Certain membrane lipids are involved in intracellular signalling processes, among them phosphoinositides and diacylglycerol (DAG). They mediate a variety of functions, including the effects of nutrients and neurohormonal stimuli on insulin secretion from pancreatic β-cells. To ensure specificity of the signal, their concentrations are maintained under tight spatial and temporal control. Here, live-cell imaging techniques were employed to investigate spatio-temporal aspects of lipid signalling in the plasma membrane of insulin-secreting β-cells. The concentration of phosphatidylinositol 4-phosphate [PtdIns(4)P] increased after stimulation with glucose or Gq protein-coupled receptor agonists. The glucose effect was Ca2+-dependent, whereas the receptor response was mediated by isoforms of novel protein kinase C (PKC). The increases in PtdIns(4)P were paralleled by lowerings of the phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] concentration. This relationship was not caused by conversion of PtdIns(4,5)P2 to PtdIns(4)P but rather reflected independent regulation of the two lipids. Stimulation of β-cells with glucose or a high K+ concentration induced pronounced, repetitive increases in plasma-membrane DAG concentration, which were locally restricted and lasted only for a few seconds. This pattern was caused by exocytotic release of ATP, which feedback-activates purinergic P2Y1-receptors and stimulates local phospholipase C-mediated DAG generation. Despite their short durations the DAG spikes triggered local activation of PKC. Novel PKCs were recruited to the plasma membrane both after glucose and muscarinic receptor stimulation. While the glucose-induced translocation was synchronized with DAG spiking, muscarinic stimulation induced sustained elevation of the DAG concentration and stable membrane association of the kinase. Also conventional PKCs translocated to the membrane after glucose and receptor stimulation. The glucose-induced response was complex with sustained membrane association mirroring the cytoplasmic Ca2+ concentration, and superimposed brief recurring translocations caused by DAG. Interruption of the purinergic feedback loop underlying DAG spiking suppressed insulin secretion. Since the DAG spikes reflected exocytosis events, a single-cell secretion assay was established, which allowed continuous recording of secretion dynamics from many cells in parallel over extended periods of time. With this approach it was possible to demonstrate that insulin exerts negative feedback on its own release via a phosphatidylinositol 3,4,5-trisphosphate-dependent mechanism.

L’existence d’une relation entre les troubles cardio-métaboliques composant le syndrome métabolique et une hyperactivité sympathique est bien admise dans la littérature sans que la relation causale entre ces deux entités soit clairement définie. Nos travaux sur un modèle murin d’hyperactivité sympathique constitutive (délétion partielle et/ou complète du transporteur de recapture de la noradrénaline) ont permis de mettre en évidence le rôle de celle-ci dans le développement de troubles glucidiques : 1) Une augmentation de l’activité sympathique est un facteur suffisant pour le développement de troubles glucidiques précoces associant une intolérance au glucose à une hyperinsulinémie basale sans hyperglycémie. 2) Ces désordres seraient dus à un retard de sécrétion d’insuline en réponse au glucose, probablement consécutif à une sous-expression du transporteur GLUT2. Ces résultats montrent que l’hyperactivité sympathique chronique pourrait constituer un facteur pronostic permettant le diagnostic précoce de patients à risque de développer des troubles de l’homéostasie glucidique et ouvre des perspectives dans le traitement du diabète de type 2. / Several studies have established an association between cardiometabolic disorders composing the metabolic syndrome and sympathetic hyperactivity. The causal relationship is however not clearly defined. Our work on a murine model of constitutive sympathetic hyperactivity (partial and / or complete deletion of the norepinephrine reuptake transporter) highlights its role in the development of carbohydrate disorders: 1) An increase in the sympathetic activity is a sufficient factor for early carbohydrate disorders associating glucose intolerance with basal hyperinsulinemia without hyperglycemia. 2) These disorder are thought to be due to a delay in insulin secretion in response to glucose stimulation, probably consecutive to a decreased expression of the GLUT2 transporter. These results show that chronic sympathetic hyperactivity may constitute a prognostic factor allowing the early diagnosis of patients at risk to develop glucose homeostasis disorders and opens perspectives in the treatment of type 2 diabetes mellitus.

Orientador: Everardo Magalhães Carneiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-13T21:03:55Z (GMT). No. of bitstreams: 1 Batista_ThiagoMartins_M.pdf: 1168177 bytes, checksum: 6c327ab4c396fab9844364b47f69ad79 (MD5) Previous issue date: 2009 / Resumo: A desnutrição ainda é um problema de saúde pública que afeta principalmente países em desenvolvimento e sua prevalência chega a ser crescente em algumas áreas. Vários estudos obtiveram êxito em correlacionar a má nutrição em estágios iniciais de vida com o desenvolvimento de doenças cardiovasculares e diabetes tipo 2 na vida adulta. No modelo de desnutrição pós desmame verifica-se menor secreção de insulina estimulada por glicose e outros agentes insulinotrópicos bem como menor expressão de várias proteínas envolvidas com a funcionalidade da célula b. Estudos realizados por nosso grupo e outros laboratórios mostram que a suplementação de camundongos com taurina aumenta a secreção de insulina além de regular o influxo de íons Ca2+ para as células b, etapa crucial para o processo secretório. Para avaliar os efeitos da taurina sobre animais desnutridos, utilizamos ratos wistar, machos com 