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Patel MS, Mahmood S, Jung J, Rideout TC. Reprogramming of aerobic glycolysis in non-transformed mouse liver with pyruvate dehydrogenase complex deficiency. Physiol Rep 2021; 9:e14684. [PMID: 33400855 PMCID: PMC7785054 DOI: 10.14814/phy2.14684] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Revised: 11/26/2020] [Accepted: 11/27/2020] [Indexed: 12/19/2022] Open
Abstract
The Pyruvate Dehydrogenase Complex (PDC), a key enzyme in glucose metabolism, catalyzes an irreversible oxidative decarboxylation reaction of pyruvate to acetyl‐CoA, linking the cytosolic glycolytic pathway to mitochondrial tricarboxylic acid cycle and oxidative phosphorylation. Earlier we reported a down‐regulation of several key hepatic lipogenic enzymes and their upstream regulators in liver‐specific PDC‐deficient mouse (L‐PDCKO model by deleting the Pdha1 gene). In this study we investigated gene expression profiles of key glycolytic enzymes and other proteins that respond to various metabolic stresses in liver from L‐PDCKO mice. Transcripts of several, such as hexokinase 2, phosphoglycerate kinase 1, pyruvate kinase muscle‐type 2, and lactate dehydrogenase B as well as those for the nonglycolysis‐related proteins, CD‐36, C/EBP homologous protein, and peroxisome proliferator‐activated receptor γ, were up‐regulated in L‐PDCKO liver whereas hypoxia‐induced factor‐1α, pyruvate dehydrogenase kinase 1 and Sirtuin 1 transcripts were down‐regulated. The protein levels of pyruvate kinase muscle‐type 2 and lactate dehydrogenase B were increased whereas that of lactate dehydrogenase A was decreased in PDC‐deficient mouse liver. Analysis of endoplasmic reticulum and oxidative stress indicators suggests that the L‐PDCKO liver showed evidence of the former but not the latter. These findings indicate that (i) liver‐specific PDC deficiency is sufficient to induce “aerobic glycolysis characteristic” in mouse liver, and (ii) the mechanism(s) responsible for these changes appears distinct from that which induces the Warburg effect in some cancer cells.
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Affiliation(s)
- Mulchand S Patel
- Department of Biochemistry, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA
| | - Saleh Mahmood
- Department of Biochemistry, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA
| | - Jiwon Jung
- Department of Biochemistry, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA
| | - Todd C Rideout
- Department of Exercise and Nutrition Sciences, School of Public Health and Health Professions, University at Buffalo, Buffalo, NY, USA
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2
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Geisler CE, Hepler C, Higgins MR, Renquist BJ. Hepatic adaptations to maintain metabolic homeostasis in response to fasting and refeeding in mice. Nutr Metab (Lond) 2016; 13:62. [PMID: 27708682 PMCID: PMC5037643 DOI: 10.1186/s12986-016-0122-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 09/15/2016] [Indexed: 12/26/2022] Open
Abstract
Background The increased incidence of obesity and associated metabolic diseases has driven research focused on genetically or pharmacologically alleviating metabolic dysfunction. These studies employ a range of fasting-refeeding models including 4–24 h fasts, “overnight” fasts, or meal feeding. Still, we lack literature that describes the physiologically relevant adaptations that accompany changes in the duration of fasting and re-feeding. Since the liver is central to whole body metabolic homeostasis, we investigated the timing of the fast-induced shift toward glycogenolysis, gluconeogenesis, and ketogenesis and the meal-induced switch toward glycogenesis and away from ketogenesis. Methods Twelve to fourteen week old male C57BL/6J mice were fasted for 0, 4, 8, 12, or 16 h and sacrificed 4 h after lights on. In a second study, designed to understand the response to a meal, we gave fasted mice access to feed for 1 or 2 h before sacrifice. We analyzed the data using mixed model analysis of variance. Results Fasting initiated robust metabolic shifts, evidenced by changes in serum glucose, non-esterified fatty acids (NEFAs), triacylglycerol, and β-OH butyrate, as well as, liver triacylglycerol, non-esterified fatty acid, and glycogen content. Glycogenolysis is the primary source to maintain serum glucose during the first 8 h of fasting, while de novo gluconeogenesis is the primary source thereafter. The increase in serum β-OH butyrate results from increased enzymatic capacity for fatty acid flux through β-oxidation and shunting of acetyl-CoA toward ketone body synthesis (increased CPT1 (Carnitine Palmitoyltransferase 1) and HMGCS2 (3-Hydroxy-3-Methylglutaryl-CoA Synthase 2) expression, respectively). In opposition to the relatively slow metabolic adaptation to fasting, feeding of a meal results in rapid metabolic changes including full depression of serum β-OH butyrate and NEFAs within an hour. Conclusions Herein, we provide a detailed description of timing of the metabolic adaptations in response to fasting and re-feeding to inform study design in experiments of metabolic homeostasis. Since fasting and obesity are both characterized by elevated adipose tissue lipolysis, hepatic lipid accumulation, ketogenesis, and gluconeogenesis, understanding the drivers behind the metabolic shift from the fasted to the fed state may provide targets to limit aberrant gluconeogenesis and ketogenesis in obesity.
