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Biomedical subjects

Y Kitamura

Publications and source records attributed to Y Kitamura.

At least 181 records · Page 10Linked to original sources
PubMed1999

Apoptotic cell death in neurons and glial cells: implications for Alzheimer's disease.

It is now generally accepted that massive neuronal death due to oxidative stress is a common characteristic of brains in neurodegenerative diseases. Recently, numerous apoptosis-regulating factors and multiple pathways have been identified, and apoptotic cell death has been implicated in neuronal loss in Alzheimer's disease. Although glial cells are more resistant to oxidative stress than neurons, extensive oxidative stress seems to cause apoptotic cell death in glial cells. In fact, signs of apoptosis are observed in both neurons and glial cells in the brains of patients with Alzheimer's disease. This review summarizes current findings regarding apoptotic processes and discusses the possible involvement of apoptosis-regulating factors in the pathology of Alzheimer's disease.

Alzheimer Disease↗
PubMed1999

Effects of glucose on lipase activity.

To establish the utility of lipase as a biocatalyst, the effects of glucose on the hydrolysis activities of lipase were investigated. Among 13 kinds of lipase from microorganisms, 6 lipases were inhibited in hydrolysis up to 50% of the original activities by 10 mM glucose. The activities of other microbial lipases and 2 kind of porcine pancreatic lipases were not affected by the addition of glucose. Six lipases that were sensitive to glucose were modified by a synthetic detergent. After they were converted to modified lipases, they were not inhibited by glucose. Even at 20 mM glucose, each modified lipase retained more than 95% activity compared with that in the absence of glucose. In the modified lipase, the detergent attached to the lipase molecule would disturb the access of glucose to the enzyme. To detect the interaction between lipase and glucose, the fluorescence of tryptophan was traced. The fluorescence intensities of lipases that were inhibited by glucose depended on the concentration of glucose, suggesting that glucose induced some structural change in the lipase molecule.

Animals↗
PubMed1999

Effects of angiotensin inhibitors on renal injury and angiotensin receptor expression in early hypertensive nephrosclerosis.

Angiotensin converting enzyme inhibitors (ACEI) are known to inhibit the progression of established renal failure. The aim of this study was to compare the efficacy of an ACEI and an AT1 receptor antagonist (AT1R-Ant) in preventing the development of renal disease, at an early stage of hypertensive nephrosclerosis. SHRSP/Izm rats (n = 61) were treated from 10 wk until 22 wk with the ACEI delapril (40 mg/kg/d) or the AT1R-Ant candesartan cilexetil (1 mg/kg/d). Proteinuria, and structural/ultrastructural changes were assessed at 14 and 22 wk. Treatment with either agent resulted in reductions in blood pressure and cardiovascular hypertrophy. Neither proteinuria nor major renal histological changes were evident at 14 wk. At 22 wk, however, proteinuria accompanied by nephrosclerotic changes was seen in the untreated SHRSP/Izm. Treatment with either ACEI or AT1R-Ant resulted in similar reductions in proteinuria (untreated, 32.2 +/- 7.4; delapril-treated, 5.5 +/- 1.2; candesartan-treated, 3.9 +/- 0.3 mg/100 g/d). Prominent sclerosis of small-to-medium sized renal arteries was seen in the untreated SHRSP/Izm at 22 wk, but was similarly attenuated by the ACEI and AT1R-Ant. The glomerular ultrastructure was comparable between the two groups. No significant changes in renal AT1a or AT1b receptor subtype mRNA expression were seen throughout the course of the study. In contrast, a decrease in AT2 receptor mRNA was seen in the drug-treated groups at 14 wk but not at 22 wk. These results suggest that both ACEI and AT1R-Ant have similar efficacy in attenuating the onset of renal injury in early hypertensive nephrosclerosis, and that treatment with either agent is associated with a transient decrease in AT2 receptor mRNA expression.

Angiotensin Receptor Antagonists↗
PubMed1999

Role of osteopontin in bone remodeling caused by mechanical stress.

