N-methyl-D-aspartate signaling to nuclear activator protein-1 through mechanisms different from those for kainate signaling in murine brain

HMGA1a: sequence-specific RNA-binding factor causing sporadic Alzheimer's disease-linked exon skipping of presenilin-2 pre-mRNA

Aberrant exon 5 skipping of presenilin-2 (PS2) pre-mRNA produces a deleterious protein isoform PS2V, which is almost exclusively observed in the brains of sporadic Alzheimer's disease patients. PS2V over-expression in vivo enhances susceptibility to various endoplasmic reticulum (ER) stresses and increases production of amyloid-beta peptides. We previously purified and identified high mobility group A protein 1a (HMGA1a) as a trans-acting factor responsible for aberrant exon 5 skipping. Using heterologous pre-mRNAs, here we demonstrate that a specific HMGA1a-binding sequence in exon 5 adjacent to the 5' splice site is necessary for HMGA1a to inactivate the 5' splice site. An aberrant HMGA1a-U1 snRNP complex was detected on the HMGA1a-binding site adjacent to the 5' splice site during the early splicing reaction. A competitor 2'-O-methyl RNA (2'-O-Me RNA) consisting of the HMGA1a-binding sequence markedly repressed exon 5 skipping of PS2 pre-mRNA in vitro and in vivo. Finally, HMGA1a-induced cell death under ER stress was prevented by transfection of the competitor 2'-O-Me RNA. These results provide insights into the molecular basis for PS2V-associated neurodegenerative diseases that are initiated by specific RNA binding of HMGA1a.

Novel interaction between HMGA1a and StIP1 in murine terminally differentiated retina

High mobility group protein A1a (HMGA1a) is expressed at high levels in embryonic cells and has been implicated in their transcriptional regulation. However, it has been reported that high levels of HMGA1a expression are normally detected in the photoreceptor of adult (terminally differentiated cells) murine retina. We showed that biochemical purification of the recombinant HMGA1a binding activity in nuclear fractions from murine retina, but not from hippocampus, resulted in STAT3 interacting protein 1 (StIP1) that formed a novel complex with HMGA1a, STAT3 and homeodomain-interacting protein kinase 2 (HIPK2). While StIP1 expressions in brain, liver, lung, heart, skeletal muscle, spleen and thymus have previously been demonstrated, this is the first report that StIP1 was expressed in nuclear fractions from murine retina, and that in murine retina there are several novel complexes of transcriptional regulators consisting of HMGA1a, StIP1, STAT3 and HIPK2.

cAMP responsive element-binding protein phosphorylation is necessary for perirhinal long-term potentiation and recognition memory

We established the importance of phosphorylation of cAMP responsive element-binding protein (CREB) to both the familiarity discrimination component of long-term recognition memory and plasticity within the perirhinal cortex of the temporal lobe. Adenoviral transduction of perirhinal cortex (and adjacent visual association cortex) with a dominant-negative inhibitor of CREB impaired the preferential exploration of novel over familiar objects at a long (24 h) but not a short (15 min) delay, disrupted the normal reduced activation of perirhinal neurons to familiar compared with novel pictures, and impaired long-term potentiation of synaptic transmission in perirhinal slices. The consistency of these effects across the behavioral, systems, and cellular levels of analysis provides strong evidence for involvement of CREB phosphorylation in synaptic plastic processes within perirhinal cortex necessary for long-term recognition memory.

Possible involvement of the expression and phosphorylation of N-Myc in the induction of HMGA1a by hypoxia in the human neuroblastoma cell line

Increased expression of N-Myc and expression of the high mobility group protein A1a (HMGA1a) were observed in the nuclei of SK-N-SH cells following exposure to hypoxia. These observations were accompanied by the appearance of additional high molecular weight bands, which were eliminated by pretreatment with alkaline phosphatase. Immunoprecipitation showed phosphorylation of serine, threonine and tyrosine residues of N-Myc in the nucleus. These results suggest that hypoxia-induced signals in SK-N-SH cells lead to persistent expression of HMGA1a, which may induce expression of the transcription factor N-Myc, and that phosphorylation at serine, threonine and tyrosine residues of N-Myc occurs at an early stage after stimulation. Such signal consolidation processes could play a role in neuronal survival after hypoxia in neurons.

