Dissociated primary nerve cell cultures as models for assessment of neurotoxicity

Sustained PGC-1α2 or PGC-1α3 expression induces astrocyte dysfunction and degeneration

Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) transcriptional coactivators are key regulators of energy metabolism-related genes and are expressed in energy-demanding tissues. There are several PGC-1α variants with different biological functions in different tissues. The brain is one of the tissues where the role of PGC-1α isoforms remains less explored. Here, we used a toxin-based mouse model of Parkinson's disease (PD) and observed that the expression levels of variants PGC-1α2 and PGC-1α3 in the nigrostriatal pathway increases at the onset of dopaminergic cell degeneration. This increase occurs concomitant with an increase in glial fibrillary acidic protein levels. Since PGC-1α coactivators regulate cellular adaptive responses, we hypothesized that they could be involved in the modulation of astrogliosis induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Therefore, we analysed the transcriptome of astrocytes transduced with expression vectors encoding PGC-1α1 to 1α4 by massively parallel sequencing (RNA-seq) and identified the main cellular pathways controlled by these isoforms. Interestingly, in reactive astrocytes the inflammatory and antioxidant responses, adhesion, migration, and viability were altered by PGC-1α2 and PGC-1α3, showing that sustained expression of these isoforms induces astrocyte dysfunction and degeneration. This work highlights PGC-1α isoforms as modulators of astrocyte reactivity and as potential therapeutic targets for the treatment of PD and other neurodegenerative disorders.

Cadmium induces mitochondrial dysfunction via SIRT1 suppression-mediated oxidative stress in neuronal cells

Cadmium is a widespread environmental contaminant and its neurotoxicity has raised serious concerns. Mitochondrial dysfunction is a key event in Cd-induced nervous system disease; however, the exact molecular mechanism involved has not been fully elucidated. Increasing evidences have shown that Sirtuin 1 (SIRT1) is the key target protein impaired in Cd-induced mitochondrial dysfunction. In this study, the role of SIRT1 in Cd-induced mitochondrial dysfunction and cell death and the underlying mechanisms were evaluated in vitro using PC12 cells and primary rat cerebral cortical neurons. The results showed that Cd exposure caused cell death by inhibiting SIRT1 expression, thus inducing oxidative stress and mitochondrial dysfunction in vitro. However, inhibition of oxidative stress by the antioxidant puerarin alleviated Cd-induced mitochondrial dysfunction. Furthermore, activation of SIRT1 using the agonist Srt1720 significantly abolished Cd-induced oxidative stress and mitochondrial dysfunction and ultimately alleviated Cd-induced neuronal cell death. Collectively, our data indicate that Cd induced mitochondrial dysfunction via SIRT1 suppression-mediated oxidative stress, leading to the death of PC12 cells and primary rat cerebral cortical neurons. These findings suggest a novel mechanism for Cd-induced neurotoxicity.

Neurotoxicity and Underlying Mechanisms of Endogenous Neurotoxins

Endogenous and exogenous neurotoxins are important factors leading to neurodegenerative diseases. In the 1980s, the discovery that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) contributes to Parkinson's disease (PD) symptoms led to new research investigations on neurotoxins. An abnormal metabolism of endogenous substances, such as condensation of bioamines with endogenous aldehydes, dopamine (DA) oxidation, and kynurenine pathway, can produce endogenous neurotoxins. Neurotoxins may damage the nervous system by inhibiting mitochondrial activity, increasing oxidative stress, increasing neuroinflammation, and up-regulating proteins related to cell death. This paper reviews the biological synthesis of various known endogenous neurotoxins and their toxic mechanisms.

Notoginsenoside R2 reduces Aβ25-35-induced neuronal apoptosis and inflammation via miR-27a/SOX8/β-catenin axis

Background: Alzheimer's disease (AD) has affected numerous elderly individuals worldwide. Panax notoginseng has been shown to ameliorate AD symptoms, and notoginsenoside R2 is a key saponin identified in this plant. Purpose: In the current study, we aimed to explore whether notoginsenoside R2 could improve the prognosis of AD. Methods: Herein, primary rat cortical neurons were isolated and they were treated with amyloid beta-peptide (Aβ) 25-35 oligomers. Cellular apoptosis was examined via flow cytometry and Western blotting. miR-27a and SOX8 mRNA expression levels were quantified by quantitative reverse transcription-polymerase chain reaction. Furthermore, the interaction between miR-27a and SOX8 was investigated by utilizing a dual-luciferase reporter assay. Finally, an AD mouse model was established to validate the in vitro findings. Results: Notoginsenoside R2 alleviated Aβ25-35-triggered neuronal apoptosis and inflammation. During this process, miR-27a expression was decreased by notoginsenoside R2, and miR-27a negatively modulated SOX8 expression. Furthermore, activation of SOX8 upregulated β-catenin expression, thus suppressing apoptosis and neuroinflammation. Conclusions: Our animal experiments revealed that notoginsenoside R2 enhanced the cognitive function of AD mice and inhibited neuronal apoptosis. Notoginsenoside R2 ameliorated AD symptoms by reducing neuronal apoptosis and inflammation, thus suggesting a novel direction for AD pharmacotherapy.

Anhydroecgonine methyl ester (AEME), a cocaine pyrolysis product, impairs glutathione-related enzymes response and increases lipid peroxidation in the hippocampal cell culture

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AEME and cocaine decreased GPx, GR and GST activities after 3 and 6 h of exposure.

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AEME and cocaine increased MDA after 48 h of exposure.

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AEME-cocaine combination decreased GPx, GR and GST activities after 3 and 6 h.

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AEME-cocaine combination showed an additive effect on MDA after 48 h of exposure.

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A higher neurotoxic effect after crack cocaine use is suggested.

