Prevention of vertebrate neuronal death by the crmA gene

Microsporidian Nosema bombycis secretes serine protease inhibitor to suppress host cell apoptosis via Caspase BmICE

Microsporidia are a group of intracellular pathogens that actively manipulate host cell biological processes to facilitate their intracellular niche. Apoptosis is an important defense mechanism by which host cell control intracellular pathogens. Microsporidia modulating host cell apoptosis has been reported previously, however the molecular mechanism is not yet clear. In this report, we describe that the microsporidia Nosema bombycis inhibits apoptosis of Bombyx mori cells through a secreted protein NbSPN14, which is a serine protease inhibitor (Serpin). An immunofluorescent assay demonstrated that upon infection with N. bombycis, NbSPN14 was initially found in the B. mori cell cytoplasm and then became enriched in the host cell nucleus. Overexpression and RNA-interference (RNAi) of NbSPN14 in B. mori' embryo cell confirmed that NbSPN14 inhibited host cells apoptosis. Immunofluorescent and Co-IP assays verified the co-localization and interaction of NbSPN14 with the BmICE, the Caspase 3 homolog in B. mori. Knocking out of BmICE or mutating the BmICE-interacting P1 site of NbSPN14, eliminated the localization of NbSPN14 into the host nucleus and prevented the apoptosis-inhibiting effect of NbSPN14, which also proved that the interaction between BmICE and NbSPN14 occurred in host cytoplasm and the NbSPN14 translocation into host cell nucleus depends on BmICE. These data elucidate that N. bombycis secretory protein NbSPN14 inhibits host cell apoptosis by directly inhibiting the Caspase protease BmICE, which provides an important insight for understanding pathogen-host interactions and a potential therapeutic target for N. bombycis proliferation.

Cell death in development, maintenance, and diseases of the nervous system

Cell death, be it of neurons or glial cells, marks the development of the nervous system. Albeit relatively less so than in tissues such as the gut, cell death is also a feature of nervous system homeostasis-especially in context of adult neurogenesis. Finally, cell death is commonplace in acute brain injuries, chronic neurodegenerative diseases, and in some central nervous system tumors such as glioblastoma. Recent studies are enumerating the various molecular modalities involved in the execution of cells. Intimately linked with cell death are mechanisms of disposal that remove the dead cell and bring about a tissue-level response. Heretofore, the association between these methods of dying and physiological or pathological responses has remained nebulous. It is envisioned that careful cartography of death and disposal may reveal novel understandings of disease states and chart new therapeutic strategies in the near future.

LncRNA H19 initiates microglial pyroptosis and neuronal death in retinal ischemia/reperfusion injury

Ischemia-reperfusion (I/R) is a common pathology when the blood supply to an organ was disrupted and then restored. During the reperfusion process, inflammation and tissue injury were triggered, which were mediated by immunocytes and cytokines. However, the mechanisms initiating I/R-induced inflammation and driving immunocytes activation remained largely unknown. In this study, we identified long non-coding RNA (lncRNA)-H19 as the key onset of I/R-induced inflammation. We found that I/R increased lncRNA-H19 expression to significantly promote NLRP3/6 inflammasome imbalance and resulted in microglial pyroptosis, cytokines overproduction, and neuronal death. These damages were effectively inhibited by lncRNA-H19 knockout. Specifically, lncRNA-H19 functioned via sponging miR-21 to facilitate PDCD4 expression and formed a competing endogenous RNA network (ceRNET) in ischemic cascade. LncRNA H19/miR-21/PDCD4 ceRNET can directly regulate I/R-induced sterile inflammation and neuronal lesion in vivo. We thus propose that lncRNA-H19 is a previously unknown danger signals in the molecular and immunological pathways of I/R injury, and pharmacological approaches to inhibit H19 seem likely to become treatment modalities for patients in the near future based on these mechanistic findings.

Necroptosis and RIPK1-mediated neuroinflammation in CNS diseases

Apoptosis is crucial for the normal development of the nervous system, whereas neurons in the adult CNS are relatively resistant to this form of cell death. However, under pathological conditions, upregulation of death receptor family ligands, such as tumour necrosis factor (TNF), can sensitize cells in the CNS to apoptosis and a form of regulated necrotic cell death known as necroptosis that is mediated by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL). Necroptosis promotes further cell death and neuroinflammation in the pathogenesis of several neurodegenerative diseases, including multiple sclerosis, amyotrophic lateral sclerosis, Parkinson disease and Alzheimer disease. In this Review, we outline the evidence implicating necroptosis in these neurological diseases and suggest that targeting RIPK1 might help to inhibit multiple cell death pathways and ameliorate neuroinflammation.

Of Molecules and Mechanisms

Without question, molecular biology drives modern neuroscience. The past 50 years has been nothing short of revolutionary as key findings have moved the field from correlation toward causation. Most obvious are the discoveries and strategies that have been used to build tools for visualizing circuits, measuring activity, and regulating behavior. Less flashy, but arguably as important are the myriad investigations uncovering the actions of single molecules, macromolecular structures, and integrated machines that serve as the basis for constructing cellular and signaling pathways identified in wide-scale gene or RNA studies and for feeding data into informational networks used in systems biology. This review follows the pathways that were opened in neuroscience by major discoveries and set the stage for the next 50 years.

