Extracellular-signal-regulated kinase signalling in neurons

Beyond PDE4 inhibition: A comprehensive review on downstream cAMP signaling in the central nervous system

Cyclic adenosine monophosphate (cAMP) is a key second messenger that regulates signal transduction pathways pivotal for numerous biological functions. Intracellular cAMP levels are spatiotemporally regulated by their hydrolyzing enzymes called phosphodiesterases (PDEs). It has been shown that increased cAMP levels in the central nervous system (CNS) promote neuroplasticity, neurotransmission, neuronal survival, and myelination while suppressing neuroinflammation. Thus, elevating cAMP levels through PDE inhibition provides a therapeutic approach for multiple CNS disorders, including multiple sclerosis, stroke, spinal cord injury, amyotrophic lateral sclerosis, traumatic brain injury, and Alzheimer's disease. In particular, inhibition of the cAMP-specific PDE4 subfamily is widely studied because of its high expression in the CNS. So far, the clinical translation of full PDE4 inhibitors has been hampered because of dose-limiting side effects. Hence, focusing on signaling cascades downstream activated upon PDE4 inhibition presents a promising strategy, offering novel and pharmacologically safe targets for treating CNS disorders. Yet, the underlying downstream signaling pathways activated upon PDE(4) inhibition remain partially elusive. This review provides a comprehensive overview of the existing knowledge regarding downstream mediators of cAMP signaling induced by PDE4 inhibition or cAMP stimulators. Furthermore, we highlight existing gaps and future perspectives that may incentivize additional downstream research concerning PDE(4) inhibition, thereby providing novel therapeutic approaches for CNS disorders.

GR/P300 Regulates MKP1 Signaling Pathway and Mediates Depression-like Behavior in Prenatally Stressed Offspring

Accumulating evidence suggests that prenatal stress (PNS) increases offspring susceptibility to depression, but the underlying mechanisms remain unclear. We constructed a mouse model of prenatal stress by spatially restraining pregnant mice from 09:00-11:00 daily on Days 5-20 of gestation. In this study, western blot analysis, quantitative real-time PCR (qRT‒PCR), immunofluorescence, immunoprecipitation, chromatin immunoprecipitation (ChIP), and mifepristone rescue assays were used to investigate alterations in the GR/P300-MKP1 and downstream ERK/CREB/TRKB pathways in the brains of prenatally stressed offspring to determine the pathogenesis of the reduced neurogenesis and depression-like behaviors in offspring induced by PNS. We found that prenatal stress leads to reduced hippocampal neurogenesis and depression-like behavior in offspring. Prenatal stress causes high levels of glucocorticoids to enter the fetus and activate the hypothalamic‒pituitary‒adrenal (HPA) axis, resulting in decreased hippocampal glucocorticoid receptor (GR) levels in offspring. Furthermore, the nuclear translocation of GR and P300 (an acetylation modifying enzyme) complex in the hippocampus of PNS offspring increased significantly. This GR/P300 complex upregulates MKP1, which is a negative regulator of the ERK/CREB/TRKB signaling pathway associated with depression. Interestingly, treatment with a GR antagonist (mifepristone, RU486) increased hippocampal GR levels and decreased MKP1 expression, thereby ameliorating abnormal neurogenesis and depression-like behavior in PNS offspring. In conclusion, our study suggested that the regulation of the MKP1 signaling pathway by GR/P300 is involved in depression-like behavior in prenatal stress-exposed offspring and provides new insights and ideas for the fetal hypothesis of mental health.

Calcium Dyshomeostasis Drives Pathophysiology and Neuronal Demise in Age-Related Neurodegenerative Diseases

This review postulates that age-related neurodegeneration entails inappropriate activation of intrinsic pathways to enable brain plasticity through deregulated calcium (Ca2+) signalling. Ca2+ in the cytosol comprises a versatile signal controlling neuronal cell physiology to accommodate adaptive structural and functional changes of neuronal networks (neuronal plasticity) and, as such, is essential for brain function. Although disease risk factors selectively affect different neuronal cell types across age-related neurodegenerative diseases (NDDs), these appear to have in common the ability to impair the specificity of the Ca2+ signal. As a result, non-specific Ca2+ signalling facilitates the development of intraneuronal pathophysiology shared by age-related NDDs, including mitochondrial dysfunction, elevated reactive oxygen species (ROS) levels, impaired proteostasis, and decreased axonal transport, leading to even more Ca2+ dyshomeostasis. These core pathophysiological processes and elevated cytosolic Ca2+ levels comprise a self-enforcing feedforward cycle inevitably spiralling toward high levels of cytosolic Ca2+. The resultant elevated cytosolic Ca2+ levels ultimately gear otherwise physiological effector pathways underlying plasticity toward neuronal demise. Ageing impacts mitochondrial function indiscriminately of the neuronal cell type and, therefore, contributes to the feedforward cycle of pathophysiology development seen in all age-related NDDs. From this perspective, therapeutic interventions to safely restore Ca2+ homeostasis would mitigate the excessive activation of neuronal destruction pathways and, therefore, are expected to have promising neuroprotective potential.

A, B, C's of Trk Receptors and Their Ligands in Ocular Repair

Neurotrophins are a family of closely related secreted proteins that promote differentiation, development, and survival of neurons, which include nerve growth factor (NGF), brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4. All neurotrophins signal through tropomyosin receptor kinases (TrkA, TrkB, and TrkC) which are more selective to NGF, brain-derived neurotrophic factor, and neurotrophin-3, respectively. NGF is the most studied neurotrophin in the ocular surface and a human recombinant NGF has reached clinics, having been approved to treat neurotrophic keratitis. Brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4 are less studied neurotrophins in the ocular surface, even though brain-derived neurotrophic factor is well characterized in glaucoma, retina, and neuroscience. Recently, neurotrophin analogs with panTrk activity and TrkC selectivity have shown promise as novel drugs for treating dry eye disease. In this review, we discuss the biology of the neurotrophin family, its role in corneal homeostasis, and its use in treating ocular surface diseases. There is an unmet need to investigate parenteral neurotrophins and its analogs that activate TrkB and TrkC selectively.

Nicotine self-administration and ERK signaling are altered in RasGRF2 knockout mice

Ras/Raf/MEK/ERK (Ras-ERK) signaling has been demonstrated to play a role in the effects of drugs of abuse such as cocaine and alcohol, but has not been extensively examined in nicotine-related reward behaviors. We examined the role of Ras Guanine Nucleotide Releasing Factor 2 (RasGRF2), an upstream mediator of the Ras-ERK signaling pathway, on nicotine self-administration (SA) in RasGRF2 KO and WT mice. We first demonstrated that acute nicotine exposure (0.4 mg/kg) resulted in an increase in phosphorylated ERK1/2 (pERK1/2) in the striatum, consistent with previous reports. We also demonstrated that increases in pERK1/2 resulting from acute (0.4 mg/kg) and repeated (0.4 mg/kg, 10 daily injections) exposure to nicotine in WT mice were not present in RasGRF2 KO mice, confirming that RasGRF2 at least partly regulates the activity of the Ras-ERK signaling pathway following nicotine exposure. We then performed intravenous nicotine SA (0.03 mg/kg/infusion for 10 days) in RasGRF2 KO and WT mice. Consistent with a previous report using cocaine SA, RasGRF2 KO mice demonstrated an increase in nicotine SA relative to WT controls. These findings suggest a role for RasGRF2 in the reinforcing effects of nicotine, and implicate the Ras-ERK signaling pathway as a common mediator of the response to drugs of abuse.

Ca2+ homeostasis maintained by TMCO1 underlies corpus callosum development via ERK signaling

Transmembrane of coiled-coil domains 1 (TMCO1) plays an important role in maintaining homeostasis of calcium (Ca²⁺) stores in the endoplasmic reticulum (ER). TMCO1-defect syndrome shares multiple features with human cerebro-facio-thoracic (CFT) dysplasia, including abnormal corpus callosum (CC). Here, we report that TMCO1 is required for the normal development of CC through sustaining Ca²⁺ homeostasis. Tmco1^-/- mice exhibit severe agenesis of CC with stalled white matter fiber bundles failing to pass across the midline. Mechanistically, the excessive Ca²⁺ signals caused by TMCO1 deficiency result in upregulation of FGFs and over-activation of ERK, leading to an excess of glial cell migration and overpopulated midline glia cells in the indusium griseum which secretes Slit2 to repulse extension of the neural fiber bundles before crossing the midline. Supportingly, using the clinical MEK inhibitors to attenuate the over-activated FGF/ERK signaling can significantly improve the CC formation in Tmco1^-/- brains. Our findings not only unravel the underlying mechanism of abnormal CC in TMCO1 defect syndrome, but also offer an attractive prevention strategy to relieve the related agenesis of CC in patients.

Tyrphostin A9 protects axons in experimental autoimmune encephalomyelitis through activation of ERKs

AIMS

Small molecule compound tyrphostin A9 (A9), an inhibitor of platelet-derived growth factor (PDGF) receptor, was previously reported by our group to stimulate extracellular signal-regulated kinase 1 (ERK1) and 2 (ERK2) in neuronal cells in a PDGF receptor-irrelevant manner. The study aimed to investigate whether A9 could protect axons in experimental autoimmune encephalomyelitis through activation of ERKs.

