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ABSTRACT: Glucose-induced insulin secretion from pancreatic ß-cells depends critically on activity of ATP-sensitive K+ channels (KATP channel). We previously generated mice lacking Kir6.2, the pore subunit of the ß-cell KATP channel (Kir6.2-/-), that show almost no insulin secretion in response to glucose in vitro. In the present study, we compared insulin secretion by voluntary feeding (self-motivated, oral nutrient ingestion) and by forced feeding (intra-gastric nutrient injection via gavage) in wild-type (Kir6.2+/+) and Kir6.2-/- mice. Under ad libitum feeding or during voluntary feeding of standard chow, blood glucose levels and plasma insulin levels were similar in Kir6.2+/+ and Kir6.2-/- mice. By voluntary feeding of carbohydrate alone, insulin secretion was induced significantly in Kir6.2-/- mice, but was markedly attenuated compared to that in Kir6.2+/+ mice. On forced feeding of standard chow or carbohydrate alone, the insulin secretory response was markedly impaired or completely absent in Kir6.2-/- mice. Pre-treatment of a muscarine receptor antagonist, atropine methyl nitrate, which does not cross the blood-brain barrier, almost completely blocked insulin secretion induced by voluntary feeding of standard chow or carbohydrate in Kir6.2-/- mice. Substantial glucose-induced insulin secretion was induced in pancreas perfusion study of Kir6.2-/- mice only in the presence of carbamylcholine. These results suggest that a KATP channel-independent mechanism mediated by the vagal nerve plays a critical role in insulin secretion in response to nutrients in vivo.
Journal of Endocrinology 04/2013; · 3.55 Impact Factor
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Journal of Human Genetics 12/2012; 57(12):809. · 2.57 Impact Factor
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ABSTRACT: The amelioration of glucose tolerance by liraglutide was associated with a significant improvement of early insulin-response during OGTT. The serum C-peptide response to glucagon challenge strongly correlated with the improvement of the early insulin-response. The C-peptide response to glucagon challenge would be useful to predict therapeutic response to liraglutide.
Diabetes research and clinical practice 10/2012; · 2.16 Impact Factor
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ABSTRACT: The aim of the present study was to explore the role of variations with modest effects (previously identified by a large-scale meta-analysis in European populations) in the genetic background of type 2 diabetes (T2D) and diabetes-related traits in a Japanese population. We enrolled 2632 Japanese subjects with T2D and 2050 non-diabetic subjects. We analyzed nine single-nucleotide polymorphisms (SNPs), including rs340874 (PROX1), rs4607517 (GCK), rs2191349 (DGKB-TMEM195), rs7034200 (GLIS3), rs10885122 (ADRA2A), rs174550 (FADS1), rs11605924 (CRY2), rs10830963 (MTNR1B) and rs35767 (IGF1). rs340874 (PROX1) and rs174550 (FADS1) were significantly associated with T2D (P=0.0078, OR: 1.12; and P=0.0071, OR: 1.12, respectively). Subjects with more risk alleles related to nine SNPs had an increased risk of T2D (P=0.0017), as well as a higher fasting plasma glucose level (P=0.018), higher HbA(1c) level (P=0.013) and lower HOMA-β (P=0.033) compared with subjects who had fewer risk alleles. We identified a significant association of a SNP of FADS1 and a SNP near PROX1 with T2D in a Japanese population. The present findings suggest that inclusion of SNPs with a tendency to increase the disease risk captured more of the genetic background of T2D than that revealed by only assessing significant SNPs.Journal of Human Genetics advance online publication, 20 September 2012; doi:10.1038/jhg.2012.110.
Journal of Human Genetics 09/2012; · 2.57 Impact Factor
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ABSTRACT: Phasic activation of the dopamine (DA) midbrain system in response to unexpected reward or novelty is critical for adaptive behavioral strategies. This activation of DA midbrain neurons occurs via a synaptically triggered switch from low-frequency background spiking to transient high-frequency burst firing. We found that, in medial DA neurons of the substantia nigra (SN), activity of ATP-sensitive potassium (K-ATP) channels enabled NMDA-mediated bursting in vitro as well as spontaneous in vivo burst firing in anesthetized mice. Cell-selective silencing of K-ATP channel activity in medial SN DA neurons revealed that their K-ATP channel-gated burst firing was crucial for novelty-dependent exploratory behavior. We also detected a transcriptional upregulation of K-ATP channel and NMDA receptor subunits, as well as high in vivo burst firing, in surviving SN DA neurons from Parkinson's disease patients, suggesting that burst-gating K-ATP channel function in DA neurons affects phenotypes in both disease and health.
