Is c-Jun involved in nerve cell death following status epilepticus and hypoxic-ischaemic brain injury?

The response of Dual-leucine zipper kinase (DLK) to nocodazole: Evidence for a homeostatic cytoskeletal repair mechanism

Genetic and pharmacological perturbation of the cytoskeleton enhances the regenerative potential of neurons. This response requires Dual-leucine Zipper Kinase (DLK), a neuronal stress sensor that is a central regulator of axon regeneration and degeneration. The damage and repair aspects of this response are reminiscent of other cellular homeostatic systems, suggesting that a cytoskeletal homeostatic response exists. In this study, we propose a framework for understanding DLK mediated neuronal cytoskeletal homeostasis. We demonstrate that low dose nocodazole treatment activates DLK signaling. Activation of DLK signaling results in a DLK-dependent transcriptional signature, which we identify through RNA-seq. This signature includes genes likely to attenuate DLK signaling while simultaneously inducing actin regulating genes. We identify alterations to the cytoskeleton including actin-based morphological changes to the axon. These results are consistent with the model that cytoskeletal disruption in the neuron induces a DLK-dependent homeostatic mechanism, which we term the Cytoskeletal Stress Response (CSR) pathway.

The response of Dual-Leucine Zipper Kinase (DLK) to nocodazole: evidence for a homeostatic cytoskeletal repair mechanism

Genetic and pharmacological perturbation of the cytoskeleton enhances the regenerative potential of neurons. This response requires Dual-leucine Zipper Kinase (DLK), a neuronal stress sensor that is a central regulator of axon regeneration and degeneration. The damage and repair aspects of this response are reminiscent of other cellular homeostatic systems, suggesting that a cytoskeletal homeostatic response exists. In this study, we propose a framework for understanding DLK mediated neuronal cytoskeletal homeostasis. We demonstrate that a) low dose nocodazole treatment activates DLK signaling and b) DLK signaling mitigates the microtubule damage caused by the cytoskeletal perturbation. We also perform RNA-seq to discover a DLK-dependent transcriptional signature. This signature includes genes likely to attenuate DLK signaling while simultaneously inducing actin regulating genes and promoting actin-based morphological changes to the axon. These results are consistent with the model that cytoskeletal disruption in the neuron induces a DLK-dependent homeostatic mechanism, which we term the Cytoskeletal Stress Response (CSR) pathway.

Analyzing pericytes under mild traumatic brain injury using 3D cultures and dielectric elastomer actuators

Traumatic brain injury (TBI) is defined as brain damage due to an external force that negatively impacts brain function. Up to 90% of all TBI are considered in the mild severity range (mTBI) but there is still no therapeutic solution available. Therefore, further understanding of the mTBI pathology is required. To assist with this understanding, we developed a cell injury device (CID) based on a dielectric elastomer actuator (DEA), which is capable of modeling mTBI via injuring cultured cells with mechanical stretching. Our injury model is the first to use patient-derived brain pericyte cells, which are ubiquitous cells in the brain involved in injury response. Pericytes were cultured in our CIDs and mechanically strained up to 40%, and by at least 20%, prior to gene expression analysis. Our injury model is a platform capable of culturing and stretching primary human brain pericytes. The heterogeneous response in gene expression changes in our result may suggest that the genes implicated in pathological changes after mTBI could be a patient-dependent response, but requires further validation. The results of this study demonstrate that our CID is a suitable tool for simulating mTBI as an in vitro stretch injury model, that is sensitive enough to induce responses from primary human brain pericytes due to mechanical impacts.

(-)-Epigallocatechin Gallate Attenuates Spinal Motoneuron Death Induced by Brachial Plexus Root Avulsion in Rats

Background:

Recent studies have indicated that epigallocatechin gallate (EGCG) benefits a variety of neurological insults. This study was performed to investigate the neuroprotective effect of EGCG after brachial plexus root avulsion in SD rats.

Methods:

One hundred twenty SD rats were randomized into the following three groups: an EGCG group, an Avulsion group, and a Sham group. There were 40 rats in each group. EGCG (100 mg/kg, i.p.) or normal saline was administered to rats immediately following the injuries. The treatment was continued from day 1 to day 7, and the animals were sacrificed on days 3, 7, 14 and 28 post-surgery for the harvesting of spinal cord samples for Nissl staining, immunohistochemistry (caspase-3, p-JNK, p-c-Jun) and western blot analysis (p-JNK, JNK, p-c-Jun, c-Jun).

Results:

EGCG treatment caused significant increases in the percentage of surviving motoneurons at days 14 and 28 (P<0.05) compared to the control animals. At days 3 and 7 after avulsion, the numbers of caspase-3-positive motoneurons in the EGCG-treated animals were significantly fewer than in the control animals (P<0.05). The numbers of p-JNK-positive motoneurons and the ratio of p-JNK/JNK were no significant differences between the Avulsion group and the EGCG-treated group after injury at any time point. The numbers of p-c-Jun-positive motoneurons and the ratio of p-c-Jun/c-Jun were significantly lower in EGCG-treated group compared with the Avulsion group at 3d and 7d after injury (p<0.05).

Conclusions:

Our results indicated that motoneurons were protected by EGCG against the cell death induced by brachial plexus root avulsion, and this effect was correlated with inhibiting c-Jun phosphorylation.

Amygdaloid complex anatomopathological findings in animal models of status epilepticus

Temporal lobe epileptic seizures are one of the most common and well-characterized types of epilepsies. The current knowledge on the pathology of temporal lobe epilepsy relies strongly on studies of epileptogenesis caused by experimentally induced status epilepticus (SE). Although several temporal lobe structures have been implicated in the epileptogenic process, the hippocampal formation is the temporal lobe structure studied in the greatest amount and detail. However, studies in human patients and animal models of temporal lobe epilepsy indicate that the amygdaloid complex can be also an important seizure generator, and several pathological processes have been shown in the amygdala during epileptogenesis. Therefore, in the present review, we systematically selected, organized, described, and analyzed the current knowledge on anatomopathological data associated with the amygdaloid complex during SE-induced epileptogenesis. Amygdaloid complex participation in the epileptogenic process is evidenced, among others, by alterations in energy metabolism, circulatory, and fluid regulation, neurotransmission, immediate early genes expression, tissue damage, cell suffering, inflammation, and neuroprotection. We conclude that major efforts should be made in order to include the amygdaloid complex as an important target area for evaluation in future research on SE-induced epileptogenesis. This article is part of the Special Issue "NEWroscience 2018".

Neurodegenerative pathways as targets for acquired epilepsy therapy development

There is a growing body of clinical and experimental evidence that neurodegenerative diseases and epileptogenesis after an acquired brain insult may share common etiological mechanisms. Acquired epilepsy commonly develops as a comorbid condition in patients with neurodegenerative diseases such as Alzheimer's disease, although it is likely much under diagnosed in practice. Progressive neurodegeneration has also been described after traumatic brain injury, stroke, and other forms of brain insults. Moreover, recent evidence has shown that acquired epilepsy is often a progressive disorder that is associated with the development of drug resistance, cognitive decline, and worsening of other neuropsychiatric comorbidities. Therefore, new pharmacological therapies that target neurobiological pathways that underpin neurodegenerative diseases have potential to have both an anti-epileptogenic and disease-modifying effect on the seizures in patients with acquired epilepsy, and also mitigate the progressive neurocognitive and neuropsychiatric comorbidities. Here, we review the neurodegenerative pathways that are plausible targets for the development of novel therapies that could prevent the development or modify the progression of acquired epilepsy, and the supporting published experimental and clinical evidence.