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Affiliation(s)
- C E Geisler
- School of Animal and Comparative Biomedical Sciences, University of Arizona, 4101 North Campbell Avenue, Tucson, AZ 85719 USA
| | - C Hepler
- School of Animal and Comparative Biomedical Sciences, University of Arizona, 4101 North Campbell Avenue, Tucson, AZ 85719 USA.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75235 USA
| | - M R Higgins
- School of Animal and Comparative Biomedical Sciences, University of Arizona, 4101 North Campbell Avenue, Tucson, AZ 85719 USA
| | - B J Renquist
- School of Animal and Comparative Biomedical Sciences, University of Arizona, 4101 North Campbell Avenue, Tucson, AZ 85719 USA
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3
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Adams AC, Astapova I, Fisher FM, Badman MK, Kurgansky KE, Flier JS, Hollenberg AN, Maratos-Flier E. Thyroid hormone regulates hepatic expression of fibroblast growth factor 21 in a PPARalpha-dependent manner. J Biol Chem 2010; 285:14078-82. [PMID: 20236931 DOI: 10.1074/jbc.c110.107375] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Thyroid hormone has profound and diverse effects on liver metabolism. Here we show that tri-iodothyronine (T3) treatment in mice acutely and specifically induces hepatic expression of the metabolic regulator fibroblast growth factor 21 (FGF21). Mice treated with T3 showed a dose-dependent increase in hepatic FGF21 expression with significant induction at doses as low as 100 microg/kg. Time course studies determined that induction is seen as early as 4 h after treatment with a further increase in expression at 6 h after injection. As FGF21 expression is downstream of the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha), we treated PPARalpha knock-out mice with T3 and found no increase in expression, indicating that hepatic regulation of FGF21 by T3 in liver is via a PPARalpha-dependent mechanism. In contrast, in white adipose tissue, FGF21 expression was suppressed by T3 treatment, with other T3 targets unaffected. In cell culture studies with an FGF21 reporter construct, we determined that three transcription factors are required for induction of FGF21 expression: thyroid hormone receptor beta (TRbeta), retinoid X receptor (RXR), and PPARalpha. These findings indicate a novel regulatory pathway whereby T3 positively regulates hepatic FGF21 expression, presenting a novel therapeutic target for diseases such as non-alcoholic fatty liver disease.
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Affiliation(s)
- Andrew C Adams
- Division of Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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4
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Bremer J. The biochemistry of hypo- and hyperlipidemic fatty acid derivatives: metabolism and metabolic effects. Prog Lipid Res 2001; 40:231-68. [PMID: 11412891 DOI: 10.1016/s0163-7827(01)00004-2] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A selection of amphipatic hyper- and hypolipidemic fatty acid derivatives (fibrates, thia- and branched chain fatty acids) are reviewed. They are probably all ligands for the peroxisome proliferation activation receptor (PPARalpha) which has a low selectivity for its ligands. These compounds give hyper- or hypolipidemic responses depending on their ability to inhibit or stimulate mitochondrial fatty acid oxidation in the liver. The hypolipidemic response is explained by the following metabolic effects: Lipoprotein lipase is induced in liver where it is normally not expressed. Apolipoprotein CIII is downregulated. These two effects in liver lead to a facilitated (re)uptake of chylomicrons and VLDL, thus creating a direct transport of fatty acids from the gut to the liver. Fatty acid metabolizing enzymes in the liver (CPT-I and II, peroxisomal and mitochondrial beta-oxidation enzymes, enzymes of ketogenesis, and omega-oxidation enzymes) are induced and create an increased capacity for fatty acid oxidation. The increased oxidation of fatty acids "drains" fatty acids from the body, reduces VLDL formation, and ultimately explains the antiadiposity and improved insulin sensitivity observed after administration of peroxisome proliferators.
