Glutamate levels control HT22 murine hippocampal cell death by regulating biphasic patterns of Erk1/2 activation: role of metabolic glutamate receptor 5

Neuroprotective Effects of Sparassis crispa Ethanol Extract through the AKT/NRF2 and ERK/CREB Pathway in Mouse Hippocampal Cells

Sparassis crispa, known as the "Cauliflower mushroom", is an edible medicinal fungus found in Asia, Europe, and North America. Its fruiting bodies contain active biological and pharmacological ingredients with antitumor and anti-inflammatory properties. In this study, we investigated the neuroprotective effect of various Sparassis crispa extract against glutamate-induced toxicity and oxidative stress in hippocampal HT22 cells. Cell viability and reactive oxygen species (ROS) analyses served to evaluate the neuroprotective effects of Sparassis crispa ethanol extract (SCE) and their fractions partitioned with ethyl acetate (EtOAc; SCE-E) and water (SCE-W) in HT22 cells. SCE and SCE-E treatment reduced glutamate-induced cell death and ROS generation. SCE-E reduced apoptosis and ROS levels by regulating anti-apoptotic proteins. Under glutamate treatment, SCE-E activated nuclear factor erythroid-derived 2-related factor 2 (Nrf2) and regulated extracellular signal-regulated kinase (ERK) and AKT signals at late stages. SCE-E increased the protein expression of cAMP response element binding (CREB), brain-derived neurotrophic factor (BDNF), and Kelch-like ECH-associated protein 1 (Keap1), and decreased the Nrf2 protein expression. Moreover, co-treatment of SCE-E and wortmannin did not activate Nrf2 expression. Thus, the neuroprotective effect of SCE-E is likely due to Nrf2 and CREB activation through AKT and ERK phosphorylation, which effectively suppress glutamate-induced oxidative stress in HT22 cells. Accordingly, a daily supplement of SCE-E could become a potential treatment for oxidative-stress-related neurological diseases.

Screening of the active Ingredients in Huanglian Jiedu decoction through amide bond-Immobilized magnetic nanoparticle-assisted cell membrane chromatography

Introduction: The Huanglian Jiedu decoction (HLJDD) is a Chinese herbal formula that exerts neuroprotective effects by alleviating oxidative stress injuries and may potentially be prescribed for treating Alzheimer's disease; however, its active ingredients have not yet been identified. Cell membrane chromatography is a high-throughput method for screening active ingredients, but traditional cell membrane chromatography requires multiple centrifugation steps, which affects its separation efficiency. Magnetic nanoparticles are unparalleled in solid-liquid separation and can overcome the shortcomings of traditional cell membrane chromatography. Methods: In this study, the neuroprotective effects of the components of HLJDD were screened through a novel magnetic nanoparticle-assisted cell membrane chromatography method. Magnetic nanoparticles and cell membranes were stably immobilized by amide bonds. Magnetic bead (MB)-immobilized cell membranes of HT-22 cells were incubated with the HLJDD extract to isolate specific binding components. The specific binding components were then identified by ultraperformance liquid chromatography (UPLC)-Orbitrap Fusion Tribrid MS after solid-phase extraction. The bioactivity of these components was analyzed in an HT-22 cellular model of glutamate-induced injury. Results and Discussion: The preparation method of the composite of cell membrane and MBs has the advantages of simple preparation and no introduction of toxic organic reagents. MBs not only provide support for cell membranes, but also greatly improve the separation efficiency compared with traditional cell membrane chromatography. Fifteen of these components were found to specifically bind to the cell membranes, and seven of them were confirmed to reduce varying degrees of glutamate-induced toxicity in HT-22 cells. In conclusion, our findings suggest that the amide bond-based immobilization of magnetic nanoparticles on cell membranes, along with solid-phase extraction and UPLC, is an effective method for isolating and discovering the bioactive components of traditional Chinese medicines.

Germinated brown rice protects against glutamate toxicity in HT22 hippocampal neurons through the jnk-mediated apoptotic pathway via the GABA(A) 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.