Peripheral Inflammation Accelerates the Onset of Mechanical Hypersensitivity after Spinal Cord Injury and Engages Tumor Necrosis Factor α Signaling Mechanisms

Previously, we showed that noxious stimulation of the tail produces numerous detrimental effects after spinal cord injury (SCI), including an earlier onset and increased magnitude of mechanical hypersensitivity. Expanding on these observations, this study sought to determine whether localized peripheral inflammation similarly impacts the expression of mechanical hypersensitivity after SCI. Adult rats received a moderate contusion injury at the thoracic level (Tl0) or sham surgery, and were administered complete Freund's adjuvant (CFA) or vehicle in one hindpaw 24 hours later. Examination of locomotor recovery (Basso, Beattie, and Bresnahan [BBB] score) showed no adverse effect of CFA. Mechanical testing with von Frey hairs was done at time-points ranging from 1 h to 28 days after CFA or vehicle treatment, and rats were sacrificed at 1, 7, or 28 days for cellular assessment. Unlike vehicle-treated SCI rats where mechanical hypersensitivity emerged at 14 days, CFA-treated SCI rats showed mechanical hypersensitivity as early as 1 h after CFA administration, which lasted at least 28 days. CFA-treated sham subjects also showed an early onset of mechanical hypersensitivity, but this was maintained up to 7 days after treatment. Cellular assessments revealed congruent findings. Expression levels of c-fos, tumor necrosis factor α (TNFα), TNF receptors, and members of the TNFα signaling pathway such as caspase 8 and phosphorylated extracellular related kinase (pERK) were preferentially upregulated in the lumbar spinal cord of SCI-CFA rats. Meanwhile, c-jun was significantly increased in both CFA-treated groups. Overall, these results together with our previous reports, suggest that peripheral noxious input after SCI facilitates the development of pain by mechanisms that may require TNFα signaling.

The role of post-translational modifications in hearing and deafness

Post-translational modifications (PTMs) are key molecular events that modify proteins after their synthesis and modulate their ultimate functional properties by affecting their stability, localisation, interaction potential or activity. These chemical changes expand the size of the proteome adding diversity to the molecular pathways governing the biological outcome of cells. PTMs are, thus, crucial in regulating a variety of cellular processes such as apoptosis, proliferation and differentiation and have been shown to be instrumental during embryonic development. In addition, alterations in protein PTMs have been implicated in the pathogenesis of many human diseases, including deafness. In this review, we summarize the recent progress made in understanding the roles of PTMs during cochlear development, with particular emphasis on the enzymes driving protein phosphorylation, acetylation, methylation, glycosylation, ubiquitination and SUMOylation. We also discuss how these enzymes may contribute to hearing impairment and deafness.

Synaptonuclear messenger PRR7 inhibits c-Jun ubiquitination and regulates NMDA-mediated excitotoxicity

Elevated c-Jun levels result in apoptosis and are evident in neurodegenerative disorders such as Alzheimer's disease and dementia and after global cerebral insults including stroke and epilepsy. NMDA receptor (NMDAR) antagonists block c-Jun upregulation and prevent neuronal cell death following excitotoxic insults. However, the molecular mechanisms regulating c-Jun abundance in neurons are poorly understood. Here, we show that the synaptic component Proline rich 7 (PRR7) accumulates in the nucleus of hippocampal neurons following NMDAR activity. We find that PRR7 inhibits the ubiquitination of c-Jun by E3 ligase SCF(FBW) (7) (FBW7), increases c-Jun-dependent transcriptional activity, and promotes neuronal death. Microarray assays show that PRR7 abundance is directly correlated with transcripts associated with cellular viability. Moreover, PRR7 knockdown attenuates NMDAR-mediated excitotoxicity in neuronal cultures in a c-Jun-dependent manner. Our results show that PRR7 links NMDAR activity to c-Jun function and provide new insights into the molecular processes that underlie NMDAR-dependent excitotoxicity.

REVIEW ■ : Jun, Fos, and CREB/ATF Transcription Factors in the Brain: Control of Gene Expression under Normal and Pathophysiological Conditions

The expression and activation of transcription factors and the control of gene transcription in the nervous system is a recent and rapidly expanding field in neurosciences. This research area may provide insights concerning the information transfer that arises from postsynaptic potentials or ligand-coupling of membrane receptors and terminates in gene expression. Visualization of both de novo synthesis of inducible transcription factors (ITFs) and phosphorylation of preexisting transcription factors have been used to mark neurons, pathways, and networks excited by various stimuli. This article summarizes basics of the transcription process and the complex functions of Jun, Fos, and CREB/ATF proteins, as well as the use of ITFs as experimental instruments in neurophysiology and neurobiology. The major focus is on the alterations in ITF expression following acute or chronic pathophysiological stimuli as mirrors of alterations in neuronal programs underlying adaptation, dysfunctions, or the development of diseases affecting the nervous system. NEUROSCIENTIST 2:153-161, 1996

REVIEW ■ : Calcium and the Pathogenesis of Traumatic CNS Injury: Cellular and Molecular Mechanisms

Under normal conditions in the central nervous system (CNS), the calcium ion (Ca2+) is known to mediate a variety of neuronal functions, including synaptic neurotransmitter release, neuronal plasticity, protein phos phorylation, and gene expression. Whereas intracellular calcium concentrations ([Ca2+]i) are precisely reg ulated through intracellular buffering, binding, and sequestration, alterations in calcium ion homeostasis and influx of Ca 2+ have been implicated in the pathogenesis of neuronal death and degeneration, as well as cerebral vasospasm associated with multiple types of CNS injury. This review revisits the "calcium hypoth esis" of neuronal death associated with traumatic injury to the CNS and examines both the direct and indirect molecular and cellular evidence for calcium-mediated neuropathology, as well as the potential for novel therapeutic strategies targeted at the downstream intracellular effects of calcium signaling and calcium- activated neutral protease (calpain) activation. NEUROSCIENTIST 3:169-175, 1997

Review : The Immediate-Early Gene Response and Neuronal Death and Regeneration

The induction of the cellular immediate-early gene (cIEG) response is the earliest known transcriptional con sequence of neuronal excitation. It is believed that the products of the cIEGs (such as c- fos and c- jun) serve to bring about persistent changes in neuronal phenotype by altering gene expression and modifying signal transduction pathways. This has led, on the one hand, to the burgeoning use of Fos immunohistochemistry as a surrogate form of neuronal activity mapping and, on the other hand, to a quest for the biochemical functions of individual cIEG products in the nervous system. Recent studies of neuronal death and regen eration have contributed substantially to our vision of the molecular and biological characteristics of the cIEG response. Indeed, they have challenged some of its long-held tenets. Therefore, we will use these results to illustrate our most contemporary view of the cIEG response in the nervous system. The Neuroscientist 1:68- 75,1995

