Kainic acid?induced excitotoxicity is associated with a complex c-Fos and c-Jun response which does not preclude either cell death or survival

Organ crosstalk during acute lung injury, acute respiratory distress syndrome, and mechanical ventilation

PURPOSE OF REVIEW

Multiple organ failure is the main cause of morbidity and mortality in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients. Moreover, survivors of both ALI and ARDS often show significant neurocognitive decline at discharge. These data suggest a deleterious organ crosstalk between lungs and distal organs. This article reviews the recent literature concerning the role of this organ crosstalk during ALI, ARDS, and mechanical ventilation, especially focusing on brain-lung communication.

RECENT FINDINGS

Numerous pulmonary and extrapulmonary disorders could predispose critically ill patients to ALI and ARDS. Mechanical ventilation, although a lifesaving intervention, could contribute by modulating the mechanisms involved in the pathophysiology of lung damage and their impact on remote organs. Emerging clinical and experimental evidence supports the hypothesis of a multidirectional organ crosstalk between lungs and distal organs.

SUMMARY

Organ crosstalk is an emerging area of research in lung disease in critically ill patients. The findings of these studies are clinically relevant and show the importance of an integrative approach in the management of critical patients. However, further studies are necessary to understand the complex interactions concurring in these pathologies.

Kainic acid-induced early genes activation and neuronal death in the medial extended amygdala of rats

The medial extended amygdala modulates pheromonal perception, influencing emotional and social behavior. As the amygdala is part of neuronal circuits that are very sensitive to excitability, its neurons are targets of seizures in temporal lobe epilepsy. It has been suggested that the hippocampus is strongly involved this pathology. There is less consistent information, however, on the effects of this disease in the amygdala. The effects of status epilepticus on the medial extended amygdala were analyzed by immunohistochemistry for neural stress and by the amino-cupric-silver technique for neuronal death in rats after kainic acid (KA) administration. Sixty adult Wistar male rats were used. Thirty animals received an injection of KA, and 30 were injected with saline. After 2, 4, 12, 24 and 48 h survival the brains were stained for Fos and FosB and for neuronal death. In the present study we show that KA induces Fos and FosB expression in neurons of the medial extended amygdala after 2, 4-48 h, with time courses that are different between them and from control animals. While Fos-IR peaks at 2-4 h post KA and then decreases, FosB-IR increases in the same period reaching its highest expression at 24-48 h. Moreover, KA injection produced massive neuronal death with a peak at 24 h. This neurodegeneration paralleled FosB-IR protein expression. These findings show that KA produces neuronal stress and activation of early genes and neuronal death in the medial extended amygdala, demonstrating the vulnerability of its neurons to the epileptogenic effects of KA.

Cajal-Retzius cells fail to trigger the developmental expression of the Cl- extruding co-transporter KCC2

Cajal-Retzius (CR) cells are transient neurons of the developing cerebral cortex that play a pivotal role in the lamination and construction of neural circuits. One physiological feature of CR cells is the failure to switch GABAergic transmission from excitation to inhibition. To examine the mechanisms underlying the persistence of the depolarizing action of GABA we analyzed the mRNA expression of the K+/Cl- co-transporter type 2 (KCC2) in mouse CR by in situ hybridization. During the second postnatal week, the developmentally regulated expression of KCC2 reached adult levels in most neurons of the cerebral cortex. Double labeling with the CR-cell marker calretinin and KCC2 in situ hybridization showed that CR cells were consistently devoid of KCC2 expression in several cortical areas such as neocortex and hippocampus. Since most cortical calretinin- and calbindin-containing non-CR neurons did express KCC2 mRNA, we conclude that CR cells specifically fail to trigger the developmental expression of the K+/Cl- co-transporter KCC2. These results suggest that absence of KCC2 preserves the depolarizing action of GABA in CR cells and support the notion that KCC2 is a key factor controlling Cl- homeostasis and preventing hyperexcitability.

