Publications by authors named "Frances M Ashcroft"

155 Publications

The KCNJ11-E23K Gene Variant Hastens Diabetes Progression by Impairing Glucose-Induced Insulin Secretion.

Diabetes 2021 Feb 10. Epub 2021 Feb 10.

Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK.

The ATP-sensitive potassium (K) channel controls blood glucose levels by coupling glucose metabolism to insulin secretion in pancreatic beta cells. E23K, a common polymorphism in the pore-forming K channel subunit ( gene, has been linked to increased risk of type 2 diabetes. Understanding the risk-allele-specific pathogenesis has the potential to improve personalized diabetes treatment, but the underlying mechanism has remained elusive. Using a genetically engineered mouse model, we now show that the K23 variant impairs glucose-induced insulin secretion and increases diabetes risk when combined with a high fat diet (HFD) and obesity. K-channels in beta cells with two K23 risk alleles (KK) showed decreased ATP inhibition and the threshold for glucose-stimulated insulin secretion from KK islets was increased. Consequently, the insulin response to glucose and glycaemic control were impaired in KK mice on a standard diet. On a HFD, the effects of the KK genotype were exacerbated, accelerating diet-induced diabetes progression and causing beta cell failure. We conclude that the K23 variant increases diabetes risk by impairing insulin secretion at threshold glucose levels, thus accelerating loss of beta cell function in the early stages of diabetes progression.
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http://dx.doi.org/10.2337/db20-0691DOI Listing
February 2021

New insights into K channel gene mutations and neonatal diabetes mellitus.

Nat Rev Endocrinol 2020 07 6;16(7):378-393. Epub 2020 May 6.

Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.

The ATP-sensitive potassium channel (K channel) couples blood levels of glucose to insulin secretion from pancreatic β-cells. K channel closure triggers a cascade of events that results in insulin release. Metabolically generated changes in the intracellular concentrations of adenosine nucleotides are integral to this regulation, with ATP and ADP closing the channel and MgATP and MgADP increasing channel activity. Activating mutations in the genes encoding either of the two types of K channel subunit (Kir6.2 and SUR1) result in neonatal diabetes mellitus, whereas loss-of-function mutations cause hyperinsulinaemic hypoglycaemia of infancy. Sulfonylurea and glinide drugs, which bind to SUR1, close the channel through a pathway independent of ATP and are now the primary therapy for neonatal diabetes mellitus caused by mutations in the genes encoding K channel subunits. Insight into the molecular details of drug and nucleotide regulation of channel activity has been illuminated by cryo-electron microscopy structures that reveal the atomic-level organization of the K channel complex. Here we review how these structures aid our understanding of how the various mutations in the genes encoding Kir6.2 (KCNJ11) and SUR1 (ABCC8) lead to a reduction in ATP inhibition and thereby neonatal diabetes mellitus. We also provide an update on known mutations and sulfonylurea therapy in neonatal diabetes mellitus.
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http://dx.doi.org/10.1038/s41574-020-0351-yDOI Listing
July 2020

Nucleotide inhibition of the pancreatic ATP-sensitive K+ channel explored with patch-clamp fluorometry.

Elife 2020 Jan 7;9. Epub 2020 Jan 7.

Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.

Pancreatic ATP-sensitive K channels (K) comprise four inward rectifier subunits (Kir6.2), each associated with a sulphonylurea receptor (SUR1). ATP/ADP binding to Kir6.2 shuts K. Mg-nucleotide binding to SUR1 stimulates K. In the absence of Mg, SUR1 increases the apparent affinity for nucleotide inhibition at Kir6.2 by an unknown mechanism. We simultaneously measured channel currents and nucleotide binding to Kir6.2. Fits to combined data sets suggest that K closes with only one nucleotide molecule bound. A Kir6.2 mutation (C166S) that increases channel activity did not affect nucleotide binding, but greatly perturbed the ability of bound nucleotide to inhibit K. Mutations at position K205 in SUR1 affected both nucleotide affinity and the ability of bound nucleotide to inhibit K. This suggests a dual role for SUR1 in K inhibition, both in directly contributing to nucleotide binding and in stabilising the nucleotide-bound closed state.
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http://dx.doi.org/10.7554/eLife.52775DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7004565PMC
January 2020

Diabetes causes marked inhibition of mitochondrial metabolism in pancreatic β-cells.

Nat Commun 2019 06 6;10(1):2474. Epub 2019 Jun 6.

Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Oxford, OX1 3PT, UK.

