Neuroprotection against ischaemic brain injury by a GluR6-9c peptide containing the TAT protein transduction sequence

Involvement of Calpain in Neurovascular Unit Damage through Up-regulating PARP-NF-κB Signaling during Experimental Ischemic Stroke

Calpain and PARP-NF-κB signaling are reported to participate in the ischemic brain injury. In this study, it was investigated whether calpain was contributed to the neurovascular unit (NVU) damage through up-regulating PARP-NF-κB signaling during experimental ischemic stroke. Male Sprague-Dawley rats were suffered from 90 min of middle cerebral artery occlusion, followed by reperfusion. The NVU damage was evaluated by the permeability of blood-brain barrier (BBB), the degradation of proteins in extracellular matrix and tight junctions, and ultrastructural changes. The inflammatory response was determined by the expression of inflammatory genes driven by PARP-NF-κB signaling and the activities of myeloperoxidase (MPO). Treatment with MDL 28,170, a calpain inhibitor, improved neurological functions, reduced TUNEL staining index, lessened brain swelling, and decreased infarct volume in ischemic rats. Moreover, it reduced the BBB permeability, enhanced the levels of laminin, collagen IV and occludin, and attenuated the ultrastructural damage of NVU in penumbra and core after induction of ischemia. Meanwhile, it enhanced the levels of cytosolic IκBα, lessened the levels of nuclear PARP and NF-κB p65, reduced the levels of ICAM-1, TNF-α, IL-1β, MMP-9, and MMP-2,and suppressed the activities of MPO in penumbra and core. These data showed that calpain inhibition suppressed PARP-NF-κB signaling-mediated inflammatory response, reduced NVU damage, and protected brain against ischemic stroke, suggesting the involvement of calpain in the NVU damage through up-regulating PARP-NF-κB signaling during brain ischemia.

Phosphorylation of 4.1N by CaMKII Regulates the Trafficking of GluA1-containing AMPA Receptors During Long-term Potentiation in Acute Rat Hippocampal Brain Slices

OBJECTIVE

GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs) inserted into postsynaptic membranes are key to the process of long-term potentiation (LTP). Some evidence has shown that 4.1N plays a critical role in the membrane trafficking of AMPARs. However, the underlying mechanism behind this is still unclear. We investigated the role of 4.1N-mediated membrane trafficking of AMPARs during theta-burst stimulation long-term potentiation (TBS-LTP), to illustrate the molecular mechanism behind LTP.

METHODS

LTP was induced by TBS in rat hippocampal CA1 neuron. Tat-GluA1 (MPR), which disrupts the association of 4.1N-GluA1, and autocamtide-2-inhibitory peptide, myristoylated (Myr-AIP), a CaMKII antagonist, were used to explore the role of 4.1N in the AMPARs trafficking during TBS-induced LTP. Immunoprecipitation (IP) and immunoblotting (IB)were used to detect protein expression, phosphorylation, and the interaction of p-CaMKII-4.1N-GluA1.

RESULTS

We found that Myr-AIP attenuated increases of p-CaMKII (T286), p-GluA1 (ser831), and 4.1N phosphorylation after TBS-LTP, and decreased the association of p-CaMKII-4.1N-GluA1, along with the expression of GluA1, at postsynaptic densities during TBS-LTP. We also designed interfering peptides to disrupt the interaction between 4.1N and GluA1, which showed that Tat-GluA1 (MPR) or Myr-AIP inhibited TBS-LTP and attenuated increases of GluA1 at postsynaptic sites, while Tat-GluA1 (MPR) or Myr-AIP had no effects on miniature excitatory postsynaptic currents (mEPSCs) in non-stimulated hippocampal CA1 neurons.

CONCLUSION

Active CaMKII enhanced the phosphorylation of 4.1N and facilitated the association of p-CaMKII with 4.1N-GluA1, which in turn resulted in GluA1 trafficking during TBS-LTP. The association of 4.1N-GluA1 is required for LTP, but not for basal synaptic transmission.

Dipeptide mimetic of BDNF ameliorates motor dysfunction and striatal apoptosis in 6-OHDA-induced Parkinson's rat model: Considering Akt and MAPKs signaling

Parkinson's disease (PD) is a progressive and debilitating neurodegenerative disorder associated with motor and non-motor complaints. Dysregulation of neurotrophic factors and related signaling cascades have been reported to be common events in PD which is accompanied by dopaminergic (DA) neuron demise. However, the restoration of neurotrophic factors has several limitations. Bis-(N-monosuccinyl-L-methionyl-L-serine) heptamethylenediamide (BHME) is a dipeptide mimetic of brain-derived neurotrophic factor (BDNF) with reported anti-oxidant and neuroprotective effects in several experimental models. The current study has investigated the effect of BHME on 6-hydroxydopamine (6-OHDA)-caused motor anomalies in Wistar rats. In this regard, rats were treated daily with BHME (0.1 or 1 mg/kg) 1 h after 6-OHDA-caused damage until the twelfth day. Afterwards, motor behavior and DA neuron survival were evaluated via behavioral tests and immunohistochemistry (IHC) staining, respectively. Moreover, the activity of Akt, mitogen-activated protein kinases (MAPKs) family, and Bax/Bcl-2 ratio were evaluated by Western blotting. Our results indicated that BHME prevents motor dysfunction and DA cell death following 6-OHDA injection, and this improvement was in parallel with an enhancement in Akt activity, decrement of P38 phosphorylation, along with a reduction in Bax/Bcl-2 ratio. In conclusion, our findings indicated that BHME, as a mimetic of BDNF, can be considered for further research and is a promising therapeutic agent for PD therapy.

Pinus massoniana needle extracts attenuate oxidative stress injury in cerebral ischemia reperfusion rats by regulating JNK3/caspase-3 signal transduction

OBJECTIVE

To investigate the effect and mechanism of Pinus massoniana needle extracts (PNE) on oxidative stress injury in cerebral ischemia reperfusion rats.

METHODS

The SD male rats were randomly divided into sham group, model control group, Edaravone (3 mg/kg) group, PNE low-dose (200 mg/kg), medium-dose (400 mg/kg) and high-dose (800 mg/kg) groups. PNE was administered by gavage for 7 d before modeling and 6 h after modeling in PNE treatment groups; Edaravone was given by intraperitoneal injection 7 d before modeling and 6 h after reperfusion. The rat model of cerebral ischemia reperfusion injury was established by middle cerebral artery occlusion method. After 24 h of reperfusion, the neurological deficit score, brain water content and cerebral infarction volume of rats were measured. The pathological changes of cerebral cortex and hippocampus were observed by HE staining, and the number of normal nerve cells was counted. The apoptosis rate of neurons in cerebral cortex was detected by TUNEL method. The content of nitric oxide (NO), malondialdehyde (MDA) and superoxide dismutase (SOD) activity in ischemic brain tissue were detected. The protein expression of c-Jun N-terminal kinase (JNK) 3, phosphorylated JNK3 (p-JNK3), B-cell lymphoma protein(Bcl) -2, Bcl-2 associated X (Bax), cytochrome C and caspase-3 in cerebral cortex were detected by Western blotting method.

RESULTS

Compared with the model control group, the behavioral score, brain water content and cerebral infarction volume in PNE groups were significantly reduced (all P<0.05), the pathological damage of cerebral cortex and hippocampal CA1 area was significantly alleviated, and the number of normal nerve cells in ischemic cortex and hippocampal CA1 area was increased (all P<0.05). The medium-dose PNE group had the best effect. Compared with the model control group, the apoptosis rate of cortical neurons, the content of NO and MDA in cerebral cortex, the ratio of p-JNK3/JNK3, the expression level of cytochrome C and caspase-3 protein in PNE medium-dose group were significantly reduced , and the activity of SOD, the Bcl-2/Bax ratio were significantly improved (all P<0.05).

