An involvement of BDNF and PI3-K/Akt in the anti-apoptotic effect of memantine on staurosporine-evoked cell death in primary cortical neurons

Ca2+-Permeable TRPV1 Receptor Mediates Neuroprotective Effects in a Mouse Model of Alzheimer's Disease via BDNF/CREB Signaling Pathway

Transient receptor potential vanilloid 1 (TRPV1) protein is a Ca2+-permeable non-selective cation channel known for its pain modulation pathway. In a previous study, it was discovered that a triple-transgenic Alzheimer's disease (AD) mouse model (3xTg-AD+/+) has anti-AD effects. The expression of proteins in the brain-derived neurotrophic factor (BDNF)/cAMP response element binding protein (CREB) pathway in a 3xTg-AD/TRPV1 transgenic mice model was investigated to better understand the AD regulatory effect of TRPV1 deficiency. The results show that TRPV1 deficiency leads to CREB activation by increasing BDNF levels and promoting phosphorylation of tyrosine receptor kinase B (TrkB), extracellular signal-regulated kinase (ERK), protein kinase B (Akt), and CREB in the hippocampus. Additionally, TRPV1 deficiency-induced CREB activation increases the antiapoptotic factor B-cell lymphoma 2 (Bcl-2) gene, which consequently downregulates Bcl-2-associated X (Bax) expression and decreases cleaved caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP), which leads to the prevention of hippocampal apoptosis. In conclusion, TRPV1 deficiency exhibits neuroprotective effects by preventing apoptosis through the BDNF/CREB signal transduction pathway in the hippocampus of 3xTg-AD mice.

The Functions of Thioredoxin 1 in Neurodegeneration

Significance: Thioredoxin 1 (Trx1) is a ubiquitous protein that is found in organisms ranging from prokaryotes to eukaryotes. Trx1 acts as reductases in redox regulation and protects proteins from oxidative aggregation and inactivation. Trx1 helps the cells to cope with various environmental stresses and inhibits programmed cell death. It is beneficial to neuroregeneration and resistance against oxidative stress-associated neuron damage. Trx1 also plays important roles in suppressing neurodegenerative disorders. Recent Advances: Trx1 is a redox regulating protein involved in neuronal protection. According to a previous study, Trx1 expression is increased by nerve growth factor (NGF) and necessary for neurite outgrowth of PC12 cells. Trx1 has been shown to promote the growth of neurons. Trx1 knockout or knockdown has the worse impact on cell viability and survival. Critical Issues: Trx1 has functions in central nervous system. Trx1 plays the defensive roles against oxidative stress in neurodegenerative diseases. Future Directions: In this review, we focus on the structure of Trx1 and basic functions of Trx1. Trx1 plays a neuroprotective role by suppressing endoplasmic reticulum stress in Parkinson's disease. Neurodegenerative diseases have no cure and carry a high cost to the health care system and patient's families. Trx1 may be taken as a new target for neurodegenerative disorder therapy. Further studies of the Trx1 roles and mechanisms on neurodegenerative diseases are needed. Antioxid. Redox Signal. 36, 1023-1036.

Transcriptomic signatures of treatment response to the combination of escitalopram and memantine or placebo in late-life depression

Drugs that target glutamate neuronal transmission, such as memantine, offer a novel approach to the treatment of late-life depression, which is frequently comorbid with cognitive impairment. The results of our recently published double-blind, randomized, placebo-controlled trial of escitalopram or escitalopram/memantine in late-life depression with subjective memory complaints (NCT01902004) indicated no differences between treatments in depression remission, but additional benefits in cognition at 12-month follow-up with combination treatment. To identify pathways and biological functions uniquely induced by combination treatment that may explain cognitive improvements, we generated transcriptional profiles of remission compared with non-remission from whole blood samples. Remitters to escitalopram compared with escitalopram/memantine combination treatment display unique patterns of gene expression at baseline and 6 months after treatment initiation. Functional enrichment analysis demonstrates that escitalopram-based remission associates to functions related to cellular proliferation, apoptosis, and inflammatory response. Escitalopram/memantine-based remission, however, is characterized by processes related to cellular clearance, metabolism, and cytoskeletal dynamics. Both treatments modulate inflammatory responses, albeit via different effector pathways. Additional research is needed to understand the implications of these results in explaining the observed superior effects of combination treatment on cognition observed with prolonged treatment.

A Shortage of FTH Induces ROS and Sensitizes RAS-Proficient Neuroblastoma N2A Cells to Ferroptosis

Ferroptosis, an iron-dependent form of programmed cell death, has excellent potential as an anti-cancer therapeutic strategy in different types of tumors, especially in RAS-mutated ones. However, the function of ferroptosis for inhibiting neuroblastoma, a common child malignant tumor with minimal treatment, is unclear. This study investigated the anti-cancer function of ferroptosis inducer Erastin or RSL3 in neuroblastoma N2A cells. Our results show that Erastin or RSL3 induces ROS level and cell death and, therefore, reduces the viability of RAS-proficient N2A cells. Importantly, inhibitors to ferroptosis, but not apoptosis, ameliorate the high ROS level and viability defect in Erastin- or RSL3-treated cells. In addition, our data also show that N2A cells are much more sensitive to ferroptosis inducers than primary mouse cortical neural stem cells (NSCs) or neurons. Moreover, a higher level of ROS and PARylation is evidenced in N2A, but not NSCs. Mechanically, ferritin heavy chain 1 (Fth), the ferroxidase function to oxidate redox-active Fe²⁺ to redox-inactive Fe³⁺, is likely responsible for the hypersensitivity of N2A to ferroptosis induction since its expression is lower in N2A compared to NSCs; ectopic expression of Fth reduces ROS levels and cell death, and induces expression of GPX4 and cell viability in N2A cells. Most importantly, neuroblastoma cell lines express a significantly low level of Fth than almost all other types of cancer cell lines. All these data suggest that Erastin or RSL3 induce ferroptosis cell death in neuroblastoma N2A cells, but not normal neural cells, regardless of RAS mutations, due to inadequate FTH. This study, therefore, provides new evidence that ferroptosis could be a promising therapeutic target for neuroblastoma.

