Brain-derived neurotrophic factor (BDNF) downregulates mRNA levels of suppressor of cancer cell invasion (SCAI) variants in cortical neurons

Suppressor of cancer cell invasion (SCAI) acts as a transcriptional repressor of serum response factor (SRF)-mediated gene expression by binding to megakaryoblastic leukemia (MKL)/myocardin-related transcription factor (MRTF), which is an SRF transcriptional coactivator. Growing evidence suggests that SCAI is a negative regulator of neuronal morphology, whereas MKL2/MRTFB is a positive regulator. The mRNA expression of SCAI is downregulated during brain development, suggesting that a reduction in SCAI contributes to the reduced suppression of SRF-mediated gene induction, thus increasing dendritic complexity and developing neuronal circuits. In the present study, we hypothesized that brain-derived neurotrophic factor (BDNF), which is important for neuronal plasticity and development, might alter SCAI mRNA levels. We therefore investigated the effects of BDNF on SCAI mRNA levels in primary cultured cortical neurons. Furthermore, because alternative splicing generates several SCAI variants in the brain, we measured SCAI variant mRNA after BDNF stimulation. Both SCAI variant 1 and total SCAI mRNA expression levels were downregulated by BDNF. Moreover, the extracellular signal-regulated protein kinase/mitogen-activated protein kinase (ERK/MAPK) pathway was involved in the BDNF-mediated decrease in SCAI mRNA expression. Our findings provide insights into the molecular mechanism underlying a neurotrophic factor switch for the repressive transcriptional complex that includes SCAI.

Endogenous SOLOIST/MRTFB i4, a neuronal isoform of MKL2/MRTFB, positively and negatively regulates SRF target immediate early genes in Neuro-2a cells

Megakaryoblastic leukemia (MKL2)/myocardin-related transcription factor-B (MRTFB) is a serum response factor (SRF) that is enriched in the brain and controls SRF target genes and neuronal morphology. There are at least four isoforms of MKL2/MRTFB. Among these, MKL2/MRTFB isoform 1 and spliced neuronal long isoform of SRF transcriptional coactivator (SOLOIST)/MRTFB isoform 4 (MRTFB i4) are highly expressed in neurons. Although, when overexpressed in neurons, isoform 1 and SOLOIST/MRTFB i4 have opposing effects on dendritic morphology and differentially regulate SRF target genes, it is unknown how endogenous SOLOIST/MRTFB i4 regulates gene expression. Using isoform-specific knockdown, we investigated the role of endogenous SOLOST/MRTFB i4 in regulating the expression of other MKL2/MRTFB isoforms and SRF-target genes in Neuro-2a cells. Knockdown of SOLOIST/MRTFB i4 downregulated SOLOIST/MRTFB i4, while it upregulated isoform 1 without affecting isoform 3. Knockdown of SOLOIST/MRTFB i4 downregulated the immediate early SRF target genes egr1 and Arc, while it upregulated c-fos. Double knockdown of isoform 1 and SOLOIST/MRTFB i4 inhibited c-fos expression. Taken together, our findings in Neuro-2a cells suggest that endogenous SOLOIST/MRTFB i4 positively regulates egr1 and Arc expression. In addition, endogenous SOLOIST/MRTFB i4 may negatively regulate c-fos expression, possibly by downregulating isoform 1 in Neuro-2a cells.

The extract based on the Kampo formula daikenchuto (Da Jian Zhong Tang) induces Bdnf expression and has neurotrophic effects in cultured cortical neurons

Reductions in brain-derived neurotrophic factor (BDNF) expression levels have been reported in the brains of patients with neurological disorders such as Alzheimer's disease. Therefore, upregulating BDNF and preventing its decline in the diseased brain could help ameliorate neurological dysfunctions. Accordingly, we sought to discover agents that increase Bdnf expression in neurons. Here, we screened a library of 42 Kampo extracts to identify those with the ability to induce Bdnf expression in cultured cortical neurons. Among the active extracts identified in the screen, we focused on the extract based on the Kampo formula daikenchuto. The extract of daikenchuto in the library used in this study was prepared using the mixture of Zingiberis Rhizoma Processum (ZIN), Zanthoxyli Piperiti Pericarpium (ZAN), and Ginseng Radix (GIN) without Koi. In this study, we defined DKT as the mixture of ZIN, ZAN, and GIN without Koi (DKT extract means the extract prepared from the mixture of ZIN, ZAN, and GIN without Koi). DKT extract significantly increased endogenous Bdnf expression by mediated, at least in part, via Ca²⁺ signaling involving L-type voltage-dependent Ca²⁺ channels in cultured cortical neurons. Furthermore, DKT extract significantly improved the survival of cultured cortical neurons and increased neurite complexity in immature neurons. Taken together, our findings suggest that DKT extract induces Bdnf expression and has a neurotrophic effect in neurons. Because BDNF inducers are expected to have therapeutic potential for neurological disorders, re-positioning of Kampo formulations such as daikenchuto may lead to clinical application in diseases associated with reduced BDNF in the brain.

