Strong c-Jun/AP-1 immunoreactivity is restricted to apoptotic cells following intracerebral ibotenic acid injection in developing rats

Colchicine induces apoptosis in organotypic hippocampal slice cultures

The microtubule-disrupting agent colchicine is known to be particular toxic for certain types of neurons, including the granule cells of the dentate gyrus. In this study we investigated whether colchicine could induce such neuron-specific degeneration in developing (1 week in vitro) and mature (3 weeks in vitro) organotypic hippocampal slice cultures and whether the induced cell death was apoptotic and/or necrotic. When applied to 1-week-old cultures for 48 h, colchicine induced primarily apoptotic, but also a minor degree of necrotic cell death in the dentate granule cells, as investigated by cellular uptake of the fluorescent dye propidium iodide (PI), immunostaining for active caspase 3 and c-Jun/AP-1 (N) and fragmentation of nuclei as seen in Hoechst 33342 staining. All four markers appeared after 12 h of colchicine exposure. Two of them, active caspase 3 and c-Jun/AP-1 (N) displayed a similar time course and reached a maximum after 24 h of exposure, 24 h ahead of both PI uptake and Hoechst 33342 staining, which together displayed similar time profiles and a close correlation. In 3-week-old cultures, colchicine did not induce apoptotic or necrotic cell death. Attempts to interfere with the colchicine-induced apoptosis in 1-week-old cultures showed that colchicine-induced PI uptake and formation of apoptotic nuclei were temporarily prevented by coapplication of the protein synthesis inhibitor cycloheximide. Application of the pancaspase inhibitor z-VAD-fmk almost completely abolished the formation of active caspase 3 protein and apoptotic nuclei induced by colchicine, but the formation of necrotic nuclei increased correspondingly and the PI uptake was unaffected. We conclude that colchicine induces caspase 3-dependent apoptotic cell death of dentate granule cells in hippocampal brain slice cultures, but the apoptotic cell death is highly dependent on the developmental stage of the cultures.

Discovery of CEP-1347/KT-7515, an inhibitor of the JNK/SAPK pathway for the treatment of neurodegenerative diseases

Apoptosis has been proposed as a mechanism of cell death in Alzheimer's, Huntington's and Parkinson's diseases and the occurrence of apoptosis in these disorders suggests a common mechanism. Events such as oxidative stress, calcium toxicity, mitochondria defects, excitatory toxicity, and deficiency of survival factors are all postulated to play varying roles in the pathogenesis of the diseases. However, the transcription factor c-jun may play a role in the pathology and cell death processes that occur in Alzheimer's disease. Parkinson's disease (PD) is also a progressive disorder involving the specific degeneration and death of dopamine neurons in the nigrostriatal pathway. In Parkinson's disease, dopaminergic neurons in the substantia nigra are hypothesized to undergo cell death by apoptotic processes. The commonality of biochemical events and pathways leading to cell death in these diseases continues to be an area under intense investigation. The current therapy for PD and AD remains targeting replacement of lost transmitter, but the ultimate objective in neurodegenerative therapy is the functional restoration and/or cessation of progression of neuronal loss. This chapter will describe a novel approach for the treatment of neurodegenerative diseases through the development of kinase inhibitors that block the active cell death process at an early transcriptional independent step in the stress activated kinase cascade. In particular, preclinical data will be presented on the c-Jun Amino Kinase pathway inhibitor, CEP-1347/KT-7515, with respect to it's properties that make it a desirable clinical candidate for treatment of various neurodegenerative diseases.