21 dias de vida. Os animais receberam dieta contendo 17% de proteína (normoprotéica) (C) ou 6% de proteína (hipoprotéica) (D). Animais C e D receberam suplementação com taurina a 2,5% na água de beber por 30 dias (CT30 e DT30) ou 90 dias (CT90 e DT90). Em seguida avaliamos parâmetros biométricos e bioquímicos, tolerância à glicose, secreção de insulina estimulada por glicose e pelo agonista colinérgico carbacol, expressão de proteínas envolvidas no controle da secreção de insulina e, finalmente, registramos os movimentos citoplasmáticos de íons Ca2+ após estímulo com glicose e carbacol. Verificamos que a restrição protéica retardou o crescimento dos animais além de reduzir a concentração plasmática de proteínas totais (C = 6,81±0,04; CT30 = 7,15±0,54; CT90 = 6,87±0,19; D = 5,35±0,24; DT30 = 5,37±0,28; DT90 = 5,70±0,09 g/dl; n = 3-5) e albumina (C = 3,20±0,11; CT30 = 3,41±0,02; CT90 = 3,18±0,05; D = 2,74±0,07; DT30 = 2,49±0,09; DT90 = 2,67±0,04 g/dl; n = 5-9) sem efeito da suplementação com taurina. Os animais D se mostraram mais tolerantes à glicose e a suplementação com taurina por 90 dias restaurou parcialmente a tolerância desses animais (C = 30249±2682; CT30 = 37255±6691; CT90 = 29365±2257; D = 16916±1609; DT30 = 18791±2859; DT90 = 23425±3856 AAC; n = 5-9). Nesse trabalho mostramos que a suplementação com taurina corrige a hipoinsulinemia verificada em animais desnutridos alimentados (C = 4,97±0,34; CT90 = 3,56±0,52; D = 1,39±0,10; DT90 = 3,31±0,70 ng/ml; n = 5-8) bem como a responsividade de ilhotas isoladas a concentrações crescentes de glicose. Verificamos também que a taurina normaliza a secreção de insulina potencializada pelo carbacol (C = 9,4+0,8; CT90 = 12,4+0,7; D = 6,4+0,5; DT90 = 9+0,7 ng/ml; n = 12). As respostas secretórias foram observadas em conjunto com a regulação da expressão das proteínas SERCA3 (C = 100+21; CT90 = 174+17; D =96+90; DT90 = 149+11 % do C; n = 6), receptor muscarínico M3 (C = 100+24; CT90 = 155+80; D = 51+10; DT90 = 108+14 % do C; n = 5) e sintaxina 1 (C = 100+30; CT90 = 92+40; D = 50+12; DT90 = 77+11 % do C; n = 5) que participam do controle de diferentes etapas do processo de secreção de insulina. Por fim, verificamos que a suplementação com taurina melhorou o padrão de oscilação de íons Ca2+ após estímulo com glicose. Concluímos então que a suplementação com taurina por 90 dias restaura a sensibilidade das ilhotas à glicose e ao carbacol possivelmente pela regulação do fluxo de cálcio para as células b bem como pela modulação da expressão de proteínas que controlam o processo de secreção de insulina. / Abstract: Malnutrition still is a public health issue, especially in developing countries. Many studies correlate malnourishment during early life and the development of cardiovascular disease and type 2 Diabetes Mellitus on latter stages. Animal models of malnutrition reveal impaired insulin secretion stimulated by glucose and other insulinotropic agents as well as lower expression of key proteins for b cell function. The literature shows that taurine supplementation increases insulin secretion and regulates calcium dynamics on b cells. Male, 21 days old, wistar rats received diet containing 17% (C) or 6% (D) of protein. Both groups received taurine supplementation on the drinking water for 30 (CT 30 and DT 30) and 90 (CT90 and DT 30) days. Next we assessed biometric and biochemical parameters, glucose tolerance, glucose and carbacholstimulated insulin secretion, protein expression of muscarinic M3 receptor, Phospholipase C b2, SERCA3, Syntaxin 1 and, finally, we registered cytoplasmic Ca2+ after stimulus with glucose and carbachol. Protein restricted rats showed lower body weight, plasma proteins (C = 6,81±0,04; CT30 = 7,15±0,54; CT90 = 6,87±0,19; D = 5,35±0,24; DT30 = 5,37±0,28; DT90 = 5,70±0,09 g/dl; n = 3-5), albumin (C = 3,20±0,11; CT30 = 3,41±0,02; CT90 = 3,18±0,05; D = 2,74±0,07; DT30 = 2,49±0,09; DT90 = 2,67±0,04 g/dl; n = 5-9) and increased glucose tolerance (C = 30249±2682; CT30 = 37255±6691; CT90 = 29365±2257; D = 16916±1609; DT30 = 18791±2859; DT90 = 23425±3856 AUC; n = 5-9). Taurine supplementation had no effect upon nutritional status parameters and partially restored glucose tolerance and insulinemia to C levels. Taurine increased secretory response to glucose and carbachol (C = 9,4+0,8; CT90 = 12,4+0,7; D = 6,4+0,5; DT90 = 9+0,7 ng/ml; n = 12). It also increased protein expression of M3 receptor (C = 100+24; CT90 = 155+80; D = 51+10; DT90 = 108+14 % of C; n = 5), SERCA 3 (C = 100+21; CT90 = 174+17; D =96+90; DT90 = 149+11 % of C; n = 6) and syntaxin 1 (C = 100+30; CT90 = 92+40; D = 50+12; DT90 = 77+11 % of C; n = 5). Finally, taurine supplementation for 90 days improved Ca2+ dynamics when the islets were stimulated with glucose. In conclusion, these data show that taurine supplementation restores secretory responsiveness to glucose and carbachol possibly through Ca2+ dynamics modulation and increased expression of key proteins for insulin secretion. / Mestrado / Fisiologia / Mestre em Biologia Funcional e Molecular

Orientador: Antonio Carlos Boschero / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-16T00:11:07Z (GMT). No. of bitstreams: 1 Vanzela_EmerielleCristine_D.pdf: 2535043 bytes, checksum: eee7b54cea5f470c5637de8c4b3385f5 (MD5) Previous issue date: 2010 / Resumo: A obesidade atingiu proporções alarmantes constituindo-se num fator de risco para o desenvolvimento de várias doenças. O aumento da resistência periférica à insulina acompanha esta patologia e a incapacidade da célula beta pancreática em suprir a maior necessidade por insulina leva ao desenvolvimento de intolerância à glicose, hiperglicemia e diabetes. Por esta razão, é importante investigar mecanismos que tornem a célula beta capaz de aumentar sua capacidade secretória. A exemplo da obesidade, resistência periférica à insulina é também observada durante a prenhez. No entanto, neste caso, a célula beta é capaz de aumentar a produção e