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Affiliation(s)
- J Bremer
- Institute of Medical Biochemistry, University of Oslo, Pb 1112 Blindern, 0317, Oslo, Norway
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5
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Mutter T, Dolinsky VW, Ma BJ, Taylor WA, Hatch GM. Thyroxine regulation of monolysocardiolipin acyltransferase activity in rat heart. Biochem J 2000; 346 Pt 2:403-6. [PMID: 10677359 PMCID: PMC1220866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Treatment of rats with thyroxine has been shown to elevate the biosynthesis and content of cardiolipin in the heart [Cao, Cheng, Angel and Hatch (1995) Biochim. Biophys. Acta 1256, 241-244]. Treatment with thyroxine resulted in a 1.8-fold increase (P<0.025) in [1-(14)C]linoleate and a 1.7-fold increase (P<0.025) in [1-(14)C]oleate incorporated into cardiolipin in perfused hearts, compared with controls. The mechanism for the elevation in incorporation of unsaturated fatty acids into cardiolipin was a 1. 6-fold (P<0.025) increase in mitochondrial monolysocardiolipin acyltransferase activity. The results demonstrate that the acylation of cardiac monolysocardiolipin is regulated by thyroid hormone. Thus an elevation in cardiolipin biosynthesis is accompanied by an elevation in monolysocardiolipin acyltransferase activity to maintain the appropriate molecular species composition of cardiolipin in the cardiac mitochondrial membrane. We postulate that monolysocardiolipin acyltransferase might be a rate-limiting enzyme for the molecular remodelling of cardiolipin in the heart.
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Affiliation(s)
- T Mutter
- Department of Pharmacology and Therapeutics, University of Manitoba, A307 Chown Building, 753 McDermot Avenue, Winnipeg, Manitoba, Canada R3E OW3
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6
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Hegardt FG. Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase: a control enzyme in ketogenesis. Biochem J 1999; 338 ( Pt 3):569-82. [PMID: 10051425 PMCID: PMC1220089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Cytosolic and mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthases were first recognized as different chemical entities in 1975, when they were purified and characterized by Lane's group. Since then, the two enzymes have been studied extensively, one as a control site of the cholesterol biosynthetic pathway and the other as an important control site of ketogenesis. This review describes some key developments over the last 25 years that have led to our current understanding of the physiology of mitochondrial HMG-CoA synthase in the HMG-CoA pathway and in ketogenesis in the liver and small intestine of suckling animals. The enzyme is regulated by two systems: succinylation and desuccinylation in the short term, and transcriptional regulation in the long term. Both control mechanisms are influenced by nutritional and hormonal factors, which explains the incidence of ketogenesis in diabetes and starvation, during intense lipolysis, and in the foetal-neonatal and suckling-weaning transitions. The DNA-binding properties of the peroxisome-proliferator-activated receptor and other transcription factors on the nuclear-receptor-responsive element of the mitochondrial HMG-CoA synthase promoter have revealed how ketogenesis can be regulated by fatty acids. Finally, the expression of mitochondrial HMG-CoA synthase in the gonads and the correction of auxotrophy for mevalonate in cells deficient in cytosolic HMG-CoA synthase suggest that the mitochondrial enzyme may play a role in cholesterogenesis in gonadal and other tissues.
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Affiliation(s)
- F G Hegardt
- Department of Biochemistry and Molecular Biology, School of Pharmacy, University of Barcelona, Av/ Diagonal 643, 08028 Barcelona, Spain.
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7
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Priestman DA, Donald E, Holness MJ, Sugden MC. Different mechanisms underlie the long-term regulation of pyruvate dehydrogenase kinase (PDHK) by tri-iodothyronine in heart and liver. FEBS Lett 1997; 419:55-7. [PMID: 9426219 DOI: 10.1016/s0014-5793(97)01430-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Antibodies to purified recombinant PDHKII were used for ELISAs of PDHKII in mitochondrial extracts. In liver, hyperthyroidism elicited a 2.3-fold increase in PDHK activity (P < 0.01) which was accompanied by a significant 1.5-fold (P < 0.001) increase in the amount of mitochondrial immunoreactive PDHKII. In contrast, despite a stable 2.0-fold increase in cardiac PDHK activity (P < 0.001), the amount of mitochondrial immunoreactive PDHKII in heart was unaffected by hyperthyroidism. The mechanisms for long-term regulation of PDHK activity by thyroid hormones therefore differ fundamentally between heart and liver.
