L'autophagie est un processus d'auto-dégradation conservé chez la plupart des eucaryotes. Généralement induit par un stress nutritif, il requiert la formation d'un compartiment à double membrane appelé l’autophagosome qui séquestre et transporte des composants intracellulaires dégradés et recyclés dans le lysosome. La protéine ATG8, qui occupe une position centrale dans ce processus, est recrutée aux membranes de l’autophagosome par un système de conjugaison très régulé. Toxoplasma gondii est un protozoaire parasite appartenant au phylum des Apicomplexes, qui contient une machinerie d'autophagie réduite. Suite à un stress nutritif, ce parasite intracellulaire obligatoire est néanmoins capable de générer des autophagosomes décorés par TgATG8. De façon surprenante, en condition normale de croissance intracellulaire, cette protéine se localise principalement à l’apicoplaste, un plaste non photosynthétique acquis par endosymbiose secondaire qui contient des voies métaboliques essentielles à la survie du parasite. Le but de ma thèse a été d’élucider les fonctions canoniques et non canoniques d‘ATG8 chez Toxoplasma. La première partie de cette étude porte sur la caractérisation fonctionnelle et spatio-temporelle de l'association de TgATG8 avec l’apicoplaste. Nous avons montré que TgATG8 est recrutée aux extrémités de l’apicoplaste en élongation, ce qui permet le maintien de l’organelle à travers les générations en le connectant aux centrosomes pour une répartition dans les deux cellules filles. La deuxième partie de ce travail vise à isoler et identifier par spectrométrie de masse des partenaires putatifs de TgATG8 qui seraient impliqués dans l’autophagie ou dans le rôle non-canonique à l’apicoplaste. Nous avons analysé la localisation subcellulaire de neuf candidats et des caractérisations fonctionnelles ont été entreprises pour trois protéines. Bien que nous n’ayons pas pu confirmer leurs interactions avec TgATG8, cela a permis l'identification de nouvelles protéines parasitaires: une phospholipase à l’apicoplaste essentielle à la survie du parasite, un régulateur potentiel du cycle cellulaire et un composant du cytosquelette du parasite. / Autophagy is a self-degradative process evolutionary conserved among eukaryotes. Typically induced by starvation, it involves the formation of a double membrane compartment called the autophagosome to sequester and deliver intracellular components for lysosomal degradation and recycling. The protein ATG8 occupies a central position in this process and is recruited to autophagosomal membranes by a highly regulated conjugation system. Toxoplasma gondii is a parasitic protist belonging to the Apicomplexa phylum, which possesses a reduced autophagy machinery. This obligate intracellular parasite is nevertheless able to generate TgATG8-decorated autophagosomes upon nutrient stress. Surprisingly, during normal intracellular parasite growth, TgATG8 mainly localizes to the apicoplast, a non-photosynthetic plastid acquired by secondary endosymbiosis which hosts essential metabolic pathways. My thesis aimed to elucidate the canonical and non-canonical roles of ATG8 in Toxoplasma. The first part of this study is the functional and spatio-temporal characterization of TgATG8 association with the apicoplast. We showed TgATG8 is recruited to both ends of the elongating plastid during parasite division, and allows the maintenance of the organelle across generations by permitting its centrosome-driven distribution into the two daughter cells. The second part of this work is the isolation and mass spectrometry-based identification of putative TgATG8-interacting proteins that would be involved in autophagy-related or non-canonical functions. We analyzed the subcellular localization of nine candidates and functional studies were conducted for three proteins. Although we were unable to confirm their interactions with TgATG8, this approach allowed the identification of novel and important parasite proteins: an essential apicoplast phospholipase, a potential regulator of the cell cycle, and a component of the parasite cytoskeleton.

