-specific OTULIN-deficient mice were diminished by deleting either Ripk3 or Nlrp3. These findings identify OTULIN as an inhibitor of RIPK3-mediated IL-1β release in mice.

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.

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.

Comprehensive analysis of necroptosis-related genes in renal ischemia-reperfusion injury

Background

Oxidative stress is the primary cause of ischemia-reperfusion injury (IRI) in kidney transplantation, leading to delayed graft function (DGF) and implications on patient health. Necroptosis is believed to play a role in renal IRI. This research presents a comprehensive analysis of necroptosis-related genes and their functional implications in the context of IRI in renal transplantation.

Methods

The necroptosis-related differentially expressed genes (NR-DEGs) were identified using gene expression data from pre- and post-reperfusion renal biopsies, and consensus clustering analysis was performed to distinguish necroptosis-related clusters. A predictive model for DGF was developed based on the NR-DEGs and patients were divided into high- and low-risk groups. We investigated the differences in functional enrichment and immune infiltration between different clusters and risk groups and further validated them in single-cell RNA-sequencing (scRNA-seq) data. Finally, we verified the expression changes of NR-DEGs in an IRI mouse model.

Results

Five NR-DEGs were identified and were involved in various biological processes. The renal samples were further stratified into two necroptosis-related clusters (C1 and C2) showing different occurrences of DGF. The predictive model had a reliable performance in identifying patients at higher risk of DGF with the area under the curve as 0.798. Additionally, immune infiltration analysis indicated more abundant proinflammatory cells in the high-risk group, which was also found in C2 cluster with more DGF patients. Validation of NR-DEG in scRNA-seq data further supported their involvement in immune cells. Lastly, the mouse model validated the up-regulation of NR-DEGs after IR and indicated the correlations with kidney function markers.

Conclusions

Our research provides valuable insights into the identification and functional characterization of NR-DEGs in the context of renal transplantation and sheds light on their involvement in immune responses and the progression of IRI and DGF.

Activation of the TNF-α-Necroptosis Pathway in Parvalbumin-Expressing Interneurons of the Anterior Cingulate Cortex Contributes to Neuropathic Pain

The hyperexcitability of the anterior cingulate cortex (ACC) has been implicated in the development of chronic pain. As one of the key causes of ACC hyperexcitation, disinhibition of the ACC may be closely related to the dysfunction of inhibitory parvalbumin (PV)-expressing interneurons (PV-INs). However, the molecular mechanism underlying the ACC PV-INs injury remains unclear. The present study demonstrates that spared sciatic nerve injury (SNI) induces an imbalance in the excitation and inhibition (E/I) of the ACC. To test whether tumor necrosis factor-α (TNF-α) upregulation in the ACC after SNI activates necroptosis and participates in PV-INs damage, we performed a differential analysis of transcriptome sequencing using data from neuropathic pain models and found that the expression of genes key to the TNF-α-necroptosis pathway were upregulated. TNF-α immunoreactivity (IR) signals in the ACCs of SNI rats were co-located with p-RIP3- and PV-IR, or p-MLKL- and PV-IR signals. We then systematically detected the expression and cell localization of necroptosis-related proteins, including kinase RIP1, RIP3, MLKL, and their phosphorylated states, in the ACC of SNI rats. Except for RIP1 and MLKL, the levels of these proteins were significantly elevated in the contralateral ACC and mainly expressed in PV-INs. Blocking the ACC TNF-α-necroptosis pathway by microinjecting TNF-α neutralizing antibody or using an siRNA knockdown to block expression of MLKL in the ACC alleviated SNI-induced pain hypersensitivity and inhibited the upregulation of TNF-α and p-MLKL. Targeting TNF-α-triggered necroptosis within ACC PV-INs may help to correct PV-INs injury and E/I imbalance in the ACC in neuropathic pain.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