Caspase-3 Mediated Cell Death in the Normal Development of the Mammalian Cerebellum

Caspase-3, onto which there is a convergence of the intrinsic and extrinsic apoptotic pathways, is the main executioner of apoptosis. We here review the current literature on the intervention of the protease in the execution of naturally occurring neuronal death (NOND) during cerebellar development. We will consider data on the most common altricial species (rat, mouse and rabbit), as well as humans. Among the different types of neurons and glia in cerebellum, there is ample evidence for an intervention of caspase-3 in the regulation of NOND of the post-mitotic cerebellar granule cells (CGCs) and Purkinje neurons, as a consequence of failure to establish proper synaptic contacts with target (secondary cell death). It seems possible that the GABAergic interneurons also undergo a similar type of secondary cell death, but the intervention of caspase-3 in this case still remains to be clarified in full. Remarkably, CGCs also undergo primary cell death at the precursor/pre-migratory stage of differentiation, in this instance without the intervention of caspase-3. Glial cells, as well, undergo a process of regulated cell death, but it seems possible that expression of caspase-3, at least in the Bergmann glia, is related to differentiation rather than death.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Apoptotic Caspases: Multiple or Mistaken Identities?

The mitochondrial caspase cascade was originally thought to be required for apoptotic death driven by Bak/Bax-mediated intrinsic apoptosis. It has also been ascribed several 'non-apoptotic' functions, including differentiation, proliferation, and cellular reprogramming. Recent work has demonstrated that, during apoptosis, the caspase cascade suppresses damage-associated molecular pattern (DAMP)-initiated production of cytokines such as type I interferon by the dying cell. The caspase cascade is not required for death to occur; instead, it shapes the immunogenic properties of the apoptotic cell. This raises questions about the role of apoptotic caspases in regulating DAMP signaling more generally, puts a new perspective on their non-apoptotic functions, and suggests that pharmacological caspase inhibitors might find new applications as antiviral or anticancer agents.

Roles of Caspases in Necrotic Cell Death

Caspases were originally identified as important mediators of inflammatory response and apoptosis. Recent discoveries, however, have unveiled their roles in mediating and suppressing two regulated forms of necrotic cell death, termed pyroptosis and necroptosis, respectively. These recent advances have significantly expanded our understanding of the roles of caspases in regulating development, adult homeostasis, and host defense response.

Vaccinia virus evasion of regulated cell death

Regulated cell death is a powerful anti-viral mechanism capable of aborting the virus replicative cycle and alerting neighbouring cells to the threat of infection. The biological importance of regulated cell death is illustrated by the rich repertoire of host signalling cascades causing cell death and by the multiple strategies exhibited by viruses to block death signal transduction and preserve cell viability. Vaccinia virus (VACV), a poxvirus and the vaccine used to eradicate smallpox, encodes multiple proteins that interfere with apoptotic, necroptotic and pyroptotic signalling. Here the current knowledge on cell death pathways and how VACV proteins interact with them is reviewed. Studying the mechanisms evolved by VACV to counteract host programmed cell death has implications for its successful use as a vector for vaccination and as an oncolytic agent against cancer.

Viruses and the Diversity of Cell Death

Cell death is a common outcome of virus infection. In some cases, cell death curbs virus replication. In others, cell death enhances virus dissemination and contributes to tissue injury, exacerbating viral disease. Three forms of cell death are observed following virus infection-apoptosis, necroptosis, and pyroptosis. In this review, I describe the core machinery needed for each of these forms of cell death. Using representative viruses, I highlight how distinct stages of virus replication initiate signaling pathways that elicit these forms of cell death. I also discuss viral strategies to overcome the deleterious effects of cell death on virus propagation and the consequences of cell death for host physiology.

■ REVIEW : Excitotoxicity, Free Radicals, Necrosis, and Apoptosis

Recent studies have shown that excitotoxicity can result in either neuronal necrosis (passive cell lysis associated with energy failure) or apoptosis (active cell death requiring energy production). The type of cell death encountered by neuronal cell cultures exposed to excessive levels of excitatory amino acids—such as glutamate, the major excitatory neurotransmitter in the central nervous system, or free radicals, such as nitric oxide (NO) and superoxide anion (O2 -), which react to form peroxynitrite (ONOO-)—depends on the intensity of the exposure and may involve two temporally distinct phases. After relatively fulminant insults, an initial phase of necrosis—associated with extreme energy depletion—may simply reflect the failure of neurons to carry out the "default" apoptotic death program used to efficiently dispose of aged or otherwise unwanted cells. Neurons that survive this initial insult recover mitochondrial membrane potential and energy charge and subsequently undergo apoptosis, which seems to be associated with a factor(s) released from mitochondria. These factors have proteolytic activity or trigger the activation of proteases (caspases), ex ecutors of the cell death program. Thus, the maintenance of balanced energy production may be a decisive factor in determining the degree, type, and progression of neuronal injury caused by excitotoxins and free radicals. Increasing evidence suggests that similar events occur in vivo after ischemia or other insults, including Alzheimer's disease, Huntington's disease, and AIDS dementia. NEUROSCIENTIST 4:345-352, 1998

REVIEW ■ : Keeping Neurons Alive: The Molecular Control of Apoptosis (Part I

Apoptosis is a form of cellular suicide in which the cell activates an intrinsic program to bring about its own demise. Recognized for years as the mechanism by which developing cells are lost naturally, it has become apparent recently that this same process may play an important role in many acute and chronic diseases in which neural cell death occurs, such as stroke and Alzheimer's disease. This growing recognition suggests that a knowledge of the gene products controlling this process may lead to improved treatments for some disease states, as well as to improved understanding of neuronal development, physiology, and pathophysiology. Some controls with important roles in neural apoptosis have been identified, and these controls, as well as their putative mechanisms of action, are described in this article. NEUROSCIENTIST 2:181-190, 1996

