Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted. Errata slip inserted. Includes bibliographical references.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted. Errata slip inserted. Includes bibliographical references.

O óxido nítrico (NO) é um mensageiro químico encontrado em diversos tipos celulares como células endoteliais, neurônios e macrófagos. A síntese do NO é realizada pela ação da enzima óxido nítrico sintase (NOS). Um dos mecanismos de ação do NO é dado pela ativação da enzima guanilato ciclase solúvel (GCs), resultando na produção de monofosfato cíclico de guanosina (GMPc), um mensageiro secundário nessa via de sinalização celular. O GMPc por sua vez é capaz de modular a atividade de algumas fosfodiesterases (PDEs), enzimas responsáveis pela degradação do GMPc e de outro nucleotídeo cíclico, o monofosfato cíclico de adenosina (AMPc). O objetivo deste trabalho foi investigar os efeitos da elevação dos níveis de NO por meio do doador de óxido nítrico (SNAP) e o uso de inibidores de diferentes isoformas de fosfodiesterases no meio de cultivo durante a maturação in vitro (MIV) de oócitos bovinos sobre a retomada da meiose, concentração de NO e níveis de GMPc e AMPc. Deste modo, os complexos cumulus-oócito (CCOs) bovinos foram cultivados por até 9 horas com o doador de NO (SNAP - 10-7 M) associado ou não ao inibidor de GCs (ODQ - 10-5 M) e associado ou não aos inibidores das fosfodiesterases, PDE5 (Sildenafil - 10µM), PDE3 (Cilostamide - 20µM) e PDE8 (Dipiridamole - 50µM). As amostras foram avaliadas quanto a taxa de retomada da meiose, níveis de NO (9h de MIV) e níveis dos nucleotídeos cíclicos GMPc e AMPc (0, 1, 2 e 3h de MIV). O SNAP retardou o rompimento da vesícula germinativa com 9horas de cultivo (P<0,05) e quando o SNAP foi associado ao ODQ o efeito foi revertido (P>0,05). A inclusão de SNAP no cultivo, os níveis de NO foram elevados (P<0,05). Os níveis de GMPc só foram influenciados positivamente pelo SNAP com 1 hora de cultivo (P<0,05) e após 2 e 3 horas, esta influência não persistiu (P>0,05), visto que o ODQ aboliu o efeito. A influência do SNAP foi devido ao estímulo da GCs. Para os níveis de AMPc, o doador de NO não foi capaz de influenciar suas concentrações durante as 3 horas de cultivo (P>0,05). Quando o SNAP foi associado ao Sildenafil (SNAP+SIL) não houve diferença em relação ao grupo imaturo (P>0,05), porém, também não se diferiu do tratamento SNAP e controle (P>0,05). Para as taxas de retomada de meiose todos os tratamentos foram eficientes e conseguiram retardar a quebra da vesícula germinativa diante do grupo controle (P<0,05), sendo o grupo SNAP+CIL mais eficiente. Para os níveis de AMPc, nem mesmo com a utilização de inibidores das PDE3 e PDE8 foi possível atenuar a queda do nucleotídeo. Em conclusão, o SNAP exerceu influência na retomada da meiose, na concentração de NO e nos níveis de GMPc sendo que sua ação se deve à atividade da GCs. Não houve influência sobre os níveis de AMPc, quando o SNAP foi associado a inibidores específicos de fosfodiesterases, mesmo quando apresentaram efeito sobre a retomada da meiose. A via NO/GCs/GMPc não parecer atuar sobre a via PDE3/AMPc, sugerindo a ação de outras vias no controle da meiose. / Nitric oxide (NO) is a chemical messenger found in many cell types such as endothelial cells, neurons and macrophages. The synthesis of NO is made by the action of nitric oxide synthase (NOS). One of the mechanisms of action of NO is given by the activation of the enzyme soluble guanylate cyclase (sGC), resulting in the production of cyclic guanosine monophosphate (cGMP), a secondary messenger in this pathway of cell signaling. The cGMP in turn is capable of modulating the activity of some phosphodiesterases (PDEs), enzymes responsible for degradation of cGMP and other cyclic nucleotide, cyclic adenosine monophosphate (cAMP). The objective of this study was to investigate the effects of elevated levels of NO via nitric oxide donor (SNAP) and the use of inhibitors of phosphodiesterase isoforms in the culture medium during in vitro maturation (IVM) of bovine oocytes on resumption of meiosis, the concentration of NO and cGMP and cAMP levels. Thus, the complexes cumulus-oocyte (COCs) were cultured for cattle up to 9 hours with the NO donor (SNAP - 10-7 M) with or without the inhibitor of sGC (ODQ - 10-5 M) and with or without to inhibitors of phosphodiesterase PDE5 (Sildenafil - 10µM), PDE3 (Cilostamide - 20µM) and PDE8 (Dipyridamole - 50µM). The samples were evaluated for the rate of resumption of meiosis, levels of NO (9h - IVM) and levels of cyclic nucleotides cGMP and cAMP (0, 1, 2 and 3h - IVM). The SNAP delayed with germinal vesicle breakdown of 9hours cultivation (P < 0.05) when SNAP was associated with ODQ was reversed the effect (P> 0.05). The inclusion of SNAP cultivation, NO levels were increased (P<0.05). cGMP levels were positively influenced only by the snap 1 hour in culture (P<0.05) and after 2 and 3 hours, this effect was not maintained (P<0.05), whereas ODQ abolished the effect. The influence of SNAP was due to stimulation of GCs. For cAMP levels, the NO donor was not able to influence their concentrations during the 3 h incubation (P>0.05). When SNAP was associated with Sildenafil (SIL+SNAP) there was no difference compared to the immature group (P>0.05), however, also did not differ from SNAP treatment and control (P>0.05). Rates for resumption of meiosis all treatments were efficient and able delay before germinal vesicle breakdown in the control group (P<0.05), with SNAP+CIL group more efficient. For cAMP levels, even with the use of inhibitors of PDE3 and PDE8 was possible to alleviate the decrease of the nucleotide. In conclusion, SNAP exerted influence on the resumption of meiosis, the concentration of NO and cGMP levels and that its action is due to a GCs activity. There was no effect on cAMP levels, when SNAP was associated with specific phosphodiesterase inhibitors, even when presented effect on the resumption of meiosis. The pathway NO/sGC/cGMP seem not act on the pathway PDE3/AMPc, suggesting the action of other pathways in the control of meiosis.

A large number of evolutionarily conserved genes have been identified by comparative genomics approaches. However, a considerable fraction of these genes lack functional characterization despite the availability of several bioinformatics approaches for prediction of protein function. Moreover, with the advent of genome sequencing efforts, numerous disease associated genes have been identified. While high throughput approaches aid in identification of genes, studying individual genes is important to understand their cellular roles. During studies on cyclic AMP metabolism in mycobacteria conducted in the laboratory, a Class III cyclic nucleotide phosphodiesterase, Rv0805 was identified from Mycobacterium tuberculosis. Interestingly, additional bioinformatics analysis identified orthologs were in higher eukaryotes. These were members of the metallophosphoesterase-domain-containing protein 1 (MPPED1) and metallophosphoesterase-domain-containing protein 2 (MPPED2) family. Class III cyclic nucleotide phosphodiesterases were previously reported only in prokaryotes and are distinct from Class I cyclic nucleotide phosphodiesterases generally found in eukaryotes. Thus MPPED1 and MPPED2 proteins were the first identified eukaryotic Class III cyclic nucleotide phosphodiesterases. In humans, MPPED2 is located on chromosome 11 in the region p13-14 that has been associated with WAGR (Wilms’ tumor, aniridia, genitourinary anomalies, and mental retardation) syndrome. Inspection of this region across sequenced mammalian genomes has revealed a shared synteny. Most interestingly, a stretch of 200 bp within the coding sequence of MPPED2 is identified to be one of 481 ultra conserved regions within the human genome. Furthermore, orthologs of MPPED2 can be traced all the way back to Drosophila melanogaster and Caenorhabditis elegans. All of these observations indicate that MPPED2 is highly conserved and hints at its likely importance in many organisms. MPPED1 and MPPED2 have been reported to be expressed in adult and fetal brain respectively and have been annotated as metallophosphoesterases. Metallophosphoesterases are a superfamily of proteins that show wide phyletic distribution and exhibit diversity in their substrate utilization and function. Previous studies from the laboratory have shown that MPPED1 and MPPED2 are indeed metallophosphoesterases and demonstrate cyclic nucleotide phosphodiesterase activity. The crystal structure of MPPED2 was obtained in collaboration with Dr. Marjetka Podobnik (National Institute of Chemistry, Slovenia). Interestingly, the crystal structure of MPPED2 revealed the presence of bound 5’GMP molecule at the active site, and this finding was investigated further in this thesis. MPPED2 bound 5’GMP and 5’AMP with high affinity (IC50 of ~70 nM) which inhibited the activity of MPPED2. Key residues involved in stabilising the 5’ nucleotide have been identified by structure guided mutational analysis. The MPPED2-G252H mutant, generated to mimic the active site of MPPED1, also bound 5’GMP or 5’AMP but with much lower affinity. Given the high affinity of MPPED2 towards 5’GMP/5’AMP, it can be speculated that MPPED2 may show poor phosphodiesterase activity in the cell, and could function in a catalytically-independent manner, perhaps as a scaffolding protein. MPPED1 on the other hand may have a catalytic role that could be regulated by intracellular levels of 5’AMP, 5’GMP and their respective cyclic nucleotides. In order to investigate the biological role of the MPPED1/MPPED2 family of proteins, Drosophila melanogaster was chosen as a model organism owing to the presence of a single ortholog, CG16717, in its genome. Biochemical characterization of CG16717 revealed that the protein was in fact a metallophosphodiesterase capable of hydrolysing cyclic AMP and cyclic GMP, albeit poorly. CG16717 could be inhibited by 5’ nucleotides at high concentrations that may seldom be achieved in-vivo, suggesting that CG16717 may have roles in the organism that depend on its catalytic activity. CG16717 has not been functionally characterized previously. In this thesis, a detailed analysis of CG16717 expression pattern has been performed. CG16717 was found to be expressed in all stages of the fly lifecycle. In adult female flies, levels of CG16717 increased across age. Moreover, CG16717 was not differentially regulated under conditions of starvation, paraquat-induced oxidative stress or in the presence of heavy metals. Spatial