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Suba K, Patel Y, Martin-Alonso A, Hansen B, Xu X, Roberts A, Norton M, Chung P, Shrewsbury J, Kwok R, Kalogianni V, Chen S, Liu X, Kalyviotis K, Rutter GA, Jones B, Minnion J, Owen BM, Pantazis P, Distaso W, Drucker DJ, Tan TM, Bloom SR, Murphy KG, Salem V. Intra-islet glucagon signalling regulates beta-cell connectivity, first-phase insulin secretion and glucose homoeostasis. Mol Metab 2024; 85:101947. [PMID: 38677509 PMCID: PMC11177084 DOI: 10.1016/j.molmet.2024.101947] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 03/26/2024] [Accepted: 04/19/2024] [Indexed: 04/29/2024] Open
Abstract
OBJECTIVE Type 2 diabetes (T2D) is characterised by the loss of first-phase insulin secretion. We studied mice with β-cell selective loss of the glucagon receptor (Gcgrfl/fl X Ins-1Cre), to investigate the role of intra-islet glucagon receptor (GCGR) signalling on pan-islet [Ca2+]I activity and insulin secretion. METHODS Metabolic profiling was conducted on Gcgrβ-cell-/- and littermate controls. Crossing with GCaMP6f (STOP flox) animals further allowed for β-cell specific expression of a fluorescent calcium indicator. These islets were functionally imaged in vitro and in vivo. Wild-type mice were transplanted with islets expressing GCaMP6f in β-cells into the anterior eye chamber and placed on a high fat diet. Part of the cohort received a glucagon analogue (GCG-analogue) for 40 days and the control group were fed to achieve weight matching. Calcium imaging was performed regularly during the development of hyperglycaemia and in response to GCG-analogue treatment. RESULTS Gcgrβ-cell-/- mice exhibited higher glucose levels following intraperitoneal glucose challenge (control 12.7 mmol/L ± 0.6 vs. Gcgrβ-cell-/- 15.4 mmol/L ± 0.0 at 15 min, p = 0.002); fasting glycaemia was not different to controls. In vitro, Gcgrβ-cell-/- islets showed profound loss of pan-islet [Ca2+]I waves in response to glucose which was only partially rescued in vivo. Diet induced obesity and hyperglycaemia also resulted in a loss of co-ordinated [Ca2+]I waves in transplanted islets. This was reversed with GCG-analogue treatment, independently of weight-loss (n = 8). CONCLUSION These data provide novel evidence for the role of intra-islet GCGR signalling in sustaining synchronised [Ca2+]I waves and support a possible therapeutic role for glucagonergic agents to restore the insulin secretory capacity lost in T2D.
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Laurent D, Vinet L, Lamprianou S, Daval M, Filhoulaud G, Ktorza A, Wang H, Sewing S, Juretschke HP, Glombik H, Meda P, Boisgard R, Nguyen DL, Stasiuk GJ, Long NJ, Montet X, Hecht P, Kramer W, Rutter GA, Hecksher-Sørensen J. Pancreatic β-cell imaging in humans: fiction or option? Diabetes Obes Metab 2016; 18:6-15. [PMID: 26228188 DOI: 10.1111/dom.12544] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 07/02/2015] [Accepted: 07/28/2015] [Indexed: 01/02/2023]
Abstract
Diabetes mellitus is a growing worldwide epidemic disease, currently affecting 1 in 12 adults. Treatment of disease complications typically consumes ∼10% of healthcare budgets in developed societies. Whilst immune-mediated destruction of insulin-secreting pancreatic β cells is responsible for Type 1 diabetes, both the loss and dysfunction of these cells underly the more prevalent Type 2 diabetes. The establishment of robust drug development programmes aimed at β-cell restoration is still hampered by the absence of means to measure β-cell mass prospectively in vivo, an approach which would provide new opportunities for understanding disease mechanisms and ultimately assigning personalized treatments. In the present review, we describe the progress towards this goal achieved by the Innovative Medicines Initiative in Diabetes, a collaborative public-private consortium supported by the European Commission and by dedicated resources of pharmaceutical companies. We compare several of the available imaging methods and molecular targets and provide suggestions as to the likeliest to lead to tractable approaches. Furthermore, we discuss the simultaneous development of animal models that can be used to measure subtle changes in β-cell mass, a prerequisite for validating the clinical potential of the different imaging tracers.
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Broichhagen J, Frank JA, Johnston NR, Mitchell RK, Šmid K, Marchetti P, Bugliani M, Rutter GA, Trauner D, Hodson DJ. A red-shifted photochromic sulfonylurea for the remote control of pancreatic beta cell function. Chem Commun (Camb) 2015; 51:6018-21. [PMID: 25744824 DOI: 10.1039/c5cc01224d] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Azobenzene photoresponsive elements can be installed on sulfonylureas, yielding optical control over pancreatic beta cell function and insulin release. An obstacle to such photopharmacological approaches remains the use of ultraviolet-blue illumination. Herein, we synthesize and test a novel yellow light-activated sulfonylurea based on a heterocyclic azobenzene bearing a push-pull system.
