Effects of insulin and cytosolic redox state on glucose production pathways in the isolated perfused mouse liver measured by integrated 2H and 13C NMR

Hausler, Natasha; Browning, Jeffrey D.; Merritt, Matthew E.; Storey, Charles; Milde, Angela; Jeffrey, F. M H; Sherry, A. Dean; Malloy, Craig R.; Burgess, Shawn C.

doi:10.1042/bj20051174

Cited by 36 publications

(42 citation statements)

References 46 publications

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“…Conversely, in mice with a liver-specific knockout of PEPCK, tricarboxylic acid cycle flux is impaired (14), despite up-regulation of some tricarboxylic acid cycle enzymes (38). Collectively, these studies indicate that cataplerosis related to GNG PEP and tricarboxylic acid cycle flux are exquisitely interdependent (14,39,40) and support the existence of bidirectional cross-talk between hepatic energy generation and gluconeogenic pathways. We propose that, in the PGC-1␣ Ϫ/Ϫ liver, impaired hepatic energy production necessarily inhibits the energetically costly process of gluconeogenesis.…”

Section: Discussionmentioning

confidence: 70%

Diminished Hepatic Gluconeogenesis via Defects in Tricarboxylic Acid Cycle Flux in Peroxisome Proliferator-activated Receptor γ Coactivator-1α (PGC-1α)-deficient Mice

Burgess

Leone

Wende

et al. 2006

Journal of Biological Chemistry

101

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The peroxisome proliferator-activated receptor ␥ (PPAR␥) coactivator 1␣ (PGC-1␣) is a highly inducible transcriptional coactivator implicated in the coordinate regulation of genes encoding enzymes involved in hepatic fatty acid oxidation, oxidative phosphorylation, and gluconeogenesis. The present study sought to assess the effects of chronic PGC-1␣ deficiency on metabolic flux through the hepatic gluconeogenic, fatty acid oxidation, and tricarboxylic acid cycle pathways. To this end, hepatic metabolism was assessed in wild-type (WT) and PGC-1␣ ؊/؊ mice using isotopomer-based NMR with complementary gene expression analyses. Hepatic glucose production was diminished in PGC-1␣ ؊/؊ livers coincident with reduced gluconeogenic flux from phosphoenolpyruvate. Surprisingly, the expression of PGC-1␣ target genes involved in gluconeogenesis was unaltered in PGC-1␣ ؊/؊ compared with WT mice under fed and fasted conditions. Flux through tricarboxylic acid cycle and mitochondrial fatty acid ␤-oxidation pathways was also diminished in PGC-1␣ ؊/؊ livers. The expression of multiple genes encoding tricarboxylic acid cycle and oxidative phosphorylation enzymes was significantly depressed in PGC-1␣ ؊/؊ mice and was activated by PGC-1␣ overexpression in the livers of WT mice. Collectively, these findings suggest that chronic wholeanimal PGC-1␣ deficiency results in defects in hepatic glucose production that are secondary to diminished fatty acid ␤-oxidation and tricarboxylic acid cycle flux rather than abnormalities in gluconeogenic enzyme gene expression per se.Flux through hepatic gluconeogenesis, fatty acid oxidation (FAO), 3 tricarboxylic acid cycle, and mitochondrial oxidative phosphorylation (OXPHOS) pathways can be modulated at multiple regulatory levels. Substrate availability, post-translational modification, and transcriptional regulation of genes encoding enzymes at various points can influence the capacity for, and the rate of flux through, each of these pathways. Moreover, flux through one pathway has an inevitable impact on the flux of the others. For instance, mitochondrial FAO is the principal source of energy in the hepatocyte, impacting the amount of chemical work that can be performed by the liver. Furthermore, the tricarboxylic acid cycle not only oxidizes acetyl-CoA generated by ␤-oxidation and produces reducing equivalents for ATP synthesis but also supplies carbons necessary for gluconeogenesis through pyruvate carboxylase (PC) and P-enolpyruvate carboxykinase (PEPCK). Thus, the tricarboxylic acid cycle is a critical hub linking FAO with gluconeogenesis and OXPHOS pathways.Recent work has shown that the peroxisome proliferatoractivated receptor ␥ (PPAR␥) coactivator-1␣ (PGC-1␣) is a highly inducible transcriptional coactivator that integrates multiple interconnected metabolic pathways in liver (1). PGC-1␣ controls transcription of genes involved in hepatic gluconeogenesis, fatty acid catabolism, oxidative phosphorylation (OXPHOS), and mitochondrial biogenesis (1-3). Although PGC-1␣ was originally identified ...

