Prion Replication in the Hematopoietic Compartment Is Not Required for Neuroinvasion in Scrapie Mouse Model

Fatal neurodegenerative prion diseases are caused by the transmissible PrPSc prion agent whose initial replication after peripheral inoculation takes place in follicular dendritic cells present in germinal centers of lymphoid organs. However, prion replication also occurs in lymphoid cells. To assess the role of the hematopoietic compartment in neuroinvasion and prion replication, we generated chimeric mice, on a uniform congenic C57/BL6J background, by bone marrow replacement with hematopoietic cells expressing different levels of PrP protein. Nine different types of chimeric mice were inoculated intraperitoneally either with the lymphotropic Rocky Mountain Laboratory (RML) strain or the non lymphotropic ME-7 scrapie strain, at different doses. Here, we clearly demonstrate that overexpression of PrP by the hematopoietic system, or the lack of PrP expression by the bone marrow derived cells, does not change the incubation time period of the disease, even when the mice are infected at limiting doses. We conclude that the hematopoietic compartment is more or less permissive to prion replication, both for RML and ME-7, but does not play a role in neuroinvasion

Toxoplasma Hypervirulence in the Rat Model Parallels Human Infection and Is Modulated by the Toxo1 Locus

Toxoplasmosis is considered as an opportunistic parasitic disease. If post-natally acquired in children or adults, it may pass unnoticed, at least with strains of European origin. However, in the wild biotopes especially in South America, Toxoplasma gondii strains display a greater genetic diversity, which correlates to higher virulence for humans, particularly along the Amazon River and its tributaries. In French Guiana, several atypical strains have been associated with severe clinical forms: ocular toxoplasmosis and acute respiratory distress syndrome both of which can result in death. Among these, the GUY008-ABE strain was responsible for an epidemic of severe disseminated toxoplasmosis in Suriname, which led to the death of one immunocompetent individual. To better understand the mechanism underlying the hypervirulence of the GUY008-ABE strain, we have tested the rat model which compared to the mouse, better reflects the immune resistance of humans to Toxoplasma infection. Here we compare the outcome of toxoplasmosis in F344 rats infected either by the GUY008-ABE strain or the type II Prugniaud strain. We show that the GUY008-ABE strain displays a higher virulence phenotype leading to the death of all infected rats observed in this study. GUY008-ABE infection was characterized by an increase of the parasite load in several organs, especially the heart and lung, and was mainly associated with severe histological changes in lungs. Moreover, correlating with its hypervirulence trait, the GUY008-ABE strain was able to form cysts in the LEW rat model otherwise known to be refractory to infection by other Toxoplasma strains. Together, these results show that the rat is a discriminating experimental model to study Toxoplasma virulence factors relevant to the pathogenesis of human infection and that the degree of virulence is linked to the Toxo1 locus

Apicoplast-localized lysophosphatidic acid precursor assembly is required for bulk phospholipid synthesis in toxoplasma gondii and relies on an algal/plant-like glycerol 3-phosphate acyltransferase

Most apicomplexan parasites possess a non-photosynthetic plastid (the apicoplast), which harbors enzymes for a number of metabolic pathways, including a prokaryotic type II fatty acid synthesis (FASII) pathway. In Toxoplasma gondii, the causative agent of toxoplasmosis, the FASII pathway is essential for parasite growth and infectivity. However, little is known about the fate of fatty acids synthesized by FASII. In this study, we have investigated the function of a plant-like glycerol 3-phosphate acyltransferase (TgATS1) that localizes to the T. gondii apicoplast. Knock-down of TgATS1 resulted in significantly reduced incorporation of FASII-synthesized fatty acids into phosphatidic acid and downstream phospholipids and a severe defect in intracellular parasite replication and survival. Lipidomic analysis demonstrated that lipid precursors are made in, and exported from, the apicoplast for de novo biosynthesis of bulk phospholipids. This study reveals that the apicoplast-located FASII and ATS1, which are primarily used to generate plastid galactolipids in plants and algae, instead generate bulk phospholipids for membrane biogenesis in T. gondii

Toxoplasma secretory granules: one population or more?