Phylum Apicomplexa comprises several thousand parasitic protozoans that cause significant disease in humans and animals worldwide. Of particular relevance to human health are Plasmodium spp., the causative agents of malaria; and Toxoplasma gondii, which infects approximately 30% of all humans on earth, and causes serious disease in immunocompromised individuals and neonatally infected fetuses. Central to the pathogenesis of apicomplexans is a unique form of substrate-dependent locomotion termed “gliding motility”, which is essential for traversing the environment and actively invading host cells. Driving motility is the class-XIV unconventional myosin motor (MyoA), which is notably divergent from canonical myosins in that it lacks a “tail” and conventional sequence motifs in both the neck and motor regions. Thus, the mechanisms that enable MyoA to function with a step size and velocity similar to canonical human myosins are not well understood. Over the past 2 decades, the apicomplexan research community has identified many of the components involved in gliding motility, resulting in a functional model of MyoA and accessory proteins forming the “glideosome” macromolecular complex. However, there was still relatively little known about the unique physical processes that drive force production and transduction in the apicomplexan motor complex. Thus, I set out to use structural and biophysical methods to interrogate this divergent molecular motor, and provide the first high-resolution model of apicomplexan motility. Towards this goal, I first used structural and biophysical methods to establish the most complete model to date of class-XIV motor complex assembly, answering key questions about the interface between MyoA and its accessory proteins. To understand the unique molecular basis of force production in apicomplexan motors, I then solved the first ever crystal structure of a class-XIV myosin, MyoA from T. gondii. Supplementing this structure with further biophysical data, I was able to determine the functional consequences of class-defining sequence polymorphisms, and elucidate the basis of phosphorylation-dependent motor regulation. The systematic dissection of apicomplexan motor complexes described herein provides crucial insight into a fundamental biological process, and may help overcome existing barriers for targeted therapeutic development. / Graduate

No description available.

Coccidia are obligate intracellular parasites belonging to the phylum Apicomplexa. Many coccidia are of medical and veterinary importance such as Cystoisospora species and Toxoplasma gondii. The need to discover new anticoccidial therapies has increased due to development of resistance by the parasite or toxicity issues in the patient. The goals of this work were to develop a model for canine coccidiosis while proving that Cystoisospora canis is a true primary pathogen in dogs and to determine the efficacy of a new anticoccidial agent. A canine coccidiosis model would be useful in evaluating new anticoccidial treatments. Oral infections with 5 X 104 (n=2) and 1 X 105 (n=20) sporulated C. canis oocysts were attempted in 22 purpose bred beagle puppies. Clinical signs associated with disease were observed in all dogs. Bacterial and viral pathogens were ruled out by transmission electron microscopy (TEM) and bacterial growth assays. Development of C. canis in cell culture was also evaluated. The efficacy of ponazuril, a new anticoccidial drug, was examined in T. gondii. In vitro studies were conducted to determine the activity of ponazuril on tachyzoites and how this agent affects development of apicomplexcan parasites. The tachyzoite production assay was conducted. Ponazuril at a dose of 1.0 µg/ml had a significant affect on tachyzoite reproduction. Comparisons were made on how ponazuril affects T. gondii and Neospora caninum. Inhibition of T. gondii tachyzoites occurred after the second round of replication and with N. caninum tachyzoites after 4 rounds of replication. Results of TEM revealed ponazuril affects replication of T. gondii and N. caninum differently. The efficacy of ponazuril to prevent and treat acute and chronic toxoplasmosis was investigated. Mice treated prophylactically with ponazuril were completely protected from developing an acute T. gondii infection. Fatal toxoplasmosis was prevented in mice starting treatment 3 and 6 days post infection at a dose of 20 mg/kg. Immunohistochemistry was used to evaluate ponazuril's effect on chronic toxoplasmosis. Sections of brain were scored according to the number of tissue cysts present. Ponazuril also proved to be highly active against toxoplasmic encephalitis in an interferon-gamma knockout mouse model. / Ph. D.