Mice with partial deficiency of c-Jun show attenuation of methamphetamine-induced neuronal apoptosis

The regional distribution of c-Jun expression and of the number of apoptotic cells was compared in various brain areas after methamphetamine administration to mice. Our results showed that there was methamphetamine-induced overexpression of c-Jun in the cortex and striatum but not in the cerebellar cortex. There was an almost totally similar regional appearance of methamphetamine-induced apoptotic cells in the mouse brain; no apoptosis was present in the cerebellum. Additionally, in the neocortical area, more positive signals for c-Jun immunoreactivity were observed in the piriform cortex, an area that also showed more positive terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) signals than the frontal and parietal cortices. These observations suggested that c-Jun might be involved in methamphetamine-induced apoptosis. This idea was confirmed by using heterozygous c-Jun knockout mice that showed much less apoptosis than wild-type controls. In addition, we found that the majority of TUNEL-positive cells were also positive for c-Jun-like immunoreactivity in both genotypes. Moreover, methamphetamine-induced caspase-3 activity and PARP cleavage were also reduced in c-Jun heterozygous knockout mice. In contrast, methamphetamine-induced hyperthermia was essentially identical in the two genotypes. When taken together, our data support the hypothesis that c-Jun is involved in methamphetamine-induced apoptosis.

3-Nitropropionic acid neurotoxicity in hippocampal slice cultures: developmental and regional vulnerability and dependency on glucose

We investigated whether neurotoxic effects of the mitochondrial toxin 3-nitropropionic acid (3-NP) in hippocampal slice cultures are dependent on glucose levels in the culture medium and whether such effects occur via apoptosis or necrosis. In addition, 3-NP toxicity was investigated at two developmental stages of the cultures, prepared from rat brain at postnatal day 5-7 and grown in Neurobasal medium for 1 or 3 weeks. Cultures were exposed to 3-NP in the presence of high (25 mM), normal (5 mM), or low (3 mM) glucose for 48 h, followed by 48 h incubation in medium without 3-NP. Cellular propidium iodide (PI) uptake and lactate dehydrogenase (LDH) efflux into the medium revealed time- and dose-dependent cell death by 3-NP, with EC(50) values of about 60 microM in high or normal glucose. Regional vulnerability, as assessed by PI uptake and MAP2 immunostaining, in 3-week-old cultures was as follows: CA1 > CA3 > fascia dentata. In low glucose much lower concentrations of 3-NP (25 microM) triggered neurotoxicity. One-week-old cultures were less susceptible to 3-NP toxicity than 3-week-old cultures, but the dentate granule cells were relatively more affected in the immature cultures. We found no evidence for apoptotic cell death by 3-NP in 3-week-old cultures, but in 1-week-old cultures the putative apoptotic marker c-JUN/AP1 and nuclear fragmentation (Hoechst) were significantly increased in the dentate granule cells.

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.

Methamphetamine causes coordinate regulation of Src, Cas, Crk, and the Jun N-terminal kinase-Jun pathway

The clinical abuse of methamphetamine (METH) is a major concern because it can cause long-lasting neurodegenerative effects in humans. Current concepts of the molecular mechanisms underlying these complications have centered on the formation of reactive oxygen species. Herein, we provide cDNA microarray evidence that METH administration caused the induction of c-Jun and of other members involved in the pathway leading to c-Jun activation [stress-activated protein kinase/Jun N-terminal kinase (JNK3), Crk-associated substrate-Cas and c-Src] after environmental stresses or cytokine stimulation. Reverse transcription-polymerase chain reaction analysis confirmed these increases and also showed that the expression of JNK1 and JNK3 but not JNK2 was also increased in the METH-treated mice. Western blot analysis showed that METH increased the expression of c-Jun phosphorylated at serine-63 and serine-73 residues. Other upstream members of the JNK pathway, including phosphorylated JNKs, mitogen-activated protein kinase kinase 4, mitogen-activated protein kinase kinase 7, Crk II, Cas, and c-Src were also increased at the protein level. These values returned to baseline by 1 week after drug treatment. These results are discussed in terms of their support for a possible role of the activation of the JNK/Jun pathway in the pathophysiological effects of METH.

Molecular and biochemical mechanisms of perinatal brain injury

Hypoxic-ischemic injury to the prenatal and perinatal brain is a major contributor to morbidity and mortality to infants, often leading to mental retardation, seizures, and cerebral palsy. The susceptibility of the immature CNS to hypoxia-ischemia is largely dependent on the temporal and regional status of critical developmental processes, as well as on the regulation of cerebral blood flow and metabolism. The molecular and biochemical mechanisms of acute injury to the neonatal brain in experimental rodent and murine models of hypoxic-ischemic and ischemic injury, including disturbances of intracellular homeostasis, role of glutamate receptors, free radicals and transitional ions, as well as the modifying role of gene expression to cell death/survival will be reviewed in this chapter.