XIAP deletion sensitizes mice to TNF-induced and RIP1-mediated death

XIAP is a caspase-inhibitory protein that blocks several cell death pathways, and mediates proper activation of inflammatory NOD2-RIP2 signaling. XIAP deficiency in patients with inflammatory diseases such as Crohn's disease, or those needing allogeneic hematopoietic cell transplantation, is associated with a worse prognosis. In this study, we show that XIAP absence sensitizes cells and mice to LPS- and TNF-mediated cell death without affecting LPS- or TNF-induced NF-κB and MAPK signaling. In XIAP deficient mice, RIP1 inhibition effectively blocks TNF-stimulated cell death, hypothermia, lethality, cytokine/chemokine release, intestinal tissue damage and granulocyte migration. By contrast, inhibition of the related kinase RIP2 does not affect TNF-stimulated events, suggesting a lack of involvement for the RIP2-NOD2 signaling pathway. Overall, our data indicate that in XIAP's absence RIP1 is a critical component of TNF-mediated inflammation, suggesting that RIP1 inhibition could be an attractive option for patients with XIAP deficiency.

Caspase-8-driven apoptotic and pyroptotic crosstalk causes cell death and IL-1β release in X-linked inhibitor of apoptosis (XIAP) deficiency

Genetic lesions in X-linked inhibitor of apoptosis (XIAP) pre-dispose humans to cell death-associated inflammatory diseases, although the underlying mechanisms remain unclear. Here, we report that two patients with XIAP deficiency-associated inflammatory bowel disease display increased inflammatory IL-1β maturation as well as cell death-associated caspase-8 and Gasdermin D (GSDMD) processing in diseased tissue, which is reduced upon patient treatment. Loss of XIAP leads to caspase-8-driven cell death and bioactive IL-1β release that is only abrogated by combined deletion of the apoptotic and pyroptotic cell death machinery. Namely, extrinsic apoptotic caspase-8 promotes pyroptotic GSDMD processing that kills macrophages lacking both inflammasome and apoptosis signalling components (caspase-1, -3, -7, -11 and BID), while caspase-8 can still cause cell death in the absence of both GSDMD and GSDME when caspase-3 and caspase-7 are present. Neither caspase-3 and caspase-7-mediated activation of the pannexin-1 channel, or GSDMD loss, prevented NLRP3 inflammasome assembly and consequent caspase-1 and IL-1β maturation downstream of XIAP inhibition and caspase-8 activation, even though the pannexin-1 channel was required for NLRP3 triggering upon mitochondrial apoptosis. These findings uncouple the mechanisms of cell death and NLRP3 activation resulting from extrinsic and intrinsic apoptosis signalling, reveal how XIAP loss can co-opt dual cell death programs, and uncover strategies for targeting the cell death and inflammatory pathways that result from XIAP deficiency.

Lentiviral Gene Transfer Corrects Immune Abnormalities in XIAP Deficiency

BACKGROUND

X-linked inhibitor of apoptosis protein (XIAP) deficiency is a severe immunodeficiency with clinical features including hemophagocytic lymphohistiocytosis (HLH) and inflammatory bowel disease (IBD) due to defective NOD2 responses. Management includes immunomodulatory therapies and hematopoietic stem cell transplant (HSCT). However, this cohort is particularly susceptible to the chemotherapeutic regimens and acutely affected by graft-vs-host disease (GvHD), driving poor long-term survival in transplanted patients. Autologous HSC gene therapy could offer an alternative treatment option and would abrogate the risks of alloreactivity.

METHODS

Hematopoietic progenitor (Lin-ve) cells from XIAPy/- mice were transduced with a lentiviral vector encoding human XIAP cDNA before transplantation into irradiated XIAP y/- recipients. After 12 weeks animals were challenged with the dectin-1 ligand curdlan and recovery of innate immune function was evaluated though analysis of inflammatory cytokines, body weight, and splenomegaly. XIAP patient-derived CD14+ monocytes were transduced with the same vector and functional recovery was demonstrated using in vitro L18-MDP/NOD2 assays.

