Specific activities of individual c-Jun N-terminal kinases in the brain

Maintaining Toll signaling in Drosophila brain is required to sustain autophagy for dopamine neuron survival

Macroautophagy/autophagy is a conserved process in eukaryotic cells to degrade and recycle damaged intracellular components. Higher level of autophagy in the brain has been observed, and autophagy dysfunction has an impact on neuronal health, but the molecular mechanism is unclear. In this study, we showed that overexpression of Toll-1 and Toll-7 receptors, as well as active Spätzle proteins in Drosophila S2 cells enhanced autophagy, and Toll-1/Toll-7 activated autophagy was dependent on Tube-Pelle-PP2A. Interestingly, Toll-1 but not Toll-7 mediated autophagy was dMyd88 dependent. Importantly, we observed that loss of functions in Toll-1 and Toll-7 receptors and PP2A activity in flies decreased autophagy level, resulting in the loss of dopamine (DA) neurons and reduced fly motion. Our results indicated that proper activation of Toll-1 and Toll-7 pathways and PP2A activity in the brain are necessary to sustain autophagy level for DA neuron survival.

Regulatory mechanisms and therapeutic potential of JAB1 in neurological development and disorders

c-Jun activation domain binding protein-1 (JAB1) is a multifunctional regulator that plays vital roles in diverse cellular processes. It regulates AP-1 transcriptional activity and also acts as the fifth component of the COP9 signalosome complex. While JAB1 is considered an oncoprotein that triggers tumor development, recent studies have shown that it also functions in neurological development and disorders. In this review, we summarize the general features of the JAB1 gene and protein, and present recent updates on the regulation of JAB1 expression. Moreover, we also highlight the functional roles and regulatory mechanisms of JAB1 in neurodevelopmental processes such as neuronal differentiation, synaptic morphogenesis, myelination, and hair cell development and in the pathogenesis of some neurological disorders such as Alzheimer's disease, multiple sclerosis, neuropathic pain, and peripheral nerve injury. Furthermore, current challenges and prospects are discussed, including updates on drug development targeting JAB1.

Neuroprotective Effect of Luteolin-7-O-Glucoside against 6-OHDA-Induced Damage in Undifferentiated and RA-Differentiated SH-SY5Y Cells

Luteolin is one of the most common flavonoids present in edible plants and its potential benefits to the central nervous system include decrease of microglia activation, neuronal damage and high antioxidant properties. The aim of this research was to evaluate the neuroprotective, antioxidant and anti-inflammatory activities of luteolin-7-O-glucoside (Lut7). Undifferentiated and retinoic acid (RA)-differentiated SH-SY5Y cells were pretreated with Lut7 and incubated with 6-hydroxydopamine (6-OHDA). Cytotoxic and neuroprotective effects were determined by MTT assay. Antioxidant capacity was determined by DPPH, FRAP, and ORAC assays. ROS production, mitochondrial membrane potential (ΔΨm), Caspase–3 activity, acetylcholinesterase inhibition (AChEI) and nuclear damage were also determined in SH-SY5Y cells. TNF-α, IL-6 and IL-10 release were evaluated in LPS-induced RAW264.7 cells by ELISA. In undifferentiated SH-SY5Y cells, Lut7 increased cell viability after 24 h, while in RA-differentiated SH-SY5Y cells, Lut7 increased cell viability after 24 and 48 h. Lut7 showed a high antioxidant activity when compared with synthetic antioxidants. In undifferentiated cells, Lut7 prevented mitochondrial membrane depolarization induced by 6-OHDA treatment, decreased Caspase-3 and AChE activity, and inhibited nuclear condensation and fragmentation. In LPS-stimulated RAW264.7 cells, Lut7 treatment reduced TNF-α levels and increased IL-10 levels after 3 and 24 h, respectively. In summary, the results suggest that Lut7 has neuroprotective effects, thus, further studies should be considered to validate its pharmacological potential in more complex models, aiming the treatment of neurodegenerative diseases.

Functional Roles of JNK and p38 MAPK Signaling in Nasopharyngeal Carcinoma

c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) family members integrate signals that affect proliferation, differentiation, survival, and migration in a cell context- and cell type-specific way. JNK and p38 MAPK activities are found upregulated in nasopharyngeal carcinoma (NPC). Studies have shown that activation of JNK and p38 MAPK signaling can promote NPC oncogenesis by mechanisms within the cancer cells and interactions with the tumor microenvironment. They regulate multiple transcription activities and contribute to tumor-promoting processes, ranging from cell proliferation to apoptosis, inflammation, metastasis, and angiogenesis. Current literature suggests that JNK and p38 MAPK activation may exert pro-tumorigenic functions in NPC, though the underlying mechanisms are not well documented and have yet to be fully explored. Here, we aim to provide a narrative review of JNK and p38 MAPK pathways in human cancers with a primary focus on NPC. We also discuss the potential therapeutic agents that could be used to target JNK and p38 MAPK signaling in NPC, along with perspectives for future works. We aim to inspire future studies further delineating JNK and p38 MAPK signaling in NPC oncogenesis which might offer important insights for better strategies in diagnosis, prognosis, and treatment decision-making in NPC patients.

Alternative Splicing of MAPKs in the Regulation of Signaling Specificity

The mitogen-activated protein kinase (MAPK) cascades transmit signals from extracellular stimuli to a variety of distinct cellular processes. The MAPKKs in each cascade specifically phosphorylate and activate their cognate MAPKs, indicating that this step funnels various signals into a seemingly linear pathway. Still, the effects of these cascades vary significantly, depending on the identity of the extracellular signals, which gives rise to proper outcomes. Therefore, it is clear that the specificity of the signals transmitted through the cascades is tightly regulated in order to secure the desired cell fate. Indeed, many regulatory components or processes that extend the specificity of the cascades have been identified. Here, we focus on a less discussed mechanism, that is, the role of distinct components in each tier of the cascade in extending the signaling specificity. We cover the role of distinct genes, and the alternatively spliced isoforms of MAPKKs and MAPKs, in the signaling specificity. The alternatively spliced MEK1b and ERK1c, which form an independent signaling route, are used as the main example. Unlike MEK1/2 and ERK1/2, this route’s functions are limited, including mainly the regulation of mitotic Golgi fragmentation. The unique roles of the alternatively spliced isoforms indicate that these components play an essential role in determining the proper cell fate in response to distinct stimulations.

Axonal injury following mild traumatic brain injury is exacerbated by repetitive insult and is linked to the delayed attenuation of NeuN expression without concomitant neuronal death in the mouse

Mild traumatic brain injury (mTBI) affects brain structure and function and can lead to persistent abnormalities. Repetitive mTBI exacerbates the acute phase response to injury. Nonetheless, its long‐term implications remain poorly understood, particularly in the context of traumatic axonal injury (TAI), a player in TBI morbidity via axonal disconnection, synaptic loss and retrograde neuronal perturbation. In contrast to the examination of these processes in the acute phase of injury, the chronic‐phase burden of TAI and/or its implications for retrograde neuronal perturbation or death have received little consideration. To critically assess this issue, murine neocortical tissue was investigated at acute (24‐h postinjury, 24hpi) and chronic time points (28‐days postinjury, 28dpi) after singular or repetitive mTBI induced by central fluid percussion injury (cFPI). Neurons were immunofluorescently labeled for NeuroTrace and NeuN (all neurons), p‐c‐Jun (axotomized neurons) and DRAQ5 (cell nuclei), imaged in 3D and quantified in automated manner. Single mTBI produced axotomy in 10% of neurons at 24hpi and the percentage increased after repetitive injury. The fraction of p‐c‐Jun+ neurons decreased at 28dpi but without neuronal loss (NeuroTrace), suggesting their reorganization and/or repair following TAI. In contrast, NeuN+ neurons decreased with repetitive injury at 24hpi while the corresponding fraction of NeuroTrace+ neurons decreased over 28dpi. Attenuated NeuN expression was linked exclusively to non‐axotomized neurons at 24hpi which extended to the axotomized at 28dpi, revealing a delayed response of the axotomized neurons. Collectively, we demonstrate an increased burden of TAI after repetitive mTBI, which is most striking in the acute phase response to the injury. Our finding of widespread axotomy in large fields of intact neurons contradicts the notion that repetitive mTBI elicits progressive neuronal death, rather, emphasizing the importance of axotomy‐mediated change.

