Browsing by Subject "Toxoplasma"
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Item Open Access Cell type- and species-specific host responses to Toxoplasma gondii and its near relatives.(International journal for parasitology, 2020-05-11) Wong, Zhee S; Borrelli, Sarah L Sokol; Coyne, Carolyn C; Boyle, Jon PToxoplasma gondii is remarkably unique in its ability to successfully infect vertebrate hosts from multiple phyla and can successfully infect most cells within these organisms. The infection outcome in each of these species is determined by the complex interaction between parasite and host genotype. As techniques to quantify global changes in cell function become more readily available and precise, new data are coming to light about how (i) different host cell types respond to parasitic infection and (ii) different parasite species impact the host. Here we focus on recent studies comparing the response to intracellular parasitism by different cell types and insights into understanding host-parasite interactions from comparative studies on T. gondii and its close extant relatives.Item Open Access Molecular Interactions between Apicomplexan Parasites and their Host Cells(2021) Toro Moreno, MariaParasitic diseases caused by pathogens of the Apicomplexan phylum result in hundreds of thousands of deaths per year, in addition to being an immense socioeconomic burden on vulnerable populations. A notorious case is that of Plasmodium parasites, the causative agents of malaria and one of the most ancient and devastating diseases known to humankind. Prior to infecting red blood cells resulting in the symptomatic stage of infection, Plasmodium parasites infect liver cells and undergo one of the most rapid replication events known in eukaryotes. Given the asymptomatic nature and technical challenges associated with studying the liver stage, this portion of the Plasmodium life cycle remains poorly understood, hindering our ability to target this stage of the life cycle for disease prevention. In particular, the host and parasite pathways that are critical to parasite infection during this hepatic phase remain unknown. The lack of effective vaccines coupled with the widespread emergence of drug-resistant parasites necessitates our understanding of host-parasite infection biology to develop improved therapeutics. To elucidate host-parasite interactions in the Plasmodium liver stage, we implemented a forward genetic screen to identify host factors within the human druggable genome that are critical to P. berghei infection in hepatoma cells, as well as RNA-seq approaches to delineate host and Plasmodium gene expression regulation during infection. Through our genetic screen, we identified the knockdown of genes involved in host trafficking pathways to be detrimental to Plasmodium infection. We additionally pursued mechanistic studies using small molecules and imaging approaches and found that both P. berghei and the related apicomplexan parasite Toxoplasma gondii hijack host trafficking by rerouting host vesicles to their parasitophorous vacuole, although with differing specificities. Our extensive RNA-Seq analysis throughout the P. berghei liver stage revealed that hundreds of parasite genes, including some coding for putative exported proteins, are differentially expressed as early as 2 hpi and that multiple genes shown to be important for later infection are upregulated as early as 12 hpi. Using co-expression analyses, we examined potential regulation of gene clusters by ApiAP2 transcription factors and found enrichment of mostly uncharacterized DNA binding motifs. This finding indicates potential liver-stage targets for these transcription factors, while also hinting at alternative uncharacterized DNA binding motifs and transcription factors during this stage. We further explored regulatory mechanisms in the liver stage by identifying differentially expressed host lncRNAs in P. berghei-infected cells, and novel putative lncRNAs in P. vivax hypnozoites. Overall, our work uncovered critical host and parasite pathways in the Plasmodium liver stage and highlights the use of high-throughput genetic and transcriptomic approaches in combination with chemical biology and classic cell biology studies to uncover host-parasite interactions in challenging infection systems.
Item Open Access Murine Immunity-Related GTPase M Proteins Regulate Immunity to Intracellular Infections(2021) Dockterman, Jacob SavageHost cells are equipped with a robust defense program to defend against intracellular pathogens. The cytokine gamma-interferon (IFNg) activates expression of hundreds of genes that identify intracellular pathogens such as Chlamydia trachomatis and Toxoplasma gondii, target pathogen-containing vacuoles (PVs) with host effector proteins, and destroy the pathogen. In mice, the IFNg-induced defense program targeting Toxoplasma and C. trachomatis is controlled by three Immunity-related GTPase M (Irgm) proteins, which coordinate host effectors to efficiently target and destroy intracellular pathogens. The mechanisms by which Irgm proteins regulate cell-autonomous immunity are not well understood. Human cell-autonomous immunity differs substantially from the mouse system, and while the sole human IRGM ortholog is not involved in cell-autonomous immunity to Toxoplasma or Chlamydia, it has been linked with a variety of inflammatory diseases including Crohn’s disease and sepsis. The mechanism linking polymorphisms in human IRGM with autoimmunity is unclear, but murine Irgm knockout models recapitulate similar phenotypes of hyperinflammation associated with human IRGM. Additionally, mouse and human Irgm proteins have been implicated in similar fundamental cellular processes including autophagy and mitochondrial function. Collectively these findings support the central hypothesis that murine Irgm proteins regulate cellular membrane biology to both coordinate cell-autonomous immunity and regulate inflammation. In order to investigate this hypothesis, I leveraged existing Irgm-/- models as well as our novel pan-Irgm-/- mouse lacking all three Irgm proteins. I demonstrated that pan-Irgm-/- cells are completely defective for the targeting of Toxoplasma gondii with host effectors, while Chlamydia trachomatis remains robustly targeted by most but not all effectors. In spite of the differences in host-directed targeting of these two vacuolar pathogens, pan-Irgm-/- mice were defective for resistance to Toxoplasma and Chlamydia trachomatis both in vitro and in vivo. In pan-Irgm-/- mice infected with Chlamydia trachomatis, adaptive immunity compensated for the defect in cell-autonomous immunity to ultimately clear the infection. Consistent with the hypothesis that Irgm proteins limit inflammation, pan-Irgm-/- mice demonstrated increased inflammation in genital Chlamydia trachomatis infection, and increased inflammation and immunopathology in infection with Chlamydia muridarum. Collectively, my findings shed light on the elusive mechanisms of murine Irgm proteins, clarifying their roles in cell-autonomous immunity, defense against intracellular pathogens in vivo, and regulation of inflammation.