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Rutter GA. Dorothy Hodgkin Lecture 2014. Understanding genes identified by genome-wide association studies for type 2 diabetes. Diabet Med 2014; 31:1480-7. [PMID: 25186316 DOI: 10.1111/dme.12579] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Accepted: 08/22/2014] [Indexed: 01/09/2023]
Abstract
Whilst the heritable nature of Type 2 diabetes has been recognized for many years, only in the past two decades have linkage analyses in families and genome-wide association studies in large populations begun to reveal the genetic landscape of the disease in detail. Whilst the former have provided a powerful means of identifying the genes responsible for monogenic forms of the disease, the latter highlight relatively large genomic regions. These often harbour multiple genes, whose relative contribution to exaggerated disease risk is uncertain. In the present study, the approaches that have been used to dissect the role of just a few (TCF7L2, SLC30A8, ADCY5, MTNR1B and CDKAL1) of the ~ 500 genes identified at dozens of implicated loci are described. These are usually selected based on the strength of their effect on disease risk, and predictions as to their likely biological role. Direct determination of the effects of identified polymorphisms on gene expression in disease-relevant tissues, notably the pancreatic islet, are then performed to identify genes whose expression is affected by a particular polymorphism. Subsequent functional analyses then involve perturbing gene expression in vitro in β-cell lines or isolated islets and in vivo in animal models. Although the majority of polymorphisms affect insulin production rather than action, and mainly affect the β cell, effects via other tissues may also contribute, requiring careful consideration in the design and interpretation of experiments in model systems. These considerations illustrate the scale of the task needed to exploit genome-wide association study data for the development of new therapeutic strategies.
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Pancholi J, Hodson DJ, Jobe K, Rutter GA, Goldup SM, Watkinson M. Biologically targeted probes for Zn 2+: a diversity oriented modular "click-S NAr-click" approach†Electronic supplementary information (ESI) available: Full experimental details including characterisation of all novel compounds can be found in the ESI. See DOI: 10.1039/c4sc01249f. Chem Sci 2014; 5:3528-3535. [PMID: 25580213 PMCID: PMC4285101 DOI: 10.1039/c4sc01249f] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 05/26/2014] [Indexed: 12/29/2022] Open
Abstract
We describe a one-pot strategy for the high yielding, operationally simple synthesis of fluorescent probes for Zn2+ that bear biological targeting groups and exemplify the utility of our method through the preparation of a small library of sensors. Investigation of the fluorescence behaviour of our library revealed that although all behaved as expected in MeCN, under biologically relevant conditions in HEPES buffer, a plasma membrane targeting sensor displayed a dramatic switch on response to excess Zn2+ as a result of aggregation phenomena. Excitingly, in cellulo studies in mouse pancreatic islets demonstrated that this readily available sensor was indeed localised to the exterior of the plasma membrane and clearly responded to the Zn2+ co-released when the pancreatic beta cells were stimulated to release insulin. Conversely, sensors that target intracellular compartments were unaffected. These results demonstrate that this sensor has the potential to allow the real time study of insulin release from living cells and exemplifies the utility of our simple synthetic approach.
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Locke JM, da Silva Xavier G, Dawe HR, Rutter GA, Harries LW. Increased expression of miR-187 in human islets from individuals with type 2 diabetes is associated with reduced glucose-stimulated insulin secretion. Diabetologia 2014; 57:122-8. [PMID: 24149837 PMCID: PMC3855472 DOI: 10.1007/s00125-013-3089-4] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Accepted: 10/04/2013] [Indexed: 02/07/2023]
Abstract
AIMS/HYPOTHESIS Type 2 diabetes is characterised by progressive beta cell dysfunction, with changes in gene expression playing a crucial role in its development. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and therefore alterations in miRNA levels may be involved in the deterioration of beta cell function. METHODS Global TaqMan arrays and individual TaqMan assays were used to measure islet miRNA expression in discovery (n = 20) and replication (n = 20) cohorts from individuals with and without type 2 diabetes. The role of specific dysregulated miRNAs in regulating insulin secretion, content and apoptosis was subsequently investigated in primary rat islets and INS-1 cells. Identification of miRNA targets was assessed using luciferase assays and by measuring mRNA levels. RESULTS In the discovery and replication cohorts miR-187 expression was found to be significantly increased in islets from individuals with type 2 diabetes compared with matched controls. An inverse correlation between miR-187 levels and glucose-stimulated insulin secretion (GSIS) was observed in islets from normoglycaemic donors. This correlation paralleled findings in primary rat islets and INS-1 cells where overexpression of miR-187 markedly decreased GSIS without affecting insulin content or apoptotic index. Finally, the gene encoding homeodomain-interacting protein kinase-3 (HIPK3), a known regulator of insulin secretion, was identified as a direct target of miR-187 and displayed reduced expression in islets from individuals with type 2 diabetes. CONCLUSIONS/INTERPRETATION Our findings suggest a role for miR-187 in the blunting of insulin secretion, potentially involving regulation of HIPK3, which occurs during the pathogenesis of type 2 diabetes.