RESULTS

In treated XIAPy/- mice, ~40% engraftment of gene-corrected Lin-ve cells led to significant recovery of weight loss, splenomegaly, and inflammatory cytokine responses to curdlan, comparable to wild-type mice. Serum IL-6, IL-10, MCP-1, and TNF were significantly reduced 2-h post-curdlan administration in non-corrected XIAPy/- mice compared to wild-type and gene-corrected animals. Appropriate reduction of inflammatory responses was observed in gene-corrected mice, whereas non-corrected mice developed an inflammatory profile 9 days post-curdlan challenge. In gene-corrected patient CD14+ monocytes, TNF responses were restored following NOD2 activation with L18-MDP.

CONCLUSION

Gene correction of HSCs recovers XIAP-dependent immune defects and could offer a treatment option for patients with XIAP deficiency.

Dysregulated inflammasome activity in intestinal inflammation - Insights from patients with very early onset IBD

Inflammatory bowel disease (IBD) is a multifactorial disorder triggered by imbalances of the microbiome and immune dysregulations in genetically susceptible individuals. Several mouse and human studies have demonstrated that multimeric inflammasomes are critical regulators of host defense and gut homeostasis by modulating immune responses to pathogen- or damage-associated molecular patterns. In the context of IBD, excessive production of pro-inflammatory Interleukin-1β has been detected in patient-derived intestinal tissues and correlated with the disease severity or failure to respond to anti-tumor necrosis factor therapy. Correspondingly, genome-wide association studies have suggested that single nucleotide polymorphisms in inflammasome components might be associated with risk of IBD development. The relevance of inflammasomes in controlling human intestinal homeostasis has been further exemplified by the discovery of very early onset IBD (VEO-IBD) patients with monogenic defects affecting different molecules in the complex regulatory network of inflammasome activity. This review provides an overview of known causative monogenic entities of VEO-IBD associated with altered inflammasome activity. A better understanding of the molecular mechanisms controlling inflammasomes in monogenic VEO-IBD may open novel therapeutic avenues for rare and common inflammatory diseases.

Death by TNF: a road to inflammation

Tumour necrosis factor (TNF) is a central cytokine in inflammatory reactions, and biologics that neutralize TNF are among the most successful drugs for the treatment of chronic inflammatory and autoimmune pathologies. In recent years, it became clear that TNF drives inflammatory responses not only directly by inducing inflammatory gene expression but also indirectly by inducing cell death, instigating inflammatory immune reactions and disease development. Hence, inhibitors of cell death are being considered as a new therapy for TNF-dependent inflammatory diseases.

Necroptosis: A Pathogenic Negotiator in Human Diseases

Over the past few decades, mechanisms of programmed cell death have attracted the scientific community because they are involved in diverse human diseases. Initially, apoptosis was considered as a crucial mechanistic pathway for programmed cell death; recently, an alternative regulated mode of cell death was identified, mimicking the features of both apoptosis and necrosis. Several lines of evidence have revealed that dysregulation of necroptosis leads to pathological diseases such as cancer, cardiovascular, lung, renal, hepatic, neurodegenerative, and inflammatory diseases. Regulated forms of necrosis are executed by death receptor ligands through the activation of receptor-interacting protein kinase (RIPK)-1/3 and mixed-lineage kinase domain-like (MLKL), resulting in the formation of a necrosome complex. Many papers based on genetic and pharmacological studies have shown that RIPKs and MLKL are the key regulatory effectors during the progression of multiple pathological diseases. This review focused on illuminating the mechanisms underlying necroptosis, the functions of necroptosis-associated proteins, and their influences on disease progression. We also discuss numerous natural and chemical compounds and novel targeted therapies that elicit beneficial roles of necroptotic cell death in malignant cells to bypass apoptosis and drug resistance and to provide suggestions for further research in this field.