expression analysis revealed that CG16717 was expressed in all adult tissues tested, with maximal expression in the brain, suggesting that neuronal expression of CG16717 may be important for its function. Attempts to identify specific cells expressing CG16717 using an enhancer-promoter analysis were not successful. In order to elucidate the physiological role of CG16717, and after having ruled out options of using a P-element insertion mutant and RNA interference approaches, a targeted knock-out of CG16717 was generated using homologous recombination based genomic engineering. CG16717KO flies generated were homozygous viable suggesting that CG16717 was dispensable for fly survival at least under normal laboratory conditions. In line with high expression of CG16717 in the brain and in-vitro ability of CG16717 to hydrolyse cAMP and cGMP, CG16717KO flies showed two to three-fold higher levels of cyclic nucleotides in the head fraction than wild-type flies. C25E10.12, one of the three C. elegans orthologs of CG16717 has been identified to be a target of the transcription factor daf-16 (FOXO) that is inhibited by active insulin signalling. Moreover, knock-down of C25E10.12 reduced the lifespan of age-1 (PI3K) mutant worms. In contrast to this, CG16717 was not found to be differentially regulated in dFOXO null flies. CG16717KO flies however, showed median lifespan that was shorter than control wild-type flies even in the presence of functional PI3K. Various genetic approaches were employed to verify if reduced lifespan was indeed a consequence of loss of CG16717. In the first approach, a wild-type copy of CG16717 was re-introduced at the genomic locus of CG16717 in the CG16717KO flies using attP-attB recombination. However, this approach could not rescue the reduced lifespan of CG16717KO flies, probably due to very low expression of CG16717. In the second approach, CG16717 was reconstituted using genomic constructs containing a copy of CG16717. Finally, CG16717 was expressed ubiquitously using the bipartite Gal4/UAS system. Both the genomic construct and the expression of CG16717 using the Gal4/UAS approach were able to restore the lifespan of CG16717KO flies. More importantly, overexpression of CG16717 in an otherwise wild-type fly led to enhanced lifespan over and above that of control flies. All of these together suggested that CG16717 plays a critical role in regulating lifespan. Mutants of the insulin and target of rapamycin (TOR) signalling pathways have previously been reported to show lifespan extension. Moreover, these mutants have also been associated with reduced growth, increased stress resistance and reduced fecundity. Given the reduction in lifespan of CG16717KO flies, the other insulin/TOR signalling associated phenotypes were tested. While CG16717KO flies showed no difference in terms of developmental growth, and resistance to starvation or paraquat induced oxidative stress, CG16717KO flies were less fecund compared to wild-type controls. Multiple approaches were adopted even in the case of reduced fecundity to verify if the observed phenotype was a consequence of loss of CG16717. However, neither reconstitution of CG16717 using the genomic construct nor ubiquitous expression of CG16717 using the bipartite Gal4/UAS system were able to rescue the reduced fecundity phenotype of CG16717KO flies. This suggested that reduced fecundity in CG16717KO flies was probably not linked to CG16717 and was a consequence of a second mutation at a site distinct from CG16717. Two other approaches were employed to confirm these observations. When CG16717KO/Deficiency lines were tested, these showed fecundity comparable to wild-type control flies despite the lack of CG16717. CG16717KO flies were extensively out-crossed in an attempt to segregate the second site mutation from the CG16717 locus and their fecundity was tested. However, these flies which retained the deletion of CG16717, showed fecundity comparable to wild-type control flies, reiterating that reduced fecundity was not linked to loss of CG16717. In an attempt to find possible links between reduced longevity of CG16717KO flies and the well-established insulin/TOR pathways, transcript levels of key players of these pathways were measured by qRT-PCR. The translational repressor 4EBP was found to be upregulated in CG16717KO flies compared to wild-type control flies. Interestingly, increased 4EBP levels have been associated with enhanced lifespan but in this case despite higher levels of 4EBP, CG16717KO flies showed reduced lifespan. Phosphorylation status of 4EBP and other players involved in the insulin/TOR phosphokinase signalling cascade would shed light on the activity of these pathways. In summary, this thesis has attempted to understand the biochemistry and physiological functions of an evolutionarily conserved metallophosphoesterase. Its apparent role in regulating life span in the fly suggests that the functions of this protein are likely to impinge on a number of diverse and important pathways involved in basic physiological processes in the organism. Further investigation would shed light on the molecular basis by which CG16717 affects lifespan, and opens up new avenues to understanding the contributions of CG16717 in regulating lifespan and diverse neurological functions.