Diabetes is a global health problem caused primarily by the inability of pancreatic β-cells to secrete adequate levels of insulin. The molecular mechanisms underlying the progressive failure of β-cells to respond to glucose in type-2 diabetes remain unresolved. Using a combination of transcriptomics and proteomics, we find significant dysregulation of major metabolic pathways in islets of diabetic βV59M mice, a non-obese, eulipidaemic diabetes model. Multiple genes/proteins involved in glycolysis/gluconeogenesis are upregulated, whereas those involved in oxidative phosphorylation are downregulated. In isolated islets, glucose-induced increases in NADH and ATP are impaired and both oxidative and glycolytic glucose metabolism are reduced. INS-1 β-cells cultured chronically at high glucose show similar changes in protein expression and reduced glucose-stimulated oxygen consumption: targeted metabolomics reveals impaired metabolism. These data indicate hyperglycaemia induces metabolic changes in β-cells that markedly reduce mitochondrial metabolism and ATP synthesis. We propose this underlies the progressive failure of β-cells in diabetes.
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http://dx.doi.org/10.1038/s41467-019-10189-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6554411PMC
June 2019

Low extracellular magnesium does not impair glucose-stimulated insulin secretion.

PLoS One 2019 4;14(6):e0217925. Epub 2019 Jun 4.

Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Centre, Nijmegen, The Netherlands.

There is an increasing amount of clinical evidence that hypomagnesemia (serum Mg2+ levels < 0.7 mmol/l) contributes to type 2 diabetes mellitus pathogenesis. Amongst other hypotheses, it has been suggested that Mg2+ deficiency affects insulin secretion. The aim of this study was, therefore, to investigate the acute effects of extracellular Mg2+ on glucose-stimulated insulin secretion in primary mouse islets of Langerhans and the rat insulinoma INS-1 cell line. Here we show that acute lowering of extracellular Mg2+ concentrations from 1.0 mM to 0.5 mM did not affect glucose-stimulated insulin secretion in islets or in insulin-secreting INS-1 cells. The expression of key genes in the insulin secretory pathway (e.g. Gck, Abcc8) was also unchanged in both experimental models. Knockdown of the most abundant Mg2+ channel Trpm7 by siRNAs in INS-1 cells resulted in a 3-fold increase in insulin secretion at stimulatory glucose conditions compared to mock-transfected cells. Our data suggest that insulin secretion is not affected by acute lowering of extracellular Mg2+ concentrations.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0217925PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548430PMC
February 2020

Correction to: Q&A: insulin secretion and type 2 diabetes: why do β-cells fail?

BMC Biol 2019 04 9;17(1):32. Epub 2019 Apr 9.

Department of Physiology, Anatomy & Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.

Upon publication of the original article [1], the authors noticed that they had accidently omitted to acknowledge funding from the European Research Council.
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http://dx.doi.org/10.1186/s12915-019-0650-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6456947PMC
April 2019

Insulin inhibits glucagon release by SGLT2-induced stimulation of somatostatin secretion.

Nat Commun 2019 01 11;10(1):139. Epub 2019 Jan 11.

Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK.

Hypoglycaemia (low plasma glucose) is a serious and potentially fatal complication of insulin-treated diabetes. In healthy individuals, hypoglycaemia triggers glucagon secretion, which restores normal plasma glucose levels by stimulation of hepatic glucose production. This counterregulatory mechanism is impaired in diabetes. Here we show in mice that therapeutic concentrations of insulin inhibit glucagon secretion by an indirect (paracrine) mechanism mediated by stimulation of intra-islet somatostatin release. Insulin's capacity to inhibit glucagon secretion is lost following genetic ablation of insulin receptors in the somatostatin-secreting δ-cells, when insulin-induced somatostatin secretion is suppressed by dapagliflozin (an inhibitor of sodium-glucose co-tranporter-2; SGLT2) or when the action of secreted somatostatin is prevented by somatostatin receptor (SSTR) antagonists. Administration of these compounds in vivo antagonises insulin's hypoglycaemic effect. We extend these data to isolated human islets. We propose that SSTR or SGLT2 antagonists should be considered as adjuncts to insulin in diabetes therapy.
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http://dx.doi.org/10.1038/s41467-018-08193-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6329806PMC
January 2019

Increased NEFA levels reduce blood Mg in hypertriacylglycerolaemic states via direct binding of NEFA to Mg.

Diabetologia 2019 02 13;62(2):311-321. Epub 2018 Nov 13.

Department of Physiology (286), Radboud Institute for Molecular Life Sciences, Radboud university medical center, P. O. Box 9101, 6500 HB, Nijmegen, the Netherlands.

Aims/hypothesis: The blood triacylglycerol level is one of the main determinants of blood Mg concentration in individuals with type 2 diabetes. Hypomagnesaemia (blood Mg concentration <0.7 mmol/l) has serious consequences as it increases the risk of developing type 2 diabetes and accelerates progression of the disease. This study aimed to determine the mechanism by which triacylglycerol levels affect blood Mg concentrations.

