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Wyatt RC, Brigatti C, Liberati D, Grace SL, Gillard BT, Long AE, Marzinotto I, Shoemark DK, Chandler KA, Achenbach P, Gillespie KM, Piemonti L, Lampasona V, Williams AJK. The first 142 amino acids of glutamate decarboxylase do not contribute to epitopes recognized by autoantibodies associated with Type 1 diabetes. Diabet Med 2018; 35:954-963. [PMID: 29577424 DOI: 10.1111/dme.13628] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [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] [Accepted: 03/19/2018] [Indexed: 01/16/2023]
Abstract
AIMS Glutamate decarboxylase (GAD) antibodies are the most widely used predictive marker for Type 1 diabetes, but many individuals currently found to be GAD antibody-positive are unlikely to develop diabetes. We have shown previously that radioimmunoassays using N-terminally truncated 35 S-GAD65 (96-585) offer better disease specificity with similar sensitivity to full-length 35 S-GAD65 (1-585). To determine whether assay performance could be improved further, we evaluated a more radically truncated 35 S-GAD65 (143-585) radiolabel. METHODS Samples from people with recent-onset Type 1 diabetes (n = 157) and their first-degree relatives (n = 745) from the Bart's-Oxford family study of childhood diabetes were measured for GAD antibodies using 35 S-labelled GAD65 (143-585). These were screened previously using a local radioimmunoassay with 35 S-GAD65 (1-585). A subset was also tested by enzyme-linked immunosorbent assay (ELISA), which performs well in international workshops, but requires 10 times more serum. Results were compared with GAD antibody measurements using 35 S-GAD65 (1-585) and 35 S-GAD65 (96-585). RESULTS Sensitivity of GAD antibody measurement was maintained using 35 S-GAD65 (143-585) compared with 35 S-GAD65 (1-585) and 35 S-GAD65 (96-585). Specificity for Type 1 diabetes was improved compared with 35 S-GAD65 (1-585), but was similar to 35 S-GAD65 (96-585). Relatives found to be GAD antibody-positive using these truncated labels were at increased risk of diabetes progression within 15 years, compared with those positive for GAD(1-585) antibody only, and at similar risk to those found GAD antibody-positive by ELISA. CONCLUSIONS The first 142 amino acids of GAD65 do not contribute to epitopes recognized by Type 1 diabetes-associated GAD antibodies. Low-volume radioimmunoassays using N-terminally truncated 35 S-GAD65 are more specific than those using full-length GAD65 and offer practical alternatives to the GAD antibody ELISA for identifying children at increased risk of Type 1 diabetes.
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Affiliation(s)
- R C Wyatt
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
| | - C Brigatti
- Diabetes Research Institute, Milan, Italy
| | - D Liberati
- Division of Genetics and Cell Biology, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - S L Grace
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
| | - B T Gillard
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
| | - A E Long
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
| | | | - D K Shoemark
- School of Biochemistry, University of Bristol, Bristol, UK
| | - K A Chandler
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
| | - P Achenbach
- Institute of Diabetes Research, Helmholtz Zentrum München, and Forschergruppe Diabetes, Klinikum rechts der Isar, Technische Universität München, Neuherberg, Germany
| | - K M Gillespie
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
| | - L Piemonti
- Division of Genetics and Cell Biology, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - V Lampasona
- Division of Genetics and Cell Biology, IRCCS San Raffaele Scientific Institute, Milan, Italy
| | - A J K Williams
- Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK
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Greenwood MP, Greenwood M, Gillard BT, Loh SY, Paton JFR, Murphy D. Epigenetic Control of the Vasopressin Promoter Explains Physiological Ability to Regulate Vasopressin Transcription in Dehydration and Salt Loading States in the Rat. J Neuroendocrinol 2016; 28. [PMID: 26833868 PMCID: PMC4855680 DOI: 10.1111/jne.12371] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 01/06/2016] [Accepted: 01/23/2016] [Indexed: 02/06/2023]
Abstract
The synthesis of arginine vasopressin (AVP) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus is sensitive to increased plasma osmolality and a decreased blood volume, and thus is robustly increased by both dehydration (increased plasma osmolality and decreased blood volume) and salt loading (increased plasma osmolality). Both stimuli result in functional remodelling of the SON and PVN, a process referred to as functional-related plasticity. Such plastic changes in the brain have recently been associated with altered patterns of DNA methylation at CpG (cytosine-phosphate-guanine) residues, a process considered to be important for the regulation of gene transcription. In this regard, the proximal Avp promoter contains a number of CpG sites and is recognised as one of four CpG islands for the Avp gene, suggesting that methylation may be regulating Avp transcription. In the present study, we show that, in an immortalised hypothalamic cell line 4B, the proximal Avp promoter is highly methylated, and treatment of these cells with the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine to demethylate DNA dramatically increases basal and stimulated Avp biosynthesis. We report no changes in the expression of DNA methyltransferases, Dnmt1 and Dnmt3a, whereas there is decreased expression of the demethylating enzyme ten-eleven-translocation 2, Tet2, in the SON by dehydration and salt loading. We found higher methylation of the SON Avp promoter in dehydrated but not salt-loaded rats. By analysis of individual CpG sites, we observed hypomethylation, hypermethylation and no change in methylation of specific CpGs in the SON Avp promoter of the dehydrated rat. Using reporter gene assays, we show that mutation of individual CpGs can result in altered Avp promoter activity. We propose that methylation of the SON Avp promoter is necessary to co-ordinate the duel inputs of increased plasma osmolality and decreased blood volume on Avp transcription in the chronically dehydrated rat.
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Affiliation(s)
- M P Greenwood
- School of Clinical Sciences, University of Bristol, Bristol, UK
| | - M Greenwood
- School of Clinical Sciences, University of Bristol, Bristol, UK
| | - B T Gillard
- School of Clinical Sciences, University of Bristol, Bristol, UK
| | - S Y Loh
- Department of Physiology, University of Malaya, Kuala Lumpur, Malaysia
| | - J F R Paton
- School of Physiology and Pharmacology, University of Bristol, Bristol, UK
| | - D Murphy
- School of Clinical Sciences, University of Bristol, Bristol, UK
- Department of Physiology, University of Malaya, Kuala Lumpur, Malaysia
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