Last Updated: 18/06/2024
Functional analysis of the autophagic pathway in Toxoplasma gondii (Autophago-Toxo)
Objectives
The aim of this project is to decipher the cellular functions of autophagy in T. gondii and their subsequent implications in the survival of these parasites.
Specific objectives are:
1) to explore the dynamics of the interactions between the autophagosomes and cellular organelles, such as the mitochondrial network or the apicoplast, during cell division
2) to use autophagosomal markers to delineate the terminal lytic compartment responsible for degradation of the autophagic material and, more precisely, the hydrolases involved. Parallel to this, the researchers aim to discover new parasite-specific autophagosomal proteins and targets
3) to screen for conditions that can trigger autophagy and whether this can be integrated in a global stress or cell death response.
In eukaryotic cells, autophagy is a usually reparative and life-sustaining process by which cytoplasmic components are sequestered in double-membrane vesicles called autophagosomes and degraded after fusion with a lysosomal compartment. Autophagy can be triggered when cells are in need of nutrients in order to recycle cellular material, but might also be involved in cell remodelling during normal eukaryotic development. Toxoplasma gondii is an obligate intracellular parasitic protist that is virtually able to infect all species of warm-blooded animals. This parasite is a member of the phylum Apicomplexa, which also includes several other notable human pathogens such as Plasmodium and Cryptosporidium. The genome of T. gondii seems to contain genes coding for the core machinery necessary for the autophagic process. Using GFP-fused TgATG8 as an autophagosomal membrane marker in order to quantify autophagy in T. gondii tachyzoites, the researchers have shown that autophagy can be induced in vitro in extracellular parasites by starving the cells in amino acid-depleted medium. However, the researchers have also followed autophagy across normal development of the parasite within the host cell and showed that it is occurring consistently, yet transiently, during cell division. Direct knock-out strategies to interfere with TgATG8 function have proven to be unsuccessful, suggesting a crucial role for this protein for the multiplication of Toxoplasma. Instead, the researchers have produced conditional knock out mutants for autophagy-related genes TgATG3 and TgATG4 (1, 2), whose products are important for regulating TgATG8 association with the membrane of the autophagosomes. Both mutant cell lines showed a severe growth defect and a several organellar defects such as fragmentation of their mitochondrial network or loss of their apicoplast (a relict, non-photosynthetic, yet metabolically important plastid found in these parasites). These converging phenotypes suggest that TgATG8-related machinery is essential for the normal development of the parasite, and seems to be more specifically involved in maintaining organellar homeostasis. There is a fundamental interest in studying a parasitic protist with an apparently reduced machinery, to bring information on autophagy as a mechanism. Beyond this, the researchers have already validated autophagy as an essential mechanism for parasite growth and the long term objectives are now to elucidate the molecular actors involved and identify putative targets that could be interfered with to modulate this cellular function. They might later be validated in other medically important Apicomplexa.
Dec 2013 — Jun 2017
$285,375
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