PubMed Health⌕ Search

Biomedical subjects

T Ohmori

Publications and source records attributed to T Ohmori.

At least 19 recordsLinked to original sources
PubMed2006

Alteration of T-cell receptor repertoires during thymic T-cell development.

The majority of thymocytes die in the thymus, whereas small populations of T cells that are able to specifically recognize an antigen are considered to survive. Although the thymic selection is thought to have a profound effect on T-cell receptor (TCR) repertoire, little is known how TCR repertoire is formed during the thymocyte developmental process. We examined TCRalpha- and beta-chain variable regions (TCRAV and TCRBV) repertoire in thymic T-cell subpopulations from mice bearing different major histocompatibility (MHC) haplotypes. In Balb/c mice, but not C57BL/6, remarkable alterations of the TCR repertoire were observed in mature T-cell subpopulations as previously reported. In contrast, there were no significant differences of TCRBV repertoire between DN3 (CD25(+)CD44(-)) and DN4 (CD25(-)CD44(-)), and between DN4 and DP. These results suggest that (1) TCR repertoire of mature T cells was formed mainly under the influence of endogenous superantigens, while MHC haplotypes played the least role; (2) the 'beta-selection' process during immature stages had little impact on TCRBV repertoire formation; and (3) TCR repertoire in immature T-cell subpopulations was extremely similar between different strains of mice. We thus consider that pre-selection TCR repertoire in immature T cells could be determined by some genetic factors conserved among different strains.

Animals↗
PubMed2006

Aspirin resistance detected with aggregometry cannot be explained by cyclooxygenase activity: involvement of other signaling pathway(s) in cardiovascular events of aspirin-treated patients.

OBJECTIVES: Although the concept of aspirin resistance is extensively reported in medical literature, its precise mechanisms and clinical outcomes are largely unknown. In this study, we examined individual thromboxane biosynthesis and platelet aggregation in aspirin-treated patients, and whether the results of a platelet aggregation test influenced clinical outcomes. RESULTS: Subjects taking 81 mg of aspirin (n = 50) and controls (n = 38) were evaluated for platelet aggregation and platelet cyclooxygenase-1 (COX-1) activity by measuring collagen-induced thromboxane B2 production. For aggregometry, both light transmission (LT) and laser-light scattering methods were employed to quantitatively evaluate aggregate sizes and numbers. Aspirin treatment resulted in the inhibition of collagen-induced platelet aggregation, particularly the transition from small to large platelet aggregates. Although platelet COX-1 activity seemed to be uniformly inhibited in all patients, platelet aggregation studies showed great inter-individual differences; variation in platelet COX-1 activity only accounted for 6-20% of the individual aggregations. Factor analysis revealed the existence of a common factor (other than platelet COX-1) that explained 48.4% of the variations in platelet aggregation induced by collagen, adenosine diphosphate (ADP), and collagen-related peptide. We then prospectively enrolled 136 aspirin-treated patients in our study, and we found that being in the upper quartile level of LT, or with large aggregate formation induced by collagen, was an independent risk factor for developing cardiovascular events within 12 months [hazard ratio (HR) = 7.98, P = 0.008 for LT; HR = 7.76, P = 0.007 for large aggregates]. On the other hand, the existence of diabetes mellitus was an independent risk factor for overall outcomes (HR 1.30-11.9, P = 0.015-0.033). CONCLUSIONS: Aspirin resistance expressed as unsuppressed platelet COX-1 activity is a rare condition in an out-patient population. Other factor(s) affecting collagen-induced platelet aggregation may influence early outcomes in aspirin-treated patients.

Aged↗
PubMed2005

Altered expression of topoisomerase IIalpha contributes to cross-resistant to etoposide K562/MX2 cell line by aberrant methylation.

