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1
Flax, Helene. "Regulation of beta-cell secretion in man." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291075.
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Stokesberry, Susan Anne. "Functional effects of temperature on pancreatic beta-cell insulin secretion and integrity." Thesis, University of Ulster, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422895.
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Owen, R. A. "The role of transglutaminase in stimulus-secretion coupling in the pancreatic #beta#-cell." Thesis, Nottingham Trent University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384731.
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Eagle, Laurence Alfanso. "Regulation of Beta-cell tropin secretion from intermediate pituitary of lean and obese mice." Thesis, University of Buckingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601360.
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B-cell tropin (BCT) is a pro-opiomelanocortin-derived peptide which is released from the pituitary neurointermediate lobe (NIL) of rodents and other mammals. It has been shown to act as a potent insulin secretagogue, has lipogenic properties both in vitro and in vivo, and its sequence has been characterized as corresponding to ACTH22-39. Perifusate of NIL can be fractionated by reverse phase HPLC into two peaks, one containing CLIP (ACTH 18-39) -related, and the other BCT-related material. BCT levels have been found to be elevated in various obese/diabetic animal models, and this, coupled with the peptide's lipogenic properties, suggests that it may have a role in the obesity commonly associated with the human disease, type II diabetes. The aim of the work described in this thesis was to assess the factors controlling the release of BCT from the pituitary in the normal and obese diabetic state. The obese (oblob) mouse and its lean (+/+) counterpart were used as the animal models for these metabolic conditions.
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Heister, Paula Maria. "The role of two pore channels (TPCs) in pancreatic beta cell stimulus-secretion coupling." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:4bed27d2-e7e4-49ff-8168-aa02b6f9b613.
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This thesis presents an investigation into the role of the recently identified two pore channels (TPCs) in β-cell stimulus-secretion coupling. TPCs are the receptors for calcium mobilising messenger nicotinic acid adenine dinucleotide phosphate (NAADP) located in the membrane of acidic intracellular calcium stores. It is proposed that they are responsible for the ATP-sensitive potassium channel (Katp channel) independent pathway of stimulus-secretion coupling; and that this pathway is not subordinate to the KAT? channel dependent pathway; but an alternative explanation of stimulus-secretion coupling in its own right. The first section of this thesis presents a characterisation of sub-membrane cal- cium signals observed in primary mouse β-cells in response to glucose and the membrane-permeable acetoxymethyl ester form of NAADP (NAADP-AM) using the non-ratiometric fluorescent calcium indicator fluo-4 and total internal reflection (TIRF) microscopy. These are compared to global cytosolic calcium changes observed with epifluorescence microscopy. Factors affecting the shape and time course of re- sponses are investigated, and pharmacological tools used to provide evidence for the role of intracellular calcium release from acidic stores mediated by NAADP. Having characterised the calcium responses of β-cells using TIRF; the second part of the thesis examines the effects of knocking out TPC2 (single KO), or both TPC1 and TPC2 (DKO) on these responses; after an initial assessment of pancreatic islet and β-cell morphology using electron microscopy. Gender differences in β-cell responses to glucose and NAADP are assessed in both wild type and knockout animals. Finally, the third section presents the discovery of elementary calcium release events in pancreatic β-cells. The current project visualises what are likely the triggering events for the global calcium signals examined in sections one and two. They take the form of localised calcium release in response to NAADP-AM and glucose; akin to sparks and puffs observed by stimulation with cADPR and IP3. Optical quantal analysis demonstrates the quantal nature of the events and estimates the size of the unitary calcium release unit (CRU) for NAADP. .
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Castell, Auví Anna. "The effects of grape seed procyanidin extract on insulin synthesis and secretion." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/79133.
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Las procianidinas son compuestos bioactivos presentes en frutas y vegetales. Aunque se conocen los efectos beneficiosos de estos compuestos en la homeostasis de la glucosa, su acción en la funcionalidad de la célula β no es clara. La presente tesis doctoral se ha centrado en describir los efectos de las procianidinas en la síntesis y secreción de insulina. Nuestros resultados muestran la capacidad de las procianidinas de modificar la funcionalidad de la célula β aumentando la relación insulina plasmática/mRNA, aunque la efectividad del tratamiento depende de la situación fisiológica. En situaciones no patológicas, las procianidinas afectan la insulinemia modificando la síntesis, secreción y/o degradación de la insulina. En situaciones de resistencia a la insulina, el tratamiento crónico con procianidinas disminuye la síntesis y secreción de insulina gracias a su acción limitando el acúmulo de lípidos. En cambio, en un modelo más dañado (obesidad genética), las procianidinas ejercen efectos similares pero no son capaces de mejorar la hipersinulinemia. En conclusión, las procianidinas, en las dosis ensayadas, pueden utilizarse únicamente como compuestos bioactivos limitando la disfuncionalidad de la célula β en sus estados iniciales.Les procianidines són compostos bioactius presents en fruites i vegetals. Tot i que es coneixen els efectes beneficiosos d’aquests compostos en l’homeòstasi de la glucosa, la seva acció en la funcionalitat de la cèl•lulaβ no és clara. La present tesi doctoral s’ha centrat en descriureels efectes de les procianidines en la síntesi i secreció d’insulina. Els nostres resultats mostren la capacitat de les procianidines de modificar la funcionalitat de la cèl•lula β augmentant la relació insulina plasmàtica/mRNA, tot i que l’efectivitat del tractamentdepèn de la situaciófisiològica. En situacions no patològiques, les procianidines afecten la insulinèmia modificant la síntesi, secreciói/o degradació d’insulina. En situacions de resistència a la insulina, el tractamentcrònicamb procianidines disminueix la síntesi i secreció d’insulina gràcies a la seva acció limitant l’acumulació de lípids. En canvi, en un model més danyat (obesitat genètica), les procianidines exerceixen efectes similars però no son capaces de millorar la hiperinsulinèmia. En conclusió, les procianidines, en les dosis assajades, podenutilitzar-seúnicament coma compostos bioactiuslimitant la disfuncionalitat de la cèl•lula β en els seus estats inicials.
Procyanidins are bioactive compounds found in fruits and vegetables widely consumed. It has been reported that procyanidins show some beneficial effects on glucose homeostasis, although their effects on β-cell functionality remain unresolved. This doctoral thesis is focus on describing the effects of procyanidins on insulin synthesis and secretion. Our results showed that procyanidins modify β-cell functionality through increasing the plasma insulin/mRNA ratio, although the effectiveness of the treatment depends on the physiological situation. Under non-pathological situation, procyanidins affected insulinaemia by modifying insulin synthesis, secretion and/or degradation activity. Under insulin-resistance situation, chronic procyanidins administration decreased insulin synthesis and secretion, thanks to its lipid-lowering effect. Otherwise in a more damaged model, Zucker fatty rat, procyanidins treatment is not able to reduce insulin plasma levels although they repress insulin expression. In conclusion, procyanidins could be used as bioactive compound to limit β-cell dysfunctions under high-palatable diets, but at the assayed doses, it is not enough to counteract a strong metabolic disruption.
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Barutcu, Seda. "Role of JIP1-JNK Signaling in Beta-Cell Function and Autophagy." eScholarship@UMMS, 2018. https://escholarship.umassmed.edu/gsbs_diss/954.
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Proper functioning of endocrine cells is crucial for organismal homeostasis. The underlying mechanisms that fine-tune the amount, and the timing of hormone secretion are not clear. JIP1 / MAPK8IP1 (JNK interacting protein 1) is a scaffold protein that mediates cellular stress response, and is highly expressed in endocrine cells, including insulin secreting b-cells in pancreas islets. However, the role of JIP1 in b-cells is unclear. This study demonstrates that b-cell specific Jip1 ablation results in decreased glucose-induced insulin secretion, without a change in Insulin1 and Insulin2 gene expression. Inhibition of both JIP1-kinesin interaction, and JIP1-JNK interaction by genetic mutations also resulted in decreased insulin secretion, suggesting that JIP1 may mediate insulin vesicle trafficking through interacting with kinesin and JNK. Autophagy is a cellular recycling mechanism and implicated in the b-cell function. Both JIP1 and JNK are proposed to regulate autophagy pathway. However, it is unclear whether JNK plays a role in the promotion or suppression of autophagy. The findings of this study show that JNK is not essential for autophagy induction, but can regulate autophagy in a cell and context specific manner. The results in this thesis implies a mechanism that link cellular trafficking and stress signaling pathways in the regulated hormone secretion. In addition to the known role of JIP1 in metabolism and insulin resistance, this finding may also be relevant to endocrine pathologies.
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Turbitt, Julie Michelle. "The role of taurine in the regulation of insulin secretion and pancreatic beta-cell function." Thesis, University of Ulster, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422896.
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Idevall, Hagren Olof. "Oscillatory Signaling and Insulin Secretion from Single ß-cells." Doctoral thesis, Uppsala universitet, Institutionen för medicinsk cellbiologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-113686.
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cAMP and Ca2+ are key regulators of exocytosis in many cells, including insulin-secreting pancreatic β-cells. Glucose-stimulated insulin secretion from β-cells is pulsatile and driven by oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i), but little is known about the kinetics of cAMP signaling and the mechanisms of cAMP action. Evanescent wave microscopy and fluorescent translocation biosensors were used to monitor plasma membrane-related signaling events in single MIN6-cells and primary mouse β-cells. Glucose stimulation of insulin secretion resulted in pronounced oscillations of the membrane phospholipid PIP3 caused by autocrine activation of insulin receptors. Glucose also triggered oscillations of the sub-plasma membrane cAMP concentration ([cAMP]pm). These oscillations were preceded and enhanced by elevations of [Ca2+]i, but conditions raising cytoplasmic ATP triggered [cAMP]pm elevations without accompanying changes in [Ca2+]i. The [cAMP]pm oscillations were also synchronized with PIP3 oscillations and both signals were suppressed after inhibition of adenylyl cyclases. Protein kinase A (PKA) was important for promoting concomitant initial elevations of [cAMP]pm and [Ca2+]i, and PKA inhibitors diminished the PIP3 response when applied before glucose stimulation, but did not affect already manifested PIP3 oscillations. The glucose-induced PIP3 oscillations were markedly suppressed in cells treated with siRNA against the cAMP-dependent guanine nucleotide exchange factor Epac2. Pharmacological activation of Epac restored PIP3 responses after adenylyl cyclase or PKA inhibition. Glucose and other cAMP-elevating stimuli induced redistribution of fluorescence-tagged Epac2 from the cytoplasm to the plasma membrane. This translocation was modulated by [Ca2+]i and depended on intact cyclic nucleotide-binding and Ras-association domains. In conclusion, glucose generates cAMP oscillations in β-cells via a concerted action of Ca2+ and metabolically generated ATP. The oscillations are important for the magnitude and kinetics of insulin secretion. While both protein kinase A and Epac is required for initiation of insulin secretion the cAMP-dependence of established pulsatility is mediated by Epac2.
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Herrero, Rodríguez Laura. "Implication of Long-Chain Fatty Acids in Glucose-Induced Insulin Secretion in the Pancreatic Beta-Cell." Doctoral thesis, Universitat de Barcelona, 2004. http://hdl.handle.net/10803/2999.
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INTRODUCTION Carnitine palmitoyltransferase I, which is expressed in the pancreas as the liver isoform (LCPTI), catalyzes the rate-limiting step in the transport of fatty acids into the mitochondria for their oxidation. To directly examine whether the availability of long-chain fatty acyl-CoA affects the regulation of insulin secretion in the Beta-cell, we infected INS(832/13) cells and rat islets with an adenovirus encoding a mutant form of LCPTI (Ad-LCPTI M593S) that is insensitive to its inhibitor malonyl-CoA. C75 is described as a potential drug for treatment of obesity and type 2 diabetes. First known as a synthetic inhibitor of fatty acid synthase, it has been also described as an activator of CPTI, increasing peripheral energy utilization and fatty acid oxidation in mice. To further investigate the C75/CPTI interaction, we have characterized the effects of C75 on CPTI in vitro and in vivo.OBJECTIVES 1) Study of the malonyl-CoA/CPTI interaction in the pancreatic Beta-cell and its involvement in glucose-stimulated insulin secretion (GSIS). 2) Construction of an INS stable cell line overexpressing LCPTI wt and LCPTI M593S. 3) Determine the effect of C75 on the CPTI activity and palmitate oxidation in pancreatic Beta-cells.
RESULTS. In Ad-LCPTI M593S infected INS(832/13) cells LCPTI activity increased six-fold. This was associated with enhanced fatty acid oxidation, at any glucose concentration, and a 60% suppression of GSIS. In isolated rat islets in which LCPTI M593S was overexpressed, GSIS decreased 40%. At high glucose concentration, overexpression of LCPTI M593S reduced partitioning of exogenous palmitate into lipid esterification products, and decreased PKC activation. Moreover, LCPTI M593S expression impaired KATP channel-independent GSIS in INS(832/13) cells.
INS-1 stable clones of LCPTIwt and LCPTImut were constructed, however none of them resulted in an increase in LCPTI protein expression compared to endogenous LCPTI nor in CPTI activity. Therefore, slight basal overexpression of LCPTI could probably be toxic for the cells, as a result of which only those cells that do not contain the LCPTI plasmids survived throughout cell passages.
When INS(823/13) cells are incubated with C75, CPTI activity is inhibited, as is fatty acid oxidation. In vivo, a single intraperitoneal injection of C75 to mice produces a short-term inhibition of CPTI activity in mitochondria from liver and pancreas.
DISCUSSION. The results with LCPTImut provide direct support for the hypothesis proposing that the malonyl-CoA/CPTI interaction is a component of a metabolic signalling network that controls insulin secretion. Overall, the findings with C75 provide compelling evidence that the drug is a potent inhibitor of CPTI.
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Ng, Ming Tak. "Effects of prominsulin C-peptide and other islet peptides on beta-cell function and insulin secretion." Thesis, University of Ulster, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.554231.