SRF and SRF cofactor mRNA expression is differentially regulated by BDNF stimulation in cortical neurons

Serum response factor (SRF) is a transcription factor that plays essential roles in multiple brain functions in concert with SRF cofactors such as ternary complex factor (TCF) and megakaryoblastic leukemia (MKL)/myocardin-related transcription factor (MRTF), which comprises MKL1/MRTFA and MKL2/MRTFB. Here, we stimulated primary cultured rat cortical neurons with brain-derived neurotrophic factor (BDNF) and investigated the levels of SRF and SRF cofactor mRNA expression. We found that SRF mRNA was transiently induced by BDNF, whereas the levels of SRF cofactors were differentially regulated: mRNA expression of Elk1, a TCF family member, and MKL1/MRTFA were unchanged, while in contrast, mRNA expression of MKL2/MRTFB was transiently decreased. Inhibitor experiments revealed that BDNF-mediated alteration in mRNA levels detected in this study was mainly due to the extracellular signal-regulated protein kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway. Collectively, BDNF mediates the reciprocal regulation of SRF and MKL2/MRTFB at the mRNA expression level through ERK/MAPK, which may fine-tune the transcription of SRF target genes in cortical neurons. Accumulating evidence regarding the alteration of SRF and SRF cofactor levels detected in several neurological disorders suggests that the findings of this study might also provide novel insights into valuable therapeutic strategies for the treatment of brain diseases.

SRF in Neurochemistry: Overview of Recent Advances in Research on the Nervous System

Serum response factor (SRF) is a representative transcription factor that plays crucial roles in various biological phenomena by regulating immediate early genes (IEGs) and genes related to cell morphology and motility, among others. Over the years, the signal transduction pathways activating SRF have been clarified and SRF-target genes have been identified. In this overview, we initially briefly summarize the basic biology of SRF and its cofactors, ternary complex factor (TCF) and megakaryoblastic leukemia (MKL)/myocardin-related transcription factor (MRTF). Progress in the generation of nervous system-specific knockout (KO) or genetically modified mice as well as genetic analyses over the last few decades has not only identified novel SRF-target genes but also highlighted the neurochemical importance of SRF and its cofactors. Therefore, here we next present the phenotypes of mice with nervous system-specific KO of SRF or its cofactors by depicting recent findings associated with brain development, plasticity, epilepsy, stress response, and drug addiction, all of which result from function or dysfunction of the SRF axis. Last, we develop a hypothesis regarding the possible involvement of SRF and its cofactors in human neurological disorders including neurodegenerative, psychiatric, and neurodevelopmental diseases. This overview should deepen our understanding, highlight promising future directions for developing novel therapeutic strategies, and lead to illumination of the mechanisms underlying higher brain functions based on neuronal structure and function.

Regulation of Dendritic Synaptic Morphology and Transcription by the SRF Cofactor MKL/MRTF

Accumulating evidence suggests that the serum response factor (SRF) cofactor megakaryoblastic leukemia (MKL)/myocardin-related transcription factor (MRTF) has critical roles in many physiological and pathological processes in various cell types. MKL/MRTF molecules comprise MKL1/MRTFA and MKL2/MRTFB, which possess actin-binding motifs at the N-terminus, and SRF-binding domains and a transcriptional activation domain (TAD) at the C-terminus. Several studies have reported that, in association with actin rearrangement, MKL/MRTF translocates from the cytoplasm to the nucleus, where it regulates SRF-mediated gene expression and controls cell motility. Therefore, it is important to elucidate the roles of MKL/MRTF in the nervous system with regard to its structural and functional regulation by extracellular stimuli. We demonstrated that MKL/MRTF is highly expressed in the brain, especially the synapses, and is involved in dendritic complexity and dendritic spine maturation. In addition to the positive regulation of dendritic complexity, we identified several MKL/MRTF isoforms that negatively regulate dendritic complexity in cortical neurons. We found that the MKL/MRTF isoforms were expressed differentially during brain development and the impacts of these isoforms on the immediate early genes including Arc/Arg3.1, were different. Here, we review the roles of MKL/MRTF in the nervous system, with a special focus on the MKL/MRTF-mediated fine-tuning of neuronal morphology and gene transcription. In the concluding remarks, we briefly discuss the future perspectives and the possible involvement of MKL/MRTF in neurological disorders such as schizophrenia and autism spectrum disorder.

Differential localization and roles of splice variants of rat suppressor of cancer cell invasion (SCAI) in neuronal cells

Suppressor of cancer cell invasion (SCAI) is a suppressor of myocardin-related transcription factor (MRTF)-mediated transcription and cancer cell invasion. However, roles of SCAI in the brain and neuronal cells are not fully resolved. In this study, we initially investigated the distribution of Scai mRNA in the developing rat brain and in neurons. We found that, although Scai mRNA levels decreased during brain development, it was highly expressed in several brain regions and in neurons but not astrocytes. Subsequently, in addition to Scai variant 1, we identified novel rat Scai variants 2 and 3 and characterized their functions in Neuro-2a cells. The novel Scai variants 2 and 3 contain unique exons that possess stop codons and therefore encode shorter proteins compared with the full-length Scai variant 1. SCAI variants 2 and 3 possess a nuclear localization signal, but do not have an MRTF-binding site. Immunostaining of green fluorescent protein (GFP)-tagged SCAI variants revealed a nuclear localization of variant 1, whereas localization of variants 2 and 3 was throughout the cytoplasm and nucleus, suggesting that other nuclear localization signals, which act in Neuro-2a cells, exist in SCAI. All three SCAI variants suppressed the neuron-like morphological change of Neuro-2a cells induced by a Rho effector, constitutively active mDia; however, the suppressive effects of variants 2 and 3 were weaker than that of full-length SCAI variant 1, indicating that the SCAI-mediated change toward a neuronal morphology appeared to be consistent with their nuclear localization. These findings indicate that generation of multiple SCAI splice variants fines-tune neuronal morphology.