MAIN METHODS

A9 treatment on the protection on neurite outgrowth in SH-SY5Y neuroblastoma cells and primary substantia nigra neuron cultures from the neurotoxin MPP+ were analyzed. Then, clinical symptoms as well as ERK1/2 activation, axonal protection induction, and the abundance increases of the regeneration biomarker GAP-43 in the CNS in the relapsing-remitting experimental autoimmune encephalomyelitis (EAE) model were verified.

KEY FINDINGS

A9 treatment could stimulate neurite outgrowth in SH-SY5Y neuroblastoma cells and protect primary substantia nigra neuron cultures from the neurotoxin MPP+. In the relapsing-remitting EAE model, oral administration of A9 successfully ameliorated clinical symptoms, activated ERK1/2, induced axonal protection, and increased the abundance of the regeneration biomarker GAP-43 in the CNS. Interestingly, gene deficiency of ERK1 or ERK2 disrupted the beneficial effects of A9 in MOG-35-55-induced EAE.

SIGNIFICANCE

These results demonstrated that small molecule compounds that stimulate persistent ERK activation in vitro and in vivo may be useful in protective or restorative treatment for neurodegenerative diseases.

Novel Synthetic Coumarin-Chalcone Derivative (E)-3-(3-(4-(Dimethylamino)Phenyl)Acryloyl)-4-Hydroxy-2H-Chromen-2-One Activates CREB-Mediated Neuroprotection in Aβ and Tau Cell Models of Alzheimer's Disease

Abnormal accumulations of misfolded Aβ and tau proteins are major components of the hallmark plaques and neurofibrillary tangles in the brains of Alzheimer's disease (AD) patients. These abnormal protein deposits cause neurodegeneration through a number of proposed mechanisms, including downregulation of the cAMP-response-element (CRE) binding protein 1 (CREB) signaling pathway. Using CRE-GFP reporter cells, we investigated the effects of three coumarin-chalcone derivatives synthesized in our lab on CREB-mediated gene expression. Aβ-GFP- and ΔK280 tau_RD-DsRed-expressing SH-SY5Y cells were used to evaluate these agents for possible antiaggregative, antioxidative, and neuroprotective effects. Blood-brain barrier (BBB) penetration was assessed by pharmacokinetic studies in mice. Of the three tested compounds, (E)-3-(3-(4-(dimethylamino)phenyl)acryloyl)-4-hydroxy-2H-chromen-2-one (LM-021) was observed to increase CREB-mediated gene expression through protein kinase A (PKA), Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), and extracellular signal-regulated kinase (ERK) in CRE-GFP reporter cells. LM-021 exhibited antiaggregative, antioxidative, and neuroprotective effects mediated by the upregulation of CREB phosphorylation and its downstream brain-derived neurotrophic factor and BCL2 apoptosis regulator genes in Aβ-GFP- and ΔK280 tau_RD-DsRed-expressing SH-SY5Y cells. Blockage of the PKA, CaMKII, or ERK pathway counteracted the beneficial effects of LM-021. LM-021 also exhibited good BBB penetration ability, with brain to plasma ratio of 5.3%, in in vivo pharmacokinetic assessment. Our results indicate that LM-021 works as a CREB enhancer to reduce Aβ and tau aggregation and provide neuroprotection. These findings suggest the therapeutic potential of LM-021 in treating AD.

Proteomic analysis of zearalenone toxicity on mouse thymic epithelial cells

Zearalenone (ZEA) is one of the most major food contaminants in cereal crops worldwide, risking health of both livestock and humans. This study aimed to assess the cytotoxicity and the underlying mechanism of ZEA on thymic epithelial cells. By using proteomics analysis, we identified 596 differentially expressed proteins in MTEC1 cells upon zearalenone exposure, of which 245 were upregulated and 351 were downregulated. Gene ontology (GO) analysis suggested that differentially expressed proteins were participated in protein synthesis, oxidative phosphorylation, and ATP binding. KEGG pathway enrichment analysis showed that differentially expressed proteins were mainly related to mitochndrial metabolism, such as citrate cycle (TCA cycle) and oxidative phosphorylation. We demonstrated that ZEA treatment was able to increase the intracellular reactive oxygen species (ROS) level, to decrease ΔΨm, ATP level, and the copy number of mtDNA, leading to necrotic cell death. Moreover, we showed that ZEA treatment inhibited cell proliferation and induced G2/M phase arrest by downregulation of proliferation-associated proteins ERK, p-ERK, CDK1, and p-CHK1. Taken together, we found that the toxicity of ZEA on thymic epithelial cells is mainly caused by the inhibition of mitochondrial dysfunction and cell proliferation. Our study might open new avenues for treatment strategies.

Paternal exposure to microcystin-LR triggers developmental neurotoxicity in zebrafish offspring via an epigenetic mechanism involving MAPK pathway

Microcystin-LR (MCLR) induced impairment to male reproductive system and revealed the effects of transgenerational toxicity on offspring. But very little is known about the inheritance of these effects to offspring and the mechanisms involved. Here, we used methylated DNA immunoprecipitation sequencing (MeDIP-Seq) and microarray to characterize whole-genome DNA methylation and mRNA expression patterns in zebrafish testis after 6-week exposure to 5 and 20 μg/L MCLR. Accompanied with these analyses it revealed that MAPK pathway and ER pathway significantly enriched in zebrafish testes. Apoptosis and testicular damage were also observed in testis. Next, we test the transmission of effects to compare control-father and MCLR exposure-father progenies. DNA methylation analyses (via reduced representation bisulfite sequencing) reveal that the enrichment of differentially methylated regions on neurodevelopment after paternal MCLR exposure. Meanwhile, several genes associated with neurodevelopment were markedly downregulated in zebrafish larvae, and swimming speed was also reduced in the larvae. Interestingly, paternal MCLR exposure also triggered activation the phosphorylation of mitogen-activated protein kinase (MAPK) pathway which is also associated with neurodevelopmental disorders. These results demonstrated the significant effect that paternal MCLR exposure may have on gene-specific DNA methylation patterns in testis. Inherited epigenetic alterations through the germline may be the mechanism leading to developmental neurotoxicity in the offspring.

Apoptotic Pathways and Alzheimer's Disease: Probing Therapeutic Potential

Apoptosis is an intrinsic biochemical, cellular process that regulates cell death and is crucial for cell survival, cellular homeostasis, and maintaining the optimum functional status. Apoptosis in a predetermined and programmed manner regulates several molecular events, including cell turnover, embryonic development, and immune system functions but may be the exclusive contributor to several disorders, including neurodegenerative manifestations, when it functions in an aberrant and disorganized manner. Alzheimer's disease (AD) is a fatal, chronic neurodegenerative disorder where apoptosis has a compelling and divergent role. The well-characterized pathological features of AD, including extracellular plaques of amyloid-beta, intracellular hyperphosphorylated tangles of tau protein (NFTs), inflammation, mitochondrial dysfunction, oxidative stress, and excitotoxic cell death, also instigate an abnormal apoptotic cascade in susceptible brain regions (cerebral cortex, hippocampus). The apoptotic players in these regions affect cellular organelles (mitochondria and endoplasmic reticulum), interact with trophic factors, and several pathways, including PI3K/AKT, JNK, MAPK, mTOR signalling. This dysregulated apoptotic cascade end with an abnormal neuronal loss which is a primary event that may precede the other events of AD progression and correlates well with the degree of dementia. The present review provides insight into the diverse and versatile apoptotic mechanisms that are indispensable for neuronal survival and constitute an integral part of the pathological progression of AD. Identification of potential targets (restoring apoptotic and antiapoptotic balance, caspases, TRADD, RIPK1, FADD, TNFα, etc.) may be valuable and advantageous to decide the fate of neurons and to develop potential therapeutics for treatment of AD.

HSP70 inhibition suppressed glioma cell viability during hypoxia/reoxygenation by inhibiting the ERK1/2 and PI3K/AKT signaling pathways

Heat shock protein 70 (HSP70) can regulate astrocyte viability under hypoxic and ischemic conditions. However, the protective mechanism involved is not completely clear. This study aimed to investigate whether HSP70 protects U87 glioma cells against hypoxic damage via the extracellular signal-regulated kinases 1/2 (ERK1/2) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) signaling pathways. Lentivirus-mediated HSP70-siRNA was used for HSP70 silencing. U87 glioma cells with lentiviral infection were exposed to hypoxia for 4, 8, 12, and 24 h, respectively, followed by a 24-h reoxygenation treatment. A Cell-Counting Kit-8 was then used to evaluate the viability of the U87 glioma cells. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting were performed to determine the mRNA and protein levels, respectively. The expression of HSP70, p-ERK1/2, p-AKT, and U87 cell viability were increased after 8 h of hypoxia/24 h of reoxygenation (P < 0.01). However, HSP70 silencing significantly decreased the U87 cell viability after the hypoxia/reoxygenation treatment (P < 0.01). The protein expressions of p-ERK1/2 and p-AKT also decreased in HSP70-silenced U87 cells (P < 0.01). In conclusion, HSP70 inhibition suppressed the viability of U87 glioma cells during hypoxia/reoxygenation (at least partially) by inhibiting the ERK1/2 and PI3K/AKT signaling pathways. This study may help to understand the molecular mechanisms underlying the progression and development of cerebral hypoxia-ischemia.