Methods: Using samples from 285 overweight individuals (BMI >27 kg/m) who participated in the 300-Obesity study (an observational cross-sectional cohort study, as part of the Human Functional Genetics Projects), we investigated the association between serum Mg with laboratory variables, including an extensive lipid profile. In a separate set of studies, hyperlipidaemia was induced in mice and in healthy humans via an oral lipid load, and blood Mg, triacylglycerol and NEFA concentrations were measured using colourimetric assays. In vitro, NEFAs harvested from albumin were added in increasing concentrations to several Mg-containing solutions to study the direct interaction between Mg and NEFAs.

Results: In the cohort of overweight individuals, serum Mg levels were inversely correlated with triacylglycerols incorporated in large VLDL particles (r = -0.159, p ≤ 0.01). After lipid loading, we observed a postprandial increase in plasma triacylglycerol and NEFA levels and a reciprocal reduction in blood Mg concentration both in mice (Δ plasma Mg -0.31 mmol/l at 4 h post oral gavage) and in healthy humans (Δ plasma Mg -0.07 mmol/l at 6 h post lipid intake). Further, in vitro experiments revealed that the decrease in plasma Mg may be explained by direct binding of Mg to NEFAs. Moreover, Mg was found to bind to albumin in a NEFA-dependent manner, evidenced by the fact that Mg did not bind to fatty-acid-free albumin. The NEFA-dependent reduction in the free Mg concentration was not affected by the presence of physiological concentrations of other cations.

Conclusions/interpretation: This study shows that elevated NEFA and triacylglycerol levels directly reduce blood Mg levels, in part explaining the high prevalence of hypomagnesaemia in metabolic disorders. We show that blood NEFA level affects the free Mg concentration, and therefore, our data challenge how the fractional excretion of Mg is calculated and interpreted in the clinic.
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http://dx.doi.org/10.1007/s00125-018-4771-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6323097PMC
February 2019

Dysregulation of Glucagon Secretion by Hyperglycemia-Induced Sodium-Dependent Reduction of ATP Production.

Cell Metab 2019 02 8;29(2):430-442.e4. Epub 2018 Nov 8.

Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK; Metabolic Research, Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Göteborg, Box 433, Göteborg 405 30, Sweden. Electronic address:

Diabetes is a bihormonal disorder resulting from combined insulin and glucagon secretion defects. Mice lacking fumarase (Fh1) in their β cells (Fh1βKO mice) develop progressive hyperglycemia and dysregulated glucagon secretion similar to that seen in diabetic patients (too much at high glucose and too little at low glucose). The glucagon secretion defects are corrected by low concentrations of tolbutamide and prevented by the sodium-glucose transport (SGLT) inhibitor phlorizin. These data link hyperglycemia, intracellular Na accumulation, and acidification to impaired mitochondrial metabolism, reduced ATP production, and dysregulated glucagon secretion. Protein succination, reflecting reduced activity of fumarase, is observed in α cells from hyperglycemic Fh1βKO and β-V59M gain-of-function K channel mice, diabetic Goto-Kakizaki rats, and patients with type 2 diabetes. Succination is also observed in renal tubular cells and cardiomyocytes from hyperglycemic Fh1βKO mice, suggesting that the model can be extended to other SGLT-expressing cells and may explain part of the spectrum of diabetic complications.
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http://dx.doi.org/10.1016/j.cmet.2018.10.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6370947PMC
February 2019

Role of the C-terminus of SUR in the differential regulation of β-cell and cardiac K channels by MgADP and metabolism.

J Physiol 2018 12 14;596(24):6205-6217. Epub 2018 Oct 14.

Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.

Key Points: β-Cell K channels are partially open in the absence of metabolic substrates, whereas cardiac K channels are closed. Using cloned channels heterologously expressed in Xenopus oocytes we measured the effect of MgADP on the MgATP concentration-inhibition curve immediately after patch excision. MgADP caused a far more striking reduction in ATP inhibition of Kir6.2/SUR1 channels than Kir6.2/SUR2A channels; this effect declined rapidly after patch excision. Exchanging the final 42 amino acids of SUR was sufficient to switch the Mg-nucleotide regulation of Kir6.2/SUR1 and Kir6.2/SUR2A channels, and partially switch their sensitivity to metabolic inhibition. Deletion of the C-terminal 42 residues of SUR abolished MgADP activation of both Kir6.2/SUR1 and Kir6.2/SUR2A channels. We conclude that the different metabolic sensitivity of Kir6.2/SUR1 and Kir6.2/SUR2A channels is at least partially due to their different regulation by Mg-nucleotides, which is determined by the final 42 amino acids.

