Rotenone-induced caspase 9/3-independent and -dependent cell death in undifferentiated and differentiated human neural stem cells

Effects of Complex I Inhibition on the Architecture of Neural Rosettes Differentiated from Human-Induced Pluripotent Stem Cells

Orchestrated changes in cell arrangements and cell-to-cell contacts are susceptible to cellular stressors during central nervous system development. Effects of mitochondrial complex I inhibition on cell-to-cell contacts have been studied in vascular and intestinal structures; however, its effects on developing neuronal cells are largely unknown. We investigated the effects of the classical mitochondrial stressor and complex I inhibitor, rotenone, on the architecture of neural rosettes-radially organized neuronal progenitor cells (NPCs)-differentiated from human-induced pluripotent stem cells. We then analyzed the effects of rotenone on the distribution of cell-contact proteins within neural rosettes. Exposure to rotenone for 24 hours led to a dose-dependent irreversible disruption of the neural rosette architecture and relocalization of the cell-contact proteins ZO-1, β-catenin, and N-cadherin from the rosette center to the pericellular region. Though the levels of nestin and SOX2 remained unchanged, NPCs showed decreased levels of the NPC marker PAX6 and exhibited impaired neurogenesis following rotenone exposure. Our study suggests that complex I inhibition leads to a rearrangement of intercellular contacts with disruptive effects on neuronal development.

Human-Induced Pluripotent Stem Cell-Derived Neural Organoids as a Novel In Vitro Platform for Developmental Neurotoxicity Assessment

There has been a recent drive to replace in vivo studies with in vitro studies in the field of toxicity testing. Therefore, instead of conventional animal or planar cell culture models, there is an urgent need for in vitro systems whose conditions can be strictly controlled, including cell-cell interactions and sensitivity to low doses of chemicals. Neural organoids generated from human-induced pluripotent stem cells (iPSCs) are a promising in vitro platform for modeling human brain development. In this study, we developed a new tool based on various iPSCs to study and predict chemical-induced toxicity in humans. The model displayed several neurodevelopmental features and showed good reproducibility, comparable to that of previously published models. The results revealed that basic fibroblast growth factor plays a key role in the formation of the embryoid body, as well as complex neural networks and higher-order structures such as layered stacking. Using organoid models, pesticide toxicities were assessed. Cells treated with low concentrations of rotenone underwent apoptosis to a greater extent than those treated with high concentrations of rotenone. Morphological changes associated with the development of neural progenitor cells were observed after exposure to low doses of chlorpyrifos. These findings suggest that the neuronal organoids developed in this study mimic the developmental processes occurring in the brain and nerves and are a useful tool for evaluating drug efficacy, safety, and toxicity.

A molecular framework for autistic experiences: Mitochondrial allostatic load as a mediator between autism and psychopathology

Molecular autism research is evolving toward a biopsychosocial framework that is more informed by autistic experiences. In this context, research aims are moving away from correcting external autistic behaviors and toward alleviating internal distress. Autism Spectrum Conditions (ASCs) are associated with high rates of depression, suicidality and other comorbid psychopathologies, but this relationship is poorly understood. Here, we integrate emerging characterizations of internal autistic experiences within a molecular framework to yield insight into the prevalence of psychopathology in ASC. We demonstrate that descriptions of social camouflaging and autistic burnout resonate closely with the accepted definitions for early life stress (ELS) and chronic adolescent stress (CAS). We propose that social camouflaging could be considered a distinct form of CAS that contributes to allostatic overload, culminating in a pathophysiological state that is experienced as autistic burnout. Autistic burnout is thought to contribute to psychopathology via psychological and physiological mechanisms, but these remain largely unexplored by molecular researchers. Building on converging fields in molecular neuroscience, we discuss the substantial evidence implicating mitochondrial dysfunction in ASC to propose a novel role for mitochondrial allostatic load in the relationship between autism and psychopathology. An interplay between mitochondrial, neuroimmune and neuroendocrine signaling is increasingly implicated in stress-related psychopathologies, and these molecular players are also associated with neurodevelopmental, neurophysiological and neurochemical aspects of ASC. Together, this suggests an increased exposure and underlying molecular susceptibility to ELS that increases the risk of psychopathology in ASC. This article describes an integrative framework shaped by autistic experiences that highlights novel avenues for molecular research into mechanisms that directly affect the quality of life and wellbeing of autistic individuals. Moreover, this framework emphasizes the need for increased access to diagnoses, accommodations, and resources to improve mental health outcomes in autism.

Metformin attenuates rotenone-induced oxidative stress and mitochondrial damage via the AKT/Nrf2 pathway

Oxidative stress and mitochondrial dysfunction are now widely accepted as the major factors involved in the pathogenesis of Parkinson's disease (PD). Rotenone, a commonly used environmental toxin also reproduces these principle pathological features of PD. Hence, it is used frequently to induce experimental PD in cells and animals. In this study, we evaluated the neuroprotective effects of metformin against rotenone-induced toxicity in SH-SY5Y cells. Metformin treatment clearly rescued these cells from rotenone-mediated cell death via the reduction of the cytosolic and mitochondrial levels of reactive oxygen species and restoration of mitochondrial function. Furthermore, metformin upregulated PGC-1α, the master regulator of mitochondrial biogenesis and key antioxidant molecules, including glutathione and superoxide dismutase. We demonstrated that the drug exerted its cytoprotective effects by activating nuclear factor erythroid 2-related factor 2 (Nrf2)/heme-oxygenase (HO)-1 pathway, which in turn, is dependent on AKT activation by metformin. Thus, our results implicate that metformin provides neuroprotection against rotenone by inhibiting oxidative stress in the cells by inducing antioxidant system via upregulation of transcription mediated by Nrf2, thereby restoring the rotenone-induced mitochondrial dysfunction and energy deficit in the cells.

High-Throughput Screening of Compound Neurotoxicity Using 3D-Cultured Neural Stem Cells on a 384-Pillar Plate

Assessing the neurotoxicity of test chemicals has typically been performed using two-dimensionally (2D)-cultured neuronal cell monolayers and animal models. The in vitro 2D cell models are simple and straightforward compared to animal models, which have the disadvantage of being relatively low throughput, expensive, and time consuming. Despite their extensive use in this area of neurotoxicology research, both models often do not accurately recapitulate human outcomes. To bridge this gap and attempt to better replicate what happens in vivo, three-dimensionally (3D) cultured neural stem cells (NSCs) encapsulated in hydrogels on a 384-pillar plate have been developed via miniature 3D bioprinting. This technology allows users to print NSCs on a pillar plate for rapid 3D cell culture as well as high-throughput compound screening. For this, the 384-pillar plate with bioprinted NSCs is sandwiched with a standard 384-well plate with growth medium for 3D culture, allowing researchers to expose the cells to test compounds and stain them with various fluorescent dyes for a suite of high-content imaging assays, including assays for DNA damage, mitochondrial impairment, cell membrane integrity, intracellular glutathione levels, and apoptosis. After acquiring cell images from an automated fluorescence microscope and extracting fluorescence intensities, researchers can obtain the IC₅₀ value of each compound to evaluate critical parameters in neurotoxicity. Here, we provide a detailed description of protocols for cell printing on a 384-pillar plate, 3D NSC culture, compound testing, 3D cell staining, and image acquisition and analysis, which altogether will allow researchers to investigate mechanisms of compound neurotoxicity with 3D-cultured NSCs in a high-throughput manner. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Three-dimensional neural stem cell culture on a 384-pillar plate Basic Protocol 2: Compound treatment and cell staining Basic Protocol 3: Image acquisition, processing, and data analysis.

