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Zhu L, Brown WC, Cai Q, Krust A, Chambon P, McGuinness OP, Stafford JM. Estrogen treatment after ovariectomy protects against fatty liver and may improve pathway-selective insulin resistance. Diabetes 2013; 62:424-34. [PMID: 22966069 PMCID: PMC3554377 DOI: 10.2337/db11-1718] [Citation(s) in RCA: 245] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Pathway-selective insulin resistance where insulin fails to suppress hepatic glucose production but promotes liver fat storage may underlie glucose and lipid abnormalities after menopause. We tested the mechanisms by which estrogen treatment may alter the impact of a high-fat diet (HFD) when given at the time of ovariectomy (OVX) in mice. Female C57BL/6J mice underwent sham operation, OVX, or OVX with estradiol (E2) treatment and were fed an HFD. Hyperinsulinemic-euglycemic clamps were used to assess insulin sensitivity, tracer incorporation into hepatic lipids, and liver triglyceride export. OVX mice had increased adiposity that was prevented with E2 at the time of OVX. E2 treatment increased insulin sensitivity with OVX and HFD. In sham and OVX mice, HFD feeding induced fatty liver, and insulin reduced hepatic apoB100 and liver triglyceride export. E2 treatment reduced liver lipid deposition and prevented the decrease in liver triglyceride export during hyperinsulinemia. In mice lacking the liver estrogen receptor α, E2 after OVX limited adiposity but failed to improve insulin sensitivity, to limit liver lipid deposition, and to prevent insulin suppression of liver triglyceride export. In conclusion, estrogen treatment may reverse aspects of pathway-selective insulin resistance by promoting insulin action on glucose metabolism but limiting hepatic lipid deposition.
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Affiliation(s)
- Lin Zhu
- Tennessee Valley Healthcare System Nashville, Tennessee
| | - William C. Brown
- Tennessee Valley Healthcare System Nashville, Tennessee
- Division of Diabetes, Endocrinology, and Metabolism, Department of Internal Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Qing Cai
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Andrée Krust
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
| | - Pierre Chambon
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
| | - Owen P. McGuinness
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - John M. Stafford
- Tennessee Valley Healthcare System Nashville, Tennessee
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Case Western Reserve Medical Center, Cleveland, Ohio
- Corresponding author: John M. Stafford,
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102
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Henriksen BS, Curtis ME, Fillmore N, Cardon BR, Thomson DM, Hancock CR. The effects of chronic AMPK activation on hepatic triglyceride accumulation and glycerol 3-phosphate acyltransferase activity with high fat feeding. Diabetol Metab Syndr 2013; 5:29. [PMID: 23725555 PMCID: PMC3679947 DOI: 10.1186/1758-5996-5-29] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 05/18/2013] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND High fat feeding increases hepatic fat accumulation and is associated with hepatic insulin resistance. AMP Activated Protein Kinase (AMPK) is thought to inhibit lipid synthesis by the acute inhibition of glycerol-3-phosphate acyltransferase (GPAT) activity and transcriptional regulation via sterol regulatory element binding protein-1c (SREBP-1c). METHODS The purpose of this study was to determine if chronic activation of AMPK prevented an increase in GPAT1 activity in rats fed a high fat diet. Rats were fed a control (C), or a high fat (HF) diet (60% fat) for 6 weeks and injected with saline or a daily aminoimidazole carboxamide ribnucleotide (AICAR) dose of 0.5 mg/g body weight. RESULTS Chronic AMPK activation by AICAR injections resulted in a significant reduction in hepatic triglyceride accumulation in both the C and HF fed animals (C, 5.5±0.7; C+AICAR, 2.7 ±0.3; HF, 21.8±3.3; and HF+AICAR, 8.0±1.8 mg/g liver). HF feeding caused an increase in total GPAT and GPAT1 activity, which was not affected by chronic AMPK activation (GPAT1 activity vs. C, C+AICAR, 92±19%; HF, 186±43%; HF+AICAR, 234±62%). Markers of oxidative capacity, including citrate synthase activity and cytochrome c abundance, were not affected by chronic AICAR treatment. Interestingly, HF feeding caused a significant increase in long chain acyl-CoA dehydrogenase or LCAD (up 66% from C), a marker of fatty acid oxidation capacity. CONCLUSIONS These results suggest that chronic AMPK activation limits hepatic triglyceride accumulation independent of a reduction in total GPAT1 activity.
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Affiliation(s)
- Bradley S Henriksen
- Department of Nutrition, Dietetics, and Food Science, Brigham Young University, Provo, UT 84602, USA
| | - Mary E Curtis
- Department of Nutrition, Dietetics, and Food Science, Brigham Young University, Provo, UT 84602, USA
| | - Natasha Fillmore
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA
| | - Brandon R Cardon
- Department of Nutrition, Dietetics, and Food Science, Brigham Young University, Provo, UT 84602, USA
| | - David M Thomson
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA
| | - Chad R Hancock
- Department of Nutrition, Dietetics, and Food Science, Brigham Young University, Provo, UT 84602, USA
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103
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Videla LA, Pettinelli P. Misregulation of PPAR Functioning and Its Pathogenic Consequences Associated with Nonalcoholic Fatty Liver Disease in Human Obesity. PPAR Res 2012; 2012:107434. [PMID: 23304111 PMCID: PMC3526338 DOI: 10.1155/2012/107434] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Accepted: 11/06/2012] [Indexed: 12/22/2022] Open
Abstract
Nonalcoholic fatty liver disease in human obesity is characterized by the multifactorial nature of the underlying pathogenic mechanisms, which include misregulation of PPARs signaling. Liver PPAR-α downregulation with parallel PPAR-γ and SREBP-1c up-regulation may trigger major metabolic disturbances between de novo lipogenesis and fatty acid oxidation favouring the former, in association with the onset of steatosis in obesity-induced oxidative stress and related long-chain polyunsaturated fatty acid n-3 (LCPUFA n-3) depletion, insulin resistance, hypoadiponectinemia, and endoplasmic reticulum stress. Considering that antisteatotic strategies targeting PPAR-α revealed that fibrates have poor effectiveness, thiazolidinediones have weight gain limitations, and dual PPAR-α/γ agonists have safety concerns, supplementation with LCPUFA n-3 appears as a promising alternative, which achieves both significant reduction in liver steatosis scores and a positive anti-inflammatory outcome. This latter aspect is of importance as PPAR-α downregulation associated with LCPUFA n-3 depletion may play a role in increasing the DNA binding capacity of proinflammatory factors, NF-κB and AP-1, thus constituting one of the major mechanisms for the progression of steatosis to steatohepatitis.
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Affiliation(s)
- Luis A. Videla
- Molecular and Clinical Pharmacology Program, Institute of Biomedical Sciences, Faculty of Medicine, University of Chile, Casilla 70000, Santiago 7, Chile
| | - Paulina Pettinelli
- Ciencias de la Salud, Nutrición y Dietética, Facultad de Medicina, Pontificia Universidad Católica de Chile, 7820436 Santiago, Chile
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104
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Lian J, Wei E, Wang SP, Quiroga AD, Li L, Di Pardo A, van der Veen J, Sipione S, Mitchell GA, Lehner R. Liver specific inactivation of carboxylesterase 3/triacylglycerol hydrolase decreases blood lipids without causing severe steatosis in mice. Hepatology 2012; 56:2154-62. [PMID: 22707181 DOI: 10.1002/hep.25881] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Accepted: 05/02/2012] [Indexed: 12/22/2022]
Abstract
UNLABELLED Carboxylesterase 3/triacylglycerol hydrolase (Ces3/TGH) participates in hepatic very low-density lipoprotein (VLDL) assembly and in adipose tissue basal lipolysis. Global ablation of Ces3/Tgh expression decreases serum triacylglycerol (TG) and nonesterified fatty acid levels and improves insulin sensitivity. To understand the tissue-specific role of Ces3/TGH in lipid and glucose homeostasis, we generated mice with a liver-specific deletion of Ces3/Tgh expression (L-TGH knockout [KO]). Elimination of hepatic Ces3/Tgh expression dramatically decreased plasma VLDL TG and VLDL cholesterol concentrations but only moderately increased liver TG levels in mice fed a standard chow diet. Significantly reduced plasma TG and cholesterol without hepatic steatosis were also observed in L-TGH KO mice challenged with a high-fat, high-cholesterol diet. L-TGH KO mice presented with increased plasma ketone bodies and hepatic fatty acid oxidation. Intrahepatic TG in L-TGH KO mice was stored in significantly smaller lipid droplets. Augmented hepatic TG levels in chow-fed L-TGH KO mice did not affect glucose tolerance or glucose production from hepatocytes, but impaired insulin tolerance was observed in female mice. CONCLUSION Our data suggest that ablation of hepatic Ces3/Tgh expression decreases plasma lipid levels without causing severe hepatic steatosis.
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Affiliation(s)
- Jihong Lian
- Group on Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada
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105
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Aicher TD, Boyd SA, McVean M, Celeste A. Novel therapeutics and targets for the treatment of diabetes. Expert Rev Clin Pharmacol 2012; 3:209-29. [PMID: 22111568 DOI: 10.1586/ecp.10.1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The microvascular complications of insufficiently controlled diabetes (neuropathy, retinopathy and nephropathy) and the marked increased risk of macrovascular events (e.g., stroke and myocardial infarction) have a dire impact on society in both human and economic terms. In Type 1 diabetes total β-cell loss occurs. In Type 2 diabetes, partial β-cell loss occurs before diagnosis, and the progressive β-cell loss during the life of the patient increases the severity of the disease. In patients with diabetes, increased insulin resistance in the muscle and liver are key pathophysiologic defects. In addition, defects in metabolic processes in the fat, GI tract, brain, pancreatic α-cells and kidney are detrimental to the overall health of the patient. This review addresses novel therapies for these deficiencies in clinical and preclinical evaluation, emphasizing their potential to address glucose homeostasis, β-cell mass and function, and the comorbidities of cardiovascular disease and obesity.
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Affiliation(s)
- Thomas D Aicher
- Principal Research Investigator, Array BioPharma Inc., 3200 Walnut Street, Boulder, CO 80301, USA.
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106
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Abstract
PURPOSE OF REVIEW This article reviews the mechanisms leading to the development of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) and the effects of hypoglycaemic and lipid-lowering therapies on NAFLD/NASH. RECENT FINDINGS The interaction of lipogenesis, fatty acid oxidation, inflammation, endoplasmic reticulum stress and hepatic insulin resistance contribute to the pathogenesis of NAFLD/NASH. Few large scale clinical trials exist with biopsy or magnetic resonance endpoints as opposed to ultrasonographic and transaminase endpoints. Trial evidence that exists supports the utility of weight loss, metformin, thiazolidinediones, fibrates, niacin, ezetimibe and statins in improving the steatosis component of NAFLD/NASH though with less or minimal effects on the fibrotic component of NASH. SUMMARY Hypoglycaemic and lipid-lowering therapies may have a role in the treatment of NAFLD/NASH but large scale endpoint trials remain to be performed.
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Affiliation(s)
- Anthony S Wierzbicki
- Department of Metabolic Medicine/Chemical Pathologyemical Pathology, Guy's and St. Thomas' Hospitals, London, UK.
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107
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MAGKOS FAIDON, SU XIONG, BRADLEY DAVID, FABBRINI ELISA, CONTE CATERINA, EAGON JCHRISTOPHER, VARELA JESTEBAN, BRUNT ELIZABETHM, PATTERSON BRUCEW, KLEIN SAMUEL. Intrahepatic diacylglycerol content is associated with hepatic insulin resistance in obese subjects. Gastroenterology 2012; 142:1444-6.e2. [PMID: 22425588 PMCID: PMC3564653 DOI: 10.1053/j.gastro.2012.03.003] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/28/2011] [Revised: 02/07/2012] [Accepted: 03/07/2012] [Indexed: 02/06/2023]
Abstract
Data from studies in animal models indicate that certain lipid metabolites, particularly diacylglycerol, ceramide, and acylcarnitine, disrupt insulin action. We evaluated the relationship between the presence of these metabolites in the liver (assessed by mass spectrometry) and hepatic insulin sensitivity (assessed using a hyperinsulinemic-euglycemic clamp with stable isotope tracer infusion) in 16 obese adults (body mass index, 48 ± 9 kg/m²). There was a negative correlation between insulin-mediated suppression of hepatic glucose production and intrahepatic diacylglycerol (r = -0.609; P = .012), but not with intrahepatic ceramide or acylcarnitine. These data indicate that intrahepatic diacylglycerol is an important mediator of hepatic insulin resistance in obese people with nonalcoholic fatty liver disease.
