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Wattanavanitchakorn S, Rojvirat P, Chavalit T, MacDonald MJ, Jitrapakdee S. CCAAT-enhancer binding protein-α (C/EBPα) and hepatocyte nuclear factor 4α (HNF4α) regulate expression of the human fructose-1,6-bisphosphatase 1 (FBP1) gene in human hepatocellular carcinoma HepG2 cells. PLoS One 2018; 13:e0194252. [PMID: 29566023 PMCID: PMC5863999 DOI: 10.1371/journal.pone.0194252] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 02/27/2018] [Indexed: 11/19/2022] Open
Abstract
Fructose-1,6-bisphosphatase (FBP1) plays an essential role in gluconeogenesis. Here we report that the human FBP1 gene is regulated by two liver-enriched transcription factors, CCAAT-enhancer binding protein-α (C/EBPα) and hepatocyte nuclear factor 4α (HNF4α) in human hepatoma HepG2 cells. C/EBPα regulates transcription of FBP1 gene via binding to the two overlapping C/EBPα sites located at nucleotide -228/-208 while HNF4α regulates FBP1 gene through binding to the classical H4-SBM site and direct repeat 3 (DR3) located at nucleotides -566/-554 and -212/-198, respectively. Mutations of these transcription factor binding sites result in marked decrease of C/EBPα- or HNF4α-mediated transcription activation of FBP1 promoter-luciferase reporter expression. Electrophoretic mobility shift assays of -228/-208 C/EBPα or -566/-554 and -212/-198 HNF4α sites with nuclear extract of HepG2 cells overexpressing C/EBPα or HNF4α confirms binding of these two transcription factors to these sites. Finally, we showed that siRNA-mediated suppression of C/EBPα or HNF4α expression in HepG2 cells lowers expression of FBP1 in parallel with down-regulation of expression of other gluconeogenic enzymes. Our results suggest that an overall gluconeogenic program is regulated by these two transcription factors, enabling transcription to occur in a liver-specific manner.
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Affiliation(s)
| | - Pinnara Rojvirat
- Division of Interdisciplinary, Mahidol University, Kanjanaburi, Thailand
| | - Tanit Chavalit
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Michael J. MacDonald
- Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States of America
| | - Sarawut Jitrapakdee
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand
- * E-mail:
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Abstract
Liver fructose-1,6-bisphosphatase (FBPase) is a regulatory enzyme in gluconeogenesis that is elevated by obesity and dietary fat intake. Whether FBPase functions only in glucose metabolism or has other metabolic roles is currently unclear. In our recently published study, we examined the importance of liver FBPase in body weight regulation by performing a series of comprehensive physiological and biochemical assessments of energy balance and specific intervention studies in our transgenic mouse line that overexpresses FBPase specifically in the liver. Compared with negative littermates, these FBPase transgenic mice weighed 10% less, had 50% less adiposity, ate 15% less food but did not have altered energy expenditure. Increased circulating leptin and cholecystokinin levels, elevated fatty acid oxidation and reduced appetite stimulating neuropeptides, neuropeptide Y (NPY) and agouti-related peptide (AGRP), underpinned this phenotype. Blocking the action of FBPase returned food intake and body weight to those of the negative littermates. Our study is the first to identify liver FBPase as a previously unknown regulator of appetite and adiposity. Importantly, this work recognizes the liver as an important organ in appetite and body weight regulation. This commentary will provide further insight and expand on this novel concept that the liver does in fact play an important role in adiposity.