Mononuclear Phagocyte-Derived Microparticulate Caspase-1 Induces Pulmonary Vascular Endothelial Cell Injury

Lung endothelial cell apoptosis and injury occurs throughout all stages of acute lung injury (ALI/ARDS) and impacts disease progression. Lung endothelial injury has traditionally been focused on the role of neutrophil trafficking to lung vascular integrin receptors induced by proinflammatory cytokine expression. Although much is known about the pathogenesis of cell injury and death in ALI/ARDS, gaps remain in our knowledge; as a result of which there is currently no effective pharmacologic therapy. Enzymes known as caspases are essential for completion of the apoptotic program and secretion of pro-inflammatory cytokines. We hypothesized that caspase-1 may serve as a key regulator of human pulmonary microvascular endothelial cell (HPMVEC) apoptosis in ALI/ARDS. Our recent experiments confirm that microparticles released from stimulated monocytic cells (THP1) induce lung endothelial cell apoptosis. Microparticles pretreated with the caspase-1 inhibitor, YVAD, or pan-caspase inhibitor, ZVAD, were unable to induce cell death of HPMVEC, suggesting the role of caspase-1 or its substrate in the induction of HPMVEC cell death. Neither un-induced microparticles (control) nor direct treatment with LPS induced apoptosis of HPMVEC. Further experiments showed that caspase-1 uptake into HPMVEC and the induction of HPMVEC apoptosis was facilitated by caspase-1 interactions with microparticulate vesicles. Altering vesicle integrity completely abrogated apoptosis of HPMVEC suggesting an encapsulation requirement for target cell uptake of active caspase-1. Taken together, we confirm that microparticle centered caspase-1 can play a regulator role in endothelial cell injury.

Sensory deprivation disrupts homeostatic regeneration of newly generated olfactory sensory neurons after injury in adult mice

Although it is well known that injury induces the generation of a substantial number of new olfactory sensory neurons (OSNs) in the adult olfactory epithelium (OE), it is not well understood whether olfactory sensory input influences the survival and maturation of these injury-induced OSNs in adults. Here, we investigated whether olfactory sensory deprivation affected the dynamic incorporation of newly generated OSNs 3, 7, 14, and 28 d after injury in adult mice. Mice were unilaterally deprived of olfactory sensory input by inserting a silicone tube into their nostrils. Methimazole, an olfactotoxic drug, was also injected intraperitoneally to bilaterally ablate OSNs. The OE was restored to its preinjury condition with new OSNs by day 28. No significant differences in the numbers of olfactory marker protein-positive mature OSNs or apoptotic OSNs were observed between the deprived and nondeprived sides 0-7 d after injury. However, between days 7 and 28, the sensory-deprived side showed markedly fewer OSNs and mature OSNs, but more apoptotic OSNs, than the nondeprived side. Intrinsic functional imaging of the dorsal surface of the olfactory bulb at day 28 revealed that responses to odor stimulation were weaker in the deprived side compared with those in the nondeprived side. Furthermore, prevention of cell death in new neurons 7-14 d after injury promoted the recovery of the OE. These results indicate that, in the adult OE, sensory deprivation disrupts compensatory OSN regeneration after injury and that newly generated OSNs have a critical time window for sensory-input-dependent survival 7-14 d after injury.

Neuronal cell death: an overview of its different forms in central and peripheral neurons

The discovery of neuronal cell death dates back to the nineteenth century. Nowadays, after a very long period of conceptual difficulties, the notion that cell death is a phenomenon occurring during the entire life course of the nervous system, from neurogenesis to adulthood and senescence, is fully established. The dichotomy between apoptosis, as the prototype of programmed cell death (PCD ), and necrosis, as the prototype of death caused by an external insult, must be carefully reconsidered, as different types of PCD: apoptosis, autophagy, pyroptosis, and oncosis have all been demonstrated in neurons (and glia ). These modes of PCD may be triggered by different stimuli, but share some intracellular pathways such that different types of cell death may affect the same population of neurons according to several intrinsic and extrinsic factors. Therefore, a mixed morphology is often observed also depending on degrees of differentiation, activity, and injury. The main histological and ultrastructural features of the different types of cell death in neurons are described and related to the cellular pathways that are specifically activated in any of these types of PCD.

Microvesicular caspase-1 mediates lymphocyte apoptosis in sepsis

Objective

Immune dysregulation during sepsis is poorly understood, however, lymphocyte apoptosis has been shown to correlate with poor outcomes in septic patients. The inflammasome, a molecular complex which includes caspase-1, is essential to the innate immune response to infection and also important in sepsis induced apoptosis. Our group has recently demonstrated that endotoxin-stimulated monocytes release microvesicles (MVs) containing caspase-1 that are capable of inducing apoptosis. We sought to determine if MVs containing caspase-1 are being released into the blood during human sepsis and induce apoptosis..

Design

Single-center cohort study

Measurements

50 critically ill patients were screened within 24 hours of admission to the intensive care unit and classified as either a septic or a critically ill control. Circulatory MVs were isolated and analyzed for the presence of caspase-1 and the ability to induce lymphocyte apoptosis. Patients remaining in the ICU for 48 hours had repeated measurement of caspase-1 activity on ICU day 3.

Main Results

Septic patients had higher microvesicular caspase-1 activity 0.05 (0.04, 0.07) AFU versus 0.0 AFU (0, 0.02) (p<0.001) on day 1 and this persisted on day 3, 0.12 (0.1, 0.2) versus 0.02 (0, 0.1) (p<0.001). MVs isolated from septic patients on day 1 were able to induce apoptosis in healthy donor lymphocytes compared with critically ill control patients (17.8±9.2% versus 4.3±2.6% apoptotic cells, p<0.001) and depletion of MVs greatly diminished this apoptotic signal. Inhibition of caspase-1 or the disruption of MV integrity abolished the ability to induce apoptosis.

