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Biomedical subjects

Hiroshi Maegawa

Publications and source records attributed to Hiroshi Maegawa.

At least 19 recordsLinked to original sources
PubMed2006

RBMX is a novel hepatic transcriptional regulator of SREBP-1c gene response to high-fructose diet.

In rodents a high-fructose diet induces metabolic derangements similar to those in metabolic syndrome. Previously we suggested that in mouse liver an unidentified nuclear protein binding to the sterol regulatory element (SRE)-binding protein-1c (SREBP-1c) promoter region plays a key role for the response to high-fructose diet. Here, using MALDI-TOF MASS technique, we identified an X-chromosome-linked RNA binding motif protein (RBMX) as a new candidate molecule. In electrophoretic mobility shift assay, anti-RBMX antibody displaced the bands induced by fructose-feeding. Overexpression or suppression of RBMX on rat hepatoma cells regulated the SREBP-1c promoter activity. RBMX may control SREBP-1c expression in mouse liver in response to high-fructose diet.

Animals↗
PubMed2006

Transcription factor activating enhancer-binding protein-2beta. A negative regulator of adiponectin gene expression.

We previously reported the association between the activating enhancer-binding protein-2beta (AP-2beta) transcription factor gene and type 2 diabetes. This gene is preferentially expressed in adipose tissue, and subjects with the disease-susceptible allele of AP-2beta showed stronger expression in adipose tissue than those without the susceptible allele. Furthermore, overexpression of AP-2beta leads to lipid accumulation by enhancing glucose transport and inducing insulin resistance in 3T3-L1 adipocytes. In this study we demonstrated that overexpression of AP-2beta in 3T3-L1 adipocytes decreased the expression and secretion of adiponectin and increased those of interleukin-6 (IL-6). Interestingly, the effects of AP-2beta on the expressions of adiponectin and IL-6 and the mechanisms by which AP-2beta modulated their expressions were different. We found that the promoter activity of adiponectin gene was inhibited by AP-2beta overexpression and enhanced by knockdown of endogenous AP-2beta, whereas IL-6 was unaffected. Electrophoretic mobility shift assays revealed the existence of putative responsive elements for AP-2beta and NF-YA in human and mouse adiponectin promoter regions, and mutation of this AP-2beta binding site abolished the inhibitory effect of AP-2beta. Furthermore, chromatin immunoprecipitation assays demonstrated that AP-2beta and NF-YA competitively bind to the same region of the adiponectin promoter. Our results clearly demonstrated that AP-2beta directly inhibits adiponectin gene expression by displacing NF-YA and binding to its promoter. We conclude that AP-2beta might modulate the expression of adiponectin by directly inhibiting its transcriptional activity.

3T3-L1 Cells↗
PubMed2006

MafA differentiates rat intestinal cells into insulin-producing cells.

Recent studies have suggested that basic leucine zipper transcription factor MafA has a crucial role in pancreatic beta-cell-specific insulin gene transcription. Thus, we investigated whether MafA overexpression in the intestine induces insulin production in small-intestinal epithelial cells in vivo. Recombinant adenovirus containing MafA gene (Ad-MafA) was prepared and administered orally to streptozocin-treated diabetic rats. Insulin gene expression was observed in the intestine by RT-PCR analysis, and then insulin protein was detected by immunohistochemical analysis after Ad-MafA administration. Furthermore, MafA overexpression in the intestine increased plasma insulin levels and ameliorated hyperglycemia. These results indicate that MafA overexpression in the intestine induces intestinal epithelial cells newly to produce and release insulin.

Animals↗
PubMed2006

Alcohol consumption and coronary artery calcium in middle-aged Japanese men.

Epidemiologic studies have investigated the relation between alcohol intake and coronary calcification, with controversial results. Furthermore, the influence of heavy drinking has not been well elucidated. In the present study, a random sample of community-based Japanese men aged 40 to 49 years without a history of cardiovascular disease (n=245) were examined for coronary artery calcium (CAC) determined by electron-beam computed tomography and drinking status. There was a J-shaped association between alcohol intake and CAC. There was an increase of CAC in heavy drinkers (>or=46 g/day), and participants who were drinking>or=69 g/day showed a significant increase in CAC compared with never drinkers after adjusting for other cardiovascular risk factors.

