Interrogating Host-Parasite Dynamics During Plasmodium Liver Stage Infection
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Malaria is a disease that poses a significant global health burden and is caused by the apicomplexan parasite Plasmodium. Plasmodium spp. are transmitted by an Anopheles mosquito and require both host and vector to complete their life cycle. Once in the host, parasites travel to the liver and undergo an obligatory and asymptomatic liver stage. This elusive stage is necessary to produce blood-infective parasites, to which the cyclical blood stage causes symptomatic disease. Understanding the liver stage of the Plasmodium life cycle is crucial for prevention of malaria but due to the technical challenges and asymptomatic nature of this stage, little is currently known about this stage. Crucially, during the liver stage of some Plasmodium spp., like the human-infective P. vivax, have the ability to form dormant parasites, termed hypnozoites, that can persist for weeks, months and even years and cause relapses in symptomatic infection. Elucidating host-parasite interactions during the liver stage, especially in these dormant hypnozoites, will be crucial for development of new therapeutics.To interrogate parasite dynamics within the host hepatocyte we conducted an RNA sequencing analysis throughout the P. berghei liver stage, covering as early as 2 hours post infection (hpi) and extending to 48 hpi. Our data revealed that hundreds of genes are differentially expressed at 2 hpi and multiple genes known to be important for later infection are upregulated as early as 12 hpi. Further, using hierarchical clustering along with coexpression analysis, we identified clusters functionally enriched for key liver stage processes and some of these clusters were highly correlated to the expression of ApiAP2 transcription factors, containing mainly uncharacterized DNA binding motifs. Beyond transcriptional profiling, host cellular structure has been shown to be altered during P. berghei infection, but this has not yet been investigated during P. vivax liver stage infection. While utilizing high-resolution microscopy to investigate parasite dynamics during the liver stage, we also characterized temporal changes of the P. vivax liver stage tubovesicular network (TVN). Our results highlight that host-parasite interactions occur in both dormant and replicating liver stage P. vivax forms and implicate a function for AQP3 in both forms. To elucidate host factors that attribute to Plasmodium liver stage we utilized genetic and chemical approaches to uncover potential mechanisms of various host factors, in particular host AQP3. We demonstrate AQP3 localizes to other apicomplexans, T. gondii and C. parvum. Investigating transcriptional regulation of host genes during infection we demonstrate preliminary evidence of two potential host transcription factors that regulate other host factors shown to be important in Plasmodium liver stage. Overall, these studies investigate host-parasite dynamics in Plasmodium liver stage though transcriptomic, high-resolution microscopy, and chemical and genetic approaches.
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