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Affiliation(s)
- FAIDON MAGKOS
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri
| | - XIONG SU
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri
| | - DAVID BRADLEY
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri
| | - ELISA FABBRINI
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri,Center for Clinical and Basic Research, Department of Medical Sciences, Instituto di Ricovero e Cura a Carattere Scientifico San Raffaele, Rome, Italy
| | - CATERINA CONTE
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri,Department of Clinical Medicine, Sapienza University of Rome, Rome, Italy
| | - J. CHRISTOPHER EAGON
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri,Department of Surgery, Washington University School of Medicine, St Louis, Missouri
| | - J. ESTEBAN VARELA
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri,Department of Surgery, Washington University School of Medicine, St Louis, Missouri
| | - ELIZABETH M. BRUNT
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri,Department of Pathology and Immunology, Washington University School of Medicine, St Louis, Missouri
| | - BRUCE W. PATTERSON
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri
| | - SAMUEL KLEIN
- Center for Human Nutrition, Washington University School of Medicine, St Louis, Missouri
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108
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Watt MJ, Hoy AJ. Lipid metabolism in skeletal muscle: generation of adaptive and maladaptive intracellular signals for cellular function. Am J Physiol Endocrinol Metab 2012; 302:E1315-28. [PMID: 22185843 DOI: 10.1152/ajpendo.00561.2011] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Fatty acids derived from adipose tissue lipolysis, intramyocellular triacylglycerol lipolysis, or de novo lipogenesis serve a variety of functions in skeletal muscle. The two major fates of fatty acids are mitochondrial oxidation to provide energy for the myocyte and storage within a variety of lipids, where they are stored primarily in discrete lipid droplets or serve as important structural components of membranes. In this review, we provide a brief overview of skeletal muscle fatty acid metabolism and highlight recent notable advances in the field. We then 1) discuss how lipids are stored in and mobilized from various subcellular locations to provide adaptive or maladaptive signals in the myocyte and 2) outline how lipid metabolites or metabolic byproducts derived from the actions of triacylglycerol metabolism or β-oxidation act as positive and negative regulators of insulin action. We have placed an emphasis on recent developments in the lipid biology field with respect to understanding skeletal muscle physiology and discuss unanswered questions and technical limitations for assessing lipid signaling in skeletal muscle.
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Affiliation(s)
- Matthew J Watt
- Biology of Lipid Metabolism Laboratory, Department of Physiology, Monash University, Clayton, Victoria 3800, Australia.
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109
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Abstract
Nonalcoholic fatty liver disease (NAFLD) is now the most frequent chronic liver disease in Western societies, affecting one in four adults in the USA, and is strongly associated with hepatic insulin resistance, a major risk factor in the pathogenesis of type 2 diabetes. Although the cellular mechanisms underlying this relationship are unknown, hepatic accumulation of diacylglycerol (DAG) in both animals and humans has been linked to hepatic insulin resistance. In this Perspective, we discuss the role of DAG activation of protein kinase Cε as the mechanism responsible for NAFLD-associated hepatic insulin resistance seen in obesity, type 2 diabetes, and lipodystrophy.
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Affiliation(s)
- François R Jornayvaz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06510, USA
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110
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Pasco MY, Léopold P. High sugar-induced insulin resistance in Drosophila relies on the lipocalin Neural Lazarillo. PLoS One 2012; 7:e36583. [PMID: 22567167 PMCID: PMC3342234 DOI: 10.1371/journal.pone.0036583] [Citation(s) in RCA: 163] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Accepted: 04/10/2012] [Indexed: 12/18/2022] Open
Abstract
In multicellular organisms, insulin/IGF signaling (IIS) plays a central role in matching energy needs with uptake and storage, participating in functions as diverse as metabolic homeostasis, growth, reproduction and ageing. In mammals, this pleiotropy of action relies in part on a dichotomy of action of insulin, IGF-I and their respective membrane-bound receptors. In organisms with simpler IIS, this functional separation is questionable. In Drosophila IIS consists of several insulin-like peptides called Dilps, activating a unique membrane receptor and its downstream signaling cascade. During larval development, IIS is involved in metabolic homeostasis and growth. We have used feeding conditions (high sugar diet, HSD) that induce an important change in metabolic homeostasis to monitor possible effects on growth. Unexpectedly we observed that HSD-fed animals exhibited severe growth inhibition as a consequence of peripheral Dilp resistance. Dilp-resistant animals present several metabolic disorders similar to those observed in type II diabetes (T2D) patients. By exploring the molecular mechanisms involved in Drosophila Dilp resistance, we found a major role for the lipocalin Neural Lazarillo (NLaz), a target of JNK signaling. NLaz expression is strongly increased upon HSD and animals heterozygous for an NLaz null mutation are fully protected from HSD-induced Dilp resistance. NLaz is a secreted protein homologous to the Retinol-Binding Protein 4 involved in the onset of T2D in human and mice. These results indicate that insulin resistance shares common molecular mechanisms in flies and human and that Drosophila could emerge as a powerful genetic system to study some aspects of this complex syndrome.
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Affiliation(s)
- Matthieu Y. Pasco
- Institute of Biology Valrose (iBV), CNRS UMR 7707, INSERM UMR 1091, University of Nice-Sophia Antipolis, Nice, France
| | - Pierre Léopold
- Institute of Biology Valrose (iBV), CNRS UMR 7707, INSERM UMR 1091, University of Nice-Sophia Antipolis, Nice, France
- * E-mail:
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111
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Samuel VT, Shulman GI. Mechanisms for insulin resistance: common threads and missing links. Cell 2012; 148:852-71. [PMID: 22385956 DOI: 10.1016/j.cell.2012.02.017] [Citation(s) in RCA: 1575] [Impact Index Per Article: 121.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Indexed: 02/07/2023]
Abstract
Insulin resistance is a complex metabolic disorder that defies explanation by a single etiological pathway. Accumulation of ectopic lipid metabolites, activation of the unfolded protein response (UPR) pathway, and innate immune pathways have all been implicated in the pathogenesis of insulin resistance. However, these pathways are also closely linked to changes in fatty acid uptake, lipogenesis, and energy expenditure that can impact ectopic lipid deposition. Ultimately, these cellular changes may converge to promote the accumulation of specific lipid metabolites (diacylglycerols and/or ceramides) in liver and skeletal muscle, a common final pathway leading to impaired insulin signaling and insulin resistance.
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Affiliation(s)
- Varman T Samuel
- Department of Medicine, Yale University School of Medicine, New Haven, CT 06510, USA.
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112
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D'souza AM, Beaudry JL, Szigiato AA, Trumble SJ, Snook LA, Bonen A, Giacca A, Riddell MC. Consumption of a high-fat diet rapidly exacerbates the development of fatty liver disease that occurs with chronically elevated glucocorticoids. Am J Physiol Gastrointest Liver Physiol 2012; 302:G850-63. [PMID: 22268100 DOI: 10.1152/ajpgi.00378.2011] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Chronically elevated glucocorticoids (GCs) and a high-fat diet (HFD) independently induce insulin resistance, abdominal obesity, and nonalcoholic fatty liver disease (NAFLD). GCs have been linked to increased food intake, particularly energy-dense "comfort" foods. Thus we examined the synergistic actions of GCs and HFD on hepatic disease development in a new rodent model of chronically elevated GCs. Six-week-old male Sprague-Dawley rats received exogenous GCs, via subcutaneous implantation of four 100-mg corticosterone (Cort) pellets, to elevate basal GC levels for 16 days (n = 8-10 per group). Another subset of animals received wax pellets (placebo) to serve as controls. Animals from each group were randomly assigned to receive a 60% HFD or a standard high-carbohydrate (13% fat and 60% carbohydrate) diet. Cort + HFD resulted in central obesity, despite a relative weight loss, a 4-fold increase in hepatic lipid content, hepatic fibrosis, and a 2.8-fold increase in plasma alanine aminotransferase levels compared with placebo + chow controls. Hepatic injury developed independent of inflammation, as plasma haptoglobin levels were reduced with Cort treatment. Insulin resistance and hepatic steatosis occurred with Cort alone; these outcomes were further exacerbated by the HFD in the presence of elevated Cort. In addition to fatty liver, the Cort + HFD group also developed severe insulin resistance, hyperinsulinemia, hyperglycemia, and hypertriglyceridemia, which were not evident with HFD or Cort alone. Thus a HFD dramatically exacerbates the development of NAFLD and characteristics of the metabolic syndrome in conditions of chronically elevated Cort.
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Affiliation(s)
- Anna M D'souza
- Muscle Health Research Center and Physical Activity and Chronic Disease Unit, School of Kinesiology and Health Science, Faculty of Health, York University, Toronto, Ontario, Canada
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113
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Ellis JM, Paul DS, Depetrillo MA, Singh BP, Malarkey DE, Coleman RA. Mice deficient in glycerol-3-phosphate acyltransferase-1 have a reduced susceptibility to liver cancer. Toxicol Pathol 2012; 40:513-21. [PMID: 22215515 PMCID: PMC3640291 DOI: 10.1177/0192623311432298] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The risk of hepatocellular carcinoma increases with the persistence of non-alcoholic fatty liver disease. Triacylglycerol synthesis is initiated by glycerol-3-phosphate acyltransferase (GPAT). Of four isoforms, GPAT1 contributes 30-50% of total liver GPAT activity, and we hypothesized that it might influence liver susceptibility to tumorigenesis. C57Bl/6 mice deficient in GPAT1 were backcrossed 6 times to C3H mice. After exposure to the carcinogen diethylnitrosamine (DEN) and the tumor promoter phenobarbital, male Gpat1⁻/⁻ mice, compared with controls (Gpat1⁺/⁺), had 93% fewer macroscopically visible nodules per liver at 21 weeks of age and 39% fewer at 34 weeks of age. Microscopically, control mice had increased numbers of foci of altered hepatocytes, particularly the basophilic subtype, as well as more, and malignant, liver neoplasms than did the Gpat1⁻/⁻ mice. At 21 weeks of age, 50% (4/8) of control mice (50%) had hepatocellular adenomas with an average multiplicity (tumors per tumor-bearing-animal) of 4.3, while none occurred in 8 Gpat1⁻/⁻ mice. At 34 weeks of age, all 15 control mice (100%) had hepatocellular adenomas with an average multiplicity of 5.2 compared to an incidence of 93% in Gpat1⁻/⁻ mice and multiplicity of 3.1. HCCs were observed in 13% of control mice and in only 6% of Gpat1⁻/⁻ mice. These data show that alterations in the formation of complex lipids catalyzed by Gpat1 reduce susceptibility to DEN-induced liver tumorigenesis.
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Affiliation(s)
- Jessica M. Ellis
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina, USA
- Department of Biological Chemistry, Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - David S. Paul
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina, USA
| | - Michael A. Depetrillo
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina, USA
| | - Bhanu P. Singh
- National Toxicology Program, National Institute of Environmental Health and Sciences, Cellular and Molecular Pathology Branch, Research Triangle Park, North Carolina, USA
- Dupont Haskell Global Centers for Health and Environmental Sciences, Newark, Delaware, USA
| | - David E. Malarkey
- National Toxicology Program, National Institute of Environmental Health and Sciences, Cellular and Molecular Pathology Branch, Research Triangle Park, North Carolina, USA
| | - Rosalind A. Coleman
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina, USA
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Monsénégo J, Mansouri A, Akkaoui M, Lenoir V, Esnous C, Fauveau V, Tavernier V, Girard J, Prip-Buus C. Enhancing liver mitochondrial fatty acid oxidation capacity in obese mice improves insulin sensitivity independently of hepatic steatosis. J Hepatol 2012; 56:632-9. [PMID: 22037024 DOI: 10.1016/j.jhep.2011.10.008] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Revised: 09/30/2011] [Accepted: 10/07/2011] [Indexed: 02/06/2023]
Abstract
BACKGROUND & AIMS Despite major public health concern, therapy for non-alcoholic fatty liver, the liver manifestation of the metabolic syndrome often associated with insulin resistance (IR), remains elusive. Strategies aiming to decrease liver lipogenesis effectively corrected hepatic steatosis and IR in obese animals. However, they also indirectly increased mitochondrial long-chain fatty acid oxidation (mFAO) by decreasing malonyl-CoA, a lipogenic intermediate, which is the allosteric inhibitor of carnitine palmitoyltransferase 1 (CPT1A), the key enzyme of mFAO. We thus addressed whether enhancing hepatic mFAO capacity, through a direct modulation of liver CPT1A/malonyl-CoA partnership, can reverse an already established hepatic steatosis and IR in obese mice. METHODS Adenovirus-mediated liver expression of a malonyl-CoA-insensitive CPT1A (CPT1mt) in high-fat/high-sucrose (HF/HS) diet-induced or genetically (ob/ob) obese mice was followed by metabolic and physiological investigations. RESULTS In association with increased hepatic mFAO capacity, liver CPT1mt expression improved glucose tolerance and insulin response to a glucose load in HF/HS and ob/ob mice, showing increased insulin sensitivity, and corrected IR in ob/ob mice. Surprisingly, hepatic steatosis was not affected in CPT1mt-expressing obese mice, indicating a clear dissociation between hepatic steatosis and IR. Moreover, liver CPT1mt expression rescued HF/HS-induced impaired hepatic insulin signaling at the level of IRS-1, IRS-2, Akt, and GSK-3β, most likely through the observed decrease in the HF/HS-induced accumulation of lipotoxic lipids, oxidative stress, and JNK activation. CONCLUSIONS Enhancing hepatic mFAO capacity is sufficient to reverse a state of IR and glucose intolerance in obese mice independently of hepatic steatosis.
