Caspase-independent cell killing by Fas-associated protein with death domain

Necrosis Links Neurodegeneration and Neuroinflammation in Neurodegenerative Disease

The mechanisms of neuronal cell death in neurodegenerative disease remain incompletely understood, although recent studies have made significant advances. Apoptosis was previously considered to be the only mechanism of neuronal cell death in neurodegenerative diseases. However, recent findings have challenged this dogma, identifying new subtypes of necrotic neuronal cell death. The present review provides an updated summary of necrosis subtypes and discusses their potential roles in neurodegenerative cell death. Among numerous necrosis subtypes, including necroptosis, paraptosis, ferroptosis, and pyroptosis, transcriptional repression-induced atypical cell death (TRIAD) has been identified as a potential mechanism of neuronal cell death. TRIAD is induced by functional deficiency of TEAD-YAP and self-amplifies via the release of HMGB1. TRIAD is a feasible potential mechanism of neuronal cell death in Alzheimer's disease and other neurodegenerative diseases. In addition to induction of cell death, HMGB1 released during TRIAD activates brain inflammatory responses, which is a potential link between neurodegeneration and neuroinflammation.

Effect of superficial adipose tissue mitochondrial and cellular functionality induced by extracorporeal shock wave therapy (ESWT)

Due to its regenerative action, extracorporeal shock wave therapy (ESWT) is applied in treating integumentary and musculoskeletal diseases. However, other potential therapeutic interventions are being investigated. It is essential to fully understand its mitochondrial signaling pathway to achieve this, which plays a fundamental role in elucidating the mechanism of action and possible therapeutic interventions. Thus, this study aimed to analyze the effect of ESWT on mitochondrial pathways through the relationship between lipolysis and adipocyte apoptosis, as well as cellular functionality. This is a non-randomized case-control clinical trial where obese women received ESWT sessions in the abdominal region, after which tissue samples were collected for histological and immunohistochemical analyses of adipose tissue. The data demonstrated positivity in the expression of mitochondrial markers related to cell apoptosis, such as FIS1 (p < 0.0203) and OPA1 (p < 0.0283), in addition to the positivity of anti-MFN1, responsible for regulating mitochondrial cell proliferation (p < 0.0003). In summary, this study demonstrates that ESWT was able to activate specific mitochondrial signaling pathways, which may be associated with its ability to stimulate lipolysis and apoptosis in superficial adipose tissue. However, no significant improvements in cellular functionality were observed.

Effects of short-term exposure to volatile pesticide dichlorvos on the olfactory systems in Spodoptera litura: Calcium homeostasis, synaptic plasticity and apoptosis

Volatile pesticides are a growing environmental and public health concern. However, little attention has been paid to its olfactory neurotoxic effect on pests and non-target organisms. Dichlorvos is a widely used organophosphorus fumigant that is ubiquitous in the environment. This study aims to explore the mode of action of the volatile dichlorvos-mediated olfactory impairment using a lepidopteran insect Spodoptera litura as a model. It was indicated that electroantennogram amplitudes of the male moths' response to sex pheromones and phenylacetaldehyde were reduced by approximately 20 % after 12-h fumigation exposure. RNA-Sequencing analysis revealed that down-regulation of trypsin and CLIC2 might be responsible for inhibition of odor recognition in the antenna, the peripheral olfactory tissue. In the head, 822 (84.05 %) of the 978 differentially expressed genes (DEGs) were up-regulated, of which seven DEGs encoding transcription factors may mainly modulate the stress-regulatory networks. Combining transcriptome with brain calcium imaging and Annexin V-mCherry staining experiments showed that volatile dichlorvos mainly disrupts Ca²⁺ homeostasis and synaptic plasticity, induces apoptosis in the central nervous system, and further leads to olfactory dysfunction. Overall, this study highlighted a comprehensive work model for dichlorvos-induced olfactory impairment in S. litura and may provide insights into toxic effects of airborne organophosphates on non-target organisms.

The web of death: the expanding complexity of necroptotic signaling

The past decade has seen the emergence of the necroptosis programmed cell death pathway as an important contributor to the pathophysiology of myriad diseases. The receptor interacting protein kinase (RIPK)1 and RIPK3, and the pseudokinase executioner protein, mixed lineage kinase domain-like (MLKL), have grown to prominence as the core pathway components. Depending on cellular context, these proteins also serve as integrators of signals, such as post-translational modifications and protein or metabolite interactions, adding layers of complexity to pathway regulation. Here, we describe the emerging picture of the web of proteins that tune necroptotic signal transduction and how these events have diverged across species, presumably owing to selective pressures of pathogens upon the RIPK3-MLKL protein pair.

Programmed Necrosis in Host Defense

Host control over infectious disease relies on the ability of cells in multicellular organisms to detect and defend against pathogens to prevent disease. Evolution affords mammals with a wide variety of independent immune mechanisms to control or eliminate invading infectious agents. Many pathogens acquire functions to deflect these immune mechanisms and promote infection. Following successful invasion of a host, cell autonomous signaling pathways drive the production of inflammatory cytokines, deployment of restriction factors and induction of cell death. Combined, these innate immune mechanisms attract dendritic cells, neutrophils and macrophages as well as innate lymphoid cells such as natural killer cells that all help control infection. Eventually, the development of adaptive pathogen-specific immunity clears infection and provides immune memory of the encounter. For obligate intracellular pathogens such as viruses, diverse cell death pathways make a pivotal contribution to early control by eliminating host cells before progeny are produced. Pro-apoptotic caspase-8 activity (along with caspase-10 in humans) executes extrinsic apoptosis, a nonlytic form of cell death triggered by TNF family death receptors (DRs). Over the past two decades, alternate extrinsic apoptosis and necroptosis outcomes have been described. Programmed necrosis, or necroptosis, occurs when receptor interacting protein kinase 3 (RIPK3) activates mixed lineage kinase-like (MLKL), causing cell leakage. Thus, activation of DRs, toll-like receptors (TLRs) or pathogen sensor Z-nucleic acid binding protein 1 (ZBP1) initiates apoptosis as well as necroptosis if not blocked by virus-encoded inhibitors. Mammalian cell death pathways are blocked by herpesvirus- and poxvirus-encoded cell death suppressors. Growing evidence has revealed the importance of Z-nucleic acid sensor, ZBP1, in the cell autonomous recognition of both DNA and RNA virus infection. This volume will explore the detente between viruses and cells to manage death machinery and avoid elimination to support dissemination within the host animal.

The resurrection of RIP kinase 1 as an early cell death checkpoint regulator-a potential target for therapy in the necroptosis era

Receptor-interacting serine threonine protein kinase 1 (RIPK1) has emerged as a central molecular switch in controlling the balance between cell survival and cell death. The pro-survival role of RIPK1 in maintaining cell survival is achieved via its ability to induce NF-κB-dependent expression of anti-apoptotic genes. However, recent advances have identified the pro-death function of RIPK1: posttranslational modifications of RIPK1 in the tumor necrosis factor receptor 1 (TNFR1)-associated complex-I, in the cytosolic complex-IIb or in necrosomes regulate the cytotoxic potential of RIPK1, forming an early cell death checkpoint. Since the kinase activity of RIPK1 is indispensable in RIPK3- and MLKL-mediated necroptosis induction, while it is dispensable in apoptosis, a better understanding of this early cell death checkpoint via RIPK1 might lead to new insights into the molecular mechanisms controlling both apoptotic and necroptotic modes of cell death and help develop novel therapeutic approaches for cancer. Here, we present an emerging view of the regulatory mechanisms for RIPK1 activity, especially with respect to the early cell death checkpoint. We also discuss the impact of dysregulated RIPK1 activity in pathophysiological settings and highlight its therapeutic potential in treating human diseases.

