RIPK1-RIPK3-MLKL-Associated Necroptosis Drives Leishmania infantum Killing in Neutrophils

Inhibition of PGAM5 hyperactivation reduces neuronal apoptosis in PC12 cells and experimental vascular dementia rats

PURPOSE

The incidence of vascular dementia (VaD), as one of the main types of dementia in old age, has been increasing year by year, and exploring its pathogenesis and seeking practical and effective treatment methods are undoubtedly the key to solving this problem. Phosphoglycerate translocase 5 (PGAM5), as a crossroads of multiple signaling pathways, can lead to mitochondrial fission, which in turn triggers the onset and development of necroptosis, and thus PGAM5 may be a novel target for the prevention and treatment of vascular dementia.

METHODS

Animal model of vascular dementia was established by Two-vessel occlusion (2-VO) method, and cellular model of vascular dementia was established by oxygen glucose deprivation (OGD) method. Neuronal damage was detected in vivo and in vitro in different groups using different concentrations of the PGAM5-specific inhibitor LFHP-1c, and necroptosis and mitochondrial dynamics-related factors were determined.

RESULTS

In vivo experiments, 10 mg/kg-1 and 20 mg/kg-1 LFHP-1c improved cognitive deficits, reduced neuronal edema and vacuoles, increased the number of nissl bodies, and it could modulate the expression of Caspase family and Bcl-2 family related proteins and mRNAs and ameliorate neuronal damage. Simultaneously, in vitro experiments, 5 μM, 10 μM and 20 μM LFHP-1c increased the activity and migration number of model cells, reduced the number of apoptotic cells, ameliorated the excessive accumulation of intracellular reactive oxygen species, inhibited the over-activation of caspase-family and Bcl-2-family related proteins and mRNAs, and improved the mitochondrial dynamics of the fission and fusion states. Moreover, in vivo and in vitro experiments have shown that LFHP-1c can also upregulate the expression level of BDNF, inhibit the expression content of TNF-α and ROS, regulate the expression of proteins and mRNAs related to the RIPK1/RIPK3/MLKL pathway and mitochondrial dynamics, and reduce neuronal apoptosis.

CONCLUSIONS

Inhibition of PGAM5 expression level can reduce neuronal damage caused by chronic cerebral ischemia and hypoxia, which mainly prevents necroptosis by targeting the RIPK1/RIPK3/MLKL signaling pathway and regulates the downstream mitochondrial dynamics homeostasis system to prevent excessive mitochondrial fission, thus improving cognition and exerting cerebroprotective effects.

Advances in understanding cisplatin-induced toxicity: Molecular mechanisms and protective strategies

Cisplatin, a widely used chemotherapeutic agent, has proven efficacy against various malignancies. However, its clinical utility is hampered by its dose-limiting toxicities, including nephrotoxicity, ototoxicity, neurotoxicity, and myelosuppression. This review aims to provide a comprehensive overview of cisplatin toxicity, encompassing its underlying mechanisms, risk factors, and emerging therapeutic strategies. The mechanisms of cisplatin toxicity are multifactorial and involve oxidative stress, inflammation, DNA damage, and cellular apoptosis. Various risk factors contribute to the interindividual variability in susceptibility to cisplatin toxicity. The risk of developing cisplatin-induced toxicity could be related to pre-existing conditions, including kidney disease, hearing impairment, neuropathy, impaired liver function, and other comorbidities. Additionally, this review highlights the emerging therapeutic strategies that could be applied to minimize cisplatin-induced toxicities and aid in optimizing cisplatin treatment regimens, improving patient outcomes, and enhancing the overall quality of cancer care.

Mechanisms regulating host cell death during Leishmania infection

Parasites from the Leishmania genus are the causative agents of leishmaniasis and primarily reside within macrophages during mammalian infection. Their ability to establish intracellular infection provides a secure niche for proliferation while evading detection. However, successful multiplication within mammalian cells requires the orchestration of multiple mechanisms that control host cell viability. In contrast, innate immune cells, such as macrophages, can undergo different forms of cell death in response to pathogenic intracellular microbes. Thus, modulation of these different forms of host cell death is crucial for Leishmaniasis development. The regulation of host cell apoptosis, a form of programmed cell death, is crucial for sustaining parasites within viable host cells. Accordingly, several studies have demonstrated evasion of apoptosis induced by dermotropic and viscerotropic Leishmania species. Conversely, the prevention of pyroptosis, an inflammatory form of cell death, ensures the establishment of infection by silencing the release of mediators that could trigger massive proinflammatory responses. This manuscript explores how Leishmania regulates various host cell death pathways and overviews seminal studies on regulating host cell apoptosis by different Leishmania species.

Necrostatin-1 protects corneal epithelial cells by inhibiting the RIPK1/RIPK3/MLKL cascade in a benzalkonium chloride-induced model of necroptosis

PURPOSE

Benzalkonium chloride (BAC) is commonly used as a preservative in ophthalmic medications, despite its potential to induce chemical injury. Extensive research has demonstrated that BAC can lead to adverse effects, including injuries to the ocular surface. Our study aimed to elucidate the underlying mechanism of necroptosis induced by BAC.

