Dynamic role of postsynaptic caspase-3 and BIRC4 in zebra finch song-response habituation

An atlas of caspase cleavage events in differentiating muscle cells

Executioner caspases, such as caspase-3, are known to induce apoptosis, but in other contexts, they can control very different fates, including cell differentiation and neuronal plasticity. While hundreds of caspase substrates are known to be specifically targeted during cell death, we know very little about how caspase activity brings about non-apoptotic fates. Here, we report the first proteome identification of cleavage events in C2C12 cells undergoing myogenic differentiation and its comparison to undifferentiated or dying C2C12 cells. These data have identified new caspase substrates, including caspase substrates specifically associated with differentiation, and show that caspases are regulating proteins involved in myogenesis in myotubes, several days after caspase-3 initiated differentiation. Cytoskeletal proteins emerged as a major group of non-apoptotic caspase substrates. We also identified proteins with well-established roles in muscle differentiation as substrates cleaved in differentiating cells.

Exploring caspase functions in mouse models

Caspases are enzymes with protease activity. Despite being known for more than three decades, caspase investigation still yields surprising and fascinating information. Initially associated with cell death and inflammation, their functions have gradually been revealed to extend beyond, targeting pathways such as cell proliferation, migration, and differentiation. These processes are also associated with disease mechanisms, positioning caspases as potential targets for numerous pathologies including inflammatory, neurological, metabolic, or oncological conditions. While in vitro studies play a crucial role in elucidating molecular pathways, they lack the context of the body's complexity. Therefore, laboratory animals are an indispensable part of successfully understanding and applying caspase networks. This paper aims to summarize and discuss recent knowledge, understanding, and challenges in caspase knock-out mice.

Cleaved caspase-3 is present in the majority of glial cells in the intact rat spinal cord during postnatal life

Cell death is an essential process that occurs during the development of the central nervous system. Despite the availability of a wide range of commercially produced antibodies against various apoptotic markers, data regarding apoptosis in intact spinal cord during postnatal development and adulthood are mostly missing. We investigated apoptosis in rat spinal cord at different stages of ontogenesis (postnatal days 8, 29, and 90). For this purpose, we applied immunofluorescent detection of two widely used apoptotic markers, cleaved caspase-3 (cC3) and cleaved poly(ADP-ribose) polymerase (cPARP). Surprisingly, we found significant discrepancy between the number of cC3+ cells and PARP+ cells, with a ratio between 500:1 and 5000:1 in rat spinal cord at all postnatal time points. The majority of cC3+ cells were glial cells and did not exhibit an apoptotic phenotype. In contrast with in vivo results, in vitro analysis of primary cell cultures derived from neonatal rat spinal cord and treated with the apoptotic inductor staurosporine revealed a similar onset of occurrence of both cC3 and cPARP in cells subjected to apoptosis. Gene expression analysis of spinal cord revealed elevated expression of the Birc4 (XIAP), Birc2, and Birc5 (Survivin) genes, which are known potent inhibitors of apoptosis. Our data indicate that cC3 is not an exclusive marker of apoptosis, especially in glial cells, owing its possible presence in inhibited forms and/or its participation in other non-apoptotic roles. Therefore, cPARP appears to be a more appropriate marker to detect apoptosis.

Pathological Impact of Tau Proteolytical Process on Neuronal and Mitochondrial Function: a Crucial Role in Alzheimer's Disease

Tau protein plays a pivotal role in the central nervous system (CNS), participating in microtubule stability, axonal transport, and synaptic communication. Research interest has focused on studying the role of post-translational tau modifications in mitochondrial failure, oxidative damage, and synaptic impairment in Alzheimer's disease (AD). Soluble tau forms produced by its pathological cleaved induced by caspases could lead to neuronal injury contributing to oxidative damage and cognitive decline in AD. For example, the presence of tau cleaved by caspase-3 has been suggested as a relevant factor in AD and is considered a previous event before neurofibrillary tangles (NFTs) formation.Interestingly, we and others have shown that caspase-cleaved tau in N- or C- terminal sites induce mitochondrial bioenergetics defects, axonal transport impairment, neuronal injury, and cognitive decline in neuronal cells and murine models. All these abnormalities are considered relevant in the early neurodegenerative manifestations such as memory and cognitive failure reported in AD. Therefore, in this review, we will discuss for the first time the importance of truncated tau by caspases activation in the pathogenesis of AD and how its negative actions could impact neuronal function.

CASP3 gene expression and the role of caspase 3 in the pathogenesis of depressive disorders

BACKGROUND

The aim of our study was to evaluate the expression of the CASP3 gene at both mRNA and protein levels in patients with depressive disorders and to determine the impact of caspase 3 in the pathogenesis of depression; METHODS: A total of 290 subjects, including 190 depressed patients and 100 healthy controls, participated in the study. Socio-demographic and clinical data were collected, and the severity of depressive symptoms was assessed using the Hamilton Depression Rating Scale. Venous blood was collected and gene expression was evaluated using RT-PCR and ELISA at the mRNA and protein levels, respectively; RESULTS: The expression of the CASP3 gene was significantly lower in depressed patients compared to healthy controls at both the mRNA and protein levels. Additionally, a positive correlation was observed between CASP3 gene expression and disease duration as well as the number of depressive episodes; CONCLUSIONS: Further studies are needed to investigate the role of caspase 3 in depressive disorders.