Crack cocaine smokers inhale, alongside with cocaine, its pyrolysis product, anhydroecgonine methyl ester (AEME). We have previously described AEME neurotoxic effect and its additive effect when co-incubated with cocaine. Our aim was to evaluate, the effect of AEME, cocaine and AEME-cocaine combination on glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) activities after 3 and 6 h of exposure, periods previous to neuronal death. Lipid peroxidation was evaluated through malonaldehyde (MDA) levels at 3, 6, 24 and 48 h of exposure. All treated groups reduced neuronal viability after 24 h of exposure. AEME and cocaine decreased GPx, GR and GST activities after 3 and 6 h, with an increase in MDA levels after 48 h. AEME-cocaine combination decreased the enzymes activities after 3 and 6 h, showing an additive effect in MDA levels after 48 h. These data show that the glutathione-related enzymes imbalance caused by AEME, cocaine or AEME-cocaine combination exposure preceded neuronal death and lipid peroxidation. Moreover, the additive effect on lipid peroxidation observed with AEME-cocaine exposure after 48 h, suggest a higher neurotoxic effect after crack cocaine use when compared to cocaine alone.

Dexmedetomidine protects PC12 cells from lidocaine-induced cytotoxicity via downregulation of Stathmin 1

Background: Understanding of lidocaine-induced neurotoxicity is not complete, resulting in the unsuccessful treatment in some clinical settings. Dexmedetomidine (DEX) has been shown to alleviate lidocaine-induced neurotoxicity in our previous cell model. However, the rationale for DEX combined with lidocaine to reduce lidocaine-induced neurotoxicity in the clinical setting remains to be further clarified in the detailed molecular mechanism. Methods: In this study, we established a cellular injury model by lidocaine preconditioning. Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) proliferation assay kit were used to analyze cell proliferation. Cell apoptosis was measured by flow cytometry and Hoechst 33342 staining. Cell cycle progression was detected by flow cytometry. The protein expression levels were detected by Western blotting and immunofluorescence staining. Results: Our results showed that DEX dose-dependently restored impaired proliferation of PC12 cells induced by lidocaine，as reflected by the increased cell viability and EdU positive cells, which were consistent with the decreased expression of tumor suppressor protein p21 and increased expression of cell cycle-related cyclin D1 and CDK1. In addition, DEX dose-dependently reduced apoptotic PC12 cells induced by lidocaine，as reflected by the decreased expression of apoptosis-related Bax, caspase-3 and caspase-9 and increased expression of anti-apoptotic Bcl-2 compared to the cells only treated with lidocaine. Mechanistically, with gain-or-loss-of-function of STMN1, we showed that DEX-mediated neuroprotection by lidocaine-induced damage is associated with downregulation of STMN1 which might be an upstream molecule involved in regulation of mitochondria death pathway. Conclusion: Our results reveal that DEX is likely to be an effective adjunct to alleviate chronic neurotoxicity induced by lidocaine.

Oxidative stress and cell death induction by amitraz and its metabolite BTS-27271 mediated through cytochrome P450 and NRF2 pathway alteration in primary hippocampal cell

Amitraz is a neurotoxic formamidine pesticide that induces cell death in hippocampal neurons, although its mechanisms are unknown. Amitraz produces reactive oxygen species (ROS), which could lead to cell death. Amitraz was shown to induce different cytochrome P450 (CYP) isoenzymes involved with ROS and apoptotic cell death induction. Finally, amitraz was described to decrease the activity of antioxidant enzymes regulated through KEAP1/NRF2 pathway, thus likely leading to a reduction of ROS elimination and to cell death induction. We evaluated the effect of amitraz or BTS-27271 co-treatment with or without the antioxidant N-acetylcysteine and/or the unspecific CYP inhibitor 1-aminobenzotriazole on cell viability and its related mechanisms in wild type and silenced primary hippocampal neurons after 24 h treatment. We observed that amitraz produced oxidative stress and CYPs induction leading to apoptotic cell death. ROS generation was partially mediated by CYPs induction and downregulation of NRF2-pathway through KEAP1 overexpression. These data could help explain the mechanism by which amitraz induces cell death and oxidative stress and provide a therapeutic strategy to protect against this effect in case of poisoning.

Models used in the study of traumatic brain injury

Traumatic brain injury (TBI) is a contemporary health problem and a leading cause of mortality and morbidity worldwide. Survivors of TBI frequently experience disabling long-term changes in cognition, sensorimotor function, and personality. A crucial step in understanding TBI and providing better treatment has been the use of models to mimic the event under controlled conditions. Here, we describe the known head injury models, which can be classified as whole animal (in vivo), in vitro, and mathematical models. We will also review the ways in which these models have advanced the knowledge of TBI.

Hydroxysafflor yellow a protects brain microvascular endothelial cells against oxygen glucose deprivation/reoxygenation injury: Involvement of inhibiting autophagy via class I PI3K/Akt/mTOR signaling pathway

The present study aimed to test whether Hydroxysafflor yellow A (HSYA) protects the brain microvascular endothelial cells (BMECs) injury induced by oxygen glucose deprivation/reoxygenation (OGD/R) via the PI3K/Akt/mTOR autophagy signaling pathway. Primary rat BMECs were cultured and identified by the expression of factor VIII-related antigen before being exposed to OGD/R to imitate ischemia/reperfusion (I/R) damage in vitro. The protective effect of HSYA was evaluated by assessing (1) cellular morphologic and ultrastructural changes; (2) cell viability and cytotoxicity; (3) transendothelial electrical resistance (TEER) of monolayer BMECs; (4) cell apoptosis; (5) fluorescence intensity of LC3B; (6) LC3 mRNA expression; (7) protein expressions of LC3, Beclin-1, Zonula occludens-1 (ZO-1), phospho-Akt (p-Akt), Akt, phospho-mTOR (p-mTOR) and mTOR. It was found that HSYA (20, 40, and 80 μM) and 3-MA effectively reversed the cellular morphological and ultrastructural changes, increased cell survival, normalized the permeability of BMECs, and suppressed apoptosis induced by OGD/R (2 h OGD followed by 24 h reoxygenation). Concurrently, HSYA and 3-MA also inhibited OGD/R-induced autophagy evidenced by the decreased number of autophagosomes and down-regulated levels of LC3 and Beclin-1 proteins and mRNAs. HSYA (80 μM), in combination with 3-MA showed a synergistic effect. Mechanistic studies revealed that HSYA (80 μM) markedly increased the levels of p-Akt and p-mTOR proteins. Blockade of PI3K activity by ZSTK474 abolished its anti-autophagic and pro-survival effect and lowered both Akt and mTOR phosphorylation levels. Taken together, these results suggest that HSYA protects BMECs against OGD/R-induced injury by inhibiting autophagy via the Class I PI3K/Akt/mTOR signaling pathway.

