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Wijesekara N, Ahrens R, Wu L, Langman T, Tandon A, Fraser PE. α-Synuclein Regulates Peripheral Insulin Secretion and Glucose Transport. Front Aging Neurosci 2021; 13:665348. [PMID: 34393754 PMCID: PMC8361797 DOI: 10.3389/fnagi.2021.665348] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Accepted: 07/05/2021] [Indexed: 11/23/2022] Open
Abstract
Aim Population based studies indicate a positive association between type 2 diabetes (T2D) and Parkinson’s disease (PD) where there is an increased risk of developing PD in patients with T2D. PD is characterized by the abnormal accumulation of intraneuronal aggregated α-synuclein (α-syn) in Lewy bodies, which negatively impact neuronal viability. α-syn is also expressed in both pancreatic islets and skeletal muscle, key players in glucose regulation. Therefore, we examined the functional role of α-syn in these tissues. Methods Using mice lacking, overexpressing or transiently injected with α-syn, effects on glucose and insulin tolerance and insulin secretion were determined, with further characterization of the effects on GLUT4 translocation using GLUT4myc myotubes. Results Mice genetically ablated for α-syn became glucose intolerant and insulin resistant with hyperinsulinemia and reduced glucose-stimulated insulin secretion (GSIS). Mice overexpressing human α-syn are more insulin senstive and glucose tolerant compared to controls with increased GSIS. Injection of purified α-syn monomers also led to improved glucose tolerance and insulin sensitivity with hightened GSIS. α-syn monomer treatments increased surface GLUT4 levels in myotubes but without any significant change in Akt phosphorylation. The increase in cell surface GLUT4 was largely due to a large reduction in GLUT4 endocytosis, however, with a compensatory reduction in GLUT4 exocytosis. Conclusion Cumulatively, this data suggests that α-syn modulates both pancreatic beta cell function and glucose transport in peripheral tissues, thereby playing a pivitol role in the maintenance of normal glucose homeostasis.
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Affiliation(s)
- Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Rosemary Ahrens
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Ling Wu
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Tammy Langman
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Anurag Tandon
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada.,Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Paul E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
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2
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Xu J, Wijesekara N, Regeenes R, Rijjal DA, Piro AL, Song Y, Wu A, Bhattacharjee A, Liu Y, Marzban L, Rocheleau JV, Fraser PE, Dai FF, Hu C, Wheeler MB. Pancreatic β cell-selective zinc transporter 8 insufficiency accelerates diabetes associated with islet amyloidosis. JCI Insight 2021; 6:143037. [PMID: 34027899 PMCID: PMC8262350 DOI: 10.1172/jci.insight.143037] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 04/21/2021] [Indexed: 01/25/2023] Open
Abstract
GWAS have shown that the common R325W variant of SLC30A8 (ZnT8) increases the risk of type 2 diabetes (T2D). However, ZnT8 haploinsufficiency is protective against T2D in humans, counterintuitive to earlier work in humans and mouse models. Therefore, whether decreasing ZnT8 activity is beneficial or detrimental to β cell function, especially under conditions of metabolic stress, remains unknown. In order to examine whether the existence of human islet amyloid polypeptide (hIAPP), a coresident of the insulin granule, affects the role of ZnT8 in regulating β cell function, hIAPP-expressing transgenics were generated with reduced ZnT8 (ZnT8B+/– hIAPP) or null ZnT8 (ZnT8B–/– hIAPP) expression specifically in β cells. We showed that ZnT8B–/– hIAPP mice on a high-fat diet had intensified amyloid deposition and further impaired glucose tolerance and insulin secretion compared with control, ZnT8B–/–, and hIAPP mice. This can in part be attributed to impaired glucose sensing and islet cell synchronicity. Importantly, ZnT8B+/– hIAPP mice were also glucose intolerant and had reduced insulin secretion and increased amyloid aggregation compared with controls. These data suggest that loss of or reduced ZnT8 activity in β cells heightened the toxicity induced by hIAPP, leading to impaired β cell function and glucose homeostasis associated with metabolic stress.
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Affiliation(s)
- Jie Xu
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Key Clinical Center for Metabolic Diseases, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China.,Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto Western Hospital, Toronto, Ontario Canada
| | - Romario Regeenes
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
| | - Dana Al Rijjal
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Anthony L Piro
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Youchen Song
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Anne Wu
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Alpana Bhattacharjee
- Division of Advanced Diagnostics, Toronto General Hospital Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
| | - Ying Liu
- Division of Advanced Diagnostics, Toronto General Hospital Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
| | - Lucy Marzban
- College of Pharmacy, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Jonathan V Rocheleau
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada.,Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.,Toronto General Research Institute, University Health Network, Toronto, Ontario, Canada
| | - Paul E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto Western Hospital, Toronto, Ontario Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Feihan F Dai
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Cheng Hu
- Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Key Clinical Center for Metabolic Diseases, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China.,Institute for Metabolic Disease, Fengxian Central Hospital Affiliated to Southern Medical University, Shanghai, China
| | - Michael B Wheeler
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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3
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Wijesekara N, Gonçalves RA, Ahrens R, Ha K, De Felice FG, Fraser PE. Combination of human tau and islet amyloid polypeptide exacerbates metabolic dysfunction in transgenic mice. J Pathol 2021; 254:244-253. [PMID: 33797777 DOI: 10.1002/path.5674] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 03/07/2021] [Accepted: 03/29/2021] [Indexed: 11/07/2022]
Abstract
Amyloid plaques and neurofibrillary tangles composed of hyperphosphorylated tau are important contributors to Alzheimer's disease (AD). Tau also impacts pancreatic beta cell function and glucose homeostasis. Amyloid deposits composed of islet amyloid polypeptide (IAPP) are a pathological feature of type 2 diabetes (T2D). The current study investigates the role of human tau (hTau) in combination with human IAPP (hIAPP) as a potential mechanism connecting AD and T2D. Transgenic mice expressing hTau and hIAPP in the absence of murine tau were generated to determine the impact of these pathological factors on glucose metabolism. Co-expression of hIAPP and hTau resulted in mice with increased hyperglycaemia, insulin resistance, and glucose intolerance. The hTau-hIAPP mice also exhibited reduced beta cell area, increased amyloid deposition, impaired insulin processing, and reduced insulin content in islets. Tau phosphorylation also increased after stimulation with high glucose. In addition, brain insulin content and signalling were reduced, and tau phosphorylation was increased in these animals. These data support a link between tau and IAPP amyloid, which seems to act co-ordinately to impair beta cell function and glucose homeostasis, and suggest that the combined pathological actions of these proteins may be a potential mechanism connecting AD and T2D. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
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Affiliation(s)
- Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - Rafaella Araujo Gonçalves
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
- Centre for Neuroscience Studies and Department of Psychiatry, Queen's University, Kingston, Canada
| | - Rosemary Ahrens
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - Kathy Ha
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - Fernanda G De Felice
- Centre for Neuroscience Studies and Department of Psychiatry, Queen's University, Kingston, Canada
- Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Paul E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
- Department of Medical Biophysics, University of Toronto, Toronto, Canada
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4
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Abstract
Microtubule-associated protein tau assists in stabilizing microtubules and has been particularly implicated in Alzheimer's disease (AD). Given the importance of tau to AD pathogenesis and therapies, it is important to understand non-classic physiological functions for this protein inside and outside the central nervous system (CNS). Our group has previously shown that tau ablation triggers glucose intolerance and pancreatic dysfunction in mice, suggesting that tau plays a role in peripheral metabolic regulation. Little is known about the role of tau in anxiety. Moreover, inconsistent results have been generated regarding the effects of tau deletion in memory. Here, we characterize systemic insulin resistance, anxiety-related behavior and memory in 15 to 20 weeks old Wild-Type (WT), Tau knockout (TauKO) and a distinct hTau mouse model consisting of tau knockout expressing the longest isoform (2N4R) of a non-mutant WT human Tau protein under the prion promoter (hTau). Our findings demonstrate that tau deletion leads to anxiety-related behavior, impaired contextual and cued fear memory. The presence of a human Tau transgene did not ameliorate the phenotypes observed in animals lacking the mouse tau protein and it elicited impairments in learning, memory, and peripheral insulin sensitivity. Our results suggest that tau protein plays a role in memory and anxiety-related behavior. Our findings also indicate that previously unrecognized functions for tau protein may be a complicating factor in using animal models on the TauKO background. Understanding the link between tau pathophysiology and cognitive and metabolic alterations is of great importance to establish the complete contribution of tau protein to AD pathogenesis.