Rotenone-induced necrosis in insect cells via the cytoplasmic membrane damage and mitochondrial dysfunction

Rotenone, a selective inhibitor of mitochondrial complex I, has been extensively studied on kinds of neuron and neuroblast in Parkinson's disease. However, little is known about the potential mechanism of this promising botanical insecticide upon insect cells. In the article, cell proliferation of two Lepidoptera cell lines, Spodoptera litura SL-1 cells and Spodoptera frugiperda Sf9 cells, were all inhibited by rotenone in a time- and dose-dependent manner. Typical necrotic characteristics of cell morphology and ultrastructure, such as plasma membrane collapses and organelle lyses, were all observed by transmission electron microscope and scanning electron microscope. Moreover, irregular DNA degradation was also detected by DNA gel electrophoresis and Hoechst 33258 staining, while the typical apoptotic feature, DNA ladder, hadn't been observed. Flow cytometric analysis showed that rotenone-induced cell death of Sf9 and SL-1 cells accompanied with the plasma membrane potential depolarization and mitochondrial membrane potential reduction. Furthermore, the activity of Na⁺-K⁺-ATPase was detected in our study. In conclusion, rotenone could cause necrosis but not apoptosis in insect cells through a mitochondrial- and plasmic membrane-dependent pattern, which shed a light on the rotenone-induced cytotoxicity on insects.

Copper Dependent Modulation of α-Synuclein Phosphorylation in Differentiated SHSY5Y Neuroblastoma Cells

Copper (Cu) dyshomeostasis plays a pivotal role in several neuropathologies, such as Parkinson's disease (PD). Metal accumulation in the central nervous system (CNS) could result in loss-of-function of proteins involved in Cu metabolism and redox cycling, generating reactive oxygen species (ROS). Moreover, neurodegenerative disorders imply the presence of an excess of misfolded proteins known to lead to neuronal damage. In PD, Cu accumulates in the brain, binds α-synuclein, and initiates its aggregation. We assessed the correlation between neuronal differentiation, Cu homeostasis regulation, and α-synuclein phosphorylation. At this purpose, we used differentiated SHSY5Y neuroblastoma cells to reproduce some of the characteristics of the dopaminergic neurons. Here, we reported that differentiated cells expressed a significantly higher amount of a copper transporter protein 1 (CTR1), increasing the copper uptake. Cells also showed a significantly more phosphorylated form of α-synuclein, further increased by copper treatment, without modifications in α-synuclein levels. This effect depended on the upregulation of the polo-like kinase 2 (PLK2), whereas the levels of the relative protein phosphatase 2A (PP2A) remained unvaried. No changes in the oxidative state of the cells were identified. The Cu dependent alteration of α-synuclein phosphorylation pattern might potentially offer new opportunities for clinical intervention.

High-content imaging of 3D-cultured neural stem cells on a 384-pillar plate for the assessment of cytotoxicity

The assessment of neurotoxicity has been performed traditionally with animals. However, in vivo studies are highly expensive and time-consuming, and often do not correlate to human outcomes. Thus, there is a need for cost-effective, high-throughput, highly predictive alternative in vitro test methods based on early markers of mechanisms of toxicity. High-content imaging (HCI) assays performed on three-dimensionally (3D) cultured cells could provide better understanding of the mechanism of toxicity needed to predict neurotoxicity in humans. However, current 3D cell culture systems lack the throughput required for screening neurotoxicity against a large number of chemicals. Therefore, we have developed miniature 3D neural stem cell (NSC) culture on a unique 384-pillar plate, which is complementary to conventional 384-well plates. Mitochondrial membrane impairment, intracellular glutathione level, cell membrane integrity, DNA damage, and apoptosis have been tested against 3D-cultured ReNcell VM on the 384-pillar plate with four model compounds rotenone, 4-aminopyridine, digoxin, and topotecan. The HCI assays performed in 3D-cultured ReNcell VM on the 384-pillar plates were highly robust and reproducible as indicated by the average Z' factor of 0.6 and CV values around 12%. From concentration-response curves and IC₅₀ values, mitochondrial membrane impairment appears to be the early stage marker of cell death by the compounds.

Biophysical and biomechanical properties of neural progenitor cells as indicators of developmental neurotoxicity

Conventional in vitro toxicity studies have focused on identifying IC₅₀ and the underlying mechanisms, but how toxicants influence biophysical and biomechanical changes in human cells, especially during developmental stages, remain understudied. Here, using an atomic force microscope, we characterized changes in biophysical (cell area, actin organization) and biomechanical (Young's modulus, force of adhesion, tether force, membrane tension, tether radius) aspects of human fetal brain-derived neural progenitor cells (NPCs) induced by four classes of widely used toxic compounds, including rotenone, digoxin, N-arachidonoylethanolamide (AEA), and chlorpyrifos, under exposure up to 36 h. The sub-cellular mechanisms (apoptosis, mitochondria membrane potential, DNA damage, glutathione levels) by which these toxicants induced biochemical changes in NPCs were assessed. Results suggest a significant compromise in cell viability with increasing toxicant concentration (p < 0.01), and biophysical and biomechanical characteristics with increasing exposure time (p < 0.01) as well as toxicant concentration (p < 0.01). Impairment of mitochondrial membrane potential appears to be the most sensitive mechanism of neurotoxicity for rotenone, AEA and chlorpyrifos exposure, but compromise in plasma membrane integrity for digoxin exposure. The surviving NPCs remarkably retained stemness (SOX2 expression) even at high toxicant concentrations. A negative linear correlation (R² = 0.92) exists between the elastic modulus of surviving cells and the number of living cells in that environment. We propose that even subtle compromise in cell mechanics could serve as a crucial marker of developmental neurotoxicity (mechanotoxicology) and therefore should be included as part of toxicology assessment repertoire to characterize as well as predict developmental outcomes.

