Browsing by Subject "Glucose -- Metabolism"

Now showing 1 - 4 of 4
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    The Orphan Nuclear Receptor ERRγ Regulates Hepatic CB1 Receptor-Mediated Fibroblast Growth Factor 21 Gene Expression
    (Plos, 2016-07-25) Jung, Yoon Seok; Lee, Ji-Min; Kim, Don-Kyu; Lee, Yong-Soo; Kim, Ki-Sun; Kim, Yong-Hoon; Kim, Jina; Lee, Myung-Shik; Lee, In-Kyu; Kim, Seong Heon; Cho, Sung Jin; Jeong, Wong-Il; Lee, Chul-Ho; Harris, Robert A.; Choi, Hueng-Sik; Department of Biochemistry & Molecular Biology, IU School of Medicine
    BACKGROUND: Fibroblast growth factor 21 (FGF21), a stress inducible hepatokine, is synthesized in the liver and plays important roles in glucose and lipid metabolism. However, the mechanism of hepatic cannabinoid type 1 (CB1) receptor-mediated induction of FGF21 gene expression is largely unknown. RESULTS: Activation of the hepatic CB1 receptor by arachidonyl-2'-chloroethylamide (ACEA), a CB1 receptor selective agonist, significantly increased FGF21 gene expression. Overexpression of estrogen-related receptor (ERR) γ increased FGF21 gene expression and secretion both in hepatocytes and mice, whereas knockdown of ERRγ decreased ACEA-mediated FGF21 gene expression and secretion. Moreover, ERRγ, but not ERRα and ERRβ, induced FGF21 gene promoter activity. In addition, deletion and mutation analysis of the FGF21 promoter identified a putative ERRγ-binding motif (AGGTGC, a near-consensus response element). A chromatin immunoprecipitation assay revealed direct binding of ERRγ to the FGF21 gene promoter. Finally, GSK5182, an ERRγ inverse agonist, significantly inhibited hepatic CB1 receptor-mediated FGF21 gene expression and secretion. CONCLUSION: Based on our data, we conclude that ERRγ plays a key role in hepatic CB1 receptor-mediated induction of FGF21 gene expression and secretion.
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    PDK regulated Warburg effect protects differentiated adipocytes against ROS
    (2014-10-06) Roell, William Christopher; March, Keith L.; Considine, Robert V.; Harris, Robert A.; Tune, Johnathan David
    Literature has demonstrated the ability of human adipose tissue to generate large amounts of lactate. However, it is not understood why adipose tissue produces lactate, how the production of lactate is regulated, and what potential benefit this has to the adipocyte or the organism. We first characterized a human model of adipogenic differentiation with minimal donor to donor variability to assess metabolic changes associated with mature adipocytes compared to their precursors. Indeed, similar to what was observed in human clinical studies, the differentiated adipocytes demonstrated increased lactate production. However, the differentiated adipocytes compared to their precursors (preadipocytes or ASCs) demonstrate an aerobic glycolysis-like (also called Warburg effect-like) increase in glycolysis characterized by a 5.2 fold increase in lactate production in normoxic conditions (atmospheric oxygen tension). Remarkably, this increase in lactate occurred even though the differentiated adipocytes simultaneously demonstrate an increase in oxidative capacity. This low fraction of oxidative capacity coupled with increased lactate production indicated regulation of oxidative rates most likely at the point of pyruvate conversion to either acetyl-CoA (oxidative metabolism) or lactate (glycolytic metabolism). To investigate the potential regulation of this metabolic phenotype, PDK isoform expression was assessed and we found PDK 1 and 4 transcript and protein elevated in the differentiated cells. Non-selective pharmacologic inhibition of the PDKs resulted in decreased lactate production, supporting a regulatory role for PDK in modulation of the observed Warburg effect. PDK inhibition also resulted in increased ROS production in the adipocytes after several hours of treatment and a decrease in cell viability when PDK inhibition was carried out over 36 hours. The resulting loss in viability could be rescued by antioxidant (Tempol) treatment, indicating the decrease in viability was ROS mediated. Similar to what is seen in cancer cells, our data demonstrate that differentiation of human adipocytes is accompanied by a PDK-dependent increase in glycolytic metabolism (Warburg effect) that not only leads to lactate production, but also seems to protect the cells from increased and detrimental generation of ROS.
