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H Maegawa

Publications and source records attributed to H Maegawa.

At least 37 records · Page 2Linked to original sources
PubMed1999

Endothelium-specific activation of NAD(P)H oxidase in aortas of exogenously hyperinsulinemic rats.

To examine the effects of chronic hyperinsulinemia on vascular tissues, we examined the production of superoxide anion (O(-2)) in the aortic tissues of control and exogenously hyperinsulinemic rats performed by the implantation of an insulin pellet for 4 wk. O(-2) production by aortic segments from hyperinsulinemic rats was 2. 4-fold (lucigenin chemiluminescence method) and 1.7-fold (cytochrome c method) of that of control rats without any differences in O(-2) degrading activities in aortic tissues, respectively (P < 0.025). The increment was completely abolished in the presence of either 100 micromol/l apocynin (an inhibitor of NADPH oxidase) or 10 micromol/l diphenyleneiodonium (an inhibitor of flavin-containing enzyme) and was exclusively endothelium dependent. Consistently, NAD(P)H oxidase activities in endothelial homogenate in hyperinsulinemic rats were dose dependently stimulated above the values of control rats, although these activities in nonendothelial homogenate were not significantly stimulated by insulin. Furthermore, an insulin effect was also demonstrated 1 h after exposing aortic tissues to insulin. These results indicate that O(-2) production specifically increases in endothelium of aortic tissues in chronic hyperinsulinemic rats through the activation of NAD(P)H oxidase.

Animals↗
PubMed1999

The 3'-untranslated region polymorphism of the gene for skeletal muscle-specific glycogen-targeting subunit of protein phosphatase 1 in the type 2 diabetic Japanese population.

A newly identified 3'-untranslated region (UTR) polymorphism of the gene for skeletal muscle-specific glycogen-targeting subunit of protein phosphatase 1 (PPP1R3) was associated with insulin resistance and type 2 diabetes in Pima Indians (Xia J, Scherers W, Cohen PTW, Majer M, Xi T, Norman RA, Knowler WC, Bogardus C, Prochazka M: A common variant in PP1R3 associated with insulin resistance and type 2 diabetes. Diabetes 47:1519-1524, 1998). Thus, we investigated the frequency of polymorphism of the adenine- and thymine-rich element (ARE-1 and its variant ARE-2) in 426 Japanese type 2 diabetic and 380 nondiabetic subjects using a polymerase chain reaction (PCR)-restriction enzyme fragment length polymorphism (RFLP) method. The allele frequency of the ARE-2 variant in diabetic subjects was higher than that in nondiabetic subjects (0.34 vs. 0.29; P < 0.05), even though its frequency in Japanese subjects was lower (P < 0.001) than the reported value in Pima Indians (0.56). An aspartate polymorphism at codon 905 was 100% coupled to the ARE-2 allele, and its allele frequency was higher also in diabetic subjects. Although a serine substitution at codon 883 was partially linked with the ARE-2 allele, there was no difference between diabetic and nondiabetic subjects. These results indicate that the frequency of polymorphism of the PPP1R3 gene (ARE-2 and Asp905) is different between two ethnic groups and is increased in Japanese people with type 2 diabetes, suggesting that these variants may be a possible marker for searching for diabetogenic genes.

3' Untranslated Regions↗
PubMed1999

[Molecular mechanism and clinical impact of insulin resistance in type 2 diabetes mellitus].

Type 2 diabetes is characterized by insulin resistance as well as impaired insulin secretion. Thus, the enhancement of insulin sensitivity is a possible treatment modality. The mechanism of insulin resistance is still unknown. However, some genetic backgrounds may be involved and modulated by environmental factors. Obesity is considered to be one of major factors to induce insulin resistance. Regarding mechanism of obesity-induced insulin resistance, the increased expression of Tumor necrosis factor alpha and abnormality in PTPase are postulated. Prolonged hyperglycemia also induces the impairment of insulin action, resulting in worsening glycemic control. Abnormal glucosamine biosynthesis and impaired receptor kinase are considered to be involved in the hyperglycemia-induced insulin resistance.

Animals↗
PubMed1999

[Glucose].

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Blood Glucose↗
PubMed1998

Opposite regulation of tyrosine-phosphorylation of p130(Cas) by insulin and insulin-like growth factor I.

