Regulation of nuclear TDP-43 by NR2A-containing NMDA receptors and PTEN

Mxene-bpV plays a neuroprotective role in cerebral ischemia-reperfusion injury by activating the Akt and promoting the M2 microglial polarization signaling pathways

Studies have shown that the inhibition of phosphatase and tensin homolog deleted on chromosome 10 (PTEN)was neuroprotective against ischemia/reperfusion(I/R) injury. Bisperoxovanadium (bpV), a derivative of vanadate, is a well-established inhibitor of PTEN. However, its function islimited due to its general inadequacy in penetrating cell membranes. Mxene(Ti3C2Tx) is a novel two-dimensional lamellar nanomaterial with an excellent ability to penetrate the cell membrane. Yet, the effects of this nanomaterial on nervous system diseases have yet to be scrutinized. Here, Mxene(Ti3C2Tx) was used for the first time to carry bpV(HOpic), creating a new nanocomposite Mxene-bpV that was probed in a cerebral I/R injury model. The findings showed that this synthetic Mxene-bpV was adequately stable and can cross the cell membraneeasily. We observed that Mxene-bpV treatment significantly increased the survival rate of oxygen glucose deprivation/reperfusion(OGD/R)--insulted neurons, reduced infarct sizes and promoted the recovery of brain function after mice cerebral I/R injury. Crucially, Mxene-bpV treatment was more therapeutically efficient than bpV(HOpic) treatment alone over the same period. Mechanistically, Mxene-bpV inhibited the enzyme activity of PTEN in vitro and in vivo. It also promoted the expression of phospho-Akt (Ser473) by repressing PTEN and then activated the Akt pathway to boost cell survival. Additionally, in PTEN transgenic mice, Mxene-bpV suppressed I/R-induced inflammatory response by promoting M2 microglial polarization through PTEN inhibition. Collectively, the nanosynthetic Mxene-bpV inhibited PTEN' enzymatic activity by activating Akt pathway and promoting M2 microglial polarization, and finally exerted neuroprotection against cerebral I/R injury.

tDCS Regulates ASBT-3-OxoLCA-PLOD2-PTEN Signaling Pathway to Confer Neuroprotection Following Rat Cerebral Ischemia-Reperfusion Injury

Humans exhibit a rich intestinal microbiome that contain high levels of bacteria capable of producing 3-oxo-lithocholic acid (3-oxoLCA) and other secondary bile acids (BAs). The molecular mechanism mediating the role of 3-oxoLCA in cerebral ischemia-reperfusion (I/R) injury remains unclear. We investigated the role of 3-oxoLCA in a rat cerebral I/R injury model. We found that the concentrations of 3-oxoLCA within the cerebrospinal fluid were increased following I/R. In the in vitro oxygen-glucose deprivation (OGD) model, the levels of intraneuronal 3-oxoLCA was elevated following OGD insult. We showed that the increase of membrane ASBT (apical sodium-dependent bile acid transporter) contributed to OGD-induced elevation of intraneuronal 3-oxoLCA. Increasing intraneuronal 3-oxoLCA promoted ischemia-induced neuronal death, whereas reducing 3-oxoLCA levels were neuroprotective. Our results revealed that PLOD2 (procollagen-lysine, 2-oxoglutarate 5-dioxygenases 2) functioned upstream of PTEN (the phosphatase and tensin homolog deleted on chromosome 10) and downstream of 3-oxoLCA to promote OGD-induced neuronal injury. We further demonstrated that direct-current stimulation (DCS) decreased the levels of intraneuronal 3-oxoLCA and membrane ASBT in OGD-insulted neurons, while bilateral transcranial DCS (tDCS) reduced brain infarct volume following I/R by inhibiting ASBT. Together, these data suggest that increased expression of ASBT promotes neuronal death via 3-oxoLCA-PLOD2-PTEN signaling pathway. Importantly, bilateral tDCS suppresses ischemia-induced increase of ASBT, thereby conferring neuroprotection after cerebral I/R injury.

