Toxoplasmic encephalitis (TE) is one of the HIV-AIDS defining opportunistic infections that is associated with the reactivation of the chronic form of te infection, mediated by bradyzoites, within tissue cysts in the CNS. Despite the central role in the pathogenesis of HIV-AIDS associated toxoplasmosis, little is known about the biology of tissue cysts and the bradyzoite stage of the parasite they contain. Among the key limitations in studying the progression of the chronic phase and the mechanisms by which latency is established, maintained and lost during reactivation has been that rigorous insights into the physiology and development of bradyzoites in vivo has not been possible. Toward removing this major limitation we have initiated a comprehensive research program to understand bradyzoite biology by the development of approaches that directly address bradyzoite replication within tissue cysts in the in vivo context. These initial studies reveal that bradyzoites possess a previously unappreciated capacity for replication and metabolism that can be exploited in the development drugs to target what has been a traditionally refractory state. With the present study we aim to establish not only a new paradigm for bradyzoite biology but also develop the experimental methodologies to dissect bradyzoite replication we have been able to conclusively detect occurs challenging the existing dogma that bradyzoites are largely dormant entities. Our initial studies provide a new window into the dynamics of bradyzoite growth within tissue cysts which exhibit a level of complexity and sophistication that has not been previously appreciated. In this exploratory and developmental study we focus on the generation of new experimental approaches to directly interrogate and dissect the progression of the cell cycle within bradyzoites. Such insights would fill a vast gap in our knowledge that has stymied the development of treatments that are targeted toward the elimination of tissue cysts and bradyzoites. Targeting of tissue cysts and bradyzoites would eliminate the primary trigger of toxoplasmic encephalitis in the HIV-AIDS.
In spite of their central role in the pathogenesis of cerebral toxoplasmosis in HIV-AIDS, the biology of bradyzoites and the tissue cysts within which they reside remain poorly understood. With this proposal apply newly developed approaches to directly investigate bradyzoite growth while defining their cell cycle within tissue cysts in vivo. This work fills a critical gap in our knowledge by applying mechanistic approaches to address fundamental questions of direct importance to the understanding of toxoplasma pathogenesis.
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| Watts, Elizabeth A; Dhara, Animesh; Sinai, Anthony P (2017) Purification Toxoplasma gondii Tissue Cysts Using Percoll Gradients. Curr Protoc Microbiol 45:20C.2.1-20C.2.19 |
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