Discovery of a Potent and Selective JNK3 Inhibitor with Neuroprotective Effect Against Amyloid β-Induced Neurotoxicity in Primary Rat Neurons

As members of the MAPK family, c-Jun-N-terminal kinases (JNKs) regulate the biological processes of apoptosis. In particular, the isoform JNK3 is expressed explicitly in the brain at high levels and is involved in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). In this study, we prepared a series of five 6-dihydroxy-1H-benzo[d]imidazoles as JNK3 inhibitors and found them have potential as neuroprotective agents. Following a previous lead scaffold, benzimidazole moiety was modified with various aryl groups and hydroxylation, and the resulting compounds exhibited JNK3 inhibitory activity with improved potency and selectivity. Out of 37 analogues synthesized, (S)-cyclopropyl(3-((4-(2-(2,3-dihydrobenzo[b][1,4]dioxin -6-yl)-5,6-dihydroxy-1H-benzo[d]imidazol-1-yl)pyrimidin-2-yl)amino) piperidin-1-yl)methanone (35b) demonstrated the highest JNK3 inhibition (IC₅₀ = 9.7 nM), as well as neuroprotective effects against Aβ-induced neuronal cell death. As a protein kinase inhibitor, it also showed excellent selectivity over other protein kinases including isoforms JNK1 (>1000 fold) and JNK2 (−10 fold).

Suppression of LPS-Induced Inflammation and Cell Migration by Azelastine through Inhibition of JNK/NF-κB Pathway in BV2 Microglial Cells

The c-Jun N-terminal kinases (JNKs) are implicated in many neuropathological conditions, including neurodegenerative diseases. To explore potential JNK3 inhibitors from the U.S. Food and Drug Administration-approved drug library, we performed structure-based virtual screening and identified azelastine (Aze) as one of the candidates. NMR spectroscopy indicated its direct binding to the ATP-binding site of JNK3, validating our observations. Although the antihistamine effect of Aze is well documented, the involvement of the JNK pathway in its action remains to be elucidated. This study investigated the effects of Aze on lipopolysaccharide (LPS)-induced JNK phosphorylation, pro-inflammatory mediators, and cell migration in BV2 microglial cells. Aze was found to inhibit the LPS-induced phosphorylation of JNK and c-Jun. It also inhibited the LPS-induced production of pro-inflammatory mediators, including interleukin-6, tumor necrosis factor-α, and nitric oxide. Wound healing and transwell migration assays indicated that Aze attenuated LPS-induced BV2 cell migration. Furthermore, Aze inhibited LPS-induced IκB phosphorylation, thereby suppressing nuclear translocation of NF-κB. Collectively, our data demonstrate that Aze exerts anti-inflammatory and anti-migratory effects through inhibition of the JNK/NF-κB pathway in BV2 cells. Based on our findings, Aze may be a potential candidate for drug repurposing to mitigate neuroinflammation in various neurodegenerative disorders, including Alzheimer’s and Parkinson’s diseases.

JNK/Elk1 signaling and PCNA protein expression in the brain of hibernating frog Pelophylax esculentus

Mitogen activated protein kinase (MAPK) activation and neurogenesis are known to play a role in neuronal survival during hibernation. Herein, we investigate the activity of c-Jun N-terminal kinases (JNK) and Ets like-1 protein (Elk1) kinase involved in cell survival, as well as the expression of proliferating cell nuclear antigen (PCNA), a cell proliferation marker, in the brain of the frog Pelophylax esculentus. The study was conducted on female and male frogs collected during the annual cycle. Our results demonstrated that JNK activity increased during the hibernating phase in relation to the active phase. Interestingly, P-Elk1 levels were positively correlated with P-JNK levels, suggesting that the JNK/Elk1 pathway is pivotal in mediating neuroprotective adaptations that are essential to successful hibernation. On the contrary, we detected higher PCNA expression levels during the active period compared with the hibernating period. A sex dimorphism was observed in the expression levels of P-JNK/P-Elk1 that were specifically higher in males, and in the expression of PCNA reporting higher levels in female brains. Much remains to be learned regarding the regulation of hibernation, however, our findings provide new insights into the role of MAPK and proliferative pathways in hibernation, adding new knowledge concerning the mechanisms activated in the brain of ectothermic species to counteract the damage resulting from extreme temperatures.

c-Jun N-Terminal Kinase Inhibitors as Potential Leads for New Therapeutics for Alzheimer's Diseases

Alzheimer's Disease (AD) is becoming more prevalent as the population lives longer. For individuals over 60 years of age, the prevalence of AD is estimated at 40.19% across the world. Regarding the cognitive decline caused by the disease, mitogen-activated protein kinases (MAPK) pathways such as the c-Jun N-terminal kinase (JNK) pathway are involved in the progressive loss of neurons and synapses, brain atrophy, and augmentation of the brain ventricles, being activated by synaptic dysfunction, oxidative stress, and excitotoxicity. Nowadays, AD symptoms are manageable, but the disease itself remains incurable, thus the inhibition of JNK3 has been explored as a possible therapeutic target, considering that JNK is best known for its involvement in propagating pro-apoptotic signals. This review aims to present biological aspects of JNK, focusing on JNK3 and how it relates to AD. It was also explored the recent development of inhibitors that could be used in AD treatment since several drugs/compounds in phase III clinical trials failed. General aspects of the MAPK family, therapeutic targets, and experimental treatment in models are described and discussed throughout this review.

Clinically Precedented Protein Kinases: Rationale for Their Use in Neurodegenerative Disease

Kinases are an intensively studied drug target class in current pharmacological research as evidenced by the large number of kinase inhibitors being assessed in clinical trials. Kinase-targeted therapies have potential for treatment of a broad array of indications including central nervous system (CNS) disorders. In addition to the many variables which contribute to identification of a successful therapeutic molecule, drug discovery for CNS-related disorders also requires significant consideration of access to the target organ and specifically crossing the blood-brain barrier (BBB). To date, only a small number of kinase inhibitors have been reported that are specifically designed to be BBB permeable, which nonetheless demonstrates the potential for success. This review considers the potential for kinase inhibitors in the context of unmet medical need for neurodegenerative disease. A subset of kinases that have been the focus of clinical investigations over a 10-year period have been identified and discussed individually. For each kinase target, the data underpinning the validity of each in the context of neurodegenerative disease is critically evaluated. Selected molecules for each kinase are identified with information on modality, binding site and CNS penetrance, if known. Current clinical development in neurodegenerative disease are summarized. Collectively, the review indicates that kinase targets with sufficient rationale warrant careful design approaches with an emphasis on improving brain penetrance and selectivity.