Impaired contextual fear conditioning in RasGRF2 mutant mice is likely Ras-ERK-dependent

Ras/Raf/MEK/ERK (Ras-ERK) signaling has been shown to play an important role in fear acquisition. However, little information is known regarding the mechanisms that contribute to the regulation of this pathway in terms of the learning of conditioned fears. Ras Guanine Nucleotide Releasing Factor 2 (RasGRF2) is one of two guanine nucleotide exchange factors (GEF) that regulates the Ras-ERK signaling pathway in a Ca²⁺-dependent manner via control of the cycling of Ras isoforms between an inactive and active state. Here we sought to determine the role of RasGRF2 on contextual fear conditioning in RasGRF2 knockout (KO) and their wild type (WT) counterparts. Male KO and WT mice underwent a single session of contextual fear conditioning (12 min, 4 unsignaled shocks), followed by either daily 12-min retention trials or the molecular analysis of Ras activation and pERK1/2 activity. KO mice showed an impaired acquisition of contextual fear, as demonstrated by reduced freezing during fear conditioning and 24-hr retention tests relative to WT mice. Ras analysis following fear conditioning demonstrated a reduction in Ras activation in the hippocampus as well as a reduction in pERK1/2 in the CA1 region of the hippocampus in KO mice, suggesting that the decrease in fear conditioning in KO mice is at least in part due to the impairment of Ras-ERK signaling in the hippocampus during learning. These data indicate a role for RasGRF2 in contextual fear conditioning in mice that may be Ras-ERK-dependent.

Crocetin ameliorates chronic restraint stress-induced depression-like behaviors in mice by regulating MEK/ERK pathways and gut microbiota

ETHNOPHARMACOLOGICAL RELEVANCE

This study aimed at determining the effects of saffron on depression as well as its neuroprotective and pharmacological effects on the intestinal function of crocetin in mice exposed to chronic restraint stress.

MATERIALS AND METHODS

Chronic stress was induced in two-week-old ICR mice by immobilizing them for 6 h per day for 28 days. The mice were orally administered with crocetin (20, 40, 80 mg/kg), fluoxetine (20 mg/kg) or distilled water. The treatments were administered daily and open field and tail suspension tests were performed. Immunofluorescent and Western-bolt (WB) assays were conducted to determine the expression of mitogen-activated protein kinase phosphatase-1 (MKP-1), the precursor of brain-derived neurotrophic factor (proBDNF), extracellular signal-regulated kinase 1/2 (ERK1/2), phosphorylated cAMP response element-binding (CREB) protein in the hippocampus. Serum levels of dopamine (DA), proBDNF, MKP-1 and CREB were measured by Elisa kits. High-throughput sequencing was carried out to analyze the composition of intestinal microbiota.

RESULTS

Crocetin ameliorated depressive-like behaviors caused by chronic restraint stress-induced depressive mice. It significantly attenuated the elevated levels of MKP-1, proBDNF, alanine transaminase, aspartate transaminase and increased the serum levels of DA as well as CREB. Histopathological analysis showed that crocetin suppressed hippocampus injury in restraint stress mice by protecting neuronal cells. Immunofluorescent and WB analysis showed elevated expression levels of ERK1/2, CREB and inhibited expression levels of MKP-1, proBDNF in the hippocampus. The intestinal ecosystem of the crocetin group partially recovered and was close to the control group.

CONCLUSIONS

Crocetin has neuroprotective properties and ameliorates the effects of stress-associated brain damage by regulating the MKP-1-ERK1/2-CREB signaling and intestinal ecosystem.

Proteomic investigation of Cbl and Cbl-b in neuroblastoma cell differentiation highlights roles for SHP-2 and CDK16

Neuroblastoma is a highly heterogeneous embryonal solid tumor of the sympathetic nervous system. As some tumors can be treated to undergo differentiation, investigating this process can guide differentiation-based therapies of neuroblastoma. Here, we studied the role of E3 ubiquitin ligases Cbl and Cbl-b in regulation of long-term signaling responses associated with extracellular signal-regulated kinase phosphorylation and neurite outgrowth, a morphological marker of neuroblastoma cell differentiation. Using quantitative mass spectrometry (MS)-based proteomics, we analyzed how the neuroblastoma cell line proteome, phosphoproteome, and ubiquitylome were affected by Cbl and Cbl-b depletion. To quantitatively assess neurite outgrowth, we developed a high-throughput microscopy assay that was applied in combination with inhibitor studies to pinpoint signaling underlying neurite outgrowth and to functionally validate proteins identified in the MS data sets. Using this combined approach, we identified a role for SHP-2 and CDK16 in Cbl/Cbl-b-dependent regulation of extracellular signal-regulated kinase phosphorylation and neurite outgrowth, highlighting their involvement in neuroblastoma cell differentiation.

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Multi-layered proteomics captures cellular changes induced by Cbl/Cbl-b depletion

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SHP-2 and CDK16 protein and phosphorylation levels increase upon Cbl/Cbl-b depletion

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SHP-2 and CDK16 regulate phospho-ERK and neurite outgrowth in neuroblastoma cells

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Inhibition of SHP-2 or CDK16 reverts Cbl/Cbl-b knockdown effects on differentiation

Synergistic efficacy and diminished adverse effect profile of composite treatment of several ADHD medications

Although attention-deficit/hyperactivity disorder (ADHD) is widely studied, problems regarding the adverse effect risks and non-responder problems still need to be addressed. Combination pharmacotherapy using standard dose regimens of existing medication is currently being practiced mainly to augment the therapeutic efficacy of each drug. The idea of combining different pharmacotherapies with different molecular targets to alleviate the symptoms of ADHD and its comorbidities requires scientific evidence, necessitating the investigation of their therapeutic efficacy and the mechanisms underlying the professed synergistic effects. Here, we injected male ICR mice with MK-801 to induce ADHD behavioral condition. We then modeled a "combined drug" using sub-optimal doses of methylphenidate, atomoxetine, and fluoxetine and investigated the combined treatment effects in MK-801-treated mice. No sub-optimal dose monotherapy alleviated ADHD behavioral condition in MK-801-treated mice. However, treatment with the combined drug attenuated the impaired behavior of MK-801-treated animals. Growth impediment, sleep disturbances, or risk of substance abuse were not observed in mice treated subchronically with the combined drugs. Finally, we observed that the combined ADHD drug rescued alterations in p-AKT and p-ERK1/2 levels in the prefrontal cortex and hippocampus, respectively, of MK-801-treated mice. Our results provide experimental evidence of a possible new pharmacotherapy option in ameliorating the ADHD behavioral condition without the expected adverse effects. The detailed mechanism of action underlying the synergistic therapeutic efficacy and reduced adverse reaction by combinatorial drug treatment should be investigated further in future studies.

Role of DNA Methyl-CpG-Binding Protein MeCP2 in Rett Syndrome Pathobiology and Mechanism of Disease

Rett Syndrome (RTT) is a severe, rare, and progressive developmental disorder with patients displaying neurological regression and autism spectrum features. The affected individuals are primarily young females, and more than 95% of patients carry de novo mutation(s) in the Methyl-CpG-Binding Protein 2 (MECP2) gene. While the majority of RTT patients have MECP2 mutations (classical RTT), a small fraction of the patients (atypical RTT) may carry genetic mutations in other genes such as the cyclin-dependent kinase-like 5 (CDKL5) and FOXG1. Due to the neurological basis of RTT symptoms, MeCP2 function was originally studied in nerve cells (neurons). However, later research highlighted its importance in other cell types of the brain including glia. In this regard, scientists benefitted from modeling the disease using many different cellular systems and transgenic mice with loss- or gain-of-function mutations. Additionally, limited research in human postmortem brain tissues provided invaluable findings in RTT pathobiology and disease mechanism. MeCP2 expression in the brain is tightly regulated, and its altered expression leads to abnormal brain function, implicating MeCP2 in some cases of autism spectrum disorders. In certain disease conditions, MeCP2 homeostasis control is impaired, the regulation of which in rodents involves a regulatory microRNA (miR132) and brain-derived neurotrophic factor (BDNF). Here, we will provide an overview of recent advances in understanding the underlying mechanism of disease in RTT and the associated genetic mutations in the MECP2 gene along with the pathobiology of the disease, the role of the two most studied protein variants (MeCP2E1 and MeCP2E2 isoforms), and the regulatory mechanisms that control MeCP2 homeostasis network in the brain, including BDNF and miR132.