Effect of puerarin on transcriptome of astrocyte during oxygen-glucose deprivation/reoxygenation injury

Stroke is a serious disease with complex pathomechanism and limited therapeutic effect in clinic. Our previous research has found obvious therapeutic effect of Puerarin (Pur) on stroke injury of rat. The aim of this study is to investigate the transcriptome changes of oxygen-glucose deprivation/reoxygenation (OGD/R)-injured astrocytes before and after the intervention of Pur. Cells activity and apoptosis detection indicated that the activity of OGD/R-injured astrocytes was improved, and the apoptosis was ameliorated by Pur. Affymetrix GeneChip Rat Genome 230 2.0 Array assays indicated that after intervention of Pur, mRNA expressions of 31 genes were up-regulated and 40 genes were down-regulated in OGD group, whereas mRNA expression of 36 genes were up-regulated, and 88 genes were down-regulated in OGD/R group. Pathway analysis indicated that the olfactory transduction pathway and the JAK (janus kinase) 2/STAT (signal transducer and activator of transcription) three pathways were down-regulated by Pur during OGD/R injury of astrocytes. These data indicated that Pur regulates transcriptome and expresses protective effect on astrocytes during OGD/R injury, and may be a potential therapeutic agent for the treatment of stroke.

Muscarinic M1 receptor partially modulates higher sensitivity to cadmium-induced cell death in primary basal forebrain cholinergic neurons: A cholinesterase variants dependent mechanism

Cadmium is a toxic compound reported to produce cognitive dysfunctions, though the mechanisms involved are unknown. In a previous work we described how cadmium blocks cholinergic transmission and induces greater cell death in primary cholinergic neurons from the basal forebrain. It also induces cell death in SN56 cholinergic neurons from the basal forebrain through M1R blockage, alterations in the expression of AChE variants and GSK-3β, and an increase in Aβ and total and phosphorylated Tau protein levels. It was observed that the silencing or blockage of M1R altered ChAT activity, GSK-3β, AChE splice variants gene expression, and Aβ and Tau protein formation. Furthermore, AChE-S variants were associated with the same actions modulated by M1R. Accordingly, we hypothesized that cholinergic transmission blockage and higher sensitivity to cadmium-induced cell death of primary basal forebrain cholinergic neurons is mediated by M1R blockage, which triggers this effect through alteration of the expression of AChE variants. To prove this hypothesis, we evaluated, in primary culture from the basal forebrain region, whether M1R silencing induces greater cell death in cholinergic neurons than cadmium does, and whether in SN56 cells M1R mediates the mechanisms described so as to play a part in the cadmium induction of cholinergic transmission blockage and cell death in this cell line through alteration of the expression of AChE variants. Our results prove that M1R silencing by cadmium partially mediates the greater cell death observed on basal forebrain cholinergic neurons. Moreover, all previously described mechanisms for blocking cholinergic transmission and inducing cell death on SN56 cells after cadmium exposure are partially mediated by M1R through the alteration of AChE expression. Thus, our results may explain cognitive dysfunctions observed in cadmium toxicity.

Activation of sodium channels by α-scorpion toxin, BmK NT1, produced neurotoxicity in cerebellar granule cells: an association with intracellular Ca2+ overloading

Voltage-gated sodium channels (VGSCs) are responsible for the action potential generation in excitable cells including neurons and involved in many physiological and pathological processes. Scorpion toxins are invaluable tools to explore the structure and function of ion channels. BmK NT1, a scorpion toxin from Buthus martensii Karsch, stimulates sodium influx in cerebellar granule cells (CGCs). In this study, we characterized the mode of action of BmK NT1 on the VGSCs and explored the cellular response in CGC cultures. BmK NT1 delayed the fast inactivation of VGSCs, increased the Na⁺ currents, and shifted the steady-state activation and inactivation to more hyperpolarized membrane potential, which was similar to the mode of action of α-scorpion toxins. BmK NT1 stimulated neuron death (EC₅₀ = 0.68 µM) and produced massive intracellular Ca²⁺ overloading (EC₅₀ = 0.98 µM). TTX abrogated these responses, suggesting that both responses were subsequent to the activation of VGSCs. The Ca²⁺ response of BmK NT1 was primary through extracellular Ca²⁺ influx since reducing the extracellular Ca²⁺ concentration suppressed the Ca²⁺ response. Further pharmacological evaluation demonstrated that BmK NT1-induced Ca²⁺ influx and neurotoxicity were partially blocked either by MK-801, an NMDA receptor blocker, or by KB-R7943, an inhibitor of Na⁺/Ca²⁺ exchangers. Nifedipine, an L-type Ca²⁺ channel inhibitor, slightly suppressed both Ca²⁺ response and neurotoxicity. A combination of these three inhibitors abrogated both responses. Considered together, these data ambiguously demonstrated that activation of VGSCs by an α-scorpion toxin was sufficient to produce neurotoxicity which was associated with intracellular Ca²⁺ overloading through both NMDA receptor- and Na⁺/Ca²⁺ exchanger-mediated Ca²⁺ influx.

M1 and M3 muscarinic receptors may play a role in the neurotoxicity of anhydroecgonine methyl ester, a cocaine pyrolysis product

The smoke of crack cocaine contains cocaine and its pyrolysis product, anhydroecgonine methyl ester (AEME). AEME possesses greater neurotoxic potential than cocaine and an additive effect when they are combined. Since atropine prevented AEME-induced neurotoxicity, it has been suggested that its toxic effects may involve the muscarinic cholinergic receptors (mAChRs). Our aim is to understand the interaction between AEME and mAChRs and how it can lead to neuronal death. Using a rat primary hippocampal cell culture, AEME was shown to cause a concentration-dependent increase on both total [³H]inositol phosphate and intracellular calcium, and to induce DNA fragmentation after 24 hours of exposure, in line with the activation of caspase-3 previously shown. Additionally, we assessed AEME activity at rat mAChR subtypes 1–5 heterologously expressed in Chinese Hamster Ovary cells. l-[N-methyl-³H]scopolamine competition binding showed a preference of AEME for the M₂ subtype; calcium mobilization tests revealed partial agonist effects at M₁ and M₃ and antagonist activity at the remaining subtypes. The selective M₁ and M₃ antagonists and the phospholipase C inhibitor, were able to prevent AEME-induced neurotoxicity, suggesting that the toxicity is due to the partial agonist effect at M₁ and M₃ mAChRs, leading to DNA fragmentation and neuronal death by apoptosis.