Conclusion

These findings suggest that microvesicular caspase-1 is important in the host response to sepsis, at least in part, via its ability to induce lymphocyte apoptosis. The ability of microvesicles to induce apoptosis requires active caspase-1 and intact microvesicles.

JNK-mediated phosphorylation of DLK suppresses its ubiquitination to promote neuronal apoptosis

Neuronal injury induces JNK phosphorylation of DLK, which reduces DLK ubiquitination and creates a positive feedback loop to enhance JNK signaling and increase apoptosis.

Neurons are highly polarized cells that often project axons a considerable distance. To respond to axonal damage, neurons must transmit a retrograde signal to the nucleus to enable a transcriptional stress response. Here we describe a mechanism by which this signal is propagated through injury-induced stabilization of dual leucine zipper-bearing kinase (DLK/MAP3K12). After neuronal insult, specific sites throughout the length of DLK underwent phosphorylation by c-Jun N-terminal kinases (JNKs), which have been shown to be downstream targets of DLK pathway activity. These phosphorylation events resulted in increased DLK abundance via reduction of DLK ubiquitination, which was mediated by the E3 ubiquitin ligase PHR1 and the de-ubiquitinating enzyme USP9X. Abundance of DLK in turn controlled the levels of downstream JNK signaling and apoptosis. Through this feedback mechanism, the ubiquitin–proteasome system is able to provide an additional layer of regulation of retrograde stress signaling to generate a global cellular response to localized external insults.

The inflammasome as a target of modulation by DNA viruses

The cellular innate immune response represents the initial reaction of a host against infecting pathogens. Host cells detect incoming microbes by way of a large and expanding array of receptors that react with evolutionarily conserved molecular patterns exhibited by microbial intruders. These receptors are responsible for initiating signaling that leads to both transcriptional activation of immunologically important genes as well as protease-dependent processing of cellular proteins. The inflammasome refers to a protein complex that functions as an activation platform for the cysteine protease caspase-1, which then processes inflammatory molecules such as IL-1β and IL-18 into functional forms. Assembly of this complex is triggered following receptor-mediated detection of pathogen-associated molecules. Receptors have been identified that are essential to inflammasome activation in response to numerous molecular patterns including virus-associated molecules such as DNA. In fact, the importance of cytoplasmic DNA as an immune stimulus is exemplified by the existence of at least nine distinct cellular receptors capable of initiating innate reactivity in response to this molecule. Viruses that employ DNA as genomic material include herpesviruses, poxviruses and adenoviruses. Each has been described as capable of inducing inflammasome-mediated activity. Interestingly, however, the cellular molecules responsible for these responses appear to vary according to host species, cell type and even viral strain. Secretion of IL-1β and IL-18 are important components of antimicrobial immunity and, as a result, pathogens have evolved factors to evade or counteract this response. This includes DNA-based viruses, many of which encode multiple redundant counteractive molecules. However, it is clear that such phenotypes are only beginning to be uncovered. The purpose of this review is to describe what is known regarding the activation of inflammasome-mediated processes in response to infection with well-examined families of DNA viruses and to discuss characterized mechanisms of manipulation and neutralization of inflammasome-dependent activity. This review aims to shed light on the biologically important phenomena regarding this virus-host interaction and to highlight key areas where important information is lacking.

Lanthanum induced primary neuronal apoptosis through mitochondrial dysfunction modulated by Ca²⁺ and Bcl-2 family

As a representative element of lanthanide, lanthanum has been widely used in various fields and eventually entered environment and accumulated in human body. Epidemiological and experimental evidences indicated that lanthanum has neurotoxicity; however, the detailed mechanism is still elusive. Here, we chose primary cerebral cortical neurons as model in vitro to investigate the mechanism underlying the toxic effects of lanthanum chloride (LaCl3). This study revealed the following findings: (1) LaCl3 treatment (0.01, 0.1, and 1.0 mM for 24 h) reduced the viability of cortical neurons and elevated apoptotic rate significantly in a dose-dependent manner. (2) LaCl3 triggered mitochondrial apoptotic pathway in cortical neurons, characterized with collapsed mitochondrial membrane potential, release of cytochrome c into cytosol, and increasing expression of activated caspase-3. (3) LaCl3 elevated intracellular Ca(2+) concentration, promoted reactive oxygen species generation, and upregulated pro-apoptotic Bax, whereas it downregulated anti-apoptotic Bcl-2 expression and consequently altered Bax/Bcl-2 ratio, which ultimately lead to neuronal mitochondrial apoptosis. Our results demonstrated that toxicity of lanthanum in cortical neurons perhaps partly attributed to enhanced mitochondrial apoptosis due to mitochondrial dysfunction modulated by Ca(2+) and Bcl-2 family.

Regulation of proteases after spinal cord injury

Spinal cord injury is a major medical problem worldwide. Unfortunately, we still do not have suitable therapeutic agents for the treatment of spinal cord injury and prevention of its devastating consequences. Scientists and physicians are baffled by the challenges of controlling progressive neurodegeneration in spinal cord injury, which has not been healed with any currently-available treatments. Although extensive work has been carried out to better understand the pathophysiology of spinal cord injury, our current understanding of the repair mechanisms of secondary injury processes is still meager. Several investigators reported the crucial role played by various proteases after spinal cord injury. Understanding the beneficial and harmful roles these proteases play after spinal cord injury will allow scientists to plan and design appropriate treatment strategies to improve functional recovery after spinal cord injury. This review will focus on various proteases such as matrix metalloproteinases, cysteine proteases, and serine proteases and their inhibitors in the context of spinal cord injury.

