Immature and mature cortical neurons engage different apoptotic mechanisms involving caspase-3 and the mitogen-activated protein kinase pathway

Predictive value of fibrinogen levels for 90-day functional outcomes after intravenous thrombolysis in patients with acute ischaemic stroke

PURPOSE

We aimed to investigate the correlation between fibrinogen levels and functional outcomes at 90 days after intravenous thrombolysis therapy (IVT) in patients with acute ischaemic stroke (AIS).

METHODS

We identified patients with AIS who received IVT (alteplase 0.6 or 0.9 mg/kg) between 1 January 2019 and 31 March 2022 in Yancheng 1st People's Hospital. Fibrinogen levels were measured before IVT, and the 90-day post-stroke functional outcome was evaluated using the modified Rankin Scale (mRS). An mRS score of 0-2 indicated functional independence, whereas an mRS score of 3-6 indicated functional dependence. Potential outcome predictors were evaluated using univariate and multivariate analyses, and receiver operating characteristic (ROC) curve analysis was performed to assess the performance of fibrinogen levels in predicting the 90-day outcome.

RESULTS

A total of 276 patients with AIS who received IVT within 4.5 h of stroke onset were enrolled, of whom 165 and 111 were categorised into the functional independence and functional dependence groups, respectively. Univariate analysis showed that the fibrinogen, homocysteine, high-density lipoprotein cholesterol, and D-dimer levels; age; National Institutes of Health Stroke Scale (NIHSS) score on admission; NIHSS score 24 h after IVT; and incidence of cardioembolism were higher in the functional dependence group than in the functional independence group (P < 0.05). Meanwhile, the thrombin time and the incidence of small-vessel occlusion in the functional dependence group were smaller than those in the functional independence group (P < 0.05). Multivariate logistic regression analysis showed that fibrinogen and homocysteine levels were both independent risk factors for 90-day functional dependence in patients with AIS (odds ratio [OR] 2.822, 95% confidence interval [95% CI]: 1.214-6.558, P = 0.016 for fibrinogen; OR 1.048, 95 %CI: 1.002-1.096, P = 0.041 for homocysteine). The area under the ROC curve of fibrinogen levels before IVT for predicting poor functional outcomes was 0.664, with a sensitivity, specificity, positive predictive value, and negative predictive value of 40.9%, 80.8%, 68.9%, and 64.3%, respectively.

CONCLUSION

In patients with AIS, fibrinogen levels have a certain predictive value for short-term functional outcomes after IVT.

Mitochondrion-Mediated Cell Death through Erk1-Alox5 Independent of Caspase-9 Signaling

Mitochondrial disruption leads to the release of cytochrome c to activate caspase-9 and the downstream caspase cascade for the execution of apoptosis. However, cell death can proceed efficiently in the absence of caspase-9 following mitochondrial disruption, suggesting the existence of caspase-9-independent cell death mechanisms. Through a genome-wide siRNA library screening, we identified a network of genes that mediate caspase-9-independent cell death, through ROS production and Alox5-dependent membrane lipid peroxidation. Erk1-dependent phosphorylation of Alox5 is critical for targeting Alox5 to the nuclear membrane to mediate lipid peroxidation, resulting in nuclear translocation of cytolytic molecules to induce DNA damage and cell death. Consistently, double knockouts of caspase-9 and Alox5 in mice, but not deletion of either gene alone, led to significant T cell expansion with inhibited cell death, indicating that caspase-9- and Alox5-dependent pathways function in parallel to regulate T cell death in vivo. This unbiased whole-genome screening reveals an Erk1-Alox5-mediated pathway that promotes membrane lipid peroxidation and nuclear translocation of cytolytic molecules, leading to the execution of cell death in parallel to the caspase-9 signaling cascade.

Immature Brain Cortical Neurons Have Low Transcriptional Competence to Activate Antiviral Defences and Control RNA Virus Infections

Virus infections of the central nervous system (CNS) cause important diseases of humans and animals. As in other tissues, innate antiviral responses mediated by type I interferons (IFNs) are crucially important in controlling CNS virus infections. The maturity of neuronal populations is an established critical factor determining the outcome of CNS virus infection. Using primary cultures of mouse cortical neurons, we investigated the relationships between neuronal maturation, type I IFN responses, and the outcome of Semliki Forest virus infection. The virus replicated better, infected more cells, and produced higher titres of infectious viruses in immature neurons. Complete transcriptome analysis demonstrated that resting immature neurons have low transcriptional competence to mount antiviral responses. They had no detectable transcription of the genes Ddx58 and Ifih1, which encode key RNA virus cytoplasmic sensors RIG-I and MDA5, and very low expression of genes encoding key regulators of associated signalling pathways. Upon infection, immature neurons failed to mount an antiviral response as evidenced by their failure to produce chemokines, IFNs, and other cytokines. Treatment of immature neurons with exogenous IFNβ prior to infection resulted in antiviral responses and lower levels of virus replication and infectious virus production. In contrast, resting mature neurons generated a robust antiviral response. This was augmented by pretreatment with IFNβ. Infection of mature neurons derived from IFNAR-/- mice did not make an antiviral response and replicated virus to high levels.

Neuroprotective derivatives of tacrine that target NMDA receptor and acetyl cholinesterase - Design, synthesis and biological evaluation

The complex and multifactorial nature of neuropsychiatric diseases demands multi-target drugs that can intervene with various sub-pathologies underlying disease progression. Targeting the impairments in cholinergic and glutamatergic neurotransmissions with small molecules has been suggested as one of the potential disease-modifying approaches for Alzheimer’s disease (AD). Tacrine, a potent inhibitor of acetylcholinesterase (AChE) is the first FDA approved drug for the treatment of AD. Tacrine is also a low affinity antagonist of N-methyl-D-aspartate receptor (NMDAR). However, tacrine was withdrawn from its clinical use later due to its hepatotoxicity. With an aim to develop novel high affinity multi-target directed ligands (MTDLs) against AChE and NMDAR, with reduced hepatotoxicity, we performed in silico structure-based modifications on tacrine, chemical synthesis of the derivatives and in vitro validation of their activities. Nineteen such derivatives showed inhibition with IC₅₀ values in the range of 18.53 ± 2.09 – 184.09 ± 19.23 nM against AChE and 0.27 ± 0.05 – 38.84 ± 9.64 μM against NMDAR. Some of the selected compounds also protected rat primary cortical neurons from glutamate induced excitotoxicity. Two of the tacrine derived MTDLs, 201 and 208 exhibited in vivo efficacy in rats by protecting against behavioral impairment induced by administration of the excitotoxic agent, monosodium glutamate. Additionally, several of these synthesized compounds also exhibited promising inhibitory activitiy against butyrylcholinesterase. MTDL-201 was also devoid of hepatotoxicity in vivo. Given the therapeutic potential of MTDLs in disease-modifying therapy, our studies revealed several promising MTDLs among which 201 appears to be a potential candidate for immediate preclinical evaluations.

Cleaved PINK1 induces neuronal plasticity through PKA-mediated BDNF functional regulation

Mutations in PTEN-induced kinase 1 (PINK1) lead to early onset autosomal recessive Parkinson's disease in humans. In healthy neurons, full-length PINK1 (fPINK1) is post-translationally cleaved into different lower molecular weight forms, and cleaved PINK1 (cPINK1) gets shuttled to the cytosolic compartments to support extra-mitochondrial functions. While numerous studies have exemplified the role of mitochondrially localized PINK1 in modulating mitophagy in oxidatively stressed neurons, little is known regarding the physiological role of cPINK1 in healthy neurons. We have previously shown that cPINK1, but not fPINK1, modulates the neurite outgrowth and the maintenance of dendritic arbors by activating downstream protein kinase A (PKA) signaling in healthy neurons. However, the molecular mechanisms by which cPINK1 promotes neurite outgrowth remain to be elucidated. In this report, we show that cPINK1 supports neuronal development by modulating the expression and extracellular release of brain-derived neurotrophic factor (BDNF). Consistent with this role, we observed a progressive increase in the level of endogenous cPINK1 but not fPINK1 during prenatal and postnatal development of mouse brains and during development in primary cortical neurons. In cultured primary neurons, the pharmacological activation of endogenous PINK1 leads to enhanced downstream PKA activity, subsequent activation of the PKA-modulated transcription factor cAMP response element-binding protein (CREB), increased intracellular production and extracellular release of BDNF, and enhanced activation of the BDNF receptor-TRKβ. Mechanistically, cPINK1-mediated increased dendrite complexity requires the binding of extracellular BDNF to TRKβ. In summary, our data support a physiological role of cPINK1 in stimulating neuronal development by activating the PKA-CREB-BDNF signaling axis in a feedforward loop.