Brain-targeted distribution and high retention of silver by chronic intranasal instillation of silver nanoparticles and ions in Sprague-Dawley rats

The wide applications of silver nanoparticles (AgNPs) have been concerned regarding their unintentional toxicities. Different exposure modes may cause distinct accumulation, retention and elimination profiles, which are closely related with their toxicities. Unlike silver accumulation profiles through other regular administration modes, the biodistribution, accumulation and elimination of AgNPs by intranasal instillation are not fully understood. This study conducted intranasal instillation of polyvinylpyrrolidone-coated AgNPs in neonatal Sprague-Dawley rats at doses of 1 and 0.1 mg kg(-1) day(-1) for 4 and 12 weeks, respectively. The 4-week recovery was also designed after the 12-week exposure. Silver concentrations in the main tissues or organs were periodically monitored. Parallel exposures using silver ion were performed for the comparative studies. No physiological alterations were observed in AgNP exposures. In comparison, 1 mg kg(-1) day(-1) silver ions decreased body weight gain and caused mortality of 18.2%, showing ionic silver had a relatively higher toxicity than AgNPs. A relatively higher silver accumulation was observed in silver ion groups than AgNP groups. The silver ion release could not fully explain silver accumulation in AgNP exposures, showing silver distribution caused by particulate silver occurred in vivo. The highest silver concentration was in the liver at week 4, while it shifted to the brain after a 12-week exposure. Dose-related silver accumulation occurred for both AgNP and silver ion groups. The time course revealed a uniquely high concentration and retention of brain silver, implying chronic intranasal instillation caused brain-targeted silver accumulation. These findings provided substantial evidence on the potential neuronal threat from the intranasal administration of AgNPs or silver colloid-based products.

GET73 Prevents Ethanol-Induced Neurotoxicity in Primary Cultures of Rat Hippocampal Neurons

AIMS

N-[(4-trifluoromethyl) benzyl] 4-methoxybutyramide (GET73) may be considered a promising therapeutic agent for the treatment of alcohol use disorders. The compound displayed anti-alcohol and anxiolytic properties in rat. In the present study, an in vitro experimental model of chronic ethanol treatment was used to investigate the ability of the compound to counteract the ethanol-induced neurotoxicity.

METHODS

Primary cultures of rat hippocampal neurons were exposed to ethanol (75 mM; 4 days) and the neuroprotective effects of GET73 were assessed by evaluating cell viability, cell morphology, glutamate levels and reactive oxygen species production.

RESULTS

The exposure to ethanol induced a reduction of cell viability, an alteration of cytoskeleton, a decrease in extracellular glutamate levels and an increase of reactive oxygen species production. The addiction of GET73 (1 and 10 µM) 1 h before and during chronic ethanol exposure prevented all the above ethanol-induced effects. Based on the proposed GET73 mechanism of action, the effects of mGlu5 receptor negative allosteric modulator, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), on ethanol-induced reduction of cell viability were also assessed. The results indicated that the addiction of MPEP (100 µM) 1 h before and during chronic ethanol exposure prevented the ethanol-induced cell viability reduction.

CONCLUSION

The present findings provide the first evidence that GET73 shows a neuroprotective role against ethanol-induced neurotoxicity in primary cultures of rat hippocampal neurons. Together with previous findings, these results suggest that GET73 possesses multifaceted properties thus lending further support to the significance of developing GET73 as a therapeutic tool for use in the treatment of alcohol use disorders.

Hydrophilic bile acids protect human blood-brain barrier endothelial cells from disruption by unconjugated bilirubin: an in vitro study

Ursodeoxycholic acid and its main conjugate glycoursodeoxycholic acid are bile acids with neuroprotective properties. Our previous studies demonstrated their anti-apoptotic, anti-inflammatory, and antioxidant properties in neural cells exposed to elevated levels of unconjugated bilirubin (UCB) as in severe jaundice. In a simplified model of the blood-brain barrier, formed by confluent monolayers of a cell line of human brain microvascular endothelial cells, UCB has shown to induce caspase-3 activation and cell death, as well as interleukin-6 release and a loss of blood-brain barrier integrity. Here, we tested the preventive and restorative effects of these bile acids regarding the disruption of blood-brain barrier properties by UCB in in vitro conditions mimicking severe neonatal hyperbilirubinemia and using the same experimental blood-brain barrier model. Both bile acids reduced the apoptotic cell death induced by UCB, but only glycoursodeoxycholic acid significantly counteracted caspase-3 activation. Bile acids also prevented the upregulation of interleukin-6 mRNA, whereas only ursodeoxycholic acid abrogated cytokine release. Regarding barrier integrity, only ursodeoxycholic acid abrogated UCB-induced barrier permeability. Better protective effects were obtained by bile acid pre-treatment, but a strong efficacy was still observed by their addition after UCB treatment. Finally, both bile acids showed ability to cross confluent monolayers of human brain microvascular endothelial cells in a time-dependent manner. Collectively, data disclose a therapeutic time-window for preventive and restorative effects of ursodeoxycholic acid and glycoursodeoxycholic acid against UCB-induced blood-brain barrier disruption and damage to human brain microvascular endothelial cells.

