Trypanosoma brucei, parasite protozoaire flagellé appartenant à l’ordre des kinétoplastidés, est responsable de la maladie du sommeil, ou trypanosomiase humaine africaine (THA). Son cycle de vie fait intervenir un insecte vecteur hématophage (la mouche tsé-tsé ou glossine) qui lors d’un repas sanguin sur un individu infecté ingère des parasites. Après plusieurs étapes de différentiation, les parasites sont injectés à un hôte lors d’un autre repas sanguin. Nous avons étudié le métabolisme intermédiaire et énergétique de la forme procyclique de T. brucei, forme présente dans l’appareil digestif de l’insecte vecteur. Chez ce parasite, la dégradation du glucose aboutit à la production d’acétate dans l’unique mitochondrie, et de succinate dans la mitochondrie et les glycosomes, organelles spécifiques des trypanosomatidés dans lesquels la glycolyse est compartimentalisée. T. brucei utilise une "navette acétate" permettant de transférer l’acétyl-CoA produit dans la mitochondrie vers le cytosol pour initier la biosynthèse de novo des acides gras et la production d’acétate est essentielle à la croissance du parasite. La navette acétate fait intervenir dans la mitochondrie l’acétate:succinate CoA-transférase (ASCT), qui converti l'acétyl-CoA produit à partir du glucose en acétate. Nous avons identifié et caractérisé une autre enzyme mitochondriale contribuant aussi à la production d’acétate à partir du glucose : l’acétyl-CoA thioesterase (ACH). Le double mutant n’exprimant ni l’ACH ni l’ASCT ne produit plus d’acétate et n’est plus viable, confirmant le rôle essentiel de la production d’acétate. Par ailleurs, nous avons montré que l’ASCT, grâce au cycle formé avec la succinyl-CoA synthétase (SCoAS), contribue à la production d’ATP par phosphorylation au niveau du substrat dans la mitochondrie, mais l’ACH n’est pas impliqué dans la production d’ATP. La thréonine est l’acide aminé le plus rapidement consommé par le parasite et sa dégradation aboutit à la production d’acétate et de glycine. En utilisant des outils de génétique inverse et des analyses métaboliques par RMN du proton et HPTLC, nous avons caractérisé la première étape enzymatique de cette voie, catalysée par la thréonine déshydrogénase (TDH), et nous avons montré que la thréonine est la principale source de carbone pour la production d’acétate, pour la biosynthèse de novo des acides gras et des stérols. L’acétyl-CoA est produit dans la mitochondrie à partir du pyruvate provenant de la dégradation du glucose par le complexe pyruvate déshydrogénase (PDH) et à partir de la thréonine dont la dégradation est initiée par la TDH. L’acétyl-CoA provenant de la dégradation du glucose ou de la thréonine est converti en acétate par les mêmes enzymes, l’ACH et l’ASCT. Nous avons montré que la voie de dégradation de la thréonine est sous régulation métabolique. L’activité et l’expression de la TDH ainsi que la production d’acétate à partir de la thréonine sont diminuées dans le mutant knock out de la phosphoenolpyruvate carboxykinase (PEPCK) dans lequel le flux glycolytique est redirigé vers la production d’acétate. De plus, contrairement au glucose, la dégradation de la thréonine ne participe pas à la production d’ATP dans la mitochondrie du parasite. Nos résultats nous amène à l’hypothèse d’un channeling mitochondrial des voies de dégradation du pyruvate et de la thréonine pour la production d’acétate. Les trypanosomes ont développé une voie de biosynthèse de novo des acides gras faisant appel aux élongases du réticulum endoplasmique et un précurseur inhabituel, le butyryl-CoA dont la voie de biosynthèse n’est à l’heure actuelle pas connue chez les trypanosomatidés. Nous avons reconstitué une voie de biosynthèse hypothétique à partir de l’acétyl-CoA dans la mitochondrie. La dernière enzyme de cette voie, l’isovaléryl-CoA déshydrogénase (IVDH), a été caractérisée, et nos premiers résultats indiquent que cette enzyme est impliquée dans la production du butyryl-CoA. / Trypanosoma brucei, a flagellated protozoan parasite of the kinetoplastidae order, is responsible for human sleeping sickness or human african trypanosomiasis (HAT). Its life cycle is complex and involves a haematophageous insect vector (tse-tse fly or Glossina), which ingests parasites during a blood meal on an infected host. After a series of differentiations, the parasites are injected to another host during another blood meal. We studied the energy and intermediary metabolism of the procyclic form of T. brucei, which is present into the midgut of the tse-tse fly. In this parasite, glucose degradation produces acetate into the mitochondria of the parasite and succinate into both the mitochondria and the glycosomes. Glycosomes are specific organites of trypanosomatids in which the glycolysis is compartimentalized. T. brucei uses an "acetate shuttle" to transfer acetyl-CoA from the mitochondrion to the cytosol to feed de novo fatty acids biosynthesis. This acetate production is essential for cell viability. The "acetate shuttle" involves inside the mitochondrion, the acetate:succinate CoA-transferase (ASCT), which converts glucose-derived acetyl-CoA into acetate. We identified and characterised a new mitochondrial enzyme involved in acetate production from glucose, in addition to ASCT: the acetyl-CoA thioesterase (ACH). Indeed, a double mutant affecting expression of both ACH and ASCT doesn’t produce anymore acetate and is lethal, which confirms the essential role of mitochondrial production of acetate. In addition, we showed that ASCT, via the ASCT/SCoAS (succinyl-CoA synthetase) cycle, contributes to mitochondrial ATP production by substrate phosphorylation, while ACH is not involved in ATP production. We also observed that contribution of the ASCT/SCoAS cycle and oxidative phosphorylation by the mitochondrial F0-F1-ATP synthase to ATP production are similar. Threonine is the most rapidly consumed amino acid by the procyclic trypanosomes and its degradation produces acetate and glycine. Using a combination of reverse genetics, proton NMR metabolic profiling and HPTLC, we characterized the first enzymatic step of the pathway, catalysed by the threonine dehydrogenase (TDH) and showed that threonine is the main carbon source for acetate production, de novo fatty acids and sterol biosynthesis. Acetyl-CoA is produced into the mitochondrion from glucose-derived pyruvate by the pyruvate dehydrogenase complex (PDH) and by the two first steps of the threonine degradation pathway, including TDH. Both glucose-derived and threonine-derived acetyl-CoA is then converted into acetate by the same enzymes, ACH and ASCT. We also found that the threonine degradation pathway is under metabolic control. Indeed, TDH activity, TDH expression and threonine-derived acetate production are reduced in the phosphoenolpyruvate carboxykinase (PEPCK) knock out mutant, in which glycolytic flux is redirected towards acetate production. In addition, we showed that, as opposed to glucose-derived acetyl-CoA, metabolism of threonine-derived acetyl-CoA doesn’t contribute to ATP production into the mitochondrion of the parasite. Our results suggest the existence of mitochondrial metabolic channelings, which disconnect pyruvate and threonine degradation pathways leading to acetate production. Trypanosomes developed a specific de novo fatty acids biosynthesis pathway using elongases located in the endoplasmic reticulum and an unusual primer, butyryl-CoA. The biosynthesic pathway of butyryl-CoA has not been investigated so far in trypanosomatids. Genomic data mining of the T. brucei database, highlights an hypothetical mitochondrial biosynthesis pathway from acetyl-CoA to butyryl-CoA. The last enzyme of this pathway, isovaleryl-CoA dehydrogenase (IVDH), was characterised and our first results suggest that this enzyme is indeed involved into butyryl-CoA production.