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Affiliation(s)
- Rafaella Araujo Gonçalves
- Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Paul E. Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
- *Correspondence: Paul E. Fraser
| | - Fernanda G. De Felice
- Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada
- Department of Psychiatry, Queen's University, Kingston, ON, Canada
- Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Fernanda G. De Felice
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5
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Gonçalves RA, Wijesekara N, Fraser PE, De Felice FG. The Link Between Tau and Insulin Signaling: Implications for Alzheimer's Disease and Other Tauopathies. Front Cell Neurosci 2019; 13:17. [PMID: 30804755 PMCID: PMC6371747 DOI: 10.3389/fncel.2019.00017] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 01/16/2019] [Indexed: 01/27/2023] Open
Abstract
The microtubule-associated protein tau (MAPT) is mainly identified as a tubulin binding protein essential for microtubule dynamics and assembly and for neurite outgrowth. However, several other possible functions for Tau remains to be investigated. Insulin signaling is important for synaptic plasticity and memory formation and therefore is essential for proper brain function. Tau has recently been characterized as an important regulator of insulin signaling, with evidence linking Tau to brain and peripheral insulin resistance and beta cell dysfunction. In line with this notion, the hypothesis of Tau pathology as a key trigger of impaired insulin sensitivity and secretion has emerged. Conversely, insulin resistance can also favor Tau dysfunction, resulting in a vicious cycle of these events. In this review article, we discuss recent evidence linking Tau pathology, insulin resistance and insulin deficiency. We further highlight the deleterious consequences of Tau pathology-induced insulin resistance to the brain and/or peripheral tissues, suggesting that these are key events mediating cognitive decline in Alzheimer’s disease (AD) and other tauopathies.
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Affiliation(s)
- Rafaella Araujo Gonçalves
- Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada.,Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada
| | - Paul E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
| | - Fernanda G De Felice
- Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada.,Department of Psychiatry, Queen's University, Kingston, ON, Canada.,Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
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6
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Bharadwaj P, Wijesekara N, Liyanapathirana M, Newsholme P, Ittner L, Fraser P, Verdile G. The Link between Type 2 Diabetes and Neurodegeneration: Roles for Amyloid-β, Amylin, and Tau Proteins. J Alzheimers Dis 2018; 59:421-432. [PMID: 28269785 DOI: 10.3233/jad-161192] [Citation(s) in RCA: 122] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A wealth of evidence indicates a strong link between type 2 diabetes (T2D) and neurodegenerative diseases such as Alzheimer's disease (AD). Although the precise mechanism remains unclear, T2D can exacerbate neurodegenerative processes. Brain atrophy, reduced cerebral glucose metabolism, and central nervous system insulin resistance are features of both AD and T2D. The T2D phenotype (glucose dyshomeostasis, insulin resistance, impaired insulin signaling) also promotes AD pathology, namely accumulation of amyloid-β (Aβ) and hyperphosphorylated tau and can induce other aspects of neuronal degeneration including inflammatory and oxidative processes. Aβ and hyperphosphorylated tau may also have roles in pancreatic β-cell dysfunction and in reducing insulin sensitivity and glucose uptake by peripheral tissues such as liver, skeletal muscle, and adipose tissue. This suggests a role for these AD-related proteins in promoting T2D. The accumulation of the islet amyloid polypeptide (IAPP, or amylin) within islet β-cells is a major pathological feature of the pancreas in patients with chronic T2D. Co-secreted with insulin, amylin accumulates over time and contributes to β-cell toxicity, ultimately leading to reduced insulin secretion and onset of overt (insulin dependent) diabetes. Recent evidence also suggests that this protein accumulates in the brain of AD patients and may interact with Aβ to exacerbate the neurodegenerative process. In this review, we highlight evidence indicating T2D in promoting Aβ and tau mediated neurodegeneration and the potential contributions of Aβ and tau in promoting a diabetic phenotype that could further exacerbate neurodegeneration. We also discuss underlying mechanisms by which amylin can contribute to the neurodegenerative processes.
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Affiliation(s)
- Prashant Bharadwaj
- School of Biomedical Sciences, Faculty of Health Sciences, Curtin Health Innovation Research Institute, Curtin University, WA, Australia.,Centre of Excellence for Alzheimer's Disease Research and Care, School of Medical Sciences, Edith Cowan University, WA, Australia
| | - Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, Krembil Discovery Tower, and Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
| | - Milindu Liyanapathirana
- School of Biomedical Sciences, Faculty of Health Sciences, Curtin Health Innovation Research Institute, Curtin University, WA, Australia
| | - Philip Newsholme
- School of Biomedical Sciences, Faculty of Health Sciences, Curtin Health Innovation Research Institute, Curtin University, WA, Australia
| | - Lars Ittner
- School of Medical Sciences, University of NSW, Kensington, NSW, Australia
| | - Paul Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, Krembil Discovery Tower, and Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
| | - Giuseppe Verdile
- School of Biomedical Sciences, Faculty of Health Sciences, Curtin Health Innovation Research Institute, Curtin University, WA, Australia.,Centre of Excellence for Alzheimer's Disease Research and Care, School of Medical Sciences, Edith Cowan University, WA, Australia.,School of Psychiatry and Clinical Neurosciences, University of Western Australia, Crawley, Australia
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7
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Wijesekara N, Gonçalves RA, Ahrens R, De Felice FG, Fraser PE. Tau ablation in mice leads to pancreatic β cell dysfunction and glucose intolerance. FASEB J 2018; 32:3166-3173. [DOI: 10.1096/fj.201701352] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative DiseasesUniversity of Toronto Toronto Ontario Canada
| | - Rafaella Araujo Gonçalves
- Tanz Centre for Research in Neurodegenerative DiseasesUniversity of Toronto Toronto Ontario Canada
- Department of Medical BiophysicsUniversity of Toronto Toronto Ontario Canada
| | - Rosemary Ahrens
- Tanz Centre for Research in Neurodegenerative DiseasesUniversity of Toronto Toronto Ontario Canada
| | - Fernanda G. De Felice
- Department of Medical BiophysicsUniversity of Toronto Toronto Ontario Canada
- Institute of Medical Biochemistry Leopoldo de MeisFederal University of Rio de Janeiro Rio de Janeiro Brazil
| | - Paul E. Fraser
- Tanz Centre for Research in Neurodegenerative DiseasesUniversity of Toronto Toronto Ontario Canada
- Department of Biomedical and Molecular SciencesCentre for Neuroscience StudiesQueen's University Kingston Ontario Canada
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8
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Wijesekara N, Gonçalves RA, De Felice FG, Fraser PE. Impaired peripheral glucose homeostasis and Alzheimer's disease. Neuropharmacology 2017; 136:172-181. [PMID: 29169962 DOI: 10.1016/j.neuropharm.2017.11.027] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Revised: 11/12/2017] [Accepted: 11/16/2017] [Indexed: 12/19/2022]
Abstract
Alzheimer's disease (AD) is the most common type of dementia. Recent studies suggest that metabolic disturbances, particularly type 2 diabetes (T2D) increase the risk of cognitive decline and AD. AD is also a risk factor for T2D, and a growing body of evidence indicates that these diseases are connected both at clinical and molecular levels. In T2D, peripheral insulin resistance, hyperglycemia and eventually insulin deficiency develops, leading to an overall decline in tissue health. More recently, brain insulin resistance has been shown to be a key feature of AD that is linked to neuronal dysfunction and cognitive impairment. Furthermore, both AD and T2D are amyloidogenic diseases, with abnormal aggregation of amyloid-β peptide (Aβ) and islet amyloid polypeptide (IAPP) respectively contributing to cellular death and disease pathogenesis. Emerging data suggests that Aβ may have peripheral effects including its co-deposition in the pancreas. In this review, we discuss how peripheral effects of Aβ and metabolic disturbances may impact AD pathogenesis. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'
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Affiliation(s)
- Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Krembil Discovery Tower, 60 Leonard Avenue, Toronto, Ontario, M5T 2S8, Canada.
| | - Rafaella Araujo Gonçalves
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Krembil Discovery Tower, 60 Leonard Avenue, Toronto, Ontario, M5T 2S8, Canada; Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil
| | - Fernanda G De Felice
- Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil; Centre for Neuroscience Studies, Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - Paul E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Krembil Discovery Tower, 60 Leonard Avenue, Toronto, Ontario, M5T 2S8, Canada; Department of Medical Biophysics, University of Toronto, Canada.
