51
|
Abstract
Although most people with type 2 diabetes are obese, most obese people never develop diabetes. They are able to compensate for the insulin resistance that usually accompanies obesity by producing more insulin. We have replicated this obesity/diabetes dichotomy in mice by studying mouse strains that differ in diabetes susceptibility when made obese with the Leptin ( ob ) mutation; the C57BL/6 (B6) mice are resistant whereas the BTBR mice are susceptible. We have used this model system to search for genes that are causal for diabetes susceptibility. To find genes whose sequence variation leads to this phenotype, we have carried out positional cloning projects. To find genes that are responsive to genetic variation with respect to gene expression and are on pathways leading to diabetes, we have studied gene expression relative to gene variation; i.e., expression quantitative trait loci. We have used these data to generate network models, which incorporate gene loci, mRNA abundance, and other phenotypes. One of these networks is involved in the regulation of β-cell proliferation.
Collapse
Affiliation(s)
- Alan D Attie
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
| | | |
Collapse
|
52
|
Abstract
Several epidemiological studies have related an increase of lipids in the postprandial state to an individual risk for the development of CVD, possibly due to the increased plasma levels of TAG and fatty acids (FA) through enzymes of FA metabolism. The interaction between nutrition and the human genome determines gene expression and metabolic response. The aim of the present study was to evaluate the influence of a fat overload on the gene mRNA levels of lipogenic regulators in peripheral blood mononuclear cells (PBMC) from patients with the metabolic syndrome. The study included twenty-one patients with criteria for the metabolic syndrome who underwent a fat overload. Measurements were made before and after the fat overload of anthropometric and biochemical variables and also the gene mRNA levels of lipogenic factors. The main results were that the fat overload led to an increased mRNA levels of sterol regulatory element binding protein-1 (SREBP1), retinoid X receptor α (RXRα) and liver X receptor α (LXRα) in PBMC, and this increase was associated with the FA synthase (FASN) mRNA levels. We also found that TAG levels correlated with FASN mRNA levels. In addition, there was a positive correlation of SREBP1 with RXRα and of LXRα with the plasma lipoperoxide concentration. The fat overload led to an increase in regulators of lipogenesis in PBMC from patients with the metabolic syndrome.
Collapse
|
53
|
Dong XY, Tang SQ. Insulin-induced gene: a new regulator in lipid metabolism. Peptides 2010; 31:2145-50. [PMID: 20817058 DOI: 10.1016/j.peptides.2010.07.020] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Revised: 07/15/2010] [Accepted: 07/15/2010] [Indexed: 10/19/2022]
Abstract
Insulin-induced genes (Insigs) including Insig-1 and Insig-2, are proteins that mediate sterol regulation of sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase). Insigs perform distinct tasks in the regulation of these effectors: they promote the endoplasmic reticulum (ER) retention of SCAP, but ubiquitin-mediated degradation of HMG-CoA reductase. Through these activities, Insig-1 and Insig-2 influence cholesterol metabolism, lipogenesis, and glucose homeostasis in diverse tissues such as adipose tissue and liver. In this article, we focus on the functions, expression and regulation, gene polymorphisms of Insigs, and their deficiency with diseases.
Collapse
Affiliation(s)
- Xiao-Ying Dong
- College of Yingdong Agricultural Science and Engineering, Shaoguan University, Daxue Avenue, Zhenjiang District, Shaoguan 512005, PR China
| | | |
Collapse
|
54
|
Keller MP, Attie AD. Physiological insights gained from gene expression analysis in obesity and diabetes. Annu Rev Nutr 2010; 30:341-64. [PMID: 20415584 DOI: 10.1146/annurev.nutr.012809.104747] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Microarray technology permits the interrogation of nearly all expressed genes under a wide range of conditions. Patterns of gene expression in response to obesity and diabetes have yielded important insights into the pathogenesis of diabetes and its relationship to obesity. In muscle, microarray studies have motivated research into mitochondrial function. In adipose tissue, clues have pointed to the importance of inflammation in obesity. New adipocyte-derived hormones involved in insulin resistance have been found; a notable example is retinol binding protein 4. In liver, genes responsive to master regulators of lipid metabolism have been identified. In beta-cells, genes involved in cell survival, cell proliferation, and insulin secretion have been identified. These studies have greatly expanded our understanding of mechanisms underlying the pathogenesis of obesity-induced diabetes. When combined with genetic information, microarray data can be used to construct causal network models linking gene expression with disease.
Collapse
Affiliation(s)
- Mark P Keller
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706-1544, USA
| | | |
Collapse
|
55
|
Yamabe N, Kim HY, Kang KS, Zhao Q, Matsumoto K, Yokozawa T. Effect of Chinese prescription Kangen-karyu on lipid metabolism in type 2 diabetic db/db mice. JOURNAL OF ETHNOPHARMACOLOGY 2010; 129:299-305. [PMID: 20363309 DOI: 10.1016/j.jep.2010.03.032] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Revised: 03/04/2010] [Accepted: 03/19/2010] [Indexed: 05/29/2023]
Abstract
AIM OF THE STUDY Chinese prescription Kangen-karyu is clinically used as a treatment for cardiovascular diseases, and we have reported the beneficial effects on chemically induced hyperlipidemic animal models. The present study was investigated to evaluate the hypolipidemic effect of Kangen-karyu in type 2 diabetic db/db mice which has not been explored yet. MATERIALS AND METHODS Male db/db mice were divided into three groups, vehicle (control), Kangen-karyu 100, or 200 mg/kg body weight/day, and orally administered for 5 weeks every day. Age-matched non-diabetic m/m mice were used as a normal group. RESULTS Serum triglyceride (TG) and total cholesterol levels in db/db mice were increased compared with those of m/m mice. However, the administration of Kangen-karyu reduced hyperlipidemia in db/db mice through a decline in the serum levels of TG and total cholesterol. The hepatic TG and total cholesterol levels of db/db mice were markedly higher than those of m/m mice, but these elevated lipid levels were significantly reduced by 200 mg/kg Kangen-karyu administration. Also, oil red O staining showed that the increased lipid deposition level in the liver of db/db control mice was improved by Kangen-karyu administration. The expression of sterol regulatory element-binding protein-1 in the liver of db/db mice was significantly down-regulated by the administration of Kangen-karyu at a dose of 200 mg/kg body weight. Kangen-karyu caused a slight elevation in the expression of peroxisome proliferator-activated receptor alpha in the liver of db/db mice. CONCLUSIONS This study provides scientific evidence that Kangen-karyu improves hyperlipidemia and lipid deposition via the regulation of hepatic SREBP-1 expression in type 2 diabetic db/db mice.
Collapse
MESH Headings
- Animals
- Blood Glucose/analysis
- Blotting, Western
- Cholesterol/blood
- Chromatography, High Pressure Liquid
- Diabetes Mellitus, Experimental/drug therapy
- Diabetes Mellitus, Experimental/metabolism
- Diabetes Mellitus, Type 2/drug therapy
- Diabetes Mellitus, Type 2/metabolism
- Drugs, Chinese Herbal/administration & dosage
- Drugs, Chinese Herbal/pharmacology
- Drugs, Chinese Herbal/therapeutic use
- Hypoglycemic Agents/administration & dosage
- Hypoglycemic Agents/pharmacology
- Hypoglycemic Agents/therapeutic use
- Lipid Metabolism/drug effects
- Liver/drug effects
- Liver/metabolism
- Liver/pathology
- Male
- Mice
- Mice, Inbred Strains
- Nuclear Proteins/metabolism
- Sterol Regulatory Element Binding Protein 1/biosynthesis
- Treatment Outcome
- Triglycerides/blood
Collapse
Affiliation(s)
- Noriko Yamabe
- Institute of Natural Medicine, University of Toyama, Sugitani, Toyama, Japan
| | | | | | | | | | | |
Collapse
|
56
|
Qin B, Dawson H, Anderson RA. Elevation of tumor necrosis factor-alpha induces the overproduction of postprandial intestinal apolipoprotein B48-containing very low-density lipoprotein particles: evidence for related gene expression of inflammatory, insulin and lipoprotein signaling in enterocytes. Exp Biol Med (Maywood) 2010; 235:199-205. [PMID: 20404035 DOI: 10.1258/ebm.2009.009169] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The aim of this study was to determine whether systemic elevation of tumor necrosis factor (TNF)-alpha induces intestinal-derived apolipoprotein B (apoB)48-containing very low-density lipoprotein (VLDL) production in hamsters after fat loading and whether TNF-alpha disturbs the related mRNA expression in inflammatory, insulin and lipoprotein signaling pathways in primary enterocytes. In vivo TNF-alpha and Triton-WR1339 infusion, Western blotting and reverse transcriptase-polymerase chain reaction were combined to explore the mechanisms underlying intestinal overproduction of apoB48-containing chylomicrons and VLDL(1) particles by TNF-alpha. TNF-alpha infusion increased intestinal production of chylomicron and VLDL(1)-apoB48 in postprandial (fat load) states. Following TNF-alpha-treatment in enterocytes, there was enhanced gene expression of Il1alpha and beta, Il6 and Tnf and decreased mRNA levels of components of the insulin signaling pathway including the insulin receptor (Ir), Ir substrate-1 and 2, PI3 k, and Akt, but increased phosphatase and tensin homolog deleted on chromosome ten (Pten) protein and mRNA expression. TNF-alpha also induced Cd36 and peroxisome proliferators-activated receptor (Ppar)gamma expression, as well as microsomal triglyceride transfer protein (Mtp) protein and mRNA, but suppressed the sterol regulatory element binding protein (Srebp)1c protein and mRNA level. Systemic elevation of TNF-alpha stimulates the postprandial overproduction of apoB48-containing chylomicrons and VLDL(1) particles by disturbing intestinal gene expression of the inflammatory, insulin and lipoprotein pathways. These findings provide mechanistic links among the inflammatory factor, TNF-alpha, intestinal inflammatory/insulin insensitivity and the overproduction of intestinal apoB48-containing lipoproteins.
Collapse
Affiliation(s)
- Bolin Qin
- Diet, Genomics, and Immunology Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, US Department of Agriculture, Beltsville, Building 307C, 10300 Baltimore Avenue, Beltsville, MD 20705-2350, USA
| | | | | |
Collapse
|
57
|
Nishiumi S, Yoshida M, Azuma T, Yoshida KI, Ashida H. 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs an insulin signaling pathway through the induction of tumor necrosis factor-alpha in adipocytes. Toxicol Sci 2010; 115:482-91. [PMID: 20181658 DOI: 10.1093/toxsci/kfq052] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes a wasting syndrome characterized by a loss of body weight accompanied by a decrease in adipose tissue weight, i.e., insulin resistance-like symptoms. Therefore, the effects of TCDD on an insulin signaling pathway in mature 3T3-L1 adipocytes were investigated to obtain insight into the underlying mechanisms. TCDD downregulated expression of insulin receptor beta-subunit (IRbeta), insulin receptor substrate 1 (IRS1), and glucose transporter 4 (GLUT4) and decreased insulin-stimulated glucose uptake activity. TCDD also upregulated expression of TNF-alpha, one of insulin resistance-inducing factors. Anti-TNF-alpha neutralization antibody and silencing of TNF-alpha receptor 1 (TNFR1) diminished the TCDD-induced downregulation of IRbeta, IRS1, and GLUT4. Moreover, the experiments using small interfering RNA for an aryl hydrocarbon receptor (AhR) revealed that the TCDD-evoked changes of IRbeta, IRS1, GLUT4, and TNF-alpha were dependent on AhR. TCDD also stimulated the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK), and their inhibitors abrogated the TCDD-induced downregulation of IRbeta, IRS1, and GLUT4; upregulation of TNF-alpha; and activation of NF-kappaB. Taken together, TCDD stimulates expression and secretion of TNF-alpha in adipocytes through activation of AhR, ERK1/2, and JNK, and the secreted TNF-alpha causes the downregulation of IRbeta, IRS1, and GLUT4 through TNFR1, resulting in insulin resistance.
