Phosphorylation of cAMP response element-binding protein in hippocampal neurons as a protective response after exposure to glutamate in vitro and ischemia in vivo

Unveiling the role of CaMKII in retinal degeneration: from biological mechanism to therapeutic strategies

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a family of broad substrate specificity serine (Ser)/threonine (Thr) protein kinases that play a crucial role in the Ca2+-dependent signaling pathways. Its significance as an intracellular Ca2+ sensor has garnered abundant research interest in the domain of neurodegeneration. Accumulating evidences suggest that CaMKII is implicated in the pathology of degenerative retinopathies such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinitis pigmentosa (RP) and glaucoma optic neuropathy. CaMKII can induce the aberrant proliferation of retinal blood vessels, influence the synaptic signaling, and exert dual effects on the survival of retinal ganglion cells and pigment epithelial cells. Researchers have put forth multiple therapeutic agents, encompassing small molecules, peptides, and nucleotides that possess the capability to modulate CaMKII activity. Due to its broad range isoforms and splice variants therapeutic strategies seek to inhibit specifically the CaMKII are confronted with considerable challenges. Therefore, it becomes crucial to discern the detrimental and advantageous aspects of CaMKII, thereby facilitating the development of efficacious treatment. In this review, we summarize recent research findings on the cellular and molecular biology of CaMKII, with special emphasis on its metabolic and regulatory mechanisms. We delve into the involvement of CaMKII in the retinal signal transduction pathways and discuss the correlation between CaMKII and calcium overload. Furthermore, we elaborate the therapeutic trials targeting CaMKII, and introduce recent developments in the zone of CaMKII inhibitors. These findings would enrich our knowledge of CaMKII, and shed light on the development of a therapeutic target for degenerative retinopathy.

Synergistic effects of citicoline and silymarin nanomicelles in restraint stress-exposed mice

This study evaluated the effects of citicoline and silymarin nanomicelles (SMnm) in repeated restraint stress (RRS).

METHOD

Mice were exposed to RRS for four consecutive days, 2 hrs. daily. On day 5 of the study, SMnm (25 and 50 mg/kg, i.p.) and citicoline (25 and 75 mg/kg), and a combination of them (25 mg/kg, i.p.) were initiated. On day 18, anxiety-like behavior, behavioral despair, and exploratory behavior were evaluated. The prefrontal cortex (PFC) and the hippocampus were dissected measuring brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), and tumor necrosis factor-alpha (TNF-α) through Western Blot and ELISA, respectively.

RESULTS

In RR-exposed mice, anxiety-like behavior in the elevated plus maze (EPM) was enhanced by reductions in open arm time (OAT%) P < 0.001, and open arm entry (OAE%) P < 0.001. In the forced swimming test (FST), the immobility increased P < 0.001 while the swimming and climbing reduced P < 0.001. In the open field test (OFT), general motor activity was raised P < 0.05. Further, body weights reduced P < 0.001, and tissue BDNF and pCREB expressions decreased P < 0.001 while TNF-α increased P < 0.001. Conversely, SMnm, citicoline and their combination could reduce anxiety-like behavior P < 0.001. The combination group reduced the depressive-like behaviors P < 0.001. Moreover, body weights were restored P < 0.001. Besides, BDNF and pCREB expressions increased while TNF-α reduced, P < 0.001.

CONCLUSION

The combination synergistically improved emotion-like behaviors, alleviating the inflammation and upregulating the hippocampal BDNF-mediated CREB signaling pathway.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Research progress and perspectives of N-methyl-D-aspartate receptor in myocardial and cerebral ischemia-reperfusion injury: A review

There is an urgent need to find common targets for precision therapy, as there are no effective preventive therapeutic measures for combined clinical heart-brain organ protection and common pathways associated with glutamate receptors are involved in heart-brain injury, but current glutamate receptor-related clinical trials have failed. Ischemia-reperfusion injury (IRI) is a common pathological condition that occurs in multiple organs, including the heart and brain, and can lead to severe morbidity and mortality. N-methyl-D-aspartate receptor (NMDAR), a type of ionotropic glutamate receptor, plays a crucial role in the pathogenesis of IRI. NMDAR activity is mainly regulated by endogenous activators, agonists, antagonists, and voltage-gated channels, and activation leads to excessive calcium influx, oxidative stress, mitochondrial dysfunction, inflammation, apoptosis, and necrosis in ischemic cells. In this review, we summarize current research advances regarding the role of NMDAR in myocardial and cerebral IRI and discuss potential therapeutic strategies to modulate NMDAR signaling to prevent and treat IRI.

β-Actin: An Emerging Biomarker in Ischemic Stroke

At present, the diagnosis of ischemic stroke mainly depends on neuroimaging technology, but it still has many limitations. Therefore, it is very important to find new biomarkers of ischemic stroke. Recently, β-actin has attracted extensive attention as a biomarker of a variety of cancers. Although several recent studies have been investigating its role in ischemic stroke and other cerebrovascular diseases, the understanding of this emerging biomarker in neurology is still limited. We examined human and preclinical studies to gain a comprehensive understanding of the literature on the subject. Most relevant literatures focus on preclinical research, and pay more attention to the role of β-actin in the process of cerebral ischemia, but some recent literatures reported that in human studies, serum β-actin increased significantly in the early stage of acute cerebral ischemia. This review will investigate the basic biology of β-actin, pay attention to the potential role of serum β-actin as an early diagnostic blood biomarker of ischemic stroke, and explore its potential mechanism in ischemic stroke and new strategies for stroke treatment in the future.

Molecular mechanisms underlying activity-dependent ischemic tolerance in the brain

Ischemic stroke is one of the leading causes of death and disability worldwide. The inhibition of cerebral blood flow triggers intertwined pathological events, resulting in cell death and loss of brain function. Interestingly, animals pre-exposed to short-term ischemia can tolerate subsequent severe ischemia. This phenomenon is called ischemic tolerance and is also triggered by other noxious stimuli. However, whether short-term exposure to non-noxious stimuli can induce ischemic tolerance remains unknown. Recently, we found that pre-exposing mice to an enriched environment for 40 min is sufficient to facilitate cell survival after a subsequent stroke. The neuroprotective process depends on the neuronal activity soon before stroke, of which the activity-dependent transcription factor Npas4 is essential. Excessive Ca²⁺ influx triggers Npas4 expression in ischemic neurons, leading to the activation of neuroprotective programs. Pre-induction of Npas4 in the normal brain effectively supports cell survival after stroke. Furthermore, our study revealed that Npas4 regulates L-type voltage-gated Ca²⁺ channels through expression of the small Ras-like GTPase Gem in ischemic neurons. Ischemic tolerance is a good model for understanding how to promote neuroprotective mechanisms in the normal and injured brain. Here, we highlight activity-dependent ischemic tolerance and discuss its role in promoting neuroprotection against stroke.

CaMKIIα as a Promising Drug Target for Ischemic Grey Matter

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a major mediator of Ca²⁺-dependent signaling pathways in various cell types throughout the body. Its neuronal isoform CaMKIIα (alpha) centrally integrates physiological but also pathological glutamate signals directly downstream of glutamate receptors and has thus emerged as a target for ischemic stroke. Previous studies provided evidence for the involvement of CaMKII activity in ischemic cell death by showing that CaMKII inhibition affords substantial neuroprotection. However, broad inhibition of this central kinase is challenging because various essential physiological processes like synaptic plasticity rely on intact CaMKII regulation. Thus, specific strategies for targeting CaMKII after ischemia are warranted which would ideally only interfere with pathological activity of CaMKII. This review highlights recent advances in the understanding of how ischemia affects CaMKII and how pathospecific pharmacological targeting of CaMKII signaling could be achieved. Specifically, we discuss direct targeting of CaMKII kinase activity with peptide inhibitors versus indirect targeting of the association (hub) domain of CaMKIIα with analogues of γ-hydroxybutyrate (GHB) as a potential way to achieve more specific pharmacological modulation of CaMKII activity after ischemia.

