Tohru Sakai

Exendin-4, a GLP-1 receptor agonist, directly induces adiponectin expression through protein kinase A pathway and prevents inflammatory adipokine expression

Exendin-4 (Ex-4) is a glucagon-like peptide-1 receptor (GLP-1R) agonist that has been used as a drug injected subcutaneously for treatment of type 2 diabetes. Many studies have revealed molecular targets of Ex-4, but its influence on adipokines has not been determined. Our study showed that Ex-4 induced secretion of adiponectin into the culture medium of 3T3-L1 adipocytes. This effect of Ex-4 is due to increased adiponectin mRNA level through the GLP-1R. Both forskolin and 3-isobutyl-1-methylxanthine (IBMX), which may finally elevate cyclic adenosine monophosphate (cAMP) concentration, prevented the induction of adiponectin expression by Ex-4. Moreover, H89, a protein kinase A inhibitor, blocked the effect of Ex-4 on adiponectin. On the other hand, Ex-4 decreased the mRNA levels of inflammatory adipokines. The results indicate that Ex-4 directly promotes adiponectin secretion via the protein kinase A pathway in 3T3-L1 adipocytes and may ameliorate insulin resistance.

Myosin IIA participates in docking of Glut4 storage vesicles with the plasma membrane in 3T3-L1 adipocytes

In adipocytes and myocytes, insulin stimulation translocates glucose transporter 4 (Glut4) storage vesicles (GSVs) from their intracellular storage sites to the plasma membrane (PM) where they dock with the PM. Then, Glut4 is inserted into the PM and initiates glucose uptake into these cells. Previous studies using chemical inhibitors demonstrated that myosin II participates in fusion of GSVs and the PM and increase in the intrinsic activity of Glut4. In this study, the effect of myosin IIA on GSV trafficking was examined by knocking down myosin IIA expression. Myosin IIA knockdown decreased both glucose uptake and exposures of myc-tagged Glut4 to the cell surface in insulin-stimulated cells, but did not affect insulin signal transduction. Interestingly, myosin IIA knockdown failed to decrease insulin-dependent trafficking of Glut4 to the PM. Moreover, in myosin IIA knockdown cells, insulin-stimulated binding of GSV SNARE protein, vesicle-associated membrane protein 2 (VAMP2) to PM SNARE protein, syntaxin 4 was inhibited. These data suggest that myosin IIA plays a role in insulin-stimulated docking of GSVs to the PM in 3T3-L1 adipocytes through SNARE complex formation.

Association between blood levels of PCDDs/PCDFs/dioxin-like PCBs and history of allergic and other diseases in the Japanese population.

BackgroundPrevious studies reported that exposure to dioxins was associated with an increased risk of various diseases in general populations.ObjectivesThe aim of this study was to examine the association between levels of dioxins in blood and allergic and other diseases.MethodsWe conducted a cross-sectional study on 1,063 men and 1,201 women (aged 15–76xa0years), who were living throughout Japan and not occupationally exposed to dioxins, during 2002–2010. In fasting blood samples, polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like PCBs (DL-PCBs) were analyzed by isotope dilution high-resolution gas chromatography/mass spectrometry. We obtained information on life style and self-reported history of diseases using a questionnaire. Blood pressure, blood levels of hemoglobin A1c, and serum lipids were also measured. Multiple logistic regression models were used to analyze the association between dioxin levels in blood and various diseases.ResultsToxic equivalents of PCDDs/PCDFs and total dioxins showed significant inverse dose–response relationships with atopic dermatitis, after adjustments for potential confounders. The highest quartile for total dioxins had an adjusted odds ratio of 0.26 (95xa0% confidence interval 0.08–0.70) compared to the reference group (first quartile). The odds ratios for hypertension, diabetes mellitus, hyperlipidemia, gout in men, and gynecologic diseases in women significantly increased with increasing toxic equivalents of PCDDs/PCDFs, DL-PCBs, and total dioxins in blood.ConclusionsThe present findings suggest that background exposure to dioxins was associated with reduced risk of atopic dermatitis. The results also support the idea that low-level exposure to dioxins is associated with an increased risk of diabetes, hypertension, and hyperlipidemia.

Sudachitin, a polymethoxylated flavone, improves glucose and lipid metabolism by increasing mitochondrial biogenesis in skeletal muscle

BackgroundObesity is a major risk factor for insulin resistance, type 2 diabetes, and stroke. Flavonoids are effective antioxidants that protect against these chronic diseases. In this study, we evaluated the effects of sudachitin, a polymethoxylated flavonoid found in the skin of the Citrus sudachi fruit, on glucose, lipid, and energy metabolism in mice with high-fat diet-induced obesity and db/db diabetic mice. In our current study, we show that sudachitin improves metabolism and stimulates mitochondrial biogenesis, thereby increasing energy expenditure and reducing weight gain.MethodsC57BL/6xa0J mice fed a high-fat diet (40% fat) and db/db mice fed a normal diet were treated orally with 5xa0mg/kg sudachitin or vehicle for 12xa0weeks. Following treatment, oxygen expenditure was assessed using indirect calorimetry, while glucose tolerance, insulin sensitivity, and indices of dyslipidemia were assessed by serum biochemistry. Quantitative polymerase chain reaction was used to determine the effect of sudachitin on the transcription of key metabolism-regulating genes in the skeletal muscle, liver, and white and brown adipose tissues. Primary myocytes were also prepared to examine the signaling mechanisms targeted by sudachitin in vitro.ResultsSudachitin improved dyslipidemia, as evidenced by reduction in triglyceride and free fatty acid levels, and improved glucose tolerance and insulin resistance. It also enhanced energy expenditure and fatty acid β-oxidation by increasing mitochondrial biogenesis and function. The in vitro assay results suggest that sudachitin increased Sirt1 and PGC-1α expression in the skeletal muscle.ConclusionsSudachitin may improve dyslipidemia and metabolic syndrome by improving energy metabolism. Furthermore, it also induces mitochondrial biogenesis to protect against metabolic disorders.

