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dc.contributor.advisor Newgard, Christopher B en_US
dc.contributor.author Ronnebaum, Sarah Marie en_US
dc.date.accessioned 2008-05-14T16:28:59Z
dc.date.available 2008-05-14T16:28:59Z
dc.date.issued 2008-02-11 en_US
dc.identifier.uri http://hdl.handle.net/10161/603
dc.description Dissertation en_US
dc.description.abstract Pancreatic β-cells secrete insulin in response to glucose. Intracellular glucose metabolism drives a cascade of events, including ATP production, calcium influx, and insulin processing, culminating in insulin granule exocytosis. However, insulin secretory mechanisms are incompletely understood. β-cells have the capacity to flow pyruvate into the TCA cycle via the anaplerotic enzyme pyruvate carboxylase to engage one of several pathways of pyruvate recycling. Previous work demonstrated that pyruvate cycling was correlated with insulin secretion, and that NADPH may be involved in granule exocytosis. We hypothesized that NADPH-producing cytosolic enzymes isocitrate dehydrogenase (ICDc) and malic enzyme (MEc) may be involved in both pyruvate cycling and insulin secretion. ICDc expression was reduced using siRNA in the INS-1 derived cell line 832/13 and in isolated rat islets, which led decreased glucose-stimulated insulin secretion (GSIS), pyruvate cycling, and NADPH. Organic acid profiling revealed that decreased pyruvate cycling was compensated by an increase in lactate and stable pyruvate levels. This work established an important role for ICDc in maintaining GSIS through pyruvate-isocitrate cycling. MEc expression was reduced using siRNA in two β-cell lines, 832/13 and 832/3, as well as isolated rat islets. MEc suppression inhibited GSIS in the 832/13 cells only, and these effects were not due to changes in pyruvate cycling, NADPH, or the organic acid profile. This suggests that in normal β-cells, MEc does not participate in pyruvate cycling. Acetyl CoA carboxylase 1 (ACC1) is essential in de novo lipogenesis, which has been implicated in GSIS by other laboratories. Chronic, but not acute, inhibition of ACC1 via siRNA reduced insulin secretion independent of lipogenesis. ACC1 siRNA decreased glucose oxidation, pyruvate cycling, and ATP:ADP, due to an unexpected decrease in glucokinase protein. This work questions the use of ACC inhibitors in obesity and diabetes therapy. In summary, these studies on ICDc, MEc, and ACC1, coupled with concurrent work in our laboratory, eliminate two potential pyruvate cycling pathways (pyruvate-malate and pyruvate-citrate) and establish that pyruvate-isocitrate cycling is the critical pathway for control of GSIS. Future work will focus on identifying the signaling intermediate generated in the pyruvate-isocitrate pathway that links to insulin granule exocytosis. en_US
dc.format.extent 1657051 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US
dc.subject Biology, Molecular en_US
dc.subject Biology, Cell en_US
dc.subject Health Sciences, Pharmacology en_US
dc.subject insulin secretion en_US
dc.subject pyruvate cycling en_US
dc.subject glucose metabolism en_US
dc.subject lipogenesis en_US
dc.title Pyruvate Cycling Pathways and Glucose-Stimulated Insulin Secretion in Pancreatic Beta Cells en_US
dc.type Dissertation en_US
dc.department Pharmacology en_US

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