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Affiliation(s)
- D A Priestman
- Department of Biochemistry, Basic Medical Sciences, St Bartholomew's and the Royal London School of Medicine and Dentistry, Queen Mary and Westfield College, UK
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8
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Sugden MC, Fryer LG, Priestman DA, Orfali KA, Holness MJ. Increased hepatic pyruvate dehydrogenase kinase activity in fed hyperthyroid rats: studies in vivo and with cultured hepatocytes. Mol Cell Endocrinol 1996; 119:219-24. [PMID: 8807641 DOI: 10.1016/0303-7207(96)03817-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Experimental hyperthyroidism induced by the administration of tri-iodothyronine (T3; 100 micrograms/100 g body wt; 3 days) increased plasma non-esterified fatty acids in the fed state in the rat. At the same time, hepatic PDH kinase responded with a persistent (1.6-fold) increase in activity. The exposure of hepatocytes from fed euthyroid rats to T3 (100 nM) in culture for 21 h increased PDH kinase activity to an extent comparable to that observed in vivo in response to hyperthyroidism. The in vitro increase in PDH kinase activity was suppressed by insulin (100 microU/ml) and by inhibition of mitochondrial fatty acid oxidation. The results demonstrate a direct hepatic action of T3 to increase PDH kinase activity, which is mediated by intramitochondrial fatty acyl-CoA or a product of beta-oxidation, and facilitated by hepatic insulin resistance.
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Affiliation(s)
- M C Sugden
- Department of Biochemistry, Queen Mary and Westfield College, (University of London), UK
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9
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Voice MW, Borthwick EB, Coughtrie MW, Burchell A. The in vivo regulation of hepatic and renal glucose-6-phosphatase by thyroxine. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1231:176-80. [PMID: 7662696 DOI: 10.1016/0005-2728(95)00081-s] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The hepatic and renal microsomal glucose-6-phosphatase enzymes are situated with their active site in the lumen of the endoplasmic reticulum and for normal enzyme activity in vivo transport systems are needed for the substrates and products of the enzyme. We have shown that thyroxine activates the kidney glucose-6-phosphatase enzyme and the liver glucose 6-phosphate transport systems. In contrast, in hypophysectomised and adrenalectomised animals, thyroxine activates the transport systems and the enzyme in both liver and kidney.
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Affiliation(s)
- M W Voice
- Department of Obstetrics and Gynaecology, University of Dundee, Ninewells Hospital and Medical School, UK
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10
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Valera A, Rodriguez-Gil JE, Bosch F. Vanadate treatment restores the expression of genes for key enzymes in the glucose and ketone bodies metabolism in the liver of diabetic rats. J Clin Invest 1993; 92:4-11. [PMID: 8100835 PMCID: PMC293515 DOI: 10.1172/jci116580] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Oral administration of vanadate to diabetic streptozotocin-treated rats decreased the high blood glucose and D-3-hydroxybutyrate levels related to diabetes. The increase in the expression of the P-enolpyruvate carboxykinase (PEPCK) gene, the main regulatory enzyme of gluconeogenesis, was counteracted in the liver and the kidney after vanadate administration to diabetic rats. Vanadate also counteracted the induction in tyrosine aminotransferase gene expression due to diabetes and was able to increase the expression of the glucokinase gene to levels even higher than those found in healthy animals. Similarly, an induction in pyruvate kinase mRNA transcripts was observed in diabetic vanadate-treated rats. These effects were correlated with changes on glucokinase and pyruvate kinase activities. Vanadate treatment caused a decrease in the expression of the liver-specific glucose transporter, GLUT-2. Thus, vanadate was able to restore liver glucose utilization and block glucose production in diabetic rats. The increase in the expression of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCoAS) gene, the key regulatory enzyme in the ketone bodies production pathway, observed in diabetic rats was also blocked by vanadate. Furthermore, a similar pattern in the expression of PEPCK, GLUT-2, HMGCoAS, and the transcription factor CCAAT/enhancer-binding protein alpha genes has been observed. All of these results suggest that the regulation of the expression of genes involved in the glucose and ketone bodies metabolism could be a key step in the normalization process induced by vanadate administration to diabetic rats.
