Artemisinin-resistant Plasmodium falciparum parasites have been reported in the Greater Mekong Subregion since 2007. Artemisinin combination therapy (ACT) is the mainstay of antimalarial treatment and is responsible for decreases in malaria-related morbidity and mortality over the past fifteen years. The slowed parasite clearance rates following ACT indicates resistance to artemisinin derivatives. This resistance places increasing selective pressure for variants or traits that confer resistance to the partner drug used in combination and has led to the rapid failure of several partner drugs. While a single nucleotide polymorphism (SNP) in kelch13 has been shown to mediate some resistance phenotypes, the complete mechanism of artemisinin resistance is poorly understood. The known mechanisms of resistance hint at a connection to autophagy, an intracellular pathway that cells use to degrade waste molecules or organelles in response to stress and starvation, which is poorly characterized in Plasmodium. In this doctoral thesis project, I investigated the role of an autophagy-like mechanism in P. falciparum in the mechanism of artemisinin resistance. I found a SNP in autophagy-related gene 18 (atg18) that was associated with clinical delayed parasite clearance half-life following ACT. This gene encodes PfAtg18, a protein that I characterized as being similar to mammalian/yeast homologues in terms of structure, binding abilities, and ability to form puncta in response to stress. In order to investigate the contribution of the mutation in this protein, I edited the atg18 gene using CRISPR/Cas9 and screened the mutant and parent parasites against a drug library of over 6000 unique compounds. I discovered that while the SNP did not change the mutant parasite's susceptibility to any of the antimalarial compounds using a 72-hour drug pulse, it did alter the susceptibility to 227 other compounds. Further, I found that the SNP offers parasites a fitness advantage by allowing them to grow better in nutrient-limited settings. Finally, I determined that neither this atg18 SNP nor several polymorphisms in kelch13 modulate a dormancy phenotype that appears to be involved in the artemisinin-resistance mechanism.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:749008 |
| Date | January 2018 |
| Creators | Breglio, Kimberly F. |
| Contributors | Rockett, Kirk ; Lee, Marcus ; Roberts, David ; Thomas, Craig ; Simon, Anna Katharina |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:e1e9eb78-cf58-473a-837e-25810db46fcf |
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