Transcranial Direct-Current Stimulation Regulates MCT1-PPA-PTEN-LONP1 Signaling to Confer Neuroprotection After Rat Cerebral Ischemia-Reperfusion Injury

Propionic acid (PPA) is a critical metabolite involved in microbial fermentation, which functions to reduce fat production, inhibit inflammation, and reduce serum cholesterol levels. The role of PPA in the context of cerebral ischemia-reperfusion (I/R) injury has yet to be clarified. Increasing evidence indicate that transcranial direct-current stimulation (tDCS) is a safe approach that confers neuroprotection in cerebral ischemia injury. Here, we show that the levels of PPA were reduced in the ischemic brain following a rat cerebral I/R injury and in the cultured rat cortical neurons after oxygen-glucose deprivation (OGD), an in vitro model of ischemic injury. We found that the decreased levels of transporter protein monocarboxylate transporter-1 (MCT1) were responsible for the OGD-induced reduction of PPA. Supplementing PPA reduced ischemia-induced neuronal death after I/R. Moreover, our results revealed that the neuroprotective effect of PPA is mediated through downregulation of phosphatase PTEN and subsequent upregulation of Lon protease 1 (LONP1). We demonstrated that direct-current stimulation (DCS) increased MCT1 expression and PPA level in OGD-insulted neurons, while tDCS decreased the brain infarct volume in the MCAO rats via increasing the levels of MCT1 expression and PPA. This study supports a potential application of tDCS in ischemic stroke.

NMDA Receptor C-Terminal Domain Signalling in Development, Maturity, and Disease

The NMDA receptor is a Ca²⁺-permeant glutamate receptor which plays key roles in health and disease. Canonical NMDARs contain two GluN2 subunits, of which 2A and 2B are predominant in the forebrain. Moreover, the relative contribution of 2A vs. 2B is controlled both developmentally and in an activity-dependent manner. The GluN2 subtype influences the biophysical properties of the receptor through difference in their N-terminal extracellular domain and transmembrane regions, but they also have large cytoplasmic Carboxyl (C)-terminal domains (CTDs) which have diverged substantially during evolution. While the CTD identity does not influence NMDAR subunit specific channel properties, it determines the nature of CTD-associated signalling molecules and has been implicated in mediating the control of subunit composition (2A vs. 2B) at the synapse. Historically, much of the research into the differential function of GluN2 CTDs has been conducted in vitro by over-expressing mutant subunits, but more recently, the generation of knock-in (KI) mouse models have allowed CTD function to be probed in vivo and in ex vivo systems without heterologous expression of GluN2 mutants. In some instances, findings involving KI mice have been in disagreement with models that were proposed based on earlier approaches. This review will examine the current research with the aim of addressing these controversies and how methodology may contribute to differences between studies. We will also discuss the outstanding questions regarding the role of GluN2 CTD sequences in regulating NMDAR subunit composition, as well as their relevance to neurodegenerative disease and neurodevelopmental disorders.

A synthetic BBB-permeable tripeptide GCF confers neuroprotection by increasing glycine in the ischemic brain

Background: We and others have previously demonstrated that glycine is neuroprotective in cerebral ischemia-reperfusion injury. But glycine has low permeability to the blood–brain barrier (BBB). To deliver glycine into the ischemic brain to confer neuroprotection, we designed a novel glycine-containing and BBB-permeable tripeptide, the H-glycine-cysteine-phenylalanine-OH (GCF).

Methods: For the synthesis of GCF, phenylalanine was included to increase the BBB permeability of the tripeptide. Cysteine was conjugated with glycine to enable the release of glycine from GCF. With the use of immunofluorescence labeling and HPLC assays, we measured the distribution and level of GCF. We used TTC labeling, LDH release, and MTT assays to evaluate the neuroprotective effect of GCF.

Results: Following intravenous injection in a rat model of cerebral ischemia-reperfusion injury, GCF was intensively distributed in the ischemic neurons. Intravenous injection of GCF, but not the non-cleavable acetyl-GCF, resulted in the elevation of glycine in the ischemic brain. GCF but not acetyl-GC conferred neuroprotection in ischemic stroke animals.

Conclusion: GCF protects against cerebral ischemia-reperfusion injury in the rat. In contrast to peptide drugs that exert therapeutic effect by interfering with signaling interaction, GCF acts as a BBB shuttle and prodrug to deliver glycine to confer neuroprotection, representing a novel therapeutic strategy for acute ischemic stroke.

miR-29a and the PTEN-GSK3β axis are involved in aluminum-induced damage to primary hippocampal neuronal networks

