Involvement of protein kinase C and RhoA in protease-activated receptor 1-mediated F-actin reorganization and cell growth in rat cardiomyocytes.

Protease-activated receptor 1 (PAR1) that can be activated by serine proteinases such as thrombin has been demonstrated to contribute to the development of cardiac remodeling and hypertrophy after myocardial injury. Here, we investigated the mechanisms by which PAR1 leads to hypertrophic cardiomyocyte growth using cultured rat neonatal ventricular myocytes. PAR1 stimulation with thrombin (1 U/ml) or a synthetic agonist peptide (TFLLR-NH(2), 50 µM) for 48 h induced an increase in cell size and myofibril formation associated with BNP (brain natriuretic peptide) production. This actin reorganization assessed by fluorescein isothiocyanate (FITC)-conjugated phalloidin staining appeared at 1 h after PAR1 stimulation, and this response was reduced by a protein kinase C (PKC) inhibitor, chelerythrine, inhibitors of Rho (simvastatin) and Rho-associated kinase (ROCK) (Y-27632), but not by pertussis toxin (PTX). By Western blot analysis, translocation of PKCα or PKCε from the cytosol to membrane fractions was observed in cells stimulated with thrombin or TFLLR-NH(2) for 2 - 5 min. In addition, PAR1 stimulation for 3 - 5 min increased the level of active RhoA. Furthermore, inhibitors of PKC and ROCK and Rho abrogated PAR1-mediated increase in cell size. Depletion of PKCα or PKCε by specific small interfering RNA also suppressed both actin reorganization and cell growth. These results suggest that PAR1 stimulation of cardiomyocytes induces cell hypertrophy with actin cytoskeletal reorganization through activation of PKCα and PKCε isoforms and RhoA via PTX-insensitive G proteins.

Involvement of Protein Kinase C and RhoA in Protease-Activated Receptor 1-Mediated F-Actin Reorganization and Cell Growth in Rat Cardiomyocytes.

Protease-activated receptor 1 (PAR1) that can be activated by serine proteinases such as thrombin has been demonstrated to contribute to the development of cardiac remodeling and hypertrophy after myocardial injury. Here, we investigated the mechanisms by which PAR1 leads to hypertrophic cardiomyocyte growth using cultured rat neonatal ventricular myocytes. PAR1 stimulation with thrombin (1 U/ml) or a synthetic agonist peptide (TFLLR-NH2, 50 µM) for 48 h induced an increase in cell size and myofibril formation associated with BNP (brain natriuretic peptide) production. This actin reorganization assessed by fluorescein isothiocyanate (FITC)-conjugated phalloidin staining appeared at 1 h after PAR1 stimulation, and this response was reduced by a protein kinase C (PKC) inhibitor, chelerythrine, inhibitors of Rho (simvastatin) and Rho-associated kinase (ROCK) (Y-27632), but not by pertussis toxin (PTX). By Western blot analysis, translocation of PKCα or PKCε from the cytosol to membrane fractions was observed in cells stimulated with thrombin or TFLLR-NH2 for 2 - 5 min. In addition, PAR1 stimulation for 3 - 5 min increased the level of active RhoA. Furthermore, inhibitors of PKC and ROCK and Rho abrogated PAR1-mediated increase in cell size. Depletion of PKCα or PKCε by specific small interfering RNA also suppressed both actin reorganization and cell growth. These results suggest that PAR1 stimulation of cardiomyocytes induces cell hypertrophy with actin cytoskeletal reorganization through activation of PKCα and PKCε isoforms and RhoA via PTX-insensitive G proteins.

[Amyloid ß hypothesis in Alzheimer's disease and Cl--ATPase-Neuronal cell death via PI4KIIα inhibition and recovery agents].

In the brains of patients with Alzheimer's disease, a decrease in phosphatidylinositol phosphate (PIP) requiring Cl--ATPase activity was found. In cultured rat hippocampal neurons, pathophysiological concentrations of amyloid ß proteins (Aßs≤10 nM) lowered PIP levels and Cl--ATPase activity with an increase in intracellular Cl- concentrations, resulting in Cl--dependent enhancements in glutamate neurotoxicity and, ultimately, neuronal cell death. Pathophysiological concentrations of Aßs(0.1-10 nM) directly lowered phosphatidylinositol-4-kinase. Non-toxic peptide fragments of Aß, such as Ile-Gly-Leu, recovered Aß-induced inhibition of recombinant human phosphatidylinositol-4-kinase IIα (PI4KIIα) and the intrahippocampally administered Aß-induced degeneration of hippocampal neurons and impairment of spatial memory in mice. Agents with the potential to block these neurotoxic mechanisms of Aß were summarized herein as (1) Aß antagonists, (2) substrates of PI4K, (3) PI4K product, (4) PI4K activators, and (5) GABAc receptor stimulants.

