Changes in activating protein 1 (AP-1) composition correspond with the biphasic profile of nerve growth factor mRNA expression in rat hippocampus after hilus lesion-induced seizures

Protective Effects of a synthetic glycosaminoglycan mimetic (OTR4132) in a rat immunotoxic lesion model of septohippocampal cholinergic degeneration

Using a partial hippocampal cholinergic denervation model, we assessed the effects of the RGTA^® named OTR4132, a synthetic heparan-mimetic biopolymer with neuroprotective/neurotrophic properties. Long-Evans male rats were injected with the cholinergic immunotoxin 192 IgG-saporin into the medial septum/diagonal band of Broca (0.37 µg); vehicle injections served as controls. Immediately after surgery, OTR4132 was injected into the lateral ventricles (0.25 µg/5 µl/rat) or intramuscularly (1.5 mg/kg). To determine whether OTR4132 reached the lesion site, some rats received intracerebroventricular (ICV) or intramuscular (I.M.) injections of fluorescent OTR4132. Rats were sacrificed at 4, 10, 20, or 60 days post-lesion (DPL). Fluorescein-labeled OTR4132 injected ICV or I.M. was found in the lesion from 4 to 20 DPL. Rats with partial hippocampal cholinergic denervation showed decreases in hippocampal acetylcholinesterase reaction products and in choline acetyltransferase-positive neurons in the medial septum. These lesions were the largest at 10 DPL and then remained stable until 60 DPL. Both hippocampal acetylcholinesterase reaction products and choline acetyltransferase-positive neurons in the medial septum effects were significantly attenuated in OTR4132-treated rats. These effects were not related to competition between OTR4132 and 192 IgG-saporin for the neurotrophin receptor P75 (p75^NTR), as OTR4132 treatment did not alter the internalization of Cy3-labelled 192 IgG. OTR4132 was more efficient at reducing the acetylcholinesterase reaction products and choline acetyltransferase-positive neurons than a comparable heparin dose used as a comparator. Using the slice superfusion technique, we found that the lesion-induced decrease in muscarinic autoreceptor sensitivity was abolished by intramuscular OTR4132. After partial cholinergic damage, OTR4132 was able to concentrate at the brain lesion site possibly due to the disruption of the blood-brain barrier and to exert structural and functional effects that hold promises for neuroprotection/neurotrophism.

Probiotic supplementation alleviates absence seizures and anxiety- and depression-like behavior in WAG/Rij rat by increasing neurotrophic factors and decreasing proinflammatory cytokines

AIM

Epilepsy is one of the most common chronic brain disorders that affect millions of people worldwide. In the present study, we investigated the effects of probiotic supplementation on absence epilepsy and anxiety-and depression-like behavior in WAG/Rij rats.

MATERIAL AND METHOD

Fourteen male WAG/Rij rats (absence-epileptic) and seven male Wistar rats (nonepileptic) were used. The effects of probiotic VSL#3 (12.86 bn living bacteria/kg/day for 30 day/gavage) on absence seizures, and related psychiatric comorbidities were evaluated in WAG/Rij rats. Anxiety-like behavior was evaluated by the open-field test and depression-like behavior by the forced swimming test. In addition, the brain tissues of rats were evaluated histopathologically for nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF], SRY sex-determining region Y-box 2 [SOX2] and biochemically for nitric oxide [NO], tumor necrosis factor-alpha [TNF-α] ,and Interleukin-6 [IL-6].

RESULTS

Compared to Wistar rats, WAG/Rij rats exhibited anxiety- and depression-like behavior, and had lower BDNF, NGF and SOX2 immunoreactivity, and higher TNF-α, IL-6 levels in brain tissue. VSL#3 supplementation reduced the duration and number of spike-wave discharges (SWDs) and exhibited anxiolytic or anti-depressive effect. VSL#3 supplement also increased the NGF immunoreactivity while decreasing IL-6, TNF-α and NO levels in WAG/Rij rat brain.

CONCLUSION

The findings of the present study showed that neurotrophins, SOX2 deficiency, and pro-inflammatory cytokines may play a role in the pathogenesis of absence epilepsy. Our data support the hypothesis that the probiotics have anti-inflammatory effect. The present study is the first to show the positive effects of probiotic bacteria on absence seizures and anxiety- and depression-like behavior.