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Affiliation(s)
- A Valera
- Department of Biochemistry and Molecular Biology, School of Veterinary Medicine, Autonomous University of Barcelona, Spain
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11
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Quant PA, Robin D, Robin P, Girard J, Brand MD. A top-down control analysis in isolated rat liver mitochondria: can the 3-hydroxy-3-methylglutaryl-CoA pathway be rate-controlling for ketogenesis? BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1156:135-43. [PMID: 8427872 DOI: 10.1016/0304-4165(93)90128-u] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We incubated isolated liver mitochondria with palmitoyl-CoA, 2,4-dinitrophenol and malonate. Under these conditions all the flux of carbon from palmitoyl-CoA was directed towards acetoacetate synthesis. We measured the rate of acetyl-CoA formation from palmitoyl-CoA (by measuring the rate of oxygen consumption) and the rate of acetoacetate production from acetyl-CoA at three different acetyl-CoA/CoA ratios. Using the top-down approach of metabolic control analysis we calculated the control over ketogenesis exerted by (a) the conversion of extramitochondrial palmitoyl-CoA to intramitochondrial acetyl-CoA and by (b) the conversion of acetyl-CoA to acetoacetate (the 'HMG-CoA pathway'). The overall flux control coefficients of the groups of enzymes involved in (a) and (b) over ketogenesis were 0.28 and 0.72, respectively. Our results show that it is possible for significant control to be exerted over ketogenesis by the enzymes of the HMG-CoA pathway.
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Affiliation(s)
- P A Quant
- Centre de Recherche sur l'Endocrinologie Moléculaire et le Développement, Centre National de la Recherche Scientifique, Meudon-Bellevue, France
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12
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Moir AM, Zammit VA. Monitoring of changes in hepatic fatty acid and glycerolipid metabolism during the starved-to-fed transition in vivo. Studies on awake, unrestrained rats. Biochem J 1993; 289 ( Pt 1):49-55. [PMID: 8424771 PMCID: PMC1132129 DOI: 10.1042/bj2890049] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
1. The technique of selective labelling of hepatic fatty acids in vivo [Moir and Zammit (1992) Biochem. J. 283, 145-149] has been used to monitor non-invasively the metabolism of fatty acids in the livers of awake unrestrained rats during the starved-to-refed transition. Values for the incorporation of labelled fatty acid into liver and plasma glycerolipids and into exhaled carbon dioxide after injection of labelled lipoprotein and Triton WR 1339 into rats with chronically cannulated jugular veins were obtained for successive 1 h periods from the start of refeeding of 24 h-starved rats. 2. Starvation for 24 h resulted in marked and reciprocal changes in the incorporation of label into glycerolipids and exhaled 14CO2, such that a 4-fold higher value was obtained for the oxidation/esterification ratio in livers of starved rats compared with fed animals. 3. Refeeding of starved rats did not return this ratio to the value observed for fed animals for at least 7 h; during the first 3 h of refeeding the ratio was at least as high as that for starved rats. Between 4 h and 6 h of refeeding the ratio was still approx. 70% of that in starved animals, and 2.5-fold higher than in fed rats. 4. These data support the hypothesis that the capacity of the liver to oxidize fatty acids is maintained at a high level during the initial stages of refeeding [Grantham and Zammit (1986) Biochem. J. 239, 485-488] and that control of the flux of hepatic fatty acids into the oxidative pathway is largely lost from the reaction catalysed by mitochondrial overt carnitine palmitoyltransferase (CPT I) during this phase of recovery from the starved state. 5. Refeeding also resulted in a rapid (< 1 h) increase in hepatic malonyl-CoA concentrations to values intermediate between those in livers of fed and starved animals. The sensitivity of CPT I to malonyl-CoA inhibition in isolated liver mitochondria was only partially reversed even after 5 h of refeeding. 6. Refeeding resulted in an acute 35% inhibition of the fraction of synthesized triacylglycerol that was secreted into the plasma; the maximal effect occurred 2-3 h after the start of refeeding. The inhibition of the fractional secretion rate was fully reversed after 5 h of refeeding. 7. The amount of 14C label that was incorporated into phospholipids as a fraction of total glycerolipid synthesis was doubled within 2 h of the start of refeeding.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A M Moir
- Hannah Research Institute, Ayr, Scotland, U.K
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13
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Glucose homeostasis in thyroxine-treated BHE/cdb rats fed corn oil or hydrogenated coconut oil. J Nutr Biochem 1993. [DOI: 10.1016/0955-2863(93)90015-o] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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14