Protection against H2O2-evoked toxicity in HT22 hippocampal neuronal cells by geissoschizine methyl ether via inhibiting ERK pathway

Oxidative stress is considered as an important mechanism underlying the pathology of neurodegenerative disorders. In this study, we utilized an in vitro model where oxidative stress process was evoked by exogenous hydrogen peroxide (H₂O₂) in HT22 murine hippocampal neurons and evaluated the neuroprotective effects of geissoschizine methyl ether (GME), a naturally occurring alkaloid from the hooks of Uncaria rhynchophylla (Miq.) Jacks. After a 24 h H₂O₂ (350 μM) insult, a significant decrease in cell survival and a sharp increase in intracellular reactive oxygen species were observed in HT22 cells. Encouragingly, GME (10-200 μM) effectively reversed these abnormal cellular changes induced by H₂O₂. Moreover, mechanistic studies using Western blot revealed that GME inhibited the increase of phospho-ERK protein expression, but not phospho-p38, caused by H₂O₂. Molecular docking simulation further revealed a possible binding mode that GME inhibited ERK protein, showing that GME favorably bound to ERK via multiple hydrophobic and hydrogen bond interactions. These findings indicate that GME provide effective neuroprotection via inhibiting ERK pathway and also encourage further ex vivo and in vivo pharmacological investigations of GME in treating oxidative stress-mediated neurological disorders.

Neuroprotective effects of an in vitro BBB permeable phenoxythiophene sulfonamide small molecule in glutamate-induced oxidative injury

Reactive oxygen species (ROS) play a central role in oxidative stress-associated neuronal cell death during ischemia. Further investigation into the inhibition of excessive ROS generation post-stroke is urgently required for the treatment of ischemic stroke. In the present study, the neuroprotective properties of the blood-brain barrier (BBB) penetrant B355227 were investigated. B355227 is a chemical analogue of B355252, and the role of the phenoxythiophene sulfonamide compound B355227 was further investigated in a glutamate-induced oxidative injury model. An in vitro model of the BBB was established in the immortalized mouse brain capillary endothelial cell line, bEnd.3. Formation of barrier in Transwell inserts was confirmed using EVOM resistance meter and Caffeine, Imatinib and Axitinib were used to validate the efficacy of the model. The validated BBB assay in combination with high performance liquid chromatography were used to analyse and verify the permeability of B355227 through the barrier. The integrity of the cell junctions after the BBB assays were confirmed using immunofluorescence to visualize the expression of the barrier junction protein zonula occludens-1. Cell survival was measured with Resazurin, a redox indicator dye, in HT22, a hippocampal neuronal cell treated with 5 mM glutamate or co-treated with the B355227 recovered from the BBB permeability experiment. Changes in glutathione levels were detected using a glutathione detection kit, while analyses of ROS, calcium (Ca2+), and mitochondrial membrane potential (MMP) were accomplished with the fluorescent dyes 2',7'-dichlorofluorescein diacetate, Fura-2 AM and MitoTracker Red dyes, respectively. Immunoblotting was also performed to detect the expression and activation of Erk1/2, p-38, JNK, Bax and Bcl-2. The results of the present study demonstrated that B355227 crossed the BBB in vitro and protected HT22 from oxidative injury induced by glutamate exposure. Treatment of cells with B355227 blocked the glutamate-dependent depletion of intracellular glutathione and significantly reduced ROS production. Increased Ca2+ influx and subsequent collapse of the MMP was attenuated by B355227. Furthermore, the results of the present study demonstrated that B355227 protected against oxidative stress via the MAPK pathway, by increasing the activation of Erk1/2, JNK and P38, and restoring anti-apoptotic Bcl-2. Collectively, the results of the present study indicate that B355227 has potent antioxidant and neuroprotective attributes in glutamate-induced neuronal cell death. Further investigation into the role of B355227 in the modulation of glutamate-dependent oxidative stress is required.

Neuroprotection by B355252 against Glutamate-Induced Cytotoxicity in Murine Hippocampal HT-22 Cells Is Associated with Activation of ERK3 Signaling Pathway