Nature Neuroscience 08/2012; 15(9):1272-80. · 15.53 Impact Factor
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Shinobu Shimizu,
Tetsuya Hosooka,
Tomokazu Matsuda,
Shun-ichiro Asahara,
Maki Koyanagi-Kimura,
Ayumi Kanno,
Alberto Bartolome,
Hiroaki Etoh,
Megumi Fuchita,
Kyoko Teruyama,
Hiroaki Takahashi,
Hiroyuki Inoue,
Yusuke Mieda,
Naoko Hashimoto, Susumu Seino,
Yoshiaki Kido
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ABSTRACT: The development of type 2 diabetes is accompanied by a progressive decline in β-cell mass and function. Vildagliptin, a dipeptidyl peptidase 4 inhibitor, is representative of a new class of antidiabetic agents that act through increasing the expression of glucagon-like peptide-1. The protective effect of this agent on β cells was studied in diabetic mice. Diabetic pancreatic β cell-specific C/EBPB transgenic (TG) mice exhibit decreased β-cell mass associated with increased apoptosis, decreased proliferation, and aggravated endoplasmic reticulum (ER) stress. Vildagliptin was orally administered to the TG mice for a period of 24 weeks, and the protective effects of this agent on β cells were examined, along with the potential molecular mechanism of protection. Vildagliptin ameliorated hyperglycemia in TG mice by increasing the serum concentration of insulin and decreasing the serum concentration of glucagon. This agent also markedly increased β-cell mass, improved aggravated ER stress, and restored attenuated insulin/IGF1 signaling. A decrease in pancreatic and duodenal homeobox 1 expression was also observed in β cells isolated from our mouse model, but this was also restored by vildagliptin treatment. The expression of C/EBPB protein, but not mRNA, was unexpectedly downregulated in vildagliptin-treated TG mice and in exenatide-treated MIN6 cells. Activation of the GLP1 pathway induced proteasome-dependent C/EBPB degradation in β cells as the proteasome inhibitor MG132 restored the downregulation of C/EBPB protein by exenatide. Vildagliptin elicits protective effects on pancreatic β cells, possibly through C/EBPB degradation, and has potential for preventing the progression of type 2 diabetes.
Journal of Molecular Endocrinology 07/2012; 49(2):125-35. · 3.48 Impact Factor
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ABSTRACT: The transforming growth factor (TGF)-β family members, bone morphogenetic protein (BMP)-2 and TGF-β that signal via the receptor-regulated Smads (R-Smads) induce bone formation in vivo. The inhibitory Smads (I-Smads), Smad6 and Smad7, negatively regulate TGF-β family ligand signaling by competing with R-Smads for binding to activated type I receptors, and preventing R-Smad activation, Hence, the I-Smads potentially act as suppressors of bone formation although their effects on phenotypic changes in mature osteoblasts are unclear. While Smad7 inhibits both BMP and TGF-β signaling, Smad6 is less effective in inhibiting TGF-β signaling. The present study was performed to examine the role of Smad7 on the phenotype of mouse osteoblastic MC3T3-E1 cells. We employed stable Smad7-transfected MC3T3-E1 cells to examine the role of Smad7 in osteoblast proliferation, differentiation and mineralization. Stable Smad7 overexpression significantly inhibited the absorbance in the MTT-dye assay and inhibited the levels of PCNA compared with those in empty vector-transfected cells. Smad7 overexpression suppressed the type 1 collagen mRNA and protein levels. Moreover, Smad7 inhibited ALP activity and mineralization of osteoblastic cells. The effects of stable overexpression of Smad6 were similar to those of Smad7 suggesting the changes mediated by either I-Smad occurred by inhibition of BMP rather than TGF-β signaling. In addition, PTH-(1-34) elevated the levels of Smad7 in parental MC3T3-E1 cells. In conclusion, the present study demonstrated that Smad7, as well as Smad6, inhibits proliferation, differentiation and mineralization of mouse osteoblastic cells. Therefore, I-Smads are important molecular targets for the negative control of bone formation.