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9
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Wijesekara N, Ahrens R, Sabale M, Wu L, Ha K, Verdile G, Fraser PE. Amyloid-β and islet amyloid pathologies link Alzheimer's disease and type 2 diabetes in a transgenic model. FASEB J 2017; 31:5409-5418. [PMID: 28808140 DOI: 10.1096/fj.201700431r] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Accepted: 07/25/2017] [Indexed: 11/11/2022]
Abstract
Alzheimer's disease (AD) and type 2 diabetes (T2D) present a significant risk to each other. AD and T2D are characterized by deposition of cerebral amyloid-β (Aβ) and pancreatic human islet amyloid polypeptide (hIAPP), respectively. We investigated the role of amyloidogenic proteins in the interplay between these diseases. A novel double transgenic mouse model combining T2D and AD was generated and characterized. AD-related amyloid transgenic mice coexpressing hIAPP displayed peripheral insulin resistance, hyperglycemia, and glucose intolerance. Aβ and IAPP amyloid co-deposition increased tau phosphorylation, and a reduction in pancreatic β-cell mass was detected in islets. Increased brain Aβ deposition and tau phosphorylation and reduced insulin levels and signaling were accompanied by extensive synaptic loss and decreased neuronal counts. Aβ immunization rescued the peripheral insulin resistance and hyperglycemia, suggesting a role for Aβ in T2D pathogenesis for individuals predisposed to AD. These findings demonstrate that Aβ and IAPP are key factors in the overlapping pathologies of AD and T2D.-Wijesekara, N., Ahrens, R., Sabale, M., Wu, L., Ha, K., Verdile, G., Fraser, P. E. Amyloid-β and islet amyloid pathologies link Alzheimer's disease and type 2 diabetes in a transgenic model.
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Affiliation(s)
- Nadeeja Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada;
| | - Rosemary Ahrens
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada
| | - Miheer Sabale
- School of Biomedical Sciences, Curtin Health and Innovation Research Institute, Curtin University, Bentley, Western Australia, Australia
| | - Ling Wu
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada
| | - Kathy Ha
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada
| | - Giuseppe Verdile
- School of Biomedical Sciences, Curtin Health and Innovation Research Institute, Curtin University, Bentley, Western Australia, Australia
| | - Paul E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
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10
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Laws SM, Gaskin S, Woodfield A, Srikanth V, Bruce D, Fraser P, Porter T, Newsholme P, Wijesekara N, Dore V, Li Q, Maruff P, Martins RN, Masters CL, Rowe CC, Salvado O, Villemagne VL, Verdile G. [P4–134]: INSULIN RESISTANCE IS ASSOCIATED WITH REDUCTIONS IN SPECIFIC COGNITIVE DOMAINS AND INCREASES IN CSF TAU IN COGNITIVELY NORMAL ADULTS. Alzheimers Dement 2017. [DOI: 10.1016/j.jalz.2017.06.2000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Simon M. Laws
- Edith Cowan UniversityJoondalupAustralia
- Cooperative Research Centre for Mental HealthMelbourneAustralia
- Curtin UniversityPerthAustralia
| | | | | | - Velandai Srikanth
- Medicine, School of Clinical SciencesMonash UniversityMelbourneAustralia
| | - David Bruce
- University of Western AustraliaPerthAustralia
| | | | | | | | | | - Vincent Dore
- CSIROMelbourneAustralia
- Austin HealthMelbourneAustralia
| | - Qiao‐Xin Li
- The Florey Institute of Neuroscience and Mental HealthParkvilleAustralia
| | - Paul Maruff
- The Florey Institute of Neuroscience and Mental HealthParkvilleAustralia
- Cogstate Ltd.MelbourneAustralia
| | | | - Colin L. Masters
- The Florey Institute of Neuroscience and Mental HealthParkvilleAustralia
- The University of MelbourneParkvilleAustralia
| | - Christopher C. Rowe
- The University of MelbourneParkvilleAustralia
- Austin HealthHeidelbergAustralia
| | - Olivier Salvado
- Commonwealth Scientific and Industrial Research OrganisationBrisbaneAustralia
| | - Victor L. Villemagne
- Austin HealthMelbourneAustralia
- The University of MelbourneParkvilleAustralia
- The Florey Institute of Neuroscience and Mental HealthMelbourneAustralia
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11
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Wijesekara N, Kaur A, Westwell-Roper C, Nackiewicz D, Soukhatcheva G, Hayden MR, Verchere CB. ABCA1 deficiency and cellular cholesterol accumulation increases islet amyloidogenesis in mice. Diabetologia 2016; 59:1242-6. [PMID: 26970755 DOI: 10.1007/s00125-016-3907-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 01/19/2016] [Indexed: 12/01/2022]
Abstract
AIMS/HYPOTHESIS Islet amyloid, a pathological feature of type 2 diabetes, forms from the aggregation of islet amyloid polypeptide (IAPP), a beta cell peptide that is produced and co-secreted with insulin. Cholesterol regulates amyloid-β processing, deposition and clearance, promoting amyloidogenesis in the brain. ATP-binding cassette transporter 1 (ABCA1) is a cholesterol efflux transporter that when absent increases and when overexpressed reduces brain amyloid-β deposition in mouse models of Alzheimer's disease. We examined whether alterations in ABCA1 expression and islet cholesterol content could also modulate islet amyloidogenesis. METHODS Thioflavin S staining for amyloid was performed in islets isolated from mice with beta cell expression of human IAPP (hIAPP (Tg/o)) and cultured for 8 days following cholesterol loading, microRNA-33 overexpression (to reduce ABCA1 expression) or palmitate treatment in the presence or absence of ABCA1 overexpression or mevastatin treatment (to reduce cholesterol synthesis). hIAPP (Tg/o) mice were crossed with beta cell-specific Abca1-knockout mice (hIAPP (Tg/o) Abca1 (βKO)) and glucose tolerance and amyloid formation were assessed. RESULTS Cholesterol loading and microRNA-33-induced reduction in islet ABCA1 expression increased Thioflavin S-positive amyloid in hIAPP (Tg/o) islets. Palmitate treatment also increased amyloid formation and this was reduced by both ABCA1 overexpression and mevastatin treatment. hIAPP (Tg/o) Abca1 (βKO) mice had increased islet cholesterol, accompanied by fasting hyperglycaemia, glucose intolerance, impaired in vivo insulin secretion and an increased islet proinsulin:insulin ratio. Amyloid area was increased in cultured hIAPP (Tg/o) Abca1 (βKO) islets compared with hIAPP (Tg/o) controls. CONCLUSIONS/INTERPRETATION These data suggest that elevations in islet cholesterol may lead to increases in IAPP aggregation and islet amyloid formation, further worsening beta cell function and glucose homeostasis.
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Affiliation(s)
- Nadeeja Wijesekara
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child & Family Research Institute, University of British Columbia, Vancouver, BC, Canada
| | - Achint Kaur
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child & Family Research Institute, University of British Columbia, Vancouver, BC, Canada
| | - Clara Westwell-Roper
- Department of Pathology & Laboratory Medicine, Child & Family Research Institute, University of British Columbia, 950 West 28th Avenue, Vancouver, BC, V5Z 4H4, Canada
| | - Dominika Nackiewicz
- Department of Surgery, Child & Family Research Institute, University of British Columbia, Vancouver, BC, Canada
| | - Galina Soukhatcheva
- Department of Pathology & Laboratory Medicine, Child & Family Research Institute, University of British Columbia, 950 West 28th Avenue, Vancouver, BC, V5Z 4H4, Canada
| | - Michael R Hayden
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child & Family Research Institute, University of British Columbia, Vancouver, BC, Canada
| | - C Bruce Verchere
- Department of Pathology & Laboratory Medicine, Child & Family Research Institute, University of British Columbia, 950 West 28th Avenue, Vancouver, BC, V5Z 4H4, Canada.