Nogo-A aggravates oxidative damage in oligodendrocytes

Nogo-A is considered one of the most important inhibitors of myelin-associated axonal regeneration in the central nervous system. It is mainly expressed by oligodendrocytes. Although previous studies have found regulatory roles for Nogo-A in neurite outgrowth inhibition, neuronal homeostasis, precursor migration, plasticity, and neurodegeneration, its functions in the process of oxidative injury are largely uncharacterized. In this study, oligodendrocytes were extracted from the cerebral cortex of newborn Sprague-Dawley rats. We used hydrogen peroxide (H₂O₂) to induce an in vitro oligodendrocyte oxidative damage model and found that endogenously expressed Nogo-A is significantly upregulated in oligodendrocytes. After recombinant virus Ad-ZsGreen-rat Nogo-A infection of oligodendrocytes, Nogo-A expression was increased, and the infected oligodendrocytes were more susceptible to acute oxidative insults and exhibited a markedly elevated rate of cell death. Furthermore, knockdown of Nogo-A expression in oligodendrocytes by Ad-ZsGreen-shRNA-Nogo-A almost completely protected against oxidative stress induced by exogenous H₂O₂. Intervention with a Nogo-66 antibody, a LINGO1 blocker, or Y27632, an inhibitor in the Nogo-66-NgR/p75/LINGO-1-RhoA-ROCK pathway, did not affect the death of oligodendrocytes. Ad-ZsGreen-shRNA-Nogo-A also increased the levels of phosphorylated extracellular signal-regulated kinase 1/2 and inhibited BCL2 expression in oligodendrocytes. In conclusion, Nogo-A aggravated reactive oxygen species damage in oligodendrocytes, and phosphorylated extracellular signal-regulated kinase 1/2 and BCL2 might be involved in this process. This study was approved by the Ethics Committee of Peking University People’s Hospital, China (approval No. 2018PHC081) on December 18, 2018.

Neurotrophic Properties of Silexan, an Essential Oil from the Flowers of Lavender-Preclinical Evidence for Antidepressant-Like Properties

BACKGROUND

Silexan, a special essential oil from flowering tops of lavandula angustifolia, is used to treat subsyndromal anxiety disorders. In a recent clinical trial, Silexan also showed antidepressant effects in patients suffering from mixed anxiety-depression (ICD-10 F41.2). Since preclinical data explaining antidepressant properties of Silexan are missing, we decided to investigate if Silexan also shows antidepressant-like effects in vitro as well as in vivo models.

METHODS

We used the forced swimming test (FST) in rats as a simple behavioral test indicative of antidepressant activity in vivo. As environmental events and other risk factors contribute to depression through converging molecular and cellular mechanisms that disrupt neuronal function and morphology-resulting in dysfunction of the circuitry that is essential for mood regulation and cognitive function-we investigated the neurotrophic properties of Silexan in neuronal cell lines and primary hippocampal neurons.

RESULTS

The antidepressant activity of Silexan (30 mg/kg BW) in the FST was comparable to the tricyclic antidepressant imipramine (20 mg/kg BW) after 9-day treatment. Silexan triggered neurite outgrowth and synaptogenesis in 2 different neuronal cell models and led to a significant increase in synaptogenesis in primary hippocampal neurons. Silexan led to a significant phosphorylation of protein kinase A and subsequent CREB phosphorylation.

CONCLUSION

Taken together, Silexan demonstrates antidepressant-like effects in cellular as well as animal models for antidepressant activity. Therefore, our data provides preclinical evidence for the clinical antidepressant effects of Silexan in patients with mixed depression and anxiety.

So-Ochim-Tang-Gamibang, a Traditional Herbal Formula, Ameliorates Depression by Regulating Hyperactive Glucocorticoid Signaling In Vitro and In Vivo

So-ochim-tang-gamibang (SOCG) is a Korean traditional medicine; it has previously been shown to be safe and effective against depression. Persistently increased levels of circulating glucocorticoids have been considered as a pathological mechanism for depression and associated with decreased neurotrophic factors in the hippocampus. This study investigated whether SOCG controls the hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis and the molecular mechanisms underlying its effects in vivo and in vitro. Wistar Kyoto (WKY) rats were subjected to restraint stress, where SOCG was orally administered to the animals for 2 weeks. An open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT) were performed to explore the antidepressant activity of SOCG in WKY rats. Plasma levels of HPA axis hormones were measured by ELISA or western blotting analysis. The expression levels or activation of HPA axis-related signaling molecules such as brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), extracellular regulated kinase (ERK), and glucocorticoid receptors (GRs) in the brain were determined by real-time PCR and western blotting analysis. Furthermore, a corticosterone- (CORT-) induced cell injury model was established using SH-SY5Y cells to explore the antidepressive effects of SOCG in vitro. The results of the OFT, FST, and SPT revealed that SOCG ameliorated depressive-like behaviors in the WKY rats. The blood plasma levels of HPA axis hormones such as CORT, CORT-releasing hormone (CRH), and adrenocorticotrophic hormone were downregulated by SOCG. On the other hand, SOCG upregulated the phosphorylation of CREB and ERK in both the rat hippocampus and CORT-treated SH-SY5Y cells. Moreover, it also increased the GR expression. These results suggested that SOCG may improve depression by controlling hyperactive glucocorticoid signaling via the downregulation of HPA axis hormones and upregulation of GR.

Pharmacological basis of the anxiolytic and antidepressant properties of Silexan®, an essential oil from the flowers of lavender

Silexan®, a proprietary essential oil manufactured by steam distillation from Lavandula angustifolia flowers showed pronounced anxiolytic effects in patients with subthreshold anxiety disorders and was also efficacious in patients with Generalized Anxiety disorder (GAD). Moreover, evidences for antidepressant-like properties of Silexan® have been observed in anxious patients suffering from comorbid depressive symptoms and in patients with mixed anxiety-depression disorder (ICD-10 F41.2). In accordance with the clinical data Silexan® is active in several behavioral models in rodents at rather low concentrations indicating potent anxiolytic and antidepressive properties. As possible mechanism of action a moderate inhibition of voltage dependent calcium channels (VDCC) has been found showing some similarities to the anxiolytic drug pregabalin. However, while pregabalin mainly inhibits P/Q-type channels by binding to a modulatory subunit, Silexan® moderately inhibits mainly T-type and N-type channels and to some extent P/Q-type channels. Unlike pregabalin Silexan® is free of hypnotic or sedative side effects and seems to be devoid of any abuse potential. With respect to its specific antidepressant like properties Silexan® improves several aspects of neuroplasticity which seems to be the common final pathway of all antidepressant drugs. As a potential mechanism of its effects on neuroplasticity an activation of the transcription factor CREB via activation of intracellular signaling kinases like PKA and MAPK has been found. Since the concentrations of Silexan® needed to inhibit VDCC function and to improve neuroplasticity are quite similar, the effects of Silexan® on PKA or MAPK could constitute a common intracellular signaling cascade leading to VDCC modulation as well as CREB activation and improved neuroplasticity.

Serum-deprivation leads to activation-like changes in primary microglia and BV-2 cells but not astrocytes

The aim of the present study was to determine the effect of serum deprivation on primary microglia, BV-2 cells and primary astrocytes. Cell morphology combined with the expression of phospho-(p-)38 and p-extracellular signal-regulated kinase (ERK) were assessed. Serum deprivation resulted in various alterations in the three cell cultures. Primary microglia and BV-2 cells exhibited alterations indicative of activation under serum treatment, as well as lipopolysaccharide (LPS) treatment. However, astrocytes did not react as fast. Regarding morphology, the processes present on the primary microglia and BV-2 cells became shorter and the cell bodies became larger, and more transparent vesicles were observed within the cell bodies, which indicated their increased phagocytic ability. At the protein level, p-p38 expression increased quickly within 1 h in the primary microglia culture in response to LPS treatment. Furthermore, the expression levels of p-p38 and p-ERK were elevated in both primary microglia and BV-2 cells under serum deprivation, as well as under LPS treatment, which was not observed in the primary astrocytes. These results suggest that serum deprivation may result in similar changes to cell morphology and the expression levels of p-p38 and p-ERK as LPS treatment in primary microglia and BV-2 cells. These observations suggest that primary microglia and BV-2 cells may become activated under serum deprivation, at least to a certain degree.

Effects of pharmacological inhibition of the centrally-projecting Edinger-Westphal nucleus on ethanol-induced conditioned place preference and body temperature

Alcohol use disorder is a chronic disease characterized in part by repeated relapsing events. Exposure to environmental stimuli or cues that have previously been associated with the effects of alcohol can promote relapse through the triggering of craving for alcohol. Therefore, identifying and characterizing neuronal populations that may regulate these associations is of the upmost importance. Previous studies have implicated the centrally-projecting Edinger Westphal nucleus (EWcp) in this process, as the EWcp is both sensitive to, and can regulate alcohol intake. To date however, it is unclear if the EWcp is involved in the formation or expression of these alcohol-cue associations. As such, the present studies examined the involvement of the EWcp in male DBA/2J mice in the acquisition and expression of place preference for an alcohol-paired cue using the conditioned place preference (CPP) procedure. Pharmacological inhibition of the EWcp via the GABAA and GABAB receptor agonists muscimol and baclofen did not affect either the acquisition or the expression of CPP. Follow up studies did find however, that pharmacological inhibition of the EWcp increased body temperature and prevented alcohol-induced increases in c-Fos expression in the EWcp. When considered in light of previous studies, the present results indicate that the EWcp may be involved in the regulation of alcohol self-administration, and not conditioned alcohol-seeking. Additionally, the present studies provide further evidence for the involvement of the EWcp in thermoregulation and help elucidate the molecular mechanisms by which alcohol increases c-Fos in the EWcp.