Endocrine Journal 05/2012; 59(8):653-62. · 2.03 Impact Factor
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ABSTRACT: Bone morphogenetic proteins (BMPs) are critical for bone regeneration and induce ectopic bone formation in vivo. The constitutively activating mutation (R206H) of the BMP type 1 receptor, activin A type 1 receptor/activin-like kinase 2 (ACVR1/ALK2), underlies the molecular pathogenesis of fibrodysplasia ossificans progressiva (FOP) in which heterotopic ossification occurs in muscle tissue. In the present study, we performed a comparative DNA microarray analysis between stable empty vector- and ALK2(R206H)-transfected mouse myoblastic C2C12 cells. Forty genes were identified whose expression was increased >3.5 times in the experimental group versus the control. The bone formation-related factor, Tmem119, was included in this group. Osteoblast differentiation markers and mineralization were enhanced in C2C12 cells stably expressing Tmem119. Differentiation of myoblastic cells into myotubes was suppressed but differentiation into chondrocytes was little affected. Transcriptional activity of the BMP-2 signaling molecules, Smad1/5, was increased even in the absence of exogenous BMP-2. Endogenous BMP-2 levels positively correlated with Tmem119 levels. A BMP-2/4 neutralizing antibody and dorsomorphin, an ALK2 inhibitor, antagonized Tmem119-enhanced alkaline phosphatase (ALP) levels. Tmem119 siRNA antagonized the BMP-2-induced ALP and osteocalcin, but not Runx2 and Osterix, mRNAs, in C2C12 cells. In conclusion, Tmem119 levels were increased by the FOP-associated constitutively activating ALK2 mutation in myoblasts. The data show that Tmem119 promotes the differentiation of myoblasts into osteoblasts and the interaction with the BMP signaling pathway likely occurs downstream of Runx2 and Osterix in myoblasts. Tmem119 may play a critical role in the commitment of myoprogenitor cells to the osteoblast lineage.
Bone 05/2012; 51(1):158-67. · 4.02 Impact Factor
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Nippon rinsho. Japanese journal of clinical medicine 05/2012; 70 Suppl 3:95-8.
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Cell metabolism 03/2012; 15(3):270. · 17.35 Impact Factor
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ABSTRACT: The interaction between muscle tissues and bone metabolism is incompletely understood. We hypothesized that there might be some humoral factors that are produced in muscle tissues and exhibit bone anabolic activity. We, therefore, performed comparative DNA microarray analysis between mouse myoblastic C2C12 cells transfected with either stable empty vector or ALK2 (R206H), the mutation that constitutively activates the bone morphogenetic protein (BMP) receptor, to search for muscle-derived bone anabolic factors. Twenty-five genes whose expression was decreased to <1/4, were identified; these included osteoglycin (OGN). Stable overexpression of OGN significantly decreased the levels of Runx2 and Osterix mRNA compared with those in cells transfected with vector alone in MC3T3-E1 cells. On the other hand, it significantly enhanced the levels of alkaline phosphatase (ALP), type I collagen (Col1), and osteocalcin (OCN) mRNA as well as β-catenin and mineralization. A reduction in endogenous OGN level showed the opposite effects to those of OGN overexpression in MC3T3-E1 and mouse calvarial osteoblastic cells. Transient OGN overexpression significantly suppressed the levels of Runx2, Osterix, ALP, Col1, and OCN mRNA induced by BMP-2 in C2C12 cells. The conditioned medium from OGN-overexpressed and OGN-suppressed myoblastic cells enhanced and decreased, respectively, the levels of ALP, Col1, and β-catenin in MC3T3-E1 cells. Moreover, OGN increased Smad3/4-responsive transcriptional activity as well as Col1 mRNA levels independently of endogenous TGF-β in these cells. In conclusion, this study suggests that OGN may be a crucial humoral bone anabolic factor that is produced by muscle tissues.
Journal of Biological Chemistry 02/2012; 287(15):11616-28. · 4.77 Impact Factor
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ABSTRACT: The interaction between muscle tissues and bone metabolism is incompletely understood. We hypothesized that there might be
some humoral factors that are produced in muscle tissues and exhibit bone anabolic activity. We therefore performed comparative
DNA microarray analysis between mouse myoblastic C2C12 cells transfected with either stable empty vector or ALK2 (R206H),
the mutation that constitutively activates the BMP receptor, to search for muscle-derived bone anabolic factors. Twenty-five
genes, whose expression was decreased to <1/4, were identified; these included osteoglycin (OGN). Stable overexpression of
OGN significantly decreased the levels of Runx2 and Osterix mRNA compared with those in cells transfected with vector alone
in MC3T3-E1 cells. On the other hand, it significantly enhanced the levels of alkaline phosphatase (ALP), type I collagen
(Col1) and osteocalcin (OCN) mRNA as well as β-catenin and mineralization. A reduction in endogenous OGN level showed the
opposite effects to those of OGN overexpression in MC3T3-E1 and mouse calvarial osteoblastic cells. Transient OGN overexpression
significantly suppressed the levels of Runx2, Osterix, ALP, Col1 and OCN mRNA induced by BMP-2 in C2C12 cells. The conditioned
medium from OGN-overexpressed and OGN-suppressed myoblastic cells enhanced and decreased the levels of ALP, Col1 and β-catenin
in MC3T3-E1 cells, respectively. Moreover, OGN increased Smad3/4-responsive transcriptional activity as well as collagen mRNA
levels independently of endogenous TGF-β in these cells. In conclusion, the present study suggests that OGN may be a crucial
humoral bone anabolic factor that is produced by muscle tissues.