- Department of Surgery, Child & Family Research Institute, University of British Columbia, Vancouver, BC, Canada.
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Wijesekara N, Ahrens R, Wu L, Ha K, Liu Y, Wheeler MB, Fraser PE. Islet amyloid inhibitors improve glucose homeostasis in a transgenic mouse model of type 2 diabetes. Diabetes Obes Metab 2015; 17:1003-6. [PMID: 26095311 DOI: 10.1111/dom.12529] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2015] [Revised: 06/03/2015] [Accepted: 06/14/2015] [Indexed: 11/29/2022]
Abstract
Increasing evidence points to the cytotoxicity of islet amyloid polypeptide (IAPP) aggregates as a major contributor to the loss of β-cell mass in type 2 diabetes. Prevention of IAPP formation represents a potential treatment to increase β-cell survival and function. The IAPP inhibitory peptide, D-ANFLVH, has been previously shown to prevent islet amyloid accumulation in cultured human islets. To assess its activity in vivo, D-ANFLVH was administered by intraperitoneal injection into a human IAPP transgenic mouse model, which replicates type 2 diabetes islet amyloid pathology. The peptide was a potent inhibitor of islet amyloid deposition, resulting in reduced islet cell apoptosis and preservation of β-cell area leading to improved glucose tolerance. These findings provide support for a key role of islet amyloid in β-cell survival and validate the application of anti-amyloid compounds as therapeutic strategies to maintain normal insulin secretion in patients with type 2 diabetes.
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Affiliation(s)
- N Wijesekara
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - R Ahrens
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - L Wu
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - K Ha
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
| | - Y Liu
- Department of Physiology, University of Toronto, Toronto, Canada
| | - M B Wheeler
- Department of Physiology, University of Toronto, Toronto, Canada
| | - P E Fraser
- Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Canada
- Department of Medical Biophysics, University of Toronto, Toronto, Canada
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13
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Kaur A, Patankar JV, de Haan W, Ruddle P, Wijesekara N, Groen AK, Verchere CB, Singaraja RR, Hayden MR. Loss of Cyp8b1 improves glucose homeostasis by increasing GLP-1. Diabetes 2015; 64:1168-79. [PMID: 25338812 DOI: 10.2337/db14-0716] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Besides their role in facilitating lipid absorption, bile acids are increasingly being recognized as signaling molecules that activate cell-signaling receptors. Targeted disruption of the sterol 12α-hydroxylase gene (Cyp8b1) results in complete absence of cholic acid (CA) and its derivatives. Here we investigate the effect of Cyp8b1 deletion on glucose homeostasis. Absence of Cyp8b1 results in improved glucose tolerance, insulin sensitivity, and β-cell function, mediated by absence of CA in Cyp8b1(-/-) mice. In addition, we show that reduced intestinal fat absorption in the absence of biliary CA leads to increased free fatty acids reaching the ileal L cells. This correlates with increased secretion of the incretin hormone GLP-1. GLP-1, in turn, increases the biosynthesis and secretion of insulin from β-cells, leading to the improved glucose tolerance observed in the Cyp8b1(-/-) mice. Thus, our data elucidate the importance of Cyp8b1 inhibition on the regulation of glucose metabolism.
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Affiliation(s)
- Achint Kaur
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jay V Patankar
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Willeke de Haan
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Piers Ruddle
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Nadeeja Wijesekara
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Albert K Groen
- Departments of Pediatrics and Laboratory Medicine, Center for Liver, Digestive and Metabolic Diseases, University Medical Center Groningen, Groningen, the Netherlands
| | - C Bruce Verchere
- Departments of Surgery and Pathology and Laboratory Medicine, Child & Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Roshni R Singaraja
- A*STAR (Agency for Science, Technology and Research) Institute and Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Michael R Hayden
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
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14
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Kang MH, Zhang LH, Wijesekara N, de Haan W, Butland S, Bhattacharjee A, Hayden MR. Regulation of ABCA1 protein expression and function in hepatic and pancreatic islet cells by miR-145. Arterioscler Thromb Vasc Biol 2013; 33:2724-32. [PMID: 24135019 DOI: 10.1161/atvbaha.113.302004] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 10/04/2013] [Indexed: 12/18/2022]
Abstract
OBJECTIVE The ATP-binding cassette transporter A1 (ABCA1) protein maintains cellular cholesterol homeostasis in several different tissues. In the liver, ABCA1 is crucial for high-density lipoprotein biogenesis, and in the pancreas ABCA1 can regulate insulin secretion. In this study, our aim was to identify novel microRNAs that regulate ABCA1 expression in these tissues. APPROACH AND RESULTS We combined multiple microRNA prediction programs to identify 8 microRNAs that potentially regulate ABCA1. A luciferase reporter assay demonstrated that 5 of these microRNAs (miR-148, miR-27, miR-144, miR-145, and miR-33a/33b) significantly repressed ABCA1 3'-untranslated region activity with miR-145 resulting in one of the larger decreases. In hepatic HepG2 cells, miR-145 can regulate both ABCA1 protein expression levels and cholesterol efflux function. In murine islets, an increase in miR-145 expression decreased ABCA1 protein expression, increased total islet cholesterol levels, and decreased glucose-stimulated insulin secretion. Inhibiting miR-145 produced the opposite effect of increasing ABCA1 protein levels and improving glucose-stimulated insulin secretion. Finally, increased glucose levels in media significantly decreased miR-145 levels in cultured pancreatic beta cells. These findings suggest that miR-145 is involved in glucose homeostasis and is regulated by glucose concentration. CONCLUSIONS Our studies demonstrate that miR-145 regulates ABCA1 expression and function, and inhibiting this microRNA represents a novel strategy for increasing ABCA1 expression, promoting high-density lipoprotein biogenesis in the liver, and improving glucose-stimulated insulin secretion in islets.
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Affiliation(s)
- Martin H Kang
- From the Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, BC, Canada
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15
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Hardy AB, Wijesekara N, Genkin I, Prentice KJ, Bhattacharjee A, Kong D, Chimienti F, Wheeler MB. Effects of high-fat diet feeding on Znt8-null mice: differences between β-cell and global knockout of Znt8. Am J Physiol Endocrinol Metab 2012; 302:E1084-96. [PMID: 22338079 PMCID: PMC3774340 DOI: 10.1152/ajpendo.00448.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Genomewide association studies have linked a polymorphism in the zinc transporter 8 (Znt8) gene to higher risk of developing type 2 diabetes. Znt8 is highly expressed in pancreatic β-cells where it is involved in the regulation of zinc transport into granules. However, Znt8 is also expressed in other tissues including α-cells, where its function is as yet unknown. Previous work demonstrated that mice lacking Znt8 globally were more susceptible to diet-induced obesity (Lemaire et al., Proc Natl Acad Sci USA 106: 14872-14877, 2009; Nicolson et al., Diabetes 58: 2070-2083, 2009). Therefore, the main goal of this study was to examine the physiological impact of β-cell-specific Znt8 deficiency in mice during high-fat high-calorie (HFHC) diet feeding. For these studies, we used β-cell-specific Znt8 knockout (Ins2Cre:Znt8loxP/loxP) and whole body Znt8 knockout (Cre-:Znt8(-/-)) mice placed on a HFHC diet for 16 wk. Ins2Cre:Znt8loxP/loxP mice on HFHC diet had similar body weights throughout the study but displayed impaired insulin biosynthesis and secretion and were glucose intolerant compared with littermate control Ins2Cre mice. In contrast, Cre-:Znt8(-/-) mice became remarkably obese, hyperglycemic, hyperinsulinemic, insulin resistant, and glucose intolerant compared with littermate control Cre- mice. These data show that β-cell Znt8 alone does not considerably aggravate weight gain and glucose intolerance during metabolic stress imposed by an HFHC diet. However, global loss of Znt8 is involved in exacerbating diet-induced obesity and resulting insulin resistance, and this may be due to the loss of Znt8 activity in a tissue other than the β-cell. Thus, our data suggest that Znt8 contributes to the risk of developing type 2 diabetes through β-cell- and non-β-cell-specific effects.
