Bax regulates neuronal Ca2+ homeostasis

Directly targeting BAX for drug discovery: Therapeutic opportunities and challenges

For over two decades, the development of B-cell lymphoma-2 (Bcl-2) family therapeutics has primarily focused on anti-apoptotic proteins, resulting in the first-in-class drugs called BH3 mimetics, especially for Bcl-2 inhibitor Venetoclax. The pro-apoptotic protein Bcl-2-associated X protein (BAX) plays a crucial role as the executioner protein of the mitochondrial regulated cell death, contributing to organismal development, tissue homeostasis, and immunity. The dysregulation of BAX is closely associated with the onset and progression of diseases characterized by pathologic cell survival or death, such as cancer, neurodegeneration, and heart failure. In addition to conducting thorough investigations into the physiological modulation of BAX, research on the regulatory mechanisms of small molecules identified through biochemical screening approaches has prompted the identification of functional and potentially druggable binding sites on BAX, as well as diverse all-molecule BAX modulators. This review presents recent advancements in elucidating the physiological and pharmacological modulation of BAX and in identifying potentially druggable binding sites on BAX. Furthermore, it highlights the structural and mechanistic insights into small-molecule modulators targeting diverse binding surfaces or conformations of BAX, offering a promising avenue for developing next-generation apoptosis modulators to treat a wide range of diseases associated with dysregulated cell death by directly targeting BAX.

A guide to cell death pathways

Regulated cell death mediated by dedicated molecular machines, known as programmed cell death, plays important roles in health and disease. Apoptosis, necroptosis and pyroptosis are three such programmed cell death modalities. The caspase family of cysteine proteases serve as key regulators of programmed cell death. During apoptosis, a cascade of caspase activation mediates signal transduction and cellular destruction, whereas pyroptosis occurs when activated caspases cleave gasdermins, which can then form pores in the plasma membrane. Necroptosis, a form of caspase-independent programmed necrosis mediated by RIPK3 and MLKL, is inhibited by caspase-8-mediated cleavage of RIPK1. Disruption of cellular homeostatic mechanisms that are essential for cell survival, such as normal ionic and redox balance and lysosomal flux, can also induce cell death without invoking programmed cell death mechanisms. Excitotoxicity, ferroptosis and lysosomal cell death are examples of such cell death modes. In this Review, we provide an overview of the major cell death mechanisms, highlighting the latest insights into their complex regulation and execution, and their relevance to human diseases.

Enlightening brain energy metabolism

Brain tissue metabolism is distributed across several cell types and subcellular compartments, which activate at different times and with different temporal patterns. The introduction of genetically-encoded fluorescent indicators that are imaged using time-lapse microscopy has opened the possibility of studying brain metabolism at cellular and sub-cellular levels. There are indicators for sugars, monocarboxylates, Krebs cycle intermediates, amino acids, cofactors, and energy nucleotides, which inform about relative levels, concentrations and fluxes. This review offers a brief survey of the metabolic indicators that have been validated in brain cells, with some illustrative examples from the literature. Whereas only a small fraction of the metabolome is currently accessible to fluorescent probes, there are grounds to be optimistic about coming developments and the application of these tools to the study of brain disease.

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

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

Advances in the knowledge on the role of apoptosis repressor with caspase recruitment domain in hemorrhagic stroke

The apoptosis repressor with caspase recruitment domain (ARC) plays a critical role in extrinsic apoptosis initiation via death receptor ligands, physiological stress, infection response in a tissue-dependent manner, endoplasmic reticulum (ER) stress, genotoxic drugs, ionizing radiation, oxidative stress, and hypoxia. Recent studies have suggested that regulating apoptosis-related pathways can improve outcomes for patients with neurological diseases, such as hemorrhagic stroke. ARC expression is significantly correlated with acute cerebral hemorrhage. However, the mechanism by which it mediates the anti-apoptosis pathway remains poorly known. Here, we discuss the function of ARC in hemorrhagic stroke and argue that it could serve as an effective target for the treatment of hemorrhagic stroke.

Systematic Review of the Therapeutic Role of Apoptotic Inhibitors in Neurodegeneration and Their Potential Use in Schizophrenia

Schizophrenia (SZ) is a deleterious brain disorder affecting cognition, emotion and reality perception. The most widely accepted neurochemical-hypothesis is the imbalance of neurotransmitter-systems. Depleted GABAergic-inhibitory function might produce a regionally-located dopaminergic and glutamatergic-storm in the brain. The dopaminergic-release may underlie the positive psychotic-symptoms while the glutamatergic-release could prompt the primary negative symptoms/cognitive deficits. This may occur due to excessive synaptic-pruning during the neurodevelopmental stages of adolescence/early adulthood. Thus, although SZ is not a neurodegenerative disease, it has been suggested that exaggerated dendritic-apoptosis could explain the limited neuroprogression around its onset. This apoptotic nature of SZ highlights the potential therapeutic action of anti-apoptotic drugs, especially at prodromal stages. If dysregulation of apoptotic mechanisms underlies the molecular basis of SZ, then anti-apoptotic molecules could be a prodromal therapeutic option to halt or prevent SZ. In fact, risk alleles related in apoptotic genes have been recently associated to SZ and shared molecular apoptotic changes are common in the main neurodegenerative disorders and SZ. PRISMA-guidelines were considered. Anti-apoptotic drugs are commonly applied in classic neurodegenerative disorders with promising results. Despite both the apoptotic-hallmarks of SZ and the widespread use of anti-apoptotic targets in neurodegeneration, there is a strikingly scarce number of studies investigating anti-apoptotic approaches in SZ. We analyzed the anti-apoptotic approaches conducted in neurodegeneration and the potential applications of such anti-apoptotic therapies as a promising novel therapeutic strategy, especially during early stages.

Brain milieu induces early microglial maturation through the BAX-Notch axis

Microglia are derived from primitive myeloid cells and gain their early identity in the embryonic brains. However, the mechanism by which the brain milieu confers microglial maturation signature remains elusive. Here, we demonstrate that the bax^cq55 zebrafish and Bax^tm1Sjk mouse embryos exhibit similarly defective early microglial maturation. BAX, a typical pro-apoptotic factor, is highly enriched in neuronal cells and regulates microglial maturation through both pro-apoptotic and non-apoptotic mechanisms. BAX regulates dlb via the CaMKII-CREB axis calcium-dependently in living neurons while ensuring the efficient Notch activation in the immigrated pre-microglia by apoptotic neurons. Notch signaling is conserved in supporting embryonic microglia maturation. Compromised microglial development occurred in the Cx3cr1^Cre/+Rbpj^fl/fl embryonic mice; however, microglia acquire their appropriate signature when incubated with DLL3 in vitro. Thus, our findings elucidate a BAX-CaMKII-CREB-Notch network triggered by the neuronal milieu in microglial development, which may provide innovative insights for targeting microglia in neuronal disorder treatment.