Les mitochondries jouent un rôle majeur dans le métabolisme de l'ATP des cellules eucaryotes. Le maintien de l'ADN mitochondrial (ADNmt) est fondamental pour la production d'énergie chez les organismes aérobie stricte. De grandes délétions de ADNmt sont à l'origine d'anomalies mitochondriales entrainant des maladies chez l'homme. Plusieurs gènes nucléaires impliqués dans le métabolisme de l’ADNmt ont été identifiés et caractérisés chez l'homme. Cependant, l’ensemble des facteurs et leurs activités requis pour le maintien de l'ADNmt reste largement inconnu. L'identification de ces facteurs et la détermination de leurs activités dans des systèmes modèles simples peuvent contribuer à l’étude du maintien de l'ADNmt et à la compréhension des mécanismes induisant des délétions de l’ADNmt chez l'homme. Le champignon filamenteux Podospora anserina est un modèle d'étude du maintien de l’ADNmt. Chez P. anserina, l’accumulation de délétions région-spécifiques de l’ADNmt (Δmt) est corrélée à la présence de la mutation AS1-4 dans le gène nucléaire codant la protéine cytosolique ribosomale S15. L'altération de la protéine S15 pourrait modifier la traduction de transcrits codant des protéines impliquées dans le maintien de l'ADNmt et indirectement causer l'accumulation des Δmt. Par une approche globale (translatome), nous avons analysé l’ensemble des transcrits associés aux ribosomes AS1-4 en cours de traduction. A partir des données obtenues, deux gènes candidats, PaIML2 et PaYHM2 potentiellement impliqués dans le maintien de l'ADNmt, ont été identifiés et étudiés. L'analyse fonctionnelle a été principalement développée pour PaYHM2. La protéine PaYHM2 partage 68% d’identité avec la protéine mitochondriale bi-fonctionnelle Yhm2 de levure, impliquée dans le transport de métabolites dans la mitochondrie et possèdant un domaine de liaison à l'ADN. J'ai démontré que le gène PaYHM2 est essentiel pour P. anserina, un organisme aérobie stricte et que la protéine PaYHM2 est mitochondriale. Par mutagénèse, j'ai montré que c'est la fonction de transport qui est essentielle à la survie du champignon et non pas la putative capacité à se lier à l'ADN. Les résultats obtenus suggèrent également que PaYHM2 participe au métabolisme de l'acétyl-CoA chez P. anserina. / Mitochondria play main role as adenosine triphosphate (ATP)-energy factories of the eukaryotic cells. To ensure energy production, mitochondrial DNA (mtDNA) maintenance is essential for all obligate-aerobe eukaryotic organisms. Large-scale mtDNA deletions are major causes of mitochondrial dysfunction in human diseases. Several nuclear genes implicated in mtDNA metabolism were identified and characterized in human. Nuclear-encoded factors and their activities required for mtDNA maintenance are, however largely unknown. Identification of these factors and discovery of their activities in simple model systems can contribute to the comprehension of mtDNA maintenance and of the mechanisms leading to mtDNA deletions in human. The filamentous fungus Podospora anserina is a useful model system for studying mtDNA maintenance. An S15 cytosolic ribosomal protein mutant in P. anserina, named AS1-4 mutant, shows a positive correlation with the accumulation of specific large mtDNA deletion (Δmt) at the time of death. Alteration of S15 protein might modify translation of transcripts encoding proteins related to mtDNA maintenance and indirectly cause Δmt accumulation. Polysome profiling (called translatome), a global approach giving genome-wide informations about modified transcripts on translation, was performed on AS1-4 mutant. From the data of this translatome, two candidate genes potentially related to mitochondrial DNA maintenance, the PaIML2 gene and PaYHM2 gene has been identified and functionally analyzed. The function of the PaYHM2 gene has been especially characterized in this project. This gene encodes a protein sharing 68% of identity with yeast Yhm2, a bi-functional protein as a mitochondrial carrier and as a protein with DNA-binding activity. I demonstrated that the PaYHM2 gene is essential for P. anserina, an obligate-aerobe organism and that the PaYHM2 protein localizes to mitochondria. Through mutagenesis approach, I showed that the transport function decides the essentiality of mitochondrial carrier PaYHM2 while the putative DNA binding activity of PaYHM2 protein is important for P. anserina. Furthermore, I found that the function of PaYHM2 probably participates in the cytosolic acetyl-CoA metabolism.

