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Bo T, Gao L, Yao Z, Shao S, Wang X, Proud CG, Zhao J. Hepatic selective insulin resistance at the intersection of insulin signaling and metabolic dysfunction-associated steatotic liver disease. Cell Metab 2024; 36:947-968. [PMID: 38718757 DOI: 10.1016/j.cmet.2024.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 01/22/2024] [Accepted: 04/09/2024] [Indexed: 06/26/2024]
Abstract
Insulin resistance (IR) is a major pathogenic factor in the progression of MASLD. In the liver, insulin suppresses gluconeogenesis and enhances de novo lipogenesis (DNL). During IR, there is a defect in insulin-mediated suppression of gluconeogenesis, but an unrestrained increase in hepatic lipogenesis persists. The mechanism of increased hepatic steatosis in IR is unclear and remains controversial. The key discrepancy is whether insulin retains its ability to directly regulate hepatic lipogenesis. Blocking insulin/IRS/AKT signaling reduces liver lipid deposition in IR, suggesting insulin can still regulate lipid metabolism; hepatic glucose metabolism that bypasses insulin's action may contribute to lipogenesis; and due to peripheral IR, other tissues are likely to impact liver lipid deposition. We here review the current understanding of insulin's action in governing different aspects of hepatic lipid metabolism under normal and IR states, with the purpose of highlighting the essential issues that remain unsettled.
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Affiliation(s)
- Tao Bo
- Key Laboratory of Endocrine Glucose & Lipids Metabolism and Brain Aging, Ministry of Education, Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Central Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Medical Science and Technology Innovation Center, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan, Shandong, China
| | - Ling Gao
- Key Laboratory of Endocrine Glucose & Lipids Metabolism and Brain Aging, Ministry of Education, Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Central Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Shandong Key Laboratory of Endocrinology and Lipid Metabolism, Jinan, Shandong, China
| | - Zhenyu Yao
- Key Laboratory of Endocrine Glucose & Lipids Metabolism and Brain Aging, Ministry of Education, Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Shandong Key Laboratory of Endocrinology and Lipid Metabolism, Jinan, Shandong, China
| | - Shanshan Shao
- Key Laboratory of Endocrine Glucose & Lipids Metabolism and Brain Aging, Ministry of Education, Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Shandong Key Laboratory of Endocrinology and Lipid Metabolism, Jinan, Shandong, China
| | - Xuemin Wang
- Lifelong Health, South Australian Health & Medical Research Institute, North Terrace, Adelaide, SA, Australia
| | - Christopher G Proud
- Lifelong Health, South Australian Health & Medical Research Institute, North Terrace, Adelaide, SA, Australia.
| | - Jiajun Zhao
- Key Laboratory of Endocrine Glucose & Lipids Metabolism and Brain Aging, Ministry of Education, Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China; Shandong Key Laboratory of Endocrinology and Lipid Metabolism, Jinan, Shandong, China.
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Molecular Mechanisms of Glucocorticoid-Induced Insulin Resistance. Int J Mol Sci 2021; 22:ijms22020623. [PMID: 33435513 PMCID: PMC7827500 DOI: 10.3390/ijms22020623] [Citation(s) in RCA: 89] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 12/29/2020] [Accepted: 01/02/2021] [Indexed: 12/12/2022] Open
Abstract
Glucocorticoids (GCs) are steroids secreted by the adrenal cortex under the hypothalamic-pituitary-adrenal axis control, one of the major neuro-endocrine systems of the organism. These hormones are involved in tissue repair, immune stability, and metabolic processes, such as the regulation of carbohydrate, lipid, and protein metabolism. Globally, GCs are presented as ‘flight and fight’ hormones and, in that purpose, they are catabolic hormones required to mobilize storage to provide energy for the organism. If acute GC secretion allows fast metabolic adaptations to respond to danger, stress, or metabolic imbalance, long-term GC exposure arising from treatment or Cushing’s syndrome, progressively leads to insulin resistance and, in fine, cardiometabolic disorders. In this review, we briefly summarize the pharmacological actions of GC and metabolic dysregulations observed in patients exposed to an excess of GCs. Next, we describe in detail the molecular mechanisms underlying GC-induced insulin resistance in adipose tissue, liver, muscle, and to a lesser extent in gut, bone, and brain, mainly identified by numerous studies performed in animal models. Finally, we present the paradoxical effects of GCs on beta cell mass and insulin secretion by the pancreas with a specific focus on the direct and indirect (through insulin-sensitive organs) effects of GCs. Overall, a better knowledge of the specific action of GCs on several organs and their molecular targets may help foster the understanding of GCs’ side effects and design new drugs that possess therapeutic benefits without metabolic adverse effects.
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Wu D, Huo M, Chen X, Zhang Y, Qiao Y. Mechanism of tanshinones and phenolic acids from Danshen in the treatment of coronary heart disease based on co-expression network. BMC Complement Med Ther 2020; 20:28. [PMID: 32020855 PMCID: PMC7076864 DOI: 10.1186/s12906-019-2712-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2019] [Accepted: 10/10/2019] [Indexed: 02/07/2023] Open
Abstract
Background The tanshinones and phenolic acids in Salvia miltiorrhiza (also named Danshen) have been confirmed for the treatment of coronary heart disease (CHD), but the action mechanisms remain elusive. Methods In the current study, the co-expression protein interaction network (Ce-PIN) was used to illustrate the differences between the tanshinones and phenolic acids of Danshen in the treatment of CHD. By integrating the gene expression profile data and protein-protein interactions (PPIs) data, the Ce-PINs of tanshinones and phenolic acids were constructed. Then, the Ce-PINs were analyzed by gene ontology enrichment analyzed based on the optimal algorithm. Results It turned out that Danshen is able to treat CHD by regulating the blood circulation, immune response and lipid metabolism. However, phenolic acids may regulate the blood circulation by Extracellular calcium-sensing receptor (CaSR), Endothelin-1 receptor (EDNRA), Endothelin-1 receptor (EDNRB), Kininogen-1 (KNG1), tanshinones may regulate the blood circulation by Guanylate cyclase soluble subunit alpha-1 (GUCY1A3) and Guanylate cyclase soluble subunit beta-1 (GUCY1B3). In addition, both the phenolic acids and tanshinones may regulate the immune response or inflammation by T-cell surface glycoprotein CD4 (CD4), Receptor-type tyrosine-protein phosphatase C (PTPRC). Conclusion Through the same targets of the same biological process and different targets of the same biological process, the tanshinones and phenolic acids synergistically treat coronary heart disease.
