Midori Fujishiro

Hiroshima University, Hiroshima-shi, Hiroshima-ken, Japan

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Publications (46)167.28 Total impact

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    ABSTRACT: Hypoglycemia is a cause of considerable morbidity. Although septic shock produces hypoglycemia and has been associated with higher mortality, hypoglycemia in infection without sepsis has not been reported in the literature. A 72-year-old Japanese woman treated with high-dose glucocorticoids for autoimmune hemolytic anemia, as well as intensive insulin therapy for type 2 diabetes, presented with severe hypoglycemia. A lung abscess was diagnosed by imaging studies and treated with intravenous antibiotics. Hypoglycemia spontaneously recurred during lung abscess exacerbations, despite appropriate de-escalation of antidiabetic therapy. Only mild sporadic episodes of hypoglycemia occurred after the lung abscess was controlled. Infection accompanied with malnutrition and immunosuppression, although in the absence of sepsis, may have contributed to hypoglycemia. Caution is warranted in the management of hypoglycemia in patients with diabetes with the conditions described here, that is malnutrition and immunosuppression, as infection may be a contributing factor.
    Journal of Medical Case Reports 02/2014; 8(1):51.
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    ABSTRACT: Gut microbiota alternations are associated with various disorders. In this study, gut microbiota changes were investigated in a methionine-choline deficient (MCD) diet-induced non-alcoholic steatohepatitis (NASH) rodent model, and the effects of administering Lactobacillus casei strain Shirota (LcS) on the development of NASH were also investigated. Mice were divided into three groups, given the normal chow diet (NCD), MCD diet, or the MCD diet plus daily oral administration of LcS for 6 weeks. Gut microbiota analyses for the three groups revealed that lactic acid bacteria such as Bifidobacterium and Lactobacillus in feces were markedly reduced by the MCD diet. Interestingly, oral administration of LcS to MCD diet-fed mice increased not only the L.casei subgroup but also other lactic acid bacteria. Subsequently, NASH development was evaluated based on hepatic histochemical findings, serum parameters and various mRNA and/or protein expression levels. LcS intervention markedly suppressed MCD-diet induced NASH development, with reduced serum lipopolysaccharide concentrations, suppression of inflammation and fibrosis in the liver, and reduced colon inflammation. Therefore, reduced populations of lactic acid bacteria in the colon may be involved in the pathogenesis of MCD diet-induced NASH, suggesting normalization of gut microbiota to be effective for treating NASH.
    AJP Gastrointestinal and Liver Physiology 10/2013; · 3.65 Impact Factor
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    ABSTRACT: Pin1 and Par14 are parvulin-type peptidyl prolyl cis/trans isomerases. While numerous proteins have been identified as Pin1 substrates, the target proteins of Par14 remain largely unknown. Par14 expression levels are increased in the livers and embryonic fibroblasts of Pin1 KO mice, suggesting a compensatory relationship between the functions of Pin1 and Par14. In this study, first, the association of Par14 with IRS-1 was demonstrated in HepG2 cells overexpressing both as well as endogenously in the mouse liver. The analysis using deletion-mutated Par14 and IRS-1 constructs revealed the N-terminal portion containing the basic domain of Par14 and the two relatively C-terminal portions of IRS-1 to be involved in these associations, in contrast to the WW domain of Pin1 and the SAIN domain of IRS-1. Par14 overexpression in HepG2 markedly enhanced insulin-induced IRS-1 phosphorylation and its downstream events; PI 3-kinase binding with IRS-1 and Akt phosphorylation. In contrast, treating HepG2 cells with Par14 siRNA suppressed these events. In addition, overexpression of Par14 in the insulin-resistant ob/ob mouse liver by adenoviral transfer significantly improved hyperglycemia with normalization of hepatic PEPCK and G6Pase mRNA levels, and gene suppression of Par14 using shRNA adenovirus significantly exacerbated the glucose intolerance in Pin1 KO mice. Therefore, although Pin1 and Par14 associate with different portions of IRS-1, the prolyl cis-trans isomerization in multiple sites of IRS-1 by these isomerases appears to be critical for efficient insulin receptor-induced IRS-1 phosphorylation. This process is likely to be one of the major mechanisms regulating insulin sensitivity and also constitutes a potential therapeutic target for novel insulin-sensitizing agents.