Neurotrophic Factor Protection against Excitotoxic Neuronal Death

Neurotrophic factors are polypeptides capable of promoting neuronal survival in both the developing and the adult brain. In addition to the neurotrophins, NGF, brain-derived neurotropic factor, and NT-3 to -6, other neurotrophic factors include ciliary neurotrophic factor, fibroblast growth factors, insulin-like growth factors, members of the transforming growth factor superfamily, members of the epidermal growth factor family, and other cytokines such as leukemia inhibitory factor, oncostatin M, and interleukins-6 and -11. One condition under which these factors promote survival is the challenge of neurons with analogs of excitatory amino acid transmitters. Such analogs, including quinolinic acid, kainic acid, and ibotenic acid, are frequently employed as models of neurological diseases such as Huntington's disease, Parkinson's disease, Alzheimer's disease, epilepsy, cerebellar degenerations, and amyotrophic lateral sclerosis. Excitotoxicity also plays a role in neu ronal death caused by focal ischemia, hypoglycemia, or trauma. Although much has been learned about the mechanisms of both the action of neurotrophic factors and of cell death in response to excitotoxins, the mechanism of protection by these factors remains uncertain. This review explores the biochemical and phys iological changes mediated by neurotrophic factors that may underlie their ability to protect against excito toxic cell death. Second messenger pathways used degenerately by both excitotoxins and neurotrophic factors are discussed as a potential site of interaction mediating the protective effects of neurotrophic factors. Particular attention is also paid to the importance of the route of neurotrophic factor delivery in conferring neuroprotection in particular excitotoxic models. The Neuroscientist 1:286-297, 1995

Review : Gene Expression after Cerebral Ischemia

Global and focal ischemias induce a variety of gene families, including immediate early genes, cytokines, neurotransmitter receptors, and heat-shock proteins. The Janus-like effects of several of these gene prod ucts promote neuronal survival and degeneration. Therefore, determining the molecular pathways respon sible for the differential regulation of these genes is of paramount importance. The discovery of apoptosis as a mediator of delayed neuronal death has led to the identification of a number of other genes involved in postischemic brain damage. Future neuroprotective therapies for cerebral ischemia may be directed at preventing alterations in gene expression. NEUROSCIENTIST 5:238-253, 1999

Peptidylarginine Deiminases as Drug Targets in Neonatal Hypoxic-Ischemic Encephalopathy

Oxygen deprivation and infection are major causes of perinatal brain injury leading to cerebral palsy and other neurological disabilities. The identification of novel key factors mediating white and gray matter damage are crucial to allow better understanding of the specific contribution of different cell types to the injury processes and pathways for clinical intervention. Recent studies in the Rice-Vannucci mouse model of neonatal hypoxic ischemia (HI) have highlighted novel roles for calcium-regulated peptidylarginine deiminases (PADs) and demonstrated neuroprotective effects of pharmacological PAD inhibition following HI and synergistic infection mimicked by lipopolysaccharide stimulation.

Peripheral noxious stimulation reduces withdrawal threshold to mechanical stimuli after spinal cord injury: role of tumor necrosis factor alpha and apoptosis

We previously showed that peripheral noxious input after spinal cord injury (SCI) inhibits beneficial spinal plasticity and impairs recovery of locomotor and bladder functions. These observations suggest that noxious input may similarly affect the development and maintenance of chronic neuropathic pain, an important consequence of SCI. In adult rats with a moderate contusion SCI, we investigated the effect of noxious tail stimulation, administered 1 day after SCI on mechanical withdrawal responses to von Frey stimuli from 1 to 28 days after treatment. In addition, because the proinflammatory cytokine tumor necrosis factor alpha (TNFα) is implicated in numerous injury-induced processes including pain hypersensitivity, we assessed the temporal and spatial expression of TNFα, TNF receptors, and several downstream signaling targets after stimulation. Our results showed that unlike sham surgery or SCI only, nociceptive stimulation after SCI induced mechanical sensitivity by 24h. These behavioral changes were accompanied by increased expression of TNFα. Cellular assessments of downstream targets of TNFα revealed that nociceptive stimulation increased the expression of caspase 8 and the active subunit (12 kDa) of caspase 3, indicative of active apoptosis at a time point consistent with the onset of mechanical allodynia. In addition, immunohistochemical analysis revealed distinct morphological signs of apoptosis in neurons and microglia at 24h after stimulation. Interestingly, expression of the inflammatory mediator NFκB was unaltered by nociceptive stimulation. These results suggest that noxious input caudal to the level of SCI can increase the onset and expression of behavioral responses indicative of pain, potentially involving TNFα signaling.

Peptidylarginine deiminases: novel drug targets for prevention of neuronal damage following hypoxic ischemic insult (HI) in neonates

Neonatal hypoxic ischaemic (HI) injury frequently causes neural impairment in surviving infants. Our knowledge of the underlying molecular mechanisms is still limited. Protein deimination is a post-translational modification caused by Ca⁺²-regulated peptidylarginine deiminases (PADs), a group of five isozymes that display tissue-specific expression and different preference for target proteins. Protein deimination results in altered protein conformation and function of target proteins, and is associated with neurodegenerative diseases, gene regulation and autoimmunity. In this study, we used the neonatal HI and HI/infection [lipopolysaccharide (LPS) stimulation] murine models to investigate changes in protein deimination. Brains showed increases in deiminated proteins, cell death, activated microglia and neuronal loss in affected brain areas at 48 h after hypoxic ischaemic insult. Upon treatment with the pan-PAD inhibitor Cl-amidine, a significant reduction was seen in microglial activation, cell death and infarct size compared with control saline or LPS-treated animals. Deimination of histone 3, a target protein of the PAD4 isozyme, was increased in hippocampus and cortex specifically upon LPS stimulation and markedly reduced following Cl-amidine treatment. Here, we demonstrate a novel role for PAD enzymes in neural impairment in neonatal HI Encephalopathy, highlighting their role as promising new candidates for drug-directed intervention in neurotrauma.

Hypoxic Ischaemic Insult (HI) results in activation of peptidylarginine deiminases (PADs) because of calcium dysregulation. Target proteins undergo irreversible changes of protein bound arginine to citrulline, resulting in protein misfolding. Infection in synergy with HI causes up-regulation of TNFα, nuclear translocation of PAD4 and change in gene regulation as a result of histone deimination. Pharmacological PAD inhibition significantly reduced HI brain damage.

The role of dopamine signaling in epileptogenesis

Clinical and experimental studies implicate most neuromodulatory systems in epileptogenesis. The dopaminergic system has a seizure-modulating effect that crucially depends on the different subtypes of dopamine (DA) receptors involved and the brain regions in which they are activated. Specifically, DA plays a major role in the control of seizures arising in the limbic system. Studies performed in a wide variety of animal models contributed to illustrate the opposite actions of D1-like and D2-like receptor signaling in limbic epileptogenesis. Indeed, signaling from D1-like receptors is generally pro-epileptogenic, whereas D2-like receptor signaling exerts an anti-epileptogenic effect. However, this view might appear quite simplistic as the complex neuromodulatory action of DA in the control of epileptogenesis likely requires a physiological balance in the activation of circuits modulated by these two major DA receptor subtypes, which determines the response to seizure-promoting stimuli. Here we will review recent evidences on the identification of molecules activated by DA transduction pathways in the generation and spread of seizures in the limbic system. We will discuss the intracellular signaling pathways triggered by activation of different DA receptors in relation to their role in limbic epileptogenesis, which lead to the activation of neuronal death/survival cascades. A deep understanding of the signaling pathways involved in epileptogenesis is crucial for the identification of novel targets for the treatment of epilepsy.