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Affiliation(s)
| | | | | | | | | | - D. Kong
- 3Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts; and
| | | | - M. B. Wheeler
- 1Department of Physiology and
- 2Department of Medicine, University of Toronto, Toronto, Ontario, Canada;
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Wijesekara N, Zhang LH, Kang MH, Abraham T, Bhattacharjee A, Warnock GL, Verchere CB, Hayden MR. miR-33a modulates ABCA1 expression, cholesterol accumulation, and insulin secretion in pancreatic islets. Diabetes 2012; 61:653-8. [PMID: 22315319 PMCID: PMC3282802 DOI: 10.2337/db11-0944] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Changes in cellular cholesterol affect insulin secretion, and β-cell-specific deletion or loss-of-function mutations in the cholesterol efflux transporter ATP-binding cassette transporter A1 (ABCA1) result in impaired glucose tolerance and β-cell dysfunction. Upregulation of ABCA1 expression may therefore be beneficial for the maintenance of normal islet function in diabetes. Studies suggest that microRNA-33a (miR-33a) expression inversely correlates with ABCA1 expression in hepatocytes and macrophages. We examined whether miR-33a regulates ABCA1 expression in pancreatic islets, thereby affecting cholesterol accumulation and insulin secretion. Adenoviral miR-33a overexpression in human or mouse islets reduced ABCA1 expression, decreased glucose-stimulated insulin secretion, and increased cholesterol levels. The miR-33a-induced reduction in insulin secretion was rescued by cholesterol depletion by methyl-β-cyclodextrin or mevastatin. Inhibition of miR-33a expression in apolipoprotein E knockout islets and ABCA1 overexpression in β-cell-specific ABCA1 knockout islets rescued normal insulin secretion and reduced islet cholesterol. These findings confirm the critical role of β-cell ABCA1 in islet cholesterol homeostasis and β-cell function and highlight modulation of β-cell miR-33a expression as a means to influence insulin secretion.
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Affiliation(s)
- Nadeeja Wijesekara
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Lin-hua Zhang
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Martin H. Kang
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Thomas Abraham
- Institute for Heart and Lung Health, St. Paul’s Hospital, Vancouver, British Columbia, Canada
| | - Alpana Bhattacharjee
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Garth L. Warnock
- Department of Surgery, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - C. Bruce Verchere
- Department of Surgery, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Pathology and Laboratory Medicine, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Michael R. Hayden
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Corresponding author: Michael R. Hayden,
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Kruit JK, Wijesekara N, Westwell-Roper C, Vanmierlo T, de Haan W, Bhattacharjee A, Tang R, Wellington CL, LütJohann D, Johnson JD, Brunham LR, Verchere CB, Hayden MR. Loss of both ABCA1 and ABCG1 results in increased disturbances in islet sterol homeostasis, inflammation, and impaired β-cell function. Diabetes 2012; 61:659-64. [PMID: 22315310 PMCID: PMC3282825 DOI: 10.2337/db11-1341] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Cellular cholesterol homeostasis is important for normal β-cell function. Disruption of cholesterol transport by decreased function of the ATP-binding cassette (ABC) transporter ABCA1 results in impaired insulin secretion. Mice lacking β-cell ABCA1 have increased islet expression of ABCG1, another cholesterol transporter implicated in β-cell function. To determine whether ABCA1 and ABCG1 have complementary roles in β-cells, mice lacking ABCG1 and β-cell ABCA1 were generated and glucose tolerance, islet sterol levels, and β-cell function were assessed. Lack of both ABCG1 and β-cell ABCA1 resulted in increased fasting glucose levels and a greater impairment in glucose tolerance compared with either ABCG1 deletion or loss of ABCA1 in β-cells alone. In addition, glucose-stimulated insulin secretion was decreased and sterol accumulation increased in islets lacking both transporters compared with those isolated from knockout mice with each gene alone. Combined deficiency of ABCA1 and ABCG1 also resulted in significant islet inflammation as indicated by increased expression of interleukin-1β and macrophage infiltration. Thus, lack of both ABCA1 and ABCG1 induces greater defects in β-cell function than deficiency of either transporter individually. These data suggest that ABCA1 and ABCG1 each make complimentary and important contributions to β-cell function by maintaining islet cholesterol homeostasis in vivo.
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Affiliation(s)
- Janine K. Kruit
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Nadeeja Wijesekara
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Clara Westwell-Roper
- Department of Pathology and Laboratory Medicine, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Tim Vanmierlo
- Laboratory for Special Lipid Diagnostics, Institute of Clinical Chemistry and Clinical Pharmacology, University Clinics of Bonn, Bonn, Germany
| | - Willeke de Haan
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Alpana Bhattacharjee
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Renmei Tang
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Cheryl L. Wellington
- Department of Pathology and Laboratory Medicine, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Dieter LütJohann
- Laboratory for Special Lipid Diagnostics, Institute of Clinical Chemistry and Clinical Pharmacology, University Clinics of Bonn, Bonn, Germany
| | - James D. Johnson
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Liam R. Brunham
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - C. Bruce Verchere
- Departments of Surgery and Pathology and Laboratory Medicine, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Michael R. Hayden
- Department of Medical Genetics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
- Corresponding author: Michael R. Hayden,
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Kruit JK, Wijesekara N, Fox JEM, Dai XQ, Brunham LR, Searle GJ, Morgan GP, Costin AJ, Tang R, Bhattacharjee A, Johnson JD, Light PE, Marsh BJ, MacDonald PE, Verchere CB, Hayden MR. Islet cholesterol accumulation due to loss of ABCA1 leads to impaired exocytosis of insulin granules. Diabetes 2011; 60:3186-96. [PMID: 21998401 PMCID: PMC3219942 DOI: 10.2337/db11-0081] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
OBJECTIVE The ATP-binding cassette transporter A1 (ABCA1) is essential for normal insulin secretion from β-cells. The aim of this study was to elucidate the mechanisms underlying the impaired insulin secretion in islets lacking β-cell ABCA1. RESEARCH DESIGN AND METHODS Calcium imaging, patch clamp, and membrane capacitance were used to assess the effect of ABCA1 deficiency on calcium flux, ion channel function, and exocytosis in islet cells. Electron microscopy was used to analyze β-cell ultrastructure. The quantity and distribution of proteins involved in insulin-granule exocytosis were also investigated. RESULTS We show that a lack of β-cell ABCA1 results in impaired depolarization-induced exocytotic fusion of insulin granules. We observed disturbances in membrane microdomain organization and Golgi and insulin granule morphology in β-cells as well as elevated fasting plasma proinsulin levels in mice in the absence of β-cell ABCA1. Acute cholesterol depletion rescued the exocytotic defect in β-cells lacking ABCA1, indicating that elevated islet cholesterol accumulation directly impairs granule fusion and insulin secretion. CONCLUSIONS Our data highlight a crucial role of ABCA1 and cellular cholesterol in β-cells that is necessary for regulated insulin granule fusion events. These data suggest that abnormalities of cholesterol metabolism may contribute to the impaired β-cell function in diabetes.
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Affiliation(s)
- Janine K. Kruit
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Nadeeja Wijesekara
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jocelyn E. Manning Fox
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Xiao-Qing Dai
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Liam R. Brunham
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Gavin J. Searle
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Garry P. Morgan
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Adam J. Costin
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Renmei Tang
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Alpana Bhattacharjee
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - James D. Johnson
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Peter E. Light
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Brad J. Marsh
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Patrick E. MacDonald
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - C. Bruce Verchere
- Departments of Pathology & Laboratory Medicine and Surgery, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Michael R. Hayden
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Corresponding author: Michael R. Hayden,
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Hardy AB, Serino AS, Wijesekara N, Chimienti F, Wheeler MB. Regulation of glucagon secretion by zinc: lessons from the β cell-specific Znt8 knockout mouse model. Diabetes Obes Metab 2011; 13 Suppl 1:112-7. [PMID: 21824264 DOI: 10.1111/j.1463-1326.2011.01451.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In type-2 diabetes, hyperglucagonaemia aggravates elevated blood glucose levels. Relative to our knowledge of the β-cell and insulin secretion, there remains a limited understanding of glucagon secretion in α-cells. Regulation of glucagon may be dependent on a combination of factors, which include direct glucose sensing by the α-cell, innervations from the autonomic nervous system and potential 'paracrine' actions by hormones and factors that are released by adjacent endocrine cells within the islets. The list of potential 'paracrine' regulators within the islet includes insulin, somatostatin, γ-aminobutyric acid, glutamate and zinc. Zinc crystallises with insulin in β-cells and is co-secreted with insulin. In the scientific literature, the effect of exogeneous zinc on glucagon secretion has been debated. Here, we confirm that an increase in exogeneous zinc does inhibit glucagon secretion. To determine if there are physiological effects of zinc on glucagon secretion we used a β-cell-specific ZnT8 knockout (Znt8BKO) mouse model. Znt8BKO mice, despite showing lower granular zinc content in β-cells, showed no changes in fasted plasma glucagon levels and glucose regulated glucagon secretion. These findings suggest that zinc secreted from β-cell does not regulate glucagon secretion.