METHODS

Human corneal epithelial (HCE) cells and mouse corneas were subjected to chemical injury, and the necrostatin-1 (Nec1) group was compared to the dimethylsulfoxide (DMSO) group. The extent of damage to HCE cells was assessed using CCK-8 and flow cytometry. Hematoxylin and eosin staining, as well as fluorescein sodium staining, were used to detect and characterize corneal injury. The activation of inflammatory cytokines and necroptosis-related proteins and genes was evaluated using Western blotting, immunofluorescence staining, and quantitative RT‒PCR.

RESULTS

In our study, the induction of necroptosis by a hypertonic solution was not observed. However, necroptosis was observed in HCE cells exposed to NaOH and BAC, which activated the receptor-interacting protein kinase 1 (RIPK1) - receptor-interacting protein kinase 3 (RIPK3) - mixed lineage kinase domain-like protein (MLKL) signaling pathway. In mouse corneal tissues, BAC could induce necroptosis and inflammation. The administration of Nec1 mitigated the inflammatory response and ocular surface damage caused by BAC-induced necroptosis in our experimental models. Furthermore, our in vivo experiments revealed that the severity of necroptosis was greater in the 3-day group than in the 7-day group.

CONCLUSIONS

Necroptosis plays a role in the pathological development of ocular surface injury caused by exposure to BAC. Furthermore, our study demonstrated that the administration of Nec1 could mitigate the pathological effects of necroptosis induced by BAC in clinical settings.

Necroptosis and autoimmunity

Autoimmunity is a normal physiological state that requires immunological homeostasis and surveillance, whereas necroptosis is a type of inflammatory cell death. When necroptosis occurs, various immune system cells must perform their appropriate duties to preserve immunological homeostasis, whether the consequence is expanding or limiting the inflammatory response and the pathological condition is cleared or progresses to the autoimmune disease stage. This article discusses necroptosis based on RIP homotypic interaction motif (RHIM) interaction under various physiological and pathological situations, with the RIPK1-RIPK3-MLKL necrosome serving as the regulatory core. In addition, the cell biology of necroptosis involved in autoimmunity and its application in autoimmune diseases were also reviewed.

A diagnostic signature developed based on the necroptosis-related genes and its association with immune infiltration in osteosarcoma

Introduction

Osteosarcoma is a bone-derived malignancy that often leads to lung metastasis and death.

Material and methods

The RNA-seq data of TARGET-osteosarcoma were collected from TARGET database. GSE16088 and GSE12865 datasets of osteosarcoma x from Gene Expression Database (GEO) were donwloaded. ConsensusClusterPlus was used for molecular subtype classification. Univariate Cox and Lasso regression was employed to develop a risk model. To analyze the regulatory effects of model feature genes on the malignant phenotype of osteosarcoma cell lines, qRT-PCR, Transwell and wound healing assays were performed. The abundance of immune cell infiltration was assessed using MCP-Counter, Gene Set Enrichment Analysis (GSEA), and ESTIMATE. The Tumor Immune Dysfunction and Exclusion (TIDE) software was employed to evaluate immunotherapy and response to conventional chemotherapy drugs.

Results

Three clusters (C1, C2 and C3) were classified using 39 necroptosis score-associated genes. In general, C1 and C2 showed better prognosis outcome and lower death rate than C3. Specifically, C2 could benefit more from immunotherapy, while C3 was more sensitive to traditional medicines, and C1 had higher immune cell infiltration. Next, an 8-gene signature and a risk score model were developed, with a low risk score indicating better survival and immune cell infiltration. ROC analysis showed that 1-, 3-, and 5-year overall survival of osteosarcoma could be correctly predicted by the risk score model. Cellular experiments revealed that the model feature gene IFITM3 promoted the osteosarcoma cell migration and invasion. Furthermore, the overall survival of osteosarcoma patients from TARGET and validation datasets can be accurately evaluated using the nomogram model.

Conclusions

Our prognostic model developed using necroptosis genes could facilitate the prognostic prediction for patients suffering from osteosarcoma, offering potential osteosarcoma targets.

EGFR-Activated JAK2/STAT3 Pathway Confers Neuroprotection in Spinal Cord Ischemia-Reperfusion Injury: Evidence from High-Throughput Sequencing and Experimental Models

This study aimed to investigate the molecular mechanisms underlying spinal cord ischemia-reperfusion (SCI/R) injury. Through RNA-Seq high-throughput sequencing and bioinformatics analysis, we found that EGFR was downregulated in the spinal cord of SCI/R mice and may function via mediating the JAK2/STAT3 signaling pathway. In vitro cell experiments indicated that overexpression of EGFR activated the JAK2/STAT3 signaling pathway and reduced neuronal apoptosis levels. In vivo animal experiments further confirmed this conclusion, suggesting that EGFR inhibits SCI/R-induced neuronal apoptosis by activating the JAK2/STAT3 signaling pathway, thereby improving SCI/R-induced spinal cord injury in mice. This study revealed the molecular mechanisms of SCI/R injury and provided new therapeutic strategies for treating neuronal apoptosis.