Caspase-1: is IL-1 just the tip of the ICEberg?

Caspase-1, formerly known as interleukin (IL)-1-converting enzyme is best established as the protease responsible for the processing of the key pro-inflammatory cytokine IL-1β from an inactive precursor to an active, secreted molecule. Thus, caspase-1 is regarded as a key mediator of inflammatory processes, and has become synonymous with inflammation. In addition to the processing of IL-1β, caspase-1 also executes a rapid programme of cell death, termed pyroptosis, in macrophages in response to intracellular bacteria. Pyroptosis is also regarded as a host response to remove the niche of the bacteria and to hasten their demise. These processes are generally accepted as the main roles of caspase-1. However, there is also a wealth of literature supporting a direct role for caspase-1 in non-infectious cell death processes. This is true in mammals, but also in non-mammalian vertebrates where caspase-1-dependent processing of IL-1β is absent because of the lack of appropriate caspase-1 cleavage sites. This literature is most prevalent in the brain where caspase-1 may directly regulate neuronal cell death in response to diverse insults. We attempt here to summarise the evidence for caspase-1 as a cell death enzyme and propose that, in addition to the processing of IL-1β, caspase-1 has an important and a conserved role as a cell death protease.

Apoptotic and non-apoptotic roles of caspases in neuronal physiology and pathophysiology

Caspases are cysteine proteases that mediate apoptosis, which is a form of regulated cell death that effectively and efficiently removes extra and unnecessary cells during development. In the mature nervous system, caspases are not only involved in mediating cell death but also regulatory events that are important for neural functions, such as axon pruning and synapse elimination, which are necessary to refine mature neuronal circuits. Furthermore, caspases can be reactivated to cause cell death as well as non-lethal changes in neurons during numerous pathological processes. Thus, although a global activation of caspases leads to apoptosis, restricted and localized activation may control normal physiology and pathophysiology in living neurons. This Review explores the multiple roles of caspase activity in neurons.

Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012

In 2009, the Nomenclature Committee on Cell Death (NCCD) proposed a set of recommendations for the definition of distinct cell death morphologies and for the appropriate use of cell death-related terminology, including 'apoptosis', 'necrosis' and 'mitotic catastrophe'. In view of the substantial progress in the biochemical and genetic exploration of cell death, time has come to switch from morphological to molecular definitions of cell death modalities. Here we propose a functional classification of cell death subroutines that applies to both in vitro and in vivo settings and includes extrinsic apoptosis, caspase-dependent or -independent intrinsic apoptosis, regulated necrosis, autophagic cell death and mitotic catastrophe. Moreover, we discuss the utility of expressions indicating additional cell death modalities. On the basis of the new, revised NCCD classification, cell death subroutines are defined by a series of precise, measurable biochemical features.

Apoptotic caspases regulate induction of iPSCs from human fibroblasts

The molecular mechanisms involved in the derivation of induced pluripotent stem cells (iPSCs) from differentiated cells are poorly understood. Here we report that caspases 3 and 8, two proteases associated with apoptotic cell death, play critical roles in induction of iPSCs from human fibroblasts. Activation of caspases 3 and 8 occurs soon after transduction of iPSC-inducing transcription factors. Oct-4, a key iPSC transcription factor, is responsible for the activation. Inhibition of caspase 3 or 8 in human fibroblast cells partially or completely (respectively) prevents the induction of iPSCs. Furthermore, retinoblastoma susceptibility (Rb) protein appears to be one of the factors that act downstream of the caspases. We propose that caspases are key facilitators of nuclear reprogramming in iPSC induction.

Monocyte derived microvesicles deliver a cell death message via encapsulated caspase-1

Apoptosis depends upon the activation of intracellular caspases which are classically induced by either an intrinsic (mitochondrial based) or extrinsic (cytokine) pathway. However, in the process of explaining how endotoxin activated monocytes are able to induce apoptosis of vascular smooth muscle cells when co-cultured, we uncovered a transcellular apoptosis inducing pathway that utilizes caspase-1 containing microvesicles. Endotoxin stimulated monocytes induce the cell death of VSMCs but this activity is found in 100,000 g pellets of cell free supernatants of these monocytes. This activity is not a direct effect of endotoxin, and is inhibited by the caspase-1 inhibitor YVADcmk but not by inhibitors of Fas-L, IL-1beta and IL-18. Importantly, the apoptosis inducing activity co-purifies with 100 nm sized microvesicles as determined by TEM of the pellets. These microvesicles contain caspase-1 and caspase-1 encapsulation is required since disruption of microvesicular integrity destroys the apoptotic activity but not the caspase-1 enzymatic activity. Thus, monocytes are capable of delivering a cell death message which depends upon the release of microvesicles containing functional caspase-1. This transcellular apoptosis induction pathway describes a novel pathway for inflammation induced programmed cell death.

