Targeting the endocytic pathway in Toxoplasma gondii

Erwin Schrödinger Fellowship J 1916 Targeting the endocytic pathway in Toxoplasma gondii Bruno ROBIBARO 26.6.2000 Underlying diseases compromising cell-mediated immunity as well as therapies central to transplantation medicine and oncology place the patients at risk of acute toxoplasmosis. While treatment regimens exist for the control of Toxoplasma gondii infections, they require long-term medication fraught with side effects. However, current therapies are not microbicidal because they do not eradicate the tissue cyst form of T. gondii, known to be the major cause for often life-threatening acute toxoplasmosis in immunocompromised individuals. The need for identifying novel drug targets is imperative. Since endocytic pathways represent potential drug delivery mechanisms, the benefit to elucidate the endocytic machinery is crucial and of clinical relevance. The specific research goal is to define mechanisms underlying endocytic membrane trafficking in T. gondii. This may potentially reveal a means to rind a novel therapeutic strategy, less harmful for patients than the established therapies, and ideally eradicating the tissue cyst form. To date neither endocytosis nor organelles involved in endocytic pathways (endosomes/lysosomes), have been proven in T. gondii. We have recently established a framework in order to characterize and derme both the morphology and function of endocytic events in T. gondii. This is underscored by the presence of a T. gondii homologue of the GTPase Rab5, known to be a key component involved in endocytosis in eukaryotic cells, as well as being the early endosomal marker par excellence, which could be isolated and cloned from T. gondii in our laboratory. The proposed experimental approaches to define the endocytic machinery in T. gondii are designed by exploiting T. gondii Rab5 and taking advantage of the recent demonstration in our laboratory that the parasite scavenges cholesterol from the host cell. Morphological and functional analyses win be monitored by immunofluorescence and electron microscopy techniques. The novelty and potentially essential role of endocytosis, makes it an excellent target for therapeutic intervention to benefit natients with toxonlasmosis.