Comprehensive analysis of necroptotic patterns and associated immune landscapes in individualized treatment of skin cutaneous melanoma

Skin cutaneous melanoma (SKCM) constitutes a malignant cutaneous neoplasm characterized by an exceedingly unfavorable prognosis. Over the past years, necroptosis, a manifestation of inflammatory programmed cell demise, has gained substantial traction in its application. However, a conclusive correlation between the expression of necroptosis-related genes (NRGs) and SKCM patient's prognosis remains elusive. In this endeavor, we have undertaken an integrative analysis of genomic data, aiming to provide an exhaustive evaluation of the intricate interplay between melanoma necroptosis and immune-infiltration nuances within the tumor microenvironment. Through meticulous scrutiny, we have endeavored to discern the prognostic potency harbored by individual necroptosis-associated genes. Our efforts culminated in the establishment of a risk stratification framework, allowing for the appraisal of necroptosis irregularities within each afflicted cutaneous melanoma patient. Notably, those SKCM patients classified within the low-risk cohort exhibited a markedly elevated survival quotient, in stark contrast to their high-risk counterparts (p < 0.001). Remarkably, the low-risk cohort not only displayed a more favorable survival rate but also exhibited an enhanced responsiveness to immunotherapeutic interventions, relative to their high-risk counterparts. The outcomes of this investigation proffer insights into a conceivable mechanistic underpinning linking necroptosis-related attributes to the intricacies of the tumor microenvironment. This prompts a conjecture regarding the plausible association between necroptosis characteristics and the broader tumor microenvironmental milieu. However, it is imperative to emphasize that the pursuit of discerning whether the expression profiles of NRG genes can indeed be regarded as viable therapeutic targets necessitates further comprehensive exploration and scrutiny. In conclusion, our study sheds light on the intricate interrelationship between necroptosis-related factors and the tumor microenvironment, potentially opening avenues for therapeutic interventions. However, the prospect of translating these findings into clinical applications mandates rigorous investigation.

SARS-CoV-2 infection of polarized human airway epithelium induces necroptosis that causes airway epithelial barrier dysfunction

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause the ongoing pandemic of coronavirus disease 2019 (COVID19). One key feature associated with COVID-19 is excessive pro-inflammatory cytokine production that leads to severe acute respiratory distress syndrome. Although the cytokine storm induces inflammatory cell death in the host, which type of programmed cell death mechanism that occurs in various organs and cells remains elusive. Using an in vitro culture model of polarized human airway epithelium (HAE), we observed that necroptosis, but not apoptosis or pyroptosis, plays an essential role in the damage of the epithelial barrier of polarized HAE infected with SARS-CoV-2. Pharmacological inhibitors of necroptosis, necrostatin-2 and necrosulfonamide, efficiently prevented cell death and epithelial barrier dysfunction caused by SARS-CoV-2 infection. Moreover, the silencing of genes that are involved in necroptosis, RIPK1, RIPK3, and MLKL, ameliorated airway epithelial damage of the polarized HAE infected with SARS-CoV-2. This study, for the first time, confirms that SARS-CoV-2 infection triggers necroptosis that disrupts the barrier function of human airway epithelia in vitro.

Leishmania major drives host phagocyte death and cell-to-cell transfer depending on intracellular pathogen proliferation rate

The virulence of intracellular pathogens relies largely on the ability to survive and replicate within phagocytes but also on release and transfer into new host cells. Such cell-to-cell transfer could represent a target for counteracting microbial pathogenesis. However, our understanding of the underlying cellular and molecular processes remains woefully insufficient. Using intravital 2-photon microscopy of caspase-3 activation in the Leishmania major-infected (L. major-infected) live skin, we showed increased apoptosis in cells infected by the parasite. Also, transfer of the parasite to new host cells occurred directly without a detectable extracellular state and was associated with concomitant uptake of cellular material from the original host cell. These in vivo findings were fully recapitulated in infections of isolated human phagocytes. Furthermore, we observed that high pathogen proliferation increased cell death in infected cells, and long-term residency within an infected host cell was only possible for slowly proliferating parasites. Our results therefore suggest that L. major drives its own dissemination to new phagocytes by inducing host cell death in a proliferation-dependent manner.

Viral-induced neuronal necroptosis: Detrimental to brain function and regulation by necroptosis inhibitors

Neuronal necroptosis (programmed necrosis) in the CNS naturally occurs through a caspase-independent way and, especially in neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parknson's disease (PD), Amyotrophic Lateral Sclerosis (ALS) and viral infections. Understanding necroptosis pathways (death receptor-dependent and independent), and its connections with other cell death pathways could lead to new insights into treatment. Receptor-interacting protein kinase (RIPK) mediates necroptosis via mixed-lineage kinase-like (MLKL) proteins. RIPK/MLKL necrosome contains FADD, procaspase-8-cellular FLICE-inhibitory proteins (cFLIPs), RIPK1/RIPK3, and MLKL. The necrotic stimuli cause phosphorylation of MLKL and translocate to the plasma membrane, causing an influx of Ca2+ and Na+ ions and, the immediate opening of mitochondrial permeability transition pore (mPTP) with the release of inflammatory cell damage-associated molecular patterns (DAMPs) like mitochondrial DNA (mtDNA), high-mobility group box1 (HMGB1), and interleukin1 (IL-1). The MLKL translocates to the nucleus to induce transcription of the NLRP3 inflammasome complex elements. MLKL-induced NLRP3 activity causes caspase-1 cleavage and, IL-1 activation which promotes neuroinflammation. RIPK1-dependent transcription increases illness-associated microglial and lysosomal abnormalities to facilitate amyloid plaque (Aβ) aggregation in AD. Recent research has linked neuroinflammation and mitochondrial fission with necroptosis. MicroRNAs (miRs) such as miR512-3p, miR874, miR499, miR155, and miR128a regulate neuronal necroptosis by targeting key components of necroptotic pathways. Necroptosis inhibitors act by inhibiting the membrane translocation of MLKL and RIPK1 activity. This review insights into the RIPK/MLKL necrosome-NLRP3 inflammasome interactions during death receptor-dependent and independent neuronal necroptosis, and clinical intervention by miRs to protect the brain from NDDs.