Abstract: ATP-sensitive potassium (K ) channels couple the metabolic state of a cell to its electrical activity and play important physiological roles in many tissues. In contrast to β-cell (Kir6.2/SUR1) channels, which open when extracellular glucose levels fall, cardiac (Kir6.2/SUR2A) channels remain closed. This is due to differences in the SUR subunit rather than cell metabolism. As ATP inhibition and MgADP activation are similar for both types of channels, we investigated channel inhibition by MgATP in the presence of 100 μm MgADP immediately after patch excision [when the channel open probability (P ) is near maximal]. The results were strikingly different: 100 μm MgADP substantially reduced MgATP inhibition of Kir6.2/SUR1, but had no effect on MgATP inhibition of Kir6.2/SUR2A. Exchanging the final 42 residues of SUR2A with that of SUR1 switched the channel phenotype (and vice versa), and deleting this region abolished Mg-nucleotide activation. This suggests the C-terminal 42 residues are important for the ability of MgADP to influence ATP inhibition at Kir6.2. This region was also necessary, but not sufficient, for activation of the K channel in intact cells by metabolic inhibition (azide). We conclude that the ability of MgADP to impair ATP inhibition at Kir6.2 accounts, in part, for the differential metabolic sensitivities of β-cell and cardiac K channels.
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http://dx.doi.org/10.1113/JP276708DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6292810PMC
December 2018

Monitoring real-time hormone release kinetics via high-content 3-D imaging of compensatory endocytosis.

Lab Chip 2018 09;18(18):2838-2848

Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK. and Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford OX3 7LE, UK and Institute of Neuroscience of Physiology, Department of Physiology, Metabolic Research Unit, University of Göteborg, Box 430, SE-405 30 Göteborg, Sweden.

High-content real-time imaging of hormone secretion in tissues or cell populations is a challenging task, which is unlikely to be resolved directly, despite immense translational value. We approach this problem indirectly, using compensatory endocytosis, a process that closely follows exocytosis in the cell, as a surrogate read-out for secretion. The tissue is immobilized in an open-air perifusion chamber and imaged using a two-photon microscope. A fluorescent polar tracer, perifused through the experimental circuit, gets trapped into the cells via endocytosis, and is quantified using a feature-detection algorithm. The signal of the tracer that accumulates into the endocytotic system reliably reflects stimulated exocytosis, which is demonstrated via co-imaging of the latter using existing reporters. A high signal-to-noise ratio and compatibility with multisensor imaging affords the real-time quantification of the secretion at the tissue/population level, whereas the cumulative nature of the signal allows imprinting of the "secretory history" within each cell. The technology works for several cell types, reflects disease progression and can be used for human tissue.
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http://dx.doi.org/10.1039/c8lc00417jDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6250124PMC
September 2018

Magnesium deficiency prevents high-fat-diet-induced obesity in mice.

Diabetologia 2018 09 9;61(9):2030-2042. Epub 2018 Jul 9.

Department of Physiology (286), Radboud Institute for Molecular Life Sciences, Radboud university medical center, P. O. Box 9101, 6500 HB, Nijmegen, the Netherlands.

Aims/hypothesis: Hypomagnesaemia (blood Mg <0.7 mmol/l) is a common phenomenon in individuals with type 2 diabetes. However, it remains unknown how a low blood Mg concentration affects lipid and energy metabolism. Therefore, the importance of Mg in obesity and type 2 diabetes has been largely neglected to date. This study aims to determine the effects of hypomagnesaemia on energy homeostasis and lipid metabolism.

Methods: Mice (n = 12/group) were fed either a low-fat diet (LFD) or a high-fat diet (HFD) (10% or 60% of total energy) in combination with a normal- or low-Mg content (0.21% or 0.03% wt/wt) for 17 weeks. Metabolic cages were used to investigate food intake, energy expenditure and respiration. Blood and tissues were taken to study metabolic parameters and mRNA expression profiles, respectively.

Results: We show that low dietary Mg intake ameliorates HFD-induced obesity in mice (47.00 ± 1.53 g vs 38.62 ± 1.51 g in mice given a normal Mg-HFD and low Mg-HFD, respectively, p < 0.05). Consequently, fasting serum glucose levels decreased and insulin sensitivity improved in low Mg-HFD-fed mice. Moreover, HFD-induced liver steatosis was absent in the low Mg group. In hypomagnesaemic HFD-fed mice, mRNA expression of key lipolysis genes was increased in epididymal white adipose tissue (eWAT), corresponding to reduced lipid storage and high blood lipid levels. Low Mg-HFD-fed mice had increased brown adipose tissue (BAT) Ucp1 mRNA expression and a higher body temperature. No difference was observed in energy expenditure between the two HFD groups.

Conclusions/interpretation: Mg-deficiency abrogates HFD-induced obesity in mice through enhanced eWAT lipolysis and BAT activity.
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http://dx.doi.org/10.1007/s00125-018-4680-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6096631PMC
September 2018

Influences: Find a friend.

J Gen Physiol 2018 07 21;150(7):895-896. Epub 2018 Jun 21.

University of Oxford, Oxford, England, UK

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http://dx.doi.org/10.1085/jgp.201812123DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6028500PMC
July 2018

Binding of sulphonylureas to plasma proteins - A KATP channel perspective.