Proteome integral solubility alteration high-throughput proteomics assay identifies Collectin-12 as a non-apoptotic microglial caspase-3 substrate

Caspases are a family of proteins mostly known for their role in the activation of the apoptotic pathway leading to cell death. In the last decade, caspases have been found to fulfill other tasks regulating the cell phenotype independently to cell death. Microglia are the immune cells of the brain responsible for the maintenance of physiological brain functions but can also be involved in disease progression when overactivated. We have previously described non-apoptotic roles of caspase-3 (CASP3) in the regulation of the inflammatory phenotype of microglial cells or pro-tumoral activation in the context of brain tumors. CASP3 can regulate protein functions by cleavage of their target and therefore could have multiple substrates. So far, identification of CASP3 substrates has been performed mostly in apoptotic conditions where CASP3 activity is highly upregulated and these approaches do not have the capacity to uncover CASP3 substrates at the physiological level. In our study, we aim at discovering novel substrates of CASP3 involved in the normal regulation of the cell. We used an unconventional approach by chemically reducing the basal level CASP3-like activity (by DEVD-fmk treatment) coupled to a Mass Spectrometry screen (PISA) to identify proteins with different soluble amounts, and consequently, non-cleaved proteins in microglia cells. PISA assay identified several proteins with significant change in their solubility after DEVD-fmk treatment, including a few already known CASP3 substrates which validated our approach. Among them, we focused on the Collectin-12 (COLEC12 or CL-P1) transmembrane receptor and uncovered a potential role for CASP3 cleavage of COLEC12 in the regulation of the phagocytic capacity of microglial cells. Taken together, these findings suggest a new way to uncover non-apoptotic substrates of CASP3 important for the modulation of microglia cell physiology.

Making the head: Caspases in life and death

The term apoptosis, as a way of programmed cell death, was coined a half century ago and since its discovery the process has been extensively investigated. The anatomy and physiology of the head are complex and thus apoptosis has mostly been followed in separate structures, tissues or cell types. This review aims to provide a comprehensive overview of recent knowledge concerning apoptosis-related molecules involved in the development of structures of head with a particular focus on caspases, cysteine proteases having a key position in apoptotic pathways. Since many classical apoptosis-related molecules, including caspases, are emerging in several non-apoptotic processes, these were also considered. The largest organ of the head region is the brain and its development has been extensively investigated, including the roles of apoptosis and related molecules. Neurogenesis research also includes sensory organs such as the eye and ear, efferent nervous system and associated muscles and glands. Caspases have been also associated with normal function of the skin and hair follicles. Regarding mineralised tissues within craniofacial morphogenesis, apoptosis in bones has been of interest along with palate fusion and tooth development. Finally, the role of apoptosis and caspases in angiogenesis, necessary for any tissue/organ development and maintenance/homeostasis, are discussed. Additionally, this review points to abnormalities of development resulting from improper expression/activation of apoptosis-related molecules.

Nonapoptotic caspases in neural development and in anesthesia-induced neurotoxicity

Apoptosis, classically initiated by caspase pathway activation, plays a prominent role during normal brain development as well as in neurodegeneration. The noncanonical, nonlethal arm of the caspase pathway is evolutionarily conserved and has also been implicated in both processes, yet is relatively understudied. Dysregulated pathway activation during critical periods of neurodevelopment due to environmental neurotoxins or exposure to compounds such as anesthetics can have detrimental consequences for brain maturation and long-term effects on behavior. In this review, we discuss key molecular characteristics and roles of the noncanonical caspase pathway and how its dysregulation may adversely affect brain development. We highlight both genetic and environmental factors that regulate apoptotic and sublethal caspase responses and discuss potential interventions that target the noncanonical caspase pathway for developmental brain injuries.

The Role of Caspase Family in Acute Brain Injury: The Potential Therapeutic Targets in the Future

The caspase family is commonly involved in the pathophysiology of acute brain injury (ABI) through complex apoptotic, pyroptotic, and inflammatory pathways. Current translational strategies for caspase modulation in ABI primarily focus on caspase inhibitors. Because there are no caspase-inhibiting drugs approved for clinical use on the market, the development of caspase inhibitors remains an attractive challenge for researchers and clinicians. Therefore, we conducted the present review with the aim of providing a comprehensive introduction of caspases in ABI. In this review, we summarized the available evidence and potential mechanisms regarding the biological function of caspases. We also reviewed the therapeutic effects of caspase inhibitors on ABI and its subsequent complications. However, various important issues remain unclear, prompting further verification of the efficacy and safety regarding clinical application of caspase inhibitors. We believe that our work will be helpful to further understand the critical role of the caspase family and will provide novel therapeutic potential for ABI treatment.

Non-Canonical Roles of Apoptotic Caspases in the Nervous System

Caspases are a family of cysteine proteases that predominantly cleave their substrates after aspartic acid residues. Much of what we know of caspases emerged from investigation a highly conserved form of programmed cell death called apoptosis. This form of cell death is regulated by several caspases, including caspase-2, caspase-3, caspase-7, caspase-8 and caspase-9. However, these “killer” apoptotic caspases have emerged as versatile enzymes that play key roles in a wide range of non-apoptotic processes. Much of what we understand about these non-apoptotic roles is built on work investigating how “killer” caspases control a range of neuronal cell behaviors. This review will attempt to provide an up to date synopsis of these roles.

Non-lethal message from the Holy Land: The first international conference on nonapoptotic roles of apoptotic proteins

Apoptosis is a major form of programmed cell death (PCD) that eliminates unnecessary and potentially dangerous cells in all metazoan organisms, thus ensuring tissue homeostasis and many developmental processes. Accordingly, defects in the activation of the apoptotic pathway often pave the way to disease. After several decades of intensive research, the molecular details controlling the apoptosis program have largely been unraveled, as well as the regulatory mechanisms of caspase activation during apoptosis. Nevertheless, an ever-growing list of studies is suggesting the essential role of caspases and other apoptotic proteins in ensuring nonlethal cellular functions during normal development, tissue repair, and regeneration. Moreover, if deregulated, these novel nonapoptotic functions can also instigate diseases. The difficulty of identifying and manipulating the caspase-dependent nonlethal cellular processes (CDPs), as well as the nonlethal functions of other cell death proteins (NLF-CDPs), meant that CDPs and NLF-CDPs have been only curiosities within the apoptotic field; however, the recent technical advancements and the latest biological findings are assigning an unanticipated biological significance to these nonapoptotic functions. Here, we summarize the various talks presented in the first international conference fully dedicated to discuss CDPs and NFL-CDPs and named 'The Batsheva de Rothschild Seminar on Non-Apoptotic Roles of Apoptotic Proteins'. The conference was organized between September 22, 2019, and 25, 2019, by Eli Arama (Weizmann Institute of Science), Luis Alberto Baena-Lopez (University of Oxford), and Howard O. Fearnhead (NUI Galway) at the Weizmann Institute of Science in Israel, and hosted a large international group of researchers.

