Differentiation of HT22 neurons induces expression of NMDA receptor that mediates homocysteine cytotoxicity

Luteolin protects mouse hippocampal neuronal cells against isoflurane-induced neurotoxicity through miR-214/PTEN/Akt pathway

Isoflurane is one of the most commonly used anaesthetic agents in surgery procedures. During the past decades, isoflurane has been found to cause impairment in neurological capabilities in new-borns and elderly patients. Luteolin is a flavonoid that has been documented to possess a neuroprotective effect. Here we investigated the putative neuroprotective effects of luteolin on isoflurane-induced neurotoxicity in mouse hippocampal neuronal HT22 cells and explored the potential mechanisms. We demonstrated that luteolin improved mitochondrial dysfunction and reduced oxidative stress and apoptosis in isoflurane-treated HT22 cells, and thus inhibiting the isoflurane-induced neuronal injury. Further investigations showed that isoflurane exposure caused miR-214 downregulation, which could be mitigated by treatment with luteolin. Knockdown of miR-214 attenuated the neuroprotection of luteolin on isoflurane-induced neuronal injury. More importantly, luteolin inhibited isoflurane-caused regulation of the PTEN/Akt pathway, while miR-214 knockdown altered the regulatory effect of luteolin on the PTEN/Akt pathway. Furthermore, the effects of miR-214 knockdown on the neuroprotection of luteolin could also be prevented by knockdown of PTEN, implying that the neuroprotective effect of luteolin was mediated by miR-214/PTEN/Akt signaling pathway. These findings provided evidence for the potential application of luteolin in preventing isoflurane-induced neurotoxicity.

γ-Oryzanol from Rice Bran Antagonizes Glutamate-Induced Excitotoxicity in an In Vitro Model of Differentiated HT-22 Cells

The excessive activation of glutamate in the brain is a factor in the development of vascular dementia. γ-Oryzanol is a natural compound that has been shown to enhance brain function, but more research is needed to determine its potential as a treatment for vascular dementia. This study investigated if γ-oryzanol can delay or improve glutamate neurotoxicity in an in vitro model of differentiated HT-22 cells and explored its neuroprotective mechanisms. The differentiated HT-22 cells were treated with 0.1 mmol/L glutamate for 24 h then given γ-oryzanol at appropriate concentrations or memantine (10 µmol/L) for another 24 h. Glutamate produced reactive oxygen species and depleted glutathione in the cells, which reduced their viability. Mitochondrial dysfunction was also observed, including the inhibition of mitochondrial respiratory chain complex I activity, the collapse of mitochondrial transmembrane potential, and the reduction of intracellular ATP levels in the HT-22 cells. Calcium influx triggered by glutamate subsequently activated type II calcium/calmodulin-dependent protein kinase (CaMKII) in the HT-22 cells. The activation of CaMKII-ASK1-JNK MAP kinase cascade, decreased Bcl-2/Bax ratio, and increased Apaf-1-dependent caspase-9 activation were also observed due to glutamate induction, which were associated with increased DNA fragmentation. These events were attenuated when the cells were treated with γ-oryzanol (0.4 mmol/L) or the N-methyl-D-aspartate receptor antagonist memantine. The results suggest that γ-oryzanol has potent neuroprotective properties against glutamate excitotoxicity in differentiated HT-22 cells. Therefore, γ-oryzanol could be a promising candidate for the development of therapies for glutamate excitotoxicity-associated neurodegenerative diseases, including vascular dementia.

Exploration of the potential neuroprotective compounds targeting GluN1-GluN2B NMDA receptors

The N-methyl-d-aspartic acid (NMDA) receptors belongs to the family of ionotropic glutamate receptors, which could mediate most excitatory synaptic transmission in the brain. It is interesting to know if some available drugs have regulatory effects on the NMDARs. Herein, the present study reports the discovery of drugs targeting NMDAR using virtual screening. In this study, talniflumate with the EC50 value at 61.49 nM was successfully screened. The interaction analysis of this compound was further explored through molecular dynamics simulation. It is indicated that talniflumate could form stable interactions with GluN1-GluN2B NMDA receptors. In particular, H-bond interactions with high occupancies between GluN1-GluN2B NMDA receptors and talniflumate were observed. Compared to de novo drug discovery, this approach could be an alternative choice for development of safety and efficiency NMDAR inhibitors from available drugs.Communicated by Ramaswamy H. Sarma.

Electro-conductive chitosan/graphene bio-nanocomposite scaffold for tissue engineering of the central nervous system

Degenerative central nervous system (CNS) disorders and traumatic brain injuries are common nowadays. These may induce the loss of neuronal cells and delicate connections essential for optimal CNS function. The CNS tissue has restricted regeneration ability, hindering the development of effective therapies. Developing cell and tissue instructive materials may bring up new treatment possibilities. In this study, chitosan-graphene nano platelets (GNPs) composite films were developed to regenerate brain cells. This study evaluates the effects of GNP concentration (0.5, 1 and 2 wt%) and their alignment on mechanical, electrical, surface, protein adsorption and biological properties of the regenerative scaffolds. Incorporating and aligning GNPs into chitosan matrix improved all the physical and biological properties. On reinforced scaffolds, HT22 cell morphology mimics pyramidal brain cells, which are responsible for the brain's highly branched neural network. Additionally, the reinforced scaffolds supported Mesenchymal Stem like Cells growth and were biocompatible in vivo. The alignment of GNPs in the chitosan matrix offered the appropriate physicochemical and biological properties to promote adhesion, proliferation and shape morphogenesis of hippocampal HT22 neuronal cells. Overall, this study delineates the enormous potential offered by the GNP-reinforced scaffolds for regeneration of central nervous system, especially the brain.

