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Novel insights into leishmania biology : the role of parasite and host-derived small non-coding RNAs

University of British Columbia

Infection with leishmania parasites causes severe chronic and potentially fatal illness in millions of people annually. Nevertheless, leishmania-host interactions remain understudied, and available treatments are sub-optimal. Pivotal to the establishment of infection, parasite replication and development of clinical disease is the subversion of microbicidal activities of host macrophages by leishmania. The overall aim of this thesis was to enhance our understanding of the modus operandi of macrophage subversion and explore the involvement of parasite- and host-derived small non-coding RNAs in this process. My first objective was to investigate whether leishmania exosomes act as shuttle vehicles to export and deliver leishmania RNAs to host macrophages, where they may contribute to pathogenesis. We used high-throughput sequencing to characterize the transcriptome of leishmania exosomes and found that leishmania exosomes are selectively and specifically enriched in small RNAs derived almost exclusively from non-coding RNAs such as rRNAs and tRNAs. In depth analysis revealed the presence of tRNA-derived small RNAs, a novel RNA type with suspected regulatory functions. Exosomes protected their RNA cargo from degradation and were competent to deliver RNAs to macrophages. Furthermore, our results demonstrated a remarkably high degree of congruence in exosomal small non-coding RNA content between two distinct leishmania species, which argues for a conserved mechanism for exosomal RNA packaging in leishmania. My second objective was to investigate whether macrophage miRNA expression is modulated during leishmania infection. Here, I was interested to know whether targeting of the host RNAi machinery is a potential novel mechanism of pathogenesis used by leishmania to control macrophage phenotype and promote chronic infection. I profiled miRNA expression in human macrophages at later stages of infection using two independent technologies. The data showed that leishmania infection induced an overall down-regulation of miRNA expression in macrophages. This down-regulation was not caused through effects on synthesis or stability of Drosha and Dicer, two essential enzymes involved in miRNA maturation. Taken together, my findings suggest that both leishmania- and host-derived small non-coding RNAs may contribute to pathogenesis. They open up new avenues of research on small RNA pathways in leishmania infection biology, which may identify novel therapeutic approaches.

Text

2016-08-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54500

Experimental Medicine

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/