Glucagon Receptor Signaling Is Essential for Control of Murine Hepatocyte Survival

doi:10.1053/j.gastro.2008.07.075

Gastroenterology

Volume 135, Issue 6, December 2008, Pages 2096-2106

https://doi.org/10.1053/j.gastro.2008.07.075 Get rights and content

Background & Aims

Glucagon action in the liver is essential for control of glucose homeostasis and the counterregulatory response to hypoglycemia. Because receptors for the related peptides glucagon-like peptide-1 and glucagon-like peptide-2 regulate β-cell and enterocyte apoptosis, respectively, we examined whether glucagon receptor (Gcgr) signaling modulates hepatocyte survival.

Methods

The importance of the Gcgr for hepatocyte cell survival was examined using Gcgr+/+ and Gcgr−/− mice in vivo, and murine hepatocyte cultures in vitro.

Results

Gcgr−/− mice showed enhanced susceptibility to experimental liver injury induced by either Fas Ligord activation or a methionine- and choline-deficient diet. Restoration of hepatic Gcgr expression in Gcgr−/− mice attenuated the development of hepatocellular injury. Furthermore, exogenous glucagon administration reduced Jo2-induced apoptosis in wild-type mice and decreased caspase activation in fibroblasts expressing a heterologous Gcgr and in primary murine hepatocyte cultures. The anti-apoptotic actions of glucagon were independent of protein kinase A, phosphatioylinositol-3K, and mitogen-activated protein kinase, and were mimicked by the exchange protein directly activated by the cyclic AMP agonist 8-(4-chloro-phenylthio)-2′-O-methyladerosine-3′, 5′-cyclic monophosphate-cAMP.

Conclusions

These findings extend the essential actions of the Gcgr beyond the metabolic control of glucose homeostasis to encompass the regulation of hepatocyte survival.

Section snippets

Materials

Tissue culture reagents were from Invitrogen (Burlington, Ontario, Canada) and chemicals were from Sigma–Aldrich (St Louis, MO). Human glucagon was purchased from California Peptides (Napa, CA). H-89, LY294002, and U0126 were from Calbiochem (Gibbstown, NJ). Primary tissue culture plates were from BD Biosciences (San Jose, CA). Anti-Fas antibody (Jo2) was from BD Pharmingen (San Jose, CA) and the exchange protein directly activated by cyclic AMP (Epac) agonist 8-pCPT-Me-cAMP was from Biolog

Results

Mouse hepatocytes showed a dose-dependent increase in levels of cAMP in response to glucagon with a half maximal effective concentration (EC₅₀) of between 0.13 and 0.8 nmol/L (supplementary Figure 1; see supplementary material online at www.gastrojournal.org). Activation of the Fas pathway with the Jo2 antibody produced characteristic morphologic signs of apoptosis, including blebbing, chromatin condensation, and cell lysis¹³ (Figure 1A,panel b); the morphologic features of apoptosis were

Discussion

Signaling through class B G-protein–coupled receptors⁸ is known to promote cell survival. For example, GLP-2 directly reduces apoptosis in cells¹⁹ and in rodents with experimental intestinal injury.²⁰ Similarly, GLP-1–receptor activation reduced cell death in rodent insulinomas and in rodent and human pancreatic islet β-cells.²¹ Conversely, Glp1r−/− β cells display enhanced susceptibility to apoptotic injury.²² Our observations extend these concepts by establishing that endogenous Gcgr

