T Imamura

Osaka City University, Ōsaka, Ōsaka, Japan

Are you T Imamura?

Claim your profile

Publications (17)95.8 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The observations that atherosclerosis often occurs in non-smokers without elevated levels of low-density lipoprotein cholesterol, and that most atherosclerosis loci so far identified in mice do not affect systemic risk factors associated with atherosclerosis, suggest that as-yet-unidentified mechanisms must contribute to vascular disease. Arterial walls undergo regional disturbances of metabolism that include the uncoupling of respiration and oxidative phosphorylation, a process that occurs to some extent in all cells and may be characteristic of blood vessels being predisposed to the development of atherosclerosis. To test the hypothesis that inefficient metabolism in blood vessels promotes vascular disease, we generated mice with doxycycline-inducible expression of uncoupling protein-1 (UCP1) in the artery wall. Here we show that UCP1 expression in aortic smooth muscle cells causes hypertension and increases dietary atherosclerosis without affecting cholesterol levels. UCP1 expression also increases superoxide production and decreases the availability of nitric oxide, evidence of oxidative stress. These results provide proof of principle that inefficient metabolism in blood vessels can cause vascular disease.
    Full-text · Article · Jun 2005 · Nature
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Although cortisone acetate is approved worldwide as corticosteroid substitution therapy in congenital adrenal hyperplasia (21-hydroxylase deficiency), its effectiveness is uncertain since its biologic activity depends on activation by 11β-hydroxysteroid dehydrogenase (11β-HSD). We sought to compare the effect of cortisone acetate with that of hydrocortisone. In 10 patients with congenital adrenal hyperplasia, cortisone acetate was replaced with hydrocortisone in substitution therapy. During this change, blood concentrations of 17-hydroxy-progesterone, adrenocorticotropin (ACTH), and requirements for each drug were monitored. Concentrations of 17-hydroxyprogesterone decreased (mean 10.1 vs. 48.6 ng/ml), as did those of ACTH. Cortisone acetate dose requirements averaged 33.9 mg/m(2), while hydrocortisone dose requirements averaged only 20.3 mg/m(2). In one of the patients resistant to cortisone acetate therapy, DNA sequences in the coding regions and promoter of the 11β-HSD gene were analyzed, detecting no genetic abnormalities. Cortisone acetate is inferior to hydrocortisone as substitution therapy in patients with congenital adrenal hyperplasia.
    Preview · Article · Jul 2004 · Clinical Pediatric Endocrinology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Pancreatitis is a common disease with substantial morbidity and mortality. To better understand the mechanisms conferring sensitivity or resistance to pancreatitis, we have initiated the analysis of novel acinar cell proteins. Integral membrane-associated protein-1 (Itmap1) is a CUB (complement subcomponents C1r/C1s, sea urchin Uegf protein, bone morphogenetic protein-1) and zona pellucida (ZP) domain-containing protein we find prominently expressed in pancreatic acinar cells. Within the acinar cell, Itmap1 localizes to zymogen granule membranes. Although roles in epithelial polarity, granule assembly, and mucosal protection have been postulated for CUB/ZP proteins, in vivo functions for these molecules have not been proven. To determine the function of Itmap1, we generated Itmap1-deficient mice. Itmap1(-/-) mice demonstrate increased severity of secretagogue- and diet-induced pancreatitis in comparison to Itmap1(+/+) mice. In contrast to previous animal models exhibiting altered severity of pancreatitis, Itmap1 deficiency results in impaired activation of trypsin, an enzyme believed critical for initiating a cascade of digestive zymogen activation during pancreatitis. Itmap1 deficiency does not alter zymogen granule size, appearance, or the composition of zymogen granule contents. Our results demonstrate that Itmap1 plays an essential role in trypsinogen activation and that both impaired and augmented trypsinogen activation can be associated with increased severity of pancreatitis.
    No preview · Article · Jan 2003 · Journal of Biological Chemistry