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Hyperglycaemia is a significant pathophysiological feature of diabetes mellitus. It has been considered to be a cause as well as a consequence of impaired pancreatic p-cell function and insulin action. The detrimental effects of a hyperglycaemic environment encourage the non-enzymatic glycation of regulatory and functional proteins. This thesis investigated the effects of pro insulin C-peptide and other important islet peptides such as insulin, somatostatin, islet amyloid polypeptide (IAPP) as well as the gut hormone gastric inhibitory polypeptide (GIP) in both native and glycated forms on insulin release and beta cell function in vitro using clonal pancreatic p-ce1ls and isolated mouse islets and in vivo, using Swiss TO lean mice. Pancreatic beta-cells not only secrete insulin into the bloodstream, but also release equimolar amounts of C-peptide. During the last decade, studies have provided definite evidence of C-peptide's active role in physiology and pathophysiology. However very little information currently exists on the direct effects of C-peptide on pancreatic beta cells. This study provides evidence that C-peptide is a biologically active endogenous peptide hormone that exerts tonic inhibitory effects on pancreatic beta cell function and these effects may be partially mediated through intracellular signalling pathways. Suppression of insulin secretion by C-peptide was observed at basal and stimulatory glucose concentrations and was shown to be concentration dependent. The ability of alanine and IBMX to potentiate glucose-induced insulin secretion was severely impaired in the pancreatic cell line and isolated islets in the presence of C-peptide. This inhibition of glucose stimulated insulin secretion may be associated with the mechanism by which cAMP and KATP channel potentiates insulin release. In vivo studies with the administration of C-peptide resulted in a decrease in plasma insulin levels and increase in plasma glucose concentrations. As proinsulin C-peptide clearly exhibited an inhibitory effect on insulin secretion, it was of interest to study the autocrine effect of the other important pancreatic p-cell peptide, insulin. Concentration dependent inhibitory effects of insulin on alanine- and IBMX-stimulated insulin secretion were observed in isolated islets. Validation of this result was confirmed in vivo using Swiss TO mice, where plasma C-peptide levels were decreased following insulin administration. In mechanistic studies, insulin not only inhibited cAMP production at stimulatory glucose concentration, but also decreased GLP-1 and forskolin-stimulated cAMP production in clonal pancreatic cells. Moreover, insulin exerted a negative effect on insulin biosynthesis by decreasing the alanine-stimulated insulin mRNA expression at basal and stimulatory glucose concentration. As expected, inhibitory effects on insulin secretion were also observed for the pancreatic peptides, somatostatin-14 and IAPP whilst the gut incretin hormone GIP exerted insulinotropic activity. Following incubation with glucose in vitro, glycated forms of C-peptide, insulin, somatostain-14 and GIP were all readily detectable by reverse-phase HPLC and MALDI- TOF mass spectrometry. The extent of glycation was shown to be time and glucose concentration dependent. G Iycated human C-peptide exerted an inhibitory effect on insulin secretion, but to a lesser extent than non-glycated C-peptide. Glycated human C- peptide in the presence of alanine, GIP and tolbutamide resulted in 22%, 12% and 27% inhibition, respectively compared to 50%, 52% and 42% inhibition with native human C- peptide. A similar trend was obtained when comparing glycated human insulin and non- glycated human insulin. Suppression of alanine- and IBMX-stimulated C-peptide release was observed with glycated insulin. Glycated insulin reduced cAMP production at stimulatory glucose concentration, GLP-l and forskolin-stimulated cAMP production. Both glycated C-peptide and glycated insulin exhibited a less potent inhibitory effect on insulin secretion. Contrastingly, glycation of somatostatin-14 increased its ability to inhibit insulin secretion. Likewise, glycated GIP was more insulinotropic than its native peptide. These studies indicate that C-peptide may be one of several players in the multifactorial regulation of the pancreatic beta cell. Insulin secretion is an important physiological process which is regulated by multiple regulatory mechanisms. C-peptide may have a compensatory regulatory effect through the fine control of insulin release. Collectively, these studies indicate the need for continuing investigation of the circulating levels of glycated peptides and their effects on the ability to modulate insulin secretion. Further investigations are thus necessary to find out the possible role of glycated peptides in the pathophysiology of type 2 diabetes.
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Patterson, Steven. "Homocysteine and the effects of other amino thiols on pancreatic beta cell function and insulin secretion." Thesis, University of Ulster, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398994.
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Wang, Xuan. "Study of the Proliferation, Function and Death of Insulin-Producing Beta-Cells in vitro: Role of the Transcription Factor ZBED6." Doctoral thesis, Uppsala universitet, Institutionen för medicinsk cellbiologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-223616.
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A thorough understanding of beta-cell proliferation, function, death and regeneration under normal condition as well as in the progression of diabetes is crucial to the conquest of this disease. The work presented in this thesis aimed to investigate the expression and role of a novel transcription factor, Zinc finger BED domain-containing protein 6 (ZBED6), in beta-cells. ZBED6 was present in mouse βTC-6 cells and human islets as a double nuclear band at 115/120 kDa and as a single cytoplasmic band at 95-100 kDa, which lacked N-terminal nuclear localization signals. Lentiviral shRNA-mediated stable silencing of ZBED6 in βTC-6 cells resulted in altered morphology, decreased proliferation, a partial S/G2 cell cycle arrest, increased expression of beta-cell specific genes, and higher rates of apoptosis. ChIP sequencing of human islets showed that ZBED6 binding was preferentially to genes that control transcription, macromolecule biosynthesis and apoptosis. We proposed that ZBED6 supported proliferation and survival of beta-cells, possibly at the expense of specialized beta-cell function, i.e. insulin production. To further investigate the role of ZBED6 in beta-cells, ChIP sequencing and whole transcriptome analysis were performed using MIN6 cells. More than 4000 putative target genes of ZBED6 were identified, including Pdx1, MafA and Nkx6.1. ZBED6-silencing resulted in differential expression of more than 700 genes, which was paralleled by an increase in the content and release of insulin in response to a high glucose concentration. Altered morphology/growth patterns as indicated by increased cell clustering were observed in ZBED6 silenced cells. We found also that ZBED6 decreased the ratio between N- and E-cadherin. A lower N- to E-cadherin ratio may hamper the formation of three-dimensional beta-cell clusters and cell-to-cell junctions with neural crest stem cells, and instead promote efficient attachment to a laminin support and monolayer growth. Thus, by controlling beta-cell adhesion and cell-to-cell junctions, ZBED6 might play an important role in beta-cell differentiation, proliferation and survival.
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Bando, Mika. "Studies on pathophysiological significance of intraislet ghrelin using transgenic animal model." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188712.
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GRANCINI, VALERIA. "RUOLO CENTRALE DELLA BETA-CELLULA NEL PROMUOVERE LA REGRESSIONE DEL DIABETE DOPO TRAPIANTO DI FEGATO IN PAZIENTI CON CIRROSI EPATICA." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/658515.
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BACKGROUND & AIMS:
Diabetes occurring as a direct consequence of loss of liver function is usually characterized by non-diabetic fasting plasma glucose (FPG) and haemoglobin A1c (HbA1c) levels and should regress after orthotopic liver transplantation (OLT). This observational, longitudinal study investigated the relationship between the time-courses of changes in all 3 direct determinants of glucose regulation, i.e., β-cell function, insulin clearance and insulin sensitivity, and diabetes regression after OLT.
METHODS:
Eighty cirrhotic patients with non-diabetic FPG and HbA1c levels underwent an extended oral glucose tolerance test (OGTT) before and 3, 6, 12 and 24 months after OLT. The OGTT data were analysed with a mathematical model to estimate derivative control (DC) and proportional control (PC) of β-cell function and insulin clearance (which determine insulin bioavailability), and with the Oral Glucose Insulin Sensitivity (OGIS)-2 h index to estimate insulin sensitivity.
RESULTS:
At baseline, 36 patients were diabetic (45%) and 44 were non-diabetic (55%). Over the 2-year follow-up, 23 diabetic patients (63.9%) regressed to non-diabetic glucose regulation, whereas 13 did not (36.1%); moreover, 4 non-diabetic individuals progressed to diabetes (9.1%), whereas 40 did not (90.9%). Both DC and PC increased in regressors (from month 3 and 24, respectively) and decreased in progressors, whereas they remained stable in non-regressors and only PC decreased in non-progressors. Insulin clearance increased in all groups, apart from progressors. Likewise, OGIS-2 h improved at month 3 in all groups, but thereafter it continued to improve only in regressors, whereas it returned to baseline values in the other groups.
CONCLUSIONS:
Increased insulin bioavailability driven by improved β-cell function plays a central role in favouring diabetes regression after OLT, in the presence of a sustained improvement of insulin sensitivity.
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Otter, Silke [Verfasser], Eckhard [Akademischer Betreuer] Lammert, and Philipp A. [Gutachter] Lang. "Regulation of insulin secretion - Role of pancreatic NMDA receptors in beta cell function / Silke Otter. Betreuer: Eckhard Lammert. Gutachter: Philipp A. Lang." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2016. http://d-nb.info/1106380991/34.
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Santos, Gustavo Jorge 1986. "Memória metabólica de células beta pancreática controla a secreção de insulina e é mediada pela CaMKII = Metabolic memory of pancreatic beta cell controls insulin secretion and is mediated by CaMKII." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/313954.
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Orientadores: Antonio Carlos Boschiero, Luiz Fernando de RezendeTese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
Made available in DSpace on 2018-08-24T14:18:46Z (GMT). No. of bitstreams: 1 Santos_GustavoJorge_D.pdf: 3129731 bytes, checksum: b00bd77f6b06be14f135a76b6977ca47 (MD5) Previous issue date: 2014
Resumo: Introdução: A Cálcio-Calmodulina quinase II (CaMKII) atua tanto na regulação da secreção de insulina com de neurotransmissores pela mesma via de sinalização. Além disso, a CaMKII é conhecida por ser a "molécula da memória", pois sua atividade é fundamental em sua formação. Portanto, hipotetizamos que células ß pancreática tem a capacidade de adquirir e estocar informações contidas em pulsos de cálcio, formando uma memória metabólica. Métodos: Para comprovar nossa hipótese, desenvolvemos um novo paradigma de exposição de células ? a pulsos de 30 mM de glicose, seguido de uma período de consolidação (24 hrs) para excluir qualquer efeito agudo do metabolismo da glicose. Após esse período analizamos a secreção de insulina (RIA), expressão proteica (Western blot), a resposta secretória frente a uma "rampa de glicose" e o Ca2+ citoplasmático induzido por glicose. Resultados: Células ß expostas a pulsos de glicose (30 mM) mostraram maior secreção de insulina estimulada por glucose, evidenciando a memória metabólica a qual foi totalmente dependente a CaMKII. Esse fenômeno foi refletido na expressão proteica de proteínas importantes na sinalização do cálcio e na secreção de insulina. Além disso, células expostas ao regime de pulsos de glucose apresentaram maior expressão do MAFA, um fator de transcrição chave para a função da célula ß. Conclusão: Em suma, assim como neurônios, células ß tumorais (MIN6), ilhotas de camundongos e de humanos são capazes de adquirir, estocar e evocar informações
Abstract: Backgroun: Ca2+/calmodulin-dependent protein kinase II (CaMKII) functions both in regulation of insulin secretion and neurotransmitter release through common downstream mediators. Memory is the ability to acquire, to store and to evocate any kind of information. In CNS, the process behind this phenomenon in the Long-Term Potentiation (LTP) and is known that it requires Ca2+ to occur. In additional, CaMKII is necessary to store information during LTP. In pancreatic ß-cells, CaMKII plays pivotal role during GSIS process. Therefore, we hypothesized that pancreatic ß-cells acquire and store the information contained in Ca2+ pulses as a form of "metabolic memory", just as neurons store cognitive information. Methods: To test this hypothesis, we developed a novel paradigm of pulsed exposure of mice and human ß-cells to intervals of high glucose, followed by a 24-hour consolidation period to eliminate any acute metabolic effects. After this period, we analyzed insulin secretion (by RIA), protein expression (by Western blot), response to a glucose-ramp and the glucose-induced Ca2+ influx. Results: Strikingly, ß-cells exposed to this high-glucose pulse paradigm exhibited significantly stronger insulin secretion. This metabolic memory was entirely dependent on CaMKII. We also observed, in pulse group, an increase in Ca2+ influx induced by glucose. In additional, metabolic memory was reflected on the protein level by increased expression of proteins involved in GSIS and Ca2+-dependent vesicle secretion, such as GCK, Cav1.2, SNAP25, pCaMKII and pSynapsin. Finally, we observed in human islet elevated levels of the key ß cell transcription factor MAFA. Discussion: Based on or findings we conclude that pancreatic ß cells, either from mice or humans, have the ability to acquire, store and retrieve information. This process is CaMKII-dependent and is due to modifications in the glucose-sensing machinery of the cell, since we observed an increase in GSIS and Ca2+ influx together with an increase in several proteins involved in this process. Our findings suggests that MAFA is the key effector in this memory, since (a) it is a potent activator of insulin gene, (b)is activated by CaMKII and (c) its expression is increased even 24 hours after the last pulse. Conclusion: In summary, like neurons, human and mouse ß-cells are able to acquire and retrieve information
Doutorado
Fisiologia
Doutor em Biologia Funcional e Molecular
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Micheletto, Francesco. "A model of beta-cell response to GLP-1 to quantify incretin effect in healthy and prediabetic subjects." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3422996.
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Glucose regulation, in healthy subjects, relies on a complex control system that keeps blood glucose level within a narrow range around its basal value. Impairment of the glucose regulatory system is the cause of several metabolic derangements, including diabetes, which is characterized by chronic hyperglycemia which leads to severe micro and macro-vascular complications. Diabetes is generally classified into two categories, type 1 and type 2 diabetes. Both arise from complex interactions between genes and the environment, and are characterized by an absolute deficiency of insulin production (type 1) or a relative deficiency of the pancreas to produce insulin in amounts sufficient to meet the body needs (type 2). The prevalence of diabetes is increasing dramatically in populations of the world, and its global incidence has been increasing steadily in the past several years. Traditional medications for type 2 diabetes, including insulin, sulfonylureas, glitinides, acarbose, metformin, and thiazolidinediones, lower blood glucose through diverse mechanisms of action. However, many of the oral hypoglycemic agents lose their efficacy over time, resulting in progressive deterioration in β-cell function and loss of glycemic control due to progressive loss of β-cell mass. Consequently, there is an increasing interest in developing therapeutic agents that preserve or restore functional β-cells mass such as the incretin hormone Glucagon-Like Peptide-1 (GLP-1). It not only acutely lowers blood glucose by promoting insulin secretion and inhibiting glucagon release, but also engages signaling pathways in the islet β-cells that leads to stimulation of β-cells proliferation and neo-genesis and inhibition of β-cell apoptosis.
Impairment of insulin secretion and glucagon suppression suggests that decreased β-cells responsiveness to GLP-1 is part of the pathogenesis of type 2 diabetes. Thus the ability to measure the effect of GLP-1 on insulin secretion can be useful to understand the pathogenesis of type 2 diabetes. Moreover it can be employed to optimized GLP-1 based therapy by determining those individuals who may benefit more from such therapy. However, a mechanistic model enabling direct quantitation of pancreatic response to GLP-1 has never been developed.