To investigate the difference in signaling between insulin and insulin-like growth factor I (IGF-I), we studied the effects of these hormones on the phosphorylation state of Crk-associated substrate (Cas) in cells expressing human insulin receptor (HIRc). In the basal state, Cas was heavily tyrosine-phosphorylated, and insulin dephosphorylated Cas in a time- and dose-dependent manner. On the other hand, IGF-I phosphorylated rather than dephosphorylated Cas in HIRc cells. In HIRY/F2 cells expressing a mutant insulin receptor lacking a binding site of SHP-2, a protein-tyrosine phosphatase containing src homology 2 (SH2) regions, insulin accelerated phosphorylation of Cas, as did IGF-I. In HIRc cells expressing a mutant SHP-2 lacking a PTPase domain (DeltaPTP), which interfered with SHP-2 function, insulin failed to dephosphorylate Cas. In whole cell lysate obtained in the basal state, Cas bound to a glutathione-S transferase fusion protein containing SH2 domains of SHP-2 and dissociated from this GST protein in response to insulin. These results indicate that the opposite regulation of Cas phosphorylation by insulin and IGF-I may be mediated through different properties of their receptors, and that the interaction of the insulin receptor with SHP-2 may play an important role in determining the tyrosine-phosphorylation state of Cas.

Animals↗
PubMed1998

High glucose-induced abnormal epidermal growth factor signaling.

We have reported that high glucose conditions (27 mM for 4 days) induces activation of protein tyrosine phosphatases (PTPases) which are associated with impaired insulin signaling in Rat 1 fibroblasts expressing human insulin receptors [Maegawa, H. et al. (1995) J. Biol. Chem. 270, 7724-7730]. In this study, we found increased mRNA-levels of a non-receptor type PTPase, protein tyrosine phosphatase 1B (PTP1B), and receptor type PTPases, leukocyte common antigen-related phosphatase (LAR), and LAR-related phosphatase (LRP), under high glucose conditions. In accordance with these results, LAR content was significantly increased, whereas LRP content was not increased. Cytosolic PTP1B content was increased, but membrane-associated PTP1B content showed no detectable change. Pioglitazone, a thiazolidinedione, normalized increased cytosolic PTPase activity through reduction of cytosolic PTP1B content, but it had no effect on mRNA levels of these PTPases. Under the high glucose condition, we also found that epidermal growth factor (EGF)-stimulated signaling, including tyrosine-phosphorylation of EGF receptor and phosphatidylinositol 3'-kinase activities, was attenuated. Nevertheless, pioglitazone failed to restore the attenuated EGF-signaling. These results indicate that the high glucose conditions cause dysfunction of EGF receptor. However, the increased cytosolic PTP1B content is not involved in the abnormal regulation of EGF-signaling, in contrast to insulin-signaling.

Animals↗
PubMed1998

Altered activities of transcription factors and their related gene expression in cardiac tissues of diabetic rats.

Gene regulation in the cardiovascular tissues of diabetic subjects has been reported to be altered. To examine abnormal activities in transcription factors as a possible cause of this altered gene regulation, we studied the activity of two redox-sensitive transcription factors--nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1)--and the change in the mRNA content of heme oxygenase-1, which is regulated by these transcription factors in the cardiac tissues of rats with streptozotocin-induced diabetes. Increased activity of NF-kappaB and AP-1 but not nuclear transcription-activating factor, as determined by an electrophoretic mobility shift assay, was found in the hearts of 4-week diabetic rats. Glycemic control by a subcutaneous injection of insulin prevented these diabetes-induced changes in transcription factor activity. In accordance with these changes, the mRNA content of heme oxygenase-1 was increased fourfold in 4-week diabetic rats and threefold in 24-week diabetic rats as compared with control rats (P < 0.01 and P < 0.05, respectively). Insulin treatment also consistently prevented changes in the mRNA content of heme oxygenase-1. The oral administration of an antioxidant, probucol, to these diabetic rats partially prevented the elevation of the activity of both NF-kappaB and AP-1, and normalized the mRNA content of heme oxygenase-1 without producing any change in the plasma glucose concentration. These results suggest that elevated oxidative stress is involved in the activation of the transcription factors NF-kappaB and AP-1 in the cardiac tissues of diabetic rats, and that these abnormal activities of transcription factors could be associated with the altered gene regulation observed in the cardiovascular tissues of diabetic rats.