Neospora caninum (filo Apicomplexa) é um parasita obrigatório intracelular como todos os membros deste filo, alguns reconhecidos por causarem doenças com impacto relevante na saúde humana (Plasmodium e Toxoplasma) e veterinária (Babesia, Eimeria e Cryptosporidium). Causador da neosporose, N. caninum vem emergindo como um dos maiores causadores de abortos infecciosos em bovinos, levando a consideráveis perdas econômicas na bovinocultura mundial. Devido à sua recente descoberta, o conhecimento sobre diversos processos bioquímicos de N.caninum ainda é limitado, demandando novas pesquisas para a compreensão de seus mecanismos de sobrevivência e consequente identificação de alvos para intervenção terapêutica. O processo de invasão celular é bastante investigado em pesquisas envolvendo apicomplexas, uma vez que a sobrevivência desses parasitas depende do sucesso de sua entrada na célula hospedeira. Proteínas secretadas de organelas filo-específicas (micronemas, roptrias e grânulos densos) estão intimamente envolvidas com a invasão celular. Elas são responsáveis pela interação inicial com a célula hospedeira, participam da junção de movimento formada no momento da invasão, e contribuem para a estabilização do vacúolo parasitóforo. Neste trabalho as proteínas secretadas por taquizoítas de N. caninum foram investigadas de duas formas: (1) por caracterização molecular de proteínas com domínio Apple; e (2) por estudo do secretoma do parasita. Os domínios proteicos do tipo Apple são caracterizados pela capacidade de interação proteína-proteína e proteína-carboidrato, e estão presentes em algumas proteínas micronêmicas com propriedades adesivas. Neste trabalho três proteínas de N. caninum contendo domínios Apple foram caracterizadas: MIC17A, MIC17B e MIC17C. A análise das sequências proteicas e das estruturas dos domínios Apple, obtidas por modelagem molecular, mostraram alta identidade sequencial e estrutural entre MIC17A e MIC17C. Apesar de ser paráloga às outras duas, MIC17B apresenta diferenças importantes em sua sequência e estrutura. Para MIC17B e MIC17C foram realizados experimentos de detecção das proteínas nativas nos extratos total e secretado do taquizoíta que sugerem diferentes formas de processamento entre essas proteínas no parasita. Para MIC17B foi confirmada a localização em micronemas, num padrão diferente do observado para MIC17C. Os ensaios de invasão combinados aos de localização indicam que estas proteínas estejam relacionadas ao processo de invasão celular, porém, suas funções permanecem desconhecidas. O secretoma é o conjunto de proteínas secretadas pelo parasita e, para explorar a composição deste extrato (ESA) no taquizoíta de N. caninum, duas abordagens complementares foram utilizadas. Na primeira abordagem foram identificadas as proteínas presentes no ESA por espectrometria de massas. Na segunda abordagem realizou-se uma ii quantificação relativa das proteínas, marcadas por dois isótopos, nos extratos totais de taquizoítas submetidos ou não ao estímulo secretório. O resultado esperado seria com as proteínas secretadas diminuídas no parasita estimulado. Em ambas as abordagens foram utilizadas técnicas de espectrometria de massas de alta resolução (nanoLC-MS/MS), o que resultou num alto número de identificações; 615 proteínas no ESA e 2011 proteínas quantificadas. A comparação das duas abordagens permitiu o reconhecimento de proteínas com maior probabilidade de secreção. Uma rede de interação entre as proteínas diferencialmente expressas foi predita, gerando resultados que, associados às informações sobre as proteínas aumentadas, permitiram uma investigação sobre proteínas potencialmente envolvidas com a regulação do metabolismo relacionado à secreção. Os resultados obtidos por ambos os estudos aqui demonstrados somam conhecimento acerca do parasita N. caninum e demonstram ser úteis para guiar a busca e seleção de alvos a serem investigados para o desenvolvimento de terapêutica contra a neosporose. / Neospora caninum (Apicomplexa phylum) is an obligatory intracellular parasite like all members from this phylum, some causing diseases with relevant impact on human (Plasmodium and Toxoplasma) and veterinary (Babesia, Eimeria and Cryptosporidium) health. Causative agent of neosporosis, N. caninum has emerged as one of the leading causes of infectious abortion in cattle, generating huge economical losses in worldwide livestock. Due to its recent discovery, knowledge of N. caninum biochemical processes remains scarce, demanding new research for comprehending its survival mechanisms and, consequently, identifying new targets for therapeutic intervention. The invasion process has often been investigated in apicomplexans since their survival depends on the success of their entry into the host cell. Proteins secreted from phylum-specific organelles (micronemes, rhoptries and dense granules) are deeply involved with invasion. They are responsible for the initial interaction with the host cell; participate of the moving junction formed in the