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Affiliation(s)
- A B Hardy
- Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
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Wijesekara N. Dihydrofolate reductase mutations-associated megaloblastic anemia and cerebral folate deficiency. Clin Genet 2011; 79:507-8. [DOI: 10.1111/j.1399-0004.2011.01662.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Wijesekara N, Krishnamurthy M, Bhattacharjee A, Suhail A, Sweeney G, Wheeler MB. Adiponectin-induced ERK and Akt phosphorylation protects against pancreatic beta cell apoptosis and increases insulin gene expression and secretion. J Biol Chem 2010; 285:33623-31. [PMID: 20709750 DOI: 10.1074/jbc.m109.085084] [Citation(s) in RCA: 169] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The functional impact of adiponectin on pancreatic beta cells is so far poorly understood. Although adiponectin receptors (AdipoR1/2) were identified, their involvement in adiponectin-induced signaling and other molecules involved is not clearly defined. Therefore, we investigated the role of adiponectin in beta cells and the signaling mediators involved. MIN6 beta cells and mouse islets were stimulated with globular (2.5 μg/ml) or full-length (5 μg/ml) adiponectin under serum starvation, and cell viability, proliferation, apoptosis, insulin gene expression, and secretion were measured. Lysates were subjected to Western blot analysis to determine phosphorylation of AMP-activated protein kinase (AMPK), Akt, or ERK. Functional significance of signaling was confirmed using dominant negative mutants or pharmacological inhibitors. Participation of AdipoRs was assessed by overexpression or siRNA. Adiponectin failed to activate AMPK after 10 min or 1- and 24-h stimulation. ERK was significantly phosphorylated after 24-h treatment with adiponectin, whereas Akt was activated at all time points examined. 24-h stimulation with adiponectin significantly increased cell viability by decreasing cellular apoptosis, and this was prevented by dominant negative Akt, wortmannin (PI3K inhibitor), and U0126 (MEK inhibitor). Moreover, adiponectin regulated insulin gene expression and glucose-stimulated insulin secretion, which was also prevented by wortmannin and U0126 treatment. Interestingly, the data also suggest adiponectin-induced changes in Akt and ERK phosphorylation and caspase-3 may occur independent of the level of AdipoR expression. This study demonstrates a lack of AMPK involvement and implicates Akt and ERK in adiponectin signaling, leading to protection against apoptosis and stimulation of insulin gene expression and secretion in pancreatic beta cells.
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Affiliation(s)
- Nadeeja Wijesekara
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, USA
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Wijesekara N, Dai FF, Hardy AB, Giglou PR, Bhattacharjee A, Koshkin V, Chimienti F, Gaisano HY, Rutter GA, Wheeler MB. Beta cell-specific Znt8 deletion in mice causes marked defects in insulin processing, crystallisation and secretion. Diabetologia 2010; 53:1656-68. [PMID: 20424817 PMCID: PMC6101216 DOI: 10.1007/s00125-010-1733-9] [Citation(s) in RCA: 219] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Accepted: 02/05/2010] [Indexed: 02/01/2023]
Abstract
AIMS/HYPOTHESIS Zinc is highly concentrated in pancreatic beta cells, is critical for normal insulin storage and may regulate glucagon secretion from alpha cells. Zinc transport family member 8 (ZnT8) is a zinc efflux transporter that is highly abundant in beta cells. Polymorphisms of ZnT8 (also known as SLC30A8) gene in man are associated with increased risk of type 2 diabetes. While global Znt8 knockout (Znt8KO) mice have been characterised, ZnT8 is also present in other islet cell types and extra-pancreatic tissues. Therefore, it is important to find ways of understanding the role of ZnT8 in beta and alpha cells without the difficulties caused by the confounding effects of ZnT8 in these other tissues. METHODS We generated mice with beta cell-specific (Znt8BKO) and alpha cell-specific (Znt8AKO) knockout of Znt8, and performed in vivo and in vitro characterisation of the phenotypes to determine the functional and anatomical impact of ZnT8 in these cells. Thus we assessed zinc accumulation, insulin granule morphology, insulin biosynthesis and secretion, and glucose homeostasis. RESULTS Znt8BKO mice are glucose-intolerant, have reduced beta cell zinc accumulation and atypical insulin granules. They also display reduced first-phase glucose-stimulated insulin secretion, reduced insulin processing enzyme transcripts and increased proinsulin levels. In contrast, Znt8AKO mice show no evident abnormalities in plasma glucagon and glucose homeostasis. CONCLUSIONS/INTERPRETATION This is the first report of specific beta and alpha cell deletion of Znt8. Our data indicate that while, under the conditions studied, ZnT8 is absolutely essential for proper beta cell function, it is largely dispensable for alpha cell function.
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Affiliation(s)
- N Wijesekara
- Department of Physiology, University of Toronto, 1 King's College Circle Room 3352, Toronto, ON, Canada M5S 1A8
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Abstract
It is well known that zinc is required in pancreatic beta-cells in the process of insulin biosynthesis and the maturation of insulin secretory granules. In fact, the zinc level in pancreatic islets is amongst the highest in the body and reduction in its levels in the pancreas has been associated with diabetes. High concentrations of zinc can also be toxic because of enhanced oxidative damage. The link between zinc, diabetes and islet dysfunction has recently been reiterated by genomewide association studies that identified an islet cell membrane zinc transporter, SLC30A8 (ZnT8), as one of the risk loci for type 2 diabetes. Here we explore the importance of both zinc and ZnT8 to islet biology and whole body glucose homeostasis.
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Affiliation(s)
- N Wijesekara
- Department of Physiology, University of Toronto, Ontario, Canada
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Fu A, Ng ACH, Depatie C, Wijesekara N, He Y, Wang GS, Bardeesy N, Scott FW, Touyz RM, Wheeler MB, Screaton RA. Loss of Lkb1 in adult beta cells increases beta cell mass and enhances glucose tolerance in mice. Cell Metab 2009; 10:285-95. [PMID: 19808021 DOI: 10.1016/j.cmet.2009.08.008] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Revised: 05/21/2009] [Accepted: 08/14/2009] [Indexed: 01/05/2023]
Abstract
The Lkb1 tumor suppressor exerts its biological effects through phosphorylation and consequent activation of the AMP kinase (AMPK) family. Extensive genetic and biochemical evidence supports a role for Lkb1 in cell cycle arrest, establishment of cell polarity, and cellular energy metabolism. However, the role of Lkb1 and the AMPK family in beta cell function in vivo has not been established. We generated conditional knockout mice with a deletion of the Lkb1 gene in the beta cell compartment of pancreatic islets; these mice display improved glucose tolerance and protection against diet-induced hyperglycemia. Lkb1(-/-) beta cells are hypertrophic because of elevated mTOR activity; they also proliferate more and secrete more insulin in response to glucose. These data indicate that inhibiting Lkb1 activity in beta cells may facilitate beta cell expansion and glucose tolerance in vivo.