Innate Immune Response and Inflammasome Activation During SARS-CoV-2 Infection

The novel coronavirus SARS-CoV-2, responsible for the COVID-19 outbreak, has become a pandemic threatening millions of lives worldwide. Recently, several vaccine candidates and drugs have shown promising effects in preventing or treating COVID-19, but due to the development of mutant strains through rapid viral evolution, urgent investigations are warranted in order to develop preventive measures and further improve current vaccine candidates. Positive-sense-single-stranded RNA viruses comprise many (re)emerging human pathogens that pose a public health problem. Our innate immune system and, in particular, the interferon response form an important first line of defense against these viruses. Flexibility in the genome aids the virus to develop multiple strategies to evade the innate immune response and efficiently promotes their replication and infective capacity. This review will focus on the innate immune response to SARS-CoV-2 infection and the virus' evasion of the innate immune system by escaping recognition or inhibiting the production of an antiviral state. Since interferons have been implicated in inflammatory diseases and immunopathology along with their protective role in infection, antagonizing the immune response may have an ambiguous effect on the clinical outcome of the viral disease. This pathology is characterized by intense, rapid stimulation of the innate immune response that triggers activation of the Nod-like receptor family, pyrin-domain-containing 3 (NLRP3) inflammasome pathway, and release of its products including the pro-inflammatory cytokines IL-6, IL-18, and IL-1β. This predictive view may aid in designing an immune intervention or preventive vaccine for COVID-19 in the near future.

Quercetin ameliorates XIAP deficiency-associated hyperinflammation

XIAP (X-linked inhibitor of apoptosis) deficiency is a rare inborn error of immunity. XIAP deficiency causes hyperinflammatory disease manifestations due to dysregulated TNF (tumor necrosis factor)-receptor signaling and NLRP3 (NOD- [nucleotide-binding oligomerization domain], LRR- [leucine-rich repeat] and pyrin domain-containing protein 3) inflammasome function. Safe and effective long-term treatments are needed and are especially important to help prevent the need for high-risk allogeneic hematopoietic cell transplantation. Here we evaluated inflammasome inhibitors as potential therapeutics with a focus on the natural flavonoid antioxidant quercetin. Bone marrow (BM)-derived macrophages were derived from XIAP-deficient or wild-type (WT) mice. Human monocytes were obtained from control or XIAP-deficient patients. Cells were stimulated with TLR (Toll-like receptor) agonists or TNF-α ± inhibitors or quercetin. For in vivo lipopolysaccharide (LPS) challenge experiments, XIAP-deficient or WT mice were fed mouse chow ± supplemental quercetin (50 mg/kg per day exposure) for 7 days followed by a challenge with 10 ng/kg LPS. IL-1β (interleukin-1β) and IL-18 were measured by ELISA (enzyme-linked immunosorbent assay). In murine studies, quercetin prevented IL-1β secretion from XIAP knockout cells following TLR agonists or TNF-α stimulation (P < .05) and strongly reduced constitutive production of IL-18 by both WT and XIAP-deficient cells (P < .05). At 4 hours after in vivo LPS challenge, blood levels of IL-1β and IL-18 were significantly decreased in mice that had received quercetin-supplemented chow (P < .05). In experiments using human cells, quercetin greatly reduced IL-1β secretion by monocytes following TNF-α stimulation (P < .05). Our data suggest that quercetin may be an effective natural therapeutic for the prevention of XIAP deficiency-associated hyperinflammation. Clinical trials, including careful pharmacokinetic and pharmacodynamic studies to ensure that effective levels of quercetin can be obtained, are warranted.