Neuroprotective effect of lithium in cold- induced traumatic brain injury in mice

Apart from its well-established therapeutic activity on bipolar disorder and depression, lithium exerts neuroprotective activity upon neurodegenerative disorders, such as traumatic brain injury (TBI). However, the cellular signaling mechanisms mediating lithium's neuroprotective activity and long-term dose- and time-dependent effects on close and remote proximity are largely unknown. Herein, we tested prophylactic and acute effects of lithium (2 mmol/kg) after cold- induced TBI. In both conditions, treatments with lithium resulted in reduced infarct volume and apoptosis. Its acute treatment resulted in the increase of Akt, ERK-1/2 and GSK-3 α/β phosphoylations. Interestingly, its prophylactic treatment instead resulted in decreased phosphorylations of Akt, ERK-1/2, p38, JNK-1 moderately and GSK-3 α/β significantly. Then, we tested subacute (35-day follow-up) role of low (0.2 mmol/kg) and high dose (2 mmol/kg) lithium and revealed that high dose lithium group was the most mobile so the least depressed in the tail suspension test. Anxiety level was assessed by light-dark test, all groups' anxiety levels were decreased with time, but lithium had no effect on anxiety like behavior. When subacute effects of injury and drug treatment were evaluated on the defined brain regions, infarct volume was decreased in the high dose lithium group significantly. In contrast to other brain regions, hippocampal atrophies were observed in both lithium treatment groups, which were significant in the low dose lithium group in both hemispheres, which was associated with the reduced cell proliferation and neurogenesis. Our data demonstrate that lithium treatment protects neurons from TBI. However, long term particularly low-dose lithium causes hippocampal atrophy and decreased neurogenesis.

Myelin-associated glycoprotein inhibits neurite outgrowth through inactivation of the small GTPase Rap1

Rap1 is a small GTPase that has been implicated in dendritic development and plasticity. In this study, we investigated the role of Rap1 in axonal growth and its activation in response to neurotrophins and myelin-associated inhibitors. We report that Rap1 is activated by brain-derived neurotrophic factor and that this activation can be blocked by myelin-associated glycoprotein (MAG) or central nervous system myelin, which also induced increases in Rap1GAP1 levels. In addition, we demonstrate that adenoviral overexpression of Rap1 enhances neurite outgrowth in the presence of MAG and myelin, while inhibition of Rap1 activity through overexpression of Rap1GAP1 blocks neurite outgrowth. These findings suggest that Rap1GAP1 negatively regulates neurite outgrowth, making it a potential therapeutic target to promote axonal regeneration.

Melatonin ameliorates cuprizone-induced reduction of hippocampal neurogenesis, brain-derived neurotrophic factor, and phosphorylation of cyclic AMP response element-binding protein in the mouse dentate gyrus

INTRODUCTION

The aim of this study was to investigate the effects of cuprizone on adult hippocampal neurogenesis in naïve mice. Additionally, we also studied how melatonin affects the neuronal degeneration induced by cuprizone.

METHODS

Eight-week-old male C57BL/6J mice were randomly divided into three groups: (a) the control group, (b) the group treated with cuprizone only, and (c) the group treated with both cuprizone and melatonin. Cuprizone was administered with food at 0.2% ad libitum for 6 weeks. Melatonin was also administered with tap water at 6 g/L ad libitum for 6 weeks; the animals were then euthanized for immunohistochemistry with Ki67, doublecortin (DCX), glucose transporter 3 (GLUT3), and phosphorylation of cyclic adenosine monophosphate (AMP) response element binding (pCREB); double immunofluorescence of neuronal nuclei (NeuN) and myelin basic protein (MBP); and Western blot analysis of brain-derived neurotrophic factor (BDNF) expression to reveal the effects of cuprizone and melatonin on cell damage and hippocampal neurogenesis.

RESULTS

Administration of cuprizone significantly decreased the number of differentiating (DCX-positive) neuroblasts and proliferating (Ki67-positive) cells in the dentate gyrus. Moreover, cuprizone administration decreased glucose utilization (GLUT3-positive cells) and cell transcription (pCREB-positive cells and BDNF protein expression) in the dentate gyrus. Administration of melatonin ameliorated the cuprizone-induced reduction of differentiating neuroblasts and proliferating cells, glucose utilization, and cell transcription.

CONCLUSION

The results of the study suggest that cuprizone treatment disrupts hippocampal neurogenesis in the dentate gyrus by reducing BDNF levels and decreasing the phosphorylation of CREB. These effects were ameliorated by melatonin treatment.

The Inhibition of RasGRF2, But Not RasGRF1, Alters Cocaine Reward in Mice

Ras/Raf/MEK/ERK (Ras-ERK) signaling has been implicated in the effects of drugs of abuse. Inhibitors of MEK1/2, the kinases upstream of ERK1/2, have been critical in defining the role of the Ras-ERK cascade in drug-dependent alterations in behavioral plasticity, but the Ras family of small GTPases has not been extensively examined in drug-related behaviors. We examined the role of Ras Guanine Nucleotide Releasing Factor 1 (RasGRF1) and 2 (RasGRF2), upstream regulators of the Ras-ERK signaling cascade, on cocaine self-administration (SA) in male mice. We first established a role for Ras-ERK signaling in cocaine SA, demonstrating that pERK1/2 is upregulated following SA in C57BL/6N mice in striatum. We then compared RasGRF1 and RasGRF2 KO mouse lines, demonstrating that cocaine SA in RasGRF2 KO mice was increased relative to WT controls, whereas RasGRF1 KO and WT mice did not differ. This effect in RasGRF2 mice is likely mediated by the Ras-ERK signaling pathway, as pERK1/2 upregulation following cocaine SA was absent in RasGRF2 KO mice. Interestingly, the lentiviral knockdown of RasGRF2 in the NAc had the opposite effect to that in RasGRF2 KO mice, reducing cocaine SA. We subsequently demonstrated that the MEK inhibitor PD325901 administered peripherally prior to cocaine SA increased cocaine intake, replicating the increase seen in RasGRF2 KO mice, whereas PD325901 administered into the NAc decreased cocaine intake, similar to the effect seen following lentiviral knockdown of RasGRF2. These data indicate a role for RasGRF2 in cocaine SA in mice that is ERK-dependent, and suggest a differential effect of global versus site-specific RasGRF2 inhibition.SIGNIFICANCE STATEMENT Exposure to drugs of abuse activates a variety of intracellular pathways, and following repeated exposure, persistent changes in these pathways contribute to drug dependence. Downstream components of the Ras-ERK signaling cascade are involved in the acute and chronic effects of drugs of abuse, but their upstream mediators have not been extensively characterized. Here we show, using a combination of molecular, pharmacological, and lentiviral techniques, that the guanine nucleotide exchange factor RasGRF2 mediates cocaine self-administration via an ERK-dependent mechanism, whereas RasGRF1 has no effect on responding for cocaine. These data indicate dissociative effects of mediators of Ras activity on cocaine reward and expand the understanding of the contribution of Ras-ERK signaling to drug-taking behavior.

MGluR5 activity is required for the induction of ethanol behavioral sensitization and associated changes in ERK MAP kinase phosphorylation in the nucleus accumbens shell and lateral habenula

Metabotropic glutamate receptor subtype-5 (mGluR5) activity regulates a variety of behavioral pathologies associated with alcohol addiction. The main goal of this study was to determine if mGluR5 regulates the induction of ethanol-induced locomotor sensitization, which is a model of experience-dependent plasticity following initial exposure to drugs of abuse. The extracellular signal-regulated kinase (ERK_1/2) pathway is downstream of mGluR5 and implicated in alcohol addiction; however, its role in sensitization remains unexplored. We sought to determine if mGluR5-mediated changes in ethanol-induced sensitization are associated with changes in ERK_1/2 phosphorylation (pERK_1/2) in specific brain regions. Adult male DBA/2 J mice were tested for acute locomotor response to ethanol (0 or 2 g/kg, IP) followed by a 9-day induction period in which the mGluR5 antagonist MPEP (0 or 30 mg/kg, IP) was administered prior to ethanol (0 or 2.5 g/kg, IP). One day later, ethanol (2 g/kg) produced a robust within- and between-group increase in locomotor activity, indicating sensitization in mice that received MPEP (0 mg/kg) during induction. MPEP (30 mg/kg) treatment during induction resulted in locomotor response to ethanol (2 g/kg) challenge that was equivalent to an acute response, indicating full blockade of sensitization. Sensitization was associated with increased pERK_1/2 immunoreactivity (IR) in nucleus accumbens shell (AcbSh) and a reduction in lateral habenula (LHb), both of which were blocked by MPEP treatment during induction. Sensitization was also associated with mGluR5-independent increases in pERK_1/2 IR in the nucleus accumbens core and decreases in the dentate gyrus and lateral septum. These data indicate that mGluR5 activity is required for the induction of ethanol locomotor sensitization and associated changes in ERK_1/2 phosphorylation in the AcbSh and LHb, which raises the hypothesis that mGluR5-mediated cell signaling in these brain regions may mediate the induction of sensitization. Elucidating mechanisms of sensitization may increase understanding of how ethanol hijacks behavioral functions during the development of addiction.