Expression of transcription factors CREB and c-Fos in the brains of terminal Creutzfeldt-Jakob disease cases

Expression levels and localization of transcription factors cAMP response element binding protein (CREB(1) and CREB(2)) and c-Fos, as well as levels of up-stream mitogen-activated protein kinases/extracellular signal-regulated kinases (ERK-1 and ERK-2) and p38 kinase, were examined in the brains (frontal cortex) of eleven cases with Creutzfeldt-Jakob disease (CJD) and five age-matched controls. Preserved expression levels of ERK-1-P, ERK-2-P and p38-P were observed in CJD. However, significantly reduced levels, as revealed by gel electrophoresis and Western blotting, and reduced numbers of immunoreactive nuclei, as seen by immunohistochemistry, to CREB, CREB-P, c-Fos and c-Fos-P were found in CJD when compared with controls. These observations point to exhausted CREB and c-Fos brain responses, in spite of preserved up-stream signaling kinases, thus favoring cell death in terminal stages of CJD.

Involvement of c-Jun-JNK pathways in the regulation of programmed cell death of developing chick embryo spinal cord motoneurons

Key features of developmentally regulated programmed cell death (PCD) have been described for the first time in the chick nervous system. JNK/c-Jun pathway was involved in early events determining normal and pathological neuronal death as shown in experimental models. In the chick embryo, PCD of motoneurons (MNs) in ovo occurs within a well-defined temporal window and can be subjected to experimental manipulation. Taking advantage of this in vivo system, we explored the role of c-Jun and JNK pathway in the regulation of PCD in MNs. By using specific antibodies against phospho-c-Jun (Ser 63, 73) and JNK we demonstrated that before MNs acquire apoptotic phenotype there is an increase in c-Jun. Blockage of neuromuscular activity by the GABA agonist muscimol reduces PCD and diminishes c-Jun immunoreactivity in MNs. Extensive induction of PCD, either due to injection of beta-bungarotoxin or limb bud removal, is also preceded by an increase in c-Jun immunoreactivity that is also associated with upregulation of phospho-c-Jun and JNK. Translocation of JNK from cytoplasm to MN nuclei was also detected. After acute application of beta-bungarotoxin, which is a strong apoptotic stimulus for MNs, c-Jun phosphorylation occurs on serine 73, whereas serine 63 is the main site for c-Jun phosphorylation after limb bud removal. These results demonstrated that the JNK/c-Jun pathway is involved in the decision phase of normal and induced apoptosis in MNs. Pharmacological interventions involving this pathway should be explored as a potential therapeutic target for promoting MN survival.

Neural Overexcitation and Implication of NMDA and AMPA Receptors in a Mouse Model of Temporal Lobe Epilepsy Implying Zinc Chelation

PURPOSE

Zinc chelation with diethyldithiocarbamate (DEDTC) during nondamaging kainic acid administration enhances excitotoxicity to the level of cell damage. The objective of this work was to study the developing of the lesion in this model of temporal lobe epilepsy and the implications of the different types of glutamate receptors.

METHODS

The antagonist of the N-methyl-D-aspartate (NMDA) receptor MK-801, and the antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor GYKI52466, were used concomitantly with intraperitoneal administration of kainic acid (15 mg/kg) followed by DEDTC (150 mg/kg) in mouse. The animals were killed at different times from 4 h to 7 days. Fos proteins were used as markers of cell overexcitation; heat-shock protein 72 (HSP72) as marker of cell stress.

RESULTS

Neither kainic acid nor DEDTC alone, at the doses used, led to cell loss, HSP72 expression, or permanent Fos protein induction. When combined, the hilus and cornu ammonis were damaged; principal cells in these areas coexpressed c-Fos and HSP72, with the exception of CA2; interneurons did not express HSP72 in any area. MK-801 completely abolished damage and HSP72 expression from the hippocampus. GYKI52466 blocked CA1 damage and HSP72 expression in the CA1 but not in the CA3.

CONCLUSIONS

Synaptic zinc increases the tolerance of hippocampus to overexcitation. All the areas that are fated to die are determined simultaneously; the damage in the CA1 is not an extension of the damage in the CA3. Damage of the CA3 is dependent on kainate and NMDA receptors, whereas the damage of the CA1 depends on AMPA and NMDA receptors.