Identification and Analysis of Necroptosis-Related Genes in COPD by Bioinformatics and Experimental Verification

Chronic obstructive pulmonary disease (COPD) is a heterogeneous and complex progressive inflammatory disease. Necroptosis is a newly identified type of programmed cell death. However, the role of necroptosis in COPD is unclear. This study aimed to identify necroptosis-related genes in COPD and explore the roles of necroptosis and immune infiltration through bioinformatics. The analysis identified 49 differentially expressed necroptosis-related genes that were primarily engaged in inflammatory immune response pathways. The infiltration of CD8+ T cells and M2 macrophages in COPD lung tissue was relatively reduced, whereas that of M0 macrophages was increased. We identified 10 necroptosis-related hub genes significantly associated with infiltrated immune cells. Furthermore, 7 hub genes, CASP8, IL1B, RIPK1, MLKL, XIAP, TNFRSF1A, and CFLAR, were validated using an external dataset and experimental mice. CFLAR was considered to have the best COPD-diagnosing capability. TF and miRNA interactions with common hub genes were identified. Several related potentially therapeutic molecules for COPD were also identified. The present findings suggest that necroptosis occurs in COPD pathogenesis and is correlated with immune cell infiltration, which indicates that necroptosis may participate in the development of COPD by interacting with the immune response.

A Novel Necroptosis-Related Gene Signature in Skin Cutaneous Melanoma Prognosis and Tumor Microenvironment

Background: Necroptosis has been identified recently as a newly recognized programmed cell death that has an impact on tumor progression and prognosis, although the necroptosis-related gene (NRGs) potential prognostic value in skin cutaneous melanoma (SKCM) has not been identified. The aim of this study was to construct a prognostic model of SKCM through NRGs in order to help SKCM patients obtain precise clinical treatment strategies.

Methods: RNA sequencing data collected from The Cancer Genome Atlas (TCGA) were used to identify differentially expressed and prognostic NRGs in SKCM. Depending on 10 NRGs via the univariate Cox regression analysis usage and LASSO algorithm, the prognostic risk model had been built. It was further validated by the Gene Expression Omnibus (GEO) database. The prognostic model performance had been assessed using receiver operating characteristic (ROC) curves. We evaluated the predictive power of the prognostic model for tumor microenvironment (TME) and immunotherapy response.

Results: We constructed a prognostic model based on 10 NRGs (FASLG, TLR3, ZBP1, TNFRSF1B, USP22, PLK1, GATA3, EGFR, TARDBP, and TNFRSF21) and classified patients into two high- and low-risk groups based on risk scores. The risk score was considered a predictive factor in the two risk groups regarding the Cox regression analysis. A predictive nomogram had been built for providing a more beneficial prognostic indicator for the clinic. Functional enrichment analysis showed significant enrichment of immune-related signaling pathways, a higher degree of immune cell infiltration in the low-risk group than in the high-risk group, a negative correlation between risk scores and most immune checkpoint inhibitors (ICIs), anticancer immunity steps, and a more sensitive response to immunotherapy in the low-risk group.

Conclusions: This risk score signature could be applied to assess the prognosis and classify low- and high-risk SKCM patients and help make the immunotherapeutic strategy decision.

A Novel Model Based on Necroptosis-Related Genes for Predicting Prognosis of Patients With Prostate Adenocarcinoma

Background: Necroptosis is a newly recognized form of cell death. Here, we applied bioinformatics tools to identify necroptosis-related genes using a dataset from The Cancer Genome Atlas (TCGA) database, then constructed a model for prognosis of patients with prostate cancer.

Methods: RNA sequence (RNA‐seq) data and clinical information for Prostate adenocarcinoma (PRAD) patients were obtained from the TCGA portal (http://tcga-data.nci.nih.gov/tcga/). We performed comprehensive bioinformatics analyses to identify hub genes as potential prognostic biomarkers in PRAD u followed by establishment and validation of a prognostic model. Next, we assessed the overall prediction performance of the model using receiver operating characteristic (ROC) curves and the area under curve (AUC) of the ROC.

Results: A total of 5 necroptosis-related genes, namely ALOX15, BCL2, IFNA1, PYGL and TLR3, were used to construct a survival prognostic model. The model exhibited excellent performance in the TCGA cohort and validation group and had good prediction accuracy in screening out high-risk prostate cancer patients.

Conclusion: We successfully identified necroptosis-related genes and constructed a prognostic model that can accurately predict 1- 3-and 5-years overall survival (OS) rates of PRAD patients. Our riskscore model has provided novel strategy for the prediction of PRAD patients’ prognosis.

Site-specific ubiquitination of MLKL targets it to endosomes and targets Listeria and Yersinia to the lysosomes

Phosphorylation of the pseudokinase mixed lineage kinase domain-like protein (MLKL) by the protein kinase RIPK3 targets MLKL to the cell membrane, where it triggers necroptotic cell death. We report that conjugation of K63-linked polyubiquitin chains to distinct lysine residues in the N-terminal HeLo domain of phosphorylated MLKL (facilitated by the ubiquitin ligase ITCH that binds MLKL via a WW domain) targets MLKL instead to endosomes. This results in the release of phosphorylated MLKL within extracellular vesicles. It also prompts enhanced endosomal trafficking of intracellular bacteria such as Listeria monocytogenes and Yersinia enterocolitica to the lysosomes, resulting in decreased bacterial yield. Thus, MLKL can be directed by specific covalent modifications to differing subcellular sites, whence it signals either for cell death or for non-deadly defense mechanisms.