Pro-caspase-3 is constitutively expressed in luteinized granulosa cells from women undergoing controlled ovarian stimulation for in vitro fertilization

Apoptosis regulation in luteinized granulosa cells (LGC) during assisted reproduction procedures is still controversial. Caspase-3 is a major apoptosis mediator encoded by CASP3 and formed through cleavage of its precursor pro-caspase-3. The aim of this study was to investigate the expression patterns of pro-caspase-3 (mRNA and protein) and cleaved caspase-3 in human LGC. Thirty-five women undergoing controlled ovarian stimulation for in vitro fertilization were prospectively enrolled in the study. LGC were isolated from follicular fluid during oocyte pickup and evaluated by immunocytochemistry for pro-caspase-3 and cleaved caspase-3, and by real-time PCR for CASP3 mRNA expression. We found a positive staining of pro-caspase-3 in 77 % of the LGC (95 % confidence interval [CI] 60%-84%), whereas cleaved caspase-3 was found in only 4% of the cells (95 % CI 3%-6%). The abundance of cells expressing pro-caspase-3 was independent from CASP3 mRNA levels (r = 0.24, p = 0.255) and did not correlate with the amount of cleaved caspase-3 (r = -0.24, p = 0.186). Multivariable logistic regression showed that pro-caspase-3 positivity was not influenced by clinical characteristics such as age, cause or length of infertility, antral follicle count or hormonal drugs used to induce ovulation. These findings suggest that pro-caspase-3 is constitutively expressed in LGC, allowing quick cleavage into active caspase-3 and apoptosis triggering whenever needed in the course of gonadotropin-induced follicular development.

Development or Disease: Caspases Balance Growth and Immunity in C. elegans

Caspase proteases execute apoptosis but also function in development. In this issue of Developmental Cell, Weaver et al. report that C. elegans CED-3 caspase promotes animal growth through PMK-1/p38 kinase cleavage, and at the expense of pathogen and stress immunity, revealing an unexpected homeostatic relationship between development and disease.

Non-apoptotic roles of apoptotic proteases: new tricks for an old dog

This Open Question article highlights current advances in the study of non-apoptotic roles of apoptotic proteins. Apoptosis is a highly regulated and energy-requiring process in which cells actively kill themselves. Apoptosis helps remove extra cells to sculpt organs during embryo development and culls damaged cells throughout the body. Apoptosis relies on evolutionarily conserved proteins that include a family of proteases called caspases. Caspases activity has long been considered a hallmark of apoptosis. Yet an emerging body of literature indicates that caspase activity is required for a number of non-lethal processes that range from sculpting cells, removing protein aggregates, changing cell identity during differentiation or de-differentiation, and rebuilding tissues. Failure in each of these processes is associated with human disease. This article is not meant to be an exhaustive review but an introduction to the subject for an educated public, with caspases as a gateway example. I propose that it is time to explore non-apoptotic roles of caspases and other apoptotic proteins, in order to better understand their non-apoptosis function and to leverage new knowledge into new therapies.

Cadmium induces mitochondrial ROS inactivation of XIAP pathway leading to apoptosis in neuronal cells

Cadmium (Cd), a heavy metal pollutant, contributes to neurodegenerative disorders. Recently, we have demonstrated that Cd induction of reactive oxygen species (ROS) causes apoptosis in neuronal cells. Whether X-linked inhibitor of apoptosis protein (XIAP) is involved in Cd-induced ROS-dependent neuronal apoptosis remains unclear. Here, we show that Cd-induced ROS reduced the expression of XIAP, which resulted in up-regulation of murine double minute 2 homolog (MDM2) and down-regulation of p53, leading to apoptosis in PC12 cells and primary neurons. Inhibition of MDM2 with Nutlin-3a reversed Cd-induced reduction of p53 and substantially rescued cells from excess ROS-dependent death. Overexpression of XIAP protected against Cd induction of ROS-dependent neuronal apoptosis. Inhibition of XIAP by Embelin strengthened Cd-induced ROS and apoptosis in the cells. Furthermore, we found that Cd inactivation of XIAP pathway was attributed to Cd induction of mitochondrial ROS, as evidenced by using a mitochondrial superoxide indicator MitoSOX and a mitochondria-targeted antioxidant Mito-TEMPO. Taken together, these results indicate that Cd induces mitochondrial ROS inactivation of XIAP-MDM2-p53 pathway leading to apoptosis in neuronal cells. Our findings suggest that activators of XIAP or modulation of XIAP-MDM2-p53 pathway by antioxidants may be exploited for the prevention of Cd-induced oxidative stress and neurodegenerative diseases.

Regulating Apoptosis by Degradation: The N-End Rule-Mediated Regulation of Apoptotic Proteolytic Fragments in Mammalian Cells

A pivotal hallmark of some cancer cells is the evasion of apoptotic cell death. Importantly, the initiation of apoptosis often results in the activation of caspases, which, in turn, culminates in the generation of proteolytically-activated protein fragments with potentially new or altered roles. Recent investigations have revealed that the activity of a significant number of the protease-generated, activated, pro-apoptotic protein fragments can be curbed via their selective degradation by the N-end rule degradation pathways. Of note, previous work revealed that several proteolytically-generated, pro-apoptotic fragments are unstable in cells, as their destabilizing N-termini target them for proteasomal degradation via the N-end rule degradation pathways. Remarkably, previous studies also showed that the proteolytically-generated anti-apoptotic Lyn kinase protein fragment is targeted for degradation by the UBR1/UBR2 E3 ubiquitin ligases of the N-end rule pathway in chronic myeloid leukemia cells. Crucially, the degradation of cleaved fragment of Lyn by the N-end rule counters imatinib resistance in these cells, implicating a possible linkage between the N-end rule degradation pathway and imatinib resistance. Herein, we highlight recent studies on the role of the N-end rule proteolytic pathways in regulating apoptosis in mammalian cells, and also discuss some possible future directions with respect to apoptotic proteolysis signaling.