Ketogenic diet decreases the level of proenkephalin mRNA induced by kainic acid in the mouse hippocampus

The ketogenic diet (KD) has been used to control medically refractory epilepsy in children for more than 80 years. Despite the clinical efficacy of the KD, its underlying bases are still obscure. Previous work from our laboratory has established that the KD has an antiepileptic and neuroprotective effect in the kainic acid (KA)-induced seizure model. The neuronal excitation caused by KA leads to increases in the expression of a variety of genes, including immediate-early genes and opioid peptides derived from proenkephalin (PENK) and prodynorphin (PDYN). In particular, the up-regulated PENK gene that is induced by KA in the hippocampal dentate granule cells has proconvulsant properties. PENK is regulated by the c-jun amino-terminal kinase (JNK) signaling pathway, the crucial role of which is involved in the regulation of transcription factors, such as Jun and Fos. In the present study, we examined the effect of the KD on the increase of PENK, Fos, Jun, AP-1 DNA-binding activity and JNK gene expression induced by KA in the mouse hippocampus. Using in situ hybridization and northern blot analysis, we found that the KD significantly decreases the level of PENK gene expression induced by KA of the granular cells in the hippocampus. In addition, we have also found that KD diminished KA-induced AP-1 DNA-binding activity, Fos and Jun expression, and phoshorylated form of the three types of JNKs. These results suggest that the KD suppresses KA-induced activation of JNK signaling pathways, followed by a decrease of PENK gene expression in the hippocampus, thereby resulting in antiepileptic effects.

PTD-XIAP protects against cerebral ischemia by anti-apoptotic and transcriptional regulatory mechanisms

Caspases play a major role in the infarction process that follows occlusion of cerebral arteries and are important targets for stroke therapy. We have generated three fusion proteins that link various domains of the X chromosome-linked inhibitor of apoptosis (XIAP), a potent caspase inhibitor, to the protein transduction domain (PTD) of HIV-1/Tat, and have tested their efficacy after distal occlusion of the middle cerebral artery (dMCAO) in mice. PTD-XIAP failed to accumulate in brain structures after intravenous (iv) delivery, but properly transduced cortical cells when applied topically. Shorter constructs efficiently targeted the lesion after iv delivery. All proteins retained their caspase inhibitory activity and significantly reduced infarct volumes. PTD-XIAP reversed long-term impairments in the water maze test. Sequential activation of transcription factors was observed, suggesting that the effects of XIAP are mediated by both direct inhibition of apoptotic mechanisms and secondary regulation of transcription factors involved in neuronal survival.

GDNF and GFRalpha1 promote differentiation and tangential migration of cortical GABAergic neurons

Cortical GABAergic neurons are generated in the ventral telencephalon and migrate dorsally into the cortex following a tangential path. GDNF signaling via GFRalpha1 was found to promote the differentiation of ventral precursors into GABAergic cells, enhancing their neuronal morphology and motility. GDNF stimulated axonal growth in cortical GABAergic neurons and acted as a potent chemoattractant of GABAergic cells. These effects required GFRalpha1 but neither RET nor NCAM, the two transmembrane signaling receptors known for GDNF. Mutant mice lacking GDNF or GFRalpha1, but neither RET nor NCAM, showed reduced numbers of GABAergic cells in the cerebral cortex and hippocampus. We conclude that one of the normal functions of GDNF signaling via GFRalpha1 in the developing brain is to promote the differentiation and migration of cortical GABAergic neurons. The lack of involvement of RET or NCAM in these processes suggests the existence of additional transmembrane effectors for GDNF.

Neuronal and astroglial alterations in the hippocampus of a mouse model for type 1 diabetes

The influence of diabetes mellitus on brain pathology is increasingly recognized. Previous contributions of our laboratory demonstrated in models of type 1 diabetes (nonobese diabetic and streptozotocin (STZ)-treated mice), a marked astrogliosis and neurogenesis deficit in hippocampus and increased expression of hypothalamic neuropeptides. In the present investigation, we further analyzed alterations of astroglia and neurons in the hippocampus of mice 1 month after STZ-induced diabetes. Results showed that these STZ-diabetic mice presented: (a) increased number of astrocytes positive for apolipoprotein-E (Apo-E), a marker of ongoing neuronal dysfunction; (b) abnormal expression of early gene products associated with neuronal activation, including a high number of Jun + neurons in CA1 and CA3 layers and dentate gyrus, and of Fos-expressing neurons in CA3 layer; (c) augmented activity of NADPH-diaphorase, linked to oxidative stress, in CA3 region. These data support the concept that uncontrolled diabetes leads to hippocampal pathology, which adjoin to changes in other brain structures such as hypothalamus and cerebral cortex.

