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Sue N, Thai LM, Saito A, Boyer CK, Fordham AM, Yan C, Davenport A, Tao J, Bensellam M, Cantley J, Shi YC, Stephens SB, Imaizumi K, Biden TJ. Independent activation of CREB3L2 by glucose fills a regulatory gap in mouse β-cells by co-ordinating insulin biosynthesis with secretory granule formation. Mol Metab 2024; 79:101845. [PMID: 38013154 PMCID: PMC10755490 DOI: 10.1016/j.molmet.2023.101845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 11/22/2023] [Accepted: 11/23/2023] [Indexed: 11/29/2023] Open
Abstract
OBJECTIVE Although individual steps have been characterized, there is little understanding of the overall process whereby glucose co-ordinates the biosynthesis of insulin with its export out of the endoplasmic reticulum (ER) and incorporation into insulin secretory granules (ISGs). Here we investigate a role for the transcription factor CREB3L2 in this context. METHODS MIN6 cells and mouse islets were analysed by immunoblotting after treatment with glucose, fatty acids, thapsigargin and various inhibitors. Knockdown of CREB3L2 was achieved using si or sh constructs by transfection, or viral delivery. In vivo metabolic phenotyping was conducted after deletion of CREB3L2 in β-cells of adult mice using Ins1-CreER+. Islets were isolated for RNAseq and assays of glucose-stimulated insulin secretion (GSIS). Trafficking was monitored in islet monolayers using a GFP-tagged proinsulin construct that allows for synchronised release from the ER. RESULTS With a Km ≈3.5 mM, glucose rapidly (T1/2 0.9 h) increased full length (FL) CREB3L2 followed by a slower rise (T1/2 2.5 h) in its transcriptionally-active cleavage product, P60 CREB3L2. Glucose stimulation repressed the ER stress marker, CHOP, and this was partially reverted by knockdown of CREB3L2. Activation of CREB3L2 by glucose was not due to ER stress, however, but a combination of O-GlcNAcylation, which impaired proteasomal degradation of FL-CREB3L2, and mTORC1 stimulation, which enhanced its conversion to P60. cAMP generation also activated CREB3L2, but independently of glucose. Deletion of CREB3L2 inhibited GSIS ex vivo and, following a high-fat diet (HFD), impaired glucose tolerance and insulin secretion in vivo. RNAseq revealed that CREB3L2 regulated genes controlling trafficking to-and-from the Golgi, as well as a broader cohort associated with β-cell compensation during a HFD. Although post-Golgi trafficking appeared intact, knockdown of CREB3L2 impaired the generation of both nascent ISGs and proinsulin condensates in the Golgi, implying a defect in ER export of proinsulin and/or its processing in the Golgi. CONCLUSION The stimulation of CREB3L2 by glucose defines a novel, rapid and direct mechanism for co-ordinating the synthesis, packaging and storage of insulin, thereby minimizing ER overload and optimizing β-cell function under conditions of high secretory demand. Upregulation of CREB3L2 also potentially contributes to the benefits of GLP1 agonism and might in itself constitute a novel means of treating β-cell failure.
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Affiliation(s)
- Nancy Sue
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Le May Thai
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Atsushi Saito
- Department of Biochemistry, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Cierra K Boyer
- Fraternal Order of Eagles Diabetes Research Center, Department of Internal Medicine, University of Iowa, Iowa City, IA 52246, USA
| | - Ashleigh M Fordham
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Chenxu Yan
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Aimee Davenport
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Jiang Tao
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Mohammed Bensellam
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - James Cantley
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Yan-Chuan Shi
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, Faculty of Medicine, The University of New South Wales, Sydney, Australia
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center, Department of Internal Medicine, University of Iowa, Iowa City, IA 52246, USA
| | - Kazunori Imaizumi
- Department of Biochemistry, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Trevor J Biden
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, Faculty of Medicine, The University of New South Wales, Sydney, Australia.
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Oberhauser L, Jiménez-Sánchez C, Madsen JGS, Duhamel D, Mandrup S, Brun T, Maechler P. Glucolipotoxicity promotes the capacity of the glycerolipid/NEFA cycle supporting the secretory response of pancreatic beta cells. Diabetologia 2022; 65:705-720. [PMID: 35018486 DOI: 10.1007/s00125-021-05633-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Accepted: 10/12/2021] [Indexed: 11/03/2022]
Abstract
AIMS/HYPOTHESIS Chronic exposure of pancreatic beta cells to high glucose and fatty acids has been proposed to induce glucolipotoxicity. However, contradictory results suggest adaptations of the beta cells, which might be instrumental for partial preservation of the secretory response. In this context, we delineated the expression pattern of genes related to lipid pathways along with fat storage/mobilisation during glucose-stimulated insulin secretion. METHODS Insulin-secreting cells were cultured for 3 days at different glucose concentrations (5.5, 11.1, 25 mmol/l) without or with BSA-complexed 0.4 mmol/l palmitate and oleate. Then, transcriptomic analyses of lipid pathways were performed in human islets by RNA-Seq and in INS-1E cells and rat islets by quantitative RT-PCR. Storage of fat was assessed in INS-1E cells by electron microscopy and Bodipy staining, which was also used for measuring lipid mobilisation rate. The secretory response was monitored during acute 15 mmol/l glucose stimulation using online luminescence assay for INS-1E cells and by radioimmunoassay for rat islets. RESULTS In human islets, chronic exposure to palmitate and oleate modified expression of a panel of genes involved in lipid handling. Culture at 25 mmol/l glucose upregulated genes encoding for enzymes of the glycerolipid/NEFA cycle and downregulated receptors implicated in fatty acid signalling. Similar results were obtained in INS-1E cells, indicating enhanced capacity of the glycerolipid/NEFA cycle under glucotoxic conditions. Exposure to unsaturated C18:1 fatty acid favoured intracellular lipid accumulation in a glucose-dependent way, an effect also observed with saturated C16:0 fatty acid when combined with the panlipase inhibitor Orlistat. After the glucolipotoxic culture, intracellular fat mobilisation was required for acute glucose-stimulated secretion, particularly in oleate-treated cells under glucotoxic culture conditions. The lipid mobilisation rate was governed chiefly by the levels of stored fat as a direct consequence of the culture conditions rather than energetic demands, except in palmitate-loaded cells. CONCLUSIONS/INTERPRETATION Glucolipotoxic conditions promote the capacity of the glycerolipid/NEFA cycle thereby preserving part of the secretory response. The cycle of fat storage/mobilisation emerges as a mechanism helping the beta cell to cope with glucotoxic conditions.
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Affiliation(s)
- Lucie Oberhauser
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Cecilia Jiménez-Sánchez
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Jesper Grud Skat Madsen
- Functional Genomics and Metabolism Research Unit, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Dominique Duhamel
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Susanne Mandrup
- Functional Genomics and Metabolism Research Unit, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Thierry Brun
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism, University of Geneva Medical Center, Geneva, Switzerland.
- Faculty Diabetes Center, University of Geneva Medical Center, Geneva, Switzerland.
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3
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Wagner R, Eckstein SS, Yamazaki H, Gerst F, Machann J, Jaghutriz BA, Schürmann A, Solimena M, Singer S, Königsrainer A, Birkenfeld AL, Häring HU, Fritsche A, Ullrich S, Heni M. Metabolic implications of pancreatic fat accumulation. Nat Rev Endocrinol 2022; 18:43-54. [PMID: 34671102 DOI: 10.1038/s41574-021-00573-3] [Citation(s) in RCA: 58] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 09/13/2021] [Indexed: 12/15/2022]
Abstract
Fat accumulation outside subcutaneous adipose tissue often has unfavourable effects on systemic metabolism. In addition to non-alcoholic fatty liver disease, which has received considerable attention, pancreatic fat has become an important area of research throughout the past 10 years. While a number of diagnostic approaches are available to quantify pancreatic fat, multi-echo Dixon MRI is currently the most developed method. Initial studies have shown associations between pancreatic fat and the metabolic syndrome, impaired glucose metabolism and type 2 diabetes mellitus. Pancreatic fat is linked to reduced insulin secretion, at least under specific circumstances such as prediabetes, low BMI and increased genetic risk of type 2 diabetes mellitus. This Review summarizes the possible causes and metabolic consequences of pancreatic fat accumulation. In addition, potential therapeutic approaches for addressing pancreatic fat accumulation are discussed.
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Affiliation(s)
- Robert Wagner
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Sabine S Eckstein
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
| | - Hajime Yamazaki
- Section of Clinical Epidemiology, Department of Community Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Felicia Gerst
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Jürgen Machann
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Section of Experimental Radiology, Department of Diagnostic and Interventional Radiology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Benjamin Assad Jaghutriz
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Annette Schürmann
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Experimental Diabetology, German Institute of Human Nutrition (DIfE), Potsdam-Rehbrücke, Germany
- Institute of Nutritional Science, University of Potsdam, Potsdam, Germany
| | - Michele Solimena
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Molecular Diabetology, University Hospital and Faculty of Medicine Carl Gustav Carus, TU Dresden, Dresden, Germany
- Paul Langerhans Institute Dresden (PLID), Helmholtz Center Munich, University Hospital and Faculty of Medicine Carl Gustav Carus, TU Dresden, Dresden, Germany
| | - Stephan Singer
- Institute of Pathology, University of Tübingen, Tübingen, Germany
| | - Alfred Königsrainer
- Department of General, Visceral, and Transplant Surgery, University Hospital Tübingen, Tübingen, Germany
| | - Andreas L Birkenfeld
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Hans-Ulrich Häring
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Andreas Fritsche
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Susanne Ullrich
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany
- German Center for Diabetes Research (DZD), Tübingen, Germany
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Martin Heni
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany.
- German Center for Diabetes Research (DZD), Tübingen, Germany.
- Department of Internal Medicine, Division of Diabetology, Endocrinology, and Nephrology, Eberhard Karls University Tübingen, Tübingen, Germany.
- Institute for Clinical Chemistry and Pathobiochemistry, Department for Diagnostic Laboratory Medicine, University Hospital Tübingen, Tübingen, Germany.