Strategic design of peptide-decorated aligned nanofibers impregnated with triiodothyronine for neural regeneration

Nerve injuries are often debilitating as its regeneration occurs in a slow and laborious manner. Remediation of nerve injury is a colossal task as functional restoration in larger gaps seldom occurs due to the complex nerve regeneration mechanism. A nanofiber-based graft material has been fabricated to provide topographical and biochemical cues to encourage neural differentiation. Laminin plays a crucial role in supporting peripheral nerve regeneration and hence aligned polyvinyl cinnamate nanofibers surface-conjugated with laminin-derived cell-adhesion peptides have been fabricated to improve selective neural adhesion and regeneration. Further, triiodothyronine has been encapsulated within the nanofibers enabling its sustained release so as to bolster regeneration and reinstate the lost functionality to the damaged nerve. The fabricated nanofibers were characterized for its physicochemical, morphological, and topographical properties. Nanofibers were biocompatible, improved cell adhesion rate, and illustrated favourable interaction with cells. Gene expression (showed 9.5 and 4.1 fold increase in β-tubulin and MAP 2 expression, respectively) and protein expression (immunofluorescence, flow cytometry, and western blot) studies confirmed the positive influence of the scaffold over cell differentiation. The studies were extrapolated to adult zebrafish model with a surgical incision in posterior lateral line. The biocomposite treated group showed earlier functional restoration of the nerve compared with control groups detected by touch-evoked response. Thus, the combination of aligned nanofibers providing topographical cue, along with the peptides and triiodothyronine serving as biochemical cues, has a robust potential to restore functionality to the injured nerve, thereby opening avenues for fabrication of regenerative nerve grafts.

Tailored release of triiodothyronine and retinoic acid from a spatio-temporally fabricated nanofiber composite instigating neuronal differentiation

Regeneration of the central and peripheral nervous system is challenging since the functional restoration of injured nerves is an incredible task. The fabrication of an ideal nerve guide that fulfills the requirement to regenerate nerve tissue is a herculean challenge requiring a combination of both biochemical and topographical cues. The present study explores the combinatorial effect of aligned nanofibers and the regulated delivery of triiodothyronine and retinoic acid on nerve regeneration. A sequential release mechanism is adopted in fabricating the nanofiber scaffold, with triiodothyronine incorporated into the nanofiber shell ensuring its prior release, followed by retinoic acid (entrapped within zein nanoparticles) from the core. The composite nanofibers thus fabricated possess excellent mechanical, physical and thermal properties and good topographical morphology and were highly biocompatible. The nanofibers were scrutinized for their efficacy in stimulating differentiation to a neuronal phenotype. The elongation factor (E-factor) of the neural cells had doubled in the bioactive incorporated composite compared to other scaffolds, as observed on phalloidin staining of their cytoskeleton, which endorsed enhanced neural differentiation on the fabricated nanofiber scaffold. There was a significant increase in the expression of neural-lineage specific markers on investigation of mRNA by real time PCR, showing a 10 fold increase in the gene expression of β-III-tubulin, a 5.5 fold increase for microtubule associated protein 2 gene and 3.5 fold for neurofilament M gene in the cells cultured over bioactive incorporated aligned nanofiber composites. Similarly protein expression was analyzed by immunofluorescence and flow cytometry studies, which showed an increase in the expression of β-III-tubulin in the composite nanofiber. This corroborates that neuronal differentiation is enhanced by the aligned nanotopography and spatio-temporal delivery of triiodothyronine and retinoic acid, opening avenues for nerve regenerative graft fabrication.

Amelioration of apoptotic events in the skeletal muscle of intra-nigrally rotenone-infused Parkinsonian rats by Morinda citrifolia--up-regulation of Bcl-2 and blockage of cytochrome c release

Parkinson's disease is a progressive neurodegenerative movement disorder with the cardinal symptoms of bradykinesia, resting tremor, rigidity, and postural instability, which lead to abnormal movements and lack of activity, which in turn cause muscular damage. Even though studies have been carried out to elucidate the causative factors that lead to muscular damage in Parkinson's disease, apoptotic events that occur in the skeletal muscle and a therapeutical approach to culminate the muscular damage have not been extensively studied. Thus, this study evaluates the impact of rotenone-induced SNPc lesions on skeletal muscle apoptosis and the efficacy of an ethyl acetate extract of Morinda citrifolia in safeguarding the myocytes. Biochemical assays along with apoptotic markers studied by immunoblot and reverse transcription-polymerase chain reaction in the current study revealed that the supplementation of Morinda citrifolia significantly reverted alterations in both biochemical and histological parameters in rotenone-infused PD rats. Treatment with Morinda citrifolia also reduced the expression of pro-apoptotic proteins Bax, caspase-3 and caspase-9 and blocked the release of cytochrome c from mitochondria induced by rotenone. In addition, it augmented the expression of Bcl2 both transcriptionally and translationally. Thus, this preliminary study paves a way to show that the antioxidant and anti-apoptotic activities of Morinda citrifolia can be exploited to alleviate skeletal muscle damage induced by Parkinsonism.

Morinda citrifolia mitigates rotenone-induced striatal neuronal loss in male Sprague-Dawley rats by preventing mitochondrial pathway of intrinsic apoptosis

OBJECTIVES

Parkinson disease (PD) is a neurodegenerative disorder affecting mainly the motor system, as a result of death of dopaminergic neurons in the substantia nigra pars compacta. The present scenario of research in PD is directed to identify novel molecules that can be administered individually or co-administered with L-Dopa to prevent the L-Dopa-Induced Dyskinesia (LID) like states that arise during chronic L-Dopa administration. Hence, in this study, we investigated whether Morinda citrifolia has therapeutic effects in rotenone-induced Parkinson's disease (PD) with special reference to mitochondrial dysfunction mediated intrinsic apoptosis.

METHODS

Male Sprague-Dawley rats were stereotaxically infused with rotenone (3 µg in both SNPc and VTA) and co-treated with the ethyl acetate extract of Morinda citrifolia and levodopa.

RESULTS

The results revealed that rotenone-induced cell death was reduced by MCE treatment as measured by decline in the levels of pro-apoptotic proteins. Moreover, MCE treatment significantly augmented the levels of anti-apoptotic Bcl2 and blocks the release of cytochrome c, thereby alleviating the rotenone-induced dopaminergic neuronal loss, as evidenced by tyrosine hydroxylase (TH) immunostaining in the striatum.

DISCUSSION

Taken together, the results suggest that Morinda citrifolia may be beneficial for the treatment of neurodegenerative diseases like PD.

Molecular Mechanism of Switching of TrkA/p75(NTR) Signaling in Monocrotophos Induced Neurotoxicity

We demonstrate the role of molecular switching of TrkA/p75(NTR) signaling cascade in organophosphate pesticide-Monocrotophos (MCP) induced neurotoxicity in stem cell derived cholinergic neurons and in rat brain. Our in-silico studies reveal that MCP followed the similar pattern of binding as staurosporine and AG-879 (known inhibitors of TrkA) with TrkA protein (PDB ID: 4AOJ) at the ATP binding sites. This binding of MCP to TrkA led to the conformational change in this protein and triggers the cell death cascades. The in-silico findings are validated by observing the down regulated levels of phosphorylated TrkA and its downstream molecules viz., pERK1/2, pAkt and pCREB in MCP-exposed cells. We observe that these MCP induced alterations in pTrkA and downstream signaling molecules are found to be associated with apoptosis and injury to neurons. The down-regulation of TrkA could be linked to increased p75(NTR). The in-vitro studies could be correlated in the rat model. The switching of TrkA/p75(NTR) signaling plays a central role in MCP-induced neural injury in rBNSCs and behavioral changes in exposed rats. Our studies significantly advance the understanding of the switching of TrkA/p75(NTR) that may pave the way for the application of TrkA inducer/p75(NTR) inhibitor for potential therapeutic intervention in various neurodegenerative disorders.