Physiopathology of ischemic stroke and its modulation using memantine: evidence from preclinical stroke

Ischemic stroke is the most common type of cerebrovascular disease and is caused by an interruption of blood flow in the brain. In this disease, two different damage areas are identifying: the lesion core, in which cells quickly die; and the penumbra (surrounding the lesion core), in which cells are functionally weakened but may recover and restore their functions. The currently approved treatments for ischemic stroke are the recombinant tissue plasminogen activator and endovascular thrombectomy, but they have a short therapeutic window (4.5 and 6 hours after stroke onset, respectively) and a low percentage of stroke patients actually receive these treatments. Memantine is an approved drug for the treatment of Alzheimer’s disease. Memantine is a noncompetitive, low affinity and use-dependent antagonist of N-methyl-D-aspartate glutamate receptor. Memantine has several advantages over developing a new drug to treat focal ischemic stroke, but the most important is that it has sufficient safe probes in preclinical models and humans, and if the preclinical studies provide more evidence about pharmacological actions in tissue protection and repair, this could help to increase the number of clinical trials. The present review summarizes the physiopathology of isquemic stroke and the pharmacological actions in neuroprotection and neuroplasticity of memantine in the post stroke stage of preclinical stroke models, to illustrate their potential to improve functional recovery in human patients.

Memantine, Simvastatin, and Epicatechin Inhibit 7-Ketocholesterol-induced Apoptosis in Retinal Pigment Epithelial Cells But Not Neurosensory Retinal Cells In Vitro

Purpose

7-ketocholesterol (7kCh), a natural byproduct of oxidation in lipoprotein deposits is implicated in the pathogenesis of diabetic retinopathy and age-related macular degeneration (AMD). This study was performed to investigate whether several clinical drugs can inhibit 7kCh-induced caspase activation and mitigate its apoptotic effects on retinal cells in vitro.

Methods

Two populations of retinal cells, human retinal pigment epithelial cells (ARPE-19) and rat neuroretinal cells (R28) were exposed to 7kCh in the presence of the following inhibitors: Z-VAD-FMK (pan-caspase inhibitor), simvastatin, memantine, epicatechin, and Z-IETD-FMK (caspase-8 inhibitor) or Z-ATAD-FMK (caspase-12 inhibitor). Caspase-3/7, -8, and -12 activity levels were measured by fluorochrome caspase assays to quantify cell death. IncuCyte live-cell microscopic images were obtained to quantify cell counts.

Results

Exposure to 7kCh for 24 hours significantly increased caspase activities for both ARPE-19 and R28 cells (P< 0.05). In ARPE cells, pretreatment with various drugs had significantly lower caspase-3/7, -8, and -12 activities, reported in % change in mean signal intensity (msi): Z-VAD-FMK (48% decrease, P< 0.01), memantine (decreased 47.8% at 1 µM, P = 0.0039 and 81.9% at 1 mM, P< 0.001), simvastatin (decreased 85.3% at 0.01 µM, P< 0.001 and 84.8% at 0.05 µM, P< 0.001) or epicatechin (83.6% decrease, P< 0.05), Z-IETD-FMK (68.1% decrease, P< 0.01), and Z-ATAD-FMK (47.7% decrease, P = 0.0017). In contrast, R28 cells exposed to 7kCh continued to have elevated caspase-3/7, -8, and -12 activities (between 25.7% decrease and 17.5% increase in msi, P> 0.05) regardless of the pretreatment.

Conclusion

Several current drugs protect ARPE-19 cells but not R28 cells from 7kCh-induced apoptosis, suggesting that a multiple-drug approach is needed to protect both cells types in various retinal diseases.

Icariside II, a PDE5 Inhibitor, Suppresses Oxygen-Glucose Deprivation/Reperfusion-Induced Primary Hippocampal Neuronal Death Through Activating the PKG/CREB/BDNF/TrkB Signaling Pathway

Background

Ischemic stroke remains the leading cause of death and adult disability. Cerebral ischemic/reperfusion (I/R) injury is caused by ischemic stroke thereafter aggravates overwhelming neuronal apoptosis and even the death of neurons. Of note, hippocampus is more susceptive to cerebral I/R injury than the other brain region. This study was designed to explore the effects and mechanism of icariside II (ICS II), a pharmacologically active compound exists in herbal Epimedii with previous study-proved as a phosphodiesterase 5 (PDE5) inhibitor, on the oxygen glucose deprivation/reoxygenation (OGD/R)-induced primary hippocampal neurons injury.

Methods

Effects of ICS II on primary hippocampal neuronal impairment and apoptosis induced by OGD/R were examined by MTT, lactate dehydrogenase (LDH) release, TUNEL staining, and flow cytometry, respectively. Activation of memory-related signaling pathways was measured using Western blot analysis. The direct interaction between ICS II and PDE5 was further evaluated by molecular docking.

Results

ICS II (12.5, 25, 50 μM) markedly abrogated OGD/R-induced hippocampal neuronal death as suggested by the increase in neurons viability and the decrease in cellular LDH release. Furthermore, ICS II not only effectively decreased the protein expression and activity of PDE5, restored the 3′5′-cyclic guanosine monophosphate (cGMP) level and its downstream target protein kinase G (PKG) activity but also increased the phosphorylation of cAMP response element binding protein (CREB) level, expressions of brain derived neurotrophic factor (BDNF), and tyrosine protein kinase B (TrkB). Mechanistically, the inhibitory effects of ICS II were abrogated by Rp-8-Br-cGMP (a PKG inhibitor) or ANA-12 (a TrkB inhibitor), which further confirmed that the favorable effects of ICS II were attributed to its activation of the PKG/CREB/BDNF signaling pathways. Intriguingly, ICS II might effectively bind and inhibited PDE5 activity as demonstrated by relatively high binding scores (−6.52 kcal/mol).