PLoS One 2018 17;13(5):e0197634. Epub 2018 May 17.

Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.

Sulphonylurea drugs stimulate insulin secretion from pancreatic β-cells primarily by inhibiting ATP sensitive potassium (KATP) channels in the β-cell membrane. The effective sulphonylurea concentration at its site of action is significantly attenuated by binding to serum albumin, which makes it difficult to compare in vitro and in vivo data. We therefore measured the ability of gliclazide and glibenclamide to inhibit KATP channels and stimulate insulin secretion in the presence of serum albumin. We used this data, together with estimates of free drug concentrations from binding studies, to predict the extent of sulphonylurea inhibition of KATP channels at therapeutic concentrations in vivo. KATP currents from mouse pancreatic β-cells and Xenopus oocytes were measured using the patch-clamp technique. Gliclazide and glibenclamide binding to human plasma were determined in spiked plasma samples using an ultrafiltration-mass spectrometry approach. Bovine serum albumin (60g/l) produced a mild, non-significant reduction of gliclazide block of KATP currents in pancreatic β-cells and Xenopus oocytes. In contrast, glibenclamide inhibition of recombinant KATP channels was dramatically suppressed by albumin (predicted free drug concentration <0.1%). Insulin secretion was also reduced. Free concentrations of gliclazide and glibenclamide in the presence of human plasma measured in binding experiments were 15% and 0.05%, respectively. Our data suggest the free concentration of glibenclamide in plasma is too low to account for the drug's therapeutic effect. In contrast, the free gliclazide concentration in plasma is high enough to close KATP channels and stimulate insulin secretion.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0197634PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5957440PMC
December 2018

Cardiac Dysfunction and Metabolic Inflexibility in a Mouse Model of Diabetes Without Dyslipidemia.

Diabetes 2018 06 2;67(6):1057-1067. Epub 2018 Apr 2.

Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Oxford, U.K.

Diabetes is a well-established risk factor for heart disease, leading to impaired cardiac function and a metabolic switch toward fatty acid usage. In this study, we investigated if hyperglycemia/hypoinsulinemia in the absence of dyslipidemia is sufficient to drive these changes and if they can be reversed by restoring euglycemia. Using the βV59M mouse model, in which diabetes can be rapidly induced and reversed, we show that stroke volume and cardiac output were reduced within 2 weeks of diabetes induction. Flux through pyruvate dehydrogenase was decreased, as measured in vivo by hyperpolarized [1-C]pyruvate MRS. Metabolomics showed accumulation of pyruvate, lactate, alanine, tricarboxyclic acid cycle metabolites, and branched-chain amino acids. Myristic and palmitoleic acid were decreased. Proteomics revealed proteins involved in fatty acid metabolism were increased, whereas those involved in glucose metabolism decreased. Western blotting showed enhanced pyruvate dehydrogenase kinase 4 (PDK4) and uncoupling protein 3 (UCP3) expression. Elevated PDK4 and UCP3 and reduced pyruvate usage were present 24 h after diabetes induction. The observed effects were independent of dyslipidemia, as mice showed no evidence of elevated serum triglycerides or lipid accumulation in peripheral organs (including the heart). The effects of diabetes were reversible, as glibenclamide therapy restored euglycemia, cardiac metabolism and function, and PDK4/UCP3 levels.
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http://dx.doi.org/10.2337/db17-1195DOI Listing
June 2018

Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men.

Physiol Rev 2018 01;98(1):117-214

Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.

The pancreatic β-cell plays a key role in glucose homeostasis by secreting insulin, the only hormone capable of lowering the blood glucose concentration. Impaired insulin secretion results in the chronic hyperglycemia that characterizes type 2 diabetes (T2DM), which currently afflicts >450 million people worldwide. The healthy β-cell acts as a glucose sensor matching its output to the circulating glucose concentration. It does so via metabolically induced changes in electrical activity, which culminate in an increase in the cytoplasmic Ca concentration and initiation of Ca-dependent exocytosis of insulin-containing secretory granules. Here, we review recent advances in our understanding of the β-cell transcriptome, electrical activity, and insulin exocytosis. We highlight salient differences between mouse and human β-cells, provide models of how the different ion channels contribute to their electrical activity and insulin secretion, and conclude by discussing how these processes become perturbed in T2DM.
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http://dx.doi.org/10.1152/physrev.00008.2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5866358PMC
January 2018

FTO demethylase activity is essential for normal bone growth and bone mineralization in mice.

Biochim Biophys Acta Mol Basis Dis 2018 Mar 2;1864(3):843-850. Epub 2017 Dec 2.

Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK. Electronic address:

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http://dx.doi.org/10.1016/j.bbadis.2017.11.027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5798602PMC
March 2018

Fumarate Hydratase Deletion in Pancreatic β Cells Leads to Progressive Diabetes.