Acetyl-Ile-Gly-Leu protects neurons from Abeta(1-42) induced toxicity in vitro and in V337M human tau-expressing mice.

AIMS: We previously reported that the neurotoxicity of amyloid beta protein (Abeta(1-42), 10 nM) was blocked by an Abeta-derived tripeptide, Abeta(32-34) (Ile-Gly-Leu, IGL), suggesting that IGL may be a lead compound in the design of Abeta antagonists. In the present study, three stable forms of IGL peptide with acetylation of its N-terminal and/or amidation of its C-terminal (acetyl-IGL, IGL-NH(2) and acetyl-IGL-NH(2)) were synthesized and examined for their effects on Abeta-induced neurotoxicity. MAIN METHODS: Phosphatidylinositol 4-kinase type II (PI4KII) activity was measured using recombinant human PI4KIIalpha kinase and cell viability was assessed in primary cultured hippocampal neurons. To test effects in vivo, 1.5 microl of 100 nM Abeta and/or 100 nM acetyl-IGL was injected into the hippocampal CA1 region of right hemisphere in transgenic mice expressing V337M human tau protein. Four weeks later, behavior performance in the Morris water maze was tested and after another 2 weeks, sections of brain were prepared for immunohistochemistry. KEY FINDINGS: Among the three modified tripeptides, acetyl-IGL attenuated the Abeta-induced inhibition of PI4KII activity as well as enhancement of glutamate neurotoxicity in primary cultured rat hippocampal neurons. Injection of Abeta into the hippocampus of mice impaired spatial memory and increased the number of degenerating neurons in bilateral hippocampal regions. Co-injection of acetyl-IGL prevented the learning impairment as well as the neuronal degeneration induced by Abeta. SIGNIFICANCE: These results suggest that a modified tripeptide, acetyl-IGL, may be effective in the treatment of Alzheimer's disease.

Anti-prolactin (PRL) autoantibodies suppress PRL bioactivity in patients with macroprolactinaemia.

OBJECTIVE: Macroprolactinaemia, mainly caused by anti-prolactin (PRL) autoantibodies, is frequently found in patients with hyperprolactinaemia. Characteristically, these patients lack clinical symptoms of hyperprolactinaemia, but the serum bioactive PRL concentrations in vitro measured by the Nb2 bioassay are usually high. In this study, we investigated the causes of the discrepancy and the true biological features of macroprolactin. SUBJECTS AND METHODS: Sixteen patients with macroprolactinaemia due to anti-PRL autoantibodies were studied. PRL bioactivity was determined by the phosphorylation of signal transducer and activator of transcription (Stat)5 in T47D human breast cancer cells and the proliferation of Nb2 rat lymphoma cells. RESULTS: PRL bioactivity by the T47D bioassay, expressed as the density of the band of phosphorylated Stat5/immunoreactive PRL, was significantly lower in sera containing anti-PRL autoantibodies (2.4 +/- 1.1) than in control sera (7.2 +/- 3.1). Dissociation of PRL from the autoantibodies by acidification resulted in an increase in phosphorylated Stat5. PRL bioactivity by the Nb2 bioassay was not significantly different between sera with and without anti-PRL autoantibodies, and free PRL in the medium gradually increased during the incubation in a time-dependent manner in sera containing anti-PRL autoantibodies. CONCLUSIONS: We conclude that the level of bioactivity of macroprolactin in the Nb2 bioassay is normal due to dissociation of PRL from the autoantibodies as a result of the longer incubation and more dilute assay conditions than in the T47D bioassay. The bioactivity of macroprolactin is low in vivo due to anti-PRL autoantibodies, but monomeric PRL dissociated from the autoantibodies retains full biological activity in patients with macroprolactinaemia.

Development of anti-PRL (prolactin) autoantibodies by homologous PRL in rats: a model for macroprolactinemia.