Post-translational redox-regulation is a well-known mechanism to regulate enzymes of the Calvin cycle, oxidative pentose phosphate cycle, NADPH export and ATP synthesis in response to light. The aim of the present thesis was to investigate whether a similar mechanism is also regulating carbon storage in leaves. <br><br> Previous studies have shown that the key-regulatory enzyme of starch synthesis, ADPglucose pyrophosphorylase (AGPase) is inactivated by formation of an intermolecular disulfide bridge between the two catalytic subunits (AGPB) of the heterotetrameric holoenzyme in potato tubers, but the relevance of this mechanism to regulate starch synthesis in leaves was not investigated. The work presented in this thesis shows that AGPase is subject to post-translational redox-regulation in leaves of pea, potato and Arabidopsis in response to day night changes. Light was shown to trigger posttranslational redox-regulation of AGPase. AGPB was rapidly converted from a dimer to a monomer when isolated pea chloroplasts were illuminated and from a monomer to a dimer when preilluminated leaves were darkened. Conversion of AGPB from dimer to monomer was accompanied by an increase in activity due to changes in the kinetik properties of the enzyme. Studies with pea chloroplast extracts showed that AGPase redox-activation is mediated by thioredoxins f and m from spinach in-vitro. In a further set of experiments it was shown that sugars provide a second input leading to AGPase redox activation and increased starch synthesis and that they can act as a signal which is independent from light. External feeding of sugars such as sucrose or trehalose to Arabidopsis leaves in the dark led to conversion of AGPB from dimer to monomer and to an increase in the rate of starch synthesis, while there were no significant changes in the level of 3PGA, an allosteric activator of the enyzme, and in the NADPH/NADP+ ratio. Experiments with transgenic Arabidopsis plants with altered levels of trehalose 6-phosphate (T6P), the precursor of trehalose synthesis, provided genetic evidence that T6P rather than trehalose is leading to AGPase redox-activation. Compared to Wt, leaves expressing E.coli trehalose-phosphate synthase (TPS) in the cytosol showed increased activation of AGPase and higher starch level during the day, while trehalose-phosphate phosphatase (TPP) overexpressing leaves showed the opposite. These changes occurred independently of changes in sugar and sugar-phosphate levels and NADPH/NADP+ ratio. External supply of sucrose to Wt and TPS-overexpressing leaves led to monomerisation of AGPB, while this response was attenuated in TPP expressing leaves, indicating that T6P is involved in the sucrose-dependent redox-activation of AGPase. To provide biochemical evidence that T6P promotes redox-activation of AGPase independently of cytosolic elements, T6P was fed to intact isolated chloroplasts for 15 min. incubation with concentrations down to 100 µM of T6P, but not with sucrose 6-phosphate, sucrose, trehalose or Pi as controls, significantly and specifically increased AGPB monomerisation and AGPase activity within 15 minutes, implying T6P as a signal reporting the cytosolic sugar status to the chloroplast. The response to T6P did not involve changes in the NADPH/NADP+ ratio consistent with T6P modulating redox-transfer to AGPase independently of changes in plastidial redox-state. <br><br> Acetyl-CoA carboxylase (ACCase) is known as key-regulatory enzyme of fatty acid and lipid synthesis in plants. At the start of the present thesis there was mainly in vitro evidence in the literature showing redox-regulation of ACCase by DTT, and thioredoxins f and m. In the present thesis the in-vivo relevance of this mechanism to regulate lipid synthesis in leaves was investigated. ACCase activity measurement in leaf tissue collected at the end of the day and night in Arabidopsis leaves revealed a 3-fold higher activation state of the enzyme in the light than in the dark. Redox-activation was accompanied by change in kinetic properties of ACCase, leading to an increase affinity to its substrate acetyl-CoA . In further experiments, DTT as well as sucrose were fed to leaves, and both treatments led to a stimulation in the rate of lipid synthesis accompanied by redox-activation of ACCase and decrease in acetyl-CoA content. <br><br> In a final approach, comparison of metabolic and transcript profiling after DTT feeding and after sucrose feeding to leaves provided evidence that redox-modification is an important regulatory mechanism in central metabolic pathways such as TCA cycle and amino acid synthesis, which acts independently of transcript levels. / Es ist bereits seit längerem bekannt, dass viele Enzyme des Calvinzyklus, des oxidativen Pentosephosphatwegs, des NAD(P)H-Exports und der ATP-Synthese durch post-translationale Redox-Modifikation in Antwort auf Licht reguliert werden. In der vorliegenden Arbeit sollte untersucht werden, ob ein ähnlicher Mechanismus auch die Kohlenstoffspeicherung in Blättern reguliert. <br><br> Vorangegangene Studien mit Kartoffelknollen zeigten, dass das Schlüsselenzym der Stärkesynthese ADP-Glukose-Pyrophosphorylase (AGPase) durch die Bildung einer Disulfidbrücke zwischen den zwei kleinen Untereinheiten (AGPB) des tetrameren Proteins inaktiviert wird, die Bedeutung dieses Mechanismus für die Stärkesynthese in Blättern blieb jedoch bislang ungeklärt. Die vorliegenden Arbeiten zeigen, das AGPase in Erbsen-, Kartoffel- und Arabidopsis-Blättern über post-translationale Redox-Modifikation in Antwort auf Tag-Nacht Änderungen reguliert wird. Dies erfolgt über ein Licht-abhängiges Signal, da, erstens, AGPB in isolierten Chloroplasten durch Belichtung sehr schnell von Dimer zu Monomer umgewandelt wird und, zweitens, ein Abdunkeln der Blätter zu einer schnellen Umwandlung von AGPB von Monomer zu Dimer führt. Die Monomerisierung von AGPB ging mit Änderungen in den kinetischen Eigenschaften des Enzyms einher, die zu einer Aktivierung führten. Studien mit Extrakten aus Erbsenchloroplasten zeigten, dass die AGPase-Redoxaktivierung in-vitro durch die Thioredoxine f und m aus Spinat vermittelt wird. In einem weiteren experimentellen Ansatz konnte gezeigt werden, dass auch Zucker zu Redox-Aktivierung der AGPase und erhöhter Stärkesynthese in Blättern führen, und dass diese unabhängig von Licht wirken. Externe Zugabe von Zuckern wie Saccharose oder Trehalose an Arabidopsis-Blätter