Concise synthesis and biological activity evaluation of novel pyrazinyl–aryl urea derivatives against several cancer cell lines, which can especially induce T24 apoptotic and necroptotic cell death

Based on structural modification of regorafenib, 28 pyrazinyl–aryl urea derivatives were synthesized and the in vitro anti-cancer effects were evaluated. Compound 5-23 possessed the strongest inhibitory activity against bladder cancer T24 cell line.

Effect of the combination of astragaloside IV and Panax notoginseng saponins on pyroptosis and necroptosis in rat models of cerebral ischemia-reperfusion

Pyroptosis and necroptosis are closely associated with the mechanism underlying cerebral ischemia-reperfusion (I/R) injury. The combination of astragaloside IV (AST IV) and Panax notoginseng saponins (PNS) has remarkable effects on the alleviation of cerebral I/R damage. However, whether inhibition of pyroptosis and necroptosis is the mechanism underlying the beneficial effects of this drug combination on cerebral I/R injury remains unclear. To explore the effects and mechanisms of drug treatment, middle cerebral artery occlusion was performed to induce I/R injury in rats, which was verified based on neurological deficit score (NDS), infarct volume and H&E staining. Activation of pyroptosis and necroptosis was detected by western blot analysis of associated proteins. The results of the present study demonstrated that treatment with AST IV and PNS, either alone or in combination, significantly reduced the NDS, cerebral infarct volume and cell injury rate in the cerebral cortex of rats. The treatments also improved pathological injury to the cerebral cortex and reduced the levels of proteins associated with pyroptosis and necroptosis. These effects were stronger in the combination drug group compared with groups treated with a single drug alone. The findings of the present study suggested that the combination of AST IV and PNS exhibited stronger neuroprotective effects in I/R injury than either drug alone, and that the underlying mechanism was associated with inhibition of pyroptosis and necroptosis.

Mutagenic Consequences of Sublethal Cell Death Signaling

Many human cancers exhibit defects in key DNA damage response elements that can render tumors insensitive to the cell death-promoting properties of DNA-damaging therapies. Using agents that directly induce apoptosis by targeting apoptotic components, rather than relying on DNA damage to indirectly stimulate apoptosis of cancer cells, may overcome classical blocks exploited by cancer cells to evade apoptotic cell death. However, there is increasing evidence that cells surviving sublethal exposure to classical apoptotic signaling may recover with newly acquired genomic changes which may have oncogenic potential, and so could theoretically spur the development of subsequent cancers in cured patients. Encouragingly, cells surviving sublethal necroptotic signaling did not acquire mutations, suggesting that necroptosis-inducing anti-cancer drugs may be less likely to trigger therapy-related cancers. We are yet to develop effective direct inducers of other cell death pathways, and as such, data regarding the consequences of cells surviving sublethal stimulation of those pathways are still emerging. This review details the currently known mutagenic consequences of cells surviving different cell death signaling pathways, with implications for potential oncogenic transformation. Understanding the mechanisms of mutagenesis associated (or not) with various cell death pathways will guide us in the development of future therapeutics to minimize therapy-related side effects associated with DNA damage.

TNF-α Triggers RIP1/FADD/Caspase-8-Mediated Apoptosis of Astrocytes and RIP3/MLKL-Mediated Necroptosis of Neurons Induced by Angiostrongylus cantonensis Infection

Angiostrongylus cantonensis (AC) can cause severe eosinophilic meningitis or encephalitis in non-permissive hosts accompanied by apoptosis and necroptosis of brain cells. However, the explicit underlying molecular basis of apoptosis and necroptosis upon AC infection has not yet been elucidated. To determine the specific pathways of apoptosis and necroptosis upon AC infection, gene set enrichment analysis (GSEA) and protein-protein interaction (PPI) analysis for gene expression microarray (accession number: GSE159486) of mouse brain infected by AC revealed that TNF-α likely played a central role in the apoptosis and necroptosis in the context of AC infection, which was further confirmed via an in vivo rescue assay after treating with TNF-α inhibitor. The signalling axes involved in apoptosis and necroptosis were investigated via immunoprecipitation and immunoblotting. Immunofluorescence was used to identify the specific cells that underwent apoptosis or necroptosis. The results showed that TNF-α induced apoptosis of astrocytes through the RIP1/FADD/Caspase-8 axis and induced necroptosis of neurons by the RIP3/MLKL signalling pathway. In addition, in vitro assay revealed that TNF-α secretion by microglia increased upon LSA stimulation and caused necroptosis of neurons. The present study provided the first evidence that TNF-α was secreted by microglia stimulated by AC infection, which caused cell death via parallel pathways of astrocyte apoptosis (mediated by the RIP1/FADD/caspase-8 axis) and neuron necroptosis (driven by the RIP3/MLKL complex). Our research comprehensively elucidated the mechanism of cell death after AC infection and provided new insight into targeting TNF-α signalling as a therapeutic strategy for CNS injury.