We previously reported that aluminum (Al) can cause a range of neurotoxic injuries including progressive irreversible synaptic structural damage and synaptic dysfunction, and eventually neuronal deaths. Mechanism of Al-induced electrophysiological and neuronal connectivity changes in neurons may indicate damage to the neuronal network. Here, mouse primary hippocampal neurons were cultured on micro-electrode array (MEA)- and high-content analysis (HCA)-related plates, showing that Al exposure significantly inhibited hippocampal neuronal electrical spike activity and neurite outgrowth characterized by a reduction in neurite branching and a decrease in the average total neurite length in relation to both Al dose and time of incubation. In recent years, miR-29a/ phosphatase and tensin homolog (PTEN) have been found to play pivotal roles in the morphogenesis of neurons, it has been confirmed in vitro and in vivo that the PTEN-Glycogen synthase kinase-3β (GSK-3β) axis regulates neurite outgrowth. The present study demonstrated that increases in Al exposure and dose gradually reduce miR-29a expression. Up-regulation of miR-29a in the hippocampal neurons by lentivirus transfection reversed the decrease in electrical spike activity and the reduction in both neurite branching and length induced by Al. Moreover, miR-29a suppressed the expression of PTEN and increased the level of phosphorylated Protein Kinase B (p-AKT) and p-GSK-3β which were inhibited by the Al treatment. This suggests that miR-29a is critically involved in the functional and structural neuronal damage induced by Al and is a potential target for Al neurotoxicity. Moreover, the reduction of neurite length and branching induced by Al exposure was regulated by miR-29a and its target neuronal PTEN-GSK3β signaling pathway, which also represents a possible mechanism of Al-induced the inhibition of the electrical activity. Collectively, Al-induced damage to the neuronal network occurred through miR-29a-mediated alterations of the PTEN-GSK3β signaling pathway.

Aagab acts as a novel regulator of NEDD4-1-mediated Pten nuclear translocation to promote neurological recovery following hypoxic-ischemic brain damage

Hypoxic-ischemic encephalopathy (HIE) is a main cause of mortality and severe neurologic impairment in the perinatal and neonatal period. However, few satisfactory therapeutic strategies are available. Here, we reported that a rapid nuclear translocation of phosphatase and tensin homolog deleted on chromosome TEN (PTEN) is an essential step in hypoxic-ischemic brain damage (HIBD)- and oxygen-glucose deprivation (OGD)-induced neuronal injures both in vivo and in vitro. In addition, we found that OGD-induced nuclear translocation of PTEN is dependent on PTEN mono-ubiquitination at the lysine 13 residue (K13) that is mediated by neural precursor cell expressed developmentally downregulated protein 4-1 (NEDD4-1). Importantly, we for the first time identified α- and γ-adaptin binding protein (Aagab) as a novel NEDD4-1 regulator to regulate the level of NEDD4-1, subsequently mediating Pten nuclear translocation. Finally, we demonstrated that genetic upregulation of Aagab or application of Tat-K13 peptide (a short interference peptide that flanks K13 residue of PTEN) not only reduced Pten nuclear translocation, but also significantly alleviated the deficits of myodynamia, motor and spatial learning and memory in HIBD model rats. These results suggest that Aagab may serve as a regulator of NEDD4-1-mediated Pten nuclear translocation to promote functional recovery following HIBD in neonatal rats, and provide a new potential therapeutic target to guide the clinical treatment for HIE.

PTEN Inhibition Protects Against Experimental Intracerebral Hemorrhage-Induced Brain Injury Through PTEN/E2F1/β-Catenin Pathway

Intracerebral hemorrhage (ICH) is a subtype of stroke with highest mortality and morbidity. We have previously demonstrated that dipotassium bisperoxo (picolinato) oxovanadate (V), (bpV[pic]) inhibits phosphatase and tensin homolog (PTEN) and activates extracellular signal-regulated kinase (ERK)1/2. In this study, we examined the effect of bpV[pic] in the rat ICH model in vivo and the hemin-induced injury model in rat cortical cultures. The rat model of ICH was created by injecting autologous blood into the striatum, and bpV[pic] was intraperitoneally injected. The effects of bpV[pic] were evaluated by neurological tests, Fluoro-Jade C (FJC) staining, and Nissl staining. We demonstrate that bpV[pic] attenuates ICH-induced brain injury in vivo and hemin-induced neuron injury in vitro. The expression of E2F1 was increased, but β-catenin expression was decreased after ICH, and the altered expressions of E2F1 and β-catenin after ICH were blocked by bpV[pic] treatment. Our results further show that bpV[pic] increases β-catenin expression through downregulating E2F1 in cortical neurons and prevents hemin-induced neuronal damage through E2F1 downregulation and subsequent upregulation of β-catenin. By testing the effect of PTEN-siRNA, PTEN cDNA, or combined use of ERK1/2 inhibitor and bpV[pic] in cultured cortical neurons after hemin-induced injury, we provide evidence suggesting that PTEN inhibition by bpV[pic] confers neuroprotection through E2F1 and β-catenin pathway, but the neuroprotective role of ERK1/2 activation by bpV[pic] cannot be excluded.