Improved understanding of the molecular mechanisms that allow a protein to control the balance between cell survival or early death could reveal new approaches to treating conditions including chronic inflammatory disease and cancer. Gang Min Hur and colleagues at Chungnam National University in Daejeon, South Korea, with Han-Ming Shen at the University of Macau in China, review emerging evidence about how the protein called receptor-interacting serine/threonine-protein kinase 1 (RIPK1) influences whether cells move towards death or survival at a key ‘checkpoint’ in cell development. Cells can undergo a natural process of programmed cell death called apoptosis, die abnormally in a disease process called necroptosis, or survive. RIPK1 appears able to influence which path is chosen depending on which genes it regulates and which proteins it interacts with. Many details are still unclear, and need further investigation.

Grb2 interacts with necrosome components and is involved in rasfonin-induced necroptosis

The underlying mechanism by which growth factor receptor-bound protein 2 (Grb2) regulates necroptosis remains unexplored. In the present study, we found that rasfonin, a fungal natural product and an activator of necroptosis, enhanced Grb2 binding to receptor-interacting serine/threonine kinase 1 (RIP1), which plays a critical role in regulating programmed necrosis. Moreover, we observed that SQSTM/p62 (p62), a protein that can form necrosomes with RIP1, increased its interaction with Grb2 upon rasfonin challenge. Although it has been used as an activator of autophagy in our previous study, here we found that a high dose of rasfonin was able to inhibit autophagic process. Inhibition of RIP1 either chemically or genetically reversed the inhibition of rasfonin on autophagy, whereas knockdown of Grb2 markedly reduced rasfonin-induced necrosis. Additionally, we found that the compound failed to upregulate the expression of RIP1 in Grb2-deprived cells. In summary, our data revealed that Grb2 actively participated in rasfonin-induced necroptosis by interacting with the components of necrosome and mediating their expression.

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.

Pan-cancer analysis of necroptosis-related gene signature for the identification of prognosis and immune significance

BACKGROUND

Necroptosis is a novel programmed cell death mode independent on caspase. A number of studies have revealed that the induction of necroptosis could act as an alternative therapeutic strategy for drug-resistant tumors as well as affect tumor immune microenvironment.

METHODS

Gene expression profiles and clinical data were downloaded from XENA-UCSC (including The Cancer Genome Atlas and Genotype-Tissue Expression), Gene Expression Omnibus, International Cancer Genome Consortium and Chinese Glioma Genome Atlas. We used non-negative matrix factorization method to conduct tumor classification. The least absolute shrinkage and selection operator regression was applied to establish risk models, whose prognostic effectiveness was examined in both training and testing sets with Kaplan-Meier analysis, time-dependent receiver operating characteristic curves as well as uni- and multi-variate survival analysis. Principal Component Analysis, t-distributed Stochastic Neighbor Embedding and Uniform Manifold Approximation and Projection were conducted to check the risk group distribution. Gene Set Enrichment Analyses, immune infiltration analysis based on CIBERSORT, EPIC, MCPcounter, ssGSEA and ESTIMATE, gene mutation and drug sensitivity between the risk groups were also taken into consideration.

RESULTS

There were eight types of cancer with at least ten differentially expressed necroptosis-related genes which could influence patients' prognosis, namely, adrenocortical carcinoma (ACC), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), acute myeloid leukemia (LAML), brain lower grade glioma (LGG), pancreatic adenocarcinoma (PAAD), liver hepatocellular carcinoma (LIHC), skin cutaneous melanoma (SKCM) and thymoma (THYM). Patients could be divided into different clusters with distinct overall survival in all cancers above except for LIHC. The risk models could efficiently predict prognosis of ACC, LAML, LGG, LIHC, SKCM and THYM patients. LGG patients from high-risk group had a higher infiltration level of M2 macrophages and cancer-associated fibroblasts. There were more CD8+ T cells, Th1 cells and M1 macrophages in low-risk SKCM patients' tumor microenvironment. Gene mutation status and drug sensitivity are also different between low- and high-risk groups in the six cancers.

CONCLUSIONS

Necroptosis-related genes can predict clinical outcomes of ACC, LAML, LGG, LIHC, SKCM and THYM patients and help to distinguish immune infiltration status for LGG and SKCM.

The emerging role of dipeptidyl peptidase 3 in pathophysiology

Dipeptidyl peptidase 3 (DPP3), a zinc-dependent aminopeptidase, is a highly conserved enzyme among higher animals. The enzyme cleaves dipeptides from the N-terminus of tetra- to decapeptides, thereby taking part in activation as well as degradation of signalling peptides critical in physiological and pathological processes such as blood pressure regulation, nociception, inflammation and cancer. Besides its catalytic activity, DPP3 moonlights as a regulator of the cellular oxidative stress response pathway, e.g., the Keap1-Nrf2 mediated antioxidative response. The enzyme is also recognized as a key modulator of the renin-angiotensin system. Recently, DPP3 has been attracting growing attention within the scientific community, which has significantly augmented our knowledge of its physiological relevance. Herein, we review recent advances in our understanding of the structure and catalytic activity of DPP3, with a focus on attributing its molecular architecture and catalytic mechanism to its wide-ranging biological functions. We further highlight recent intriguing reports that implicate a broader role for DPP3 as a valuable biomarker in cardiovascular and renal pathologies and furthermore discuss its potential as a promising drug target.

Cell Death and Survival Pathways Involving ATM Protein Kinase

Cell death is the ultimate form of cellular dysfunction, and is induced by a wide range of stresses including genotoxic stresses. During genotoxic stress, two opposite cellular reactions, cellular protection through DNA repair and elimination of damaged cells by the induction of cell death, can occur in both separate and simultaneous manners. ATM (ataxia telangiectasia mutated) kinase (hereafter referred to as ATM) is a protein kinase that plays central roles in the induction of cell death during genotoxic stresses. It has long been considered that ATM mediates DNA damage-induced cell death through inducing apoptosis. However, recent research progress in cell death modality is now revealing ATM-dependent cell death pathways that consist of not only apoptosis but also necroptosis, ferroptosis, and dysfunction of autophagy, a cellular survival mechanism. In this short review, we intend to provide a brief outline of cell death mechanisms in which ATM is involved, with emphasis on pathways other than apoptosis.

The role of iron homeostasis and iron-mediated ROS in cancer

As an important trace element, iron plays an essential role in many biology processes like cell proliferation, metabolism, and mitochondrial function. However, the disruption of iron homeostasis tends to cells death and human diseases due to it servers as mediator to promote the production of reactive oxygen species (ROS). In this review, first we introduced the mechanism of complex iron-mediated ROS involved in apoptosis, necroptosis, ferroptosis and pyroptosis. Next, we discussed the controversial role of excess iron and iron deficiency in tumor. Finally, we discussed the anti-cancer effects of iron on both sides, and novel iron-related strategies. This review outlined the mechanisms and regulation of iron homeostasis and iron-mediated ROS in tumors, and discussed the iron-related treatments.