Conclusions

ICS II significantly rescues OGD/R-induced hippocampal neuronal injury. The mechanism is, at least partly, due to inhibition of PDE5 and activation of PKG/CREB/BDNF/TrkB signaling pathway. Hence it is thought that ICS II might be a potential naturally PDE5 inhibitor to combat cerebral I/R injury.

Vildagliptine protects SH-SY5Y human neuron-like cells from Aβ 1-42 induced toxicity, in vitro

The amyloid β (Aβ) toxic fibrils is thought to play a central role in the onset and progression of Alzheimer's disease (AD) because of it is a main formation of senile plaques. Diabetic patients are more vulnerable to caught Alzheimer's disease. Vildagliptine, a novel anti diabetic agent, has been reported to exert protective effects on AD rat models in restricted study. We aimed to investigate any protective effects of vildagliptine against Aβ fibrils on SH-SY5Y cell line. Vildagliptine decreased PSEN1 and PSEN2 mRNA levels which enroll Aβ production. In addition, vildagliptin was downregulated caspase-3 and caspase-9 expression levels which were evoked by Aβ. Also we confirmed cellular viability with real time cell analyzer and MTT assay. Our data exposed that vildagliptine has lowering effect on GSK3β and Tau phosphorylation. However we did not get protective effect of vildagliptine against Aβ toxicity on mitochondrial membrane potential. These results indicate that vildagliptine exerts a protective effect against Aβ by decreasing apoptosis related proteins, lowering GSK3β and Tau phosphorylation levels in addition to expression of PSEN1 and PSEN2 mRNA downregulation effect.

The role of memantine in the treatment of major depressive disorder: Clinical efficacy and mechanisms of action

A developing body of evidence indicates that disturbed glutamate neurotransmission especially through N-methyl-d-aspartate (NMDA) is central to the pathophysiology of major depressive disorder (MDD) and NMDA receptor antagonists have shown therapeutic potential in the MDD treatment. Memantine is an uncompetitive NMDA receptor antagonist, approved for treatment of Alzheimer's disease (AD) that in contrast to other NMDA receptor antagonists at therapeutic doses does not induce highly undesirable side effects. Neuroprotective properties and well tolerability of memantine have been attributed to its unique pharmacological features such as moderate affinity, rapid blocking kinetics and strongly voltage-dependency. In this review we summarized clinical trial evidence of antidepressant effectiveness of memantine and its mechanisms of action. Available data indicate contradictory findings relating to clinical efficacy suggesting further research is necessary in determining as to whether memantine will eventually be an advantageous therapy for MDD. Preclinical data proposed various neurobiological mechanisms underlying antidepressant-like properties of memantine that are responsible for synaptic plasticity and cell survival.

Molecular mechanisms of brain-derived neurotrophic factor in neuro-protection: Recent developments

Neuronal cell injury, as a consequence of acute or chronic neurological trauma, is a significant cause of mortality around the world. On a molecular level, the condition is characterized by widespread cell death and poor regeneration, which can result in severe morbidity in survivors. Potential therapeutics are of major interest, with a promising candidate being brain-derived neurotrophic factor (BDNF), a ubiquitous agent in the brain which has been associated with neural development and may facilitate protective and regenerative effects following injury. This review summarizes the available information on the potential benefits of BDNF and the molecular mechanisms involved in several pathological conditions, including hypoxic brain injury, stroke, Alzheimer's disease and Parkinson's disease. It further explores the methods in which BDNF can be applied in clinical and therapeutic settings, and the potential challenges to overcome.

The ATM kinase inhibitor KU-55933 provides neuroprotection against hydrogen peroxide-induced cell damage via a γH2AX/p-p53/caspase-3-independent mechanism: Inhibition of calpain and cathepsin D

The role of the kinase ataxia-telangiectasia mutated (ATM), a well-known protein engaged in DNA damage repair, in the regulation of neuronal responses to oxidative stress remains unexplored. Thus, the neuroprotective efficacy of KU-55933, a potent inhibitor of ATM, against cell damage evoked by oxidative stress (hydrogen peroxide, H₂O₂) has been studied in human neuroblastoma SH-SY5Y cells and compared with the efficacy of this agent in models of doxorubicin (Dox)- and staurosporine (St)-evoked cell death. KU-55933 inhibited the cell death induced by H₂O₂ or Dox but not by St in undifferentiated (UN-) and retinoic acid-differentiated (RA)-SH-SY5Y cells, with a more pronounced effect in the latter cell phenotype. Furthermore, this ATM inhibitor attenuated the Dox- but not H₂O₂-induced caspase-3 activity in both UN- and RA-SH-SY5Y cells. Although KU-55933 inhibited the H₂O₂- and Dox-induced activation of ATM, it attenuated the toxin-induced phosphorylation of the proteins H2AX and p53 only in the latter model of cell damage. Moreover, the ATM inhibitor prevented the H₂O₂-evoked increases in calpain and cathepsin D activity and attenuated cell damage to a similar degree as inhibitors of calpain (MDL28170) and cathepsin D (pepstatin A). Finally, we confirmed the neuroprotective potential of KU-55933 against the H₂O₂- and Dox-evoked cell damage in primary mouse cerebellar granule cells and in the mouse hippocampal HT-22 cell line. Altogether, our results extend the neuroprotective portfolio of KU-55933 to a model of oxidative stress, with this effect not involving inhibition of the γH2AX/p-p53/caspase-3 pathway and instead associated with the attenuation of calpain and cathepsin D activity.