In this contribution a mathematical model which describes the mechanism of GLP-1 action on insulin secretion is proposed. It provides a direct measure of the β-cells responsivity indexes to glucose and GLP-1. Three databases were used to develop, test and validate the model.
Data of 88 healthy individuals, who underwent a hyperglycemic clamp with a concomitant GLP-1 intravenous infusion, were used for model formulation. A set of models of increasing complexity describing GLP-1 action on insulin secretion were tested. All models share the common assumption that insulin secretion is made up of two components, one proportional to glucose rate of change through dynamic responsivity, Φd, and one proportional to glucose through static responsivity, Φs, but differ in the modality of GLP-1 control on β-cells. For each model potentiation index П was derived representing the percent increase in secretion due to 1 pmol/l of circulating GLP-1. All the models fit the data well, as confirmed by the run test, which supported randomness of residuals in 70% of the subjects and provide precise estimate of model parameters. Model selection was tackled using standard criteria (e.g. ability to describe the data, precision of parameter estimates, model parsimony, residual independence). The most parsimonious model in most subjects assumes that above-basal insulin secretion depends linearly on GLP-1 concentration and its rate of change.
However, the hyperglycemic clamp with concomitant intravenous infusion of GLP-1, is not physiological and easy to perfume in large scale studies. Thus data of 22 impairing fasting glucose (IFG) subjects, studied twice with a mixed meal, were used to test the model performance in a more physiological condition. We found that during an oral test, a simpler model is sufficient to describe the data.
Validation of the model was performed using both simulations and real data of 10 healthy subjects studied with an OGTT and matched intravenous glucose challenge (I-IVG). The protocol allows to calculate a model-independent index (PI) from the comparison of insulin secretion rate estimated in these two occasions. The comparison between model-derived Π and incretin potentiation index PI shows that they are very similar (П = 6.55, CV = 65%; PI = 6.15 % per pmol/l). In addition in silico validation proved the ability of the model to single out the effect of GLP-1 on insulin secretion since it correctly estimated П in the 93 ± 1% of the simulations.La regolazione della glicemia in soggetti sani, si basa su un complesso sistema di controllo che permette di mantenere il livello di glucosio nel sangue all’interno di un range ristretto che oscilla attorno al suo valore basale. Il mal funzionamento di tale sistema è la causa di patologie metaboliche, ad esempio il diabete. Questa patologia è caratterizzata da iperglicemia cronica che, se non curata, a lungo termine comporta gravi complicanze micro e marco vascolari. Il diabete è comunemente classificato in tipo 1 e tipo 2. Entrambi derivano da complesse interazioni tra ambente e geni, e sono caratterizzati da una totale mancanza di produzione di insulina, nel tipo 1, o da una carenza da parte del pancreas nel produrre insulina in quantità sufficiente per soddisfare le necessità dell’organismo, nel tipo 2. La prevalenza del diabete è in costante aumento in tutto il mondo, così come la sua incidenza è in costante crescita negli ultimi anni. I farmaci tradizionali per la terapia del diabete di tipo 2, come l’insulina, sulfaniluree, metformina e tiazolidinedioni, riducono la glicemia attraverso diversi meccanismi di azione. Tuttavia, molti degli agenti ipoglicemizzanti assunti per via orale, perdono di efficacia con il tempo causando un progressivo deterioramento della funzionalità e riduzione della massa delle β-cellule con conseguente riduzione del controllo glicemico. Di conseguenza vi è un crescente interesse nello sviluppo di nuovi agenti terapeutici che preservino la massa e ripristino la funzionalità delle β-cellule. Uno di questi è l’ormone Glucagon-Like Peptide-1 (GLP-1), che non solo riduce la glicemia aumentando la secrezione di insulina, ma agisce anche nel signaling nelle isole di Langherans stimolando la proliferazione e la neo-genesi delle β-cellule e inibendone l’apoptosi. La ridotta secrezione di insulina e la mancata soppressione del glucagone inducono ad ipotizzare che la diminuita risposata delle β-cellule al GLP-1 possa essere parte della patogenesi del diabete di tipo 2. Pertanto la capacità di misurare l’effetto del GLP-1 sulla secrezione dell’insulina è utile per studiare la patogenesi della malattia ed ottimizzare valutare l’efficacia delle terapie basate sul GLP-1. Infatti è cruciale determinare quali soggetti possono beneficiare maggiormente di tale terapia per ottimizzare le risorse. Tuttavia, non è ancora disponibile un modello che descriva l’azione del GLP-1 sulla secrezione di insulina e permetta di quantificarne l’entità. In questo lavoro viene proposto un modello matematico che descrive i meccanismi di azione del GLP-1 sulla secrezione di insulina, fornendo una misura diretta dell’aumento della secrezione dell’insulina dovuto all’effetto del GLP-1. Sono stati utilizzati tre database per sviluppare, testare e validare i modelli proposti. I dati di 88 soggetti sani sottoposti ad un clamp iperglicemico con contemporanea infusione intravenosa di GLP-1, sono stati utilizzati per lo sviluppo del modello. Sono stati testati una serie di modelli dell’azione del GLP-1 sulla secrezione di insulina di complessità crescente. Tutti i modelli si basano sulla comune assunzione che la secrezione di insulina è costituita da due componenti, una proporzionale alla concentrazione ed una alla velocità di variazione del glucosio plasmatico, modulate rispettivamente dalla responsività statica Φs e dalla responsività dinamica Φd. Ogni modello differisce dagli altri nella descrizione della modalità di azione del GLP-1. Per ciascun modello è stato derivato un indice di potenziamento, П, che rappresenta l’aumento percentuale della secrezione di insulina dovuta ad 1 pmol/l di GLP-1. I modelli predicono bene i dati (infatti il run test conferma la casualità dei residui nel 70% dei soggetti) e forniscono stime precise dei parametri . La selezione del modello ottimo è stata affrontata confrontando le prestazioni dei modelli sulla base di criteri standard (capacità di descrivere i dati, la precisione della stima dei parametri, la parsimonia, la casualità dei residui). Il modello più parsimonioso ipotizza che la secrezione sopra basale di insulina dipenda linearmente sia dalla concentrazione di GLP-1 sia dalla sua variazione. Tuttavia le condizioni sperimentali di tale protocollo non sono fisiologiche e applicabili su larga scala. Pertanto, i dati di 22 soggetti IFG (Impaired Fasting Glucose), studiati due volte con un pasto misto, sono stati utilizzati per testare il modello in una condizione sperimentale più vicina alla fisiologia. I risultati dimostrano che per descrivere i dati di un test orale, è sufficiente un modello più semplice. La validazione del modello è stata effettuata sia in simulazione sia utilizzando i dati reali di 10 soggetti, studiati due volte: una prima volta utilizzando un test orale di tolleranza al glucosio (OGTT) e successivamente un test intravenoso di tolleranza al glucosio durante il quale il glucosio è stato infuso in modo tale da riprodurre la glicemia osservata durante l’OGTT. Questo protocollo permette di calcolare un indice di potenziamento (PI) modello-indipendente dal confronto tra la secrezione di insulina stimata nelle due occasioni. Il confronto tra il potenziamento stimato con il modello, П, e l’indice di potenziamento PI mostra che i due indici sono molto simili (П = 6.55, CV = 65%; PI = 6.15 % per pmol/l). Inoltre nel 93 ± 1% delle simulazioni effettuate il modello è in grado di quantificare correttamente l’effetto del GLP-1 sulla secrezione di insulina.
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Cohrs, Christian M., Julia K. Panzer, Denise M. Drotar, Stephen J. Enos, Nicole Kipke, Chunguang Chen, Robert Bozsak, et al. "Dysfunction of Persisting β Cells Is a Key Feature of Early Type 2 Diabetes Pathogenesis." Elsevier, 2020. https://tud.qucosa.de/id/qucosa%3A73294.
Full textAbstract:
Type 2 diabetes is characterized by peripheral insulin resistance and insufficient insulin release from pancreatic islet β cells. However, the role and sequence of β cell dysfunction and mass loss for reduced insulin levels in type 2 diabetes pathogenesis are unclear. Here, we exploit freshly explanted pancreas specimens from metabolically phenotyped surgical patients using an in situ tissue slice technology. This approach allows assessment of β cell volume and function within pancreas samples of metabolically stratified individuals. We show that, in tissue of pre-diabetic, impaired glucose-tolerant subjects, β cell volume is unchanged, but function significantly deteriorates, exhibiting increased basal release and loss of first-phase insulin secretion. In individuals with type 2 diabetes, function within the sustained β cell volume further declines. These results indicate that dysfunction of persisting β cells is a key factor in the early development and progression of type 2 diabetes, representing a major target for diabetes prevention and therapy.
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Xie, Lanyi. "Population pharmacokinetic/pharmacodynamic modeling of insulin kinetics." Diss., University of Iowa, 2011. https://ir.uiowa.edu/etd/2791.
Full textAbstract:
The development of type 2 diabetes over time involves defects in insulin action and insulin secretion. Defects in insulin action alone can be compensated with appropriate hyperinsulinemia. However, the progressive loss of pancreatic beta-cell function leads eventually to the development of persistent hyperglycemia that characterizes type 2 diabetes. Insulin secretion patterns reflect two phases when beta-cells are exposed to acute and sustained glucose stimulation. Through the study and understanding of the roles of these two phases in the regulation of glucose homeostasis, it is clear that insulin must not only be secreted in sufficient amounts, but also at the right time. In type 2 diabetes, the timing and magnitude of insulin secretion are altered, and an abnormal first-phase release initiates before the onset of the disease. Only a few pharmacokinetic/pharmacodynamic (PK/PD) models have considered the biphasic nature of insulin secretion. This study is aimed at describing the biphasic dynamics of insulin secretion through developing a PK/PD model based on current knowledge of the cellular mechanism of biphasic insulin secretion.
The objectives of this work are to 1) evaluate the insulin-glucose kinetics using nonparametric analysis, 2) develop a physiologically based mechanistic PK/PD model to dynamically describe the biphasic insulin secretion, 3) evaluate the impact of ethnicity on insulin secretion kinetics following an intravenous glucose administration using population analysis and 4) extend the proposed model to oral glucose administration and utilize the co-secretion kinetics of insulin and C-peptide in a population PK/PD analysis of the prehepatic insulin secretion. Population analysis was done using a nonlinear mixed-effects model combined with the proposed PK/PD model to estimate population parameters and their variations between- and within-subjects and the covariates' effects on model parameters. The proposed model describes biphasic insulin behavior, accounts for first-phase insulin secretion, and also applies to oral glucose administration for estimating prehepatic insulin secretion in vivo and in liver extraction. This is done by an analysis that simultaneously uses plasma insulin and C-peptide concentrations. A significant higher first-phase insulin secretion was identified in healthy youths of African-American compared to Caucasians. The analysis showed no significant differences in the clearance of insulin from the plasma and the liver extraction of insulin between subjects with various levels of glucose tolerance. Obesity leads to a higher insulin production rate and lower elimination rate from the plasma than normal weight subjects. Also, type 2 diabetes and impaired glucose tolerance were found to reduce insulin production rate and resulted in a delayed insulin secretion from the beta-cells.
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Oliveira, Ricardo Beltrame de. "Proliferação e disfunção da célula beta pancreática em modelo animal de Diabetes Melito tipo 2. Envolvimento da via de sinalização WNT/Beta-Catenina." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/317134.