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Prostaglandins are essential for the initiation of parturition in mice. The peak in uterine prostaglandin F(2)(alpha) levels occurs at d 19.0 of gestation, just before the onset of labor. Our studies set out to determine the important regulatory step(s) involved in this increase of prostaglandin F(2)(alpha). We show that cytosolic phospholipase A(2) mRNA, protein, and activity do not significantly vary during mouse gestation. Rather, our studies demonstrate that cyclooxygenase-1 mRNA is abruptly induced at d 15.5 of gestation, but cyclooxygenase-1 protein levels only gradually increase throughout gestation. In contrast, cyclooxygenase-2 protein remains constant during gestation. We find that prostaglandin F synthase protein increases significantly during gestation reaching peak levels between d 15.5 and d 17.5 of gestation. We also find that the level of prostaglandin dehydrogenase, responsible for degradation of prostaglandins, decreases during late gestation. Taken together these results suggest that the regulation of prostaglandin F(2)(alpha) is a complex process involving the coordinate induction of synthetic enzymes along with a decrease in degradative enzymes involved in prostaglandin metabolism.
    Preview · Article · Aug 2002 · Endocrinology
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Galactokinase (GALK) deficiency is an autosomal recessive disorder characterized by hypergalactosemia and cataract formation. Through mass screening of newborn infants, we identified a novel and prevalent GALK variant (designated here as the “Osaka” variant) associated with an A198V mutation in three infants with mild GALK deficiency. GALK activity and the amount of immunoreactive protein in the mutant were both 20% of normal construct in expression analysis. The Km values for galactose and ATP-Mg2+ in erythrocytes with homozygous A198V were similar to those of the healthy adult control subjects. A population study for A198V revealed prevalences of 4.1% in Japanese and 2.8% in Koreans, lower incidence in Taiwanese and Chinese, no incidence in blacks and whites from the United States, and a significantly high frequency (7.8%; P<.023) in Japanese individuals with bilateral cataract. This variant probably originated in Japanese and Korean ancestors and is one of the genetic factors that causes cataract in elderly individuals.
    Full-text · Article · May 2001 · The American Journal of Human Genetics
  • T Imamura · C E Luedke · S K Vogt · L J Muglia
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent analysis of mice deficient in both oxytocin (OT) and cyclooxygenase-1 has shown that OT exerts significant effects on both the ovarian corpus luteum and the uterine myometrium during pregnancy. To better define the roles of OT during pregnancy, we evaluated OT action and OT receptor regulation in wild-type and OT-deficient knockout (KO) mice. Continuous infusion of OT revealed that OT can either delay labor at low doses or initiate preterm labor at high doses. The infusion rates of OT necessary for these effects were reduced in OT KO mice. The dose of OT that delayed labor also delayed the normal decrease in plasma progesterone late in gestation, implicating a primary effect on the corpus luteum. Consistent with this hypothesis, luteal OT receptor expression exceeded that of the myometrium until luteolysis occurred. We propose that the downregulation of OT receptors in the corpus luteum and induction of OT receptors in the myometrium serve to shift the predominant consequence of OT action during murine pregnancy from labor inhibition to labor promotion.
    No preview · Article · Oct 2000 · AJP Regulatory Integrative and Comparative Physiology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Prostaglandins (PGs) have proven important during parturition, but inhibition of PG production treating preterm labor (PTL) results in significant maternal and fetal side effects. We hypothesize that specific inhibition of either cyclooxygenase (COX)-1 or -2 may result in separation of therapeutic and toxic effects. We demonstrate that COX-2, but not COX-1, is induced during inflammation-mediated PTL caused by lipopolysaccharide (LPS) administration. A two- to threefold increase in uterine and ovarian PG concentrations coincides with this induction of COX-2. The COX-2-selective inhibitor SC-236 proved effective in stopping preterm delivery and the increases in PGs. The COX-1-selective inhibitor SC-560 also attenuated uterine and ovarian PG production after LPS but did not inhibit PTL as efficiently as SC-236. COX-1-deficient mice, which show delay in the onset of term labor, exhibited no delay in onset of PTL after LPS. These findings suggest that the mechanisms for initiation of inflammation-mediated PTL and term labor differ and that selective COX-2 inhibition may provide a means of stopping inflammation-induced PTL in humans.