The neuroprotective effects of orthosteric agonists of group II and III mGluRs in primary neuronal cell cultures are dependent on developmental stage

Activation of metabotropic glutamate receptors (mGluRs) modulates neuronal excitability. Here, we evaluated the neuroprotective potential of four structurally diverse activators of group II and III mGluRs: an orthosteric agonist of group II (LY354740), an orthosteric agonist of group III (ACPT-I), an allosteric agonist of mGluR7 (AMN082) and a positive allosteric modulator (PAM) of mGluR4 (VU0361737). Neurotoxicity was induced by the pro-apoptotic agents: staurosporine (St) and doxorubicin (Dox) or the excitotoxic factor glutamate (Glu). The effects were analyzed in primary hippocampal (HIP) and cerebellar granule cell (CGC) cultures at two developmental stages, at 7 and 12 days in vitro (DIV). The data reveal a general neuroprotective effect of group II and III mGluR activators against the St- and Glu- but not Dox-induced cell damage. We found that neuroprotective effects of group II and III mGluR orthosteric agonists (LY354740 and ACPT-I) were higher at 12 DIV when compared to 7 DIV cells. In contrast, the efficiency of allosteric mGluR agents (AMN082 and VU0361737) did not differ between 7 and 12 DIV in both, St and Glu models of neuronal cell damage. Interestingly, the protective effects of activators of group II and III mGluRs were blocked by relevant antagonists only against Glu-induced neurotoxicity. Moreover, the observed neuroprotective action of group II and III mGluR activators in the St model was associated with a decreased number of PI-positive cells and no alterations in the caspase-3 activity. Finally, we showed that MAPK/ERK pathway activation was potentially involved in the mechanism of ACPT-I- and AMN082-induced neuroprotection against the St-evoked cellular damage. Our comparative study demonstrated the developmental stage-dependent neuroprotective effect of orthosteric group II and III mGluR agonists. In comparison to allosteric modulators, orthosteric compounds may provide more specific tools for suppression of neuronal cell loss associated with various chronic neurodegenerative conditions. Our results also suggest that the inhibition of intracellular pathways mediating necrotic, rather than apoptotic cascades, may be involved in neuroprotective effects of activators of group II and III mGluRs.

An Involvement of PI3-K/Akt Activation and Inhibition of AIF Translocation in Neuroprotective Effects of Undecylenic Acid (UDA) Against Pro-Apoptotic Factors-Induced Cell Death in Human Neuroblastoma SH-SY5Y Cells

Undecylenic acid (UDA), a naturally occurring 11-carbon unsaturated fatty acid, has been used for several years as an economical antifungal agent and a nutritional supplement. Recently, the potential usefulness of UDA as a neuroprotective drug has been suggested based on the ability of this agent to inhibit μ-calpain activity. In order to verify neuroprotective potential of UDA, we tested protective efficacy of this compound against cell damage evoked by pro-apoptotic factors (staurosporine and doxorubicin) and oxidative stress (hydrogen peroxide) in human neuroblastoma SH-SY5Y cells. We showed that UDA partially protected SH-SY5Y cells against the staurosporine- and doxorubicin-evoked cell death; however, this effect was not connected with its influence on caspase-3 activity. UDA decreased the St-induced changes in mitochondrial and cytosolic AIF level, whereas in Dox-model it affected only the cytosolic AIF content. Moreover, UDA (1-40 μM) decreased the hydrogen peroxide-induced cell damage which was connected with attenuation of hydrogen peroxide-mediated necrotic (PI staining, ADP/ATP ratio) and apoptotic (mitochondrial membrane potential, caspase-3 activation, AIF translocation) changes. Finally, we demonstrated that an inhibitor of PI3-K/Akt (LY294002) but not MAPK/ERK1/2 (U0126) pathway blocked the protection mediated by UDA in all tested models of SH-SY5Y cell injury. These in vitro data point to UDA as potentially effective neuroprotectant the utility of which should be further validated in animal studies.

The Effects of Astilbin on Cognitive Impairments in a Transgenic Mouse Model of Alzheimer's Disease

Bioflavonoids are being utilised as neuroprotectants in the treatment of various neurological disorders, including Alzheimer's disease (AD). Astilbin, a bioflavanoid, has been reported to have potent neuroprotective effects, but its preventive effects on amyloid-β (Aβ)-induced, Alzheimer's disease-related, cognitive impairment, and the underlying mechanisms of these effects have not been well characterised. Five-month-old APPswe/PS1dE9 transgenic mice were randomly assigned to a vehicle group and two astilbin (either 20 or 40 mg/kg per day, intraperitoneally) groups. After 8 weeks of treatment, we observed beneficial effects of astilbin (40 mg/kg per day), including lessening learning and memory deficits and reducing plaque burden and Aβ levels. Furthermore, the expressions of both the cAMP responsive element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) were significantly increased and the disturbance of AKT/GSK-3β signalling pathway was markedly ameliorated in the hippocampus of astilbin-treated (40 mg/kg per day) group. Our data suggest that astilbin might be a potential therapeutic agent against AD.

A novel mechanism of hepatocellular carcinoma cell apoptosis induced by lupeol via Brain-Derived Neurotrophic Factor Inhibition and Glycogen Synthase Kinase 3 beta reactivation

Lupeol is a naturally available triterpenoid with selective anticancerous potential on various human cancer cells. The present study shows that lupeol can inhibit cell proliferation of hepatocellular carcinoma (HCC) HCCLM3 cells in a time- and dose-dependent manner, through caspase-3 dependent activation and Poly ADP-Ribose Polymerase (PARP) cleavage. Lupeol-induced cell death is associated with a marked decrease in the protein expression of Brain-Derived Neurotrophic Factor (BDNF) and ser-9-phosphoryltion of Glycogen Synthase Kinase 3 Beta (GSK-3β), with concomitant suppression of Akt1, phosphatidyl inositol 3-kinase (PI3K), β-catenin, c-Myc and Cyclin D1 mRNA expression. Suppressing overexpression of BDNF by lupeol results in decreased protein expression of p-Akt and PI3K (p110α), as well as reactivation of GSK-3β function in HepG2 cells. Lupeol treatment also inhibits LiCl-induced activation of Wnt signaling pathway and exerts the in vitro anti-invasive activity in Huh-7 cells. LiCl-triggered high expression of β-catenin, c-Myc and Cyclin D1 protein is reduced followed by lupeol exposure. The findings suggest a mechanistic link between caspase dependent pathway, BDNF secretion and Akt/PI3K/GSK-3β in HCC cells. These results indicate that lupeol can suppress HCC cell proliferation by inhibiting BDNF secretion and phosphorylation of GSK-3β(Ser-9), cooperated with blockade of Akt/PI3K and Wnt signaling pathway.