Higher sensitivity to cadmium induced cell death of basal forebrain cholinergic neurons: a cholinesterase dependent mechanism

Cadmium is an environmental pollutant, which is a cause of concern because it can be greatly concentrated in the organism causing severe damage to a variety of organs including the nervous system which is one of the most affected. Cadmium has been reported to produce learning and memory dysfunctions and Alzheimer like symptoms, though the mechanism is unknown. On the other hand, cholinergic system in central nervous system (CNS) is implicated on learning and memory regulation, and it has been reported that cadmium can affect cholinergic transmission and it can also induce selective toxicity on cholinergic system at peripheral level, producing cholinergic neurons loss, which may explain cadmium effects on learning and memory processes if produced on central level. The present study is aimed at researching the selective neurotoxicity induced by cadmium on cholinergic system in CNS. For this purpose we evaluated, in basal forebrain region, the cadmium toxic effects on neuronal viability and the cholinergic mechanisms related to it on NS56 cholinergic mourine septal cell line. This study proves that cadmium induces a more pronounced, but not selective, cell death on acetylcholinesterase (AChE) on cholinergic neurons. Moreover, MTT and LDH assays showed a dose dependent decrease of cell viability in NS56 cells. The ACh treatment of SN56 cells did not revert cell viability reduction induced by cadmium, but siRNA transfection against AChE partially reduced it. Our present results provide new understanding of the mechanisms contributing to the harmful effects of cadmium on the function and viability of neurons, and the possible relevance of cadmium in the pathogenesis of neurodegenerative diseases.

Neurotoxicity of coral snake phospholipases A2 in cultured rat hippocampal neurons

The neurotoxicity of two secreted Phospholipases A2 from Brazilian coral snake venom in rat primary hippocampal cell culture was investigated. Following exposure to Mlx-8 or Mlx-9 toxins, an increase in free cytosolic Ca(2+) and a reduction in mitochondrial transmembrane potential (ΔΨm) became evident and occurred prior to the morphological changes and cytotoxicity. Exposure of hippocampal neurons to Mlx-8 or Mlx-9 caused a decrease in the cell viability as assessed by MTT and LDH assays. Inspection using fluorescent images and ultrastructural analysis by scanning and transmission electron microscopy showed that multiphase injury is characterized by overlapping cell death phenotypes. Shrinkage, membrane blebbing, chromatin condensation, nucleosomal DNA fragmentation and the formation of apoptotic bodies were observed. The most striking alteration observed in the electron microscopy was the fragmentation and rarefaction of the neuron processes network. Degenerated terminal synapses, cell debris and apoptotic bodies were observed among the fragmented fibers. Numerous large vacuoles as well as swollen mitochondria and dilated Golgi were noted. Necrotic signs such as a large amount of cellular debris and membrane fragmentation were observed mainly when the cells were exposed to highest concentration of the PLA2-neurotoxins. PLA2s exposed cultures showed cytoplasmic vacuoles filled with cell debris, clusters of mitochondria presented mitophagy-like structures that are in accordance to patterns of programmed cell death by autophagy. Finally, we demonstrated that the sPLA2s, Mlx-8 and Mlx-9, isolated from the Micrurus lemniscatus snake venom induce a hybrid cell death with apoptotic, autophagic and necrotic features. Furthermore, this study suggests that the augment in free cytosolic Ca(2+) and mitochondrial dysfunction are involved in the neurotoxicity of Elapid coral snake venom sPLA2s.

Autism-specific maternal autoantibodies recognize critical proteins in developing brain

Autism spectrum disorders (ASDs) are neurodevelopmental in origin, affecting an estimated 1 in 88 children in the United States. We previously described ASD-specific maternal autoantibodies that recognize fetal brain antigens. Herein, we demonstrate that lactate dehydrogenase A and B (LDH), cypin, stress-induced phosphoprotein 1 (STIP1), collapsin response mediator proteins 1 and 2 (CRMP1, CRMP2) and Y-box-binding protein to comprise the seven primary antigens of maternal autoantibody-related (MAR) autism. Exclusive reactivity to specific antigen combinations was noted in 23% of mothers of ASD children and only 1% of controls. ASD children from mothers with specific reactivity to LDH, STIP1 and CRMP1 and/or cypin (7% vs 0% in controls; P<0.0002; odds ratios of 24.2 (95% confidence interval: 1.45-405)) had elevated stereotypical behaviors compared with ASD children from mothers lacking these antibodies. We describe the first panel of clinically significant biomarkers with over 99% specificity for autism risk thereby advancing our understanding of the etiologic mechanisms and therapeutic possibilities for MAR autism.

Determination of the detectable concentration of manganese used in neuronal MEMRI and its effect on cortical neurons in vitro

OBJECTIVE

Manganese (Mn(2+))-enhanced magnetic resonance imaging (MEMRI) has received increasing attention because of its functional and anatomic value in brain studies. However, the contrast agent, Mn(2+), will lead to neurotoxicity at high concentrations, which limits its use in biomedical research. This study was designed to determine whether Mn(2+) can significantly enhance the signal intensity (SI) of primary cultured cortical neurons at non-toxic levels.

METHOD

Neurons were incubated with different concentrations of Mn(2+) (control and 0.01, 0.05, 0.10, and 0.20 mM), then a cellular MRI was performed in vitro and the intracellular Mn(2+) concentrations were analyzed by ICP-MS. At the same time, the cell viability, LDH release assay, intracellular ROS level, and apoptosis were measured 24 h after treatment.

RESULTS

(1) After the neurons were treated with Mn(2+) at a low concentration (0.01 mM), there was no impact on cell viability and cytotoxicity, and no significant signal was enhanced on MEMRI. (2) When the neurons were exposed to higher concentrations of Mn(2+) (0.05, 0.1, and 0.2 mM), a significant increase in signal quality was achieved, but cell viability was significantly reduced and the intracellular ROS formation and percentage of TUNEL-positive cells were increased significantly.

CONCLUSION

At Mn(2+) concentrations > 0.05 mM, significant enhancement of MEMRI SI occurred, but with overt cytotoxicity.