Collapse
Affiliation(s)
- Shin Nishiumi
- Division of Gastroenterology, Department of Internal Medicine, Graduate School of Medicine, Kobe University, Kobe, Hyogo 650-0017, Japan.
| | | | | | | | | |
Collapse
|
58
|
Fernández-Alvarez A, Soledad Alvarez M, Cucarella C, Casado M. Characterization of the human insulin-induced gene 2 (INSIG2) promoter: the role of Ets-binding motifs. J Biol Chem 2010; 285:11765-74. [PMID: 20145255 DOI: 10.1074/jbc.m109.067447] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin-induced gene 2 (INSIG2) and its homolog INSIG1 encode closely related endoplasmic reticulum proteins that regulate the proteolytic activation of sterol regulatory element-binding proteins, transcription factors that activate the synthesis of cholesterol and fatty acids in animal cells. Several studies have been carried out to identify INSIG2 genetic variants associated with metabolic diseases. However, few data have been published regarding the regulation of INSIG2 gene expression. Two Insig2 transcripts have been described in rodents through the use of different promoters that produce different noncoding first exons that splice into a common second exon. Herein we report the cloning and characterization of the human INSIG2 promoter and the detection of an INSIG2-specific transcript homologous to the Insig2b mouse variant in human liver. Deletion analyses on 3 kb of 5'-flanking DNA of the human INSIG2 gene revealed the functional importance of a 350-bp region upstream of the transcription start site. Mutated analyses, chromatin immunoprecipitation assays, and RNA interference analyses unveiled the significance of an Ets-consensus motif in the proximal region and the interaction of the Ets family member SAP1a (serum response factor (SRF) accessory protein-1a) with this region of the human INSIG2 promoter. Moreover, our findings suggest that insulin activated the human INSIG2 promoter in a process mediated by phosphorylated SAP1a. Overall, these results map the functional elements in the human INSIG2 promoter sequence and suggest an unexpected regulation of INSIG2 gene expression in human liver.
Collapse
Affiliation(s)
- Ana Fernández-Alvarez
- Instituto de Biomedicina de Valencia (Consejo Superior de Investigaciones Científicas), Valencia, Spain
| | | | | | | |
Collapse
|
59
|
PAYNE VA, AU WS, LOWE CE, RAHMAN SM, FRIEDMAN JE, O’RAHILLY S, ROCHFORD JJ. C/EBP transcription factors regulate SREBP1c gene expression during adipogenesis. Biochem J 2009; 425:215-23. [PMID: 19811452 PMCID: PMC2913385 DOI: 10.1042/bj20091112] [Citation(s) in RCA: 140] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The transcription factor SREBP1c (sterol-regulatory-element-binding protein 1c) is highly expressed in adipose tissue and plays a central role in several aspects of adipocyte development including the induction of PPARgamma (peroxisome-proliferator-activated receptor gamma), the generation of an endogenous PPARgamma ligand and the expression of several genes critical for lipid biosynthesis. Despite its significance, the regulation of SREBP1c expression during adipogenesis is not well characterized. We have noted that in several models of adipogenesis, SREBP1c expression closely mimics that of known C/EBPbeta (CCAAT/enhancer-binding protein beta) targets. Inhibition of C/EBP activity during adipogenesis by expressing either the dominant-negative C/EBPbeta LIP (liver-enriched inhibitory protein) isoform, the co-repressor ETO (eight-twenty one/MTG8) or using siRNAs (small interfering RNAs) targeting either C/EBPbeta or C/EBPdelta significantly impaired early SREBP1c induction. Furthermore, ChIP (chromatin immunoprecipitation) assays identified specific sequences in the SREBP1c promoter to which C/EBPbeta and C/EBPdelta bind in intact cells, demonstrating that these factors may directly regulate SREBP1c expression. Using cells in which C/EBPalpha expression is inhibited using shRNA (short hairpin RNA) and ChIP assays we show that C/EBPalpha replaces C/EBPbeta and C/EBPdelta as a regulator of SREBP1c expression in maturing adipocytes. These results provide novel insight into the induction of SREBP1c expression during adipogenesis. Moreover, the findings of the present study identify an important additional mechanism via which the C/EBP transcription factors may control a network of gene expression regulating adipogenesis, lipogenesis and insulin sensitivity.
Collapse
Affiliation(s)
- Victoria A. PAYNE
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 0QQ, U.K
| | - Wo-Shing AU
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 0QQ, U.K
| | - Christopher E. LOWE
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 0QQ, U.K
| | - Shaikh M. RAHMAN
- Department of Pediatrics, University of Colorado Health Sciences Center, Denver, CO 80262, U.S.A
| | - Jacob E. FRIEDMAN
- Department of Pediatrics, University of Colorado Health Sciences Center, Denver, CO 80262, U.S.A
| | - Stephen O’RAHILLY
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 0QQ, U.K
| | - Justin J. ROCHFORD
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 0QQ, U.K
| |
Collapse
|
60
|
Abstract
Adiponectin is an adipose-tissue-derived hormone with anti-diabetic, anti-atherogenic and anti-inflammatory functions. Adiponectin circulates in the bloodstream in trimeric, hexameric and high-molecular-mass species, and different forms of adiponectin have been found to play distinct roles in the regulation of energy homoeostasis. The serum levels of adiponectin are negatively correlated with obesity and insulin resistance, yet the underlying mechanisms remain elusive. In the present review, we summarize recent progress made on the mechanisms regulating adiponectin gene transcription, multimerization and secretion. We also discuss the potential relevance of these studies to the development of new clinical therapy for insulin resistance, Type 2 diabetes and other obesity-related metabolic disorders.
Collapse
|
61
|
Thrush AB, Brindley DN, Chabowski A, Heigenhauser GJ, Dyck DJ. Skeletal muscle lipogenic protein expression is not different between lean and obese individuals: a potential factor in ceramide accumulation. J Clin Endocrinol Metab 2009; 94:5053-61. [PMID: 19837942 DOI: 10.1210/jc.2008-2565] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
CONTEXT Skeletal muscle lipid content is increased in obesity. Recent evidence suggests that fatty acid (FA) storage as triacylglycerol (TAG) represents a metabolically safe pool compared to the more bioactive diacylglycerol (DAG) and ceramide. OBJECTIVE/DESIGN The purpose of this study was to compare the expression of lipogenic proteins and ceramide and DAG content in skeletal muscle of lean and obese humans. We hypothesized that lipogenic protein expression would be increased in obese to facilitate the storage of excess FA as TAG. PARTICIPANTS Eighteen lean (BMI < or = 26 kg/m(2)) and 15 obese (BMI > 29 kg/m(2)) women participated in this study. RESULTS There was no difference in the expression of any lipogenic (stearoyl-CoA desaturase-1, stearoyl retinol binding protein-1c, mitochondrial glycerol-3-phosphate acyltransferase, diacylglycerol acyltransferase-1) or sphingolipid proteins measured between lean and obese humans. Total ceramide was increased in muscle from obese humans (lean vs. obese, 529.4 +/- 54.8 vs. 672.4 +/- 57.4 nmol/g; P < 0.05), but there was no difference in total DAG content (lean vs. obese, 2244.1 +/- 278.2 vs. 1941.4 +/- 165.0 nmol/g). Content of protein phosphatase 2A, a ceramide target, was increased in muscle of obese humans (P < 0.05). CONCLUSIONS We propose that in muscle of obese humans there is an insufficient lipogenic response to the lipid oversupply, allowing more FA to be stored as reactive lipid species, particularly ceramide, potentially contributing to subsequent metabolic complications.
Collapse
Affiliation(s)
- A Brianne Thrush
- Department of Human Health and Nutritional Sciences, Animal Science and Nutrition Building, Room 203, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
| | | | | | | | | |
Collapse
|
62
|
Granjon A, Gustin MP, Rieusset J, Lefai E, Meugnier E, Güller I, Cerutti C, Paultre C, Disse E, Rabasa-Lhoret R, Laville M, Vidal H, Rome S. The microRNA signature in response to insulin reveals its implication in the transcriptional action of insulin in human skeletal muscle and the role of a sterol regulatory element-binding protein-1c/myocyte enhancer factor 2C pathway. Diabetes 2009; 58:2555-64. [PMID: 19720801 PMCID: PMC2768160 DOI: 10.2337/db09-0165] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
OBJECTIVE Factors governing microRNA expressions in response to changes of cellular environment are still largely unknown. Our aim was to determine whether insulin, the major hormone controlling whole-body energy homeostasis, is involved in the regulation of microRNA expressions in human skeletal muscle. RESEARCH DESIGN AND METHODS We carried out comparative microRNA (miRNA) expression profiles in human skeletal muscle biopsies before and after a 3-h euglycemic-hyperinsulinemic clamp, with TaqMan low-density arrays. Then, using DNA microarrays, we determined the response to insulin of the miRNA putative target genes in order to determine their role in the transcriptional action of insulin. We further characterized the mechanism of action of insulin on two representative miRNAs, miR-1 and miR-133a, in human muscle cells. RESULTS Insulin downregulated the expressions of 39 distinct miRNAs in human skeletal muscle. Their potential target mRNAs coded for proteins that were mainly involved in insulin signaling and ubiquitination-mediated proteolysis. Bioinformatic analysis suggested that combinations of different downregulated miRNAs worked in concert to regulate gene expressions in response to insulin. We further demonstrated that sterol regulatory element-binding protein (SREBP)-1c and myocyte enhancer factor 2C were involved in the effect of insulin on miR-1 and miR-133a expression. Interestingly, we found an impaired regulation of miRNAs by insulin in the skeletal muscle of type 2 diabetic patients, likely as consequences of altered SREBP-1c activation. CONCLUSIONS This work demonstrates a new role of insulin in the regulation of miRNAs in human skeletal muscle and suggests a possible implication of these new modulators in insulin resistance.
Collapse
Affiliation(s)
- Aurélie Granjon
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
| | | | - Jennifer Rieusset
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
| | - Etienne Lefai
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
| | - Emmanuelle Meugnier
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
| | - Isabelle Güller
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
| | - Catherine Cerutti
- INSERM ERI22/EA 4173, Biostatistiques, Université Lyon, Lyon, France
| | - Christian Paultre
- INSERM ERI22/EA 4173, Biostatistiques, Université Lyon, Lyon, France
| | - Emmanuel Disse
- Hospices Civils de Lyon, Service de Diabétologie et Nutrition, Hôpital Edouard-Herriot, Lyon, France
- Centre de Recherche en Nutrition Humaine Rhône-Alpes, Oullins, France
| | - Rémi Rabasa-Lhoret
- Chaire de recherche J-A DeSève, Institut de Recherches Cliniques de Montréal, Montréal, Québec, Canada
| | - Martine Laville
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
- Hospices Civils de Lyon, Service de Diabétologie et Nutrition, Hôpital Edouard-Herriot, Lyon, France
- Centre de Recherche en Nutrition Humaine Rhône-Alpes, Oullins, France
| | - Hubert Vidal
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
- Hospices Civils de Lyon, Service de Diabétologie et Nutrition, Hôpital Edouard-Herriot, Lyon, France
- Centre de Recherche en Nutrition Humaine Rhône-Alpes, Oullins, France
| | - Sophie Rome
- Institut de la Recherche Agronomique (INRA) 1235, INSERM 870, INSA-Lyon, Régulations Métaboliques Nutrition et Diabète, Université Lyon, Oullins, France
- Corresponding author: Sophie Rome,
| |
Collapse
|
63
|
Simonyte K, Rask E, Näslund I, Angelhed JE, Lönn L, Olsson T, Mattsson C. Obesity is accompanied by disturbances in peripheral glucocorticoid metabolism and changes in FA recycling. Obesity (Silver Spring) 2009; 17:1982-7. [PMID: 19360009 DOI: 10.1038/oby.2009.99] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The glucocorticoid activating enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) is of major interest in obesity-related morbidity. Alterations in tissue-specific cortisol levels may influence lipogenetic and gluco/glyceroneogenetic pathways in fat and liver. We analyzed the expression and activity of 11betaHSD1 as well as the expression of phosphoenolpyruvate carboxykinase (PEPCK), sterol regulatory element binding protein (SREBP), and fatty acid synthase (FAS) in adipose and liver and investigated putative associations between 11betaHSD1 and energy metabolism genes. A total of 33 obese women (mean BMI 44.6) undergoing gastric bypass surgery were enrolled. Subcutaneous adipose tissue (SAT), omental fat (omental adipose tissue (OmAT)), and liver biopsies were collected during the surgery. 11betaHSD1 gene expression was higher in SAT vs. OmAT (P = 0.013), whereas the activity was higher in OmAT (P = 0.009). The SAT 11betaHSD1 correlated with waist circumference (P = 0.045) and was an independent predictor for the OmAT area in a linear regression model. Energy metabolism genes had AT depot-specific expression; higher leptin and SREBP in SAT than OmAT, but higher PEPCK in OmAT than SAT. The expression of 11betaHSD1 correlated with PEPCK in both AT depots (P = 0.05 for SAT and P = 0.0001 for OmAT). Hepatic 11betaHSD1 activity correlated negatively with abdominal adipose area (P = 0.002) and expression positively with PEPCK (P = 0.003). In human obesity, glucocorticoid regeneration in the SAT is associated with central fat accumulation indicating that the importance of this specific fat depot is underestimated. Central fat accumulation is negatively associated with hepatic 11betaHSD1 activity. A disturbance in peripheral glucocorticoid metabolism is associated with changes in genes involved in fatty acid (FA) recycling in adipose tissue (AT).
