Structure-functional changes in eNAMPT at high concentrations mediate mouse and human beta cell dysfunction in type 2 diabetes.

Autor: Sayers SR; Diabetes Research Group, Department of Diabetes, School of Life Course Sciences, King's College London, Hodgkin Building, Guy's Campus, London, SE1 1UL, UK., Beavil RL; Protein Production Facility, Randall Centre for Cell and Molecular Biophysics, King's College London, London, UK., Fine NHF; Institute of Metabolism and Systems Research (IMSR), University of Birmingham, Birmingham, UK.; Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK.; Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, UK., Huang GC; Diabetes Research Group, Department of Diabetes, School of Life Course Sciences, King's College London, Hodgkin Building, Guy's Campus, London, SE1 1UL, UK., Choudhary P; Diabetes Research Group, Department of Diabetes, School of Life Course Sciences, King's College London, Hodgkin Building, Guy's Campus, London, SE1 1UL, UK., Pacholarz KJ; Michael Barber Centre for Collaborative Mass Spectrometry, School of Chemistry, Manchester Institute of Biotechnology, Manchester, UK., Barran PE; Michael Barber Centre for Collaborative Mass Spectrometry, School of Chemistry, Manchester Institute of Biotechnology, Manchester, UK., Butterworth S; Division of Pharmacy and Optometry, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK., Mills CE; Department of Nutritional Sciences, School of Life Course Sciences, King's College London, London, UK.; Nutrition Research Group, University of Reading, Reading, UK., Cruickshank JK; Department of Nutritional Sciences, School of Life Course Sciences, King's College London, London, UK., Silvestre MP; Human Nutrition Unit, School of Biological Sciences, University of Auckland, Auckland, New Zealand., Poppitt SD; Human Nutrition Unit, School of Biological Sciences, University of Auckland, Auckland, New Zealand., McGill AT; Human Nutrition Unit, School of Biological Sciences, University of Auckland, Auckland, New Zealand.; School of Health & Human Sciences, Southern Cross University, Lismore, NSW, Australia., Lavery GG; Institute of Metabolism and Systems Research (IMSR), University of Birmingham, Birmingham, UK.; Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK.; Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, UK., Hodson DJ; Institute of Metabolism and Systems Research (IMSR), University of Birmingham, Birmingham, UK.; Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK.; Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, UK., Caton PW; Diabetes Research Group, Department of Diabetes, School of Life Course Sciences, King's College London, Hodgkin Building, Guy's Campus, London, SE1 1UL, UK. paul.w.caton@kcl.ac.uk.; Department of Nutritional Sciences, School of Life Course Sciences, King's College London, London, UK. paul.w.caton@kcl.ac.uk.
Jazyk: angličtina
Zdroj: Diabetologia [Diabetologia] 2020 Feb; Vol. 63 (2), pp. 313-323. Date of Electronic Publication: 2019 Nov 15.
DOI: 10.1007/s00125-019-05029-y
Abstrakt: Aims/hypothesis: Progressive decline in functional beta cell mass is central to the development of type 2 diabetes. Elevated serum levels of extracellular nicotinamide phosphoribosyltransferase (eNAMPT) are associated with beta cell failure in type 2 diabetes and eNAMPT immuno-neutralisation improves glucose tolerance in mouse models of diabetes. Despite this, the effects of eNAMPT on functional beta cell mass are poorly elucidated, with some studies having separately reported beta cell-protective effects of eNAMPT. eNAMPT exists in structurally and functionally distinct monomeric and dimeric forms. Dimerisation is essential for the NAD-biosynthetic capacity of NAMPT. Monomeric eNAMPT does not possess NAD-biosynthetic capacity and may exert distinct NAD-independent effects. This study aimed to fully characterise the structure-functional effects of eNAMPT on pancreatic beta cell functional mass and to relate these to beta cell failure in type 2 diabetes.
Methods: CD-1 mice and serum from obese humans who were without diabetes, with impaired fasting glucose (IFG) or with type 2 diabetes (from the Body Fat, Surgery and Hormone [BodyFatS&H] study) or with or at risk of developing type 2 diabetes (from the VaSera trial) were used in this study. We generated recombinant wild-type and monomeric eNAMPT to explore the effects of eNAMPT on functional beta cell mass in isolated mouse and human islets. Beta cell function was determined by static and dynamic insulin secretion and intracellular calcium microfluorimetry. NAD-biosynthetic capacity of eNAMPT was assessed by colorimetric and fluorescent assays and by native mass spectrometry. Islet cell number was determined by immunohistochemical staining for insulin, glucagon and somatostatin, with islet apoptosis determined by caspase 3/7 activity. Markers of inflammation and beta cell identity were determined by quantitative reverse transcription PCR. Total, monomeric and dimeric eNAMPT and nicotinamide mononucleotide (NMN) were evaluated by ELISA, western blot and fluorometric assay using serum from non-diabetic, glucose intolerant and type 2 diabetic individuals.
Results: eNAMPT exerts bimodal and concentration- and structure-functional-dependent effects on beta cell functional mass. At low physiological concentrations (~1 ng/ml), as seen in serum from humans without diabetes, eNAMPT enhances beta cell function through NAD-dependent mechanisms, consistent with eNAMPT being present as a dimer. However, as eNAMPT concentrations rise to ~5 ng/ml, as in type 2 diabetes, eNAMPT begins to adopt a monomeric form and mediates beta cell dysfunction, reduced beta cell identity and number, increased alpha cell number and increased apoptosis, through NAD-independent proinflammatory mechanisms.
Conclusions/interpretation: We have characterised a novel mechanism of beta cell dysfunction in type 2 diabetes. At low physiological levels, eNAMPT exists in dimer form and maintains beta cell function and identity through NAD-dependent mechanisms. However, as eNAMPT levels rise, as in type 2 diabetes, structure-functional changes occur resulting in marked elevation of monomeric eNAMPT, which induces a diabetic phenotype in pancreatic islets. Strategies to selectively target monomeric eNAMPT could represent promising therapeutic strategies for the treatment of type 2 diabetes.
Databáze: MEDLINE
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