Novel function of PS2V: change in conformation of tau proteins

Neurofibrillary tangles (NFTs) are associated with many neurodegenerative disorders, such as Alzheimer's disease (AD). The major components of NFTs are hyper-phosphorylated tau proteins. The alternatively spliced form of the presenilin-2 (PS2) gene (PS2V) has been observed in sporadic AD brains. However, it is not known whether there is a relationship between tau aggregation/hyper-phosphorylation and PS2V expression. In this manuscript, we make the first report of PS2V alterations in the conformation of the tau protein (unknown form of tau) in the human neuroblastoma cell line.

Metals accelerate production of the aberrant splicing isoform of the presenilin-2

Oxidative stress is a major risk factor for Alzheimer's disease (AD) and other neurodegenerative disorders. Metals are known to be one of the factors that contribute to oxidative stress. Recently, we reported that the aberrant splicing isoform (PS2V) generated by skipping exon5 of the presenilin-2 (PS2) gene is a diagnostic feature of sporadic AD (SAD). PS2V is inducible by exposure of human neuroblastoma to hypoxia. We examined whether this aberrant splicing was caused by metal-induced oxidative stress, such as exposure to aluminum. As a result, we demonstrated that exposure to aluminum accelerated PS2V production induced by hypoxia. This acceleration of the production of PS2V to hypoxia was caused by chronic aluminum exposure, but was not related to the intracellular content of aluminum. HMGA1a is a mediator of PS2V production, and it was induced by aluminum as well as by hypoxia. Induction of HMGA1a was increased by chronic exposure to aluminum, and a nuclear extract containing HMGA1a bound to a specific sequence on exon5 of PS2 pre-mRNA, as reported previously. Finally, the acceleration of PS2V production induced by aluminum under hypoxic conditions reflected, but has not yet been directly shown to cause, vulnerability to endoplasmic reticulum stress. These results suggest that exposure to some metals can accelerate and enhance PS2V generation, and that hypoxia plus chronic exposure to metals may promote the development of AD.

Enhanced binding activity of nuclear antioxidant-response element through possible formation of Nrf2/Fos-B complex after in vivo treatment with kainate in murine hippocampus

To evaluate whether in vivo glutamate signals modulate signaling processes mediated by antioxidant-response element (ARE), we examined ARE binding in nuclear extracts from the hippocampus after in vivo treatment of mice with kainate. Enhancement of ARE binding was found at 2 h to 3 days after kainate treatment. Supershift analysis indicated possible involvement of Nrf2, Fos-B, and c-Fos in ARE binding in hippocampal nuclear extracts obtained from kainate-treated animals. On super-supershift analysis by combination of these antibodies, ARE probe/protein complex was shifted by the anti-Fos-B antibody alone, but not by the anti-c-Fos antibody alone, and further addition of the anti-Nrf2 antibody dramatically eliminated binding of the complex shifted by the anti-Fos-B antibody in hippocampal nuclear extracts from kainate-treated animals. Kainate treatment induced a profound increase in levels of c-Fos and Fos-B, without markedly affecting that of Nrf2 in nuclear extracts from the hippocampus. Co-localization of Nrf2 with both Fos-B and c-Fos was found in neuronal cell layers of the hippocampus in kainate-treated animals. RT-PCR analysis revealed that kainate treatment increases glutathione-S-transferase mRNA level in the hippocampus. Taken together, kainate signals may enhance nuclear ARE binding through an interaction between constitutive Nrf2 with inducible Fos-B expressed in murine hippocampus.