Carbosilane dendrimers inhibit α-synuclein fibrillation and prevent cells from rotenone-induced damage

This study investigates the role of carbosilane dendrimers in fibrillation of α-synuclein and prevention of the mouse hippocampal cell (mHippoE-18) from rotenone-induced damage. Examining the interaction between carbosilane dendrimers and α-synuclein, we found that the dendrimers inhibit fibril formation. We also investigated cell viability, the production of reactive oxygen species (ROS), and mitochondrial membrane potential. mHippoE-18 cells were preincubated with carbosilane dendrimers before rotenone was added. All the dendrimers possess potential protection activity. Preincubation with dendrimers contributed to: increased viability, higher mitochondrial membrane potential, and reduced ROS level in cells. The probable mechanism of cell protection lies in the ability of dendrimers to capture rotenone by encapsulating or binding to its surface groups. The fact that dendrimers have prevention potential is important in the search for new pharmacological strategies against neurodegenerative disorders.

Nlrx1 regulates neuronal cell death

Background

Regulation of cell death during neurodegeneration is one of the key factors that play a role in the speed at which a disease progresses. Out of several cellular pathways responsible for this progression, necrosis and apoptosis are situated on the opposite spectrum of cell death regulation. Necrosis produces an environment that promotes inflammation and cytotoxicity and apoptosis is a highly organized process that maintains tissue homeostasis. A recently discovered protein, Nlrx1, regulates inflammatory and cell death responses during infection.

Findings

Using transfections of N2A cell line, we demonstrate that Nlrx1 redirects cells away from necrosis and towards an apoptotic pathway following rotenone treatments. In addition, Nlrx1 promotes DRP1 phosphorylation and increases mitochondrial fission.

Conclusion

Our results suggest a novel molecular pathway for regulating mitochondrial dynamics and neuronal death. Nlrx1 may play an important role in neurodegenerative diseases, where necrosis is a prominent factor.

Water-soluble coenzyme q10 inhibits nuclear translocation of apoptosis inducing factor and cell death caused by mitochondrial complex I inhibition

The objectives of the study were to explore the mechanism of rotenone-induced cell damage and to examine the protective effects of water-soluble Coenzyme Q10 (CoQ10) on the toxic effects of rotenone. Murine hippocampal HT22 cells were cultured with mitochondrial complex I inhibitor rotenone. Water-soluble CoQ10 was added to the culture media 3 h prior to the rotenone incubation. Cell viability was determined by alamar blue, reactive oxygen species (ROS) production by dihydroethidine (DHE) and mitochondrial membrane potential by tetramethyl rhodamine methyl ester (TMRM). Cytochrome c, caspase-9 and apoptosis-inducing factor (AIF) were measured using Western blotting after 24 h rotenone incubation. Rotenone caused more than 50% of cell death, increased ROS production, AIF nuclear translocation and reduction in mitochondrial membrane potential, but failed to cause mitochondrial cytochrome c release and caspase-9 activation. Pretreatment with water-soluble CoQ10 enhanced cell viability, decreased ROS production, maintained mitochondrial membrane potential and prevented AIF nuclear translocation. The results suggest that rotenone activates a mitochondria-initiated, caspase-independent cell death pathway. Water-soluble CoQ10 reduces ROS accumulation, prevents the fall of mitochondrial membrane potential, and inhibits AIF translocation and subsequent cell death.

Rapamycin does not inhibit human cytomegalovirus reactivation from dendritic cells in vitro

Human cytomegalovirus (HCMV) infection and reactivation are a major cause of morbidity in immune-suppressed patients. Interestingly, epidemiological studies have shown that patients administered the mammalian target of rapamycin (mTOR) inhibitor, sirolimus (rapamycin), exhibit more favourable outcomes, suggestive of activity against HCMV in vivo. Given its relative lack of activity against lytic infection, it is postulated that rapamycin inhibits HCMV reactivation. Here, we showed that rapamycin administered acutely or chronically has little impact on induction of immediate early (IE) gene expression in experimentally latent dendritic cells or cells from naturally latent individuals. Furthermore, we extended these observations to include other inhibitors of mTORC1 and mTORC 2, which similarly have minimal effects on induction of IE gene expression from latency. Taken together, these data suggest that favourable outcomes associated with sirolimus are attributable to indirect effects that influence HCMV reactivation, rather than a direct mechanistic action against HCMV itself.

DJ-1 deficiency triggers microglia sensitivity to dopamine toward a pro-inflammatory phenotype that is attenuated by rasagiline

DJ-1 is an oxidative stress sensor that localizes to the mitochondria when the cell is exposed to oxidative stress. DJ-1 mutations that result in gene deficiency are linked to increased risk of Parkinson's disease (PD). Activation of microglial stress conditions that are linked to PD may result in neuronal death. We postulated that DJ-1 deficiency may increase microglial neurotoxicity. We found that down-regulation of DJ-1 in microglia using an shRNA approach increased cell sensitivity to dopamine as measured by secreted pro-inflammatory cytokines such as IL-1β and IL-6. Furthermore, we discovered that DJ-1-deficient microglia had increased monoamine oxidase activity that resulted in elevation of intracellular reactive oxygen species and nitric oxide leading to increased dopaminergic neurotoxicity. Rasagaline, a monoamine oxidase inhibitor approved for treatment of PD, reduced the microglial pro-inflammatory phenotype and significantly reduced neurotoxicity. Moreover, we discovered that DJ-1-deficient microglia have reduced expression of triggering receptor expressed on myeloid cells 2 (TREM2), previously suggested as a risk factor for pro-inflammation in neurodegenerative diseases. Further studies of DJ-1-mediated cellular pathways in microglia may contribute useful insights into the development of PD providing future avenues for therapeutic intervention

In vitro neuroprotective potential of four medicinal plants against rotenone-induced toxicity in SH-SY5Y neuroblastoma cells

BACKGROUND

Lannea schweinfurthii, Zanthoxylum capense, Scadoxus puniceus and Crinum bulbispermum are used traditionally to treat neurological disorders. The aim of this study was to evaluate the cytoprotective potential of the four plants, after induction of toxicity using rotenone, in SH-SY5Y neuroblastoma cells.