NMDA Receptor Activation Stimulates Hypoxia-Induced TRPM2 Channel Activation, Mitochondrial Oxidative Stress, and Apoptosis in Neuronal Cell Line: Modular Role of Memantine

TRPM2 channel is activated by the increase of hypoxia (HYP)-mediated excessive mitochondrial (mROS) and cytosolic (cROS) free reactive oxygen species generation and intracellular free Ca²⁺ ([Ca²⁺]_i) influx. The stimulations of the N-methyl-d-aspartate(NMDA) receptor and TRPM2 channel induce mROS and apoptosis in the neurons, although their inhibitions via the treatments of memantine (MEM) and MK-801 decrease mROS and apoptosis. However, the molecular mechanisms underlying MEM treatment and NMDA inhibition' neuroprotection via TRPM2 inhibition in the HYP remain elusive. We investigated the modulator role of MEM and NMDA via the modulation of TRPM2 on oxidative neurodegeneration and apoptosis in SH-SY5Y neuronal cells. Six groups were induced in the SH-SY5Y and HEK293 cells as follows: Control, MEM, NMDA blocker (MK-801), HYP (CoCl₂), HYP + MEM, and HYP + MK-801. The HYP caused to the increases of TRPM2 and PARP-1 expressions, and TRPM2 agonist (H₂O₂ and ADP-ribose)-induced TRPM2 current density and [Ca²⁺]_i concentration via the upregulation of mitochondrial membrane potential, cROS, and mROS generations. The alterations were not observed in the absence of TRPM2 in the HEK293 cells. The increase of cROS, mROS, lipid peroxidation, cell death (propidium iodide/Hoechst) rate, apoptosis, caspase -3, caspase -8, and caspase -9 were restored via upregulation of glutathione and glutathione peroxidase by the treatments of TRPM2 antagonists (ACA or 2-APB), MEM, and MK-801. In conclusion, the inhibition of NMDA receptor via MEM treatment modulated HYP-mediated mROS, apoptosis, and TRPM2-induced excessive [Ca²⁺]_i and may provide an avenue for protecting HYP-mediated neurodegenerative diseases associated with the increase of mROS, [Ca²⁺]_i, and apoptosis.

Differentiated HT22 cells as a novel model for in vitro screening of serotonin reuptake inhibitors

The mouse hippocampal neuronal cell line HT22 is frequently used as an in vitro model to investigate the role of hippocampal cholinergic neurons in cognitive functions. HT22 cells are derived from hippocampal neuronal HT4 cells. However, whether these cells exhibit the serotonergic neuronal phenotype observed in mature hippocampal neurons has not been determined yet. In this present study, we examined whether the differentiation of HT22 cells enhances the serotonergic neuronal phenotype, and if so, whether it can be used for antidepressant screening. Our results show that differentiation of HT22 cells promoted neurite outgrowth and upregulation of N-methyl-D-aspartate receptor and choline acetyltransferase, which is similar to that observed in primary cultured hippocampal neurons. Furthermore, proteins required for serotonergic neurotransmission, such as tryptophan hydroxylase 2, serotonin (5-hydroxytryptamine, 5-HT)_1a receptor, and serotonin transporter (SERT), were significantly upregulated in differentiated HT22 cells. The transcription factor Pet-1 was upregulated during HT22 differentiation and was responsible for the regulation of the serotonergic neuronal phenotype. Differentiation also enhanced the functional serotonergic properties of HT22 cells, as evidenced by increase in intracellular 5-HT levels, serotonin transporter SERT glycosylation, and 5-HT reuptake activity. The sensitivity of 5-HT reuptake inhibition by venlafaxine in differentiated HT22 cells (IC_50, 27.21 nM) was comparable to that in HEK293 cells overexpressing serotonin transporter SERT (IC_50, 30.65 nM). These findings suggest that the differentiation of HT22 cells enhances their functional serotonergic properties, and these cells could be a potential in vitro system for assessing the efficacy of antidepressant 5-HT reuptake inhibitors.