Full textAbstract:
Orientador: Carla Beatriz Collares BuzatoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Tem havido um grande interesse na determinação das vias envolvidas na proliferação e função/disfunção da célula beta e a aplicação deste conhecimento em terapias moleculares e celulares da diabetes. A patogênese da diabetes melito tipo 2 (T2DM) é complexa, mas frequentemente está associada com obesidade e distúrbios do metabolismo de lipídios (hipercolesterolemia e hipertrigliceridemia). A T2DM envolve o desenvolvimento de um quadro de resistência periférica à insulina parcialmente compensada por hiperinsulinemia e hiperplasia da célula beta pancreática, resultando em intolerância à glicose e hiperglicemia. Os mecanismos interligando os estados de obesidade/hipercolesterolemia e resistência à insulina ao fenômeno da hiperplasia da célula beta não são completamente conhecidos. A presente dissertação teve como objetivos: 1) caracterizar um modelo animal adequado para se estudar a proliferação e disfunção da célula beta pancreática, e 2) avaliar, no pâncreas endócrino desses animais, a possível ativação da via de sinalização Wnt/beta-catenina, conhecida por estar envolvida no processo de proliferação celular em outros tecidos/órgãos. Para tal, foram empregados camundongos C57BL/6, wild-type (WT) e knockout para receptor de lipoproteína LDL (LDLr-/-), os quais foram submetidos à dieta hiperlipídica (HF) por 60 dias. Após a dieta HF, os animais WT tornaram-se obesos e hipercolesterolêmicos, bem como moderadamente hiperglicêmicos, hiperinsulinêmicos, intolerantes à glicose e resistentes à insulina, caracterizando-os como pré-diabéticos. Além disso, os animais alimentados com dieta HF apresentaram uma diminuição significativa na resposta secretora das células beta à glicose. De modo geral, os animais LDLr-/- apresentaram uma susceptibilidade relativamente mais alta à dieta HF, sugerida pela acentuada hipercolesterolemia, intolerância à glicose, e reduzida secreção de insulina estimulada por glicose observadas nestes animais. No entanto, a dieta HF induziu, de forma semelhante em animais WT e LDLr-/-, uma diminuição significativa no conteúdo celular de Cx36, uma proteína associada à junção comunicante e um marcador de diferenciação terminal da célula beta. Ambos os grupos WT e LDLr-/- alimentados com dieta HF mostraram aumento na proliferação de células beta, como avaliada pela imunomarcação das ilhotas para a proteína Ki67, mas apenas os animais WT exibiram alterações morfométricas indicativas de hiperplasia do pâncreas endócrino, tais como aumento na massa total de ilhotas e de células beta. Uma vez estabelecido que camundongos WT alimentados com dieta HF por 60 dias consistiam em um modelo adequado para a segunda etapa deste estudo, fomos investigar a possível ativação da via Wnt/beta-catenina nas ilhotas pancreáticas desses animais, avaliando-se a distribuição e expressão celular das proteínas beta-catenina total, beta-catenina ativada, c-Myc e ciclina D. A análise por imunofluorescência para beta-catenina não mostrou acúmulo citoplasmático ou translocação para o núcleo desta proteína em ilhotas pancreáticas, que poderia indicar ativação da via Wnt/beta-catenina no nosso modelo de hiperplasia do pâncreas endócrino. No entanto, a análise por Western Blot revelou um aumento significativo na expressão de beta-catenina ativada e ciclina D em ilhotas de animais alimentados com dieta HF em relação ao grupo controle. Concluindo, a dieta HF por 60 dias induz alterações metabólicas típicas da pré-diabetes em animais WT e LDLr-/-. O estado de pré-diabetes está associado a uma diminuição da expressão de Cx36 nas células beta pancreáticas, sugerindo um possível papel da comunicação intercelular mediada pelas junções comunicantes na patogênese da T2DM. A maior susceptibilidade metabólica à dieta HF apresentada por camundongos LDLr-/-, em relação aos WT, pode ser explicada pela maior deficiência na secreção de insulina em resposta à glicose e ausência de hiperplasia compensatória do pâncreas endócrino. Ainda, a análise preliminar de expressão protéica de algumas proteínas da via Wnt/beta-catenina sugere que esta via parece estar ativada durante o processo de hiperplasia do pâncreas endócrino observada no nosso modelo animal
Abstract: The pathogenesis of type 2 diabetes mellitus (T2DM) is often associated with obesity and dyslipidemia (hypercholesterolemia and hypertriglyceridemia). T2DM involves intolerance to glucose and insulin resistance partially compensated by hyperinsulinemia and pancreatic beta cell hyperplasia. The mechanisms linking obesity/hypercholesterolemia and insulin resistance to beta cell hyperplasia are not fully known. The Wnt/beta-catenin signaling pathway has been reported to be involved in cell growth and differentiation in several tissues/organs but its role in endocrine pancreas development and function is still unclear. This work aimed at: 1) establishing an appropriate animal model of T2DM to study pancreatic beta cell proliferation and dysfunction and, 2) investigating a putative involvement of the Wnt/beta-catenin signaling pathway in the beta cell hyperplasia in this model. To this end, we employed C57BL/6 wild-type (WT) and LDL lipoprotein receptor knockout (LDLr-/-) mice, fed a high fat (HF) diet for 60 days. After feeding a HF diet, WT mice became obese, hypercholesterolemic and moderately hyperglycemic, hyperinsulinemic, glucose intolerant and insulin resistant, characterizing them as pre-diabetics. Moreover, animals fed a HF diet showed a significant decrease in beta-cell secretory response to glucose. In general, LDLr-/- animals showed a relatively higher susceptibility to HF diet, as suggested by a marked hypercholesterolemia, glucose intolerance and reduced insulin secretion stimulated by glucose observed in these animals as compared to the control ones. However, HF diet induced similarly in both WT and LDLr-/- mice a significant decrease in cellular content of Cx36, a gap junctional protein and marker of terminally differentiated beta cell. Both WT and LDLr-/- fed a HF diet showed increased proliferation of beta cells, as assessed by Ki67 immunostaining, but only WT mice exhibited morphometric changes indicative of endocrine pancreas hyperplasia, such as increased total islet and beta cell masses. After we investigated a possible activation of Wnt/beta-catenin signaling pathway in these hyperplasic pancreatic islets of WT animals fed a HF diet. This was done by assessing the distribution and cellular protein expression of some proteins associated to this pathway (i.e., total and activated beta-catenin, c-Myc and cyclin D) in islets of our animal model. Beta-catenin immunofluorescence showed no cytoplasmic accumulation or translocation into the nucleus of beta cells in HF-fed mice. However, immunoblotting revealed a significant increase of unphosphorylated beta-catenin (activated) and cyclin D expression in islets of HF diet-fed animals when compared to its control group. In conclusion, a HF diet for 60d induced pre-diabetes state in both WT and LDLr-/- mice. The pre-diabetes state is associated with a decreased expression of Cx36 in pancreatic beta cells, suggesting a possible role of intercellular communication mediated by gap junctions in the pathogenesis of T2DM. The relatively high metabolic susceptibility to the HF diet showed by LDLr-/- mice, as compared to WT, may be explained by a marked impairment of glucosestimulated insulin secretion and a lack of compensatory hyperplasia of the endocrine pancreas. In addition, the protein expression analysis suggests that the Wnt/beta-catenin pathway may be activated during the islet hyperplasia process in our animal model
Mestrado
Histologia
Mestre em Biologia Celular e Estrutural
22
Solimena, Michele, Anke M. Schulte, Lorella Marselli, Florian Ehehalt, Daniela Richter, Manuela Kleeberg, Hassan Mziaut, et al. "Systems biology of the IMIDIA biobank from organ donors and pancreatectomised patients defines a novel transcriptomic signature of islets from individuals with type 2 diabetes." Springer, 2017. https://tud.qucosa.de/id/qucosa%3A33350.
Full textAbstract:
Pancreatic islet beta cell failure causes type 2 diabetes in humans. To identify transcriptomic changes in type 2 diabetic islets, the Innovative Medicines Initiative for Diabetes: Improving beta-cell function and identification of diagnostic biomarkers for treatment monitoring in Diabetes (IMIDIA) consortium (www.imidia.org) established a comprehensive, unique multicentre biobank of human islets and pancreas tissues from organ donors and metabolically phenotyped pancreatectomised patients (PPP).
23
Tomita, Tsutomu. "Expression of the gene for a membrane-bound fatty acid receptor in the pancreas and islet cell tumours in humans : evidence for GPR40 expression in pancreatic beta cells and implications for insulin secretion." Kyoto University, 2006. http://hdl.handle.net/2433/135624.
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Santos-Silva, Junia Carolina Rebelo 1983. "Expressão e distribuição celular de proteínas associadas às junções intercelulares no pâncreas endócrino durante o desenvolvimento animal e na diabetes tipo 2." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/317145.
Full textAbstract:
Orientador: Carla Beatriz Collares-BuzatoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: As junções intercelulares são especializações da membrana plasmática através das quais células dentro de um tecido podem interagir e aderirem-se umas às outras. Nas ilhotas pancreáticas, as diferentes células endócrinas se interconectam por meio das junções de oclusão, comunicante, aderente e desmossomos. Tais contatos intercelulares parecem ser cruciais para o perfeito funcionamento deste órgão, porém, pouco se sabe sobre a função fisiopatológica e composição das junções intercelulares no pâncreas endócrino. O objetivo geral desta dissertação foi estudar a importância funcional da adesão e reconhecimento celular mediados pelas junções de oclusão (JO) e de adesão (JA) nos processos de maturação e disfunção da célula beta do pâncreas endócrino, ao longo do desenvolvimento do animal e na patogênese da diabetes tipo 2, respectivamente. Nossos dados mostram que as ilhotas de fetos e recém-nascidos de ratos Wistar, cuja resposta secretora de insulina à glicose é significativamente menor, apresentam uma morfologia menos organizada, caracterizada por um formato menos definido e uma associação mais freqüente com ductos, quando comparadas às ilhotas de jovens e adultos, que são responsivas à esse secretagogo. Na ausência de contato intercelular, quando as células das ilhotas de adultos foram dispersas, a resposta secretora de insulina foi completamente inibida, porém parcialmente restabelecida quando as células foram reagregadas. Quando comparado às ilhotas de adultos, o impacto da ausência de contatos intercelulares sobre a resposta secretora de insulina à glicose foi consideravelmente menor no caso das ilhotas de ratos recém-nascidos. A imunofluorescência para NCAM e pan-caderina revelou uma distribuição diferencial destas moléculas de adesão somente nas células das ilhotas pancreáticas de jovens e adultos, o que pode estar relacionada com a citoarquitetura típica (células beta, ocupando a região central e os outros tipos celulares na periferia da ilhota) adquirida no período pré-natal. Das proteínas associadas à JA e JO estudadas, ?- e ?-cateninas e ZO-1 (mas não a ocludina) foram expressas nas células endócrinas das ilhotas de todos os grupos experimentais. De forma geral, a imunofluorescência para tais proteínas revelou uma marcação intercelular menos definida nas células beta de ilhotas de recém-nascidos e fetos em comparação com os animais jovens e adultos. Isto pode indicar uma menor interação/adesão celular, que por sua vez, pode estar relacionada com a resposta secretora deficitária de insulina das ilhotas pancreáticas verificada na fase perinatal. Como modelo de diabetes do tipo 2, utilizamos camundongos C57, machos, alimentados com dieta hiperlipídica por 8 meses desde os 21 dias de idade. Após este período em dieta, os animais tornaram-se obesos e pré-diabéticos, apresentando moderada hiperglicemia e significativa hiperinsulinemia ao final desta dieta. Não observamos diferenças morfológicas marcantes entre os grupos e nem alterações significativas na distribuição intercelular da ZO-1, ?- e ?-cateninas nas ilhotas do grupo tratado em comparação ao grupo controle. Entretanto, verificou-se uma maior marcação intercelular para Ecaderina e uma maior associação de F-actina à membrana na região de contato intercelular nas células endócrinas das ilhotas do grupo pré-diabético em relação ao controle. Em conclusão, os contatos intercelulares mediados pelas proteínas associadas à JA e à JO parecem desempenhar um papel no processo de maturação do pâncreas do endócrino durante o desenvolvimento animal e na patogênese da diabetes do tipo 2
Abstract: Intercellular junctions are specializations of the plasma membrane that allow cells within a tissue to interact and adhere to each other. In endocrine pancreas, the different endocrine cells are interconnected by tight, gap and adherens-type junctions. Such intercellular contacts seem to be crucial for the function of this organ, however, little is known about the pathophysiological role and biochemistry of intercellular junctions in the endocrine pancreas. The aim of this thesis was to study the importance of cell-cell recognition and adhesion mediated by proteins associated to tight and adherens junctions in pancreatic islets, with emphasis on the process of insulin secretion, along the animal development and in pathogenesis of type 2 diabetes. Pancreatic islets of foetuses (F) and newborn (N) Wistar rats, that display a relatively poor insulin secretory response to glucose, present an immature morphology and a less defined cytoarchitecture when compared to islets from young (Y) and adult (A) rats, that are responsive to glucose. The immunofluorescence for N-CAM and pan-cadherin, adhesion molecules that are important in cell segregation, revealed a differential distribution of these proteins only in cells of the islets from Y and A. A lower junctional content of ?-and ?-catenins and ZO-1 in islet cells was seen in F and N in comparison with Y and A. In addition, we found that in the absence of intercellular contact, the glucose-stimulated insulin secretion was completely blocked in A islets. In contrast, the impact of the disruption of cell-cell adhesion on insulin secretory response of N islets was relatively small. As a model of type 2 diabetes, we employed male C57 mice, fed on high-fat (HF) diet for 8 months since they were 21 days old. After HF diet, these mice became obese and pre-diabetic (displaying moderate hyperglycemia and marked hyperinsulinaemia). We did not observe marked differences either in morphology either in the intercellular distribution of ZO-1, ?- and ?-catenins in islets between the HF-treated and control groups. However, there was a stronger immunoreaction for Ecadherin at the cell-cell contact site and an increased association of F-actin to the plasma membrane of islet endocrine cells from pre-diabetic mice as compared to control ones. In conclusion, the intercellular contacts mediated by adherens and tight junction and their constitutive proteins seem to play a role in the developmental maturation of the endocrine pancreas and in the pathogenesis of type 2 diabetes
Mestrado
Histologia
Mestre em Biologia Celular e Estrutural
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Bardy, Guillaume. "Effets insulino-sécrétoires et protecteurs de la quercétine au niveau de la cellule beta pancréatique : implication du calcium intracellulaire et de ERK1/2." Thesis, Montpellier 1, 2012. http://www.theses.fr/2012MON13515/document.
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Dans le diabète de type 2 établi, l'hyperglycémie chronique, un taux élevé d'acides gras libres et l'inflammation induisent un stress oxydatif (SO) au niveau de la cellule beta. Le SO, qui apparaît dès le stade de pré-diabète, peut induire un dysfonctionnement précoce de cette cellule. Ainsi, la protection de la cellule β par des molécules anti-oxydantes pourrait ralentir la progression du pré-diabète au diabète.La quercétine, un flavonoïde, a présenté des propriétés antidiabétiques dans plusieurs études in vivo. Cependant, très peu de données traitent de son mécanisme d'action directement au niveau de la cellule beta. Dans ce contexte, nous avons étudié les effets de la quercétine au niveau de la cellule beta dans des conditions physiologiques et des conditions de SO.Nos résultats montrent qu'en présence de concentrations stimulantes de sécrétagogue, la quercétine potentialise la sécrétion d'insuline par un mécanisme impliquant l'augmentation de calcium intracellulaire et la potentialisation de ERK1/2 via l'activation des voies de la PKA et de la CaMK II. De plus, la quercétine protège la cellule beta du SO en sur-activant ERK1/2. Le resvératrol et la NAC, deux antioxydants de référence, sont inactifs dans ces conditions expérimentales.En absence de concentrations stimulantes de sécrétagogue, la quercétine induit une sécrétion d'insuline modérée en augmentant le calcium intracellulaire suite à une activation directe des CaV de type L. Dans ces conditions, l'activation de ERK1/2 induite par la quercétine, qui est indépendante de l'activation des voies de la PKA et de la CaMK II, ne serait pas impliquée dans le mécanisme sécrétoire. Nos résultats indiquent que le mécanisme d'action de la quercétine au niveau de la cellule β ne repose pas uniquement sur ses capacités anti-oxydantes mais fait intervenir des cibles pharmacologiques et la régulation de voies de signalisation intracellulairesIn type 2 diabetes, chronic hyperglycaemia, elevated free fatty acids and inflammation induce oxidative stress (OS) in pancreatic β cell. SO, which appears at the stage of pre-diabetes, may induce early dysfunction of this cell. Thus, the β cell protection by antioxidant molecules could slow the progression of pre-diabetes to diabetes.Quercetin, a flavonoid, has shown antidiabetic properties in several in vivo studies. However, very few data address its mechanism of action directly at the β cell. In this context, we studied the effects of quercetin at the β cell under physiological conditions and conditions of OS.Our results show that in the presence of stimulating concentrations of secretagogue, quercetin potentiates insulin secretion by a mechanism involving increased intracellular calcium and potentiation of ERK1 / 2 via activation of the PKA and the CaMK II pathways. In addition, quercetin protects beta cell from OS via a suractivation of ERK1/2. Resveratrol and NAC, two antioxidants of reference are inactive under these experimental conditions.In the absence of stimulating concentration of secretagogue, quercetin induced moderate insulin secretion by increasing the intracellular calcium via a direct activation of L-type CaV Under these conditions, the activation of ERK1/2 induced by quercetin, which is independent of the activation pathways of PKA and CaMK II to, would not be involved in the secretory mechanism.Our results indicate that the mechanism of action of quercetin at the β cell not only based on its antioxidant capacity but involves pharmacological targets and the regulation of intracellular signaling pathways
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Amouyal, Chloé. "Restaurer la fonction bêta pancréatique de la souris leptine déficiente par la chirurgie bariatrique." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS010.