Glutamate differentially affects the levels extracellular signal-regulated kinase (ERK)1/2 and ERK3 and the protective effect of B355252, an aryl thiophene compound, 4-chloro-N-(naphthalen-1-ylmethyl)-5-(3-(piperazin-1-yl)phenoxy)thiophene-2-sulfonamide, is associated with suppression of ERK1/2. The objectives of this study were to further investigate the impact of B355252 on ERK3 and its downstream signaling pathways affected by glutamate exposure in the mouse hippocampal HT-22 neuronal cells. Murine hippocampal HT22 cells were incubated with glutamate and treated with B355252. Cell viability was assessed, protein levels of pERK3, ERK3, mitogen-activated protein kinase-activated protein kinase-5 (MAPKAPK-5), steroid receptor coactivator 3 (SRC-3), p-S6 and S6 were measured using Western blotting, and immunoreactivity of p-S6 was determined by immunocytochemistry. The results reveal that glutamate markedly diminished the protein levels of p-ERK3 and its downstream targets MK-5 and SRC-3 and increased p-S6, an indicator for mechanistic target of rapamycin (mTOR) activation. Conversely, treatment with B355252 protected the cells from glutamate-induced damage and prevented the glutamate-caused declines of p-ERK3, MK-5 and SRC-3 and increase of p-S6. Our study demonstrates that one of the mechanisms that glutamate mediates its cytotoxicity is through suppression of ERK3 and that B355252 rescues the cells from glutamate toxicity by reverting ERK3 level.

Protective Effects of Active Compounds from Salviae miltiorrhizae Radix against Glutamate-Induced HT-22 Hippocampal Neuronal Cell Death

Oxidative stress is considered one of the factors that cause dysfunction and damage of neurons, causing diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer’s disease (AD), and Parkinson’s disease (PD).Recently, natural antioxidant sources have emerged as one of the main research areas for the discovery of potential neuroprotectants that can be used to treat neurological diseases. In this research, we assessed the neuroprotective effect of a 70% ethanol Salvia miltiorrhiza Radix (SMR) extract and five of its constituent compounds (tanshinone IIA, caffeic acid, salvianolic acid B, rosmarinic acid, and salvianic acid A) in HT-22 hippocampal cells. The experimental data showed that most samples were effective in attenuating the cytotoxicity caused by glutamate in HT-22 cells, except for rosmarinic acid and salvianolic acid B. Of the compounds tested, tanshinone IIA (TS-IIA) exerted the strongest effect in protecting HT-22 cells against glutamate neurotoxin. Treatment with 400 nM TS-IIA restored HT-22 cell viability almost completely. TS-IIA prevented glutamate-induced oxytosis by abating the accumulation of calcium influx, reactive oxygen species, and phosphorylation of mitogen-activated protein kinases. Moreover, TS-IIA inhibited glutamate-induced cytotoxicity by reducing the activation and phosphorylation of p53, as well as by stimulating Akt expression. This research suggested that TS-IIA is a potential neuroprotective component of SMR, with the ability to protect against neuronal cell death induced by excessive amounts of glutamate.

Glutamate affects cholesterol homeostasis within the brain via the up-regulation of CYP46A1 and ApoE

Chronic glutamate excitotoxicity has been thought to be involved in numerous neurodegenerative disorders. A small but significant loss of membrane cholesterol has been reported following a short stimulation of ionotropic glutamate receptors (iGluRs). We investigated the alteration of brain cholesterol following chronic glutamate treatment. The alteration of cholesterol levels was evaluated in the hippocampus from the adult rats that received the subcutaneous injection with monosodium l-glutamate at 1, 3, 5, and 7 days of age. The regulation of CYP46A1, LXRα, and ApoE levels were assayed following subtoxic glutamate treatment in SH-SY5Y cells as well as HT-22 cells lacking iGluRs. The ratio of 24S-hydroxycholesterol to cholesterol was elevated in the adult rats exposed to monosodium l-glutamate before the weaning age, compared to the control. The blockers of NMDA receptor (MK801) and mGluR5 (MPEP) attenuated the glutamate-induced loss of cholesterol and elevation of 24S-hydroxycholesterol level in SH-SY5Y cells. The induction of the mRNA levels of CYP46A1, LXRα, and ApoE by glutamate was observed in both SH-SY5Y cells and HT-22 cells; additionally, MK801 and MPEP attenuated the increases in these genes in SH-SY5Y cells. The increase in the binding of LXRα proteins with ApoE promoter following glutamate treatment was attenuated by MK801. The luciferase assay indicated the binding of CREB protein with CYP46A1 promoter, and the glutamate-induced CREB expression was inhibited by MK801. The results suggest that glutamate, the major excitatory neurotransmitter, may affect the metabolism and redistribution of cholesterol in the neuronal cells via its specific receptors during chronic exposure.