Modulation of α7nAchR by Melatonin Alleviates Ischemia and Reperfusion-Compromised Integrity of Blood-Brain Barrier Through Inhibiting HMGB1-Mediated Microglia Activation and CRTC1-Mediated Neuronal Loss

The only food and drug administration (FDA)-approved drug currently available for the treatment of acute ischemic stroke is tissue plasminogen activator (tPA), yet the therapeutic benefits of this drug are partially outweighed by the increased risk of hemorrhagic transformation (HT). Analysis of the NIH trial has shown that cigarette smoking protected tPA-treated patients from HT; however, the underlying mechanism is not clear. Nicotinic acetylcholine receptors (nAChR) has shown anti-inflammatory effect and modulation nAChR could be a strategy to reduce ischemia/reperfusion-induced blood-brain barrier (BBB) damage. Since melatonin could regulate the expression of α7nAchR and melatonin's neuroprotective effect against ischemic injury is mediated via α7nAChR modulation, here, we aim to test the hypothesis that melatonin reduces ischemia and reperfusion (I/R)-induced BBB damage through modulation of α7nACh receptor (α7nAChR). Mice were subjected to 1.5 h ischemia and 24 h reperfusion and at the onset of reperfusion, mice received intraperitoneal administration (i.p.) of either drug or saline. Mice were randomly assigned into five groups: Saline; α7nAChR agonist PNU282987; Melatonin; Melatonin+Methyllycaconitine (MLA, α7nAChR antagonist), and MLA group. BBB permeability was assessed by detecting the extravasation of Evan's blue and IgG. Our results showed that I/R significantly increased BBB permeability accompanied by occludin degradation, microglia activation, and high mobility group box 1 (HMGB1) release from the neuron. In addition, I/R significantly induced neuronal loss accompanied by the decrease of CREB-regulated transcriptional coactivator 1 (CRTC1) and p-CREB expression. Melatonin treatment significantly inhibited the above changes through modulating α7nAChR. Taken together, these results demonstrate that melatonin provides a protective effect on ischemia/reperfusion-induced BBB damage, at least in part, depending on the modulation of α7nAChR.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer’s and Parkinson’s disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer’s and Parkinson’s disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

Glutamate excitotoxicity: Potential therapeutic target for ischemic stroke

Glutamate-mediated excitotoxicity is an important mechanism leading to post ischemic stroke damage. After acute stroke, the sudden reduction in cerebral blood flow is most initially followed by ion transport protein dysfunction and disruption of ion homeostasis, which in turn leads to impaired glutamate release, reuptake, and excessive N-methyl-D-aspartate receptor (NMDAR) activation, promoting neuronal death. Despite extensive evidence from preclinical studies suggesting that excessive NMDAR stimulation during ischemic stroke is a central step in post-stroke damage, NMDAR blockers have failed to translate into clinical stroke treatment. Current treatment options for stroke are very limited, and there is therefore a great need to develop new targets for neuroprotective therapeutic agents in ischemic stroke to extend the therapeutic time window. In this review, we highlight recent findings on glutamate release, reuptake mechanisms, NMDAR and its downstream cellular signaling pathways in post-ischemic stroke damage, and review the pathological changes in each link to help develop viable new therapeutic targets. We then also summarize potential neuroprotective drugs and therapeutic approaches for these new targets in the treatment of ischemic stroke.

Neuroprotection in Acute Ischemic Stroke: A Battle Against the Biology of Nature

Stroke is the second most common cause of global death following coronary artery disease. Time is crucial in managing stroke to reduce the rapidly progressing insult of the ischemic penumbra and the serious neurologic deficits that might follow it. Strokes are mainly either hemorrhagic or ischemic, with ischemic being the most common of all types of strokes. Thrombolytic therapy with recombinant tissue plasminogen activator and endovascular thrombectomy are the main types of management of acute ischemic stroke (AIS). In addition, there is a vital need for neuroprotection in the setting of AIS. Neuroprotective agents are important to investigate as they may reduce mortality, lessen disability, and improve quality of life after AIS. In our review, we will discuss the main types of management and the different modalities of neuroprotection, their mechanisms of action, and evidence of their effectiveness after ischemic stroke.

Novel interaction between neurotrophic factor-α1/carboxypeptidase E and serotonin receptor, 5-HTR1E, protects human neurons against oxidative/neuroexcitotoxic stress via β-arrestin/ERK signaling

Protecting neurons from death during oxidative and neuroexcitotoxic stress is key for preventing cognitive dysfunction. We uncovered a novel neuroprotective mechanism involving interaction between neurotrophic factor-α1 (NF-α1/carboxypeptidase E, CPE) and human 5-HTR1E, a G protein-coupled serotonin receptor with no previously known neurological function. Co-immunoprecipitation and pull-down assays confirmed interaction between NFα1/CPE and 5-HTR1E and 125I NF-α1/CPE-binding studies demonstrated saturable, high-affinity binding to 5-HTR1E in stably transfected HEK293 cells (Kd = 13.82 nM). Treatment of 5-HTR1E stable cells with NF-α1/CPE increased pERK 1/2 and pCREB levels which prevented a decrease in pro-survival protein, BCL2, during H2O2-induced oxidative stress. Cell survival assay in β-arrestin Knockout HEK293 cells showed that the NF-α1/CPE-5-HTR1E-mediated protection against oxidative stress was β-arrestin-dependent. Molecular dynamics studies revealed that NF-α1/CPE interacts with 5-HTR1E via 3 salt bridges, stabilized by several hydrogen bonds, independent of the serotonin pocket. Furthermore, after phosphorylating the C-terminal tail and intracellular loop 3 (ICL3) of NF-α1/CPE-5-HTR1E, it recruited β-arrestin1 by forming numerous salt bridges and hydrogen bonds to ICL2 and ICL3, leading to activation of β-arrestin1. Immunofluorescence studies showed 5-HTR1E and NF-α1/CPE are highly expressed and co-localized on cell surface of human hippocampal neurons. Importantly, knock-down of 5-HTR1E in human primary neurons diminished the NF-α1/CPE-mediated protection of these neurons against oxidative stress and glutamate neurotoxicity-induced cell death. Thus, NF-α1/CPE uniquely interacts with serotonin receptor 5-HTR1E to activate the β-arrestin/ERK/CREB/BCL2 pathway to mediate stress-induced neuroprotection.

Cofilin Signaling in the CNS Physiology and Neurodegeneration

All eukaryotic cells are composed of the cytoskeleton, which plays crucial roles in coordinating diverse cellular functions such as cell division, morphology, migration, macromolecular stabilization, and protein trafficking. The cytoskeleton consists of microtubules, intermediate filaments, and actin filaments. Cofilin, an actin-depolymerizing protein, is indispensable for regulating actin dynamics in the central nervous system (CNS) development and function. Cofilin activities are spatiotemporally orchestrated by numerous extra- and intra-cellular factors. Phosphorylation at Ser-3 by kinases attenuate cofilin’s actin-binding activity. In contrast, dephosphorylation at Ser-3 enhances cofilin-induced actin depolymerization. Cofilin functions are also modulated by various binding partners or reactive oxygen species. Although the mechanism of cofilin-mediated actin dynamics has been known for decades, recent research works are unveiling the profound impacts of cofilin dysregulation in neurodegenerative pathophysiology. For instance, oxidative stress-induced increase in cofilin dephosphorylation is linked to the accumulation of tau tangles and amyloid-beta plaques in Alzheimer’s disease. In Parkinson’s disease, cofilin activation by silencing its upstream kinases increases α-synuclein-fibril entry into the cell. This review describes the molecular mechanism of cofilin-mediated actin dynamics and provides an overview of cofilin’s importance in CNS physiology and pathophysiology.