Valproic acid protection against the brachial plexus root avulsion-induced death of motoneurons in rats

In this study, the role of valproic acid (VPA) in protecting motoneuron after brachial plexus root avulsion was investigated in adult rats. Sixty rats were used in this study, and underwent the brachial plexus root avulsion injury, which was created by using a micro-hemostat forceps to pull out brachial plexus root from the intervertebral foramen. The animals were divided into two groups, VPA group administered with VPA dissolved in drinking water (300 mg/kg) daily, and control group had drinking water every day. The spinal cords (C5-T1) were harvested at day 1, 2, 3, 7, 14, and 28 for immunohistochemistry analysis, TUNEL staining, Nissl staining, and electron microscopy, respectively. The results showed that with VPA administration, the survival of motoneurons was promoted and the cell apoptosis was inhibited. The number of c-Jun and Bcl-2 positive motoneurons was increased immediately after avulsion both in control and VPA group, however, the percent of c-Jun positive motoneurons was decreased and the percent of Bcl-2 positive motoneurons was increased by VPA treatment significantly. Our results indicated that motoneurons were protected by VPA against cell death induced by brachial plexus root avulsion through c-Jun inhibition and Bcl-2 induction.

Time courses of changes in phospho- and total- MAP kinases in the cochlea after intense noise exposure

Mitogen-activated protein kinases (MAP kinases) are intracellular signaling kinases activated by phosphorylation in response to a variety of extracellular stimuli. Mammalian MAP kinase pathways are composed of three major pathways: MEK1 (mitogen-activated protein kinase kinase 1)/ERK 1/2 (extracellular signal-regulated kinases 1/2)/p90 RSK (p90 ribosomal S6 kinase), JNK (c-Jun amino (N)-terminal kinase)/c-Jun, and p38 MAPK pathways. These pathways coordinately mediate physiological processes such as cell survival, protein synthesis, cell proliferation, growth, migration, and apoptosis. The involvement of MAP kinase in noise-induced hearing loss (NIHL) has been implicated in the cochlea; however, it is unknown how expression levels of MAP kinase change after the onset of NIHL and whether they are regulated by transient phosphorylation or protein synthesis. CBA/J mice were exposed to 120-dB octave band noise for 2 h. Auditory brainstem response confirmed a component of temporary threshold shift within 0–24 h and significant permanent threshold shift at 14 days after noise exposure. Levels and localizations of phospho- and total- MEK1/ERK1/2/p90 RSK, JNK/c-Jun, and p38 MAPK were comprehensively analyzed by the Bio-Plex® Suspension Array System and immunohistochemistry at 0, 3, 6, 12, 24 and 48 h after noise exposure. The phospho-MEK1/ERK1/2/p90 RSK signaling pathway was activated in the spiral ligament and the sensory and supporting cells of the organ of Corti, with peaks at 3–6 h and independently of regulations of total-MEK1/ERK1/2/p90 RSK. The expression of phospho-JNK and p38 MAPK showed late upregulation in spiral neurons at 48 h, in addition to early upregulations with peaks at 3 h after noise trauma. Phospho-p38 MAPK activation was dependent on upregulation of total-p38 MAPK. At present, comprehensive data on MAP kinase expression provide significant insight into understanding the molecular mechanism of NIHL, and for developing therapeutic models for acute sensorineural hearing loss.

Co-localization of activating transcription factor 3 and phosphorylated c-Jun in axotomized facial motoneurons

Activating transcription factor 3 (ATF3) and c-Jun play key roles in either cell death or cell survival, depending on the cellular background. To evaluate the functional significance of ATF3/c-Jun in the peripheral nervous system, we examined neuronal cell death, activation of ATF3/c-Jun, and microglial responses in facial motor nuclei up to 24 weeks after an extracranial facial nerve axotomy in adult rats. Following the axotomy, neuronal survival rate was progressively but significantly reduced to 79.1% at 16 weeks post-lesion (wpl) and to 65.2% at 24 wpl. ATF3 and phosphorylated c-Jun (pc-Jun) were detected in the majority of ipsilateral facial motoneurons with normal size and morphology during the early stage of degeneration (1-2 wpl). Thereafter, the number of facial motoneurons decreased gradually, and both ATF3 and pc-Jun were identified in degenerating neurons only. ATF3 and pc-Jun were co-localized in most cases. Additionally, a large number of activated microglia, recognized by OX6 (rat MHC II marker) and ED1 (phagocytic marker), gathered in the ipsilateral facial motor nuclei. Importantly, numerous OX6- and ED1-positive, phagocytic microglia closely surrounded and ingested pc-Jun-positive, degenerating neurons. Taken together, our results indicate that long-lasting co-localization of ATF3 and pc-Jun in axotomized facial motoneurons may be related to degenerative cascades provoked by an extracranial facial nerve axotomy.

The c-Jun N-terminal kinase inhibitor SP600125 is neuroprotective in amygdala kindled rats

c-Jun N-terminal kinase (JNK) is implicated in cell death in neurodegenerative disorders and has been taken as a critical point between the physiological and pathological status. JNK specific inhibitor SP600125 has been found to have a protective effect against transient brain ischemia/reperfusion-induced neuronal death in rat hippocampal CA1 region. Former studies have shown the relation between JNK phosphorylation and neuronal damage in models of brain ischemia or in chemically or acute electrically kindled animal in which the stimulus-induced JNK phosphorylation was temporary or transient. In this study, the effect of repeated activation of JNK was examined in the amygdala kindled rats, under or without intraventrical infusion of SP600125, compared with the sham control. JNK phosphorylation was detected by Western blot and immunofluorescent staining in hippocampal extracts and in slices respectively. Nissl staining was performed to detect the neuronal defect. We found that the level of JNK phosphorylation (46KD) in the hippocampus increased in the amygdala kindled rats, whereas such JNK phosphorylation could be inhibited by SP600125. Expression of total JNK in the hippocampus remained unchanged in kindled rats compared with the sham control, and was not affected by SP600125. Neuronal defect was marked in the kindling group and in the vehicle DMSO group, and was alleviated under the administration of SP600125. These findings suggest that JNK phosphorylation is involved in the process of hippocampal sclerosis in the mesial temporal lobe epilepsy (TLE). JNK signaling pathway may be a new target to interfere with the development of hippocampal sclerosis in the temporal lobe epilepsy. The JNK inhibitor SP600125 can show a protective effect on hippocampal neurons in TLE by inhibiting JNK activation.

Gentamicin-induced spiral ganglion cell death: apoptosis mediated by ROS and the JNK signaling pathway

CONCLUSION

Reactive oxygen species (ROS) and the c-Jun N-terminal kinase (JNK) signaling pathway may be involved in secondary apoptosis of spiral ganglion cells (SGCs) induced by intracochlear gentamicin injection.

OBJECTIVES

The purpose of this study was to ascertain the role of ROS and the JNK signaling pathway in secondary apoptosis of SGCs induced by intracochlear gentamicin treatment.