METHODS

Cytotoxicity of the plant extracts and rotenone was assessed using the sulforhodamine B (SRB) assay. Fluorometry was used to measure intracellular redox state (reactive oxygen species (ROS) and intracellular glutathione content), mitochondrial membrane potential (MMP) and caspase-3 activity, as a marker of apoptotic cell death.

RESULTS

Of the tested plants, the methanol extract of Z. capense was the least cytotoxic; LC50 121.3 ± 6.97 μg/ml, while S. puniceus methanol extract was the most cytotoxic; LC50 20.75 ± 1.47 μg/ml. Rotenone reduced intracellular ROS levels after 24 h exposure. Pre-treating cells with S. puniceus and C. bulbispermum extracts reversed the effects of rotenone on intracellular ROS levels. Rotenone exposure also decreased intracellular glutathione levels, which was counteracted by pre-treatment with any one of the extracts. MMP was reduced by rotenone, which was neutralized by pre-treatment with C. bulbispermum ethyl acetate extract. All extracts inhibited rotenone-induced activation of caspase-3.

CONCLUSION

The studied plants demonstrated anti-apoptotic activity and restored intracellular glutathione content following rotenone treatment, suggesting that they may possess neuroprotective properties.

Impairment of Atg5-dependent autophagic flux promotes paraquat- and MPP⁺-induced apoptosis but not rotenone or 6-hydroxydopamine toxicity

Controversial reports on the role of autophagy as a survival or cell death mechanism in dopaminergic cell death induced by parkinsonian toxins exist. We investigated the alterations in autophagic flux and the role of autophagy protein 5 (Atg5)-dependent autophagy in dopaminergic cell death induced by parkinsonian toxins. Dopaminergic cell death induced by the mitochondrial complex I inhibitors 1-methyl-4-phenylpyridinium (MPP⁺) and rotenone, the pesticide paraquat, and the dopamine analog 6-hydroxydopamine (6-OHDA) was paralleled by increased autophagosome accumulation. However, when compared with basal autophagy levels using chloroquine, autophagosome accumulation was a result of impaired autophagic flux. Only 6-OHDA induced an increase in autophagosome formation. Overexpression of a dominant negative form of Atg5 increased paraquat- and MPP⁺-induced cell death. Stimulation of mammalian target of rapamycin (mTOR)-dependent signaling protected against cell death induced by paraquat, whereas MPP⁺-induced toxicity was enhanced by wortmannin, a phosphoinositide 3-kinase class III inhibitor, rapamycin, and trehalose, an mTOR-independent autophagy activator. Modulation of autophagy by either pharmacological or genetic approaches had no effect on rotenone or 6-OHDA toxicity. Cell death induced by parkinsonian neurotoxins was inhibited by the pan caspase inhibitor (Z-VAD), but only caspase-3 inhibition was able to decrease MPP⁺-induced cell death. Finally, inhibition of the lysosomal hydrolases, cathepsins, increased the toxicity by paraquat and MPP⁺, supporting a protective role of Atg5-dependent autophagy and lysosomes degradation pathways on dopaminegic cell death. These results demonstrate that in dopaminergic cells, Atg5-dependent autophagy acts as a protective mechanism during apoptotic cell death induced by paraquat and MPP⁺ but not during rotenone or 6-OHDA toxicity.

MicroRNA-195 targets ADP-ribosylation factor-like protein 2 to induce apoptosis in human embryonic stem cell-derived neural progenitor cells

Neural progenitor cells (NPCs) derived from human embryonic stem cells (hESCs) have great potential in cell therapy, drug screening and toxicity testing of neural degenerative diseases. However, the molecular regulation of their proliferation and apoptosis, which needs to be revealed before clinical application, is largely unknown. MicroRNA miR-195 is known to be expressed in the brain and is involved in a variety of proapoptosis or antiapoptosis processes in cancer cells. Here, we defined the proapoptotic role of miR-195 in NPCs derived from two independent hESC lines (human embryonic stem cell-derived neural progenitor cells, hESC-NPCs). Overexpression of miR-195 in hESC-NPCs induced extensive apoptotic cell death. Consistently, global transcriptional microarray analyses indicated that miR-195 primarily regulated genes associated with apoptosis in hESC-NPCs. Mechanistically, a small GTP-binding protein ADP-ribosylation factor-like protein 2 (ARL2) was identified as a direct target of miR-195. Silencing ARL2 in hESC-NPCs provoked an apoptotic phenotype resembling that of miR-195 overexpression, revealing for the first time an essential role of ARL2 for the survival of human NPCs. Moreover, forced expression of ALR2 could abolish the cell number reduction caused by miR-195 overexpression. Interestingly, we found that paraquat, a neurotoxin, not only induced apoptosis but also increased miR-195 and reduced ARL2 expression in hESC-NPCs, indicating the possible involvement of miR-195 and ARL2 in neurotoxin-induced NPC apoptosis. Notably, inhibition of miR-195 family members could block neurotoxin-induced NPC apoptosis. Collectively, miR-195 regulates cell apoptosis in a context-dependent manner through directly targeting ARL2. The finding of the critical role of ARL2 for the survival of human NPCs and association of miR-195 and ARL2 with neurotoxin-induced apoptosis have important implications for understanding molecular mechanisms that control NPC survival and would facilitate our manipulation of the neurological pathogenesis.

Mechanisms to prevent caspase activation in rotenone-induced dopaminergic neurodegeneration: role of ATP depletion and procaspase-9 degradation

The evidence implicating a mode of cell death that either favors or argues against caspase-dependent apoptosis is available in studies that used experimental models of Parkinson's disease. We sought to investigate the mechanisms by which release of cytochrome c is not linked to caspase activation during rotenone-induced dopaminergic (DA) neurodegeneration. Unlike caspase activation in 6-hydroxydopamine-treated cells, both MN9D DA neuronal cells and primary cultures of mesencephalic neurons showed no obvious signs of caspase activation upon exposure to rotenone. We found that intracellular levels of ATP significantly decreased at the early phase of neurodegeneration (<~24 h) and therefore external addition of ATP to the lysates obtained at this stage reconstituted caspase-3 activity. At a later phase of cell death (>~24 h), both decreased levels of ATP and procaspase-9 contributed to the lack of caspase-3 activation. Under this condition, calpain and the proteasome system were responsible for the degradation of procaspase-9. Consequently, external addition of ATP and procaspase-9 to the lysates harvested at the later phase was required for activation of caspase-3. Similarly, caspase-3 activity was also reconstituted in the lysates harvested from cells co-treated with inhibitors of these proteases and incubated in the presence of external ATP. Taken together, our findings provided a sequential mechanism underlying how DA neurons may undergo caspase-independent cell death, even in the presence of cytoplasmic cytochrome c following inhibition of mitochondrial complex I.