Visualizing physiological parameters in cells and tissues using genetically encoded indicators for metabolites

The study of metabolism is undergoing a renaissance. Since the year 2002, over 50 genetically-encoded fluorescent indicators (GEFIs) have been introduced, capable of monitoring metabolites with high spatial/temporal resolution using fluorescence microscopy. Indicators are fusion proteins that change their fluorescence upon binding a specific metabolite. There are indicators for sugars, monocarboxylates, Krebs cycle intermediates, amino acids, cofactors, and energy nucleotides. They permit monitoring relative levels, concentrations, and fluxes in living systems. At a minimum they report relative levels and, in some cases, absolute concentrations may be obtained by performing ad hoc calibration protocols. Proper data collection, processing, and interpretation are critical to take full advantage of these new tools. This review offers a survey of the metabolic indicators that have been validated in mammalian systems. Minimally invasive, these indicators have been instrumental for the purposes of confirmation, rebuttal and discovery. We envision that this powerful technology will foster metabolic physiology.

Calpain Inhibitors as Potential Therapeutic Modulators in Neurodegenerative Diseases

It is considered a significant challenge to understand the neuronal cell death mechanisms with a suitable cure for neurodegenerative disorders in the coming years. Calpains are one of the best-considered "cysteine proteases activated" in brain disorders. Calpain is an important marker and mediator in the pathophysiology of neurodegeneration. Calpain activation being the essential neurodegenerative factor causing apoptotic machinery activation, it is crucial to develop reliable and effective approaches to prevent calpain-mediated apoptosis in degenerating neurons. It has been recently seen that the "inhibition of calpain activation" has appeared as a possible therapeutic target for managing neurodegenerative diseases. A systematic literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was conducted. The present article reviews the basic pathobiology and role of selective calpain inhibitors used in various neurodegenerative diseases as a therapeutic target.

Optimization of Long-Term Human iPSC-Derived Spinal Motor Neuron Culture Using a Dendritic Polyglycerol Amine-Based Substrate

Human induced pluripotent stem cells (hiPSCs) derived from healthy and diseased individuals can give rise to many cell types, facilitating the study of mechanisms of development, human disease modeling, and early drug target validation. In this context, experimental model systems based on hiPSC-derived motor neurons (MNs) have been used to study MN diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis. Modeling MN disease using hiPSC-based approaches requires culture conditions that can recapitulate in a dish the events underlying differentiation, maturation, aging, and death of MNs. Current hiPSC-derived MN-based applications are often hampered by limitations in our ability to monitor MN morphology, survival, and other functional properties over a prolonged timeframe, underscoring the need for improved long-term culture conditions. Here we describe a cytocompatible dendritic polyglycerol amine (dPGA) substrate-based method for prolonged culture of hiPSC-derived MNs. We provide evidence that MNs cultured on dPGA-coated dishes are more amenable to long-term study of cell viability, molecular identity, and spontaneous network electrophysiological activity. The present study has the potential to improve hiPSC-based studies of human MN biology and disease.We describe the use of a new coating substrate providing improved conditions for long-term cultures of human iPSC-derived motor neurons, thus allowing evaluation of cell viability, molecular identity, spontaneous network electrophysiological activity, and single-cell RNA sequencing of mature motor neurons.

Mitochondrial Carrier Homolog 2 Functionally Co-operates With BH3 Interacting-Domain Death Agonist in Promoting Ca2+-Induced Neuronal Injury

The BH3 interacting-domain death agonist (BID) is a pro-apoptotic member of the Bcl-2 protein family. While proteolytic processing of BID links death receptor-induced apoptosis to the mitochondrial apoptosis pathway, we previously showed that full length BID also translocates to mitochondria during Ca²⁺-induced neuronal cell death. Moreover, mitochondrial carrier homolog 2 (MTCH2) was identified as a mitochondrial protein that interacts with BID during cell death. We started our studies by investigating the effect of Mtch2 silencing in a well-established model of Ca²⁺-induced mitochondrial permeability transition pore opening in non-neuronal HCT116 cells. We found that silencing of Mtch2 inhibited mitochondrial swelling and the associated decrease in mitochondrial energetics, suggesting a pro-death function for MTCH2 during Ca²⁺-induced injury. Next, we explored the role of BID and MTCH2 in mediating Ca²⁺-induced injury in primary cortical neurons triggered by prolonged activation of NMDA glutamate receptors. Analysis of intracellular Ca²⁺ transients, using time-lapse confocal microscopy, revealed that neurons lacking Bid showed markedly reduced Ca²⁺ levels during the NMDA excitation period. These Ca²⁺ transients were further decreased when Mtch2 was also silenced. Collectively, our data suggest that BID and MTCH2 functionally interact to promote Ca²⁺-induced neuronal injury.

Too much death can kill you: inhibiting intrinsic apoptosis to treat disease

Apoptotic cell death is implicated in both physiological and pathological processes. Since many types of cancerous cells intrinsically evade apoptotic elimination, induction of apoptosis has become an attractive and often necessary cancer therapeutic approach. Conversely, some cells are extremely sensitive to apoptotic stimuli leading to neurodegenerative disease and immune pathologies. However, due to several challenges, pharmacological inhibition of apoptosis is still only a recently emerging strategy to combat pathological cell loss. Here, we describe several key steps in the intrinsic (mitochondrial) apoptosis pathway that represent potential targets for inhibitors in disease contexts. We also discuss the mechanisms of action, advantages and limitations of small-molecule and peptide-based inhibitors that have been developed to date. These inhibitors serve as important research tools to dissect apoptotic signalling and may foster new treatments to reduce unwanted cell loss.

Pharmacological Targeting of Executioner Proteins: Controlling Life and Death

Small-molecule mediated modulation of protein interactions of Bcl-2 (B-cell lymphoma-2) family proteins was clinically validated in 2015 when Venetoclax, a selective inhibitor of the antiapoptotic protein BCL-2, achieved breakthrough status designation by the FDA for treatment of lymphoid malignancies. Since then, substantial progress has been made in identifying inhibitors of other interactions of antiapoptosis proteins. However, targeting their pro-apoptotic counterparts, the "executioners" BAX, BAK, and BOK that both initiate and commit the cell to dying, has lagged behind. However, recent publications demonstrate that these proteins can be positively or negatively regulated using small molecule tool compounds. The results obtained with these molecules suggest that pharmaceutical regulation of apoptosis will have broad implications that extend beyond activating cell death in cancer. We review recent advances in identifying compounds and their utility in the exogenous control of life and death by regulating executioner proteins, with emphasis on the prototype BAX.