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Mridha AR, Dargaville TR, Dalton PD, Carroll L, Morris MB, Vaithilingam V, Tuch BE. Prevascularized Retrievable Hybrid Implant to Enhance Function of Subcutaneous Encapsulated Islets. Tissue Eng Part A 2020; 28:212-224. [PMID: 33081600 DOI: 10.1089/ten.tea.2020.0179] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Replacement of pancreatic β-cells is one of the most promising treatment options for treatment of type 1 diabetes (T1D), even though, toxic immunosuppressive drugs are required. In this study, we aim to deliver allogeneic β-cell therapies without antirejection drugs using a bioengineered hybrid device that contains microencapsulated β-cells inside 3D polycaprolactone (PCL) scaffolds printed using melt electrospin writing (MEW). Mouse β-cell (MIN6) pseudoislets and QS mouse islets are encapsulated in alginate microcapsules, without affecting viability and insulin secretion. Microencapsulated MIN6 cells are then seeded within 3D MEW scaffolds, and these hybrid devices implanted subcutaneously in streptozotocin-treated diabetic NOD/SCID and BALB/c mice. Similar to NOD/SCID mice, blood glucose levels (BGL) are lowered from 30.1 to 4.8 mM in 25-41 days in BALB/c. In contrast, microencapsulated islets placed in prevascularized MEW scaffold 3 weeks after implantation in BALB/c mice normalize BGL (<12 mM) more rapidly, lasting for 60-105 days. The lowering of glucose levels is confirmed by an intraperitoneal glucose tolerance test. Vascularity within the implanted grafts is demonstrated and quantified by 3D-doppler ultrasound, with a linear increase over 4 weeks (r = 0.65). Examination of the device at 5 weeks shows inflammatory infiltrates of neutrophils, macrophages, and B-lymphocytes on the MEW scaffolds, but not on microcapsules, which have infrequent profibrotic walling. In conclusion, we demonstrate the fabrication of an implantable and retrievable hybrid device for vascularization and enhancing the survival of encapsulated islets implanted subcutaneously in an allotransplantation setting without immunosuppression. This study provides proof-of-concept for the application of such devices for human use, but, will require modifications to allow translation to people with T1D. Impact statement The retrievable 3D printed PCL scaffold we have produced promotes vascularization when implanted subcutaneously and allows seeded microencapsulated insulin-producing cells to normalize blood glucose of diabetic mice for at least 2 months, without the need for antirejection drugs to be administered. The scaffold is scalable for possible human use, but will require modification to ensure that normalization of blood glucose levels can be maintained long term.
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Affiliation(s)
- Auvro R Mridha
- Discipline of Physiology, Faculty of Medicine and Health, School of Medical Sciences, The University of Sydney, Sydney, Australia.,Australian Foundation for Diabetes Research, Sydney, Australia.,Bosch Institute, The University of Sydney, Sydney, Australia
| | - Tim R Dargaville
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Queensland, Australia
| | - Paul D Dalton
- Department of Functional Materials in Medicine and Dentistry, University of Würzburg, Würzburg, Germany
| | - Luke Carroll
- Discipline of Physiology, Faculty of Medicine and Health, School of Medical Sciences, The University of Sydney, Sydney, Australia.,Australian Foundation for Diabetes Research, Sydney, Australia.,Now Based at NHMRC Clinical Trials Centre, The University of Sydney, Sydney, Australia
| | - Michael B Morris
- Discipline of Physiology, Faculty of Medicine and Health, School of Medical Sciences, The University of Sydney, Sydney, Australia.,Bosch Institute, The University of Sydney, Sydney, Australia
| | - Vijayaganapathy Vaithilingam
- Australian Foundation for Diabetes Research, Sydney, Australia.,Cell Biology Inspired Tissue Engineering (CBITE), MERLN Institute for Technology-Inspired Regenerative Medicine, Maastricht University, Maastricht, The Netherlands
| | - Bernard E Tuch
- Discipline of Physiology, Faculty of Medicine and Health, School of Medical Sciences, The University of Sydney, Sydney, Australia.,Australian Foundation for Diabetes Research, Sydney, Australia
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5
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Schmitz-Peiffer C. Deconstructing the Role of PKC Epsilon in Glucose Homeostasis. Trends Endocrinol Metab 2020; 31:344-356. [PMID: 32305097 DOI: 10.1016/j.tem.2020.01.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 01/22/2020] [Accepted: 01/24/2020] [Indexed: 02/06/2023]
Abstract
The failure of insulin to suppress glucose production by the liver is a key aspect of the insulin resistance seen in type 2 diabetes. Lipid-activated protein kinase C epsilon has long been identified as an important mediator of diet-induced glucose intolerance and hepatic insulin resistance and the current view emphasizes a mechanism involving phosphorylation of the insulin receptor by the kinase to inhibit downstream insulin action. However, the significance of this direct effect in the liver has now been challenged by tissue-specific deletion of PKCε, which demonstrated a more prominent role for the kinase in adipose tissue to promote glucose intolerance. New insights regarding the role of PKCε therefore contribute to the understanding of indirect effects on hepatic glucose metabolism.
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Affiliation(s)
- Carsten Schmitz-Peiffer
- Garvan Institute of Medical Research, Darlinghurst Sydney, NSW 2010, Australia; St Vincent's Clinical School, University of New South Wales, Sydney, NSW 2010, Australia.
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6
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Lytrivi M, Castell AL, Poitout V, Cnop M. Recent Insights Into Mechanisms of β-Cell Lipo- and Glucolipotoxicity in Type 2 Diabetes. J Mol Biol 2019; 432:1514-1534. [PMID: 31628942 DOI: 10.1016/j.jmb.2019.09.016] [Citation(s) in RCA: 219] [Impact Index Per Article: 43.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2019] [Revised: 09/15/2019] [Accepted: 09/16/2019] [Indexed: 12/24/2022]
Abstract
The deleterious effects of chronically elevated free fatty acid (FFA) levels on glucose homeostasis are referred to as lipotoxicity, and the concurrent exposure to high glucose may cause synergistic glucolipotoxicity. Lipo- and glucolipotoxicity have been studied for over 25 years. Here, we review the current evidence supporting the role of pancreatic β-cell lipo- and glucolipotoxicity in type 2 diabetes (T2D), including lipid-based interventions in humans, prospective epidemiological studies, and human genetic findings. In addition to total FFA quantity, the quality of FFAs (saturation and chain length) is a key determinant of lipotoxicity. We discuss in vitro and in vivo experimental models to investigate lipo- and glucolipotoxicity in β-cells and describe experimental pitfalls. Lipo- and glucolipotoxicity adversely affect many steps of the insulin production and secretion process. The molecular mechanisms underpinning lipo- and glucolipotoxic β-cell dysfunction and death comprise endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, impaired autophagy, and inflammation. Crosstalk between these stress pathways exists at multiple levels and may aggravate β-cell lipo- and glucolipotoxicity. Lipo- and glucolipotoxicity are therapeutic targets as several drugs impact the underlying stress responses in β-cells, potentially contributing to their glucose-lowering effects in T2D.
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Affiliation(s)
- Maria Lytrivi
- ULB Center for Diabetes Research, Medical Faculty, Université Libre de Bruxelles, Brussels, Belgium; Division of Endocrinology, Erasmus Hospital, Université Libre de Bruxelles, Brussels, Belgium
| | - Anne-Laure Castell
- CRCHUM, Montréal, QC, Canada; Department of Medicine, Université de Montréal, Montréal, QC, Canada
| | - Vincent Poitout
- CRCHUM, Montréal, QC, Canada; Department of Medicine, Université de Montréal, Montréal, QC, Canada.
| | - Miriam Cnop
- ULB Center for Diabetes Research, Medical Faculty, Université Libre de Bruxelles, Brussels, Belgium; Division of Endocrinology, Erasmus Hospital, Université Libre de Bruxelles, Brussels, Belgium.
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7
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Srivastava S, Pandey H, Singh SK, Tripathi YB. Anti-oxidant, anti-apoptotic, anti-hypoxic and anti-inflammatory conditions induced by PTY-2 against STZ-induced stress in islets. Biosci Trends 2019; 13:382-393. [PMID: 31597821 DOI: 10.5582/bst.2019.01181] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The earlier assessment of Pueraria tuberosa (PT) has shown anti-diabetic effects through enhancing incretin action and DPP-IV (Dipeptidyl peptidase-IV) inhibition. The aim of this work was to further explore the protective role of aqueous extract of Pueraria tuberosa tuber (PTY-2) against streptozotocin (STZ) induced islet stress in rats. Diabetes was induced by STZ (65 mg/kg body weight) in charles foster male rats. After 60 days of STZ administration, animals with blood glucose levels > 200 g/dL were considered as diabetic. All the rats were later divided into three groups: Group-1 (STZ untreated normal rats), Group-2 (Diabetic control), and Group-3 (PTY-2 [50 mg/100 g bw treatment for next 10 days to diabetic rats). The rats were then sacrificed after the 10th day of treatment accordingly. STZ treatment led to an increase in expression of Matrix metalloproteinases-9 (MMP-9), Tumour necrosis factor-α (Tnf-α), Hypoxia inducible factor-α (HIF-1α), Vascular endothelial growth factor (VEGF), Interleukin-6 (IL-6), Protein kinase C-ε (PKC-ε), Nuclear factor kappa-light-chain-enhancer of activated B-cells (NFkB), and Caspase-3. Reverse Transcriptase-PCR (RT-PCR), Immunohistochemistry and Western-Blot analysis showed an increase in the expressions of Superoxide Dismutase (SOD) and Nephrin, and a decrease in the expressions of NFkB, PKC-ε, TNF-α, MMP-9, HIF-1α, VEGF, Caspase-3 and IL-6 after 10 days of PTY-2 treatment. The results showed that PTY-2 favorably changed all the expressions via anti-oxidant, anti-apoptotic, anti-hypoxic and anti-inflammatory pathways, making itself as a protective agent against STZ induced islet stress. Further evaluation of PTY-2 might be helpful in establishing its role in the management of diabetes mellitus.