Animals↗
PubMed1997

Oxidized lipoproteins found in patients with NIDDM stimulate radical-induced monocyte chemoattractant protein-1 mRNA expression in cultured human endothelial cells.

Although oxidized low density lipoprotein (LDL) exists in plasma from diabetic patients, there are few studies on its biological activity. Thus, we investigated the biological potency of LDL plus intermediate density lipoprotein fraction isolated from 12 non-diabetic and 24 non-insulin-dependent diabetic subjects of similar age and body mass index, in order to induce monocyte chemoattractant protein-1 (MCP-1) mRNA expression in cultured human endothelial cells. MCP-1 mRNA content in the cells exposed to the lipoproteins isolated from the diabetic patients was significantly higher than that from the control subjects (p < 0.001). The increment of MCP-1 mRNA content was positively correlated with not only HbA1c (r = 0.58, p < 0.0001) but also lysophosphatidylcholine (LPC) content in the lipoprotein (r = 0.46, p < 0.005) and was negatively correlated with diene formation lag time as a marker of oxidizability of the lipoprotein (r = -0.33, p < 0.05). Treatments of the cells with either 50 mumol/l probucol, 50 mumol/l alpha-tocopherol, or 0.1 mmol/l deferoxamine suppressed the increase in MCP-1 mRNA content induced by diabetic lipoproteins, respectively. Furthermore, the diabetic lipoproteins activated nuclear transcription factor NF-kappa B in the cells, which was inhibited by pre-treatment of cells with 50 mumol/l probucol. These data indicate that oxidatively modified lipoproteins found in diabetic plasma stimulate MCP-1 gene expression in endothelial cells. The LPC content which reflects oxidative modification of lipoprotein is at least a possible marker of biological activity to increase an atherogenic cytokine in endothelial cells.

Antioxidants↗
PubMed1997

beta-Sitosterolemia with generalized eruptive xanthomatosis.

The clinical features of the first case of a patient with sitosterolemia and generalized eruptive xanthomatosis are described. A six-year-old girl with generalized eruption was referred to the lipid clinic because of the high plasma cholesterol levels determined by the enzymatic method. Neither clinical signs nor results of laboratory examinations appeared to be abnormal, except for the eruption and the increase in the plasma cholesterol concentration. A family survey revealed high plasma cholesterol concentrations in the mother and one of two other siblings. Histological examination showed the eruption to be a xanthoma. Plasma sterol analysis by high-performance liquid chromatography revealed a noticeable increase in plasma plant sterol as well as cholestanol concentrations in the proband and the hypercholesterolemic sibling. The other family members had slightly high plasma sterol concentrations. This is the first case of a sitosterolemic patient with eruptive xanthomatosis. The case indicates that the clinical features of the xanthoma in sitosterolemia are not only tuberous or tendon but also eruptive, and also suggests that sitosterolemia should be considered in the differential diagnosis of hypercholesterolemia in almost every case with tuberous or eruptive xanthoma. The diagnosis is clinically important, since the disease can be treated successfully by diet therapy and bile acid binding resins.

Child↗
PubMed1997

[CT-guided biopsy of small lung nodules: usefulness of frozen-section pathologic diagnosis].

PURPOSE: To improve the diagnostic accuracy of computed tomography (CT)-guided biopsy of small lung nodules. MATERIALS AND METHODS: The usefulness of fine-needle core biopsy combined with immediate frozen-section diagnosis by pathologists was prospectively studied. Forty-six biopsies of small lung nodules (less than 3 cm in greatest diameter) were performed under CT guidance in 46 patients with 31 malignant and 15 benign processes. Initial biopsy was always attempted with a 20 or 21G histological needle; tissue samples were sent to the pathology department immediately after biopsy for pathologic diagnosis of the frozen sections. RESULTS: In 41 of 46 lesions (89.1%), sufficient material was obtained for diagnosis, permitting a correct final diagnosis. For malignancy, the sensitivity was 100%, whereas 81.8% of the benign lesions were diagnosed as specifically benign. Pneumothorax occurred in 41.3%. CONCLUSION: Histological diagnosis using frozen sections is a useful adjunct for CT-guided biopsy of the chest.

Adenocarcinoma↗
PubMed1996

SHPTP2 serves adapter protein linking between Janus kinase 2 and insulin receptor substrates.