Macroprolactinemia is hyperprolactinemia in humans mainly due to anti-PRL (prolactin) autoantibodies and is a pitfall for the differential diagnosis of hyperprolactinemia. Despite its high prevalence, the pathogenesis remains unclear. In this study, we examined whether anti-PRL autoantibodies develop via immunization with homologous rat pituitary PRL in rats to elucidate what mechanisms are involved and whether they cause hyperprolactinemia with low PRL bioactivity, as seen in human macroprolactinemia. Anti-PRL antibodies were developed in 19 of 20 rats immunized with homologous rat pituitary PRL and 29 of 30 rats with heterogeneous bovine or porcine pituitary PRL but did not develop in 25 control rats. In rats with anti-PRL antibodies, the basal serum PRL levels were elevated, and a provocative test for PRL secretion using dopamine D2 receptor antagonist (metoclopramide) showed a normal rising response with a slower clearance of PRL because of the accumulation of macroprolactin in blood. Antibodies developed by porcine or rat pituitary PRL reduced the bioactivity of rat serum PRL, and gonadal functions in these rats were normal despite hyperprolactinemia. Anti-PRL antibodies were stable and persisted for at least 5 wk after the final injection of PRL. These findings suggest that pituitary PRL, even if homologous, has antigenicity, leading to the development of anti-PRL autoantibodies. We successfully produced an animal model of human macroprolactinemia, with which we can explain the mechanisms of its clinical characteristics, i.e. asymptomatic hyperprolactinemia.

Proteinase-activated receptor 4 stimulation-induced epithelial-mesenchymal transition in alveolar epithelial cells.

BACKGROUND: Proteinase-activated receptors (PARs; PAR1-4) that can be activated by serine proteinases such as thrombin and neutrophil catepsin G are known to contribute to the pathogenesis of various pulmonary diseases including fibrosis. Among these PARs, especially PAR4, a newly identified subtype, is highly expressed in the lung. Here, we examined whether PAR4 stimulation plays a role in the formation of fibrotic response in the lung, through alveolar epithelial-mesenchymal transition (EMT) which contributes to the increase in myofibroblast population. METHODS: EMT was assessed by measuring the changes in each specific cell markers, E-cadherin for epithelial cell, alpha-smooth muscle actin (alpha-SMA) for myofibroblast, using primary cultured mouse alveolar epithelial cells and human lung carcinoma-derived alveolar epithelial cell line (A549 cells). RESULTS: Stimulation of PAR with thrombin (1 U/ml) or a synthetic PAR4 agonist peptide (AYPGKF-NH2, 100 muM) for 72 h induced morphological changes from cobblestone-like structure to elongated shape in primary cultured alveolar epithelial cells and A549 cells. In immunocytochemical analyses of these cells, such PAR4 stimulation decreased E-cadherin-like immunoreactivity and increased alpha-SMA-like immunoreactivity, as observed with a typical EMT-inducer, tumor growth factor-beta (TGF-beta). Western blot analyses of PAR4-stimulated A549 cells also showed similar changes in expression of these EMT-related marker proteins. Such PAR4-mediated changes were attenuated by inhibitors of epidermal growth factor receptor (EGFR) kinase and Src. PAR4-mediated morphological changes in primary cultured alveolar epithelial cells were reduced in the presence of these inhibitors. PAR4 stimulation increased tyrosine phosphorylated EGFR or tyrosine phosphorylated Src level in A549 cells, and the former response being inhibited by Src inhibitor. CONCLUSION: PAR4 stimulation of alveolar epithelial cells induced epithelial-mesenchymal transition (EMT) as monitored by cell shapes, and epithelial or myofibroblast marker at least partly through EGFR transactivation via receptor-linked Src activation.

Down-regulation of Cl- pump ClP55 subunit induced enhancement of glutamate neurotoxicity in cultured rat hippocampal neurons.

To test whether the increased intracellular Cl- concentration ([Cl-]i) is responsible for the enhanced glutamate toxicity, antisense oligonucleotide of ClP55, a Cl- -ATPase/pump associated protein, was transfected in cultured rat hippocampal neurons. Neuronal [Cl-]i in the antisense oligonucleotide-transfected culture increased to a level 3- to 4-fold higher than that in control. Glutamate exposure (10 microM, 10 min) increased neuronal apoptosis and decreased Akt-pS473 level in the antisense oligonucleotide-transfected neurons, but not in control or sense oligonucleotide-transfected ones, suggesting the responsibility of elevated [Cl-]i in the enhancement of glutamate neurotoxicity.