METHODS

Gentamicin (40 mg/ml) was injected into the cochlea of guinea pigs (n = 18) to destroy the hair cells and induce secondary apoptosis of SGCs. At 1 (n = 6), 2 (n = 6), and 3 (n = 6) weeks after gentamicin treatment, the cochleas were removed and stained with hematoxylin and eosin, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling to observe the morphologic changes and apoptosis of SGCs. A dihydroethidium (DHE) assay was performed to detect ROS generation, and RT-PCR and Western blot analysis were used to assess the expression of Fas ligand (FasL), JNK, and c-Jun.

RESULTS

After gentamicin was injected into the cochlea, apoptosis and progressive loss of SGCs were observed. RT-PCR and Western blot analysis showed increased expression of FasL after gentamicin treatment. ROS generation detected by DHE fluorescence increased progressively, and the expression of JNK, phospho-JNK, c-Jun, and phospho-c-Jun also increased.

Induction of apoptosis in nutrient-deprived cultures of hybridoma and myeloma cells

In the present study, cell death was investigated in cultures of NS/0 myelomas and SP2/0-derived D5 hybridomas through morphological examination of cells stained with acridine orange and ethidium bromide. The relative contribution of elevated levels of lactic acid and ammonia, as well as deprivation of glutamine, cystine, and glucose on the induction of necrosis or apoptosis, was investigated. In batch culture of D5 hybridoma cells, induction of apoptotic cell death correlated with the exhaustion of glutamine, while in the case of NS/0 myelomas, it coincided with exhaustion of cystine. To determine whether limiting nutrients were the actual triggering factors for apoptosis in batch culture, exponentially growing cells were resuspended in glutamine or cystine-free media. Within 30 to 40 h, viability decreased to 50% and the nonviable cell population displayed typical apoptotic morphology, with crescents of condensed chromatin around the periphery of the nucleus, or with the entire nucleus present as one or a group of featureless, brightly staining spherical beads. Similarly, D5 hybridomas and NS/0 myelomas cultivated in glucose-free medium died mainly from apoptosis. Cells were also cultivated in fresh medium supplemented with elevated concentrations of ammonia (3.0 mM) and/or lactate (35 mM, 50 mM). This resulted in decreased viabilities and necrotic death in both cell lines. From these results, we conclude that D5 hybridomas and NS/0 myelomas deprived of essential nutrients die by apoptosis, whereas incubation in the presence of elevated levels of metabolic byproducts such as ammonia and lactate will induce necrotic cell death in these cells.

Anandamide inhibits cholangiocyte hyperplastic proliferation via activation of thioredoxin 1/redox factor 1 and AP-1 activation

The endocannabinoid system regulates various aspects of hepatic fibrosis; however, nothing is known about its role in regulating cholangiocyte proliferation and function. We evaluated the effects of anandamide (AEA) on cholangiocyte proliferation and explored the effects of AEA on the thioredoxin 1 (TRX1)/redox factor 1 (Ref1)/activator protein-1 (AP-1) pathway. Mice underwent bile duct ligation (BDL) and were infused with AEA for 3 days postsurgery. Proliferation and apoptosis were evaluated in liver sections. Effects of in vitro AEA treatment on cholangiocyte proliferation and apoptosis were studied in purified cholangiocytes. The relative expression of cannabinoid receptors was also assessed in liver sections and cholangiocytes. mRNA expression of the cannabinoid receptors Cb1 and VR1 was decreased after BDL, whereas there was an upregulation of Cb2 mRNA. AEA decreased cholangiocyte growth and induced accumulation of reactive oxygen species, upregulation of TRX1, Ref1, c-Fos, and c-Jun expression, increased nuclear localization of TRX1, and increased AP-1 transcriptional activity. Specific knockdown of TRX1 or Ref1 expression ablated the AP-1 transcriptional activity and AEA-induced cell death but not expression of c-Fos and c-Jun. Knockdown of c-Fos and c-Jun expression also ablated AEA-induced apoptosis. We conclude that AEA suppresses cholangiocyte proliferation during cholestasis via a Cb2-dependent mechanism. Modulation of the endocannabinoid system may be important in the treatment of cholangiopathies.

Inhibition of mitogen-activated protein kinase and stimulation of Akt kinase signaling pathways: Two approaches with therapeutic potential in the treatment of neurodegenerative disease

The neurodegenerative diseases of adulthood, including Alzheimer's disease (AD) and Parkinson's disease (PD), pose an enormous and growing public health burden. Although effective symptomatic treatments exist for PD, and, to a lesser extent, for AD, there is no therapy for these disorders which will forestall their progression. With the rise of the concept of programmed cell death (PCD) came the realization that even in the absence of complete knowledge of proximate causes neuroprotection may nevertheless be possible by targeting the pathways of PCD. One set of signaling pathways that have been implicated in cell death are the mitogen-activated protein kinase (MAPK) pathways. The possibility of blocking these pathways and thereby providing neuroprotection has recently been put to the test in a clinical trial of a mixed lineage kinase inhibitor in the treatment of PD. Unfortunately, this trial failed to demonstrate a protective effect. Based on considerations related to the implementation of the trial, it would be premature to conclude that inhibition of MAPK signaling is a failed strategy. In spite of these negative results, the MAPK and related kinase pathways retain their importance as potential targets in PD. In relation to pathogenesis, the discovery of mutations in the mixed lineage kinase (MLK)-like kinase leucine-rich repeat kinase 2 (LRRK2) suggests a role for these kinases in regulating the viability of dopamine neurons. In relation to treatment, the survival signaling kinase Akt has been demonstrated in vivo to mediate striking neurotrophic and antiapoptotic effects. Thus, it is likely that therapeutic targets related to these kinase signaling pathways will emerge.

Astrocyte-derived transgene GDNF promotes complete and long-term survival of adult facial motoneurons following avulsion and differentially regulates the expression of transcription factors of AP-1 and ATF/CREB families

Glial-cell-line-derived neurotrophic factor (GDNF) is a potent survival factor for motoneurons (MNs). We have previously demonstrated that overexpression of GDNF in astrocytes of GFAP-GDNF mice promotes long-term survival of neonatal MNs after facial nerve axotomy. In the present study, we investigated whether astrocyte-derived GDNF could also have a neuroprotective effect on adult MNs following facial nerve avulsion. We also examined avulsion- and GDNF-induced changes in the expression pattern of several members of the AP-1 and ATF/CREB families of transcription factors, which are involved in the fate determination of neurons following injury. We demonstrated that GDNF promotes complete rescue of avulsed MNs for at least 4 months post-injury. Transgene GDNF significantly upregulates c-Jun expression in naive MNs, further upregulates injury-induced c-Jun expression in facial MNs, and results in its activation in most surviving MNs. No significant changes were found in c-Fos expression. We found that GDNF has an opposing effect on ATF2 and ATF3 expression. It dramatically downregulates increased levels of ATF3 in response to injury, whereas the expression of ATF2, which is normally reduced after injury, is completely preserved in GFAP-GDNF mice. Our data suggest that maintenance of high levels of ATF2 in injured MNs could be crucial in modulating c-Jun function, and c-Jun/ATF2 signaling could be involved in GDNF-mediated survival of mature MNs.