KRN 8602 (MX2) is a novel morpholino anthracycline derivative having the chemical structure 3'-deamino-3'-morpholino-13-deoxo-10-hydroxycarminomycin hydrochloride. To investigate the mechanisms of resistance to MX2, we established an MX2-resistant phenotype (K562/MX2) of the human myelogeneous leukaemia cell line (K562/P), by continuously exposing a suspension culture to increasing concentrations of MX2. K562/MX2 cells were more resistant to MX2 than the parent cells, and also showed cross-resistance to etoposide and doxorubicin. Topoisomerase (Topo) IIalpha protein levels in K562/MX2 cells were lower of those in K562/P cells on immunoblot analysis and decreased expression of Topo IIalpha mRNA was seen in K562/MX2 cells. Topoisomerase II catalytic activity was also reduced in the nuclear extracts from K562/MX2 cells when compared with K562/P cells. Aberrant methylated CpG of Topo IIalpha gene was observed in K562/MX2 cells when compared with the parent line on methylation-specific restriction enzyme analysis. To overcome the drug resistance to MX2 and etoposide, we investigated treatment with 5-Aza-2'-deoxycytidine (5AZ), which is a demethylating agent, in K562/MX2 cells. 5-Aza-2'-deoxycytidine treatment increased Topo IIalpha mRNA expression in K562/MX2 cells, but not in K562/P cells, and increased the cytotoxicity of MX2 and etoposide. Methylated CpG was decreased in K562/MX2 cells after 5AZ treatment. We concluded that the mechanism of drug resistance to MX2 and etoposide in K562/MX2 cells might be the combination of decreased expression of Topo IIalpha gene and increased methylation, and that 5AZ could prove to be a novel treatment for etoposide-resistant cell lines, such as K562/MX2.

Antigens, Neoplasm↗
PubMed2005

Relation between estradiol and negative symptoms in men with schizophrenia.

The authors tested the hypothesis that estradiol would be associated with negative symptoms in 30 male schizophrenia inpatients. Medications were switched from typical to atypical antipsychotics. Estradiol concentrations were inversely correlated with negative symptoms significantly before the switch and at a trend level of significance after the switch. Changes in negative symptoms were positively correlated with those in estradiol concentrations at a trend level of significance. Estradiol could be a biological marker for negative symptoms even in male schizophrenia patients.

Adult↗
PubMed2004

The intracellular action of sphingosine 1-phosphate in GPVI-mediated Ca2+ mobilization in platelets.

We analyzed the intracellular action of sphingosine 1-phosphate (Sph-1-P), formed from sphingosine (Sph) by sphingosine kinase (SPHK), in platelets. When sphingosine kinase activity was inhibited by N,N-dimethylsphingosine (DMS), Ca2+ mobilization induced by convulxin, an agonist of the collagen receptor glycoprotein VI (GPVI), was moderately but specifically abolished; that induced via G protein-coupled receptors was not affected. Under the same conditions, however, tyrosine phosphorylation of Syk and phospholipase Cgamma2, which is essential for the GPVI-mediated signaling, was not inhibited. Sphingosine kinase activity of the platelet membrane fraction increased specifically upon stimulation with convulxin or collagen. Our results suggest that intracellular sphingosine 1-phosphate is related to Ca2+ mobilization in GPVI-mediated signaling pathways.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2001

The serotonin syndrome: investigation using the Japanese version of the Serotonin Syndrome Scale.

This preliminary study was performed to investigate the prevalence of the serotonin syndrome in a group of Japanese patients in a clinical setting and to test the reliability and value of the Serotonin Syndrome Scale (SSS) as an assessment tool in a Japanese-language version (JSSS). Twenty-three patients, all being treated with serotonin agonists, gave informed consent to participate. Only one patient fulfilled strict diagnostic criteria of the serotonin syndrome and none of the JSSS scores reached the cutoff point of the SSS. Cronbach's alpha coefficient for the JSSS was 0.56. All inter-rater reliability coefficients were in the excellent range, and the JSSS had a high stability over time. The mean dose of fluvoxamine in the subgroup with high scores on the JSSS was significantly larger than that in the subgroup with low scores and there was a positive but non-significant correlation between total JSSS scores and doses of fluvoxamine. This preliminary study indicates that (1) a full serotonin syndrome was a rare phenomenon in a group of Japanese patients in a clinical setting and (2) the JSSS is a simple and reliable scale for evaluating the serotonin syndrome.