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Visinoni S, Khalid NFI, Joannides CN, Shulkes A, Yim M, Whitehead J, Tiganis T, Lamont BJ, Favaloro JM, Proietto J, Andrikopoulos S, Fam BC. The role of liver fructose-1,6-bisphosphatase in regulating appetite and adiposity. Diabetes 2012; 61:1122-32. [PMID: 22517657 PMCID: PMC3331739 DOI: 10.2337/db11-1511] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Liver fructose-1,6-bisphosphatase (FBPase) is a regulatory enzyme in gluconeogenesis that is elevated by obesity and dietary fat intake. Whether FBPase functions only to regulate glucose or has other metabolic consequences is not clear; therefore, the aim of this study was to determine the importance of liver FBPase in body weight regulation. To this end we performed comprehensive physiologic and biochemical assessments of energy balance in liver-specific transgenic FBPase mice and negative control littermates of both sexes. In addition, hepatic branch vagotomies and pharmacologic inhibition studies were performed to confirm the role of FBPase. Compared with negative littermates, liver-specific FBPase transgenic mice had 50% less adiposity and ate 15% less food but did not have altered energy expenditure. The reduced food consumption was associated with increased circulating leptin and cholecystokinin, elevated fatty acid oxidation, and 3-β-hydroxybutyrate ketone levels, and reduced appetite-stimulating neuropeptides, neuropeptide Y and Agouti-related peptide. Hepatic branch vagotomy and direct pharmacologic inhibition of FBPase in transgenic mice both returned food intake and body weight to the negative littermates. This is the first study to identify liver FBPase as a previously unknown regulator of appetite and adiposity and describes a novel process by which the liver participates in body weight regulation.
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Affiliation(s)
- Sherley Visinoni
- Department of Medicine, University of Melbourne, Heidelberg, Victoria, Australia
| | | | | | - Arthur Shulkes
- Department of Surgery, Austin Health, University of Melbourne, Heidelberg, Victoria, Australia
| | - Mildred Yim
- Department of Surgery, Austin Health, University of Melbourne, Heidelberg, Victoria, Australia
| | - Jon Whitehead
- Mater Medical Research Institute, Brisbane, Queensland, Australia
| | - Tony Tiganis
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Benjamin J. Lamont
- Department of Medicine, University of Melbourne, Heidelberg, Victoria, Australia
| | - Jenny M. Favaloro
- Department of Medicine, University of Melbourne, Heidelberg, Victoria, Australia
| | - Joseph Proietto
- Department of Medicine, University of Melbourne, Heidelberg, Victoria, Australia
| | | | - Barbara C. Fam
- Department of Medicine, University of Melbourne, Heidelberg, Victoria, Australia
- Corresponding author: Barbara C. Fam,
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Wong N, Fam BC, Cempako GR, Steinberg GR, Walder K, Kay TW, Proietto J, Andrikopoulos S. Deficiency in interferon-gamma results in reduced body weight and better glucose tolerance in mice. Endocrinology 2011; 152:3690-9. [PMID: 21791564 DOI: 10.1210/en.2011-0288] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Obesity is a chronic low-grade inflammatory disease caused by increased energy intake and reduced energy expenditure. Studies using animal models with deletion of inflammatory cytokines have produced conflicting results with some showing increased weight gain and others showing no effect or even reduced body weights. Clearly, more work is necessary to understand the role of cytokines on body weight control. The aim of this study was to determine the effect of interferon-γ deletion (IFNγ(-/-)) on body weight regulation and glucose metabolism. Male IFNγ(-/-) and wild-type C57BL/6 mice were fed a low-fat chow diet, and body weight, food intake, and energy expenditure were monitored over 20 wk. At the end of the study, ip glucose tolerance test, insulin tolerance test, basal glucose turnover, and hyperinsulinemic/euglycemic clamps were performed. Expression levels of arcuate nucleus neuropeptide Y, Agouti-related peptide, and proopiomelanocortin mRNA as well as circulating leptin levels were also determined. IFNγ(-/-) mice had improved glucose tolerance with reduced rate of glucose appearance and increased insulin sensitivity due to greater suppression of endogenous glucose output, which was associated with decreased hepatic glucose-6-phosphatase activity. In addition, we also observed reduced body weight associated with decreased food intake and increased physical activity. Neuropeptide Y and Agouti-related peptide mRNA expression was reduced, whereas proopiomelanocortin mRNA expression was increased, as were plasma leptin levels. Global deletion of IFNγ in mice resulted in reduced body weight associated with negative energy balance, improved glucose tolerance, and hepatic insulin sensitivity. Our findings demonstrate that IFNγ plays a critical role in the regulation of body weight and glucose metabolism.
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Affiliation(s)
- Nicole Wong
- University of Melbourne, Department of Medicine (Austin Health and Northern Health), Heidelberg Repatriation Hospital, 300 Waterdale Road, Heidelberg Heights, Victoria 3081, Australia.