Paeoniflorin, a natural neuroprotective agent, modulates multiple anti-apoptotic and pro-apoptotic pathways in differentiated PC12 cells

Numerous studies have shown robust neuroprotective effects of paeoniflorin (PF), a natural compound derived from the herbal medicine Paeony radix. In the present study, we determined associations of PF neuroprotection with its modulation of various apoptotic and anti-apoptotic pathways. PF (50-400 μM) pretreatment significantly improved viability of differentiated PC12 cells exposed to methyl-4-phenylpyridine ion (MPP(+)), a neurotoxin, and inhibited over-release of lactate dehydrogenase, a biomarker of neuronal cell death. PF also ameliorated MPP(+)-induced nuclear and mitochondrial apoptotic alteration and intracellular calcium overload. PF treatment reversed MPP(+) suppression of activity of B cell lymphoma-extra large, which is a mitochondrial membrane molecule that protects cells from DNA damage-induced apoptosis, and strikingly inhibited the enhanced level of cleaved poly(ADP-ribose)polymerase, which is involved in the process of apoptosis. PF alone and coadministration with MPP(+) enhanced phospho activation of extracellular signal-regulated kinases, Akt, and its downstream element glycogen synthase kinase-3, but the effects were completely abolished in the presence of their blockers PD98059 and LY294002. The presence of the blockers also diminished the potency of PF in improving viability of MPP(+)-exposed cells. These results indicate that neuroprotective effects of PF are related to its modulation of multiple anti-apoptotic and pro-apoptotic pathways, including blockade of intracellular calcium overload, prevention of mitochondrial membrane integrity, inhibition of pro-apoptotic molecules, and up-regulation of anti-apoptotic proteins associated with cell survival and proliferation. The study provides evidence supporting PF as a potential therapeutic agent used for the treatment of neurodegenerative diseases and neural injury.

A novel brain neurovascular unit model with neurons, astrocytes and microvascular endothelial cells of rat

A novel triple cell neurovascular unit (NVU) model co-culturing with neurons, brain microvascular endothelial cells (BMECs) and astrocytes was established in this study for investigating the cerebral diseases and screening the candidates of therapeutic drug. We have first performed the cell identification and morphological characterization, analyzed the specific protein expression and determined the blood-brain barrier (BBB) function of the co-culture model under normal condition. Then, we further determined the BBB function, inflammation, cell injury and the variation of neuroprotective factor in this model after anoxia-reoxygenation. The results suggest that this model exhibited a better BBB function and significantly increased expression of P-glycoprotein (Pg-P) and ZO-1 compared with BMECs only or co-culture with astrocytes or neurons. After anoxia-reoxygenation, the pathological changes of this model were basically resemblance to the pathological changes of brain cells and BBB in vivo. And nimodipine, an antagonist of calcium, could reverse those changes as well. According to our observations, we deduce that this triple cell co-culture model exhibits the basic structure, function and cell-cell interaction of NVU, which may offer a more proper in vitro system of NVU for the further investigation of cerebral diseases and drug screening.

Three-dimensional scaffolding to investigate neuronal derivatives of human embryonic stem cells

Access to unlimited numbers of live human neurons derived from stem cells offers unique opportunities for in vitro modeling of neural development, disease-related cellular phenotypes, and drug testing and discovery. However, to develop informative cellular in vitro assays, it is important to consider the relevant in vivo environment of neural tissues. Biomimetic 3D scaffolds are tools to culture human neurons under defined mechanical and physico-chemical properties providing an interconnected porous structure that may potentially enable a higher or more complex organization than traditional two-dimensional monolayer conditions. It is known that even minor variations in the internal geometry and mechanical properties of 3D scaffolds can impact cell behavior including survival, growth, and cell fate choice. In this report, we describe the design and engineering of 3D synthetic polyethylene glycol (PEG)-based and biodegradable gelatin-based scaffolds generated by a free form fabrication technique with precise internal geometry and elastic stiffnesses. We show that human neurons, derived from human embryonic stem (hESC) cells, are able to adhere to these scaffolds and form organoid structures that extend in three dimensions as demonstrated by confocal and electron microscopy. Future refinements of scaffold structure, size and surface chemistries may facilitate long term experiments and designing clinically applicable bioassays.

A neuroprotective mechanism of YGY-E in cerebral ischemic injury in rats

AIMS

To investigate the anticerebral ischemic properties of YGY-E (apigenin-7-O-β-D-glucopyranosy l-4'-O-α-L-rhamnopy-ranosid, a flavonoid glycoside extracted from plant phoenix-tail fern), focusing on its effects on neuronal apoptosis.

METHODS

In vitro YGY-E treatment was examined in primary cultured rat hippocampal neurons subjected to hypoxia-reoxygenation (H-R) injury. In addition, in vivo effects of YGY-E on neuronal apoptosis were measured by Hoechst staining and in situ DNA end labeling (TUNEL). Finally, B cell lymphoma/lewkmia-2 (Bcl-2) level in ischemic rat brain tissue was evaluated with immunohistochemistry and western blot analyses.

RESULTS

In vitro YGY-E (50-100 μg/mL) treatment increased the survival rate compared to that of the vehicle-treated group (P < 0.05 and P < 0.01, respectively). In in vivo experiments, YGY-E (2.5-10 mg/kg) decreased the percentage of apoptotic neurons (P < 0.01), increased Bcl-2 (P < 0.01) in ischemic rat brain tissue. These effects were dose dependent.

CONCLUSIONS

Our findings indicate that YGY-E's neuroprotective effects may be because of its inhibition of neuronal apoptosis by increasing Bcl-2 expression.

Exposure to lipopolysaccharide and/or unconjugated bilirubin impair the integrity and function of brain microvascular endothelial cells

Background

Sepsis and jaundice are common conditions in newborns that can lead to brain damage. Though lipopolysaccharide (LPS) is known to alter the integrity of the blood-brain barrier (BBB), little is known on the effects of unconjugated bilirubin (UCB) and even less on the joint effects of UCB and LPS on brain microvascular endothelial cells (BMEC).

Methodology/Principal Findings

Monolayers of primary rat BMEC were treated with 1 µg/ml LPS and/or 50 µM UCB, in the presence of 100 µM human serum albumin, for 4 or 24 h. Co-cultures of BMEC with astroglial cells, a more complex BBB model, were used in selected experiments. LPS led to apoptosis and UCB induced both apoptotic and necrotic-like cell death. LPS and UCB led to inhibition of P-glycoprotein and activation of matrix metalloproteinases-2 and -9 in mono-cultures. Transmission electron microscopy evidenced apoptotic bodies, as well as damaged mitochondria and rough endoplasmic reticulum in BMEC by either insult. Shorter cell contacts and increased caveolae-like invaginations were noticeable in LPS-treated cells and loss of intercellular junctions was observed upon treatment with UCB. Both compounds triggered impairment of endothelial permeability and transendothelial electrical resistance both in mono- and co-cultures. The functional changes were confirmed by alterations in immunostaining for junctional proteins β-catenin, ZO-1 and claudin-5. Enlargement of intercellular spaces, and redistribution of junctional proteins were found in BMEC after exposure to LPS and UCB.