Inferior Colliculus Transcriptome After Status Epilepticus in the Genetically Audiogenic Seizure-Prone Hamster GASH/Sal

The Genetic Audiogenic Seizure Hamster from Salamanca (GASH/Sal), an animal model of reflex epilepsy, exhibits generalized tonic–clonic seizures in response to loud sound with the epileptogenic focus localized in the inferior colliculus (IC). Ictal events in seizure-prone strains cause gene deregulation in the epileptogenic focus, which can provide insights into the epileptogenic mechanisms. Thus, the present study aimed to determine the expression profile of key genes in the IC of the GASH/Sal after the status epilepticus. For such purpose, we used RNA-Seq to perform a comparative study between the IC transcriptome of GASH/Sal and that of control hamsters both subjected to loud sound stimulation. After filtering for normalization and gene selection, a total of 36 genes were declared differentially expressed from the RNA-seq analysis in the IC. A set of differentially expressed genes were validated by RT-qPCR showing significant differentially expression between GASH/Sal hamsters and Syrian control hamsters. The confirmed differentially expressed genes were classified on ontological categories associated with epileptogenic events similar to those produced by generalized tonic seizures in humans. Subsequently, based on the result of metabolomics, we found the interleukin-4 and 13-signaling, and nucleoside transport as presumably altered routes in the GASH/Sal model. This research suggests that seizures in GASH/Sal hamsters are generated by multiple molecular substrates, which activate biological processes, molecular processes, cellular components and metabolic pathways associated with epileptogenic events similar to those produced by tonic seizures in humans. Therefore, our study supports the use of the GASH/Sal as a valuable animal model for epilepsy research, toward establishing correlations with human epilepsy and searching new biomarkers of epileptogenesis.

Immunohistochemical evaluation of the protein expression of nerve growth factor and its TrkA receptor in rat limbic regions following electroshock seizures

Repeated (but not acute) exposure to brief, non-injurious seizures evoked by minimal electroconvulsive shock (ECS) decreases neuronal death in limbic system and increases mRNA levels for nerve growth factor (NGF). Thus, the induction of NGF is a potential mechanism for the neuroprotection evoked by repeated ECS. The neuroprotective action of NGF is mediated by the TrkA receptor. This study determined whether repeated ECS exposure increased TrkA and NGF protein levels. To determine the functional significance of changes in these proteins, we compared the effects of ECS given daily either for 7 days (chronic ECS) or for 1 day (acute ECS). After chronic ECS, upregulation of both NGF and TrkA was found in perirhinal cortex, thalamus, and amygdala. In hippocampus, TrkA was upregulated in CA2, CA3 and CA4. NGF increase in hippocampus was found in CA1 and dentate gyrus. In frontal cortex and substantia innominata, an increase in NGF (but not in TrkA) was found. In most brain regions, TrkA and NGF remained unchanged after acute ECS. Our results demonstrate that repeated exposure to ECS causes an upregulation of TrkA and NGF proteins in several limbic areas in which neuroprotective effects are observed suggesting that NGF contributes to ECS-evoked neuroprotection.

JunB is a repressor of MMP-9 transcription in depolarized rat brain neurons

Matrix Metalloproteinase-9 (MMP-9) is an extracellularly operating enzyme involved in the synaptic plasticity, hippocampal-dependent long term memory and neurodegeneration. Previous studies have shown its upregulation following seizure-evoking stimuli. Herein, we show that in the rat brain, MMP-9 mRNA expression in response to pentylenetetrazole-evoked neuronal depolarization is transient. Furthermore, we demonstrate that in the rat hippocampus neuronal activation strongly induces JunB expression, simultaneously leading to an accumulation of JunB/FosB complexes onto the -88/-80 bp site of the rat MMP-9 gene promoter in vivo. Surprisingly, manipulations with JunB expression levels in activated neurons revealed its moderate repressive action onto MMP-9 gene expression. Therefore, our study documents the active repressive influence of AP-1 onto MMP-9 transcriptional regulation by the engagement of JunB.