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Affiliation(s)
- Dongxue Wu
- Beijing University of Chinese Medicine, State Administration of Traditional Chinese Medicine, Research Center of TCM-Information Engineering, Beijing, 100102, China
| | - Mengqi Huo
- Beijing University of Chinese Medicine, State Administration of Traditional Chinese Medicine, Research Center of TCM-Information Engineering, Beijing, 100102, China
| | - Xi Chen
- Beijing University of Chinese Medicine, State Administration of Traditional Chinese Medicine, Research Center of TCM-Information Engineering, Beijing, 100102, China
| | - Yanling Zhang
- Beijing University of Chinese Medicine, State Administration of Traditional Chinese Medicine, Research Center of TCM-Information Engineering, Beijing, 100102, China.
| | - Yanjiang Qiao
- Beijing University of Chinese Medicine, State Administration of Traditional Chinese Medicine, Research Center of TCM-Information Engineering, Beijing, 100102, China.
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Petersen MC, Shulman GI. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev 2018; 98:2133-2223. [PMID: 30067154 PMCID: PMC6170977 DOI: 10.1152/physrev.00063.2017] [Citation(s) in RCA: 1430] [Impact Index Per Article: 238.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 03/22/2018] [Accepted: 03/24/2018] [Indexed: 12/15/2022] Open
Abstract
The 1921 discovery of insulin was a Big Bang from which a vast and expanding universe of research into insulin action and resistance has issued. In the intervening century, some discoveries have matured, coalescing into solid and fertile ground for clinical application; others remain incompletely investigated and scientifically controversial. Here, we attempt to synthesize this work to guide further mechanistic investigation and to inform the development of novel therapies for type 2 diabetes (T2D). The rational development of such therapies necessitates detailed knowledge of one of the key pathophysiological processes involved in T2D: insulin resistance. Understanding insulin resistance, in turn, requires knowledge of normal insulin action. In this review, both the physiology of insulin action and the pathophysiology of insulin resistance are described, focusing on three key insulin target tissues: skeletal muscle, liver, and white adipose tissue. We aim to develop an integrated physiological perspective, placing the intricate signaling effectors that carry out the cell-autonomous response to insulin in the context of the tissue-specific functions that generate the coordinated organismal response. First, in section II, the effectors and effects of direct, cell-autonomous insulin action in muscle, liver, and white adipose tissue are reviewed, beginning at the insulin receptor and working downstream. Section III considers the critical and underappreciated role of tissue crosstalk in whole body insulin action, especially the essential interaction between adipose lipolysis and hepatic gluconeogenesis. The pathophysiology of insulin resistance is then described in section IV. Special attention is given to which signaling pathways and functions become insulin resistant in the setting of chronic overnutrition, and an alternative explanation for the phenomenon of ‟selective hepatic insulin resistanceˮ is presented. Sections V, VI, and VII critically examine the evidence for and against several putative mediators of insulin resistance. Section V reviews work linking the bioactive lipids diacylglycerol, ceramide, and acylcarnitine to insulin resistance; section VI considers the impact of nutrient stresses in the endoplasmic reticulum and mitochondria on insulin resistance; and section VII discusses non-cell autonomous factors proposed to induce insulin resistance, including inflammatory mediators, branched-chain amino acids, adipokines, and hepatokines. Finally, in section VIII, we propose an integrated model of insulin resistance that links these mediators to final common pathways of metabolite-driven gluconeogenesis and ectopic lipid accumulation.
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Affiliation(s)
- Max C Petersen
- Departments of Internal Medicine and Cellular & Molecular Physiology, Howard Hughes Medical Institute, Yale University School of Medicine , New Haven, Connecticut
| | - Gerald I Shulman
- Departments of Internal Medicine and Cellular & Molecular Physiology, Howard Hughes Medical Institute, Yale University School of Medicine , New Haven, Connecticut
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The transcription factor carbohydrate-response element-binding protein (ChREBP): A possible link between metabolic disease and cancer. Biochim Biophys Acta Mol Basis Dis 2016; 1863:474-485. [PMID: 27919710 DOI: 10.1016/j.bbadis.2016.11.029] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 11/24/2016] [Accepted: 11/29/2016] [Indexed: 12/19/2022]
Abstract
Carbohydrate-response element-binding protein (ChREBP) has been identified as a transcription factor that binds to carbohydrate response element in the promoter of pyruvate kinase, liver and red blood cells. ChREBP is activated by metabolites derived from glucose and suppressed by adenosine monophosphate (AMP), ketone bodies and cyclic cAMP. ChREBP regulates gene transcription related to glucose and lipid metabolism. Findings from knockout mice and human subjects suggest that ChREBP helps to induce hepatic steatosis, dyslipidemia, and glucose intolerance. Moreover, in tumor cells, ChREBP promotes aerobic glycolysis through p53 inhibition, resulting in tumor cell proliferation. Anti-diabetic and anti-lipidemic drugs such as atorvastatin, metformin, bile acid sequestrants, docosahexaenoic acid and eicosapentaenoic acid may affect ChREBP transactivity. Secretory proteins such as fibroblast growth factor 21 and ANGPTL8 (Betatrophin) may be promising candidates for biologic markers reflecting ChREBP transactivity. Thus, ChREBP is associated with metabolic diseases and cancers, and may be a link between them.