1-O-Hexyl-2,3,5-Trimethylhydroquinone Ameliorates l-DOPA-Induced Cytotoxicity in PC12 Cells

1-O-Hexyl-2,3,5-trimethylhydroquinone (HTHQ) has previously been found to have effective anti-oxidant and anti-lipid-peroxidative activity. We aimed to elucidate whether HTHQ can prevent dopaminergic neuronal cell death by investigating the effect on l-DOPA-induced cytotoxicity in PC12 cells. HTHQ protected from both l-DOPA-induced cell death and superoxide dismutase activity reduction. When assessing the effect of HTHQ on oxidative stress-related signaling pathways, HTHQ inhibited l-DOPA-induced phosphorylation of sustained extracellular signal-regulated kinases (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK1/2). HTHQ also normalized l-DOPA-reduced Bcl-2-associated death protein (Bad) phosphorylation and Bcl-2-associated X protein (Bax) expression, promoting cell survival. Taken together, HTHQ exhibits protective effects against l-DOPA-induced cell death through modulation of the ERK1/2-p38MAPK-JNK1/2-Bad-Bax signaling pathway in PC12 cells. These results suggest that HTHQ may show ameliorative effects against oxidative stress-induced dopaminergic neuronal cell death, although further studies in animal models of Parkinson’s disease are required to confirm this.

Ketamine-induced hypnosis and neuroplasticity in mice is associated with disrupted p-MEK/p-ERK sequential activation and sustained upregulation of survival p-FADD in brain cortex: Involvement of GABAA receptor

Ketamine (KET) is an antidepressant and hypnotic drug acting as an antagonist at excitatory NMDA glutamate receptors. The working hypothesis postulated that KET-induced sleep in mice results in dysregulation of mitogen-activated protein kinases (MAPK) MEK-ERK sequential phosphorylation and upregulation of survival p-FADD and other neuroplastic markers in brain. Low (5-15 mg/kg) and high (150 mg/kg) doses of KET on target proteins were assessed by Western immunoblot in mouse brain cortex. During the time course of KET (150 mg/kg)-induced sleep (up to 50 min) p-MEK was increased (up to +79%) and p-ERK decreased (up to -46%) indicating disruption of MEK to ERK signal. Subhypnotic KET (5-15 mg/kg) also revealed uncoupling of p-MEK (+13-81%) to p-ERK (unchanged content). KET did not alter contraregulatory MAPK mechanisms such as inactivated p-MEK1 (ERK dampening) and phosphatases MKP1/2/3 (ERK dephosphorylation). As other relevant findings, KET (5, 15 and 150 mg/kg) upregulated p-FADD in a dose-dependent manner, and for the hypnotic dose the effect paralleled the time course of sleep which resulted in increased p-FADD/FADD ratios. KET (150 mg/kg) also increased NF-κΒ and PSD-95 neuroplastic markers. Flumazenil (a neutral allosteric antagonist at GABA_A receptor) prolonged KET sleep and blocked p-MEK upregulation, indicating the involvement of this receptor as a negative modulator. SL-327 (a MEK inhibitor) augmented KET sleep, further indicating the relevance of reduced p-ERK1/2 in KET-induced hypnosis. These findings suggest that hypnotic and subhypnotic doses of KET inducing uncoupling of p-MEK to p-ERK signal and regulation of p-ERK (downregulation) and p-FADD (upregulation) may participate in the expression of some of its adverse effects (e.g. amnesia, dissociative effects).

Neuroprotective Mechanism of Hypoxic Post-conditioning Involves HIF1-Associated Regulation of the Pentose Phosphate Pathway in Rat Brain

Post-conditioning is exposure of an injured organism to the same harmful factors but of milder intensity which mobilizes endogenous protective mechanisms. Recently, we have developed a novel noninvasive post-conditioning (PostC) protocol involving three sequential episodes of mild hypobaric hypoxia which exerts pronounced neuroprotective action. In particular, it prevents development of pathological cascades caused by severe hypobaric hypoxia (SH) such as cellular loss, lipid peroxidation, abnormal neuroendocrine responses and behavioural deficit in experimental animals. Development of these post-hypoxic pathological effects has been associated with the delayed reduction of hypoxia-inducible factor 1 (HIF1) regulatory α-subunit levels in rat hippocampus, whereas PostC up-regulated it. The present study has been aimed at experimental examination of the hypothesis that intrinsic mechanisms underlying the neuroprotective and antioxidant effects of PostC involves HIF1-dependent stimulation of the pentose phosphate pathway (PPP). We have observed that SH leads to a decrease of glucose-6-phosphate dehydrogenase (G6PD) activity in the hippocampus and neocortex of rats as well as to a reduction in NADPH and total glutathione levels. This depletion of the antioxidant defense system together with excessive lipid peroxidation during the reoxygenation phase resulted in increased oxidative stress and massive cellular death observed after SH. In contrast, PostC led to normalization of G6PD activity, stabilization of the NADPH and total glutathione levels and thereby resulted in recovery of the cellular redox state and prevention of neuronal death. Our data suggest that stabilization of the antioxidant system via HIF1-associated PPP regulation represents an important neuroprotective mechanism enabled by PostC.

Synergistic activation of ERK1/2 between A-fiber neurons and glial cells in the DRG contributes to pain hypersensitivity after tissue injury

Background

Intense nociceptive signaling arising from ongoing injury activates primary afferent nociceptive systems to generate peripheral sensitization. ERK1/2 phosphorylation in dorsal root ganglion can be used to visualize intracellular signal activity immediately after noxious stimulation. The aim of this study was to investigate spatiotemporal characteristics of ERK1/2 phosphorylation against tissue injury in the primary afferent neurons.

Methods

Plantar incisions were made in the hind paws of Sprague-Dawley rats (n =150). Levobupivacaine was injected into the plantar aspect of the paws and ankles, Mitogen-activated protein kinase kinase (MEK) inhibitor was injected into the paw, and carbenoxolone, dual inhibitor of the gap junction and pannexin channel, was intraperitoneally injected. Pain hypersensitivity was investigated by a behavioral study, while phosphorylated ERK1/2 was detected in dorsal root ganglion and hind paw using immunohistochemistry and Western blot.

Results

Phosphorylated ERK1/2 was induced in dorsal root ganglion (26.8 ± 2.9% at baseline, 65.6 ± 3.6% at 2 min, and 26.3 ± 3.4% at 2 h) after the incision. NF-200 positive A-fiber neurons and satellite glial cells were positive for phosphorylated ERK1/2. Injury-induced pain hypersensitivity was abolished by MEK inhibitor. Levobupivacaine treatment inhibited phosphorylated ERK1/2 induction, carbenoxolone treatment inhibited glial phosphorylated ERK1/2 at 2 min after the injury, and carbenoxolone inhibited pain hypersensitivity and neuronal phosphorylated ERK1/2 at 1 h after the injury.

Conclusion

ERK1/2 phosphorylation in A-fiber neurons and satellite glial cells immediately after injury contributes to the generation of pain hypersensitivity. Signal communication between neurons and satellite glial cells expands the duration of neuronal ERK1/2 phosphorylation and pain hypersensitivity at 1 h after tissue injury.

Lavandula angustifolia Essential Oil and Linalool Counteract Social Aversion Induced by Social Defeat

Many vegetable extracts, essential oils, and their main constituents are active on the Central Nervous System (CNS). In fact, they have been used as sedatives, hypnotics, or tranquilizers for their activity in treating CNS disorders. In this research, we studied the possible activities of Lavandula angustifolia (LA) essential oil and of its main constituent, linalool, as anti-stress compounds on anxiety and social interaction and their in vitro effects on proteins (pERK and PKA) involved in the transmission of the signal. An acute intraperitoneal injection of linalool (100 mg/kg) and of LA essential oil (200 mg/kg) reduced motor activity without any anxiolytic effect, but significantly increased social interaction. Stressed mice, after being exposed to a social defeat encounter, showed heightened anxiety and social avoidance. Acute administration of LA essential oil blocked stress-induced anxiety, while linalool showed no effects. However, both compounds were capable of reversing social aversion, acting as antidepressant agents. Our results showed that linalool inhibits pERK and PKA expression in the SH-SY5Y cell, but no effect was detected with the LA essential oil. Therefore, the LA essential oil and linalool may be considered as useful alternative tools to the available traditional treatments for social stress-induced mental illnesses.

Tau Pathology of Alzheimer Disease: Possible Role of Sleep Deprivation

Sleep deprivation is a common complaint in modern societies. Insufficient sleep has increased the risk of catching neurodegenerative diseases such as Alzheimer’s. Several studies have indicated that restricted sleep increases the level of deposition of β-amyloid and formation of neurofibrillary tangles, the major brain microstructural hallmarks for Alzheimer disease. The mechanisms by which sleep deprivation affects the pathology of Alzheimer disease has not yet been fully and definitively identified. However, risk factors like apolipoprotein E risk alleles, kinases and phosphatases dysregulation, reactive oxygen species, endoplasmic reticulum damages, glymphatic system dysfunctions and orexinergic system inefficacy have been identified as the most important factors which mediates between the two conditions. In this review, these factors are briefly discussed.