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Section: Discussionmentioning

confidence: 70%

Diminished Hepatic Gluconeogenesis via Defects in Tricarboxylic Acid Cycle Flux in Peroxisome Proliferator-activated Receptor γ Coactivator-1α (PGC-1α)-deficient Mice

Burgess

Leone

Wende

et al. 2006

Journal of Biological Chemistry

101

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“…13 CO 2 following pyruvate carboxylation. It is also notable that 50-75% of PEPCK flux is cycled back to the TCA cycle (i.e., pyruvate cycling) rather than supporting gluconeogenesis (8)(9)(10)18). Indeed, the lack of statistical significance between [ 13 C]bicarbonate production in the fed and fasted states (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Recently, DNP was used to observe altered cytosolic redox state in liver following ethanol administration (3), and hyperpolarized bicarbonate was observed in vivo after administration of [1-13 C]lactate, but analysis of oxidative versus biosynthetic metabolism in the liver has not been reported. In contrast to the heart, hepatic anaplerosis is four-to sixfold higher than acetyl-CoA oxidation (8)(9)(10). Consequently, the appearance of hyperpolarized [ 13 (Fig.…”

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confidence: 99%

Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized ¹³ C magnetic resonance

Merritt

Harrison

Sherry

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

141

190

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In the heart, detection of hyperpolarized [ 13 H epatic metabolism is comprised of a network of exergonic reactions that facilitate energy capture, such as fatty acid oxidation, carbohydrate oxidation and flux through the tricarboxylic acid (TCA) cycle, and endergonic reactions required for gluconeogenesis, lipogenesis, and amino acid biosynthesis. The dysregulation of these pathways underlie the pathology of a variety of diseases, including diabetes, cancer, and inborn errors of metabolism, making their diagnostic evaluation critically important. In particular, the hepatic TCA cycle is an important diagnostic target because its intermediates integrate lipid, carbohydrate, and amino acid metabolism during normal physiology. As examples, oxaloacetate is the common intermediate by which all noncarbohydrate sources enter gluconeogenesis; citrate is required to shuttle acetyl-CoA from the mitochondria for cytosolic lipogenesis; and the ketoacids of the TCA cycle serve as intermediates of amino acid synthesis and catabolism. The interconnectivity of these hepatic pathways makes their examination difficult but worthwhile because technologies that detect these fluxes provide important advances for basic and clinical investigation of mechanisms of disease.Dynamic nuclear polarization (DNP) of 13 C is a powerful molecular imaging technology that uses principles of magnetic resonance (MR) (1). Prepolarization of 13 C-labeled tracers enhances the sensitivity of MR by 10,000-fold or more and enables studies of cancer (2), hepatic metabolism (3, 4), and cardiac metabolism (5-7). In the heart, metabolism of hyperpolarized [1-13 C]pyruvate to 13 CO 2 and [ 13 C]bicarbonate is caused exclusively by flux through the pyruvate dehydrogenase complex (PDH). Consequently, 13 CO 2 detection is not necessarily indicative of flux in the TCA cycle, because non-PDH sources of acetyl-CoA (e.g., fat oxidation) dominate the metabolism of certain tissues, like the liver. Recently, DNP was used to observe altered cytosolic redox state in liver following ethanol administration (3), and hyperpolarized bicarbonate was observed in vivo after administration of [1-13 C]lactate, but analysis of oxidative versus biosynthetic metabolism in the liver has not been reported. In contrast to the heart, hepatic anaplerosis is four-to sixfold higher than acetyl-CoA oxidation (8)(9)(10) C]pyruvate, followed by rapid but incomplete "backwards" equilibration with the symmetric intermediate, fumarate. The polarization profiles of these hepatic metabolites changed as anticipated during feeding and fasting. Signal from hyperpolarized [ 13 C]bicarbonate was also observed. A 13 C isotopomer analysis of glutamate isolated from separate livers demonstrated that flux through PEPCK is ∼sevenfold higher than flux through PDH, indicating that flux through PEPCK may be a significant source of the The authors declare no conflict of interest.