Conditioned media of mouse macrophages modulates neuronal dynamics in mouse hippocampal cells

Many neurodegenerative diseases display both neuroinflammation and impaired neuron production in hippocampus. Although immunotherapeutic strategies indicate a promising avenue for combating neuroinflammation-induced diseases, directly targeting microglia, principle immune cells of CNS for such therapeutic purposes might be problematic due to invasive procedures. Instructing monocytes/macrophages from the periphery can be a less invasive and advantageous strategy compared to reaching microglia. But interplay between CNS neurons and macrophages even under normal conditions is poorly understood. To explore the experimental platform of how CNS derived neuronal cells respond to overall soluble factors of a non-CNS derived immune cell type, we introduced the conditioned media (CM) of unstimulated, and lipopolysaccharide stimulated RAW264.7 mouse macrophages to immortalized HT-22 mouse hippocampal cells during and after they were exposed to neuronal differentiation media. First, we recorded the cell viability of HT-22 cell study groups by using a real time cell analyzer. Then, we assessed the immunocytochemical expression of CR and CB proteins and mRNA levels of Ascl1, Bdnf, CB, Grn, Nrf2 and Rac1 genes via semi quantitative image analysis and q-RT-PCR among the different groups of HT-22 cells. Real time cell monitoring provided a solid physiological evidence regarding how various cell culture treatments affected the cell viability of HT-22 cells over time. Our further findings suggested that culturing HT-22 cells with unstimulated CM of macrophages markedly increased the immunocytochemical expression of CR and mRNA expression of Ascl1, Bdnf, CB and Grn genes, while the latter media resulted in decreases of those expressions. Overall, our results imply that HT-22 cells are meaningfully responsive to the secretome of RAW264.7 macrophages and using the interaction of macrophage with CNS derived neuronal cells is an instructive platform for deciphering the molecular mechanisms of cellular communication between immune system cells and neurons.

Germinated brown rice protects against glutamate toxicity in HT22 hippocampal neurons through the jnk-mediated apoptotic pathway via the GABAA receptor

The anti-apoptosis effect of germinated brown rice (GBR) focusing on differentiated HT22 cells results in improved nutritional values after the germination process of GBR which contains total phenolic compounds and γ-aminobutyric acid (GABA). Cell death induced by 5 mM glutamate was investigated for 24 h to determine whether GBR mediates cell death through GABA receptors by using antagonists. The results showed that GBR (100 µg/ml) suppressed glutamate-induced cytotoxicity and caused arrest at the G1/S phase of the cell cycle in differentiated HT22 cells. Furthermore, GBR significantly decreased the expression level of c-Jun, while its active form, p-c-Jun, is the downstream product of the JNK-mediated apoptotic pathway and causes subsequent cell death. In addition, bicuculline (12.5 nM), a GABA_A antagonist, could eliminate GBR effects, but phaclofen (1 mM), a GABA_B antagonist, could not. Surprisingly, GBR exhibited a better neuroprotective effect than a pure commercial GABA compound (0.115 µM). These results indicated that GBR possessed high anti-apoptotic activity and inhibited cell death in differentiated HT22 cells by perturbing re-entry of the cell cycle and apoptosis via the GABA_A receptor. Hence, GBR could be further used as a valuable nutritional compound to prevent apoptosis-induced neurodegenerative diseases.

The Combination of Salidroside and Hedysari Radix Polysaccharide Inhibits Mitochondrial Damage and Apoptosis via the PKC/ERK Pathway

Background. Beta-amyloid (Aβ) peptide is a widely recognized pathological marker of Alzheimer’s disease (AD). Salidroside and Hedysari Radix polysaccharide (HRP) were extracted from Chinese herb medicine Rhodiola rosea L and Hedysarum polybotrys Hand-Mazz, respectively. The neuroprotective effects and mechanisms of the combination of salidroside and Hedysari Radix polysaccharide (CSH) against Aβ25–35 induced neurotoxicity remain unclear. Objective. This study aims to investigate the neuroprotective effects and pharmacological mechanisms of CSH on Aβ25–35-induced HT22 cells. Materials and Methods. HT22 cells were pretreated with various concentrations of salidroside or HRP for 24 h, followed by exposed to 20 μm Aβ25–35 in the presence of salidroside or RHP for another 24 h. In a CSH protective assay, HT22 cells were pretreated with 40 μm salidroside and 20 μg/mL HRP for 24 h. The cell viability assay, cell morphology observation, determination of mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and cell apoptosis rate were performed. The mRNA expression of protein kinase C-beta (PKCβ), Bax, and Bcl-2 were measured by qRT-PCR. The protein expression levels of cleaved caspase-3, Cyt-C, PKCβ, phospho-ERK1/2, Bax, and Bcl-2 were measured by Western blot. Results. CSH treatment increased cell viability, MMP, and decreased ROS generation in Aβ25–35-induced HT22 cells. PKCβ and Bcl-2 mRNA expression were elevated by CSH while Bax was decreased. CSH increased the protein expression levels of PKCβ, Bcl-2, and phospho-ERK1/2, and decreased those of Bax, Cyt-C, and cleaved caspase-3. Conclusions. CSH treatment have protective effects against Aβ25–35-induced cytotoxicity through decreasing ROS levels, increasing MMP, inhibiting early apoptosis, and regulating PKC/ERK pathway in HT22 cells. CSH may be a potential therapeutic agent for treating or preventing neurodegenerative diseases.