Adult↗
PubMed2001

Wheat germ agglutinin-induced platelet activation via platelet endothelial cell adhesion molecule-1: involvement of rapid phospholipase C gamma 2 activation by Src family kinases.

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is a 130K transmembrane glycoprotein that belongs to the immunoglobulin gene superfamily and is expressed on the surface of hematological or vascular cells, including platelets and endothelial cells. Although the importance of this adhesion molecule in various cell-cell interactions is established, its function in platelets remains ill-defined. In the process of clarifying the mechanism by which the lectin wheat germ agglutinin (WGA) activates platelets, we unexpectedly discovered that PECAM-1 is involved in signal transduction pathways elicited by this N-acetyl-D-glucosamine (NAGlu)-reactive lectin. WGA, which is a very potent platelet stimulator, elicited a rapid surge in Syk and phospholipase C (PLC)-gamma 2 tyrosine phosphorylation and the resultant intracellular Ca(2+) mobilization; collagen, as reported, induced these responses, but in a much slower and weaker manner. WGA strongly induced tyrosine phosphorylation of a 130-140K protein, which was confirmed to be PECAM-1 by immunoprecipitation and immunodepletion studies. WGA-induced PECAM-1 tyrosine phosphorylation occurred rapidly, strongly and in a manner independent of platelet aggregation or cell-cell contact; these characteristics of PECAM-1 phosphorylation were not mimicked at all by receptor-mediated platelet agonists. In addition, WGA was found to associate with PECAM-1 itself, and anti-PECAM-1 antibody, as well as NAGlu, specifically inhibited WGA-induced platelet aggregation. In PECAM-1 immunoprecipitates, Src family tyrosine kinases existed, and a kinase activity was detected, which increased upon WGA stimulation. Furthermore, the Src family kinase inhibitor PP2 inhibited WGA-induced platelet aggregation, Ca(2+) mobilization, and PLC-gamma 2 tyrosine phosphorylation. Finally, WGA induced PECAM-1 tyrosine phosphorylation and cytoskeletal reorganization in vascular endothelial cells. Our results suggest that (i) PECAM-1 is involved in WGA-induced platelet activation, (ii) PECAM-1 clustering by WGA activates unique and strong platelet signaling pathways, leading to a rapid PLC activation via Src family kinases, and (iii) WGA is a useful tool for elucidating PECAM-1-mediated signaling with wide implications not confined to platelets.

Acetylglucosamine↗
PubMed2001

Involvement of Hic-5 in platelet activation: integrin alphaIIbbeta3-dependent tyrosine phosphorylation and association with proline-rich tyrosine kinase 2.

Hic-5 and paxillin, members of the LIM protein family, have been shown to be localized in focal adhesion and to have a role in integrin-mediated signalling. In the present study we examined the involvement of Hic-5 in human platelet activation: platelets express Hic-5 but not paxillin, whereas human umbilical-vein vascular endothelial cells and MEG-01 cells express mainly paxillin. When platelets were stimulated with thrombin, collagen or the stable thromboxane A(2) analogue U46619, Hic-5 was markedly tyrosine-phosphorylated, in a manner dependent on integrin alphaIIbbeta3-mediated aggregation. In addition, direct activation of protein kinase C with PMA resulted in tyrosine phosphorylation of Hic-5 only when platelets were fully aggregated with the exogenous addition of fibrinogen. Furthermore, PMA-induced Hic-5 tyrosine phosphorylation was also observed when platelets adhered to immobilized fibrinogen. In studies on immunoprecipitation and immunodepletion, Hic-5 seemed to associate with proline-rich tyrosine kinase 2 (Pyk2) but only marginally with focal adhesion kinase. When platelets were stimulated with thrombin, both Hic-5 and Pyk2 translocated to the cytoskeleton from the cytosol and membrane fractions in a manner dependent on alphaIIbbeta3-mediated aggregation. Finally, on stimulation with PMA, Hic-5, as well as Pyk2, translocated to the cell periphery, where a meshwork of actin filaments assembled after adhesion to immobilized fibrinogen. Our results suggest that Hic-5 might be important in platelet aggregation and adhesion, in a manner dependent on alphaIIbbeta3-mediated outside-in signalling, through association with Pyk2.