secreção do hormônio, mantendo a tolerância à glicose em condições adequadas. Diante disso,decidimos investigar a sensibilidade à insulina e a consequente resposta das células beta pancreáticas durante a prenhez em ratas obesas. Observamos que a alimentação com a dieta de cafeteria aumentou o ganho de peso, bem como os depósitos de gordura das ratas. Ratas obesas não-prenhes (Caf) e prenhes (CafP) apresentaram tolerância à glicose diminuída, associada a um aumento da insulina plasmática em resposta à sobrecarga de glicose no grupo CafP. Apesar disso, as glicemias de jejum e pós-prandial foram normais nos dois grupos. No entanto, as ratas Caf e CafP apresentaram hiperinsulinemia (jejum e alimentado), aumento do índice insulina/glicose e do AGL plasmático (alimentado). Ainda, houve redução na sinalização da insulina no fígado e músculo esquelético das ratas Caf e CafP, aos 15 e aos 19 dias de prenhez, de forma mais exacerbada do que a redução observada nas ratas controle prenhes. Em paralelo, as ilhotas isoladas das ratas Caf secretaram menos insulina em resposta a diferentes estímulos. Contudo, o conteúdo total de insulina, a secreção estimulada por PMA (ativador da PKC), a produção decompostos redutores e a oxidação de glicose, na presença de 11,1 mmol/L do açúcar, foram similares entre as ratas Caf e as controle não-prenhes. Entretanto, as ilhotas isoladas das ratas Caf apresentaram redução na mobilização do Ca2+ citoplasmático livre frente à glicose ou tolbutamida, acompanhada pela redução da expressão gênica da subunidade ?1.2 do canal de cálcio voltagem-dependente (CaVa1.2), e da Ca2+- ATPase do retículo endoplasmático tipo 2a. Independente da dieta, a prenhez aumentou a secreção de insulina em resposta à glicose, a produção de compostos redutores, a oxidação de glicose, a amplitude e a frequência das oscilações do Ca2+ citoplasmático e, a expressão gênica do CaVa1.2. Concluindo, a prenhez nas ratas obesas melhorou o manejo do Ca2+ e restaurou a secreção de insulina por ilhotas isoladas. Contudo, esta restauração não foi suficiente para vencer o aumento da resistência periférica à insulina e normalizar a tolerância à glicose nas ratas obesas / Abstract: The incidence of obesity reached alarming levels worldwide. This illness constitutes a risk factor for the development of several other diseases. The augmented peripheral insulin resistance accompanies this pathology, and the failure of the pancreatic beta cell to overcome the higher demand for insulin causes glucose intolerance, hyperglycemia and diabetes. For this reason, it became interesting to investigate mechanisms that make the beta cell capable to increases its secretory capacity. As obesity, peripheral insulin resistance is also observed during pregnancy. Nevertheless, in this situation, the beta cell is capable to enhance insulin production and release, maintaining glucose tolerance at adequate levels. Therefore, we decided to investigate insulin sensibility and the consequent beta cell response during pregnancy in obese rats. We observed that cafeteria diet enhanced weight gain and fat pads in rats. Despite no differences were noticed in obese non-pregnant (Caf) and pregnant (CafP) rats, during fast and fed states, the glucose tolerance was diminished in these rats, associated with an augmented plasma insulin levels in response to a glucose load inCafP rats. However, Caf and CafP rats had hyperinsulemia (fast and fed), higher insulin/glucose index, and enhanced plasma FFA (fed state). In addition, we observed a reduction in insulin signaling in liver and skeletal muscle from Caf and CafP rats, at15th and 19th days of pregnancy, higher than that registered in control pregnant rats. Also, there was a reduction in insulin secretion induced by different stimuli in is lets from Caf rats. However, total islet insulin content, PMA-stimulated insulin secretion, production of reducing equivalents, and glucose oxidation in the presence of 11.1mmol/L glucose, were similar between islets from Caf and non-pregnant control rats .Nevertheless, glucose- and tolbutamide-induced Ca2+ mobilization, a1.2 subunit of thevoltage sensitive Ca2+ channel (CaVa1.2), and sarcoendoplasmic reticulum Ca2+ATPase 2a gene expression were reduced in islets from Caf rats. Independently of the diet, pregnancy enhanced glucose stimulated insulin secretion, reducing equivalents production, glucose oxidation, amplitude and frequency of cytoplasm Ca2+ oscillations, and CaVa1.2 gene expression. In conclusion, although pregnancy improved Ca2+ handling and restored insulin secretion in cafeteria diet-induced obese rats, this restoration was not enough to overcome the increase in peripheral resistance and normalize glucose tolerance in these obese rats / Doutorado / Fisiologia / Doutor em Biologia Funcional e Molecular

Orientador: Jose Roberto Bosqueiro / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-10T23:23:58Z (GMT). No. of bitstreams: 1 Giozzet_VanessaAparecidaGoncalves_D.pdf: 2125921 bytes, checksum: 5e1d4923fcc0268442cc60af14fa58dd (MD5) Previous issue date: 2008 / Resumo: A desnutrição e a resistência periférica à insulina induzida por administração de glicocorticóides induzem compensações funcionais e morfológicas em ilhotas pan creáticas a fim de manter a homeostase glicêmica. Deste modo, investigamos as alterações desenvolvidas pelo tratamento com dexametasona (Dex) em animais submetidos à restrição protéica. Foram analisados: parâmetros metabólicos, secreção de insulina em resp osta a glicose e proteínas envolvidas na via de sinalização da insulina em ilhotas pancreáticas isoladas. Ratos submetidos à dieta hipoprotéica (LP) apresentaram características padrões que caracterizam a desnutrição como: diminuição de ganho de massa corp oral, redução dos níveis séricos de albumina, proteína total e insulina. Adicionalmente, os ratos LP exibiram aumento da sensibilidade periférica à insulina e redução da área das ilhotas pancreáticas