To investigate the role of Janus kinase family (JAK1 and JAK2) in insulin signaling, we assessed their insulin-induced associations with other molecules in the cells overexpressing insulin receptors (HIRc and CHO-IR). After insulin stimulation, pp185 proteins (insulin receptor substrate, IRS) were co-immunoprecipitated with both kinases by alpha JAK1 and alpha JAK2 antibodies. However, JAK2 constitutively associated with pp95 protein (IR beta). Moreover, JAK2 also constitutively bound to a protein tyrosine phosphatase containing Src 2 regions (SHPTP2), but JAK1 did not. In HIRc cells expressing PTPase-negative mutant SHPTP2, no association of JAK2 with either pp185 or pp95 was detected. Thus, SHPTP2 might serve as an adapter protein linking between JAK2 and IRS. These results suggest that JAK1 and JAK2 behave differently and they may constitute a new regulatory component in insulin signaling.

Animals↗
PubMed1996

Expression of dominant negative mutant SHPTP2 attenuates phosphatidylinositol 3'-kinase activity via modulation of phosphorylation of insulin receptor substrate-1.

To clarify the role of protein-tyrosine phosphatase (PTPase) containing Src homology 2 regions (SHPTP2) in insulin signaling, either wild-type or mutant SHPTP2 (delta PTP; lacking full PTPase domain) was expressed in Rat 1 fibroblasts overexpressing human insulin receptors. In response to insulin, phosphorylation of insulin receptor substrate 1 (IRS-1), IRS-1-associated PTPase activities and phosphatidylinositol (PI) 3'-kinase activities were slightly enhanced in wild-type cells when compared with those in the parent cells transfected with hygromycin-resistant gene alone. In contrast, introduction of delta PTP inhibited insulin-induced association of IRS-1 with endogenous SHPTP2 and impaired both insulin-stimulated phosphorylation of IRS-1 and activation of PI 3'-kinase. Furthermore, decreased content of p85 subunit of PI 3'-kinase was also found in mutant cells. Consistently, the insulin-stimulated mitogen-activated protein kinase activities and DNA synthesis were also enhanced in wild-type cells, but impaired in mutant cells. Thus, the interaction of SHPTP2 with IRS-1 may be associated with modulation of phosphorylation levels of IRS-1, resulting in the changes of PI 3'-kinase and mitogen-activated protein kinase activity. Furthermore, an impaired insulin signaling in mutant cells may be partly reflected in a decreased content of p85 protein of PI 3'-kinase.

Animals↗
PubMed1996

Lysophosphatidylcholine stimulates the expression and production of MCP-1 by human vascular endothelial cells.

Lysophosphatidylcholine (LPC increased monocyte chemoattractant protein-1 (MCP-1) messenger RNA concentrations in human umbilical vein endothelial cells (HUVECs). A time-course study showed that the increase in MCP-1 mRNA levels peaked at 6 hours after treatment with LPC. The effect of LPC on the accumulation of MCP-I mRNA levels in HUVECs depended on LPC concentration, and the maximal effect was obtained at 50 micromol / L LPC, which induced a sixfold increase in MCP-1 mRNA levels. The amount of MCP-1 released from HUVECs measured using an enzyme-linked immunosorbent assay (ELISA) showed a 38% increase in the presence of 50 micromol/L LPC, but not in the presence of phosphatidylcholine or lysophosphatidylethanolamine. Coincubation with staurosporine, a potent inhibitor of protein kinase C (PKC) activity, attenuated the LPC-induced increase in MCP-1 mRNA levels by 53%. These results indicate that LPC can induce an increase in MCP-1 mRNA concentrations and stimulate the release of MCP-1 protein from HUVECs, and that the effect of LPC on the MCP-1 gene may be mediated through activation of the PKC pathway.

Base Sequence↗
PubMed1996

Insulin signaling and its regulation of system A amino acid uptake in cultured rat vascular smooth muscle cells.