    No preview · Article · Jul 2000 · AJP Regulatory Integrative and Comparative Physiology
  • G Gross · T Imamura · L J Muglia
    [Show abstract] [Hide abstract]
    ABSTRACT: To review recent studies of parturition control in mice with relevance to understanding the control of human parturition. Assimilation of published studies of gene knockout mice with mutations in neuropeptides, prostaglandin synthetic enzymes and receptors, and other molecules implicated in parturition. The central role of prostaglandins in murine labor is demonstrated by mice with gene mutations at multiple levels of the prostaglandin synthetic pathway. In addition, novel molecules such as steroid 5 alpha-reductase are found to play an essential role in the progression of labor. Surprisingly, deficiency of neuropeptides such as oxytocin and corticotropin-releasing hormone have little effect on parturition. Molecular genetic analyses in mice provide an efficient way to define molecules critical for murine parturition. Extrapolation of the importance of these molecules to human parturition provides the next challenge.
    No preview · Article · Mar 2000 · Journal of the Society for Gynecologic Investigation
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Galactokinase (GALK) deficiency is an autosomal recessive disorder, which causes cataract formation in children not maintained on a lactose-free diet. We characterized the human GALK gene by screening a Japanese genomic DNA phage library, and found that several nucleotides in the 5'-untranslated region and introns 1,2, and 5 in our GALK genomic analysis differed from published data. A 20-bp tandem repeat was found in three places in intron 5, which were considered insertion sequences. We identified five novel mutations in seven unrelated Japanese patients with GALK deficiency. There were three missense mutations and two deletions. All three missense mutations (R256W, T344M, and G349S) occurred at CpG dinucleotides, and the T344M and G349S mutations occurred in the conserved region. The three missense mutations led to a drastic reduction in GALK activity when individual mutant cDNAs were expressed in a mammalian cell system. These findings indicated that these missense mutations caused GALK deficiency. The two deletions, of 410delG and 509-510delGT, occurred at the nucleotide repeats GGGGGG and GTGTGT, respectively, and resulted in in-frame nonsense codons at amino acids 163 and 201. These mutations arose by slipped strand mispairing. All five mutations occurred at hot spots in the CpG dinucleotide for missense mutations and in short direct repeats for deletions. These five mutations in Japanese have not yet been identified in Caucasians. We speculate that the origin of GALK mutations in Japanese is different from that in Caucasians.
    Preview · Article · Feb 1999 · Journal of Human Genetics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We identified three mutations in four Japanese patients with central type 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. One missense mutation was a C-to-T transition, resulting in the substitution of Pro by Ser at codon 87 (P87S) in exon 5. Another missense mutation was a G-to-A transition, resulting in the substitution of Asp by Asn at codon 96 (D96N) in exon 5. A splicing mutation was found by skipping of exon 4 on PTPS mRNA analysis, and a G-to-A transition at the third base of codon 81 (E81E) and at the terminal base in exon 4 were detected on genomic PTPS DNA analysis. The E81E mutation affected the splice donor site of exon 4 and caused the splicing error. In COS cell expression analysis, the P87S and D96N mutant constructs revealed, respectively, 52% and 10% of wild-type activity. Patients with P87S/P87S (52%/52% in-vitro PTPS activity) exhibited 0.11 and 0 microU/g hemoglobin [Hb] in erythrocyte PTPS activity (wild-type control: 11-29 microU/gHb) erythrocyte PTPS activity, and the patient with P87S/D96N mutations (52%/10%) had 0.97 microU/gHb in PTPS erythrocyte activity. The PTPS erythrocyte activity did not coincide with the in-vitro PTPS activity based on patient genotype.