moment of invasion; and contribute for the stabilization of the parasitophorus vacuole. In this study, the proteins secreted by N. caninum tachyzoites were investigated in two ways: (1) the molecular characterization of Apple domaincontaining proteins; and (2) exploring the parasite secretome. The Apple protein domains are characterized by the ability to interact as protein-protein and proteincarbohydrate, and are present in some microneme proteins with adhesive properties. Here three N. caninum proteins containing Apple domains were characterized: MIC17A, MIC17B and MIC17C. Analyses of the Apple domains sequences and structures, obtained by molecular modeling, revealed high sequential and structural identities between MIC17A and MIC17C. Although being a paralog of the other two proteins, MIC17B presents significant differences in its sequence and structure. Experiments were performed for native MIC17B and MIC17C detection in the total and secreted tachyzoite extracts, suggesting different processing forms for these proteins in the parasite. For MIC17B, the microneme localization was confirmed, differently from the pattern observed for MIC17C. Invasion and localization assays indicated that these proteins are related to the cell invasion process; nevertheless, their functions remain unknown. The secretome is the set of proteins secreted by the parasite and, to explore this extract (ESA) composition in N. caninum, two complementary approaches were used. Firstly proteins present in ESA were identified by mass spectrometry. In the second approach, a relative quantification was performed on the proteomes of ethanol stimulated/non stimulated tachyzoites, expecting that the secreted proteins would be down regulated at the stimulated parasite. Both approaches were performed with high resolution mass spectrometry techniques (nanoLC-MS/MS), reaching a high number of identifications: 615 proteins iv in ESA and 2011 quantified proteins. The comparison between both approaches allowed the recognition of the most likely secreted proteins. An interaction network was predicted, involving the differentially expressed proteins. These results, associated with the information of up regulated proteins, allowed the investigation of proteins potentially involved with the secretion metabolism regulation. The findings from our two studies add up knowledge about N. caninum and demonstrate to be useful in guiding the search and selection for new targets for therapeutic development against neosporosis.

Neospora caninum (filo Apicomplexa) é um parasita obrigatório intracelular como todos os membros deste filo, alguns reconhecidos por causarem doenças com impacto relevante na saúde humana (Plasmodium e Toxoplasma) e veterinária (Babesia, Eimeria e Cryptosporidium). Causador da neosporose, N. caninum vem emergindo como um dos maiores causadores de abortos infecciosos em bovinos, levando a consideráveis perdas econômicas na bovinocultura mundial. Devido à sua recente descoberta, o conhecimento sobre diversos processos bioquímicos de N.caninum ainda é limitado, demandando novas pesquisas para a compreensão de seus mecanismos de sobrevivência e consequente identificação de alvos para intervenção terapêutica. O processo de invasão celular é bastante investigado em pesquisas envolvendo apicomplexas, uma vez que a sobrevivência desses parasitas depende do sucesso de sua entrada na célula hospedeira. Proteínas secretadas de organelas filo-específicas (micronemas, roptrias e grânulos densos) estão intimamente envolvidas com a invasão celular. Elas são responsáveis pela interação inicial com a célula hospedeira, participam da junção de movimento formada no momento da invasão, e contribuem para a estabilização do vacúolo parasitóforo. Neste trabalho as proteínas secretadas por taquizoítas de N. caninum foram investigadas de duas formas: (1) por caracterização molecular de proteínas com domínio Apple; e (2) por estudo do secretoma do parasita. Os domínios proteicos do tipo Apple são caracterizados pela capacidade de interação proteína-proteína e proteína-carboidrato, e estão presentes em algumas proteínas micronêmicas com propriedades adesivas. Neste trabalho três proteínas de N. caninum contendo domínios Apple foram caracterizadas: MIC17A, MIC17B e MIC17C. A análise das sequências proteicas e das estruturas dos domínios Apple, obtidas por modelagem molecular, mostraram alta identidade sequencial e estrutural entre MIC17A e MIC17C. Apesar de ser paráloga às outras duas, MIC17B apresenta diferenças importantes em sua sequência e estrutura. Para MIC17B e MIC17C foram realizados experimentos de detecção das proteínas nativas nos extratos total e secretado do taquizoíta que sugerem diferentes formas de processamento entre essas proteínas no parasita. Para MIC17B foi confirmada a localização em micronemas, num padrão diferente do observado para MIC17C. Os ensaios de invasão combinados aos de localização indicam que estas proteínas estejam relacionadas ao processo de invasão celular, porém, suas