Platelet-derived growth factor (PDGF) receptor-alpha-activated c-Jun NH2-terminal kinase-1 is critical for PDGF-induced p21WAF1/CIP1 promoter activity independent of p53

Platelet-derived growth factor (PDGF) is a potent mitogen for mesenchymal cells. PDGF AA functions as a "competent factor" that stimulates cell cycle entry but requires additional (progression) factors in serum to transit the cell cycle beyond the G1/S checkpoint. Unlike PDGF AA, PDGF B-chain (c-sis) homodimer (PDGF BB) and its viral counterpart v-sis can serve as both competent and progression factors. PDGF BB activates alpha- and beta-receptor subunits (alpha-PDGFR and beta-PDGFR) and induces phenotypic transformation in NIH 3T3 cells, whereas PDGF AA activates alpha-PDGFR only and fails to induce transformation. We showed previously that alpha-PDGFR antagonizes beta-PDGFR-mediated transformation through activation of stress-activated protein kinase-1/c-Jun NH2-terminal kinase-1, whereas both alpha-PDGFR and beta-PDGFR induce mitogenic signals. These studies revealed a striking feature of PDGF signaling; the specificity and the strength of the PDGF growth signal is modulated by alpha-PDGFR-mediated simultaneous activation of growth stimulatory and inhibitory signals, whereas beta-PDGFR mainly induces a growth-promoting signal. Here we demonstrate that PDGF BB activation of beta-PDGFR alone results in more efficient cell cycle transition from G1 to S phase than PDGF BB activation of both alpha-PDGFR and beta-PDGFR. PDGF AA activation of alpha-PDGFR or PDGF BB activation of both alpha- and beta-PDGFRs up-regulates expression of p21WAF1/CIP1, an inhibitor of cell cycle-dependent kinases and a downstream mediator of the tumor suppressor gene product p53. However, beta-PDGFR activation alone fails to induce p21WAF1/CIP1 expression. We also demonstrate that alpha-PDGFR-activated JNK-1 is a critical signaling component for PDGF induction of p21WAF1/CIP1 promoter activity. The ability of PDGF/JNK-1 to induce p21WAF1/CIP1 promoter activity is independent of p53, although the overall p21WAF1/CIP1 promoter activities are greatly reduced in the absence of p53. These results provide a molecular basis for differential regulation of the cell cycle and transformation by alpha- and beta-PDGFRs.

Increased vulnerability to kainic acid-induced epileptic seizures in mice underexpressing the scaffold protein Islet-Brain 1/JIP-1

Islet-Brain 1, also known as JNK-interacting protein-1 (IB1/JIP-1) is a scaffold protein mainly involved in the regulation of the pro-apoptotic signalling cascade mediated by c-Jun-N-terminal kinase (JNK). IB1/JIP-1 organizes JNK and upstream kinases in a complex that facilitates JNK activation. However, overexpression of IB1/JIP-1 in neurons in vitro has been reported to result in inhibition of JNK activation and protection against cellular stress and apoptosis. The occurrence and the functional significance of stress-induced modulations of IB1/JIP-1 levels in vivo are not known. We investigated the regulation of IB1/JIP-1 in mouse hippocampus after systemic administration of kainic acid (KA), in wild-type mice as well as in mice hemizygous for the gene MAPK8IP1, encoding for IB1/JIP-1. We show here that IB1/JIP-1 is upregulated transiently in the hippocampus of normal mice, reaching a peak 8 h after seizure induction. Heterozygous mutant mice underexpressing IB1/JIP-1 showed a higher vulnerability to the epileptogenic properties of KA, whereas hippocampal IB1/JIP-1 levels remained unchanged after seizure induction. Subsequently, an increasing activation of JNK in the 8 h following seizure induction was observed in IB1/JIP-1 haploinsufficient mice, which also underwent more severe excitotoxic lesions in hippocampal CA3, as assessed histologically 3 days after KA administration. Taken together, these data indicate that IB1/JIP-1 in hippocampus participates in the regulation of the neuronal response to excitotoxic stress in a level-dependent fashion.