Role of cAMP-responsive element-binding protein (CREB)-regulated transcription coactivator 3 (CRTC3) in the initiation of mitochondrial biogenesis and stress response in liver cells

Peroxisome proliferator-activated receptor α, coactivator 1α (PGC-1α) is the master regulator of mitochondrial biogenesis. PGC-1α expression is under the control of the transcription factor, cAMP-responsive element-binding protein (CREB). In searching for candidate transcription factors that mediate mitochondrial stress-initiated mitochondria-to-nucleus signaling in the regulation of mitochondrial biogenesis, we assessed the effect of silencing CREB-regulated transcription co-activators (CRTC). CRTC isoforms are co-activators of CREB-regulated transcription by a CREB phosphorylation-independent pathway. Using cultured HepG2 cells and primary mouse hepatocytes, we determined that mitochondrial stress imposed by the complex I inhibitor rotenone elicited mitochondrial biogenesis, which was dependent on an induction of PGC-1α, which was inhibited by silencing PGC-1α. PGC-1α induction in response to rotenone was inhibited by silencing the expression of CRTC3, which blocked downstream mitochondria biogenesis. In contrast, silencing CRTC2 did not affect the induction of this pathway in response to rotenone. Thus, CRTC3 plays a selective role in mitochondrial biogenesis in response to rotenone.

Purinergic signaling in embryonic and stem cell development

Nucleotides are of crucial importance as carriers of energy in all organisms. However, the concept that in addition to their intracellular roles, nucleotides act as extracellular ligands specifically on receptors of the plasma membrane took longer to be accepted. Purinergic signaling exerted by purines and pyrimidines, principally ATP and adenosine, occurs throughout embryologic development in a wide variety of organisms, including amphibians, birds, and mammals. Cellular signaling, mediated by ATP, is present in development at very early stages, e.g., gastrulation of Xenopus and germ layer definition of chick embryo cells. Purinergic receptor expression and functions have been studied in the development of many organs, including the heart, eye, skeletal muscle and the nervous system. In vitro studies with stem cells revealed that purinergic receptors are involved in the processes of proliferation, differentiation, and phenotype determination of differentiated cells. Thus, nucleotides are able to induce various intracellular signaling pathways via crosstalk with other bioactive molecules acting on growth factor and neurotransmitter receptors. Since normal development is disturbed by dysfunction of purinergic signaling in animal models, further studies are needed to elucidate the functions of purinoceptor subtypes in developmental processes.

Molecular mechanisms of pesticide-induced neurotoxicity: Relevance to Parkinson's disease

Pesticides are widely used in agricultural and other settings, resulting in continued human exposure. Pesticide toxicity has been clearly demonstrated to alter a variety of neurological functions. Particularly, there is strong evidence suggesting that pesticide exposure predisposes to neurodegenerative diseases. Epidemiological data have suggested a relationship between pesticide exposure and brain neurodegeneration. However, an increasing debate has aroused regarding this issue. Paraquat is a highly toxic quaternary nitrogen herbicide which has been largely studied as a model for Parkinson's disease providing valuable insight into the molecular mechanisms involved in the toxic effects of pesticides and their role in the progression of neurodegenerative diseases. In this work, we review the molecular mechanisms involved in the neurotoxic action of pesticides, with emphasis on the mechanisms associated with the induction of neuronal cell death by paraquat as a model for Parkinsonian neurodegeneration.

Synphilin-1 exhibits trophic and protective effects against Rotenone toxicity

Synphilin-1 is a cytoplasmic protein with unclear function. Synphilin-1 has been identified as an interaction partner of alpha-synuclein. The interaction between synphilin-1 and alpha-synuclein has implications in Parkinson's disease. In this study, we stably overexpressed human synphilin-1 in mouse N1E-115 neuroblastoma cells. We found that overexpression of synphilin-1 shortened cell growth doubling time and increased neurite outgrowth. Knockdown of endogenous synphilin-1 caused neuronal toxicity and shortened neurite outgrowth. We further found that synphilin-1 increased activation of the extracellular signal-regulated kinases (ERK1/2) and mediated neurite outgrowth. Rotenone, mitochondrial complex I inhibitor, has been shown previously to induce dopaminergic neurodegeneration and Parkinsonism in rats and Drosophila. We found that Rotenone induced apoptotic cell death in N1E-115 cells via caspase-3 activation and poly (ADP-ribose) polymerase (PARP) cleavage. Overexpression of synphilin-1 significantly reduced Rotenone-induced cell death, caspase-3 activation and PARP cleavage. The results indicate that synphilin-1 displays trophic and protective effects in vitro, suggesting that synphilin-1 may play a protective role in Parkinson's disease (PD) pathogenesis and may lead to a potential therapeutic target for PD intervention.

VPS41, a protein involved in lysosomal trafficking, is protective in Caenorhabditis elegans and mammalian cellular models of Parkinson's disease

VPS41 is a protein identified as a potential therapeutic target for Parkinson's disease (PD) as a result of a high-throughput RNAi screen in Caenorhabditis elegans. VPS41 has a plausible mechanistic link to the pathogenesis of PD, as in yeast it is known to participate in trafficking of proteins to the lysosomal system and several recent lines of evidence have pointed to the importance of lysosomal system dysfunction in the neurotoxicity of alpha-synuclein (alpha-syn). We found that expression of the human form of VPS41 (hVPS41) prevents dopamine (DA) neuron loss induced by alpha-syn overexpression and 6-hydroxydopamine (6-OHDA) neurotoxicity in C. elegans. In SH-SY5Y neuroblastoma cell lines stably transfected with hVPS41, we determined that presence of this protein conferred protection against the neurotoxins 6-OHDA and rotenone. Overexpression of hVPS41 did not alter the mitochondrial membrane depolarization induced by these neurotoxins. hVPS41 did, however, block downstream events in the apoptotic cascade including activation of caspase-9 and caspase-3, and PARP cleavage. We also observed that hVPS41 reduced the accumulation of insoluble high-molecular weight forms of alpha-syn in SH-SY5Y cells after treatment with rotenone. These data show that hVPS41 is protective against both alpha-syn and neurotoxic-mediated injury in invertebrate and cellular models of PD. These protective functions may be related to enhanced clearance of misfolded or aggregated protein, including alpha-syn. Our studies indicate that hVPS41 may be a useful target for developing therapeutic strategies for human PD.

Autophagy and exosomes in the aged retinal pigment epithelium: possible relevance to drusen formation and age-related macular degeneration

Age-related macular degeneration (AMD) is a major cause of loss of central vision in the elderly. The formation of drusen, an extracellular, amorphous deposit of material on Bruch's membrane in the macula of the retina, occurs early in the course of the disease. Although some of the molecular components of drusen are known, there is no understanding of the cell biology that leads to the formation of drusen. We have previously demonstrated increased mitochondrial DNA (mtDNA) damage and decreased DNA repair enzyme capabilities in the rodent RPE/choroid with age. In this study, we found that drusen in AMD donor eyes contain markers for autophagy and exosomes. Furthermore, these markers are also found in the region of Bruch's membrane in old mice. By in vitro modeling increased mtDNA damage induced by rotenone, an inhibitor of mitochondrial complex I, in the RPE, we found that the phagocytic activity was not altered but that there were: 1) increased autophagic markers, 2) decreased lysosomal activity, 3) increased exocytotic activity and 4) release of chemoattractants. Exosomes released by the stressed RPE are coated with complement and can bind complement factor H, mutations of which are associated with AMD. We speculate that increased autophagy and the release of intracellular proteins via exosomes by the aged RPE may contribute to the formation of drusen. Molecular and cellular changes in the old RPE may underlie susceptibility to genetic mutations that are found in AMD patients and may be associated with the pathogenesis of AMD in the elderly.