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Affiliation(s)
- Accalia Fu
- Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
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Nicolson TJ, Bellomo EA, Wijesekara N, Loder MK, Baldwin JM, Gyulkhandanyan AV, Koshkin V, Tarasov AI, Carzaniga R, Kronenberger K, Taneja TK, da Silva Xavier G, Libert S, Froguel P, Scharfmann R, Stetsyuk V, Ravassard P, Parker H, Gribble FM, Reimann F, Sladek R, Hughes SJ, Johnson PR, Masseboeuf M, Burcelin R, Baldwin SA, Liu M, Lara-Lemus R, Arvan P, Schuit FC, Wheeler MB, Chimienti F, Rutter GA. Insulin storage and glucose homeostasis in mice null for the granule zinc transporter ZnT8 and studies of the type 2 diabetes-associated variants. Diabetes 2009; 58:2070-83. [PMID: 19542200 PMCID: PMC2731533 DOI: 10.2337/db09-0551] [Citation(s) in RCA: 284] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Accepted: 06/02/2009] [Indexed: 12/03/2022]
Abstract
OBJECTIVE Zinc ions are essential for the formation of hexameric insulin and hormone crystallization. A nonsynonymous single nucleotide polymorphism rs13266634 in the SLC30A8 gene, encoding the secretory granule zinc transporter ZnT8, is associated with type 2 diabetes. We describe the effects of deleting the ZnT8 gene in mice and explore the action of the at-risk allele. RESEARCH DESIGN AND METHODS Slc30a8 null mice were generated and backcrossed at least twice onto a C57BL/6J background. Glucose and insulin tolerance were measured by intraperitoneal injection or euglycemic clamp, respectively. Insulin secretion, electrophysiology, imaging, and the generation of adenoviruses encoding the low- (W325) or elevated- (R325) risk ZnT8 alleles were undertaken using standard protocols. RESULTS ZnT8(-/-) mice displayed age-, sex-, and diet-dependent abnormalities in glucose tolerance, insulin secretion, and body weight. Islets isolated from null mice had reduced granule zinc content and showed age-dependent changes in granule morphology, with markedly fewer dense cores but more rod-like crystals. Glucose-stimulated insulin secretion, granule fusion, and insulin crystal dissolution, assessed by total internal reflection fluorescence microscopy, were unchanged or enhanced in ZnT8(-/-) islets. Insulin processing was normal. Molecular modeling revealed that residue-325 was located at the interface between ZnT8 monomers. Correspondingly, the R325 variant displayed lower apparent Zn(2+) transport activity than W325 ZnT8 by fluorescence-based assay. CONCLUSIONS ZnT8 is required for normal insulin crystallization and insulin release in vivo but not, remarkably, in vitro. Defects in the former processes in carriers of the R allele may increase type 2 diabetes risks.
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Affiliation(s)
- Tamara J. Nicolson
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | - Elisa A. Bellomo
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | | | - Merewyn K. Loder
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | - Jocelyn M. Baldwin
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K
| | | | - Vasilij Koshkin
- Department of Physiology, University of Toronto, Toronto, Canada
| | - Andrei I. Tarasov
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | | | | | - Tarvinder K. Taneja
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | | | | | - Philippe Froguel
- Section of Genomic Medicine, Division of Medicine, Imperial College London, London, U.K
- Centre National de la Recherche Scientifique Unite Mixte de Recherche 8090, Institute of Biology, Lille, France
| | | | | | - Philippe Ravassard
- Centre National de la Recherche Scientifique and Université Pierre et Marie Curie, Paris, France
| | - Helen Parker
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Fiona M. Gribble
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Frank Reimann
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Robert Sladek
- Department of Human Genetics, McGill University, Montreal, Canada
| | - Stephen J. Hughes
- Nuffield Department of Surgery, University of Oxford, Oxfordshire, U.K
| | - Paul R.V. Johnson
- Nuffield Department of Surgery, University of Oxford, Oxfordshire, U.K
| | - Myriam Masseboeuf
- Institut de Medecine Moleculaire de Rangueil, INSERM U858, IFR31, Toulouse III University, CHU Rangueil, Toulouse Cedex, Toulouse, France
| | - Remy Burcelin
- Institut de Medecine Moleculaire de Rangueil, INSERM U858, IFR31, Toulouse III University, CHU Rangueil, Toulouse Cedex, Toulouse, France
| | - Stephen A. Baldwin
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K
| | - Ming Liu
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan
| | - Roberto Lara-Lemus
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan
| | - Peter Arvan
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan
| | - Frans C. Schuit
- Gene Expression Unit, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Michael B. Wheeler
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K
| | - Fabrice Chimienti
- Section of Genomic Medicine, Division of Medicine, Imperial College London, London, U.K
| | - Guy A. Rutter
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
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Hardy AB, Fox JEM, Giglou PR, Wijesekara N, Bhattacharjee A, Sultan S, Gyulkhandanyan AV, Gaisano HY, MacDonald PE, Wheeler MB. Characterization of Erg K+ channels in alpha- and beta-cells of mouse and human islets. J Biol Chem 2009; 284:30441-52. [PMID: 19690348 DOI: 10.1074/jbc.m109.040659] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated eag-related gene (Erg) K(+) channels regulate the electrical activity of many cell types. Data regarding Erg channel expression and function in electrically excitable glucagon and insulin producing cells of the pancreas is limited. In the present study Erg1 mRNA and protein were shown to be highly expressed in human and mouse islets and in alpha-TC6 and Min6 cells alpha- and beta-cell lines, respectively. Whole cell patch clamp recordings demonstrated the functional expression of Erg1 in alpha- and beta-cells, with rBeKm1, an Erg1 antagonist, blocking inward tail currents elicited by a double pulse protocol. Additionally, a small interference RNA approach targeting the kcnh2 gene (Erg1) induced a significant decrease of Erg1 inward tail current in Min6 cells. To investigate further the role of Erg channels in mouse and human islets, ratiometric Fura-2 AM Ca(2+)-imaging experiments were performed on isolated alpha- and beta-cells. Blocking Erg channels with rBeKm1 induced a transient cytoplasmic Ca(2+) increase in both alpha- and beta-cells. This resulted in an increased glucose-dependent insulin secretion, but conversely impaired glucagon secretion under low glucose conditions. Together, these data present Erg1 channels as new mediators of alpha- and beta-cell repolarization. However, antagonism of Erg1 has divergent effects in these cells; to augment glucose-dependent insulin secretion and inhibit low glucose stimulated glucagon secretion.
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Affiliation(s)
- Alexandre B Hardy
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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Lu H, Yang Y, Allister EM, Wijesekara N, Wheeler MB. The identification of potential factors associated with the development of type 2 diabetes: a quantitative proteomics approach. Mol Cell Proteomics 2008; 7:1434-51. [PMID: 18448419 DOI: 10.1074/mcp.m700478-mcp200] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Type 2 diabetes (T2D) arises when pancreatic beta-cells fail to compensate for systemic insulin resistance with appropriate insulin secretion. However, the link between insulin resistance and beta-cell failure in T2D is not fully understood. To explore this association, we studied transgenic MKR mice that initially develop insulin resistance in skeletal muscle but by 8 weeks of age have T2D. In the present study, global islet protein and gene expression changes were characterized in diabetic MKR versus non-diabetic control mice at 10 weeks of age. Using a quantitative proteomics approach (isobaric tags for relative and absolute quantification (iTRAQ)), 159 proteins were differentially expressed in MKR compared with control islets. Marked up-regulation of protein biosynthesis and endoplasmic reticulum stress pathways and parallel down-regulation in insulin processing/secretion, energy utilization, and metabolism were observed. A fraction of the differentially expressed proteins identified (including GLUT2, DNAJC3, VAMP2, RAB3A, and PC1/3) were linked previously to insulin-secretory defects and T2D. However, many proteins for the first time were associated with islet dysfunction, including the unfolded protein response proteins (ERP72, ERP44, ERP29, PPIB, FKBP2, FKBP11, and DNAJB11), endoplasmic reticulum-associated degradation proteins (VCP and UFM1), and multiple proteins associated with mitochondrial energy metabolism (NDUFA9, UQCRH, COX2, COX4I1, COX5A, ATP6V1B2, ATP6V1H, ANT1, ANT2, ETFA, and ETFB). The mRNA expression level corresponding to these proteins was examined by microarray, and then a small subset was validated using quantitative real time PCR and Western blot analyses. Importantly approximately 54% of differentially expressed proteins in MKR islets (including proteins involved in proinsulin processing, protein biosynthesis, and mitochondrial oxidation) showed changes in the proteome but not transcriptome, suggesting post-transcriptional regulation. These results underscore the importance of integrated mRNA and protein expression measurements and validate the use of the iTRAQ method combined with microarray to assess global protein and gene changes involved in the development of T2D.