Detection and monitoring of the neuroprotective behavior of curcumin micelles based on an AIEgen probe

In recent years, the role of mitochondrial injury in the pathogenesis of Alzheimer's disease (AD) has attracted extensive attention. Studies have shown that curcumin (Cur) can protect nerve cells from beta-amyloid (Aβ)-induced mitochondrial damage. However, natural Cur encounters limited application due to its poor biocompatibility and bioavailability. To improve the solubility and biocompatibility of natural Cur, we prepared water-soluble curcumin micelles (CurM). Furthermore, the mitochondria-specific aggregation-induced emission (AIE) probe (TPE-Ph-In) was employed to observe the protective effect of CurM on the damage of mitochondrial morphology, distribution, and membrane potential caused by Aβ. Results showed that CurM had higher solubility, stronger stability and retention effect, and better cellular uptake than that of natural Cur. Furthermore, the inhibitory effects of CurM on mitochondrial morphology, distribution, and membrane potential damage induced by Aβ25-35 were observed utilizing TPE-Ph-In as an indicator of mitochondrial morphology and membrane potential. Thus, this method provides a useful strategy for experimental research and clinical treatment of AD with mitochondrial damage as the pathogenic mechanism.

Effects of ketamine on neurogenesis, extracellular matrix homeostasis and proliferation in hypoxia-exposed HT22 murine hippocampal neurons

Ketamine is a widely used drug in pediatric anesthesia, and both neurotoxic and neuroprotective effects have been associated with its use. There are only a few studies to date which have examined the effects of ketamine on neurons under hypoxic conditions, which may lead to severe brain damage and poor neurocognitive outcomes in neonates. In the present study, the effects of ketamine on cellular pathways associated with neurogenesis, extracellular matrix homeostasis and proliferation were examined in vitro in hypoxia-exposed neurons. Differentiated HT22 murine hippocampal neurons were treated with 1, 10 and 20 µM ketamine and cultured under hypoxic or normoxic conditions for 24 h followed by quantitative PCR analysis of relevant candidate genes. Ketamine treatment did not exert any notable effects on the mRNA expression levels of markers of neurogenesis (neuronal growth factor and syndecan 1), extracellular matrix homeostasis (matrix-metalloproteinase 2 and 9, tenascin C and tenascin R) or proliferation markers (Ki67 and proliferating cell nuclear antigen) compared with the respective untreated controls. However, there was a tendency towards downregulation of multiple cellular markers under hypoxic conditions and simultaneous ketamine treatment. No dose-dependent association was found in the ketamine treated groups for genetic markers of neurogenesis, extracellular matrix homeostasis or proliferation. Based on the results, ketamine may have increased the vulnerability of hippocampal neurons in vitro to hypoxia, independent of the dose. The results of the present study contribute to the ongoing discussion on the safety concerns around ketamine use in pediatric clinical practice from a laboratory perspective.

Neuroprotective mechanisms of DNA methyltransferase in a mouse hippocampal neuronal cell line after hypoxic preconditioning

Hypoxic preconditioning has been shown to improve hypoxic tolerance in mice, accompanied by the downregulation of DNA methyltransferases (DNMTs) in the brain. However, the roles played by DNMTs in the multiple neuroprotective mechanisms associated with hypoxic preconditioning remain poorly understood. This study aimed to establish an in vitro model of hypoxic preconditioning, using a cultured mouse hippocampal neuronal cell line (HT22 cells), to examine the effects of DNMTs on the endogenous neuroprotective mechanisms that occur during hypoxic preconditioning. HT22 cells were divided into a control group, which received no exposure to hypoxia, a hypoxia group, which was exposed to hypoxia once, and a hypoxic preconditioning group, which was exposed to four cycles of hypoxia. To test the ability of hypoxic preadaptation to induce hypoxic tolerance, cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethonyphenol)-2-(4-sulfophenyl)-2H-tetrazolium assay. Cell viability improved in the hypoxic preconditioning group compared with that in the hypoxia group. The effects of hypoxic preconditioning on the cell cycle and apoptosis in HT22 cells were examined by western blot assay and flow cytometry. Compared with the hypoxia group, the expression levels of caspase-3 and spectrin, which are markers of early apoptosis and S-phase arrest, respectively, noticeably reduced in the hypoxic preconditioning group. Finally, enzyme-linked immunosorbent assay, real-time polymerase chain reaction, and western blot assay were used to investigate the changes in DNMT expression and activity during hypoxic preconditioning. The results showed that compared with the control group, hypoxic preconditioning downregulated the expression levels of DNMT3A and DNMT3B mRNA and protein in HT22 cells and decreased the activities of total DNMTs and DNMT3B. In conclusion, hypoxic preconditioning may exert anti-hypoxic neuroprotective effects, maintaining HT22 cell viability and inhibiting cell apoptosis. These neuroprotective mechanisms may be associated with the inhibition of DNMT3A and DNMT3B.