Stereological estimation of gap junction surface area per neuron in the developing nervous system of the invertebrate Mesocestoides corti

As a major morphological feature in establishing the form of the nervous system, it is recognized that neurons are initially overproduced, then naturally occurring cell death reduces the neuron number to the functional requirement. However, the mechanisms controlling the selective elimination of certain neurons during a general phase of cell death are not fully understood. One event that seems to be pivotal is the establishment of neural connections, the degree of which may be influential regarding the fate of specific neurons. However, little quantitative evidence is available to either support or refute this theory. In this current study, a Stereological measurement of gap junction per neuron was carried out within the invertebrate model system of the tapeworm metacestode Mesocestoides corti, which has previously been shown to overproduce neurons during the asexual reproduction stage of its life-cycle. Novel Stereological estimation methods with ‘ vertical sections’ indicated that prior to asexual division the cerebral ganglion possessed approximately 268 neurons, each with a gap junction surface area of 250 μm2. As division progressed, the neuron number increased to approximately 700, while the total surface area of gap junction remained statistically unchanged. As a result the surface area of gap junction per neuron decreased to 106 μm2, less than half that in the undividing stage. These results provide the first non-biased quantitative data regarding changes in the mean surface area of gap junction per neuron in a developing cerebral ganglion.

Cowpea bruchid midgut transcriptome response to a soybean cystatin--costs and benefits of counter-defence

The insect digestive system is the first line of defence protecting cells and tissues of the body from a broad spectrum of toxins and antinutritional factors in its food. To gain insight into the nature and breadth of genes involved in adaptation to dietary challenge, a collection of 20 352 cDNAs was prepared from the midgut tissue of cowpea bruchid larvae (Callosobruchus maculatus) fed on regular diet and diets containing antinutritional compounds. Transcript responses of the larvae to dietary soybean cystatin (scN) were analysed using cDNA microarrays, followed by quantitative real-time PCR (RT-PCR) confirmation with selected genes. The midgut transcript profile of insects fed a sustained sublethal scN dose over the larval life was compared with that of insects treated with an acute high dose of scN for 24 h. A total of 1756 scN-responsive cDNAs was sequenced; these clustered into 967 contigs, of which 653 were singletons. Many contigs (451) did not show homology with known genes, or had homology only with genes of unknown function in a Blast search. The identified differentially regulated sequences encoded proteins presumptively involved in metabolism, structure, development, signalling, defence and stress response. Expression patterns of some scN-responsive genes were consistent in each larval stage, whereas others exhibited developmental stage-specificity. Acute (24 h), high level exposure to dietary scN caused altered expression of a set of genes partially overlapping with the transcript profile seen under chronic lower level exposure. Protein and carbohydrate hydrolases were generally up-regulated by scN whereas structural, defence and stress-related genes were largely down-regulated. These results show that insects actively mobilize genomic resources in the alimentary tract to mitigate the impact of a digestive protease inhibitor. The enhanced or restored digestibility that may result is possibly crucial for insect survival, yet may be bought at the cost of weakened response to other stresses.

Regulation of caspase activation in apoptosis: implications for transformation and drug resistance

Recent developments in the apoptosis field have uncovered a family of cysteine proteases, the Caspases, that act as signalling components as well as effectors of the cell death machinery. Caspases are constitutively present as inactive precursors within most cells and undergo proteolytic processing in response to diverse death-inducing stimuli to initiate the death programme. Active caspases can process other caspases of the same type as well as process caspases further downstream in the pathway that ultimately leads to collapse of the cell. This cellular collapse is thought to occur as a consequence of caspase-mediated cleavage of a diverse array of cellular substrates. Regulation of entry into the death programme is controlled at a number of levels by members of the Bcl-2 family, as well as by other cell death regulatory proteins. Recent data has shed light upon the mechanism of action of these regulatory molecules and suggests that the point of caspase activation is a major checkpoint in the cell death programme. Because many transformed cell populations possess derangements in cell death-regulatory genes, such as bcl-2, such cells frequently exhibit elevated resistance to cytotoxic chemotherapy. Thus, a deeper understanding of how apoptosis is normally regulated has therapeutic implications for disease states where the normal controls on the cell death machinery have been subverted.

Inflammation in the nervous system--physiological and pathophysiological aspects

There is ample evidence for the occurrence of inflammatory processes in most major neurodegenerative disorders, both in acute conditions such as traumatic brain injury and stroke, and in chronic disorders such as Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis and Parkinson's disease. Studies on inflammatory factors such as pro- and antiinflammatory cytokines in experimental models of neurodegenerative disorders suggest that they are not merely bystanders, but may be involved in the neurodegenerative process. In addition, there are findings indicating that inflammatory factors may have beneficial effects on the nervous system, particularly during development of the nervous system. The challenge is to understand when, where and during which circumstances inflammation and inflammatory factors are positive or negative for neuronal survival and functioning. Some of our studies on cytokines, particularly the interleukin-1 system, are summarised and discussed in relation to neurodegeneration, cognition, and temperature changes.

Divergence from a dedicated cellular suicide mechanism: exploring the evolution of cell death

The developmental cell death in the nematode C. elegans is controlled by a simple and dedicated genetic program. This genetic program is evolutionarily conserved in higher organisms, including mammals. However, although mammalian homologs of C. elegans cell death gene products continue to regulate apoptosis, they are no longer dedicated regulators of cell death. On the other hand, multiple cellular noncell death-related mechanisms have been recruited to regulate cell death under different conditions. Such evidence suggests that evolution has led to an extensive integration of mammalian apoptosis machinery with multiple cellular physiological processes.

Caspase-1 regulates Escherichia coli sepsis and splenic B cell apoptosis independently of interleukin-1beta and interleukin-18

RATIONALE

Caspase-1 processes interleukin 1beta (IL-1beta) and IL-18 but may also contribute to apoptosis. In this context, caspase-1 knockout mice have been shown to be protected from endotoxin-induced mortality, whereas IL-1beta knockout mice are not protected.