CONCLUSION

PNE ameliorates brain injury after cerebral ischemia reperfusion in rats, which may be related to scavenging NO and MDA, inhibiting oxidative stress-mediated JNK3/caspase-3 signsal transduction to inhibit neuronal apoptosis.

LAMP-2A ablation in hippocampal CA1 astrocytes confers cerebroprotection and ameliorates neuronal injury after global brain ischemia

Reactive astrogliosis and neuronal death are major features of brain tissue damage after transient global cerebral ischemia/reperfusion (I/R). The CA1 subfield in the hippocampus is particularly susceptible to cell death after I/R. Recently, attention has focused on the relationship between the autophagy-lysosomal pathway and cerebral ischemia. Lysosomal-associated membrane protein type-2A (LAMP-2A) is a key protein in chaperone-mediated autophagy (CMA). However, LAMP-2A expression in astrocytes of the hippocampus and its influence on brain injury following I/R remain unknown. Here, we show that LAMP-2A is elevated in astrocytes of the CA1 hippocampal subfield after I/R and in primary cultured astrocytes after transient oxygen-glucose deprivation (OGD). Conditional LAMP-2A knockdown in CA1 astrocytes inhibited astrocyte activation and prevented neuronal death by inhibiting the mitochondrial pathway of apoptosis after I/R, suggesting that elevated astrocytic LAMP-2A contributes to regional ischemic vulnerability. Furthermore, astrocytic LAMP-2A ablation ameliorated the spatial learning and memory deficits caused by I/R. Conditional astrocytic LAMP-2A knockdown also prevented the loss of hippocampal synapses and dendritic spines, improved the synaptic ultrastructure, and inhibited the reduced expression of synaptic proteins after ischemia. Thus, our findings demonstrate that astrocytic LAMP-2A expression increases upon I/R and that LAMP-2A ablation specifically in hippocampal astrocytes contributes to cerebroprotection, suggesting a novel neuroprotective strategy for patients with global ischemia.

Inhibition of the postsynaptic density protein 95 on the protective effect of Ang-(1-7)-Mas on cerebral ischaemia injury

BACKGROUND

Postsynaptic density protein-95 (PSD95) plays an important role in cerebral ischaemia injury, but its mechanism needs further research. This study aimed to explore the role of PSD95 in (Ang-(1-7))-Mas-mediated cerebral ischaemia protection and its regulatory mechanism.

METHODS

Oxygen-glucose deprivation (OGD) neuron and rat middle cerebral artery occlusion (MCAO) models were used as in vitro and in vivo models, respectively. TAT-MAS9C was used to disrupt the interaction between PSD95 and Mas. The recombinant PSD95 adenovirus (Ad-PSD95) was used to overexpress PSD95 in neurons.

RESULTS

Results showed that in OGD neurons, Ang-(1-7) could promote cell viability; reduce cell apoptosis; reduce the cell membrane localisation of Mas; upregulate the expression levels of pAKT, bcl-2 and I-κB; and downregulate the expression levels of Bax, pI-κB, tumour necrosis factor alpha and interleukin-1β. TAT-MAS9C could enhance the aforementioned effects of Ang-(1-7). However, the PSD95 overexpression inhibited the aforementioned effects of Ang-(1-7). In the MCAO rat model, the 2,3,5-triphenyltetrazolium chloride (TTC) staining showed that Ang-(1-7) reduced the infarct volume. The Morris water maze test showed that the number of crossings over the platform area in the Ang-(1-7) group was significantly increased. TAT-MAS9C could promote the protective effect of Ang-(1-7).

CONCLUSIONS

Results suggested that PSD95 alleviated the activation of AKT and the inhibition of nuclear factor kappa B signalling pathway mediated by the Ang-(1-7)-Mas complex, thereby reducing neuronal activity, increasing apoptosis and inhibiting the Ang-(1-7)-Mas-mediated cerebral ischaemia protection.

Kainate receptors: from synaptic activity to disease

Kainate receptors (KARs) are glutamate receptors that participate in the postsynaptic transmission of information and in the control of neuronal excitability, as well as presynaptically modulating the release of the neurotransmitters GABA and glutamate. These modulatory effects, general follow a biphasic pattern, with low KA concentrations provoking an increase in GABA and glutamate release, and higher concentrations mediating a decrease in the release of these neurotransmitters. In addition, KARs are involved in different forms of long- and short-term plasticity. Importantly, altered activity of these receptors has been implicated in different central nervous system diseases and disturbances. Here, we describe the pre- and postsynaptic actions of KARs, and the possible role of these receptors in disease, a field that has seen significant progress in recent years.

PTD4 Peptide Increases Neural Viability in an In Vitro Model of Acute Ischemic Stroke

Ischemic stroke is a disturbance in cerebral blood flow caused by brain tissue ischemia and hypoxia. We optimized a multifactorial in vitro model of acute ischemic stroke using rat primary neural cultures. This model was exploited to investigate the pro-viable activity of cell-penetrating peptides: arginine-rich Tat(49–57)-NH₂ (R⁴⁹KKRRQRRR⁵⁷-amide) and its less basic analogue, PTD4 (Y⁴⁷ARAAARQARA⁵⁷-amide). Our model included glucose deprivation, oxidative stress, lactic acidosis, and excitotoxicity. Neurotoxicity of these peptides was excluded below a concentration of 50 μm, and PTD4-induced pro-survival was more pronounced. Circular dichroism spectroscopy and molecular dynamics (MD) calculations proved potential contribution of the peptide conformational properties to neuroprotection: in MD, Tat(49–57)-NH₂ adopted a random coil and polyproline type II helical structure, whereas PTD4 adopted a helical structure. In an aqueous environment, the peptides mostly adopted a random coil conformation (PTD4) or a polyproline type II helical (Tat(49–57)-NH₂) structure. In 30% TFE, PTD4 showed a tendency to adopt a helical structure. Overall, the pro-viable activity of PTD4 was not correlated with the arginine content but rather with the peptide’s ability to adopt a helical structure in the membrane-mimicking environment, which enhances its cell membrane permeability. PTD4 may act as a leader sequence in novel drugs for the treatment of acute ischemic stroke.

Yixin-Shu Capsules Ameliorated Ischemia-Induced Heart Failure by Restoring Trx2 and Inhibiting JNK/p38 Activation

Traditional Chinese medicine has shown great safety and efficacy in the treatment of heart failure (HF), whereas the mechanism remains unclear. In this study, the protective effect of Yixin-shu (YXS) capsules, a conventional medicine for various cardiovascular diseases, against myocardial ischemia-induced HF in rats was systematically investigated by RNA-seq technology. HF rats treated with YXS (0.8 or 1.6 g/kg/d, ig) for 6 weeks had significantly decreased brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) and collagen III and attenuated cardiac structure rupture and collagen deposition. Additionally, YXS treatment decreased the levels of interleukin-1β (IL-1β), interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and lactate dehydrogenase (LDH) and TUNEL-positive rate and the nitrotyrosine staining, but increased levels of glutathione (GSH), total antioxidant capacity (T-AOC) activity, and mitochondrial membrane potential. Further experiments demonstrated that YXS restored Trx2 and inhibited the phosphorylation of JNK and p38, thereby improving cardiac function in the rats with HF. Silencing Trx2 decreased the protection of YXS in the response to H2O2 as evidenced by the increase of caspase-3 activity and decrease of GSH level. Thus, YXS enhanced heart function and decreased myocardial damage through restoring Trx2 and inhibiting JNK and p38 activation in ischemia-induced HF.