Toll-like receptor 4-mediated signaling participates in apoptosis of hippocampal neurons

The phosphatidylinositol 3 kinase (PI3K)/protein kinase B (AKT) signaling pathway is considered important for cell survival and has been shown to mediate various anti-apoptotic biological effects. This study explored the role of the Toll-like receptor 4 (TLR4)-mediated PI3K/AKT-glycogen syn-thase kinase 3β (GSK-3β) signaling pathways in lipopolysaccharide-induced apoptosis in a primary culture of hippocampal neurons. Results demonstrated that the apoptotic ratio of hippocampal neurons stimulated by lipopolysaccharide was significantly higher compared with the control group. Both the expression of P-AKT^Ser473 and P-GSK-3β^Ser9 in hippocampal neurons stimulated by lipopo-polysaccharide decreased compared with the control, while the level of active Caspase-3 and the ratio of Bax/Bcl-2 were significantly increased. The level of active Caspase-3 and the ratio of Bax/Bcl-2 in hippocampal neurons treated with TLR4 antibody or the GSK-3β inhibitor, LiCl, creased before intervention with lipopolysaccharide, but increased after treatment with the AKT hibitor, LY294002. These findings suggest that the TLR4-PI3K/AKT-GSK3β signaling pathway may be involved in lipopolysaccharide-induced apoptosis of hippocampal neurons.

Memantine improves spatial learning and memory impairments by regulating NGF signaling in APP/PS1 transgenic mice

Memantine (MEM) is used for improving the cognitive impairments of the patients suffering from Alzheimer's disease (AD) by multiple neuroprotective mechanisms. However, it is still not clear whether nerve growth factor (NGF) signaling is involved in the mechanisms of MEM. The present study investigated the neuroprotective effects of MEM treatment on the cognitive performance and amyloidosis in APP/PS1 transgenic mice, and disclosed the NGF-related mechanism of MEM. We found that MEM treatment improved the cognitive performance by decreasing the escape latency and path length in the navigation test, by shortening the duration in target quadrant and reducing the frequency to pass through the target in probe trial, and by prolonging the latency and decreasing the frequencies of entering the dark compartment in passive avoidance test. The over-expressions of Aβ(1-42) and amyloid precursor protein (APP) were also decreased in the brains of APP/PS1 mice. Interestingly, MEM treatment improved the decreased NGF levels in APP/PS1 mice. Furthermore, NGF/TrkA signaling was activated by increasing the phosphorylation levels of tyrosine kinase (TrkA), proto-oncogene serine/threonine-protein kinase, Raf1 (c-Raf), extracellular regulated protein kinases (ERK)1/2 and cAMP-response element binding protein (CREB) after MEM treatment. Simultaneously, MEM also inhibited NGF/p75(NTR) signaling via decreasing the cleavage substrate of p75(NTR), increasing the JNK2 phosphorylation and decreasing the levels of p53 and cleaved-caspase 3. Therefore, the dual-regulation on NGF signaling was attributed to the improvements of cognitive deficits and Aβ depositions in APP/PS1 mice. In conclusion, MEM treatment activated the NGF/TrkA signaling, and inhibited the p75(NTR) signaling in APP/PS1 mice to ameliorate the behavioral deficits and amyloidosis, indicating that NGF signaling was a new potential target of MEM treatment for AD therapy.

Memantine enhances recovery from stroke

BACKGROUND AND PURPOSE

Stroke treatment is constrained by limited treatment windows and the clinical inefficacy of agents that showed preclinical promise. Yet animal and clinical data suggest considerable poststroke plasticity, which could allow treatment with recovery-modulating agents. Memantine is a well-tolerated N-methyl-D-aspartate glutamate receptor antagonist in common use for Alzheimer disease.

METHODS

Memantine, 30 mg/kg per day, or vehicle, was delivered chronically in drinking water beginning >2 hours after photothrombotic stroke.

RESULTS

Although there was no difference in infarct size, behavior, or optical intrinsic signal maps in the first 7 days after stroke, mice treated chronically with memantine showed significant improvements in motor control, measured by cylinder test and grid-walking performance, compared with vehicle-treated animals. Optical intrinsic signal revealed an increased area of forepaw sensory maps at 28 days after stroke. There was decreased reactive astrogliosis and increased vascular density around the infarcted cortex. Peri-infarct Western blots revealed increased brain-derived neurotrophic factor and phosphorylated-tropomyosin-related kinase-B receptor expression.

CONCLUSIONS

Our results suggest that memantine improves stroke outcomes in an apparently non-neuroprotective manner involving increased brain-derived neurotrophic factor signaling, reduced reactive astrogliosis, and improved vascularization, associated with improved recovery of sensory and motor cortical function. The clinical availability and tolerability of memantine make it an attractive candidate for clinical translation.

The predominant protective effect of tianeptine over other antidepressants in models of neuronal apoptosis: the effect blocked by inhibitors of MAPK/ERK1/2 and PI3-K/Akt pathways

Tianeptine (Tian) possesses neuroprotective potential, however, little is known about the effect of this drug in models of neuronal apoptosis. In the present study, we aimed (1) to compare the neuroprotective capacities of some antidepressants (ADs) in the models of staurosporine (St)- and doxorubicin (Dox)-evoked cell death, activating the intracellular and the extracellular apoptotic pathway, respectively; (2) to identify the Tian-modulated steps underlying its neuroprotective action; (3) to test the effect of various ADs against Dox-evoked cell damage in glia cells. Primary neuronal and glia cell cultures and retinoic acid-differentiated human neuroblastoma SH-SY5Y (RA-SH-SY5Y) cells were co-treated with imipramine, fluoxetine, citalopram, reboxetine, mirtazapine or Tian and St or Dox. The data showed the predominant neuroprotective effect of Tian over other tested ADs against St- and Dox-induced cell damage in primary neurons and in RA-SH-SY5Y cells. This effect was shown to be caspase-3-independent but connected with attenuation of DNA fragmentation. Moreover, neuroprotection elicited by Tian was blocked by pharmacological inhibitors of MAPK/ERK1/2 and PI3-K/Akt signaling pathways as well by inhibitor of necroptosis, necrostatin-1. Interestingly, the protective effects of all tested ADs were demonstrated in primary glia cells against the Dox-evoked cell damage. The obtained data suggests the glial cells as a common target for protective action of various ADs whereas in relation to neuronal cells only Tian possesses such properties, at least against St- and Dox-induced cell damage. Moreover, this neuroprotective effect of Tian is caspase-3-independent and engages the regulation of survival pathways (MAPK/ERK1/2 and PI3-K/Akt).