Conclusions

LPS and/or UCB exert direct toxic effects on BMEC, with distinct temporal profiles and mechanisms of action. Therefore, the impairment of brain endothelial integrity upon exposure to these neurotoxins may favor their access to the brain, thus increasing the risk of injury and requiring adequate clinical management of sepsis and jaundice in the neonatal period.

Hyaluronan tetrasaccharide in the cerebrospinal fluid is associated with self-repair of rats after chronic spinal cord compression

The objective of this study was to explore changes in hyaluronan levels in the cerebrospinal fluid (CSF) in a spinal cord compression model, to investigate whether hyaluronan tetrasaccharide was involved in this process, and to test the effects of hyaluronan tetrasaccharide on neuron and oligodendrocyte repair. We developed a chronic spinal cord compression model with various sizes of polymer sheets (1.5×0.7×0.3 mm(3); 5×1.5×0.7 mm(3)) that were implanted microsurgically underneath the C(5-6) laminae. The rats were divided into three groups: a sham group, a mildly compressed (MC) group, and a widely compressed (WC) group. Locomotor functional evaluations revealed that the behavioral function of the MC and WC groups dropped to their lowest level from the fourth to fifth week and gradually recovered thereafter. The hyaluronan levels in the CSF gradually increased after spinal cord compression. Furthermore, hyaluronan tetrasaccharide was involved in the hyaluronan change. In addition, we found that nuclear factor kappa B (NF-κB) and cellular inhibitor-of-apoptosis protein 2 (c-IAP(2)) were co-expressed in neurons and oligodendrocytes, and caspase-3 expression gradually decreased in the compression model. The brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) expression was upregulated in astrocytes at the fourth week post-compression. Hyaluronan tetrasaccharide (HA(4)) induced NF-κB and c-IAP(2) to suppress the H(2)O(2)-induced apoptosis in primary neuronal cultures and increased BDNF and VEGF expression in astrocytic cultures in vitro. These findings suggest that HA(4) in the CSF may associate with behavioral recovery by increasing the levels of NF-κB, c-IAP(2), and neurotrophic factors after chronic spinal cord compression.

Astrocyte reactivity to unconjugated bilirubin requires TNF-α and IL-1β receptor signaling pathways

Jaundice and sepsis are common neonatal conditions that can lead to neurodevelopment sequelae, namely if present at the same time. We have reported that tumor necrosis factor (TNF)-α and interleukin (IL)-1β are produced by cultured neurons and mainly by glial cells exposed to unconjugated bilirubin (UCB). The effects of these cytokines are mediated by cell surface receptors through a nuclear factor (NF)-κB-dependent pathway that we have showed to be activated by UCB. The present study was designed to evaluate the role of TNF-α and IL-1β signaling on astrocyte reactivity to UCB in rat cortical astrocytes. Exposure of astrocytes to UCB increased the expression of both TNF-α receptor (TNFR)1 and IL-1β receptor (IL-1R)1, but not TNFR2, as well as their activation, observed by augmented binding of receptors' molecular adaptors, TRAF2 and TRAF6, respectively. Silencing of TNFR1, using siRNA technology, or blockade of IL-1β cascade, using its endogenous antagonist, IL-1 receptor antagonist (IL-1ra), prevented UCB-induced cytokine release and NF-κB activation. Interestingly, lack of TNF-α signal transduction reduced UCB-induced cell death for short periods of incubation, although an increase was observed after extended exposure; in contrast, inhibition of IL-1β cascade produced a sustained blockade of astrocyte injury by UCB. Together, our data show that inflammatory pathways are activated during in vitro exposure of rat cortical astrocytes to UCB and that this activation is prolonged in time. This supports the concept that inflammatory pathways play a role in brain damage by UCB, and that they may represent important pharmacological targets.

N-methyl-aspartate receptor and neuronal nitric oxide synthase activation mediate bilirubin-induced neurotoxicity

Hyperbilirubinemia may lead to neurotoxicity and neuronal death. Although the mechanisms of nerve cell damage by unconjugated bilirubin (UCB) appear to involve a disruption of the redox status and excitotoxicity, the contribution of nitric oxide (NO·) and of N-methyl-D-aspartate (NMDA) glutamate receptors is unclear. We investigated the role of NO· and NMDA glutamate receptors in the pathways of nerve cell demise by UCB. Neurons were incubated with 100 micromol/L UCB, in the presence of 100 micromol/L human serum albumin for 4 h at 37ºC, alone or in combination with N-ω-nitro-L-arginine methyl ester (L-NAME) (an inhibitor of neuronal nitric oxide synthase [nNOS]), hemoglobin (an NO· scavenger) or (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) (an NMDA-receptor antagonist). Exposure to UCB led to increased expression of nNOS and production of both NO· and cyclic guanosine 3',5'-monophosphate (cGMP), along with protein oxidation and depletion of glutathione. These events concurred for cell dysfunction and death and were counteracted by L-NAME. Moreover, the UCB-induced loss of neuronal viability was abolished by hemoglobin, whereas the activation of nNOS and production of both NO· and cGMP were counteracted by MK-801, resulting in significant protection from cell dysfunction and death. These results reinforce the involvement of oxidative stress by showing that nerve cell damage by UCB is mediated by NO· and therefore is counteracted by NO· inhibitors or scavengers. Our findings strongly suggest that the activation of nNOS and neurotoxicity occur through the engagement of NMDA receptors. These data reveal a role for overstimulation of glutamate receptors in mediating oxidative damage by UCB.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Cytotoxicity and apoptosis induction on RTG-2 cells of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209)