The role of Bcl-2 proteins in modulating neuronal Ca2+ signaling in health and in Alzheimer's disease

The family of B-cell lymphoma-2 (Bcl-2) proteins exerts key functions in cellular health. Bcl-2 primarily acts in mitochondria where it controls the initiation of apoptosis. However, during the last decades, it has become clear that this family of proteins is also involved in controlling intracellular Ca2+ signaling, a critical process for the function of most cell types, including neurons. Several anti- and pro-apoptotic Bcl-2 family members are expressed in neurons and impact neuronal function. Importantly, expression levels of neuronal Bcl-2 proteins are affected by age. In this review, we focus on the emerging roles of Bcl-2 proteins in neuronal cells. Specifically, we discuss how their dysregulation contributes to the onset, development, and progression of neurodegeneration in the context of Alzheimer's disease (AD). Aberrant Ca2+ signaling plays an important role in the pathogenesis of AD, and we propose that dysregulation of the Bcl-2-Ca2+ signaling axis may contribute to the progression of AD and that herein, Bcl-2 may constitute a potential therapeutic target for the treatment of AD.

BCL(X)L and BCL2 increase the metabolic fitness of breast cancer cells: a single-cell imaging study

The BCL2 family of proteins regulate apoptosis by controlling mitochondrial outer membrane permeability. However, the effects on mitochondrial structure and bioenergetics have also been reported. Here we comprehensively characterized the effects of BCL2 and BCL(X)L on cellular energetics in MCF7 breast cancer cells using time-lapse confocal single-cell imaging and mitochondrial and cytosolic FRET reporters. We found that BCL2 and BCL(X)L increase the metabolic robustness of MCF7 cells, and that this was associated with increased mitochondrial NAD(P)H and ATP levels. Experiments with the F₁F₀ synthase inhibitor oligomycin demonstrated that BCL2 and in particular BCL(X)L, while not affecting ATP synthase activity, more efficiently coupled the mitochondrial proton motive force with ATP production. This metabolic advantage was associated with an increased resistance to nutrient deprivation and enhanced clonogenic survival in response to metabolic stress, in the absence of profound effects on cell death. Our data suggest that a primary function of BCL(X)L and BCL2 overexpression in tumor cells is to increase their resistance to metabolic stress in the tumor microenvironment, independent of cell death signaling.

Bcl-2 Family of Proteins in the Control of Mitochondrial Calcium Signalling: An Old Chap with New Roles

Bcl-2 family proteins are considered as one of the major regulators of apoptosis. Indeed, this family is known to control the mitochondrial outer membrane permeabilization (MOMP): a central step in the mitochondrial pathway of apoptosis. However, in recent years Bcl-2 family members began to emerge as a new class of intracellular calcium (Ca²⁺) regulators. At mitochondria-ER contacts (MERCs) these proteins are able to interact with major Ca²⁺ transporters, thus controlling mitochondrial Ca²⁺ homeostasis and downstream Ca²⁺ signalling pathways. Beyond the regulation of cell survival, this Bcl-2-dependent control over the mitochondrial Ca²⁺ dynamics has far-reaching consequences on the physiology of the cell. Here, we review how the Bcl-2 family of proteins mechanistically regulate mitochondrial Ca²⁺ homeostasis and how this regulation orchestrates cell death/survival decisions as well as the non-apoptotic process of cell migration.

Excitotoxicity Revisited: Mitochondria on the Verge of a Nervous Breakdown

Excitotoxicity is likely to occur in pathological scenarios in which mitochondrial function is already compromised, shaping neuronal responses to glutamate. In fact, mitochondria sustain cell bioenergetics, tune intracellular Ca²⁺ dynamics, and regulate glutamate availability by using it as metabolic substrate. Here, we suggest the need to explore glutamate toxicity in the context of specific disease models in which it may occur, re-evaluating the impact of mitochondrial dysfunction on glutamate excitotoxicity. Our aim is to signpost new approaches, perhaps combining glutamate and pathways to rescue mitochondrial function, as therapeutic targets in neurological disorders.

Neuronal cell life, death, and axonal degeneration as regulated by the BCL-2 family proteins

Axonal degeneration and neuronal cell death are fundamental processes in development and contribute to the pathology of neurological disease in adults. Both processes are regulated by BCL-2 family proteins which orchestrate the permeabilization of the mitochondrial outer membrane (MOM). MOM permeabilization (MOMP) results in the activation of pro-apoptotic molecules that commit neurons to either die or degenerate. With the success of small-molecule inhibitors targeting anti-apoptotic BCL-2 proteins for the treatment of lymphoma, we can now envision the use of inhibitors of apoptosis with exquisite selectivity for BCL-2 family protein regulation of neuronal apoptosis in the treatment of nervous system disease. Critical to this development is deciphering which subset of proteins is required for neuronal apoptosis and axon degeneration, and how these two different outcomes are separately regulated. Moreover, noncanonical BCL-2 family protein functions unrelated to the regulation of MOMP, including impacting necroptosis and other modes of cell death may reveal additional potential targets and/or confounders. This review highlights our current understanding of BCL-2 family mediated neuronal cell death and axon degeneration, while identifying future research questions to be resolved to enable regulating neuronal survival pharmacologically.

Calcium Export from Neurons and Multi-Kinase Signaling Cascades Contribute to Ouabain Neuroprotection in Hyperhomocysteinemia

Pathological homocysteine (HCY) accumulation in the human plasma, known as hyperhomocysteinemia, exacerbates neurodegenerative diseases because, in the brain, this amino acid acts as a persistent N-methyl-d-aspartate receptor agonist. We studied the effects of 0.1–1 nM ouabain on intracellular Ca²⁺ signaling, mitochondrial inner membrane voltage (φ_mit), and cell viability in primary cultures of rat cortical neurons in glutamate and HCY neurotoxic insults. In addition, apoptosis-related protein expression and the involvement of some kinases in ouabain-mediated effects were evaluated. In short insults, HCY was less potent than glutamate as a neurotoxic agent and induced a 20% loss of φ_mit, whereas glutamate caused a 70% decrease of this value. Subnanomolar ouabain exhibited immediate and postponed neuroprotective effects on neurons. (1) Ouabain rapidly reduced the Ca²⁺ overload of neurons and loss of φ_mit evoked by glutamate and HCY that rescued neurons in short insults. (2) In prolonged 24 h excitotoxic insults, ouabain prevented neuronal apoptosis, triggering proteinkinase A and proteinkinase C dependent intracellular neuroprotective cascades for HCY, but not for glutamate. We, therefore, demonstrated here the role of PKC and PKA involving pathways in neuronal survival caused by ouabain in hyperhomocysteinemia, which suggests existence of different appropriate pharmacological treatment for hyperhomocysteinemia and glutamate excitotoxicity.