Protective effects of Abeta-derived tripeptide, Abeta(32-34), on Abeta(1-42)-induced phosphatidylinositol 4-kinase inhibition and neurotoxicity.

We previously reported that the neurotoxicity of pathophysiological concentrations of amyloid beta proteins (Abetas, 0.1-10nM) as assessed by the inhibition of type II phosphatidylinositol 4-kinase (PI4KII) activity and the enhancement of glutamate toxicity was blocked by a short fragment of Abeta, Abeta(31-35). Such protective effects of shorter fragments derived from Abeta(31-35) were examined in this study to reach the shortest effective peptide, using recombinant human PI4KII and primary cultured rat hippocampal neurons. Among the peptides tested (Abeta(31-34), Abeta(31-33), Abeta(31-32), Abeta(32-35), Abeta(33-35), Abeta(34-35), Abeta(32-34), Abeta(33-34) and Abeta(32-33)), Abeta(31-34), Abeta(32-35) and Abeta(32-34) blocked both the Abeta(1-42)-induced inhibition of PI4KII activity and enhancement of glutamate toxicity on cell viability. The shortest peptide among them, Abeta(32-34), showed a dose-dependent protective effect with 50% effective concentration near 1nM, while Abeta(34-32), with a reverse amino acid sequence for Abeta(32-34), showed no protective effects. Thus, a tripeptide, Abeta(32-34) i.e. Ile-Gly-Leu, may be available as a lead compound for designing effective Abeta antagonists.

Protease-activated receptor 4-mediated Ca2+ signaling in mouse lung alveolar epithelial cells.

Protease-activated receptor (PAR)-4 is a recently identified low-affinity thrombin receptor that plays a pathophysiological role in many types of tissues including the lung. Here, we showed for the first time that PAR4 mRNA and protein are expressed on primary cultured mouse lung alveolar epithelial cells by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemical analyses. In a fura 2-AM-loaded single epithelial cell, stimulation with thrombin (1 U/ml) and a PAR4 agonist peptide (AYPGKF-NH(2), 1-100 microM) increased intracellular Ca(2+) concentration ([Ca(2+)](i)), which consisted of an initial peak phase followed by a slowly decaying delayed phase, while a PAR1 agonist peptide, TFLLR-NH(2) (1-100 microM), induced a transient increase in [Ca(2+)](i). AYPGKF-NH(2) (10 microM)-induced [Ca(2+)](i) response was attenuated by a PAR4 antagonist peptide (tcY-NH(2)), a phospholipase C inhibitor, U-73122 (1-10 microM) or a Ca(2+)-ATPase inhibitor, thapsigargin (1 microM). Removal of extracellular Ca(2+) or an inhibitor of store-operated Ca(2+) entry, trans-resveratrol (1 microM) shortened the time to shut off the Ca(2+) response without any significant effects on the magnitude of the peak [Ca(2+)](i). Thus, stimulation of PAR4 appeared to mobilize Ca(2+) from intracellular stores in the initial peak response and to enhance Ca(2+) entry through the store depletion-operated pathway in the delayed phase. The latter mechanism probably contributed to the longer responsiveness of PAR4 stimulation.

Soybean-derived phosphatidylinositol inhibits in vivo low concentrations of amyloid beta protein-induced degeneration of hippocampal neurons in V337M human tau-expressing mice.

In our previous reports using primary cultured rat hippocampal neurons, pathophysiological concentrations (< or =10 nM) of amyloid beta proteins (Abetas) showed neurotoxicity via a phosphatidylinositol metabolism disorder, and soybean-derived phosphatidylinositol protected the neurons against the Abeta's neurotoxicity. In the present study, such a neurotoxic effect of Abeta and a neuroprotective effect of phosphatidylinositol were examined in vivo using transgenic mice expressing V337 M human tau. Intrahippocampal CA1 injection of 1.5 mul of 100 nM or 1 microM Abeta25-35 increased the number of degenerating neurons with an apoptotic feature in bilateral hippocampal CA1, CA2, CA3 and dentate gyrus regions in 1 month, demonstrating an in vivo neurotoxic effect of Abeta at lower concentrations after diffusion. Intrahippocampal co-injection or intracerebroventricular administration of 1.5 microl of 500 nM phosphatidylinositol prevented the Abeta25-35-induced neuronal degeneration in all the hippocampal regions, while co-injection of another acidic phospholipid, phosphatidylserine (1.5 microl, 500 nM) with Abeta25-35 showed no protective effects. Thus, exogenously applied phosphatidylinositol appeared to minimize the toxic effects of Abeta in vivo. These results suggest that soybean-derived phosphatidylinositol may be effective in the treatment of Alzheimer's disease.