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115
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Loss of regulator of G protein signaling 5 exacerbates obesity, hepatic steatosis, inflammation and insulin resistance. PLoS One 2012; 7:e30256. [PMID: 22272317 PMCID: PMC3260252 DOI: 10.1371/journal.pone.0030256] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Accepted: 12/12/2011] [Indexed: 01/22/2023] Open
Abstract
Background The effect of regulator of G protein signaling 5 (RGS5) on cardiac hypertrophy, atherosclerosis and angiogenesis has been well demonstrated, but the role in the development of obesity and insulin resistance remains completely unknown. We determined the effect of RGS5 deficiency on obesity, hepatic steatosis, inflammation and insulin resistance in mice fed either a normal-chow diet (NC) or a high-fat diet (HF). Methodology/Principal Findings Male, 8-week-old RGS5 knockout (KO) and littermate control mice were fed an NC or an HF for 24 weeks and were phenotyped accordingly. RGS5 KO mice exhibited increased obesity, fat mass and ectopic lipid deposition in the liver compared with littermate control mice, regardless of diet. When fed an HF, RGS5 KO mice had a markedly exacerbated metabolic dysfunction and inflammatory state in the blood serum. Meanwhile, macrophage recruitment and inflammation were increased and these increases were associated with the significant activation of JNK, IκBα and NF-κBp65 in the adipose tissue, liver and skeletal muscle of RGS5 KO mice fed an HF relative to control mice. These exacerbated metabolic dysfunction and inflammation are accompanied with decreased systemic insulin sensitivity in the adipose tissue, liver and skeletal muscle of RGS5 KO mice, reflected by weakened Akt/GSK3β phosphorylation. Conclusions/Significance Our data suggest that loss of RGS5 exacerbates HF-induced obesity, hepatic steatosis, inflammation and insulin resistance.
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Glycerolipid signals alter mTOR complex 2 (mTORC2) to diminish insulin signaling. Proc Natl Acad Sci U S A 2012; 109:1667-72. [PMID: 22307628 DOI: 10.1073/pnas.1110730109] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Increased flux through the glycerolipid synthesis pathway impairs the ability of insulin to inhibit hepatic gluconeogenesis, but the exact mechanism remains unknown. To determine the mechanism by which glycerolipids impair insulin signaling, we overexpressed glycerol-3-phosphate acyltransferase-1 (GPAT1) in primary mouse hepatocytes. GPAT1 overexpression impaired insulin-stimulated phosphorylation of Akt-S473 and -T308, diminished insulin-suppression of glucose production, significantly inhibited mTOR complex 2 (mTORC2) activity and decreased the association of mTOR and rictor. Conversely, in hepatocytes from Gpat1(-/-) mice, mTOR-rictor association and mTORC2 activity were enhanced. However, this increase in mTORC2 activity in Gpat1(-/-) hepatocytes was ablated when rictor was knocked down. To determine which lipid intermediate was responsible for inactivating mTORC2, we overexpressed GPAT1, AGPAT, or lipin to increase the cellular content of lysophosphatidic acid (LPA), phosphatidic acid (PA), or diacylglycerol (DAG), respectively. The inhibition of mTOR/rictor binding and mTORC2 activity coincided with the levels of PA and DAG species that contained 16:0, the preferred substrate of GPAT1. Furthermore, di-16:0-PA strongly inhibited mTORC2 activity and disassociated mTOR/rictor in vitro. Taken together, these data reveal a signaling pathway by which phosphatidic acid synthesized via the glycerol-3-phosphate pathway inhibits mTORC2 activity by decreasing the association of rictor and mTOR, thereby down-regulating insulin action. These data demonstrate a critical link between nutrient excess, TAG synthesis, and hepatic insulin resistance.
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Jurczak MJ, Lee AH, Jornayvaz FR, Lee HY, Birkenfeld AL, Guigni BA, Kahn M, Samuel VT, Glimcher LH, Shulman GI. Dissociation of inositol-requiring enzyme (IRE1α)-mediated c-Jun N-terminal kinase activation from hepatic insulin resistance in conditional X-box-binding protein-1 (XBP1) knock-out mice. J Biol Chem 2011; 287:2558-67. [PMID: 22128176 PMCID: PMC3268415 DOI: 10.1074/jbc.m111.316760] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Hepatic insulin resistance has been attributed to both increased endoplasmic reticulum (ER) stress and accumulation of intracellular lipids, specifically diacylglycerol (DAG). The ER stress response protein, X-box-binding protein-1 (XBP1), was recently shown to regulate hepatic lipogenesis, suggesting that hepatic insulin resistance in models of ER stress may result from defective lipid storage, as opposed to ER-specific stress signals. Studies were designed to dissociate liver lipid accumulation and activation of ER stress signaling pathways, which would allow us to delineate the individual contributions of ER stress and hepatic lipid content to the pathogenesis of hepatic insulin resistance. Conditional XBP1 knock-out (XBP1Δ) and control mice were fed fructose chow for 1 week. Determinants of whole-body energy balance, weight, and composition were determined. Hepatic lipids including triglyceride, DAGs, and ceramide were measured, alongside markers of ER stress. Whole-body and tissue-specific insulin sensitivity were determined by hyperinsulinemic-euglycemic clamp studies. Hepatic ER stress signaling was increased in fructose chow-fed XBP1Δ mice as reflected by increased phosphorylated eIF2α, HSPA5 mRNA, and a 2-fold increase in hepatic JNK activity. Despite JNK activation, XBP1Δ displayed increased hepatic insulin sensitivity during hyperinsulinemic-euglycemic clamp studies, which was associated with increased insulin-stimulated IRS2 tyrosine phosphorylation, reduced hepatic DAG content, and reduced PKCε activity. These studies demonstrate that ER stress and IRE1α-mediated JNK activation can be disassociated from hepatic insulin resistance and support the hypothesis that hepatic insulin resistance in models of ER stress may be secondary to ER stress modulation of hepatic lipogenesis.
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Affiliation(s)
- Michael J Jurczak
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06536-8012, USA
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Kamath S, Chavez AO, Gastaldelli A, Casiraghi F, Halff GA, Abrahamian GA, Davalli AM, Bastarrachea RA, Comuzzie AG, Guardado-Mendoza R, Jimenez-Ceja LM, Mattern V, Paez AM, Ricotti A, Tejero ME, Higgins PB, Rodriguez-Sanchez IP, Tripathy D, DeFronzo RA, Dick EJ, Cline GW, Folli F. Coordinated defects in hepatic long chain fatty acid metabolism and triglyceride accumulation contribute to insulin resistance in non-human primates. PLoS One 2011; 6:e27617. [PMID: 22125617 PMCID: PMC3220682 DOI: 10.1371/journal.pone.0027617] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Accepted: 10/20/2011] [Indexed: 01/07/2023] Open
Abstract
Non-Alcoholic fatty liver disease (NAFLD) is characterized by accumulation of triglycerides (TG) in hepatocytes, which may also trigger cirrhosis. The mechanisms of NAFLD are not fully understood, but insulin resistance has been proposed as a key determinant.
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Affiliation(s)
- Subhash Kamath
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Alberto O. Chavez
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Amalia Gastaldelli
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Institute of Clinical Physiology, National Research Council, Pisa, Italy
| | - Francesca Casiraghi
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Glenn A. Halff
- The UT Transplant Center, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Gregory A. Abrahamian
- The UT Transplant Center, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Alberto M. Davalli
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Department of Internal Medicine, Diabetes & Endocrinology Unit, San Raffaele Scientific Institute, Milano, Italy
| | - Raul A. Bastarrachea
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Anthony G. Comuzzie
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Rodolfo Guardado-Mendoza
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Lilia M. Jimenez-Ceja
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Vicki Mattern
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Ana Maria Paez
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Andrea Ricotti
- Institute of Clinical Physiology, National Research Council, Pisa, Italy
| | - Mary E. Tejero
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Paul B. Higgins
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Iram Pablo Rodriguez-Sanchez
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Devjit Tripathy
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Ralph A. DeFronzo
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Edward J. Dick
- Southwest National Primate Research Center/Texas Biomedical Research Institute, San Antonio, Texas, United States of America
| | - Gary W. Cline
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Franco Folli
- Department of Medicine/Division of Diabetes. The University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Department of Internal Medicine, Diabetes & Endocrinology Unit, San Raffaele Scientific Institute, Milano, Italy
- * E-mail:
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Affiliation(s)
- Rosalind A Coleman
- Department of Nutrition, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
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Cellular mechanism of insulin resistance in nonalcoholic fatty liver disease. Proc Natl Acad Sci U S A 2011; 108:16381-5. [PMID: 21930939 DOI: 10.1073/pnas.1113359108] [Citation(s) in RCA: 435] [Impact Index Per Article: 31.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Insulin resistance is associated with nonalcoholic fatty liver disease (NAFLD) and is a major factor in the pathogenesis of type 2 diabetes. The development of hepatic insulin resistance has been ascribed to multiple causes, including inflammation, endoplasmic reticulum (ER) stress, and accumulation of hepatocellular lipids in animal models of NAFLD. However, it is unknown whether these same cellular mechanisms link insulin resistance to hepatic steatosis in humans. To examine the cellular mechanisms that link hepatic steatosis to insulin resistance, we comprehensively assessed each of these pathways by using flash-frozen liver biopsies obtained from 37 obese, nondiabetic individuals and correlating key hepatic and plasma markers of inflammation, ER stress, and lipids with the homeostatic model assessment of insulin resistance index. We found that hepatic diacylglycerol (DAG) content in cytoplasmic lipid droplets was the best predictor of insulin resistance (R = 0.80, P < 0.001), and it was responsible for 64% of the variability in insulin sensitivity. Hepatic DAG content was also strongly correlated with activation of hepatic PKCε (R = 0.67, P < 0.001), which impairs insulin signaling. In contrast, there was no significant association between insulin resistance and other putative lipid metabolites or plasma or hepatic markers of inflammation. ER stress markers were only partly correlated with insulin resistance. In conclusion, these data show that hepatic DAG content in lipid droplets is the best predictor of insulin resistance in humans, and they support the hypothesis that NAFLD-associated hepatic insulin resistance is caused by an increase in hepatic DAG content, which results in activation of PKCε.
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The increased activity of liver lysosomal lipase in nonalcoholic Fatty liver disease contributes to the development of hepatic insulin resistance. Biochem Res Int 2011; 2012:135723. [PMID: 21904679 PMCID: PMC3163129 DOI: 10.1155/2012/135723] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 05/10/2011] [Accepted: 06/02/2011] [Indexed: 12/15/2022] Open
Abstract
We tested the hypothesis that TAG accumulation in the liver induced by short-term high-fat diet (HFD) in rats leads to the dysregulation of endogenous TAG degradation by lysosomal lipase (LIPA) via lysosomal pathway and is causally linked with the onset of hepatic insulin resistance. We found that LIPA could be translocated between qualitatively different depots (light and dense lysosomes). In contrast to dense lysosomal fraction, LIPA associated with light lysosomes exhibits high activity on both intracellular TAG and exogenous substrate and prandial- or diet-dependent regulation. On standard diet, LIPA activity was upregulated in fasted and downregulated in fed animals. In the HFD group, we demonstrated an increased TAG content, elevated LIPA activity, enhanced production of diacylglycerol, and the abolishment of prandial-dependent LIPA regulation in light lysosomal fraction. The impairment of insulin signalling and increased activation of PKCε was found in liver of HFD-fed animals. Lipolysis of intracellular TAG, mediated by LIPA, is increased in steatosis probably due to the enhanced formation of phagolysosomes. Consequent overproduction of diacylglycerol may represent the causal link between HFD-induced hepatic TAG accumulation and hepatic insulin resistance via PKCε activation.