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Pullen TJ, Rutter GA. When less is more: the forbidden fruits of gene repression in the adult β-cell. Diabetes Obes Metab 2013; 15:503-12. [PMID: 23121289 DOI: 10.1111/dom.12029] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Revised: 10/08/2012] [Accepted: 10/28/2012] [Indexed: 12/15/2022]
Abstract
Outside of the biological arena the term 'repression' often has a negative connotation. However, in the pancreatic β-cell a small group of genes, which are abundantly expressed in most if not all other mammalian tissues, are highly selectively repressed, with likely functional consequences. The two 'founder' members of this group, lactate dehydrogenase A (Ldha) and monocarboxylate transporter-1 (MCT-1/Slc16a1), are inactivated by multiple mechanisms including histone modifications and microRNA-mediated silencing. Their inactivation ensures that pyruvate and lactate, derived from muscle during exercise, do not stimulate insulin release inappropriately. Correspondingly, activating mutations in the MCT-1 promoter underlie 'exercise-induced hyperinsulinism' (EIHI) in man, a condition mimicked by forced over-expression of MCT-1 in the β-cell in mice. Furthermore, LDHA expression in the β-cell is upregulated in both human type 2 diabetes and in rodent models of the disease. Recent work by us and by others has identified a further ∼60 genes which are selectively inactivated in the β-cell, a list which we refine here up to seven by detailed comparison of the two studies. These genes include key regulators of cell proliferation and stimulus-secretion coupling. The present, and our earlier results, thus highlight the probable importance of shutting down a subset of 'disallowed' genes for the differentiated function of β-cells, and implicate previously unsuspected signalling pathways in the control of β-cell expansion and insulin secretion. Targeting of deregulated 'disallowed' genes in these cells may thus, in the future, provide new therapeutic avenues for type 2 diabetes.
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da Silva Xavier G, Mondragon A, Sun G, Chen L, McGinty JA, French PM, Rutter GA. Abnormal glucose tolerance and insulin secretion in pancreas-specific Tcf7l2-null mice. Diabetologia 2012; 55:2667-2676. [PMID: 22717537 PMCID: PMC6101215 DOI: 10.1007/s00125-012-2600-7] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Accepted: 05/04/2012] [Indexed: 12/15/2022]
Abstract
AIMS/HYPOTHESIS Individuals carrying type 2 diabetes risk alleles in TCF7L2 display decreased beta cell levels of T cell factor 7 like-2 (TCF7L2) immunoreactivity, and impaired insulin secretion and beta cell sensitivity to glucagon-like peptide 1 (GLP-1). Here, we sought to determine whether selective deletion of Tcf7l2 in mouse pancreas impairs insulin release and glucose homeostasis. METHODS Pancreas-specific Tcf7l2-null (pTcf7l2) mice were generated by crossing mice carrying conditional knockout alleles of Tcf7l2 (Tcf7l2-flox) with mice expressing Cre recombinase under the control of the Pdx1 promoter (Pdx1.Cre). Gene expression was assessed by real-time quantitative PCR and beta cell mass by optical projection tomography. Glucose tolerance, insulin secretion from isolated islets, and plasma insulin, glucagon and GLP-1 content were assessed by standard protocols. RESULTS From 12 weeks of age, pTcf7l2 mice displayed decreased oral glucose tolerance vs control littermates; from 20 weeks they had glucose intolerance upon administration of glucose by the intraperitoneal route. pTcf7l2 islets displayed impaired insulin secretion in response to 17 (vs 3.0) mmol/l glucose (54.6 ± 4.6%, p < 0.01) or to 17 mmol/l glucose plus 100 nmol/l GLP-1 (44.3 ± 4.9%, p < 0.01) compared with control islets. Glp1r (42 ± 0.08%, p < 0.01) and Ins2 (15.4 ± 4.6%, p < 0.01) expression was significantly lower in pTcf7l2 islets than in controls. Maintained on a high-fat (but not on a normal) diet, pTcf7l2 mice displayed decreased expansion of pancreatic beta cell volume vs control littermates. No differences were observed in plasma insulin, proinsulin, glucagon or GLP-1 concentrations. CONCLUSIONS/INTERPRETATION Selective deletion of Tcf7l2 in the pancreas replicates key aspects of the altered glucose homeostasis in human carriers of TCF7L2 risk alleles, indicating the direct role of this factor in controlling beta cell function.
