Induction of tetradecanoyl phorbol acetate-inducible sequence (TIS) genes by electroconvulsive shock in rat brain

Electroconvulsive seizure inhibits the mTOR signaling pathway via AMPK in the rat frontal cortex

RATIONALE

Accumulating evidence indicates critical involvement of mammalian target of rapamycin (mTOR) in the treatment of depressive disorders, epilepsy, and neurodegenerative disorders through its signal transduction mechanisms related to protein translation, autophagy, and synaptic remodeling. Electroconvulsive seizure (ECS) treatment is a potent antidepressive, anti-convulsive, and neuroprotective therapeutic modality; however, its effects on mTOR signaling have not yet been clarified.

METHODS

The effect of ECS on the mTOR complex 1 (mTORC1) pathway was investigated in the rat frontal cortex. ECS or sham treatment was administered once per day for 10 days (E10X or sham), and compound C was administered through the intracerebroventricular cannula. Changes in mTORC1-associated signaling molecules and their interactions were analyzed.

RESULTS

E10X reduced phosphorylation of mTOR downstream substrates, including p70S6K, S6, and 4E-BP1, and increased inhibitory phosphorylation of mTOR at Thr2446 compared to the sham group in the rat frontal cortex, indicating E10X-induced inhibition of mTORC1 activity. Akt and ERK1/2, upstream kinases that activate mTORC1, were not inhibited; however, AMPK, which can inhibit mTORC1, was activated. AMPK-responsive phosphorylation of Raptor at Ser792 and TSC2 at Ser1387 inhibiting mTORC1 was increased by E10X. Moreover, intrabrain inhibition of AMPK restored E10X-induced changes in the phosphorylation of S6, Raptor, and TSC2, indicating mediation of AMPK in E10X-induced mTOR inhibition.

CONCLUSIONS

Repeated ECS treatments inhibit mTORC1 signaling by interactive crosstalk between mTOR and AMPK pathways, which could play important roles in the action of ECS via autophagy induction.

Electroconvulsive Seizure Alters the Expression and Daily Oscillation of Circadian Genes in the Rat Frontal Cortex

OBJECTIVE

Electroconvulsive therapy (ECT) is the most effective treatment for mood disorders. Accumulating evidence has suggested the important role of circadian genes in mood disorders. However, the effects of ECT on circadian genes have not been systemically investigated.

METHODS

We examined the expression and daily oscillation of major circadian genes in the rat frontal cortex after electroconvulsive seizure (ECS).

RESULTS

Firstly, mRNA and protein level were investigated at 24 hr after single ECS (E1X) and repeated ECS treatements for 10 days (E10X), which showed more remarkable changes after E10X than E1X. mRNA expression of Rorα, Bmal1, Clock, Per1, and Cry1 was decreased, while Rev-erbα expression was increased at 24 hr after E10X compared to sham. The proteins showed similar pattern of changes. Next, the effects on oscillation and rhythm properties (mesor, amplitude, and acrophase) were examined, which also showed more prominent changes after E10X than E1X. After E10X, mesor of Rorα, Bmal1, and Cry1 was reduced, and that of Rev-erbα was increased. Five genes, Rev-erbα, Bmal1, Per1, Per2, and Cry2, showed earlier acrophase after E10X.

CONCLUSION

The findings suggest that repeated ECS induces reduced expression and phase advance of major circadian genes in the in vivo rat frontal cortex.

Long-term decrease in immediate early gene expression after electroconvulsive seizures

Electroconvulsive therapy (ECT) is a well-established psychiatric treatment for severe depression. Despite its clinical utility, post-ECT memory deficits are a common side effect. Neuronal plasticity and memory consolidation are intimately related to the expression of immediate early genes (IEG), such as Egr1, Fos and Arc. Changes in IEG activation have been postulated to underlie long-term neuronal adaptations following electroconvulsive seizures (ECS), an animal model of ECT. To test this hypothesis, we used real-time PCR to examine the effect of acute and chronic ECS (8 sessions, one every other day) on the long-term (>24 h) expression of IEG Egr1, Fos and Arc in the hippocampus, a brain region implicated both in the pathophysiology of depression as well as in memory function. We observed a transient increase in Egr1 and Fos expression immediately after ECS, followed by a long-term decrease of IEG levels after both acute and chronic ECS. A separate group of animals, submitted to the same chronic ECS protocol and then subjected to open field or passive avoidance tasks, confirmed robust memory deficits 2 weeks after the last chronic ECS. The possible role of IEG downregulation on long-term learning deficits observed following ECS are discussed.