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Fructose-1, 6-bisphosphatase inhibitors for reducing excessive endogenous glucose production in type 2 diabetes. Handb Exp Pharmacol 2011:279-301. [PMID: 21484576 DOI: 10.1007/978-3-642-17214-4_12] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Fructose-1,6-bisphosphatase (FBPase), a rate-controlling enzyme of gluconeogenesis, has emerged as an important target for the treatment of type 2 diabetes due to the well-recognized role of excessive endogenous glucose production (EGP) in the hyperglycemia characteristic of the disease. Inhibitors of FBPase are expected to fulfill an unmet medical need because the majority of current antidiabetic medications act primarily on insulin resistance or insulin insufficiency and do not reduce gluconeogenesis effectively or in a direct manner. Despite significant challenges, potent and selective inhibitors of FBPase targeting the allosteric site of the enzyme were identified by means of a structure-guided design strategy that used the natural inhibitor, adenosine monophosphate (AMP), as the starting point. Oral delivery of these anionic FBPase inhibitors was enabled by a novel diamide prodrug class. Treatment of diabetic rodents with CS-917, the best characterized of these prodrugs, resulted in a reduced rate of gluconeogenesis and EGP. Of note, inhibition of gluconeogenesis by CS-917 led to the amelioration of both fasting and postprandial hyperglycemia without weight gain, incidence of hypoglycemia, or major perturbation of lactate or lipid homeostasis. Furthermore, the combination of CS-917 with representatives of the insulin sensitizer or insulin secretagogue drug classes provided enhanced glycemic control. Subsequent clinical evaluations of CS-917 revealed a favorable safety profile as well as clinically meaningful reductions in fasting glucose levels in patients with T2DM. Future trials of MB07803, a second generation FBPase inhibitor with improved pharmacokinetics, will address whether this novel class of antidiabetic agents can provide safe and long-term glycemic control.
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Kim EJ, Kim E, Kwon EY, Jang HS, Hur CG, Choi MS. Network analysis of hepatic genes responded to high-fat diet in C57BL/6J mice: nutrigenomics data mining from recent research findings. J Med Food 2010; 13:743-56. [PMID: 20553184 DOI: 10.1089/jmf.2009.1350] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Obesity and its associated complications, including diabetes, dyslipidemia, atherosclerosis, and some cancers, have been a global health problem with a rapid increase of the obese population. In this study, we selected 31 obesity candidate genes in the liver of high-fat-induced obese C57BL/6J mice through investigation of literature search and analyzed functional protein-protein interaction of the genes using the STRING database. Most of the obesity candidate genes were closely connected through lipid metabolism, and in particular acyl-coenzyme A oxidase 1 appeared to be a core obesity gene. Overall, genes involved in fatty acid beta-oxidation, fatty acid synthesis, and gluconeogenesis were up-regulated, and genes involved in sterol biosynthesis, insulin signaling, and oxidative stress defense system were down-regulated with a high-fat diet. Future identification of core obesity genes and their functional targets is expected to provide a new way to prevent obesity by phytochemicals or functional foods on the basis of food and nutritional genomics.
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Affiliation(s)
- Eun Jung Kim
- Department of Food Science and Nutrition, Food and Nutritional Genomics Research Center, Kyungpook National University, Daegu, Republic of Korea
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Andrikopoulos S. Obesity and type 2 diabetes: slow down!--Can metabolic deceleration protect the islet beta cell from excess nutrient-induced damage? Mol Cell Endocrinol 2010; 316:140-6. [PMID: 19815054 DOI: 10.1016/j.mce.2009.09.031] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2009] [Revised: 09/08/2009] [Accepted: 09/28/2009] [Indexed: 01/09/2023]
Abstract
Islet beta-cell dysfunction is a characteristic and the main cause of hyperglycaemia of Type 2 diabetes. Understanding the mechanisms that cause beta-cell dysfunction will lead to better therapeutic outcomes for patients with Type 2 diabetes. Chronic fatty acid exposure of susceptible islet beta-cells causes dysfunction and death and this is associated with increased reactive oxygen species production leading to oxidative stress and increased endoplasmic reticulum stress. We present the hypothesis that metabolic deceleration can reduce both oxidative and endoplasmic reticulum stress and lead to improved beta-cell function and viability when exposed to a deleterious fat milieu. This is illustrated by the C57BL/6J mouse which is characterised by reduced insulin secretion and glucose intolerance associated with a mutation in nicotinamide nucleotide transhydrogenase (Nnt) but is resistant to obesity induced diabetes. On the other hand the DBA/2 mouse has comparatively higher insulin secretion and better glucose tolerance associated with increased Nnt activity but is susceptible to obesity-induced diabetes, possibly as a result of increased oxidative stress. We therefore suggest that in states of excess nutrient load, a reduced ability to metabolise this load may protect both the function and viability of beta-cells. Strategies that reduce metabolic flux when beta-cells are exposed to nutrient excess need to be considered when treating Type 2 diabetes.