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Le bypass gastrique (RYGB) a démontré un effet bénéfique sur le diabète de type 2. L’EGA (entéro-gastro-anastomose) est une procédure de bypass gastrique adaptée au modèle murin. Chez les souris ob-ob (déficientes pour la leptine), l’EGA améliore la tolérance au glucose en augmentant le contenu pancréatique en insuline et la sécrétion d’insuline induite par le glucose in vivo en l’absence de perte de poids, de restriction alimentaire, de modification de composition corporelle, sans modifier le nombre ni dans la taille des ilots. L’expression du gène de l’insuline, la prolifération beta cellulaire et l’infiltration immunitaire insulaire sont également inchangés. De plus, la chirurgie bariatrique régule l’expression de 193 gènes et 27 miRs intra-ilots. Certaines anomalies moléculaires observées dans les îlots pancréatiques des souris ob-ob (régulation négative du canal ionique TRPM5, du transporteur GLUT2, de la glucokinase, de la connexine 36) et fonctionnelles (sensibilité élevée des îlots à de faibles taux de glucose) ont été modulées par la chirurgie bariatrique. La chirurgie a favorisé l’enrichissement de 227 processus biologiques, notamment 21 gènes impliqués dans le transport hormonal et 20 gènes impliqués dans la sécrétion hormonale. Sept des 27 miRs (324-3p, 380-3p, 671-5p, 1927, 6904-5p, 6918-5p et 7682-3p) sont des noyaux dans le réseau de prédiction d’interaction gène-miRs. Globalement, nos données ont mis en évidence de nouveaux mécanismes moléculaires dans la résolution du diabète après une chirurgie bariatrique. De manière importante, notre modèle démontre que la résolution du diabète après la chirurgie bariatrique peut être indépendante de la perte de poidsEGA (entero-gastro-anastomosis) is a gastric bypass procedure adapted to rodent. EGA in leptin deficient ob/ob mice improves glucose tolerance by increasing pancreatic insulin content and glucose stimulated insulin secretion in vivo without persistent body weight loss dietary restriction, modification of body composition / energy expenditure. We do not observe differences in islets ‘number or size after EGA. Insulin gene expression, beta-cell proliferation (Ki67 index) and insular immune infiltration are also unchanged. Transcriptomic analysis of pancreatic islets showed that bariatric surgery differentially regulated 193 genes and 27 miRs. Interestingly, the surgery normalized molecular defects (down regulation of TRPM5, GLUT2, GCK, connexin 36) and functional alteration (high sensitivity of islets to low glucose levels) observed in diabetic ob pancreatic islets. In addition, the surgery promoted the enrichment of 227 biological process, composed of genes with known or undetermined beta cell function, especially 21 genes are involved in the hormone transport and 20 genes in the hormone secretion biological process. Computational analysis predicted that 7 of 27 miRs (324-3p, 380-3p, 671-5p, 1927, 6904-5p, 6918-5p and 7682-3p) are hubs in the miRs-gene interaction network. Altogether, our data highlighted novel molecular mechanisms in the resolution of diabetes after bariatric surgery. Overall, diabetes resolution in our model appears to be totally independent of body weight
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Papas, Klearchos Kyriacos. "Bioenergetics, metabolism, and secretion of immunoisolated endocrine cell preparations." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/11001.
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Mezghenna, Karima. "No synthase neuronale pancréatique et musculaire dans la pathogénie des états prédiabétiques." Thesis, Montpellier 1, 2010. http://www.theses.fr/2010MON13503.
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Le diabète de type 2, défini par une hyperglycémie chronique, résulte d'un déficit de la sécrétion d'insuline et d'une insulinorésistance. Durant le prédiabète qui précède la maladie, la cellule ß pancréatique est capable d'établir une hyperactivité sécrétoire compensatrice de l'insulinorésistance. Les NO synthases neuronales (nNOS) pancréatique et musculaire contrôlent respectivement la sécrétion d'insuline induite par le glucose dans la cellule ß et la force contractile, la captation et l'utilisation du glucose dans les myocytes. Dans le modèle génétique du rat obèse Zucker fa/fa mimant l'état prédiabétique associant un hyperinsulinisme et une insulinorésistance, nous avons retrouvé au niveau de la cellule ß une forte augmentation du complexe entre la nNOS et son inhibiteur endogène PIN (Protein Inhibitor of Neuronal NOS) au niveau des granules de sécrétion d'insuline. Ce complexe, grâce à une interaction accrue avec la myosine V, participe à l'hyperactivité sécrétoire de la cellule ß pancréatique. En effet, des molécules inhibant spécifiquement l'interaction nNOS-PIN permettent de rétablir, chez le rat fa/fa, une sécrétion d'insuline normale. Au niveau musculaire, nous avons observé, dans ce modèle animal, une diminution d'expression de la nNOS sans variation du taux d'ARNm, traduisant une protéolyse accrue de la protéine. L'inhibition de la dégradation protéasomale permet de restaurer l'expression et l'activité catalytique de la nNOS dans le muscle squelettique. Cette perte de fonctionnalité de l'enzyme participerait à l'installation de l'insulinorésistance. Ces travaux ont permis de valider la nNOS comme une cible potentielle pour la prévention du diabète de type 2Type 2 diabetes is a chronic disorder defined by chronic hyperglycemia resulting from a deficiency of insulin secretion and an insulin resistance in peripheral tissues and liver. A long lasting silent phase, called prediabetes, precedes the disease and in which pancreatic ß cell is able to improve insulin secretion to compensate for the insulin resistance. The pancreatic and muscular neuronal nitric oxide synthases (nNOS) control respectively glucose-induced insulin secretion in pancreatic ß cell and glucose uptake and utilization in myocytes. In the genetic model of obese Zucker fa/fa rat mimicking the prediabetic state characterized by hyperinsulinemia and insulin resistance, we found a high increase in the amount of the complex between nNOS and its endogenous inhibitor PIN (Protein Inhibitor of Neuronal NOS) at the level of insulin secretory granules within the ß cell. This complex, through an increased interaction with myosin V, participates in the secretory hyperactivity of the pancreatic ß cell, observed in this model of prediabetes. Indeed, molecules that specifically inhibit nNOS-PIN interaction allow to restore a normal insulin secretion in fa/fa rat. In skeletal muscle of this model, we observed a decreased expression of nNOS protein with no change in mRNA levels, suggesting an increased proteolysis of the protein. Inhibition of proteasomal degradation restores the expression and the catalytic activity of nNOS in skeletal muscle. Thus, this loss of functionality of the enzyme could participate in the installation of insulin resistance. This work therefore validated nNOS as a potential target for the prevention of type 2 diabetes
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Debuyser, Anne. "Etude du controle noradrenergique de la cellule beta du pancreas de souris par des techniques electrophysiologique, radioimmunologique et radioisotopiques." Poitiers, 1988. http://www.theses.fr/1988POIT2324.
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LOCATELLI, LUIGI. "Expression of aVB6 integrin by Pkhd1-defective cholangiocytes links enhanced ductal secretion of Macrophage chemokines to progressive portal fibrosis in Congenital Hepatic Fibrosis." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2013. http://hdl.handle.net/10281/41733.
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BACKGROUND AND AIMS: Congenital Hepatic Fibrosis (CHF) is caused by mutations in PKHD1, a gene encoding for fibrocystin, a protein of unknown function, expressed in cholangiocyte cilia and centromers. In CHF, biliary dysgenesis is accompanied by severe progressive portal fibrosis and portal hypertension. The mechanisms responsible for portal fibrosis in CHF are unclear. The αvβ6 integrin mediates local activation of TGFβ1 and is expressed by reactive cholangiocytes during cholestasis. To understand the mechanisms of fibrosis in CHF we studied the expression of αvβ6 integrin and its regulation in Pkhd1del4/del4 mice.
METHODS: In Pkhd1del4/del4 mice we studied, at different ages (1-12 months): a) portal fibrosis (Sirius Red) and portal hypertension (spleen weight/body weight); b) αvβ6 mRNA and protein expression (RT-PCR, IHC); c) α-SMA and TGFβ1 mRNA expression (RT-PCR); d) portal inflammatory infiltrate (IHC for CD45 and FACS analysis of whole liver infiltrate); f) cytokines secretion from cultured monolayers of primary cholangiocytes (Luminex assay); g) cytokine effects on monocyte/macrophage proliferation (MTS assay) and migration (Boyden chamber); h) TGFβ1 and TNFα effects on β6 integrin mRNA expression by cultured cholangiocytes before and after inhibition of the TGFβ receptor type II (TGFβRII); i) TGFβ1 effects on collagen type I (COLL1) mRNA expression by cultured cholangiocytes.
RESULTS: Pkhd1del4/del4 mice showed a progressive increase in αvβ6 integrin expression on biliary cyst epithelia. Expression of αvβ6 correlated with portal fibrosis (r=0.94, p<0.02) and with enrichment of a CD45+ve cell infiltrate in the portal space (r=0.97, p<0.01). Gene expression of TGFβ1 showed a similar age-dependent increase. FACS analysis showed that 50-75% of the CD45+ve cells were macrophages (CD45/CD11b/F4/80+ve). Cultured polarized Pkhd1del4/del4 cholangiocytes secreted from the basolateral side significantly increased amounts of CXCL1 and CXCL10 (p<0.05). Both cytokines were able to stimulate macrophage migration (p<0.05). Basal expression of β6 mRNA by cultured Pkhd1del4/del4 cholangiocytes (0.015±0.002 2^-dCt) was potently stimulated by the macrophage-derived cytokines TGFβ1 (0.017±0.002 2^-dCt, p<0.05) and TNFα (0.018±0.003 2^-dCt, p<0.05). Inhibition of TGFβRII completely blunted TGFβ1 (0.014±0.003 2^-dCt, p<0.05) but not TNFα effects (0.017±0.001 2^-dCt, p=ns) on β6 mRNA. COLL1 mRNA expression by cultured Pkhd1del4/del4 cholangiocytes (0.0009±0.0003 2^-dCt) was further and significantly increased after TGFβ1 stimulation (0.002±0.0005 2^-dCt, p<0.05).
CONCLUSIONS: Pkhd1del4/del4 cholangiocytes possess increased basolateral secretory functions of chemokines (CXCL1, CXCL10) able to orchestrate macrophage homing to the peribiliary microenvironment. In turn, by releasing TGFβ1 and TNFα, macrophages up-regulate αvβ6 integrin in Pkhd1del4/del4 cholangiocytes. αvβ6 integrin activates latent TGFβ1, further increasing the fibrogenic properties of cholangiocytes.
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Schisler, Jonathan Cummings. "New roles of the transcription factor NKX6.1 in beta cell biology." Access to abstract only; dissertation is embargoed until after 5/15/2007, 2006. http://www4.utsouthwestern.edu/library/ETD/etdDetails.cfm?etdID=164.
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Holmberg, Hanna. "Autoantibodies as markers of beta-cell autoimmunity in children." Doctoral thesis, Linköping : Univ, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7092.
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Masserini, B. "ANALISI DEL METABOLISMO GLUCIDICO IN PAZIENTI CIRROTICI SOTTOPOSTI A TRAPIANTO EPATICO: RUOLO DELLA SECREZIONE BETA CELLULARE E DELL'INSULINORESISTENZA." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/246332.
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Impaired glucose metabolism is frequently described in cirrhotic patients. The pathogenesis of diabetes mellitus (DM) in this population is complex and not precisely known. Insulin resistance (IR) plays a central role in the glucose metabolism disturbance and it has been speculated that genetic and environmental factors and some etiologic agents in liver disease impair insulin secretion.
Aim of the study: evaluate β cell secretion and insulin sensitivity in a cohort of cirrhotic patients undergoing liver transplantation (LT).
107 cirrhotic patients (31 female e 76 male) were evaluated before LT. The patients who underwent LT were evaluated 3, 6, 12 months after surgery. To evaluate insulin resistance HOMA-IR was used. To assess the β cell secretion, a state-of-art modelling of glucose/C-peptide curves during OGTT was used. Two outputs were provided: dynamic evaluation (1st phase) and proportional evaluation (2nd phase).
Before LT the prevalence of DM and prediabetes (pre DM) were 50.5% and 31.8 % respectively. DM patients showed a lower insulin secretion (both 1st and 2nd phase) and tended to have higher HOMA-IR when compared to pre DM and non DM subjects.
After LT glucose metabolism improved (impaired glucose metabolism: 6 months 61.1%, 12 months 65.6%). HOMA-IR was decreased (pre LT: 5.48±5.14, 3 months post LT: 2.17±1.62, 6 months post LT: 2.28±1.44, 12 months post LT: 2.36±1.73 P=0.0017). No differences in β cell secretion was found.
When the population who underwent LT was divided in 2 groups according to the improvement or not of glucose metabolism, higher insulin secretion was found in improved subjects (2nd phase). No differences in HOMA-IR, age, duration of hepatic disease, family history of type 2 DM, immunosuppressive therapy were observed.
In conclusion IR and reduced insulin secretion was observed in cirrhotic diabetic patients. After LT an improved glucose metabolism was observed. Insulin sensitivity was increased in all patients and higher β cell secretion was observed only in subjects with improved glucose metabolism.
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Makeeva, Natalia. "Role of MAP Kinases in the Life and Death of Beta-cells." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6317.
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Guo, Hong. "Investigation of the cellular and molecular characteristics of four novel human insulin-secreting beta cell lines in vitro and in vivo." Thesis, University of Ulster, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494356.
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Liu, Hui-Kang. "Modification of the function of insulin-secreting cells by beta-cell toxins, differentiation drugs, insulin mimetics, steroids, and incretic hormones and their stable analogues." Thesis, University of Ulster, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399055.
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O'Sullivan-Murphy, Bryan M. "Contribution of WFS1 to Pancreatic Beta Cell Survival and Adaptive Alterations in WFS1 Deficiency: A Dissertation." eScholarship@UMMS, 2012. https://escholarship.umassmed.edu/gsbs_diss/590.