Immune-mediated inflammatory diseases with chronic excess of serum interleukin-18

Review: Interleukin-18 (IL-18) is a proinflammatory cytokine that promotes various innate immune processes related to infection, inflammation, and autoimmunity. Patients with systemic juvenile idiopathic arthritis and adult-onset Still’s disease exhibit chronic excess of serum IL-18, which is associated with a high incidence of macrophage activation syndrome (MAS), although the mechanisms of IL-18 regulation in such diseases remain largely unknown. Similar elevation of serum IL-18 and susceptibility to MAS/hemophagocytic lymphohistiocytosis (HLH) have been reported in monogenic diseases such as X-linked inhibitor of apoptosis deficiency (i.e., X-linked lymphoproliferative syndrome type 2) and NLRC4-associated autoinflammatory disease. Recent advances in molecular and cellular biology allow the identification of other genetic defects such as defects in CDC42, PSTPIP1, and WDR1 that result in high serum IL-18 levels and hyperinflammation. Among these diseases, chronic excess of serum IL-18 appears to be linked with severe hyperinflammation and/or predisposition to MAS/HLH. In this review, we focus on recent findings in inflammatory diseases associated with and probably attributable to chronic excess of serum IL-18 and describe the clinical and therapeutical relevance of understanding the pathology of this group of diseases.

Macrophages in Renal Injury, Repair, Fibrosis Following Acute Kidney Injury and Targeted Therapy

Acute kidney injury (AKI) is a renal disease with a high incidence and mortality. Currently, there are no targeted therapeutics for preventing and treating AKI. Macrophages, important players in mammalian immune response, are involved in the multiple pathological processes of AKI. They are dynamically activated and exhibit a diverse spectrum of functional phenotypes in the kidney after AKI. Targeting the mechanisms of macrophage activation significantly improves the outcomes of AKI in preclinical studies. In this review, we summarize the role of macrophages and the underlying mechanisms of macrophage activation during kidney injury, repair, regeneration, and fibrosis and provide strategies for macrophage-targeted therapies.

Unleashing Cell-Intrinsic Inflammation as a Strategy to Kill AML Blasts

Leukemic blasts are immune cells gone awry. We hypothesized that dysregulation of inflammatory pathways contributes to the maintenance of their leukemic state and can be exploited as cell-intrinsic, self-directed immunotherapy. To this end, we applied genome-wide screens to discover genetic vulnerabilities in acute myeloid leukemia (AML) cells implicated in inflammatory pathways. We identified the immune modulator IRF2BP2 as a selective AML dependency. We validated AML cell dependency on IRF2BP2 with genetic and protein degradation approaches in vitro and genetically in vivo. Chromatin and global gene-expression studies demonstrated that IRF2BP2 represses IL1β/TNFα signaling via NFκB, and IRF2BP2 perturbation results in an acute inflammatory state leading to AML cell death. These findings elucidate a hitherto unexplored AML dependency, reveal cell-intrinsic inflammatory signaling as a mechanism priming leukemic blasts for regulated cell death, and establish IRF2BP2-mediated transcriptional repression as a mechanism for blast survival.

SIGNIFICANCE

This study exploits inflammatory programs inherent to AML blasts to identify genetic vulnerabilities in this disease. In doing so, we determined that AML cells are dependent on the transcriptional repressive activity of IRF2BP2 for their survival, revealing cell-intrinsic inflammation as a mechanism priming leukemic blasts for regulated cell death. See related commentary by Puissant and Medyouf, p. 1617. This article is highlighted in the In This Issue feature, p. 1599.

Biological Effects and Mechanisms of Caspases in Early Brain Injury after Subarachnoid Hemorrhage