Amelioration of lipopolysaccharide-induced memory impairment in equilibrative nucleoside transporter-2 knockout mice is accompanied by the changes in glutamatergic pathways

Neuroinflammation has been implicated in cognitive deficits in neurological and neurodegenerative diseases. Lipopolysaccharide (LPS)-induced neuroinflammation and the breakdown of the blood-brain barrier can be attenuated in mice with equilibrative nucleoside transporter-2 (ENT2/Ent2) deletion. The present study was aimed to investigate the role of ENT2 in cognitive and neuronal functions under physiological and inflammatory conditions, in terms of behavioral performance and synaptic plasticity in saline- and LPS-treated Ent2 knockout (KO) mice and their wild-type (WT) littermate controls. Repeated administrations of LPS significantly impaired spatial memory formation in Morris water maze and hippocampal-dependent long-term potentiation (LTP) in WT mice. The LPS-treated WT mice exhibited significant synaptic and neuronal damage in the hippocampus. Notably, the LPS-induced impairment in spatial memory and LTP performance were attenuated in Ent2 KO mice, along with the preservation of neuronal survival. The beneficial effects were accompanied by the normalization of excessive extracellular glutamate and aberrant downstream signaling of glutamate receptor activation, including the upregulation of phosphorylated p38 mitogen-activated protein kinase and the downregulation of phosphorylated cyclic adenosine monophosphate-response element-binding protein. There was no significant difference in behavioral outcome and all tested parameters between these two genotypes under physiological condition. These results suggest that ENT2 plays an important role in regulating inflammation-associated cognitive decline and neuronal damage.

PAK4 suppresses motor neuron degeneration in hSOD1G93A -linked amyotrophic lateral sclerosis cell and rat models

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons (MN). CREB pathway-mediated inhibition of apoptosis contributes to neuron protection, and PAK4 activates CREB signalling in diverse cell types. This study aimed to investigate PAK4's effect and mechanism of action in ALS.

METHODS

We analysed RNA levels by qRT-PCR, protein levels by immunofluorescence and Western blotting, and apoptosis by flow cytometry and TUNEL staining. Cell transfection was performed for in vitro experiment. Mice were injected intraspinally to evaluate PAK4 function in vivo experiment. Rotarod test was performed to measure motor function.

RESULTS

The expression and activation of PAK4 significantly decreased in the cell and mouse models of ALS as the disease progressed, which was caused by the negative regulation of miR-9-5p. Silencing of PAK4 increased the apoptosis of MN by inhibiting CREB-mediated neuroprotection, whereas overexpression of PAK4 protected MN from hSOD1^G93A -induced degeneration by activating CREB signalling. The neuroprotective effect of PAK4 was markedly inhibited by CREB inhibitor. In ALS models, the PAK4/CREB pathway was inhibited, and cell apoptosis increased. In vivo experiments revealed that PAK4 overexpression in the spinal neurons of hSOD1^G93A mice suppressed MN degeneration, prolonged survival and promoted the CREB pathway.

CONCLUSIONS

PAK4 protects MN from degeneration by activating the anti-apoptotic effects of CREB signalling, suggesting it may be a therapeutic target in ALS.

Activation of the Akt1-CREB pathway promotes RNF146 expression to inhibit PARP1-mediated neuronal death

Progressive degeneration of dopaminergic neurons characterizes Parkinson's disease (PD). This neuronal loss occurs through diverse mechanisms, including a form of programmed cell death dependent on poly(ADP-ribose) polymerase-1 (PARP1) called parthanatos. Deficient activity of the kinase Akt1 and aggregation of the protein α-synuclein are also implicated in disease pathogenesis. Here, we found that Akt1 suppressed parthanatos in dopaminergic neurons through a transcriptional mechanism. Overexpressing constitutively active Akt1 in SH-SY5Y cells or culturing cells with chlorogenic acid (a polyphenol found in coffee that activates Akt1) stimulated the CREB-dependent transcriptional activation of the gene encoding the E3 ubiquitin ligase RNF146. RNF146 inhibited PARP1 not through its E3 ligase function but rather by binding to and sequestering PAR, which enhanced the survival of cultured cells exposed to the dopaminergic neuronal toxin 6-OHDA or α-synuclein aggregation. In mice, intraperitoneal administration of chlorogenic acid activated the Akt1-CREB-RNF146 pathway in the brain and provided neuroprotection against both 6-OHDA and combinatorial α-synucleinopathy in an RNF146-dependent manner. Furthermore, dysregulation of the Akt1-CREB pathway was observed in postmortem brain samples from patients with PD. The findings suggest that therapeutic restoration of RNF146 expression, such as by activating the Akt1-CREB pathway, might halt neurodegeneration in PD.

Natural products improve healthspan in aged mice and rats: A systematic review and meta-analysis

Over the last decades a decrease in mortality has paved the way for late onset pathologies such as cardiovascular, metabolic or neurodegenerative diseases. This evidence has led many researchers to shift their focus from researching ways to extend lifespan to finding ways to increase the number of years spent in good health; "healthspan" is indeed the emerging concept of such quest for ageing without chronic or disabling diseases and dysfunctions. Regular consumption of natural products might improve healthspan, although the mechanisms of action are still poorly understood. Since preclinical studies aimed to assess the efficacy and safety of these compounds are growing, we performed a systematic review and meta-analysis on the effects of natural products on healthspan in mouse and rat models of physiological ageing. Results indicate that natural compounds show robust effects improving stress resistance and cognitive abilities. These promising data call for further studies investigating the underlying mechanisms in more depth.

Safflor Yellow B Attenuates Ischemic Brain Injury via Downregulation of Long Noncoding AK046177 and Inhibition of MicroRNA-134 Expression in Rats

Stroke breaks the oxidative balance in the body and causes extra reactive oxygen species (ROS) generation, leading to oxidative stress damage. Long noncoding RNAs (lncRNAs) and microRNAs play pivotal roles in oxidative stress-mediated brain injury. Safflor yellow B (SYB) was able to effectively reduce ischemia-mediated brain damage by increasing antioxidant capacity and inhibiting cell apoptosis. In this study, we investigated the putative involvement of lncRNA AK046177 and microRNA-134 (miR-134) regulation in SYB against ischemia/reperfusion- (I/R-) induced neuronal injury. I/R and oxygen-glucose deprivation/reoxygenation (OGD/R) were established in vivo and in vitro. Cerebral infarct volume, neuronal apoptosis, and protein expression were detected. The effects of SYB on cell activity, cell respiration, nuclear factor erythroid 2-related factor 2 (Nrf2), antioxidant enzymes, and ROS were evaluated. I/R or OGD/R upregulated the expression of AK046177 and miR-134 and subsequently inhibited the activation and expression of CREB, which caused ROS generation and brain/cell injury. SYB attenuated the effects of AK046177, inhibited miR-134 expression, and promoted CREB activation, which in turn promoted Nrf2 expression, and then increased antioxidant capacities, improved cell respiration, and reduced apoptosis. We suggested that the antioxidant effects of SYB were driven by an AK046177/miR-134/CREB-dependent mechanism that inhibited this pathway, and that SYB has potential use in reducing or possibly preventing I/R-induced neuronal injury.

Impact of a Histone Deacetylase Inhibitor-Trichostatin A on Neurogenesis after Hypoxia-Ischemia in Immature Rats

Hypoxia-ischemia (HI) in the neonatal brain frequently results in neurologic impairments, including cognitive disability. Unfortunately, there are currently no known treatment options to minimize ischemia-induced neural damage. We previously showed the neuroprotective/neurogenic potential of a histone deacetylase inhibitor (HDACi), sodium butyrate (SB), in a neonatal HI rat pup model. The aim of the present study was to examine the capacity of another HDACi—Trichostatin A (TSA)—to stimulate neurogenesis in the subgranular zone of the hippocampus. We also assessed some of the cellular/molecular processes that could be involved in the action of TSA, including the expression of neurotrophic factors (glial cell line-derived neurotrophic factor (GDNF), nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF)) as well as the TrkB receptor and its downstream signalling substrate— cAMP response element-binding protein (CREB). Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by hypoxia for 1 h. TSA was administered directly after the insult (0.2 mg/kg body weight). The study demonstrated that treatment with TSA restored the reduced by hypoxia-ischemia number of immature neurons (neuroblasts, BrdU/DCX-positive) as well as the number of oligodendrocyte progenitors (BrdU/NG2+) in the dentate gyrus of the ipsilateral damaged hemisphere. However, new generated cells did not develop the more mature phenotypes. Moreover, the administration of TSA stimulated the expression of BDNF and increased the activation of the TrkB receptor. These results suggest that BDNF-TrkB signalling pathways may contribute to the effects of TSA after neonatal hypoxic-ischemic injury.

