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Gray CW, Coster ACF. Periodic insulin stimulation of Akt: Dynamic steady states and robustness. Math Biosci 2024; 367:109113. [PMID: 38056823 DOI: 10.1016/j.mbs.2023.109113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 11/29/2023] [Accepted: 12/01/2023] [Indexed: 12/08/2023]
Abstract
The periodic secretion of insulin is a salient feature of the blood glucose control system in vivo. Insulin levels in the blood exhibit oscillations on multiple time scales - rapid, ultradian, and circadian - and the improved metabolic regulation resulting from pulsatile insulin release has been well established. Although numerous mathematical models investigating the causal mechanisms of insulin oscillations have appeared in the literature, to date there has been comparatively little attention given to the influence of periodic insulin stimulation on downstream components of the insulin signalling pathway. In this paper, we explore the effect of high frequency periodic insulin stimulation on Akt (also known as PKB), a crucial crosstalk node in the insulin signalling pathway that coordinates metabolic and mitogenic processes in the cell. We analyse a mathematical model of Akt translocation to the plasma membrane under both single step insulin perturbations and periodic insulin stimulation with an emphasis on - but not limited to - the physiological range of parameter values. It was shown that the system rapidly attains a robust dynamic steady state entrained to the periodic insulin stimulation. Moreover, the translocation of Akt to the plasma membrane in the model permits a sufficient level of phosphorylation to trigger downstream metabolic regulators. However, the modelling also indicated that further investigation of this activation process is required to determine whether the response of Akt is a key determinant of the enhanced metabolic control observed under periodic insulin stimulation.
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Affiliation(s)
- Catheryn W Gray
- School of Mathematics and Statistics, The University of New South Wales, Sydney, 2052, New South Wales, Australia.
| | - Adelle C F Coster
- School of Mathematics and Statistics, The University of New South Wales, Sydney, 2052, New South Wales, Australia.
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2
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Roy JR, Janaki CS, Jayaraman S, Periyasamy V, Balaji T, Vijayamalathi M, Veeraraghavan VP. Carica papaya Reduces Muscle Insulin Resistance via IR/GLUT4 Mediated Signaling Mechanisms in High Fat Diet and Streptozotocin-Induced Type-2 Diabetic Rats. Antioxidants (Basel) 2022; 11:antiox11102081. [PMID: 36290804 PMCID: PMC9598374 DOI: 10.3390/antiox11102081] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2022] [Revised: 10/15/2022] [Accepted: 10/17/2022] [Indexed: 11/19/2022] Open
Abstract
In the management of type 2 diabetes, oral antidiabetic drugs have several side effects, which in turn have led the pharmaceutical industry to search for good therapeutic, non-toxic and reliable drugs. Carica papaya (C. papaya) is one of several plants in nature that have been found to possess anti-diabetic properties. Despite studies being focused on the antidiabetic activity of C. papaya, the molecular mechanism against high fat diet induced insulin resistance is yet to be identified. The role of C. papaya was evaluated on insulin signaling molecules, such as the insulin receptor (IR) and glucose transporter-4 (GLUT4) in high fat, diet-streptozotocin induced type 2 diabetic rats, and analyzed the bioactive compounds of C. papaya against IR and GLUT4 via molecular docking and dynamics. The ethanolic extract of C. papaya leaves (600 mg/kg of body weight) was given daily to male wistar rats for 45 days and we observed the various biochemical parameters, gene expression analysis and histopathology of skeletal muscle. Molecular docking and dynamics were undertaken to understand the bioactive compounds with the greatest hit rate. C. papaya treatment was able to control blood glucose levels, the lipid profile and serum insulin, but it facilitated tissue antioxidant enzymes and IR and GLUT4 levels. The in-silico study showed that kaempferol, quercitin and transferulic acid were the top three ligands with the greatest hit rate against the protein targets. Our preliminary findings, for the first time, showed that C. papaya reinstates the glycemic effect in the diabetic skeletal muscle by accelerating the expression of IR and GLUT4.
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Affiliation(s)
- Jeane Rebecca Roy
- Department of Anatomy, Bhaarath Medical College and Hospital, Bharath Institute of Higher Education and Research (BIHER), Chennai 600 073, Tamil Nadu, India
- Correspondence: (J.R.R.); (S.J.)
| | - Coimbatore Sadagopan Janaki
- Department of Anatomy, Bhaarath Medical College and Hospital, Bharath Institute of Higher Education and Research (BIHER), Chennai 600 073, Tamil Nadu, India
| | - Selvaraj Jayaraman
- Centre of Molecular Medicine and Diagnostics (COMManD), Department of Biochemistry, Saveetha Dental College & Hospitals, Saveetha Institute of Medical & Technical Sciences, Saveetha University, Chennai 600 077, Tamil Nadu, India
- Correspondence: (J.R.R.); (S.J.)
| | - Vijayalakshmi Periyasamy
- Department of Biotechnology and Bioinformatics, Holy Cross College, Trichy 620 002, Tamil Nadu, India
| | - Thotakura Balaji
- Department of Anatomy, Chettinad Hospital and Research Institute, Chettinad Academy of Research and Education, Chennai 603 103, Tamil Nadu, India
| | - Madhavan Vijayamalathi
- Department of Physiology, Bhaarath Medical College and Hospital, Bharath Institute of Higher Education and Research (BIHER), Chennai 600 073, Tamil Nadu, India
| | - Vishnu Priya Veeraraghavan
- Centre of Molecular Medicine and Diagnostics (COMManD), Department of Biochemistry, Saveetha Dental College & Hospitals, Saveetha Institute of Medical & Technical Sciences, Saveetha University, Chennai 600 077, Tamil Nadu, India
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3
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Rojano-Toimil A, Rivera-Esteban J, Manzano-Nuñez R, Bañares J, Martinez Selva D, Gabriel-Medina P, Ferrer R, Pericàs JM, Ciudin A. When Sugar Reaches the Liver: Phenotypes of Patients with Diabetes and NAFLD. J Clin Med 2022; 11:jcm11123286. [PMID: 35743358 PMCID: PMC9225139 DOI: 10.3390/jcm11123286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 06/03/2022] [Accepted: 06/06/2022] [Indexed: 01/27/2023] Open
Abstract
Type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD) have been traditionally linked to one another. Recent studies suggest that NAFLD may be increasingly common in other types of diabetes such as type 1 diabetes (T1DM) and less frequently ketone-prone and Maturity-onset Diabetes of the Young (MODY) diabetes. In this review, we address the relationship between hyperglycemia and insulin resistance and the onset and progression of NAFLD. In addition, despite the high rate of patients with T2DM and other diabetes phenotypes that can alter liver metabolism and consequently develop steatosis, fibrosis, and cirrhosis, NALFD screening is not still implemented in the daily care routine. Incorporating a clinical algorithm created around a simple, non-invasive, cost-effective model would identify high-risk patients. The principle behind managing these patients is to improve insulin resistance and hyperglycemia states with lifestyle changes, weight loss, and new drug therapies.
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Affiliation(s)
- Alba Rojano-Toimil
- Endocrinology Department, Vall d’Hebron University Hospital, 08035 Barcelona, Spain;
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
| | - Jesús Rivera-Esteban
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
- Medicine Department Bellaterra, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain
- Liver Unit, Vall d’Hebron University Hospital, 08035 Barcelona, Spain
| | - Ramiro Manzano-Nuñez
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
- Liver Unit, Vall d’Hebron University Hospital, 08035 Barcelona, Spain
| | - Juan Bañares
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
- Liver Unit, Vall d’Hebron University Hospital, 08035 Barcelona, Spain
| | - David Martinez Selva
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
- Spanish Network of Biomedical Research Centers, Diabetes and Metabolic Associated Disorders (CIBERdem), 28029 Madrid, Spain
| | - Pablo Gabriel-Medina
- Biochemistry Department, Vall d’Hebron University Hospital, 08035 Barcelona, Spain; (P.G.-M.); (R.F.)
- Biochemistry and Molecular Biology Department, Universitat Autònoma de Barcelona (UAB), Bellaterra, 08193 Barcelona, Spain
| | - Roser Ferrer
- Biochemistry Department, Vall d’Hebron University Hospital, 08035 Barcelona, Spain; (P.G.-M.); (R.F.)
| | - Juan M Pericàs
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
- Liver Unit, Vall d’Hebron University Hospital, 08035 Barcelona, Spain
- Spanish Network of Biomedical Research Centers, Liver and Digestive Diseases (CIBERehd), 28801 Madrid, Spain
- Correspondence: (J.M.P.); (A.C.)
| | - Andreea Ciudin
- Endocrinology Department, Vall d’Hebron University Hospital, 08035 Barcelona, Spain;
- Vall d’Hebron Institut de Recerca (VHIR), 08035 Barcelona, Spain; (J.R.-E.); (R.M.-N.); (J.B.); (D.M.S.)
- Medicine Department Bellaterra, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain
- Spanish Network of Biomedical Research Centers, Diabetes and Metabolic Associated Disorders (CIBERdem), 28029 Madrid, Spain
- Correspondence: (J.M.P.); (A.C.)
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Prasad M, Jayaraman S, Eladl MA, El-Sherbiny M, Abdelrahman MAE, Veeraraghavan VP, Vengadassalapathy S, Umapathy VR, Jaffer Hussain SF, Krishnamoorthy K, Sekar D, Palanisamy CP, Mohan SK, Rajagopal P. A Comprehensive Review on Therapeutic Perspectives of Phytosterols in Insulin Resistance: A Mechanistic Approach. Molecules 2022; 27:molecules27051595. [PMID: 35268696 PMCID: PMC8911698 DOI: 10.3390/molecules27051595] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 02/24/2022] [Accepted: 02/25/2022] [Indexed: 02/04/2023] Open
Abstract
Natural products in the form of functional foods have become increasingly popular due to their protective effects against life-threatening diseases, low risk of adverse effects, affordability, and accessibility. Plant components such as phytosterol, in particular, have drawn a lot of press recently due to a link between their consumption and a modest incidence of global problems, such as Type 2 Diabetes mellitus (T2DM), cancer, and cardiovascular disease. In the management of diet-related metabolic diseases, such as T2DM and cardiovascular disorders, these plant-based functional foods and nutritional supplements have unquestionably led the market in terms of cost-effectiveness, therapeutic efficacy, and safety. Diabetes mellitus is a metabolic disorder categoriszed by high blood sugar and insulin resistance, which influence major metabolic organs, such as the liver, adipose tissue, and skeletal muscle. These chronic hyperglycemia fallouts result in decreased glucose consumption by body cells, increased fat mobilisation from fat storage cells, and protein depletion in human tissues, keeping the tissues in a state of crisis. In addition, functional foods such as phytosterols improve the body’s healing process from these crises by promoting a proper physiological metabolism and cellular activities. They are plant-derived steroid molecules having structure and function similar to cholesterol, which is found in vegetables, grains, nuts, olive oil, wood pulp, legumes, cereals, and leaves, and are abundant in nature, along with phytosterol derivatives. The most copious phytosterols seen in the human diet are sitosterol, stigmasterol, and campesterol, which can be found in free form, as fatty acid/cinnamic acid esters or as glycosides processed by pancreatic enzymes. Accumulating evidence reveals that phytosterols and diets enriched with them can control glucose and lipid metabolism, as well as insulin resistance. Despite this, few studies on the advantages of sterol control in diabetes care have been published. As a basis, the primary objective of this review is to convey extensive updated information on the possibility of managing diabetes and associated complications with sterol-rich foods in molecular aspects.