Gamma-aminobutyric acid (GABA)-C receptor stimulation increases prolactin (PRL) secretion in cultured rat anterior pituitary cells.

Gamma-aminobutyric acid (GABA) reportedly inhibits secretion of anterior pituitary hormones by directly acting on GABA-A and GABA-B receptors on anterior pituitary cells, but the roles of GABA-C receptors are little known. In this study, involvement of GABA-C receptors in the secretion of prolactin (PRL) was examined using cultured rat anterior pituitary cells. GABA-C receptor agonist, cis-4-aminocrotonic acid (CACA, 0.1-1 mM) increased PRL secretion dose-dependently, while GABA-A receptor agonist, 100 microM muscimol, but not GABA-B receptor agonist, 100 microM baclofen, decreased the secretion. GABA-C receptor antagonist, 15 microM (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA), and GABA-A receptor antagonist, 100 microM bicuculline, not only reversed such an agonist-induced increase or decrease in PRL secretion, but also suppressed or enhanced spontaneous PRL secretion, raising a possibility of GABA-C or GABA-A receptor stimulation by intrinsic pituitary-derived GABA. GABA-C receptor subunits (rho1, rho2, rho3) and GABA synthesizing enzymes (GAD 65 and GAD 67) were shown to be expressed as assayed by RT-PCR, and GABA-C receptor stimulation by CACA obviously increased intracellular Ca2+ concentration in the anterior pituitary cells. Thus, PRL secretion from anterior pituitary cells appears to be enhanced via direct GABA-C receptor stimulation by GABA originating from the anterior pituitary cells besides well-known hypothalamic GABA.

Involvement of Rho signaling in PAR2-mediated regulation of neutrophil adhesion to lung epithelial cells.

Protease-activated receptor 2 (PAR2) has been implicated in the pathogenesis of airway inflammation. We report that epithelial PAR2 stimulation with trypsin (0.05-1 U/ml) or an agonist peptide (SLIGKV-NH2, 1-100 microM) for 0.5-3 h dose- and time-dependently enhanced neutrophil adhesion to alveolar type II epithelial cells (A549 cells) and that this stimulation also induced the formation of epithelial actin filaments. Both responses in neutrophil adhesion and epithelial actin reorganization were reduced by a Rho inhibitor, mevastatin and by a Rho-associated kinase (ROCK) inhibitor, Y-27632 ((R)-(+)-trans-N-(4-Pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide). Neutrophil adherence was also inhibited by an inhibitor of actin polymerization, cytochalasin D and a tyrosine kinase inhibitor, genistein. Further, the PAR2-mediated tyrosine phosphorylation of focal adhesion kinase (FAK), a major cytoskeleton protein, was detected, and this response was inhibited by mevastatin or Y-27632. These results suggest that PAR2 stimulation of alveolar epithelial cells enhances neutrophil adhesion presumably at least in part through Rho/ROCK signal-mediated actin cytoskeleton reorganization associated with the tyrosine phosphorylation of FAK.

Attenuation of amyloid beta (Abeta)-induced inhibition of phosphatidylinositol 4-kinase activity by Abeta fragments, Abeta20-29 and Abeta31-35.

We previously reported that pathophysiological concentrations of amyloid beta protein (Abeta25-35, 0.1-10 nM) directly inhibited type II phosphatidylinositol 4-kinase (PI4KII) activity in neuronal plasma membranes, which resulted in the enhanced glutamate neurotoxicity. In the present study, we examined the effects of Abeta fragments, Abeta20-29 and Abeta31-35, on the 10 nM Abeta25-35- or Abeta1-42-induced inhibition of PI4KII activity. Both of the peptide fragments recovered the inhibition of rat brain plasma membrane PI4KII activity over the concentration range of 0.1-5 nM. Such protection by the Abeta fragments was observed in the 10 nM Abeta25-35-induced inhibition of recombinant human PI4KII, suggesting that these Abeta fragments blocked the inhibition on PI4KII molecule. The Abeta25-35-induced enhancement of glutamate neurotoxicity was also completely inhibited in the presence of these fragments. Thus, Abeta20-29 and Abeta31-35 ameliorated the Abeta-enhanced glutamate neurotoxicity probably through attenuation of Abeta-induced inhibition of PI4KII activity.