RbAp48 expression and neuronal damage in the gerbil hippocampus following 5 min of transient ischemia

Histone-binding protein RbAp48 has been known to be involved in histone acetylation, and epigenetic alterations of histone modifications are closely associated with the pathogenesis of ischemic reperfusion injury. In the current study, we investigated chronological change of RbAp48 expression in the hippocampus following 5 min of transient ischemia in gerbils. RbAp48 expression was examined 1, 2, 5, and 10 days after transient ischemia using immunohistochemistry. In sham operated gerbils, RbAp48 immunoreactivity was strong in pyramidal and non-pyramidal cells in the hippocampus. After transient ischemia, RbAp48 immunoreactivity was changed in the cornu ammonis 1 subfield (CA1), not in CA2/3. RbAp48 immunoreactivity in CA1 pyramidal neurons was gradually decreased and not detected at 5 and 10 days after ischemia. RbAp48 immunoreactivity in non-pyramidal cells was maintained until 2 days post-ischemia and significantly increased from 5 days post-ischemia. Double immunohistofluorescence staining revealed that RbAp48 immunoreactive non-pyramidal cells were astrocytes. At 5 days post-ischemia, death of pyramidal neurons occurred only in the CA1. These results showed that RbAp48 immunoreactivity was distinctively altered in pyramidal neurons and astrocytes in the hippocampal CA1 following 5 mins of transient ischemia. Ischemia-induced change in RbAp48 expression may be closely associated with neuronal death and astrocyte activation following 5 min of transient ischemia.

Strength exercise suppresses STZ-induced spatial memory impairment and modulates BDNF/ERK-CAMKII/CREB signalling pathway in the hippocampus of mice

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that has generated scientific interest because of its prevalence in the population. Studies indicate that physical exercise promotes neuroplasticity and improves cognitive function in animal models and in human beings. The aim of the present study was to investigate the effects of strength exercise on the hippocampal protein contents and memory performance in mice subjected to a model of sporadic AD induced by streptozotocin (STZ). Swiss mice received two injections of STZ (3 mg/kg, intracerebroventricular). After 21 days, they began physical training using a ladde. Mice performed this protocol for 4 weeks. After the last exercise training session, mice performed the Morris Water Maze test. The samples of hippocampus were excised and used to determine protein contents of brain-derived neurotrophic factor (BDNF), extracellular signal-regulated kinase-Ca²⁺ (ERK), calmodulin-dependent protein kinase (CAMKII) and cAMP-response element-binding protein (CREB) signalling pathway. Strength exercise was effective against the decrease in the time spent and distance travelled in the target quadrant by STZ-injected mice. Strength exercise was also effective against the reduction of mature BDNF, tropomyosin receptor kinase B and neuronal nuclear antigen (NeuN) hippocampal protein levels in STZ mice. The decrease in the hippocampal ratio of pERK/ERK, pCAMKII/CAMKII and pCREB/CREB induced by STZ was reversed by strength exercise. Strength exercise decreased Bax/Bcl2 ratio in the hippocampus of STZ-injected mice. The present study demonstrates that strength exercise modulated the hippocampal BDNF/ERK-CAMKII/CREB signalling pathway and suppressed STZ-induced spatial memory impairment in mice.

Pharmacological Potential of Cilostazol for Alzheimer's Disease

Alzheimer’s disease (AD), a slow progressive form of dementia, is clinically characterized by cognitive dysfunction and memory impairment and neuropathologically characterized by the accumulation of extracellular plaques containing amyloid β-protein (Aβ) and neurofibrillary tangles containing tau in the brain, with neuronal degeneration and high level of oxidative stress. The current treatments for AD, e.g., acetylcholinesterase inhibitors (AChEIs), have efficacies limited to symptom improvement. Although there are various approaches to the disease modifying therapies of AD, none of them can be used alone for actual treatment, and combination therapy may be needed for amelioration of the progression. There are reports that cilostazol (CSZ) suppressed cognitive decline progression in patients with mild cognitive impairment or stable AD receiving AChEIs. Previously, we showed that CSZ suppressed Aβ-induced neurotoxicity in SH-SY5Y cells via coincident inhibition of oxidative stress, as demonstrated by reduced activity of nicotinamide adenine dinucleotide phosphate oxidase, accumulation of reactive oxygen species, and signaling of mitogen-activated protein kinase. CSZ also rescued cognitive impairment and promoted soluble Aβ clearance in a mouse model of cerebral amyloid angiopathy. Mature Aβ fibrils have long been considered the primary neurodegenerative factors in AD; however, recent evidence indicates soluble oligomers to initiate the neuronal and synaptic dysfunction related to AD and other protein-misfolding diseases. Further underscoring the potential of CSZ for AD treatment, we recently described the inhibitory effects of CSZ on Aβ oligomerization and aggregation in vitro. In this review, we discuss the possibility of CSZ as a potential disease-modifying therapy for the prevention or delay of AD.

Therapeutic strategy against ischemic stroke with the concept of neurovascular unit

Stroke is one of the leading causes of death and disability globally. Although thrombolytic therapy by t-PA and mechanical thrombectomy have improved outcomes of ischemic stroke patients, both of these approaches are applicable to limited numbers of patients owing to their time constraints. Therefore, development of other treatment approaches such as developing neuroprotective drugs and nerve regeneration therapy is required to overcome ischemic stroke. The concept of the neurovascular unit (NVU) was formalized by the Stroke Progress Review Group of the National Institute of Neurological Disorders and Stroke in 2001. This concept emphasizes the importance not just of neurons but of the interactions between neurons, endothelial cells, astroglia, microglia and associated tissue matrix proteins to investigate the pathological condition of ischemic stroke. Many reports have been published about these interactions. This review focuses on the roles of cells that surround cerebral vasculature, especially endothelial cells, and reports therapeutic strategies against ischemic stroke from four points of view including angiogenesis, neurotrophic effects, protection of NVU components and regenerative therapy.

Effect of the HDAC Inhibitor, Sodium Butyrate, on Neurogenesis in a Rat Model of Neonatal Hypoxia-Ischemia: Potential Mechanism of Action

Neonatal hypoxic-ischemic (HI) brain injury likely represents the major cause of long-term neurodevelopmental disabilities in surviving babies. Despite significant investigations, there is not yet any known reliable treatment to reduce brain damage in suffering infants. Our recent studies in an animal model of HI revealed the therapeutic potential of a histone deacetylase inhibitor (HDACi). The neuroprotective action was connected with the stimulation of neurogenesis in the dentate gyrus subgranular zone. In the current study, we investigated whether HDACi-sodium butyrate (SB)-would also lead to neurogenesis in the subventricular zone (SVZ). By using a neonatal rat model of hypoxia-ischemia, we found that SB treatment stimulated neurogenesis in the damaged ipsilateral side, based on increased DCX labeling, and restored the number of neuronal cells in the SVZ ipsilateral to lesioning. The neurogenic effect was associated with inhibition of inflammation, expressed by a transition of microglia to the anti-inflammatory phenotype (M2). In addition, the administration of SB increased the activation of the TrkB receptor and the phosphorylation of the transcription factor-CREB-in the ipsilateral hemisphere. In contrast, SB administration reduced the level of HI-induced p75^NTR. Together, these results suggest that BDNF-TrkB signaling plays an important role in SB-induced neurogenesis after HI. These findings provide the basis for clinical approaches targeted at protecting the newborn brain damage, which may prove beneficial for treating neonatal hypoxia-ischemia.