Potassium bisperoxo (1,10-phenanthroline) oxovanadate suppresses proliferation of hippocampal neuronal cell lines by increasing DNA methyltransferases

Bisperoxo (1,10-phenanthroline) oxovanadate (BpV) can reportedly block the cell cycle. The present study examined whether BpV alters gene expression by affecting DNA methyltransferases (DNMTs), which would impact the cell cycle. Immortalized mouse hippocampal neuronal precursor cells (HT22) were treated with 0.3 or 3 μM BpV. Proliferation, morphology, and viability of HT22 cells were detected with an IncuCyte real-time video imaging system or inverted microscope and 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethonyphenol)-2-(4-sulfophenyl)-2H-tetrazolium, respectively. mRNA and protein expression of DNMTs and p21 in HT22 cells was detected by real-time polymerase chain reaction and immunoblotting, respectively. In addition, DNMT activity was measured with an enzyme-linked immunosorbent assay. Effects of BpV on the cell cycle were analyzed using flow cytometry. Results demonstrated that treatment with 0.3 μM BpV did not affect cell proliferation, morphology, or viability; however, treatment with 3 μM BpV decreased cell viability, increased expression of both DNMT3B mRNA and protein, and inhibited the proliferation of HT22 cells; and 3 μM BpV also blocked the cell cycle and increased expression of the regulatory factor p21 by increasing DNMT expression in mouse hippocampal neurons.

Alpha-naphthoflavone induces apoptosis through endoplasmic reticulum stress via c-Src-, ROS-, MAPKs-, and arylhydrocarbon receptor-dependent pathways in HT22 hippocampal neuronal cells

α-Naphthoflavone (αNF) is a prototype flavone, also known as a modulator of aryl hydrocarbon receptor (AhR). In the present study, we investigated the molecular mechanisms of αNF-induced cytotoxic effects in HT22 mouse hippocampal neuronal cells. αNF induced apoptotic cell death via activation of caspase-12 and -3 and increased expression of endoplasmic reticulum (ER) stress-associated proteins, including C/EBP homologous protein (CHOP). Inhibition of ER stress by treatment with the ER stress inhibitor, salubrinal, or by CHOP siRNA transfection reduced αNF-induced cell death. αNF activated mitogen-activated protein kinases (MAPKs), such as p38, JNK, and ERK, and inhibition of MAPKs reduced αNF-induced CHOP expression and cell death. αNF also induced accumulation of reactive oxygen species (ROS) and an antioxidant, N-acetylcysteine, reduced αNF-induced MAPK phosphorylation, CHOP expression, and cell death. Furthermore, αNF activated c-Src kinase, and inhibition of c-Src by a kinase inhibitor, SU6656, or siRNA transfection reduced αNF-induced ROS accumulation, MAPK activation, CHOP expression, and cell death. Inhibition of AhR by an AhR antagonist, CH223191, and siRNA transfection of AhR and AhR nuclear translocator reduced αNF-induced AhR-responsive luciferase activity, CHOP expression, and cell death. Finally, we found that inhibition of c-Src and MAPKs reduced αNF-induced transcriptional activity of AhR. Taken together, these findings suggest that αNF induces apoptosis through ER stress via c-Src-, ROS-, MAPKs-, and AhR-dependent pathways in HT22 cells.

Involvement of nerve growth factor in mouse hippocampal neuronal cell line (HT22) differentiation and underlying role of DNA methyltransferases

DNA methylation is an epigenetic event involved in regulation of gene transcription during cell differentiation. DNA methyltransferases (DNMT) play a role in differentiation of neural stem cells into neurons. The aim of this study was to determine whether nerve growth factor (NGF) was involved in differentiation of mouse hippocampal neuronal cell line (HT22) as assessed by IncuCyte. Quantitative PCR and western blot were used to measure gene and protein expression of DNMT as well as the activity of DNMTs. Treatment with NGF was found to upregulate both gene and protein expressions as well as total activity of DNMTs in differentiating HT22 cells. Compared to undifferentiating cells, the percentage of differentiating cells at S phase increased significantly when incubated with NGF. In undifferentiated cells, NGF failed to induce gene and protein expressions and activity of DNMTs. Data demonstrate that differentiation of HT22 cells by exposure to NGF involve the activation of DNMTs pathway.

Effects of 5-Aza on p-Y1472 NR2B related to learning and memory in the mouse hippocampus

BACKGROUND

We have previously reported that 5-Aza-2-deoxycytidine (5-Aza-cdR) can repress protein serine/threonine phosphatase-1γ (PP1γ) expression and activity in the mouse hippocampus and affect the behaviour of mice in a water maze. It is well known that the phosphorylation of N-methyl-d-aspartate receptor 2B subunit (NR2B) plays a role in behaviour. In this study, we examined whether 5-Aza-cdR affects NR2B phosphorylation at tyrosine 1472 (p-Y1472 NR2B) and whether it affected the responses of the mice in a passive avoidance test.