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Affiliation(s)
- Monisha Prasad
- Centre of Molecular Medicine and Diagnostics (COMManD), Department of Biochemistry, Saveetha Dental College & Hospital, Saveetha Institute of Medical & Technical Sciences, Chennai 600077, India; (M.P.); (K.K.)
| | - Selvaraj Jayaraman
- Centre of Molecular Medicine and Diagnostics (COMManD), Department of Biochemistry, Saveetha Dental College & Hospital, Saveetha Institute of Medical & Technical Sciences, Chennai 600077, India; (M.P.); (K.K.)
- Correspondence: (S.J.); (V.P.V.); (P.R.)
| | - Mohamed Ahmed Eladl
- Department of Basic Medical Sciences, College of Medicine, University of Sharjah, Sharjah 27272, United Arab Emirates;
| | - Mohamed El-Sherbiny
- Department of Basic Medical Sciences, College of Medicine, AlMaarefa University, Riyadh 71666, Saudi Arabia; (M.E.-S.); (M.A.E.A.)
| | | | - Vishnu Priya Veeraraghavan
- Centre of Molecular Medicine and Diagnostics (COMManD), Department of Biochemistry, Saveetha Dental College & Hospital, Saveetha Institute of Medical & Technical Sciences, Chennai 600077, India; (M.P.); (K.K.)
- Correspondence: (S.J.); (V.P.V.); (P.R.)
| | - Srinivasan Vengadassalapathy
- Department of Pharmacology, Saveetha Medical College and Hospital, Saveetha Institute of Medical & Technical Sciences, Chennai 602105, India;
| | - Vidhya Rekha Umapathy
- Department of Public Health Dentistry, Sree Balaji Dental College and Hospital, Pallikaranai, Chennai 600100, India;
| | | | - Kalaiselvi Krishnamoorthy
- Centre of Molecular Medicine and Diagnostics (COMManD), Department of Biochemistry, Saveetha Dental College & Hospital, Saveetha Institute of Medical & Technical Sciences, Chennai 600077, India; (M.P.); (K.K.)
| | - Durairaj Sekar
- Cellular and Molecular Research Centre, Saveetha Dental College & Hospitals, Saveetha Institute of Medical & Technical Sciences, Saveetha University, Chennai 600077, India;
| | - Chella Perumal Palanisamy
- State Key Laboratory of Biobased Material and Green Papermaking, College of Food Science and Engineering, Qilu University of Technology, Shandong Academy of Science, Jinan 250353, China;
| | - Surapaneni Krishna Mohan
- Departments of Biochemistry, Molecular Virology, Research, Clinical Skills & Simulation, Panimalar Medical College Hospital & Research Institute, Varadharajapuram, Poonamallee, Chennai 600123, India;
| | - Ponnulakshmi Rajagopal
- Department of Central Research Laboratory, Meenakshi Ammal Dental College and Hospitals, Chennai 600095, India
- Correspondence: (S.J.); (V.P.V.); (P.R.)
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5
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Mertens J, De Block C, Spinhoven M, Driessen A, Francque SM, Kwanten WJ. Hepatopathy Associated With Type 1 Diabetes: Distinguishing Non-alcoholic Fatty Liver Disease From Glycogenic Hepatopathy. Front Pharmacol 2021; 12:768576. [PMID: 34759828 PMCID: PMC8573337 DOI: 10.3389/fphar.2021.768576] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 10/06/2021] [Indexed: 12/14/2022] Open
Abstract
Autoimmune destruction of pancreatic β-cells results in the permanent loss of insulin production in type 1 diabetes (T1D). The daily necessity to inject exogenous insulin to treat hyperglycemia leads to a relative portal vein insulin deficiency and potentiates hypoglycemia which can induce weight gain, while daily fluctuations of blood sugar levels affect the hepatic glycogen storage and overall metabolic control. These, among others, fundamental characteristics of T1D are associated with the development of two distinct, but in part clinically similar hepatopathies, namely non-alcoholic fatty liver disease (NAFLD) and glycogen hepatopathy (GlyH). Recent studies suggest that NAFLD may be increasingly common in T1D because more people with T1D present with overweight and/or obesity, linked to the metabolic syndrome. GlyH is a rare but underdiagnosed complication hallmarked by extremely brittle metabolic control in, often young, individuals with T1D. Both hepatopathies share clinical similarities, troubling both diagnosis and differentiation. Since NAFLD is increasingly associated with cardiovascular and chronic kidney disease, whereas GlyH is considered self-limiting, awareness and differentiation between both condition is important in clinical care. The exact pathogenesis of both hepatopathies remains obscure, hence licensed pharmaceutical therapy is lacking and general awareness amongst physicians is low. This article aims to review the factors potentially contributing to fatty liver disease or glycogen storage disruption in T1D. It ends with a proposal for clinicians to approach patients with T1D and potential hepatopathy.
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Affiliation(s)
- Jonathan Mertens
- Department of Gastroenterology and Hepatology, Antwerp University Hospital, Edegem, Belgium.,Department of Endocrinology, Diabetology and Metabolism, Antwerp University Hospital, Edegem, Belgium.,Laboratory of Experimental Medicine and Pediatrics, University of Antwerp, Wilrijk, Belgium
| | - Christophe De Block
- Department of Endocrinology, Diabetology and Metabolism, Antwerp University Hospital, Edegem, Belgium.,Laboratory of Experimental Medicine and Pediatrics, University of Antwerp, Wilrijk, Belgium
| | - Maarten Spinhoven
- Department of Radiology, Antwerp University Hospital, Edegem, Belgium
| | - Ann Driessen
- Department of Pathology, Antwerp University Hospital, Antwerp, Belgium.,CORE, Faculty of Medicine and Health Sciences, University of Antwerp, Wilrijk, Belgium
| | - Sven M Francque
- Department of Gastroenterology and Hepatology, Antwerp University Hospital, Edegem, Belgium.,Laboratory of Experimental Medicine and Pediatrics, University of Antwerp, Wilrijk, Belgium
| | - Wilhelmus J Kwanten
- Department of Gastroenterology and Hepatology, Antwerp University Hospital, Edegem, Belgium.,Laboratory of Experimental Medicine and Pediatrics, University of Antwerp, Wilrijk, Belgium
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Mertens J, Van Gaal LF, Francque SM, De Block C. NAFLD in type 1 diabetes: overrated or underappreciated? Ther Adv Endocrinol Metab 2021; 12:20420188211055557. [PMID: 34840719 PMCID: PMC8613893 DOI: 10.1177/20420188211055557] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 10/04/2021] [Indexed: 12/18/2022] Open
Abstract
Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in western countries, affecting 25-30% of the general population and up to 65% in those with obesity and/or type 2 diabetes. Accumulation of visceral adipose tissue and insulin resistance (IR) contributes to NAFLD. NAFLD is not an innocent entity as it not only may cause nonalcoholic steatohepatitis and cirrhosis but also contribute to cardiovascular morbidity and mortality. More and more people with type 1 diabetes (T1D) are becoming overweight and present with features of IR, but the prevalence and impact of NAFLD in this population are still unclear. The utility of noninvasive screening tools for NAFLD in T1D is being explored. Recent data indicate that based upon ultrasonographic criteria NAFLD is present in 27% (ranging between 19% and 31%) of adults with T1D. Magnetic resonance imaging data indicate a prevalence rate of 8.6% (ranging between 2.1% and 18.6%). There are, however, multiple factors affecting these data, ranging from study design and referral bias to discrepancies in between diagnostic modalities. Individuals with T1D have a 7-fold higher risk of cardiovascular disease (CVD) and cardiovascular mortality is the most prominent cause of death in T1D. Patients with T1D and NALFD are also more prone to develop CVD, but the independent contribution of NAFLD to cardiovascular events has to be determined in this population. Furthermore, limited data in T1D also point towards a 2 to 3 times higher risk for microvascular complications in those with NAFLD. In this article, we will discuss epidemiological and diagnostic challenges of NAFLD in T1D, explore the link between IR and NAFLD and chronic complications, and examine the independent contribution of NAFLD to the presence of macro-, and microvascular complications.
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Affiliation(s)
- Jonathan Mertens
- Department of Endocrinology, Diabetology and Metabolism, Antwerp University Hospital, Drie Eikenstraat 655, 2650 Edegem, Belgium
- Laboratory of Experimental Medicine and Pediatrics and Member of the Infla-Med Centre of Excellence, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
- Department of Gastroenterology & Hepatology, Antwerp University Hospital, Edegem, Belgium
| | - Luc F. Van Gaal
- Department of Endocrinology, Diabetology and Metabolism, Antwerp University Hospital, Edegem, Belgium
- Laboratory of Experimental Medicine and Pediatrics and Member of the Infla-Med Centre of Excellence, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
| | - Sven M. Francque
- Department of Gastroenterology & Hepatology, Antwerp University Hospital, Drie Eikenstraat 655, 2650 Edegem, Belgium
- Laboratory of Experimental Medicine and Pediatrics and Member of the Infla-Med Centre of Excellence, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
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Bassols J, Serino M, Carreras-Badosa G, Burcelin R, Blasco-Baque V, Lopez-Bermejo A, Fernandez-Real JM. Gestational diabetes is associated with changes in placental microbiota and microbiome. Pediatr Res 2016; 80:777-784. [PMID: 27490741 DOI: 10.1038/pr.2016.155] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 06/03/2016] [Indexed: 12/18/2022]
Abstract
BACKGROUND The human microbiota is a modulator of the immune system. Variations in the placental microbiota could be related with pregnancy disorders. We profiled the placental microbiota and microbiome in women with gestational diabetes (GDM) and studied its relation to maternal metabolism and placental expression of anti-inflammatory cytokines. METHODS Placental microbiota and microbiome and expression of anti-inflammatory cytokines (IL10, TIMP3, ITGAX, and MRC1MR) were analyzed in placentas from women with GDM and from control women. Fasting insulin, glucose, O'Sullivan glucose, lipids, and blood cell counts were assessed at second and third trimester of pregnancy. RESULTS Bacteria belonging to the Pseudomonadales order and Acinetobacter genus showed lower relative abundance in women with GDM compared to control (P < 0.05). In GDM, lower abundance of placental Acinetobacter associated with a more adverse metabolic (higher O'Sullivan glucose) and inflammatory phenotype (lower blood eosinophil count and lower placental expression of IL10 and TIMP3) (P < 0.05 to P = 0.001). Calcium signaling pathway was increased in GDM placental microbiome. CONCLUSION A distinct microbiota profile and microbiome is present in GDM. Acinetobacter has been recently shown to induce IL-10 in mice. GDM could constitute a state of placental microbiota-driven altered immunologic tolerance, making placental microbiota a new target for therapy in GDM.