Glutamate activatesc-fos in glial cells via a novel mechanism involving the glutamate receptor subtype mGlu5 and the transcriptional repressor DREAM

Activation of c-fos in brain is related to coupling of neuronal activity to gene expression, but also to pathological conditions such as seizures or excitotoxicity-induced cell death. Glutamate activates c-fos in neurons through the calcium-dependent phosphorylation of CREB by ERK and/or CaMKIV kinase pathways downstream NMDA-receptors. In glial cells, however, the activation of c-fos by glutamate is poorly understood. Because glial cells actively modulate neuronal excitability and the brain's response to injury, we studied the mechanisms by which glutamate activates c-fos in rat cortical glial cells. Glutamate potently induced c-fos mRNA in a calcium-dependent manner, as demonstrated by using the calcium chelator BAPTA-AM. Glutamate-induced c-fos mRNA expression was not sensitive to inhibitors of ERK, p38(MAPK), or CaMK pathways, indicating that glial c-fos is activated by a distinct mechanism. Thapsigargin abolished the glutamate effect on c-fos mRNA, indicating ER calcium mobilization. Additionally, glutamate induction of c-fos mRNA was sensitive to the mGluR5 antagonist MPEP but not the NMDA-R antagonist MK-801. In luciferase reporter assays, DRE, which actively represses c-fos by binding the calcium-binding transcriptional repressor DREAM, was activated by glutamate, whereas SRE and CRE were not. Finally, glutamate caused the nuclear export of DREAM in astrocytes, and transfection of astrocytes with a mutant variant of DREAM that constitutively binds DNA inhibited glutamate-induced c-Fos expression. These findings are in sharp contrast to the mechanism described in neurons and suggest a novel pathway activated by glutamate in glial cells that employs mGluR5, ER calcium, and the derepression of c-fos at the DRE.

Activation of the stress-activated MAP kinase, p38, but not JNK in cortical motor neurons during early presymptomatic stages of amyotrophic lateral sclerosis in transgenic mice

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder, characterized by the degeneration of upper and lower motor neurons (MNs). Central nervous system features include a loss of Betz cells and other pyramidal cells from sensorimotor cortex. The intrinsic mechanism underlying this selective motor neuron loss has not been identified. A recent in vitro study has provided evidence of a novel programmed cell death (PCD) pathway that is unique to spinal cord MNs and is exacerbated by superoxide dismutase (SOD) mutations. This PCD pathway is triggered through the Fas receptor and involves the apoptosis signal-regulating kinase 1 (ASK1), the p38 MAP kinase, and the neuronal form of nitric oxide synthase (nNOS). Previously, we found significant increases in the numbers of ventral horn MNs immunopositive for these enzymes in the spinal cords of mutant SOD transgenic (G93A) mice as early as 60 days of age, suggesting that this pathway may be active in vivo. Since the upper MNs of ALS patients and G93A mice are also known to degenerate, the purpose of the present study was to investigate the possible activation of this PCD pathway in the MNs of the sensorimotor cortex of G93A transgenic mice. Compared to non-transgenic littermates, the G93A mice showed significant increases in the numbers of MNs immunopositive for the active (phosphorylated) forms of ASK1, p38, MKK3/6 (the known activator of p38), and also active caspase-3, as early as 60 days of age. Another stress-activated protein kinase, c-Jun N-terminal kinase (JNK), commonly activated in other neurodegenerative disorders such as Alzheimer's disease, showed no increases in G93A mice at any age. These results suggest that, not only has a PCD pathway been activated in the cortical MNs, but one that may be unique to ALS. Moreover, these findings suggest that earlier diagnosis and therapeutic intervention may be possible for successful treatment of ALS. Consequently, these enzymes may provide the biochemical markers to enable earlier diagnosis of ALS and molecular targets for the development of new therapeutic compounds.

Mixed lineage kinase-c-jun N-terminal kinase signaling pathway: A new therapeutic target in Parkinson's disease

There is growing evidence that the molecular pathways of programmed cell death play a role in neurodegenerative disease, including Parkinson's disease, so there has been increased interest in them as therapeutic targets for the development of neuroprotective strategies. One pathway of cell death that has attracted particular attention is the mixed lineage kinase (MLK) -c-jun N-terminal kinase (JNK) signaling cascade, which leads to the phosphorylation and activation of the transcription factor c-jun. There is much evidence, from in vitro and in vivo studies, that this cascade can mediate cell death. In addition, there is evidence that it is operative upstream in the death process. It is possible that abrogation of this pathway may forestall death before irreversible cellular injury. One class of compounds that has shown promise for their ability to block cell death by inhibiting this cascade are the inhibitors of the MLKs, which are upstream in the activation of c-jun. One of these compounds, CEP1347, is now in a Phase II/III clinical trial for neuroprotection in PD. Whether this trial is successful or not, this signaling cascade is likely to be a focus of future therapeutic development. This review, therefore, outlines the principles of signaling within this kinase pathway, and the evidence for its role in cell death. We review the evidence that inhibition of the MLKs can prevent dopamine neuron cell death and the degeneration of their axons. These studies suggest important future directions for the development of therapies that will target this important cell death pathway.

Angiotensin II accelerates functional recovery in the rat sciatic nerve in vivo: role of the AT2 receptor and the transcription factor NF-kappaB

The AT2 receptor regulates several functions of nerve cells, e.g., ionic fluxes, cell differentiation, and axonal regeneration, but also modulates programmed cell death. We tested the hypothesis that angiotensin II (ANG II) via its AT2 receptor not only promotes regeneration but also functional recovery after sciatic nerve crush in adult rats. ANG II (10(-7), 10(-9), 10(-11) M) applied locally via osmotic minipumps promoted functional recovery with maximal effects after the lowest concentration. The toe spread distance as a parameter for re-innervation after 20 days was significantly (P<0.01) greater (10.2+/-10.27 mm) compared with the control group (8.73+/-0.16 mm). The response to local electrical stimulation (return of sensorimotor function) was reduced to 14.6 days vs. 17.9 days in the control group (P<0.01). The AT2 receptor antagonist PD 123319 administered alone or in combination with ANG II completely prevented the ANG II-induced recovery, whereas the AT1 receptor antagonist losartan had no effect. Furthermore, ANG II induces, via the AT2 receptor, activation of the transcription factor NF-kappaB in Schwann cells. Histological criteria, morphometric analyses, and electron microscopy confirmed the functional data. These results are the first to present direct evidence for an involvement of the AT2 receptor and NF-kappaB in peripheral nerve regeneration.

Biphasic expression of activating transcription factor-3 in neurons after cerebral infarction

It has been demonstrated that some of immediate early genes such as c-Jun are induced immediately and transiently following focal cerebral ischemia. Here we newly characterize the activating transcription factor (ATF)-3 as a focal ischemia associated immediate early gene. Using in situ hybridization and immunohistochemistry, we compared the expression profile of ATF-3 with those of ATF-2 and c-Jun after middle cerebral artery (MCA) occlusion. Focal cerebral ischemia induced two temporal and spatial patterns of ATF-3 expression. Early and transient induction of ATF-3 mRNA was observed in the core and margins of the cortex immediately after MCA occlusion. Late-onset and prolonged expression of ATF-3 mRNA and its protein were specifically identified in the peri-infarct cortex and thalamus where neurons survive at least 1 month. The expression profiles of ATF-3 and c-Jun were virtually similar, but c-Jun expression was also observed in other regions of the brain in control rats. Expression of ATF-2 was ubiquitously seen in neuronal cells throughout the brain in normal rats, but was suppressed in ischemic regions. Double immunohistochemical labeling revealed concurrent expression of ATF-3 and phospho-c-Jun in neurons. We conclude that the transcription factor ATF-3 is a suitable marker of neurons subjected to ischemic insult directly and indirectly, and that cooperative works of ATF-3 and c-Jun may be crucial triggers of various transcriptional responses to the ischemic insult.