Role of apoptosis repressor with caspase recruitment domain (ARC) in cell death and cardiovascular disease

Apoptosis repressor with caspase recruitment domain (ARC) is a highly effective and multifunctional inhibitor of apoptosis that is mainly expressed in postmitotic cells such as cardiomyocytes and skeletal muscle cells. ARC contains a C-terminal region rich in proline and glutamic acid residues and an N-terminal caspase recruitment domain (CARD). The CARD is originally described as a protein-binding motif that interacts with caspase through a CARD-CARD interaction. Initially, the inhibitory effect of ARC was only found in apoptosis, however, it was later found that ARC also played a regulatory role in other types of cell death. As a powerful cardioprotective factor, ARC can protect the heart by inhibiting the death of cardiomyocytes in various ways. ARC can reduce the cardiomyocyte apoptotic response to various stresses and injuries, including extrinsic apoptosis induced by death receptor ligands, cellular Ca2+ homeostasis and the dysregulation of endoplasmic reticulum (ER) stress, oxidative stress and hypoxia. In addition, changes in ARC transcription and translation levels in the heart can cause a series of physiological and pathological changes, and ARC can also perform corresponding functions through interactions with other molecules. Although there has been much research on ARC, the functional redundancy among proteins shows that ARC still has much research value. This review summarizes the molecular characteristics of ARC, its roles in the various death modes in cardiomyocytes and the roles of ARC in cardiac pathophysiology. This article also describes the potential therapeutic effect and research prospects of ARC.

A Putative Serine Protease is Required to Initiate the RIPK3-MLKL-Mediated Necroptotic Death Pathway in Neutrophils

Adhesion receptors, such as CD44, have been shown to activate receptor interacting protein kinase-3 (RIPK3)—mixed lineage kinase-like (MLKL) signaling, leading to a non-apoptotic cell death in human granulocyte/macrophage colony-stimulating factor (GM-CSF) – primed neutrophils. The signaling events of this necroptotic pathway, however, remain to be investigated. In the present study, we report the design, synthesis, and characterization of a series of novel serine protease inhibitors. Two of these inhibitors, compounds 1 and 3, were able to block CD44-triggered necroptosis in GM-CSF-primed neutrophils. Both inhibitors prevented the activation of MLKL, p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3’—kinase (PI3K), hence blocking the increased levels of reactive oxygen species (ROS) required for cell death. Although compounds one and three partially inhibited isolated human neutrophil elastase (HNE) activity, we obtained no pharmacological evidence that HNE is involved in the initiation of this death pathway within a cellular context. Interestingly, neither serine protease inhibitor had any effect on FAS receptor-mediated apoptosis. Taken together, these results suggest that a serine protease is involved in non-apoptotic CD44-triggered RIPK3-MLKL-dependent neutrophil cell death, but not FAS receptor-mediated caspase-dependent apoptosis. Thus, a pharmacological block on serine proteases might be beneficial for preventing exacerbation of disease in neutrophilic inflammatory responses.

The diverse roles of RIP kinases in host-pathogen interactions

Receptor Interacting Protein Kinases (RIPKs) are cellular signaling molecules that are critical for homeostatic signaling in both communicable and non-communicable disease processes. In particular, RIPK1, RIPK2, RIPK3 and RIPK7 have emerged as key mediators of intracellular signal transduction including inflammation, autophagy and programmed cell death, and are thus essential for the early control of many diverse pathogenic organisms. In this review, we discuss the role of each RIPK in host responses to bacterial and viral pathogens, with a focus on studies that have used pathogen infection models rather than artificial stimulation with purified pathogen associated molecular patterns. We also discuss the intricate mechanisms of host evasion by pathogens that specifically target RIPKs for inactivation, and finally, we will touch on the controversial issue of drug development for kinase inhibitors to treat chronic inflammatory and neurological disorders, and the implications this may have on the outcome of pathogen infections.

In vitro analysis reveals necroptotic signaling does not provoke DNA damage or HPRT mutations

Most anticancer drugs provoke apoptotic signaling by damaging DNA or other means. Genotoxic therapies may enhance a patient’s risk of developing “therapy-related cancers” due to the accumulation of oncogenic mutations that may occur in noncancerous cells. Mutations can also form upon apoptotic signaling due to sublethal caspase activity, implying that apoptosis activating drugs may also be oncogenic. Necroptosis is a different way of killing cancer cells: this version of caspase-independent cell death is characterized by receptor-interacting protein kinase-3 (RIPK3) and mixed lineage kinase-like domain protein (MLKL) activation, leading to cell membrane rupture and controlled cell lysis. The mutagenic potential of sublethal necroptotic signaling has not yet been directly investigated. Smac mimetics drugs, which activate apoptotic or necroptotic cell death, do not induce mutations but the mechanistic basis for this lack of mutagenic activity has not been determined. In this study, we compared the mutagenic potential of these two cell death pathways by engineering cells to activate either apoptotic or necroptotic signaling by exposing them to Smac mimetics with or without TNFα, and/or enforcing or preventing expression of apoptotic or necroptotic regulators. We discovered that sublethal concentrations of Smac mimetics in contexts that activated apoptotic signaling provoked DNA damage and mutations in surviving cells. Mutagenesis was dependent on executioner caspase activation of the nuclease CAD. In contrast, RIPK3- and MLKL-dependent necroptotic signaling following Smac mimetic treatment was not mutagenic. Likewise, DNA damage was not provoked in cells expressing a lethal constitutively active MLKL mutant. These data reveal that cells surviving sublethal necroptotic signaling do not sustain genomic damage and provide hope for a reduced risk of therapy-related malignancies in patients treated with necroptosis-inducing drugs.