DJ-1 Suppresses Cytoplasmic TDP-43 Aggregation in Oxidative Stress-Induced Cell Injury

DJ-1 (also called PARK7) is a multifunctional redox-sensitive protein that is protective against oxidative stress-induced cell death. TAR DNA-binding protein 43 (TDP-43) is a major protein component of pathological inclusions in amyotrophic lateral sclerosis and frontotemporal dementia. Reducing aberrant aggregation of TDP-43 is a potential approach to prevent cell death. To investigate whether DJ-1 might inhibit TDP-43 aggregation to exert a protective effect in oxidative stress-induced injury, we tested the protein level and subcellular localization of TDP-43 and DJ-1 in SH-SY5Y cells transfected with wild-type DJ-1, DJ-1 mutant (L166P) cDNA, or DJ-1 siRNA. We show that oxidative stress induced by paraquat leads to the formation of cytosolic TDP-43 aggregation in SH-SY5Y cells. DJ-1 overexpression decreases paraquat-induced cytoplasmic accumulation of TDP-43 in SH-SY5Y cells and protects against paraquat-induced cell death. Transfection of DJ-1 L166P mutant or DJ-1 siRNA leads to increased cytosolic aggregation of TDP-43 in paraquat-treated SH-SY5Y cells and promotes cell death. These data suggest that DJ-1 may protect against oxidative stress-induced cell death through the suppression of cytoplasmic TDP-43 aggregation.

Harpagoside Rescues the Memory Impairments in Chronic Cerebral Hypoperfusion Rats by Inhibiting PTEN Activity

Vascular dementia (VaD) is the second most common dementia worldwide. Unlike Alzheimer's disease, VaD does not yet have effective therapeutic drugs. Harpagoside is the most important component extracted from Harpagophytum procumbens, a traditional Chinese medicine that has been widely used. The neuroprotective effects of harpagoside have been studied in Aβ- and MPTP-induced neurotoxicity. However, whether harpagoside is protective against VaD is not clear. In this study, with the use of chronic cerebral hypoperfusion rats, a well-known VaD model, we demonstrated that chronic administration (two months) of harpagoside was able to restore both the spatial learning/memory and fear memory impairments. Importantly, the protective effects of harpagoside were not due to alterations in the physiological conditions, metabolic parameters, or locomotor abilities of the rats. Meanwhile, we found that harpagoside suppressed the overactivation of PTEN induced by CCH by enhancing PTEN phosphorylation. Furthermore, harpagoside elevated the activity of Akt and inhibited the activity of GSK-3β, downstream effectors of PTEN. Overall, our study suggested that harpagoside treatment might be a potential therapeutic drug targeting the cognitive impairments of VaD.

The neuroprotective effect of bisperoxovandium (pyridin-2-squaramide) in intracerebral hemorrhage

Background: The authors have recently designed a new compound bisperoxovandium (pyridin-2-squaramide) [bpV(pis)] and verified that bpV(pis) confers neuroprotection through suppressing PTEN and activating ERK1/2, respectively. Intracerebral hemorrhage (ICH) is the second most common cause of stroke and has severe clinical outcome. In this study, we investigate the effect of bpV(pis) in ICH model both in vivo and in vitro.

Materials and methods: The novel drug bpV(pis) was synthesized in the Faculty of Pharmacy, Wuhan University School of Medicine. An ICH model was generated on both SD rats and cells. bpV(pis) was injected into intracerebroventricular or culture media. Western blotting was applied to test the signal pathway. To determine the effect of bpV(pis) on PTEN inhibition and ERK1/2 activation, we measured the phosphorylation level of AKT (a direct downstream target of PTEN that negatively regulates AKT) and ERK1/2. FJC, MTT, and LDH were applied to measure the cell viability. Neurobehavioral tests were performed to measure the effect of bpV(pis).

Results: The in vivo results showed that intracerebroventricular administration of bpV(pis) significantly alleviates hematoma, the damage of brain–blood barrier and brain edema. The in vitro results demonstrated that bpV(pis) treatment reduces ICH-induced neuronal injury. Western blotting results identified that bpV(pis) exerts a neuroprotective effect by significantly increasing the phosphorylation level of AKT and ERK1/2 after experimental ICH. Neurobehavioral tests indicate that bpV(pis) promotes functional recovery in ICH animals.

Conclusion: This study provides first and direct evidence for a potential role of bpV(pis) in ICH therapy.