Blood Platelets↗
PubMed2001

Skeletal malformations caused by overexpression of Cbfa1 or its dominant negative form in chondrocytes.

During skeletogenesis, cartilage develops to either permanent cartilage that persists through life or transient cartilage that is eventually replaced by bone. However, the mechanism by which cartilage phenotype is specified remains unclarified. Core binding factor alpha1 (Cbfa1) is an essential transcription factor for osteoblast differentiation and bone formation and has the ability to stimulate chondrocyte maturation in vitro. To understand the roles of Cbfa1 in chondrocytes during skeletal development, we generated transgenic mice that overexpress Cbfa1 or a dominant negative (DN)-Cbfa1 in chondrocytes under the control of a type II collagen promoter/enhancer. Both types of transgenic mice displayed dwarfism and skeletal malformations, which, however, resulted from opposite cellular phenotypes. Cbfa1 overexpression caused acceleration of endochondral ossification due to precocious chondrocyte maturation, whereas overexpression of DN-Cbfa1 suppressed maturation and delayed endochondral ossification. In addition, Cbfa1 transgenic mice failed to form most of their joints and permanent cartilage entered the endochondral pathway, whereas most chondrocytes in DN-Cbfa1 transgenic mice retained a marker for permanent cartilage. These data show that temporally and spatially regulated expression of Cbfa1 in chondrocytes is required for skeletogenesis, including formation of joints, permanent cartilages, and endochondral bones.

Animals↗
PubMed2001

Rhodocytin induces platelet aggregation by interacting with glycoprotein Ia/IIa (GPIa/IIa, Integrin alpha 2beta 1). Involvement of GPIa/IIa-associated src and protein tyrosine phosphorylation.

Although glycoprotein Ia/IIa (GPIa/IIa, integrin alpha(2)beta(1)) has established its role as a collagen receptor, it remains unclear whether GPIa/IIa mediates activation signals. In this study, we show that rhodocytin, purified from the Calloselasma rhodostoma venom, induces platelet aggregation, which can be blocked by anti-GPIa monoclonal antibodies. Studies with rhodocytin-coupled beads and liposomes loaded with recombinant GPIa/IIa demonstrated that rhodocytin directly binds to GPIa/IIa independently of divalent cations. In vitro kinase assays and Western blotting of GPIa immunoprecipitates revealed that Src and Lyn constitutively associate with GPIa/IIa and that Src activity increases transiently after rhodocytin stimulation. Src specifically associates with p130 Crk-associated substrate (Cas) in a manner dependent upon Cas phosphorylation, suggesting that Src is responsible for Cas tyrosine phosphorylation. While all these phenomena occur early after rhodocytin stimulation in a cAMP-resistant manner, tyrosine phosphorylation of Syk and phospholipase Cgamma2, intracellular Ca(2+) mobilization, and platelet aggregation occur later in a cAMP-sensitive manner. Cytochalasin D, which interferes with actin polymerization and blocks receptor clustering, inhibits all the rhodocytin-mediated signals we examined in this study. We suggest that rhodocytin, by clustering GPIa/IIa, activates GPIa/IIa-associated Src, which then mediates downstream activation signals.

Animals↗
PubMed2001

Development of stratum intermedium and its role as a Sonic hedgehog-signaling structure during odontogenesis.