Reactive Oxygen Species/Caspase 3 Promotes Autophagy of Nigral Dopaminergic Neuron in Parkinson’s Disease

Parkinson’s disease (PD) is characterized as bradykinesia and sleep disorder, troubling numerous people. In the present study, we aimed to explore whether reactive oxygen species (ROS)/caspase 3 promotes PD to provide a basis for novel treatments of PD. Firstly, we applied 1-methyl-4-phenylpyridinium (MPP+) to stimulate PC12 cell lines to establish a PD cell model. Western blot and qRT-PCR analyses detected protein and mRNA expression of caspase 3, IL-1β, Bax, and BCL2. Finally, ROS detection kit determined ROS content. Compared with the controls, MPP+-treated PC12 exhibited significantly elevated caspase 3, caspase 3, and IL-1β at the protein level (p < 0.001). In addition, MMP + treatment increased Bax protein level in vitro, while decreased Bcl-2 protein expression (p <0.001). Moreover, MPP + induced oxidative stress which contributes to autophagy. The ROS in MPP + group was increased significantly (p < 0.001). ROS and caspase 3 participate in the pathogenesis of PD and enhances autophagy of nigral dopaminergic neuron.

A New Vision for Therapeutic Hypothermia in the Era of Targeted Temperature Management: A Speculative Synthesis

Three decades of animal studies have reproducibly shown that hypothermia is profoundly cerebroprotective during or after a central nervous system (CNS) insult. The success of hypothermia in preclinical acute brain injury has not only fostered continued interest in research on the classic secondary injury mechanisms that are prevented or blunted by hypothermia but has also sparked a surge of new interest in elucidating beneficial signaling molecules that are increased by cooling. Ironically, while research into cold-induced neuroprotection is enjoying newfound interest in chronic neurodegenerative disease, conversely, the scope of the utility of therapeutic hypothermia (TH) across the field of acute brain injury is somewhat controversial and remains to be fully defined. This has led to the era of Targeted Temperature Management, which emphasizes a wider range of temperatures (33–36°C) showing benefit in acute brain injury. In this comprehensive review, we focus on our current understandings of the novel neuroprotective mechanisms activated by TH, and discuss the critical importance of developmental age germane to its clinical efficacy. We review emerging data on four cold stress hormones and three cold shock proteins that have generated new interest in hypothermia in the field of CNS injury, to create a framework for new frontiers in TH research. We make the case that further elucidation of novel cold responsive pathways might lead to major breakthroughs in the treatment of acute brain injury, chronic neurological diseases, and have broad potential implications for medicines of the distant future, including scenarios such as the prevention of adverse effects of long-duration spaceflight, among others. Finally, we introduce several new phrases that readily summarize the essence of the major concepts outlined by this review—namely, Ultramild Hypothermia, the “Responsivity of Cold Stress Pathways,” and “Hypothermia in a Syringe.”

Sirtuins in Neuroendocrine Regulation and Neurological Diseases

Silent information regulator 1 (SIRT1) is a mammalian homolog of the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin family. Sirtuin was originally studied as the lifespan-extending gene, silent information regulator 2 (SIRT2) in budding yeast. There are seven mammalian homologs of sirtuin (SIRT1–7), and SIRT1 is the closest homolog to SIRT2. SIRT1 modulates various key targets via deacetylation. In addition to histones, these targets include transcription factors, such as forkhead box O (FOXO), Ku70, p53, NF-κB, PPAR-gamma co-activator 1-alpha (PGC-1α), and peroxisome proliferator-activated receptor γ (PPARγ). SIRT1 has many biological functions, including aging, cell survival, differentiation, and metabolism. Genetic and physiological analyses in animal models have shown beneficial roles for SIRT1 in the brain during both development and adulthood. Evidence from in vivo and in vitro studies have revealed that SIRT1 regulates the cellular fate of neural progenitors, axon elongation, dendritic branching, synaptic plasticity, and endocrine function. In addition to its importance in physiological processes, SIRT1 has also been implicated in protection of neurons from degeneration in models of neurological diseases, such as traumatic brain injury and Alzheimer’s disease. In this review, we focus on the role of SIRT1 in the neuroendocrine system and neurodegenerative diseases. We also discuss the potential therapeutic implications of targeting the sirtuin pathway.

DNA Damage Response and Repair, DNA Methylation, and Cell Death in Human Neurons and Experimental Animal Neurons Are Different

Neurological disorders affecting individuals in infancy to old age elude interventions for meaningful protection against neurodegeneration, and preclinical work has not translated to humans. We studied human neuron responses to injury and death stimuli compared to those of animal neurons in culture under similar settings of insult (excitotoxicity, oxidative stress, and DNA damage). Human neurons were differentiated from a cortical neuron cell line and the embryonic stem cell-derived H9 line. Mouse neurons were differentiated from forebrain neural stem cells and embryonic cerebral cortex; pig neurons were derived from forebrain neural stem cells. Mitochondrial morphology was different in human and mouse neurons. Human and mouse neurons challenged with DNA-damaging agent camptothecin showed different chromatin condensation, cell death, and DNA damage sensor activation. DNA damage accumulation and repair kinetics differed among human, mouse, and pig neurons. Promoter CpG island methylation microarrays showed significant differential DNA methylation in human and mouse neurons after injury. Therefore, DNA damage response, DNA repair, DNA methylation, and autonomous cell death mechanisms in human neurons and experimental animal neurons are different.

Mitogen- and Stress-Activated Protein Kinase 1 Regulates Status Epilepticus-Evoked Cell Death in the Hippocampus

Mitogen-activated protein kinase (MAPK) signaling has been implicated in a wide range of neuronal processes, including development, plasticity, and viability. One of the principal downstream targets of both the extracellular signal-regulated kinase/MAPK pathway and the p38 MAPK pathway is Mitogen- and Stress-activated protein Kinase 1 (MSK1). Here, we sought to understand the role that MSK1 plays in neuroprotection against excitotoxic stimulation in the hippocampus. To this end, we utilized immunohistochemical labeling, a MSK1 null mouse line, cell viability assays, and array-based profiling approaches. Initially, we show that MSK1 is broadly expressed within the major neuronal cell layers of the hippocampus and that status epilepticus drives acute induction of MSK1 activation. In response to the status epilepticus paradigm, MSK1 KO mice exhibited a striking increase in vulnerability to pilocarpine-evoked cell death within the CA1 and CA3 cell layers. Further, cultured MSK1 null neurons exhibited a heighted level of N-methyl-D-aspartate-evoked excitotoxicity relative to wild-type neurons, as assessed using the lactate dehydrogenase assay. Given these findings, we examined the hippocampal transcriptional profile of MSK1 null mice. Affymetrix array profiling revealed that MSK1 deletion led to the significant (>1.25-fold) downregulation of 130 genes and an upregulation of 145 genes. Notably, functional analysis indicated that a subset of these genes contribute to neuroprotective signaling networks. Together, these data provide important new insights into the mechanism by which the MAPK/MSK1 signaling cassette confers neuroprotection against excitotoxic insults. Approaches designed to upregulate or mimic the functional effects of MSK1 may prove beneficial against an array of degenerative processes resulting from excitotoxic insults.