Journal of Biological Chemistry 02/2012; · 4.77 Impact Factor
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ABSTRACT: Muscle mass is related to higher bone mass and a reduction in fracture risk. However, the interactions between muscle tissues and bone metabolism are incompletely understood and there might be some humoral factors that are produced in muscle tissues and exhibit bone anabolic activity. We therefore investigated the role of FAM5C in osteoblast differentiation and the interactions between muscle and bone. A reduction of endogenous FAM5C by siRNA reduced the levels of osterix, alkaline phosphatase (ALP) and osteocalcin (OCN) mRNA as well as the levels of type 1 collagen and β-catenin in mouse osteoblastic MC3T3-E1 cells and mouse calvarial osteoblasts, although FAM5C overexpression significantly antagonized the levels of osterix, ALP and OCN mRNA induced by bone morphogenetic protein-2 in C2C12 cells. The conditioned medium from FAM5C-overexpressed and -suppressed C2C12 cells increased and decreased the levels of osterix, ALP and OCN mRNA in MC3T3-E1 cells, respectively. In conclusion, the present study is the first to show that FAM5C enhances osteoblast differentiation in differentiated osteoblasts, and that the effects of the conditioned medium from FAM5C-modulated myoblastic cells were positively correlated with the effects of FAM5C on osteoblast phenotype in osteoblasts. FAM5C might be an important humoral bone anabolic factor produced from muscle cells.
Biochemical and Biophysical Research Communications 02/2012; 418(1):134-9. · 2.48 Impact Factor
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Toshiya Matsubara,
Ayako Mita,
Kohtaro Minami,
Tetsuya Hosooka,
Sohei Kitazawa,
Kenichi Takahashi,
Yoshikazu Tamori,
Norihide Yokoi,
Makoto Watanabe,
Ei-Ichi Matsuo,
Osamu Nishimura, Susumu Seino
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ABSTRACT: Adipose tissue secretes adipokines that mediate insulin resistance, a characteristic feature of obesity and type 2 diabetes. By differential proteome analysis of cellular models of insulin resistance, we identified progranulin (PGRN) as an adipokine induced by TNF-α and dexamethasone. PGRN in blood and adipose tissues was markedly increased in obese mouse models and was normalized with treatment of pioglitazone, an insulin-sensitizing agent. Ablation of PGRN (Grn(-/-)) prevented mice from high fat diet (HFD)-induced insulin resistance, adipocyte hypertrophy, and obesity. Grn deficiency blocked elevation of IL-6, an inflammatory cytokine, induced by HFD in blood and adipose tissues. Insulin resistance induced by chronic administration of PGRN was suppressed by neutralizing IL-6 in vivo. Thus, PGRN is a key adipokine that mediates HFD-induced insulin resistance and obesity through production of IL-6 in adipose tissue, and may be a promising therapeutic target for obesity.
Cell metabolism 01/2012; 15(1):38-50. · 17.35 Impact Factor
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ABSTRACT: Insulin secretion is a highly dynamic process regulated by various factors including nutrients, hormones, and neuronal inputs. The dynamics of insulin secretion can be studied at different levels: the single β cell, pancreatic islet, whole pancreas, and the intact organism. Studies have begun to analyze cellular and molecular mechanisms underlying dynamics of insulin secretion. This review focuses on our current understanding of the dynamics of insulin secretion in vitro and in vivo and discusses their clinical relevance.