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Affiliation(s)
- Judit Bassols
- Department of Pediatrics, Dr. Josep Trueta Hospital and Girona Institute for Biomedical Research, Girona, Spain
| | - Matteo Serino
- Institut National de la Santé et de la Recherche Médicale (INSERM), Toulouse, France.,Institut de Maladies Métaboliques et Cardiovasculaires (I2MC), Université Paul Sabatier (UPS), Toulouse, France
| | - Gemma Carreras-Badosa
- Department of Pediatrics, Dr. Josep Trueta Hospital and Girona Institute for Biomedical Research, Girona, Spain
| | - Rémy Burcelin
- Institut National de la Santé et de la Recherche Médicale (INSERM), Toulouse, France.,Institut de Maladies Métaboliques et Cardiovasculaires (I2MC), Université Paul Sabatier (UPS), Toulouse, France
| | - Vincent Blasco-Baque
- Institut National de la Santé et de la Recherche Médicale (INSERM), Toulouse, France.,Institut de Maladies Métaboliques et Cardiovasculaires (I2MC), Université Paul Sabatier (UPS), Toulouse, France.,Faculté de Chirurgie Dentaire de Toulouse, Université Paul Sabatier, Toulouse, France
| | - Abel Lopez-Bermejo
- Department of Pediatrics, Dr. Josep Trueta Hospital and Girona Institute for Biomedical Research, Girona, Spain
| | - José-Manuel Fernandez-Real
- Department of Endocrinology, Dr. Josep Trueta Hospital and Girona Institute for Biomedical Research and CIBERobn, Girona, Spain
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Corbin KL, Waters CD, Shaffer BK, Verrilli GM, Nunemaker CS. Islet Hypersensitivity to Glucose Is Associated With Disrupted Oscillations and Increased Impact of Proinflammatory Cytokines in Islets From Diabetes-Prone Male Mice. Endocrinology 2016; 157:1826-38. [PMID: 26943366 PMCID: PMC4870867 DOI: 10.1210/en.2015-1879] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pulsatile insulin release is the primary means of blood glucose regulation. The loss of pulsatility is thought to be an early marker and possible factor in developing type 2 diabetes. Another early adaptation in islet function to compensate for obesity is increased glucose sensitivity (left shift) associated with increased basal insulin release. We provide evidence that oscillatory disruptions may be linked with overcompensation (glucose hypersensitivity) in islets from diabetes-prone mice. We isolated islets from male 4- to 5-week-old (prediabetic) and 10- to 12-week-old (diabetic) leptin-receptor-deficient (db/db) mice and age-matched heterozygous controls. After an overnight incubation in media with 11 mM glucose, we measured islet intracellular calcium in 5, 8, 11, or 15 mM glucose. Islets from heterozygous 10- to 12-week-old mice were quiescent in 5 mM glucose and displayed oscillations with increasing amplitude and/or duration in 8, 11, and 15 mM glucose, respectively. Islets from diabetic 10- to 12-week-old mice, in contrast, showed robust oscillations in 5 mM glucose that declined with increasing glucose. Similar trends were observed at 4-5-weeks of age. A progressive left shift in maximal insulin release was also observed in islets as db/db mice aged. Reducing glucokinase activity with 1 mM D-mannoheptulose restored oscillations in 11 mM glucose. Finally, overnight low-dose cytokine exposure negatively impacted oscillations preferentially in high glucose in diabetic islets compared with heterozygous controls. Our findings suggest the following: 1) islets from frankly diabetic mice can produce oscillations, 2) elevated sensitivity to glucose prevents diabetic mouse islets from producing oscillations in normal postprandial (11-15 mM glucose) conditions, and 3) hypersensitivity to glucose may magnify stress effects from inflammation or other sources.
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Affiliation(s)
- Kathryn L Corbin
- Department of Biomedical Sciences (K.L.C., C.S.N.), Heritage College of Osteopathic Medicine, and Diabetes Institute (K.L.C., C.S.N.), Ohio University, Athens, Ohio 45701; and Departments of Medicine (C.D.W., B.K.S., G.M.V.) and Biomedical Engineering (C.D.W.), University of Virginia, Charlottesville, Virginia 22908
| | - Christopher D Waters
- Department of Biomedical Sciences (K.L.C., C.S.N.), Heritage College of Osteopathic Medicine, and Diabetes Institute (K.L.C., C.S.N.), Ohio University, Athens, Ohio 45701; and Departments of Medicine (C.D.W., B.K.S., G.M.V.) and Biomedical Engineering (C.D.W.), University of Virginia, Charlottesville, Virginia 22908
| | - Brett K Shaffer
- Department of Biomedical Sciences (K.L.C., C.S.N.), Heritage College of Osteopathic Medicine, and Diabetes Institute (K.L.C., C.S.N.), Ohio University, Athens, Ohio 45701; and Departments of Medicine (C.D.W., B.K.S., G.M.V.) and Biomedical Engineering (C.D.W.), University of Virginia, Charlottesville, Virginia 22908
| | - Gretchen M Verrilli
- Department of Biomedical Sciences (K.L.C., C.S.N.), Heritage College of Osteopathic Medicine, and Diabetes Institute (K.L.C., C.S.N.), Ohio University, Athens, Ohio 45701; and Departments of Medicine (C.D.W., B.K.S., G.M.V.) and Biomedical Engineering (C.D.W.), University of Virginia, Charlottesville, Virginia 22908
| | - Craig S Nunemaker
- Department of Biomedical Sciences (K.L.C., C.S.N.), Heritage College of Osteopathic Medicine, and Diabetes Institute (K.L.C., C.S.N.), Ohio University, Athens, Ohio 45701; and Departments of Medicine (C.D.W., B.K.S., G.M.V.) and Biomedical Engineering (C.D.W.), University of Virginia, Charlottesville, Virginia 22908
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Reduced insulin secretion function is associated with pancreatic islet redistribution of cell adhesion molecules (CAMS) in diabetic mice after prolonged high-fat diet. Histochem Cell Biol 2016; 146:13-31. [PMID: 27020567 DOI: 10.1007/s00418-016-1428-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/15/2016] [Indexed: 01/09/2023]
Abstract
Intercellular junctions play a role in regulating islet cytoarchitecture, insulin biosynthesis and secretion. In this study, we investigated the animal metabolic state as well as islet histology and cellular distribution/expression of CAMs and F-actin in the endocrine pancreas of C57BL/6/JUnib mice fed a high-fat diet (HFd) for a prolonged time period (8 months). Mice fed a HFd became obese and type 2 diabetic, displaying significant peripheral insulin resistance, hyperglycemia and moderate hyperinsulinemia. Isolated islets of HFd-fed mice displayed a significant impairment of glucose-induced insulin secretion associated with a diminished frequency of intracellular calcium oscillations compared with control islets. No marked change in islet morphology and cytoarchitecture was observed; however, HFd-fed mice showed higher beta cell relative area in comparison with controls. As shown by immunohistochemistry, ZO-1, E-, N-cadherins, α- and β-catenins were expressed at the intercellular contact site of endocrine cells, while VE-cadherin, as well as ZO-1, was found at islet vascular compartment. Redistribution of N-, E-cadherins and α-catenin (from the contact region to the cytoplasm in endocrine cells) associated with increased submembranous F-actin cell level as well as increased VE-cadherin islet immunolabeling was observed in diabetic mice. Increased gene expression of VE-cadherin and ZO-1, but no change for the other proteins, was observed in islets of diabetic mice. Only in the case of VE-cadherin, a significant increase in islet content of this CAM was detected by immunoblotting in diabetic mice. In conclusion, CAMs are expressed by endocrine and endothelial cells of pancreatic islets. The distribution/expression of N-, E- and VE-cadherins as well as α-catenin and F-actin is significantly altered in islet cells of obese and diabetic mice.
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10
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Nunemaker CS, Satin LS. Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH. Endocrine 2014; 47:49-63. [PMID: 24610206 PMCID: PMC4382805 DOI: 10.1007/s12020-014-0212-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2014] [Accepted: 02/13/2014] [Indexed: 01/01/2023]
Abstract
Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.
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Affiliation(s)
- Craig S. Nunemaker
- Division of Endocrinology and Metabolism, Department of, Medicine, University of Virginia, P.O. Box 801413, Charlottesville, VA 22901, USA,
| | - Leslie S. Satin
- Pharmacology Department, University of Michigan Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
- Brehm Diabetes Research Center, University of Michigan, Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
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11
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Liang K, Du W, Lu J, Li F, Yang L, Xue Y, Hille B, Chen L. Alterations of the Ca²⁺ signaling pathway in pancreatic beta-cells isolated from db/db mice. Protein Cell 2014; 5:783-94. [PMID: 25053525 PMCID: PMC4180459 DOI: 10.1007/s13238-014-0075-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 04/20/2014] [Indexed: 11/16/2022] Open
Abstract
Upon glucose elevation, pancreatic beta-cells secrete insulin in a Ca2+-dependent manner. In diabetic animal models, different aspects of the calcium signaling pathway in beta-cells are altered, but there is no consensus regarding their relative contributions to the development of beta-cell dysfunction. In this study, we compared the increase in cytosolic Ca2+ ([Ca2+]i) via Ca2+ influx, Ca2+ mobilization from endoplasmic reticulum (ER) calcium stores, and the removal of Ca2+ via multiple mechanisms in beta-cells from both diabetic db/db mice and non-diabetic C57BL/6J mice. We refined our previous quantitative model to describe the slow [Ca2+]i recovery after depolarization in beta-cells from db/db mice. According to the model, the activity levels of the two subtypes of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) pump, SERCA2 and SERCA3, were severely down-regulated in diabetic cells to 65% and 0% of the levels in normal cells. This down-regulation may lead to a reduction in the Ca2+ concentration in the ER, a compensatory up-regulation of the plasma membrane Na+/Ca2+ exchanger (NCX) and a reduction in depolarization-evoked Ca2+ influx. As a result, the patterns of glucose-stimulated calcium oscillations were significantly different in db/db diabetic beta-cells compared with normal cells. Overall, quantifying the changes in the calcium signaling pathway in db/db diabetic beta-cells will aid in the development of a disease model that could provide insight into the adaptive transformations of beta-cell function during diabetes development.
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Affiliation(s)
- Kuo Liang
- Department of General Surgery, XuanWu Hospital, Capital Medical University, Beijing, 100053, China
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12
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Bursting synchronization dynamics of pancreatic β-cells with electrical and chemical coupling. Cogn Neurodyn 2014; 7:197-212. [PMID: 24427201 DOI: 10.1007/s11571-012-9226-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2012] [Revised: 09/17/2012] [Accepted: 10/11/2012] [Indexed: 10/27/2022] Open
Abstract
Based on bifurcation analysis, the synchronization behaviors of two identical pancreatic β-cells connected by electrical and chemical coupling are investigated, respectively. Various firing patterns are produced in coupled cells when a single cell exhibits tonic spiking or square-wave bursting individually, irrespectively of what the cells are connected by electrical or chemical coupling. On the one hand, cells can burst synchronously for both weak electrical and chemical coupling when an isolated cell exhibits tonic spiking itself. In particular, for electrically coupled cells, under the variation of the coupling strength there exist complex transition processes of synchronous firing patterns such as "fold/limit cycle" type of bursting, then anti-phase continuous spiking, followed by the "fold/torus" type of bursting, and finally in-phase tonic spiking. On the other hand, it is shown that when the individual cell exhibits square-wave bursting, suitable coupling strength can make the electrically coupled system generate "fold/Hopf" bursting via "fold/fold" hysteresis loop; whereas, the chemically coupled cells generate "fold/subHopf" bursting. Especially, chemically coupled bursters can exhibit inverse period-adding bursting sequence. Fast-slow dynamics analysis is applied to explore the generation mechanism of these bursting oscillations. The above analysis of bursting types and the transition may provide us with better insight into understanding the role of coupling in the dynamic behaviors of pancreatic β-cells.
