UBC Theses and Dissertations
Pathogenesis of leishmania infection in human macrophages : role of leishmania chaperonin 10 and modulation of host miRNA Colineau, Lucie
Protozoan parasites of the genus Leishmania infect macrophages in their mammalian hosts causing a spectrum of diseases known as the leishmaniases. The search for parasite and host factors that support macrophage infection is a focus of significant interest. Here, I studied two aspects of the host-pathogen interaction: the role of the leishmania protein chaperonin 10 (CPN10) and the impact of leishmania infection on host cell micro RNA (miRNA) expression. The heat shock protein CPN10 is secreted by leishmania in exosomes and its human homolog has immunosuppressive properties. Two genetically modified strains of Leishmania donovani (Ld) were generated: one overexpressing CPN10 (CPN10+++) and the second, a CPN10 single allele knockdown (CPN10+/−). When compared with the wild-type (WT) parental strain, CPN10+/− Ld showed higher infection rates and parasite loads in human macrophages after 24 h of infection. Conversely, CPN10+++ Ld was associated with lower initial infection rates. We found that this unexpected apparent gain-of-function for the knockdown was a result of CPN10+/− Ld being more readily internalized than WT Ld. However, the CPN10+/- strain also displayed significantly impaired intracellular survival. Taken together, these findings identify leishmania CPN10 as a novel effector that negatively regulates the rate of parasite uptake by macrophages while being required for intracellular survival. miRNAs have recently emerged as ubiquitous regulators of gene expression. Here, we used miRNA expression profiling to ask whether leishmania target their host cell miRNA machinery as a novel virulence strategy. The data show that leishmania infection of human macrophages induces a genome-wide downregulation of host miRNAs. This repression takes place at the level of miRNA gene transcription as the synthesis rates of primary miRNAs are markedly decreased in infected cells. Expression of the host transcription factor c-Myc is markedly upregulated by infection and silencing of c-Myc both reverses miRNA suppression and brings about a significant reduction in leishmania survival. These findings identify c-Myc as a novel and essential leishmania virulence factor by proxy that targets the host miRNA machinery and promotes pathogen survival.
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