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    Regulation of endoplasmic reticulum calcium homeostasis in pancreatic β cells
    (2016-06-21) Tong, Xin; Evans-Molina, Carmella; Day, Richard; Tune, Johnathan; Fueger, Patrick T.; Dong, X. Charlie
    Diabetes mellitus is a group of metabolic diseases characterized by disordered insulin secretion from the pancreatic β cell and chronic hyperglycemia. In order to maintain adequate levels of insulin secretion, the β cell relies on a highly developed and active endoplasmic reticulum (ER). Calcium localized in this compartment serves as a cofactor for key proteins and enzymes involved in insulin production and maturation and is critical for ER health and function. The ER Ca2+ pool is maintained largely through activity of the sarco-endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) pump, which pumps two Ca2+ ions into the ER during each catalytic cycle. The goal of our research is to understand the molecular mechanisms through which SERCA2 maintains β cell function and whole body glucose metabolism. Our previous work has revealed marked dysregulation of β cell SERCA2 expression and activity under diabetic conditions. Using a mixture of pro-inflammatory cytokines to model the diabetic milieu, we found that SERCA2 activity and protein stability were decreased through nitric oxide and AMP-activated protein kinase (AMPK)mediated signaling pathways. Moreover, SERCA2 expression, intracellular Ca2+ storage, and β cell death under diabetic conditions were rescued by pharmacologic or genetic inhibition of AMPK. These findings provided novel insight into pathways leading to altered β cell Ca2+ homeostasis and reduced β cell survival in diabetes. To next define the role of SERCA2 in the regulation of whole body glucose homeostasis, SERCA2 heterozygous mice (S2HET) were challenged with high fat diet (HFD). Compare to wild-type controls, S2HET mice had lower serum insulin and significantly reduced glucose tolerance with similar adiposity and systemic and tissue specific insulin sensitivity, suggesting an impairment in insulin secretion rather than insulin action. Consistent with this, S2HET mice exhibited reduced β cell mass, decreased β cell proliferation, increased ER stress, and impaired insulin production and processing. Furthermore, S2HET islets displayed impaired cytosolic Ca2+ oscillations and reduced glucose-stimulated insulin secretion, while a small molecule SERCA2 activator was able to rescue these defects. In aggregate, these data suggest a critical role for SERCA2 and the maintenance of ER Ca2+ stores in the β cell compensatory response to diet induced obesity.
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    Syntaxin 4 Overexpression Ameliorates Effects of Aging and High-Fat Diet on Glucose Control and Extends Lifespan
    (Elsevier, 2015-09-01) Oh, Eunjin; Miller, Richard A.; Thurmond, Debbie C.; Department of Pediatrics, IU School of Medicine
    Indirect evidence suggests that improved insulin sensitivity may contribute to improved lifespan of mice in which aging has been slowed by mutations, drugs, or dietary means, even in stocks of mice that do not show signs of late-life diabetes. Peripheral responses to insulin can be augmented by overexpression of Syntaxin 4 (Syn4), a plasma-membrane-localized SNARE protein. We show here that Syn4 transgenic (Tg) mice with high level expression of Syn4 had a significant extension of lifespan (33% increase in median) and showed increased peripheral insulin sensitivity, even at ages where controls exhibited age-related insulin resistance. Moreover, skeletal muscle GLUT4 and islet insulin granule exocytosis processes were fully protected in Syn4 Tg mice challenged with a high-fat diet. Hence, high-level expressing Syn4 Tg mice may exert better glycemic control, which slows multiple aspects of aging and extends lifespan, even in non-diabetic mice.