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Diabetes mellitus comprises a cohort of genetic and metabolic diseases which are characterized by the hallmark symptom of hyperglycemia. Diabetic subtypes are based on their pathogenetic origins: the most prevalent subtypes are the autoimmune-mediated type 1 diabetes mellitus (T1DM) and the metabolic disease of type 2 diabetes mellitus (T2DM). Genetic factors are major contributory aspects to diabetes development, particularly in T2DM where there is close to 80% concordance rates between monozygotic twins. However, the functional state of the pancreatic β cell is of paramount importance to the development of diabetes. Perturbations that lead to β cell dysfunction impair insulin production and secretion and precede diabetes onset.
The endoplasmic reticulum (ER) is a subcellular organelle network of tubes and cisternae with multifaceted roles in cellular metabolism. Alterations to ER function such as those begotten by the accumulation of misfolded and unfolded ER client proteins upset the ER homeostatic balance, leading to a condition termed ER stress. Subsequent sensing of ER stress by three ER transmembrane proteins, initiates an adaptive reaction to alleviate ER stress: this is known as the unfolded protein response (UPR). Divergent cascades of the UPR attempt to mitigate ER stress and restore ER homeostasis: Failing that, the UPR initiates pro-apoptotic pathways. The demand of insulin production on the β cell necessitates the presence of a highly functional ER. However, the consequence of dependence on the ER for insulin synthesis and secretion portends disaster for the functional state of the β cell. Disturbances to the ER that elicit ER stress and UPR activation causes β cell dysfunction and may lead to apoptosis. There are numerous well-characterized models of ER stress-mediated diabetes, including genetic mutations in UPR transducers and insulin. Recently, polymorphisms in Wolfram syndrome 1 (WFS1), an ER transmembrane protein involved in the UPR, were suggested to contribute to T2DM risk.
In this thesis, one of the highlighted WFS1 polymorphism, H611R, was examined to identify its contribution to β cell function and viability, and hence, diabetes risk. It was revealed that augmentation of WFS1 expression increased insulin secretion and cellular content. In addition, WFS1 protected β cells against ER stress-mediated dysfunction, with a more pronounced effect in the WFS1-R611 protective allele. Subsequent gene expression analysis identified netrin-1 as a WFS1-induced survival factor.
As a contributory factor to diabetes progression, ER stress and UPR are potential drug and biomarker targets. In this dissertation, a novel UPR-regulating microRNA (miRNA) family was uncovered in ER stressed, WFS1-deficient islets. These miRNAs, the miR-29 family, are induced in WFS1 -/- islets as a possible adaptive alteration to chronic ER stress conditions, and indirectly decreases the expression of UPR transducers, while directly targeting downstream ER stress-related pro-apoptotic factors. Collectively, this work extends the function of WFS1 as a protective factor in the pancreatic β cell through the induction of netrin-1 signaling. Additionally, it further strengthens the role of miRNA as regulatory members of the UPR which contribute to cell survival.
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Selander, Lars. "In vivo and in vitro approaches to induce beta cells from stem and progenitor cells." Doctoral thesis, Umeå : Umeå University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-25813.
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Schubert, Sandra. "The Role of [beta]2-Syntrophin Phosphorylation in Secretory Granule Exocytosis." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1146851994562-42414.
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The trafficking of insulin secretory granules(SGs) of pancreatic b-cells is a tightly controlled complex network. Increasing evidence indicates that the cortical actin cytoskeleton modulates the mobility and exocytosis of SGs,yet the mechanisms anchoring SGs to the cytoskeleton is not completely understood.It has been shown by Ort et al.(2000,2001) that the cytoplasmic tail of an intrinsic membrane protein of the SGs named ICA512/IA-2 binds the PDZ domain of b2-syntrophin,which in turn binds to the F-actin-binding protein utrophin. These data also indicate that stimulation of SG exocytosis affects the phosphorylation of b2-syntrophin,hence altering its binding to ICA512.Therefore a model was proposed whereby SGs are anchored to the actin cytoskeleton through the ICA512/b2-syntrophin complex, whose dynamics are regulated by phosphorylation.To test this model GFP-b2-syntrophin stable INS-1 cell clones were generated.GFP-b2-syntrophin expression and localization pattern were similar to those of the endogenous protein. Electron microscopy showed that in GFP-b2-syntrophin INS-1 cells the number of SGs with a pear-like shape was increased relative to control cells. Insulin content and stimulated secretion were increased in three GFP-â2-syntrophin INS-1 cell clones,compared to non-transfected INS-1 cells and INS-1 cells expressing GFP. These increments correlated with the different expression levels of GFP-b2-syntrophin in the three GFP-b2-syntrophin INS-1 cell clones. These findings support the hypothesis that b2-syntrophin regulates the trafficking and exocytosis of SGs by modulating their tethering to the actin cytoskeleton.In order to confirm the proposed model, the phosphorylation of b2-syntrophin was investigated in more detail. Similar to endogenous b2-syntrophin,GFP-b2-syntrophin underwent Ca2+-dependent and okadaic acid-sensitive dephosphorylation upon stimulation of insulin secretion. Stimulation-dependent dephosphorylation was confirmed by immunoprecipitation of 32P-labeled GFP-b2-syntrophin.Mass spectrometry of immunoprecipitated GFP-b2-syntrophin allowed the identification of four serine-phosphorylation sites (S75,S90,S213,S373) that could affect the binding to ICA512.Mutants,in which all four phosphoserines, were replaced by either asp or ala to mimic(S/D) or prevent(S/A) phosphorylation were expressed in INS-1 cells. All S/D mutants retained a cortical localization,but by immunoblotting the pattern of the S75D allele differed from wild type and all other S/D alleles.Conversely, all S/A alleles were diffused cytosolically, except S213A,which was still restricted to the cortex. Finally, pull down assays showed increased binding of ICA512 to the S75A and S90D alleles compared to wild type b2-syntrophin,while the opposite was observed with the S75D and S90A mutants.Additionally,both the S75 and the S213 allele conform a consensus for phosphorylation by Cdk5,which is known to modulate insulin secretion. The phosphorylation of GFP-b2-syntrophin and particularly the S75 allele by Cdk5 was exhibited with pharmacological inhibitors,by in vitro phosphorylation and by RNAi. Taken together, these findings are consistent with the model by which phosphorylation of b2-syntrophin modulates the tethering of SGs to the cytoskeleton, and thereby their mobility and exocytosis. Specifically, the data of this thesis suggest that Cdk5-dependent phosphorylation of the S75 site of GFP-b2-syntrophin facilitates insulin secretion by reducing the interaction of b2-syntrophin with ICA512,thereby decreasing the actin cytoskeleton constrain on SG mobility. This process could occur in combination with the phosphatase-dependent dephosphorylation of b2-syntrophin at phosphosites other than S75Der Transport Insulin-gefüllter sekretorische Granula(SG) ist ein streng kontrollierter komplexer Prozess.Es gibt vermehrt Beweise,dass das kortikale Actinzytoskelett die Ausschüttung der SGs beeinflusst.Bisher ist der Mechanismus der Verankerung von SGs am Zytoskelett noch nicht vollständig aufgeklärt.Ort et al.(2000,2001) haben gezeigt,daß der zytosoplasmatische Teil des trans-membranen SG-Proteins ICA512 mit der PDZ-Domäne von b2-Syntrophin interagiert.Dieses Protein bindet das F-Actin-Bindeprotein Utrophin.Die Ergebnisse zeigen außerdem,daß durch Stimulation der SG-Exozytose der Phosphorilierungsstatus von b2-Syntrophin beeinflusst wird,woraus ein verändertes Bindungsvermögen zu ICA512 resultiert.Es wurde ein Funktionsmodel vorgestellt,in dem sich SGs durch die Interaktion des ICA512/b2-Syntrophin Komplexes an das Actinzytoskelett binden.Dabei wird die Bindedynamik durch Phosphorilierung reguliert.Um dieses Model zu etablieren,wurden stabile GFP-b2-Syntrophin produzierende INS-1-Zellklone erzeugt.Die zelluläre Lokalisation und das Expressionsmuster von GFP-b2-Syntrophin stimmen mit dem des endogenen Proteins überein.Elektronenmikroskopie zeigte eine größe Anzahl oval-verformter SGs in GFP-b2-Syntrophin INS-1-Zellen im Vergleich zu Kontrollzellen.Verglichen mit nicht-transfizierten INS-1 Zellen waren in drei GFP-b2-Syntrophin INS-1-Zellklonen der Insulingehalt der Zellen und die stimulierte Insulinsekretion erhöht.Die Werte korrelierten mit den unterschiedlichen GFP-b2-Syntrophin Expressionsmengen der Klone.Diese Ergebnisse untermauern die Hypothese,daß b2-Syntrophin den Transport und die Sekretion der SGs durch Modulation ihres Bindevermögens an Actin reguliert.Um das postulierte Model genauer zu prüfen,wurde die Phosphorilierung von b2-Syntrophin detaillierter untersucht.Das GFP-Protein wurde,ähnlich dem endogenen b2-Syntrophin,durch Stimulation der Insulinausschüttung dephosphoriliert.Diese Dephosphorilierung ist Ca2+-abhängig und Okadeinsäuresensitiv.Die stimulationsabhängige Dephosphorilierung wurde durch Immunoprezipitation von 32P-markiertem GFP-b2-Syntrophin bestätigt.Massenspektrometrie des präzipitierten Proteins ermöglichte die Identifikation von vier Serin-Phosphorilierungsstellen(S75,S90,S213,S373),welche die Bindung zu ICA512 beeinflussen könnten.Mutanten,in denen die vier Phosphoserine durch Asp beziehungsweise Ala ersetzt wurden,um entweder eine Phosphorilierung(S/D) oder Dephosphorilierung(S/A) nachzuahmen,wurden in INS-1-Zellen exprimiert.Alle S/D Mutanten blieben kortikal lokalisiert.Das Expressionsmuster des S75D Allels unterschied sich jedoch von denen des Wild-Typs(wt).Im Gegensatz dazu waren alle S/A Allele zytosolisch verteilt.Eine Ausnahme bildete S213A,das an der Zellkortex lokalisiert blieb.Im Vergleich zu wt b2-Syntrophin zeigten PullDown-Assays eine erhöhte Bindung von ICA512 zu den S75A und S90D Allelen.Das Gegenteil konnte für die S75D und S90A Mutanten nachgewiesen werden.S75,S90 und S213 sind in einer Konsensussequenz für Cdk5-Phosphorilierung enthalten.Diese Kinase kann die Insulinsekretion regulieren.Die Phosphorilierung von b2-Syntrophin,insbesondere des S75 Allels durch Cdk5 wurde durch pharmakologische Inhibitoren,in vitro-Phosphorilierung und RNAi demonstriert.Zusammenfassend stimmen diese Erkenntnisse mit dem Model überein,daß die Phosphorilierung von b2-Syntrophin die Vernetzung von SGs mit Actin und dadurch deren Mobilität und Exozytose moduliert.Im Speziellen postulieren die Ergebnisse dieser Arbeit eine Cdk5-abhängige Phosphorilierung der S75 Stelle des b2-Syntrophins.Durch eine verminderte Interaktion von b2-Syntrophin und ICA512 erleichtert diese Mutante vermutlich die Insulinsekretion,da der Einfluss des Actinzytoskeletts auf die Granulamobilität vermindert ist.Dieser Prozess ereignet sich möglicherweise in Kombination mit einer Dephosphorilierung des b2-Syntrophins.in Kombination mit einer Dephosphorilierung des b2-Syntrophins
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Schubert, Sandra. "The Role of [beta]2-Syntrophin Phosphorylation in Secretory Granule Exocytosis." Doctoral thesis, Technische Universität Dresden, 2005. https://tud.qucosa.de/id/qucosa%3A23710.