Proteome profiling of different rat brain regions reveals the modulatory effect of prolonged maternal separation on proteins involved in cell death-related processes

Background

Early-life stress in the form of maternal separation can be associated with alterations in offspring neurodevelopment and brain functioning. Here, we aimed to investigate the potential impact of prolonged maternal separation on proteomic profiling of prefrontal cortex, hippocampus and cerebellum of juvenile and young adult rats. A special attention was devoted to proteins involved in the process of cell death and redox state maintenance.

Methods

Long-Evans pups were separated from their mothers for 3 h daily over the first 3 weeks of life (during days 2–21 of age). Brain tissue samples collected from juvenile (22-day-old) and young adult (90-day-old) rats were used for label-free quantitative (LFQ) proteomic analysis. In parallel, selected oxidative stress markers and apoptosis-related proteins were assessed biochemically and by Western blot, respectively.

Results

In total, 5526 proteins were detected in our proteomic analysis of rat brain tissue. Approximately one tenth of them (586 proteins) represented those involved in cell death processes or regulation of oxidative stress balance. Prolonged maternal separation caused changes in less than half of these proteins (271). The observed alterations in protein expression levels were age-, sex- and brain region-dependent. Interestingly, the proteins detected by mass spectrometry that are known to be involved in the maintenance of redox state were not markedly altered. Accordingly, we did not observe any significant differences between selected oxidative stress markers, such as the levels of hydrogen peroxide, reduced glutathione, protein carbonylation and lipid peroxidation in brain samples from rats that underwent maternal separation and from the corresponding controls. On the other hand, a number of changes were found in cell death-associated proteins, mainly in those involved in the apoptotic and autophagic pathways. However, there were no detectable alterations in the levels of cleaved products of caspases or Bcl-2 family members. Taken together, these data indicate that the apoptotic and autophagic cell death pathways were not activated by maternal separation either in adolescent or young adult rats.

Conclusion

Prolonged maternal separation can distinctly modulate expression profiles of proteins associated with cell death pathways in prefrontal cortex, hippocampus and cerebellum of juvenile rats and the consequences of early-life stress may last into adulthood and likely participate in variations in stress reactivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-021-00327-5.

Inhibition of EZH2 attenuates inhibitory synaptic transmission via the pro-inflammatory pathway in rats

Enhancer of zeste homolog 2 (EZH2), a subunit of the polycomb repressive complex 2 (PRC2), is associated with seizure development and epileptogenesis, however, the underlying mechanism of the process remains to be elucidated. This study focused on exploring whether EZH2 regulated gamma-aminobutyric acid (GABA)-mediated neurotransmission during seizure generation. Hyperthermia-induced seizures were generated in Sprague-Dawley (SD) rats using a hot (43.5 °C) bath method, and seizure severity was evaluated according to the Racine scale. The effect of treatment with the EZH2 pharmacological inhibitor GSK 126 on the GABA and pro-inflammatory cytokine levels was tested using enzyme-linked immunosorbent assay (ELISA). Miniature inhibitory postsynaptic currents (mIPSCs) were recorded using whole-cell patch clamp. In this study, our results showed that intracerebroventricular (i.c.v) injection of the EZH2 pharmacological inhibitor GSK 126 (10 nM) increased seizure severity and shortened seizure latency in a rat model of FS, and these effects were accompanied by reduced GABA content. Furthermore, GSK 126 (1 μM) treatment decreased the mean amplitude and frequency of the mIPSCs in cultured hippocampal neurons subjected to hyperthermia. Importantly, the same results were also obtained in cultured neurons infected with lentivirus carrying EZH2 shRNA. In addition, a significant increase in the pro-inflammatory cytokine (IL-1β and TNF-α) levels was observed in rats after GSK 126 treatment, and IL-1β administration increased seizure severity, suggesting that the inflammatory response was involved in the regulation of seizure development by EZH2. This study helps clarify the role of EZH2 in FS and supports EZH2 administration as an effective target for the management of seizure generation.

Cationic Arginine-Rich Peptides (CARPs): A Novel Class of Neuroprotective Agents With a Multimodal Mechanism of Action

There are virtually no clinically available neuroprotective drugs for the treatment of acute and chronic neurological disorders, hence there is an urgent need for the development of new neuroprotective molecules. Cationic arginine-rich peptides (CARPs) are an expanding and relatively novel class of compounds, which possess intrinsic neuroprotective properties. Intriguingly, CARPs possess a combination of biological properties unprecedented for a neuroprotective agent including the ability to traverse cell membranes and enter the CNS, antagonize calcium influx, target mitochondria, stabilize proteins, inhibit proteolytic enzymes, induce pro-survival signaling, scavenge toxic molecules, and reduce oxidative stress as well as, having a range of anti-inflammatory, analgesic, anti-microbial, and anti-cancer actions. CARPs have also been used as carrier molecules for the delivery of other putative neuroprotective agents across the blood-brain barrier and blood-spinal cord barrier. However, there is increasing evidence that the neuroprotective efficacy of many, if not all these other agents delivered using a cationic arginine-rich cell-penetrating peptide (CCPPs) carrier (e.g., TAT) may actually be mediated largely by the properties of the carrier molecule, with overall efficacy further enhanced according to the amino acid composition of the cargo peptide, in particular its arginine content. Therefore, in reviewing the neuroprotective mechanisms of action of CARPs we also consider studies using CCPPs fused to a putative neuroprotective peptide. We review the history of CARPs in neuroprotection and discuss in detail the intrinsic biological properties that may contribute to their cytoprotective effects and their usefulness as a broad-acting class of neuroprotective drugs.

Antiapoptotic and Anti-Inflammatory Effects of CPCGI in Rats with Traumatic Brain Injury

BACKGROUND

Compound porcine cerebroside and ganglioside injection (CPCGI) has been used for the treatment of certain brain disorders. Apoptosis and inflammation were reported to be involved in the pathogenesis of traumatic brain injury (TBI). Therefore, this study primarily investigated the effects of CPCGI on mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling in a rat model of controlled cortical impact (CCI).

MATERIALS AND METHODS

CPCGI (0.6 mL/kg) was administered intraperitoneally 30 min after the induction of CCI. Mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling were evaluated 24 h after CCI, and apoptotic cell death, neutrophil infiltration, and astrocyte and microglial activation were determined by TUNEL and immunofluorescent staining 3 days after CCI.

RESULTS

1) CPCGI markedly enhanced cytosolic and mitochondrial Bcl-xL levels, the mitochondrial Bcl-xL/Bax ratio, and mitochondrial cytochrome (cyt) c levels and reduced cytosolic cyt c levels, caspase-3 activity, and nuclear AIF levels in brain tissues after traumatic injury; however, CPCGI had no significant effects on cytosolic or mitochondrial Bax levels, the cytosolic Bcl-xL/Bax ratio, or mitochondrial AIF levels. Moreover, CPCGI markedly reduced the TUNEL staining score in the contusion region. 2) CPCGI markedly reduced cytosolic and nuclear PARP levels and nuclear NF-κB p65 levels in brain tissues after traumatic injury but had no significant effect on cytosolic NF-κB p65 levels. In addition, CPCGI markedly reduced caspase-1 activity and the levels of caspase-1, ICAM-1, TNF-α, and IL-1β in brain tissues after traumatic injury and decreased the immunoreactivities of neutrophils, GFAP and Iba-1 in the region of CCI-induced contusion.

CONCLUSION

These data suggest that CPCGI can reduce brain injury due to trauma by suppressing both mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling.