Fos protein expression following acute administration of diethyldithiocarbamate in rats

Dithiocarbamates are compounds commonly used in medicine and in agriculture and their prolonged use is known to result in neurotoxicity. Whether this response may be related to early gene expression has not been investigated. We have addressed this issue by mapping Fos expression in rats acutely injected with diethyldithiocarbamate (DDTC) and correlating these data to neural damage in the hippocampus as determined by pyknotic nuclei count. In comparison to saline injected rats, DDTC treatment induced a marked Fos expression in most brain regions at 1 and 3 h. In the hippocampus, a high Fos expression was followed by a variable number of pyknotic nuclei at 6 h, depending on the subregion. The data suggest that, in this model of neurotoxicity, c-fos induction does not reflect a cell commitment to die or survive, but rather a cell response to the DDTC-induced oxidative disorder.

Vagal afferents are necessary for the establishment but not the maintenance of kainic acid-induced hyperalgesia in mice

Systemic administration of a single, sub-convulsive dose (20mg/kg) of kainic acid (KA) produces long-term hyperalgesia. The robustness and reproducibility of this effect makes this a valuable model of chronic pain. However, the mechanism by which KA produces hyperalgesia remains unknown. We evaluated the role of vagal afferents on KA-induced hyperalgesia in mice by assessing the influence of bilateral subdiaphragmatic vagotomy and of direct application of KA to vagal afferents on the development of hyperalgesia. The hot plate and tail flick tests were used to assess pain behavior. Central nervous system (CNS) activity evoked by acute administration of KA or exposure to a nociceptive stimulus was also determined by the immunocytochemical detection of Fos and of phosphorylated extracellular signal-regulated protein kinases 1 and 2 (pErk). Mice exhibited a persistent hyperalgesia after either systemic application of KA or topical treatment with KA on vagal afferents. Vagotomy performed 2 weeks before the application of KA was able to prevent the establishment of hyperalgesia, but vagotomy performed 2 weeks after the application of KA was unable to reverse the already established hyperalgesia. This result establishes that vagal afferents are pivotal to the onset of hyperalgesia. Consistent with this, KA evoked the expression of Fos in vagal related areas of the brainstem, including the nucleus tractus solitarius (NTS) and area postrema (AP), as well as widespread areas of the forebrain. Vagotomy selectively decreased KA-evoked Fos in the NTS while sparing that in other brain areas. In addition to hyperalgesia, weeks after KA treatment, stimulus induced pErk was increased in spinal nociceptive neurons and the medial hypothalamus, a phenomenon that was prevented by prior vagotomy. No signs of cell death were detected using in situ nick end-labeling (TUNEL) assay and Nissl staining at 1, 5, 24, 36 h and 12 days post-KA. These findings suggest that the mechanism underlying KA-induced hyperalgesia is a long-term dysfunction of CNS areas that are activated by vagal afferents and involved in descending control of spinal nociceptive neurons.

To die or not to die for neurons in ischemia, traumatic brain injury and epilepsy: a review on the stress-activated signaling pathways and apoptotic pathways

After a severe episode of ischemia, traumatic brain injury (TBI) or epilepsy, it is typical to find necrotic cell death within the injury core. In addition, a substantial number of neurons in regions surrounding the injury core have been observed to die via the programmed cell death (PCD) pathways due to secondary effects derived from the various types of insults. Apart from the cell loss in the injury core, cell death in regions surrounding the injury core may also contribute to significant losses in neurological functions. In fact, it is the injured neurons in these regions around the injury core that treatments are targeting to preserve. In this review, we present our cumulated understanding of stress-activated signaling pathways and apoptotic pathways in the research areas of ischemic injury, TBI and epilepsy and that gathered from concerted research efforts in oncology and other diseases. However, it is obvious that our understanding of these pathways in the context of acute brain injury is at its infancy stage and merits further investigation. Hopefully, this added research effort will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat these acute brain injuries.