CBX2 Inhibits Neurite Development by Regulating Neuron-Specific Genes Expression

Polycomb group (PcG) proteins regulate the epigenetic status of transcription regulatory states during development. Progression from pluripotency to differentiation requires the sequential activation and repression of different PcG target genes, however, the relationship between early patterning signals, PcG expression, and the development of the central nervous system is still unclear. Using various models of neuronal differentiation, we provide evidence that CBX2 is a negative regulator of neuronal differentiation. Knock-down of CBX2 expression promotes neurite development, while overexpression of CBX2 inhibits neurite development. Further, we found that CBX2 is a direct target gene of miR-124. During neuronal differentiation, CBX2 was decreased while miR-124 was increased. Mechanistically, CBX2 directly interacts with the promoter region of several neuro-associated genes and regulates their expression. We found that the neuron-specific GAP-43 gene could contribute to the stimulating effect on neurite development associated with inhibition of CBX2.

Sexually Dimorphic Outcomes after Neonatal Stroke and Hypoxia-Ischemia

Cohort studies have demonstrated a higher vulnerability in males towards ischemic and/or hypoxic-ischemic injury in infants born near- or full-term. Male sex was also associated with limited brain repair following neonatal stroke and hypoxia-ischemia, leading to increased incidence of long-term cognitive deficits compared to females with similar brain injury. As a result, the design of pre-clinical experiments considering sex as an important variable was supported and investigated because neuroprotective strategies to reduce brain injury demonstrated sexual dimorphism. While the mechanisms underlining these differences between boys and girls remain unclear, several biological processes are recognized to play a key role in long-term neurodevelopmental outcomes: gonadal hormones across developmental stages, vulnerability to oxidative stress, modulation of cell death, and regulation of microglial activation. This review summarizes the current evidence for sex differences in neonatal hypoxic-ischemic and/or ischemic brain injury, considering the major pathways known to be involved in cognitive and behavioral deficits associated with damages of the developing brain.

Enforced DNA repair enzymes rescue neurons from apoptosis induced by target deprivation and axotomy in mouse models of neurodegeneration

It is unknown whether DNA damage accumulation is an upstream instigator or secondary effect of the cell death process in different populations of adult postmitotic neurons in the central nervous system. In two different mouse models of injury-induced neurodegeneration characterized by relatively synchronous accumulation of mitochondria, oxidative stress, and DNA damage prior to neuronal apoptosis, we enforced the expression of human 8-oxoguanine DNA glycosylase (hOGG1) and human apurinic-apyrimidinic endonuclease-1/Ref1 (hAPE) using recombinant adenoviruses (Ad). Thalamic lateral geniculate neurons and lumbar spinal cord motor neurons were transduced by Ad-hOGG1 and Ad-hAPE injections into the occipital cortex and skeletal muscle, respectively, prior to their target deprivation- and axotomy-induced retrograde apoptosis. Enforced expression of hOGG1 and hAPE in thalamus and spinal cord was confirmed by western blotting and immunohistochemistry. In injured populations of neurons in thalamus and spinal cord, a DNA damage response (DDR) was registered, as shown by localization of phospho-activated p53, Rad17, and replication protein A-32 immunoreactivities, and this DDR was attenuated more effectively by enforced hAPE expression than by hOGG1 expression. Enforced expression of hOGG1 and hAPE significantly protected thalamic neurons and motor neurons from retrograde apoptosis induced by target deprivation and axotomy. We conclude that a DDR response is engaged pre-apoptotically in different types of injured mature CNS neurons and that DNA repair enzymes can regulate the survival of retrogradely dying neurons, suggesting that DNA damage and activation of DDR are upstream mechanisms for this form of adult neurodegeneration in vivo, thus identifying DNA repair as a therapeutic target for neuroprotection.

Beneficial Effect of Astragaloside on Alzheimer's Disease Condition Using Cultured Primary Cortical Cells Under β-amyloid Exposure

β-amyloid (Aβ)-mediated neuronal apoptosis contributes to the pathogenesis of Alzheimer's disease (AD). This study aimed to investigate whether astragalosides (AST) could inhibit Aβ-induced apoptosis in vivo and in vitro and to explore the underlying mechanisms. Amyloid β-protein fragment 25-35 (Aβ_25-35) was administered to cerebral lateral ventricle of rats to make the AD models in vivo. AST was able to attenuate both cortical cell degeneration and memory deficits in the AD rats. AST also inhibited Aβ_25-35-induced cytotoxicity (e.g., decreased cell viability); apoptosis (e.g., increased caspase-3 expression, increased DNA fragmentation, and Tau hyperphosphorylation); synaptotoxicity (e.g., increased loss of both a dendritic marker, microtubule-associated protein 2 (MAP-2) and synaptic proteins, synaptophysins); and mitochondrial dysfunction (e.g., increased mitochondrial membrane potential) in cultured primary rat cortical cells. The beneficial effect of AST in reducing Aβ-induced cytotoxicity, apoptosis, and mitochondrial dysfunction in cortical cells were blocked by inhibition of phosphoinositide 3-kinase (PI3K)-dependent protein kinase B (PKB, as known as AKT) activation with LY294002. In addition, inhibition of extracellular protein kinase (ERK) with U0126 shared with the AST the same beneficial effects in reducing Aβ-induced apoptosis. Our data suggest that the cortical PI3K/AKT and MAPK (or ERK) pathways as appealing therapeutic targets in treating AD, and AST may have a positive impact on AD treatment via modulation of both PI3K/AKT and ERK pathways.

Upregulated Ras/Raf/ERK1/2 signaling pathway: a new hope in the repair of spinal cord injury

An increasing number of studies report that the Ras/Raf/extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway has a death-promoting apoptotic function in neural cells. We hypothesized that the Ras/Raf/ERK1/2 signaling pathway may be abnormally regulated in rat injured spinal cord models. The weight drop method was used to establish rat spinal cord injury at T₉. Western blot analysis and immunohistochemical staining revealed Ras expression was dramatically elevated, and the phosphorylations of A-Raf, B-Raf and C-Raf were all upregulated in the injured spinal cord. Both mitogen-activated protein kinase kinase 1/2 and ERK1/2, which belong to the Ras/Raf signaling kinases, were upregulated. These results indicate that Ras/Raf/ERK1/2 signaling may be upregulated in injured spinal cord and are involved in recovery after spinal cord injury.

Rewarming from therapeutic hypothermia induces cortical neuron apoptosis in a swine model of neonatal hypoxic-ischemic encephalopathy

The consequences of therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy are poorly understood. Adverse effects from suboptimal rewarming could diminish neuroprotection from hypothermia. Therefore, we tested whether rewarming is associated with apoptosis. Piglets underwent hypoxia-asphyxia followed by normothermic or hypothermic recovery at 2 hours. Hypothermic groups were divided into those with no rewarming, rewarming at 0.5 °C/hour, or rewarming at 4 °C/hour. Neurodegeneration at 29 hours was assessed by hematoxylin and eosin staining, TUNEL assay, and immunoblotting for cleaved caspase-3. Rewarmed piglets had more apoptosis in motor cortex than did those that remained hypothermic after hypoxia-asphyxia. Apoptosis in piriform cortex was greater in hypoxic-asphyxic, rewarmed piglets than in naive/sham piglets. Caspase-3 inhibitor suppressed apoptosis with rewarming. Rapidly rewarmed piglets had more caspase-3 cleavage in cerebral cortex than did piglets that remained hypothermic or piglets that were rewarmed slowly. We conclude that rewarming from therapeutic hypothermia can adversely affect the newborn brain by inducing apoptosis through caspase mechanisms.

Automated quantification of neuronal networks and single-cell calcium dynamics using calcium imaging

BACKGROUND

Recent advances in genetically engineered calcium and membrane potential indicators provide the potential to estimate the activation dynamics of individual neurons within larger, mesoscale networks (100s-1000+neurons). However, a fully integrated automated workflow for the analysis and visualization of neural microcircuits from high speed fluorescence imaging data is lacking.

NEW METHOD

Here we introduce FluoroSNNAP, Fluorescence Single Neuron and Network Analysis Package. FluoroSNNAP is an open-source, interactive software developed in MATLAB for automated quantification of numerous biologically relevant features of both the calcium dynamics of single-cells and network activity patterns. FluoroSNNAP integrates and improves upon existing tools for spike detection, synchronization analysis, and inference of functional connectivity, making it most useful to experimentalists with little or no programming knowledge.