funções permanecem desconhecidas. O secretoma é o conjunto de proteínas secretadas pelo parasita e, para explorar a composição deste extrato (ESA) no taquizoíta de N. caninum, duas abordagens complementares foram utilizadas. Na primeira abordagem foram identificadas as proteínas presentes no ESA por espectrometria de massas. Na segunda abordagem realizou-se uma ii quantificação relativa das proteínas, marcadas por dois isótopos, nos extratos totais de taquizoítas submetidos ou não ao estímulo secretório. O resultado esperado seria com as proteínas secretadas diminuídas no parasita estimulado. Em ambas as abordagens foram utilizadas técnicas de espectrometria de massas de alta resolução (nanoLC-MS/MS), o que resultou num alto número de identificações; 615 proteínas no ESA e 2011 proteínas quantificadas. A comparação das duas abordagens permitiu o reconhecimento de proteínas com maior probabilidade de secreção. Uma rede de interação entre as proteínas diferencialmente expressas foi predita, gerando resultados que, associados às informações sobre as proteínas aumentadas, permitiram uma investigação sobre proteínas potencialmente envolvidas com a regulação do metabolismo relacionado à secreção. Os resultados obtidos por ambos os estudos aqui demonstrados somam conhecimento acerca do parasita N. caninum e demonstram ser úteis para guiar a busca e seleção de alvos a serem investigados para o desenvolvimento de terapêutica contra a neosporose. / Neospora caninum (Apicomplexa phylum) is an obligatory intracellular parasite like all members from this phylum, some causing diseases with relevant impact on human (Plasmodium and Toxoplasma) and veterinary (Babesia, Eimeria and Cryptosporidium) health. Causative agent of neosporosis, N. caninum has emerged as one of the leading causes of infectious abortion in cattle, generating huge economical losses in worldwide livestock. Due to its recent discovery, knowledge of N. caninum biochemical processes remains scarce, demanding new research for comprehending its survival mechanisms and, consequently, identifying new targets for therapeutic intervention. The invasion process has often been investigated in apicomplexans since their survival depends on the success of their entry into the host cell. Proteins secreted from phylum-specific organelles (micronemes, rhoptries and dense granules) are deeply involved with invasion. They are responsible for the initial interaction with the host cell; participate of the moving junction formed in the moment of invasion; and contribute for the stabilization of the parasitophorus vacuole. In this study, the proteins secreted by N. caninum tachyzoites were investigated in two ways: (1) the molecular characterization of Apple domaincontaining proteins; and (2) exploring the parasite secretome. The Apple protein domains are characterized by the ability to interact as protein-protein and proteincarbohydrate, and are present in some microneme proteins with adhesive properties. Here three N. caninum proteins containing Apple domains were characterized: MIC17A, MIC17B and MIC17C. Analyses of the Apple domains sequences and structures, obtained by molecular modeling, revealed high sequential and structural identities between MIC17A and MIC17C. Although being a paralog of the other two proteins, MIC17B presents significant differences in its sequence and structure. Experiments were performed for native MIC17B and MIC17C detection in the total and secreted tachyzoite extracts, suggesting different processing forms for these proteins in the parasite. For MIC17B, the microneme localization was confirmed, differently from the pattern observed for MIC17C. Invasion and localization assays indicated that these proteins are related to the cell invasion process; nevertheless, their functions remain unknown. The secretome is the set of proteins secreted by the parasite and, to explore this extract (ESA) composition in N. caninum, two complementary approaches were used. Firstly proteins present in ESA were identified by mass spectrometry. In the second approach, a relative quantification was performed on the proteomes of ethanol stimulated/non stimulated tachyzoites, expecting that the secreted proteins would be down regulated at the stimulated parasite. Both approaches were performed with high resolution mass spectrometry techniques (nanoLC-MS/MS), reaching a high number of identifications: 615 proteins iv in ESA and 2011 quantified proteins. The comparison between both approaches allowed the recognition of the most likely secreted proteins. An interaction network was predicted, involving the differentially expressed proteins. These results, associated with the information of up regulated proteins, allowed the investigation of proteins potentially involved with the secretion metabolism regulation. The findings from our two studies add up knowledge about N. caninum and demonstrate to be useful in guiding the search and selection for new targets for therapeutic development against neosporosis.