Glycine site N-methyl-D-aspartate receptor antagonist 7-CTKA produces rapid antidepressant-like effects in male rats

BACKGROUND

Glutamate N-methyl-D-aspartate (NMDA) receptor antagonists exert fast-acting antidepressant effects, providing a promising way to develop a new classification of antidepressant that targets the glutamatergic system. In the present study, we examined the potential antidepressant action of 7-chlorokynurenic acid (7-CTKA), a glycine recognition site NMDA receptor antagonist, in a series of behavioural models of depression and determined the molecular mechanisms that underlie the behavioural actions of 7-CTKA.

METHODS

We administered the forced swim test, novelty-suppressed feeding test, learned helplessness paradigm and chronic mild stress (CMS) paradigm in male rats to evaluate the possible rapid antidepressant-like actions of 7-CTKA. In addition, we assessed phospho-glycogen synthase kinase-3β (p-GSK3β) level, mammalian target of rapamycin (mTOR) function, and postsynaptic protein expression in the medial prefrontal cortex (mPFC) and hippocampus.

RESULTS

Acute 7-CTKA administration produced rapid antidepressant-like actions in several behavioural tests. It increased p-GSK3β, enhanced mTOR function and increased postsynaptic protein levels in the mPFC. Activation of GSK3β by LY294002 completely blocked the antidepressant-like effects of 7-CTKA. Moreover, 7-CTKA did not produce rewarding properties or abuse potential.

LIMITATIONS

It is possible that 7-CTKA modulates glutamatergic transmission, thereby causing enduring alterations of GSK3β and mTOR signalling, although we did not provide direct evidence to support this possibility. Thus, the therapeutic involvement of synaptic adaptions engaged by 7-CTKA requires further study.

CONCLUSION

Our findings demonstrate that acute 7-CTKA administration produced rapid antidepressant-like effects, indicating that the behavioural response to 7-CTKA is mediated by GSK3β and mTOR signalling function in the mPFC.

Free and nanoencapsulated curcumin suppress β-amyloid-induced cognitive impairments in rats: involvement of BDNF and Akt/GSK-3β signaling pathway

Alzheimer's disease (AD), a neurodegenerative disorder exhibiting progressive loss of memory and cognitive functions, is characterized by the presence of neuritic plaques composed of neurofibrillary tangles and β-amyloid (Aβ) peptide. Drug delivery to the brain still remains highly challenging for the treatment of AD. Several studies have been shown that curcumin is associated with anti-amyloidogenic properties, but therapeutic application of its beneficial effects is limited. Here we investigated possible mechanisms involved in curcumin protection against Aβ(1-42)-induced cognitive impairment and, due to its poor bioavailability, we developed curcumin-loaded lipid-core nanocapsules in an attempt to improve the neuroprotective effect of this polyphenol. Animals received a single intracerebroventricular injection of Aβ(1-42) and they were administered either free curcumin or curcumin-loaded lipid-core nanocapsules (Cur-LNC) intraperitoneally for 10days. Aβ(1-42)-infused animals showed a significant impairment on learning-memory ability, which was paralleled by a significant decrease in hippocampal synaptophysin levels. Furthermore, animals exhibited activated astrocytes and microglial cells, as well as disturbance in BDNF expression and Akt/GSK-3β signaling pathway, beyond tau hyperphosphorylation. Our findings demonstrate that administration of curcumin was effective in preventing behavioral impairments, neuroinflammation, tau hyperphosphorylation as well as cell signaling disturbances triggered by Aβ in vivo. Of high interest, Cur-LNC in a dose 20-fold lower presented similar neuroprotective results compared to the effective dose of free curcumin. Considered overall, the data suggest that curcumin is a potential therapeutic agent for neurocognition and nanoencapsulation of curcumin in LNC might constitute a promising therapeutic alternative in the treatment of neurodegenerative diseases such as AD.

Upregulation of anti-apoptotic factors in upper motor neurons after spinal cord injury in adult zebrafish

Unlike mammals, fish motor function can recover within 6-8weeks after spinal cord injury (SCI). The motor function of zebrafish is regulated by dual control; the upper motor neurons of the brainstem and motor neurons of the spinal cord. In this study, we aimed to investigate the framework behind the regeneration of upper motor neurons in adult zebrafish after SCI. In particular, we investigated the cell survival of axotomized upper motor neurons and its molecular machinery in zebrafish brain. As representative nuclei of upper motor neurons, we retrogradely labeled neurons in the nucleus of medial longitudinal fasciculus (NMLF) and the intermediate reticular formation (IMRF) using a tracer injected into the lesion site of the spinal cord. Four to eight neurons in each thin sections of the area of NMLF and IMRF were successfully traced at least 1-15days after SCI. TUNEL staining and BrdU labeling assay revealed that there was no apoptosis or cell proliferation in the axotomized neurons of the brainstem at various time points after SCI. In contrast, axotomized neurons labeled with a neurotracer showed increased expression of anti-apoptotic factors, such as Bcl-2 and phospho-Akt (p-Akt), at 1-6days after SCI. Such a rapid increase of Bcl-2 and p-Akt protein levels after SCI was quantitatively confirmed by western blot analysis. These data strongly indicate that upper motor neurons in the NMLF and IMRF can survive and regrow their axons into the spinal cord through the rapid activation of anti-apoptotic molecules after SCI. The regrowing axons from upper motor neurons reached the lesion site at 10-15days and then crossed at 4-6weeks after SCI. These long-distance descending axons from originally axotomized neurons have a major role in restoration of motor function after SCI.