Non-canonical activation of CREB mediates neuroprotection in a Caenorhabditis elegans model of excitotoxic necrosis

Excitotoxicity, caused by exaggerated neuronal stimulation by Glutamate (Glu), is a major cause of neurodegeneration in brain ischemia. While we know that neurodegeneration is triggered by overstimulation of Glu-receptors (GluRs), the subsequent mechanisms that lead to cellular demise remain controversial. Surprisingly, signaling downstream of GluRs can also activate neuroprotective pathways. The strongest evidence involves activation of the transcription factor cAMP response element-binding protein (CREB), widely recognized for its importance in synaptic plasticity. Canonical views describe CREB as a phosphorylation-triggered transcription factor, where transcriptional activation involves CREB phosphorylation and association with CREB-binding protein. However, given CREB's ubiquitous cross-tissue expression, the multitude of cascades leading to CREB phosphorylation, and its ability to regulate thousands of genes, it remains unclear how CREB exerts closely tailored, differential neuroprotective responses in excitotoxicity. A non-canonical, alternative cascade for activation of CREB-mediated transcription involves the CREB co-factor cAMP-regulated transcriptional co-activator (CRTC), and may be independent of CREB phosphorylation. To identify cascades that activate CREB in excitotoxicity we used a Caenorhabditis elegans model of neurodegeneration by excitotoxic necrosis. We demonstrated that CREB's neuroprotective effect was conserved, and seemed most effective in neurons with moderate Glu exposure. We found that factors mediating canonical CREB activation were not involved. Instead, phosphorylation-independent CREB activation in nematode excitotoxic necrosis hinged on CRTC. CREB-mediated transcription that depends on CRTC, but not on CREB phosphorylation, might lead to expression of a specific subset of neuroprotective genes. Elucidating conserved mechanisms of excitotoxicity-specific CREB activation can help us focus on core neuroprotective programs in excitotoxicity. Cover Image for this issue: doi: 10.1111/jnc.14494.

iPlasticity: Induced juvenile-like plasticity in the adult brain as a mechanism of antidepressants

The network hypothesis of depression proposes that mood disorders reflect problems in information processing within particular neural networks. Antidepressants (AD), including selective serotonin reuptake inhibitors (SSRI), function by gradually improving information processing within these networks. AD have been shown to induce a state of juvenile-like plasticity comparable to that observed during developmental critical periods: Such critical-period-like plasticity allows brain networks to better adapt to extrinsic and intrinsic signals. We have coined this drug-induced state of juvenile-like plasticity 'iPlasticity.' A combination of iPlasticity induced by chronic SSRI treatment together with training, rehabilitation, or psychotherapy improves symptoms of neuropsychiatric disorders and issues underlying the developmentally or genetically malfunctioning networks. We have proposed that iPlasticity might be a critical component of AD action. We have demonstrated that iPlasticity occurs in the visual cortex, fear erasure network, extinction of aggression caused by social isolation, and spatial reversal memory in rodent models. Chronic SSRI treatment is known to promote neurogenesis and to cause dematuration of granule cells in the dentate gyrus and of interneurons, especially parvalbumin interneurons enwrapped by perineuronal nets in the prefrontal cortex, visual cortex, and amygdala. Brain-derived neurotrophic factor (BDNF), via its receptor tropomyosin kinase receptor B, is involved in the processes of synaptic plasticity, including neurogenesis, neuronal differentiation, weight of synapses, and gene regulation of synaptic formation. BDNF can be activated by both chronic SSRI treatment and neuronal activity. Accordingly, the BDNF/tropomyosin kinase receptor B pathway is critical for iPlasticity, but further analyses will be needed to provide mechanical insight into the processes of iPlasticity.

Effects of intravenous anesthetics on the phosphorylation of cAMP response element‑binding protein in hippocampal slices of adult mice

cAMP response‑element binding protein (CREB) functions in hippocampal synaptic plasticity and memory formation. However, it remains unknown whether intravenous anesthetics modulate CREB. The present study aimed to examine the effects of intravenous anesthetics on CREB phosphorylation in the mouse hippocampus. CREB phosphorylation was examined in hippocampal slices with and without pharmacological or intravenous anesthetics via immunoblotting. In a dose‑response experiment, the concentrations of intravenous anesthetics ranged from 10‑9 to 10‑4 mol/l for 1 h. For the time‑response experiment, these slices were incubated with 5x10‑6 mol/l of propofol for 0, 1, 2, 5, 7, 9, 12, 15, 30 and 60 min. In order to examine whether CREB phosphorylation could be recovered following washing out the propofol, the slices were incubated in plain artificial cerebrospinal fluid at different time durations following 5 min incubation with propofol. Propofol, etomidate, ketamine and midazolam inhibited CREB phosphorylation (P<0.05) in a time‑ and dose‑dependent manner. This inhibition was reversible following the removal of propofol, and was rescued by CREB phosphorylation (P<0.05). The decrease in CREB phosphorylation revealed additive effects with 100 µM of chelerythrine and 20 µM of PD‑98059, and the etomidate‑induced decrease in CREB phosphorylation was blocked by 1 mM of NMDA. However, 0.1 µM of phorbol 12‑myristate 13‑acetate, 50 µM of U 73122, 100 µM of carbachol and 10 µM of MK801 were ineffective in the anesthetic‑induced decrease in CREB phosphorylation. Intravenous anesthetics markedly decreased CREB phosphorylation in the mouse hippocampus, which was most likely via the protein kinase C and mitogen activated protein kinase pathways. This suggests that CREB represents a target for anesthetic action in the brain.

Expression of Hypoxia Inducible Factor 1alpha Is Protein Kinase A-dependent in Primary Cortical Astrocytes Exposed to Severe Hypoxia

The hypoxia inducible factor 1 (HIF-1) and the cyclic AMP-responsive element binding protein (CREB) are two transcription factors that have been studied in the context of neuronal survival and neurodegeneration. HIF-1 upregulation and CREB activation have been observed not only in neurons but also in astrocytes under conditions of hypoxia. We hypothesized that activation of CREB regulate HIF-1α expression in the nucleus of cortical astrocytes under in vitro ischemic condition. To test the hypothesis, we determined the effects of inhibiting the CREB activation pathway on the expression of HIF-1α protein in astrocytes exposed to CoCl₂ and severe hypoxia (near anoxia, 0.1% O₂). The results demonstrated that inhibition of CaMKII and CaMKIV had no effect on both HIF-1α and pCREB expression in cortical astrocytes exposed to CoCl₂ and anoxia. In contrast, PKA inhibition lowered the expression of HIF-1α and pCREB expression. Furthermore, the inhibition of PKA but not CaMKII or CaMKIV increased cell death of astrocytes exposed to near anoxia. The results suggest that PKA plays an important role in the cell survival signaling pathways in astrocytes.

Nigral dopaminergic PAK4 prevents neurodegeneration in rat models of Parkinson's disease

Parkinson's disease (PD) is characterized by progressive loss of dopaminergic (DA) neurons in the substantia nigra. No neuroprotective treatments have successfully prevented the progression of this disease. We report that p21-activated kinase 4 (PAK4) is a key survival factor for DA neurons. We observed PAK4 immunoreactivity in rat and human DA neurons in brain tissue, but not in microglia or astrocytes. PAK4 activity was markedly decreased in postmortem brain tissue from PD patients and in rodent models of PD. Expression of constitutively active PAK4^S445N/S474E (caPAK4) protected DA neurons in both the 6-hydroxydopamine and α-synuclein rat models of PD and preserved motor function. This neuroprotective effect of caPAK4 was mediated by phosphorylation of CRTC1 [CREB (adenosine 3',5'-monophosphate response element-binding protein)-regulated transcription coactivator] at S215. The nonphosphorylated form of CRTC1^S215A compromised the ability of caPAK4 to induce the expression of the CREB target proteins Bcl-2, BDNF, and PGC-1α. Our results support a neuroprotective role for the PAK4-CRTC1^S215-CREB signaling pathway and suggest that this pathway may be a useful therapeutic target in PD.