    Journal of Biological Chemistry 05/2013; · 4.65 Impact Factor
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    ABSTRACT: OBJECTIVE: Resistin-like molecule (RELM) β is a secretory protein homologous to resistin and reportedly contributes to local immune response regulation in gut and bronchial epithelial cells. However, we found that activated macrophages also express RELMβ and thus investigated the role of RELMβ in the development of atherosclerosis. APPROACH AND RESULTS: It was demonstrated that foam cells in atherosclerotic lesions of the human coronary artery abundantly express RELMβ. RELMβ knockout ((-/-)) and wild-type mice were mated with apolipoprotein E-deficient background mice. RELMβ(-/-) apolipoprotein E-deficient mice exhibited less lipid accumulation in the aortic root and wall than RELMβ(+/+) apolipoprotein E-deficient mice, without significant changes in serum lipid parameters. In vitro, RELMβ(-/-) peritoneal macrophages (PCPMs) exhibited weaker lipopolysaccharide-induced nuclear factor-κB classical pathway activation and inflammatory cytokine secretion than RELMβ(+/+), whereas stimulation with RELMβ upregulated inflammatory cytokine expressions and increased expressions of many lipid transporters and scavenger receptors in PCPMs. Flow cytometric analysis revealed inflammatory stimulation-induced RELMβ in F4/80(+) CD11c(+) PCPMs. In contrast, the expressions of CD11c and tumor necrosis factor were lower in RELMβ(-/-) PCPMs, but both were restored by stimulation with recombinant RELMβ. CONCLUSIONS: RELMβ is abundantly expressed in foam cells within plaques and contributes to atherosclerosis development via lipid accumulation and inflammatory facilitation.
    Arteriosclerosis Thrombosis and Vascular Biology 05/2013; · 6.34 Impact Factor
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    ABSTRACT: The dynamic process of adipose differentiation involves stepwise expressions of transcription factors and proteins specific to the mature fat cell phenotype. In this study, it was revealed that expression levels of IntS6 and IntS11, subunits of the Integrator complex, were increased in 3T3-L1 cells in the period when the cells reached confluence and differentiated into adipocytes, while being reduced to basal levels after the completion of differentiation. Suppression of IntS6 or IntS11 expression using siRNAs in 3T3-L1 preadipocytes markedly inhibited differentiation into mature adipocytes, based on morphological findings as well as mRNA analysis of adipocyte-specific genes such as Glut4, perilipin and Fabp4. Although Pparγ2 protein expression was suppressed in IntS6 or IntS11-siRNA treated cells, adenoviral forced expression of Pparγ2 failed to restore the capacity for differentiation into mature adipocytes. Taken together, these findings demonstrate that increased expression of Integrator complex subunits is an indispensable event in adipose differentiation. Although further study is necessary to elucidate the underlying mechanism, the processing of U1, U2 small nuclear RNAs may be involved in cell differentiation steps.
    Biochemical and Biophysical Research Communications 03/2013; · 2.41 Impact Factor
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    ABSTRACT: Inflammation involving adipose tissue is regarded as one of the major molecular mechanisms underlying obesity-related insulin resistance. Recent studies have suggested a series of angiotensin II receptor blockers (ARBs) to improve insulin resistance or protect against the development of diabetes mellitus. We previously demonstrated that valsartan suppresses the inflammatory response of macrophages. Interestingly, however, this effect did not occur via peroxisome proliferator-activated receptor (PPAR) γ or the AT1a receptor. This suppression appears to secondarily lead to amelioration of insulin resistance and reductions in abnormal gene expressions in adipocytes. In addition to these in vitro findings, we herein demonstrate the in vivo effects of valsartan, using mice constitutively infused with lipopolysaccharide (LPS) for 4 weeks. Oral administration of valsartan to LPS-infused mice normalized the increased expressions of inflammatory cytokines in adipose and liver tissues. These results raise the possibility that valsartan not only contributes to normalization of obesity-related insulin resistance, but is also beneficial for the treatment of other diseases with inflammation related to the metabolic syndrome such as atherosclerosis and non-alcoholic steatohepatitis. Further study is necessary to clarify these issues.
    Adipocyte. 01/2013; 2(1):28-32.