comparadas ao grupo controle ( P < 0,05). Todos estes parâmetros apresentaram valores similares ao grupo controle nos ratos submetidos à dieta hipoprotéica e submetidos ao tratamento com Dex (LPD), exceto para o peso corpóreo ( P < 0,05). A secreção de insulina em ilhotas pancreáticas isoladas de ratos LPD aprese ntou maior responsividade à glicose, em níveis estimulatórios, comparados a secreção em ilhotas de ratos LP (P < 0,05). Paralelo aos resultados de secreção, os ratos LPD exibiram redução do conteúdo protéico de IRS-1, IRS-2 e aumento dos níveis protéicos d e p-FoxO1, p-ERK e PKC comparados ao grupo LP (P < 0,05). Concomitantemente, as ilhotas dos ratos LPD mostraram ¿se hipertrofiadas comparadas com ilhotas de ratos LP ( P < 0,05). Em conclusão, o tratamento com dexametasona reverte, ao menos parcialmente, os efeitos no metabolismo analisados e no funcionamento das ilhotas pancreáticas causados pela restrição protéica, confirmando a grande plasticidade das células ß frente a condições adversas facultativas e/ou permanentes / Abstract: Malnutrition caused by protein restriction and dexamethasone -induced insulin resistance, in vivo treatment (Dex) are conditions associated with morphological and functional alterations in pancreatic islets. Thus, the present study evaluated the dexamethasone treatment effects on the metabolic parameters, glucose-stimulated insulin secretion and proteins involved in the insulin - signalling pathway over low protein diet fed rats (LP). LP rats showed decrease in body weight, serum insulin, total serum protein, and serum albumin, patte rns that characterize the LP rats. Moreover, LP rats presented improved peripheral insulin sensibility and reduced islets area (P < 0,05). Except for the body weight (P < 0,05), all these parameters were proned to be normalized in rats exposed to a low protein diet and treated with dexamethasone (LPD), whose islets showed increased glucose stimulated insulin secretion (GSIS). In addition, LPD rats showed lower protein expression of IRS-1, IRS-2 and higher in p-FoxO1, p-ERK and PKC, while presenting pancreatic islet hypertrophy compared to LP rats islet. In conclusion, dexamethasone treatment revert the effects related to metabolism and islet function caused by diet protein restriction, confirming ß-cells wide plasticity, even in transient or lasting adverse conditions / Doutorado / Fisiologia / Doutor em Biologia Funcional e Molecular

O hiperinsulinismo congênito (CHI) é um distúrbio do pâncreas endócrino, mais freqüentemente causado por alterações dos canais de membrana KATP das células , resultando em secreção inapropriada de insulina e hipoglicemia severa e persistente nos recém-nascidos, que leva ao óbito ou a seqüelas neurológicas graves, se não diagnosticado a tempo. O diagnóstico depende da análise dos dados clínicos, laboratoriais, morfológicos e genético-moleculares (50% apresentam mutações dos canais KATP). As duas formas histopatológicas descritas requerem cirurgias radicalmente opostas: pancreatectomia quase-total (95-98%) na forma difusa que acomete todo o pâncreas, ou apenas exerese do foco adenomatoso de células , medindo em média 4,5 mm, na forma focal, e portanto a sua distinção é essencial durante o exame intra-operatório de congelação ou através de [18F]-L-Dopa PET-CT. Dez pacientes com CHI difuso e um com CHI focal, submetidos a pancreatectomia, foram analisados em relação a parâmetros clínicos, histopatológicos, de proliferação das células (IHQ de dupla marcação Ki-67 / insulina) e quanto à presença de mutações nos genes das únicas duas proteínas (SUR 1 e Kir 6.2) que formam os canais KATP, e comparados a 19 pâncreas controles normais da mesma faixa etária. Pacientes e controles foram estratificados em 3 meses e > 3 meses de idade. Nucleomegalia, ausente nos controles, foi observada apenas na forma difusa. Os critérios histológicos de maturação normalmente mais freqüentes nos controles 3 meses, foram freqüentemente observados nos recém-nascidos com CHI difuso > 3 meses, sugerindo um retardo na maturação do pâncreas endócrino destes pacientes. O índice de proliferação das células (Ki-67- LI), muito elevado nos focos adenomatosos da forma focal, foi útil na distinção destes focos dos agregados frouxos de ilhotas, histologicamente muito semelhantes, observados em dois casos difusos e um controle, que apresentam níveis de Ki-67-LI cerca de 10 vezes menor. Na forma difusa o Ki-67-LI também foi estatisticamente mais alto do que nos controles. Este é o primeiro estudo de pacientes com CHI no Brasil, e embora existam diferenças epidemiológicas entre os países relacionadas à determinação genética do CHI, não foram constatadas mutações ou novos polimorfismos nos exons 33-37 do gene ABCC8 (SUR 1) de 10/10 pacientes ou no único exon do gene KCNJ11 (Kir 6.2) de 4/10 pacientes / Congenital hyperinsulinism (CHI) is a rare pancreatic endocrine cell disease which most severe cases are found to be, at least in half of patients, associated with genetic defects in the -cell KATP channels. The aim of this study was to evaluate eleven Brazilian patients diagnosed, by standard criteria, as CHI non responsive to clinical therapy, and submitted to pancreatectomy, regarding: histology, -cell proliferation (IHC Ki-67 / insulin) and -cell KATP channels genes mutations in blood samples. For comparison of histology and -cell proliferation, 19 pancreatic control samples were included. According histology, ten patients were classified as diffuse and one as focal form. Nucleomegaly and -cells with abundant cytoplasm were absent in controls, and observed only in the group of diffuse CHI patients. Ki- 67-LI was useful to differentiate the adenomatous areas of the focal form CHI neonate from loose clusters of islets found in two diffuse form and one control samples. Proliferation was much higher in the focal CHI adenomatous areas, but diffuse CHI patients also have statistically higher Ki-67-LI than controls. This is the first genetic study of CHI patients in Brazil, and no mutations or new polymorphisms were found in the ABCC8 gene (SUR 1) (exons 33-37) or in the only exon of KCNJ11 gene (Kir 6.2) in 4/4 patients evaluated. On the other hand, enhanced -cell proliferation seems to be a constant feature in these patients both in diffuse and focal forms