Development of a high-throughput screening assay for chemical effects on proliferation and viability of immortalized human neural progenitor cells

There is considerable public concern that the majority of commercial chemicals have not been evaluated for their potential to cause developmental neurotoxicity. Although several chemicals are assessed annually under the current developmental neurotoxicity guidelines, time, resource, and animal constraints prevent testing of large numbers of chemicals using this approach. Thus, incentive is mounting to develop in vitro methods to screen chemicals for their potential to harm the developing human nervous system. As an initial step toward this end, the present studies evaluated an automated, high-throughput method for screening chemical effects on proliferation and viability using ReNcell CX cells, a human neural progenitor cell (hNPC) line. ReNcell CX cells doubled in approximately 36 h and expressed the neural progenitor markers nestin and SOX2. High-throughput assays for cell proliferation (5-bromo-2'-deoxyuridine incorporation) and viability (propidium iodide exclusion) were optimized and tested using known antiproliferative compounds. The utility of this in vitro screen was evaluated further using a set of compounds containing eight known to cause developmental neurotoxicity and eight presumably nontoxic compounds. Six out of eight developmental neurotoxicants significantly inhibited ReNcell CX cell proliferation and/or viability, whereas two out of eight nontoxic chemicals caused only minimal effects. These results demonstrate that chemical effects on cell proliferation and viability can be assessed via high-throughput methods using hNPCs. Further development of this approach as part of a strategy to screen compounds for potential effects on nervous system development is warranted.

Complex I binding by a virally encoded RNA regulates mitochondria-induced cell death

Human cytomegalovirus infection perturbs multiple cellular processes that could promote the release of proapoptotic stimuli. Consequently, it encodes mechanisms to prevent cell death during infection. Using rotenone, a potent inhibitor of the mitochondrial enzyme complex I (reduced nicotinamide adenine dinucleotide-ubiquinone oxido-reductase), we found that human cytomegalovirus infection protected cells from rotenone-induced apoptosis, a protection mediated by a 2.7-kilobase virally encoded RNA (beta2.7). During infection, beta2.7 RNA interacted with complex I and prevented the relocalization of the essential subunit genes associated with retinoid/interferon-induced mortality-19, in response to apoptotic stimuli. This interaction, which is important for stabilizing the mitochondrial membrane potential, resulted in continued adenosine triphosphate production, which is critical for the successful completion of the virus' life cycle. Complex I targeting by a viral RNA represents a refined strategy to modulate the metabolic viability of the infected host cell.

Workgroup report: incorporating in vitro alternative methods for developmental neurotoxicity into international hazard and risk assessment strategies

This is the report of the first workshop on Incorporating In Vitro Alternative Methods for Developmental Neurotoxicity (DNT) Testing into International Hazard and Risk Assessment Strategies, held in Ispra, Italy, on 19-21 April 2005. The workshop was hosted by the European Centre for the Validation of Alternative Methods (ECVAM) and jointly organized by ECVAM, the European Chemical Industry Council, and the Johns Hopkins University Center for Alternatives to Animal Testing. The primary aim of the workshop was to identify and catalog potential methods that could be used to assess how data from in vitro alternative methods could help to predict and identify DNT hazards. Working groups focused on two different aspects: a) details on the science available in the field of DNT, including discussions on the models available to capture the critical DNT mechanisms and processes, and b) policy and strategy aspects to assess the integration of alternative methods in a regulatory framework. This report summarizes these discussions and details the recommendations and priorities for future work.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

Simultaneous age-related depolarization of mitochondrial membrane potential and increased mitochondrial reactive oxygen species production correlate with age-related glutamate excitotoxicity in rat hippocampal neurons

Mitochondria are implicated in glutamate excitotoxicity by causing bioenergetic collapse, loss of Ca(2+) homeostasis, and generation of reactive oxygen species (ROS), all of which become increasingly important clinically with age. Little is known about how aging affects the relative importance of mitochondrial membrane potential (DeltaPsi(m)) and ROS production. To determine aging affects on DeltaPsi(m) and ROS production in individual somal and axonal/dendritic mitochondria, we compared ROS production while simultaneously monitoring DeltaPsi(m) before and after glutamate treatment of live neurons from embryonic (day 18), middle-aged (9-12 months), and old (24 months) rats. At rest, old neuronal mitochondria 1) showed a higher rate of ROS production that was particularly strong in axonal/dendritic mitochondria relative to that in middle-age neurons, 2) were more depolarized in comparison with neurons of other ages, and 3) showed no differences in ROS or DeltaPsi(m) as a function of distance from the nucleus. All DeltaPsi(m) grouped into three classes of high (less than -120 mV), medium (-85 to -120 mV), and low (greater than -85 mV) polarization that shifted toward the lower classes with age at rest. Glutamate exposure dramatically depolarized the DeltaPsi(m) in parallel with greatly increased ROS production, with a surprising absence of an effect of age or distance from the nucleus on these mitochondrial parameters. These data suggest that old neurons are more susceptible to glutamate excitotoxicity because of an insidious depolarization of DeltaPsi(m) and rate of ROS generation at rest that lead to catastrophic failure of phosphorylative and reductive energy supplies under stress.

Divergent Mechanisms of Paraquat, MPP+, and Rotenone Toxicity: Oxidation of Thioredoxin and Caspase-3 Activation

Paraquat, N-methyl-4-phenyl-1,2,3,6 tetrahydropyridine, and rotenone have been shown to reproduce several features of Parkinson's disease in animal and cell culture models. Although these chemicals are known to perturb dopamine homeostasis and induce dopaminergic cell death, their molecular mechanisms of action are not well defined. We have previously shown that paraquat does not require functional dopamine transporter and does not inhibit mitochondrial complex I in order to mediate its toxic action (Richardson et al., 2005). In this study, we show that paraquat specifically oxidized the cytosolic form of thioredoxin and activated Jun N-terminal kinase (JNK), followed by caspase-3 activation. Conversely, 1-methyl-4-phenylpyridinium (MPP(+)) and rotenone oxidized the mitochondrial form of thioredoxin but did not activate JNK-mitogen-activated protein kinase and caspase-3. Loading cells with exogenous dopamine did not exacerbate the toxicity of any of these compounds. These data suggest that oxidative modification of cytosolic proteins is critical to paraquat toxicity, while oxidation of mitochondrial proteins is important for MPP(+) and rotenone toxicity. In addition, intracellular dopamine does not seem to exacerbate the toxicity of these dopaminergic neurotoxicants in this model.

