Investigating Host-Parasite Interactions Supporting Plasmodium Liver Stage Nutrient Acquisition

Abstract

Malaria remains a significant global health challenge, with nearly half the world’s population at risk of infection. Plasmodium, the apicomplexan parasite responsible for the disease, follows a complex life cycle involving a mosquito vector and two developmental stages in the human host. During the liver stage, Plasmodium develops within a parasitophorous vacuole (PV), where it rapidly proliferates into tens of thousands of merozoites that then infect red blood cells, leading to the clinical manifestation of malaria. The PV protects the parasite against host immune responses but also restricts nutrient exchange with the host cell. To overcome these challenges, Plasmodium remodels the host cell to effectively scavenge resources for its development. While the processes involved in host cell remodeling are well documented, the specific nutrients acquired and how they are transported into the PV remain poorly understood. This dissertation aims to elucidate the interactions between Plasmodium and its host cell, focusing on the mechanisms by which the parasite acquires essential nutrients during the liver stage.We first examined the role of host lipids, discovering that sphingolipids are critical for Plasmodium liver stage development and invasion. Using live microscopy studies with NBD-labeled sphingolipids, we found that exogenous sphingolipids are actively trafficked into the PV and promote parasite development. Additionally, we identified key host sphingolipid pathways that support Plasmodium viability, including the ceramide transporter, CERT1. We then explored how Plasmodium and the related parasite Toxoplasma gondii interact with host Arf GTPases and partner proteins of the vesicular trafficking system. Overexpression studies coupled with immunofluorescence microscopy revealed that host Arfs are internalized by the T. gondii PV and colocalize with sphingolipids, suggesting a role in nutrient acquisition. While Plasmodium did not internalize host Arfs, these proteins were enriched around the PV and were essential for parasite viability. Finally, we applied ultrastructure expansion microscopy to the Plasmodium liver stage, providing new structural insights into the parasitophorous vacuole membrane and its interactions with host organelles. Overall, these findings enhance our understanding of how Plasmodium interacts with its host cell during the liver stage and offer new directions for identifying therapeutic targets to disrupt parasite development and reduce disease burden.