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The trafficking of insulin secretory granules(SGs) of pancreatic b-cells is a tightly controlled complex network. Increasing evidence indicates that the cortical actin cytoskeleton modulates the mobility and exocytosis of SGs,yet the mechanisms anchoring SGs to the cytoskeleton is not completely understood.It has been shown by Ort et al.(2000,2001) that the cytoplasmic tail of an intrinsic membrane protein of the SGs named ICA512/IA-2 binds the PDZ domain of b2-syntrophin,which in turn binds to the F-actin-binding protein utrophin. These data also indicate that stimulation of SG exocytosis affects the phosphorylation of b2-syntrophin,hence altering its binding to ICA512.Therefore a model was proposed whereby SGs are anchored to the actin cytoskeleton through the ICA512/b2-syntrophin complex, whose dynamics are regulated by phosphorylation.To test this model GFP-b2-syntrophin stable INS-1 cell clones were generated.GFP-b2-syntrophin expression and localization pattern were similar to those of the endogenous protein. Electron microscopy showed that in GFP-b2-syntrophin INS-1 cells the number of SGs with a pear-like shape was increased relative to control cells. Insulin content and stimulated secretion were increased in three GFP-â2-syntrophin INS-1 cell clones,compared to non-transfected INS-1 cells and INS-1 cells expressing GFP. These increments correlated with the different expression levels of GFP-b2-syntrophin in the three GFP-b2-syntrophin INS-1 cell clones. These findings support the hypothesis that b2-syntrophin regulates the trafficking and exocytosis of SGs by modulating their tethering to the actin cytoskeleton.In order to confirm the proposed model, the phosphorylation of b2-syntrophin was investigated in more detail. Similar to endogenous b2-syntrophin,GFP-b2-syntrophin underwent Ca2+-dependent and okadaic acid-sensitive dephosphorylation upon stimulation of insulin secretion. Stimulation-dependent dephosphorylation was confirmed by immunoprecipitation of 32P-labeled GFP-b2-syntrophin.Mass spectrometry of immunoprecipitated GFP-b2-syntrophin allowed the identification of four serine-phosphorylation sites (S75,S90,S213,S373) that could affect the binding to ICA512.Mutants,in which all four phosphoserines, were replaced by either asp or ala to mimic(S/D) or prevent(S/A) phosphorylation were expressed in INS-1 cells. All S/D mutants retained a cortical localization,but by immunoblotting the pattern of the S75D allele differed from wild type and all other S/D alleles.Conversely, all S/A alleles were diffused cytosolically, except S213A,which was still restricted to the cortex. Finally, pull down assays showed increased binding of ICA512 to the S75A and S90D alleles compared to wild type b2-syntrophin,while the opposite was observed with the S75D and S90A mutants.Additionally,both the S75 and the S213 allele conform a consensus for phosphorylation by Cdk5,which is known to modulate insulin secretion. The phosphorylation of GFP-b2-syntrophin and particularly the S75 allele by Cdk5 was exhibited with pharmacological inhibitors,by in vitro phosphorylation and by RNAi. Taken together, these findings are consistent with the model by which phosphorylation of b2-syntrophin modulates the tethering of SGs to the cytoskeleton, and thereby their mobility and exocytosis. Specifically, the data of this thesis suggest that Cdk5-dependent phosphorylation of the S75 site of GFP-b2-syntrophin facilitates insulin secretion by reducing the interaction of b2-syntrophin with ICA512,thereby decreasing the actin cytoskeleton constrain on SG mobility. This process could occur in combination with the phosphatase-dependent dephosphorylation of b2-syntrophin at phosphosites other than S75.Der Transport Insulin-gefüllter sekretorische Granula(SG) ist ein streng kontrollierter komplexer Prozess.Es gibt vermehrt Beweise,dass das kortikale Actinzytoskelett die Ausschüttung der SGs beeinflusst.Bisher ist der Mechanismus der Verankerung von SGs am Zytoskelett noch nicht vollständig aufgeklärt.Ort et al.(2000,2001) haben gezeigt,daß der zytosoplasmatische Teil des trans-membranen SG-Proteins ICA512 mit der PDZ-Domäne von b2-Syntrophin interagiert.Dieses Protein bindet das F-Actin-Bindeprotein Utrophin.Die Ergebnisse zeigen außerdem,daß durch Stimulation der SG-Exozytose der Phosphorilierungsstatus von b2-Syntrophin beeinflusst wird,woraus ein verändertes Bindungsvermögen zu ICA512 resultiert.Es wurde ein Funktionsmodel vorgestellt,in dem sich SGs durch die Interaktion des ICA512/b2-Syntrophin Komplexes an das Actinzytoskelett binden.Dabei wird die Bindedynamik durch Phosphorilierung reguliert.Um dieses Model zu etablieren,wurden stabile GFP-b2-Syntrophin produzierende INS-1-Zellklone erzeugt.Die zelluläre Lokalisation und das Expressionsmuster von GFP-b2-Syntrophin stimmen mit dem des endogenen Proteins überein.Elektronenmikroskopie zeigte eine größe Anzahl oval-verformter SGs in GFP-b2-Syntrophin INS-1-Zellen im Vergleich zu Kontrollzellen.Verglichen mit nicht-transfizierten INS-1 Zellen waren in drei GFP-b2-Syntrophin INS-1-Zellklonen der Insulingehalt der Zellen und die stimulierte Insulinsekretion erhöht.Die Werte korrelierten mit den unterschiedlichen GFP-b2-Syntrophin Expressionsmengen der Klone.Diese Ergebnisse untermauern die Hypothese,daß b2-Syntrophin den Transport und die Sekretion der SGs durch Modulation ihres Bindevermögens an Actin reguliert.Um das postulierte Model genauer zu prüfen,wurde die Phosphorilierung von b2-Syntrophin detaillierter untersucht.Das GFP-Protein wurde,ähnlich dem endogenen b2-Syntrophin,durch Stimulation der Insulinausschüttung dephosphoriliert.Diese Dephosphorilierung ist Ca2+-abhängig und Okadeinsäuresensitiv.Die stimulationsabhängige Dephosphorilierung wurde durch Immunoprezipitation von 32P-markiertem GFP-b2-Syntrophin bestätigt.Massenspektrometrie des präzipitierten Proteins ermöglichte die Identifikation von vier Serin-Phosphorilierungsstellen(S75,S90,S213,S373),welche die Bindung zu ICA512 beeinflussen könnten.Mutanten,in denen die vier Phosphoserine durch Asp beziehungsweise Ala ersetzt wurden,um entweder eine Phosphorilierung(S/D) oder Dephosphorilierung(S/A) nachzuahmen,wurden in INS-1-Zellen exprimiert.Alle S/D Mutanten blieben kortikal lokalisiert.Das Expressionsmuster des S75D Allels unterschied sich jedoch von denen des Wild-Typs(wt).Im Gegensatz dazu waren alle S/A Allele zytosolisch verteilt.Eine Ausnahme bildete S213A,das an der Zellkortex lokalisiert blieb.Im Vergleich zu wt b2-Syntrophin zeigten PullDown-Assays eine erhöhte Bindung von ICA512 zu den S75A und S90D Allelen.Das Gegenteil konnte für die S75D und S90A Mutanten nachgewiesen werden.S75,S90 und S213 sind in einer Konsensussequenz für Cdk5-Phosphorilierung enthalten.Diese Kinase kann die Insulinsekretion regulieren.Die Phosphorilierung von b2-Syntrophin,insbesondere des S75 Allels durch Cdk5 wurde durch pharmakologische Inhibitoren,in vitro-Phosphorilierung und RNAi demonstriert.Zusammenfassend stimmen diese Erkenntnisse mit dem Model überein,daß die Phosphorilierung von b2-Syntrophin die Vernetzung von SGs mit Actin und dadurch deren Mobilität und Exozytose moduliert.Im Speziellen postulieren die Ergebnisse dieser Arbeit eine Cdk5-abhängige Phosphorilierung der S75 Stelle des b2-Syntrophins.Durch eine verminderte Interaktion von b2-Syntrophin und ICA512 erleichtert diese Mutante vermutlich die Insulinsekretion,da der Einfluss des Actinzytoskeletts auf die Granulamobilität vermindert ist.Dieser Prozess ereignet sich möglicherweise in Kombination mit einer Dephosphorilierung des b2-Syntrophins.in Kombination mit einer Dephosphorilierung des b2-Syntrophins.
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Aslamy, Arianne. "DOC2B enhancement of beta cell function and survival." Diss., 2018. https://doi.org/10.7912/C25W7M.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)Diabetes mellitus is a complex metabolic disease that currently affects an estimated 422 million people worldwide, with incidence rates rising annually. Type 1 diabetes (T1D) accounts for 5-10% of these cases. Its complications remain a major cause of global deaths. T1D is characterized by autoimmune destruction of β-cell mass. Efforts to preserve and protect β-cell mass in the preclinical stages of T1D are limited by few blood-borne biomarkers of β-cell destruction. In healthy β-cells, insulin secretion requires soluble n-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) complexes and associated accessory regulatory proteins to promote the docking and fusion of insulin vesicles at the plasma membrane. Two target membrane (t)-SNARE proteins, Syntaxin 1/4 and SNAP25/23, and one vesicle-associated (v)-SNARE protein, VAMP2, constitute the SNARE core complex. SNARE complex assembly is also facilitated by the regulatory protein, Double C2-domain protein β (DOC2B). I hypothesized that DOC2B deficiency may underlie β-cell susceptibility to T1D damage; conversely , overexpression of DOC2B may protect β-cell mass. Indeed, with regard to DOC2B abundance, my studies show reduced levels of DOC2B in platelets and islets of prediabetic rodents and new-onset T1D humans. Remarkably, clinical islet transplantation in T1D humans restores platelet DOC2B levels, indicating a correlation With regard to protection/functional effects, DOC2B deficiency enhances susceptibility to T1D in mice, while overexpression of DOC2B selectively in β-cells protects mice from chemically induced T1D; this correlates with preservation of functional β-cell mass. Mechanistically, overexpression of DOC2B and the DOC2B peptide, C2AB, protects clonal β-cell against cytokine or thapsigargin-induced apoptosis and reduces ER stress; this is dependent on C2AB’s calcium binding capacity. C2AB is sufficient to enhance glucose stimulated insulin secretion (GSIS) and SNARE activation in clonal β-cells to the same extent as full-length DOC2B. In summary, these studies identify DOC2B as a potential biomarker and novel therapeutic target for prevention/management of T1D.
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Joseph, Jamie W. "Beta-cell stimulus-secretion coupling : a role for uncoupling protein 2." 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=94794&T=F.
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Xia, Fuzhen. "Lipid Rafts in Pancreatic Beta- and Alpha-cell Stimulus-secretion Coupling." Thesis, 2008. http://hdl.handle.net/1807/17314.
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Type 2 diabetes is hallmarked by insufficient beta-cell insulin secretion and inappropriate alpha-cell glucagon secretion concomitant to peripheral insulin resistance. However, the mechanisms underlying dysregulation of pancreatic beta- and alpha-cells in type 2 diabetes require further investigation. Whereas triglycerides and saturated free fatty acids have been well recognized to cause beta-cell dysfunction, the physiological and/or pathological role of cholesterol on beta- and alpha-cells is less well examined. Cholesterol is the major component of membrane microdomains, termed lipid rafts. Numerous signaling and transport proteins have been found to be targeted to lipid raft microdomains, where the function of the associated membrane proteins could be distinctly regulated.
I have identified the expression of lipid raft constituent proteins, caveolin-1/2 in pancreatic beta-cells; and caveolin-2 in alpha-cells. A variety of membrane proteins (ion channels and SNARE proteins) critical for beta- and alpha-cell stimulus-secretion coupling were found to be associated with cholesterol-rich lipid raft microdomians, and the properties of those ion channels (Kv2.1, Kv4.1/4.3, and Cav1.2 channels) and SNARE proteins were closely regulated by cholesterol-rich lipid rafts. Acute depletion of cholesterol from the plasma membrane with methyl-beta-cyclodextrin caused an elevated basal hormone secretion from both beta- and alpha-cells and a loss of glucose-stimulated insulin secretion, implicating that cholesterol-rich lipid rafts play an important role in regulating exocytosis of these two types of islet cells. Chronic pharmacological inhibition of beta-cell endogenous cholesterol biosynthesis with squalene epoxidase inhibitor caused an impairment of both Cav channels and SNARE protein exocytotic machinery, indicating that intracellular cholesterol and its homeostasis are critical for maintaining normal beta-cell function.
The work presented in this thesis provided clear evidence that cholesterol-rich lipid rafts play a critical role in maintaining the normal function of pancreatic ion channels and SNARE proteins to regulate pancreatic beta- and alpha-cells stimulus-secretion coupling. Manipulation of cholesterol level of beta- and alpha-cells could be a potential target for a therapeutic intervention in the treatment of type 2 diabetes.
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Koo, Ellen. "Syntaxin-3 Regulates Biphasic Glucose Stimulated Insulin Secretion in the Pancreatic Beta Cell." Thesis, 2010. http://hdl.handle.net/1807/25732.
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Our study aims to investigate the role of Syntaxin-3 in glucose stimulated insulin secretion (GSIS) and how it regulates the recruitment to plasma membrane and/or exocytotic fusion of insulin granules. We examined endogenous Syn-3 function by down-regulating its expression using siRNA/lenti-shRNA, which impaired GSIS. Although Syn-3 depleted cells showed no change in the number and fusion of docked granules, there was a reduction in newcomer granules and their subsequent exocytotic fusion. We then examined the effects of overexpressing Syn-3-WT, which enhanced biphasic GSIS. Since open conformation (OF) Syn-1A was reported to enhance exocytosis by promoting SNARE complex formation, we constructed OF Syn-3. Exogenous OF Syn-3 had no effect on secretion as it is unable to be trafficked to insulin granules. Taken together, we conclude that Syn-3 facilitates mobilization of newcomer insulin granules to the plasma membrane, to contribute to both first and second phase of GSIS in pancreatic beta cells.
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Erion, Karel Arnt. "Nutrient regulation of insulin secretion: implications for hyperinsulinemia." Thesis, 2016. https://hdl.handle.net/2144/16726.
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Pancreatic beta-cells regulate blood glucose by secreting insulin in response to nutrients. The development of Type 2 Diabetes (T2D) is characterized by elevated insulin secretion in the fasted state and a failure to adequately respond to nutrient influx, particularly glucose. Current dogma states that insulin resistance is the initiating event in the development of T2D, with compensation by beta-cells necessary to maintain glucose homeostasis. An alternative model, which will be a central theme throughout this thesis, is that hypersecretion of insulin is the initiating and sustaining event in the development of T2D.
The underlying cause of insulin hypersecretion is unclear. Determining this is important in order to test this alternative model as a viable target for prevention and treatment of T2D. Because of the association between obesity and hyperinsulinemia, we hypothesized that exposure of the β-cell to high levels of nutrients stimulates insulin hypersecretion. We found that chronic incubation of β-cells in high glucose and/or oleate, which mimics nutrient conditions in obesity, lowered the half-maximal response for glucose to stimulate insulin secretion. The degree of the left-shift correlated with lipid stores. We determined that heightened sensitivity of granule exocytosis to Ca2+ was driving this left-shift. Thus glucose, while not necessarily abnormal in obesity, may cause hypersecretion of insulin due to altered sensitivity of the β-cell to this secretagogue. Iron stores are increased in obesity and are predictive of T2D development. We found that iron acutely stimulated both basal and glucose-stimulated insulin secretion (GSIS) in a reactive oxygen species dependent manner. Interestingly, iron did not increase insulin secretion via Ca2+ influx. Thus, both iron and glucose/oleate induce insulin hypersecretion via an aspect of the triggering pathway that is not Ca2+, the putative triggering signal. Previous work in our laboratory documented that exogenous mono-oleoyl-glycerol, an endogenous lipid signaling molecule and food additive, increases basal insulin secretion. We found that inhibition of monoacylglycerol lipase, which increases cellular monacylglycerol species, reduced GSIS, possibly via a reduction in long-chain CoA. Collectively, our works supports the hypothesis that chronic exposure to high nutrient levels drives insulin hypersecretion in obesity.2018-06-15T00:00:00Z
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Allen, Ronald Wayne. "Fatty acid required for glucose-induced change in beta cell plasma membrane potential leading to insulin secretion." Thesis, 2019. https://hdl.handle.net/2144/34890.