Cell Rep 2017 Sep;20(13):3135-3148

Radcliffe Department of Medicine, OCDEM, Churchill Hospital, University of Oxford, Oxford OX3 7LE, UK; Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, 405 30 Göteborg, Sweden. Electronic address:

We explored the role of the Krebs cycle enzyme fumarate hydratase (FH) in glucose-stimulated insulin secretion (GSIS). Mice lacking Fh1 in pancreatic β cells (Fh1βKO mice) appear normal for 6-8 weeks but then develop progressive glucose intolerance and diabetes. Glucose tolerance is rescued by expression of mitochondrial or cytosolic FH but not by deletion of Hif1α or Nrf2. Progressive hyperglycemia in Fh1βKO mice led to dysregulated metabolism in β cells, a decrease in glucose-induced ATP production, electrical activity, cytoplasmic [Ca] elevation, and GSIS. Fh1 loss resulted in elevated intracellular fumarate, promoting succination of critical cysteines in GAPDH, GMPR, and PARK 7/DJ-1 and cytoplasmic acidification. Intracellular fumarate levels were increased in islets exposed to high glucose and in islets from human donors with type 2 diabetes (T2D). The impaired GSIS in islets from diabetic Fh1βKO mice was ameliorated after culture under normoglycemic conditions. These studies highlight the role of FH and dysregulated mitochondrial metabolism in T2D.
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http://dx.doi.org/10.1016/j.celrep.2017.08.093DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5637167PMC
September 2017

Is Type 2 Diabetes a Glycogen Storage Disease of Pancreatic β Cells?

Cell Metab 2017 Jul;26(1):17-23

Department of Physiology, Anatomy, and Genetics and OXION, University of Oxford, Parks Road, Oxford OX1 3PT, UK.

Elevated plasma glucose leads to pancreatic β cell dysfunction and death in type 2 diabetes. Glycogen accumulation, due to impaired metabolism, contributes to this "glucotoxicity" via dysregulated biochemical pathways promoting β cell dysfunction. Here, we review emerging data, and re-examine published findings, on the role of glycogen in β cells in normoglycemia and in diabetes.
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http://dx.doi.org/10.1016/j.cmet.2017.05.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5890904PMC
July 2017

An Nonsense Mutation Causing Neonatal Diabetes Through Altered Transcript Expression.

J Clin Res Pediatr Endocrinol 2017 Sep 30;9(3):260-264. Epub 2017 Jun 30.

University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom.

The pancreatic ATP-sensitive K+ (K-ATP) channel is a key regulator of insulin secretion. Gain-of-function mutations in the genes encoding the Kir6.2 (KCNJ11) and SUR1 (ABCC8) subunits of the channel cause neonatal diabetes, whilst loss-of-function mutations in these genes result in congenital hyperinsulinism. We report two patients with neonatal diabetes in whom we unexpectedly identified recessively inherited loss-of-function mutations. The aim of this study was to investigate how a homozygous nonsense mutation in ABCC8 could result in neonatal diabetes. The ABCC8 p.Glu747* was identified in two unrelated Vietnamese patients. This mutation is located within the in-frame exon 17 and RNA studies confirmed (a) the absence of full length SUR1 mRNA and (b) the presence of the alternatively spliced transcript lacking exon 17. Successful transfer of both patients to sulphonylurea treatment suggests that the altered transcript expression enhances the sensitivity of the K-ATP channel to Mg-ADP/ATP. This is the first report of an ABCC8 nonsense mutation causing a gain-of-channel function and these findings extend the spectrum of K-ATP channel mutations observed in patients with neonatal diabetes.
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http://dx.doi.org/10.4274/jcrpe.4624DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5596808PMC
September 2017

Functional identification of islet cell types by electrophysiological fingerprinting.

J R Soc Interface 2017 03;14(128)

Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK.

The α-, β- and δ-cells of the pancreatic islet exhibit different electrophysiological features. We used a large dataset of whole-cell patch-clamp recordings from cells in intact mouse islets ( = 288 recordings) to investigate whether it is possible to reliably identify cell type (α, β or δ) based on their electrophysiological characteristics. We quantified 15 electrophysiological variables in each recorded cell. Individually, none of the variables could reliably distinguish the cell types. We therefore constructed a logistic regression model that included all quantified variables, to determine whether they could together identify cell type. The model identified cell type with 94% accuracy. This model was applied to a dataset of cells recorded from hyperglycaemic βV59M mice; it correctly identified cell type in all cells and was able to distinguish cells that co-expressed insulin and glucagon. Based on this revised functional identification, we were able to improve conductance-based models of the electrical activity in α-cells and generate a model of δ-cell electrical activity. These new models could faithfully emulate α- and δ-cell electrical activity recorded experimentally.
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http://dx.doi.org/10.1098/rsif.2016.0999DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5378133PMC
March 2017

Neonatal Diabetes and the K Channel: From Mutation to Therapy.