Adult↗
PubMed2006

Higher levels of adiponectin in American than in Japanese men despite obesity.

Levels of adiponectin are inversely associated with obesity levels. We examined the levels of adiponectin in American (n = 98) and Japanese (n = 92) men aged 40 to 49 years. Contrary to our expectations, the American men had higher levels of adiponectin than the Japanese men (13.3 +/- 5.8 vs 7.3 +/- 4.2 (microg/mL) despite higher levels of obesity. Smaller areas of visceral adipose tissue in American than in Japanese men may have resulted in the higher levels of adiponectin.

Adiponectin↗
PubMed2006

Enhanced sodium sensitivity and disturbed circadian rhythm of blood pressure in essential hypertension.

OBJECTIVE: To assess whether an association between sodium-sensitive hypertension and metabolic syndrome exists; and whether, in patients with metabolic syndrome, the nocturnal fall of blood pressure decreases and salt restriction affects the circadian blood pressure rhythm. METHODS: Japanese patients with essential hypertension, who were treated without any antihypertensive agent, were maintained on a high-sodium diet and a low-sodium diet for 1 week each. On the last day of each diet, the 24-h blood pressures were measured. A diagnosis of metabolic syndrome was made according to the International Diabetes Foundation definition RESULTS: Among the 56 patients with essential hypertension, 15 patients were complicated with metabolic syndrome while 41 patients were not. The nocturnal blood pressure fall was significant in patients without metabolic syndrome, while it was not so in patients with metabolic syndrome. Only in patients with metabolic syndrome was the nocturnal blood pressure fall enhanced by sodium restriction. The prevalence of sodium-sensitive hypertension in patients with metabolic syndrome was significantly higher than in those without metabolic syndrome (70.6 versus 36.0%, respectively; P = 0.017). A multiple logistic regression analysis revealed central obesity to be an independent risk factor for sodium-sensitive hypertension (odds ratio, 1.41; 95% confidence interval, 1.04-1.91). CONCLUSIONS: In patients with essential hypertension, an inter-relationship exists among metabolic syndrome, enhanced sodium sensitivity of the blood pressure and non-dipping. The elevated risk of cardiovascular diseases in patients with metabolic syndrome may be related to sodium-sensitive hypertension and non-dipping.

Adult↗
PubMed2006

Low blood flow estimates in lower-leg arteries predict cardiovascular events in Japanese patients with type 2 diabetes with normal ankle-brachial indexes.

OBJECTIVE: To examine the association of baseline measures in lower-leg arteries and conventional cardiovascular risk factors with the incidence of cardiovascular disease (CVD) events in type 2 diabetic patients with normal ankle-brachial indexes (ABIs) (>0.9). RESEARCH DESIGN AND METHODS: We studied 129 type 2 diabetic patients and 35 age-matched nondiabetic subjects with no apparent CVD consecutively admitted to our hospital. At baseline, total flow volume and resistive index, as an index of vascular resistance, at the popliteal artery was evaluated using gated two-dimensional cine-mode phase-contrast magnetic resonance imaging. Patients were followed 4.8 +/- 1.5 years (range 3.0-8.2) or until their first event of CVD. RESULTS: On follow-up, 16 patients developed primary CVD events. Patients with CVD had lower blood flow (P < 0.01) and higher vascular resistance (P < 0.05) than patients without CVD. When the patients were grouped into tertiles according to their levels of total flow volume (129.6-85.5, 85.3-63.3, and 62.7-23.8 ml/min), Kaplan-Meier analysis showed a higher probability of developing CVD events in patients in the lowest than in patients in the highest (P = 0.0199, log-rank test) tertile. Multivariate Cox proportional hazards analysis revealed that the lowest tertile for flow volume (hazard ratio [HR] 8.60, 95% CI 1.61-45.97, P = 0.012), hypertension (3.99, 1.12-14.25, P = 0.033), and smoking status (12.01, 1.21-119.28, P = 0.034) were significant independent predictors of CVD events. CONCLUSIONS: We have demonstrated that low blood flow estimates in lower-leg arteries may be predictive for CVD events among Japanese patients with type 2 diabetes even though they have a normal ABI.