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Affiliation(s)
- Hongfang Lu
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto M5S 1A8, Canada
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Gyulkhandanyan AV, Lu H, Lee SC, Bhattacharjee A, Wijesekara N, Fox JEM, MacDonald PE, Chimienti F, Dai FF, Wheeler MB. Investigation of transport mechanisms and regulation of intracellular Zn2+ in pancreatic alpha-cells. J Biol Chem 2008; 283:10184-97. [PMID: 18250168 DOI: 10.1074/jbc.m707005200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During insulin secretion, pancreatic alpha-cells are exposed to Zn(2+) released from insulin-containing secretory granules. Although maintenance of Zn(2+) homeostasis is critical for cell survival and glucagon secretion, very little is known about Zn(2+)-transporting pathways and the regulation of Zn(2+) in alpha-cells. To examine the effect of Zn(2+) on glucagon secretion and possible mechanisms controlling the intracellular Zn(2+) level ([Zn(2+)](i)), we employed a glucagon-producing cell line (alpha-TC6) and mouse islets where non-beta-cells were identified using islets expressing green fluorescent protein exclusively in beta-cells. In this study, we first confirmed that Zn(2+) treatment resulted in the inhibition of glucagon secretion in alpha-TC6 cells and mouse islets in vitro. The inhibition of secretion was not likely via activation of K(ATP) channels by Zn(2+). We then determined that Zn(2+) was transported into alpha-cells and was able to accumulate under both low and high glucose conditions, as well as upon depolarization of cells with KCl. The nonselective Ca(2+) channel blocker Gd(3+) partially inhibited Zn(2+) influx in alpha-TC cells, whereas the L-type voltage-gated Ca(2+) channel inhibitor nitrendipine failed to block Zn(2+) accumulation. To investigate Zn(2+) transport further, we profiled alpha-cells for Zn(2+) transporter transcripts from the two families that work in opposite directions, SLC39 (ZIP, Zrt/Irt-like protein) and SLC30 (ZnT, Zn(2+) transporter). We observed that Zip1, Zip10, and Zip14 were the most abundantly expressed Zips and ZnT4, ZnT5, and ZnT8 the dominant ZnTs. Because the redox state of cells is also a major regulator of [Zn(2+)](i), we examined the effects of oxidizing agents on Zn(2+) mobilization within alpha-cells. 2,2'-Dithiodipyridine (-SH group oxidant), menadione (superoxide generator), and SIN-1 (3-morpholinosydnonimine) (peroxynitrite generator) all increased [Zn(2+)](i) in alpha-cells. Together these results demonstrate that Zn(2+) inhibits glucagon secretion, and it is transported into alpha-cells in part through Ca(2+) channels. Zn(2+) transporters and the redox state also modulate [Zn(2+)](i).
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Abstract
Contracting skeletal muscle increases glucose uptake to sustain energy demand. This is achieved through a gain in GLUT4 at the membrane, but the traffic mechanisms and regulatory signals involved are unknown. Muscle contraction is elicited by membrane depolarization followed by a rise in cytosolic Ca2+ and actomyosin activation, drawing on ATP stores. It is unknown whether one or more of these events triggers the rise in surface GLUT4. Here, we investigate the effect of membrane depolarization on GLUT4 cycling using GLUT4myc-expressing L6 myotubes devoid of sarcomeres and thus unable to contract. K+-induced membrane depolarization elevated surface GLUT4myc, and this effect was additive to that of insulin, was not prevented by inhibiting phosphatidylinositol 3-kinase (PI3K) or actin polymerization, and did not involve Akt activation. Instead, depolarization elevated cytosolic Ca2+, and the surface GLUT4myc elevation was prevented by dantrolene (an inhibitor of Ca2+ release from sarcoplasmic reticulum) and by extracellular Ca2+ chelation. Ca2+-calmodulin-dependent protein kinase-II (CaMKII) was not phosphorylated after 10 min of K+ depolarization, and the CaMK inhibitor KN62 did not prevent the gain in surface GLUT4myc. Interestingly, although 5'-AMP-activated protein kinase (AMPK) was phosphorylated upon depolarization, lowering AMPKalpha via siRNA did not alter the surface GLUT4myc gain. Conversely, the latter response was abolished by the PKC inhibitors bisindolylmaleimide I and calphostin C. Unlike insulin, K+ depolarization caused only a small increase in GLUT4myc exocytosis and a major reduction in its endocytosis. We propose that K+ depolarization reduces GLUT4 internalization through signals and mechanisms distinct from those engaged by insulin. Such a pathway(s) is largely independent of PI3K, Akt, AMPK, and CaMKII but may involve PKC.
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Affiliation(s)
- Nadeeja Wijesekara
- Programme in Cell Biology, The Hospital for Sick Children, 555 University Ave., Toronto, ON, Canada M5G 1X8
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Wijesekara N, Konrad D, Eweida M, Jefferies C, Liadis N, Giacca A, Crackower M, Suzuki A, Mak TW, Kahn CR, Klip A, Woo M. Muscle-specific Pten deletion protects against insulin resistance and diabetes. Mol Cell Biol 2005; 25:1135-45. [PMID: 15657439 PMCID: PMC544010 DOI: 10.1128/mcb.25.3.1135-1145.2005] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Pten (phosphatase with tensin homology), a dual-specificity phosphatase, is a negative regulator of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. Pten regulates a vast array of biological functions including growth, metabolism, and longevity. Although the PI3K/Akt pathway is a key determinant of the insulin-dependent increase in glucose uptake into muscle and adipose cells, the contribution of this pathway in muscle to whole-body glucose homeostasis is unclear. Here we show that muscle-specific deletion of Pten protected mice from insulin resistance and diabetes caused by high-fat feeding. Deletion of muscle Pten resulted in enhanced insulin-stimulated 2-deoxyglucose uptake and Akt phosphorylation in soleus but, surprisingly, not in extensor digitorum longus muscle compared to littermate controls upon high-fat feeding, and these mice were spared from developing hyperinsulinemia and islet hyperplasia. Muscle Pten may be a potential target for treatment or prevention of insulin resistance and diabetes.
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Affiliation(s)
- Nadeeja Wijesekara
- Programme in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 2N9
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Rudich A, Konrad D, Török D, Ben-Romano R, Huang C, Niu W, Garg RR, Wijesekara N, Germinario RJ, Bilan PJ, Klip A. Indinavir uncovers different contributions of GLUT4 and GLUT1 towards glucose uptake in muscle and fat cells and tissues. Diabetologia 2003; 46:649-58. [PMID: 12712244 DOI: 10.1007/s00125-003-1080-1] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/28/2002] [Revised: 01/20/2003] [Indexed: 12/21/2022]
Abstract
AIMS/HYPOTHESIS Insulin-dependent glucose influx in skeletal muscle and adipocytes is believed to rely largely on GLUT4, but this has not been confirmed directly. We assessed the relative functional contribution of GLUT4 in experimental models of skeletal muscle and adipocytes using the HIV-1 protease inhibitor indinavir. METHODS Indinavir (up to 100 micro mol/l) was added to the glucose transport solution after insulin stimulation of wild-type L6 muscle cells, L6 cells over-expressing either GLUT4myc or GLUT1myc, 3T3-L1 adipocytes, isolated mouse brown or white adipocytes, and isolated mouse muscle preparations. RESULTS 100 micro mol/l indinavir inhibited 80% of both basal and insulin-stimulated 2-deoxyglucose uptake in L6GLUT4myc myotubes and myoblasts, but only 25% in L6GLUT1myc cells. Cell-surface density of glucose transporters was not affected. In isolated soleus and extensor digitorum longus muscles, primary white and brown adipocytes, insulin-stimulated glucose uptake was inhibited 70 to 80% by indinavir. The effect of indinavir on glucose uptake was variable in 3T3-L1 adipocytes, averaging 45% and 67% inhibition of basal and maximally insulin-stimulated glucose uptake, respectively. In this cell, fractional inhibition of glucose uptake by indinavir correlated positively with the fold-stimulation of glucose uptake by insulin, and was higher with sub-maximal insulin concentrations. The latter finding coincided with an increase only in GLUT4, but not GLUT1, in plasma membrane lawns. CONCLUSION/INTERPRETATION Indinavir is a useful tool to assess different functional contributions of GLUT4 to glucose uptake in common models of skeletal muscle and adipocytes.
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Affiliation(s)
- A Rudich
- Programme in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada
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