Toxoplasma gondii is an obligate intracellular parasite that invaginates the host plasma membrane upon invasion to form a parasitophorous vacuole inside which the parasite replicates and survives. Like the related malaria parasite, Plasmodium falciparum, we recently discovered that T. gondii ingests host cytosolic proteins and targets them for degradation in a lysosome-like organelle called the vacuolar compartment or VAC. This discovery challenges the longstanding notion that T. gondii lacks endocytosis, because of its isolation in a non-fusogenic vacuole. Preliminary studies show that ingestion- deficient parasites display attenuated virulence and defective chronic infection in vivo. Further, these parasites are more vulnerable to killing by interferon gamma-dependent mechanisms, implying a role in immune evasion. Genetic and live cell imaging studies of intracellular parasites suggest a vesicular pathway for uptake from the intravacuolar network, a specialized structure in the parasitophorous vacuole. Immunofluorescence analysis indicates that ingested material traverses the late endosome of the parasite en route to the VAC. Our central hypothesis is that host protein-containing vesicles, generated from the intravacuolar network, are trafficked to the VAC via clathrin- mediated endocytosis. I have designed two specific aims to test this hypothesis.
In Aim 1, I will use live-cell imaging to directly visualize vesicular trafficking fromthe parasitophorous vacuole membrane to the VAC to determine if the intravacuolar network is a conduit for ingestion.
In Aim 2, I will use state of the art Stimulated Emission Depletion Microscopy to localize ingested host proteins within the parasite endosomal system of wild type parasites or parasites expressing dominant negative forms of suspected endocytic players to elucidate the pathway of trafficking within T. gondii.

Public Health Relevance

Reactivated chronic toxoplasmosis results in severe ocular and neural disease in congenitally infected infants and immunodeficient people. Current drugs are effective against the acute but not the chronic stage of infection, leaving approximately 2 billion infected people potentially vulnerable to reactivated toxoplasmosis. My work will identify players important for host cytosolic protein ingestion, which may reveal new targets for expanding treatment options for management of toxoplasmosis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Predoctoral Individual National Research Service Award (F31)
Project #
1F31AI118274-01
Application #
8908567
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Adger-Johnson, Diane S
Project Start
2015-09-01
Project End
2017-08-31
Budget Start
2015-09-01
Budget End
2016-08-31
Support Year
1
Fiscal Year
2015
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Di Cristina, Manlio; Dou, Zhicheng; Lunghi, Matteo et al. (2017) Toxoplasma depends on lysosomal consumption of autophagosomes for persistent infection. Nat Microbiol 2:17096