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Affiliation(s)
- S Andrikopoulos
- Department of Medicine (AH/NH), University of Melbourne, Heidelberg Repatriation Hospital, Heidelberg Heights, Victoria, Australia.
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Kebede M, Favaloro J, Gunton JE, Laybutt DR, Shaw M, Wong N, Fam BC, Aston-Mourney K, Rantzau C, Zulli A, Proietto J, Andrikopoulos S. Fructose-1,6-bisphosphatase overexpression in pancreatic beta-cells results in reduced insulin secretion: a new mechanism for fat-induced impairment of beta-cell function. Diabetes 2008; 57:1887-95. [PMID: 18375435 PMCID: PMC2453625 DOI: 10.2337/db07-1326] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2007] [Accepted: 03/23/2008] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme that is upregulated in islets or pancreatic beta-cell lines exposed to high fat. However, whether specific beta-cell upregulation of FBPase can impair insulin secretory function is not known. The objective of this study therefore is to determine whether a specific increase in islet beta-cell FBPase can result in reduced glucose-mediated insulin secretion. RESEARCH DESIGN AND METHODS To test this hypothesis, we have generated three transgenic mouse lines overexpressing the human FBPase (huFBPase) gene specifically in pancreatic islet beta-cells. In addition, to investigate the biochemical mechanism by which elevated FBPase affects insulin secretion, we made two pancreatic beta-cell lines (MIN6) stably overexpressing huFBPase. RESULTS FBPase transgenic mice showed reduced insulin secretion in response to an intravenous glucose bolus. Compared with the untransfected parental MIN6, FBPase-overexpressing cells showed a decreased cell proliferation rate and significantly depressed glucose-induced insulin secretion. These defects were associated with a decrease in the rate of glucose utilization, resulting in reduced cellular ATP levels. CONCLUSIONS Taken together, these results suggest that upregulation of FBPase in pancreatic islet beta-cells, as occurs in states of lipid oversupply and type 2 diabetes, contributes to insulin secretory dysfunction.
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Affiliation(s)
- Melkam Kebede
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Jenny Favaloro
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Jenny E. Gunton
- Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
- Diabetes and Endocrinology, Westmead Hospital, Westmead, New South Wales, Australia
| | - D. Ross Laybutt
- Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia
| | - Margaret Shaw
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Nicole Wong
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Barbara C. Fam
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Kathryn Aston-Mourney
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Christian Rantzau
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Anthony Zulli
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Joseph Proietto
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
| | - Sofianos Andrikopoulos
- Department of Medicine, Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
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von Geldern TW, Lai C, Gum RJ, Daly M, Sun C, Fry EH, Abad-Zapatero C. Benzoxazole benzenesulfonamides are novel allosteric inhibitors of fructose-1,6-bisphosphatase with a distinct binding mode. Bioorg Med Chem Lett 2006; 16:1811-5. [PMID: 16442285 DOI: 10.1016/j.bmcl.2006.01.015] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 01/04/2006] [Accepted: 01/05/2006] [Indexed: 10/25/2022]
Abstract
We have identified benzoxazole benzenesulfonamide 1 as a novel allosteric inhibitor of fructose-1,6-bisphosphatase (FBPase-1). X-ray crystallographic and biological studies of 1 indicate a distinct binding mode that recapitulates features of several previously reported FBPase-1 inhibitor classes.