Orientador: Antonio Carlos Boschiero / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-27T05:10:32Z (GMT). No. of bitstreams: 1 Ferreira_SandraMara_D.pdf: 2032504 bytes, checksum: da4ca0c7e913b98f9a0ec91b1a14ba82 (MD5) Previous issue date: 2015 / Resumo: A ARHGAP21 é uma proteína da família das RhoGAPs (Proteínas ativadoras de GTPases Rho) que, em diferentes tipos de células, controla múltiplas funções tais como: migração, proliferação, diferenciação e tráfego intracelular de vesículas. Em ilhotas de camundongo Swiss neonato o knockdown da ARHGAP21 aumentou a secreção de insulina estimulada por glicose (GSIS), por mecanismos ainda desconhecidos. Contudo, não se conhece os efeitos da ARHGAP21 sobre a secreção de insulina e sobre a homeostase glicêmica em camundongos adultos. Assim, o objetivo do trabalho foi avaliar: a) em ilhotas pancreáticas de camundongo Swiss neonato knockdown para ARHGAP21, a expressão de genes envolvidos com a proliferação, maturação e extrusão de grânulos de insulina, bem como o rearranjo do citoesqueleto de actina; b) em camundongos C57BL/6 adultos, o efeito do knockdown da ARHGAP21 sobre GSIS e sobre alguns genes que codificam proteínas envolvidas na função secretória (maturação e extrusão) e sobre a homeostase glicêmica. Os neonatos foram tratados (i.p.) com 1 nmol de antisense anti-ARHGAP21 (neonato AS) ou mismatch (CTL) por dois dias (redução da expressão de 60%). Os adultos foram tratados (i.p.) com 1,5 nmol/g de antisense (adulto AS) ou mismatch (adulto CTL) por 3 dias consecutivos (redução de 50%). A secreção de insulina foi avaliada na presença de concentrações crescentes de glicose (2,8 - 22,2 mM). A F-actina (polímero) foi medida através da marcação com faloidina. A expressão gênica foi avaliada por PCR em tempo real. Tolerância à glicose e ao Piruvato foi medida através de ipGTT e ipPTT, respectivamente, e a sensibilidade à insulina através do ipITT, clamp hiperinsulinêmico-euglicêmico e, AKT fosforilada. Como já descrito, ilhotas de neonatos AS apresentaram maior secreção basal de insulina (2,8 mM) bem como menor presença de F-actina. Observamos também maior expressão dos genes da VAMP2 e SNAP25. Ilhotas de adultos AS apresentaram maior secreção de insulina apenas na presença de 22,2 mM. Contudo, o aumento do [Ca2+]i, induzido por glicose, foi similar ao CTL. Observou-se também aumento da expressão dos genes da SYT VII (SYNAPTOTAGMINA VII) e CX 36 (CONEXINA 36). Adultos AS apresentaram intolerância à glicose e aumento da insulinemia durante o ipGTT, acompanhado de resistência à insulina específica no músculo, além de menor produção de glicose pelo fígado. Concluímos que a ARHGAP21 modula negativamente a secreção de insulina em neonato provavelmente através do rearranjo da actina e da redução da expressão de VAMP2 e SNAP25. Em ilhotas isoladas de camundongos adultos, a ARHGAP21 modula negativamente a expressão de genes envolvidos na sensibilidade ao cálcio e resposta secretória (SYT VII e CX 36). Apesar da melhora na secreção de insulina, os adultos AS apresentaram intolerância à glicose com discreta resistência à insulina no músculo que parece ser compensada pela menor liberação de glicose pelo fígado / Abstract: ARHGAP21 is a protein of the RhoGAPs (Rho GTPases activating proteins) family that exerts several functions such as: migration, proliferation, differentiation and intracellular traffic of vesicles, in multiple cell types. In islets from Swiss mice knockdown for ARHGAP21 the glucose-induced insulin secretion (GSIS) was significantly increased, by mechanisms not yet elucidated. Although, it is still unknown the effects of ARHGAP21 knockdown on the insulin secretion and glucose homeostasis in adult mice. Here, we evaluated: a) in islets from ARHGAP21 knockdown mice the expression of genes involved in proliferation, maturation, and extrusion of the insulin containing granules, as well as on the rearrangement of the actin cytoskeleton, and b) the effect of ARHGAP21 knockdown on GSIS and on the expression of genes that encode proteins involved with the secretory function (maturation and extrusion), as well as on the glucose homeostasis in adult C57BL/6 mice. Neonatal Swiss mice received (i.p.) 1 nmol of anti-ARHGAP21 anti-sense (neonate AS) (reduction of 60%) or mismatch (neonate CTL), subcutaneously, for two days. Adult C57BL/6 mice received (i.p.) 1.5 nmol/g of anti-ARHGAP21 anti-sense (adult AS) (50% reduction) or mismatch (adult CTL) for three consecutive days. Insulin secretion was measured in the presence of increasing concentrations of glucose (2.8 ¿ 22.2 mM). F-actin (polymer) was measured using phalloidin. Gene expression was assessed by Real Time PCR. Glucose and Piruvate tolerance were measured by ipGTT and ipPTT, respectively, and insulin sensitivity by ipITT, hyperinsulinemic-euglycemic clamp, and AKT phosphorylation. Islets from neonate AS displayed higher insulin secretion at 2.8 mM glucose, and lower expression of F-actin. Higher expression of VAMP2 and SNAP25 genes was also observed. Islets from adult AS showed higher insulin secretion at 22.2 mM glucose. However, glucose-induced increase in [Ca2+]i was not different from CTL. The expression of SYT VII and CX 36 genes was also increased. Adult AS mice displayed glucose intolerance and higher insulinemia during ipGTT, accompanied by insulin resistance specifically in skeletal muscle, and a lower hepatic glucose production. In conclusion, ARHGAP21 negatively modulates insulin secretion in neonatal mice through the rearrangement of the actin cytoskeleton and reduction of the expression of VAMP2 e SNAP25 genes. ARHGAP21 also may negatively modulate the expression of genes involved in the Ca2+ sensitivity and secretory response (SYT VII and CX 36, respectively) in adult mice. Despite the higher insulin secretion, adult AS mice showed glucose intolerance associated with a mild insulin resistance in the skeletal muscle, which may be compensated by a lower glucose production in the liver / Doutorado / Fisiologia / Doutora em Biologia Funcional e Molecular

