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Biomedical subjects

N Yamada

Publications and source records attributed to N Yamada.

At least 55 records · Page 3Linked to original sources
PubMed2001

Low M(r) protein tyrosine phosphatase inhibits growth and migration of vascular smooth muscle cells induced by platelet-derived growth factor.

Vascular smooth muscle cell (VSMC) migration and growth are positively regulated by protein tyrosine phosphorylation. Therefore, a dephosphorylation process controlled by protein tyrosine phosphatases (PTPs) must also be critical. The present study identified six cytoplasmic PTPs expressed in VSMCs: low M(r) protein tyrosine phosphatase (LMW-PTP), SHP-2, PTP36, PTP2, PTP1B, and FAP1. We further examined the functions of LMW-PTP in VSMCs using the adenovirus-mediated gene transfer of recombinant LMW-PTP. PDGF-induced activation of p38, but not of ERK MAP kinase, was blocked by LMW-PTP. LMW-PTP as well as the p38 inhibitor SB203580 inhibited DNA synthesis and cell migration upon PDGF stimulation. LMW-PTP dephosphorylated activated PDGF receptors in NIH3T3 cells, but not in VSMCs. Thus, LMW-PTP negatively regulates PDGF functions by inhibiting the p38 pathway in VSMCs although its substrate is unclear. These findings strongly demonstrate that PTPs are important as negative regulators for VSMC growth and migration, processes that are closely related to the progression of atherosclerosis.

3T3 Cells↗
PubMed2001

Elevated levels of vascular endothelial growth factor in the sera of patients with rheumatoid arthritis correlation with disease activity.

To evaluate vascular endothelial growth factor (VEGF) levels in relation to disease activity in rheumatoid arthritis (RA), VEGF in the serum of 155 patients with RA and 75 healthy control subjects was quantified by our highly sensitive enzyme-linked immunosorbent assay. VEGF levels were found to correlate with the articular index (AI) and Lansbury's activity index (LI). Patients with RA had a mean serum VEGF concentration of 153.5+/-111.8 pg/ml, which was significantly higher than control subjects (104.8+/-65.7 pg/ml; P<0.01). VEGF concentration was elevated significantly according to disease progression as expressed by stages I to IV and correlated with AI (r=0.530, P<0.0001) and LI (r=0.688, P<0.0001) in stages I and II as well as with the conventional erythrocyte sedimentation rate or serum C-reactive protein concentration. Serum VEGF levels may therefore be valuable as a marker of disease activity in patients with early RA, and this cytokine may play a significant role in the pathophysiology of RA.

Arthritis, Rheumatoid↗
PubMed2001

[(Dihydroindenyl)oxy]alkonic acid inhibits the cystic fibrosis transmembrane conductance regulator.

We investigated the effects of [(dihydroindenyl)oxy]alkaonic acid (DIOA) on the Cl(-) secretion in Calu-3 human airway epithelial cells that exclusively express the cystic fibrosis transmembrane conductance regulator (CFTR) as an apical Cl(-) channel. The 5'-nitro-2-(3-phenylpropylamino) benzoate (NPPB)-sensitive short-circuit current (I(sc)) and apical conductance were markedly reduced by DIOA (100 microM) in the presence and absence of isoproterenol (10 nM). Replacement of the butyl group in DIOA with a methyl group attenuated the inhibitory effects. The ED(50) of DIOA (17.0+/-1.0 microM) was almost equivalent to that of NPPB (15.6+/-2.1 microM). In conclusion, DIOA inhibits CFTR as strongly as NPPB does.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2001

Sterol regulatory element-binding proteins induce an entire pathway of cholesterol synthesis.

To evaluate the effects of sterol regulatory element-binding proteins (SREBPs) on the expression of the individual enzymes in the cholesterol synthetic pathway, we examined expression of these genes in the livers from wild-type and transgenic mice overexpressing nuclear SREBP-1a or -2. As estimated by a Northern blot analysis, overexpression of nuclear SREBP-1a or -2 caused marked increases in mRNA levels of the whole battery of cholesterogenic genes. This SREBP activation covers not only rate-limiting enzymes such as HMG CoA synthase and reductase that have been well established as SREBP targets, but also all the enzyme genes in the cholesterol synthetic pathway tested here. The activated genes include mevalonate kinase, mevalonate pyrophosphate decarboxylase, isopentenyl phosphate isomerase, geranylgeranyl pyrophosphate synthase, farnesyl pyrophosphate synthase, squalene synthase, squalene epoxidase, lanosterol synthase, lanosterol demethylase, and 7-dehydro-cholesterol reductase. These results demonstrate that SREBPs activate every step of cholesterol synthetic pathway, contributing to an efficient cholesterol synthesis.

Animals↗
PubMed2001

Overexpression of lipoprotein lipase in transgenic rabbits inhibits diet-induced hypercholesterolemia and atherosclerosis.

