The obligate intracellular protozoan Toxoplasma gondii is the etiological agent of toxoplasmic encephalitis that remains a major cause of death in AIDS patients. The currently available treatment for toxoplasmosis shows no efficacy against Toxoplasma long-term chronic infections, resulting in the recrudescence of active infections. New drugs are imperatively needed. During mammalian cell invasion, the parasite creates a specialized parasitophorous vacuole (PV) that is demarcated from the host cytoplasm by a unique membrane containing parasite proteins. Toxoplasma is notorious for extensively modifying the host cell and rerouting host organelles to its PV, largely for purposes of nutrient acquisition. The parasite usually establishes its 'nest'near the host peri-Golgi microtubule-organizing center. This region is at the intersection of the endocytic and biosynthetic pathways, and PV positioning in this area of the cell could facilitate the interception of vesicular traffic and satisfy parasite requirements for nutrients and lipid membranes. In support of this hypothesis, we demonstrated that T. gondii has a marked requirement for host cell lipids derived both from lysosomes (e.g. cholesterol) and the Golgi (e.g. sphingolipids). The PV does not fuse with host organelles, and the mechanisms by which the parasite retrieves lipids from endocytic and exocytic organelles are still poorly understood. The overall goal of our proposal is to decipher the molecular details of host lysosome and Golgi exploitation by Toxoplasma. We previously showed that Toxoplasma uses the host microtubular network to redirect host lysosomes to its vacuole and sequester these organelles within PV membrane invaginations formed by microtubules. This strategy allows the parasite to have access to nutrients provided by organelles of the endocytic cascade. However, extensive gaps remain in our current model.
Specific Aim 1 proposes experiments to better understand the intersection of T. gondii with the host endocytic pathway. We will clarify the nature and contribution of the endocytic structures intercepted by Toxoplasma to parasite development. We will examine the molecular mechanism of implicated in host microtubule-PV interaction and PV membrane transformations for lysosome sequestration. Almost nothing is known about the role of host Golgi during Toxoplasma infection. Our preliminary data show that the parasite associates with the Golgi, fragments this organelle into Golgi ministacks that align along the PV and intercepts the Golgi vesicular trafficking by engulfing secretory vesicles into the PV. This strategy may allow the parasite to retrieve Golgi lipids from sequestered Golgi vesicles.
Specific Aim 2 combines experiments to verify our hypothetic model on host- Golgi-PV interaction. We will study the mechanisms leading to host Golgi breakdown and the delivery of Golgi vesicles to the PV by identifying the host Golgi proteins that are targeted by the parasite. We will explore the connection between Golgi remodeling and lipid salvage by the parasite. Our results may raise the provocative notion of novel treatments against Toxoplasma based on interference with host organelle functions.

Public Health Relevance

The human parasite Toxoplasma is the most common cause of brain lesions in HIV/AIDS patients. This pathogen invades mammalian cells and develops within a specialized niche that serves as a platform for modulation of host cell functions. Our proposal focuses on the identification of unique features of lipid uptake from host organelles developed by the parasite in order to uncover targets for new therapeutics.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI060767-09
Application #
8681296
Study Section
AIDS-associated Opportunistic Infections and Cancer Study Section (AOIC)
Program Officer
Mcgugan, Glen C
Project Start
2004-06-01
Project End
2015-06-30
Budget Start
2014-07-01
Budget End
2015-06-30
Support Year
9
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Microbiology/Immun/Virology
Type
Schools of Public Health
DUNS #
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Coppens, Isabelle; Romano, Julia D (2018) Hostile intruder: Toxoplasma holds host organelles captive. PLoS Pathog 14:e1006893
Coleman, Bradley I; Saha, Sudeshna; Sato, Seiko et al. (2018) A Member of the Ferlin Calcium Sensor Family Is Essential for Toxoplasma gondii Rhoptry Secretion. MBio 9:
Coppens, Isabelle; Romano, Julia D (2018) Correction: Hostile intruder: Toxoplasma holds host organelles captive. PLoS Pathog 14:e1007018
Nolan, Sabrina J; Romano, Julia D; Kline, John T et al. (2018) Novel Approaches To Kill Toxoplasma gondii by Exploiting the Uncontrolled Uptake of Unsaturated Fatty Acids and Vulnerability to Lipid Storage Inhibition of the Parasite. Antimicrob Agents Chemother 62:
Nolan, Sabrina J; Romano, Julia D; Coppens, Isabelle (2017) Host lipid droplets: An important source of lipids salvaged by the intracellular parasite Toxoplasma gondii. PLoS Pathog 13:e1006362
Di Cristina, Manlio; Dou, Zhicheng; Lunghi, Matteo et al. (2017) Toxoplasma depends on lysosomal consumption of autophagosomes for persistent infection. Nat Microbiol 2:17096
Romano, Julia D; Nolan, Sabrina J; Porter, Corey et al. (2017) The parasite Toxoplasma sequesters diverse Rab host vesicles within an intravacuolar network. J Cell Biol 216:4235-4254
Pszenny, Viviana; Ehrenman, Karen; Romano, Julia D et al. (2016) A Lipolytic Lecithin:Cholesterol Acyltransferase Secreted by Toxoplasma Facilitates Parasite Replication and Egress. J Biol Chem 291:3725-46
Romano, Julia D; de Beaumont, Catherine; Carrasco, Jose A et al. (2013) A novel co-infection model with Toxoplasma and Chlamydia trachomatis highlights the importance of host cell manipulation for nutrient scavenging. Cell Microbiol 15:619-46
Lige, Bao; Sampels, Vera; Coppens, Isabelle (2013) Characterization of a second sterol-esterifying enzyme in Toxoplasma highlights the importance of cholesterol storage pathways for the parasite. Mol Microbiol 87:951-67

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