Does the developmental neurotoxicity of chlorpyrifos involve glial targets? Macromolecule synthesis, adenylyl cyclase signaling, nuclear transcription factors, and formation of reactive oxygen in C6 glioma cells

The widespread use of chlorpyrifos (CPF) has raised major concerns about its potential to cause fetal or neonatal neurobehavioral damage, even at doses that do not evoke acute toxicity. CPF has been shown to inhibit replication of brain cells, to elicit alterations in neurotrophic signaling governing cell differentiation and apoptosis, and to evoke oxidative stress. However, the specific cell types targeted by CPF have not been clarified, an issue of vital importance in establishing the boundaries of the critical period in which the developing brain is vulnerable. In the current study, we evaluated the effects of CPF on C6 glioma cells, a well-established glial model. In undifferentiated C6 cells, CPF inhibited DNA synthesis in a concentration-dependent manner, with greater potency than had been seen previously with neuronal cell lines. Just as found after in vivo CPF treatment or with neuronal cell lines, the effects on cell replication were independent of cholinergic stimulation, as cholinergic antagonists did not block CPF-induced inhibition. CPF interfered with cell signaling mediated through adenylyl cyclase at the level of G-protein function; the effects again were greater in undifferentiated C6 cells but were still detectable in differentiating cells. In contrast, differentiation enhanced the ability of CPF to elicit the formation of reactive oxygen species and to evoke deficits in Sp1, a nuclear transcription factor essential for differentiation. These results indicate that glial-type cells are targeted by CPF through the same multiple mechanisms that have been demonstrated for the effects of CPF on brain development in vivo. Because glial development continues long after the conclusion of neurogenesis, and given that CPF targets events in both glial cell replication and the later stages of differentiation, the vulnerable period for developmental neurotoxicity of CPF is likely to extend well into childhood.

Prolonged c-Jun expression in the basolateral amygdala following bulbectomy: possible implications for antidepressant activity and time of onset

Olfactory bulbectomy is a well established animal model of depression. Neurochemical and behavioral alterations observed following olfactory bulbectomy, are due, in part, to the neurodegeneration of specific brain structures. Amygdaloid dysfunction in particular, is known to play a substantial role in the syndrome of the olfactory bulbectomized rat. The present study examined both short- and long-term alterations in immediate early gene expression, tyrosine hydroxylase and serotonin immunoreactivity, and classical silver staining, following olfactory bulbectomy in the basolateral amygdala. The results indicated no consistent change in Fos expression observed over the experimental period. Following bulbectomy, long term (up to 64 days post-lesion) Jun expression, not coincident with silver staining, was observed in the basolateral nucleus. The basolateral nucleus was also intensely immunoreactive for serotonin at this timepoint post-bulbectomy. Thus, following bulbectomy long term alterations in Jun expression occurs in the serotonin rich basolateral amygdala. As a site of action for antidepressant compounds, alterations at the immediate early gene level in this region may have implications both for the model, and antidepressant drug action therein.

Developmental neurotoxicity of chlorpyrifos in vivo and in vitro: effects on nuclear transcription factors involved in cell replication and differentiation