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Locke JM, Da Silva Xavier G, Rutter GA, Harries LW. An alternative polyadenylation signal in TCF7L2 generates isoforms that inhibit T cell factor/lymphoid-enhancer factor (TCF/LEF)-dependent target genes. Diabetologia 2011; 54:3078-82. [PMID: 21913056 PMCID: PMC3210366 DOI: 10.1007/s00125-011-2290-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2011] [Accepted: 08/01/2011] [Indexed: 11/08/2022]
Abstract
AIMS/HYPOTHESIS Intronic single nucleotide polymorphisms within the transcription factor 7-like 2 (TCF7L2) gene are associated with risk of type 2 diabetes. It is widely hypothesised that the predisposing variation is involved in cis-regulation of TCF7L2 activity. The aim of this study was to seek evidence for the existence of novel TCF7L2 isoforms encoded within the type 2 diabetes-associated genomic region. METHODS We searched expressed sequence tag (EST) databases for novel TCF7L2 transcripts and sought to validate the function and integrity of any isoforms found using a combination of RT-PCR, western blotting and reporter gene techniques. RESULTS Analysis of EST databases suggested the presence of an alternative polyadenylation site located in intron 4 of TCF7L2. We used 3' rapid amplification of cDNA ends and real-time PCR to validate the integrity of this polyadenylation signal and show its wide use across human tissues. Western blotting results are consistent with the use of this polyadenylation signal to generate novel protein isoforms. The alternative polyadenylation signal results in the production of isoforms that retain the β-catenin binding domain but do not possess the high-mobility group box DNA-binding domain. Promoter-reporter gene assays suggest that these isoforms inhibit TCF7L2-dependent target genes by sequestering β-catenin. CONCLUSIONS/INTERPRETATION We have identified a novel polyadenylation signal within TCF7L2 that can result in the production of isoforms that act to repress TCF/LEF-dependent target genes. These findings may provide new insights into the association of TCF7L2 with susceptibility to type 2 diabetes.
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da Silva Xavier G, Farhan H, Kim H, Caxaria S, Johnson P, Hughes S, Bugliani M, Marselli L, Marchetti P, Birzele F, Sun G, Scharfmann R, Rutter J, Siniakowicz K, Weir G, Parker H, Reimann F, Gribble FM, Rutter GA. Per-arnt-sim (PAS) domain-containing protein kinase is downregulated in human islets in type 2 diabetes and regulates glucagon secretion. Diabetologia 2011; 54:819-27. [PMID: 21181396 PMCID: PMC3052475 DOI: 10.1007/s00125-010-2010-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2010] [Accepted: 11/12/2010] [Indexed: 10/27/2022]
Abstract
AIMS/HYPOTHESIS We assessed whether per-arnt-sim (PAS) domain-containing protein kinase (PASK) is involved in the regulation of glucagon secretion. METHODS mRNA levels were measured in islets by quantitative PCR and in pancreatic beta cells obtained by laser capture microdissection. Glucose tolerance, plasma hormone levels and islet hormone secretion were analysed in C57BL/6 Pask homozygote knockout mice (Pask-/-) and control littermates. Alpha-TC1-9 cells, human islets or cultured E13.5 rat pancreatic epithelia were transduced with anti-Pask or control small interfering RNAs, or with adenoviruses encoding enhanced green fluorescent protein or PASK. RESULTS PASK expression was significantly lower in islets from human type 2 diabetic than control participants. PASK mRNA was present in alpha and beta cells from mouse islets. In Pask-/- mice, fasted blood glucose and plasma glucagon levels were 25 ± 5% and 50 ± 8% (mean ± SE) higher, respectively, than in control mice. At inhibitory glucose concentrations (10 mmol/l), islets from Pask-/- mice secreted 2.04 ± 0.2-fold (p < 0.01) more glucagon and 2.63 ± 0.3-fold (p < 0.01) less insulin than wild-type islets. Glucose failed to inhibit glucagon secretion from PASK-depleted alpha-TC1-9 cells, whereas PASK overexpression inhibited glucagon secretion from these cells and human islets. Extracellular insulin (20 nmol/l) inhibited glucagon secretion from control and PASK-deficient alpha-TC1-9 cells. PASK-depleted alpha-TC1-9 cells and pancreatic embryonic explants displayed increased expression of the preproglucagon (Gcg) and AMP-activated protein kinase (AMPK)-alpha2 (Prkaa2) genes, implying a possible role for AMPK-alpha2 downstream of PASK in the control of glucagon gene expression and release. CONCLUSIONS/INTERPRETATION PASK is involved in the regulation of glucagon secretion by glucose and may be a useful target for the treatment of type 2 diabetes.