METHODS

5-Aza-cdR (10 μM) was administered to mice via intracerebroventricular injection (i.c.v). The learning and memory behaviour of the mice were evaluated by measuring their response in a step-down type passive avoidance test 24 h after the injection. The mRNA level of NR2B was measured by real-time PCR. NR2B and p-Y1472 NR2B protein expression in the mouse hippocampus was detected by western blot and immunofluorescence. CDK5 activity was detected by the ADP-Glo™ + CDK5/p35 Kinase Enzyme System. To further clarify whether the 5-Aza-cdR effects on behaviour were dependent on cellular proliferation or not, the effect of 5-Aza-cdR on the expression level of NR2B, the phosphorylation level of p-Y1472 NR2B, cell viability and the cell cycle were analysed using the immortalized mouse hippocampal neuronal cells neural cell line HT22 treated with 10 μM 5-Aza-cdR compared with an untreated control group.

RESULTS

After injection with 5-Aza-cdR, the behaviour of the mice in the step-down test was improved, while their phosphorylation level of p-Y1472 NR2B was increased and their CDK5 activity was decreased in the hippocampus. In vitro experiments showed 10 μM 5-Aza-cdR increased the p-Y1472 NR2B phosphorylation level with inhibition of cell viability and cell cycle arrest.

CONCLUSIONS

Our results suggested that the effect of 5-Aza-cdR on behaviour may be related to the increase in phosphorylation of p-Y1472 NR2B in the hippocampus.

AAV-Syn-BDNF-EGFP Virus Construct Exerts Neuroprotective Action on the Hippocampal Neural Network during Hypoxia In Vitro

Brain-derived neurotrophic factor (BDNF) is one of the key signaling molecules that supports the viability of neural cells in various brain pathologies, and can be considered a potential therapeutic agent. However, several methodological difficulties, such as overcoming the blood–brain barrier and the short half-life period, challenge the potential use of BDNF in clinical practice. Gene therapy could overcome these limitations. Investigating the influence of viral vectors on the neural network level is of particular interest because viral overexpression affects different aspects of cell metabolism and interactions between neurons. The present work aimed to investigate the influence of the adeno-associated virus (AAV)-Syn-BDNF-EGFP virus construct on neural network activity parameters in an acute hypobaric hypoxia model in vitro. Materials and methods. An adeno-associated virus vector carrying the BDNF gene was constructed using the following plasmids: AAV-Syn-EGFP, pDP5, DJvector, and pHelper. The developed virus vector was then tested on primary hippocampal cultures obtained from C57BL/6 mouse embryos (E18). Acute hypobaric hypoxia was induced on day 21 in vitro. Spontaneous bioelectrical and calcium activity of neural networks in primary cultures and viability tests were analysed during normoxia and during the posthypoxic period. Results. BDNF overexpression by AAV-Syn-BDNF-EGFP does not affect cell viability or the main parameters of spontaneous bioelectrical activity in normoxia. Application of the developed virus construct partially eliminates the negative hypoxic consequences by preserving cell viability and maintaining spontaneous bioelectrical activity in the cultures. Moreover, the internal functional structure, including the activation pattern of network bursts, the number of hubs, and the number of connections within network elements, is also partially preserved. BDNF overexpression prevents a decrease in the number of cells exhibiting calcium activity and maintains the frequency of calcium oscillations. Conclusion. This study revealed the pronounced antihypoxic and neuroprotective effects of AAV-Syn-BDNF-EGFP virus transduction in an acute normobaric hypoxia model.

The Aminopyridinol Derivative BJ-1201 Protects Murine Hippocampal Cells against Glutamate-Induced Neurotoxicity via Heme Oxygenase-1

Glutamate is the major excitatory neurotransmitter in the brain. It can cause neuronal cell damage in the context of oxidative stress. BJ-1201 is a derivative of the compound aminopyridinol, which is known for its antioxidant activity. In this study, we examined the effect of BJ-1201, a 6-(diphenylamino)-2,4,5-trimethylpyridin-3-ol compound, on neuroprotection in HT22 cells. Our data showed that BJ-1201 can protect HT22 cells against glutamate-induced cell cytotoxicity. In addition, BJ-1201 upregulated heme oxygenase-1 (HO-1) to levels comparable to those of the CoPP-treated group. BJ-1201 treatment induced phosphorylation of JNK, but not p38-MAPK or ERK. It also increased the signal in the reporter assay based on β-galactosidase activity driven by the nuclear transcription factor erythroid-2 related factor 2 (Nrf2) promoter harboring antioxidant response elements (AREs) and induced the translocation of Nrf2. These results demonstrate that BJ-1201 may be a good therapeutic platform against neurodegenerative diseases induced by oxidative stress.

PI3K/AKT/mTOR/p70S6K Pathway Is Involved in Aβ25-35-Induced Autophagy

Disruption or deregulation of the autophagy system has been implicated in neurodegenerative disorders such as Alzheimer's disease (AD). Aβ plays an important role in this autophagic system. In many cases, autophagy is regulated by the phosphatidylinositol 3-phosphate kinase/AKT/mammalian target of rapamycin/p70 ribosomal protein S6 kinase (PI3K/AKT/mTOR/p70S6K) signaling pathway. However, whether this signaling pathway is involved in Aβ-induced autophagy in neuronal cells is not known. Here, we studied whether Aβ25-35 induces autophagy in HT22 cells and C57 mice and investigated whether PI3K is involved in the autophagy induction. We found that Aβ25-35 inhibited HT22 cell viability in a dose- and time-dependent manner. Aβ25-35 induced autophagosome formation, the conversion of microtubule-associated protein light chain 3 (LC3), and the suppression of the mTOR pathway both in vitro and in vivo. Furthermore, Aβ25-35 impaired the learning abilities of C57 mice. Our study suggests that Aβ25-35 induces autophagy and the PI3K/AKT/mTOR/p70S6K pathway is involved in the process, which improves our understanding of the pathogenesis of AD and provides an additional model for AD research.