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Glucagon
2021, Handbook of Hormones: Comparative Endocrinology for Basic and Clinical Research
Glucagon is a linear peptide hormone consisting of 29 amino acid residues, secreted from the pancreatic α cells. Glucagon shares the same precursor, proglucagon, with GLP-1 and GLP-2. By tissue-specific posttranslational processing, glucagon is secreted from pancreatic α cells whereas GLP-1 and GLP-2 are secreted from intestinal L cells. All these peptides have considerable sequence homology and form the glucagon family, a subfamily of the secretin-glucagon superfamily. Among the glucagon family members, the primary structure of glucagon is most highly conserved in vertebrates. Glucagon is the principal hyperglycemic hormone, and acts as a counterbalancing hormone to insulin. Glucagon generally elevates the blood glucose levels by promoting gluconeogenesis and glycogenolysis. Glucagon has the greatest effect on the liver, although it affects many different organs in the body such as the adipose tissue, pancreas, brain, and kidney.
Pancreatic Hormones
2020, Hormonal Signaling in Biology and Medicine: Comprehensive Modern Endocrinology
The pancreas has both an exocrine (digestive) function exerted by acinar cells and endocrine functions exerted by five different cell types secreting at least eight peptide hormones: insulin, glucagon, somatostatin, neuronostatin, pancreatic polypeptide, amylin, ghrelin, urocortin III, and stanniocalcin 2. In this chapter, we discuss the development, general organization, and cellular composition of the endocrine islets of Langerhans, the paracrine relationships between the different cell types, and the structure and function and mechanism of action of the various peptide hormones, and their role in metabolic pathophysiology.
Pancreatic Hormones
2019, Hormonal Signaling in Biology and Medicine: Comprehensive Modern Endocrinology
The pancreas has both an exocrine (digestive) function exerted by acinar cells and endocrine functions exerted by five different cell types secreting at least eight peptide hormones: insulin, glucagon, somatostatin, neuronostatin, pancreatic polypeptide, amylin, ghrelin, urocortin III, and stanniocalcin 2. In this chapter, we discuss the development, general organization, and cellular composition of the endocrine islets of Langerhans, the paracrine relationships between the different cell types, and the structure and function and mechanism of action of the various peptide hormones, and their role in metabolic pathophysiology.
Hepatocyte Toll-Like Receptor 5 Promotes Bacterial Clearance and Protects Mice Against High-Fat Diet–Induced Liver Disease
2016, Cellular and Molecular Gastroenterology and Hepatology
Innate immune dysfunction can promote chronic inflammatory diseases of the liver. For example, mice lacking the flagellin receptor Toll-like receptor 5 (TLR5) show microbial dysbiosis and predisposition to high-fat diet (HFD)-induced hepatic steatosis. The extent to which hepatocytes play a direct role in detecting bacterial products in general, or flagellin in particular, is poorly understood. In the present study, we investigated the role of hepatocyte TLR5 in recognizing flagellin, policing bacteria, and protecting against liver disease.
Mice were engineered to lack TLR5 specifically in hepatocytes (TLR5^ΔHep) and analyzed relative to sibling controls (TLR5^fl/fl). TLR5 messenger RNA levels, responses to exogenous flagellin, elimination of circulating motile bacteria, and susceptibility of liver injury (concanavalin A, carbon tetrachloride, methionine- and choline-deficient diet, and HFD) were measured.
TLR5^ΔHep expressed similar levels of TLR5 as TLR5^fl/fl in all organs examined, except in the liver, which showed a 90% reduction in TLR5 levels, indicating that hepatocytes accounted for the major portion of TLR5 expression in this organ. TLR5^ΔHep showed impairment in responding to purified flagellin and clearing flagellated bacteria from the liver. Although TLR5^ΔHep mice did not differ markedly from sibling controls in concanavalin A or carbon tetrachloride–induced liver injury models, they showed exacerbated disease in response to a methionine- and choline-deficient diet and HFD. Such predisposition of TLR5^ΔHep to diet-induced liver pathology was associated with increased expression of proinflammatory cytokines, which was dependent on the Nod-like-receptor C4 inflammasome and rescued by microbiota ablation.
Hepatocyte TLR5 plays a critical role in protecting liver against circulating gut bacteria and against diet-induced liver disease.
Cardiomyocyte glucagon receptor signaling modulates outcomes in mice with experimental myocardial infarction
2015, Molecular Metabolism
Citation Excerpt :
Activation of glucagon receptor (Gcgr) signaling promotes glycogenolysis and enhanced gluconeogenesis, and regulates pathways controlling hepatic lipid oxidation and lipid secretion. Although the actions of glucagon are classically viewed as essential for prevention of hypoglycemia in the face of limited nutrient availability or excess insulin action [1], Gcgr signaling also controls cell survival pathways, as genetic interruption of Gcgr signaling increases the susceptibility to hepatic injury [2]. A single Gcgr is expressed not only in liver, but in extrahepatic tissues including the central and peripheral nervous system, pancreatic islets, adipose tissue, kidney, blood vessels and heart [3,4].
Glucagon is a hormone with metabolic actions that maintains normoglycemia during the fasting state. Strategies enabling either inhibition or activation of glucagon receptor (Gcgr) signaling are being explored for the treatment of diabetes or obesity. However, the cardiovascular consequences of manipulating glucagon action are poorly understood.
We assessed infarct size and the following outcomes following left anterior descending (LAD) coronary artery ligation; cardiac gene and protein expression, acylcarnitine profiles, and cardiomyocyte survival in normoglycemic non-obese wildtype mice, and in newly generated mice with selective inactivation of the cardiomyocyte Gcgr. Complementary experiments analyzed Gcgr signaling and cell survival in cardiomyocyte cultures and cell lines, in the presence or absence of exogenous glucagon.
Exogenous glucagon administration directly impaired recovery of ventricular pressure in ischemic mouse hearts ex vivo, and increased mortality from myocardial infarction after LAD coronary artery ligation in mice in a p38 MAPK-dependent manner. In contrast, cardiomyocyte-specific reduction of glucagon action in adult Gcgr^CM−/− mice significantly improved survival, and reduced hypertrophy and infarct size following myocardial infarction. Metabolic profiling of hearts from Gcgr^CM−/− mice revealed a marked reduction in long chain acylcarnitines in both aerobic and ischemic hearts, and following high fat feeding, consistent with an essential role for Gcgr signaling in the control of cardiac fatty acid utilization.
Activation or reduction of cardiac Gcgr signaling in the ischemic heart produces substantial cardiac phenotypes, findings with implications for therapeutic strategies designed to augment or inhibit Gcgr signaling for the treatment of metabolic disorders.
Glucagon
2015, Handbook of Hormones: Comparative Endocrinology for Basic and Clinical Research
Glucagon is a linear peptide hormone of 29 amino acids secreted from α cells of the pancreas. Glucagon shares the same precursor molecule, proglucagon, with GLP-1 and GLP-2. By tissue-specific posttranslational processing, glucagon is secreted from pancreatic α cells whereas GLP-1 and GLP-2 are secreted from intestinal L cells. All these peptides have considerable sequence homology and form a subfamily within the secretin family. Among the members of the glucagon subfamily, the glucagon sequence is most highly conserved throughout vertebrates. Glucagon is the principal hyperglycemic hormone, and acts as a counterbalancing hormone to insulin. Glucagon generally elevates the level of blood glucose by promoting gluconeogenesis and glycogenolysis. Glucagon has the greatest effect on the liver although it affects many different organs in the body, such as adipose tissue, pancreas, brain, and kidney.