CPCGI Reduces Gray and White Matter Injury by Upregulating Nrf2 Signaling and Suppressing Calpain Overactivation in a Rat Model of Controlled Cortical Impact

BACKGROUND

Compound porcine cerebroside and ganglioside injection (CPCGI), which involves injection of a neurotrophic drug, has been widely used to treat certain brain disorders in the clinic; however, the detailed mechanism is unknown. This study investigated whether CPCGI protects the brain from trauma by stimulating antioxidative nuclear factor erythroid-2-related factor 2 (Nrf2) signaling and suppressing calpain overactivation in a rat model of controlled cortical impact (CCI).

MATERIALS AND METHODS

The rat model of CCI was used. Neurological deficits, contusion, and white matter damage were evaluated 3 days after CCI. Calpain activation, Nrf2 signaling and oxidative stress were determined 24 h after CCI.

RESULTS

CPCGI dose-dependently reduced neurological deficits, attenuated axonal and myelin sheath injury, and decreased contusion volume 3 days post-CCI. Moreover, CPCGI reduced calpain activity, and enhanced the cytosolic levels of calpastatin, αII-spectrin, microtubule-associated protein 2 (MAP2), neurofilament heavy chain (NF-H) and myelin basic protein (MBP) in traumatic tissues 24 h post-CCI. Furthermore, CPCGI reduced the levels of nuclear Kelch-like ECH-associated protein 1 (Keap1) and thioredoxin interacting protein (TXNIP); increased the levels of cytosolic Nrf2 and thioredoxin 1 (Trx 1) and nuclear Nrf2; increased the cytosolic and nuclear Nrf2/Keap1 and Trx 1/TXNIP ratios; enhanced the levels of heme oxygenase 1 (HO-1), glutathione (GSH), superoxide dismutase activity, and total antioxidative capacity; and reduced the levels of malondialdehyde in TBI tissues.

CONCLUSION

These data confirm the neuroprotective effect of CPCGI against gray and white matter damage due to CCI and suggest that activating Nrf2 signaling and alleviating oxidative stress-mediated calpain activation could be one mechanism by which CPCGI protects against brain trauma.

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.

Mitochondria and neuroprotection in stroke: Cationic arginine-rich peptides (CARPs) as a novel class of mitochondria-targeted neuroprotective therapeutics

Stroke is the second leading cause of death globally and represents a major cause of devastating long-term disability. Despite sustained efforts to develop clinically effective neuroprotective therapies, presently there is no clinically available neuroprotective agent for stroke. As a central mediator of neurodamaging events in stroke, mitochondria are recognised as a critical neuroprotective target, and as such, provide a focus for developing mitochondrial-targeted therapeutics. In recent years, cationic arginine-rich peptides (CARPs) have been identified as a novel class of neuroprotective agent with several demonstrated mechanisms of action, including their ability to target mitochondria and exert positive effects on the organelle. This review provides an overview on neuronal mitochondrial dysfunction in ischaemic stroke pathophysiology and highlights the potential beneficial effects of CARPs on mitochondria in the ischaemic brain following stroke.

Inhibition of DPP4 enhances inhibitory synaptic transmission through activating the GLP-1/GLP-1R signaling pathway in a rat model of febrile seizures

Dipeptidyl peptidase-IV (DPP4) is a cell surface serine peptidase widely expressed in the brain. Recent studies suggest that DPP4 contributes to the development of febrile seizures (FS); however, the underlying mechanism is still unclear. Thus, we investigated the role of DPP4 in the progression of FS at the molecular and electrophysiological levels using FS models in vivo and in vitro. Herein, we found that both the mRNA and protein levels of DPP4 were upregulated in the FS model. Administration of the pharmacological DPP4 inhibitor sitagliptin suppressed the hyperthermia-induced neuronal excitability as determined via whole-cell patch-clamp recordings in vitro. Interestingly, sitagliptin administration activated the glucagon-like peptide-1 (GLP-1)/GLP-1 receptor (GLP-1R) pathway by increasing the expression of GLP-1 and GLP-1R in a rat model of FS. Moreover, administration of the GLP-1R inhibitor exendin9-39 increased seizure severity, and sitagliptin reversed the effect, as shown in the electroencephalogram (EEG) and patch-clamp results in a rat model of FS. Furthermore, the GLP-1R-mediated reduction in GABAergic transmission was enhanced by sitagliptin and DPP4 knockdown through increasing miniature inhibitory post-synaptic currents (mIPSCs) in vitro accompanied by increased synaptic release of GABA in vivo. Taken together, our results demonstrate a role of DPP4 in regulating GABAergic transmission via the GLP-1/GLP-1R pathway. These findings indicated that DPP4 may represent a novel therapeutic strategy and target for FS.

c-Jun N-Terminal Kinases (JNKs) in Myocardial and Cerebral Ischemia/Reperfusion Injury

In this article, we review the literature regarding the role of c-Jun N-terminal kinases (JNKs) in cerebral and myocardial ischemia/reperfusion injury. Numerous studies demonstrate that JNK-mediated signaling pathways play an essential role in cerebral and myocardial ischemia/reperfusion injury. JNK-associated mechanisms are involved in preconditioning and post-conditioning of the heart and the brain. The literature and our own studies suggest that JNK inhibitors may exert cardioprotective and neuroprotective properties. The effects of modulating the JNK-depending pathways in the brain and the heart are reviewed. Cardioprotective and neuroprotective mechanisms of JNK inhibitors are discussed in detail including synthetic small molecule inhibitors (AS601245, SP600125, IQ-1S, and SR-3306), ion channel inhibitor GsMTx4, JNK-interacting proteins, inhibitors of mixed-lineage kinase (MLK) and MLK-interacting proteins, inhibitors of glutamate receptors, nitric oxide (NO) donors, and anesthetics. The role of JNKs in ischemia/reperfusion injury of the heart in diabetes mellitus is discussed in the context of comorbidities. According to reviewed literature, JNKs represent promising therapeutic targets for protection of the brain and the heart against ischemic stroke and myocardial infarction, respectively. However, different members of the JNK family exert diverse physiological properties which may not allow for systemic administration of non-specific JNK inhibitors for therapeutic purposes. Currently available candidate JNK inhibitors with high therapeutic potential are identified. The further search for selective JNK3 inhibitors remains an important task.

Anticonvulsant agent DPP4 inhibitor sitagliptin downregulates CXCR3/RAGE pathway on seizure models

Epilepsy is a common neurological disorder with a complex etiology. Our previous study demonstrated that dipeptidyl peptidase IV (DPP4) may be associated with the pathogenesis of epilepsy. However, whether the DPP4 inhibitor sitagliptin has an anticonvulsant effect and the underlying mechanism remain to be elucidated. In this study, we determined that sitagliptin remarkably attenuated the severity of seizures in a pentylenetetrazole (PTZ)-induced rat model. In addition, sitagliptin decreased epileptiform activity measured by electroencephalography (EEG) recordings and patch-clamp methods. Interestingly, sitagliptin pretreatment downregulated the RAGE-JAK2/STAT3 pathway and decreased the expression of CXCL4 and CXCR3. Moreover, CXCR3 knockdown decreased the expression of RAGE, JAK2 and STAT3 in cultured neurons, which suggests that CXCR3 is upstream of the RAGE-JAK2/STAT3 pathway. Altogether, our present data suggest that sitagliptin has an anticonvulsant effect, which might act via downregulation of the CXCL4/CXCR3 axis, followed by a decrease in RAGE and JAK2/STAT3 expression. Considering these effects, sitagliptin could be considered as a novel potential anticonvulsant drug.