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Affiliation(s)
- Shivani Srivastava
- Department of Medicinal Chemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
| | - Harsh Pandey
- Department of Medicinal Chemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
| | - Surya Kumar Singh
- Department of Endocrinology and Metabolism, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
| | - Yamini Bhusan Tripathi
- Department of Medicinal Chemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
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8
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Montgomery MK, Osborne B, Brandon AE, O'Reilly L, Fiveash CE, Brown SHJ, Wilkins BP, Samsudeen A, Yu J, Devanapalli B, Hertzog A, Tolun AA, Kavanagh T, Cooper AA, Mitchell TW, Biden TJ, Smith NJ, Cooney GJ, Turner N. Regulation of mitochondrial metabolism in murine skeletal muscle by the medium-chain fatty acid receptor Gpr84. FASEB J 2019; 33:12264-12276. [PMID: 31415180 DOI: 10.1096/fj.201900234r] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Fatty acid receptors have been recognized as important players in glycaemic control. This study is the first to describe a role for the medium-chain fatty acid (MCFA) receptor G-protein-coupled receptor (Gpr) 84 in skeletal muscle mitochondrial function and insulin secretion. We are able to show that Gpr84 is highly expressed in skeletal muscle and adipose tissue. Mice with global deletion of Gpr84 [Gpr84 knockout (KO)] exhibit a mild impairment in glucose tolerance when fed a MCFA-enriched diet. Studies in mice and pancreatic islets suggest that glucose intolerance is accompanied by a defect in insulin secretion. MCFA-fed KO mice also exhibit a significant impairment in the intrinsic respiratory capacity of their skeletal muscle mitochondria, but at the same time also exhibit a substantial increase in mitochondrial content. Changes in canonical pathways of mitochondrial biogenesis and turnover are unable to explain these mitochondrial differences. Our results show that Gpr84 plays a crucial role in regulating mitochondrial function and quality control.-Montgomery, M. K., Osborne, B., Brandon, A. E., O'Reilly, L., Fiveash, C. E., Brown, S. H. J., Wilkins, B. P., Samsudeen, A., Yu, J., Devanapalli, B., Hertzog, A., Tolun, A. A., Kavanagh, T., Cooper, A. A., Mitchell, T. W., Biden, T. J., Smith, N. J., Cooney, G. J., Turner, N. Regulation of mitochondrial metabolism in murine skeletal muscle by the medium-chain fatty acid receptor Gpr84.
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Affiliation(s)
- Magdalene K Montgomery
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia.,Department of Physiology, School of Biomedical Sciences, University of Melbourne, Melbourne, Victoria, Australia
| | - Brenna Osborne
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Amanda E Brandon
- Diabetes and Metabolism Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia.,Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia
| | - Liam O'Reilly
- Diabetes and Metabolism Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - Corrine E Fiveash
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Simon H J Brown
- School of Biological Sciences, University of Wollongong, Wollongong, New South Wales, Australia.,Illawarra Health and Medical Research Institute, Wollongong, New South Wales, Australia
| | - Brendan P Wilkins
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia.,Division of Molecular Cardiology and Biophysics, Victor Chang Cardiac Research Institute, Sydney, New South Wales, Australia
| | - Azrah Samsudeen
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Josephine Yu
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Beena Devanapalli
- New South Wales (NSW) Biochemical Genetics Laboratory, Sydney Children's Hospital Network, Westmead, New South Wales, Australia
| | - Ashley Hertzog
- New South Wales (NSW) Biochemical Genetics Laboratory, Sydney Children's Hospital Network, Westmead, New South Wales, Australia
| | - Adviye A Tolun
- New South Wales (NSW) Biochemical Genetics Laboratory, Sydney Children's Hospital Network, Westmead, New South Wales, Australia.,Discipline of Genomic Medicine, and Child and Adolescent Health, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, Australia.,Discipline of Child and Adolescent Health, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, Australia
| | - Tomas Kavanagh
- Neuroscience Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - Antony A Cooper
- Neuroscience Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia.,St. Vincent's Clinical School, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Todd W Mitchell
- Illawarra Health and Medical Research Institute, Wollongong, New South Wales, Australia.,School of Medicine, University of Wollongong, Wollongong, New South Wales, Australia
| | - Trevor J Biden
- Diabetes and Metabolism Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia.,St. Vincent's Clinical School, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Nicola J Smith
- Division of Molecular Cardiology and Biophysics, Victor Chang Cardiac Research Institute, Sydney, New South Wales, Australia.,St. Vincent's Clinical School, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
| | - Gregory J Cooney
- Diabetes and Metabolism Division, Garvan Institute of Medical Research, Sydney, New South Wales, Australia.,Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia
| | - Nigel Turner
- Department of Pharmacology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, New South Wales, Australia
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9
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Cantley J, Davenport A, Vetterli L, Nemes NJ, Whitworth PT, Boslem E, Thai LM, Mellett N, Meikle PJ, Hoehn KL, James DE, Biden TJ. Disruption of beta cell acetyl-CoA carboxylase-1 in mice impairs insulin secretion and beta cell mass. Diabetologia 2019; 62:99-111. [PMID: 30334081 PMCID: PMC6290731 DOI: 10.1007/s00125-018-4743-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 08/22/2018] [Indexed: 11/29/2022]
Abstract
AIMS/HYPOTHESIS Pancreatic beta cells secrete insulin to maintain glucose homeostasis, and beta cell failure is a hallmark of type 2 diabetes. Glucose triggers insulin secretion in beta cells via oxidative mitochondrial pathways. However, it also feeds mitochondrial anaplerotic pathways, driving citrate export and cytosolic malonyl-CoA production by the acetyl-CoA carboxylase 1 (ACC1) enzyme. This pathway has been proposed as an alternative glucose-sensing mechanism, supported mainly by in vitro data. Here, we sought to address the role of the beta cell ACC1-coupled pathway in insulin secretion and glucose homeostasis in vivo. METHODS Acaca, encoding ACC1 (the principal ACC isoform in islets), was deleted in beta cells of mice using the Cre/loxP system. Acaca floxed mice were crossed with Ins2cre mice (βACC1KO; life-long beta cell gene deletion) or Pdx1creER mice (tmx-βACC1KO; inducible gene deletion in adult beta cells). Beta cell function was assessed using in vivo metabolic physiology and ex vivo islet experiments. Beta cell mass was analysed using histological techniques. RESULTS βACC1KO and tmx-βACC1KO mice were glucose intolerant and had defective insulin secretion in vivo. Isolated islet studies identified impaired insulin secretion from beta cells, independent of changes in the abundance of neutral lipids previously implicated as amplification signals. Pancreatic morphometry unexpectedly revealed reduced beta cell size in βACC1KO mice but not in tmx-βACC1KO mice, with decreased levels of proteins involved in the mechanistic target of rapamycin kinase (mTOR)-dependent protein translation pathway underpinning this effect. CONCLUSIONS/INTERPRETATION Our study demonstrates that the beta cell ACC1-coupled pathway is critical for insulin secretion in vivo and ex vivo and that it is indispensable for glucose homeostasis. We further reveal a role for ACC1 in controlling beta cell growth prior to adulthood.
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Affiliation(s)
- James Cantley
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
| | - Aimee Davenport
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
| | - Laurène Vetterli
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Nandor J Nemes
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - P Tess Whitworth
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
| | - Ebru Boslem
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
| | - Le May Thai
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
| | - Natalie Mellett
- Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia
| | - Peter J Meikle
- Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia
| | - Kyle L Hoehn
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, Australia
| | - David E James
- The Charles Perkins Centre, School of Molecular Biosciences, School of Medicine, University of Sydney, Sydney, NSW, Australia
| | - Trevor J Biden
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Darlinghurst, NSW, Australia
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10
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Zhou K, Yao P, He J, Zhao H. Lipophagy in nonliver tissues and some related diseases: Pathogenic and therapeutic implications. J Cell Physiol 2018; 234:7938-7947. [PMID: 30537019 DOI: 10.1002/jcp.27988] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 11/21/2018] [Indexed: 12/24/2022]
Abstract
Lipid autophagy (lipophagy) is defined as a selective autophagy process in which some intracellular lipid droplets are selectively degraded by autophagic lysosomes pathway. The occurrence of lipophagy was first discovered in liver tissues. Additionally, abundant evidence indicated that the occurrence of hepatic lipophagy has been implicated in many liver diseases including fatty liver diseases, nonalcoholic fatty liver diseases, liver fibrosis, and liver cirrhosis. However, recent studies suggested that hepatic lipophagy occurs not only in liver tissue but also in other nonliver tissues and cells. Furthermore, the occurrence of lipophagy plays a crucial role in nonliver tissues and some related diseases. For instance, lipophagy relieves insulin resistance in adipose tissue from obesity patient with type 2 diabetes. Additionally, lipophagy has the ability to remit neurodegenerative diseases by reducing activity-dependent neurodegeneration in nervous tissue. Lipophagy decreases muscle lipid accumulation and accordingly improves lipid storage myopathy in muscle tissue. Moreover, lipophagy alleviates the malignancy and metastasis of cancer in clear renal cell carcinoma tissue. Lipophagy is also involved in other processes, such as spermatogenesis, osteoblastogenesis, and mucosal ulceration. In conclusion, targeting lipophagy may be a critical regulator and a new therapeutic strategy for nonliver tissues and some related diseases.