Trends Endocrinol Metab 2017 05 3;28(5):377-387. Epub 2017 Mar 3.

Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, OX1 3PT, UK.

Activating mutations in one of the two subunits of the ATP-sensitive potassium (K) channel cause neonatal diabetes (ND). This may be either transient or permanent and, in approximately 20% of patients, is associated with neurodevelopmental delay. In most patients, switching from insulin to oral sulfonylurea therapy improves glycemic control and ameliorates some of the neurological disabilities. Here, we review how K channel mutations lead to the varied clinical phenotype, how sulfonylureas exert their therapeutic effects, and why their efficacy varies with individual mutations.
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http://dx.doi.org/10.1016/j.tem.2017.02.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5582192PMC
May 2017

Hyperglycaemia induces metabolic dysfunction and glycogen accumulation in pancreatic β-cells.

Nat Commun 2016 11 24;7:13496. Epub 2016 Nov 24.

Department of Physiology, Anatomy and Genetics and OXION, University of Oxford, Parks Road, Oxford OX1 3PT, UK.

Insulin secretion from pancreatic β-cells is impaired in all forms of diabetes. The resultant hyperglycaemia has deleterious effects on many tissues, including β-cells. Here we show that chronic hyperglycaemia impairs glucose metabolism and alters expression of metabolic genes in pancreatic islets. In a mouse model of human neonatal diabetes, hyperglycaemia results in marked glycogen accumulation, and increased apoptosis in β-cells. Sulphonylurea therapy rapidly normalizes blood glucose levels, dissipates glycogen stores, increases autophagy and restores β-cell metabolism. Insulin therapy has the same effect but with slower kinetics. Similar changes are observed in mice expressing an activating glucokinase mutation, in in vitro models of hyperglycaemia, and in islets from type-2 diabetic patients. Altered β-cell metabolism may underlie both the progressive impairment of insulin secretion and reduced β-cell mass in diabetes.
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http://dx.doi.org/10.1038/ncomms13496DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5123088PMC
November 2016

Pancreatic β-Cells Express the Fetal Islet Hormone Gastrin in Rodent and Human Diabetes.

Diabetes 2017 02 18;66(2):426-436. Epub 2016 Nov 18.

Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel

β-Cell failure in type 2 diabetes (T2D) was recently proposed to involve dedifferentiation of β-cells and ectopic expression of other islet hormones, including somatostatin and glucagon. Here we show that gastrin, a stomach hormone typically expressed in the pancreas only during embryogenesis, is expressed in islets of diabetic rodents and humans with T2D. Although gastrin in mice is expressed in insulin cells, gastrin expression in humans with T2D occurs in both insulin and somatostatin cells. Genetic lineage tracing in mice indicates that gastrin expression is turned on in a subset of differentiated β-cells after exposure to severe hyperglycemia. Gastrin expression in adult β-cells does not involve the endocrine progenitor cell regulator neurogenin3 but requires membrane depolarization, calcium influx, and calcineurin signaling. In vivo and in vitro experiments show that gastrin expression is rapidly eliminated upon exposure of β-cells to normal glucose levels. These results reveal the fetal hormone gastrin as a novel marker for reversible human β-cell reprogramming in diabetes.
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http://dx.doi.org/10.2337/db16-0641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5248995PMC
February 2017

Running out of time: the decline of channel activity and nucleotide activation in adenosine triphosphate-sensitive K-channels.

Philos Trans R Soc Lond B Biol Sci 2016 08;371(1700)

Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK

KATP channels act as key regulators of electrical excitability by coupling metabolic cues-mainly intracellular adenine nucleotide concentrations-to cellular potassium ion efflux. However, their study has been hindered by their rapid loss of activity in excised membrane patches (rundown), and by a second phenomenon, the decline of activation by Mg-nucleotides (DAMN). Degradation of PI(4,5)P2 and other phosphoinositides is the strongest candidate for the molecular cause of rundown. Broad evidence indicates that most other determinants of rundown (e.g. phosphorylation, intracellular calcium, channel mutations that affect rundown) also act by influencing KATP channel regulation by phosphoinositides. Unfortunately, experimental conditions that reproducibly prevent rundown have remained elusive, necessitating post hoc data compensation. Rundown is clearly distinct from DAMN. While the former is associated with pore-forming Kir6.2 subunits, DAMN is generally a slower process involving the regulatory sulfonylurea receptor (SUR) subunits. We speculate that it arises when SUR subunits enter non-physiological conformational states associated with the loss of SUR nucleotide-binding domain dimerization following prolonged exposure to nucleotide-free conditions. This review presents new information on both rundown and DAMN, summarizes our current understanding of these processes and considers their physiological roles.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.
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http://dx.doi.org/10.1098/rstb.2015.0426DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4938026PMC
August 2016

Neonatal diabetes caused by a homozygous KCNJ11 mutation demonstrates that tiny changes in ATP sensitivity markedly affect diabetes risk.