Refocusing Neuroprotection in Cerebral Reperfusion Era: New Challenges and Strategies

Pathophysiological processes of stroke have revealed that the damaged brain should be considered as an integral structure to be protected. However, promising neuroprotective drugs have failed when translated to clinical trials. In this review, we evaluated previous studies of neuroprotection and found that unsound patient selection and evaluation methods, single-target treatments, etc., without cerebral revascularization may be major reasons of failed neuroprotective strategies. Fortunately, this may be reversed by recent advances that provide increased revascularization with increased availability of endovascular procedures. However, the current improved effects of endovascular therapy are not able to match to the higher rate of revascularization, which may be ascribed to cerebral ischemia/reperfusion injury and lacking of neuroprotection. Accordingly, we suggest various research strategies to improve the lower therapeutic efficacy for ischemic stroke treatment: (1) multitarget neuroprotectant combinative therapy (cocktail therapy) should be investigated and performed based on revascularization; (2) and more efforts should be dedicated to shifting research emphasis to establish recirculation, increasing functional collateral circulation and elucidating brain–blood barrier damage mechanisms to reduce hemorrhagic transformation. Therefore, we propose that a comprehensive neuroprotective strategy before and after the endovascular treatment may speed progress toward improving neuroprotection after stroke to protect against brain injury.

The role of S-nitrosylation of kainate-type of ionotropic glutamate receptor 2 in epilepsy induced by kainic acid

Epilepsy is a chronic brain disease affecting millions of individuals. Kainate receptors, especially kainate-type of ionotropic glutamate receptor 2 (GluK2), play an important role in epileptogenesis. Recent data showed that GluK2 could undergo post-translational modifications in terms of S-nitrosylation (SNO), and affect the signaling pathway of cell death in cerebral ischemia-reperfusion. However, it is unclear whether S-nitrosylation of GluK2 (SNO-GluK2) contributes to cell death induced by epilepsy. Here, we report that kainic acid-induced SNO-GluK2 is mediated by GluK2 itself, regulated by neuronal nitric oxide synthase (nNOS) and the level of cytoplasmic calcium in vivo and in vitro hippocampus neurons. The whole-cell patch clamp recordings showed the influence of SNO-GluK2 on ion channel characterization of GluK2-Kainate receptors. Moreover, immunohistochemistry staining results showed that inhibition of SNO-GluK2 by blocking nNOS or GluK2 or by reducing the level of cytoplasmic calcium-protected hippocampal neurons from kainic acid-induced injury. Finally, immunoprecipitation and western blotting data revealed the involvement of assembly of a GluK2-PSD95-nNOS signaling complex in epilepsy. Taken together, our results showed that the SNO-GluK2 plays an important role in neuronal injury of epileptic rats by forming GluK2-PSD95-nNOS signaling module in a cytoplasmic calcium-dependent way, suggesting a potential therapeutic target site for epilepsy.

Prolonged hippocampal cell death following closed-head traumatic brain injury in rats

Traumatic brain injury (TBI) leads to enduring cognitive disorders. Although recent evidence has shown that controlled cortical impact in a rodent may induce memory deficits with prolonged cell death in the dentate gyrus (DG) of the hippocampus, few studies have reported long-term chronic hippocampal cell death following 'closed-head' TBI (cTBI), the predominant form of human TBI. Therefore, the aim of this study was to quantify terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)(+) apoptotic hippocampal cells as well as hippocampal cells with hallmark morphological features of degenerating cells in a chronic setting of cTBI in rats. TUNEL assays and Cresyl violet staining were performed using 6-month post-TBI fixed hippocampal sections. Evidence of prolonged hippocampal cell death was shown by the presence of a significantly increased number of TUNEL(+) cells in the cornu ammonis 1-3 (CA1-CA3) and DG of the hippocampus compared with intact controls. In addition, Cresyl violet staining indicated a significantly elevated number of cells with the degenerative morphological features in all hippocampal subregions (CA1-CA3, hilus, and DG). These results suggest that prolonged cell death may occur in multiple regions of the hippocampus following cTBI.

Geldanamycin inhibits Fas signaling pathway and protects neurons against ischemia

The inhibitor of Heat shock proteins 90, geldanamycin (GA), has been reported neuroprotective against both global and focal brain ischemia. To understand the mechanisms underlies the neuroprotection effect of GA, we investigated the relationship between GA pretreatment and Fas signaling pathway in rat global brain ischemia/reperfusion model in the present study. Results showed that GA attenuated neuron loss significantly in hippocampal CA1 region. Upon GA pretreatment, Mixed Lineage Kinase 3 (MLK3) expression and activation and FasL expression was decreased, the assembly of death-inducing signaling complex and activation of downstream apoptosis-associating proteins were inhibited along with neuroprotection. Based on the facts that MLK3 is one client protein of HSP90 and MLK3 pathway induces FasL expression in ischemic brain injury, our study suggests one of the mechanisms of neuroprotection against brain ischemia from GA.

TrkB-enhancer facilitates functional recovery after traumatic brain injury

Brain-derived neurotrophic factor (BDNF), a key player in regulating synaptic strength and learning, is dysregulated following traumatic brain injury (TBI), suggesting that stimulation of BDNF signaling pathways may facilitate functional recovery. This study investigates whether CN2097, a peptidomimetic ligand which targets the synaptic scaffold protein, postsynaptic density protein 95, to enhance downstream signaling of tropomyosin-related kinase B, a receptor for BDNF, can improve neurological function after TBI. Moderate to severe TBI elicits neuroinflammation and c-Jun-N-terminal kinase (JNK) activation, which is associated with memory deficits. Here we demonstrate that CN2097 significantly reduces the post-traumatic synthesis of proinflammatory mediators and inhibits the post-traumatic activation of JNK in a rodent model of TBI. The recordings of field excitatory post-synaptic potentials in the hippocampal CA1 subfield demonstrate that TBI inhibits the expression of long-term potentiation (LTP) evoked by high-frequency stimulation of Schaffer collaterals, and that CN2097 attenuates this LTP impairment. Lastly, we demonstrate that CN2097 significantly improves the complex auditory processing deficits, which are impaired after injury. The multifunctionality of CN2097 strongly suggests that CN2097 could be highly efficacious in targeting complex secondary injury processes resulting from neurotrauma.

Protective roles of bioactive peptides during ischemia-reperfusion injury: From bench to bedside

Ischemia-reperfusion (I/R) is a well-known pathological condition which may lead to disability and mortality. I/R injury remains an unresolved and complicated situation in a number of clinical conditions, such as cardiac arrest with successful reanimation, as well as ischemic events in brain and heart. Peptides have many attractive advantages which make them suitable candidate drugs in treating I/R injury, such as low toxicity and immunogenicity, good solubility property, distinct tissue distribution pattern, and favorable pharmacokinetic profile. An increasing number of studies indicate that peptides could protect against I/R injury in many different organs and tissues. Peptides also face several therapeutic challenges that limit their clinical application. In this review, we present the mechanisms of action of peptides in reducing I/R injury, as well as further discuss modification strategies to improve the functional properties of bioactive peptides.

Protein Kinases and Parkinson's Disease

Currently, the lack of new drug candidates for the treatment of major neurological disorders such as Parkinson’s disease has intensified the search for drugs that can be repurposed or repositioned for such treatment. Typically, the search focuses on drugs that have been approved and are used clinically for other indications. Kinase inhibitors represent a family of popular molecules for the treatment and prevention of various cancers, and have emerged as strong candidates for such repurposing because numerous serine/threonine and tyrosine kinases have been implicated in the pathobiology of Parkinson’s disease. This review focuses on various kinase-dependent pathways associated with the expression of Parkinson’s disease pathology, and evaluates how inhibitors of these pathways might play a major role as effective therapeutic molecules.