Autonomous CaMKII Activity as a Drug Target for Histological and Functional Neuroprotection after Resuscitation from Cardiac Arrest

The Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a major mediator of physiological glutamate signaling, but its role in pathological glutamate signaling (excitotoxicity) remains less clear, with indications for both neurotoxic and neuro-protective functions. Here, the role of CaMKII in ischemic injury is assessed utilizing our mouse model of cardiac arrest and cardiopulmonary resuscitation (CA/CPR). CaMKII inhibition (with tatCN21 or tatCN19o) at clinically relevant time points (30 min after resuscitation) greatly reduces neuronal injury. Importantly, CaMKII inhibition also works in combination with mild hypothermia, the current standard of care. The relevant drug target is specifically Ca²⁺-independent “autonomous” CaMKII activity generated by T286 autophosphorylation, as indicated by substantial reduction in injury in autonomy-incompetent T286A mutant mice. In addition to reducing cell death, tatCN19o also protects the surviving neurons from functional plasticity impairments and prevents behavioral learning deficits, even at extremely low doses (0.01 mg/kg), further highlighting the clinical potential of our findings.

Efficacy of alogliptin combined with motor imagery under hyperbaric oxygen in diabetic nephropathy with silent cerebral infarction

In the present study, we evaluated the curative effect of dipeptidyl peptidase-IV (DPP-IV) inhibitor alogliptin combined with motor imagery under hyperbaric oxygen in diabetic nephropathy (DN) with silent cerebral infarction (SCI). Two-hundred newly diagnosed DN patients with and without SCI were included. The SCI patients were divided into two treatment groups: Alogliptin (A group, n=50) and alogliptin combined with motor imagery under hyperbaric oxygen (B group, n=50). The degrees of neurocognitive dysfunction were evaluated at baseline and after 6 months of treatment. Thromboelastograms (TEGs) mapping were conducted. Serum glycoprotein VI (GPVI) mRNA expression and urine 11-DH-TXB₂ levels were determined. Compared to group A patients, the severity of neurofunctional defects, GPVI mRNA expression and 11-DH-TXB₂ levels were significantly lower in group B (P<0.05), while comprehensive, MoCA scores were higher in group B. The MoCA subscores of visuospatial/executive function, attention and concentration were significantly higher compared to group A (P<0.05). The sub-scores of computation, abstract thinking, language competence, memory and orientation were also higher in group B but the differences were not significant (P>0.05). TEG indexes were improved in both groups after treatment as manifested by increased R and K values, but there was significant improvement in group B. Intra-group comparisons revealed a time-dependent effect of treatment. In conclusion, the treatment of alogliptin combined with motor imagery under hyperbaric oxygen can better promote thrombolysis absorption, restore brain damage and improve neurocognitive function in DN with silent cerebral infarction.

Cilostazol ameliorates collagenase-induced cerebral hemorrhage by protecting the blood-brain barrier

Intracranial hemorrhage remains a devastating disease. Among antiplatelet drugs, cilostazol, a phosphodiesterase 3 inhibitor, was recently reported to prevent secondary hemorrhagic stroke in patients in a clinical trial. The aim of this study was to evaluate whether pre-treatment with cilostazol could decrease the intracranial hemorrhage volume and examine the protective mechanisms of cilostazol. We evaluated the pre-treatment effects of the antiplatelet drug cilostazol on the collagenase-induced intracranial hemorrhage volume and neurological outcomes in mice. To estimate the mechanism of collagenase injury, we evaluated various vascular components in vitro, including endothelial cells, vascular smooth muscle cells, pericytes, and a blood-brain barrier model. Cilostazol pre-treatment reduced the intracranial hemorrhage volume with sufficient inhibition of platelet aggregation, and motor function was improved by cilostazol treatment. Blood-brain barrier permeability was increased by collagenase-induced intracranial hemorrhage, and cilostazol attenuated blood-brain barrier leakage. Terminal deoxynucleotidyl transferase dUTP nick-end labeling and western blot analysis showed that cilostazol prevented pericyte cell death by inducing cyclic adenosine monophosphate-responsive element-binding protein phosphorylation. Cilostazol also prevented endothelial cell death and protected collagen type 4, laminin, and vascular endothelial- and N-cadherins from collagenase injury. In conclusion, cilostazol reduced collagenase-induced intracranial hemorrhage volume by protecting the blood-brain barrier.

Electroacupuncture Ameliorates Learning and Memory and Improves Synaptic Plasticity via Activation of the PKA/CREB Signaling Pathway in Cerebral Hypoperfusion

Electroacupuncture (EA) has shown protective effects on cognitive decline. However, the underlying molecular mechanisms are ill-understood. The present study was undertaken to determine whether the cognitive function was ameliorated in cerebral hypoperfusion rats following EA and to investigate the role of PKA/CREB pathway. We used a rat 2-vessel occlusion (2VO) model and delivered EA at Baihui (GV20) and Dazhui (GV14) acupoints. Morris water maze (MWM) task, electrophysiological recording, Golgi silver stain, Nissl stain, Western blot, and real-time PCR were employed. EA significantly (1) ameliorated the spatial learning and memory deficits, (2) alleviated long-term potentiation (LTP) impairment and the reduction of dendritic spine density, (3) suppressed the decline of phospho-CREB (pCREB) protein, brain-derived neurotrophic factor (BDNF) protein, and microRNA132 (miR132), and (4) reduced the increase of p250GAP protein of 2VO rats. These changes were partially blocked by a selective protein kinase A (PKA) inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide (H89), suggesting that the PKA/CREB pathway is potentially involved in the effects of EA. Moreover, any significant damage to the pyramidal cell layer of CA1 subregion was absent. These results demonstrated that EA could ameliorate learning and memory deficits and alleviate hippocampal synaptic plasticity impairment of cerebral hypoperfusion rats, potentially mediated by PKA/CREB signaling pathway.

Serine racemase inhibition induces nitric oxide-mediated neurovascular protection during cerebral ischemia

There are no effective neuroprotectant drugs for acute cerebral ischemia. Serine racemase (SR) synthesizes d-serine, which is involved in N-methyl-d-aspartate (NMDA) receptor-induced neurotoxicity. Recently, SR deletion was reported to protect against focal cerebral ischemia. However, regulatory mechanisms controlling SR-activity in the neurovascular unit (NVU) during cerebral ischemia remain to be clarified. We investigated the effects of SR inhibition on neurovascular protection after ischemia. The SR inhibitor phenazine methosulfate (PMS) alleviated neuronal damage in an ex vivo ischemic model (oxygen glucose deprivation [OGD]) using primary neuronal cultures, and in an in vivo mouse model of ischemia (middle cerebral artery occlusion [MCAO]). Ischemic preconditioning (IP) and PMS-treatment inhibited SR phosphorylation after ischemia ex vivo. In addition, SR phosphorylation after MCAO was also decreased in PMS-treated mice. Reductions in regional cerebral blood flow (CBF) after MCAO were improved by administration of PMS. Treatment with PMS increased phosphorylation of endothelial nitric oxide synthase (eNOS) in the ischemic core and penumbra region. In neuron-endothelial cell co-cultures, PMS promoted nitric oxide production after OGD. These findings indicate that SR inhibition acts as a neuroprotectant in the NVU and ameliorant of CBF abnormalities post-stroke. Thus, pharmacologic SR inhibition has potential clinical applications.