Ferrostatin-1 protects HT-22 cells from oxidative toxicity

Ferroptosis is a type of programmed cell death dependent on iron. It is different from other forms of cell death such as apoptosis, classic necrosis and autophagy. Ferroptosis is involved in many neurodegenerative diseases. The role of ferroptosis in glutamate-induced neuronal toxicity is not fully understood. To test its toxicity, glutamate (1.25–20 mM) was applied to HT-22 cells for 12 to 48 hours. The optimal experimental conditions occurred at 12 hours after incubation with 5 mM glutamate. Cells were cultured with 3–12 μM ferrostatin-1, an inhibitor of ferroptosis, for 12 hours before exposure to glutamate. The cell viability was detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Autophagy was determined by monodansylcadaverine staining and apoptosis by caspase 3 activity. Damage to cell structures was observed under light and by transmission electron microscopy. The release of lactate dehydrogenase was detected by the commercial kit. Reactive oxygen species were measured by flow cytometry. Glutathione peroxidase activity, superoxide dismutase activity and malondialdehyde level were detected by the appropriate commercial kit. Prostaglandin peroxidase synthase 2 and glutathione peroxidase 4 gene expression was detected by real-time quantitative polymerase chain reaction. Glutathione peroxidase 4 and nuclear factor erythroid-derived-like 2 protein expression was detected by western blot analysis. Results showed that ferrostatin-1 can significantly counter the effects of glutamate on HT-22 cells, improving the survival rate, reducing the release of lactate dehydrogenase and reducing the damage to mitochondrial ultrastructure. However, it did not affect the caspase-3 expression and monodansylcadaverine-positive staining in glutamate-injured HT-22 cells. Ferrostatin-1 reduced the levels of reactive oxygen species and malondialdehyde and enhanced superoxide dismutase activity. It decreased gene expression of prostaglandin peroxidase synthase 2 and increased gene expression of glutathione peroxidase 4 and protein expressions of glutathione peroxidase 4 and nuclear factor (erythroid-derived)-like 2 in glutamate-injured HT-22 cells. Treatment of cultured cells with the apoptosis inhibitor Z-Val-Ala-Asp (OMe)-fluoromethyl ketone (2–8 μM), autophagy inhibitor 3-methyladenine (100–400 μM) or necrosis inhibitor necrostatin-1 (10–40 μM) had no effect on glutamate induced cell damage. However, the iron chelator deferoxamine mesylate salt inhibited glutamate induced cell death. Thus, the results suggested that ferroptosis is caused by glutamate-induced toxicity and that ferrostatin-1 protects HT-22 cells from glutamate-induced oxidative toxicity by inhibiting the oxidative stress.

Neuroprotective effects of myristargenol A against glutamate-induced apoptotic HT22 cell death

Glutamate is an important neurotransmitter in the central nervous system; however, at high concentrations, it causes excitotoxicity and many neurological disorders. Excitotoxicity induces cell death by apoptosis. Thus, factors that can inhibit the apoptotic pathways are a target of drug development for the treatment and prevention of neurodegenerative diseases. Herein, the antioxidative and neuroprotective effects of myristargenol A were examined in glutamate-induced mouse hippocampal neuronal HT22 cells. When the HT22 cells were stressed with glutamate, cell viability decreased to 44.4 ± 5.6% when compared with the case of the control cells (100 ± 4.8%); however, when these cells were treated with myristargenol A (10 μM), the cell viability was increased by 113.6 ± 2.3%. The protective effect of myristargenol A against the apoptosis of glutamate-induced HT22 cells was also confirmed using FITC-annexin V/propidium iodide double staining. In addition, myristargenol A protected the mitochondrial membrane potential (ΔΨ m). Subsequently, the expression levels of proteins in the caspase pathway related with the induction of apoptosis were decreased. Moreover, the expression levels of mitochondrial-related proteins, such as Bcl-2 and Bax, were examined, and it was found that the expression ratio of Bax/Bcl-2 decreased. In addition, myristargenol A inhibited the activity of mitogen-activated protein kinases, including p38 and c-Jun N-terminal kinase, for an oxidative stress protection effect but increased the activity of the extracellular signal-regulated kinases 1 and 2 for cell proliferation. These results reveal that myristargenol A possesses a neuroprotective effect against the neuronal cell damage caused by glutamate.