Indiana University-Purdue University Indianapolis (IUPUI) / Histone acetylation has been linked to developmental changes in gene expression and is a validated drug target of apicomplexan parasites, but little is known about the roles of individual histone modifying enzymes and how they are recruited to target genes. The protozoan parasite Toxoplasma gondii (phylum Apicomplexa) is unusual among invertebrates in possessing two GCN5-family lysine acetyltransferases (KATs). While GCN5a is required for gene expression in response to alkaline stress, this KAT is dispensable for parasite proliferation in normal culture conditions. In contrast, GCN5b cannot be disrupted, suggesting it is essential for Toxoplasma viability. To further explore the function of GCN5b, we generated clonal parasites expressing an inducible HA-tagged form of GCN5b containing a point mutation that ablates enzymatic activity (E703G). Stabilization of this dominant-negative form of GCN5b was mediated through ligand-binding to a destabilization domain (dd) fused to the protein. Induced accumulation of the ddHAGCN5b(E703G) protein led to a rapid arrest in parasite replication. Growth arrest was accompanied by a decrease in histone H3 acetylation at specific lysine residues as well as reduced expression of GCN5b target genes in GCN5b(E703G) parasites, which were identified using chromatin immunoprecipitation coupled with microarray hybridization (ChIP-chip). We also demonstrate that GCN5b interacts with AP2-domain proteins, which are plant-like transcription factors in Apicomplexa. The interactions between GCN5b, AP2IX-7, and AP2X-8 were confirmed by reciprocal co-immunoprecipitation and revealed a “core complex” that includes the co-activator ADA2-A, TFIID subunits, LEO1 polymerase-associated factor (Paf1) subunit, and RRM proteins. The dominant-negative phenotype of ddHAGCN5b(E703G) parasites, considered with the proteomics and ChIP-chip data, indicate that GCN5b plays a central role in transcriptional and chromatin remodeling complexes. We conclude that GCN5b has a non-redundant and indispensable role in regulating gene expression required during the Toxoplasma lytic cycle.

Wir nutzten in dieser Studie den apikomplexen Parasiten Eimeria falciformis als Modell. Unsere Ergebnisse zeigen, dass das in infizierten Wildtypmäusen dominierende Zytokin IFN-γ für Immunschutz und für die Entwicklung der Darmpathologie entbehrlich war. E. falciformis-infizierte IFN-γR-/- and IFN-γ-/- Mäuse zeigten extremen Körpergewichtsverlust und starke Pathologie im Darm. Die Entwicklung des Parasiten in diesen Mäusen war überraschenderweise reduziert. Diese Beobachtungen gingen mit einer drastisch erhöhten Produktion von parasiten-spezifischem IL-17A und IL-22 durch CD4+ T Zellen einher. Gleichzeitige Neutralisierung von IL-17A und IL-22 in E. falciformis-infizierten IFN-γR-/- Mäusen verringerte den Körpergewichtsverlust und die Darmpathologie, und führte zu einer erhöhten Ausscheidung von Parasiten. Die Behandlung einer E. falciformis-infizierten intestinalen Epithelzelllinie mit IL-17A oder IL-22 führte zu einer signifikant reduzierten Entwicklung von E. falciformis in vitro. Diese Daten demonstrieren erstmalig einen anti-parasitären Effekt von IL-22 im Darm und deuten auf redundante Rollen von IL-17A und IL-22 im Hinblick auf die Förderung von Darmpathologie in Abwesenheit von IFN-γ hin. Um E. falciformis als Modellsystem weiter zu entwickeln, haben wir die Transfektion von E. falciformis Sporozoiten mit verschiedenen Plasmiden die den Reporter YFP und den Resistenzmarker DHTS enthalten etabliert. Rektal in Mäuse injizierte Sporozoiten entwickelten sich erfolgreich zu Oocysten, wenn auch mit geringerer Effizienz im Vergleich zur oralen Infektion mit Oozysten. Wiederholte in vivo Selektion YFP-exprimierender Oozysten führte zu Populationen mit maximal 34 % YFP-exprimierenden Parasiten. Wir demonstrieren in dieser Arbeit zum ersten Mal die Transfektion von E. falciformis und zeigen Perspektiven im Hinblick auf die Etablierung einer stabil transgenen Parasitenlinie auf. / The roles of Th1 and Th17 responses as mediators of