A Coral-Derived Compound Improves Functional Recovery after Spinal Cord Injury through Its Antiapoptotic and Anti-Inflammatory Effects

Background: Our previous in vitro results demonstrated that 11-dehydrosinulariolide significantly reduced 6-hydroxydopamine-induced cytotoxicity and apoptosis in a human neuroblastoma cell line, SH-SY5Y, and suppressed the expression of inducible NO synthase (iNOS) and cyclooxygenase 2 in lipopolysaccharide-stimulated macrophage cells. The neuroprotective and anti-inflammatory effects of 11-dehydrosinulariolide may be suitable for treating spinal cord injury (SCI). Methods: In the present study, Wistar rats were pretreated with 11-dehydrosinulariolide or saline through intrathecal injection after a thoracic spinal cord contusion injury induced using a New York University (NYU) impactor. The apoptotic cells were assessed using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The expression and localization of proinflammatory, apoptosis-associated and cell survival-related pathway proteins were examined through immunoblotting and immunohistochemistry. Results: 11-Dehydrosinulariolide attenuated SCI-induced cell apoptosis by upregulating the antiapoptotic protein Bcl-2 and cell survival-related pathway proteins p-Akt and p-ERK, 8 h after SCI. Furthermore, the transcription factor p-CREB, which regulates Bcl-2 expression, was upregulated after 11-dehydrosinulariolide treatment. On day 7 after SCI, 11-dehydrosinulariolide exhibited an anti-inflammatory effect, attenuating SCI-induced upregulation of the inflammatory proteins iNOS and tumor necrosis factor-α. 11-Dehydrosinulariolide also induced an increase in the expression of arginase-1 and CD206, markers of M2 microglia, in the injured spinal cord on day 7 after SCI. Thus, the anti-inflammatory effect of 11-dehydrosinulariolide may be related to the promotion of an alternative pathway of microglia activation. Conclusion: The results show that 11-dehydrosinulariolide exerts antiapoptotic effects at 8 h after SCI and anti-inflammatory effects at 7 days after SCI. We consider that this compound may be a promising therapeutic agent for SCI.

Ferulic Acid Administered at Various Time Points Protects against Cerebral Infarction by Activating p38 MAPK/p90RSK/CREB/Bcl-2 Anti-Apoptotic Signaling in the Subacute Phase of Cerebral Ischemia-Reperfusion Injury in Rats

Objectives

This study aimed to evaluate the effects of ferulic acid (FA) administered at various time points before or after 30 min of middle cerebral artery occlusion (MCAo) followed by 7 d of reperfusion and to examine the involvement of mitogen-activated protein kinase (MAPK) signaling pathways in the cortical penumbra.

Methods

FA was intravenously administered to rats at a dose of 100 mg/kg 24 h before ischemia (B-FA), 2 h before ischemia (P-FA), immediately after ischemic insult (I-FA), 2 h after reperfusion (R-FA), or 24 h after reperfusion (D-FA).

Results

Our study results indicated that P-FA, I-FA, and R-FA effectively reduced cerebral infarct areas and neurological deficits. P-FA, I-FA, and R-FA significantly downregulated glial fibrillary acidic protein (GFAP), mitochondrial Bax, cytochrome c, and cleaved caspase-3 expression, and effectively restored the phospho-p38 MAPK (p-p38 MAPK)/p38 MAPK ratio, phospho-90 kDa ribosomal S6 kinase (p-p90RSK) expression, phospho-Bad (p-Bad) expression, the phospho-cAMP response element-binding protein (p-CREB)/CREB ratio, the cytosolic and mitochondrial Bcl-2/Bax ratios, and the cytosolic Bcl-xL/Bax ratio in the cortical penumbra 7 d after reperfusion. SB203580, a specific inhibitor of p38 MAPK, administered 30 min prior to ischemia abrogated the downregulating effects of I-FA on cerebral infarction, and mitochondrial Bax and cleaved caspase-3 expression, and the upregulating effects of I-FA on the p-p38 MAPK/p38 MAPK ratio, p-p90RSK expression, p-Bad expression, and the p-CREB/CREB, and cytosolic and mitochondrial Bcl-2/Bax ratios.

Conclusions

Our study results thus indicate that P-FA, I-FA, and R-FA effectively suppress reactive astrocytosis and exert neuroprotective effects against cerebral infarction by activating p38 MAPK signaling. The regulating effects of P-FA, I-FA, and R-FA on Bax-induced apoptosis result from activation of the p38 MAPK/p90RSK/CREB/Bcl-2 signaling pathway, and eventually contribute to inhibition of the cytochrome c-mediated caspase-3-dependent apoptotic pathway in the cortical penumbra 7 d after reperfusion.

Luteolin rescues pentylenetetrazole-induced cognitive impairment in epileptic rats by reducing oxidative stress and activating PKA/CREB/BDNF signaling

Most antiepileptic drugs (AEDs) interfere with cognitive function, and there is therefore an urgent need for AEDs that are effective but do not have this side effect. Various studies have reported the antiinflammatory and cytoprotective properties of the natural flavonoid luteolin (LU); however, none has examined systematically its antiseizure potential. The current study investigated the effects of LU on pentylenetetrazole (PTZ)-induced cognitive impairment in rats and the underlying mechanisms. Seizures were induced in rats by daily injection of PTZ for 36 days. Two other groups were pretreated with LU (50 or 100 mg/kg/day by oral administration) 30 min prior to PTZ administration. Seizure severity was scored, and cognitive function was tested in the Morris water maze. Neuronal damage, mitochondrial generation of reactive oxygen species, oxidative stress, phosphoactivation of the protein kinase A (PKA)-cyclic AMP response element-binding protein (CREB) pathway, and brain-derived neurotrophic factor (BDNF) expression were measured in the hippocampus. Pretreatment with LU suppressed seizure induction, duration, and severity following PTZ injection, reversed cognitive impairment, reduced neuronal and oxidative stress damage, and increased phosphoactivation of PKA and CREB as well as BDNF expression. These results indicate that LU should be further investigated as a treatment for epilepsy.

Cofilin as a Promising Therapeutic Target for Ischemic and Hemorrhagic Stroke

Neurovascular unit (NVU) is considered as a conceptual framework for investigating the mechanisms as well as developing therapeutic targets for ischemic and hemorrhagic stroke. From a molecular perspective, oxidative stress, excitotoxicity, inflammation, and disruption of the blood brain barrier are broad pathophysiological frameworks on the basis on which potential therapeutic candidates for ischemic and hemorrhagic stroke could be discussed. Cofilin is a potent actin-binding protein that severs and depolymerizes actin filaments in order to generate the dynamics of the actin cytoskeleton. Although studies of the molecular mechanisms of cofilin-induced reorganization of the actin cytoskeleton have been ongoing for decades, the multicellular functions of cofilin and its regulation in different molecular pathways are expanding beyond its primary role in actin cytoskeleton. This review focuses on the role of cofilin in oxidative stress, excitotoxicity, inflammation, and disruption of the blood brain barrier in the context of NVU as well as how and why cofilin could be studied further as a potential target for ischemic and hemorrhagic stroke.

Transcription factor cyclic adenosine monophosphate responsive element binding protein negatively regulates tumor necrosis factor alpha-induced protein 1 expression

Tumor necrosis factor alpha (TNFα)-induced protein 1 (TNFAIP1) was originally identified as a protein involved in DNA replication, DNA damage repair, apoptosis and the progression of certain diseases, such as Alzheimer's disease. In the present study, forskolin, a stimulant of cyclic adenosine monophosphate (cAMP), was found to significantly reduce human TNFAIP1 mRNA levels and TNFAIP1 promoter activity in the SKNSH human neuroblastoma cell line as indicated by polymerase chain reaction analysis and a luciferase reporter assay. The association between transcription factor cAMP response element‑binding protein (CREB) and TNFAIP1 was further investigated using loss- and gain of function-studies with western blot analysis and luciferase reporter assays. The CREB-specific inhibitor KG‑501 significantly increased TNFAIP1 protein levels, while overexpression of wild‑type CREB, but not CREB mutated at ser133a or its DNA-binding site, significantly decreased human TNFAIP1 protein levels and TNFAIP1 promoter activity in SKNSH cells. Furthermore, two CRE sites located at ‑285 and ‑425 bp of the human TNFAIP1 promoter were identified to be responsible for CREB‑induced inhibition of human TNFAIP1 promoter activity. Chromatin immunoprecipitation assays confirmed that CREB bound to the TNFAIP1 promoter region harboring these two CRE sites. A further luciferase reporter assay demonstrated that CREB phosphorylation on ser133 was responsible for forskolin‑induced inhibition of TNFAIP1 expression. In conclusion, the present study suggested that CREB is a negative regulator of the TNFAIP1 gene.