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Birkenfeld AL, Lee HY, Guebre-Egziabher F, Alves TC, Jurczak MJ, Jornayvaz FR, Zhang D, Hsiao JJ, Martin-Montalvo A, Fischer-Rosinsky A, Spranger J, Pfeiffer AF, Jordan J, Fromm MF, König J, Lieske S, Carmean CM, Frederick DW, Weismann D, Knauf F, Irusta PM, De Cabo R, Helfand SL, Samuel VT, Shulman GI. Deletion of the mammalian INDY homolog mimics aspects of dietary restriction and protects against adiposity and insulin resistance in mice. Cell Metab 2011; 14:184-95. [PMID: 21803289 PMCID: PMC3163140 DOI: 10.1016/j.cmet.2011.06.009] [Citation(s) in RCA: 173] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2010] [Revised: 12/24/2010] [Accepted: 06/07/2011] [Indexed: 01/07/2023]
Abstract
Reduced expression of the Indy (I'm Not Dead, Yet) gene in D. melanogaster and its homolog in C. elegans prolongs life span and in D. melanogaster augments mitochondrial biogenesis in a manner akin to caloric restriction. However, the cellular mechanism by which Indy does this is unknown. Here, we report on the knockout mouse model of the mammalian Indy (mIndy) homolog, SLC13A5. Deletion of mIndy in mice (mINDY(-/-) mice) reduces hepatocellular ATP/ADP ratio, activates hepatic AMPK, induces PGC-1α, inhibits ACC-2, and reduces SREBP-1c levels. This signaling network promotes hepatic mitochondrial biogenesis, lipid oxidation, and energy expenditure and attenuates hepatic de novo lipogenesis. Together, these traits protect mINDY(-/-) mice from the adiposity and insulin resistance that evolve with high-fat feeding and aging. Our studies demonstrate a profound effect of mIndy on mammalian energy metabolism and suggest that mINDY might be a therapeutic target for the treatment of obesity and type 2 diabetes.
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Affiliation(s)
- Andreas L Birkenfeld
- Howard Hughes Medical Institute, Yale School of Medicine, New Haven, CT 06520, USA
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Kiefer FW, Neschen S, Pfau B, Legerer B, Neuhofer A, Kahle M, Hrabé de Angelis M, Schlederer M, Mair M, Kenner L, Plutzky J, Zeyda M, Stulnig TM. Osteopontin deficiency protects against obesity-induced hepatic steatosis and attenuates glucose production in mice. Diabetologia 2011; 54:2132-42. [PMID: 21562757 PMCID: PMC3131508 DOI: 10.1007/s00125-011-2170-0] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2010] [Accepted: 04/04/2011] [Indexed: 02/07/2023]
Abstract
AIMS/HYPOTHESIS Obesity is strongly associated with the development of non-alcoholic fatty liver disease (NAFLD). The cytokine osteopontin (OPN) was recently shown to be involved in obesity-induced adipose tissue inflammation and reduced insulin response. Accumulating evidence links OPN to the pathogenesis of NAFLD. Here we aimed to identify the role of OPN in obesity-associated hepatic steatosis and impaired hepatic glucose metabolism. METHODS Wild-type (WT) and Opn (also known as Spp1) knockout (Opn (-/-)) mice were fed a high-fat or low-fat diet to study OPN effects in obesity-driven hepatic alterations. RESULTS We show that genetic OPN deficiency protected from obesity-induced hepatic steatosis, at least in part, by downregulating hepatic triacylglycerol synthesis. Conversely, absence of OPN promoted fat storage in adipose tissue thereby preventing the obesity-induced shift to ectopic fat accumulation in the liver. Euglycaemic-hyperinsulinaemic clamp studies revealed that insulin resistance and excess hepatic glucose production in obesity were significantly attenuated in Opn (-/-) mice. OPN deficiency markedly improved hepatic insulin signalling as shown by enhanced insulin receptor substrate-2 phosphorylation and prevented upregulation of the major hepatic transcription factor Forkhead box O1 and its gluconeogenic target genes. In addition, obesity-driven hepatic inflammation and macrophage accumulation was blocked by OPN deficiency. CONCLUSIONS/INTERPRETATION Our data strongly emphasise OPN as mediator of obesity-associated hepatic alterations including steatosis, inflammation, insulin resistance and excess gluconeogenesis. Targeting OPN action could therefore provide a novel therapeutic strategy to prevent obesity-related complications such as NAFLD and type 2 diabetes.
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Affiliation(s)
- F. W. Kiefer
- Department of Medicine III, Clinical Division of Endocrinology and Metabolism, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria
| | - S. Neschen
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - B. Pfau
- Department of Medicine III, Clinical Division of Endocrinology and Metabolism, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria
| | - B. Legerer
- Department of Medicine III, Clinical Division of Endocrinology and Metabolism, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria
| | - A. Neuhofer
- Department of Medicine III, Clinical Division of Endocrinology and Metabolism, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria
| | - M. Kahle
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - M. Hrabé de Angelis
- Institute of Experimental Genetics, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Neuherberg, Germany
| | - M. Schlederer
- Ludwig Boltzmann Institute for Cancer Research, Vienna, Austria
| | - M. Mair
- Ludwig Boltzmann Institute for Cancer Research, Vienna, Austria
| | - L. Kenner
- Ludwig Boltzmann Institute for Cancer Research, Vienna, Austria
| | - J. Plutzky
- Department of Medicine, Brigham and Women’s Hospital Boston, Cardiovascular Division, Harvard Medical School, Boston, MA USA
| | - M. Zeyda
- Department of Medicine III, Clinical Division of Endocrinology and Metabolism, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria
| | - T. M. Stulnig
- Department of Medicine III, Clinical Division of Endocrinology and Metabolism, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria
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Liver X Receptor: an oxysterol sensor and a major player in the control of lipogenesis. Chem Phys Lipids 2011; 164:500-14. [PMID: 21693109 DOI: 10.1016/j.chemphyslip.2011.06.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Revised: 06/04/2011] [Accepted: 06/06/2011] [Indexed: 01/12/2023]
Abstract
De novo fatty acid biosynthesis is also called lipogenesis. It is a metabolic pathway that provides the cells with fatty acids required for major cellular processes such as energy storage, membrane structures and lipid signaling. In this article we will review the role of the Liver X Receptors (LXRs), nuclear receptors that sense oxysterols, in the transcriptional regulation of genes involved in lipogenesis.
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Kuhajda FP, Aja S, Tu Y, Han WF, Medghalchi SM, El Meskini R, Landree LE, Peterson JM, Daniels K, Wong K, Wydysh EA, Townsend CA, Ronnett GV. Pharmacological glycerol-3-phosphate acyltransferase inhibition decreases food intake and adiposity and increases insulin sensitivity in diet-induced obesity. Am J Physiol Regul Integr Comp Physiol 2011; 301:R116-30. [PMID: 21490364 DOI: 10.1152/ajpregu.00147.2011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Storage of excess calories as triglycerides is central to obesity and its associated disorders. Glycerol-3-phosphate acyltransferases (GPATs) catalyze the initial step in acylglyceride syntheses, including triglyceride synthesis. We utilized a novel small-molecule GPAT inhibitor, FSG67, to investigate metabolic consequences of systemic pharmacological GPAT inhibition in lean and diet-induced obese (DIO) mice. FSG67 administered intraperitoneally decreased body weight and energy intake, without producing conditioned taste aversion. Daily FSG67 (5 mg/kg, 15.3 μmol/kg) produced gradual 12% weight loss in DIO mice beyond that due to transient 9- to 10-day hypophagia (6% weight loss in pair-fed controls). Continued FSG67 maintained the weight loss despite return to baseline energy intake. Weight was lost specifically from fat mass. Indirect calorimetry showed partial protection by FSG67 against decreased rates of oxygen consumption seen with hypophagia. Despite low respiratory exchange ratio due to a high-fat diet, FSG67-treated mice showed further decreased respiratory exchange ratio, beyond pair-fed controls, indicating enhanced fat oxidation. Chronic FSG67 increased glucose tolerance and insulin sensitivity in DIO mice. Chronic FSG67 decreased gene expression for lipogenic enzymes in white adipose tissue and liver and decreased lipid accumulation in white adipose, brown adipose, and liver tissues without signs of damage. RT-PCR showed decreased gene expression for orexigenic hypothalamic neuropeptides AgRP or NPY after acute and chronic systemic FSG67. FSG67 given intracerebroventricularly (100 and 320 nmol icv) produced 24-h weight loss and feeding suppression, indicating contributions from direct central nervous system sites of action. Together, these data point to GPAT as a new potential therapeutic target for the management of obesity and its comorbidities.
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Affiliation(s)
- Francis P Kuhajda
- Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, 855 N. Wolfe St., Baltimore, MD 21205, USA
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Leavens KF, Birnbaum MJ. Insulin signaling to hepatic lipid metabolism in health and disease. Crit Rev Biochem Mol Biol 2011; 46:200-15. [PMID: 21599535 DOI: 10.3109/10409238.2011.562481] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The increasing prevalence of overnutrition and reduced activity has led to a worldwide epidemic of obesity. In many cases, this is associated with insulin resistance, an inability of the hormone to direct its physiological actions appropriately. A number of disease states accompany insulin resistance such as type 2 diabetes mellitus, the metabolic syndrome, and non-alcoholic fatty liver disease. Though the pathways by which insulin controls hepatic glucose output have been of intense study in recent years, considerably less attention has been devoted to how lipid metabolism is regulated. Thus, both the proximal signaling pathways as well as the more distal targets of insulin remain uncertain. In this review, we consider the signaling pathways by which insulin controls the synthesis and accumulation of lipids in the mammalian liver and, in particular, how this might lead to abnormal triglyceride deposition in liver during insulin-resistant states.
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Affiliation(s)
- Karla F Leavens
- Department of Medicine, Institute for Diabetes, Obesity and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
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Alves TC, Befroy DE, Kibbey RG, Kahn M, Codella R, Carvalho RA, Petersen KF, Shulman GI. Regulation of hepatic fat and glucose oxidation in rats with lipid-induced hepatic insulin resistance. Hepatology 2011; 53:1175-81. [PMID: 21400553 PMCID: PMC3077048 DOI: 10.1002/hep.24170] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Accepted: 12/22/2010] [Indexed: 12/24/2022]
Abstract
UNLABELLED Pyruvate dehydrogenase plays a critical role in the regulation of hepatic glucose and fatty acid oxidation; however, surprisingly little is known about its regulation in vivo. In this study we examined the individual effects of insulin and substrate availability on the regulation of pyruvate dehydrogenase flux (V(PDH) ) to tricarboxylic acid flux (V(TCA) ) in livers of awake rats with lipid-induced hepatic insulin resistance. V(PDH) /V(TCA) flux was estimated from the [4-(13) C]glutamate/[3-(13) C]alanine enrichments in liver extracts and assessed under conditions of fasting and during a hyperinsulinemic-euglycemic clamp, whereas the effects of increased plasma glucose concentration on V(PDH) /V(TCA) flux was assessed during a hyperglycemic clamp in conjunction with infusions of somatostatin and insulin to maintain basal concentrations of insulin. The effects of increases in both glucose and insulin on V(PDH) /V(TCA) were examined during a hyperinsulinemic-hyperglycemic clamp. The effects of chronic lipid-induced hepatic insulin resistance on this flux were also examined by performing these measurements in rats fed a high-fat diet for 3 weeks. Using this approach we found that fasting V(PDH) /V(TCA) was reduced by 95% in rats with hepatic insulin resistance (from 17.2 ± 1.5% to 1.3 ± 0.7%, P < 0.00001). Surprisingly, neither hyperinsulinemia per se or hyperglycemia per se were sufficient to increase V(PDH) /V(TCA) flux. Only under conditions of combined hyperglycemia and hyperinsulinemia did V(PDH) /V(TCA) flux increase (44.6 ± 3.2%, P < 0.0001 versus basal) in low-fat fed animals but not in rats with chronic lipid-induced hepatic insulin resistance. CONCLUSION These studies demonstrate that the combination of both hyperinsulinemia and hyperglycemia are required to increase V(PDH) /V(TCA) flux in vivo and that this flux is severely diminished in rats with chronic lipid-induced hepatic insulin resistance.