im Dunkeln führten zu Monomerisierung von AGPB und einer Erhöhung der Stärkesyntheserate / während die Spiegel des allosterischen Aktivators 3PGA unverändert blieben und keine Änderungen im NADPH/NADP+-Verhältnis auftraten. Experimente mit transgenen Arabidopsis-Pflanzen mit veränderten Spiegeln des Vorläufers der Trehalosesynthese, Trehalose-6-phosphat (T6P), zeigten, dass T6P und nicht Trehalose zu Redox-Aktivierung von AGPase führt. Expression einer E. coli T6P synthase (TPS) im Zytosol führte zu erhöhter Redox-Aktivierung von AGPase und erhöhter Stäreksynthese in Blättern, während die Expression einer T6P-Phosphatase (TPP) gegenteilige Änderungen bewirkte. Diese Auswirkungen erfolgten unabhängig von Änderungen in den Spiegeln von Zuckern und Zuckerphosphaten oder im NADPH/NADP+-Verhältnis. Externe Zugabe von Saccharose führte zu Monomerisierung von AGPB in Wildtyp und TPS exprimierenden Blättern, während diese Antwort in TPP exprimierenden Blättern stark abgeschwächt war. Dies zeigt, dass T6P eine wesentliche Komponente darstellt, die die Redox-Aktivierung der AGPase in Antwort auf Saccharose vermittelt. T6P wurde auch für 15 min direkt an intakte, isolierte Erbsenchloroplasten gefüttert. T6P Konzentrationen im Bereich von 100 µM bis 10 mM führten zu einem signifikanten und spezifischen Anstieg der AGPB-Monomersierung und der AGPase Aktivität. Dies zeigt, dass T6P auch ohne zytosolische Elemente die Redox-Aktivierung der AGPase stimuliert und somit ein Signal zwischen Zytosol und Plastid darstellt. Diese Antwort erfolgte ohne Änderungen im NADPH/NADP+-Verhältnis, was zeigt, dass T6P eher den Redox-Transfer zu AGPase als den Redoxzustand des Chloroplasten moduliert. <br><br> Acetyl-CoA-Carboxylase (ACCase) ist als Schlüsselenzym der Fettsäure- und Lipidsynthese in Pflanzen bekannt. Zu Beginn der vorliegenden Arbeit lagen hauptsächlich in-vitro Befunde vor, die zeigten, dass ACCase durch DTT und thioredoxine f und m über Redox-Modulation reguliert wird. In der Arbeit sollte daher die in-vivo Relevanz dieses Mechanismus für die Regulation der Lipidsynthese in Blättern untersucht werden. ACCase zeigte einen höheren Redox-Aktivierungszustand in Arabidopsis-Blätter, die während des Tages im Vergleich zur Nacht geerntet wurden. Die Redox-Aktivierung der ACCase wurde von Änderungen in den kinetischen Eigenschaften begleitet und führte zu einer erhöhten Affinität des Enzymes gegenüber Acetyl-CoA als Substrat. <br><br> In weiteren Versuchen wurde sowohl DTT als auch Saccharose an Blätter gefüttert, und beide Behandlungen führten zu Redox-Aktivierung von ACCase, was mit erhöhten Lipidsynthesraten und einem Rückgang des Acetyl-CoA-Spiegels einherging.

Made available in DSpace on 2015-03-26T13:51:45Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2830202 bytes, checksum: 646d57cf2258798f7f8bcfe375e2b6ab (MD5) Previous issue date: 2009-03-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Hydnangium sp. is a basidiomycetous fungus that is capable of forming ectomycorrhiza with Eucalyptus species. The in vitro mycorrhization system is widely used for mycorrhizal interactions studies, becoming a simple and reproducible system for the symbiosis-regulated genes expression analysis. In this work, the in vitro mycorrhization system for the Hydnangium sp. and Eucalyptus grandis interaction was performed for the colonization, differentiation and functioning phases for the ectomicorriza formation. The colonization phase were verified after five days of inoculation with the Hydnangium sp., the differentiation phase after ten days and the functioning phase after 20 days of inoculation. The extern morphology was analyzed by stereomicroscopy and the section microscopy was performed for the mantle and Hartig net detection. The total RNA extraction was performed for each phase, with the objective of to analyze genes expression. However, the material quantity from roots of 130 seedlings for each phase was insufficient for the transcripts detection through RTPCR. The intron analysis of the partial sequences of the genes that encode ATP sintase (atp) and acetyl-CoA acetyltransferase (aat) of Hydnangium sp. enabled two introns identification in partial sequence of atp gene (53 and 65 bp), while in partial sequence of aat gene were identified three introns (52, 52 e 46 bp). All introns analyzed have the canonical sequence 5 GT 3 AG on splicing sites, ranging the adjacent nucleotides. The phylogenetic analysis, using the partial sequences of amino acids of atp and aat genes, enabled the correct group separation, corroborating the Hydnangium sp. classification as belonging the same family of Laccaria bicolor. / Hydnangium sp. é um fungo basidiomiceto capaz de formar ectomicorriza com espécies de Eucalyptus. Os sistemas de micorrização in vitro vêm sendo largamente utilizados para estudar interações micorrízicas, tornando-se um sistema simples e reproduzível para as análises de expressão de genes envolvidos na interação. Neste trabalho, a técnica de micorrização in vitro para a interação do fungo Hydnangium sp. com E. grandis foi realizada para as fases de colonização, diferenciação e funcionamento da ectomicorriza. A fase de colonização foi verificada após cinco dias de inoculação com Hydnangium sp., a fase de diferenciação após 10 dias e a fase de funcionamento após 20 dias de inoculação. A morfologia externa foi analisada por lupa e foram avaliados cortes microscópicos para a detecção do manto e da rede de Hartig. A extração de RNA total foi realizada para cada uma das fases, com o objetivo de analisar a expressão gênica. Entretanto, a quantidade de material proveniente de raízes de 130 plântulas para cada fase, foi insuficiente para a detecção de transcritos por meio de RTPCR. A análise dos íntrons das seqüências parciais dos genes que codificam ATP sintase (atp) e acetil-CoA acetiltransferase (aat) de Hydnangium sp. permitiu a identificação de dois íntrons na seqüência parcial do gene atp (53 e 65 pb), enquanto que na seqüência parcial do gene aat foram identificados três íntrons (52, 52 e 46 pb). Todos os íntrons analisados possuem a seqüência padrão 5 GT 3 AG no sítio de processamento, variando os nucleotídeos adjacentes. A análise filogenética, utilizando as seqüências parciais de aminoácidos deduzidas dos genes atp e aat, permitiu a separação correta dos grupos, corroborando a classificação do fungo Hydnangium sp. como pertencente à mesma família de Laccaria bicolor.