    Full-text · Article · Feb 1999 · Journal of Human Genetics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Prostaglandins (PGs) have been recently proven essential for parturition in mice. To dissect the contributions of the two cyclooxygenase (COX) isoforms to the synthesis of PGs during pregnancy, we have characterized the parturition phenotype of COX-1-deficient mice. We find that mice with targeted disruption of the COX-1 gene have delayed parturition resulting in neonatal death. Results of matings of COX-1-deficient females with COX-1 intact males, and blastocyst transfer of COX-1-deficient or -intact embryos into wild-type foster mothers, proved necessity and sufficiency of maternal COX-1 for the normal onset of labor. COX-1 expression is induced in gravid murine uterus and by in situ hybridization; this induction is localized to the decidua. Measurement of uterine PGs further confirmed that COX-1 accounted for the majority of PGF2alpha production. To evaluate the interaction of PGs with oxytocin during murine labor, we generated mice deficient in both oxytocin and COX-1. Surprisingly, the combined oxytocin and COX-1-deficient mice initiated labor at the normal time. COX-1-deficient mice demonstrated impaired luteolysis, as evidenced by elevated serum progesterone concentration and ovarian histology late in gestation, and delayed induction of uterine oxytocin receptors. In contrast, simultaneous oxytocin and COX-1 deficiency restored the normal onset of labor by allowing luteolysis in the absence of elevated PGF2alpha production. These findings demonstrate that COX-1 is essential for normal labor in the mouse, with a critical function being to overcome the luteotrophic action of oxytocin in late gestation.
    Preview · Article · Oct 1998 · Proceedings of the National Academy of Sciences
  • [Show abstract] [Hide abstract]
    ABSTRACT: CRP was determined for 110 cord bloods and peripheral blood of 36 newborns collected within 72 hours after delivery for the early diagnosis of newborn infection. The determination of CRP was done by a counting immunoassay method using PAMIA-30(Sysmex, Kobe, Japan). Sample volume needed was small and the time for determination was short. Within-run and between-run precisions were satisfactory, with CV values being approximately 6%. The CRP of healthy newborns was lower than that of cord blood, and the mean value was 33.4 +/- 4.2 ng/ml and the value was not significantly different from that obtained from the newborn babies with turbid amnionic fluid or early rupture of a sac. The CRP gradually increased after delivery had a peak at 24 to 48 hours after delivery. This tendency was observed both in healthy and infected newborns. The data were divided into 6 groups depending on the time collected after delivery (6, 12, 24, 48, and 72 hours). The CRP of blood from infected newborns tended to have higher CRP than that of healthy newborns in each group. Increased amount of CRP (ng/ml/hrs) was calculated as ((CRP of peripheral blood at time x)--(CRP of cord blood))/x, and this value was significantly higher (p < 0.05) in infected newborns than in healthy newborns 12hrs and more after delivery. Thus, CRP might be useful for monitoring the newborn infection.
    No preview · Article · Jul 1995 · Rinsho byori. The Japanese journal of clinical pathology
  • H Shintaku · K J Hsiao · T T Liu · T Imamura · Y Hase · R G Chen · G Isshiki · T Oura

    No preview · Article · Feb 1994 · Journal of Inherited Metabolic Disease

  • No preview · Article · Feb 1993 · Advances in Experimental Medicine and Biology
  • H Shintaku · T Nakajima · T Imamura · Y Sawada · G Isshiki · T Oura

    No preview · Article · Feb 1993 · Advances in Experimental Medicine and Biology

  • No preview · Article · Feb 1993 · Advances in Experimental Medicine and Biology

  • No preview · Article · Feb 1993 · Advances in Experimental Medicine and Biology