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Abels M, Riva M, Bennet H, Ahlqvist E, Dyachok O, Nagaraj V, Shcherbina L, Fred RG, Poon W, Sörhede-Winzell M, Fadista J, Lindqvist A, Kask L, Sathanoori R, Dekker-Nitert M, Kuhar MJ, Ahrén B, Wollheim CB, Hansson O, Tengholm A, Fex M, Renström E, Groop L, Lyssenko V, Wierup N. CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion. Diabetologia 2016; 59:1928-37. [PMID: 27338624 DOI: 10.1007/s00125-016-4020-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 05/23/2016] [Indexed: 11/30/2022]
Abstract
AIMS/HYPOTHESIS Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart (-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice. METHODS CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca(2+) oscillation patterns and exocytosis were studied in mouse islets. RESULTS We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca(2+) signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis. CONCLUSIONS/INTERPRETATION We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.
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Affiliation(s)
- Mia Abels
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Matteo Riva
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Hedvig Bennet
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Emma Ahlqvist
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Oleg Dyachok
- Department of Medical Cell Biology, Uppsala University Biomedical Centre, Uppsala, Sweden
| | - Vini Nagaraj
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Liliya Shcherbina
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Rikard G Fred
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Wenny Poon
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | | | - Joao Fadista
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Andreas Lindqvist
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Lena Kask
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Ramasri Sathanoori
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | | | - Michael J Kuhar
- The Yerkes Research Center of Emory University, Atlanta, GA, USA
| | - Bo Ahrén
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Claes B Wollheim
- Department of Cell Physiology and Metabolism, University Medical Centre, Geneva, Switzerland
| | - Ola Hansson
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Anders Tengholm
- Department of Medical Cell Biology, Uppsala University Biomedical Centre, Uppsala, Sweden
| | - Malin Fex
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Erik Renström
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Leif Groop
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
| | - Valeriya Lyssenko
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden
- Steno Diabetes Center A/S, Gentofte, Denmark
| | - Nils Wierup
- Lund University Diabetes Centre, Skåne University Hospital, Lund and Malmö, Sweden.
- Lund University Diabetes Centre, Skåne University Hospital, Department of Clinical Sciences in Malmö, Unit of Neuroendocrine Cell Biology, Lund University, Clinical Research Centre 91:12, Jan Waldenströms gata 35, 20502, Malmö, Sweden.
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Omar B, Sörhede-Winzell M, Ahrén B. Conditional glucagon receptor overexpression has multi-faceted consequences for beta-cell function. Metabolism 2014; 63:1568-76. [PMID: 25301258 DOI: 10.1016/j.metabol.2014.09.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Revised: 08/28/2014] [Accepted: 09/19/2014] [Indexed: 12/24/2022]
Abstract
BACKGROUND Although it is known that the islet expression of glucagon receptors is increased in type 2 diabetes, its implication for beta-cell function is not known. OBJECTIVE To determine whether increased beta cell glucagon receptor expression and action influences multiple aspects of beta cell function. MATERIALS/METHODS Mice with beta cell specific overexpression of the glucagon receptor (RIP-Gcgr) were subjected to intravenous glucose tolerance tests with acute injections of glucagon or GLP-1. Mice were also subjected to intravenous arginine and carbachol tests and insulin secretory responses were evaluated. RESULTS The specific beta-cell overexpression of glucagon receptors has a complex and diverse consequence with dissociated consequences on beta-cell secretion depending on the stimulatory secretagogue in that whereas the potentiating effects of GLP-1 and arginine on glucose-stimulated insulin secretion were completely lost, the response to the muscarinic receptor agonist carbachol was largely unaffected and the insulin secretory response to glucose was exaggerated. CONCLUSION This suggests that glucagon receptor overexpression, which is seen in hyperglycemia, may have dissociated consequence on beta cell function in its regulation under fasting, after meal and in response to autonomic nervous activation.
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Affiliation(s)
- Bilal Omar
- Lund University, Department of Clinical Sciences, Lund, Sweden.
| | | | - Bo Ahrén
- Lund University, Department of Clinical Sciences, Lund, Sweden
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Fex M, Olofsson CS, Fransson U, Bacos K, Lindvall H, Sörhede-Winzell M, Rorsman P, Holm C, Mulder H. Hormone-sensitive lipase deficiency in mouse islets abolishes neutral cholesterol ester hydrolase activity but leaves lipolysis, acylglycerides, fat oxidation, and insulin secretion intact. Endocrinology 2004; 145:3746-53. [PMID: 15142983 DOI: 10.1210/en.2003-1673] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Lipids are thought to serve as coupling factors in insulin secretion. Hormone-sensitive lipase (HSL) is expressed in pancreatic beta-cells and could potentially regulate insulin secretion via mobilization of stored triglycerides. Here, we examined the impact of HSL deficiency on fuel metabolism and insulin secretion in mouse islets. Lack of HSL resulted in abrogation of neutral cholesterol ester hydrolase activity, whereas diglyceride lipase activity remained intact. Although glucose stimulates lipolysis in rat islets, elevation of glucose with or without addition of cAMP failed to increase lipolysis in mouse islets regardless of genotype, as indicated by release of glycerol from islets. Storage of lipids, assayed as total acylglycerides, was unaltered in HSL null islets, and oxidation of fatty acids or glucose was not different. The intracellular rise in Ca(2+) triggered by glucose and its subsequent oscillations was unaffected in HSL null islets. Accordingly, insulin secretion in static incubations of islets, in response to fuel- and nonfuel secretagogues, was in no instance significantly different between wild-type and HSL null mice. The lacking impact of HSL deficiency on insulin secretion may be attributed to the failure of insulin secretagogues to stimulate lipolysis. Consequently, a regulatory function of lipid mobilization in insulin secretion in the mouse appears unlikely.