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Affiliation(s)
- Tiago C. Alves
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Biochemistry, Faculty of Sciences and Technology, University of Coimbra, Portugal
| | - Douglas E. Befroy
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Richard G. Kibbey
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Mario Kahn
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Roberto Codella
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Rui A. Carvalho
- Department of Biochemistry, Faculty of Sciences and Technology, University of Coimbra, Portugal
| | - Kitt Falk Petersen
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gerald I. Shulman
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
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Perfield JW, Lee Y, Shulman GI, Samuel VT, Jurczak MJ, Chang E, Xie C, Tsichlis PN, Obin MS, Greenberg AS. Tumor progression locus 2 (TPL2) regulates obesity-associated inflammation and insulin resistance. Diabetes 2011; 60:1168-76. [PMID: 21346175 PMCID: PMC3064090 DOI: 10.2337/db10-0715] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
OBJECTIVE Obesity-associated low-grade systemic inflammation resulting from increased adipose mass is strongly related to the development of insulin resistance and type 2 diabetes as well as other metabolic complications. Recent studies have demonstrated that the obese metabolic state can be improved by ablating certain inflammatory signaling pathways. Tumor progression locus 2 (TPL2), a kinase that integrates signals from Toll receptors, cytokine receptors, and inhibitor of κ-B kinase-β is an important regulator of inflammatory pathways. We used TPL2 knockout (KO) mice to investigate the role of TPL2 in mediating obesity-associated inflammation and insulin resistance. RESEARCH DESIGN AND METHODS Male TPL2KO and wild-type (WT) littermates were fed a low-fat diet or a high-fat diet to investigate the effect of TPL2 deletion on obesity, inflammation, and insulin sensitivity. RESULTS We demonstrate that TPL2 deletion does not alter body weight gain or adipose depot weight. However, hyperinsulinemic euglycemic clamp studies revealed improved insulin sensitivity with enhanced glucose uptake in skeletal muscle and increased suppression of hepatic glucose output in obese TPL2KO mice compared with obese WT mice. Consistent with an improved metabolic phenotype, immune cell infiltration and inflammation was attenuated in the adipose tissue of obese TPL2KO mice coincident with reduced hepatic inflammatory gene expression and lipid accumulation. CONCLUSIONS Our results provide the first in vivo demonstration that TPL2 ablation attenuates obesity-associated metabolic dysfunction. These data suggest TPL2 is a novel target for improving the metabolic state associated with obesity.
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Affiliation(s)
- James W. Perfield
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Yunkyoung Lee
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Gerald I. Shulman
- Howard Hughes Medical Institute, Departments of Internal Medicine and Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Varman T. Samuel
- Howard Hughes Medical Institute, Departments of Internal Medicine and Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
- West Haven VAMC, West Haven, Connecticut
| | - Michael J. Jurczak
- Howard Hughes Medical Institute, Departments of Internal Medicine and Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Eugene Chang
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Chen Xie
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Phillip N. Tsichlis
- Molecular Oncology Research Institute, Tufts University School of Medicine, Boston, Massachusetts
| | - Martin S. Obin
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
- Corresponding author: Andrew S. Greenberg, , or Martin S. Obin,
| | - Andrew S. Greenberg
- Obesity and Metabolism Laboratory, JM-USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
- Corresponding author: Andrew S. Greenberg, , or Martin S. Obin,
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Li GY, Li CP, Zhong XL, Kang M. Role of PI-3K, DGAT2 and PKC-ε in pathogenesis of non-alcoholic fatty liver disease in rats. Shijie Huaren Xiaohua Zazhi 2011; 19:782-788. [DOI: 10.11569/wcjd.v19.i8.782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To investigate the role of phosphatidylinositol 3-kinase (PI-3K), acyl-CoA: diacylgycerol acyltransferase 2 (DGAT2) and protein kinase C-ε (PKC-ε) in the pathogenesis of non-alcoholic fatty liver disease (NAFLD) in rats.
METHODS: Forty-eight Sprague-Dawley rats were randomly divided into normal control group and high-fat diet group. Rats of the high-fat diet group were fed a high-fat diet for 4, 8 or 12 weeks, while the normal control group was fed a normal diet. Liver slices were prepared to grade the degree of fatty change, inflammation and fibrosis. The expression of PKC-ε protein was determined by immunohistochemistry (IHC), while the mRNA levels of PI-3K (p85) and DGAT2 were measured by reverse transcription-polymerase chain reaction (RT-PCR).
RESULTS: Feeding a high-fat diet caused the development of NAFLD in rats. The degree of fatty change and inflammation was significantly more severe in the high-fat die group than in the normal control group. The degree of inflammation, fibrosis and ballooning degeneration was significantly more severe in rats fed a high-fat diet for 8 and 12 wk than for 4 wk. The expression of PKC-ε in rats feeding a high-fat diet for 8 and 12 wk was significantly higher than that in the normal control group (7.68 ± 1.32 vs 6.68 ± 2.16, 8.46 ± 1.19 vs 5.52 ± 1.05, P < 0.05 or 0.01). The expression of PI-3K (p85a) was significantly lower in the high-fat diet group than in the normal control group and in rats fed a high-fat diet for 8 and 12 wk than for 4 wk. In contrast, the expression of DGAT2 was significantly higher in the high-fat diet group than in the normal control group and in rats fed a high-fat diet for 8 and 12 wk than for 4 wk.
CONCLUSION: PI-3K and its associated proteins DGAT2 and PKC-ε may be critically involved in the pathogenesis of NAFLD.
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Guo H, Li D, Ling W, Feng X, Xia M. Anthocyanin inhibits high glucose-induced hepatic mtGPAT1 activation and prevents fatty acid synthesis through PKCζ. J Lipid Res 2011; 52:908-22. [PMID: 21343633 DOI: 10.1194/jlr.m013375] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Mitochondrial acyl-CoA:glycerol-sn-3-phosphate acyltransferase 1 (mtGPAT1) controls the first step of triacylglycerol (TAG) synthesis and is critical to the understanding of chronic metabolic disorders such as primary nonalcoholic fatty liver disease (NAFLD). Anthocyanin, a large group of polyphenols, was negatively correlated with hepatic lipid accumulation, but its impact on mtGPAT1 activity and NAFLD has yet to be determined. Hepatoma cell lines and KKAy mice were used to investigate the impact of anthocyanin on high glucose-induced mtGPAT1 activation and hepatic steatosis. Treatment with anthocyanin cyanidin-3-O-β-glucoside (Cy-3-g) reduced high glucose-induced GPAT1 activity through the prevention of mtGPAT1 translocation from the endoplasmic reticulum to the outer mitochondrial membrane (OMM), thereby suppressing intracellular de novo lipid synthesis. Cy-3-g treatment also increased protein kinase C ζ phosphorylation and membrane translocation in order to phosphorylate the mtF0F1-ATPase β-subunit, reducing its enzymatic activity and thus inhibiting mtGPAT1 activation. In vivo studies further showed that Cy-3-g treatment significantly decreases hepatic mtGPAT1 activity and its presence in OMM isolated from livers, thus ameliorating hepatic steatosis in diabetic KKAy mice. Our findings reveal a novel mechanism by which anthocyanin regulates lipogenesis and thereby inhibits hepatic steatosis, suggesting its potential therapeutic application in diabetes and related steatotic liver diseases.
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Affiliation(s)
- Honghui Guo
- Guangdong Provincial Key Laboratory of Food, Nutrition and Health, Department of Nutrition, School of Public Health, Sun Yat-Sen University (Northern Campus), Guangzhou, Guangdong Province, PR China
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131
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Samuel VT. Fructose induced lipogenesis: from sugar to fat to insulin resistance. Trends Endocrinol Metab 2011; 22:60-5. [PMID: 21067942 DOI: 10.1016/j.tem.2010.10.003] [Citation(s) in RCA: 185] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Revised: 10/13/2010] [Accepted: 10/13/2010] [Indexed: 12/23/2022]
Abstract
Increasing consumption of sugars is one of the contributing factors to the obesity epidemic. Both cane sugar and high-fructose corn syrup contain glucose and fructose. Fructose, in contrast to glucose, is known to potently stimulate lipogenesis, but the mechanisms responsible are not yet fully known. This paper reviews several possible pathways that might be involved, such as activation of pyruvate dehydrogenase, and transcriptional activation of sterol regulatory element binding protein 1c by key regulators such as peroxisome proliferator activated receptor-γ co-activator 1β and the splice variant of X-box binding protein 1. Together, these pathways might establish a feed forward cycle that can rapidly increase hepatic lipogenesis. As a result, dietary fructose might promote the development of nonalcoholic fatty liver disease, which in and of itself, can result in hepatic insulin resistance, a key feature of type 2 diabetes mellitus.
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Affiliation(s)
- Varman T Samuel
- Departments of Internal Medicine, Yale University School of Medicine, New Haven, CT 06536-8012, USA.
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132
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Mouse cardiac acyl coenzyme a synthetase 1 deficiency impairs Fatty Acid oxidation and induces cardiac hypertrophy. Mol Cell Biol 2011; 31:1252-62. [PMID: 21245374 DOI: 10.1128/mcb.01085-10] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Long-chain acyl coenzyme A (acyl-CoA) synthetase isoform 1 (ACSL1) catalyzes the synthesis of acyl-CoA from long-chain fatty acids and contributes the majority of cardiac long-chain acyl-CoA synthetase activity. To understand its functional role in the heart, we studied mice lacking ACSL1 globally (Acsl1(T-/-)) and mice lacking ACSL1 in heart ventricles (Acsl1(H-/-)) at different times. Compared to littermate controls, heart ventricular ACSL activity in Acsl1(T-/-) mice was reduced more than 90%, acyl-CoA content was 65% lower, and long-chain acyl-carnitine content was 80 to 90% lower. The rate of [(14)C]palmitate oxidation in both heart homogenate and mitochondria was 90% lower than in the controls, and the maximal rates of [(14)C]pyruvate and [(14)C]glucose oxidation were each 20% higher. The mitochondrial area was 54% greater than in the controls with twice as much mitochondrial DNA, and the mRNA abundance of Pgc1α and Errα increased by 100% and 41%, respectively. Compared to the controls, Acsl1(T-/-) and Acsl1(H-/-) hearts were hypertrophied, and the phosphorylation of S6 kinase, a target of mammalian target of rapamycin (mTOR) kinase, increased 5-fold. Our data suggest that ACSL1 is required to synthesize the acyl-CoAs that are oxidized by the heart, and that without ACSL1, diminished fatty acid (FA) oxidation and compensatory catabolism of glucose and amino acids lead to mTOR activation and cardiac hypertrophy without lipid accumulation or immediate cardiac dysfunction.
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133
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Turpin SM, Hoy AJ, Brown RD, Rudaz CG, Honeyman J, Matzaris M, Watt MJ. Adipose triacylglycerol lipase is a major regulator of hepatic lipid metabolism but not insulin sensitivity in mice. Diabetologia 2011; 54:146-56. [PMID: 20842343 DOI: 10.1007/s00125-010-1895-5] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Accepted: 08/04/2010] [Indexed: 01/04/2023]
Abstract
AIMS/HYPOTHESIS Hepatic steatosis is characterised by excessive triacylglycerol accumulation and is strongly associated with insulin resistance. An inability to efficiently mobilise liver triacylglycerol may be a key event mediating hepatic steatosis. Adipose triacylglycerol lipase (ATGL) is a key triacylglycerol lipase in the liver and we hypothesised that liver-specific overproduction of ATGL would reduce steatosis and enhance insulin action in obese rodents. METHODS Studies of fatty acid metabolism were conducted in primary hepatocytes isolated from wild-type and Atgl (also known as Pnpla2)⁻(/)⁻ mice. An ATGL adenovirus was utilised to overproduce ATGL in the livers of obese insulin-resistant C57Bl/6 mice (Ad-ATGL). Blood chemistry, hepatic lipid content and insulin sensitivity were assessed in mice. RESULTS Triacylglycerol content was increased in Atgl⁻(/)⁻ hepatocytes and was associated with increased fatty acid uptake and impaired fatty acid oxidation. ATGL adenovirus administration in obese mice increased the production of hepatic ATGL protein and reduced triacylglycerol, diacylglycerol and ceramide content in the liver. Overproduction of ATGL improved insulin signal transduction in the liver but did not affect fasting glycaemia or insulinaemia. Inflammatory signalling was not suppressed by ATGL overproduction. While ATGL overproduction increased plasma non-esterified fatty acids, neither lipid deposition nor insulin-stimulated glucose uptake were affected in skeletal muscle. CONCLUSIONS/INTERPRETATION Liver ATGL overproduction decreases hepatic steatosis and mildly enhances liver insulin sensitivity. These effects are not sufficient to improve fasting glycaemia or insulinaemia in rodent obesity.