Genetic association of the EGR2 gene with bipolar disorder in Korea

The early growth response gene 2 (EGR2) is located at chromosome 10q21, one of the susceptibility loci in bipolar disorder (BD). EGR2 is involved in cognitive function, myelination, and signal transduction related to neuregulin-ErbB receptor, Bcl-2 family proteins, and brain-derived neurotrophic factor. This study investigated the genetic association of the EGR2 gene with BD and schizophrenia (SPR) in Korea. In 946 subjects (350 healthy controls, 352 patients with BD, and 244 with SPR), nine single nucleotide polymorphisms (SNPs) in the EGR2 gene region were genotyped. Five SNPs showed nominally significant allelic associations with BD (rs2295814, rs61865882, rs10995315, rs2297488, and rs2297489), and the positive associations of all except rs2297488 remained significant after multiple testing correction. Linkage disequilibrium structure analysis revealed two haplotype blocks. Among the common identified haplotypes (frequency > 5%), 'T-G-A-C-T (block 1)' and 'A-A-G-C (block 2)' haplotypes were over-represented, while 'C-G-G-T-T (block 1)' haplotype was under-represented in BD. In contrast, no significant associations were found with SPR. Although an extended analysis with a larger sample size or independent replication is required, these findings suggest a genetic association of EGR2 with BD. Combined with a plausible biological function of EGR2, the EGR2 gene is a possible susceptibility gene in BD.

Imipramine activates glial cell line-derived neurotrophic factor via early growth response gene 1 in astrocytes

Recent evidence has suggested that deficits in glial plasticity contribute to the pathophysiology of depressive disorders. The present study explored early growth response 1 (EGR-1) transcriptional regulation of imipramine-induced glial cell line-derived neurotrophic factor (GDNF) expression in astrocytes. After we observed the induction of GDNF mRNA expression in rat astrocytes in response to imipramine, deletion mutant studies showed that the proximal region between -493 and -114 of the GDNF promoter, which contains three binding sites for EGR-1, was essential for maximal imipramine-induced activation of GDNF promoter. The dose-dependent upregulation of EGR-1 by imipramine, the activation of GDNF by the over-expression of EGR-1 without imipramine and the reduction in the imipramine-induced GDNF mRNA expression after silencing of endogenous EGR-1 demonstrated that EGR-1 is upregulated by imipramine to activate the GDNF promoter. Furthermore, imipramine-induced GDNF mRNA expression was strongly attenuated in primary astrocytes from Egr-1(-/-) mice, and the immunoreactivity to an anti-GDNF antibody in glial fibrillary acidic protein-positive cells was lower in imipramine-treated astrocytes from Egr-1(-/-) mice than in those from Egr-1(+/-) mice. To determine whether mitogen-activated protein kinases (MAPKs) were associated with imipramine-induced EGR-1 expression, we examined the induction of MAPK phosphorylation in response to imipramine. Pretreatment of rat primary astrocytes with the MAPK kinase inhibitor U0126 or the JNK inhibitor SP600125 strongly inhibited imipramine-stimulated EGR-1 expression. In conclusion, we found that imipramine induction of EGR-1 upregulated GDNF in astrocytes in a dose-dependent manner. This upregulation may occur through the MEK/ERK and JNK MAPK pathways, which suggests a new therapeutic mechanism of action for depressive disorders.