Mechanisms of Ferroptosis and Application to Head and Neck Squamous Cell Carcinoma Treatments

Many kinds of cancer cells are intrinsically sensitive to ferroptosis, and research interest regarding ferroptosis has been sparked by its significant role in many detrimental diseases. Ferroptosis is a novel type of iron-dependent cell death mediated by accumulation of reactive oxygen species and lipid peroxidation. Furthermore, a large number of small agents can induce ferroptosis in numerous kinds of cancer cells, including prostate cancer, pancreatic cancer, breast cancer, lymphomas, and renal cancer. These insights may help discover novel approaches for cancer therapeutic strategies; however, there is considerable uncertainty regarding ferroptosis in head and neck cancer (HNC). So far, no review of the current studies on this topic has been published. Therefore, we here elaborate the mechanisms of ferroptosis and summarize the latest findings regarding its role in HNC according to current literature. The respective findings shed light on the role of ferroptosis in HNC treatment with a number of important implications for future practice in HNC management, as outlined in this review.

Mechanisms of neuronal cell death in ischemic stroke and their therapeutic implications

Ischemic stroke caused by arterial occlusion is the most common type of stroke, which is among the most frequent causes of disability and death worldwide. Current treatment approaches involve achieving rapid reperfusion either pharmacologically or surgically, both of which are time-sensitive; moreover, blood flow recanalization often causes ischemia/reperfusion injury. However, even though neuroprotective intervention is urgently needed in the event of stroke, the exact mechanisms of neuronal death during ischemic stroke are still unclear, and consequently, the capacity for drug development has remained limited. Multiple cell death pathways are implicated in the pathogenesis of ischemic stroke. Here, we have reviewed these potential neuronal death pathways, including intrinsic and extrinsic apoptosis, necroptosis, autophagy, ferroptosis, parthanatos, phagoptosis, and pyroptosis. We have also reviewed the latest results of pharmacological studies on ischemic stroke and summarized emerging drug targets with a focus on clinical trials. These observations may help to further understand the pathological events in ischemic stroke and bridge the gap between basic and translational research to reveal novel neuroprotective interventions.

Loss of FADD and Caspases Affects the Response of T-Cell Leukemia Jurkat Cells to Anti-Cancer Drugs

Programmed cell death (PCD) pathways play a crucial role in the response of cancer cells to treatment. Their dysregulation is one of the cancer hallmarks and one of the reasons of drug resistance. Here, we studied the significance of the individual members of PCD signaling pathways in response to treatment with common anti-cancer drugs using the T-cell leukemia Jurkat cells with single or double knockouts of necroptosis and/or apoptosis genes. We identified apoptosis as the primary cell death pathway upon anti-cancer drugs treatment. The cells with knocked out either Fas-associated protein with death domain (FADD) or all executioner caspases were resistant. This resistance could be partially overcome by induction of RIP1-dependent necroptosis through TNFR1 activation using combined treatment with TNF-α and smac mimetic (LCL161). RIP1 was essential for cellular response to TNF-α and smac mimetic, but dispensable for the response to anti-cancer drugs. Here, we demonstrated the significance of FADD and executioner caspases in carrying out programmed cell death upon anti-cancer drug treatments and the ability of combined treatment with TNF-α and smac mimetic to partially overcome drug resistance of FADD and/or CASP3/7/6-deficient cells via RIP1-dependent necroptosis. Thus, a combination of TNF-α and smac mimetic could be a suitable strategy for overcoming resistance to therapy in cells unable to trigger apoptosis.

Altered mitochondrial calcium handling and cell death by necroptosis: An emerging paradigm

The classical necroptosis signaling is mediated by death receptors (DRs) that work in synergy with traditional caspase inhibitory signals. Currently, potential therapeutic molecules are in various phases of clinical trials for a spectrum of pathological conditions associated with necroptosis. However, a non-classical model of necroptosis has also emerged over the last decade with a relatively unexplored molecular mechanism. Although in vitro studies and preclinical models have shown its close association with mitochondrial dysfunction (mito-dysfunction), contradictory reports have emerged which complicate its definitiveness. Though impaired mitochondrial calcium ([Ca²⁺]_m) handling is established in necrotic cell death, how this interplay regulates necroptosis is yet to be elucidated. Taking these questions into consideration, we have discussed various molecular aspects of necroptosis with the emerging role of mito-dysfunction. Based on the central role of altered [Ca²⁺]_m handling in mito-dysfunction mediated necroptosis, we have provided a comprehensive molecular insight into this emerging paradigm. Potential reasons for the contradictory findings regarding the role of mito-dysfunction in necroptosis in general and mitochondrial-dependent necroptosis in specific are discussed. We also provide insights into the current understanding of how [Ca²⁺]_m can be a critical determinant in deciding the cell fate under certain pathological conditions, while under others it may be dispensable. Lastly, we have highlighted the key molecular targets which have a direct implication for therapeutic intervention in conditions that are associated with impaired [Ca²⁺]_m handling and cell death by necroptosis.

The molecular mechanisms of MLKL-dependent and MLKL-independent necrosis

Necrosis, a type of unwanted and passive cell demise, usually occurs under the excessive external stress and is considered to be unregulated. However, under some special conditions such as caspase inhibition, necrosis is regulable in a well-orchestrated way. The term 'regulated necrosis' has been proposed to describe such programed necrosis. Recently, several forms of necrosis, including necroptosis, pyroptosis, ferroptosis, parthanatos, oxytosis, NETosis, and Na+/K+-ATPase-mediated necrosis, have been identified, and some crucial regulators governing regulated necrosis have also been discovered. Mixed lineage kinase domain-like pseudokinase (MLKL), a core regulator in necroptosis, acts as an executioner in response to ligands of death receptor family. Its activation requires the receptor-interacting protein kinases, RIP1 and RIP3. However, MLKL is only involved in necroptosis, i.e. MLKL is dispensable for necrosis. Therefore, this review is aimed at summarizing the molecular mechanisms of MLKL-dependent and MLKL-independent necrosis.

Varicella zoster virus encodes a viral decoy RHIM to inhibit cell death

Herpesviruses are known to encode a number of inhibitors of host cell death, including RIP Homotypic Interaction Motif (RHIM)-containing proteins. Varicella zoster virus (VZV) is a member of the alphaherpesvirus subfamily and is responsible for causing chickenpox and shingles. We have identified a novel viral RHIM in the VZV capsid triplex protein, open reading frame (ORF) 20, that acts as a host cell death inhibitor. Like the human cellular RHIMs in RIPK1 and RIPK3 that stabilise the necrosome in TNF-induced necroptosis, and the viral RHIM in M45 from murine cytomegalovirus that inhibits cell death, the ORF20 RHIM is capable of forming fibrillar functional amyloid complexes. Notably, the ORF20 RHIM forms hybrid amyloid complexes with human ZBP1, a cytoplasmic sensor of viral nucleic acid. Although VZV can inhibit TNF-induced necroptosis, the ORF20 RHIM does not appear to be responsible for this inhibition. In contrast, the ZBP1 pathway is identified as important for VZV infection. Mutation of the ORF20 RHIM renders the virus incapable of efficient spread in ZBP1-expressing HT-29 cells, an effect which can be reversed by the inhibition of caspases. Therefore we conclude that the VZV ORF20 RHIM is important for preventing ZBP1-driven apoptosis during VZV infection, and propose that it mediates this effect by sequestering ZBP1 into decoy amyloid assemblies.