Hyperinsulinemia has been recognized as an independent risk factor for atherosclerosis. However, its exact mechanisms are still unclear. In our previous work, we showed that 10 nmol/L insulin stimulated neither mitogen-activated protein kinase (MAP kinase) activity nor [3H]thymidine incorporation but did stimulated S6 kinase through the specific insulin receptors in cultured rat vascular smooth muscle cells (VSMCs). In this study, we observed that > or = 1 nmol/L insulin stimulated tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and activated IRS-1-dependent phosphatidylinositol 3'-kinase (PI 3'-kinase) and p70 S6 kinase (p70S6K) but not MAP kinase (extracellular signal-regulated kinase 2) and p90 S6 kinase (p90RSK). However, 10 nmol/L insulin-like growth factor I stimulated all these pathways. Finally, 10 nmol/L insulin stimulated alpha-amino-isobutyric acid (AIB) uptake, and wortmannin (100 nmol/L) completely inhibited insulin-stimulated AIB uptake, whereas rapamycin (20 nmol/L) had no such effect. Furthermore, cycloheximide (10 micrograms/mL) completely inhibited insulin-stimulated AIB uptake, but actinomycin D (5 micrograms/mL) failed to inhibit this. Thus, we reached the following conclusions: (1) Insulin (1 nmol/L) induced phosphorylation of IRS-1 and activated the PI 3'-kinase and p70S6K pathways in VSMCs, even though 10 nmol/L insulin did not significantly stimulate MAP kinase or p90RSK. (2) Stimulation of AIB uptake by insulin was regulated at the translational level via wortmannin-sensitive pathways but not p70S6K pathways.

Aminoisobutyric Acids↗
PubMed1996

[A quantitative of serum biotin with microplate-assay using affinity streptavidin].

We modified Bayer's method of micro-plate assay for quantitation of biotin concentration. Biotin concentration in the solution and serum which cannot be quantitated directly by a microorganism assay (bio-assay), was easily determined by this method, which showed a high affinity of streptavidin for biotin this method and had a wide measurement range (0.9-60,000 pg/ml). We measured the concentration of biotin in 150 sera from 44 patients (21 males and 23 females) with active hepatitis (high level of both GOT and GPT, over 100 IU/l), 15 patients (7 males and 8 females) with inactive hepatitis (positive HCV-Ab but within normal limits of both GOT and GPT level), 17 patients (8 males and 9 females) with hepatoma and liver cirrhosis and 71 healthy persons (34 males and 37 females). The biotin concentration of sera in the healthy persons was 243.5 +/- 184.6 pg/ml, there being no sex difference. The biotin concentration in sera was higher in the patients than in healthy persons. It was high in the hepatoma and cirrhosis group (4,394.0 +/- 6,176.3), the active hepatitis group (2,397.4 +/- 2,785.5), and the inactive hepatitis group (1,873.2 +/- 1,523.7). These findings suggest that the biotin concentration is not significantly correlated with an escape enzyme such as GOT and GPT. These findings suggest that a high biotin concentration reflects other mechanisms such as escape from damaged liver cells.

Adult↗
PubMed1995

Localization of the insulin-like growth factor I receptor binding sites for the SH2 domain proteins p85, Syp, and GTPase activating protein.

Potential signaling substrates for the insulin-like growth factor I (IGF-I) receptor are SH2 domain proteins including the p85 subunit of phosphatidylinositol 3-kinase, the tyrosine phosphatase Syp, GTPase activating protein (GAP), and phospholipase C-gamma (PLC-gamma). In this study, we demonstrate an association between the IGF-I receptor and p85, Syp, and GAP, but not with PLC-gamma in lysates of cells overexpressing the human IGF-I receptor. We further investigated these interactions using glutathione S-transferase (GST) fusion proteins containing the amino-terminal SH2 domains of p85 or GAP, or both SH2 domains of Syp or PLC-gamma to precipitate the IGF-I receptor from purified receptor preparations and from whole cell lysates. p85-, Syp-, and GAP-GSTs precipitated the IGF-I receptor, whereas the PLC-gamma-GST did not. Using phosphopeptides corresponding to IGF-I receptor phosphorylation sites, we determined that the p85- and Syp-GST association with the IGF-I receptor could be inhibited by a carboxyl-terminal peptide containing pY1316 and that the GAP-GST association could be inhibited by a NPXY domain peptide. The GAP-GST binding site was confirmed by showing that a mutant IGF-I receptor with a deletion of the NPXY domain including tyrosine 950 was poorly precipitated by the GAP-GST. We conclude that p85 and Syp may bind directly to the IGF-I receptor at tyrosine 1316, and that GAP may bind to the IGF-I receptor at and PLC-gamma was not evident. p85, Syp, and GAP are potential modulators of IGF-I receptor signal transduction.

Amino Acid Sequence↗