Aged↗
PubMed2005

The transcription factor AP-2beta causes cell enlargement and insulin resistance in 3T3-L1 adipocytes.

We have reported the association of variations in the activating protein-2beta (AP-2beta) transcription factor gene with type 2 diabetes. This gene was preferentially expressed in 3T3-L1 adipocytes in a differentiation stage-dependent manner, and preliminary experiments showed that subjects with the disease-susceptible allele showed stronger expression in adipose tissue than those without the susceptible allele. Thus, we overexpressed the AP-2beta gene in 3T3-L1 adipocytes to clarify whether AP-2beta might play a crucial role in the pathogenesis of type 2 diabetes through dysregulation of adipocyte function. In cells overexpressing AP-2beta, cells increased in size by accumulation of triglycerides accompanied by enhanced glucose uptake. On the contrary, suppression of AP-2beta expression by small interfering RNA inhibited glucose uptake. Enhancement of glucose uptake by AP-2beta overexpression was attenuated by inhibitors of phospholipase C (PLC) and atypical protein kinase Czeta/lambda (PKCzeta/lambda), but not by a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Consistently, we found activation of PLC and atypical PKC, but not PI3-K, by AP-2beta expression. Furthermore, overexpression of PLCgamma enhanced glucose uptake, and this activation was inhibited by an atypical PKC inhibitor, suggesting that the enhanced glucose uptake may be mediated through PLC and atypical PKCzeta/lambda, but not PI3-K. Moreover, we observed the increased tyrosine phosphorylation of Grb2-associated binder-1 (Gab1) and its association with PLCgamma, indicating that Gab1 may be involved in AP-2beta-induced PLCgamma activation. Finally, AP-2beta overexpression was found to relate to the impaired insulin signaling. We propose that AP-2beta is a candidate gene for producing adipocyte hypertrophy and may relate to the abnormal characteristics of adipocytes observed in obesity.

3T3-L1 Cells↗
PubMed2005

Intronic polymorphisms within TFAP2B regulate transcriptional activity and affect adipocytokine gene expression in differentiated adipocytes.

We have identified a gene encoding transcription factor activating enhancer binding protein-2beta (TFAP2B) as a candidate for conferring susceptibility to type 2 diabetes. Although we have also found that TFAP2B was preferentially expressed in adipose cells in a differentiation-dependent manner, the mechanisms by which the gene and gene polymorphisms contribute to conferring susceptibility to the disease have not yet been elucidated. The aim of this study was to evaluate the impact of the polymorphisms within the TFAP2B gene on conferring susceptibility to type 2 diabetes. We identified that a 300-bp DNA fragment in intron 1 of TFAP2B had significant enhancer activity, and the variations of this region affected this enhancer activity in differentiated adipocytes. In an experiment using adenovirus vectors encoding TFAP2B, the expression of TNF-alpha gene was shown to be elevated in the TFAP2B overexpressing cells compared with those in control cells. Furthermore, we demonstrated that the expression of TFAP2B was increased in the adipose tissues of subjects with the disease-susceptibility allele, and the plasma levels of TNF-alpha and high sensitivity C-reactive peptide were significantly elevated in the patients with the disease-susceptibility allele. These results suggest that TFAP2B may contribute to the pathogenesis of type 2 diabetes through regulation of adipocytokine gene expression, and that TFAP2B may be a promising target for treatment or prevention of this disease.

3T3-L1 Cells↗
PubMed2005

Abnormal peripheral circulation in type 2 diabetic patients with normal ankle-brachial index associates with coronary atherosclerosis, large artery stiffness, and peripheral vascular resistance.