A novel genomic region on chromosome 11 associated with fearfulness in dogs

The complex phenotypic and genetic nature of anxieties hampers progress in unravelling their molecular etiologies. Dogs present extensive natural variation in fear and anxiety behaviour and could advance the understanding of the molecular background of behaviour due to their unique breeding history and genetic architecture. As dogs live as part of human families under constant care and monitoring, information from their behaviour and experiences are easily available. Here we have studied the genetic background of fearfulness in the Great Dane breed. Dogs were scored and categorised into cases and controls based on the results of the validated owner-completed behavioural survey. A genome-wide association study in a cohort of 124 dogs with and without socialisation as a covariate revealed a genome-wide significant locus on chromosome 11. Whole exome sequencing and whole genome sequencing revealed extensive regions of opposite homozygosity in the same locus on chromosome 11 between the cases and controls with interesting neuronal candidate genes such as MAPK9/JNK2, a known hippocampal regulator of anxiety. Further characterisation of the identified locus will pave the way for molecular understanding of fear in dogs and may provide a natural animal model for human anxieties.

Discovery of 1-Pyrimidinyl-2-Aryl-4,6-Dihydropyrrolo [3,4-d]Imidazole-5(1H)-Carboxamide as a Novel JNK Inhibitor

We designed and synthesized 1-pyrimidinyl-2-aryl-4, 6-dihydropyrrolo [3,4-d] imidazole-5(1H)-carboxamide derivatives as selective inhibitors of c-Jun-N-terminal Kinase 3 (JNK3), a target for the treatment of neurodegenerative diseases. Based on the compounds found in previous studies, a novel scaffold was designed to improve pharmacokinetic characters and activity, and compound 18a, (R)-1-(2-((1-(cyclopropanecarbonyl)pyrrolidin-3-yl)amino)pyrimidin-4-yl)-2-(3,4-dichlorophenyl)-4,6-dihydro pyrrolo [3,4-d]imidazole-5(1H)-carboxamide, showed the highest IC₅₀ value of 2.69 nM. Kinase profiling results also showed high selectivity for JNK3 among 38 kinases, having mild activity against JNK2, RIPK3, and GSK3β, which also known to involve in neuronal apoptosis.

Discovery of 3-alkyl-5-aryl-1-pyrimidyl-1H-pyrazole derivatives as a novel selective inhibitor scaffold of JNK3

3-alkyl-5-aryl-1-pyrimidyl-1H-pyrazole derivatives were designed and synthesised as selective inhibitors of JNK3, a target for the treatment of neurodegenerative diseases. Following previous studies, we have designed JNK3 inhibitors to reduce the molecular weight and successfully identified a lead compound that exhibits equipotent activity towards JNK3. Kinase profiling results also showed high selectivity for JNK3 among 38 kinases. Among the derivatives, the IC₅₀ value of 8a, (R)-2-(1-(2-((1-(cyclopropanecarbonyl)pyrrolidin-3-yl)amino)pyrimidin-4-yl)-5-(3,4-dichlorophenyl)-1H-pyrazol-3-yl)acetonitrile exhibited 227 nM, showing the highest inhibitory activity against JNK3.

The Y172 Monoclonal Antibody Against p-c-Jun (Ser63) Is a Marker of the Postsynaptic Compartment of C-Type Cholinergic Afferent Synapses on Motoneurons

C-bouton-type cholinergic afferents exert an important function in controlling motoneuron (MN) excitability. During the immunocytochemical analysis of the role of c-Jun in MNs with a monoclonal (clone Y172) antibody against phospho (p)-c-Jun (serine [Ser]63), unexpected labeling was identified in the cell body cytoplasm. As predicted for c-Jun in adult spinal cord, very few, if any MNs exhibited nuclear immunoreactivity with the Y172 antibody; conversely, virtually all MNs displayed strong Y172 immunostaining in cytoplasmic structures scattered throughout the soma and proximal dendrites. The majority of these cytoplasmic Y172-positive profiles was closely associated with VAChT-positive C-boutons, but not with other types of nerve afferents contacting MNs. Ultrastructural analysis revealed that cytoplasmic Y172 immunostaining was selectively located at the subsurface cistern (SSC) of C-boutons and also in the inner areas of the endoplasmic reticulum (ER). We also described changes in cytoplasmic Y172 immunoreactivity in injured and degenerating MNs. Moreover, we noticed that MNs from NRG1 type III-overexpressing transgenic mice, which show abnormally expanded SSCs, exhibited an increase in the density and size of peripherally located Y172-positive profiles. A similar immunocytochemical pattern to that of the Y172 antibody in MNs was found with a polyclonal antibody against p-c-Jun (Ser63) but not with another polyclonal antibody that recognizes c-Jun phosphorylated at a different site. No differential band patterns were found by western blotting with any of the antibodies against c-Jun or p-c-Jun used in our study. In cultured MNs, Y172-positive oval profiles were distributed in the cell body and proximal dendrites. The in vitro lentiviral-based knockdown of c-Jun resulted in a dramatic decrease in nuclear Y172 immunostaining in MNs without any reduction in the density of cytoplasmic Y172-positive profiles, suggesting that the synaptic antigen recognized by the antibody corresponds to a C-bouton-specific protein other than p-c-Jun. Our results lay the foundation for further studies aimed at identifying this protein and determining its role in this particular type of synapse.

Role of c-Jun N-Terminal Kinases (JNKs) in Epilepsy and Metabolic Cognitive Impairment

Previous studies have reported that the regulatory function of the different c-Jun N-terminal kinases isoforms (JNK1, JNK2, and JNK3) play an essential role in neurological disorders, such as epilepsy and metabolic-cognitive alterations. Accordingly, JNKs have emerged as suitable therapeutic strategies. In fact, it has been demonstrated that some unspecific JNK inhibitors exert antidiabetic and neuroprotective effects, albeit they usually show high toxicity or lack therapeutic value. In this sense, natural specific JNK inhibitors, such as Licochalcone A, are promising candidates. Nonetheless, research on the understanding of the role of each of the JNKs remains mandatory in order to progress on the identification of new selective JNK isoform inhibitors. In the present review, a summary on the current gathered data on the role of JNKs in pathology is presented, as well as a discussion on their potential role in pathologies like epilepsy and metabolic-cognitive injury. Moreover, data on the effects of synthetic small molecule inhibitors that modulate JNK-dependent pathways in the brain and peripheral tissues is reviewed.

Role of brain c-Jun N-terminal kinase 2 in the control of the insulin receptor and its relationship with cognitive performance in a high-fat diet pre-clinical model

Insulin resistance has negative consequences on the physiological functioning of the nervous system. The appearance of type 3 diabetes in the brain leads to the development of the sporadic form of Alzheimer's disease. The c-Jun N-terminal kinases (JNK), a subfamily of the Mitogen Activated Protein Kinases, are enzymes composed by three different isoforms with differential modulatory activity against the insulin receptor (IR) and its substrate. This research focused on understanding the regulatory role of JNK2 on the IR, as well as study the effect of a high-fat diet (HFD) in the brain. Our observations determined how JNK2 ablation did not induce compensatory responses in the expression of the other isoforms but led to an increase in JNKs total activity. HFD-fed animals also showed an increased activity profile of the JNKs. These animals also displayed endoplasmic reticulum stress and up-regulation of the protein tyrosine phosphatase 1B (PTP1B) and the suppressor of cytokine signalling 3 protein. Consequently, a reduction in insulin sensitivity was detected and it is correlated with a decrease on the signalling of the IR. Moreover, cognitive impairment was observed in all groups but only wild-type genotype animals fed with HFD showed neuroinflammatory responses. In conclusion, HFD and JNK2 absence cause alterations in normal cognitive activity by altering the signalling of the IR. These affectations are related to the appearance of endoplasmic reticulum stress and an increase in the levels of inhibitory proteins like PTP1B and suppressor of cytokine signalling 3 protein. Cover Image for this issue: doi: 10.1111/jnc.14502.