Collapse
Affiliation(s)
- Kotryna Simonyte
- Department of Public Health and Clinical Medicine, Umeå University Hospital, Umeå, Sweden.
| | | | | | | | | | | | | |
Collapse
|
64
|
Bi Y, Cai M, Liang H, Sun W, Li X, Wang C, Zhu Y, Chen X, Li M, Weng J. Increased carnitine palmitoyl transferase 1 expression and decreased sterol regulatory element-binding protein 1c expression are associated with reduced intramuscular triglyceride accumulation after insulin therapy in high-fat-diet and streptozotocin-induced diabetic rats. Metabolism 2009; 58:779-86. [PMID: 19375767 DOI: 10.1016/j.metabol.2009.01.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Accepted: 01/27/2009] [Indexed: 01/06/2023]
Abstract
We previously reported that early insulin treatment reduced intramuscular triglyceride content in type 2 diabetes mellitus Sprague-Dawley rats; the underlying mechanisms are, however, not completely understood. Here we investigated the regulation of insulin on molecular expressions involved in lipid metabolism pathways in skeletal muscle of high-fat-diet and streptozotocin-induced diabetic Sprague-Dawley rats. Neutral protamine Hagedorn insulin and gliclazide were initiated at the third day after streptozotocin injection and lasted for 3 weeks. Compared with normal rats, untreated diabetic rats had a 30% and 61% increase in lipoprotein lipase protein expression and activity, which were decreased by insulin and gliclazide (P < .05). Fatty acid translocase protein was down-regulated by 45% in untreated diabetic rats, which was up-regulated by 31% and 26% with insulin and gliclazide, respectively (P < .05). Insulin failed to affect fatty acid transport protein 1 and fatty acid binding protein expressions. Carnitine palmitoyl transferase 1 had a 47% decrease in untreated diabetic rats, which was normalized by insulin (P < .05). Moreover, compared with normal rats, untreated diabetic rats had higher expressions of sterol regulatory element-binding protein 1c, tumor necrosis factor alpha, and Tyr(705) phosphorylation of signal transducer and activator of transcription 3 levels, which all were down-regulated after insulin treatment. These results suggested that early insulin reduced intramuscular triglyceride levels in diabetic rats potentially through amelioration of lipid dysfunction and inhibition of lipid synthesis.
Collapse
Affiliation(s)
- Yan Bi
- Department of Endocrinology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou 510630, PR China
| | | | | | | | | | | | | | | | | | | |
Collapse
|
65
|
Motallebipour M, Enroth S, Punga T, Ameur A, Koch C, Dunham I, Komorowski J, Ericsson J, Wadelius C. Novel genes in cell cycle control and lipid metabolism with dynamically regulated binding sites for sterol regulatory element-binding protein 1 and RNA polymerase II in HepG2 cells detected by chromatin immunoprecipitation with microarray detection. FEBS J 2009; 276:1878-90. [PMID: 19292868 DOI: 10.1111/j.1742-4658.2009.06914.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Sterol regulatory element-binding proteins 1 and 2 (SREBP-1 and SREBP-2) are important regulators of genes involved in cholesterol and fatty acid metabolism, but have also been implicated in the regulation of the cell cycle and have been associated with the pathogenesis of type 2 diabetes, atherosclerosis and obesity, among others. In this study, we aimed to characterize the binding sites of SREBP-1 and RNA polymerase II through chromatin immunoprecipitation and microarray analysis in 1% of the human genome, as defined by the Encyclopaedia of DNA Elements consortium, in a hepatocellular carcinoma cell line (HepG2). Our data identified novel binding sites for SREBP-1 in genes directly or indirectly involved in cholesterol metabolism, e.g. apolipoprotein C-III (APOC3). The most interesting biological findings were the binding sites for SREBP-1 in genes for host cell factor C1 (HCFC1), involved in cell cycle regulation, and for filamin A (FLNA). For RNA polymerase II, we found binding sites at classical promoters, but also in intergenic and intragenic regions. Furthermore, we found evidence of sterol-regulated binding of SREBP-1 and RNA polymerase II to HCFC1 and FLNA. From the results of this work, we infer that SREBP-1 may be involved in processes other than lipid metabolism.
Collapse
Affiliation(s)
- Mehdi Motallebipour
- Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala University, Uppsala, Sweden
| | | | | | | | | | | | | | | | | |
Collapse
|
66
|
Bhonagiri P, Pattar GR, Horvath EM, Habegger KM, McCarthy AM, Elmendorf JS. Hexosamine biosynthesis pathway flux contributes to insulin resistance via altering membrane phosphatidylinositol 4,5-bisphosphate and cortical filamentous actin. Endocrinology 2009; 150:1636-45. [PMID: 19036880 PMCID: PMC2659275 DOI: 10.1210/en.2008-1102] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We recently found that plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP(2))-regulated filamentous actin (F-actin) polymerization was diminished in hyperinsulinemic cell culture models of insulin resistance. Here we delineated whether increased glucose flux through the hexosamine biosynthesis pathway (HBP) causes the PIP(2)/F-actin dysregulation and insulin resistance induced by hyperinsulinemia. Increased HBP activity was detected in 3T3-L1 adipocytes cultured under conditions closely resembling physiological hyperinsulinemia (5 nm insulin for 12 h) and in cells where HBP activity was amplified by 2 mm glucosamine (GlcN). Both the physiological hyperinsulinemia and experimental GlcN challenge induced comparable losses of PIP(2) and F-actin. In addition to protecting against the insulin-induced membrane/cytoskeletal abnormality and insulin-resistant state, exogenous PIP(2) corrected the GlcN-induced insult on these parameters. Moreover, in accordance with HBP flux directly weakening PIP(2)/F-actin structure, inhibition of the rate-limiting HBP enzyme (glutamine:fructose-6-phosphate amidotransferase) restored PIP(2)-regulated F-actin structure and insulin responsiveness. Conversely, overexpression of glutamine:fructose-6-phosphate amidotransferase was associated with a loss of detectable plasma membrane PIP(2) and insulin sensitivity. A slight decrease in intracellular ATP resulted from amplifying HBP by hyperinsulinemia and GlcN. However, experimental maintenance of the intracellular ATP pool under both conditions with inosine did not reverse the PIP(2)/F-actin-based insulin-resistant state. Furthermore, less invasive challenges with glucose, in the absence of insulin, also led to PIP(2)/F-actin dysregulation. Accordingly, we suggest that the functionality of cell systems dependent on PIP(2) and/or F-actin status, such as the glucose transport system, can be critically compromised by inappropriate HBP activity.
Collapse
Affiliation(s)
- Padma Bhonagiri
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, VanNuys Medical Science Building Room 308A, Indianapolis, Indiana 46202.
| | | | | | | | | | | |
Collapse
|
67
|
Retinol saturase promotes adipogenesis and is downregulated in obesity. Proc Natl Acad Sci U S A 2009; 106:1105-10. [PMID: 19139408 DOI: 10.1073/pnas.0812065106] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Adipocyte differentiation is controlled by many transcription factors, but few known downstream targets of these factors are necessary for adipogenesis. Here we report that retinol saturase (RetSat), which is an enzyme implicated in the generation of dihydroretinoid metabolites, is induced during adipogenesis and is directly regulated by the transcription factor peroxisome proliferator activated receptor gamma (PPARgamma). Ablation of RetSat dramatically inhibited adipogenesis but, surprisingly, this block was not overcome by the putative product of RetSat enzymatic activity. On the other hand, ectopic RetSat with an intact, but not a mutated, FAD/NAD dinucleotide-binding motif increased endogenous PPARgamma transcriptional activity and promoted adipogenesis. Indeed, RetSat was not required for adipogenesis when cells were provided with exogenous PPARgamma ligands. In adipose tissue, RetSat is expressed in adipocytes but is unexpectedly downregulated in obesity, most likely owing to infiltration of macrophages that we demonstrate to repress RetSat expression. Thiazolidinedione treatment reversed low RetSat expression in adipose tissue of obese mice. Thus, RetSat plays an important role in the biology of adipocytes, where it favors normal differentiation, yet is reduced in the obese state. RetSat is thus a novel target for therapeutic intervention in metabolic disease.
Collapse
|
68
|
White adipose tissue as endocrine organ and its role in obesity. Arch Med Res 2008; 39:715-28. [PMID: 18996284 DOI: 10.1016/j.arcmed.2008.09.005] [Citation(s) in RCA: 272] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Accepted: 09/19/2008] [Indexed: 02/08/2023]
Abstract
Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity.
Collapse
|
69
|
Liu JX, Liu J, Li PQ, Xie XD, Guo Q, Tian LM, Ma XQ, Zhang JP, Liu J, Gao JY. Association of sterol regulatory element-binding protein-1c gene polymorphism with type 2 diabetes mellitus, insulin resistance and blood lipid levels in Chinese population. Diabetes Res Clin Pract 2008; 82:42-7. [PMID: 18692268 DOI: 10.1016/j.diabres.2008.06.017] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Revised: 03/04/2008] [Accepted: 06/30/2008] [Indexed: 11/23/2022]
Abstract
AIMS The sterol regulatory element-binding protein (SREBP)-1c gene has been identified as a susceptibility gene in metabolic diseases such as type 2 diabetes mellitus (T2DM), obesity, dyslipidemia and insulin resistance. Previous studies suggest that SNP17 (rs2297508, exon18c and G952G) of SREBP-1c gene and a common SREBP-1c SNP6 (rs11868035) are associated with an increased risk of T2DM. The present study aimed to confirm the previously reported association in a Chinese population and to examine the two SREBP-1c SNPs for their associations with insulin resistance and blood lipid. METHODS We genotyped two SREBP-1c SNPs in a case-control study (n=327) from Chinese, including 156 patients with T2DM and 171 healthy controls, using polymerase chain reaction-denaturing high-performance liquid chromatography (PCR-DHPLC) and tested for association with type 2 diabetes, insulin resistance and blood lipid, respectively. Genotype and allele distributions and haplotype construction were analysed. RESULTS The genotype and allele distributions of rs2297508 and rs11868035 polymorphisms were significantly different in type 2 diabetic patients compared to controls (P=0.002 and P=0.013; 0.00 and 0.001, respectively). Haplotype analyses showed significant association with diabetes risk and confirmed the results of the single SNP analyses. The plasma levels of LDL-c of the minor allele-C carriers of the two SNPs were both significantly higher than the noncarriers in the control group (P<0.05). Furthermore, insulin resistance index (HOMA-IRI) of the rare homozygotes C/C of rs11868035 was significantly lower than that of T/T in the T2DM group (P<0.05). CONCLUSIONS These findings indicate that the SREBP-1c SNPs rs2297508 and rs11868035 are associated with a significantly increased risk of T2DM and dyslipidemia in the Chinese population. Moreover, the SNP (rs11868035) is closely related to insulin resistance (IR) in diabetic patients.