Synergistic neuroprotection by epicatechin and quercetin: Activation of convergent mitochondrial signaling pathways

In view of evidence that increased consumption of epicatechin (E) and quercetin (Q) may reduce the risk of stroke, we have measured the effects of combining E and Q on mitochondrial function and neuronal survival following oxygen-glucose deprivation (OGD). Relative to mouse cortical neuron cultures pretreated (24h) with either E or Q (0.1-10μM), E+Q synergistically attenuated OGD-induced neuronal cell death. E, Q and E+Q (0.3μM) increased spare respiratory capacity but only E+Q (0.3μM) preserved this crucial parameter of neuronal mitochondrial function after OGD. These improvements were accompanied by corresponding increases in cyclic AMP response element binding protein (CREB) phosphorylation and the expression of CREB-target genes that promote neuronal survival (Bcl-2) and mitochondrial biogenesis (PGC-1α). Consistent with these findings, E+Q (0.1 and 1.0μM) elevated mitochondrial gene expression (MT-ND2 and MT-ATP6) to a greater extent than E or Q after OGD. Q (0.3-3.0μM), but not E (3.0μM), elevated cytosolic calcium (Ca(2+)) spikes and the mitochondrial membrane potential. Conversely, E and E+Q (0.1 and 0.3μM), but not Q (0.1 and 0.3μM), activated protein kinase B (Akt). Nitric oxide synthase (NOS) inhibition with L-N(G)-nitroarginine methyl ester (1.0μM) blocked neuroprotection by E (0.3μM) or Q (1.0μM). Oral administration of E+Q (75mg/kg; once daily for 5days) reduced hypoxic-ischemic brain injury. These findings suggest E and Q activate Akt- and Ca(2+)-mediated signaling pathways that converge on NOS and CREB resulting in synergistic improvements in neuronal mitochondrial performance which confer profound protection against ischemic injury.

Gene Transfer of Glutamic Acid Decarboxylase 67 by Herpes Simplex Virus Vectors Suppresses Neuropathic Pain Induced by Human Immunodeficiency Virus gp120 Combined with ddC in Rats

BACKGROUND

Human immunodeficiency virus (HIV)-related painful sensory neuropathies primarily consist of the HIV infection-related distal sensory polyneuropathy and antiretroviral toxic neuropathies. Pharmacotherapy provides only partial relief of pain in patients with HIV/acquired immune deficiency syndrome because little is known about the exact neuropathological mechanisms for HIV-associated neuropathic pain (NP). Hypofunction of γ-aminobutyric acid (GABA) GABAergic inhibitory mechanisms has been reported after peripheral nerve injury. In this study, we tested the hypothesis that HIV gp120 combined with antiretroviral therapy reduces spinal GABAergic inhibitory tone and that restoration of GABAergic inhibitory tone will reduce HIV-related NP in a rat model.

METHODS

The application of recombinant HIV-1 envelope protein gp120 into the sciatic nerve plus systemic ddC (one antiretroviral drug) induced mechanical allodynia. The hind paws of rats were inoculated with replication-defective herpes simplex virus (HSV) vectors genetically encoding gad1 gene to express glutamic acid decarboxylase 67 (GAD67), an enzyme that catalyzes the decarboxylation of glutamate to GABA. Mechanical threshold was tested using von Frey filaments before and after treatments with the vectors. The expression of GAD67 in both the lumbar spinal cord and the L4-5 dorsal root ganglia was examined using western blots. The expression of mitochondrial superoxide in the spinal dorsal horn was examined using MitoSox imaging. The immunoreactivity of spinal GABA, pCREB, and pC/EBPβ was tested using immunohistochemistry.

RESULTS

In the gp120 with ddC-induced neuropathic pain model, GAD67 expression mediated by the HSV vector caused an elevation of mechanical threshold that was apparent on day 3 after vector inoculation. The antiallodynic effect of the single HSV vector inoculation expressing GAD67 lasted >28 days. The area under the time-effect curves in the HSV vector expressing GAD67 was increased compared with that in the control vectors (P = 0.0005). Intrathecal GABA-A/B agonists elevated mechanical threshold in the pain model. The HSV vectors expressing GAD67 reversed the lowered GABA immunoreactivity in the spinal dorsal horn in the neuropathic rats. HSV vectors expressing GAD67 in the neuropathic rats reversed the increased signals of mitochondrial superoxide in the spinal dorsal horn. The vectors expressing GAD67 reversed the upregulated immunoreactivity expression of pCREB and pC/EBPβ in the spinal dorsal horn in rats exhibiting NP.

CONCLUSIONS

Based on our results, we suggest that GAD67 mediated by HSV vectors acting through the suppression of mitochondrial reactive oxygen species and transcriptional factors in the spinal cord decreases pain in the HIV-related neuropathic pain model, providing preclinical evidence for gene therapy applications in patients with HIV-related pain states.

AMPA receptor desensitization is the determinant of AMPA receptor mediated excitotoxicity in purified retinal ganglion cells

The ionotropic glutamate receptors (iGLuR) have been hypothesized to play a role in neuronal pathogenesis by mediating excitotoxic death. Previous studies on iGluR in the retina have focused on two broad classes of receptors: NMDA and non-NMDA receptors including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) and kainate receptor. In this study, we examined the role of receptor desensitization on the specific excitotoxic effects of AMPAR activation on primary retinal ganglion cells (RGCs). Purified rat RGCs were isolated from postnatal day 4-7 Sprague-Dawley rats. Calcium imaging was used to identify the functionality of the AMPARs and selectivity of the s-AMPA agonist. Phosphorylated CREB and ERK1/2 expression were performed following s-AMPA treatment. s-AMPA excitotoxicity was determined by JC-1 mitochondrial membrane depolarization assay, caspase 3/7 luciferase activity assay, immunoblot analysis for α-fodrin, and Live (calcein AM)/Dead (ethidium homodimer-1) assay. RGC cultures of 98% purity, lacking Iba1 and GFAP expression were used for the present studies. Isolated prenatal RGCs expressed calcium permeable AMPAR and s-AMPA (100 μM) treatment of cultured RGCs significantly increased phosphorylation of CREB but not that of ERK1/2. A prolonged (6 h) AMPAR activation in purified RGCs using s-AMPA (100 μM) did not depolarize the RGC mitochondrial membrane potential. In addition, treatment of cultured RGCs with s-AMPA, both in the presence and absence of trophic factors (BDNF and CNTF), did not increase caspase 3/7 activities or the cleavage of α-fodrin (neuronal apoptosis marker), as compared to untreated controls. Lastly, a significant increase in cell survival of RGCs was observed after s-AMPA treatment as compared to control untreated RGCs. However, preventing the desensitization of AMPAR with the treatment with either kainic acid (100 μM) or the combination of s-AMPA and cyclothiazide (50 μM) significantly reduced cell survivability. Activation of the AMPAR in RGCs does not appear to activate a signaling cascade to apoptosis, suggesting that RGCs in vitro are not susceptible to AMPA excitotoxicity as previously hypothesized. Conversely, preventing AMPAR desensitization through differential agonist activation caused AMPAR mediated excitotoxicity. Activation of the AMPAR in increasing CREB phosphorylation was dependent on the presence of calcium, which may help explain this action in increasing RGC survival.