The Nuclear Translocation of Mitogen-Activated Protein Kinases: Molecular Mechanisms and Use as Novel Therapeutic Target

The mitogen-activated protein kinase (MAPK) cascades are central signaling pathways that play a central role in the regulation of most stimulated cellular processes including proliferation, differentiation, stress response and apoptosis. Currently 4 such cascades are known, each termed by its downstream MAPK components: the extracellular signal-regulated kinase 1/2 (ERK1/2), cJun-N-terminal kinase (JNK), p38 and ERK5. One of the hallmarks of these cascades is the stimulated nuclear translocation of their MAPK components using distinct mechanisms. ERK1/2 are shuttled into the nucleus by importin7, JNK and p38 by a dimer of importin3 with either importin9 or importin7, and ERK5 by importin-α/β. Dysregulation of these cascades often results in diseases, including cancer and inflammation, as well as developmental and neurological disorders. Much effort has been invested over the years in developing inhibitors to the MAPK cascades to combat these diseases. Although some inhibitors are already in clinical use or clinical trials, their effects are hampered by development of resistance or adverse side-effects. Recently, our group developed 2 myristoylated peptides: EPE peptide, which inhibits the interaction of ERK1/2 with importin7, and PERY peptide, which prevents JNK/p38 interaction with either importin7 or importin9. These peptides block the nuclear translocation of their corresponding kinases, resulting in prevention of several cancers, while the PERY peptide also inhibits inflammation-induced diseases. These peptides provide a proof of concept for the use of the nuclear translocation of MAPKs as therapeutic targets for cancer and/or inflammation.

Growth Cone Phosphoproteomics Reveals that GAP-43 Phosphorylated by JNK Is a Marker of Axon Growth and Regeneration

Neuronal growth cones are essential for nerve growth and regeneration, as well as for the formation and rearrangement of the neural network. To elucidate phosphorylation-dependent signaling pathways and establish useful molecular markers for axon growth and regeneration, we performed a phosphoproteomics study of mammalian growth cones, which identified >30,000 phosphopeptides of ∼1,200 proteins. The phosphorylation sites were highly proline directed and primarily MAPK dependent, owing to the activation of JNK, suggesting that proteins that undergo proline-directed phosphorylation mediate nerve growth in the mammalian brain. Bioinformatics analysis revealed that phosphoproteins were enriched in microtubules and the cortical cytoskeleton. The most frequently phosphorylated site was S96 of GAP-43 (growth-associated protein 43-kDa), a vertebrate-specific protein involved in axon growth. This previously uncharacterized phosphorylation site was JNK dependent. S96 phosphorylation was specifically detected in growing and regenerating axons as the most frequent target of JNK signaling; thus it represents a promising new molecular marker for mammalian axonal growth and regeneration.

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Phosphoproteomics of mammalian growth cone membranes reveals activation of MAPK

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JNK is the activated MAPK in growth cones and phosphorylates S96 of GAP-43

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pS96 of GAP-43, the most frequent site, is observed in growing axons

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pS96 is biochemically detected in the regenerating axons of the peripheral nerves

The impact of neuronal Notch-1/JNK pathway on intracerebral hemorrhage-induced neuronal injury of rat model

Notch signaling is a highly conserved pathway that regulates cell fate decisions during embryonic development. Notch activation endangers neurons by modulating NF-κB and HIF-1α pathways, however, the role of Notch signaling in activating JNK/c-Jun following intracerebral hemorrhage (ICH) has not been investigated. In this study, we used rat ICH models and thrombin-induced cell models to investigate the potential role of Notch-1/JNK signals. Our findings revealed that Notch-1 and JNK increased in hematoma-surrounding neurons tissues following ICH during ischemic conditions (all p<0.05). Besides, the expression of active caspase-3 protein was also up-regulated after ICH. According to in-vitro assays, the expression of Notch-1, p-JNK, and active caspase-3 were all up-regulated in cell viability-decreasing ICH cell models (all p<0.05). However, blocking of either Notch-1 or JNK suppressed the phosphorylation of JNK and the expression of active caspase-3, and cell viability was obviously ameliorated. In conclusion, this work suggested Notch-1 activates JNK pathway to induce the active caspase-3, leading to neuronal injury when intracerebral hemorrhage or ischemia occurred. Thus the Notch-1/JNK signal pathway has an important role in ICH process, and may be a therapeutic target to prevent brain injury.

MAPK pathway mediates the anti-oxidative effect of chicoric acid against cerebral ischemia-reperfusion injury in vivo

The aim of the present study was to investigate the protective effect of chicoric acid on oxidative stress and inflammation in rats with cerebral ischemia-reperfusion injury. A cerebral ischemia-reperfusion injury rat model was created via transient middle cerebral artery occlusion (MCAO) and rats were treated with various doses of chicoric acid (0, 1, 10 and 100 mg/kg). Neurological deficits and infarct volume were used to estimate the protective effects of chicoric acid treatment. Levels of reactive oxygen species (ROS), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, nitric oxide (NO) and prostaglandin E2 (PGE2) were assessed. Western blot analysis was also used to measure the expression of cyclooxygenase (COX)-2, p38-mitogen activated protein kinase (MAPK), c-Jun, phosphorylated protein kinase B (p-AKT) and AKT. Chicoric acid exposure was observed to reduce neurological deficits and infarct volume in rats with cerebral ischemia-reperfusion injury. In addition, ROS production and inflammation were significantly suppressed following treatment with chicoric acid. Chicoric acid was demonstrated to significantly inhibit the upregulation of NO and PGE2 levels in rats following MCAO. Furthermore, chicoric acid significantly suppressed the MCAO-induced promotion of COX-2, p38-MAPK and c-Jun protein expression and enhanced the inhibition of p-AKT/AKT. These results suggest that chicoric acid has a protective effect, preventing oxidative stress and inflammation in rats with cerebral ischemia-reperfusion injury via the p38-MAPK, c-Jun and AKT signaling pathways.

Imidazole improves cognition and balances Alzheimer's-like intracellular calcium homeostasis in transgenic Drosophila model

AIMS

The characteristic of Alzheimer's disease (AD) is the accumulation and aggregation of amyloid-β (Aβ). So far, we already know that the dysregulation of intracellular calcium homeostasis is considered to be associated with Aβ neurotoxicity. Meantime, we also found that the channels formed by Aβ are electronegative as calcium channels. Base on this hypothesis, the formation of Aβ channels will provide us with a new therapeutic direction for AD. Aβ channel hypothesis is proposed that the axis of Aβ channel's pore was encompasses by the His¹³ -His¹⁴ diad. Imidazole especially the imidazole ring was supposed binding to the side chains of Aβ peptides.

METHODS

In our study, we adopted Gal4/UAS system to establish transgenic drosophila model which lay a good foundation to explore the imidazole's function and mechanism of action.

RESULTS

The results suggested that Imidazole could not only improve the cognition of Aβ42-expressing flies, but also decreases p-JNK activation in whole brain of Aβ42-expressing flies.

CONCLUSIONS

Furthermore, freshly prepared oligomeric Aβ42 peptide ascended primary pupal neuronal calcium concentration and this phenomenon was alleviated by Imidazole and Zn²⁺ .

Critical Roles of Dual-Specificity Phosphatases in Neuronal Proteostasis and Neurological Diseases

Protein homeostasis or proteostasis is a fundamental cellular property that encompasses the dynamic balancing of processes in the proteostasis network (PN). Such processes include protein synthesis, folding, and degradation in both non-stressed and stressful conditions. The role of the PN in neurodegenerative disease is well-documented, where it is known to respond to changes in protein folding states or toxic gain-of-function protein aggregation. Dual-specificity phosphatases have recently emerged as important participants in maintaining balance within the PN, acting through modulation of cellular signaling pathways that are involved in neurodegeneration. In this review, we will summarize recent findings describing the roles of dual-specificity phosphatases in neurodegeneration and offer perspectives on future therapeutic directions.