We tested the hypothesis that impaired peripheral circulation in diabetes arises from different aspects of vascular abnormalities even when accompanied by a normal ankle-brachial index (ABI>0.9). One hundred fourteen type 2 diabetic patients with normal ABI and 33 age-matched non-diabetic subjects consecutively admitted to our hospital were enrolled. The Agatston coronary artery calcium score (CACS), as a marker of coronary atherosclerosis, was obtained using electron-beam computed tomography. An automatic device was used to measure brachial-ankle pulse wave velocity (baPWV) as an index of arterial distensibility. Total flow volume and resistive index (RI), as a marker of peripheral vascular resistance, at the popliteal artery were evaluated using gated two-dimensional cine-mode phase-contrast magnetic resonance imaging. Diabetic patients had baPWV (P<0.001) and RI (P<0.001) higher than those in the non-diabetic subjects, indicating that those parameters are characteristically altered in diabetic patients. When diabetic patients were grouped into three subgroups according to their levels of total flow volume, those with the lowest range showed the highest log-transformed CACS (P<0.001), baPWV (P<0.001), and RI (P<0.001) among the groups. Total flow volume was negatively correlated with log-transformed CACS (P<0.001), baPWV (P<0.001), and RI (P<0.001). Waveform at the popliteal artery could be clearly separated into systolic and early and late diastolic blood flows, which were negatively correlated with log-transformed CACS (P<0.001), RI (P<0.001), and baPWV (P<0.001), respectively. These results suggest that impaired peripheral circulation in diabetes is attributable to coronary atherosclerosis, large artery stiffness, and peripheral vascular resistance even when ABI is normal.

Aged↗
PubMed2005

Genetic variations in the gene encoding TFAP2B are associated with type 2 diabetes mellitus.

To search a gene(s) conferring susceptibility to type 2 diabetes mellitus, we genotyped nearly 60,000 gene-based SNPs for Japanese patients and found evidence that the gene at chromosome 6p12 encoding transcription-factor-activating protein 2beta (TFAP2B) was a likely candidate in view of significant association of polymorphism in this gene with type 2 diabetes. Extensive analysis of this region identified that several variations within TFAP2B were significantly associated with type 2 diabetes [a variable number of tandem repeat locus: chi(2)=10.9, P=0.0009; odds ratio=1.57, 95% CI 1.20-2.06, intron 1+774 (G/T); chi(2)=11.6, P=0.0006; odds ratio=1.60, 95% CI 1.22-2.09, intron 1+2093 (A/C); chi(2)=12.2, P=0.0004; odds ratio=1.61, 95% CI 1.23-2.11]. The association of TFAP2B with type 2 diabetes was also observed in the UK population. These results suggest that TFAP2B might be a new candidate for conferring susceptibility to type 2 diabetes and contribute to the pathogenesis of type 2 diabetes.

Base Sequence↗
PubMed2005

Bidirectional regulation of monocyte chemoattractant protein-1 gene at distinct sites of its promoter by nitric oxide in vascular smooth muscle cells.

We have previously reported that chronic activation of phosphatidylinositol 3-kinase (PI3-kinase) by the overexpression of membrane-targeted p110CAAX induced proinflammatory gene expression in rat vascular smooth muscle cells (VSMCs) through the induction of CCAAT/enhancer binding protein-beta (C/EBP-beta) and C/EBP-delta. To examine the anti-inflammatory effect of nitric oxide (NO) on proinflammatory gene expression, we have investigated the effects of sodium nitroprusside (SNP) on the monocyte chemoattractant protein-1 (MCP-1) gene expression in VSMCs under chronic activation of PI3-kinase. At low concentrations (0.05 mM) of SNP, but not at high concentrations (0.5-1.0 mM), MCP-1 mRNA and protein expression as well as its transcriptional activity were significantly reduced. We found that SNP induced C/EBP homologous protein (CHOP) expression, which inhibited C/EBP binding activity and reduced the C/EBP activity induced by chronic activation of PI3-kinase in a dose-dependent manner up to 1.0 mM. Consistently, the increase in CHOP expression significantly reduced the MCP-1 promoter activity induced by PI3-kinase. However, the overexpression of CHOP alone upregulated MCP-1 promoter activity in a dose-dependent manner up to high concentrations. Deletion analysis of MCP-1 promoter and electrophoretic mobility shift assay identified the CHOP-response element (CHOP-RE) at the region between -190 and -179 bp of MCP-1 promoter. By using CHOP-RE as a decoy, we significantly suppressed the increase in promoter activity of MCP-1 induced by either CHOP or SNP. Thus CHOP induced by an NO donor has bidirectional effects on MCP-1 gene expression: it decreases gene expression by inhibition of C/EBPs, and it increases the gene expression through CHOP-RE.