RIP homotypic interaction motifs (RHIMs) are found in host proteins that can signal for programmed cell death and in viral proteins that can prevent it. Complexes stabilized by intermolecular interactions involving RHIMs have a fibrillar amyloid structure. We have identified a novel RHIM within the ORF20 protein expressed by Varicella zoster virus (VZV) that forms amyloid-based complexes with human cellular RHIMs. Whereas other herpesvirus RHIMs inhibit necroptosis, this new VZV RHIM targets the host RHIM-containing protein ZBP1 to inhibit apoptosis during infection. This is the first study to demonstrate the importance of the ZBP1 pathway in VZV infection and to identify the role of a viral RHIM in apoptosis inhibition. It broadens our understanding of host defense pathways and demonstrates how a decoy amyloid strategy is employed by pathogens to circumvent the host response.

Autophagy as a decisive process for cell death

Autophagy is an intracellular catabolic pathway in which cellular constituents are engulfed by autophagosomes and degraded upon autophagosome fusion with lysosomes. Autophagy serves as a major cytoprotective process by maintaining cellular homeostasis and recycling cytoplasmic contents. However, emerging evidence suggests that autophagy is a primary mechanism of cell death (autophagic cell death, ACD) and implicates ACD in several aspects of mammalian physiology, including tumor suppression and psychological disorders. However, little is known about the physiological roles and molecular mechanisms of ACD. In this review, we document examples of ACD and discuss recent progress in our understanding of its molecular mechanisms.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

Programmed necrosis in cardiomyocytes: mitochondria, death receptors and beyond

Excessive death of cardiac myocytes leads to many cardiac diseases, including myocardial infarction, arrhythmia, heart failure and sudden cardiac death. For the last several decades, most work on cell death has focused on apoptosis, which is generally considered as the only form of regulated cell death, whereas necrosis has been regarded to be an unregulated process. Recent findings reveal that necrosis also occurs in a regulated manner and that it is closely related to the physiology and pathophysiology of many organs, including the heart. The recognition of necrosis as a regulated process mandates a re-examination of cell death in the heart together with the mechanisms and therapy of cardiac diseases. In this study, we summarize the regulatory mechanisms of the programmed necrosis of cardiomyocytes, that is, the intrinsic (mitochondrial) and extrinsic (death receptor) pathways. Furthermore, the role of this programmed necrosis in various heart diseases is also delineated. Finally, we describe the currently known pharmacological inhibitors of several of the key regulatory molecules of regulated cell necrosis and the opportunities for their therapeutic use in cardiac disease. We intend to systemically summarize the recent progresses in the regulation and pathological significance of programmed cardiomyocyte necrosis along with its potential therapeutic applications to cardiac diseases. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Single-Cell and Population-Level Analyses Using Real-Time Kinetic Labeling Couples Proliferation and Cell Death Mechanisms

Quantifying cytostatic and cytotoxic outcomes are integral components of characterizing perturbagens used as research tools and in drug discovery pipelines. Furthermore, data-rich acquisition, coupled with robust methods for analysis, is required to properly assess the function and impact of these perturbagens. Here, we present a detailed and versatile method for single-cell and population-level analyses using real-time kinetic labeling (SPARKL). SPARKL integrates high-content live-cell imaging with automated detection and analysis of fluorescent reporters of cell death. We outline several examples of zero-handling, non-disruptive protocols for detailing cell death mechanisms and proliferation profiles. Additionally, we suggest several methods for mathematically analyzing these data to best utilize the collected kinetic data. Compared to traditional methods of detection and analysis, SPARKL is more sensitive, accurate, and high throughput while substantially eliminating sample processing and providing richer data.

RIP3 participates in early brain injury after experimental subarachnoid hemorrhage in rats by inducing necroptosis

Necroptosis is a regulated form of necrosis that is mediated by a variety of proteins including tumor necrosis factor-α (TNF-α) and receptor-interacting proteins (RIPs). TNF-α, a critical inflammatory molecule, is one of the initiating signals in the necroptosis pathway, and RIP3 acts as a switch that commits the cell to necroptosis. Subarachnoid hemorrhage (SAH) is a common type of hemorrhagic stroke with high mortality and disability rates. RIP3 has been studied in many central nervous system (CNS) diseases, but its role in SAH has not been investigated in depth. Here, we used an autologous-blood injection model to study the role of RIP3 in brain injury induced by SAH in rats. Several indexes such as brain edema, loss of blood-brain barrier (BBB) integrity, and behavioral tests of neurological function were used to evaluate brain damage in SAH-injured rats. We found that the expression of RIP3 was increased in the rat brain after SAH, reaching the highest point 24 h post-injury. We also showed that genetic or pharmacological inhibition of RIP3 or TNF-α reduced the brain damage induced by SAH, whereas overexpression of RIP3 aggravated brain injury and neurological damage. Additionally, we verified the presence of RIP3-mediated necroptosis in an in vitro SAH model of primary cultured neurons treated with conditioned medium from primary microglia activated by oxygen hemoglobin (OxyHb). Collectively, our findings indicated that RIP3 contributed to brain damage after SAH by inducing necroptosis.

Necroptosis Signaling Pathways in Stroke: From Mechanisms to Therapies

It has been confirmed that apoptosis, autophagy and necrosis are the three major modes of cell death. For a long time, necrosis is regarded as a deranged or accidental cell demise. In recent years, there is evidence showing that necrotic cell death can be a well regulated and orchestrated event, which is also known as programmed cell death or “necroptosis”. Necroptosis can be triggered by a variety of external stimuli and regulated by a caspase-independent pathway. It plays a key role in the pathogenesis of some diseases including neurological diseases. In the past two decades, a variety of studies have revealed that the necroptosis related pathway is activated in stroke, and plays a crucial role in the pathogenesis of stroke. Moreover, necroptosis may serve as a potential target in the therapy of stroke because genetic or pharmacological inhibition of necroptosis has been shown to be neuroprotective in stroke in vitro and in vivo. In this review, we briefly summarize re-cent advances in necroptosis, introduce the mechanism and strategies targeting necroptosis in stroke, and finally propose some issues in the treatment of stroke by targeting necroptosis

Rs217727 polymorphism in H19 promotes cell apoptosis by regulating the expressions of H19 and the activation of its downstream signaling pathway

BACKGROUND

The objective of the current study was to explore the role of H19 rs217727 polymorphism in the control of hepatocellular carcinoma (HCC).