Fos-B expression is required for polyamine-induced increase in nuclear activator protein-1 DNA binding in discrete structures of murine brain

Spermidine (SPD) and spermine (SPN) have been shown to be endogenous agonists for N-methyl-D-aspartate (NMDA) receptors that could lead to expression of the nuclear transcription factor activator protein-1 (AP1) complex in the mammalian central nervous system both in vitro and in vivo. In nuclear extracts of murine whole brain, AP1 DNA binding increased significantly in a concentration-dependent manner with the addition of either SPD or SPN at a concentration range of 50-500 microM. Similarly, the nuclear proteins histone and dephosphorylated casein, but not phosphorylated casein, significantly increased AP1 DNA binding alone but in the presence of either SPD or SPN did not increase further binding. By contrast, another endogenous polyamine, putrescine, significantly prevented AP1 DNA binding increases by histone and dephosphorylated casein, but did not by itself significantly alter binding. Invariably, SPD and SPN effected significantly increased AP1 DNA binding in neocortex, hippocampus, striatum, midbrain, hypothalamus and cerebellum, but not in medulla-pons and spinal cord. Supershift and Western blotting analyses revealed relatively high constitutive expression of Fos-B protein in neocortex and hippocampus, but not in medulla-pons and spinal cord. Immunoprecipitation of Fos-B led to complete abolition of the ability of SPN and SPD to increase AP1 DNA binding in neocortical and hippocampal nuclear extracts. These results suggest that expression of Fos-B protein may be required for modulation of nuclear gene transcription by both SPD and SPN through stimulation DNA-binding activity of AP1 complex in murine central structures.

Transcription factor activator protein-1 expressed by kainate treatment can bind to the non-coding region of mitochondrial genome in murine hippocampus

We have demonstrated previously that the transcription factor activator protein-1 (AP-1) complex is translocated into mitochondria into the nucleus in murine hippocampus after systemic kainate injection (Ogita et al. [2002] J. Neurosci. 22:2561-2570). The present study investigates whether the mitochondrial AP-1 complex translocated in response to kainate treatment binds to AP-1-like sites located at the non-coding region of the mitochondrial genome in mouse hippocampus. There are 10 sites with sequences similar to the nuclear AP-1 site in the non-coding region. Of 10 pieces (MT-1-MT-10) of synthesized double-stranded oligonucleotides, each containing a mitochondrial AP-1-like site, MT-3, MT-4, and MT-9 were effective in inhibiting mitochondrial AP-1 DNA binding enhanced by kainate. Electrophoresis mobility shift analysis using radiolabeled MT-3 and MT-9 probes demonstrated marked enhancement with binding of these 2 probes in hippocampal mitochondrial extracts prepared 2-6 hr after kainate treatment. Unlabeled AP-1 probe was more potent than unlabeled MT-9 probe in inhibiting the mitochondrial MT-9 binding. Supershift analysis revealed participation of particular Fos/Jun family proteins, such as c-Fos, Fos-B, c-Jun, Jun-B, and Jun-D, in MT-9 binding in hippocampal mitochondrial extracts prepared 4 hr after kainate treatment. Immunoprecipitation analysis using anti-c-Fos antibody demonstrated that c-Fos associated with the mitochondrial genome in hippocampal mitochondria prepared from kainate-treated animals. These results suggest that the AP-1 complex expressed by in vivo kainate treatment would bind to AP-1-like sites in the non-coding region of the mitochondrial genome after translocation into mitochondria from murine hippocampus.

In vivo neuroprotective role of NMDA receptors against kainate-induced excitotoxicity in murine hippocampal pyramidal neurons

Activation of NMDA receptors has been shown to induce either neuronal cell death or neuroprotection against excitotoxicity in cultured cerebellar granule neurons in vitro. We have investigated the effects of pretreatment with NMDA on kainate-induced neuronal cell death in mouse hippocampus in vivo. The systemic administration of kainate (30 mg/kg), but not NMDA (100 mg/kg), induced severe damage in pyramidal neurons of the hippocampal CA1 and CA3 subfields 3-7 days later, without affecting granule neurons in the dentate gyrus. An immunohistochemical study using an anti-single-stranded DNA antibody and TdT-mediated dUTP nick end labeling analysis both revealed that kainate, but not NMDA, induced DNA fragmentation in the CA1 and CA3 pyramidal neurons 1-3 days after administration. Kainate-induced neuronal loss was completely prevented by the systemic administration of NMDA (100 mg/kg) 1 h to 1 day previously. No pyramidal neuron was seen with fragmented DNA in the hippocampus of animals injected with kainate 1 day after NMDA treatment. The neuroprotection mediated by NMDA was prevented by the non-competitive NMDA receptor antagonist MK-801. Taken together these results indicate that in vivo activation of NMDA receptors is capable of protecting against kainate-induced neuronal damage through blockade of DNA fragmentation in murine hippocampus.