Mir-17∼92 Confers Motor Neuron Subtype Differential Resistance to ALS-Associated Degeneration

Progressive degeneration of motor neurons (MNs) is the hallmark of amyotrophic lateral sclerosis (ALS). Limb-innervating lateral motor column MNs (LMC-MNs) seem to be particularly vulnerable and are among the first MNs affected in ALS. Here, we report association of this differential susceptibility with reduced expression of the mir-17∼92 cluster in LMC-MNs prior to disease onset. Reduced mir-17∼92 is accompanied by elevated nuclear PTEN in spinal MNs of presymptomatic SOD1^G93A mice. Selective dysregulation of the mir-17∼92/nuclear PTEN axis in degenerating SOD1^G93A LMC-MNs was confirmed in a double-transgenic embryonic stem cell system and recapitulated in human SOD1^+/L144F-induced pluripotent stem cell (iPSC)-derived MNs. We further show that overexpression of mir-17∼92 significantly rescues human SOD1^+/L144F MNs, and intrathecal delivery of adeno-associated virus (AAV)9-mir-17∼92 improves motor deficits and survival in SOD1^G93A mice. Thus, mir-17∼92 may have value as a prognostic marker of MN degeneration and is a candidate therapeutic target in SOD1-linked ALS. VIDEO ABSTRACT.

Phased Treatment Strategies for Cerebral Ischemia Based on Glutamate Receptors

Extracellular glutamate accumulation following cerebral ischemia leads to overactivation of glutamate receptors, thereby resulting in intracellular Ca²⁺ overload and excitotoxic neuronal injury. Multiple attempts have been made to counteract such effects by reducing glutamate receptor function, but none have been successful. In this minireview, we present the available evidence regarding the role of all types of ionotropic and metabotropic glutamate receptors in cerebral ischemia and propose phased treatment strategies based on glutamate receptors in both the acute and post-acute phases of cerebral ischemia, which may help realize the clinical application of glutamate receptor antagonists.

ERK 1/2 Activation Mediates the Neuroprotective Effect of BpV(pic) in Focal Cerebral Ischemia-Reperfusion Injury

Bisperoxovanadium (pyridine-2-carboxyl) [bpV(pic)] is a commercially available PTEN inhibitor. Previous studies from us and others have shown that bpV(pic) confers neuroprotection in cerebral ischemia injury. We set up to determine whether ERK 1/2 activation plays a role in bpV(pic)-induced neuroprotective effect in cerebral ischemia injury. We found that the phosphorylation levels of Akt (p-AKT) and ERK1/2 (p-ERK 1/2) were down-regulated after cerebral ischemia–reperfusion injury. The injection of bpV(pic) after injury not only increased the level of p-AKT but also the level of p-ERK 1/2. While the inhibition of PTEN mediated the up-regulatation of p-AKT and p-ERK 1/2 by bpV(pic). Interestingly, the ERK 1/2 activation induced by bpV(pic) was also independent of the inhibition of PTEN. Our results indicate that bpV(pic) protects against OGD-induced neuronal death and promotes the functional recovery of stroke animals through PTEN inhibition and ERK 1/2 activation, respectively. This study suggests that the effect of bpV(pic) on ERK 1/2 signaling should be considered while using bpV(pic) as a PTEN inhibitor.

Glycine confers neuroprotection through PTEN/AKT signal pathway in experimental intracerebral hemorrhage

Glycine has been shown to protect against ischemic stroke through various mechanisms. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) which antagonize Akt-dependent cell survival has been linked to neuronal damage. However, whether glycine has a neuroprotective property in intracerebral hemorrhage (ICH) was unknown. This study aimed to determine the protective effect of glycine in rats ICH. Adult male Sprague-Dawley (SD) rats were subjected to left striatum infusion of autologous blood. ICH animals received glycine (0.2-3 mg/kg, icv) at 1 h after ICH with or without pre-injection of Akt Inhibitor IV (100 μM, 2 μl, icv) 0.5 h prior to glycine treatment. Our results showed that in the perihematomal area PTEN was up-regulated in the early stage after ICH. However, glycine treatment decreased PTEN protein level and increased the phosphorylation level of AKT (p-AKT) in the perihematomal area. With the administration of glycine, neuronal death was significantly reduced and Evans blue leakage was alleviated as well as the brain edema after ICH. Moreover, hematoma volume was decreased and neurobehavioral outcome was improved. Nevertheless, Akt Inhibitor IV abolished the neuroprotective effects of glycine after ICH. Together, our findings demonstrate, for the first time, the protective role of glycine on ICH rats, and suggest that the neuroprotective effect of glycine was mediated through PTEN/Akt signal pathway.