Repeated electroconvulsive seizure treatment in rats reduces inducibility of early growth response genes and hyperactivity in response to cocaine administration

Regulated expression of immediate early genes (IEGs) in the brain reflects neuronal activity in response to various stimuli and recruits specific gene programs involved in long-term neuronal modification and behavioral alterations. Repeated electroconvulsive seizure (ECS) treatment reduces the expression level of several IEGs, such as c-fos, which play important roles in psychostimulant-induced behavioral changes. In this study, we investigated the effects of repeated ECS treatment on the basal expression level of IEGs and its effects on cocaine-induced activation of IEGs and locomotor activity in rats. Repeated ECS treatment for 10days (E10×) reduced Egr1, Egr2, Egr3, and c-fos mRNA and protein levels in the rat frontal cortex at 24h after the last ECS treatment, and these changes were evident in the neuronal cells of the prefrontal cortex. In particular, downregulation of Egr1 and c-fos was evident until 5days after the last ECS treatment. Moreover, E10× pretreatment attenuated the cocaine-induced increase in Egr1, Egr2, and c-fos expression in the rat frontal cortex, whereas phosphorylation of ERK1/2, one of the representative upstream activators of these genes, increased significantly following cocaine treatment. Additionally, E10× pretreatment attenuated the increase in locomotor activity in response to a cocaine injection. In conclusion, repeated ECS treatment reduced the expression and inducibility of Egrs and c-fos, which could attenuate the response of the brain to psychostimulants.

EGR3 as a potential susceptibility gene for schizophrenia in Korea

Early growth response (EGR) genes play critical roles in signal transduction in the brain, which is involved in neuronal activation, brain development, and synaptic plasticity. EGR genes, including EGR2, EGR3, and EGR4, showed significant association with schizophrenia in Japanese schizophrenic pedigrees. In particular, EGR3, which resides at the chromosomal location 8p21.3, was suggested to be a potential susceptibility gene in schizophrenia based on a study of Japanese cases. However, this requires further replication with an independent sample set. We investigated the association of the EGR3 and EGR2 genes, which were suggested as potential susceptibility genes for schizophrenia supported by both genetic association and postmortem brain expression studies, with schizophrenia in Korean patients. Along with 350 healthy individuals, 244 schizophrenic patients were analyzed. Among the four examined single-nucleotide polymorphisms (SNPs) of EGR3 (rs1008949, rs7009708, rs35201266, and rs3750192), SNP rs35201266 in intron 1 of the EGR3 gene showed a significant association with schizophrenia (P = 0.0008, χ(2) = 11.156, OR = 1.493), which withstands multiple testing correction. In addition, the "T-G-C-G" haplotype of EGR3 was under-represented in the patients with schizophrenia (P = 0.0073, χ(2) = 7.188, OR = 0.697). However, an association between the SNPs of EGR2 (rs2295814 and rs2297488) and schizophrenia was not found. These findings are consistent with the previous genetic association of the EGR3 gene in Japanese cohorts, which is the first replication concerning the association of EGR3 with schizophrenia in an independent cohort. Taken together, EGR3 could be suggested as a compelling susceptibility gene in schizophrenia.

Effects of FG7142 and immobilization stress on the gene expression in the neocortex of mice

Several psychiatric disorders are often precipitated or exacerbated by exposure to stressors. FG7142 (N-methyl-beta-carboline-3-carboxamide), a partial inverse agonist of benzodiazepine receptors, mimics the physiological (an increased release in the adrenal steroid hormone) and neurochemical (an enhanced neurotransmission of monoamines) changes induced by stressful stimuli. We examined the effects of FG7142 and immobilization stress on the gene expression of the mouse neocortex in order to obtain a new insight into the molecular stress-responsive system. The effect of FG7142 (20 mg/kg, i.p.) on the gene expression of the brain area was examined using a DNA microarray method. The genes showing a significant change in expression were investigated in further experiments using the quantitative RT-PCR method. There was an increase in the mRNA of seven genes in the neocortex of mice 1h after treatment with FG7142. In addition, there was an increase in the mRNAs of five of the seven genes (Fos, Cyr61, Btg2, Adamts1, and Gem) in the neocortex of mice exposed to the stress for 1h. The up-regulation of these five genes by both FG7142 and immobilization stress indicates that these genes may be involved in the stress-responsive system. Dysfunctions of the system may be associated with the pathophysiology of psychiatric disorders.