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13
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Stamper IJ, Jackson E, Wang X. Phase transitions in pancreatic islet cellular networks and implications for type-1 diabetes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:012719. [PMID: 24580269 PMCID: PMC4172977 DOI: 10.1103/physreve.89.012719] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Indexed: 06/03/2023]
Abstract
In many aspects the onset of a chronic disease resembles a phase transition in a complex dynamic system: Quantitative changes accumulate largely unnoticed until a critical threshold is reached, which causes abrupt qualitative changes of the system. In this study we examine a special case, the onset of type-1 diabetes (T1D), a disease that results from loss of the insulin-producing pancreatic islet β cells. Within each islet, the β cells are electrically coupled to each other via gap-junctional channels. This intercellular coupling enables the β cells to synchronize their insulin release, thereby generating the multiscale temporal rhythms in blood insulin that are critical to maintaining blood glucose homeostasis. Using percolation theory we show how normal islet function is intrinsically linked to network connectivity. In particular, the critical amount of β-cell death at which the islet cellular network loses site percolation is consistent with laboratory and clinical observations of the threshold loss of β cells that causes islet functional failure. In addition, numerical simulations confirm that the islet cellular network needs to be percolated for β cells to synchronize. Furthermore, the interplay between site percolation and bond strength predicts the existence of a transient phase of islet functional recovery after onset of T1D and introduction of treatment, potentially explaining the honeymoon phenomenon. Based on these results, we hypothesize that the onset of T1D may be the result of a phase transition of the islet β-cell network.
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Affiliation(s)
- I. J. Stamper
- Department of Physics, the University of Alabama at Birmingham, Birmingham, Alabama, USA
- The Comprehensive Diabetes Center, the University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Elais Jackson
- Department of Computer and Information Sciences, the University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Xujing Wang
- Department of Physics, the University of Alabama at Birmingham, Birmingham, Alabama, USA
- The Comprehensive Diabetes Center, the University of Alabama at Birmingham, Birmingham, Alabama, USA
- Systems Biology Center, the National Heart, Lung, and Blood Institute, the National Institutes of Health, Bethesda, Maryland, USA
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14
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Hosking J, Metcalf BS, Jeffery AN, Streeter AJ, Voss LD, Wilkin TJ. Evidence of early beta-cell deficiency among children who show impaired fasting glucose: 10-yr cohort study (EarlyBird 56). Pediatr Diabetes 2013; 14:481-9. [PMID: 23721587 DOI: 10.1111/pedi.12049] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Revised: 03/18/2013] [Accepted: 04/09/2013] [Indexed: 12/22/2022] Open
Abstract
OBJECTIVE Impaired fasting glucose (IFG) is a predictor of future diabetes and is increasingly common in children, but the extent to which it results from excess insulin demand or failure of supply is unclear. Our aim was to compare the behaviour of insulin sensitivity and beta-cell function in children who developed IFG with those whose glucose levels remained within the normal range. METHODS We examined trends in fasting glucose, insulin sensitivity (HOMA-S) and beta-cell function (HOMA-B) in 327 healthy children annually from 5 to 15 yr, and the parents at baseline. RESULTS Fifty-five children showed IFG, mostly after age 11 yr. Fasting glucose rose progressively and was higher throughout in those who developed IFG compared with those who did not (p < 0.001). Beta-cell function was lower from the age of 5 yr in those who developed IFG (p = 0.006), but there was no difference in BMI (p = 0.71). A difference in insulin sensitivity was revealed on adjustment for covariates (p = 0.03). Glucose was higher (p < 0.001), beta-cell function lower (p = 0.01), and insulin sensitivity the same (p = 0.86) in the mothers of children who showed IFG, compared with those who did not. CONCLUSIONS IFG is common in contemporary children, and appears to be related to a defect in beta-cell function already present at 5 yr. Similar findings in the mothers of IFG children suggest that the beta-cell defect may be transmissible.
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Affiliation(s)
- Joanne Hosking
- University Medicine, Level 07 Derriford Hospital, Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, UK
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15
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Abstract
Islet autoimmunity in type 1 diabetes results in the loss of the pancreatic β-cells. The consequences of insulin deficiency in the portal vein for liver fat are poorly understood. Under normal conditions, the portal vein provides 75% of the liver blood supply. Recent studies suggest that non-alcoholic fatty liver disease (NAFLD) may be more common in type 1 diabetes than previously thought, and may serve as an independent risk marker for some chronic diabetic complications. The pathogenesis of NAFLD remains obscure, but it has been hypothesized that hepatic fat accumulation in type 1 diabetes may be due to lipoprotein abnormalities, hyperglycemia-induced activation of the transcription factors carbohydrate response element-binding protein (ChREBP) and sterol regulatory element-binding protein 1c (SREBP-1c), upregulation of glucose transporter 2 (GLUT2) with subsequent intrahepatic fat synthesis, or a combination of these mechanisms. Novel approaches to non-invasive determinations of liver fat may clarify the consequences for liver metabolism when the pancreas has ceased producing insulin. This article aims to review the factors potentially contributing to hepatic steatosis in type 1 diabetes, and to assess the feasibility of using liver fat as a prognostic and/or diagnostic marker for the disease. It provides a background and a case for possible future studies in the field.
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Affiliation(s)
- Simon E Regnell
- Lund University, CRC, Department of Clinical Sciences, Diabetes and Celiac Disease Unit, Skåne University Hospital, Malmö, Sweden.
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16
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Guo LX, Xia ZN, Gao X, Yin F, Liu JH. Glucagon-like peptide 1 receptor plays a critical role in geniposide-regulated insulin secretion in INS-1 cells. Acta Pharmacol Sin 2012; 33:237-41. [PMID: 22101168 DOI: 10.1038/aps.2011.146] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
AIM To explore the role of the glucagon-like peptide 1 receptor (GLP-1R) in geniposide regulated insulin secretion in rat INS-1 insulinoma cells. METHODS Rat INS-1 insulinoma cells were cultured. The content of insulin in the culture medium was measured with ELISA assay. GLP-1R gene in INS-1 cells was knocked down with shRNA interference. The level of GLP-1R protein in INS-1 cells was measured with Western blotting. RESULTS Geniposide (0.01-100 μmol/L) increased insulin secretion from INS-1 cells in a concentration-dependent manner. Geniposide (10 μmol/L) enhanced acute insulin secretion in response to both the low (5.5 mmol/L) and moderately high levels (11 mmol/L) of glucose. Blockade of GLP-1R with the GLP-1R antagonist exendin (9-39) (200 nmol/L) or knock-down of GLP-1R with shRNA interference in INS-1 cells decreased the effect of geniposide (10 μmol/L) on insulin secretion stimulated by glucose (5.5 mmol/L). CONCLUSION Geniposide increases insulin secretion through glucagon-like peptide 1 receptors in rat INS-1 insulinoma cells.
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17
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Zhang X, Grimley A, Bertram R, Roper MG. Microfluidic system for generation of sinusoidal glucose waveforms for entrainment of islets of Langerhans. Anal Chem 2010; 82:6704-11. [PMID: 20617825 DOI: 10.1021/ac101461x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A microfluidic system was developed to produce sinusoidal waveforms of glucose to entrain oscillations of intracellular [Ca(2+)] in islets of Langerhans. The work described is an improvement to a previously reported device where two pneumatic pumps delivered pulses of glucose and buffer to a mixing channel. The mixing channel acted as a low pass filter to attenuate these pulses to produce the desired final concentration. Improvements to the current device included increasing the average pumping frequency from 0.83 to 3.33 Hz by modifying the on-chip valves to minimize adhesion between the PDMS and glass within the valve. The cutoff frequency of the device was increased from 0.026 to 0.061 Hz for sinusoidal fluorescein waves by shortening the length of the mixing channel to 3.3 cm. The value of the cutoff frequency was chosen between the average pumping frequency and the low frequency (approximately 0.0056 Hz) glucose waves that were needed to entrain the islets of Langerhans. In this way, the pulses from the pumps were attenuated greatly but the low-frequency glucose waves were not. With the use of this microfluidic system, a total flow rate of 1.5 +/- 0.1 microL min(-1) was generated and used to deliver sinusoidal waves of glucose concentration with a median value of 11 mM and amplitude of 1 mM to a chamber that contained an islet of Langerhans loaded with the Ca(2+)-sensitive fluorophore, indo-1. Entrainment of the islets was demonstrated by pacing the rhythm of intracellular [Ca(2+)] oscillations to oscillatory glucose levels produced by the device. The system should be applicable to a wide range of cell types to aid understanding cellular responses to dynamically changing stimuli.
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Affiliation(s)
- Xinyu Zhang
- Department of Chemistry and Biochemistry and Program in Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, USA
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18
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Jahanshahi P, Wu R, Carter JD, Nunemaker CS. Evidence of diminished glucose stimulation and endoplasmic reticulum function in nonoscillatory pancreatic islets. Endocrinology 2009; 150:607-15. [PMID: 18818288 PMCID: PMC2646533 DOI: 10.1210/en.2008-0773] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pulsatility is a fundamental feature of pancreatic islets and a hallmark of hormone secretion. Isolated pancreatic islets endogenously generate rhythms in secretion, metabolic activity, and intracellular calcium ([Ca(2+)](i)) that are important to normal physiological function. Few studies have directly compared oscillatory and nonoscillatory islets to identify possible differences in function. We investigated the hypothesis that the loss of these oscillations is a leading indicator of islet dysfunction by comparing oscillatory and nonoscillatory mouse islets for multiple parameters of function. Nonoscillatory islets displayed elevated basal [Ca(2+)](i) and diminished [Ca(2+)](i) response and insulin secretory response to 3-28 mm glucose stimulation compared with oscillatory islets, suggesting diminished glucose sensitivity. We investigated several possible mechanisms to explain these differences. No differences were observed in mitochondrial membrane potential, estimated ATP-sensitive potassium channel and L-type calcium channel activity, or cell death rates. Nonoscillatory islets, however, showed a reduced response to the sarco(endo)plasmic reticulum calcium ATPase inhibitor thapsigargin, suggesting a disruption in calcium homeostasis in the endoplasmic reticulum (ER) compared with oscillatory islets. The diminished ER calcium homeostasis among nonoscillatory islets was also consistent with the higher cytosolic calcium levels observed in 3 mm glucose. Inducing mild damage with low-dose proinflammatory cytokines reduced islet oscillatory capacity and produced similar effects on glucose-stimulated [Ca(2+)](i), basal [Ca(2+)](i), and thapsigargin response observed among untreated nonoscillatory islets. Our data suggest the loss of oscillatory capacity may be an early indicator of diminished islet glucose sensitivity and ER dysfunction, suggesting targets to improve islet assessment.
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Affiliation(s)
- Pooya Jahanshahi
- Department of Medicine, Division of Endocrinology and Metabolism, University of Virginia, Charlottesville, VA 22908-1413, USA
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19
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Farhy LS, McCall AL. System-level control to optimize glucagon counterregulation by switch-off of α-cell suppressing signals in β-cell deficiency. J Diabetes Sci Technol 2009; 3:21-33. [PMID: 20046648 PMCID: PMC2769841 DOI: 10.1177/193229680900300104] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND Glucagon counterregulation (GCR) is a key protection against hypoglycemia that is compromised in diabetes. In β-cell-deficient rats, GCR pulsatility can be amplified if insulin (INS) or somatostatin (SS) are infused in the pancreatic artery and then switched off during hypoglycemia. The data indicate that these signals act by different mechanisms, and here we analyze the differences between the two switch offs (SOs) and predict the GCR-amplifying effect of their individual or combined application. METHODS A minimal control network (MCN) of α/δ-cell interactions is approximated by differential equations to explain the GCR response to a SO and test in silico the hypotheses: (i) INS SO suppresses basal and pulsatile, while SS SO blocks only pulsatile glucagon release and (ii) simultaneous application of the two switch offs will augment the individual GCR response. RESULTS The mechanism postulated in (i) explains the differences in the GCR responses between the SOs. The MCN predicts that simultaneous application of INS and SS decreases basal glucagon but increases post-SO amplitude, thus doubling the response of GCR achieved by each of the individual signals. CONCLUSION The current analyses predict that INS and SS SOs improve defective GCR in β-cell deficiency through different but complementary mechanisms and suggest SO strategies to maximally enhance GCR in type 1 diabetes by simultaneous manipulation of the network control. These results are clinically relevant, as they could have application to design of an artificial pancreas by providing ways to augment GCR that would not require glucagon infusion.