Expression of SOLOIST/MRTFB i4, a novel neuronal isoform of the mouse serum response factor coactivator myocardin-related transcription factor-B, negatively regulates dendritic complexity in cortical neurons

Megakaryoblastic leukemia 2 (MKL2)/myocardin-related transcription factor-B (MRTFB), a serum response factor (SRF) coactivator, is an important regulator of gene expression and neuronal morphology. Here, we show that different mouse MRTFB splice isoforms, including a novel fourth MRTFB isoform named spliced neuronal long isoform of SRF transcriptional coactivator (SOLOIST)/MRTFB isoform 4 (MRTFB i4), play distinct roles in this process. SOLOIST/MRTFB i4 has a short exon that encodes 21 amino acid residues ahead of the first RPXXXEL (RPEL) motif in MRTFB isoform 3. Quantitative PCR revealed that SOLOIST/MRTFB i4 and isoform 1 were enriched in the forebrain and neurons, and up-regulated during brain development. Conversely, isoform 3 was detected in various tissues, including both neurons and astrocytes, and was down-regulated in the developing brain. Reporter assays supported the SRF-coactivator function of SOLOIST/MRTFB i4 as well as isoform 1. Acute expression of MRTFB isoform 1, but not isoform 3 or SOLOIST/MRTFB i4, in neuronal cells within 24 hr drastically increased endogenous immediate early gene [c-fos, egr1, and activity-regulated cytoskeleton-associated protein] expression, but not endogenous actinin α1, β-actin, gelsolin, or srf gene expression measured by qPCR. Over-expression of SOLOIST/MRTFB i4 reduced the dendritic complexity of cortical neurons, whereas over-expression of isoform 1 increased this complexity. Co-expression of isoform 1 and SOLOIST/MRTFB i4 in cortical neurons revealed that isoform 1 competitively counteracted down-regulation by SOLOIST/MRTFB i4. Our findings indicate that MRTFB isoforms have unique expression patterns and differential effects on gene expression and dendritic complexity, which contribute to shaping neuronal circuits, at least in part.

Productivity and bioactivity of enokipodins A-D of Flammulina rossica and Flammulina velutipes

Enokipodins are antimicrobial sesquiterpenes produced by Flammulina velutipes in a mycelial culture medium. To date, enokipodin production has not been reported in other members of the genus Flammulina. Hence, in this study, the production of enokipodins A, B, C, and D by F. velutipes and F. rossica was investigated. Some strains of F. rossica were confirmed to produce at least one of the four enokipodins in the culture medium. However, some strains of F. velutipes did not produce any of the enokipodins. In an antibacterial assay using liquid medium, enokipodin B showed the strongest growth inhibitory activity against Bacillus subtilis among the four types of enokipodins. Enokipodin B inhibited the spore germination of some plant pathogenic fungi. Enokipodins B and D exerted moderate anti-proliferative activity against some cancer cell lines, and enokipodins A and C inhibited the proliferation of the malarial parasite, Plasmodium falciparum.

Screening inducers of neuronal BDNF gene transcription using primary cortical cell cultures from BDNF-luciferase transgenic mice

Brain-derived neurotrophic factor (BDNF) is a key player in synaptic plasticity, and consequently, learning and memory. Because of its fundamental role in numerous neurological functions in the central nervous system, BDNF has utility as a biomarker and drug target for neurodegenerative and neuropsychiatric disorders. Here, we generated a screening assay to mine inducers of Bdnf transcription in neuronal cells, using primary cultures of cortical cells prepared from a transgenic mouse strain, specifically, Bdnf-Luciferase transgenic (Bdnf-Luc) mice. We identified several active extracts from a library consisting of 120 herbal extracts. In particular, we focused on an active extract prepared from Ginseng Radix (GIN), and found that GIN activated endogenous Bdnf expression via cAMP-response element-binding protein-dependent transcription. Taken together, our current screening assay can be used for validating herbal extracts, food-derived agents, and chemical compounds for their ability to induce Bdnf expression in neurons. This method will be beneficial for screening of candidate drugs for ameliorating symptoms of neurological diseases associated with reduced Bdnf expression in the brain, as well as candidate inhibitors of aging-related cognitive decline.

Involvement of SRF coactivator MKL2 in BDNF-mediated activation of the synaptic activity-responsive element in the Arc gene

The expression of immediate early genes (IEGs) is thought to be an essential molecular basis of neuronal plasticity for higher brain function. Many IEGs contain serum response element in their transcriptional regulatory regions and their expression is controlled by serum response factor (SRF). SRF is known to play a role in concert with transcriptional cofactors. However, little is known about how SRF cofactors regulate IEG expression during the process of neuronal plasticity. We hypothesized that one of the SRF-regulated neuronal IEGs, activity-regulated cytoskeleton-associated protein (Arc; also termed Arg3.1), is regulated by an SRF coactivator, megakaryoblastic leukemia (MKL). To test this hypothesis, we initially investigated which binding site of the transcription factor or SRF cofactor contributes to brain-derived neurotrophic factor (BDNF)-induced Arc gene transcription in cultured cortical neurons using transfection and reporter assays. We found that BDNF caused robust induction of Arc gene transcription through a cAMP response element, binding site of myocyte enhancer factor 2, and binding site of SRF in an Arc enhancer, the synaptic activity-responsive element (SARE). Regardless of the requirement for the SRF-binding site, the binding site of a ternary complex factor, another SRF cofactor, did not affect BDNF-mediated Arc gene transcription. In contrast, chromatin immunoprecipitation revealed occupation of MKL at the SARE. Furthermore, knockdown of MKL2, but not MKL1, significantly decreased BDNF-mediated activation of the SARE. Taken together, these findings suggest a novel mechanism by which MKL2 controls the Arc SARE in response to BDNF stimulation.