RESULTS

We apply FluoroSNNAP to characterize the activity patterns of neuronal microcircuits undergoing developmental maturation in vitro. Separately, we highlight the utility of single-cell analysis for phenotyping a mixed population of neurons expressing a human mutant variant of the microtubule associated protein tau and wild-type tau.

COMPARISON WITH EXISTING METHOD(S)

We show the performance of semi-automated cell segmentation using spatiotemporal independent component analysis and significant improvement in detecting calcium transients using a template-based algorithm in comparison to peak-based or wavelet-based detection methods. Our software further enables automated analysis of microcircuits, which is an improvement over existing methods.

CONCLUSIONS

We expect the dissemination of this software will facilitate a comprehensive analysis of neuronal networks, promoting the rapid interrogation of circuits in health and disease.

Insulin protects against Aβ-induced spatial memory impairment, hippocampal apoptosis and MAPKs signaling disruption

Alzheimer disease (AD) is a progressive neurodegenerative disease characterized by extracellular deposits of beta amyloid (Aβ) and neuronal loss particularly in the hippocampus. Accumulating evidences have implied that insulin signaling impairment plays a key role in the pathology of AD; as much as it is considered as type 3 Diabetes. MAPKs are a group of signaling molecules which are involved in pathobiology of AD. Therefore this study was designed to investigate if intrahippocampal insulin hinders Aβ-related memory deterioration, hippocampal apoptosis and MAPKs signaling alteration induced by Aβ. Adult male Sprague-Dawely rats weighing 250-300 g were used in this study. The canules were implanted bilaterally into CA1 region. Aβ25-35 was administered during first 4 days after surgery (5 μg/2.5 μL/daily). Insulin treatment (0.5 or 6 mU) was done during days 4-9. The animal's learning and memory capability was assessed on days 10-13 using Morris water maze. After finishing of behavioral studies the hippocampi was isolated and the amount of hippocampal cleaved caspase 3 (the landmark of apoptosis) and the phosphorylated (activated) forms of P38, JNK and ERK was analyzed by western blot. The results showed that insulin in 6 but not 0.5 mU reversed the memory loss induced by Aβ25-35. Western blot analysis revealed that Aβ25-35 induced elevation of caspase-3 and all 3 MAPks subfamily activity, while insulin in 6 mu restored ERK and P38 activation but has no effect on JNK. This study disclosed that intrahippocampal insulin treatment averts not only Aβ-induced memory deterioration but also hippocampal caspase-3, ERK and P38 activation.

The developmental pattern of the RAS/RAF/Erk1/2 pathway in the BTBR autism mouse model

BTBR mice exhibit several autistic-like behaviors and are currently used as a model for understanding mechanisms that may be responsible for the pathogenesis of autism. Ras/Raf/ERK1/2 signaling has been suggested to play an important role in neural development, learning, memory, and cognition. Two studies reported that a deletion of a locus on chromosome 16 containing the mitogen-activated protein kinase 3 (MAPK3) gene, which encodes ERK1, is associated with autism. In the present study, Ras/Raf/ERK1/2 signaling was found to be up-regulated in BTBR mice relative to matched control B6 mice, to further suggest involvement in the pathogenesis of autism. To further characterize the developmental pattern of Ras/Raf/ERK1/2 signaling, varying stages during development were sampled to reveal an up-regulation in newborn and 2-week old BTBR mice relative to age-matched B6 mice. By the age of 3-week, Ras/Raf/ERK1/2 signaling in the brain of BTBR mice was unaltered relative to B6 mice, with this trend maintained in 6-week samples. These results suggest that the alteration of Ras/Raf/ERK signaling in the early developmental stages in mice could contribute to the noted autistic phenotype. Furthermore, these findings support the value of BTBR mice to serve as a human analog for autistic etiological research and aid in a better understanding of the developmental mechanisms of autism.

Knockdown of cyclin-dependent kinase 10 (cdk10) gene impairs neural progenitor survival via modulation of raf1a gene expression

In this study, we used zebrafish as an animal model to elucidate the developmental function of cdk10 in vertebrates. In situ hybridization analyses demonstrated that cdk10 is expressed throughout development with a relative enrichment in the brain in the late stages. Similar to its mammalian ortholog, cdk10 can interact with the transcription factor ETS2 and exhibit kinase activity by phosphorylating histone H1. Morpholino-based loss of cdk10 expression caused apoptosis in sox2-positive cells and decreased the expression of subsequent neuronal markers. Acetylated tubulin staining revealed a significant reduction in the number of Rohon-Beard sensory neurons in cdk10 morphants. This result is similar to that demonstrated by decreased islet2 expression in the dorsal regions. Moreover, cdk10 morphants exhibited a marked loss of huC-positive neurons in the telencephalon and throughout the spinal cord axis. The population of retinal ganglion cells was also diminished in cdk10 morphants. These phenotypes were rescued by co-injection of cdk10 mRNA. Interestingly, the knockdown of cdk10 significantly elevated raf1a mRNA expression. Meanwhile, an MEK inhibitor (U0126) recovered sox2 and ngn1 transcript levels in cdk10 morphants. Our findings provide the first functional characterization of cdk10 in vertebrate development and reveal its critical function in neurogenesis by modulation of raf1a expression.

An adeno-associated virus-based intracellular sensor of pathological nuclear factor-κB activation for disease-inducible gene transfer

Stimulation of resident cells by NF-κB activating cytokines is a central element of inflammatory and degenerative disorders of the central nervous system (CNS). This disease-mediated NF-κB activation could be used to drive transgene expression selectively in affected cells, using adeno-associated virus (AAV)-mediated gene transfer. We have constructed a series of AAV vectors expressing GFP under the control of different promoters including NF-κB -responsive elements. As an initial screen, the vectors were tested in vitro in HEK-293T cells treated with TNF-α. The best profile of GFP induction was obtained with a promoter containing two blocks of four NF-κB -responsive sequences from the human JCV neurotropic polyoma virus promoter, fused to a new tight minimal CMV promoter, optimally distant from each other. A therapeutical gene, glial cell line-derived neurotrophic factor (GDNF) cDNA under the control of serotype 1-encapsidated NF-κB -responsive AAV vector (AAV-NF) was protective in senescent cultures of mouse cortical neurons. AAV-NF was then evaluated in vivo in the kainic acid (KA)-induced status epilepticus rat model for temporal lobe epilepsy, a major neurological disorder with a central pathophysiological role for NF-κB activation. We demonstrate that AAV-NF, injected in the hippocampus, responded to disease induction by mediating GFP expression, preferentially in CA1 and CA3 neurons and astrocytes, specifically in regions where inflammatory markers were also induced. Altogether, these data demonstrate the feasibility to use disease-activated transcription factor-responsive elements in order to drive transgene expression specifically in affected cells in inflammatory CNS disorders using AAV-mediated gene transfer.

Tissue-type plasminogen activator protects neurons from excitotoxin-induced cell death via activation of the ERK1/2-CREB-ATF3 signaling pathway

The release of the serine proteinase tissue-type plasminogen activator (tPA) from cerebral cortical neurons has a neuroprotective effect in the ischemic brain. Because excitotoxicity is a basic mechanism of ischemia-induced cell death, here we investigated the effect of tPA on excitotoxin-induced neuronal death. We report that genetic overexpression of neuronal tPA or treatment with recombinant tPA renders neurons resistant to the harmful effects of an excitotoxic injury in vitro and in vivo. We found that at concentrations found in the ischemic brain, tPA interacts with synaptic but not extrasynaptic NMDARs. This effect is independent of tPA's proteolytic properties and leads to a rapid and transient phosphorylation of the extracellular signal regulated kinases1/2 (ERK1/2), with ERK1/2-mediated activation of the cAMP response element binding protein (CREB) and induction of the neuroprotective CREB-regulated activating transcription factor 3 (Atf3). In line with these observations, Atf3 down-regulation abrogates the protective effect of tPA against excitotoxin-induced neuronal death. Our data indicate that tPA preferentially activates synaptic NMDARs via a plasminogen-independent mechanism turning on a cell signaling pathway that protects neurons from the deleterious effects of excitotoxicity.