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Affiliation(s)
- Leon S Farhy
- Department of Medicine, Center for Biomathematical Technology, University of Virginia, Charlottesville, Virginia 22908, USA.
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20
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Schmitz O, Rungby J, Edge L, Juhl CB. On high-frequency insulin oscillations. Ageing Res Rev 2008; 7:301-5. [PMID: 18583199 DOI: 10.1016/j.arr.2008.04.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Revised: 04/24/2008] [Accepted: 04/24/2008] [Indexed: 11/16/2022]
Abstract
Insulin is released in a pulsatile manner, which results in oscillatory concentrations in blood. The oscillatory secretion improves release control and enhances the hormonal action. Insulin oscillates with a slow ultradian periodicity (approximately 140 min) and a high-frequency periodicity (approximately 6-10 min). Only the latter is reviewed in this article. At least 75% of the insulin secretion is released in a pulsatile manner. Individuals prone to developing diabetes or with overt type 2 diabetes are characterized by irregular oscillations of plasma insulin. Many factors have impact on insulin pulsatility such as age, insulin resistance and glycemic level. In addition, tiny glucose oscillations are capable of entraining insulin oscillations in healthy people in contrast to type 2 diabetic individuals emphasizing a profound disruption of the beta-cells in type 2 diabetes to sense or respond to physiological glucose excursions. A crucial question is how approximately 1,000,000 islets, each containing from a few to several thousand beta-cells, can be coordinated to secrete insulin in a pulsatile manner. This is blatantly a very complex operation to control involving an intra-pancreatic neural network, an intra-islet communication and metabolic oscillations in the beta-cell itself. Overnight beta-cell rest, e.g. during somatostatin administration, improves the disordered pulsatile insulin secretion in type 2 diabetes. Acute as well as long-term administration of sulphonylureas (SU) leads to substantial amplification (approximately 50%) of the pulsatile insulin secretion in type 2 diabetes. This is probably cardinal in terms of governing the hepatic glucose release in type 2 diabetes. Whether sulfonylureas also improve the ability of the beta-cells to sense glucose fluctuations remains to be explored. Thiazolidinediones reduce the pulsatile insulin secretion without affecting regularity, but appear to improve the ability of the beta-cell to be entrained by small glucose excursions. Finally, similar to SUs, the incretin hormone GLP-1 also results in an augmented pulsatile burst mass in both healthy and diabetic individuals, in the latter group, however, without influencing the disorderliness of pulses. This review will briefly describe the high-frequency insulin pulsatility during physiologic and pathophysiologic conditions as well as the influence of some hypoglycemic compounds on the insulin oscillations.
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Affiliation(s)
- Ole Schmitz
- Department of Diabetes, University Hospital of Aarhus and Institute of Pharmacology, University of Aarhus, 8000 Aarhus C, Denmark.
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21
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Farhy LS, Du Z, Zeng Q, Veldhuis PP, Johnson ML, Brayman KL, McCall AL. Amplification of pulsatile glucagon counterregulation by switch-off of alpha-cell-suppressing signals in streptozotocin-treated rats. Am J Physiol Endocrinol Metab 2008; 295:E575-85. [PMID: 18577688 PMCID: PMC2536740 DOI: 10.1152/ajpendo.90372.2008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Glucagon counterregulation (GCR) is a key protection against hypoglycemia that is compromised in diabetes via an unknown mechanism. To test the hypothesis that alpha-cell-inhibiting signals that are switched off during hypoglycemia amplify GCR, we studied streptozotocin (STZ)-treated male Wistar rats and estimated the effect on GCR of intrapancreatic infusion and termination during hypoglycemia of saline, insulin, and somatostatin. Times 10 min before and 45 min after the switch-off were analyzed. Insulin and somatostatin, but not saline, switch-off significantly increased the glucagon levels (P = 0.03), and the fold increases relative to baseline were significantly higher (P < 0.05) in the insulin and somatostatin groups vs. the saline group. The peak concentrations were also higher in the insulin (368 pg/ml) and somatostatin (228 pg/ml) groups vs. the saline (114 pg/ml) group (P < 0.05). GCR was pulsatile in most animals, indicating a feedback regulation. After the switch-off, the number of secretory events and the total pulsatile production were lower in the saline group vs. the insulin and somatostatin groups (P < 0.05), indicating enhancement of glucagon pulsatile activity by insulin and somatostatin compared with saline. Network modeling analysis demonstrates that reciprocal interactions between alpha- and delta-cells can explain the amplification by interpreting the GCR as a rebound response to the switch-off. The model justifies experimental designs to further study the intrapancreatic network in relation to the switch-off phenomenon. The results of this proof-of-concept interdisciplinary study support the hypothesis that GCR develops as a rebound pulsatile response of the intrapancreatic endocrine feedback network to switch-off of alpha-cell-inhibiting islet signals.
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Affiliation(s)
- Leon S Farhy
- University of Virginia Health System, Charlottesville, VA 22908, USA.
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22
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Guillausseau PJ, Meas T, Virally M, Laloi-Michelin M, Médeau V, Kevorkian JP. Abnormalities in insulin secretion in type 2 diabetes mellitus. DIABETES & METABOLISM 2008; 34 Suppl 2:S43-8. [PMID: 18640585 DOI: 10.1016/s1262-3636(08)73394-9] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Type 2 diabetes mellitus is a multifactorial disease, due to decreased glucose peripheral uptake, and increased hepatic glucose production, due to reduced both insulin secretion and insulin sensitivity. Multiple insulin secretory defects are present, including absence of pulsatility, loss of early phase of insulin secretion after glucose, decreased basal and stimulated plasma insulin concentrations, excess in prohormone secretion, and progressive decrease in insulin secretory capacity with time. beta-cell dysfunction is genetically determined and appears early in the course of the disease. The interplay between insulin secretory defect and insulin resistance is now better understood. In subjects with normal beta-cell function, increase in insulin is compensated by an increase in insulin secretion and plasma glucose levels remain normal. In subjects genetically predisposed to type 2 diabetes, failure of beta-cell to compensate leads to a progressive elevation in plasma glucose levels, then to overt diabetes. When permanent hyperglycaemia is present, progressive severe insulin secretory failure with time ensues, due to glucotoxicity and lipotoxicity, and oxidative stress. A marked reduction in beta-cell mass at post-mortem examination of pancreas of patients with type 2 diabetes has been reported, with an increase in beta-cell apoptosis non-compensated by neogenesis.
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Affiliation(s)
- P-J Guillausseau
- AP-HP, Department of Internal Medicine B, Hôpital Lariboisière, 2, rue Ambroise Raré, 75010, Paris, France.
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23
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Long lasting synchronization of calcium oscillations by cholinergic stimulation in isolated pancreatic islets. Biophys J 2008; 95:4676-88. [PMID: 18708464 DOI: 10.1529/biophysj.107.125088] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Individual mouse pancreatic islets exhibit oscillations in [Ca(2+)](i) and insulin secretion in response to glucose in vitro, but how the oscillations of a million islets are coordinated within the human pancreas in vivo is unclear. Islet to islet synchronization is necessary, however, for the pancreas to produce regular pulses of insulin. To determine whether neurohormone release within the pancreas might play a role in coordinating islet activity, [Ca(2+)](i) changes in 4-6 isolated mouse islets were simultaneously monitored before and after a transient pulse of a putative synchronizing agent. The degree of synchronicity was quantified using a novel analytical approach that yields a parameter that we call the "Synchronization Index". Individual islets exhibited [Ca(2+)](i) oscillations with periods of 3-6 min, but were not synchronized under control conditions. However, raising islet [Ca(2+)](i) with a brief application of the cholinergic agonist carbachol (25 microM) or elevated KCl in glucose-containing saline rapidly synchronized islet [Ca(2+)](i) oscillations for >/=30 min, long after the synchronizing agent was removed. In contrast, the adrenergic agonists clonidine or norepinephrine, and the K(ATP) channel inhibitor tolbutamide, failed to synchronize islets. Partial synchronization was observed, however, with the K(ATP) channel opener diazoxide. The synchronizing action of carbachol depended on the glucose concentration used, suggesting that glucose metabolism was necessary for synchronization to occur. To understand how transiently perturbing islet [Ca(2+)](i) produced sustained synchronization, we used a mathematical model of islet oscillations in which complex oscillatory behavior results from the interaction between a fast electrical subsystem and a slower metabolic oscillator. Transient synchronization simulated by the model was mediated by resetting of the islet oscillators to a similar initial phase followed by transient "ringing" behavior, during which the model islets oscillated with a similar frequency. These results suggest that neurohormone release from intrapancreatic neurons could help synchronize islets in situ. Defects in this coordinating mechanism could contribute to the disrupted insulin secretion observed in Type 2 diabetes.
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Insulin resistance: a proinflammatory state mediated by lipid-induced signaling dysfunction and involved in atherosclerotic plaque instability. Mediators Inflamm 2008; 2008:767623. [PMID: 18604303 PMCID: PMC2442435 DOI: 10.1155/2008/767623] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Accepted: 06/09/2008] [Indexed: 11/23/2022] Open
Abstract
The dysregulation of the insulin-glucose axis represents the crucial event in insulin resistance syndrome. Insulin resistance increases atherogenesis and atherosclerotic plaque instability by inducing proinflammatory activities on vascular and immune cells. This condition characterizes several diseases, such as type 2 diabetes, impaired glucose tolerance (IGT), impaired fasting glucose (IFG), obesity, hypertension, dyslipidemia, and other endocrinopathies, but also cancer. Recent studies suggest that the pathophysiology of insulin resistance is closely related to interferences with insulin-mediated intracellular signaling on skeletal muscle cells, hepatocytes, and adipocytes. Strong evidence supports the role of free fatty acids (FFAs) in promoting insulin resistance. The FFA-induced activation of protein kinase C (PKC) delta, inhibitor kappaB kinase (IKK), or c-Jun N-terminal kinase (JNK) modulates insulin-triggered intracellular pathway (classically known as PI3-K-dependent). Therefore, reduction of FFA levels represents a selective target for modulating insulin resistance.
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Nittala A, Wang X. The hyperbolic effect of density and strength of inter beta-cell coupling on islet bursting: a theoretical investigation. Theor Biol Med Model 2008; 5:17. [PMID: 18673579 PMCID: PMC2538510 DOI: 10.1186/1742-4682-5-17] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2008] [Accepted: 08/03/2008] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Insulin, the principal regulating hormone of blood glucose, is released through the bursting of the pancreatic islets. Increasing evidence indicates the importance of islet morphostructure in its function, and the need of a quantitative investigation. Recently we have studied this problem from the perspective of islet bursting of insulin, utilizing a new 3D hexagonal closest packing (HCP) model of islet structure that we have developed. Quantitative non-linear dependence of islet function on its structure was found. In this study, we further investigate two key structural measures: the number of neighboring cells that each beta-cell is coupled to, nc, and the coupling strength, gc. RESULTS BETA-cell clusters of different sizes with number of beta-cells nbeta ranging from 1-343, nc from 0-12, and gc from 0-1000 pS, were simulated. Three functional measures of islet bursting characteristics--fraction of bursting beta-cells fb, synchronization index lambda, and bursting period Tb, were quantified. The results revealed a hyperbolic dependence on the combined effect of nc and gc. From this we propose to define a dimensionless cluster coupling index or CCI, as a composite measure for islet morphostructural integrity. We show that the robustness of islet oscillatory bursting depends on CCI, with all three functional measures fb, lambda and Tb increasing monotonically with CCI when it is small, and plateau around CCI = 1. CONCLUSION CCI is a good islet function predictor. It has the potential of linking islet structure and function, and providing insight to identify therapeutic targets for the preservation and restoration of islet beta-cell mass and function.