Astrocytes and radial glia-like cells, but not neurons, display a nonapoptotic increase in caspase-3 expression following exercise

BACKGROUND

Exercise induces plasticity in the hippocampus, which includes increases in neurogenesis, the proliferation of new neurons, and angiogenesis, the sprouting of new capillaries from preexisting blood vessels. Following exercise, astrocytes also undergo morphological changes that parallel the events occurring in the neurovascular system. Interestingly, there have also been reports of apoptosis in the hippocampus following aerobic exercise. This experiment aimed to identify which population of hippocampal cells undergoes apoptosis after an acute bout of exercise.

METHODS

Cleaved caspase-3, a terminal protein in the apoptotic cascade, was initially used to identify apoptotic cells in the hippocampus after rats completed an acute bout of exercise. Next, the proportion of immature neurons, adult neurons, astrocytes, or radial glia-like cells expressing cleaved caspase-3 was quantified. TUNEL staining was completed as a second measure of apoptosis.

RESULTS

Following exercise, cleaved caspase-3 expression was increased in the CA1 and DG regions of the hippocampus. Cleaved caspase-3 was not highly expressed in neuronal populations, and expression was not increased in these cells postexercise. Instead, cleaved caspase-3 was predominantly expressed in astrocytes. Following exercise, there was an increased number of cleaved caspase-3 positive astrocytes in DG and CA1, and cleaved caspase-3 positive radial glia-like cells located in the subgranular zone. To determine whether cleaved caspase-3 expression in these glial cells was associated with apoptosis, a TUNEL assay was completed. TUNEL staining was negligible in all groups and did not mirror the pattern of caspase-3 labeling.

CONCLUSIONS

Cleaved caspase-3 expression was detected largely in non-neuronal cell populations, and the pattern of cleaved caspase-3 expression did not match that of TUNEL. This suggests that after exercise, cleaved caspase-3 expression may serve a nonapoptotic role in these hippocampal astrocytes and radial glia-like cells. It will be important to identify the function of exercise-induced cleaved caspase-3 expression in the future experiments.

Long-term Reductions in the Population of GABAergic Interneurons in the Mouse Hippocampus following Developmental Ethanol Exposure

Developmental exposure to ethanol leads to a constellation of cognitive and behavioral abnormalities known as Fetal Alcohol Spectrum Disorders (FASDs). Many cell types throughout the central nervous system are negatively impacted by gestational alcohol exposure, including inhibitory, GABAergic interneurons. Little evidence exists, however, describing the long-term impact of fetal alcohol exposure on survival of interneurons within the hippocampal formation, which is critical for learning and memory processes that are impaired in individuals with FASDs. Mice expressing Venus yellow fluorescent protein in inhibitory interneurons were exposed to vaporized ethanol during the third trimester equivalent of human gestation (postnatal days 2-9), and the long-term effects on interneuron numbers were measured using unbiased stereology at P90. In adulthood, interneuron populations were reduced in every hippocampal region examined. Moreover, we found that a single exposure to ethanol at P7 caused robust activation of apoptotic neurodegeneration of interneurons in the hilus, granule cell layer, CA1 and CA3 regions of the hippocampus. These studies demonstrate that developmental ethanol exposure has a long-term impact on hippocampal interneuron survivability, and may provide a mechanism partially explaining deficits in hippocampal function and hippocampus-dependent behaviors in those afflicted with FASDs.

Characterization of the caspase family in zebrafish

First discovered for their role in mediating programmed cell death and inflammatory responses, caspases have now emerged as crucial regulators of other cellular and physiological processes including cell proliferation, differentiation, migration, and survival. In the developing nervous system, for instance, the non-apoptotic functions of caspases have been shown to play critical roles in the formation of neuronal circuits by regulating axon outgrowth, guidance and pruning. How caspase activity is spatially and temporally maintained at sub-lethal levels within cells remains however poorly understood, especially in vivo. Thanks to its transparency and accessibility, the zebrafish offers the unique ability to directly visualize caspase activation in vivo. Yet, detailed information about the caspase family in zebrafish is lacking. Here, we report the identification and characterization of 19 different caspase genes in zebrafish, and show that caspases have diverse expression profiles from cleavage to larval stages, suggesting highly specialized and/or redundant functions during embryonic development.

Dendritic Spine Elimination: Molecular Mechanisms and Implications

Dynamic modification of synaptic connectivity in response to sensory experience is a vital step in the refinement of brain circuits as they are established during development and modified during learning. In addition to the well-established role for new spine growth and stabilization in the experience-dependent plasticity of neural circuits, dendritic spine elimination has been linked to improvements in learning, and dysregulation of spine elimination has been associated with intellectual disability and behavioral impairment. Proper brain function requires a tightly regulated balance between spine formation and spine elimination. Although most studies have focused on the mechanisms of spine formation, considerable progress has been made recently in delineating the neural activity patterns and downstream molecular mechanisms that drive dendritic spine elimination. Here, we review the current state of knowledge concerning the signaling pathways that drive dendritic spine shrinkage and elimination in the cerebral cortex and we discuss their implication in neuropsychiatric and neurodegenerative disease.