Inhibition of hippocampal Jun N-terminal kinase enhances short-term memory but blocks long-term memory formation and retrieval of an inhibitory avoidance task

Learning initiates a series of plastic events the occurrence of which are required for the storage of information related to the training experience. Several lines of evidence indicate that, in the rat hippocampus, different members of the family of mitogen-activated protein kinases (MAPK) play a key role in the onset of such plastic events. Using SP600125, the newly developed inhibitor of the MAPK c-Jun amino-terminal kinase (JNK), we show a direct involvement of this protein kinase in mnemonic processes. The intra-CA1 infusion of SP600125, at a dose that in naïve animals significantly reduced the phosphorylation levels of c-Jun without affecting the activity of ERK1/2 or p38 MAPK, enhanced short-term memory (STM) but blocked long-term memory (LTM) formation and retrieval of an inhibitory avoidance learning task. No action of this drug on locomotor/exploratory activity or general anxiety state could be detected. The significance of these results is discussed in the context of others describing the independence of LTM from STM.

c-Jun-like immunoreactivity in apoptosis is the result of a crossreaction with neoantigenic sites exposed by caspase-3-mediated proteolysis

Previous reports in various cells and species have shown that apoptotic cells are specifically and strongly labeled by certain c-Jun/N-terminal antibodies, such as c-Jun/sc45. This kind of immunoreactivity is confined to the cytoplasm. It is not due to c-Jun but appears to be related to c-Jun-like neoepitopes generated during apoptosis. This study was planned to gain further information about c-Jun-like immunostaining during apoptosis and to evaluate these antibodies as possible tools for characterizing cell death. Most of the experiments were performed in chick embryo spinal cord. When the apoptotic c-Jun-like immunoreactivity and caspase-3 immunostaining patterns were compared, we found that both antibodies immunostained the same dying cells in a similar pattern. In contrast to TUNEL staining, which reveals a positive reaction in both apoptotic and necrotic dying cells, active caspase-3 and c-Jun/sc45 antibodies are more selective because they stained only apoptotic cells. When cytosolic extracts from normal tissues were digested in vitro with caspase-3, c-Jun/sc45 immunoreactivity was strongly induced in several proteins, as demonstrated by Western blotting. Similar results were found when normal tissue sections were treated with caspase-3. Our results show that c-Jun/sc45 antibodies react with neoepitopes generated from cell proteins cleaved by activated caspases during apoptosis. We conclude that c-Jun/sc45 antibodies may be useful for detecting apoptosis. They can even be used in archival paraffin-embedded tissue samples.

Effect of melatonin on the regulation of proenkephalin and prodynorphin mRNA levels induced by kainic acid in the rat hippocampus

The in vivo short-term effect of melatonin on kainic acid (KA)-induced proenkephalin (proENK) or prodynorphin (proDYN) mRNA, and on AP-1 protein levels in the rat hippocampus, were studied. Melatonin (5 mg/kg) or saline was administered intraperitoneally (i.p.) to rats 30 min prior to and immediately after i.p. injection of KA (10 mg/kg). Rats were sacrificed 1 and 3 h after KA injection. The proENK and proDYN mRNA levels were significantly increased 3 h after KA administration. The elevations of both proENK and proDYN mRNA levels induced by KA were significantly inhibited by the preadministration with melatonin. The increases of proENK and proDYN mRNA levels induced by KA were well-correlated with the increases of c-Fos, Fra-2, FosB, c-Jun, and JunB protein levels, which were significantly increased 3 h after KA administration and effectively inhibited by administration with melatonin. In an electrophoretic mobility shift assay, both AP-1 and ENKCRE-2 DNA binding activities were increased by KA, which were also attenuated by the administration of melatonin. In addition, cross-competition studies revealed that AP-1 or ENKCRE-2 DNA binding activity was effectively reduced by the 50x unlabeled cross-competitor. Therefore, these data suggest that melatonin has an inhibitory role in KA-induced gene expression, such as proENK and proDYN mRNA expression, and this may be due to a reduction of KA-induced AP-1 or ENKCRE-2 DNA binding activity.