Release of mitochondrial Opa1 following oxidative stress in HT22 cells

Cellular mechanisms involved in multiple neurodegenerative diseases converge on mitochondria to induce overproduction of reactive oxygen species, damage to mitochondria, and subsequent cytochrome c release. Little is currently known regarding the contribution mitochondrial dynamics play in cytochrome c release following oxidative stress in neurodegenerative disease. Here we induced oxidative stress in the HT22 cell line with glutamate and investigated key mediators of mitochondrial dynamics to determine the role this process may play in oxidative stress induced neuronal death. We report that glutamate treatment in HT22 cells induces increase in reactive oxygen species (ROS), release of the mitochondrial fusion protein Opa1 into the cytosol, with concomitant release of cytochrome c. Furthermore, following the glutamate treatment alterations in cell signaling coincide with mitochondrial fragmentation which culminates in significant cell death in HT22 cells. Finally, we report that treatment with the antioxidant tocopherol attenuates glutamate induced-ROS increase, release of mitochondrial Opa1 and cytochrome c, and prevents cell death.

Endocannabinoid 2-arachidonylglycerol protects primary cultured neurons against homocysteine-induced impairments in rat caudate nucleus through CB1 receptor

Homocysteine (Hcy) is a high risk factor for Alzheimer's disease (AD). Caudate nucleus (CN), the major component of basal ganglia in the brain, is also involved in many neurological disorders. 2-Arachidonoylglycerol (2-AG), the true natural ligand for cannabinoid type-1 (CB1) receptors and the most abundant endogenous cannabinoid, has been shown to exhibit neuroprotective effects through its anti-inflammatory action from proinflammatory stimuli in the hippocampus and CN. However, it is still not well understood whether that 2-AG is also able to protect CN neurons from Hcy harmful insults. In the present work, we explored that 2-AG significantly protects CN neurons in culture against Hcy-induced response. 2-AG is capable of inhibiting elevation of Hcy-induced cyclooxygenase-2 expression associated with nuclear factor-kappaB/p38MAPK/ERK1/2 signaling pathway through CB1 receptors-dependent way in primary cultured CN neurons. Our study reveals the therapeutic potential for 2-AG for the treatment of neurodegenerative diseases, such as AD.

The neuroprotective effects of cordycepin inhibit glutamate-induced oxidative and ER stress-associated apoptosis in hippocampal HT22 cells

Glutamate toxicity increases the formation of reactive oxygen species (ROS) and intracellular calcium levels, resulting in neuronal dysfunction, neurodegenerative disorders, and death. Cordycepin is a derivative of the nucleoside adenosine, and is believed to exert neuroprotective effects against glutamate-induced oxidative toxicity in HT22 neuronal cells. Excessive glutamate induces oxidative and endoplasmic reticulum (ER) stress, gradually increasing ER-related pro-apoptotic transcription factor C/EBP homologous protein (CHOP) expression, and eventually up-regulating expression of the pro-apoptotic factor Bax. Cordycepin inhibits CHOP and Bax expressions, as well as p-ERK, p-JNK, and p-p38, all of which are involved in oxidative or ER stress-induced apoptosis. In addition, the increased production of ROS from excessive glutamate leads to elevation of mitochondrial membrane potential (MMP), a hallmark of mitochondrial dysfunction. Cordycepin retains MMP and reduces the elevated levels of ROS and Ca(2+) induced by glutamate. Caspases are crucial mediators involved in mitochondrial apoptosis, and while glutamate disrupts mitochondrial function, it does not change expression levels of caspase 3 and caspase 9. Similarly, cordycepin has no effect on caspase 3 and caspase 9 expressions; however, it decreases the expression of ER stress-specific caspase 12, which plays a key role in the initiation of ER stress-induced apoptosis. Finally, we found that the anti-apoptotic effects of cordycepin are partially dependent on activation of the adenosine A1 receptor, whereas an antagonist selectively attenuated the neuroprotective effects of cordycepin. Collectively, these results suggest that cordycepin could be a potential future therapeutic agent for neuronal disorders.