Orientador: Helena Coutinho Franco de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-19T14:08:09Z (GMT). No. of bitstreams: 1 Kato_LarissaSayuri_M.pdf: 3085711 bytes, checksum: 2c9b592f72e52ceb332be3af215a87fe (MD5) Previous issue date: 2011 / Resumo: O estudo das vias de sinalização envolvidas no metabolismo energético é de grande relevância fisiológica, uma vez que um desequilíbrio da homeostase energética pode resultar em obesidade e/ou síndrome metabólica e aumento da mortalidade por doença cardiovascular. Estudos recentes de nosso grupo em três modelos experimentais que exibem distintos tipos de dislipidemias revelaram alterações significativas da composição corporal, gasto energético e padrão de ingestão alimentar. Neste trabalho estudamos a homeostase energética desses modelos dislipidêmicos avaliando: (1) a expressão e fosforilação da proteína quinase dependente de AMP (AMPK), um importante regulador do metabolismo energético, bem como de seu alvo, a enzima acetil-CoA carboxilase (ACC), em fígado e músculo esquelético de camundongos hipoalfalipoproteinêmicos e hipercolesterolêmicos e (2) o efeito da alimentação pareada em animais hipertrigliceridêmicos que apresentam alterações de comportamento alimentar, metabolismo corporal e maior atividade do canal mitocondrial de potássio sensível ao ATP (mitoKATP). Considerando os animais hipoalfalipoproteinêmicos (transgênicos para CETP), os quais apresentam aumento de gasto energético global, verificamos que estes apresentam redução da massa relativa dos depósitos adiposos quando comparados os controles wild type (WT). O estudo da ativação da AMPK e da ACC mostra que o estado energético dos tecidos muscular e hepático parece não diferir nos animais CETP e WT. Tanto no fígado como no músculo dos animais CETP não houve alteração da massa e do estado de ativação da AMPK e da ACC. Estes resultados sugerem que não ocorrem variações significativas na síntese, armazenamento e "exportação" de lípides no fígado destes animais. Em relação ao músculo sóleo, pode-se concluir que não há alteração de síntese e catabolismo lipídico nos animais CETP. De modo geral, podemos dizer que a sinalização da AMPK não está ativada nestes tecidos e, portanto, que o maior metabolismo corporal observado nestes animais deve estar sendo causado por outros tecidos do organismo, por exemplo, o próprio tecido adiposo. Em animais machos e fêmeas hipercolesterolêmicas (LDLR0) observamos redução da massa corporal, porém sem alteração significativa da massa relativa dos depósitos adiposos quando comparados aos animais controles wild type. Os resultados sobre ativação da AMPK e da ACC mostram que o estado energético em tecidos periféricos é diferente nos animais LDLR0 e controles (WT). No fígado das fêmeas hipercolesterolêmicas observamos aumento da ativação da AMPK sem alteração significativa da fosforilação da ACC. Isso significa que não houve inibição da lipogênese ou ativação da beta-oxidação no fígado dos animais hipercolesterolêmicos, embora possa ter havido aumento de catabolismo de outros nutrientes. No músculo sóleo das fêmeas e dos machos não houve alteração de fosforilação de ambas AMPK e ACC. Pode-se então concluir que não há deprivação energética no músculo destes animais. Considerando o estudo em animais hipertrigliceridêmicos (HTG), quando submetidos ao regime de paired feeding (PF) observamos uma redução de 17% no consumo alimentar nas fêmeas e nos machos HTG quando comparados aos HTG alimentados ad libitum (ad lib). Isso levou a uma redução significativa do ganho de peso dos HTG-PF comparados aos WT-ad lib, em ambos os sexos. Os animais HTG-PF mantiveram a massa dos depósitos adiposos da carcaça semelhantes aos WT-ad lib e HTG-ad lib. No entanto, o depósito adiposo visceral das fêmeas HTG-ad lib é menor que dos WT-ad lib, enquanto nos machos, os HGT-PF apresentaram maior adiposo visceral que os HTG-ad lib. Quando comparados aos WT-ad lib, verificamos que as fêmeas HTG-PF mantiveram aumento significativo da atividade (abertura) do canal de potássio mitocondrial sensível ao ATP (mitoKATP) e da produção corporal de CO2. No entanto, nos machos HTG-PF houve fechamento dos mitoKATP, redução da produção de CO2 e manutenção da massa corporal. Assim, pode-se inferir que o metabolismo corporal (produção de CO2) reflete o aumento do metabolismo celular causado por aumento da atividade do mitoKATP que desacopla levemente as mitocôndrias e que estas adaptações são revertidas pela restrição alimentar nos machos, mas não nas fêmeas HTG / Abstract: An imbalance of energy homeostasis can result in obesity and/or metabolic syndrome and increased mortality from cardiovascular disease. Recent studies by our group in three experimental models that exhibit different types of dyslipidemia have shown significant changes in body composition, energy expenditure and food intake. In this work we studied the energy homeostasis in these models through: (1) quantifying the expression and phosphorylation of AMP-dependent protein kinase (AMPK), a key regulator of energy metabolism, as well as its target, the enzyme acetyl-CoA carboxylase (ACC) in liver and skeletal muscle in hypoalphalipoproteinemic and hypercholesterolemic mice and (2) the effect of paired feeding regimen on hypertriglyceridemic mice that present increased food intake, body CO2 production and increased activity of the mitochondrial potassium channel sensitive to ATP (mitoKATP). Considering the hypoalphalipoproteinemic mice (transgenic for CETP), which show an increased overall energy expenditure, we found that these mice have reduced relative fat depot mass when compared to wild type controls (WT). Western blot analyses showed that, in both tissues, liver and muscle, there were no changes in mass and state of activation of AMPK and ACC in CETP compared to WT mice. These results suggest that no significant variations in the synthesis, storage and secretion of lipids in the liver of these mice. Regarding the soleus muscle, these results suggest that there is no change in lipid synthesis and catabolism in CETP mice. Overall we may say that AMPK signaling is not activated in liver and muscle tissues and, therefore, that the increased body metabolism observed in these CETP mice must be caused by other body tissues, for example, the adipose tissue itself. In hypercholesterolemic male and female mice (LDLR0) we observed a reduction in body mass, but no significant change in the relative mass of fat depots when compared to WT. The results on activation of AMPK and ACC show that the liver of LDLR0 females had increased activation of AMPK without significant change in the phosphorylation of ACC. This means that there was no inhibition of lipogenesis and activation of ?