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Affiliation(s)
- Kebing Zhou
- Department of Emergency Medicine, Affiliated Nanhua Hospital, University of South China, Hengyang, China
| | - Pingbo Yao
- Department of Emergency Medicine, Affiliated Nanhua Hospital, University of South China, Hengyang, China
| | - Jun He
- Department of Emergency Medicine, Affiliated Nanhua Hospital, University of South China, Hengyang, China
| | - Hong Zhao
- Department of Basic nursing, Nursing College, University of South China, Hengyang, China
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11
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Chu KY, O'Reilly L, Mellet N, Meikle PJ, Bartley C, Biden TJ. Oleate disrupts cAMP signaling, contributing to potent stimulation of pancreatic β-cell autophagy. J Biol Chem 2018; 294:1218-1229. [PMID: 30518550 DOI: 10.1074/jbc.ra118.004833] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Revised: 11/19/2018] [Indexed: 12/12/2022] Open
Abstract
Autophagy is critical for maintaining cellular function via clearance of excess nutrients and damaged organelles. In pancreatic β-cells, it helps counter the endoplasmic reticulum (ER) stress that impairs insulin secretory capacity during Type 2 diabetes. Chronic exposure of β-cells to saturated fatty acids (FAs) such as palmitate stimulates ER stress and modulates autophagy, but the effects of unsaturated FAs such as oleate, which are also elevated during obesity, are less well understood. We therefore treated MIN6 cells and mouse islets for 8-48 h with either palmitate or oleate, and then monitored autophagic flux, signaling pathways, lysosomal biology, and phospholipid profiles. Compared with palmitate, oleate more effectively stimulated both autophagic flux and clearance of autophagosomes. The flux stimulation occurred independently of ER stress, nutrient-sensing (mTOR) and signaling pathways (protein kinases A, C, and D). Instead the mechanism involved the exchange factor directly activated by cAMP 2 (EPAC2). Oleate reduced cellular cAMP, and its effects on autophagic flux were reproduced or inhibited, respectively, by Epac2 knockdown or activation. Oleate also increased lysosomal acidity and increased phospholipid saturation, consistent with improved autophagosomal fusion with lysosomes. We conclude that a potent stimulation of autophagy might help explain the known benefits of unsaturated FAs in countering the toxicity of saturated FAs in β-cells during obesity and lipid loading.
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Affiliation(s)
- Kwan Yi Chu
- Division of Diabetes and Metabolism, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010; St. Vincent's Clinical School, Faculty of Medicine, UNSW Sydney, NSW 2052
| | - Liam O'Reilly
- Division of Diabetes and Metabolism, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010
| | - Natalie Mellet
- Baker IDI Heart and Diabetes Institute, Prahran, Victoria 3004, Australia
| | - Peter J Meikle
- Baker IDI Heart and Diabetes Institute, Prahran, Victoria 3004, Australia
| | - Clarissa Bartley
- Division of Diabetes and Metabolism, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010
| | - Trevor J Biden
- Division of Diabetes and Metabolism, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010; St. Vincent's Clinical School, Faculty of Medicine, UNSW Sydney, NSW 2052.
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12
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Zheng J, Wang Y, Han S, Luo Y, Sun X, Zhu N, Zhao L, Li J. Identification of Protein Kinase C Isoforms Involved in Type 1 Diabetic Encephalopathy in Mice. J Diabetes Res 2018; 2018:8431249. [PMID: 29744369 PMCID: PMC5878894 DOI: 10.1155/2018/8431249] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Accepted: 01/23/2018] [Indexed: 12/12/2022] Open
Abstract
Diabetic encephalopathy is a complication of diabetes mellitus characterized by impaired cognitive functions. Protein kinase C (PKC) isoforms are rarely reported on diabetic encephalopathy, although they have been believed to play crucial roles in other diabetic complications. In this study, streptozotocin- (STZ-) induced diabetic mice were found to exhibit learning and memory deficits in the Morris water maze test. Meanwhile, the expression of cPKCβII, nPKCε, and cPKCγ did not change in the hippocampus, cortex, and striatum at 2 and 8 weeks after STZ injection. The nPKCε translocation to the membrane, where it is activated, was not altered in the above brain regions at 2 and 8 weeks after STZ injection. Nevertheless, cPKCβII translocation to the membrane was significantly decreased in the cortex and hippocampus at 8 weeks after STZ injection. The translocation of cPKCγ from the cytosol to the membrane was remarkably decreased in the hippocampus at 2 and 8 weeks and in the cortex and striatum at 8 weeks after STZ injection. In addition, deletion of cPKCγ aggravated the impairment of spatial learning and memory. In conclusion, our results suggest that the decrease in the activity of cPKCβII and cPKCγ, especially cPKCγ, may play key roles in the pathogenesis of diabetic encephalopathy.
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Affiliation(s)
- Jiayin Zheng
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Yue Wang
- Department of Neurology, Beijing Chaoyang Hospital, Capital Medical University, Beijing, China
| | - Song Han
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Yanlin Luo
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Xiuli Sun
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Ning Zhu
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Li Zhao
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Junfa Li
- Department of Neurobiology and Center of Stroke, Beijing Institute for Brain Disorders, Capital Medical University, Beijing 100069, China
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13
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Vaithilingam V, Evans MDM, Lewy DM, Bean PA, Bal S, Tuch BE. Co-encapsulation and co-transplantation of mesenchymal stem cells reduces pericapsular fibrosis and improves encapsulated islet survival and function when allografted. Sci Rep 2017; 7:10059. [PMID: 28855611 PMCID: PMC5577272 DOI: 10.1038/s41598-017-10359-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 08/09/2017] [Indexed: 12/22/2022] Open
Abstract
Pericapsular fibrotic overgrowth (PFO) is associated with poor survival of encapsulated islets. A strategy to combat PFO is the use of mesenchymal stem cells (MSC). MSC have anti-inflammatory properties and their potential can be enhanced by stimulation with proinflammatory cytokines. This study investigated whether co-encapsulation or co-transplantation of MSC with encapsulated islets would reduce PFO and improve graft survival. Stimulating MSC with a cytokine cocktail of IFN-γ and TNF-α enhanced their immunosuppressive potential by increasing nitric oxide production and secreting higher levels of immunomodulatory cytokines. In vitro, co-encapsulation with MSC did not affect islet viability but significantly enhanced glucose-induced insulin secretion. In vivo, normoglycemia was achieved in 100% mice receiving islets co-encapsulated with stimulated MSC as opposed to 71.4% receiving unstimulated MSC and only 9.1% receiving encapsulated islets alone. Microcapsules retrieved from both unstimulated and stimulated MSC groups had significantly less PFO with improved islet viability and function compared to encapsulated islets alone. Levels of peritoneal immunomodulatory cytokines IL-4, IL-6, IL-10 and G-CSF were significantly higher in MSC co-encapsulated groups. Similar results were obtained when encapsulated islets and MSC were co-transplanted. In summary, co-encapsulation or co-transplantation of MSC with encapsulated islets reduced PFO and improved the functional outcome of allotransplants.
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Affiliation(s)
- Vijayaganapathy Vaithilingam
- Biomedical Manufacturing Research Program, Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing Flagship, North Ryde, New South Wales, Australia.
| | - Margaret D M Evans
- Biomedical Manufacturing Research Program, Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing Flagship, North Ryde, New South Wales, Australia
| | - Denise M Lewy
- Biomedical Manufacturing Research Program, Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing Flagship, North Ryde, New South Wales, Australia
| | - Penelope A Bean
- Biomedical Manufacturing Research Program, Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing Flagship, North Ryde, New South Wales, Australia
| | - Sumeet Bal
- Biomedical Manufacturing Research Program, Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing Flagship, North Ryde, New South Wales, Australia
| | - Bernard E Tuch
- Biomedical Manufacturing Research Program, Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing Flagship, North Ryde, New South Wales, Australia
- Australian Foundation for Diabetes Research, Sydney, New South Wales, Australia, previously at CSIRO Manufacturing Flagship, North Ryde, New South Wales, Australia
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14
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Xie Y, Cui C, Nie A, Wang Y, Ni Q, Liu Y, Yin Q, Zhang H, Li Y, Wang Q, Gu Y, Ning G. The mTORC2/PKC pathway sustains compensatory insulin secretion of pancreatic β cells in response to metabolic stress. Biochim Biophys Acta Gen Subj 2017; 1861:2039-2047. [DOI: 10.1016/j.bbagen.2017.04.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2016] [Revised: 03/31/2017] [Accepted: 04/18/2017] [Indexed: 12/24/2022]
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15
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Pepin É, Al-Mass A, Attané C, Zhang K, Lamontagne J, Lussier R, Madiraju SRM, Joly E, Ruderman NB, Sladek R, Prentki M, Peyot ML. Pancreatic β-Cell Dysfunction in Diet-Induced Obese Mice: Roles of AMP-Kinase, Protein Kinase Cε, Mitochondrial and Cholesterol Metabolism, and Alterations in Gene Expression. PLoS One 2016; 11:e0153017. [PMID: 27043434 PMCID: PMC4820227 DOI: 10.1371/journal.pone.0153017] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 03/22/2016] [Indexed: 12/27/2022] Open
Abstract
Diet induced obese (DIO) mice can be stratified according to their weight gain in response to high fat diet as low responders (LDR) and high responders (HDR). This allows the study of β-cell failure and the transitions to prediabetes (LDR) and early diabetes (HDR). C57BL/6N mice were fed for 8 weeks with a normal chow diet (ND) or a high fat diet and stratified as LDR and HDR. Freshly isolated islets from ND, LDR and HDR mice were studied ex-vivo for mitochondrial metabolism, AMPK activity and signalling, the expression and activity of key enzymes of energy metabolism, cholesterol synthesis, and mRNA profiling. Severely compromised glucose-induced insulin secretion in HDR islets, as compared to ND and LDR islets, was associated with suppressed AMP-kinase activity. HDR islets also showed reduced acetyl-CoA carboxylase activity and enhanced activity of 3-hydroxy-3-methylglutaryl-CoA reductase, which led respectively to elevated fatty acid oxidation and increased cholesterol biosynthesis. HDR islets also displayed mitochondrial membrane hyperpolarization and reduced ATP turnover in the presence of elevated glucose. Expression of protein kinase Cε, which reduces both lipolysis and production of signals for insulin secretion, was elevated in DIO islets. Genes whose expression increased or decreased by more than 1.2-fold were minor between LDR and ND islets (17 differentially expressed), but were prominent between HDR and ND islets (1508 differentially expressed). In HDR islets, particularly affected genes were related to cell cycle and proliferation, AMPK signaling, mitochondrial metabolism and cholesterol metabolism. In conclusion, chronically reduced AMPK activity, mitochondrial dysfunction, elevated cholesterol biosynthesis in islets, and substantial alterations in gene expression accompany β-cell failure in HDR islets. The β-cell compensation process in the prediabetic state (LDR) is largely independent of transcriptional adaptive changes, whereas the transition to early diabetes (HDR) is associated with major alterations in gene expression.