Presynaptic GLP-1 receptors enhance the depolarization-evoked release of glutamate and GABA in the mouse cortex and hippocampus

Glucagon-like peptide-1 receptors (GLP-1Rs) have been shown to mediate cognitive-enhancing and neuroprotective effects in the central nervous system. However, little is known about their physiological roles on central neurotransmission, especially at the presynaptic level. Using purified synaptosomal preparations and immunofluorescence techniques, here we show for the first time that GLP-1Rs are localized on mouse cortical and hippocampal synaptic boutons, in particular on glutamatergic and GABAergic nerve terminals. Their activation by the selective agonist exendin-4 (1-100 nM) was able to increase the release of either [³ H]d-aspartate or [³ H]GABA. These effects were abolished by 10 nM of the selective GLP1-R antagonist exendin-3 (9-39) and were prevented by the selective adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (10 µM), indicating the involvement of classic GLP-1Rs coupled to G_s protein stimulating cAMP synthesis. Our data demonstrate the existence and activity of presynaptic receptors for GLP-1 that could represent additional mechanisms by which this neurohormone exerts its effects in the CNS. © 2017 BioFactors, 44(2):148-157, 2018.

Bisperoxovandium (pyridin-2-squaramide) targets both PTEN and ERK1/2 to confer neuroprotection

BACKGROUND AND PURPOSE

We and others have shown that inhibiting phosphatase and tensin homolog deleted on chromosome 10 (PTEN) or activating ERK1/2 confer neuroprotection. As bisperoxovanadium compounds are well-established inhibitors of PTEN, we designed bisperoxovandium (pyridin-2-squaramide) [bpV(pis)] and determined whether and how bpV(pis) exerts a neuroprotective effect in cerebral ischaemia-reperfusion injury.

EXPERIMENTAL APPROACH

Malachite green-based phosphatase assay was used to measure PTEN activity. A western blot assay was used to measure the phosphorylation level of Akt and ERK1/2 (p-Akt and p-ERK1/2). Oxygen-glucose deprivation (OGD) was used to injure cultured cortical neurons. Cell death and viability were assessed by LDH and MTT assays. To verify the effects of bpV(pis) in vivo, Sprague-Dawley rats were subjected to middle cerebral artery occlusion, and brain infarct volume was measured and neurological function tests performed.

KEY RESULTS

bpV(pis) inhibited PTEN activity and increased p-Akt in SH-SY5Y cells but not in PTEN-deleted U251 cells. bpV(pis) also elevated p-ERK1/2 in both SH-SY5Y and U251 cells. These data indicate that bpV(pis) enhances Akt activation through PTEN inhibition but increases ERK1/2 activation independently of PTEN signalling. bpV(pis) prevented OGD-induced neuronal death in vitro and reduced brain infarct volume and promoted functional recovery in stroke animals. This neuroprotective effect of bpV(pis) was blocked by inhibiting Akt and/or ERK1/2.

CONCLUSIONS AND IMPLICATIONS

bpV(pis) confers neuroprotection in OGD-induced injury in vitro and in cerebral ischaemia in vivo by suppressing PTEN and activating ERK1/2. Thus, bpV(pis) is a bi-target neuroprotectant that may be developed as a drug candidate for stroke treatment.

Glycine confers neuroprotection through microRNA-301a/PTEN signaling

Background

Glycine is known to protect against neuronal death. However, the underlying mechanism remains to be elucidated. The microRNA-301a is involved in both biological and pathological processes. But it is not known whether microRNA-301a has a neuroprotective property. In this study, we aimed to determine whether glycine-induced neuroprotection requires microRNA-301a-dependent signaling.

Results

We provided the first evidence that glycine increased the expression of microRNA-301a in cultured rat cortical neurons and protected against cortical neuronal death through up-regulation of microRNA-301a after oxygen-glucose deprivation. MicroRNA-301a directly bound the predicted 3′UTR target sites of PTEN and reduced PTEN expression in cortical neurons. We revealed that PTEN down-regulation by microRNA-301a mediated glycine-induced neuroprotective effect following oxygen-glucose deprivation.

Conclusions

Our results suggest that 1) microRNA-301a is neuroprotective in oxygen-glucose deprivation-induced neuronal injury; 2) glycine is an upstream regulator of microRNA-301a; 3) glycine confers neuroprotection through microRNA-301a/PTEN signal pathway.

Induction of COX-2-PGE2 synthesis by activation of the MAPK/ERK pathway contributes to neuronal death triggered by TDP-43-depleted microglia

Neuroinflammation is a striking hallmark of amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Previous studies have shown the contribution of glial cells such as astrocytes in TDP-43-linked ALS. However, the role of microglia in TDP-43-mediated motor neuron degeneration remains poorly understood. In this study, we show that depletion of TDP-43 in microglia, but not in astrocytes, strikingly upregulates cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE2) production through the activation of MAPK/ERK signaling and initiates neurotoxicity. Moreover, we find that administration of celecoxib, a specific COX-2 inhibitor, greatly diminishes the neurotoxicity triggered by TDP-43-depleted microglia. Taken together, our results reveal a previously unrecognized non-cell-autonomous mechanism in TDP-43-mediated neurodegeneration, identifying COX-2-PGE2 as the molecular events of microglia- but not astrocyte-initiated neurotoxicity and identifying celecoxib as a novel potential therapy for TDP-43-linked ALS and possibly other types of ALS.