L’objectif de cette thèse était de caractériser le rôle des différentes familles de phosphodiestérases (PDEs), les enzymes de dégradation du 3'-5'- adénosine monophosphate cyclique (AMPc), dans la régulation de la signalisation de l’AMPc dans deux types de cellules musculaires lisses (CMLs), l’aorte de rat (CMLAR) et la vessie de rat néonatal (CMLVRN). Dans les CMLARs en culture, nous avons déterminé le profil d’expression et d’activité des PDE-AMPc. Nous avons alors montré, à l’aide de la technique de FRET basée sur une sonde sensible à l’AMPc pour mesurer l’AMPc en temps réel dans une cellule isolée, que l’inhibition de la PDE4 démasque un effet d’hydrolyse de l’AMPc cytosolique par la PDE1 et la PDE3, alors que les PDE3 et PDE4 agissent de façon synergistique dans le compartiment sous-membranaire. Les mécanismes de cette compartimentation subcellulaire des signaux restent à caractériser.Dans les CMLVRNs, les PDE3 et PDE4 régulent les contractions phasiques, par des mécanismes différents. L’inhibition de la PDE4 limite les contractions stimulées par le carbachol par un mécanisme dépendant de la protéine kinase A, impliquant une augmentation de la fréquence des sparks calciques, qui entrainent l’activation des canaux potassiques BK, assurant en final une diminution des transitoires calciques. Au contraire, l’effet de l’inhibition de la PDE3 implique la protéine kinase G mais par un mécanisme qui reste à définir.En conclusion, ce travail montre que dans les CMLs, les différents familles de PDE-AMPc sont douées de spécificité de fonction et/ou de mécanisme d’action, et participent ainsi à une compartimentation subcellulaire des voies de signalisation. / The aim of the present thesis was to characterize the role of the different families of phosphodiesterases (PDEs), the enzymes degrading 3'-5'-cyclic adenosine monophosphate (cAMP), in controlling the cAMP signalling in two distinct smooth muscle cells (SMCs), the rat aorta SMC (RASMCs) and the rat bladder SMC (RBSMCs).In cultured RASMCs, we firstly characterized the pattern of cAMP-PDE expression and activity. We then showed, by using a FRET-based cAMP sensor to explore cAMP signals in living cells, that PDE4 inhibition unmasks an effect of PDE1 and PDE3 on cytosolic cAMP hydrolyzis, whereas PDE3 and PDE4 act synergistically at the submembrane compartment. The mechanisms of this subcellular compartmentation need to be characterized. In neonatal RBSMCs, we showed that both PDE3 and PDE4 are involved in regulating the phasic contractions albeit through distinct mechanisms. PDE4 inhibition inhibits the carbachol-enhanced contractions through a protein kinase A-dependent pathway involving an increase in Ca2+ sparks frequency which activates BK channels to ultimately decrease Ca2+ transients, whereas PDE3 inhibition acts through a protein kinase G-dependent pathway through a still unknown mechanism.In conclusion, our work shows that in the SMC, the different cAMP-PDE families exhibit a specificity in their function and/or mechanism of action, thus participating to a subcellular signaling compartmentation.

Kam Man Fai Afia. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves [195]-224). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.v / Publications --- p.vi / Abbreviations --- p.vii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- The Mast Cell --- p.2 / Chapter 1.1.1 --- Historical Perspective --- p.2 / Chapter 1.1.2 --- Mast Cell Origin and Development --- p.3 / Chapter 1.1.3 --- Mast Cell Heterogeneity --- p.5 / Chapter 1.1.3.1 --- Rodent Mast Cell Heterogeneity --- p.5 / Chapter 1.1.3.2 --- Human Mast Cell Heterogeneity --- p.7 / Chapter 1.1.4 --- Mast Cell Mediators --- p.10 / Chapter 1.1.4.1 --- Preformed Mediators --- p.11 / Chapter 1.1.4.2 --- Newly Synthesized Lipid Mediators --- p.14 / Chapter 1.1.4.3 --- Cytokines --- p.16 / Chapter 1.1.5 --- Mast Cell Activation --- p.17 / Chapter 1.1.5.1 --- Immunological Activation --- p.19 / Chapter 1.1.5.1.1 --- FcεIR Activation and Protein Tyrosine Phosphorylation --- p.19 / Chapter 1.1.5.1.2 --- Activation of Phospholipases --- p.20 / Chapter 1.1.5.1.3 --- The Role of Calcium --- p.22 / Chapter 1.1.5.1.3.1 --- Intracellular Calcium Mobilization --- p.23 / Chapter 1.1.5.1.3.2 --- Calcium Influx --- p.24 / Chapter 1.1.5.1.3.3 --- Mechanisms of Action of Calcium in Mast Cells --- p.28 / Chapter 1.1.5.1.4 --- The Role of G-proteins --- p.30 / Chapter 1.1.5.1.5. --- The Role of Cylic AMP --- p.33 / Chapter 1.1.5.1.2.1 --- Mechanisms of Action of Cyclic AMP in Mast Cells --- p.36 / Chapter 1.1.5.1.2.2 --- Implications for the Inhibitory Role of Cyclic AMP in Mast Cell Activation --- p.37 / Chapter 1.2 --- The Cyclic Nucleotide Phosphodiesterases --- p.39 / Chapter 1.2.1 --- Introduction --- p.39 / Chapter 1.2.2 --- Classification and Structure --- p.41 / Chapter 1.2.3 --- Distribution and Physiological Functions of the Different PDE Families --- p.45 / Chapter 1.2.4 --- Phosphodiesterase Inhibitors --- p.49 / Chapter 1.2.4.1 --- Non-selective PDE Inhibitors --- p.50 / Chapter 1.2.4.2 --- Selective PDE Inhibitors --- p.52 / Chapter 1.2.4.2.1 --- PDE1 and PDE2 Inhibitors --- p.52 / Chapter 1.2.4.2.2 --- PDE3 Inhibitors --- p.53 / Chapter 1.2.4.2.3 --- PDE4 Inhibitors --- p.54 / Chapter 1.2.4.2.4.1 --- PDE5 Inhibitors --- p.56 / Chapter 2. --- Materials and Methods --- p.59 / Chapter 2.1 --- Materials --- p.60 / Chapter 2.1.1 --- Drugs --- p.60 / Chapter 2.1.1.1 --- Phosphodiesterase Inhibitors --- p.60 / Chapter 2.1.1.2 --- Mast Cell Secretagogues --- p.61 / Chapter 2.1.2 --- Materials for Rat Peritoneal Mast Cell Experiments --- p.61 / Chapter 2.1.2.1 --- Materials for Rat Sensitization --- p.61 / Chapter 2.1.2.2 --- Materials for Buffers --- p.62 / Chapter 2.1.2.3 --- Materials for Histamine Assay --- p.62 / Chapter 2.1.2.4 --- Miscellaneous --- p.63 / Chapter 2.1.3 --- Materials for RBL-2H3 Cell Line Experiments --- p.63 / Chapter 2.1.3.1 --- Materials for Cell Culture --- p.63 / Chapter 2.1.3.2 --- Materials for Cell Sensitization and Enzyme Release --- p.64 / Chapter 2.1.3.3 --- Materials for β-Hexosaminidase Assay --- p.64 / Chapter 2.1.3.4 --- Miscellaneous --- p.64 / Chapter 2.2 --- Rat Peritoneal Mast Cell Experiments --- p.65 / Chapter 2.2.1 --- Preparation of Buffers --- p.65 / Chapter 2.2.2 --- Preparation of Stock Solutions --- p.66 / Chapter 2.2.2.1 --- Mast Cell Secretagogue Stock Solutions --- p.66 / Chapter 2.2.2.2 --- Phosphodiesterase Inhibitor Stock Solutions --- p.66 / Chapter 2.2.3 --- Animals and Cell Isolation --- p.71 / Chapter 2.2.3.1 --- Animals --- p.71 / Chapter 2.2.3.2 --- Sensitization of Animals --- p.71 / Chapter 2.2.3.3 --- Cell Isolation --- p.71 / Chapter 2.2.3.4 --- Cell Purification --- p.72 / Chapter 2.2.3.5 --- Determination of Cell Number and Viability --- p.73 / Chapter 2.2.4 --- General Protocol for Histamine Release and Histamine Measurement --- p.75 / Chapter 2.2.4.1 --- Histamine Release --- p.75 / Chapter 2.2.4.2 --- Spectrofluorometric Determination of Histamine Content --- p.76 / Chapter 2.2.4.2.1 --- Manual Histamine Assay --- p.76 / Chapter 2.2.4.2.2 --- Automated Histamine Assay --- p.78 / Chapter 2.2.4.3 --- Calculation of Histamine Levels --- p.78 / Chapter 2.2.4.4 --- Presentation and Statistics --- p.79 / Chapter 2.3 --- RBL-2H3 Cell Line Experiments --- p.80 / Chapter 2.3.1 --- Preparation of Stock Solutions --- p.80 / Chapter 2.3.2 --- Preparation of Materials for Enzyme Release and Assay --- p.81 / Chapter 2.3.2.1 --- Cell Culture --- p.81 / Chapter 2.3.2.2 --- Preparation of Cells for β-Hexosaminidase Release Experiments --- p.82 / Chapter 2.3.2.3 --- β-Hexosaminidase Release --- p.82 / Chapter 2.3.2.4 --- β-Hexosaminidase Assay --- p.83 / Chapter 3. --- Effects of Phosphodiesterase Inhibitors on Mediator Release from Rat Mast Cells --- p.84 / Chapter 3.1 --- Introduction --- p.85 / Chapter 3.2 --- Materials and Methods --- p.87 / Chapter 3.2.1 --- Rat Peritoneal Mast Cells --- p.87 / Chapter 3.2.1.1 --- Experiments Employing Immunological Stimulus in RPMCs --- p.87 / Chapter 3.2.1.2 --- Experiments Employing Non-Immunological Stimuli in RPMCs --- p.88 / Chapter 3.2.2 --- Rat Basophilic Leukemia Cells --- p.88 / Chapter 3.3 --- Results --- p.89 / Chapter 3.3.1 --- Rat Peritoneal Mast Cells --- p.89 / Chapter 3.3.1.1 --- Immunologically Activated Rat Peritoneal Mast Cells --- p.89 / Chapter 3.3.1.1.1 --- Effects of Non-Selective PDE Inhibitors on Anti-IgE-Mediated Histamine Release from RPMCs --- p.89 / Chapter 3.3.1.1.2 --- Effects of Selective