Interactions between SIRT1 and MAPK/ERK regulate neuronal apoptosis induced by traumatic brain injury in vitro and in vivo

Traumatic brain injury (TBI) is a serious insult that frequently leads to neurological dysfunction or death. Silent information regulator family protein 1 (SIRT1), as the founding member of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases, has recently been demonstrated to have neuroprotective effect in several models of neurodegenerative diseases. The present study attempts to determine whether SIRT1 has a neuroprotective effect in the model of TBI, and further to investigate the possible regulatory mechanism of neuron death. Thus, we employ transection model in vitro and weight-drop model in vivo to mimic the insults of TBI. The study shows that the expressions of SIRT1, phosphorylation extracellular signal-regulated kinase (p-ERK) and cleaved Caspase-3 are induced after trauma injury in vitro or in vivo. Furthermore, inhibiting SIRT1 by pharmacological inhibitor salermide or SIRT1 siRNA significantly promotes apoptotic neuron death and reduces ERK1/2 activation induced by mechanical injury in vitro and in vivo. Inhibition of ERK1/2 activation with PD98059 or U0126 (two mitogen activated protein kinase kinase inhibitors) in vitro and in vivo significantly attenuates the SIRT1 and cleaved Caspase-3 expression to protect neuron against TBI-induced apoptosis. These results reveal that SIRT1 plays a neuroprotective effect against neuronal apoptosis induced by TBI. The interactions between SIRT1 and MAPK/ERK pathway regulate neuronal apoptosis induced by mechanical trauma injury in vitro and in vivo.

Up-regulation of Ras/Raf/ERK1/2 signaling impairs cultured neuronal cell migration, neurogenesis, synapse formation, and dendritic spine development

The Ras/Raf/ERK1/2 signaling pathway controls many cellular responses such as cell proliferation, migration, differentiation, and death. In the nervous system, emerging evidence also points to a death-promoting role for ERK1/2 in both in vitro and in vivo models of neuronal death. Recent studies have suggested that abnormal apoptosis in the central nervous system may be involved in the pathogenesis of autism. Two studies reported that both a microdeletion and microduplication on chromosome 16, which includes the MAPK3 gene that encodes ERK1, are associated with autism. In addition, our recent work showed that Ras/Raf/ERK1/2 signaling activities were significantly up-regulated in the frontal cortex of autistic individuals and in the BTBR murine model of autism. To further investigate how Ras/Raf/ERK1/2 up-regulation may lead to the development of autism, we developed a cellular model of Raf/ERK up-regulation by over-expressing c-Raf in cultured cortical neurons (CNs) and cerebellar granule cells (CGCs). We found that Raf/ERK up-regulation stimulates the migration of both CNs and CGCs, and impairs the formation of excitatory synapses in CNs. In addition, we found that Raf/ERK up-regulation inhibits the development of mature dendritic spines in CNs. Investigating the possible mechanisms through which Raf/ERK up-regulation affects excitatory synapse formation and dendritic spine development, we discovered that Raf/ERK up-regulation suppresses the development and maturation of CNs. Together, these results suggest that the up-regulation of the Raf/ERK signaling pathway may contribute to the pathogenesis of autism through both its impairment of cortical neuron development and causing neural circuit imbalances.

Caspase-3 activation as a bifurcation point between plasticity and cell death

Death-mediating proteases such as caspases and caspase-3 in particular, have been implicated in neurodegenerative processes, aging and Alzheimer's disease. However, emerging evidence suggests that in addition to their classical role in cell death, caspases play a key role in modulating synaptic function. It is remarkable that active caspases-3, which can trigger widespread damage and degeneration, aggregates in structures as delicate as synapses and persists in neurons without causing acute cell death. Here, we evaluate this dichotomy, and discuss the hypothesis that caspase-3 may be a bifurcation point in cellular signaling, able to orient the neuronal response to stress down either pathological/apoptotic pathways or towards physiological cellular remodeling. We propose that temporal, spatial and other regulators of caspase activity are key determinants of the ultimate effect of caspase-3 activation in neurons. This concept has implications for differential roles of caspase-3 activation across the lifespan. Specifically, we propose that limited caspase-3 activation is critical for synaptic function in the healthy adult brain while chronic activation is involved in degenerative processes in the aging brain.

Epigenetic regulation of motor neuron cell death through DNA methylation

DNA methylation is an epigenetic mechanism for gene silencing engaged by DNA methyltransferase (Dnmt)-catalyzed methyl group transfer to cytosine residues in gene-regulatory regions. It is unknown whether aberrant DNA methylation can cause neurodegeneration. We tested the hypothesis that Dnmts can mediate neuronal cell death. Enforced expression of Dnmt3a induced degeneration of cultured NSC34 cells. During apoptosis of NSC34 cells induced by camptothecin, levels of Dnmt1 and Dnmt3a increased fivefold and twofold, respectively, and 5-methylcytosine accumulated in nuclei. Truncation mutation of the Dnmt3a catalytic domain and Dnmt3a RNAi blocked apoptosis of cultured neurons. Inhibition of Dnmt catalytic activity with RG108 and procainamide protected cultured neurons from excessive DNA methylation and apoptosis. In vivo, Dnmt1 and Dnmt3a are expressed differentially during mouse brain and spinal cord maturation and in adulthood when Dnmt3a is abundant in synapses and mitochondria. Dnmt1 and Dnmt3a are expressed in motor neurons of adult mouse spinal cord, and, during their apoptosis induced by sciatic nerve avulsion, nuclear and cytoplasmic 5-methylcytosine immunoreactivity, Dnmt3a protein levels and Dnmt enzyme activity increased preapoptotically. Inhibition of Dnmts with RG108 blocked completely the increase in 5-methycytosine and the apoptosis of motor neurons in mice. In human amyotrophic lateral sclerosis (ALS), motor neurons showed changes in Dnmt1, Dnmt3a, and 5-methylcytosine similar to experimental models. Thus, motor neurons can engage epigenetic mechanisms to drive apoptosis, involving Dnmt upregulation and increased DNA methylation. These cellular mechanisms could be relevant to human ALS pathobiology and disease treatment.

Anthocyanins extracted from black soybean seed coat protect primary cortical neurons against in vitro ischemia

The present study investigated the neuroprotective effects of anthocyanins extracted from black soybean (cv. Cheongja 3, Glycine max (L.) MERR.) seed coat against oxygen-glucose deprivation (OGD) and glutamate-induced cell death in rat primary cortical neurons. Lactate dehydrogenase (LDH) release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assays were employed to assess cell membrane damage and viability of primary neurons, respectively. OGD-induced cell death in 7 d in vitro primary cortical neurons was found to be OGD duration-dependent, and approximately 3.5 h of OGD resulted in ≈60% cell death. Treatment with black soybean anthocyanins dose-dependently prevented membrane damage and increased the viability of primary neurons that were exposed to OGD. Glutamate-induced neuronal cell death was dependent on the glutamate concentration at relatively low concentrations and the number of days the cells remained in culture. Interestingly, black soybean anthocyanins did not protect against glutamate-induced neuronal cell death. They did, however, inhibit the excessive generation of reactive oxygen species (ROS) and preserve mitochondrial membrane potential (MMP) in primary neurons exposed to OGD. In agreement with the neuroprotective effect of crude black soybean anthocyanins, purified cyanidin-3-glucoside (C3G), the major component of anthocyanins, also offered dose-dependent neuroprotection against OGD-induced neuronal cell death. Moreover, black soybean C3G markedly prevented excessive generation of ROS and preserved MMP in primary neurons that were exposed to OGD. Collectively, these results suggest that the neuroprotection of primary rat cortical neurons by anthocyanins that were extracted from black soybean seed coat might be mediated through oxidative stress inhibition and MMP preservation but not through glutamate-induced excitotoxicity attenuation.