Caspases are an evolutionarily conserved family of proteases responsible for mediating and initiating cell death signals. In the past, the dysregulated activation of caspases was reported to play diverse but equally essential roles in neurodegenerative diseases, such as brain injury and neuroinflammatory diseases. A subarachnoid hemorrhage (SAH) is a traumatic event that is either immediately lethal or induces a high risk of stroke and neurological deficits. Currently, the prognosis of SAH after treatment is not ideal. Early brain injury (EBI) is considered one of the main factors contributing to the poor prognosis of SAH. The mechanisms of EBI are complex and associated with oxidative stress, neuroinflammation, blood-brain barrier disruption, and cell death. Based on mounting evidence, caspases are involved in neuronal apoptosis or death, endothelial cell apoptosis, and increased inflammatory cytokine-induced by apoptosis, pyroptosis, and necroptosis in the initial stages after SAH. Caspases can simultaneously mediate multiple death modes and regulate each other. Caspase inhibitors (including XIAP, VX-765, and Z-VAD-FMK) play an essential role in ameliorating EBI after SAH. In this review, we explore the related pathways mediated by caspases and their reciprocal regulation patterns after SAH. Furthermore, we focus on the extensive crosstalk of caspases as a potential area of research on therapeutic strategies for treating EBI after SAH.

Ubiquitylation of RIPK3 beyond-the-RHIM can limit RIPK3 activity and cell death

Pathogen recognition and TNF receptors signal via receptor interacting serine/threonine kinase-3 (RIPK3) to cause cell death, including MLKL-mediated necroptosis and caspase-8-dependent apoptosis. However, the post-translational control of RIPK3 is not fully understood. Using mass-spectrometry, we identified that RIPK3 is ubiquitylated on K469. The expression of mutant RIPK3 K469R demonstrated that RIPK3 ubiquitylation can limit both RIPK3-mediated apoptosis and necroptosis. The enhanced cell death of overexpressed RIPK3 K469R and activated endogenous RIPK3 correlated with an overall increase in RIPK3 ubiquitylation. Ripk3^K469R/K469R mice challenged with Salmonella displayed enhanced bacterial loads and reduced serum IFNγ. However, Ripk3^K469R/K469R macrophages and dermal fibroblasts were not sensitized to RIPK3-mediated apoptotic or necroptotic signaling suggesting that, in these cells, there is functional redundancy with alternate RIPK3 ubiquitin-modified sites. Consistent with this idea, the mutation of other ubiquitylated RIPK3 residues also increased RIPK3 hyper-ubiquitylation and cell death. Therefore, the targeted ubiquitylation of RIPK3 may act as either a brake or accelerator of RIPK3-dependent killing.

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RIPK3 can be ubiquitylated on K469 to limit RIPK3-induced necroptosis and apoptosis

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Ripk3^K469R/K469R mice are more susceptible to Salmonella infection

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Several ubiquitylated or surface exposed lysines can limit RIPK3-induced cell death

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Hyper-ubiquitylated RIPK3 correlates with RIPK3 signaling and cell death

Neuroimmune Mechanisms Underlying Neuropathic Pain: The Potential Role of TNF-α-Necroptosis Pathway

The neuroimmune mechanism underlying neuropathic pain has been extensively studied. Tumor necrosis factor-alpha (TNF-α), a key pro-inflammatory cytokine that drives cytokine storm and stimulates a cascade of other cytokines in pain-related pathways, induces and modulates neuropathic pain by facilitating peripheral (primary afferents) and central (spinal cord) sensitization. Functionally, TNF-α controls the balance between cell survival and death by inducing an inflammatory response and two programmed cell death mechanisms (apoptosis and necroptosis). Necroptosis, a novel form of programmed cell death, is receiving increasing attraction and may trigger neuroinflammation to promote neuropathic pain. Chronic pain is often accompanied by adverse pain-associated emotional reactions and cognitive disorders. Overproduction of TNF-α in supraspinal structures such as the anterior cingulate cortex (ACC) and hippocampus plays an important role in pain-associated emotional disorders and memory deficits and also participates in the modulation of pain transduction. At present, studies reporting on the role of the TNF-α–necroptosis pathway in pain-related disorders are lacking. This review indicates the important research prospects of this pathway in pain modulation based on its role in anxiety, depression and memory deficits associated with other neurodegenerative diseases. In addition, we have summarized studies related to the underlying mechanisms of neuropathic pain mediated by TNF-α and discussed the role of the TNF-α–necroptosis pathway in detail, which may represent an avenue for future therapeutic intervention.