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    ABSTRACT: Non-alcoholic steatohepatitis (NASH) is a disorder characterized by simultaneous fat accumulation and chronic inflammation in the liver. In this study, Pin1 expression was revealed to be markedly increased in the livers of mice with MCDD (Methionine choline-deficient diet)-induced NASH, a rodent model of NASH. In addition, Pin1 KO mice were highly resistant to MCDD-induced NASH, based on a series of data showing simultaneous fat accumulation, chronic inflammation and fibrosis in the liver. In terms of Pin1-induced fat accumulation, it was revealed that the expression levels of PPARα and its target genes were higher in the livers of Pin1 KO mice than in controls. Thus, resistance of Pin1 KO mice to hepatic steatosis is partially attributable to lack of Pin1-induced down-regulation of PPARα, although multiple other mechanisms are apparently involved. Another mechanism involves the enhancing effect of hematopoietic Pin1 on the expressions of inflammatory cytokines such as tumor necrosis factorαand monocyte chemoattractant protein 1 through NF-κB activation, eventually leading to hepatic fibrosis. Finally, to distinguish the roles of hematopoietic or non-hematopoietic Pin1 in NASH development, mice lacking Pin1 in either non-hematopoietic or hematopoietic cells were produced by bone marrow transplantation between wild-type and Pin1 KO mice. The mice having non-hematopoietic Pin1 exhibited fat accumulation without liver fibrosis on the MCD diet. Thus, hepatic Pin1 appears to be directly involved in the fat accumulation in hepatocytes, while Pin1 in hematopoietic cells contribute to inflammation and fibrosis. In summary, this is the first study to demonstrate that Pin1 plays critical roles in NASH development. This report also raises the possibility that hepatic Pin1 inhibition to the appropriate level might provide a novel therapeutic strategy for NASH.
    Journal of Biological Chemistry 10/2012; · 4.65 Impact Factor
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    ABSTRACT: Hyperuricemia is common in patients with metabolic syndrome. We investigated the role of xanthine oxidoreductase (XOR) in atherosclerosis development, and the effects of the XOR inhibitor allopurinol on this process. Oral administration of allopurinol to ApoE knockout mice markedly ameliorated lipid accumulation and calcification in the aorta and aortic root. In addition, allopurinol treatment or siRNA-mediated gene knockdown of XOR suppressed transformation of J774.1 murine macrophage cells, treated with acetylated LDL or very low density lipoprotein (VLDL) into foam cells. This inhibitory effect of allopurinol was also observed in primary cultured human macrophages. In contrast, overexpression of XOR promoted transformation of J774.1 cells into foam cells. Interestingly, SR-A1, SR-B1, SR-B II, and VLDL receptors in J774.1 cells were reduced by XOR knockdown, and increased by XOR overexpression. Conversely, expressions of ABCA1 and ABCG1 were increased by XOR knockdown and suppressed by XOR overexpression. Finally, productions of inflammatory cytokines accompanied by foam cell formation were also reduced by allopurinol administration. These results strongly suggest XOR activity and/or its expression level to contribute to macrophage foam cell formation. Thus, XOR inhibitors may be useful for preventing atherosclerosis.
    Arteriosclerosis Thrombosis and Vascular Biology 11/2011; 32(2):291-8. · 6.34 Impact Factor
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    ABSTRACT: Macrophages are integrated into adipose tissues and interact with adipocytes in obese subjects, thereby exacerbating adipose insulin resistance. This study aimed to elucidate the molecular mechanism underlying the insulin-sensitizing effect of the angiotensin II receptor blocker (ARB) valsartan, as demonstrated in clinical studies. Insulin signaling, i.e., insulin receptor substrate-1 and Akt phosphorylations, in 3T3-L1 adipocytes was impaired markedly by treatment with tumor necrosis factor-α (TNFα) or in the culture medium of lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages, and valsartan had no effects on these impairments. However, in contrast, when cocultured with RAW 264.7 cells using a transwell system, the LPS-induced insulin signaling impairment in 3T3-L1 adipocytes showed almost complete normalization with coaddition of valsartan. Furthermore, valsartan strongly suppressed LPS-induced productions of cytokines such as interleukin (IL)-1β, IL-6, and TNFα with nuclear factor-κB activation and c-Jun NH(2)-terminal kinase phosphorylation in RAW 264.7 and primary murine macrophages. Very interestingly, this effect of valsartan was also observed in THP-1 cells treated with angiotensin II type 1 (AT1) siRNA or a peroxisome proliferator-activated receptor-γ (PPARγ) antagonist as well as macrophages from AT1a receptor-knockout mice. We conclude that valsartan suppresses the inflammatory response of macrophages, albeit not via PPARγ or the AT1a receptor. This suppression appears to secondarily improve adipose insulin resistance.