A network of RNA and protein interactions in Fronto Temporal Dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by degeneration of the fronto temporal lobes and abnormal protein inclusions. It exhibits a broad clinicopathological spectrum and has been linked to mutations in seven different genes. We will provide a picture, which connects the products of these genes, albeit diverse in nature and function, in a network. Despite the paucity of information available for some of these genes, we believe that RNA processing and post-transcriptional regulation of gene expression might constitute a common theme in the network. Recent studies have unraveled the role of mutations affecting the functions of RNA binding proteins and regulation of microRNAs. This review will combine all the recent findings on genes involved in the pathogenesis of FTD, highlighting the importance of a common network of interactions in order to study and decipher the heterogeneous clinical manifestations associated with FTD. This approach could be helpful for the research of potential therapeutic strategies.

Parkin reverses TDP-43-induced cell death and failure of amino acid homeostasis

The E3 ubiquitin ligase Parkin plays a central role in the pathogenesis of many neurodegenerative diseases. Parkin promotes specific ubiquitination and affects the localization of transactivation response DNA-binding protein 43 (TDP-43), which controls the translation of thousands of mRNAs. Here we tested the effects of lentiviral Parkin and TDP-43 expression on amino acid metabolism in the rat motor cortex using high frequency ¹³C NMR spectroscopy. TDP-43 expression increased glutamate levels, decreased the levels of other amino acids, including glutamine, aspartate, leucine and isoleucine, and impaired mitochondrial tricarboxylic acid cycle. TDP-43 induced lactate accumulation and altered the balance between excitatory (glutamate) and inhibitory (GABA) neurotransmitters. Parkin restored amino acid levels, neurotransmitter balance and tricarboxylic acid cycle metabolism, rescuing neurons from TDP-43-induced apoptotic death. Furthermore, TDP-43 expression led to an increase in 4E-BP levels, perhaps altering translational control and deregulating amino acid synthesis; while Parkin reversed the effects of TDP-43 on the 4E-BP signaling pathway. Taken together, these data suggest that Parkin may affect TDP-43 localization and mitigate its effects on 4E-BP signaling and loss of amino acid homeostasis.

Excitotoxicity and stroke: identifying novel targets for neuroprotection

Excitotoxicity, the specific type of neurotoxicity mediated by glutamate, may be the missing link between ischemia and neuronal death, and intervening the mechanistic steps that lead to excitotoxicity can prevent stroke damage. Interest in excitotoxicity began fifty years ago when monosodium glutamate was found to be neurotoxic. Evidence soon demonstrated that glutamate is not only the primary excitatory neurotransmitter in the adult brain, but also a critical transmitter for signaling neurons to degenerate following stroke. The finding led to a number of clinical trials that tested inhibitors of excitotoxicity in stroke patients. Glutamate exerts its function in large by activating the calcium-permeable ionotropic NMDA receptor (NMDAR), and different subpopulations of the NMDAR may generate different functional outputs, depending on the signaling proteins directly bound or indirectly coupled to its large cytoplasmic tail. Synaptic activity activates the GluN2A subunit-containing NMDAR, leading to activation of the pro-survival signaling proteins Akt, ERK, and CREB. During a brief episode of ischemia, the extracellular glutamate concentration rises abruptly, and stimulation of the GluN2B-containing NMDAR in the extrasynaptic sites triggers excitotoxic neuronal death via PTEN, cdk5, and DAPK1, which are directly bound to the NMDAR, nNOS, which is indirectly coupled to the NMDAR via PSD95, and calpain, p25, STEP, p38, JNK, and SREBP1, which are further downstream. This review aims to provide a comprehensive summary of the literature on excitotoxicity and our perspectives on how the new generation of excitotoxicity inhibitors may succeed despite the failure of the previous generation of drugs.