When dying is not the end: Apoptotic caspases as drivers of proliferation

Caspases are well known for their role as executioners of apoptosis. However, recent studies have revealed that these lethal enzymes also have important mitogenic functions. Caspases can promote proliferation through autonomous regulation of the cell cycle, as well as by induction of secreted signals, which have a profound impact in neighboring tissues. Here, I review the proliferative role of caspases during development and homeostasis, in addition to their key regenerative function during tissue repair upon injury. Furthermore, the emerging properties of apoptotic caspases as drivers of carcinogenesis are discussed, as well as their involvement in other diseases. Finally, I examine further effects of caspases regulating death and survival in a non-autonomous manner.

Physiological functions of non-apoptotic caspase activity in the nervous system

Caspases are cysteine proteases that play important and well-defined roles in apoptosis and inflammation. Increasing evidence point to alternative functions of caspases where restricted and localized caspase activation within neurons allows for a variety of non-apoptotic and non-inflammatory processes required for brain development and function. In this review, we highlight sublethal caspase functions in axon and dendrite pruning, neurite outgrowth and dendrite branches formation, as well as in long-term depression and synaptic plasticity. Importantly, as non-apoptotic activity of caspases is often confined in space and time in neurons, we also discuss the mechanisms that restrict caspase activity in order to maintain the neuronal networks in a healthy and functional state.

More alive than dead: non-apoptotic roles for caspases in neuronal development, plasticity and disease

Nervous systems are arguably the most fascinating and complex structures in the known universe. How they are built, changed by experience and then degenerate are some of the biggest questions in biology. Regressive phenomena, such as neuron pruning and programmed cell death, have a key role in the building and maintenance of the nervous systems. Both of these cellular mechanisms deploy the caspase family of protease enzymes. In this review, we highlight the non-apoptotic function of caspases during nervous system development, plasticity and disease, particularly focussing on their role in structural remodelling. We have classified pruning as either macropruning, where complete branches are removed, or micropruning, where individual synapses or dendritic spines are eliminated. Finally we discuss open questions and possible future directions within the field.

Characterization and functional analysis of two inhibitor of apoptosis genes in Zhikong scallop Chlamys farreri

The proteins of inhibitor of apoptosis (IAP) family play important roles in regulation of apoptosis, immunological response and cell proliferation. Here we reported two IAP genes (named CfIAP1 and CfIAP2) in Zhikong scallop Chlamys farreri. The full-length CfIAP1 cDNA contained 1552 nucleotides, encoding a predicted protein of 251 amino acids with two BIR domains. The full-length CfIAP2 cDNA contained 1243 nt, encoding a 356-aa protein with one BIR domain and one RING domain. The two genes are ubiquitously expressed in six types of tissue of C. farreri. The expression levels of CfIAP1 and CfIAP2 were significantly up-regulated after challenged with acute viral necrobiotic disease virus, lipopolysaccharide and exposure to air. Subcellular localization assay showed that CfIAP1 was mainly distributed in cytoplasm and CfIAP2 was in cytoplasm and nucleus. As assessed using a kit designed to test Caspase3 function in mammalian cells, the activity of CfCaspase3 was enhanced as a result of the down-regulation of CfIAP2 expression by dsRNA-mediated gene silencing. Our study indicated that CfIAP1 and CfIAP2 may participate in the innate immunity and stress responses and that CfIAP2 might block apoptosis via inhibiting CfCaspase3 indirectly through an unexplored mechanism in C. farreri.

The X-linked inhibitor of apoptosis regulates long-term depression and learning rate

Hippocampal long-term depression (LTD) is an active form of synaptic plasticity that is necessary for consolidation of spatial memory, contextual fear memory, and novelty acquisition. Recent studies have shown that caspases (CASPs) play an important role in NMDA receptor-dependent LTD and are involved in postsynaptic remodeling and synaptic maturation. In the present study, we examined the role of X-linked inhibitor of apoptosis (XIAP), a putative endogenous CASP inhibitor, in synaptic plasticity in the hippocampus. Analysis in acute brain slices and in cultured hippocampal neurons revealed that XIAP deletion increases CASP-3 activity, enhances α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor internalization, sharply increases LTD, and significantly reduces synapse density. In vivo behaviors related to memory were also altered in XIAP(-/-) mice, with faster acquisition of spatial object location and increased fear memory observed. Together, these results indicate that XIAP plays an important physiologic role in regulating sublethal CASP-3 activity within central neurons and thereby facilitates synaptic plasticity and memory acquisition.-Gibon, J., Unsain, N., Gamache, K., Thomas, R. A., De Leon, A., Johnstone, A., Nader, K., Séguéla, P., Barker, P. A. The X-linked inhibitor of apoptosis regulates long-term depression and learning rate.

A Krebs Cycle Component Limits Caspase Activation Rate through Mitochondrial Surface Restriction of CRL Activation

How cells avoid excessive caspase activity and unwanted cell death during apoptotic caspase-mediated removal of large cellular structures is poorly understood. We investigate caspase-mediated extrusion of spermatid cytoplasmic contents in Drosophila during spermatid individualization. We show that a Krebs cycle component, the ATP-specific form of the succinyl-CoA synthetase β subunit (A-Sβ), binds to and activates the Cullin-3-based ubiquitin ligase (CRL3) complex required for caspase activation in spermatids. In vitro and in vivo evidence suggests that this interaction occurs on the mitochondrial surface, thereby limiting the source of CRL3 complex activation to the vicinity of this organelle and reducing the potential rate of caspase activation by at least 60%. Domain swapping between A-Sβ and the GTP-specific SCSβ (G-Sβ), which functions redundantly in the Krebs cycle, show that the metabolic and structural roles of A-Sβ in spermatids can be uncoupled, highlighting a moonlighting function of this Krebs cycle component in CRL activation.