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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: 228] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [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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Rutter GA, Loder MK, Ravier MA. Rapid three-dimensional imaging of individual insulin release events by Nipkow disc confocal microscopy. Biochem Soc Trans 2007; 34:675-8. [PMID: 17052172 DOI: 10.1042/bst0340675] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Minute-to-minute control of the release of insulin by pancreatic beta-cells in response to glucose or other stimuli requires the precise delivery of large dense-core vesicles to the plasma membrane and regulated exocytosis. At present, the precise spatial organization at the cell surface and the nature of these events ('transient' versus 'full fusion') are debated. In order to monitor secretory events simultaneously over most of the surface of clusters of single MIN6 beta-cells, we have expressed recombinant neuropeptide Y-Venus (an enhanced and vesicle-targeted form of yellow fluorescent protein) as an insulin surrogate. Individual exocytotic events were monitored using Nipkow spinning disc confocal microscopy, with acquisition of a three-dimensional complete image (eight to twelve confocal slices) in <1 s, in response to cell depolarization. Corroborating earlier studies using TIRF (total internal reflection fluorescence) microscopy, this approach indicates that events occur with roughly equal probability over the entire cell surface, with only minimal clustering in individual areas, and provides no evidence for multiple events at the same site. Nipkow disc confocal imaging may thus provide a useful tool to determine whether event types occur at different sites at the cell surface and to explore the role of endocytic proteins including dynamin-1 and -2 in terminating individual exocytotic events.
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An R, da Silva Xavier G, Hao HX, Semplici F, Rutter J, Rutter GA. Regulation by Per-Arnt-Sim (PAS) kinase of pancreatic duodenal homeobox-1 nuclear import in pancreatic beta-cells. Biochem Soc Trans 2007; 34:791-3. [PMID: 17052199 DOI: 10.1042/bst0340791] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The transcription factor PDX-1 (pancreatic duodenal homeobox-1) is required for normal pancreatic development and for the function of insulin-producing islet beta-cells in mammals. We have shown previously that glucose regulates insulin gene expression in part through the activation and translocation of PDX-1 from the nuclear periphery to the nucleoplasm. We have also found that PASK [PAS (Per-Arnt-Sim) kinase], a member of the nutrient-regulated family of protein kinases, is activated in response to glucose challenge in beta-cells and is involved in the regulation of expression of PDX-1. Purified PASK efficiently phosphorylated recombinant PDX-1 in vitro on a single site (Thr-152). To determine the impact of phosphorylation at this site, we generated wild-type and mutant (T152A, T152D and T152E) forms of PDX-1 and examined the distribution of each of these in clonal MIN6 beta-cells by immunocytochemical analysis. Unexpectedly, only the T152D mutation significantly affected subcellular distribution, increasing the ratio of nuclear/cytosolic labelling at low and high glucose concentrations, suggesting that phosphorylation at Thr-152 inhibits nuclear uptake in response to glucose. Based on these results, experiments to examine the contribution of Thr-152 to the overall phosphorylation of PDX-1 in intact cells will be undertaken.
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Mountjoy PD, Bailey SJ, Rutter GA. Inhibition by glucose or leptin of hypothalamic neurons expressing neuropeptide Y requires changes in AMP-activated protein kinase activity. Diabetologia 2007; 50:168-77. [PMID: 17093945 DOI: 10.1007/s00125-006-0473-3] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2006] [Accepted: 09/04/2006] [Indexed: 12/31/2022]
Abstract
AIMS/HYPOTHESIS Changes in the activity of glucose-excited and glucose-inhibited neurons within the basomedial hypothalamus are key to the central regulation of satiety. However, the molecular mechanisms through which these cells respond to extracellular stimuli remain poorly understood. Here, we investigate the role of 5'-AMP-activated protein kinase (AMPK), a trimeric complex encoded by seven distinct genes of the PRKA family, in the responses to glucose and leptin of each cell type. METHODS The activity of isolated rat basomedial hypothalamic neurons was assessed by: (1) recording cellular voltage responses under current clamp; (2) measuring intracellular free Ca(2+) with fluo-3 or fura-2; and (3) developing a neuropeptide Y (NPY) promoter-driven adenovirally produced ratiometric 'pericam' (a green fluorescent protein-based Ca(2+) sensor) to monitor [Ca(2+)] changes selectively in NPY-positive neurons. RESULTS The stimulatory effects of decreased (0 or 1.0 vs 15 mmol/l) glucose on glucose-inhibited neurons were mimicked by the AMPK activator, 5-amino-imidazole-4-carboxamide riboside (AICAR) and blocked by the inhibitor Compound C. Similarly, AICAR reversed the inhibitory effects of leptin in the majority of glucose-inhibited neurons. The responses to glucose of Npy-expressing cells, which represented approximately 40 % of all glucose-inhibited neurons, were also sensitive to Compound C or AICAR. Forced changes in AMPK activity had no effect on glucose-excited and non-glucose-responsive neurons. CONCLUSIONS/INTERPRETATION Changes in AMPK activity are involved in the responses of glucose-inhibited neurons to large fluctuations in glucose concentration, and possibly also to leptin. This mechanism may contribute to the acute reduction of electrical activity and Ca(2+) oscillation frequency in these, but not other neurons, in the basomedial hypothalamus.