-oxidation in the liver of hypercholesterolemic mice, although there may have been increased catabolism of other nutrients. In the soleus muscle of females and males there were no changes in the phosphorylation state of both AMPK and ACC. Then, we can conclude that there is no energy deprivation in the muscle of these LDLR0 mice. Considering the study with hypertriglyceridemic (HTG) mice, when subjected to the paired feeding (PF) we observed a 17% reduction in food intake of females and males when compared to HTG mice fed ad libitum (ad lib). This led to a significant reduction in HTG-PF weight gain compared to WT-ad lib in both sexes. HTG-PF mice retained the mass of carcass fat deposits similar to WT and HTG ad lib. Compared to WT-ad lib, HTG-PF mice maintained significant increased activity (opening) of the mitoKATP and body CO2 production. These data showed that the regimen of paired feeding in which HTG mice were submitted did not change the high rate body metabolism and mitochondrial resting respiration observed in HTG-ad lib mice. These results suggest that the metabolic adaptation of HTG (higher activity of mitoKATP) is not sensitive to changes in food restriction and compromises the rate of body growth / Mestrado / Fisiologia / Mestre em Biologia Funcional e Molecular

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In der vorliegenden Arbeit werden zwei Enzymsysteme – Ni-haltige Kohlenmonoxid-Dehydrogenase (CODH) und [NiFe]-haltige Hydrogenase – strukturell untersucht. Im 1. Teil werden die Untersuchungen des ACDS-Komplexes aus A. fulgidus mittels Transmissionselektronenmikroskopie (Negativkontrastierung und der Kryo-Einbettung) geschildert. Die 3D-Rekonstruktion mit einer Auflösung von 29 Å wird de novo ermittelt und drei mögliche Positionen für die CODH-Untereinheit vorgeschlagen. Im 2. Teil wird die Röntgenkristallstrukturanalyse der CODH-Untereinheit des ACDS Komplexes aus A. fulgidus geschildert. Das Protein besteht aus α- und ε-Untereinheiten, die zusammen eine α2ε2-Stöchiometrie bilden (Afα2ε). Während die Gesamtstruktur von Afα2ε2 jener von M. barkeri (Mbα2ε2) ähnelt, führt der Austausch der koordinierenden Cys zu Asp und Glu zu einer Deletion des verbrückenden FeS-Zentrums. Die Rolle der ε-Untereinheit wird durch kinetische Studien untersucht. Die CO-abhängige FAD-Reduktionsaktivität von Afα2ε2 folgt einer Michaelis-Menten Kinetik. Die Mbα2ε2 hat ein ähnliches Kinetikverhalten. Im Gegensatz dazu weist die CODH-II von C. hydrogenoformans, die keine ε-Untereinheit hat, eine lineare Abhängigkeit der CO-abhängigen FAD-Reduktionsaktivität von Flavin auf. Diese Beobachtungen sind im Einklang mit der Annahme, dass die ε-Untereinheit ein Gerüst für die Flavinbindung bereitstellt. Der 3. Teil ist der F420-reduzierenden Hydrogenase aus M. barkeri (MbFRH) gewidmet. Die Struktur von MbFRH wird mittels Röntgenkristallographie bestimmt und ergibt eine dodekamerische Anordnung von ca. 1.2 MDa. Zusammen mit der etablierten Elektronenübertragungskette, beobachtet in FRH aus M. marburgensis, wird in MbFRH auch ein [2Fe2S]-Cluster und eine Fe-Stelle detektiert. Schließlich führen die schwingungsspektroskopischen Analysen zusammen mit der Röntgenkristallographie zu dem Schluss, dass MbFRH in einem bisher strukturell nicht charakterisierten, katalytisch aktiven Nia-S Zustand isoliert wird. / In this work, we structurally characterize two metal-based enzyme systems from archaea: Ni-containing CO dehydrogenase (CODH) and [NiFe] containing hydrogenase. In the first chapter we investigate, using transmission electron microscopy, the ACDS complex from A. fulgidus (AfACDS). The purified ACDS complex can be visualized as an intact globular protein particle by negative stain and vitrification techniques. The 3D reconstruction is determined de novo to 29 Å-resolution by single-particle analysis. We suggest three possible positions for the CODH subunit within ACDS by rigid-body fitting. In the second chapter we determine the X-ray crystal structure of the CODH subunit. The 220 kDa protein is composed of α- and ε-subunits that form a heterodimer with (α2ε2) stoichiometry (Afα2ε2). While the overall structure of Afα2ε2 resembles the previously reported structure of the α2ε2-subunit from M. barkeri (Mbα2ε2), the naturally-occurring exchange of the Cys to Asp and Glu results in a depletion of the bridging iron-sulfur cluster. The role of the ε-subunit is investigated by kinetics studies. CO-dependent FAD reduction activity of Afα2ε2 exhibits Michaelis-Menten type kinetics. The same kinetic type is demonstrated for the Mbα2ε2-subunit. In contrast, the ε-subunit lacking CODH-II from C. hydrogenoformans shows linear dependency between CO-dependent FAD reduction activity and flavin concentration. The data suggests that the ε-subunit provides a scaffold for the flavin binding. In the third chapter we study the F420-reducing hydrogenase from M. barkeri (MbFRH). Its structure is solved by X-ray crystallography, revealing a dodecameric arrangement of 1.2 MDa. Along with the established ET chain observed in FRH from M. marburgensis, one solvent-exposed [2Fe2S] cluster and an additional Fe metal site are detected. The combined approach of X-ray crystallography and vibrational spectroscopy reveals that MbFRH is isolated in the previously structurally uncharacterized Nia-S state.