How Neutrophils Meet Their End

Neutrophil death can transpire via diverse pathways and is regulated by interactions with commensal and pathogenic microorganisms, environmental exposures, and cell age. At steady state, neutrophil turnover and replenishment are continually maintained via a delicate balance between host-mediated responses and microbial forces. Disruptions in this equilibrium directly impact neutrophil numbers in circulation, cell trafficking, antimicrobial defenses, and host well-being. How neutrophils meet their end is physiologically important and can result in different immunologic consequences. Whereas nonlytic forms of neutrophil death typically elicit anti-inflammatory responses and promote healing, pathways ending with cell membrane rupture may incite deleterious proinflammatory responses, which can exacerbate local tissue injury, lead to chronic inflammation, or precipitate autoimmunity. This review seeks to provide a contemporary analysis of mechanisms of neutrophil death.

miR-425 deficiency promotes necroptosis and dopaminergic neurodegeneration in Parkinson's disease

A major hallmark of Parkinson’s disease (PD) is the degeneration of dopaminergic neurons in the substantia nigra, and the causative mechanism is thought to be the activation of programmed neuronal death. Necroptosis is a regulated process of cell death triggered by RIPK1. Although the pathophysiology of PD has been studied extensively, the cellular mechanism underlying dopaminergic neuron death remains unclear. In this study, we detected a specific miRNA, miR-425, in response to MPTP toxicity and dopaminergic degeneration. In MPTP-treated mice, we observed necroptosis activation and miR-425 deficiency in the substantia nigra, which is correlated with dopaminergic neuron loss. This miRNA targeted RIPK1 transcripts and promoted the phosphorylation of MLKL and necroptosis. Similarly, in the brains of PD patients, miR-425 deficiency and necroptosis activation were also confirmed in dopaminergic neuron. Furthermore, we found that genetic knockdown of miR-425 aggravated MPTP-induced motor deficits and dopaminergic neurodegeneration via early upregulation of necroptotic genes. Intracerebral miR-425 mimics (AgomiR-425) treatment attenuated necroptosis activation and dopaminergic neuron loss, and improved locomotor behaviors. In conclusion, our study suggests that miR-425 deficiency triggers necroptosis of dopaminergic neurons, and targeting miR-425 in MPTP-treated mice restored dysfunctional dopaminergic neurodegeneration and ameliorated behavioral deficits. These findings identify brain delivery of miR-425 as a potential therapeutic approach for the treatment of PD.

The Caspase Inhibitor Z-VAD-FMK Alleviates Endotoxic Shock via Inducing Macrophages Necroptosis and Promoting MDSCs-Mediated Inhibition of Macrophages Activation

Macrophages play a critical role in the pathogenesis of endotoxin shock by producing excessive amounts of pro-inflammatory cytokines. A pan-caspase inhibitor, zVAD, can be used to induce necroptosis under certain stimuli. The role of zVAD in both regulating the survival and activation of macrophages, and the pathogenesis of endotoxin shock remains not entirely clear. Here, we found that treatment of mice with zVAD could significantly reduce mortality and alleviate disease after lipopolysaccharide (LPS) challenge. Notably, in LPS-challenged mice, treatment with zVAD could also reduce the percentage of peritoneal macrophages by promoting necroptosis and inhibiting pro-inflammatory responses in macrophages. In vitro studies showed that pretreatment with zVAD promoted LPS-induced nitric oxide-mediated necroptosis of bone marrow-derived macrophages (BMDMs), leading to reduced pro-inflammatory cytokine secretion. Interestingly, zVAD treatment promoted the accumulation of myeloid-derived suppressor cells (MDSCs) in a mouse model of endotoxin shock, and this process inhibited LPS-induced pro-inflammatory responses in macrophages. Based on these findings, we conclude that treatment with zVAD alleviates LPS-induced endotoxic shock by inducing macrophage necroptosis and promoting MDSC-mediated inhibition of macrophage activation. Thus, this study provides insights into the effects of zVAD treatment in inflammatory diseases, especially endotoxic shock.

Infection of Human Neutrophils With Leishmania infantum or Leishmania major Strains Triggers Activation and Differential Cytokines Release

Leishmaniases are neglected diseases, caused by intracellular protozoan parasites of the Leishmania (L.) genus. Although the principal host cells of the parasites are macrophages, neutrophils are the first cells rapidly recruited to the site of parasites inoculation, where they play an important role in the early recognition and elimination of the parasites. The nature of early interactions between neutrophils and Leishmania could influence the outcome of infection. Herein we aimed to evaluate whether different Leishmania strains, responsible for distinct clinical manifestations, could influence ex vivo functional activity of neutrophils. Human polymorphonuclear leukocytes were isolated from 14 healthy volunteers and the ex vivo infection of these cells was done with two L. infantum and one L. major strains. Infection parameters were determined and neutrophils activation was assessed by oxidative burst, degranulation, DNA release and apoptosis; cytokine production was measured by a multiplex flow cytometry analysis. Intracellular amastigotes were rescued to determine Leishmania strains survival. The results showed that L. infantum and L. major promastigotes similarly infected the neutrophils. Oxidative burst, neutrophil elastase, myeloperoxidase activity and apoptosis were significantly increased in infected neutrophils but with no differences between strains. The L. infantum-infected neutrophils induced more DNA release than those infected by L. major. Furthermore, Leishmania strains induced high amounts of IL-8 and stimulated the production of IL-1β, TNF-α, and TGF-β by human neutrophils. We observed that only one strain promoted IL-6 release by these neutrophils. The production of TNF-α was also differently induced by the parasites strains. All these results demonstrate that L. infantum and L. major strains were able to induce globally a similar ex vivo activation and apoptosis of neutrophils; however, they differentially triggered cytokines release from these cells. In addition, rescue of intracellular parasites indicated different survival rates further emphasizing on the influence of parasite strains within a species on the fate of infection.