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Sugden MC, Holness MJ, Liu YL, Smith DM, Fryer LG, Kruszynska YT. Mechanisms regulating cardiac fuel selection in hyperthyroidism. Biochem J 1992; 286 ( Pt 2):513-7. [PMID: 1530584 PMCID: PMC1132927 DOI: 10.1042/bj2860513] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Starvation (48 h) decreases fructose 2,6-bisphosphate (Fru-2,6-P2) concentrations and the ratio of free to acylated carnitine in hearts of euthyroid rats. These decreases, which are indicative of increased lipid fuel oxidation, are accompanied by decreased rates of glucose uptake and phosphorylation, assessed by using radioactive 2-deoxyglucose. Cardiac concentrations of acylated carnitines were increased at the expense of free carnitine even in the fed state in response to experimental hyperthyroidism, but neither Fru-2,6-P2 concentrations nor rates of glucose utilization were suppressed. Starvation (48 h) did not further increase the proportion of acylated carnitine in the heart in hyperthyroidism, and suppression of Fru-2,6-P2 concentrations and glucose utilization rates by starvation was attenuated. Although glucose utilization rates were decreased, starvation did not decrease immunoreactive GLUT 4 protein concentrations. Furthermore, although hyperthyroidism was associated with a statistically significant (30-40%) increase in relative abundance of GLUT 4 mRNA, the amount of GLUT 4 protein was not increased by hyperthyroidism in either the fed or the starved state. The results demonstrate a significant effect of hyperthyroidism to enhance cardiac glucose utilization in starvation by a mechanism which does not involve changes in GLUT 4 expression but may be secondary to changes in glucose-lipid interactions at the tissue level.
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Affiliation(s)
- M C Sugden
- Department of Biochemistry, Faculty of Basic Medical Sciences, Queen Mary and Westfield College, London, U.K
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15
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Ayté J, Gil-Gómez G, Haro D, Marrero PF, Hegardt FG. Rat mitochondrial and cytosolic 3-hydroxy-3-methylglutaryl-CoA synthases are encoded by two different genes. Proc Natl Acad Sci U S A 1990; 87:3874-8. [PMID: 1971108 PMCID: PMC54006 DOI: 10.1073/pnas.87.10.3874] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
We report the isolation and characterization of a 1994-base-pair cDNA that encompasses the entire transcription unit of the mitochondrial 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase (EC 4.1.3.5.) gene from rat. Analysis of the nucleotide sequence reveals that the cDNA encodes a polypeptide of 508 residues and 56,918-Da molecular mass. Identify of the cDNA clone isolated as mitochondrial HMG-CoA synthase was confirmed by the following criteria: (i) Amino acid residues are 65% homologous with hamster cytosolic HMG-CoA synthase. (ii) A 19-amino acid sequence probably corresponding to the catalytic site is highly homologous (90%) to that reported for chicken liver mitochondrial HMG-CoA synthase. (iii) The expression product of the cDNA in Escherichia coli has HMG-CoA synthase activity. (iv) The protein includes a sequence of 37 amino acid residues at the N terminus that is not present in the cytosolic enzyme. The predominantly basic, hydrophobic, and hydroxylated nature of the residues of this sequence suggests that it is a leader peptide to target HMG-CoA synthase inside mitochondria. These data plus the hybridization pattern in genomic Southern blot analysis, the different transcript size (2.0 kilobases versus 3.4 kilobases for the cytosolic enzyme), and the different expression pattern shown in RNA blot experiments suggest the presence of two HMG-CoA synthase genes, one for the cytosolic and another for the mitochondrial enzyme.
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Affiliation(s)
- J Ayté
- Unitat de Bioquímica, Facultat de Farmàcia, Universitat de Barcelona, Spain
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16
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Quant PA, Tubbs PK, Brand MD. Glucagon activates mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase in vivo by decreasing the extent of succinylation of the enzyme. EUROPEAN JOURNAL OF BIOCHEMISTRY 1990; 187:169-74. [PMID: 1967579 DOI: 10.1111/j.1432-1033.1990.tb15291.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
1. 3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (EC 4.1.3.5) in extracts of rat liver mitochondria can be inactivated by succinyl-CoA and activated by incubation in a medium designed to cause desuccinylation ('desuccinylation medium'). 2. The enzyme is less active in extracts of whole liver from control rats than from rats treated with glucagon or mannoheptulose. Incubation in desuccinylation medium raises the activity in extracts from control rats to the same value as treated rats, suggesting that the extent of succinylation in vivo is greater in controls than in hormone-treated animals. 3. This result is also obtained in liver homogenates and in isolated mitochondria. 4. Increasing the succinyl-CoA content of mitochondria to the same high level lowers the enzyme activity to the same value in mitochondria isolated from control or treated rats. In each case subsequent incubation of the lysates in desuccinylation medium raises the enzyme activity by the same extent. 5. Measurement of the incorporation of radiolabel from 2-oxo[5-14C]glutarate into protein is consistent with the proposal that all these changes in activity in isolated mitochondria may be explained by changes in the extent of succinylation of the enzyme. 6. From these data and our earlier work we conclude that, in vivo, mitochondrial HMG-CoA synthase in fed rats is normally substantially succinylated (about 40%) and inactivated, and that glucagon increases the activity of HMG-CoA synthase by lowering the concentration of succinyl-CoA and thus decreasing the extent of succinylation of the enzyme (to less than 10%). This may be an important control mechanism in ketogenesis.