Cell Death-Related Ubiquitin Modifications in Inflammatory Syndromes: From Mice to Men

Aberrant cell death can cause inflammation and inflammation-related diseases. While the link between cell death and inflammation has been widely established in mouse models, evidence supporting a role for cell death in the onset of inflammatory and autoimmune diseases in patients is still missing. In this review, we discuss how the lessons learnt from mouse models can help shed new light on the initiating or contributing events leading to immune-mediated disorders. In addition, we discuss how multiomic approaches can provide new insight on the soluble factors released by dying cells that might contribute to the development of such diseases.

Programmed Cell Death in Sepsis Associated Acute Kidney Injury

Sepsis-associated acute kidney injury (SA-AKI) is common in patients with severe sepsis, and has a high incidence rate and high mortality rate in ICU patients. Most patients progress to AKI before drug treatment is initiated. Early studies suggest that the main mechanism of SA-AKI is that sepsis leads to vasodilation, hypotension and shock, resulting in insufficient renal blood perfusion, finally leading to renal tubular cell ischemia and necrosis. Research results in recent years have shown that programmed cell death such as apoptosis, necroptosis, pyroptosis and autophagy play important roles. In the early stage of sepsis-related AKI, autophagy bodies form and inhibit various types of programmed cell death. With the progress of disease, programmed cell death begins. Apoptosis promoter represents caspase-8-induced apoptosis and apoptosis effector represents caspase-3-induced apoptosis, however, caspase-11 and caspase-1 regulate gasdermin D-mediated pyroptosis. Caspase-8 and receptor interacting kinase 1 bodies mediate necroptosis. This review focuses on the pathophysiological mechanisms of various programmed cell death in sepsis-related AKI.

Receptor-Interacting Protein Kinase 3 Inhibition Relieves Mechanical Allodynia and Suppresses NLRP3 Inflammasome and NF-κB in a Rat Model of Spinal Cord Injury

Background

Neuroinflammation is critical in developing and maintaining neuropathic pain after spinal cord injury (SCI). The receptor-interacting protein kinase 3 (RIPK3) has been shown to promote inflammatory response by exerting its non-necroptotic functions. In this study, we explored the involvement of RIPK3 in neuropathic pain after SCI.

Methods

Thoracic (T10) SCI rat model was conducted, and the mechanical threshold in rats was measured. The expressions of RIPK3, nod-like receptor family pyrin domain-containing protein 3 (NLRP3), caspase-1, and nuclear factor-κB (NF-κB) were measured with western blotting analysis or quantitative real-time polymerase chain reaction (qRT-PCR). Double immunofluorescence staining was used to explore the colabeled NLRP3 with NeuN, glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (IBA1). In addition, enzyme-linked immunosorbent assay (ELISA) was applied to analyze the levels of proinflammatory factors interleukin 1 beta (IL-1β), interleukin 18 (IL-18), and tumor necrosis factor alpha (TNF-α).

Results

The expression of RIPK3 was elevated from postoperative days 7–21, which was consistent with the development of mechanical allodynia. Intrathecal administration of RIPK3 inhibitor GSK872 could alleviate the mechanical allodynia in SCI rats and reduce the expression levels of RIPK3. The activation of NLRP3 inflammasome and NF-κB was attenuated by GSK872 treatment. Furthermore, immunofluorescence suggested that NLRP3 had colocalization with glial cells and neurons in the L4–L6 spinal dorsal horns. In addition, GSK872 treatment reduced the production of inflammatory cytokines.

Conclusion

Our findings indicated that RIPK3 was an important facilitated factor for SCI-induced mechanical allodynia. RIPK3 inhibition might relieve mechanical allodynia by inhibiting NLRP3 inflammasome, NF-κB, and the associated inflammation.