Ca2+/calmodulin-dependent protein kinase II regulation by inhibitor 1 of protein phosphatase 1 alleviates necroptosis in high glucose-induced cardiomyocytes injury

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays an important role in the cardiovascular system. However, the potential protective role of inhibitor 1 of protein phosphatase 1 (I1PP1), which is able to regulate CaMKII, in high glucose-induced cardiomyocytes injury remains unknown. In the present study, cardiomyocytes were transfected with I1PP1 adenovirus to inhibit protein phosphatase 1 (PP1) expression. After the cardiomyocytes were subjected to high glucose stimulation for 48 h, quantitative real-time PCR was used to detect CaMKIIδ alternative splicing. Lactate dehydrogenase (LDH) release and adenosine triphosphate (ATP) level were measured to assess cell damage and energy metabolism respectively. CaMKII activity was represented as phospholamban (PLB) phosphorylation, CaMKII phosphorylation (p-CaMKII) and oxidation (ox-CaMKII). Dihydroethidium (DHE), MitoSOX and JC-1 staining were used to assess oxidative stress and mitochondrial membrane potential. Necroptosis was evaluated by receptor interacting protein kinase 3 (RIPK3) expression, TUNEL and cleaved-caspase 3 levels. RIPK3, mixed lineage kinase domain like protein (MLKL) and dynamin-related protein 1 (DRP1) expressions were also detected. We found that high glucose disordered CaMKIIδ alternative splicing. I1PP1 over-expression suppressed PLB phosphorylation, ox-CaMKII, DRP1, RIPK3 and cleaved-caspase 3 proteins expression, decreased LDH release, attenuated necroptosis, increased ATP level, inhibited oxidative stress, and elevated mitochondrial membrane potential in high glucose-stimulated cardiomyocytes. However, there was no effect on phosphorylation of MLKL (p-MLKL), p-CaMKII, and receptor interacting protein kinase 1 (RIPK1) expression. Altogether, I1PP1 over-expression alleviated CaMKIIδ alternative splicing disorder, suppressed CaMKII oxidation, reduced reactive oxygen species (ROS) accumulation and inhibited necroptosis to attenuate high glucose-induced cardiomyocytes injury.

Neutrophil Degranulation, Plasticity, and Cancer Metastasis

Neutrophils are the first responders to inflammation and infection. Recently, an elevated neutrophil-to-lymphocyte ratio has generally become a prognostic indicator of poor overall survival in cancer. Accordingly, heterogeneous ill-defined neutrophil-like populations have been increasingly recognized as important players in cancer development. In addition, neutrophil granule proteins released upon cell activation have been associated with tumor progression; this differential granule mobilization may allow neutrophils - and possibly associated cancer cells - to leave the bloodstream and enter inflamed/infected tissues. This review discusses and proposes how granule mobilization may facilitate neutrophil-mediated transport of cancer cells into different tissues as well as leading to different cellular phenotypes that underlie remarkable neutrophil plasticity. This concept might inform novel neutrophil-centered approaches to putative cancer therapies.

Role of pyroptosis in cardiovascular disease

Cardiac function is determined by the dynamic equilibrium of various cell types and the extracellular matrix that composes the heart. Cardiovascular diseases (CVDs), especially atherosclerosis and myocardial infarction, are often accompanied by cell death and acute/chronic inflammatory reactions. Caspase‐dependent pyroptosis is characterized by the activation of pathways leading to the activation of NOD‐like receptors, especially the NLRP3 inflammasome and its downstream effector inflammatory factors interleukin (IL)‐1β and IL‐18. Many studies in the past decade have investigated the role of pyroptosis in CVDs. The findings of these studies have led to the development of therapeutic approaches based on the regulation of pyroptosis, and some of these approaches are in clinical trials. This review summarizes the molecular mechanisms, regulation and cellular effects of pyroptosis briefly and then discusses the current pyroptosis studies in CVD research.

Leishmania braziliensis Subverts Necroptosis by Modulating RIPK3 Expression

Leishmania braziliensis infection causes skin ulcers, typically found in localized cutaneous leishmaniasis (LCL). This tissue pathology associates with different modalities of cell necrosis, which are subverted by the parasite as a survival strategy. Herein we examined the participation of necroptosis, a specific form of programmed necrosis, in LCL lesions and found reduced RIPK3 and PGAM5 gene expression compared to normal skin. Assays using infected macrophages demonstrated that the parasite deactivates both RIPK3 and MLKL expression and that these molecules are important to control the intracellular L. braziliensis replication. Thus, LCL-related necroptosis may be targeted to control infection and disease immunopathology.