OBJECTIVES

We therefore sought to delineate the mechanisms responsible for the differential responses between caspase-1 and IL-1beta knockout mice.

METHODS

Caspase-1 knockout, IL-1beta knockout, and IL-1beta/IL-18 double knockout mice were compared with wild-type mice for survival after intraperitoneal challenge with live Escherichia coli.

MEASUREMENTS AND MAIN RESULTS

Caspase-1 knockout animals were protected from bacterial challenge, whereas wild-type, IL-1beta knockout, and IL-1beta/IL-18 double knockout animals were not. Wild-type animals and both IL-1beta knockout and IL-1beta/IL-18 double knockout mice demonstrated significant splenic B lymphocyte apoptosis, which was absent in the caspase-1 knockout mice. Importantly, IL-1beta/IL-18 double knockout mice were protected from splenic cell apoptosis and sepsis-induced mortality by the caspase inhibitor zVAD-fmk. Furthermore, wild-type but not caspase-1 knockout splenic B lymphocytes induced peritoneal macrophages to assume an inhibitory phenotype.

CONCLUSION

Taken together, these findings suggest that caspase-1 is important in the host response to sepsis at least in part via its ability to regulate sepsis-induced splenic cell apoptosis.

A Novel Function of Plasminogen Activator Inhibitor-1 in Modulation of the AKT Pathway in Wild-type and Plasminogen Activator Inhibitor-1-deficient Endothelial Cells

Cell proliferation, an event associated with angiogenesis, involves coordinated activities of a number of proteins. The role of plasminogen activator inhibitor-1 (PAI-1) in angiogenesis remains controversial. Utilizing proliferating PAI-1-/- endothelial cells (EC), the impact of a host PAI-1 deficiency on Akt activation was evaluated. Hyperactivation of Akt(Ser(P)473) was observed in PAI-1-/- EC, and this was probably due to enhanced inactivation of tumor suppressor PTEN, thus rendering the cells resistant to apoptotic signals. Higher levels of inactivated caspase-9 in PAI-1-/- EC led to lower levels of procaspase-3 and cleaved caspase-3, thereby promoting survival. These effects were reversed when recombinant PAI-1 was added to PAI-1-/- EC. Additional studies demonstrated that regulation of proliferation is dependent on its interaction with low density lipoprotein receptor-related protein. Thus, PAI-1 is a negative regulator of cell growth, exerting its effect on the phosphatidylinositol 3-kinase/Akt pathway and allowing controlled cell proliferation.

Nedd4-WW domain-binding protein 5 (Ndfip1) is associated with neuronal survival after acute cortical brain injury

Understanding the transcriptional response to neuronal injury after trauma is a necessary prelude to formulation of therapeutic strategies. We used Serial Analysis of Gene Expression (SAGE) to identify 50,000 sequence tags representing 18,000 expressed genes in the cortex 2 h after traumatic brain injury (TBI). A similar tag library was obtained from sham-operated cortex. The SAGE data were validated on biological replicates using quantitative real-time-PCR on multiple samples at 2, 6, 12, and 24 h after TBI. This analysis revealed that the vast majority of genes showed a downward trend in their pattern of expression over 24 h. This was confirmed for a subset of genes using in situ hybridization and immunocytochemistry on brain sections. Of the overexpressed genes in the trauma library, Nedd4-WW (neural precursor cell expressed, developmentally downregulated) domain-binding protein 5 (N4WBP5) (also known as Ndfip1) is strongly expressed in surviving neurons around the site of injury. Overexpression of N4WBP5 in cultured cortical neurons increased the number of surviving neurons after gene transfection and growth factor starvation compared with control transfections. These results identify N4WBP5 as a neuroprotective protein and, based on its known interaction with the ubiquitin ligase Nedd4, would suggest protein ubiquitination as a possible survival strategy in neuronal injury.

Expression of c-Jun and Bcl-2 Family Proteins in Apoptotic Photoreceptors of RCS Rats

PURPOSE

To determine if c-Jun and Bcl-2 family proteins play a role in photoreceptor apoptosis in Royal College of Surgeons (RCS) rats.

METHODS

RCS and Sprague-Dawley rats were used. Cryosections of retinas harvested at various postnatal periods were immunostained with antibodies against c-Jun, Bcl-2, and Bax. Double staining with TdT-dUTP nick-end labeling (TUNEL) or propidium iodide (PI) and antibodies was also done. To study the time course of gene and protein expression, semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblotting analyses were carried out.

RESULTS

TUNEL-positive photoreceptors of RCS rats were stained strongly with antibodies against c-Jun and Bax. The number of immunoreactive cells increased on days 21 and 28 after birth (P21 and P28) and decreased on P45. Semiquantitative RT-PCR analysis showed that mRNAs for c-Jun and Bax were upregulated at P21 and P28, but those for Bcl-2 were unchanged. On immunoblotting, a 43-kDa band was revealed by the anti-c-Jun antibody and a 21-kDa band, by the anti-Bax antibody. Protein expression of c-Jun and Bax were increased at both P21 and P28. The temporal profiles of immunoreactivity, protein expression, and mRNA expression were similar.

CONCLUSION

c-Jun and Bax may play a role in photoreceptor apoptosis in RCS rats.