Evidence that activation of P2X7R does not exacerbate neuronal death after optic nerve transection and focal cerebral ischemia in mice

Conflicting data in the literature about the function of P2X7R in survival following ischemia necessitates the conductance of in-depth studies. To investigate the impacts of activation vs inhibition of the receptor on neuronal survival as well as the downstream signaling cascades, in addition to optic nerve transection (ONT), 30min and 90min of middle cerebral artery occlusion (MCAo) models were performed in mice. Intracellular calcium levels were assessed in primary cortical neuron cultures. Here, we show that P2X7R antagonist Brilliant Blue G (BBG) decreased DNA fragmentation, infarct volume, brain swelling, neurological deficit scores and activation of microglial cells after focal cerebral ischemia. BBG also significantly increased the number of surviving retinal ganglion cells (RGCs) after ONT and the number of surviving neurons following MCAo. Importantly, receptor agonist BzATP resulted in increased activation of microglial cells and induced phosphorylation of ERK, AKT and JNK. These results indicated that inhibition of P2X7R with BBG promoted neuronal survival, not through the activation of survival kinase pathways, but possibly by improved intracellular Ca²⁺ overload and decreased the levels of Caspase 1, IL-1β and Bax proteins. On the other hand, BzATP-mediated increased number of activated microglia and increased survival kinase levels in addition to increased caspase-1 and IL-1β levels indicate the complex nature of the P2X7 receptor-mediated signaling in neuronal injury.

The Influence of Fluorine on the Disturbances of Homeostasis in the Central Nervous System

Fluorides occur naturally in the environment, the daily exposure of human organism to fluorine mainly depends on the intake of this element with drinking water and it is connected with the geographical region. In some countries, we can observe the endemic fluorosis-the damage of hard and soft tissues caused by the excessive intake of fluorine. Recent studies showed that fluorine is toxic to the central nervous system (CNS). There are several known mechanisms which lead to structural brain damage caused by the excessive intake of fluorine. This element is able to cross the blood-brain barrier, and it accumulates in neurons affecting cytological changes, cell activity and ion transport (e.g. chlorine transport). Additionally, fluorine changes the concentration of non-enzymatic advanced glycation end products (AGEs), the metabolism of neurotransmitters (influencing mainly glutamatergic neurotransmission) and the energy metabolism of neurons by the impaired glucose transporter-GLUT1. It can also change activity and lead to dysfunction of important proteins which are part of the respiratory chain. Fluorine also affects oxidative stress, glial activation and inflammation in the CNS which leads to neurodegeneration. All of those changes lead to abnormal cell differentiation and the activation of apoptosis through the changes in the expression of neural cell adhesion molecules (NCAM), glial fibrillary acidic protein (GFAP), brain-derived neurotrophic factor (BDNF) and MAP kinases. Excessive exposure to this element can cause harmful effects such as permanent damage of all brain structures, impaired learning ability, memory dysfunction and behavioural problems. This paper provides an overview of the fluoride neurotoxicity in juveniles and adults.

c-Jun Amino-Terminal Kinase is Involved in Valproic Acid-Mediated Neuronal Differentiation of Mouse Embryonic NSCs and Neurite Outgrowth of NSC-Derived Neurons

Valproic acid (VPA), an anticonvulsant and mood-stabilizing drug, can induce neuronal differentiation, promote neurite extension and exert a neuroprotective effect in central nervous system (CNS) injuries; however, comparatively little is known regarding its action on mouse embryonic neural stem cells (NSCs) and the underlying molecular mechanism. Recent studies suggested that c-Jun N-terminal kinase (JNK) is required for neurite outgrowth and neuronal differentiation during neuronal development. In the present study, we cultured mouse embryonic NSCs and treated the cells with 1 mM VPA for up to 7 days. The results indicate that VPA promotes the neuronal differentiation of mouse embryonic NSCs and neurite outgrowth of NSC-derived neurons; moreover, VPA induces the phosphorylation of c-Jun by JNK. In contrast, the specific JNK inhibitor SP600125 decreased the VPA-stimulated increase in neuronal differentiation of mouse embryonic NSCs and neurite outgrowth of NSC-derived neurons. Taken together, these results suggest that VPA promotes neuronal differentiation of mouse embryonic NSCs and neurite outgrowth of NSC-derived neurons. Moreover, JNK activation is involved in the effects of VPA stimulation.

Antiepileptic action of c-Jun N-terminal kinase (JNK) inhibition in an animal model of temporal lobe epilepsy

Several phosphorylation signaling pathways have been implicated in the pathogenesis of epilepsy arising from both genetic causes and acquired insults to the brain. Identification of dysfunctional signaling pathways in epilepsy may provide novel targets for antiepileptic therapies. We previously described a deficit in phosphorylation signaling mediated by p38 mitogen-activated protein kinase (p38 MAPK) that occurs in an animal model of temporal lobe epilepsy, and that produces neuronal hyperexcitability measured in vitro. We asked whether in vivo pharmacological manipulation of p38 MAPK activity would influence seizure frequency in chronically epileptic animals. Administration of a p38 MAPK inhibitor, SB203580, markedly worsened spontaneous seizure frequency, consistent with prior in vitro results. However, anisomycin, a non-specific p38 MAPK activator, significantly increased seizure frequency. We hypothesized that this unexpected result was due to activation of a related MAPK, c-Jun N-terminal kinase (JNK). Administration of JNK inhibitor SP600125 significantly decreased seizure frequency in a dose-dependent manner without causing overt behavioral abnormalities. Biochemical analysis showed increased JNK expression and activity in untreated epileptic animals. These results show for the first time that JNK is hyperactivated in an animal model of epilepsy, and that phosphorylation signaling mediated by JNK may represent a novel antiepileptic target.

Differential Activation of Mitogen-Activated Protein Kinases, ERK 1/2, p38(MAPK) and JNK p54/p46 During Postnatal Development of Rat Hippocampus

Mitogen-activated protein kinases (MAPKs) are a group of serine-threonine kinases, including p38(MAPK), ERK 1/2 and JNK p54/p46, activated by phosphorylation in response to extracellular stimuli. The early postnatal period is characterized by significant changes in brain structure as well as intracellular signaling. In the hippocampus MAPKs have been involved in the modulation of development and neural plasticity. However, the temporal profile of MAPK activation throughout the early postnatal development is incomplete. An understanding of this profile is important since slight changes in the activity of these enzymes, in response to environmental stress in specific developmental windows, might alter the course of development. The present study was undertaken to investigate the hippocampal differential activation of MAPK during postnatal period. MAPK activation and total content were evaluated by Western blotting of hippocampal tissue obtained from male Wistar rats at postnatal days (P) 1, 4, 7, 10, 14, 21, 30 and 60. The total content and phosphorylation of each MAPK was expressed as mean ± SEM and then calculates as a percentile compared to P1 (set at 100 %). The results showed: (1) phosphorylation peaks of p38(MAPK) at PN4 (p = 0.036) and PN10 to PN60; (2) phosphorylation of ERK1 and ERK2 were increased with age (ERK1 p = 0.0000005 and ERK2 p = 0.003); (3) phosphorylation profile of JNK p54/p46 was not changed during the period analyzed (JNKp56 p = 0.716 and JNKp46 p = 0.192). Therefore, the activity profile of ERK 1/2 and p38(MAPK) during postnatal development of rat hippocampus are differentially regulated. Our results demonstrate that ERK 1/2 and p38(MAPK) are dynamically regulated during postnatal neurodevelopment, suggesting temporal correlation of MAPK activity with critical periods when programmed cell death and synaptogenesis are occurring. This suggests an important role for these MAPKs in postnatal development of rat hippocampus.