PDE1 and PDE2 Inhibitors on Anti-IgE- Mediated Histamine Release from RPMCs --- p.90 / Chapter 3.3.1.1.3 --- Effects of Selective PDE3 Inhibitors on Anti-IgE-Mediated Histamine Release from RPMCs --- p.90 / Chapter 3.3.1.1.4 --- Effects of Selective PDE4 Inhibitors on Anti-IgE-Mediated Histamine Release from RPMCs --- p.91 / Chapter 3.3.1.1.5 --- Effects of Selective PDE5 Inhibitors on Anti-IgE-Mediated Histamine Release from RPMCs --- p.91 / Chapter 3.3.1.2 --- Non-Immunologically Activated Rat Peritoneal Mast Cells --- p.92 / Chapter 3.3.1.2.1 --- Effects of Selective PDE Inhibitors on Compound 48/80- Mediated Histamine Release from RPMCs --- p.92 / Chapter 3.3.1.2.2 --- Effects of Selective PDE Inhibitors on Histamine Release from RPMCs Stimulated by Calcium Ionophores --- p.93 / Chapter 3.3.2 --- Rat Basophilic Leukemia Cells --- p.93 / Chapter 3.3.2.1 --- Effects of Non-Selective PDE Inhibitors on Antigen-Mediated β-Hexosaminidase Release from RBL-2H3 Cells --- p.93 / Chapter 3.3.2.2 --- Effects of Selective PDE Inhibitors on Antigen-Mediated β-Hexosaminidase Release from RBL-2H3 Cells --- p.94 / Chapter 3.4 --- Discussion --- p.95 / Chapter 3.4.1 --- Rat Peritoneal Mast Cells --- p.95 / Chapter 3.4.1.1 --- Immunologically Activated RPMCs --- p.95 / Chapter 3.4.1.2 --- Non-Immunologically Activated RPMCs --- p.99 / Chapter 3.4.2 --- Rat Basophilic Leukemia Cells --- p.103 / Chapter 4. --- Combined Effects of Selective Phosphodiesterase Inhibitors on Immunologically Induced Histamine from Rat Mast Cells --- p.143 / Chapter 4.1 --- Introduction --- p.144 / Chapter 4.2 --- Materials and Methods --- p.144 / Chapter 4.2.1 --- Simultaneous Addition of PDE3 and PDE4 Inhibitors --- p.145 / Chapter 4.2.2 --- Sequential Addition of PDE3 and PDE4 Inhibitors --- p.145 / Chapter 4.3 --- Results --- p.146 / Chapter 4.3.1 --- Effects of the Selective Inhibitors for PDE3 and PDE4 Alone: Calculation of the Expected Inhibition Curve --- p.146 / Chapter 4.3.2 --- Effects of the Simultaneous Addition of PDE3 and PDE4 Inhibitors on Anti-IgE-Mediated Histamine Release from RPMCs --- p.148 / Chapter 4.3.2.1 --- Rolipram and Siguazodan --- p.148 / Chapter 4.3.2.2 --- Ro 20-1724 and Siguazodan --- p.149 / Chapter 4.3.2.3 --- Rolipram and Quazinone --- p.149 / Chapter 4.3.2.4 --- Ro 20-1724 and Quazinone --- p.150 / Chapter 4.3.3 --- Effects of the Sequential Addition of PDE3 and PDE4 Inhibitors on Anti-IgE-Mediated Histamine Release from RPMCs --- p.150 / Chapter 4.3.3.1 --- Rolipram and Siguazodan --- p.150 / Chapter 4.3.3.2 --- Ro 20-1724 and Siguazodan --- p.151 / Chapter 4.3.3.3 --- Rolipram and Quazinone --- p.151 / Chapter 4.3.3.4 --- Ro 20-1724 and Quazinone --- p.152 / Chapter 4.4 --- Discussion --- p.153 / Chapter 5. --- Future Directions --- p.191 / Chapter 5.1 --- Future Directions --- p.192 / References --- p.195

The aim of the present thesis was to characterize the role of the different families of phosphodiesterases (PDEs), the enzymes degrading 3'-5'-cyclic adenosine monophosphate (cAMP), in controlling the cAMP signalling in two distinct smooth muscle cells (SMCs), the rat aorta SMC (RASMCs) and the rat bladder SMC (RBSMCs).In cultured RASMCs, we firstly characterized the pattern of cAMP-PDE expression and activity. We then showed, by using a FRET-based cAMP sensor to explore cAMP signals in living cells, that PDE4 inhibition unmasks an effect of PDE1 and PDE3 on cytosolic cAMP hydrolyzis, whereas PDE3 and PDE4 act synergistically at the submembrane compartment. The mechanisms of this subcellular compartmentation need to be characterized. In neonatal RBSMCs, we showed that both PDE3 and PDE4 are involved in regulating the phasic contractions albeit through distinct mechanisms. PDE4 inhibition inhibits the carbachol-enhanced contractions through a protein kinase A-dependent pathway involving an increase in Ca2+ sparks frequency which activates BK channels to ultimately decrease Ca2+ transients, whereas PDE3 inhibition acts through a protein kinase G-dependent pathway through a still unknown mechanism.In conclusion, our work shows that in the SMC, the different cAMP-PDE families exhibit a specificity in their function and/or mechanism of action, thus participating to a subcellular signaling compartmentation.