METHOD

The Student's t test, Cox regression, and Kaplan-Meier analyses were used to clarify whether the H19 rs217727 polymorphism played an important role in the development of HCC. Real-time polymerase chain reaction (PCR) and western-blot analysis were carried out to measure the levels of H19, microRNA (miR)-675, FAS-associated death domain (FADD), caspase-8, and caspase-3 among H19 CC, CT, and TT groups, as well as in cells transfected with H19/si-H19, or miR-675 mimic/inhibitor. The MTT assay, colony formation assay, and flow cytometry assay were performed to detect the effect of H19/miR-675 on cell viability, cell colony formation, and cell apoptosis.

RESULT

T allele of H19 rs217727 polymorphism apparently increased the survival rate of patients with HCC. Meanwhile, H19 enhanced miR-675 expression but reduced the mRNA and protein levels of FADD, caspase-3, and caspase-8. The T allele of H19 rs217727 polymorphism apparently increased the apoptotic rate of HCC cells. Furthermore, FADD was a virtual target gene of miR-675 with a potential "hit" located in the 3'-untranslated region (UTR) of FADD, whereas H19 inhibited FADD expression via increasing the expression of miR-675. Moreover, H19 upregulated the expression of miR-675 whereas reducing the expression of FADD, caspase-3, and caspase-8. Finally, H19 and miR-675 promoted cell proliferation and cell colony formation but repressed cell apoptosis.

CONCLUSION

In summary, the above findings demonstrated that the polymorphism of rs217727 in H19 was associated with HCC via the H19/miR-675/FADD/caspase-8/caspase-3/apoptosis signaling pathway.

Pathophysiological Roles of Intracellular Proteases in Neuronal Development and Neurological Diseases

Proteases are classified into six distinct classes (cysteine, serine, threonine, aspartic, glutamic, and metalloproteases) on the basis of catalytic mechanism. The cellular control of protein quality senses misfolded or damaged proteins principally by selective ubiquitin-proteasome pathway and non-selective autophagy-lysosome pathway. The two pathways do not only maintain cell homeostasis physiologically, but also mediate necrosis and apoptosis pathologically. Proteasomes are threonine proteases, whereas cathepsins are lysosomal aspartic proteases. Calpains are non-lysosomal cysteine proteases and calcium-dependent papain-like enzyme. Calpains and cathepsins are involved in the neuronal necrosis, which are accidental cell death. Necrosis is featured by the disruption of plasma membranes and lysosomes, the loss of ATP and ribosomes, the lysis of cell and nucleus, and the caspase-independent DNA fragmentation. On the other hand, caspases are cysteine endoproteases and mediate neuronal cell death such as apoptosis and pyroptosis, which are programmed cell death. In the central nervous system, necroptosis, ferroptosis and autophagic cell death are also classified into programmed cell death. Neuronal apoptosis is characterized by cell shrinkage, plasma membrane blebbing, karyorrhexis, chromatin condensation, and DNA fragmentation. Necroptosis and pyroptosis are necrotic and lytic forms of programmed cell death, respectively. Although autophagy is involved in cell survival, it fails to maintain cellular homeostasis, resulting in autophagic cell death. Ferroptosis is induced by reactive oxygen species in excitotoxicity of glutamate and ischemia-reperfusion. Apoptosis and pyroptosis are dependent on caspase-3 and caspase-1, respectively. Autophagic cell death and necroptosis are dependent on calpain and cathepsin, respectively, but independent of caspase. Although apoptosis has been defined by the absence of morphological features of necrosis, the two deaths are both parts of a continuum. The intracellular proteases do not only maintain cell homeostasis but also regulate neuronal maturation during the development of embryonic brain. Furthermore, neurodegenerative diseases are caused by the impairment of quality control mechanisms for a proper folding and function of protein.

The Pathogenesis of Necroptosis-Dependent Signaling Pathway in Cerebral Ischemic Disease

Necroptosis is the best-described form of regulated necrosis at present, which is widely recognized as a component of caspase-independent cell death mediated by the concerted action of receptor-interacting protein kinase 1 (RIPK1) and receptor-interacting protein kinase 3 (RIPK3). Mixed-lineage kinase domain-like (MLKL) was phosphorylated by RIPK3 at the threonine 357 and serine 358 residues and then formed tetramers and translocated onto the plasma membrane, which destabilizes plasma membrane integrity leading to cell swelling and membrane rupture. Necroptosis is downstream of the tumor necrosis factor (TNF) receptor family, and also interaction with NOD-like receptor pyrin 3 (NLRP3) induced inflammasome activation. Multiple inhibitors of RIPK1 and MLKL have been developed to block the cascade of signal pathways for procedural necrosis and represent potential leads for drug development. In this review, we highlight recent progress in the study of roles for necroptosis in cerebral ischemic disease and discuss how these modifications delicately control necroptosis.

HIV Protease-Generated Casp8p41, When Bound and Inactivated by Bcl2, Is Degraded by the Proteasome

HIV protease is known to cause cell death, which is dependent upon cleavage of procaspase 8. HIV protease cleavage of procaspase 8 generates Casp8p41, which directly binds Bak with nanomolar affinity, causing Bak activation and consequent cell death. Casp8p41 can also bind Bcl2 with nanomolar affinity, in which case cell death is averted. Central memory CD4 T cells express high levels of Bcl2, possibly explaining why those cells do not die when they reactivate HIV. Here, we determine that the Casp8p41-Bcl2 complex is polyubiquitinated and degraded by the proteasome. Ixazomib, a proteasome inhibitor in clinical use, blocks this pathway, increasing the abundance of Casp8p41 and causing more cells to die in a Casp8p41-dependent manner.

IMPORTANCE The Casp8p41 pathway of cell death is unique to HIV-infected cells yet is blocked by Bcl2. Once bound by Bcl2, Casp8p41 is polyubiquitinated and degraded by the proteasome. Proteasome inhibition blocks degradation of Casp8p41, increasing Casp8p41 levels and causing more HIV-infected cells to die.

Necrostatin-1 inhibits the cell death of osteoblasts induced by glucocorticoid

Glucocorticoids have been shown to induce apoptosis in different cell types. Recent studies have indicated that apoptosis may not be the only form of death that is activated in osteoblasts in response to glucocorticoids. The aim of this study was to investigate whether necrostatin-1 could protect osteoblasts from glucocorticoid-induced cell death. Dexamethasone could induce both apoptotic and necrotic cell death in MC3T3-E1 cells, in a dose- and time-dependent manner. Necrotic cell death was induced by dexamethasone in MC3T3-E1 cells and was characterized by caspase independence, delayed externalization of phosphatidylserine, cellular swelling and plasma membrane disruption. Blockages of necroptotic induction by a special inhibitor (Necrostatin-1) succeed to protect cells against dexamethasone induced cell death. The levels of RIP-1 production and loss of mitochondrial membrane potential were also determined to assess the effects of dexamethasone. This study showed, for the first time, that high-doses of dexamethasone can induce necrotic-like cell death in osteoblastic MC3T3-E1 cells, and this induction could be inhibited by necrostatin-1.