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

The excessive extracellular accumulation of glutamate in the ischemic brain leads to an overactivation of glutamate receptors with consequent excitotoxic neuronal death. Neuronal demise is largely due to a sustained activation of NMDA receptors for glutamate, with a consequent increase in the intracellular Ca(2+) concentration and activation of calcium- dependent mechanisms. Calpains are a group of Ca(2+)-dependent proteases that truncate specific proteins, and some of the cleavage products remain in the cell, although with a distinct function. Numerous studies have shown pre- and post-synaptic effects of calpains on glutamatergic and GABAergic synapses, targeting membrane- associated proteins as well as intracellular proteins. The resulting changes in the presynaptic proteome alter neurotransmitter release, while the cleavage of postsynaptic proteins affects directly or indirectly the activity of neurotransmitter receptors and downstream mechanisms. These alterations also disturb the balance between excitatory and inhibitory neurotransmission in the brain, with an impact in neuronal demise. In this review we discuss the evidence pointing to a role for calpains in the dysregulation of excitatory and inhibitory synapses in brain ischemia, at the pre- and post-synaptic levels, as well as the functional consequences. Although targeting calpain-dependent mechanisms may constitute a good therapeutic approach for stroke, specific strategies should be developed to avoid non-specific effects given the important regulatory role played by these proteases under normal physiological conditions.

PDZ1 inhibitor peptide protects neurons against ischemia via inhibiting GluK2-PSD-95-module-mediated Fas signaling pathway

Respecting the selective inhibition of peptides on protein-protein interactions, they might become potent methods in ischemic stroke therapy. In this study, we investigated the effect of PDZ1 inhibitor peptide on ischemic neuron apoptosis and the relative mechanism. Results showed that PDZ1 inhibitor peptide, which significantly disrupted GluK2-PSD-95 interaction, efficiently protected neuron from ischemia/reperfusion-induced apoptosis. Further, PDZ1 inhibited FasL expression, DISC assembly and activation of Caspase 8, Bid, Caspase 9 and Caspase 3 after global brain ischemia. Based on our previous report that GluK2-PSD-95 pathway increased FasL expression after global brain ischemia, the neuron protection effect of PDZ1 inhibitor peptide was considered to be achieved by disrupting GluK2-PSD-95 interaction and subsequently inhibiting FasL expression and Fas apoptosis pathway.

Conventional protein kinase Cβ-mediated phosphorylation inhibits collapsin response-mediated protein 2 proteolysis and alleviates ischemic injury in cultured cortical neurons and ischemic stroke-induced mice

We previously reported that conventional protein kinase C (cPKC)β participated in hypoxic preconditioning-induced neuroprotection against cerebral ischemic injury, and collapsin response-mediated protein 2 (CRMP2) was identified as a cPKCβ interacting protein. In this study, we explored the regulation of CRMP2 phosphorylation and proteolysis by cPKCβ, and their role in ischemic injury of oxygen-glucose deprivation (OGD)-treated cortical neurons and brains of mice with middle cerebral artery occlusion-induced ischemic stroke. The results demonstrated that cPKCβ-mediated CRMP2 phosphorylation via the cPKCβ-selective activator 12-deoxyphorbol 13-phenylacetate 20-acetate (DOPPA) and inhibition of calpain-mediated CRMP2 proteolysis by calpeptin and a fusing peptide containing TAT peptide and the calpain cleavage site of CRMP2 (TAT-CRMP2) protected neurons against OGD-induced cell death through inhibiting CRMP2 proteolysis in cultured cortical neurons. The OGD-induced nuclear translocation of the CRMP2 breakdown product was inhibited by DOPPA, calpeptin, and TAT-CRMP2 in cortical neurons. In addition, both cPKCβ activation and CRMP2 proteolysis inhibition by hypoxic preconditioning and intracerebroventricular injections of DOPPA, calpeptin, and TAT-CRMP2 improved the neurological deficit in addition to reducing the infarct volume and proportions of cells with pyknotic nuclei in the peri-infact region of mice with ischemic stroke. These results suggested that cPKCβ modulates CRMP2 phosphorylation and proteolysis, and cPKCβ activation alleviates ischemic injury in the cultured cortical neurons and brains of mice with ischemic stroke through inhibiting CRMP2 proteolysis by phosphorylation. Focal cerebral ischemia induces a large flux of Ca(2+) to activate calpain which cleaves collapsin response mediator (CRMP) 2 into breakdown product (BDP). Inhibition of CRMP2 cleavage by calpeptin and TAT-CRMP2 alleviates ischemic injury. Conventional protein kinase C (cPKC)β-mediated phosphorylation could inhibit CRMP2 proteolysis and alleviate ischemic injury in cultured cortical neurons and ischemic stroke-induced mice.

Neuroprotective peptides fused to arginine-rich cell penetrating peptides: Neuroprotective mechanism likely mediated by peptide endocytic properties

Several recent studies have demonstrated that TAT and other arginine-rich cell penetrating peptides (CPPs) have intrinsic neuroprotective properties in their own right. Examples, we have demonstrated that in addition to TAT, poly-arginine peptides (R8 to R18; containing 8-18 arginine residues) as well as some other arginine-rich peptides are neuroprotective in vitro (in neurons exposed to glutamic acid excitotoxicity and oxygen glucose deprivation) and in the case of R9 in vivo (after permanent middle cerebral artery occlusion in the rat). Based on several lines of evidence, we propose that this neuroprotection is related to the peptide's endocytosis-inducing properties, with peptide charge and arginine residues being critical factors. Specifically, we propose that during peptide endocytosis neuronal cell surface structures such as ion channels and transporters are internalised, thereby reducing calcium influx associated with excitotoxicity and other receptor-mediated neurodamaging signalling pathways. We also hypothesise that a peptide cargo can act synergistically with TAT and other arginine-rich CPPs due to potentiation of the CPPs endocytic traits rather than by the cargo-peptide acting directly on its supposedly intended intracellular target. In this review, we systematically consider a number of studies that have used CPPs to deliver neuroprotective peptides to the central nervous system (CNS) following stroke and other neurological disorders. Consequently, we critically review evidence that supports our hypothesis that neuroprotection is mediated by carrier peptide endocytosis. In conclusion, we believe that there are strong grounds to regard arginine-rich peptides as a new class of neuroprotective molecules for the treatment of a range of neurological disorders.

Overexpression of C-terminal fragment of glutamate receptor 6 prevents neuronal injury in kainate-induced seizure via disassembly of GluR6-PSD-95-MLK3 signaling module

Our previous study showed that when glutamate receptor (GluR)6 C terminus-containing peptide conjugated with the human immunodeficiency virus Tat protein (GluR6)-9c is delivered into hippocampal neurons in a brain ischemic model, the activation of mixed lineage kinase 3 (MLK3) and c-Jun NH2-terminal kinase (JNK) is inhibited via GluR6-postsynaptic density protein 95 (PSD95). In the present study, we investigated whether the recombinant adenovirus (Ad) carrying GluR6c could suppress the assembly of the GluR6-PSD95-MLK3 signaling module and decrease neuronal cell death induced by kainate in hippocampal CA1 subregion. A seizure model in Sprague-Dawley rats was induced by intraperitoneal injections of kainate. The effect of Ad-Glur6-9c on the phosphorylation of JNK, MLK3 and mitogen-activated kinase kinase 7 (MKK7) was observed with western immunoblots and immunohistochemistry. Our findings revealed that overexpression of GluR6c inhibited the interaction of GluR6 with PSD95 and prevented the kainate-induced activation of JNK, MLK3 and MKK7. Furthermore, kainate-mediated neuronal cell death was significantly suppressed by GluR6c. Taken together, GluR6 may play a pivotal role in neuronal cell death.