Résumé : Durant les dernières années, l’encapsulation d’îlots pancréatiques endocriniens a reçu une grande attention parce qu’elle pourrait constituer une solution pour diminuer les taux d'échecs des transplantations. Dans le contexte de la perte de la matrice extracellulaire (MEC) native des îlots lors de leur isolation et le rejet de greffes par le système immunitaire du receveur, cette thèse vise à améliorer la compréhension des interactions entre la MEC et les cellules des îlots pancréatiques endocriniens ainsi qu’à étudier les effets de stress apoptotiques associés à des éléments du système immunitaire sur la survie et les fonctions des îlots. Ces études pourraient permettre de raffiner notre compréhension des mécanismes associés au rejet des greffes d'îlots de Langerhans. Dans cette thèse, le premier chapitre constitue une revue de la littérature permettant de mettre en lumière les rôles réciproques de la MEC dans l'action des cellules immunitaires et l'influence de ces rôles sur le diabète de type 1 (DT1) et sur la transplantation d'îlots. Ce premier chapitre a été publié dans la revue Pathologie Biologie. Le premier travail expérimental comprend la culture de cellules d'insulinomes de rat (INS-1) sur des surfaces composées de carboxyméthyl dextrane (CMD) recouvertes de fibronectine, RGD ou YIGSR, un peptide synthétique de la laminine. Dans cette étude, l'effet bénéfique d’éléments de la MEC sur ces cellules productrices d'insuline a été démontré. Les cellules INS-1 ont davantage proliféré sur ces surfaces et sécrétaient plus d’insuline que les cellules INS-1 cultivées sur les surfaces contrôle de CMD, CMD+RGE et dans les plaques à multi-puits de polystyrène vendues pour la culture tissulaire (TCPS). Cette première étude a été publiée dans Acta Biomaterialia. La deuxième étude expérimentale avait pour objectif d’étudier l’effet protecteur de gels de fibrine pour enrober des îlots pancréatiques endocriniens isolés de jeunes porcs et exposés à deux concentrations de peroxyde d'hydrogène (H[indice inférieur 2]O[indice inférieur 2]). L’enrobage dans la fibrine a permis de réduire l'apoptose chez les cellules des îlots et d’améliorer la sécrétion d'insuline par ceux-ci lorsque les résultats étaient comparés à ceux des îlots non-enrobés. Ce travail a été publié dans la revue Islets. Dans la troisième étude expérimentale, des îlots porcins étaient enrobés dans des gels de fibrine et d'alginate et exposés à des monocytes humains pour comparer l’effet de l’enrobage par ces deux matériaux sur la survie et les fonctions des îlots. Les monocytes sécrétaient des concentrations importantes de cytokines TNFα, IL-6, IL-1β en réponse à la fibrine seule et aux îlots. Les cellules des îlots enrobés dans les gels de fibrine et d'alginate étaient moins apoptotiques et sécrétaient plus d'insuline que leurs contrôles respectifs non-enrobés. Cette étude a été acceptée dans la revue Pathologie Biologie. // Abstract : In recent years, the encapsulation of endocrine pancreatic islets has received enhanced attention as it might constitute a solution for islet transplantation failure. In the context of the loss of the native islet extracellular matrix (ECM) and graft rejection by the recipient’s immune system, this thesis aims to improve the understanding of ECM-islet cell interactions and immune system-related implications in islet survival and function in the context of type 1 diabetes mellitus (T1DM) and islet graft rejection. In the first chapter, a literature review introduces the reciprocal roles of the ECM in immune cell action and the influence of these interactions on T1DM and islet transplantation. The most important ECM components are discussed followed by an overview of immune cells and their possible implication in diabetes. Immune cell integrins and cytokines and their communication with and influence on ECM are highlighted, concluding in a brief discussion of the significance of these interactions for islet transplantation and encapsulation. This review has been accepted for publication by Pathologie Biologie. The first experimental work comprises the culture of rat insulinoma cells (INS-1) on welldefined low-fouling carboxymethyl-dextran (CMD) surfaces covalently grafted with fibronectin, RGD and YIGSR, a synthetic laminin peptide, resulting in higher cell proliferation and insulin secretion of INS-1 cells when compared to the controls CMD, CMD+RGE and tissue culture polystyrene (TCPS) plates. With this work, the beneficial effect of ECM cues on insulin-producing cells was proven. This study has been published in Acta Biomaterialia. The second experimental work aimed to study the effect of fibrin gels when used to embed endocrine pancreatic islets isolated from young pigs and exposed to hydrogen peroxide (H[subscript 2]O[subscript 2]). Fibrin-embedded islets showed less apoptosis and higher relative insulin secretion than islets on TCPS, verifying the protective effect of fibrin towards islets. This study has been published in Islets. In the third experimental study, porcine islets were encapsulated in fibrin and alginate gels and exposed to human monocytes to compare the two materials and to further investigate the immune protective properties of fibrin and alginate. Monocytes secreted high concentrations of TNFα, IL-6, and IL-1β in response to fibrin, but at the same time islets in both fibrin and alginate gels were less apoptotic and secreted more insulin then their TCPS controls. This study has been submitted to Pathologie Biologie.