Deltamethrin Increases Neurite Outgrowth in Cortical Neurons through Endogenous BDNF/TrkB Pathways

Deltamethrin (DM), a type II pyrethroid, robustly increases brain-derived neurotrophic factor (Bdnf) expression and has a neurotrophic effect in primary cultures of rat cortical neurons. In this study, we investigated the effect of DM on neurite morphology in cultured rat cortical neurons. DM significantly increased neurite outgrowth, but this increase was abolished when the BDNF scavenger tropomyosin receptor kinase B (TrkB)-Fc was added 10 min before the DM treatment. In contrast, the addition of TrkB-Fc 1 h after the treatment did not affect DM-induced neurite outgrowth. Our previous research has indicated that type II, but not type I, pyrethroids have the ability to induce Bdnf mRNA expression, but neither permethrin nor cypermethrin, which are type I and type II pyrethroids, respectively, affected neurite outgrowth in the current study. These results suggest that this effect is not due to increased Bdnf expression, and the effect is unique to DM. We previously demonstrated that calcineurin plays a role in the DM-mediated induction of Bdnf expression. However, the calcineurin inhibitor FK506 did not significantly affect DM-induced neurite outgrowth. DM-induced neurite outgrowth was abolished by U0126 and rapamycin, indicating the involvement of the mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) pathways. Taken together, these findings suggest that DM activates endogenous BDNF/TrkB-mediated MAPK and mTOR pathways, thereby increasing neurite outgrowth.Key words: BDNF, Deltamethrin, MAPK, mTOR, Neurite outgrowth.

Distinct regulation of activity-dependent transcription of immediate early genes in cultured rat cortical neurons

The activity-regulated expression of immediate early genes (IEGs) contributes to long-lasting neuronal functions underlying long-term memory. However, their response properties following neuronal activity are unique and remain poorly understood. To address this knowledge gap, here we further investigated the response properties of two representative IEGs, c-fos and brain-derived neurotrophic factor (Bdnf). Treatment of cultured cortical cells with KCl produces a depolarization process that results in the increase of intracellular calcium concentration in a KCl concentration-dependent manner. Consistent with this increase, c-fos expression was induced in a KCl concentration-dependent manner. In contrast, however, Bdnf expression was optimally activated by both 25 and 50 mM concentration of KCl. Similar results were observed when the cells were treated with okadaic acid, which inhibits protein phosphatases and elicits the hyper-phosphorylation of signaling molecules. Thus, Bdnf expression is strictly regulated by a neuronal activity threshold in an all or nothing manner, whereas c-fos expression is activated in a neuronal activity-dependent manner. Our findings also suggest that these differential responses might be due to the presence or absence of a TATA box.

Balance between cAMP and Ca(2+) signals regulates expression levels of pituitary adenylate cyclase-activating polypeptide gene in neurons

Mice lacking the gene encoding pituitary adenylate cyclase-activating polypeptide (PACAP) or its specific receptor, PAC1, show abnormal behaviors related to schizophrenia. However, the regulation of PACAP expression in neurons remains unclear. Here, we report that Pacap mRNA levels are regulated transcriptionally and post-transcriptionally by cAMP and Ca(2+) signals in cultured rat cortical cells. Pacap mRNA levels decreased proportionately with the intensity of cAMP signaling, and this decrease was accelerated by N-methyl-D-aspartate (NMDA) receptor blockade, suggesting that cAMP signaling enhances the degradation of Pacap mRNA, whereas NMDA receptor-mediated signals inhibit its degradation. However, depolarization (which produced a robust increase in Ca(2+) signals) together with cAMP signaling resulted in a synergistic induction of Pacap mRNA through calcineurin and its substrate, cAMP-response element-binding protein (CREB)-regulated transcription coactivator 1. These results strongly support the concept that while cAMP signaling can accelerate the degradation of Pacap mRNA, it can also synergistically enhance Ca(2+) signaling-induced transcriptional activation of Pacap. Taken together, our findings suggest that a balance between Ca(2+) and cAMP signals regulates PACAP levels in neurons and that a perturbation of this balance may result in psychiatric disorders, such as schizophrenia.

Successful control of an outbreak of GES-5 extended-spectrum β-lactamase-producing Pseudomonas aeruginosa in a long-term care facility in Japan

BACKGROUND

Little is known about multidrug-resistant Pseudomonas aeruginosa (MDRP) outbreaks in long-term care facilities (LTCFs).

AIM

To describe an MDRP outbreak in an LTCF and to clarify risk factors for MDRP acquisition.

METHODS

Patients who were positive for MDRP at an LTCF from January 2013 to January 2014 were analysed. A descriptive analysis, a case-control study, and a microbiological analysis were performed.

FINDINGS

A total of 23 MDRP cases were identified, 16 of which were confirmed in sputum samples. Healthcare workers were observed violating hand hygiene procedures when performing oral, wound, and genital care. Nasogastric tube and oxygen mask use was associated with MDRP acquisition in the respiratory tract, which might have been confounded by poor hand hygiene. Sharing unhygienic devices, such as portable oral suction devices for oral care, and washing bottles and ointments for wound and genital care with inadequate disinfection could explain the transmission of MDRP in some cases. Isolates from 11 patients were found to be indistinguishable or closely related by pulsed-field gel electrophoresis and harbouring the blaGES-5 gene. Subsequent enhanced infection control measures were supported by nearby hospitals and a local public health centre. No additional cases were identified for a year after the last case occurred in January 2014.

CONCLUSION

An outbreak of MDRP with an antimicrobial resistance gene, blaGES-5, occurred in a Japanese LTCF. It was successfully controlled by enhanced infection control measures, which neighbouring hospitals and a local public health centre supported.