Novel Nexus with NFκB, β-catenin, and RB1 empowers PSMD10/Gankyrin to counteract TNF-α induced apoptosis establishing its oncogenic role

NFκB is a critical rapid-acting transcription factor that protects cancer cells from programmed cell death induced by stress or therapy. While NFκB works in nexus with non-classical oncoproteins such as STAT3 and AKT under a variety of conditions, it is a major antiapoptotic factor activated by TNF-α of the tumor microenvironment. Therefore, it is surprising that PSMD10, an oncoprotein overexpressed in several cancers and a marker of poor prognosis, is reported to inhibit the NFκB pathway. In this study, we explore the role of PSMD10 in cancer cells exposed to TNF-α. We screen several breast and colon cancer cell lines and select SW480, a colon cancer cell line highly resistant to TNF-α, and demonstrate that PSMD10 knockdown sensitizes these cells to TNF-α induced cell death. One of the mechanisms involves transcriptional regulation of β-catenin and RB1, two key colon cancer cell specific anti-apoptotic factors. Surprisingly, we find that PSMD10 is required for optimal phosphorylation and transcriptional activation of NFκB (RELA). Thus, upon PSMD10 knockdown, there is significant downregulation of anti-apoptotic NFκB target genes TNFAIP3 (A20), BIRC2 (cIAP1), BIRC3 (cIAP2), and XIAP. Our study, for the first time, shows that PSMD10 is required for the activation of the pro-survival arm via NFκB transcriptional activation to prevent cancer cells from succumbing to TNF-induced cell death. In addition by transcriptional regulation of two major antiapoptotic players RB1 and β-catenin, PSMD10 proves to be a coveted oncoprotein with a key role in tumorigenesis.

A Review of the Current Impact of Inhibitors of Apoptosis Proteins and Their Repression in Cancer

The Inhibitor of Apoptosis (IAP) family possesses the ability to inhibit programmed cell death through different mechanisms; additionally, some of its members have emerged as important regulators of the immune response. Both direct and indirect activity on caspases or the modulation of survival pathways, such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), have been implicated in mediating its effects. As a result, abnormal expression of inhibitor apoptosis proteins (IAPs) can lead to dysregulated apoptosis promoting the development of different pathologies. In several cancer types IAPs are overexpressed, while their natural antagonist, the second mitochondrial-derived activator of caspases (Smac), appears to be downregulated, potentially contributing to the acquisition of resistance to traditional therapy. Recently developed Smac mimetics counteract IAP activity and show promise in the re-sensitization to apoptosis in cancer cells. Given the modest impact of Smac mimetics when used as a monotherapy, pairing of these compounds with other treatment modalities is increasingly being explored. Modulation of molecules such as tumor necrosis factor-α (TNF-α) present in the tumor microenvironment have been suggested to contribute to putative therapeutic efficacy of IAP inhibition, although published results do not show this consistently underlining the complex interaction between IAPs and cancer.

The Roles of circRNAs in Intervertebral Disc Degeneration: Inflammation, Extracellular Matrix Metabolism, and Apoptosis

Low back pain (LBP) is seriously harmful to human health and produces heavy economic burden. And most scholars hold that intervertebral disc degeneration (IDD) is the primary cause of LBP. With the study of IDD, aberrant expression of gene has become an important pathogenic factor of IDD. Circular RNAs (circRNAs), as a kind of noncoding RNA (ncRNA), participate in the regulation of genetic transcription and translation and further affect the expression of inflammatory cytokine, metabolism of extracellular matrix (ECM), the proliferation and apoptosis of cells, etc. Therefore, maybe it will become a new therapeutic target for IDD. At present, our understanding of the mechanism of circRNAs in IDD is limited. The purpose of this review is to summarize the mechanism and related signaling pathways of circRNAs in IDD reported in the past. Particularly, the roles of circRNAs in inflammation, ECM metabolism, and apoptosis are emphasized.