Chloride-dependency of amyloid beta protein-induced enhancement of glutamate neurotoxicity in cultured rat hippocampal neurons.

In our previous studies, pathophysiological concentrations of amyloid-beta (Abeta) proteins increased intracellular Cl(-) concentration ([Cl(-)]i) and enhanced glutamate neurotoxicity in primary cultured neurons, suggesting Cl(-)-dependent changes in glutamate signaling. To test this possibility, we examined the effects of isethionate-replaced low Cl(-) medium on the Abeta-induced enhancement of glutamate neurotoxicity in the primary cultured rat hippocampal neurons. In a normal Cl(-) (135 mM) medium, treatment with 10 nM Abeta25-35 for 2 days increased neuronal [Cl(-)]i to a level three times higher than that of control as assayed using a Cl(-)-sensitive fluorescent dye, while in a low Cl(-) (16 mM) medium such an Abeta25-35-induced increase in [Cl(-)]i was not observed. The Abeta treatment aggravated glutamate neurotoxicity in a normal Cl(-) medium as measured by mitochondrial reducing activity and lactate dehydrogenase (LDH) release, while in a low Cl(-) medium the Abeta treatment did not enhance glutamate toxicity. Upon such Abeta plus glutamate treatment under a normal Cl(-) condition, activated anti-apoptotic molecule Akt (Akt-pS473) level monitored by Western blot significantly decreased to 74% of control. Under a low Cl(-) condition, a resting Akt-pS473 level was higher than that under a normal Cl(-) condition and did not significantly change upon Abeta plus glutamate treatment. Tyrosine phosphorylation levels of 110 and 60 kDa proteins (pp110 and pp60) increased upon Abeta plus glutamate treatment under a normal Cl(-), but not low Cl(-), condition. These findings indicated that Abeta-induced enhancement of glutamate neurotoxicity is Cl(-)-dependent. Chloride-sensitive Akt pathway and tyrosine phosphorylation of proteins (pp110 and pp60) may be involved in this process.

Immunoglobulin G subclasses and prolactin (PRL) isoforms in macroprolactinemia due to anti-PRL autoantibodies.

Although macroprolactinemia due to antiprolactin (anti-PRL) autoantibodies is not uncommon among hyperprolactinemic patients, the pathogenesis of such macroprolactinemia is still unknown. We examined IgG subclasses of anti-PRL autoantibodies by enzyme immunoassay, and PRL phosphorylation and isoforms by Western blotting, mass spectrometry, and two-dimensional electrophoresis in six patients with anti-PRL autoantibodies and in 29 controls. PRL-specific IgG subclasses in patients with anti-PRL autoantibodies were heterogeneous, but five of six patients showed IgG4 predominance, which is known to be produced by chronic antigen stimulation. Western blot and mass spectrometric analyses revealed that human pituitary PRL was phosphorylated at serine 194 and serine 163, whereas serine 163 in serum PRL was dephosphorylated. On two-dimensional electrophoresis, serum PRL mainly consisted of isoform with isoelectric point (pI) 6.58 in control hyperprolactinemic patients, whereas acidic isoforms (pIs 6.43 and 6.29) were also observed in patients with anti-PRL autoantibodies. Our data first demonstrate that human pituitary PRL is serine phosphorylated and partially dephosphorylated in serum, and suggest that the acidic isoforms may give rise to chronic antigen stimulation in patients with anti-PRL autoantibodies.

Anxiolytic agent, dihydrohonokiol-B, recovers amyloid beta protein-induced neurotoxicity in cultured rat hippocampal neurons.