Discovery of novel N-substituted carbazoles as neuroprotective agents with potent anti-oxidative activity

Carbazole moiety is an important scaffold with a variety of biological applications, for example, anti-oxidative stress. Our previous synthesized carbazoles were screened for their neuroprotective properties against two individual oxidative stresses. Some of the new carbazole derivatives were observed with modest to good neuroprotective effects on neuronal cells HT22 against cell injury induced by glutamate or homocysteic acid (HCA). Substituents introduced to the carbazole ring system play crucial roles in their biological activities. In particular, a bulky group favors the neuroprotective activity of the compounds. One of the new compounds, 6, showed the best neuroprotective effects, which might result from its anti-oxidative activity with a GSH-independent mechanism. These findings might provide an alternative strategy for the development of novel carbazole derivatives for the treatment of CNS diseases such as Alzheimer's disease.

Peptidergic drugs for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is a devastating medical condition that has an enormous socioeconomic impact because it affects more than 10 million people annually worldwide and is associated with high rates of hospitalization, mortality and disability. Although TBI survival has improved continuously for decades, particularly in developing countries, implementation of an effective drug therapy for TBI represents an unmet clinical need. All confirmatory trials conducted to date with drugs targeting a single TBI pathological pathway failed to show clinical efficacy, probably because TBI pathophysiology involves multiple cellular and molecular mechanisms of secondary brain damage. According to current scientific evidence of the participation of peptide-mediated mechanisms in the processes of brain injury and repair after TBI, peptidergic drugs represent a multimodal therapy alternative to improve acute outcome and long-term recovery in TBI patients. Preliminary randomized-controlled clinical trials and open-label studies conducted to date with the peptidergic drug Cerebrolysin® (Ever Neuro Pharma GmbH, Unterach, Austria) and with the endogenous neuropeptides progesterone and erythropoietin, showed positive clinical results. Cerebrolysin-treated patients had a faster clinical recovery, a shorter hospitalization time and a better long-term outcome. Treatment with progesterone showed advantages over placebo regarding TBI mortality and clinical outcome, whereas erythropoietin only reduced mortality. Further validation of these promising findings in confirmatory randomized-controlled clinical trials is warranted. This article reviews the scientific basis and clinical evidence on the development of multimodal peptidergic drugs as a therapeutic option for the effective treatment of TBI patients.

Basic fibroblast growth factor protects C17.2 cells from radiation-induced injury through ERK1/2

AIMS

To establish a radiation-induced neural injury model using C17.2 neural stem cells (NSCs) and to investigate whether basic fibroblast growth factor (bFGF) can protect the radiation-induced injury of C17.2 NSCs. Furthermore, we aim to identify the possible mechanisms involved in this model.

METHODS

C17.2 NSCs received a single exposure (3, 6, and 9 Gy, respectively) at a dose rate of 300 cGy/min with a control group receiving 0 Gy. Different concentrations of bFGF were added for 24 h, 5 min postirradiation. The MTS assay and flow cytometry were used to detect cytotoxicity and apoptosis. Expression of FGFR1, ERK1/2, and p-ERK1/2 proteins was detected with or without U0126 was pretreated prior to C17.2 NSCs receiving irradiation.

RESULTS

C17.2 NSCs showed a dose-dependent cell death as the dose of radiation was increased. Additionally, the rate of apoptosis in the C17.2 NSCs reached 31.2 ± 1.23% in the 6 Gy irradiation group, which was the most significant when compared to the other irradiation treated groups. bFGF showed protective effect on cell apoptosis in a dose-dependent manner. The mean percentage of apoptotic cells decreased to 7.83 ± 1.75% when 100 ng/mL bFGF was given. Furthermore, U0126 could block the protective effect of bFGF by inhibiting the phosphorylation of ERK1/2.

CONCLUSIONS

An in vitro cellular model of radiation-induced apoptosis of NSCs, in C17.2 NSCs, was developed successfully. Additionally, bFGF can protect neurons from radiation injury in vitro via the ERK1/2 signal transduction pathway.

Edaravone protects HT22 neurons from H2O2-induced apoptosis by inhibiting the MAPK signaling pathway

AIMS

Oxidative stress is frequently implicated in the pathology of neurodegenerative diseases. This study aimed to investigate the effects and their underlying mechanism(s) of edaravone upon hydrogen peroxide (H2O2)-induced oxidative stress and apoptosis in HT22 cells, a murine hippocampal neuronal model.

METHODS

HT22 cells were treated with H2O2 in the presence of various concentrations of edaravone or in its absence. A CCK-8 assay, Hoechst 33342 staining, and flow cytometry were used to detect cytotoxicity and apoptosis. In addition, the levels of reactive oxygen species (ROS) and the expression of Bcl-2, Bax, p-ERK 1/2, p-JNK, and p-P38 proteins in HT22 cells were examined.

RESULTS

Exogenous H2O2 decreased cell viability in a concentration-dependent manner and was associated with increased apoptosis and ROS production. Moreover, H2O2 significantly activated and upregulated the expression of p-ERK 1/2, p-JNK, and p-P38, while edaravon protected HT22 cells against H2O2-induced injury by inhibiting the production of ROS and activating the MAPK signaling pathway.

CONCLUSIONS

Our results provide the first evidence that edaravone can protect H2O2-induced cell injury in HT22 neurons via its antioxidant action. These findings suggest that edaravone may be useful in the treatment of neurodegenerative disorders in which oxidative stress has been principally implicated.