AMPA receptor expression in mouse testis and spermatogonial GC-1 cells: A study on its regulation by excitatory amino acids

Excitatory amino acids (EAAs) are found present in the nervous and reproductive systems of animals. Numerous studies have demonstrated a regulatory role for Glutamate (Glu), d-aspartate ( d-Asp) and N-methyl- d-aspartate (NMDA) in the control of spermatogenesis. EAAs are able to stimulate the Glutamate receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Here in, we assess expression of the main AMPAR subunits, GluA1 and GluA2/3, in the mouse testis and in spermatogonial GC-1 cells. The results showed that both GluA1 and GluA2/3 were localized in mouse testis prevalently in spermatogonia. The subunit GluA2/3 was more highly expressed compared with GluA1 in both the testis and the GC-1 cells. Subsequently, GC-1 cells were incubated with medium containing l-Glu, d-Glu, d-Asp or NMDA to determine GluA1 and GluA2/3 expressions. At 30 minutes and 2 hours of incubation, EAA-treated GC-1 cells showed significantly higher expression levels of both GluA1 and GluA2/3. Furthermore, p-extracellular signal-regulated kinase (ERK), p-Akt, proliferating cell nuclear antigen (PCNA), and Aurora B expressions were assayed in l-Glu-, d-Glu-, and NMDA-treated GC-1 cells. At 30 minutes and 2 hours of incubation, treated GC-1 cells showed significantly higher expression levels of p-ERK and p-Akt. A consequent increase of PCNA and Aurora B expressions was induced by l-Glu and NMDA, but not by d-Glu. Our study demonstrates a direct effect of the EAAs on spermatogonial activity. In addition, the increased protein expression levels of GluA1 and GluA2/3 in EAA-treated GC-1 cells suggest that EAAs could activate ERK and Akt pathways through the AMPAR. Finally, the increased PCNA and Aurora B levels may imply an enhanced proliferative activity.

Protective effect of casuarinin against glutamate-induced apoptosis in HT22 cells through inhibition of oxidative stress-mediated MAPK phosphorylation

Glutamate is the major excitatory neurotransmitter in the central nervous system and is involved in oxidative stress during neurodegeneration. In the present study, casuarinin prevented glutamate-induced HT22 murine hippocampal neuronal cell death by inhibiting intracellular reactive oxygen species (ROS) production. Moreover, casuarinin reduced chromatin condensation and annexin-V-positive cell production induced by glutamate. We also confirmed the underlying protective mechanism of casuarinin against glutamate-induced neurotoxicity. Glutamate markedly increased the phosphorylation of extracellular signal regulated kinase (ERK)-1/2 and p38, which are crucial in oxidative stress-mediated neuronal cell death. Conversely, treatment with casuarinin diminished the phosphorylation of ERK1/2 and P38. In conclusion, the results of this study suggest that casuarinin, obtained from natural products, acts as potent neuroprotective agent by suppressing glutamate-mediated apoptosis through the inhibition of ROS production and activation of the mitogen activated protein kinase (MAPK) pathway. Thus, casuarinin can be a potential therapeutic agent in the treatment of neurodegenerative diseases.

Glucose deprivation regulates the progranulin-sortilin axis in PC12 cells

Progranulin (PGRN) is a growth factor implicated in several neurodegenerative diseases, such as frontotemporal lobar degeneration. Despite its important role in the central nervous system (CNS), the mechanisms controlling PGRN expression in the CNS are largely unknown. Recent evidence, however, suggested that several stressors, such as hypoxia, acidosis, or oxidative stress, induce PGRN expression. The present study was mainly aimed at determining whether and, if so, how glucose deprivation affects PGRN expression in PC12 cells. Initially, it was found that glucose deprivation gradually induced PGRN gene expression in PC12 cells. To elucidate the underlying molecular mechanisms, several intracellular signalings that were modified in response to glucose deprivation were examined. Both adenosine monophosphate kinase (AMPK) activation and changes in osmotic pressure, which are modified by extracellular glucose concentration, had no effect on PGRN gene expression; on the other hand, p38 activation in response to glucose deprivation played an important role in inducing PGRN gene expression. It was also found that expression of sortilin, a PGRN receptor implicated in PGRN endocytosis, was dramatically reduced by glucose deprivation. In contrast to glucose‐dependent regulation of PGRN gene expression, AMPK activation played a central role in reducing sortilin expression. Overall, the present study suggests that the PGRN–sortilin axis is modulated by glucose deprivation via two distinct mechanisms. As PGRN is neuroprotective, this system may represent a new neuroprotective mechanism activated by glucose deprivation in the CNS.