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Affiliation(s)
- Thomas W von Geldern
- Metabolic Disease Research, GPRD, Abbott Laboratories, Abbott Park, IL 60064, USA.
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Proietto J, Andrikopoulos S. Molecular Mechanisms of Increased Glucose Production: Identifying Potential Therapeutic Targets. J Investig Med 2004. [DOI: 10.1177/108155890405200633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/16/2023]
Abstract
Many patients with type 2 diabetes go on to require insulin therapy to achieve adequate control. A need remains to develop new classes of oral hypoglycemic agents to complement those already in use. A useful target is the inappropriately elevated endogenous glucose production present in patients with type 2 diabetes. This review discusses mechanisms of increased glucose production and possible strategies and targets for its suppression. Several approaches are being investigated, including inhibitors of glycogenolysis and gluconeogenesis, inhibitors of stimulatory hormones or their receptors, metabolic modulators, and agents that alter gene expression. There is a high probability that one of these approaches will soon result in a safe and effective inhibitor of glucose production.
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Affiliation(s)
- Joseph Proietto
- Department of Medicine (J.P., S.A.), Repatriation Hospital, Heidelberg, Australia
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Koza RA, Flurkey K, Graunke DM, Braun C, Pan HJ, Reifsnyder PC, Kozak LP, Leiter EH. Contributions of dysregulated energy metabolism to type 2 diabetes development in NZO/H1Lt mice with polygenic obesity. Metabolism 2004; 53:799-808. [PMID: 15164332 DOI: 10.1016/j.metabol.2003.12.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
New Zealand Obese (NZO) male mice develop a polygenic juvenile-onset obesity and maturity-onset hyperinsulinemia and hyperglycemia (diabesity). Here we report on metabolic and molecular changes associated with the antidiabesity action of CL316,243 (CL), a beta(3)-adrenergic receptor agonist. Dietary CL treatment initiated at weaning reduced the peripubertal rise in body weight and adiposity while promoting growth without suppressing hyperphagia. The changes in adiposity, in turn, suppressed development of hyperinsulinemia, hyperleptinemia, hyperlipidemia, and hyperglycemia. These CL-induced alterations were reflected by decreased adipose tissue mass, increased expression of transcripts for uncoupling protein-1 (UCP-1), peroxisome proliferator-activated receptor alpha (PPARalpha), peroxisome proliferater-activated receptor coactivator-1 (PGC-1), and robust development of brown adipocyte function in white fat. Increased drug-mediated energy dissipation elicited a 1.5 degrees C increase in whole body temperature under conditions of increased food intake but with no change in physical activity. Indirect calorimetry of mice treated with CL showed both increased energy expenditure and a restoration of a prominent diurnal pattern in the respiratory exchange ratio suggesting improved nutrient sensing. Our data suggest that CL promotes increased energy dissipation in white and brown fat depots by augmenting thermogenesis and by metabolic re-partitioning of energy in a diabesity-protective fashion. This is the first report demonstrating the effects of dietary beta(3)-agonist in preventing the onset of diabesity in a polygenic rodent model of type 2 diabetes.
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Affiliation(s)
- Robert A Koza
- Pennington Biomedical Research Center, Baton Rouge, LA, USA
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Leiter EH, Reifsnyder PC. Differential levels of diabetogenic stress in two new mouse models of obesity and type 2 diabetes. Diabetes 2004; 53 Suppl 1:S4-11. [PMID: 14749259 DOI: 10.2337/diabetes.53.2007.s4] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The genetic basis for the more common forms of human obesity predisposing to insulin resistance and development of type 2 diabetes is multigenic rather than monogenic in origin. New mouse "diabesity" models have been created by combining independent diabetes risk-conferring quantitative trait loci from two unrelated parental strains: New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/Lt). F1 hybrid males, heterozygous at all polymorphic autosomal loci distinguishing the two parental strains, are driven to obesity-induced diabetes (diabesity) at high frequencies. This review focuses on two new recombinant congenic strains (RCSs) developed by introgressing multiple NZO/HlLt chromosomal segments into the nominally diabesity-resistant NON/Lt strain background. Both RCSs gain more weight than NON animals. Although exhibiting comparable weight gain and adiposity, only one of the two RCSs develops diabetes. Hence, these two RCSs will be instructive in elucidating genetic and pathophysiological differences underlying uncomplicated obesity syndromes versus diabetogenic obesity (diabesity) syndromes. Unlike mice with null mutations in a single gene producing morbid obesity, the new models develop a more moderate obesity produced by the interaction of numerous genes with relatively small effects. These RCSs are differentially sensitive to adverse side effects of thiazolidinediones and thus should be particularly useful for pharmacogenetic analyses.