Collapse
Affiliation(s)
- Ju-Xiang Liu
- Key Laboratory of Preclinical Study for New Drugs of Gansu Province, School of Basic Medical Science, 222 South Tianshui Road, Lanzhou University, Lanzhou City, Gansu Province 730000, China
| | | | | | | | | | | | | | | | | | | |
Collapse
|
70
|
Lim JY, Kim WH, Park SI. GO6976 prevents TNF-alpha-induced suppression of adiponectin expression in 3T3-L1 adipocytes: putative involvement of protein kinase C. FEBS Lett 2008; 582:3473-8. [PMID: 18804108 DOI: 10.1016/j.febslet.2008.09.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Revised: 08/19/2008] [Accepted: 09/09/2008] [Indexed: 01/15/2023]
Abstract
Adiponectin, one of the adipokines secreted by adipocytes, possesses insulin sensitizing and anti-atherosclerotic properties. Tumor necrosis factor-alpha (TNF-alpha) is known to suppress the expression and secretion of adiponectin in adipocytes; however, the underlying mechanism remains poorly understood. Here, we demonstrate that GO6976 (a selective inhibitor of conventional protein kinase C (PKC)) prevents TNF-alpha-induced suppression of adiponectin secretion and expression in fully differentiated 3T3-L1 adipocytes, accompanied by attenuation of c-Jun N-terminal kinase (JNK) activation. Additionally, the transcriptional activity of peroxisome proliferator-activated receptor-gamma (PPARg) (a strong inducer of adiponectin) on the adiponectin promoter was inhibited in a PKC isoform-specific manner. These results raise the possibility that PKC is involved in TNF-alpha-induced suppression of adiponectin in 3T3-L1 adipocytes.
Collapse
Affiliation(s)
- Joong-Yeon Lim
- Division of Intractable Diseases, Center for Biomedical Sciences, National Institute of Health, 194 Tongillo, Eunpyeong-gu, Seoul 122-701, Republic of Korea
| | | | | |
Collapse
|
71
|
Kim SJ, Jung JY, Kim HW, Park T. Anti-obesity effects of Juniperus chinensis extract are associated with increased AMP-activated protein kinase expression and phosphorylation in the visceral adipose tissue of rats. Biol Pharm Bull 2008; 31:1415-21. [PMID: 18591785 DOI: 10.1248/bpb.31.1415] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study evaluates the protective effect of Juniperus chinensis hot water extract (JCE) against high-fat-diet (HFD)-induced obesity and its molecular mechanisms in the visceral adipose tissue of rats. JCE supplementation significantly lowered body weight gain, visceral fat-pad weights, blood lipid levels, and blood insulin and leptin levels of rats rendered obese by an HFD. Feeding with JCE significantly reversed the HFD-induced down-regulation of the epididymal adipose tissue genes implicated in adipogenesis, such as the peroxisome proliferator-activated receptors gamma2 (PPARgamma2), adipocyte protein 2 (aP2), sterol regulatory element binding protein 1c (SREBP1c), fatty acid synthase (FAS), and HMG-CoA reductase (HMGR), as well as those involved in uncoupled respiration, such as the uncoupling protein 2 (UCP2) and uncoupling protein 3 (UCP3). Dietary supplementation with JCE also reversed the HFD-induced decreases in the AMP-activated protein kinase (AMPK) and the acetyl-CoA carboxylase 2 (ACC2) expressions at both the mRNA and protein levels and restored the HFD-induced inhibitions in the AMPK and ACC2 phosphorylation, which are related to fatty acid beta-oxidation, in the epididymal adipose tissue. This study reports, for the first time, that the JCE can have an anti-obesity effect in a rodent model with HFD-induced obesity through an enhanced gene transcription of the uncoupling protein as well as an elevated AMPK protein expression and phosphorylation in the visceral adipose tissue.
Collapse
Affiliation(s)
- Seung-Jin Kim
- Department of Food and Nutrition, Brain Korea 21 Project, Yonsei University, Seoul, Korea
| | | | | | | |
Collapse
|
72
|
Miranda M, Chacón MR, Gutiérrez C, Vilarrasa N, Gómez JM, Caubet E, Megía A, Vendrell J. LMNA mRNA expression is altered in human obesity and type 2 diabetes. Obesity (Silver Spring) 2008; 16:1742-8. [PMID: 18497734 DOI: 10.1038/oby.2008.276] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
OBJECTIVE The aim of this study was to analyze lamin A/C mRNA levels in abdominal subcutaneous adipose tissue in two conditions-obesity and type 2 diabetes-that share common inflammatory and metabolic features, and to assess their relationship with selected inflammatory and adipogenic genes. METHODS AND PROCEDURES This is a cross-sectional study involving 52 nondiabetic and 54 type 2 diabetes patients. Anthropometrical and analytical measurements (glycemic, lipidic, and inflammatory profiles) were performed, and mRNA expression was determined using real-time PCR. RESULTS Lamin A and C isoforms are expressed differentially. Lamin A/C mRNA levels were increased in obese and in type 2 diabetes patients. We also observed a strong relationship between both isoforms (B = 2.218, P < 0.001) and among lamin C mRNA expression and adipogenic (sterol-responsive element binding protein-1 (SREBP1c)) and inflammatory (interleukin-6 (IL-6)) markers (B = 0.854, P = 0.001, and B = 0.557, P < 0.001, respectively). DISCUSSION These data suggest that lamin A/C may be involved in the adipocyte gene profile observed in obesity and type 2 diabetes.
Collapse
Affiliation(s)
- Merce Miranda
- Endocrinology and Diabetes Unit, Research Department, University Hospital of Tarragona Joan XXIII, Pere Virgili Institute, Rovira i Virgili University, Tarragona, Spain.
| | | | | | | | | | | | | | | |
Collapse
|
73
|
Jääskeläinen J, Korhonen S, Kuulasmaa T, Kurl S, Niskanen L, Vanhala M, Hippeläinen M, Voutilainen R, Heinonen S. Androgen receptor gene CAG repeat length in women with metabolic syndrome. Gynecol Endocrinol 2008; 24:411-6. [PMID: 18645714 DOI: 10.1080/09513590802210865] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
OBJECTIVE The length of the androgen receptor gene CAG repeat [AR (CAG)(n)] modulates the activity of the androgen receptor (AR), and this polymorphism has been shown to modulate body fat mass and serum concentrations of insulin in men. We hypothesized that shorter AR (CAG)(n) is associated with metabolic syndrome (MBS) or its components in women. DESIGN, PATIENTS AND MEASUREMENTS In a cross-sectional controlled study we studied 52 Finnish women aged 34-55 years with MBS and 69 age-matched controls. All participants were recruited from a sample of women drawn from the Finnish population register. We compared the mean AR (CAG)(n) in the two groups. Furthermore, we correlated the AR (CAG)(n) with serum testosterone, androstenedione, dehydroepiandrosterone sulfate and several parameters of glucose and lipid metabolism in each group and in all 121 women. RESULTS There was no difference in the biallelic mean AR (CAG)(n) between the MBS and the control group (21.6+/-0.2 vs. 21.8+/-0.2, not significant). The AR (CAG)(n) did not correlate significantly with any of the clinical or biochemical parameters of glucose or fat metabolism. However, it correlated negatively with serum testosterone (-0.195, p = 0.04) and androstenedione concentrations (-0.205, p = 0.03) in all studied women. CONCLUSIONS The AR (CAG)(n) is not a major determinant of MBS in women but it contributes to ovarian androgen production.
Collapse
Affiliation(s)
- Jarmo Jääskeläinen
- Department of Pediatrics, University of Kuopio and Kuopio University Hospital, Kuopio, Finland
| | | | | | | | | | | | | | | | | |
Collapse
|
74
|
Qin B, Anderson RA, Adeli K. Tumor necrosis factor-alpha directly stimulates the overproduction of hepatic apolipoprotein B100-containing VLDL via impairment of hepatic insulin signaling. Am J Physiol Gastrointest Liver Physiol 2008; 294:G1120-9. [PMID: 18372392 DOI: 10.1152/ajpgi.00407.2007] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Insulin-resistant states are commonly associated with both increased circulating levels of tumor necrosis factor (TNF)-alpha and hepatic overproduction of very low density lipoproteins (VLDL). Here, we provide evidence that increased TNF-alpha can directly stimulate the hepatic assembly and secretion of apolipoprotein B (apoB) 100-containing VLDL(1), using the Syrian golden hamster, an animal model that closely resembles humans in hepatic VLDL-apoB100 metabolism. In vivo TNF-alpha infusion for 4 h in chow-fed hamsters induced whole-body insulin resistance on the basis of euglycemic hyperinsulinemic clamp studies. Immunoprecipitation and immunoblotting analysis of livers from TNF-alpha-treated hamsters indicated decreased tyrosine phosphorylation of insulin receptor (IR)-beta, IR substrate-1 (Tyr), Akt (Ser(473)), p38, ERK1/2, and JNK but increased serine phosphorylation of IRS-1 (Ser(307)) and Shc. TNF-alpha infusion also significantly increased hepatic production of total circulating apoB100 and VLDL-apoB100 in both fasting and postprandial (fat load) states. Ex vivo experiments, using cultured primary hepatocytes from hamsters, also showed TNF-alpha-induced VLDL-apoB100 oversecretion, an effect that was blocked by TNF receptor 2 antibody. Unexpectedly, TNF-alpha decreased the sterol regulatory element-binding protein-1c mass and mRNA levels but significantly increased microsomal triglyceride transfer protein mass and mRNA levels in primary hepatocytes. In summary, these data provide direct evidence that TNF-alpha induces whole-body insulin resistance and impairs hepatic insulin signaling accompanied by overproduction of apoB100-containing VLDL particles, an effect likely mediated via TNF receptor 2.
Collapse
Affiliation(s)
- Bolin Qin
- Department of Laboratory Medicine and Pathobiology, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
| | | | | |
Collapse
|
75
|
Grarup N, Stender-Petersen KL, Andersson EA, Jørgensen T, Borch-Johnsen K, Sandbaek A, Lauritzen T, Schmitz O, Hansen T, Pedersen O. Association of variants in the sterol regulatory element-binding factor 1 (SREBF1) gene with type 2 diabetes, glycemia, and insulin resistance: a study of 15,734 Danish subjects. Diabetes 2008; 57:1136-42. [PMID: 18192539 DOI: 10.2337/db07-1534] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE We evaluated the association of variants in the sterol regulatory element-binding factor 1 gene (SREBF1) with type 2 diabetes. Due to the previous inconclusive quantitative trait associations, we also did studies of intermediate quantitative phenotypes. RESEARCH DESIGN AND METHODS We genotyped four variants in SREBF1 in the population-based Inter99 cohort (n = 6,070), the Danish ADDITION study (n = 8,662), and in additional type 2 diabetic patients (n = 1,002). The case-control studies involved 2,980 type 2 diabetic patients and 4,522 glucose-tolerant subjects. RESULTS The minor alleles of rs2297508, rs11868035, and rs1889018 (linkage disequilibrium R(2) = 0.6-0.8) associated with a modestly increased risk of type 2 diabetes (rs2297508: OR 1.17 [95% CI 1.05-1.30], P = 0.003), which was confirmed in meta-analyses of all published studies (rs2297508 G-allele: 1.08 [1.03-1.14] per allele, P = 0.001). The diabetes-associated alleles also associated strongly with a higher plasma glucose at 30 and 120 min and serum insulin at 120 min during an oral glucose tolerance test (all P < 0.006) and the minor allele of rs1889018 with a surrogate measure of insulin sensitivity (P = 0.03). Furthermore, the diabetes-associated alleles associated with a modestly increased A1C level in the population-based Inter99 of middle-aged subjects and in the ADDITION study of high-risk individuals (P = 0.006 and P = 0.008, respectively). CONCLUSIONS We associate sequence variation in SREBF1 with a modestly increased predisposition to type 2 diabetes. In the general population, the diabetes-associated alleles are discreetly associated with hyperglycemia presumably due to decreased insulin sensitivity. Because sterol regulatory element-binding protein-1c is a mediator of insulin action, the findings are consistent with the presence of a yet undefined subtle loss-of-function SREBF1 variant.