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Affiliation(s)
- P A Quant
- Department of Biochemistry, University of Cambridge, England
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17
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Sugden MC, Holness MJ. The role of regulation of tissue pyruvate dehydrogenase complex activity during the starved-to-fed transition. Ann N Y Acad Sci 1989; 573:314-36. [PMID: 2699403 DOI: 10.1111/j.1749-6632.1989.tb15008.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- M C Sugden
- Department of Biochemistry, London Hospital Medical College, United Kingdom
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18
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Sugden MC, Holness MJ, Palmer TN. Fuel selection and carbon flux during the starved-to-fed transition. Biochem J 1989; 263:313-23. [PMID: 2688629 PMCID: PMC1133432 DOI: 10.1042/bj2630313] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- M C Sugden
- Department of Biochemistry and Chemical Pathology, London Hospital Medical College, U.K
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19
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Quant PA, Tubbs PK, Brand MD. Treatment of rats with glucagon or mannoheptulose increases mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase activity and decreases succinyl-CoA content in liver. Biochem J 1989; 262:159-64. [PMID: 2573345 PMCID: PMC1133242 DOI: 10.1042/bj2620159] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
1. The activity of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (EC 4.1.3.5) in extracts of rapidly frozen rat livers was doubled in animals treated in various ways to increase ketogenic flux. 2. Some 90% of the activity measured was mitochondrial, and changes in mitochondrial activity dominated changes in total enzyme activity. 3. The elevated HMG-CoA synthase activities persisted throughout the isolation of liver mitochondria. 4. Intramitochondrial succinyl-CoA content was lower in whole liver homogenates and in mitochondria isolated from animals treated with glucagon or mannoheptulose. 5. HMG-CoA synthase activity in mitochondria from both ox and rat liver was negatively correlated with intramitochondrial succinyl-CoA levels when these were manipulated artificially. Under these conditions, the differences between mitochondria from control and hormone-treated rats were abolished. 6. These findings show that glucagon can decrease intramitochondrial succinyl-CoA concentration, and that this in turn can regulate mitochondrial HMG-CoA synthase. They support the hypothesis that the formation of ketone bodies from acetyl-CoA may be regulated by the extent of succinylation of mitochondrial HMG-CoA synthase.
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Affiliation(s)
- P A Quant
- Department of Biochemistry, University of Cambridge, U.K
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20
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McGarry JD, Woeltje KF, Kuwajima M, Foster DW. Regulation of ketogenesis and the renaissance of carnitine palmitoyltransferase. DIABETES/METABOLISM REVIEWS 1989; 5:271-84. [PMID: 2656156 DOI: 10.1002/dmr.5610050305] [Citation(s) in RCA: 239] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- J D McGarry
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas
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21
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Effects of thyroid hormone on lipogenesis and glucose flux. Nutr Rev 1988; 46:356-8. [PMID: 3067142 DOI: 10.1111/j.1753-4887.1988.tb05362.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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22
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Holness MJ, MacLennan PA, Palmer TN, Sugden MC. The disposition of carbohydrate between glycogenesis, lipogenesis and oxidation in liver during the starved-to-fed transition. Biochem J 1988; 252:325-30. [PMID: 3415654 PMCID: PMC1149147 DOI: 10.1042/bj2520325] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A comparison was made between the time courses of restoration of pyruvate dehydrogenase activities, fructose 2,6-bisphosphate concentrations and lipogenic rates, together with net hepatic glucose flux and glycogen synthesis/deposition in livers of 48 h-starved rats provided with laboratory chow ad libitum for up to 24 h. Increased glycogenesis, lipogenesis and net glucose uptake were observed after 1 h of re-feeding, preceding re-activation of pyruvate dehydrogenase, which occurred after 3-4 h. Increased concentrations of fructose 2,6-bisphosphate were only observed after 5-6 h. The implication of the temporal relationship between these parameters is discussed.