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The pancreatic β−cell secretes insulin through a combination of triggering and amplification pathways in response to glucose. Glucose metabolism is known to increase intracellular calcium and trigger insulin secretion from the β−cell while fatty acid (FA), an essential component of glucose stimulated insulin secretion (GSIS), is known to amplify secretion through varied mechanisms. Orlistat, a lipase inhibitor, blocks GSIS although the mechanism has not been clearly elucidated. We show that orlistat can also inhibit basal insulin secretion. FA can prevent/reverse orlistat-induced inhibition of secretion but fails to amplify GSIS after orlistat treatment. Here we test the hypothesis that FA is required to maintain normal plasma membrane potential and calcium influx in the β−cell. Clonal pancreatic β−cells (INS-1 832/13) were cultured in RPMI media containing 11 mM glucose and 10% FBS. Insulin secretion was measured over 2 hours with and without FA and orlistat (200 µM) using homogeneous time resolved fluorescence insulin assay (HTRF, Cisbio) and reported as ng/million cells. Intracellular calcium was measured in single cells using fura-2 AM. Single cell membrane potential was measured with virally expressed ARC Lite protein (Montana molecular). High glucose (8 mM) stimulated insulin secretion at least 3-fold over basal glucose (2 mM) and addition of FA enhanced GSIS. Orlistat almost completely abolished GSIS. This inhibition was mostly prevented in the presence of FA. Orlistat blocked calcium influx required for triggering insulin release while addition of FA recovered normal calcium homeostasis. The monoacylglycerol lipase inhibitor JZL 184 reduced both calcium influx and the increase in plasma membrane potential induced by KCl. FA recovered plasma membrane potential inhibited by JZL 184. Our results suggest that reducing β−cell intracellular FA availability by lipase inhibition blocks GSIS by preventing the glucose-induced rise in plasma membrane potential required to induce β−cell calcium influx through voltage dependent calcium channels (VDCC). FA is thus required to maintain normal nutrient metabolic coupling to insulin secretion. Whether the effect of FA to modulate plasma membrane potential plays a role in β−cell insulin hypersecretion resulting from excess nutrients requires further investigation.
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Ronnebaum, Sarah Marie. "Pyruvate Cycling Pathways and Glucose-Stimulated Insulin Secretion in Pancreatic Beta Cells." Diss., 2008. http://hdl.handle.net/10161/603.
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Yang, Wei-Ti, and 楊惟蒂. "The Effects of Momordica charantia Linn. Water Extracts and Fractions on Glucose Uptake of Hepatic Cell Line and Insulin Secretion of Islet Beta Cell Line." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/55625661937437677029.
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碩士國立臺灣大學
微生物與生化學研究所
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Metabolic syndromes predict a high risk of cardiovascular diseases and type 2 diabetes. Insulin resistance and abnormal regulation of glucose homeostasis are major part of metabolic syndromes. Tissue-specific knockouts of the insulin receptor in liver and islet beta cells in mice resulted in impaired plasma glucose control, indicating that both liver and islet beta cells are indispensible in the regulation of body glucose homeostasis and metabolism. Bitter gourd (BG, Momordica charantia) is known for its hypoglycemic activity, but the active compounds and molecular target have not been clearly understood. This study aimed at examining effects of wild BG (Hualien No.4) water extract and fraction on the glucose uptake of hepatocytes (FL83B hepatic cell line) and on the insulin secretion of islet beta cells (RIN-m5F and HIT-T15 cell line). Glucose uptake by FL83B cells was measured by the reduction of glucose concentration in the culture media after cells were treated with insulin (positive control) or MC extract/fractions for 16 or 20 hrs. Insulin secretion was measured after RIN-m5F and HIT-T15 cells were treated with 10mM glucose (positive control) or MC extract/fractions for 1 hour. Insulin secretion was also measured in HIT-T15 cells pretreated with 100uM palmitic acid for 48 hours to blunt the response of insulin secretion to glucose. The results shows that the P-fraction (containing insulin-like peptide), the WE (water extract) and its low MW (<3kD) fractions (WES) of MC significantly enhanced the glucose uptake of FL83B and the insulin secretion in both of the two beta cell lines (p<0.05). WE and WES were further hydrolyzed by incubation with β-glucosidase. The hydrolyzed products were sequentially extracted by ethyl acetate (EA) and butanol(B). The two extracts of WE also significantly enhanced glucose uptake of FL83B and insulin secretion of HIT-T15 (P<0.05). In addition, the EA extract of theβ-glucosidase hydrolyzed WES also increased the glucose uptake of FL83B and the insulin secretion in both of the beta cells (P <0.05). It was found that one fraction obtained from the prepared HPLC separation of the EA extract of the β-glucosidase hydrolyzed WES significantly improved the impaired insulin secretion of HIT-T15 pretreated with palmitic acid. In conclusion, these results suggest that the hypoglycemic effect of Hualien No. 4 wild BG is attributed, at least in part, to its active component(s) that enhanced the glucose uptake of liver and the insulin secretion of islet beta cells.
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Zhao, Shangang. "Monoacylglycerol, alpha/beta-hydrolase domain-6, and the regulation of insulin secretion and energy metabolism." Thèse, 2015. http://hdl.handle.net/1866/13533.
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Le cycle glycérolipides/acides gras libres (GL/FFA) est une voie métabolique clé qui relie le métabolisme du glucose et des acides gras et il est composé de deux processus métaboliques appelés lipogenèse et lipolyse. Le cycle GL/FFA, en particulier la lipolyse des triglycérides, génère diverses molécules de signalisation pour réguler la sécrétion d'insuline dans les cellules bêta pancréatiques et la thermogenèse non-frissonnante dans les adipocytes. Actuellement, les lipides provenant spécifiquement de la lipolyse impliqués dans ce processus sont mal connus.
L’hydrolyse des triglycérides dans les cellules β est réalisée par les actions successives de la triglycéride lipase adipocytaire pour produire le diacylglycérol, ensuite par la lipase hormono-sensible pour produire le monoacylglycérol (MAG) et enfin par la MAG lipase (MAGL) qui relâche du glycerol et des acides gras. Dans les cellules bêta, la MAGL classique est très peu exprimée et cette étude a démontré que l’hydrolyse de MAG dans les cellules β est principalement réalisée par l'α/β-Hydrolase Domain-6 (ABHD6) nouvellement identifiée. L’inhibition d’ABHD6 par son inhibiteur spécifique WWL70, conduit à une accumulation des 1-MAG à longues chaines saturées à l'intérieur des cellules, accompagnée d’une augmentation de la sécrétion d'insuline stimulée par le glucose (GSIS). Baisser les niveaux de MAG en surexprimant ABHD6 dans la lignée cellulaire bêta INS832/13 réduit la GSIS, tandis qu’une augmentation des niveaux de MAG par le « knockdown » d’ABHD6 améliore la GSIS. L'exposition aiguë des monoacylglycérols exogènes stimule la sécrétion d'insuline de manière dose-dépendante et restaure la GSIS supprimée par un inhibiteur de lipases appelé orlistat. En outre, les souris avec une inactivation du gène ABHD6 dans tous les tissus (ABHD6-KO) et celles avec une inactivation du gène ABHD6 spécifiquement dans la cellule β présentent une GSIS stimulée, et leurs îlots montrent une augmentation de la production de monoacylglycérol et de la sécrétion d'insuline en réponse au glucose. L’inhibition d’ABHD6 chez les souris diabétiques (modèle induit par de faibles doses de streptozotocine) restaure la GSIS et améliore la tolérance au glucose. De plus, les résultats montrent que les MAGs non seulement améliorent la GSIS, mais potentialisent également la sécrétion d’insuline induite par les acides gras libres ainsi que la sécrétion d’insuline induite par divers agents et hormones, sans altération de l'oxydation et l'utilisation du glucose ainsi que l'oxydation des acides gras. Nous avons démontré que le MAG se lie à la protéine d’amorçage des vésicules appelée Munc13-1 et l’active, induisant ainsi l’exocytose de l'insuline. Sur la base de ces observations, nous proposons que le 1-MAG à chaines saturées agit comme facteur de couplage métabolique pour réguler la sécrétion d'insuline et que ABHD6 est un modulateur négatif de la sécrétion d'insuline.
En plus de son rôle dans les cellules bêta, ABHD6 est également fortement exprimé dans les adipocytes et son niveau est augmenté avec l'obésité. Les souris dépourvues globalement d’ABHD6 et nourris avec une diète riche en gras (HFD) montrent une faible diminution de la prise alimentaire, une diminution du gain de poids corporel et de la glycémie à jeun et une amélioration de la tolérance au glucose et de la sensibilité à l'insuline et ont une activité locomotrice accrue. En outre, les souris ABHD6-KO affichent une augmentation de la dépense énergétique et de la thermogenèse induite par le froid. En conformité avec ceci, ces souris présentent des niveaux élevés d’UCP1 dans les adipocytes blancs et bruns, indiquant le brunissement des adipocytes blancs. Le phénotype de brunissement est reproduit dans les souris soit en les traitant de manière chronique avec WWL70 (inhibiteur d’ABHD6) ou des oligonucléotides anti-sense ciblant l’ABHD6. Les tissus adipeux blanc et brun isolés de souris ABHD6-KO montrent des niveaux très élevés de 1-MAG, mais pas de 2-MAG. L'augmentation des niveaux de MAG soit par administration exogène in vitro de 1-MAG ou par inhibition ou délétion génétique d’ABHD6 provoque le brunissement des adipocytes blancs. Une autre évidence indique que les 1-MAGs sont capables de transactiver PPARα et PPARγ et que l'effet de brunissement induit par WWL70 ou le MAG exogène est aboli par les antagonistes de PPARα et PPARγ. L’administration in vivo de l’antagoniste de PPARα GW6471 à des souris ABHD6-KO inverse partiellement les effets causés par l’inactivation du gène ABHD6 sur le gain de poids corporel, et abolit l’augmentation de la thermogenèse, le brunissement du tissu adipeux blanc et l'oxydation des acides gras dans le tissu adipeux brun. L’ensemble de ces observations indique que ABHD6 régule non seulement l’homéostasie de l'insuline et du glucose, mais aussi l'homéostasie énergétique et la fonction des tissus adipeux.
Ainsi, 1-MAG agit non seulement comme un facteur de couplage métabolique pour réguler la sécrétion d'insuline en activant Munc13-1 dans les cellules bêta, mais régule aussi le brunissement des adipocytes blancs et améliore la fonction de la graisse brune par l'activation de PPARα et PPARγ. Ces résultats indiquent que ABHD6 est une cible prometteuse pour le développement de thérapies contre l'obésité, le diabète de type 2 et le syndrome métabolique.The glycerolipid/ free fatty acid (GL/FFA) cycle is a key metabolic pathway that links glucose and fatty acid metabolism and it consists of lipogenesis and lipolysis. GL/FFA cycling, especially in its lipolysis arm, generates various lipid signaling molecules to regulate insulin secretion in pancreatic ß-cells and non-shivering thermogenesis in adipocytes. Currently, the lipolysis-derived lipid signals involved in this process are uncertain. Triglyceride hydrolysis in mammalian cells is accomplished by the sequential actions of adipose triglyceride lipase to produce diacylglycerol, by hormone sensitive lipase to produce monoacylglycerol (MAG) and by MAG lipase (MAGL) that releases free fatty acid and glycerol. Our work shows that in pancreatic ß-cell, the classical MAGL is poorly expressed and that MAG hydrolysis is mainly conducted by the newly identified α/β-Hydrolase Domain-6 (ABHD6). Inhibition of ABHD6 by its specific inhibitor WWL70, leads to long-chain saturated 1-MAG accumulation inside the cells, accompanied by enhanced glucose-stimulated insulin secretion (GSIS). Decreasing the MAG levels by overexpression of ABHD6 in the ß-cell line INS832/13 reduces GSIS, while increasing MAG levels by ABHD6 knockdown enhances GSIS. Acute exposure of INS832/13 cells to various MAG species dose-dependently stimulates insulin secretion and restores GSIS suppressed by the pan-lipase inhibitor orlistat. Also, various biochemical and pharmacological experiments show that saturated 1-MAG levels species rather than unsaturated or 2-MAG species best correlate with insulin secretion. Furthermore, whole-body and β-cell-specific ABHD6-KO mice exhibit enhanced GSIS in vivo, and their isolated islets show elevated MAG production and GSIS. Inhibition of ABHD6 in low dose streptozotocin diabetic mice restores GSIS and improves glucose tolerance. Results further show that ABHD6-accessible MAGs not only enhance GSIS, but also potentiate fatty acid and non-fuel-induced insulin secretion without alteration in glucose oxidation and utilization as well as fatty acid oxidation. We have identified that MAG binds and activates the vesicle priming protein Munc13-1, thereby inducing insulin exocytosis. Based on all these observations, we propose that lipolysis-derived saturated 1-MAG acts as a metabolic coupling factor to regulate insulin secretion and ABHD6 is a negative modulator of insulin secretion. Besides its role in ß-cells, ABHD6 is also highly expressed in adipocytes and its level is increased with obesity. Mice globally lacking ABHD6 on high fat diet (HFD) show modestly reduced food intake, decreased body weight gain, insulinemia and fasting glycemia and improved glucose tolerance and insulin sensitivity and enhanced locomotor activity. In addition, ABHD6-KO mice display increased energy expenditure and cold-induced thermogenesis. In accordance with this, these mice show elevated UCP1 level in white and brown adipocytes, indicating browning of white adipocytes. The browning phenotype is reproduced in the mice either chronically treated with the ABHD6 inhibitor WWL70 or an antisense oligonucleotides targeting ABHD6. White and brown adipose tissues isolated from whole body ABHD6 KO mice show greatly elevated levels of 1-MAG, but not 2-MAG. Increasing MAG levels by either exogenous administration of 1-MAG or ABHD6 inhibition or genetic deletion induces browning of white adipocytes in a cell-autonomous manner. Further evidence indicates that 1-MAGs can transactivate PPARα and PPARγ and the browning effect induced by WWL70 or exogenous MAG is abolished by PPARα and PPARγ antagonists. In vivo administration of the PPARα antagonist GW6471 to ABHD6 KO mice partially reversed the ABHD6-KO effects on body weight gain, and abolishes the enhanced thermogenesis, white adipose browning and fatty acid oxidation in brown adipose tissue. All these observations indicate that ABHD6 regulates not only insulin and glucose homeostasis but also energy homeostasis and adipose tissue function. Thus, ABHD6-accessible 1-MAG not only acts as a metabolic coupling factor to regulate fuel and non-fuel induced insulin secretion by activating Munc13-1 in beta cells, but also regulates glucose, insulin and energy homeostasis. The latter effects are mediated at least in part via browning of white adipocytes and enhanced brown fat function through the activation of PPARα and PPARγ. Collectively these findings suggest that ABHD6 is a promising target for developing therapeutics against obesity, type 2 diabetes and metabolic syndrome.
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Rose, Tobias. "Stimulus-secretion coupling in pancreatic β-cells of healthy and diabetic rats in tissue slice preparation." Doctoral thesis, 2006. http://hdl.handle.net/11858/00-1735-0000-0006-B6DF-F.
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