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Affiliation(s)
- Aparna Nittala
- Max McGee National Research Center for Juvenile Diabetes & Human and Molecular Genetics Center, Medical College of Wisconsin and Children's Research Institute of the Children's Hospital of Wisconsin, Milwaukee, WI 53226, USA.
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Dror V, Kalynyak TB, Bychkivska Y, Frey MHZ, Tee M, Jeffrey KD, Nguyen V, Luciani DS, Johnson JD. Glucose and endoplasmic reticulum calcium channels regulate HIF-1beta via presenilin in pancreatic beta-cells. J Biol Chem 2008; 283:9909-16. [PMID: 18174159 DOI: 10.1074/jbc.m710601200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Pancreatic beta-cell death is a critical event in type 1 diabetes, type 2 diabetes, and clinical islet transplantation. We have previously shown that prolonged block of ryanodine receptor (RyR)-gated release from intracellular Ca(2+) stores activates calpain-10-dependent apoptosis in beta-cells. In the present study, we further characterized intracellular Ca(2+) channel expression and function in human islets and the MIN6 beta-cell line. All three RyR isoforms were identified in human islets and MIN6 cells, and these endoplasmic reticulum channels were observed in close proximity to mitochondria. Blocking RyR channels, but not sarco/endoplasmic reticulum ATPase (SERCA) pumps, reduced the ATP/ADP ratio. Blocking Ca(2+) flux through RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of hypoxia-inducible factor (HIF-1beta). Moreover, inhibition of RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of presenilin-1. Both HIF-1beta and presenilin-1 expression were also induced by low glucose. Overexpression of presenilin-1 increased HIF-1beta, suggesting that HIF is downstream of presenilin. Our results provide the first evidence of a presenilin-HIF signaling network in beta-cells. We demonstrate that this pathway is controlled by Ca(2+) flux through intracellular channels, likely via changes in mitochondrial metabolism and ATP. These findings provide a mechanistic understanding of the signaling pathways activated when intracellular Ca(2+) homeostasis and metabolic activity are suppressed in diabetes and islet transplantation.
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Affiliation(s)
- Vardit Dror
- Laboratory of Molecular Signaling in Diabetes, Diabetes Research Group, Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
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Nittala A, Ghosh S, Wang X. Investigating the role of islet cytoarchitecture in its oscillation using a new beta-cell cluster model. PLoS One 2007; 2:e983. [PMID: 17912360 PMCID: PMC1991600 DOI: 10.1371/journal.pone.0000983] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Accepted: 09/07/2007] [Indexed: 12/02/2022] Open
Abstract
The oscillatory insulin release is fundamental to normal glycemic control. The basis of the oscillation is the intercellular coupling and bursting synchronization of β cells in each islet. The functional role of islet β cell mass organization with respect to its oscillatory bursting is not well understood. This is of special interest in view of the recent finding of islet cytoarchitectural differences between human and animal models. In this study we developed a new hexagonal closest packing (HCP) cell cluster model. The model captures more accurately the real islet cell organization than the simple cubic packing (SCP) cluster that is conventionally used. Using our new model we investigated the functional characteristics of β-cell clusters, including the fraction of cells able to burst fb, the synchronization index λ of the bursting β cells, the bursting period Tb, the plateau fraction pf, and the amplitude of intracellular calcium oscillation [Ca]. We determined their dependence on cluster architectural parameters including number of cells nβ, number of inter-β cell couplings of each β cell nc, and the coupling strength gc. We found that at low values of nβ, nc and gc, the oscillation regularity improves with their increasing values. This functional gain plateaus around their physiological values in real islets, at nβ∼100, nc∼6 and gc∼200 pS. In addition, normal β-cell clusters are robust against significant perturbation to their architecture, including the presence of non-β cells or dead β cells. In clusters with nβ>∼100, coordinated β-cell bursting can be maintained at up to 70% of β-cell loss, which is consistent with laboratory and clinical findings of islets. Our results suggest that the bursting characteristics of a β-cell cluster depend quantitatively on its architecture in a non-linear fashion. These findings are important to understand the islet bursting phenomenon and the regulation of insulin secretion, under both physiological and pathological conditions.
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Affiliation(s)
- Aparna Nittala
- Max McGee National Research Center for Juvenile Diabetes, Human and Molecular Genetics Center, Medical College of Wisconsin, Children's Research Institute of the Children's Hospital of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Soumitra Ghosh
- Max McGee National Research Center for Juvenile Diabetes, Human and Molecular Genetics Center, Medical College of Wisconsin, Children's Research Institute of the Children's Hospital of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Xujing Wang
- Max McGee National Research Center for Juvenile Diabetes, Human and Molecular Genetics Center, Medical College of Wisconsin, Children's Research Institute of the Children's Hospital of Wisconsin, Milwaukee, Wisconsin, United States of America
- * To whom correspondence should be addressed. E-mail:
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Heart E, Smith PJS. Rhythm of the beta-cell oscillator is not governed by a single regulator: multiple systems contribute to oscillatory behavior. Am J Physiol Endocrinol Metab 2007; 292:E1295-300. [PMID: 17213468 DOI: 10.1152/ajpendo.00648.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pulsatile insulin output, paralleled by oscillations in intracellular Ca(2+), reflect oscillating metabolism within beta-cells in response to secretory fuels. Here we question whether oscillatory periodicity is conserved or varied from stimulation to stimulation, whether glycolysis is essential for the manifestation of an oscillatory response, and if an environment of nutrient oversupply affects oscillatory regularity. We have determined that a beta-cell oscillatory Ca(2+) pattern is independent of the type of applied secretory fuel (glucose, methyl-pyruvate, or alpha-ketoisocaproate). In addition, single cells respond with the same pattern when repeatedly stimulated, regardless of the type of stimulatory fuel. Presence of substimulatory glucose is not necessary to obtain an oscillatory responses to methyl-pyruvate or alpha-ketoisocaproate. Glucose-6-phosphate, as a measure of glycolytic flux, is not detectable under these conditions. These data suggest that multiple systems, rather than a single enzyme component, can contribute to the beta-cell oscillatory behavior. Prolonged exposure to high levels of palmitate impaired oscillatory regularity in the individual beta-cells. This supports the hypothesis that a high-fat environment might contribute to loss of regular oscillatory pattern in diabetic subjects, acting, at least in part, at the level of the single beta-cell.
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Affiliation(s)
- Emma Heart
- BioCurrents Research Center, Molecular Physiology Program, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
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29
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Manning Fox JE, Gyulkhandanyan AV, Satin LS, Wheeler MB. Oscillatory membrane potential response to glucose in islet beta-cells: a comparison of islet-cell electrical activity in mouse and rat. Endocrinology 2006; 147:4655-63. [PMID: 16857746 DOI: 10.1210/en.2006-0424] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In contrast to mouse, rat islet beta-cell membrane potential is reported not to oscillate in response to elevated glucose despite demonstrated oscillations in calcium and insulin secretion. We aim to clarify the electrical activity of rat islet beta-cells and characterize and compare the electrical activity of both alpha- and beta-cells in rat and mouse islets. We recorded electrical activity from alpha- and beta-cells within intact islets from both mouse and rat using the perforated whole-cell patch clamp technique. Fifty-six percent of both mouse and rat beta-cells exhibited an oscillatory response to 11.1 mm glucose. Responses to both 11.1 mm and 2.8 mm glucose were identical in the two species. Rat beta-cells exhibited incremental depolarization in a glucose concentration-dependent manner. We also demonstrated electrical activity in human islets recorded under the same conditions. In both mouse and rat alpha-cells 11 mm glucose caused hyperpolarization of the membrane potential, whereas 2.8 mm glucose produced action potential firing. No species differences were observed in the response of alpha-cells to glucose. This paper is the first to demonstrate and characterize oscillatory membrane potential fluctuations in the presence of elevated glucose in rat islet beta-cells in comparison with mouse. The findings promote the use of rat islets in future electrophysiological studies, enabling consistency between electrophysiological and insulin secretion studies. An inverse response of alpha-cell membrane potential to glucose furthers our understanding of the mechanisms underlying glucose sensitive glucagon secretion.
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30
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Manning Fox JE, Karaman G, Wheeler MB. Alkali pH directly activates ATP-sensitive K+ channels and inhibits insulin secretion in beta-cells. Biochem Biophys Res Commun 2006; 350:492-7. [PMID: 17011513 DOI: 10.1016/j.bbrc.2006.09.084] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Accepted: 09/19/2006] [Indexed: 11/20/2022]
Abstract
Glucose stimulation of pancreatic beta-cells is reported to lead to sustained alkalization, while extracellular application of weak bases is reported to inhibit electrical activity and decrease insulin secretion. We hypothesize that beta-cell K(ATP) channel activity is modulated by alkaline pH. Using the excised patch-clamp technique, we demonstrate a direct stimulatory action of alkali pH on recombinant SUR1/Kir6.2 channels due to increased open probability. Bath application of alkali pH similarly activates native islet beta-cell K(ATP) channels, leading to an inhibition of action potentials, and hyperpolarization of membrane potential. In situ pancreatic perfusion confirms that these cellular effects of alkali pH are observable at a functional level, resulting in decreases in both phase 1 and phase 2 glucose-stimulated insulin secretion. Our data are the first to report a stimulatory effect of a range of alkali pH on K(ATP) channel activity and link this to downstream effects on islet beta-cell function.
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Affiliation(s)
- Jocelyn E Manning Fox
- Department of Physiology, 3352 Medical Sciences Building, 1 King's College Circle, University of Toronto, Toronto, Ont., Canada.
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31
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Tsaneva-Atanasova K, Zimliki CL, Bertram R, Sherman A. Diffusion of calcium and metabolites in pancreatic islets: killing oscillations with a pitchfork. Biophys J 2006; 90:3434-46. [PMID: 16500973 PMCID: PMC1440728 DOI: 10.1529/biophysj.105.078360] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cell coupling is important for the normal function of the beta-cells of the pancreatic islet of Langerhans, which secrete insulin in response to elevated plasma glucose. In the islets, electrical and metabolic communications are mediated by gap junctions. Although electrical coupling is believed to account for synchronization of the islets, the role and significance of diffusion of calcium and metabolites are not clear. To address these questions we analyze two different mathematical models of islet calcium and electrical dynamics. To study diffusion of calcium, we use a modified Morris-Lecar model. Based on our analysis, we conclude that intercellular diffusion of calcium is not necessary for islet synchronization, at most supplementing electrical coupling. Metabolic coupling is investigated with a recent mathematical model incorporating glycolytic oscillations. Bifurcation analysis of the coupled system reveals several modes of behavior, depending on the relative strength of electrical and metabolic coupling. We find that whereas electrical coupling always produces synchrony, metabolic coupling can abolish both oscillations and synchrony, explaining some puzzling experimental observations. We suggest that these modes are generic features of square-wave bursters and relaxation oscillators coupled through either the activation or recovery variable.