    AJP Endocrinology and Metabolism 11/2011; 302(3):E286-96. · 4.51 Impact Factor
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    ABSTRACT: Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) is a unique enzyme that associates with the pSer/Thr-Pro motif and catalyzes cis-trans isomerization. We identified Pin1 in the immunoprecipitates of overexpressed IRS-1 with myc and FLAG tags in mouse livers and confirmed the association between IRS-1 and Pin1 by not only overexpression experiments but also endogenously in the mouse liver. The analysis using deletion- and point-mutated Pin1 and IRS-1 constructs revealed the WW domain located in the N terminus of Pin1 and Ser-434 in the SAIN (Shc and IRS-1 NPXY binding) domain of IRS-1 to be involved in their association. Subsequently, we investigated the role of Pin1 in IRS-1 mediation of insulin signaling. The overexpression of Pin1 in HepG2 cells markedly enhanced insulin-induced IRS-1 phosphorylation and its downstream events: phosphatidylinositol 3-kinase binding with IRS-1 and Akt phosphorylation. In contrast, the treatment of HepG2 cells with Pin1 siRNA or the Pin1 inhibitor Juglone suppressed these events. In good agreement with these in vitro data, Pin1 knock-out mice exhibited impaired insulin signaling with glucose intolerance, whereas adenoviral gene transfer of Pin1 into the ob/ob mouse liver mostly normalized insulin signaling and restored glucose tolerance. In addition, it was also demonstrated that Pin1 plays a critical role in adipose differentiation, making Pin1 knock-out mice resistant to diet-induced obesity. Importantly, Pin1 expression was shown to be up-regulated in accordance with nutrient conditions such as food intake or a high-fat diet. Taken together, these observations indicate that Pin1 binds to IRS-1 and thereby markedly enhances insulin action, essential for adipogenesis.
    Journal of Biological Chemistry 06/2011; 286(23):20812-20822. · 4.65 Impact Factor
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    ABSTRACT: Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) is a unique enzyme that associates with the pSer/Thr-Pro motif and catalyzes cis-trans isomerization. We identified Pin1 in the immunoprecipitates of overexpressed IRS-1 with myc and FLAG tags in mouse livers and confirmed the association between IRS-1 and Pin1 by not only overexpression experiments but also endogenously in the mouse liver. The analysis using deletion- and point-mutated Pin1 and IRS-1 constructs revealed the WW domain located in the N terminus of Pin1 and Ser-434 in the SAIN (Shc and IRS-1 NPXY binding) domain of IRS-1 to be involved in their association. Subsequently, we investigated the role of Pin1 in IRS-1 mediation of insulin signaling. The overexpression of Pin1 in HepG2 cells markedly enhanced insulin-induced IRS-1 phosphorylation and its downstream events: phosphatidylinositol 3-kinase binding with IRS-1 and Akt phosphorylation. In contrast, the treatment of HepG2 cells with Pin1 siRNA or the Pin1 inhibitor Juglone suppressed these events. In good agreement with these in vitro data, Pin1 knock-out mice exhibited impaired insulin signaling with glucose intolerance, whereas adenoviral gene transfer of Pin1 into the ob/ob mouse liver mostly normalized insulin signaling and restored glucose tolerance. In addition, it was also demonstrated that Pin1 plays a critical role in adipose differentiation, making Pin1 knock-out mice resistant to diet-induced obesity. Importantly, Pin1 expression was shown to be up-regulated in accordance with nutrient conditions such as food intake or a high-fat diet. Taken together, these observations indicate that Pin1 binds to IRS-1 and thereby markedly enhances insulin action, essential for adipogenesis.