The Neuroprotective Potential of Cyanidin-3-glucoside Fraction Extracted from Mulberry Following Oxygen-glucose Deprivation

In this study, cyanidin-3-glucoside (C3G) fraction extracted from the mulberry fruit (Morus alba L.) was investigated for its neuroprotective effects against oxygen-glucose deprivation (OGD) and glutamate-induced cell death in rat primary cortical neurons. Cell membrane damage and mitochondrial function were assessed by LDH release and MTT reduction assays, respectively. A time-course study of OGD-induced cell death of primary cortical neurons at 7 days in vitro (DIV) indicated that neuronal death was OGD duration-dependent. It was also demonstrated that OGD for 3.5 h resulted in approximately 50% cell death, as determined by the LDH release assay. Treatments with mulberry C3G fraction prevented membrane damage and preserved the mitochondrial function of the primary cortical neurons exposed to OGD for 3.5 h in a concentration-dependent manner. Glutamate-induced cell death was more pronounced in DIV-9 and DIV-11 cells than that in DIV-7 neurons, and an application of 50µM glutamate was shown to induce approximately 40% cell death in DIV-9 neurons. Interestingly, treatment with mulberry C3G fraction did not provide a protective effect against glutamate-induced cell death in primary cortical neurons. On the other hand, treatment with mulberry C3G fraction maintained the mitochondrial membrane potential (MMP) in primary cortical neurons exposed to OGD as assessed by the intensity of rhodamine-123 fluorescence. These results therefore suggest that the neuroprotective effects of mulberry C3G fraction are mediated by the maintenance of the MMP and mitochondrial function but not by attenuating glutamate-induced excitotoxicity in rat primary cortical neurons.

Upregulation of Ras/Raf/ERK1/2 signaling and ERK5 in the brain of autistic subjects

Autism is a neurodevelopmental disorder characterized by impairments in social interaction, verbal communication and repetitive behaviors. A number of studies have shown that the Ras/Raf/ERK1/2 (extracellular signal-regulated kinase) signaling pathway plays important roles in the genesis of neural progenitors, learning and memory. Ras/Raf/ERK1/2 and ERK5 have also been shown to have death-promoting apoptotic roles in neural cells. Recent studies have shown a possible association between neural cell death and autism. In addition, two recent studies reported that a deletion of a locus on chromosome 16, which included the mitogen-activated protein kinase 3 (MAPK3) gene that encodes ERK1, is associated with autism. Most recently, our laboratory detected that Ras/Raf/ERK1/2 signaling activities were significantly enhanced in the brain of BTBR mice that model autism, as they exhibit many autism-like behaviors. We thus hypothesized that Ras/Raf/ERK1/2 signaling and ERK5 could be abnormally regulated in the brain of autistic subjects. In this study, we show that the expression of Ras protein was significantly elevated in the frontal cortex of autistic subjects. C-Raf phosphorylation was increased in the frontal cortex, while both C-Raf and A-Raf activities were enhanced in the cerebellum of autistic subjects. We also detected that both the protein expression and activities of ERK1/2 were significantly upregulated in the frontal cortex of autistic subjects, but not in the cerebellum. Furthermore, we showed that ERK5 protein expression is upregulated in both frontal cortex and cerebellum of autistic subjects. These results suggest that the upregulation of Ras/Raf/ERK1/2 signaling and ERK5 activities mainly found in the frontal cortex of autistic subjects may be critically involved in the pathogenesis of autism.

Specific correction of a splice defect in brain by nutritional supplementation

Recent studies emphasize the importance of mRNA splicing in human genetic disease, as 20-30% of all disease-causing mutations are predicted to result in mRNA splicing defects. The plasticity of the mRNA splicing reaction has made these mutations attractive candidates for the development of therapeutics. Familial dysautonomia (FD) is a severe neurodegenerative disorder, and all patients have an intronic IVS20+6T>C splice site mutation in the IKBKAP gene, which results in tissue-specific skipping of exon 20 and a corresponding reduction in ikappaB kinase complex associated protein (IKAP) levels. We created transgenic mouse lines using a human IKBKAP bacterial artificial chromosome (BAC) into which we inserted the IKBKAP splice mutation (FD BAC) and have shown that the transgenic mice exhibit the same tissue-specific aberrant splicing patterns as seen in FD patients. We have previously demonstrated that the plant cytokinin kinetin can significantly improve the production of wild-type IKBKAP transcripts in FD lymphoblast cell lines by improving exon inclusion. In this study, we tested the ability of kinetin to alter IKBKAP splicing in the transgenic mice carrying the FD BAC and show that it corrects IKBKAP splicing in all major tissues assayed, including the brain. The amount of wild-type IKBKAP mRNA and IKAP protein was significantly higher in the kinetin-treated mice. These exciting results prove that treatment of FD, as well as other mechanistically related splicing disorders, with kinetin holds great promise as a potential therapeutic aimed at increasing normal protein levels, which may, in turn, slow disease progression.

Lipopolysaccharide-induced preconditioning against ischemic injury is associated with changes in toll-like receptor 4 expression in the rat developing brain

Lipopolysaccharide (LPS) preconditioning reduces ischemic injury in adult brain by activating Toll-like receptor 4 (TLR-4). We sought to investigate the effect of brain maturity on the efficacy of LPS preconditioning against hypoxic-ischemic (HI) injury in the developing rat brain. Rat pups at the specified age were randomly assigned to LPS-treated (0.1 mg/kg) or saline-treated groups. HI injury was induced 48 h later by occluding the right common carotid artery followed by transient hypoxia. Brains were removed 1 wk after HI injury, and infarct volumes were compared between the two groups. TLR-4 expression was also compared among different ages. We found that LPS treated P7, P9, and P14 rat pups had significantly smaller infarct volume compared with saline-treated pups (p = 0.006, 0.03, and 0.01, respectively). This significant reduction in infarct volume was not observed in P3 and P5 rats. TLR-4 expression was significantly higher in older rats compared with P3 and P5 rats (p < 0.01). These findings indicate that LPS-induced preconditioning is a robust neuroprotective phenomenon in the ischemic developing brain that is age dependent. Pattern of TLR-4 expression is also affected by brain maturity and likely to be responsible for differences in the efficacy of LPS preconditioning.

Neuronal cell death in neonatal hypoxia-ischemia

Perinatal hypoxic-ischemic encephalopathy (HIE) is a significant cause of mortality and morbidity in infants and young children. Therapeutic opportunities are very limited for neonatal and pediatric HIE. Specific neural systems and populations of cells are selectively vulnerable in HIE; however, the mechanisms of degeneration are unresolved. These mechanisms involve oxidative stress, excitotoxicity, inflammation, and the activation of several different cell death pathways. Decades ago the structural and mechanistic basis of the cellular degeneration in HIE was thought to be necrosis. Subsequently, largely due to advances in cell biology and to experimental animal studies, emphasis has been switched to apoptosis or autophagy mediated by programmed cell death (PCD) mechanisms as important forms of degeneration in HIE. We have conceptualized based on morphological and biochemical data that this degeneration is better classified according to an apoptosis-necrosis cell death continuum and that programmed cell necrosis has prominent contribution in the neurodegeneration of HIE in animal models. It is likely that neonatal HIE evolves through many cell death chreodes influenced by the dynamic injury landscape. The relevant injury mechanisms remain to be determined in human neonatal HIE, though preliminary work suggests a complexity in the cell death mechanisms greater than that anticipated from experimental animal models. The accurate identification of the various cell death chreodes and their mechanisms unfolding within the immature brain matrix could provide fresh insight for developing meaningful therapies for neonatal and pediatric HIE.

Loss of caspase-2-dependent apoptosis induces autophagy after mitochondrial oxidative stress in primary cultures of young adult cortical neurons

Mitochondrial dysfunctions have been associated with neuronal apoptosis and are characteristic of neurodegenerative conditions. Caspases play a central role in apoptosis; however, their involvement in mitochondrial dysfunction-induced neuronal apoptosis remains elusive. In the present report using rotenone, a complex I inhibitor that causes mitochondrial dysfunction, we determined the initiator caspase and its role in cell death in primary cultures of cortical neurons from young adult mice (1-2 months old). By pretreating the cells with a cell-permeable, biotinylated pan-caspase inhibitor that irreversibly binds to and traps the active caspase, we identified caspase-2 as an initiator caspase activated in rotenone-treated primary neurons. Loss of caspase-2 inhibited rotenone-induced apoptosis; however, these neurons underwent a delayed cell death by necrosis. We further found that caspase-2 acts upstream of mitochondria to mediate rotenone-induced apoptosis in neurons. The loss of caspase-2 significantly inhibited rotenone-induced activation of Bid and Bax and the release of cytochrome c and apoptosis inducing factor from mitochondria. Rotenone-induced downstream activation of caspase-3 and caspase-9 were also inhibited in the neurons lacking caspase-2. Autophagy was enhanced in caspase-2 knock-out neurons after rotenone treatment, and this response was important in prolonging neuronal survival. In summary, the present study identifies a novel function of caspase-2 in mitochondrial oxidative stress-induced apoptosis in neurons cultured from young adult mice.