Characterization of Human iPSC-derived Spinal Motor Neurons by Single-cell RNA Sequencing

Human induced pluripotent stem cells (iPSCs) offer the opportunity to generate specific cell types from healthy and diseased individuals, allowing the study of mechanisms of early human development, modelling a variety of human diseases, and facilitating the development of new therapeutics. Human iPSC-based applications are often limited by the variability among iPSC lines originating from a single donor, as well as the heterogeneity among specific cell types that can be derived from iPSCs. The ability to deeply phenotype different iPSC-derived cell types is therefore of primary importance to the successful and informative application of this technology. Here we describe a combination of motor neuron (MN) derivation and single-cell RNA sequencing approaches to generate and characterize specific MN subtypes obtained from human iPSCs. Our studies provide evidence for rapid and robust generation of MN progenitor cells that can give rise to a heterogenous population of MNs. Approximately 58% of human iPSC-derived MNs display molecular characteristics of lateral motor column MNs, with a number of molecularly distinct subpopulations present within this MN group. Roughly 19% of induced MNs resemble hypaxial motor column MNs, while ∼6% of induced MNs have features of median motor column MNs. The present study has the potential to improve our understanding of iPSC-derived MN subtype function and dysfunction, possibly leading to improved iPSC-based applications for the study of human MN biology and disease.

Mitochondrial MPTP: A Novel Target of Ethnomedicine for Stroke Treatment by Apoptosis Inhibition

Mammalian mitochondrial permeability transition pore (MPTP), across the inner and outer membranes of mitochondria, is a nonspecific channel for signal transduction or material transfer between mitochondrial matrix and cytoplasm such as maintenance of Ca²⁺ homeostasis, regulation of oxidative stress signals, and protein translocation evoked by some of stimuli. Continuous MPTP opening has been proved to stimulate neuronal apoptosis in ischemic stroke. Meanwhile, inhibition of MPTP overopening-induced apoptosis has shown excellent efficacy in the treatment of ischemic stroke. Among of which, the potential molecular mechanisms of drug therapy for stroke has also been gradually revealed by researchers. The characteristics of multi-components or multi-targets for ethnic drugs also provide the possibility to treat stroke from the perspective of mitochondrial MPTP. The advantages mentioned above make it necessary for us to explore and clarify the new perspective of ethnic medicine in treating stroke and to determine the specific molecular mechanisms through advanced technologies as much as possible. In this review, we attempt to uncover the relationship between abnormal MPTP opening and neuronal apoptosis in ischemic stroke. We further summarized currently authorized drugs, ethnic medicine prescriptions, herbs, and identified monomer compounds for inhibition of MPTP overopening-induced ischemic neuron apoptosis. Finally, we strive to provide a new perspective and enlightenment for ethnic medicine in the prevention and treatment of stroke by inhibition of MPTP overopening-induced neuronal apoptosis.

L-type Ca2+ channel-mediated Ca2+ influx adjusts neuronal mitochondrial function to physiological and pathophysiological conditions

L-type voltage-gated Ca2+ channels (LTCCs) are implicated in neurodegenerative processes and cell death. Accordingly, LTCC antagonists have been proposed to be neuroprotective, although this view is disputed, because intentional LTCC activation can also have beneficial effects. LTCC-mediated Ca2+ influx influences mitochondrial function, which plays a crucial role in the regulation of cell viability. Hence, we investigated the effect of modulating LTCC-mediated Ca2+ influx on mitochondrial function in cultured hippocampal neurons. To activate LTCCs, neuronal activity was stimulated by increasing extracellular K+ or by application of the GABAA receptor antagonist bicuculline. The activity of LTCCs was altered by application of an agonistic (Bay K8644) or an antagonistic (isradipine) dihydropyridine. Our results demonstrated that activation of LTCC-mediated Ca2+ influx affected mitochondrial function in a bimodal manner. At moderate stimulation strength, ATP synthase activity was enhanced, an effect that involved Ca2+-induced Ca2+ release from intracellular stores. In contrast, high LTCC-mediated Ca2+ loads led to a switch in ATP synthase activity to reverse-mode operation. This effect, which required nitric oxide, helped to prevent mitochondrial depolarization and sustained increases in mitochondrial Ca2+ Our findings indicate a complex role of LTCC-mediated Ca2+ influx in the tuning and maintenance of mitochondrial function. Therefore, the use of LTCC inhibitors to protect neurons from neurodegeneration should be reconsidered carefully.

NDRG4 prevents cerebral ischemia/reperfusion injury by inhibiting neuronal apoptosis

Cerebral ischemia is a major cause of mortality and long-term morbidity worldwide. NDRG4 has been shown to protect against cerebral ischemia, although the underlying mechanisms remain largely unclear. Here we found that NDRG4 expression was decreased in the brain tissues of ischemia/reperfusion (IR) rats, indicating increased apoptosis rates among cerebral cells. NDRG4 restoration via an adenovirus significantly attenuated cerebral infarct sizes and impairments in IR rats. Furthermore, adenovirus-mediated NDRG4 inhibited cell apoptosis in the brains of IR rats and regulated the expression of Bcl-2, Bax, caspase-3, and c-Fos. Moreover, we found that NDRG4 increased expression of BDNF, which is strongly related to cerebral ischemia and cellular apoptosis. Altogether, our findings demonstrate that NDRG4 protects cerebral IR injury by inhibiting cell apoptosis and regulates cerebral cell apoptosis by increasing BDNF expression. These results suggest that NDRG4 may be a therapeutic target for IR treatment.

NMDA Receptor Activation Underlies the Loss of Spinal Dorsal Horn Neurons and the Transition to Persistent Pain after Peripheral Nerve Injury

Peripheral nerve lesions provoke apoptosis in the dorsal horn of the spinal cord. The cause of cell death, the involvement of neurons, and the relevance for the processing of somatosensory information are controversial. Here, we demonstrate in a mouse model of sciatic nerve injury that glutamate-induced neurodegeneration and loss of γ-aminobutyric acid (GABA)ergic interneurons in the superficial dorsal horn promote the transition from acute to chronic neuropathic pain. Conditional deletion of Grin1, the essential subunit of N-methyl-d-aspartate-type glutamate receptors (NMDARs), protects dorsal horn neurons from excitotoxicity and preserves GABAergic inhibition. Mice deficient in functional NMDARs exhibit normal nociceptive responses and acute pain after nerve injury, but this initial increase in pain sensitivity is reversible. Eliminating NMDARs fully prevents persistent pain-like behavior. Reduced pain in mice lacking proapoptotic Bax confirmed the significance of neurodegeneration. We conclude that NMDAR-mediated neuron death contributes to the development of chronic neuropathic pain.