    Journal of Biological Chemistry 03/2011; 286(23):20812-22. · 4.65 Impact Factor
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    ABSTRACT: Glucose transporter 1 (GLUT1) is widely distributed throughout various tissues and contributes to insulin-independent basal glucose uptake. Using a split-ubiquitin membrane yeast two-hybrid system, we newly identified 4F2 heavy chain (4F2hc) as a membrane protein interacting with GLUT1. Though 4F2hc reportedly forms heterodimeric complexes between amino acid transporters, such as LAT1 and LAT2, and regulates amino acid uptake, we investigated the effects of 4F2hc on GLUT1 expression and the associated glucose uptake. First, FLAG-tagged 4F2hc and hemagglutinin-tagged GLUT1 were overexpressed in human embryonic kidney 293 cells and their association was confirmed by coimmunoprecipitation. The green fluorescent protein-tagged 4F2hc and DsRed-tagged GLUT1 showed significant, but incomplete, colocalization at the plasma membrane. In addition, an endogenous association between GLUT1 and 4F2hc was demonstrated using mouse brain tissue and HeLa cells. Interestingly, overexpression of 4F2hc increased the amount of GLUT1 protein in HeLa and HepG2 cells with increased glucose uptake. In contrast, small interfering RNA (siRNA)-mediated 4F2hc gene suppression markedly reduced GLUT1 protein in both cell types, with reduced glucose uptake. While GLUT1 mRNA levels were not affected by overexpression or gene silencing of 4F2hc, GLUT1 degradation after the addition of cycloheximide was significantly suppressed by 4F2hc overexpression and increased by 4F2hc siRNA treatment. Taken together, these observations indicate that 4F2hc is likely to be involved in GLUT1 stabilization and to contribute to the regulation of not only amino acid but also glucose metabolism.
    AJP Cell Physiology 01/2011; 300(5):C1047-54. · 3.71 Impact Factor
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    ABSTRACT: Pin1 is a unique regulator, which catalyzes the conversion of a specific phospho-Ser/Thr-Pro-containing motif in target proteins. Herein, we identified CRTC2 as a Pin1-binding protein by overexpressing Pin1 with Myc and FLAG tags in mouse livers and subsequent purification of the complex containing Pin1. The association between Pin1 and CRTC2 was observed not only in overexpression experiments but also endogenously in the mouse liver. Interestingly, Ser(136) in the nuclear localization signal of CRTC2 was shown to be involved in the association with Pin1. Pin1 overexpression in HepG2 cells attenuated forskolin-induced nuclear localization of CRTC2 and cAMP-responsive element (CRE) transcriptional activity, whereas gene knockdown of Pin1 by siRNA enhanced both. Pin1 also associated with CRTC1, leading to their cytosol localization, essentially similar to the action of CRTC2. Furthermore, it was shown that CRTC2 associated with Pin1 did not bind to CREB. Taken together, these observations indicate the association of Pin1 with CRTC2 to decrease the nuclear CBP·CRTC·CREB complex. Indeed, adenoviral gene transfer of Pin1 into diabetic mice improved hyperglycemia in conjunction with normalizing phosphoenolpyruvate carboxykinase mRNA expression levels, which is regulated by CRE transcriptional activity. In conclusion, Pin1 regulates CRE transcriptional activity, by associating with CRTC1 or CRTC2.
    Journal of Biological Chemistry 10/2010; 285(43):33018-27. · 4.65 Impact Factor
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    ABSTRACT: Pin1 is a unique regulator, which catalyzes the conversion of a specific phospho-Ser/Thr-Pro-containing motif in target proteins. Herein, we identified CRTC2 as a Pin1-binding protein by overexpressing Pin1 with Myc and FLAG tags in mouse livers and subsequent purification of the complex containing Pin1. The association between Pin1 and CRTC2 was observed not only in overexpression experiments but also endogenously in the mouse liver. Interestingly, Ser136 in the nuclear localization signal of CRTC2 was shown to be involved in the association with Pin1. Pin1 overexpression in HepG2 cells attenuated forskolin-induced nuclear localization of CRTC2 and cAMP-responsive element (CRE) transcriptional activity, whereas gene knockdown of Pin1 by siRNA enhanced both. Pin1 also associated with CRTC1, leading to their cytosol localization, essentially similar to the action of CRTC2. Furthermore, it was shown that CRTC2 associated with Pin1 did not bind to CREB. Taken together, these observations indicate the association of Pin1 with CRTC2 to decrease the nuclear CBP·CRTC·CREB complex. Indeed, adenoviral gene transfer of Pin1 into diabetic mice improved hyperglycemia in conjunction with normalizing phosphoenolpyruvate carboxykinase mRNA expression levels, which is regulated by CRE transcriptional activity. In conclusion, Pin1 regulates CRE transcriptional activity, by associating with CRTC1 or CRTC2.
    Journal of Biological Chemistry 10/2010; 285(43):33018-33027. · 4.65 Impact Factor
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    ABSTRACT: A 59-year-old female with type 1 diabetes and RS3PE had HLA types known to be associated with both diseases. Type 1 diabetes patients suffering from polyarthritis and pitting edema should be examined for possible RS3PE and glucocorticoid therapy may be indicated despite the diabetes.