Lipoprotein lipase (LPL) is a key enzyme in the hydrolysis of TG-rich lipoproteins. To elucidate the physiological roles of LPL in lipid and lipoprotein metabolism, we generated transgenic rabbits expressing human LPL. In postheparinized plasma of transgenic rabbits, the human LPL protein levels were about 650 ng/ml, and LPL enzymatic activity was found at levels up to 4-fold greater than that in nontransgenic littermates. Increased LPL activity in transgenic rabbits was associated with as much as an 80% decrease in plasma triglycerides and a 59% decrease in high density lipoprotein-cholesterol. Analysis of the lipoprotein density fractions revealed that increased expression of the LPL transgene resulted in a remarkable reduction in the level of very low density lipoproteins as well as in the level of intermediate density lipoproteins. In addition, LDL cholesterol levels in transgenic rabbits were significantly increased. When transgenic rabbits were fed a cholesterol-rich diet, the development of hypercholesterolemia and aortic atherosclerosis was dramatically suppressed in transgenic rabbits. These results demonstrate that systemically increased LPL activity functions in the metabolism of all classes of lipoproteins, thereby playing a crucial role in plasma triglyceride hydrolysis and lipoprotein conversion, and that overexpression of LPL protects against diet-induced hypercholesterolemia and atherosclerosis.

Animals↗
PubMed2001

Severe hypercholesterolemia, hypertriglyceridemia, and atherosclerosis in mice lacking both leptin and the low density lipoprotein receptor.

Leptin-deficient mice (ob/ob) are an excellent murine model for obesity, insulin resistance, and diabetes, all of which are components of a multiple risk factor syndrome that, along with hypercholesterolemia, precipitates a potential high risk for atherosclerosis. In the current study, we show an unexpectedly severe hyperlipidemia in ob/ob mice on a background of low density lipoprotein receptor (LDLR) deficiency (-/-). Doubly mutant mice (LDLR-/-;ob/ob) exhibited striking elevations in both total plasma cholesterol (TC) and triglyceride (TG) levels (1715 +/- 87 and 1016 +/- 172 mg/dl, respectively), at age 3-4 months, resulting in extensive atherosclerotic lesions throughout the aorta by 6 months. Lipoprotein analyses revealed the elevated TC and TG levels to be due to a large increase in an apoB-containing broad-beta remnant lipoprotein fraction. While fasting, diet restriction, and low level leptin treatment significantly lowered TG levels, they caused only slight changes in TC levels. Hepatic cholesterol and triglyceride contents as well as mRNA levels of cholesterologenic and lipogenic enzymes suggest that leptin deficiency increased hepatic triglyceride production but did not change cholesterol production in ob/ob mice regardless of their LDLR genotype. These data provide evidence that the hypertriglyceridemia and hypercholesterolemia in the doubly mutant mice are caused by distinct mechanisms and point to the possibility that leptin might have some impact on plasma cholesterol metabolism, possibly through an LDLR-independent pathway. This model will be an excellent tool for future studies on the relationship between impaired fuel metabolism, increased plasma remnant lipoproteins, diabetes, and atherosclerosis.

Animals↗
PubMed2001

Insulin up-regulates tumor necrosis factor-alpha production in macrophages through an extracellular-regulated kinase-dependent pathway.

Hyperinsulinemia has recently been reported as a risk factor for atherosclerotic diseases such as coronary heart disease; however, the effect of insulin on the development of atherosclerosis is not well understood. Here we have investigated the direct effect of insulin on macrophages, which are known to be important in the atherosclerotic process. We treated THP-1 macrophages with insulin (10(-7) m) and examined the gene expression using nucleic acid array systems. The results of array analysis showed that insulin stimulated gene expression of tumor necrosis factor-alpha (TNF-alpha) the most among all genes in the analysis. In addition, insulin administration to macrophages enhanced both mRNA expression and protein secretion of TNF-alpha in a dose-dependent manner. To determine the signaling pathway involved in this TNF-alpha response to insulin, we pretreated the cells with three distinct protein kinase inhibitors: wortmannin, PD98059, and SB203580. Only PD98059, which inhibits extracellular signal-regulated kinases, suppressed insulin-induced production of TNF-alpha mRNA and protein in THP-1 macrophages. These observations indicate that insulin stimulates TNF-alpha production in macrophages by regulating the expression of TNF-alpha mRNA and that the extracellular signal-regulated kinase signaling pathway may have a critical role in stimulating the production of TNF-alpha in response to insulin in macrophages.

Cell Line↗
PubMed2001

Analysis of pain-related somatosensory evoked magnetic fields using the MUSIC (multiple signal classification) algorithm for magnetoencephalography.

We evaluated the effectiveness of the Multiple Signal Classification (MUSIC) algorithm by analysing pain-related somatosensory-evoked magnetic fields (SEFs) by 148-channel whole-head-type magnetoencephalography. MUSIC peaks of middle latency components were located around the primary somatosensory cortex (SI), contralateral to the stimulated finger. Long latency components were located around the bilateral secondary somatosensory cortices (SII) and cingulate gyri. Peaks at the SII and cingulate gyri were more prominent on very painful and moderately painful stimulation than on weak stimulation. The results were in very good agreement with results from single dipole estimation. These findings suggest that the MUSIC algorithm could be a useful tool for analysis of pain-related SEFs.