The effects of anxiolytic honokiol derivative, dihydrohonokiol-B (DHH-B), on amyloid beta protein (Abeta(25-35), 10 nM)-induced changes in Cl(-)-ATPase activity, intracellular Cl- concentration ([Cl-]i) and glutamate neurotoxicity were examined in cultured rat hippocampal neurons. DHH-B (10 ng/ml) recovered Abeta-induced decrease in neuronal Cl(-)-ATPase activity without any changes in the activities of Na+/K+-ATPase and anion-insensitive Mg2+-ATPase. A GABA(C) receptor antagonist (1,2,5,6,-tetrahydropyridin-4-yl) methyl-phosphinic acid (TPMPA, 15 microM), inhibited the protective effects of DHH-B on Cl(-)-ATPase activity. DHH-B reduced Abeta-induced elevation of [Cl-]i as assayed using a Cl(-)-sensitive fluorescent dye, and prevented Abeta-induced aggravation of glutamate neurotoxicity. These data suggest that DHH-B exerts the neuroprotective action against Abeta through GABA(C) receptor stimulation.

Regulation of the expression of lysyl oxidase mRNA in cultured rabbit retinal pigment epithelium cells.

Lysyl oxidase, an extracellular amine oxidase, controls the maturation of collagen and elastin. We examined the regulation of lysyl oxidase mRNA in cultured rabbit retinal pigment epithelium (RPE) cells in relation to the changes in subretinal fluid transport and phenotype of RPE cells. The level of the mRNA in cells grown on microporous membranes was markedly increased by application of hyperosmotic mannitol solution on the apical side (191% of control), implying that RPE cells express more lysyl oxidase in the condition which may cause the accumulation of subretinal fluid. Platelet-derived growth factor increased the mRNA level in subconfluent cells in culture (137% of control) and basic fibroblast growth factor decreased it (79% of control). In addition, exposure of cells to retinoic acid alone or in combination with dibutyryl cAMP for 22 days markedly decreased the level of lysyl oxidase mRNA (52 or 35% of control) while increasing the level of mRNA of N-acetylglucosaminidase (NAG), a marker enzyme for lysosomes (162 or 142% of control). Moreover, the level of lysyl oxidase mRNA in cells grown on microporous membranes was lower than that in cells grown on plastic dishes, while the level of NAG mRNA in the former cells was higher than that in the latter. Taken together, the expression of lysyl oxidase seemed to increase during proliferation of RPE cells and decrease toward differentiation. beta-Aminopropionitrile, an inhibitor of lysyl oxidase, significantly inhibited the contraction of collagen gels by fetal calf serum, suggesting that lysyl oxidase may be involved in pathogenesis caused by RPE cells.

Single cell RT-PCR demonstrates differential expression of GABAC receptor rho subunits in rat hippocampal pyramidal and granule cells.

Although gamma-aminobutyric acid (GABA)C receptor rho1, rho2 and rho3 subunits are reportedly expressed in pyramidal and granule cells in the hippocampus at various developmental stages, it is not clear whether these three rho subunits are coexpressed in a single neuron. To attempt to answer this question, we performed single-cell RT-PCR for rho subunits from neurons of rat brain hippocampus. In hippocampal cultures, pyramidal cells were positive for rho1 mRNA expression in 89%, rho2 in 94% and rho3 in 94%, while granule cells were positive for rho1 mRNA in only 6%, rho2 in 36% and rho3 in 91%. Intensive amplification of the RT-PCR products by the second PCR revealed that all the three rho subunits were coexpressed in a single pyramidal and granule cells from both of the cultures and the slices. These results suggest that all the three GABAC receptor rho1, rho2 and rho3 subunits are present probably in different compositions in pyramidal and granule cells in the rat hippocampus.

Suppression of cell proliferation with induction of p21 by Cl(-) channel blockers in human leukemic cells.

The existence of Cl(-) channels in lymphocytes and neutrophils has been increasingly recognized, but the biological functions are not yet clear. We examined the effects of Cl(-) channel blockers on the cell proliferation and the cell cycle of human leukemic cell lines. The growth of leukemic cells was suppressed most efficiently by NPPB (5-nitro-2-(3-phenylpropylamino) benzoic acid), partially by 9-AC (9-anthracenecarboxylic acid) and tamoxifen, but not by stilbene compounds. NPPB increased the G0/G1 population and induced the expression of p21, one of the critical molecules for G1/S checkpoint. Antisense oligonucleotide for a NPPB-sensitive and stilbene-insensitive Cl(-) channel, ClC-2, sufficiently suppressed the ClC-2 protein synthesis, but did not affect the growth of leukemic cells. These findings suggest that NPPB-sensitive and stilbene-insensitive Cl(-) channels other than ClC-2 play important roles in cell cycles and cell proliferation of human leukemic cells.