New Views on the Misconstrued: Executioner Caspases and Their Diverse Non-apoptotic Roles

Initially characterized for their roles in apoptosis, executioner caspases have emerged as important regulators of an array of cellular activities. This is especially true in the nervous system, where sublethal caspase activity has been implicated in axonal pathfinding and branching, axonal degeneration, dendrite pruning, regeneration, long-term depression, and metaplasticity. Here we examine the roles of sublethal executioner caspase activity in nervous system development and maintenance, consider the mechanisms that locally activate and restrain these potential killers, and discuss how their activity be subverted in neurodegenerative disease.

Mitochondrial Damage and Apoptosis Induced by Adenosine Deaminase Inhibition and Deoxyadenosine in Human Neuroblastoma Cell Lines

The treatment with deoxycoformycin, a strong adenosine deaminase inhibitor, in combination with deoxyadenosine, causes apoptotic cell death of two human neuroblastoma cell lines, SH-SY5Y and LAN5. Herein we demonstrate that, in SH-SY5Y cells, this combination rapidly decreases mitochondrial reactive oxygen species and, in parallel, increases mitochondrial mass, while, later, induces nuclear fragmentation, and activation of caspase-8, -9, and -3. In previous papers we have shown that a human astrocytoma cell line, subjected to the same treatment, undergoes apoptotic death as well. Therefore, both astrocytoma and neuroblastoma cell lines undergo apoptotic death following the combined treatment with deoxycoformycin and deoxyadenosine, but several differences have been found in the mode of action, possibly reflecting a different functional and metabolic profile of the two cell lines. Overall this work indicates that the neuroblastoma cell lines, like the line of astrocytic origin, are very sensitive to purine metabolism perturbation thus suggesting new therapeutic approaches to nervous system tumors. J. Cell. Biochem. 117: 1671-1679, 2016. © 2015 Wiley Periodicals, Inc.

The Cellular Apoptosis Susceptibility Protein (CAS) Promotes Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL)-induced Apoptosis and Cell Proliferation

A signature event during the cell intrinsic apoptotic pathway is mitochondrial outer membrane permeabilization, leading to formation of the apoptosome, a caspase activation complex. The cellular apoptosis susceptibility protein (CAS) can facilitate apoptosome assembly by stimulating nucleotide exchange on Apaf-1 following binding of cytochrome c. We report here that CAS expression itself is up-regulated during tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, and knockdown of CAS renders cells resistant to TRAIL. We find that TRAIL induces up-regulation of CAS in a posttranscriptional, caspase-8-dependent manner through degradation of cIAP1, an E3 ligase that targets CAS for ubiquitin-dependent proteasomal degradation. We identified a novel signaling pathway whereby caspase-8 engages a feedforward cascade that leads to CAS up-regulation and amplifies the apoptotic signal. Furthermore, in silico analysis revealed that expression of CAS is up-regulated at both the mRNA and DNA levels in human breast tumors, consistent with its role in promoting cell proliferation. Overexpression of various oncogenes led to CAS up-regulation in non-transformed cells. Intriguingly, oncogene-induced CAS up-regulation also resulted in greater susceptibility to TRAIL-induced cell death, consistent with its proapoptotic function. These findings suggest that CAS plays contrasting roles in proliferation and apoptosis and that overexpression of CAS in tumors could serve as a potential biomarker to guide therapeutic choices.

The Cell Death Pathway Regulates Synapse Elimination through Cleavage of Gelsolin in Caenorhabditis elegans Neurons

Synapse elimination occurs in development, plasticity, and disease. Although the importance of synapse elimination has been documented in many studies, the molecular mechanisms underlying this process are unclear. Here, using the development of C. elegans RME neurons as a model, we have uncovered a function for the apoptosis pathway in synapse elimination. We find that the conserved apoptotic cell death (CED) pathway and axonal mitochondria are required for the elimination of transiently formed clusters of presynaptic components in RME neurons. This function of the CED pathway involves the activation of the actin-filament-severing protein, GSNL-1. Furthermore, we show that caspase CED-3 cleaves GSNL-1 at a conserved C-terminal region and that the cleaved active form of GSNL-1 promotes its actin-severing ability. Our data suggest that activation of the CED pathway contributes to selective elimination of synapses through disassembly of the actin filament network.

Caspase-3 deficiency results in disrupted synaptic homeostasis and impaired attention control

The ability to attend to relevant stimuli and to adapt dynamically as demands change is a core aspect of cognition, and one that is impaired in several neuropsychiatric diseases, including attention deficit/hyperactivity disorder. However, the cellular and molecular mechanisms underlying such cognitive adaptability are poorly understood. We found that deletion of the caspase-3 gene, encoding an apoptosis protease with newly discovered roles in neural plasticity, disrupts attention in mice while preserving multiple learning and memory capabilities. Attention-related deficits include distractibility, impulsivity, behavioral rigidity, and reduced habituation to novel stimuli. Excess exploratory activity in Casp3(-/-) mice was correlated with enhanced novelty-induced activity in the dentate gyrus, which may be related to our findings that caspase-3 is required for homeostatic synaptic plasticity in vitro and homeostatic expression of AMPA receptors in vivo in response to chronic or repeated stimuli. These results suggest an important role for caspase-3 in synaptic suppression of irrelevant stimuli.

Interactions between mitochondria and the transcription factor myocyte enhancer factor 2 (MEF2) regulate neuronal structural and functional plasticity and metaplasticity

The classical view of mitochondria as housekeeping organelles acting in the background to simply maintain cellular energy demands has been challenged by mounting evidence of their direct and active participation in synaptic plasticity in neurons. Time-lapse imaging has revealed that mitochondria are motile in dendrites, with their localization and fusion and fission events regulated by synaptic activity. The positioning of mitochondria directly influences function of nearby synapses through multiple pathways including control over local concentrations of ATP, Ca(2+) and reactive oxygen species. Recent studies have also shown that mitochondrial protein cascades, classically associated with apoptosis, are involved in neural plasticity in healthy cells. These findings link mitochondria to the plasticity- and metaplasticity-associated activity-dependent transcription factor myocyte enhancer factor 2 (MEF2), further repositioning mitochondria as potential command centres for regulation of synaptic plasticity. Intriguingly, MEF2 and mitochondrial functions appear to be intricately intertwined, as MEF2 is a target of mitochondrial apoptotic caspases and, in turn, MEF2 regulates mitochondrial genome transcription essential for production of superoxidase and hydrogen peroxidase. Here, we review evidence supporting mitochondria as central organelles controlling the spatiotemporal expression of neuronal plasticity, and attempt to disentangle the MEF2-mitochondria relationship mediating these functions.