An approach to experimental synaptic pathology using green fluorescent protein-transgenic mice and gene knockout mice to show mitochondrial permeability transition pore-driven excitotoxicity in interneurons and motoneurons

Researchers used transgenic mice expressing enhanced-green fluorescent protein (eGFP) driven by either the glycine transporter-2 gene promoter to specifically visualize glycinergic interneurons or the homeobox-9 (Hb9) gene promoter to visualize motoneurons for assessing their vulnerabilities to excitotoxins in vivo. Stereotaxic excitotoxic lesions were made in adult male and female mouse lumbar spinal cord with the specific N-methyl-D-aspartate (NMDA) receptor agonist quinolinic acid (QA) and the non-NMDA ion channel glutamate receptor agonist kainic acid (KA). QA and KA induced large-scale degeneration of glycinergic interneurons in spinal cord. Glycinergic interneurons were more sensitive than motoneurons to NMDA receptor-mediated and non-NMDA glutamate receptor-mediated excitotoxicity. Outcome after spinal cord excitotoxicity was gender-dependent, with males showing greater sensitivity than females. Excitotoxic degeneration of spinal interneurons resembled apoptosis, while motoneuron degeneration appeared non-apoptotic. Perikaryal mitochondrial accumulation was antecedent to both NMDA and non-NMDA receptor-mediated excitotoxic stimulation of interneurons and motoneurons. Genetic ablation of cyclophilin D, a regulator of the mitochondrial permeability transition pore (mPTP), protected both interneurons and motoneurons from excitotoxicity. The results demonstrate in adult mouse spinal cord that glycinergic interneurons are more sensitive than motoneurons to excitotoxicity that stimulates mitochondrial accumulation, and that the mPTP has pro-death functions mediating apoptotic and non-apoptotic neuronal degeneration in vivo.

Protein S protects neurons from excitotoxic injury by activating the TAM receptor Tyro3-phosphatidylinositol 3-kinase-Akt pathway through its sex hormone-binding globulin-like region

The anticoagulant factor protein S (PS) protects neurons from hypoxic/ischemic injury. However, molecular mechanisms mediating PS protection in injured neurons remain unknown. Here, we show mouse recombinant PS protects dose-dependently mouse cortical neurons from excitotoxic NMDA-mediated neuritic bead formation and apoptosis by activating the phosphatidylinositol 3-kinase (PI3K)-Akt pathway (EC(50) = 26 ± 4 nm). PS stimulated phosphorylation of Bad and Mdm2, two downstream targets of Akt, which in neurons subjected to pathological overstimulation of NMDA receptors (NMDARs) increased the antiapoptotic Bcl-2 and Bcl-X(L) levels and reduced the proapoptotic p53 and Bax levels. Adenoviral transduction with a kinase-deficient Akt mutant (Ad.Akt(K179A)) resulted in loss of PS-mediated neuronal protection, Akt activation, and Bad and Mdm2 phosphorylation. Using the TAM receptors tyrosine kinases Tyro3-, Axl-, and Mer-deficient neurons, we showed that PS protected neurons lacking Axl and Mer, but not Tyro3, suggesting a requirement of Tyro3 for PS-mediated protection. Consistent with these results, PS dose-dependently phosphorylated Tyro3 on neurons (EC(50) = 25 ± 3 nm). In an in vivo model of NMDA-induced excitotoxic lesions in the striatum, PS dose-dependently reduced the lesion volume in control mice (EC(50) = 22 ± 2 nm) and protected Axl(-/-) and Mer(-/-) transgenic mice, but not Tyro3(-/-) transgenic mice. Using different structural PS analogs, we demonstrated that the C terminus sex hormone-binding globulin-like (SHBG) domain of PS is critical for neuronal protection in vitro and in vivo. Thus, our data show that PS protects neurons by activating the Tyro3-PI3K-Akt pathway via its SHGB domain, suggesting potentially a novel neuroprotective approach for acute brain injury and chronic neurodegenerative disorders associated with excessive activation of NMDARs.

Novel role of KCNQ2/3 channels in regulating neuronal cell viability

Overactivation of certain K(+) channels can mediate excessive K(+) efflux and intracellular K(+) depletion, which are early ionic events in apoptotic cascade. The present investigation examined a possible role of the KCNQ2/3 channel or M-channel (also named Kv7.2/7.3 channels) in the pro-apoptotic process. Whole-cell recordings detected much larger M-currents (212 ± 31 pA or 10.5 ± 1.5 pA/pF) in cultured hippocampal neurons than that in cultured cortical neurons (47 ± 21 pA or 2.4 ± 0.8 pA/pF). KCNQ2/3 channel openers N-ethylmaleimide (NEM) and flupirtine caused dose-dependent K(+) efflux, intracellular K(+) depletion, and cell death in hippocampal cultures, whereas little cell death was induced by NEM in cortical cultures. The NEM-induced cell death was antagonized by co-applied KCNQ channel inhibitor XE991 (10 μM), or by elevated extracellular K(+) concentration. Supporting a mediating role of KCNQ2/3 channels in apoptosis, expression of KCNQ2 or KCNQ2/3 channels in Chinese hamster ovary (CHO) cells initiated caspase-3 activation. Consistently, application of NEM (20 μM, 8 h) in hippocampal cultures similarly caused caspase-3 activation assessed by immunocytochemical staining and western blotting. NEM increased the expression of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), induced mitochondria membrane depolarization, cytochrome c release, formation of apoptosome complex, and apoptosis-inducing factor (AIF) translocation into nuclear. All these events were attenuated by blocking KCNQ2/3 channels. These findings provide novel evidence that KCNQ2/3 channels could be an important regulator in neuronal apoptosis.

Mitochondrial and Cell Death Mechanisms in Neurodegenerative Diseases

Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS) are the most common human adult-onset neurodegenerative diseases. They are characterized by prominent age-related neurodegeneration in selectively vulnerable neural systems. Some forms of AD, PD, and ALS are inherited, and genes causing these diseases have been identified. Nevertheless, the mechanisms of the neuronal cell death are unresolved. Morphological, biochemical, genetic, as well as cell and animal model studies reveal that mitochondria could have roles in this neurodegeneration. The functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress and overlying genetic variations, triggering neurodegeneration according to a cell death matrix theory. In AD, alterations in enzymes involved in oxidative phosphorylation, oxidative damage, and mitochondrial binding of Aβ and amyloid precursor protein have been reported. In PD, mutations in putative mitochondrial proteins have been identified and mitochondrial DNA mutations have been found in neurons in the substantia nigra. In ALS, changes occur in mitochondrial respiratory chain enzymes and mitochondrial cell death proteins. Transgenic mouse models of human neurodegenerative disease are beginning to reveal possible principles governing the biology of selective neuronal vulnerability that implicate mitochondria and the mitochondrial permeability transition pore. This review summarizes how mitochondrial pathobiology might contribute to neuronal death in AD, PD, and ALS and could serve as a target for drug therapy.