Collapse
|
76
|
Chapman MJ, Sposito AC. Hypertension and dyslipidaemia in obesity and insulin resistance: Pathophysiology, impact on atherosclerotic disease and pharmacotherapy. Pharmacol Ther 2008; 117:354-73. [DOI: 10.1016/j.pharmthera.2007.10.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Accepted: 10/01/2007] [Indexed: 01/12/2023]
|
77
|
Nadeau KJ, Ehlers LB, Aguirre LE, Reusch JEB, Draznin B. Discordance between intramuscular triglyceride and insulin sensitivity in skeletal muscle of Zucker diabetic rats after treatment with fenofibrate and rosiglitazone. Diabetes Obes Metab 2007; 9:714-23. [PMID: 17697064 DOI: 10.1111/j.1463-1326.2006.00696.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
AIM Intramyocellular triglyceride (IMTG) correlates with insulin resistance, but there is no clear causal relationship. Insulin resistance and associated hyperinsulinaemia may increase IMTG, via the insulin-regulated transcription factor, sterol regulatory element-binding protein 1 (SREBP-1). PPAR agonists may also affect IMTG via changes in insulin sensitivity, SREBP-1 or other factors. METHODS We examined skeletal muscle IMTG and SREBP-1 expression, and metabolic parameters in Zucker diabetic fatty rats (ZDF) after 25 weeks of PPAR-gamma or PPAR-alpha administration. RESULTS Compared with Zucker lean rats (ZL), untreated ZDF had significantly higher weights, serum glucose, insulin, free fatty acids, total cholesterol and triglycerides. IMTG and SREBP-1c messenger RNA (mRNA) were also higher in untreated ZDF; both were decreased by fenofibrate (FF). Rosiglitazone (Rosi), despite marked improvement in glycaemia, hyperinsulinaemia and hyperlipidaemia, failed to affect SREBP-1 expression, and increased body weight and IMTG. Rosi/FF combination caused less weight gain and no IMTG increase, despite metabolic effects similar to Rosi alone. CONCLUSIONS IMTG and SREBP-1c mRNA are high in the ZDF. FF and Rosi both improved insulin sensitivity but had opposite effects on IMTG. Thus, there was a clear discordance between insulin sensitivity and IMTG with PPAR agonists, indicating that IMTG and insulin sensitivity do not share a simple relationship.
Collapse
Affiliation(s)
- K J Nadeau
- Division of Pediatric Endocrinology, Department of Pediatrics, University of Colorado Health Sciences Center, Denver, CO, USA.
| | | | | | | | | |
Collapse
|
78
|
Rosa G, Mingrone G, Manco M, Euthine V, Gniuli D, Calvani R, Calvani M, Favuzzi AMR, Castagneto M, Vidal H. Molecular mechanisms of diabetes reversibility after bariatric surgery. Int J Obes (Lond) 2007; 31:1429-36. [PMID: 17515913 DOI: 10.1038/sj.ijo.0803630] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
OBJECTIVE Insulin resistance is a strong biological marker of both obesity and type 2 diabetes. Abnormal fat deposition within skeletal muscle has been identified as a mechanism of obesity-associated insulin resistance. Biliopancreatic diversion (BPD), inducing a massive lipid malabsorption, leads to a reversion of type 2 diabetes. To elucidate the mechanisms of diabetes reversibility, the expression of genes involved in glucose and free fatty acids (FFAs) metabolism was investigated in skeletal muscle biopsies from obese, type 2 diabetic subjects. Peripheral insulin sensitivity and insulin secretion was also measured. SUBJECTS Eight Caucasian obese diabetic patients (BMI 52.1+/-1.85 kg/m(2)) were studied before and 3 years after BPD. MEASUREMENTS The mRNA levels were estimated by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR), insulin sensitivity by the euglycemic-hyperinsulinemic clamp and insulin secretion using a model describing the relationship between insulin secretion and glucose concentration. RESULTS Whole-body glucose uptake (M), normalized by fat-free mass, significantly increased in post-obese subjects (P<0.0001). Total insulin output decreased (P<0.05) in association with a significant improvement of beta-cells glucose sensitivity (P<0.05). mRNA levels of FABP3 (P<0.05), FACL (P<0.05), ACC2 (P<0.05), HKII (P<0.05) and PDK4 (P<0.05) were significantly decreased, while SREBP1c mRNA increased (P<0.05) after BPD. CONCLUSION Reversibility of type 2 diabetes after BPD is dependent on the improvement of skeletal muscle insulin sensitivity, mediated by changes in the expression of genes regulating glucose and fatty acid metabolism in response to nutrient availability.
Collapse
Affiliation(s)
- G Rosa
- Department of Internal Medicine, Catholic University S Cuore, Rome, Italy.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
79
|
Gregor MF, Hotamisligil GS. Thematic review series: Adipocyte Biology. Adipocyte stress: the endoplasmic reticulum and metabolic disease. J Lipid Res 2007; 48:1905-14. [PMID: 17699733 DOI: 10.1194/jlr.r700007-jlr200] [Citation(s) in RCA: 416] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In the context of obesity and its related maladies, the adipocyte plays a central role in the balance, or imbalance, of metabolic homeostasis. An obese, hypertrophic adipocyte is challenged by many insults, including surplus energy, inflammation, insulin resistance, and considerable stress to various organelles. The endoplasmic reticulum (ER) is one such vital organelle that demonstrates significant signs of stress and dysfunction in obesity and insulin resistance. Under normal conditions, the ER must function in the unique and trying environment of the adipocyte, adapting to meet the demands of increased protein synthesis and secretion, energy storage in the form of triglyceride droplet formation, and nutrient sensing that are particular to the differentiated fat cell. When nutrients are in pathological excess, the ER is overwhelmed and the unfolded protein response (UPR) is activated. Remarkably, the consequences of UPR activation have been causally linked to the development of insulin resistance through a multitude of possible mechanisms, including c-jun N-terminal kinase activation, inflammation, and oxidative stress. This review will focus on the function of the ER under normal conditions in the adipocyte and the pathological effects of a stressed ER contributing to adipocyte dysfunction and a thwarted metabolic homeostasis.
Collapse
Affiliation(s)
- Margaret F Gregor
- Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, MA 02115, USA
| | | |
Collapse
|
80
|
Xiang CC, Wu YJ, Ma L, Ding L, Lisinski I, Brownstein MJ, Cushman SW, Chen X. Characterisation of insulin-resistant phenotype of cultured rat primary adipose cells. Diabetologia 2007; 50:1070-9. [PMID: 17380319 DOI: 10.1007/s00125-007-0626-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Accepted: 01/26/2007] [Indexed: 11/28/2022]
Abstract
AIMS/HYPOTHESIS We characterised insulin resistance, metabolic defects and endocrine dysfunction in cultured adipose cells and examined the autocrine or paracrine roles of cytokines/adipokines in the progression of insulin resistance. MATERIALS AND METHODS Rat primary adipose cells were prepared and cultured for 24 and 48 h. Insulin resistance and gene expression were examined by glucose uptake assay, cDNA microarray and real-time RT-PCR. RESULTS After 24 h in culture, the fold increase of insulin-stimulated glucose uptake in adipose cells was markedly reduced; after 48 h the response of the cells to insulin decreased. cDNA microarray analysis showed that the expression of 514 genes was altered in adipose cells after 24 h in culture. The dysregulated genes included those involved in the citric acid cycle and in fatty acid and pyruvate metabolism. Specifically, the following genes were all downregulated: genes encoding lipolytic and lipogenic enzymes; uncoupling protein 1 and 2 genes; peroxisome proliferator-activated receptor gamma, coactivator 1 alpha gene. This indicates that lipolytic and lipogenic activity, as well as mitochondria capacity decline in adipose cells cultured for 24 h. The mRNAs encoding 40 adipokines were also dysregulated in cultured cells. Strikingly, the dysregulated adipokines in cultured cells and in freshly isolated adipose cells from insulin-resistant Zucker fa/fa rats displayed a similar pattern with regard to protein functions. Also striking was the fact that progression of insulin resistance was promoted by the adipokines secreted from insulin-resistant adipose tissue or cells. CONCLUSIONS/INTERPRETATION Our data demonstrate that the impairment of metabolism and endocrine dysfunction in cultured adipose cells mimics the insulin resistance occurring in vivo. Cytokines and adipokines appear to play a critical role in the progression of insulin resistance in adipose cells.
Collapse
Affiliation(s)
- C C Xiang
- Laboratory of Functional Genomics, J. Craig Venter Institute, Rockville, MD, USA
| | | | | | | | | | | | | | | |
Collapse
|
81
|
Cartwright MJ, Tchkonia T, Kirkland JL. Aging in adipocytes: potential impact of inherent, depot-specific mechanisms. Exp Gerontol 2007; 42:463-71. [PMID: 17507194 PMCID: PMC1961638 DOI: 10.1016/j.exger.2007.03.003] [Citation(s) in RCA: 212] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Revised: 02/28/2007] [Accepted: 03/06/2007] [Indexed: 12/25/2022]
Abstract
Fat mass and tissue distribution change dramatically throughout life. Fat depot sizes reach a peak by middle or early old age, followed by a substantial decline, together with fat tissue dysfunction and redistribution in advanced old age. These changes are associated with health complications, including type 2 diabetes, atherosclerosis, dyslipidemia, thermal dysregulation, and skin ulcers, particularly in advanced old age. Fat tissue growth occurs through increases in size and number of fat cells. Fat cells turn over throughout the lifespan, with new fat cells developing from preadipocytes, which are of mesenchymal origin. The pool of preadipocytes comprises 15-50% of the cells in fat tissue. Since fat tissue turns over throughout life, characteristics of these cells very likely have a significant impact on fat tissue growth, plasticity, function, and distribution. The aims of this review are to highlight recent findings regarding changes in preadipocyte cell dynamics and function with aging, and to consider how inherent characteristics of these cells potentially contribute to age- and depot-dependent changes in fat tissue development and function.
Collapse
Affiliation(s)
- Mark J Cartwright
- Department of Medicine, Section of Geriatrics, Boston University Medical Center, 650 Albany St., Boston, MA 02118, USA
| | | | | |
Collapse
|
82
|
Renaville B, Mullen A, Moloney F, Larondelle Y, Schneider YJ, Roche HM. Eicosapentaenoic acid and 3,10 dithia stearic acid inhibit the desaturation oftrans-vaccenic acid intocis-9,trans-11-conjugated linoleic acid through different pathways in Caco-2 and T84 cells. Br J Nutr 2007; 95:688-95. [PMID: 16571147 DOI: 10.1079/bjn20061717] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Stearoyl-CoA desaturase (SCD) is a key enzyme that determines the composition and metabolic fate of ingested fatty acids, in particular the conversion oftrans-vaccenic acid (TVA) to conjugated linoleic acid (CLA). The present study addressed the hypothesis that intestinal TVA absorption and biotransformation into CLA can be modulated by EPA and 3,10-dithia stearic acid (DSA) via altered SCD mRNA levels and desaturation indices (cis-9,trans-11-CLA:TVA and oleic acid:stearic acid ratios) in Caco-2 and T84 cells, two well-establishedin vitromodels of the human intestinal epithelium. The study determined the effect of acute (3h with 0·3mm-EPA or 0·3mm-DSA) and acute-on-chronic (1 week with 0·03mm-EPA or -DSA, followed by respectively, 0·3mm-EPA or -DSA for 3h) treatments. In both cell lines, acute EPA treatment did not alter SCD desaturation indices, whereas the acute-on-chronic treatment affected these surrogate markers of SCD activity. This was associated with reduced sterol regulatory-element binding protein-1c and SCD mRNA levels. In contrast, acute and acute-on-chronic DSA treatments significantly reduced SCD desaturation indices without affecting SCD mRNA levels in Caco-2 cells. The present study on intestinal cells shows that the conversion rate of TVA to c9, t11-CLA is affected by other fatty acids present in the diet such as EPA, confirming previous observations in hepatic and mammary cell models.