Caspases: therapeutic targets in neurologic disease

Specific therapies for neurologic diseases such as Alzheimer's disease provide the potential for better clinical outcomes. Expression of caspases in the brain is developmentally regulated, and dysregulated in neurologic disease, supporting that caspases may be therapeutic targets. The activity of caspases is carefully regulated via binding partners, cleavage, or endogenous inhibitors to prevent spontaneous activation, which could lead to aberrant cell death. This review serves as a brief examination of the current understanding of the regulation and function of caspases, and approaches to specifically target aberrant caspase activity. The use of proper tools to investigate individual caspases is addressed. Moreover, it summarizes the reports of various caspases in Alzheimer's disease studies. A better understanding of specific caspase pathways in heath and neurodegenerative disease is crucial for identifying specific targets for the development of therapeutic interventions.

Transcriptomic analysis unveils correlations between regulative apoptotic caspases and genes of cholesterol homeostasis in human brain

Regulative circuits controlling expression of genes involved in the same biological processes are frequently interconnected. These circuits operate to coordinate the expression of multiple genes and also to compensate dysfunctions in specific elements of the network. Caspases are cysteine-proteases with key roles in the execution phase of apoptosis. Silencing of caspase-2 expression in cultured glioblastoma cells allows the up-regulation of a limited number of genes, among which some are related to cholesterol homeostasis. Lysosomal Acid Lipase A (LIPA) was up-regulated in two different cell lines in response to caspase-2 down-regulation and cells silenced for caspase-2 exhibit reduced cholesterol staining in the lipid droplets. We expanded this observation by large-scale analysis of mRNA expression. All caspases were analyzed in terms of co-expression in comparison with 166 genes involved in cholesterol homeostasis. In the brain, hierarchical clustering has revealed that the expression of regulative apoptotic caspases (CASP2, CASP8 CASP9, CASP10) and of the inflammatory CASP1 is linked to several genes involved in cholesterol homeostasis. These correlations resulted in altered GBM (Glioblastoma Multiforme), in particular for CASP1. We have also demonstrated that these correlations are tissue specific being reduced (CASP9 and CASP10) or different (CASP2) in the liver. For some caspases (CASP1, CASP6 and CASP7) these correlations could be related to brain aging.

Non-apoptotic role of caspase-3 in synapse refinement

Caspases, a family of cysteine proteases, mediate programmed cell death during early neural development and neurodegeneration, as well as following neurotoxic insults. Notably, accumulating lines of evidence have shown non-apoptotic roles of caspases in the structural and functional plasticity of neuronal circuits under physiological conditions, such as growth-cone dynamics and axonal/dendritic pruning, as well as neuronal excitability and plasticity. Here, we summarize recent progress on the roles of caspases in synaptic refinement.

Caspase inhibition in select olfactory neurons restores innate attraction behavior in aged Drosophila

Sensory and cognitive performance decline with age. Neural dysfunction caused by nerve death in senile dementia and neurodegenerative disease has been intensively studied; however, functional changes in neural circuits during the normal aging process are not well understood. Caspases are key regulators of cell death, a hallmark of age-related neurodegeneration. Using a genetic probe for caspase-3-like activity (DEVDase activity), we have mapped age-dependent neuronal changes in the adult brain throughout the lifespan of Drosophila. Spatio-temporally restricted caspase activation was observed in the antennal lobe and ellipsoid body, brain structures required for olfaction and visual place memory, respectively. We also found that caspase was activated in an age-dependent manner in specific subsets of Drosophila olfactory receptor neurons (ORNs), Or42b and Or92a neurons. These neurons are essential for mediating innate attraction to food-related odors. Furthermore, age-induced impairments of neural transmission and attraction behavior could be reversed by specific inhibition of caspase in these ORNs, indicating that caspase activation in Or42b and Or92a neurons is responsible for altering animal behavior during normal aging.

Caspase-3 cleavage of dishevelled induces elimination of postsynaptic structures

During the development of vertebrate neuromuscular junction (NMJ), agrin stabilizes, whereas acetylcholine (ACh) destabilizes AChR clusters, leading to the refinement of synaptic connections. The intracellular mechanism underlying this counteractive interaction remains elusive. Here, we show that caspase-3, the effector protease involved in apoptosis, mediates elimination of AChR clusters. We found that caspase-3 was activated by cholinergic stimulation of cultured muscle cells without inducing cell apoptosis and that this activation was prevented by agrin. Interestingly, inhibition of caspase-3 attenuated ACh agonist-induced dispersion of AChR clusters. Furthermore, we identified Dishevelled1 (Dvl1), a Wnt signaling protein involved in AChR clustering, as the substrate of caspase-3. Blocking Dvl1 cleavage prevented induced dispersion of AChR clusters. Finally, inhibition or genetic ablation of caspase-3 or expression of a caspase-3-resistant form of Dvl1 caused stabilization of aneural AChR clusters. Thus, caspase-3 plays an important role in the elimination of postsynaptic structures during the development of NMJs.