Kainic acid induces 14-3-3 zeta expression in distinct regions of rat brain

Areas of the limbic system of adult male Wistar rats were screened for kainic-acid-induced gene expression. Polymerase-chain-reaction-based differential display identified a 147-bp cDNA fragment, which represented an mRNA that was upregulated in the entorhinal cortex and hippocampus in the kainic-acid-treated animals. The sequence was 97.8% homologous to rat 14-3-3 zeta isoform mRNA. Detailed Northern analysis revealed increased mRNA levels in the entorhinal cortex 1 h after kainic acid exposure and continued elevation 24 h post-injection in both the entorhinal cortex and hippocampus. Western blot analyses confirmed that the protein product of this gene was also present in increased amounts over the same time period. Immunohistochemistry and terminal transferase-mediated dUTP nick end labelling (TUNEL) detected expression of 14-3-3 zeta protein exclusively in the entorhinal cortex and hippocampus, and only in TUNEL-positive neuronal cells. Expression of the tumor suppressor protein, p53 was also induced by kainate injection, and was co-localized with 14-3-3 zeta protein in selected cells only in the affected brain regions. The increase gene expression of 14-3-3 zeta represents a transcription-mediated response associated with region selective neuronal damage induced by kainic acid.

Increased expression and activation of c-Jun contributes to human amylin-induced apoptosis in pancreatic islet beta-cells

The role of c-Jun in apoptosis evoked by human amylin was investigated using human and rat insulinoma beta-cell lines. Two transient increases in the levels of c-jun mRNA were detected at 30 minutes and eight hours after treatment with human amylin. The level of c-Jun protein was also up-regulated in a time-dependent manner, reaching maximal levels after eight hours of exposure. However, no c-Jun induction was detected in cells treated with vehicle only or with rat amylin, indicating that the amyloidogenic feature of the human peptide may be important for c-Jun induction. We found that c-Jun was activated by phosphorylation specifically at Ser63 at four hours, but not at Ser73, after treatment with human amylin, preceding increased c-Jun protein. Furthermore, expression of an antisense c-jun (AS-c-jun), which suppressed protein levels of both c-Jun and phosphorylated-c-Jun, caused a marked reduction in apoptotic cell death, whereas the corresponding sense c-jun (S-c-jun) had no effect on changes of either c-Jun production or apoptosis. This indicated that increased expression and activation of c-Jun is required for human amylin-induced apoptosis. Immunocytochemical studies showed a significant increase in nuclear staining for c-Jun, phosphorylated-c-Jun (Ser63) and phosphorylated-JNK, suggesting that c-Jun may be activated through activation of JNK. In addition, electrophoretic mobility-shift assays showed that the increase in expression and phosphorylation of c-Jun was associated with increased AP-1 DNA binding activity. Supershift assays demonstrated that c-Jun, c-Fos and ATF-2 are part of the AP-1 complex, indicating that activated c-Jun is dimerized with c-Fos or ATF-2 for control of its target gene expression. Finally, we showed that human amylin triggers AP-1-mediated transcriptional activation. Our results suggest strongly that human amylin induces apoptosis through stimulation of expression and activation of c-Jun, and that co-expression and dimerization of c-Jun and c-fos or ATF-2 may be important for activation of the downstream apoptotic process.

Inhibition of the c-Jun N-terminal kinase signaling pathway influences neurite outgrowth of spiral ganglion neurons in vitro

OBJECTIVES

Inhibitors of the c-Jun N-terminal kinase (JNK) signaling pathway have been demonstrated to protect hair cells of the auditory system and different types of neurons from various insults, and their use for future therapeutic applications has been proposed. In the study, we evaluated the effects of inhibition of the JNK pathway on process outgrowth from spiral ganglion neurons.

METHODS

Spiral ganglion explants from rats (postnatal days 3-5) that were cultured on laminin were treated with neurotrophin-3 and/or the JNK signaling pathway inhibitor CEP-11004. Both neurite length and number of the explants were evaluated and statistically analyzed by analysis of variance.

RESULTS

Inhibition of the JNK signaling pathway reduced process outgrowth from spiral ganglion explants. The reduction, both in length and number of neurites, was reversed by the application of neurotrophin-3.

CONCLUSIONS

The results indicate that an intact JNK signaling pathway is important for process outgrowth of spiral ganglion neurons. However, neurotrophin-3 stimulates process extension by a JNK independent pathway. Our results demonstrate that inhibition of the JNK pathway can have adverse effects on the extension of spiral ganglion neurons, but that the negative effects can be ameliorated by appropriate treatment.

Expression profiling following traumatic brain injury: a review

Traumatic brain injury (TBI) elicits a complex sequence of putative autodestructive and neuroprotective cellular cascades. It is hypothesized that the genomic responses of cells in the injured brain serve as the basis for these cascades. Traditional methods for analyzing differential gene expression following brain trauma demonstrate that immediate early genes, cytokines, transcription factors, and neurotrophic factors can all participate in the brain's active and directed response to injury, and may do so concurrently. It is this complexity and multiplicity of interrelated molecular mechanisms that has demanded new methods for comprehensive and parallel evaluation of putative as well as novel gene targets. Recent advances in DNA microarray technology have enabled the simultaneous evaluation of thousands of genes and the subsequent generation of massive amounts of biological data relevant to CNS injury. This emerging technology can serve to further current knowledge regarding recognized molecular cascades as well as to identify novel molecular mechanisms that occur throughout the post-traumatic period. The elucidation of the complex alterations in gene expression underlying the pathological sequelae following TBI is of central importance in the design of future therapeutic agents.

Exposure to short-lasting impulse noise causes neuronal c-Jun expression and induction of apoptosis in the adult rat brain

Exposure to impulse noise, above a certain intensity, is harmful to auditory function. Effects of impulse noise on the central nervous system (CNS) are largely unexplored, and there is little information on critical threshold values and time factors. We have recently shown that neurofilament proteins are affected in the cerebral cortex and the hippocampus. Now we show that impulse noise induces expression of the immediate early gene c-Jun products, proposed to play a role in the initiation of neuronal death, and apoptosis as revealed by TUNEL staining. Rat brains were investigated immunohistochemically 2 h to 21 days after exposure to impulse noise of 198 dB or 202 dB. c-Jun was expressed in neuronal perikarya in layers II-VI of the temporal cortex, the cingulate and the piriform cortices at 2 h to 21 days after both exposure levels. Granule neurons of the dentate gyrus and the CA1-3 in the hippocampus pyramidal neurons were similarly affected. The elevated expression of c-Jun products remained high at all postexposure times. TUNEL staining was positive among the same nerve cell populations 6 h after exposure and persisted even at 7 days at both exposure levels.