Dabrafenib, an inhibitor of RIP3 kinase-dependent necroptosis, reduces ischemic brain injury

Ischemic brain injury triggers neuronal cell death by apoptosis via caspase activation and by necroptosis through activation of the receptor-interacting protein kinases (RIPK) associated with the tumor necrosis factor-alpha (TNF-α)/death receptor. Recent evidence shows RIPK inhibitors are neuroprotective and alleviate ischemic brain injury in a number of animal models, however, most have not yet undergone clinical trials and safety in humans remains in question. Dabrafenib, originally identified as a B-raf inhibitor that is currently used to treat melanoma, was later revealed to be a potent RIPK3 inhibitor at micromolar concentrations. Here, we investigated whether Dabrafenib would show a similar neuroprotective effect in mice subjected to ischemic brain injury by photothrombosis. Dabrafenib administered intraperitoneally at 10 mg/kg one hour after photothrombosis-induced focal ischemic injury significantly reduced infarct lesion size in C57BL6 mice the following day, accompanied by a markedly attenuated upregulation of TNF-α. However, subsequent lower doses (5 mg/kg/day) failed to sustain this neuroprotective effect after 4 days. Dabrafenib blocked lipopolysaccharides-induced activation of TNF-α in bone marrow-derived macrophages, suggesting that Dabrafenib may attenuate TNF-α-induced necroptotic pathway after ischemic brain injury. Since Dabrafenib is already in clinical use for the treatment of melanoma, it might be repurposed for stroke therapy.

Staphylococcus aureus triggers a shift from influenza virus-induced apoptosis to necrotic cell death

Superinfections with Staphylococcus aureus are a major complication of influenza disease, causing excessive inflammation and tissue damage. This enhanced cell-damaging effect is also observed in superinfected tissue cultures, leading to a strong decrease in overall cell viability. In our analysis of the underlying molecular mechanisms, we observed that, despite enhanced cell damage in superinfection, S. aureus did not increase but rather inhibited influenza virus (IV)-induced apoptosis in cells on the level of procaspase-8 activation. This apparent contradiction was solved when we observed that S. aureus mediated a switch from apoptosis to necrotic cell death of IV-infected cells, a mechanism that was dependent on the bacterial accessory gene regulator ( agr) locus that promotes bacterial survival and spread. This so far unknown action may be a bacterial strategy to enhance dissemination of intracellular S. aureus and may thereby contribute to increased tissue damage and severity of disease.-Van Krüchten, A., Wilden, J. J., Niemann, S., Peters, G., Löffler, B., Ludwig, S., Ehrhardt, C. Staphylococcus aureus triggers a shift from influenza virus-induced apoptosis to necrotic cell death.

Necroptosis in cancer: An angel or a demon?

In the past few decades, apoptosis has been regarded as the only form of programmed cell death. However, the traditional view has been challenged by the identification of several forms of regulated necrosis, including necroptosis. Necroptosis is typified by a necrotic cell death morphology and is controlled by RIP1, RIP3, and mixed lineage kinase domain-like protein. The physiological role of necroptosis is to serve as a "fail-safe" form of cell death for cells that fail to undergo apoptosis during embryonic development and disease defense. Currently, established studies have indicated that necroptosis is involved in cancer initiation and progression. Although elevated necroptosis contributes to cancer cell death, extensive cell death also increases the risk of proliferation and metastasis of the surviving cells by inducing the generation reactive oxygen species, activation of inflammation, and suppression of the immune response. Thus, questions regarding the overall impact of necroptosis on cancer remain open. In this review, we introduce the basic knowledge regarding necroptosis, summarize its dual effects on cancer progression, and analyze its advantages and disadvantages in clinical applications.

SUMO-Modified FADD Recruits Cytosolic Drp1 and Caspase-10 to Mitochondria for Regulated Necrosis

Fas-associated protein with death domain (FADD) plays a key role in extrinsic apoptosis. Here, we show that FADD is SUMOylated as an essential step during intrinsic necrosis. FADD was modified at multiple lysine residues (K120/125/149) by small ubiquitin-related modifier 2 (SUMO2) during necrosis caused by calcium ionophore A23187 and by ischemic damage. SUMOylated FADD bound to dynamin-related protein 1 (Drp1) in cells both in vitro and in ischemic tissue damage cores, thus promoting Drp1 recruitment by mitochondrial fission factor (Mff) to accomplish mitochondrial fragmentation. Mitochondrial-fragmentation-associated necrosis was blocked by FADD or Drp1 deficiency and SUMO-defective FADD expression. Interestingly, caspase-10, but not caspase-8, formed a ternary protein complex with SUMO-FADD/Drp1 on the mitochondria upon exposure to A23187 and potentiated Drp1 oligomerization for necrosis. Moreover, the caspase-10 L285F and A414V mutants, found in autoimmune lymphoproliferative syndrome and non-Hodgkin lymphoma, respectively, regulated this necrosis. Our study reveals an essential role of SUMOylated FADD in Drp1- and caspase-10-dependent necrosis, providing insights into the mechanism of regulated necrosis by calcium overload and ischemic injury.

Involvement of necroptosis, a newly recognized cell death type, in steroid-induced osteonecrosis in a rabbit model

We investigated the role of programmed necrosis (necroptosis), a newly recognized form of cell necrosis that has been implicated in the development of steroid-induced osteonecrosis. We used an osteonecrosis model in which 30 Japanese white rabbits each weighing 3.5kg were injected once with methylprednisolone at 20 mg/kg body weight into the right gluteal muscle. Ten animals killed 14 days thereafter were designated as S14d groups, while another 10 animals injected with necroptosis, a specific inhibitor of necrostatin-1 i.v. at 1.65mg/kg on the same day as the steroid were also killed on the 14^th day and designated as SN14d group. As a control, 10 animals injected only with physiological saline were studied as N group. After the animals were sacrificed the bilateral femoral bone was examined histopathologically and the presence of osteonecrosis determined. Furthermore, animals subjected to the same treatment and killed on the 3^rd day after drug administration were set up as S3d group and SN3d group, and Western blotting of Receptor-interacting protein ( RIP ) 1 and RIP3 in femoral bone performed. The osteonecrosis rate was 70% in S14d group, and 0% in both N and SN groups. In 2 of 10 animals in SN group fatty marrow was found. On Western blotting significantly increased expression of both RIP1 and RIP3 was noted in S3d group, confirming that Nec-1 was suppressed. Necroptosis mediated by RIP1 and RIP3 expression was thought to be implicated in the development of steroid-induced osteonecrosis. Also, by suppressing expression of RIP1 and 3 with the administration of Nec-1 the osteonecrosis rate was significantly decreased. These results suggest that necroptosis may have potential as a novel target for both elucidating the mechanisms underlying steroid-induced osteonecrosis and establishing more effective prophylactic countermeasures.

Influenza virus infection induces translocation of apoptosis-inducing factor (AIF) in A549 cells: role of AIF in apoptosis and viral propagation

It is recognized that influenza virus induces caspase-dependent apoptosis by activating caspase-3. Apoptosis-inducing factor (AIF) is a caspase-independent cell death effector, and its mitochondrial-nuclear translocation plays an important role in apoptosis. It is demonstrated in this study how influenza virus infection can induce caspase-independent apoptosis in the human alveolar epithelial cell line A549. AIF is translocated from the mitochondria to the nucleus in a caspase-independent manner in response to infection with influenza virus. Knockdown of AIF expression by small interfering RNA (siRNA) led to a reduction in virus-infection-induced apoptosis and virus yield. These results indicate that AIF translocation has a role in influenza-virus-induced apoptosis.