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Affiliation(s)
- S M Turpin
- Department of Physiology, Monash University, Clayton, Victoria, Australia
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Bharadwaj KG, Hiyama Y, Hu Y, Huggins LA, Ramakrishnan R, Abumrad NA, Shulman GI, Blaner WS, Goldberg IJ. Chylomicron- and VLDL-derived lipids enter the heart through different pathways: in vivo evidence for receptor- and non-receptor-mediated fatty acid uptake. J Biol Chem 2010; 285:37976-86. [PMID: 20852327 PMCID: PMC2992231 DOI: 10.1074/jbc.m110.174458] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2010] [Revised: 09/15/2010] [Indexed: 12/17/2022] Open
Abstract
Lipids circulate in the blood in association with plasma lipoproteins and enter the tissues either after hydrolysis or as non-hydrolyzable lipid esters. We studied cardiac lipids, lipoprotein lipid uptake, and gene expression in heart-specific lipoprotein lipase (LpL) knock-out (hLpL0), CD36 knock-out (Cd36(-/-)), and double knock-out (hLpL0/Cd36(-/-)-DKO) mice. Loss of either LpL or CD36 led to a significant reduction in heart total fatty acyl-CoA (control, 99.5 ± 3.8; hLpL0, 36.2 ± 3.5; Cd36(-/-), 57.7 ± 5.5 nmol/g, p < 0.05) and an additive effect was observed in the DKO (20.2 ± 1.4 nmol/g, p < 0.05). Myocardial VLDL-triglyceride (TG) uptake was reduced in the hLpL0 (31 ± 6%) and Cd36(-/-) (47 ± 4%) mice with an additive reduction in the DKO (64 ± 5%) compared with control. However, LpL but not CD36 deficiency decreased VLDL-cholesteryl ester uptake. Endogenously labeled mouse chylomicrons were produced by tamoxifen treatment of β-actin-MerCreMer/LpL(flox/flox) mice. Induced loss of LpL increased TG levels >10-fold and reduced HDL by >50%. After injection of these labeled chylomicrons in the different mice, chylomicron TG uptake was reduced by ∼70% and retinyl ester by ∼50% in hLpL0 hearts. Loss of CD36 did not alter either chylomicron TG or retinyl ester uptake. LpL loss did not affect uptake of remnant lipoproteins from ApoE knock-out mice. Our data are consistent with two pathways for fatty acid uptake; a CD36 process for VLDL-derived fatty acid and a non-CD36 process for chylomicron-derived fatty acid uptake. In addition, our data show that lipolysis is involved in uptake of core lipids from TG-rich lipoproteins.
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Affiliation(s)
- Kalyani G. Bharadwaj
- From the Divisions of Preventive Medicine and Nutrition, and Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, and
| | - Yaeko Hiyama
- From the Divisions of Preventive Medicine and Nutrition, and Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, and
| | - Yunying Hu
- From the Divisions of Preventive Medicine and Nutrition, and Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, and
| | - Lesley Ann Huggins
- From the Divisions of Preventive Medicine and Nutrition, and Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, and
| | | | - Nada A. Abumrad
- the Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, and
| | - Gerald I. Shulman
- the Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06510
| | - William S. Blaner
- From the Divisions of Preventive Medicine and Nutrition, and Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, and
| | - Ira J. Goldberg
- From the Divisions of Preventive Medicine and Nutrition, and Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, and
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Lee HY, Choi CS, Birkenfeld AL, Alves TC, Jornayvaz FR, Jurczak MJ, Zhang D, Woo DK, Shadel GS, Ladiges W, Rabinovitch PS, Santos JH, Petersen KF, Samuel VT, Shulman GI. Targeted expression of catalase to mitochondria prevents age-associated reductions in mitochondrial function and insulin resistance. Cell Metab 2010; 12:668-74. [PMID: 21109199 PMCID: PMC3013349 DOI: 10.1016/j.cmet.2010.11.004] [Citation(s) in RCA: 259] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Revised: 07/31/2010] [Accepted: 10/01/2010] [Indexed: 01/07/2023]
Abstract
Aging-associated muscle insulin resistance has been hypothesized to be due to decreased mitochondrial function, secondary to cumulative free radical damage, leading to increased intramyocellular lipid content. To directly test this hypothesis, we examined both in vivo and in vitro mitochondrial function, intramyocellular lipid content, and insulin action in lean healthy mice with targeted overexpression of the human catalase gene to mitochondria (MCAT mice). Here, we show that MCAT mice are protected from age-induced decrease in muscle mitochondrial function (∼30%), energy metabolism (∼7%), and lipid-induced muscle insulin resistance. This protection from age-induced reduction in mitochondrial function was associated with reduced mitochondrial oxidative damage, preserved mitochondrial respiration and muscle ATP synthesis, and AMP-activated protein kinase-induced mitochondrial biogenesis. Taken together, these data suggest that the preserved mitochondrial function maintained by reducing mitochondrial oxidative damage may prevent age-associated whole-body energy imbalance and muscle insulin resistance.
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Affiliation(s)
- Hui-Young Lee
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Cheol Soo Choi
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
- Lee Gil Ya Cancer and Diabetes Institute Gachon University of Medicine and Science, Incheon, Korea
| | - Andreas L. Birkenfeld
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Tiago C. Alves
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Francois R. Jornayvaz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Michael J. Jurczak
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Dongyan Zhang
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Dong Kyun Woo
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA
| | - Gerald S. Shadel
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA
| | - Warren Ladiges
- Department of Comparative Medicine, University of Washington, Seattle, WA, USA
| | | | - Janine H. Santos
- Department of Pharmacology & Physiology UMDNJ - New Jersey Medical School, Newark, NJ, USA
| | - Kitt F. Petersen
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Varman T. Samuel
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Gerald I. Shulman
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
- Department of Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA
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Sachithanandan N, Fam BC, Fynch S, Dzamko N, Watt MJ, Wormald S, Honeyman J, Galic S, Proietto J, Andrikopoulos S, Hevener AL, Kay TWH, Steinberg GR. Liver-specific suppressor of cytokine signaling-3 deletion in mice enhances hepatic insulin sensitivity and lipogenesis resulting in fatty liver and obesity. Hepatology 2010; 52:1632-42. [PMID: 20799351 DOI: 10.1002/hep.23861] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
UNLABELLED Obesity is associated with chronic inflammation and contributes to the development of insulin resistance and nonalcoholic fatty liver disease. The suppressor of cytokine signaling-3 (SOCS3) protein is increased in inflammation and is thought to contribute to the pathogenesis of insulin resistance by inhibiting insulin and leptin signaling. Therefore, we studied the metabolic effects of liver-specific SOCS3 deletion in vivo. We fed wild-type (WT) and liver-specific SOCS3 knockout (SOCS3 LKO) mice either a control diet or a high-fat diet (HFD) for 6 weeks and examined their metabolic phenotype. We isolated hepatocytes from WT and SOCS3 LKO mice and examined the effects of tumor necrosis factor α and insulin on Akt phosphorylation and fatty acid metabolism and lipogenic gene expression. Hepatocytes from control-fed SOCS3 LKO mice were protected from developing tumor necrosis factor α-induced insulin resistance but also had increased lipogenesis and expression of sterol response element-binding protein-1c target genes. Lean SOCS3 LKO mice fed a control diet had enhanced hepatic insulin sensitivity; however, when fed an HFD, SOCS3 LKO mice had increased liver fat, inflammation, and whole-body insulin resistance. SOCS3 LKO mice fed an HFD also had elevated hypothalamic SOCS3 and fatty acid synthase expression and developed greater obesity due to increased food intake and reduced energy expenditure. CONCLUSION Deletion of SOCS3 in the liver increases liver insulin sensitivity in mice fed a control diet but paradoxically promotes lipogenesis, leading to the development of nonalcoholic fatty liver disease, inflammation, and obesity.
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Affiliation(s)
- Nirupa Sachithanandan
- St. Vincent's Institute of Medical Research and Department of Medicine, University of Melbourne, Fitzroy, Victoria, Australia
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Jornayvaz FR, Jurczak MJ, Lee HY, Birkenfeld AL, Frederick DW, Zhang D, Zhang XM, Samuel VT, Shulman GI. A high-fat, ketogenic diet causes hepatic insulin resistance in mice, despite increasing energy expenditure and preventing weight gain. Am J Physiol Endocrinol Metab 2010; 299:E808-15. [PMID: 20807839 PMCID: PMC2980360 DOI: 10.1152/ajpendo.00361.2010] [Citation(s) in RCA: 168] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Low-carbohydrate, high-fat ketogenic diets (KD) have been suggested to be more effective in promoting weight loss than conventional caloric restriction, whereas their effect on hepatic glucose and lipid metabolism and the mechanisms by which they may promote weight loss remain controversial. The aim of this study was to explore the role of KD on liver and muscle insulin sensitivity, hepatic lipid metabolism, energy expenditure, and food intake. Using hyperinsulinemic-euglycemic clamps, we studied insulin action in mice fed a KD or regular chow (RC). Body composition was assessed by ¹H magnetic resonance spectroscopy. Despite being 15% lighter (P < 0.001) than RC-fed mice because of a 17% increase in energy expenditure (P < 0.001), KD-fed mice manifested severe hepatic insulin resistance, as reflected by decreased suppression (0% vs. 100% in RC-fed mice, P < 0.01) of endogenous glucose production during the clamp. Hepatic insulin resistance could be attributed to a 350% increase in hepatic diacylglycerol content (P < 0.001), resulting in increased activation of PKCε (P < 0.05) and decreased insulin receptor substrate-2 tyrosine phosphorylation (P < 0.01). Food intake was 56% (P < 0.001) lower in KD-fed mice, despite similar caloric intake, and could partly be attributed to a more than threefold increase (P < 0.05) in plasma N-acylphosphatidylethanolamine concentrations. In conclusion, despite preventing weight gain in mice, KD induces hepatic insulin resistance secondary to increased hepatic diacylglycerol content. Given the key role of nonalcoholic fatty liver disease in the development of type 2 diabetes and the widespread use of KD for the treatment of obesity, these results may have potentially important clinical implications.
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Affiliation(s)
- François R Jornayvaz
- Depts. of Internal Medicine, Yale Univ. School of Medicine, New Haven, CT 06536, USA
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138
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Jornayvaz FR, Samuel VT, Shulman GI. The role of muscle insulin resistance in the pathogenesis of atherogenic dyslipidemia and nonalcoholic fatty liver disease associated with the metabolic syndrome. Annu Rev Nutr 2010; 30:273-90. [PMID: 20645852 DOI: 10.1146/annurev.nutr.012809.104726] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The metabolic syndrome is a clustering of cardiovascular risk factors, including insulin resistance, abdominal obesity, dyslipidemia, and hypertension, and is associated with other comorbidities such as a proinflammatory state and nonalcoholic fatty liver disease (NAFLD). Its prevalence is high, especially among developed countries, and mainly reflects overnutrition and sedentary lifestyle. Moreover, the developing countries are not spared, as obesity and its related problems such as the metabolic syndrome are increasing quickly. We review the potential primary role of skeletal muscle insulin resistance in the pathophysiology of the metabolic syndrome, showing that in lean, young, insulin-resistant individuals, impaired muscle glucose transport and glycogen synthesis redirect energy derived from carbohydrate into hepatic de novo lipogenesis, promoting the development of atherogenic dyslipidemia and NAFLD. The demonstration of a link between skeletal muscle insulin resistance and the metabolic syndrome offers opportunities in targeting early defects in muscle insulin action in order to counteract the development of the disease and its related complications.
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Affiliation(s)
- François R Jornayvaz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06536, USA
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139
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Santoro N, Kursawe R, D’Adamo E, Dykas DJ, Zhang CK, Bale AE, Calí AM, Narayan D, Shaw MM, Pierpont B, Savoye M, Lartaud D, Eldrich S, Cushman SW, Zhao H, Shulman GI, Caprio S. A common variant in the patatin-like phospholipase 3 gene (PNPLA3) is associated with fatty liver disease in obese children and adolescents. Hepatology 2010; 52:1281-90. [PMID: 20803499 PMCID: PMC3221304 DOI: 10.1002/hep.23832] [Citation(s) in RCA: 179] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
UNLABELLED The genetic factors associated with susceptibility to nonalcoholic fatty liver disease (NAFLD) in pediatric obesity remain largely unknown. Recently, a nonsynonymous single-nucleotide polymorphism (rs738409), in the patatin-like phospholipase 3 gene (PNPLA3) has been associated with hepatic steatosis in adults. In a multiethnic group of 85 obese youths, we genotyped the PNLPA3 single-nucleotide polymorphism, measured hepatic fat content by magnetic resonance imaging and insulin sensitivity by the insulin clamp. Because PNPLA3 might affect adipogenesis/lipogenesis, we explored the putative association with the distribution of adipose cell size and the expression of some adipogenic/lipogenic genes in a subset of subjects who underwent a subcutaneous fat biopsy. Steatosis was present in 41% of Caucasians, 23% of African Americans, and 66% of Hispanics. The frequency of PNPLA3(rs738409) G allele was 0.324 in Caucasians, 0.183 in African Americans, and 0.483 in Hispanics. The prevalence of the G allele was higher in subjects showing hepatic steatosis. Surprisingly, subjects carrying the G allele showed comparable hepatic glucose production rates, peripheral glucose disposal rate, and glycerol turnover as the CC homozygotes. Carriers of the G allele showed smaller adipocytes than those with CC genotype (P = 0.005). Although the expression of PNPLA3, PNPLA2, PPARγ2(peroxisome proliferator-activated receptor gamma 2), SREBP1c(sterol regulatory element binding protein 1c), and ACACA(acetyl coenzyme A carboxylase) was not different between genotypes, carriers of the G allele showed lower leptin (LEP)(P = 0.03) and sirtuin 1 (SIRT1) expression (P = 0.04). CONCLUSION A common variant of the PNPLA3 gene confers susceptibility to hepatic steatosis in obese youths without increasing the level of hepatic and peripheral insulin resistance. The rs738409 PNPLA3 G allele is associated with morphological changes in adipocyte cell size.