Recently, the environmental residues of polybrominated diphenyl ethers (PBDEs) have markedly increased. In particular, the levels of certain PBDE congeners in fish have raised concern regarding potential risks associated with dietary PBDEs exposures. However, little is known regarding PBDE-mediated cell injury in relevant in vitro fish cell models. In this study, the cytotoxic effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209) on RTG-2 cells were investigated. RTG-2 cells were incubated with different concentrations of BDE-47 and BDE-209 (1-100 microM) for 72 h, and a set of bioassays were conducted to measure: cell viability (evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and neutral red (NR) uptake), lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation and cell apoptosis. The results showed that BDE-47 and BDE-209 inhibited the cells viability, increased LDH leakage, and induced cell apoptosis in time and concentration-dependent manner. All significant effects were observed at concentrations of 12.5 microM and above for BDE-47 and 25 microM and above for BDE-209 (P<0.05). At the concentration of 100 microM BDE-47 and BDE-209, the cell viability of the exposed cells dropped to about 40% and 50% of the control, and the apoptotic rates were 52.6% and 34.6%, respectively. After 12h exposure, a concentration-dependent increases of BDE-47 and BDE-209 (12.5-100 microM) in ROS formation were observed. Collectively, the results of cell viability, LDH leakage, cell apoptosis and ROS formation demonstrated that the toxic mechanism of PBDEs on RTG-2 might be mediated by oxidative stress.

L-Ascorbate protects rat hepatocytes against sodium arsenite--induced cytotoxicity and oxidative damage

Sodium arsenite-exposed hepatocytes of rat showed higher production of nitric oxide (NO) and increased lipid peroxidation (LPO) level vis-a-vis activity of superoxide dismutase (SOD) and catalase (CAT) were significantly lowered. Subsequently, the cell proliferation index (CPI) and cell viability were also reduced. Treatment with L-ascorbate was found effective in normalizing the arsenic-induced alteration of SOD and CAT activity and LPO level in rat hepatocytes. These observations indicated that L-ascorbate also has potent cytoprotective role as it could reduce the NO production and normalize the cell proliferation and viability of hepatocytes. Therefore, the in vitro study suggested that ascorbic acid is helpful to ameliorate the arsenic-induced cytotoxicity and oxidative stress of rat hepatocytes.

Bilirubin as a determinant for altered neurogenesis, neuritogenesis, and synaptogenesis

Elevated levels of serum unconjugated bilirubin (UCB) in the first weeks of life may lead to long-term neurologic impairment. We previously reported that an early exposure of developing neurons to UCB, in conditions mimicking moderate to severe neonatal jaundice, leads to neuritic atrophy and cell death. Here, we have further analyzed the effect of UCB on nerve cell differentiation and neuronal development, addressing how UCB may affect the viability of undifferentiated neural precursor cells and their fate decisions, as well as the development of hippocampal neurons in terms of dendritic and axonal elongation and branching, the axonal growth cone morphology, and the establishment of dendritic spines and synapses. Our results indicate that UCB reduces the viability of proliferating neural precursors, decreases neurogenesis without affecting astrogliogenesis, and increases cellular dysfunction in differentiating cells. In addition, an early exposure of neurons to UCB decreases the number of dendritic and axonal branches at 3 and 9 days in vitro (DIV), and a higher number of neurons showed a smaller growth cone area. UCB-treated neurons also reveal a decreased density of dendritic spines and synapses at 21 DIV. Such deleterious role of UCB in neuronal differentiation, development, and plasticity may compromise the performance of the brain in later life.

Twenty-First Century Challenges for In Vitro Neurotoxicity

During the last 40 years, studies incorporating in vitro methodologies have greatly advanced our understanding of human nerve cell biology. Attempts have been made to apply these to investigations of neurotoxicity. Due to the complexity of the nervous system, underpinned by an array of integrated interactions between a host of cell types, it is concluded that, at present, alternative neural models are most successful in determining the underlying mechanisms which can cause perturbation of normal functioning of the nervous system, both in adults and during the embryonic period. The use of tiered batteries of test models has been proposed in screening programmes for neurotoxicity, with the generation of much encouraging data in laboratories across the globe. This review aims to discuss the development of neural alternatives, considers the various model systems available, and highlights specific neuronal endpoints which can be tested, in addition to the cytotoxic evaluation of neuronal viability. Developments in molecular and stem cell biology, which are appropriate to neural tissue, and which offer the prospect of exciting advances for the next decade, are cited.

Suppressive effects of cadmium on neurons and affected proteins in cultured developing cortical cells

The purpose of the present study was to examine the in vitro effects of low-dose cadmium (Cd) on developing cortical cells. The cortical cells removed from fetuses (embryonic day 15) were treated with 10nM of Cd for 24h. The effects of Cd on dendritic and synaptic development were immunocytochemically observed with anti-microtubule associated protein-2 (MAP2) and anti-synapsin I antibodies, respectively. Administration of Cd suppressed dendritic as well as synaptic development at 10nM. By two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometric (LC/MS/MS) analysis, we identified three proteins with different expression after Cd-treatment; dihydropyrimidinase-related protein 2 (DRP-2/CRMP-2), 14-3-3-epsillon and calmodulin (CaM). Though the number of identified proteins was small, these proteins are known to be involved in neuronal development. The present study demonstrated the morphological effects as well as affected proteins in Cd-treated cortical cells, providing tools and insights in elucidating mechanisms how low-dose Cd distorts brain development.

Stable isotopic labeling by amino acids in cultured primary neurons: application to brain-derived neurotrophic factor-dependent phosphotyrosine-associated signaling

Cultured primary neurons are a well established model for the study of neuronal function in vitro. Here we demonstrated that stable isotope labeling by amino acids in cell culture (SILAC) can be applied to a differentiated, non-dividing cell type such as primary neurons, and we applied this technique to assess changes in the neuronal phosphotyrosine proteome in response to stimulation by brain-derived neurotrophic factor (BDNF), an important molecule for the development and regulation of neuronal connections. We found that 13 proteins had SILAC ratios above 1.50 or below 0.67 in phosphotyrosine immunoprecipitations comparing BDNF-treated and control samples, and an additional 18 proteins had ratios above 1.25 or below 0.80. These proteins include TrkB, the receptor tyrosine kinase for BDNF, and others such as hepatocyte growth factor-regulated tyrosine kinase substrate and signal-transducing adaptor molecule, which are proteins known to regulate intracellular trafficking of receptor tyrosine kinases. These results demonstrate that the combination of primary neuronal cell culture and SILAC can be a powerful tool for the study of the proteomes of neuronal molecular and cellular dynamics.