Role of TIS7 family of transcriptional regulators in differentiation and regeneration

The regulation of gene expression plays an important role not only during embryonic development but also in the course of cell differentiation and regeneration processes of various tissues, e.g. skeletal muscles, intestines, or nerves. Tightly regulated gene expression in particular cell types requires a sophisticated interplay between the basic transcriptional machinery and specific transcriptional regulators--activators, repressors, co-activators, and co-repressors. The last category includes the TPA Induced Sequence 7 (TIS7) protein family, recently characterized as transcriptional co-repressors. The expression of these proteins is regulated on the mRNA level and directly correlates with the processes of cell and tissue differentiation not only during embryonic development but mainly throughout the regeneration events in adult organisms. The expression of TIS7 and its homologue SKMc15 is ubiquitous and according to current knowledge, as summarized in this review, TIS7 plays a role in the differentiation of various cell types, e.g. epithelial cells, myoblasts, hematopoietic cells, or neurons. Here, we not only focus on the description of TIS7 expression in various systems (species, organs) but also try to provide current state of knowledge of the regulatory mechanisms in which TIS7 is involved. The clarification of biochemical mechanisms directed by the TIS7 family members during regeneration events, e.g. following injury, will additionally provide us with the opportunity to intervene therapeutically.

Region-specific phosphorylation of ERK5-MEF2C in the rat frontal cortex and hippocampus after electroconvulsive shock

ERK5-MEF2C has been implicated in many aspects of neuronal survival and neuroprotection. Neurotrophic effects have been considered as one of the mechanisms in therapeutic electroconvulsive shock (ECS). To investigate whether ECS activates ERK5-MEF2C, we examined the phosphorylation of ERK5, along with its downstream molecule MEF2C, after ECS in the rat frontal cortex and hippocampus. Increased phosphorylation of ERK5 was observed immediately after ECS, but was barely detectable from 2 min after ECS in both the frontal cortex and the hippocampus. The level of MEF2C phosphorylation was decreased immediately after ECS in both regions. It was increased from 2 min and maintained until 10 min after ECS in the frontal cortex, but it returned to the basal level from 2 min after ECS in the hippocampus. Taken together, these results suggest that ECS can regulate the region-specific activity of ERK5-MEF2C pathways in the rat brain.

Nxf and Fbxo33: novel seizure-responsive genes in mice

Much is understood about the response of the brain to seizure but little is known in relation to the underlying molecular mechanisms involved. We used microarray technology to investigate the complex genetic response of the brain to generalized seizure. For this investigation a seizure-specific mouse brain cDNA library was generated and spotted onto microarray slides with the aim of increasing the likelihood of identifying novel genes responsive to seizure. Microarray analysis was performed on mouse hippocampus 1 h after generalized seizure pharmacologically induced by pentylenetetrazol (PTZ). Using the custom microarray slides, six genes were identified as being up-regulated in this seizure model and results were validated by real-time PCR. Four of the seizure-responsive genes had previously-reported roles in apoptosis, proliferation or differentiation of neural cells. Two of the genes were novel and in situ hybridization analysis demonstrated heightened mRNA expression in the hippocampus 1 h following generalized convulsive seizure, in a pattern which is typical for other activity-dependant genes expressed in this structure. In addition to being up-regulated postseizure, the genes described in this paper appear to be expressed normally in the adult hippocampus and during development.

Region-specific phosphorylation of ATF-2, Elk-1 and c-Jun in rat hippocampus and cerebellum after electroconvulsive shock

There have been reports of regional differences in the activation of mitogen activated protein kinases (MAPKs) and in the induction of immediate early genes after electroconvulsive shock (ECS) in the rat brain. This study was performed to determine whether ECS induce the region-specific phosphorylation of MAPK-downstream transcription factors, ATF-2, Elk-1, c-Jun, in rat hippocampus and cerebellum. Following ECS, the phosphorylation of ATF-2 was highly increased in the hippocampus but slightly in the cerebellum. The phosphorylation of Elk-1 was increased in the cerebellum but not in the hippocampus. In contrast, the phosphorylation of c-Jun was increased only in the hippocampus. These results indicate that ECS can induce the region-specific phosphorylation of MAPK-downstream transcription factors in rat hippocampus and cerebellum.