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Affiliation(s)
- Nicola Santoro
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Romy Kursawe
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Ebe D’Adamo
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
- Department of Pediatrics, University of Chieti, Chieti, Italy
| | - Daniel J. Dykas
- Department of Genetics, Yale University School of Medicine, New Haven, CT
| | | | - Allen E. Bale
- Department of Genetics, Yale University School of Medicine, New Haven, CT
| | - Anna M. Calí
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Deepak Narayan
- Department of Plastic Surgery, Yale University School of Medicine, New Haven, CT
| | - Melissa M. Shaw
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Bridget Pierpont
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Mary Savoye
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Derek Lartaud
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | - Samuel Eldrich
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
| | | | - Hongyu Zhao
- Yale Center for Statistical Genomics and Proteomics, New Haven, CT
| | - Gerald I. Shulman
- Departments of Internal Medicine and Cellular and Molecular Physiology, Howard Hughes Medical Institute, New Haven, CT
| | - Sonia Caprio
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT
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140
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Choi CS, Ghoshal P, Srinivasan M, Kim S, Cline G, Patel MS. Liver-Specific Pyruvate Dehydrogenase Complex Deficiency Upregulates Lipogenesis in Adipose Tissue and Improves Peripheral Insulin Sensitivity. Lipids 2010; 45:987-95. [DOI: 10.1007/s11745-010-3470-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Accepted: 08/25/2010] [Indexed: 10/19/2022]
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141
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Brown JM, Betters JL, Lord C, Ma Y, Han X, Yang K, Alger HM, Melchior J, Sawyer J, Shah R, Wilson MD, Liu X, Graham MJ, Lee R, Crooke R, Shulman GI, Xue B, Shi H, Yu L. CGI-58 knockdown in mice causes hepatic steatosis but prevents diet-induced obesity and glucose intolerance. J Lipid Res 2010; 51:3306-15. [PMID: 20802159 DOI: 10.1194/jlr.m010256] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Mutations of Comparative Gene Identification-58 (CGI-58) in humans cause triglyceride (TG) accumulation in multiple tissues. Mice genetically lacking CGI-58 die shortly after birth due to a skin barrier defect. To study the role of CGI-58 in integrated lipid and energy metabolism, we utilized antisense oligonucleotides (ASOs) to inhibit CGI-58 expression in adult mice. Treatment with two distinct CGI-58-targeting ASOs resulted in ∼80-95% knockdown of CGI-58 protein expression in both liver and white adipose tissue. In chow-fed mice, ASO-mediated depletion of CGI-58 did not alter weight gain, plasma TG, or plasma glucose, yet raised hepatic TG levels ∼4-fold. When challenged with a high-fat diet (HFD), CGI-58 ASO-treated mice were protected against diet-induced obesity, but their hepatic contents of TG, diacylglycerols, and ceramides were all elevated, and intriguingly, their hepatic phosphatidylglycerol content was increased by 10-fold. These hepatic lipid alterations were associated with significant decreases in hepatic TG hydrolase activity, hepatic lipoprotein-TG secretion, and plasma concentrations of ketones, nonesterified fatty acids, and insulin. Additionally, HFD-fed CGI-58 ASO-treated mice were more glucose tolerant and insulin sensitive. Collectively, this work demonstrates that CGI-58 plays a critical role in limiting hepatic steatosis and maintaining hepatic glycerophospholipid homeostasis and has unmasked an unexpected role for CGI-58 in promoting HFD-induced obesity and insulin resistance.
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Affiliation(s)
- J Mark Brown
- Departments of Pathology Section on Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
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142
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Zhang L, Ussher JR, Oka T, Cadete VJJ, Wagg C, Lopaschuk GD. Cardiac diacylglycerol accumulation in high fat-fed mice is associated with impaired insulin-stimulated glucose oxidation. Cardiovasc Res 2010; 89:148-56. [PMID: 20729341 DOI: 10.1093/cvr/cvq266] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
AIMS the molecular processes leading to cardiac insulin resistance induced via a high-fat diet (HFD) remain unclear. We examined the changes in cardiac insulin sensitivity and the potential mechanism(s) involved following HFD in mice. METHODS AND RESULTS C57BL/6 mice were fed either a low-fat diet (LFD, 4% kcal fat) or a HFD (60% kcal fat) for 3 or 10 weeks. Insulin-stimulated glucose oxidation in isolated working hearts was decreased at 10 weeks of HFD compared with mice on LFD (249 ± 19 to 399 ± 46 vs. 551 ± 97 to 1464 ± 243 nmol/g dry wt/min; P < 0.05). The accumulation of myocardial diacylglycerol (DAG; 479 ± 174 vs. 266 ± 29 micromol/g wet wt; P < 0.05), but not long-chain acyl CoA, ceramide, or triacylglycerol, correlated with the development of insulin resistance. The accumulation of DAG occurred concomitantly with an increase in glycerol phosphate acyltransferase activity, a decrease in DAG acyltransferase activity, as well as an increase in the translocation of protein kinase C-α (PKCα) and phosphorylation of p70s6k. Neither HFD-induced accumulation of cardiac DAG nor up-regulation of phosphorylated p70s6k occurred in mice lacking malonyl CoA decarboxylase which are resistant to the development of HFD-induced insulin resistance. CONCLUSION the activation of myocardial p70s6k and PKCα is closely associated with cardiac insulin resistance in which the accumulation of intra-myocardial DAG could be responsible.
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Affiliation(s)
- Liyan Zhang
- Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, 423 Heritage Medical Research Center, Edmonton, AB, Canada T6G 2S2
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143
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Fuchs H, Gailus-Durner V, Adler T, Aguilar-Pimentel JA, Becker L, Calzada-Wack J, Da Silva-Buttkus P, Neff F, Götz A, Hans W, Hölter SM, Horsch M, Kastenmüller G, Kemter E, Lengger C, Maier H, Matloka M, Möller G, Naton B, Prehn C, Puk O, Rácz I, Rathkolb B, Römisch-Margl W, Rozman J, Wang-Sattler R, Schrewe A, Stöger C, Tost M, Adamski J, Aigner B, Beckers J, Behrendt H, Busch DH, Esposito I, Graw J, Illig T, Ivandic B, Klingenspor M, Klopstock T, Kremmer E, Mempel M, Neschen S, Ollert M, Schulz H, Suhre K, Wolf E, Wurst W, Zimmer A, Hrabě de Angelis M. Mouse phenotyping. Methods 2010; 53:120-35. [PMID: 20708688 DOI: 10.1016/j.ymeth.2010.08.006] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 08/06/2010] [Accepted: 08/06/2010] [Indexed: 12/13/2022] Open
Abstract
Model organisms like the mouse are important tools to learn more about gene function in man. Within the last 20 years many mutant mouse lines have been generated by different methods such as ENU mutagenesis, constitutive and conditional knock-out approaches, knock-down, introduction of human genes, and knock-in techniques, thus creating models which mimic human conditions. Due to pleiotropic effects, one gene may have different functions in different organ systems or time points during development. Therefore mutant mouse lines have to be phenotyped comprehensively in a highly standardized manner to enable the detection of phenotypes which might otherwise remain hidden. The German Mouse Clinic (GMC) has been established at the Helmholtz Zentrum München as a phenotyping platform with open access to the scientific community (www.mousclinic.de; [1]). The GMC is a member of the EUMODIC consortium which created the European standard workflow EMPReSSslim for the systemic phenotyping of mouse models (http://www.eumodic.org/[2]).
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Affiliation(s)
- Helmut Fuchs
- Institute of Experimental Genetics, Helmholtz Zentrum München, German Research Center for Environmental Health, Ingolstädter Landstraße 1, 85764 München/Neuherberg, Germany
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144
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Rong X, Li Y, Ebihara K, Zhao M, Naowaboot J, Kusakabe T, Kuwahara K, Murray M, Nakao K. Angiotensin II type 1 receptor-independent beneficial effects of telmisartan on dietary-induced obesity, insulin resistance and fatty liver in mice. Diabetologia 2010; 53:1727-31. [PMID: 20390403 DOI: 10.1007/s00125-010-1744-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
AIMS/HYPOTHESIS Evidence suggests that telmisartan, an angiotensin II type 1 receptor (AT1) blocker and peroxisome proliferator-activated receptor-gamma partial agonist, has beneficial actions that limit development of the metabolic syndrome and diabetes. However, the role played by AT1 inhibition in metabolic effects elicited by telmisartan remains uncertain. Here we isolated the metabolic effects of telmisartan from AT1 antagonism. METHODS Male At1a (also known as Agtr1a)-deficient mice were fed a standard diet or 60% high-fat diet; those on high-fat diet were co-administered telmisartan (3 mg kg(-1) day(-1) by oral gavage) or vehicle for 12 weeks. RESULTS In At1a-null mice, telmisartan prevented high-fat-diet-induced increases in (1) body weight, epididymal and inguinal white adipose tissue weight, adipocyte size and plasma leptin concentration; (2) plasma glucose and insulin concentrations and HOMA index; and (3) liver weight and triacylglycerol content. Insulin tolerance testing also indicated that telmisartan improved the high-fat-diet-induced reduction of glucose-lowering by insulin. CONCLUSIONS/INTERPRETATION The present findings demonstrate beneficial, AT1-independent effects of the AT1 blocker telmisartan on dietary-induced obesity, insulin resistance and fatty liver in animals.
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MESH Headings
- Adipocytes/pathology
- Adipose Tissue, White/pathology
- Angiotensin II Type 1 Receptor Blockers
- Animals
- Benzimidazoles/administration & dosage
- Benzoates/administration & dosage
- Blood Glucose/analysis
- Cell Size
- Diet, High-Fat
- Fatty Liver/drug therapy
- Fatty Liver/pathology
- Insulin/blood
- Insulin Resistance
- Leptin/blood
- Lipids/analysis
- Liver/chemistry
- Liver/pathology
- Male
- Metabolic Syndrome/prevention & control
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Muscle, Skeletal/chemistry
- Obesity, Abdominal/drug therapy
- Obesity, Abdominal/etiology
- Organ Size
- PPAR gamma/agonists
- Receptor, Angiotensin, Type 1/deficiency
- Receptor, Angiotensin, Type 1/physiology
- Telmisartan
- Triglycerides/analysis
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Affiliation(s)
- X Rong
- Department of Medicine and Clinical Science, Kyoto University Graduate School of Medicine, Kyoto, 606-8507, Japan
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145
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Kars M, Yang L, Gregor MF, Mohammed BS, Pietka TA, Finck BN, Patterson BW, Horton JD, Mittendorfer B, Hotamisligil GS, Klein S. Tauroursodeoxycholic Acid may improve liver and muscle but not adipose tissue insulin sensitivity in obese men and women. Diabetes 2010; 59:1899-905. [PMID: 20522594 PMCID: PMC2911053 DOI: 10.2337/db10-0308] [Citation(s) in RCA: 317] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
OBJECTIVE Insulin resistance is commonly associated with obesity. Studies conducted in obese mouse models found that endoplasmic reticulum (ER) stress contributes to insulin resistance, and treatment with tauroursodeoxycholic acid (TUDCA), a bile acid derivative that acts as a chemical chaperone to enhance protein folding and ameliorate ER stress, increases insulin sensitivity. The purpose of this study was to determine the effect of TUDCA therapy on multiorgan insulin action and metabolic factors associated with insulin resistance in obese men and women. RESEARCH DESIGN AND METHODS Twenty obese subjects ([means +/- SD] aged 48 +/- 11 years, BMI 37 +/- 4 kg/m2) were randomized to 4 weeks of treatment with TUDCA (1,750 mg/day) or placebo. A two-stage hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled tracer infusions and muscle and adipose tissue biopsies were used to evaluate in vivo insulin sensitivity, cellular factors involved in insulin signaling, and cellular markers of ER stress. RESULTS Hepatic and muscle insulin sensitivity increased by approximately 30% (P < 0.05) after treatment with TUDCA but did not change after placebo therapy. In addition, therapy with TUDCA, but not placebo, increased muscle insulin signaling (phosphorylated insulin receptor substrate(Tyr) and Akt(Ser473) levels) (P < 0.05). Markers of ER stress in muscle or adipose tissue did not change after treatment with either TUDCA or placebo. CONCLUSIONS These data demonstrate that TUDCA might be an effective pharmacological approach for treating insulin resistance. Additional studies are needed to evaluate the target cells and mechanisms responsible for this effect.