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Affiliation(s)
- Malin Fex
- Department of Cell and Molecular Biology, Lund University, SE-221 84, Lund Sweden
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Mulder H, Sörhede-Winzell M, Contreras JA, Fex M, Ström K, Ploug T, Galbo H, Arner P, Lundberg C, Sundler F, Ahrén B, Holm C. Hormone-sensitive lipase null mice exhibit signs of impaired insulin sensitivity whereas insulin secretion is intact. J Biol Chem 2003; 278:36380-8. [PMID: 12835327 DOI: 10.1074/jbc.m213032200] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Lipid metabolism plays an important role in glucose homeostasis under normal and pathological conditions. In adipocytes, skeletal muscle, and pancreatic beta-cells, lipids are mobilized from acylglycerides by the hormone-sensitive lipase (HSL). Here, the consequences of a targeted disruption of the HSL gene for glucose homeostasis were examined. HSL null mice were slightly hyperglycemic in the fasted, but not fed state, which was accompanied by moderate hyperinsulinemia. During glucose challenges, however, disposal of the sugar was not affected in HSL null mice, presumably because of release of increased amounts of insulin. Impaired insulin sensitivity was further indicated by retarded glucose disposal during an insulin tolerance test. A euglycemic hyperinsulinemic clamp revealed that hepatic glucose production was insufficiently blocked by insulin in HSL null mice. In vitro, insulin-stimulated glucose uptake into soleus muscle, and lipogenesis in adipocytes were moderately reduced, suggesting additional sites of insulin resistance. Morphometric analysis of pancreatic islets revealed a doubling of beta-cell mass in HSL null mice, which is consistent with an adaptation to insulin resistance. Insulin secretion in vitro, examined by perifusion of isolated islets, was not impacted by HSL deficiency. Thus, HSL deficiency results in a moderate impairment of insulin sensitivity in multiple target tissues of the hormone but is compensated by hyperinsulinemia.
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Affiliation(s)
- Hindrik Mulder
- Department of Cell and Molecular Biology, Physiological Sciences, and Medicine, Lund University, SE-221 84 Lund, Sweden.
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Grober J, Lucas S, Sörhede-Winzell M, Zaghini I, Mairal A, Contreras JA, Besnard P, Holm C, Langin D. Hormone-sensitive lipase is a cholesterol esterase of the intestinal mucosa. J Biol Chem 2003; 278:6510-5. [PMID: 12482847 DOI: 10.1074/jbc.m208513200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The identity of the enzymes responsible for lipase and cholesterol esterase activities in the small intestinal mucosa is not known. Because hormone-sensitive lipase (HSL) catalyzes the hydrolysis of acylglycerols and cholesteryl esters, we sought to determine whether HSL could be involved. HSL mRNA and protein were detected in all segments of the small intestine by Northern and Western blot analyses, respectively. Immunocytochemistry experiments revealed that HSL was expressed in the differentiated enterocytes of the villi and was absent in the undifferentiated cells of the crypt. Diacylglycerol lipase and cholesterol esterase activities were found in the different segments. Analysis of gut from HSL-null mice showed that diacylglycerol lipase activity was unchanged in the duodenum and reduced in jejunum. Neutral cholesterol esterase activity was totally abolished in duodenum, jejunum, and ileum of HSL-null mice. Analysis of HSL mRNA structure showed two types of transcripts expressed in equal amounts with alternative 5'-ends transcribed from two exons. This work demonstrates that HSL is expressed in the mucosa of the small intestine. The results also reveal that the enzyme participates in acylglycerol hydrolysis in jejunal enterocytes and cholesteryl ester hydrolysis throughout the small intestine.
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Affiliation(s)
- Jacques Grober
- Laboratoire de Physiologie de la Nutrition, Ecole Nationale Supérieure de Biologie Appliquée à la Nutrition et à l'Alimentation, FRE2328 CNRS/Université de Bourgogne 1, Dijon 21000, France
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Abstract
OBJECTIVE To discover a possible absorption and/or secretion of enterostatin into the circulating blood, as well as to compare the levels of circulating enterostatin after high-fat feeding and low-fat feeding. RESEARCH METHODS AND PROCEDURES Using a specific enzyme-linked immunosorbent assay, plasma enterostatin levels were determined after feeding a high-fat, a high-fat/-sucrose, or a low-fat meal to Sprague-Dawley rats deprived of food overnight. RESULTS The enterostatin levels were increased by all diets; the response to the high-fat and the high-fat/-sucrose meals was greater in magnitude and duration than that to the low-fat meal. In addition, enterostatin levels correlated with the intake of dietary fat. Plasma enterostatin levels after high-fat feeding were found to be similar to those after intravenous administration of exogenous enterostatin known to inhibit high-fat food intake. Gel chromatography of pooled postprandial plasma extracts followed by high-performance liquid chromatography analysis showed that plasma enterostatin was identical to synthetic enterostatin. Affinity cross-linking of plasma proteins with 125I-enterostatin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by autoradiography, revealed a single band with a molecular weight of about 66 kDa, indicating the presence of a potential enterostatin-binding protein in plasma. DISCUSSION The measurements of plasma enterostatin may be a sensitive indicator for the measurement of fat intake.
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Affiliation(s)
- Jie Mei
- Department of Cell and Molecular Biology, University of Lund, Lund, Sweden
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