In search of a function for the TIS21/PC3/BTG1/TOB family

The Btg family of anti-proliferative gene products includes Pc 3/Tis 21/Btg 2, Btg 1, Tob, Tob2, Ana/Btg3, Pc3k and others. These proteins are characterized by similarities in their amino-terminal region: the Btg1 homology domain. However, the pleiotropic nature of these family proteins has been observed and no common physiological function among family members was suggested from the history of their identification. Recent progress in the search for Btg family functions has come from the analysis of cell regulation and of cell differentiation. It is now emerging that every member of this family has a potential to regulate cell growth. We would like to propose here to use a nomenclature APRO as a new term for the family.

The gene PC3(TIS21/BTG2), prototype member of the PC3/BTG/TOB family: regulator in control of cell growth, differentiation, and DNA repair?

PC3(TIS21/BTG2) is the founding member of a family of genes endowed with antiproliferative properties, namely BTG1, ANA/BTG3, PC3B, TOB, and TOB2. PC3 was originally isolated as a gene induced by nerve growth factor during neuronal differentiation of rat PC12 cells, or by TPA in NIH3T3 cells (named TIS21), and is a marker for neuronal birth in vivo. This and other findings suggested its implication in the process of neurogenesis as mediator of the growth arrest before differentiation. Remarkably, its human homolog, named BTG2, was shown to be p53-inducible, in conditions of genotoxic damage. PC3(TIS21/BTG2) impairs G(1)-S progression, either by a Rb-dependent pathway through inhibition of cyclin D1 transcription, or in a Rb-independent fashion by cyclin E downregulation. PC3(TIS21/BTG2) might also control the G(2) checkpoint. Furthermore, PC3(TIS21/BTG2) interacts with carbon catabolite repressor protein-associated factor 1 (CAF-1), a molecule that associates to the yeast transcriptional complex CCR4 and might influence cell cycle, with the transcription factor Hoxb9, and with the protein-arginine methyltransferase 1, that might control transcription through histone methylation. Current evidence suggests a physiological role of PC3(TIS21/BTG2) in the control of cell cycle arrest following DNA damage and other types of cellular stress, or before differentiation of the neuron and other cell types. The molecular function of PC3(TIS21/BTG2) is still unknown, but its ability to modulate cyclin D1 transcription, or to synergize with the transcription factor Hoxb9, suggests that it behaves as a transcriptional co-regulator.

MKP-1 induced in rat brain after electroconvulsive shock is independent of regulation of 42- and 44-kDa MAPK activity

Electroconvulsive shock (ECS) activates MAPKs in rat brain and also induces immediate early genes. We investigated whether ECS induces MKP-1, a specific MAPK phosphatase and an immediate early gene, for feedback regulation of MAPK activity. ECS induced MKP-1 in the cortex, but MAPK activity returned to its basal level before MKP-1 protein increased, within 10 min of ECS. MKP-1 protein amount peaked 1 hr after ECS. MKP-1 induced did not lower the basal level of MAPK activity or attenuate MAPK activation by second ECS. MAPK activation in cerebellum was very weak, but the MKP-1 induction was faster and more prominent than in the cortex. These results suggest that ECS induces MKP-1 in various rat brain regions, however, the induction may not be related to the activation of MAPK and the MKP-1 induced may be independent of the regulation of MAPK activity after ECS.

Electroconvulsive shock does not induce c-fos and junB, but TIS1 and TIS8/zif-268, in neonatal rat hippocampus

The induction in the animal brain of immediate early genes (IEGs) is known to be age-dependent, and it was suggested that, during neonatal period, signaling pathways for the induction of IEGs are immature. In this study, we investigated the induction of various IEGs in neonatal rat hippocampus after electroconvulsive shock (ECS). ECS did not induce c-fos and junB in the hippocampus of 7-day-old rat, but these genes were weakly induced at postnatal 14 days and to an adult level at postnatal 21 days; two other IEGs, TIS1 (NGFI-B, nur77) and TIS8 (zif-268, Egr-1, Krox-24, NGFI-A), were induced at postnatal 7 days, however. Our results suggested that during the neonatal period, signaling pathways for TIS1 and TIS8 induction in rat hippocampus after ECS are complete, while those for c-fos and junB are immature.