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Affiliation(s)
- Marleen Kars
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Ling Yang
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts
| | - Margaret F. Gregor
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts
| | - B. Selma Mohammed
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Terri A. Pietka
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Brian N. Finck
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Bruce W. Patterson
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Jay D. Horton
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Bettina Mittendorfer
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Gökhan S. Hotamisligil
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts
| | - Samuel Klein
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, Missouri
- Corresponding author: Samuel Klein,
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146
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Lee JY, Cho HK, Kwon YH. Palmitate induces insulin resistance without significant intracellular triglyceride accumulation in HepG2 cells. Metabolism 2010; 59:927-34. [PMID: 20006364 DOI: 10.1016/j.metabol.2009.10.012] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 10/15/2009] [Accepted: 10/15/2009] [Indexed: 12/20/2022]
Abstract
Previous studies showed that increased release of free fatty acids from adipocytes leads to insulin resistance and triglyceride (TG) accumulation in the liver, which may progress into hepatic steatohepatitis. We and other investigators have previously reported that palmitate induces endoplasmic reticulum stress-mediated toxicity in several tissues. This work investigated whether palmitate could induce insulin resistance and steatosis in HepG2 cells. We treated cells with either saturated fatty acid (palmitate) or unsaturated fatty acid (oleate), and observed that palmitate significantly activated c-jun N-terminal kinase and inactivated protein kinase B. Both 4-phenylbutyric acid and glycerol significantly activated protein kinase B, confirming the involvement of endoplasmic reticulum stress in palmitate-mediated insulin resistance. Oleate, but not palmitate, significantly induced intracellular TG deposition and activated sterol regulatory element binding protein-1. Instead, diacylglycerol level and protein kinase C epsilon activity were significantly increased by palmitate, suggesting the possible role of diacylglycerol in palmitate-mediated lipotoxicity. Therefore, the present study clearly showed that palmitate impairs insulin resistance, but does not induce significant TG accumulation in HepG2 cells.
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Affiliation(s)
- Jin-young Lee
- Department of Food and Nutrition, Seoul National University, Seoul, Korea
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147
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Phillips CM, Goumidi L, Bertrais S, Field MR, Cupples LA, Ordovas JM, Defoort C, Lovegrove JA, Drevon CA, Gibney MJ, Blaak EE, Kiec-Wilk B, Karlstrom B, Lopez-Miranda J, McManus R, Hercberg S, Lairon D, Planells R, Roche HM. Gene-nutrient interactions with dietary fat modulate the association between genetic variation of the ACSL1 gene and metabolic syndrome. J Lipid Res 2010; 51:1793-800. [PMID: 20176858 PMCID: PMC2882737 DOI: 10.1194/jlr.m003046] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Revised: 02/17/2010] [Indexed: 12/14/2022] Open
Abstract
Long-chain acyl CoA synthetase 1 (ACSL1) plays an important role in fatty acid metabolism and triacylglycerol (TAG) synthesis. Disturbance of these pathways may result in dyslipidemia and insulin resistance, hallmarks of the metabolic syndrome (MetS). Dietary fat is a key environmental factor that may interact with genetic determinants of lipid metabolism to affect MetS risk. We investigated the relationship between ACSL1 polymorphisms (rs4862417, rs6552828, rs13120078, rs9997745, and rs12503643) and MetS risk and determined potential interactions with dietary fat in the LIPGENE-SU.VI.MAX study of MetS cases and matched controls (n = 1,754). GG homozygotes for rs9997745 had increased MetS risk {odds ratio (OR) 1.90 [confidence interval (CI) 1.15, 3.13]; P = 0.01}, displayed elevated fasting glucose (P = 0.001) and insulin concentrations (P = 0.002) and increased insulin resistance (P = 0.03) relative to the A allele carriers. MetS risk was modulated by dietary fat, whereby the risk conferred by GG homozygosity was abolished among individuals consuming either a low-fat (<35% energy) or a high-PUFA diet (>5.5% energy). In conclusion, ACSL1 rs9997745 influences MetS risk, most likely via disturbances in fatty acid metabolism, which was modulated by dietary fat consumption, particularly PUFA intake, suggesting novel gene-nutrient interactions.
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Affiliation(s)
- Catherine M. Phillips
- Nutrigenomics Research Group, UCD School of Public Health and Population Science, UCD Conway Institute, and Institute of Food and Health, University College Dublin, Ireland
| | - Louisa Goumidi
- INSERM 476, Lipid nutrients and prevention of metabolic diseases, INRA, 1260, Université de la Méditerranée, Faculté de Médecine, 27 Bd Jean Moulin, Marseille, France
| | | | | | | | - Jose M. Ordovas
- Nutrition and Genomics Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA
| | - Catherine Defoort
- INSERM 476, Lipid nutrients and prevention of metabolic diseases, INRA, 1260, Université de la Méditerranée, Faculté de Médecine, 27 Bd Jean Moulin, Marseille, France
| | - Julie A. Lovegrove
- Hugh Sinclair Unit of Human Nutrition, Department of Food Biosciences, Institute for Cardiovascular and Metabolic Research, University of Reading, Reading, UK
| | - Christian A. Drevon
- Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Norway
| | | | - Ellen E. Blaak
- Department of Human Biology, Nutrition and Toxicology Research Institute Maastricht, Maastricht, The Netherlands
| | - Beata Kiec-Wilk
- Department of Clinical Biochemistry, Jagiellonian University Medical College, Kopernika 15A, Krakow, Poland
| | - Britta Karlstrom
- Department of Public Health and Caring Sciences/Clinical Nutrition and Metabolism, Uppsala University, Uppsala Science Park, 751 85 Uppsala, Sweden
| | - Jose Lopez-Miranda
- Lipid and Atherosclerosis Unit, Department of Medicine, Reina Sofia University Hospital, School of Medicine, University of Cordoba, Spain
| | - Ross McManus
- Institute of Molecular Medicine, Trinity College Dublin, Ireland
| | - Serge Hercberg
- INSERM U557, INRA:CNAM, Université Paris 13, Bobigny, France
| | - Denis Lairon
- INSERM 476, Lipid nutrients and prevention of metabolic diseases, INRA, 1260, Université de la Méditerranée, Faculté de Médecine, 27 Bd Jean Moulin, Marseille, France
| | - Richard Planells
- INSERM 476, Lipid nutrients and prevention of metabolic diseases, INRA, 1260, Université de la Méditerranée, Faculté de Médecine, 27 Bd Jean Moulin, Marseille, France
| | - Helen M. Roche
- Nutrigenomics Research Group, UCD School of Public Health and Population Science, UCD Conway Institute, and Institute of Food and Health, University College Dublin, Ireland
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148
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Abstract
De novo lipogenesis (DNL) is a complex yet highly regulated metabolic pathway, and transcription factors such as liver X receptor (LXR), sterol regulatory element-binding protein-1c (SREBP-1c), and carbohydrate response element binding protein (ChREBP) exert significant control over the de novo synthesis of fatty acids. An increase in de novo lipogenesis (DNL) is an important contributor to increased fat mass, while a reduction in lipogenesis may be protective against the development of obesity. In this review, we explore fatty acid synthesis in the context of new insights gleaned from global and tissue-specific gene knockout mouse models of enzymes involved in fatty acid synthesis, namely acetyl-CoA carboxylase, fatty acid synthase, fatty acid elongase 6, and stearoyl-CoA desaturase 1. A disruption in fatty acid synthesis, induced by the deficiency of any one of these enzymes, affects lipid metabolism and in some cases may protect against obesity in a tissue and gene-specific manner, as discussed in detail in this review.
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Affiliation(s)
- Maggie S. Strable
- Department of Nutritional Sciences, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA
| | - James M. Ntambi
- Department of Nutritional Sciences, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA
- Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA
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149
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Wendel AA, Li LO, Li Y, Cline GW, Shulman GI, Coleman RA. Glycerol-3-phosphate acyltransferase 1 deficiency in ob/ob mice diminishes hepatic steatosis but does not protect against insulin resistance or obesity. Diabetes 2010; 59:1321-9. [PMID: 20200319 PMCID: PMC2874692 DOI: 10.2337/db09-1380] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2009] [Accepted: 02/22/2010] [Indexed: 12/14/2022]
Abstract
OBJECTIVE Hepatic steatosis is strongly associated with insulin resistance, but a causal role has not been established. In ob/ob mice, sterol regulatory element binding protein 1 (SREBP1) mediates the induction of steatosis by upregulating target genes, including glycerol-3-phosphate acyltransferase-1 (Gpat1), which catalyzes the first and committed step in the pathway of glycerolipid synthesis. We asked whether ob/ob mice lacking Gpat1 would have reduced hepatic steatosis and improved insulin sensitivity. RESEARCH DESIGN AND METHODS Hepatic lipids, insulin sensitivity, and hepatic insulin signaling were compared in lean (Lep(+/?)), lean-Gpat1(-/-), ob/ob (Lep(ob/ob)), and ob/ob-Gpat1(-/-) mice. RESULTS Compared with ob/ob mice, the lack of Gpat1 in ob/ob mice reduced hepatic triacylglycerol (TAG) and diacylglycerol (DAG) content 59 and 74%, respectively, but increased acyl-CoA levels. Despite the reduction in hepatic lipids, fasting glucose and insulin concentrations did not improve, and insulin tolerance remained impaired. In both ob/ob and ob/ob-Gpat1(-/-) mice, insulin resistance was accompanied by elevated hepatic protein kinase C-epsilon activation and blunted insulin-stimulated Akt activation. CONCLUSIONS These results suggest that decreasing hepatic steatosis alone does not improve insulin resistance, and that factors other than increased hepatic DAG and TAG contribute to hepatic insulin resistance in this genetically obese model. They also show that the SREBP1-mediated induction of hepatic steatosis in ob/ob mice requires Gpat1.
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Affiliation(s)
- Angela A. Wendel
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina
| | - Lei O. Li
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina
| | - Yue Li
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina
| | - Gary W. Cline
- Departments of Internal Medicine and Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut; and
| | - Gerald I. Shulman
- Departments of Internal Medicine and Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut; and
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut
| | - Rosalind A. Coleman
- Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina
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150
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Zhang D, Christianson J, Liu ZX, Tian L, Choi CS, Neschen S, Dong J, Wood PA, Shulman GI. Resistance to high-fat diet-induced obesity and insulin resistance in mice with very long-chain acyl-CoA dehydrogenase deficiency. Cell Metab 2010; 11:402-11. [PMID: 20444420 PMCID: PMC3146169 DOI: 10.1016/j.cmet.2010.03.012] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2009] [Revised: 10/18/2009] [Accepted: 03/24/2010] [Indexed: 01/06/2023]
Abstract
Mitochondrial fatty acid oxidation provides an important energy source for cellular metabolism, and decreased mitochondrial fatty acid oxidation has been implicated in the pathogenesis of type 2 diabetes. Paradoxically, mice with an inherited deficiency of the mitochondrial fatty acid oxidation enzyme, very long-chain acyl-CoA dehydrogenase (VLCAD), were protected from high-fat diet-induced obesity and liver and muscle insulin resistance. This was associated with reduced intracellular diacylglycerol content and decreased activity of liver protein kinase Cvarepsilon and muscle protein kinase Ctheta. The increased insulin sensitivity in the VLCAD(-/-) mice were protected from diet-induced obesity and insulin resistance due to chronic activation of AMPK and PPARalpha, resulting in increased fatty acid oxidation and decreased intramyocellular and hepatocellular diacylglycerol content.
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Affiliation(s)
- Dongyan Zhang
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT
| | | | - Zhen-Xiang Liu
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT
| | - Liqun Tian
- Department of Genetics, University of Alabama at Birmingham, Birmingham, AL
| | - Cheol Soo Choi
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT
| | - Susanne Neschen
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT
| | - Jianying Dong
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT
| | - Philip A. Wood
- Department of Genetics, University of Alabama at Birmingham, Birmingham, AL
- Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Orlando, FL
| | - Gerald I. Shulman
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT
- Department of Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, CT
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