Changes in the number and proportion of osteopontin mRNA (Opn) expressing osteocytes and osteoclasts caused by the mechanical stress applied during experimental tooth movement were examined in the present study. Opn expression was detected in the osteocytes on the pressure side at the early stage, and gradually spread to those on the tension side and also to the osteoblasts and bone-lining cells in the alveolar bone. Only 3.3% of the osteocytes located on the pressure side expressed Opn in the interradicular septum of control rats; in contrast, the value was increased to 87.5% at 48 h after the initiation of tooth movement. These results indicate that these cells responded to mechanical stress loaded on the bone with expression of the osteopontin gene. Following the increased expression of Opn in these cells, a 17-fold greater number of osteoclasts compared with the control and numerous resorption pits were observed on the pressure side of the alveolar bone. Injection of arginine-glycine-aspartic acid-serine peptide but not that of arginine-glycine-glutamic acid-serine peptide strongly inhibited the increase in the number of osteoclasts. Furthermore, an in vitro migration assay demonstrated the chemotactic activity of osteopontin (OPN) on the precursor of osteoclasts. Our study strongly suggests that OPN is an important factor triggering bone remodeling caused by mechanical stress.

Animals↗
PubMed1999

Mechanical tension-stress induces expression of bone morphogenetic protein (BMP)-2 and BMP-4, but not BMP-6, BMP-7, and GDF-5 mRNA, during distraction osteogenesis.

Bone lengthening with osteotomy and gradual distraction was achieved in 57 rats, and the effect of mechanical tension-stress on gene expression of bone morphogenetic proteins (BMPs) was investigated by in situ hybridization and Northern blot analysis using probes of BMP-2, BMP-4, BMP-6, BMP-7, and growth/differentiation factor (GDF)-5. There was a lag phase for 7 days after femoral osteotomy until gradual distraction was carried out for 21 days at a rate of 0. 25 mm/12 h using a small external fixator. The signals of the above BMPs mRNA were not detected in the intact rat bone but they were induced after osteotomy except those for BMP-7. By 4 days after osteotomy, BMP-2 and BMP-4 mRNAs were detected in chondrogenic precursor cells in the subperiosteal immature callus. BMP-6 and GDF-5 mRNA were detected in more differentiated cells in chondroid bone. By 7 days after osteotomy, cartilaginous external callus and bony endosteal callus were formed. Meanwhile, the signals of BMP-2 and BMP-4 mRNAs declined to preoperative levels, whereas the signals of BMP-6 and GDF-5 mRNAs were rather elevated. As distraction was started, the callus elongated and eventually separated into proximal and distal segments forming a fibrous interzone in the middle. Expression of BMP-2 and BMP-4 mRNAs was markedly induced at this stage. Their signals were detected widely among chondrogenic and osteogenic cells and their precursor cells sustaining mechanical tension-stress at the fibrous interzone. BMP-6 and GDF-5 mRNAs were detected exclusively in chondrogenic cells at both ends of the fibrous interzone, where endochondral ossification occurred. But neither mRNA was detected in terminally differentiated hypertrophic chondrocytes. As distraction advanced, the cartilage was progressively resorbed from both ends and new bone was formed directly by intramembranous ossification. There was no new cartilage formation in the advanced stage of distraction. The signals of BMP-6 and GDF-5 mRNA declined by this stage, while those of BMP-2 and BMP-4 were maintained at high level for as long as distraction was continued. After completion of distraction, the fibrous interzone fused and the lengthened segment was consolidated. BMP-2, BMP-4, BMP-6, nor GDF-5 was expressed at this stage. The signals of BMP-7 were not detected throughout the experiment. The present results suggest that excellent and uninterrupted bone formation during distraction osteogenesis owes to enhanced expression of BMP-2 and BMP-4 genes by mechanical tension-stress. Abundant gene products of BMP-2 and BMP-4 could induce in situ bone formation by paracrine and autocrine mechanisms.

Animals↗
PubMed1998

Human papillomavirus-induced carcinogenesis with p53 deficiency in mouse: novel lymphomagenesis in HPV16E6E7 transgenic mice mimicking p53 defect.