Regenerative and survival capabilities of Purkinje cells overexpressing c-Jun

Following axotomy, cerebellar Purkinje cells (PCs) do not elongate their axons, even in a favourable environment, and are resistant to death. They have no constitutive presence of common growth-associated proteins, such as GAP-43 and c-Jun. Previous experiments show that injured transgenic PCs overexpressing GAP-43 exhibit a profuse sprouting along the axon and at its severed end. Nevertheless, the lesioned axons are unable to regenerate either spontaneously or into growth-permissive environments. In addition, a considerable number of GAP-43 transgenic PCs degenerate after injury. c-Jun is an inducible transcription factor expressed in axotomized central neurons and regenerating peripheral neurons. It also contributes to programmed cell death during development. To test whether c-Jun could modify the response of PCs to axotomy or enhance the growth/death phenomena of GAP-43 Purkinje neurons, we generated transgenic mice overexpressing c-Jun in PCs. However, c-Jun upregulation did not affect the adult intact phenotype of these neurons and their regenerative and survival capabilities after axotomy. Also in the cross-bred GAP-43/c-Jun mice, c-Jun did not modify the response of GAP-43 PCs to axotomy. By contrast, in organotypic cultures of cerebellum taken from 9-day-old-pups, the survival capabilities of PCs overexpressing c-Jun decreased, in association with a consistent c-Jun phosphorylation. On the whole our data show that c-Jun alone is unable to trigger regenerative or degenerative phenomena in PCs and suggest that the cellular action of this early gene in developing and mature neurons strongly depends on interplaying intracellular signals.

c-Jun mediates axotomy-induced dopamine neuron death in vivo

Expression of the transcription factor c-Jun is induced in neurons of the central nervous system (CNS) in response to injury. Mechanical transection of the nigrostriatal pathway at the medial forebrain bundle (MFB) results in the delayed retrograde degeneration of the dopamine neurons in the substantia nigra pars compacta (SNc) and induces protracted expression and phosphorylation of c-Jun. However, the role of c-Jun after axotomy of CNS neurons is unclear. Here, we show that adenovirus-mediated expression of a dominant negative form of c-Jun (Ad.c-JunDN) inhibited axotomy-induced dopamine neuron death and attenuated phosphorylation of c-Jun in nigral neurons. Ad.c-JunDN also delayed the degeneration of dopaminergic nigral axons in the striatum after MFB axotomy. Taken together, these findings suggest that activation of c-Jun mediates the loss of dopamine neurons after axotomy injury.

Signalling for survival and death in neurones: the role of stress-activated kinases, JNK and p38

The pathways involved in neuronal survival or death have been extensively studied mainly in cell lines. Recent evidence has suggested that activation of the stress activated pathways, jun N-terminal kinase (JNK) and p38 may play important roles in neuronal cell death or regeneration. In this review we will discuss these pahtways in detail. We will examine the evidence that these pathways are important in neuronal cell death. Finally we will review the evidence that inhibitors of these pathways have a neuroprotective effect both in vitro and in vivo.

Early c-Fos induction after cerebral ischemia: a possible neuroprotective role

The role of c-Fos in neurodegeneration or neuroprotection after cerebral ischemia is controversial. To investigate whether early c-Fos induction after ischemia is associated with neuroprotection, rats were subjected to 10 minutes of transient forebrain ischemia and c-Fos expression was examined. Resistant dentate granule cells and neurons in CA2-4 displayed more robust immunoreactivity than vulnerable neurons in the CA1 region of hippocampus during early hours of reperfusion. By 6 hours after reperfusion, c-Fos immunoreactivity was greatly diminished in all areas of the hippocampus. Administration of N-acetyl-O-methyldopamine (NAMDA), a compound previously shown to protect CA1 neurons against ischemia, increased c-Fos immunoreactivity in the CA1 vulnerable region at 6 hours after ischemia and protected SK-N-BE(2)C neurons from oxygen glucose deprivation. Further in vitro study showed that NAMDA potentiated phorbol-12 myristate-13 acetate (PMA)-induced c-Fos expression, AP1 binding activity, and late gene expression determined by chloramphenicol acetyltransferase (CAT) activity from AP1 containing tyrosine hydroxylase promoter-CAT fusion gene in SK-N-BE(2)C neurons. In vivo and in vitro results showed that a neuroprotectant, NAMDA, in concert with another stimulus (for example, ischemia or PMA) up-regulates c-Fos expression and suggested that the early rise of NAMDA-induced c-Fos expression in vulnerable CA1 neurons may account for neuroprotection by means of up-regulating late gene expression for survival.

Kainate-induced genes in the hippocampus: lessons from expression patterns

Kainate, the analog of the excitatory amino acid L-glutamate, upon binding to non-NMDA glutamate receptors, causes depolarization of neurons followed by severe status epilepticus, neurodegeneration, plasticity and gliosis. These events are best observed in hippocampus, the limbic structure implicated in learning and long-term memory formation. Neurons in all hippocampal structures undergo hyper-activation, however, whereas the cells in the CA subfields degenerate within 2--3 days following the application of kainate, the granule cells of the dentate gyrus are resistant to any form of neurodegeneration and even initiate new synaptic contacts. These physiological and histological changes are modulated by short-term and long-term alterations in gene expression. Perhaps close examination of the changing spatio-temporal patterns of mRNAs of various genes may help in generating a clearer picture of the molecular events leading to complex cognitive functions.

The mammalian Jun proteins: redundancy and specificity

The AP-1 transcription factor is composed of a mixture of homo- and hetero-dimers formed between Jun and Fos proteins. The different Jun and Fos family members vary significantly in their relative abundance and their interactions with additional proteins generating a complex network of transcriptional regulators. Thus, the functional activity of AP-1 in any given cell depends on the relative amount of specific Jun/Fos proteins which are expressed, as well as other potential interacting proteins. This diversity of AP-1 components has complicated our understanding of AP-1 function and resulted in a paucity of information about the precise role of individual AP-1 members in distinct cellular processes. We shall discuss recent studies which suggest that different Jun and Fos family members may have both opposite and overlapping functions in cellular proliferation and cell fate.

A new model for diffuse brain injury by rotational acceleration: II. Effects on extracellular glutamate, intracranial pressure, and neuronal apoptosis

The aim of this study is to monitor excitatory amino acids (EAAs) in the extracellular fluids of the brain and to characterize regional neuronal damage in a new experimental model for brain injury, in which rabbits were exposed to 180-260 krad/s2 rotational head acceleration. This loading causes extensive subarachnoid hemorrhage, focal tissue bleeding, reactive astrocytosis, and axonal damage. Animals were monitored for intracranial pressure (ICP) and for amino acids in the extracellular fluids. Immunohistochemistry was used to study expression of the gene c-Jun and apoptosis with the terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) technique. Extracellular glutamate, glycine, and taurine increased significantly in the hippocampus within a few hours and remained high after 24 h. Neuronal nuclei in the granule layers of the hippocampus and cerebellum were positive for c-Jun after 24 h. Little immunoreactivity was detected in the cerebral cortex. c-Jun-positive neuronal perikarya and processes were found in granule and pyramidal CA4 layers of the hippocampus and among the Purkinje cells of the cerebellum. Also some microglial cells stained positively for c-Jun. TUNEL reactivity was most intense at 10 days after trauma and was extensive in neurons of the cerebral cortex, hippocampus, and cerebellum. The initial response of the brain after rotational head injury involves brain edema after 24 h and an excitotoxic neuronal microenvironment in the first hour, which leads to extensive delayed neuronal cell death by apoptosis necrosis in the cerebral cortex, hippocampus and cerebellum.