Seizure-induced neuronal death is associated with induction of c-Jun N-terminal kinase and is dependent on genetic background

Previous studies have shown that expression of c-Jun protein, as well as the c-Jun amino-terminal kinase (JNK) group of mitogen-activated protein kinases, may play a critical role in the pathogenesis of glutamate neurotoxicity. In order to define the molecular cascade that leads to c-Jun activation following excitotoxic injury and delineate whether induction of protein synthesis is related to cell death signaling cascades or those changes associated with increased seizure activity, we examined the expression of JNK-1, as well as its substrate, c-Jun and N-terminal phosphorylated c-Jun following kainic acid (KA) administration in two strains of mice. In the present study, we assessed the immunohistochemical expression of these proteins at time points between 2 h and 7 days, in excitotoxic cell death-resistant (C57BL/6) and -susceptible (FVB/N) mouse strains that were systemically injected with saline or kainic acid. No strain-related differences in the immunohistochemical expression of any of the proteins were observed in intact control mice. However, following KA administration, the magnitude and period of induction of JNK-1 protein was associated with impending cell death, while increased phosphorylation of c-Jun protein was associated with resistance to cell death. In contrast, expression of c-Jun protein does not appear to be a reliable indicator of impending cell death, as it was expressed in resistant and vulnerable subfields in mice susceptible to kainate injury. These results provide the first evidence that JNK-1 expression may be involved in producing the neuronal cell death response following excitotoxin-induced injury.

Accumulation of phosphorylated neurofilaments and increase in apoptosis-specific protein and phosphorylated c-Jun induced by proteasome inhibitors

The ubiquitin-proteasome system has been regarded as being important in the progression of neurodegenerative diseases, although its exact role remains uncertain. This in vitro study using PC12h cell cultures examined whether interference with the ubiquitin-proteasome system by proteasome inhibitors induces the neuropathological features of neurodegenerative diseases. Perikaryal accumulation of phosphorylated neurofilaments and an increase in c-Jun as well as phosphorylated form of c-Jun and apoptosis-specific protein were induced by the proteasome inhibitors lactacystin and N-carbobenzoxy-leucyl-leucyl-leucinal. These changes were not observed when only calpain was inhibited. The present study therefore suggests the possibility that a perturbation of the ubiquitin-proteasome system may be one of the causes that result in the development of neuropathological features. Additionally, activity assays showed that the proteasome inhibitor caused an increase in the activity of c-Jun N-terminal kinase (JNK/SAPK), which can phosphorylate neurofilaments and c-Jun, suggesting the possible involvement of JNK in phosphorylation of these proteins.

Nitrone spin trapping compound N-tert-butyl-alpha-phenylnitrone prevents seizures induced by anticholinesterases

The neuroprotection afforded by spin trapping agents such as N-tert-butyl-alpha-phenylnitrone (PBN) has lent support to the hypothesis that increased production of reactive oxygen species (ROS) is a major contributing factor to excitotoxicity, aging and cognitive decline. Little is known, however, about the pharmacological properties of PBN. We have compared the acute effects of PBN on the development of seizures induced by the irreversible acetylcholinesterase (AChE) inhibitor diisopropylphosphorofluoridate (DFP), the reversible AChE inhibitor physostigmine (PHY), the muscarinic cholinergic receptor agonist pilocarpine (PIL) and the glutamatergic receptor agonist kainic acid (KA). Rats were sacrificed 90 min after the injection of seizure-inducing agents. In situ hybridization was used to detect the induction of immediate early gene (IEG) c-fos and c-jun mRNA's and the levels of AChE mRNA. The activity of AChE was visualized by AChE staining and quantified using an in vitro AChE assay. The seizures correlated with the induction of IEG mRNA's with all agents used. The pre-treatment with 150 mg/kg of PBN prevented DFP- and PHY-induced seizures and the related expression of IEG mRNA's, but had no effect on PIL- or KA-induced seizures and associated IEG mRNA's changes. PBN prevented seizures and significantly protected AChE activity against DFP inhibition when given before, but not when given after DFP. This study shows that PBN specifically protects against anticholinesterase-induced seizures by reversible protection of AChE activity and not by the blockade of muscarinic or glutamate receptors, reactivation of AChE or scavenging of ROS. The anticholinesterase properties should be considered when using PBN in studies of cholinergic dysfunction.