Memantine treatment reverses anhedonia, normalizes corticosterone levels and increases BDNF levels in the prefrontal cortex induced by chronic mild stress in rats

Memantine is a N-methyl-D-aspartate (NMDA) receptor antagonist and several studies have pointed to the NMDA receptor antagonists as a potential therapeutic target for the treatment of depression. The present study was aimed to evaluate the behavioral and physiological effects of administration of memantine in rats exposed to the chronic mild stress (CMS) model. To this aim, after 40 days of exposure to CMS procedure, rats were treated with memantine (20 mg/kg) for 7 days. In this study, sweet food consumption, adrenal gland weight, corticosterone levels, and brain-derived-neurotrophic factor (BDNF) protein levels in the prefrontal cortex, hippocampus and amygdala were assessed. Our results demonstrated that chronic stressful situations induced anhedonia, hypertrophy of adrenal gland weight, and an increase of corticosterone levels in rats, but did not alter BDNF protein levels in the rat brain. Memantine treatment reversed anhedonia and the increase of adrenal gland weight, normalized corticosterone levels and increased BDNF protein levels in the prefrontal cortex in stressed rats. Finally, these findings further support the hypothesis that NMDA receptor antagonists such as memantine could be helpful in the pharmacological treatment of depression.

Gastrocnemius-derived BDNF promotes motor function recovery in spinal cord transected rats

This study evaluated the role of gastrocnemius-derived brain-derived neurotrophic factor (BDNF) and possible mechanism in motor improvement in T10 spinal cord transection (SCT) rats. There was complete paralysis in hindlimbs immediately after SCT, followed by partial functional restoration with time going. The level of BDNF but not its mRNA gradually increased in caudal stump after SCT, whereas a significant increase in both BDNF and its mRNA was simultaneously seen in gastrocnemius. Injection of BDNF antibody into the gastrocnemius significantly decreased hindlimb locomotor function, downregulated the level of BDNF and its mRNA together with extracellular signal-regulated kinase 1/2 (Erk1/2). Moreover, ventral root ligation led to decrease both BDNF and Erk in caudal stump, indicating BDNF transportation from gastrocnemius into the spinal cord. We concluded that gastrocnemius-derived BDNF reduced motor functional deficits in SCT rats through Erk signaling pathway. These novel findings suggested the usage of BDNF in muscle for the treatment of spinal cord injury in clinic.

Excitatory and Mitogenic Signaling in Cell Death, Blood-brain Barrier Breakdown, and BBB Repair after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) results in the release of a large number of endogenous molecules, including glutamate, Ca(2+), ROS, thrombin, heme, iron, TNF-α, and others. These molecules participate in excitatory and mitogenic signaling transduction in which N-methyl-D-aspartate (NMDA) receptors and Src family kinases (SFKs) are implicated. Mitogenic signaling initiates the cell cycle for normal cell division of microglia and neural progenitor cells, whereas aberrant mitogenic signaling causes toxicity, killing neurons, astrocytes, and brain microvascular endothelial cells in neurological diseases including ICH. In this review, we summarize (1) how SFKs modulate NMDA receptors to kill neurons following ICH and (2) how SFKs modulate mitogenic signaling transduction to kill neurons and play a role in disrupting the blood-brain barrier (BBB) immediately following ICH and in repairing the BBB during the recovery phases weeks following ICH.

The adaptor protein SH2B3 (Lnk) negatively regulates neurite outgrowth of PC12 cells and cortical neurons

SH2B adaptor protein family members (SH2B1-3) regulate various physiological responses through affecting signaling, gene expression, and cell adhesion. SH2B1 and SH2B2 were reported to enhance nerve growth factor (NGF)-induced neuronal differentiation in PC12 cells, a well-established neuronal model system. In contrast, SH2B3 was reported to inhibit cell proliferation during the development of immune system. No study so far addresses the role of SH2B3 in the nervous system. In this study, we provide evidence suggesting that SH2B3 is expressed in the cortex of embryonic rat brain. Overexpression of SH2B3 not only inhibits NGF-induced differentiation of PC12 cells but also reduces neurite outgrowth of primary cortical neurons. SH2B3 does so by repressing NGF-induced activation of PLCγ, MEK-ERK1/2 and PI3K-AKT pathways and the expression of Egr-1. SH2B3 is capable of binding to phosphorylated NGF receptor, TrkA, as well as SH2B1β. Our data further demonstrate that overexpression of SH2B3 reduces the interaction between SH2B1β and TrkA. Consistent with this finding, overexpressing the SH2 domain of SH2B3 is sufficient to inhibit NGF-induced neurite outgrowth. Together, our data demonstrate that SH2B3, unlike the other two family members, inhibits neuronal differentiation of PC12 cells and primary cortical neurons. Its inhibitory mechanism is likely through the competition of TrkA binding with the positive-acting SH2B1 and SH2B2.

Effects of ethylene glycol ethers on cell viability in the human neuroblastoma SH-SY5Y cell line

Ethylene glycol ethers (EGEs) are a class of chemicals used extensively in the manufacture of a wide range of domestic and industrial products, which may result in human exposure and toxicity. Hematologic and reproductive toxicity of EGEs are well known whereas their action on neuronal cell viability has not been studied so far. In the present study, we investigated the effects of some EGEs on cell viability and on the hydrogen peroxide-induced damage in the human neuroblastoma (SH-SY5Y) cells. It has been found that 2-phenoxyethanol in a concentration-dependent manner (5-25 mM, 24 h) increased the basal and H(2)O(2)-induced lactate dehydrogenase (LDH) release and 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyl tetrazolium bromide (MTT) reduction. 2-Butoxyethanol given alone did not affect LDH release and MTT reduction but concentration-dependently enhanced the cytotoxic effect of H(2)O(2). 2-Isopropoxyethanol significantly and concentration-dependently (1-25 mM) increased the basal LDH release and attenuated MTT reduction, but did not potentiate the cytotoxic effect of H(2)O(2). Contrary to this, 2-methoxyethanol did not show a cytotoxic effect while 2-ethoxyethanol at high concentrations intensified the hydrogen peroxide action. This study demonstrated that among the EGEs studied, 2-phenoxyethanol showed the most consistent cytotoxic effect on neurons in in vitro conditions and enhanced the hydrogen peroxide action. 2-Isopropoxyethanol had also a potent cytotoxic effect, but it did not enhance the hydrogen peroxide action, whereas 2-butoxyethanol only potentiated cytotoxic effect of H(2)O(2). It is concluded that the results of the present study should be confirmed in in vivo conditions and that some EGEs, especially 2-phenoxyethanol, 2-butoxyethanol and 2-isopropoxyethanol, may be responsible for initiation or exacerbation of neuronal cell damage.