To investigate the transforming activity of human papillomavirus (HPV) E6 and E7 genes in vivo, we previously established transgenic mouse lines containing HPV16E6E7, in which male mice develop a Leydig cell tumors with a very high incidence. Because HPV-induced carcinogenesis is highly related to p53, we changed the dose of p53 gene in the transgenic lines by the mice crossing with p53-disrupted mice. The transgenic mice with homozygous wild-type p53 alleles developed only the testicular tumor, whereas novel T cell lymphomagenesis occurred in the heterozygous p53-disrupted E6E7 (p53+/-E6E7) transgenic mice. In this tumor and even in the normal spleen, the absence of p53 protein was observed, whereas the p53 mRNA was expressed with a normal size, suggesting the degradation of p53 protein in these tissues. These results suggest that HPV16E6 could stimulate p53 protein degradation in mouse cells and induced the lymphomagenesis in a manner indistinguishable from p53 deficiency.

Animals↗
PubMed1998

Effects of ACTH on adrenal angiotensin II receptor subtype expression in vivo.

Control of adrenal aldosterone secretion is an important endocrine mechanism mediated by angiotensin II (Ang. II). Recently three subtypes of angiotensin receptors have been demonstrated in the rat adrenal. Our aim was to examine if these receptors are affected by hormone treatment in vivo. Treatment of rats with ACTH resulted in a decrease in AT2 receptor binding from 766 +/- 95 to 310 +/- 51 fmol/mg protein (P < 0.05), without significant changes in AT1 receptors. AT2 receptor mRNA was also decreased (18 +/- 2%, of control, P < 0.05; 25+/-7% of control, P < 0.05) after both 2 and 7 day treatment with ACTH. Changes in AT1a receptor mRNA or total AT1 mRNA did not reach statistical significance. Moreover, treatment with dexamethasone or aldosterone did not affect AT1a, AT1b, or AT2 mRNA. These results demonstrate that ACTH treatment results in subtype-specific changes in adrenal AT receptor gene expression in vivo.

Adrenal Glands↗
PubMed1998

Kainic acid-induced neuronal loss and glial changes in the hippocampal CA3 of p53-deficient mouse.

We examined kainic acid (KA)-induced neuronal death and changes in glial cells in p53-deficient (p53-/-) and wild-type (p53+/+) mice which were CBA and C57BL/6 background. The p53-/- mouse exhibited a KA-induced loss of CA3 pyramidal neurons similar to that in wild-type mouse. Before neuronal death, c-Jun protein was expressed, phosphorylated and translocated into several nuclei of CA3 pyramidal neurons. In p53-/- mouse, microglial activation was slightly faster and more continuous after 1-7 days than that in p53+/+ mouse. On the other hand, p53-/- astrocytes were relatively resistant to KA cytotoxicity, and marked astrocytosis also occurred after 7 days. These observations suggest that p53-null mutation may influence the activation and proliferation of glial cells rather than neuronal death.

Animals↗
PubMed1998

Adrenal angiotensin II type 1 and type 2 receptors in Cushing's and Conn's syndromes.

Cushing's and Conn's syndromes are well recognised endocrine diseases, but the pathobiology of the tumors causing these disorders is unclear. In this study we examined AT1 and AT2 gene expression in adrenal adenomas of Cushing's and Conn's syndromes. AT1 and AT2 receptor mRNA, as well as alternatively spliced AT1 transcripts, were detected by RT-PCR using adjacent adrenal cortex tissue as controls. Whereas no consistent differences in AT1 mRNA were seen compared to control adrenal cortex, AT2 mRNA levels were significantly decreased in the adenomas of Cushing's and Conn's syndromes. No changes in alternative splicing of AT1 mRNA were observed in the adrenal tumors. The fact that no consistent changes were seen in AT1 mRNA or its splicing, whereas AT2 mRNA were reduced in both forms of hormone producing adrenal tumor suggests that the AT2 receptor, rather than the AT1 subtype, may be correlated with adrenal tumorigenesis.

Adrenal Cortex↗
PubMed1998

Transcriptional regulation of osteopontin gene in vivo by PEBP2alphaA/CBFA1 and ETS1 in the skeletal tissues.