Momordica charantia polysaccharides could protect against cerebral ischemia/reperfusion injury through inhibiting oxidative stress mediated c-Jun N-terminal kinase 3 signaling pathway

Momordica charantia (MC) is a medicinal plant for stroke treatment in Traditional Chinese Medicine, but its active compounds and molecular targets are unknown yet. M. charantia polysaccharide (MCP) is one of the important bioactive components in MC. In the present study, we tested the hypothesis that MCP has neuroprotective effects against cerebral ischemia/reperfusion injury through scavenging superoxide (O2(-)), nitric oxide (NO) and peroxynitrite (ONOO(-)) and inhibiting c-Jun N-terminal protein kinase (JNK3) signaling cascades. We conducted experiments with in vivo global and focal cerebral ischemia/reperfusion rat models and in vitro oxygen glucose deprivation (OGD) neural cells. The effects of MCP on apoptotic cell death and infarction volume, the bioactivities of scavenging O2(-), NO and ONOO(-), inhibiting lipid peroxidation and modulating JNK3 signaling pathway were investigated. Major results are summarized as below: (1) MCP dose-dependently attenuated apoptotic cell death in neural cells under OGD condition in vitro and reduced infarction volume in ischemic brains in vivo; (2) MCP had directing scavenging effects on NO, O2(-) and ONOO(-) and inhibited lipid peroxidation; (3) MCP inhibited the activations of JNK3/c-Jun/Fas-L and JNK3/cytochrome C/caspases-3 signaling cascades in ischemic brains in vivo. Taken together, we conclude that MCP could be a promising neuroprotective ingredient of M. charantia and its mechanisms could be at least in part attributed to its antioxidant activities and inhibiting JNK3 signaling cascades during cerebral ischemia/reperfusion injury.

Induction of GADD45α protects M17 neuroblastoma cells against MPP*

Growth arrest and DNA-damage-inducible protein 45α (GADD45α) is an important member of the family of growth arrest and DNA damage-inducible (GADD) proteins. The expression patterns and possible roles of GADD45α in Parkinson's disease (PD) are so far less understood. In this study, we found that 1-methyl-4-phenylpyridinium (MPP+) treatment up-regulates the expression of GADD45α in both a time-dependent manner and a dose-dependent manner in human dopamine neuroblastoma M17 cells. The up-regulation of GADD45α was abolished by pretreatment with the c-Jun N-terminal kinases (JNK) inhibitor SP600125 but not the p38 specific inhibitor SB203580. Further study revealed that c-Jun silencing abolished the effects of MPP+ on the expression of GADD45α. Important, ChIP studies verified the ability of c-Jun to bind to the GADD45 promoter. In addition, we found that inhibition of GADD45α by small RNA interference exacerbates the impaired cell viability, LDH release, and apoptosis induced by MPP+. Correspondingly, silence of GADD45 exacerbated Caspase-3 activation induced by MPP+. These data suggested a neuroprotective effect of GADD45α against MPP+ neurotoxicity.

Tyrosine phosphorylation of GluK2 up-regulates kainate receptor-mediated responses and downstream signaling after brain ischemia

Although kainate receptors play important roles in ischemic stroke, the molecular mechanisms underlying postischemic regulation of kainate receptors remain unclear. In this study we demonstrate that Src family kinases contribute to the potentiation of kainate receptor function. Brain ischemia and reperfusion induce rapid and sustained phosphorylation of the kainate receptor subunit GluK2 by Src in the rat hippocampus, implicating a critical role for Src-mediated GluK2 phosphorylation in ischemic brain injury. The NMDA and kainate receptors are involved in the tyrosine phosphorylation of GluK2. GluK2 binds to Src, and the tyrosine residue at position 590 (Y590) on GluK2 is a major site of phosphorylation by Src kinases. GluK2 phosphorylation at Y590 is responsible for increases in whole-cell currents and calcium influx in response to transient kainate stimulation. In addition, GluK2 phosphorylation at Y590 facilitates the endocytosis of GluK2 subunits, and the activation of JNK3 and its substrate c-Jun after long-term kainate treatment. Thus, Src phosphorylation of GluK2 plays an important role in the opening of kainate receptor channels and downstream proapoptosis signaling after brain ischemia. The present study reveals an additional mechanism for the regulation of GluK2-containing kainate receptors by Src family kinases, which may be of pathological significance in ischemic stroke.

Trafficking of kainate receptors

Ionotropic glutamate receptors (iGluRs) mediate the vast majority of excitatory neurotransmission in the central nervous system of vertebrates. In the protein family of iGluRs, kainate receptors (KARs) comprise the probably least well understood receptor class. Although KARs act as key players in the regulation of synaptic network activity, many properties and functions of these proteins remain elusive until now. Especially the precise pre-, extra-, and postsynaptic localization of KARs plays a critical role for neuronal function, as an unbalanced localization of KARs would ultimately lead to dysregulated neuronal excitability. Recently, important advances in the understanding of the regulation of surface expression, function, and agonist-dependent endocytosis of KARs have been achieved. Post-translational modifications like PKC-mediated phosphorylation and SUMOylation have been reported to critically influence surface expression and endocytosis, while newly discovered auxiliary proteins were shown to shape the functional properties of KARs.

Protective effect of N-acetylcysteine (NAC) on renal ischemia/reperfusion injury through Nrf2 signaling pathway

The aim of this study was to investigate whether N-acetylcysteine (NAC), a known antioxidant, can protect kidney against ischemic injury through regulating Nrf2 signaling pathway. The expression of Nrf2, HO-1 and cleaved caspase 3 were analyzed by Western blot analysis. Apoptosis of renal tubular epithelial cells was assessed by the TUNEL method. Malondialdehyde (MDA) levels were measured by the thiobarbituric acid reaction. Blood serum creatinine and blood urea nitrogen levels were measured with an Olympus automatic multi-analyzer. We found that NAC significantly increased Nrf2 and downstream HO-1 expression. Furthermore, NAC significantly decreased cleaved caspase 3, p53 and renal epithelial tubular cell apoptosis. In addition, NAC reduced the MDA level. These findings suggest that the protective action of NAC on ischemia renal injury is associated closely with Nrf2 signaling pathway.

Increased glutamate receptor and transporter expression in the cerebral cortex and striatum of gcdh-/- mice: possible implications for the neuropathology of glutaric acidemia type I

We determined mRNA expression of the ionotropic glutamate receptors NMDA (NR1, NR2A and NR2B subunits), AMPA (GluR2 subunit) and kainate (GluR6 subunit), as well as of the glutamate transporters GLAST and GLT1 in cerebral cortex and striatum of wild type (WT) and glutaryl-CoA dehydrogenase deficient (Gchh^-/-) mice aged 7, 30 and 60 days. The protein expression levels of some of these membrane proteins were also measured. Overexpression of NR2A and NR2B in striatum and of GluR2 and GluR6 in cerebral cortex was observed in 7-day-old Gcdh^-/-. There was also an increase of mRNA expression of all NMDA subunits in cerebral cortex and of NR2A and NR2B in striatum of 30-day-old Gcdh^-/- mice. At 60 days of life, all ionotropic receptors were overexpressed in cerebral cortex and striatum of Gcdh^-/- mice. Higher expression of GLAST and GLT1 transporters was also verified in cerebral cortex and striatum of Gcdh^-/- mice aged 30 and 60 days, whereas at 7 days of life GLAST was overexpressed only in striatum from this mutant mice. Furthermore, high lysine intake induced mRNA overexpression of NR2A, NR2B and GLAST transcripts in striatum, as well as of GluR2 and GluR6 in both striatum and cerebral cortex of Gcdh^-/- mice. Finally, we found that the protein expression of NR2A, NR2B, GLT1 and GLAST were significantly greater in cerebral cortex of Gcdh^-/- mice, whereas NR2B and GLT1 was similarly enhanced in striatum, implying that these transcripts were translated into their products. These results provide evidence that glutamate receptor and transporter expression is higher in Gcdh^-/- mice and that these alterations may be involved in the pathophysiology of GA I and possibly explain, at least in part, the vulnerability of striatum and cerebral cortex to injury in patients affected by GA I.