Ferroptosis, a new form of cell death, and its relationships with tumourous diseases

Ferroptosis is a newly discovered type of cell death that differs from traditional apoptosis and necrosis and results from iron‐dependent lipid peroxide accumulation. Ferroptotic cell death is characterized by cytological changes, including cell volume shrinkage and increased mitochondrial membrane density. Ferroptosis can be induced by two classes of small‐molecule substances known as class 1 (system X_c⁻ inhibitors) and class 2 ferroptosis inducers [glutathione peroxidase 4 (GPx4) inhibitors]. In addition to these small‐molecule substances, a number of drugs (e.g. sorafenib, artemisinin and its derivatives) can induce ferroptosis. Various factors, such as the mevalonate (MVA) and sulphur‐transfer pathways, play pivotal roles in the regulation of ferroptosis. Ferroptosis plays an unneglectable role in regulating the growth and proliferation of some types of tumour cells, such as lymphocytoma, ductal cell cancer of the pancreas, renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). Here, we will first introduce the discovery of and research pertaining to ferroptosis; then summarize the induction mechanisms and regulatory pathways of ferroptosis; and finally, further elucidate the roles of ferroptosis in human tumourous diseases.

Cancer and necroptosis: friend or foe?

Regulated cell death is one major factor to ensure homoeostasis in multicellular organisms. For decades, apoptosis was considered as the sole form of regulated cell death, whereas necrosis was believed to be accidental and unregulated. Due to this view, research on necrosis was somewhat neglected, especially in the field of anti-cancer treatment. However, new interest in necrosis has been sparked by the recent discovery of different forms of necrosis that show indeed regulated pathways. More and more studies now address the molecular pathways of regulated necrosis and its connections within the cellular signaling networks. Necroptosis, a subform of regulated necrosis, has so far hardly been focused on with regard to a future treatment of cancer patients and may emerge as a novel and effective approach to eliminate tumor cells. However, and similar to apoptosis, tumor cells can develop resistances against necroptosis to ensure their own survival. In this context, new molecules that enhance necroptosis are currently being identified to overcome such resistances. This review discusses cancer and necroptosis as friends or foes, i.e. the options to exploit necroptosis in anti-cancer therapies ("foes"), but also potential limitations that may block or actually cause necroptosis to act in a protumoral manner ("friends"). The balance between these two possible roles will determine whether necroptosis can indeed be used as a promising tool for early diagnosis of tumors, prevention of metastasis and anti-cancer treatment.

Necrosome core machinery: MLKL

In the study of regulated cell death, the rapidly expanding field of regulated necrosis, in particular necroptosis, has been drawing much attention. The signaling of necroptosis represents a sophisticated form of a death pathway. Anti-caspase mechanisms (e.g., using inhibitors of caspases, or genetic ablation of caspase-8) switch cell fate from apoptosis to necroptosis. The initial extracellular death signals regulate RIP1 and RIP3 kinase activation. The RIP3-associated death complex assembly is necessary and sufficient to initiate necroptosis. MLKL was initially identified as an essential mediator of RIP1/RIP3 kinase-initiated necroptosis. Recent studies on the signal transduction using chemical tools and biomarkers support the idea that MLKL is able to make more functional sense for the core machinery of the necroptosis death complex, called the necrosome, to connect to the necroptosis execution. The experimental data available now have pointed that the activated MLKL forms membrane-disrupting pores causing membrane leakage, which extends the prototypical concept of morphological and biochemical events following necroptosis happening in vivo. The key role of MLKL in necroptosis signaling thus sheds light on the logic underlying this unique "membrane-explosive" cell death pathway. In this review, we provide the general concepts and strategies that underlie signal transduction of this form of cell death, and then focus specifically on the role of MLKL in necroptosis.

Control of adult neurogenesis by programmed cell death in the mammalian brain

The presence of neural stem cells (NSCs) and the production of new neurons in the adult brain have received great attention from scientists and the public because of implications to brain plasticity and their potential use for treating currently incurable brain diseases. Adult neurogenesis is controlled at multiple levels, including proliferation, differentiation, migration, and programmed cell death (PCD). Among these, PCD is the last and most prominent process for regulating the final number of mature neurons integrated into neural circuits. PCD can be classified into apoptosis, necrosis, and autophagic cell death and emerging evidence suggests that all three may be important modes of cell death in neural stem/progenitor cells. However, the molecular mechanisms that regulate PCD and thereby impact the intricate balance between self-renewal, proliferation, and differentiation during adult neurogenesis are not well understood. In this comprehensive review, we focus on the extent, mechanism, and biological significance of PCD for the control of adult neurogenesis in the mammalian brain. The role of intrinsic and extrinsic factors in the regulation of PCD at the molecular and systems levels is also discussed. Adult neurogenesis is a dynamic process, and the signals for differentiation, proliferation, and death of neural progenitor/stem cells are closely interrelated. A better understanding of how adult neurogenesis is influenced by PCD will help lead to important insights relevant to brain health and diseases.

Autophagy for the quality control of adult hippocampal neural stem cells

Autophagy plays an important role in neurodegeneration, as well as in normal brain development and function. Recent studies have also implicated autophagy in the regulation of stemness and neurogenesis in neural stem cells (NSCs). However, little is known regarding the roles of autophagy in NSC biology. It has been shown that in addition to cytoprotective roles of autophagy, pro-death autophagy, or ׳autophagic cell death (ACD),' regulates the quantity of adult NSCs. A tight regulation of survival and death of NSCs residing in the neurogenic niches through programmed cell death (PCD) is critical for maintenance of adult neurogenesis. ACD plays a primary role in the death of adult hippocampal neural stem (HCN) cells following insulin withdrawal. Despite the normal apoptotic capability of HCN cells, they are committed to death by autophagy following insulin withdrawal, suggesting the existence of a unique regulatory program that controls the mode of cell death. We propose that dual roles of autophagy for maintenance of NSC pluripotency, as well as for elimination of defective NSCs, may serve as a combined NSC quality control mechanism. This article is part of a Special Issue entitled SI:Autophagy.

Activation of necroptosis in multiple sclerosis

Multiple sclerosis (MS), a common neurodegenerative disease of the CNS, is characterized by the loss of oligodendrocytes and demyelination. Tumor necrosis factor α (TNF-α), a proinflammatory cytokine implicated in MS, can activate necroptosis, a necrotic cell death pathway regulated by RIPK1 and RIPK3 under caspase-8-deficient conditions. Here, we demonstrate defective caspase-8 activation, as well as activation of RIPK1, RIPK3, and MLKL, the hallmark mediators of necroptosis, in the cortical lesions of human MS pathological samples. Furthermore, we show that MS pathological samples are characterized by an increased insoluble proteome in common with other neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson’s disease (PD), and Huntington's disease (HD). Finally, we show that necroptosis mediates oligodendrocyte degeneration induced by TNF-α and that inhibition of RIPK1 protects against oligodendrocyte cell death in two animal models of MS and in culture. Our findings demonstrate that necroptosis is involved in MS and suggest that targeting RIPK1 may represent a therapeutic strategy for MS.