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“…13 C labeling and isotopomer analysis is an effective methodology to quantify fluxes in mammalian metabolic pathways, as evidenced by several research articles and reviews [41][42][43][44][45][46][47][48][49][50][51][52]. There has been increasing emphasis on comprehensive isotopomer balancing, global optimization, and meticulous selection of a 13 C carbon source mixture [28,30,33,36] in the accurate interpretation of 13 C labeling data and evaluation of fluxes.…”

Section: Discussionmentioning

confidence: 99%

Global metabolic effects of glycerol kinase overexpression in rat hepatoma cells

Sriram

Rahib

et al. 2008

Molecular Genetics and Metabolism

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Glycerol kinase has several diverse activities in mammalian cells. Glycerol kinase deficiency is a complex, single-gene, inborn error of metabolism wherein no genotype-phenotype correlation has been established. Since glycerol kinase has been suggested to exhibit additional activities than glycerol phosphorylation, expression level perturbation in this enzyme may affect cellular physiology globally. To investigate this possibility, we conducted metabolic investigations of wild type and two glycerol kinase-overexpressing H4IIE rat hepatoma cell lines constructed in this study. The glycerol kinase-overexpressing cell lines exhibited a significantly higher consumption of carbon sources per cell, suggesting excess carbon expenditure. Furthermore, we quantified intracellular metabolic fluxes by employing stable isotope ( 13 C) labeling with a mathematically designed substrate mixture, gas chromatography-mass spectrometry, and comprehensive isotopomer balancing. This flux analysis revealed that the pentose phosphate pathway flux in the glycerol kinase-overexpressing cell lines was two-fold higher than that in the wild type, in addition to subtler flux changes in other pathways of carbohydrate metabolism. Furthermore, the activity and transcript level of the lipogenic enzyme glucose-6-phosphate dehydrogenase, the rate-limiting enzyme of the pentose phosphate pathway, were also about two-fold higher than that of the wild type; these data corroborate the flux analysis results. This study shows that glycerol kinase affects carbon metabolism globally, possibly through its additional functions, and highlights glycerol kinase's multifaceted role in cellular physiology.

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Effects of insulin and cytosolic redox state on glucose production pathways in the isolated perfused mouse liver measured by integrated 2H and 13C NMR

Cited by 36 publications

References 46 publications

Diminished Hepatic Gluconeogenesis via Defects in Tricarboxylic Acid Cycle Flux in Peroxisome Proliferator-activated Receptor γ Coactivator-1α (PGC-1α)-deficient Mice

Diminished Hepatic Gluconeogenesis via Defects in Tricarboxylic Acid Cycle Flux in Peroxisome Proliferator-activated Receptor γ Coactivator-1α (PGC-1α)-deficient Mice

Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized ¹³ C magnetic resonance

Global metabolic effects of glycerol kinase overexpression in rat hepatoma cells

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Effects of insulin and cytosolic redox state on glucose production pathways in the isolated perfused mouse liver measured by integrated 2H and 13C NMR

Cited by 36 publications

References 46 publications

Diminished Hepatic Gluconeogenesis via Defects in Tricarboxylic Acid Cycle Flux in Peroxisome Proliferator-activated Receptor γ Coactivator-1α (PGC-1α)-deficient Mice

Diminished Hepatic Gluconeogenesis via Defects in Tricarboxylic Acid Cycle Flux in Peroxisome Proliferator-activated Receptor γ Coactivator-1α (PGC-1α)-deficient Mice

Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized 13 C magnetic resonance

Global metabolic effects of glycerol kinase overexpression in rat hepatoma cells

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Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized ¹³ C magnetic resonance