Acoustic overstimulation facilitates the expression of glutamate-cysteine ligase catalytic subunit probably through enhanced DNA binding of activator protein-1 and/or NF-kappaB in the murine cochlea

Glutamate-cysteine ligase (GCL), previously known as gamma-glutamylcysteine synthetase, is the rate-limiting enzyme for GSH synthesis. The expression of GCL is mediated by activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappaB), which are known to participate in stress-induced apoptotic pathways in neuronal cells. In this study, we investigated the changes in the level of these transcription factors as well as of GCL catalytic subunit in the cochlea in response to acoustic overstimulation. Nuclear extracts were prepared from the cochlear at various time points after intense noise exposure (4kHz octave band, 125dB sound pressure level, 5h), and then determined DNA binding activity of the transcription factors. AP-1 DNA binding was markedly increased 2-12h after the noise exposure, with a peak at 2h after the exposure. NF-kappaB DNA binding was also increased immediately after the exposure. Semi-quantitative RT-PCR revealed that the catalytic subunit of GCL mRNA was elevated in the cochlea 2-24h post the exposure. Further immunohistochemical study revealed that increased level of GCL catalytic subunit observed at least in the spiral ganglion cells after the exposure. These results suggest that intense noise exposure facilitates the expression of GCL catalytic subunit in the cochlea possibly through the activation of transcription factors including AP-1 and NF-kappaB.

Transcriptional Factors in the Cochlea Within the Inner Ear

Differential regulation of gene expression by transcription factors is widely viewed as one of the principal mechanisms guiding development. Although numerous DNA binding proteins have been identified in various tissues, the role of individual transcription factors in the differentiation of specific cell groups, such as those populating the inner ear, is just beginning to be elucidated. It is known that transcription factors are induced in response to many signals that lead to cell growth, differentiation, inflammatory responses, the regulation of apoptosis, and neoplastic transformation. There are various transcription factors in the cochlea of the inner ear. These include activator protein-1 and nuclear factor-kappa B, glucocorticoid receptor, and so on. Based on recent reports and our investigation, in this article we review possible functions and expression of these transcription factors.

Modulation of activator protein 1/DNA binding activity by acoustic overstimulation in the guinea-pig cochlea

Changes in gene expression are part of the homeostatic machinery with which cells respond to external stimuli or assaults. The activity of the early response transcriptional factor activator protein-1 (AP-1) can be modulated by a variety of environmental stimuli including those that alter the cellular oxidation/reduction status. This study investigates the activation of AP-1/DNA binding in the guinea-pig cochlea in response to acoustic overstimulation which produces reactive oxygen species. Electrophoretic mobility shift assays revealed that binding of AP-1 to its radiolabeled oligonucleotide probe markedly changed in nuclear extracts of inner ear tissues following intense noise exposure (4 kHz octave band, 115 dB, 5 h). AP-1/DNA binding increased in the organ of Corti and the lateral wall tissues immediately after the exposure, returning to near-baseline levels 5 h later. At 15 h after noise, a second peak of binding activity occurred in the organ of Corti whereas stria vascularis showed a lesser but more sustained activity. Binding in nuclear extracts from the spiral ganglion did not change. Incubation of nuclear extracts with antibodies against Fos/Jun family proteins prior to a supershift assay showed Fra-2 as a major component of the AP-1 complex immediately after the noise exposure. In the organ of Corti, Fra-2 immunoreactivity was localized to the middle turn, i.e. the region which is most affected by the 4-kHz octave band exposure. The results suggest the modulation of gene expression via the activation of AP-1 as a consequence of noise trauma but also demonstrate differential responses in cochlear tissues.

Chronic elevation of brain-derived neurotrophic factor by ampakines

The ampakine CX614 positively modulates alpha-amino-3-hydroxy-5methyl-4-isoxazolepropionic acid (AMPA) receptor-gated currents and increases brain-derived neurotrophic factor (BDNF) expression. In rat hippocampal slice cultures, CX614 rapidly increases BDNF gene expression but with time, mRNA levels fall despite the continued presence of active drug. The present study examined this apparent refractory period and the possibility that spaced ampakine treatments could sustain elevated BDNF protein levels. In cultured hippocampal slices, CX614, a second ampakine CX546, and the cholinergic agonist carbachol each increased BDNF mRNA levels with acute (3-h) treatment. After 4-day pretreatment with CX614, fresh ampakine (CX614 or CX546) did not induce BDNF mRNA, whereas carbachol did. Western blots confirmed that after an extended period of ampakine treatment, AMPA receptor protein levels are indeed reduced, suggesting that with longer treatments receptor down-regulation mediates ampakine insensitivity. Finally, using a "24-h on/24-h off" CX614 treatment protocol, the ampakine refractory state was circumvented, BDNF mRNA was induced with each ampakine application, and elevated BDNF protein levels were maintained through 5 days in vitro. These results suggest that spaced ampakine treatments can be used to sustain elevated neurotrophin levels and to test the utility of this manipulation for neuroprotection by endogenous neurotrophins.