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Affiliation(s)
- Krasimira Tsaneva-Atanasova
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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32
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Schmitt CP, Hömme M, Schaefer F. Structural organization and biological relevance of oscillatory parathyroid hormone secretion. Pediatr Nephrol 2005; 20:346-51. [PMID: 15700141 DOI: 10.1007/s00467-004-1767-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2004] [Accepted: 11/09/2004] [Indexed: 10/25/2022]
Abstract
Parathyroid gland secretory activity exhibits seasonal and circadian fluctuations, which are in synchrony with changes in serum calcium, phosphate, and bone turnover. In addition, an ultradian rhythm exists, which comprises seven pulses per hour, accounts for 30% of basal parathyroid hormone (PTH) release, and is highly sensitive to changes in ionized calcium. Acute hypocalcemia induces a selective, severalfold increase in pulse frequency and amplitude, whereas hypercalcemia suppresses the pulsatile secretion component, as does prolonged calcitriol therapy. Chronic renal failure is associated with a GFR dependent decrease in metabolic PTH clearance accounting for a two- to threefold increase in plasma PTH concentrations, a consistent increase of PTH burst mass and frequency, and a markedly reduced capacity to counteract changes in ionized calcium by modulation of pulsatile PTH release. Continuous PTH excess destroys bone, whereas intermittent administration of pharmacological doses of PTH improves bone morphology and strength in experimental and clinical settings. The molecular mechanisms of the exposure pattern dependent, contrasting biological effects of PTH may involve differential regulation of osteoblastic G protein signaling feedback circuits. In this context, calcimimetic and calcilytic agents are promising new therapeutic tools allowing for tight control of plasma PTH and restoration of circadian PTH rhythmicity.
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Affiliation(s)
- C P Schmitt
- Division of Pediatric Nephrology, University Children's Hospital, Im Neuenheimer Feld 153, 69120 Heidelberg, Germany.
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33
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Katzman SM, Messerli MA, Barry DT, Grossman A, Harel T, Wikstrom JD, Corkey BE, Smith PJS, Shirihai OS. Mitochondrial metabolism reveals a functional architecture in intact islets of Langerhans from normal and diabetic Psammomys obesus. Am J Physiol Endocrinol Metab 2004; 287:E1090-9. [PMID: 15339741 DOI: 10.1152/ajpendo.00044.2004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cells within the intact islet of Langerhans function as a metabolic syncytium, secreting insulin in a coordinated and oscillatory manner in response to external fuel. With increased glucose, the oscillatory amplitude is enhanced, leading to the hypothesis that cells within the islet are secreting with greater synchronization. Consequently, non-insulin-dependent diabetes mellitus (NIDDM; type 2 diabetes)-induced irregularities in insulin secretion oscillations may be attributed to decreased intercellular coordination. The purpose of the present study was to determine whether the degree of metabolic coordination within the intact islet was enhanced by increased glucose and compromised by NIDDM. Experiments were performed with isolated islets from normal and diabetic Psammomys obesus. Using confocal microscopy and the mitochondrial potentiometric dye rhodamine 123, we measured mitochondrial membrane potential oscillations in individual cells within intact islets. When mitochondrial membrane potential was averaged from all the cells in a single islet, the resultant waveform demonstrated clear sinusoidal oscillations. Cells within islets were heterogeneous in terms of cellular synchronicity (similarity in phase and period), sinusoidal regularity, and frequency of oscillation. Cells within normal islets oscillated with greater synchronicity compared with cells within diabetic islets. The range of oscillatory frequencies was unchanged by glucose or diabetes. Cells within diabetic (but not normal) islets increased oscillatory regularity in response to glucose. These data support the hypothesis that glucose enhances metabolic coupling in normal islets and that the dampening of oscillatory insulin secretion in NIDDM may result from disrupted metabolic coupling.
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Affiliation(s)
- S M Katzman
- Dept. of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111, USA
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Abstract
UNLABELLED "Common" type 2 diabetes mellitus is a multifactorial disease. Hyperglycemia is related to a decrease in glucose peripheral uptake, and to an increase in hepatic glucose production, due to reduced insulin secretion and insulin sensitivity. Multiple insulin secretory defects are present, including loss of basal pulsatility, lack of early phase of insulin secretion after intravenous glucose administration, decreased basal and stimulated plasma insulin concentrations, excess in prohormone secretion, and progressive decrease in insulin secretory capacity with time. These genetically determined abnormalities appear early in the course of the disease. Insulin resistance affects muscle, liver, and adipose tissue. For the same plasma insulin levels, peripheral glucose uptake and hepatic glucose production suppressibility are lower in diabetic patients than in controls. It results from aging of the population and from "western" lifestyle, with progressive increase in mean body weight, due to excess in energy intake, decreased energy expenses and low physical activity level. NEW ASPECTS The role of beta-cell dysfunction, as well as the interplay between insulin secretory defect and insulin resistance are now better understood. In subjects with normal beta-cell function, increase in insulin needs secondary to insulin resistance is compensated by an increase in insulin secretion adjusted to maintain plasma glucose levels to normal. In subjects genetically predisposed to type 2 diabetes, failure of beta-cell to compensate for increased needs is responsible for a progressive elevation in plasma glucose levels, then for overt type 2 diabetes. This adaptative phenomenon is called beta-cell compensation of insulin resistance. The lack of compensation is responsible for type 2 diabetes. When permanent hyperglycemia is present, progressive insulin secretory failure with time ensues, due to glucotoxicity and to lipotoxicity. PERSPECTIVES Simple changes in lifestyle, such regular moderate physical activity, and control of body weight, should permit to avoid the explosion in prevalence of type 2 diabetes. This has been evidenced by the results of prospective studies aiming at preventing conversion from impaired glucose tolerance to diabetes. In patients with permanent hyperglycemia not controlled by lifestyle changes, metabolic defects are the targets of specific therapy intervention with antidiabetic oral agents, such as insulin secretagogues, insulin sensitizers, and inhibitors of hepatic glucose production.
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Affiliation(s)
- P-J Guillausseau
- Service de médecine interne B, hôpital Lariboisière, 2, rue Ambroise-Paré, 75475 Paris 10, France.
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Caton D, Calabrese A, Mas C, Serre-Beinier V, Charollais A, Caille D, Zufferey R, Trono D, Meda P. Lentivirus-mediated transduction of connexin cDNAs shows level- and isoform-specific alterations in insulin secretion of primary pancreatic beta-cells. J Cell Sci 2003; 116:2285-94. [PMID: 12697840 DOI: 10.1242/jcs.00442] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We have generated novel lentiviral vectors to integrate various connexin cDNAs into primary, non-dividing cells. We have used these vectors to test whether proper control of insulin secretion depends on a specific connexin isoform and/or on its level of expression. We have observed that transduced connexin32, connexin36 and connexin43 were expressed by primary adult beta-cells at membrane interfaces, were packed into typical gap junction plaques and formed functional channels that allowed a variable coupling, depending on the type and level of connexin expressed. The infected cells spontaneously reaggregated into three-dimensional pseudo-islet organs that could be maintained in culture. We have found that pseudo-islets made by cells transduced with either GFP- or connexin43-expressing lentivirus released insulin in response to various secretagogues similarly to controls. By contrast, pseudo-islets made by cells expressing connexin32, a connexin exogenous to pancreatic islets, or over-expressing connexin36, the endogenous islet connexin, featured a marked decrease in the secretory response to glucose. The data show: (1) that lentiviral vectors allow stable modulation of various connexin in primary, non-proliferating cells; (2) that specific connexin isoforms affect insulin secretion differently; and (3) that adequate levels of coupling via connexin36 channels are required for proper beta-cell function.
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Affiliation(s)
- David Caton
- Department of Morphology, University of Geneva Medical School, 1211 Geneva 4, Switzerland.
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Fogdell-Hahn A, Soldan SS, Jacobson S. Association of chronic progressive neurological disease and ubiquitous viral agents: lessons from human herpesvirus 6 and multiple sclerosis. Mol Psychiatry 2003; 7 Suppl 2:S29-31. [PMID: 12142941 DOI: 10.1038/sj.mp.4001172] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- A Fogdell-Hahn
- Neuroimmunology Branch, National Institute of Neurological Disorders and Stroke/NIH, 9000 Rockville Pike, Building 10, Room 5B-16, Bethesda, MD 20892, USA
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Lin JM, Fabregat ME, Gomis R, Bergsten P. Pulsatile insulin release from islets isolated from three subjects with type 2 diabetes. Diabetes 2002; 51:988-93. [PMID: 11916916 DOI: 10.2337/diabetes.51.4.988] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Plasma insulin in healthy subjects shows regular oscillations, which are important for the hypoglycemic action of the hormone. In individuals with type 2 diabetes, these regular variations are altered, which has been implicated in the development of insulin resistance and hyperglycemia. The origin of the change is unknown, but derangement of the islet secretory pattern has been suggested as a contributing cause. In the present study, we show the dynamics of insulin release from individually perifused islets isolated from three subjects with type 2 diabetes. Insulin release at 3 mmol/l glucose was 10.5 +/- 4.5 pmol.g(-1).s(-1) and pulsatile (0.26 +/- 0.05 min(-1)). In islets from one subject, 11 mmol/l glucose transiently increased insulin release by augmentation of the insulin pulses without affecting the frequency. Addition of 1 mmol/l tolbutamide did not increase insulin release. In islets from the remaining subjects, insulin release was not affected by 11 mmol/l glucose. Tolbutamide transiently increased insulin release in islets from one subject. Insulin release from four normal subjects at 3 mmol/l glucose was 4.3 +/- 0.8 pmol.g(-1).s(-1) and pulsatile (0.23 +/- 0.03 min(-1)). At 11 mmol/l glucose, insulin release increased in islets from all subjects. Tolbutamide further increased insulin release in islets from two subjects. It is concluded that islets from the three individuals with type 2 diabetes release insulin in pulses. The impaired secretory response to glucose may be related to impaired metabolism before mitochondrial degradation of the sugar.
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Affiliation(s)
- Jian-Man Lin
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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Abstract
The role of metabolism in the generation of plasma insulin oscillations was investigated by simultaneous in vivo recordings of oxygen tension (pO(2)) in the endocrine and exocrine pancreas and portal blood insulin concentrations in the anesthetized rat. At the start of the experiment, the blood glucose concentration of seven rats was 6.2 +/- 0.1 mmol/l and the arterial blood pressure was 116 +/- 5 mmHg. These values did not differ from those obtained at the end of the experiment. Islet pO(2) was measured by impaling superficially located islets with a miniaturized Clark electrode. The pO(2) measurements revealed slow (0.21 +/- 0.03 min(-1)) with superimposed rapid (3.1 +/- 0.3 min(-1)) oscillations. The average pO(2) was 39 +/- 5 mmHg. Simultaneous recordings of pO(2) in the exocrine pancreas were significantly lower (16 +/- 6 mmHg), but showed a slow and a rapid oscillatory activity with similar frequencies as seen in the endocrine pancreas. Corresponding measurements of portal insulin concentrations revealed insulin oscillations at a frequency of 0.22 +/- 0.02 min(-1). The results are the first in vivo recordings of an oscillatory islet parameter with a frequency corresponding to that of plasma insulin oscillations; they support a primary role of metabolic oscillations in the induction of plasma insulin oscillations.
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Affiliation(s)
- Peter Bergsten
- Department of Medical Cell, Uppsala University, Uppsala, Sweden.