Mechanisms of cell death of neural progenitor cells caused by trophic support deprivation

Cell death of neural progenitor cells is the primary problem limiting the value of neural progenitor cell-based therapy for central nervous system disorders. However, little is known about the mechanism of cell death of neural progenitor cells. In this study, we investigated the mechanisms of cell death of a multipotent cell line, MEB5, caused by deprivation of epidermal growth factor (EGF). When EGF was removed from the culture medium, the total number of viable MEB5 cells reduced, and nuclear condensation and elevation of caspase-3-like enzyme activity were observed in MEB5 cells. Treatment with a broad-range caspase inhibitor reduced cell death in a concentration-dependent manner, indicating that MEB5 cells undergo caspase-mediated apoptotic cell death caused by EGF deprivation. We also investigated the effects of glutamate receptor antagonists, antioxidants and nitric oxide synthase inhibitor on EGF deprivation-induced cell death. N-methyl-D-aspartate (NMDA) glutamate receptor antagonists, alpha-amino-3-hydrozy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptor antagonist and nitric oxide synthase inhibitor failed to reduce cell death. In contrast, two antioxidants with different chemical structures reduced cell death in a concentration-dependent manner. The production of reactive oxygen species was detected in MEB5 cells after EGF deprivation by monitoring dichlorodihydrofluorescein fluorescence as a marker of reactive oxygen species-related radicals. Our results suggest that oxidative stress triggers caspase-mediated apoptosis of neural progenitor cells by trophic support deprivation.

Basic fibroblast growth factor protects against rotenone-induced dopaminergic cell death through activation of extracellular signal-regulated kinases 1/2 and phosphatidylinositol-3 kinase pathways

Administration of rotenone to rats reproduces many features of Parkinson's disease, including dopaminergic neuron degeneration, and provides a useful model to study the pathogenesis of Parkinson's disease. However, the cell death mechanisms induced by rotenone and potential neuroprotective mechanisms against rotenone are not well defined. Here we report that rotenone-induced apoptosis in human dopaminergic SH-SY5Y cells is attenuated by pretreatment with several growth factors, most notably basic fibroblast growth factor (bFGF). bFGF activated both extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol-3 kinase (PI3-kinase) pathways in SH-SY5Y cells. Ectopic activation of ERK1/2 or PI3-kinase protected against rotenone, whereas inhibition of either pathway attenuated bFGF protection. Reducing the expression of the proapoptotic protein Bcl-2-associated death protein (BAD) by small interfering RNA rendered SH-SY5Y cells resistant to rotenone, implicating BAD in rotenone-induced cell death. Interestingly, bFGF induced a long-lasting phosphorylation of BAD at serine 112, suggesting BAD inactivation through the ERK1/2 signaling pathway. Moreover, primary cultured dopaminergic neurons from mesencephalon were more sensitive to rotenone-induced cell death than nondopaminergic neurons in the same culture. The loss of dopaminergic neurons was blocked by bFGF, an inhibition dependent on ERK1/2 and PI3-kinase signaling. These data suggest that rotenone-induced dopaminergic cell death requires BAD and identify bFGF and its activation of ERK1/2 and PI3-kinase signaling pathways as novel intervention strategies to block cell death in the rotenone model of Parkinson's disease.

Simultaneous detection of L-glutamate and nitric oxide from adherently growing cells at known distance using disk shaped dual electrodes

An ex vivo system for simultaneous detection of nitric oxide (NO) and L-glutamate using integrated dual 250 microm platinum disk electrodes modified individually with suitable sensing chemistries has been developed. One of the sensors was coated with an electrocatalytic layer of Ni tetrasulfonate phthalocyanine tetrasodium salt (Ni-TSPc) covered by second layer of Nafion, which stabilises on the one hand the primary oxidation product NO(+) and prevents interferences from negatively charged compounds such as NO(2)(-). For glutamate determination, the second electrode was modified with a crosslinked redox hydrogel consisting of Os complex modified poly(vinylimidazol), glutamate oxidase and peroxidase. A manual x-y-z micromanipulator on top of an inverted optical microscope was used to position the dual electrode sensor at a defined distance of 5 microm from a cell population under visual control. C6 glioma cells were stimulated simultaneously with bradykinin or VEGF to release NO while KCl was used to invoke glutamate release. For evaluation of the glutamate sensors, in some experiments HN10 cells were used. To investigate the sensitivity and reliability of the system, several drugs were applied to the cells, e.g. Ca(2+)-channel inhibitors for testing Ca(2+)-dependence of the release of NO and glutamate, rotenone for inducing oxidative stress and glutamate antagonists for analysing glutamate release. With these drugs the NO and glutamate release was modulated in a similar way then expected from previously described systems or even in-vivo measurements. We therefore conclude that our system is suitable to analyse stress-induced mechanisms in cell lines.

Mitochondrial dysfunction in choline deficiency-induced apoptosis in cultured rat hepatocytes

Our recent studies have demonstrated that generation of ROS is associated with choline deficiency (CD)-induced apoptosis in CWSV-1 cells, an immortalized rat hepatocyte that becomes tumorigenic by stepwise culturing in decreasing levels of choline. In the present study, we investigated the effect of CD on loss of mitochondrial membrane potential (MMP), using the JC-1 probe by FASCAN assay. Our data demonstrate that MMP in CD-cultured cells was decreased in a time- and dose-dependent manner and that significant disruption occurred at 24 h, relative to high choline (HC, 70 microM) cultured cells. In order to investigate further the relationship among the CD-induced ROS, MMP collapse, and apoptosis, we examined the effects of different inhibitors on ROS production, MMP disruption, and apoptosis in CD or HC-cultured CWSV-1 cells. These data indicate that the disruption of MMP is an upstream event in CD-induced apoptosis, and mitochondrial dysfunction plays a key role in mediating CD-induced apoptosis in CWSV-1 cells.

Zinc induced apoptosis in HEP-2 cancer cells: the role of oxidative stress and mitochondria

Induction of apoptosis by zinc sulfate was investigated during 96 h exposure on the cancer Hep-2 cell line. During 48 h of exposure, zinc translocated into mitochondria and stimulated production of reactive oxygen species (ROS), affected cellular GSH management and induced moderate activation of p53 and dissipation of mitochondrial membrane potential. In Zn-exposed cells, mitochondria released cytochrome c and AIF, whose translocation to the cytoplasm or the nucleus coincided with the activation of apoptosis. The use of various pharmacological inhibitors inhibiting particular apoptotic targets (antioxidants such as N-acetyl-cysteine and coenzyme Q, the caspase inhibitors z-DEVD-fmk and z-VAD-fmk, cyclosporin A and bonkgrekic acid) proved that Zn acts both directly and indirectly on mitochondria and observed apoptosis is executed by caspase-dependent and caspase-independent pathways.