Adult↗
PubMed2001

Extension of glial processes by activation of Ca2+-permeable AMPA receptor channels.

AMPA type-glutamate receptor channels (AMPARs) assembled without the GluR2 (GluR-B) subunit are characterized by high Ca2+ permeability, and are expressed abundantly in cerebellar Bergmann glial cells. Here we show that the morphology of cultured Bergmann glia-like fusiform cells derived from the rat cerebellum was changed by manipulating expression of Ca2+-permeable AMPARs using adenoviral vector-mediated gene transfer. Converting endogenous Ca2+-permeable AMPARs into Ca2+-impermeable channels by viral-mediated transfer of GluR2 gene induced retraction of glial processes. In contrast, overexpression of Ca2+-permeable AMPARs markedly elongated glial processes. The process extension was blocked by 2,3-Dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX), a specific antagonist of AMPAR. These results indicate that glutamate regulates the morphology of glial processes by activating Ca2+-permeable AMPARs.

Adenoviridae↗
PubMed2001

Interleukin-18 up-regulates osteoprotegerin expression in stromal/osteoblastic cells.

Osteoprotegerin (OPG) and osteoclast differentiation factor (ODF) are crucial regulators of osteoclastogenesis. To determine the biological role of interleukin (IL)-18 produced by stromal/osteoblastic cells in osteoclastogenesis, we examined the effects of IL-18 on the OPG and ODF mRNA levels in these cells. When bone marrow stromal ST2 cells, osteoblastic MC3T3-E1 cells, and mouse calvarial osteoblasts were stimulated with IL-18, the expression of OPG mRNA, but not ODF mRNA, was transiently increased, its expression reaching a maximal level at 3 h after the beginning of the culture. In accordance with this observation, all these cells expressed the mRNAs of two IL-18 receptor components and MyD88, an adapter molecule involved in IL-18 signaling. Moreover, in these cells, mitogen-activated protein kinase was phosphorylated after stimulation with IL-18. These results suggest that stromal/osteoblastic cells are IL-18-responsive cells and that IL-18 may inhibit osteoclastogenesis by up-regulating OPG expression, without stimulation of ODF production, in stromal/osteoblastic cells.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Neutralization of vascular endothelial growth factor prevents collagen-induced arthritis and ameliorates established disease in mice.

Vascular endothelial growth factor (VEGF) is implicated in the pathogenesis of inflammatory joint diseases, including rheumatoid arthritis (RA). To determine the importance of this cytokine in vivo, the effect of administering VEGF-neutralizing antibodies to mice with collagen-induced arthritis (CIA), which has many immunological and pathological similarities to human RA, has been investigated. Either saline, normal rabbit immunoglobulin or anti-human VEGF121 rabbit polyclonal antibody was administered to mice subcutaneously either before the onset of arthritis or after the establishment of clinical disease. Anti-VEGF antibody administered prior to disease onset significantly delayed the development of arthritis and decreased clinical score and paw thickness as well as histological severity. On the other hand, the frequency of occurrence of disease compared to either the control group administered saline or normal rabbit immunoglobulin was not altered. Anti-VEGF antibody also significantly ameliorated clinical and histological parameters even when administered after disease onset. These results indicate a possible therapeutical potential for anti-VEGF treatment in human arthritis.

Animals↗
PubMed2001

Asialoglycoprotein receptor deficiency in mice lacking the major receptor subunit. Its obligate requirement for the stable expression of oligomeric receptor.

The asialoglycoprotein receptor is an abundant hetero-oligomeric endocytic receptor that is predominantly expressed on the sinusoidal surface of the hepatocytes. A number of physiological and pathophysiological functions have been ascribed to this hepatic lectin (HL), the removal of desialylated serum glycoproteins and apoptotic cells, clearance of lipoproteins, and the sites of entry for hepatotropic viruses. The assembly of two homologous subunits, HL-1 and HL-2, is required to form functional, high affinity receptors on the cell surface. However, the importance of the individual subunits for receptor transport to the cell surface is controversial. We have previously generated HL-2-deficient mice and showed that the expression of HL-1 was significantly reduced, and the functional activity as the asialoglycoprotein receptor was virtually eliminated. However, we failed to detect phenotypic abnormalities. To explore the significance of the major HL-1 subunit for receptor expression and function in vivo, we have disrupted the HL-1 gene in mice. Homozygous HL-1-deficient animals are superficially normal. HL-2 expression in the liver is virtually abrogated, indicating that HL-1 is strictly required for the stable expression of HL-2. Although these mice are almost unable to clear asialo-orosomucoid, a high affinity ligand for asialoglycoprotein receptor, they do not accumulate desialylated glycoproteins or lipoproteins in the plasma.

Animals↗