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Affiliation(s)
- Émilie Pepin
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
| | - Anfal Al-Mass
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
- Departments of Medicine and Human Genetics, McGill University, Montreal, Québec, Canada
| | - Camille Attané
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
| | - Kezhuo Zhang
- Departments of Medicine and Human Genetics, McGill University, Montreal, Québec, Canada
| | - Julien Lamontagne
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
| | - Roxane Lussier
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
| | - S. R. Murthy Madiraju
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
| | - Erik Joly
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
| | - Neil B. Ruderman
- Departments of Medicine and Physiology and Biophysics, Boston University School of Medicine and Diabetes Unit, Boston Medical Center, Boston, MA, United States of America
| | - Robert Sladek
- Departments of Medicine and Human Genetics, McGill University, Montreal, Québec, Canada
| | - Marc Prentki
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
- Departments of Nutrition, Biochemistry and Molecular Medicine, Faculty of Medicine, University of Montréal, Montreal, Québec, Canada
- * E-mail: (MP); (MLP)
| | - Marie-Line Peyot
- Montreal Diabetes Research Center and Centre de Recherche du CHUM, Montréal, Québec, Canada
- * E-mail: (MP); (MLP)
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16
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Cai Y, Lydic TA, Turkette T, Reid GE, Olson LK. Impact of alogliptin and pioglitazone on lipid metabolism in islets of prediabetic and diabetic Zucker Diabetic Fatty rats. Biochem Pharmacol 2015; 95:46-57. [PMID: 25801003 DOI: 10.1016/j.bcp.2015.03.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 03/13/2015] [Indexed: 12/30/2022]
Abstract
Prolonged exposure of pancreatic beta (β) cells to elevated glucose and free fatty acids (FFA) as occurs in type 2 diabetes results in loss of β cell function and survival. In Zucker Diabetic Fatty (ZDF) rats, β cell failure is associated with increased triacylglyceride (TAG) synthesis and disruption of the glycerolipid/FFA (GL/FFA) cycle, a critical arm of glucose-stimulated insulin secretion (GSIS). The aim of this study was to determine the impact of activation of PPARγ and increased incretin action via dipeptidyl-peptidase inhibition using pioglitazone and/or alogliptin, respectively, on islet lipid metabolism in prediabetic and diabetic ZDF rats. Transition of control prediabetic ZDF rats to diabetes was associated with reduced plasma insulin levels, reduced islet insulin content and GSIS, reduced stearoyl-CoA desaturase 2 (SCD 2) expression, and increased islet TAG, diacylglyceride (DAG) and ceramides species containing saturated FA. Treatment of prediabetic ZDF rats with a combination of pioglitazone and alogliptin, but not individually, prevented the transition to diabetes and was associated with marked lowering of islet TAG and DAG levels. Pioglitazone and alogliptin, however, did not restore SCD2 expression, the degree of FA saturation in TAG, DAG or ceramides, islet insulin content, or lower ceramide levels. These findings are consistent with activation of PPARγ and increased incretin action working in concert to restore GL/FFA cycle in β cells of ZDF rats. Restoration of the GL/FFA cycle without correcting islet FA desaturation, production of islet ceramides, and/or insulin sensitivity, however, may place these islets at risk for β cell failure.
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Affiliation(s)
- Ying Cai
- Department of Physiology, Michigan State University, East Lansing, MI 48824, USA.
| | - Todd A Lydic
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
| | - Thomas Turkette
- Department of Physiology, Michigan State University, East Lansing, MI 48824, USA.
| | - Gavin E Reid
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA; Department of Chemistry, Michigan State University, East Lansing, MI 48824 USA.
| | - L Karl Olson
- Department of Physiology, Michigan State University, East Lansing, MI 48824, USA.
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17
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Kaneko YK, Ishikawa T. Diacylglycerol Signaling Pathway in Pancreatic β-Cells: An Essential Role of Diacylglycerol Kinase in the Regulation of Insulin Secretion. Biol Pharm Bull 2015; 38:669-73. [DOI: 10.1248/bpb.b15-00060] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Yukiko K. Kaneko
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka
| | - Tomohisa Ishikawa
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka
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18
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Li J, Cantley J, Burchfield JG, Meoli CC, Stöckli J, Whitworth PT, Pant H, Chaudhuri R, Groffen AJA, Verhage M, James DE. DOC2 isoforms play dual roles in insulin secretion and insulin-stimulated glucose uptake. Diabetologia 2014; 57:2173-82. [PMID: 25005332 DOI: 10.1007/s00125-014-3312-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 05/28/2014] [Indexed: 01/08/2023]
Abstract
AIMS/HYPOTHESIS Glucose-stimulated insulin secretion (GSIS) and insulin-stimulated glucose uptake are processes that rely on regulated intracellular vesicle transport and vesicle fusion with the plasma membrane. DOC2A and DOC2B are calcium-sensitive proteins that were identified as key components of vesicle exocytosis in neurons. Our aim was to investigate the role of DOC2 isoforms in glucose homeostasis, insulin secretion and insulin action. METHODS DOC2 expression was measured by RT-PCR and western blotting. Body weight, glucose tolerance, insulin action and GSIS were assessed in wild-type (WT), Doc2a (-/-) (Doc2aKO), Doc2b (-/-) (Doc2bKO) and Doc2a (-/-)/Doc2b (-/-) (Doc2a/Doc2bKO) mice in vivo. In vitro GSIS and glucose uptake were assessed in isolated tissues, and exocytotic proteins measured by western blotting. GLUT4 translocation was assessed by epifluorescence microscopy. RESULTS Doc2b mRNA was detected in all tissues tested, whereas Doc2a was only detected in islets and the brain. Doc2aKO and Doc2bKO mice had minor glucose intolerance, while Doc2a/Doc2bKO mice showed pronounced glucose intolerance. GSIS was markedly impaired in Doc2a/Doc2bKO mice in vivo, and in isolated Doc2a/Doc2bKO islets in vitro. In contrast, Doc2bKO mice had only subtle defects in insulin secretion in vivo. Insulin action was impaired to a similar degree in both Doc2bKO and Doc2a/Doc2bKO mice. In vitro insulin-stimulated glucose transport and GLUT4 vesicle fusion were defective in adipocytes derived from Doc2bKO mice. Surprisingly, insulin action was not altered in muscle isolated from DOC2-null mice. CONCLUSIONS/INTERPRETATION Our study identifies a critical role for DOC2B in insulin-stimulated glucose uptake in adipocytes, and for the synergistic regulation of GSIS by DOC2A and DOC2B in beta cells.
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Affiliation(s)
- Jia Li
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
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19
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Pearson GL, Mellett N, Chu KY, Cantley J, Davenport A, Bourbon P, Cosner CC, Helquist P, Meikle PJ, Biden TJ. Lysosomal acid lipase and lipophagy are constitutive negative regulators of glucose-stimulated insulin secretion from pancreatic beta cells. Diabetologia 2014; 57:129-39. [PMID: 24149836 DOI: 10.1007/s00125-013-3083-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 09/26/2013] [Indexed: 12/20/2022]
Abstract
AIMS/HYPOTHESIS Lipolytic breakdown of endogenous lipid pools in pancreatic beta cells contributes to glucose-stimulated insulin secretion (GSIS) and is thought to be mediated by acute activation of neutral lipases in the amplification pathway. Recently it has been shown in other cell types that endogenous lipid can be metabolised by autophagy, and this lipophagy is catalysed by lysosomal acid lipase (LAL). This study aimed to elucidate a role for LAL and lipophagy in pancreatic beta cells. METHODS We employed pharmacological and/or genetic inhibition of autophagy and LAL in MIN6 cells and primary islets. Insulin secretion following inhibition was measured using RIA. Lipid accumulation was assessed by MS and confocal microscopy (to visualise lipid droplets) and autophagic flux was analysed by western blot. RESULTS Insulin secretion was increased following chronic (≥ 8 h) inhibition of LAL. This was more pronounced with glucose than with non-nutrient stimuli and was accompanied by augmentation of neutral lipid species. Similarly, following inhibition of autophagy in MIN6 cells, the number of lipid droplets was increased and GSIS was potentiated. Inhibition of LAL or autophagy in primary islets also increased insulin secretion. This augmentation of GSIS following LAL or autophagy inhibition was dependent on the acute activation of neutral lipases. CONCLUSIONS/INTERPRETATION Our data suggest that lysosomal lipid degradation, using LAL and potentially lipophagy, contributes to neutral lipid turnover in beta cells. It also serves as a constitutive negative regulator of GSIS by depletion of substrate for the non-lysosomal neutral lipases that are activated acutely by glucose.
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Affiliation(s)
- Gemma L Pearson
- Diabetes and Obesity Department, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia
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20
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Abstract
The pancreatic islet β cell senses circulating levels of calorigenic nutrients to secrete insulin according to the needs of the organism. Altered insulin secretion is linked to various disorders such as diabetes, hypoglycemic states, and cardiometabolic diseases. Fuel stimuli, including glucose, free fatty acids, and amino acids, promote insulin granule exocytosis primarily via their metabolism in β cells and the production of key signaling metabolites. This paper reviews our current knowledge of the pathways involved in both positive and negative metabolic signaling for insulin secretion and assesses the role of established and candidate metabolic coupling factors, keeping recent developments in focus.
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Affiliation(s)
- Marc Prentki
- Molecular Nutrition Unit, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, QC, Canada.
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Boslem E, Weir JM, MacIntosh G, Sue N, Cantley J, Meikle PJ, Biden TJ. Alteration of endoplasmic reticulum lipid rafts contributes to lipotoxicity in pancreatic β-cells. J Biol Chem 2013; 288:26569-82. [PMID: 23897822 DOI: 10.1074/jbc.m113.489310] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Chronic saturated fatty acid exposure causes β-cell apoptosis and, thus, contributes to type 2 diabetes. Although endoplasmic reticulum (ER) stress and reduced ER-to-Golgi protein trafficking have been implicated, the exact mechanisms whereby saturated fatty acids trigger β-cell death remain elusive. Using mass spectroscopic lipidomics and subcellular fractionation, we demonstrate that palmitate pretreatment of MIN6 β-cells promoted ER remodeling of both phospholipids and sphingolipids, but only the latter was causally linked to lipotoxic ER stress. Thus, overexpression of glucosylceramide synthase, previously shown to protect against defective protein trafficking and ER stress, partially reversed lipotoxic reductions in ER sphingomyelin (SM) content and aggregation of ER lipid rafts, as visualized using Erlin1-GFP. Using both lipidomics and a sterol response element reporter assay, we confirmed that free cholesterol in the ER was also reciprocally modulated by chronic palmitate and glucosylceramide synthase overexpression. This is consistent with the known coregulation and association of SM and free cholesterol in lipid rafts. Inhibition of SM hydrolysis partially protected against ATF4/C/EBP homology protein induction because of palmitate. Our results suggest that loss of SM in the ER is a key event for initiating β-cell lipotoxicity, which leads to disruption of ER lipid rafts, perturbation of protein trafficking, and initiation of ER stress.