Les cellules beta pancréatiques sécrètent l’insuline lors d’une augmentation post-prandiale du glucose dans le sang. Ce processus essentiel est contrôlé par des facteurs physiologiques, nutritionnels et pathologiques. D’autres sources d’énergie, comme les acides aminés (leucine et glutamine) ou les acides gras potentialisent la sécrétion d’insuline. Une sécrétion d’insuline insuffisante au besoin du corps déclanche le diabète. Le rôle que joue l’augmentation du calcium intracellulaire et les canaux K+/ATP dans la sécrétion d’insuline est bien connu. Bien que le mécanisme exact de la potentialisation de la sécrétion d’insuline par les lipides est inconnu, le cycle Glycérolipides/Acides gras (GL/FFA) et son segment lipolytique ont été reconnu comme un composant essentiel de la potentialisation lipidique de la sécrétion d’insuline. Le diacylglycérol, provenant de la lipolyse, a été proposé comme un signal lipidique important d’amplification. Cependant, l’hydrolyse des triglycérides et des diacylglycérides a été démontrée essentielle pour la sécrétion d’insuline stimulée par le glucose, en suggérant un rôle du monoacylglycérol (MAG) dans ce processus. Dans cette étude, on démontre que la réduction de la sécrétion d’insuline stimulée par le glucose, lors d’une inhibition de la lipolyse, est restaurée par l’addition de MAG. Dans les cellules beta pancréatiques, le niveau de MAG augmente en présence des concentrations élevées du glucose, et également lorsqu’on inhibe l’enzyme MAG hydrolase abhydrolase-6 (ABHD6) avec l’inhibiteur spécifique WWL70. L’analyse lipidomique a démontré qu’après la stimulation des cellules beta pancréatiques avec le glucose et aussi avec le WWL70, l’espèce la plus accumulée de MAG était le 1-stearoylglycérol (1-SG). L’addition de 1-SG, de 1-palmitoylglycérol (1-PG) ou de WWL70 augmente la sécrétion d’insuline stimulée par le glucose, et cette augmentation est indépendante de la génération de acides gras à partir de MAG. Cela suggère que le MAG est un signal lipidique pour la potentialisation de la sécrétion d’insuline stimulée par le glucose. De plus, la surexpression du gène d’ABHD6 dans les cellules INS832/13 cause une réduction de la sécrétion d’insuline, due probablement à la diminution des niveaux intracellulaire de MAG. Avec le but de comprendre le mécanisme moléculaire impliqué dans la potentialisation de la sécrétion d’insuline par le MAG, on a bloqué l’action du récepteur vanilloid-1 (TRPV1) liant le MAG par l’agent pharmacologiste, AMG9810. Le traitement des cellules beta pancréatique par AMG9810 entraîne une diminution de la potentialisation de la sécrétion de l’insuline induite par le MAG. Il est a noter que le MAG pourrait activer TRPV1 par une liaison physique dans la membrane cellulaire interne; ce qui entraînerai l’entrée du calcium dans la cellule, et ensuite la stimulation de l’exocytose des granules à insuline. En soutien de cette hypothèse, on a trouvé une diminution du calcium intracellulaire lorsqu’on traite au AMG9810 des cellules beta pancréatique de rat (provenant des îlots dispersés) stimulées au glucose et au WWL70. L’ensemble des résultats suggère que le MAG est un médiateur de la potentialisation lipidique de la sécrétion d’insuline stimulée par le glucose. Vu que l’inhibition pharmacologique d’ABHD6 augmente la sécrétion d’insuline, on pourra conclure que cette enzyme représente une cible thérapeutique potentielle dans le développement des médicaments anti-diabétiques, visant une augmentation de la sécrétion d’insuline. / Insulin secretion by the pancreatic b-cell in response to post-prandial increase in blood glucose levels is an essential physiological process that is governed by cellular, nutritional and pathological factors. Other fuels including amino acids like leucine and glutamine and also fatty acids contribute to further augment insulin secretion. Failure to secrete adequate amount of insulin according to the changing demands of the body by b-cell is a key determinant of diabetes. The role played by the elevated Ca2+ influx and K+-ATP channels in insulin secretion is well known. Even though the precise mechanism of the lipid amplification of insulin secretion and the involved molecular signals are not clear, Glycerolipid/Free fatty acid (GL/FFA) cycle and its lipolytic segment have been recognized as essential components in the lipid amplification pathway of insulin secretion. Diacylglycerol produced by lipolysis was proposed as an important lipid amplification signal. However, hydrolysis of triglycerides and also of diacylglycerols is shown to be essential for glucose stimulated insulin secretion (GSIS), indicating a possible role for monoacylglycerol (MAG) in this process. In the present study we demonstrate that the obliterated GSIS due to lipolysis inhibition in b-cells can be restored by providing exogenous MAG. In the b-cells MAG levels increase significantly in the presence of high glucose concentration and specific inhibition of the major MAG hydrolase, abhydrolase-6 (ABHD6), in b-cells and islets with WWL70 leads to accumulation of MAG with concomitant increase in insulin secretion. Lipidomics analysis indicated that the major MAG species that is elevated by high glucose as well as WWL70 addition is 1-stearoylglycerol (1-SG). Exogenously added 1-SG and also 1-palmitoylglycerol (1-PG) strongly enhanced GSIS and this augmentation is not dependent on the generation of FFA by these MAGs. This indicates that MAG is a potential candidate for being the lipid signal for GSIS amplification. Further evidence for this was provided by the observation that overexpression of the MAG hydrolase ABHD6 in INS832/13 cells, resulted in decreased insulin secretion, probably owing to the lowered MAG level inside the b-cells. Pharmacological studies using AMG9810, a specific antagonist of transient receptor potential vanilloid-1 (TRPV1) receptor that binds MAG, revealed that a blockade of TRPV1 strongly attenuated the MAG-augmented insulin secretion. Since MAG is a potential activator of TRPV1, it is likely that MAG binds on the inner surface of the cell membrane to TRPV1, which in turn triggers rapid influx of Ca2+ thereby promoting insulin granule exocytosis. Thus, AMG9810 was found to lower Ca2+ influx into dispersed rat islet cells that was induced by high glucose and also WWL70. These results collectively suggest that MAG is the potential mediator of the lipid amplification of glucose-stimulated insulin secretion. Our results also indicate that pharmacological intervening at the ABHD6 hydrolysis step enhances insulin secretion; this enzyme protein can be a promising thrapeutic target for the development of anti-diabetic drugs that promote insulin secretion.