Convergent effects of Ca(2+) and cAMP signals on the expression of immediate early genes in neurons

How the expression of immediate early genes (IEGs) is controlled in response to neurotransmissions is unknown. Using cultured rat cortical cells, we investigated the expression of IEGs regulated by Ca(2+) and/or cAMP signals. The expression of c-fos was transiently induced by treatment of cells with high potassium (high K(+)), which evoked depolarization, or forskolin, an adenylate cyclase activator. c-fos expression was persistently and synergistically induced by simultaneous treatment with high K(+) and forskolin via cAMP-response element (CRE). Microarray analysis indicated the expression profiles of IEGs caused by depolarization in the presence or absence of forskolin. When a novel index was included to investigate the profile of IEGs, we found that high K(+)-induced expression of IEGs was stimulatory or negatively changed in the presence of forskolin, suggesting distinct convergent effects of Ca(2+) and cAMP signals on the expression of IEGs.

Class I histone deacetylase-mediated repression of the proximal promoter of the activity-regulated cytoskeleton-associated protein gene regulates its response to brain-derived neurotrophic factor

We examined the transcriptional regulation of the activity-regulated cytoskeleton-associated protein gene (Arc), focusing on BDNF-induced Arc expression in cultured rat cortical cells. Although the synaptic activity-responsive element (SARE), located -7 kbp upstream of the Arc transcription start site, responded to NMDA, BDNF, or FGF2, the proximal region of the promoter (Arc/-1679) was activated by BDNF or FGF2, but not by NMDA, suggesting the presence of at least two distinct Arc promoter regions, distal and proximal, that respond to extracellular stimuli. Specificity protein 4 (SP4) and early growth response 1 (EGR1) controlled Arc/-1679 transcriptional activity via the region encompassing -169 to -37 of the Arc promoter. We found that trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, significantly enhanced the inductive effects of BDNF or FGF2, but not those of NMDA on Arc expression. Inhibitors of class I/IIb HDACs, SAHA, and class I HDACs, MS-275, but not of class II HDACs, MC1568, enhanced BDNF-induced Arc expression. The enhancing effect of TSA was mediated by the region from -1027 to -1000 bp, to which serum response factor (SRF) and HDAC1 bound. The binding of HDAC1 to this region was reduced by TSA. Thus, Arc expression was suppressed by class I HDAC-mediated mechanisms via chromatin modification of the proximal promoter whereas the inhibition of HDAC allowed Arc expression to be markedly enhanced in response to BDNF or FGF2. These results contribute to our understanding of the physiological role of Arc expression in neuronal functions such as memory consolidation.

Excitatory GABA induces BDNF transcription via CRTC1 and phosphorylated CREB-related pathways in immature cortical cells

Although the excitatory action of GABA has been shown to activate the expression of brain-derived neurotrophic factor (BDNF), its molecular mechanisms remain unclear. Using cultured rat cortical cells, we here demonstrated that GABA induced Bdnf mRNA expression mainly via L-type voltage-dependent Ca(2+) channels (L-VDCC) at the early stage and inhibited it at the late stage of the culture, which corresponded to the excitatory and inhibitory states of cortical cells. The excitatory GABA-induced Bdnf mRNA expression was controlled by multiple Ca(2+) signaling pathways including Ca(2+) /calmodulin-dependent protein kinase (CaMK), mitogen-activated protein kinase (MAPK) and calcineurin (CN). The Bdnf-promoter IV (Bdnf-pIV) was activated by GABA, mainly via cAMP-response element (CRE)/CREB, and this was prevented by the over-expression of a dominant negative CREB. The nuclear translocation of CREB-regulated transcriptional coactivator 1 (CRTC1) was selectively induced by the GABA-induced CN pathway to activate Bdnf-pIV. On the other hand, GABA-induced Gal4-CREB-dependent transcription, which was controlled by multiple Ca(2+) signaling pathways, was prevented when the serine at position 133 of Gal4-CREB was mutated to alanine. Taken together, the excitatory action of GABA transcriptionally activated Bdnf expression through the combination of nuclear-localized CRTC1 and phosphorylated CREB in immature cortical cells, and may be the molecular mechanisms underlying Bdnf expression to control neuronal development. We demonstrated that GABA induced Bdnf expression at the early stage of the culture, in which GABA exerted its excitatory action. The excitatory GABA-induced Bdnf expression was controlled by multiple Ca(2+) signaling pathways evoked via L-VDCC. Both the CREB coactivator, CRTC1 and CREB phosphorylation participated in excitatory GABA-induced Bdnf transcription. Our present study indicates the mechanism underlying the excitatory GABA-induced Bdnf expression in immature neurons and provide new insights into molecular mechanisms underlying Bdnf expression to control neuronal development.

Type II pyrethroid deltamethrin produces antidepressant-like effects in mice

Pyrethroids, which are widely used insecticides with low acute toxicity in mammals, affect sodium channels in neurons. In primary culture of rat cortical neurons, the type II pyrethroid deltamethrin (DM) markedly enhances the expression of the mRNA of brain-derived neurotrophic factor (BDNF) and exerts neurotrophic effects. In this study, we investigated the antidepressant-like effect of DM in mice. The effects of DM were assessed using the forced swimming test (FST) and were compared with those of type I pyrethroid permethrin (PM). Intraperitoneal administration of DM (5 and 10mg/kg), but not of PM (10mg/kg), increased the expression of BDNF mRNA in the hippocampus. DM, but not PM, significantly decreased the immobility time in the FST, and did not affect locomotor activity and motor coordination, suggesting that DM has an antidepressant-like effect. This effect of DM was inhibited by intracerebroventricular injection of K252a, which is an inhibitor of the BDNF receptor TrkB, indicating that the antidepressant-like effects of DM are mediated by BDNF/TrkB signaling pathways. Repeated administration of DM, but not of PM, also exerted antidepressant-like effects, which were long lasting. The results of the present study suggest that DM possesses antidepressant-like properties, and may be a possible source for the development of drugs to treat neurodegenerative and psychiatric disorders including depression.