Animals↗
PubMed2005

Diet high in lipid hydroperoxide by vitamin E deficiency induces insulin resistance and impaired insulin secretion in normal rats.

To clarify the effect of dietary lipid hydroperoxide (LPO) on development of glucose intolerance, we fed Sprague-Dawley rats on a diet containing elevated LPO level for 10 weeks and measured both insulin sensitivity and insulin secretion. The contents of LPO in both plasma and skeletal muscle in the LPO-fed rats were significantly higher than those in the controls. Both insulin resistance evaluated by steady-state blood glucose (SSBG) methods and impaired insulin secretion evaluated by oral glucose tolerance test (OGTT) were found in the LPO-fed rats as compared with control rats. Furthermore, the levels of insulin receptor substrate (IRS)-1 protein in the skeletal muscle were significantly lower in the LPO-fed rats. Those impairments were not reversed in LPO-fed rats with supernormal levels of plasma vitamin E following vitamin E supplementation for 5 weeks. Moreover, the immunohistochemical study revealed that NF-kappaB-p50 protein was found in the nucleus of pancreatic beta-cells of the LPO-fed rats, whereas it was not observed in the nucleus of the islets in the control rats. These findings indicate that NF-kappaB is activated in response to oxidative stress in pancreatic islet cells in LPO-fed rats. In conclusion, our studies reveal that diet high in LPO by vitamin E deficiency accelerates glucose intolerance through impairments of both sensitivity and secretion of insulin.

Animals↗
PubMed2004

Much lower prevalence of coronary calcium detected by electron-beam computed tomography among men aged 40-49 in Japan than in the US, despite a less favorable profile of major risk factors.

BACKGROUND: Since World War II (WWII), exposures to westernized lifestyle have occurred in many non-Western countries, including Japan. National surveys showed that risk factor profiles for atherosclerosis around 1990 were similar in men in the post WWII birth cohorts in the US and Japan. We compared the degree of coronary calcium and other factors in men in the post WWII birth cohort: men aged 40-49 in the US and Japan. METHODS: We conducted a cross-sectional study examining randomly selected 100 men from Kusatsu, Japan, and 100 men from Allegheny County, US. Coronary calcium was assessed using electron-beam computed tomography. RESULTS: Systolic blood pressure, total cholesterol, low density lipoprotein (LDL)-cholesterol, and smoking rates were higher among the Japanese (122.6 +/- 14.1 versus 113.7 +/- 9.6 mmHg, P < 0.01; 5.72 +/- 0.90 versus 4.99 +/- 0.81 mmol/l (220.9 +/- 34.6 versus 192.8 +/- 31.3 mg/dl), P < 0.01; 3.52 +/- 1.01 versus 3.10 +/- 0.78 mmol/l (136.0 +/- 39.0 versus 119.7 +/- 30.0 mg/dl), P < 0.01; and 48 versus 15%, P < 0.01, respectively). Triglycerides and fibrinogen were similar. High density lipoprotein (HDL)-cholesterol was higher among the Japanese. Body mass index, fasting insulin, and C-reactive protein were higher among the Americans. Prevalence of coronary artery calcium score >0 was strikingly lower among the Japanese than the Americans (13% versus 47%, P < 0.01). CONCLUSIONS: Much lower prevalence of coronary calcium despite a less favourable profile of many major independent risk factors in the Japanese might imply that there are strong protective factors against atherosclerosis in the Japanese. Further investigation is of critical importance.

Adult↗
PubMed2004

Regulation of ATP-sensitive potassium channel subunit Kir6.2 expression in rat intestinal insulin-producing progenitor cells.