INTRODUCTION : Il a été démontré que le nombre de lipoprotéines apolipoprotéine B (apoB) est un prédicteur du développement du diabète de type 2 (DT2), mais le mécanisme est inconnu. La résistance à l'insuline (RI) et l'hyperinsulinémie compensatoire (HI) entraînent l’épuisement des cellules β et la progression vers le DT2. De plus, l'activation du système de l'interleukine -1β (IL- 1β) est impliquée dans la pathophysiologie du DT2. Notre objectif était donc d'étudier si l’apoB est associé à la RI et à l’HI chez les humains et si cette corrélation est médiée par l’activation du système IL-1β. MÉTHODOLOGIE : 47 femmes ménopausées, non diabétiques, obèses ou en surpoids et 28 hommes, âgés de 45 à 74 ans ont été recrutés. La sécrétion d'insuline (SI) et la sensibilité à l'insuline ont été mesurées par un clamp Botnia modifié. La 1ère et 2ème phase de SI furent mesurées lors d'un test de tolérance au glucose intraveineux (IVGTT) d’une heure, suivi d’un clamp hyperinsulinémique euglycémique (HEIC) de 3 heures (taux de perfusion d'insuline de 75 mU/m2/min) pour mesurer la sensibilité à l'insuline lors des 30 dernières minutes du clamp (état d'équilibre). La sensibilité à l'insuline est exprimée comme étant le taux de perfusion de glucose (GIR) seul ou divisé par le taux d’insuline à l’état d’équilibre (M/I). RÉSULTATS : Chez les femmes, l’apoB à jeun corrélait avec une augmentation de la 2e phase de SI, la SI totale et la sécrétion totale de C-peptide (r=0,202; r=0,168; r=0,204) et avec une diminution de la sensibilité à l'insuline (GIR r=-0,299; M/I r=-0,180) indépendamment de l'adiposité. L’IL-1Ra à jeun (indicateur de l’activation du système IL-1β) corrélait positivement avec la 2e phase, la SI totale et la sécrétion totale de C-peptide (r=0,217; r=0,154; r=0,198) et négativement avec la sensibilité à l'insuline (GIR r=-0,304; M/I r=-0,214). L’IL-1Ra était également corrélée avec l'apoB (r=0,352). Une fois corrigé pour l'IL-1Ra, toutes les associations entre l'apoB et les indices de sensibilité à l'insuline et de SI ont été perdues. Malgré des glycémies similaires, il n’y avait pas de corrélation de l’apoB avec les indices mesurés chez les hommes. CONCLUSION : L’apoB est associé à l’HI et la RI chez les femmes non diabétiques obèses et en surpoids, potentiellement via l'activation du système IL-1β. Ces différences sexuelles doivent être prises en compte dans l'exploration de la physiopathologie du DT2. / INTRODUCTION: The number of plasma apolipoprotein B lipoproteins (apoB) is reported to predict the development of type 2 diabetes (T2D); however the underlying mechanism is unknown. Insulin resistance (IR) and compensatory hyperinsulinemia (HI) are believed to promote β-cell exhaustion and progression to T2D. Moreover, the activation of the interleukin-1β (IL-1β) system is implicated in the pathophysiology of T2D. Our aim was thus to investigate whether plasma apoB associates with IR and HI in humans and whether this is mediated through the IL-1β system. METHODOLOGY: 47 non-diabetic overweight and obese postmenopausal women and 28 men, 45-74 years old were recruited. Insulin secretion (IS) and insulin sensitivity were examined by a modified Botnia clamp. 1st and 2nd phase IS were measured during a 1 hour intravenous glucose tolerance test (IVGTT), followed by a 3 hour hyperinsulinemic-euglycemic clamp (HEIC, insulin infusion rate of 75 mU/m2/min) to measure insulin sensitivity during the last 30 minutes of the clamp (steady state). Insulin sensitivity was expressed as steady state glucose infusion rate (GIR) alone or divided over steady state plasma insulin (M/I). RESULTS: In women, fasting plasma apoB correlated positively with increased 2nd phase and total IS and with total C-peptide secretion (r=0.202; r=0.168; r=0.204 respectively) and negatively with insulin sensitivity (r: GIR= -0.299 and M/I =-0.180) independent of adiposity. Similar to plasma apoB, fasting plasma IL-Ra (indicator of activated IL-1β system) correlated positively with 2nd phase and total IS and with total C-peptide secretion (r=0.217; r=0.154; r=0.198 respectively) and negatively with insulin sensitivity (GIR r=-0.304; M/I r=-0.214). Fasting plasma IL-Ra also correlated with apoB r=0.352). Once corrected for IL-1Ra, the associations between apoB and the indexes of insulin sensitivity and IS were all lost. Despite similar fasting glucose, plasma apoB did not correlate with any indices of insulin secretion or sensitivity in men. CONCLUSION: ApoB is associated with HI and IR in non-diabetic overweight and obese women, which may be mediated through activation of the IL-1β system. Gender differences may need to be considered in exploring the pathophysiology of T2D in humans.