The parasitic protozoan Trypanosoma brucei is the causative agent of African trypanosomiasis which causes sleeping sickness in humans and Nagana in farm animals. The World Health Organization projects that the current disease burden of human African trypanosomiasis is about two million """"""""Disability Adjusted Life Years"""""""" (with 300,000 new cases each year). Coupled with the profound effect on the economy caused by Nagana, T. brucei is one of the leading impediments to development in much of Africa. While related parasites utilize protected niches after they enter their mammalian host, T. brucei thrives in the mammalian bloodstream, where it must survive the onslaught of the humoral immune response. The parasite does this by virtue of its dense surface coat, consisting of ~5 x 106 variable surface glycoprotein (VSG) homodimers. While this VSG coat is exposed to and recognized by antibodies, T. brucei periodically replaces it (in a process called """"""""VSG switching"""""""") enabling a subpopulation of parasites to survive by evading complement-mediated lysis. Little is known about VSG switching at the molecular level. Work over the last 25 years has determined (a) that the majority of switching occurs by duplicative gene conversion and (b) that there is semi-predictable hierarchy with regard to the types of VSGs that appear early vs. late after infection. We have recently established a robust experimental system, which we have used to successfully reproduce many of the features of in vivo infection. Here, we propose to use this system toward two specific aims: 1) Determine the mechanism that initiates VSG switching. There is a long-standing hypothesis that VSG switching is initiated by an endonuclease. Alternatively, switching could be a result of spontaneous but frequent DNA breaks that can arise from endogenous processes peculiar to chromosome ends (which is where all expressed VSGs are located). We propose experiments to evaluate both hypotheses. 2) Understand the rules that govern choice of donor VSG, leading to the observed hierarchy of switching. In the early stages of VSG switching, the new (donor) VSGs arising in the course of infection are not random. For example, cells expressing VSG221 tend to switch to VSG224, both in vivo (Robinson et al., 1999) and in vitro (our preliminary data). We will evaluate two mechanisms that could explain this consistent finding: (a) initial preference could be due to sequence similarity in conserved elements (such as the 70-bp repeat tracts) of expression sites, and (b) this preference could be the result of proximity of the two expression sites in the context of the nucleus. African trypanosomiasis is always fatal unless treated. The few therapeutic treatment options that do exist are expensive, have serious side effects and are increasingly inefficient as drug resistant T. brucei strains begin to emerge. The work we propose centers upon understanding and eventually disrupting the major known pathway of immune evasion by this parasite which is also the cause of pathogen persistence. As such, in the long term the research we propose could lead to a novel and effective way to protect against this neglected disease.

Public Health Relevance

The parasite Trypanosoma brucei is the causative agent of African sleeping sickness in humans and of Nagana in cattle, and one of the leading impediments to development in much of sub-Saharan Africa. T. brucei is transmitted to the mammalian bloodstream through the bite of the tse-tse vector, and once there, it quickly elicits an antibody mediated immune response which is capable of eliminating the parasite by binding to its exposed surface coat. However, the parasite has evolved a survival strategy that hinges upon its ability to change its surface coat, to evade the host immune response. The work we propose aims to understand the mechanism of T. brucei surface coat switching, which is the sole cause of pathogen persistence and chronic infection.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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Special Emphasis Panel (ZRG1-IDM-S (02))
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Mcgugan, Glen C
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Rockefeller University
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New York
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Pinger, Jason; NeŇ°i?, Dragana; Ali, Liaqat et al. (2018) African trypanosomes evade immune clearance by O-glycosylation of the VSG surface coat. Nat Microbiol 3:932-938
Pinger, Jason; Chowdhury, Shanin; Papavasiliou, F Nina (2017) Variant surface glycoprotein density defines an immune evasion threshold for African trypanosomes undergoing antigenic variation. Nat Commun 8:828
Mugnier, Monica R; Papavasiliou, F Nina; Schulz, Danae (2016) Vesicles as Vehicles for Virulence. Trends Parasitol 32:435-436
Schulz, Danae; Mugnier, Monica R; Boothroyd, Catherine E et al. (2016) Detection of Trypanosoma brucei Variant Surface Glycoprotein Switching by Magnetic Activated Cell Sorting and Flow Cytometry. J Vis Exp :
Schulz, Danae; Zaringhalam, Maryam; Papavasiliou, F Nina et al. (2016) Base J and H3.V Regulate Transcriptional Termination in Trypanosoma brucei. PLoS Genet 12:e1005762
Schulz, Danae; Papavasiliou, F Nina (2016) The VEXing problem of monoallelic expression in the African trypanosome. Proc Natl Acad Sci U S A 113:7017-9
Mugnier, Monica R; Stebbins, C Erec; Papavasiliou, F Nina (2016) Masters of Disguise: Antigenic Variation and the VSG Coat in Trypanosoma brucei. PLoS Pathog 12:e1005784
Hovel-Miner, Galadriel; Mugnier, Monica R; Goldwater, Benjamin et al. (2016) A Conserved DNA Repeat Promotes Selection of a Diverse Repertoire of Trypanosoma brucei Surface Antigens from the Genomic Archive. PLoS Genet 12:e1005994
Schulz, Danae; Mugnier, Monica R; Paulsen, Eda-Margaret et al. (2015) Bromodomain Proteins Contribute to Maintenance of Bloodstream Form Stage Identity in the African Trypanosome. PLoS Biol 13:e1002316
Hovel-Miner, Galadriel; Mugnier, Monica; Papavasiliou, F Nina et al. (2015) A Host-Pathogen Interaction Reduced to First Principles: Antigenic Variation in T. brucei. Results Probl Cell Differ 57:23-46

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