Identification, expression and characterization of rat isoforms of the serum response factor (SRF) coactivator MKL1

Megakaryoblastic leukemia 1 (MKL1) is a member of the MKL family of serum response factor (SRF) coactivators. Here we have identified three rat MKL1 transcripts: two are homologues of mouse MKL1 transcripts, full-length MKL1 (FLMKL1) and basic, SAP, and coiled-coil domains (BSAC), the third is a novel transcript, MKL1-elongated derivative of yield (MELODY). These rat MKL1 transcripts are differentially expressed in a wide variety of tissues with highest levels in testis and brain. During brain development, these transcripts display differential patterns of expression. The FLMKL1 transcript encodes two isoforms that utilize distinct translation start sites. The longer form possesses three actin-binding RPXXXEL (RPEL) motifs and the shorter form, MKL1met only has two RPEL motifs. All four rat MKL1 isoforms, FLMKL1, BSAC, MKL1met and MELODY increased SRF-mediated transcription, but not CREB-mediated transcription. Accordingly, the differential expression of MKL1 isoforms may help fine-tune gene expression during brain development.

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Megakaryoblastic leukemia 1 (MKL1) is a serum response factor (SRF) coactivator.

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We have identified multiple rat MKL1 isoforms, including a novel one named MELODY.

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Rat MKL1 isoforms are enriched in testis and brain.

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Expression of rat MKL1 isoforms is regulated during brain development.

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All rat MKL1 isoforms act as SRF transcriptional coactivators.

Up-regulation of L-type amino acid transporter 1 (LAT1) in cultured rat retinal capillary endothelial cells in response to glucose deprivation

We investigated the regulation of L-type amino acid transporter 1 (LAT1) in a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2 cells) in response to glucose deprivation. The amounts of LAT1 and 4F2 heavy chain (4F2hc) mRNA in TR-iBRB2 cells exposed to glucose-free culture medium for 8 to 24 h were significantly elevated compared with those in control medium. Concomitantly, [³H]L-leucine uptake activity was increased, suggesting that LAT1 transport activity is induced under glucose-deprivation. To determine the transcriptional activity of the LAT1 gene under glucose-free conditions, the promoter activity of the LAT1 gene of approximately 2 kbp (-1958 bp to +70 bp) in TR-iBRB2 cells was assayed using a dual-luciferase reporter assay system. The transcriptional activity of the 2 kbp LAT1 promoter under the glucose-free conditions was 1.7-fold greater than that under normal glucose conditions. The presence of an activator site(s) between -162 bp and -155 bp was indicated by the low activities exhibited by the construct spanning this region and mutagenesis. These results suggest that the glucose deprivation sensitivity of LAT1 expression is transcriptionally regulated, and cis-elements within the LAT1 promoter region from -162 bp to -155 bp mediate this regulation.

Deltamethrin, a type II pyrethroid insecticide, has neurotrophic effects on neurons with continuous activation of the Bdnf promoter

Pyrethroids, widely used insecticides with low acute toxicity in mammals, affect sodium channels in neurons. In a primary culture of rat cortical neurons, deltamethrin (DM), a type II pyrethroid, markedly enhanced the expression of brain-derived neurotrophic factor (BDNF) exon IV-IX (Bdnf eIV-IX) mRNA. In this study, we found that DM has a neurotrophic effect on cultured neurons and investigated the mechanisms responsible for it. One μM DM increased cell survival, neurite complexity and length. Neurite complexity and length were reduced not only by a blockade of cellular excitation with GABA or Ca(2+) influx via L-type voltage-dependent calcium channels with nicardipine, but also by a blockade of TrkB, a specific receptor for BDNF, with TrkB/Fc. These data indicate DM has neurotrophic actions. DM-induced Bdnf eIV-IX mRNA expression through the calcineurin and ERK/MAPK pathways, the increase of which was reduced by GABA(A) receptor activation. Using a promoter assay, we found that Ca(2+)-responsive elements including a CRE are involved in the DM-induced activation of the Bdnf promoter IV (Bdnf-pIV). The intracellular concentration of Ca(2+) and activation of Bdnf-pIV remained elevated for, at least, 1 and 24 h, respectively. Moreover, GABA(A) receptor activation or a blockade of Ca(2+) influx even after starting the incubation with DM reduced the elevated activity of Bdnf-pIV. These data demonstrated that the prolonged activation of Bdnf-pIV occurred because of this continuous increase in the intracellular Ca(2+) concentration. Thus, DM has neurotrophic effects on neurons, likely due to prolonged activation of Bdnf promoter in neurons. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Involvement of the serum response factor coactivator megakaryoblastic leukemia (MKL) in the activin-regulated dendritic complexity of rat cortical neurons

Dynamic changes in neuronal morphology and transcriptional regulation play crucial roles in the neuronal network and function. Accumulating evidence suggests that the megakaryoblastic leukemia (MKL) family members, which function not only as actin-binding proteins but also as serum response factor (SRF) transcriptional coactivators, regulate neuronal morphology. However, the extracellular ligands and signaling pathways, which activate MKL-mediated morphological changes in neurons, remain unresolved. Here, we demonstrate that in addition to MKL1, MKL2, highly enriched in the forebrain, strongly contributes to the dendritic complexity, and this process is triggered by stimulation with activin, a member of the transforming growth factor β (TGF-β) superfamily. Activin promoted dendritic complexity in a SRF- and MKL-dependent manner without drastically affecting MKL localization and protein levels. In contrast, activin promoted the nuclear export of suppressor of cancer cell invasion (SCAI), which is a corepressor for SRF and MKL. Furthermore, overexpression of SCAI blocked activin-induced SRF transcriptional responses and dendritic complexity. Collectively, these results strongly suggest that activin-SCAI-MKL signaling is a novel pathway that regulates the dendritic morphology of rat cortical neurons by excluding SCAI from the nucleus and activating MKL/SRF-mediated gene expression.