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Motakis ES, Nason GP, Fryzlewicz P, Rutter GA. Variance stabilization and normalization for one-color microarray data using a data-driven multiscale approach. Bioinformatics 2006; 22:2547-53. [PMID: 16877753 DOI: 10.1093/bioinformatics/btl412] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
MOTIVATION Many standard statistical techniques are effective on data that are normally distributed with constant variance. Microarray data typically violate these assumptions since they come from non-Gaussian distributions with a non-trivial mean-variance relationship. Several methods have been proposed that transform microarray data to stabilize variance and draw its distribution towards the Gaussian. Some methods, such as log or generalized log, rely on an underlying model for the data. Others, such as the spread-versus-level plot, do not. We propose an alternative data-driven multiscale approach, called the Data-Driven Haar-Fisz for microarrays (DDHFm) with replicates. DDHFm has the advantage of being 'distribution-free' in the sense that no parametric model for the underlying microarray data is required to be specified or estimated; hence, DDHFm can be applied very generally, not just to microarray data. RESULTS DDHFm achieves very good variance stabilization of microarray data with replicates and produces transformed intensities that are approximately normally distributed. Simulation studies show that it performs better than other existing methods. Application of DDHFm to real one-color cDNA data validates these results. AVAILABILITY The R package of the Data-Driven Haar-Fisz transform (DDHFm) for microarrays is available in Bioconductor and CRAN.
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Varadi A, Grant A, McCormack M, Nicolson T, Magistri M, Mitchell KJ, Halestrap AP, Yuan H, Schwappach B, Rutter GA. Intracellular ATP-sensitive K+ channels in mouse pancreatic beta cells: against a role in organelle cation homeostasis. Diabetologia 2006; 49:1567-77. [PMID: 16752175 DOI: 10.1007/s00125-006-0257-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Accepted: 02/28/2006] [Indexed: 11/30/2022]
Abstract
AIMS/HYPOTHESIS ATP-sensitive K(+) (K(ATP)) channels located on the beta cell plasma membrane play a critical role in regulating insulin secretion and are targets for the sulfonylurea class of antihyperglycaemic drugs. Recent reports suggest that these channels may also reside on insulin-containing dense-core vesicles and mitochondria. The aim of this study was to explore these possibilities and to test the hypothesis that vesicle-resident channels play a role in the control of organellar Ca(2+) concentration or pH. METHODS To quantify the subcellular distribution of the pore-forming subunit Kir6.2 and the sulfonylurea binding subunit SUR1 in isolated mouse islets and clonal pancreatic MIN6 beta cells, we used four complementary techniques: immunoelectron microscopy, density gradient fractionation, vesicle immunopurification and fluorescence-activated vesicle isolation. Intravesicular and mitochondrial concentrations of free Ca(2+) were measured in intact or digitonin-permeabilised MIN6 cells using recombinant, targeted aequorins, and intravesicular pH was measured with the recombinant fluorescent probe pHluorin. RESULTS SUR1 and Kir6.2 immunoreactivity were concentrated on dense-core vesicles and on vesicles plus the endoplasmic reticulum/Golgi network, respectively, in both islets and MIN6 cells. Reactivity to neither subunit was detected on mitochondria. Glibenclamide, tolbutamide and diazoxide all failed to affect Ca(2+) uptake into mitochondria, and K(ATP) channel regulators had no significant effect on intravesicular free Ca(2+) concentrations or vesicular pH. CONCLUSIONS/INTERPRETATION A significant proportion of Kir6.2 and SUR1 subunits reside on insulin-secretory vesicles and the distal secretory pathway in mouse beta cells but do not influence intravesicular ion homeostasis. We propose that dense-core vesicles may serve instead as sorting stations for the delivery of channels to the plasma membrane.
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Rutter GA, Varadi A, Tsuboi T, Parton L, Ravier M. Insulin secretion in health and disease: genomics, proteomics and single vesicle dynamics. Biochem Soc Trans 2006; 34:247-50. [PMID: 16545086 DOI: 10.1042/bst20060247] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Defective insulin secretion from pancreatic islet beta-cells is a sine qua non of Type II (non-insulin-dependent) diabetes. Digital imaging analysis of the nanomechanics of individual exocytotic events, achieved using total internal reflection fluorescence microscopy, has allowed us to demonstrate that insulin is released via transient or 'cavicapture' events whereby the vesicle and plasma membranes fuse transiently and reversibly. Such studies reveal that an increase in the number of abortive fusion events contributes to defective insulin secretion in in vitro models of Type II diabetes. Complementary analyses of genome-wide changes in beta-cell gene expression, at both the mRNA and protein levels, are now facilitating the identification of key molecular players whose altered expression may contribute to the secretory defects in the diabetic beta-cell.