Collapse
Affiliation(s)
- Bénédicte Renaville
- Fisiologia Veterinaria e Nutrizione, Dept Science degli Alimenti, Università degli Studi di Udine, Italy
| | | | | | | | | | | |
Collapse
|
83
|
Felder TK, Oberkofler H, Weitgasser R, Mackevics V, Krempler F, Paulweber B, Patsch W. The SREBF-1 locus is associated with type 2 diabetes and plasma adiponectin levels in a middle-aged Austrian population. Int J Obes (Lond) 2006; 31:1099-103. [PMID: 17160088 DOI: 10.1038/sj.ijo.0803505] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
CONTEXT The sterol regulatory element-binding protein-1c (SREBP-1c) is a transcription factor involved in the regulation of lipid and glucose metabolism and has been implicated in the pathophysiology of type 2 diabetes mellitus (T2DM). OBJECTIVE We aimed to confirm associations of the SREBF-1 gene with T2DM in an Austrian population and to study possible associations with diabetes-related quantitative traits. DESIGN, SETTINGS AND PARTICIPANTS We genotyped a diabetic cohort (n=446) along with a control group (n=1524) for a common C/G variation that is located in exon 18c (rs2297508) and has been associated with obesity and T2DM in French populations. MAIN OUTCOME MEASURES Body mass index (BMI), indices of insulin sensitivity and beta-cell function, plasma adiponectin, T2DM and single-nucleotide polymorphism rs2297508. RESULTS Genotype distributions associated with rs2297508 differed by T2DM status (P=0.0045), but not by BMI. The variant G allele was associated with a modest, but significant, increase in the prevalence of T2DM after adjustment for age, sex and BMI (G/G: odds ratios (OR) (95% confidence intervals)=1.45 (0.99-2.11) and G/C: OR=1.37 (1.04-1.81)). In a cross-sectional population of non-diabetic subjects, associations of rs2297508 genotypes with plasma adiponectin levels adjusted for age, sex and BMI (P=0.0017) were observed in that the risk G/G genotype displayed the lowest adiponectin levels. CONCLUSIONS We observed associations of rs2297508 with T2DM prevalence and plasma adiponectin. SREBP-1c has been implicated in the regulation of adiponectin gene expression. Our results therefore raise the possibility that sequence variations at the SREBF-1 gene locus might contribute to T2DM risk, at least in part, by altering circulating adiponectin levels.
Collapse
Affiliation(s)
- T K Felder
- Department of Laboratory Medicine, Paracelsus Private Medical University, Salzburg, Austria
| | | | | | | | | | | | | |
Collapse
|
84
|
Harding AH, Loos RJF, Luan J, O'Rahilly S, Wareham NJ, Barroso I. Polymorphisms in the gene encoding sterol regulatory element-binding factor-1c are associated with type 2 diabetes. Diabetologia 2006; 49:2642-8. [PMID: 17019602 PMCID: PMC2668914 DOI: 10.1007/s00125-006-0430-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2006] [Accepted: 07/24/2006] [Indexed: 10/24/2022]
Abstract
AIMS/HYPOTHESIS The sterol regulatory element-binding factor (SREBF)-1c is a transcription factor involved in the regulation of lipid and glucose metabolism. We have previously found evidence that a common SREBF1c single-nucleotide polymorphism (SNP), located between exons 18c and 19c, is associated with an increased risk of type 2 diabetes. The present study aimed to replicate our previously reported association in a larger case-control study and to examine an additional five SREBF1c SNPs for their association with diabetes risk and plasma glucose concentrations. METHODS We genotyped six SREBF1c SNPs in two case-control studies (n=1,938) and in a large cohort study (n=1,721) and tested for association with type 2 diabetes and with plasma glucose concentrations (fasting and 120-min post-glucose load), respectively. RESULTS In the case-control studies, carriers of the minor allele of the previously reported SNP (rs11868035) had a significantly increased diabetes risk (odds ratio [OR]=1.20 [95% CI 1.04-1.38], p=0.015). Also, three other SNPs (rs2236513, rs6502618 and rs1889018), located in the 5' region, were significantly associated with diabetes risk (OR > or =1.21, p< or =0.006). Furthermore, two SNPs (rs2236513 and rs1889018) in the 5' region were weakly (p<0.09) associated with plasma glucose concentrations in the cohort study. Rare homozygotes had increased (p< or =0.05) 120-min post-load glucose concentrations compared with carriers of the wild-type allele. Haplotype analyses showed significant (p=0.04) association with diabetes risk and confirmed the single SNP analyses. CONCLUSIONS/INTERPRETATION In summary, we replicated our previous finding and found evidence for SNPs in the 5' region of the SREBF1c gene to be associated with the risk of type 2 diabetes and plasma glucose concentration.
Collapse
|
85
|
Dubois SG, Heilbronn LK, Smith SR, Albu JB, Kelley DE, Ravussin E. Decreased expression of adipogenic genes in obese subjects with type 2 diabetes. Obesity (Silver Spring) 2006; 14:1543-52. [PMID: 17030965 PMCID: PMC2677804 DOI: 10.1038/oby.2006.178] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
OBJECTIVE Our objective was to delineate the potential role of adipogenesis in insulin resistance and type 2 diabetes. Obesity is characterized by an increase in adipose tissue mass resulting from enlargement of existing fat cells (hypertrophy) and/or from increased number of adipocytes (hyperplasia). The inability of the adipose tissue to recruit new fat cells may cause ectopic fat deposition and insulin resistance. RESEARCH METHODS AND PROCEDURES We examined the expression of candidate genes involved in adipocyte proliferation and/or differentiation [CCAAT/enhancer-binding protein (C/EBP) alpha, C/EBPdelta, GATA domain-binding protein 3 (GATA3), C/EBPbeta, peroxisome proliferator-activated receptor (PPAR) gamma2, signal transducer and activator of transcription 5A (STAT5A), Wnt-10b, tumor necrosis factor alpha, sterol regulatory element-binding protein 1c (SREBP1c), 11 beta-hydroxysteroid dehydrogenase, PPARG angiopoietin-related protein (PGAR), insulin-like growth factor 1, PPARgamma coactivator 1alpha, PPARgamma coactivator 1beta, and PPARdelta] in subcutaneous adipose tissue from 42 obese individuals with type 2 diabetes and 25 non-diabetic subjects matched for age and obesity. RESULTS Insulin sensitivity was measured by a 3-hour 80 mU/m2 per minute hyperinsulinemic glucose clamp (100 mg/dL). As expected, subjects with type 2 diabetes had lower glucose disposal (4.9 +/- 1.9 vs. 7.5 +/- 2.8 mg/min per kilogram fat-free mass; p < 0.001) and larger fat cells (0.90 +/- 0.26 vs. 0.78 +/- 0.17 microm; p = 0.04) as compared with obese control subjects. Three genes (SREBP1c, p < 0.01; STAT5A, p = 0.02; and PPARgamma2, p = 0.02) had significantly lower expression in obese type 2 diabetics, whereas C/EBPbeta only tended to be lower (p = 0.07). DISCUSSION This cross-sectional study supports the hypothesis that impaired expression of adipogenic genes may result in impaired adipogenesis, potentially leading to larger fat cells in subcutaneous adipose tissue and insulin resistance.
Collapse
Affiliation(s)
| | | | - Steven R. Smith
- Pennington Biomedical Research Center, Baton Rouge, Louisiana
| | | | - David E. Kelley
- Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Eric Ravussin
- Pennington Biomedical Research Center, Baton Rouge, Louisiana
| | | |
Collapse
|
86
|
Broers JLV, Ramaekers FCS, Bonne G, Yaou RB, Hutchison CJ. Nuclear Lamins: Laminopathies and Their Role in Premature Ageing. Physiol Rev 2006; 86:967-1008. [PMID: 16816143 DOI: 10.1152/physrev.00047.2005] [Citation(s) in RCA: 441] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
It has been demonstrated that nuclear lamins are important proteins in maintaining cellular as well as nuclear integrity, and in maintaining chromatin organization in the nucleus. Moreover, there is growing evidence that lamins play a prominent role in transcriptional control. The family of laminopathies is a fast-growing group of diseases caused by abnormalities in the structure or processing of the lamin A/C ( LMNA) gene. Mutations or incorrect processing cause more than a dozen different inherited diseases, ranging from striated muscular diseases, via fat- and peripheral nerve cell diseases, to progeria. This broad spectrum of diseases can only be explained if the responsible A-type lamin proteins perform multiple functions in normal cells. This review gives an overview of current knowledge on lamin structure and function and all known diseases associated with LMNA abnormalities. Based on the knowledge of the different functions of A-type lamins and associated proteins, explanations for the observed phenotypes are postulated. It is concluded that lamins seem to be key players in, among others, controlling the process of cellular ageing, since disturbance in lamin protein structure gives rise to several forms of premature ageing.
Collapse
Affiliation(s)
- J L V Broers
- Department of Molecular Cell Biology, University of Maastricht, Research Institutes CARIM, GROW, and EURON, The Netherlands
| | | | | | | | | |
Collapse
|
87
|
Nadeau KJ, Ehlers LB, Aguirre LE, Moore RL, Jew KN, Ortmeyer HK, Hansen BC, Reusch JEB, Draznin B. Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride in skeletal muscle. Am J Physiol Endocrinol Metab 2006; 291:E90-8. [PMID: 16449296 DOI: 10.1152/ajpendo.00543.2005] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Intramuscular triglyceride (IMTG) deposition in skeletal muscle is associated with obesity and type 2 diabetes (T2DM) and is thought to be related to insulin resistance (IR). Curiously, despite enhanced skeletal muscle insulin sensitivity, highly trained athletes and calorie-restricted (CR) monkeys also have increased IMTG. Sterol regulatory element-binding proteins (SREBPs) are transcription factors that regulate the biosynthesis of cholesterol and fatty acids. SREBP-1 is increased by insulin in skeletal muscle in vitro and in skeletal muscle of IR subjects, but SREBP-1 expression has not been examined in exercise training or calorie restriction. We examined the relationship between IMTG and SREBP-1 expression in animal models of exercise and calorie restriction. Gastrocnemius and soleus muscle biopsies were obtained from 38 Sprague-Dawley rats (18 control and 20 exercise trained). Triglyceride content was higher in the gastrocnemius and soleus muscles of the trained rats. SREBP-1c mRNA, SREBP-1 precursor and mature proteins, and fatty acid synthase (FAS) protein were increased with exercise training. Monkeys (Macaca mulatta) were CR for a mean of 10.4 years, preventing weight gain and IR. Vastus lateralis muscle was obtained from 12 monkeys (6 CR and 6 controls). SREBP-1 precursor and mature proteins and FAS protein were higher in the CR monkeys. In addition, phosphorylation of ERK1/ERK2 was increased in skeletal muscle of CR animals. In summary, SREBP-1 protein and SREBP-1c mRNA are increased in interventions that increase IMTG despite enhanced insulin sensitivity. CR and exercise-induced augmentation of SREBP-1 expression may be responsible for the increased IMTG seen in skeletal muscle of highly conditioned athletes.