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.

Mitochondrial Division Inhibitor 1 (mdivi-1) Protects Neurons against Excitotoxicity through the Modulation of Mitochondrial Function and Intracellular Ca2+ Signaling

Excessive dynamin related protein 1 (Drp1)-triggered mitochondrial fission contributes to apoptosis under pathological conditions and therefore it has emerged as a promising therapeutic target. Mitochondrial division inhibitor 1 (mdivi-1) inhibits Drp1-dependent mitochondrial fission and is neuroprotective in several models of brain ischemia and neurodegeneration. However, mdivi-1 also modulates mitochondrial function and oxidative stress independently of Drp1, and consequently the mechanisms through which it protects against neuronal injury are more complex than previously foreseen. In this study, we have analyzed the effects of mdivi-1 on mitochondrial dynamics, Ca2+ signaling, mitochondrial bioenergetics and cell viability during neuronal excitotoxicity in vitro. Time-lapse fluorescence microscopy revealed that mdivi-1 blocked NMDA-induced mitochondrial fission but not that triggered by sustained AMPA receptor activation, showing that mdivi-1 inhibits excitotoxic mitochondrial fragmentation in a source specific manner. Similarly, mdivi-1 strongly reduced NMDA-triggered necrotic-like neuronal death and, to a lesser extent, AMPA-induced toxicity. Interestingly, neuroprotection provided by mdivi-1 against NMDA, but not AMPA, correlated with a reduction in cytosolic Ca2+ ([Ca2+]cyt) overload and calpain activation indicating additional cytoprotective mechanisms. Indeed, mdivi-1 depolarized mitochondrial membrane and depleted ER Ca2+ content, leading to attenuation of mitochondrial [Ca2+] increase and enhancement of the integrated stress response (ISR) during NMDA receptor activation. Finally, lentiviral knockdown of Drp1 did not rescue NMDA-induced mitochondrial fission and toxicity, indicating that neuroprotective activity of mdivi-1 is Drp1-independent. Together, these results suggest that mdivi-1 induces a Drp1-independent protective phenotype that prevents predominantly NMDA receptor-mediated excitotoxicity through the modulation of mitochondrial function and intracellular Ca2+ signaling.

Cell Death Mechanisms in Stroke and Novel Molecular and Cellular Treatment Options

As a result of ischemia or hemorrhage, blood supply to neurons is disrupted which subsequently promotes a cascade of pathophysiological responses resulting in cell loss. Many mechanisms are involved solely or in combination in this disorder including excitotoxicity, mitochondrial death pathways, and the release of free radicals, protein misfolding, apoptosis, necrosis, autophagy and inflammation. Besides neuronal cell loss, damage to and loss of astrocytes as well as injury to white matter contributes also to cerebral injury. The core problem in stroke is the loss of neuronal cells which makes recovery difficult or even not possible in the late states. Acute treatment options that can be applied for stroke are mainly targeting re-establishment of blood flow and hence, their use is limited due to the effective time window of thrombolytic agents. However, if the acute time window is exceeded, neuronal loss starts due to the activation of cell death pathways. This review will explore the most updated cellular death mechanisms leading to neuronal loss in stroke. Ischemic and hemorrhagic stroke as well as subarachnoid hemorrhage will be debated in the light of cell death mechanisms and possible novel molecular and cellular treatment options will be discussed.

Neuroprotective effects of orientin on oxygen-glucose deprivation/reperfusion-induced cell injury in primary culture of rat cortical neurons

Orientin (luteolin-8-C-glucoside) is a phenolic compound found abundantly in millet, juice, and peel of passion fruit and has been shown to have antioxidant properties. In the present study, we explored the effects of orientin on oxygen-glucose deprivation/reperfusion (OGD/RP)-induced cell injury in primary culture of rat cortical neurons using an in vitro model of neonatal ischemic brain injury. The reduced cell viability and elevated lactate dehydrogenase leakage were observed after OGD/RP exposure, which were then reversed by orientin (10, 20, and 30 µM) pretreatment in a dose-dependent manner. Additionally, OGD/RP treatment resulted in significant oxidative stress, accompanied by enhanced intracellular reactive oxygen species (ROS) generation, and obvious depletion in the activities of intracellular Mn-superoxide dismutase, catalase, and glutathione peroxidase antioxidases. However, these effects were dose dependently restored by orientin pretreatment. We also found that orientin pretreatment dose dependently suppressed [Ca²⁺]_i increase and mitochondrial membrane potential dissipation caused by OGD/RP in primary culture of rat cortical neurons. Western blot analysis showed that OGD/RP exposure induced a distinct decrease of Bcl-2 protein and a marked elevation of Bax, caspase-3, and cleaved caspase-3 proteins; whereas these effects were dose dependently reversed by orientin incubation. Both the caspase-3 activity and the apoptosis rate were increased under OGD/RP treatment, but was then dose dependently down-regulated by orientin (10, 20, and 30 µM) incubation. Moreover, orientin pretreatment dose dependently inhibited OGD/RP-induced phosphorylation of JNK and ERK1/2. Notably, JNK inhibitor SP600125 and ERK1/2 inhibitor PD98059 also dramatically attenuated OGD/RP-induced cell viability loss and ROS generation, and further, orientin failed to protect cortical neurons with the interference of JNK activator anisomycin or ERK1/2 activator FGF-2. Taken together, these results demonstrated that orientin has significant neuroprotective effects against OGD/RP-induced cell injury via JNK and ERK1/2 signaling pathways in primary culture of rat cortical neurons. Impact statement Orientin has been used in traditional eastern medicine and reported to possess antioxidant properties. However, the effects of orientin on neonatal ischemic brain injury and the underlying mechanisms involved have not been studied. Our results showed that orientin exerts significant neuroprotective effects on cell injury caused by oxygen-glucose deprivation/reperfusion via the JNK and ERK1/2 signaling pathways in primary culture of rat cortical neurons, implying the potential therapeutic application of orientin via the suppression of oxidative stress and cell apoptosis. This research suggested that orientin may be used as a therapeutic and preventive option for newborn cerebral ischemia/reperfusion injury.