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Rutter GA. Moving Ca2+ from the endoplasmic reticulum to mitochondria: is spatial intimacy enough? Biochem Soc Trans 2006; 34:351-5. [PMID: 16709159 DOI: 10.1042/bst0340351] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A number of studies in recent years have demonstrated that the ER (endoplasmic reticulum) makes intimate contacts with mitochondria, the latter organelles existing both as individual organelles and occasionally as a more extensive interconnected network. Demonstrations that mitochondria take up Ca2+ more avidly upon its mobilization from the ER than when delivered to permeabilized cells as a buffered solution also indicate that a shielded conduit for Ca2+ may exist between the two organelle types, perhaps comprising the inositol 1,4,5-trisphosphate receptor and mitochondrial outer membrane proteins including the VDAC (voltage-dependent anion channel). Although the existence of such intracellular ER–mitochondria ‘synapses’, or of an ER–mitochondria Ca2+ ‘translocon’, is an exciting idea, more definitive experiments are needed to test this possibility.
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Richards SK, Parton LE, Leclerc I, Rutter GA, Smith RM. Over-expression of AMP-activated protein kinase impairs pancreatic {beta}-cell function in vivo. J Endocrinol 2005; 187:225-35. [PMID: 16293770 DOI: 10.1677/joe.1.06413] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Treatment of type 1 diabetes by islet transplantation is currently limited by loss of functional beta-cell mass after transplantation. We investigated here whether adenovirus-mediated changes in AMP-activated protein kinase (AMPK) activity, previously shown to affect insulin secretion in vitro, might affect islet graft function in vivo. In isolated mouse and rat islets, insulin secretion stimulated by 17 (vs 3) mmol/l glucose was inhibited by 36.5% (P<0.01) and 43% (P<0.02) respectively after over-expression of constitutively-active AMPK- (AMPK CA) versus null (eGFP-expressing) viruses, and glucose oxidation was decreased by 38% (P<0.05) and 26.6% (P<0.05) respectively. Increases in apoptotic index (terminal deoxynucleotide transferase-mediated deoxyuridine trisphosphate biotin nick end-labelling) (TUNEL)) were also observed in AMPK CA- (22.8 +/- 3.6% TUNEL-positive cells, P<0.001), but not AMPK DN- (2.72 +/- 3.9%, positive cells, P=0.05) infected islets, versus null adenovirus-treated islets (0.68 +/- 0.36% positive cells). Correspondingly, transplantation of islets expressing AMPK CA into streptozotocin-diabetic C57 BL/6 mice improved glycaemic control less effectively than transplantation with either null (P<0.02) or AMPK-DN-infected (P<0.01) islets. We conclude that activation of AMPK inhibits beta-cell function in vivo and may represent a target for therapeutic intervention during islet transplantation.
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Rutter GA. Visualising insulin secretion. The Minkowski Lecture 2004. Diabetologia 2004; 47:1861-72. [PMID: 15551048 DOI: 10.1007/s00125-004-1541-1] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Accepted: 09/04/2004] [Indexed: 01/09/2023]
Abstract
Insulin secretion from pancreatic islet beta cells is a tightly regulated process, under the close control of blood glucose concentrations, neural inputs and circulating hormones. Defects in glucose-triggered insulin secretion, possibly exacerbated by a decrease in beta cell mass, are ultimately responsible for the development of type 2 diabetes. A full understanding of the mechanisms by which glucose and other nutrients trigger insulin secretion will probably be essential to allow for the development of new therapies of type 2 diabetes and for the derivation of "artificial" beta cells from embryonic stem cells as a treatment for type 1 diabetes. I focus here on recent developments in our understanding of beta cell glucose sensing, achieved in part through the development of recombinant targeted probes (luciferase, green fluorescent protein) that allow islet beta cell metabolism and Ca(2+) handling to be imaged in situ in the intact islet with single cell resolution. Combined with classical biochemistry, these techniques show that the beta cell is uniquely poised, thanks to the expression of low levels of lactate dehydrogenase and plasma membrane lactate/monocarboxylate transporters, to channel glucose carbons towards oxidative metabolism, ATP synthesis and inhibition of AMP-activated protein kinase, a newly defined regulator of insulin release. I also discuss the molecular basis of the recruitment of secretory vesicles to the cell surface, analysed by the use of new imaging techniques including total internal reflection of fluorescence, as well as the "nanomechanics" of the exocytotic event itself.