Induced HMGA1a expression causes aberrant splicing of Presenilin-2 pre-mRNA in sporadic Alzheimer's disease

The aberrant splicing isoform (PS2V), generated by exon 5 skipping of the Presenilin-2 (PS2) gene transcript, is a diagnostic feature of sporadic Alzheimer's disease (AD). We found PS2V is hypoxia-inducible in human neuroblastoma SK-N-SH cells. We purified a responsible trans-acting factor based on its binding to an exon 5 fragment. The factor was identified as the high mobility group A1a protein (HMGA1a; formerly HMG-I). HMGA1a bound to a specific sequence on exon 5, located upstream of the 5' splice site. HMGA1a expression was induced by hypoxia and the protein was accumulated in the nuclear speckles with the endogenous splicing factor SC35. Overexpression of HMGA1a generated PS2V, but PS2V was repressed by cotransfection with the U1 snRNP 70K protein that has a strong affinity to HMGA1a. HMGA1a could interfere with U1 snRNP binding to the 5' splice site and caused exon 5 skipping. HMGA1a levels were significantly increased in the brain tissue from sporadic AD patients. We propose a novel mechanism of sporadic AD that involves HMGA1a-induced aberrant splicing of PS2 pre-mRNA in the absence of any mutations.

Modulation of DNA binding of nuclear transcription factors with leucine-zipper motifs by particular endogenous polyamines in murine central and peripheral excitable tissues

Transcriptional regulation is one of the most important functions of polyamines in the nucleus of eukaryotic cells. The addition of the endogenous polyamines spermine and spermidine markedly increased DNA binding activity of the transcription factor activator protein-1 (AP1) in a concentration-dependent manner at a concentration range of 50 to 500 microM in nuclear extracts of murine whole brain when determined in the absence of added MgCl(2) on gel retardation electrophoresis. Similar but less potent potentiation was seen with DNA binding of cAMP responsive element binding protein (CREB), while both polyamines were ineffective in affecting that of c-Myc irrespective of the addition of MgCl(2). Unlabeled AP1 probe was invariably more potent in competing for AP1 binding than unlabeled CREB probe in either the presence or absence of spermine and spermidine. In addition to whole brain, both polyamines significantly increased AP1 binding in retina, adrenal and pituitary, without significantly affecting that in spleen. Moreover, ultraviolet and circular dichroism spectra analyses revealed that these two polyamines induced DNA topological transition of AP1 probe under the conditions favorable for the increase in AP1 binding. These results suggest that both spermine and spermidine may modulate gene transcription through cis- and trans-actions on AP1 binding in the nucleus in murine central and peripheral structures with high excitability.

Inhibition of endogenous thyroid hormone receptor-beta and peroxisome proliferator-activated receptor-alpha activities by humic acid in a human-derived liver cell line

Humic acid (HA), know to be ubiquitous in the natural environment, is present in almost all soil, surface water, and plants. Earlier studies indicate that HA can affect thyroid economy via binding with iodide, inhibiting both thyroid peroxidase and hepatic 5'-deiodinase in rodents. However, the effect of HA, a peroxisome proliferator in rodents, on thyroid hormone receptor (TR) and peroxisome proliferator-activated receptor (PPAR) in human cells has not yet been examined. In this study, we demonstrate that the malic enzyme activity and the transcriptional activities of endogenous TR and PPAR were inhibited after treatment with HA in human hepatocyte Chang liver cell line. Although the protein expression levels of TR-beta, PPAR-alpha and retinoid X receptor-alpha (RXRalpha) were not changed significantly by HA treatment, both the binding abilities of endogenous TR-beta on thyroid hormone response element (TRE) and PPAR-alpha on the PPAR response element (PPRE) were inhibited by HA treatment. The study of the subcellular distribution of HA, relying on the inherent HA fluorescence, showed that HA distributed in the intracellular compartments including cytoplasm and nucleus. The 50% binding inhibition values (CI(50)) of HA on ME-TRE (malic enzyme gene-TRE) and ACOX-PPRE (acylCoA oxidase gene-PPRE) were 19.31 and 19.94 microg/mL, respectively. These results suggest that HA-induced endemic goiter may link in part to the disruption of TRbeta and PPARalpha function in human Chang liver cells. This model may be useful in the investigation of environmental goitrogens.