Collapse
Affiliation(s)
- Kristen J Nadeau
- The Children's Hospital, Dept. of Pediatric Endocrinology, Box 265, 1056 East 19th Ave, Denver, CO 80218, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
88
|
Tsintzas K, Jewell K, Kamran M, Laithwaite D, Boonsong T, Littlewood J, Macdonald I, Bennett A. Differential regulation of metabolic genes in skeletal muscle during starvation and refeeding in humans. J Physiol 2006; 575:291-303. [PMID: 16763003 PMCID: PMC1819428 DOI: 10.1113/jphysiol.2006.109892] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
This study investigated the molecular alterations underlying the physiological adaptations to starvation and refeeding in human skeletal muscle. Forty-eight hours' starvation reduced whole-body insulin sensitivity by 42% and produced marked changes in expression of key carbohydrate (CHO) regulatory genes and proteins: SREBP1c and hexokinase II (HKII) were downregulated 2.5- and 5-fold, respectively, whereas the pyruvate dehydrogenase kinase 4 (PDK4) was upregulated 4-fold. These responses were not dependent on the phosphorylation status of Akt and FOXO1. On the other hand, starvation and the concomitant increase in circulating free fatty acids did not upregulate the expression of transcription factors and genes involved in fat metabolism. Twenty-four hours' refeeding with a CHO-rich diet completely reversed the changes in PDK4, HKII and SREBP1c expression in human skeletal muscle but failed to fully restore whole-body insulin sensitivity. Thus, during starvation in healthy humans, unlike rodents, regulation of fat metabolism does not require an adaptive response at transcriptional level, but adaptive changes in gene expression are required to switch off oxidative glucose disposal. Lack of effect on key proteins in the insulin-signalling pathway may indicate that changes in intracellular substrate availability/flux may be responsible for these adaptive changes in glucose metabolism. This may represent an important aspect of the molecular basis of the development of insulin resistance in metabolic conditions characterized by energy restriction.
Collapse
Affiliation(s)
- Kostas Tsintzas
- Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, University of Nottingham, Nottingham NG7 2UH, UK.
| | | | | | | | | | | | | | | |
Collapse
|
89
|
Abstract
The safest place to store lipids is the white adipose tissue, but its storage capacity may become saturated resulting in excess of fat "overspilled" to non-adipose tissues. This overspill of fat occurs in apparently opposite pathological states such as lipodistrophy or obesity. When the excess of energy is redirected towards peripheral organs, their initial response is to facilitate the storage of the surplus in the form of triacylglycerol, but the limited triacylglycerol buffer capacity becomes saturated soon. Under these conditions excess of lipids enter alternative non-oxidative pathways that result in production of toxic reactive lipid species that induce organ-specific toxic responses leading to apoptosis. Reactive lipids can accumulate in non-adipose tissues of metabolically relevant organs such as pancreatic beta-cells, liver, heart and skeletal muscle leading to lipotoxicity, a process that contributes substantially to the pathophysiology of insulin resistance, type 2 diabetes, steatotic liver disease and heart failure. The effects of this lipotoxic insult can be minimised by several strategies: (a) decreased incorporation of energy, (b) a less orthodox approach such as increased adipose tissue expandability and/or (c) increased oxidation of fat in peripheral organs. Aging should be considered as physiological degenerative process potentially accelerated by concomitant lipotoxic insults. Conversely, the process of aging can sensitise cells to effects of lipid toxicity.
Collapse
Affiliation(s)
- Marc Slawik
- Department of Clinical Biochemistry, University of Cambridge, UK
| | | |
Collapse
|
90
|
Sugden MC, Holness MJ. Skeletal muscle lipid metabolism and the adipomuscular axis. ACTA ACUST UNITED AC 2006. [DOI: 10.2217/17460875.1.2.153] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
91
|
Avramoglu RK, Basciano H, Adeli K. Lipid and lipoprotein dysregulation in insulin resistant states. Clin Chim Acta 2006; 368:1-19. [PMID: 16480697 DOI: 10.1016/j.cca.2005.12.026] [Citation(s) in RCA: 188] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Revised: 12/15/2005] [Accepted: 12/20/2005] [Indexed: 12/30/2022]
Abstract
Insulin resistant states are commonly associated with an atherogenic dyslipidemia that contributes to significantly higher risk of atherosclerosis and cardiovascular disease. Indeed, disorders of carbohydrate and lipid metabolism co-exist in the majority of subjects with the "metabolic syndrome" and form the basis for the definition and diagnosis of this complex syndrome. The most fundamental defect in these patients is resistance to cellular actions of insulin, particularly resistance to insulin-stimulated glucose uptake. Insulin insensitivity appears to cause hyperinsulinemia, enhanced hepatic gluconeogenesis and glucose output, reduced suppression of lipolysis in adipose tissue leading to a high free fatty acid flux, and increased hepatic very low density lipoprotein (VLDL) secretion causing hypertriglyceridemia and reduced plasma levels of high density lipoprotein (HDL) cholesterol. Although the link between insulin resistance and dysregulation of lipoprotein metabolism is well established, a significant gap of knowledge exists regarding the underlying cellular and molecular mechanisms. Emerging evidence suggests that insulin resistance and its associated metabolic dyslipidemia result from perturbations in key molecules of the insulin signaling pathway, including overexpression of key phosphatases, downregulation and/or activation of key protein kinase cascades, leading to a state of mixed hepatic insulin resistance and sensitivity. These signaling changes in turn cause an increased expression of sterol regulatory element binding protein (SREBP) 1c, induction of de novo lipogensis and higher activity of microsomal triglyceride transfer protein (MTP), which together with high exogenous free fatty acid (FFA) flux collectively stimulate the hepatic production of apolipoprotein B (apoB)-containing VLDL particles. VLDL overproduction underlies the high triglyceride/low HDL-cholesterol lipid profile commonly observed in insulin resistant subjects.
Collapse
Affiliation(s)
- Rita Kohen Avramoglu
- Clinical Biochemistry Division, Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada M5G 1X8
| | | | | |
Collapse
|
92
|
Jones SP, Qazi N, Morelese J, Lebrecht D, Sutinen J, Yki-Jărvinen H, Back DJ, Pirmohamed M, Gazzard BG, Walker UA, Moyle GJ. Assessment of adipokine expression and mitochondrial toxicity in HIV patients with lipoatrophy on stavudine- and zidovudine-containing regimens. J Acquir Immune Defic Syndr 2006; 40:565-72. [PMID: 16284533 DOI: 10.1097/01.qai.0000187443.30838.3e] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
OBJECTIVES Despite evidence for the role of adipokines such as adiponectin in the metabolic toxicities of protease inhibitor (PI)-treated patients, little is known about their role in nucleoside reverse transcriptase inhibitor (NRTI)-induced lipoatrophy (LA). We analyzed the relations between mitochondrial toxicity, adipokine expression, and clinical LA in peripheral blood mononuclear cells (PBMCs) and adipose samples from individuals treated with stavudine (d4T) or zidovudine (ZDV) in comparison to patients undergoing highly active antiretroviral therapy (HAART) as well as HIV-negative individuals. METHODS In this cross-sectional analysis, we studied 18 PI-naive HIV-infected patients with LA treated with d4T (d4T+LA+ [n = 12]) or zidovudine (ZDV+LA+ [n = 6]) in comparison to HAART-treated patients with (HAART+LA+ [n = 8]) and without (HAART+LA- [n = 8]) LA as well as HIV-negative controls (n = 12). Adipose samples were assessed for protein and/or messenger RNA (mRNA) levels of adiponectin, tumor necrosis factor-alpha (TNFalpha), interleukin (IL)-6, and sterol regulatory element-binding protein (SREBP) 1a/c in all groups, whereas adipose and PBMC samples from the d4T+LA+, ZDV+LA+, and HIV-negative subgroups were assessed for mitochondrial DNA (mtDNA) depletion and cytochrome c-oxidase (COX) II/COX IV ratios. RESULTS There was no change in mtDNA levels in adipose or PBMC samples in NRTI-treated patients with LA, although patients treated with d4T had reduced COX II/COX IV ratios in adipose and PBMC samples. Adipose tissue adiponectin mRNA and plasma levels were reduced in the d4T- and ZDV-treated patients regardless of the use of PIs. Tissue SREBP1c mRNA levels were also significantly reduced in both NRTI groups when compared with the HIV-negative controls. Significant reductions in SREBP1c levels were also evident with the HAART+LA+ group when compared with HAART+LA- controls. CONCLUSIONS Patients with LA on d4T-based regimens show evidence of mitochondrial respiratory chain dysfunction, whereas the d4T- and ZDV-based regimens also demonstrated reduced SREBP1c and adiponectin levels, findings that have previously been shown with PIs.
Collapse
Affiliation(s)
- Simon P Jones
- Department of Pharmacology and Therapeutics, University of Liverpool, Liverpool, United Kingdom
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
93
|
Kelley GL, Azhar S. Reversal of high dietary fructose-induced PPARalpha suppression by oral administration of lipoxygenase/cyclooxygenase inhibitors. Nutr Metab (Lond) 2005; 2:18. [PMID: 16091142 PMCID: PMC1188072 DOI: 10.1186/1743-7075-2-18] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2005] [Accepted: 08/09/2005] [Indexed: 12/11/2022] Open
Abstract
High fructose feeding causes diet-induced alterations of lipid metabolism and decreased insulin sensitivity, hallmark of which is a rapid and profound hypertriglyceridemia. One of the mechanisms that contribute to serum hypertriglyceridemia in this model is suppression of hepatic PPARα. HMG-CoA inhibitors, which reduce serum triglycerides in these animals, also elevate/restore hepatic PPARα. Previously we demonstrated that two known lipoxygenase/cyclooxygenase inhibitors reversed diet-induced hypertriglyceridemia in this model and that reversal of certain inflammatory markers in the liver correlated with the metabolic benefit. In this paper we extended these studies by examining the impact of these compounds on expression of PPARα, both at the level of transcription and expression. Our data show that diet-induced suppression of hepaic PPARα is reversed upon treatment with lipoxygenase/cyclooxygenase compounds. We then tested one of these compounds, BW-755c, over a range of doses from 10 mg/kg to 100 mg/kg to establish a dose-response relationship with the reduction of serum hypertriglyceridemia in this model. These experiments support the concept of using anti-inflammatory medications as one method to correct metabolic dysfunction.
Collapse
Affiliation(s)
| | - Salman Azhar
- Geriatric Research, Education and Clinical Center, VA Palo Alto Health Care System & Stanford University School of Medicine, Palo Alto, CA, USA
| |
Collapse
|
94
|
Dulloo AG, Gubler M, Montani JP, Seydoux J, Solinas G. Substrate cycling between de novo lipogenesis and lipid oxidation: a thermogenic mechanism against skeletal muscle lipotoxicity and glucolipotoxicity. Int J Obes (Lond) 2005; 28 Suppl 4:S29-37. [PMID: 15592483 DOI: 10.1038/sj.ijo.0802861] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Life is a combustion, but how the major fuel substrates that sustain human life compete and interact with each other for combustion has been at the epicenter of research into the pathogenesis of insulin resistance ever since Randle proposed a 'glucose-fatty acid cycle' in 1963. Since then, several features of a mutual interaction that is characterized by both reciprocality and dependency between glucose and lipid metabolism have been unravelled, namely: the inhibitory effects of elevated concentrations of fatty acids on glucose oxidation (via inactivation of mitochondrial pyruvate dehydrogenase or via desensitization of insulin-mediated glucose transport),the inhibitory effects of elevated concentrations of glucose on fatty acid oxidation (via malonyl-CoA regulation of fatty acid entry into the mitochondria), and more recentlythe stimulatory effects of elevated concentrations of glucose on de novo lipogenesis, that is, synthesis of lipids from glucose (via SREBP1c regulation of glycolytic and lipogenic enzymes). This paper first revisits the physiological significance of these mutual interactions between glucose and lipids in skeletal muscle pertaining to both blood glucose and intramyocellular lipid homeostasis. It then concentrates upon emerging evidence, from calorimetric studies investigating the direct effect of leptin on thermogenesis in intact skeletal muscle, of yet another feature of the mutual interaction between glucose and lipid oxidation: that of substrate cycling between de novo lipogenesis and lipid oxidation. It is proposed that this energy-dissipating substrate cycling that links glucose and lipid metabolism to thermogenesis could function as a 'fine-tuning' mechanism that regulates intramyocellular lipid homeostasis, and hence contributes to the protection of skeletal muscle against lipotoxicity.