Osteopontin (Opn) and polyoma enhancer-binding protein (PEBP) 2alphaA/core binding factor (CBFA) 1 have been suggested to play important roles in ossification. The overlapping localization of opn and PEBP2alphaA/CBFA1 mRNA, and the marked decrease of opn mRNA expression in PEBP2alphaA knockout mice, indicated that the transcription of opn gene was controlled by PEBP2alphaA. In the present study, we determined the direct regulation of PEBP2alphaA on the opn promoter activity. Opn promoter activity was markedly enhanced by PEBP2alphaA and ETS1 in a synergistic manner. The synergistic effect was diminished when either the PEBP2alphaA or ETS1 binding site was mutated, or the spatial arrangement of these sites was mutated by a 4-nt insertion. The distance between these sites was important for transactivation but not protein-DNA binding. The direct interaction between PEBP2alphaA and ETS1 was depended on protein-DNA binding. These results suggested that the specific spatial arrangement of both sites and direct interaction between PEBP2alphaA and ETS1, were essential for promoter function. Furthermore, endogenous opn mRNA was decreased with the introduction of dominant negative PEBP2alphaA to MC3T3/E1 cells expressing endogenous PEBP2alphaA, ETS1 and opn. These findings suggest that PEBP2alphaA and ETS1 cooperate in vivo to regulate expression of the opn gene in the skeletal tissue. Cell type-specific regulation of Opn gene expression will also be discussed.

3T3 Cells↗
PubMed1998

Impaired expression of integrin alpha-4 subunit in cultured mast cells derived from mutant mice of mi/mi genotype.

The mi locus encodes a member of the basic-helix-loop-helix-leucine zipper protein family of transcription factors (hereafter called MITF). We have reported that expression of several genes was impaired in cultured mast cells (CMCs) of mi/mi mice due to a defective transactivation ability of mutant MITF (mi-MITF). Because attachment of mi/mi CMCs to fibroblasts is impaired, we examined the expression of integrin genes in mi/mi CMCs in the present study. Among the integrin genes examined, the expression of integrin alpha4 subunit was barely detectable in mi/mi CMCs, and the alpha4 protein was not detected by flow cytometry either. The specific adhesion to vascular cell adhesion molecule-1 (VCAM-1), the ligand for alpha4 subunit, was observed in +/+ CMCs but not in mi/mi CMCs, indicating that the expression of integrin alpha4 subunit at a functional level did not occur in mi/mi CMCs. In the promoter region of the alpha4 subunit gene, there was a CACTTG motif to which normal MITF (+- MITF) bound. The coexpression of +-MITF but not of mi-MITF transactivated the promoter of the alpha4 subunit gene. The deletion or mutation of the CACTTG motif abolished the transactivation by +-MITF, suggesting that +-MITF directly transactivated the gene encoding alpha4 subunit of integrin.

Animals↗
PubMed1998

Characterization of the hatching enzyme from embryos of an anuran amphibian, Rana pirica.

The culture medium in which prehatching embryos of the frog, Rana pirica, were cultured (hatching medium) solubilized the vitelline coat (VC) of unfertilized eggs and contained molecules reactive to antibodies (anti-UVS.2) against the Xenopus hatching enzyme (HE). The hydrolyzing activity of the hatching medium against Pro-Phe-Arg-MCA was inhibited dose-dependently by the same antibodies. Using anti-UVS.2 as a probe, we purified two distinct 56 kDa molecules exhibiting Pro-Phe-Arg-MCA hydrolyzing activity. These 56 kDa molecules, which were separable on anion exchange chromatography, were the same with respect to VC solubilizing activity and a substrate specificity for various MCA-peptides, and they were regarded as charge isomers that function as the HE. The hydrolyzing activity against Pro-Phe-Arg-MCA of HE was optimal at pH of 7.6, with the apparent Km value of 250 microM at 30 degreesC. The activity was strongly inhibited by DFP and EDTA, and was accelerated by extremely low concentrations of Mg2+ and Zn2+, indicating the serine protease and metalloprotease nature of the HE. The HE was glycosylated and was present as a putative proenzyme form of 63 kDa.

Animals↗
PubMed1998

The influence of mast cells on pathways of transepithelial antigen transport in rat intestine.