L’objectif de ces travaux de thèse était de rechercher un potentiel effet inhibiteur de l’acide acétique endogène sur le métabolisme oxydo réductif de Saccharomyces cerevisiae, afin d’évaluer la pertinence d’une stratégie d’amélioration des capacités de production d’éthanol par la modulation de la synthèse de cet acide. Ces travaux devaient également permettre d’approfondir la compréhension des principaux facteurs commandant la synthèse de l’acide acétique et plus largement des acides organiques. La stratégie de modulation de la synthèse d’acide acétique mise en place reposait sur des approches microbiologique et génétique, consistant en l’ajout d’acide oléique et / ou de carnitine dans le milieu de culture ainsi que la surexpression du gène CIT2 ou la suppression du gène ALD6.Cette démarche a permis de montrer que, contrairement à la version exogène, l’acide acétique endogène ne présentait pas d’effet inhibiteur du métabolisme oxydo réductif de Saccharomyces cerevisiae ou qu’il était négligeable par rapport au stress éthanol. En outre, la modulation de la production de cet acide ne semble pas être une stratégie envisageable en vue de l’amélioration des capacités de production d’éthanol de cette levure, bien qu’une corrélation ait été observée entre les titres finaux de ces deux molécules.En outre, il a été montré que l’isoforme 6 de l’acétaldéhyde déshydrogénase (Ald6p) était essentiel pour assurer la croissance cellulaire normale ainsi que les mécanismes de résistance au stress éthanol dans ces conditions de culture. Plus largement, l’interrelation entre les différents isoformes ne paraissait pas aussi flexible qu’en anaérobiose. Saccharomyces cerevisiae semblait également présenter un métabolisme flexible en réponse à une modulation de la synthèse d’acide acétique. La voie des pentoses phosphates serait ainsi capable de prendre le relais de l’Ald6p pour assurer la régénération du NADPH cytosolique, bien que le flux à travers cette voie semble avoir été limité par le ratio NADP+ / NADPH. Enfin, les cellules paraissaient capables de réguler la synthèse de l’acétyl coA à partir d’acide acétique en réaction à une évolution des besoins anaboliques lors de la fin de la phase de croissance. Elles seraient toutefois incapables de pallier le manque d’acétyl coA suite à la suppression du gène ALD6. La modulation de la synthèse des acides pyruvique et succinique a également fait l’objet de discussions. / The aim of this work was to investigate a potential inhibitory effect of endogenous acetic acid on the oxido-reductive metabolism of Saccharomyces cerevisiae, to assess the relevance of a strategy based of the modulation of the synthesis of this acid, to improve ethanol production capacities. This work should also help to broaden the understanding of the main factors controlling the synthesis of acetic acid, and more generally organic acids. The strategy to modulate the synthesis of acetic acid was based on microbiological and genetic approaches, consisting in the addition of oleic acid and / or carnitine in the medium as well as the overexpression of the gene CIT2 or the deletion of the gene ALD6.This approach has shown that, contrary to exogenous version, endogenous acetic acid did not induce inhibitory effects on the oxido-reductive metabolism of Saccharomyces cerevisiae, or was negligible compared to stress caused by ethanol. Moreover, the modulation of the synthesis of this acid appear to be not an attractive strategy to improve ethanol production capacities of the yeast, although a correlation was observed between the end-culture titer of these two molecules.In addition, it has been shown that the isoform 6 of acetaldehyde dehydrogenase (Ald6p) was essential to ensure regular growth and mechanisms of ethanol stress resistance under these conditions of culture. More broadly, the interrelation between the different isoforms did not seem as flexible as under anaerobic conditions. Saccharomyces cerevisiae also seemed to have a flexible metabolism in response to a modulation of the synthesis of acetic acid. The pentose-phosphate way would be able to take over from Ald6p for regeneration of cytosolic NADPH, although the ratio NADP+ / NADPH seemed to lessen the flux through this pathway. Finally, the cells appeared to be able to regulate the synthesis of acetyl-CoA from acetic acid in response to changing in anabolic needs at the end of the growth phase. However, yeasts would be unable to overcome the lack of acetyl-CoA following the suppression of the gene ALD6. The modulation of the synthesis of pyruvic and succinic acids has also been discussed.

Les triacylglycérols d'algues (TAG) représentent une source prometteuse de biocarburants. Les principales étapes de la synthèse des acides gras et du métabolisme du TAG des algues ont été déduites de celles des plantes terrestres, mais on en sait peu sur les sources de carbones et d’énergie intervenant dans la synthèse de lipides de réserve. Nous avons donc étudié la synthèse des acides gras chez l’algue modèle Chlamydomonas reinhardtii en utilisant une combinaison d'approches génétiques, biochimiques et microscopiques. Plus précisément, j'ai d'abord examiné la localisation subcellulaire de gouttelettes de lipides dans des cellules d'algues exposées à une forte lumière, conditions où une plus grande quantité de pouvoir réducteur est produite. J'ai ensuite contribué à mettre en évidence que la bêta-oxydation des acides gras est un processus peroxysomal, et que pendant une carence en azote réalisée en conditions photoautotrophe, des mutants dépourvus de la malate déshydrogénase 2 peroxysomale (mdh2) accumulent 50% plus TAG que les souches parentales. Ces résultats nous ont permis de mettre en évidence l'importance du contexte redox cellulaire sur la synthèse lipidique. Cette étude a également permis de révéler l’existence d'un échange d’énergie entre le peroxysome et le chloroplaste. Enfin, en caractérisant des mutants déficients dans la dégradation des acides aminés à chaîne ramifiée (BCAA), j'ai montré que le catabolisme des BCAAs joue un double rôle dans la synthèse de TAG en fournissant des précurseurs carbonés et de l'ATP. L'ensemble de ces travaux ouvert de nouvelles pistes pour l'amélioration génétique future de souches d'algues pour la production de biocarburants. / Algal triacylglycerols (TAG) represent a promising source for biofuel. The major steps for fatty acid synthesis and TAG metabolism have been deduced based on that of land plants, but little is known about carbon and energy sources. To address this question, we investigated fatty acid synthesis in algal cells using a combination of genetic, biochemical and microscopic approaches in the model microalga Chlamydomonas reinhardtii. Specifically, I first examined subcellular localization of lipid droplets in algal cells exposed to high light, a condition favoring production of reducing power. Secondly, I contributed to put on evidence that the beta-oxidation of fatty acids is a peroxisomal process, and that during photoautotrophic nitrogen starvation, knock-out mutants of the peroxisomal malate dehydrogenase 2 (mdh2) made 50% more TAG than parental strains, highlighting the importance of cellular redox context on lipid synthesis. This study also revealed for the first time the occurrence of an energy trafficking pathway from peroxisome to chloroplast. And finally, by characterizing mutants defected in degradation of branched-chain amino acids (BCAAs), I showed that BCAA catabolism plays a dual role in TAG synthesis via providing carbon precursors and ATP. Taken together, this work highlighted the complex interplay between carbon and energy metabolism in green photosynthetic cells, and pointed future directions for genetic improvement of algal strains for biofuel productions.