Nuclear trafficking of Pten after brain injury leads to neuron survival not death

There is controversy whether accumulation of the tumor suppressor PTEN protein in the cell nucleus under stress conditions such as trauma and stroke causes cell death. A number of in vitro studies have reported enhanced apoptosis in neurons possessing nuclear PTEN, with the interpretation that its nuclear phosphatase activity leads to reduction of the survival protein phospho-Akt. However, there have been no in vivo studies to show that nuclear PTEN in neurons under stress is detrimental. Using a mouse model of injury, we demonstrate here that brain trauma altered the nucleo-cytoplasmic distribution of Pten, resulting in increased nuclear Pten but only in surviving neurons near the lesion. This event was driven by Ndfip1, an adaptor and activator of protein ubiquitination by Nedd4 E3 ligases. Neurons next to the lesion with nuclear PTEN were invariably negative for TUNEL, a marker for cell death. These neurons also showed increased Ndfip1 which we previously showed to be associated with neuron survival. Biochemical assays revealed that overall levels of Pten in the affected cortex were unchanged after trauma, suggesting that Pten abundance globally had not increased but rather Pten subcellular location in affected neurons had changed. Following experimental injury, the number of neurons with nuclear Pten was reduced in heterozygous mice (Ndfip1(+/-)) although lesion volumes were increased. We conclude that nuclear trafficking of Pten following injury leads to neuron survival not death.

Critical role of increased PTEN nuclear translocation in excitotoxic and ischemic neuronal injuries

Stroke is the leading cause of disability in developed countries. However, no treatment is available beyond 3 h post-ictus. Here, we report that nuclear translocation of PTEN (phosphatase and tensin homolog deleted on chromosome TEN) is a delayed step causatively leading to excitotoxic (in vitro) and ischemic (in vivo) neuronal injuries. We found that excitotoxic stimulation of N-methyl-d-aspartate (NMDA) resulted in PTEN nuclear translocation in cultured neurons, a process requiring mono-ubiquitination at the lysine 13 residue (K13), as the translocation was prevented by mutation of K13 or a short interfering peptide (Tat-K13) that flanks the K13 residue. More importantly, using a rat model of focal ischemia, we demonstrated that systemic application of Tat-K13, even 6 h after stroke, not only reduced ischemia-induced PTEN nuclear translocation, but also strongly protected against ischemic brain damage. Our study suggests that inhibition of PTEN nuclear translocation may represent a novel after stroke therapy.

GluN2A versus GluN2B: twins, but quite different

N-Methyl-D-aspartate receptors (NMDARs) play vital roles in the central nervous system, as they are primary mediators of Ca(2+) influx during synaptic activity. The subunits that compose NMDARs share similar topological structures but are distinct in distribution and pharmacological properties, as well as physiological and pathological functions, which make the NMDAR one of the most complex and elusive ionotropic glutamate receptors. In this review, we focus on GluN2A and GluN2B, the primary NMDAR subunits in the cortex and hippocampus, and discuss their differences in developmental expression, brain distribution, trafficking, and functional properties during neuronal activity.

RNA-mediated toxicity in neurodegenerative disease

Cellular viability depends upon the well-orchestrated functions carried out by numerous protein-coding and non-coding RNAs, as well as RNA-binding proteins. During the last decade, it has become increasingly evident that abnormalities in RNA processing represent a common feature among many neurodegenerative diseases. In "RNAopathies", which include diseases caused by non-coding repeat expansions, RNAs exert toxicity via diverse mechanisms: RNA foci formation, bidirectional transcription, and the production of toxic RNAs and proteins by repeat associated non-ATG translation. The mechanisms of toxicity in "RNA-binding proteinopathies", diseases in which RNA-binding proteins like TDP-43 and FUS play a prominent role, have yet to be fully elucidated. Nonetheless, both loss of function of the RNA binding protein, and a toxic gain of function resulting from its aggregation, are thought to be involved in disease pathogenesis. As part of the special issue on RNA and Splicing Regulation in Neurodegeneration, this review intends to explore the diverse RNA-related mechanisms contributing to neurodegeneration, with a special emphasis on findings emerging from animal models.

Differential roles of GluN2A- and GluN2B-containing NMDA receptors in neuronal survival and death

Glutamate-induced neurotoxicity is the primary molecular mechanism that induces neuronal death in a variety of pathologies in central nervous system (CNS). Toxicity signals are relayed from extracellular space to the cytoplasm by N-methyl-D-aspartate receptors (NMDARs) and regulate a variety of survival and death signaling. Differential subunit combinations of NMDARs confer neuroprotection or trigger neuronal death pathways depending on the subunit arrangements of NMDARs and its localization on the cell membrane. It is well-known that GluN2B-contaning NMDARs (GluN2BRs) preferentially link to signaling cascades involved in CNS injury promoting neuronal death and neurodegeneration. Conversely, less well-known mechanisms of neuronal survival signaling are associated with GluN2A-comtaining NMDARs (GluN2AR)-dependent signal pathways. This review will discuss the most recent signaling cascades associated with GluN2ARs and GluN2BRs.