Mitochondrial mechanisms of neuronal rescue by F-68, a hydrophilic Pluronic block co-polymer, following acute substrate deprivation

Global brain ischemia can lead to widespread neuronal death and poor neurologic outcomes in patients. Despite detailed understanding of the cellular and molecular mechanisms mediating neuronal death following focal and global brain hypoxia-ischemia, treatments to reduce ischemia-induced brain injury remain elusive. One pathway central to neuronal death following global brain ischemia is mitochondrial dysfunction, one consequence of which is the cascade of intracellular events leading to mitochondrial outer membrane permeabilization. A novel approach to rescuing injured neurons from death involves targeting cellular membranes using a class of synthetic molecules called Pluronics. Pluronics are triblock copolymers of hydrophilic poly[ethylene oxide] (PEO) and hydrophobic poly[propylene oxide] (PPO). Evidence is accumulating to suggest that hydrophilic Pluronics rescue injured neurons from death following substrate deprivation by preventing mitochondrial dysfunction. Here, we will review current understanding of the nature of interaction of Pluronic molecules with biological membranes and the efficacy of F-68, an 80% hydrophilic Pluronic, in rescuing neurons from injury. We will review data indicating that F-68 reduces mitochondrial dysfunction and mitochondria-dependent death pathways in a model of neuronal injury in vitro, and present new evidence that F-68 acts directly on mitochondria to inhibit mitochondrial outer membrane permeabilization. Finally, we will present results of a pilot, proof-of-principle study suggesting that F-68 is effective in reducing hippocampal injury induced by transient global ischemia in vivo. By targeting mitochondrial dysfunction, F-68 and other Pluronic molecules constitute an exciting new approach to rescuing neurons from acute injury.

Mitochondria in the nervous system: From health to disease, Part I

In Part I of this Special Issue on "Mitochondria in the Nervous System: From Health to Disease", the editors bring together contributions from experts in brain mitochondrial research to provide an up-to-date overview of mitochondrial functioning in physiology and pathology. The issue provides cutting edge reviews on classical areas of mitochondrial biology that include energy substrate utilization, calcium handling, mitochondria-endoplasmic reticulum communication, and cell death regulation. Additional reviews and original research articles touch upon key mitochondrial defects seen across multiple neurodegenerative conditions, including fragmentation, loss of respiratory capacity, calcium overload, elevated reactive oxygen species generation, perturbed NAD⁺ metabolism, altered protein acetylation, and compromised mitophagy. Emerging links between the genetics of neurodegenerative disorders and disruption in mitochondrial function are discussed, and a new mouse model of Complex I deficiency is described. Finally, novel ways to rescue mitochondrial structure and function in acute and chronic brain injury are explored.

Glyceryl 1,3-Dipalmitate Produced from Lactobacillus paracasei subspecies. paracasei NTU 101 Inhibits Oxygen-Glucose Deprivation and Reperfusion-Induced Oxidative Stress via Upregulation of Peroxisome Proliferator-Activated Receptor γ in Neuronal SH-SY5Y Cells

Glyceryl 1,3-dipalmitate (GD) purified from Lactobacillus paracasei subsp. paracasei NTU 101-fermented products has been demonstrated to possess neuroprotective properties. We determined the effect of GD on oxygen-glucose deprivation and reperfusion (OGD/R)-induced SH-SY5Y neuroblastoma cell death. GD ameliorated OGD/R-induced apoptosis by elevating the protein expression of nuclear peroxisome proliferator-activated receptor γ (PPARγ) and nuclear factor erythroid 2-related factor 2 (Nrf2), thereby attenuating reactive oxygen species (ROS) generation. Pretreatment with GD reduced nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) expression from 1.54 ± 0.27 to 0.84 ± 0.46, thereby attenuating the induction of pro-inflammatory mediators, and increased the plasma membrane Ca²⁺ ATPase (PMCA) levels from 0.81 ± 0.02 to 1.08 ± 0.06, thus reducing the levels of cytosolic Ca²⁺; this also correlated with reduced cell death. We conclude that GD prevents SH-SY5Y cells from injury after OGD/R insult, possibly by modulating oxidative stress and inflammatory response.

Autophagy-regulated AMPAR subunit upregulation in in vitro oxygen glucose deprivation/reoxygenation-induced hippocampal injury

Autophagy has been implicated to mediate experimental cerebral ischemia/reperfusion-induced neuronal death; the underlying molecular mechanisms, though, are poorly understood. In this study, we investigated the role of autophagy in regulating the expression of AMPAR subunits (GluR1, GluR2, and GluR3) in oxygen glucose deprivation/reperfusion (OGD/R)-mediated injury of hippocampal neurons. Our results showed that, OGD/R-induced hippocampal neuron injury was accompanied by accumulation of autophagosomes and autolysosomes in cytoplasm alongside a dramatic increase in expression of autophagy-related genes, LC3 and Beclin 1 and increased intracellular Ca²⁺ levels. Pre-treatment with autophagy inhibitor 3-methyladenine (3-MA) significantly reduced this effect. Moreover, the OGD/R-induced upregulation of mRNA and protein expressions of GluR1, GluR2, and GluR3 were also effectively reversed in cells pretreated with 3-MA. Our findings indicate that OGD/R induced the expression of GluRs by activating autophagy in in vitro cultured hippocampal neurons, which could be effectively reversed by the administration of 3-MA.

Connecting mitochondrial dynamics and life-or-death events via Bcl-2 family proteins

The morphology of a population of mitochondria is the result of several interacting dynamical phenomena, including fission, fusion, movement, elimination and biogenesis. Each of these phenomena is controlled by underlying molecular machinery, and when defective can cause disease. New understanding of the relationships between form and function of mitochondria in health and disease is beginning to be unraveled on several fronts. Studies in mammals and model organisms have revealed that mitochondrial morphology, dynamics and function appear to be subject to regulation by the same proteins that regulate apoptotic cell death. One protein family that influences mitochondrial dynamics in both healthy and dying cells is the Bcl-2 protein family. Connecting mitochondrial dynamics with life-death pathway forks may arise from the intersection of Bcl-2 family proteins with the proteins and lipids that determine mitochondrial shape and function. Bcl-2 family proteins also have multifaceted influences on cells and mitochondria, including calcium handling, autophagy and energetics, as well as the subcellular localization of mitochondrial organelles to neuronal synapses. The remarkable range of physical or functional interactions by Bcl-2 family proteins is challenging to assimilate into a cohesive understanding. Most of their effects may be distinct from their direct roles in apoptotic cell death and are particularly apparent in the nervous system. Dual roles in mitochondrial dynamics and cell death extend beyond BCL-2 family proteins. In this review, we discuss many processes that govern mitochondrial structure and function in health and disease, and how Bcl-2 family proteins integrate into some of these processes.