Synergistic Inhibition of ERK1/2 and JNK, Not p38, Phosphorylation Ameliorates Neuronal Damages After Traumatic Brain Injury

Mitogen-activated protein (MAP) kinases are serine/threonine protein kinases that play a critical role in signal transduction and are activated by phosphorylation in response to a variety of pathophysiology stimuli. While MAP kinase signaling has a significant role in the pathophysiology of several neurodegenerative diseases, the precise function of activation of MAP kinase in traumatic brain injury (TBI) is unknown. Therefore, it is important to study the role of MAP kinase signaling in TBI-associated neurological ailments. In this study, using an in vitro stretch injury model in rat embryo neuronal cultures and the in vivo fluid percussion injury (FPI) model in rats, we explored the role of MAP kinase signaling in the mechanisms of cell death in TBI. Our study demonstrated that the stretch injury in vitro and FPI in vivo upregulated the phosphorylation of MAP kinase proteins ERK1/2 and JNK, but not p38. Using ERK1/2 inhibitor U0126, JNK inhibitor SP600125, and p38 inhibitor SB203580, we validated the role of MAP kinase proteins in the activation of NF-kB and caspase-3. By immunofluorescence and western blotting, further, we demonstrated the role of ERK1/2 and JNK phosphorylation in neurodegeneration by analyzing cell death proteins annexin V and Poly-ADP-Ribose-Polymerase p85. Interestingly, combined use of ERK1/2 and JNK inhibitors further attenuated the cell death in stretch-injured neurons. In conclusion, this study could establish the significance of MAP kinase signaling in the pathophysiology of TBI and may have significant implications for developing therapeutic strategies using ERK1/2 and JNK inhibitors for TBI-associated neurological complications.

Bumetanide blocks the acquisition of conditioned fear in adult rats

BACKGROUND AND PURPOSE

Bumetanide has anxiolytic effects in rat models of conditioned fear. As a loop diuretic, bumetanide blocks cation-chloride co-transport and this property may allow bumetanide to act as an anxiolytic by modulating GABAergic synaptic transmission in the CNS. Its potential for the treatment of anxiety disorders deserves further investigation. In this study, we evaluated the possible involvement of the basolateral nucleus of the amygdala in the anxiolytic effect of bumetanide.

EXPERIMENTAL APPROACH

Brain slices were prepared from Wistar rats. extracellular recording, stereotaxic surgery, fear-potentiated startle response, locomotor activity monitoring and Western blotting were applied in this study.

KEY RESULTS

Systemic administration of bumetanide (15.2 mg·kg-1 , i.v.), 30 min prior to fear conditioning, significantly inhibited the acquisition of the fear-potentiated startle response. Phosphorylation of ERK in the basolateral nucleus of amygdala was reduced after bumetanide administration. In addition, suprafusion of bumetanide (5 or 10 μM) attenuated long-term potentiation in the amygdala in a dose-dependent manner. Intra-amygdala infusion of bumetanide, 15 min prior to fear conditioning, also blocked the acquisition of the fear-potentiated startle response. Finally, the possible off-target effect of bumetanide on conditioned fear was excluded by side-by-side control experiments.

CONCLUSIONS AND IMPLICATIONS

These results suggest the basolateral nucleus of amygdala plays a critical role in the anxiolytic effects of bumetanide.

Expression and activation of mitogen-activated protein kinases in the optic nerve head in a rat model of ocular hypertension

BACKGROUND

Glaucoma is a leading cause of irreversible blindness manifesting as an age-related, progressive optic neuropathy with associated retinal ganglion cell (RGC) loss. Mitogen-activated protein kinases (MAPKs: p42/44 MAPK, SAPK/JNK, p38 MAPK) are activated in various retinal disease models and likely contribute to the mechanisms of RGC death. Although MAPKs play roles in the development of retinal pathology, their action in the optic nerve head (ONH), where the initial insult to RGC axons likely resides in glaucoma, remains unexplored.

METHODS

An experimental paradigm representing glaucoma was established by induction of chronic ocular hypertension (OHT) via laser-induced coagulation of the trabecular meshwork in Sprague-Dawley rats. MAPKs were subsequently investigated over the following days for expression and activity alterations, using RT-PCR, immunohistochemistry and Western immunoblot.

RESULTS

p42/44 MAPK expression was unaltered after intraocular pressure (IOP) elevation, but there was a significant activation of this enzyme in ONH astrocytes after 6-24 h. Activated SAPK/JNK isoforms were present throughout healthy RGC axons but after IOP elevation or optic nerve crush, they both accumulated at the ONH, likely due to RGC axon transport disruption, and were subject to additional activation. p38 MAPK was expressed by a population of microglia which were significantly more populous following IOP elevation. However it was only significantly activated in microglia after 3 days, and then only in the ONH and optic nerve; in the retina it was solely activated in RGC perikarya.

CONCLUSIONS

In conclusion, each of the MAPKs showed a specific spatio-temporal expression and activation pattern in the retina, ONH and optic nerve as a result of IOP elevation. These findings likely reflect the roles of the individual enzymes, and the cells in which they reside, in the developing pathology following IOP elevation. These data have implications for understanding the mechanisms of ocular pathology in diseases such as glaucoma.

Drug Targets in Neurotrophin Signaling in the Central and Peripheral Nervous System

Neurotrophins are a family of proteins that play an important role in the regulation of the growth, survival, and differentiation of neurons in the central and peripheral nervous system. Neurotrophins were earlier characterized by their role in early development, growth, maintenance, and the plasticity of the nervous system during development, but recent findings also indicate their complex role during normal physiology in both neuronal and non-neuronal tissues. Therefore, it is important to recognize a deficiency in the expression of neurotrophins, a major factor driving the debilitating features of several neurologic and psychiatric diseases/disorders. On the other hand, overexpression of neurotrophins is well known to play a critical role in pathogenesis of chronic pain and afferent sensitization, underlying conditions such as lower urinary tract symptoms (LUTS)/disorders and osteoarthritis. The existence of a redundant receptor system of high-and low-affinity receptors accounts for the diverse, often antagonistic, effects of neurotrophins in neurons and non-neuronal tissues in a spatial and temporal manner. In addition, studies looking at bladder dysfunction because of conditions such as spinal cord injury and diabetes mellitus have found alterations in the levels of these neurotrophins in the bladder, as well as in sensory afferent neurons, which further opens a new avenue for therapeutic targets. In this review, we will discuss the characteristics and roles of key neurotrophins and their involvement in the central and periphery nervous system in both normal and diseased conditions.

Differences in the expression of long noncoding RNAs at different time points in the PTSD-like syndrome rat hippocampus

The aim of this study was to characterize the expression profiles at different time points in the PTSD-like syndrome rat hippocampus and perform analyses. PTSD rat models were made as reported by Rau, and we collected the hippocampus at different time points. The lncRNAs at different time points were compared by microarray and listed. We used quantitative real-time PCR to confirm the lncRNA profiling expression data. Bioinformatics analysis was performed on EU056364_P1. Compare with control, a total of 948 lncRNAs and 2514 mRNAs were found (fold-change > 2.0) among the four time points. Additionally, bioinformatics analysis of EU056364_P1 suggested it might be involved in memory development through the target gene Camk2a.This study revealed different lncRNAs expressed at different time points in PTSD and explored the targets of PTSD.

Nasal TRPA1 mediates irritant-induced bradypnea in mice

Transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily, exists in sensory neurons such as trigeminal neurons innervating the nasal cavity and vagal neurons innervating the trachea and the lung. Although TRPA1 has been proposed as an irritant receptor that, when stimulated, triggers bradypnea, precise locations of the receptors responsible have not been elucidated. Here, we examined the relative importance of TRPA1 located in the upper airway (nasal) and the lower airway (trachea/lungs) in urethane-anesthetized mice. To stimulate the upper and lower airways separately, two cannulas were inserted through a hole made in the trachea just caudal to the thyroid cartilage, one into the nasal cavity and the second into the lower trachea. A vapor of one of the TRPA1-agonists, allyl isothiocyanate (AITC), was introduced by placing a piece of cotton paper soaked with AITC solution into the airline. AITC decreased the respiratory frequency when applied to the upper airway (ca -30%) but not to the lower airway (ca -5%). No response was observed in TRPA1 knockout mice. Contribution of the olfactory nerve seemed minimal because olfactory bulbectomized wild-type mice showed a similar response to that of the intact mice. AITC-induced bradypnea seemed to be mediated, at least in part, by the trigeminal nerve because trigeminal ganglion neurons were activated by AITC as revealed by an increase in the phosphorylated form of extracellular signal-regulated kinase in the neurons. These data clearly show that trigeminal TRPA1 in the nasal cavity play an essential role in irritant-induced bradypnea.