Necroptotic Cell Death Signaling and Execution Pathway: Lessons from Knockout Mice

Under stress conditions, cells in living tissue die by apoptosis or necrosis depending on the activation of the key molecules within a dying cell that either transduce cell survival or death signals that actively destroy the sentenced cell. Multiple extracellular (pH, heat, oxidants, and detergents) or intracellular (DNA damage and Ca(2+) overload) stress conditions trigger various types of the nuclear, endoplasmic reticulum (ER), cytoplasmatic, and mitochondrion-centered signaling events that allow cells to preserve the DNA integrity, protein folding, energetic, ionic and redox homeostasis, thus escaping from injury. Along the transition from reversible to irreversible injury, death signaling is highly heterogeneous and damaged cells may engage autophagy, apoptotic, or necrotic cell death programs. Studies on multiple double- and triple- knockout mice identified caspase-8, flip, and fadd genes as key regulators of embryonic lethality and inflammation. Caspase-8 has a critical role in pro- and antinecrotic signaling pathways leading to the activation of receptor interacting protein kinase 1 (RIPK1), RIPK3, and the mixed kinase domain-like (MLKL) for a convergent execution pathway of necroptosis or regulated necrosis. Here we outline the recent discoveries into how the necrotic cell death execution pathway is engaged in many physiological and pathological outcome based on genetic analysis of knockout mice.

Reactive oxygen species, heat stress and oxidative-induced mitochondrial damage. A review

In recent years there has been enormous interest in researching oxidative stress. Reactive oxygen species (ROS) are derived from the metabolism of oxygen as by-products of cell respiration, and are continuously produced in all aerobic organisms. Oxidative stress occurs as a consequence of an imbalance between ROS production and the available antioxidant defence against them. Nowadays, a variety of diseases and degenerative processes such as cancer, Alzheimer's and autoimmune diseases are mediated by oxidative stress. Heat stress was suggested to be an environmental factor responsible for stimulating ROS production because of similarities in responses observed following heat stress compared with that occurring following exposure to oxidative stress. This manuscript describes the main mitochondrial sources of ROS and the antioxidant defences involved to prevent oxidative damage in all the mitochondrial compartments. It also deals with discussions concerning the cytotoxic effect of heat stress, mitochondrial heat-induced alterations, as well as heat shock protein (HSP) expression as a defence mechanism.

The recent progress of the mechanism and regulation of tumor necrosis in colorectal cancer

In colorectal cancer (CRC), despite the complex inducing and regulating mechanism in necrosis progress, the prognostic value of tumor necrosis has been reported. It is generally recognized that necrosis is associated with many process involving severe hypoxia, inflammatory responses and angiogenesis, all of which contribute to promote tumor growth and poor prognosis. In addition to local hypoxia, regulation by RIP kinase and the conversion from apoptosis to necrosis can result in necrosis also. Recent studies showed necrosis can be a histopathologic characteristic for special molecular phenotype of CRC. A novel and attractive complementary treatment, tumor necrosis therapy, using radiolabelled compounds avid for necrosis has emerged. However, the complicated regulatory mechanisms of tumor necrosis were rarely reported in CRC, and we collected and reviewed these effect and relevance in CRC.

Efficient Multiple Genome Modifications Induced by the crRNAs, tracrRNA and Cas9 Protein Complex in Zebrafish

The type II clustered regularly interspaced short palindromic repeats (CRISPR) associated with Cas9 endonuclease (CRISPR/Cas9) has become a powerful genetic tool for understanding the function of a gene of interest. In zebrafish, the injection of Cas9 mRNA and guide-RNA (gRNA), which are prepared using an in vitro transcription system, efficiently induce DNA double-strand breaks (DSBs) at the targeted genomic locus. Because gRNA was originally constructed by fusing two short RNAs CRISPR RNA (crRNA) and trans-activating crRNA (tracrRNA), we examined the effect of synthetic crRNAs and tracrRNA with Cas9 mRNA or Cas9 protein on the genome editing activity. We previously reported that the disruption of tyrosinase (tyr) by tyr-gRNA/Cas9 mRNA causes a retinal pigment defect, whereas the disruption of spns2 by spns2-gRNA1/Cas9 mRNA leads to a cardiac progenitor migration defect in zebrafish. Here, we found that the injection of spns2-crRNA1, tyr-crRNA and tracrRNA with Cas9 mRNA or Cas9 protein simultaneously caused a migration defect in cardiac progenitors and a pigment defect in retinal epithelial cells. A time course analysis demonstrated that the injection of crRNAs and tracrRNA with Cas9 protein rapidly induced genome modifications compared with the injection of crRNAs and tracrRNA with Cas9 mRNA. We further show that the crRNA-tracrRNA-Cas9 protein complex is functional for the visualization of endogenous gene expression; therefore, this is a very powerful, ready-to-use system in zebrafish.

Sphingolipids as cell fate regulators in lung development and disease

Sphingolipids are a diverse class of signaling molecules implicated in many important aspects of cellular biology, including growth, differentiation, apoptosis, and autophagy. Autophagy and apoptosis are fundamental physiological processes essential for the maintenance of cellular and tissue homeostasis. There is great interest into the investigation of sphingolipids and their roles in regulating these key physiological processes as well as the manifestation of several disease states. With what is known to date, the entire scope of sphingolipid signaling is too broad, and a single review would hardly scratch the surface. Therefore, this review attempts to highlight the significance of sphingolipids in determining cell fate (e.g. apoptosis, autophagy, cell survival) in the context of the healthy lung, as well as various respiratory diseases including acute lung injury, acute respiratory distress syndrome, bronchopulmonary dysplasia, asthma, chronic obstructive pulmonary disease, emphysema, and cystic fibrosis. We present an overview of the latest findings related to sphingolipids and their metabolites, provide a short introduction to autophagy and apoptosis, and then briefly highlight the regulatory roles of sphingolipid metabolites in switching between cell survival and cell death. Finally, we describe functions of sphingolipids in autophagy and apoptosis in lung homeostasis, especially in the context of the aforementioned diseases.

Deletion of FADD in macrophages and granulocytes results in RIP3- and MyD88-dependent systemic inflammation

Myeloid cells, which include monocytes, macrophages, and granulocytes, are important innate immune cells, but the mechanism and downstream effect of their cell death on the immune system is not completely clear. Necroptosis is an alternate form of cell death that can be triggered when death receptor-mediated apoptosis is blocked, for example, in stimulated Fas-associated Death Domain (FADD) deficient cells. We report here that mice deficient for FADD in myeloid cells (mFADD^-/-) exhibit systemic inflammation with elevated inflammatory cytokines and increased levels of myeloid and B cell populations while their dendritic and T cell numbers are normal. These phenotypes were abolished when RIP3 deficiency was introduced, suggesting that systemic inflammation is caused by RIP3-dependent necroptotic and/or inflammatory activity. We further found that loss of MyD88 can rescue the systemic inflammation observed in these mice. These phenotypes are surprisingly similar to that of dendritic cell (DC)-specific FADD deficient mice with the exception that DC numbers are normal in mFADD^-/- mice. Together these data support the notion that innate immune cells are constantly being stimulated through the MyD88-dependent pathway and aberrations in their cell death machinery can result in systemic effects on the immune system.