Local caspase activation interacts with Slit-Robo signaling to restrict axonal arborization

In addition to being critical for apoptosis, components of the apoptotic pathway, such as caspases, are involved in other physiological processes in many types of cells, including neurons. However, very little is known about their role in dynamic, nonphysically destructive processes, such as axonal arborization and synaptogenesis. We show that caspases were locally active in vivo at the branch points of young, dynamic retinal ganglion cell axonal arbors but not in the cell body or in stable mature arbors. Caspase activation, dependent on Caspase-3, Caspase-9, and p38 mitogen-activated protein kinase (MAPK), rapidly increased at branch points corresponding with branch tip addition. Time-lapse imaging revealed that knockdown of Caspase-3 and Caspase-9 led to more stable arbors and presynaptic sites. Genetic analysis showed that Caspase-3, Caspase-9, and p38 MAPK interacted with Slit1a-Robo2 signaling, suggesting that localized activation of caspases lie downstream of a ligand receptor system, acting as key promoters of axonal branch tip and synaptic dynamics to restrict arbor growth in vivo in the central nervous system.

Plasma rich in growth factors (PRGF-Endoret) reduces neuropathologic hallmarks and improves cognitive functions in an Alzheimer's disease mouse model

Impaired growth factor function is thought to drive many of the alterations observed in Alzheimer's disease (AD) patients. Endogenous regenerative technology, PRGF (plasma rich in growth factor)-Endoret, is designed for the delivery of a complex pool of patient's own active morphogens that may stimulate tissue regeneration. We obtained and characterized PRGF-Endoret preparations from human blood. We used, as experimental approach in vivo, APP/PS1 mice, characterized by age-dependent brain amyloid-β (Aβ) accumulation. Intranasal administration of PRGF-Endoret to APP/PS1 mice resulted in an important decrease in brain Aβ deposition and tau phosphorylation. PRGF-Endoret-treated APP/PS1 mice also showed decreased astrocyte reactivity, and prevented protein synaptic loss. In vitro approaches demonstrated that PRGF-Endoret treatment modulated astrocyte activation, reducing inflammatory responses, and promoted Aβ degradation. Furthermore, PRGF-Endoret stimulated global improvements in anxiety, learning, and memory behaviors. Our findings show that PRGF-Endoret exerts multifunctional and complementary effects that result in the reversal of the broad range of cognitive deficits in AD, suggesting that PRGF-Endoret may hold promise as an innovative therapy in AD.

Long-term depression: a cell biological view

Recent studies of the molecular mechanisms of long-term depression (LTD) suggest a crucial role for the signalling pathways of apoptosis (programmed cell death) in the weakening and elimination of synapses and dendritic spines. With this backdrop, we suggest that LTD can be considered as the electrophysiological aspect of a larger cell biological programme of synapse involution, which uses localized apoptotic mechanisms to sculpt synapses and circuits without causing cell death.

Modulation of gene expression in contextual fear conditioning in the rat

In contextual fear conditioning (CFC) a single training leads to long-term memory of context-aversive electrical foot-shocks association. Mid-temporal regions of the brain of trained and naive rats were obtained 2 days after conditioning and screened by two-directional suppression subtractive hybridization. A pool of differentially expressed genes was identified and some of them were randomly selected and confirmed with qRT-PCR assay. These transcripts showed high homology for rat gene sequences coding for proteins involved in different cellular processes. The expression of the selected transcripts was also tested in rats which had freely explored the experimental apparatus (exploration) and in rats to which the same number of aversive shocks had been administered in the same apparatus, but temporally compressed so as to make the association between painful stimuli and the apparatus difficult (shock-only). Some genes resulted differentially expressed only in the rats subjected to CFC, others only in exploration or shock-only rats, whereas the gene coding for translocase of outer mitochondrial membrane 20 protein and nardilysin were differentially expressed in both CFC and exploration rats. For example, the expression of stathmin 1 whose transcripts resulted up regulated was also tested to evaluate the transduction and protein localization after conditioning.

Neuronal repair: Apoptotic proteins make good

The potential of the central nervous system (CNS) to regenerate is regulated by a complex interaction of neuronal intrinsic and extrinsic factors that remain poorly understood. Significant research has been dedicated to identifying these factors to facilitate design of therapies that will treat the functional impairment associated with CNS injuries. Over the last decade, the development of in vivo laser severing of single axons in C. elegans has established an invaluable model for the genetic identification of novel regeneration factors. In a recent study we report the unexpected identification of the core apoptotic proteins CED-4/Apaf-1 and the executioner caspase CED-3 as important factors that promote early events in regeneration in C. elegans. Other upstream regulators of apoptosis do not influence regeneration, indicating the existence of a novel mechanism for activation of CED-4 and CED-3 in neuronal repair. CED-4 and CED-3 function downstream of injury-induced calcium transients and appear to act through the conserved DLK-1 pathway to promote regeneration. We propose a working model for calcium-dependent localized activation of CED-4 and CED-3 caspase and discuss questions raised including mechanisms for spatially regulating activated CED-3 and the possible substrates that it might cleave to initiate regeneration.

The novel caspase-3 substrate Gap43 is involved in AMPA receptor endocytosis and long-term depression

The cysteine protease caspase-3, best known as an executioner of cell death in apoptosis, also plays a non-apoptotic role in N-methyl-d-aspartate receptor-dependent long-term depression of synaptic transmission (NMDAR-LTD) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor endocytosis in neurons. The mechanism by which caspase-3 regulates LTD and AMPA receptor endocytosis, however, remains unclear. Here, we addressed this question by using an enzymatic N-terminal peptide enrichment method and mass spectrometry to identify caspase-3 substrates in neurons. Of the many candidates revealed by this proteomic study, we have confirmed BASP1, Dbn1, and Gap43 as true caspase-3 substrates. Moreover, in hippocampal neurons, Gap43 mutants deficient in caspase-3 cleavage inhibit AMPA receptor endocytosis and LTD. We further demonstrated that Gap43, a protein well-known for its functions in axons, is also localized at postsynaptic sites. Our study has identified Gap43 as a key caspase-3 substrate involved in LTD and AMPA receptor endocytosis, uncovered a novel postsynaptic function for Gap43 and provided new insights into how long-term synaptic depression is induced.