The Journal of clinical investigation 06/2011; 121(6):2118-25. · 15.39 Impact Factor
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ABSTRACT: Some class I antiarrhythmic drugs induce a sporadic hypoglycemia by producing insulin secretion via inhibition of ATP-sensitive K(+) (K(ATP)) channels of pancreatic β-cells. It remains undetermined whether amiodarone produces insulin secretion by inhibiting K(ATP) channels. In this study, effects of amiodarone on K(ATP) channels, L-type Ca(2+) channel, membrane potential, and insulin secretion were examined and compared with those of quinidine in a β-cell line (MIN6). Amiodarone as well as quinidine inhibited the openings of the K(ATP) channel in a concentration-dependent manner without affecting its unitary amplitude in inside-out membrane patches of single MIN6 cells, and the IC(50) values were 0.24 and 4.9 µM, respectively. The L-type Ca(2+) current was also inhibited by amiodarone as well as quinidine in a concentration-dependent manner. Although glibenclamide (0.1 µM) or quinidine (10 µM) significantly potentiated the insulin secretion from MIN6 cells, amiodarone (1-30 µM) failed to increase insulin secretion. Amiodarone (30 µM) and nifedipine (10 µM) significantly inhibited the increase in insulin secretion produced by 0.1 µM glibenclamide. Amiodarone (30 µM) produced a gradual decrease of the membrane potential, but did not produce repetitive electrical activity in MIN6 cells. Glibenclamide (1 µM) produced a slow depolarization, followed by spiking activity which was inhibited by 30 µM amiodarone. Thus, amiodarone is unlikely to produce hypoglycemia in spite of potent inhibitory action on K(ATP) channels in insulin-secreting cells, possibly due to its Ca(2+) channel-blocking action.
Journal of Pharmacological Sciences 05/2011; 116(1):73-80. · 2.08 Impact Factor
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Nihon Naika Gakkai Zasshi 05/2011; 100(5):1418-24.
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ABSTRACT: Incretin hormones GIP(glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) improve glycemic control by potentiating glucose-induced insulin secretion in pancreatic beta-cells and also have beneficial effects on appetite control and body weight. In response to food ingestion, GIP and GLP-1 are secreted from enteroendocrine K- and L-cells, respectively. In these cells, it is shown that a variety of molecular sensors are involved in the detection of carbohydrates, lipids, and proteins. In view of development of new incretin-related drugs, these sensors are attractive targets to enhance the endogenous pools of incretins.
Nippon rinsho. Japanese journal of clinical medicine 05/2011; 69(5):803-7.
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ABSTRACT: The mechanisms whereby the parathyroid hormone (PTH) exerts its anabolic action on bone are incompletely understood. We previously
showed that inhibition of ERK1/2 enhanced Smad3-induced bone anabolic action in osteoblasts. These findings suggested the
hypothesis that changes in gene expression associated with the altered Smad3-induced signaling brought about by an ERK1/2
inhibitor would identify novel bone anabolic factors in osteoblasts. We therefore performed a comparative DNA microarray analysis
between empty vector-transfected mouse osteoblastic MC3T3-E1 cells and PD98059-treated stable Smad3-overexpressing MC3T3-E1
cells. Among the novel factors, Tmem119 was selected on the basis of its rapid induction by PTH independent of later increases
in endogenous TGF-β. The levels of Tmem119 increased with time in cultures of MC3T3-E1 cells and mouse mesenchymal ST-2 cells
committed to the osteoblast lineage by BMP-2. PTH stimulated Tmem119 levels within 1 h as determined by Western blot analysis
and immunocytochemistry in MC3T3-E1 cells. MC3T3-E1 cells stably overexpressing Tmem119 exhibited elevated levels of Runx2,
osteocalcin, alkaline phosphatase, and β-catenin, whereas Tmem119 augmented BMP-2-induced Runx2 levels in mesenchymal cells.
Tmem119 interacted with Runx2, Smad1, and Smad5 in C2C12 cells. In conclusion, we identified a Smad3-related factor, Tmem119,
that is induced by PTH and promotes differentiation in mouse osteoblastic cells. Tmem119 is an important molecule in the pathway
downstream of PTH and Smad3 signaling in osteoblasts.
Journal of Biological Chemistry 03/2011; 286(11):9787-9796. · 4.77 Impact Factor
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ABSTRACT: Transplantation of surrogate β-cells is a promising option for the treatment of insulin-deficient diabetes mellitus in the future. Although pancreatic exocrine cells of rodents have been shown to transdifferentiate into insulin-secreting cells, no studies are reported on human exocrine cells. Here, we report the generation of insulin-secreting cells from exocrine cells of the human pancreas. When cultured in suspension with epidermal growth factor, human pancreatic exocrine cells readily formed spherical cell clusters. Expression of Pdx1 was induced in all 19 cases in which we successfully isolated exocrine cells, and insulin expression was induced in 11 cases. In addition, insulin secretion was evaluated in four cases, and the newly-made cells were found to secrete insulin in response to various stimuli. Although further studies are required to improve both the quality and quantity of such insulin-secreting cells, our data suggest that pancreatic exocrine cells represent a potential source of insulin-secreting cells for treatment of type 1 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00095.x, 2011)
Journal of Diabetes Investigation. 01/2011; 2(4):271 - 275.