Luminal Ag challenge of intestinal segments from sensitized rats results in a rapid (approximately 3 min) secretory response. We previously showed in horseradish peroxidase (HRP)-sensitized rats that the initial phase of transepithelial Ag transport occurred via a transcellular route and was enhanced by sensitization. However, following the hypersensitivity reaction, Ag also crossed between epithelial cells. The aim of this study was to determine the role of mast cells in the altered transepithelial Ag transport. White spotting mast cell-deficient rats and +/+ littermate controls were sensitized to HRP. After 10 to 14 days, jejunal segments were resected, mounted in Ussing chambers, and challenged with HRP on the luminal side. Electron microscopy of jejunum fixed at 2 min showed a similarly enhanced endocytic transport of HRP in sensitized +/+ and Ws/Ws rats compared with naive controls. In sensitized +/+ rats, a secretory response occurred approximately 3 min after challenge, and tissue conductance increased thereafter. Naive +/+ and sensitized Ws/Ws rats did not demonstrate a secretory response to HRP challenge, and conductance remained at baseline levels. The flux of HRP was elevated across tissue from sensitized +/+ rats but not across tissue from naive controls or sensitized Ws/Ws rats. The results indicate that sensitization enhances the initial phase of transepithelial uptake of Ag by transcytosis in a mast cell-independent manner. However, subsequent recruitment of the paracellular pathway for Ag transport in sensitized rats is dependent upon the presence of mast cells and occurs after the activation of such cells.

Animals↗
PubMed1998

Tissue and cell type specificity of the human neurotrophin-3 promoter region in transgenic mice.

To examine the tissue and cell type specificity of the human neurotrophin-3 (NT-3) promoter, we generated transgenic mice bearing the 3.3 kbp upstream region of the human NT-3 gene linked to the bacterial chloramphenicol acetyltransferase (CAT) gene as a reporter. Eight independent founders of transgenic mice were obtained, and four of them transmitted the transgene to their offsprings. Among three lines of four transgenic mice at 6 weeks of age, a high level of production of CAT protein was detected in the spleen and a low level in the brain. By in situ hybridization analysis, CAT gene expression was detected in the hippocampal neurons and in the cerebellar granular neurons of the transgenic mouse brain. These results suggest that the 3.3 kbp 5' flanking region of the human NT-3 gene has adequate promoter activity in vivo and that its expression pattern resembles the endogenous gene.

Animals↗
PubMed1998

D-serine content and D-[3H]serine binding in the brain regions of the senescence-accelerated mouse.

An established senescence-accelerated model mouse strain, SAMP8, shows the deterioration of learning and memory compared with a normal control strain, SAMR1. D-Serine binds to strychnine-insensitive glycine binding sites of the N-methyl-D-aspartate (NMDA) receptor complex, and enhances glutamate binding to the receptor complex. To investigate the relationship of endogenous brain D-serine and the brain dysfunction caused by aging, the level of brain free D-serine and the D-[3H]serine binding to the brain samples were examined using the SAMP8 and SAMR1 mice. The free D-serine level was highest in the cerebral frontal and occipital cortices in both the SAMP8 and SAMR1; no difference in the D-serine level was shown between the two strains. A receptor autoradiographical analysis showed that the D-[3H]serine binding to the brain section was highest in the hippocampus, and the binding in the SAMP8 brains was lower than that of the SAMR1. The D-[3H]serine binding to the crude cerebral membranes indicated that the value of the total binding sites for the SAMP8 was lower than that for the SAMR1, whereas the value of the dissociation constant Kd for the SAMP8 was similar to that of the SAMR1. These results suggest that the number of D-[3H]serine binding sites was decreased in the SAMP8 compared to the SAMR1, but the affinity of D-[3H]serine to the binding sites was not altered. These results support the view that a decrease of NMDA receptor complex is involved in the age-related neural dysfunction of SAMP8 mice.

Aging↗
PubMed1998

Induction of plasminogen in rat hippocampal pyramidal neurons by kainic acid.

Tissue plasminogen activator (tPA) is used to treat acute stroke, but tPA- and plasminogen-gene-deficient mice exhibit resistance to neurodegeneration. Thus, it is unclear whether the tPA-plasminogen system, an extracellular proteolytic cascade plays a helpful or harmful role, and whether plasminogen is induced by neurodegeneration. In the CA3, kainic acid (KA)-injection caused neuronal damage after 6 h, and almost all of the neurons were lost after 7 days. Plasminogen mRNA was strongly induced 6 h after injection, then gradually decreased, and was very weak at 2 days after injection. Plasminogen protein was expressed after 6 h and localized in abnormally shaped neurons. The in vivo expression of plasminogen was synchronous with morphological changes in neurons. These results suggest that the expression of plasminogen induced by KA-injection may disrupt of neuron-extracellular matrix interaction and thereby contribute to cell death in neurons in the hippocampus.

Animals↗