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Reimann F, Williams L, da Silva Xavier G, Rutter GA, Gribble FM. Glutamine potently stimulates glucagon-like peptide-1 secretion from GLUTag cells. Diabetologia 2004; 47:1592-601. [PMID: 15365617 DOI: 10.1007/s00125-004-1498-0] [Citation(s) in RCA: 188] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2004] [Accepted: 06/02/2004] [Indexed: 01/28/2023]
Abstract
AIMS/HYPOTHESIS Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are secreted from enteroendocrine L cells in response to nutrient ingestion. As glutamine is an important metabolic fuel for the gut, the aim of this study was to investigate the effect of glutamine on the GLP-1-secreting cell line, GLUTag. METHODS GLP-1 release was measured following incubation of GLUTag cells under a range of conditions. Single cells were studied by electrophysiology, calcium imaging and cytosolic ATP measurement using recombinant luciferase. RESULTS Glutamine was a more potent GLP-1 secretagogue than glucose or other amino acids, increasing GLP-1 release 7.1+/-0.7-fold ( n=19) at 10 mmol/l, with an estimated median effective concentration of between 0.1 and 1 mmol/l. Glutamine (10 mmol/l) induced a sodium-dependent inward current of 3.2+/-1.2 pA per cell ( n=9), which triggered membrane depolarisation and an increase in intracellular calcium. Asparagine and alanine produced electrophysiological and calcium changes that were at least as large as those caused by glutamine, but they were less effective GLP-1 secretagogues, suggesting that glutamine also potentiates secretion downstream of the calcium signal. This was confirmed by measuring secretion in the presence of 30 mmol/l KCl + diazoxide, or in alpha-haemolysin-permeabilised cells. Glutamine increased cytosolic ATP, but was less effective than glucose. CONCLUSIONS/INTERPRETATION Glutamine acts as a trigger and potentiator of GLP-1 release, consistent with its role as the major metabolic fuel for the gut. The results suggest that nutritional agents like glutamine might have beneficial effects in diabetes and obesity.
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Tsuboi T, Rutter GA. Insulin secretion by 'kiss-and-run' exocytosis in clonal pancreatic islet beta-cells. Biochem Soc Trans 2003; 31:833-6. [PMID: 12887316 DOI: 10.1042/bst0310833] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Exocytotic release of neuropeptides and hormones is generally believed to involve the complete merger of the secretory vesicle with the plasma membrane. However, recent data have suggested that 'kiss-and-run' mechanisms may also play a role. To analyse secretory events in neuroendocrine beta-cells, we imaged chimaeric reporters targeted to either the vesicle membrane [chimaeras of synaptobrevin-2 and pH-sensitive green fluorescent protein (synapto.pHluorin) or of phogrin (phosphatase on the granule of insulinoma) and enhanced green fluorescent protein (EGFP) (phogrin.EGFP)] or the lumen [neuropeptide Y (NPY).pH-insensitive yellow fluorescent protein (Venus)] by evanescent wave microscopy. Unexpectedly, the frequency of NPY.Venus release events was only 17-27% of that of vesicle fusion reported with synapto.pHluorin, but not phogrin.EGFP, indicating that exocytosis of cargo peptides that is likely to require complete collapse of the vesicle into the plasma membrane is relatively rare. However, both the frequency and the kinetics of NPY.Venus release were modulated by stimulus strength or by overexpression of synaptotagmin IV, demonstrating the plasticity of 'kiss-and-run' fusion.
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Varadi A, Ainscow EK, Allan VJ, Rutter GA. Molecular mechanisms involved in secretory vesicle recruitment to the plasma membrane in beta-cells. Biochem Soc Trans 2002; 30:328-332. [PMID: 12023874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Glucose stimulates the release of insulin in part by activating the recruitment of secretory vesicles to the cell surface. While this movement is known to be microtubule-dependent, the molecular motors involved are undefined. Active kinesin was found to be essential for vesicle translocation in live beta-cells, since microinjection of cDNA encoding dominant-negative KHC(mut) (motor domain of kinesin heavy chain containing a Thr(93)-->Asn point mutation) blocked vesicular movements. Moreover, expression of KHC(mut) strongly inhibited the sustained, but not acute, stimulation of secretion by glucose. Thus, vesicles released during the first phase of insulin secretion exist largely within a translocation-independent pool. Kinesin-driven anterograde movement of vesicles is then necessary for the sustained (second phase) of insulin release. Kinesin may, therefore, represent a novel target for increases in intracellular ATP concentrations in response to elevated extracellular glucose and may be involved in the ATP-sensitive K+channel-independent stimulation of secretion by the sugar.
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Porcelli AM, Pinton P, Ainscow EK, Chiesa A, Rugolo M, Rutter GA, Rizzuto R. Targeting of reporter molecules to mitochondria to measure calcium, ATP, and pH. Methods Cell Biol 2002; 65:353-80. [PMID: 11381603 DOI: 10.1016/s0091-679x(01)65021-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
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