Nicotinic modulation of hippocampal cell signaling and associated effects on learning and memory

The hippocampus is a key brain structure involved in synaptic plasticity associated with long-term declarative memory formation. Importantly, nicotine and activation of nicotinic acetylcholine receptors (nAChRs) can alter hippocampal plasticity and these changes may occur through modulation of hippocampal kinases and transcription factors. Hippocampal kinases such as cAMP-dependent protein kinase (PKA), calcium/calmodulin-dependent protein kinases (CAMKs), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-jun N-terminal kinase 1 (JNK1), and the transcription factor cAMP-response element-binding protein (CREB) that are activated either directly or indirectly by nicotine may modulate hippocampal plasticity and in parallel hippocampus-dependent learning and memory. Evidence suggests that nicotine may alter hippocampus-dependent learning by changing the time and magnitude of activation of kinases and transcription factors normally involved in learning and by recruiting additional cell signaling molecules. Understanding how nicotine alters learning and memory will advance basic understanding of the neural substrates of learning and aid in understanding mental disorders that involve cognitive and learning deficits.

Valproic acid induces neuronal cell death through a novel calpain-dependent necroptosis pathway

A growing body of evidence indicates that valproic acid (VPA), a histone deacetylase inhibitor used to treat epilepsy and mood disorders, has histone deacetylase-related and -unrelated neurotoxic activity, the mechanism of which is still poorly understood. We report that VPA induces neuronal cell death through an atypical calpain-dependent necroptosis pathway that initiates with downstream activation of c-Jun N-terminal kinase 1 (JNK1) and increased expression of receptor-interacting protein 1 (RIP-1) and is accompanied by cleavage and mitochondrial release/nuclear translocation of apoptosis-inducing factor, mitochondrial release of Smac/DIABLO, and inhibition of the anti-apoptotic protein X-linked inhibitor of apoptosis (XIAP). Coinciding with apoptosis-inducing factor nuclear translocation, VPA induces phosphorylation of the necroptosis-associated histone H2A family member H2AX, which is known to contribute to lethal DNA degradation. These signals are inhibited in neuronal cells that express constitutively activated MEK/ERK and/or PI3-K/Akt survival pathways, allowing them to resist VPA-induced cell death. The data indicate that VPA has neurotoxic activity and identify a novel calpain-dependent necroptosis pathway that includes JNK1 activation and RIP-1 expression. A growing body of evidence indicates that valproic acid (VPA) has neurotoxic activity, the mechanism of which is still poorly understood. We report, for the first time, that VPA activates a previously unrecognized calpain-dependent necroptosis cascade that initiates with JNK1 activation and involves AIF cleavage/nuclear translocation and H2AX phosphorylation as well as an altered Smac/DIABLO to XIAP balance.

Design and synthesis of highly potent and isoform selective JNK3 inhibitors: SAR studies on aminopyrazole derivatives

The c-jun N-terminal kinase 3 (JNK3) is expressed primarily in the brain. Numerous reports have shown that inhibition of JNK3 is a promising strategy for treatment of neurodegeneration. The optimization of aminopyrazole-based JNK3 inhibitors with improved potency, isoform selectivity, and pharmacological properties by structure–activity relationship (SAR) studies utilizing biochemical and cell-based assays, and structure-based drug design is reported. These inhibitors had high selectivity over JNK1 and p38α, minimal cytotoxicity, potent inhibition of 6-OHDA-induced mitochondrial membrane potential dissipation and ROS generation, and good drug metabolism and pharmacokinetic (DMPK) properties for iv dosing. 26n was profiled against 464 kinases and was found to be highly selective hitting only seven kinases with >80% inhibition at 10 μM. Moreover, 26n showed good solubility, good brain penetration, and good DMPK properties. Finally, the crystal structure of 26k in complex with JNK3 was solved at 1.8 Å to explore the binding mode of aminopyrazole based JNK3 inhibitors.

Quantitative proteomics reveals dynamic interaction of c-Jun N-terminal kinase (JNK) with RNA transport granule proteins splicing factor proline- and glutamine-rich (Sfpq) and non-POU domain-containing octamer-binding protein (Nono) during neuronal differentiation

The c-Jun N-terminal kinase (JNK) is an important mediator of physiological and pathophysiological processes in the central nervous system. Importantly, JNK not only is involved in neuronal cell death, but also plays a significant role in neuronal differentiation and regeneration. For example, nerve growth factor induces JNK-dependent neuronal differentiation in several model systems. The mechanism by which JNK mediates neuronal differentiation is not well understood. Here, we employed a proteomic strategy to better characterize the function of JNK during neuronal differentiation. We used SILAC-based quantitative proteomics to identify proteins that interact with JNK in PC12 cells in a nerve growth factor-dependent manner. Intriguingly, we found that JNK interacted with neuronal transport granule proteins such as Sfpq and Nono upon NGF treatment. We validated the specificity of these interactions by showing that they were disrupted by a specific peptide inhibitor that blocks the interaction of JNK with its substrates. Immunoprecipitation and Western blotting experiments confirmed the interaction of JNK1 with Sfpq/Nono and demonstrated that it was RNA dependent. Confocal microscopy indicated that JNK1 associated with neuronal granule proteins in the cytosol of PC12 cells, primary cortical neurons, and P19 neuronal cells. Finally, siRNA experiments confirmed that Sfpq was necessary for neurite outgrowth in PC12 cells and that it most likely acted in the same pathway as JNK. In summary, our data indicate that the interaction of JNK1 with transport granule proteins in the cytosol of differentiating neurons plays an important role during neuronal development.

Cortical interneurons require Jnk1 to enter and navigate the developing cerebral cortex

Proper assembly of cortical circuitry relies on the correct migration of cortical interneurons from their place of birth in the ganglionic eminences to their place of terminal differentiation in the cerebral cortex. Although molecular mechanisms mediating cortical interneuron migration have been well studied, intracellular signals directing their migration are largely unknown. Here we illustrate a novel and essential role for c-Jun N-terminal kinase (JNK) signaling in guiding the pioneering population of cortical interneurons into the mouse cerebral cortex. Migrating cortical interneurons express Jnk proteins at the entrance to the cortical rudiment and have enriched expression of Jnk1 relative to noninterneuronal cortical cells. Pharmacological blockade of JNK signaling in ex vivo slice cultures resulted in dose-dependent and highly specific disruption of interneuron migration into the nascent cortex. Time-lapse imaging revealed that JNK-inhibited cortical interneurons advanced slowly and assumed aberrant migratory trajectories while traversing the cortical entry zone. In vivo analyses of JNK-deficient embryos supported our ex vivo pharmacological data. Deficits in interneuron migration were observed in Jnk1 but not Jnk2 single nulls, and those migratory deficits were further exacerbated when homozygous loss of Jnk1 was combined with heterozygous reduction of Jnk2. Finally, genetic ablation of Jnk1 and Jnk2 from cortical interneurons significantly perturbed migration in vivo, but not in vitro, suggesting JNK activity functions to direct their guidance rather than enhance their motility. These data suggest JNK signaling, predominantly mediated by interneuron expressed Jnk1, is required for guiding migration of cortical interneurons into and within the developing cerebral cortex.