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Song S, Andrikopoulos S, Filippis C, Thorburn AW, Khan D, Proietto J. Mechanism of fat-induced hepatic gluconeogenesis: effect of metformin. Am J Physiol Endocrinol Metab 2001; 281:E275-82. [PMID: 11440903 DOI: 10.1152/ajpendo.2001.281.2.e275] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
High-fat feeding has been shown to cause hepatic insulin resistance. The aims of this study were to investigate the biochemical steps responsible for enhanced gluconeogenesis as a result of increased dietary fat intake and the site or sites at which the antihyperglycemic agent metformin acts to inhibit this process. Male Hooded Wistar rats were fed either a standard chow diet (5% fat by weight) or a high-fat diet (60% fat by weight) for 14 days with or without metformin. Total endogenous glucose production and gluconeogenesis were determined using [6-(3)H]glucose and [U-(14)C]alanine, respectively. Gluconeogenic enzyme activity and, where appropriate, protein and mRNA levels were measured in liver tissues. The high-fat diet increased endogenous glucose production (21.9 +/- 4.4 vs. 32.2 +/- 4.8 micromol x kg(-1) x min(-1), P < 0.05) and alanine gluconeogenesis (4.5 +/- 0.9 vs. 9.6 +/- 1.9 micromol x kg(-1) x min(-1), P < 0.05). Metformin reduced both endogenous glucose production (32.2 +/- 4.8 vs. 16.1 +/- 2.1 micromol x kg(-1) x min(-1), P < 0.05) and alanine gluconeogenesis (9.6 +/- 1.9 vs. 4.7 +/- 0.8 micromol x kg(-1) x min(-1), P < 0.05) after high-fat feeding. These changes were reflected in liver fructose-1,6-bisphosphatase protein levels (4.5 +/- 0.9 vs. 9.6 +/- 1.9 arbitrary units, P < 0.05 chow vs. high-fat feeding; 9.5 +/- 1.9 vs. 4.7 +/- 0.8 arbitrary units, P < 0.05 high fat fed in the absence vs. presence of metformin) but not in changes to the activity of other gluconeogenic enzymes. There was a significant positive correlation between alanine gluconeogenesis and fructose-1,6-bisphosphatase protein levels (r = 0.56, P < 0.05). Therefore, excess supply of dietary fat stimulates alanine gluconeogenesis via an increase in fructose-1,6-bisphosphatase protein levels. Metformin predominantly inhibits alanine gluconeogenesis by preventing the fat-induced changes in fructose-1,6-bisphosphatase levels.
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Affiliation(s)
- S Song
- Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia
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14
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Abstract
Recent studies have shown that increased hepatic gluconeogenesis is the predominant contributor to fasting hyperglycemia - the hallmark of type 2 diabetes. Although it has been known for a long time that over-supply of fat is able to stimulate gluconeogenesis both in-vitro and in-vivo, neither the leading substrate nor the mechanism responsible for this phenomenon have been fully identified. Recent observations that the glyoxylate pathway may exist in animals has shed light on this question. The glyoxylate pathway is able to convert fatty acid into glucose but has been thought to be absent in animals. Although further evidence is needed, current available data does suggest a possible mechanism which, by integrating both glucose and lipid metabolism together rather than interpreting them separately, may explain the role of fatty acids in hepatic insulin resistance. This hypothesis is based on current understanding of insulin resistance and supported by many laboratory observations.
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Affiliation(s)
- S Song
- Department of Medicine, University of Melbourne, Australia
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