We have reported that the combined expression of Pdx-1 (pancreatic duodenal homeobox 1) and Isl-1 (islet 1) enables immature rat enterocytes (IEC-6) to produce and release insulin. A key component regulating the release of insulin is the ATP-sensitive potassium channel subunit Kir6.2. To investigate the regulation of Kir6.2 gene expression, we assessed Kir6.2 expression in IEC-6 cells expressing Pdx-1 and/or Isl-1. We observed that Kir6.2 protein was expressed de novo in IEC-6 cells expressing both Pdx-1 and Isl-1 but not in cells expressing Pdx-1 alone. Next, we analyzed the regions of the Kir6.2 promoter (-1677/-45) by performing a luciferase assay and electrophoretic mobility shift assay. The results have demonstrated that Kir6.2 promoter possesses two regions regulating the promoter activity: a Foxa2-binding site (-1364 to -1210) and an Sp1/Sp3-binding site (-1035 to -939). The additional expression of Isl-1 in IEC-6 cells expressing Pdx-1 attenuated overexpression of Foxa2 protein and enhanced Kir6.2 expression. Finally, knockdown of Isl-1 using the iRNA technique resulted in decreased expression of Kir6.2 protein in a rat pancreatic beta-cell line (RIN-5F cells). These results indicate that expression of Kir6.2 in the rat intestine is moderated by Isl-1.

Adenosine Triphosphate↗
PubMed2004

Reduction of insulin-stimulated glucose uptake by peroxynitrite is concurrent with tyrosine nitration of insulin receptor substrate-1.

Inducible nitric oxide synthetase plays an essential role in insulin resistance induced by a high-fat diet. The reaction of nitric oxide with superoxide leads to the formation of peroxynitrite (ONOO-), which can modify several proteins. In this study, we investigated whether peroxynitrite impairs insulin-signalling pathway. Our experiments showed that 3-(4-morpholinyl)sydnonimine hydrochloride (SIN-1), a constitutive producer of peroxynitrite, dose-dependently inhibited insulin-stimulated glucose uptake. While SIN-1 did not affect the insulin receptor protein level and tyrosine phosphorylation, it reduced the insulin receptor substrate-1 (IRS-1) protein level, and IRS-1 associated phosphatidylinositol-3 kinase (PI-3 kinase) activity. Although SIN-1 did not induce Ser307 phosphorylation of IRS-1, tyrosine nitration of IRS-1 was detected in SIN-1-treated-Rat1 fibroblasts expressing human insulin receptors. Mass spectrometry showed that peroxynitrite induced at least four nitrated tyrosine residues in rat IRS-1, including Tyr939, which is critical for association of IRS-1 with the p85 subunit of PI-3 kinase. Our results suggest that peroxynitrite reduces the IRS-1 protein level and decreases phosphorylation of IRS-1 concurrent with nitration of its tyrosine residues.

3T3-L1 Cells↗
PubMed2004

A simple and sensitive method for glutamine:fructose-6-phosphate amidotransferase assay.

For measuring glutamine:fructose-6-phosphate amidotransferase (GFAT) activity in cultured cells, an enzyme method -GDH method- was set up with high-efficiency, high-sensitivity and simple operation by determining the formed glutamate. During the process of making samples, reduced glutathione (GSH, 5 mM) and glucose-6-phosphate Na2 (5 mM) were added to the buffer for scraping the cells. The range of protein content in the samples was 80-150 microg. In the GFAT activity assay, the end product reduced acetylpyridine adenine dinucleotide (APADH) was determined at 370 nm directly. The suitable concentrations of the reactants fructose-6-phosphate (F-6-P), glutamine, acetylpyridine adenine dinucleotide (APAD) and glutamate dehydrogenase (GDH) were 0.8, 6 and 0.3 mM and 6 U, respectively. However, the excess of APAD may interfere with the APADH measurement. The reaction time course was 90 min. The GFAT activity in 3T3-L1, L6, HepG2 and HIRc cells were 1.84-8.51 nmol glutamate/mg protein.min.

3T3-L1 Cells↗