Regulatory role of the JNK-STAT1/3 signaling in neuronal differentiation of cultured mouse embryonic stem cells

Stem cell transplantation therapy has provided promising hope for the treatment of a variety of neurodegenerative disorders. Among challenges in developing disease-specific stem cell therapies, identification of key regulatory signals for neuronal differentiation is an essential and critical issue that remains to be resolved. Several lines of evidence suggest that JNK, also known as SAPK, is involved in neuronal differentiation and neural plasticity. It may also play a role in neurite outgrowth during neuronal development. In cultured mouse embryonic stem (ES) cells, we test the hypothesis that the JNK pathway is required for neuronal differentiation. After neural induction, the cells were plated and underwent differentiation for up to 5 days. Western blot analysis showed a dramatic increase in phosphorylated JNKs at 1-5 days after plating. The phosphorylation of JNK subsequently induced activation of STAT1 and STAT3 that lead to expressions of GAP-43, neurofilament, βIII-tubulin, and synaptophysin. NeuN-colabelled with DCX, a marker for neuroblast, was enhanced by JNK signaling. Neuronal differentiation of ES cells was attenuated by treatment with SP600125, which inhibited the JNK activation and decreased the activation of STAT1 and STAT3, and consequently suppressed the expressions of GAP-43, neurofilament, βIII-tubulin, and the secretion of VEGF. Data from immunocytochemistry indicated that the nuclear translocation of STAT3 was reduced, and neurites of ES-derived neurons were shorter after treatment with SP600125 compared with control cells. These results suggest that the JNK-STAT3 pathway is a key regulator required for early neuronal differentiation of mouse ES cells. Further investigation on expression of JNK isoforms showed that JNK-3 was significantly upregulated during the differentiation stage, while JNK-1 and JNK-2 levels decreased. Our study provided interesting information on JNK functions during ES cell neuronal differentiation.

Axon-soma communication in neuronal injury

The extensive lengths of neuronal processes necessitate efficient mechanisms for communication with the cell body. Neuronal regeneration after nerve injury requires new transcription; thus, long-distance retrograde signalling from axonal lesion sites to the soma and nucleus is required. In recent years, considerable progress has been made in elucidating the mechanistic basis of this system. This has included the discovery of a priming role for early calcium waves; confirmation of central roles for mitogen-activated protein kinase signalling effectors, the importin family of nucleocytoplasmic transport factors and molecular motors such as dynein; and demonstration of the importance of local translation as a key regulatory mechanism. These recent findings provide a coherent mechanistic framework for axon-soma communication in the injured nerve and shed light on the integration of cytoplasmic and nuclear transport in all eukaryotic cells.

c-Jun N-terminal kinase phosphorylation of heterogeneous nuclear ribonucleoprotein K regulates vertebrate axon outgrowth via a posttranscriptional mechanism

c-Jun N-terminal kinase (JNK) mediates cell signaling essential for axon outgrowth, but the associated substrates and underlying mechanisms are poorly understood. We identified in Xenopus laevis embryos a novel posttranscriptional mechanism whereby JNK regulates axonogenesis by phosphorylating a specific site on heterogeneous nuclear ribonucleoprotein K (hnRNP K). Both JNK inhibition and hnRNP K knockdown inhibited axon outgrowth and translation of hnRNP K-regulated cytoskeletal RNAs (tau and neurofilament medium), effects that were alleviated by expressing phosphomimetic, but not phosphodeficient, forms of hnRNP K. Immunohistochemical and biochemical analyses indicated that JNK phosphorylation of hnRNP K occurred within the cytoplasm and was necessary for the translational initiation of hnRNP K-targeted RNAs but not for hnRNP K intracellular localization or RNA binding. Thus, in addition to its known roles in transcription and cytoskeletal organization, JNK acts posttranscriptionally through hnRNP K to regulate translation of proteins crucial for axonogenesis.

Multisite phosphorylation of c-Jun at threonine 91/93/95 triggers the onset of c-Jun pro-apoptotic activity in cerebellar granule neurons

Cerebellar granule cell (CGC) apoptosis by trophic/potassium (TK) deprivation is a model of election to study the interplay of pro-apoptotic and pro-survival signaling pathways in neuronal cell death. In this model, the c-Jun N-terminal kinase (JNK) induces pro-apoptotic genes through the c-Jun/activator protein 1 (AP-1) transcription factor. On the other side, a survival pathway initiated by lithium leads to repression of pro-apoptotic c-Jun/AP-1 target genes without interfering with JNK activity. Yet, the mechanism by which lithium inhibits c-Jun activity remains to be elucidated. Here, we used this model system to study the regulation and function of site-specific c-Jun phosphorylation at the S63 and T91/T93 JNK sites in neuronal cell death. We found that TK-deprivation led to c-Jun multiphosphorylation at all three JNK sites. However, immunofluorescence analysis of c-Jun phosphorylation at single cell level revealed that the S63 site was phosphorylated in all c-Jun-expressing cells, whereas the response of T91/T93 phosphorylation was more sensitive, mirroring the switch-like apoptotic response of CGCs. Conversely, lithium prevented T91T93 phosphorylation and cell death without affecting the S63 site, suggesting that T91T93 phosphorylation triggers c-Jun pro-apoptotic activity. Accordingly, a c-Jun mutant lacking the T95 priming site for T91/93 phosphorylation protected CGCs from apoptosis, whereas it was able to induce neurite outgrowth in PC12 cells. Vice versa, a c-Jun mutant bearing aspartate substitution of T95 overwhelmed lithium-mediate protection of CGCs from TK-deprivation, validating that inhibition of T91/T93/T95 phosphorylation underlies the effect of lithium on cell death. Mass spectrometry analysis confirmed multiphosphorylation of c-Jun at T91/T93/T95 in cells. Moreover, JNK phosphorylated recombinant c-Jun at T91/T93 in a T95-dependent manner. On the basis of our results, we propose that T91/T93/T95 multiphosphorylation of c-Jun functions as a sensitivity amplifier of the JNK cascade, setting the threshold for c-Jun pro-apoptotic activity in neuronal cells.

JNK inhibitors as anti-inflammatory and neuroprotective agents

JNK is involved in a broad range of physiological processes. Several inflammatory and neurodegenerative diseases, such as multiple sclerosis, Alzheimer's and Parkinson's disease have been linked with the dysregulated JNK pathway. Research on disease models using the relevant knockout mice has highlighted the importance of specific JNK isoformsin-particular disorders and has stimulated further efforts in the drug-discovery area. However, most of the experimental evidence for the efficacy of JNK inhibition in animal models is from studies using JNK inhibitors, which are not isoform selective. Some of the more recent compounds exhibit good oral bioavailability, CNS penetration and selectivity against the rest of the kinome. Efforts to design isoform-selective inhibitors have produced a number of examples with various selectivity profiles. This article presents recent progress in this area and comment on the role of isoform selectivity for efficacy.

c-Jun N-terminal kinase 1 (JNK1) is required for coordination of netrin signaling in axon guidance

The JNK family of MAPKs is involved in a large variety of physiological and pathological processes in brain development, such as neural survival, migration, and polarity as well as axon regeneration. However, whether JNK activation is involved in axon guidance remains unknown. Here, we provide evidence indicating the JNK pathway is required for Netrin signaling in the developing nervous system. Netrin-1 increased JNK1, not JNK2 or JNK3, activity in the presence of deleted in colorectal cancer (DCC) or Down syndrome cell adhesion molecule (DSCAM), and expression of both of them further enhanced Netrin-1-induced JNK1 activity in vitro. Inhibition of JNK signaling either by a JNK inhibitor, SP600125, or expression of a dominant negative form of MKK4, a JNK upstream activator, blocked Netrin-1-induced JNK1 activation in HEK293 cells. Netrin-1 increased endogenous JNK activity in primary neurons. Netrin-1-induced JNK activation was inhibited either by the JNK inhibitor or an anti-DCC function-blocking antibody. Combination of the anti-DCC function-blocking antibody with expression of DSCAM shRNA in primary neurons totally abolished Netrin-1-induced JNK activation, whereas knockdown of DSCAM partially inhibited the Netrin-1 effect. In the developing spinal cord, phospho-JNK was strongly expressed in commissural axons before and as they crossed the floor plate, and Netrin-1 stimulation dramatically increased the level of endogenous phospho-JNK in commissural axon growth cones. Inhibition of JNK signaling either by JNK1 RNA interference (RNAi) or the JNK inhibitor suppressed Netrin-1-induced neurite outgrowth and axon attraction. Knockdown of JNK1 in ovo caused defects in spinal cord commissural axon projection and pathfinding. Our study reveals that JNK1 is important in the coordination of DCC and DSCAM in Netrin-mediated attractive signaling.