host protection and pathology in the intestine are the subjects of intense research. Here we investigated a model of intestinal inflammation driven by the intracellular apicomplexan parasite Eimeria falciformis. Although IFN-γ was the predominant cytokine during E. falciformis infection in wild type mice, it was found to be dispensable for host defence and the development of infection-driven intestinal inflammation. E. falciformis-infected IFN-γR-/- and IFN-γ-/- mice developed dramatically exacerbated body weight loss and intestinal pathology, but surprisingly harboured fewer parasites. This was associated with a striking increase in parasite-specific IL-17A and IL-22 production in the mesenteric lymph nodes and at the site of infection. Concurrent neutralisation of IL-17A and IL-22 in E. falciformis infected IFN-γR-/- mice resulted in a reduction in infection induced body weight loss and inflammation and significantly increased parasite shedding. Taken together these data demonstrate for the first time an anti-parasitic effect of IL-22 during an intestinal infection and suggest that IL-17A and IL-22 have redundant roles in driving intestinal pathology in the absence of IFN-γ signalling. To further develop E. falciformis as a model system, we established transfection of E. falciformis sporozoites using various plasmids that contain the fluorescent reporter YFP and the resistance marker DHTS. Sporozoites applied rectally to mice were shown to complete their life cycle, albeit with a lower efficiency in comparison to oral infection with oocysts. Repeated in vivo selection using pyrimethamine and/or FACS and manual sorting led to a maximum percentage of 34 % YFP-expressing oocysts. Taken together, we demonstrate for the first time transfection of E. falciformis and provide perspectives for further work on the establishment of a stable transgenic parasite line.

Toxoplasma gondii ist ein obligat intrazellulärer protozoischer Parasit, der Toxoplasmose beim Menschen und bei Warmblütern verursacht. Die Signalübertragung durch zyklische Nukleotide ist entscheidend für das erfolgreiche intrazelluläre Überleben und die Vermehrung der Parasiten. Hier haben wir die physiologische und biochemische Bedeutung der wesentlichen Phosphodiesterasen (PDEs) in Toxoplasma gondii Tachyzoiten untersucht. Durch C-terminale Markierung von 18 PDEs konnten wir die Expression von 11 PDEs nachweisen. Die Immunogold-Färbung zeigte, dass TgPDE1, TgPDE2 und TgPDE9 im gesamten Parasitenkörper verteilt sind, einschließlich des inneren Membrankomplexes, des apikalen Pols, der Plasmamembran, des Zytosols, der dichten Granula und der Rhoptry, was auf eine räumliche Kontrolle der Signalübertragung innerhalb der Tachyzoiten hindeutet. Anschließend stellten wir fest, dass die meisten Enzyme berüchtigte dual-spezifische Phosphodiesterasen sind, wobei TgPDE2 anders als T.gondii cAMP-spezifisch ist, während T.gondii keine cGMP-spezifische Phosphodiesterase besitzt. Unsere enzymkinetischen Daten zeigen, dass TgPDE2 die höchste Affinität zu seinem Substrat aufweist, während die dualen PDEs (TgPDE1, TgPDE7 und TgPDE9) eine höhere Affinität zu cGMP als zu cAMP haben. Ein Screening der Hemmung gängiger PDE-Inhibitoren auf TgPDEs ergab, dass TgPDE1 das Ziel von BIPPO und Zaprinast ist. Darüber hinaus ergab die biologische Bedeutung, dass TgPDE1 und TgPDE2 einzeln für das Wachstum des Parasiten notwendig sind und ihr Verlust zum Tod des Parasiten führt, was auf ihre funktionelle Redundanz hindeutet. Darüber hinaus identifizierten wir Kinasen und Phosphatasen innerhalb der TgPDE1- und TgPDE2-Interaktome, die die enzymatische Aktivität über Protein-Protein-Interaktionen oder posttranslationale Modifikationen steuern könnten. Insgesamt unterstreichen unsere Erkenntnisse über die subzelluläre Lokalisierung, die katalytische Funktion, die medikamentöse Hemmung und die physiologische Bedeutung der wichtigsten Phosphodiesterasen die unvorhersehbare Plastizität und das therapeutische Potenzial der zyklischen Nukleotid-Signalübertragung in T. gondii. Der Datensatz der cAMP-bindenden Interaktoren, den wir in einem anderen