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Gilon P, Ravier MA, Jonas JC, Henquin JC. Control mechanisms of the oscillations of insulin secretion in vitro and in vivo. Diabetes 2002; 51 Suppl 1:S144-51. [PMID: 11815474 DOI: 10.2337/diabetes.51.2007.s144] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The mechanisms driving the pulsatility of insulin secretion in vivo and in vitro are still unclear. Because glucose metabolism and changes in cytosolic free Ca(2+) ([Ca(2+)](c)) in beta-cells play a key role in the control of insulin secretion, and because oscillations of these two factors have been observed in single isolated islets and beta-cells, pulsatile insulin secretion could theoretically result from [Ca(2+)](c) or metabolism oscillations. We could not detect metabolic oscillations independent from [Ca(2+)](c) changes in beta-cells, and imposed metabolic oscillations were poorly effective in inducing oscillations of secretion when [Ca(2+)](c) was kept stable, which suggests that metabolic oscillations are not the direct regulator of the oscillations of secretion. By contrast, tight temporal and quantitative correlations between the changes in [Ca(2+)](c) and insulin release strongly suggest that [Ca(2+)](c) oscillations are the direct drivers of insulin secretion oscillations. Metabolism may play a dual role, inducing [Ca(2+)](c) oscillations (via changes in ATP-sensitive K(+) channel activity and membrane potential) and amplifying the secretory response by increasing the efficiency of Ca(2+) on exocytosis. The mechanisms underlying the oscillations of insulin secretion by the isolated pancreas and those observed in vivo remain elusive. It is not known how the functioning of distinct islets is synchronized, and the possible role of intrapancreatic ganglia in this synchronization requires confirmation. That pulsatile insulin secretion is beneficial in vivo, by preventing insulin resistance, is suggested by the greater hypoglycemic effect of exogenous insulin when it is infused in a pulsatile rather than continuous manner. The observation that type 2 diabetic patients have impaired pulsatile insulin secretion has prompted the suggestion that such dysregulation contributes to the disease and justifies the efforts toward understanding of the mechanism underlying the pulsatility of insulin secretion both in vitro and in vivo.
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Affiliation(s)
- Patrick Gilon
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, Brussels, Belgium.
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Bergsten P. Role of oscillations in membrane potential, cytoplasmic Ca2+, and metabolism for plasma insulin oscillations. Diabetes 2002; 51 Suppl 1:S171-6. [PMID: 11815477 DOI: 10.2337/diabetes.51.2007.s171] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
A model for the relationship between ionic and metabolic oscillations and plasma insulin oscillations is presented. It is argued that the pancreatic beta-cell in vivo displays two intrinsic frequencies that are important for the regulation of plasma insulin oscillations. The rapid oscillatory activity (2--7 oscillations [osc] per minute), which is evident in both ionic and metabolic events, causes the required elevation in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) for the exocytosis of insulin granules. This activity is important for regulation of the amplitude of plasma insulin oscillations. The frequency of the rapid oscillatory ionic activities is regulated by glucose and allows the beta-cell to respond in an analogous way, with gradual changes in [Ca(2+)](i) and insulin release in response to the alterations in glucose concentration. The slower oscillatory activity (0.2--0.4 osc/min), which is evident in the metabolism of the beta-cell, has a frequency corresponding to the frequency observed in plasma insulin oscillations. The frequency is not affected by changes in the glucose concentration. This activity is suggested to generate energy in a pulsatile fashion, which sets the frequency of the plasma insulin oscillations. It is proposed that the slow oscillations in [Ca(2+)](i) observed in vitro are a manifestation of the metabolic oscillations and do not represent an in vivo phenomenon.
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Affiliation(s)
- Peter Bergsten
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.
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Kjems LL, Ravier MA, Jonas JC, Henquin JC. Do oscillations of insulin secretion occur in the absence of cytoplasmic Ca2+ oscillations in beta-cells? Diabetes 2002; 51 Suppl 1:S177-82. [PMID: 11815478 DOI: 10.2337/diabetes.51.2007.s177] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
That oscillations of the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in beta-cells induce oscillations of insulin secretion is not disputed, but whether metabolism-driven oscillations of secretion can occur in the absence of [Ca(2+)](i) oscillations is still debated. Because this possibility is based partly on the results of experiments using islets from aged, hyperglycemic, hyperinsulinemic ob/ob mice, we compared [Ca(2+)](i) and insulin secretion patterns of single islets from 4- and 10-month-old, normal NMRI mice to those of islets from 7- and 10-month-old ob/ob mice (Swedish colony) and their lean littermates. The responses were subjected to cluster analysis to identify significant peaks. Control experiments without islets and with a constant insulin concentration were run to detect false peaks. Both ob/ob and NMRI islets displayed large synchronous oscillations of [Ca(2+)](i) and insulin secretion in response to repetitive depolarizations with 30 mmol/l K(+) in the presence of 0.1 mmol/l diazoxide and 12 mmol/l glucose. Continuous depolarization with high K(+) steadily elevated [Ca(2+)](i) in all types of islets, with no significant oscillation, and caused a biphasic insulin response. In islets from young (4-month-old) NMRI mice and 7-month-old lean mice, the insulin profile did not show significant peaks when [Ca(2+)](i) was stable. In contrast, two or more peaks were detected over 20 min in the response of most ob/ob islets. Similar insulin peaks appeared in the insulin response of 10-month-old lean and NMRI mice. However, the size of the insulin peaks detected in the presence of stable [Ca(2+)](i) was small, so that no more than 10-13% of total insulin secretion occurred in a pulsatile manner. In conclusion, insulin secretion does not oscillate when [Ca(2+)](i) is stably elevated in beta-cells from young normal mice. Some oscillations are observed in aged mice and are seen more often in ob/ob islets. These fluctuations of the insulin secretion rate at stably elevated [Ca(2+)](i), however, are small compared with the large oscillations induced by [Ca(2+)](i) oscillations in beta-cells.
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Affiliation(s)
- Lise L Kjems
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, Brussels, Belgium
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Lin JM, Ortsäter H, Fakhrai-Rad H, Galli J, Luthman H, Bergsten P. Phenotyping of individual pancreatic islets locates genetic defects in stimulus secretion coupling to Niddm1i within the major diabetes locus in GK rats. Diabetes 2001; 50:2737-43. [PMID: 11723056 DOI: 10.2337/diabetes.50.12.2737] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The major diabetes quantitative trait locus (Niddm1), which segregates in crosses between GK rats affected with spontaneous type 2-like diabetes and normoglycemic F344 rats, encodes at least two different diabetes susceptibility genes. Congenic strains for the two subloci (Niddm1f and Niddm1i) have been generated by transfer of GK alleles onto the genome of F344 rats. Whereas the Niddm1f phenotype implicated insulin resistance, the Niddm1i phenotype displayed diabetes related to insulin deficiency. Individual islets from 16-week-old congenic rats were characterized for insulin release and oxygen tension (pO(2)). In the presence of 3 mmol/l glucose, insulin release from Niddm1f and Niddm1i islets was approximately 5 pmol. g(-1). s(-1) and pO(2) was 120 mmHg. Similar recordings were obtained from GK and F344 islets. When glucose was raised to 11 mmol/l, insulin release increased significantly in Niddm1f and F344 islets but was essentially unchanged in islets from GK and Niddm1i. The high glucose concentration lowered pO(2) to the same extent in islets from all strains. Addition of 1 mmol/l tolbutamide to the perifusion medium further increased pulsatile insulin release threefold in all islets. The pulse frequency was approximately 0.4 min(-1). alpha-Ketoisocaproate (11 mmol/l) alone increased pulsatile insulin release eightfold in islets from Niddm1f, Niddm1i, and control F344 rats but had no effect on insulin release from GK islets. These secretory patterns in response to alpha-ketoisocaproate were paralleled by reduction of pO(2) in Niddm1f, Niddm1i, and control F344 islets and no change of pO(2) in GK islets. The results demonstrate that Niddm1i carries alleles of gene(s) that reduce glucose-induced insulin release and that are amenable to molecular identification by genetic fine mapping.
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Affiliation(s)
- J M Lin
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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Affiliation(s)
- B Goichot
- Service de medecine interne et nutrition, hopitaux universitaires de Strasbourg, France
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Shiraishi S, Yamamoto R, Yanagita T, Yokoo H, Kobayashi H, Uezono Y, Wada A. Down-regulation of cell surface insulin receptors by sarco(endo)plasmic reticulum Ca2+-ATPase inhibitor in adrenal chromaffin cells. Brain Res 2001; 898:152-7. [PMID: 11292458 DOI: 10.1016/s0006-8993(01)02193-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Long-term (> or =12 h) treatment of cultured bovine adrenal chromaffin cells with thapsigargin (TG), an inhibitor of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), caused a time (t(1/2)=16.3 h)- and concentration (IC50=37.8 nM)-dependent decrease of cell surface 125I-insulin binding by 35%, but did not change the Kd value. TG caused a sustained increase of cytoplasmic concentration of Ca2+ ([Ca2+]c) in a biphasic manner, and the effect of TG on 125I-insulin binding was abolished by BAPTA-AM. Western blot analysis showed that TG lowered insulin receptor (IR) beta-subunit level in membrane, but did not alter total cellular levels of IR precursor and IR beta-subunit. Internalization of cell surface IR, as measured by using brefeldin A, an inhibitor of vesicular exit from the trans-Golgi network (TGN), was not changed by TG. These results suggest that inhibition of SERCA by TG and the subsequent increase of [Ca2+]c down-regulates cell surface IR by retarding externalization of IR from the TGN.
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Affiliation(s)
- S Shiraishi
- Department of Pharmacology, Miyazaki Medical College, 889-1692, Miyazaki, Japan
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Wang XY, Bergdahl K, Heijbel A, Liljebris C, Bleasdale JE. Analysis of in vitro interactions of protein tyrosine phosphatase 1B with insulin receptors. Mol Cell Endocrinol 2001; 173:109-20. [PMID: 11223182 DOI: 10.1016/s0303-7207(00)00402-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
One strategy to treat the insulin resistance that is central to type II diabetes mellitus may be to maintain insulin receptors (IR) in the active (tyrosine phosphorylated) form. Because protein tyrosine phosphatase 1B (PTP1B) binds and subsequently dephosphorylates IR, inhibitors of PTP1B-IR binding are potential insulin 'sensitizers.' A Scintillation Proximity Assay (SPA) was developed to characterize and quantitate PTP1B-IR binding. Human IR were solubilized and captured on wheat germ agglutinin (WGA)-coated SPA beads. Subsequent binding of human, catalytically inactive [35S] PTP1B Cys(215)/Ser (PTP1B(C215S)) to the lectin-anchored IR results in scintillation from the SPA beads that can be quantitated. Binding of PTP1B to IR was pH- and divalent cation-sensitive. Ca(2+) and Mn(2+), but not Mg(2+), dramatically attenuated the loss of PTP1B-IR binding observed when pH was raised from 6.2 to 7.8. PTP1B binding to IR from insulin-stimulated cells was much greater than to IR from unstimulated cells and was inhibited by either an antiphosphotyrosine antibody or treatment of IR with alkaline phosphatase, suggesting that tyrosine phosphorylation of IR is required for PTP1B binding. Phosphopeptides modeled after various IR phosphotyrosine domains each only partially inhibited PTP1B-IR binding, indicating that multiple domains of IR are likely involved in binding PTP1B. However, competitive displacement of [35S]PTP1B(C215S) by PTP1B(C215S) fitted best to a single binding site with a K(d) in the range 100-1000 nM, depending upon pH and divalent cations. PNU-200898, a potent and selective inhibitor of PTP1B whose orientation in the active site of PTP1B has been solved, competitively inhibited catalysis and PTP1B-IR binding with equal potency. The results of this novel assay for PTP1B-IR binding suggest that PTP1B binds preferentially to tyrosine phosphorylated IR through its active site and that binding may be susceptible to therapeutic disruption by small molecules.
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Affiliation(s)
- X Y Wang
- Cell & Molecular Biology, Research & Development, Pharmacia & Upjohn, Kalamazoo, MI 49007, USA
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