Localization of activator protein-1 complex with DNA binding activity in mitochondria of murine brain after in vivo treatment with kainate

To elucidate mechanisms underlying mitochondrial dysfunctions induced by glutamate, we have examined the effects of in vivo treatment with the ionotropic glutamate receptor agonist kainate on localization of the transcription factor activator protein-1 (AP-1) in mitochondria as well as nuclei of murine brain. A systemic administration of kainate dramatically enhanced AP-1 DNA binding in both mitochondrial and nuclear extracts of mouse cerebral cortex and hippocampus 1 hr to 3 d later. Unlabeled AP-1 probe selectively competed for AP-1 DNA binding in mitochondrial extracts of cortex and hippocampus obtained from mice injected with kainate. Supershift and immunoblotting analyses revealed participation of c-Fos, Fos-B, and Jun-B proteins in potentiation by kainate of mitochondrial AP-1 DNA binding in cortex and hippocampus. An immunohistochemical study demonstrated marked expression by kainate of c-Fos protein in the pyramidal and dentate granular layers, whereas an immunoelectron microscopic analysis showed localization of c-Fos protein within mitochondria, as well as nuclei, of the CA1 pyramidal and dentate granular cells in hippocampus obtained 2 hr after the administration of kainate. Mitochondrial AP-1 DNA binding was inhibited by particular unlabeled oligonucleotides containing sequences similar to the AP-1 site found in the noncoding region of mitochondrial DNA. Kainate markedly potentiated binding of radiolabeled oligonucleotide probes containing sequences effective in competing for AP-1 DNA binding in hippocampal mitochondrial extracts. These results suggest that kainate may facilitate expression of the AP-1 complex and subsequent translocation into mitochondria to participate in mechanisms associated with transcriptional regulation of mitochondrial DNA in murine hippocampus.

Nuclear degradation of particular Fos family members expressed following injections of NMDA and kainate in murine hippocampus

Transient glutamate signaling often leads to long lasting and permanent alterations of a variety of cellular functions through particular membrane receptors in the brain. For elucidation of mechanisms underlying long-term consolidation of transient extracellular signals, we have examined expression and degradation of particular Fos family member proteins required for assembly to the nuclear transcription factor activator protein-1 in this study. Transcription factors could modulate the activity of RNA polymerase II responsible for the formation of mRNA from genomic DNA in the nucleus and therefore regulate de novo synthesis of particular target functional proteins. Mice were intraperitoneally injected with 100 mg/kg N-methyl-D-aspartic acid (NMDA) or 40 mg/kg kainic acid (KA), followed by homogenization of hippocampus in the presence of different protease and phosphatase inhibitors 2 h after administration, and subsequent preparation of nuclear and cytosolic fractions. The systemic administration of both NMDA and KA induced marked expression of particular Fos family members, including c-Fos and Fra-2 proteins, in hippocampal nuclear and cytosolic fractions. Incubation at 30 degrees C for 1 to 18 h led to differential degradation profiles of each Fos family member protein in nuclear fractions in a manner peculiar to the individual excitants. Degradation rate was also affected by dialysis and subsequent addition of inhibitors for phosphatases and proteases. These results suggest that in vivo NMDA and KA signals may additionally modulate the activity of heterologous machineries responsible for breakdown of each Fos family member in a unique manner in nuclear fractions, rather than cytosolic fractions, of murine hippocampus.