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Affiliation(s)
- Loranne Agius
- Institutes of Cellular Medicine and Ageing and Health, Medical School, Newcastle University, Newcastle upon Tyne, NE2 4HH United Kingdom;
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Guan HP, Chen G. Factors affecting insulin-regulated hepatic gene expression. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 121:165-215. [PMID: 24373238 DOI: 10.1016/b978-0-12-800101-1.00006-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Obesity has become a major concern of public health. A common feature of obesity and related metabolic disorders such as noninsulin-dependent diabetes mellitus is insulin resistance, wherein a given amount of insulin produces less than normal physiological responses. Insulin controls hepatic glucose and fatty acid metabolism, at least in part, via the regulation of gene expression. When the liver is insulin-sensitive, insulin can stimulate the expression of genes for fatty acid synthesis and suppress those for gluconeogenesis. When the liver becomes insulin-resistant, the insulin-mediated suppression of gluconeogenic gene expression is lost, whereas the induction of fatty acid synthetic gene expression remains intact. In the past two decades, the mechanisms of insulin-regulated hepatic gene expression have been studied extensively and many components of insulin signal transduction pathways have been identified. Factors that alter these pathways, and the insulin-regulated hepatic gene expression, have been revealed and the underlying mechanisms have been proposed. This chapter summarizes the recent progresses in our understanding of the effects of dietary factors, drugs, bioactive compounds, hormones, and cytokines on insulin-regulated hepatic gene expression. Given the large amount of information and progresses regarding the roles of insulin, this chapter focuses on findings in the liver and hepatocytes and not those described for other tissues and cells. Typical insulin-regulated hepatic genes, such as insulin-induced glucokinase and sterol regulatory element-binding protein-1c and insulin-suppressed cytosolic phosphoenolpyruvate carboxyl kinase and insulin-like growth factor-binding protein 1, are used as examples to discuss the mechanisms such as insulin regulatory element-mediated transcriptional regulation. We also propose the potential mechanisms by which these factors affect insulin-regulated hepatic gene expression and discuss potential future directions of the area of research.
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Affiliation(s)
- Hong-Ping Guan
- Department of Diabetes, Merck Research Laboratories, Kenilworth, New Jersey, USA
| | - Guoxun Chen
- Department of Nutrition, University of Tennessee at Knoxville, Knoxville, Tennessee, USA
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Wang Y, Guo T, Zhao S, Li Z, Mao Y, Li H, Wang X, Wang R, Xu W, Song R, Jin L, Li X, Irwin DM, Niu G, Tan H. Expression of the human glucokinase gene: important roles of the 5' flanking and intron 1 sequences. PLoS One 2012; 7:e45824. [PMID: 23029263 PMCID: PMC3447760 DOI: 10.1371/journal.pone.0045824] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2012] [Accepted: 08/24/2012] [Indexed: 02/07/2023] Open
Abstract
Background Glucokinase plays important tissue-specific roles in human physiology, where it acts as a sensor of blood glucose levels in the pancreas, and a few other cells of the gut and brain, and as the rate-limiting step in glucose metabolism in the liver. Liver-specific expression is driven by one of the two tissue-specific promoters, and has an absolute requirement for insulin. The sequences that mediate regulation by insulin are incompletely understood. Methodology/Principal Findings To better understand the liver-specific expression of the human glucokinase gene we compared the structures of this gene from diverse mammals. Much of the sequence located between the 5′ pancreatic beta-cell-specific and downstream liver-specific promoters of the glucokinase genes is composed of repetitive DNA elements that were inserted in parallel on different mammalian lineages. The transcriptional activity of the liver-specific promoter 5′ flanking sequences were tested with and without downstream intronic sequences in two human liver cells lines, HepG2 and L-02. While glucokinase liver-specific 5′ flanking sequences support expression in liver cell lines, a sequence located about 2000 bases 3′ to the liver-specific mRNA start site represses gene expression. Enhanced reporter gene expression was observed in both cell lines when cells were treated with fetal calf serum, but only in the L-02 cells was expression enhanced by insulin. Conclusions/Significance Our results suggest that the normal liver L-02 cell line may be a better model to understand the regulation of the liver-specific expression of the human glucokinase gene. Our results also suggest that sequences downstream of the liver-specific mRNA start site have important roles in the regulation of liver-specific glucokinase gene expression.
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Affiliation(s)
- Yi Wang
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Tingting Guo
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Shuyong Zhao
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Zhixin Li
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Yiqing Mao
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Hui Li
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Xi Wang
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Rong Wang
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Wei Xu
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Rongjing Song
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Ling Jin
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
| | - Xiuli Li
- Department of Pharmacology, Chifeng College, Chifeng, China
| | - David M. Irwin
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
- * E-mail: (HT); (DMI)
| | - Gang Niu
- Beijing N&N Genetech Company, Beijing, China
| | - Huanran Tan
- Department of Pharmacology, Peking University, Health Science Center, Beijing, China
- * E-mail: (HT); (DMI)
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Velazquez-Arellano A, Ortega-Cuellar D, Hernandez-Mendoza A, Moreno-Arriola E. A heuristic model for paradoxical effects of biotin starvation on carbon metabolism genes in the presence of abundant glucose. Mol Genet Metab 2011; 102:69-77. [PMID: 20869286 DOI: 10.1016/j.ymgme.2010.08.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2010] [Revised: 08/25/2010] [Accepted: 08/26/2010] [Indexed: 11/17/2022]
Abstract
We recently showed that in biotin starvation in yeast Saccharomyces cerevisiae, nematode Caenorhabditis elegans and rat Rattus norvegicus, despite abundant glucose provision, the expression of genes for glucose utilization and lipogenesis were lowered, and for fatty acid β-oxidation and gluconeogenesis were raised, and glycolytic/fermentative flow was reduced. This work explored the mechanisms of these results. We show that they are associated with ATP deficit and activation of the energy stress sensor AMP kinase (AMPK; Snf1 in yeast). Analysis of microarray results revealed extensive changes of transcripts for signal transduction pathways and transcription factors AMPK, SREBP-1c, ChREBP, NAMPT, PGC-1α, mTORC1 in rat, and their homologs in worm. In yeast the altered factor transcripts were Adr1, Cat8, Sip4, Mig1, HXK2, and Rgt1. The insulin pathway was negatively enriched (in rat and worm), whereas the adiponectins and JAK/STAT pathways were increased (present only in the rat; they activate AMPK). Together, all these changes explain the effects of biotin starvation on glucose utilization, energy status and carbon metabolism gene expression in a coherent manner across three phylogenetically distant eukaryotes and may have clinical significance in humans, since the effects are reminiscent of insulin resistance. We propose a general model for integrating these results in regulatory circuitries, according to the biology of each species, based on impaired anaplerosis due to pyruvate carboxylase deficiency, that have a basic underlying logic. In a preliminary test in yeast, aspartate corrects all the alterations produced by biotin starvation.
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Affiliation(s)
- Antonio Velazquez-Arellano
- Unidad de Genética de la Nutrición, Instituto de Investigaciones Biomédicas de la Universidad Nacional Autónoma de México, Mexico.
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Zhu LL, Liu Y, Cui AF, Shao D, Liang JC, Liu XJ, Chen Y, Gupta N, Fang FD, Chang YS. PGC-1alpha coactivates estrogen-related receptor-alpha to induce the expression of glucokinase. Am J Physiol Endocrinol Metab 2010; 298:E1210-8. [PMID: 20215575 DOI: 10.1152/ajpendo.00633.2009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) is a key regulator of cellular energy metabolism and regulates processes such as adaptive thermogenesis, hepatic gluconeogenesis, fatty acid oxidation, and mitochondrial biogenesis by coactivating numerous nuclear receptors and transcription factors. Here, we demonstrate the presence of the ERRalpha binding site in the regulatory sequence of the glucokinase gene and that PGC-1alpha coactivates ERRalpha to stimulate the transcription of glucokinase. Simultaneous overexpression of PGC-1alpha and ERRalpha potently induced the glucokinase gene expression and its enzymatic activity in primary hepatocytes; however, expression of either PGC-1alpha or ERRalpha alone had no significant effect. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed the interaction of ERRalpha with the glucokinase promoter. Finally, the knockdown of endogenous ERRalpha with specific siRNA (siERRalpha) or pharmacological inhibition of ERRalpha with XCT790 attenuated insulin-induced glucokinase expression. Taken together, this research identifies glucokinase as a novel target of PGC-1alpha/ERRalpha and underscores the regulatory function of ERRalpha in insulin-dependent enzyme regulation.
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Affiliation(s)
- Liu-Luan Zhu
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China
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Anti-diabetic effects of lemon balm (Melissa officinalis) essential oil on glucose- and lipid-regulating enzymes in type 2 diabetic mice. Br J Nutr 2010; 104:180-8. [DOI: 10.1017/s0007114510001765] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The antioxidant activity of lemon balm (Melissa officinalis) essential oil (LBEO) on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and its hypoglycaemic effect in db/db mice were investigated. LBEO scavenged 97 % of DPPH radicals at a 270-fold dilution. Mice administered LBEO (0·015 mg/d) for 6 weeks showed significantly reduced blood glucose (65 %; P < 0·05) and TAG concentrations, improved glucose tolerance, as assessed by an oral glucose tolerance test, and significantly higher serum insulin levels, compared with the control group. The hypoglycaemic mechanism of LBEO was further explored via gene and protein expression analyses using RT-PCR and Western blotting, respectively. Among all glucose metabolism-related genes studied, hepatic glucokinase and GLUT4, as well as adipocyte GLUT4, PPAR-γ, PPAR-α and SREBP-1c expression, were significantly up-regulated, whereas glucose-6-phosphatase and phosphoenolpyruvate carboxykinase expression was down-regulated in the livers of the LBEO group. The results further suggest that LBEO administered at low concentrations is an efficient hypoglycaemic agent, probably due to enhanced glucose uptake and metabolism in the liver and adipose tissue and the inhibition of gluconeogenesis in the liver.
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Transcriptional regulation of glucose sensors in pancreatic β-cells and liver: an update. SENSORS 2010; 10:5031-53. [PMID: 22399922 PMCID: PMC3292162 DOI: 10.3390/s100505031] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Revised: 05/07/2010] [Accepted: 05/13/2010] [Indexed: 01/17/2023]
Abstract
Pancreatic β-cells and the liver play a key role in glucose homeostasis. After a meal or in a state of hyperglycemia, glucose is transported into the β-cells or hepatocytes where it is metabolized. In the β-cells, glucose is metabolized to increase the ATP:ADP ratio, resulting in the secretion of insulin stored in the vesicle. In the hepatocytes, glucose is metabolized to CO(2), fatty acids or stored as glycogen. In these cells, solute carrier family 2 (SLC2A2) and glucokinase play a key role in sensing and uptaking glucose. Dysfunction of these proteins results in the hyperglycemia which is one of the characteristics of type 2 diabetes mellitus (T2DM). Thus, studies on the molecular mechanisms of their transcriptional regulations are important in understanding pathogenesis and combating T2DM. In this paper, we will review a recent update on the progress of gene regulation of glucose sensors in the liver and β-cells.
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Chen G, Zhang Y, Lu D, Li NQ, Ross AC. Retinoids synergize with insulin to induce hepatic Gck expression. Biochem J 2009; 419:645-53. [PMID: 19173678 PMCID: PMC3789248 DOI: 10.1042/bj20082368] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hepatic GK (glucokinase) plays a key role in maintaining glucose homoeostasis. Many stimuli regulate GK activity by controlling its gene transcription. We hypothesized that endogenous lipophilic molecules modulate hepatic Gck expression. Lipophilic molecules were extracted from rat livers, saponified and re-constituted as an LE (lipophilic extract). LE synergized with insulin to induce primary hepatocyte, but not beta-cell, Gck expression in an SREBP-1c (sterol-regulatory-element-binding protein-1c)-independent manner. The dramatic induction of Gck mRNA resulted in a significant increase in GK activity. Subsequently, the active molecules were identified as retinol and retinal by MS after the purification of the active LE fractions. Retinoids synergized with insulin to induce Gck expression by the activation of both RAR [RA (retinoic acid) receptor] and RXR (retinoid X receptor). Inhibition of RAR activation completely abolished the effect of retinal. The hepatic GK specific activity and Gck mRNA levels of Zucker lean rats fed with a VAD [VA (vitamin A)-deficient] diet were significantly lower than those of rats fed with VAS (VA-sufficient) diet. Additionally, the hepatic Gck mRNA expression of Sprague-Dawley rats fed with a VAD diet was lower than that of rats fed with VA-marginal, -adequate or -supplemented diets. The reduced expression of Gck mRNA was increased after an intraperitoneal dose of RA in VAD rats. Furthermore, an intravenous injection of RA rapidly raised hepatic Gck expression in rats fed with a VAS control diet. Understanding the underlying mechanism that mediates the synergy may be helpful for developing a treatment strategy for patients with diabetes.
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Affiliation(s)
- Guoxun Chen
- Department of Nutrition, University of Tennessee at Knoxville, Knoxville, TN 37996, U.S.A.
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Bhatnagar S, Damron HA, Hillgartner FB. Fibroblast growth factor-19, a novel factor that inhibits hepatic fatty acid synthesis. J Biol Chem 2009; 284:10023-33. [PMID: 19233843 DOI: 10.1074/jbc.m808818200] [Citation(s) in RCA: 152] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Previous studies have shown that administration of fibroblast growth factor-19 (FGF-19) reverses diabetes, hepatic steatosis, hyperlipidemia, and adipose accretion in animal models of obesity. To investigate the mechanism for this effect, we determined whether FGF-19 modulated hepatic fatty acid synthesis, a key process controlling glucose tolerance and triacylglycerol accumulation in liver, blood, and adipose tissue. Incubating primary hepatocyte cultures with recombinant FGF-19 suppressed the ability of insulin to stimulate fatty acid synthesis. This effect was associated with a reduction in the expression of lipogenic enzymes. FGF-19 also suppressed the insulin-induced expression of sterol regulatory element-binding protein-1c (SREBP-1c), a key transcriptional activator of lipogenic genes. FGF-19 inhibition of lipogenic enzyme expression was not mediated by alterations in the activity of the insulin signal transduction pathway or changes in the activity of ERK, p38 MAPK, and AMP-activated protein kinase (AMPK). In contrast, FGF-19 increased the activity of STAT3, an inhibitor of SREBP-1c expression and decreased the expression of peroxisome proliferator-activated receptor-gamma coactivator-1beta (PGC-1beta), an activator of SREBP-1c activity. FGF-19 also increased the expression of small heterodimer partner (SHP), a transcriptional repressor that inhibits lipogenic enzyme expression via a SREBP-1c-independent mechanism. Inhibition of SREBP-1c activity by changes in STAT3 and PGC-1beta activity and inhibition of gene transcription by an elevation in SHP expression can explain the inhibition of lipogenesis caused by FGF-19. In summary, the inhibitory effect of FGF-19 on insulin activation of hepatic fatty acid synthesis constitutes a mechanism that would explain the beneficial effect of FGF-19 on metabolic syndrome.
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Affiliation(s)
- Sushant Bhatnagar
- Department of Biochemistry, West Virginia University, Morgantown, West Virginia 26506, USA
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15
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Kaiser JP, Beier JI, Zhang J, David Hoetker J, von Montfort C, Guo L, Zheng Y, Monia BP, Bhatnagar A, Arteel GE. PKCepsilon plays a causal role in acute ethanol-induced steatosis. Arch Biochem Biophys 2008; 482:104-11. [PMID: 19022218 DOI: 10.1016/j.abb.2008.11.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 10/27/2008] [Accepted: 11/03/2008] [Indexed: 12/17/2022]
Abstract
Steatosis is a critical stage in the pathology of alcoholic liver disease (ALD), and preventing steatosis could protect against later stages of ALD. PKCepsilon has been shown to contribute to hepatic steatosis in experimental non-alcoholic fatty liver disease (NAFLD); however, the role of PKCepsilon in ethanol-induced steatosis has not been determined. The purpose of this study was to therefore test the hypothesis that PKCepsilon contributes to ethanol-induced steatosis. Accordingly, the effect of acute ethanol on indices of hepatic steatosis and insulin signaling were determined in PKCepsilon knockout mice and in wild-type mice that received an anti-sense oligonucleotide (ASO) to knockdown PKCepsilon expression. Acute ethanol (6g/kg i.g.) caused a robust increase in hepatic non-esterified free fatty acids (NEFA), which peaked 1h after ethanol exposure. This increase in NEFA was followed by elevated diacylglycerols (DAG), as well as by the concomitant activation of PKCepsilon. Acute ethanol also changed the expression of insulin-responsive genes (i.e. increased G6Pase, downregulated GK), in a pattern indicative of impaired insulin signaling. Acute ethanol exposure subsequently caused a robust increase in hepatic triglycerides. The accumulation of triglycerides caused by ethanol was blunted in ASO-treated or in PKCepsilon(-/-) mice. Taken together, these data suggest that the increase in NEFA caused by hepatic ethanol metabolism leads to an increase in DAG production via the triacylglycerol pathway. DAG then subsequently activates PKCepsilon, which then exacerbates hepatic lipid accumulation by inducing insulin resistance. These data also suggest that PKCepsilon plays a causal role in at least the early phases of ethanol-induced liver injury.
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Affiliation(s)
- J Phillip Kaiser
- Department of Pharmacology and Toxicology, University of Louisville Health Sciences Center, Louisville, KY 40292, USA
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16
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Gómez-Valadés AG, Méndez-Lucas A, Vidal-Alabró A, Blasco FX, Chillon M, Bartrons R, Bermúdez J, Perales JC. Pck1 gene silencing in the liver improves glycemia control, insulin sensitivity, and dyslipidemia in db/db mice. Diabetes 2008; 57:2199-210. [PMID: 18443203 PMCID: PMC2494684 DOI: 10.2337/db07-1087] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
OBJECTIVE Cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; encoded by Pck1) catalyzes the first committed step in gluconeogenesis. Extensive evidence demonstrates a direct correlation between PEPCK-C activity and glycemia control. Therefore, we aimed to evaluate the metabolic impact and their underlying mechanisms of knocking down hepatic PEPCK-C in a type 2 diabetic model. RESEARCH DESIGN AND METHODS PEPCK-C gene targeting was achieved using adenovirus-transduced RNAi. The study assessed several clinical symptoms of diabetes and insulin signaling in peripheral tissues, in addition to changes in gene expression, protein, and metabolites in the liver. Liver bioenergetics was also evaluated. RESULTS Treatment resulted in reduced PEPCK-C mRNA and protein. After treatment, improved glycemia and insulinemia, lower triglyceride, and higher total and HDL cholesterol were measured. Unsterified fatty acid accumulation was observed in the liver, in the absence of de novo lipogenesis. Despite hepatic lipidosis, treatment resulted in improved insulin signaling in the liver, muscle, and adipose tissue. O(2) consumption measurements in isolated hepatocytes demonstrated unaltered mitochondrial function and a consequent increased cellular energy charge. Key regulatory factors (FOXO1, hepatocyte nuclear factor-4alpha, and peroxisome proliferator-activated receptor-gamma coactivator [PGC]-1alpha) and enzymes (G6Pase) implicated in gluconeogenesis were downregulated after treatment. Finally, the levels of Sirt1, a redox-state sensor that modulates gluconeogenesis through PGC-1alpha, were diminished. CONCLUSIONS Our observations indicate that silencing PEPCK-C has direct impact on glycemia control and energy metabolism and provides new insights into the potential significance of the enzyme as a therapeutic target for the treatment of diabetes.
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Affiliation(s)
- Alicia G Gómez-Valadés
- Biophysics Unit, Department de Ciències Fisiològuiques II, IDIBELL-University of Barcelona, Barcelona, Spain
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17
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Iizuka K, Horikawa Y. ChREBP: a glucose-activated transcription factor involved in the development of metabolic syndrome. Endocr J 2008; 55:617-24. [PMID: 18490833 DOI: 10.1507/endocrj.k07e-110] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Excess carbohydrate intake leads to fat accumulation and insulin resistance. Glucose and insulin coordinately regulate de novo lipogenesis from glucose in the liver, and insulin activates several transcription factors including SREBP1c and LXR, while those activated by glucose remain unknown. Recently, a carbohydrate response element binding protein (ChREBP), which binds to the carbohydrate response element (ChoRE) in the promoter of rat liver type pyruvate kinase (LPK), has been identified. The target genes of ChREBP are involved in glycolysis, lipogenesis, and gluconeogenesis. Although the regulation of ChREBP remains unknown in detail, the transactivity of ChREBP is partly regulated by a phosphorylation/dephosphorylation mechanism. During fasting, protein kinase A and AMP-activated protein kinase phosphorylate ChREBP and inactivate its transactivity. During feeding, xylulose-5-phosphate in the hexose monophosphate pathway activates protein phosphatase 2A, which dephosphorylates ChREBP and activates its transactivity. ChREBP controls 50% of hepatic lipogenesis by regulating glycolytic and lipogenic gene expression. In ChREBP (-/-) mice, liver triglyceride content is decreased and liver glycogen content is increased compared to wild-type mice. These results indicate that ChREBP can regulate metabolic gene expression to convert excess carbohydrate into triglyceride rather than glycogen. Furthermore, complete inhibition of ChREBP in ob/ob mice reduces the effects of the metabolic syndrome such as obesity, fatty liver, and glucose intolerance. Thus, further clarification of the physiological role of ChREBP may be useful in developing treatments for the metabolic syndrome.
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Affiliation(s)
- Katsumi Iizuka
- Laboratory of Medical Genomics, the Institute for Molecular and Cellular Regulation, Gunma University, Maebashi-shi, Japan.
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18
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Denechaud PD, Bossard P, Lobaccaro JMA, Millatt L, Staels B, Girard J, Postic C. ChREBP, but not LXRs, is required for the induction of glucose-regulated genes in mouse liver. J Clin Invest 2008; 118:956-64. [PMID: 18292813 DOI: 10.1172/jci34314] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Accepted: 12/19/2007] [Indexed: 11/17/2022] Open
Abstract
The transcription factor carbohydrate-responsive element-binding protein (ChREBP) has emerged as a central regulator of lipid synthesis in liver because it is required for glucose-induced expression of the glycolytic enzyme liver-pyruvate kinase (L-PK) and acts in synergy with SREBP to induce lipogenic genes such as acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). Liver X receptors (LXRs) are also important regulators of the lipogenic pathway, and the recent finding that ChREBP is a direct target of LXRs and that glucose itself can bind and activate LXRs prompted us to study the role of LXRs in the induction of glucose-regulated genes in liver. Using an LXR agonist in wild-type mice, we found that LXR stimulation did not promote ChREBP phosphorylation or nuclear localization in the absence of an increased intrahepatic glucose flux. Furthermore, the induction of ChREBP, L-PK, and ACC by glucose or high-carbohydrate diet was similar in LXRalpha/beta knockout compared with wild-type mice, suggesting that the activation of these genes by glucose occurs by an LXR-independent mechanism. We used fluorescence resonance energy transfer analysis to demonstrate that glucose failed to promote the interaction of LXRalpha/beta with specific cofactors. Finally, siRNA silencing of ChREBP in LXRalpha/beta knockout hepatocytes abrogated glucose-induced expression of L-PK and ACC, further demonstrating the central role of ChREBP in glucose signaling. Taken together, our results demonstrate that glucose is required for ChREBP functional activity and that LXRs are not necessary for the induction of glucose-regulated genes in liver.
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Affiliation(s)
- Pierre-Damien Denechaud
- Institut Cochin, Département d'Endocrinologie, Métabolisme et Cancer, Université Paris Descartes, CNRS, UMR 8104, Paris, France
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19
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Egea M, Metón I, Córdoba M, Fernández F, Baanante IV. Role of Sp1 and SREBP-1a in the insulin-mediated regulation of glucokinase transcription in the liver of gilthead sea bream (Sparus aurata). Gen Comp Endocrinol 2008; 155:359-67. [PMID: 17686483 DOI: 10.1016/j.ygcen.2007.06.018] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 06/07/2007] [Accepted: 06/22/2007] [Indexed: 01/14/2023]
Abstract
Insulin induction of glucokinase (GCK) transcription in the liver is essential for maintaining glucose homeostasis. To study the molecular mechanism underlying the regulation of hepatic GCK expression in the carnivorous fish gilthead sea bream (Sparus aurata), we analysed the role of sterol regulatory element binding protein-1a (SREBP-1a) and specificity protein (Sp) 1 in insulin-dependent GCK transcription. Transient transfection experiments performed in HepG2 cells and electrophoretic mobility shift assays allowed us to identify a cis-element in the proximal region of GCK promoter implicated in transactivation by SREBP-1a. Consistently, mutations in the SRE binding site completely abolished the enhancing effect of SREBP-1a. These results and previous findings suggest that SREBP-1a plays a role in the transcriptional regulation of key enzymes in glycolysis-gluconeogenesis. Since SREBP-1a and Sp1 may mediate insulin action on S. aurata GCK transcription, we analysed the effect of insulin on HepG2 cells transfected with GCK promoter reporter constructs carrying intact or mutated SRE or Sp boxes. Insulin transactivated GCK irrespective of the presence of an intact or mutated SRE box. However, insulin failed to induce GCK transcription when using reporter constructs that had either a mutated Sp site or no Sp site. Our findings indicate that Sp1, rather than SREBP-1a, mediates the insulin-dependent induction of S. aurata GCK.
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Affiliation(s)
- Miriam Egea
- Departament de Bioquímica i Biologia Molecular, Facultat de Farmàcia, Universitat de Barcelona, Diagonal 643, 08028 Barcelona, Spain
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20
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Yang LH, Chen TM, Yu ST, Chen YH. Olanzapine induces SREBP-1-related adipogenesis in 3T3-L1 cells. Pharmacol Res 2007; 56:202-8. [PMID: 17651982 DOI: 10.1016/j.phrs.2007.05.007] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Revised: 05/11/2007] [Accepted: 05/23/2007] [Indexed: 12/20/2022]
Abstract
Olanzapine is a second-generation atypical antipsychotic drug (AAPD). Major side effects of olanzapine are weight gain and development of diabetes mellitus, which are risk factors of cardiovascular diseases. The possible causes of metabolic adverse effects are known as poor satiety and increased food intake due to blockade of receptors such as 5-HT(2C) in CNS. In this study, we examine the effect of olanzapine on peripheral adipogenesis using cultured 3T3-L1 cell model. Olanzapine increased triacylglyceride (TG) accumulation during 3T3-L1 preadipocyte differentiation to mature adipocyte phenotype. TG accumulation was accompanied by overexpression of fatty acid synthase and adiponectin that are the downstream genes of sterol regulatory element binding protein-1 (SREBP-1), one of the key transcription factors in lipid homeostasis. We further consisted that mostly SREBP-1 and at a lesser extent peroxisome proliferator-activated receptor gamma (PPAR-gamma), but not CCAAT/enhancer binding protein-alpha (C/EBP-alpha), were overexpressed and activated in 3T3-L1 adipocytes exposed to olanzapine. Furthermore, we showed that olanzapine enhanced the activity of SRE-1-containing LDLR promoter in transfected 3T3-L1 adipocytes and HepG2 cells. Taken together, olanzapine may cause body weight gain not only through influencing CNS receptors, but also affecting the peripheral adipogenesis regulated by SREBP-1.
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Affiliation(s)
- Li-Hung Yang
- Institute of Pharmaceutical Sciences, College of Medicine, National Taiwan University, Taipei 10051, Taiwan
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21
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Krapivner S, Chernogubova E, Ericsson M, Ahlbeck-Glader C, Hamsten A, van 't Hooft FM. Human evidence for the involvement of insulin-induced gene 1 in the regulation of plasma glucose concentration. Diabetologia 2007; 50:94-102. [PMID: 17106696 DOI: 10.1007/s00125-006-0479-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2006] [Accepted: 08/14/2006] [Indexed: 10/23/2022]
Abstract
AIMS/HYPOTHESIS Insulin-induced gene 1 (INSIG1) is a protein that blocks proteolytic activation of sterol regulatory element-binding proteins (SREBPs), transcription factors that activate genes regulating cholesterol and fatty acid metabolism and possibly genes involved in glucose homeostasis. In search of genetic regulation of these processes we examined human INSIG1 for common polymorphisms and analysed their associations with biochemical parameters related to lipid and glucose metabolism. METHODS Associations between common polymorphisms in INSIG1 and several biochemical parameters were analysed in a group of 618 healthy, 50-year-old men. A replication analysis was performed in a cohort of 472 healthy, middle-aged men. The impact of one promoter polymorphism on oral glucose tolerance was analysed in a subset of 181 subjects. Small interfering RNA (siRNA) inhibition was used to test the significance of INSIG1 for gene expression in human Huh7 hepatoma cells. RESULTS A potentially functional polymorphism, a C to T substitution at position -169, was discovered in a highly conserved section of the promoter. Significant relationships between the -169C>T polymorphism and plasma glucose concentration were found in two cohorts of healthy, middle-aged men (p < 0.01 and p < 0.02, respectively). The -169T allele was associated with significantly lower post-load plasma glucose concentrations. A significant (p = 0.02) reduction in expression of phosphoenolpyruvate carboxykinase (PCK2) was observed following siRNA inhibition of INSIG1 in human Huh7 hepatoma cells. CONCLUSIONS/INTERPRETATION Population studies demonstrate that INSIG1 plays a role in glucose homeostasis. Experiments with siRNA suggest that this action of INSIG1 is related to SREBP-mediated regulation of PCK2.
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MESH Headings
- Adult
- Animals
- Base Sequence
- Blood Glucose/genetics
- Blood Glucose/metabolism
- Carcinoma, Hepatocellular/metabolism
- Carcinoma, Hepatocellular/pathology
- Cell Line, Tumor
- Cohort Studies
- Homeostasis/physiology
- Humans
- Intracellular Signaling Peptides and Proteins/antagonists & inhibitors
- Intracellular Signaling Peptides and Proteins/genetics
- Intracellular Signaling Peptides and Proteins/metabolism
- Liver Neoplasms/metabolism
- Liver Neoplasms/pathology
- Male
- Membrane Proteins/antagonists & inhibitors
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Mice
- Middle Aged
- Molecular Sequence Data
- Polymorphism, Genetic/genetics
- Polymorphism, Genetic/physiology
- Promoter Regions, Genetic/genetics
- Promoter Regions, Genetic/physiology
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Small Interfering/pharmacology
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Affiliation(s)
- S Krapivner
- Atherosclerosis Research Unit, King Gustaf V Research Institute, Karolinska University Hospital, 17176, Stockholm, Sweden
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22
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Hall RK, Wang XL, George L, Koch SR, Granner DK. Insulin represses phosphoenolpyruvate carboxykinase gene transcription by causing the rapid disruption of an active transcription complex: a potential epigenetic effect. Mol Endocrinol 2006; 21:550-63. [PMID: 17095578 DOI: 10.1210/me.2006-0307] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Insulin represses gluconeogenesis, in part, by inhibiting the transcription of genes that encode rate-determining enzymes, such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase). Glucocorticoids stimulate expression of the PEPCK gene but the repressive action of insulin is dominant. Here, we show that treatment of H4IIE hepatoma cells with the synthetic glucocorticoid, dexamethasone (dex), induces the accumulation of glucocorticoid receptor, as well as many transcription factors, coregulators, and RNA polymerase II, on the PEPCK gene promoter. The addition of insulin to dex-treated cells causes the rapid dissociation of glucocorticoid receptor, polymerase II, and several key transcriptional regulators from the PEPCK gene promoter. These changes are temporally related to the reduced rate of PEPCK gene transcription. A similar disruption of the G-6-Pase gene transcription complex was observed. Additionally, insulin causes the rapid demethylation of arginine-17 on histone H3 of both genes. This rapid, insulin-induced, histone demethylation is temporally related to the disruption of the PEPCK and G-6-Pase gene transcription complex, and may be causally related to the mechanism by which insulin represses transcription of these genes.
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Affiliation(s)
- Robert K Hall
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 707 Light Hall, Nashville, Tennessee 37232-0615, USA
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23
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Hansmannel F, Mordier S, Iynedjian P. Insulin induction of glucokinase and fatty acid synthase in hepatocytes: analysis of the roles of sterol-regulatory-element-binding protein-1c and liver X receptor. Biochem J 2006; 399:275-83. [PMID: 16834571 PMCID: PMC1609914 DOI: 10.1042/bj20060811] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The transcription activator SREBP-1c (sterol-regulatory-element-binding protein-1c) is induced by insulin in the liver and is considered a master regulator of lipogenic genes such as FASN (fatty acid synthase). The question of whether SREBP-1c is also a mediator of insulin action on the regulatory enzyme of glucose metabolism GCK (glucokinase) is controversial. In the present paper, we induced SREBP-1c to various levels with insulin or the liver X receptor ligand T0901317 in primary hepatocytes and asked if these levels correlated with those of GCK or FASN mRNA expression, using the latter as positive control. Insulin and T0901317 triggered the accumulation of precursor and processed forms of SREBP-1c to similar levels and with comparable kinetics, and both effectors together caused synergistic increases in SREBP-1c protein levels. These effects were accompanied by commensurate elevation of FASN mRNA, notably by a synergistic response to both effectors. By contrast, GCK mRNA was unresponsive to T0901317 and was induced only by insulin. Treatment of hepatocytes with insulin and/or T0901317 resulted in the recruitment of SREBP-1c to the FASN promoter as shown by chromatin immunoprecipitation, whereas SREBP-1c did not bind to the GCK promoter. Lastly, we observed that the glycogen synthase kinase-3 inhibitor SB216763 produced a small increase in SREBP-1c protein level, which was further augmented in the presence of T0901317. The level of FASN mRNA varied in parallel with SREBP-1c, while GCK mRNA was unaffected. Collectively, these results showed that increases in SREBP-1c were neither necessary nor sufficient for GCK induction in hepatocytes, while at the same time they underscored the role of SREBP-1c as a key regulator of FASN.
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Affiliation(s)
- Franck Hansmannel
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland
| | - Sylvie Mordier
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland
| | - Patrick B. Iynedjian
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland
- To whom correspondence should be addressed (email )
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