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Affiliation(s)
- Ebru Boslem
- From the Diabetes and Obesity Program, Garvan Institute of Medical Research, 384 Victoria St., Darlinghurst, New South Wales 2010, Australia and
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Schmitz-Peiffer C. The tail wagging the dog--regulation of lipid metabolism by protein kinase C. FEBS J 2013; 280:5371-83. [PMID: 23587021 DOI: 10.1111/febs.12285] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2013] [Revised: 03/19/2013] [Accepted: 04/11/2013] [Indexed: 12/12/2022]
Abstract
Upon their discovery almost 40 years ago, isoforms of the lipid-activated protein kinase C (PKC) family were initially regarded only as downstream effectors of the second messengers calcium and diacylglycerol, undergoing activation upon phospholipid hydrolysis in response to acute stimuli. Subsequently, several isoforms were found to be associated with the inhibitory effects of lipid over-supply on glucose homeostasis, especially the negative cross-talk with insulin signal transduction, observed upon accumulation of diacylglycerol in insulin target tissues. The PKC family has therefore attracted much attention in diabetes and obesity research, because intracellular lipid accumulation is strongly correlated with defective insulin action and the development of type 2 diabetes. Causal roles for various isoforms in the generation of insulin resistance have more recently been confirmed using PKC-deficient mice. However, during characterization of these animals, it became increasingly evident that the enzymes play key roles in the modulation of lipid metabolism itself, and may control the supply of lipids between tissues such as adipose and liver. Molecular studies have also demonstrated roles for PKC isoforms in several aspects of lipid metabolism, such as adipocyte differentiation and hepatic lipogenesis. While the precise mechanisms involved, especially the identities of protein substrates, are still unclear, the emerging picture suggests that the currently held view of the contribution of PKC isoforms to metabolism is an over-simplification. Although PKCs may inhibit insulin signal transduction, these enzymes are not merely downstream effectors of lipid accumulation, but in fact control the fate of fatty acids, thus the tail wags the dog.
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Affiliation(s)
- Carsten Schmitz-Peiffer
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, NSW, Australia; St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia
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Chandarana K, Gelegen C, Irvine EE, Choudhury AI, Amouyal C, Andreelli F, Withers DJ, Batterham RL. Peripheral activation of the Y2-receptor promotes secretion of GLP-1 and improves glucose tolerance. Mol Metab 2013; 2:142-52. [PMID: 24049729 DOI: 10.1016/j.molmet.2013.03.001] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 03/04/2013] [Accepted: 03/05/2013] [Indexed: 12/15/2022] Open
Abstract
The effect of peptide tyrosine-tyrosine (PYY) on feeding is well established but currently its role in glucose homeostasis is poorly defined. Here we show in mice, that intraperitoneal (ip) injection of PYY3-36 or Y2R agonist improves nutrient-stimulated glucose tolerance and enhances insulin secretion; an effect blocked by peripheral, but not central, Y2R antagonist administration. Studies on isolated mouse islets revealed no direct effect of PYY3-36 on insulin secretion. Bariatric surgery in mice, enterogastric anastomosis (EGA), improved glucose tolerance in wild-type mice and increased circulating PYY and active GLP-1. In contrast, in Pyy-null mice, post-operative glucose tolerance and active GLP-1 levels were similar in EGA and sham-operated groups. PYY3-36 ip increased hepato-portal active GLP-1 plasma levels, an effect blocked by ip Y2R antagonist. Collectively, these data suggest that PYY3-36 therefore acting via peripheral Y2R increases hepato-portal active GLP-1 plasma levels and improves nutrient-stimulated glucose tolerance.
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Key Words
- AUC, area under the curve
- CNS, central nervous system
- DPP-4, di-peptidyl peptidase-4
- EGA, entero-gastric anastomosis
- GLP-1
- Glucose homeostasis
- HFD, high-fat diet
- ICV, intracerebroventricular
- IPGTT, intraperitoneal glucose tolerance test
- PYY
- PYY, peptide tyrosine–tyrosine
- T2DM, type 2 diabetes mellitus
- WT, wild-type
- Y2-receptor
- Y2R, Y2-receptor
- aCSF, artificial cerebrospinal fluid
- active GLP-1, glucagon-like peptide-1(7-36)amide
- ip, intraperitoneal
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Affiliation(s)
- Keval Chandarana
- Centre for Obesity Research, Department of Medicine, University College London, Rayne Institute, 5 University Street, WC1E 6JJ, London, UK
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Mourad NI, Nenquin M, Henquin JC. Amplification of insulin secretion by acetylcholine or phorbol ester is independent of β-cell microfilaments and distinct from metabolic amplification. Mol Cell Endocrinol 2013; 367:11-20. [PMID: 23246352 DOI: 10.1016/j.mce.2012.12.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Revised: 11/23/2012] [Accepted: 12/04/2012] [Indexed: 11/30/2022]
Abstract
Insulin secretion (IS) triggered by β-cell [Ca(2+)](c) is amplified by metabolic and receptor-generated signals. Diacylglycerol largely mediates acetylcholine (ACh) effects through protein-kinase C and other effectors, which can be directly activated by phorbol-ester (PMA). Using mouse islets, we investigated the possible role of microfilaments in ACh/PMA-mediated amplification of IS. PMA had no steady-state impact on actin microfilaments. Although ACh slightly augmented and PMA diminished glucose- and tolbutamide-induced increases in β-cell [Ca(2+)](c), both amplified IS in control islets and after microfilament disruption (latrunculin) or stabilization (jasplakinolide). Both phases of IS were larger in response to glucose than tolbutamide, although [Ca(2+)](c) was lower. This difference in secretion, which reflects metabolic amplification, persisted in presence of ACh/PMA and was independent of microfilaments. Amplification of IS by ACh/PMA is thus distinct from metabolic amplification, but both pathways promote acquisition of release competence by insulin granules, which can access exocytotic sites without intervention of microfilaments.
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Affiliation(s)
- Nizar I Mourad
- Unit of Endocrinology and Metabolism, University of Louvain, Faculty of Medicine, B-1200 Brussels, Belgium
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25
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The role of fatty acid metabolism and lipotoxicity in pancreatic β-cell injury: Identification of potential therapeutic targets. Acta Pharm Sin B 2012. [DOI: 10.1016/j.apsb.2012.05.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Oleanolic acid reduces hyperglycemia beyond treatment period with Akt/FoxO1-induced suppression of hepatic gluconeogenesis in type-2 diabetic mice. PLoS One 2012; 7:e42115. [PMID: 22860063 PMCID: PMC3408432 DOI: 10.1371/journal.pone.0042115] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Accepted: 07/02/2012] [Indexed: 12/31/2022] Open
Abstract
The present study investigated the chronic efficacy of oleanolic acid (OA), a triterpenoid selected from our recent screening, on hyperglycemia in type-2 diabetic mice. C57BL/6J mice were fed a high-fat diet followed by low doses of streptozotocin to generate a type-2 diabetic model. OA (100 mg/kg/day) was administered orally for 2 weeks with its effects monitored for 6 weeks. High-fat feeding and streptozotocin generated a steady hyperglycemia (21.2±1.1 mM) but OA administration reversed the hyperglycemia by ∼60%. Interestingly, after the cessation of OA administration, the reversed hyperglycemia was sustained for the entire post-treatment period of the study (4 weeks) despite the reoccurrence of dyslipidemia. Examination of insulin secretion and pancreas morphology did not indicate improved β-cell function as a likely mechanism. Urine glucose loss was decreased with substantial improvement of diabetic nephropathy after the OA treatment. Pair-feeding the OA-treated mice to an untreated group ruled out food intake as a main factor attributable for this sustained reduction in hyperglycemia. Studies with the use of glucose tracers revealed no increase in glucose influx into muscle, adipose tissue or liver in the OA-treated mice. Finally, we analyzed key regulators of gluconeogenesis in the liver and found significant increases in the phosphorylation of both Akt and FoxO1 after treatment with OA. Importantly, these increases were significantly correlated with a down-regulation of glucose-6-phosphatase expression. Our findings suggest triterpenoids are a potential source of new efficacious drugs for sustained control of hyperglycemia. The liver appears to be a major site of action, possibly by the suppression of hepatic glucose production via the Akt/FoxO1 axis.
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Prentki M, Madiraju SRM. Glycerolipid/free fatty acid cycle and islet β-cell function in health, obesity and diabetes. Mol Cell Endocrinol 2012; 353:88-100. [PMID: 22108437 DOI: 10.1016/j.mce.2011.11.004] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Revised: 11/07/2011] [Accepted: 11/07/2011] [Indexed: 12/16/2022]
Abstract
Pancreatic β-cells secrete insulin in response to fluctuations in blood fuel concentrations, in particular glucose and fatty acids. However, chronic fuel surfeit can overwhelm the metabolic, signaling and secretory capacity of the β-cell leading to its dysfunction and death - often referred to as glucolipotoxicity. In β-cells and many other cells, glucose and lipid metabolic pathways converge into a glycerolipid/free fatty acid (GL/FFA) cycle, which is driven by the substrates, glycerol-3-phosphate and fatty acyl-CoA, derived from glucose and fatty acids, respectively. Although the overall operation of GL/FFA cycle, consisting of lipolysis and lipogenesis, is "futile" in terms of energy expenditure, this metabolic cycle likely plays an indispensable role for various β-cell functions, in particular insulin secretion and excess fuel detoxification. In this review, we discuss the significance of GL/FFA cycle in the β-cell, its regulation and role in generating essential metabolic signals that participate in the lipid amplification arm of glucose stimulated insulin secretion and in β-cell growth. We propose the novel concept that the lipolytic segment of GL/FFA cycle is instrumental in producing signals for insulin secretion, whereas, the lipogenic segment generates signals relevant for β-cell survival/death and growth/proliferation.