No description available.

Les nucléotides cycliques (NC) apparaissent comme des régulateurs majeurs du tonus vasculaire. Produits dans les cellules musculaires lisses (CMLs) par les cyclases, les NC agissent par l’intermédiaire des protéines effectrices qui modulent de nombreux mécanismes régulateurs de la vasomotricité. Les phoshodiestérases (PDEs) qui dégradent les NC assurent le contrôle spatiotemporel de leur réponse biologique. L’objectif de mon travail était de préciser les mécanismes par lesquels le tonus artériel est contrôlé par certaines PDEs. J’ai réalisé cette exploration en utilisant des artères coronaires ou mésentériques de rat, en situation physiologique puis dans un modèle d’insuffisance cardiaque (IC) chronique.Dans la première partie de mon travail, nous nous sommes intéressés au mécanisme par lequel les PDE3 et PDE4 régulent le tonus de l’artère coronaire.Par une approche expérimentale plus intégrée de réactivité vasculaire sur artère coronaires isolées, nous avons montré l’importance du canal potassique BK(Ca) dans l’effet relaxant des inhibiteurs de PDE3 et PDE4. De plus, nous avons constaté une contribution différentielle de ces canaux selon le mode de stimulation de la génération d’un NC, l’AMPc. A l’échelle de la CML, notre étude a permis de suggérer l’existence d’un signalosome impliquant les PDE3/PDE4 et du canal potassique BK(Ca), indiqué par la technique de Proximity Ligation Assay. En accord avec cette hypothèse, le contrôle des BK(Ca) par ces PDEs a pu être mis en évidence par la technique du Patch-Clamp. De manière intéressante, la contribution du couplage fonctionnel entre le canal BKCa et les PDE3 et PDE4 n’a pas été retrouvée dans les artères isolées de rats atteints d’IC. Ceci pourrait être expliqué par une diminution de l’expression des canaux BK(Ca) ainsi que, au moins partiellement, par une raréfaction de leur localisation à proximité de la PDE4B.Dans la deuxième partie de mon travail nous avons exploré les rôles des PDE3, PDE4 et de la PDE2 en particulier, dans la régulation du tonus de l’artère mésentérique de rats atteints d’IC, en comparaison aux rats contrôles. En effet, la contribution de la PDE2 est suggérée par la capacité d’un inhibiteur sélectif de cette enzyme à diminuer la réponse des artères isolées à une stimulation vasocontractante. Nous avons ensuite exploré les effets de cet inhibiteur dans d’autres types de réponses impliquant les NC.L’ensemble de ces travaux ajoute un niveau de complexité à la compréhension des mécanismes de la régulation de la vasomotricité des artères de résistance par les PDEs. Les altérations de cette voie de signalisation que nous avons mises en évidence dans l’IC pourraient contribuer à la dysfonction vasculaire qui accompagne la maladie. / Cyclic nucleotides (CN) appears to be important regulator of vascular tone. Produced in smooth muscle cells (SMCs) by cyclases, CN act through activation of key effectors involved in the regulation of vascular tone. Phoshodiesterases (PDEs), which degrade CN, provide spatiotemporal control of their biological responses. The aim of my work was to understand how vascular tone is controlled by some PDEs and how it is altered during heart failure (HF). For this, I used rat coronary and mesenteric arteries.In the first part of my work, we were interested in defining the contribution of PDE3 and PDE4 in the regulation of coronary tone. Using vascular reactivity technique, we demonstrate the importance of large-conductance Ca2+-activated potassium channel (BK(Ca)) channel in the relaxant effect of PDE3 and PDE4 inhibitor. Moreover, their contribution was different depending on the mode of cAMP production, a type of CN. At the cellular level, Proximity Ligation Assay experiments suggest the existence of a signalosome that involves PDE3/PDE4 andBK(Ca). According to this result, the control of BK(Ca) activity by these PDEs was demonstrated using the Patch-Clamp technique. Interestingly, the contribution of the functional coupling involving the BK(Ca) and PDE3/PDE4 is lost during HF. This may be explained by the decrease of BK(Ca) expression and [BK(Ca)-PDE4B] duplex signal in coronary arteries isolated from HF rat.In the second part of my work, we investigated the role of PDE3, PDE4 and PDE2 particularly, in the regulation of rat mesenteric artery tone during HF. In fact, PDE2 selective inhibitor, decreased the contractile response of isolated arteries. Then, we investigated the effect of PDE2 inhibition in other pathway that involve CN.Our findings underline the complexity of PDEs in the regulation of resistance artery tone. During HF, some CN signaling pathway are impaired leading to vascular dysfunction which can aggravate the pathology.