Decrease in level of APG-2, a member of the heat shock protein 110 family, in murine brain following systemic administration of kainic acid

APG-2 belongs to the heat shock protein 110 family. Although kainic acid (KA)-induced seizures are known to elicit expression of inducible heat shock protein 70 (HSP70) in the brain, no investigation has been carried out on the APG-2 level after excitatory amino acid-induced seizures. By means of an immunoblot assay, we determined the levels of HSP70 and APG-2 in discrete brain structures of mice after a single intraperitoneal injection of KA or N-methyl-D-aspartic acid (NMDA). APG-2 level was significantly decreased in frontal cortex, hippocampus, and striatum three days after the administration of KA, while HSP70 level was increased in these regions following the administration. In any of these regions, APG-2 levels were returned to the control levels 10 days after the administration. However, no significant changes were observed in levels of both HSP70 and APG-2 in hypothalamus, midbrain, medulla-pons, and cerebellum of the mice. By contrast, NMDA administration did not significantly affect both levels in any of the regions examined. These findings indicate that the transient decrease in APG-2 expression is one of the intracellular events elicited by signals peculiar to KA, but not by those peculiar to NMDA, in telencephalon of murine brain.

Consolidation of transient ionotropic glutamate signals through nuclear transcription factors in the brain

Long-lasting alterations of neuronal functions could involve mechanisms associated with consolidation of transient extracellular signals through modulation of de novo synthesis of particular functional proteins in the brain. In eukaryotes, protein de novo synthesis is mainly under the control at the level of gene transcription by transcription factors in the cell nucleus. Transcription factors are nuclear proteins with an ability to recognize particular core nucleotides at the upstream and/or downstream of target genes, and thereby to modulate the activity of RNA polymerase II that is responsible for the formation of mRNA from double stranded DNA. Gel retardation electrophoresis is widely employed for conventional detection of DNA binding activities of a variety of transcription factors with different protein motifs. Extracellular ionotropic glutamate (Glu) signals lead to rapid and selective potentiation of DNA binding of the nuclear transcription factor activator protein-1 (AP1) that is a homo- and heterodimeric complex between Jun and Fos family members, in addition to inducing expression of the corresponding proteins, in a manner unique to each Glu signal in murine hippocampus. Therefore, extracellular Glu signals may be differentially transduced into the nucleus to express AP1 with different assemblies between Jun and Fos family members, and thereby to modulate de novo synthesis of the individual target proteins at the level of gene transcription in the hippocampus. Such mechanisms may be operative on synaptic plasticity as well as delayed neuronal death through consolidation of alterations of a variety of cellular functions induced by transient extracellular signals in the brain.

Effects of glutathione depletion by 2-cyclohexen-1-one on excitatory amino acids-induced enhancement of activator protein-1 DNA binding in murine hippocampus

We have investigated the role of glutathione in mechanisms associated with excitatory amino acid signaling to the nuclear transcription factor activator protein-1 (AP1) in the brain using mice depleted of endogenous glutathione by prior treatment with 2-cyclohexen-1-one (CHX). In the hippocampus of animals treated with CHX 2 h before, a significant increase was seen in enhancement of AP1 DNA binding when determined 2 h after the injection of kainic acid (KA) at low doses. The sensitization to KA was not seen in animals injected with CHX 24 h before, in coincidence with the recovery of glutathione contents to the normal levels. By contrast, CHX did not significantly affect the potentiation by NMDA of AP1 binding under any experimental conditions. Prior treatment with CHX resulted in facilitation of behavioral changes induced by KA without affecting those induced by NMDA. These results suggest that endogenous glutathione may be at least in part involved in molecular mechanisms underlying transcriptional control by KA, but not by NMDA, signals of cellular functions.