Vimentin binds IRAP and is involved in GLUT4 vesicle trafficking

Insulin-responsive aminopeptidase (IRAP) and GLUT4 are two major cargo proteins of GLUT4 storage vesicles (GSVs) that are translocated from a postendosomal storage compartment to the plasma membrane (PM) in response to insulin. The cytoplasmic region of IRAP is reportedly involved in retention of GSVs. In this study, vimentin was identified using the cytoplasmic domain of IRAP as bait. The validity of this interaction was confirmed by pull-down assays and immunoprecipitation in 3T3-L1 adipocytes. In addition, it was shown that GLUT4 translocation to the PM by insulin was decreased in vimentin-depleted adipocytes, presumably due to dispersing GSVs away from the cytoskeleton. These findings suggest that the IRAP binding protein, vimentin, plays an important role in retention of GSVs.

Soy Isoflavone Equol Perpetuates Dextran Sulfate Sodium-Induced Acute Colitis in Mice

The effects of the soy isoflavones, genistein, daidzein and equol, on experimental colitis were examined. Equol severely perpetrated dextran sulfate sodium (DSS)-induced colitis as evaluated by the weight loss. Production of the anti-inflammatory cytokine, IL-10, from T cells was decreased in the equol-treated mice. The results show that the soy isoflavone, equol, played an important role in the inflammatory response in the gastrointestinal tract.

Effects of chemotherapy on gene expression of lingual taste receptors in patients with head and neck cancer.

We aimed to test the hypothesis that chemotherapy changes the gene expression of taste receptors in the tongue to induce dysgeusia in patients with head and neck cancer.

Dietary Ribonucleic Acid Suppresses Inflammation of Adipose Tissue and Improves Glucose Intolerance That Is Mediated by Immune Cells in C57BL/6 Mice Fed a High-Fat Diet

Recent evidence suggests that immune cells play an important role in differentiation of inflammatory macrophages in adipose tissue, which contributes to systemic chronic inflammation. Dietary ribonucleic acid (RNA) has been shown to modulate immune function. We hypothesized that RNA affects immune cell function in adipose tissue and then improves inflammatory response in adipose tissue. C57/BL6 mice and recombination activating gene-1 (RAG-1) knockout mice on a C57BL/6 mice background were fed a high-fat diet containing 1% RNA for 12 wk. An oral glucose tolerance test was performed. Supplementation of dietary RNA in C57BL/6 mice fed a high-fat diet resulted in a smaller area under the curve (AUC) after oral glucose administration than that for control mice. The mRNA expression levels of inflammation-related cytokines in adipose tissue and serum interleukin-6 levels were reduced by dietary RNA supplementation. Interestingly, reduction of the AUC value by RNA supplementation was abolished in T and B cell-deficient RAG-1 knockout mice. These results indicate that RNA improves inflammation in adipose tissue and reduces the AUC value following oral glucose administration in a T and B cell-dependent manner.

Vitamin A Deficiency Impairs Induction of Oral Tolerance in Mice

Oral tolerance is a phenomenon of induction of systemic unresponsiveness to antigens ingested by the oral route and loss of immune response. Studies have shown the importance of vitamin A in oral tolerance in vitro but not in an in vivo experimental model. Therefore, we carried out experiments to determine how vitamin A deficiency affects tolerance induction and the ability of mesenteric lymph node (MLN) CD11c(+) cells to induce regulatory T cells (Tregs). Immunological tolerance was induced by oral ovalbumin (OVA) administration in vitamin A-sufficient mice. OVA-specific antibody and cytokine production were significantly reduced. On the other hand, in vitamin A-deficient mice, both OVA-specific antibody and cytokine production were not suppressed by oral OVA administration. Regarding induction of Tregs, the conversion rate of Foxp3(+) cells from naïve CD4(+) cell by CD11c(+) cells was decreased in vitamin A-deficient mice. Our study indicates that vitamin A deficiency causes the breakdown of oral tolerance in vivo.

High phosphate diet reduces atherosclerosis formation in apolipoprotein E-deficient mice.

Although higher serum phosphate level is a risk factor for cardiovascular diseases in general population as well as chronic kidney disease patients, it has not been clarified whether higher phosphate can affect atherosclerotic plaque formation. In this study, we investigated the effect of prolonged-intake of different concentrations of phosphate on atherosclerosis formation using apolipoprotein E-deficient mice. Apolipoprotein E-deficient mice were fed with high fat diet including 0.6%, 1.2% or 1.8% phosphate. After 20-week treatment, atherosclerotic plaque formation in aorta in 1.8% phosphate diet group was unexpectedly less than that in the other groups. To elucidate mechanisms of suppression of plaque formation by high phosphate diet, we hypothesized that high phosphate diet may modify a profile of monocytes/macrophages suppressing plaque formation. We confirmed that elevated peripheral monocytes (CD11b+, F4/80+ cell numbers) in apolipoprotein E-deficient mice were decreased by feeding with 1.8% P diet. In addition, ex vivo study indicated that high dose of phosphate induced macrophage apoptosis. These observations suggest that excess phosphate intake decreased atherosclerosis formation, at least in part, by changing the profile of peripheral monocytes or inducing apoptosis of macrophages in apolipoprotein E-deficient mice.