Half-value layer measurement: simple process method using radiochromic film

Although the half-value layer (HVL) is one of the important parameters for QA and QC, constant monitoring has not been performed because the measurements using an ionization chamber (IC) are time-consuming and complicated. To solve these problems, the use of radiochromic film (GAFCHROMIC XR TYPE R: GAF-R) with step-shaped aluminum (Al) filters, referred to herein as the simple process method, has been developed. The measurement X-ray tube voltages were 120 kV, 100 kV, and 80 kV. The Al filter area, the full exposure area, and the unexposed area were set on the GAF-R so as to obtain correct data. The HVL was evaluated using the density attenuation ratio. The HVLs obtained using the GAF-R and an 1C dosimeter were compared. HVLs with X-ray tube voltages of 120 kV, 100 kV, and 80 kV using the GAF-R were 4.10 mm, 3.55 mm and 2.97 mm, respectively. The difference ratios of the HVLs using the GAF-R and the IC were 1.2%, 7.6%, and 10.0%, respectively. The HVL at 120 kV can be routinely and quickly measured using the simple process method. Therefore, an IC dosimeter is not needed for HVL measurements for QA and QC. However, the HVL measurements of low energy (100 kV and 80 kV) need attention.

Persistent BDNF exon I-IX mRNA expression following the withdrawal of neuronal activity in neurons

It is still unclear whether an active state of transcription once established in chromatin persists in neurons. Here, we focused on BDNF exon I-IX mRNA expression because of its marked induction upon the treatment of rat cortical neurons with trichostatin A, suggesting strong repression of the expression through histone deacetylase activity. Acetylation of histones H3 and H4 in promoter-I of the BDNF gene (BDNF-PI) was induced by membrane depolarization time- and dose-dependently, corresponding with the increase in mRNA expression. Following withdrawal of the depolarization, the mRNA level remained elevated for at least 6h, the persistence of which depended upon the strength of depolarization, whereas the BDNF exon IV-IX expression did not. The acetylation of histones was also maintained with BDNF-PI. Thus, BDNF exon I-IX mRNA expression remained increased after depolarization was withdrawn, suggesting that once activated, the BDNF-PI transcription persists due to chromatin remodeling.

Valproic acid induces up- or down-regulation of gene expression responsible for the neuronal excitation and inhibition in rat cortical neurons through its epigenetic actions

Valproic acid (VPA), a drug used to treat epilepsy and bipolar mood disorder, inhibits histone deacetylase (HDAC), which is associated with the epigenetic regulation of gene expression. Using a microarray, we comprehensively examined which genes are affected by stimulating cultured rat cortical neurons with VPA, and found that the VPA-treatment markedly altered gene expression (up-regulated; 726 genes, down-regulated; 577 genes). The mRNA expression for brain-derived neurotrophic factor (BDNF) and the alpha4 subunit of the GABA(A) receptor (GABA(A)Ralpha4), known to be involved in epileptogenesis, was up-regulated, with the increase in BDNF exon I-IX mRNA expression being remarkable, whereas that for GABA(A)Rgamma2, GAD65 and 67, and the K(+)/Cl(-) co-transporter KCC2, which are responsible for the development of GABAergic inhibitory neurons, was down-regulated. The number of GAD67-positive neurons decreased upon VPA-treatment. Similar changes of up- and down-regulation were obtained by trichostatin A. VPA did not affect the intracellular Ca(2+) concentration and the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), suggesting its direct action on HDAC. The acetylation of histones H3 and H4 was increased in the promoters of up-regulated but not down-regulated genes. Thus, VPA may disrupt a balance between excitatory and inhibitory neuronal activities through its epigenetic effect.

Remote control of activity-dependent BDNF gene promoter-I transcription mediated by REST/NRSF

To know the role of repressor element-1 (RE-1)-silencing transcription factor (REST) in activity-dependent gene transcription in neurons, we investigated whether the Ca2+ signal-induced transcription of brain-derived neurotrophic factor promoter-I (BDNF-PI) is repressed by RE-1 located in exon II from far downstream of BDNF promoter-II (BDNF-PII). By constructing plasmids in which the location between BDNF-PI, -PII, and -RE-1 is maintained, we found, by conducting promoter assays with cortical neurons, that the promoter activity was constitutively repressed through the actions of BDNF-RE-1 but activated by Ca2+ signals evoked via membrane depolarization, which was due to BDNF-PI but not to BDNF-PII. The over-expression of REST reduced the level of transcriptional activation through the N- and C-terminals, suggesting the recruitment of a histone deacetylase. On over-expression of REST, an increased depolarization did not allow the activation. Thus, REST remotely represses activity-dependent gene transcription, the level of which controls the magnitude of the repression.