Differential expression and phosphorylation of particular fos family members by kainate in nuclear and cytosolic fractions of murine hippocampus

An i.p. injection of kainate resulted in severe losses of neuronal cells stained by Cresyl Violet in the CA1 and CA3 pyramidal layers of the murine hippocampus within two weeks, without affecting those in the dentate granule layer up to six weeks. Immunohistochemical analysis revealed marked and predominant expression of Fos family members, including c-Fos, Fos-B and Fra-2 proteins, in the dentate granule layer of the hippocampus, but not in the pyramidal layers, 2-18h after administration. Immunoblotting experiments showed that kainate induced more potent expression of c-Fos protein in nuclear fractions obtained 2h after injection than those obtained 18h later, with similar expression between cytosolic fractions obtained 2 and 18h after administration. Both Fos-B and Fra-2 proteins were more potently expressed in nuclear and cytosolic fractions 18h after administration than 2h when determined on immunoblotting analysis. Two-dimensional electrophoresis revealed expression of several proteins immunoreactive to the anti-c-Fos antibody with different isoelectric points in response to kainate in nuclear and cytosolic fractions of the hippocampus for 2-18h after a single injection. Immunoprecipitation analysis using the anti-c-Fos antibody showed phosphorylation of c-Fos protein on serine residues in hippocampal nuclear fractions 2h after administration, with additional phosphorylation on tyrosine residues 18h later. Prior treatment of the protein synthesis inhibitor cycloheximide prevented the expression of immunoreactivities to the anti-c-Fos antibody detected on two-dimensional electrophoresis in hippocampal nuclear fractions obtained 2h after administration.These results suggest that in vivo kainate signals may lead to persistent expression of the transcription factor activator protein-1 that consists of different Fos family members, as well as of c-Fos protein phosphorylated on serine and/or tyrosine residues, at an early stage after administration. Such signal consolidation processes could play a role in mechanisms associated with neuronal survival after kainate in the dentate granular layer of murine hippocampus.

Toll-like receptor 4-mediated signal pathway induced by Porphyromonas gingivalis lipopolysaccharide in human gingival fibroblasts

The lipopolysaccharide (LPS) secreted by Porphyromonas gingivalis is implicated in the initiation and progression of periodontitis. Human gingival fibroblasts (HGFs) are the major constituent of gingival connective tissue. In this study, we examined the expression of Toll-like receptor 4 (TLR4) on HGFs by flow cytometric analysis, and studied the signal transduction induced by LPS stimulation of HGFs by enzyme-linked immunosorbent assay, Western blotting, and immunoprecipitation. We show that LPS binds to HGFs, and that HGFs express TLR4 and myeloid differentiation primary response gene 88 (MyD88). P. gingivalis LPS-induced interleukin (IL)-1 production in HGFs was inhibited by anti-TLR4 antibody. P. gingivalis LPS treatment of HGFs activated several intracellular proteins including protein tyrosine kinases, and upregulated the expression of IL-1 receptor-associated kinase (IRAK), nuclear factor-kappaB (NF-kappaB), and activating protein-1 (AP-1), and these events were suppressed by anti-TLR4 monoclonal antibody. Our findings suggest that the binding of P. gingivalis LPS to TLR4 on HGFs activates various second messenger systems.

Sustained potentiation of AP1 DNA binding is not always associated with neuronal death following systemic administration of kainic acid in murine hippocampus

Mice were intraperitoneally injected with kainic acid (KA), followed by dissection of frozen coronal sections and subsequent punching out of the pyramidal and granular cell layers in the hippocampus under a binocular microscope. Systemic administration of KA resulted in marked and sustained potentiation of binding of a radiolabeled double stranded oligonucleotide probe for the nuclear transcription factor activator protein-1 (AP1) in the pyramidal cell layers of the CA1 and CA3 subfields and the granule cell layers of the dentate gyrus 2-18 h later. Morphological evaluation using cresyl violet revealed marked losses of neuronal layers in the pyramidal CA1 and CA3 subfields, but not in the granular dentate gyrus, within 6 weeks after administration. Supershift analysis using antibodies against different Jun and Fos family members differentiated between AP1 DNA binding in hippocampal nuclear extracts obtained 2 and 18 h after the administration of KA. These results suggest that neuronal death may not always follow modulation of de novo synthesis of particular proteins through sustained potentiation of AP1 DNA binding which involves expression of different Jun and Fos family members in response to systemic administration of KA in murine hippocampus.