Collapse
Affiliation(s)
- A G Dulloo
- Department of Medicine, Division of Physiology, University of Fribourg, Switzerland.
| | | | | | | | | |
Collapse
|
95
|
Basciano H, Federico L, Adeli K. Fructose, insulin resistance, and metabolic dyslipidemia. Nutr Metab (Lond) 2005; 2:5. [PMID: 15723702 PMCID: PMC552336 DOI: 10.1186/1743-7075-2-5] [Citation(s) in RCA: 530] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Accepted: 02/21/2005] [Indexed: 12/31/2022] Open
Abstract
Obesity and type 2 diabetes are occurring at epidemic rates in the United States and many parts of the world. The "obesity epidemic" appears to have emerged largely from changes in our diet and reduced physical activity. An important but not well-appreciated dietary change has been the substantial increase in the amount of dietary fructose consumption from high intake of sucrose and high fructose corn syrup, a common sweetener used in the food industry. A high flux of fructose to the liver, the main organ capable of metabolizing this simple carbohydrate, perturbs glucose metabolism and glucose uptake pathways, and leads to a significantly enhanced rate of de novo lipogenesis and triglyceride (TG) synthesis, driven by the high flux of glycerol and acyl portions of TG molecules from fructose catabolism. These metabolic disturbances appear to underlie the induction of insulin resistance commonly observed with high fructose feeding in both humans and animal models. Fructose-induced insulin resistant states are commonly characterized by a profound metabolic dyslipidemia, which appears to result from hepatic and intestinal overproduction of atherogenic lipoprotein particles. Thus, emerging evidence from recent epidemiological and biochemical studies clearly suggests that the high dietary intake of fructose has rapidly become an important causative factor in the development of the metabolic syndrome. There is an urgent need for increased public awareness of the risks associated with high fructose consumption and greater efforts should be made to curb the supplementation of packaged foods with high fructose additives. The present review will discuss the trends in fructose consumption, the metabolic consequences of increased fructose intake, and the molecular mechanisms leading to fructose-induced lipogenesis, insulin resistance and metabolic dyslipidemia.
Collapse
Affiliation(s)
- Heather Basciano
- Clinical Biochemistry Division, Department of Laboratory Medicine and Pathobiology, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Lisa Federico
- Clinical Biochemistry Division, Department of Laboratory Medicine and Pathobiology, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| | - Khosrow Adeli
- Clinical Biochemistry Division, Department of Laboratory Medicine and Pathobiology, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
96
|
Lelliott C, Vidal-Puig AJ. Lipotoxicity, an imbalance between lipogenesis de novo and fatty acid oxidation. Int J Obes (Lond) 2004; 28 Suppl 4:S22-8. [PMID: 15592482 DOI: 10.1038/sj.ijo.0802854] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Obesity and type 2 diabetes mellitus are the major noncommunicable public health problem of the 21st century. The best strategy to tackle this problem is to develop strategies to prevent/treat obesity. However, it is becoming clear that despite successful research identifying weight regulatory pathways, the development of the obesity epidemic is outpacing scientific progress. The lack of success controlling the obesity epidemic in an aging population will result in another subsequent uncontrolled epidemic of complications. Our research focuses on the mechanisms causing lipotoxicity aiming to identify suitable strategies to prevent or at least retard the development of the metabolic syndrome. Previous work using transgenic and knockout mouse models has shown an interplay between white adipose tissue and skeletal muscle linking fatty acid (FA) synthesis with reciprocal effects on FA oxidation. Work from our lab and others suggests that defective adipose tissue is a key link between obesity, insulin resistance and type 2 diabetes mellitus by promoting the development of lipotoxicity in peripheral tissues. We propose a series of models to describe the process by which the adipose tissue could react to an energy-rich environment and responds depending on genetic and physiological factors, impacting on the functions of other peripheral tissues. We suggest that by examining hypotheses that encompass multiple organs and the partitioning of energy between these organs, a suitable strategy can be devised for the treatment of chronic obesity.
Collapse
Affiliation(s)
- C Lelliott
- Department of Clinical Biochemistry and Medicine, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK
| | | |
Collapse
|
97
|
von Eyben FE, Kroustrup JP, Larsen JF, Celis J. Comparison of Gene Expression in Intra-Abdominal and Subcutaneous Fat: A Study of Men with Morbid Obesity and Nonobese Men Using Microarray and Proteomics. Ann N Y Acad Sci 2004; 1030:508-36. [PMID: 15659836 DOI: 10.1196/annals.1329.063] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Extent of intra-abdominal fat had significant linear relations with six metabolic coronary risk factors: systolic and diastolic blood pressure, fasting blood concentrations of glucose, high density lipoprotein (HDL) cholesterol, triglyceride, and plasminogen activator inhibitor-1. Tumor necrosis factor-alpha and adiponectin can be biological mediators from the intra-abdominal fat to the metabolic coronary risk factors. Complementarily, we describe a new study that will analyze the gene expression in intra-abdominal and subcutaneous fat on mRNA and protein level using high throughput methods. The study will elucidate further whether intra-abdominal obesity is the common denominator for the different components of the metabolic syndrome.
Collapse
|
98
|
Eberlé D, Hegarty B, Bossard P, Ferré P, Foufelle F. SREBP transcription factors: master regulators of lipid homeostasis. Biochimie 2004; 86:839-48. [PMID: 15589694 DOI: 10.1016/j.biochi.2004.09.018] [Citation(s) in RCA: 1050] [Impact Index Per Article: 52.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2004] [Accepted: 09/27/2004] [Indexed: 02/08/2023]
Abstract
Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate lipid homeostasis by controlling the expression of a range of enzymes required for endogenous cholesterol, fatty acid (FA), triacylglycerol and phospholipid synthesis. The three SREBP isoforms, SREBP-1a, SREBP-1c and SREBP-2, have different roles in lipid synthesis. In vivo studies using transgenic and knockout mice suggest that SREBP-1c is involved in FA synthesis and insulin induced glucose metabolism (particularly in lipogenesis), whereas SREBP-2 is relatively specific to cholesterol synthesis. The SREBP-1a isoform seems to be implicated in both pathways. SREBP transcription factors are synthetized as inactive precursors bound to the endoplasmic reticulum (ER) membranes. Upon activation, the precursor undergoes a sequential two-step cleavage process to release the NH(2)-terminal active domain in the nucleus (designated nSREBPs). SREBP processing is mainly controlled by cellular sterol content. When sterol levels decrease, the precursor is cleaved to activate cholesterogenic genes and maintain cholesterol homeostasis. This sterol-sensitive process appears to be a major point of regulation for the SREBP-1a and SREBP-2 isoforms but not for SREBP-1c. Moreover, the SREBP-1c isoform seems to be mainly regulated at the transcriptional level by insulin. The unique regulation and activation properties of each SREBP isoform facilitate the co-ordinate regulation of lipid metabolism; however, further studies are needed to understand the detailed regulation pathways that specifically regulate each SREBP isoform.
Collapse
Affiliation(s)
- Delphine Eberlé
- Inserm U465, Université Pierre et Marie Curie, 15, rue de l'Ecole de médecine, 75270 Paris cedex 06, France
| | | | | | | | | |
Collapse
|
99
|
Eberlé D, Clément K, Meyre D, Sahbatou M, Vaxillaire M, Le Gall A, Ferré P, Basdevant A, Froguel P, Foufelle F. SREBF-1 gene polymorphisms are associated with obesity and type 2 diabetes in French obese and diabetic cohorts. Diabetes 2004; 53:2153-7. [PMID: 15277400 DOI: 10.2337/diabetes.53.8.2153] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Sterol regulatory element-binding protein (SREBP)-1 transcription factors play a central role in energy homeostasis by promoting glycolysis, lipogenesis, and adipogenesis. The sterol regulatory element-binding protein gene (SREBF)-1 is a good candidate gene for obesity and obesity-related metabolic traits such as type 2 diabetes and dyslipidemia. The SREBF-1 molecular screening of 40 unrelated obese patients by PCR/single-strand conformation polymorphism revealed 19 single nucleotide polymorphisms (SNPs). Six SNPs were genotyped for an association study in large French obese and nonobese cohorts. Case-control studies using two independent nonobese cohorts indicated that SNP17 (54G/C, exon 18c) is associated with morbid obesity (odds ratio 1.5, P = 0.006 and P = 0.02, respectively). SNP3 (-150G/A, exon 1a), SNP5 (-36delG, exon 1a), and SNP17 are found in high linkage disequilibrium (D' > 0.8). The haplotype including wild-type alleles of these SNPs (C/G/G/T/C/G, HAP2) is identified as a risk factor for morbid obesity (P = 0.003). In the obese group, SNP3, SNP5, and SNP17 are associated with male-specific hypertriglyceridemia (P = 0.07, P = 0.01, and P = 0.05, respectively). SNP17 is also associated with type 2 diabetes (P = 0.03) and increased prevalence of nephropathy (P = 0.028) in a diabetic cohort. Our results indicate a role of the SREBF-1 gene in genetic predisposition of metabolic diseases such as obesity, type 2 diabetes, and dyslipidemia.
Collapse
Affiliation(s)
- Delphine Eberlé
- INSERM Unit 465, University Pierre et Marie Curie, Paris, France
| | | | | | | | | | | | | | | | | | | |
Collapse
|
100
|
Nadeau KJ, Leitner JW, Gurerich I, Draznin B. Insulin Regulation of Sterol Regulatory Element-binding Protein-1 Expression in L-6 Muscle Cells and 3T3 L1 Adipocytes. J Biol Chem 2004; 279:34380-7. [PMID: 15187085 DOI: 10.1074/jbc.m403596200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sterol regulatory element-binding proteins (SREBPs) are transcription factors that regulate enzymes required for cholesterol and fatty acid synthesis. Expression of SREBP-1 is enhanced by insulin; however, the actual insulin-signaling cascades employed are yet unclear. We determined the roles of the phosphatidylinositol (PI) 3-kinase and mitogen-activated protein (MAP) kinase-dependent pathways in the effect of mediating insulin on SREBP-1 in L-6 skeletal muscle cells and 3T3 L1 adipocytes, using wortmannin or LY294002 to inhibit the PI 3-kinase pathway, and PD98059 to inhibit the MAP kinase-dependent pathway. In myocytes, insulin increased SREBP-1 protein in a dose-dependent manner. 1 and 10 nm insulin significantly increased expression of total cellular SREBP-1 protein at 24 and 48 h, nuclear SREBP-1 protein at 24 h, and SREBP-1a mRNA at 24 h. Although wortmannin and LY294002 had no effect on this aspect of insulin action, PD98059 completely blocked each of these responses. Transfection of a dominant negative mutant of Ras similarly blocked the insulin effect on SREBP-1. In contrast, in adipocytes, the insulin effect on SREBP-1 was mediated via the PI 3-kinase and not the MAP kinase pathway. In conclusion, although insulin increases skeletal muscle SREBP-1 expression in a dose-dependent fashion via the MAP kinase-dependent signaling pathway, insulin action on adipocyte SREBP-1 is mediated via the PI 3-kinase signaling pathway. In the state of insulin resistance, characterized by selective inhibition of the PI 3-kinase pathway, the usual stimulation of lipogenesis by insulin in adipocytes may be inhibited, whereas intramyocellular lipogenesis via the MAP kinase pathway of insulin may continue unabated.
Collapse
Affiliation(s)
- Kristen J Nadeau
- Division of Pediatric Endocrinology, Department of Pediatrics, University of Colorado Health Sciences Center, 1056 East 19th Avenue, Denver, CO 80218, USA.
| | | | | | | |
Collapse
|