A Small-Molecule Inhibitor of Bax and Bak Oligomerization Prevents Genotoxic Cell Death and Promotes Neuroprotection

Aberrant apoptosis can lead to acute or chronic degenerative diseases. Mitochondrial outer membrane permeabilization (MOMP) triggered by the oligomerization of the Bcl-2 family proteins Bax/Bak is an irreversible step leading to execution of apoptosis. Here, we describe the discovery of small-molecule inhibitors of Bax/Bak oligomerization that prevent MOMP. We demonstrate that these molecules disrupt multiple, but not all, interactions between Bax dimer interfaces thereby interfering with the formation of higher-order oligomers in the MOM, but not recruitment of Bax to the MOM. Small-molecule inhibition of Bax/Bak oligomerization allowed cells to evade apoptotic stimuli and rescued neurons from death after excitotoxicity, demonstrating that oligomerization of Bax is essential for MOMP. Our discovery of small-molecule Bax/Bak inhibitors provides novel tools for the investigation of the mechanisms leading to MOMP and will ultimately facilitate development of compounds inhibiting Bax/Bak in acute and chronic degenerative diseases.

Control of mitochondrial physiology and cell death by the Bcl-2 family proteins Bax and Bok

Neuronal cell death is often triggered by events that involve intracellular increases in Ca²⁺. Under resting conditions, the intracellular Ca²⁺ concentration is tightly controlled by a number of extrusion and sequestering mechanisms involving the plasma membrane, mitochondria, and ER. These mechanisms act to prevent a disruption of neuronal ion homeostasis. As these processes require ATP, excessive Ca²⁺ overloading may cause energy depletion, mitochondrial dysfunction, and may eventually lead to Ca²⁺-dependent cell death. Excessive Ca²⁺ entry though glutamate receptors (excitotoxicity) has been implicated in several neurologic and chronic neurodegenerative diseases, including ischemic stroke, epilepsy, and Alzheimer's disease. Recent evidence has revealed that excitotoxic cell death is regulated by the B-cell lymphoma-2 (Bcl-2) family of proteins. Bcl-2 proteins, comprising of both pro-apoptotic and anti-apoptotic members, have been shown to not only mediate the intrinsic apoptosis pathway by controlling mitochondrial outer membrane (MOM) integrity, but to also control neuronal Ca²⁺ homeostasis and energetics. In this review, the role of Bcl-2 family proteins in the regulation of apoptosis, their expression in the central nervous system and how they control Ca²⁺-dependent neuronal injury are summarized. We review the current knowledge on Bcl-2 family proteins in the regulation of mitochondrial function and bioenergetics, including the fusion and fission machinery, and their role in Ca²⁺ homeostasis regulation at the mitochondria and ER. Specifically, we discuss how the 'pro-apoptotic' Bcl-2 family proteins, Bax and Bok, physiologically expressed in the nervous system, regulate such 'non-apoptotic/daytime' functions.

Bcl-2 family proteins: master regulators of cell survival

The most prominent function of proteins of the Bcl-2 family is regulation of the initiation of intrinsic (mitochondrial) pathways of apoptosis. However, recent research has revealed that in addition to regulation of mitochondrial apoptosis, proteins of the Bcl-2 family play important roles in regulating other cellular pathways with a strong impact on cell survival like autophagy, endoplasmic reticulum (ER) stress response, intracellular calcium dynamics, cell cycle progression, mitochondrial dynamics and energy metabolism. This review summarizes the recent knowledge about functions of Bcl-2 family proteins that are related to cell survival.

Bok Is Not Pro-Apoptotic But Suppresses Poly ADP-Ribose Polymerase-Dependent Cell Death Pathways and Protects against Excitotoxic and Seizure-Induced Neuronal Injury

Bok (Bcl-2-related ovarian killer) is a Bcl-2 family member that, because of its predicted structural homology to Bax and Bak, has been proposed to be a pro-apoptotic protein. In this study, we demonstrate that Bok is highly expressed in neurons of the mouse brain but that bok was not required for staurosporine-, proteasome inhibition-, or excitotoxicity-induced apoptosis of cultured cortical neurons. On the contrary, we found that bok-deficient neurons were more sensitive to oxygen/glucose deprivation-induced injury in vitro and seizure-induced neuronal injury in vivo Deletion of bok also increased staurosporine-, excitotoxicity-, and oxygen/glucose deprivation-induced cell death in bax-deficient neurons. Single-cell imaging demonstrated that bok-deficient neurons failed to maintain their neuronal Ca(2+)homeostasis in response to an excitotoxic stimulus; this was accompanied by a prolonged deregulation of mitochondrial bioenergetics.bok deficiency led to a specific reduction in neuronal Mcl-1 protein levels, and deregulation of both mitochondrial bioenergetics and Ca(2+)homeostasis was rescued by Mcl-1 overexpression. Detailed analysis of cell death pathways demonstrated the activation of poly ADP-ribose polymerase-dependent cell death in bok-deficient neurons. Collectively, our data demonstrate that Bok acts as a neuroprotective factor rather than a pro-death effector during Ca(2+)- and seizure-induced neuronal injury in vitro and in vivo

SIGNIFICANCE STATEMENT

Bcl-2 proteins are essential regulators of the mitochondrial apoptosis pathway. The Bcl-2 protein Bok is highly expressed in the CNS. Because of its sequence similarity to Bax and Bak, Bok has long been considered part of the pro-apoptotic Bax-like subfamily, but no studies have yet been performed in neurons to test this hypothesis. Our study provides important new insights into the functional role of Bok during neuronal apoptosis and specifically in the setting of Ca(2+)- and seizure-mediated neuronal injury. We show that Bok controls neuronal Ca(2+)homeostasis and bioenergetics and, contrary to previous assumptions, exerts neuroprotective activities in vitro and in vivo Our results demonstrate that Bok cannot be placed unambiguously into the Bax-like Bcl-2 subfamily of pro-apoptotic proteins.

Involvement of calcium/calmodulin-dependent protein kinase II in methamphetamine-induced neural damage

Methamphetamine (METH), an illicit drug, is widely abused in many parts of the world. Mounting evidence shows that METH exposure contributes to neurotoxicity, particularly for the monoaminergic neurons. However, to date, only a few studies have tried to unravel the mechanisms involved in METH-induced non-monoaminergic neural damage. Therefore, in the present study, we tried to explore the mechanisms for METH-induced neural damage in cortical neurons. Our results showed that METH significantly increased intracellular [Ca(2) (+) ]i in Ca(2) (+) -containing solution rather than Ca(2) (+) -free solution. Moreover, METH also upregulated calmodulin (CaM) expression and activated CaM-dependent protein kinase II (CaMKII). Significantly, METH-induced neural damage can be partially retarded by CaM antagonist W7 as well as CaMKII blocker KN93. In addition, L-type Ca(2) (+) channel was also proved to be involved in METH-induced cell damage, as nifedipine, the L-type Ca(2) (+) channel-specific inhibitor, markedly attenuated METH-induced neural damage. Collectively, our results suggest that Ca(2) (+) -CaM-CaMKII is involved in METH-mediated neurotoxicity, and it might suggest a potential target for the development of therapeutic strategies for METH abuse. Copyright © 2016 John Wiley & Sons, Ltd.