    Diabetes research and clinical practice 10/2010; 91(2):e43-4. · 2.74 Impact Factor
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    ABSTRACT: Aims: Energy sensing systems including AMPK and SIRT1 play important roles in the regulation of hepatic gluconeogenesis and fatty acid oxidation. In this study, we investigated how hepatic LKB1-AMPK signaling and SIRT1 expression are altered after 2 or 8 weeks of HFD feeding.Methods: The livers of male mice fed a HFD or a standard diet for 2 or 8 weeks were removed. The expression and phosphorylation levels of LKB1, AMPK, ACC and TORC2, and SIRT1 expression levels were examined by immunoblotting.Results: In mice fed a HFD for 2 weeks, the phosphorylations of AMPKα and ACC were decreased without significant alterations in LKB1 phosphorylation or SIRT1 protein levels, while TORC2 protein levels were increased. In mice fed a HFD for 8 weeks, marked reductions in LKB1 phosphorylation and SIRT1 protein amount were observed in addition to the decreased phosphorylations of AMPKα and ACC.Conclusions: The mechanisms underlying impaired energy sensing signaling differ with the duration of HFD feeding. In the early phase of HFD feeding, LKB1 and SIRT1 were not impaired, while in the later phase of HFD feeding, decreased SIRT1 expression and LKB1 phosphorylation may be involved in the development of severe glucose and lipid intolerance.
    Obesity Research & Clinical Practice 01/2010; 4(3):e163-e246. · 0.51 Impact Factor
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    ABSTRACT: The differentiation of macrophages into cytokine-secreting foam cells plays a critical role in the development of diabetic angiopathy. J774.1, a murine macrophage cell line, reportedly differentiates into foam cells when incubated with oxidized LDL, ApoE-rich VLDL or WHHLMI (myocardial infarction-prone Watanabe heritable hyperlipidemic) rabbit serum. In this study, serum samples from Type 2 diabetic patients were added to the medium with J774.1 cells and the degree of foam cell induction was quantified by measuring lipid accumulation. These values were calculated relative to the activities of normal and WHHLMI rabbit sera as 0% and 100%, respectively, and termed the MMI (Macrophage Maturation Index). These MMI values reflected intracellular lipids, including cholesteryl ester assayed by GC/MS. Statistical analysis revealed MMI to correlate positively and independently with serum triglycerides, the state of diabetic retinopathy, nephropathy and obesity, but negatively with administration of alpha-glucosidase inhibitors or thiazolidinediones. Taken together, our results suggest that this novel assay may be applicable to the identification of patients at risk for rapidly progressive angiopathic disorders.
    Diabetes research and clinical practice 11/2009; 87(1):57-63. · 2.74 Impact Factor
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    ABSTRACT: AMP-activated protein kinase (AMPK) activation reportedly suppresses transcriptional activity of the cAMP-responsive element (CRE) in the phosphoenolpyruvate carboxykinase C (PEPCK-C) promoter and reduces hepatic PEPCK-C expression. Although a previous study found TORC2 phosphorylation to be involved in the suppression of AMPK-mediated CRE transcriptional activity, we herein present evidence that glycogen synthase kinase 3beta (GSK3beta) phosphorylation induced by AMPK also plays an important role. We initially found that injecting fasted mice with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) markedly increased Ser-9 phosphorylation of hepatic GSK3beta within 15 min. Stimulation with AICAR or the GSK3beta inhibitor SB-415286 strongly inhibited CRE-containing promoter activity in HepG2 cells. Using the Gal4-based transactivation assay system, the transcriptional activity of cAMP-response element-binding protein (CREB) was suppressed by both AICAR and SB415286, whereas that of TORC2 was repressed significantly by AICAR but very slightly by SB415286. These results show inactivation of GSK3beta to directly inhibit CREB but not TORC2. Importantly, the AICAR-induced suppression of PEPCK-C expression was shown to be blunted by overexpression of GSK3beta(S9G) but not wild-type GSK3beta. In addition, AICAR stimulation decreased, whereas Compound C (AMPK inhibitor) increased CREB phosphorylation (Ser-129) in HepG2 cells. The time-courses of decreased CREB phosphorylation (Ser-129) and increased GSK3beta phosphorylation were very similar. Furthermore, AMPK-mediated GSK3beta phosphorylation was inhibited by an Akt-specific inhibitor in HepG2 cells, suggesting involvement of the Akt pathway. In summary, phosphorylation (Ser-9) of GSK3beta is very likely to be critical for AMPK-mediated PEPCK-C gene suppression. Reduced CREB phosphorylation (Ser-129) associated with inactivation of GSK3beta by Ser-9 phosphorylation may be the major mechanism underlying PEPCK-C gene suppression by AMPK-activating agents such as biguanide.