Chlorpyrifos is a widely used organophosphate insecticide that is a suspected developmental neurotoxin. Although chlorpyrifos exerts some effects through cholinesterase inhibition, recent studies suggest additional, direct actions on developing cells. We assessed the effects of chlorpyrifos on nuclear transcription factors involved in cell replication and differentiation using in vitro and in vivo models. HeLa nuclear protein extracts were incubated with the labeled consensus oligonucleotides for AP-1 and Sp1 transcription factors in the presence and absence of chlorpyrifos. In concentrations previously shown to affect cell development, chlorpyrifos reduced AP-1, but not Sp1 DNA-binding activity. Next, chlorpyrifos was incubated with PC12 cells either during cell replication or after initiation of differentiation with NGF. Chlorpyrifos evoked stage-specific interference with the expression of the transcription factors: Sp1 was reduced in replicating and differentiating cells, whereas AP-1 was affected only during differentiation. Finally, neonatal rats were given apparently subtoxic doses of chlorpyrifos either on postnatal days 1-4 or 11-14 and the effects were evaluated in the forebrain (an early-developing, cholinergic target region) and cerebellum (late-developing region, poor in cholinergic innervation). Again, chlorpyrifos evoked stage-specific changes in transcription factor expression and binding activity, with greater effects on Sp1 during active neurogenesis, and effects on AP-1 during differentiation. The changes were present in both forebrain and cerebellum and were gender-specific. These results indicate that chlorpyrifos interferes with brain development, in part by multiple alterations in the activity of transcription factors involved in the basic machinery of cell replication and differentiation. Noncholinergic actions of chlorpyrifos that are unique to brain development reinforce the need to examine endpoints other than cholinesterase inhibition.

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.

Strain-related brain injury in neonatal mice subjected to hypoxia-ischemia

The development of transgenic mice has led to an increase in the use of mice as models for human disease. We hypothesized that the degree of brain damage sustained by animals in a neonatal mouse model of hypoxia-ischemia depends on the strain used. We compared three strains of mice commonly used to generate transgenic strains (C57Bl/6, 129Sv and CD1), as well as three hybrids of these strains (C57Bl/6x129Sv, CD1xC57Bl/6, and CD1x129Sv). At postnatal day 7 (P7), pups were subjected to a modified Vannucci procedure for hypoxia-ischemia as follows: permanent ligation of right common carotid artery under halothane anesthesia, 2-h recovery period, exposure to 8% oxygen at 37 degreesC for varying durations (30, 60 or 90 min). After 5 days, animals were perfused with 4% paraformaldehyde, brains were removed, postfixed and examined histologically with cresyl violet and Perl's iron stain to assess the degree of damage. Damage was assessed blindly using a score ranging from 0 (none) to 3 (infarct) in eight regions (ant-, mid-, and post- cortex, CA1, CA2, CA3 and dentate gyrus of the hippocampus, and striatum). We found significant differences in susceptibility to brain damage and mortality depending on the strain used. While determining the maximal degree of injury with the least amount of mortality for each strain, it was found that some strains (CD1) are particularly susceptible to brain damage in this model, while others (129Sv) are resistant.

Differential expression of SAPK isoforms in the rat brain. An in situ hybridisation study in the adult rat brain and during post-natal development

MAPK pathways transduce a broad variety of extracellular signals into cellular responses. Despite their pleiotropic effects and their ubiquitous distribution, surprisingly little is known about their involvement in the communication network of nerve cells. As a first step to elucidate the role of MAPK pathways in neuronal signalling, we studied the distribution of SAPK alpha/JNK2, SAPK beta/JNK3, and SAPK gamma/JNK1, three isoforms of SAPK/JNK, a stress-activated MAPK subfamily. We compared the mRNA localisation of the three main isoforms in the adult and developing rat brain using in situ hybridisation. In the adult brain, SAPK alpha and beta were widely but heterogeneously distributed, reproducing the pattern of a probe that does not discriminate the isoforms. Differently, high labelling for the SAPK gamma probe was exclusively localised in the endopiriform nucleus and medial habenula. Intermediate staining was detected in the hippocampus. During post-natal development, SAPK beta showed the same localisation as in the adult. Nevertheless, the semi-quantitative analysis of optical densities showed significantly different mRNA levels. In the adult, SAPK gamma signal was weak, whereas in newborn rats the labelling was intense and widely distributed. SAPK gamma mRNA levels decreased during development, to reach the low signals detected in the adult. These results suggest that in the central nervous system SAPK-type MAP kinases perform significant physiological functions which are particularly relevant during post-natal development. The distinct distribution patterns of SAPK isoforms in the adult rat brain support the hypothesis that separate functions are performed by the products of the three SAPK genes.