L’AMPc est un messager important de la régulation neurohormonale du cœur. En activant ses effecteurs, l’AMPc régule de nombreuses fonctions cellulaires telles que l'expression de gènes, le couplage excitation-contraction et le métabolisme cellulaire. Chez les mammifères, l'AMPc est produit par une famille d’adénylate cyclases au sein de plusieurs compartiments subcellulaires solubles ou membranaires. L'existence et le rôle de la signalisation des nucléotides cycliques dans les mitochondries ont été postulés, mais n'ont pas encore été démontrés. De plus, son implication dans la régulation de la mort cellulaire est encore inconnue. Dans cette thèse, nous avons démontré l'expression locale de plusieurs acteurs de la signalisation de l'AMPc dans les mitochondries cardiaques, à savoir une forme tronquée soluble AC (sACt) et la protéine d'échange directement activées par AMPc 1 (Epac1). Nous avons montré un rôle protecteur pour sACt contre la mort cellulaire, l'apoptose, ainsi que la nécrose de cardiomyocytes primaires. Lors de la stimulation par du bicarbonate (HCO3-) et du Ca2+, la sACt produit de l’AMPc, qui à son tour stimule la consommation d'oxygène, une augmentation du potentiel mitochondrial de membrane (ΔΨm) et la production d'ATP. L’AMPc est limitant pour l’entrée matricielle de Ca2+ via l’uniport calcique mitochondrial (MCU) et, en conséquence, prévient la transition de perméabilité mitochondriale (MPT). En outre, dans les mitochondries isolées de cœurs de rats défaillants, la stimulation de la voie de l'AMPc par le HCO3- prévient la sensibilisation des mitochondries au Ca2+. Nous avons également constaté que les familles de phosphodiestérases (PDE), PDE2, 3 et 4, sont exprimées dans les mitochondries cardiaques régulant le taux d’AMPc. Ainsi, ces protéines forment une voie de signalisation locale dans la matrice régulant la fonction mitochondriale cardiaque. Finalement, notre étude a permis d’identifier un lien entre l'AMPc mitochondrial, le métabolisme, certaines PDEs et la mort cellulaire dans le cœur, qui est indépendant de la signalisation AMPc cytosolique. Ceci pourrait constituer un nouveau mécanisme cardioprotecteur via la préservation de la fonction mitochondriale dans un contexte physiopathologique. / CAMP is an important messenger in neurohormonal regulation of the heart. By activating its effectors, cAMP regulates many cellular functions such as gene expression, excitation-contraction coupling and cellular metabolism. In mammals, cAMP is produced by a family of adenylyl cyclase with various subcellular locations and membrane anchorage. The existence and role of cyclic nucleotide signaling in mitochondria has been postulated, but has not yet been demonstrated. Moreover, its implication in the regulation of cell death is still unknown. In this thesis, we demonstrated the local expression of several actors of cAMP signaling within cardiac mitochondria, namely a truncated form of soluble AC (sACt) and the exchange protein directly activated by cAMP 1 (Epac1) and showed a protective role for sACt against cell death, apoptosis as well as necrosis, in primary cardiomyocytes. Upon stimulation with bicarbonate (HCO3-) and Ca2+, sACt produces cAMP, which in turn stimulates oxygen consumption, increased the mitochondrial membrane potential (∆Ψm) and ATP production. cAMP is rate-limiting for matrix Ca2+ entry via the mitochondrial calcium uniporter (MCU) and, as a consequence, prevented mitochondrial permeability transition (MPT). In addition, in mitochondria isolated from failing rat hearts, stimulation of the mitochondrial cAMP pathway by HCO3- rescued the sensitization of mitochondria to Ca2+-induced MPT. We also found that PDE2, 3 and 4 families are located in cardiac mitochondria. They form a local signaling pathway with soluble AC in the matrix, which regulates cardiac mitochondrial functions. Thus, our study identifies a link between mitochondrial cAMP, mitochondrial metabolism, some PDEs and cell death in the heart, which is independent of cytosolic cAMP signaling. This might constitute a novel cardioprotective mechanism through mitochondrial function preservation in pathophysiological conditions.