    Journal of Biological Chemistry 10/2008; 283(49):33902-10. · 4.65 Impact Factor
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    ABSTRACT: Several serine/threonine kinases reportedly phosphorylate serine residues of IRS-1 and thereby induce insulin resistance. In this study, to investigate the effect of mTOR/raptor on insulin signaling and metabolism in K/KAy mice with genetic obesity-associated insulin resistance, a dominant negative raptor, COOH-terminally deleted raptor (raptor-DeltaC(T)), was overexpressed in the liver via injection of its adenovirus into the circulation. Hepatic raptor-DeltaC(T) expression levels were 1.5- to 4-fold that of endogenously expressed raptor. Glucose tolerance in raptor-DeltaC(T)-overexpressing mice improved significantly compared with that of LacZ-overexpressing mice. Insulin-induced activation of p70S6 kinase (p70(S6k)) was significantly suppressed in the livers of raptor-DeltaC(T) overexpressing mice. In addition, insulin-induced IRS-1, Ser(307), and Ser(636/639) phosphorylations were significantly suppressed in the raptor-DeltaC(T)-overexpressing liver, whereas tyrosine phosphorylation of IRS-1 was increased. PI 3-kinase activation in response to insulin stimulation was increased approximately twofold, and Akt phosphorylation was clearly enhanced under both basal and insulin-stimulated conditions in the livers of raptor-DeltaC(T) mice. Thus, our data indicate that suppression of the mTOR/p70(S6k) pathway leads to improved glucose tolerance in K/KAy mice. These observations may contribute to the development of novel antidiabetic agents.
    AJP Endocrinology and Metabolism 05/2008; 294(4):E719-25. · 4.51 Impact Factor
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    ABSTRACT: Resistin was initially identified as a protein, secreted by adipocytes, which inhibits insulin action and adipose differentiation. The three proteins homologous to resistin were identified and given the names resistin-like molecules (RELM) alpha, beta and gamma. Resistin and RELMalpha are abundantly expressed in adipose, but RELMbeta and RELMgamma are secreted mainly from the gut. Since nutrient composition greatly affects insulin sensitivity, we investigated the regulatory effects of various nutritional factors in food on the expressions of resistin family proteins. First, mice were given diets with different nutritional compositions (high-carbohydrate, high-protein and high-fat) for 2 weeks. RELMbeta mRNA expression in the intestines was markedly suppressed by the high-protein and high-carbohydrate diets, while slightly but not significantly upregulated by the high-fat diet. In the epididymal fat, resistin expression was unchanged, while RELMalpha expression was markedly decreased by the high-carbohydrate diet. Taking into consideration that humans have neither RELMalpha nor RELMgamma, our subsequent studies focused on RELMbeta expression. We used the human colon cancer cell line LS174T. Treatments with insulin and TNFalpha as well as stearic acid, a saturated free fatty acid, upregulated RELMbeta expression, while d-glucose downregulated RELMbeta. These results suggest RELMbeta expression to be regulated directly by nutrients such as glucose and saturated free fatty acids including stearic acid, as well as by hormones including insulin and TNFalpha. These regulations may play an important role in the nutrient-associated induction of insulin resistance.
    Diabetes research and clinical practice 02/2008; 79(1):2-10. · 2.74 Impact Factor

Publication Stats

964 Citations
167.28 Total Impact Points

Institutions

  • 2009–2013
    • Hiroshima University
      • • Department of Dental and Medical Biochemistry
      • • School of Medicinal Sciences
      Hiroshima-shi, Hiroshima-ken, Japan
  • 2001–2013
    • The University of Tokyo
      • • Division of Internal Medicine
      • • Department of Internal Medicine
      Edo, Tōkyō, Japan
  • 2006
    • Nagoya University
      • Graduate School of Medicine
      Nagoya-shi, Aichi-ken, Japan