Mesenchymal stem cells inhibition of chronic ethanol-induced oxidative damage via upregulation of phosphatidylinositol-3-kinase/Akt and modulation of extracellular signal-regulated kinase 1/2 activation in PC12 cells and neurons

It is well known that chronic ethanol consumption damages CNS through oxidative stress which results in many dysfunctions. Recently, it has been demonstrated that as a promising strategy to treat several neurological diseases, transplanted bone marrow-derived mesenchymal stem cells (MSCs) can secrete lots of protective factors that in turn promote function recovery. In the present study, we assessed the potential effects of MSCs conditioned medium (MSC-CM) against chronic ethanol-associated damage on PC12 cells and primary cortical neurons. We found that pretreatment with MSC-CM notably improved cell survival, prevented chronic ethanol-associated apoptosis and abolished the robust deterioration in oxidative status. In addition, we also discovered that chronic ethanol exposure induced an inactivation of phosphatidylinositol-3-kinase (PI3K)/Akt and a lasting activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in both PC12 cells and primary cortical neurons which were able to be reversed by MSC-CM. The PI3K inhibitor (LY294002) was able to reduce the antioxidative and cytoprotective effects conferred by MSC-CM, in part, and the ERK1/2 inhibitor (PD98059) was able to elicit significant protection from chronic ethanol cytotoxicity but not rescue the deterioration in oxidative status induced by chronic ethanol. Taken together, these findings provide the first evidence that MSCs might have potent antioxidant action to shield the apoptotic impairment from chronic ethanol exposure in PC12 cells and neurons, which is involved in upregulation of PI3K/Akt and modulation of ERK1/2 activation, at least partially.

JNK contributes to Hif-1alpha regulation in hypoxic neurons

Hypoxia is an established factor of neurodegeneration. Nowadays, attention is directed at understanding how alterations in the expression of stress-related signaling proteins contribute to age dependent neuronal vulnerability to injury. The purpose of this study was to investigate how Hif-1alpha, a major neuroprotective factor, and JNK signaling, a key pathway in neurodegeneration, relate to hypoxic injury in young (6DIV) and adult (12DIV) neurons. We could show that in young neurons as compared to mature ones, the protective factor Hif-1alpha is more induced while the stress protein phospho-JNK displays lower basal levels. Indeed, changes in the expression levels of these proteins correlated with increased vulnerability of adult neurons to hypoxic injury. Furthermore, we describe for the first time that treatment with the D-JNKI1, a JNK-inhibiting peptide, rescues adult hypoxic neurons from death and contributes to Hif-1alpha upregulation, probably via a direct interaction with the Hif-1alpha protein.

ERK and cell death: ERK1/2 in neuronal death

Extracellular signal-regulated kinase (ERK) is a versatile protein kinase that regulates many cellular functions. Growing evidence suggests that ERK1/2 plays a crucial role in promoting cell death in a variety of neuronal systems, including neurodegenerative diseases. It is believed that the magnitude and the duration of ERK1/2 activity determine its cellular function. In this review, we summarize recent evidence for a role of ERK1/2 in neuronal death. Furthermore, we discuss the mechanisms involved in ERK1/2 mediating neuronal death.

Homocysteine-NMDA receptor-mediated activation of extracellular signal-regulated kinase leads to neuronal cell death

Hyperhomocysteinemia is an independent risk factor for stroke and neurological abnormalities. However, the underlying cellular mechanisms by which elevated homocysteine can promote neuronal death is not clear. In the present study we have examined the role of NMDA receptor-mediated activation of the extracellular signal-regulated kinase-mitogen-activated protein (ERK-MAP) kinase pathway in homocysteine-dependent neurotoxicity. The study demonstrates that in neurons l-homocysteine-induced cell death was mediated through activation of NMDA receptors. The study also shows that homocysteine-dependent NMDA receptor stimulation and resultant Ca2+ influx leads to rapid and sustained phosphorylation of ERK-MAP kinase. Inhibition of ERK phosphorylation attenuates homocysteine-mediated neuronal cell death thereby demonstrating that activation of ERK-MAP kinase signaling pathway is an intermediate step that couples homocysteine-mediated NMDA receptor stimulation to neuronal death. The findings also show that cAMP response-element binding protein (CREB), a pro-survival transcription factor and a downstream target of ERK, is only transiently activated following homocysteine exposure. The sustained activation of ERK but a transient activation of CREB together suggest that exposure to homocysteine initiates a feedback loop that shuts off CREB signaling without affecting ERK phosphorylation and thereby facilitates homocysteine-mediated neurotoxicity.

Selective vulnerability of neurons in primary cultures and in neurodegenerative diseases

Primary neuronal cultures are commonly used to dissect the molecular and cellular mechanisms that underlie human brain diseases. Neurons dissociated from an embryonic brain and grown in culture dishes are almost by definition different from those residing inside a living brain. Not only are the individual cells stripped of their normal chemical and physical contacts, but the cellular composition of the cultures (the ratio of cell types) can be affected by many intrinsic and extrinsic factors, including brain region, neuronal birthday, gender, genetic background and in vitro age. Changes in any of these factors may have a strong impact on the outcome of the experiment. In a recent study, Romito-DiGiacomo et al. /54/ demonstrated that when neurons were harvested from murine embryonic cortex, the typical protocol favored cells that were just finishing cell division at the time of harvest. By taking advantage of the fact that the date of the final cell division (birthday) of a neuron correlates with its final position in the cortical plate they were able to assay deeper layer neurons (layers V-VI) separately from the more superficial layers (layers II-III). They reported that while the superficial cells were sensitive to the toxic effect of beta-amyloid, the deeper layer neurons were virtually resistant to death in its presence. The findings recapitulate selective vulnerability in the neocortex of Alzheimer's disease. This is a beautiful example of how to turn the apparent weakness of primary cultures into strength through experimental design and data interpretation. Selective vulnerability is a common feature of neurodegenerative disease, thus it is critical to use the right primary culture. Do you know what is in your culture?

Role of the sodium hydrogen exchanger in maitotoxin-induced cell death in cultured rat cortical neurons

Maitotoxin (MTX) is one of the most potent toxins known to date. It causes massive calcium (Ca(2+)) influx and necrotic cell death in various tissues. However, the exact mechanism(s) underlying its cellular toxicity is not fully understood. In the present study, the role of the sodium hydrogen exchanger (NHE) in MTX-induced increases in intracellular Ca(2+) and subsequent cell death were investigated in cultured rat cortical neurons. Intracellular Ca(2+) concentrations ([Ca(2+)](i)) were measured fluorimetrically using FURA-2 as the fluorescence indicator. Cell death was measured with the alamarBlue cell viability assay and the vital dye ethidium bromide (EB) uptake assay. Results showed that MTX increased, in a concentration dependent manner, both [Ca(2+)](i) and cell death in cortical neurons. Decreasing the pH of the treatment medium from 7.5 to 6.0 diminished MTX-induced cell death. The protection offered by lowering extracellular pH was not due to MTX degradation, because it was still effective even if the cells were treated with MTX in normal pH and then switched to a lower pH. Pretreatment of cells with the specific NHE inhibitor, 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), prevented MTX-induced increases in [Ca(2+)](i), as well as cell death in a concentration dependent manner. Furthermore, knockdown of NHE1 by SiRNA transfection suppressed MTX-induced cell death in human embryonic kidney (HEK) cells. Together, these results suggest that NHE1 plays a major role in MTX-induced neurotoxicity.

Protective effects of N-methyl-D-aspartate receptor antagonism on VX-induced neuronal cell death in cultured rat cortical neurons

Exposure of the central nervous system to organophosphorus (OP) nerve agents induces seizures and neuronal cell death. Here we report that the OP nerve agent, VX, induces apoptotic-like cell death in cultured rat cortical neurons. The VX effects on neurons were concentration-dependent, with an IC(50) of approximately 30 microM. Blockade of N-methyl-D-aspartate receptors (NMDAR) with 50 microM. D-2-amino-5-phosphonovalerate (APV) diminished 30 microM VX-induced total cell death, as assessed by alamarBlue assay and Hoechst staining. In contrast, neither antagonists of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) nor metabotropic glutamate receptors (mGluRs) had any effect on VX-induced neurotoxicity. VX-induced neuronal cell death could not be solely attributed to acetylcholinesterase (AChE) inhibition, since neither the reversible pharmacological cholinesterase inhibitor, physostigmine, nor the muscarinic receptor antagonist, atropine, affected VX-induced cell death. Importantly, APV was found to be therapeutically effective against VX-induced cell death up to 2 h post VX exposure. These results suggest that NMDARs, but not AMPARs or mGluRs, play important roles in VX-induced cell death in cultured rat cortical neurons. Based on their therapeutic effects, NMDAR antagonists may be beneficial in the treatment of VX-induced neurotoxicities.