Integrins regulate neuronal neurotrophin gene expression through effects on voltage-sensitive calcium channels

Integrin adhesion receptors regulate gene expression during growth and differentiation in various cell types. Recent work, implicating integrins in functional synaptic plasticity, suggest they may have similar activities in adult brain. The present study tested if integrins binding the arginine-glycine-aspartate (RGD) matrix sequence regulate neurotrophin and neurotrophin receptor gene expression in cultured hippocampal slices. The soluble RGD-containing peptide glycine-arginine-glycine-aspartate-serine-proline (GRGDSP) increased neurotrophin mRNA levels in transcript- and subfield-specific fashions. Integrin ligand effects were greatest for brain-derived neurotrophic factor transcripts I and II and barely detectable for transcript III. In accordance with increased nerve growth factor mRNA levels, GRGDSP increased c-fos expression as well. In contrast, growth-associated protein-43, amyloid precursor protein and fibroblast growth factor-1 mRNAs were not elevated. Ligand effects on brain-derived neurotrophic factor transcript II and c-fos mRNA did not depend on the integrity of the actin cytoskeleton, neuronal activity, or various signaling pathways but were blocked by L-type voltage-sensitive calcium-channel blockers. These results indicate that in mature hippocampal neurons integrin engagement regulates expression of a subset of growth-related genes at least in part through effects on calcium influx. Accordingly, these synaptic adhesion receptors may play the same role in maintaining an adult, differentiated state in brain as they do in other tissues and changes in integrin activation and/or engagement may contribute to dynamic changes in neurotrophin expression and to neuronal calcium signaling.

A functional polymorphism in the prodynorphin gene promotor is associated with temporal lobe epilepsy

The prodynorphin gene (PDYN) encoding the anticonvulsant peptide dynorphin is a strong candidate for a seizure suppressor gene and thus a possible modulator of susceptibility to temporal lobe epilepsy. We performed a case control association study in 155 patients with nonlesional temporal lobe epilepsy and 202 controls and found that PDYN promotor low-expression L-alleles confer an increased risk for temporal lobe epilepsy in patients with a family history for seizures. Irrespective of the familial background, L-homozygotes display a higher risk for secondarily generalized seizures and status epilepticus.

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.

AP-1 proteins in the adult brain: facts and fiction about effectors of neuroprotection and neurodegeneration

Jun and Fos proteins are induced and activated following most physiological and pathophysiological stimuli in the brain. Only few data allow conclusions about distinct functions of AP-1 proteins in neurodegeneration and neuroregeneration, and these functions mainly refer to c-Jun and its activation by JNKs. Apoptotic functions of activated c-Jun affect hippocampal, nigral and primary cultured neurons following excitotoxic stimulation and destruction of the neuron-target-axis including withdrawal of trophic molecules. The inhibition of JNKs might exert neuroprotection by subsequent omission of c-Jun activation. Besides endogenous neuronal functions, the c-Jun/AP-1 proteins can damage the nervous system by upregulation of harmful programs in non-neuronal cells (e.g. microglia) with release of neurodegenerative molecules. In contrast, the differentiation with neurite extension and maturation of neural cells in vitro indicate physiological and potentially neuroprotective functions of c-Jun and JNKs including sensoring for alterations in the cytoskeleton. This review summarizes the multiple molecular interfunctions which are involved in the shift from the physiological role to degenerative effects of the Jun/JNK-axis such as cell type-specific expression and intracellular localization of scaffold proteins and upstream activators, antagonistic phosphatases, interaction with other kinase systems, or the activation of transcription factors competing for binding to JNK proteins and AP-1 DNA elements.