Signaling pathways and genes that inhibit pathogen-induced macrophage apoptosis--CREB and NF-kappaB as key regulators

Certain microbes evade host innate immunity by killing activated macrophages with the help of virulence factors that target prosurvival pathways. For instance, infection of macrophages with the TLR4-activating bacterium Bacillus anthracis triggers an apoptotic response due to inhibition of p38 MAP kinase activation by the bacterial-produced lethal toxin. Other pathogens induce macrophage apoptosis by preventing activation of NF-kappaB, which depends on IkappaB kinase beta (IKKbeta). To better understand how p38 and NF-kappaB maintain macrophage survival, we searched for target genes whose products prevent TLR4-induced apoptosis and a p38-dependent transcription factor required for their induction. Here we describe key roles for transcription factor CREB, a target for p38 signaling, and the plasminogen activator 2 (PAI-2) gene, a target for CREB, in maintenance of macrophage survival.

Pleiotropic mechanisms of virus survival and persistence

Viruses are enormously efficient infectious agents that have been implicated in causing human disease for centuries. Transmission of these pathogens continues to be from one life form to another in the form of isolated cases, epidemics, and pandemics. Each infection requires entry into a susceptible host, replication, and evasion of the immune system. Viruses are successful pathogens because they target specific cells for their attack, exploit the cellular machinery, and are efficient in circumventing and/or inhibiting key cellular events required of survival. This article reviews some of the advances that have taken place in human virology in the past 50 years, emphasizing mechanisms that contribute to, and are involved with, virus survival and persistence.

Insulin-like growth factor-I decreased etoposide-induced apoptosis in glioma cells by increasing bcl-2 expression and decreasing CPP32 activity

AIMS

In a variety of tumors, the susceptibility of the tumor cells to apoptotic cell death following chemotherapy is a major determinant of therapeutic outcome. Gliomas are resistant to most chemotherapeutic agents, and its mechanism is not known in detail. In an attempt to understand the mechanism of chemo-resistance, we investigated the roles of insulin-like growth factor-I (IGF-I), IGF-I receptors (IGF-IR), and their relationship with the apoptotic response of two glioma cell lines to etoposide, a chemotherapeutic agent for malignant gliomas.

METHODS

Two human glioma cell lines, U-87MG and KNS-42, were used. Etoposide-induced cell growth inhibition was quantified using a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide), colorimetric assay. Hoechst 33258 staining, DNA fragmentation assay, and western blot were used for the evaluation of apoptosis. ApoAlert caspase assay was used for measuring the activity of caspase-3 (CPP32) and interleukin-1 beta -converting enzyme (ICE) protease. In addition, the effect of IGF-IR antisense was tested in U-87MG and KNS-42 glioma cell lines.

RESULTS

Etoposide inhibited the growth of U-87MG and KNS-42 cells in a concentration-dependent manner. Etoposide increased the expression of wild-type p53, activated CPP32 (but not ICE) activity, and induced apoptosis in these cells. IGF-I prevented etoposide-induced apoptosis by increasing the expression of bcl-2 and decreasing the activity of CPP32. IGF-IR antisense enhanced the apoptotic effect of etoposide.

CONCLUSIONS

IGF-I decreased etoposide-induced apoptosis in glioma cells by increasing the expression of bcl-2 and decreasing the activity of CPP32. The antisense of IGF-IR increased etoposide-induced apoptosis. The anti-apoptotic effect of IGF-I and IGF-IR might be related to the chemo-resistance of glioma to chemotherapeutic agents.

Vascular low-flow malformations in children: current concepts for classification, diagnosis and therapy

Congenital vascular malformations (CVM) are made of dysplastic vessels with no cellular proliferation. Low- or slow-flow malformations (LFM) consist predominantly of venous and/or lymphatic vessels. Correct terminology is necessary for differentiating vascular malformations from tumours such as haemangiomas, in order to prevent ineffective or even adverse therapy. The role of the radiologist in the management of patients is two-fold: making the diagnosis with the use of ultrasound and magnetic resonance imaging, and performing sclerotherapy, which is the treatment of choice. Prior to sclerotherapy, percutaneous phlebography is necessary to visualize the dynamic situation inside the lesion and the flow into the adjacent vascular system. The double-needle technique is a useful therapy option reducing the risk of embolisation of the sclerosing agent. Large lesions might need subsequent surgical treatment. A multidisciplinary approach is substantial for optimal patient management.

The cowpox virus host range gene, CP77, affects phosphorylation of eIF2 alpha and vaccinia viral translation in apoptotic HeLa cells

Host restriction of vaccinia virus has been previously described in CHO and RK13 cells in which a cowpox virus CP77 gene rescues vaccinia virus growth at the viral protein translation level. Here we investigate the restrictive stage of vaccinia virus in HeLa cells using a vaccinia mutant virus (VV-hr) that contains a deletion of 18-kb genome sequences resulting in no growth in HeLa cells. Insertion of CP77 gene into VV-hr generated a recombinant virus (VV-36hr) that multiplied well in HeLa cells. Both viruses could enter cells, initiate viral DNA replication and intermediate gene transcription. However, translation of viral intermediate gene was only detected in cells infected with VV-36hr, indicating that CP77 relieves host restriction at the intermediate gene translation stage in HeLa cells. Caspase-2 and -3 activation was observed in HeLa cells infected with VV-hr coupled with dramatic morphological alterations and cleavage of the translation initiation factor eIF4G. Caspase activation was reduced in HeLa cells infected with VV-36hr, indicating that CP77 acts upstream of caspase activation. Enhanced phosphorylation of PKR and eIF2alpha was also observed in cells infected with VV-hr and was suppressed by CP77. Suppression of eIF4G cleavage with the caspase inhibitor ZVAD did not rescue virus translation, whereas expression of a mutant eIF2alpha protein with an alanine substitution of serine at amino acid position 51 (eIF2alphaS51A) partially restored viral translation and moderately increased virus growth in HeLa cells.