International audienc

Safe living within a parasitophorous vacuole: The recipe of success by Toxoplasma gondii

International audienceWhile most intracellular pathogens typically enter mammalian cells by phagocytosis or by induced-uptake, leading to the engulfment of the microbe into a membrane-bound vacuole, the protozoan parasite Toxoplasma gondii drives its own entrance, using a multiple step process which gives rise to a newly formed, fusion-incompetent compartment, the so-called "parasitophorous vacuole" (PV). The parasite-mediated vacuole formation is governed by highly coordinated molecular events which involve parasite specific organelles such as three types of specialized secretory organelles, namely the micronemes, the rhoptries and the dense granules. In this chapter, we will review the several molecular steps which allow the parasite to propel itself into the host cell and form its PV, highlighting the recent molecular studies on the subject. In the last part of this chapter, we will review what is currently known on the gradual transformation of PVs into intracellular dormant cysts which persist in muscles and in the brain. Thanks to these mechanisms, Toxoplasma gondii stands as one of the most successful parasites: it can indeed infect virtually any kind of nucleated cell and it establishes a long lasting chronic infection in any warm-blooded animal, including human beings

Le rat LEW, un modèle d'étude de la résistance à l'infection toxoplasmique (analyses génétiques et immunologiques)

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

Etude de l adressage des protéines GRAs transmembranaires de Toxoplasma gondii aux granules denses et de leur insertion membranaire post-sécrétoire

Parmi les mécanismes de survie intracellulaire connus, l export de protéines solubles ou transmembranaires visant à modifier différents compartiments de la cellule-hôte est une stratégie employée par de nombreux pathogènes. Chez Toxoplasma gondii, il a été montré que les granules denses (GD) constituent la voie de sécrétion par défaut pour les protéines solubles. Par contre, le tri de protéines transmembranaires vers les GD et leur maintien sous forme soluble avant insertion membranaire post-sécrétoire font appel à des mécanismes originaux qui ont fait l objet de ces travaux. Chez le Toxoplasme, la protéine de GD GRA5 est adressée à la membrane de la vacuole parasitophore (MVP) après sécrétion. Exprimée en cellules de mammifères, GRA5 est adressée à la membrane plasmique avec une topologie de type I, ce qui démontre la particularité des mécanismes de sécrétion chez T. gondii. Par une approche basée sur des protéines chimériques présentant des domaines spécifiques de GRA5 et d une protéine transmembranaire de la membrane plasmique parasitaire (MPP), nous avons pu identifier les déterminants de l adressage à la MPP versus à la MVP. Nous avons ainsi pu démontrer que le domaine Nt de GRA5 est impliqué dans l adressage soluble aux GD et est essentiel pour l insertion membranaire post-sécrétoire dans la MVP. Ces résultats, qui ont été étendus à une autre protéine GRA transmembranaire (GRA6), divergent de l idée largement répandue selon laquelle les signaux d adressage des protéines transmembranaires seraient présents dans la queue C-terminale et/ou dépendraient de la longueur du domaine transmembranaire de ces protéines.The success of many intracellular pathogens relies on the export of both soluble and membrane-bound proteins that are destined to modify various compartments of the host cell. In Toxoplasma gondii, it is well established that the dense granules (DG) constitute the default constitutive pathway for soluble proteins. By contrast, the mechanism by which transmembrane proteins are sorted to the DG and are maintained in a soluble state while adopting a transmembrane topology after secretion is not known. The GRA5 DG protein of T. gondii is targeted to the parasitophorous vacuole membrane (PVM) after soluble secretion. Expression of GRA5 in mammalian cells revealed that the protein is targeted to the cell surface with a type I topology, providing evidence that soluble trafficking of GRA5 within the parasite is peculiar. By using chimeric proteins containing specific domains of GRA5 and of a parasite plasma membrane (PPM) targeted transmembrane protein, we investigated which are the determinant(s) of PPM versus PVM targeting. We demonstrated that the GRA5 Nt domain is involved in soluble targeting within the DG and is essential for insertion into the PVM. These results, that were extented to another transmembrane GRA protein (GRA6), contrast with the broad acceptance that sorting signals are present within the cytoplasmic tail of membranous proteins and/or depend on the size of their transmembrane domain.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF