Lower blood glucose, hyperglucagonemia, and pancreatic α cell hyperplasia in glucagon receptor knockout mice
04 Feb 2003-Proceedings of the National Academy of Sciences of the United States of America (National Academy of Sciences)-Vol. 100, Iss: 3, pp 1438-1443
TL;DR: The data indicate that glucagon is essential for maintenance of normal glycemia and postnatal regulation of islet and α and δ cell numbers and the lean phenotype of Gcgr−/− mice suggests glucagon action may be involved in the regulation of whole body composition.
Abstract: Glucagon, the counter-regulatory hormone to insulin, is secreted from pancreatic α cells in response to low blood glucose. To examine the role of glucagon in glucose homeostasis, mice were generated with a null mutation of the glucagon receptor (Gcgr−/−). These mice display lower blood glucose levels throughout the day and improved glucose tolerance but similar insulin levels compared with control animals. Gcgr−/− mice displayed supraphysiological glucagon levels associated with postnatal enlargement of the pancreas and hyperplasia of islets due predominantly to α cell, and to a lesser extent, δ cell proliferation. In addition, increased proglucagon expression and processing resulted in increased pancreatic glucogen-like peptide 1 (GLP-1) (1–37) and GLP-1 amide (1–36 amide) content and a 3- to 10-fold increase in circulating GLP-1 amide. Gcgr−/− mice also displayed reduced adiposity and leptin levels but normal body weight, food intake, and energy expenditure. These data indicate that glucagon is essential for maintenance of normal glycemia and postnatal regulation of islet and α and δ cell numbers. Furthermore, the lean phenotype of Gcgr−/− mice suggests glucagon action may be involved in the regulation of whole body composition.
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TL;DR: This review focuses on the mechanisms regulating the synthesis, secretion, biological actions, and therapeutic relevance of the incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1).
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TL;DR: The main actions of GLP-1 are to stimulate insulin secretion and to inhibit glucagon secretion, thereby contributing to limit postprandial glucose excursions and acts as an enterogastrone and part of the "ileal brake" mechanism.
Abstract: Glucagon-like peptide 1 (GLP-1) is a 30-amino acid peptide hormone produced in the intestinal epithelial endocrine L-cells by differential processing of proglucagon, the gene which is expressed in ...
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Cites background from "Lower blood glucose, hyperglucagone..."
...In agreement with this, animals in which the PC2 gene is disrupted cannot cleave proglucagon in the alpha cells (73) and, as a result, have lower glucose levels than wild-type animals and improved tolerance to glucose, and they develop alpha cell hyperplasia, features that also characterize mice with a deletion of the glucagon receptor gene (77)....
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TL;DR: The liver is an essential metabolic organ, and its metabolic function is controlled by insulin and other metabolic hormones, so controlling liver energy metabolism is tightly regulated by neuronal and hormonal signals.
Abstract: The liver is an essential metabolic organ, and its metabolic function is controlled by insulin and other metabolic hormones. Glucose is converted into pyruvate through glycolysis in the cytoplasm, and pyruvate is subsequently oxidized in the mitochondria to generate ATP through the TCA cycle and oxidative phosphorylation. In the fed state, glycolytic products are used to synthesize fatty acids through de novo lipogenesis. Long-chain fatty acids are incorporated into triacylglycerol, phospholipids, and/or cholesterol esters in hepatocytes. These complex lipids are stored in lipid droplets and membrane structures, or secreted into the circulation as very low-density lipoprotein particles. In the fasted state, the liver secretes glucose through both glycogenolysis and gluconeogenesis. During pronged fasting, hepatic gluconeogenesis is the primary source for endogenous glucose production. Fasting also promotes lipolysis in adipose tissue, resulting in release of nonesterified fatty acids which are converted into ketone bodies in hepatic mitochondria though β-oxidation and ketogenesis. Ketone bodies provide a metabolic fuel for extrahepatic tissues. Liver energy metabolism is tightly regulated by neuronal and hormonal signals. The sympathetic system stimulates, whereas the parasympathetic system suppresses, hepatic gluconeogenesis. Insulin stimulates glycolysis and lipogenesis but suppresses gluconeogenesis, and glucagon counteracts insulin action. Numerous transcription factors and coactivators, including CREB, FOXO1, ChREBP, SREBP, PGC-1α, and CRTC2, control the expression of the enzymes which catalyze key steps of metabolic pathways, thus controlling liver energy metabolism. Aberrant energy metabolism in the liver promotes insulin resistance, diabetes, and nonalcoholic fatty liver diseases.
1,444 citations
Cites background from "Lower blood glucose, hyperglucagone..."
...Systemic deletion of glucagon receptors decreases blood glucose levels and improves glucose tolerance (66, 205)....
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TL;DR: More effective therapies to slow progressive loss of β-cell function are needed and additional long-term studies of drugs and bariatric surgery are needed to identify new ways to prevent and treat type 2 diabetes and thereby reduce the harmful effects of this disease.
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TL;DR: The 12th update of the human obesity gene map is presented, which incorporates published results up to the end of October 2005, and shows putative loci on all chromosomes except Y.
Abstract: This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.
1,205 citations
References
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TL;DR: The aim of this monograph is to clarify the role of Incretin in the development of Glucagon-Related Peptides in women and to provide a mechanistic basis for future research into their role in women's health.
Abstract: I. Introduction II. History of the Incretin Concept: Discovery of Gastric Inhibitory Polypeptide III. Discovery of GLP-1 IV. Structures of GLPs and Family of Glucagon-Related Peptides V. Tissue Distribution of the Expression of GLPs A. Pancreatic α-cells B. Intestinal L cells C. Central nervous system VI. Proglucagon Biosynthesis A. Organization/structure of the proglucagon gene B. Regulation of glucagon gene expression C. Posttranslational processing of proglucagon VII. Regulation of GLP Secretion A. Overview B. Intracellular signals C. Carbohydrates D. Fats E. Proteins F. Endocrine G. Neural H. GLP-2 VIII. Metabolism of GLPs A. GLP-1 B. GLP-2 IX. Physiological Actions of GLPs A. Overview B. Pancreatic islets C. Counterregulatory actions of GLP-1 and leptin on β-cells D. Stomach E. Lung F. Brain G. Liver, skeletal muscle, and fat H. Pituitary, hypothalamus, and thyroid I. Cardiovascular system J. GLP-2 X. GLP Receptors A. Structure B. Signaling C. Distribution D. Regulation E. GLP-2 XI. Pathophysiology o...
1,308 citations
Book•
01 Jan 1993
TL;DR: Biology experimental models pancreatitis endocrine and exocrine pancreatic relationships pancreatic neoplasms congenital and hereditary diseases imaging of the pancreas.
Abstract: Biology experimental models pancreatitis endocrine and exocrine pancreatic relationships pancreatic neoplasms congenital and hereditary diseases imaging of the pancreas.
546 citations
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TL;DR: This review focuses on the serine proteases that process protein precursors (proproteins) traversing the secretory pathway and the early development of this field is reviewed.
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TL;DR: It is demonstrated that functional GLUT4 protein is not required for maintaining nearly normal glycaemia but that GLLJT4 is absolutely essential for sustained growth, normal cellular glucose and fat metabolism, and expected longevity.
Abstract: THE insulin-sensitive glucose transporter, GLUT4, is the most abundant facilitative glucose transporter in muscle and adipose tissue, the major sites for postprandial glucose disposal. To assess the role of GLUT4 in glucose homeostasis, we have disrupted the murine GLUT4 gene. Because GLUT4 has been shown to be dysregulated in pathological states such as diabetes and obesity, it was expected that genetic ablation of GLUT4 would result in abnormal glucose homeostasis. The mice deficient in GLUT4 (GLUT4-null) are growth-retarded and exhibit decreased longevity associated with cardiac hypertrophy and severely reduced adipose tissue deposits. Blood glucose levels in female GLUT4-null mice are not significantly elevated in either the fasting or fed state; in contrast, male GLUT4-null mice have moderately reduced glycaemias in the fasted state and increased glycaemias in the fed state. However, both female and male GLUT4-null mice exhibit postprandial hyperinsulinaemia, indicating possible insulin resistance. Increased expression of other glucose transporters is observed in the liver (GLUT2) and heart (GLUT1) but not skeletal muscle. Oral glucose tolerance tests show that both female and male GLUT4-null mice clear glucose as efficiently as controls, but insulin tolerance tests indicate that these mice are less sensitive to insulin action. The GLUT4-null mice demonstrate that functional GLUT4 protein is not required for maintaining nearly normal glycaemia but that GLLJT4 is absolutely essential for sustained growth, normal cellular glucose and fat metabolism, and expected longevity.
475 citations