L’acétyl-coA occupe une place centrale dans le métabolisme intermédiaire. Il constitue le point de jonction de plusieurs voies métaboliques telles que la .-oxydation, la glycolyse, le catabolisme de certains acides aminés, la cétolyse, la cétogenèse et la synthèse d’acides gras. Il est également impliqué dans d’autres processus tels que l’acétylation des protéines. Au cours de mon travail de thèse, je me suis attachée à étudier différents aspects du métabolisme de l’acétyl-coA. La première partie de mon travail a porté sur la modulation pharmacologique de la .- oxydation dans le but de corriger des déficits de cette voie métabolique. L’intérêt de traitements par 400µM de bézafibrate ou 75µM de resvératrol dans les formes modérées de déficit en VLCAD et en CPT2 avait été montré précédemment. Par des méthodes de référence et grâce à la mise au point de nouvelles techniques, j’ai pu montrer sur des fibroblastes de patients déficitaires en LCHAD que des traitements par une combinaison de 35µM de bézafibrate et 30µM de resvératrol permettent d’augmenter les capacités d’oxydation du palmitate en stimulant la synthèse protéique. L’effet de cette combinaison était comparable à celui d’un traitement par 400µM de bézafibrate. Dans un second temps, je me suis intéressée à deux cofacteurs impliqués dans le métabolisme de l’acétyl-coA : l’acide lipoïque, cofacteur de quatre .-cétoacides déshydrogénases (PDHc, BCKDHc, .- KGDHc et GCS) et la riboflavine, cofacteur d’acyl-coA déshydrogénases de la .-oxydation et de déshydrogénases impliquées dans le catabolisme des acides aminés ramifiés. Ainsi, j’ai participé à la description d’anomalies du métabolisme de l’acide lipoïque, un nouveau groupe de maladies héréditaires du métabolisme caractérisé par un déficit combiné en .-cétoacides déshydrogénases. Par ailleurs, j’ai pu montrer qu’une hyperprolinémie constitue un biomarqueur intéressant pour le diagnostic d’acidurie glutarique de type II primaire ou secondaire, ces dernières pouvant se rencontrer en cas d’anomalie du métabolisme de la riboflavine. J’ai également évalué l’utilisation d’un mélange racémique de L,D-3-hydroxybutyrate afin de corriger les déficits énergétiques induits par un déficit en PDHc ou GLUT1. Via la cétolyse, le L,D-3- hydroxybutyrate génère de l’acétyl-coA. De façon surprenante, l’administration de ce composé s’est traduite par une amélioration de l’état clinique des patients atteints de déficits en PDHc, alors qu’une dégradation a été observée chez les patients atteints de déficits en GLUT1. Cette évolution différente pourrait souligner l’importance de l’anaplérose chez les patients déficitaires en GLUT1. Enfin, la dernière partie de mon travail de thèse porte sur la description d’un patient atteint d’une forme modérée de déficit en pyruvate carboxylase, cette enzyme étant régulée par l’acétyl-coA. Les difficultés diagnostiques rencontrées devant ces formes modérées sont rapportées, ainsi que des essais de traitement par des composés anaplérotiques et par le bézafibrate, malheureusement sans bénéfice net que ce soit in vitro ou in vivo. En conclusion, le métabolisme de l’acétyl-coA est altéré dans de nombreuses maladies héréditaires du métabolisme, dont certaines sont de description récente. Il peut être modulé par différentes approches pharmacologiques. Le développement de nouvelles techniques et notamment les analyses de flux métaboliques fournissent des outils utiles à son exploration et à l’étude de nouveaux traitements. / Acetyl-CoA is crucial for intermediary metabolism. It is at the crossroad of several metabolic pathways such as beta-oxidation, glycolysis, aminoacid catabolism, ketolysis, and fatty acid synthesis. It is also involved in other processes such as protein acetylation. In this document I studied different aspects of acetyl-CoA metabolism. First, I tried to correct fatty acid oxidation defects through pharmacological approach. Thanks to well- known methods and new ones, I showed that a combination of 30µM resveratrol and 35µM bezafibrate increased fatty acid oxidation capacities by increasing protein synthesis, as well as 400µM bezafibrate. Acetyl-CoA metabolism is also altered due to cofactors defects such as lipoic acid or riboflavine deficiency. I was involved in new diseases description and research for new biomarkers in this context. PDHc and GLUT1 deficiency are two different diseases with the same consequence : a defect in acetyl- CoA production from glucose. In order to improve patients’ quality of life, I evaluated the substitution of ketogenic diet with a racemic mix of L,D-3-hydroxybutyrate in PDHc and GLUT1 deficiency. The clinical evolution of patients was strikingly different, with an improvement in PDHc patients, whereas a degradation was noticed in GLUT1 patients. This difference might underline the role of anaplerosis in GLUT1 deficiency. Finally, I evaluated anaplerotic treatment and bezafibrate treatment in pyruvate carboxylase deficiency, an enzyme allosterically regulated by acetyl-CoA. To conclude, acetyl-CoA metabolism is altered in numerous inherited errors of metabolism, some of them being recently described. It can be modulated by pharmacological approaches. The development of new techniques such as metabolic flux analysis are useful for its study and for new treatments evaluation.