Extracellular adenosine 5'-triphosphate elicits the expression of brain-derived neurotrophic factor exon IV mRNA in rat astrocytes

A growing body of recent evidence indicates that ATP plays an important role in neuronal-glial communications. In this study, the authors demonstrated that extracellular ATP elicits the gene expression of brain-derived neurotrophic factor (BDNF), especially BDNF exon IV mRNA, in primary cultured rat cortical astrocytes but not in neurons. To investigate the mechanism by which ATP induces BDNF exon IV mRNA expression, the authors used immortalized astrocyte cell line RCG-12. ATP dose-dependently increased the expression of BDNF exon IV mRNA and activated BDNF promoter IV. P2Y receptor agonists (ADP and 2MeS-ADP) but not a P2X receptor agonist (alphabetaMeATP) induced the expression of BDNF exon IV mRNA. Moreover, ATP-induced BDNF exon IV mRNA upregulation was inhibited by a P2Y antagonist (MRS2179) but not by P2X antagonists (TNP-ATP and PPADS). These findings suggest the involvement of P2Y receptors in the ATP-induced transcription of the BDNF gene. Among the signal transduction inhibiters examined in this study, intracellular Ca(2+) chelator (BAPTA-AM) and Ca(2+)/calmodulin-dependent kinase (CaM kinase) inhibitors (KN-93 and W-7) attenuated ATP-induced BDNF exon IV mRNA upregulation. ATP transiently induced the phosphorylation of cAMP-responsive element-binding protein (CREB). ATP-induced CREB phosphorylation was repressed by P2Y antagonists, BAPTA-AM, and CaM kinase inhibitors. Overexpression of dominant negative CREB mutants reduced the activation of BDNF promoter IV and attenuated the upregulation of BDNF exon IV mRNA expression. These results suggest that ATP induces BDNF expression through P2Y receptor followed by the activation of CaM kinase and CREB in astrocytes. These mechanisms are likely to contribute to the enhancement of neuronal-glial networks.

[Subtraction image for dynamic liver MRI using free breath-hold at functional residual capacity: a clinical trial]

PURPOSE

Dynamic liver MRI images have been obtained under expiration breath holding (BH). However, problems with obtaining reproducible liver positions often observed. This study investigated ways to improve the reproducibility of liver position on dynamic liver MRI.

MATERIALS AND METHODS

After giving informed consent, 60 patients (32 males and 28 females, ages 33-85, median age 69) were examined by liver dynamic MRI under two types of BH. The BH phases were voluntary expiration (VE) phase without any explanations and functional residual capacity (FRC) phase after careful explanation was provided. Plain images, arterial phase images, portal phase images and parenchymal phase images were obtained. For statistical evaluation of reproducibility, the area of the 2nd or 3rd images from top of the liver was measured in each phase using a threshold value of half maximum. Misregistration areas were calculated by finding the remainder of the liver area in the plain-arterial (Pl-A) phase, arterial-portal (A-Po) phase, plain-parenchymal (Pl-Pa) phase. Contingency table analysis was done due to the misregistration was occurred or not.

RESULTS

Misregistration of liver image on the VE and the FRC of three phase types were statistical significant on the Pl-A (p < 0.01), on the A-Po (p < 0.01) and on the Pl-Pa (p < 0.05), respectively.

CONCLUSION

The FRC phase following careful explanation of the BH provided significantly improved reproducibility of liver position on dynamic liver MRI. Therefore, precise subtraction images could be obtained for routine clinical examinations without slice matching.

Synaptic plasticity-regulated gene expression: a key event in the long-lasting changes of neuronal function

"Neuronal activity"-dependent transcriptional activation is required for the long-lasting, functional changes that are involved in memory consolidation or drug addiction. Elucidation of the molecular mechanisms underlying the neuronal activity-dependent transcription of synaptic plasticity-related genes has helped towards understanding neuronal function and disorders as well in identifying new target molecules for drug design. In this study, we focused on neurotrophin and neuropeptide, which both have the ability to modulate neuronal survival and function. We also examined the molecular mechanisms by which underlying neurotrophin genes are regulated by neuronal activity. Brain-derived neurotrophic factor (BDNF) is a neurotrophin family member that has important roles in neuronal survival and plasticity as well as in psychiatric disorders. Transcriptional activation of the BDNF gene is commonly regulated by a key transcription factor, cAMP response element-binding protein (CREB), and this at least in part contributes to neuronal activity-dependent neuronal survival. Among at least four distinct promoters of the BDNF gene, promoters I and III are differentially activated by Ca2+ signals via NMDA receptors and L-type voltage-dependent Ca2+ channels. Especially, BDNF gene promoter I activation requires the cooperative binding of and upstream stimulatory factor (USF) and CREB to a CRE/USF binding site. By contrast, NT-3 gene transcription is regulated by Sp3/4. An important future direction will be to elucidate how long-lasting changes in neuronal plasticity are "epigenetically" and "structurally" controlled. Our studies on the relationships between long-lasting neuronal responses and gene expressions should help guide research into novel drugs for neuronal or psychiatric disorders.

Robust stimulation of TrkB induces delayed increases in BDNF and Arc mRNA expressions in cultured rat cortical neurons via distinct mechanisms

In cultures of rat cortical neurons, we found that stimulation of tyrosine receptor kinase B (TrkB) with brain-derived neurotrophic factor (BDNF) induced a biphasic expression of BDNF exon IV-IX mRNA, which became obvious 1-3 h (primary induction) and 24-72 h (delayed induction) after the stimulation, and characterized the delayed induction in relation to the mRNA expression of activity-regulated cytoskeleton-associated protein (Arc). Withdrawal of BDNF from the medium after stimulation for 3 h allowed the delayed induction, which was caused at the transcriptional level and dependent upon the initial contact between exogenously added BDNF and TrkB, the effect of which was time- and dose-dependent. The primary induction was controlled by the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) whereas the secondary induction by the calcium (Ca(2+)) signaling pathway. The enhanced Arc or Zif268 mRNA expression was controlled by activation of the ERK/MAPK pathway, both of which were repressed by blocking the binding of endogenously synthesized BDNF to TrkB. Thus, robust stimulation of TrkB autonomously induces delayed BDNF mRNA expression in an activity-dependent manner in rat cortical neurons, resulting in the stimulation of Arc mRNA expression through endogenously synthesized BDNF, the process being orchestrated by the Ca(2+) and ERK/MAPK signaling pathways.