Activity and expression of JNK1, p38 and ERK kinases, c-Jun N-terminal phosphorylation, and c-jun promoter binding in the adult rat brain following kainate-induced seizures

The activity and/or expression of the mitogen-activated protein kinases c-Jun N-terminal kinase 1, p38 and extracellular signal-regulated kinases 1/2, as well as their substrates, the transcription factors c-Jun and activating transcription factor-2, were examined following systemic application of kainate in the cortex and hippocampus of the adult rat brain. The protein expression levels of all three mitogen-activated protein kinases remained constant during the observation period. Unexpectedly, c-Jun N-terminal kinase 1 was the only mitogen-activated protein kinase activated in this model of excitotoxicity, its activity raised from between 1 and 3 h moderate basal to maximal levels between 6 and 12 h. In contradistinction, activity of extracellular signal-regulated kinases 1/2 fell from their substantial basal levels and did not recover; activity of p38 was characterized by a high basal level that almost entirely disappeared and did not return to basal levels even 10 days after kainate application. c-Jun protein was rapidly expressed, with a maximum after 3 h and a slow decline after 12 h. Supershift assays revealed that, during the early induction phase of the c-jun gene, the proximal activator protein-1 (jun1) site of the c-jun promoter was mainly occupied by the constitutively expressed activating transcription factor-2, whereas the late induction correlated with the predominant binding of c-Jun and, to a lesser extent, activating transcription factor-2 to the distal activator protein-1 (jun2) site. The time-course of the N-terminal phosphorylation of c-Jun as determined by immunocytochemistry paralleled the activity of c-Jun N-terminal kinase 1 and showed a compartment-specific regulation between 3 and 12 h. A second set of supershift experiments demonstrated that c-Jun, but not activating transcription factor 2, bound to activator protein-1 sites in the promoter of substance P and collagenase genes, but not of the cyclo-oxygenase-2 gene. Our results demonstrate that activation of c-Jun N-terminal kinase 1, phosphorylation of c-Jun and selective occupation of the c-jun promoter by activating transcription factor-2 or c-Jun are part of the neuronal response following excitotoxicity that is considered as the mechanism for neuronal apoptosis in vivo. Some of these findings differ substantially from in vitro experiments and underline the necessity to analyse the neuronal stress pathways in the adult brain.

C-Fos, Jun D and HSP72 immunoreactivity, and neuronal injury following lithium-pilocarpine induced status epilepticus in immature and adult rats

In order to follow the maturation-related evolution of neuronal damage, cellular activation and stress response subsequent to Li-Pilo seizures in the 10- (P10), 21-day-old (P21) and adult rat, we analyzed the expression of the c-Fos protein as a marker of cellular activation, HSP72 immunoreactivity as the stress response and silver staining for the assessment of neuronal damage in 20 selected brain regions. The early wave of c-Fos measured at 2 h after the onset of seizures was present in most structures of the animals at the three ages studied and particularly strong in the cerebral cortex, hippocampus and amygdala. The late wave of c-Fos measured at 24 h after the onset of seizures and that was shown to correlate to neuronal damage was absent from the P10 rat brain, and present mainly in the cerebral cortex and hippocampus of P21 and adult rats. The expression of the stress response, assessed by the immunoreactivity of HSP72 at 24 h after the seizures was absent from the P10 rat brain and present in the entorhinal cortex, amygdala, hippocampus and thalamus of P21 and adult rats. The expression of Jun D at 24 h after the seizures was discrete and present in most brain regions at all ages. Neuronal injury assessed by silver staining at 6 h after the onset of seizures was very discrete in the brain of the P10 rat and limited to a few neurons in the piriform and entorhinal cortices. In older animals, marked neuronal degeneration occurred in the cerebral cortex, amygdala, hippocampus, lateral septum and thalamus. Thus the immediate cell activation induced by lithium-pilocarpine seizures which is present at all ages translates only into a late wave of c-Fos and the expression of HSP72 in P21 and adult animals in which there will be extensive cell damage.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.