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: The authors disclose the following: Dr Drucker consults for companies developing diabetes therapeutics as disclosed at http://www.glucagon.com/druckerlab.html. These studies were supported by an operating grant from the Canadian Institutes for Health Research MOP-10903, the Canada Research Chairs Program (D.J.D.), and by National Institutes of Health grant RO1 DK47425 (M.C.).

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Basic—Liver, Pancreas, and Biliary TractGlucagon Receptor Signaling Is Essential for Control of Murine Hepatocyte Survival

Background & Aims

Methods

Results

Conclusions

Section snippets

Materials

Results

Discussion

Biochem Biophys Res Commun

Gastroenterology

J Biol Chem

J Hepatol

Gastroenterology

Best Pract Res Clin Gastroenterol

J Biol Chem

J Biol Chem

Arch Biochem Biophys

Glucagon and regulation of glucose metabolism

Am J Physiol Endocrinol Metab

Lower blood glucose, hyperglucagonemia, and pancreatic {alpha} cell hyperplasia in glucagon receptor knockout mice

Proc Natl Acad Sci U S A

Glucagon receptor knockout mice display increased insulin sensitivity and impaired {beta}-cell function

Diabetes

Glucagon receptor knockout mice are resistant to diet-induced obesity and streptozotocin-mediated beta cell loss and hyperglycaemia

Diabetologia

Emerging therapies mimicking the effects of amylin and glucagon-like peptide 1

Diabetes Care

Basic—Liver, Pancreas, and Biliary Tract
Glucagon Receptor Signaling Is Essential for Control of Murine Hepatocyte Survival