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Affiliation(s)
- Marc Prentki
- Departments of Nutrition and Biochemistry, University of Montreal, Montreal Diabetes Research Center, CR-CHUM, Technopôle Angus, 2901, Montreal, Canada QC H1W 4A4.
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Watson ML, Macrae K, Marley AE, Hundal HS. Chronic effects of palmitate overload on nutrient-induced insulin secretion and autocrine signalling in pancreatic MIN6 beta cells. PLoS One 2011; 6:e25975. [PMID: 21998735 PMCID: PMC3187833 DOI: 10.1371/journal.pone.0025975] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 09/14/2011] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Sustained exposure of pancreatic β cells to an increase in saturated fatty acids induces pleiotropic effects on β-cell function, including a reduction in stimulus-induced insulin secretion. The objective of this study was to investigate the effects of chronic over supply of palmitate upon glucose- and amino acid-stimulated insulin secretion (GSIS and AASIS, respectively) and autocrine-dependent insulin signalling with particular focus on the importance of ceramide, ERK and CaMKII signalling. PRINCIPAL FINDINGS GSIS and AASIS were both stimulated by >7-fold resulting in autocrine-dependent activation of protein kinase B (PKB, also known as Akt). Insulin release was dependent upon nutrient-induced activation of calcium/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) as their pharmacological inhibition suppressed GSIS/AASIS significantly. Chronic (48 h, 0.4 mM) palmitate treatment blunted glucose/AA-induced activation of CaMKII and ERK and caused a concomitant reduction (~75%) in GSIS/AASIS and autocrine-dependent activation of PKB. This inhibition could not be attributed to enhanced mitochondrial fatty acid uptake/oxidation or ceramide synthesis, which were unaffected by palmitate. In contrast, diacylglycerol synthesis was elevated suggesting increased palmitate esterification rather than oxidation may contribute to impaired stimulus-secretion coupling. Consistent with this, 2-bromopalmitate, a non-oxidisable palmitate analogue, inhibited GSIS as effectively as palmitate. CONCLUSIONS Our results exclude changes in ceramide content or mitochondrial fatty acid handling as factors initiating palmitate-induced defects in insulin release from MIN6 β cells, but suggest that reduced CaMKII and ERK activation associated with palmitate overload may contribute to impaired stimulus-induced insulin secretion.
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Affiliation(s)
- Maria L. Watson
- Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Katherine Macrae
- Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Anna E. Marley
- AstraZeneca, CVGI, Alderley Park, Macclesfield, Cheshire, United Kingdom
| | - Harinder S. Hundal
- Division of Cell Signalling and Immunology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, United Kingdom
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Taguchi K, Kobayashi T, Matsumoto T, Kamata K. Dysfunction of endothelium-dependent relaxation to insulin via PKC-mediated GRK2/Akt activation in aortas of ob/ob mice. Am J Physiol Heart Circ Physiol 2011; 301:H571-83. [DOI: 10.1152/ajpheart.01189.2010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In diabetic states, hyperinsulinemia may negatively regulate Akt/endothelial nitric oxide synthase (eNOS) activation. Our main aim was to investigate whether and how insulin might negatively regulate Akt/eNOS activities via G protein-coupled receptor kinase 2 (GRK2) in aortas from ob/ob mice. Endothelium-dependent relaxation was measured in aortic rings from ob/ob mice (a type 2 diabetes model). GRK2, β-arrestin2, and Akt/eNOS signaling-pathway protein levels and activities were mainly assayed by Western blotting. Plasma insulin was significantly elevated in ob/ob mice. Insulin-induced relaxation was significantly decreased in the ob/ob aortas [vs. age-matched control (lean) ones]. The response in ob/ob aortas was enhanced by PKC inhibitor or GRK2 inhibitor. Akt (at Thr308) phosphorylation and eNOS (at Ser1177) phosphorylation, and also the β-arrestin2 protein level, were markedly decreased in the membrane fraction of insulin-stimulated ob/ob aortas (vs. insulin-stimulated lean ones). These membrane-fraction expressions were enhanced by GRK2 inhibitor and by PKC inhibitor in the ob/ob group but not in the lean group. PKC activity was much greater in ob/ob than in lean aortas. GRK2 protein and activity levels were increased in ob/ob and were greatly reduced by GRK2 inhibitor or PKC inhibitor pretreatment. These results suggest that in the aorta in diabetic mice with hyperinsulinemia an upregulation of GRK2 and a decrease in β-arrestin2 inhibit insulin-induced stimulation of the Akt/eNOS pathway and that GRK2 overactivation may result from an increase in PKC activity.
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Affiliation(s)
- Kumiko Taguchi
- Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Shinagawa-ku, Tokyo, Japan
| | - Tsuneo Kobayashi
- Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Shinagawa-ku, Tokyo, Japan
| | - Takayuki Matsumoto
- Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Shinagawa-ku, Tokyo, Japan
| | - Katsuo Kamata
- Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Shinagawa-ku, Tokyo, Japan
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Raddatz K, Turner N, Frangioudakis G, Liao BM, Pedersen DJ, Cantley J, Wilks D, Preston E, Hegarty BD, Leitges M, Raftery MJ, Biden TJ, Schmitz-Peiffer C. Time-dependent effects of Prkce deletion on glucose homeostasis and hepatic lipid metabolism on dietary lipid oversupply in mice. Diabetologia 2011; 54:1447-56. [PMID: 21347625 DOI: 10.1007/s00125-011-2073-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/29/2010] [Accepted: 01/10/2011] [Indexed: 02/06/2023]
Abstract
AIMS/HYPOTHESIS We examined the time-dependent effects of deletion of the gene encoding protein kinase C epsilon (Prkce) on glucose homeostasis, insulin secretion and hepatic lipid metabolism in fat-fed mice. METHODS Prkce(-/-) and wild-type (WT) mice were fed a high-fat diet for 1 to 16 weeks and subjected to i.p. glucose tolerance tests (ipGTT) and indirect calorimetry. We also investigated gene expression and protein levels by RT-PCR, quantitative protein profiling (isobaric tag for relative and absolute quantification; iTRAQ) and immunoblotting. Lipid levels, mitochondrial oxidative capacity and lipid metabolism were assessed in liver and primary hepatocytes. RESULTS While fat-fed WT mice became glucose intolerant after 1 week, Prkce(-/-) mice exhibited normal glucose and insulin levels. iTRAQ suggested differences in lipid metabolism and oxidative phosphorylation between fat-fed WT and Prkce(-/-) animals. Liver triacylglycerols were increased in fat-fed Prkce(-/-) mice, resulting from altered lipid partitioning which promoted esterification of fatty acids in hepatocytes. In WT mice, fat feeding elevated oxygen consumption in vivo and in isolated liver mitochondria, but these increases were not seen in Prkce(-/-) mice. Prkce(-/-) hepatocytes also exhibited reduced production of reactive oxygen species (ROS) in the presence of palmitate. After 16 weeks of fat feeding, however, the improved glucose tolerance in fat-fed Prkce(-/-) mice was instead associated with increased insulin secretion during ipGTT, as we have previously reported. CONCLUSIONS/INTERPRETATION Prkce deletion ameliorates diet-induced glucose intolerance via two temporally distinct phenotypes. Protection against insulin resistance is associated with changes in hepatic lipid partitioning, which may reduce the acute inhibitory effects of fatty acid catabolism, such as ROS generation. In the longer term, enhancement of glucose-stimulated insulin secretion prevails.
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Affiliation(s)
- K Raddatz
- Garvan Institute of Medical Research, 384 Victoria Street, Sydney, NSW 2010, Australia.
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A lipidomic screen of palmitate-treated MIN6 β-cells links sphingolipid metabolites with endoplasmic reticulum (ER) stress and impaired protein trafficking. Biochem J 2011; 435:267-76. [PMID: 21265737 DOI: 10.1042/bj20101867] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Saturated fatty acids promote lipotoxic ER (endoplasmic reticulum) stress in pancreatic β-cells in association with Type 2 diabetes. To address the underlying mechanisms we employed MS in a comprehensive lipidomic screen of MIN6 β-cells treated for 48 h with palmitate. Both the overall mass and the degree of saturation of major neutral lipids and phospholipids were only modestly increased by palmitate. The mass of GlcCer (glucosylceramide) was augmented by 70% under these conditions, without any significant alteration in the amounts of either ceramide or sphingomyelin. However, flux into ceramide (measured by [3H]serine incorporation) was augmented by chronic palmitate, and inhibition of ceramide synthesis decreased both ER stress and apoptosis. ER-to-Golgi protein trafficking was also reduced by palmitate pre-treatment, but was overcome by overexpression of GlcCer synthase. This was accompanied by increased conversion of ceramide into GlcCer, and reduced ER stress and apoptosis, but no change in phospholipid desaturation. Sphingolipid alterations due to palmitate were not secondary to ER stress since they were neither reproduced by pharmacological ER stressors nor overcome using the chemical chaperone phenylbutyric acid. In conclusion, alterations in sphingolipid, rather than phospholipid, metabolism are more likely to be implicated in the defective protein trafficking and enhanced ER stress and apoptosis of lipotoxic β-cells.
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Epac2-dependent rap1 activation and the control of islet insulin secretion by glucagon-like peptide-1. VITAMINS AND HORMONES 2011; 84:279-302. [PMID: 21094904 DOI: 10.1016/b978-0-12-381517-0.00010-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Glucagon-like peptide-1 (GLP-1) binds its Class II G protein-coupled receptor to stimulate cyclic adenosine monophosphate (cAMP) production and to potentiate the glucose metabolism-dependent secretion of insulin from pancreatic β cells located within the islets of Langerhans. Prior clinical studies demonstrate that this cAMP-mediated action of GLP-1 to potentiate glucose-stimulated insulin secretion (GSIS) is of major therapeutic importance when evaluating the abilities of GLP-1 receptor (GLP-1R) agonists to lower levels of blood glucose in type 2 diabetic subjects. Surprisingly, recent in vitro studies of human or rodent islets of Langerhans provide evidence for the existence of a noncanonical mechanism of β cell cAMP signal transduction, one that may explain how GLP-1R agonists potentiate GSIS. What these studies demonstrate is that a cAMP-regulated guanine nucleotide exchange factor designated as Epac2 couples β cell cAMP production to the protein kinase A-independent stimulation of insulin exocytosis. Provided here is an overview of the Epac2 signal transduction system in β cells, with special emphasis on Rap1, a Ras-related GTPase that is an established target of Epac2.