Diabetologia 2016 07 27;59(7):1430-1436. Epub 2016 Apr 27.

Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.

Aims/hypothesis: The pancreatic ATP-sensitive potassium (KATP) channel plays a pivotal role in linking beta cell metabolism to insulin secretion. Mutations in KATP channel genes can result in hypo- or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, respectively. To date, all patients affected by neonatal diabetes due to a mutation in the pore-forming subunit of the channel (Kir6.2, KCNJ11) are heterozygous for the mutation. Here, we report the first clinical case of neonatal diabetes caused by a homozygous KCNJ11 mutation.

Methods: A male patient was diagnosed with diabetes shortly after birth. At 5 months of age, genetic testing revealed he carried a homozygous KCNJ11 mutation, G324R, (Kir6.2-G324R) and he was successfully transferred to sulfonylurea therapy (0.2 mg kg(-1) day(-1)). Neither heterozygous parent was affected. Functional properties of wild-type, heterozygous and homozygous mutant KATP channels were examined after heterologous expression in Xenopus oocytes.

Results: Functional studies indicated that the Kir6.2-G324R mutation reduces the channel ATP sensitivity but that the difference in ATP inhibition between homozygous and heterozygous channels is remarkably small. Nevertheless, the homozygous patient developed neonatal diabetes, whereas the heterozygous parents were, and remain, unaffected. Kir6.2-G324R channels were fully shut by the sulfonylurea tolbutamide, which explains why the patient's diabetes was well controlled by sulfonylurea therapy.

Conclusions/interpretation: The data demonstrate that tiny changes in KATP channel activity can alter beta cell electrical activity and insulin secretion sufficiently to cause diabetes. They also aid our understanding of how the Kir6.2-E23K variant predisposes to type 2 diabetes.
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http://dx.doi.org/10.1007/s00125-016-3964-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4901145PMC
July 2016

Successful transfer to sulfonylureas in KCNJ11 neonatal diabetes is determined by the mutation and duration of diabetes.

Diabetologia 2016 06 31;59(6):1162-6. Epub 2016 Mar 31.

Department of Diabetes and Endocrinology, Royal Devon and Exeter NHS Foundation Trust, Exeter, UK.

Aims/hypothesis: The finding that patients with diabetes due to potassium channel mutations can transfer from insulin to sulfonylureas has revolutionised the management of patients with permanent neonatal diabetes. The extent to which the in vitro characteristics of the mutation can predict a successful transfer is not known. Our aim was to identify factors associated with successful transfer from insulin to sulfonylureas in patients with permanent neonatal diabetes due to mutations in KCNJ11 (which encodes the inwardly rectifying potassium channel Kir6.2).

Methods: We retrospectively analysed clinical data on 127 patients with neonatal diabetes due to KCNJ11 mutations who attempted to transfer to sulfonylureas. We considered transfer successful when patients completely discontinued insulin whilst on sulfonylureas. All unsuccessful transfers received ≥0.8 mg kg(-1) day(-1) glibenclamide (or the equivalent) for >4 weeks. The in vitro response of mutant Kir6.2/SUR1 channels to tolbutamide was assessed in Xenopus oocytes. For some specific mutations, not all individuals carrying the mutation were able to transfer successfully; we therefore investigated which clinical features could predict a successful transfer.

Results: In all, 112 out of 127 (88%) patients successfully transferred to sulfonylureas from insulin with an improvement in HbA1c from 8.2% (66 mmol/mol) on insulin, to 5.9% (41 mmol/mol) on sulphonylureas (p = 0.001). The in vitro response of the mutation to tolbutamide determined the likelihood of transfer: the extent of tolbutamide block was <63% for the p.C166Y, p.I296L, p.L164P or p.T293N mutations, and no patients with these mutations successfully transferred. However, most individuals with mutations for which tolbutamide block was >73% did transfer successfully. The few patients with these mutations who could not transfer had a longer duration of diabetes than those who transferred successfully (18.2 vs 3.4 years, p = 0.032). There was no difference in pre-transfer HbA1c (p = 0.87), weight-for-age z scores (SD score; p = 0.12) or sex (p = 0.17).

Conclusions/interpretation: Transfer from insulin is successful for most KCNJ11 patients and is best predicted by the in vitro response of the specific mutation and the duration of diabetes. Knowledge of the specific mutation and of diabetes duration can help predict whether successful transfer to sulfonylureas is likely. This result supports the early genetic testing and early treatment of patients with neonatal diabetes aged under 6 months.
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http://dx.doi.org/10.1007/s00125-016-3921-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4869695PMC
June 2016