Neuroprotective effects of MAPK/ERK1/2 and calpain inhibitors on lactacystin-induced cell damage in primary cortical neurons

The dysfunction of the proteasome system is implicated in the pathomechanism of several chronic neurodegenerative diseases. Lactacystin (LC), an irreversible proteasome inhibitor, induces cell death in primary cortical neurons, however, the molecular mechanisms of its neurotoxic action has been only partially unraveled. In this study we aimed to elucidate an involvement of the key enzymatic pathways responsible for LC-induced neuronal cell death. Incubation of primary cortical neurons with LC (0.25-50 μg/ml) evoked neuronal cell death in concentration- and time-dependent manner. Lactacystin (2.5 μg/ml; 6.6μM) enhanced caspase-3 activity, but caspase-3 inhibitor, Ac-DEVD-CHO did not attenuate the LC-evoked cell damage. Western blot analysis showed a time-dependent, prolonged activation of MAPK/ERK1/2 pathway after LC exposure. Moreover, inhibitors of MAPK/ERK1/2 signaling, U0126 and PD98052 attenuated the LC-evoked cell death. We also found that LC-treatment resulted in the induction of calpains and calpain inhibitors (MDL28170 and calpeptin) protected neurons against the LC-induced cell damage. Neuroprotective action of MAPK/ERK1/2 and calpain inhibitors were connected with attenuation of LC-induced DNA fragmentation measured by Hoechst 33342 staining and TUNEL assay. However, only MAPK/ERK1/2 but not calpain inhibitors, attenuated the LC-induced AIF (apoptosis inducing factor) release. Further studies showed no synergy between neuroprotective effects of MAPK/ERK1/2 and calpain inhibitors given in combination when compared to their effects alone. The obtained data provided evidence for neuroprotective potency of MAPK/ERK1/2 and calpain, but not caspase-3 inhibition against the neurotoxic effects of LC in primary cortical neurons and give rationale for using these inhibitors in the treatment of neurodegenerative diseases connected with proteasome dysfunction.

Lithium chloride and staurosporine potentiate the accumulation of phosphorylated glycogen synthase kinase 3β/Tyr216, resulting in glycogen synthase kinase 3β activation in SH-SY5Y human neuroblastoma cell lines

Glycogen synthase kinase 3β (GSK3β) activity is regulated by phosphorylation processes and regulates in turn through phosphorylation several proteins, including eukaryotic initiation factor 2B (eIF2B). Serine 9 phosphorylation of GSK3β (pGSK3βSer9), usually promoted by activation of the PI3K/Akt survival pathway, triggers GSK3β inhibition. By contrast, tyrosine 216 phosphorylation of GSK3β (pGSK3βTyr216) increases under apoptotic conditions, leading to GSK3β activation. Lithium chloride (LiCl) is usually described to increase pGSK3βSer9 through the PI3K/Akt pathway, resulting in GSK3β inhibition. The purpose of this study is to demonstrate that in some cases LiCl is also able to increase pGSK3βTyr216, resulting in GSK3β activation. For this, we used SH-SY5Y cells and primary neuronal cultures and investigated the effects of LiCl on the two phosphorylated forms of GSK3β under staurosporine (STS)-intoxicated conditions. The ratios between the phosphorylated and total forms of GSK3β and eIF2B were determined by Western blotting. Our results revealed that, besides its ability to increase pGSK3βSer9, LiCl is also able to increase pGSK3βTyr216 greatly in STS-intoxicated SH-SY5Y cells but not in STS-intoxicated primary neuronal cultures. This accumulation of both Ser9 and Tyr216 phosphorylation results in GSK3β activation in STS-intoxicated SH-SY5Y cells in spite of the presence of LiCl. These findings indicate that LiCl treatment is not necessarily correlated with GSK3β inhibition even though it generates Ser9 phosphorylation. Consequently, the ratio pGSK3βSer9/pGSK3βTyr216, which takes into account the balance between the two inactive (Ser9) and active (Tyr216) forms of GSK3β, could be more useful for predicting GSK3β inhibition.

STIM2 regulates capacitive Ca2+ entry in neurons and plays a key role in hypoxic neuronal cell death

Excessive cytosolic calcium ion (Ca(2+)) accumulation during cerebral ischemia triggers neuronal cell death, but the underlying mechanisms are poorly understood. Capacitive Ca(2+) entry (CCE) is a process whereby depletion of intracellular Ca(2+) stores causes the activation of plasma membrane Ca(2+) channels. In nonexcitable cells, CCE is controlled by the endoplasmic reticulum (ER)-resident Ca(2+) sensor STIM1, whereas the closely related protein STIM2 has been proposed to regulate basal cytosolic and ER Ca(2+) concentrations and make only a minor contribution to CCE. Here, we show that STIM2, but not STIM1, is essential for CCE and ischemia-induced cytosolic Ca(2+) accumulation in neurons. Neurons from Stim2(-/-) mice showed significantly increased survival under hypoxic conditions compared to neurons from wild-type controls both in culture and in acute hippocampal slice preparations. In vivo, Stim2(-/-) mice were markedly protected from neurological damage in a model of focal cerebral ischemia. These results implicate CCE in ischemic neuronal cell death and establish STIM2 as a critical mediator of this process.