Computational Analysis of AMPK-Mediated Neuroprotection Suggests Acute Excitotoxic Bioenergetics and Glucose Dynamics Are Regulated by a Minimal Set of Critical Reactions

Loss of ionic homeostasis during excitotoxic stress depletes ATP levels and activates the AMP-activated protein kinase (AMPK), re-establishing energy production by increased expression of glucose transporters on the plasma membrane. Here, we develop a computational model to test whether this AMPK-mediated glucose import can rapidly restore ATP levels following a transient excitotoxic insult. We demonstrate that a highly compact model, comprising a minimal set of critical reactions, can closely resemble the rapid dynamics and cell-to-cell heterogeneity of ATP levels and AMPK activity, as confirmed by single-cell fluorescence microscopy in rat primary cerebellar neurons exposed to glutamate excitotoxicity. The model further correctly predicted an excitotoxicity-induced elevation of intracellular glucose, and well resembled the delayed recovery and cell-to-cell heterogeneity of experimentally measured glucose dynamics. The model also predicted necrotic bioenergetic collapse and altered calcium dynamics following more severe excitotoxic insults. In conclusion, our data suggest that a minimal set of critical reactions may determine the acute bioenergetic response to transient excitotoxicity and that an AMPK-mediated increase in intracellular glucose may be sufficient to rapidly recover ATP levels following an excitotoxic insult.

BID Mediates Oxygen-Glucose Deprivation-Induced Neuronal Injury in Organotypic Hippocampal Slice Cultures and Modulates Tissue Inflammation in a Transient Focal Cerebral Ischemia Model without Changing Lesion Volume

The BH3 interacting-domain death agonist (BID) is a pro-apoptotic protein involved in death receptor-induced and mitochondria-mediated apoptosis. Recently, it has also been suggested that BID is involved in the regulation of inflammatory responses in the central nervous system. We found that BID deficiency protected organotypic hippocampal slice cultures in vitro from neuronal injury induced by oxygen-glucose deprivation. In vivo, BID-knockout (KO) mice and wild type (WT) mice were subjected to 60 min of transient middle cerebral artery occlusion (tMCAO) to induce focal cerebral ischemia, and allowed to recover for 24 h. Infarct volumes and functional outcome were assessed and the inflammatory response was evaluated using immunofluorescence, Western blotting, quantitative PCR (qPCR) and Mesoscale multiplex analysis. We observed no difference in the infarct volume or neurological outcome between BID-KO and WT mice. The inflammatory response was reduced by BID deficiency as indicated by a change in microglial/leukocyte response. In conclusion, our data suggest that BID deficiency is neuroprotective in an in vitro model and modulates the inflammatory response to focal cerebral ischemia in vivo. However, this is not translated into a robust neuroprotection in vivo.

Protection against Oxygen-Glucose Deprivation/Reperfusion Injury in Cortical Neurons by Combining Omega-3 Polyunsaturated Acid with Lyciumbarbarum Polysaccharide

Ischemic stroke, characterized by the disturbance of the blood supply to the brain, is a severe worldwide health threat with high mortality and morbidity. However, there is no effective pharmacotherapy for ischemic injury. Currently, combined treatment is highly recommended for this devastating injury. In the present study, we investigated neuroprotective effects of the combination of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) and Lyciumbarbarum polysaccharide (LBP) on cortical neurons using an in vitro ischemic model. Our study demonstrated that treatment with docosahexaenoic acid (DHA), a major component of the ω-3 PUFAs family, significantly inhibited the increase of intracellular Ca²⁺ in cultured wild type (WT) cortical neurons subjected to oxygen-glucose deprivation/reperfusion (OGD/R) injury and promoted their survival compared with the vehicle-treated control. The protective effects were further confirmed in cultured neurons with high endogenous ω-3 PUFAs that were isolated from fat-1 mice, in that a higher survival rate was found in fat-1 neurons compared with wild-type neurons after OGD/R injury. Our study also found that treatment with LBP (50 mg/L) activated Trk-B signaling in cortical neurons and significantly attenuated OGD/R-induced cell apoptosis compared with the control. Notably, both combining LBP treatment with ω-3 PUFAs administration to WT neurons and adding LBP to fat-1 neurons showed enhanced effects on protecting cortical neurons against OGD/R injury via concurrently regulating the intracellular calcium overload and neurotrophic pathway. The results of the study suggest that ω-3 PUFAs and LBP are promising candidates for combined pharmacotherapy for ischemic stroke.

Interleukin-6 reduces NMDAR-mediated cytosolic Ca²⁺ overload and neuronal death via JAK/CaN signaling

Cytosolic Ca(2+) overload induced by N-methyl-D-aspartate (NMDA) is one of the major causes for neuronal cell death during cerebral ischemic insult and neurodegenerative disorders. Previously, we have reported that the cytokine interleukin-6 (IL-6) reduces NMDA-induced cytosolic Ca(2+) overload by inhibiting both L-type voltage-gated calcium channel (L-VGCC) activity and intracellular Ca(2+) store release in cultured cerebellar granule neurons (CGNs). Here we aimed to show that NMDA-gated receptor channels (i.e., NMDA receptors, NMDARs) are an inhibitory target of IL-6 via a mediation of calcineurin (CaN) signaling. As expected, IL-6 decreased NMDAR-mediated cytosolic Ca(2+) overload and inward current in cultured CGNs. The NMDAR subunits, NR1, NR2A, NR2B and NR2C, were expressed in CGNs. Blocking either of NR2A, NR2B and NR2C with respective antagonist reduced NMDA-induced extracellular Ca(2+) influx and neuronal death. Importantly, the reduced percentages in extracellular Ca(2+) influx and neuronal death by either NR2B or NR2C antagonist were weaker in the presence of IL-6 than in the absence of IL-6, while the reduced percentage by NR2A antagonist was not significantly different between the presence and the absence of IL-6. AG490, an inhibitor of Janus kinase (JAK), abolished IL-6 protection against extracellular Ca(2+) influx, mitochondrial membrane depolarization, neuronal death, and CaN activity impairment induced by NMDA. The CaN inhibitor FK506 reduced these IL-6 neuroprotective properties. Collectively, these results suggest that IL-6 exerts neuroprotection by inhibiting activities of the NMDAR subunits NR2B and NR2C (but not NR2A) via the intermediation of JAK/CaN signaling.