Stressor-like effects of c-Jun N-terminal kinase (JNK) inhibition

There is an urgent need for novel treatment strategies for stressor related disorders, particularly depression and anxiety disorders. Indeed, existing drug treatments are only clinically successful in a subset of patients and relapse is common. This likely stems from the fact that stressor disorders are heterogeneous with multiple biological pathways being affected. To this end, the present investigation sought to assess in mice the contribution of the c-Jun N terminal kinase (JNK) pathway to the behavioral, hormonal and neurochemical effects of an acute stressor. Indeed, although JNK has been shown to modulate glucocorticoid receptors in vitro, virtually nothing is known of the role for JNK in affecting stressor induced pathology. We presently found that the JNK antagonist, SP600125, (but not the p38 antagonist, SB203580) increased plasma corticosterone levels under resting conditions and in the context of an acute stressor (wet bedding + restraint). SP600125 also reduced exploration in an open field arena, but prevented the stressor induced increase in open arm exploration in an elevated plus maze. Finally, SP600125 affected noradrenergic activity in the central amygdala and locus coruleus under resting condition, but prevented the noradrenergic effects within the paraventricular nucleus of the hypothalamus that were induced by the acute stressor exposure. These data suggest inhibiting endogenous JNK can have stressor-like corticoid, behavioral and central monoamine effects under basal conditions, but can actually reverse some behavioral and neurochemical effects of an acute stressor. Thus, endogenous JNK appears to affect stress relevant processes in a context-dependent manner.

Endothelial cells and astrocytes: a concerto en duo in ischemic pathophysiology

The neurovascular/gliovascular unit has recently gained increased attention in cerebral ischemic research, especially regarding the cellular and molecular changes that occur in astrocytes and endothelial cells. In this paper we summarize the recent knowledge of these changes in association with edema formation, interactions with the basal lamina, and blood-brain barrier dysfunctions. We also review the involvement of astrocytes and endothelial cells with recombinant tissue plasminogen activator, which is the only FDA-approved thrombolytic drug after stroke. However, it has a narrow therapeutic time window and serious clinical side effects. Lastly, we provide alternative therapeutic targets for future ischemia drug developments such as peroxisome proliferator- activated receptors and inhibitors of the c-Jun N-terminal kinase pathway. Targeting the neurovascular unit to protect the blood-brain barrier instead of a classical neuron-centric approach in the development of neuroprotective drugs may result in improved clinical outcomes after stroke.

Neuronal c-Jun is required for successful axonal regeneration, but the effects of phosphorylation of its N-terminus are moderate

Although neural c-Jun is essential for successful peripheral nerve regeneration, the cellular basis of this effect and the impact of c-Jun activation are incompletely understood. In the current study, we explored the effects of neuron-selective c-Jun deletion, substitution of serine 63 and 73 phosphoacceptor sites with non-phosphorylatable alanine, and deletion of Jun N-terminal kinases 1, 2 and 3 in mouse facial nerve regeneration. Removal of the floxed c-jun gene in facial motoneurons using cre recombinase under control of a neuron-specific synapsin promoter (junΔS) abolished basal and injury-induced neuronal c-Jun immunoreactivity, as well as most of the molecular responses following facial axotomy. Absence of neuronal Jun reduced the speed of axonal regeneration following crush, and prevented most cut axons from reconnecting to their target, significantly reducing functional recovery. Despite blocking cell death, this was associated with a large number of shrunken neurons. Finally, junΔS mutants also had diminished astrocyte and microglial activation and T-cell influx, suggesting that these non-neuronal responses depend on the release of Jun-dependent signals from neighboring injured motoneurons. The effects of substituting serine 63 and 73 phosphoacceptor sites (junAA), or of global deletion of individual kinases responsible for N-terminal c-Jun phosphorylation were mild. junAA mutants showed decrease in neuronal cell size, a moderate reduction in post-axotomy CD44 levels and slightly increased astrogliosis. Deletion of Jun N-terminal kinase (JNK)1 or JNK3 showed delayed functional recovery; deletion of JNK3 also interfered with T-cell influx, and reduced CD44 levels. Deletion of JNK2 had no effect. Thus, neuronal c-Jun is needed in regeneration, but JNK phosphorylation of the N-terminus mostly appears to not be required for its function.

The JNK inhibitor XG-102 protects against TNBS-induced colitis

The c-Jun N-terminal kinase (JNK)-inhibiting peptide D-JNKI-1, syn. XG-102 was tested for its therapeutic potential in acute inflammatory bowel disease (IBD) in mice. Rectal instillation of the chemical irritant trinitrobenzene sulfonic acid (TNBS) provoked a dramatic acute inflammation in the colon of 7–9 weeks old mice. Coincident subcutaneous application of 100 µg/kg XG-102 significantly reduced the loss of body weight, rectal bleeding and diarrhoea. After 72 h, the end of the study, the colon was removed and immuno-histochemically analysed. XG-102 significantly reduced (i) pathological changes such as ulceration or crypt deformation, (ii) immune cell pathology such as infiltration and presence of CD3- and CD68-positive cells, (iii) the production of tumor necrosis factor (TNF)-α in colon tissue cultures from TNBS-treated mice, (iv) expression of Bim, Bax, FasL, p53, and activation of caspase 3, (v) complexation of JNK2 and Bim, and (vi) expression and activation of the JNK substrate and transcription factor c-Jun. A single application of subcutaneous XG-102 was at least as effective or even better depending on the outcome parameter as the daily oral application of sulfasalazine used for treatment of IBD.

The successful and substantial reduction of the severe, TNBS-evoked intestinal damages and clinical symptoms render the JNK-inhibiting peptide XG-102 a powerful therapeutic principle of IBD.

NR2A and NR2B subunits differentially mediate MAP kinase signaling and mitochondrial morphology following excitotoxic insult

NMDA receptors are essential for neurotransmission and key mediators of synaptic signaling, but they can also trigger deleterious degenerative processes that lead to cell death. Growing evidence suggests that selective blockade of the heterogeneous subunits that comprise the NMDA receptor may enable better control of pharmacotherapies for treating neurological diseases and injuries. We investigated the relationship between NMDAR activation, MAPK signaling, and mitochondrial shape following an excitotoxic insult. NR2A- and NR2B-containing NMDARs differentially mediated acute changes in cytosolic calcium, alterations in mitochondrial morphology, and phosphorylation of the MAPKs ERK and JNK. Activation of NR2A-containing NMDARs was associated with JNK phosphorylation that was neuroprotective in neuronal cultures subjected to excitotoxicity. In contrast, activation of NR2B-containing NMDARs triggered calcium accumulation in mitochondria that was strongly associated with mitochondrial swelling and neuronal cell death. Indeed, while blockade of NR2B-containing receptors was neuroprotective, this protection was lost when NR2A-initiated JNK phosphorylation was inhibited. Given the modest selectivity of the NR2A inhibitor, NVP-AAM077, the results highlight the significance of the relative, rather than absolute, activation of these two NMDA subtypes in modulating cell death pathways. Therefore, the balance between concurrent activation of NR2B-containing and NR2A-containing NMDARs dictates neuronal fate following excitotoxicity.