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Affiliation(s)
- M J Holness
- Department of Chemical Pathology, London Hospital Medical College, U.K
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23
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Holness MJ, Cook EB, Sugden MC. Regulation of hepatic fructose 2,6-bisphosphate concentrations and lipogenesis after re-feeding in euthyroid and hyperthyroid rats. A regulatory role for glycogenesis. Biochem J 1988; 252:357-62. [PMID: 3415658 PMCID: PMC1149152 DOI: 10.1042/bj2520357] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The time courses of restoration of fructose 2,6-bisphosphate (Fru-2,6-P2) concentrations and rates of lipogenesis after chow re-feeding were correlated with glycogen concentrations and rates of glycogen synthesis in livers of 48 h-starved euthyroid and hyperthyroid rats. Although a regulatory function for glycogen in the regulation of Fru-2,6-P2 concentrations was excluded, an inverse relationship between rates of glycogenesis and Fru-2,6-P2 concentrations indicated a role for glycogenesis in the suppression of Fru-2,6-P2 concentrations during the early (0-4 h) period of re-feeding. There was also a negative correlation between rates of glycogenesis and lipogenesis, and a positive correlation between glycogen concentrations and the lipogenic rate. Decreased rates of glycogenesis in hyperthyroid rats were associated with increased rates of lipogenesis. The response of Fru-2,6-P2 to changes in the glycogenic rate was modified by hyperthyroidism, although a negative correlation was again observed.
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Affiliation(s)
- M J Holness
- Department of Chemical Pathology, London Hospital Medical College, U.K
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24
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French TJ, Holness MJ, MacLennan PA, Sugden MC. Effects of nutritional status and acute variation in substrate supply on cardiac and skeletal-muscle fructose 2,6-bisphosphate concentrations. Biochem J 1988; 250:773-9. [PMID: 3291855 PMCID: PMC1148923 DOI: 10.1042/bj2500773] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We examined the long-term effects of nutritional status and the acute effects of changes in exogenous carbohydrate- and lipid-substrate supply and utilization on fructose 2,6-bisphosphate (Fru-2,6-P2) concentrations in heart, gastrocnemius and soleus. Starvation decreased Fru-2,6-P2 concentrations in all three muscles. The acute administration of insulin and glucose increased skeletal-muscle Fru-2,6-P2 in the fed, but not in the starved, state, but cardiac Fru-2,6-P2 was unchanged. Cardiac and skeletal-muscle Fru-2,6-P2 concentrations were unaffected by acute increases in fatty acid supply produced by the administration of corn oil plus heparin, or by acute decreases in fatty acid supply produced by inhibition of lipolysis. Differences in cardiac and skeletal-muscle Fru-2,6-P2 concentrations observed in response to starvation were not reversed by administration of glucose or glucose plus insulin, or by inhibition of lipolysis, even though changes in citrate (heart), acylcarnitine (heart) and glycogen (skeletal muscle) were observed. Concentrations remained low for at least 8 h after chow re-feeding, but the fed value was restored by 24 h.
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Affiliation(s)
- T J French
- Department of Chemical Pathology, London Hospital Medical College, U.K
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25
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Holness MJ, Palmer TN, Worrall EB, Sugden MC. Hepatic carbon flux after re-feeding in the glycogen-storage-disease (gsd/gsd) rat. Biochem J 1987; 248:969-72. [PMID: 3481265 PMCID: PMC1148646 DOI: 10.1042/bj2480969] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In this study we utilized the phosphorylase b kinase-deficient (gsd/gsd) rat as a model of hepatic substrate utilization where there is a constraint on glycogenesis imposed by the maintenance of high glycogen concentrations. Glucose re-feeding of 48 h-starved gsd/gsd rats led to suppression of hepatic glucose output. In contrast with the situation in normal rats, activation of the pyruvate dehydrogenase complex and lipogenesis was observed. It is suggested that impeding glycogenic flux may divert substrate into lipogenesis, possibly via activation of the pyruvate dehydrogenase complex.
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Affiliation(s)
- M J Holness
- Department of Chemical Pathology, London Hospital Medical College, U.K
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