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.

GluR6-FasL-Trx2 mediates denitrosylation and activation of procaspase-3 in cerebral ischemia/reperfusion in rats

Global cerebral ischemia/reperfusion (I/R) facilitates the activation of procaspase-3 and promotes apoptosis in hippocampus. But the mechanisms have remained uncharacterized. Protein S-nitrosylation and denitrosylation is an important reversible posttranslational modification, which is a common mechanism in signal transduction and affects numerous physiological and pathophysiological events. However, it is not known whether S-nitrosylation/denitrosylation modification of procaspase-3 serves as a component of apoptosis and cell death induced by cerebral I/R. Here we show that procaspase-3 is significantly denitrosylated and activated after I/R in rat hippocampus. NS102, a glutamate receptor 6 (GluR6) antagonist, can inhibit the denitrosylation of procaspase-3 and diminish the increased Fas ligand (FasL) and thioredoxin (Trx)-2 expression induced by cerebral I/R. Moreover, downregulation of FasL expression by antisense oligodeoxynucleotides inhibits the denitrosylation and activation of procaspase-3. Auranofin, a TrxR inhibitor or TrxR2 antisense oligodeoxynucleotide, has similar effects. In primary hippocampal cultures, Lentiviral-mediated knockdown of FasL and TrxR2 before the oxygen and glucose deprivation/reoxygenation further verifies that FasL and TrxR2 are involved in the denitrosylation of procaspase-3. In situ TUNEL staining and cresyl violet staining validate that inhibiting denitrosylation of procaspase-3 may exert neuroprotective effect on apoptosis and cell death induced by cerebral I/R in hippocampal CA1 pyramidal neurons. This is the first evidence that cerebral I/R mediates procaspase-3 denitrosylation and activation through GluR6-FasL-Trx2 pathway, which leads to neuronal apoptosis and cell death.

Molecular targets underlying SUMO-mediated neuroprotection in brain ischemia

SUMOylation (small ubiquitin-like modifier conjugation) is an important post-translational modification which is becoming increasingly implicated in the altered protein dynamics associated with brain ischemia. The function of SUMOylation in cells undergoing ischemic stress and the identity of small ubiquitin-like modifier (SUMO) targets remain in most cases unknown. However, the emerging consensus is that SUMOylation of certain proteins might be part of an endogenous neuroprotective response. This review brings together the current understanding of the underlying mechanisms and downstream effects of SUMOylation in brain ischemia, including processes such as autophagy, mitophagy and oxidative stress. We focus on recent advances and controversies regarding key central nervous system proteins, including those associated with the nucleus, cytoplasm and plasma membrane, such as glucose transporters (GLUT1, GLUT4), excitatory amino acid transporter 2 glutamate transporters, K+ channels (K2P1, Kv1.5, Kv2.1), GluK2 kainate receptors, mGluR8 glutamate receptors and CB1 cannabinoid receptors, which are reported to be SUMO-modified. A discussion of the roles of these molecular targets for SUMOylation could play following an ischemic event, particularly with respect to their potential neuroprotective impact in brain ischemia, is proposed.

ATPA induced GluR5-containing kainite receptor S-nitrosylation via activation of GluR5-Gq-PLC-IP(3)R pathway and signalling module GluR5·PSD-95·nNOS

GluR5-containing kainite receptor (GluR5-KAR) plays an important role in the pathophysiology of nervous system diseases, while S-nitrosylation exerts a variety of effects on biological systems. However, the mechanism of GluR5-KAR S-nitrosylation is still unclear up to now. Here our researches found that GluR5-KAR selective agonist ATPA stimulation activated the nonclassical GluR5-KAR-Gq-PLC-IP(3)R pathway and the signalling module GluR5·PSD-95·nNOS (the former is more important), led to Ca(2+) release from intracellular calcium stores endoplasmic reticulum (ER) to cytoplasm and extracellular calcium indrawal, respectively, which further resulted in nNOS activation and GluR5-KAR S-nitrosylation, and then inhibited GluR5-mediated whole-cell current attenuation and induced apoptosis in primary cultured hippocampal neurons. Clarification of the primary mechanisms of GluR5-KAR S-nitrosylation induced by ATPA and identification of critical cysteine for GluR5-2a S-nitrosylation (Cys231 and Cys804) open up a brand-new field for revealing downstream signalling pathway of GluR5-KAR and its molecular characteristics, exploring the pathogenesis of neurological diseases and searching for promising therapies.

Curcumin inhibition of JNKs prevents dopaminergic neuronal loss in a mouse model of Parkinson's disease through suppressing mitochondria dysfunction

Curcumin,a natural polyphenol obtained from turmeric,has been implicated to be neuroprotective in a variety of neurodegenerative disorders although the mechanism remains poorly understood. The results of our recent experiments indicated that curcumin could protect dopaminergic neurons from apoptosis in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease (PD). The death of dopaminergic neurons and the loss of dopaminergic axon in the striatum were significantly suppressed by curcumin in MPTP mouse model. Further studies showed that curcumin inhibited JNKs hyperphosphorylation induced by MPTP treatment. JNKs phosphorylation can cause translocation of Bax to mitochondria and the release of cytochrome c which both ultimately contribute to mitochondria-mediated apoptosis. These pro-apoptosis effect can be diminished by curcumin. Our experiments demonstrated that curcumin can prevent nigrostriatal degeneration by inhibiting the dysfunction of mitochondrial through suppressing hyperphosphorylation of JNKs induced by MPTP. Our results suggested that JNKs/mitochondria pathway may be a novel target in the treatment of PD patients.

Kinases and kinase signaling pathways: potential therapeutic targets in Parkinson's disease

Complex molecular mechanisms underlying the pathogenesis of Parkinson's disease (PD) are gradually being elucidated. Accumulating genetic evidence implicates dysfunction of kinase activities and phosphorylation pathways in the pathogenesis of PD. Causative and risk gene products associated with PD include protein kinases (such as PINK1, LRRK2 and GAK) and proteins related phosphorylation signaling pathways (such as SNCA, DJ-1). PINK1, LRRK2 and several PD gene products have been associated with mitogen-activated protein (MAP) and protein kinase B (AKT) kinase signaling pathways. C-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERK) and p38, signaling pathways downstream of MAP, are particularly important in PD. JNK and p38 play an integral role in neuronal death. Targeting JNK or p38 signaling may offer an effective therapy for PD. Inhibitors of the ERK signaling pathway, which plays an important role in the development of l-DOPA-induced dyskinesia (LID), have been shown to attenuate this condition in animal models. In this review, we summarize experimental evidence gathered over the last decade on the role of PINK1, LRRK2 and GAK and their related phosphorylation signaling pathways (JNK, ERK, p38 and PI3K/AKT) in PD. It is speculated that improvement or modulation of these signaling pathways will reveal potential therapeutic targets for attenuation of the cardinal symptoms and motor complications in patients with PD in the future.