Stratum intermedium is a transient and subtle epithelial structure closely associated with inner dental epithelium in tooth germs. Little is known about its development and roles. To facilitate analysis, we used bovine tooth germs, predicting that they may contain a more conspicuous stratum intermedium. Indeed, early bell stage bovine tooth germs already displayed an obvious stratum intermedium with a typical multilayered organization and flanking the enamel knot. Strikingly, with further development, the cuspally located stratum intermedium underwent thinning and involution, whereas a multilayered stratum intermedium formed at successive sites along the cusp-to-cervix axis of odontogenesis. In situ hybridization and immunohistochemistry showed that stratum intermedium produces the signaling molecule Sonic hedgehog (Shh). Maximal Shh expression was invariably seen in its thickest multilayered portions. Shh was also produced by inner dental epithelium; expression was not constant but varied with development and cytodifferentiation of ameloblasts along the cusp-to-cervix axis. Interestingly, maximal Shh expression in inner dental epithelium did not coincide with that in stratum intermedium. Both stratum intermedium and inner dental epithelium expressed the Shh receptor Patched2 (Ptch2), an indication of autocrine signaling loops. Shh protein, but not RNA, was present in underlying dental mesenchyme, probably resulting from gradual diffusion from epithelial layers and reflecting paracrine loops of action. To analyze the regulation of Shh expression, epithelial and mesenchymal layers were separated and maintained in organ culture. Shh expression decreased over time, but was maintained in unoperated specimens. Our data show for the first time that stratum intermedium is a highly regulated and Shh-expressing structure. Given its dynamic and apparently interactive properties, stratum intermedium may help orchestrate progression of odontogenesis from cusp to cervix.

Animals↗
PubMed2001

Effect of low doses of L-NAME on methamphetamine-induced dopaminergic depletion in the rat striatum.

The toxic dose of methamphetamine (METH) (5 mg/kg, s.c., x4, 2 hr intervals) decreased contents of dopamine, dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in striatum, and decreased contents of serotonin (5-HT) in both striatum and nucleus accumbens. Administration of low doses of a non-selective endothelial and neuronal nitric oxide synthase (NOS) inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME) (5 and 10 mg/kg, i.p., x1) intensified the METH-induced decreases in contents of dopamine and its metabolites in striatum. NO substrate, L-arginine (500 mg/kg, i.p., x4) reversed these effects of L-NAME on the METH-neurotoxicity. L-NAME did not change the METH-induced hyperthermia. These findings, which are contrary to our previous study with a high dose of L-NAME, suggest that the inhibition of endothelial or neuronal NOS-mediated NO production by low doses of L-NAME enhanced the METH-induced neurotoxicity. The finding that L-NAME can have opposite effects on the METH-neurotoxicity according to the dosing is important, however, additional experiments should be performed to clarify which type of NOS is related to these effects.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2001

Sphingosine 1-phosphate: synthesis and release.

Sphingosine 1-phosphate (Sph-1-P) is a bioactive sphingolipid, acting both as an intracellular second messenger and extracellular mediator, in mammalian cells. In cell types where Sph-1-P acts as an intracellular messenger, stimulation-dependent synthesis of Sph-1-P, possibly resulting from sphingosine (Sph) kinase activation, is essential. Since this important kinase has recently been cloned, precise regulation of intracellular Sph-1-P synthesis will be clarified in the near future. As an intercellular mediator, elucidation of sources for extracellular Sph-1-P is important, in addition to identification of the cell surface receptors for this phospholipid. Blood platelets are very unique in that they store Sph-1-P abundantly (possibly due to the existence of highly active Sph kinase and a lack of Sph-1-P lyase) and release this bioactive lipid extracellularly upon stimulation. It is likely that platelets are an important source for extracellular Sph-1-P, especially for plasma and serum Sph-1-P. Platelet-derived Sph-1-P seems to play an important role in vascular biology.

Animals↗
PubMed2001

Comparison of oligosaccharides derived from salivary mucin of Japanese secretor and non-secretor individuals of blood group type-A.

Comparison of oligosaccharide components derived from salivary mucin was performed between secretor and non-secretor individuals. Salivary mucin was collected from four secretors and three non-secretors having blood group type-A. Compositional analysis showed that the contents of galactose and N-acetylglucosamine in the non-secretor were higher than those in the secretor. The O-linked oligosaccharides obtained by treatment with alkaline borohydride were separated by gel filtration using Sephadex G-50. The results indicated that the size of the type-A active oligosaccharides from the secretor was similar to or smaller than that of the non-secretor. Ion-exchange chromatography showed that the secretors had strong type-A activities in both the neutral and acidic fractions but the non-secretors showed type-A activity mainly in the neutral fraction. These results suggest that compositional differences in blood group substances exist between secretors and non-secretors.

ABO Blood-Group System↗