MK-STYX Alters the Morphology of Primary Neurons, and Outgrowths in MK-STYX Overexpressing PC-12 Cells Develop a Neuronal Phenotype

We previously reported that the pseudophosphatase MK-STYX (mitogen activated kinase phosphoserine/threonine/tyrosine binding protein) dramatically increases the number of what appeared to be primary neurites in rat pheochromocytoma (PC-12) cells; however, the question remained whether these MK-STYX-induced outgrowths were bona fide neurites, and formed synapses. Here, we report that microtubules and microfilaments, components of the cytoskeleton that are involved in the formation of neurites, are present in MK-STYX-induced outgrowths. In addition, in response to nerve growth factor (NGF), MK-STYX-expressing cells produced more growth cones than non-MK-STYX-expressing cells, further supporting a model in which MK-STYX has a role in actin signaling. Furthermore, immunoblot analysis demonstrates that MK-STYX modulates actin expression. Transmission electron microscopy confirmed that MK-STYX-induced neurites form synapses. To determine whether these MK-STYX-induced neurites have pre-synaptic or post-synaptic properties, we used classical markers for axons and dendrites, Tau-1 and MAP2 (microtubule associated protein 2), respectively. MK-STYX induced neurites were dopaminergic and expression of both Tau-1 and MAP2 suggests that they have both axonal and dendritic properties. Further studies in rat hippocampal primary neurons demonstrated that MK-STYX altered their morphology. A significant number of primary neurons in the presence of MK-STYX had more than the normal number of primary neurites. Our data illustrate the novel findings that MK-STYX induces outgrowths in PC-12 cells that fit the criteria for neurites, have a greater number of growth cones, form synapses, and have pre-synaptic and post-synaptic properties. It also highlights that the pseudophosphatase MK-STYX significantly alters the morphology of primary neurons.

Cannabinoid Receptor Type 1 Agonist ACEA Protects Neurons from Death and Attenuates Endoplasmic Reticulum Stress-Related Apoptotic Pathway Signaling

Neurodegeneration is the result of progressive destruction of neurons in the central nervous system, with unknown causes and pathological mechanisms not yet fully elucidated. Several factors contribute to neurodegenerative processes, including neuroinflammation, accumulation of neurotoxic factors, and misfolded proteins in the lumen of the endoplasmic reticulum (ER). Endocannabinoid signaling has been pointed out as an important modulatory system in several neurodegeneration-related processes, inhibiting the inflammatory response and increasing neuronal survival. Thus, we investigated the presumptive protective effect of the selective cannabinoid type 1 (CB1) receptor agonist arachidonyl-2'-chloroethylamide (ACEA) against inflammatory (lipopolysaccharide, LPS) and ER stress (tunicamycin) stimuli in an in vitro neuronal model (Neuro-2a neuroblastoma cells). Cell viability analysis revealed that ACEA was able to protect against cell death induced by LPS and tunicamycin. This neuroprotective effect occurs via the CB1 receptor in the inflammation process and via the transient receptor potential of vanilloid type-1 (TRPV1) channel in ER stress. Furthermore, the immunoblotting analyses indicated that the neuroprotective effect of ACEA seems to involve the modulation of eukaryotic initiation factor 2 (eIF2α), transcription factor C/EBP homologous protein (CHOP), and caspase 12, as well as the survival/death p44/42 MAPK, ERK1/2-related signaling pathways. Together, these data suggest that the endocannabinoid system is a potential therapeutic target in neurodegenerative processes, especially in ER-related neurodegenerative diseases.

Association analysis between mitogen-activated protein/extracellular signal-regulated kinase (MEK) gene polymorphisms and depressive disorder in the Han Chinese population

BACKGROUND

Recent research findings suggest that BDNF and BDNF signaling pathways participate in the development of major depressive disorder. Mitogen-activated extracellular signal-regulated kinase (MEK) is the most important kinase in the extracellular signal-regulated kinase pathway, and the extracellular signal-regulated kinase pathway is the key signaling pathway of BDNF, so it may play a role in development of depressive disorder. The aim of this study is to investigate the association between polymorphisms of the MAP2K1 (also known as MEK) gene and depressive disorder.

RESULTS

Three single nucleotide polymorphisms (SNPs), were significantly associated with depressive disorder: rs1549854 (p = 0.006), rs1432441 (p = 0.025), and rs7182853 (p = 0.039). When subdividing the sample by gender, two of the SNPs remained statistically associated with depressive disorder in females: rs1549854 (p = 0.013) and rs1432441 (p = 0.04).

CONCLUSION

The rs1549854 and rs1432441 polymorphisms of the MAP2K1 gene may be associated with major depressive disorder, especially in females. This study is the first to report that the MAP2K1 gene may be a genetic marker for depressive disorder.

Calreticulin promotes EGF-induced EMT in pancreatic cancer cells via Integrin/EGFR-ERK/MAPK signaling pathway

Our previous study showed that Calreticulin (CRT) promoted the development of pancreatic cancer (PC) through ERK/MAPK pathway. We next investigate whether CRT promotes EGF-induced epithelial-mesenchymal transition (EMT) in PC via Integrin/EGFR-ERK/MAPK signaling, which has not been reported yet to our knowledge. EGF simultaneously induced EMT and activated Integrin/EGFR-ERK/MAPK signaling pathway in 3 PC cells. However, CRT silencing significantly inhibited EGF function, including inhibiting EGF-induced EMT-like cell morphology, EGF-enhanced cell invasion and migration, and EGF induced the decrease of E-cadherin, ZO-1, and β-catenin and the increase of the key proteins in Integrin/EGFR-ERK/MAPK signaling (pEGFR-tyr1173, Fibronectin, Integrinβ1, c-Myc and pERK). Conversely, CRT overexpression rescued the change of EMT-related proteins induced by EGF in CRT silencing PC cells. Additionally, CRT was co-stained with pEGFR1173 (with EGF), Fibronectin and Integrinβ1 by IF under confocal microscopy and was co-immunoprecipitated with Fibronectin, Integrinβ1 and c-Myc in both PC cells, all of which indicating a close interaction of CRT with Integrin/EGFR-ERK/MAPK signaling pathway in PC. In vivo, CRT silencing inhibited subcutaneous tumor growth and liver metastasis of pancreatic tumor. A positive relationship of CRT with Fibronectin, Integrinβ1, c-Myc and pERK and a negative association of CRT with E-cad was also observed in vivo and clinical samples. Meanwhile, overexpression of the above proteins was closely associated with multiple aggressive clinicopathological characteristics and the poor prognosis of PC patients. CRT promotes EGF-induced EMT in PC cells via Integrin/EGFR-ERK/MAPK signaling pathway, which would be a promising therapy target for PC.

LPA1 is a key mediator of intracellular signalling and neuroprotection triggered by tetracyclic antidepressants in hippocampal neurons

Both lysophosphatidic acid (LPA) and antidepressants have been shown to affect neuronal survival and differentiation, but whether LPA signalling participates in the action of antidepressants is still unknown. In this study, we examined the role of LPA receptors in the regulation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) activity and neuronal survival by the tetracyclic antidepressants, mianserin and mirtazapine in hippocampal neurons. In HT22 immortalized hippocampal cells, antidepressants and LPA induced a time- and concentration-dependent stimulation of ERK1/2 phosphorylation. This response was inhibited by either LPA₁ and LPA_1/3 selective antagonists or siRNA-induced LPA₁ down-regulation, and enhanced by LPA₁ over-expression. Conversely, the selective LPA₂ antagonist H2L5186303 had no effect. Antidepressants induced cyclic AMP response element binding protein phosphorylation and this response was prevented by LPA₁ blockade. ERK1/2 stimulation involved pertussis toxin-sensitive G proteins, Src tyrosine kinases and fibroblast growth factor receptor (FGF-R) activity. Tyrosine phosphorylation of FGF-R was enhanced by antidepressants through LPA₁ . Serum withdrawal induced apoptotic death, as indicated by increased annexin V staining, caspase activation and cleavage of poly-ADP-ribose polymerase. Antidepressants inhibited the apoptotic cascade and this protective effect was curtailed by blockade of either LPA₁ , ERK1/2 or FGF-R activity. Moreover, in primary mouse hippocampal neurons, mianserin acting through LPA₁ increased phospho-ERK1/2 and protected from apoptosis induced by removal of growth supplement. These data indicate that in neurons endogenously expressed LPA₁ receptors mediate intracellular signalling and neuroprotection by tetracyclic antidepressants.

Noxious, but not innocuous, thermal stimuli evoke pERK expression in dorsal horn neurons after spared nerve injury in adult rats

Noxious stimulation of sensory afferents evokes phosphorylated extracellular signal regulated kinase (pERK) expression in spinal cord neurons. This study investigated the expression of pERK in the dorsal horn neurons in response to innocuous and noxious cold stimuli in naïve versus spared nerve injury (SNI) rats. Noxious cold or hot stimuli (0 or 45°C) elicited pERK expression in laminae I-II whereas cooling stimuli from 32°C to 25, 15 or 5°C produced no or little pERK expression in dorsal horn neurons. Five days after SNI, a time when these animals showed heat hyperalgesia, cold and mechanical hypersensitivity, only noxious heat stimuli produced a significant increase in pERK expression compared to naïve rats in spinal cord neurons. Thus, pERK cannot be used as an activity marker for neurons responding to cooling stimuli or cold allodynia; however, these results confirm the role of pERK as an activity marker for heat hyperalgesia.