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Identification of a small molecule activator of novel PKCs for promoting glucose-dependent insulin secretion. Cell Res 2010; 21:588-99. [PMID: 20877311 DOI: 10.1038/cr.2010.137] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Using an image-based screen for small molecules that can affect Golgi morphology, we identify a small molecule, Sioc145, which can enlarge the Golgi compartments and promote protein secretion. More importantly, Sioc145 potentiates insulin secretion in a glucose-dependent manner. We show that Sioc145 selectively activates novel protein kinase Cs (nPKCs; δ and ɛ) but not conventional PKCs (cPKCs; α, βI and βII) in INS-1E insulinoma cells. In contrast, PMA, a non-selective activator of cPKCs and nPKCs, promotes insulin secretion independent of glucose concentrations. Furthermore, we demonstrate that Sioc145 and PMA show differential abilities in depolarizing the cell membrane, and suggest that Sioc145 promotes insulin secretion in the amplifying pathway downstream of K(ATP) channels. In pancreatic islets, the treatment with Sioc145 enhances the second phase of insulin secretion. Increased insulin granules close to the plasma membrane are observed after Sioc145 treatment. Finally, the administration of Sioc145 to diabetic GK rats increases their serum insulin levels and improves glucose tolerance. Collectively, our studies identify Sioc145 as a novel glucose-dependent insulinotropic compound via selectively activating nPKCs.
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Peyot ML, Pepin E, Lamontagne J, Latour MG, Zarrouki B, Lussier R, Pineda M, Jetton TL, Madiraju SRM, Joly E, Prentki M. Beta-cell failure in diet-induced obese mice stratified according to body weight gain: secretory dysfunction and altered islet lipid metabolism without steatosis or reduced beta-cell mass. Diabetes 2010; 59:2178-87. [PMID: 20547980 PMCID: PMC2927940 DOI: 10.2337/db09-1452] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
OBJECTIVE C57Bl/6 mice develop obesity and mild hyperglycemia when fed a high-fat diet (HFD). Although diet-induced obesity (DIO) is a widely studied model of type 2 diabetes, little is known about beta-cell failure in these mice. RESEARCH DESIGN AND METHODS DIO mice were separated in two groups according to body weight gain: low- and high-HFD responders (LDR and HDR). We examined whether mild hyperglycemia in HDR mice is due to reduced beta-cell mass or function and studied islet metabolism and signaling. RESULTS HDR mice were more obese, hyperinsulinemic, insulin resistant, and hyperglycemic and showed a more altered plasma lipid profile than LDR. LDR mice largely compensated insulin resistance, whereas HDR showed perturbed glucose homeostasis. Neither LDR nor HDR mice showed reduced beta-cell mass, altered islet glucose metabolism, and triglyceride deposition. Insulin secretion in response to glucose, KCl, and arginine was impaired in LDR and almost abolished in HDR islets. Palmitate partially restored glucose- and KCl-stimulated secretion. The glucose-induced rise in ATP was reduced in both DIO groups, and the glucose-induced rise in Ca(2+) was reduced in HDR islets relatively to LDR. Glucose-stimulated lipolysis was decreased in LDR and HDR islets, whereas fat oxidation was increased in HDR islets only. Fatty acid esterification processes were markedly diminished, and free cholesterol accumulated in HDR islets. CONCLUSIONS beta-Cell failure in HDR mice is not due to reduced beta-cell mass and glucose metabolism or steatosis but to a secretory dysfunction that is possibly due to altered ATP/Ca(2+) and lipid signaling, as well as free cholesterol deposition.
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Affiliation(s)
- Marie-Line Peyot
- Montreal Diabetes Research Center and CRCHUM, Montreal, QC, Canada.
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35
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López S, Bermúdez B, Abia R, Muriana FJG. The influence of major dietary fatty acids on insulin secretion and action. Curr Opin Lipidol 2010; 21:15-20. [PMID: 19915461 DOI: 10.1097/mol.0b013e3283346d39] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
PURPOSE OF REVIEW To briefly summarize recent advances towards understanding the influence of major dietary fatty acids on beta-cell function and evaluate their implications for insulin resistance. RECENT FINDINGS Studies in humans have shown that beta-cell function and insulin sensitivity improve progressively in the postprandial period as the proportion of monounsaturated fatty acids (MUFAs) with respect to saturated fatty acids (SFAs) in dietary fats increases. However, cell-culture experiments have revealed a dichotomy in the ability of fatty acids to moderate hyperactivity of, and induce lipotoxicity in, beta-cells. There are also some novel findings regarding the ability of HDL to protect beta-cells against oxidized LDL-induced apoptosis in vitro and of reconstituted HDL to attenuate insulin resistance in vivo. These findings raise new questions regarding the contribution of dietary fatty acids to insulin secretion and action. SUMMARY These new findings point to a critical role for major dietary fatty acids in the etiology and pathogenesis of diabetes, which appears to be of particular relevance during postprandial periods and mainly depends on the fatty acid type. This underscores the importance of dietary fatty acids in standard diabetes management.
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Affiliation(s)
- Sergio López
- Cellular and Molecular Nutrition, Instituto de la Grasa (CSIC), Seville, Spain
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36
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Affiliation(s)
- Carsten Schmitz-Peiffer
- Garvan Institute of Medical Research, Sydney, Australia
- St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Trevor J. Biden
- Garvan Institute of Medical Research, Sydney, Australia
- St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
- Corresponding author: Trevor J. Biden,
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Poitout V, Amyot J, Semache M, Zarrouki B, Hagman D, Fontés G. Glucolipotoxicity of the pancreatic beta cell. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1801:289-98. [PMID: 19715772 DOI: 10.1016/j.bbalip.2009.08.006] [Citation(s) in RCA: 269] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Revised: 08/13/2009] [Accepted: 08/13/2009] [Indexed: 02/07/2023]
Abstract
The concept of glucolipotoxicity refers to the combined, deleterious effects of elevated glucose and fatty acid levels on pancreatic beta-cell function and survival. Significant progress has been made in recent years towards a better understanding of the cellular and molecular basis of glucolipotoxicity in the beta cell. The permissive effect of elevated glucose on the detrimental actions of fatty acids stems from the influence of glucose on intracellular fatty acid metabolism, promoting the synthesis of cellular lipids. The combination of excessive levels of fatty acids and glucose therefore leads to decreased insulin secretion, impaired insulin gene expression, and beta-cell death by apoptosis, all of which probably have distinct underlying mechanisms. Recent studies from our laboratory have identified several pathways implicated in fatty acid inhibition of insulin gene expression, including the extracellular-regulated kinase (ERK1/2) pathway, the metabolic sensor Per-Arnt-Sim kinase (PASK), and the ATF6 branch of the unfolded protein response. We have also confirmed in vivo in rats that the decrease in insulin gene expression is an early defect which precedes any detectable abnormality in insulin secretion. While the role of glucolipotoxicity in humans is still debated, the inhibitory effects of chronically elevated fatty acid levels has been clearly demonstrated in several studies, at least in individuals genetically predisposed to developing type 2 diabetes. It is therefore likely that glucolipotoxicity contributes to beta-cell failure in type 2 diabetes as well as to the decline in beta-cell function observed after the onset of the disease.
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Affiliation(s)
- Vincent Poitout
- Montreal Diabetes Research Center, CRCHUM, Department of Medicine, University of Montreal, Montreal, QC, Canada.
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Lockerbie RO, Eddé B, Prochiantz A. Cyclic AMP-dependent protein phosphorylation in isolated neuronal growth cones from developing rat forebrain. J Neurochem 1989; 31:202-14. [PMID: 2537377 DOI: 10.1016/j.devcel.2014.08.028] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Revised: 07/07/2014] [Accepted: 08/28/2014] [Indexed: 12/19/2022]
Abstract
We have shown recently that neuronal growth cones isolated from developing rat forebrain possess an appreciable activity of adenylate cyclase, which produces cyclic AMP and can be stimulated by various neurotransmitter receptor agonists and by forskolin. To investigate cyclic AMP-mediated biochemical mechanisms in isolated growth cones, we have centered the present study on cyclic AMP-dependent protein phosphorylation. One-dimensional gel electrophoretic analysis showed that cyclic AMP analogs increased incorporation of 32P into several phosphoproteins in molecular mass ranges of 50-58 and 76-82 kilodaltons, including those of 82, 76, and 51 kilodaltons. Two-dimensional electrophoresis, using isoelectric focusing in the first dimension, resolved phosphorylated alpha- and beta-tubulin species, actin, a very acidic protein (isoelectric point 4.0) with a molecular mass of 93 kilodaltons, and two proteins (x and x') closely neighboring beta-tubulin. Two other phosphoproteins seen in the gels had molecular masses of 56 and 51 kilodaltons (respective isoelectric points, 4.5 and 4.4) and, along with the 93-kilodalton phosphoprotein, were highly enriched in the isolated growth cones. Only the tubulin and actin species were major proteins in the isolated growth cones. Cyclic AMP analogs enhanced incorporation of 32P into phosphoproteins x and x', and, as assessed by immunoprecipitation, into beta-tubulin. Peptide digest experiments suggested that phosphoproteins x and x' are unrelated to beta-tubulin. Nonequilibrium two-dimensional electrophoresis resolved many phosphoproteins, of which a 79- and 75-kilodalton doublet, a 74-kilodalton species, and a 58-kilodalton doublet showed enhanced incorporation of 32P in the presence of cyclic AMP.
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Affiliation(s)
- R O Lockerbie
- Chaire de Neuropharmacologie, INSERM U 114, Collège de France, Paris
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