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      Cinnamon Extract Enhances Glucose Uptake in 3T3-L1 Adipocytes and C2C12 Myocytes by Inducing LKB1-AMP-Activated Protein Kinase Signaling

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          Abstract

          We previously demonstrated that cinnamon extract (CE) ameliorates type 1 diabetes induced by streptozotocin in rats through the up-regulation of glucose transporter 4 (GLUT4) translocation in both muscle and adipose tissues. This present study was aimed at clarifying the detailed mechanism(s) with which CE increases the glucose uptake in vivo and in cell culture systems using 3T3-L1 adipocytes and C2C12 myotubes in vitro. Specific inhibitors of key enzymes in insulin signaling and AMP-activated protein kinase (AMPK) signaling pathways, as well as small interference RNA, were used to examine the role of these kinases in the CE-induced glucose uptake. The results showed that CE stimulated the phosphorylation of AMPK and acetyl-CoA carboxylase. An AMPK inhibitor and LKB1 siRNA blocked the CE-induced glucose uptake. We also found for the first time that insulin suppressed AMPK activation in the adipocyte. To investigate the effect of CE on type 2 diabetes in vivo, we further performed oral glucose tolerance tests and insulin tolerance tests in type 2 diabetes model rats administered with CE. The CE improved glucose tolerance in oral glucose tolerance tests, but not insulin sensitivity in insulin tolerance test. In summary, these results indicate that CE ameliorates type 2 diabetes by inducing GLUT4 translocation via the AMPK signaling pathway. We also found insulin antagonistically regulates the activation of AMPK.

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          Most cited references 39

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          Global prevalence of diabetes: estimates for the year 2000 and projections for 2030.

          The goal of this study was to estimate the prevalence of diabetes and the number of people of all ages with diabetes for years 2000 and 2030. Data on diabetes prevalence by age and sex from a limited number of countries were extrapolated to all 191 World Health Organization member states and applied to United Nations' population estimates for 2000 and 2030. Urban and rural populations were considered separately for developing countries. The prevalence of diabetes for all age-groups worldwide was estimated to be 2.8% in 2000 and 4.4% in 2030. The total number of people with diabetes is projected to rise from 171 million in 2000 to 366 million in 2030. The prevalence of diabetes is higher in men than women, but there are more women with diabetes than men. The urban population in developing countries is projected to double between 2000 and 2030. The most important demographic change to diabetes prevalence across the world appears to be the increase in the proportion of people >65 years of age. These findings indicate that the "diabetes epidemic" will continue even if levels of obesity remain constant. Given the increasing prevalence of obesity, it is likely that these figures provide an underestimate of future diabetes prevalence.
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            Calmodulin-dependent protein kinase kinase-beta is an alternative upstream kinase for AMP-activated protein kinase.

            The AMP-activated protein kinase (AMPK) is a critical regulator of energy balance at both the cellular and whole-body levels. Two upstream kinases have been reported to activate AMPK in cell-free assays, i.e., the tumor suppressor LKB1 and calmodulin-dependent protein kinase kinase. However, evidence that this is physiologically relevant currently only exists for LKB1. We now report that there is a significant basal activity and phosphorylation of AMPK in LKB1-deficient cells that can be stimulated by Ca2+ ionophores, and studies using the CaMKK inhibitor STO-609 and isoform-specific siRNAs show that CaMKKbeta is required for this effect. CaMKKbeta also activates AMPK much more rapidly than CaMKKalpha in cell-free assays. K(+)-induced depolarization in rat cerebrocortical slices, which increases intracellular Ca2+ without disturbing cellular adenine nucleotide levels, activates AMPK, and this is blocked by STO-609. Our results suggest a potential Ca(2+)-dependent neuroprotective pathway involving phosphorylation and activation of AMPK by CaMKKbeta.
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              Complexes between the LKB1 tumor suppressor, STRADα/β and MO25α/β are upstream kinases in the AMP-activated protein kinase cascade

              Background The AMP-activated protein kinase (AMPK) cascade is a sensor of cellular energy charge that acts as a 'metabolic master switch' and inhibits cell proliferation. Activation requires phosphorylation of Thr172 of AMPK within the activation loop by upstream kinases (AMPKKs) that have not been identified. Recently, we identified three related protein kinases acting upstream of the yeast homolog of AMPK. Although they do not have obvious mammalian homologs, they are related to LKB1, a tumor suppressor that is mutated in the human Peutz-Jeghers cancer syndrome. We recently showed that LKB1 exists as a complex with two accessory subunits, STRADα/β and MO25α/β. Results We report the following observations. First, two AMPKK activities purified from rat liver contain LKB1, STRADα and MO25α, and can be immunoprecipitated using anti-LKB1 antibodies. Second, both endogenous and recombinant complexes of LKB1, STRADα/β and MO25α/β activate AMPK via phosphorylation of Thr172. Third, catalytically active LKB1, STRADα or STRADβ and MO25α or MO25β are required for full activity. Fourth, the AMPK-activating drugs AICA riboside and phenformin do not activate AMPK in HeLa cells (which lack LKB1), but activation can be restored by stably expressing wild-type, but not catalytically inactive, LKB1. Fifth, AICA riboside and phenformin fail to activate AMPK in immortalized fibroblasts from LKB1-knockout mouse embryos. Conclusions These results provide the first description of a physiological substrate for the LKB1 tumor suppressor and suggest that it functions as an upstream regulator of AMPK. Our findings indicate that the tumors in Peutz-Jeghers syndrome could result from deficient activation of AMPK as a consequence of LKB1 inactivation.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2014
                14 February 2014
                : 9
                : 2
                Affiliations
                [1 ]Department of Chemistry and Life Science, Nihon University College of Bioresource Sciences, Nihon University Graduate School of Bioresource Sciences, Kanagawa, Japan
                [2 ]School of Pharmacy, Nihon University, Chiba, Japan
                [3 ]Department of Food and Nutrition, Japan Women’s University, Tokyo, Japan
                Virginia Tech, United States of America
                Author notes

                Competing Interests: The Cinnamon ( Cinnamomum zeylanicum) used in this study was a gift from House Foods Corporation (Tokyo). This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials. The authors have declared that no other competing interests exist.

                Conceived and designed the experiments: YS. Performed the experiments: YS NH KK. Analyzed the data: YS NH KK. Wrote the paper: YS. Contribution to the discussion section of the manuscript: LNJ KS TH TS. Conducted some of the research: TH. Reviewed/edited the manuscript: TA TS.

                Article
                PONE-D-13-39530
                10.1371/journal.pone.0087894
                3925101

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Pages: 9
                Funding
                This work was supported by grants from the Nihon University individual research grant program (to T.S.). This work was also supported by grants from the Japan Scienceand Technology Agency (JST) A-STEP program (to T.H.). Y.S. is supported by a Fellowship from the Academic Frontier Project from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology
                Biochemistry
                Model organisms
                Animal models
                Rat
                Molecular cell biology
                Signal transduction
                Signaling cascades
                Protein kinase signaling cascade
                Medicine
                Complementary and alternative medicine
                Endocrinology
                Diabetic endocrinology
                Diabetes mellitus type 2
                Nutrition
                Obesity

                Uncategorized

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