Aspekt dieser Studie offengelegt haben, wird wertvolle Einblicke in die allgegenwärtige Natur der cAMP-vermittelten Signalübertragung in T. gondii Tachyzoiten liefern. / Toxoplasma gondii is an obligate intracellular protozoan parasite that causes toxoplasmosis in human and warm-blood organisms. Cyclic nucleotide signaling is crucial for the successful intracellular survival and replication of the parasites. Here, we dissected the physiological and biochemical importance of the essential phosphodiesterases (PDEs) in Toxoplasma gondii tachyzoite. By C-terminal tagging of 18 PDEs, we detected the expression of 11 PDEs. Immunogold staining revealed that TgPDE1, TgPDE2 and TgPDE9 are distributed throughout the parasite body, including the inner membrane complex, the apical pole, the plasma membrane, the cytosol, dense granules, and rhoptry, suggesting the spatial control of signaling within tachyzoites. Subsequently, we identified that most enzymes are notorious dual-specific phosphodiesterases, and TgPDE2 is cAMP specific differently, whilst T.gondii lacks of cGMP specific phosphodiesterase. Our enzyme kinetic data demonstrated that the highest affinity to its substrate belongs to TgPDE2, while the dual PDEs (TgPDE1, TgPDE7 and TgPDE9) have higher affinity with cGMP than cAMP. Inhibition screening of commonly-used PDE inhibitors on TgPDEs, signifying TgPDE1 as the target of BIPPO and zaprinast. Furthermore, the biological significance revealed TgPDE1 and TgPDE2 are individually necessary for parasite growth, and their loss associatively results in parasite death, implying their functional redundancy. In addition, we identified kinases and phosphatases within the TgPDE1 and TgPDE2 interactomes, which may operate the enzymatic activity via protein-protein interactions or posttranslational modifications. Collectively, our findings on subcellular localization, catalytic function, drug inhibition, and physiological relevance of major phosphodiesterases highlight the unforeseeable plasticity and therapeutic potential of cyclic nucleotide signaling in T. gondii. The data set of cAMP-binding interactors, which we disclosed in another aspect of this study, will provide valuable insight into the pervasive nature of cAMP-mediated signaling in T. gondii tachyzoites.

Small molecule screening is commonly used to discover lead compounds for drug development, but it can also be a powerful way to identify chemical probes for studying biological mechanisms. Our lab uses small molecules to study the mechanisms by which the protozoan parasite Toxoplasma gondii infects and replicates within its hosts. In this work, we employed a fluorescence-based assay to screen the Medicines for Malaria Venture (MMV) Open Access Malaria box for compounds that affect T. gondii growth. The box contains 400 previously identified small-molecule inhibitors of the related parasite, Plasmodium falciparum. We identified 79 hits, including a 2,4-diaminoquinazoline (MMV006169; IC50=1.15µM) that strongly inhibits T. gondii intracellular replication and invasion with no evidence of toxicity to mammalian cells. Extensive structure-activity relationship analyses with T. gondii identified a number of analogs with changed potency and altered effects on replication and invasion. These structure-activity analyses provided the information necessary to synthesize a bivalent chemical inducer of dimerization (CID) containing MMV006169 for use in yeast three-hybrid experiments. Yeast growth competition assays showed that this CID is capable of entering the yeast nucleus, as required for yeast three-hybrid screening. Yeast three-hybrid was used in a targeted format to test the hypothesis that MMV006169 works by inhibiting parasite CDC48, an ATPase involved in trafficking and the degradation of misfolded proteins. Large-scale cDNA library screening by yeast three-hybrid suggests that the compound may instead be working through inhibition of a host cell target. This work has provided insight into how MMV006169 affects the parasite's lytic cycle and generated a testable hypothesis for the biologically relevant target of the compound.